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Chalmers University of Technology is a Swedish university located in Gothenburg that focuses on research and education in technology, natural science, architecture, maritime and other management areas. Wikipedia.

Chen X.,Chalmers University of Technology
International Journal of Antennas and Propagation | Year: 2012

It has previously been shown that a reverberation chamber can conveniently be used to measure ergodic multiple-input multiple-output (MIMO) capacity for over-the-air (OTA) tests. However, the MIMO channel in the reverberation chamber has not been fully studied before. In this paper, the spatial correlation of the MIMO channel in the chamber is studied by comparing the measured channel with two popular MIMO channel models. It is shown that the models can accurately predict the ergodic MIMO capacity of the channel in the reverberation chamber, but not the outage capacity (especially at high signal-to-noise regime). It is verified that the capacity estimation error is due to the fact that the measured MIMO channel in the chamber does not satisfy multivariate normality (MVN), which causes the capacity error increases additively with MIMO size and multiplicatively with signal-to-noise (SNR). Copyright © 2012 Xiaoming Chen. Source

Stotsky A.A.,Chalmers University of Technology
Proceedings of the Institution of Mechanical Engineers. Part I: Journal of Systems and Control Engineering | Year: 2012

A new frequency domain system identification method based on a multi-frequency input signal is proposed. Frequency contents of the oscillating signal are estimated using a modified Kaczmarz algorithm proposed in this paper. Lyapunov stability analysis is performed for this new Kaczmarz algorithm and transient bounds for estimation error are established. Moreover, a new method for estimation of the variance of the measurement noise in Kaczmarz algorithms is also described. A comparison of a transient performance of modified Kaczmarz algorithm and a recursive least-squares algorithm is presented. The results are applied to a frequency domain identification of a DC motor. © Author 2011. Source

Rinaldini C.A.,University of Modena and Reggio Emilia | Mattarelli E.,University of Modena and Reggio Emilia | Golovitchev V.I.,Chalmers University of Technology
Applied Energy | Year: 2013

The paper explores, by means of CFD simulations, the potential of the Miller cycle, applied to High Speed Direct Injection (HSDI) Diesel engines, facing the challenge of emissions reduction enforced by the near-term regulations, with particular reference to Euro VI. In fact, a valuable benefit of the Miller technique is the strong reduction of combustion temperature, thus the abating of NO. x emissions, compared to a traditional cycle with the same values of AFR and EGR rate.The practical application of the Miller cycle yields a number of critical issues, which are generally addressed in the paper. However, the goal of the study is to assess the potential and the limits of this technique, more than develop a specific engine configuration.For the analysis, a 2.8. L 4-cylinder turbocharged engine produced by VM Motori was selected, carrying out a comprehensive experimental campaign, at both full and partial load. The experimental data allowed the authors to calibrate two types of numerical models, one for the whole engine analyses (0/1D), the other for the combustion process simulation (CFD-3D). The integrated use of these computational tools provides a reliable comparison between the base engine and the one modified according to the Miller cycle, in terms of both emissions and fuel consumption in the European Driving Cycle. It was found a reduction of NO. x and Soot of 25% and 60%, respectively, and a worsening of fuel efficiency of 2%. The abating of NO. x can be further enhanced, since it is demonstrated that the engine operated according to the Miller cycle can tolerate higher rates of EGR. © 2013 Elsevier Ltd. Source

Dahlin A.B.,Chalmers University of Technology
Analyst | Year: 2015

A review of sensing applications based on plasmonic nanopores is given. Many new types of plasmonic nanopores have recently been fabricated, including pores penetrating multilayers of thin films, using a great variety of fabrication techniques based on either serial nanolithography or self-assembly. One unique advantage with nanopores compared to other plasmonic sensors is that sample liquids can flow through the surface, which increases the rate of binding and improves the detection limit under certain conditions. Also, by utilizing the continuous metal films, electrical control can be implemented for electrochemistry, dielectrophoresis and resistive heating. Much effort is still spent on trying to improve sensor performance in various ways, but the literature uses inconsistent benchmark parameters. Recently plasmonic nanopores have been used to analyse targets of high clinical or academic interest. Although this is an important step forward, one should probably reflect upon whether the same results could have been achieved with another optical technique. Overall, this critical review suggests that the research field would benefit by focusing on applications where plasmonic nanopores truly can offer unique advantages over similar techniques. This journal is © The Royal Society of Chemistry. Source

Rosengren H.,Chalmers University of Technology
Journal of Combinatorial Theory. Series A | Year: 2016

We obtain an explicit formula for a certain weighted enumeration of lozenge tilings of a hexagon with an arbitrary triangular hole. The complexity of our expression depends on the distance from the hole to the center of the hexagon. This proves and generalizes conjectures of Ciucu et al., who considered the case of plain enumeration when the triangle is located at or very near the center. Our proof uses Askey-Wilson polynomials as a tool to relate discrete and continuous Selberg-type integrals. © 2015 Elsevier Inc. Source

Garnier J.,University Paris Diderot | Lisak M.,Chalmers University of Technology | Picozzi A.,University of Burgundy
Journal of the Optical Society of America B: Optical Physics | Year: 2012

During this last decade, several remarkable phenomena inherent to the nonlinear propagation of incoherent optical waves have been reported in the literature. This article is aimed at providing a generalized wave turbulence kinetic formulation of random nonlinear waves governed by the nonlinear Schrödinger equation in the presence of a nonlocal or a noninstantaneous nonlinear response function. Depending on the amount of nonlocal (noninstantaneous) nonlinear interaction and the amount of inhomogeneous (nonstationary) statistics of the incoherent wave, different types of kinetic equations are obtained. In the spatial domain, when the incoherent wave exhibits fluctuations that are statistically homogeneous in space, the relevant kinetic equation is the wave turbulence (Hasselmann) kinetic equation. It describes, in particular, the process of optical wave thermalization to thermodynamic equilibrium, which slows down significantly as the interaction becomes highly nonlocal. When the incoherent wave is characterized by inhomogeneous statistical fluctuations, different forms of the Vlasov equation are derived, which depend on the amount of nonlocality in the system. This Vlasov approach describes, in particular, the processes of incoherent modulational instability and the formation of localized incoherent soliton structures. In the temporal domain, the noninstantaneous nonlinear response function is constrained by the causality condition. It turns out that the relevant kinetic equation has a form analogous to the weak Langmuir turbulence equation, which describes, in particular, the formation of nonlocalized spectral incoherent solitons. In the regime of a highly noninstantaneous nonlinear response and a stationary statistics of the incoherent wave, the weak Langmuir turbulence equation reduces to the Korteweg-de Vries equation. Conversely, in the regime of a highly noninstantaneous response in the presence of a nonstationary statistics, we derive a long-range Vlasov-like kinetic equation in the temporal domain, whose self-consistent potential is constrained by the causality condition. From a broader perspective, this work indicates that the wave turbulence theory may constitute the appropriate theoretical framework to formulate statistical nonlinear optics. © 2012 Optical Society of America. Source

Lind M.,Gothenburg University | Bounias I.,NU Hospital Organisation | Olsson M.,Chalmers University of Technology | Gudbjornsdottir S.,Sahlgrenska University Hospital | Rosengren A.,Gothenburg University
The Lancet | Year: 2011

Poor glycaemic control is associated with microvascular and macrovascular complications in type 1 diabetes, but whether glycaemic control is associated with heart failure in such patients is not known. We aimed to assess this association in a large cohort of patients with type 1 diabetes identified from the Swedish national diabetes registry. We identified all patients (aged ≥18 years) with type 1 diabetes and no known heart failure who were registered in the national diabetes registry between January, 1998, and December, 2003. These patients were followed up until hospital admission for heart failure, death, or end of follow-up on Dec 31, 2009. We calculated incidence categorised by glycated haemoglobin A1c (HbA1c) values, and we assessed the association between patients' characteristics, including HbA1c, and heart failure. In a cohort of 20 985 patients with mean age of 38·6 years (SD 13·3) at baseline, 635 patients (3) were admitted to hospital with a primary or secondary diagnosis of heart failure during a median follow-up of 9·0 years (IQR 7·3-11·0), with an incidence of 3·38 events per 1000 patient-years (95 CI 3·12-3·65). Incidence increased monotonically with HbA1c, with a range of 1·42-5·20 per 1000 patient-years between patients in the lowest (<6·5) and highest (≥10·5) categories of HbA1c. In a Cox regression analysis, with adjustment for age, sex, duration of diabetes, cardiovascular risk factors, and baseline or intervening acute myocardial infarction and other comorbidities, the hazard ratio for development of heart failure was 3·98 (95 CI 2·23-7·14) in patients with HbA1c of 10·5 or higher compared with a reference group of patients with HbA1c of less than 6·5. Risk of heart failure increased with age and duration of diabetes. Other modifiable factors associated with increased risk of heart failure were smoking, high systolic blood pressure, and raised body-mass index. In a subgroup of 18 281 patients (87) with data for blood lipids, higher HDL cholesterol was associated with lower risk of heart failure, but there was no association with LDL cholesterol. The positive association between HbA1c and risk of heart failure in fairly young patients with type 1 diabetes indicates a potential for prevention of heart failure with improved glycaemic control. AstraZeneca, Novo Nordisk Scandinavia, Swedish Heart and Lung Foundation, and Swedish Research Council. © 2011 Elsevier Ltd. Source

Ahlgren C.,Sahlgrenska University Hospital | Oden A.,Chalmers University of Technology | Lycke J.,Sahlgrenska University Hospital
Multiple Sclerosis Journal | Year: 2011

Background: Few nationwide multiple sclerosis (MS) prevalence studies have been published. In Scandinavia, the nationwide MS prevalence was 173/100,000 in Denmark 2005 and 100/100,000 in Iceland 1990.Objective: Our aim with the present study was to determine the first population-based nationwide MS prevalence in Sweden, based on observed, registered patients and to investigate the presence of a north-south gradient of MS prevalence.Methods: By linking the Swedish National Patient Register, the Swedish Multiple Sclerosis Registry and the Swedish Total Population Register we obtained the number of patients who were diagnosed with MS before 2009, and who were registered, alive and resident in Sweden on the prevalence date 31 December 2008. We calculated the gender-specific nationwide MS prevalence in 1-year age intervals. The relationship between MS risk and latitude was studied in a logistic regression model including all individuals in the population of Sweden.Results: The number of registered MS patients in 2008 was 17,485 out of the Swedish population of 9,256,347. The overall MS prevalence was 188.9/100,000 (95% CI 186.1-191.7), 113.4 (95% CI 110.3-116.5) for men and 263.6 (95% CI 258.9-268.3) for women. The female to male ratio was 2.35:1. The prevalence of MS significantly increased for each degree of north latitude with 1.5% in men (p = 0.013) and 1% in women (p = 0.015).Conclusions: The MS prevalence of 188.9/100,000 in Sweden is among the highest nationwide prevalence estimates in the world. In Sweden, the risk of MS increases with increasing north latitude for both men and women. © The Author(s) 2011. Source

Lagerwall S.T.,Chalmers University of Technology
Advances in Colloid and Interface Science | Year: 2014

Since the early investigations on liquid crystals it was realized how the confining surfaces often determine the textures and even properties of the material. This influence is particularly complex and important for chiral materials. When we come to chiral smectics the surfaces may have dramatic effects. These are illustrated on the ferroelectric liquid crystals; they then again increase in importance for the antiferroelectric liquid crystals where the most recent example is given by the orthoconic liquid crystals. © 2014 Elsevier B.V. Source

Karlsson M.,Chalmers University of Technology
Physical Chemistry Chemical Physics | Year: 2015

Torres-Company V.,Chalmers University of Technology | Weiner A.M.,Purdue University
Laser and Photonics Reviews | Year: 2014

The outstanding phase-noise performance of optical frequency combs has led to a revolution in optical synthesis and metrology, covering a myriad of applications, from molecular spectroscopy to laser ranging and optical communications. However, the ideal characteristics of an optical frequency comb are application dependent. In this review, the different techniques for the generation and processing of high-repetition-rate (>10 GHz) optical frequency combs with technologies compatible with optical communication equipment are covered. Particular emphasis is put on the benefits and prospects of this technology in the general field of radio-frequency photonics, including applications in high-performance microwave photonic filtering, ultra-broadband coherent communications, and radio-frequency arbitrary waveform generation. The outstanding phase-noise performance of optical frequency combs has led to a revolution in optical synthesis and metrology. In this review, the techniques for the generation and processing of high-repetition-rate (>10 GHz) optical frequency combs with technologies compatible with optical communication equipment are covered. Particular emphasis is put on the benefits and prospects of this technology in the general field of radio-frequency photonics, including applications in high-performance microwave photonic filtering, ultra-broadband coherent communications, and radio-frequency arbitrary waveform generation. © 2013 by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Pusztai I.,Chalmers University of Technology | Catto P.J.,Massachusetts Institute of Technology
Plasma Physics and Controlled Fusion | Year: 2010

In tokamak pedestals with subsonic flows the radial scale of plasma profiles can be comparable to the ion poloidal Larmor radius, thereby making the radial electrostatic field so strong that the E × B drift has to be retained in the ion kinetic equation in the same order as the parallel streaming. The modifications of neoclassical plateau regime transport - such as the ion heat flux and the poloidal ion and impurity flows - are evaluated in the presence of a strong radial electric field. The altered poloidal ion flow can lead to a significant increase in the bootstrap current in the pedestal where the spatial profile variation is strong because of the enhanced coefficient of the ion temperature gradient term near the electric field minimum. Unlike the banana regime, orbit squeezing does not affect the plateau regime results. © 2010 IOP Publishing Ltd. Source

Azar C.,Chalmers University of Technology
Wiley Interdisciplinary Reviews: Climate Change | Year: 2011

Bioenergy can come to play a significant role in the global energy system and perhaps account for one fifth of global energy supply in 50 years in response to ambitions to reduce carbon dioxide emissions. But bioenergy is complicated. There are both traditional and modern forms. In this article, I will exclusively look at modern forms, i.e., biomass for electricity, transport and heat, and process heat (not traditional forms used for cooking in developing countries). Furthermore, there are both 'good' and 'bad' kinds, expensive and inexpensive technologies, bioenergy systems that lead to massive carbon dioxide emissions and systems that are carbon neutral, and even ones that remove carbon dioxide from the atmosphere while delivering energy. There is concern that certain bioenergy forms will, in response to increasing carbon prices, become so attractive that food prices increase significantly, that poor people are evicted from their lands, and that rainforest and other sensitive ecosystem are destroyed in order to pave the way for bioenergy plantations. This article offers a survey of these risks, and the policy instruments intended to deal with the challenges. © 2011 John Wiley & Sons, Ltd. Source

Krivoruchko A.,Chalmers University of Technology | Storey K.B.,Carleton University
Biochimica et Biophysica Acta - General Subjects | Year: 2013

Background The forkhead class O (FoxO) transcription factors are important regulators of multiple aspects of cellular metabolism. We hypothesized that activation of these transcription factors could play crucial roles in low oxygen survival in the anoxia-tolerant turtle, Trachemys scripta elegans. Methods Two FoxOs, FoxO1 and FoxO3, were examined in turtle tissues in response to 5 and 20 h of anoxic submergence using techniques of RT-PCR, western immunoblotting and DNA-binding assays to assess activation. Transcript levels of FoxO-responsive genes were also quantified using RT-PCR. Results FoxO1 was anoxia-responsive in the liver, with increases in transcript levels, protein levels, nuclear levels and DNA-binding of 1.7-4.8 fold in response to anoxia. Levels of phosphorylated FoxO1 also decreased to 57% of control values in response to 5 h of anoxia, indicating activation. FoxO3 was activated in the heart, kidney and liver in response to anoxia, with nuclear levels increasing by 1.5-3.7 fold and DNA-binding activity increasing by 1.3-2.9 fold. Transcript levels of two FoxO-target genes, p27kip1 and catalase, also rose by 2.4-2.5 fold in the turtle liver under anoxia. Conclusions The results suggest that the FoxO transcription factors are activated in response to anoxia in T. scripta elegans, potentially contributing to the regulation of stress resistance and metabolic depression. General significance This study provides the first demonstration of activation of FoxOs in a natural model for vertebrate anoxia tolerance, further improving understanding of how tissues can survive without oxygen. © 2013 Elsevier B.V. Source

Davidson L.,Chalmers University of Technology
Journal of Turbulence | Year: 2016

The partially Reynolds-averaged Navier-Stokes (PANS) model can be used to simulate turbulent flows either as RANS, large eddy simulation (LES) or DNS. Its main parameter is fk whose physical meaning is the ratio of the modelled to the total turbulent kinetic energy. In RANS fk = 1, in DNS fk = 0 and in LES fk takes values between 0 and 1. Three different ways of prescribing fk are evaluated for decaying grid turbulence and fully developed channel flow: fk = 0.4, fk = k3/2 tot/ε and, from its definition, fk = k/ktot where ktot is the sum of the modelled, k, and resolved, kres, turbulent kinetic energy. It is found that the fk = 0.4 gives the best results. In Girimaji and Wallin, a method was proposed to include the effect of the gradient of fk. This approach is used at RANS-LES interface in the present study. Four different interface models are evaluated in fully developed channel flow and embedded LES of channel flow: in both cases, PANS is used as a zonal model with fk = 1 in the unsteady RANS (URANS) region and fk = 0.4 in the LES region. In fully developed channel flow, the RANS-LES interface is parallel to the wall (horizontal) and in embedded LES, it is parallel to the inlet (vertical). The importance of the location of the horizontal interface in fully developed channel flow is also investigated. It is found that the location-and the choice of the treatment at the interface-may be critical at low Reynolds number or if the interface is placed too close to the wall. The reason is that the modelled turbulent shear stress at the interface is large and hence the relative strength of the resolved turbulence is small. In RANS, the turbulent viscosity-and consequently also the modelled Reynolds shear stress-is only weakly dependent on Reynolds number. It is found in the present work that it also applies in the URANS region. © 2015 Taylor and Francis. Source

Pallavicini P.,University of Pavia | Dacarro G.,University of Pavia | Diaz-Fernandez Y.A.,Chalmers University of Technology | Taglietti A.,University of Pavia
Coordination Chemistry Reviews | Year: 2014

Antibacterial metal complex monolayers covalently grafted on bulk surfaces are reviewed, focusing on the experimental values found for metal:ligand surface stoichiometry, on the surface concentration of the complexes, on time-regulated cation release and on the relation with the observed antibacterial properties. Stability, geometry and coordination features of the surface-grafted complexes are discussed where available, and compared with the classical ligand/metal behavior found in solution. In the applicable cases, comparison is made also with surfaces bearing monolayers of silver nanoparticles as antibacterial agents, evidencing the advantages of the coordination complex monolayers in obtaining fast release, efficient antibacterial action and null or negligible risks as regards toxicity. © 2014 Elsevier B.V. Source

Physical Review B - Condensed Matter and Materials Physics | Year: 2012

A detailed analysis of the in-plane magnetoresistance anisotropy in single-orientation thin-film SrRuO 3 grown on (001)SrTiO 3 is presented. The resistivity is measured in strips along [001], [1̄10], and [1̄11̄] with an in-plane rotating magnetic field. The data show additional details in the transfer from negative to positive magnetoresistance when the field is rotated in the plane. They show that the magnetoresistance is anisotropic with respect to the crystalline directions rather than with respect to the direction of the current. The data suggest an anisotropic spin-orbit interaction and can possibly be a sign of in-plane weak antilocalization. © 2012 American Physical Society. Source

Hyldgaard P.,Chalmers University of Technology
Journal of Physics Condensed Matter | Year: 2012

The standard formulation of tunneling transport rests on an open-boundary modeling. There, conserving approximations to nonequilibrium Green function or quantum statistical mechanics provide consistent but computational costly approaches; alternatively, the use of density-dependent ballistic-transport calculations (e.g., Lang 1995 Phys. Rev.B 52 5335), here denoted DBT, provides computationally efficient (approximate) atomistic characterizations of the electron behavior but has until now lacked a formal justification. This paper presents an exact, variational nonequilibrium thermodynamic theory for fully interacting tunneling and provides a rigorous foundation for frozen-nuclei DBT calculations as a lowest-order approximation to an exact nonequilibrium thermodynamic density functional evaluation. The theory starts from the complete electron nonequilibrium quantum statistical mechanics and I identify the operator for the nonequilibrium Gibbs free energy which, generally, must be treated as an implicit solution of the fully interacting many-body dynamics. I demonstrate a minimal property of a functional for the nonequilibrium thermodynamic grand potential which thus uniquely identifies the solution as the exact nonequilibrium density matrix. I also show that the uniqueness-of-density proof from a closely related Lippmann-Schwinger collision density functional theory (Hyldgaard 2008 Phys.Rev.B 78 165109) makes it possible to express the variational nonequilibrium thermodynamic description as a single-particle formulation based on universal electron-density functionals; the full nonequilibrium single-particle formulation improves the DBT method, for example, by a more refined account of Gibbs free energy effects. I illustrate a formal evaluation of the zero-temperature thermodynamic grand potential value which I find is closely related to the variation in the scattering phase shifts and hence to Friedel density oscillations. This paper also discusses the difference between the here-presented exact thermodynamic forces and the often-used electrostatic forces. Finally the paper documents an inherent adiabatic nature of the thermodynamic forces and observes that these are suited for a nonequilibrium implementation of the Born-Oppenheimer approximation. © 2012 IOP Publishing Ltd. Source

Atalaya J.,Chalmers University of Technology
Journal of Physics Condensed Matter | Year: 2012

This paper presents a study of dephasing of an underdamped nanomechanical resonator subject to random mass loading of small particles. A frequency noise model is presented which describes dephasing due to the attachment and detachment of particles at random points and particle diffusion along the resonator. This situation is commonly encountered in current mass measurement experiments using nanoelectromechanical (NEM) resonators. The conditions which can lead to inhomogeneous broadening and fine structure in the modes absorption spectra are discussed. It is also shown that the spectra of the higher-order cumulants of the (complex) vibrational mode amplitude are sensitive to the parameters characterizing the frequency noise process. Hence, measurement of these cumulants can provide information not only about the mass but also about other parameters of the particles (diffusion coefficient and attachment-detachment rates). © 2012 IOP Publishing Ltd. Source

Torgrimsson G.,Chalmers University of Technology
Few-Body Systems | Year: 2015

We consider signals of photon–photon scattering in laser-based, low energy experiments. In particular, we consider the ellipticity induced on a probe beam by a strong background field, and compare it with a recent worldline expression for the photon polarisation flip amplitude. When the probe and the background are plane waves, the ellipticity is equal to the flip amplitude. Here we investigate the ellipticity–amplitude relation for more physical fields. © 2015, Springer-Verlag Wien. Source

Lui H.-S.,Chalmers University of Technology | Shuley N.V.,Queensland University of Technology
IEEE Transactions on Antennas and Propagation | Year: 2012

Automated target recognition based on resonances embedded in the ultrawideband transient signatures has been of significant research interest throughout the years. In most studies, targets are usually illuminated and measured using a linear polarized basis. This could lead to an incorrect result for target recognition as some resonant modes may not be well excited at that particular incident aspect and polarization state. In this communication, the possibility of using a full-polarimetric ultrawideband target signature is investigated. Target recognition of some simple wire targets using the extinction pulse technique demonstrate that it would be easier to fully excite all of the important resonances using a circular polarization basis with due consideration of the co- and cross-polarized target signatures. © 1963-2012 IEEE. Source

Stotsky A.,Chalmers University of Technology
Proceedings of the Institution of Mechanical Engineers. Part I: Journal of Systems and Control Engineering | Year: 2012

New algorithms for estimation of the frequencies of oscillating waveform signals are described. A model of the signals is presented in the form of a linear difference equation with unknown coefficients, which define the frequencies and amplitudes. Coefficients are estimated utilizing the property of the persistence of excitation of oscillating signals. Exponentially damped and oscillating signals are described in a unified framework. A property of excitation is proved for an exponentially damped signal that contains a single frequency via diagonal dominance of an information matrix. Two applications of this frequency estimation technique are considered. The first one is filtering of the wind speed signal in wind turbine control applications, and the second one is the frequency estimation of exponentially damped signals motivated by the engine knock detection applications. © 2012 IMechE. Source

Andreasson J.,Chalmers University of Technology | Pischel U.,University of Huelva
Chemical Society Reviews | Year: 2015

In this tutorial review, the most recent developments in the field of molecular logic and information processing are discussed. Special emphasis is given to the report of progress in the concatenation of molecular logic devices and switches, the design of memory systems working according to the principles of sequential logic, the mimicking of transistors, and the research on photochromic platforms with an unprecedented degree of functional integration. Furthermore, a series of achievements that add up to the conceptual diversity of molecular logic is introduced, such as the realization of highly complex and logically reversible Toffoli and Fredkin gates by the action of DNAzymes or the use of a multifluorophoric platform as a viable approach towards keypad lock functions. This journal is © The Royal Society of Chemistry. Source

Sarasini S.,Chalmers University of Technology
Energy Policy | Year: 2013

This paper utilises qualitative methods to examine factors that influence corporate political actions (CPA) linked to climate policy in the Swedish electricity industry. CPA strategies are examined in connection to two policy instruments-the EU emission-trading scheme and the Swedish electricity certificate scheme. These instruments are the main drivers of climate-related investments in the sector. The study treats CPA as a form of institutional work and examines reasons for companies to seek to maintain/disrupt institutions. The study finds that CPA is driven primarily by the need to manage external resource dependencies and that where risks are more acute, companies are more likely to seek to disrupt regulative institutions. However, the study also shows that respondents' appraisals of policy instruments are based on a convergent set of shared values (cognitive institutions) that form the basis of CPA and which actors do not seek to disrupt despite resource-based risks. CPA is thus characterised as a means to transmute cognitively held values and beliefs into regulative institutions. The study concludes with implications for policymakers and theory. © 2013 Elsevier Ltd. Source

Ni W.,Chinese University of Hong Kong | Ambjornsson T.,Lund University | Apell S.P.,Chalmers University of Technology | Chen H.,Chinese University of Hong Kong | Wang J.,Chinese University of Hong Kong
Nano Letters | Year: 2010

Strong plasmonic-molecular resonance coupling occurs between noble metal nanocrystals and organic adsorbates when the plasmonic resonance is degenerate with the molecular one. This interaction forms the basis for many fundamental studies and practical applications. We describe here the first direct measurement of the resonance coupling on single gold nanorods. The darkfield scattering technique is employed. The nanorods are embedded in hydrogel to facilitate uniform dye adsorption. The adsorbed dye molecules exhibit both monomer and H-aggregate absorption bands. The same gold nanorods are measured before and after the dye adsorption. Both strong and weak coupling are investigated by selecting nanorods with different longitudinal plasmon bands. Excellent agreement between the experiments and an analytic theory is obtained. The resonance coupling reveals a unique threeband structure. The tunability of the coupling on individual nanorods is further demonstrated by photodecomposing the adsorbed dye molecules. © 2010 American Chemical Society. Source

Anderson L.,Chalmers University of Technology | Zarembo K.,KTH Royal Institute of Technology | Zarembo K.,Uppsala University
Journal of High Energy Physics | Year: 2014

Abstract: When mass-deformed ABJM theory is considered on S3, the partition function of the theory localises, and is given by a matrix model. At large N, we solve this model in the decompactification limit, where the radius of the three-sphere is taken to infinity. In this limit, the theory exhibits a rich phase structure with an infinite number of third-order quantum phase transitions, accumulating at strong coupling. © 2014, The Author(s). Source

Bargmann S.,TU Dortmund | Svendsen B.,RWTH Aachen | Ekh M.,Chalmers University of Technology
Computational Mechanics | Year: 2011

In this contribution, a computational approach to modeling size-dependent self- and latent hardening in polycrystals is presented. Latent hardening is the hardening of inactive slip systems due to active slip systems. We focus attention on the investigation of glide system interaction, latent hardening and excess dislocation development. In particular, latent hardening results in a transition to patchy slip as a first indication and expression of the development of dislocation microstructures. To this end, following Nye (Acta Metall 1:153-162, 1953), Kondo (in Proceedings of the second Japan national congress for applied mechanics. Science Council of Japan, Tokyo, pp. 41-47, 1953), and many others, local deformation incompatibility in the material is adopted as a measure of the density of geometrically necessary dislocations. Their development results in additional energy being stored in the material, leading to additional kinematic-like hardening effects. A large-deformation model for latent hardening is introduced. This approach is based on direct exploitation of the dissipation principle to derive all field relations and (sufficient) forms of the constitutive relations as based on the free energy density and dissipation potential. The numerical implementation is done via a dual-mixed finite element method. A numerical example for polycrystals is presented. © 2011 Springer-Verlag. Source

Von Borgstede C.,Gothenburg University | Andersson M.,Gothenburg University | Johnsson F.,Chalmers University of Technology
Energy Policy | Year: 2013

This work explores public opinions regarding climate change and mitigation options and examines how psychological factors, such as attitudes, norms, and willingness to pay, determine self-reported energy-efficient behaviour. The aim is to create knowledge for the design and implementation of policy measures. The results of an opinion poll conducted in 2005 and 2010 are compared. The number of respondents favouring new technologies as a way to reduce emissions was substantially lower in 2010 than in 2005, whereas there was an increase in the number of people who acknowledged that lifestyle changes are necessary to counteract climate changes. This indicates an increased awareness among the public of the need for lifestyle changes, which could facilitate implementation of policies promoting environmental behaviour. Renewable energy and energy saving measures were ranked as the top two measures for mitigating climate change in both polls. In determining which energy behaviours of the public are determined by psychological factors, an analysis of the 2010 survey revealed that respondents with pro-environmental attitudes towards global warming favour significantly increased use of renewable energy technologies and greater engagement in energy-efficient behaviours. © 2013 Elsevier Ltd. Source

Kirsten F.,University of Bonn | Kirsten F.,Max Planck Institute for Radio Astronomy | Vlemmings W.H.T.,Chalmers University of Technology
Astronomy and Astrophysics | Year: 2012

Intermediate mass black holes (IMBHs) with expected masses M • ≈ 10 4 M ⊙ are thought to bridge the gap between stellar mass black holes (M • ≈ 3-100 M ⊙) and supermassive black holes found at the centre of galaxies (M • > 10 6 M ⊙). Until today, no IMBH has been confirmed observationally. The most promising objects to host an IMBH as their central mass are globular clusters. Here, we present high sensitivity multi-epoch 1.6 GHz very long baseline interferometry observations of the globular cluster M 15 that has been suggested to host an IMBH. Assuming the IMBH to be accreting matter from its surrounding we expect to detect it as a point source moving with the global motion of the cluster. However, we do not detect any such object within a radius of 6000 AU of the cluster centre in any of the five observations spread over more than one year. This rules out any variability of the putative IMBH on the time scale of one to two months. To get the most stringent upper limit for the flux density of the putative IMBH we concatenate the data of all five epochs. In this data we measure a 3σ upper flux limit of 10 μJy for a central source. We employ the fundamental plane of black hole activity to estimate the mass of the central IMBH candidate. Based on previous X-ray observations of M 15 our measurements indicate a 3σ upper mass limit of ≈ 500 M ⊙. © 2012 ESO. Source

Matthaiou M.,Chalmers University of Technology | Zhong C.,Zhejiang University | McKay M.R.,Hong Kong University of Science and Technology | Ratnarajah T.,University of Edinburgh
IEEE Journal on Selected Areas in Communications | Year: 2013

The performance of single-cell distributed multiple-input multiple-output (D-MIMO) systems is not only affected by small-scale Rayleigh fading but also from large-scale fading and path-loss. In this paper, we elaborate on the sum rate of D-MIMO systems employing linear zero-forcing receivers, accounting for both large and small-scale fading effects, as well as spatial correlation at the transmit side. In particular, we consider the classical lognormal model and propose closed-form upper and lower bounds on the achievable sum rate. Using these bounds as a starting point, we pursue a "large-system" analysis and provide asymptotic expressions when the number of antennas at the base station (BS) grow large, and when the number of antennas at both ends grow large with a fixed and finite ratio. A detailed characterization in the asymptotically high and low signal to noise ratio regimes is also provided. An interesting observation from our results is that in order to maximize the sum rate, the RPs should be placed at unequal distances to the BS when they experience the same level of shadowing. The resulting closed-form expressions are compared with the corresponding results on MIMO optimal receivers. © 1983-2012 IEEE. Source

Kahnert M.,Swedish Meteorological and Hydrological Institute | Kahnert M.,Chalmers University of Technology
Journal of Quantitative Spectroscopy and Radiative Transfer | Year: 2016

Numerical solution methods for electromagnetic scattering by non-spherical particles comprise a variety of different techniques, which can be traced back to different assumptions and solution strategies applied to the macroscopic Maxwell equations. One can distinguish between time- and frequency-domain methods; further, one can divide numerical techniques into finite-difference methods (which are based on approximating the differential operators), separation-of-variables methods (which are based on expanding the solution in a complete set of functions, thus approximating the fields), and volume integral-equation methods (which are usually solved by discretisation of the target volume and invoking the long-wave approximation in each volume cell). While existing reviews of the topic often tend to have a target audience of program developers and expert users, this tutorial review is intended to accommodate the needs of practitioners as well as novices to the field. The required conciseness is achieved by limiting the presentation to a selection of illustrative methods, and by omitting many technical details that are not essential at a first exposure to the subject. On the other hand, the theoretical basis of numerical methods is explained with little compromises in mathematical rigour; the rationale is that a good grasp of numerical light scattering methods is best achieved by understanding their foundation in Maxwell's theory. © 2015 Elsevier Ltd. Source

Chen X.,Chalmers University of Technology
Progress in Electromagnetics Research | Year: 2012

In this paper, evaluations of diversity gains and capacities of multi-element antenna based on limited channel samples in a reverberation chamber (RC) are studied. It is shown that, for a large antenna array, the classical sample estimation based on finite channel samples tends to underestimate its diversity gain and capacity. An improved (yet slightly more complicated) eigenvalue estimation method is applied in both diversity gain and capacity calculations, which effectively alleviates the estimation bias. The findings of the present paper are applicable for measurements where the maximum independent channel samples per antenna element are limited. Apart from simulations, we also evaluate the performances of the classical and improved eigenvalue estimators based on measurements in a RC. Based on the results of this paper, the performance of the RC measurement (with limited samples) for multi-element antennas can be readily enhanced. Source

Chen X.,Chalmers University of Technology
IEEE Transactions on Electromagnetic Compatibility | Year: 2012

The turn-table platform stirring technique is used to improve the measurement accuracy of a reverberation chamber (RC). It is usually assumed that the half-wavelength platform spatial sampling results in independent samples, which can be used to approximate the independent platform sample number. But the approximation is rather coarse. This paper presents a measurement-based method to determine the independent platform sample number. This method is simple and accurate. In contrast to the half-wavelength coarse approximation that depends only on frequency, this method in addition illustrates the dependence of the independent platform sample number on RC loading and mode stirring. © 1964-2012 IEEE. Source

Enoksson P.,Chalmers University of Technology
IEEE Sensors Journal | Year: 2012

Self contained closed circuit rebreathers are life supporting breathing systems, where the exhaled gas is recycled by filtering CO 2 and replacing metabolized O 2. For the O 2 injection control galvanic O 2 sensors are used to measure the partial pressure of O 2. A malfunction of the sensors can lead to a gas mixture beyond life supporting limits which is life threatening. Galvanic O 2 sensors are often used in anaesthetic machines in hospitals. Also in this case, a malfunction of the sensors can cause severe injury to a person. It is obvious that such sensors are key elements in life supporting equipment and as such must be designed in order to achieve high functional safety. However these sensors are consuming sensors, and with that, will fail at a certain time. Failure modes include current limitation, non linearity, electrolyte evaporation or leakage, etc. Within this paper a novel low cost read out electronic circuit for galvanic O 2 sensors is presented, which allows not only digital readout, digital temperature compensation, on board storage of calibration and manufacturing data, but also can be used for performing voltammetry cycles to test the Pb anode for exhaustion. First measurements are presented and compared to data from a Solartron SI 1287 impedance analyzer, which is state-of-the-art in electrochemical sensor characterization. © 2001-2012 IEEE. Source

Rajo-Iglesias E.,Charles III University of Madrid | Kildal P.-S.,Chalmers University of Technology
IET Microwaves, Antennas and Propagation | Year: 2011

Recently it has been shown that so-called gap waveguides can be generated in the gap between parallel metal plates. The gap waveguides are formed by metal ridges or strips along which local waves propagate, and parallel plate modes are prohibited from propagating by providing one of the surfaces with a texture that generates an artificial magnetic conductor (AMC) or an electromagnetic bandgap (EBG) surface on both sides of the ridges or strips. The bandwidth of the gap waveguide is determined by the cut-off bandwidth of a parallel-plate waveguide where one surface has such a texture (and no ridges or strips). This paper studies the bandwidths (or stop bands) of such parallel-plate cut-offs when the AMC or EBG is realised by a metal pin surface, corrugations or a mushroom surface. It is shown that cut-off bandwidths of up to 4:1 are potentially available, and thereby similar bandwidths should be achievable also for gap waveguides. © 2011 The Institution of Engineering and Technology. Source

Dozza M.,Chalmers University of Technology
Accident Analysis and Prevention | Year: 2013

Distraction and inattention contribute to 80% of traffic accidents by delaying or hindering driver responses. However, distraction and inattention are not the only factors increasing response times. In addition, the extent to which different factors-related to the driver, the vehicle, or the environmentinfluence response times in real traffic is still uncertain. Such knowledge may significantly help the development of countermeasures to distraction and inattention. Naturalistic driving data promises to help determine the causes of distraction and inattention by understanding driver behavior in real traffic. Further, large naturalistic datasets are now publically available from a few sources such as UMTRI (University of Michigan Transportation Institute) and VTTI (Virginia Tech Transportation Institute). However, analysis of such data is made difficult by the intrinsic nature of the data: it is large and complex and the variables of interest are hard to control. This study used the public 100-car and 8-truck naturalistic data from VTTI to show how the NatWare toolkit developed at SAFER (Vehicle and Traffic Safety Center at Chalmers) can be used to determine the influence of several factors on response time. Among these factors, attendance to secondary tasks and eyes-off-road, which are indicators of driver's distraction and inattention, significantly delayed response times; the type of incident and response maneuver also affected response times; and finally, truck drivers responded more quickly than car drivers. © 2012 Elsevier Ltd. All rights reserved. Source

Johnsson F.,Chalmers University of Technology
Greenhouse Gases: Science and Technology | Year: 2011

The last decade has seen a signifi cant increase in the research and development of CO 2 capture and storage (CCS) technology. CCS is now considered to be one of the key options for climate change mitigation. This perspective provides a brief summary of the state of the art regarding CCS development and discusses the implications for the further development of CCS, particularly with respect to climate change policy. The aim is to provide general perspectives on CCS, although examples used to illustrate the prospects for CCS are mainly taken from Europe. The rationale for developing CCS should be the over-abundance of fossil fuel reserves (and resources) in a climate change context. However, CCS will only be implemented if society is willing to attach a suffi ciently high price to CO 2 emissions. Although arguments have been put forward both in favor and against CCS, the author of this perspective argues that the most important outcome from the successful commercialization of CCS will be that fossil-fuel-dependent economies will fi nd it easier to comply with stringent greenhouse gas (GHG) reduction targets. In contrast, failure to implement CCS will require that the global community agrees almost immediately to start phasing out the use of fossil fuels; such an agreement seems more unrealistic than reaching a global agreement on stringent GHG reductions. Thus, in the near term, it is crucial to initiate demonstration projects, such as those supported by the EU. If this is not done, there is a risk that the introduction of CCS will be signifi cantly delayed. Among the stakeholders in CCS technologies (R&D actors in industry and academia), the year 2020 is typically considered to be the year in which CCS will be commercially available. Considering the lead times for CCS development and the slow pace of implementation of climate policy (post-Copenhagen), the target year of 2020 seems rather optimistic. © 2011 Society of Chemical Industry and John Wiley & Sons, Ltd. Source

Leckner B.,Chalmers University of Technology | Szentannai P.,Budapest University of Technology and Economics | Winter F.,Vienna University of Technology
Fuel | Year: 2011

Methods for scaling of fluidized-bed combustors are reviewed. It is found that a general scaling methodology, including simultaneously fluid-dynamic and combustion scaling, cannot be applied in practical scaling tests. Simplifications are needed. The approach followed here is to differentiate between fluid-dynamic scaling, combustion scaling, both related to the basic equations describing the phenomena, and boiler scaling that means scale-up from one boiler size to another, where established design elements can be utilized in the scaling procedure. © 2011 Elsevier Ltd. All rights reserved. Source

Eriksson A.M.,Chalmers University of Technology
New Journal of Physics | Year: 2015

Nonresonant high-frequency electrostatic actuation of a movable quantum dot (QD) is investigated analytically. The electronic dot state is in tunneling contact with a continuum of electronic states in bulk electrodes. Gate electrodes induce an electric ac-field at the dot. Absorbtion of the field is accompanied by increment or decrement of one vibrational quantum in the QD. It is shown that the rate of increment overcomes the rate of decrement of vibrational quanta when the driving frequency exceeds the inverse tunneling time between the bulk electrodes and the QD. This results in a mechanical instability, leading to relatively large amplitude oscillations of the QD, which are saturated by nonlinear dissipation. © 2015 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft. Source

Ivarsson M.,Chalmers University of Technology | Gorschek T.,Blekinge Institute of Technology
Empirical Software Engineering | Year: 2011

One of the main goals of an applied research field such as software engineering is the transfer and widespread use of research results in industry. To impact industry, researchers developing technologies in academia need to provide tangible evidence of the advantages of using them. This can be done trough step-wise validation, enabling researchers to gradually test and evaluate technologies to finally try them in real settings with real users and applications. The evidence obtained, together with detailed information on how the validation was conducted, offers rich decision support material for industry practitioners seeking to adopt new technologies and researchers looking for an empirical basis on which to build new or refined technologies. This paper presents model for evaluating the rigor and industrial relevance of technology evaluations in software engineering. The model is applied and validated in a comprehensive systematic literature review of evaluations of requirements engineering technologies published in software engineering journals. The aim is to show the applicability of the model and to characterize how evaluations are carried out and reported to evaluate the state-of-research. The review shows that the model can be applied to characterize evaluations in requirements engineering. The findings from applying the model also show that the majority of technology evaluations in requirements engineering lack both industrial relevance and rigor. In addition, the research field does not show any improvements in terms of industrial relevance over time. © Springer Science+Business Media, LLC 2010. Source

Black J.H.,Chalmers University of Technology
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences | Year: 2012

The H 3 + molecular ion has been used by Oka and collaborators to trace the rate of ionization by cosmic rays in the interstellar medium. More energetic cosmic rays also produce diffuse g-radiation. Now that several supernova remnants (SNRs) have been identified as g-ray sources, it is possible to use spectroscopy of molecular ions to search for enhanced ionization rates that would pinpoint the SNRs as the accelerators of cosmic rays. It is proposed that the warm, dilute molecular gas revealed by H 3 + absorption in the central molecular zone of the Galaxy can also be investigated via radio recombination lines of atoms and possibly triatomic hydrogen. © 2012 The Royal Society. Source

Engstrom O.,Chalmers University of Technology
Journal of Applied Physics | Year: 2012

A model has been developed to describe the emission of electrons from silicon across the oxide energy barrier of metal-oxide-silicon structures. An optical absorption coefficient, exclusively describing the transmission of electrons which are emitted across the barrier, is split from the corresponding experimental quantity for the entire absorption range. This makes it possible to approximate the photo yield in terms of absorption coefficients and density of states without need for explicitly calculated matrix elements of optical transitions. Using this method, theoretical emission yield curves are found in good agreement with measured data. An important conclusion from this work is that values of oxide energy barrier heights should be extracted from different features of the yield data than most often done in the literature. This replaces a commonly used practice for determining the barrier heights, which is shown to be based on optical bulk properties of the silicon crystal. © 2012 American Institute of Physics. Source

McKinley A.W.,Imperial College London | Lincoln P.,Chalmers University of Technology | Tuite E.M.,Northumbria University
Dalton Transactions | Year: 2013

The luminescence of DNA-bound [Ru(phen)2dppz]2+ is shown to be highly sensitive to environmental conditions such as ionic strength, temperature, and the sequence and secondary structure of the nucleic acid, although not to bulky DNA substituents in the major groove. Each enantiomer has two characteristic lifetimes with any polynucleotide and their relative amplitudes vary as a function of binding ratio. For [poly(dA-dT)]2 as a model sequence, the longer lifetime for Δ-[Ru(phen)2dppz] 2+ has been assigned to canted intercalation of the complex and the shorter lifetime is ascribed to symmetric intercalation. At a fixed binding ratio, the longer lifetime amplitude increases with increasing ionic strength, without significant change in lifetimes. Increasing temperature has a similar effect, but also affects lifetimes. In general, emission is strongest with AT-rich polynucleotides and with higher-order secondary structures, with intensity increasing as single-stranded < duplex < triplex. However, sequence-context and secondary duplex structure also influence the photophysics since emission with [poly(dA)]·[poly(dT)] is significantly higher than with [poly(dA-dT)]2 or [poly(rA)]·[poly(rU)]. The strong influence of different environmental conditions on the emission of nucleic acid-bound [Ru(phen)2dppz]2+ reflects subtle heterogeneities that are inherent elements of DNA recognition by small molecules, amplified by large changes in photophysics caused by differential exposure of the dppz nitrogens to groove hydration. This journal is © 2013 The Royal Society of Chemistry. Source

Fang Y.,CAS Institute of Physics | Fang Y.,Chalmers University of Technology | Sun M.,CAS Institute of Physics
Light: Science and Applications | Year: 2015

The properties of propagating surface plasmon polaritons (SPPs) along one-dimensional metal structures have been investigated for more than 10 years and are now well understood. Because of the high confinement of electromagnetic energy, propagating SPPs have been considered to represent one of the best potential ways to construct next-generation circuits that use light to overcome the speed limit of electronics. Many basic plasmonic components have already been developed. In this review, researches on plasmonic waveguides are reviewed from the perspective of plasmonic circuits. Several circuit components are constructed to demonstrate the basic function of an optical digital circuit. In the end of this review, a prototype for an SPP-based nanochip is proposed, and the problems associated with building such plasmonic circuits are discussed. A plasmonic chip that can be practically applied is expected to become available in the near future. © 2015 CIOMP. Source

Petersen N.,University of Virginia | Gatenholm P.,Wake forest University | Gatenholm P.,Bc Genesis, Llc | Gatenholm P.,Chalmers University of Technology
Applied Microbiology and Biotechnology | Year: 2011

Bacterial cellulose (BC) is a unique and promising material for use as implants and scaffolds in tissue engineering. It is composed of a pure cellulose nanofiber mesh spun by bacteria. It is remarkable for its strength and its ability to be engineered structurally and chemically at nano-, micro-, and macroscales. Its high water content and purity make the material biocompatible for multiple medical applications. Its biocompatibility, mechanical strength, chemical and morphologic controllability make it a natural choice for use in the body in biomedical devices with broader application than has yet been utilized. This paper reviews the current state of understanding of bacterial cellulose, known methods for controlling its physical and chemical structure (e.g., porosity, fiber alignment, etc.), biomedical applications for which it is currently being used, or investigated for use, challenges yet to be overcome, and future possibilities for BC. © 2011 Springer-Verlag. Source

Weiland J.,Chalmers University of Technology
Physics of Plasmas | Year: 2014

We have simulated the L-H transition on the EAST tokamak [Baonian Wan, EAST and HT-7 Teams, and International Collaborators, "Recent experiments in the EAST and HT-7 superconducting tokamaks," Nucl. Fusion 49, 104011 (2009)] using a predictive transport code where ion and electron temperatures, electron density, and poloidal and toroidal momenta are simulated self consistently. This is, as far as we know, the first theory based simulation of an L-H transition including the whole radius and not making any assumptions about where the barrier should be formed. Another remarkable feature is that we get H-mode gradients in agreement with the α - αd diagram of Rogers et al. [Phys. Rev. Lett. 81, 4396 (1998)]. Then, the feedback loop emerging from the simulations means that the L-H power threshold increases with the temperature at the separatrix. This is a main feature of the C-mod experiments [Hubbard et al., Phys. Plasmas 14, 056109 (2007)]. This is also why the power threshold depends on the direction of the grad B drift in the scrape off layer and also why the power threshold increases with the magnetic field. A further significant general H-mode feature is that the density is much flatter in H-mode than in L-mode. © 2014 AIP Publishing LLC. Source

Eskilsson C.,Chalmers University of Technology
International Journal for Numerical Methods in Fluids | Year: 2011

An adaptive spectral/hp discontinuous Galerkin method for the two-dimensional shallow water equations is presented. The model uses an orthogonal modal basis of arbitrary polynomial order p defined on unstructured, possibly non-conforming, triangular elements for the spatial discretization. Based on a simple error indicator constructed by the solutions of approximation order p and p-1, we allow both for the mesh size, h, and polynomial approximation order to dynamically change during the simulation. For the h-type refinement, the parent element is subdivided into four similar sibling elements. The time-stepping is performed using a third-order Runge-Kutta scheme. The performance of the hp-adaptivity is illustrated for several test cases. It is found that for the case of smooth flows, p-adaptivity is more efficient than h-adaptivity with respect to degrees of freedom and computational time. © 2010 John Wiley & Sons, Ltd. Source

Matthaiou M.,Chalmers University of Technology | Zhong C.,Queens University of Belfast | Ratnarajah T.,Queens University of Belfast
IEEE Transactions on Signal Processing | Year: 2011

This paper introduces some novel upper and lower bounds on the achievable sum rate of multiple-input multiple-output (MIMO) systems with zero-forcing (ZF) receivers. The presented bounds are not only tractable but also generic since they apply for different fading models of interest, such as uncorrelated/ correlated Rayleigh fading and Ricean fading. We further formulate a new relationship between the sum rate and the first negative moment of the unordered eigenvalue of the instantaneous correlation matrix. The derived expressions are explicitly compared with some existing results on MIMO systems operating with optimal and minimum mean-squared error (MMSE) receivers. Based on our analytical results, we gain valuable insights into the implications of the model parameters, such as the number of antennas, spatial correlation and Ricean-K factor, on the sum rate of MIMO ZF receivers. © 2011 IEEE. Source

Hansbo P.,Chalmers University of Technology
International Journal for Numerical Methods in Biomedical Engineering | Year: 2010

We propose an interior penalty discontinuous finite element method for small strain elasto-plasticity using triangular or tetrahedral meshes. A new penalty formulation suitable for plasticity, in particular allowing for inter-element slip, is introduced. The method is also locking free, which is crucial as the plastic zone may exhibit an incompressible response. Numerical results are presented. Copyright © 2008 John Wiley & Sons, Ltd. Source

Rodriguez K.,Virginia Polytechnic Institute and State University | Renneckar S.,Virginia Polytechnic Institute and State University | Gatenholm P.,Virginia Polytechnic Institute and State University | Gatenholm P.,Chalmers University of Technology
ACS Applied Materials and Interfaces | Year: 2011

Novel cellulose based-scaffolds were studied for their ability to nucleate bioactive calcium phosphate crystals for future bone healing applications. Cellulose-based scaffolds were produced by electrospinning cellulose acetate (CA) dissolved in a mixture of acetone/dimethylacetamide (DMAc). The resulting nonwoven CA mats containing fibrils with diameters in the range of 200 nm to 1.5 μm were saponified by NaOH/ethanol for varying times to produce regenerated cellulose scaffolds. Biomimetic crystal growth nucleated from the fiber surface was studied as a function of surface chemistry. Regenerated cellulose scaffolds of varying treatments were soaked in simulated body fluid (SBF) solution. Scaffolds that were treated with CaCl 2, a mixture of carboxymethyl cellulose (CMC) and CaCl 2, and NaOH and CaCl 2, were analyzed using X-ray photoelectron spectroscopy, X-ray powder diffraction, and scanning electron microscopy to understand the growth of bioactive calcium phosphate (Ca-P) crystals as a function of surface treatment. The crystal structure of the nucleated Ca-P crystals had a diffraction pattern similar to that of hydroxyapatite, the mineralized component of bone. The study shows that the scaffold surface chemistry can be manipulated, providing numerous routes to engineer cellulosic substrates for the requirements of scaffolding. © 2011 American Chemical Society. Source

Tymchenko N.,Chalmers University of Technology
Biointerphases | Year: 2012

The mechanical properties and responses of cells to external stimuli (including drugs) are closely connected to important phenomena such as cell spreading, motility, activity, and potentially even differentiation. Here, reversible changes in the viscoelastic properties of surface-attached fibroblasts were induced by the cytoskeleton-perturbing agent cytochalasin D, and studied in real-time by the quartz crystal microbalance with dissipation (QCM-D) technique. QCM-D is a surface sensitive technique that measures changes in (dynamically coupled) mass and viscoelastic properties close to the sensor surface, within a distance into the cell that is usually only a fraction of its size. In this work, QCM-D was combined with light microscopy to study in situ cell attachment and spreading. Overtone-dependent changes of the QCM-D responses (frequency and dissipation shifts) were first recorded, as fibroblast cells attached to protein-coated sensors in a window equipped flow module. Then, as the cell layer had stabilised, morphological changes were induced in the cells by injecting cytochalasin D. This caused changes in the QCM-D signals that were reversible in the sense that they disappeared upon removal of cytochalasin D. These results are compared to other cell QCM-D studies. Our results stress the combination of QCM-D and light microscopy to help interpret QCM-D results obtained in cell assays and thus suggests a direction to develop the QCM-D technique as an even more useful tool for real-time cell studies. Source

Konkoli Z.,Chalmers University of Technology
Journal of Theoretical Biology | Year: 2012

A novel computational method for modeling reaction noise characteristics has been suggested. The method can be classified as a moment closure method. The approach is based on the concept of correlation forms which are used for describing spatially extended many body problems where particle numbers change in space and time. In here, it was shown how the formalism of spatially extended correlation forms can be adapted to study well mixed reaction systems. Stochastic fluctuations in particle numbers are described by selectively capturing correlation effects up to the desired order, ξ. The method is referred to as the ξ-level Approximation Reaction Noise Estimator method (XARNES). For example, the ξ = 1 description is equivalent to the mean field theory (first-order effects), the ξ = 2 case corresponds to the previously developed PARNES method (pair effects), etc. The main idea is that inclusion of higher order correlation effects should lead to better (more accurate) results. Several models were used to test the method, two versions of a simple complex formation model, the Michaelis-Menten model of enzymatic kinetics, the smallest bistable reaction network, a gene expression network with negative feedback, and a random large network. It was explicitly demonstrated that increase in ξ indeed improves accuracy in all cases investigated. The approach has been implemented as automatic software using the Mathematica programming language. The user only needs to input reaction rates, stoichiometry coefficients, and the desired level of computation ξ. © 2012 Elsevier Ltd. Source

Hellman A.,Chalmers University of Technology | Pala R.G.S.,Indian Institute of Technology Kanpur
Journal of Physical Chemistry C | Year: 2011

Photoinduced water-splitting on hematite (Fe2O3) is investigated by first-principles calculations. (HO)3-Fe-H 3O3-R, (HO)3-Fe-O3-R, O 3-Fe-O3-R, (HO)3-Fe-R and O3-R terminations are considered, where R represents the bulk stacking sequence. The stability under photoelectrochemical conditions and the free energy of all reaction intermediates in a simple one-electron transfer reaction mechanism is calculated and the ability of different surface terminations to function as a photoanode is analyzed. Our results show that (i) under relevant photoelectrochemical conditions only O3-Fe-O3-R and O 3-R are stable and that (ii) the water-oxidation is only allowed on (HO)3-Fe-H3O3-R, (HO)3-Fe-O 3-R, O3-Fe-O3-R from thermodynamic considerations. The results suggest that hematite, as long as the (HO) 3-Fe-H3O3-R termination is present under normal conditions, is a promising candidate for the photoanode. © 2011 American Chemical Society. Source

Vikstrom A.,Chalmers University of Technology
Low Temperature Physics | Year: 2015

We consider a graphene sheet with a zigzag edge subject to a perpendicular magnetic field and investigate the propagation of in-plane acoustic edge waves. In particular it is shown that propagation is significantly blocked for certain frequencies defined by the resonant absorption due to electronic-acoustic interaction. We study absorption of acoustic energy as a function of magnetic field and find that, for a finite gate voltage and fixed acoustic frequency, tuning the magnetic field may bring the system through a number of electronic resonances. We suggest that the strong interaction between the acoustic and electronic edge states in graphene may generate significant nonlinear effects leading to the existence of acoustic solitons in such systems. © 2015 AIP Publishing LLC. Source

Torres-Company V.,Chalmers University of Technology | Castello-Lurbe D.,University of Valencia | Silvestre E.,University of Valencia
Optics Express | Year: 2014

Microresonator combs exploit parametric oscillation and nonlinear mixing in an ultrahigh-Q cavity. This new comb generator offers unique potential for chip integration and access to high repetition rates. However, time-domain studies reveal an intricate spectral coherence behavior in this type of platform. In particular, coherent, partially coherent or incoherent combs have been observed using the same microresonator under different pumping conditions. In this work, we provide a numerical analysis of the coherence dynamics that supports the above experimental findings and verify particular design rules to achieve spectrally coherent microresonator combs. A particular emphasis is placed in understanding the differences between so-called Type I and Type II combs. © 2014 Optical Society of America. Source

Fermvik A.,Chalmers University of Technology
Journal of Radioanalytical and Nuclear Chemistry | Year: 2011

Solvent extraction is a separation technique suitable for the treatment of used nuclear fuel. Two immiscible phases are contacted and the metals of interest are extracted from one phase into the other, most often using so called extractants. One group of extractants is the bis(triazine)-bipyridine (BTBP) type molecules. These molecules have been developed within EU research programs for the separation of actinides from lanthanides. During such an extraction process, the components of the two phases will be exposed to ionizing radiation, since the used fuel contains many highly radioactive species. Radiolytic reactions can alter the chemistry of the extracting system, and affect the metal extraction by degradation of the extractant and the formation of degradation products. In this paper the effect of irradiation with alpha particles and gamma rays, respectively, has been studied for one of the BTBP type molecules, C5-BTBP. © 2011 Akadémiai Kiadó, Budapest, Hungary. Source

Zomer P.J.,Zernike Institute for Advanced Materials | Dash S.P.,Zernike Institute for Advanced Materials | Tombros N.,Chalmers University of Technology | Van Wees B.J.,Zernike Institute for Advanced Materials
Applied Physics Letters | Year: 2011

We present electronic transport measurements of single and bilayer graphene on commercially available hexagonal boron nitride. We extract mobilities as high as 125 000 cm 2 V -1 s -1 at room temperature and 275 000 cm 2 V -1 s -1 at 4.2 K. The excellent quality is supported by the early development of the v = 1 quantum Hall plateau at a magnetic field of 5 T and temperature of 4.2 K. We also present a fast, simple, and accurate transfer technique of graphene to hexagonal boron nitride crystals. This technique yields atomically flat graphene on boron nitride which is almost completely free of bubbles or wrinkles. The potential of commercially available boron nitride combined with our transfer technique makes high mobility graphene devices more accessible. © 2011 American Institute of Physics. Source

Chakraborty N.,Northumbria University | Lipatnikov A.N.,Chalmers University of Technology
Physics of Fluids | Year: 2013

The effects of global Lewis number Le on the statistics of fluid velocity components conditional in unburned reactants and fully burned products in the context of Reynolds Averaged Navier Stokes simulations have been analysed using a Direct Numerical Simulations (DNS) database of statistically planar turbulent premixed flames with a low Damköhler number and Lewis number ranging from 0.34 to 1.2. The conditional velocity statistics extracted from DNS data have been analysed with respect to the well-known Bray-Moss-Libby (BML) expressions which were derived based on bi-modal probability density function of reaction progress variable for high Damköhler number flames. It has been shown that the Lewis number substantially affects the mean velocity and the velocity fluctuation correlation conditional in products, with the effect being particularly pronounced for low Le. As far as the mean velocity and the velocity fluctuation correlation conditional in reactants are concerned, the BML expressions agree reasonably well with the DNS data reported in the present work. Based on a priori analysis of present and previously reported DNS data, the BML expressions have been empirically modified here in order to account for Lewis number effects, and the non-bimodal distribution of reaction progress variable. Moreover, it has been demonstrated for the first time that surface averaged velocity components and Reynolds stresses conditional in unburned reactants can be modelled without invoking expressions involving the Lewis number, as these surface averaged conditional quantities remain approximately equal to their conditionally averaged counterparts in the unburned mixture. © 2013 American Institute of Physics. Source

Lyngfelt A.,Chalmers University of Technology
Applied Energy | Year: 2014

Chemical-looping combustion (CLC) of solid fuels is a technology with the potential of reducing the costs and energy penalty dramatically for CO2 capture. The potential for low costs is based on the similarity to coal combustion in fluidized beds. However, this assumes reaching high performance with respect to fuel and gas conversion, or that inadequate performance can be readily mitigated by downstream options. There are uncertainties with respect to the performance that can be reached in large-scale units, as well as with the extra costs needed to compensate for inadequate performance. Performance will be dependent on both reactor design and oxygen carrier properties. The status of chemical-looping combustion of solid fuels is discussed with respect to performance and experiences from pilot operation. © 2013 Elsevier Ltd. Source

Jacobsson S.,Chalmers University of Technology | Bergek A.,Linkoping University
Environmental Innovation and Societal Transitions | Year: 2011

This paper argues (1) that technology-specific policies are necessary if we are to meet the climate challenge and (2) that a main contribution of innovation system (IS) analysis to the study of sustainability transitions is that it allows policy makers to identify the processes and components in a system where intervention is likely to matter most. We demonstrate that an IS framework can identify a diverse set of system weaknesses in the field of environmental innovation and identify five venues for further research that can help strengthen the framework and improve its application to environmental innovations. © 2011 Elsevier B.V. All rights reserved. Source

IEEE Journal on Selected Topics in Quantum Electronics | Year: 2011

The vertical-cavity surface-emitting laser (VCSEL) has become a light source of great importance for industrial and consumer applications. This includes communication and sensing in particular, where dynamics and optical mode behavior are key performance characteristics. This tutorial treats relevant VCSEL basics, performance requirements and recent progress toward higher speed, higher single-mode power, and polarization control. © 2006 IEEE. Source

Sedarsky D.,Lund University | Berrocal E.,Lund University | Linne M.,Chalmers University of Technology
Optics Express | Year: 2011

Experimental work in turbid media has shown that trans-illumination images can be significantly improved by limiting light collection to a subset of photons which are minimally distorted by scattering. The literature details numerous schemes (commonly termed ballistic imaging), most often based on time-gating and/or spatially filtering the detected light. However, due to the complex nature of the detected signal, analysis of this optical filtering process has been heretofore limited to qualitative comparisons of image results. In this article we present the implementation of a complete system model for the simulation of light propagation, including both the scattering medium and all stages of the optical train. Validation data from ballistic imaging (BI) measurements of monodisperse scatterers with diameter, d = 0.7 μm, at optical depths 5, 10, and 14, are compared with model results, showing excellent agreement. In addition, the validated model is subsequently applied to a modified time-gated optical system to probe the comparative performance of the BI system used in validation and the modified BI system. This instrument comparison examines scatterers with diameters of 0.7 and 15 μm at optical depths 10 and 14, and highlights the benefits of each system design for these specific scattering conditions. These results show that the modified optics configuration is more suitable for particles which are much larger than the incident wavelength, D, while the configuration employed in the validation system provides a better contrast for particle diameters on the order of the wavelength, d ~?, where the scattering process exhibits a more homogeneous phase function. The insights and predictions made available by the full numerical model are important for the design of optimized imaging systems suited to specific turbid media, and make possible the quantitative understanding of both the effects of light propagation in the measurement and the performance of the complete imaging system. © 2011 Optical Society of America. Source

Karlsson M.,Chalmers University of Technology
Journal of Lightwave Technology | Year: 2014

To model electromagnetic wave propagation for coherent communications without polarization dependent losses, the unitary 2 \times 2 Jones transfer matrix formalism is typically used. In this study, we propose an alternative formalism to describe such transformations based on rotations in four-dimensional (4d) Euclidean space. This formalism is usually more attractive from a communication theoretical perspective, since decisions and symbol errors can be related to geometric concepts such as Euclidean distances between points and decision boundaries. Since 4d rotations is a richer description than the conventional Jones calculus, having six rather than four degrees of freedom (DOF), we propose an extension of the Jones calculus to handle all six DOF. In addition, we show that the two extra DOF in the 4d description represents transformations that are nonphysical for propagating photons, since they does not obey the fundamental quantum mechanical boson commutation relations. Finally, we exemplify on how the nonphysical rotations can change the polarization-phase degeneracy of well-known constellations such as single-polarization QPSK, polarization-multiplexed (PM-)QPSK and polarization-switched (PS-) QPSK. For example, we show how PM-QPSK, which is well known to consist of four polarization states each having four-fold phase degeneracy, can be represented as eight states of polarizations, each with binary phase degeneracy. © 2014 IEEE. Source

Begel A.,Microsoft | Bosch J.,Chalmers University of Technology | Storey M.-A.,University of Victoria
IEEE Software | Year: 2013

Many successful software companies use social networking as a way to improve the services or products they provide. To gain an understanding of the role social networking plays in today's software development world, the guest editors of the January/February 2013 issue conducted semistructured interviews with leaders from four successful companies: Brian Doll, an engineer who manages GitHub's marketing; Doug Laundry, a principal group program manager at Microsoft; David Fullerton, vice president of engineering at Stack Exchange; and Robert Hughes, the president and chief operating officer of TopCoder. The first Web extra at http://try.github.com is a video of Joel Spolsky discussing the structure, software, technology, and culture of Stack Exchange. The second Web extra at http://blip.tv/play/gvUBgqLbRgI.html is a video of Matthew McCullough and Tim Berglund demonstrating how Git not only incorporates the best features of existing source control systems but also includes unique distributed capabilities that make version control commands available without connectivity, allowing you to choose when to interact with a network. The third Web extra at http://blip.tv/play/gvUBgqLbRgI.html is a video of Matthew McCullough and Tim Berglund demonstrating how to leverage Git's powerful yet underused advanced features. The last Web extra at http://youtu.be/SK6TBI1bNLI is a video of Thomas Baden, Chief Information Officer, State of Minnesota, Department of Human Services, describing the experience of working on the TopCoder Platform and with the members of the TopCoder Community. © 1984-2012 IEEE. Source

Wittung-Stafshede P.,Chalmers University of Technology
Israel Journal of Chemistry | Year: 2016

Enzymes need to fold into unique three-dimensional structures in order to function. Copper ions are cofactors in many essential enzymes. Such enzymes need to couple polypeptide folding with metal incorporation, as the metal sites are often integrated within the folded structure. Since free copper ions are toxic, most organisms have highly specialized copper transport systems. The human cytoplasmic copper chaperone Atox1 delivers copper to P1B-type ATPases in the Golgi, for incorporation into copper-dependent enzymes following the secretory path. Copper plays key roles in cancer development, as copper-dependent enzymes are needed for tumor growth and metastasis. In addition, platinum-based drugs are exported out of cells by the copper transport machinery. Recent findings also imply that some copper transport proteins regulate cell growth and development. In this brief journey of my later career, I will discuss the roles of copper in protein folding, mechanisms of copper ion transport, and cisplatin hitchhiking. The identification of new partners for Atox1 underscore the importance of further research in this area for combating cancer. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.. Source

Axelsson E.,Chalmers University of Technology
Proceedings of the ACM SIGPLAN International Conference on Functional Programming, ICFP | Year: 2012

Representing a syntax tree using a data type often involves having many similar-looking constructors. Functions operating on such types often end up having many similar-looking cases. Different languages often make use of similar-looking constructions. We propose a generic model of abstract syntax trees capable of representing a wide range of typed languages. Syntactic constructs can be composed in a modular fashion enabling reuse of abstract syntax and syntactic processing within and across languages. Building on previous methods of encoding extensible data types in Haskell, our model is a pragmatic solution to Wadler's "expression problem". Its practicality has been confirmed by its use in the implementation of the embedded language Feldspar. © 2012 ACM. Source

Guerriero M.,University of Connecticut | Svensson L.,Chalmers University of Technology | Willett P.,University of Connecticut
IEEE Transactions on Signal Processing | Year: 2010

In this correspondence, we study different approaches for Bayesian data fusion for distributed target detection in sensor networks. Due to communication and bandwidth constraints, we assume that each sensor can only transmit a local decision to the fusion center (FC), which is in charge to take the final decision about the presence of a target. The optimal Bayesian test statistic at the FC is derived in the case where both the number and locations of the sensors are known. On the other hand, if both the number and the locations of the sensors are unknown, the optimal Bayesian test statistic is computed based on the same observations that the Scan Statistic test utilizes. The performances of the different approaches are compared through simulation. © 2010 IEEE. Source

Dahlin A.B.,Chalmers University of Technology
Sensors | Year: 2012

There is no doubt that the recent advances in nanotechnology have made it possible to realize a great variety of new sensors with signal transduction mechanisms utilizing physical phenomena at the nanoscale. Some examples are conductivity measurements in nanowires, deflection of cantilevers and spectroscopy of plasmonic nanoparticles. The fact that these techniques are based on the special properties of nanostructural entities provides for extreme sensor miniaturization since a single structural unit often can be used as transducer. This review discusses the advantages and problems with such small sensors, with focus on biosensing applications and label-free real-time analysis of liquid samples. Many aspects of sensor design are considered, such as thermodynamic and diffusion aspects on binding kinetics as well as multiplexing and noise issues. Still, all issues discussed are generic in the sense that the conclusions apply to practically all types of surface sensitive techniques. As a counterweight to the current research trend, it is argued that in many real world applications, better performance is achieved if the active sensor is larger than that in typical nanosensors. Although there are certain specific sensing applications where nanoscale transducers are necessary, it is argued herein that this represents a relatively rare situation. Instead, it is suggested that sensing on the microscale often offers a good compromise between utilizing some possible advantages of miniaturization while avoiding the complications. This means that ensemble measurements on multiple nanoscale sensors are preferable instead of utilizing a single transducer entity. © 2012 by the author. Source

Bosch J.,Chalmers University of Technology
Journal of Systems and Software | Year: 2012

The Special Issue 2012 of The Journal of Systems and Software offers articles regarding the development in the software ecosystems. Geir Hanssen presents a longitudinal case study of an emerging ecosystem. The paper raises interesting aspects of a theory of software ecosystems, including the role of a central referent organization, self-regulation, networked character as well as the importance of sharing values, control and the business and technology aspects of successful ecosystem adoption. The second paper, by Terhi Kilamo and co-authors, takes a different perspective and studies the challenge of putting software developed as closed source into the open-source domain with the intent of building a software ecosystem around it. The fourth paper, by Slinger Jansen and co-authors, raises a very important challenge to many organizations and external developers looking to determine whether to invest in a software ecosystem. The fifth paper, by Rick Kazman and co-authors, focuses on software architecture analysis and how analysis techniques can be applied to software ecosystems. Source

Hanke F.,University of Liverpool | Haq S.,University of Liverpool | Raval R.,University of Liverpool | Persson M.,University of Liverpool | Persson M.,Chalmers University of Technology
ACS Nano | Year: 2011

Recent experiments demonstrated the assembly of unfunctionalized porphyrin molecules into organometallic wires on the Cu(110) surface through the formation of stable C-Cu-C bonds involving Cu adatoms. The remarkable property of the observed structures is that they adopt a clear direction, despite the lack of functional ligands to direct the assembly. Here we use density functional theory calculations and scanning tunneling microscopy to clarify the mechanism for the highly one-dimensional assembly of the observed nanostructures. An energetic preference for the formation of C-Cu-C bonds is found in several lattice directions, but self-assembly critically relies on the commensurability of appropriate adsorption sites for the Cu atoms involved in the coupling. The experimentally observed structures arise from a geometric self-limitation of the assembly process, which proceeds in the energetically and geometrically most preferred direction. A further extension of the structure in the orthogonal dimension to form 2D assemblies is prevented by the lattice mismatch between the repeat lengths in the 001 and 110 directions of the underlying (110) lattice and the apparent rigidity of the molecules involved. However, the fusing of two parallel chains is geometrically allowed and leads to some of the energetically most favorable configurations. Finally, the role of van der Waals forces is investigated for the covalent couplings and chemisorbed interactions found in this system. © 2011 American Chemical Society. Source

Grigorenko L.V.,Helmholtz Center for Heavy Ion Research | Grigorenko L.V.,RAS Research Center Kurchatov Institute | Mukha I.G.,Helmholtz Center for Heavy Ion Research | Zhukov M.V.,Chalmers University of Technology
Physical Review Letters | Year: 2013

The structure and decay of O26 are investigated in a three-body O24+n+n model suitable for studies of the long-lived (including radioactivity time scale) states. We have found extremely strong effects of the subbarrier configuration mixing on the decay width of true 2n emitters due to core recoil and neutron-neutron final state interaction. This effect far exceeds the analogous effect in the true 2p emitters. Our calculations provide reasonably narrow boundaries for the lifetime vs decay energy dependence for the true 2n emission. An upper limit of ∼1 keV for the decay energy of the unbound O26 is inferred based on the recent experimental lifetime value. © 2013 American Physical Society. Source

Bejger M.,Copernicus Astronomical Center | Piran T.,Hebrew University of Jerusalem | Abramowicz M.,Copernicus Astronomical Center | Abramowicz M.,Gothenburg University | Hakanson F.,Chalmers University of Technology
Physical Review Letters | Year: 2012

Collisions of particles in black hole ergospheres may result in an arbitrarily large center-of-mass energy. This led recently to the suggestion that black holes can act as ultimate particle accelerators. If the energy of an outgoing particle is larger than the total energy of the infalling particles, the energy excess must come from the rotational energy of the black hole and hence, a Penrose process is involved. However, while the center-of-mass energy diverges, the position of the collision makes it impossible for energetic particles to escape to infinity. Following an earlier work on collisional Penrose processes, we show that even under the most favorable idealized conditions the maximal energy of an escaping particle is only a modest factor above the total initial energy of the colliding particles. This implies that one should not expect collisions around a black hole to act as spectacular cosmic accelerators. © 2012 American Physical Society. Source

Linne M.,Chalmers University of Technology
Experiments in Fluids | Year: 2012

Recent studies of spray-related flowfields using synchrotron-based X-ray radiography at the Advanced Photon Source (APS), Argonne National Lab, have produced useful results related to fuel mass. A companion article to this one analyzed X-ray phase contrast imaging and it identified several problems. Those results could potentially raise questions about radiography as well. Here, we simulate X-ray radiography using the same computational tools as before, but we reach a different set of conclusions. One important finding is the demonstration that radiography detects the total liquid mass along a line-of-sight, including both drops and intact liquid. As such, it can reveal liquid mass fraction, which is related to the spray breakup rate and gas entrainment; both critical for understanding of sprays. The potential for confusion between local signal reduction by diffraction and local signal reduction by absorption is also discussed. The issue is not unusual in such circumstances. This potential background problem can be avoided by careful arrangement of the experiment, and it is clear that it does not affect the results produced by the APS. © 2012 Springer-Verlag. Source

Linne M.,Chalmers University of Technology
Experiments in Fluids | Year: 2012

Recent studies of spray-related flow fields using synchrotron-based X-ray phase contrast imaging have produced results that are sometimes straightforward to interpret in terms of the fluid structure, but in other cases the images do not reflect generally accepted physics of fluid motion. It has been unclear why some images have the appearance of a normal fluid stream while others depart significantly from expectation. The detailed numerical modeling presented here is meant to explain the images and resolve common questions about the technique. The simulations show that collimated X-ray beams will always contain signatures from every possible encounter, from the input plane to the exit plane, and these signatures generate overlapping phase contrast patterns that can prove at times impossible to interpret. Clouds of moderate- to large-size drops produce a complex, mottled X-ray phase contrast image indicating the presence of the cloud; but it is an image that cannot be interpreted further. Small drops generate something akin to one gray pixel image each, and their size is close to the resolution limit of the instrument, so the diffraction pattern is broadened by the instrument response into something more like a small diffuse blob. Dense clouds of small drops produce a composite image that is a fairly uniform gray mass indicating the presence of a drop cloud that cannot be interpreted further. Moreover, it is not possible to image intact liquid structures behind clouds of drops. Whenever a significant number of drops are present, therefore, X-ray phase contrast images are dominated by unavoidable artifacts of the technique. Sprays, by definition, consist of droplet clouds and this means that internal features in the spray formation region cannot be investigated using X-ray phase contrast imaging. © Springer-Verlag 2011. Source

Polemi A.,University of Modena and Reggio Emilia | MacI S.,University of Siena | Kildal P.-S.,Chalmers University of Technology
IEEE Transactions on Antennas and Propagation | Year: 2011

The newly introduced parallel-plate ridge gap waveguide consists of a metal ridge in a metamaterial surface, covered by a metallic plate at a small height above it. The gap waveguide is simple to manufacture, especially at millimeter and sub-millimeter wave frequencies. The metamaterial surface is designed to provide a frequency band where normal global parallel-plate modes are in cutoff, thereby allowing a confined gap wave to propagate along the ridge. This paper presents an approximate analytical solution for this confined quasi-TEM dominant mode of the ridge gap waveguide, when the metamaterial surface is an artificial magnetic conductor in the form of a bed of nails. The modal solution is found by dividing the field problem in three regions, the central region above the ridge and the two surrounding side regions above the nails. The fields within the side regions are expressed in terms of two evanescent TE and TM modes obtained by treating the bed of nails as an isotropic impedance surface, and the field in the central ridge region is expanded as a fundamental TEM parallel-plate mode with unknown longitudinal propagation constant. The field solutions are linked together by equalizing longitudinal propagation constants and imposing point-continuity of fields across the region interfaces, resulting in a transcendental dispersion equation. This is solved and presented in a dispersion diagram, showing good agreement with a numerical solution using a general electromagnetic solver. Both the lower and upper cutoff frequencies of the normal global parallel-plate modes are predicted, as well as the quasi-TEM nature of the gap mode between these frequencies, and the evanescent fields in the two side regions decay very rapidly away from the ridge. © 2010 IEEE. Source

Leckner B.,Chalmers University of Technology | Gomez-Barea A.,University of Seville
Applied Energy | Year: 2014

The conditions for CO2 reduction in a circulating fluidized bed (CFB) oxy-boiler are studied, that is, operation with pure oxygen, diluted by recirculated flue gases to moderate the combustion process. Two cases are analyzed: the ready-to-convert case, a normal air-fired CFB boiler, only slightly modified to be operated with oxygen instead of air for CO2 capture, and a more general option, an entirely new design, employing high oxygen concentration in the input to the oxy-fuel CFB boiler. It is found that at a given fuel load, the relevant parameters for maintaining the CFB performance (bed temperature and fluidization velocity) in the ready-to-convert case cannot be kept entirely equal to those in the air-fired case, and some compromise has to be found. The new-design case results in a smaller boiler than that of the comparable air-fired case, depending on the oxygen concentration and the corresponding flue-gas recirculation. This case is expected to contribute favorably to reduction of the cost of CO2 removal. © 2014 Elsevier Ltd. Source

Krajnovic S.,Chalmers University of Technology
Journal of Fluid Mechanics | Year: 2011

The flow around a finite circular cylinder with a height-to-diameter ratio of 6 was studied using large eddy simulation (LES). The cylinder was mounted on a ground plane where a thin boundary layer with a thickness of only 7% of the cylinder's diameter was formed. The flow resulting from the present LES was used to present a detailed picture of both the instantaneous and the time-averaged flow. Among the results of the present study is the explanation for the formation of two time-averaged tip vortices from two pairs of instantaneous vortices. The main recirculation region on the cylinder's top was found to be one vortex with both legs attached to the top surface, in agreement with some previous investigations. The mean flow in the near wake region was found to contain two horseshoe vortices, one large arch vortex stretching from the cylinder's top and another vortex resulting from the flow moving down below the rear stagnation point on the cylinder. The instantaneous horseshoe vortex near the ground was found to be unsteady and changed shape over time. The time-averaged flow showed three complete horseshoe vortices, in agreement with previous knowledge. The downwash process above the free end into the near wake occurs at a rather constant angle with respect to the plane normal to the streamwise direction. The same angle was preserved in the inclination of the arch vortex in the time-averaged flow. © 2011 Cambridge University Press. Source

Linderholm K.,Swedish University of Agricultural Sciences | Tillman A.-M.,Chalmers University of Technology | Mattsson J.E.,Swedish University of Agricultural Sciences
Resources, Conservation and Recycling | Year: 2012

Phosphorus is an important nutrient in plant cultivation. Global reserves of phosphate rock worth mining are limited. Reuse of phosphorus in wastewater is therefore important. This LCA study assessed the environmental impact of four ways to supply Swedish agriculture with phosphorus fertiliser of acceptable quality as regards cadmium content: mineral fertiliser; certified sewage sludge; struvite (MgNH 4PO 4·6H 2O) precipitated from wastewater; and phosphorus recovered from sludge incineration. These were examined with respect to impacts on global warming, eutrophication, energy demand and cadmium flows to farmland. The functional unit chosen was 11 kg P (25.2 kg P 2O 5) to agricultural land, which was the average phosphorus output (removal with harvest) per hectare from Swedish farmland in 2007. Using sewage sludge directly on farmland was the most efficient option in terms of energy and emissions of greenhouse gases, but also added most cadmium to the soil. Phosphorus recovery from incinerated sludge was the most energy demanding option and gave most emissions of greenhouse gases. Despite great concerns about cadmium in Swedish fertilisers and sludge, it was found that almost no regular analyses for cadmium are made on imported food by the authorities, although food imports are constantly increasing. Total imports of cadmium with food are therefore unknown. © 2012 Elsevier B.V. Source

Carozzi T.D.,Chalmers University of Technology
Monthly Notices of the Royal Astronomical Society: Letters | Year: 2015

I present an exact and explicit solution to the scalar (Stokes flux intensity) radio interferometer imaging equation on a spherical surface which is valid also for non-coplanar interferometer configurations. This imaging equation is comparable to ω-term imaging algorithms, but by using a spherical rather than a Cartesian formulation this term has no special significance. The solution presented also allows direct identification of the scalar (spin 0 weighted) spherical harmonics on the sky. The method should be of interest for future multispacecraft interferometers, wide-field imaging with non-coplanar arrays, and cosmic microwave background spherical harmonic measurements using interferometers. © 2015 The Authors. Source

Gerlee P.,Gothenburg University | Gerlee P.,Chalmers University of Technology
Cancer Research | Year: 2013

In this article, we will trace the historical development of tumor growth laws, which in a quantitative fashion describe the increase in tumor mass/volume over time. These models are usually formulated in terms of differential equations that relate the growth rate of the tumor to its current state and range from the simple one-parameter exponential growth model to more advanced models that contain a large number of parameters. Understanding the assumptions and consequences of such models is important, as they often underpin more complex models of tumor growth. The conclusion of this brief survey is that although much improvement has occurred over the last century, more effort and new models are required if we are to understand the intricacies of tumor growth. Cancer Res; 73(8); 2407-11. © 2013 American Association for Cancer Research. Source

Fulop T.,Chalmers University of Technology | Landreman M.,Massachusetts Institute of Technology
Physical Review Letters | Year: 2013

Runaway ions can be produced in plasmas with large electric fields, where the accelerating electric force is augmented by the low mean ionic charge due to the imbalance between the number of electrons and ions. Here we derive an expression for the high-energy tail of the ion distribution function in lightning discharges and investigate the energy range that the ions can reach. We also estimate the corresponding energetic proton and neutron production due to fusion reactions. © 2013 American Physical Society. Source

Guo S.,Chalmers University of Technology
Materials Science and Technology (United Kingdom) | Year: 2015

This paper summarises existing phase selection rules for cast high entropy alloys. Essentially, they are almost all based on the parametric approach, utilising various descriptors comprising mixing enthalpy, configuration entropy, mismatch entropy, melting points, atomic size mismatch, electronegativity and valence electron concentration. The overview starts from phase selection rules for solid solutions, intermetallic compounds and the amorphous phase in high entropy alloys. Further discussions are relevant to selection rules for solid solution phases in high entropy alloys, more specifically, for face centred cubic and body centred cubic type solid solutions. Finally, some challenges and future prospects of phase selection rules for high entropy alloys are addressed. © 2015 Institute of Materials, Minerals and Mining Published by Maney on behalf of the Institute. Source

Lofgren B.,Skf Sverige Ab | Tillman A.-M.,Chalmers University of Technology
Journal of Cleaner Production | Year: 2011

To meet the increasing need for practical life-cycle thinking in manufacturing, this paper proposes a method that includes the life-cycle perspective in manufacturing decision making. This method combines discrete-event simulation (DES) - commonly used for the conceptual evaluation of manufacturing systems - with life-cycle assessment (LCA). This combination captures the dynamic interrelationships between manufacturing processes in order to analyse systemic responses to configuration changes, something static LCA modelling cannot do. The method evolved when a bearing production line at SKF was being examined to relate manufacturing decision making to environmental consequences. This was done using DES to investigate how parameters normally used to optimize traditional manufacturing system performance influence energy use and material losses in manufacturing systems. The environmental consequences of this material loss and energy use are further calculated using LCA methodology. Results indicate that while the combination of the two methods increases the data collection workload, it uncovers previously hidden environmental consequences of manufacturing decision making and introduces a way to assess an industrial actor's manufacturing system using relevant LCA scenarios. © 2011 Elsevier Ltd. All rights reserved. Source

Cederwall M.,Chalmers University of Technology
Journal of High Energy Physics | Year: 2014

Abstract: Generalised diffeomorphisms in double field theory rely on an O(d, d) structure defined on tangent space. We show that any (pseudo-)Riemannian metric on the doubled space defines such a structure, in the sense that the generalised diffeomorphisms defined using such a metric form an algebra, provided a covariant section condition is fulfilled. Consistent solutions of the section condition gives further restrictions. The case previously considered corresponds to a flat metric. The construction makes it possible to apply double geometry to a larger class of manifolds. Examples of curved defining metrics are given. We also comment on the rôle of the defining geometry for the symmetries of double field theory, and on the continuation of the present construction to the U-duality setting. © 2014, The Author(s). Source

Ilderton A.,Chalmers University of Technology
Journal of High Energy Physics | Year: 2014

Abstract: The nonperturbative probability of pair production in electric fields depending on lightfront time is given exactly by the locally constant approximation. We explain this by showing that the worldline path integral defining the effective action contains a constraint, which localises contributing paths on hypersurfaces of constant lightfront time. These paths are lightfront zero-modes and there can be no pair production without them; the effective action vanishes if they are projected out. © 2014, The Author(s). Source

Mijakovic I.,Chalmers University of Technology | Deutscher J.,French National Center for Scientific Research | Deutscher J.,French National Institute for Agricultural Research
Frontiers in Microbiology | Year: 2015

The discovery of tyrosine-phosphorylated proteins in Bacillus subtilis in the year 2003 was followed by a decade of intensive research activity. Here we provide an overview of the lessons learned in that period. While the number of characterized kinases and phosphatases involved in reversible protein-tyrosine phosphorylation in B. subtilis has remained essentially unchanged, the number of proteins known to be targeted by this post-translational modification has increased dramatically. This is mainly due to phosphoproteomics and interactomics studies, which were instrumental in identifying new tyrosine-phosphorylated proteins. Despite their structural similarity, the two B. subtilis protein-tyrosine kinases (BY-kinases), PtkA and PtkB (EpsB), seem to accomplish different functions in the cell. The PtkB is encoded by a large operon involved in exopolysaccharide production, and its main role appears to be the control of this process. The PtkA seems to have a more complex role; it phosphorylates and regulates a large number of proteins involved in the DNA, fatty acid and carbon metabolism and engages in physical interaction with other types of kinases (Ser/Thr kinases), leading to mutual phosphorylation. PtkA also seems to respond to several activator proteins, which direct its activity toward different substrates. In that respect PtkA seems to function as a highly connected signal integration device. © 2015 Mijakovic and Deutscher. Source

Romeo A.B.,Chalmers University of Technology | Agertz O.,University of Surrey
Monthly Notices of the Royal Astronomical Society | Year: 2014

Gravitational instabilities play a primary role in shaping the clumpy structure and powering the star formation activity of gas-rich high-redshift galaxies. Here, we analyse the stability of such systems, focusing on the size and mass ranges of unstable regions in the disc. Our analysis takes into account the mass-size and linewidth-size scaling relations observed in molecular gas, originally discovered by Larson. We show that such relations can have a strong impact on the size and mass of star-forming clumps, as well as on the stability properties of the disc at all observable scales, making the classical Toomre parameter a highly unreliable indicator of gravitational instability. For instance, a disc with Q = 1 can be far from marginal instability, while a disc with Q ≪ 1 can be marginally unstable. Our work raises an important caveat: if clumpy discs at high redshift have scale-dependent surface densities and velocity dispersions, as implied by the observed clump scaling relations, then we cannot thoroughly understand their stability and star formation properties unless we perform multiscale observations. This will soon be possible thanks to dedicated Atacama Large Millimeter/submillimeter Array surveys, which will explore the physical properties of supergiant molecular clouds at the peak of cosmic star formation and beyond. © 2014 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. Source

Rosado L.,Chalmers University of Technology | Niza S.,University of Lisbon | Ferrao P.,University of Lisbon
Journal of Industrial Ecology | Year: 2014

Summary: This article describes a new methodological framework to account for urban material flows and stocks, using material flow accounting (MFA) as the underlying method. The proposed model, urban metabolism analyst (UMAn), bridges seven major gaps in previous urban metabolism studies: lack of a unified methodology; lack of material flows data at the urban level; limited categorizations of material types; limited results about material flows as they are related to economic activities; limited understanding of the origin and destination of flows; lack of understanding about the dynamics of added stock; and lack of knowledge about the magnitude of the flow of materials that are imported and then, to a great extent, exported. To explore and validate the UMAn model, a case study of the Lisbon Metropolitan Area was used. An annual time series of material flows from 2003 to 2009 is disaggregated by the model into 28 material types, 55 economic activity categories, and 18 municipalities. Additionally, an annual projection of the obsolescence of materials for 2010-2050 was performed. The results of the case study validate the proposed methodology, which broadens the contribution of existing urban MFA studies and presents pioneering information in the field of urban metabolism. In particular, the model associates material flows with economic activities and their spatial location within the urban area. © 2014 by Yale University. Source

Kopylov S.,Lancaster University | Tzalenchuk A.,National Physical Laboratory United Kingdom | Kubatkin S.,Chalmers University of Technology | Fal'Ko V.I.,Lancaster University
Applied Physics Letters | Year: 2010

We analyze doping of graphene grown on SiC in two models which differ by the source of charge transferred to graphene, namely, from SiC surface and from bulk donors. For each of the two models, we find the maximum electron density induced in monolayer and bilayer graphene, which is determined by the difference between the work function for electrons in pristine graphene and donor states on/in SiC, and analyze the responsivity of graphene to the density variation by means of electrostatic gates. © 2010 American Institute of Physics. Source

Horellou C.,Chalmers University of Technology | Fletcher A.,Northumbria University
Monthly Notices of the Royal Astronomical Society | Year: 2014

Tong L.,Chinese Academy of Sciences | Xu H.,Chinese Academy of Sciences | Kall M.,Chalmers University of Technology
MRS Bulletin | Year: 2014

The nanogap is possibly the single most important physical entity in surface-enhanced Raman scattering. Nanogaps between noble metal nanostructures deliver extremely high electric field-enhancement, resulting in an extraordinary amplification of both the excitation rate and the emission rate of Raman active molecules situated in the gap. In some cases, the resulting surface-enhancement in the gap can be so high that Raman spectra from single molecules can be measured. Here, we briefly review some important concepts and experimental results on nanoscale gaps for SERS applications. © 2014 Materials Research Society. Source

Construction Management and Economics | Year: 2010

The relationship between trust and control in client-contractor interactions is explored, focusing on the control mechanisms used in a construction project. A longitudinal case study of a large laboratory construction project found that the client used a variety of control mechanisms to ensure that the contractor behaved trustworthily. Empirical data were gathered through interviews and non-participant observation. The results indicate that the use of control mechanisms is part of a complex and dynamic socially constructed process that requires ongoing discussion and evaluation, and to which informal control mechanisms are central. Business relationships built solely on trust are seemingly rare; even in trust-based collaborative settings, such as partnering arrangements; the contracting parties must pay attention to trust-nurturing actions. © 2010 Taylor & Francis. Source

Podgorski K.,Lund University | Rychlik I.,Chalmers University of Technology
Journal of Marine Systems | Year: 2014

Significant wave heights are modeled by means of a spatial-temporal random Gaussian field. Its dependent structure can be localized by introduction of time and space dependent parameters in the spectrum. The model has the advantage of having a relatively small number of parameters. These parameters have natural physical interpretation and are statistically fitted to represent variability of observed significant wave height records. The fitted spatial-temporal significant wave field allows for prediction of fatigue accumulation in ship details and of extreme responses encountered. The method is exemplified by analyzing a container ship data relevant for North Atlantic trade and the results show a high agreement with actual on-board measurements. © 2013 Elsevier B.V. Source

Rootzen H.,Chalmers University of Technology | Katz R.W.,U.S. National Center for Atmospheric Research
Water Resources Research | Year: 2013

In the past, the concepts of return levels and return periods have been standard and important tools for engineering design. However, these concepts are based on the assumption of a stationary climate and do not apply to a changing climate, whether local or global. In this paper, we propose a refined concept, Design Life Level, which quantifies risk in a nonstationary climate and can serve as the basis for communication. In current practice, typical hydrologic risk management focuses on a standard (e.g., in terms of a high quantile corresponding to the specified probability of failure for a single year). Nevertheless, the basic information needed for engineering design should consist of (i) the design life period (e.g., the next 50 years, say 2015-2064); and (ii) the probability (e.g., 5% chance) of a hazardous event (typically, in the form of the hydrologic variable exceeding a high level) occurring during the design life period. Capturing both of these design characteristics, the Design Life Level is defined as an upper quantile (e.g., 5%) of the distribution of the maximum value of the hydrologic variable (e.g., water level) over the design life period. We relate this concept and variants of it to existing literature and illustrate how they, and some useful complementary plots, may be computed and used. One practically important consideration concerns quantifying the statistical uncertainty in estimating a high quantile under nonstationarity. Key Points The concepts return level and return period do not apply to a changing climate We propose a concept, Design Life Level, which gives key information for design We illustrate by rainfall in Western Australia and warm winters in Fort Collins ©2013. American Geophysical Union. All Rights Reserved. Source

Gomez-Barea A.,University of Seville | Ollero P.,University of Seville | Leckner B.,Chalmers University of Technology
Fuel | Year: 2013

In fluidized-bed gasification (FBG) of biomass and waste the temperature is maintained relatively low to prevent agglomeration. This slows down carbon conversion in conventional FBG, and a gas with relatively high concentration of tar is generated. Then the gasification efficiency is reduced and utilization of the gas is difficult in applications where the gas is cooled or compressed. In the present work the conversion of char and tar is studied to identify the main factors hindering complete conversion of the fuel into a product gas that is free from tar. It is concluded that char conversion can be increased by solids recirculation in directly heated FBG (stand-alone units) or by burning the char in a separate chamber in indirectly heated FBG. However, the tar content of the gas remains high, making gas cleaning necessary. Downstream cleaning of gas by catalytic cracking and/or scrubbing is complex and/or expensive for small to medium gasification plants, so conversion of tar within the gasifier is preferred. The optimization of conventional directly heated FBG by use of in-bed catalyst and distribution of the gasification agent to various zones of the gasifier, although improving the process, is not sufficient to attain the gas purity required for cold gas applications. Staged gasification is a suitable way to reach high char conversion, while yielding a gas with low concentration of heavy tar. Most of the staged-gasification developments proposed up to date have been based on fixed-beds, thus having relatively small capacity. A recently proposed concept to achieve almost complete tar and char conversion in fluidized bed is presented. © 2012 Elsevier Ltd. All rights reserved. Source

Hkansson B.,Chalmers University of Technology
Advances in Oto-Rhino-Laryngology | Year: 2011

The bone-anchored hearing aid (Baha) is today an important rehabilitation alternative for patients with mixed and conductive hearing loss and where air conduction devices should not or cannot be used. Some patients with single-sided deafness are also successfully treated with a Baha. Despite successful treatment of these patient groups, there is always a need for future improvements. First, it is well known that Baha are associated with some drawbacks related to skin infections, accidental or spontaneous loss of the bone implant, and patient refusal for treatment due to stigma. Therefore, in this chapter some alternatives to the Baha which have the potential to reduce these drawbacks are generally discussed. They all have the common feature that they do not need a permanent skin penetration. The alternatives to the Baha are: (1) improved conventional bone conduction (BC) devices, (2) devices with an implanted transducer referred to as BC implants (BCI), (3) dental-attached devices. Disregarding skin complication issues, direct BC devices like the Baha, have a superior advantage of better sound quality in the high-frequency range. How these devices might be improved in the future is also discussed. Finally, some recent advances in the development of a new BCI system will be presented, where the implanted transducer uses a non-screw attachment to a hollow recess of the temporal bone. Some preclinical studies have been performed showing that a BCI system can provide similar or higher output as compared with a Baha. Copyright © 2011 S. Karger AG, Basel. Source

Ferretti G.,Chalmers University of Technology
Journal of High Energy Physics | Year: 2014

We present a model of partial compositeness arising as the IR limit of a SU(4) gauge theory with only fermionic matter. This group is one of the most promising ones among a handful of possible choices allowing a symmetry breaking pattern incorporating custodial symmetry and a top partner candidate, while retaining asymptotic freedom. It is favored for not giving rise to lepto-quarks or Landau poles in the SM gauge couplings. The minimal UV theory consists of five hyperfermions in the anti-symmetric representation and three in the fundamental and anti-fundamental. The IR theory is centered around the coset SU(5)/SO(5), with top partners in the fundamental of SO(5), giving rise to one composite fermion of electric charge 5/3, three of charge 2/3 and one of charge -1/3. Electro-Weak symmetry breaking occurs via top-quark-driven vacuum misalignment. The top quark mass is generated via the mechanism of partial compositeness, while the remaining fermions acquire a mass via a standard quadratic coupling to the Higgs. We compute the top and bottom quark mass matrix and the Electro-Weak currents of the composite fermions. The model does not give rise to unacceptably large deviations from the SM Z → b b ̄ decay width. © 2014 The Author(s). Source

Ramstedt S.,Uppsala University | Olofsson H.,Chalmers University of Technology
Astronomy and Astrophysics | Year: 2014

Karlsson M.,Chalmers University of Technology
Dalton Transactions | Year: 2013

Understanding the fundamental properties of materials of relevance for alternative energy technologies is crucial in addressing the global challenge of cleaner sources of energy. This Perspective article aims to demonstrate the important role that neutron scattering now plays in advancing the state of the art of the basic understanding of proton conducting oxides, which show potential as electrolytes in next-generation intermediate temperature fuel cells. In particular, the breadth of neutron scattering work on perovskite structured oxides, which continue to be the most promising class of electrolytes for intermediate-temperature applications, is reviewed. Key fundamental properties that are addressed include structures, proton sites, hydrogen-bonding interactions, proton dynamics, and concentration of protons in materials. Furthermore, the perspectives for future neutron studies within this field of research are discussed. © 2013 The Royal Society of Chemistry. Source

Kann N.,Chalmers University of Technology
Current Organic Chemistry | Year: 2012

The Nicholas reaction involves the treatment of a cobalt carbonyl-stabilized propargylic cation with a variety of nucleophiles to form a new carbon-carbon or carbon-heteroatom bond. Several features of this reaction make it especially well suited for applications in natural product synthesis, in particular when cyclic and polycyclic target molecules are involved. This review summarizes the results in this area from the last ten years, including approaches towards terpenes, alkaloids and marine natural products. © 2012 Bentham Science Publishers. Source

Lindholm M.,Chalmers University of Technology
European Transport - Trasporti Europei | Year: 2013

On the path towards sustainability for the urban area, local authorities make decisions that affect freight transport. However, in many ways, urban freight transport is a neglected issue. The purpose of this paper is to map out the current status of urban freight transport research from a local authority perspective. A literature review is performed, looking through research in urban freight transport during the last 15 years. The review presents a large amount of references and it is clear that the area of urban freight transport has gained a larger interest during the later part of the time period studied. Research mainly focuses on freight measures (pilot actions) performed in an urban context, but the local authority perspective is lacking in many aspects. The review shows some areas that local authorities need to consider when working with freight transport in the urban area, according to the literature: measures; monitoring and evaluation; performance indicators; transfer of knowledge between cities/countries; and, stakeholder involvement. Source

Sabel'Nikov V.A.,ONERA | Lipatnikov A.N.,Chalmers University of Technology
Combustion Science and Technology | Year: 2011

A simple model is proposed to evaluate (a) the divergence of velocity vector conditioned on unburned mixture, and (b) the vector component normal to the mean flame brush in the flamelet regime of premixed turbulent combustion. The model involves a single constant and does not invoke an extra balance equation. To perform the first test of the model, six flames stabilized in impinging jets and experimentally investigated by 4 research groups were numerically simulated. In the computations, (a) approximations of the measured axial profiles of the mean combustion progress variable were invoked, (b) the well-known (Bray et al., 1998, and 2000) statistically steady and 1-dimensional Favre-averaged continuity and Euler equations were numerically integrated in order to approximate the measured axial profiles of the mean axial velocity, and, then, (c) the approximations were utilized in order to evaluate conditioned velocities and turbulent scalar flux using the proposed model supplemented with the BML approach and balance equation for the Favre-averaged combustion progress variable. The obtained agreement between the measured and computed axial profiles of the conditioned axial velocities or axial turbulent scalar flux was encouraging, thus, indicating that the proposed simple model is promising. Since the correlation between fluctuations of velocity and unity normal vectors, conditioned to flamelet surface, plays a key role in the model, the encouraging test results call for studying this correlation in future DNS. Moreover, further research into the difference in velocity conditioned on unburned mixture and velocity conditioned on the unburned side of flamelets is necessary for improving the model at the leading edge of a turbulent flame brush. Copyright © Taylor & Francis Group, LLC. Source

Beilina L.,Chalmers University of Technology | Klibanov M.V.,University of North Carolina at Charlotte
Inverse Problems | Year: 2010

A synthesis of a globally convergent numerical method for a coefficient inverse problem and the adaptivity technique is presented. First, the globally convergent method provides a good approximation for the unknown coefficient. Next, this approximation is refined via the adaptivity technique. The analytical effort is focused on a posteriori error estimates for the adaptivity. A numerical test is presented. © 2010 IOP Publishing Ltd. Source

Ljung Aust M.,Chalmers University of Technology
Accident Analysis and Prevention | Year: 2010

To define pre-crash scenarios for evaluation of active safety functions, data from crash investigations is often used. Typical data sources include official databases with police reported crashes (macroscopic data) and in-depth case studies (microscopic data). Macroscopic data is often representative but has little detail on causation, while the opposite is true of microscopic data. Combining the sources by coupling causation information from a set of case studies to a macroscopic crash type would therefore seem ideal. For the coupling to be valid however, it must be verified that the selected case study set is representative of the crash type. The aim of this study is to describe and test a new methodology for such verification by means of an intermediate layer of representatively sampled crash information (questionnaire responses from crash involved drivers). The methodology was applied to intersection crashes. For the data sets used, the similarity in crash causation for case studies and questionnaire crashes, together with the context similarity for questionnaire crashes and the macroscopic crash type, was sufficient to argue that the case studies were representative of the crash type. While results must be considered preliminary given the limited data sets used, the proposed methodology shows promise for future work related to defining pre-crash scenarios for ADAS evaluation. © 2009 Elsevier Ltd. All rights reserved. Source

Cederwall M.,Chalmers University of Technology
Journal of High Energy Physics | Year: 2010

We investigate the possibility of writing a manifestly supersymmetric action for 11-dimensional supergravity. The construction involves an explicit relation between the fields in the super-vielbein and the super-3-form, and uses non-minimal pure spinors. A simple cubic interaction term for a single scalar superfield is found. © SISSA 2010. Source

Henningson M.,Chalmers University of Technology
Journal of High Energy Physics | Year: 2010

We consider ADE-type (2,0) theory on a family of flat six-tori endowed with flat Sp(4) connections coupled to the R-symmetry. Our main objects of interest are the components of the 'partition vector' of the theory. These constitute an element of a certain finite dimensional vector space, carrying an irreducible representation of a discrete Heisenberg group related to the 't Hooft fluxes of the theory. Covariance under the SL 6(ℤ) mapping class group of a six-torus amounts to a certain automorphic transformation law for the partition vector, which we derive. Because of the absence of a Lagrangian formulation of (2,0) theory, this transformation property is not manifest, and gives useful non-trivial constraints on the partition vector. As an application, we derive a shifted quantization law for the spatial momentum of (2,0) theory on a space-time of the form ℝ × T 5. This quantization law is in agreement with an earlier result based on the relationship between (2, 0) theory and maximally supersymmetric Yang-Mills theory together with certain geometric facts about gauge bundles. © SISSA 2010. Source

Mucke T.,Carl von Ossietzky University | Kleinhans D.,Chalmers University of Technology | Peinke J.,Carl von Ossietzky University
Wind Energy | Year: 2011

Analysis of measurements on atmospheric turbulence with respect to the statistics of velocity increments reveals that the statistics are not Gaussian but highly intermittent. Here, we demonstrate that the higher quantity of extreme events in atmospheric wind fields transfers to alternating loads on the airfoil and on the main shaft in the form of torque fluctuations. For this purpose, alternating loads are discussed with respect to their increment statistics. Our conjecture is that the anomalous wind statistics are responsible for load changes, which may potentially contribute to additional loads and may cause additional fatigue. Our analysis is performed on three different wind field data sets: measured fields, data generated by a standard wind field model and data generated by an alternative model based on continuous time random walks, which grasps the intermittent structure of atmospheric turbulence in a better way. Our findings suggest that fluctuations in the loads might not be reflected properly by the standard wind field models. © 2010 John Wiley & Sons, Ltd. Source

Agrell E.,Chalmers University of Technology | Alvarado A.,University of Cambridge
IEEE Transactions on Information Theory | Year: 2011

Optimal binary labelings, input distributions, and input alphabets are analyzed for the so-called bit-interleaved coded modulation (BICM) capacity, paying special attention to the low signal-to-noise ratio (SNR) regime. For 8-ary pulse amplitude modulation (PAM) and for 0.75 bit/symbol, the folded binary code results in a higher capacity than the binary reflected Gray code (BRGC) and the natural binary code (NBC). The 1 dB gap between the additive white Gaussian noise (AWGN) capacity and the BICM capacity with the BRGC can be almost completely removed if the input symbol distribution is properly selected. First-order asymptotics of the BICM capacity for arbitrary input alphabets and distributions, dimensions, mean, variance, and binary labeling are developed. These asymptotics are used to define first-order optimal (FOO) constellations for BICM, i.e., constellations that make BICM achieve the Shannon limit -1.59 dB. It is shown that the Eb/N0 required for reliable transmission at asymptotically low rates in BICM can be as high as infinity, that for uniform input distributions and 8-PAM there are only 72 classes of binary labelings with a different first-order asymptotic behavior, and that this number is reduced to only 26 for 8-ary phase shift keying (PSK). A general answer to the question of FOO constellations for BICM is also given: using the Hadamard transform, it is found that for uniform input distributions, a constellation for BICM is FOO if and only if it is a linear projection of a hypercube. A constellation based on PAM or quadrature amplitude modulation input alphabets is FOO if and only if they are labeled by the NBC; if the constellation is based on PSK input alphabets instead, it can never be FOO if the input alphabet has more than four points, regardless of the labeling. © 2011 IEEE. Source

Nilsson B.E.W.,Chalmers University of Technology
Journal of High Energy Physics | Year: 2014

In this paper we discuss some special (critical) background solutions that arise in topological gauged N= 8 three-dimensional CFTs with SO(N) gauge group. Depending on how many scalar fields are given a VEV the theory has background solutions for certain values of μl, where μ and l are parameters in the TMG Lagrangian. Apart from Minkowski, chiral round AdS 3 and null-warped AdS 3 (or Schrödinger(z = 2)) we identify also a more exotic solution recently found in TMG by Ertl, Grumiller and Johansson. We also discuss the spectrum, symmetry breaking pattern and the supermultiplet structure in the various backgrounds and argue that some properties are due to their common origin in a conformal phase. Some of the scalar fields, including all higgsed ones, turn out to satisfy three-dimensional field equations similar to those of the singleton. Finally, we note that topologically gauged N= 6 ABJ(M) theories have a similar, but more restricted, set of background solutions. © 2014 The Author(s). Source

Etzlinger B.,Johannes Kepler University | Wymeersch H.,Chalmers University of Technology | Springer A.,Johannes Kepler University
IEEE Transactions on Signal Processing | Year: 2014

Synchronization is a key functionality in wireless networks, enabling a wide variety of services. We consider a Bayesian inference framework whereby network nodes can achieve phase and skew synchronization in a fully distributed way. In particular, under the assumption of Gaussian measurement noise, we derive two message passing methods (belief propagation and mean field), analyze their convergence behavior, and perform a qualitative and quantitative comparison with a number of competing algorithms. We also show that both methods can be applied in networks with and without master nodes. Our performance results are complemented by, and compared with, the relevant Bayesian Cramér-Rao bounds. © 2014 IEEE. Source

Hansbo P.,Chalmers University of Technology
Computer Methods in Applied Mechanics and Engineering | Year: 2011

In this paper we construct an approximation that uses midpoints of edges on tetrahedra in three dimensions. The construction is based on the three-dimensional version of the rotated Q1-approximation proposed by Rannacher and Turek (1992) [6]. We prove a priori error estimates for finite element solutions of the elasticity equations using the new element. Since it contains (rotated) bilinear terms it performs substantially better than the standard constant strain element in bending. It also allows for under-integration (in the form of one point Gauss integration of volumetric terms) in near incompressible situations. Numerical examples are included. © 2010 Elsevier B.V. Source

Sasic Kalagasidis A.,Chalmers University of Technology
Journal of Building Performance Simulation | Year: 2014

Integration of phase-change materials (PCMs) in building envelopes is a way to enhance heat storage capacity of buildings and thereby to rationalize the use of energy for heating and cooling of buildings. This work presents a numerical model of a building envelope with PCMs, verifications of the model according to a normative benchmark and measurements and a tentative case study that exemplifies the effects of such a building envelope on the thermal performance of a whole building. Simulations have been carried out using a modular environment of the International Building Physics Toolbox in Simulink®. As for the effects of PCMs in buildings, it is concluded that they are rather case sensitive; in the tentative case study, the annual savings of total energy for heating and cooling vary between 5% and 21%, depending mainly on the thermal comfort and the placement of PCM in the building envelope. © 2013 © 2013 International Building Performance Simulation Association (IBPSA). Source

Chakraborty N.,Newcastle University | Lipatnikov A.N.,Chalmers University of Technology
Proceedings of the Combustion Institute | Year: 2013

The statistics of fluid velocity components conditional in unburned reactants and fully burned products in the context of Reynolds Averaged Navier Stokes (RANS) simulations have been analysed using a Direct Numerical Simulation (DNS) database of statistically planar turbulent premixed flames for both high and low values of Damkohler number for different values of heat release parameter. It has been found that the contributions arising from chemical reaction to the conditional mean velocities and the conditional Reynolds stresses remain strong under high values of Damkohler number. The expressions for conditional mean velocity components and conditional Reynolds stresses, which are derived based on bi-modal probability density function of reaction progress variable for unity Lewis number flames, are modified in this study in such a manner that the new expressions can be used for low Damkohler number flames where bi-modal distribution is not realised. Suitable models for conditional surface-averaged velocity components and the Reynolds stresses have been identified, which are shown to work satisfactorily for all values of Damkohler number and heat release parameter considered in this analysed. © 2012 The Combustion Institute. Source

Yoshimura K.,Japan National Institute of Advanced Industrial Science and Technology | Langhammer C.,Chalmers University of Technology | Dam B.,Technical University of Delft
MRS Bulletin | Year: 2013

The hydrogenation of metals often leads to changes in optical properties in the visible range. This allows for fundamental studies of the hydrogenation process, as well as the exploration of various applications using these optical effects. Here, we focus on recent developments in metal hydride-based optical fiber and plasmonic sensors and smart windows. Both applications benefit from the existence of a reflective metallic state, which is lost on hydrogenation and allows for large reversible optical changes. In this article, we review the status of both technologies and their prospects for applications. © 2013 Materials Research Society. Source

Danielsson N.A.,Chalmers University of Technology
Proceedings of the ACM SIGPLAN International Conference on Functional Programming, ICFP | Year: 2012

The operational semantics of a partial, functional language is often given as a relation rather than as a function. The latter approach is arguably more natural: if the language is functional, why not take advantage of this when defining the semantics? One can immediately see that a functional semantics is deterministic and, in a constructive setting, computable. This paper shows how one can use the coinductive partiality monad to define big-step or small-step operational semantics for lambda-calculi and virtual machines as total, computable functions (total definitional interpreters). To demonstrate that the resulting semantics are useful type soundness and compiler correctness results are also proved. The results have been implemented and checked using Agda, a dependently typed programming language and proof assistant. © 2012 ACM. Source

Armelles G.,Imm Institute Microelectronica Of Madrid Cnm Csic | Dmitriev A.,Chalmers University of Technology
New Journal of Physics | Year: 2014

In this 'focus on' collection, a snapshot of the new, fast emerging field of magnetoplasmonics is presented. The research in the field deals with the combination of plasmonics and magnetism to elucidate the fundamentals of spin - plasmon interactions and reach new functionalities such as the enhancement of magneto-optical activity in various materials, active control of plasmons with weak magnetic fields, magnetoplasmonics-based bio- and chemical sensing, magnetophotonic and magnetoplasmonic crystals as modulators of light transmission and reflection, and many others. © 2014 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft. Source

Matic A.,Chalmers University of Technology | Scrosati B.,Helmholtz Institute Ulm
MRS Bulletin | Year: 2013

There is an urgent need for new energy storage and conversion systems in order to tackle the environmental problems we face today and to make the transition to a fossil fuel-free society. New batteries, supercapacitors, and fuel cells have the potential to be key devices for large-scale energy storage systems for load leveling and electric vehicles. In many cases, the concepts are known, but the right materials solutions are lacking. Ionic liquids (ILs) have been highlighted as suitable materials to be included in new devices, most commonly as electrolytes. Attractive features of ILs such as high ionic conductivity, low vapor pressure, high thermal and electrochemical stability, large temperature range for the liquid phase, and flexibility in molecular design have drawn the attention of researchers from many different fields. In addition, there is the possibility of designing new materials and morphologies using electrochemical synthesis with ILs. In this article, we provide an introduction to ILs and their properties, serving as a base for the topical articles in this issue. © 2013 Materials Research Society. Source

Rychlik I.,Chalmers University of Technology
Fatigue and Fracture of Engineering Materials and Structures | Year: 2013

This note reviews the means for fatigue damage rates estimation using scaled Laplace distributed loads. The model is suitable for the description of stresses containing transients of random amplitudes and locations. Moment method to estimate model parameters is given. Explicit formulas to compute rainflow damage rate as a function of excess kurtosis are presented. Laplace model is used to describe the variability of forces measured at some location on a cultivator frame. Validation of the model and uncertainty analysis in fatigue damage predictions is given. © 2013 Wiley Publishing Ltd. Source

Davidson L.,Chalmers University of Technology
International Journal of Heat and Fluid Flow | Year: 2014

A new approach to use the partially averaged Navier-Stokes (PANS) model as a hybrid RANS-LES model is presented. It is evaluated in fully developed channel flow and embedded LES in a hump flow. For the channel flow, the two RANS-LES interfaces are parallel to the walls. In the URANS region, fk is set to one. In the LES region, fk is set to a constant value (the baseline value is fk=0.4) or it is computed. It is found that the new model gives good results for channel flow for a large span of Reynolds numbers (4000≤Reτ. ≤. 32,000). In the channel flow simulations, three different grids are used in the wall-parallel planes, 322,642 and 1282, and the model yields virtually grid-independent flow fields and turbulent viscosities. Embedded LES is used for the hump flow which is well predicted. The RANS-LES interface is normal to the flow from the inlet. RANS is used upstream of the interface. Downstream this interface, RANS is used near the wall and LES is used away from the wall. © 2014 Elsevier Inc. Source

Fernando M.A.R.M.,University of Peradeniya | Gubanski S.M.,Chalmers University of Technology
IEEE Transactions on Dielectrics and Electrical Insulation | Year: 2010

This paper presents investigations on the performance of 33 kV silicone rubber insulators characterized by different creepage lengths, which aimed to find out whether the insulators could permanently work when electrically stressed beyond the recommended limits in polluted and clean tropical environments. The study was performed under natural field and laboratory conditions. The insulators tested included eight types of silicone rubber composite insulators, one type of hybrid siliconeceramic insulator and one semi-conducting glazed porcelain insulator, while ordinary porcelain and glass insulators were used as reference. During the field investigation, two sets of the insulators were separately installed and energized in coastal and inland parts of Sri Lanka, being by that exposed to marine and clean tropical environments. Their performances were periodically evaluated by visual inspections and measurements of hydrophobicity class. After five years of field exposure, the insulator performances were evaluated in laboratory by measurements of leakage currents under clean fog conditions and of wet flashover voltage. A third set of the insulators was aged in laboratory for 1000 hours inside a salt fog chamber where the insulators were continuously energized and daily sprayed with salt solution for eight hours and left to rest for remaining 16 hours. This treatment represented conditions similar as those in the field i.e. insulators exposed to salt sprays during monsoons. The insulator performances were investigated by measurements of leakage currents and classifying their patterns into different categories, i.e. capacitive, resistive, non-linear, discharge and strong discharge types, by means of fast Fourier transform and short time Fourier transform analyses. It was found that the long-term field exposure yielded weaker insulator deterioration than the salt fog chamber ageing, which indicated for a possibility to increase the electric stress on silicone rubber insulators to levels higher than the ones used today on glass and porcelain counterparts. © 2010 IEEE. Source

Karandikar Y.B.,Chalmers University of Technology
IEEE Antennas and Wireless Propagation Letters | Year: 2010

The patterns of dual dipoles above a ground plane in the so-called Eleven configuration are presented. It is shown that these patterns can be shaped to get different beamwidths to better fit reflectors with different F/D ratios while maintaining beam symmetry. Linear as well as curved dipoles are considered. The effect of finite ground plane is also discussed. © 2006 IEEE. Source

Johansson D.J.A.,Chalmers University of Technology | Johansson D.J.A.,Gothenburg University
Climatic Change | Year: 2011

Gronbeck H.,Chalmers University of Technology
Nanoscale | Year: 2012

Density functional theory calculations are used to evaluate Au4f core level shifts of methyl thiolate protected Au 25, Au 102 and Au 144 nanoparticles. The shifts are found to provide sensitive fingerprints of the chemical environment. In particular, Au atoms in protective gold-thiolate complexes have higher binding energies than Au atoms with solely metal neighbors. The core level shifts for the nanoparticles are compared to the corresponding results for methyl thiolates adsorbed on Au(111) and implications for the understanding of the gold-sulfur bond is discussed. This journal is © 2012 The Royal Society of Chemistry. Source

McKinstrie C.J.,Alcatel - Lucent | Karlsson M.,Chalmers University of Technology
Optics Express | Year: 2013

Parametric devices based on four-wave mixing in fibers perform many signal-processing functions required by optical communication systems. In these devices, strong pumps drive weak signal and idler sidebands, which can have one or two polarization components, and one or many frequency components. The evolution of these components (modes) is governed by a system of coupled-mode equations. Schmidt decompositions of the associated transfer matrices determine the natural input and output mode vectors of such systems, and facilitate the optimization of device performance. In this paper, the basic properties of Schmidt decompositions are derived from first principles and are illustrated by two simple examples (one- and two-mode parametric amplification). In a forthcoming paper, several nontrivial examples relevant to current research (including four-mode parametric amplification) will be discussed. © 2013 Optical Society of America. Source

Demaziere C.,Chalmers University of Technology
International Journal of Nuclear Energy Science and Technology | Year: 2013

Current practices in the nuclear industry to model the transient behaviour of nuclear reactors are based on the use of different solvers for resolving the different physical fields, and to some extent the different scales. The overall time-dependence is computed by a coarse-mesh neutronic solver coupled to a coarse-mesh thermal-hydraulic solver. The meso-scale information in the thermal-hydraulic solver is provided by empirically-derived correlations, which are strongly dependent on the flow regime. The neutronic solver makes use of homogenised and condensed macroscopic cross-sections, which are tabulated in advance as functions of local instantaneous and history variables. The pre-computation of such macroscopic cross-sections is carried out by a neutron transport solver modelling an infinite lattice of a single fuel assembly. The entire modelling procedure involves many intertwined steps, each step having its own set of approximations. The purpose of the present paper is to clearly highlight such steps and the corresponding approximations. Copyright © 2013 Inderscience Enterprises Ltd. Source

Linne M.,Chalmers University of Technology
Progress in Energy and Combustion Science | Year: 2013

Since the year 2000, a number of very different techniques to image spray formation in optically dense regions of atomizing sprays have appeared in the literature, been further developed, and applied to sprays. Three of them are transillumination techniques (meaning a beam is passed all the way through the spray and imaged on the other side, often called 'line-of-sight'), one technique is internally illuminated (the signal originates inside the spray), and one is a planar laser imaging technique. Researchers intending to use these new results need to understand with clarity what exactly the measurements provide and how reliably they can provide them. This article intends, therefore, to bring some order to the discussion of techniques. It includes a description of each of the five techniques, a review of advantages and limitations for each of them, a comparison, and a discussion of future trends. Most of the techniques are certain to evolve and improve further, but this article can provide a snapshot in time and help create a context for understanding. © 2013 Elsevier Ltd. All rights reserved. Source

Wynstra F.,Erasmus University Rotterdam | Von Corswant F.,Chalmers University of Technology | Wetzels M.,Maastricht University
Journal of Product Innovation Management | Year: 2010

In the literature on interorganizational collaboration in product development, considerable attention is given to supplier role classifications. Such classifications often link to a supplier's position in the overall supply chain, but the claim that this position has a substantial impact on its product development activities has seldom been empirically validated. The results from the present survey among Swedish automotive suppliers demonstrate that supplier product development activity is significantly affected by the position of the supplier in the supply chain and the supplier's strategic focus on innovation. While the latter has a stronger impact on product development activities, there is also an interaction effect implying that the effects of a supplier's innovation strategy are contingent on its supply chain position. Contrary to expectations, customer development commitment does not have any significant direct effect on supplier product development activities. Instead, this relation is fully mediated by supplier innovation strategy. These findings imply that, in contrast to conventional wisdom, product development activities are not strictly organized in "chains." Although supply chains can be useful metaphors for understanding the distribution of regular production activities between firms, they arguably apply less to the distribution of product development activities. © 2010 Product Development & Management Association. Source

Konkoli Z.,Chalmers University of Technology
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2010

A generic model of complex formation in small volumes was studied under the assumption of perfect mixing. Particles A react in clusters, and each reaction converts k A particles into a P particle. The back reaction is also allowed. The equilibrium state of the model is solved exactly. Fluctuations in product particle number are reduced by increasing the degree of cooperativity k. Three qualitatively distinct reactant fluctuation characteristics emerge. © 2010 The American Physical Society. Source

Braaten E.,Ohio State University | Kang D.,Ohio State University | Platter L.,University of Washington | Platter L.,Chalmers University of Technology
Physical Review Letters | Year: 2011

Systems consisting of identical bosons with a large scattering length satisfy universal relations determined by 2-body physics that are similar to those for fermions with two spin states. They require the momentum distribution to have a large-momentum 1/k4 tail and the radio-frequency transition rate to have a high-frequency 1/ω3/2 tail, both of which are proportional to the 2-body contact. Identical bosons also satisfy additional universal relations that are determined by 3-body physics and involve the 3-body contact, which measures the probability of 3 particles being very close together. The coefficients of the 3-body contact in the 1/k5 tail of the momentum distribution and in the 1/ω2 tail of the radio-frequency transition rate are log-periodic functions of k and ω that depend on the Efimov parameter. © 2011 American Physical Society. Source

Hansbo P.,Chalmers University of Technology | Larson M.G.,Umea University
Computer Methods in Applied Mechanics and Engineering | Year: 2011

We present energy norm a posteriori error estimates for continuous/discontinuous Galerkin (c/dG) approximations of the Kirchhoff-Love plate problem. The method is based on a continuous displacement field inserted into a symmetric discontinuous Galerkin formulation of the fourth order partial differential equation governing the deflection of a thin plate. We also give explicit formulas for the penalty parameter involved in the formulation. © 2011 Elsevier B.V. Source

Hansbo P.,Chalmers University of Technology | Larson M.G.,Umea University
Computer Methods in Applied Mechanics and Engineering | Year: 2011

We present a residual-based a posteriori error estimate in an energy norm of the error in a family of discontinuous Galerkin approximations of linear elasticity problems. The theory is developed in two and three spatial dimensions and general nonconvex polygonal domains are allowed. We also present some illustrating numerical examples. © 2011 Elsevier B.V. Source

Baran J.D.,Tyndall National Institute | Baran J.D.,Chalmers University of Technology | Larsson J.A.,Tyndall National Institute
Journal of Physical Chemistry C | Year: 2012

Berland K.,Chalmers University of Technology
Superlattices and Microstructures | Year: 2011

A general, system-independent, formulation of the parabolic Schrödinger-Poisson equation is presented for a charged hard wall in the limit of complete screening by the ground state. It is solved numerically using iteration and asymptotic boundary conditions. The solution gives a simple relation between the band bending and sheet charge density at an interface. Approximative analytical expressions for the potential profile and wave function are developed based on properties of the exact solution. Specific tests of the validity of the assumptions leading to the general solution are made. The assumption of complete screening by the ground state is found be a limitation; however, the general solution provides a fair approximate account of the potential profile when the bulk is doped. The general solution is further used in a simple model for the potential profile of an AlN/GaN barrier structure. The result compares well with the solution of the full Schrödinger-Poisson equation. © 2011 Elsevier Ltd. All rights reserved. Source

Linder M.,Chalmers University of Technology
International Journal of Innovation and Sustainable Development | Year: 2012

The paper outlines a framework of value creation and appropriation strategies available to firms that address environmental problems. It does so by utilising the idea that valuable problem-solution pairs correspond to opportunities and by describing why many environmental problems are 'valuable' problems as defined by the problem-solving perspective of the firm. Considering social dilemmas as the main hurdle for the appropriation of environmental value by firms, the paper derives four appropriation strategies for environmental innovations by drawing on the literature on economic institutions. The appropriation strategies are labelled eco-lean, eco-branding, eco-lobbyism and eco-transaction design. Copyright © 2012 Inderscience Enterprises Ltd. Source

Ferrighi L.,University of Aarhus | Pan Y.-X.,University of Aarhus | Gronbeck H.,Chalmers University of Technology | Hammer B.,University of Aarhus
Journal of Physical Chemistry C | Year: 2012

We present a density functional theory study of the structure and stability of self-assembled monolayers (SAMs) of alkylthiolate on Au(111) as a function of the alkyl chain length. The most favorable structure of the SAMs involves an RS-Au-SR complex (S being sulfur, R being an alkyl chain) formed through sandwiching one Au adatom by two alkylthiolates (RSs). Comparing a generalized gradient (GGA-PBE) and a meta-GGA (MGGA-M06-L) exchange-correlation functional we find that only the meta-GGA functional predicts the experimentally observed attractive intermolecular interactions within the SAMs. In particular, the use of M06-L yields an increased stability of the SAMs with increasing alkyl chain length and an increased attractive interaction between RS-Au-SR complexes at shorter distances. © 2012 American Chemical Society. Source

Hansson T.,University of Brescia | Hansson T.,Chalmers University of Technology | Wabnitz S.,University of Brescia
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2014

A study is made of the nonlinear dynamics of bichromatically pumped microresonator Kerr frequency combs described by a driven and damped nonlinear Schrödinger equation, with an additional degree of freedom in the form of the modulation frequency. A truncated four-wave model is derived for the pump modes and the dominant sideband pair, which is found to be able to describe much of the essential dynamical behavior of the full equation. The stability of stationary states within the four-wave model is investigated, and numerical simulations are made to demonstrate that a large range of solutions, including cavity solitons, are possible beyond previously considered low-intensity patterns. © 2014 American Physical Society. Source

Bocker S.,Friedrich - Schiller University of Jena | Damaschke P.,Chalmers University of Technology
Information Processing Letters | Year: 2011

Cluster Deletion and Cluster Editing ask to transform a graph by at most k edge deletions or edge edits, respectively, into a cluster graph, i.e., disjoint union of cliques. Equivalently, a cluster graph has no conflict triples, i.e., two incident edges without a transitive edge. We solve the two problems in time Oâ'Ž(1.415k) and Oâ'Ž(1.76k), respectively. These results round off our earlier work by considerably improved time bounds. For Cluster Deletion we use a technique that cuts away small connected components that do no longer contribute to the exponential part of the time complexity. As this idea is simple and versatile, it may lead to improvements for several other parameterized graph problems. The improvement for Cluster Editing is achieved by using the full power of an earlier structure theorem for graphs where no edge is in three conflict triples. © 2011 Elsevier B.V. Source

Brchner J.,Chalmers University of Technology | Olofsson T.,Lule University of Technology
Journal of Construction Engineering and Management | Year: 2012

A 30-year retrospective analysis of resource use in a range of new construction and repair projects reveals insignificant productivity increase when applying traditional narrow measures, as shown in a case study of beam bridges. It appears as necessary to estimate hidden quality changes in both outputs and inputs. Changes in government regulations, in specifications, and the development of nonprice criteria for contract award emerge as important. Schemes for benchmarking the performance of construction projects as well as life-cycle analyses suggest that customer risk aversion and effects on customer productivity should be taken into account. The outcome is a set of measurements that can be applied to the selection of any type of proposed new construction or repair technology innovation according to their potential impact on industry productivity. © 2012 American Society of Civil Engineers. Source

Busch M.,Gothenburg University | Ahlberg E.,Gothenburg University | Panas I.,Chalmers University of Technology
Catalysis Today | Year: 2013

The energy profiles of the di-hydroxo - di-oxo - peroxo pathway are discussed for a set of 3d transition metal oxides comprising V(III-V), Cr(III-V), Mn(II-IV, Mn(III-V), Fe(II-IV), Co(II-IV) and Ni(II-IV) using density functional theory (DFT). Two classes of oxides were identified. The first class, comprising V(III-V), Cr(III-V) and Fe(II-IV), displays exothermicity for the oxidation of di-hydroxo to di-oxo versus the tyrosine/tyrosyl-radical (TyrOH/TyrO) couple and endothermicity for the subsequent OO bond formation ([-/+] class), while the second class, comprising Mn(III-V), Co(II-IV) and Ni(II-IV), shows endothermicity with respect to the oxidation step and exothermicity for the OO bond formation ([+/-] class). The energetics of the endothermicity (exothermicity) for the oxidation step is reflected in the exothermicity (endothermicity) of the subsequent OO bond formation step. Mn(II-IV) is not part of any of the two classes. Instead it shows zero exothermicity with respect to TyrOH/TyrO for the oxidation step and a small endothermicity for the OO bond formation step. Despite the promising energy profile Mn(II-IV) is argued to be inactive due to a large activation barrier. A set of improved hetero-nuclear candidate catalysts is predicted by mixing [-/+] with [+/-] transition metal oxides. A simple and efficient method to estimate the energy profile of mixed transition metal oxides from the homo-nuclear systems is demonstrated. The validity of this procedure is checked and agreement with the explicitly calculated values is found. All considered heteronuclear candidate catalysts display enhanced performance compared to the pure homonuclear systems. © 2012 Elsevier B.V. Source

Bosch J.,Chalmers University of Technology | Capilla R.,Rey Juan Carlos University
Computer | Year: 2012

Dynamic software product lines address many of the challenges of building highly configurable software and use runtime variability mechanisms to support automatic decision making. © 2012 IEEE. Source

Brochner J.,Chalmers University of Technology
Building Research and Information | Year: 2010

As in the manufacturing and services industries, a mix of technological and non-technological innovation should be expected in construction. This study ascertains the relative importance of a set of internal and external factors for the intensity of technological and non-technological innovation among construction contracting firms. Seventeen types of contractor activities, associated with three levels of service content, are identified and a characteristics-based theory of service innovation with four innovation trajectories (material, informational, methodological, contractual or relational) is applied. Data collected from a questionnaire survey of 44 of the 50 largest construction contractors in Sweden indicate that 30 contractors had carried out research and development during 2003-2005 and that 11 had made at least one innovation new to the country. The lowest level of innovation intensity was mostly linked to the methodological trajectory (28 contractors), while the material trajectory dominated innovation 'new to the country' (eight contractors). Analysing data per activity where research and development or innovation had been reported shows that collaboration with another type of contractor is associated with a higher intensity of innovation, regardless of trajectory. The level of employee education is significant for relational innovation. The consequences for policies in firms and central government are identified. © 2010 Taylor & Francis. Source

Busch M.,Gothenburg University | Ahlberg E.,Gothenburg University | Panas I.,Chalmers University of Technology
Journal of Physical Chemistry C | Year: 2013

The critical steps in water oxidation at a binuclear Mn(II-IV) oxide site are revisited. Ideal stabilities of intermediates are confirmed by comparing to results for a binuclear Ir(III-V) system. The latter in turn is known to be an excellent water oxidation catalyst. The inefficiency of the binuclear Mn(II-IV) site is owing to the high activation energy for the chemical step whereby MnIV-O double bonds on adjacent sites are broken prior to forming the MnIII -O -O -MnIII peroxy moiety. A rationale for Mn(II-IV) -Mn(III-V) mixed oxidation state for water oxidation catalysis, analogous to mixed transition metal oxide systems, is offered. Possible virtues of the kinetic stability of the binuclear MnIV-O moiety are discussed, utilizing its oxidizing power by sidestepping oxygen evolution. © 2012 American Chemical Society. Source

Cederwall M.,Chalmers University of Technology
Modern Physics Letters A | Year: 2010

The complete supersymmetric classical Batalin-Vilkovisky action for 11-dimensional supergravity is presented. The action is polynomial in the scalar fermionic pure spinor superfield, and contains only a minor modification to the recently proposed three-point coupling. © 2010 World Scientific Publishing Company. Source

Zhdanov V.P.,Chalmers University of Technology | Zhdanov V.P.,RAS Boreskov Institute of Catalysis
Chemical Physics Letters | Year: 2015

Rupture of single adsorbed lipid vesicles is believed to occur via pore formation in the membrane. The latter process is related to the support-induced membrane strain. It includes membrane bending primarily near the rim of the vesicle-substrate contact area and tension distributed over the whole membrane. Herein, the relative role of these two factors is scrutinized from the perspectives of general theory and available experiments. The former factor is concluded to dominate. © 2015 Elsevier B.V. All rights reserved. Source

Kim J.-K.,Chalmers University of Technology
Journal of Power Sources | Year: 2013

A micro-fibrous organic electrode has been prepared by electrospinning process using poly(2,2,6,6-tetramethylpiperidinyloxy-4-ylmethacrylate) (PTMA), poly(vinylidene fluoride-co-hexafluoropropylene) (P(VdF-HFP)) and carbon black powder. The micro-fibrous PTMA electrode (MPE) film is investigated by FT-IR, TGA, SEM, TEM and electrochemical tests. The MPE shows excellent rate-capability and cycle performance. The MPE based lithium cell displays a high discharge capacity of 111 mAh g-1 at 1C. Even at a high current density of 50C, the MPE cell presents a discharge capacity of 109 mAh g-1. Moreover, the MPE have remarkably improved the volumetric capacity (209 mAh cm -3 at 10C) compared with a nano-fibrous PTMA electrode. The excellent electrochemical performance is ascribed to the microstructure that promotes fast ion transport through short diffusion pathways and at the same time facilitates electron transport. © 2013 Elsevier B.V. All rights reserved. Source

Ivert L.K.,Chalmers University of Technology
Production Planning and Control | Year: 2012

The purpose of this article is to investigate how the manufacturing process, the shop type and the data quality, i.e. the shop floor characteristics, influence the use of advanced planning and scheduling (APS) systems in production activity and control (PAC). The methodology implemented is a multiple case study at three case companies. Each company has different shop floor characteristics, but all use a scheduling module in an APS system, which supports production scheduling. A theoretical framework is developed suggesting how APS system are used in the PAC activities, and which major aspect to consider. The case analysis shows that the scheduling module in APS system, foremost supports sequencing and dispatching. In particular, the shop type is influenced by the decision of how often the APS runs and what freedom is given to the shop floor. The manufacturing process influences how the dispatch list is created. Contrary to the literature presuming that APS systems are most suitable in job shop processes, it is found that the manufacturing process is not a crucial factor when deciding whether APS systems are an appropriate investment. It is found that the level of data quality needed in the APS system depends to a large extent on how the dispatch list is used. For example, is the dispatch list used as a guideline, not a regulation, the need for accurate data in the module is reduced. This article extends the previous literature concerning APS systems by analysing how APS systems influence PAC as a whole and increase the understanding of the challenges of using APS systems in PAC. © 2012 Taylor & Francis. Source

Diamond and Related Materials | Year: 2012

Synthetic and natural diamonds containing small amounts of boron are conducting with apparent activation energy of 0.37 eV at high temperature and ≈ 0.01 eV at low temperature. If the boron/carbon ratio is increased above about 1‰, the higher activation energy starts to decrease to zero. By applying high pressure and high temperature Ekimov et al. managed to raise the B/C ratio above 1%. This material is superconducting below a few Kelvin. It is shown here that at low B/C ratio the MIR absorption at 0.37 eV can be identified with vertical Hubbard-U. Increasing the boron concentration Hubbard-U decreases to zero. Apparently B +/B - becomes more stable than B/B as a sub-lattice phase. It is shown that this is due to the smaller distance between the boron sites. The presence of B +, B, and B - in highly boron doped diamond is supported by NMR, Raman, and IR data in combination with simple calculations. © 2012 Elsevier B.V. All rights reserved. Source

Hornikx M.,Catholic University of Leuven | Forssen J.,Chalmers University of Technology
Applied Acoustics | Year: 2011

Hansson T.,Chalmers University of Technology | Wabnitz S.,University of Brescia
Journal of the Optical Society of America B: Optical Physics | Year: 2015

The generation of optical frequency combs in microresonators is considered without resorting to the mean-field approximation. New dynamical regimes are found to appear for high intracavity power that cannot be modeled using the Lugiato-Lefever equation. Using the Ikeda map, we show the existence of multi-valued stationary states and analyze their stability. Period doubled patterns are considered, and a novel type of super cavity soliton associated with the multi-stable states is predicted. © 2015 Optical Society of America. Source

Gustavsson S.M.K.,Chalmers University of Technology
International Journal of Health Care Quality Assurance | Year: 2014

Purpose – The purpose of this paper is to identify and improve patient care processes by collaborating patients, relatives and healthcare professionals. Design/methodology/approach – To identify and improve patient care processes by collaborating patients, relatives and healthcare professionals. Findings – Healthcare problems captured from collaboration between patients and healthcare professionals fall into simple, complicated and complex problems. Healthcare staff and patient experiences with patient processes differ, and a collaborative approach is needed to capture all areas needing improvement. Research limitations/implications – The conclusions are drawn from a project with few participants in a context that probably influenced the results. In contrast, other studies in the same area confirm the results. Practical implications – The study outcomes have direct implications for healthcare professionals who can learn from patients involved in quality improvements such as this experience-based co-design (EBCD) project. Originality/value – The paper contributes to limited studies on EBCD involving patients in healthcare quality improvements. © Emerald Group Publishing Limited. Source

Jagers P.,Chalmers University of Technology
Journal of Mathematical Biology | Year: 2010

It is argued that biological populations are finite and consisting of individuals with varying life span and reproduction, and that they should be thus modelled. Modern probability theory provides tools for this. © 2010 Springer-Verlag. Source

Olsson P.,Chalmers University of Technology
Wave Motion | Year: 2011

Recently, some explicit results were obtained regarding non-uniqueness for the traction to displacement maps of bounded elastic bodies in 2D and 3D, under the assumption of an internal kinematic constraint. The approach utilized is that of transformation optics. As the approach could, under the usual continuum assumptions, handle all frequencies without resorting to active materials, it could potentially be directly applied also to time domain problems. In the present paper we cover the extension to the time domain of these recent results in the case of reflection from a composite slab of rather general anisotropy, and derive the required material properties of different slabs with identical reflection properties. In particular we describe how homogeneous and inhomogeneous slabs of very different thicknesses may be indistinguishable with respect to elastic wave reflection properties. It should be noted that the approach retains both the minor and major symmetries of the stiffness tensor, and does not require an anisotropic mass density tensor to be used. © 2011 Elsevier B.V. Source

Hansen T.F.,University of Oslo | Bartoszek K.,Chalmers University of Technology
Systematic Biology | Year: 2012

Regressions of biological variables across species are rarely perfect. Usually, there are residual deviations from the estimated model relationship, and such deviations commonly show a pattern of phylogenetic correlations indicating that they have biological causes. We discuss the origins and effects of phylogenetically correlated biological variation in regression studies. In particular, we discuss the interplay of biological deviations with deviations due to observational or measurement errors, which are also important in comparative studies based on estimated species means. We show how bias in estimated evolutionary regressions can arise from several sources, including phylogenetic inertia and either observational or biological error in the predictor variables. We show how all these biases can be estimated and corrected for in the presence of phylogenetic correlations. We present general formulas for incorporating measurement error in linear models with correlated data. We also show how alternative regression models, such as major axis and reduced major axis regression, which are often recommended when there is error in predictor variables, are strongly biased when there is biological variation in any part of the model. We argue that such methods should never be used to estimate evolutionary or allometric regression slopes. © 2012 The Author(s). Source

International Journal of Project Management | Year: 2011

This paper aims to increase our understanding of collective outcomes by exploring both micro- and macro-level strategies for dealing with problems arising from incomplete contracts. By combining theories dealing with risk-sharing under various degrees of uncertainty (financial incentives and long-term relationships) with respect to social influence tactics involved in negotiations concerning additional work and changes, a useful framework was created. Case data regarding Swedish interorganizational development projects from both the construction and IT industries are used to illustrate the theoretical arguments. Findings indicate that social norms and the work-related values and attitudes of key negotiators significantly affect project outcomes. Efforts to increase the sophistication of financial incentives and long-term arrangements (e.g., standardized routines concerning risk-sharing and collaborative initiatives) do not seem to pay-off. © 2010 Elsevier Ltd. Source

Dozza M.,Chalmers University of Technology
Accident Analysis and Prevention | Year: 2016

Crash databases are commonly queried to infer crash causation, prioritize countermeasures to prevent crashes, and evaluate safety systems. However, crash databases, which may be compiled from police and hospital records, alone cannot provide estimates of crash risk. Moreover, they fail to capture road user behavior before the crash. In Sweden, as in many other countries, crash databases are particularly sterile when it comes to bicycle crashes. In fact, not only are bicycle crashes underreported in police reports, they are also poorly documented in hospital reports. Nevertheless, these reports are irreplaceable sources of information, clearly highlighting the surprising prevalence of single-bicycle crashes and hinting at some cyclist behaviors, such as alcohol consumption, that may increase crash risk.In this study, we used exposure data from 11 roadside stations measuring cyclist flow in Gothenburg to help explain crash data and estimate risk. For instance, our results show that crash risk is greatest at night on weekends, and that this risk is larger for single-bicycle crashes than for crashes between a cyclist and another motorist. This result suggests that the population of night-cyclists on weekend nights is particularly prone to specific crash types, which may be influenced by specific contributing factors (such as alcohol), and may require specific countermeasures. Most importantly, our results demonstrate that detailed exposure data can help select, filter, aggregate, highlight, and normalize crash data to obtain a sharper view of the cycling safety problem, to achieve a more fine-tuned intervention. © 2016 Elsevier Ltd. Source

Perzon M.,Chalmers University of Technology
Biomass and Bioenergy | Year: 2010

Oats are a new biofuel possible to use in modified residential wood pellet combustion appliances. The emissions of organic compounds from five sequential combustion stages; initial smouldering, early flaming, late flaming, after-flame smouldering and final glowing, for incomplete burning of oats on a laboratory scale were determined by gas chromatography and compared to those of softwood pellets. High concentrations of 1,6-anhydroglucose and furan-related compounds were released from the initial smouldering of oats, while high concentrations of methoxyphenols were released during the initial smouldering of wood pellets. The results indicate that oats are a biofuel with relatively low emissions during combustion, almost as low as those from wood pellets. After-flame smouldering of oats released lower concentrations of methane, alkenes and aromatic hydrocarbons than the after-flame smouldering of wood pellets. The large differences in emissions from the various combustion stages should be considered when evaluating the environmental aspects and health effects of residential burning of oats and wood pellets. © 2010 Elsevier Ltd. Source

Hansson T.,University of Brescia | Hansson T.,Chalmers University of Technology | Modotto D.,University of Brescia | Wabnitz S.,University of Brescia
Optics Letters | Year: 2014

We numerically study the mechanisms of frequency comb generation in the mid-infrared spectral region from cw-pumped silicon microring resonators. Coherent soliton comb generation may be obtained even for a pump with zero linear cavity detuning, through suitable control of the effective lifetime of free carriers from multiphoton absorption, which introduces a nonlinear cavity detuning via free-carrier dispersion. Conditions for optimal octave spanning Raman comb generation are also described. © 2014 Optical Society of America. Source

Bordes R.,Chalmers University of Technology | Hook F.,SE
Analytical Chemistry | Year: 2010

The assessment of adsorbed surfactant mass by quartz crystal microbalance with dissipation (QCM-D) monitoring is often complicated due to large bulk responses, particularly for surfactants with high critical micelle concentration (CMC). We present in this work means to interpret QCM-D data that enables the response from the bulk contribution to be separated from the response originating from adsorbed mass. Adsorption of two surfactants, Triton X100 and C12AspNa 2 with low and high CMCs, respectively, at the gold-liquid interface surface has been evaluated. Two different approaches to quantify the bulk response are compared. The first approach involves the use of a nonadsorbing surface (silica), yielding a calibration curve for the concentration dependent bulk response. The second method is based on the fact that the overtone-dependent QCM-D response that originates from changes in the bulk differs from that induced by the adsorbed layer of the surfactants. Under the reasonable assumption that the bulk solution and the adsorbed surfactants can be treated as a Newtonian liquid and an acoustically rigid film, it is demonstrated that the bulk contribution can be quantified without control measurements involving inert surfaces. An excellent agreement between the two methods is reported. © 2010 American Chemical Society. Source

Ferretti G.,Chalmers University of Technology | Karateev D.,International School for Advanced Studies
Journal of High Energy Physics | Year: 2014

We classify the four-dimensional purely fermionic gauge theories that give a UV completion of composite Higgs models. Our analysis is at the group theoretical level, addressing the necessary (but not sufficient) conditions for the viability of these models, such as the existence of top partners and custodial symmetry. The minimal cosets arising are those of type SU(5)/SO(5) and SU(4)/Sp(4). We list all the possible "hyper-color" groups allowed and point out the simplest and most promising ones. © 2014 The Author(s). Source

Henningson M.,Chalmers University of Technology
Journal of High Energy Physics | Year: 2011

Six-dimensional (2, 0) theory can be defined on a large class of six-manifolds endowed with some additional topological and geometric data (i.e. an orientation, a spin structure, a conformal structure, and an R-symmetry bundle with connection). We discuss the nature of the object that generalizes the partition function of a more conventional quantum theory. This object takes its values in a certain complex vector space, which fits together into the total space of a complex vector bundle (the 'partition bundle') as the data on the six-manifold is varied in its infinite-dimensional parameter space. In this context, an important role is played by the middle-dimensional intermediate Jacobian of the six-manifold endowed with some additional data (i.e. a symplectic structure, a quadratic form, and a complex structure). We define a certain hermitian vector bundle over this finite-dimensional parameter space. The partition bundle is then given by the pullback of the latter bundle by the map from the parameter space related to the six-manifold to the parameter space related to the intermediate Jacobian. © SISSA 2011. Source

Cederwall M.,Chalmers University of Technology
Journal of High Energy Physics | Year: 2016

Abstract: A geometry of superspace corresponding to double field theory is developed, with type II supergravity in D = 10 as the main example. The formalism is based on an orthosymplectic extension OSp(d, d|2s) of the continuous T-duality group. Covariance under generalised super-diffeomorphisms is manifest. Ordinary superspace is obtained as a solution of the orthosymplectic section condition. A systematic study of curved superspace Bianchi identities is performed, and a relation to a double pure spinor superfield cohomology is established. A Ramond-Ramond superfield is constructed as an infinite-dimensional orthosymplectic spinor. Such objects in minimal orbits under the OSp supergroup (“pure spinors”) define super-sections. © 2016, The Author(s). Source

Sjoblom J.,Chalmers University of Technology
Topics in Catalysis | Year: 2013

A new experimental set-up applied to engine emission experiments is presented which enables experiments where reactor conditions can be varied independently. These conditions include residence time, which can be varied via flow reduction and the possibility to use very different sizes of catalyst, temperature (using cooler or heaters) and concentrations (by dilution or adding gases). The system is designed to enhance knowledge transfer between lab scale and engine bench scale catalysis experimentation and to enable efficient design of experiments and catalytic reactor modeling. Two examples are presented dealing with capture of particulates and selective NOX reduction over a silver-alumina catalyst. Different experimental issues and their resolutions are also presented. © 2013 Springer Science+Business Media New York. Source

Dyer M.S.,University of Liverpool | Persson M.,University of Liverpool | Persson M.,Chalmers University of Technology
New Journal of Physics | Year: 2010

A free-electron-like band has recently been observed in a monolayer of 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA) molecules on Ag(111) by two-photon photoemission (Schwalb et al 2008 Phys. Rev. Lett. 101 146801) and scanning tunneling spectroscopy (Temirov et al 2006 Nature 444 350). Using density functional theory calculations, we find that the observed free-electron-like band originates from the Shockley surface state band being dramatically shifted up in energy by the interaction with the adsorbed molecules, while it also acquires a substantial admixture with a molecular band. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft. Source

Wilhelmsson L.M.,Chalmers University of Technology
Quarterly Reviews of Biophysics | Year: 2010

The use of fluorescent nucleic acid base analogues is becoming increasingly important in the fields of biology, biochemistry and biophysical chemistry as well as in the field of DNA nanotechnology. The advantage of being able to incorporate a fluorescent probe molecule close to the site of examination in the nucleic acid-containing system of interest with merely a minimal perturbation to the natural structure makes fluorescent base analogues highly attractive. In recent years, there has been a growing interest in developing novel candidates in this group of fluorophores for utilization in various investigations. This review describes the different classes of fluorophores that can be used for studying nucleic acid-containing systems, with an emphasis on choosing the right kind of probe for the system under investigation. It describes the characteristics of the large group of base analogues that has an emission that is sensitive to the surrounding microenvironment and gives examples of investigations in which this group of molecules has been used so far. Furthermore, the characterization and use of fluorescent base analogues that are virtually insensitive to changes in their microenvironment are described in detail. This group of base analogues can be used in several fluorescence investigations of nucleic acids, especially in fluorescence anisotropy and fluorescence resonance energy transfer (FRET) measurements. Finally, the development and characterization of the first nucleic base analogue FRET pair, tCO-tCnitro, and its possible future uses are discussed. © 2010 Cambridge University Press. Source

Palmkvist J.,Solvay Group | Palmkvist J.,Chalmers University of Technology
Journal of High Energy Physics | Year: 2011

We write the Lagrangian of the general N = 5 three-dimensional superconformal Chern-Simons theory, based on a basic Lie superalgebra, in terms of our recently introduced N = 5 three-algebras. These include N = 6 and N = 8 three-algebras as special cases. When we impose an antisymmetry condition on the triple product, the supersymmetry automatically enhances, and the N = 5 Lagrangian reduces to that of the well known N = 6 theory, including the ABJM and ABJ models. © SISSA 2011. Source

Ferretti G.,Chalmers University of Technology
Journal of High Energy Physics | Year: 2016

Abstract: We continue our investigation of gauge theories in which the Higgs boson arises as a pseudo-Nambu-Goldstone boson (pNGB) and top-partners arise as bound states of three hyperfermions. All models have additional pNGBs in their spectrum that should be accessible at LHC. We analyze the patterns of symmetry breaking and present all relevant couplings of the pNGBs with the gauge fields. We discuss how vacuum misalignment and a mass for the pNGBs is generated by a loop-induced potential. Finally, we paint a very broad, qualitative, picture of the kind of experimental signatures these models give rise to, setting the stage for further analysis. © 2016, The Author(s). Source

Ghazawneh A.,Jonkoping International Business School | Henfridsson O.,Chalmers University of Technology
Information Systems Journal | Year: 2013

Prior research documents the significance of using platform boundary resources (e.g. application programming interfaces) for cultivating platform ecosystems through third-party development. However, there are few, if any, theoretical accounts of this relationship. To this end, this paper proposes a theoretical model that centres on two drivers behind boundary resources design and use - resourcing and securing - and how these drivers interact in third-party development. We apply the model to a detailed case study of Apple's iPhone platform. Our application of the model not only serves as an illustration of its plausibility but also generates insights about the conflicting goals of third-party development: the maintenance of platform control and the transfer of design capability to third-party developers. We generate four specialised constructs for understanding the actions taken by stakeholders in third-party development: self-resourcing, regulation-based securing, diversity resourcing and sovereignty securing. Our research extends and complements existing platform literature and contributes new knowledge about an alternative form of system development. © 2012 Wiley Publishing Ltd. Source

Verburg R.M.,Technical University of Delft | Bosch-Sijtsema P.,Chalmers University of Technology | Vartiainen M.,Aalto University
International Journal of Project Management | Year: 2013

What conditions do project managers perceive as the most important to get the work done when working in fully dispersed settings? Rather than focusing on problems that managers experience when working in dispersed settings, our study highlights the conditions that are important for successful task accomplishment. We applied a Means-End-Chain (MEC) method to investigate the links between task accomplishment and relevant conditions that are attributes, benefits and values among a sample of experienced project managers (N=30). Our results show that important conditions for successful project execution in a dispersed setting include rules of communication and its clarity; project management style and goal-setting; and managers' competences and trust in a team. In addition to these internal conditions, project managers also stress the importance of both corporate and technology support. These four conditions are all perceived as vital for task accomplishment in global dispersed projects. © 2012 Elsevier Ltd. APM and IPMA. Source

Shumeiko V.S.,Chalmers University of Technology
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2016

We propose theory for a reversible quantum transducer connecting superconducting qubits and optical photons using acoustic waves in piezoelectrics. The proposed device consists of an integrated acousto-optic resonator that utilizes stimulated Brillouin scattering for phonon-photon conversion and piezoelectric effect for coupling of phonons to qubits. We evaluate the phonon-photon coupling rate and show that the required power of the optical pump as well as the other device parameters providing full and faithful quantum conversion is feasible for implementation with the state-of-the-art integrated acousto-optics. © 2016 American Physical Society. Source

Berman R.J.,Chalmers University of Technology
Journal of High Energy Physics | Year: 2011

We propose a statistical mechanical derivation of Kähler-Einstein metrics, i.e. solutions to Einstein's vacuum field equations in Euclidean signature (with a cosmological constant) on a compact Kähler manifold X. The microscopic theory is given by a canonical free fermion gas on X whose one-particle states are pluricanonical holomorphic sections on X (coinciding with higher spin states in the case of a Riemann surface) defined in background free manner. A heuristic, but hopefully physically illuminating, argument for the convergence in the thermodynamical (large N) limit is given, based on a recent mathematically rigorous result about exponentially small fluctuations of Slater determinants. Relations to higher-dimensional effective bosonization, the Yau-Tian-Donaldson program in Kähler geometry and quantum gravity are explored. The precise mathematical details will be investigated elsewhere. © SISSA 2011. Source

Sheeran M.,Chalmers University of Technology
Journal of Functional Programming | Year: 2011

A parallel prefix network of width n takes n inputs, a1, a 2,..., an, and computes each yi = a1 oa2 o...oai for 1 ≤ i ≤ n, for an associative operator. This is one of the fundamental problems in computer science, because it gives insight into how parallel computation can be used to solve an apparently sequential problem. As parallel programming becomes the dominant programming paradigm, parallel prefix or scan is proving to be a very important building block of parallel algorithms and applications. There are many different parallel prefix networks, with different properties such as number of operators, depth and allowed fanout from the operators. In this paper, ideas from functional programming are combined with search to enable a deep exploration of parallel prefix network design. Networks that improve on the best known previous results are generated. It is argued that precise modelling in a functional programming language, together with simple visualization of the networks, gives a new, more experimental, approach to parallel prefix network design, improving on the manual techniques typically employed in the literature. The programming idiom that marries search with higher order functions may well have wider application than the network generation described here. © Cambridge University Press 2010. Source

Johansson D.J.A.,Chalmers University of Technology | Johansson D.J.A.,Gothenburg University
Climatic Change | Year: 2012

A range of alternatives to the Global Warming Potential (GWP) have been suggested in the scientific literature. One of the alternative metrics that has received attention is the cost-effective relative valuation of greenhouse gases, recently denoted Global Cost Potential (GCP). However, this metric is based on complex optimising integrated assessment models that are far from transparent to the general scientist or policymaker. Here we present a new analytic metric, the Cost-Effective Temperature Potential (CETP) which is based on an approximation of the GCP. This new metric is constructed in order to enhance general understanding of the GCP and elucidate the links between physical metrics and metrics that take economics into account. We show that this metric has got similarities with the purely physical metric, Global Temperature change Potential (GTP). However, in contrast with the GTP, the CETP takes the long-term temperature response into account. © 2011 Springer Science+Business Media B.V. Source

Rohman I.K.,Chalmers University of Technology
Telecommunications Policy | Year: 2013

Recent studies of European countries indicate that the contribution of the ICT sectors to the regional economy is weakening and slowing economic growth. The present study investigates the contribution of the ICT sectors to economic performance in the European economies using Input-Output (10) methodology. The results indicate that: (1) the multiplier effect of the ICT sectors on the rest of the economy declined significantly during the period 2000-2005 compared with 1995-2000; and (2) the decline in the output of the ICT sectors can be attributed to the loss of export advantages and technical change gains in the sectors. The results show an inability of the sectors to grasp the international market, most likely a consequence of the lack of anticipation of more rapid innovation in emerging countries. © 2012 Elsevier Ltd. Source

Production Planning and Control | Year: 2013

This article publishes the results of a study of surgery time estimations. The study examines the estimating accuracy of the duration of future surgeries between a surgeon-based estimating system and a computer-based system that examine data from previously made surgeries. The relative estimating accuracy of the two systems is evaluated by using two hypothesis tests. This article also investigates whether the surgeons option to include additional factors in their estimations result in more accurate estimates for procedures requiring longer-than-normal surgery time. The results show that the surgeon-based estimation system is less accurate in general than the computer-based system. However, in cases where median surgery time is exceeded, the surgeon-based system is more accurate than a calculated average value of the previous surgeries. © 2013 Copyright Taylor and Francis Group, LLC. Source

Rusek F.,Lund University | Persson D.,Chalmers University of Technology | Lau B.K.,Lund University | Larsson E.G.,Linkoping University | And 3 more authors.
IEEE Signal Processing Magazine | Year: 2013

Multiple-input multiple-output (MIMO) technology is maturing and is being incorporated into emerging wireless broadband standards like long-term evolution (LTE). Very large MIMO entails an unprecedented number of antennas simultaneously serving a much smaller number of terminals. Larger numbers of terminals can always be accommodated by combining very large MIMO technology with conventional time- and frequency-division multiplexing via orthogonal frequency-division multiplexing (OFDM). A point-to-point MIMO link consists of a transmitter having an array of antennas, a receiver having an array of n t antennas, with both arrays connected by a channel such that every receive antenna is subject to the combined action of all transmit antennas. If we split up the antenna array at one end of a point-to-point MIMO link into autonomous antennas, we obtain the qualitatively different MU-MIMO. As the number of base station antennas grows, the system gets almost entirely limited from the reuse of pilots in neighboring cells, the so-called pilot contamination concept. Source

Agrell E.,Chalmers University of Technology
IEEE Transactions on Information Theory | Year: 2011

Most of the calculations in standard sphere decoders are redundant in the sense that they either calculate quantities that are never used or calculate some quantities more than once. A new method, which is applicable to lattices as well as finite constellations, is proposed to avoid these redundant calculations while still returning the same result. Pseudocode is given to facilitate immediate implementation. Simulations show that the speed gain with the proposed method increases linearly with the lattice dimension. At dimension 60, the new algorithms avoid about 75% of all floating-point operations. © 2011 IEEE. Source

Rosnes E.,University of Bergen | Graell I Amat A.,Chalmers University of Technology
IEEE Transactions on Information Theory | Year: 2011

In this work, we consider the minimum distance properties and convergence thresholds of 3-D turbo codes (3D-TCs), recently introduced by Berrou Here, we consider binary 3D-TCs while the original work of Berrou considered double-binary codes. In the first part of the paper, the minimum distance properties are analyzed from an ensemble perspective, both in the finite-length regime and in the asymptotic case of large block lengths. In particular, we analyze the asymptotic weight distribution of 3D-TCs and show numerically that their typical minimum distance dmin may, depending on the specific parameters, asymptotically grow linearly with the block length, i.e., the 3D-TC ensemble is asymptotically good for some parameters. In the second part of the paper, we derive some useful upper bounds on the dmin when using quadratic permutation polynomial (QPP) interleavers with a quadratic inverse. Furthermore, we give examples of interleaver lengths where an upper bound appears to be tight. The best codes (in terms of estimated dmin ) obtained by randomly searching for good pairs of QPPs for use in the 3D-TC are compared to a probabilistic lower bound on the dmin when selecting codes from the 3D-TC ensemble uniformly at random. This comparison shows that the use of designed QPP interleavers can improve the dmin significantly. For instance, we have found a (6144,2040) 3D-TC with an estimated dmin of 147, while the probabilistic lower bound is 69. Higher rates are obtained by puncturing nonsystematic bits, and optimized periodic puncturing patterns for rates 1/2, 2/3, and 4/5 are found by computer search. Finally, we give iterative decoding thresholds, computed from an extrinsic information transfer chart analysis, and present simulation results on the additive white Gaussian noise channel to compare the error rate performance to that of conventional turbo codes. © 2011 IEEE. Source

Weidow J.,Chalmers University of Technology | Weidow J.,Vienna University of Technology
Ultramicroscopy | Year: 2013

A tantalum doped tungsten carbide powder, (W,Ta)C, was prepared with the purpose to maximise the amount of Ta in the hexagonal mixed crystal carbide. Atom probe tomography (APT) was considered to be the best technique to quantitatively measure the amount of Ta within this carbide. As the carbide powder consisted in the form of very small particles (<1. μm), a method to produce APT specimens of such a powder was developed. The powder was at first embedded in copper and a FIB-SEM workstation was used to make an in-situ lift-out from a selected powder particle. The powder particle was then deposited on a post made from a WC-Co based cemented carbide specimen. With the use of a laser assisted atom probe, it was shown that the method is working and the Ta content of the (W,Ta)C could be measured quantitatively. © 2013 Elsevier B.V. Source

Bosch J.,Chalmers University of Technology
Computer | Year: 2013

Increased system complexity has historically been treated as an inevitable consequence of architecture evolution over time. The three-layer product model offers an innovative framework for managing system growth that encourages greater efficiency, nimbler responsiveness, and more opportunities for innovation during all stages of the software development life cycle. © 2013 IEEE. Source

Journal of Supply Chain Management | Year: 2013

The latest century has witnessed two major transformations of the business landscape through which the boundaries of firms were modified substantially. The first was the establishment of the large-scale integrated hierarchies, like the Ford Motor Company, in the beginning of the 20th century. The second was the disintegration of these hierarchies at the end of the same century. In both cases, the objective of the boundary movement was to improve the opportunities for innovative redesign. Because the strategic approaches to achieve this objective were quite different, the interplay between innovative redesign and changes of the boundaries of firms deserves further exploration. This article is based empirically on previous research on these two types of transformations. The information from these studies is used to formulate seven propositions concerning the interplay between innovative redesign and corporate boundaries. Three main findings spring from this study. First, the boundaries of firms are multifaceted. In addition to the ownership boundary, it is demonstrated that influence boundaries and awareness boundaries are central in innovative redesign. Second, corporate boundaries are dynamic. The study shows that sometimes they function as buffers in relation to other firms, while in other situations, they serve as bridges. Third, for the individual firm's boundary setting, two issues appear to be critical: one concerns the trade-off between specialization and integration, and the other relates to the interaction between the internal capabilities of the firm and those that are accessible from business partners. © 2013 Institute for Supply Management, Inc. Source

Damaschke P.,Chalmers University of Technology
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2012

A vector with at most k nonzeros is called k-sparse. We show that enumerating the support vectors of k-sparse solutions to a system Ax = b of r-sparse linear equations (i.e., where the rows of A are r-sparse) is fixed-parameter tractable (FPT) in the combined parameter r,k. For r = 2 the problem is simple. For 0,1-matrices A we can also compute an O(rk r ) kernel. For systems of linear inequalities we get an FPT result in the combined parameter d,k, where d is the total number of minimal solutions. This is achieved by interpeting the problem as a case of group testing in the complex model. The problems stem from the reconstruction of chemical mixtures by observable reaction products. © 2012 Springer-Verlag. Source

Fang Y.,Chongqing University | Fang Y.,Chalmers University of Technology | Huang Y.,Chongqing University
Applied Physics Letters | Year: 2013

Combining simulation and experiment, we demonstrate that a metal nanoparticle dimer on a gold film substrate can confine more energy in the particle/film gap because of the hybridization of the dimer resonant lever and the continuous state of the film. The hybridization may even make the electric field enhancement in the dimer/film gap stronger than in the gap between particles. The resonant peak can be tuned by varying the size of the particles and the film thickness. This electromagnetic field redistribution has tremendous applications in sensor, photocatalysis and solar cell, etc., especially considering ultrasensitive detection of tracing molecule on substrates. © 2013 AIP Publishing LLC. Source

Weiland J.,Chalmers University of Technology
Physica Scripta | Year: 2015

The difference between simple drift waves driven by the density gradient and thermal instabilities driven by the temperature gradient is discussed. It is shown that thermal instabilities basically are of a kinetic nature although they can also be accurately described by an advanced fluid model. © 2015 The Royal Swedish Academy of Sciences. Source

Rosengren H.,Chalmers University of Technology
Communications in Mathematical Physics | Year: 2015

We introduce and study symmetric polynomials, which as very special cases include polynomials related to the supersymmetric eight-vertex model, and other elliptic lattice models with $${\Delta=\pm 1/2}$$Δ=±1/2. There is also a close relation to affine Lie algebra characters. After a natural change of variables, our polynomials satisfy a non-stationary Schrödinger equation with elliptic potential, which is related to the Knizhnik–Zamolodchikov–Bernard equation and to the canonical quantization of Painlevé VI. Moreover, specializations of our polynomials can be identified with tau functions of Painlevé VI, obtained from one of Picard’s algebraic solutions by acting with a four-dimensional lattice of Bäcklund transformations. In the present work, our results on these topics are summarized with a minimum of technical details. © 2015, Springer-Verlag Berlin Heidelberg. Source

Koch C.,Chalmers University of Technology
Construction Management and Economics | Year: 2013

Accidents in construction have motivated a range of prevention methods and efforts with more or less success. Cultural explanations are of crucial importance in understanding risk at work and this contribution adds to the growing body of qualitative studies of safety culture. Symbolic interactionism is used as a conceptual ethnographic framework to include integration, differentiation, ambiguity and the multiple configuration of safety cultures. The primary case is a carpenter's crew of 28 men engaged in renovation work. The analysis reveals the overarching common integrative culture to be characterized by pride in work. This culture overlaps with four cultures named mastering, framework and rules, drawing board and plan, and ties that bind, found using the differentiation perspective. Ambiguous perceptions are found regarding possibilities for prevention and risk, which differ according to time, place and actor. This result is juxtaposed with cultures found in four other ethnographic studies from Denmark covering 10 companies. Although these studies find 25 different safety cultures, a national pattern showing a configuration of reactive and proactive safety cultures does seem prevalent. Accident prevention methods need to be more sensitive to different safety cultures, on site and in companies, but can also use national mechanisms such as training. © 2013 Taylor and Francis Group, LLC. Source

Konkoli Z.,Chalmers University of Technology
Journal of Theoretical Biology | Year: 2011

Noise characteristics of a simple multiparticle reaction model were investigated. The model can describe strongly cooperative reactions and is defined as follows. Particles A react in clusters of size k and each reaction forms a product molecule P. The back reaction is also allowed, and each cluster can dissociate into k reactants A. To describe a situation where the reaction is part of a pathway, the system is made open by assuming that particles A are injected and that particles P decay. This is a continuation study. The model is studied by using the same technique as employed previously, the pair approach reaction noise estimator (PARNES) method. Several new issues have been addressed. (i) In the previous work closeness to the Poisson distribution was used as a noise measure. In this work a more traditional noise measure, the ratio of the variance and the mean, was used to analyze stochastic features of the problem. (ii) The dependence of the new noise measure on k has been analyzed in detail, with an emphasis of investigating reactions with large k values. (iii) The previous study focused on understanding time-dependent issues, while this study focuses on describing the equilibrium state of the system. (iv) An exact solution (published elsewhere), available for closed system only, was used to re-investigate the validity of the PARNES method for describing reactions with large k. It was found that the PARNES method cannot describe fine details of the noise characteristics of such reactions. © 2011 Elsevier Ltd. Source

Bjornberg J.E.,Chalmers University of Technology
Communications in Mathematical Physics | Year: 2015

Adapting the recent argument of Aizenman, Duminil-Copin and Sidoravicius for the classical Ising model, it is shown here that the magnetization in the transverse-field Ising model vanishes at the critical point. The proof applies to the ground state in dimension d ≥ 2 and to positive-temperature states in dimension d ≥ 3, and relies on graphical representations as well as an infrared bound. © 2015, Springer-Verlag Berlin Heidelberg. Source

Kim J.-K.,Ulsan National Institute of Science and Technology | Kim J.-K.,Chalmers University of Technology
CrystEngComm | Year: 2014

A short synthesis time and high tap density are key conditions for the commercialization of electrode materials. Carbon coated three-dimensional porous LiFePO4 microspheres are synthesized by a supercritical and spray-dry combination method in a significantly short processing time (about 10 min). The three-dimensional (3D) porous morphology is composed of nanocrystallites tightly compacted to form three-dimensional electronic and ionic channels, which enhances their electrochemical properties. The obtained porous LiFePO4 microspheres are intensively analyzed by XRD, SEM, TGA, and FT-IR techniques. The porous microspheres, which are 60 μm in size, show uniform morphology with the carbon coating. Moreover, at a 0.1 C rate the 3D porous microspheres of LiFePO4 exhibit a high initial capacity with a high tap density (1.7 g cm-3) and high active material content (~90% without carbon), which corresponds to 94% and 79% of the theoretical capacity at 0.1 and 1 C. This journal is © 2014 The Royal Society of Chemistry. Source

Ershov S.N.,Joint Institute for Nuclear Research | Vaagen J.S.,University of Bergen | Zhukov M.V.,Chalmers University of Technology
Physical Review C - Nuclear Physics | Year: 2012

An unusually large value of the 22C matter radius has recently been extracted from measured reaction cross sections. The giant size can be explained by a very loose binding that is, however, not known experimentally yet. Within the three-body cluster model we have explored the sensitivity of the s-motion-dominated 22C geometry to the two-neutron separation energy. A low energy of a few tens of keV is required to reach the alleged experimental lower value of the matter radius, while the experimental mean radius requires an extremely tiny binding. The dependence of the 22C charge radius on the two-neutron separation energy is also presented. The soft dipole mode in 22C is shown to be strongly affected by the loose binding and should be studied in the process of Coulomb fragmentation. © 2012 American Physical Society. Source

Computers and Fluids | Year: 2016

There are several well-established methods to achieve solver speed-up for finite-volume solvers for compressible flows. These methods are more or less difficult to implement and more or less suitable for implementation in a parallel unstructured type of solver. This article presents a non-intrusive solver acceleration technique applicable for steady-state problems. The proposed technique is based on Dynamic Mode Decomposition (DMD) and does not depend on data format or mesh structure and is thus as straightforward to implement in an unstructured parallel code as in a structured sequential one. The main idea behind the method is that it is possible to use the information available in global flow-field modes to find a correction that will bring the solution closer to a steady-state condition. The DMD-based acceleration technique has been implemented in a massively parallel block-structured finite-volume Navier-Stokes solver for compressible flows and tested on a turbine cascade case with promising results. © 2016. Source

Johansen K.S.,Chalmers University of Technology
Biochemical Society Transactions | Year: 2016

The recent discovery of copper-dependent lytic polysaccharide mono-oxygenases (LPMOs) has opened up a vast area of research covering several fields of application. The biotech company Novozymes A/S holds patents on the use of these enzymes for the conversion of steam-pre-treated plant residues such as straw to free sugars. These patents predate the correct classification of LPMOs and the striking synergistic effect of fungal LPMOs when combined with canonical cellulases was discovered when fractions of fungal secretomes were evaluated in industrially relevant enzyme performance assays. Today, LPMOs are a central component in the Cellic CTec enzyme products which are used in several large-scale plants for the industrial production of lignocellulosic ethanol. LPMOs are characterized by an N-terminal histidine residue which, together with an internal histidine and a tyrosine residue, co-ordinates a single copper atom in a so-called histidine brace. The mechanism by which oxygen binds to the reduced copper atom has been reported and the general mechanism of copper-oxygen-mediated activation of carbon is being investigated in the light of these discoveries. LPMOs are widespread in both the fungal and the bacterial kingdoms, although the range of action of these enzymes remains to be elucidated. However, based on the high abundance of LPMOs expressed by microbes involved in the decomposition of organic matter, the importance of LPMOs in the natural carbon-cycle is predicted to be significant. In addition, it has been suggested that LPMOs play a role in the pathology of infectious diseases such as cholera and to thus be relevant in the field of medicine. © 2016 Authors; published by Portland Press Limited. Source

Bjornberg J.E.,Chalmers University of Technology | Stefansson S.O.,University of Iceland
Journal of Statistical Physics | Year: 2015

We study site percolation on uniform quadrangulations of the upper half plane. The main contribution is a method for applying Angel’s peeling process, in particular for analyzing an evolving boundary condition during the peeling. Our method lets us obtain rigorous and explicit upper and lower bounds on the percolation threshold $$p_\mathrm {c}$$pc, and thus show in particular that $$0.5511\le p_\mathrm {c}\le 0.5581$$0.5511≤pc≤0.5581. The method can be extended to site percolation on other half-planar maps with the domain Markov property. © 2015, Springer Science+Business Media New York. Source

Lofwander T.,Chalmers University of Technology | San-Jose P.,CSIC - Institute for the Structure of Matter | Prada E.,CSIC - Institute of Materials Science
Physical Review B - Condensed Matter and Materials Physics | Year: 2013

We analyze the quantum Hall effect in single layer graphene with bilayer stripe defects. Such defects are often encountered at steps in the substrate of graphene grown on silicon carbide. We show that AB or AA stacked bilayer stripes result in large Hall conductivity fluctuations that destroy the quantum Hall plateaux. The fluctuations are a result of the coupling of edge states at opposite edges through currents traversing the stripe. Upon rotation of the second layer with respect to the continuous monolayer (a twisted-bilayer stripe defect), such currents decouple from the extended edge states and develop into long-lived discrete quasibound states circulating around the perimeter of the stripe. Backscattering of edge modes then occurs only at precise resonant energies, and hence the quantum Hall plateaux are recovered as twist angle grows. © 2013 American Physical Society. Source

Bergek A.,Linkoping University | Jacobsson S.,Chalmers University of Technology
Energy Policy | Year: 2010

In the European policy debate, tradable green certificates (TGC) have been suggested to be a superior regulatory framework for promoting the diffusion of renewable electricity technologies. The purpose of this paper is to assess the performance of the Swedish TGC system, contributing to the European debate on the suitability of different types of frameworks. The expectations of the TGC system were that it would: (a) be effective in terms of increasing the supply of "green" electricity; (b) do this in a cost effective manner (from both a social and a consumer perspective); (c) generate an equitable distribution of costs and benefits and (d) drive technical change. So far, it has performed adequately in terms of effectiveness and social cost effectiveness. However, consumer costs have been substantially higher than expected, very large rents are generated and, at best, it contributes marginally to technical change. Thus, a TGC framework should be selected if the overriding concern is to minimize short term social costs of reaching a certain goal with a high degree of predictability. However, it cannot be expected to also drive technical change, keep consumer costs down and be equitable. Such trade-offs need to be revealed and not obscured by analysts. © 2009 Elsevier Ltd. Source

Caprioli S.,Chalmers University of Technology
Engineering Fracture Mechanics | Year: 2015

The relative severity of radial (thermal) and inclined rolling contact fatigue surface cracks of equal depth in a railway wheel is investigated by three-dimensional elastoplastic finite element analyses of a cracked wheel sector subjected to contact loading. Response is quantified by relative displacements of nodes close to crack tip and at the crack mouth. Highly inclined cracks give the highest magnitudes of crack tip shear displacements, which is the dominant deformation mode. Braking conditions are found to open the crack mouth. Initially higher temperatures on thermal cracks cause increased crack tip deformation and opening of the crack, whereafter subsequent mechanical load cycles impose crack closure. © 2015 Elsevier Ltd. Source

Pankratov A.L.,Nizhny Novgorod State Technical University | Gordeeva A.V.,Nizhny Novgorod State Technical University | Kuzmin L.S.,Chalmers University of Technology
Physical Review Letters | Year: 2012

The fluctuational propagation of solitons (magnetic fluxons) in long Josephson junctions is studied both numerically and analytically. It is demonstrated that operation in conditions where solitons are subjected to Lorentz contraction for a significant part of the junctions length leads to drastic suppression of thermal jitter at the output junction end. Specifically, for large-to-critical damping and small values of bias current, the physically obvious dependence of the jitter versus length σ∼√L is confirmed, while for small damping starting from the experimentally relevant α=0.1 and below, strong deviation from σ∼√L is observed, up to nearly complete independence of the jitter versus length, which is supported by the obtained theory. © 2012 American Physical Society. Source

Muller C.,Chalmers University of Technology
Chemistry of Materials | Year: 2015

The glass transition temperature is a critical processing parameter that governs the kinetics of molecular organization of polymer semiconductors during solidification. Yet, little attention is paid to the resulting structure-processing-property relationships that lead to optimal optoelectronic performance, which is usually obtained with nonequilibrium nanostructures. This review elucidates the interplay of molecular design and glass transition phenomena that are common to the most well-studied families of conjugated polymers, including polyfluorenes, polythiophenes, and poly(p-phenylenevinylene)s. The influence of key structural factors - known from classical polymer science - such as molecular weight, chain rigidity, side-chain architecture, and intermolecular π-π interactions, is explored in order to provide rationales that can guide the synthesis of new polymer semiconductors with tailored glass transition temperatures. Moreover, the discussion is anchored in an overview of the main measurement techniques with emphasis on rate-dependency and sub-glass transition phenomena as well as differences between bulk and thin films. The second half of the review focuses on the glass transition temperature(s) of polymer:fullerene bulk-heterojunction blends, which represent the most promising active layer architecture for organic solar cells, and highlights the relevance of fullerene diffusion. A challenging perspective is provided with regard to the thermal stability of the blend nanostructure vs the mechanical robustness and ductility of the active layer material. Conflicting demands on the blend glass transition temperature, i.e., higher vs lower than the processing and operating temperature, require a satisfactory compromise that must be achieved before truly flexible polymer solar cells with a high light-harvesting efficiency can be realized. © 2015 American Chemical Society. Source

Alvelid M.,Trelleborg Sealing Solutions Kalmar AB | Alvelid M.,Chalmers University of Technology
Composite Structures | Year: 2013

A 6th order differential equation for the dynamic analysis of the deflection of a three-layer sandwich beam with a viscoelastic middle layer is developed. Transverse shear deformation as well as rotational inertia effects of the covering layers are taken into account. The same boundary conditions as in the Euler-Bernoulli case are used for the covering layers, making the method straightforward to use. The material in the viscoelastic layer is modeled using a fractional derivative material model. The parameters of the model are fit to experimental data for a rubber in industrial use. A cantilever beam is analyzed, and it is shown that taking the effects of transverse shear and rotational inertia into account can have a significant effect on the response at the resonances even if length to thickness ratio is over 30 for the covering layers. © 2013 Elsevier Ltd. Source

Kalenkov M.S.,Nizhny Novgorod State Technical University | Zaikin A.D.,Karlsruhe Institute of Technology | Kuzmin L.S.,Chalmers University of Technology
Physical Review Letters | Year: 2012

We argue that parametrically strong enhancement of a thermoelectric current can be observed in conventional superconductors doped by magnetic impurities. This effect is caused by the violation of the symmetry between electronlike and holelike excitations due to formation of subgap bound Andreev states in the vicinity of magnetic impurities. We develop a quantitative theory of this effect and demonstrate that it can be detected in modern experiments. © 2012 American Physical Society. Source

Yang Z.-J.,Chalmers University of Technology
Journal of Physical Chemistry C | Year: 2015

The coherent couplings between plasmon modes have attracted significant research interest recently as they can dramatically modify the light-matter interactions and have many applications such as sensor and metamaterial. In this work, the energy transfer properties in a radiant and weakly radiant plasmon mode coupled system are investigated in the time domain. The phase difference between the two modes is found to vary from π to 0 with wavelength, and it is about π/2 near the resonance. The plasmon energy transfers back and forth between the two modes, and the transfer cycles increase with the coupling strength. Therefore, the system can undergo from enhanced absorption to Fano resonance phenomena on the optical spectra. Furthermore, the total energy transfer efficiency from the radiant plasmon mode to the weakly radiant one is also studied, and it shows a Förster resonance energy transfer (FRET)-like behavior. © 2015 American Chemical Society. Source

Zhuang K.,University of Toronto | Vemuri G.N.,Chalmers University of Technology | Mahadevan R.,University of Toronto
Molecular Systems Biology | Year: 2011

The simultaneous utilization of efficient respiration and inefficient fermentation even in the presence of abundant oxygen is a puzzling phenomenon commonly observed in bacteria, yeasts, and cancer cells. Despite extensive research, the biochemical basis for this phenomenon remains obscure. We hypothesize that the outcome of a competition for membrane space between glucose transporters and respiratory chain (which we refer to as economics of membrane occupancy) proteins influences respiration and fermentation. By incorporating a sole constraint based on this concept in the genome-scale metabolic model of Escherichia coli, we were able to simulate respiro-fermentation. Further analysis of the impact of this constraint revealed differential utilization of the cytochromes and faster glucose uptake under anaerobic conditions than under aerobic conditions. Based on these simulations, we propose that bacterial cells manage the composition of their cytoplasmic membrane to maintain optimal ATP production by switching between oxidative and substrate-level phosphorylation. These results suggest that the membrane occupancy constraint may be a fundamental governing constraint of cellular metabolism and physiology, and establishes a direct link between cell morphology and physiology. © 2011 EMBO and Macmillan Publishers Limited. All rights reserved. Source

Henningson M.,Chalmers University of Technology
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2012

We consider topologically twisted N=4 supersymmetric Yang-Mills theory on a four-manifold of the form V=W×R + or V=W×I, where W is a Riemannian three-manifold. Different kinds of boundary conditions apply at infinity or at finite distance. We verify that each of these conditions defines a "middle-dimensional" subspace of the space of all bulk solutions. Taking the two boundaries of V into account should thus generically give a discrete set of solutions. We explicitly find the spherically symmetric solutions when W=S3 endowed with the standard metric. For widely separated boundaries, these consist of a pair of solutions which coincide for a certain critical value of the boundary separation and disappear for even smaller separations. © 2012 American Physical Society. Source

Bartoszek K.,Chalmers University of Technology
Mathematical Biosciences | Year: 2014

An ongoing debate in evolutionary biology is whether phenotypic change occurs predominantly around the time of speciation or whether it instead accumulates gradually over time. In this work I propose a general framework incorporating both types of change, quantify the effects of speciational change via the correlation between species and attribute the proportion of change to each type. I discuss results of parameter estimation of Hominoid body size in this light. I derive mathematical formulae related to this problem, the probability generating functions of the number of speciation events along a randomly drawn lineage and from the most recent common ancestor of two randomly chosen tip species for a conditioned Yule tree. Additionally I obtain in closed form the variance of the distance from the root to the most recent common ancestor of two randomly chosen tip species. © 2014 Elsevier Inc. Source

Lagerwall S.T.,Chalmers University of Technology
Liquid Crystals | Year: 2013

Before 1910, the study of liquid crystals was dominated by Lehmann and the German school of chemists. The point of gravity then moved to France with Friedel as a leading figure. While there are many studies about Lehmann, there are fewer about Friedel. He has written about himself, so to speak, and more people have cited him than read his original papers. In the first part of this historical review, I will, after a close reading of the original papers, trace the development on French soil between 1910 and 1922.After 1922, the progress stopped in France, but a renewal of interest in liquid crystals came from Germany in the late 1920s and the first international symposium was organised there in 1931, closely followed by one in England 1933. After the Second World War, a new symposium in 1958 revived the field and then came a new outburst of turbulent productivity in the late 1960s. My aim is to focus on some of the most prominent persons and some turning points also in this modern era. But my foremost aim is to illustrate that nothing happened in the straightforward way in which most texts tend to outline the history. © 2013 © Taylor & Francis. Source

Chen X.,Chalmers University of Technology
IEEE Transactions on Electromagnetic Compatibility | Year: 2013

Due to the complicated and time-varying boundary conditions, reverberation chamber (RC) measurements are usually studied using statistical analysis. Hence, it is of importance to know the number of independent samples of the measurements. Different methods for estimating the number of independent samples has been proposed in the literature. This paper uses the spatial degrees of freedom method to estimate the independent sample number. Comparing with the commonly used autocorrelation function method, the proposed method requires less computation time and provides a smaller estimation bias for correlated samples and a smaller estimation variance once above a certain sample number. The estimated independent sample number can be used to explain the dependences of the measurement uncertainty on frequency, mode stirrers, and RC loading. Finally, the estimated independent sample number is used to predict the standard deviation (STD) of the average power level for different loading configurations, where good agreements are observed. © 2013 IEEE. Source

Sandstrom J.,Chalmers University of Technology | Sandstrom J.,Epsilon Utvecklingscentrum Vast AB
International Journal of Fatigue | Year: 2012

A numerical model for predicting the probability of subsurface initiated rolling contact fatigue failure in railway wheels subjected to operational loading is presented. The loading is evaluated through simulations of dynamic train-track interaction incorporating the influence of, e.g., corrugation. Contact stresses are found from Hertzian theory and the resulting stress field from theory of elasticity. Fatigue damage is evaluated by use of a Wöhler curve where the fatigue strength is decreased due to the influence of material defects, which are presumed to be of random size and occurrence in the stressed volume of the wheel rim. Damage accumulation is performed using the Palmgren-Miner rule, extending the model to cases of variable loading. The results show how a combination of rail corrugation and high train speeds have a significant impact on the probability of fatigue failure. A sensitivity analysis reveals a strong influence of the fatigue strength and the material defect distribution on the probability of fatigue failure. © 2011 Elsevier Ltd. All rights reserved. Source

Chen X.,Chalmers University of Technology
IEEE Transactions on Electromagnetic Compatibility | Year: 2013

Previous studies on modeling the random field (amplitude) in a reverberation chamber (RC) were conducted either by fitting a given distribution to measured data or by comparing different distributions using goodness-of-fit (GOF) tests. However, the GOF tests are inappropriate for comparing different distribution candidates in that they are meant to check if a given distribution provides an adequate fit for a set of data or not and they cannot provide correct relative fitness between different candidate distributions in general. A fair comparison of different distributions in modeling the RC field is missing in the literature. In this paper, Akaike's information criterion (AIC), which allows fair comparisons of different distributions, is introduced. With Rayleigh, Rician, Nakagami, Bessel K, and Weibull distributions as the candidate set, the AIC approach is applied to measured data in an RC. Results show that the Weibull distribution provides the best fit to the field in an undermoded RC and that the Rayleigh distribution provides the best approximation of the field in an overmoded RC. In addition, it is found that both the Rician and Weibull distributions provide improved approximations of the field in an RC loaded with lossy objects. This study provides correct complementary results to the previous RC studies. © 1964-2012 IEEE. Source

Grigorenko L.V.,National Research Nuclear University MEPhI | Golubkova T.A.,Moscow State University | Zhukov M.V.,Chalmers University of Technology
Physical Review C - Nuclear Physics | Year: 2015

The dynamic mechanism of the Thomas-Ehrman shift in three-cluster systems is studied by using the example of Ne16 and C16 isobaric mirror partners. We predict configuration mixings for 0+ and 2+ states in Ne16 and C16. Large isospin symmetry breaking on the level of wave function component weights is demonstrated for these states and discussed as a three-body mechanism of the Thomas-Ehrman shift. It is shown that the description of the Coulomb displacement energies requires consistency among three parameters: the Ne16 decay energy ET, the F15 ground-state energy Er, and the configuration mixing parameters for the Ne16 and C160+ and 2+ states. Based on this analysis we infer the F151/2+ ground-state energy to be Er=1.39-1.42 MeV. © 2015 American Physical Society. Source

Ballantyne E.E.F.,University of Leeds | Lindholm M.,Chalmers University of Technology | Whiteing A.,University of Leeds
Journal of Transport Geography | Year: 2013

Over the last decade, research in the area of urban freight transport has increased and local authorities are slowly beginning to acknowledge the need to consider freight in their overall transport planning. Most urban freight studies to date consider specific solutions and measures, as opposed to ways in which the local authorities could and should consider this issue in the wider transport planning and decision making process. The aim of this paper is to examine cities that differ in context in order to demonstrate that urban freight transport planning can be improved by involving a wider range of stakeholders. Interview data from Sweden, the UK and the Baltic Sea Region has been analysed to draw out the factors that influence the perceptions of local authorities and freight operators of freight transport issues in urban areas. The findings show that the issues faced by the freight industry are still not fully understood. The paper contradicts earlier research results that suggest differences in the ways that local authorities consider freight transport, and goes some way towards demonstrating that the problems faced by local authorities are not unique to one country or any specific category of urban area, and hence a generic decision-making framework would be of value. A framework is developed to facilitate meaningful interaction between the various urban freight actors and stakeholders. © 2013 Elsevier Ltd. Source

Grigorenko L.V.,National Research Nuclear University MEPhI | Zhukov M.V.,Chalmers University of Technology
Physical Review C - Nuclear Physics | Year: 2015

The structure and decay dynamics for 0+ and 2+ continuum excitations of O26 are investigated in a three-body O24+n+n model. The validity of a simple approximation for the cross section profile for long-lived 2n emission is demonstrated. A sequence of three 0+ monopole ("breathing mode" type) excited states is predicted. These states could probably be interpreted as analogs of Efimov states pushed in the continuum due to insufficient binding. The calculated energies of the 2+ states are related to the excitation spectrum of O25. We discuss the correlation between the predicted O26 spectrum and experimental observations. © 2015 American Physical Society. Source

Tong L.,CAS Beijing National Laboratory for Molecular | Tong L.,Chalmers University of Technology | Zhu T.,CAS Beijing National Laboratory for Molecular | Liu Z.,CAS Beijing National Laboratory for Molecular
Chemical Society Reviews | Year: 2011

Surface-enhanced Raman scattering (SERS) has been intensively explored both in theory and applications and has been widely used in chemistry, physics and biology for decades. A variety of SERS substrates have been developed in order to investigate the mechanisms behind, which give rise to the enormous enhancement even enabling single molecule detection. The Raman enhancement, which involves an electromagnetic enhancement (EM) and a chemical enhancement (CM), reflects both the physical principle of light/metal interactions and the molecule/metal interactions. In this tutorial review, we focus on the EM enhancement of SERS active substrates made of colloidal gold nanoparticles (GNPs), varying from self-assembled arrays down to single particles, for the purpose of investigating the EM coupling effect and probing the distribution of the induced electric field of single GNPs. © 2011 The Royal Society of Chemistry. Source

Bohstrom Z.,Chalmers University of Technology
Journal of Porous Materials | Year: 2012

Amorphous and long range ordered cubic and hexagonal silica impregnated with heteropolyacids was investigated as catalyst for nitration of anisol using HNO3 as nitrating agent. The use of HNO3 together with a solid acid catalyst is an environmentally attractive alternative to the conventional procedure that employs HNO3 together with H 2SO4. The aqueous nitric acid was loaded in the pores of the mesoporous material and the HNO3 filled particles were subsequently dispersed in anisol. The reaction took place at the interface between the two liquid phases, i.e., at the pore openings. It was shown that ordered mesoporous silica is more efficient than amorphous silica and that silica with cubic geometry is the most efficient. Two heteropolyacids of Keggin type, phosphotungstic acid and phosphomolybdic acid, were tested. One Wells-Dawson type of phosphotungstic acid was included as well as cesium exchanged heteropolyacid acids of Keggin type. The best yield was obtained with mesoporous cubic silica impregnated with cesium exchanged phosphotungstic acid. The amount of heteropolyacid used in the impregnation turned out to be critical. Above a certain loading the activity went down, probably due to clogging of the pores. The preferred catalyst could also be reused with retained activity. © Springer Science+Business Media, LLC 2011. Source

Werner E.,Gothenburg University | Westerlund F.,Chalmers University of Technology | Tegenfeldt J.O.,Lund University | Mehlig B.,Gothenburg University
Macromolecules | Year: 2013

We study the conformations of a self-avoiding polymer confined to a channel by computing the cross-sectional distributions of the positions of its monomers. By means of Monte Carlo simulations for a self-avoiding, freely jointed chain, we determine how the cross-sectional distribution for a given monomer depends on its location in the polymer and how strongly this distribution is affected by self-avoidance. To this end we analyze how the frequency of intrachain collisions between monomers depends on their spatial position in the channel and on their location within the polymer. We show that most collisions occur between closely neighboring monomers. As a consequence, the collision probability depends only weakly on the spatial position of the monomers. Our results explain why the effect of self-avoidance on the monomer distributions is weaker than predicted by mean-field theory. We discuss the relevance of our results for studies of DNA conformations in nanofluidic channels. © 2013 American Chemical Society. Source

Olsson P.,Chalmers University of Technology
Inverse Problems | Year: 2016

A new directional decomposition of the acoustic 3D wave equation is derived for spherically symmetric geometries, where the wave fields do not need to possess such a symmetry. This provides an alternative basis for various applications of techniques like invariant embedding and time domain Green functions in spherically symmetric geometries. Contrary to previous results on spherical wave splittings, the new decomposition is given in a very explicit form. The wave equation considered incorporates effects from radially varying compressibility and density, but also from anisotropic density, a property of certain so called metafluids. By applying the new spherical wave splitting, we show that all spherically symmetric acoustic metafluid cloaks are diffeomorphic images of a homogeneous and isotropic spherical ball of perfect fluid. © 2016 IOP Publishing Ltd. Source

Konkoli Z.,Chalmers University of Technology
Journal of Theoretical Biology | Year: 2011

A simple multiparticle reaction model was studied where reactants A react with (a possibly large) stoichiometric coefficient k. Each reaction forms a product molecule P, and every product molecule can be split into k A particles through the back reaction. To study the fluctuations in particle numbers a novel approach has been developed; to be referred to as the Pair approach based Reaction Noise EStimator (PARNES) method. The PARNES method is based on the full Kirkwood superposition approximation implemented at the pair level. Kirkwood's method has been adapted to study stochastic properties of an arbitrary reaction network in a perfectly mixed reaction volume. PARNES works well for large particle numbers. It provides qualitative description when particle numbers are low. The PARNES method can easily augment mean field calculations. Extension of the method beyond the pair approach level is straightforward. Both stationary and non-stationary properties of the model were investigated, and the findings of this work point to two possible scenarios of intracellular noise control. When k is increased, the fluctuations in the number of product molecules become smaller (sub-Poissonian) in a stationary state, and relaxation to a stationary state becomes faster. © 2010 Elsevier Ltd. Source

Lindgren E.,Chalmers University of Technology
Eurasip Journal on Advances in Signal Processing | Year: 2014

Anderson L.,Chalmers University of Technology | Russo J.G.,Catalan Institution for Research and Advanced Studies | Russo J.G.,University of Barcelona
Journal of High Energy Physics | Year: 2015

Abstract: The phase structure of ABJM theory with mass m deformation and non-vanishing Fayet-Iliopoulos (FI) parameter, ζ, is studied through the use of localisation on S$$\mathbb{S}$$3. The partition function of the theory then reduces to a matrix integral, which, in the large N limit and at large sphere radius, is exactly computed by a saddle-point approximation. When the couplings are analytically continued to real values, the phase diagram of the model becomes immensely rich, with an infinite series of third-order phase transitions at vanishing FI-parameter [1]. As the FI term is introduced, new effects appear. For any given 0 < ζ < m/2, the number of phases is finite and for ζ ≥ m/2 the theory does not have any phase transitions at all. Finally, we argue that ABJM theory with physical couplings does not undergo phase transitions and investigate the case of U(2) × U(2) gauge group in detail by an explicit calculation of the partition function. © 2015, The Author(s). Source

Kuppinger P.,ETH Zurich | Durisi G.,Chalmers University of Technology | Bolcskei H.,ETH Zurich
IEEE Transactions on Information Theory | Year: 2012

We present an uncertainty relation for the representation of signals in two different general (possibly redundant or incomplete) signal sets. This uncertainty relation is relevant for the analysis of signals containing two distinct features each of which can be described sparsely in a suitable general signal set. Furthermore, the new uncertainty relation is shown to lead to improved sparsity thresholds for recovery of signals that are sparse in general dictionaries. Specifically, our results improve on the well-known $(1+1/d)/2$ -threshold for dictionaries with coherence $d$ by up to a factor of two. Furthermore, we provide probabilistic recovery guarantees for pairs of general dictionaries that also allow us to understand which parts of a general dictionary one needs to randomize over to weed out the sparsity patterns that prohibit breaking the square-root bottleneck. © 2006 IEEE. Source

Cederwall M.,Chalmers University of Technology
Journal of High Energy Physics | Year: 2015

Abstract: As a means of examining the section condition and its possible solutions and relaxations, we perform twistor transforms related to versions of exceptional field theory with Minkowski signature. The spinor parametrisation of the momenta naturally solves simultaneously both the mass-shell condition and the (weak) section condition. It is shown that the incidence relations for multi-particle twistors force them to share a common section, but not to be orthogonal. The supersymmetric extension contains additional scalar fermionic variables shown to be kappa-symmetry invariants. We speculate on some implications, among them a possible relation to higher spin theory. © 2015, The Author(s). Source

Johansson M.,Chalmers University of Technology
GRAPP 2013 IVAPP 2013 - Proceedings of the International Conference on Computer Graphics Theory and Applications and International Conference on Information Visualization Theory and Applications | Year: 2013

This paper presents an efficient approach for integrating occlusion culling and hardware instancing. The work is primarily targeted at Building Information Models (BIM), which typically share characteristics addressed by these two acceleration techniques separately - high level of occlusion and frequent reuse of building components. Together, these two acceleration techniques complement each other and allows large and complex BIMs to be rendered in real-time. Specifically, the proposed method takes advantage of temporal coherence and uses a lightweight data transfer strategy to provide an efficient hardware instancing implementation. Compared to only using occlusion culling, additional speedups of 1.25x-1.7x is achieved for rendering large BIMs received from real-world projects. These speedups are measured in viewpoints that represents the worst case scenarios in terms of rendering performance when only occlusion culling is utilized. Source

Gomez-Barea A.,Polytechnic University of Valencia | Leckner B.,Chalmers University of Technology
Fuel | Year: 2013

A method is presented to predict the conversion of biomass in a fluidized bed gasifier. The model calculates the yields of CO, H2, CO 2, N2, H2O, CH4, tar (represented by one single lump), and char, from fuel properties, reactor geometry and some kinetic data. The equilibrium approach is taken as a frame for the gas-phase calculation, corrected by kinetic models to estimate the deviation of the conversion processes from equilibrium. The yields of char, methane, and other gas species are estimated using devola-tilization data from literature. The secondary conversion of methane and tar, as well as the approach to equilibrium of the water-gas-shift reaction, are taken into account by simple kinetic models. Char conversion is calculated accounting for chemical reaction, attrition and elutriation. The model is compared with measurements from a 100 kWth bubbling fluidized bed gasifier, operating with different gasification agents. A sensitivity analysis is conducted to establish the applicability of the model and to underline its advantages compared to existing quasi-equilibrium models. © 2012 Elsevier Ltd. All rights reserved. Source

Electronic Journal of Combinatorics | Year: 2011

The 2-player impartial game of Wythoff Nim is played on two piles of tokens. A move consists in removing any number of tokens from precisely one of the piles or the same number of tokens from both piles. The winner is the player who removes the last token. We study this game with a blocking maneuver, that is, for each move, before the next player moves the previous player may declare at most a predetermined number, k - 1 ≥ 0, of the options as forbidden. When the next player has moved, any blocking maneuver is forgotten and does not have any further impact on the game. We resolve the winning strategy of this game for k = 2 and k = 3 and, supported by computer simulations, state conjectures of 'sets of aggregation points' for the P-positions whenever 4 ≤ k ≤ 20. Certain comply variations of impartial games are also discussed. Source

Vogelgesang R.,Max Planck Institute for Solid State Research | Dmitriev A.,Chalmers University of Technology
Analyst | Year: 2010

Resonant nanoplasmonic structures have long been recognized for their unique applications in subwavelength control of light for enhanced transmission, focussing, field confinement, decay rate management, etc. Increasingly, they are also integrated in electro-optical analytical sensors, shrinking the active volume while at the same time improving sensitivity and specificity. The microscopic imaging of resonances in such structures and also their dynamic variations has seen dramatic advances in recent years. In this Minireview we outline the current status of this rapidly evolving field, discussing both optical and electron microscopy approaches, the limiting issues in spatial resolution and data interpretation, the quantities that can be recorded, as well as the growing importance of time-resolving methods. © The Royal Society of Chemistry 2010. Source

Andreasson J.,Chalmers University of Technology | Pischel U.,University of Huelva
Israel Journal of Chemistry | Year: 2013

The use of photochromes for the implementation of molecular logic operations is a very promising approach toward molecular computing. This statement is based on a) the possibility of operating such molecular devices exclusively with photonic signals and b) spatiotemporally and remotely controlled switching, which is characteristic for photochromes. Herein, a brief overview of the application of simple photochromes and multi-photochromic conjugates for the small-scale functional integration of complicated logic circuits is given. This complements and extends efforts to design molecular photochromic memories for data storage described by many research groups worldwide. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Bhadauria M.,Cornell University | McKee S.A.,Chalmers University of Technology
Proceedings of the International Conference on Supercomputing | Year: 2010

We develop real-time scheduling techniques for improving performance and energy for multiprogrammed workloads that scale non-uniformly with increasing thread counts. Multithreaded programs generally deliver higher throughput than single-threaded programs on chip multiprocessors, but performance gains from increasing threads decrease when there is contention for shared resources. We use analytic metrics to derive local search heuristics for creating efficient multiprogrammed, multithreaded workload schedules. Programs are allocated fewer cores than requested, and scheduled to space-share the CMP to improve global throughput. Our holistic approach attempts to co-schedule programs that complement each other with respect to shared resource consumption. We find application co-scheduling for performance and energy in a resource-aware manner achieves better results than solely targeting total throughput or concurrently co-scheduling all programs. Our schedulers improve overall energy delay (E*D) by a factor of 1.5 over time-multiplexed gang scheduling. © 2010 ACM. Source

Ota J.J.,Federal University of Parana | Perrusquia G.S.,Chalmers University of Technology
Water Science and Technology | Year: 2013

This paper focuses on the sediment particle while it is transported at the limit of deposition in storm sewers, i.e. as bed load at the limit of concentration that leads to sediment deposition. Although many empirical sediment transport equations are known in the literature, there is only limited knowledge concerning particle velocity. Sediment particle and sphere velocity measurements were carried out in two pipe channels and these results led to the development of a semi-theoretical equation for sediment transport at the limit of deposition in sewers. Even in the transport process without deposition, sediment movement is slower than water velocity and depends on the angle of repose of sediment with a diameter d on the roughness k of the pipe channel. Instead of classical dimensionless bed shear stress ψ, a modified dimensionless bed shear stress ψ(d/k)2/3 was suggested, based on the angle of repose and this parameter was proved to be significant for quantifying the transport capacity. The main purpose of this article is to emphasize the importance of careful observation of experiments. Not only number of tests, but physical understanding are essential for better empirical equations. Copyright © IWA Publishing 2013. Source

Liang H.-L.,Martin Luther University of Halle Wittenberg | Schymura S.,Martin Luther University of Halle Wittenberg | Rudquist P.,Chalmers University of Technology | Rudquist P.,Seoul National University of Science and Technology | Lagerwall J.,Martin Luther University of Halle Wittenberg
Physical Review Letters | Year: 2011

We carry out the first study of smectic liquid crystalline colloidal shells and investigate how their complex internal structure depends on the director configuration in the nematic phase, preceding the smectic phase on coo