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Berlin, Germany

The Technische Universität Berlin, known as TU Berlin for short and unofficially as the Technical University of Berlin or Berlin Institute of Technology, is a research university located in Berlin, Germany and one of the largest and most prestigious research and education institutions in Germany. The university was founded in 1879. It has the highest proportion of foreign students out of universities in Germany, with 20.9% in the summer semester of 2007, roughly 5,598 students. The university alumni and professor list include National Academies elections, two National Medal of Science laureates and ten Nobel Prize winners.The TU Berlin is a member of TU9, an incorporated society of the largest and most notable German institutes of technology and of the Top Industrial Managers for Europe network, which allows for student exchanges between leading European engineering schools. It also belongs to the Conference of European Schools for Advanced Engineering Education and Research. As of 2013, TU Berlin is ranked 41st in the world in the field of Engineering & Technology and 1st in Germany in Mathematics according to QS World University Rankings.The university is known for its high ranked engineering programmes, especially in mechanical engineering and engineering management. Wikipedia.

Brfull T.,TU Berlin
Systems and Control Letters | Year: 2011

In this paper we consider linear systems given through a kernel representation P together with a quadratic cost functional H. We will see that the solvability of the associated infinite-horizon optimal control problem is equivalent to cyclo-dissipativity and that the solution of the optimal control problem can be obtained from the kernel representation of a para-Hermitian matrix polynomial which can be easily constructed from P and H. In contrast to previous work on this topic we avoid image representations as far as possible. The results can be applied to descriptor systems (see Section 4) to obtain results which so far were only known for regular descriptor systems with index 1. © 2011 Elsevier B.V. All rights reserved. Source

Von Falkenhausen P.,TU Berlin | Harks T.,Maastricht University
Mathematics of Operations Research | Year: 2013

Joint use of resources with usage-dependent cost raises the question: who pays how much? We study cost sharing in resource selection games where the strategy spaces are either singletons or bases of a matroid defined on the ground set of resources. Our goal is to design cost sharing protocols so as to minimize the resulting price of anarchy and price of stability. We investigate three classes of protocols: basic protocols guarantee the existence of at least one pure Nash equilibrium; separable protocols additionally require that the resulting cost shares only depend on the set of players on a resource; uniform protocols are separable and require that the cost shares on a resource may not depend on the instance, that is, they remain the same even if new resources are added to or removed from the instance. We find optimal basic and separable protocols that guarantee the price of stability and price of anarchy to grow logarithmically in the number of players, except for the case of matroid games induced by separable protocols where the price of anarchy grows linearly with the number of players. For uniform protocols we show that the price of anarchy is unbounded even for singleton games. ©2013 INFORMS. Source

Chepoi V.,CNRS Laboratory of Fundamental Informatics of Marseille (LIF) | Felsner S.,TU Berlin
Computational Geometry: Theory and Applications | Year: 2013

In this note, we present a simple combinatorial factor 6 algorithm for approximating the minimum hitting set of a family R={R1,⋯, Rn} of axis-parallel rectangles in the plane such that there exists an axis-monotone curve γ that intersects each rectangle in the family. The quality of the hitting set is shown by comparing it to the size of a packing (set of pairwise non-intersecting rectangles) that is constructed along, hence, we also obtain a factor 6 approximation for the maximum packing of R. In cases where the axis-monotone curve γ intersects the same side (e.g. the bottom side) of each rectangle in the family the approximation factor for hitting set and packing is 3. © 2013 Elsevier B.V. Source

Sullivan G.J.,Microsoft | Ohm J.-R.,RWTH Aachen | Han W.-J.,Gachon University | Wiegand T.,Fraunhofer Institute for Telecommunications, Heinrich-Hertz-Institut | Wiegand T.,TU Berlin
IEEE Transactions on Circuits and Systems for Video Technology | Year: 2012

High Efficiency Video Coding (HEVC) is currently being prepared as the newest video coding standard of the ITU-T Video Coding Experts Group and the ISO/IEC Moving Picture Experts Group. The main goal of the HEVC standardization effort is to enable significantly improved compression performance relative to existing standards-in the range of 50% bit-rate reduction for equal perceptual video quality. This paper provides an overview of the technical features and characteristics of the HEVC standard. © 1991-2012 IEEE. Source

The potential contribution of remote sensing and GIS techniques to earthquake hazard analysis was investigated in SW-Haiti in order to improve the systematic, standardized inventory of those areas that are more susceptible to earthquake ground motions or to earthquake related secondary effects such as landslides, liquefaction, soil amplifications, compaction or even tsunami-waves. Geophysical, topographical, geological data and satellite images were collected, processed, and integrated into a spatial database using Geoinformation Systems (GIS) and image processing techniques. The GIS integrated evaluation of satellite imageries, of digital topographic data and of various open-source geodata can contribute to the acquisition of those specific tectonic, geomorphologic/topographic settings influencing local site conditions in Haiti and, thus, to a first data base stock. Using the weighted overlay techniques in GIS susceptibility maps were produced indicating areas where causal factors influencing surface-near earthquake shock occur aggregated and interfering each other and, thus, rise the susceptibility to soil amplification. This approach was used as well to create landslide and flooding susceptibility maps. © Author(s) 2010. Source

Two informal sporomorph assemblage zones can be distinguished in the dinosaur-bearing Tendaguru Beds of southeast Tanzanian. The first zone, the ClassopollisAraucariacitesShanbeipollenites Assemblage Zone, ranges from the Lower to the Upper Saurian Bed, and a mid-Oxfordian to Tithonian age is suggested based on the presence of Shanbeipollenites quadratus. The second zone, the ClassopollisCicatricosisporitesRuffordiaspora Assemblage Zone, is restricted in the Trigonia schwarzi Bed, which overlies the Upper Saurian Bed. The combined ranges of Cicatricosisporites hughesii, Ruffordiaspora australiensis and Trilobosporites obsitus would be consistent with a late Berriasian to Hauterivian age of this zone. This is refined further to late Valanginian to Hauterivian on the basis of already existing evidence from fauna and dinoflagellate cysts. From a phytogeographic point of view the Tendaguru locality belongs to the southern Gondwana Trisaccates Province because of the presence of trisaccate podocarpaceous pollen. The quantitative composition of the palynofloras is characterized by the dominance or abundance of pollen produced by the two conifer families Cheirolepidiaceae (Classopollis) and Araucariaceae (mainly Araucariacites). Pollen of Cheirolepidiaceae, typically xerophytic, drought-resistant, thermophilic plants, is dominant throughout the Tendaguru Beds except in parts of the Middle Saurian Bed where pollen of Araucariaceae, a presumably mesic group, becomes most abundant. Classopollis attains the highest degree of dominance in the shallow marine deposits associated with the saurian beds. This may be related to paleoecological and taphonomic factors, namely abundance of Classopollis-producing plants in low-lying coastal environments close to the lagoonlike depositional sites and transportational sorting of sporomorphs leading to a relative enrichment of small and/or anemophilous pollen. The abundance of Araucariacites in the Middle Saurian Bed suggests that araucarians existed in coastal plain environments that were stable enough to allow the growth of large trees. This open araucarian forest, which may have been a source of food for high-browsing dinosaurs, was situated landward of the cheirolepidiacean belt not far from the depositional sites. Pteridophytes and bryophytes were concentrated at moist places and around water bodies. Podocarpaceous conifers producing bisaccate and trisaccate pollen grew in local uplands, while gnetaleans related to Ephedra and Welwitschia may have been present in dry places. The palynological evidence is consistent with a seasonally dry, tropical to sub-tropical paleoclimate. Three new combinations, Equisetosporites certus (Bolkhovitina), Jugella caichigensis (Volkheimer and Quattrocchio) and Trichotomosulcites microsaccatus (Couper), are proposed, and Jugella semistriata is described as a new species. © 2010 AASP-The Palynological Society. Source

Brull T.,TU Berlin
Mathematics of Control, Signals, and Systems | Year: 2011

The behavior approach and the problem of dissipativity have both been introduced and studied extensively by Willems and others. Current methods to check dissipativity will either check the solvability of a linear matrix inequality or rely on symbolic computations with image representations via computer algebra packages. We will discuss a new characterization for linear behavior systems in kernel representation that allows to check dissipativity via the solution of structured eigenvalue problems. The complexity and efficiency of our new method will be compared to the existing methods. © 2011 Springer-Verlag London Limited. Source

Financing decentralized renewable energy infrastructures in Germany is a complex issue due to the fact that public authorities lack the needed capital and institutional private investors are generally averse to restraints such as high transaction costs and risk-return-concerns. Consequently, alternative financing concepts must be developed to keep the energy transition going. An approach that has recently gained attention in Germany is the concept of financial citizen participation. The concept entails that private individuals contribute to the realization of infrastructure projects by investing in renewable energy projects via various business models and financing concepts. This article illustrates empirical results on the relevance of financial citizen participation within the German renewable energy sector, briefly reviews the technical, political and legal framework that led to the significant development in the field of financial citizen participation and analyzes different business models and citizen participation schemes from Germany with a particular focus on so called energy cooperatives and closed-end funds. © 2014 Elsevier Ltd. Source

Tautz R.C.,TU Berlin
Physics of Plasmas | Year: 2011

Three linear kinetic plasma instabilities are investigated for a counterstreaming Maxwellian distribution function with anisotropic temperatures such that aperiodic modes are generated. Concentration is focused on the instability condition, which is characterized by the marginally positive growth rate, and on the maximum growth rate and the associated fastest growing wavenumber. It is demonstrated that the simultaneous numerical solution of the dispersion relation and its derivative facilitates parameter studies for quantities such as the temperature anisotropy, thermal and streaming velocities, and the background magnetic field strength. Similarities and differences in the behavior of the three aperiodic modes are exemplified and implications for applications such as numerical simulations are illustrated. © 2011 American Institute of Physics. Source

Slawik M.,TU Berlin
Proceedings of the International Conference on Cloud Computing Technology and Science, CloudCom | Year: 2013

Contemporary cloud computing solutions incorporate HTTP intermediaries, such as reverse proxies, load balancers, and intrusion prevention systems. These act as TLS server connection ends and access HTTP/TLS plaintext to carry out their functions. This raises many concerns: increased security efforts, the risk of losing confidentiality and integrity, and potentially unauthorized data access. Current HTTP entity-body encryption technologies address these concerns by providing end-to-end security between user agents and origin servers. However, they present disparate deficiencies, e.g., inefficient presentation languages, message-flow vulnerabilities, and the circumvention of HTTP streaming. This paper introduces the Trusted Cloud Transfer Protocol (TCTP), which presents a novel approach to entity-body encryption overcoming these deficiencies. The pivotal idea of TCTP are HTTP application layer encryption channels (HALECs), which integrate TLS functionality into the HTTP application layer. TCTP can be deployed immediately, as it is fully HTTP compliant, and rapidly implemented, as required TLS libraries are widely available. The reliance upon the mature TLS protocol minimizes the risk of introducing new security threats. Furthermore, TLS brings the benefit of relative efficiency, which is demonstrated on the basis of an example TCTP implementation. © 2013 IEEE. Source

Finkbeiner M.,TU Berlin
Biomass and Bioenergy | Year: 2014

The 'food vs. fuel' debate inspired the concept of indirect land use change (iLUC). Greenhouse gas (GHG) emission factors for iLUC are proposed for inclusion into carbon footprints (CF) of biofuels. The range of published iLUC values is enormous: from about 200% below, up to 1700% above the CF values of fossil fuels. From the perspective of life cycle assessment (LCA) and CF science, single iLUC factors are currently more representative for the approach or model used than for the crop or biofuel assessed. The scientific robustness is not sufficient for political and corporate decision making. None of the relevant international standards of LCA or CF require the inclusion of iLUC. The iLUC concept deserves credit for raising awareness of a relevant problem but it is not the solution. Science and policy should focus on proactive real world mitigation of iLUC rather than reactive and theoretical iLUC factors. © 2014 The Author. Source

Li Z.,Huazhong University of Science and Technology | Jiang Y.,Huazhong University of Science and Technology | Jiang Y.,Hubei Engineering University | Yuan L.,Huazhong University of Science and Technology | And 5 more authors.
ACS Nano | Year: 2015

For lithium-sulfur batteries, commercial application is hindered by the insulating nature of sulfur and the dissolution of the reaction intermediates of polysulfides. Here, we present an ordered meso-microporous core-shell carbon (MMCS) as a sulfur container, which combines the advantages of both mesoporous and microporous carbon. With large pore volume and highly ordered porous structure, the "core" promises a sufficient sulfur loading and a high utilization of the active material, while the "shell" containing microporous carbon and smaller sulfur acts as a physical barrier and stabilizes the cycle capability of the entire S/C composite. Such a S/MMCS composite exhibits a capacity as high as 837 mAh g-1 at 0.5 C after 200 cycles with a capacity retention of 80% vs the second cycle (a decay of only 0.1% per cycle), demonstrating that the diffusion of the polysulfides into the bulk electrolyte can be greatly reduced. We believe that the tailored highly ordered meso-microporous core-shell structured carbon can also be applicable for designing some other electrode materials for energy storage. © 2014 American Chemical Society. Source

Choudhury N.R.,University of Edinburgh | Alves F.L.,University of Edinburgh | de Andres-Aguayo L.,Center for Genomic Regulation Barcelona | Graf T.,Center for Genomic Regulation Barcelona | And 4 more authors.
Genes and Development | Year: 2013

MicroRNA (miRNA) biogenesis is a highly regulated process in eukaryotic cells. Several mature miRNAs exhibit a tissue-specific pattern of expression without an apparent tissue-specific pattern for their corresponding primary transcripts. This discrepancy is suggestive of post-transcriptional regulation of miRNA abundance. Here, we demonstrate that the brain-enriched expression of miR-7, which is processed from the ubiquitous hnRNP K pre-mRNA transcript, is achieved by inhibition of its biogenesis in nonbrain cells in both human and mouse systems. Using stable isotope labeling by amino acids in cell culture (SILAC) mass spectrometry combined with RNase-assisted RNA pull-down, we identified Musashi homolog 2 (MSI2) and Hu antigen R (HuR) proteins as inhibitors of miR-7 processing in nonneural cells. This is achieved through HuR-mediated binding of MSI2 to the conserved terminal loop of pri-miR-7. Footprinting and electrophoretic gel mobility shift analysis (EMSA) provide further evidence for a direct interaction between pri-miR-7-1 and the HuR/MSI2 complex, resulting in stabilization of the pri-miR-7-1 structure. We also confirmed the physiological relevance of this inhibitory mechanism in a neuronal differentiation system using human SH-SY5Y cells. Finally, we show elevated levels of miR-7 in selected tissues from MSI2 knockout (KO) mice without apparent changes in the abundance of the pri-miR-7 transcript. Altogether, our data provide the first insight into the regulation of brain-enriched miRNA processing by defined tissue-specific factors. Copyright © 2013 by Cold Spring Harbor Laboratory Press. Source

De Avillez M.A.,University of Evora | Breitschwerdt D.,TU Berlin
Astronomy and Astrophysics | Year: 2012

Aims. We present the first high-resolution non-equilibrium ionization simulation of the joint evolution of the Local Bubble (LB) and Loop I superbubbles in the turbulent supernova-driven interstellar medium (ISM). The time variation and spatial distribution of the Li-like ions Civ, Nv, and Ovi inside the LB are studied in detail. Methods. This work uses the parallel adaptive mesh refinement code EAF-PAMR coupled to the newly developed atomic and molecular plasma emission module E(A+M)PEC, featuring the time-dependent calculation of the ionization structure of H through Fe, using the latest revision of solar abundances. The finest AMR resolution is 1 pc within a grid that covers a representative patch of the Galactic disk (with an area of 1 kpc 2 in the midplane) and halo (extending up to 10 kpc above and below the midplane). Results. The evolution age of the LB is derived by the match between the simulated and observed absorption features of the Li-like ions Civ, Nv, and Ovi. The modeled LB current evolution time is bracketed between 0.5 and 0.8 Myr since the last supernova reheated the cavity in order to have N(Ovi) < 8 × 10 12 cm -2, log[N(Civ)/N(Ovi)] <-0.9 and log[N(Nv)/N(Ovi)] <-1 inside the simulated LB cavity, as found in Copernicus, IUE, GHRS-IST and FUSE observations. © 2012 ESO. Source

Khan M.A.,TU Berlin | Tembine H.,Supelec | Vasilakos A.V.,University of Western Macedonia
IEEE Journal on Selected Areas in Communications | Year: 2012

In this paper, we study game dynamics and learning schemes for heterogeneous 4G networks. We introduce a novel learning scheme called cost-to-learn that incorporates the cost to switch, the switching delay, and the cost of changing to a new action and, captures the realistic behavior of the users that we have experimented on OPNET simulations. Considering a dynamic and uncertain environment where the users and operators have only a numerical value of their own payoffs as information, we construct various heterogeneous combined fully distributed payoff and strategy reinforcement learning (CODIPAS-RL): the users try to learn their own optimal payoff and their optimal strategy simultaneously. We establish the asymptotic pseudo-trajectories as solution of differential equations. Using evolutionary game dynamics, we prove the convergence and stability properties in specific classes of dynamic robust games. We provide various numerical examples and OPNET simulations in the context network selection in wireless local area networks (WLAN) and Long Term Evolution (LTE). © 2012 IEEE. Source

Contemporary RDBMS-based systems for visualization of high-volume numerical data have difficulty to cope with the hard latency requirements and high ingestion rates of interactive visualizations. Existing solutions for lowering the volume of large data sets disregard the spatial properties of visualizations, resulting in visualization errors. In this work, we introduce VDDA, a visualization-driven data aggregation that models visual aggregation at the pixel level as data aggregation at the query level. Based on the M4 aggregation for producing pixel-perfect line charts from highly reduced data subsets, we define a complete set of data reduction operators that simulate the overplotting behavior of the most frequently used chart types. Relying only on the relational algebra and the common data aggregation functions, our approach is generic and applicable to any visualization system that consumes data stored in relational databases. We demonstrate our visualization-driven data aggregation using real-world data sets from high-tech manufacturing, stock markets, and sports analytics, reducing data volumes by up to two orders of magnitude, while preserving pixel-perfect visualizations, as producible from the raw data. © 2015 Springer-Verlag Berlin Heidelberg Source

The impact of the Late Palaeozoic glaciation of Gondwana is documented in northern Ethiopia both by glaciogenic sediments and by palaeolandforms of glacial erosion, yet the palaeoglaciological conditions that existed in this region during the glaciation haven't been investigated so far. In northern Ethiopia, erosional landforms of the Late Palaeozoic glaciation are exposed over an area of at least several tens of km2. These palaeolandforms are described for the first time and their origin and significance as indicators of regional ice-flow direction, glacial palaeolandscape and ice dynamics are discussed. The palaeolandforms of glacial erosional occur mainly on Precambrian basement rocks being directly overlain by glaciogenic sediments of latest Carboniferous to Early Permian age. Landforms are highly diverse and include, among others, chatter marks, muschelbrüche, whalebacks and rock drumlins. All these palaeolandforms indicate that the region was occupied by predominantly wet-based, temperate and relatively mobile continental glaciers during the Late Palaeozoic. The erosional surface that occurs at the base of the glaciogenic sediments represents a palaeolandscape of areal scour formed mainly by glacial abrasion and to a lesser extent by quarrying beneath a continental ice sheet, whereas meltwater erosion played only a minor role in its genesis. A northward-directed palaeo-ice flow is indicated by the orientation of palaeolandforms such as wedge striae, crescentic gouges, lunate fractures and roche moutonnées. This suggests, that the glaciers were sourced by ice sheets located in central Africa or in the Horn of Africa. Glacial advances might have extended into Arabia, albeit this scenario is not yet proven. © 2009 International Association for Gondwana Research. Source

Alpcan T.,TU Berlin | Buchegger S.,KTH Royal Institute of Technology
IEEE Transactions on Mobile Computing | Year: 2011

Vehicular networks (VANETs) can be used to improve transportation security, reliability, and management. This paper investigates security aspects of VANETs within a game-theoretic framework where defensive measures are optimized with respect to threats posed by malicious attackers. The formulations are chosen to be abstract on purpose in order to maximize applicability of the models and solutions to future systems. The security games proposed for vehicular networks take as an input centrality measures computed by mapping the centrality values of the car networks to the underlying road topology. The resulting strategies help locating most valuable or vulnerable points (e.g., against jamming) in vehicular networks. Thus, optimal deployment of traffic control and security infrastructure is investigated both in the static (e.g., fixed roadside units) and dynamic cases (e.g., mobile law enforcement units). Multiple types of security games are studied under varying information availability assumptions for the players, leading to fuzzy game and fictitious play formulations in addition to classical zero-sum games. The effectiveness of the security game solutions is evaluated numerically using realistic simulation data obtained from traffic engineering systems. © 2011 IEEE. Source

Dorfi E.A.,University of Vienna | Breitschwerdt D.,TU Berlin
Astronomy and Astrophysics | Year: 2012

Context. Cosmic rays (CRs) are transported out of the galaxy by diffusion and advection due to streaming along magnetic field lines and resonant scattering off self-excited MHD waves. Thus momentum is transferred to the plasma via the frozen-in waves as a mediator assisting the thermal pressure in driving a galactic wind. Aims. The bulk of the Galactic CRs (GCRs) are accelerated by shock waves generated in supernova remnants (SNRs), a significant fraction of which occur in OB associations on a timescale of several 10 7 years. We examine the effect of changing boundary conditions at the base of the galactic wind due to sequential SN explosions on the outflow. Thus pressure waves will steepen into shock waves leading to in situ post-acceleration of GCRs. Methods. We performed hydrodynamical simulations of galactic winds in flux tube geometry appropriate for disk galaxies, describing the CR diffusive-advective transport in a hydrodynamical fashion (by taking appropriate moments of the Fokker-Planck equation) along with the energy exchange with self-generated MHD waves. Results. Our time-dependent CR hydrodynamic simulations confirm the existence of time asymptotic outflow solutions (for constant boundary conditions), which are in excellent the agreement with the steady state galactic wind solutions described by Breitschwerdt et al. (1991, A&A, 245, 79). It is also found that high-energy particles escaping from the Galaxy and having a power-law distribution in energy (∞ E -2.7) similar to the Milky Way with an upper energy cut-off at ∼10 15 eV are subjected to efficient and rapid post-SNR acceleration in the lower galactic halo up to energies of 10 17-10 18 eV by multiple shock waves propagating through the halo. The particles can gain energy within less than 3 kpc from the galactic plane corresponding to flow times less than 5 × 10 6 years. Since particles are advected downstream of the shocks, i.e. towards the galactic disk, they should be easily observable, and their flux should be fairly isotropic. Conclusions. The mechanism described here offers a natural and elegant solution to explain the power-law distribution of CRs between the "knee" and the "ankle". © 2012 ESO. Source

Renger G.,TU Berlin
Biochimica et Biophysica Acta - Bioenergetics | Year: 2012

The reactions of light induced oxidative water splitting were analyzed within the framework of the empirical rate constant-distance relationship of non-adiabatic electron transfer in biological systems (C. C. Page, C. C. Moser, X. Chen, P. L. Dutton, Nature 402 (1999) 47-52) on the basis of structure information on Photosystem II (PS II) (A. Guskov, A. Gabdulkhakov, M. Broser, C. Glöckner, J. Hellmich, J. Kern, J. Frank, W. Saenger, A. Zouni, Chem. Phys. Chem. 11 (2010) 1160-1171, Y. Umena, K. Kawakami, J-R Shen, N. Kamiya, Crystal structure of oxygen-evolving photosystem II at a resolution of 1.9 Å. Nature 47 (2011) 55-60). Comparison of these results with experimental data leads to the following conclusions: 1) The oxidation of tyrosine Y z by the cation radical P680+ · in systems with an intact water oxidizing complex (WOC) is kinetically limited by the non-adiabatic electron transfer step and the extent of this reaction is thermodynamically determined by relaxation processes in the environment including rearrangements of hydrogen bond network(s). In marked contrast, all Yz ox induced oxidation steps in the WOC up to redox state S3 are kinetically limited by trigger reactions which are slower by orders of magnitude than the rates calculated for non-adiabatic electron transfer. 3) The overall rate of the triggered reaction sequence of Yz ox reduction by the WOC in redox state S3 eventually leading to formation and release of O2 is kinetically limited by an uphill electron transfer step. Alternative models are discussed for this reaction. The protein matrix of the WOC and bound water molecules provide an optimized dynamic landscape of hydrogen bonded protons for catalyzing oxidative water splitting energetically driven by light induced formation of the cation radical P680 + ·. In this way the PS II core acts as a molecular machine formed during a long evolutionary process. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: from Natural to Artificial. © 2011 Elsevier B.V. All rights reserved. Source

Enculescu M.,TU Berlin | Falcke M.,Max Delbruck Center for Molecular Medicine
New Journal of Physics | Year: 2011

We propose a mathematical model of the actin-based propulsion of spatially extended obstacles. It starts from the properties of individual actin filaments and includes transient attachment to the obstacle, polymerization as well as cross-linking. Two particular geometries are discussed, which apply to the motion of protein-coated beads in a cell-like medium and the leading edge of a cell protrusion, respectively. The model gives rise to both steady and saltatory movement of beads and can explain the experimentally observed transitions of the dynamic regime with changing bead radius and protein surface density. Several spatiotemporal patterns are obtained with a soft obstacle under tension, including the experimentally observed spontaneous emergence of lateral traveling waves in crawling cells. Thus, we suggest a unifying mechanism for systems that are currently described by differential concepts. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft. Source

Concerns regarding supply security are increasingly raised in reaction to the transition of the German energy system towarda renewable and nuclear-free system called "Energiewende". The goal of this work is to contribute to a measurability of supply security by quantifying the consequences of power interruptions monetarily. The focus lies within the investigation of power interruption costs in private households. An online survey with 859 participants in 2011 is used to gather the necessary data. Based on this data, a two-staged bottom-up regression model was estimated to describe interruption costs for durations of 15min, 1h, 4h, 1 day and 4 days. Finally, micro-data from 55,000 households were used to perform Monte Carlo simulations to increase the representativeness of the estimations. The frequency distributions of the estimated interruption costs indicate potentials for load-shedding measures. Such measures could be an economically viable contribution to a successful integration of large shares of renewable fluctuating generation like wind or solar power. © 2014 The Authors. Source

Widyan M.S.,Hashemite University | Hanitsch R.E.,TU Berlin
International Journal of Electrical Power and Energy Systems | Year: 2014

This paper presents the operating point stability analysis of a Single Machine Infinite Bus (SMIB) power system equipped with high Photovoltaic (PV) penetration. The detailed dynamical model of the synchronous generator in dq reference frame is considered including the dynamics of the damper windings and Automatic Voltage Regulator (AVR). A DC-DC buck-boost switch mode converter is placed as an intermediate stage between the PV array and the inverter. The main function of this implementation is to inject the voltage corresponding to the PV generator Maximum Power Point (MPP) by automatic adjusting its duty cycle. The PV array is designed to provide a maximum output power of about 0.78 pu at the full solar irradiance. The nonlinearity of the output characteristics of the PV generator is taken into account. Operating point stability analysis is performed by extracting the eigenvalues of the linearized model around the operating point at different solar irradiances. System response after successive step changes on the synchronous generator input mechanical power at three solar irradiances based on the complete nonlinear dynamical model is investigated. For given synchronous generator input parameters, the response of the system after successive step changes on the solar intensity is addressed. It is found that high PV penetration via DC-DC buck-boost converter and DC-AC inverter is practically possible, experiences a stable operating point and can withstand successive step changes on system parameters in case of practical solar irradiance levels. All numerical simulations are conducted using MATLAB software package by building the code required. © 2013 Elsevier Ltd. All rights reserved. Source

Tautz R.C.,TU Berlin | Shalchi A.,University of Manitoba
Journal of Geophysical Research: Space Physics | Year: 2013

Reproducing measurements of the scattering mean free paths for energetic particles propagating through the solar system has been a major problem in space physics. The pioneering work of Bieber et al. (1994) provided a theoretical explanation of such observations, which, however, was based on assumptions such as the questionable hypothesis that quasi-linear theory is correct for parallel diffusion. By employing a hybrid plasma-wave/magnetostatic turbulence model, a test-particle code is used to investigate the scattering of energetic particles. The results show excellent agreement with solar wind observations. Key PointsCosmic-ray mean-free paths are reproduced with test-particle simulationsA new hybrid plasma wave/magnetostatic models the Solar wind turbulenceThe results show excellent agreement with Palmer consensus range observations ©2013. American Geophysical Union. All Rights Reserved. Source

Mehta S.K.,Panjab University | Kumar S.,Government College | Gradzielski M.,TU Berlin
Journal of Colloid and Interface Science | Year: 2011

The interaction between organic molecules and the surface of nanoparticles (NPs) strongly affects the size, properties and applications of surface-modified metal sulfide semiconductor nanocrystals. From this viewpoint, we compared the influence of cationic surfactants with various chain lengths and anionic surfactants with different head groups, as surface modifiers during synthesis of ZnS NPs in aqueous medium. The surfactant adsorbs on the surface of the particles as micelle-like aggregates. These aggregates can form even at the concentration lower than critical micelle concentration (cmc) due to interaction between the polar groups and the NPs. The nature of interaction depends specifically on the surfactant polar group. The ability of surfactant to form the micelle-like aggregates on the surface of the NPs correlates with their cmc. This leads to the fact that the surfactant with longer tail stabilizes the NPs better since its cmc is lower. The adsorption of the surfactant on the NPs also stabilizes them by the change of their charge which is in accordance with the correlation of zeta potential with the particles stability. The energetics of surface states generating interesting photoluminescence (PL) properties in ZnS NPs has been governed by the nature of surfactant molecules. In general, the size, structure, and stability of the ZnS NPs can be controlled by the choice of suitable surfactant. © 2011 Elsevier Inc. Source

Emary C.,TU Berlin
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2013

We consider maximal violations of the Leggett-Garg inequality, obtained by maximizing over all possible measurement operators, in relation to nonunitary aspects of the system dynamics. We model the action of an environment on a qubit in terms of generic quantum channels and relate the maximal value of the Leggett-Garg correlator to the channel parameters. We focus on unital channels and hence on decoherence. In certain important cases, exact relations between the channel parameters and maximal violations can be found. Moreover, we demonstrate the existence of distinct thresholds for the channel parameters, below which no violation of the Leggett-Garg inequality can occur. © 2013 American Physical Society. Source

Dopfer O.,TU Berlin
EAS Publications Series | Year: 2011

In this contribution, we summarize the recent progress made in recording laboratory infrared (IR) spectra of protonated polycyclic aromatic hydrocarbon molecules (H+PAH) in the gas phase. The IR spectra of a large variety of H+PAH species ranging from benzene to coronene have been obtained by various variants of photodissociation spectroscopy. The employed techniques include single-photon IR photodissociation (IRPD) of tagged H+PAH ions and IR multiple-photon dissociation (IRMPD) of bare H+PAH ions. The comparison of the laboratory IR spectra with astronomical spectra supports the hypothesis that H+PAH ions are possible carriers of the unidentified IR emission (UIR) bands. Moreover, the spectra provide detailed information about the geometric and electronic structure as well as the chemical reactivity and stability of these fundamental hydrocarbon ions. © EAS, EDP Sciences 2011. Source

Emary C.,TU Berlin | Aguado R.,CSIC - Institute of Materials Science
Physical Review B - Condensed Matter and Materials Physics | Year: 2011

We discuss the description of full counting statistics in quantum transport with a non-Markovian master equation. We focus on differences arising from whether charge is considered as a classical or a quantum degree of freedom. These differences manifest themselves in the inhomogeneous term of the master equation which describes initial correlations. We describe the influence on current and in particular, the finite-frequency shotnoise. We illustrate these ideas by studying transport through a quantum dot and give results that include both sequential and cotunneling processes. Importantly, the noise spectra derived from the classical description are essentially frequency independent and all quantum noise effects are absent. These effects are fully recovered when charge is considered as a quantum degree of freedom. © 2011 American Physical Society. Source

A consistent model of the rheology of polymer melts and concentrated solutions is presented, based on the idea that the pressures exerted by a polymer chain on the walls of an anisotropic confinement are anisotropic (Doi and Edwards. The Theory of Polymer Dynamics, Oxford University Press, 1986). In a tube model with variable tube diameter, chain stretch and tube diameter reduction are related, and at deformation rates larger than the inverse Rouse time τR, the chain is stretched and its confining tube becomes increasingly anisotropic. Tube diameter reduction leads to an interchain pressure in the lateral direction of the tube (Marrucci and Ianniruberto. Macromolecules 37:3934-3942, 2004). Chain stretch is balanced by interchain tube pressure in the lateral direction, which is proportional to the third power of stretch, and by a spring force in the longitudinal direction of the tube, which is linear in stretch. Analyzing elongational viscosity data of Huang et al. (Macromolecules 46:5026-5035, 2013a; ACS Macro Letters 2:741-744, 2013b) shows that dilution of polystyrene by oligomeric styrene does not change the relative interchain tube pressure. Based on this extended interchain pressure concept, scaling relations for linear viscoelasticity and elongational viscosity of polystyrene melts and concentrated solutions of polystyrene in oligomeric styrene are presented based exclusively on the relaxation modulus of a reference polymer melt, the volume fraction of polymer in the solution, and the time-molar-mass shift as well as the time-temperature shift caused by the reduction of the glass transition temperature Tg of the polymer in a solution relative to Tg of the melt. © 2014, Springer-Verlag Berlin Heidelberg. Source

Subramanian L.,University of Edinburgh | Toda N.R.T.,University of Edinburgh | Rappsilber J.,University of Edinburgh | Rappsilber J.,TU Berlin | Allshire R.C.,University of Edinburgh
Open Biology | Year: 2014

CENP-A chromatin forms the foundation for kinetochore assembly. Replicationindependent incorporation of CENP-A at centromeres depends on its chaperone HJURPScm3, and Mis18 in vertebrates and fission yeast. The recruitment of Mis18 and HJURPScm3 to centromeres is cell cycle regulated. Vertebrate Mis18 associates with Mis18BP1KNL2, which is critical for the recruitment ofMis18 and HJURPScm3. We identify two novel fission yeastMis18-interacting proteins (Eic1 and Eic2), components of the Mis18 complex. Eic1 is essential to maintain Cnp1CENP-A at centromeres and is crucial for kinetochore integrity; Eic2 is dispensable. Eic1 also associates with Fta7CENP-Q/Okp1, Cnl2Nkp2and Mal2CENP-O/Mcm21, components of the constitutive CCAN/Mis6/Ctf19 complex. No Mis18BP1KNL2 orthologue has been identified in fission yeast, consequently it remains unknown how the key Cnp1CENP-A loading factor Mis18 is recruited. Our findings suggest that Eic1 serves a function analogous to that of Mis18BP1KNL2, thus representing the functional counterpart of Mis18BP1KNL2 in fission yeast that connects with a module within the CCAN/Mis6/Ctf19 complex to allow the temporally regulated recruitment of the Mis18/Scm3HJURP Cnp1CENP-A loading factors. The novel interactions identified between CENP-A loading factors and the CCAN/Mis6/Ctf19 complex are likely to also contribute to CENP-A maintenance in other organisms. © 2014 The Authors. Source

Aubram D.,TU Berlin
Journal of Non-Newtonian Fluid Mechanics | Year: 2016

Multi-material flow generally describes a situation where several distinct materials separated by sharp material interfaces undergo large deformations. In order to model such flow situations in the context of geomechanics and geotechnical engineering, a theoretical framework is presented which introduces a possible two-phase coupled saturated granular material behavior among the different materials. This is achieved by extending the technique of local volume averaging to a hierarchy of three spatial scales, based on a product of two indicator functions. A homogeneous equilibrium mixture model is subsequently derived for an example flow consisting of bulk solid, bulk fluid, and undrained granular material with compressible constituents. The closure relations are provided at the macroscale, including those describing granular behavior covering the full frictional-collisional flow regime and bulk material volume fraction evolution. The paper discusses the advantages and restrictions of the proposed mixture model and addresses its application and full-scale numerical implementation. © 2016 Elsevier B.V. Source

Recent progress in the gas-phase activation of methane is discussed. We demonstrate that cluster size, charge state, and ligands crucially affect both the reactivity and selectivity of metal-mediated bond activation processes. We outline the important role that relativistic effects and spin densities play and discuss the paradigm of two-state reactivity in thermal reactions. State-of-the-art mass-spectrometry based experiments, in conjunction with electronic structure calculations, permit identification of the elementary steps at a strictly molecular level and thus allow to uncover mechanistic features for four types of reactions: (i) metal-mediated dehydrogenation of methane, (ii) ligand-switch processes of the type ML + CH4 → M(CH3) + HL, (iii) hydrogen-atom abstraction as the crucial step in the oxidative coupling of methane, and (iv) the mechanism of the challenging CH4→CH3OH conversion. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Morosuk T.,Maritime University Of Szczecin | Tsatsaronis G.,TU Berlin
Energy | Year: 2011

During the last two decades the total cost of LNG technology has decreased significantly due to improvements of the liquefaction process. However, the regasification system has not been considerably improved. It is known that for the regasification process about 1.5% of LNG is used. Two novel, gas-turbine-based concepts for combining LNG regasification with the generation of electricity are discussed in this paper. These concepts have relatively low investment costs and high efficiencies. An advanced exergetic analysis is applied to one of these attractive LNG-based cogeneration systems to identify the potential for improvement and the interactions among components. In an advanced exergetic analysis, the exergy destruction within each component is split into unavoidable/avoidable and endogenous/exogenous parts. The advantages of this analysis over a conventional one are demonstrated. Some new developments in the advanced exergetic analysis and options for improving the concepts are also presented. © 2010 Elsevier Ltd. Source

Jabs A.,TU Berlin
Foundations of Physics | Year: 2010

The spin-statistics connection is derived in a simple manner under the postulates that the original and the exchange wave functions are simply added, and that the azimuthal phase angle, which defines the orientation of the spin part of each single-particle spin-component eigenfunction in the plane normal to the spin-quantization axis, is exchanged along with the other parameters. The spin factor (-1)2s belongs to the exchange wave function when this function is constructed so as to get the spinor ambiguity under control. This is achieved by effecting the exchange of the azimuthal angle by means of rotations and admitting only rotations in one sense. The procedure works in Galilean as well as in Lorentz-invariant quantum mechanics. Relativistic quantum field theory is not required. © 2009 Springer Science+Business Media, LLC. Source

Mani P.,University of Houston | Mani P.,NRC Institute for Fuel Cell Innovation | Srivastava R.,University of Houston | Strasser P.,TU Berlin | Strasser P.,Gwangju Institute of Science and Technology
Journal of Power Sources | Year: 2011

Dealloyed Pt bimetallic nanoparticles are highly active electrocatalysts for the electroreduction of molecular oxygen (ORR), the key barrier to more efficient polymer electrolyte membrane fuel cells (PEMFCs). Most previous studies of dealloyed Pt alloys focused on the structure and mechanism of dealloyed Pt-Cu bimetallic materials. Also, stability concerns related to Cu prompted the search for alternative non-noble metal components for dealloying. Here, we report on a comparative study of dealloyed binary PtM3 (M = Co, Cu, Ni) electrocatalyst for use in PEMFC cathodes. We also study synergistic effects of a third metal in ternary PtNi3M (M = Co, Cu, Fe, Cr) cathode electrocatalysts. All catalyst precursor materials were prepared by an impregnation, freeze-drying, annealing route. After deployment of the catalyst precursor in single PEM cells, the active dealloyed form of the catalysts was obtained through a voltammetric dealloying protocol. Dealloyed binary PtM 3 catalysts showed more than a threefold activity improvement for ORR for M = Co, Cu, and close to a threefold improvement for M = Ni in terms of the Pt-mass activity (AmgPt-1) of the single fuel cell, compared to a 45 wt% Pt/C reference cathode catalyst. Improvements in specific surface area normalized activities (AcmPt-2) followed those in Pt-mass activity. All ternary catalysts, except the Fe containing one, showed clearly improved catalytic ORR performance compared to PtNi3, in particular PtNi3Co and PtNi3Cu. A previously unachieved four- to fivefold activity improvement in real single MEAs was observed. Near-surface (XPS) and bulk (EDS/ICP) compositional characterizations suggested that the degree of dealloying of Pt-Co and Pt-Ni binary precursors is lower than that of Pt-Cu compounds. Pt-Co and Pt-Ni still showed 15-20 at.% non-noble metal near the surface and in the bulk of the dealloyed particles, whereas, under the chosen dealloying conditions, Pt-Cu formed core-shell structures with a Pt-rich surface and a Pt-Cu core. Of the selectively characterized Pt-Ni-Co and Pt-Ni-Cu ternaries, the near-surface composition of dealloyed Pt-Ni compounds showed an atomic ratio of about 1:1, compared to about 5:1 in the bulk, pointing to a Ni enrichment at the surface with only small residual amounts of Co or Cu. Our study highlights a number of novel active cathode catalyst compositions and underscores the sensitive dependence of the ORR activity of dealloyed Pt binary and ternary nanoparticle electrocatalysts on the nature and initial composition of the non-noble alloy component. © 2010 Elsevier B.V. Source

Betsch C.,University of Erfurt | Sachse K.,TU Berlin
Health Psychology | Year: 2013

Objective: Information about risks is often contradictory, especially in the health domain. A vast amount of bizarre information on vaccine-adverse events (VAE) can be found on the Internet; most are posted by antivaccination activists. Several actors in the health sector struggle against these statements by negating claimed risks with scientific explanations. The goal of the present work is to find optimal ways of negating risk to decrease risk perceptions. Methods: In two online experiments, we varied the extremity of risk negations and their source. Perception of the probability of VAE, their expected severity (both variables serve as indicators of perceived risk), and vaccination intentions. Results: Paradoxically, messages strongly indicating that there is "no risk" led to a higher perceived vaccination risk than weak negations. This finding extends previous work on the negativity bias, which has shown that information stating the presence of risk decreases risk perceptions, while information negating the existence of risk increases such perceptions. Several moderators were also tested; however, the effect occurred independently of the number of negations, recipient involvement, and attitude. Solely the credibility of the information source interacted with the extremity of risk negation: For credible sources (governmental institutions), strong and weak risk negations lead to similar perceived risk, while for less credible sources (pharmaceutical industries) weak negations lead to less perceived risk than strong negations. Conclusions: Optimal risk negation may profit from moderate rather than extreme formulations as a source's trustworthiness can vary. © 2012 American Psychological Association. Source

Yang R.,SLAC | Strasser P.,TU Berlin | Toney M.F.,SLAC
Journal of Physical Chemistry C | Year: 2011

The structural evolution during dissolution of Cu from Cu 3Pt (111) single crystal surfaces under potential control has been studied by X-ray scattering. An epitaxial, compressively strained, Pt-rich overlayer is formed upon Cu dissolution and thickens as the potential increases (more anodic). The compressive lattice strain in the Pt-rich overlayers decreases as the potential and overlayer thickness increase. The Pt-rich overlayers exhibit same fcc stacking sequence as the substrate. We compare and contrast the behavior of the dealloyed single crystals with similarly dealloyed Cu 3Pt thin films and nanoparticles. © 2011 American Chemical Society. Source

Enthaler S.,TU Berlin
Catalysis Letters | Year: 2014

The recycling of polymers continues to be a significant matter for a sustainable society. In particular, the conversion of end-of-life polymers to monomers or suitable low-molecular weight chemicals creates a feedstock for new high-quality polymeric materials and contributes to conserve resources and allow overall an efficient waste-managing system. In the present study, we have set up a straightforward methodology for the depolymerization of artificial polyethers applying cheap and abundant zinc( II) salts as precatalysts. In the presence of bio-based fatty acid chlorides as depolymerization reagent well-defined chloroesters were accessible in good to excellent yields. Moreover, acetic anhydride and fatty acids were applied as depolymerization reagents resulting in the formation of diacetates in moderate yields. In both cases the obtained products (chloroesters, diacetates) can be useful building blocks in polymerization chemistry. Noteworthy, overall a recycling of polyethers are possible. © Springer Science+Business Media New York 2014. Source

Cytochrome c oxidase (CcO) catalyzes the four electron reduction of molecular oxygen to water while avoiding the formation of toxic peroxide; a quality that is of high relevance for the development of oxygen-reducing catalysts. Resonance Raman spectroscopy has been used since many years as a technique to identify electron transfer pathways in cytochrome c oxidase and to identify the key intermediates in the catalytic cycle. This information can be compared to artificial systems such as modified heme-copper enzymes, molecular heme-copper catalysts or CcO/electrode complexes in order to shed light into the reaction mechanism of these non-natural systems. Understanding the structural commonalities and differences of CcO with its non-natural analogs is of great value for designing efficient oxygen-reducing catalysts. In this review therefore Raman spectroscopic measurements on artificial heme-copper enzymes and model complexes are summarized and compared to the natural enzyme cytochrome c oxidase. This article is part of a Special Issue entitled: Vibrational spectroscopies and bioenergetic systems. © 2014 Elsevier B.V. All rights reserved. Source

Tran B.L.,University of California at Berkeley | Driess M.,TU Berlin | Hartwig J.F.,University of California at Berkeley
Journal of the American Chemical Society | Year: 2015

We report copper-catalyzed oxidative dehydrogenative carboxylation (ODC) of unactivated alkanes with various substituted benzoic acids to produce the corresponding allylic esters. Spectroscopic studies (EPR, UV-vis) revealed that the resting state of the catalyst is [(BPI)Cu(O2CPh)] (1-O2CPh), formed from [(BPI)Cu(PPh3)2], oxidant, and benzoic acid. Catalytic and stoichiometric reactions of 1-O2CPh with alkyl radicals and radical probes imply that C-H bond cleavage occurs by a tert-butoxy radical. In addition, the deuterium kinetic isotope effect from reactions of cyclohexane and d12-cyclohexane in separate vessels showed that the turnover-limiting step for the ODC of cyclohexane is C-H bond cleavage. To understand the origin of the difference in products formed from copper-catalyzed amidation and copper-catalyzed ODC, reactions of an alkyl radical with a series of copper-carboxylate, copper-amidate, and copper-imidate complexes were performed. The results of competition experiments revealed that the relative rate of reaction of alkyl radicals with the copper complexes follows the trend Cu(II)-amidate > Cu(II)-imidate > Cu(II)-benzoate. Consistent with this trend, Cu(II)-amidates and Cu(II)-benzoates containing more electron-rich aryl groups on the benzamidate and benzoate react faster with the alkyl radical than do those with more electron-poor aryl groups on these ligands to produce the corresponding products. These data on the ODC of cyclohexane led to preliminary investigation of copper-catalyzed oxidative dehydrogenative amination of cyclohexane to generate a mixture of N-alkyl and N-allylic products. © 2014 American Chemical Society. Source

Tetrapodal pentadentate ligands occupy five coordination positions in a coordination octahedron, thereby providing the metal ion with a square-pyramidal "coordination cap": In such complexes, all reactivity is focused on a single coordination site. The review highlights recent advances in the coordination chemistry of iron. With a variety of NN4 ligands, the concept is being used to model non-heme active sites in biomolecules. Tetraphosphane ligands (donor set: NP4) undergo, depending on the solvent, remarkably specific P-C bond activation reactions, which may be reversed under suitable conditions. © The Royal Society of Chemistry 2010. Source

Lommatzsch A.,TU Berlin
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2014

With the rapidly growing amount of items and news articles on the internet, recommender systems are one of the key technologies to cope with the information overload and to assist users in finding information matching the their individual preferences. News and domain-specific information portals are important knowledge sources on the Web frequently accessed by millions of users. In contrast to product recommender systems, news recommender systems must address additional challenges, e.g. short news article lifecycles, heterogonous user interests, strict time constraints, and context-dependent article relevance. Since news articles have only a short time to live, recommender models have to be continuously adapted, ensuring that the recommendations are always up-to-date, hampering the pre-computations of suggestions. In this paper we present our framework for providing real-time news recommendations. We discuss the implemented algorithms optimized for the news domain and present an approach for estimating the recommender performance. Based on our analysis we implement an agent-based recommender system, aggregation several different recommender strategies. We learn a context-aware delegation strategy, allowing us to select the best recommender algorithm for each request. The evaluation shows that the implemented framework outperforms traditional recommender approaches and allows us to adapt to the specific properties of the considered news portals and recommendation requests. © 2014 Springer International Publishing Switzerland. Source

Grein A.,TU Berlin | Pehnt M.,Institute for Energy Research of Germany
Energy Policy | Year: 2011

As a strategy to deal with the increasing intermittent input of renewable energy sources in Germany, the adaptation of power consumption is complementary to power-plant regulation, grid expansion and physical energy storage. One demand sector that promises strong returns for load management efforts is cooling and refrigeration. In these processes, thermal inertia provides a temporal buffer for shifting and adjusting the power consumption of cooling systems. We have conducted an empirical investigation to obtain a detailed and time-resolved bottom-up analysis of load management for refrigeration systems in the city of Mannheim, Germany. We have extrapolated our results to general conditions in Germany. Several barriers inhibit the rapid adoption of load management strategies for cooling systems, including informational barriers, strict compliance with legal cooling requirements, liability issues, lack of technical experience, an inadequate rate of return and organizational barriers. Small commercial applications of refrigeration in the food-retailing and cold storage in hotels and restaurants are particularly promising starting points for intelligent load management. When our results are applied to Germany, suitable sectors for load management have theoretical and achievable potential values of 4.2 and 2.8. GW, respectively, amounting to about 4-6% of the maximum power demand in Germany. © 2011 Elsevier Ltd. Source

He F.,Shandong University of Technology | Behrendt F.,TU Berlin
Combustion and Flame | Year: 2011

Combining a volume reaction model and front reaction approximation is proposed to simulate the combustion of a large biomass particle. Two intraparticle processes-drying and char oxidation-are simplified as front reaction because they are transport controlled. The other intraparticle process-pyrolysis-is described as the volume reaction because it is controlled by both heat transfer and kinetics. A new numerical method based on the basic mechanism of the process is applied to mitigate oscillations of the solution of the front reactions. To compare the calculation results with the experimental results presented in the literature, combustion of cubic wood particles between 5 and 25. mm is chosen to test the new method. Drying, pyrolysis, char oxidation, vapor condensation, shrinkage of the process, heat transfer via conduction, diffusion, convection, radiation and mass transfer via diffusion, and convection inside particle are taken into account. Finite volumes attached to solid materials are used to discretize the domain and explicit method with variable time step is used to calculate the process. A program was written and the calculation showed that the conversion of a particle is almost independent of computational mesh from 10 cells on. However there is significant instability in the mass loss rate curve when the number of cells is less than 20. Predictions for different particle sizes, furnace temperatures and moisture contents were compared with measurements and they agree reasonably well. The results highlight the significance of pyrolysis kinetics on prediction. Thus, the front reaction model of pyrolysis assuming a constant reaction temperature of 773. K is sometimes inadequate. The proposed method also showed that moisture content and pyrolysis reactivity significantly affect the thickness of devolatilizing fuel. © 2011 The Combustion Institute. Source

Rolon-Garrido V.H.,TU Berlin
Rheologica Acta | Year: 2014

The molecular stress function (MSF) model is an integral constitutive equation introduced more than two decades ago. It is based on the time-deformation separability principle. The time contribution encloses the linear viscoelastic information, which can be provided by the phenomenological models or any molecular theory. The deformation contribution is defined in the MSF model as a strain measure describing the orientation and the stretch of the strands of the chain as independent processes. The orientation is described by the second-order tensor of the Doi-Edwards model, considering the independent alignment assumption. The stretch is taken into account by the molecular stress function, the main characteristic being that it is included inside the integral and it is the solution of an evolution equation. Since its proposal, the MSF model has been used to describe quantitatively the non-linear rheology of a broad variety of materials such as rubbers, linear and long-chain branched polymer melts and blends of polydisperse samples relevant to the industry. Nearly, monodisperse systems in solution and melt states have also been studied in samples with different structures like linear, bidisperse blends with linear components, combs and pom-pom molecules. Predictions have been obtained for a variety of deformations like uniaxial, equibiaxial and planar extensional flow as well as for steady, medium and large amplitude oscillatory and exponential shear flow. The quantitative description of polymer melts in transient elongation is crucial for numerical simulations. Therefore, the MSF model has been applied to perform finite element simulations for different processes and freesurface deformations, due to its flexibility, reliability and reduced number of material parameters. The integral constitutive equation and its physical interpretation remains the same since it was first published. The evolution equation of the molecular stress function is material dependent because it considers different molecular mechanisms occurring in different structures. Given its importance to rheology, it is the objective of this contribution to review the antecedents, physical basis and applications of the MSF model. © 2014, Springer-Verlag Berlin Heidelberg. Source

Anand K.,TU Berlin | Bianconi G.,Northeastern University | Severini S.,University College London
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2011

Entropic measures of complexity are able to quantify the information encoded in complex network structures. Several entropic measures have been proposed in this respect. Here we study the relation between the Shannon entropy and the von Neumann entropy of networks with given expected degree sequence. We find in different examples of network topologies that when the degree distribution contains some heterogeneity, an intriguing correlation emerges between the two entropic quantities. This results seems to suggest that heterogeneity in the expected degree distribution is implying an equivalence between a quantum and a classical description of networks, which respectively corresponds to the von Neumann and the Shannon entropy. © 2011 American Physical Society. Source

In this study, the load-carrying capacities of reinforced concrete (RC) beams strengthened with carbon-fibre-reinforced polymer (CFRP) and external tendons were compared. The effective stress of the RC beams was estimated by analysing the experimental reinforcing effect and the resulting behaviour of each specimen. It was found that the strengthening effect of CFRP was affected by the initial damage in the RC beams. On the other hand, in external post-tensioning, application of strain induced an initial effective stress in the RC beams. As a result, the effective stress of these RC beams was reduced and their performance was improved. Furthermore, it was found that the strengthening effect of external tendons used to strengthen in-service RC beams can be predicted by a finite element analysis. © 2013 © 2013 Taylor & Francis. Source

The commonly used hydraulic models only account for capillary water retention and conductivity. Adsorptive water retention and film conductivity is neglected. This leads to erroneous description of hydraulic properties in the dry range. The few existing models, which account for film conductivity and adsorptive retention are either difficult to use or physically inconsistent. A new set of empirical hydraulic models for an effective description of water dynamics from full saturation to complete dryness is introduced. The models allow a clear partitioning between capillary and adsorptive water retention as well as between capillary and film conductivity. The number of adjustable parameters for the new retention model is not increased compared to the commonly used models, whereas only one extra parameter for quantifying the contribution of film conductivity is required for the new conductivity model. Both models are mathematically simple and thus easy to use in simulation studies. The new liquid conductivity model is coupled with an existing vapor conductivity model to describe conductivity in the complete moisture range. The new models were successfully applied to literature data, which all reach the dry to very dry range and cannot be well described with the classic capillary models. The investigated soils range from pure sands to clay loams. A simulation study with steady-state water transport scenarios shows that neglecting either film or vapor conductivity or both can lead to significant underestimation of water transport at low water contents. Key Points Empirical models distinguish between capillary, adsorptive and film components New models are easy to use in parameter estimation procedures and simulations Neglecting film flow can lead to a significant underestimation of water fluxes ©2013. American Geophysical Union. All Rights Reserved. Source

Astudillo R.F.,Spoken Language Systems Laboratory | Orglmeister R.,TU Berlin
IEEE Transactions on Audio, Speech and Language Processing | Year: 2013

In this paper we demonstrate how uncertainty propagation allows the computation of minimum mean square error (MMSE) estimates in the feature domain for various feature extraction methods using short-time Fourier transform (STFT) domain distortion models. In addition to this, a measure of estimate reliability is also attained which allows either feature re-estimation or the dynamic compensation of automatic speech recognition (ASR) models. The proposed method transforms the posterior distribution associated to a Wiener filter through the feature extraction using the STFT Uncertainty Propagation formulas. It is also shown that non-linear estimators in the STFT domain like the Ephraim-Malah filters can be seen as special cases of a propagation of the Wiener posterior. The method is illustrated by developing two MMSE-Mel-frequency Cepstral Coefficient (MFCC) estimators and combining them with observation uncertainty techniques. We discuss similarities with other MMSE-MFCC estimators and show how the proposed approach outperforms conventional MMSE estimators in the STFT domain on the AURORA4 robust ASR task. © 2006-2012 IEEE. Source

Gradzielski M.,TU Berlin
Current Opinion in Colloid and Interface Science | Year: 2011

The presence of amphiphilic bilayers in the form of vesicles and disks typically has a profound effect on the rheology of the corresponding surfactant solutions. For instance such aggregates often show pronounced effects of shear thinning. These effects not only depend on the type of structure present, such as uni- or multilamellar vesicles, but in addition become more complicated due to the fact that shear may largely affect the structures present and thereby the rheological behaviour may depend to a large extent on the shear history of the given system. Such shear induced structural changes of bilayer systems are by themselves already very interesting and in addition lead to pronounced effects on the rheological behaviour. © 2010 Elsevier Ltd. Source

Tekin T.,TU Berlin
IEEE Journal on Selected Topics in Quantum Electronics | Year: 2011

Packaging is a core technology to leverage the functions and the performances of micro- and nano-structures in a system. In order to bring them to application, the gap between component and environment has to be bridged by providing reliable interfaces. This paper reviews the packaging of optoelectronic, photonic, and microelectromechanical systems (MEMS) components. State-of-the-art requirements, standard technologies, and approaches are considered. Recent trends and research results in the packaging of advanced photonic, MEMS, Si-photonic components, and in 3-D, heterogeneous integration, and SiP are discussed. © 2006 IEEE. Source

Schrank E.,TU Berlin
Review of Palaeobotany and Palynology | Year: 2013

This paper describes a rich assemblage of winteraceous pollen tetrads from the independently dated Albian Upper Hatira Formation at Makhtesh Qatan, northern Negev, Israel. Previously similar winteraceous tetrads have been reported from the upper Aptian-middle Albian of the Zohar 1 well north of Makhtesh Qatan. These pollen grains were widely recognized as early stem group representatives of the primitive angiosperm family Winteraceae, and a centre of origin in Northern Gondwana was postulated for a family, which is today mainly austral in distribution. On the basis of the new material from Makhtesh Qatan the new genus and species Qatanipollis valentini is proposed. In addition to its type this genus contains at present the two species Qatanipollis sp. A (formerly Walkeripollis sp. A) and Qatanipollis sp. B, both recovered from core samples of the Zohar 1 well. © 2013 Elsevier B.V. Source

Kock A.,TU Berlin
Journal of Product Innovation Management | Year: 2011

This study addresses the contradiction that, although technological innovativeness of new products is often seen as a major driver of competitive advantage and commercial success, empirical research is not always able to show a significant performance influence. In order to find an explanation, the effects of technological innovativeness are decomposed as its influence on the market, the innovating firm, and the firm's environment is considered. The proposed model is tested on a sample of new product development projects. In order to avoid systematic biases, this paper uses a longitudinal survey design with two informants and a sample that includes both incremental and highly innovative projects. The results show that technological innovativeness has both positive and negative effects on the commercial success of new products. On the one hand, technological innovativeness can increase customer value, which in turn has a positive effect on success. On the other hand, incorporating new technologies into new products also implies changes in the innovating firm and potentially in its environment. These changes have a negative impact on commercial success. The positive and negative effects compensate for each other, so that the total effect of technological innovativeness on commercial success is close to zero. The findings imply that firms developing new products through incorporating radically new technologies often seem to underestimate the inherent complexities with respect to both internal and external changes. Developing and introducing new products with a radically changed technology also implies anticipating the need for new competences, processes, structures, and network partners. Social and political resistance against technological changes, large investments in new infrastructures, and the long duration of these changes additionally become frequent features of such innovation endeavors. Hence, firms embarking on a path of exploiting radically new technologies should consider those complexities very carefully when making their new product development decisions. © 2011 Product Development & Management Association. Source

Schwarz H.,TU Berlin
Angewandte Chemie - International Edition | Year: 2011

Four seemingly simple transformations related to the chemistry of methane will be addressed from mechanistic and conceptual points of view: 1) metal-mediated dehydrogenation to form metal carbene complexes, 2) the hydrogen-atom abstraction step in the oxidative dimerization of methane, 3) the mechanisms of the CH4→CH3OH conversion, and 4) the initial bond scission (C-H vs. O-H) as well as the rate-limiting step in the selective CH3OH→CH2O oxidation. State-of-the-art gas-phase experiments, in conjunction with electronic-structure calculations, permit identification of the elementary reactions at a molecular level and thus allow us to unravel detailed mechanistic aspects. Where appropriate, these results are compared with findings from related studies in solution or on surfaces. Elementary steps associated with the activation of methane are addressed from experimental and computational viewpoints; what matters most are relativistic effects, two-state reactivity scenarios, and cluster-size and ligand effects, which all play a role in the organometallic chemistry of methane at ambient conditions. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Laneuville M.,CNRS Paris Institute of Global Physics | Wieczorek M.A.,CNRS Paris Institute of Global Physics | Breuer D.,German Aerospace Center | Tosi N.,TU Berlin
Journal of Geophysical Research E: Planets | Year: 2013

The Moon possesses a clear dichotomy in geological processes between the nearside and farside hemispheres. The most pronounced expressions of this dichotomy are the strong concentration of radioactive heat sources on the nearside in a region known as the Procellarum KREEP Terrane (PKT) and the mare basaltic lava flows that erupted in or adjacent to this terrane. We model the thermochemical evolution of the Moon using a 3-D spherical thermochemical convection code in order to assess the consequences of a layer enriched in heat sources below the PKT on the Moon's global evolution. We find that in addition to localizing most of the melt production on the nearside, such an enriched concentration of heat sources in the PKT crust has an influence down to the core-mantle boundary and leaves a present-day temperature anomaly within the nearside mantle. Moderate gravitational and topographic anomalies that are predicted in the PKT, but not observed, may be masked either by crustal thinning or gravitational anomalies from dense material in the underlying mantle. Our models also predict crystallization of an inner core for sulfur concentrations less than 6 wt %. Key Points The thermochemical consequences of the PKT are consistent with the observations A thermal anomaly is present today in the mantle below the PKT Heat sources enrichment in the PKT has an influence down to the CMB ©2013. American Geophysical Union. All Rights Reserved. Source

Wegener M.,TU Berlin | Paschedag A.R.,University of Applied Sciences, Berlin
International Journal of Heat and Mass Transfer | Year: 2012

The toluene/acetone/water system without surfactants shows strong Marangoni instabilities with distinct fluid dynamics and enhanced mass transfer. The present study investigates the impact of an anionic surfactant (SDS) on rise velocity and mass transfer both in the spherical and the oscillating droplet regime in time resolved measurements. Results are compared with the respective pure system and with correlations from literature. Velocity measurements reveal that the smaller the droplets are the lower is the surfactant concentration where the terminal velocity of the corresponding rigid sphere is attained. Mass transfer measurements show that mass transfer is still significantly enhanced by Marangoni convection although the surfactant concentration was believed to be high enough to hinder interfacial movement. © 2011 Elsevier Ltd. All rights reserved. Source

Siurkus J.,Thermo Fisher Scientific | Neubauer P.,TU Berlin
Microbial Cell Factories | Year: 2011

Background: Eukaryotic Ribonuclease inhibitor (RI), belonging to the RNH1 family, is distinguished by unique features - a high sensitivity to oxidation due to the large number of reduced cysteins and a high hydrophobicity, which made most production approaches so far unsuccessful or resulted in very low yields. In this work efficient in vivo folding of native RI in the Escherichia coli cytoplasm was obtained by external addition of a reducing agent in tandem with oxygen limitation and overproduction of a molecular chaperonin. After optimisation of the production conditions in the shake flask scale the process was scaled up to high cell densities by applying a glucose limited fed-batch procedure.Results: RI production in a T7 RNA polymerase based system results in accumulation of aggregated inactive product in inclusion bodies. Combination of addition of the reductant DTT, low production temperature and coexpression of the chaperonin GroELS resulted in high level production of approximately 25 mg g-1CDW active RI in E. coli ER2566 pET21b, corresponding to approximately 800 kU g-1cell wet weight. Further conditional screening under fed-batch-like conditions with the EnBase®technology and scale up into the bioreactor scale resulted in an efficient high cell density glucose and oxygen limited fed-batch process with a final cell dry weight of 25 g L-1and a total RI yield of app. 625 mg L-1(volumetric activity of 80,000 kU L-1). The E. coli based production constructs showed a very high robustness. The recombinant culture maintained its productivity despite the combination of the toxic growth conditions, the substrate limited production mode in tandem with a high level expression of several recombinant proteins, the set of molecular chaperonins and the target protein (RI).Conclusions: High level production of active RI in E. coli in a T7 RNA polymerase expression system depends on the following factors: (i) addition of a reducing agent, (ii) low production temperature, (iii) oxygen limitation, and (iii) co-overexpression of the chaperonin GroELS. The study indicates the strength of applying fed-batch cultivation techniques for the efficient optimisation of production factors already at the screening stage for fast and straight forward bioprocess development even for target proteins which show a complex folding behaviour. In our case none of the approaches alone would have resulted in significant accumulation of active RI. © 2011 Šiurkus and Neubauer; licensee BioMed Central Ltd. Source

Kowarik I.,TU Berlin
Environmental Pollution | Year: 2011

With increasing urbanization the importance of cities for biodiversity conservation grows. This paper reviews the ways in which biodiversity is affected by urbanization and discusses the consequences of different conservation approaches. Cities can be richer in plant species, including in native species, than rural areas. Alien species can lead to both homogenization and differentiation among urban regions. Urban habitats can harbor self-sustaining populations of rare and endangered native species, but cannot replace the complete functionality of (semi-)natural remnants. While many conservation approaches tend to focus on such relict habitats and native species in urban settings, this paper argues for a paradigm shift towards considering the whole range of urban ecosystems. Although conservation attitudes may be challenged by the novelty of some urban ecosystems, which are often linked to high numbers of nonnative species, it is promising to consider their associated ecosystem services, social benefits, and possible contribution to biodiversity conservation. © 2011 Elsevier Ltd. All rights reserved. Source

Chang C.S.T.,Helmholtz Center Berlin | Banhart J.,TU Berlin
Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science | Year: 2011

The clustering behavior at room temperature of a pure ternary Al-0.59 wt pct Mg-0.82 wt pct Si alloy was investigated by low-temperature differential scanning calorimetry (DSC). We find three clustering reactions that take place in two stages. The first two reactions are linked to each other and are completed after 1 hour. The third reaction starts around 1 hour after quenching and is completed after 2 weeks. Only the latter reaction exhibits a strong shift of the peak position of the thermal signal, indicating a change in the activation energy during aging at room temperature caused by changing solute supersaturation or increasing trapping of vacancies. The first two stages are closely linked to the known adverse effect of room-temperature preaging on the ensuing age-hardening step, since 60 to 80 pct of cluster formation is sufficient to establish the full negative effect. © 2010 The Minerals, Metals & Materials Society and ASM International. Source

Tommaseo C.E.,TU Berlin
Journal of Structural Geology | Year: 2015

This paper presents the microstructural and structural properties of two natural salt samples from Iran and Portugal. Their strength-ductility behavior is explored by uniaxial compression experiments that, demonstrate that the observed differences lie not only in the inhomogeneous composition of the samples and their different grain sizes but also in their internal microstructural inhomogeneities. Microstructural inhomogeneities and substructural changes were observed with the SEM method (Scanning Electron Microscopy), the thin section microscope investigations and the EXAFS (Extended X-ray Absorption Fine Structure) spectroscopy. EBSD (Electron backscattered diffraction) analyses show maximum in the [100] or [110] directions in the inverse pole figure. This demonstrates that recrystallization and grain growth processes took place together. A weak [111] texture sometimes observed nearby indicates that residual stress is still present in the recrystallized sample.Comparison of the textural and structural results show that local structural rearrangements take place during textural development; this is attributed to different orientations influencing the deformation and recrystallization of adjacent grains influencing the bulk final texture. © 2015 Elsevier Ltd. Source

A group of engineering students at the Technical University of Berlin, Germany, designed a course on engineering ethics. The core element of the developed Blue Engineering course are self-contained teaching-units, "building blocks". These building blocks typically cover one complex topic and make use of various teaching methods using moderators who lead discussions, rather than experts who lecture. Consequently, the students themselves started to offer the credited course to their fellow students who take an active role in further developing the course themselves. © 2013 Springer Science+Business Media Dordrecht. Source

Few studies have been conducted to date on the importance of water availability (in-stream flows, water levels) for demand for a recreation site in Europe. In this paper we combine data on actual trips taken to a site (revealed behaviour) with data on anticipated trips that are stated as a response to hypothetical scenarios constructed for survey respondents (contingent behaviour). We combine these two sources of data in order to assess whether, and to what extent, the maintenance of minimum in-stream flows for boating matter in demand for trips to a wetland recreation site. The data from the on-site survey are used to estimate an aggregate count data travel cost model. Our findings indicate that variations in navigability significantly affect demand and associated welfare measures. © 2011 University of Newcastle upon Tyne. Source

Siurkus J.,Thermo Fisher Scientific | Neubauer P.,TU Berlin
Microbial Cell Factories | Year: 2011

Background: The eukaryotic RNase ribonuclease/angiogenin inhibitors (RI) are a protein group distinguished by a unique structure - they are composed of hydrophobic leucine-rich repeat motifs (LRR) and contain a high amount of reduced cysteine residues. The members of this group are difficult to produce in E. coli and other recombinant hosts due to their high aggregation tendency.Results: In this work dithiothreitol (DTT) was successfully applied for improving the yield of correctly folded ribonuclease/angiogenin inhibitor in E. coli K12 periplasmic and cytoplasmic compartments. The feasibility of the in vivo folding concepts for cytoplasmic and periplasmic production were demonstrated at batch and fed-batch cultivation modes in shake flasks and at the bioreactor scale.Firstly, the best secretion conditions of RI in the periplasmic space were evaluated by using a high throughput multifactorial screening approach of a vector library, directly with the Enbase fed-batch production mode in 96-well plates. Secondly, the effect of the redox environment was evaluated in isogenic dsbA+and dsbA-strains at the various cultivation conditions with reducing agents in the cultivation medium. Despite the fusion to the signal peptide, highest activities were found in the cytoplasmic fraction. Thus by removing the signal peptide the positive effect of the reducing agent DTT was clearly proven also for the cytoplasmic compartment. Finally, optimal periplasmic and cytoplasmic RI fed-batch production processes involving externally added DTT were developed in shake flasks and scaled up to the bioreactor scale.Conclusions: DTT highly improved both, periplasmic and cytoplasmic accumulation and activity of RI at low synthesis rate, i.e. in constructs harbouring weak recombinant synthesis rate stipulating genetic elements together with cultivation at low temperature. In a stirred bioreactor environment RI folding was strongly improved by repeated pulse addition of DTT at low aeration conditions. © 2011 Šiurkus and Neubauer; licensee BioMed Central Ltd. Source

Enthaler S.,TU Berlin
Catalysis Science and Technology | Year: 2011

In the present study, the zinc-catalysed reduction of a variety of sulfoxides with silanes as reductant to the corresponding sulfide has been examined in detail. With the straightforward and commercially available zinc(ii) triflate as pre-catalyst, excellent yields and chemoselectivities were feasible. After studying the reaction conditions and the scope and limitations several attempts were undertaken to shed light on the reaction mechanism. © 2011 The Royal Society of Chemistry. Source

Stockfleth E.,TU Berlin | Meyer T.,University of Hamburg
Expert Opinion on Biological Therapy | Year: 2012

Introduction: Sinecatechins is a standardized extract of green tea leaves, containing a mixture of catechin compounds. The 15% ointment has been approved for the topical treatment of condylomata acuminata (CA), caused by particular human papillomaviruses (HPV), mainly HPV types 6 and 11. Objective: To update the use of sinecatechins for treatment of CA and to describe possible mechanisms involved in the mode of action. Areas covered: The clearance rate of wart lesions after treatment with sinecatechins is similar to other topically applied drugs, like imiquimod and podophyllotoxin, but recurrences are seen less frequently after treatment with sinecatechins. The molecular mode of action underlying the clinical efficacy has yet not been characterized, but the following properties are likely to be involved in the regression of genital warts: activation of cellular immune reactions, induction of cell cycle arrest and apoptosis, inhibition of HPV gene expression. Expert opinion: Sinecatechins is a safe and effective treatment option for CA. Due to the variety of molecular activities of catechins the product has great potential for application to other viral and tumor lesions in the future. © 2012 Informa UK, Ltd. Source

Heinkenschloss M.,Rice University | Reis T.,TU Berlin | Antoulas A.C.,Rice University
Automatica | Year: 2011

We present a rigorous approach to extend balanced truncation model reduction (BTMR) to systems with inhomogeneous initial conditions, we provide an estimate for the error between the inputoutput maps of the original and of the reduced initial value system, and we illustrate numerically the superiority of our approach over the naive application of BTMR. When BTMR is applied to linear time invariant systems with inhomogeneous initial conditions, it is crucial that the initial data are well represented by the subspaces generated by BTMR. This requirement is often ignored or it is avoided by making the restrictive assumption that the initial data are zero. To ensure that the initial data are well represented by the BTMR subspaces, we add auxiliary inputs determined by the initial data. © 2010 Elsevier Ltd. All rights reserved. Source

Hubel N.,TU Berlin | Dahlem M.A.,Humboldt University of Berlin
PLoS Computational Biology | Year: 2014

The classical Hodgkin-Huxley (HH) model neglects the time-dependence of ion concentrations in spiking dynamics. The dynamics is therefore limited to a time scale of milliseconds, which is determined by the membrane capacitance multiplied by the resistance of the ion channels, and by the gating time constants. We study slow dynamics in an extended HH framework that includes time-dependent ion concentrations, pumps, and buffers. Fluxes across the neuronal membrane change intra- and extracellular ion concentrations, whereby the latter can also change through contact to reservoirs in the surroundings. Ion gain and loss of the system is identified as a bifurcation parameter whose essential importance was not realized in earlier studies. Our systematic study of the bifurcation structure and thus the phase space structure helps to understand activation and inhibition of a new excitability in ion homeostasis which emerges in such extended models. Also modulatory mechanisms that regulate the spiking rate can be explained by bifurcations. The dynamics on three distinct slow times scales is determined by the cell volume-to-surface-area ratio and the membrane permeability (seconds), the buffer time constants (tens of seconds), and the slower backward buffering (minutes to hours). The modulatory dynamics and the newly emerging excitable dynamics corresponds to pathological conditions observed in epileptiform burst activity, and spreading depression in migraine aura and stroke, respectively. © 2014 Hübel, Dahlem. Source

Tietje I.C.,TU Berlin
Journal of Physics: Conference Series | Year: 2012

A detailed overview of the conventional (van Hove) neutron scattering theory and its specification to the Impulse Approximation (IA) are given. The IA constitutes the basis of all interpretations of results from neutron scattering experiments in the Compton regime, in which is widely believed that single-particle properties are probed. Here the validity of this approximation is carefully scrutinized and it is shown that there are several different steps in the derivation, whose validity can be questioned: (1) the scattering system is a closed system (in the quantum mechanical sense); (2) all entanglement in the scattering system is absent (N-body operators are replaced by single particle operators); (3) consequently the one-body momentum distribution n(p) is introduced ad hoc; (4) the δ-function in energy assumed in the derivation is not valid when the interaction times underlying the IA are so short that the uncertainty relation allows a noticeable spread in the energy balance. Additionally, (5) the entanglement due to the direct interaction of the neutron with a nucleus is completely absent in the general formalism. The concrete experimental context of recent neutron Compton scattering (NCS) experiments at the ISIS neutron spallation source is considered and emphasis is put on the ultrafast (attosecond) scattering time for the neutron-proton scattering. Recent modern theoretical developments are shortly mentioned in the discussion, which take into account the neutron's coherence length being larger than the de Broglie wavelength, or decoherence phenomena during the short but finite scattering time. © Published under licence by IOP Publishing Ltd. Source

Jankowiak R.,Kansas State University | Reppert M.,Kansas State University | Zazubovich V.,Concordia University at Montreal | Pieper J.,TU Berlin | And 2 more authors.
Chemical Reviews | Year: 2011

Spectral hole burning (SHB) remains an active and expanding area of spectroscopy. SHB spectroscopy provides information on the static inhomogeneous broadening of S0fS1 transition, electron phonon coupling parameters, intermolecular Franck-Condon factors via vibronic satellite hole structure, the extent of correlation between the SDFs of different electronic states, radiative lifetimes, dephasing time and the excitation energy transfer time, electron transfer rates from the zero point level, and energy landscape barrier distribution parameters. SHB can also provide information on the interaction of the probe with the protein environment, the range of these interactions, and on spectral diffusion, i.e. on the protein motion in conformational phase space. It has been demonstrated that SHB can be performed on electronic transition in diffuse reflection mode. In particular, the diffuse reflection SHB should be used to study opaque materials with very low luminescence quantum yield. Source

Harks T.,Maastricht University | Miller K.,TU Berlin
Operations Research | Year: 2011

Resource allocation problems play a key role in many applications, including traffic networks, telecommunication networks, and economics. In most applications, the allocation of resources is determined by a finite number of independent players, each optimizing an individual objective function. An important question in all these applications is the degree of suboptimality caused by selfish resource allocation. We consider the worst-case efficiency of cost sharing methods in resource allocation games in terms of the ratio of the minimum guaranteed surplus of a Nash equilibrium and the maximal surplus. Our main technical result is an upper bound on the efficiency loss that depends on the class of allowable cost functions and the class of allowable cost sharing methods. We demonstrate the power of this bound by evaluating the worst-case efficiency loss for three well-known cost sharing methods: incremental cost sharing, marginal cost pricing, and average cost sharing. © 2011 INFORMS. Source

The V2X simulation runtime infrastructure - VSimRTI - enables the preparation and execution of V2X simulations. It is a flexible system which simulates traffic flow dynamically. VSimRTI couples different simulators, thus, allowing the simulation of the various aspects of future intelligent transportation systems. The easy integration and exchange of simulators enables the utilization of the most relevant simulators for a realistic presentation of vehicle traffic, emissions, wireless communication, and the execution of V2X applications. © 2011 Elsevier B.V. All rights reserved. Source

Crane K.,California Institute of Technology | Pinkall U.,TU Berlin | Schroder P.,California Institute of Technology
ACM Transactions on Graphics | Year: 2011

We introduce a new method for computing conformal transformations of triangle meshes in R 3. Conformal maps are desirable in digital geometry processing because they do not exhibit shear, and therefore preserve texture fidelity as well as the quality of the mesh itself. Traditional discretizations consider maps into the complex plane, which are useful only for problems such as surface parameterization and planar shape deformation where the target surface is flat. We instead consider maps into the quaternions H, which allows us to work directly with surfaces sitting in R 3. In particular, we introduce a quaternionic Dirac operator and use it to develop a novel integrability condition on conformal deformations. Our discretization of this condition results in a sparse linear system that is simple to build and can be used to efficiently edit surfaces by manipulating curvature and boundary data, as demonstrated via several mesh processing applications. © 2011 ACM. Source

Centner M.,Siemens AG | Schafer U.,TU Berlin
IEEE Transactions on Industrial Electronics | Year: 2010

This paper presents the design of highly efficient high-speed induction motors with optimally exploited magnetic materials. First, new combined numerical-analytical design methods are presented and validated, which closely relate to the classical way of machine design but allow the designer to precisely account for material properties. Second, it is shown how two optimized 20-kW 30 000-r/min induction machines have been realized, i.e., one incorporating cobalt-iron alloy, and the other one using siliconized steel. Finally, the influence of the electrical steel grade on their performance is evaluated on the basis of electrical, thermal, vibrational, and noise measurements. Copyright © 2010 IEEE. Source

Schreuder M.,TU Berlin
Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference | Year: 2011

Brain-computer interfaces based on event-related potentials face a trade-off between the speed and accuracy of the system, as both depend on the number of iterations. Increasing the number of iterations leads to a higher accuracy but reduces the speed of the system. This trade-off is generally dealt with by finding a fixed number of iterations that give a good result on the calibration data. We show here that this method is sub optimal and increases the performance significantly in only one out of five datasets. Several alternative methods have been described in literature, and we test the generalization of four of them. One method, called rank diff, significantly increased the performance over all datasets. These findings are important, as they show that 1) one should be cautious when reporting the potential performance of a BCI based on post-hoc offline performance curves and 2) simple methods are available that do boost performance. Source

Marwede M.,TU Berlin | Reller A.,Universitatsstr 1a
Resources, Conservation and Recycling | Year: 2012

According to the European Photovoltaic Industry Association, photovoltaic energy has the potential to contribute up to 13% to the global electricity supply by 2040. A part of this electricity production will come from thin-film photovoltaic technologies. From various thin-film technologies available on the market today, low-cost cadmium telluride photovoltaics (CdTe-PV) can be considered the market leader with a market share of 5% at annual production. There are however two major concerns about this technology: first, the potential negative environmental impacts of cadmium contamination from CdTe-PV; and second, the possible shortage of the metal tellurium in the future. Because of these concerns, the recycling of production scrap and end-of-life PV modules is essential. In this paper we estimate how much tellurium will be recovered from PV scrap to substitute for primary tellurium. In order to estimate global tellurium flows until 2040, we have created a dynamic material flow model for the life-cycle of CdTe-PV modules. Three scenarios, which describe different market developments and technology trajectories, show how material efficiency measures - higher material utilization in production, decrease of material content in PV modules, and recycling of production scrap and end-of-life modules - will affect demand, waste flows, and recycling flows of semiconductor grade tellurium. The results depict that efficiency measures at process and cell level will reduce the specific tellurium demand per watt peak such that total tellurium demand starts to decline after 2020 despite further market growth. Thus, the CdTe-PV industry has the potential to fully rely on tellurium from recycled end-of-life modules by 2038. However, in order to achieve this goal, material efficiency must be substantially improved and efficient collection and recycling systems have to be built up. © 2012 Elsevier B.V. All rights reserved. Source

Rieck K.,TU Berlin
Wiley Interdisciplinary Reviews: Data Mining and Knowledge Discovery | Year: 2011

Expressive comparison of strings is a prerequisite for analysis of sequential data in many areasof computer science. However, comparing strings and assessing their similarity is not a trivial task and there exists several contrasting approaches for defining similarity measures over sequential data. Inthis paper, we review three major classes of such similarity measures: edit distances, bag-of-word models, and string kernels. Each of these classes originates from a particular application domain andmodels similarity of strings differently. We present these classes and underlying comparisons in detail, highlight advantages, and differences as well as provide basic algorithms supporting practical applications. © 2011 John Wiley & Sons, Inc. Source

Renger T.,Johannes Kepler University | Schlodder E.,TU Berlin
Journal of Photochemistry and Photobiology B: Biology | Year: 2011

In this review we discuss structure-function relationships of the core complex of photosystem II, as uncovered from analysis of optical spectra of the complex and its subunits. Based on descriptions of optical difference spectra including site directed mutagenesis we propose a revision of the multimer model of the symmetrically arranged reaction center pigments, described by an asymmetric exciton Hamiltonian. Evidence is provided for the location of the triplet state, the identity of the primary electron donor, the localization of the cation and the secondary electron transfer pathway in the reaction center. We also discuss the stationary and time-dependent optical properties of the CP43 and CP47 subunits and the excitation energy transfer and trapping-by-charge- transfer kinetics in the core complex. © 2011 Elsevier B.V. All rights reserved. Source

In this review, the phenomenology of hysteresis is discussed, including both empirical and mathematical models, and some examples are presented. The focus lies on soil-moisture hysteresis, where the capillary pressure exhibits different values depending on the initial state of saturation. An historical overview is given of the investigation of this phenomenon, of various empirical models, and also of some mathematical approaches to soil-moisture hysteresis. All these studies are aimed at accurately fitting experimental results - not only the main hysteresis curves but also the inner hysteresis curves that occur upon re-wetting and re-drying. Finally, a comparison is made to another field in which hysteresis appears, the deformation of pseudoelastic bodies such as shape memory alloys. © 2014 Springer-Verlag Wien. Source

Fazelpour F.,Islamic Azad University at South Tehran | Morosuk T.,TU Berlin
International Journal of Refrigeration | Year: 2014

In the last two decades many scientific papers and reports have been published in the field of the application of the carbon dioxide as a refrigerant for refrigeration (heat pump) systems. A simple transcritical CO2 refrigeration machine is evaluated from the perspectives of energetic, exergetic, economic and exergoeconomic analyses. Special attention has been paid to the transcritical cycle under hot climatic conditions. The main goal of this paper is to define the energy and cost efficient transcritical CO2 refrigeration machine, therefore the options for the structure and parametric improvements are discussed. Introducing the economizer as an auxiliary component for one-stage transcritical CO2 refrigeration machine helps us to decrease the total cost of the final product by approximately 14%. © 2013 Elsevier Ltd and IIR. All rights reserved. Source

Kratsch S.,TU Berlin | Philip G.,Max Planck Institute for Informatics | Ray S.,Ben - Gurion University of the Negev
Proceedings of the Annual ACM-SIAM Symposium on Discrete Algorithms | Year: 2014

The input to the NP-hard Point Line Cover problem (PLC) consists of a set V of n points on the plane and a positive integer k, and the question is whether there exists a set of at most k lines which pass through all points in V. By straightforward reduction rules one can efficiently reduce any input to one with at most k2 points. We show that this easy reduction is already essentially tight under standard assumptions. More precisely, unless the polynomial hierarchy collapses to its third level, for any ε > 0, there is no polynomial-time algorithm that reduces every instance (P, k) of PLC to an equivalent instance with O(k2-ε) points. This answers, in the negative, an open problem posed by Lokshtanov (PhD Thesis, 2009). Our proof uses the notion of a kernel from parameterized complexity, and the machinery for deriving lower bounds on the size of kernels developed by Dell and van Melkebeek (STOC 2010). It has two main ingredients: We first show, by reduction from Vertex Cover, that-unless the polynomial hierarchy collapses-PLC has no kernel of total size O(k2-ε) bits. This does not directly imply the claimed lower bound on the number of points, since the best known polynomial-time encoding of a PLC instance with n points requires ω(n 2) bits. To get around this hurdle we build on work of Goodman, Pollack and Sturmfels (STOC 1989) and devise an oracle communication protocol of cost O(n log n) for PLC; its main building blocks are a bound of O(N O(n)) for the order types of n points that are not necessarily in general position and an explicit (albeit slow) algorithm that enumerates a superset of size NO(n) of all possible order types of n points. This protocol, together with the lower bound on the total size (which also holds for such protocols), yields the stated lower bound on the number of points. While a number of essentially tight polynomial lower bounds on total sizes of kernels are known, our result is-to the best of our knowledge-the first to show a nontrivial lower bound for structural/secondary parameters. Copyright © 2014 by the Society for Industrial and Applied Mathematics. Source

Muller M.,TU Berlin
Theoretical Computer Science | Year: 2010

Kolmogorov complexity and algorithmic probability are defined only up to an additive resp. multiplicative constant, since their actual values depend on the choice of the universal reference computer. In this paper, we analyze a natural approach to eliminate this machine-dependence. Our method is to assign algorithmic probabilities to the different computers themselves, based on the idea that "unnatural" computers should be hard to emulate. Therefore, we study the Markov process of universal computers randomly emulating each other. The corresponding stationary distribution, if it existed, would give a natural and machine-independent probability measure on the computers, and also on the binary strings. Unfortunately, we show that no stationary distribution exists on the set of all computers; thus, this method cannot eliminate machine-dependence. Moreover, we show that the reason for failure has a clear and interesting physical interpretation, suggesting that every other conceivable attempt to get rid of those additive constants must fail in principle, too. However, we show that restricting to some subclass of computers might help to get rid of some amount of machine-dependence in some situations, and the resulting stationary computer and string probabilities have beautiful properties. © 2009 Elsevier B.V. All rights reserved. Source

Voss M.,TU Berlin
International Journal of Project Management | Year: 2012

The growing number of company projects requires comprehensive management, project portfolio management (PPM), for strategic alignment and efficient use of resources. In parallel, companies face customers demanding higher value, and joint value creation with customers is considered a key success factor in the future. Project portfolios delivering products and services for customers implicate a link between PPM and an increased customer focus. Combining the research fields of marketing and PPM for the first time, this study proposes customer integration into PPM. I develop a framework describing the impact of customer integration into PPM on project portfolio success mediated through relationship value. Furthermore, the study describes relevant aspects for customer integration on the project portfolio level and identifies interfaces for cross-functional integration of a customer portfolio representative within the PPM process. The findings and limitations of this study are discussed, and further research is suggested. © 2012 Elsevier Ltd. Source

Got ammo? In the search for sustainable and environmentally benign primary aniline synthesis, the application of ammonia instead of currently applied ammonia surrogates is one major challenge in catalysis. Recent efforts in palladium- and copper-catalyzed transformations of ammonia to anilines are discussed in this Highlight. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Weinland D.,TU Berlin | Ronfard R.,French Institute for Research in Computer Science and Automation | Boyer E.,French Institute for Research in Computer Science and Automation
Computer Vision and Image Understanding | Year: 2011

Action recognition has become a very important topic in computer vision, with many fundamental applications, in robotics, video surveillance, human-computer interaction, and multimedia retrieval among others and a large variety of approaches have been described. The purpose of this survey is to give an overview and categorization of the approaches used. We concentrate on approaches that aim on classification of full-body motions, such as kicking, punching, and waving, and we categorize them according to how they represent the spatial and temporal structure of actions; how they segment actions from an input stream of visual data; and how they learn a view-invariant representation of actions. © 2010 Elsevier Inc. All rights reserved. Source

Heising W.,TU Berlin
International Journal of Project Management | Year: 2012

Effective management of single projects is no longer sufficient. In today's business market, proactive management of the whole project portfolio has become increasingly important for achieving long-term success and competitive advantage. At the front end of projects, opportunities are discovered, ideas are created, and the foundation for later project, portfolio, and, eventually, corporate success is laid. This paper contributes to the project management body of knowledge by combining the front end view on projects with the holistic view of managing project portfolio landscapes. It focuses on establishing a framework for conceptualization of the relationship between ideation and project portfolio management in product development environment by relating . ideation portfolio management, . front end success, and . project portfolio success, and lays the groundwork for further empirical research. The overarching topic I address is the conceptualization of how ideation can facilitate and sustainably improve portfolio success in the product development environment in the long-term. © 2012 Elsevier Ltd. Source

Alexa M.,TU Berlin | Wardetzky M.,University of Gottingen
ACM Transactions on Graphics | Year: 2011

While the theory and applications of discrete Laplacians on triangulated surfaces are well developed, far less is known about the general polygonal case. We present here a principled approach for constructing geometric discrete Laplacians on surfaces with arbitrary polygonal faces, encompassing non-planar and non-convex polygons. Our construction is guided by closely mimicking structural properties of the smooth Laplace-Beltrami operator. Among other features, our construction leads to an extension of the widely employed cotan formula from triangles to polygons. Besides carefully laying out theoretical aspects, we demonstrate the versatility of our approach for a variety of geometry processing applications, embarking on situations that would have been more difficult to achieve based on geometric Laplacians for simplicial meshes or purely combinatorial Laplacians for general meshes. © 2011 ACM. Source

Gillis N.,University of Mons | Luce R.,TU Berlin
Journal of Machine Learning Research | Year: 2014

Nonnegative matrix factorization (NMF) has been shown recently to be tractable under the separability assumption, under which all the columns of the input data matrix belong to the convex cone generated by only a few of these columns. Bittorf, Recht, Re and Tropp (̀Factoring nonnegative matrices with linear programs', NIPS 2012) proposed a linear programming (LP) model, referred to as Hottopixx, which is robust under any small perturbation of the input matrix. However, Hottopixx has two important drawbacks: (i) the input matrix has to be normalized, and (ii) the factorization rank has to be known in advance. In this paper, we generalize Hottopixx in order to resolve these two drawbacks, that is, we propose a new LP model which does not require normalization and detects the factorization rank automatically. Moreover, the new LP model is more exible, signi ficantly more tolerant to noise, and can easily be adapted to handle outliers and other noise models. Finally, we show on several synthetic data sets that it outperforms Hottopixx while competing favorably with two state-of-the-art methods. © 2014 Nicolas Gillis and Robert Luce. Source

Peltola M.,Finnish National Institute for Health and Welfare | Quentin W.,TU Berlin
Cerebrovascular Diseases | Year: 2013

Background: Diagnosis-related groups (DRGs) are increasingly being used for various purposes in many countries. However, there are no studies comparing different DRG systems in the care of stroke. As part of the EuroDRG project, researchers from 11 countries (i.e. Austria, England, Estonia, Finland, France, Germany, Ireland, the Netherlands, Poland, Sweden and Spain) compared how their DRG systems deal with stroke patients. The study aims to assist clinicians and national authorities to optimize their DRG systems. Methods: National or regional databases were used to identify hospital cases with a diagnosis of stroke. DRG classification algorithms and indicators of resource consumption were compared for those DRGs that individually represent at least 1% of stroke cases. In addition, standardized case vignettes were defined, and quasi prices according to national DRG-based hospital payment systems were ascertained. Results: European DRG systems vary widely: they classify stroke patients according to different sets of variables (between 1 and 7 classification variables) into diverging numbers of DRGs (between 1 and 10 DRGs). In 6 of the countries more than half of the patients are concentrated within a single DRG. The countries' systems also vary with respect to the evaluation of different kinds of stroke patients. The most complex DRG is considered 3.8 times more resource intensive than an index case in Finland. By contrast, in England, the DRG system does not account for complex cases. Comparisons of quasi prices for the case vignettes show that hypothetical payments for the index case amount to only EUR 907 in Poland but to EUR 7,881 in Ireland. Conclusions: Large variations in the classification of stroke patients raise concerns whether all systems rely on the most appropriate classification variables and whether the DRGs adequately reflect differences in the complexity of treating different groups of patients. Learning from other DRG systems may help in improving the national systems. Clinicians and national DRG authorities should consider how other countries' DRG systems classify stroke patients in order to optimize their DRG system and to ensure fair and appropriate reimbursement. In future, quantitative research is needed to verify whether the most important determinants of cost are considered in different patient classification systems, and whether differences between systems reflect country-specific differences in treatment patterns and, most importantly, what influence they have on patient outcomes. Copyright © 2013 S. Karger AG, Basel. Source

Barjenbruch M.,TU Berlin
Desalination and Water Treatment | Year: 2012

In rural areas, the quality of the water bodies will continue to be influenced by the purification performances of small and smaller wastewater treatment plants (WWTPs). In this paper, the different methods of wastewater discharge and treatment currently available for rural areas were presented. Today, both technical and natural methods achieve purification results which are equivalent to, if less stable than those of larger technical pants, provided that dimensioning, design, and operation are optimally cared for. The general question will be to decide for a centralized wastewater system or for local, on-site solution installing small treatment plants. Important criteria for this decision as the distance between the houses and also crucial dimensioning parameters like the amount of wastewater will be given within the report. Several wastewater treatment technologies will be explained and also results from the SBR-System, which are applied in Germany special in smaller communities, are discussed. The evaluation of monitoring values showed that on average the required effluent qualities could be obtained. But still one has to consider that there are technical and economic limits of the degree to which WWTPs can be cared for in rural areas. For on-site treatment the main reasons is the organization of a good operation, maintenance and surveillance. © 2012 Desalination Publications. Source

Jun Y.-S.,University of California at Santa Barbara | Lee E.Z.,Korea Advanced Institute of Science and Technology | Wang X.,Fuzhou University | Hong W.H.,Korea Advanced Institute of Science and Technology | And 2 more authors.
Advanced Functional Materials | Year: 2013

Graphitic carbon nitride (g-CN) is a promising heterogeneous metal-free catalyst for organic photosynthesis, solar energy conversion, and photodegradation of pollutants. Its catalytic performance is easily adjustable by modifying texture, optical, and electronic properties via nanocasting, doping, and copolymerization. However, simultaneous optimization has yet to be achieved. Here, a facile synthesis of mesoporous g-CN using molecular cooperative assembly between triazine molecules is reported. Flower-like, layered spherical aggregates of melamine cyanuric acid complex (MCA) are formed by precipitation from equimolecular mixtures in dimethyl sulfoxide (DMSO). Thermal polycondensation of MCA under nitrogen at 550°C produces mesoporous hollow spheres comprised of tri-s-triazine based g-CN nanosheets (MCA-CN) with the composition of C3N4.14H1.98. The layered structure succeeded from MCA induces stronger optical absorption, widens the bandgap by 0.16 eV, and increases the lifetime of photoexcited charge carriers by twice compared to that of the bulk g-CN, while the chemical structure remains similar to that of the bulk g-CN. As a result of these simultaneous modifications, the photodegradation kinetics of rhodamine B on the catalyst surface can be improved by 10 times. Simple molecular engineering of triazine precursors enables simultaneous optimization of the texture and photoelectric properties of graphitic carbon nitride (g-CN). Thermolysis of flower-like supramolecular aggregates of melamine and cyanuric acid yields the formation of mesoporous g-CN hollow spheres with the typical nanosheet-type structure preserved in the microspheres. Such structures are highly active in the photocatalytic degradation of organic pollutants. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Illge L.,TU Berlin | Preuss L.,Royal Holloway, University of London
Corporate Social Responsibility and Environmental Management | Year: 2012

This case study examines the strategies by two very different types of textile companies for supplying garments in a more sustainable way: Sweden-based H&M, a large international firm, and hessnatur of Germany, a small niche player. In particular, the case discusses the strategies the two companies have adopted with regard to managing supplier relations and monitoring adherence to social and environmental standards. The case also discusses the respective implications the two companies' strategies have on society. It aims to stimulate critical thinking regarding the multiple ways in which corporate strategies affect the sustainability footprint of both the company and the wider society in which the company is embedded. The case study should thus be of interest to students of strategic management, but also be useful to those interested in sustainable development or supply chain management. © 2012 John Wiley & Sons, Ltd and ERP Environment. Source

Tsatsaronis G.,TU Berlin | Morosuk T.,Maritime University Of Szczecin
Energy | Year: 2010

LNG technology has been in use since the 1960s. During the last 20 years the total cost of LNG technology has decreased by 30% due mainly to improvements of the liquefaction process and shipping. However, the regasification system has not been significantly improved. The paper presents a detailed advanced exergetic analysis of a novel co-generation concept that combines LNG regasification with the generation of electricity. The analysis includes splitting the exergy destruction within each component into its unavoidable, avoidable, endogenous and exogenous parts as well as a detailed splitting of the avoidable exogenous exergy destruction. The results of the advanced exergetic analysis are confirmed through a sensitivity analysis. Finally, some suggestions for improving the overall system efficiency are developed. © 2009 Elsevier Ltd. All rights reserved. Source

Hohne J.,TU Berlin
2010 Annual International Conference of the IEEE Engineering in Medicine and Biology Society, EMBC'10 | Year: 2010

P300-based Brain Computer Interfaces offer communication pathways which are independent of muscle activity. Mostly visual stimuli, e.g. blinking of different letters are used as a paradigm of interaction. Neural degenerative diseases like amyotrophic lateral sclerosis (ALS) also cause a decrease in sight, but the ability of hearing is usually unaffected. Therefore, the use of the auditory modality might be preferable. This work presents a multiclass BCI paradigm using two-dimensional auditory stimuli: cues are varying in pitch (high/medium/low) and location (left/middle/right). The resulting nine different classes are embedded in a predictive text system, enabling to spell a letter with a 9-class decision. Moreover, an unbalanced subtrial selection is investigated and compared to the wellestablished sequence-wise paradigm. Twelve healthy subjects participated in an online study to investigate these approaches. © 2010 IEEE. Source

Reck B.K.,Yale University | Rotter V.S.,TU Berlin
Journal of Industrial Ecology | Year: 2012

This study introduces the 2005 life cycle data for nickel in 50 countries and presents a comparative analysis of the 2000 and 2005 nickel and stainless steel cycles for these countries. The life cycles of the two metals are linked by nickel's role as a major alloying element in most stainless steels. Between 2000 and 2005, the global use of both metals grew, driven by China's extraordinary growth and despite the fact that many industrialized countries decreased their metal use during that time. China's and India's growth of stainless steel use was greater than that of nickel use, a result of price-driven substitution away from nickel-containing stainless steels. The intensity of use (IU) in industrialized countries is about 30 to 50 kilograms (kg) nickel/million U.S. dollars (USD), and 300 to 500 kg stainless steel/million USD. High-income countries decreased their IU of both metals between 2000 and 2005, while low- and medium-income countries increased their IU of stainless steel. At the per capita level, average industrialized countries use about 1 kg of nickel and 11 kg of stainless steel. Were China's and India's projected urban areas in 2025 to use similar amounts of the two metals, they alone would require the equivalent of global nickel production in 2000, and 200% of the world's stainless steel production in 2005. In China, substantial nickel and stainless steel end-of-life flows will arise between 2015 and 2020, and efficient collection and separation systems should be prepared now to maximize the potential environmental and resource benefits of recycling. © 2012 by Yale University. Source

Stantchev V.,TU Berlin | Malek M.,Humboldt University of Berlin
IEEE Transactions on Services Computing | Year: 2011

Dependability should be considered throughout the phases of the SOA life cycle. This article proposes the application of a service level management approach to address dependability and presents dependability-related activities for every stage (Model, Assemble, Deploy, and Manage) of the SOA life cycle. Furthermore, we describe the concepts and the formalisms that are behind these activities. Following these activities service providers and aggregators can offer optimized levels of dependability from their existing services and thus better meet user requirements. © 2011 IEEE. Source

Schultz C.,TU Berlin
Journal of Combinatorial Theory. Series A | Year: 2011

The stable Kneser graph SGn,k, n≥1, k≥0, introduced by Schrijver (1978) [19], is a vertex critical graph with chromatic number k+2, its vertices are certain subsets of a set of cardinality m=2n+k. Björner and de Longueville (2003) [5] have shown that its box complex is homotopy equivalent to a sphere, Hom(K2,SGn,k)≃Sk. The dihedral group D2m acts canonically on SGn,k, the group C2 with 2 elements acts on K2. We almost determine the (C2×D2m)-homotopy type of Hom(K2,SGn,k) and use this to prove the following results. The graphs SG2s,4 are homotopy test graphs, i.e. for every graph H and r≥0 such that Hom(SG2s,4,H) is (r-1)-connected, the chromatic number χ(H) is at least r+6.If k∉{0,1,2,4,8} and n≥N(k) then SGn,k is not a homotopy test graph, i.e. there are a graph G and an r≥1 such that Hom(SGn,k,G) is (r-1)-connected and χ(G) Source

Harks T.,TU Berlin
Theory of Computing Systems | Year: 2011

We study the impact of collusion in network games with splittable flow and focus on the well established price of anarchy as a measure of this impact. We first investigate symmetric load balancing games and show that the price of anarchy is at most m, where m denotes the number of coalitions. For general networks, we present an instance showing that the price of anarchy is unbounded, even in the case of two coalitions. If latencies are restricted to polynomials with nonnegative coefficients and bounded degree, we prove upper bounds on the price of anarchy for general networks, which improve upon the current best ones except for affine latencies. In light of the negative results even for two coalitions, we analyze the effectiveness of Stackelberg strategies as a means to improve the quality of Nash equilibria. In this setting, an α fraction of the entire demand is first routed centrally by a Stackelberg leader according to a predefined Stackelberg strategy and the remaining demand is then routed selfishly by the coalitions (followers). For a single coalitional follower and parallel arcs, we develop an efficiently computable Stackelberg strategy that reduces the price of anarchy to one. For general networks and a single coalitional follower, we show that a simple strategy, called SCALE, reduces the price of anarchy to 1+α. Finally, we investigate SCALE for multiple coalitional followers, general networks, and affine latencies. We present the first known upper bound on the price of anarchy in this case. Our bound smoothly varies between 1.5 for α=0 and full efficiency for α=1. © 2010 Springer Science+Business Media, LLC. Source

Schulze B.,TU Berlin | Whiteley W.,York University
Discrete and Computational Geometry | Year: 2011

A number of recent papers have studied when symmetry causes frameworks on a graph to become infinitesimally flexible, or stressed, and when it has no impact. A number of other recent papers have studied special classes of frameworks on generically rigid graphs which are finite mechanisms. Here we introduce a new tool, the orbit matrix, which connects these two areas and provides a matrix representation for fully symmetric infinitesimal flexes, and fully symmetric stresses of symmetric frameworks. The orbit matrix is a true analog of the standard rigidity matrix for general frameworks, and its analysis gives important insights into questions about the flexibility and rigidity of classes of symmetric frameworks, in all dimensions. With this narrower focus on fully symmetric infinitesimal motions, comes the power to predict symmetry-preserving finite mechanisms-giving a simplified analysis which covers a wide range of the known mechanisms, and generalizes the classes of known mechanisms. This initial exploration of the properties of the orbit matrix also opens up a number of new questions and possible extensions of the previous results, including transfer of symmetry based results from Euclidean space to spherical, hyperbolic, and some other metrics with shared symmetry groups and underlying projective geometry. © 2010 Springer Science+Business Media, LLC. Source

Tautz R.C.,TU Berlin
Astronomy and Astrophysics | Year: 2016

The random walk of energetic charged particles in turbulent magnetic fields is investigated. Special focus is placed on transport across the mean magnetic field, which had been found to be subdiffusive on many occasions. Therefore, a characterization using the concept of ergodicity is attempted by noting the connection to the time evolution of the mean-square displacement. Methods. Based on the test-particle approach, a numerical Monte Carlo simulation code is used to integrate the equation of motion for particles that are scattered by magnetic turbulence. The turbulent fields are generated by superposing plane waves with a Kolmogorov-type power spectrum. The individual particle trajectories are then used to calculate a variety of statistical quantities. Results. The simulation results clearly demonstrate how the heterogeneity of the particle ensemble causes the system to be weakly non-ergodic. In addition, it is shown how the step length distribution varies with the particle energy. In conclusion, cross-field transport is non-Gaussian but still almost diffusive. © 2016 ESO. Source

Markl V.,TU Berlin
Proceedings of the VLDB Endowment | Year: 2014

Data management research, systems, and technologies have drastically improved the availability of data analysis capa-bilities, particularly for non-experts, due in part to low-en-try barriers and reduced ownership costs (e.g., for data management infrastructures and applications). Major reasons for the widespread success of database systems and today's multi-billion dollar data management market include data independence, separating physical representation and storage from the actual information, and declarative languages, separating the program specification from its intended execution environment. In contrast, today's big data solutions do not offer data independence and declarative specification. As a result, big data technologies are mostly employed in newly-established companies with IT-savvy employees or in large well-estab-lished companies with big IT departments. We argue that current big data solutions will continue to fall short of widespread adoption, due to usability problems, despite the fact that in-situ data analytics technologies achieve a good degree of schema independence. In particular, we consider the lack of a declarative specification to be a major road-block, contributing to the scarcity in available data scien-tists available and limiting the application of big data to the IT-savvy industries. In particular, data scientists currently have to spend a lot of time on tuning their data analysis programs for specific data characteristics and a specific execution environment. We believe that the research com-munity needs to bring the powerful concepts of declarative specification to current data analysis systems, in order to achieve the broad big data technology adoption and effectively deliver the promise that novel big data technolo-gies offer. © 2014 VLDB Endowment 2150-8097/14/08. Source

Ghazisaidi N.,INRS - Institute National de la Recherche Scientifique | Scheutzow M.,TU Berlin | Maier M.,INRS - Institute National de la Recherche Scientifique
IEEE Transactions on Reliability | Year: 2011

Passive optical networks (PONs) are currently evolving into next-generation PONs (NG-PONs) which aim at achieving higher data rates, wavelength channel counts, number of optical network units (ONUs), and extended coverage compared to their conventional counterparts. Due to the increased number of stages and ONUs, NG-PONs face significant challenges to provide the same level of survivability like conventional PONs without exceeding the budget constraints of cost-sensitive access networks. Toward this end, partial optical protection, in combination with interconnecting a subset of ONUs through a wireless mesh network (WMN) front-end, are promising solutions to render NG-PONs survivable in a cost-effective manner. In this paper, we present a probabilistic analysis of the survivability of NG-PONs and hybrid fiber-wireless (FiWi) access networks, taking both optical and wireless protection into account. In addition, we propose different selection schemes to wirelessly upgrade a subset of ONUs, and investigate their performance for a wide range of fiber link failure scenarios and different NG-PON topologies. © 2011 IEEE. Source

Su Q.,University of Washington | Strunz K.,TU Berlin
IEEE Transactions on Power Electronics | Year: 2011

With the introduction of variable-frequency generators in next-generation more-electric aircraft, both voltage and frequency are to reveal significant tolerance levels. In this study, a method based on the combination of polynomial chaos and nodal analysis is developed to identify and quantify the impact of such tolerance in ac/dc diode rectifiers and dc/dc switch-mode converters. The resulting stochastic average models track the transients of the tolerance limits and related information in the time domain both accurately and efficiently. The relative merits of the method are substantiated through a comparative analysis with the Monte Carlo and root-sum-square methods. © 2011 IEEE. Source

Typically the cooling capacity of absorption chillers is controlled by adjusting the driving hot water temperature according to the load. Meanwhile the cooling water temperature is controlled to a constant set value. In order to increase the solar cooling fraction and/or to decrease the operating costs of solar assisted cooling systems (SAC-systems) a new control strategy has been developed which controls hot and cooling water temperature simultaneously. Hereby the specific cost of cold - generated from solar or conventional heat - can be reduced. The basic concept of the strategy is explained and results are shown for the SAC-system at the Federal Environment Agency in Dessau, Germany. Here a recently developed absorption chiller is now used instead of a former adsorption chiller. With the new absorption chiller and the control strategy the seasonal energy efficiency ratio SEER is above 0.75, electric efficiency is 35% higher and water consumption is reduced by 70%. © 2013 Elsevier Ltd and IIR. All rights reserved. Source

Grigor'eva and Nakoryakov presented an analytical solution for combined heat and mass transfer in laminar falling films by means of the Fourier method. The obtained solutions exhibited mathematical instabilities for small flow length, such as oscillations in the mass fraction profile and a mismatch of the inlet temperature. Grigor'eva and Nakoryakov explained these instabilities with the inconsistency of the inlet and boundary conditions and therefore an additional short term solution was introduced. In the present study the established tangent function, that is used to determine the eigenvalues within the Fourier method, is rearranged to a term without domain restrictions. Consequently, more eigenvalues are found, leading to a physical valid solution even for small flow lengths, matching the results of the short term solution perfectly. © 2014 Elsevier Ltd and IIR. All rights reserved. Source

Objective This paper provides a comprehensive overview of hospital payment systems based on diagnosis-related groups (DRGs) in low- and middle-income countries. It also explores design and implementation issues and the related challenges countries face. Methods A literature research for papers on DRG-based payment systems in low- and middle-income countries was conducted in English, French and Spanish through Pubmed, the Pan American Health Organization's Regional Library of Medicine and Google. Findings Twelve low- and middle-income countries have DRG-based payment systems and another 17 are in the piloting or exploratory stage. Countries have chosen from a wide range of imported and self-developed DRG models and most have adapted such models to their specific contexts. All countries have set expenditure ceilings. In general, systems were piloted before being implemented. The need to meet certain requirements in terms of coding standardization, data availability and information technology made implementation difficult. Private sector providers have not been fully integrated, but most countries have managed to delink hospital financing from public finance budgeting. Conclusion Although more evidence on the impact of DRG-based payment systems is needed, our findings suggest that (i)the greater portion of health-care financing should be public rather than private; (ii)it is advisable to pilot systems first and to establish expenditure ceilings; (iii)countries that import an existing variant of a DRG-based system should be mindful of the need for adaptation; and (iv)countries should promote the cooperation of providers for appropriate data generation and claims management. Source

Strekalova E.G.,Boston University | Mazza M.G.,TU Berlin | Stanley H.E.,Boston University | Franzese G.,University of Barcelona
Physical Review Letters | Year: 2011

Using MonteCarlo simulations, we study a coarse-grained model of a water layer confined in a fixed disordered matrix of hydrophobic nanoparticles at different particle concentrations c. For c=0, we find a first-order liquid-liquid phase transition (LLPT) ending in one critical point at low pressure P. For c>0, our simulations are consistent with a LLPT line ending in two critical points at low and high P. For c=25%, at high P and low temperature, we find a dramatic decrease of compressibility, thermal expansion coefficient, and specific heat. Surprisingly, the effect is present also for c as low as 2.4%. We conclude that even a small presence of hydrophobic nanoparticles can drastically suppress thermodynamic fluctuations, making the detection of the LLPT more difficult. © 2011 American Physical Society. Source

Hildebrandt P.,TU Berlin
Angewandte Chemie - International Edition | Year: 2010

(Figure Presented) A view of the room : A novel application of Raman microscopy takes advantage of a spectral window to map the uptake and distribution of metal-carbonyl-based drugs in single cells. The approach provides information on cell structure and molecular structure simultaneously and may have significant impact on drug screening and on the analysis of cellular processes in general. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

If we take for granted that introspection is indispensable for the study of conscious mental states, the question arises what criteria have to be met in order for introspective reports to qualify as scientific evidence. There have been some attempts to argue (implicitly or explicitly) that it is possible to provide a satisfactory answer to this question while remaining agnostic with respect to questions about the nature of consciousness. Focusing on the aim of using introspection in order to generate phenomenological descriptions of conscious mental states, this paper argues that such an agnostic stance cannot be maintained, because the very meaning of "introspection" remains fuzzy as long as we don't have a clear understanding of how the mind does it. I show that current debates revolve around some of the same issues that were already in the background of debates around 1900, and I argue that a satisfactory treatment of introspection as a method cannot be separated from the aim of providing a satisfactory treatment of introspection as a feature of consciousness. © 2012 Copyright Taylor and Francis Group, LLC. Source

Jakob M.,Potsdam Institute for Climate Impact Research | Marschinski R.,Potsdam Institute for Climate Impact Research | Marschinski R.,TU Berlin
Nature Climate Change | Year: 2013

Most industrialized countries are net importers of carbon emissions, that is, they release fewer emissions for the production of their total exported goods and services than the amount generated (by their trading partners) for producing their total imported goods and services. But what do such carbon trade-deficits imply in terms of global CO 2 emissions and the design of carbon trade-policies? Drawing on trade theory, this Perspective argues that a deeper understanding of these observed net emission transfers is required to assess how international trade affects global emissions and proposes a method to disentangle the underlying determinants of such transfers. © 2013 Macmillan Publishers Limited. All rights reserved. Source

Chiavarino B.,University of Rome La Sapienza | Crestoni M.E.,University of Rome La Sapienza | Dopfer O.,TU Berlin | Maitre P.,University Paris - Sud | Fornarini S.,University of Rome La Sapienza
Angewandte Chemie - International Edition | Year: 2012

Definitely different: The path towards sorting out a long-standing dichotomy in carbocation chemistry is disclosed by infrared multiple photon dissociation spectroscopy of tropylium and benzylium isomers of C 8H 9 + ions (see picture). Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Kurreck J.,TU Berlin
Angewandte Chemie - International Edition | Year: 2010

Great hope is placed in the use of RNA interference in the development of novel therapeutics. Recently, small interfering RNAs (siRNAs) were delivered to tumor cells of melanoma patients by nanoparticles consisting of a cyclodextrin polymer, and polyethylene glycol coupled to adamantane and transferrin (see picture). It was demonstrated that the target mRNA in the patients was degraded by a specific RNA interference mechanism. Copyright © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Kratsch S.,TU Berlin
Leibniz International Proceedings in Informatics, LIPIcs | Year: 2013

Integer linear programs (ILPs) are a widely applied framework for dealing with combinatorial problems that arise in practice. It is known, e.g., by the success of CPLEX, that preprocessing and simplification can greatly speed up the process of optimizing an ILP. The present work seeks to further the theoretical understanding of preprocessing for ILPs by initiating a rigorous study within the framework of parameterized complexity and kernelization. A famous result of Lenstra (Mathematics of Operations Research, 1983) shows that feasibility of any ILP with n variables and m constraints can be decided in time O(cn3 · mc0 ). Thus, by a folklore argument, any such ILP admits a kernelization to an equivalent instance of size O(cn3 ). It is known, that unless NP ⊆ coNP/poly and the polynomial hierarchy collapses, no kernelization with size bound polynomial in n is possible. However, this lower bound only applies for the case when constraints may include an arbitrary number of variables since it follows from lower bounds for SAT and Hitting Set, whose bounded arity variants admit polynomial kernelizations. We consider the feasibility problem for ILPs Ax ≤ b where A is an r-row-sparse matrix parameterized by the number of variables. We show that the kernelizability of this problem depends strongly on the range of the variables. If the range is unbounded then this problem does not admit a polynomial kernelization unless NP ⊆ coNP/poly. If, on the other hand, the range of each variable is polynomially bounded in n then we do get a polynomial kernelization. Additionally, this holds also for the more general case when the maximum range d is an additional parameter, i.e., the size obtained is polynomial in n + d. Source

Bar M.,Physikalisch - Technische Bundesanstalt | Scholl E.,TU Berlin | Torcini A.,CNR Institute for Complex Systems
Angewandte Chemie - International Edition | Year: 2012

Finger on the pulse: A systematic experimental study of pulse-coupled chemical oscillators with delay has confirmed a surprisingly large number of theoretical and mathematical predictions (see the dynamics for a pair of pulse-coupled oscillators; AP=antiphase (AP) and IP=in-phase oscillations, C=complex bursting dynamics, and OS=oscillator suppression). These results have implications for neuroscience and other biological fields. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Rucker C.,TU Berlin | Gunther T.,Leibniz Institute for Applied Geophysics
Geophysics | Year: 2011

Direct-current resistivity surveys usually are performed using steel rods of finite extent and grounding resistance. However, in modeling, electrodes are commonly treated as ideal point sources. We present an approach for numerical computation applying the complete electrode model (CEM), which is known from medical imaging. The electrode surface was discretized, and the partial-differential equations were extended by additional relations incorporating a contact impedance and a condition for the current flow through the electrode surface. We verified the modeling of the electrical potential using an analytical solution for a perfectly coupled half-ellipsoid current source. To quantify the influence of a finite electrode, we computed the electrode effect as the ratio between CEM and point-source solution and investigated its dependence on geometry and contact impedance. Surface measurements using rods of typical spatial extent showed electrode effects on the order of the measuring accuracy for an electrode length/spacing ratio lower than 0.2. However, the effects are more significant for closed geometries such as experimental tanks. A comparison with a point approximation for finite electrodes using point-source locations along the electrode axis showed the best agreement, with points at about 60% of the electrode extension. The contact impedance played a minor role for four-point measurements, contributing only a few percent to the electrode effect. In addition to penetrating electrodes, we investigated surface electrodes with galvanic or capacitive coupling, showing electrode effects on the same order as for penetrating electrodes. An inhomogeneous resistivity distribution clearly increased the size of the effects. We also investigate the use of CEM to simulate current injected through steel-cased boreholes. Finally, we applied the approach with buried ring electrodes to calculate effects caused mainly by geometric disturbances from the borehole. © 2011 Society of Exploration Geophysicists. Source

Albers B.,TU Berlin
Transport in Porous Media | Year: 2011

Due to its propitious material properties sandstone is the most studied porous medium for the investigation of linear wave propagation. However, in practical applications the behavior of other soil types, i.e., especially the three main soil types sand, silt, and clay, are much more important. Therefore, the model for partially saturated soils introduced by Albers (Habilitation Thesis, 2010a) is applied to 11 soil types classified in the German standard DIN 4220 to obtain information on the phase velocities and attenuations of the three longitudinal waves and the shear wave appearing in such media. © 2010 Springer Science+Business Media B.V. Source

Maertens M.,TU Berlin
Journal of vision | Year: 2013

A fundamental question in visual perception research is whether the sensitivity to stimulus differences is limited by the sensory representation of the external stimulus, that is, the proximal stimulus, or by its perceptual representation, i.e., stimulus appearance. In the domain of lightness perception, the question translates into whether discrimination thresholds depend on the local luminance in the retinal image or on the apparent lightness of the corresponding image region. The majority of findings seem to indicate that sensitivity is limited by the sensory stimulus representation, which would imply different mechanisms for stimulus discrimination and appearance. We think this conclusion needs to be qualified. We report data suggesting that the relationship between discrimination and appearance judgments depends on how exactly they are being measured. We propose a theoretical account that provides a common mechanism for appearance and sensitivity. An interesting corollary of this model is that it also accounts for the perceptual phenomenon of assimilation. Source

Emary C.,TU Berlin
Journal of Physics Condensed Matter | Year: 2011

We develop a self-consistent version of perturbation theory in Liouville space which seeks to combine the advantages of master equation approaches in quantum transport with the nonperturbative features that a self-consistent treatment brings. We describe how counting fields may be included in a self-consistent manner in this formalism such that the full counting statistics can be calculated. Non-Markovian effects are also incorporated. Several different self-consistent approximations are introduced and we discuss their relative strengths with a simple example. © 2011 IOP Publishing Ltd. Source

Erdmann L.,TU Berlin | Graedel T.E.,Yale University
Environmental Science and Technology | Year: 2011

The criticality of nonfuel minerals is an emerging research subject that captures both the supply risks and the vulnerability of a system to a potential supply disruption. The significance of material criticality for the mass deployment of sustainable and other key technologies is currently obscured by diverse, often immature, and still evolving methodologies. This review explores why principal studies agree or disagree in designating the criticality of certain nonfuel minerals. We survey the literature and analyze several well documented studies in depth, demonstrating that the platinum group metals (e.g., essential for catalytic reduction of air pollutants), and the rare earth elements (e.g., essential for efficient electricity generation in wind turbines) are frequently singled out as critical, albeit by differing criteria. We also discuss the impacts of methodological choices on the designation of raw materials as critical. The treatment of substitutability, time horizons, and the aggregation level of criticality indicators are shown to be significant in this regard. We determine several important issues that have thus far been largely disregarded, especially the justification of methodological components, and policy responses to criticality designation. © 2011 American Chemical Society. Source

Widyan M.S.,Hashemite University | Hanitsch R.E.,TU Berlin
International Journal of Electrical Power and Energy Systems | Year: 2012

Compared with conventional electrical machines, permanent-magnet (PM) machines experience higher efficiency, higher power-to-weight ratio and simpler construction. In this paper, a new three-slot three-phase four-pole rare-earth radial-flux PM variable-speed electrical generator is proposed, designed using Finite Element Technique (FET) and is investigated. In this topology, the soft magnetic material of the rotor is placed at the pole faces of the rectangular high-energy magnets. An air-gap flux density distribution very close to sinusoidal is achieved by curving the faces of the rotor soft magnetic pieces. The steady-state characteristics at different rotational speeds and loading conditions are addressed and compared. Basically, slotted PM electrical machines suffer from cogging torque. The cogging torque of this generator is predicted and compared to the rated value of the machine. The windings, located at flat slots, have short ends which therefore adds further improvements on the efficiency, power-to-weight ratio, operational performance and cost of active material. The obtained output operational performance characteristics of this generator along with the acceptable peak value of the cogging torque demonstrate the success of the topology and the effectiveness of the design methodology. © 2012 Elsevier Ltd. All rights reserved. Source

This paper presents an application of an indirect method, the alternative or replacement cost method to value a regulatory ecosystem service: the retention of river nutrient loads by floodplain wetlands. The paper presents a cost-minimisation model for nutrient abatement measures for the River Elbe. The model is applied to estimate the shadow price of phosphate and nitrogen nutrient retention services by restored floodplains. It is shown that the shadow price of restored floodplain area is a function of the nutrient load reduction target for the river basin. The scope of the floodplain restoration projects is shown to have a lesser impact on the estimated shadow price.In addition, this paper presents an empirical cost function for the costs of floodplain restoration measures in the Elbe Basin. In conjunction with the shadow prices, this allows for a rapid strategic assessment of the costs and benefits of 45 potential restoration sites along the Elbe trajectory. In spite of the large investment costs for dike realignments, the nutrient retention effects alone may in many cases generate sufficient benefits to generate an economic efficiency gain. Floodplain restoration may therefore, under advantageous circumstances, constitute a cost effective nutrient abatement measure. However the key thrust of the argument is that floodplain restoration projects have to be assessed as multifunctional projects, with the positive impacts on water quality being one of several benefit dimensions. © 2012 . Source

Peuckert J.,TU Berlin
Environmental Innovation and Societal Transitions | Year: 2014

In diametrical opposition to standard predictions, the theory of lead markets conjectures potential competitiveness gains from environmental regulation. Evidence for the actual impact direction and its determinants has however so far been inconclusive. Examining different regulation characteristics and distinguishing between their long-term and short-term effects brings the two seemingly contradictory concepts in line. Based on Executive Opinion Surveys that are annually conducted by the WEF and the IMD, country-level competitiveness effects are evaluated and the determinants are estimated in a panel regression. The estimation results call for a flexible regulation design that allows for different ways of achieving compliance. The fact that regulatory pressure is found to be strongly associated with a more positive perception of long-term impacts lends support to the induced-innovation-hypothesis. While controlling for potential effects from affluence, market size and trade openness, the impact on long-term competitiveness seems also to be affected by environmental quality institutions. © 2013 Elsevier B.V. All rights reserved. Source

Groh S.,TU Berlin
Energy for Sustainable Development | Year: 2014

This paper empirically assesses energy poverty from an end-user perspective. The concept of an energy poverty penalty is developed arguing that people that are deprived of a certain level of energy service quality (e.g. lack access to the grid) spend more money on energy relative to their total income than people who enjoy better energy service quality. Additionally, it is tested whether these people also pay more in absolute terms given the same income level measured by asset indices. Both conditions are met in the analysis of a conducted dataset consisting of 342 households and micro-businesses in the rural area of Arequipa, Peru. Mobile phone network coverage is used as proxy for remoteness criteria and to build data strata, thus facilitating model replication for different geographical areas and a systematic measurement of structural handicaps. It is further shown that it serves as a better proxy for remoteness than the mere measure of distance to the capital. Income is proxied by two forms of asset indices further representing pure asset poverty and multidimensional poverty. The penalty is found to be most prevalent in the lowest income segments. The paper sheds light on the relationship between energy poverty, remoteness and implications for the people's development opportunities. The proof of the energy poverty penalty has strong implications for the present perception of energy poverty. Its existence raises questions on the impact of this penalty with respect to causing a trap that is delaying (rural) development at the household level or even prohibiting the development path. It leads to further discussion on the causality between energy service quality and economic development at low-income segments in a country. © 2013 International Energy Initiative. Published by Elsevier Ltd. All rights reserved. Source

The potential role of bioenergy in the future energy mix and the performance of bioenergy conversion and use is a controversial issue. Life cycle assessment (LCA) is the key tool to assess the performance and impacts of bioenergy systems and services. As a fairly complex and costly tool, LCAs are rarely applied on small-scale rural settings, which at the same time make up for the largest share of global bioenergy demand. This study proposes an analytical model for rural energy service pathways (RESPs), which supports a simplified and manageable small-scale bioenergy planning by comparing energy and cost efficiencies as well as by pre-assessing possible livelihood impacts of rural energy service pathways for lighting, cooking and mechanical power. The model has been applied on a case study on the Indonesian island Sumbawa that uses the oil bearing scrub . Jatropha curcas L. to provide rural energy services. Results of the quantitative and qualitative analyses are combined to evaluate different energy service pathways. Results show strong differences for the investigated service pathways. Cooking with plant oil or biogas cannot compete with firewood from the energy and cost analysis while the negative health impact of particulate matter support liquid and gaseous fuels as long as no low-emission wood stoves are available. Lighting with plant oil or biogas is not supported by both the quantitative and qualitative analyses. The provision of mechanical power shows the greatest potential if the technical service pathways can be further optimised and the institutional challenges can be solved. © 2012 International Energy Initiative. Source

Emary C.,University of Hull | Emary C.,TU Berlin
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences | Year: 2013

Feedback control in quantum transport has been predicted to give rise to several interesting effects, among them quantum state stabilization and the realization of a mesoscopic Maxwell's daemon. These results were derived under the assumption that control operations on the system are affected instantaneously after the measurement of electronic jumps through it. In this contribution, I describe how to include a delay between detection and control operation in the master equation theory of feedback-controlled quantum transport. I investigate the consequences of delay for the state stabilization and Maxwell's daemon schemes. Furthermore, I describe how delay can be used as a tool to probe coherent oscillations of electrons within a transport system and how this formalism can be used to model finite detector bandwidth. © 2013 The Author(s) Published by the Royal Society. All rights reserved. Source

Schwarz H.,TU Berlin
Angewandte Chemie - International Edition | Year: 2015

Gas-phase investigations of judiciously doped oxide clusters permit to address fundamental challenges related to, for example, the lowerature oxidation of CO or the selective conversion of hydrocarbons. Modifying the size and composition of a free cluster in a controlled way enables the modification of local charge effects and of spin states, and spectroscopic studies in combination with computational work help to identify the active site of a catalyst and to unravel mechanistic details. Also, the interplay of the support material with the reactive part of a composite catalyst cluster can be addressed. Examples will be presented demonstrating how and why the gas-phase reactivities of heteronuclear clusters, in comparison with their homonuclear counterparts, toward small, generally rather inert molecules can be increased, decreased, or not significantly affected. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Nolte G.,Intelligent Group | Muller K.-R.,TU Berlin
Frontiers in Human Neuroscience | Year: 2010

Estimating brain connectivity and especially causality between different brain regions from EEG or MEG is limited by the fact that the data are a largely unknown superposition of the actual brain activities. Any method, which is not robust to mixing artifacts, is prone to yield false positive results. We here review a number of methods that allow for addressing this problem. They are all based on the insight that the imaginary part of the cross-spectra cannot be explained as a mixing artifact. First, a joined decomposition of these imaginary parts into pairwise activities separates subsystems containing different rhythmic activities. Second, assuming that the respective source estimates are least overlapping, yields a separation of the rhythmic interacting subsystem into the source topographies themselves. Finally, a causal relation between these sources can be estimated using the newly proposed measure Phase Slope Index (PSI). This work, for the first time, presents the above methods in combination; all illustrated using a single, simulated data set. © 2010 Nolte and Mueller. Source

Fleck C.,TU Berlin | Eifler D.,University of Kaiserslautern
International Journal of Fatigue | Year: 2010

In recent years, implants have gained growing importance in all areas of medicine. Of these, orthopaedic and dental implants are routinely exposed to high mechanical loads such as friction and wear together with multiaxial, multistep fatigue. Sustaining these loads is one prime challenge of these implants which is complicated by the need to survive in body electrolytes (proteins, enzymes, salts) that are very corrosive. Even though titanium and its alloys form a very stable oxide layer in physiological environments bestowing them exceptional biocompatibility as compared to other metal implant materials, surface reactions do take place. Such reactions, for example ion exchange or adsorption of proteins, determine the quality and stability of the bone-implant-interface, and consequently mechanical activation of the surface plays an important role. The present paper reviews the current knowledge on the corrosion, fatigue, and corrosion fatigue behaviour of titanium and its alloys, with a special emphasis on the influence of simulated in vivo conditions. © 2009 Elsevier Ltd. All rights reserved. Source

Grote M.,TU Berlin
Journal of the History of Biology | Year: 2013

In the context of 1960s research on biological membranes, scientists stumbled upon a curiously coloured material substance, which became called the "purple membrane." Interactions with the material as well as chemical analyses led to the conclusion that the microbial membrane contained a photoactive molecule similar to rhodopsin, the light receptor of animals' retinae. Until 1975, the find led to the formation of novel objects in science, and subsequently to the development of a field in the molecular life sciences that comprised biophysics, bioenergetics as well as membrane and structural biology. Furthermore, the purple membrane and bacteriorhodopsin, as the photoactive membrane transport protein was baptized, inspired attempts at hybrid bio-optical engineering throughout the 1980s. A central motif of the research field was the identification of a functional biological structure, such as a membrane, with a reactive material substance that could be easily prepared and manipulated. Building on this premise, early purple membrane research will be taken as a case in point to understand the appearance and transformation of objects in science through work with material substances. Here, the role played by a perceptible material and its spontaneous change of colour, or reactivity, casts a different light on objects and experimental practices in the late twentieth century molecular life sciences. With respect to the impact of chemical working and thinking, the purple membrane and rhodopsins represent an influential domain straddling the life and chemical sciences as well as bio- and material technologies, which has received only little historical and philosophical attention. Re-drawing the boundary between the living and the non-enlivened, these researches explain and model organismic activity through the reactivity of macromolecular structures, and thus palpable material substances. © 2012 Springer Science+Business Media B.V. Source

Demirel G.B.,Gazi University | Von Klitzing R.,TU Berlin
ChemPhysChem | Year: 2013

This paper addresses the synthesis and characterization of a novel temperature- and pH-responsive nanogel system based on poly(vinylcaprolactam-co- 2-dimethylaminoethyl methacrylate) [P(VCL-co-DMAEMA)] by using a surfactant-free emulsion polymerization procedure for the multiresponsive drug delivery of hydrophobic drugs. The effects of solvent, monomer, pH, and temperature were studied to tailor the average particle hydrodynamic diameters and the polydispersity index of the final particles. According to dynamic light-scattering measurements, the obtained nanogels show a narrow particle-size distribution and their hydrodynamic diameters can be varied from 81 to 368 nm. The nanogels display a re-entrant phase-transition state, and the equilibrium volume swelling ratio of the nanogels decreases drastically down to 47 °C and then increases up to 65°C. In addition, the nanogels show pH-dependent behavior. They exhibit a maximum size at pH 5.0. Rhodamine B (RhB) was chosen as a model compound for drug loading and release studies from P(VCL-co-DMAEMA) on the basis of particles in different phosphate buffer solutions at different temperatures. The temperature/pH-dependent cumulative release and ultrasound-enhanced pulsatile release properties were investigated for RhB-loaded nanogels for long-term and one-shot delivery. The nanogels display efficient delivery for both long-term and one-shot delivery systems. We provide here a proof of concept for the novel use of multiresponsive nanogels having an overall size below 200 nm as a cargo system for hydrophobic drugs and for controlled release mediated by temperature/pH and ultrasound. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Altmann R.,TU Berlin
ZAMM Zeitschrift fur Angewandte Mathematik und Mechanik | Year: 2013

In space semi-discretized equations of elastodynamics with weakly enforced Dirichlet boundary conditions lead to differential algebraic equations (DAE) of index 3. We rewrite the continuous model as operator DAE and present an index reduction technique on operator level. This means that a semi-discretization leads directly to an index-1 system. We present existence results for the operator DAE with nonlinear damping term and show that the reformulated operator DAE is equivalent to the original equations of elastodynamics. Furthermore, we show that index reduction and semi-discretization in space commute if the discretization schemes are chosen in an appropriate way. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Suris Y.B.,TU Berlin
Journal of Geometric Mechanics | Year: 2013

Recently, Lobb and Nijhoff initiated the study of variational (Lagrangian) structure of discrete integrable systems from the perspective of multidimensional consistency. In the present work, we follow this line of research and develop a Lagrangian theory of integrable one-dimensional systems. We give a complete solution of the following problem: one looks for a function of several variables (interpreted as multi-time) which delivers critical points to the action functionals obtained by integrating a Lagrangian 1-form along any smooth curve in the multi-time. The Lagrangian 1-form is supposed to depend on the first jet of the sought-after function. We derive the corresponding multitime Euler-Lagrange equations and show that, under the multi-time Legendre transform, they are equivalent to a system of commuting Hamiltonian flows. Involutivity of the Hamilton functions turns out to be equivalent to closeness of the Lagrangian 1-form on solutions of the multi-time Euler-Lagrange equations. In the discrete time context, the analogous extremal property turns out to be characteristic for systems of commuting symplectic maps. For one-parameter families of commuting symplectic maps (Bäcklund transformations), we show that their spectrality property, introduced by Kuznetsov and Sklyanin, is equivalent to the property of the Lagrangian 1-form to be closed on solutions of the multi-time Euler-Lagrange equations, and propose a procedure of constructing Lax representations with the only input being the maps themselves. © American Institute of Mathematical Sciences. Source

Rymanov V.,University of Duisburg - Essen | Stohr A.,University of Duisburg - Essen | Dulme S.,University of Duisburg - Essen | Tekin T.,TU Berlin
Optics Express | Year: 2014

We report on a novel triple transit region (TTR) layer structure for 1.55 μm waveguide photodiodes (PDs) providing high output power in the millimeter wave (mmW) regime. Basically, the TTR-PD layer structure consists of three transit layers, in which electrons drift at saturation velocity or even at overshoot velocity. Sufficiently strong electric fields (>3000 V/cm) are achieved in all three transit layers even in the undepleted absorber layer and even at very high optical input power levels. This is achieved by incorporating three 10 nm thick p-doped electric field clamp layers. Numerical simulations using the drift-diffusion model (DDM) indicate that for optical intensities up to ∼500 kW/cm2, no saturation effects occur, i.e. the electric field exceeds the critical electric field in all three transit layers. This fact in conjunction with a high-frequency doublemushroom cross-section of the waveguide TTR-PD ensures high output power levels at mmW frequencies. Fabricated 1.55 μm InGaAs(P)/InP waveguide TTR-PDs exhibit output power levels exceeding 0 dBm (1 mW) and a return loss (RL) up to ∼24 dB. Broadband operation with a 3 dB bandwidth beyond 110 GHz is achieved. © 2014 Optical Society of America. Source

Bojdys M.J.,Max Planck Institute of Colloids and Interfaces | Jeromenok J.,Max Planck Institute of Colloids and Interfaces | Thomas A.,TU Berlin | Antonietti M.,Max Planck Institute of Colloids and Interfaces
Advanced Materials | Year: 2010

Figure Presented A layered, covalent, triazine-based framework (CTF) was synthesized via the condensation of 2,6-naphthalenedicarbonitrile under ionothermal conditions. The polytrimerization of this bi functional carbon nitrile in zinc chloride at lower temperatures yields a well-ordered, closepacked framework. At elevated temperatures an amorphous, yet porous solid is obtained, which shows remarkable thermal stability (640°C) and a high surface area (2255 m2 g-1 and 1.51 cm3 g -1). © 2010 WILEY-VCH Verlag GmbH & Co. KGaA. Source

Giese C.,ProBioGen AG | Marx U.,TU Berlin
Advanced Drug Delivery Reviews | Year: 2014

It has been widely recognised that the phylogenetic distance between laboratory animals and humans limits the former's predictive value for immunogenicity testing of biopharmaceuticals and nanostructure-based drug delivery and adjuvant systems. 2D in vitro assays have been established in conventional culture plates with little success so far. Here, we detail the status of various 3D approaches to emulate innate immunity in non-lymphoid organs and adaptive immune response in human professional lymphoid immune organs in vitro. We stress the tight relationship between the necessarily changing architecture of professional lymphoid organs at rest and when activated by pathogens, and match it with the immunity identified in vitro. Recommendations for further improvements of lymphoid tissue architecture relevant to the development of a sustainable adaptive immune response in vitro are summarized. In the end, we sketch a forecast of translational innovations in the field to model systemic innate and adaptive immunity in vitro. © 2014 Elsevier B.V. Source

Reitzenstein S.,TU Berlin
IEEE Journal on Selected Topics in Quantum Electronics | Year: 2012

In this paper, exciting progress of quantum optics in solid state is reviewed. The focus is on semiconductor microcavities with self-assembled quantum dots embedded in the active layer. Due to enormous progress in semiconductor nanotechnology, such photonic structures have become a model system for the study of quantum optics on a scalable and integrable technology platform with high potential for future applications in quantum information technology. Quantum optical phenomena have become accessible due to 3-D confinement of light and matter on the length scale of their wavelength in state-of-the-art semiconductor micro-and nanostructures. This confinement leads to a quantization of the associated photonic and electronic energy levels and requires a quantum mechanical description of the system in the framework of cavity quantum electrodynamics (cQED). This approach considers the dipole interaction between two-level quantum emitters and discrete photonic states of a microcavity. Within the well-known Jaynes-Cummings model, the dipole interaction is described in terms of a coherent exchange of energy between the emitter and the resonator mode. This coherent interaction in the so-called strong coupling regime of cQED is reflected in a normal mode splitting, the vacuum Rabi splitting, of the involved modes and represents a central feature of quantum optics in solid state. Another important example of quantum optics in semiconductor nanostructures is the generation of nonclassical light in specific quantum devices. Of particular interest is the realization of Fock states which represent states containing a well-defined number of photons. Single-photon sources, for instance, allow for the generation of single photons on demand, which is highly desirable for quantum communication systems. In this context, this review paper will present recent experimental studies of quantum optics in solid state. This paper is meant for readers who would like to become familiar with this topic and for experts being interested in the progress in this field. It will cover a broad range of studies ranging from examples of fundamental light-matter interaction in the quantum limit to devices capable of emitting single photons and entangled photon pairs on demand. © 2012 IEEE. Source

Zaharieva I.,Free University of Berlin | Chernev P.,Free University of Berlin | Risch M.,Free University of Berlin | Klingan K.,Free University of Berlin | And 3 more authors.
Energy and Environmental Science | Year: 2012

In the sustainable production of non-fossil fuels, water oxidation is pivotal. Development of efficient catalysts based on manganese is desirable because this element is earth-abundant, inexpensive, and largely non-toxic. We report an electrodeposited Mn oxide (MnCat) that catalyzes electrochemical water oxidation at neutral pH at rates that approach the level needed for direct coupling to photoactive materials. By choice of the voltage protocol we could switch between electrodeposition of inactive Mn oxides (deposition at constant anodic potentials) and synthesis of the active MnCat (deposition by voltage-cycling protocols). Electron microscopy reveals that the MnCat consists of nanoparticles (100 nm) with complex fine-structure. X-ray spectroscopy reveals that the amorphous MnCat resembles the biological paragon, the water-splitting Mn4Ca complex of photosynthesis, with respect to mean Mn oxidation state (ca. +3.8 in the MnCat) and central structural motifs. Yet the MnCat functions without calcium or other bivalent ions. Comparing the MnCat with electrodeposited Mn oxides inactive in water oxidation, we identify characteristics that likely are crucial for catalytic activity. In both inactive Mn oxides and active ones (MnCat), extensive di-μ-oxo bridging between Mn ions is observed. However in the MnCat, the voltage-cycling protocol resulted in formation of MnIII sites and prevented formation of well-ordered and unreactive MnIVO2. Structure-function relations in Mn-based water-oxidation catalysts and strategies to design catalytically active Mn-based materials are discussed. Knowledge-guided performance optimization of the MnCat could pave the road for its technological use. © 2012 The Royal Society of Chemistry. Source

Schulze B.,TU Berlin
Discrete and Computational Geometry | Year: 2010

Recent work has shown that if an isostatic bar-and-joint framework possesses nontrivial symmetries, then it must satisfy some very simply stated restrictions on the number of joints and bars that are "fixed" by various symmetry operations of the framework. For the group C3 which describes 3-fold rotational symmetry in the plane, we verify the conjecture proposed by Connelly et al. (Int. J. Solids Struct. 46:762-773, 2009) that these restrictions on the number of fixed structural components, together with the Laman conditions, are also sufficient for a framework with C3 symmetry to be isostatic, provided that its joints are positioned as generically as possible subject to the given symmetry constraints. In addition, we establish symmetric versions of Henneberg's theorem and Crapo's theorem for C3 which provide alternate characterizations of "generically" isostatic graphs with C3 symmetry. As shown in (Schulze, Combinatorial and geometric rigidity with symmetry constraints, Ph. D. thesis, York University, Toronto, Canada, 2009; Schulze, Symmetrized Laman theorems for the groups C2 and Cs, in preparation, 2009), our techniques can be extended to establish analogous results for the symmetry groups C2 and Cs which are generated by a half-turn and a reflection in the plane, respectively. © 2009 Springer Science+Business Media, LLC. Source

Jain B.J.,TU Berlin
Machine Learning | Year: 2015

The majority of machine learning algorithms assumes that objects are represented as vectors. But often the objects we want to learn on are more naturally represented by other data structures such as sequences and time series. For these representations many standard learning algorithms are unavailable. We generalize gradient-based learning algorithms to time series under dynamic time warping. To this end, we introduce elastic functions, which extend functions on Euclidean spaces to time series spaces. Necessary conditions are sketched under which generalized gradient learning on time series is consistent. Specifically, four linear classifiers are extended to time series under dynamic time warping and applied to benchmark datasets. Results indicate that generalized gradient learning via elastic functions have the potential to complement the state-of-the-art in pattern recognition on time series. © 2015, The Author(s). Source

Jun Y.-S.,University of California at Santa Barbara | Park J.,University of California at Santa Barbara | Lee S.U.,Korea Advanced Institute of Science and Technology | Thomas A.,TU Berlin | And 2 more authors.
Angewandte Chemie - International Edition | Year: 2013

Simple organic cooperative assembly of triazine molecules leads to three-dimensional macroscopic assemblies of low-dimensional graphitic carbon nitrides (g-CNs), for example, nanoparticles, nanotubes, and nanosheets. The approach enables the characterization of the cooperative properties and photocatalytic activities of low-dimensional g-CN materials in hydrogen evolution reactions from water under visible light. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

In hybrid systems which are self-assembled in solution from surface treated CdSe/ZnS quantum dots (QDs) and isolated phycobiliprotein (PBP) complexes from the cyanobacterium Acaryochloris marina, excitation energy transfer (EET) from the QDs to the PBP complexes was observed. The EET from the QDs to attached PBPs was analyzed with time integrated fluorescence spectroscopy and time-correlated single photon counting (TCSPC) at different temperatures. This functional connection between QDs and PBPs via EET is interrupted at temperatures below 273 K (0 °C) (Schmitt et al 2010 Photon. Nanostruct. submitted). The evaluation of the temperature-dependent fluorescence spectra of the QDs showed that the change of the excitation energy transfer efficiency at temperatures below 273 K cannot be explained by the change of the spectral overlap integral alone. Therefore the value of κ 2/R 12 6 must change at 273 K. We assume that micro crystals of water, formed in between the QDs and the PBP antenna structures, lead to a structural change of the hybrid complex. Our results show that TCSPC is suitable to distinguish strongly coupled and weakly coupled QD-PBP complexes at different temperatures. © 2010 IOP Publishing Ltd. Source

Schonfelder V.H.,TU Berlin
The Journal of the Acoustical Society of America | Year: 2012

As a prerequisite to quantitative psychophysical models of sensory processing it is necessary to learn to what extent decisions in behavioral tasks depend on specific stimulus features, the perceptual cues. Based on relative linear combination weights, this study demonstrates how stimulus-response data can be analyzed in this regard relying on an L(1)-regularized multiple logistic regression, a modern statistical procedure developed in machine learning. This method prevents complex models from over-fitting to noisy data. In addition, it enforces "sparse" solutions, a computational approximation to the postulate that a good model should contain the minimal set of predictors necessary to explain the data. In simulations, behavioral data from a classical auditory tone-in-noise detection task were generated. The proposed method is shown to precisely identify observer cues from a large set of covarying, interdependent stimulus features--a setting where standard correlational and regression methods fail. The proposed method succeeds for a wide range of signal-to-noise ratios and for deterministic as well as probabilistic observers. Furthermore, the detailed decision rules of the simulated observers were reconstructed from the estimated linear model weights allowing predictions of responses on the basis of individual stimuli. Source

Hobiger K.,University of Marburg | Friedrich T.,TU Berlin
Frontiers in Pharmacology | Year: 2015

The transmembrane protein Ci-VSP from the ascidian Ciona intestinalis was described as first member of a fascinating family of enzymes, the voltage sensitive phosphatases (VSPs). Ci-VSP and its voltage-activated homologs from other species are stimulated by positive membrane potentials and dephosphorylate the head groups of negatively charged phosphoinositide phosphates (PIPs). In doing so, VSPs act as control centers at the cytosolic membrane surface, because they intervene in signaling cascades that are mediated by PIP lipids. The characteristic motif CX5RT/S in the active site classifies VSPs as members of the huge family of cysteine-based protein tyrosine phosphatases (PTPs). Although PTPs have already been well-characterized regarding both, structure and function, their relationship to VSPs has drawn only limited attention so far. Therefore, the intention of this review is to give a short overview about the extensive knowledge about PTPs in relation to the facts known about VSPs. Here, we concentrate on the structural features of the catalytic domain which are similar between both classes of phosphatases and their consequences for the enzymatic function. By discussing results obtained from crystal structures, molecular dynamics simulations, and mutagenesis studies, a possible mechanism for the catalytic cycle of VSPs is presented based on that one proposed for PTPs. In this way, we want to link the knowledge about the catalytic activity of VSPs and PTPs. © 2015 Hobiger and Friedrich. Source

Nurutdinova I.,TU Berlin | Fitzgibbon A.,Microsoft
Proceedings of the IEEE International Conference on Computer Vision | Year: 2016

Modern structure from motion (SfM) remains dependent on point features to recover camera positions, meaning that reconstruction is severely hampered in low-texture environments, for example scanning a plain coffee cup on an uncluttered table. We show how 3D curves can be used to refine camera position estimation in challenging low-texture scenes. In contrast to previous work, we allow the curves to be partially observed in all images, meaning that for the first time, curve-based SfM can be demonstrated in realistic scenes. The algorithm is based on bundle adjustment, so needs an initial estimate, but even a poor estimate from a few point correspondences can be substantially improved by including curves, suggesting that this method would benefit many existing systems. © 2015 IEEE. Source

Durand A.,University Paris Diderot | Mengel S.,TU Berlin
Journal of Computer and System Sciences | Year: 2014

This paper is a study of weighted counting of the solutions of acyclic conjunctive queries (ACQ). The unweighted quantifier free version of this problem is known to be tractable (for combined complexity), but it is also known that introducing even a single quantified variable makes it #P-hard. We first show that weighted counting for quantifier free ACQ is still tractable and that even minimalistic extensions of the problem lead to hard cases. We then introduce a new parameter for quantified queries that permits to isolate a large island of tractability. We show that, up to a standard assumption from parameterized complexity, this parameter fully characterizes tractable subclasses for counting weighted solutions for ACQs. Thus we completely determine the tractability frontier for weighted counting for ACQ. © 2013 Elsevier Inc. Source

Schaller G.,TU Berlin | Schutzhold R.,University of Duisburg - Essen
Quantum Information and Computation | Year: 2010

Exploiting the similarity between adiabatic quantum algorithms and quantum phase transitions, we argue that second-order transitions - typically associated with broken or restored symmetries - should be advantageous in comparison to first-order transitions. Guided by simple examples we construct an alternative adiabatic algorithm for the NP-complete problem Exact Cover 3. We show numerically that its average performance (for the considered cases up to O{20} qubits) is better than that of the conventional scheme. The run-time of adiabatic algorithms is not just determined by the minimum value of the fundamental energy gap (between the ground state and the exited states), but also by its curvature at the critical point. The proposed symmetry-restoring adiabatic quantum algorithm only contains contributions linear and quadratic in the Pauli matrices and can be generalized to other problem Hamiltonians which are decomposed of terms involving one and two qubits. We show how the factoring problem can be cast into such a quadratic form. These findings suggest that adiabatic quantum algorithms can solve a large class of NP problems much faster than the Grover search routine (which corresponds to a first-order transition and yields a quadratic enhancement only). © Rinton Press. Source

Bulteau L.,French National Center for Scientific Research | Komusiewicz C.,TU Berlin
Proceedings of the Annual ACM-SIAM Symposium on Discrete Algorithms | Year: 2014

The NP-hard Minimum Common String Partition problem asks whether two strings x and y can each be partitioned into at most k substrings such that both partitions use exactly the same substrings in a different order. We present the first fixed-parameter algorithm for Minimum Common String Partition using only parameter k. Copyright © 2014 by the Society for Industrial and Applied Mathematics. Source

Kratzer J.,TU Berlin
Journal of Product Innovation Management | Year: 2016

The field of lead user research has seen a great deal of attention from academics and practitioners alike. However, we still lack a full understanding of the nature of users with high potential for innovation. In this paper, we employ a social network perspective on lead users. Increasing the realism of our research in three empirical studies with different empirical settings and methods, we provide robust evidence that lead users have a distinctive social network position: They exhibit an unusually high level of "betweenness centrality," meaning that they are positioned as bridges between different social groups. This finding has two major implications for lead user theory. First, it consolidates seminal conceptual work on lead users and their embeddedness in social networks. And second, the findings extend and validate prior work on the social network perspective of lead users by combining theoretical insights from cognitive psychology, research on creativity, and network theory. As the social network positions of individuals can be mapped quickly and at low cost with modern Web mining tools, our findings may point to a new and readily applicable approach for the efficient and effective identification of lead users in real-life projects, an aspect that is usually emphasized as the most crucial activity in lead user projects. © 2015 The Authors. Journal of Product Innovation Management published by Wiley Periodicals, Inc. on behalf of Product Development and Management Association. Source

Beck-Sickinger A.G.,University of Leipzig | Budisa N.,TU Berlin
Angewandte Chemie - International Edition | Year: 2012

The genetic code was expanded with orthogonal pairs to introduce photoactivatable amino acids into G-protein-coupled receptors (GPCRs) in a noninvasive manner. In this way the receptor surface could be mapped by searching for specific ligand interaction sites and the complex dynamics could be studied. This method is also useful for probing the structure of GPCR complexes in living cells. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

In this invited review we address, from a mechanistic point of view, three fundamental reactions of carbon dioxide transformation in the gas phase: (i) its reduction to carbon monoxide via oxygen-atom transfer to a suitable oxygen acceptor, (ii) translocation of a hydride from metal hydrides to generate a formate ligand, and (iii) coupling processes with CO2 to make CC and CO bonds. Where appropriate, the findings are compared with related reactions in the condensed phase. The gas-phase studies described, in conjunction with computational work, permit to uncover numerous mechanistic aspects of elementary steps in the making and breaking of bonds, reactions which, by definition, are obscured in solution due to ill-defined effects of the environment. © 2016 Elsevier B.V. Source

Bimberg D.,TU Berlin
IEEE Photonics Journal | Year: 2010

Vertical-cavity surface-emitting lasers (VCSELs) are broadly used as low-cost reliable light sources for high-speed data communication in local area and storage area networks (LANs/SANs), as well as for computer and consumer applications. The rapid increase of the serial transmission speed and the limitations of copper-based links at bit rates beyond 10 Gb/s and distances beyond 1 m extend the applications of fiber-optic interconnects to progressively shorter distances. The wavelength of 850 nm is standard for LAN/SAN applications over OM3 and OM4 multimode fibers and will continue playing an important role in future standards. In the last year, impressive results were achieved with oxide-confined VCSELs emitting at 850 nm. The data transmission rate could be shifted from 30 to 38 Gb/s, which is presently the highest data rate for any oxide-confined VCSELs. © 2010 IEEE. Source

MacKe J.H.,University College London | MacKe J.H.,University of Tubingen | Opper M.,TU Berlin | Bethge M.,University of Tubingen
Physical Review Letters | Year: 2011

Simultaneously recorded neurons exhibit correlations whose underlying causes are not known. Here, we use a population of threshold neurons receiving correlated inputs to model neural population recordings. We show analytically that small changes in second-order correlations can lead to large changes in higher-order redundancies, and that the resulting interactions have a strong impact on the entropy, sparsity, and statistical heat capacity of the population. Our findings for this simple model may explain some surprising effects recently observed in neural population recordings. © 2011 American Physical Society. Source

Herm S.,TU Berlin
Journal of Product Innovation Management | Year: 2013

Consumers understand product preannouncements as credible promises to bring innovations to market at a given time. However, a majority of preannounced products are introduced with some delay. This study investigates potential loss in brand trust due to delay and the role of brand commitment in this process. Building on the Commitment-Trust Theory of Relationship Marketing, which posits trust as a crucial antecedent of the commitment construct, this study extends this common perspective and proposes an additional reversal path from commitment to trust. That is, in the case of a delayed launch, the more stable commitment should buffer a loss in brand trust, which is more fragile. In three studies, this research finds consistent evidence that consumers lose trust in brands as a result of delayed launches. Surprisingly, high brand commitment does not mitigate such losses. In contrast, a long-term relationship with a launching brand proves to be a buffer against losses in brand trust. Different operationalizations of brand commitment in laboratory and field experiments with brands from different product categories contribute to the generalizabilty of this work's findings. © 2012 Product Development & Management Association. Source

Downes T.G.,Queensland University of Technology | Fuentes I.,University of Nottingham | Fuentes I.,TU Berlin | Ralph T.C.,Queensland University of Technology
Physical Review Letters | Year: 2011

An open question in the field of relativistic quantum information is how parties in arbitrary motion may distribute and store quantum entanglement. We propose a scheme for storing quantum information in the field modes of cavities moving in flat space-time and analyze it in a quantum field theoretical framework. In contrast with previous work that found entanglement degradation between observers moving with uniform acceleration, we find the quantum information in such systems is protected. We further discuss a method for establishing the entanglement in the first place and show that in principle it is always possible to produce maximally entangled states between the cavities. © 2011 American Physical Society. Source

Filippov A.E.,NASU Institute of Physics | Popov V.L.,TU Berlin | Urbakh M.,Tel Aviv University
Physical Review Letters | Year: 2011

We propose a model for a description of formation of quasiperiodic nanoscale patterns induced by scratching a surface with an atomic force microscope tip. The simulations demonstrate that the interplay between the developing surface corrugation and the frictional stress produced by the moving tip plays a decisive role in the formation of the regular ripples. Our model reveals the size and shape of the tip as the main factors that determine periodicity and amplitudes of the patterns, and it allows experimental observations to be explained. It is shown that the wear at the nanoscale cannot be explained by conventional macroscopic wear theories. © 2011 American Physical Society. Source

Ruhl A.S.,BAM Federal Institute of Materials Research and Testing | Ruhl A.S.,TU Berlin | Kranzmann A.,BAM Federal Institute of Materials Research and Testing
Journal of Supercritical Fluids | Year: 2012

Carbon capture and storage (CCS) includes processing of supercritical carbon dioxide (scCO 2). The carbon dioxide (CO 2) stemming from flue gases contains acid forming impurities, especially in the case of coal fired power plants. In the present work, the mobility and reactivity of acids in supercritical scCO 2 was investigated. The corrosive attack of low alloyed carbon steel (material 1.0484) by water (H 2O) alone in scCO 2 was negligible. Nitric acid (HNO 3) was very mobile and corrosive towards the carbon steel while sulfuric acid did not migrate through the scCO 2 to react with the steel surface. Hydrochloric acid in scCO 2 was very mobile and reactive towards both carbon steel and high alloyed test equipment. Gravimetric analyses revealed a severe material loss after corrosion in the presence of HNO 3. Thickness measurements showed localized material losses. © 2012 Elsevier B.V. All rights reserved. Source

Schloder T.,Albert Ludwigs University of Freiburg | Kaupp M.,TU Berlin | Riedel S.,Albert Ludwigs University of Freiburg
Journal of the American Chemical Society | Year: 2012

Very recently, a thermochemically stable Zn III complex has been predicted by Samanta and Jena (J. Am. Chem. Soc. 2012, 134, 8400-8403). In contrast to their conclusions we show here by quantum chemical calculations that (a) Zn(AuF 6) 3 is not a thermochemically feasible compound, and (b) even if it could be made, it would not represent a Zn III oxidation state by any valid definition. © 2012 American Chemical Society. Source

Fink K.,TU Berlin | Bernet S.,TU Dresden
IEEE Transactions on Power Electronics | Year: 2013

This paper describes the design and the experimental investigation of a gate drive unit with closed-loop control of the collector current slope diC/dt for multichip insulated-gate bipolar transistors (IGBTs). Compared to a pure resistive gate drive, the proposed diC/dt control offers the ability to adjust the collector current slope freely which helps to find an optimized relation between switching losses and secure operation of the freewheeling diode for every type of IGBT. Based on the description of IGBTs switching behavior, the design and the realization of the gate drive are presented. The test setup and the comparison of switching tests with and without the proposed diC/dt control are discussed. © 1986-2012 IEEE. Source

Talke K.,TU Berlin
Journal of Product Innovation Management | Year: 2013

This research investigates how the adoption of new high-tech consumer products can be stimulated by communicating product-related information in launch messages. In an initial pilot study, the authors find that for making an adoption decision, consumers require different types of product-related information, i.e., technical information, financial information, and personal/social information. In three experiments, the authors then examine how adoption intention and behavior is affected by communicating these information types. The first experiment shows that communicating personal/social information results in the highest adoption intention. This effect is moderated by the way in which the information is represented in the message. Adoption intention is highest when personal/social information is communicated in an abstract manner, while financial and technical information are most effective when communicated in a concrete manner. The second experiment shows that the effects hold for actual adoption behavior. In addition, visual imagination is found to mediate these effects. In the last experiment, visual imagination is directly manipulated by thematic priming and has a direct effect on adoption behavior. The results emphasize that activating the imagination in a product-relevant situation stimulates adoption behavior. © 2013 Product Development & Management Association. Source

In the track design and behavior prediction, the variable contribution of wheel load was evaluated by considering the design load for the tracks. Further, the track impact factor was used to calculate the dynamic wheel load as a single value, which was chosen according to the rail type (i.e., continuous welded rail or joint rail) and the design speed but did not take into consideration the track conditions (i.e., the ballast condition good or bad), train type (i.e., tilting train and EMU), and track components (i.e., sleeper type and fastening type). In this study, the measured track impact factor was applied to the time history function of the FE analysis in order to predict the displacement of ballasted tracks under real conditions, which included curved and the deteriorated tracks, thus increasing the train speed by approximately 20-30% of the existing train speed. Therefore, the dynamic wheel load and the rail and sleeper displacement were measured for two different trains running on four conventional curved track sections with two different sleeper types. The track impact factor was estimated from the measured dynamic wheel load, and the empirical dynamic wheel load was calculated using the measured track impact factor at each site. The measured track impact factors were used for simulating the dynamic wheel loads applied on the derived time history function for fast trains. A finite element analysis model using the derived time history function based on the empirical dynamic wheel load was used to predict the train-induced track displacement. The numerical simulations and field test results were compared with German and Japanese regulations for train-induced track displacement, and the speedup effect of a tilting train was compared with that of a general train (EMU).The empirical track impact factors were 17-18% higher in the R400 sections than in the R600 sections. As the track curvature decreased, the impact on the track increased. Therefore, the empirical track impact factors were 21-23% higher in the WT sections than in the PCT sections. At 70. km/h, the impact on the track from a tilting train was 7-11% less than that from EMU. Although the tilting train sped up by 30% (90. km/h), its response level was similar to or less than that of the EMU. The analytical results reproduced the experimental results well within about 2-5% difference in the values. Therefore, the derived time history function based on the measured track impact factors is considered to provide sufficiently reliable FEA results in the investigation of the behavior of ballasted tracks. The difference between the maximum displacements for both train types on all the sections was about 15-20%.The analytical results show that the speed limits of the tilting train were higher than those of the EMU by approximately 8-23. km/h at each test site. Therefore, the speed limit of each test site was estimated by considering the limit of sleeper displacement. It was shown that the time history function derived using the measured track impact factor on a small track curvature with wooden sleepers was higher than that in other test sections. Therefore, it would be advantageous to increase the weight of sleepers on existing lines to increase the train speed through the speedup effect without increasing the track curvature. The increase in the speed of a tilting train with a small track curvature was much better than that by a track curvature increased by approximately 10%. © 2013 Elsevier Ltd. Source

Tautz R.C.,TU Berlin | Dosch A.,University of Alabama in Huntsville
Physics of Plasmas | Year: 2013

A modified method is presented to generate artificial magnetic turbulence that is used for test-particle simulations. Such turbulent fields are obtained from the superposition of a set of wave modes with random polarizations and random directions of propagation. First, it is shown that the new method simultaneously fulfils requirements of isotropy, equal mean amplitude and variance for all field components, and vanishing divergence. Second, the number of wave modes required for a stochastic particle behavior is investigated by using a Lyapunov approach. For the special case of slab turbulence, it is shown that already for 16 wave modes the particle behavior agrees with that shown for considerably larger numbers of wave modes. © 2013 American Institute of Physics. Source

Meyerhoff J.,TU Berlin | Morkbak M.R.,University of Southern Denmark | Olsen S.B.,Copenhagen University
Environmental and Resource Economics | Year: 2014

It is a well-known empirical finding that some percentage of respondents participating in Stated Preference surveys will not give responses that reflect their true preferences. One reason is protest behaviour. If the distribution of protest responses is not independent of respondent or survey characteristics, then simply expelling protesters from surveys can lead to sample selection bias. Furthermore, WTP estimates will not be comparable across surveys. This paper seeks to explore potential causes of protest behaviour through a meta-study based on full datasets from 38 different surveys. The objective of the study is to examine the effect of respondent specific variables as well as survey specific variables on protest behaviour. Our results suggest that some of the differences in WTP typically observed between different demographic groups, different elicitation formats and different question formats might actually be attributed to inherent differences in the propensity to protest. Our results indicate that the propensity for respondents to exhibit protest behaviour when asked a stated preference type valuation question depends on a number of specific factors, respondent specific as well as survey specific-knowledge which could be used in order to reduce protest behaviour. © 2013 Springer Science+Business Media Dordrecht. Source

Behboodi A.,TU Berlin | Piantanida P.,Supelec
IEEE Transactions on Information Theory | Year: 2015

The problem of communicating a single message to a destination in presence of multiple relay nodes, referred to as cooperative unicast network, is considered. First, we introduce mixed noisy network coding (MNNC) scheme which generalizes noisy network coding where relays are allowed to decode-and-forward (DF) messages while all of them (without exception) transmit noisy descriptions of their observations. These descriptions are exploited at the destination and DF relays aim to decode the transmitted messages while creating full cooperation among the nodes. Moreover, the destination and DF relays can independently select the set of descriptions to be decoded or treated as interference. This concept is further extended to multihopping scenarios, referred to as layered MNNC, where DF relays are organized into disjoint groups representing one hop in the network. For cooperative unicast additive white Gaussian noise (AWGN) networks, we show that - provided DF relays are properly chosen - MNNC improves over all previously established constant gaps to the cut-set bound. Second, we consider the composite cooperative unicast network where the channel parameters are randomly drawn before communication starts and remain fixed during the transmission. Each draw is assumed to be unknown at the source and fully known at the destination but only partly known at the relays. We introduce through MNNC scheme the concept of selective coding strategy (SCS) that enables relays to decide dynamically whether, in addition to communicate noisy descriptions, is possible to decode and forward messages. It is demonstrated through slow-fading AWGN relay networks that SCS clearly outperforms conventional coding schemes. © 1963-2012 IEEE. Source

Eilzer S.,Max Born Institute for Nonlinear Optics and Short Pulse Spectroscopy | Zimmermann H.,Max Born Institute for Nonlinear Optics and Short Pulse Spectroscopy | Eichmann U.,Max Born Institute for Nonlinear Optics and Short Pulse Spectroscopy | Eichmann U.,TU Berlin
Physical Review Letters | Year: 2014

Laser induced strong-field phenomena in atoms and molecules on the femtosecond (fs) time scale have been almost exclusively investigated with traveling wave fields. In almost all cases, approximation of the strong electromagnetic field by an electric field purely oscillating in time suffices to describe experimental observations. Spatially dependent electromagnetic fields, as they occur in a standing light wave, allow for strong energy and momentum transfer and are expected to extend strong-field dynamics profoundly. Here we report a strong-field version of the Kapitza-Dirac effect for neutral atoms where we scatter neutral He atoms in an intense short pulse standing light wave with fs duration and intensities well in the strong-field tunneling regime. We observe substantial longitudinal momentum transfer concomitant with an unprecedented atomic photon scattering rate greater than 1016s-1. © 2014 American Physical Society. Source

Paraknowitsch B.J.P.,Max Planck Institute of Colloids and Interfaces | Zhang J.,Fritz Haber Institute of the Max Planck Society | Su D.,Fritz Haber Institute of the Max Planck Society | Thomas A.,TU Berlin | Antonietti M.,Max Planck Institute of Colloids and Interfaces
Advanced Materials | Year: 2010

Nitrogen-doped carbons are prepared by thermolysis of two organic, nitrogen-rich ionic liquids (see figure). The nitrogen content can be adjusted by the thermolysis temperature. As the precursors are liquids at room temperature they represent ideal precursors for the direct synthesis of carbon nanostructures and coatings with flexible geometry controlled by the processing of liquids. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA,. Source

Ordas I.,University of California at San Diego | Ordas I.,University of Barcelona | Eckmann L.,University of California at San Diego | Talamini M.,University of California at San Diego | And 2 more authors.
The Lancet | Year: 2012

Ulcerative colitis is an idiopathic, chronic inflammatory disorder of the colonic mucosa, which starts in the rectum and generally extends proximally in a continuous manner through part of, or the entire, colon; however, some patients with proctitis or left-sided colitis might have a caecal patch of inflammation. Bloody diarrhoea is the characteristic symptom of the disease. The clinical course is unpredictable, marked by alternating periods of exacerbation and remission. In this Seminar we discuss the epidemiology, pathophysiology, diagnostic approach, natural history, medical and surgical management, and main disease-related complications of ulcerative colitis, and briefly outline novel treatment options. Enhanced understanding of how the interaction between environmental factors, genetics, and the immune system results in mucosal inflammation has increased knowledge of disease pathophysiology. We provide practical therapeutic algorithms that are easily applicable in daily clinical practice, emphasising present controversies in treatment management and novel therapies. © 2012 Elsevier Ltd. Source

Bian W.,Soochow University of China | Yang Z.,Soochow University of China | Strasser P.,TU Berlin | Yang R.,Soochow University of China
Journal of Power Sources | Year: 2014

Development of efficient electrocatalysts for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) remain key issues for the commercialization of fuel cells and metal-air batteries. In this study, A CoFe2O4/graphene nanohybrid is facilely synthesized via a two-step process and applied as an electrocatalyst for the ORR and the OER. The as-prepared CoFe2O4/graphene nanohybrid demonstrates excellent catalytic activity for the ORR. At the same mass loading, the Tafel slope of CoFe2O4/graphene electrocatalyst for the ORR is comparable to that of the commercial Pt/C (20 wt% Pt on Vulcan XC-72, Johnson Matthey). The ORR on CoFe2O4/graphene mainly favours a direct 4e- reaction pathway. The CoFe2O 4/graphene nanohybrid also affords high catalytic activity for the OER. The chronoamperometric tests show that CoFe2O 4/graphene catalyst exhibits excellent stability for both the ORR and the OER, outperforming the commercial Pt/C. The high electrocatalytic activity and durability of CoFe2O4/graphene nanohybrid are attributed to the strong coupling between CoFe2O4 nanoparticles and graphene. © 2013 Elsevier B.V. All rights reserved. Source

Mallison H.,TU Berlin
Fossil Record | Year: 2014

It has been hypothesized that the pronounced differences of stegosaur humeral shapes, with large forms having more slender and small forms having more robust humeri, may be explained by a difference in relative centre of mass (COM) placement caused by differing distributions of osteoderms. To test this hypothesis, digital 3-D models of the bones and osteoderms of the Tanzanian stegosaurKentrosaurus aethiopicusand of the North American stegosaurStegosaurus armatuswere used to create a 3-D computer-aided design life reconstruction. On these models osteoderm placement was varied drastically, recreating both existing and hypothetical forms. These models show that COM position varies somewhat with realistic osteoderm distributions, but insufficiently to explain major differences in humeral shape. The uniform weight distribution between forelimbs and hindlimbs found between the two taxa also casts doubt on the hypothesis that differences in relative COM position caused by other factors than osteoderm distribution can explain differences in humeral robustness. © Author(s) 2014. CC Attribution 3.0 License. Source

Mueller W.-D.,Charite - Medical University of Berlin | Lucia Nascimento M.,TU Berlin | Lorenzo De Mele M.F.,and University la Plata
Acta Biomaterialia | Year: 2010

The aim of this work was to collect and compare data from different published reports which focused on the description of the influence of different electrochemical setups for the assessment of magnesium corrosion. Based on this, a comparison with our own results, obtained for LAE 442 and AZ 31, was made and discussed. As the collection of data has shown, the reported inconsistencies between in vivo and electrochemical data depend greatly on the electrochemical medium used, on the alloy composition and on surface preparation. Nevertheless, these differences also exist when comparing different in vitro results using different methodologies and even different Mg alloys, and need therefore to be discussed more thoroughly in the future. The simulation of transport conditions of the in vivo interface should become a focus of research interest in order to gain a better understanding of the influence of connecting processes on the degradation of the biomaterials. © 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Source

Meyer T.,University of Hamburg | Surber C.,University of Basel | French L.E.,University of Zurich | Stockfleth E.,TU Berlin
Expert Opinion on Investigational Drugs | Year: 2013

Introduction: Resiquimod is an immune response modifier which stimulates cells through a toll-like receptors (TLR) 7 and 8 dependent pathway resulting in activation of immune responses that are effective against viral and tumor lesions. Areas covered: Studies on genital herpes, hepatitis C and actinic keratosis (AK) as well as papers of molecular activities of resiquimod were identified by a PubMed search. Although effective against genital HSV-2 in animal models, development of topical resiquimod for the treatment of recurrent genital herpes in humans was stopped due to inconsistent results in clinical trials. Reduction of HCV viral load was achieved by oral application but was associated with unacceptable side effects. Topical treatment of AK was well tolerated and effective with clearance rates higher compared to imiquimod. The molecular mode of action underlying the clinical efficacy primarily depends on cytokine induction in TLR7/8 expressing dendritic cells in the skin. Expert opinion: Topical resiquimod was shown to be a safe and effective treatment option for AK and appears to have potential as a treatment modality for patients with extended skin areas affected with AK (field cancerization). Resiquimod may also have potential for the therapy or prevention of epithelial viral infections. © 2012 Informa UK, Ltd. Source

Fellinger T.-P.,Max Planck Institute of Colloids and Interfaces | Thomas A.,TU Berlin | Yuan J.,Max Planck Institute of Colloids and Interfaces | Antonietti M.,Max Planck Institute of Colloids and Interfaces
Advanced Materials | Year: 2013

This review surveys recent work on the use of ionic liquids (ILs) and polymerized ionic liquids (PILs) as precursors to synthesize functional carbon materials. As solvents or educts with negligible vapour pressure, these systems enable simple processing, composition, and structural control of the resulting carbons under rather simple and green synthesis conditions. Recent applications of the resulting nanocarbons across a multitude of fields, such as fuel cells, energy storage in batteries and supercapacitors, catalysis, separation, and sorption materials are highlighted. Ionic liquids (ILs) and polymerized ionic liquids (PILs) are flexible and versatile precursors for the synthesis of functional carbon materials. Heteroatom doping and various morphologies, such as powder, film, hollow spheres, fibers, and monoliths, are all accessible when proper structures and processing methods are coupled with this IL/PIL route. Applications in energy storage, catalysis, separation, and sorption are highlighted. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Jonas D.,TU Berlin
International Journal of Project Management | Year: 2010

Along with the increasing diffusion of project portfolio management a new managerial role evolves: the project portfolio manager. This new role is supposed to be pivotal in planning and controlling complex project landscapes more effectively and more efficiently, in implementing project portfolio management practices as a management innovation, and in coping with traditional conflicts between line and project managers in matrix organizations. However, by empowering project portfolio managers and giving their role more clarity and significance, the complex power balance between senior managers, line managers, and project managers also has to change. These changes are assumed to lead to new tensions between traditional key players and the new role which will reduce the overall project portfolio performance. This paper uses the new role of the project portfolio manager and its interplay with line and senior management to explain how management involvement can positively and negatively impact project portfolio success at the same time. It therefore offers practitioners an initial point for designing organizational governance structures and job descriptions to increase the portfolio management performance while implementing or reconfiguring the formal role definition of involved managers. For scholars this article paves the way for an empirical study on the impact of power re-distribution in project (portfolio) management. © 2010 Elsevier Ltd and IPMA. Source

Meskendahl S.,TU Berlin
International Journal of Project Management | Year: 2010

Firms are facing more difficulties with the implementation of strategies than with its formulation. Therefore, this paper examines the linkage between business strategy, project portfolio management, and business success to close the gap between strategy formulation and implementation. Earlier research has found some supporting evidence of a positive relationship between isolated concepts, but so far there is no coherent and integral framework covering the whole cycle from strategy to success. Therefore, the existing research on project portfolio management is extended by the concept of strategic orientation. Based on a literature review, a comprehensive conceptual model considering strategic orientation, project portfolio structuring, project portfolio success, and business success is developed. This model can be used for future empirical research on the influence of strategy on project portfolio management and its success. Furthermore, it can easily be extended e.g. by contextual factors. © 2010 Elsevier Ltd and IPMA. Source

Holzle K.,TU Berlin
International Journal of Project Management | Year: 2010

Many project managers do not feel adequately respected and compensated for their work. They often see their role as a temporary one and focus more on their advancement in traditional leadership career paths. Although a lot has been done with respect to qualification and certification programs for project managers, the special role of motivation and retention of project managers has not extensively been researched in the past. Moreover, human resource management has neglected career possibilities and career design for project managers so far. Consequently, our research builds on different streams of research from human resource management, project management, and motivational theory to identify the key ingredients for a project managers' career path. A qualitative study with 20 companies that have already implemented a project managers' career path has been conducted. The findings of this research are used to derive key success factors for the design and implementation of a project managers' career path. © 2010. Source

Ripl W.,TU Berlin
International Journal of Water | Year: 2010

Under natural conditions order is created by interactions between water, temperature, chemical gradients, ground surface, and organisms. However, in the 'developed' landscape, order is replaced by randomness. The de-coupling of energy and water cycles is observed in eutrophication, as irreversible matter losses break closed metabolic cycles in coenotic structures. Another cause of landscape entropy is the lowered water table, which decreases surface flows. Applying the Energy-Transport-Reaction Model to the River Stor Catchment in Germany, the paper shows how dissipative structures balance terrestrial and aquatic ecosystems, returning short water cycles to the atmosphere. This ecosystem integrity benefits food production as well as climate. © 2010 Inderscience Enterprises Ltd. Source

Scholler-Schwedes O.,TU Berlin
Journal of Transport Geography | Year: 2010

In order to reach a sustainable traffic development, the European Union follows the central idea of an integrated transport policy. In contrast to the widely accepted concept, the EU recently had to admit that in fact transport development goes in the opposite direction. This contradiction has to be explained. The article describes the long lasting succession of efforts to implement a far-reaching cooperation in the transport sector as is aspired to by an integrated transport policy. In each case, though, the political idea of cooperation was superseded by the economic one of competition. Therefore, the author argues in favour of a detailed scientific analysis of the necessary political conditions for an integrated transport policy, instead of continuing an untested concept. © 2009 Elsevier Ltd. All rights reserved. Source

Krugel U.,University of Zurich | Kuhn C.,TU Berlin
Frontiers in Plant Science | Year: 2013

Sucrose transporters are essential membrane proteins for the allocation of carbon resources in higher plants and protein-protein interactions play a crucial role in the post-translational regulation of sucrose transporters affecting affinity, transport capacity, oligomerization, localization, and trafficking. Systematic screening for protein interactors using sucrose transporters as bait proteins helped identifying several proteins binding to sucrose transporters from apple, Arabidopsis, potato, or tomato using the split ubiquitin system. This mini-review summarizes known sucrose transporter-interacting proteins and their potential function in plants. Not all of the identified interaction partners are postulated to be located at the plasma membrane, but some are predicted to be endoplasmic reticulum-residing proteins such as a protein disulfide isomerase and members of the cytochrome b5 family. Many of the SUT1-interacting proteins are secretory proteins or involved in metabolism. Identification of actin and actin-related proteins as SUT1-interacting proteins confirmed the observation that movement of SUT1-containing intracellular vesicles can be blocked by inhibition of actin polymerization using specific inhibitors. Manipulation of expression of these interacting proteins represents one possible way to modify resource allocation by post-translational regulation of sucrose transporters. © 2013 Krügel and Kühn. Source

Over H.,Justus Liebig University | Schomacker R.,TU Berlin
ACS Catalysis | Year: 2013

The Deacon process is a sustainable way to recover chlorine from HCl by its oxidation with molecular oxygen. Deacon catalysts need to fulfill both selection criteria: high activity and high stability. In this Review, we introduce and discuss simple descriptors for assessing activity and stability of catalyst materials. A promising descriptor for ranking the experimental activities of Deacon catalysts and other oxidation catalysts in the form of oxides represents the dissociation energy of molecular oxygen as introduced by Studt et al. (ChemCatChem.2010, 2, 98). The resulting volcano plot allows for identifying promising catalyst materials for the Deacon process, such as exemplified with La2O3. © 2013 American Chemical Society. Source

Enthaler S.,TU Berlin
ACS Catalysis | Year: 2013

During the past years a number of interesting zinc catalyzed reactions have been reported, spanning a range from reduction to oxidation, (de)polymerization, synthesis of amines, or cyclopropanation reactions. This Perspective will focus on a selection of recent achievements applying catalytic amounts of zinc in organic transformations and raise the question if zinc can be a future option or tool for organic synthesis. © 2013 American Chemical Society. Source

The number of constituent amino acids in ribosomally synthetized and post-translationally modified peptide natural products (RiPPs) is restricted to the 20 canonical amino acids. Microorganisms with an engineered genetic code are capable of delivering the biological, chemical, or physical properties of many unnatural or synthetic noncanonical amino acids, ncAAs (in different combinations of their numbers and chemistry) precisely defined by the chemist at the bench. In this way, post-translational modifications (PTMs) which make RiPPs chemically extremely rich can be augmented by the co-translational insertion of ncAAs. This will dramatically expand the chemical and functional space of these molecules and enable the design of novel and unique sequence combinations with improved specificity, stability, membrane permeability and even better oral availability. © 2013 Elsevier Ltd. Source

Banhart J.,Helmholtz Center Berlin | Banhart J.,TU Berlin
Advanced Engineering Materials | Year: 2013

The history of metallic foams and the key innovations that have led to the variety of processing methods known today are reviewed. It is evident that the idea of foaming metals is very old and that most of the techniques used today have been proposed already in the 1950s. The most important milestones in the development of foaming technologies and the some of the attempts to commercialize metal foams are reviewed. The history of metallic foams dates back to 1926. Most of the techniques used today were proposed in the 1950s, but refinement of methods to a state allowing for industrial application has taken place only recently. Based on earlier developments, many new processing routes have been proposed. These and attempts to commercialize metal foams are reviewed. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Busing C.,TU Berlin
Networks | Year: 2012

In this article, we investigate two different recoverable robust (RR) models to deal with cost uncertainties in a shortest path problem. RR extends the classical concept of robustness to deal with uncertainties by incorporating limited recovery actions after the full data are revealed. Our first model focuses on the case where the recovery actions are quite restricted: after a simple path is fixed in the first stage, in the second stage, after all data are revealed, any path containing at most k new arcs may be chosen. Thus, the parameter k can be interpreted as a mediator between robust optimization-no changes allowed-and optimization on the fly-an arbitrary solution can be chosen. Considering three classical scenario sets, which model uncertainties in the cost function, we show that this new problem is strongly NP-hard in all these cases and is not approximable, unless P = NP. This is in contrast to the robust shortest path problem, where, for example, an optimal solution can be computed efficiently for interval and γ -scenarios. For series-parallel graphs and interval scenarios, we present a polynomial time algorithm for this RR setting. In our second model, the recovery set, that is, the set of paths selectable in the second stage is not limited, but deviating from the previous choice comes at extra cost. Thus, a path chosen in the first stage produces renting costs modeled as an α -fraction of the scenario cost. For an arc taken in the second stage, the remaining cost needs to be paid in addition to some extra inflation cost modeled by a β -fraction of the scenario cost, if the arc was not reserved beforehand. The complexity status of this problem is similar to the robust case. Yet, for γ -scenarios, the problem is again strongly NP -hard, but can be approximated with a min{2+β,1/α} factor. © 2011 Wiley Periodicals, Inc. Source

Weingarten E.,TU Berlin
Environmental Policy and Governance | Year: 2010

Under the maxim of 'better regulation', the European Commission is aiming to simplify and improve the European regulatory framework in order to reduce bureaucracy and to foster economic growth. Against this background, the integration of requirements presents one option for responding to the challenge of carrying out various environmental assessments stipulated by a number of European environmental directives. Although integrative, cross-sectional approaches have been established by some European directives, such as the Directive on Environmental Impact Assessment, the member states currently make little use of these options when implementing the directives into national law. Based on a review of European directives as well as related German regulations, this article outlines an approach for an integrative environmental assessment that aims to enhance the integrative effects and reduce duplication resulting from different environmental assessments. The investigation shows that the different assessment procedures as outlined by European and German legislation can be successfully integrated without necessarily lowering the standards set by these regulations. Given that the relevant directives are binding for all member states, the proposed assessment structure can easily be applied to other member states and, where necessary, modied to suit national requirements. Copyright © 2010 John Wiley & Sons, Ltd and ERP Environment. Source

Schirmel J.,University of Greifswald | Buchholz S.,TU Berlin
Biodiversity and Conservation | Year: 2011

We analyzed the impacts of succession and grass encroachment on carabid beetle and spider assemblages in a coastal heathland. Further, indicator species for different successional stages (grey dunes, dwarf-shrub heath, grassy heath, heath with shrubs, birch forest) were identified, and their relations to habitat parameters were analyzed. The study was conducted on the Baltic island of Hiddensee, Germany. Ground-dwelling arthropods were sampled using pitfall traps along a successional gradient containing five stages. Ordination by nonmetric multidimensional scaling (NMDS) and analysis of similarities (ANOSIM) revealed a clear separation of species composition among the successional stages. Both in carabid beetles and spiders, most indicator species were obtained in the youngest stage (grey dunes) and fewest in the intermediate stages (grassy heath, heath with shrubs). Also the proportion of endangered species was highest in grey dunes. Based on our results, conservation management of coastal heathlands should preserve a mosaic of different successional stages with a clear preference on younger stages (grey dunes and dwarf-shrub heath). © 2011 Springer Science+Business Media B.V. Source

Yamaguchi T.,University of Tsukuba | Sekiguchi A.,University of Tsukuba | Driess M.,TU Berlin
Journal of the American Chemical Society | Year: 2010

The reaction of disilyne 1 with 1,3,4,5-tetramethylimidazol-2-ylidene (an N-heterocyclic carbene, NHC) produced the disilyne-NHC complex 2, RLSi SiR: (R = SiiPr[CH(SiMe3)2]2, L = NHC), with a trans geometry of the Si Si moiety and lone-pair electrons residing on one of the double-bonded Si atoms. Upon complexation of 2 with ZnCl2, the disilyne-NHC-ZnCl2 complex 3 was produced, in which the Si Si bond adopted the cis geometry. © 2010 American Chemical Society. Source

Grimm A.,National University of Singapore | Stark H.,TU Berlin
Soft Matter | Year: 2011

We investigate how hydrodynamic interactions between Brownian particles influence the performance of a fluctuating ratchet. For this purpose, we perform Brownian dynamics simulations of particles that move in a toroidal trap under the influence of a sawtooth potential which fluctuates between two states (on and off). Hydrodynamic interactions are included in the Rotne-Prager approximation. We first consider spatially constant transition rates between the two ratchet states and observe that hydrodynamic interactions significantly increase the mean velocity of the particles but only when they are allowed to change their ratchet states individually. If in addition the transition rate to the off state is localized at the minimum of the ratchet potential, particles form characteristic transient clusters that travel with remarkably high velocities. The clusters form since drifting particles have the ability to push but also pull neighboring particles due to hydrodynamic interactions. © The Royal Society of Chemistry 2011. Source

Enthaler S.,TU Berlin
Chemistry - A European Journal | Year: 2011

Easy for U! The efficient uranium-catalyzed dehydration of a variety of primary amides, using N-methyl-N-(trimethylsilyl)trifluoroacetamide (MSTFA) as a dehydration reagent, to the corresponding nitriles has been investigated. With this catalyst system, extraordinary catalyst activities and selectivities were feasible (see scheme; DME=dimethoxyethane). Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Producing and interpreting functional brain data is part of the negotiation we imagine our brain. To take a closer look at the idea of brain imaging as a form of visual knowledge, it is necessary to put the research of today into a historical context. In my article I will point to a specific approach of functional imaging which depends on historical shifts entangled with the visual aspect of producing pictures of the brain. I will bring out the interaction of issues like techniques, models and historical assumptions of the brain and link them with the way the brain images are presented. The aesthetic dimensions (Rancière) in the pictures are also questions of ethics and normativity. © Springer Science+Business Media B.V. 2011. Source

Chalcogenide and chalcopyrite photovoltaic (PV) technologies are highly suitable for solar energy conversion because of their high efficiency, long-term stable performance, and low-cost production. However, the absorber materials that are used, such as indium, gallium, and tellurium, are regarded as critical, and their limited availability can hinder market expansion. Therefore, we assess how material efficiency measures along the PV module's life cycle can reduce the net material demand of the absorber materials and thus the material costs. In order to estimate the material flows, we developed a closed-loop model for the life cycle representing the phases module production, module collection, module recycling, and refinement. In order to reflect the variety and uncertainty in each phase, we compose three different efficiency scenarios by varying material efficiency measures on process and product levels. For each scenario, we compute the life cycle material costs based on the computed material flows. The results show that, in the long term, the material demand can be reduced down to one fourth of the required feedstock for module manufacturing that is, three fourths of the absorber material stays in the life cycle in a very efficient scenario. Thus, total material costs along the life cycle could be significantly reduced, because the costs for material recycling are lower than the costs for "new" technical-grade material. This reduction in life cycle material costs means that cadmium telluride- and copper indium gallium diselenide-PV can still be financially viable even if the price of the absorber materials increases significantly. Hence those technologies will still be competitive against crystalline silicon PV in the mid to long term. © 2014 by Yale University. Source

Flinth A.,TU Berlin
IEEE Transactions on Information Theory | Year: 2016

Compressed sensing deals with the recovery of sparse signals from linear measurements. Without any additional information, it is possible to recover an s-sparse signal using m \gtrsim s \log (d/s) measurements in a robust and stable way. Some applications provide additional information, such as on the location the support of the signal. Using this information, it is conceivable that the threshold amount of measurements can be lowered. A proposed algorithm for this task is weighted \ell -{1}-minimization. Put shortly, one modifies standard \ell -{1}-minimization by assigning different weights to different parts of the index set [1, \ldots d]. The task of choosing the weights is, however, non-Trivial. This paper provides a complete answer to the question of an optimal choice of the weights. In fact, it is shown that it is possible to directly calculate unique weights that are optimal in the sense that the threshold amount of measurements needed for exact recovery is minimized. The proof uses recent results about the connection between convex geometry and compressed sensing-Type algorithms. © 1963-2012 IEEE. Source

Harding D.J.,University of Gottingen | Harding D.J.,Max Planck Institute for Chemistry | Fielicke A.,TU Berlin
Chemistry - A European Journal | Year: 2014

Transition-metal clusters have long been proposed as model systems to study heterogeneous catalysts. In this Concept article we show how advanced spectroscopic techniques can be used to determine the structures of gas-phase transition-metal clusters and their complexes with small molecules. Combined with computational studies, this can help to develop an understanding of the reactivity of these catalytic models. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Busse R.,World Health Organization | Stahl J.,TU Berlin | Stahl J.,German Institute for Economic Research
Health Affairs | Year: 2014

Care for people with chronic conditions is an issue of increasing importance in industrialized countries. This article examines three recent efforts at care coordination that have been evaluated but not yet included in systematic reviews. The first is Germany's Gesundes Kinzigtal, a population-based approach that organizes care across all health service sectors and indications in a targeted region. The second is a program in the Netherlands that bundles payments for patients with certain chronic conditions. The third is England's integrated care pilots, which take a variety of approaches to care integration for a range of target populations. Results have been mixed. Some intermediate clinical outcomes, process indicators, and indicators of provider satisfaction improved; patient experience improved in some cases and was unchanged or worse in others. Across the English pilots, emergency hospital admissions increased compared to controls in a difference-in-difference analysis, but planned admissions declined. Using the same methods to study all three programs, we observed savings in Germany and England. However, the disease-oriented Dutch approach resulted in significantly increased costs. The Kinzigtal model, including its shared-savings incentive, may well deserve more attention both in Europe and in the United States because it combines addressing a large population and different conditions with clear but simple financial incentives for providers, the management company, and the insurer. © 2014 Project HOPE-The People-to-People Health Foundation, Inc. Source

Reis T.,TU Berlin
International Journal of Circuit Theory and Applications | Year: 2010

In this work we consider the problem of multiport passive reciprocal network synthesis by descriptor systems. A numerical method is presented that leads to circuit equations in modified nodal analysis. Copyright © 2008 John Wiley & Sons, Ltd. Source

Harks T.,Maastricht University | Klimm M.,TU Berlin
Mathematics of Operations Research | Year: 2012

We study the existence of pure Nash equilibria in weighted congestion games. Let C denote a set of cost functions. We say that C is consistent if every weighted congestion game with cost functions in C possesses a pure Nash equilibrium. Our main contribution is a complete characterization of consistency of continuous cost functions. We prove that a set C of continuous functions is consistent for two-player games if and only if C contains only monotonic functions and for all nonconstant functions c11 c2 2C, there are constants a1 b 2 ε R such that c14x5 D a c24x5Cb for all x 2 ε R 0. For games with at least three players, we prove that C is consistent if and only if exactly one of the following cases holds: (a) C contains only affine functions; (b) C contains only exponential functions such that c4x5 D ac e?x C bc for some ac1 bc1θ 2 ε R, where ac and bc may depend on c, while θ must be equal for every c 2 C. The latter characterization is even valid for three-player games. Finally, we derive several characterizations of consistency of cost functions for games with restricted strategy spaces, such as weighted network congestion games or weighted congestion games with singleton strategies. © 2012 INFORMS. Source

Baumgart D.C.,TU Berlin | Sandborn W.J.,University of California at San Diego
The Lancet | Year: 2012

Crohn's disease is a relapsing systemic inflammatory disease, mainly affecting the gastrointestinal tract with extraintestinal manifestations and associated immune disorders. Genome wide association studies identified susceptibility loci that - triggered by environmental factors - result in a disturbed innate (ie, disturbed intestinal barrier, Paneth cell dysfunction, endoplasmic reticulum stress, defective unfolded protein response and autophagy, impaired recognition of microbes by pattern recognition receptors, such as nucleotide binding domain and Toll like receptors on dendritic cells and macrophages) and adaptive (ie, imbalance of effector and regulatory T cells and cytokines, migration and retention of leukocytes) immune response towards a diminished diversity of commensal microbiota. We discuss the epidemiology, immunobiology, amd natural history of Crohn's disease; describe new treatment goals and risk stratification of patients; and provide an evidence based rational approach to diagnosis (ie, work-up algorithm, new imaging methods [ie, enhanced endoscopy, ultrasound, MRI and CT] and biomarkers), management, evolving therapeutic targets (ie, integrins, chemokine receptors, cell-based and stem-cell-based therapies), prevention, and surveillance. © 2012 Elsevier Ltd. Source

D'Adderio M.,Max Planck Institute For Mathematik | Moci L.,TU Berlin
European Journal of Combinatorics | Year: 2012

We prove that the Ehrhart polynomial of a zonotope is a specialization of the arithmetic Tutte polynomial introduced by Moci (2012) [16]. We derive some formulae for the volume and the number of integer points of the zonotope. © 2012 Elsevier Ltd. Source

Gabay C.,University of Geneva | Emery P.,University of Leeds | Van Vollenhoven R.,Karolinska Institutet | Dikranian A.,San Diego Arthritis Medical Clinic | And 7 more authors.
The Lancet | Year: 2013

Background Roughly a third of patients with rheumatoid arthritis treated with biological treatments receive them as monotherapy. Tocilizumab - an inhibitor of interleukin 6 receptor signalling - has been studied as monotherapy in several clinical trials. We assessed the efficacy and safety of tocilizumab monotherapy compared with adalimumab monotherapy for patients with rheumatoid arthritis. Methods We did this randomised, double-blind, parallel-group, phase 4 superiority study in 76 centres in 15 countries in North and South America, Australasia, and Europe. We enrolled patients who were aged at least 18 years, had severe rheumatoid arthritis for 6 months or more, and were intolerant to methotrexate or were inappropriate for continued methotrexate treatment. Patients were randomly assigned (1:1; block size of four) to receive tocilizumab 8 mg per kg bodyweight intravenously every 4 weeks plus placebo subcutaneously every 2 weeks or adalimumab 40 mg subcutaneously every 2 weeks plus placebo intravenously every 4 weeks for 24 weeks. Investigators, patients, and sponsor personnel were masked to assignment. The primary endpoint was change in disease activity score using 28 joints (DAS28) from baseline to week 24. This trial is registered with ClinicalTrials.gov, number NCT01119859. Findings We screened 452 patients and enrolled 326 patients. The intention-to-treat population contained 325 patients (163 assigned to tocilizumab, 162 assigned to adalimumab). Week 24 mean change from baseline in DAS28 was significantly greater in the tocilizumab group (-3·3) than in the adalimumab group (-1·8) patients (difference -1·5, 95% CI -1·8 to -1·1; p<0·0001). 16 of 162 (10%) patients in the adalimumab group versus 19 of 162 (12%) in the tocilizumab group had serious adverse events. More patients in the tocilizumab group than in the adalimumab group had increased LDL-cholesterol, increased alanine aminotransferase concentrations, and reduced platelet and neutrophil counts. Interpretation Tocilizumab monotherapy was superior to adalimumab monotherapy for reduction of signs and symptoms of rheumatoid arthritis in patients for whom methotrexate was deemed inappropriate. The adverse event profiles of tocilizumab and adalimumab were consistent with previous findings. Funding F Hoffmann-La Roche. © 2013 Elsevier Ltd. Source

Casas E.,University of Cantabria | Troltzsch F.,TU Berlin
SIAM Journal on Optimization | Year: 2012

An abstract optimization problem of minimizing a functional on a convex subset of a Banach space is considered. We discuss natural assumptions on the functional that permit establishing sufficient second-order optimality conditions with minimal gap with respect to the associated necessary ones. Though the two-norm discrepancy is taken into account, the obtained results exhibit the same formulation as the classical ones known from finite-dimensional optimization. We demonstrate that these assumptions are fulfilled, in particular, by important optimal control problems for partial differential equations. We prove that, in contrast to a widespread common belief, the standard second-order conditions formulated for these control problems imply strict local optimality of the controls not only in the sense of L∞, but also of L 2. © 2012 Society for Industrial and Applied Mathematics. Source

Kreutzer S.,TU Berlin
Logical Methods in Computer Science | Year: 2012

One of Courcelle's celebrated results states that if C is a class of graphs of bounded tree-width, then model-checking for monadic second order logic (MSO2) is fixedparameter tractable (fpt) on C by linear time parameterized algorithms, where the parameter is the tree-width plus the size of the formula. An immediate question is whether this is best possible or whether the result can be extended to classes of unbounded tree-width. In this paper we show that in terms of tree-width, the theorem cannot be extended much further. More specifically, we show that if C is a class of graphs which is closed under colourings and satisfies certain constructibility conditions and is such that the treewidth of C is not bounded by log84 n then MSO2-model checking is not fpt unless Sat can be solved in sub-exponential time. If the tree-width of C is not poly-logarithmically bounded, then MSO2-model checking is not fpt unless all problems in the polynomial-time hierarchy can be solved in sub-exponential time. © S. Kreutzer. Source

Cavalcante R.L.G.,Fraunhofer Institute for Telecommunications, Heinrich-Hertz-Institut | Stanczak S.,Fraunhofer Institute for Telecommunications, Heinrich-Hertz-Institut | Stanczak S.,TU Berlin
IEEE Journal on Selected Topics in Signal Processing | Year: 2013

We consider a convex optimization problem for nonhierarchical agent networks where each agent has access to a local or private time-varying function, and the network-wide objective is to find a time-invariant minimizer of the sum of these functions, provided that such a minimizer exists. Problems of this type are common in dynamic systems where the objective function is timevarying because of, for instance, the dependency on measurements that arrive continuously to each agent. A typical outer-loop optimization iteration for optimization problems of this type consists of a local optimization step based on the information provided by neighboring agents, followed by a consensus step to exchange and fuse local estimates of the agents. A great deal of research effort has been directed towards developing and better understanding such algorithms, which find many applications in distinct areas such as cognitive radio networks, distributed acoustic source localization, coordination of unmanned vehicles, and environmental modeling. Contrasting with existing work, which considers either dynamic systems or noisy links (but not both jointly), in this study we devise and analyze a novel distributed online algorithm for dynamic optimization problems in noisy communication environments. The main result of the study proves sufficient conditions for almost sure convergence of the algorithm as the number of iterations tends to infinity. The algorithm is applicable to a wide range of distributed optimization problems with time-varying cost functions and consensus updates corrupted by additive noise. Our results therefore extend previous work to include recently proposed schemes that merge the processes of computation and data transmission over noisy wireless networks for fast and efficient consensus protocols. To give a concrete example of an application, we show how to apply our general technique to the problem of distributed detection with adaptive filters. © 2013 IEEE. Source

Wittmann N.,TU Berlin
Energy Policy | Year: 2013

Global discussions on the reduction of Co2 emissions and the increasing interest in alternative energy sources and production technologies have started to concern oil exporting nations. International discussions on projects such as Desert Tec might also have sparked their interest to explore a possible diversification of their energy resource production portfolio. However, extremely low in-country retail prices of fossil fuels to date present a significant economic hurdle to such developments. This paper uses a formal model setup accompanied by intuitive graphical illustrations as well as a numerical example to analyze fossil fuel abundant nations' potential to transition to a supplier of renewable energy as well as possible pitfalls resulting from their status quo situation. © 2013 Elsevier Ltd. Source

Peuckert J.,TU Berlin
International Journal of Technology and Globalisation | Year: 2011

We compare newly industrialising countries as to their capabilities for integrating sustainability innovations into their catching-up processes. We thereby provide an approach to assess their absorption potential for sustainability innovations. The conditions that favour the exploitation of imitation opportunities are separated into general innovation capabilities and the sustainability selection environment. Using principal component analysis to aggregate numerous subjective indicators, we construct two composite indices that measure the functioning of the national innovation system and the societal anchoring of sustainability, respectively. Both indices have a strong positive correlation, suggesting that the development of certain institutions promotes both innovation and sustainability. Copyright © 2011 Inderscience Enterprises Ltd. Source

Voss J.-P.,TU Berlin | Bornemann B.,Luneburg University
Ecology and Society | Year: 2011

New concepts of governance take account of ambivalence, uncertainty, and distributed power in societal change. They aim for reflexivity regarding the limits of prognostic knowledge and actual control of complex processes of change. Adaptive management and transition management are two examples that evolved from the analysis of social-ecological and sociotechnical systems, respectively. Both feature strategies of collective experimentation and learning. In this paper, we ask how these two designs of reflexive governance consider politics. Based on a framework of different dimensions and levels of politics, we show that they are mainly concerned with problem solving by a focal process, but conflict and asymmetric power relations, as well as the embedding of processes within broader political contexts, are neglected. We suggest two routes for integrating politics into the design of reflexive governance: (1) recognize the politics of learning for sustainable development and develop safeguards against domination and capture by powerful actors, and (2) systematically consider the embedding of governance designs in political contexts and their ongoing dynamics for political fit. © 2011 by the author(s). Source

Tautz R.C.,TU Berlin | Lerche I.,Martin Luther University of Halle Wittenberg
Physics Reports | Year: 2012

This Review is concerned with summarizing known properties of the linear and non-linear Weibel instabilities including radiation from particles constrained by non-linear waves. In view of the purported importance of the Weibel instability for astrophysical objects (such as AGNs and relativistic jets) and for which only the emitted radiation field is available to help determine the existence of such Weibel modes, it seems appropriate to discuss the extent to which such modes are relevant. The first observation is that only for gyrotropic particle distribution functions (where the gyrotropy is perpendicular to the wave direction) can one have decoupled longitudinal and transverse linear Weibel modes that exist over a continuum of wavenumbers. For any asymmetry, no matter how small, the longitudinal and transverse linear modes are coupled and the continuum of wavenumbers collapses to isolated wavenumbers allowing Weibel modes as is determined both analytically and also with numerical simulations. This isolation of the wavenumbers suggests that any Weibel-like modes are non-linear and so a discussion of transverse non-linear Weibel modes is then given. Within the framework of such non-linear modes the emitted radiation of charged particles constrained by such modes is discussed. The spectrum of the emitted radiation tends to be concentrated in an emission cone centered on the direction of propagation of the soliton-like structure; the frequency spectrum tends to have emission at the highest frequencies allowed by the total emitted power limitations suggesting gamma-ray emission is dominantly prevalent. The polarization tends to be dominated by the parallel component of emission and has the electric vectors plane polarized. These basic properties of the emission spectra are the only components related to the underlying Weibel non-linear mode that are at all observable and can be used to indicate the appropriateness of such Weibel modes in the physical description of the astrophysical objects in question. © 2012 Elsevier B.V. Source

Papageorgiou N.S.,National Technical University of Athens | Winkert P.,TU Berlin
Advanced Nonlinear Studies | Year: 2014

We study a nonlinear parametric elliptic equation (nonlinear eigenvalue problem) driven by a nonhomogeneous differential operator. Our setting incorporates equations driven by the p-Laplacian, the (p, q)-Laplacian, and the generalized p-mean curvature differential operator. Applying variational methods we show that for λ > 0 (the parameter) sufficiently large the problem has at least three nontrivial smooth solutions whereby one is positive, one is negative and the last one has changing sign (nodal). In the particular case of (p, 2)-equations, using Morse theory, we produce another nodal solution for a total of four nontrivial smooth solutions. Source

Yavari M.H.,TU Berlin | Ahmadi V.,Tarbiat Modares University
IEEE Journal on Selected Topics in Quantum Electronics | Year: 2011

The important tradeoff between frequency bandwidth and single-mode behavior of multimode self-assembled InAs-GaAs quantum-dot (QD) laser by increasing temperature or homogeneous broadening is addressed. The effects of carrier dynamics on the frequency response of columnar-shaped self-assembled QD laser are analyzed. The phonon bottleneck problem is simulated. It is shown that to prevent the effect of phonon bottleneck on the frequency behavior, carrier relaxation lifetime must be less than a critical value about a few pico seconds, which is in agreement with the experimental results. Results show that carrier recombination in wetting layer has no important effect on the modulation response; however, carrier recombination inside dots degrades frequency response drastically. © 2011 IEEE. Source

Van Bevern R.,TU Berlin
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2012

A sunflower in a hypergraph is a set of hyperedges pairwise intersecting in exactly the same vertex set. Sunflowers are a useful tool in polynomial-time data reduction for problems formalizable as d-Hitting Set, the problem of covering all hyperedges (of cardinality at most d) of a hypergraph by at most k vertices. Additionally, in fault diagnosis, sunflowers yield concise explanations for "highly defective structures". We provide a linear-time algorithm that, by finding sunflowers, transforms an instance of d-Hitting Set into an equivalent instance comprising at most O(k d) hyperedges and vertices. In terms of parameterized complexity, we show a problem kernel with asymptotically optimal size (unless coNP ⊆ NP/poly). We show that the number of vertices can be reduced to O(k d-1) with additional processing in O(k 1.5d) time-nontrivially combining the sunflower technique with problem kernels due to Abu-Khzam and Moser. © 2012 Springer-Verlag. Source

Sanabria-Chinchilla J.,University of Houston | Asazawa K.,Daihatsu Motor Co. | Sakamoto T.,Daihatsu Motor Co. | Yamada K.,Daihatsu Motor Co. | And 2 more authors.
Journal of the American Chemical Society | Year: 2011

We report the discovery of a highly active Ni-Co alloy electrocatalyst for the oxidation of hydrazine (N2H4) and provide evidence for competing electrochemical (faradaic) and chemical (nonfaradaic) reaction pathways. The electrochemical conversion of hydrazine on catalytic surfaces in fuel cells is of great scientific and technological interest, because it offers multiple redox states, complex reaction pathways, and significantly more favorable energy and power densities compared to hydrogen fuel. Structure-reactivity relations of a Ni60Co40 alloy electrocatalyst are presented with a 6-fold increase in catalytic N 2H4 oxidation activity over todays benchmark catalysts. We further study the mechanistic pathways of the catalytic N2H 4 conversion as function of the applied electrode potential using differentially pumped electrochemical mass spectrometry (DEMS). At positive overpotentials, N2H4 is electrooxidized into nitrogen consuming hydroxide ions, which is the fuel cell-relevant faradaic reaction pathway. In parallel, N2H4 decomposes chemically into molecular nitrogen and hydrogen over a broad range of electrode potentials. The electroless chemical decomposition rate was controlled by the electrode potential, suggesting a rare example of a liquid-phase electrochemical promotion effect of a chemical catalytic reaction ("EPOC"). The coexisting electrocatalytic (faradaic) and heterogeneous catalytic (electroless, nonfaradaic) reaction pathways have important implications for the efficiency of hydrazine fuel cells.(Figure Presented) © 2011 American Chemical Society. Source

Lober J.,TU Berlin
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2014

We consider the stability of position control of traveling waves in reaction-diffusion systems as proposed in Löber and Engel [Phys. Rev. Lett. 112, 148305 (2014)PRLTAO0031-900710.1103/PhysRevLett.112.148305]. Instead of analyzing the controlled reaction-diffusion system, stability is studied on the reduced level of the equation of motion for the position over time of perturbed traveling waves. We find an interval of perturbations of initial conditions for which position control is stable. This interval can be interpreted as a localized region where traveling waves are susceptible to perturbations. For stationary solutions of reaction-diffusion systems with reflection symmetry, this region does not exist. Analytical results are in qualitative agreement with numerical simulations of the controlled Schlögl model. © 2014 American Physical Society. Source

Opper M.,TU Berlin | Sanguinetti G.,University of Edinburgh
Bioinformatics | Year: 2010

Motivation: mRNA transcriptional dynamics is governed by a complex network of transcription factor (TF) proteins. Experimental and theoretical analysis of this process is hindered by the fact that measurements of TF activity in vivo is very challenging. Current models that jointly infer TF activities and model parameters rely on either of the two main simplifying assumptions: either the dynamics is simplified (e.g. assuming quasi-steady state) or the interactions between TFs are ignored, resulting in models accounting for a single TF. Results: We present a novel approach to reverse engineer the dynamics of multiple TFs jointly regulating the expression of a set of genes. The model relies on a continuous time, differential equation description of transcriptional dynamics where TFs are treated as latent on/off variables and are modelled using a switching stochastic process (telegraph process). The model can not only incorporate both activation and repression, but allows any non-trivial interaction between TFs, including AND and OR gates. By using a factorization assumption within a variational Bayesian treatment we formulate a framework that can reconstruct both the activity profiles of the TFs and the type of regulation from time series gene expression data. We demonstrate the identifiability of the model on a simple but non-trivial synthetic example, and then use it to formulate non-trivial predictions about transcriptional control during yeast metabolism. Availability: http://homepages.inf.ed.ac.uk/gsanguin/. Contact: g.sanguinetti@ed.ac.uk. © The Author 2010. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org. Source

Tautz R.C.,TU Berlin | Shalchi A.,University of Manitoba
Astrophysical Journal | Year: 2011

Previous diffusion theories make diverse predictions concerning the ability of slab modes to scatter charged particles across the mean magnetic field. Whereas the original nonlinear guiding center theory provides a strong contribution of slab modes if a two-component model is employed, improved nonlinear guiding center theories describe cross-field transport due to slab modes as a subdiffusive process. Therefore, the slab fluctuations do not explicitly contribute to the perpendicular spatial diffusion coefficient in the late time limit. In the present article, numerical simulations are used to explore the validity of the different predictions. Only a very weak contribution is found due to slab modes. The numerical results confirm improved nonlinear guiding center theories. This conclusion has also implications for cross-field diffusion in three-dimensional turbulence. © 2011. The American Astronomical Society. All rights reserved.. Source

Beery M.,TU Berlin
Computer Aided Chemical Engineering | Year: 2010

Sustainable development is usually presented using the three pillar model: economy, environment and society. This research uses life cycle based assessments in conjunction with process system engineering methods for the design and analysis of sustainable processes with the example of pretreatment of seawater membrane desalination. At the first step, the sustainability potential of several state of the art process alternatives is analyzed (namely granular media- and membrane-based filtration). Conducting a broad environmental life cycle assessment (LCA, using GaBi4® software) together with a life cycle costs assessment (LCC, according to SETAC guidelines) forms the so called eco-efficiency analysis (based on a definition by Germany's institute for applied Ecology) which together with a qualitative process performance assessment gives a good idea about the sustainability potential of the different process alternatives. The results show that the current trend of using a membrane based pre-treatment is proven here to not always be a more sustainable process solution. © 2010 Elsevier B.V. All rights reserved. Source

The strong international growth of biofuels in the last decade brought the interest in bioenergy back on the agenda. While many life cycle assessments for biofuels mainly focus on environmental impacts and costs, over the last decade especially the energy balance of biofuel production chains has been a major point of criticism. This study applies a specially adapted and LCA-based analytical framework for rural energy service pathways (RESPs) to compare the use of Jatropha plant oil and biogas with other small-scale RESPs for lighting, cooking and mechanical power. The aim is to analyse their technological feasibility and economical viability by comparing the energy and cost efficiency. Results show strong differences for the investigated plant oil production and processing pathways, while the comparison with a baseline and a competitive renewable energy scenario reveals a weak performance of plant oil and even biogas in the categories of lighting and cooking. The potential for mechanical power depends largely on the careful optimisation of the energy service pathway by balancing the capital, energy, labour, and transport intensity. For the present case, the village scale production of Jatropha plant oil and biogas and their simultaneous use in a dual fuel engine to locally provide power and electricity would be the service pathway with the highest potential in terms of energy and cost efficiency. © 2012 Elsevier Ltd. Source

Ehrig R.,Bioenergy 2020+ GmbH | Behrendt F.,TU Berlin
Energy Policy | Year: 2013

In this paper the energy and carbon footprints of pellet imports from Australia, West Canada, and Russia for co-firing in Europe are investigated. Their ecologic and economic performances are proven by applying the Belgian and UK co-firing subsidy systems, which require dedicated sustainability evaluations. Based on the modelling of different subsidy schemes and price scenarios, the present paper identifies favourable conditions for the use of biomass co-firing in Germany and Austria, which currently do not have dedicated co-firing incentives. The present paper shows that under present conditions, co-firing has a narrow financial gap to coal with -3 to 4€ Cent/kWhel and has low CO2 mitigation costs compared to other renewables. Moreover, it is shown that co-firing is one of the most cost-attractive options to reach the EU-2020 targets. For policy makers, the support of co-firing is found to be very efficient in terms of cost-benefit ratio. It is proven that the co-firing subsidy schemes might direct supply chain decisions towards options with low energy and carbon impacts. © 2013 Elsevier Ltd. Source

Wassen E.,TU Berlin
Notes on Numerical Fluid Mechanics and Multidisciplinary Design | Year: 2010

An active flow control approach was investigated in order to reduce the aerodynamic drag of a generic square-back vehicle. Using Large Eddy Simulations, it could be shown that steady blowing along the rear edges of the vehicle can reduce the drag by more than 10%. The blowing angle was varied, and a most effective angle of 45°. was found. The control method leads to a delay of shear layer vortex generation and to changes in the wake structure that cause a pressure increase on the rear surface of the vehicle. A simple estimation of the energy balance showed that the energy input needed for the active control is relatively large. Only for one case investigated in this study a small net power gain was found. © 2010 Springer-Verlag Berlin Heidelberg. Source

Brandes T.,TU Berlin
Physical Review Letters | Year: 2010

The current through nanostructures like quantum dots can be stabilized by a classical feedback loop that continuously adjusts system parameters as a function of the number of tunnelled particles n. At large times, the feedback loop freezes the fluctuations of n, which leads to highly accurate, continuous single particle transfers. For the simplest case of feedback acting simultaneously on all system parameters, we show how to reconstruct the original full counting statistics from the frozen distribution. © 2010 The American Physical Society. Source

Oestreich M.,TU Berlin
Angewandte Chemie - International Edition | Year: 2014

Glowing results with less phosphorus: Tremendous progress has been made recently in asymmetric intermolecular Heck chemistry. Previously unprecedented enantioselective Heck-Matsuda reactions have been accomplished, and mixed phosphine/phosphine oxides have been shown to be superior ligands in enantioselective Mizoroki-Heck reactions. All of this was achieved with chiral ligands containing few or even no phosphorus donors (see scheme). Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Enthaler S.,TU Berlin
Angewandte Chemie - International Edition | Year: 2014

Polymers occupy an important role in our current society. Besides their great success, an issue is the accumulation of huge amounts of end-of-life polymers. Currently, the waste management is based primarily on landfills, thermal recycling, and downcycling. Notably, only a small portion of end-of-life materials is recycled by depolymerization, which refers to the creation of synthetic precursors that can be polymerized to new polymers to close the cycle. Widely used polymers in modern times are silicones (polysiloxanes), the intrinsic properties of which make their depolymerization demanding; only a few high-temperature or less environmentally friendly processes have been reported. In this regard, we have established an efficient low-temperature protocol for the depolymerization of silicones with benzoyl fluoride in the presence of cheap zinc salts as precatalysts to yield defined products. Notably, the products can be useful synthetic precursors for the preparation of new polymers, so that an overall recycling process is feasible. Reclaiming resources: Straightforward zinc-catalyzed depolymerization of a range of polysiloxanes produced difluorodimethylsilanes and 1,3-difluoro-1,1,3,3-tetramethyldisiloxanes, which are appropriate starting materials for new polymers. In the presence of simple zinc salts, extraordinary catalytic activity and selectivity were feasible at low temperature (see scheme). © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Uhlig S.,TU Berlin
Telecommunication Systems | Year: 2010

Most studies of Internet traffic rely on observations from a single link. The corresponding traffic dynamics has been studied for more than a decade and is well understood. The study of how traffic on the Internet topology, on the other hand, is poorly understood and has been largely limited to the distribution of traffic among source-destination pairs inside the studied network, also called the traffic matrix. In this paper, we make a first step towards understanding the way traffic gets distributed onto the whole topology of the Internet. For this, we rely on the traffic seen by a transit network, for a period of more than a week. As we are still at the stage of understanding the topological traffic distribution, we do not try to model the traffic dynamics. Rather we concentrate on understanding the complexity of describing the traffic observed by a transit network, how it maps onto the AS-level topology of the Internet and how it changes over time. For this, we rely on well-known tools of multi-variate analysis and multi-resolution analysis. Our first observation is that the structure of the Internet topology highly impacts the traffic distribution. Second, our attempts at compressing the traffic on the topology through dimension reduction suggests two options for traffic modeling: (1) to ignore links on the topology for which we do not see much traffic, or (2) to ignore time scales smaller than a few hours. In either case, important properties of the traffic might be lost, so might not be an option to build realistic models of Internet traffic. Realistic models of Internet traffic on the topology are not out of reach though. In this paper, we identify two prop- erties such models should have: (1) use a compact representation of the dependencies of the traffic on the topology, and (2) be able to capture the complex multi-scale nature of traffic dynamics on different types of links. © Springer Science + Business Media, LLC 2009. Source

Khader O.,TU Berlin | Willig A.,University of Canterbury
Computer Communications | Year: 2013

In this paper we analyze in detail the energy consumption characteristics of the Wireless HART protocol when operated with a popular transceiver, the ChipCon CC2420. We analyze how much various factors contribute to the overall energy consumption over a longer period of 12 h. These factors include the amount of management traffic and the power levels required for various transceiver activities (transmit, receive, listen, sleep). It turns out that in light traffic scenarios and with only a minimum-complexity level of exploitation of the transceivers sleeping capabilities the energy spent in the sleep state over 12 h is quite substantial. We then proceed to analyze the energy consumption characteristics with a more complex usage of the transceivers sleeping capabilities in which each node individually selects its next sleep state according to its transmission/reception schedule. With this scheme the energy consumption in the sleep state (over 12 h) can be reduced substantially. © 2013 Elsevier B.V. All rights reserved. Source

Ziegler F.,TU Berlin
International Journal of Refrigeration | Year: 2010

The Stefan-number is one out of the multitude of dimensionless numbers which predominantly are used in chemical engineering or heat and mass transfer problems. It relates sensible heat to latent heat and is a key number in solving the problem of heat transfer during solidification or melting. However, numbers similar to this show up also when several thermodynamic problems or relationships in refrigeration engineering are analyzed. Using the Stefan-number it can be distinguished if a refrigerant superheats or condenses during compression, it gives the size of the throttling loss, and it helps to decide if a suction line heat exchanger is beneficial or not. For absorption heat pumping, it allows to quantify the most important loss mechanism, the solution heat exchanger loss. Of course, all this information can be acquired in different ways - and maybe in more precise ways - also, but at least for teaching the basics of refrigeration the Stefan-number is simple to use and very easy to understand. In this paper, the different ways of how to use the Stefan-number in teaching and understanding thermodynamics of refrigerants are presented. © 2010 Elsevier Ltd and IIR. All rights reserved. Source

Crane K.,California Institute of Technology | Pinkall U.,TU Berlin | Schroder P.,California Institute of Technology
ACM Transactions on Graphics | Year: 2013

We present a formulation of Willmore flow for triangulated surfaces that permits extraordinarily large time steps and naturally preserves the quality of the input mesh. The main insight is that Willmore flow becomes remarkably stable when expressed in curvature space - we develop the precise conditions under which curvature is allowed to evolve. The practical outcome is a highly efficient algorithm that naturally preserves texture and does not require remeshing during the flow. We apply this algorithm to surface fairing, geometric modeling, and construction of constant mean curvature (CMC) surfaces. We also present a new algorithm for length-preserving flow on planar curves, which provides a valuable analogy for the surface case. Copyright © ACM 2013. Source