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The Technical University of Denmark , often simply referred to as DTU, is a university in Kongens Lyngby, just north of Copenhagen, Denmark. It was founded in 1829 at the initiative of Hans Christian Ørsted as Denmark's first polytechnic, and is today ranked among Europe's leading engineering institutions, and the best engineering university in the Nordic countries. Wikipedia.

Laegsgaard J.,Technical University of Denmark
Journal of the Optical Society of America B: Optical Physics | Year: 2010

The possibility of second-harmonic generation based on surface dipole and bulk multipole nonlinearities in silica nanowires is investigated numerically. Both circular and microstructured nanowires are considered. Phase matching is provided by propagating the pump field in the fundamental mode, while generating the second harmonic in one of the modes of the LP 11 multiplet. This is shown to work in both circular and microstructured nanowires, although only one of the LP 11 modes can be phase-matched in the microstructure. The prospect of obtaining large conversion efficiencies in silica-based nanowires is critically discussed, based on simulations of second-harmonic generation in nanowires with a fluctuating phase-matching wavelength. It is concluded that efficient wavelength conversion will require strong improvements in the nanowire uniformity, peak powers well in excess of 10 KW, increase of the second-order nonlinearity by an order of magnitude by use of a different base material, or highly polarizable surface coatings. © 2010 Optical Society of America.

Mabit S.L.,Technical University of Denmark
Transportation Research Part A: Policy and Practice | Year: 2014

Differentiated vehicle taxes are considered by many a useful tool for promoting environmentally friendly vehicles. Various structures have been implemented in several countries, e.g. Ireland, France, The Czech Republic, and Denmark. In many countries the tax reforms have been followed by a steep change in new vehicle purchases toward more diesel vehicles and more fuel-efficient vehicles. The paper analyses to what extent a vehicle tax reform similar to the Danish 2007 reform may explain changes in purchasing behaviour. The paper investigates the effects of a tax reform, fuel price changes, and technological development on vehicle type choice using a mixed logit model. The model allows a simulation of the effect of car price changes that resemble those induced by the tax reform. This effect is compared to the effects of fuel price changes and technology improvements. The simulations show that the effect of the tax reform on fuel efficiency is similar to the effect of rising fuel prices while the effect of technological development is much larger. The conclusion is that while the tax reform appeared in the same year as a large increase in fuel efficiency, it seems likely that it only explains a small part of the shift in fuel efficiency that occurred and that the main driver was the technological development. © 2014 Elsevier Ltd.

Prato C.G.,Technical University of Denmark
Transportation | Year: 2014

The discrete choice paradigm of random regret minimization (RRM) has been recently proposed in several choice contexts. In the route choice context, the paradigm has been used to model the choice among three routes and to formulate regret-based stochastic user equilibrium. However, in the same context the RRM literature has not confronted three major challenges: (i) accounting for similarities across alternative routes, (ii) analyzing choice set composition effects on choice probabilities, and (iii) comparing RRM-based models with advanced RUM-based models. This paper looks into RRM-based route choice models from these three perspectives by (i) proposing utility-based and regret-based correction terms to account for similarities across alternatives, (ii) analyzing the variation of choice set probabilities with the choice set composition, and (iii) comparing RRM-based route choice models with C-Logit, Path Size Logit and Paired Combinatorial Logit. The results illustrate the definition of the correction terms within the regret function, the effect of the choice set specificity of RRM-based route choice models, and the positive performance of these models when compared to advanced RUM-based models. © 2013, Springer Science+Business Media New York.

Andersen J.E.T.,Technical University of Denmark
TrAC - Trends in Analytical Chemistry | Year: 2014

Contemporary research in quality assurance indicates that large uncertainties observed in interlaboratory comparisons to a large extent originate from a lack of competence of laboratory staff. This explanation is challenged by the present article for which six technologies and multiple series of experiments were investigated with respect to uncertainty of measurement and treatment of outliers. It was found that long-term precision was poor in comparison to short-term precision. The ratio of predicted uncertainty to observed uncertainty was determined as significantly above 1, and it was suggested that a correction factor is needed for the predicted uncertainty. This indicates that statistical control could be obtained only by treating many independent series of experiments and using pooled calibrations in the method validation. Retention of outliers in calculation of contents and calculation of uncertainties of certified reference materials (CRMs) gave results that differed significantly from those in the certificates of the CRMs. © 2014 Elsevier B.V.

Hagen A.,Technical University of Denmark
Journal of the Electrochemical Society | Year: 2013

Investigation of fuels containing sulfur impurities is important regarding durability of solid oxide fuel cells (SOFC) because they are present in various potential fuels for SOFC applications. The effect of H2S in the ppm range on the performance of state-of-the-art anode supported SOFC at 850 and 750°C is evaluated in either hydrogen/steam or hydrogen/steam/CO fuel. It was found that the poisoning effect is more severe in H2/H 2O/CO vs. H2/H2O fuel. Only ̃8 ppm H 2S can be allowed in the CO containing fuel without risking damage to the anode, whereas 90 ppm (or even more) is possible in H2/H 2O. Impedance spectroscopy revealed that the poisoning effect in H2/H2O is due to an increase of the polarization resistance in the high frequency range, which is related to the electrochemical anode reaction. In H2/H2O/CO, both the polarization and serial resistance increase. Furthermore, the polarization resistance increased both in the high and low frequency region, which indicates a strong poisoning of the water gas shift reaction and thus a lack of hydrogen fuel in addition to the poisoning of the electrochemical hydrogen oxidation. All poisoning effects are reversible under the applied operating conditions. © 2012 The Electrochemical Society.

Andersen K.H.,Technical University of Denmark | Pedersen M.,Lund University
Proceedings of the Royal Society B: Biological Sciences | Year: 2010

The largest perturbation on upper trophic levels of many marine ecosystems stems from fishing. The reaction of the ecosystem goes beyond the trophic levels directly targeted by the fishery. This reaction has been described either as a change in slope of the overall size spectrum or as a trophic cascade triggered by the removal of top predators. Here we use a novel size- and trait-based model to explore how marine ecosystems might react to perturbations from different types of fishing pressure. The model explicitly resolves the whole life history of fish, from larvae to adults. The results show that fishing does not change the overall slope of the size spectrum, but depletes the largest individuals and induces trophic cascades. A trophic cascade can propagate both up and down in trophic levels driven by a combination of changes in predation mortality and food limitation. The cascade is damped as it comes further away from the perturbed trophic level. Fishing on several trophic levels leads to a disappearance of the signature of the trophic cascade. Differences in fishing patterns among ecosystems might influence whether a trophic cascade is observed. © 2009 The Royal Society.

Gautier L.,Technical University of Denmark
BMC Bioinformatics | Year: 2010

Background: Computer languages can be domain-related, and in the case of multidisciplinary projects, knowledge of several languages will be needed in order to quickly implements ideas. Moreover, each computer language has relative strong points, making some languages better suited than others for a given task to be implemented. The Bioconductor project, based on the R language, has become a reference for the numerical processing and statistical analysis of data coming from high-throughput biological assays, providing a rich selection of methods and algorithms to the research community. At the same time, Python has matured as a rich and reliable language for the agile development of prototypes or final implementations, as well as for handling large data sets.Results: The data structures and functions from Bioconductor can be exposed to Python as a regular library. This allows a fully transparent and native use of Bioconductor from Python, without one having to know the R language and with only a small community of translators required to know both. To demonstrate this, we have implemented such Python representations for key infrastructure packages in Bioconductor, letting a Python programmer handle annotation data, microarray data, and next-generation sequencing data.Conclusions: Bioconductor is now not solely reserved to R users. Building a Python application using Bioconductor functionality can be done just like if Bioconductor was a Python package. Moreover, similar principles can be applied to other languages and libraries. Our Python package is available at: http://pypi.python.org/pypi/rpy2-bioconductor-extensions/. © 2010 Gautier; licensee BioMed Central Ltd.

Rothausen B.W.,Technical University of Denmark
Public health nutrition | Year: 2012

To compare differences in children's diet quality on weekdays (Monday-Thursday), Fridays and weekend days. A representative cross-sectional study in which participants completed a 7 d pre-coded food record. Mean intakes of energy, macronutrients and selected food items (g/10 MJ) as well as energy density were compared between weekdays, Fridays and weekend days for each gender in three age groups (4-6, 7-10 and 11-14 years) using Tobit analysis to account for zero intakes. The Danish National Survey of Dietary Habits and Physical Activity 2003-2008. Children (n 784; 49·9 % boys) aged 4-14 years. For both genders in all age groups (P < 0·05), energy intake was higher during weekends than on weekdays, and intakes of sugar-sweetened beverages and white bread were higher, whereas intake of rye bread was lower. This contributed to a higher percentage of energy from added sugars, a lower fibre content and a higher energy density on weekend days v. weekdays. In children aged 4-6 and 7-10 years, the diet on weekend days was also characterized by higher intakes of sweets and chocolate and lower intakes of fruit and vegetables. Overall, the diet on Fridays appeared as a mix of the diets on weekdays and weekend days. Significant differences and distinct characteristic patterns were found in children's diet quality during weekdays, Fridays and weekend days. The present study suggests that in prevention of childhood overweight and obesity, more attention should be paid to the higher energy intake, especially from sugar-rich foods and beverages, on Fridays and weekend days.

Jensen J.S.,Technical University of Denmark
Structural and Multidisciplinary Optimization | Year: 2011

This paper considers the design of nonlinear photonic devices. The nonlinearity stems from a nonlinear material model with a permittivity that depends on the local time-averaged intensity of the electric field. A finite element model is developed for time-harmonic wave propagation and an incremental complex Newton-Raphson scheme is used to solve the nonlinear equations. The sensitivities of the objective function with respect to element-wise design variables are found using an adjoint approach and iterative design updates are performed using the method of moving asymptotes. The optimization procedure is exemplified by the design of two nonlinear devices. A one-dimensional optical diode is created by distributing a linear and a nonlinear material. The diode allows for higher transmission in one propagation direction compared to the other. The second example illustrates a two-dimensional optical limiter. Here, air, a linear and a nonlinear material are distributed so that the wave transmission displays a strong sensitivity to the amplitude of the incoming wave. © 2011 Springer-Verlag.

Skov C.,Technical University of Denmark
Biology letters | Year: 2013

The importance of predation risk in shaping patterns of animal migration is not well studied, mostly owing to difficulties in accurately quantifying predation risk for migratory versus resident individuals. Here, we present data from an extensive field study, which shows that migration in a freshwater fish (roach, Rutilus rutilus) that commonly migrates from lakes to streams during winter confers a significant survival benefit with respect to bird (cormorant, Phalacrocorax carbo spp.) predation. We tagged over 2000 individual fish in two Scandinavian lakes over 4 years and monitored migratory behaviour using passive telemetry. Next, we calculated the predation vulnerability of fish with differing migration strategies, by recovering data from passive integrated transponder tags of fish eaten by cormorants at communal roosts close to the lakes. We show that fish can reduce their predation risk from cormorants by migrating into streams, and that probability of being preyed upon by cormorants is positively related to the time individuals spend in the lake during winter. Our data add to the growing body of evidence that highlights the importance of predation for migratory dynamics, and, to our knowledge, is one of the first studies to directly quantify a predator avoidance benefit to migrants in the field.

Rokni M.,Technical University of Denmark
Energy Conversion and Management | Year: 2010

Hybrid systems consisting of solid oxide fuel cells (SOFC) on the top of a steam turbine (ST) are investigated. The plants are fired by natural gas (NG). A desulfurization reactor removes the sulfur content in the fuel while a pre-reformer breaks down the heavier hydro-carbons. The pre-treated fuel enters then into the anode side of the SOFC. The remaining fuels after the SOFC stacks enter a burner for further burning. The off-gases are then used to produce steam for a Rankine cycle in a heat recovery steam generator (HRSG). Different system setups are suggested. Cyclic efficiencies up to 67% are achieved which is considerably higher than the conventional combined cycles (CC). Both adiabatic steam reformer (ASR) and catalytic partial oxidation (CPO) fuel pre-reformer reactors are considered in this investigation. © 2010 Elsevier Ltd. All rights reserved.

Zvingilaite E.,Technical University of Denmark
Applied Energy | Year: 2011

This paper discusses methodology of energy system modelling when reduction of local externalities, such as damage to the human health from energy production-related air pollution, is in focus. Ideally, the local energy externalities should be analysed by adopting the impact pathway approach of ExternE study, and following the pollutants from their release to the personal uptake and resulting health effects. This would require inclusion of air pollution modelling and monetary valuation of the impacts into an energy system optimisation process. However, this approach involves a complex study and generalisations are needed. The way local externalities are included in the existing energy system models is identified and discussed in the paper. Only a few studies include localisation aspects when internalising local externalities in an energy system optimisation. The performed analysis of the Danish heat and power sector verifies that it is cheaper for the society to include externalities in the planning of an energy system than to pay for the resulting damages later. Total health costs decrease by around 18% and total system costs decrease by nearly 4% when health externalities are included in the optimisation. Furthermore, including localisation aspects can reduce health costs of the heat and power sector in Denmark by additional 7%. © 2010 Elsevier Ltd.

Hou X.,Technical University of Denmark
Applied Microbiology and Biotechnology | Year: 2012

A cost-effective conversion of lignocellulosic biomass into bioethanol requires that the xylose released from the hemicellulose fraction (20-40% of biomass) can be fermented. Baker's yeast, Saccharomyces cerevisiae, efficiently ferments glucose but it lacks the ability to ferment xylose. Xylose-fermenting yeast such as Pichia stipitis requires accurately controlled microaerophilic conditions during the xylose fermentation, rendering the process technically difficult and expensive. In this study, it is demonstrated that under anaerobic conditions Spathaspora passalidarum showed high ethanol production yield, fast cell growth, and rapid sugar consumption with xylose being consumed after glucose depletion, while P. stipitis was almost unable to utilize xylose under these conditions. It is further demonstrated that for S. passalidarum, the xylose conversion takes place by means of NADH-preferred xylose reductase (XR) and NAD+-dependent xylitol dehydrogenase (XDH). Thus, the capacity of S. passalidarum to utilize xylose under anaerobic conditions is possibly due to the balance between the cofactor's supply and demand through this XR-XDH pathway. Only few XRs with NADH preference have been reported so far. 2-Deoxy glucose completely inhibited the conversion of xylose by S. passalidarum under anaerobic conditions, but only partially did that under aerobic conditions. Thus, xylose uptake by S. passalidarum may be carried out by different xylose transport systems under anaerobic and aerobic conditions. The presence of glucose also repressed the enzymatic activity of XR and XDH from S. passalidarum as well as the activities of those enzymes from P. stipitis. © 2011 Springer-Verlag.

Kim O.S.,Technical University of Denmark
IEEE Transactions on Antennas and Propagation | Year: 2012

Theoretically, the minimum radiation quality factor Q of an isolated resonance can be achieved in a spherical electrically small antenna by combining TM 1m and TE 1m spherical modes, provided that the stored energy in the antenna spherical volume is totally suppressed. Using closed-form expressions for the stored energies obtained through the vector spherical wave theory, it is shown that a magnetic-coated metal core reduces the internal stored energy of both TM 1m and TE 1m modes simultaneously, so that a self-resonant antenna with the Q approaching the fundamental minimum is created. Numerical results for a multiarm spherical helix antenna confirm the theoretical predictions. For example, a 4-arm spherical helix antenna with a magnetic-coated perfectly electrically conducting core (ka=0.254)exhibits the Q of 0.66 times the Chu lower bound, or 1.25 times the minimum Q. © 1963-2012 IEEE.

A novel hybrid power system (~10kW) for an average family home is proposed. The system investigated contains a solid oxide fuel cell (SOFC) on top of a Stirling engine. The off-gases produced in the SOFC cycle are fed to a bottoming Stirling engine, at which additional power is generated. Simulations of the proposed system were conducted using different fuels, which should facilitate the use of a variety of fuels depending on availability. Here, the results for natural gas (NG), ammonia, di-methyl ether (DME), methanol and ethanol are presented and analyzed. The system behavior is further investigated by comparing the effects of key factors, such as the utilization factor and the operating conditions under which these fuels are used. Moreover, the effect of using a methanator on the plant efficiency is also studied. The combined system improves the overall electrical efficiency relative to that of a stand-alone Stirling engine or SOFC plant. For the combined SOFC and Stirling configuration, the overall power production was increased by approximately 10% compared to that of a stand-alone SOFC plant. System efficiencies of approximately 60% are achieved, which is remarkable for such small plant sizes. Additionally, heat is also produced to heat the family home when necessary. © 2013 Elsevier Ltd.

Santos A.,Novo Nordisk AS | Wernersson R.,Technical University of Denmark | Jensen L.J.,Novo Nordisk AS
Nucleic Acids Research | Year: 2015

The eukaryotic cell division cycle is a highly regulated process that consists of a complex series of events and involves thousands of proteins. Researchers have studied the regulation of the cell cycle in several organisms, employing a wide range of high-throughput technologies, such as microarraybased mRNA expression profiling and quantitative proteomics. Due to its complexity, the cell cycle can also fail or otherwise change in many different ways if important genes are knocked out, which has been studied in several microscopy-based knockdown screens. The data from these many large-scale efforts are not easily accessed, analyzed and combined due to their inherent heterogeneity. To address this, we have created Cyclebase-available at http://www.cyclebase.org-an online database that allows users to easily visualize and download results from genome-wide cell-cycle-related experiments. In Cyclebase version 3.0, we have updated the content of the database to reflect changes to genome annotation, added new mRNA and protein expression data, and integrated cell-cycle phenotype information from high-content screens and modelorganism databases. The new version of Cyclebase also features a new web interface, designed around an overview figure that summarizes all the cell-cyclerelated data for a gene. © The Author(s) 2014.

Bellomare F.,University of Padua | Rokni M.,Technical University of Denmark
Renewable Energy | Year: 2013

An interesting source of producing energy with low pollutants emission and reduced environmental impact are the biomasses; particularly using Municipal Solid Waste (MSW) as fuel, can be a competitive solution not only to produce energy with negligible costs but also to decrease the storage in landfills. A Municipal Solid Waste Gasification Plant Integrated with Solid Oxide Fuel Cell (SOFC) and Gas Turbine (GT) has been studied and the plant is called IGSG (Integrated Gasification SOFC and GT). Gasification plant is fed by MSW to produce syngas by which the anode side of an SOFC is fed wherein it reacts with air and produces electricity. The exhausted gases out of the SOFC enter a burner for further fuel combusting and finally the off-gases are sent to a gas turbine to produce additional electricity. Different plant configurations have been studied and the best one found to be a regenerative gas turbine. Under optimized condition, the thermodynamic efficiency of 52% is achieved. Variations of the most critical parameters have been studied and analyzed to evaluate plant features and find out an optimized configuration. © 2013 Elsevier Ltd.

Tabatabaeipour S.M.,Technical University of Denmark | Bak T.,University of Aalborg
Journal of the Franklin Institute | Year: 2014

In this paper a new integrated observer-based fault estimation and accommodation strategy for discrete-time piecewise linear (PWL) systems subject to actuator faults is proposed. A robust estimator is designed to simultaneously estimate the state of the system and the actuator fault. Then, the estimate of fault is used to compensate for the effect of the fault. By using the estimate of fault and the states, a fault tolerant controller using a PWL state feedback is designed. The observer-based fault-tolerant controller is obtained by the interconnection of the estimator and the state feedback controller. We show that separate design of the state feedback and the estimator results in the stability of the overall closed-loop system. In addition, the input-to-state stability (ISS) gain for the closed-loop system is obtained and a procedure for minimizing it is given. All of the design conditions are formulated in terms of linear matrix inequalities (LMI) which can be solved efficiently. Also, performance of the estimator and the state feedback controller are minimized by solving convex optimization problems. The efficiency of the method is demonstrated by means of a numerical example. © 2013 The Franklin Institute. Published by Elsevier Ltd. All rights reserved.

Mosegaard K.,Technical University of Denmark
Geophysics | Year: 2011

On 6 December 2009, the distinguished Spanish-French physicist and geoscientist, Albert Tarantola, passed away at the age of 60. Born in Barcelona in 1949, he went to Paris where he lived most of his life, and worked as a professor at Institut de Physique du Globe de Paris. His extensive scientific production and remarkable achievements in inverse problem theory and geophysical data analysis established him as one of the most influential mathematical geoscientists of our time. He became the father of probabilistic inverse theory, a theory that he passionately defended against severe criticism and managed to propagate to a major part of the geophysical community. Another major achievement was his contributions to the theory of seismic waveform inversion_a work that right now is unfolding its potential in large-scale computations. Albert's contributions were not limited to geoscience. He started his career in astrophysics, and later in his life he wrote several papers and books on physics and probability, including new formulations of fluid dynamics, elasticity theory, global positioning, and scientific inference. Albert possessed a unique combination of exceptional skills and remarkable mental energy. He was a veritable powerhouse with an unusual work ethic, and his passion for science will remain an ideal for all those who worked with him. © 2011 Society of Exploration Geophysicists.

Sigmund O.,Technical University of Denmark | Maute K.,University of Colorado at Boulder
Structural and Multidisciplinary Optimization | Year: 2013

Topology optimization has undergone a tremendous development since its introduction in the seminal paper by Bendsøe and Kikuchi in 1988. By now, the concept is developing in many different directions, including "density", "level set", "topological derivative", "phase field", "evolutionary" and several others. The paper gives an overview, comparison and critical review of the different approaches, their strengths, weaknesses, similarities and dissimilarities and suggests guidelines for future research. © 2013 Springer-Verlag Berlin Heidelberg.

Sigmund O.,Technical University of Denmark
Structural and Multidisciplinary Optimization | Year: 2011

Topology optimization is a highly developed tool for structural design and is by now being extensively used in mechanical, automotive and aerospace industries throughout the world. Gradient-based topology optimization algorithms may efficiently solve fine-resolution problems with thousands and up to millions of design variables using a few hundred (finite element) function evaluations (and even less than 50 in some commercial codes). Nevertheless, non-gradient topology optimization approaches that require orders of magnitude more function evaluations for extremely low resolution examples keep appearing in the literature. This forum article discusses the practical and scientific relevance of publishing papers that use immense computational resources for solving simple problems for which there already exist efficient solution techniques. © 2011 Springer-Verlag.

Kiil S.,Technical University of Denmark
Journal of Coatings Technology Research | Year: 2010

The mechanisms of simultaneous solvent evaporation and film formation in high-solids thermoset coatings are considered. The relevant phenomena, chemical reactions, solvent diffusion and evaporation, gelation, vitrification, network mobility restrictions, and crosslinking, are quantified and a mathematical model for a curing film is presented, which does not violate the local volume balance. For model verification, a previous investigation with a polyisocyanate and a polyol in methyl amyl ketone solvent, catalyzed by an organotin compound, was selected. In contrast to earlier modelling studies, simulations can match and explain detailed experimental data. For exemplification, simulations are used to analyse the influence of the various rate phenomena on the behavior of the solvent-based polyisocyanate/polyol film. © 2010 FSCT and OCCA.

Kim O.S.,Technical University of Denmark
IEEE Transactions on Antennas and Propagation | Year: 2012

The radiation properties of spherical electric dipole antennas with electric current excitation and material-coated perfectly electrically conducting (PEC) cores are investigated analytically using vector spherical wave functions. Closed-form expressions for electric and magnetic stored energy as well as the radiation quality factor Q are derived. Using these, it is shown that properly selected magnetic coating and radius of the PEC core vastly reduce the internal stored energy, and thus make the Q of an electric dipole antenna approach the Chu lower bound. © 2006 IEEE.

Kusano Y.,Technical University of Denmark
Journal of Adhesion | Year: 2014

Atmospheric pressure plasma processing has attracted significant interests over decades due to its usefulness and a variety of applications. Adhesion improvement of polymer surfaces is among the most important applications of atmospheric pressure plasma treatment. Reflecting recent significant development of the atmospheric pressure plasma processing, this work presents its fundamental aspects, applications, and characterization techniques relevant to adhesion. © 2014 Copyright Taylor & Francis Group, LLC.

Langer S.,IVL Svenska Miljoinstitutet AB | Beko G.,Technical University of Denmark
Building and Environment | Year: 2013

Data from a recent Swedish survey on the status of the housing stock and indoor air quality were placed in the public domain by the Swedish National Board of Housing, Building and Planning in 2011. The available parameters included the year of construction, dwelling location, type of ventilation system, temperature, relative humidity, air exchange rate (AER), and concentrations of nitrogen dioxide (NO2), formaldehyde and Total Volatile Organic Compounds (TVOC) from 157 single-family houses and 148 apartments. The median AER was lower in the single-family houses than in apartments (0.33h-1 vs. 0.47h-1). The majority of houses (80%) did not comply with the building code that requires 0.5 air changes per hour. The median concentrations in single-family houses and apartments were 6.0 and 10μg/m3, respectively, for NO2, 22 and 13μg/m3 for formaldehyde, and 236 and 143μg/m3 for TVOC. All of these differences between single-family houses and apartments were statistically significant. The median values for AER and the median values for the concentrations of NO2, formaldehyde and TVOC were similar to those found in other Scandinavian studies. Multivariate linear regression models revealed that air exchange rate was a significant predictor of the concentrations of all three indoor pollutants. While ventilation seemed to be a source of NO2, increased ventilation rate appeared to decrease the indoor concentrations of formaldehyde and TVOC. © 2013 Elsevier Ltd.

Sumer B.M.,Technical University of Denmark
Journal of Hydraulic Research | Year: 2014

Flow-structure-seabed interaction in coastal and marine environments is a rapidly growing area of research and applications. In this vision paper, this area is discussed with a view of identifying its state of the art and current research challenges. The discussion draws attention to key issues related to structures such as marine pipelines, offshore windfarms, and multiuse offshore platforms. Tsunamis, which received considerable attention after two recent extreme events (2004 Indonesia tsunami and 2011 Japan tsunami) are also included in the discussion. Marine hydro-geomechanics is highlighted, among other areas, as an emerging branch of Marine Civil Engineering. Predictions of the field development for the forthcoming years are also briefly outlined. © 2014 International Association for Hydro-Environment Engineering and Research.

Jiang H.,Woods Hole Oceanographic Institution | Kiorboe T.,Technical University of Denmark
Journal of the Royal Society Interface | Year: 2011

Copepods swim either continuously by vibrating their feeding appendages or erratically by repeatedly beating their swimming legs, resulting in a series of small jumps. The two swimming modes generate different hydrodynamic disturbances and therefore expose the swimmers differently to rheotactic predators. We developed an impulsive stresslet model to quantify the jump-imposed flow disturbance. The predicted flow consists of two counter-rotating viscous vortex rings of similar intensity, one in the wake and one around the body of the copepod. We showed that the entire jumping flow is spatially limited and temporally ephemeral owing to jump-impulsiveness and viscous decay. In contrast, continuous steady swimming generates two well-extended long-lasting momentum jets both in front of and behind the swimmer, as suggested by the well-known steady stresslet model. Based on the observed jump-swimming kinematics of a small copepod Oithona davisae, we further showed that jump-swimming produces a hydrodynamic disturbance with much smaller spatial extension and shorter temporal duration than that produced by a same-size copepod cruising steadily at the same average translating velocity. Hence, small copepods in jump-swimming are in general much less detectable by rheotactic predators. The present impulsive stresslet model improves a previously published impulsive Stokeslet model that applies only to the wake vortex. © 2011 The Royal Society.

Diaz A.R.,Michigan State University | Sigmund O.,Technical University of Denmark
Structural and Multidisciplinary Optimization | Year: 2010

A methodology based on topology optimization for the design of metamaterials with negative permeability is presented. The formulation is based on the design of a thin layer of copper printed on a dielectric, rectangular plate of fixed dimensions. An effective media theory is used to estimate the effective permeability, obtained after solving Maxwell's equations on a representative cell of a periodic arrangement using a full 3D finite element model. The effective permeability depends on the layout of copper, and the subject of the topology optimization problem is to find layouts that result in negative (real) permeability at a prescribed frequency. A SIMP-like model is invoked to represent the conductivity of regions of intermediate density. A number of different filtering strategies are invoked to facilitate convergence to binary solutions. Examples of designs for S-band applications are presented for illustration. New metamaterial concepts are uncovered, beyond the classical split-ring inspired layouts. Copyright © 2009 Springer-Verlag.

Carlquist M.,Technical University of Denmark
Microbial cell factories | Year: 2012

Traditionally average values of the whole population are considered when analysing microbial cell cultivations. However, a typical microbial population in a bioreactor is heterogeneous in most phenotypes measurable at a single-cell level. There are indications that such heterogeneity may be unfavourable on the one hand (reduces yields and productivities), but also beneficial on the other hand (facilitates quick adaptation to new conditions--i.e. increases the robustness of the fermentation process). Understanding and control of microbial population heterogeneity is thus of major importance for improving microbial cell factory processes. In this work, a dual reporter system was developed and applied to map growth and cell fitness heterogeneities within budding yeast populations during aerobic cultivation in well-mixed bioreactors. The reporter strain, which was based on the expression of green fluorescent protein (GFP) under the control of the ribosomal protein RPL22a promoter, made it possible to distinguish cell growth phases by the level of fluorescence intensity. Furthermore, by exploiting the strong correlation of intracellular GFP level and cell membrane integrity it was possible to distinguish subpopulations with high and low cell membrane robustness and hence ability to withstand freeze-thaw stress. A strong inverse correlation between growth and cell membrane robustness was observed, which further supports the hypothesis that cellular resources are limited and need to be distributed as a trade-off between two functions: growth and robustness. In addition, the trade-off was shown to vary within the population, and the occurrence of two distinct subpopulations shifting between these two antagonistic modes of cell operation could be distinguished. The reporter strain enabled mapping of population heterogeneities in growth and cell membrane robustness towards freeze-thaw stress at different phases of cell cultivation. The described reporter system is a valuable tool for understanding the effect of environmental conditions on population heterogeneity of microbial cells and thereby to understand cell responses during industrial process-like conditions. It may be applied to identify more robust subpopulations, and for developing novel strategies for strain improvement and process design for more effective bioprocessing.

Jensen J.A.,Technical University of Denmark
IEEE International Ultrasonics Symposium, IUS | Year: 2013

A method for making Vector Flow Images using the transverse oscillation (TO) approach on a convex array is presented. The paper presents optimization schemes for TO fields for convex probes and evaluates their performance using Field II simulations and measurements using the SARUS experimental scanner. A 3 MHz 192 elements convex array probe (pitch 0.33 mm) is used in both simulations and measurements. An F-number of 5 is used in transmit and two 32 element wide peaks are used in receive separated by 96 elements between peaks. Parabolic velocity profiles are simulated at beam-to-flow angles from 90 to 45 degrees in steps of 15 degrees. The optimization routine changes the lateral oscillation period λx to yield the best possible estimates based on the energy ratio between positive and negative spatial frequencies in the ultrasound field. The basic equation for λx gives 1.14 mm at 40 mm, and 1.51 mm from the simulated point spread function. This results in a bias of 35% as λx directly scales the estimated velocities. Optimizing the focusing yields a λx of 1.61 mm. The energy ratio is reduced from -12.8 dB to -20.1 dB and the spectral bandwidth from 115.1 m-1 to 96.5 m-1. λx is maintained between 1.47 and 1.70 mm from 25 mm to 70 mm and is increased to 2.8 mm at a depth of 100 mm. Parabolic profiles are estimated using 16 emissions. The optimization gives a reduction in std. from 8.5% to 5.9% with a reduction in bias from 35% to 1.02% at 90 degrees (transverse flow) at a depth of 40 mm. Measurements have been made using the SARUS experimental ultrasound scanner and a BK Medical 8820e convex array transducer. Sixty-four elements was used in transmit and 2 × 32 elements in receive for creating a color flow map image of a flow rig phantom with a laminar, parabolic flow. At 75 degrees a bias of less than 1% was obtained. © 2013 IEEE.

Broberg O.,Technical University of Denmark
International Journal of Technology Management | Year: 2010

The Danish workspace design (WSD) research program is aimed to develop and trial a potential new concept for ergonomists and other workplace consultants who are to engage in socio-technical design processes. The objective of this paper is to report on the trial of the workspace design concept in a case involving the design and implementation of a new mixing technology in an industrial plant. The case showed how the WSD concept can contribute to an engineering design process. The WSD team took the role as workspace designer and by the participatory workshops achieved an impact on the technology project. In the role as workspace designer, it was important for the WSD team to make sure that the achievements in the workshops were 'transmitted' to and susTWNned in the ordinary engineering design process. In this case, it turned out that the artefacts such as a layout game board and documents with compilations of ideas and requirements from use scenarios served as appropriate transmitter devices or inscriptions. Copyright © 2010 Inderscience Enterprises Ltd.

Here, we document microbial communities in rapid gravity filtration units, specifically serial rapid sand filters (RSFs), termed prefilters (PFs) and after- filters (AFs), fed with anoxic groundwaters low in organic carbon to prepare potable waters. A comprehensive 16S rRNA-based amplicon sequencing survey revealed a core RSF microbiome comprising few bacterial taxa (29–30 genera) dominated by Nitrospirae, Proteobacteria and Acidobacteria, with a strikingly high abundance (75–87±18%) across five examined waterworks in Denmark. Lineages within the Nitrospira genus consistently comprised the second most and most abundant fraction in PFs (27±23%) and AFs (45.2±23%), respectively, and were far more abundant than typical proteobacterial ammonium-oxidizing bacteria, suggesting a physiology beyond nitrite oxidation for Nitrospira. Within the core taxa, sequences closely related to types with ability to oxidize ammonium, nitrite, iron, manganese and methane as primary growth substrate were identified and dominated in both PFs (73.6±6%) and AFs (61.4±21%), suggesting their functional importance. Surprisingly, operational taxonomic unit richness correlated strongly and positively with sampling location in the drinking water treatment plant (from PFs to AFs), and a weaker negative correlation held for evenness. Significant spatial heterogeneity in microbial community composition was detected in both PFs and AFs, and was higher in the AFs. This is the first comprehensive documentation of microbial community diversity in RSFs treating oligotrophic groundwaters. We have identified patterns of local spatial heterogeneity and dispersal, documented surprising energy–diversity relationships, observed a large and diverse Nitrospira fraction and established a core RSF microbiome. © 2016 International Society for Microbial Ecology

Mean outcrossing rates can be used as a basis for decision support for ships in severe sea. The article describes a procedure for calculating the mean outcrossing rate of non-Gaussian processes with stochastic input parameters. The procedure is based on the first-order reliability method (FORM) and stochastic parameters are incorporated by carrying out a number of FORM calculations corresponding to combinations of specific values of the stochastic parameters. Subsequently, the individual FORM calculation is weighted according to the joint probability with which the specific combination of parameter values is expected to occur, and the final result, the mean outcrossing rate, is obtained by summation. The derived procedure is illustrated by an example considering the forces in containers stowed on ships and, in particular, results are presented for the so-called racking failure in the containers. The results of the procedure are compared with brute force simulations obtained by Monte Carlo simulation (MCS) and good agreement is observed. Importantly, the procedure requires significantly less CPU time compared to MCS to produce mean outcrossing rates. © 2009 Elsevier Ltd. All rights reserved.

Kepp K.P.,Technical University of Denmark
Journal of Inorganic Biochemistry | Year: 2012

Metallothioneins (MT) are small, metal-binding proteins with diverse functions related to metal ion homeostasis. This paper presents the full 384-388-atom structures of the two native Zn(II)- and the Cd(II)-containing domains of human MT2, optimized with density functional theory. The presented structures are accurate to ~ 0.03 Å for bond lengths and thus provide new physical insight into the detailed electronic structures of MTs, in particular with accurate accounts of bridging vs. terminal bonds not available from NMR or EXAFS. The MT protein enhances the asymmetry, as compared to the protein-free clusters, causing a hierarchy in binding that most likely allows MTs to transfer ions to multiple targets in vivo. The protein polarization is substantial and occurs primarily via the terminal sulfurs, a key mechanism in providing domain-specific electronic structures. The β-domain polarizes its smaller cluster less on average, due to its less polarizable, higher negative charge density, as reflected in longer MS bond lengths and smaller bond orders. This may explain why MT2β is more reactive and dynamic and why MTs have evolved two different-size, asymmetric domains with different metal binding affinities fit for different molecular targets of metal ion transfer. © 2011 Elsevier Inc. All rights reserved.

Stromann-Andersen J.,Technical University of Denmark | Sattrup P.A.,k-Technology
Energy and Buildings | Year: 2011

The link between urban density and building energy use is a complex balance between climatic factors and the spatial, material and use patterns of urban spaces and the buildings that constitute them. This study uses the concept of the urban canyon to investigate the ways that the energy performance of low-energy buildings in a north-European setting is affected by their context. This study uses a comprehensive suite of climate-based dynamic thermal and daylight simulations to describe how these primary factors in the passive energy properties of buildings are affected by increases in urban density. It was found that the geometry of urban canyons has an impact on total energy consumption in the range of up to +30% for offices and +19% for housing, which shows that the geometry of urban canyons is a key factor in energy use in buildings. It was demonstrated how the reflectivity of urban canyons plays an important, previously underestimated role, which needs to be taken into account when designing low-energy buildings in dense cities. Energy optimization of urban and building design requires a detailed understanding of the complex interplay between the temporal and spatial phenomena taking place, merging qualitative and quantitative considerations. © 2011 Elsevier B.V. All rights reserved.

Haglind F.,Technical University of Denmark
Applied Thermal Engineering | Year: 2011

The part-load performance of combined cycles intended for naval use is of great importance, and it is influenced by the gas turbine configuration and load control strategy. This paper is aimed at quantifying the effects of variable geometry gas turbines on the part-load efficiency for combined cycles used for ship propulsion. Moreover, the paper is aimed at developing methodologies and deriving models for part-load simulations suitable for energy system analysis of various components within combined cycle power plants. Two different gas turbine configurations are studied, a two-shaft aero-derivative configuration and a single-shaft industrial configuration. The results suggest that by the use of variable geometry gas turbines, the combined cycle part-load performance can be improved. In order to minimise the voyage fuel consumption, a combined cycle featuring two-shaft gas turbines with VAN control is a promising alternative for container ships, while a cycle with single-shaft gas turbine configurations with VGV control is indicated to be an equally good choice for tankers and carriers. © 2010 Elsevier Ltd. All rights reserved.

Jensen J.J.,Technical University of Denmark
Probabilistic Engineering Mechanics | Year: 2011

In the analysis of structures subjected to stationary stochastic load processes the mean out-crossing rate plays an important role as it can be used to determine the extreme value distribution of any response, usually assuming that the sequence of mean out-crossings can be modelled as a Poisson process. The mean out-crossing rate of a response level r can be expressed in terms of the reliability index, which for linear systems is r divided by the standard deviation of the response in question. For non-linear processes the reliability index depends non-linearly on r and a good estimate can be found using the First Order Reliability Method (FORM). The FORM analysis also shows that the reliability index is strictly inversely proportional to the square root of the magnitude of the load spectrum, irrespectively of the non-linearity in the system. However, the FORM analysis only gives an approximation to the mean out-crossing rate. Better accuracy can be obtained by Monte Carlo simulations, but the necessary length of the time domain simulations for very low out-crossing rates might be prohibitively long. In such cases the property mentioned above for the FORM reliability index might be assumed to be valid in the Monte Carlo simulations, making it possible to increase the out-crossing rates and thus reduce the necessary length of the time domain simulations by applying a larger load spectrum than relevant from a design point of view. The mean out-crossing rate thus obtained can then afterwards be scaled down to its actual value. In the present paper the usefulness of this approach is investigated, considering problems related to wave loads on marine structures. Here the load scale parameter is conveniently taken as the square of the significant wave height. © 2010 Elsevier Ltd. All rights reserved.

We have tested the performance of statistical extrapolation methods in predicting the extreme response of a multi-megawatt wind turbine generator. We have applied the peaks-over-threshold, block maxima and average conditional exceedance rates (ACER) methods for peaks extraction, combined with four extrapolation techniques: The Weibull, Gumbel and Pareto distributions and a double-exponential asymptotic extreme value function based on the ACER method. For the successful implementation of a fully automated extrapolation process, we have developed a procedure for automatic identification of tail threshold levels, based on the assumption that the response tail is asymptotically Gumbel distributed. Example analyses were carried out, aimed at comparing the different methods, analysing the statistical uncertainties and identifying the factors, which are critical to the accuracy and reliability of the extrapolation. The present paper describes the modelling procedures and makes a comparison of extrapolation methods based on the results from the example calculations. Copyright © 2015 John Wiley & Sons, Ltd.

A mathematical model, describing coating degradation mechanisms of thermoset coatings exposed to ultraviolet radiation and humidity at constant temperature, was extended to simulate the behavior of a coating with a low glass transition temperature. The effects of adding light stabilizers (a UV absorber and a radical scavenger) to the coating were also explored. The extended model includes photoinitiated oxidation reactions, intrafilm oxygen permeability, water absorption and diffusion, reduction of crosslink density, absorption of ultraviolet radiation, a radical scavenger reaction, and simulates the transient development of an oxidation zone. Simulations are in good agreement with experimental data for a fast degrading epoxy-amine coating with a glass transition temperature of -50 °C. It was found that the degradation rate of the non-stabilized coating was influenced significantly by the diffusion rate of oxygen in the oxidation zone, whereas light absorption by the photoproducts formed was only a secondary effect. On the other hand, the degradation rate of the stabilized coating was mainly influenced by the light absorption capability of the coating and in this case there was no oxygen diffusion resistance. Finally, simulations showed that the rate constants of the photoinitiating and oxidation reactions, taking place within the epoxy-amine family of coatings, are strong functions of the specific crosslinker used and must be estimated, in each case, by calibration of the model against adequate experimental data series. © 2013 Elsevier B.V. All rights reserved.

Melikov A.K.,Technical University of Denmark | Kaczmarczyk J.,Silesian University of Technology
Building and Environment | Year: 2012

The impact of air movement on perceived air quality (PAQ) and sick building syndrome (SBS) symptoms was studied. In total, 124 human subjects participated in four series of experiments performed in climate chambers at different combinations of room air temperature (20, 23, 26 and 28 °C), relative humidity (30, 40 and 70%) and pollution level (low and high). Most of the experiments were performed with and without facially applied airflow at elevated velocity. The importance of the use of recirculated room air and clean, cool and dry outdoor air was studied. The exposures ranged from 60. min to 235. min. Acceptability of PAQ and freshness of the air improved when air movement was applied. The elevated air movement diminished the negative impact of increased air temperature, relative humidity and pollution level on PAQ. The degree of improvement depended on the pollution level, the temperature and the humidity of the room air. At a low humidity level of 30% an increased velocity could compensate for the decrease in perceived air quality due to an elevated temperature ranging from 20 °C to 26 °C. In a room with 26 °C, increased air movement was also able to compensate for an increase in humidity from 30% to 60%, but not to 70%. The elevated velocity of recirculated polluted room air did not decrease the intensity of SBS symptoms, but movement of clean, cool and dry air did so. Energy-saving strategy of improving occupants' comfort in rooms by moving room air at high velocity and maintaining room temperature high at reduced supply of outdoor air or by a decrease of indoor air enthalpy should be cautiously implemented in buildings because the pollution level may still cause negative health effects. © 2011 Elsevier Ltd.

Bruus H.,Technical University of Denmark
Lab on a Chip - Miniaturisation for Chemistry and Biology | Year: 2012

In this paper, Part 7 of the thematic tutorial series "Acoustofluidics - exploiting ultrasonic standing waves, forces and acoustic streaming in microfluidic systems for cell and particle manipulation ", we present the theory of the acoustic radiation force; a second-order, time-averaged effect responsible for the acoustophoretic motion of suspended, micrometre-sized particles in an ultrasound field. © 2012 The Royal Society of Chemistry.

Kutter J.P.,Technical University of Denmark
Journal of Chromatography A | Year: 2012

Over the past twenty years, the field of microfluidics has emerged providing one of the main enabling technologies to realize miniaturized chemical analysis systems, often referred to as micro-Total Analysis Systems (uTAS), or, more generally, Lab-on-a-Chip Systems (LOC) [1,2]. While microfluidics was driven forward a lot from the engineering side, especially with respect to ink jet and dispensing technology, the initial push and interest from the analytical chemistry community was through the desire to develop miniaturized sensors, detectors, and, very early on, separation systems. The initial almost explosive development of, in particular, chromatographic separation systems on microchips, has, however, slowed down in recent years. This review takes a closer, critical look at how liquid phase chromatography has been implemented in miniaturized formats over the past several years, what is important to keep in mind when developing or working with separations in a miniaturized format, and what challenges and pitfalls remain. © 2011 Elsevier B.V.

Jeong C.-H.,Technical University of Denmark
Journal of the Acoustical Society of America | Year: 2010

Measured absorption coefficients in reverberation chambers often differ from theoretical random incidence absorption coefficients, because ideal assumptions for the theoretical random incidence absorption coefficient are not fulfilled during measurements in actual reverberation chambers. Therefore sound intensity distributions on absorber under measurement conditions have been simulated using a phased beam tracing, and used as correction functions for reducing discrepancies between the measured and theoretical absorption coefficients. Two reverberation rooms were investigated by assuming that a test specimen was attached to a vertical surface and the floor. The frequency-dependent sound intensity distributions on absorbers were found to be affected by the reverberation chamber geometry and dimensions, the absorption capability of the specimen, and the placement of the specimen. High frequency intensity distributions above 1 kHz were similar for all studied cases, but some variations in low frequency intensity distributions were observed. If the non-uniform intensity distribution and a finite size effect are taken into account for correcting the theoretical absorption coefficients, a good agreement is found between corrected and measured statistical absorption coefficients. The non-uniform sound intensity can account for the discrepancy at high frequencies. © 2010 Acoustical Society of America.

Li R.,University of California at Berkeley | Wu Q.,Technical University of Denmark | Oren S.S.,University of California at Berkeley
IEEE Transactions on Power Systems | Year: 2014

This paper presents an integrated distribution locational marginal pricing (DLMP) method designed to alleviate congestion induced by electric vehicle (EV) loads in future power systems. In the proposed approach, the distribution system operator (DSO) determines distribution locational marginal prices (DLMPs) by solving the social welfare optimization of the electric distribution system which considers EV aggregators as price takers in the local DSO market and demand price elasticity. Nonlinear optimization has been used to solve the social welfare optimization problem in order to obtain the DLMPs. The efficacy of the proposed approach was demonstrated by using the bus 4 distribution system of the Roy Billinton Test System (RBTS) and Danish driving data. The case study results show that the integrated DLMP methodology can successfully alleviate the congestion caused by EV loads. It is also shown that the socially optimal charging schedule can be implemented through a decentralized mechanism where loads respond autonomously to the posted DLMPs by maximizing their individual net surplus. © 2013 IEEE.

Brander K.M.,Technical University of Denmark
Journal of Fish Biology | Year: 2010

Environmental factors act on individual fishes directly and indirectly. The direct effects on rates and behaviour can be studied experimentally and in the field, particularly with the advent of ever smarter tags for tracking fishes and their environment. Indirect effects due to changes in food, predators, parasites and diseases are much more difficult to estimate and predict. Climate can affect all life-history stages through direct and indirect processes and although the consequences in terms of growth, survival and reproductive output can be monitored, it is often difficult to determine the causes. Investigation of cod Gadus morhua populations across the whole North Atlantic Ocean has shown large-scale patterns of change in productivity due to lower individual growth and condition, caused by large-scale climate forcing. If a population is being heavily exploited then a drop in productivity can push it into decline unless the level of fishing is reduced: the idea of a stable carrying capacity is a dangerous myth. Overexploitation can be avoided by keeping fishing mortality low and by monitoring and responding rapidly to changes in productivity. There are signs that this lesson has been learned and that G. morhua will continue to be a mainstay of the human diet. © 2010 The Author. Journal of Fish Biology © 2010 The Fisheries Society of the British Isles.

Weschler C.J.,Rutgers University | Weschler C.J.,Technical University of Denmark
Indoor Air | Year: 2011

In the two decades since the first issue of Indoor Air, there have been over 250 peer-reviewed publications addressing chemical reactions among indoor pollutants. The present review has assembled and categorized these publications. It begins with a brief account of the state of our knowledge in 1991 regarding 'indoor chemistry', much of which came from corrosion and art conservation studies. It then outlines what we have learned in the period between 1991 and 2010 in the context of the major reference categories: gas-phase chemistry, surface chemistry, health effects and reviews/workshops. The indoor reactions that have received the greatest attention are those involving ozone-with terpenoids in the gas-phase as well as with the surfaces of common materials, furnishings, and the occupants themselves. It has become clear that surface reactions often have a larger impact on indoor settings than do gas-phase processes. This review concludes with a subjective list of major research needs going forward, including more information on the decomposition of common indoor pollutants, better understanding of how sorbed water influences surface reactions, and further identification of short-lived products of indoor chemistry. Arguably, the greatest need is for increased knowledge regarding the impact that indoor chemistry has on the health and comfort of building occupants. © 2011 John Wiley & Sons A/S.

Poulsen H.F.,Technical University of Denmark
Journal of Applied Crystallography | Year: 2012

Three-dimensional X-ray diffraction microscopy is a fast and nondestructive structural characterization technique aimed at studies of the individual crystalline elements (grains or subgrains) within millimetre-sized polycrystalline specimens. It is based on two principles: the use of highly penetrating hard X-rays from a synchrotron source and the application of tomographic reconstruction algorithms for the analysis of the diffraction data. In favourable cases, the position, morphology, phase and crystallographic orientation can be derived for up to 1000 elements simultaneously. For each grain its average strain tensor may also be derived, from which the type II stresses can be inferred. Furthermore, the dynamics of the individual elements can be monitored during typical processes such as deformation or annealing. A review of the field is provided, with a viewpoint from materials science. © 2012 International Union of Crystallography Printed in Singapore-all rights reserved.

Storrle H.,Technical University of Denmark
Journal of Visual Languages and Computing | Year: 2011

In large scale model based development, analysis level models are more like knowledge bases than engineering artifacts. Their effectiveness depends, to a large degree, on the ability of domain experts to retrieve information from them ad-hoc. For large scale models, however, existing query facilities are inadequate. The visual model query language (VMQL) is a novel approach that uses the respective modeling language of the source model as the query language, too. The semantics of VMQL is defined formally based on graphs, so that query execution can be defined as graph matching. VMQL has been applied to several visual modeling languages, implemented, and validated in small case studies, and several controlled experiments. © 2010 Elsevier Ltd.

Sorensen J.N.,Technical University of Denmark
Journal of Fluid Mechanics | Year: 2011

The conditions for the appearance of instabilities in systems of helical vortices constitute an intriguing problem that still remains partly unsolved. The experimental study of Felli, Camussi & Di Felice (J. Fluid Mech., this issue, vol. 682, 2011, pp. 5-53) has shed new light on some of the basic mechanisms governing the instability mechanisms. © Cambridge University Press 2011.

Erler J.T.,Copenhagen University | Linding R.,Technical University of Denmark
Cell | Year: 2012

Drug development for complex diseases is shifting from targeting individual proteins or genes to systems-based attacks targeting dynamic network states. Lee et al. now reveal how the progressive rewiring of a signaling network over time following EGF receptor inhibition leaves triple-negative breast tumors vulnerable to a second, later hit with DNA-damaging drugs, demonstrating that time- and order-dependent drug combinations can be more efficacious in killing cancer cells. © 2012 Elsevier Inc.

Tvergaard V.,Technical University of Denmark
International Journal of Solids and Structures | Year: 2010

Crack growth is analyzed numerically under combined mode I, II and III loading, or under loading in one of these modes alone. The solid is a ductile metal modelled as elastic-plastic, and the fracture process is represented in terms of a cohesive zone model. The analyses are carried out for conditions of small-scale yielding, with the elastic mixed mode solution applied as boundary conditions on the outer edge of the region analyzed. For pure mode I loading crack growth continued far beyond the maximum fracture toughness shows that the predicted subsequent steady-state toughness is well below the maximum. The reason for this is discussed in terms of the local stress and strain fields around the tip. For pure mode II or mode III loading it is shown that there is no maximum before the steady-state. Also results for different mixed mode conditions are presented and discussed in relation to the results for loading in only one mode. Most of the results are based on assuming that the peak tractions for tangential separation are equal to that for normal separation, but it is shown that a relatively smaller peak traction for tangential separation may significantly affect the predictions. © 2010 Elsevier Ltd. All rights reserved.

Meier S.,Technical University of Denmark | Meier S.,Carlsberg Laboratory | Beeren S.R.,Carlsberg Laboratory
Journal of the American Chemical Society | Year: 2014

We describe a simple method for the simultaneous determination of association constants for a guest binding to seven different hosts in a mixture of more than 20 different oligosaccharides. If the binding parameters are known for one component in the mixture, a single NMR titration suffices to determine binding constants for all other detectable and resolvable hosts. With the use of high-resolution 1H-13C HSQC experiments, complexes of amphiphiles with more than 10 different maltooligosaccharides can be resolved. Hereby, the binding capabilities of a set of structurally related hosts can be quantitatively studied to systematically explore noncovalent interactions without the need to isolate each host. © 2014 American Chemical Society.

Brander K.,Technical University of Denmark
Climatic Change | Year: 2013

Human impacts on marine fisheries go back many centuries or even thousands of years in some coastal areas. Full global exploitation of the most productive fish stocks probably occurred around 1990. Many stocks have been overexploited and the assessment and management required to rein this in and to combat other human pressures, such as pollution, has been slow to mature, but is showing positive trends. The need to protect marine ecosystems for their intrinsic value and for the services they provide has also been recognised and is being embodied in legislation and turned into operational tools. As with terrestrial systems, it will not be easy to find acceptable balances between food production and conservation objectives. Climate change imposes a new set of pressures on marine ecosystems; increasing temperature, reduced salinity in some enclosed seas and coastal areas, changing windfields and seasonality, acidification, deoxygenation and rising sea level will all affect the productivity and distribution of marine life. We can detect some of the consequences already but prediction is very difficult for a variety of reasons. In spite of these difficulties it is possible to map out robust guidance on the kind of research that will help us to adapt and on the development of practices and management that will insure against future change. © 2012 Springer Science+Business Media B.V.

Espinosa N.,Technical University of Cartagena | Garcia-Valverde R.,Technical University of Cartagena | Krebs F.C.,Technical University of Denmark
Energy and Environmental Science | Year: 2011

A life cycle analysis (LCA) on a product integrated polymer solar module is carried out in this study. These assessments are well-known to be useful in developmental stages of a product in order to identify the bottlenecks for the up-scaling in its production phase for several aspects spanning from economics through design to functionality. An LCA study was performed to quantify the energy use and greenhouse gas (GHG) emissions from electricity use in the manufacture of a light-weight lamp based on a plastic foil, a lithium-polymer battery, a polymer solar cell, printed circuitry, blocking diode, switch and a white light emitting semiconductor diode. The polymer solar cell employed in this prototype presents a power conversion efficiency in the range of 2 to 3% yielding energy payback times (EPBT) in the range of 1.3-2 years. Based on this it is worthwhile to undertake a life-cycle study on the complete product integrated polymer solar cell. We have compared this portable lighting system with other lighting solutions, namely: a kerosene lamp in a remote rural area in Africa (Ethiopia), as a replacement of a silicon PV based lamp, in place of a torch with non-rechargeable lead-acid battery and instead of a battery charging station. The analysis reveals that the OPV lamp has a significant advantage provided that some of the challenges facing this novel technology are efficiently met such that it can enter the market of portable lighting devices. © The Royal Society of Chemistry 2011.

Sommer M.O.A.,Technical University of Denmark
Current Opinion in Microbiology | Year: 2015

Culture-independent approaches have driven the field of microbiome research and illuminated intricate relationships between the gut microbiota and human health. However, definitively associating phenotypes to specific strains or elucidating physiological interactions is challenging for metagenomic approaches. Recently a number of new approaches to gut microbiota cultivation have emerged through the integration of high-throughput phylogenetic mapping and new simplified cultivation methods. These methodologies are described along with their potential use within microbiome research. Deployment of novel cultivation approaches should enable improved studies of xenobiotic tolerance and modification phenotypes and allow a drastic expansion of the gut microbiota reference genome catalogues. Furthermore, the new cultivation methods should facilitate systematic studies of the causal relationship between constituents of the microbiota and human health accelerating new probiotic development. © 2015 Elsevier Ltd.

Aarestrup F.M.,Technical University of Denmark
Philosophical Transactions of the Royal Society B: Biological Sciences | Year: 2015

The purpose of this review was to provide an updated overview on the use of antimicrobial agents in livestock, the associated problems for humans and current knowledge on the effects of reducing resistance in the livestock reservoir on both human health and animal production. There is still limiting data on both use of antimicrobial agents, occurrence and spread of resistance as well as impact on human health. However, in recent years, emerging issues related to methicillin-resistant Staphylococcus aureus, Clostridium difficile, Escherichia coli and horizontally transferred genes indicates that the livestock reservoir has a more significant impact on human health than was estimated 10 years ago, where the focus was mainly on resistance in Campylobacter and Salmonella. Studies have indicated that there might only be a marginal if any benefit from the regular use of antibiotics and have shown that it is possible to substantially reduce the use of antimicrobial agents in livestock production without compromising animal welfare or health or production. In some cases, this should be done in combination with other measures such as biosecurity and use of vaccines. To enable better studies on both the global burden and the effect of interventions, there is a need for global harmonized integrated and continuous surveillance of antimicrobial usage and antimicrobial resistance, preferably associated with data on production and animal diseases to determine the positive and negative impact of reducing antimicrobial use in livestock. © 2015 The Author(s).

Nielsen C.H.,Technical University of Denmark
Advances in Experimental Medicine and Biology | Year: 2010

Biological membranes define the structural and functional boundaries in living cells and their organelles.The integrity of the cell depends on its ability to separate inside from outside and yet at the same time allow massive transport of matter in and out the cell.Nature has elegantly met this challenge by developing membranes in the form of lipid bilayers in which specialized transport proteins are incorporated.This raises the question:is it possible to mimic biological membranes and create a membrane based sensor and/or separation device? In the development of a biomimetic sensor/separation technology,a unique class of membrane transport proteins is especially interesting -the major intrinsic proteins (MIPs).Generally,MIPs conduct water molecules and selected solutes in and out of the cell while preventing the passage of other solutes,a property critical for the conservation of the cells internal pH and salt concen-tration.Also known as water channels or aquaporins they are highly efficient membrane pore proteins some of which are capable of transporting water at very high rates up to 109 molecules per second.Some MIPs transport other small,uncharged solutes,such as glycerol and other permeants such as carbon dioxide,nitric oxide,ammonia,hydrogen peroxide and the metalloids antimonite, arsenite, silicic and boric acid depending on the effective restriction mechanism of the protein.The flux properties of MIPs thus lead to the question if MIPs can be used in separation devices or as sensor devices based on e.g.,the selective permeation of metalloids. In principle a MIP based membrane sensor/separation device requires the supporting bio-mimetic matrix to be virtually impermeable to anything but water or the solute in question.In practice,however,a biomimetic support matrix will generally have finite permeabilities to both electrolytes and non-electrolytes.The feasibility of a biomimetic MIP device thus depends on the relative transport contribution from both protein and biomimetic support matrix.Also the biomimetic matrix must be encapsulated in order to protect it and make it sufficiently stable in a final application.Here,I specifically discuss the feasibility of developing osmotic biomimetic MIP membranes,but the technical issues are of general concern in the design of biomimetic membranes capable of supporting selective transmembrane fluxes. © 2010 Landes Bioscience and Springer Science+Business Media.

Zhurbenko V.,Technical University of Denmark
Advances in Electrical and Computer Engineering | Year: 2011

Among the various breast imaging modalities for breast cancer detection, microwave imaging is attractive due to the high contrast in dielectric properties between the cancerous and normal tissue. Due to this reason, this modality has received a significant interest and attention from the microwave community. This paper presents the survey of the ongoing research in the field of microwave imaging of biological tissues, with major focus on the breast tumor detection application. The existing microwave imaging systems are categorized on the basis of the employed measurement concepts. The advantages and disadvantages of the implemented imaging techniques are discussed. The fundamental tradeoffs between the various system requirements are indicated. Some strategies to overcome these limitations are outlined.© 2011 AECE.

Frandsen R.J.N.,Technical University of Denmark
Journal of Microbiological Methods | Year: 2011

Agrobacterium tumefaciens-mediated transformation (ATMT) of fungi has become a common technique for the study of a wide variety of different fungal species over the past 12. years. The discovery that the host range of A. tumefaciens could be extended to include fungi provided an efficient transformation tool for species in which it was previously impossible to conduct molecular genetics experiments. ATMT experiments can be divided into three groups: i) Forward genetics (i.e., random mutagenesis), ii) Reverse genetics (i.e., targeted genome modification and random integration) and iii) the introduction of reporter genes (e.g., GFP, RFP and GUS) that allow in situ monitoring of the fungus. The use of ATMT for forward genetics experiments has primarily included classic random insertional inactivation strategies to obtain loss-of-function mutants. For reverse genetics experiments, ATMT has been used to introduce targeted genome modifications (e.g., disruptions, replacements, overexpression and complementation) and to generate random integrations for complementation, heterologous expression, expression of transcriptional and translational fusion reporters and RNAi-mediated down-regulation of gene expression. This review summarizes the technical advances within the field from 1998 to the summer of 2011, focusing on the development of binary vectors that are compatible with fungal transformation (over 180 general vectors) and methods for constructing binary vectors for targeted integration of T-DNA into fungal genomes. © 2011 Elsevier B.V.

Alapetite A.,Technical University of Denmark
Personal and Ubiquitous Computing | Year: 2010

This article introduces a novel Web architecture that supports session migration in multi-device Web applications, particularly the case when a user starts a Web session on a computer and wishes to continue on a mobile phone. The proposed solution for transferring the needed session identifiers across devices is to dynamically generate pictures of 2D-barcodes containing a Web address and a session ID in an encoded form. 2D-barcodes are a cheap, fast and robust approach to the problem. They are widely known and used in Japan, and are spreading in other countries. Variations on the topic are covered in the article, including a possible migration from a mobile device to a computer (opposite direction), and between two or more mobile phones (possibly back and forth). The results show that this HCI approach is inexpensive, efficient, and works with most camera-phones on the market; the author does see any other mature technique with such assets. © 2009 Springer-Verlag London Limited.

Nakai H.,Niigata University | Kitaoka M.,Japan National Agriculture and Food Research Organization | Svensson B.,Technical University of Denmark | Ohtsubo K.,Niigata University
Current Opinion in Chemical Biology | Year: 2013

Phosphorylases are one group of carbohydrate active enzymes involved in the cleavage and formation of glycosidic linkages together with glycoside hydrolases and sugar nucleotide-dependent glycosyltransferases. Noticeably, the catalyzed phosphorolysis is reversible, making phosphorylases suitable catalysts for efficient synthesis of particular oligosaccharides from a donor sugar 1-phosphate and suitable carbohydrate acceptors with strict regioselectivity. Although utilization of phosphorylases for oligosaccharide synthesis has been limited because only few different enzymes are known, recently the number of reported phosphorylases has gradually increased, providing the variation making these enzymes useful tools for efficient synthesis of diverse oligosaccharides. © 2013 Elsevier Ltd.

Ohlrich M.,Technical University of Denmark
Journal of Sound and Vibration | Year: 2011

Structure-borne sound generated by audible vibration of machines in vehicles, equipment and house-hold appliances is often a major cause of noise. Such vibration of complex machines is mostly determined and quantified by measurements. It has been found that characterization of the vibratory source strength and the prediction of power transmission to a supporting structure or the machine casing itself can be greatly simplified if all mobility cross-terms and spatial cross-coupling of source velocities can be neglected in the analysis. In many cases this gives an acceptable engineering accuracy, especially at mid- and high-frequencies. For structurally compact machines, however, the influence of cross-coupling cannot always be ignored. The present paper addresses this problem and examines the transmission of structure-borne sound power by including spatial cross-coupling between pairs of translational terminals in a global plane. This paired or bi-coupled power transmission represents the simplest case of cross-coupling. The procedure and quality of the predicted transmission using this improved technique is demonstrated experimentally for an electrical motor unit with an integrated radial fan that was mounted resiliently in a vacuum cleaner casing. It is found that cross-coupling plays a significant role, but only at frequencies below 100 Hz for the examined system. © 2011 Elsevier Ltd. All rights reserved.

Negendahl K.,Technical University of Denmark
Automation in Construction | Year: 2015

Abstract Designing with building performance simulation feedback in the early design stage has existed since the early days of computational modeling. However, as a consequence of a fragmented building industry building performance simulations (BPSs) in the early design stage are closely related to who is creating and operating the BPS models. This paper critically reviews the different ways designers and analysts use BPS in the early design stage. One of the key findings is that most tools and methods used in the early design stages are insufficient to provide valid feedback while in the same time being flexible enough to accommodate a rapid changing design process. The main concern points to the way geometrical models and analytical models are combined and how this affects the way the buildings are designed and perform. This paper concludes that integrated dynamic models may combine a design tool, a visual programming language and a BPS to provide better support for the designer during the early stages of design as opposed to alternatives such as the current implementation of IFC or gbXML or the unaccompanied use of simulation packages. © 2015 Elsevier B.V. All rights reserved.

Jensen P.B.,Copenhagen University | Jensen L.J.,Copenhagen University | Brunak S.,Copenhagen University | Brunak S.,Technical University of Denmark
Nature Reviews Genetics | Year: 2012

Clinical data describing the phenotypes and treatment of patients represents an underused data source that has much greater research potential than is currently realized. Mining of electronic health records (EHRs) has the potential for establishing new patient-stratification principles and for revealing unknown disease correlations. Integrating EHR data with genetic data will also give a finer u-derstanding of genotype-phenotype relationships. However, a broad range of ethical, legal and technical reasons currently hinder the systematic deposition of these data in EHRs and their mining. Here, we consider the potential for furthering medical research and clinical care using EHR data and the challenges that must be overcome before this is a reality. © 2012 Macmillan Publishers Limited. All rights reserved.

Munk P.,Technical University of Denmark
Deep-Sea Research Part II: Topical Studies in Oceanography | Year: 2014

The reproduction and early life history of many fish species are linked to the physical and biological characteristics of fronts. In order to ascertain linkages between frontal physics and fish larvae, we investigated distributional differences among gadoid fish larvae comparing these to both horizontal and vertical variability in hydrography and abundances of potential copepod prey The investigation was carried out at a frontal zone along the Norwegian Trench in the northern North Sea, and was based on a series of cross-bathymetric sampling transects. Tows with a large ring net and an opening-closing net were used for describing fish larval horizontal and vertical distributions, while a submersible pump was used for describing vertical distributions of copepods. Hydrographic profiles and current velocity measurements were used to outline variability in temperature, salinity and current structure. Measurements demonstrated a distinct bottom front at the southern slope of the Trench with deepening isopycnals and high chlorphyll a concentrations. Abundances of both gadoid fish larvae and copepods peaked in vicinity of the front around mid-depth, and findings points to an inter-connection between the vertical and horizontal distributions of each species. However, the three-dimensional pattern of distribution differed significantly among species of larvae and species of copepods. The study underlines the complexity of bio-physical interrelationships in the frontal zone, and indicates that the zone encompasses specific ecological niches to which each species of fish larvae is adapted. © 2014 Elsevier Ltd.

Stamate E.,Technical University of Denmark
Plasma Physics and Controlled Fusion | Year: 2012

Charge flux distribution on the surface of biased electrodes of different geometries immersed in a plasma is investigated by three-dimensional simulations and experiments. It is demonstrated that the sheath surrounding the electrodes that interface insulators acts as an electrostatic lens, focusing the charges to distinct locations on the electrode surface depending on the entrance coordinates at the sheath edge. Two focusing effects are identified. Discrete focusing leads to the formation of a passive surface of no ion impact, near the edge of the electrodes interfacing insulators. Modal focusing results in the formation of certain 'modal spots' and/or 'modal lines'. Several phenomenological aspects and potential applications are reviewed and further discussed, including charge focusing by a three-dimensional plasma-sheath-lens, ion dose uniformity during plasma immersion ion implantation, mass spectrometry and plasma monitoring. © 2012 IOP Publishing Ltd.

Norgard J.S.,Technical University of Denmark
Journal of Cleaner Production | Year: 2013

This paper outlines a simple, aggregate, descriptive model of what is here termed a "whole economy", covering all human involvement in the economy, from ultimate means or ecological sacrifices, to the ultimate ends of human satisfaction. The model embraces not only the formal "professional economy" driven by money, but also the parallel non-paid, voluntary economy, here termed "amateur economy", driven by peoples' affective motivations. The input of work to the economy plays an essential role in the paper's analysis of options for reducing ecological sacrifices. Hence, part of the paper is devoted to a brief historical overview of the role of work, including turning points in the 1930s in the United States, when work sharing was displaced by work creation through consumerism, and, in the post-war economy when GDP became the dominant economic indicator. The paper proposes the aim of a happy and sustainable degrowth for affluent countries, implying the transfer of some activities from the professional economy to the less 'labor' productive amateur economy. This will tend to reduce overall labor productivity and hence resource throughput, but increase satisfaction and happiness. A key element in the analysis is combining a reduction in consumption with a reduction in production, which is obtainable through lowering either working time or work productivity and turning some of the leisure time into voluntary activities. Economic growth is not a law of nature but the consequence of explicit political decisions taken. Hence growth is also open to new political decisions in recognition of physical limits to growth and the human quest for replacing economic growth with life satisfaction, including increased free time. © 2011 Elsevier Ltd. All rights reserved.

Huang X.,Technical University of Denmark
Jinshu Xuebao/Acta Metallurgica Sinica | Year: 2014

The grain size effect and the specimen size effect on the strength of metals are briefly reviewed with respect to their history and current status of research. It is revealed that the fundamental strengthening mechanisms responsible for these two types of size effect are to increase the resistance to dislocation motion and to dislocation generation, respectively. It is shown that both strengthening mechanisms take place in some nanostructured metals, which leads to a suggestion to use these two mechanisms for optimizing the strength and ductility of nanostructured metals. This suggestion is verified by some results obtained in nanostructured pure aluminum. © Copyright.

Niordson C.F.,Technical University of Denmark | Kysar J.W.,Columbia University
Journal of the Mechanics and Physics of Solids | Year: 2014

A numerical method for viscous strain gradient crystal plasticity theory is presented, which incorporates both energetic and dissipative gradient effects. The underlying minimum principles are discussed as well as convergence properties of the proposed finite element procedure. Three problems of plane crystal plasticity are studied: pure shear of a single crystal between rigid platens as well as plastic deformation around cylindrical voids in hexagonal close packed and face centered cubic crystals. Effective in-plane constitutive slip parameters for plane strain deformation of specifically oriented face centered cubic crystals are developed in terms of the crystallographic slip parameters. The effect on geometrically necessary dislocation structures introduced by plastic deformation is investigated as a function of the ratio of void radius to plasticity length scale. © 2013 Elsevier Ltd. All rights reserved.

The effect of polymicrobial interactions on pathogen physiology and how it can act either to limit pathogen colonization or to potentiate pathogen expansion and virulence are not well understood. Pseudomonas aeruginosa and Staphylococcus aureus are opportunistic pathogens commonly found together in polymicrobial human infections. However, we have previously shown that the interactions between these two bacterial species are strain dependent. Whereas P. aeruginosa PAO1, a commonly used laboratory strain, effectively suppressed S. aureus growth, we observed a commensal-like interaction between the human host-adapted strain, DK2-P2M24-2003, and S. aureus. In this study, characterization by matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) imaging mass spectrometry (IMS) and mass spectral (MS) molecular networking revealed a significant metabolic divergence between P. aeruginosa PAO1 and DK2-P2M24-2003, which comprised several virulence factors and signaling 4-hydroxy-2-alkylquinoline (HAQ) molecules. Strikingly, a further modulation of the HAQ profile was observed in DK2-P2M24-2003 during interaction with S. aureus, resulting in an area with thickened colony morphology at the P. aeruginosa–S. aureus interface. In addition, we found an HAQ-mediated protection of S. aureus by DK2-P2M24-2003 from the killing effect of tobramycin. Our findings suggest a model where the metabolic divergence manifested in human host-adapted P. aeruginosa is further modulated during interaction with S. aureus and facilitate a proto-cooperative P. aeruginosa–S. aureus relationship. © 2015 International Society for Microbial Ecology

Dehli T.,Technical University of Denmark
Sub-cellular biochemistry | Year: 2012

Synthetic and systems biologists need standardized, modular and orthogonal tools yielding predictable functions in vivo. In systems biology such tools are needed to quantitatively analyze the behavior of biological systems while the efficient engineering of artificial gene networks is central in synthetic biology. A number of tools exist to manipulate the steps in between gene sequence and functional protein in living cells, but out of these the most straight-forward approach is to alter the gene expression level by manipulating the promoter sequence. Some of the promoter tuning tools available for accomplishing such altered gene expression levels are discussed here along with examples of their use, and ideas for new tools are described. The road ahead looks very promising for synthetic and systems biologists as tools to achieve just about anything in terms of tuning and timing multiple gene expression levels using libraries of synthetic promoters now exist.

Tvergaard V.,Technical University of Denmark
Mechanics of Materials | Year: 2015

For voids in a shear field unit cell model analyses have been used to show that ductile failure is predicted even though the stress triaxiality is low or perhaps negative, so that the void volume fraction does not grow during deformation. Here, the effect of the void shape is studied by analyzing materials where the voids have initially ellipsoidal shapes. The cell models are in plane strain, so that the voids are modeled as cylindrical holes. Periodic boundary conditions are used to represent a material with a periodic distribution of voids having different spacings in the two in-plane coordinate directions, and subjected to different average stress states. Depending on the initial orientation of the ellipsoidal voids, the principal axes of the elongated voids rotate initially in different directions relative to the shear field. After some deformation the behavior is much like that found for voids with circular cross-section, i.e. the voids in shear flatten out to micro-cracks, which rotate and elongate until interaction with neighboring micro-cracks gives coalescence. Even though the mechanism of ductile failure is the same, the load carrying capacity predicted, for the same initial void volume fraction, is rather different for different initial orientations of the ellipsoidal voids. © 2014 Elsevier Ltd. All rights reserved.

Frosz M.H.,Technical University of Denmark
Optics Express | Year: 2010

A new model of pump noise in supercontinuum and rogue wave generation is presented. Simulations are compared with experiments and show that the new model provides significantly better agreement than the currently ubiquitously used one-photon-per-mode model. The new model also allows for a study of the influence of the pump spectral line width on the spectral broadening mechanisms. Specifically, it is found that for four-wave mixing (FWM) a narrow spectral line width (≲ 0.1 nm) initially leads to a build-up of FWM from quantum noise, whereas a broad spectral line width (≳ 1 nm) initially leads to a gradual broadening of the pump spectrum. Since the new model provides better agreement with experiments and is still simple to implement, it is particularly important that it is used for future studies of the statistical properties of nonlinear spectral broadening, such as the formation of rogue waves. © 2010 Optical Society of America.

Dufva M.,Technical University of Denmark
Journal of Histochemistry and Cytochemistry | Year: 2011

The use of short, high-affinity probes consisting of a combination of DNA and locked nucleic acid (LNA) has enabled the specific detection of microRNAs (miRNAs) by in situ hybridization (ISH). However, detection of low-copy number miRNAs is still not always possible. Here the authors show that probes consisting of 2′-O-methyl RNAs (2OMe) and LNA at every third base (2:1 ratio), under optimized hybridization conditions, excluding yeast RNA from the hybridization buffer, can provide superior performance in detection of miRNA targets in terms of sensitivity and signal-to-noise ratio compared to DNA + LNA probes. Furthermore, they show that hybridizations can be performed in buffers of 4M urea instead of 50% formamide, thereby yielding an equally specific but nontoxic assay. The use of 2OMe + LNA-based probes and the optimized ISH assay enable simple and fast detection of low-copy number miRNA targets, such as miR-130a in mouse brain. © The Author(s) 2011.

Meyer A.S.,Technical University of Denmark
Annals of the New York Academy of Sciences | Year: 2010

A number of naturally occurring dietary substances may exert physiological benefits. The production of enhanced levels or particularly tailored versions of such candidate functional compounds can be targeted by enzymatic catalysis. The recent literature contains examples of enhancing bioavailability of iron via enzyme-catalyzed degradation of phytate in wheat bran, increasing diacyl-glycerol and conjugated linoleic acid levels by lipase action, enhancing the absorption of the citrus flavonoid hesperetin via rhamnosidase treatment, and obtaining solubilized dietary fiber via enzymatic modification of potato starch processing residues. Such targeted enzyme-catalyzed reactions provide new invention opportunities for designing functional foods with significant health benefits. The provision of well-defined naturally structured compounds can, moreover, assist in obtaining the much-needed improved understanding of the physiological benefits of complex natural substances. © 2010 New York Academy of Sciences.

Johannesson B.,Technical University of Denmark
Cement and Concrete Composites | Year: 2010

Samples of concrete at different water-to-cement ratios and air contents subjected to freeze/thaw cycles with the lowest temperature at about -80 °C are investigated. By adopting a novel technique, a scanning calorimeter is used to obtain data from which the ice contents at different freeze temperatures can be calculated. The length change caused by temperature and ice content changes during test is measured by a separate experiment using the same types of freeze-thaw cycles as in the calorimetric tests. In this way it was possible to compare the amount of formed ice at different temperatures and the corresponding measured length changes. The development of cracks in the material structure was indicated by an ultra-sonic technique by measuring on the samples before and after the freeze-thaw tests. Further the air void structure was investigated using a microscopic technique in which air 'bubble' size distributions and the so-called spacing factor, indicating the mean distance between air bubbles, were measured. By analyzing the experimental result, it is concluded that damages occur in the temperature range of about -10 °C to -55 °C, when the air content is lower than about 4% of the total volume. For a totally water-saturated concrete, damages always occur independently of the use of entrained air or low water-to-cement ratios. It is, further, concluded that the length changes of these samples correspond to the calculated ice contents at different temperatures in a linear fashion. © 2009 Elsevier Ltd. All rights reserved.

Marvig R.L.,Technical University of Denmark
Nature Genetics | Year: 2014

Little is known about how within-host evolution compares between genotypically different strains of the same pathogenic species. We sequenced the whole genomes of 474 longitudinally collected clinical isolates of Pseudomonas aeruginosa sampled from 34 children and young individuals with cystic fibrosis. Our analysis of 36 P. aeruginosa lineages identified convergent molecular evolution in 52 genes. This list of genes suggests a role in host adaptation for remodeling of regulatory networks and central metabolism, acquisition of antibiotic resistance and loss of extracellular virulence factors. Furthermore, we find an ordered succession of mutations in key regulatory networks. Accordingly, mutations in downstream transcriptional regulators were contingent upon mutations in upstream regulators, suggesting that remodeling of regulatory networks might be important in adaptation. The characterization of genes involved in host adaptation may help in predicting bacterial evolution in patients with cystic fibrosis and in the design of future intervention strategies. © 2014 Nature Publishing Group, a division of Macmillan Publishers Limited. All Rights Reserved.

Lehre P.K.,Technical University of Denmark
Genetic and Evolutionary Computation Conference, GECCO'11 | Year: 2011

This paper introduces an easy to use technique for deriving upper bounds on the expected runtime of non-elitist population-based evolutionary algorithms (EAs). Applications of the technique show how the efficiency of EAs is critically dependant on having a sufficiently strong selective pressure. Parameter settings that ensure sufficient selective pressure on commonly considered benchmark functions are derived for the most popular selection mechanisms. Together with a recent technique for deriving lower bounds, this paper contributes to a much-needed analytical tool-box for the analysis of evolutionary algorithms with populations. Copyright 2011 ACM.

Meyer K.E.,Technical University of Denmark
Flow Measurement and Instrumentation | Year: 2011

In this work we demonstrate the construction of an 'inside-out' sensor geometry for electrical capacitance tomography (ECT). The inside-out geometry has the electrodes placed around a tube, as usual, but measuring 'outwards'. The flow between the electrodes and an outer tube is reconstructed; allowing the inside-out sensor to move inside the outer tube. A test sensor was constructed and capacitances were measured using the charge transfer technique. Sensitivity matrices for the inside-out sensor were calculated with a finite element approach and some special issues with the sensitivity matrices are discussed. An adaptation of the Landweber algorithm, which works very well for the inside-out geometry, is presented and a definition of the spatial resolution of an ECT sensor is suggested. Tomograms from a test run of an inside-out sensor are presented and measurements of watercut are compared with images obtained by a camera and a simple direct result based on the capacitance vector. © 2010 Elsevier Ltd.

Bacteria play a central role in the cycling of carbon, yet our understanding of the relationship between the taxonomic composition and the degradation of dissolved organic matter (DOM) is still poor. In this experimental study, we were able to demonstrate a direct link between community composition and ecosystem functioning in that differently structured aquatic bacterial communities differed in their degradation of terrestrially derived DOM. Although the same amount of carbon was processed, both the temporal pattern of degradation and the compounds degraded differed among communities. We, moreover, uncovered that low-molecular-weight carbon was available to all communities for utilisation, whereas the ability to degrade carbon of greater molecular weight was a trait less widely distributed. Finally, whereas the degradation of either low- or high-molecular-weight carbon was not restricted to a single phylogenetic clade, our results illustrate that bacterial taxa of similar phylogenetic classification differed substantially in their association with the degradation of DOM compounds. Applying techniques that capture the diversity and complexity of both bacterial communities and DOM, our study provides new insight into how the structure of bacterial communities may affect processes of biogeochemical significance.The ISME Journal advance online publication, 21 August 2015; doi:10.1038/ismej.2015.131. © 2015 International Society for Microbial Ecology

Rothausen B.W.,Technical University of Denmark
The British journal of nutrition | Year: 2013

Little is known about dietary patterns on weekdays and weekend days in children, and the aim of the present study was to investigate 4-14-year-old children's dietary patterns specifically on weekdays (Monday-Thursday) and weekend days (Saturday-Sunday). Dietary data were derived from the Danish National Survey of Dietary Habits and Physical Activity 2003-8, where a total of 784 children aged 4-14 years completed a 7 d pre-coded food record. Principal component analysis was used to identify dietary patterns in the age groups 4-6, 7-10 and 11-14 years. Consistently, two dietary patterns, labelled 'processed' and 'health conscious', emerged on both weekdays and weekend days. Factor scores from corresponding dietary patterns were significantly correlated between weekdays and weekend days with the exception of the 'health conscious' pattern in the 7-10-year-olds. Within each age group, children with high agreement for the 'processed' pattern had a significantly higher dietary energy density, which was reflected in significantly higher intakes of sugar-sweetened beverages and lower intakes of fruit and vegetables, compared with children with high agreement for the 'health conscious' pattern (P< 0·05). Moreover, these variables indicated less healthy dietary intakes on weekend days than on weekdays for both patterns. In conclusion, two distinct dietary patterns, labelled 'processed' and 'health conscious', were identified on both weekdays and weekend days for each age group. While overall major dietary patterns may somewhat track between weekdays and weekends, the specific foods actually eaten became less healthy during weekends.

Hughes D.A.,Sandia National Laboratories | Hansen N.,Technical University of Denmark
Physical Review Letters | Year: 2014

A twofold decrease to an unexplored scale of 5 nm was produced in Cu by applying a large sliding load in liquid nitrogen. Statistical and universal scaling analyses of deformation induced high angle boundaries, dislocation boundaries, and individual dislocations observed by high resolution electron microscopy reveal that dislocation processes still dominate. Dislocation based plasticity continues far below the transition suggested by experiment and molecular dynamics simulations, with a limit below 5 nm. Very high strength metals may emerge based on this enhanced structural refinement. © 2014 American Physical Society.

Novitsky A.,Technical University of Denmark | Qiu C.-W.,National University of Singapore | Wang H.,Data Storage Institute Singapore
Physical Review Letters | Year: 2011

Usually a light beam pushes a particle when the photons act upon it. We investigate the optical forces by nonparaxial gradientless beams and find that the forces can drag suitable particles all the way towards the light source. The major criterion of realizing the backward dragging force is the strong nonparaxiality of the light beam, which contributes to the pulling force owing to momentum conservation. The nonparaxiality of the Bessel beam can be manipulated to possess a dragging force along both the radial longitudinal directions, i.e., a "tractor beam" with stable trajectories is achieved. © 2011 American Physical Society.

Henriksen L.C.,Technical University of Denmark
Wind Energy | Year: 2013

As a service to readers, Wind Energy regularly conducts literature surveys and publishes lists of relevant articles drawn from recent issues of a large number of periodicals including the following: Journal of Wind Engineering and Industrial Aerodynamics, International Journal of Energy Research, Renewable Energy, Energy Sources, Journal of Solar Energy Engineering, American Institute of Aeronautics and Astronautics Journal and Electric Power Components and Systems along with a number of periodicals published by the Institute of Electrical and Electronics Engineers, etc. The list is limited exclusively to journals not specifically devoted to wind energy and its applications. To assist the reader, the list is separated into broad categories. Although many papers fit several categories, each paper is listed only once under the category thought most appropriate. Please note that the inclusion in the list is not an endorsement of a paper's quality. Please e-mail any suggestions to corresponding author. © 2013 John Wiley & Sons, Ltd.

Hvilsted S.,Technical University of Denmark
Polymer International | Year: 2014

The versatility of the atom transfer radical polymerization (ATRP) of pentafluorostyrene (FS) is comprehensively evaluated. The ATRP of a wide range of monomers derived from FS is likewise discussed with emphasis on the potential polymer applications. A large number of block and star copolymers centred around polypentafluorostyrene (PFS) and prepared primarily using the bromomacroinitiator concept is surveyed. Here the main emphasis is on the feasibility of the polymer design, but also the very many different applications are highlighted. The potential grafting onto PFS and PFS block copolymers by exploitation of the very labile para-fluorine demonstrates new material architecture possibilities through very mild reaction conditions. Finally the utility of PFS in various conducting materials is elaborated. The amphiphilic nature of PFS in triblock copolymers with polyethers has been exploited for Li+ ion electrolytes. The convenient grafting of PFS through 'click' chemistry to a polysulfone and subsequent phosphonation of the PFS grafts seem very beneficial for the fabrication of proton conducting materials with high conductivity. © 2013 Society of Chemical Industry.

Jansen T.,Technical University of Denmark
ICES Journal of Marine Science | Year: 2014

The largest observed change in mackerel (Scomber scombrus) abundance in the North Atlantic happened when the so-called "North Sea mackerel" collapsed due to overfishing. Despite protection, it has remained in a depleted state. Central to this interpretation was that the "North Sea mackerel" was considered to be a distinct spawning component. However, a recent study has shown that this is not likely. In the light of this study, a review of the history of mackerel spawning in the North Sea found that the traditional explanation of the collapse did not account for a range of unfavourable environmental changes: high fishing pressure was followed by decreasing temperatures that reduced the spawning migration into the North Sea. This was further supplemented by unfavourable changes in food and wind-induced turbulence. On the population level, this was, therefore, not a local stock collapse, but a southwest shift in spawning distribution combined with a reduction in that portion of the population cline with an affinity for spawning in the northeastern part of the spawning area, including the North Sea. No indication of irreversible genetic or behavioural losses caused by the events was found. The previously unexplained lack of rebuilding of spawning in the North Sea consequently seems related to two environmental factors that have remained unfavourable: (i) zooplankton concentration, and (ii) wind-induced turbulence. Furthermore, the large commercial autumn-winter fishery in the North Sea continues to land unknown quantities of mackerel that have an affinity for spawning in the northeastern part of the spawning area, including the North Sea. © 2013 © 2013 International Council for the Exploration of the Sea. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Andersen U.L.,Technical University of Denmark | Ralph T.C.,Queensland University of Technology
Physical Review Letters | Year: 2013

Traditional continuous-variable teleportation can only approach unit fidelity in the limit of an infinite (and unphysical) amount of squeezing. We describe a new method for continuous-variable teleportation that approaches unit fidelity with finite resources. The protocol is not based on squeezed states as in traditional teleportation but on an ensemble of single photon entangled states. We characterize the teleportation scheme with coherent states, mesoscopic superposition states, and two-mode squeezed states and we find several situations in which near-unity teleportation fidelity can be obtained with modest resources. © 2013 American Physical Society.

Villanueva L.G.,Ecole Polytechnique Federale de Lausanne | Schmid S.,Technical University of Denmark
Physical Review Letters | Year: 2014

Silicon nitride (SiN) micro- and nanomechanical resonators have attracted a lot of attention in various research fields due to their exceptionally high quality factors (Qs). Despite their popularity, the origin of the limiting loss mechanisms in these structures has remained controversial. In this Letter we propose an analytical model combining acoustic radiation loss with intrinsic loss. The model accurately predicts the resulting mode-dependent Qs of low-stress silicon-rich and high-stress stoichiometric SiN membranes. The large acoustic mismatch of the low-stress membrane to the substrate seems to minimize radiation loss and Qs of higher modes (nm≥3) are limited by intrinsic losses. The study of these intrinsic losses in low-stress membranes reveals a linear dependence with the membrane thickness. This finding was confirmed by comparing the intrinsic dissipation of arbitrary (membranes, strings, and cantilevers) SiN resonators extracted from literature, suggesting surface loss as ubiquitous damping mechanism in thin SiN resonators with Qsurf=βh and β=6×1010±4×1010m-1. Based on the intrinsic loss the maximal achievable Qs and Qf products for SiN membranes and strings are outlined. © 2014 American Physical Society.

Zania V.,Technical University of Denmark
Soil Dynamics and Earthquake Engineering | Year: 2014

Offshore wind turbine (OWT) is a typical example of a slender engineering structure founded on large diameter rigid piles (monopiles). The natural vibration characteristics of these structures are of primary interest since the dominant loading conditions are dynamic. A rigorous analytical solution of the modified SSI eigenfrequency and damping is presented, which accounts for the cross coupling stiffness and damping terms of the soil-pile system and is applicable but not restrictive to OWTs. A parametric study was performed to illustrate the sensitivity of the eigenfrequency and damping on the foundation properties, the latter being expressed using the notion of dimensionless parameters (slenderness ratio and flexibility factor). The application of the approximate solution that disregards the off diagonal terms of the dynamic impedance matrix was found to overestimate the eigenfrequency and underestimate the damping. The modified SSI eigenfrequency and damping was mostly affected by the soil-pile properties, when the structural eigenfrequency was set between the first and second eigenfrequency of the soil layer. Caution is suggested when selecting one of the popular design approaches for OWTs, since the dynamic SSI effects may drive even a conservative design to restrictive frequency ranges, nonetheless along with advantageous - from a designers perspective - increased damping. © 2014 Elsevier Ltd.

Schroder S.T.,Technical University of Denmark
Wind Energy | Year: 2013

Different capacity allocation regimes have a strong impact on the economics of offshore wind farms and on interconnectors in offshore grids. Integrating offshore generation in offshore grids is currently a subject of discussion for different regions, e.g. the North Sea. A novel question is how the interconnector capacity should be allocated for wind generation and for international power trading. The main difficulty arises from the stochastic nature of wind generation: in a case with radial connections to the national coast, the wind park owner has the possibility of aggregating the offshore wind park with onshore installations to reduce balancing demand. This is not necessarily the case if the interconnector capacity is sold through implicit or explicit auctions. Different design options are discussed and quantified for a number of examples based on Danish, Dutch, German and Norwegian power markets. It is concluded that treating offshore generation as a single price zone within the interconnector reduces the wind operator's ability to pool it with other generation. Furthermore, a single offshore price zone between two markets will always receive the lower spot market price of the neighbouring zones, although its generation flows only to the high-price market. Granting the high-price market income for wind generation as the opposite design option reduces congestion rents. Otherwise, compensation measures through support schemes or different balancing responsibilities may be discussed. © 2012 John Wiley & Sons, Ltd. © 2012 John Wiley & Sons, Ltd.

Frimmer M.,FOM Institute for Atomic and Molecular Physics | Chen Y.,Technical University of Denmark | Koenderink A.F.,FOM Institute for Atomic and Molecular Physics
Physical Review Letters | Year: 2011

We report an experimental technique to map and exploit the local density of optical states of arbitrary planar nanophotonic structures. The method relies on positioning a spontaneous emitter attached to a scanning probe deterministically and reversibly with respect to its photonic environment while measuring its lifetime. We demonstrate the method by imaging the enhancement of the local density of optical states around metal nanowires. By nanopositioning, the decay rate of a pointlike source of fluorescence can be reversibly and repeatedly changed by a factor of 2 by coupling it to the guided plasmonic mode of the wire. © 2011 American Physical Society.

Henriksen L.C.,Technical University of Denmark
Wind Energy | Year: 2013

As a service to readers, Wind Energy regularly conducts literature surveys and publishes lists of relevant articles drawn from recent issues of a large number of periodicals including: Journal of Wind Engineering and Industrial Aerodynamics, International Journal of Energy Research, Renewable Energy, Energy Sources, Journal of Solar Energy Engineering, American Institute of Aeronautics and Astronautics Journal, and Electric Power Components and Systems along with a number of periodicals published by the Institute of Electrical and Electronics Engineers and so on. The list is limited exclusively to journals not specifically devoted to wind energy and its applications. To assist the reader, the list is separated into broad categories. Although many papers fit several categories, each paper is listed only once under the category thought most appropriate. Please note that the inclusion in the list is not an endorsement of a paper's quality. © 2013 John Wiley & Sons, Ltd.

Xu Z.,Hong Kong Polytechnic University | Ostergaard J.,Technical University of Denmark | Togeby M.,Ea Energianalyse A S
IEEE Transactions on Power Systems | Year: 2011

Relying on generation side alone is deemed insufficient to fulfill the system balancing needs for future Danish power system, where a 50% wind penetration is outlined by the government for year 2025. This paper investigates use of the electricity demand as frequency controlled reserve (DFR), which has a high potential and can provide many advantages. Firstly, the background of the research is reviewed, including conventional power system reserves and the demand side potentials. Subsequently, the control logics and corresponding design considerations for the DFR technology have been developed and analyzed, based on which simulation models have been built using the DIgSILENT Power Factory. The simulation studies of different scenarios confirm that the DFR can provide reliable performance of frequency control. Furthermore, relevant issues regarding implementing DFR in reality have been discussed. © 2011 IEEE.

Andersen J.E.T.,Technical University of Denmark
Central European Journal of Chemistry | Year: 2014

A detailed method validation of graphite-furnace atomic absorption spectrometry (GFAAS) with Zeeman background correction was performed. The aim is to perform a detailed investigation of short-term precision as opposed to long-term precision. It was suggested that release of graphite flakes into the light path during measurement significantly influenced the performance of the method. It was found that significant deviations with respect to the certified values were frequent and an estimate of reliable uncertainties was obtained only after a high number of repetitions. Uncertainty of Interlaboratory testing was evaluated as a method to estimate uncertainties that are comparable to uncertainties that were obtained by Interlaboratory testing and to uncertainties predicted by the Horwitz curve. To a large extent, the uncertainty in measurement that was predicted by pooled calibrations corresponded to the uncertainties that were obtained from multiple determinations of unknowns. It was thus proposed that a large proportion of the difference in uncertainty in measurement between laboratories could be explained by properties of the different detectors. In order to support accuracy, it is suggested that a higher level of uncertainty should be accepted in analytical investigations. © 2014 Versita Warsaw and Springer-Verlag Wien.

Qian X.,Illinois Institute of Technology | Sigmund O.,Technical University of Denmark
Computer Methods in Applied Mechanics and Engineering | Year: 2011

In this paper, we present an approach that extends isogeometric shape optimization from optimization of rectangular-like NURBS patches to the optimization of topologically complex geometries. We have successfully applied this approach in designing photonic crystals where complex geometries have been optimized to maximize the band gaps. Salient features of this approach include the following: (1) multi-patch Coons representation of design geometry. The design geometry is represented as a collection of Coons patches where the four boundaries of each patch are represented as NURBS curves. The use of multiple patches is motivated by the need for representing topologically complex geometries. The Coons patches are used as a design representation so that designers do not need to specify interior control points and they provide a mechanism to compute analytical sensitivities for internal nodes in shape optimization, (2) exact boundary conversion to the analysis geometry with guaranteed mesh injectivity. The analysis geometry is a collection of NURBS patches that are converted from the multi-patch Coons representation with geometric exactness in patch boundaries. The internal NURBS control points are embedded in the parametric domain of the Coons patches with a built-in mesh rectifier to ensure the injectivity of the resulting B-spline geometry, i.e. every point in the physical domain is mapped to one point in the parametric domain, (3) analytical sensitivities. Sensitivities of objective functions and constraints with respect to design variables are derived through nodal sensitivities. The nodal sensitivities for the boundary control points are directly determined by the design parameters and those for internal nodes are obtained via the corresponding Coons patches. © 2011 Elsevier B.V.

Bache M.,Technical University of Denmark | Eilenberger F.,Friedrich - Schiller University of Jena | Minardi S.,Friedrich - Schiller University of Jena
Optics Letters | Year: 2012

The higher-order Kerr effect (HOKE) has recently been advocated to explain measurements of the saturation of the nonlinear refractive index in gases. Here we show that cascaded third-harmonic generation results in an effective fifth-order nonlinearity that is negative and significant. Higher-order harmonic cascading will also occur from the HOKE, and the cascading contributions may significantly modify the observed nonlinear index change. At lower wavelengths, cascading increases the HOKE saturation intensity, while for longer wavelengths cascading will decrease the HOKE saturation intensity. © 2012 Optical Society of America.

Halasa T.,Technical University of Denmark
Journal of Dairy Science | Year: 2012

The objective of this study was to assess the epidemiologic and economic consequences of intervention against contagious clinical mastitis during lactation. A bioeconomic model of intramammary infections (IMI) was used to simulate contagious spread of Staphylococcus aureus, Streptococcus uberis, and Streptococcus dysgalactiae, and an environmental spread of Escherichia coli IMI in a 100-cow dairy herd during 1 quota year. The costs of clinical IMI, subclinical IMI, and intervention were calculated into the total annual net costs of IMI during lactation per scenario and compared with a default scenario. Input parameter values were based on the scientific literature. The scenarios were 3-d intramammary lactational treatment (default), 5-d intramammary treatment, 5-d intramammary treatment and 3-d systemic treatment, 3-d intramammary treatment and culling bacteriologically unrecovered clinical IMI cows, and 5-d intramammary treatment and culling bacteriologically unrecovered clinical IMI cows. Sensitivity analysis was conducted on parameter input values. The results showed that interventions including antibiotic treatment combined with culling unrecovered clinical IMI cows resulted in the lowest transmission, number of IMI cases, and persistent subclinical IMI cases. Nonetheless, the high associated costs of culling bacteriologically unrecovered clinical IMI cows made the other scenarios with a long and intensive antibiotic treatment, but without culling, the most cost effective. The model was sensitive to changes to the cure rate of clinical IMI following treatment, but the ranking of the intervention scenarios did not change. The model was most sensitive to the changes to the transmission rate of Staph. aureus. The ranking of the intervention scenarios changed at low transmission rate of this pathogen, in which the default scenario became the most cost-effective scenario. In case of high transmission of contagious IMI pathogens, long and intensive treatment of clinical IMI should be preceded by strategies that lower the transmission. © 2012 American Dairy Science Association.

A novel numerical method based on the finite element approach is established for the zero current method approach for calculating multi-species ionic diffusion. The proposed numerical method uses the direct calculation of the coupled set of equations in favor of the staggering approach. A one-step truly implicit time stepping scheme is adopted together with an implementation of a modified Newton-Raphson iteration scheme for search of equilibrium at each considered time step calculation. Results from the zero current case are compared with existing results from the solutions of the more general Gauss' law method. © 2010 Elsevier Ltd.

Cheng C.-C.,Technical University of Denmark
Energy Policy | Year: 2010

This paper presents a new approach for a nationally appropriate mitigation actions (NAMA) framework that can unlock the huge potential for greenhouse gas mitigation in dispersed energy end-use sectors in developing countries; specifically, the building sector and the industrial sector. These two sectors make up the largest portions of energy consumption in developing countries. However, due to multiple barriers and lack of effective polices, energy efficiency in dispersed energy end-use sectors has not been effectively put into practice. The new NAMA framework described in this paper is designed to fulfill the demand for public policies and public sector investment in developing countries and thereby boost private sector investment through project based market mechanisms, such as CDM. The new NAMA framework is designed as a need-based mechanism which effectively considers the conditions of each developing country. The building sector is used as an example to demonstrate how NAMA measures can be registered and implemented. The described new NAMA framework has the ability to interface efficiently with Kyoto Protocol mechanisms and to facilitate a systematic uptake for GHG emission reduction investment projects. This is an essential step to achieve the global climate change mitigation target and support sustainable development in developing countries. © 2010 Elsevier Ltd. All rights reserved.

Zhang J.,Kings College London | Zhang J.,Technical University of Denmark | Zayats A.,Kings College London
Optics Express | Year: 2013

Multiple plasmonic Fano resonances are generally considered to require complex nanostructures, such as multilayer structure, to provide several dark modes that can couple with the bright mode. In this paper, we show the existence of multiple Fano resonances in single layer core-shell nanostructures where the multiple dark modes appear due to the geometrical symmetry breaking induced by axial offset of the core. Both dielectric-core-metal-shell (DCMS) and metal-core-dielectric-shell (MCDS) configurations have been studied. Compared to the MCDS structure, the DCMS configuration provides higher modulation depth. Analytical studies based on transformation optics and numerical simulations have been performed to investigate the role of geometrical and material parameters on the optical properties of the proposed nanostructures. Refractive index sensing with higher-order Fano resonances has also been described, providing opportunity for multiwavelength sensing with high figure of merit. © 2013 Optical Society of America.

Kiviluoma J.,VTT Technical Research Center of Finland | Meibom P.,Technical University of Denmark
Energy | Year: 2010

Due to rising fuel costs, the substantial price for CO2 emissions and decreasing wind power costs, wind power might become the least expensive source of power for an increasing number of power systems. This poses the questions of how wind power might change optimal investments in other forms of power production and what kind of means could be used to increase power system flexibility in order to incorporate the variable power production from wind power in a cost-effective manner. We have analysed possible effects using an investment model that combines heat and power production and simulates electric vehicles. The model runs in an hourly time scale in order to accommodate the impact of variable power production from wind power. Electric vehicles store electricity for later use and can thus serve to increase the flexibility of the power system. Flexibility can also be upgraded by using heat storages with heat from heat pumps, electric heat boilers and combined heat and power (CHP) plants. Results show that there is great potential for additional power system flexibility in the production and use of heat. © 2009 Elsevier Ltd. All rights reserved.

Leuzinger S.,ETH Zurich | Luo Y.,University of Oklahoma | Beier C.,Technical University of Denmark | Dieleman W.,University of Antwerp | And 2 more authors.
Trends in Ecology and Evolution | Year: 2011

In recent decades, many climate manipulation experiments have investigated biosphere responses to global change. These experiments typically examined effects of elevated atmospheric CO2, warming or drought (driver variables) on ecosystem processes such as the carbon and water cycle (response variables). Because experiments are inevitably constrained in the number of driver variables tested simultaneously, as well as in time and space, a key question is how results are scaled up to predict net ecosystem responses. In this review, we argue that there might be a general trend for the magnitude of the responses to decline with higher-order interactions, longer time periods and larger spatial scales. This means that on average, both positive and negative global change impacts on the biosphere might be dampened more than previously assumed. © 2011 Elsevier Ltd.

Bille P.,Technical University of Denmark
Journal of Discrete Algorithms | Year: 2011

Given strings P and Q the (exact) string matching problem is to find all positions of substrings in Q matching P. The classical Knuth-Morris-Pratt algorithm [SIAM J. Comput. 6 (2) (1977) 323-350] solves the string matching problem in linear time which is optimal if we can only read one character at the time. However, most strings are stored in a computer in a packed representation with several characters in a single word, giving us the opportunity to read multiple characters simultaneously. In this paper we study the worst-case complexity of string matching on strings given in packed representation. Let m≤n be the lengths P and Q, respectively, and let σ denote the size of the alphabet. On a standard unit-cost word-RAM with logarithmic word size we present an algorithm using timeO(nlogσn+m+occ). Here occ is the number of occurrences of P in Q. For m=o(n) this improves the O(n) bound of the Knuth-Morris-Pratt algorithm. Furthermore, if m=O(n/logσn) our algorithm is optimal since any algorithm must spend at least Ω((n+m) logσlogn+occ)=Ω(nlogσn+occ) time to read the input and report all occurrences. The result is obtained by a novel automaton construction based on the Knuth-Morris-Pratt algorithm combined with a new compact representation of subautomata allowing an optimal tabulation-based simulation. © 2010 Elsevier B.V. All rights reserved.

Macmillan S.,British Geological Survey | Olsen N.,Technical University of Denmark
Earth, Planets and Space | Year: 2013

The ESA Swarm mission to identify and measure very accurately the different magnetic signals that arise in the Earth's core, mantle, crust, oceans, ionosphere and magnetosphere, which together form the magnetic field around the Earth, has increased interest in magnetic data collected on the surface of the Earth at observatories. The scientific use of Swarm data and Swarm-derived products is greatly enhanced by combination with observatory data and indices. As part of the Swarm Level-2 data activities plans are in place to distribute such ground-based data along with the Swarm data as auxiliary data products. We describe here the preparation of the data set of ground observatory hourly mean values, including procedures to check and select observatory data spanning the modern magnetic survey satellite era. We discuss other possible combined uses of satellite and observatory data, in particular those that may use higher cadence 1-second and 1-minute data from observatories. Copyright © NERC, 2013. All Rights Reserved.

Jeong C.-H.,Technical University of Denmark
Acta Acustica united with Acustica | Year: 2015

The Sabine absorption coefficient is calculated via Sabine's formula based on the reverberation time measurements with and without an absorber specimen in a reverberation chamber. The Sabine absorption coefficient has two main problems, such as it can exceed unity and is likely to be higher than the random incidence absorption coefficient and it has a poor inter-chamber reproducibility. Investigations are conducted to report the discrepancy between predictions of the Sabine absorption coefficient using the finite surface radiation impedance and round robin test data. The investigations also clarify the grounds for the use of the complex conjugate of the radiation impedance in an earlier study.

Rokni M.,Technical University of Denmark
Energy | Year: 2010

Plant characteristics of a system containing a solid oxide fuel cell (SOFC) cycle on the top of a Rankine cycle were investigated. A desulfurization reactor removes the sulfur content in the fuel, while a pre-reformer broke down the heavier hydrocarbons in an adiabatic steam reformer (ASR). The pre-treated fuel then entered to the anode side of the SOFC. The remaining fuels after the SOFC stacks entered a catalytic burner for further combusting. The burned gases from the burner were then used to produce steam for the Rankine cycle in a heat recovery steam generator (HRSG). The remaining energy of the off-gases was recycled back to the topping cycle for further utilization. Several parameter studies were carried out to investigate the sensitivity of the suggested plant. It was shown that the operation temperature of the desulfurization and the pre-reformer had no effect on the plant efficiency, which was also true when decreasing the anode temperature. However, increasing the cathode temperature had a significant effect on the plant efficiency. In addition, decreasing the SOFC utilization factor from 0.8 to 0.7, increases the plant efficiency by about 6%. An optimal plant efficiency of about 71% was achieved by optimizing the plant. © 2010 Elsevier Ltd.

Jessen L.E.,Technical University of Denmark
Nucleic acids research | Year: 2013

Identifying which mutation(s) within a given genotype is responsible for an observable phenotype is important in many aspects of molecular biology. Here, we present SigniSite, an online application for subgroup-free residue-level genotype-phenotype correlation. In contrast to similar methods, SigniSite does not require any pre-definition of subgroups or binary classification. Input is a set of protein sequences where each sequence has an associated real number, quantifying a given phenotype. SigniSite will then identify which amino acid residues are significantly associated with the data set phenotype. As output, SigniSite displays a sequence logo, depicting the strength of the phenotype association of each residue and a heat-map identifying 'hot' or 'cold' regions. SigniSite was benchmarked against SPEER, a state-of-the-art method for the prediction of specificity determining positions (SDP) using a set of human immunodeficiency virus protease-inhibitor genotype-phenotype data and corresponding resistance mutation scores from the Stanford University HIV Drug Resistance Database, and a data set of protein families with experimentally annotated SDPs. For both data sets, SigniSite was found to outperform SPEER. SigniSite is available at: http://www.cbs.dtu.dk/services/SigniSite/.

Ennis J.M.,The Institute for Perception | Christensen R.H.B.,Technical University of Denmark
Food Quality and Preference | Year: 2014

Interest in the Tetrad test has increased recently as it has become apparent that this methodology can be a more powerful alternative to the Triangle test within the standard difference testing paradigm. But when products are tested following an ingredient or process change, a pressing question is whether a sensory difference is large enough to be meaningful. To this end, in this paper we examine the precision of measurement offered by the Tetrad test as compared to two other standard forced-choice discrimination testing procedures - the Triangle and 2-AFC tests. This comparison is made from a Thurstonian perspective. In particular, for all three methods we compare: (1) The variances in the maximum-likelihood estimates of the Thurstonian measure of sensory difference, (2) The expected widths of the corresponding likelihood-based confidence intervals, and (3) The power of the tests when used for equivalence testing. We find that the Tetrad test is consistently more precise than the Triangle test and is sometimes even more precise than the 2-AFC. As a result of this precision, we discover that the Tetrad test is typically more powerful than the Triangle test for equivalence testing purposes and can, under certain conditions, even be more powerful than the 2-AFC. © 2013 Elsevier Ltd.

Duijm N.J.,Technical University of Denmark
Safety Science | Year: 2015

Risk matrices are widely used in risk management. They are a regular feature in various risk management standards and guidelines and are also used as formal corporate risk acceptance criteria. It is only recently, however, that scientific publications have appeared that discuss the weaknesses of the risk matrix. The objective of this paper is to explore these weaknesses, and provide recommendations for the use and design of risk matrices. The paper reviews the few relevant publications and adds some observations of its own in order to emphasize existing recommendations and add some suggestions. The recommendations cover a range of issues, among them: the relation between coloring the risk matrix and the definition of risk and major hazard aversion; the qualitative, subjective assessment of likelihood and consequence; the scaling of the discrete likelihood and consequence categories; and the use of corporate risk matrix standards. Finally, it proposes a probability consequence diagram with continuous scales; providing, in some instances, an alternative to the risk matrix. © 2015 Elsevier Ltd.

Jorgensen K.,Technical University of Denmark
Safety Science | Year: 2016

The concept "simple accidents" is understood as traumatic events with one victim. In the last 10 years many European countries have seen a decline in the number of fatalities, but there still remain many severe accidents at work. In the years 2009-2010 in European countries 2.0-2.4. million occupational accidents a year were notified leading to 4500 fatalities and 90,000 permanent disabilities each year. The article looks at the concept "accident" to find similarities and distinctions between major and simple accident characteristics. The purpose is to find to what extent the same kinds of prevention or safety methodologies and procedures established for major accidents are applicable to simple accidents. The article goes back to basics about accidents causes, to review the nature of successful prevention techniques and to analyze what have been constraints to getting this knowledge used more broadly. This review identifies gaps in the prevention of simple accidents, relating to safety barriers for risk control and the management processes that need to be in place to deliver those risk controls in a continuingly effective state. The article introduces the "INFO cards" as a tool for the systematic observation of hazard sources in order to ascertain whether safety barriers and management deliveries are present. Safety management and safety culture, together with the INFO cards are important factors in the prevention process. The conclusion is that we must look at safety as a part of being a professional in all kinds of jobs and occupations as well as at management level. © 2015 Elsevier Ltd.

The SAFE FOODS framework proposes an integrated five-step procedure for the risk analysis. The five steps are: framing, risk assessment, evaluation, risk management, and review. The framework is designed to address both risks and benefits. The SAFE FOODS approach introduces a 20-member Interface Committee, headed by a risk manager, to run the procedure. First third of the members is risk managers, second third is independent scientific experts and the last third is stakeholders with economic interests and with consumer interests. The role of the different steps in the procedure and the role of each category of Committee Members during the process are described. The proposal suggests a strict separation of responsibilities between managerial members on one side and scientific members and stakeholder members on the other side. This division of responsibilities in the committee opens up new possibilities for transparency, openness and participation without violation of the delegation-of-power rule. For the communication with the interested parties and the public at large during the process it is foreseen to create an Internet Forum, and use press conferences, press releases and interviews. Overall the SAFE FOODS proposal shall be seen as an invitation for rethinking the current risk assessment/risk management system in EU. © 2010 Elsevier Ltd.

Laegsgaard J.,Technical University of Denmark | Tu H.,University of Illinois at Urbana - Champaign
Optics Letters | Year: 2013

The generation of wavelengths above 3 μm by nonlinear processes in short silica photonic crystal fibers is investigated numerically. It was found that wavelengths in the 3-3.5 μm range may be generated quite efficiently in centimeter-long fiber pieces when pumping with femtosecond pulses in the 1.55-2 μm range. Wavelengths in the range of 3.5-4 μm can in principle be generated, but these require shorter fiber lengths for efficient extraction. The results indicate that useful 3 μm sources may be fabricated with existing silica-based fiber technology. © 2013 Optical Society of America. phenomena.

Kontogeorgis G.M.,Technical University of Denmark
Chemical Engineering Research and Design | Year: 2013

Thermodynamics of complex systems (e.g. with associating molecules, multicomponent mixtures, multiphase equilibria, wide ranges of conditions, estimation of many different properties simultaneously) is a topic of great importance in chemical engineering and for a wide range of industrial applications. While specialized models can handle different cases, even complex ones, with the advent of powerful theories and computers there is the hope that a single or a few models could be suitable for a general modeling of complex thermodynamics. After more than 100 years with active use of thermodynamic models, we have now come to the understanding that simple one-fluid theories like the cubic equations of state or the various forms of local composition models will never be able to model a wide range of complex systems with sufficient accuracy. While various modern approaches have appeared, one very promising direction for a general and useful for engineering purposes modeling of complex thermodynamics is via the use of association theories e.g. those based on chemical theory (like APACT), or on the lattice theory (like NRHB) or those based on perturbation theory (like SAFT and CPA). The purpose of this review is two-fold: first to illustrate some of the significant capabilities of these association theories and why indeed they have already been extensively used and are expected to find even more applications in the future. The second and most important aspect of this review is to outline many of the non-answered questions about these association theories, provide answers to some of these questions and limitations based on recent research and highlight areas where further research is needed. © 2013 The Institution of Chemical Engineers.

Einsiedl F.,Technical University of Denmark
Applied Geochemistry | Year: 2012

The geochemistry and isotopic composition of a karstic coastal aquifer in western Ireland has shed light on the effect of sea-water/groundwater interactions on the water quality of Ireland's Atlantic coastal zone. The use of stable isotope data from the IAEA precipitation station in Valentia, located in SW Ireland has facilitated the characterization of groundwater recharge conditions in the western part of Ireland and suggests that groundwater is mostly replenished by the isotopically light winter precipitation. The dissolved SO42- in the karstic groundwater that was collected during baseflow conditions with δ 34S values between 4.6‰ and 18‰ may be composed of S stemming from three principal sources: SO42- derived from precipitation which is composed of both sea-spray S (δ 34S: 20‰) and an isotopically light anthropogenic source (δ 34S: 1-5‰), SO42-stemming from animal slurries (δ 34S: ~5‰), and intruding sea-water SO42- (δ 34S: 20.2‰). The isotopic composition of δ 18O in dissolved groundwater SO42- collected during baseflow conditions is interpreted as reflecting sea-water intrusion to the karstic coastal groundwater system. The highest δ 18O values in dissolved groundwater SO42- were in samples collected near the coast (4.8±0.4‰) and the lowest (2±0.5‰) were collected further inland. The δ 15N and δ 18O values of groundwater NO3- were between 3.4‰ and 11.4‰ and approximately 7.7‰, respectively, and reflect geochemical conditions in the aquifer that do not promote attenuation of NO3- through denitrification. As a result N loading to Kinvara Bay that is controlled by submarine groundwater discharge (SGD) was calculated as 5tons/day on average compared to an estimated N-input that derives from precipitation of approximately 2.5tons/a. SGD into the bay may result in near coastal sea-water quality changes. These results represent one of the first studies addressing the effect of groundwater quality in Ireland on the European Atlantic coastal zone. © 2011 Elsevier Ltd.

Petersen R.,University of Aalborg | Pedersen T.G.,University of Aalborg | Jauho A.-P.,Technical University of Denmark | Jauho A.-P.,Aalto University
ACS Nano | Year: 2011

Pristine graphene is a semimetal and thus does not have a band gap. By making a nanometer scale periodic array of holes in the graphene sheet a band gap may form; the size of the gap is controllable by adjusting the parameters of the lattice. The hole diameter, hole geometry, lattice geometry, and the separation of the holes are parameters that all play an important role in determining the size of the band gap, which, for technological applications, should be at least of the order of tenths of an eV. We investigate four different hole configurations: the rectangular, the triangular, the rotated triangular, and the honeycomb lattice. It is found that the lattice geometry plays a crucial role for size of the band gap: the triangular arrangement displays always a sizable gap, while for the other types only particular hole separations lead to a large gap. This observation is explained using Clar sextet theory, and we find that a sufficient condition for a large gap is that the number of sextets exceeds one-third of the total number of hexagons in the unit cell. Furthermore, we investigate nonisosceles triangular structures to probe the sensitivity of the gap in triangular lattices to small changes in geometry. © 2011 American Chemical Society.

Tvergaard V.,Technical University of Denmark
International Journal of Solids and Structures | Year: 2011

Numerical, axisymmetric cell model analyses are used to study the growth of voids in ductile metals, until the mechanism of coalescence with neighbouring voids sets in. A special feature of the present analyses is that extremely small values of the initial void volume fraction are considered, down to 10 -10, which means that the metal undergoes huge strains before coalescence. This is accounted for in the present analyses by using remeshing techniques. The evolution of the void shape during the large deformations is a natural outcome of the numerical analysis. Also the effect of different initial void shapes is considered, as well as the effect of different spacings between the voids in the axial and transverse directions. While these first analyses are carried out for voids in a homogeneous metal, a second set of cell model studies are carried out for voids that initiate from a crack in a hard second phase particle. As the particle deforms relatively little the void growth is here dominated by strong blunting of the metal at the tip of the initial penny-shaped crack. These analyses are used to estimate how well the void shape evolution would be approximated by assuming that the presence of the particle in the material adjacent to the void can be neglected. © 2010 Elsevier Ltd. All rights reserved.

Modi A.,Technical University of Denmark | Perez-Segarra C.D.,Polytechnic University of Catalonia
Solar Energy | Year: 2014

Concentrated solar power plants have attracted increasing interest from researchers and governments all over the world in recent years. An important part of these plants is the storage system which improves dispatchability and makes the plant more reliable. In this paper, a one-dimensional transient mathematical model for a single-tank thermocline thermal energy storage system is presented. The model used temperature dependent correlations to obtain the thermophysical properties for the heat transfer fluid and considered heat loss through the tank wall. The effect of variation in important system parameters like the type of heat transfer fluid, the storage temperature difference and the cycle cut-off criterion on system performance was investigated. The results suggest that two important aspects for assessing the performance of the system are the cyclic behaviour of the system and the time required to attain equilibrium conditions. These aspects directly influence the discharge capacity and discharge power of the storage system, and therefore play an essential role in understanding the start-up characteristics of the system and provide an insight regarding the availability of storage when designing the power cycle for concentrated solar power applications. It was also observed that the cycle durations and the time required to attain cyclic conditions are highly sensitive to not only the storage temperature difference, but also the cut-off temperature difference. © 2013 Elsevier Ltd.

Naik G.V.,Purdue University | Shalaev V.M.,Purdue University | Shalaev V.M.,Russian Quantum Center | Boltasseva A.,Purdue University | Boltasseva A.,Technical University of Denmark
Advanced Materials | Year: 2013

Materials research plays a vital role in transforming breakthrough scientific ideas into next-generation technology. Similar to the way silicon revolutionized the microelectronics industry, the proper materials can greatly impact the field of plasmonics and metamaterials. Currently, research in plasmonics and metamaterials lacks good material building blocks in order to realize useful devices. Such devices suffer from many drawbacks arising from the undesirable properties of their material building blocks, especially metals. There are many materials, other than conventional metallic components such as gold and silver, that exhibit metallic properties and provide advantages in device performance, design flexibility, fabrication, integration, and tunability. This review explores different material classes for plasmonic and metamaterial applications, such as conventional semiconductors, transparent conducting oxides, perovskite oxides, metal nitrides, silicides, germanides, and 2D materials such as graphene. This review provides a summary of the recent developments in the search for better plasmonic materials and an outlook of further research directions. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A theoretical study of differences in broadband high-indexcontrast grating (HCG) reflectors for TM and TE polarizations is presented, covering various grating parameters and properties of HCGs. It is shown that the HCG reflectors for TM polarization (TM HCG reflectors) have much thicker grating thicknesses and smaller grating periods than the TE HCG reflectors. This difference is found to originate from the different boundary conditions met for the electric field of each polarization. Due to this difference, the TM HCG reflectors have much shorter evanescent extension of HCG modes into low-refractive-index media surrounding the HCG. This enables to achieve a very short effective cavity length for VC-SELs, which is essential for ultrahigh speed VCSELs and MEMS-tunable VCSELs. The obtained understandings on polarization dependences will be able to serve as important design guidelines for various HCG-based devices. © 2015 Optical Society of America.

Aarestrup F.M.,Technical University of Denmark
Emerging infectious diseases | Year: 2012

The rapid advancement of genome technologies holds great promise for improving the quality and speed of clinical and public health laboratory investigations and for decreasing their cost. The latest generation of genome DNA sequencers can provide highly detailed and robust information on disease-causing microbes, and in the near future these technologies will be suitable for routine use in national, regional, and global public health laboratories. With additional improvements in instrumentation, these next- or third-generation sequencers are likely to replace conventional culture-based and molecular typing methods to provide point-of-care clinical diagnosis and other essential information for quicker and better treatment of patients. Provided there is free-sharing of information by all clinical and public health laboratories, these genomic tools could spawn a global system of linked databases of pathogen genomes that would ensure more efficient detection, prevention, and control of endemic, emerging, and other infectious disease outbreaks worldwide.

Jeong C.-H.,Technical University of Denmark
Acta Acustica united with Acustica | Year: 2011

Room surfaces have been extensively modeled as locally reacting in room acoustic predictions although such modeling could yield significant errors under certain conditions. Therefore, this study aims to propose a guideline for adopting the local reaction assumption by comparing predicted random incidence acoustical characteristics of typical building elements made of porous materials assuming extended and local reaction. For each surface reaction, five well-established wave propagation models, the Delany-Bazley, Miki, Beranek, Allard-Champoux, and Biot model, are employed. Effects of the flow resistivity and the absorber thickness on the difference between the two surface reaction models are examined and discussed. For a porous absorber backed by a rigid surface, the assumption of local reaction always underestimates the random incidence absorption coefficient and the local reaction models give errors of less than 10% if the thickness exceeds 120 mm for a flow resistivity of 5000 Nm-4s. As the flow resistivity doubles, a decrease in the required thickness by 25 mm is observed to achieve the same amount of error. For an absorber backed by an air gap, the thickness ratio between the material and air cavity is important, since the thicker the cavity, the more extendedly reacting the absorber. If the absorber thickness is approximately 40% of the cavity depth, the local reaction models give errors below 10% even for a low flow resistivity case. © S. Hirzel Verlag · EAA.

Leekitcharoenphon P.,Technical University of Denmark
BMC genomics | Year: 2012

The advances and decreasing economical cost of whole genome sequencing (WGS), will soon make this technology available for routine infectious disease epidemiology. In epidemiological studies, outbreak isolates have very little diversity and require extensive genomic analysis to differentiate and classify isolates. One of the successfully and broadly used methods is analysis of single nucletide polymorphisms (SNPs). Currently, there are different tools and methods to identify SNPs including various options and cut-off values. Furthermore, all current methods require bioinformatic skills. Thus, we lack a standard and simple automatic tool to determine SNPs and construct phylogenetic tree from WGS data. Here we introduce snpTree, a server for online-automatic SNPs analysis. This tool is composed of different SNPs analysis suites, perl and python scripts. snpTree can identify SNPs and construct phylogenetic trees from WGS as well as from assembled genomes or contigs. WGS data in fastq format are aligned to reference genomes by BWA while contigs in fasta format are processed by Nucmer. SNPs are concatenated based on position on reference genome and a tree is constructed from concatenated SNPs using FastTree and a perl script. The online server was implemented by HTML, Java and python script.The server was evaluated using four published bacterial WGS data sets (V. cholerae, S. aureus CC398, S. Typhimurium and M. tuberculosis). The evaluation results for the first three cases was consistent and concordant for both raw reads and assembled genomes. In the latter case the original publication involved extensive filtering of SNPs, which could not be repeated using snpTree. The snpTree server is an easy to use option for rapid standardised and automatic SNP analysis in epidemiological studies also for users with limited bioinformatic experience. The web server is freely accessible at http://www.cbs.dtu.dk/services/snpTree-1.0/.

Jensen K.,Technical University of Denmark | Panagiotou G.,University of Hong Kong | Kouskoumvekaki I.,University of Hong Kong
PLoS Computational Biology | Year: 2014

Awareness that disease susceptibility is not only dependent on genetic make up, but can be affected by lifestyle decisions, has brought more attention to the role of diet. However, food is often treated as a black box, or the focus is limited to few, well-studied compounds, such as polyphenols, lipids and nutrients. In this work, we applied text mining and Naïve Bayes classification to assemble the knowledge space of food-phytochemical and food-disease associations, where we distinguish between disease prevention/amelioration and disease progression. We subsequently searched for frequently occurring phytochemical-disease pairs and we identified 20,654 phytochemicals from 16,102 plants associated to 1,592 human disease phenotypes. We selected colon cancer as a case study and analyzed our results in three directions; i) one stop legacy knowledge-shop for the effect of food on disease, ii) discovery of novel bioactive compounds with drug-like properties, and iii) discovery of novel health benefits from foods. This works represents a systematized approach to the association of food with health effect, and provides the phytochemical layer of information for nutritional systems biology research. © 2014 Jensen et al.

Sorensen J.N.,Technical University of Denmark
Annual Review of Fluid Mechanics | Year: 2011

This article reviews the most important aerodynamic research topics in the field of wind energy. Wind turbine aerodynamics concerns the modeling and prediction of aerodynamic forces, such as performance predictions of wind farms, and the design of specific parts of wind turbines, such as rotor-blade geometry. The basics of the blade-element momentum theory are presented along with guidelines for the construction of airfoil data. Various theories for aerodynamically optimum rotors are discussed, and recent results on classical models are presented. State-of-the-art advanced numerical simulation tools for wind turbine rotors and wakes are reviewed, including rotor predictions as well as models for simulating wind turbine wakes and flows in wind farms. © 2011 by Annual Reviews. All rights reserved.

Peterson A.A.,Stanford University | Peterson A.A.,Technical University of Denmark | Norskov J.K.,Stanford University | Norskov J.K.,SLAC
Journal of Physical Chemistry Letters | Year: 2012

The electrochemical reduction of CO 2 into hydrocarbons and alcohols would allow renewable energy sources to be converted into fuels and chemicals. However, no electrode catalysts have been developed that can perform this transformation with a low overpotential at reasonable current densities. In this work, we compare trends in binding energies for the intermediates in CO 2 electrochemical reduction and present an activity "volcano" based on this analysis. This analysis describes the experimentally observed variations in transition-metal catalysts, including why copper is the best-known metal electrocatalyst. The protonation of adsorbed CO is singled out as the most important step dictating the overpotential. New strategies are presented for the discovery of catalysts that can operate with a reduced overpotential. © 2012 American Chemical Society.

Markou G.,Agricultural University of Athens | Angelidaki I.,Technical University of Denmark | Georgakakis D.,Agricultural University of Athens
Applied Microbiology and Biotechnology | Year: 2012

Microalgal biomass seems to be a promising feedstock for biofuel generation. Microalgae have relative high photosynthetic efficiencies, high growth rates, and some species can thrive in brackish water or seawater and wastewater from the food- and agro-industrial sector. Today, the main interest in research is the cultivation of microalgae for lipids production to generate biodiesel. However, there are several other biological or thermochemical conversion technologies, in which microalgal biomass could be used as substrate. However, the high protein content or the low carbohydrate content of the majority of the microalgal species might be a constraint for their possible use in these technologies. Moreover, in the majority of biomass conversion technologies, carbohydrates are the main substrate for production of biofuels. Nevertheless, microalgae biomass composition could be manipulated by several cultivation techniques, such as nutrient starvation or other stressed environmental conditions, which cause the microalgae to accumulate carbohydrates. This paper attempts to give a general overview of techniques that can be used for increasing the microalgal biomass carbohydrate content. In addition, biomass conversion technologies, related to the conversion of carbohydrates into biofuels are discussed. © Springer-Verlag 2012.

The development of effective vaccines against zoonotic pathogens represents a priority in public health protection programs. The design of clinical trials and appropriate data analysis of the experiments results are crucial for the assessment of vaccine effectiveness. This manuscript reviews important issues related to the assessment of the effectiveness of vaccines designed to obtain a quantitative reduction of the pathogen in animals or animal products. An effective vaccine will reduce the risk of human infections and therefore the number of human cases. Important considerations will be illustrated using a vaccination trial of a new campylobacter vaccine candidate developed to reduce the numbers of campylobacter in chickens and consequently the numbers of human campylobacteriosis cases. The design of the author's vaccination trial was based on the use of isolators, a parallel group design and several rotations. The effect of clustering or design effect was considered in the sample size calculations. Chickens were randomly assigned to different isolators (treatments) and challenged with Campylobacter jejuni. Samples were obtained at different intervals and processed in the laboratory. C. jejuni counts were determined as colony-forming unit-per-gram of chicken cecum or fecal mass in order to assess vaccine effectiveness. A desired vaccine effect of 2 logs reduction on the numbers of C. jejuni recovered from vaccinated chickens was selected. Sample-size calculations, desired vaccine effect, biological and epidemiological aspects, experimental design and appropriate statistical analysis of data considering group or clustering effects will be the focus of this manuscript.

Kiviluoma J.,VTT Technical Research Center of Finland | Meibom P.,Technical University of Denmark
Energy | Year: 2011

The article estimates the costs of plug-in electric vehicles (EVs) in a future power system as well as the benefits from smart charging and discharging EVs (smart EVs). To arrive in a good estimate, a generation planning model was used to create power plant portfolios, which were operated in a more detailed unit commitment and dispatch model. In both models the charging and discharging of EVs is optimised together with the rest of the power system. Neither the system cost nor the market price of electricity for EVs turned out to be high (36-263 €/vehicle/year in the analysed scenarios). Most of the benefits of smart EVs come from smart timing of charging although benefits are also accrued from provision of reserves and lower power plant portfolio cost. The benefits of smart EVs are 227 €/vehicle/year. This amount has to cover all expenses related to enabling smart EVs and need to be divided between different actors. Additional benefits could come from the avoidance of grid related costs of immediate charging, but these were not part of the analysis. © 2011 Elsevier Ltd.

Jeong C.-H.,Technical University of Denmark
Acta Acustica united with Acustica | Year: 2013

For room acoustic simulations, the acoustic characteristics of room boundary surfaces are typically calculated under the assumption that the surfaces are sufficiently large. In this study, a reflection coefficient for finite surfaces is suggested and its performance is assessed through case studies involving simulation of rectangular rooms using a phased beam tracing method. The suggested reflection coefficient employs the radiation impedance of a finite surface by combining the radiation impedance of an infinitely large surface and that of the finite surface backed by an infinite rigid baffle. For 28 surface impedance values that are assigned to all the boundary surfaces, the suggested reflection coefficient is found to improve low frequency responses compared to the infinite panel theory; larger improvements are found for a more disproportionate room, more absorptive surfaces, and surfaces having larger negative phase angles of the surface impedance. A larger improvement is also found for a nonuniform absorption case than for a uniform absorption setting having a similar equivalent absorption coefficient. © S. Hirzel Verlag.

Smith A.,Technical University of Denmark
European Physical Journal H | Year: 2013

A magnetic body changes its thermal state when subjected to a changing magnetic field. In particular, if done under adiabatic conditions, its temperature changes. For the past 15 years the magnetocaloric effect has been the focus of significant research due to its possible application for efficient refrigeration near room temperature. At the same time, it has become common knowledge within the magnetic refrigeration research community that the magnetocaloric effect was discovered by the German physicist E. Warburg in 1881. We reexamine the original literature and show that this is a misleading reading of what Warburg did, and we argue that the discovery of the effect should instead be attributed to P. Weiss and A. Piccard in 1917. © EDP Sciences, Springer-Verlag 2013.

Santurette S.,Technical University of Denmark
The Journal of the Acoustical Society of America | Year: 2012

The ability of eight normal-hearing listeners and fourteen listeners with sensorineural hearing loss to detect and identify pitch contours was measured for binaural-pitch stimuli and salience-matched monaurally detectable pitches. In an effort to determine whether impaired binaural pitch perception was linked to a specific deficit, the auditory profiles of the individual listeners were characterized using measures of loudness perception, cognitive ability, binaural processing, temporal fine structure processing, and frequency selectivity, in addition to common audiometric measures. Two of the listeners were found not to perceive binaural pitch at all, despite a clear detection of monaural pitch. While both binaural and monaural pitches were detectable by all other listeners, identification scores were significantly lower for binaural than for monaural pitch. A total absence of binaural pitch sensation coexisted with a loss of a binaural signal-detection advantage in noise, without implying reduced cognitive function. Auditory filter bandwidths did not correlate with the difference in pitch identification scores between binaural and monaural pitches. However, subjects with impaired binaural pitch perception showed deficits in temporal fine structure processing. Whether the observed deficits stemmed from peripheral or central mechanisms could not be resolved here, but the present findings may be useful for hearing loss characterization.

The concept of the multifunctional platform for rural energy access has increasingly been supported by donors in five West African countries since 1994. While it is often referred to as a highly successful concept, recent reviews and interviews with local stakeholders in Mali and Burkina Faso indicate that the high aspirations to be found in project descriptions and early evaluations are only partly reflected in activities on the ground. This paper illustrates how the multipurpose aspects of the platform have made the concept a nexus of potential achievements that are highly valued in the dominant discourse of development, and how including concerns, such as poverty alleviation, gender equity, local democracy, decentralisation and the environment, have attracted donors outside the energy sector. The paper thus argues that, while the integration of multiple technical functions, preconceived organisational set-ups and local fuel production have in fact had limited or even adverse effects on the outcome of the multifunctional platform programme, these virtues have proved essential in presenting the concept at the policy level. This analysis of the dilemma between mobilizing funding and implementing practical programmes provides an argument for building development aid on existing structures instead of inventing new complicated concepts and approaches. © 2009 Elsevier Ltd. All rights reserved.

The part-load performance of gas and steam turbine combined cycles intended for naval use is of great importance, and it is influenced by the gas turbine configuration and load control strategy. This paper is aimed at quantifying the effects of variable geometry on the gas turbine part-load performance. Subsequently, in another paper, the effects of variable geometry on the part-load performance for combined cycles used for ship propulsion will be presented. Moreover, this paper is aimed at developing methodologies and deriving models for part-load simulations suitable for energy system analysis of various components within gas turbines. Two different gas turbine configurations are studied, a two-shaft aero-derivative configuration and a single-shaft industrial configuration. When both gas turbine configurations are running in part-load using fuel flow control, the results indicate better part-load performance for the two-shaft gas turbine. Reducing the load this way is accompanied by a much larger decrease in exhaust gas temperature for the single-shaft gas turbine than for the two-shaft configuration. As used here, the results suggest that variable geometry generally deteriorates the gas turbine part-load performance. © 2009 Elsevier Ltd. All rights reserved.

Hoorfar J.,Technical University of Denmark
APMIS. Supplementum | Year: 2011

As food safety management further develops, microbiological testing will continue to play an important role in assessing whether Food Safety Objectives are achieved. However, traditional microbiological culture-based methods are limited, particularly in their ability to provide timely data. The present review discusses the reasons for the increasing interest in rapid methods, current developments in the field, the research needs, and the future trends. The advent of biotechnology has introduced new technologies that led to the emergence of rapid diagnostic methods and altered food testing practices. Rapid methods are comprised of many different detection technologies, including specialized enzyme substrates, antibodies and DNA, ranging from simple differential plating media to the use of sophisticated instruments. The use of non-invasive sampling techniques for live animals especially came into focus with the 1990s outbreak of bovine spongiform encephalopathy that was linked to the human outbreak of Creutzfeldt Jakob's Disease. Serology is still an important tool in preventing foodborne pathogens to enter the human food supply through meat and milk from animals. One of the primary uses of rapid methods is for fast screening of large number of samples, where most of them are expected to be test-negative, leading to faster product release for sale. This has been the main strength of rapid methods such as real-time Polymerase Chain Reaction (PCR). Enrichment PCR, where a primary culture broth is tested in PCR, is the most common approach in rapid testing. Recent reports show that it is possible both to enrich a sample and enumerate by pathogen-specific real-time PCR, if the enrichment time is short. This can be especially useful in situations where food producers ask for the level of pathogen in a contaminated product. Another key issue is automation, where the key drivers are miniaturization and multiple testing, which mean that not only one instrument is flexible enough to test for many pathogens but also many pathogens can be detected with one test. The review is mainly based on the author's scientific work that has contributed with the following new developments to this field: (i) serologic tests for large-scale screening, surveillance, or eradication programs, (ii) same-day detection of Salmonella that otherwise was considered as difficult to achieve, (iii) pathogen enumeration following a short log-phase enrichment, (iv) detection of foodborne pathogens in air samples, and finally (v) biotracing of pathogens based on mathematical modeling, even in the absence of isolate. Rapid methods are discussed in a broad global health perspective, international food supply, and for improvement of quantitative microbial risk assessments. The need for quantitative sample preparation techniques, culture-independent, metagenomic-based detection, online monitoring, a global validation infrastructure has been emphasized. The cost and ease of use of rapid assays remain challenging obstacles to surmount. © 2011 The Author. APMIS © 2011 APMIS.

Stolpe M.,Technical University of Denmark
Structural and Multidisciplinary Optimization | Year: 2010

We study some fundamental mathematical properties of discretized structural topology optimization problems. Either compliance is minimized with an upper bound on the volume of the structure, or volume is minimized with an upper bound on the compliance. The design variables are either continuous or 0-1. We show, by examples which can be solved by hand calculations, that the optimal solutions to the problems in general are not unique and that the discrete problems possibly have inactive volume or compliance constraints. These observations have immediate consequences on the theoretical convergence properties of penalization approaches based on material interpolation models. Furthermore, we illustrate that the optimal solutions to the considered problems in general are not symmetric even if the design domain, the external loads, and the boundary conditions are symmetric around an axis. The presented examples can be used as teaching material in graduate and undergraduate courses on structural topology optimization. © 2010 Springer-Verlag.

Andersen M.R.,Technical University of Denmark
BMC genomics | Year: 2012

The degradation of plant materials by enzymes is an industry of increasing importance. For sustainable production of second generation biofuels and other products of industrial biotechnology, efficient degradation of non-edible plant polysaccharides such as hemicellulose is required. For each type of hemicellulose, a complex mixture of enzymes is required for complete conversion to fermentable monosaccharides. In plant-biomass degrading fungi, these enzymes are regulated and released by complex regulatory structures. In this study, we present a methodology for evaluating the potential of a given fungus for polysaccharide degradation. Through the compilation of information from 203 articles, we have systematized knowledge on the structure and degradation of 16 major types of plant polysaccharides to form a graphical overview. As a case example, we have combined this with a list of 188 genes coding for carbohydrate-active enzymes from Aspergillus niger, thus forming an analysis framework, which can be queried. Combination of this information network with gene expression analysis on mono- and polysaccharide substrates has allowed elucidation of concerted gene expression from this organism. One such example is the identification of a full set of extracellular polysaccharide-acting genes for the degradation of oat spelt xylan. The mapping of plant polysaccharide structures along with the corresponding enzymatic activities is a powerful framework for expression analysis of carbohydrate-active enzymes. Applying this network-based approach, we provide the first genome-scale characterization of all genes coding for carbohydrate-active enzymes identified in A. niger.

Markussen T.,Technical University of Denmark
Nano Letters | Year: 2012

Ge-Si core-shell nanowires with surface disorder are shown to be very promising candidates for thermoelectric applications. In atomistic calculations we find that surface roughness decreases the phonon thermal conductance significantly. On the contrary, the hole states are confined to the Ge core and are thereby shielded from the surface disorder, resulting in large electronic conductance values even in the presence of surface disorder. This decoupling of the electronic and phonon transport is very favorable for thermoelectric purposes, giving rise to promising room temperature figure of merits ZT > 2. It is also found that the Ge-Si core-shell wires perform better than pure Si nanowires. © 2012 American Chemical Society.

Witt C.,Technical University of Denmark
Theoretical Computer Science | Year: 2012

Recently, various randomized search heuristics have been studied for the solution of the minimum vertex cover problem, in particular for sparse random instances according to the G(n,cn) model, where c>0 is a constant. Methods from statistical physics suggest that the problem is easy if c

Stolpe M.,Technical University of Denmark
Structural and Multidisciplinary Optimization | Year: 2014

The equivalent static loads algorithm is an increasingly popular approach to solve dynamic response structural optimization problems. The algorithm is based on solving a sequence of related static response structural optimization problems with the same objective and constraint functions as the original problem. The optimization theoretical foundation of the algorithm is mainly developed in Park and Kang (J Optim Theory Appl 118(1):191–200, 2003). In that article it is shown, for a certain class of problems, that if the equivalent static loads algorithm terminates then the KKT conditions of the original problem and the final sub-problem are identical. The proof of this important theoretical result is unfortunately both incomplete and incorrect and the result is generally not valid. The missing parts of the proof are herein identified and corrected and the critical mistake in the proof is located and explained. We suggest a modified method in the same spirit for which the requested result is proved. © 2014, Springer-Verlag Berlin Heidelberg.

Thomassen C.,Technical University of Denmark | Thomassen C.,King Abdulaziz University
Journal of Combinatorial Theory. Series B | Year: 2012

We show that, for each natural number k>1, every graph (possibly with multiple edges but with no loops) of edge-connectivity at least 2k 2+k has an orientation with any prescribed outdegrees modulo k provided the prescribed outdegrees satisfy the obvious necessary conditions. For k=3 the edge-connectivity 8 suffices. This implies the weak 3-flow conjecture proposed in 1988 by Jaeger (a natural weakening of Tutte's 3-flow conjecture which is still open) and also a weakened version of the more general circular flow conjecture proposed by Jaeger in 1982. It also implies the tree-decomposition conjecture proposed in 2006 by Bárat and Thomassen when restricted to stars. Finally, it is the currently strongest partial result on the (2+ε)-flow conjecture by Goddyn and Seymour. © 2011 Elsevier Inc..

Enz S.,Technical University of Denmark
Flow Measurement and Instrumentation | Year: 2010

Coriolis flowmeters (CFM) are forced to vibrate by a periodic excitation usually applied midpipe through an electromagnetic actuator. From hands-on experience with industrial CFMs it appears, that the electromagnetic actuator has to be located as symmetric as possible. For CFM design and trouble-shooting it is of relevance to know how and if imperfections, related to the excitation location, influence the dynamic behavior of the vibrating fluid-conveying pipes employed in CFMs. A simple model of an imperfectly excited, simply supported, straight, single pipe CFM is investigated using a multiple time scaling perturbation analysis. The result is a simple analytical expression for the approximated phase shift, which offers a direct insight into how the location of the actuator influences the phase shift. It appears, that asymmetrical forcing combined with fluctuating pipe damping could be a factor contributing to lack of zero shift stability observed with some industrial CFMs. Tests of the approximated solution against results obtained by pure numerical analysis using Galerkin expansion show very good agreement. The effect of asymmetric detector positions is also investigated. Any asymmetry in the detectors position, e.g. due to manufacturing variations or improper handling of the CFM, induces a phase shift that leads to changes of the meter's sensitivity, and could therefore result into erroneous measurements of the mass flow. This phase shift depends on the mass flow and does not contribute to a lacking zero-point stability. The validity of the hypotheses, which are assumed to be basically similar for more complicated geometries, e.g. bended and/or dual pipe CFMs, with or without multiple actuators, is suggested to be tested using laboratory experiments with purpose built non-ideal CFMs. © 2010 Elsevier Ltd.

Pinson P.,Technical University of Denmark
Quarterly Journal of the Royal Meteorological Society | Year: 2012

Ensemble forecasts of (u,v)-wind are of crucial importance for a number of decision-making problems related to e.g. air traffic control, ship routeing and energy management. The skill of these ensemble forecasts as generated by NWP-based models can be maximised by correcting for their lack of sufficient reliability. The original framework introduced here allows for an adaptive bivariate calibration of these ensemble forecasts. The originality of this methodology lies in the fact that calibrated ensembles still consist of a set of (space-time) trajectories, after translation and dilation. In parallel, the parameters of the models employed for improving the stochastic properties of the generating processes involved are adaptively and recursively estimated to accommodate smooth changes in the process characteristics and to lower computational costs. The approach is applied and evaluated based on the adaptive calibration of ECMWF ensemble forecasts of (u,v)-wind at 10 m above ground level over Europe over a three-year period between December 2006 and December 2009. Substantial improvements in (bivariate) reliability and in various deterministic/probabilistic scores are observed. Finally, the maps of translation and dilation factors are discussed. © 2012 Royal Meteorological Society.

Rokni M.,Technical University of Denmark
Energy | Year: 2014

An integrated gasification solid oxide fuel cell (SOFC) and Stirling engine for combined heat and power application is analyzed. The target for electricity production is 120kW. Woodchips are used as gasification feedstock to produce syngas, which is then used to feed the SOFC stacks for electricity production. Unreacted hydrocarbons remaining after the SOFC are burned in a catalytic burner, and the hot off-gases from the burner are recovered in a Stirling engine for electricity and heat production. Domestic hot water is used as a heat sink for the Stirling engine. A complete balance-of-plant is designed and suggested. Thermodynamic analysis shows that a thermal efficiency of 42.4% based on the lower heating value (LHV) can be achieved if all input parameters are selected conservatively. Different parameter studies are performed to analyze the system behavior under different conditions. The analysis shows that the decreasing number of stacks from a design viewpoint, indicating that plant efficiency decreases but power production remains nearly unchanged. Furthermore, the analysis shows that there is an optimum value for the utilization factor of the SOFC for the suggested plant design with the suggested input parameters. This optimum value is approximately 65%, which is a rather modest value for SOFC. In addition, introducing a methanator increases plant efficiency slightly. If SOFC operating temperature decreases due to new technology then plant efficiency will slightly be increased. Decreasing gasifier temperature, which cannot be controlled, causes the plant efficiency to increase also. © 2014 Elsevier Ltd.

Mowat A.M.,University of Glasgow | Agace W.W.,Lund University | Agace W.W.,Technical University of Denmark
Nature Reviews Immunology | Year: 2014

The intestine represents the largest compartment of the immune system. It is continually exposed to antigens and immunomodulatory agents from the diet and the commensal microbiota, and it is the port of entry for many clinically important pathogens. Intestinal immune processes are also increasingly implicated in controlling disease development elsewhere in the body. In this Review, we detail the anatomical and physiological distinctions that are observed in the small and large intestines, and we suggest how these may account for the diversity in the immune apparatus that is seen throughout the intestine. We describe how the distribution of innate, adaptive and innate-like immune cells varies in different segments of the intestine and discuss the environmental factors that may influence this. Finally, we consider the implications of regional immune specialization for inflammatory disease in the intestine. © 2014 Macmillan Publishers Limited. All rights reserved.

Laegsgaard J.,Technical University of Denmark
Journal of the Optical Society of America B: Optical Physics | Year: 2011

Nonlinear propagation in slow-light states of high-index photonic crystal fibers (PCFs) is studied numerically. To avoid divergencies in dispersion and nonlinear parameters around the zero-velocity mode, a time-propagating generalized nonlinear Schrödinger equation is formulated. Calculated slow-light modes in a solid core chalcogenide PCF are used to parameterize the model, which is shown to support standing and moving spatial solitons. Inclusion of Raman scattering slows down moving solitons exponentially, so that the zero-velocity soliton becomes an attractor state. An analytical expression for the deceleration rate that compares favorably with the numerical results is derived. Collisions of successive solitons due to the Raman deceleration are studied numerically, and it is found that the soliton interaction is mostly repulsive, as expected from the established theory of fiber solitons. © 2010 Optical Society of America.

Bekiaris V.,Lund University | Persson E.K.,Lund University | Agace W.W.,Lund University | Agace W.W.,Technical University of Denmark
Immunological Reviews | Year: 2014

The intestine presents a huge surface area to the outside environment, a property that is of critical importance for its key functions in nutrient digestion, absorption, and waste disposal. As such, the intestine is constantly exposed to dietary and microbial-derived foreign antigens, to which immune cells within the mucosa must suitably respond to maintain intestinal integrity, while also providing the ability to mount effective immune responses to potential pathogens. Dendritic cells (DCs) are sentinel immune cells that play a central role in the initiation and differentiation of adaptive immune responses. In the intestinal mucosa, DCs are located diffusely throughout the intestinal lamina propria, within gut-associated lymphoid tissues, including Peyer's patches and smaller lymphoid aggregates, as well as in intestinal-draining lymph nodes, including mesenteric lymph nodes. The recognition that dietary nutrients and microbial communities in the intestine influence both mucosal and systemic immune cell development and function as well as immune-mediated disease has led to an explosion of literature in mucosal immunology in recent years and a growing interest in the functionality of intestinal DCs. In the current review, we discuss recent findings from our group and others that have provided important insights regarding murine and human intestinal lamina propria DCs and highlighted marked developmental and functional heterogeneity within this compartment. A thorough understanding of the role these subsets play in the regulation of intestinal immune homeostasis and inflammation will help to define novel strategies for the treatment of intestinal pathologies and contribute to improved rational design of mucosal vaccines. © 2014 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

Jensen P.A.,Technical University of Denmark
Facilities | Year: 2010

Purpose: The purpose of this paper is to present a conceptual framework - the FM Value Map - to understand and explain the different ways in which FM can add value to a core business, and possibly to the surroundings. Design/methodology/approach: The value map has been developed based on inductive reasoning from an analysis of a large number of cases in an explorative empirical study of FM best practice in the Nordic countries of Europe. It has been tested and modified from discussions with practitioners in a Nordic FM project group and aligned with the current European standardisation of taxonomy for FM. Findings: The FM Value Map was successfully tested in a number of case studies from companies in the five Nordic countries. Research limitations/implications: The present version of the FM Value Map is not seen as a final model, but as a result of an initial development. The model should be tested and validated further and also refined. Practical implications: The FM Value Map can be used in general to provide a better understanding of the value and contributions of FM, for instance by FM organisations in the dialogue with their customers. Originality/value: The FM Value Map is a unique conceptual framework, and a comparison with other models shows that it provides the most holistic framework by including the impacts on the surroundings and all relevant stakeholders. © Emerald Group Publishing Limited.

Hilgers G.,Technical University of Denmark
Journal of applied clinical medical physics / American College of Medical Physics | Year: 2014

Philips Healthcare released a novel metal artifact reduction algorithm for large orthopedic implants (O-MAR). Little information was available about its CT number accuracy. Since CT numbers are used for tissue heterogeneity corrections in external beam radiotherapy treatment planning, we performed a phantom study to assess the CT number accuracy of O-MAR. Two situations were simulated: a patient with a unilateral metallic hip prosthesis and a patient with bilateral metallic hip prostheses. We compared the CT numbers in the O-MAR reconstructions of the simulations to those in the nonO-MAR reconstruction and to those in a metal-free baseline reconstruction. In both simulations, the CT number accuracy of the O-MAR reconstruction was better than the CT number accuracy of the nonO- MAR reconstruction. In the O-MAR reconstruction of the unilateral simulation, all CT numbers were accurate within ± 5 HU (AAPM criterion). In the O-MAR reconstruction of the bilateral simulation, CT numbers were found that differed more than ± 5 HU from the metal-free baseline values. However, none of these differences were clinically relevant.

Nielsen F.A.,Technical University of Denmark
Neuroinformatics | Year: 2014

As open science neuroinformatics databases the Brede Database and Brede Wiki seek to make distribution and federation of their content as easy and transparent as possible. The databases rely on simple formats and allow other online tools to reuse their content. This paper describes the possible interconnections on different levels between the Brede tools and other databases. © 2013 Springer Science+Business Media New York.

Flyvbjerg H.,Technical University of Denmark
Bioinformatics | Year: 2014

Motivation: Next-generation sequencing produces vast amounts of data with errors that are difficult to distinguish from true biological variation when coverage is low. Results: We demonstrate large reductions in error frequencies, especially for high-error-rate reads, by three independent means: (i) filtering reads according to their expected number of errors, (ii) assembling overlapping read pairs and (iii) for amplicon reads, by exploiting unique sequence abundances to perform error correction. We also show that most published paired read assemblers calculate incorrect posterior quality scores. Availability and implementation: These methods are implemented in the USEARCH package. Binaries are freely available at http://drive5.com/usearch. © The Author 2015. Published by Oxford University Press. All rights reserved.

Kiil S.,Technical University of Denmark
Journal of Coatings Technology Research | Year: 2012

Coating degradation mechanisms of thermoset coatings exposed to ultraviolet radiation and humidity at constant temperature are investigated. The essential processes, photoinitiated oxidation reactions, intrafilm oxygen permeability, water absorption and diffusion, reduction of crosslink density, and development of a thin surface oxidation zone are quantified and a mathematical model for degrading coatings developed. Front-Tracking techniques are used to determine the rate of movement of the oxidation and ablation fronts, the positions of which define the extension of the surface oxidation zone. Three previous and independent experimental investigations with two-component, densely crosslinked, epoxy-Amine model coatings were selected for verification of the mathematical model. Simulations can match and explain transient mass loss and coating thickness reduction data and are in agreement with infrared measurements of carbonyl groups formed in the surface zone. The thickness of the stable surface oxidation zone, which is established after an initial ablation lag time, is estimated by the model to 0.5- 2 lm in good agreement with previous measurements. Simulated concentration profiles of active groups, oxygen, and radicals in the stable surface oxidation zone are presented and analyzed. The mathematical model can be used for obtaining a quantitative insight into the degradation of thermoset coatings and has potential, after further development, to complete commercial coatings and dynamic exposure conditions, to become a supplementing tool for predicting in-service coating behavior based on accelerated laboratory measurements. © The Author(s) 2011.

Laegsgaard J.,Technical University of Denmark
Journal of the Optical Society of America B: Optical Physics | Year: 2012

A full-vectorial nonlinear propagation equation for short pulses in tapered optical fibers is developed. Specific emphasis is placed on the importance of the field normalization convention for the structure of the equations, and the interpretation of the resulting field amplitudes. Different numerical schemes for interpolation of fiber parameters along the taper are discussed and tested in numerical simulations on soliton propagation and generation of continuum radiation in short photonic-crystal fiber tapers. © 2012 Optical Society of America.

Grivel J.-C.,Technical University of Denmark
Journal of Thermal Analysis and Calorimetry | Year: 2014

The thermal decomposition of Dy(III), Tb(III), Gd(III), Eu(III), and Sm(III) propionate monohydrates was studied in argon by means of simultaneous differential thermal analysis and thermogravimetry, infrared-spectroscopy, X-ray diffraction, and optical microscopy. After dehydration, which takes place below 120 C, all salts decompose into dioxycarbonates with simultaneous release of CO2 and C2H5COC2H5 (3-pentanone) between 250 and 460 C. However, whereas the anhydrous Dy-, Tb-, and Gd-propionates appear to transform into RE2O2CO 3 (rare earth [RE] = Dy, Tb, Gd) in a single step, an intermediate stage involving a RE2O(C2H5CO2) 4 composition was evidenced in the case of the Eu- and Sm-propionates. For all compounds, further decomposition of RE2O 2CO3 into the corresponding sesquioxides (RE 2O3) is accompanied by the release of CO2. The thermal decomposition of Dy- and Tb-propionates occurs entirely in the solid state. In contrast the dehydrated Gd-, Eu-, and Sm-propionates melt at increasingly higher temperatures. Evidence for recrystallization was found in conjunction with the onset of decomposition of these three propionates. © 2013 Akadémiai Kiadó, Budapest, Hungary.

Different support instruments for renewable energy expose investors differently to market risks. This has implications on the attractiveness of investment. We use mean-variance portfolio analysis to identify the risk implications of two support instruments: feed-in tariffs and feed-in premiums. Using cash flow analysis, Monte Carlo simulations and mean-variance analysis, we quantify risk-return relationships for an exemplary offshore wind park in a simplified setting. We show that feed-in tariffs systematically require lower direct support levels than feed-in premiums while providing the same attractiveness for investment, because they expose investors to less market risk. These risk implications should be considered when designing policy schemes. © 2013 Elsevier Ltd.

Laegsgaard J.,Technical University of Denmark
Optics Express | Year: 2016

A coupled-mode formalism, earlier used to describe transverse mode instabilities in single-pass optical fiber amplifiers, is extended to the case of double-pass amplifiers. Contrary to the single-pass case, it is shown that the thermo-optic nonlinearity can couple light at the same frequency between the LP01 and LP11 modes, leading to a static deformation of the output beam profile. This novel phenomenon is caused by the interaction of light propagating in either direction with thermo-optic index perturbations caused by light propagating in the opposite direction. The threshold power for the static deformation is found to be several times lower than what is typically found for the dynamic modal instabilities observed in single-pass amplifiers. © 2016 Optical Society of America.

Integrated and external torrefaction is analyzed and compared via thermodynamic modeling. In this paper, integrated torrefaction is defined as torrefaction integrated with entrained flow gasification. External torrefaction is defined as the decentralized production of torrefied wood pellets and centralized conversion of the pellets by entrained flow gasification. First, the syngas production of the two methods was compared. Second, the two methods were compared by considering complete biorefineries with either integrated torrefaction or external torrefaction. The first part of the analysis showed that the biomass to syngas efficiency can be increased from 63% to 86% (LHV-dry) when switching from external torrefaction to integrated torrefaction. The second part of the analysis showed that the total energy efficiency (biomass to methanol+net electricity) could be increased from 53% to 63% when switching from external torrefaction to integrated torrefaction. The costs of this increase in energy efficiency are as follows: 1) more difficult transport, storage and handling of the biomass feedstock (wood chips vs. torrefied wood pellets); 2) reduced plant size; 3) no net electricity production; and 4) a more complex plant design. © 2014 Elsevier Ltd.

Grivel J.-C.,Technical University of Denmark
Journal of Analytical and Applied Pyrolysis | Year: 2010

The thermal decomposition of lutetium(III) propionate monohydrate (Lu(C2H5CO2)3·H2O) in argon was studied by means of thermogravimetry, differential thermal analysis, IR-spectroscopy and X-ray diffraction. Dehydration takes place around 90 °C. It is followed by the decomposition of the anhydrous propionate to Lu2O2CO3 with evolution of CO2 and 3-pentanone (C2H5COC2H5) between 300 °C and 400 °C. The further decomposition of Lu2O 2CO3 to Lu2O3 is characterized by an intermediate constant mass plateau corresponding to a Lu2O 2.5(CO3)0.5 overall composition and extending from approximately 550 °C to 720 °C. Full conversion to Lu 2O3 is achieved at about 1000 °C. Whereas the temperatures and solid reaction products of the first two decomposition steps are similar to those previously reported for the thermal decomposition of lanthanum(III) propionate monohydrate, the final decomposition of the oxycarbonate to the rare-earth oxide proceeds in a different way, which is here reminiscent of the thermal decomposition path of Lu(C3H 5O2)·2CO(NH2)2·2H 2O. © 2010 Elsevier B.V. All rights reserved.

Zawadzki P.,Technical University of Denmark
Journal of Physical Chemistry C | Year: 2013

Charge transport to surface reactive sites is a crucial step in any photocatalytic process. In the most popular photocatalyst - the anatase TiO 2-this step is complicated by the fact that photogenerated carriers can trap. Studies of charge trapping and transfer in anatase often employ transient absorption spectroscopy (TAS), but the understanding of the optical absorption due to trapped carriers in TiO2 is incomplete. On the basis of the generalized Δ self-consistent field density functional theory (Δ-SCF DFT) calculations, we attribute the experimentally observed absorption band at 430-550 nm to the interpolaron transitions of the stable surface and subsurface O- centers and associate the blue shift of the spectra after the photoexcitation with holes migration to surfaces. We also suggest that subsurface hole trapping may contribute to generally lower photocatalytic performance of the anatase (101) surface compared to the (001) surface. © 2013 American Chemical Society.

Evgrafov A.,Technical University of Denmark | Evgrafov A.,Norwegian University of Science and Technology
Computer Methods in Applied Mechanics and Engineering | Year: 2014

We introduce a new algorithm for solving certain classes of topology optimization problems, which enjoys fast local convergence normally achieved by the full space methods while working in a smaller reduced space. The computational complexity of Newton's direction finding subproblem in the algorithm is comparable with that of finding the steepest descent direction in the traditional first order nested/reduced space algorithms for topology optimization. That is, the space reduction is computationally inexpensive, and more importantly it does not ruin the sparsity of the full-space system of optimality conditions.The fast local convergence of the algorithm allows one to efficiently solve a sequence of optimization problems for varying parameters (numerical continuation). This can be utilized for eliminating the errors introduced by the approximate enforcement of the boundary conditions or 0/1-type constraints on the design field through penalties in many topology optimization approaches.We test the algorithm on the benchmark problems of dissipated power minimization for Stokes flows, and in all cases the algorithm outperforms the traditional first order reduced space/nested approaches by a factor varying from two to almost twenty in terms of the number of iterations while attaining an almost unprecedented accuracy in solving the discretized topology optimization problem. Finally we present a few extensions to the algorithm, one involving computations on adaptively refined meshes and another related to solving topology optimization problems for non-Newtonian fluids. © 2014 Elsevier B.V.

Pedersen P.T.,Technical University of Denmark
Marine Structures | Year: 2010

It is the purpose of the paper to present a review of prediction and analysis tools for collision and grounding analyses and to outline a probabilistic procedure for which these tools can be used by the maritime industry to develop performance based rules to reduce the risk associated with human, environmental and economic costs of collision and grounding events. The main goal of collision and grounding research should be to identify the most economic risk control options associated with prevention and mitigation of collision and grounding events. © 2010 Elsevier Ltd.

Brunskog J.,Technical University of Denmark
Journal of the Acoustical Society of America | Year: 2012

The single wall is the simplest element of concern in building acoustics, but there still remain some open questions regarding the sound insulation of this simple case. The two main reasons for this are the effects on the excitation and sound radiation of the wall when it has a finite size, and the fact that the wave field in the wall is consisting of two types of waves, namely forced waves due to the exciting acoustic field, and free bending waves due to reflections in the boundary. The aim of the present paper is to derive simple analytical formulas for the forced part of the airborne sound insulation of a single homogeneous wall of finite size, using a variational technique based on the integral-differential equation of the fluid loaded wall. The so derived formulas are valid in the entire audible frequency range. The results are compared with full numerical calculations, measurements and alternative theory, with reasonable agreement. © 2012 Acoustical Society of America.

Jeong C.-H.,Technical University of Denmark
Journal of the Acoustical Society of America | Year: 2012

Defining accurate acoustical boundary conditions is of crucial importance for room acoustic simulations. In predicting sound fields using phased geometrical acoustics methods, both absorption coefficients and surface impedances of the boundary surfaces can be used, but no guideline has been developed on which boundary condition produces accurate results. In this study, various boundary conditions in terms of normal, random, and field incidence absorption coefficients and normal incidence surface impedance are used in a phased beam tracing model, and the simulated results are validated with boundary element solutions. Two rectangular rooms with uniform and non-uniform absorption distributions are tested. Effects of the neglect of reflection phase shift are also investigated. It is concluded that the impedance, random incidence, and field incidence absorption boundary conditions produce reasonable results with some exceptions at low frequencies for acoustically soft materials. © 2012 Acoustical Society of America.

Nymand M.,University of Southern Denmark | Andersen M.A.E.,Technical University of Denmark
IEEE Transactions on Industrial Electronics | Year: 2010

A new design approach achieving very high conversion efficiency in low-voltage high-power isolated boost dcdc converters is presented. The transformer eddy-current and proximity effects are analyzed, demonstrating that an extensive interleaving of primary and secondary windings is needed to avoid high winding losses. The analysis of transformer leakage inductance reveals that extremely low leakage inductance can be achieved, allowing stored energy to be dissipated. Power MOSFETs fully rated for repetitive avalanches allow primary-side voltage clamp circuits to be eliminated. The oversizing of the primary-switch voltage rating can thus be avoided, significantly reducing switch-conduction losses. Finally, silicon carbide rectifying diodes allow fast diode turn-off, further reducing losses. Detailed test results from a 1.5-kW full-bridge boost dcdc converter verify the theoretical analysis and demonstrate very high conversion efficiency. The efficiency at minimum input voltage and maximum power is 96.8%. The maximum efficiency of the proposed converter is 98%. © 2009 IEEE.

Kadkhodazadeh S.,Technical University of Denmark
Micron | Year: 2013

This article reviews the application of high resolution scanning transmission electron microscopy (STEM) to semiconductor quantum dots (QDs) and quantum wires (QWRs). Different imaging and analytical techniques in STEM are introduced and key examples of their application to QDs and QWRs are presented. In addition, the benefits offered by aberration correction are discussed and an outlook for future developments of high resolution STEM analysis of QDs and QWRs is given. © 2012 Elsevier Ltd.

Olsen C.A.,Technical University of Denmark
Biopolymers | Year: 2011

The field of peptoid (i.e., N-alkylglycine) research has been thriving since the first publications on this molecular design appeared in 1992. A highly efficient and modular synthetic platform, which is compatible with automation and ready generation of combinatorial libraries, was published the same year. This has enabled the investigation of numerous compounds with this architecture, and ligands with a wide variety of interesting biological targets have thus been discovered. Furthermore, detailed biophysical and structural studies focusing on the investigation of the conformational space adopted and three-dimensional folding of these peptide mimics have been undertaken. The same is true for beta-peptides (i.e., oligomers composed of beta-amino acids). Since the first publication describing peptide mimics combining these two structural modifications [the N-alkyl-beta-alanines (beta-peptoids)] in 1998, on the other hand, the application of this backbone construct has appeared much more sparsely in the literature. The present perspective article will provide an overview of the data obtained for beta-peptoid-containing peptide mimics as well as a discussion of the future challenges associated with this type of backbone modification.

Azizi R.,Technical University of Denmark
Engineering Fracture Mechanics | Year: 2012

Damage evolution at the fiber matrix interface in Metal Matrix Composites (MMCs) is studied using strain gradient theory of plasticity. The study includes the rate independent formulation of energetic strain gradient plasticity for the matrix, purely elastic model for the fiber and cohesive zone model for the fiber-matrix interface. For the micro structure, free energy holds both elastic strains and plastic strain gradients. Due to the gradient theory, higher order boundary conditions must be considered. A unit cell with a circular elastic fiber is studied by the numerical finite element cell model under simple shear and transverse uniaxial tension using plane strain and periodic boundary conditions. The result of the overall response curve, effective plastic strain, effective stress and higher order stress distributions are shown. The effect of the material length scale, maximum stress carried by the interface and the work of separation per unit interface area on the composites overall behavior are investigated. The results are compared with those for strong interface. © 2012 Elsevier Ltd.

Melikov A.K.,Technical University of Denmark
Indoor Air | Year: 2016

Indoor environment affects the health, comfort, and performance of building occupants. The energy used for heating, cooling, ventilating, and air conditioning of buildings is substantial. Ventilation based on total volume air distribution in spaces is not always an efficient way to provide high-quality indoor environments at the same time as low-energy consumption. Advanced air distribution, designed to supply clean air where, when, and as much as needed, makes it possible to efficiently achieve thermal comfort, control exposure to contaminants, provide high-quality air for breathing and minimizing the risk of airborne cross-infection while reducing energy use. This study justifies the need for improving the present air distribution design in occupied spaces, and in general the need for a paradigm shift from the design of collective environments to the design of individually controlled environments. The focus is on advanced air distribution in spaces, its guiding principles and its advantages and disadvantages. Examples of advanced air distribution solutions in spaces for different use, such as offices, hospital rooms, vehicle compartments, are presented. The potential of advanced air distribution, and individually controlled macro-environment in general, for achieving shared values, that is, improved health, comfort, and performance, energy saving, reduction of healthcare costs and improved well-being is demonstrated. Performance criteria are defined and further research in the field is outlined. © 2016 John Wiley & Sons A/S.

Parisio G.,University of Padua | Sperotto M.M.,Technical University of Denmark | Ferrarini A.,University of Padua
Journal of the American Chemical Society | Year: 2012

The transverse motion of molecules from one leaflet to the other of a lipid bilayer, or flip-flop, represents a putative mechanism for their transmembrane transport and may contribute to the asymmetric distribution of components in biomembranes. However, a clear understanding of this process is still missing. The scarce knowledge derives from the difficulty of experimental determination. Because of its slow rate on the molecular time scale, flip-flop is challenging also for computational techniques. Here, we report a study of the passive transbilayer diffusion of steroids, based on a kinetic model derived from the analysis of their free energy surface, as a function of their position and orientation in the bilayer. An implicit membrane description is used, where the anisotropy and the nonuniformity of the bilayer environment are taken into account in terms of the gradients of density, dielectric permittivity, acyl chain order parameters, and lateral pressure. The flip-flop rates are determined by solving the Master Equation that governs the time evolution of the system, with transition rates between free energy minima evaluated according to the Kramers theory. Considering various steroids (cholesterol, lanosterol, ketosterone, 5-cholestene, 25-hydroxycholesterol, and testosterone), we can discuss how differences in molecular shape and polarity affect the pathway and the rate of flip-flop in a liquid crystalline 1,2-dipalmitoyl-sn-glycero-3- phosphatidylcholine (DPPC) bilayer, at low steroid concentration. We predict time scales ranging from microseconds to milliseconds, strongly affected by the presence of polar substituents and by their position in the molecular skeleton. © 2012 American Chemical Society.

Payne M.R.,Technical University of Denmark
ICES Journal of Marine Science | Year: 2010

The North Sea autumn-spawning herring (Clupea harengus) stock consists of a set of different spawning components. The dynamics of the entire stock have been well characterized, but although time-series of larval abundance indices are available for the individual components, study of the dynamics at the component level has historically been hampered by missing observations and high sampling noise. A simple state-space statistical model is developed that is robust to these problems, gives a good fit to the data, and proves capable of both handling and predicting missing observations well. Furthermore, the sum of the fitted abundance indices across all components proves an excellent proxy for the biomass of the total stock, even though the model utilizes information at the individual-component level. The Orkney-Shetland component appears to have recovered faster from historic depletion events than the other components, whereas the Downs component has been the slowest. These differences give rise to changes in stock composition, which are shown to vary widely within a relatively short time. The modelling framework provides a valuable tool for studying and monitoring the dynamics of the individual components of the North Sea herring stock. © 2010 International Council for the Exploration of the Sea. Published by Oxford Journals. All rights reserved.

Andersen M.R.,Technical University of Denmark
Briefings in Functional Genomics | Year: 2014

Primary metabolism affects all phenotypical traits of filamentous fungi. Particular examples include reacting to extracellular stimuli, producing precursor molecules required for cell division and morphological changes as well as providing monomer building blocks for production of secondary metabolites and extracellular enzymes. In this review, all annotated genes from four Aspergillus species have been examined. In this process, it becomes evident that 80-96% of the genes (depending on the species) are still without verified function. A significant proportion of the genes with verified metabolic functions are assigned to secondary or extracellular metabolism, leaving only 2-4% of the annotated genes within primary metabolism. It is clear that primary metabolism has not received the same attention in the post-genomic area asmany other research areasc-despite its role at the very centre of cellular function. However, several methods can be employed to use the metabolic networks in tandem with comparative genomics to accelerate functional assignment of genes in primary metabolism. In particular, gaps in metabolic pathways can be used to assign functions to orphan genes. In this review, applications of this from the Aspergillus genes will be examined, and it is proposed that, where feasible, this should be a standard part of functional annotation of fungal genomes. © The Author 2014.

Pedersen N.L.,Technical University of Denmark
Mechanism and Machine Theory | Year: 2010

Bending stress plays a significant role in gear design wherein its magnitude is controlled by the nominal bending stress and the stress concentration due to the geometrical shape. The bending stress is indirectly related to shape changes made to the cutting tool. This work shows that the bending stress can be reduced significantly by using asymmetric gear teeth and by shape optimizing the gear through changes made to the tool geometry. However, to obtain the largest possible stress reduction a custom tool must be designed depending on the number of teeth, but the stress reductions found are not very sensitive to small design changes. This observation suggests the use of two new standard cutting tools. © 2010 Elsevier Ltd. All rights reserved.

Nielsen A.A.,Technical University of Denmark
IEEE Transactions on Image Processing | Year: 2011

This paper introduces kernel versions of maximum autocorrelation factor (MAF) analysis and minimum noise fraction (MNF) analysis. The kernel versions are based upon a dual formulation also termed Q-mode analysis in which the data enter into the analysis via inner products in the Gram matrix only. In the kernel version, the inner products of the original data are replaced by inner products between nonlinear mappings into higher dimensional feature space. Via kernel substitution also known as the kernel trick these inner products between the mappings are in turn replaced by a kernel function and all quantities needed in the analysis are expressed in terms of this kernel function. This means that we need not know the nonlinear mappings explicitly. Kernel principal component analysis (PCA), kernel MAF, and kernel MNF analyses handle nonlinearities by implicitly transforming data into high (even infinite) dimensional feature space via the kernel function and then performing a linear analysis in that space. Three examples show the very successful application of kernel MAF/MNF analysis to: 1) change detection in DLR 3K camera data recorded 0.7 s apart over a busy motorway, 2) change detection in hyperspectral HyMap scanner data covering a small agricultural area, and 3) maize kernel inspection. In the cases shown, the kernel MAF/MNF transformation performs better than its linear counterpart as well as linear and kernel PCA. The leading kernel MAF/MNF variates seem to possess the ability to adapt to even abruptly varying multi and hypervariate backgrounds and focus on extreme observations. © 2011 IEEE.

Xydis G.,Technical University of Denmark
Energy and Buildings | Year: 2013

In this paper wind energy to thermal and cold storage scenarios was examined to enable high wind integration through converting renewable electricity excess into thermal or cooling energy, saving part of the energy used in an area and eliminating the need to possibly build a new coal fired plant. Case studies in Crete Island (not interconnected to the power grid of Greek mainland) with onshore wind power installed were investigated. The aim of this work was to review the options for greater integration of renewables into the grid and the main idea was to analyze the wind to thermal and to cold storage according to the needs of two small municipalities. © 2012 Elsevier B.V. All rights reserved.

Modersheim S.A.,Technical University of Denmark
Proceedings of the ACM Conference on Computer and Communications Security | Year: 2010

The abstraction and over-approximation of protocols and web services by a set of Horn clauses is a very successful method in practice. It has however limitations for protocols and web services that are based on databases of keys, contracts, or even access rights, where revocation is possible, so that the set of true facts does not monotonically grow with state transitions. We extend the scope of these over-approximation methods by defining a new way of abstraction that can handle such databases, and we formally prove that the abstraction is sound. We realize a translator from a convenient specification language to standard Horn clauses and use the verifier ProVerif and the theorem prover SPASS to solve them. We show by a number of examples that this approach is practically feasible for wide variety of verification problems of security protocols and web services. Copyright 2010 ACM.

Hansen K.K.,Technical University of Denmark
Applied Catalysis B: Environmental | Year: 2010

The literature on direct electrochemical reduction of NOx in a solid state cell has been reviewed. It is shown that the reduction of nitric oxide either occurs on the electrode or on the electrolyte if F-centers are formed. It is also shown that some oxide based electrodes has a high apparent selectivity towards the reduction of nitric oxide in a net oxidizing atmosphere. The activity and apparent selectivity of oxide based electrodes is strongly dependent on the composition of the oxide. The selectivity of noble metal based electrodes is generally very low. However, coating of noble metal based electrodes can give current efficiencies of up to 20% even in the presence of large amounts of oxygen. © 2010 Elsevier B.V.

In recent years, several authors have proposed easier numerical methods to find the critical speed in railway dynamical problems. Actually, the methods do function in some cases, but in most cases it is really a gamble. In this article, the methods are discussed and the pros and contras are commented upon. I also address the questions when a linearisation is allowed and the curious fact that the hunting motion is more robust than the ideal stationary-state motion on the track. Concepts such as multiple attractors, subcritical and supercritical bifurcations, permitted linearisation, the danger of running at supercritical speeds and chaotic motion are addressed. © 2013 Taylor and Francis Group, LLC.

Thompson M.K.,Technical University of Denmark
CIRP Annals - Manufacturing Technology | Year: 2013

This paper introduces a model to integrate the traditional requirements process into Axiomatic Design Theory and proposes a method to structure the requirements process. The method includes a requirements classification system to ensure that all requirements information can be included in the Axiomatic Design process, a stakeholder classification system to reduce the chances of excluding one or more key stakeholders, and a table to visualize the mapping between the stakeholders and their requirements. © 2013 CIRP.

Pedersen J.G.,Technical University of Denmark | Pedersen T.G.,University of Aalborg
Physical Review B - Condensed Matter and Materials Physics | Year: 2013

We study graphene antidot lattices (GALs) in magnetic fields. Using a tight-binding model and a recursive Green's function technique that we extend to deal with periodic structures, we calculate Hofstadter butterflies of GALs. We compare the results to those obtained in a simpler gapped graphene model. A crucial difference emerges in the behavior of the lowest Landau level, which in a gapped graphene model is independent of magnetic field. In stark contrast to this picture, we find that in GALs the band gap can be completely closed by applying a magnetic field. While our numerical simulations can only be performed on structures much smaller than can be experimentally realized, we find that the critical magnetic field for which the gap closes can be directly related to the ratio between the cyclotron radius and the neck width of the GAL. In this way, we obtain a simple scaling law for extrapolation of our results to more realistically sized structures and find resulting quenching magnetic fields that should be well within reach of experiments. © 2013 American Physical Society.

Zhu X.,Technical University of Denmark
Nature Nanotechnology | Year: 2015

Colour generation by plasmonic nanostructures and metasurfaces has several advantages over dye technology: reduced pixel area, sub-wavelength resolution and the production of bright and non-fading colours. However, plasmonic colour patterns need to be pre-designed and printed either by e-beam lithography (EBL) or focused ion beam (FIB), both expensive and not scalable processes that are not suitable for post-processing customization. Here we show a method of colour printing on nanoimprinted plasmonic metasurfaces using laser post-writing. Laser pulses induce transient local heat generation that leads to melting and reshaping of the imprinted nanostructures. Depending on the laser pulse energy density, different surface morphologies that support different plasmonic resonances leading to different colour appearances can be created. Using this technique we can print all primary colours with a speed of 1 ns per pixel, resolution up to 127,000 dots per inch (DPI) and power consumption down to 0.3 nJ per pixel. © 2015 Nature Publishing Group

Morup M.,Technical University of Denmark
Wiley Interdisciplinary Reviews: Data Mining and Knowledge Discovery | Year: 2011

Tensor (multiway array) factorization and decomposition has become an important tool for datamining. Fueled by the computational power of modern computer researchers can now analyze large-scale tensorial structured data that only a few years ago would have been impossible. Tensor factorizations have several advantages over two-way matrix factorizations including uniqueness of the optimal solution and component identification even when most of the data is missing. Furthermore, multiway decomposition techniques explicitly exploit the multiway structure that is lost when collapsing some of the modes of the tensor in order to analyze the data by regular matrix factorization approaches. Multiway decomposition is being applied to new fields every year and there is no doubt that the future will bring many exciting new applications. The aim of this overview is to introduce the basic concepts of tensor decompositions and demonstrate some of themany benefits and challenges of modeling data multiway for a wide variety of data and problem domains. © 2011 John Wiley & Sons, Inc.

McCutcheon D.P.S.,Technical University of Denmark
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2016

We derive an extension to the quantum regression theorem which facilitates the calculation of two-time correlation functions and emission spectra for systems undergoing non-Markovian evolution. The derivation exploits projection operator techniques, with which we obtain explicit equations of motion for the correlation functions, making only a second-order expansion in the system-environment coupling strength and invoking the Born approximation at a fixed initial time. The results are used to investigate a driven semiconductor quantum dot coupled to an acoustic phonon bath, where we find the non-Markovian nature of the dynamics has observable signatures in the form of phonon sidebands in the resonance fluorescence emission spectrum. Furthermore, we use recently developed non-Markovianity measures to demonstrate an associated flow of information from the phonon bath back into the quantum dot exciton system. © 2016 American Physical Society.

Bogomolny M.,Technical University of Denmark
International Journal for Numerical Methods in Engineering | Year: 2010

This study shows how the Combined Approximations (CA) can be used for reducing the computational effort in Topology Optimization for free vibrations. The previously developed approach is based on the integration of several concepts and methods, including matrix factorization, series expansion, and reduced basis. In this paper the CA method is used for repeated eigenvalue analysis. Adjoint sensitivity analysis is developed such that the inaccuracies of the approximation are taken into consideration. Several 2-D and 3-D numerical examples show how optimal topology designs can be achieved by the reduced computational effort compared with the exact eigenvalue analysis. © 2009 John Wiley & Sons, Ltd.

The Yb concentration of double-clad optical fiber amplifiers is numerically optimized with respect to maximizing the transverse modal instability threshold in the presence of absorption arising from photodarkening. The pump cladding area is scaled with the Yb concentration to approximately maintain the pump absorption in operation. It is found that approximate analytical expressions can predict the optimized concentration levels found in numerical simulations with sufficient accuracy to be useful in fiber design. © 2016 Optical Society of America.

Janssen H.,Technical University of Denmark
International Journal for Numerical Methods in Engineering | Year: 2010

Efficient simulation of unsaturated moisture flow in porous media is of great importance in many engineering fields. The highly non-linear character of unsaturated flow typically gives sharp moving moisture fronts during wetting and drying of materials with strong local moisture permeability and capacity variations as result. It is shown that these strong variations conflict with the common preference for low-order numerical integration in finite element simulations of unsaturated moisture flow: inaccurate numerical integration leads to errors that are often far more important than errors from inappropriate discretization. In response, this article develops adaptive integration, based on nested Kronrod-Patterson-Gauss integration schemes: basically, the integration order is adapted to the locally observed grade of non-linearity. Adaptive integration is developed based on a standard infiltration problem, and it is demonstrated that serious reductions in the numbers of required integration points and discretization nodes can be obtained, thus significantly increasing computational efficiency. The multi-dimensional applicability is exemplified with two-dimensional wetting and drying applications. While developed for finite element unsaturated moisture transfer simulation, adaptive integration is similarly applicable for other non-linear problems and other discretization methods, and whereas perhaps outperformed by mesh-adaptive techniques, adaptive integration requires much less implementation and computation. Both techniques can moreover be easily combined. © 2009 John Wiley & Sons, Ltd.

Jeong C.-H.,Technical University of Denmark
Journal of the Acoustical Society of America | Year: 2013

Absorption coefficients measured by the chamber method are referred to as Sabine absorption coefficients, which sometimes exceed unity due to the finite size of a sample and non-uniform intensity in the reverberation chambers under test. In this study, conversion methods from Sabine absorption coefficients to random incidence absorption coefficients are proposed. The overestimations of the Sabine absorption coefficient are investigated theoretically based on Miki's model for porous absorbers backed by a rigid wall or an air cavity, resulting in conversion factors. Additionally, three optimizations are suggested: An optimization method for the surface impedances for locally reacting absorbers, the flow resistivity for extendedly reacting absorbers, and the flow resistance for fabrics. With four porous type absorbers, the conversion methods are validated. For absorbers backed by a rigid wall, the surface impedance optimization produces the best results, while the flow resistivity optimization also yields reasonable results. The flow resistivity and flow resistance optimization for extendedly reacting absorbers are also found to be successful. However, the theoretical conversion factors based on Miki's model do not guarantee reliable estimations, particularly at frequencies below 250 Hz and beyond 2500 Hz. © 2013 Acoustical Society of America.

Alessandrini S.,RSE SpA | Sperati S.,RSE SpA | Pinson P.,Technical University of Denmark
Applied Energy | Year: 2013

Wind power forecasting (WPF) represents a crucial tool to reduce problems of grid integration and to facilitate energy trading. By now it is advantageous to associate a deterministic forecast with a probabilistic one, in order to give to the end-users information about prediction uncertainty together with a single forecast power value for each future time horizon. A comparison between two different ensemble forecasting models, ECMWF EPS (Ensemble Prediction System in use at the European Centre for Medium-Range Weather Forecasts) and COSMO-LEPS (Limited-area Ensemble Prediction System developed within COnsortium for Small-scale MOdelling) applied for power forecasts on a real case in Southern Italy is presented. The approach is based on retrieving meteorological ensemble variables (i.e. wind speed, wind direction), using them to create a power Probability Density Function (PDF) for each 0-72. h ahead forecast horizon. A statistical calibration of the ensemble wind speed members based on the use of past wind speed measurements is explained. The two models are compared using common verification indices and diagrams. The higher horizontal resolution model (COSMO-LEPS) shows slightly better performances, especially for lead times from 27 to 48. h ahead. For longer lead times the increase in resolution does not seem crucial to obtain better results. A deterministic application using the mean of each ensemble system is also presented and compared with a higher resolution 0-72. h ahead power forecast based on the ECMWF deterministic model. It is noticeable that, in a deterministic approach, a higher resolution of the ensemble system can lead to slightly better results that are comparable with those of the high resolution deterministic model. © 2013 Elsevier Ltd.

Riisgard H.U.,University of Southern Denmark | Larsen P.S.,Technical University of Denmark
Marine Ecology Progress Series | Year: 2010

A large number of suspension-feeding aquatic animals (e.g. bivalves, polychaetes, ascidians, bryozoans, crustaceans, sponges, echinoderms, cnidarians) have specialized in grazing on not only the 2 to 200 μm phytoplankton but frequently also the 0.5 to 2 μm free-living bacteria, or they have specialized in capturing larger prey, e.g. zooplankton organisms. We review the different particle capture mechanisms in order to illustrate the many solutions to the common problem of obtaining nourishment from a dilute suspension of microscopic food particles. Despite the many differences in morphology and living conditions, particle capture mechanisms may be divided into 2 main types. (1) Filtering or sieving (e.g. through mucus nets, stiff cilia, filter setae), which is found in passive suspension feeders that rely on external currents to bring suspended particles to the filter, and in active suspension feeders that themselves produce a feeding flow by a variety of pump systems. Here the inventiveness of nature does not lie in the capture mechanism but in the type of pump system and filter pore-size. (2) A paddle-like flow manipulating system (e.g. cilia, cirri, tentacles, hair-bearing appendages) that acts to redirect an approaching suspended particle, often along with a surrounding 'fluid parcel', to a strategic location for arrest or further transport. Examples include (1) sieving (e.g. by microvilli in sponge choanocytes, mucus nets in polychaetes, acidians, and salps among others), filter setae in crustaceans, 'ciliary sieving' by stiff laterofrontal cilia in bryozoans and phoronids; and (2) 'cirri trapping' in mussels and other bivalves with eu-laterofrontal cirri, ciliary 'catch-up' in bivalve and gastropod veliger larvae, some polychaetes, entroprocts, and cycliophores. These capture mechanisms may involve contact with a particle, and possibly mechanoreception or chemore-ception, or may include redirection of particles by the interaction of multiple currents (e.g. in scallops and other bivalves without eu-laterofrontal cirri). Based on the review, we discuss the current physical and biological understanding of the capture process and suggest a number of specific problems related to particle capture, which may be solved in the future using advanced theoretical, computational and experimental techniques. © Inter-Research 2010.

Garcia-Lastra J.M.,University of the Basque Country | Garcia-Lastra J.M.,Technical University of Denmark
Physical Review B - Condensed Matter and Materials Physics | Year: 2010

The band gap of periodically doped graphene with hydrogen is investigated. It is found through a tight-binding (TB) model that for certain periodicities, called here nongap periodicities (NGPs), no gap is opened at the Dirac point. Density-functional-theory calculations show that a tiny gap is opened for NGPs due to exchange effects, not taken into account in the TB model. However, this tiny gap is one order of magnitude smaller than the gap opened for other periodicities different from NGPs. This remarkable reduction in the band-gap opening for NGPs provokes a crossing of the midgap and the conduction bands and, consequently, the metallization of the system. This result is also valid for other adsorbates different from atomic hydrogen. © 2010 The American Physical Society.

Kepp K.P.,Technical University of Denmark
ChemPhysChem | Year: 2013

This paper reports the computed O2 binding to heme, which for the first time explains experimental enthalpies for this process of central importance to bioinorganic chemistry. All four spin states along the relaxed Fe-O2-binding curves were optimized using the full heme system with dispersion, thermodynamic, and scalar-relativistic corrections, applying several density functionals. When including all these physical terms, the experimental enthalpy of O2 binding (-59 kJ mol-1) is closely reproduced by TPSSh-D3 (-66 kJ mol-1). Dispersion changes the potential energy surfaces and leads to the correct electronic singlet and heptet states for bound and dissociated O2. The experimental activation enthalpy of dissociation (∼82 kJ mol-1) was also accurately computed (∼75 kJ mol-1) with an actual barrier height of ∼60 kJ mol-1 plus a vibrational component of ∼10 and ∼5 kJ mol-1 due to the spin-forbidden nature of the process, explaining the experimentally observed difference of ∼20 kJ mol-1 in enthalpies of binding and activation. Most importantly, the work shows how the nearly degenerate singlet and triplet states increase crossover probability up to ∼0.5 and accelerate binding by ∼100 times, explaining why the spin-forbidden binding of O2 to heme, so fundamental to higher life forms, is fast and reversible. Crossing borders: The paper reports how close-lying spin states and resulting broad crossing regions enable fast, reversible oxygen binding to heme (see picture), despite the small spin-orbit coupling of this biologically important spin-forbidden process. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Boomsma W.,Copenhagen University | Ferkinghoff-Borg J.,Technical University of Denmark | Lindorff-Larsen K.,Copenhagen University
PLoS Computational Biology | Year: 2014

A key component of computational biology is to compare the results of computer modelling with experimental measurements. Despite substantial progress in the models and algorithms used in many areas of computational biology, such comparisons sometimes reveal that the computations are not in quantitative agreement with experimental data. The principle of maximum entropy is a general procedure for constructing probability distributions in the light of new data, making it a natural tool in cases when an initial model provides results that are at odds with experiments. The number of maximum entropy applications in our field has grown steadily in recent years, in areas as diverse as sequence analysis, structural modelling, and neurobiology. In this Perspectives article, we give a broad introduction to the method, in an attempt to encourage its further adoption. The general procedure is explained in the context of a simple example, after which we proceed with a real-world application in the field of molecular simulations, where the maximum entropy procedure has recently provided new insight. Given the limited accuracy of force fields, macromolecular simulations sometimes produce results that are at not in complete and quantitative accordance with experiments. A common solution to this problem is to explicitly ensure agreement between the two by perturbing the potential energy function towards the experimental data. So far, a general consensus for how such perturbations should be implemented has been lacking. Three very recent papers have explored this problem using the maximum entropy approach, providing both new theoretical and practical insights to the problem. We highlight each of these contributions in turn and conclude with a discussion on remaining challenges. © 2014 Boomsma et al.

Leander G.,Technical University of Denmark
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2011

We discuss complexities of advanced linear attacks. In particular, we argue why it is often more appropriate to examine the median of the complexity than the average value. Moreover, we apply our methods to the block ciphers PUFFIN and PRESENT. For PUFFIN, a 128 bit key cipher, we present an attack which breaks the cipher for at least a quarter of the keys with a complexity less than 258. In the case of PRESENT we show that the design is sound. The design criteria are sufficient to ensure the resistance against linear attacks, taking into account the notion of linear hulls. Finally, we show that statistical saturation attacks and multi dimensional linear attacks are almost identical. © 2011 International Association for Cryptologic Research.

Thygesen U.H.,Technical University of Denmark
Journal of Marine Systems | Year: 2011

Many oceanographic studies perform individual-based simulations of the transport and dispersal of particles such as fish larvae and eggs. An increasing number of these studies take place in reverse time, for example as to locate the origins of a particle observed at a given time and position. This paper demonstrates that when turbulent dispersal is taken into account, such backtracking can be done in different ways, which have different justifications and which may yield quite different results. We discuss three methods for reversing time: First, following the streamlines backwards while letting the eddy diffusivity perturb the trajectory; next, considering the initial position of an unknown parameter and estimating it using the maximum likelihood principle; and finally; assuming the trajectory to be a path in a stationary stochastic process and identifying the reversed-time transition probabilities. We illustrate the conceptual and algorithmic differences between the approaches. © 2011 Elsevier B.V.

A variety of approaches to attribute foodborne diseases to specific sources are available, including hazard occurrence analysis, epidemiological methods, intervention studies, and expert elicitations. The usefulness of each method to attribute disease caused by a foodborne hazard depends on the public health question being addressed, on the data requirements, on advantages and limitations of the method, and on the data availability of the country or region in question. Previous articles have described available methods for source attribution, but have focused only on foodborne microbiological hazards. These articles have described strengths and weaknesses of each method, but no guidance on how to choose the most appropriate tool to address different public health questions has thus far been provided. We reviewed available source attribution methods; assessed their applicability to attribute illness caused by enteric, parasitic, and chemical foodborne hazards to the responsible sources; and renamed some of the approaches. The main objective was to make recommendations on the most appropriate method(s) to attribute human disease caused by different foodborne hazards. We concluded that the proportion of disease that can be attributed to specific foods items or transmission routes may be estimated for the majority of the evaluated hazards by applying one or more of the source attribution methods assessed. It was also recognized that the use of source attribution methods may be limited to specific countries, reflecting the data availability. © Mary Ann Liebert, Inc.

Visser A.W.,Technical University of Denmark | Fiksen O.,University of Bergen
Marine Ecology Progress Series | Year: 2013

One of the most troubling aspects of ecosystem models is the use of rather arbitrary feeding and preference functions. The predictions of plankton functional type models have been shown to be highly sensitive to the choice of foraging model, particularly in multiple prey situations. Here we propose ecological mechanics and evolutionary logic as a solution to diet selection in ecosystem models. When a predator can consume a range of prey items, it has to choose which foraging mode to use, which prey to ignore and which ones to pursue, and animals are known to be particularly skilled in adapting their diets towards the most profitable prey items. We present a simple algorithm for plankton feeding on a size-spectrum of prey with particular energetic content, handling times and capture probabilities. We show that the optimal diet breadth changes with relative densities, but in a different way to the preference functions commonly used in models today. Indeed, depending on prey class resolution, optimal foraging can yield feeding rates that are considerably different from the 'switching functions' often applied in marine ecosystem models. Dietary inclusion is dictated by 2 optimality choices: (1) the diet breadth and (2) the actual feeding mode. The optimality model does not generate 'safety in low densities' for prey, as the 'switching function' does in ecosystem models, unless predators are shifting feeding mode adaptively. The actual diet, feeding rate and energy flux in ecosystem models can be determined by letting predators maximise energy intake or more properly, some measure of fitness where predation risk and cost are also included. An optimal foraging or fitness-maximising approach will give marine ecosystem models a sound principle to determine trophic interactions. © Inter-Research 2013.

Jacobsen N.S.,Technical University of Denmark
Proceedings. Biological sciences / The Royal Society | Year: 2014

Balanced harvesting, where species or individuals are exploited in accordance with their productivity, has been proposed as a way to minimize the effects of fishing on marine fish communities and ecosystems. This calls for a thorough examination of the consequences balanced harvesting has on fish community structure and yield. We use a size- and trait-based model that resolves individual interactions through competition and predation to compare balanced harvesting with traditional selective harvesting, which protects juvenile fish from fishing. Four different exploitation patterns, generated by combining selective or unselective harvesting with balanced or unbalanced fishing, are compared. We find that unselective balanced fishing, where individuals are exploited in proportion to their productivity, produces a slightly larger total maximum sustainable yield than the other exploitation patterns and, for a given yield, the least change in the relative biomass composition of the fish community. Because fishing reduces competition, predation and cannibalism within the community, the total maximum sustainable yield is achieved at high exploitation rates. The yield from unselective balanced fishing is dominated by small individuals, whereas selective fishing produces a much higher proportion of large individuals in the yield. Although unselective balanced fishing is predicted to produce the highest total maximum sustainable yield and the lowest impact on trophic structure, it is effectively a fishery predominantly targeting small forage fish.

Wisthaler A.,University of Innsbruck | Weschler C.J.,Rutgers University | Weschler C.J.,Technical University of Denmark
Proceedings of the National Academy of Sciences of the United States of America | Year: 2010

This study has used proton transfer reaction-mass spectrometry (PTR-MS) for direct air analyses of volatile products resulting from the reactions of ozone with human skin lipids. An initial series of small-scale in vitro and in vivo experiments were followed by experiments conducted with human subjects in a simulated office. The latter were conducted using realistic ozone mixing ratios (≈15 ppb with occupants present). Detected products included monoand bifunctional compounds that contain carbonyl, carboxyl, or α-hydroxy ketone groups. Among these, three previously unreported dicarbonyls have been identified, and two previously unreported α-hydroxy ketones have been tentatively identified. The compounds detected in this study (excepting acetone) have been overlooked in surveys of indoor pollutants, reflecting the limitations of the analytical methods routinely used to monitor indoor air. The results are fully consistent with the Criegee mechanism for ozone reactingwith squalene, the singlemost abundantunsaturated constituent of skin lipids, and several unsaturated fatty acidmoieties in their free or esterified forms. Quantitative product analysis confirms that squalene is the major scavenger of ozone at the interface between room air and the human envelope. Reactions between ozone and human skin lipids reduce the mixing ratio of ozone in indoor air, but concomitantly increase the mixing ratios of volatile products and, presumably, skin surface concentrations of less volatile products. Some of the volatile products, especially the dicarbonyls, may be respiratory irritants. Some of the less volatile products may be skin irritants.

Schlechtingen M.,EnBW | Santos I.F.,Technical University of Denmark | Achiche S.,Ecole Polytechnique de Montreal
IEEE Transactions on Sustainable Energy | Year: 2013

Four data-mining approaches for wind turbine power curve monitoring are compared. Power curve monitoring can be applied to evaluate the turbine power output and detect deviations, causing financial loss. In this research, cluster center fuzzy logic, neural network, and k-nearest neighbor models are built and their performance compared against literature. Recently developed adaptive neuro-fuzzy-interference system models are set up and their performance compared with the other models, using the same data. Literature models often neglect the influence of the ambient temperature and the wind direction. The ambient temperature can influence the power output up to 20%. Nearby obstacles can lower the power output for certain wind directions. The approaches proposed in literature and the ANFIS models are compared by using wind speed only and two additional inputs. The comparison is based on the mean absolute error, root mean squared error, mean absolute percentage error, and standard deviation using data coming from three pitch regulated turbines rating 2 MW each. The ability to highlight performance deviations is investigated by use of real measurements. The comparison shows the decrease of error rates and of the ANFIS models when taking into account the two additional inputs and the ability to detect faults earlier. © 2010-2012 IEEE.

Kepp K.P.,Technical University of Denmark
Journal of Physical Chemistry B | Year: 2014

Protein stability is affected in several diseases and is of substantial interest in efforts to correlate genotypes to phenotypes. Superoxide dismutase 1 (SOD1) is a suitable test case for such correlations due to its abundance, stability, available crystal structures and thermochemical data, and physiological importance. In this work, stability changes of SOD1 mutations were computed with five methods, CUPSAT, I-Mutant2.0, I-Mutant3.0, PoPMuSiC, and SDM, with emphasis on structural sensitivity as a potential issue in structure-based protein calculation. The large correlation between experimental literature data of SOD1 dimers and monomers (r = 0.82) suggests that mutations in separate protein monomers are mostly additive. PoPMuSiC was most accurate (typical MAE ∼ 1 kcal/mol, r ∼ 0.5). The relative performance of the methods was not very structure-dependent, and the more accurate methods also displayed less structural sensitivity, with the standard deviation from different high-resolution structures down to ∼0.2 kcal/mol. Structures of variable resolution and number of protein copies locally affected specific sites, emphasizing the use of state-relevant crystal structures when such sites are of interest, but had little impact on overall batch estimates. Protein-interaction effects (as a mimic of crystal packing) were small for the more accurate methods. Thus, batch computations, relevant to, e.g., comparisons of disease/nondisease mutant sets or different clades in phylogenetic trees, are much more significant than single mutant calculations and may be the only meaningful way to computationally bridge the genotype-phenotype gap of proteomics. Finally, mutations involving glycine were most difficult to model, of relevance to future method improvement. This could be due to structure changes (glycine has a low structural propensity) or water colocalization with glycine. © 2014 American Chemical Society.

Xydis G.,Technical University of Denmark
Renewable and Sustainable Energy Reviews | Year: 2012

In the present paper a Linear Programming (LP) methodology for the city of Athens, Attica region is implemented trying to identify the energy supply levels based on the energy use, aiming to determine the optimal way for the energy needs to be covered. The final aim was to find the best solution/s to meet the (metropolitan) city's energy needs using Renewable Energy Sources (RES) and additionally implement a techno-economic analysis through a developed tool, in order to find which RES should participate in the city's energy system examining different scenarios focusing not only on the projects' economical success but also on minimizing the cost for the society. © 2012 Elsevier Ltd.

Xydis G.,Technical University of Denmark | Koroneos C.,Aristotle University of Thessaloniki
Renewable and Sustainable Energy Reviews | Year: 2012

In the present paper the mismatch between the energy supply levels and the end use, in a broader sense, was studied for the Hellenic energy system. The ultimate objective was to optimize the way to meet the country's energy needs in every different administrative and geographical region using renewable energy sources (RES) and at the same time to define the remaining available space for energy recovery units from municipal solid waste (MSW) in each region to participate in the energy system. Based on the results of the different scenarios examined for meeting the electricity needs using linear programming and by using the exergoeconomic analysis the penetration grade was found for the proposed energy recovery units from MSWs in each region. © 2011 Elsevier Ltd. All rights reserved.

Lehre P.K.,Technical University of Denmark | Yao X.,University of Birmingham
IEEE Transactions on Evolutionary Computation | Year: 2012

The interplay between mutation and selection plays a fundamental role in the behavior of evolutionary algorithms (EAs). However, this interplay is still not completely understood. This paper presents a rigorous runtime analysis of a non-elitist population-based EA that uses the linear ranking selection mechanism. The analysis focuses on how the balance between parameter η, controlling the selection pressure in linear ranking, and parameter χ controlling the bit-wise mutation rate, impacts the runtime of the algorithm. The results point out situations where a correct balance between selection pressure and mutation rate is essential for finding the optimal solution in polynomial time. In particular, it is shown that there exist fitness functions which can only be solved in polynomial time if the ratio between parameters η and χ is within a narrow critical interval, and where a small change in this ratio can increase the runtime exponentially. Furthermore, it is shown quantitatively how the appropriate parameter choice depends on the characteristics of the fitness function. In addition to the original results on the runtime of EAs, this paper also introduces a very useful analytical tool, i.e., multi-type branching processes, to the runtime analysis of non-elitist population-based EAs. © 2011 IEEE.

Brander K.,Technical University of Denmark
Current Opinion in Environmental Sustainability | Year: 2010

Pathways for moving towards the goals of biodiversity conservation and food security in terrestrial systems include the application of trait-based ecology to develop highly productive agroecosystems with less negative effects on biodiversity. Although marine ecosystems have been impacted by human activity over several centuries, the changes have been unintentional and undirected; we have not learned how to enhance food production from the sea and are reliant, as hunter-gatherers, on natural production. The goals of maximising fisheries production and maintaining biodiversity may be difficult to achieve simultaneously, but studies of marine ecosystem responses and models of multispecies interactions provide a basis for new ecosystem approaches. © 2010 Elsevier B.V.

Tvergaard V.,Technical University of Denmark
Journal of the Mechanics and Physics of Solids | Year: 2014

Bifurcation into a shear band is studied for a porous ductile material subject to a combination of shear loading and tensile or compressive loading in different directions. The material with a periodic array of voids is studied by numerical solutions for a plane strain unit cell model with fully periodic boundary conditions. The fundamental pre-bifurcation solution has been studied before, with focus on ductile fracture under conditions of low stress triaxiality. In the previous studies it has been shown that voids in shear are flattened out to micro-cracks, which rotate and elongate until interaction with neighboring micro-cracks gives coalescence. These failure mechanisms are included in the present study, but here the focus is on the possibility that failure may occur earlier, if bifurcation leads to a shear band crossing over many cells, where the plastic strains inside the band will grow very large, while the overall strains in the material will not increase any further. The unit cell analysis with full periodicity is used both inside and outside the band to find the average behavior in the two material regions. This does not allow for point-wise satisfaction of compatibility and equilibrium along the interface between the two regions, but these conditions can be satisfied on the average. The bifurcation analysis includes determination of the direction along which a shear band is first critical. © 2014 Elsevier Ltd.

Rezanova N.J.,Technical University of Denmark | Ryan D.M.,University of Auckland
Computers and Operations Research | Year: 2010

The need to recover a train driver schedule occurs during major disruptions in the daily railway operations. Based on data from the Danish passenger railway operator DSB S-tog A/S, a solution method to the train driver recovery problem (TDRP) is developed. The TDRP is formulated as a set partitioning problem. We define a disruption neighbourhood by identifying a small set of drivers and train tasks directly affected by the disruption. Based on the disruption neighbourhood, the TDRP model is formed and solved. If the TDRP solution provides a feasible recovery for the drivers within the disruption neighbourhood, we consider that the problem is solved. However, if a feasible solution is not found, the disruption neighbourhood is expanded by adding further drivers or increasing the recovery time period. Fractional solutions to the LP relaxation of the TDRP are resolved with a constraint branching strategy using the depth-first search of the Branch & Bound tree. The LP relaxation of the TDRP possesses strong integer properties. We present test scenarios generated from the historical real-life operations data of DSB S-tog A/S. The numerical results show that all but one tested instances produce integer solutions to the LP relaxation of the TDRP and solutions are found within a few seconds. © 2009 Elsevier Ltd. All rights reserved.

Schmidt S.,Technical University of Denmark
Journal of Applied Crystallography | Year: 2014

A new approach for indexing multigrain diffraction data is presented. It is based on the use of a monochromatic beam simultaneously illuminating all grains. By operating in sub-volumes of Rodrigues space, a powerful vertex-finding algorithm can be applied, with a running time that is compatible with online analysis. The resulting program, GrainSpotter, is sufficiently fast to enable online analysis during synchrotron sessions. The program applies outlier rejection schemes, leading to more robust and accurate data. By simulations it is shown that several thousand grains can be retrieved. A new method to derive partial symmetries, called pseudo-twins, is introduced. Uniquely, GrainSpotter includes an analysis of pseudo-twins, which is shown to be critical to avoid erroneous grains resulting from the indexing. © 2014 International Union of Crystallography.

A gasification plant is integrated on the top of a solid oxide fuel cell (SOFC) cycle, while a steam turbine (ST) cycle is used as a bottoming cycle for the SOFC plant. The gasification plant was fueled by woodchips to produce biogas and the SOFC stacks were fired with biogas. The produced gas was rather clean for feeding to the SOFC stacks after a simple cleaning step. Because all the fuel cannot be burned in the SOFC stacks, a burner was used to combust the remaining fuel. The off-gases from the burner were then used to produce steam for the bottoming steam cycle in a heat recovery steam generator (HRSG). The steam cycle was modeled with a simple single pressure level. In addition, a hybrid recuperator was used to recover more energy from the HRSG and send it back to the SOFC cycle. Thus two different configurations were investigated to study the plants characteristic. Such system integration configurations are completely novel and have not been studied elsewhere. Plant efficiencies of 56% were achieved under normal operation which was considerably higher than the IGCC (Integrated Gasification Combined Cycle) in which a gasification plant is integrated with a gas turbine and a steam turbine. Furthermore, it is shown that under certain operating conditions, plant efficiency of about 62 is also possible to achieve. Copyright © 2012 De Gruyter.

The effect of stocking density on indicators of welfare has been investigated by several studies on farmed rainbow trout Oncorhynchus mykiss. However, the densities at which welfare are compromised remain ambiguous. Here three different stocking density treatments were selected based on the results of a previous study, where levels of crowding where determined using the spatial distribution of fish in two-tank systems. An un-crowded low density of 25 kgm(-3), the highest density accepted by the fish without showing indications of crowding stress of 80 kgm(-3) as the intermediate density, and the highest density accepted by the fish showing indications of crowding stress of 140 kgm(-3) as the high density were investigated. The aim of the present study was to examine the effect of being held at these densities on indicators of welfare. This was achieved through oxygen consumption measurements using automated respirometry, recording fin erosion, determining scale loss and analysing plasma cortisol and brain serotonergic activity levels. The results obtained in the present study indicated that at the lowest density the fish had the space and opportunity to display their natural aggressive behaviour and that the fish held at the highest density were exposed to a situation of confinement. © 2013.

Mohlmann D.,German Aerospace Center | Thomsen K.,Technical University of Denmark
Icarus | Year: 2011

Brines, i.e. aqueous salty solutions, increasingly play a role in a better understanding of physics and chemistry (and eventually also putative biology) of the upper surface of Mars. Results of physico-chemical modeling and experimentally determined data to characterize properties of cryobrines of potential interest with respect to Mars are described. Eutectic diagrams, the related numerical eutectic values of composition and temperature, the water activity of Mars-relevant brines of sulfates, chlorides, perchlorides and carbonates, including related deliquescence relative humidity, are parameters and properties, which are described here in some detail. The results characterize conditions for liquid low-temperature brines (" cryobrines") to evolve and to exist, at least temporarily, on present Mars. © 2010 Elsevier Inc.

Hagen A.,Technical University of Denmark
Chemical Physics Letters | Year: 2011

The potential NOx-reduction electro catalyst lanthanum strontium cuprate has been characterized with an in situ X-ray spectrochemical gas reaction cell. In a series of samples with increasing substitution of trivalent lanthanum by divalent strontium ions, the oxidation state of copper increased, maintaining charge neutrality, with the concentration of oxygen vacancies likely increasing at substitution ratios larger than Sr/La > 0.08. During heating in air, the valence of copper ions in the structure increased. Upon exposure to NO at 500 °C the valence of copper ions in a lanthanum strontium cuprate sample decreased, whereas it remained unchanged in the strontium-free lanthanum cuprate sample. © 2010 Elsevier B.V. All rights reserved.

Matzen R.,Technical University of Denmark
International Journal for Numerical Methods in Engineering | Year: 2011

The perfectly matched layer (PML) technique has demonstrated very high efficiency as absorbing boundary condition for the elastic wave equation recast as a first-order system in velocity and stress in attenuating non-grazing bulk and surface waves. This paper develops a novel convolutional PML formulation based on the second-order wave equation with displacements as the only unknowns to annihilate spurious reflections from near-grazing waves. The derived variational form allows for the use of e.g. finite element and the spectral element methods as spatial discretization schemes. A recursive convolution update scheme of second-order accuracy is employed such that highly stable, effective time integration with the Newmark-beta (implicit and explicit with mass lumping) method is achieved. The implementation requires minor modifications of existing displacement-based finite element software, and the stability and efficiency of the proposed formulation is verified by relevant two-dimensional benchmarks that accommodate bulk and surface waves. © 2011 John Wiley & Sons, Ltd.

Lehre P.K.,University of Nottingham | Witt C.,Technical University of Denmark
Algorithmica | Year: 2012

The complexity theory for black-box algorithms, introduced by Droste, Jansen, and Wegener (Theory Comput. Syst. 39:525-544, 2006), describes common limits on the efficiency of a broad class of randomised search heuristics. There is an obvious trade-off between the generality of the black-box model and the strength of the bounds that can be proven in such a model particular, the original black-box model provides for well-known benchmark problems relatively small lower bounds, which seem unrealistic in certain cases and are typically not met by popular search heuristics this paper, we introduce a more restricted black-box model for optimisation of pseudo-Boolean functions which we claim captures the working principles of many randomised search heuristics including simulated annealing, evolutionary algorithms, randomised local search, and others. The key concept worked out is an unbiased variation operator. Considering this class of algorithms, significantly better lower bounds on the black-box complexity are proved, amongst them an (nlog n) bound for functions with unique optimum. Moreover, a simple unimodal function and plateau functions are considered. We show that a simple (1 + 1) EA is able to match the runtime bounds in several cases. © 2011 The Author(s).

A numerical scheme for the transient solution of a generalized version of the Poisson-Nernst-Planck (PNP) equations is presented. The finite element method is used to establish the coupled non-linear matrix system of equations capable of solving the present problem iteratively. The PNP equations represent a set of diffusion equations for charged species, i.e. dissolved ions, present in the pore solution of a rigid porous material in which the surface charge can be assumed neglectable. These equations are coupled to the 'internally' induced electrical field and to the velocity field of the fluid. The Nernst-Planck equations describing the diffusion of the ionic species and Gauss' law in use are, however, coupled in both directions. The governing set of equations is derived from a simplified version of the so-called hybrid mixture theory (HMT). The simplifications used here mainly concerns ignoring the deformation and stresses in the porous material in which the ionic diffusion occurs. The HMT is a special version of the more 'classical' continuum mixture theories in the sense that it works with averaged equations at macroscale and that it includes the volume fractions of phases in its structure. The background to the PNP equations can by the HMT approach be described by using the postulates of mass conservation of constituents together with Gauss' law used together with consistent constitutive laws. The HMT theory includes the constituent forms of the quasistatic version of Maxwell's equations making it suitable for analyses of the kind addressed in this work. Within the framework of HTM, constitutive equations have been derived using the postulate of entropy inequality together with the technique of identifying properties by Lagrange multipliers. These results will be used in obtaining a closed set of equations for the present problem. © Springer Science+Business Media B.V. 2010.

Kepp K.P.,Technical University of Denmark
Journal of Inorganic Biochemistry | Year: 2011

Porphyrins are much studied due to their biochemical relevance and many applications. The density functional TPSSh has previously accurately described the energy of close-lying electronic states of transition metal systems such as porphyrins. However, a recent study questioned this conclusion based on calculations of five iron(III) porphines. Here, we compute the geometries of 80 different electronic configurations and the free energies of the most stable configurations with the functionals TPSSh, TPSS, and B3LYP. Zero-point energies and entropy favor high-spin by ~ 4 kJ/mol and 0-10 kJ/mol, respectively. When these effects are included, and all electronic configurations are evaluated, TPSSh correctly predicts the spin of all the four difficult phenylporphine cases and is within the lower bound of uncertainty of any known theoretical method for the fifth, iron(III) chloroporphine. Dispersion computed with DFT-D3 favors low-spin by 3-53 kJ/mol (TPSSh) or 4-15 kJ/mol (B3LYP) due to the attractive r - 6 term and the shorter distances in low-spin. The very large and diverse corrections from TPSS and TPSSh seem less consistent with the similarity of the systems than when calculated from B3LYP. If the functional-specific corrections are used, B3LYP and TPSSh are of equal accuracy, and TPSS is much worse, whereas if the physically reasonable B3LYP-computed dispersion effect is used for all functionals, TPSSh is accurate for all systems. B3LYP is significantly more accurate when dispersion is added, confirming previous results. © 2011 Elsevier Inc. All rights reserved.

Jacobsen C.,Technical University of Denmark
Annals of the New York Academy of Sciences | Year: 2010

Enrichment of foods with marine omega-3 polyunsaturated fatty acids (PUFA) poses a multidisciplinary challenge to food industry and academia. Although our knowledge about possible health effects of omega-3 PUFA has increased tremendously during the last 30 years, there is still a lot to be learned about these healthy fatty acids. Moreover, consumer acceptance and lipid oxidation of omega-3 PUFA-enriched food are other major challenges that the food industry meet when developing omega-3-enriched foods. Two examples on multidisciplinary research projects to overcome some of these challenges are given in this article together with cases studies illustrating how lipid oxidation can be prevented in a range of different omega-3-enriched foods. © 2010 New York Academy of Sciences.

Rorig-Dalgaard I.,Technical University of Denmark
Materials and Structures/Materiaux et Constructions | Year: 2013

Salt induced deterioration of structures and stones are generally recognized as a frequent and serious problem. The deterioration is especially undesired in relation to cultural heritage as it is impossible to recreate original material (e.g. original murals). By presence of salts in decorated vaults two different techniques are applied: poultices or establishment of climate chambers. Both techniques can result in ion transport away from the valuable surfaces with murals, but satisfying desalination has not been obtained according to conservators from the Danish National Museums mural preservation section in consistence with the present available literature. In the present paper the possibility for salt removal by utilizing a well known and accepted transport process, electromigration, is investigated, i.e. movement of ions in a solution in an applied electric DC field. An experimental laboratory setup was designed to approximate real conditions in vaults and with ion contents corresponding to normal heavily polluted church vaults (1.0 wt% Chloride, added as NaCl). During the electromigration process acid and base is produced at the electrodes due to electrode reactions and in a clarifying experiment with a traditional poultice significant pH changes and an absence of satisfying high desalination effect was measured. The new idea in the present paper was to introduce a calculated amount of buffer components corresponding to the productions during the electrode processes to a poultice (a solid) to minimize the adverse effects and to optimize on the effects. The results showed good ability to retain neutral pH values in the substrate which is of major importance when the method should be applied on existing structures. Also the desalination process continued until a very low and harmless salt content was reached after introduction of the buffer components. © 2012 RILEM.

Qing H.,Technical University of Denmark | Qing H.,Siemens AG
Materials and Design | Year: 2013

The influence of interface strength and loading conditions on the mechanical behavior of the metal-matrix composites is investigated in this paper. A program is developed to generate automatically 2D micromechanical Finite element (FE) models including interface, in which both the locations and dimensions of Silicon-Carbide (SiC) particles are randomly distributed. Finite element simulations of the deformation and damage evolution of SiC particle reinforced Aluminum (Al) alloy composite are carried out for different microstructures and interphase strengths under tensile, shear and combined tensile/shear loads. 2D cohesive element is applied to describe the fracture and failure process of interphase, while the damage models based on maximum principal stress criterion and the stress triaxial indicator are developed within Abaqus/Standard Subroutine USDFLD to simulate the failure process of SiC particles and aluminum alloy matrix, respectively. A series of computational experiments are performed to study the influence of particle arrangements, interface strengths and loading conditions of the representative volume element (RVE) on composite stiffness and strength properties. © 2013 Elsevier Ltd.

Two-dimensional finite element (FE) simulations of the deformation and damage evolution of Silicon- Carbide (SiC) particle reinforced aluminum alloy composite including interphase are carried out for different microstructures and particle volume fractions of the composites. A program is developed for the automatic generation of 2D micromechanical FE-models with randomly distributed SiC particles. In order to simulate the damage process in aluminum alloy matrix and SiC particles, a damage parameter based on the stress triaxial indicator and the maximum principal stress criterion based elastic brittle damage model are developed within Abaqus/Standard Subroutine USDFLD, respectively. An Abaqus/Standard Subroutine MPC, which allows defining multi-point constraints, is developed to realize the symmetric boundary condition (SBC) and periodic boundary condition (PBC). A series of computational experiments are performed to study the influence of boundary condition, particle number and volume fraction of the representative volume element (RVE) on composite stiffness and strength properties. © 2012 Elsevier Ltd.

Holdt S.L.,Technical University of Denmark | Kraan S.,Galway Technology Park
Journal of Applied Phycology | Year: 2011

Seaweed is more than the wrap that keeps rice together in sushi. Seaweed biomass is already used for a wide range of other products in food, including stabilising agents. Biorefineries with seaweed as feedstock are attracting worldwide interest and include low-volume, high value-added products and vice versa. Scientific research on bioactive compounds in seaweed usually takes place on just a few species and compounds. This paper reviews worldwide research on bioactive compounds, mainly of nine genera or species of seaweed, which are also available in European temperate Atlantic waters, i. e. Laminaria sp., Fucus sp., Ascophyllum nodosum, Chondrus crispus, Porphyra sp., Ulva sp., Sargassum sp., Gracilaria sp. and Palmaria palmata. In addition, Undaria pinnatifida is included in this review as this is globally one of the most commonly produced, investigated and available species. Fewer examples of other species abundant worldwide have also been included. This review will supply fundamental information for biorefineries in Atlantic Europe using seaweed as feedstock. Preliminary selection of one or several candidate seaweed species will be possible based on the summary tables and previous research described in this review. This applies either to the choice of high value-added bioactive products to be exploited in an available species or to the choice of seaweed species when a bioactive compound is desired. Data are presented in tables with species, effect and test organism (if present) with examples of uses to enhance comparisons. In addition, scientific experiments performed on seaweed used as animal feed are presented, and EU, US and Japanese legislation on functional foods is reviewed. © 2011 Springer Science+Business Media B.V.

Hussy K.,Technical University of Denmark
ICES Journal of Marine Science | Year: 2011

Important processes in the recruitment dynamics of western Baltic cod (Gadus morhua) are identified. Spawning areas are in the deep, saline waters below 2040 m, depending on area topography. Spatial distribution remains relatively stable over time. Peak spawning shows an area-specific pattern, with progressively later spawning towards the east. Genetic stock structure and tagging indicate some degree of natal homing for spawning. The highly variable hydrodynamic conditions and the fact that cod eggs float in the water column cause their entrainment by currents, and their destination is determined by the prevailing winds and currents. Drift is almost exclusively to the east, but the magnitude and its impact on the structure of the affected stocks (Kattegat, western Baltic, and eastern Baltic) remains unresolved. Salinity limits the eastwest exchange of eggs as a consequence of the stocks differential requirement for neutral buoyancy. Superimposed on this, oxygen content and temperature have a significant effect on fertilization, egg/larva development, and survival. Within the Baltic Sea ecosystem, mixing of stocks may be anticipated and is particularly pronounced in the Arkona Basin because of its use for spawning by both western and eastern stocks, the advection of early life stages from the west and immigration/emigration from the east. © 2011 International Council for the Exploration of the Sea.

Brander K.,Technical University of Denmark
Journal of Marine Systems | Year: 2010

Evidence of the impacts of anthropogenic climate change on marine ecosystems is accumulating, but must be evaluated in the context of the "normal" climate cycles and variability which have caused fluctuations in fisheries throughout human history. The impacts on fisheries are due to a variety of direct and indirect effects of a number of physical and chemical factors, which include temperature, winds, vertical mixing, salinity, oxygen, pH and others. The direct effects act on the physiology, development rates, reproduction, behaviour and survival of individuals and can in some cases be studied experimentally and in controlled conditions. Indirect effects act via ecosystem processes and changes in the production of food or abundance of competitors, predators and pathogens. Recent studies of the effects of climate on primary production are reviewed and the consequences for fisheries production are evaluated through regional examples. Regional examples are also used to show changes in distribution and phenology of plankton and fish, which are attributed to climate. The role of discontinuous and extreme events (regime shifts, exceptional warm periods) is discussed. Changes in fish population processes can be investigated in experiments and by analysis of field data, particularly by assembling comparative data from regional examples. Although our existing knowledge is in many respects incomplete it nevertheless provides an adequate basis for improved management of fisheries and of marine ecosystems and for adapting to climate change. In order to adapt to changing climate, future monitoring and research must be closely linked to responsive, flexible and reflexive management systems. © 2009 Elsevier B.V. All rights reserved.

Guillot G.,Technical University of Denmark | Rousset F.,Montpellier University
Methods in Ecology and Evolution | Year: 2013

The simple and partial Mantel tests are routinely used in many areas of evolutionary biology to assess the significance of the association between two or more matrices of distances relative to the same pairs of individuals or demes. Partial Mantel tests rather than simple Mantel tests are widely used to assess the relationship between two variables displaying some form of structure. We show that contrary to a widely shared belief, partial Mantel tests are not valid in this case, and their bias remains close to that of the simple Mantel test. We confirm that strong biases are expected under a sampling design and spatial correlation parameter drawn from an actual study. The Mantel tests should not be used in case autocorrelation is suspected in both variables compared under the null hypothesis. We outline alternative strategies. The R code used for our computer simulations is distributed as supporting material. © 2012 British Ecological Society.

Wegener H.C.,Technical University of Denmark
Meat Science | Year: 2010

During the last two decades the major food safety problems in Denmark, as determined by the number of human patients, has been associated with bacterial infections stemming from meat products and eggs. The bacterial pathogens causing the majority of human infections has been Salmonella and Campylobacter, and to a lesser extent Yersinia, Escherichia coli O157 and Listeria. Danish initiatives to improve the safety of meat products have focused on the entire production chain from the farm to the consumer, with a special emphasis on the pre-harvest stage of production. The control of bacterial pathogens which are resistant to antibiotics has been a new area of attention in the recent decade, and recently, the increasing globalization of the domestic food supply has called for a complete rethinking of the national food safety strategies. The implementations of a "case-by-case" risk assessment system, as well as increased international collaboration on surveillance, are both elements in this new strategy. © 2009 Elsevier Ltd. All rights reserved.

Nielsen K.L.,Technical University of Denmark
Computational Materials Science | Year: 2010

The plug failure modes of resistance spot welded shear-lab and cross-tension test specimens are studied, using recent extensions to the Gurson model. A comparison of the predicted mechanical response is presented when using either: (i) the Gurson-Tvergaard-Needleman model (GTN-model), (ii) the shear-modified GTN-model by Nahshon and Hutchinson that also describes damage development at low triaxiality (NH-model) or (iii) the Gologanu-Leblond-Devaux model (GLD-model) accounting for non-spherical void growth. The failure responses predicted by the various models are discussed in relation to their approximate description of the nucleation, growth and coalescence of microvoids. Using the void shape factor of the GLD-model, a simple approach for approximating void nucleation by either particle fracture or particle-matrix decohesion is applied and a study of the subsequent void shape evolution is presented. The models are applied to predict failure of specimens containing a fully intact weld nugget as well as a partly removed weld nugget to address the problems of shrinkage voids or larger weld defects. All analysis are carried out by full 3D finite element modelling. © 2009 Elsevier B.V. All rights reserved.

Hellgren L.I.,Technical University of Denmark
Annals of the New York Academy of Sciences | Year: 2010

Phytanic acid is a multibranched fatty acid with reported retinoid X receptor (RXR) and peroxisome proliferator-activated receptor-α (PPAR-α) agonist activity, which have been suggested to have preventive effects on metabolic dysfunctions. Serum level in man is strongly correlated to the intake of red meat and dairy products and the concentration in these products is strongly correlated to the chlorophyll content in the feed of the cattle. Available data suggest that phytanic acid is a natural agonist for RXR at physiological concentrations, while it is more likely that it is the metabolite pristanic acid, rather than phytanic acid itself, that acts as PPAR-α agonist. Animal studies show increased expression of genes involved in fatty acid oxidation, after intake of phytol, the metabolic precursor of phytanic acid, but it is at present not possible to deduce whether phytanic acid is useful in the prevention of ectopic lipid deposition. Phytanic acid is an efficient inducer of the expression of uncoupler protein 1 (UCP1). UCP1 is expressed in human skeletal muscles, were it might be important for the total energy balance. Therefore, phytanic acid may be able to stimulate energy dissipation in skeletal muscles. Phytanic acid levels in serum are associated with an increased risk of developing prostate cancer, but the available data do not support a general causal link between circulating phytanic acid and prostate cancer risk. However, certain individuals, with specific single-nucleotide polymorphisms in the gene for the enzyme alpha-methylacyl-CoA racemase, might be susceptible to raised phytanic acid levels. © 2010 New York Academy of Sciences.

Kiorboe T.,Technical University of Denmark
Journal of Plankton Research | Year: 2011

Three features that are unique or almost unique to pelagic copepods among zooplankton may account for their numerical dominance in the pelagic realm of the oceans: (i) the torpedo-shaped body, the sensory armed antennules and the 'gearing' of the muscle motor make pelagic copepods very efficient in detecting and escaping predators. The specific force production and velocities during escape jumps are both about an order of magnitude higher than for other similarly sized organisms. (ii) The capability to remotely detect prey and to either capture these as they arrive in a scanning current, or as they swim through the perceptive sphere of the copepod, releases the copepods from the penalties associated filtering sticky water for prey particles. Scanning currents and active attack jumps are found in only few other zooplankters. (iii) Efficient mate finding in a mate-dilute environment allows for sexual reproduction with actual mating in each generation, otherwise uncommon in the plankton, and yields advantages in terms of deleting bad mutations and promoting 'good genes' through sexual selection. © The Author 2010. Published by Oxford University Press. All rights reserved.

Kiorboe T.,Technical University of Denmark
Limnology and Oceanography | Year: 2013

I compiled literature on zooplankton body composition, from protozoans to gelatinous plankton, and report allometric relations and average body composition. Zooplankton segregate into gelatinous and non-gelatinous forms, with few intermediate taxa (chaetognaths, polychaetes, and pteropods). In most groups body composition is size independent. Exceptions are protozoans, chaetognaths, and pteropods, where larger individuals become increasingly watery. I speculate about the dichotomy in body composition and argue that differences in feeding mechanisms and predator avoidance strategies favor either a watery or a condensed body form, and that in the intermediate taxa the moderately elevated water content is related to buoyancy control and ambush feeding. © 2013, by the Association for the Sciences of Limnology and Oceanography, Inc.

Silva G.T.,Federal University of Alagoas | Bruus H.,Technical University of Denmark
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2014

We present a theoretical expression for the acoustic interaction force between small spherical particles suspended in an ideal fluid exposed to an external acoustic wave. The acoustic interaction force is the part of the acoustic radiation force on one given particle involving the scattered waves from the other particles. The particles, either compressible liquid droplets or elastic microspheres, are considered to be much smaller than the acoustic wavelength. In this so-called Rayleigh limit, the acoustic interaction forces between the particles are well approximated by gradients of pair-interaction potentials with no restriction on the interparticle distance. The theory is applied to studies of the acoustic interaction force on a particle suspension in either standing or traveling plane waves. The results show aggregation regions along the wave propagation direction, while particles may attract or repel each other in the transverse direction. In addition, a mean-field approximation is developed to describe the acoustic interaction force in an emulsion of oil droplets in water. © 2014 American Physical Society.

Kinnunen M.,Technical University of Denmark
ISME Journal | Year: 2016

There is a growing interest in controlling—promoting or avoiding—the invasion of microbial communities by new community members. Resource availability and community structure have been reported as determinants of invasion success. However, most invasion studies do not adhere to a coherent and consistent terminology nor always include rigorous interpretations of the processes behind invasion. Therefore, we suggest that a consistent set of definitions and a rigorous conceptual framework are needed. We define invasion in a microbial community as the establishment of an alien microbial type in a resident community and argue how simple criteria to define aliens, residents, and alien establishment can be applied for a wide variety of communities. In addition, we suggest an adoption of the community ecology framework advanced by Vellend (2010) to clarify potential determinants of invasion. This framework identifies four fundamental processes that control community dynamics: dispersal, selection, drift and diversification. While selection has received ample attention in microbial community invasion research, the three other processes are often overlooked. Here, we elaborate on the relevance of all four processes and conclude that invasion experiments should be designed to elucidate the role of dispersal, drift and diversification, in order to obtain a complete picture of invasion as a community process.The ISME Journal advance online publication, 3 May 2016; doi:10.1038/ismej.2016.75. © 2016 International Society for Microbial Ecology

Rapid gravity sand filtration is a drinking water production technology widely used around the world. Microbially catalyzed processes dominate the oxidative transformation of ammonia, reduced manganese and iron, methane and hydrogen sulfide, which may all be present at millimolar concentrations when groundwater is the source water. In this study, six metagenomes from various locations within a groundwater-fed rapid sand filter (RSF) were analyzed. The community gene catalog contained most genes of the nitrogen cycle, with particular abundance in genes of the nitrification pathway. Genes involved in different carbon fixation pathways were also abundant, with the reverse tricarboxylic acid cycle pathway most abundant, consistent with an observed Nitrospira dominance. From the metagenomic data set, 14 near-complete genomes were reconstructed and functionally characterized. On the basis of their genetic content, a metabolic and geochemical model was proposed. The organisms represented by draft genomes had the capability to oxidize ammonium, nitrite, hydrogen sulfide, methane, potentially iron and manganese as well as to assimilate organic compounds. A composite Nitrospira genome was recovered, and amo-containing Nitrospira genome contigs were identified. This finding, together with the high Nitrospira abundance, and the abundance of atypical amo and hao genes, suggests the potential for complete ammonium oxidation by Nitrospira, and a major role of Nitrospira in the investigated RSFs and potentially other nitrifying environments.The ISME Journal advance online publication, 29 April 2016; doi:10.1038/ismej.2016.63. © 2016 International Society for Microbial Ecology

Jabbari M.,Technical University of Denmark
Computational Materials Science | Year: 2014

In this paper, a thermal model is developed and used to simulate the friction stir welding of pure copper plates with the thickness of 4 mm in the constant traverse speed of 25 mm/min and five different rotation speeds. The mechanical deformation (plastic deformation) is neglected in the developed thermal model, hence the mechanical force in the process is taken to account in the heat generation equations. A moving coordinate system is used for modeling of the tool movement during the welding process. The generated heat is then used to model the grain growth in the copper plates, and consequently the mechanical properties of the copper plates. We then compare the numerical results with the results obtained from the series of experiments. Analysis of metallographic images show that increasing of the rotation speed results in increase of grain size in the nugget zone, which confirmes the numerical results. Vickers hardness tests were conducted on the weld samples and the maximum hardness obtained in rotation speed of 900 rpm. Results of the tensile tests and their comparison with that of the base metal showed that the maximum strength and the minimum elongation achieved again in this rotation speed. Yield strength and ultimate tensile strength increased with decrease in grain size in the nugget region and the yield strength obeyed the new proposed Hall-Petch relationship. © 2013 Elsevier B.V. All rights reserved.

Hoffmann M.C.,University of Hamburg | Turchinovich D.,Technical University of Denmark
Applied Physics Letters | Year: 2010

We demonstrate saturable absorber behavior of n-type semiconductors GaAs, GaP, and Ge in the terahertz (THz) frequency range at room temperature using nonlinear THz spectroscopy. The saturation mechanism is based on a decrease in electron conductivity of semiconductors at high electron momentum states, due to conduction band nonparabolicity and scattering into satellite valleys in strong THz fields. Saturable absorber parameters, such as linear and nonsaturable transmission, and saturation fluence, are extracted by fits to a classic saturable absorber model. Further, we observe THz pulse shortening, and an increase in the group refractive index of the samples at higher THz pulse peak fields. © 2010 American Institute of Physics.

Kim O.S.,Technical University of Denmark
IEEE Transactions on Antennas and Propagation | Year: 2014

It is shown how modern rapid prototyping technologies can be applied for quick and inexpensive, but still accurate, fabrication of electrically small wire antennas. A well known folded spherical helix antenna and a novel spherical zigzag antenna have been fabricated and tested, exhibiting the impedance and radiation characteristics in close agreement with those predicted numerically. © 1963-2012 IEEE.

Chen J.,ETH Zurich | Walther J.H.,ETH Zurich | Walther J.H.,Technical University of Denmark | Koumoutsakos P.,ETH Zurich
Nano Letters | Year: 2014

We demonstrate through molecular dynamics simulations that the Kapitza resistance in few-layer graphene (FLG) can be controlled by applying mechanical strain. For unstrained FLG, the Kapitza resistance decreases with the increase of thickness and reaches an asymptotic value of 6 × 10-10 m2K/W at a thickness about 16 nm. Uniaxial cross-plane strain is found to increase the Kapitza resistance in FLG monotonically, when the applied strain varies from compressive to tensile. Moreover, uniaxial strain couples the in-plane and out-of-plane strain/stress when the surface of FLG is buckled. We find that with a compressive cross-plane stress of 2 GPa, the Kapitza resistance is reduced by about 50%. On the other hand it is almost tripled with a tensile cross-plane stress of 1 GPa. Remarkably, compressive in-plane strain can either increase or reduce the Kapitza resistance, depending on the specific way it is applied. Our study suggests that graphene can be exploited for both heat dissipation and insulation through strain engineering. © 2014 American Chemical Society.

Reisner W.,McGill University | Pedersen J.N.,Technical University of Denmark | Pedersen J.N.,Princeton University | Austin R.H.,Princeton University
Reports on Progress in Physics | Year: 2012

DNA is the central storage molecule of genetic information in the cell, and reading that information is a central problem in biology. While sequencing technology has made enormous advances over the past decade, there is growing interest in platforms that can readout genetic information directly from long single DNA molecules, with the ultimate goal of single-cell, single-genome analysis. Such a capability would obviate the need for ensemble averaging over heterogeneous cellular populations and eliminate uncertainties introduced by cloning and molecular amplification steps (thus enabling direct assessment of the genome in its native state). In this review, we will discuss how the information contained in genomic-length single DNA molecules can be accessed via physical confinement in nanochannels. Due to self-avoidance interactions, DNA molecules will stretch out when confined in nanochannels, creating a linear unscrolling of the genome along the channel for analysis. We will first review the fundamental physics of DNA nanochannel confinement - including the effect of varying ionic strength - and then discuss recent applications of these systems to genomic mapping. Apart from the intense biological interest in extracting linear sequence information from elongated DNA molecules, from a physics view these systems are fascinating as they enable probing of single-molecule conformation in environments with dimensions that intersect key physical length-scales in the 1nm to 100m range. © 2012 IOP Publishing Ltd.

Svensmark H.,Technical University of Denmark
Monthly Notices of the Royal Astronomical Society | Year: 2012

Observations of open star clusters in the solar neighbourhood are used to calculate local supernova (SN) rates for the past 510Myr. Peaks in the SN rates match passages of the Sun through periods of locally increased cluster formation which could be caused by spiral arms of the Galaxy. A statistical analysis indicates that the Solar system has experienced many large short-term increases in the flux of Galactic cosmic rays (GCR) from nearby SNe. The hypothesis that a high GCR flux should coincide with cold conditions on the Earth is borne out by comparing the general geological record of climate over the past 510Myr with the fluctuating local SN rates. Surprisingly, a simple combination of tectonics (long-term changes in sea level) and astrophysical activity (SN rates) largely accounts for the observed variations in marine biodiversity over the past 510Myr. An inverse correspondence between SN rates and carbon dioxide (CO 2) levels is discussed in terms of a possible drawdown of CO 2 by enhanced bio-productivity in oceans that are better fertilized in cold conditions - a hypothesis that is not contradicted by data on the relative abundance of the heavy isotope of carbon, 13C. © 2012 The Author Monthly Notices of the Royal Astronomical Society © 2012 RAS.

Sigmund O.,Technical University of Denmark | Maute K.,University of Colorado at Boulder
Structural and Multidisciplinary Optimization | Year: 2012

Abstract In topology optimization filtering is a popular approach for preventing numerical instabilities. This short note shows that the well-known sensitivity filtering technique, that prevents checkerboards and ensures mesh-independent designs in density-based topology optimization, is equivalent to minimizing compliance for nonlocal elasticity problems known from continuum mechanics. Hence, the note resolves the long-standing quest for finding an explanation and physical motivation for the sensitivity filter. © Springer-Verlag 2012.

Niemann H.,Technical University of Denmark
International Journal of Applied Mathematics and Computer Science | Year: 2012

A model-based controller architecture for Fault-Tolerant Control (FTC) is presented in this paper. The controller architecture is based on a general controller parameterization. The FTC architecture consists of two main parts, a Fault Detection and Isolation (FDI) part and a controller reconfiguration part. The theoretical basis for the architecture is given followed by an investigation of the single parts in the architecture. It is shown that the general controller parameterization is central in connection with both fault diagnosis as well as controller reconfiguration. Especially in relation to the controller reconfiguration part, the application of controller parameterization results in a systematic technique for switching between different controllers. This also allows controller switching using different sets of actuators and sensors.

Mishnaevsky L.,Technical University of Denmark
Computational Mechanics | Year: 2012

The strength and reliability of wind turbine blades depend on the properties, mechanical behavior and strengths of the material components (glass or carbon fibers and polymer matrix), and the interaction between them under loading. In this paper, ideas, methods and concepts of micromechanical modelling of materials for wind turbine blades are briefly reviewed. Using the variety of the modeling methods reviewed here, one can predict the strength, stiffness and lifetime of the materials, optimize their microstructures with view on the better usability for wind turbines, or compare the applicability of different groups of the materials to the application in wind turbine blades. Some examples of the analysis of the microstructural effects on the strength and fatigue life of composites are shown. © 2012 Springer-Verlag.

Traerup S.L.M.,Technical University of Denmark
Global Environmental Change | Year: 2012

This article contributes to the understanding of how to proceed with the development of index-insurance in order to reach extended population coverage with the insurance. The approach is applied to an example from a region in Tanzania. One of the main coping strategies that resource-poor households rely on to manage risks related to fluctuations in income flows is risk-sharing in informal networks. An informal network is an ideal way of managing idiosyncratic shocks, but once such shocks become covariate and affect whole communities, as is the case with most climate change impacts, informal networks become insufficient since the majority of risk-sharers will be affected by the shock at the same time. This paper proposes a collective approach to index-insurance in which the members of an informal network will be insured as one insurance taker. The paper raises a conceptual argument that targeting households through existing informal networks will remove a number of prevailing barriers to the take-up of insurance and consequently the approach has the potential to increase households' resilience to climate change impacts. The policy implications of the conclusions are significant since the number of covariate shocks is predicted to increase with climate change. © 2011 Elsevier Ltd.

In this paper, the most important energy and exergy characteristics of wind energy were examined. Atmospheric variables as air temperature, humidity and pressure and their effects on the wind turbine output were investigated toward wind energy exploitation. It was shown that these usually disregarded meteorological parameters while planning new WFs (Wind Farms), in fact, do play an important role in the farm's overall exergetic efficiency. The wind potential around a coastal mountainous area was studied based on field measurements. Understanding atmospheric parameters variation appears to be of great importance for estimating energy yield in rough terrain and in this paper special focus was given to that. © 2011 Elsevier Ltd.

Witt C.,Technical University of Denmark
Leibniz International Proceedings in Informatics, LIPIcs | Year: 2012

The analysis of randomized search heuristics on classes of functions is fundamental for the understanding of the underlying stochastic process and the development of suitable proof techniques. Recently, remarkable progress has been made in bounding the expected optimization time of the simple (1+1) EA on the class of linear functions. We improve the best known bound in this setting from (1.39 + o(1))enln n to en ln n + O(n) in expectation and with high probability, which is tight up to lower-order terms. Moreover, upper and lower bounds for arbitrary mutations probabilities p are derived, which imply expected polynomial optimization time as long as p = O((ln n)/n) and which are tight if p = c/n for a constant c. As a consequence, the standard mutation probability p = 1/n is optimal for all linear functions, and the (1+1) EA is found to be an optimal mutation-based algorithm. Furthermore, the algorithm turns out to be surprisingly robust since large neighborhood explored by the mutation operator does not disrupt the search. © Carsten Witt.

Arnbjerg-Nielsen K.,Technical University of Denmark
Urban Water Journal | Year: 2012

Design of urban drainage structures should include the climatic changes anticipated over the technical lifetime of the system. In Northern Europe climate changes implies increasing occurrences of extreme rainfall. Three approaches to quantify the impact of climate changes on extreme rainfall are studied, all based on output from historical rain series of the present climate and output from Regional Climate Models. Two models are applied, one being based on an extreme value model, the Partial Duration Series Approach, and the other based on a stochastic rainfall generator model. Finally an approach is based on identification of areas, where the present climate resembles the anticipated future climate for the region in question. The results indicate that design intensities in Denmark are likely to be increased by 10-50% within the next 100 years. The increase in design intensities depend on the duration and the return period in question. © 2012 Copyright Taylor and Francis Group, LLC.

Anyfantis K.N.,Technical University of Denmark
Engineering Fracture Mechanics | Year: 2014

Bonded structure, can be either considered a multilayer material system, where its sublayers are held together through media that provide adhesion, or an adhesive joint designated for the assembly of different parts involved in a structure. For the assessment of the adhesion strength that characterizes a given bondline, both its cohesive strength and fracture toughness material parameters must be experimentally defined. Based on these properties, failure analysis of the bondline can be done either through stress- or energy-based criteria. The aim of this work is to investigate the effectiveness of each criteria type to effectively predict debonding initiation/propagation of different bondlines (brittle, quasi-brittle, ductile), which are eventually utilized for the evaluation of the joint's failure load. By representing a bondline according to its cohesive length scale, an effort is made to classify the wide range of bondlines with respect to the failure theory that best describes the debonding process. Cohesive length scale effects are first demonstrated by modeling end notch flexure geometries and later by modeling double strap joint geometries within the framework of a wide numerical experimentation programme. Fracture initiation and propagation of the bondlines was numerically simulated by cohesive zone models. © 2014 Elsevier Ltd.

Rasmussen H.K.,Technical University of Denmark
Journal of Non-Newtonian Fluid Mechanics | Year: 2013

Numerical flow modeling has been applied to study the break of monodisperse polymer melts during extension. These continuum mechanical based computations are within the ideas of the microstructural 'interchain pressure' theory. Calculated breaks, a result of small initial sample imperfections, agree with experimental observations. © 2013.

Juul N.,Technical University of Denmark
Energy | Year: 2012

The increase in fluctuating power production requires an increase in flexibility in the system as well. Flexibility can be found in generation technologies with fast response times or in storage options. In the transport sector, the proportion of electric drive vehicles is expected to increase over the next decade or two. These vehicles can provide some of the flexibility needed in the power system, in terms of both flexible demand and electricity storage. However, what are the batteries worth to the power system? And does the value depend on battery capacity? This article presents an analysis of the integrated power and transport system, focusing on the sensitivity of the power system configuration according to battery capacity and price of the electric drive vehicle. The value of different battery capacities is estimated, given that the batteries are used for both driving and storage. Likewise, the prices at which the electric drive vehicles become of interest to the power system are found. Smart charge, including the opportunity to discharge (vehicle-to-grid) is used in all scenarios. Analyses show that the marginal benefits decrease the larger the battery. For very high battery prices, large batteries imply that diesel vehicles are preferable to electric drive vehicles. © 2012 Elsevier Ltd.

Blasques J.P.,Technical University of Denmark
Composite Structures | Year: 2014

This paper describes a methodology for simultaneous topology and material optimization in optimal design of laminated composite beams with eigenfrequency constraints.