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Richter S.,ETH Zurich | Jones C.N.,Ecole Polytechnique Federale de Lausanne | Morari M.,ETH Zurich
IEEE Transactions on Automatic Control | Year: 2012

This paper proposes to use Nesterov's fast gradient method for the solution of linear quadratic model predictive control (MPC) problems with input constraints. The main focus is on the method's a priori computational complexity certification which consists of deriving lower iteration bounds such that a solution of pre-specified suboptimality is obtained for any possible state of the system. We investigate cold- and warm-starting strategies and provide an easily computable lower iteration bound for cold-starting and an asymptotic characterization of the bounds for warm-starting. Moreover, we characterize the set of MPC problems for which small iteration bounds and thus short solution times are expected. The theoretical findings and the practical relevance of the obtained lower iteration bounds are underpinned by various numerical examples and compared to certification results for a primal-dual interior point method. © 2011 IEEE. Source


Canto C.,Nestle | Auwerx J.,Ecole Polytechnique Federale de Lausanne
Cold Spring Harbor Symposia on Quantitative Biology | Year: 2011

The ability of NAD + to act as a metabolic cofactor and as a rate-limiting cosubstrate for many enzymes, particularly the sirtuins, has led to the identification of a pivotal role of NAD + levels in the control of whole-body metabolic homeostasis. Bioavailability and compartmentalization of NAD + have become highly relevant issues that we need to understand in order to elucidate how NAD + acts both as a readout of the metabolic milieu and as an effector triggering appropriate cellular adaptations. © 2011 Cold Spring Harbor Laboratory Press. Source


Garny M.,German Electron Synchrotron | Kartavtsev A.,Max Planck Institute for Nuclear Physics | Hohenegger A.,Ecole Polytechnique Federale de Lausanne
Annals of Physics | Year: 2013

The lepton asymmetry generated by the out-of-equilibrium decays of heavy Majorana neutrinos with a quasi-degenerate mass spectrum is resonantly enhanced. In this work, we study this scenario within a first-principle approach. The quantum field theoretical treatment is applicable for mass splittings of the order of the width of the Majorana neutrinos, for which the enhancement is maximally large. The non-equilibrium evolution of the mixing Majorana neutrino fields is described by a formal analytical solution of the Kadanoff-Baym equations, that is obtained by neglecting the back-reaction. Based on this solution, we derive approximate analytical expressions for the generated asymmetry and compare them to the Boltzmann result. We find that the resonant enhancement obtained from the Kadanoff-Baym approach is smaller compared to the Boltzmann approach, due to additional contributions that describe coherent transitions between the Majorana neutrino species. We also discuss corrections to the masses and widths of the degenerate pair of Majorana neutrinos that are relevant for very small mass splitting, and compare the approximate analytical result for the lepton asymmetry with numerical results. © 2012 Elsevier Inc. Source


Tschopp P.,University of Geneva | Duboule D.,University of Geneva | Duboule D.,Ecole Polytechnique Federale de Lausanne
Annual Review of Genetics | Year: 2011

The evolution of vertebrate genomes was accompanied by an astounding increase in the complexity of their regulatory modalities. Genetic redundancy resulting from large-scale genome duplications at the base of the chordate tree was repeatedly exploited by the functional redeployment of paralogous genes via innovations in their regulatory circuits. As a paradigm of such regulatory evolution, we have extensively studied those control mechanisms at work in-cis over vertebrate Hox gene clusters. Here, we review the portfolio of genetic strategies that have been developed to tackle the intricate relationship between genomic topography and the transcriptional activities in this gene family, and we describe some of the mechanistic insights we gained by using the HoxD cluster as an example. We discuss the high heuristic value of this system in our general understanding of how changes in transcriptional regulation can diversify gene function and thereby fuel morphological evolution. © 2011 by Annual Reviews. All rights reserved. Source


Banerji N.,Ecole Polytechnique Federale de Lausanne
Journal of Materials Chemistry C | Year: 2013

In this feature article, we review and examine evidence that the primary photoexcited species in conjugated polymers is considerably delocalized. Localization occurs via a series of complex relaxation mechanisms on the <200 femtosecond time scale. We show that short-lived delocalization in the neutral excited state and charge separated state of bulk heterojunction blends might play an essential role in ensuring efficient formation of free charge carriers for photovoltaic applications. Finally, the additional parameter of intramolecular charge transfer character in the excited state of more recently developed donor-acceptor copolymers is discussed. Both delocalization and partial charge transfer reduce the binding of the electron and hole in photoexcited organic semiconductors and can help to overcome the bottleneck to macroscopic current generation in polymer solar cells. © 2013 The Royal Society of Chemistry. Source


Wigginton K.R.,University of Maryland University College | Kohn T.,Ecole Polytechnique Federale de Lausanne
Current Opinion in Virology | Year: 2012

Drinking waters are treated for enteric virus via a number of disinfection techniques including chemical oxidants, irradiation, and heat, however the inactivation mechanisms during disinfection remain elusive. Owing to the fact that a number of significant waterborne virus strains are not readily culturable in vitro at this time (e.g. norovirus, hepatitis A), the susceptibility of these viruses to disinfection is largely unknown. An in-depth understanding of the mechanisms involved in virus inactivation would aid in predicting the susceptibility of non-culturable virus strains to disinfection and would foster the development of improved disinfection methods. Recent technological advances in virology research have provided a wealth of information on enteric virus compositions, structures, and biological functions. This knowledge will allow for physical/chemical descriptions of virus inactivation and thus further our understanding of virus disinfection to the most basic mechanistic level. © 2011 Elsevier B.V. All rights reserved. Source


Song J.,McGill University | Curtin W.A.,Ecole Polytechnique Federale de Lausanne
Acta Materialia | Year: 2014

Atomistic simulations of the effects of H on edge dislocation mobility and pile-ups are performed to investigate possible nanoscale mechanisms for hydrogen-enhanced localized plasticity (HELP). α-Fe is used as a model system because H diffusion is fast enough to capture kinetics within the time scales of molecular dynamics and because edge dislocation glide in α-Fe is similar to glide in face-centered cubic metals. Results over a wide range of H concentrations sufficient to generate a range of sizes in the Cottrell atmospheres show that the Cottrell atmospheres follow the moving dislocations, leading to a resistance to dislocation motion that is consistent with solute drag theory; thus, H reduces the dislocation mobility. Furthermore, once motion stops and a pile-up is established, the H Cottrell atmospheres do not affect the equilibrium spacing of dislocations in the pile-up; thus, the H atmosphere provides no "shielding" of dislocation-dislocation interactions. This result is consistent with conclusions from previous continuum calculations. Two oft-proposed mechanisms for HELP (H-induced increase in true dislocation mobility and decrease in dislocation-dislocation pile-up interactions) are therefore not supported by the present simulations. A mechanistic understanding of HELP phenomena observed in various experiments thus requires evaluation of more complex H-dislocation interactions. © 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Source


Gonseth C.,Ecole Polytechnique Federale de Lausanne
Climatic Change | Year: 2013

With its numerous mountain regions and its well developed winter tourism infrastructures, Switzerland is a country whose tourism sector is known to be sensitive to snowpack variability. With climate change-which is predicted to have negative impacts on snow depths and duration-the need for accurately assessing the sensitivity of winter tourism consumption to changing snow conditions is reinforced. Taking advantage of newly available data on visitation rates at Swiss ski areas, we analyze the effect of snow conditions on skier visits using standard panel data regression techniques. We assume the magnitude of this effect to be conditional on the level of snowmaking investments. Higher snowmaking investments should lead to a lower sensitivity. Our results validate this hypothesis and also shed light on the competitive interactions between lower and higher lying ski areas located in the same tourism region. In fact, our results show that better snow conditions in the former reduces visitation rates in the latter. Eventually, we find that ski areas benefiting from sunny conditions tend to have, ceteris paribus, more skier visits. This suggests additional impacts if climate change were to modify sunshine duration in mountain regions. © 2013 Springer Science+Business Media Dordrecht. Source


Hebert D.N.,University of Massachusetts Amherst | Molinari M.,Institute for Research in Biomedicine | Molinari M.,Ecole Polytechnique Federale de Lausanne
Trends in Biochemical Sciences | Year: 2012

Nascent polypeptides entering the endoplasmic reticulum (ER) are covalently modified with pre-assembled oligosaccharides. The terminal glucose and mannose residues are immediately removed after transfer of the oligosaccharide onto newly synthesized polypeptides. This processing determines whether the polypeptide will be retained in the ER, transported along the secretory pathway, or dislocated across the ER membrane for destruction. New avenues of research and some issues of controversy have recently been opened by the discovery that lectin-oligosaccharide interactions stabilize supramolecular complexes between regulators of ER-associated degradation (ERAD). In this Opinion article, we propose a unified model that depicts carbohydrates acting both as flags signaling the fitness of a maturing protein and as docking sites that regulate the assembly and stability of the ERAD machinery. © 2012 Elsevier Ltd. Source


Mischler S.,Ecole Polytechnique Federale de Lausanne | Munoz A.I.,Polytechnic University of Valencia
Wear | Year: 2013

A good biocompatibility, excellent mechanical properties and high corrosion resistance characterize CoCrMo alloys. Therefore they are widely used for artificial joints in biomedical implants. However, the degradation of the implants during service life leads to the release into the body of toxic ions and wear particles. This continuous degradation is of concern for long-term stability of the implants. Published literature has highlighted the relevance of lubrication as well as metallurgical and contact mechanical factors on the degradation of CoCrMo implant alloys. Recent experimental investigations have proposed tribocorrosion, i.e., the interplay of mechanical wear and corrosion by the body fluids, as one of the crucial degradation mechanism of implants. Tribocorrosion is sub-discipline of tribology and corrosion that recently made significant progresses in mechanistic understanding and modelling. The present work aims at evaluating published results on the degradation of CoCrMo alloys using existing tribocorrosion concepts. Results show that wear accelerated corrosion due to mechanical removal of the passive film during sliding is a major contribution to the overall degradation. Further, a transition from low (10-6N/mm3m) to high (10-4N/mm3m) wear coefficients was found at a threshold electrode potential close to 0.2 VSHE These findings clearly show that electrochemical phenomena play a key role on the tribological behaviour of biomedical CoCrMo alloy implants. © 2012 Elsevier B.V. Source


Tuia D.,Ecole Polytechnique Federale de Lausanne | Munoz-Mari J.,University of Valencia
IEEE Transactions on Geoscience and Remote Sensing | Year: 2013

In this paper, we study the applicability of active learning (AL) in operative scenarios. More particularly, we consider the well-known contradiction between the AL heuristics, which rank the pixels according to their uncertainty, and the user's confidence in labeling, which is related to both the homogeneity of the pixel context and user's knowledge of the scene. We propose a filtering scheme based on a classifier that learns the confidence of the user in labeling, thus minimizing the queries where the user would not be able to provide a class for the pixel. The capacity of a model to learn the user's confidence is studied in detail, also showing that the effect of resolution in such a learning task. Experiments on two QuickBird images of different resolutions (with and without pansharpening) and considering committees of users prove the efficiency of the filtering scheme proposed, which maximizes the number of useful queries with respect to traditional AL. © 1980-2012 IEEE. Source


Chergui M.,Ecole Polytechnique Federale de Lausanne
Faraday Discussions | Year: 2014

I discuss the recent developments concerning emerging ultrafast sources of short wavelength radiation, as well as the new methods they generate. I then dwell on a few examples of recent results and the way the new sources will bring major advancements in our understanding of fundamental chemical dynamics. © The Royal Society of Chemistry 2014. Source


Chergui M.,Ecole Polytechnique Federale de Lausanne
Dalton Transactions | Year: 2012

This perspective presents some recent results concerning ultrafast intramolecular relaxation processes in metal-based molecular complexes. Ultrafast electronic/vibrational relaxation at sub-vibrational time scales, ultrafast intersystem crossing processes and ultrafast structure changes are discussed, stressing the questions that still need to be solved in order to arrive at a rationale that describes these processes. We will also discuss some new techniques, based on core-level spectroscopies that can provide new insights into the ultrafast intramolecular relaxation in these systems. © 2012 The Royal Society of Chemistry. Source


Chen X.,University of Missouri - Kansas City | Li C.,CAS Dalian Institute of Chemical Physics | Gratzel M.,Ecole Polytechnique Federale de Lausanne | Kostecki R.,Lawrence Berkeley National Laboratory | Mao S.S.,Lawrence Berkeley National Laboratory
Chemical Society Reviews | Year: 2012

Over the past decades, there have been many projections on the future depletion of the fossil fuel reserves on earth as well as the rapid increase in green-house gas emissions. There is clearly an urgent need for the development of renewable energy technologies. On a different frontier, growth and manipulation of materials on the nanometer scale have progressed at a fast pace. Selected recent and significant advances in the development of nanomaterials for renewable energy applications are reviewed here, and special emphases are given to the studies of solar-driven photocatalytic hydrogen production, electricity generation with dye-sensitized solar cells, solid-state hydrogen storage, and electric energy storage with lithium ion rechargeable batteries. This journal is © The Royal Society of Chemistry 2012. Source


Ancey C.,Ecole Polytechnique Federale de Lausanne
European Physical Journal: Special Topics | Year: 2012

Predicting the occurrence and spatial extent of extreme avalanches is a longstanding issue. Using field data pooled from various sites within the same mountain range, authors showed that the avalanche size distribution can be described using either an extreme value distribution or a thick-tailed distribution, which implies that although they are much larger than common avalanches, extreme avalanches belong to the same population of events as "small" avalanches. Yet, when looking at historical records of catastrophic avalanches, archives reveal that a few avalanches had features that made them "extra-ordinary." Applying avalanche-dynamics or statistical models to simulate these past events runs into considerable difficulty since the model parameters or the statical properties are very different from the values usually set to model extreme avalanches. Were these events genuine outliers (also called "dragon-kings")? What were their distinctive features? This paper reviews some of the concepts in use to model extreme events, gives examples of processes that were at play in extreme avalanches, and shows that the concept of dragon-king avalanches is of particular relevance to describing some extreme avalanches. © 2012 EDP Sciences and Springer. Source


Corminboeuf C.,Ecole Polytechnique Federale de Lausanne
Accounts of Chemical Research | Year: 2014

Kohn-Sham density functional theory offers a powerful and robust formalism for investigating the electronic structure of many-body systems while providing a practical balance of accuracy and computational cost unmatched by other methods. Despite this success, the commonly used semilocal approximations have difficulties in properly describing attractive dispersion interactions that decay with R-6 at large intermolecular distances. Even in the short to medium range, most semilocal density functionals fail to give an accurate description of weak interactions. The omnipresence of dispersion interactions, which are neglected in the most popular electronic structure framework, has stimulated intense developments during the past decade.In this Account, we summarize our effort to develop and implement dispersion corrections that dramatically reduce the failures of both inter- and intramolecular interaction energies. The proposed schemes range from improved variants of empirical atom pairwise dispersion correction (e.g., dD10) to robust formulations dependent upon the electron density. Emphasis has been placed on introducing more physics into a modified Tang and Toennies damping function and deriving accurate dispersion coefficients. Our most sophisticated and established density-dependent correction, dDsC, is based on a simple generalized gradient approximation (GGA)-like reformulation of the exchange hole dipole moment introduced by Becke and Johnson. Akin to its empirical precursor, dDsC dramatically improves the interaction energy of a variety of standard density functionals simultaneously for typical intermolecular complexes and shorter-range interactions occurring within molecules. The broad applicability and robustness of the dDsC scheme is demonstrated on various representative reaction energies, geometries, and molecular dynamic simulations. The suitability of the a posteriori correction is also established through comparisons with the more computationally demanding self-consistent implementation. The proposed correction is then exploited to identify the key factors at the origin of the errors in thermochemistry beyond van der Waals complexes. Particular focus is placed on charge-transfer and mixed-valence complexes, which are relevant to the field of organic electronics. These types of complexes represent insightful examples for which the delocalization error may partially counterbalance the missing dispersion. Our devised methodology reveals the true performance of standard density functional approximations and the subtle interplay between the two types of errors. The analysis presented provides guidance for future functional development that could further improve the modeling of the structures and properties of molecular materials. Overall, the proposed state-of-the-art approaches have contributed to stress the crucial role of dispersion and improve their description in both straightforward van der Waals complexes and more challenging chemical situations. For the treatment of the latter, we have also provided relevant insights into which type of density functionals to favor. © 2014 American Chemical Society. Source


Montavon T.,Ecole Polytechnique Federale de Lausanne
Philosophical transactions of the Royal Society of London. Series B, Biological sciences | Year: 2013

During development, a properly coordinated expression of Hox genes, within their different genomic clusters is critical for patterning the body plans of many animals with a bilateral symmetry. The fascinating correspondence between the topological organization of Hox clusters and their transcriptional activation in space and time has served as a paradigm for understanding the relationships between genome structure and function. Here, we review some recent observations, which revealed highly dynamic changes in the structure of chromatin at Hox clusters, in parallel with their activation during embryonic development. We discuss the relevance of these findings for our understanding of large-scale gene regulation. Source


Gnansounou E.,Ecole Polytechnique Federale de Lausanne
Energy | Year: 2011

Over the last decade, the production and consumption of biofuels increased rapidly worldwide, in an attempt to reduce GHG (greenhouse gas) emissions, diversify transportation fuels, promote renewable energy, and create or maintain employment, especially in rural areas and developing countries. Although policy instruments being currently implemented in industrialized regions focus on sustainable biofuels, the definition and assessment of sustainability remains a highly debated issue. Several countries have adopted compulsory targets or financial incentives for promoting biofuels, and only a few countries have accounted for sustainability certification schemes for those biofuels within their policy framework. In this paper, a logic-based model for assessing the sustainability of biofuels is presented. The model uses a hierarchical structure to link multiple factors from the more specific variables to the most general one, sustainability performance. The strengths and limitations of the model are discussed and the anticipated improvements are provided. © 2010 Elsevier Ltd. Source


Rachidi F.,Ecole Polytechnique Federale de Lausanne
IEEE Transactions on Electromagnetic Compatibility | Year: 2012

We discuss the transmission line (TL) theory and its application to the problem of lightning electromagnetic field coupling to TLs. We start with the derivation of the general field-to-TL coupling equations for the case of a single-wire line above a perfectly conducting ground. The derived equations are solely based on the thin-wire approximation and they do take into account high-frequency radiation effects. Under the TL approximation, the general equations reduce to the Agrawal et al. field-to-TL coupling equations. After a short discussion on the underlying assumptions of the TL theory, three seemingly different but completely equivalent approaches that have been proposed to describe the coupling of electromagnetic fields to TLs are presented. The derived equations are then extended to deal with the presence of losses and multiple conductors and expressions for the line parameters, including the ground impedance and admittance, are presented. The time-domain representation of the field-to-TL coupling equations, which allows for a straightforward treatment of nonlinear phenomena as well as the variation in the line topology, is also described. Solution methods in the frequency domain and in the time domain are given and application examples with reference to lightning-induced voltages are presented and discussed. Specifically, the effects of ground losses and corona are illustrated and discussed. When the traveling voltage and current waves are originated from lumped excitation sources located at a specific location along a TL (direct lightning strike), both the corona phenomenon and ground losses result, in general, in an attenuation and dispersion of propagating surges along TLs. However, when distributed sources representing the action of the electromagnetic field from a nearby lightning illuminating the line are present, ground losses and corona phenomenon could result in important enhancement of the induced voltage magnitude. © 2012 IEEE. Source


Hu X.,Ecole Polytechnique Federale de Lausanne
Chemical Science | Year: 2011

Cross coupling of non-activated alkyl halides is a potentially transformative methodology in organic synthesis. Herein we review the recent development of nickel-catalyzed coupling of non-activated alkyl halides. The current understanding of the mechanism of these coupling reactions is highlighted. As the mechanism is ligand-dependant, the perspective is organized according to the types of ligands employed in the catalysis. © The Royal Society of Chemistry 2011. Source


Chakareski J.,Ecole Polytechnique Federale de Lausanne
IEEE Transactions on Multimedia | Year: 2011

We investigate two important problems in media delivery via active network agents. First, we consider streaming multiple video assets over a shared backbone network through an intermediate proxy-server to a set of receiving clients. The proxy is located at the junction of the backbone network and the last hop to each of the clients and coordinates the delivery of the videos from the origin media server to the clients. We propose an optimization framework that enables the proxy to coordinate the streaming process such that the overall end-to-end performance of the video streams is maximized for the given data rate resources on the backbone and the last hop links. Prospective video quality requirements for the associated media sessions are also taken into consideration in the analysis. Through experiments, we study in detail the operation of the framework and the influence of the various constraints that it considers. Furthermore, we measure its performance gains relative to a sender-driven system where the media server controls the delivery of the data with no assistance from an intervening proxy. We establish an analytical relationship between the relative improvement of the proxy-based system, the network conditions on the backbone and the last hops, and the number of streams served. The gains of the proxy-driven system measured in our experiments closely match their expected values predicted by this relationship. © 2006 IEEE. Source


Yazyev O.V.,Ecole Polytechnique Federale de Lausanne | Chen Y.P.,Purdue University
Nature Nanotechnology | Year: 2014

Graphene, a single atomic layer of graphitic carbon, has attracted intense attention because of its extraordinary properties that make it a suitable material for a wide range of technological applications. Large-area graphene films, which are necessary for industrial applications, are typically polycrystalline-that is, composed of single-crystalline grains of varying orientation joined by grain boundaries. Here, we present a review of the large body of research reported in the past few years on polycrystalline graphene. We discuss its growth and formation, the microscopic structure of grain boundaries and their relations to other types of topological defect such as dislocations. The Review further covers electronic transport, optical and mechanical properties pertaining to the characterizations of grain boundaries, and applications of polycrystalline graphene. We also discuss research, still in its infancy, performed on other two-dimensional materials such as transition metal dichalcogenides, and offer perspectives for future directions of research. © 2014 Macmillan Publishers Limited. Source


Kamada K.,Ecole Polytechnique Federale de Lausanne
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2015

Higgs G-inflation is an inflation model that takes advantage of a Galileon-like derivative coupling. It is a non-renormalizable operator and is strongly coupled at high energy scales. Perturbative analysis does not have a predictive power any longer there. In general, when the Lagrangian is expanded around the vacuum, the strong coupling scale is identified as the mass scale that appears in non-renormalizable operators. In inflationary models, however, the identification of the strong coupling scale is subtle, since the structures of the kinetic term as well as the interaction itself can be modified by the background inflationary dynamics. Therefore, the strong coupling scale depends on the background. In this letter, we evaluate the strong coupling scale of the fluctuations around the background in the Higgs G-inflation including the Nambu-Goldstone modes associated with the symmetry breaking. We find that the system is sufficiently weakly coupled when the scales which we now observe exit the horizon during inflation and the observational predictions with the semiclassical treatment are valid. However, we also find that the inflaton field value at which the strong coupling scale and the Hubble scale meet is less than the Planck scale. Therefore, we cannot describe the model from the Planck scale, or the chaotic initial condition. © 2015 The Author. Source


Karananas G.K.,Ecole Polytechnique Federale de Lausanne
Classical and Quantum Gravity | Year: 2015

In this paper we investigate the physical spectrum of the gravitational theory based on the Poincaré group with terms that are at most quadratic in tetrad and spin connection, allowing for the presence of parity-even as well as parity-odd invariants. We determine restrictions on the parameters of the action so that all degrees of freedom propagate and are neither ghosts nor tachyons. We show that the addition of parity non-conserving invariants extends the healthy parameter space of the theory. To accomplish our goal, we apply the weak field approximation around flat spacetime and in order to facilitate the analysis, we separate the bilinear action for the excitations into completely independent spin sectors. For this purpose, we employ the spin-projection operator formalism and extend the original basis built previously, to be able to handle the parity-odd pieces. © 2015 IOP Publishing Ltd. Source


Tosic I.,University of California at Berkeley | Frossard P.,Ecole Polytechnique Federale de Lausanne
IEEE Signal Processing Magazine | Year: 2011

Huge amounts of high-dimensional information are captured every second by diverse natural sensors such as the eyes or ears, as well as artificial sensors like cameras or microphones. This information is largely redundant in two main aspects: it often contains multiple correlated versions of the same physical world and each version is usually densely sampled by generic sensors. The relevant information about the underlying processes that cause our observations is generally of much reduced dimensionality compared to such recorded data sets. The extraction of this relevant information by identifying the generating causes within classes of signals is the central topic of this article. © 2006 IEEE. Source


Kiritsis D.,Ecole Polytechnique Federale de Lausanne
CAD Computer Aided Design | Year: 2011

With the advent of the information and related emerging technologies, such as RFID, small size sensors and sensor networks or, more generally, product embedded information devices (PEID), a new generation of products called smart or intelligent products is available in the market. Although various definitions of intelligent products have been proposed, we introduce a new definition of the notion of Intelligent Product inspired by what happens in nature with us as human beings and the way we develop intelligence and knowledge. We see an intelligent product as a product system which contains sensing, memory, data processing, reasoning and communication capabilities at four intelligence levels. This future generations of Intelligent Products will need new Product Data Technologies allowing the seamless interoperability of systems and exchange of not only Static but of Dynamic Product Data as well. Actual standards for PDT cover only lowest intelligence of today's products. In this context, we try to shape the actual state and a possible future of the Product Data Technologies from a Closed-Loop Product Lifecycle Management (C-L PLM) perspective. Our approach is founded in recent findings of the FP6 IP 507100 project PROMISE and follow-up research work. Standards of the STEP family, covering the product lifecycle to a certain extend (PLCS) as well as MIMOSA and ISO 15926 are discussed together with more recent technologies for the management of ID and sensor data such as EPCglobal, OGC-SWE and relevant PROMISE propositions for standards. Finally, the first efforts towards ontology based semantic standards for product lifecycle management and associated knowledge management and sharing are presented and discussed. © 2010 Elsevier Ltd. All rights reserved. Source


Munch M.,Ecole Polytechnique Federale de Lausanne | Bromundt V.,University of Basel
Dialogues in Clinical Neuroscience | Year: 2012

Environmental light synchronizes the primary mammalian biological clock in the suprachiasmatic nuclei, as well as many peripheral clocks in tissues and cells, to the solar 24-hour day. Light is the strongest synchronizing agent (zeitgeber) for the circadian system, and therefore keeps most biological and psychological rhythms internally synchronized, which is important for optimum function. Circadian sleep-wake disruptions and chronic circadian misalignment, as often observed in psychiatric and neurodegenerative illness, can be treated with light therapy. The beneficial effect on circadian synchronization, sleep quality, mood, and cognitive performance depends on timing, intensity, and spectral composition of light exposure. Tailoring and optimizing indoor lighting conditions may be an approach to improve wellbeing, alertness, and cognitive performance and, in the long term, producing health benefits. © 2012 LLS SAS. Source


Davis B.A.S.,Ecole Polytechnique Federale de Lausanne
Vegetation History and Archaeobotany | Year: 2013

Modern pollen samples provide an invaluable research tool for helping to interpret the quaternary fossil pollen record, allowing investigation of the relationship between pollen as the proxy and the environmental parameters such as vegetation, land-use, and climate that the pollen proxy represents. The European Modern Pollen Database (EMPD) is a new initiative within the European Pollen Database (EPD) to establish a publicly accessible repository of modern (surface sample) pollen data. This new database will complement the EPD, which at present holds only fossil sedimentary pollen data. The EMPD is freely available online to the scientific community and currently has information on almost 5,000 pollen samples from throughout the Euro-Siberian and Mediterranean regions, contributed by over 40 individuals and research groups. Here we describe how the EMPD was constructed, the various tables and their fields, problems and errors, quality controls, and continuing efforts to improve the available data. © 2013 Springer-Verlag Berlin Heidelberg. Source


Yazyev O.V.,Ecole Polytechnique Federale de Lausanne
Solid State Communications | Year: 2012

Recent experimental investigations show that large-area samples of graphene tend to be polycrystalline. Physical properties of such samples are strongly affected by the presence of intrinsic topological defects of polycrystalline materials - dislocations and grain boundaries. This article reviews recent progress in understanding dislocations and grain boundaries in graphene. First, a systematic approach towards constructing topological defects in graphene is introduced. Then, the review discusses the formation energies of these defects, stressing the dramatic stabilization of dislocations and small-angle grain boundaries in graphene due to the two-dimensional nature of this material. Finally, the electronic transport properties of polycrystalline graphene are considered, showing that topological defects may present novel opportunities towards engineering electronic devices based on graphene. © 2012 Elsevier Ltd. All rights reserved. Source


Bunzli J.C.G.,Ecole Polytechnique Federale de Lausanne | Bunzli J.C.G.,CAS Fujian Institute of Research on the Structure of Matter
Coordination Chemistry Reviews | Year: 2015

Presently, phosphors and luminescent materials for lighting, telecommunications, displays, security inks and marking, as well as for probes in biosciences represent one third of the total value of the lanthanides used worldwide. If optical glasses and laser materials are added, this figure is close to 40%, explaining the large interest that the scientific community is devoting to such materials. The present review focuses on the design of highly luminescent lanthanide complexes and discusses all aspects needing optimization. Reference is made to the mastering of the various energy migration processes in luminescence sensitization by organic ligands, to minimizing non-radiative deactivation mechanisms, as well as to other parameters such as the radiative lifetime, the refractive index, and the benefit of inserting luminescent complexes into inorganic-hybrid structures. Comparative tables list the most luminescent complexes emitting in the visible and near-infrared ranges and the best chromophores are pointed out. © 2014 Elsevier B.V. Source


Ijspeert A.J.,Ecole Polytechnique Federale de Lausanne
Science | Year: 2014

The graceful and agile movements of animals are difficult to analyze and emulate because locomotion is the result of a complex interplay of many components: The central and peripheral nervous systems, the musculoskeletal system, and the environment. The goals of biorobotics are to take inspiration from biological principles to design robots that match the agility of animals, and to use robots as scientific tools to investigate animal adaptive behavior. Used as physical models, biorobots contribute to hypothesis testing in fields such as hydrodynamics, biomechanics, neuroscience, and prosthetics. Their use may contribute to the design of prosthetic devices that more closely take human locomotion principles into account. © 2014 by the American Association for the Advancement of Science; all rights reserved. Source


Hersch R.D.,Ecole Polytechnique Federale de Lausanne
Applied Optics | Year: 2014

We present a spectral model for predicting the fluorescent emission and the total reflectance of color halftones printed on optically brightened paper. By relying on extended Neugebauer models, the proposed model accounts for the attenuation by the ink halftones of both the incident exciting light in the UV wavelength range and the emerging fluorescent emission in the visible wavelength range. The total reflectance is predicted by adding the predicted fluorescent emission relative to the incident light and the pure reflectance predicted with an ink-spreading enhanced Yule-Nielsen modified Neuge-bauer reflectance prediction model. The predicted fluorescent emission spectrum as a function of the amounts of cyan, magenta, and yellow inks is very accurate. It can be useful to paper and ink manufacturers who would like to study in detail the contribution of the fluorescent brighteners and the attenuation of the fluorescent emission by ink halftones. © 2014 Optical Society of America. Source


Mitchell J.S.,Ecole Polytechnique Federale de Lausanne | Harris S.A.,University of Leeds
Physical Review Letters | Year: 2013

DNA supercoiling plays a role in genetic control by imposing torsional stress. This can induce writhe, which changes the global shape of the DNA. We have used atomistic molecular dynamics simulations to partition the free energy changes driving the writhing and unwrithing transitions in supercoiled minicircle DNA. The calculations show that while writhing is energetically driven, the unwrithing transition occurs because the circular state has a higher configurational entropy than the plectoneme. Writhing improves the van der Waals interactions between stacked bases, but can be suppressed by electrostatic repulsion within the negatively charged backbone strands in low salt conditions where electrostatic screening is poor. The free energy difference between circular and plectonemic DNA is determined by such a delicate balance of opposing thermodynamic terms that any perturbation in the environment, such as a change in salt concentration, can be sufficient to convert between these two states. This switchable behavior provides a mechanism for supercoiled DNA to store and communicate biological information physically as well as chemically. © 2013 American Physical Society. Source


Irvine D.J.,Massachusetts Institute of Technology | Irvine D.J.,Howard Hughes Medical Institute | Swartz M.A.,Ecole Polytechnique Federale de Lausanne | Szeto G.L.,Massachusetts Institute of Technology
Nature Materials | Year: 2013

Vaccines aim to protect against or treat diseases through manipulation of the immune response, promoting either immunity or tolerance. In the former case, vaccines generate antibodies and T cells poised to protect against future pathogen encounter or attack diseased cells such as tumours; in the latter case, which is far less developed, vaccines block pathogenic autoreactive T cells and autoantibodies that target self tissue. Enormous challenges remain, however, as a consequence of our incomplete understanding of human immunity. A rapidly growing field of research is the design of vaccines based on synthetic materials to target organs, tissues, cells or intracellular compartments; to co-deliver immunomodulatory signals that control the quality of the immune response; or to act directly as immune regulators. There exists great potential for well-defined materials to further our understanding of immunity. Here we describe recent advances in the design of synthetic materials to direct immune responses, highlighting successes and challenges in prophylactic, therapeutic and tolerance-inducing vaccines. © 2013 Macmillan Publishers Limited. All rights reserved. Source


Svensson O.,Ecole Polytechnique Federale de Lausanne
Proceedings of the Annual ACM Symposium on Theory of Computing | Year: 2013

We present a novel approximation algorithm for k-median that achieves an approximation guarantee of 1 + √3 + ε, improving upon the decade-old ratio of 3+ε. Our approach is based on two components, each of which, we believe, is of independent interest. First, we show that in order to give an α-approximation algorithm for k-median, it is sufficient to give a pseudo- approximation algorithm that finds an α-approximate solu- tion by opening k+O(1) facilities. This is a rather surprising result as there exist instances for which opening k + 1 facil- ities may lead to a significant smaller cost than if only k facilities were opened. Second, we give such a pseudo-approximation algorithm with α = 1+ √3+ε. Prior to our work, it was not even known whether opening k + o(k) facilities would help improve the approximation ratio. Copyright 2013 ACM. Source


Obermeier B.,Johannes Gutenberg University Mainz | Wurm F.,Ecole Polytechnique Federale de Lausanne | Mangold C.,Johannes Gutenberg University Mainz | Frey H.,Johannes Gutenberg University Mainz
Angewandte Chemie - International Edition | Year: 2011

In the rapidly evolving multidisciplinary field of polymer therapeutics, tailored polymer structures represent the key constituent to explore and harvest the potential of bioactive macromolecular hybrid structures. In light of the recent developments for anticancer drug conjugates, multifunctional polymers are becoming ever more relevant as drug carriers. However, the potentially best suited polymer, poly(ethylene glycol) (PEG), is unfavorable owing to its limited functionality. Therefore, multifunctional linear copolymers (mf-PEGs) based on ethylene oxide (EO) and appropriate epoxide comonomers are attracting increased attention. Precisely engineered via living anionic polymerization and defined with state-of-the-art characterization techniques-for example real-time 1H NMR spectroscopy monitoring of the EO polymerization kinetics-this emerging class of polymers embodies a powerful platform for bio- and drug conjugation. © 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim. Source


Lothenbach B.,Empa - Swiss Federal Laboratories for Materials Science and Technology | Scrivener K.,Ecole Polytechnique Federale de Lausanne | Hooton R.D.,University of Toronto
Cement and Concrete Research | Year: 2011

The use of silica rich SCMs influences the amount and kind of hydrates formed and thus the volume, the porosity and finally the durability of these materials. At the levels of substitution normally used, major changes are the lower Ca/Si ratio in the C-S-H phase and consumption of portlandite. Alumina-rich SCMs increase the Al-uptake in C-S-H and the amounts of aluminate containing hydrates. In general the changes in phase assemblages are well captured by thermodynamic modelling, although better knowledge of the C-S-H is needed. At early ages, "filler" effects lead to an increased reaction of the clinker phases. Reaction of SCMs starts later and is enhanced with pH and temperature. Composition, fineness and the amount of glassy phase play also an important role. Due to the diverse range of SCM used, generic relations between composition, particle size, exposure conditions as temperature or relative humidity become increasingly crucial. © 2010 Elsevier Ltd. All rights reserved. Source


Gonczy P.,Ecole Polytechnique Federale de Lausanne
Nature Reviews Molecular Cell Biology | Year: 2012

The centriole is an evolutionarily conserved macromolecular structure that is crucial for the formation of flagella, cilia and centrosomes. The ultrastructure of the centriole was first characterized decades ago with the advent of electron microscopy, revealing a striking ninefold radial arrangement of microtubules. However, it is only recently that the molecular mechanisms governing centriole assembly have begun to emerge, including the elucidation of the crucial role of spindle assembly abnormal 6 (SAS-6) proteins in imparting the ninefold symmetry. These advances have brought the field to an exciting era in which architecture meets function. © 2012 Macmillan Publishers Limited. All rights reserved. Source


Ozgur A.,Stanford University | Leveque O.,Ecole Polytechnique Federale de Lausanne | Tse D.,University of California at Berkeley
IEEE Journal on Selected Areas in Communications | Year: 2013

We consider a large distributed MIMO system where wireless users with single transmit and receive antenna cooperate in clusters to form distributed transmit and receive antenna arrays. We characterize how the capacity of the distributed MIMO transmission scales with the number of cooperating users, the area of the clusters and the separation between them, in a line-of-sight propagation environment. We use this result to answer the following question: can distributed MIMO provide significant capacity gain over traditional multi-hop in large adhoc networks with n source-destination pairs randomly distributed over an area A? Two diametrically opposite answers and have emerged in the current literature. We show that neither of these two results are universal and their validity depends on the relation between the number of users n and A, which we identify as the spatial degrees of freedom in the network. λ is the carrier wavelength. When A≥ n, there are n degrees of freedom in the network and distributed MIMO with hierarchical cooperation can achieve a capacity scaling linearly in n as in , while capacity of multihop scales only as n. On the other hand, when Aλ≤ n as in , there are only n degrees of freedom in the network and they can be readily achieved by multihop. Our results also reveal a third regime where n≤A/λ≤ n. Here, the number of degrees of freedom are smaller than n but larger than what can be achieved by multi-hop. We construct scaling optimal architectures for this intermediate regime. © 2012 IEEE. Source


The amyloid cascade hypothesis, supported by strong evidence from genetics, pathology and studies using animal models, implicates amyloid-beta (Abeta) oligomerization and fibrillogenesis as central causative events in the pathogenesis of Alzheimer's disease (AD). Today, significant efforts in academia, biotechnology and the pharmaceutical industry are devoted to identifying the mechanisms by which the process of Abeta aggregation contributes to neurodegeneration in AD and to the identity of the toxic Abeta species. In this paper, we describe methods and detailed protocols for reproducibly preparing Abeta aggregates of defined size distribution and morphology, including monomers, protofibrils and fibrils, using size exclusion chromatography. In addition, we describe detailed biophysical procedures for elucidating the structural features, aggregation kinetics and toxic properties of the different Abeta aggregation states, with special emphasis on protofibrillar intermediates. The information provided by this approach allows for consistent correlation between the properties of the aggregates and their toxicity toward primary neurons and/or cell lines. A better understanding of the molecular and structural basis of Abeta aggregation and toxicity is crucial for the development of effective strategies aimed at prevention and/or treatment of AD. Furthermore, the identification of specific aggregation states, which correlate with neurodegeneration in AD, could lead to the development of diagnostic tools to detect and monitor disease progression. The procedures described can be performed in as little as 1 day, or may take longer, depending on the exact toxicity assays used. Source


Hantschel O.,Ecole Polytechnique Federale de Lausanne | Grebien F.,Austrian Academy of Sciences | Superti-Furga G.,Austrian Academy of Sciences
Cancer Research | Year: 2012

The BCR-ABL fusion kinase is the driving mutation of chronic myelogenous leukemias and is also expressed in a subset of acute lymphoblastic leukemias. Recent advances in elucidating the structure, regulation, and signaling of BCR-ABL have led to the identification of allosteric sites that are distant from the ATP-binding pocket and are critical for BCR-ABL-dependent oncogenic transformation. Here, we review the available data regarding the molecular mechanism of action and the specificity of ATP-competitive tyrosine kinase inhibitors targeting BCR-ABL. In addition, we discuss how targeting of allosteric sites could provide new opportunities to inhibit resistant BCR-ABL mutants, either alone or in combination with conventional ATP-competitive inhibitors. ©2012 AACR. Source


Jensen J.D.,Ecole Polytechnique Federale de Lausanne | Jensen J.D.,Swiss Institute of Bioinformatics
Nature Communications | Year: 2014

Underlying any understanding of the mode, tempo and relative importance of the adaptive process in the evolution of natural populations is the notion of whether adaptation is mutation limited. Two very different population genetic models have recently been proposed in which the rate of adaptation is not strongly limited by the rate at which newly arising beneficial mutations enter the population. However, empirical and experimental evidence to date challenges the recent enthusiasm for invoking these models to explain observed patterns of variation in humans and Drosophila. © 2014 Macmillan Publishers Limited. All rights reserved. Source


Baillod P.,Ecole Polytechnique Federale de Lausanne
Biochemistry | Year: 2013

The doppel (Dpl) and prion (PrP) proteins share a very similar fold (three helices and two short β-strands), while they differ significantly in sequence (only 25% homologous) and in disease-related β-rich conformations that occur for PrP only. In a previous study [Baillod, P., et al. (2012) Biochemistry 51, 9891-9899], we investigated the misfolding and rare, β-rich folds of monomeric PrP with replica-exchange molecular dynamics (REMD) simulations. In the work presented here, we perform analogous simulations for Dpl with the aim of comparing the two systems and characterizing possible specificities of PrP for misfolding and amyloidogenesis. Our extensive simulations, which allow us to overcome high energy barriers via the REMD approach, sample several β-rich folds, some of which are stable at room temperature, for both proteins. Per residue secondary structure propensities reveal that novel β-sheets of Dpl and PrP are formed by amino acids belonging to the helices that are the least stable in the respective native structure, H1 for Dpl and H2 and H3 for PrP, in agreement with experimental data. Using a specific clustering method that allows discrimination against different β-strand arrangements, seven β-rich folds could be characterized for PrP and five for Dpl, which are clearly distinct and share only one single similar fold. A major difference between the two proteins is found in the free energy barriers leading to misfolded structures: they are approximately 3 times higher for Dpl than for PrP. This suggests that the difference in amyloidogenic behavior between PrP and Dpl might be due to kinetic reasons. Source


Perruisseau-Carrier J.,Ecole Polytechnique Federale de Lausanne
IEEE Antennas and Wireless Propagation Letters | Year: 2012

This letter relates to the development of satellite reflectarrays able to scan a single dual-polarized beam, based on monolayer resonating cells embedding digital microelectromechanical systems (MEMS). We study general topology constraints to be imposed on the elementary cell to ensure dual-polarized operation, minimal cross-polarization, and a reduced number of MEMS for a given phase resolution. It is shown that an element electrically invariant to a 90° rotation is the most favorable one, and the theoretical considerations are verified by a design example under both normal and oblique incidence. © 2012 IEEE. Source


Chakrabarti S.,Ecole Polytechnique Federale de Lausanne
Cell host & microbe | Year: 2012

Typically, immune responses control the pathogen, while repair and stress pathways limit damage caused by pathogenesis. The relative contribution of damage to the outcome of pathogenesis and the mechanistic links between the immune and repair pathways are poorly understood. Here, we analyze how the entomopathogenic bacterium Pseudomonas entomophila induces irreversible damage to the Drosophila gut. We find that P. entomophila ingestion induces a global translational blockage that impairs both immune and repair programs in the fly gut. P. entomophila-induced translational inhibition is dependent on bacterial pore forming toxins and reactive oxygen species produced by the host in response to infection. Translational arrest is mediated through activation of the GCN2 kinase and inhibition of the TOR pathway as a consequence of host damage. Together, our study draws a model of pathogenesis in which bacterial inhibition of translation by excessive activation of stress responsive pathways inhibits both immune and regenerative epithelial responses. Copyright © 2012 Elsevier Inc. All rights reserved. Source


Bunzli J.-C.G.,Ecole Polytechnique Federale de Lausanne | Bunzli J.-C.G.,Korea University
Chemical Reviews | Year: 2010

The problematic issues of lanthanide luminescent bioprobes (LLB) from the standpoint of their photophysical and biochemical properties are studied. Quenching of the lanthanide luminescence by high-energy vibrational overtones is a major concern in the design of luminescent probes. On the other hand, it allows one to assess the number of water molecules q interacting in the inner coordination sphere from lifetimes measured in water and deuterated water. Several phenomenological equations have been proposed, based on the assumptions that O-D oscillators contribute little to deactivation and that all the other deactivation paths are the same in water and in deuterated water. Efficient lanthanide luminescent bioprobes must meet several stringent requirements, chemical, photophysical, and biochemical. A growing number of bioanalyses require specific targeting of the analyte, and therefore the lanthanide luminescent probes have to be fitted with adequate functionalities able to couple with biological material. Source


Chakareski J.,Ecole Polytechnique Federale de Lausanne
IEEE Communications Magazine | Year: 2013

Delivering multiview video content over present packet networks poses multiple challenges. First, the best effort nature of the Internet exposes media packets to variable bandwidth, loss, and delay as they traverse the network. Second, the prediction dependencies employed to maximize compression efficiency make the reconstruction process at the client extremely vulnerable to missing data. Third, the heterogeneity of client devices in terms of computing power, display capabilities, and access link capacity necessitates customizing the streaming process per user. My article reviews existing opportunities for addressing these challenges from within each of the three main stages of the content delivery pipeline (i.e., encoding, transmission, and reconstruction). Concretely, I first describe adaptive source coding techniques that construct a compressed representation of the multiview video source that exhibits resilience to network bandwidth variations and client view selection uncertainty. Then I discuss intelligent methods for error protection, caching, and packet scheduling that organize the transmission of multiview data in a bandwidth-effective way. Here, I also review prospective multipath and cloud-assisted techniques for multiview video streaming. Finally, I identify robust client-side content reconstruction schemes and adaptive media playout methods that can minimize the impact of missing data and enhance the useri's interactive experience. Then I proceed to describe community-driven streaming techniques for delivering interactive multiview content over a population of social peers. The article concludes with an outline of approaches for synergistic exploitation of the techniques I will present theretofore, jointly across the different layers of the network protocol stack at which they individually operate. Here, I also highlight the main deployment challenges for some of these techniques, and how their design should be addressed accordingly, to overcome them. © 2013 IEEE. Source


Ramdya P.,University of Lausanne | Ramdya P.,Ecole Polytechnique Federale de Lausanne | Benton R.,University of Lausanne
Trends in Genetics | Year: 2010

The detection of odour stimuli in the environment is universally important for primal behaviours such as feeding, mating, kin interactions and escape responses. Given the ubiquity of many airborne chemical signals and the similar organisation of animal olfactory circuits, a fundamental question in our understanding of the sense of smell is how species-specific behavioural responses to odorants can evolve. Recent comparative genomic, developmental and physiological studies are shedding light on this problem by providing insights into the genetic mechanisms that underlie anatomical and functional evolution of the olfactory system. Here we synthesise these data, with a particular focus on insect olfaction, to address how new olfactory receptors and circuits might arise and diverge, offering glimpses into how odour-evoked behaviours could adapt to an ever-changing chemosensory world. © 2010 Elsevier Ltd. Source


Hering J.G.,Eawag - Swiss Federal Institute of Aquatic Science and Technology | Hering J.G.,ETH Zurich | Hering J.G.,Ecole Polytechnique Federale de Lausanne | Ingold K.M.,Eawag - Swiss Federal Institute of Aquatic Science and Technology | Ingold K.M.,University of Bern
Science | Year: 2012

Appropriately bounded integration can be a basis for sustainable management of water resources. Source


Blokesch M.,Ecole Polytechnique Federale de Lausanne
Journal of Visualized Experiments | Year: 2012

Several methods are available to manipulate bacterial chromosomes. Most of these protocols rely on the insertion of conditionally replicative plasmids (e.g. harboring pir-dependent or temperature-sensitive replicons). These plasmids are integrated into bacterial chromosomes based on homology-mediated recombination. Such insertional mutants are often directly used in experimental settings. Alternatively, selection for plasmid excision followed by its loss can be performed, which for Gram-negative bacteria often relies on the counter-selectable levan sucrase enzyme encoded by the sacB gene. The excision can either restore the pre-insertion genotype or result in an exchange between the chromosome and the plasmid-encoded copy of the modified gene. A disadvantage of this technique is that it is time-consuming. The plasmid has to be cloned first; it requires horizontal transfer into V. cholerae (most notably by mating with an E. coli donor strain) or artificial transformation of the latter; and the excision of the plasmid is random and can either restore the initial genotype or create the desired modification if no positive selection is exerted. Here, we present a method for rapid manipulation of the V. cholerae chromosome(s) (Figure 1). This TransFLP method is based on the recently discovered chitin-mediated induction of natural competence in this organism and other representative of the genus Vibrio such as V. fischeri. Natural competence allows the uptake of free DNA including PCR-generated DNA fragments. Once taken up, the DNA recombines with the chromosome given the presence of a minimum of 250-500 bp of flanking homologous region. Including a selection marker in-between these flanking regions allows easy detection of frequently occurring transformants. This method can be used for different genetic manipulations of V. cholerae and potentially also other naturally competent bacteria. We provide three novel examples on what can be accomplished by this method in addition to our previously published study on single gene deletions and the addition of affinity-tag sequences. Several optimization steps concerning the initial protocol of chitin-induced natural transformation are incorporated in this TransFLP protocol. These include among others the replacement of crab shell fragments by commercially available chitin flakes, the donation of PCR-derived DNA as transforming material, and the addition of FLP-recombination target sites (FRT). FRT sites allow site-directed excision of the selection marker mediated by the Flp recombinase. Source


Carney R.P.,Ecole Polytechnique Federale de Lausanne
Biointerphases | Year: 2012

Nanoparticles (NPs) are gaining increasing attention for potential application in medicine; consequently, studying their interaction with cells is of central importance. We found that both ligand arrangement and composition on gold nanoparticles play a crucial role in their cellular internalization. In our previous investigation, we showed that 66-34OT nanoparticles coated with stripe-like domains of hydrophobic (octanethiol, OT, 34%) and hydrophilic (11-mercaptoundecane sulfonate, MUS, 66%) ligands permeated through the cellular lipid bilayer via passive diffusion, in addition to endo-/pino-cytosis. Here, we show an analysis of NP internalization by DC2.4, 3T3, and HeLa cells at two temperatures and multiple time points. We study four NPs that differ in their surface structures and ligand compositions and report on their cellular internalization by intracellular fluorescence quantification. Using confocal laser scanning microscopy we have found that all three cell types internalize the 66-34OT NPs more than particles coated only with MUS, or particles coated with a very similar coating but lacking any detectable ligand shell structure, or 'striped' particles but with a different composition (34-66OT) at multiple data points. Source


Finger M.,Ecole Polytechnique Federale de Lausanne
Utilities Policy | Year: 2014

Based on extensive qualitative research, this article analyzes the governance of competition in European railways and relates this to their performance via five case studies covering the Netherlands, France, Germany, Sweden and the UK. Even though some trends can be identified, such as regionalization, system fragmentation, and the strengthening of the regulatory function, each country's governance appears to be a type of its own, with a unique relationship between governance and railway performance. © 2014 Elsevier Ltd. Source


Beyer K.,Ecole Polytechnique Federale de Lausanne
Engineering Structures | Year: 2012

Unreinforced masonry (URM) walls comprise vertical piers and horizontal spandrels, which together form the lateral load resisting system. Whereas past research yielded significant advances in the understanding of the force-deformation characteristics of masonry piers, knowledge of the behaviour of masonry spandrels is lacking. This paper makes a contribution to our understanding of the seismic behaviour of brick masonry spandrel elements by describing typical behaviour modes and analysing the boundary condition of spandrel elements in URM walls. The main part of the paper concerns the development of simple mechanical models for estimating the peak and residual strength of brick masonry spandrels, which are supported either by a timber lintel or a shallow masonry arch. The proposed models are compared against results from experimental tests on four masonry spandrels. It is found that predicted and experimental values agree well. © 2012 Elsevier Ltd. Source


Schwarzenbach D.,Ecole Polytechnique Federale de Lausanne
Acta Crystallographica Section A: Foundations of Crystallography | Year: 2012

Diffractionists usually place the birth of crystallography in 1912 with the first X-ray diffraction experiment of Friedrich, Knipping and Laue. This discovery propelled the mathematical branch of mineralogy to global importance and enabled crystal structure determination. Knowledge of the geometrical structure of matter at atomic resolution had revolutionary consequences for all branches of the natural sciences: physics, chemistry, biology, earth sciences and material science. It is scarcely possible for a single person in a single article to trace and appropriately value all of these developments. This article presents the limited, subjective view of its author and a limited selection of references. The bulk of the article covers the history of X-ray structure determination from the NaCl structure to aperiodic structures and macromolecular structures. The theoretical foundations were available by 1920. The subsequent success of crystallography was then due to the development of diffraction equipment, the theory of the solution of the phase problem, symmetry theory and computers. The many structures becoming known called for the development of crystal chemistry and of data banks. Diffuse scattering from disordered structures without and with partial long-range order allows determination of short-range order. Neutron and electron scattering and diffraction are also mentioned. Source


Hantschel O.,Ecole Polytechnique Federale de Lausanne
Genes and Cancer | Year: 2012

Abl kinases are prototypic cytoplasmic tyrosine kinases and are involved in a variety of chromosomal aberrations in different cancers. This causes the expression of Abl fusion proteins, such as Bcr-Abl, that are constitutively activated and drivers of tumorigenesis. Over the past decades, biochemical and functional studies on the molecular mechanisms of Abl regulation have gone hand in hand with progression of our structural understanding of autoinhibited and active Abl conformations. In parallel, Abl oncoproteins have become prime molecular targets for cancer therapy, using adenosine triphosphate (ATP)-competitive kinase inhibitors, such as imatinib. Abl-targeting drugs serve as a paradigm for our understanding of kinase inhibitor action, specificity, and resistance development. In this review article, I will review the molecular mechanisms that are responsible for the regulation of Abl kinase activity and how oncogenic Abl fusions signal. Furthermore, past and ongoing efforts to target Abl oncoproteins using ATP-competitive and allosteric inhibitors, as well as future possibilities using combination therapy, will be discussed. © The Author(s) 2012. Source


Maerkl S.J.,Ecole Polytechnique Federale de Lausanne
Current Opinion in Biotechnology | Year: 2011

DNA technologies such as cloning, DNA microarrays, and next generation sequencing have transformed the life sciences. Protein technologies on the other hand have not seen such explosive progress. This is mainly due to the inherent difficulty of working with proteins because of their manifold physical characteristics as opposed to the well behaved and well understood DNA polymer. Recent technological advancements have increased the throughput of protein biochemistry to levels where it is becoming of interest to systems biology. Here I review methods for high-throughput in situ synthesis and characterization of proteins and their integration with microfluidic devices. In the near future, the use of gene synthesis, microfluidic based protein synthesis and characterization will give rise to a resurgence of protein biochemistry in the current world of high-throughput genomics. © 2010 Elsevier Ltd. Source


Lu H.,University of Minnesota | Porte-Agel F.,Ecole Polytechnique Federale de Lausanne
Physics of Fluids | Year: 2011

When deployed as large arrays, wind turbines significantly interact among themselves and with the atmospheric boundary layer. In this study, we integrate a three-dimensional large-eddy simulation with an actuator line technique to examine the characteristics of wind-turbine wakes in an idealized wind farm inside a stable boundary layer (SBL). The wind turbines, with a rotor diameter of 112m and a tower height of 119m, were "immersed" in a well-known SBL case that bears a boundary layer height of approximately 175m. Two typical spacing setups were adopted in this investigation. The super-geostrophic low-level jet near the top of the boundary layer was eliminated owing to the energy extraction and the enhanced mixing of momentum. Non-axisymmetric wind-turbine wakes were observed in response to the non-uniform incoming turbulence, the Coriolis effect the rotational effects induced by blade motion. The Coriolis force caused a skewed spatial structure and drove a part of the turbulence energy away from the center of the wake. The SBL height was increased, while the magnitude of the surface momentum flux was reduced by more than 30% the magnitude of the surface buoyancy flux was reduced by more than 15%. The wind farm was also found to have a strong effect on vertical turbulent fluxes of momentum and heat, an outcome that highlights the potential impact of wind farms on local meteorology. © 2011 American Institute of Physics. Source


Van De Vosse F.N.,TU Eindhoven | Stergiopulos N.,Ecole Polytechnique Federale de Lausanne
Annual Review of Fluid Mechanics | Year: 2011

The beating heart creates blood pressure and flow pulsations that propagate as waves through the arterial tree that are reflected at transitions in arterial geometry and elasticity. Waves carry information about the matter in which they propagate. Therefore, modeling of arterial wave propagation extends our knowledge about the functioning of the cardiovascular system and provides a means to diagnose disorders and predict the outcome of medical interventions. In this review we focus on the physical and mathematical modeling of pulse wave propagation, based on general fluid dynamical principles. In addition we present potential applications in cardiovascular research and clinical practice. Models of short- and long-term adaptation of the arterial system and methods that deal with uncertainties in personalized model parameters and boundary conditions are briefly discussed, as they are believed to be major topics for further study and will boost the significance of arterial pulse wave modeling even more. © 2011 by Annual Reviews. All rights reserved. Source


Harris N.,Ecole Polytechnique Federale de Lausanne
Nature | Year: 2015

Acute infection of mice with an intestinal pathogen leads to long-lasting inflammation that is maintained by intestinal microorganisms. This observation reveals a path by which infection history can affect long-term immune function. Source


Coda S.,Ecole Polytechnique Federale de Lausanne
Nuclear Fusion | Year: 2011

The TCV tokamak has the dual mission of supporting ITER and exploring alternative paths to a fusion reactor. Its most unique tools are a 4.5 MW electron cyclotron resonance heating system with seven real-time controllable launchers and a plasma control system with 16 independent shaping coils. Recent upgrades in temperature, density and rotation diagnostics are being followed by new turbulence and suprathermal electron diagnostics, and a new digital real-time network has been commissioned. The shape control flexibility of TCV has enabled the generation and control of the first 'snowflake' divertor, characterized by a null point in which both the poloidal field and its gradient vanish. The predicted increases in flux expansion and edge magnetic shear have been verified experimentally, and stable EC-heated snowflake ELMy H-modes have been obtained and characterized. ECCD modulation techniques have been used to study the role of the current profile in energy transport, and simulations reproduce the results robustly. The relation between impurity and electron density gradients in L-mode is explained in terms of neoclassical and turbulent drives. Studies of torqueless plasma rotation have continued, highlighting the important role of MHD and sawtooth relaxations in determining the rotation profiles. A newly predicted mechanism for turbulent momentum transport associated with up-down plasma asymmetry has been verified in TCV. Sawtooth period control, neoclassical tearing mode control and soft x-ray emission profile control have been demonstrated in TCV using the new digital control hardware, as a step on the way to more complex applications. © 2011 IAEA, Vienna. Source


Snellings R.,Ecole Polytechnique Federale de Lausanne
Journal of the American Ceramic Society | Year: 2013

Supplementary cementitious materials (SCMs) are widely used to partially replace portland clinker in blended cements. Reducing clinker contents further without compromising the development of early strength necessitates a better assessment and enhancement of the reactivity of the available SCMs. To this purpose, the reactivity of synthesized calcium aluminosilicate glasses covering a compositional range from blast-furnace slags (BFS) over fly ashes to silica fume was analyzed by dissolution experiments. Initial glass dissolution rates were measured at 20°C and pH 13, and with varying initial concentrations of aqueous Al, Ca, and Si. At pH 13, glass dissolution rates were observed to scale linearly with the glass Ca/(Al + Si) molar ratio. Ca-rich blast-furnace type glass dissolution was shown to be up to one order of magnitude faster than tectosilicate fly ash and silica fume type glass dissolution, supporting different pathways to dissolution. In solutions that are strongly undersaturated with respect to hydrous glass and hydration products, glass dissolution rates are independent of changes in solution undersaturation and aqueous Si activity. In contrast, dissolution rates decrease with aqueous Ca concentration for all glasses and with aqueous Al concentration for tectosilicate-type glasses. The insights gained are instrumental in finding ways to enhance SCM reactivity. © 2013 The American Ceramic Society. Source


Krawczyk M.,Adam Mickiewicz University | Grundler D.,TU Munich | Grundler D.,Ecole Polytechnique Federale de Lausanne
Journal of Physics Condensed Matter | Year: 2014

Research efforts addressing spin waves (magnons) in micro- and nanostructured ferromagnetic materials have increased tremendously in recent years. Corresponding experimental and theoretical work in magnonics faces significant challenges in that spin-wave dispersion relations are highly anisotropic and different magnetic states might be realized via, for example, the magnetic field history. At the same time, these features offer novel opportunities for wave control in solids going beyond photonics and plasmonics. In this topical review we address materials with a periodic modulation of magnetic parameters that give rise to artificially tailored band structures and allow unprecedented control of spin waves. In particular, we discuss recent achievements and perspectives of reconfigurable magnonic devices for which band structures can be reprogrammed during operation. Such characteristics might be useful for multifunctional microwave and logic devices operating over a broad frequency regime on either the macro- or nanoscale. © 2014 IOP Publishing Ltd. Source


Broderick N.A.,Ecole Polytechnique Federale de Lausanne
Gut microbes | Year: 2012

There is growing interest in using Drosophila melanogaster to elucidate mechanisms that underlie the complex relationships between a host and its microbiota. In addition to the many genetic resources and tools Drosophila provides, its associated microbiota is relatively simple (1-30 taxa), in contrast to the complex diversity associated with vertebrates (> 500 taxa). These attributes highlight the potential of this system to dissect the complex cellular and molecular interactions that occur between a host and its microbiota. In this review, we summarize what is known regarding the composition of gut-associated microbes of Drosophila and their impact on host physiology. We also discuss these interactions in the context of their natural history and ecology and describe some recent insights into mechanisms by which Drosophila and its gut microbiota interact. Source


Svensson O.,Ecole Polytechnique Federale de Lausanne
SIAM Journal on Computing | Year: 2012

One of the classic results in scheduling theory is the 2-approximation algorithm by Lenstra, Shmoys, and Tardos for the problem of scheduling jobs to minimize makespan on unrelated machines; i.e., job j requires time p ij if processed on machine i. More than two decades after its introduction it is still the algorithm of choice even in the restricted model where processing times are of the form p ij ∈ {p j, ∞}. This problem, also known as the restricted assignment problem, is NP-hard to approximate within a factor less than 1.5, which is also the best known lower bound for the general version. Our main result is a polynomial time algorithm that estimates the optimal makespan of the restricted assignment problem within a factor 33/17 + ε = 1.9412 + ε, where ε > 0 is an arbitrarily small constant. The result is obtained by upper bounding the integrality gap of a certain strong linear program, known as the configuration LP, that was previously successfully used for the related Santa Claus problem. Similar to the strongest analysis for that problem our proof is based on a local search algorithm that will eventually find a schedule of the mentioned approximation guarantee but is not known to converge in polynomial time. © 2012 Society for Industrial and Applied Mathematics. Source


Lei C.-H.,CAS Beijing National Laboratory for Molecular | Wang D.-X.,CAS Beijing National Laboratory for Molecular | Zhao L.,Tsinghua University | Zhu J.,Ecole Polytechnique Federale de Lausanne | Wang M.-X.,Tsinghua University
Journal of the American Chemical Society | Year: 2013

A novel strategy for de novo synthesis of pyridines featuring an unprecedented α-addition of aldehyde and enamide to isonitrile as a key step is described. Under mild conditions, a cascade reaction involving Zn(OTf)2-promoted [1 + 5] cycloaddition of isonitrile with N-formylmethyl-substituted enamide, facile aerobic oxidative aromatization and intermolecular acyl transfer from the pyridinium nitrogen to the 5-hydroxy oxygen, and finally acylation of the 4-amino group by an external acyl chloride efficiently afforded 2-substituted 4-acylamino-5-acyloxypyridines in good to excellent yields. © 2013 American Chemical Society. Source


Leiman P.G.,Ecole Polytechnique Federale de Lausanne | Shneider M.M.,RAS Shemyakin Ovchinnikov Institute of Bioorganic Chemistry
Advances in Experimental Medicine and Biology | Year: 2012

Bacteriophages with contractile tails epitomize the concepts of "virus" and "phage" for many because the tails of these phages undergo a large conformational change - resembling the action of a syringe - upon the attachment to the host cell. The contractile tails belong to the recently recognized class of "contractile systems," which includes phage tails, their close relatives R-type pyocins, the bacterial type VI secretion system, and the virulence cassette of Photorhabdus. Their function is to deliver large proteins and/or DNA into the cytoplasm of a bacterial or eukaryotic cell. The structure of the core components of all contractile tail-like systems is conserved, but the corresponding genes have diverged to such a degree that the common ancestry can no longer be easily detected at the level of amino acid sequence. At present, it is unclear, whether the contractile systems originated in bacteria or in phages. This chapter describes the structure and function of phage contractile tails and compares them with other phage tails and with other known contractile systems. © 2012 Springer Science+Business Media, LLC. Source


Martinez-Duarte R.,Ecole Polytechnique Federale de Lausanne
Electrophoresis | Year: 2012

DEP is an established technique for particle manipulation. Although first demonstrated in the 1950s, it was not until the development of miniaturization techniques in the 1990s that DEP became a popular research field. The 1990s saw an explosion of DEP publications using microfabricated metal electrode arrays to sort a wide variety of cells. The concurrent development of microfluidics enabled devices for flow management and better understanding of the interaction between hydrodynamic and electrokinetic forces. Starting in the 2000s, alternative techniques have arisen to overcome common problems in metal-electrode DEP, such as electrode fouling, and to increase the throughput of the system. Insulator-based DEP and light-induced DEP are the most significant examples. Most recently, new 3D techniques such as carbon-electrode DEP, contactless DEP, and the use of doped PDMS have further simplified the fabrication process. The constant desire of the community to develop practical solutions has led to devices which are more user friendly, less expensive, and are capable of higher throughput. The state-of-the-art of fabricating DEP devices is critically reviewed in this work. The focus is on how different fabrication techniques can boost the development of practical DEP devices to be used in different settings such as clinical cell sorting and infection diagnosis, industrial food safety, and enrichment of particle populations for drug development. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source


Brisken C.,Ecole Polytechnique Federale de Lausanne
Nature Reviews Cancer | Year: 2013

Understanding the biology of the breast and how ovarian hormones impinge on it is key to rational new approaches in breast cancer prevention and therapy. Because of the success of selective oestrogen receptor modulators (SERMs), such as tamoxifen, and aromatase inhibitors in breast cancer treatment, oestrogens have long received the most attention. Early progesterone receptor (PR) antagonists, however, were dismissed because of severe side effects, but awareness is now increasing that progesterone is an important hormone in breast cancer. Oestrogen receptor-α (ERα) signalling and PR signalling have distinct roles in normal mammary gland biology in mice; both ERα and PR delegate many of their biological functions to distinct paracrine mediators. If the findings in the mouse model translate to humans, new preventive and therapeutic perspectives might open up. © 2013 Macmillan Publishers Limited. All rights reserved. Source


Damjanovic D.,Ecole Polytechnique Federale de Lausanne
Applied Physics Letters | Year: 2010

Many ferroelectric solid solutions exhibit enhanced electromechanical properties at the morphotropic boundary separating two phases with different orientations of polarization. The mechanism of properties enhancement is associated with easy paths for polarization rotation in anisotropically flattened free energy profile. Another mechanism of properties enhancement related to free energy flattening is polarization extension. It is best known at temperature-driven ferroelectric-paraelectric phase transitions and may lead to exceedingly large properties. Its disadvantage is temperature instability of the enhancement. In this paper a temperature-composition phase diagram is proposed that exhibits compositionally driven-phase transitions with easy paths for both polarization rotation and polarization extension. © 2010 American Institute of Physics. Source


Lemaitre B.,Ecole Polytechnique Federale de Lausanne | Miguel-Aliaga I.,Imperial College London
Annual Review of Genetics | Year: 2013

The digestive tract plays a central role in the digestion and absorption of nutrients. Far from being a passive tube, it provides the first line of defense against pathogens and maintains energy homeostasis by exchanging neuronal and endocrine signals with other organs. Historically neglected, the gut of the fruit fly Drosophila melanogaster has recently come to the forefront of Drosophila research. Areas as diverse as stem cell biology, neurobiology, metabolism, and immunity are benefitting from the ability to study the genetics of development, growth regulation, and physiology in the same organ. In this review, we summarize our knowledge of the Drosophila digestive tract, with an emphasis on the adult midgut and its functional underpinnings. © 2013 by Annual Reviews. All rights reserved. Source


De Palma M.,Ecole Polytechnique Federale de Lausanne | Lewis C.E.,University of Sheffield
Cancer Cell | Year: 2013

Tumor-associated macrophages (TAMs) promote key processes in tumor progression, like angiogenesis, immunosuppression, invasion, and metastasis. Increasing studies have also shown that TAMs can either enhance or antagonize the antitumor efficacy of cytotoxic chemotherapy, cancer-cell targeting antibodies, and immunotherapeutic agents-depending on the type of treatment and tumor model. TAMs also drive reparative mechanisms in tumors after radiotherapy or treatment with vascular-targeting agents. Here, we discuss the biological significance and clinical implications of these findings, with an emphasis on novel approaches that effectively target TAMs to increase the efficacy of such therapies. © 2013 Elsevier Inc. Source


Hannestad S.,University of Aarhus | Hansen R.S.,University of Aarhus | Tram T.,Ecole Polytechnique Federale de Lausanne
Physical Review Letters | Year: 2014

Short baseline neutrino oscillation experiments have shown hints of the existence of additional sterile neutrinos in the eV mass range. However, such neutrinos seem incompatible with cosmology because they have too large of an impact on cosmic structure formation. Here we show that new interactions in the sterile neutrino sector can prevent their production in the early Universe and reconcile short baseline oscillation experiments with cosmology. © 2014 American Physical Society. Source


Vicario C.,Paul Scherrer Institute | Monoszlai B.,Paul Scherrer Institute | Hauri C.P.,Paul Scherrer Institute | Hauri C.P.,Ecole Polytechnique Federale de Lausanne
Physical Review Letters | Year: 2014

We report on compact and efficient laser-based THz generation in the terahertz frequency gap (1-10 THz). The radiation is generated by optical rectification of a midinfrared laser in a large-size, partitioned nonlinear organic crystal assembly. This enables up-scaling of presently field-limited tabletop THz sources to GV/m electric and several tesla magnetic field at millijoule pulse energy. In agreement with simulations, the THz beam properties at focus are shown to be not deteriorated by the discontinuity of the emitter surface. The high laser-to-THz energy conversion efficiency exceeds the Manley-Rowe limit and is explained by a cascaded χ(2) process in the organic crystals accompanied by a significant redshift of the pump spectrum. The scheme provides a compact, tabletop THz source for single-cycle transients at field strength equivalent or even higher to linear accelerator and FEL-based THz sources. This opens an avenue toward novel nonlinear THz applications. © 2014 American Physical Society. Source


Pomarol A.,Autonomous University of Barcelona | Riva F.,Ecole Polytechnique Federale de Lausanne
Journal of High Energy Physics | Year: 2014

With the discovery of the Higgs at the LHC, experiments have finally addressed all aspects of the Standard Model (SM). At this stage, it is important to understand which windows for beyond the SM (BSM) physics are still open, and which are instead tightly closed. We address this question by parametrizing BSM effects with dimension-six operators and performing a global fit to the SM. We separate operators into different groups constrained at different levels, and provide independent bounds on their Wilson coefficients taking into account only the relevant experiments. Our analysis allows to assert in a model-independent way where BSM effects can appear in Higgs physics. In particular, we show that deviations from the SM in the differential distributions of $ h\ \to\ V\overline{f}f $ are related to other observables, such as triple gauge-boson couplings, and are then already constrained by present data. On the contrary, BR(h → Zγ) can still hide large deviations from the SM. © 2014 The Author(s). Source


Bellouard Y.,TU Eindhoven | Hongler M.-O.,Ecole Polytechnique Federale de Lausanne
Optics Express | Year: 2011

By continuously scanning a femtosecond laser beam across a fused silica specimen, we demonstrate the formation of self-organized bubbles buried in the material. Rather than using high intensity pulses and high numerical aperture to induce explosions in the material, here bubbles form as a consequence of cumulative energy deposits. We observe a transition between chaotic and self-organized patterns at high scanning rate (above 10 mm/s). Through modeling the energy exchange, we outline the similarities of this phenomenon with other non-linear dynamical systems. Furthermore, we demonstrate with this method the high-speed writing of two- and three- dimensional bubble "crystals" in bulk silica. © 2011 Optical Society of America. Source


Ribordy M.,Ecole Polytechnique Federale de Lausanne | Smirnov A.Y.,Abdus Salam International Center For Theoretical Physics
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2013

Multimegaton scale in under-ice and underwater detectors of atmospheric neutrinos with a few GeV energy threshold (PINGU, ORCA) open up new possibilities in the determination of neutrino properties, and in particular the neutrino mass hierarchy. With a dense array of optical modules it will be possible to determine the inelasticity, y, of the charged current νμ events in addition to the neutrino energy Eν and the muon zenith angle θμ. The discovery potential of the detectors will substantially increase with the measurement of y. It will enable (i) a partial separation of the neutrino and antineutrino signals, (ii) a better reconstruction of the neutrino direction, (iii) the reduction of the neutrino parameters degeneracy, (iv) a better control of systematic uncertainties, and (v) a better identification of the νμ events. It will improve the sensitivity to the CP-violation phase. The three-dimensional (Eν,θμ,y), νμ oscillograms with the kinematical as well as the experimental smearing are computed. We present the asymmetry distributions in the Eν-θμ plane for different intervals of y and study their properties. We show that the inelasticity information reduces the effect of degeneracy of parameters by 30%. With the inelasticity, the total significance of establishing mass hierarchy may increase by (20-50)%, thus effectively increasing the volume of the detector by a factor of 1.5-2. © 2013 American Physical Society. Source


Gerlach H.,Ecole Polytechnique Federale de Lausanne | von der Mosel H.,RWTH Aachen
Archive for Rational Mechanics and Analysis | Year: 2011

We consider the variational problem of finding the longest closed curves of given minimal thickness on the unit sphere. After establishing the existence of solutions for any given thickness between 0 and 1, we explicitly construct for each given thickness n: sinπ (2n),nN, exactly (N) solutions, where is Euler's totient function from number theory. Then we prove that these solutions are unique, and also provide a complete characterisation of sphere filling curves on the unit sphere; that is of those curves whose spherical tubular neighbourhood completely covers the surface area of the unit sphere exactly once. All of these results carry over to open curves as well, as indicated in the last section. © 2011 Springer-Verlag. Source


Bonnet N.,Massachusetts Institute of Technology | Marzari N.,Ecole Polytechnique Federale de Lausanne
Physical Review Letters | Year: 2013

A first-principles model of the electrochemical double layer is applied to study surface energies and surface coverage under realistic electrochemical conditions and to determine the equilibrium shape of metal nanoparticles as a function of applied potential. The potential bias is directly controlled by adding electronic charge to the system, while total energy calculations and thermodynamic relations are used to predict electrodeposition curves and changes in surface energies and coverage. This approach is applied to Pt surfaces subject to hydrogen underpotential deposition. The shape of Pt nanoparticles under a cathodic scan is shown to undergo an octahedric-to-cubic transition, which is more pronounced in alkaline media due to the interaction energy of the pH-dependent surface charge with the surface dipole. © 2013 American Physical Society. Source


Ruchert C.,Paul Scherrer Institute | Vicario C.,Paul Scherrer Institute | Hauri C.P.,Paul Scherrer Institute | Hauri C.P.,Ecole Polytechnique Federale de Lausanne
Physical Review Letters | Year: 2013

High-field terahertz (THz) single-cycle pulses with 1.5 MV/cm are generated by optical rectification in the stilbazolium salt crystal 4-N,N-dimethylamino- 4'-N'-methyl-stilbazolium 2,4,6-trimethylbenzenesulfonate. We show experimentally that the generated THz transient carrying 5 octaves (0.15 to 5.5 THz) undergoes a complex time-frequency evolution when tightly focused, and we present a model based on three independent oscillating dipoles capable to describe this anomalous field evolution. Finally, we present a method to control the absolute phase of such supercontinuum THz pulses as an essential tool for future field-sensitive investigations. © 2013 American Physical Society. Source


Corboz P.,ETH Zurich | Mila F.,Ecole Polytechnique Federale de Lausanne
Physical Review Letters | Year: 2014

Using infinite projected entangled-pair states, we show that the Shastry-Sutherland model in an external magnetic field has low-magnetization plateaus which, in contrast to previous predictions, correspond to crystals of bound states of triplets, and not to crystals of triplets. The first sizable plateaus appear at magnetization 1/8, 2/15 and 1/6, in agreement with experiments on the orthogonal-dimer antiferromagnet SrCu2(BO3)2, and they can be naturally understood as regular patterns of bound states, including the intriguing 2/15 one. We also show that, even in a confined geometry, two triplets bind into a localized bound state with Sz=2. Finally, we discuss the role of competing domain-wall and supersolid phases, as well as that of additional anisotropic interactions. © 2014 American Physical Society. Source


Pinsker F.,University of Cambridge | Flayac H.,Ecole Polytechnique Federale de Lausanne
Physical Review Letters | Year: 2014

We theoretically demonstrate the generation of dark soliton trains in a one-dimensional exciton-polariton condensate within experimentally accessible schemes. In particular, we show that the frequency of the train can be finely tuned fully optically or electrically to provide a stable and efficient output signal modulation. Taking the polarization of the condensate into account, we elucidate the possibility of forming on-demand half-soliton trains. © 2014 American Physical Society. Source


Unnikrishnan J.,Ecole Polytechnique Federale de Lausanne
IEEE International Symposium on Information Theory - Proceedings | Year: 2012

Suppose we are given two independent strings of data from a known finite alphabet. We are interested in testing the null hypothesis that both the strings were drawn from the same distribution, assuming that the samples within each string are mutually independent. Among statisticians, the most popular solution for such a homogeneity test is the two sample chi-square test, primarily due to its ease of implementation and the fact that the limiting null hypothesis distribution of the associated test statistic is known and easy to compute. Although tests that are asymptotically optimal in error probability have been proposed in the information theory literature, such optimality results are not well-known and such tests are rarely used in practice. In this paper we seek to bridge the gap between theory and practice. We study two different optimal tests proposed by Shayevitz [1] and Gutman [2]. We first obtain a simplified structure of Shayevitz's test and then obtain limiting distributions of the test statistics used in both the tests. These results provide guidelines for choosing thresholds that guarantee an approximate false alarm constraint for finite length observation sequences, thus making these tests easy to use in practice. The approximation accuracies are demonstrated using simulations. We argue that such homogeneity tests with provable optimality properties could potentially be better choices than the chi-square test in practice. © 2012 IEEE. Source


Deveaud B.,Ecole Polytechnique Federale de Lausanne
Annual Review of Condensed Matter Physics | Year: 2015

Exciton-polaritons, mixed light-matter quasiparticles in semiconductors, have recently shown evidence for Bose-Einstein condensation. Some of the properties of condensates of exciton-polaritons are reviewed in this article. We first discuss the spontaneous appearance of long-range order and the way this can be easily accessed in the case of polariton fluids. We show that the Penrose-Onsager criterion is valid even for such a very special case of condensate. We then describe the experiments that allow observation of topological defects in the fluid: quantized vortices, half vortices, and hyperbolic spin vortices. We demonstrate through the comparison with the gross Pitaevskii equation that the appearance and stability of such vortices are linked with the dissipative nature of the condensate together with the presence of disorder. We then briefly summarize the experiments on erfluid behavior of the polaritons at large-enough densities and expand somewhat more on the dynamical behavior of turbulence in the wake of an obstacle, with the appearance of vortex streets. We finally show that the Bogoliubov transformation has been revealed through four-wave mixing experiments. © 2015 by Annual Reviews. Source


Lucchi A.,Ecole Polytechnique Federale de Lausanne
Medical image computing and computer-assisted intervention : MICCAI ... International Conference on Medical Image Computing and Computer-Assisted Intervention | Year: 2010

While there has been substantial progress in segmenting natural images, state-of-the-art methods that perform well in such tasks unfortunately tend to underperform when confronted with the different challenges posed by electron microscope (EM) data. For example, in EM imagery of neural tissue, numerous cells and subcellular structures appear within a single image, they exhibit irregular shapes that cannot be easily modeled by standard techniques, and confusing textures clutter the background. We propose a fully automated approach that handles these challenges by using sophisticated cues that capture global shape and texture information, and by learning the specific appearance of object boundaries. We demonstrate that our approach significantly outperforms state-of-the-art techniques and closely matches the performance of human annotators. Source


Kuhn L.C.,Ecole Polytechnique Federale de Lausanne
Metallomics | Year: 2015

Cellular iron homeostasis is regulated by post-transcriptional feedback mechanisms, which control the expression of proteins involved in iron uptake, release and storage. Two cytoplasmic proteins with mRNA-binding properties, iron regulatory proteins 1 and 2 (IRP1 and IRP2) play a central role in this regulation. Foremost, IRPs regulate ferritin H and ferritin L translation and thus iron storage, as well as transferrin receptor 1 (TfR1) mRNA stability, thereby adjusting receptor expression and iron uptake via receptor-mediated endocytosis of iron-loaded transferrin. In addition splice variants of iron transporters for import and export at the plasma-membrane, divalent metal transporter 1 (DMT1) and ferroportin are regulated by IRPs. These mechanisms have probably evolved to maintain the cytoplasmic labile iron pool (LIP) at an appropriate level. In certain tissues, the regulation exerted by IRPs influences iron homeostasis and utilization of the entire organism. In intestine, the control of ferritin expression limits intestinal iron absorption and, thus, whole body iron levels. In bone marrow, erythroid heme biosynthesis is coordinated with iron availability through IRP-mediated translational control of erythroid 5-aminolevulinate synthase mRNA. Moreover, the translational control of HIF2α mRNA in kidney by IRP1 coordinates erythropoietin synthesis with iron and oxygen supply. Besides IRPs, body iron absorption is negatively regulated by hepcidin. This peptide hormone, synthesized and secreted by the liver in response to high serum iron, downregulates ferroportin at the protein level and thereby limits iron absorption from the diet. Hepcidin will not be discussed in further detail here. © The Royal Society of Chemistry 2015. Source


Tavernelli I.,Ecole Polytechnique Federale de Lausanne
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2013

We derive a Bohmian trajectory-based quantum dynamics approach for the calculation of adiabatic and nonadiabatic quantum effects in ab initio on-the-fly molecular dynamics simulations. The method is designed for calculations in the full, unconstrained, phase space of molecular systems described within density functional theory and time-dependent density functional theory. The problem of solving quantum hydrodynamic equations using trajectories in high dimensions is addressed using an expansion of the nuclear amplitude in atom centered Gaussians that are propagated along the quantum trajectories. In this work, we investigate the adiabatic limit of this theory, even though the full nonadiabatic case is derived. The method is first tested on the H2 molecule and then applied to the study of the proton transfer dynamics in the phase space of the molecular complex (H3N-H-NH 3)+. © 2013 American Physical Society. Source


Tronci C.,Ecole Polytechnique Federale de Lausanne
Journal of Physics A: Mathematical and Theoretical | Year: 2010

The Hamiltonian structures of several hybrid kinetic-fluid models are identified explicitly, upon considering collisionless Vlasov dynamics for the hot particles interacting with a bulk fluid. After presenting different pressure-coupling schemes for an ordinary fluid interacting with a hot gas, the paper extends the treatment to account for a fluid plasma interacting with an energetic ion species. Both current-coupling and pressure-coupling MHD schemes are treated extensively. In particular, pressure-coupling schemes are shown to require a transport-like term in the Vlasov kinetic equation, in order for the Hamiltonian structure to be preserved. The last part of the paper is devoted to studying the more general case of an energetic ion species interacting with a neutralizing electron background (hybrid Hall-MHD). Circulation laws and Casimir functionals are presented explicitly in each case. © 2010 IOP Publishing Ltd. Source


Sayim B.,Ecole Polytechnique Federale de Lausanne
Journal of vision | Year: 2011

Contextual elements can strongly modulate visual performance. For example, performance deteriorates when a vernier is flanked by neighboring lines. On a neural level, such contextual modulation is often explained by local spatial interactions such as lateral inhibition or pooling. However, these mechanisms cannot account for a number of recent results which showed that global rather than local factors play a key role in contextual modulation. On a level of perceptual organization, we proposed that contextual modulation increases when the target groups with the flankers and decreases when the target stands out from the flankers. To quantify this "standing out" in foveal vision, here, we performed both a visual search and a vernier offset discrimination task on the same stimulus configurations. Stimulus configurations yielding short reaction times in visual search yielded good vernier discrimination performance. Stimulus configurations yielding long reaction times yielded weaker discrimination. Hence, vernier offset discrimination is superior for targets that are efficiently searched and vice versa. Source


Brisken C.,Ecole Polytechnique Federale de Lausanne
Cold Spring Harbor perspectives in biology | Year: 2010

A woman's breast cancer risk is affected by her reproductive history. The hormonal milieu also influences the course of the disease. The female reproductive hormones, estrogens, progesterone, and prolactin, have a major impact on breast cancer and control postnatal mammary gland development. Analysis of hormone receptor mutant mouse strains combined with tissue recombination techniques and proteomics revealed that sequential activation of hormone signaling in the mammary epithelium is required for progression of morphogenesis. Hormones impinge on a subset of luminal mammary epithelial cells (MECs) that express hormone receptors and act as sensor cells translating and amplifying systemic signals into local stimuli. Proliferation is induced by paracrine mechanisms mediated by distinct factors at different stages. Tissue and stage specificity of hormonal signaling is achieved at the molecular level by different chromatin contexts and differential recruitment of coactivators and corepressors. Source


Kruchkov A.,Ecole Polytechnique Federale de Lausanne
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2014

The paper considers Bose-Einstein condensation (BEC) of light in a cavity with a medium. In the framework of a two-level model we show the effect of gaseous medium on the critical temperature of light condensation in the system. Transition of the system to the state with released light condensate is illustrated in consequent stages. Analytical expressions for a typical spatial extent of the condensed cloud of photons, as well for spectral characteristics of the condensate peak are derived. Energy and heat capacity of photons as functions of temperature are obtained. Finally, we demonstrate that the energy of light can be accumulated in the BEC state. © 2014 American Physical Society. Source


Loshchilov I.,Ecole Polytechnique Federale de Lausanne
2013 IEEE Congress on Evolutionary Computation, CEC 2013 | Year: 2013

This paper investigates the performance of 6 versions of Covariance Matrix Adaptation Evolution Strategy (CMA-ES) with restarts on a set of 28 noiseless optimization problems (including 23 multi-modal ones) designed for the special session on real-parameter optimization of CEC 2013. The experimental validation of the restart strategies shows that: i). The versions of CMA-ES with weighted active covariance matrix update outperform the original versions of CMA-ES, especially on ill-conditioned problems; ii). The original restart strategies with increasing population size (IPOP) are usually outperformed by the bi-population restart strategies where the initial mutation step-size is also varied; iii). The recently proposed alternative restart strategies for CMA-ES demonstrate a competitive performance and are ranked first w.r.t. The proportion of function-target pairs solved after the full run on all 10-, 30-and 50-dimensional problems. © 2013 IEEE. Source


Abbe E.,Ecole Polytechnique Federale de Lausanne | Zheng L.,Massachusetts Institute of Technology
IEEE Transactions on Information Theory | Year: 2012

This paper investigates network information theory problems where the external noise is Gaussian distributed. In particular, the Gaussian broadcast channel with coherent fading and the Gaussian interference channel are considered. It is shown that in these problems, non-Gaussian code ensembles can achieve higher rates than the Gaussian ones. It is also shown that the strong Shamai-Laroia conjecture on the Gaussian ISI channel does not hold. In order to analyze non-Gaussian code ensembles over Gaussian networks, a geometrical tool using the Hermite polynomials is proposed. This tool provides a coordinate system to analyze a class of non-Gaussian input distributions that are invariant over Gaussian networks. © 2011 IEEE. Source


Sivula K.,Ecole Polytechnique Federale de Lausanne
Journal of Physical Chemistry Letters | Year: 2013

The photoelectrochemical reduction of water or CO2 is a promising route to sustainable solar fuels but hinges on the identification of a stable photoanode for water oxidation. Semiconductor oxides like Fe 2O3 and BiVO4 have been gaining significant attention as promising materials. However, they exhibit a major drawback of a large required overpotential for solar water oxidation. In this Perspective, recent efforts to characterize and reduce the overpotential are critically examined. The accumulation of photogenerated holes at the semiconductor-liquid interface, recently observed with multiple techniques, is rationalized with surface state models. Transient absorption spectroscopy and electrochemical impedance spectroscopy suggest that surface treatments designed to either passivate surface traps or increase reaction rates (as catalysts) actually perform identically. This calls into question the definition of a catalyst when coupled to a semiconductor photoelectrode. In contrast, results from transient photocurrent spectroscopy suggest that two separate loss mechanisms are indeed occurring and can be addressed separately. © 2013 American Chemical Society. Source


Scanlon M.D.,Ecole Polytechnique Federale de Lausanne
ChemCatChem | Year: 2013

A just cause: Fukuzumi and co-workers have employed experimental methods to tease out "cause and effect" relationships between subtle modification of the catalyst design or reaction conditions, and the resultant changes in the homogeneous oxygen-reduction mechanistic pathways. © 2013 WILEY-VCH Verlag GmbH & Co. Source


Falkowski A.,University Paris - Sud | Riva F.,Ecole Polytechnique Federale de Lausanne
Journal of High Energy Physics | Year: 2015

Abstract: We discuss electroweak precision constraints on dimension-6 operators in the effective theory beyond the standard model. We identify the combinations of these operators that are constrained by the pole observables (the W and Z masses and on-shell decays) and by the W boson pair production. To this end, we define a set of effective couplings of W and Z bosons to fermions and to itself, which capture the effects of new physics corrections. This formalism clarifies which operators are constrained by which observable, independently of the adopted basis of operators. We obtain numerical constraints on the coefficients of dimension-6 operator in a form that can be easily adapted to any particular basis of operators, or any particular model with new heavy particles. © 2015, The Author(s). Source


Garg J.,Massachusetts Institute of Technology | Bonini N.,Kings College London | Marzari N.,Ecole Polytechnique Federale de Lausanne
Nano Letters | Year: 2011

The thermal conductivity of ideal short-period superlattices is computed using harmonic and anharmonic force constants derived from density-functional perturbation theory and by solving the Boltzmann transport equation in the single-mode relaxation time approximation, using silicon-germanium as a paradigmatic case. We show that in the limit of small superlattice period the computed thermal conductivity of the superlattice can exceed that of both the constituent materials. This is found to be due to a dramatic reduction in the scattering of acoustic phonons by optical phonons, leading to very long phonon lifetimes. By variation of the mass mismatch between the constituent materials in the superlattice, it is found that this enhancement in thermal conductivity can be engineered, providing avenues to achieve high thermal conductivities in nanostructured materials. © 2011 American Chemical Society. Source


Boyarsky A.,Leiden University | Ruchayskiy O.,Ecole Polytechnique Federale de Lausanne | Iakubovskyi D.,NASU Bogolyubov Institute for Theoretical Physics | Iakubovskyi D.,National University of Kyiv-Mohyla Academy | Franse J.,Leiden University
Physical Review Letters | Year: 2014

We report a weak line at 3.52±0.02keV in x-ray spectra of the Andromeda galaxy and the Perseus galaxy cluster observed by the metal-oxide-silicon (MOS) and p-n (PN) CCD cameras of the XMM-Newton telescope. This line is not known as an atomic line in the spectra of galaxies or clusters. It becomes stronger towards the centers of the objects; is stronger for Perseus than for M31; is absent in the spectrum of a deep "blank sky" data set. Although for each object it is hard to exclude that the feature is due to an instrumental effect or an atomic line, it is consistent with the behavior of a dark matter decay line. Future (non-)detections of this line in multiple objects may help to reveal its nature. © 2014 American Physical Society. Source


Lukinavicius G.,Ecole Polytechnique Federale de Lausanne
Current opinion in chemical biology | Year: 2011

Numerous synthetic fluorophores have been developed that can switch their spectroscopic properties upon interaction with other molecules or by irradiation with light. In recent years, protein-labeling techniques have been introduced that permit the specific attachment of such molecules to proteins of interest in living cells. We review here how the attachment of switchable fluorophores to selected proteins of interest via self-labeling protein tags enables new applications in different areas of biology and discuss how these molecules could be further improved. Copyright © 2011 Elsevier Ltd. All rights reserved. Source


Magistretti P.J.,Ecole Polytechnique Federale de Lausanne | Magistretti P.J.,Center for Psychiatric Neuroscience
Cell Metabolism | Year: 2014

Functional brain imaging studies show that in certain brain regions glucose utilization exceeds oxygen consumption, indicating the predominance of aerobic glycolysis. In this issue, Goyal et al. (2014) report that this metabolic profile is associated with an enrichment in the expression of genes involved in synaptic plasticity and remodeling processes. © 2014 Elsevier Inc. Source


Auerbach J.E.,Ecole Polytechnique Federale de Lausanne | Bongard J.C.,University of Vermont
PLoS Computational Biology | Year: 2014

Whether, when, how, and why increased complexity evolves in biological populations is a longstanding open question. In this work we combine a recently developed method for evolving virtual organisms with an information-theoretic metric of morphological complexity in order to investigate how the complexity of morphologies, which are evolved for locomotion, varies across different environments. We first demonstrate that selection for locomotion results in the evolution of organisms with morphologies that increase in complexity over evolutionary time beyond what would be expected due to random chance. This provides evidence that the increase in complexity observed is a result of a driven rather than a passive trend. In subsequent experiments we demonstrate that morphologies having greater complexity evolve in complex environments, when compared to a simple environment when a cost of complexity is imposed. This suggests that in some niches, evolution may act to complexify the body plans of organisms while in other niches selection favors simpler body plans. © 2014 Auerbach, Bongard. Source


Balasubramanian K.,Max Planck Institute for Solid State Research | Kern K.,Max Planck Institute for Solid State Research | Kern K.,Ecole Polytechnique Federale de Lausanne
Advanced Materials | Year: 2014

Nanostructures are promising candidates for use as active materials for the detection of chemical and biological species, mainly due to the high surface-to-volume ratio and the unique physical properties arising at the nanoscale. Among the various nanostructures, materials comprised of sp 2-carbon enjoy a unique position due to the possibility to readily prepare them in various dimensions ranging from 0D, through 1D to 2D. This review focuses on the use of 1D (carbon nanotubes) and 2D (graphene) carbon nanostructures for the detection of biologically relevant molecules. A key advantage is the possibility to perform the sensing operation without the use of any labels or complex reaction schemes. Along this spirit, various strategies reported for the label-free electrical detection of biomolecules using carbon nanostructures are discussed. With their promise for ultimate sensitivity and the capability to attain high selectivity through controlled chemical functionalization, carbon-based nanobiosensors are expected to open avenues to novel diagnostic tools as well as to obtain new fundamental insight into biomolecular interactions down to the single molecule level. The current state-of-the-art of carbonbased nanostructures (carbon nanotubes and graphene) for the label-free electrical detection of biomolecules is presented. Challenges in their use are also outlined. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source


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

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


Hanahan D.,Ecole Polytechnique Federale de Lausanne | Coussens L.,Oregon Health And Science University
Cancer Cell | Year: 2012

Mutationally corrupted cancer (stem) cells are the driving force of tumor development and progression. Yet, these transformed cells cannot do it alone. Assemblages of ostensibly normal tissue and bone marrow-derived (stromal) cells are recruited to constitute tumorigenic microenvironments. Most of the hallmarks of cancer are enabled and sustained to varying degrees through contributions from repertoires of stromal cell types and distinctive subcell types. Their contributory functions to hallmark capabilities are increasingly well understood, as are the reciprocal communications with neoplastic cancer cells that mediate their recruitment, activation, programming, and persistence. This enhanced understanding presents interesting new targets for anticancer therapy. © 2012 Elsevier Inc. Source


Gupta R.S.,Autonomous University of Barcelona | Pomarol A.,Autonomous University of Barcelona | Riva F.,Ecole Polytechnique Federale de Lausanne
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2015

Using the predictive power of the effective field theory approach, we present a physical parametrization of the leading effects beyond the standard model (BSM), which gives us at present the best way to constrain heavy new physics at low energies. We show that other BSM effects are not independent from these ones, and we provide the explicit correlations. This information is useful to know where to primarily look for new physics in future experiments, and to know how this new physics is related to previous measurements, most importantly in electroweak symmetry breaking processes or Higgs physics. © 2015 American Physical Society. Source


Berne A.,Ecole Polytechnique Federale de Lausanne | Krajewski W.F.,University of Iowa
Advances in Water Resources | Year: 2013

Hydrology requires accurate and reliable rainfall input. Because of the strong spatial and temporal variability of precipitation, estimation of spatially distributed rain rates is challenging. Despite the fact that weather radars provide high-resolution (but indirect) observations of precipitation, they are not used in hydrological applications as extensively as one could expect. The goal of the present review paper is to investigate this question and to provide a clear view of the opportunities (e.g., for flash floods, urban hydrology, rainfall spatial extremes) the limitations (e.g., complicated error structure, need for adjustment) and the challenges for the use of weather radar in hydrology (i.e., validation studies, precipitation forecasting, mountainous precipitation, error propagation in hydrological models). © 2012 Elsevier Ltd. Source


Cudalbu C.,Ecole Polytechnique Federale de Lausanne
Metabolic Brain Disease | Year: 2013

Hepatic encephalopathy (HE) is a common and severe neuropsychiatric complication present in acute and chronic liver disease. The unique advantages of high field 1H MRS provide a method for assessing pathogenic mechanism, diagnosis and monitoring of HE, as well as for treatment assessment or recovery after liver transplantation, in a reproducible and reliable non-invasive way. The purpose of the present review is to present some new features of in vivo proton Magnetic Resonance Spectroscopy (1H MRS) at high magnetic fields combined with some basic requirements for reliable metabolic profiling. Finally, in vivo applications of 1H MRS in different HE animal models are presented. © 2012 Springer Science+Business Media New York. Source


Gonczy P.,Ecole Polytechnique Federale de Lausanne
Nature Reviews Cancer | Year: 2015

Over a century ago, centrosome aberrations were postulated to cause cancer by promoting genome instability. The mechanisms governing centrosome assembly and function are increasingly well understood, allowing for a timely reappraisal of this postulate. This Review discusses recent advances that shed new light on the relationship between centrosomes and cancer, and raise the possibility that centrosome aberrations contribute to this disease in different ways than initially envisaged. © 2015 Macmillan Publishers Limited. All rights reserved. Source


Sivula K.,Ecole Polytechnique Federale de Lausanne
Chimia | Year: 2013

Efficiently and inexpensively converting solar energy into chemical fuels is an important goal towards a sustainable energy economy. An integrated tandem cell approach could reasonably convert over 20% of the sun's energy directly into chemical fuels like H2 via water splitting. Many different systems have been investigated using various combinations of photovoltaic cells and photoelectrodes, but in order to be economically competitive with the production of H2 from fossil fuels, a practical water splitting tandem cell must optimize cost, longevity and performance. In this short review, the practical aspects of solar fuel production are considered from the perspective of a semiconductor-based tandem cell and the latest advances with a very promising technology - metal oxide photoelectrochemical tandem cells - are presented. © Schweizerische Chemische Gesellschaft. Source


Davison A.C.,Ecole Polytechnique Federale de Lausanne | Gholamrezaee M.M.,Center hospitalier University Vaudois
Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences | Year: 2012

We describe a prototype approach to flexible modelling for maxima observed at sites in a spatial domain, based on fitting of max-stable processes derived from underlying Gaussian random fields. The models we propose have generalized extreme-value marginal distributions throughout the spatial domain, consistent with statistical theory for maxima in simpler cases, and can incorporate both geostatistical correlation functions and random set components. Parameter estimation and fitting are performed through composite likelihood inference applied to observations from pairs of sites, with occurrence times of maxima taken into account if desired, and competing models are compared using appropriate information criteria. Diagnostics for lack of model fit are based on maxima from groups of sites. The approach is illustrated using annual maximum temperatures in Switzerland, with risk analysis proposed using simulations from the fitted max-stable model. Drawbacks and possible developments of the approach are discussed. © 2011 The Royal Society. Source


Fallahi A.,University of Hamburg | Perruisseau-Carrier J.,Ecole Polytechnique Federale de Lausanne
Physical Review B - Condensed Matter and Materials Physics | Year: 2012

Periodic structures with subwavelength features are instrumental in the versatile and effective control of electromagnetic waves from radio frequencies up to optics. In this paper, we theoretically evaluate the potential applications and performance of electromagnetic metasurfaces made of periodically patterned graphene. Several graphene metasurfaces are presented, thereby demonstrating that such ultrathin surfaces can be used to dynamically control the electromagnetic wave reflection, absorption, or polarization. Indeed, owing to the graphene properties, the structure performance in terms of resonance frequencies and bandwidths changes with the variation of electrostatic bias fields. To demonstrate the applicability of the concept at different frequency ranges, the examples provided range from microwave to infrared, corresponding to graphene features with length scales of a few millimeters down to about a micrometer, respectively. The results are obtained using a full-vector semianalytical numerical technique developed to accurately model the graphene-based multilayer periodic structures under study. © 2012 American Physical Society. Source


Spadoni A.,Ecole Polytechnique Federale de Lausanne | Ruzzene M.,Georgia Institute of Technology
Journal of the Mechanics and Physics of Solids | Year: 2012

Auxetic materials expand when stretched, and shrink when compressed. This is the result of a negative Poissons ratio ν. Isotropic configurations with ν≈-1 have been designed and are expected to provide increased shear stiffness G. This assumes that Youngs modulus and ν can be engineered independently. In this article, a micropolar-continuum model is employed to describe the behavior of a representative auxetic structural network, the chiral lattice, in an attempt to remove the indeterminacy in its constitutive law resulting from ν=-1. While this indeterminacy is successfully removed, it is found that the shear modulus is an independent parameter and, for certain configurations, it is equal to that of the triangular lattice. This is remarkable as the chiral lattice is subject to bending deformation of its internal members, and thus is more compliant than the triangular lattice which is stretch dominated. The derived micropolar model also indicates that this unique lattice has the highest characteristic length scale lc of all known lattice topologies, as well as a negative first Lamé constant without violating bounds required for thermodynamic stability. We also find that hexagonal arrangements of deformable rings have a coupling number N=1. This is the first lattice reported in the literature for which couple-stress or Mindlin theory is necessary rather than being adopted a priori. © 2011 Elsevier Ltd. All rights reserved. Source


Necsulea A.,Ecole Polytechnique Federale de Lausanne | Kaessmann H.,University of Lausanne | Kaessmann H.,Swiss Institute of Bioinformatics
Nature Reviews Genetics | Year: 2014

Gene expression changes may underlie much of phenotypic evolution. The development of high-throughput RNA sequencing protocols has opened the door to unprecedented large-scale and cross-species transcriptome comparisons by allowing accurate and sensitive assessments of transcript sequences and expression levels. Here, we review the initial wave of the new generation of comparative transcriptomic studies in mammals and vertebrate outgroup species in the context of earlier work. Together with various large-scale genomic and epigenomic data, these studies have unveiled commonalities and differences in the dynamics of gene expression evolution for various types of coding and non-coding genes across mammalian lineages, organs, developmental stages, chromosomes and sexes. They have also provided intriguing new clues to the regulatory basis and phenotypic implications of evolutionary gene expression changes. © 2014 Macmillan Publishers Limited. All rights reserved. Source


Osorio C.,Massachusetts Institute of Technology | Bierlaire M.,Ecole Polytechnique Federale de Lausanne
Operations Research | Year: 2013

This paper proposes a simulation-based optimization (SO) method that enables the efficient use of complex stochastic urban traffic simulators to address various transportation problems. It presents a metamodel that integrates information from a simulator with an analytical queueing network model. The proposed metamodel combines a general-purpose component (a quadratic polynomial), which provides a detailed local approximation, with a physical component (the analytical queueing network model), which provides tractable analytical and global information. This combination leads to an SO framework that is computationally efficient and suitable for complex problems with very tight computational budgets. We integrate this metamodel within a derivative-free trust region algorithm. We evaluate the performance of this method considering a traffic signal control problem for the Swiss city of Lausanne, different demand scenarios, and tight computational budgets. The method leads to well-performing signal plans. It leads to reduced, as well as more reliable, average travel times. © 2013 INFORMS. Source


Mainero C.,Harvard University | Boshyan J.,Harvard University | Hadjikhani N.,Harvard University | Hadjikhani N.,Ecole Polytechnique Federale de Lausanne
Annals of Neurology | Year: 2011

Objective: The periaqueductal gray matter (PAG), a known modulator of somatic pain transmission, shows evidence of interictal functional and structural abnormalities in migraineurs, which may contribute to hyperexcitability along spinal and trigeminal nociceptive pathways, and lead to the migraine attack. The aim of this study was to examine functional connectivity of the PAG in migraine. Methods: Using resting-state functional MRI, we compared functional connectivity between PAG and a subset of brain areas involved in nociceptive/somatosensory processing and pain modulation in 17 subjects with migraine, during a pain-free state, versus 17 gender- and age-matched controls. We also assessed the relation between intrinsic resting-state correlations within PAG networks and the average monthly frequency of migraine attacks, as well as allodynia. Results: Our findings show stronger connectivity between the PAG and several brain areas within nociceptive and somatosensory processing pathways in migraineurs versus controls. In addition, as the monthly frequency of migraine attacks worsens, the strength of the connectivity in some areas within these pathways increases, whereas a significant decrease in functional resting-state connectivity between the PAG and brain regions with a predominant role in pain modulation (prefrontal cortex, anterior cingulate, amygdala) can be evidenced. Finally, migraineurs with a history of allodynia exhibit significantly reduced connectivity between PAG, prefrontal regions, and anterior cingulate compared to migraineurs without allodynia. Interpretation: These data reveal interictal dysfunctional dynamics within pain pathways in migraine manifested as an impairment of the descending pain modulatory circuits, likely leading to loss of pain inhibition, and hyperexcitability primarily in nociceptive areas. ANN NEUROL 2011 Copyright © 2011 American Neurological Association. Source


Hu X.,Ecole Polytechnique Federale de Lausanne
Chimia | Year: 2010

Non-activated alkyl halides are challenging substrates for cross-coupling reactions because they are reluctant to undergo oxidative addition and because metal alkyl intermediates are prone to β-H elimination. Despite recent progress, well-defined catalysts are rare. We recently prepared Ni complexes with a chelating pincer-type bis(amino)amide ligand. The chloride complex [(MeNN2)NiCl] is an active (pre)catalyst for the coupling of non-activated alkyl halides with alkyl, aryl, and heteroaryl Grignard reagents. The catalysis tolerates a wide range of functional groups such as keto, ester, amide, acetal, indole, furan, nitrile, etc. The Ni complex also catalyzes direct alkylation of alkynes and aromatic heterocycles. © Schweizerische Chemische Gesellschaft. Source


Gerace D.,University of Pavia | Savona V.,Ecole Polytechnique Federale de Lausanne
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2014

It is shown that noncentrosymmetric materials with bulk second-order nonlinear susceptibility can be used to generate strongly antibunched radiation at an arbitrary wavelength, solely determined by the resonant behavior of suitably engineered coupled microcavities. The proposed scheme exploits the unconventional photon blockade of a coherent driving field at the input of a coupled cavity system, where one of the two cavities is engineered to resonate at both fundamental and second harmonic frequencies, respectively. Remarkably, the unconventional blockade mechanism occurs with reasonably low quality factors at both harmonics, and does not require a sharp doubly resonant condition for the second cavity, thus proving its feasibility with current semiconductor technology. © 2014 American Physical Society. Source


Hanahan D.,Ecole Polytechnique Federale de Lausanne | Hanahan D.,University of California at San Francisco | Weinberg R.A.,Whitehead Institute For Biomedical Research
Cell | Year: 2011

The hallmarks of cancer comprise six biological capabilities acquired during the multistep development of human tumors. The hallmarks constitute an organizing principle for rationalizing the complexities of neoplastic disease. They include sustaining proliferative signaling, evading growth suppressors, resisting cell death, enabling replicative immortality, inducing angiogenesis, and activating invasion and metastasis. Underlying these hallmarks are genome instability, which generates the genetic diversity that expedites their acquisition, and inflammation, which fosters multiple hallmark functions. Conceptual progress in the last decade has added two emerging hallmarks of potential generality to this list - reprogramming of energy metabolism and evading immune destruction. In addition to cancer cells, tumors exhibit another dimension of complexity: they contain a repertoire of recruited, ostensibly normal cells that contribute to the acquisition of hallmark traits by creating the "tumor microenvironment." Recognition of the widespread applicability of these concepts will increasingly affect the development of new means to treat human cancer. © 2011 Elsevier Inc. Source


Constam D.B.,Ecole Polytechnique Federale de Lausanne
Seminars in Cell and Developmental Biology | Year: 2014

Secreted cytokines of the TGFβ family are found in all multicellular organisms and implicated in regulating fundamental cell behaviors such as proliferation, differentiation, migration and survival. Signal transduction involves complexes of specific type I and II receptor kinases that induce the nuclear translocation of Smad transcription factors to regulate target genes. Ligands of the BMP and Nodal subgroups act at a distance to specify distinct cell fates in a concentration-dependent manner. These signaling gradients are shaped by multiple factors, including proteases of the proprotein convertase (PC) family that hydrolyze one or several peptide bonds between an N-terminal prodomain and the C-terminal domain that forms the mature ligand. This review summarizes information on the proteolytic processing of TGFβ and related precursors, and its spatiotemporal regulation by PCs during development and various diseases, including cancer. Available evidence suggests that the unmasking of receptor binding epitopes of TGFβ is only one (and in some cases a non-essential) function of precursor processing. Future studies should consider the impact of proteolytic maturation on protein localization, trafficking and turnover in cells and in the extracellular space. © 2014 The Author. Source


Oosterveer M.H.,University of Groningen | Schoonjans K.,Ecole Polytechnique Federale de Lausanne
Cellular and Molecular Life Sciences | Year: 2014

The hepatic glucose-sensing system is a functional network of enzymes and transcription factors that is critical for the maintenance of energy homeostasis and systemic glycemia. Here we review the recent literature on its components and metabolic actions. Glucokinase (GCK) is generally considered as the initial postprandial glucose-sensing component, which acts as the gatekeeper for hepatic glucose metabolism and provides metabolites that activate the transcription factor carbohydrate response element binding protein (ChREBP). Recently, liver receptor homolog 1 (LRH-1) has emerged as an upstream regulator of the central GCK-ChREBP axis, with a critical role in the integration of hepatic intermediary metabolism in response to glucose. Evidence is also accumulating that O-linked β-N-acetylglucosaminylation (O-GlcNAcylation) and acetylation can act as glucose-sensitive modifications that may contribute to hepatic glucose sensing by targeting regulatory proteins and the epigenome. Further elucidation of the components and functional roles of the hepatic glucose-sensing system may contribute to the future treatment of liver diseases associated with deregulated glucose sensors. © 2013 Springer. Source


Cayron C.,Ecole Polytechnique Federale de Lausanne
Acta Materialia | Year: 2016

This work generalizes the one-step model previously developed on fcc → bcc martensitic transformations to the larger family of phase transitions in the fcc-bcc-hcp system. The angular distortive matrices are calculated for the bcc → fcc, bcc → hcp and fcc → hcp transitions, and for fcc → fcc mechanical twinning. The analytical expressions of the continuous atomic displacements, lattice distortion and lattice correspondence matrices result directly from the orientation relationships; the unique assumption is that the atoms are hard-spheres that can't interpenetrate each other. The displacive transformations occur in one-step by the change of the unique parameter which is the angle of distortion, without any defined intermediate phase or lattice shearing. The matrices of complete distortion form an algebra over the number field ℚ (6). The habit planes are predicted on the simple criterion that they are untilted by the distortion; the results are compared to experimental observations published in literature. Shuffle is required for bcc → hcp and fcc → hcp transitions because the hcp primitive Bravais lattice contains two atoms instead of one for the fcc and bcc phases; the analytical expressions of the shuffle trajectories are determined. Different crystallographic aspects are discussed. The steric barriers on dense planes are calculated and compared for fcc → fcc mechanical twining and fcc → bcc martensitic transformation. A distinction between the orientational and distortional variants is introduced, with an example given for the fcc → hcp transformation. Some crystallographic properties that could help the understanding of the transformation reversibility are also detailed. This approach is directly applicable to mechanical twinning in bcc and hcp crystals, and probably to diffusion-limited displacive transformations. This work gives a unified approach of the crystallography of displacive phase transformations and mechanical twinning in hard-sphere packed metallic alloys. © 2016 Acta Materialia Inc. Source


Gratzel M.,Ecole Polytechnique Federale de Lausanne
Pure and Applied Chemistry | Year: 2013

This article deals with artificial (non biological) systems that achieve fuel generation by visible light. Intrinsic features of light driven redox processes in organized assemblies such as surfactant micelles and colloidal semiconductors are discussed. When coupled with suitable highly active redox catalysts these devices can be employed to accomplish cleavage of water or hydrogen sulfide by visible light. © 2013, Walter de Gruyter. All rights reserved. Source


Cole S.T.,Ecole Polytechnique Federale de Lausanne
Philosophical Transactions of the Royal Society B: Biological Sciences | Year: 2014

The golden age of antimicrobial drug development is a distant memory, and the likelihood of there being another seems slim. In part, this is because the pharmaceutical industry, which has now adopted an unsustainable business model, abandoned the anti-infective sector, and the pipeline is almost empty. The contribution to this crisis of national governments, health agencies and funders also merits discussion. Much of the basis for drug discovery is funded by the public sector, thereby generating intellectual property and leads for drug development that are often not pursued owing to funding gaps. In particular, the cost of testing drug efficacy in clinical trials is beyond the means of most companies and organizations. Lack of a concerted international effort to develop new antimicrobials is particularly alarming at a time when multidrug-resistant bacteria threaten all areas of human medicine globally. Here, the steps that led to this situation are retraced, and some possible solutions to the dilemma are proposed. © 2014 The Author(s) Published by the Royal Society. All rights reserved. Source


Mosig J.,Ecole Polytechnique Federale de Lausanne
IEEE Transactions on Antennas and Propagation | Year: 2012

The classic weighted averages (WA) algorithm for the evaluation of Sommerfeld-like integrals is reviewed and reappraised. As a result, a new version of the WA algorithm, called generalized WA, is introduced. The new version can be considered as a generalization of the well established Hlder and Csaro means, used to sum divergent series. Generalized WA exhibits a more compact formulation, devoid of iterative and recursive steps, and a wider range of applications. It is more robust, as it provides a unique formulation, valid for monotonic and oscillating functions. The implementation of the new version is easier and more economical in terms of basic operations. Preliminary numerical examples show that generalized WA also outperforms in terms of accuracy the classic WA algorithm, which is currently recognized as the most competitive algorithm to evaluate Sommerfeld integral tails. © 2012 IEEE. Source


Oberli D.Y.,Ecole Polytechnique Federale de Lausanne
Physical Review B - Condensed Matter and Materials Physics | Year: 2012

We present an experimental study and develop a group theoretical analysis of the Zeeman effect on excitons in pyramidal semiconductor quantum dots possessing the symmetries of the C 3v point group. The magnetic field dependence of the emission pattern originating from neutral exciton states is investigated in both the Faraday and Voigt configurations. The Zeeman doublet splitting of the "bright" exciton states varies linearly with the magnetic field strength in each configuration while the intensity of the "dark" exciton transitions exhibit a nonlinear dependence. We demonstrate that these observations originate from the intertwining of the Zeeman and Coulomb interactions, which provides clear spectral signatures of this effect for highly symmetric quantum dots. We uncover a large anisotropy of the Zeeman doublet splittings for longitudinal and transverse magnetic fields, revealing the ubiquitous role of a symmetry elevation in our pyramidal quantum dots. These results suggest that the common description of the Zeeman effect based on effective g factors for electrons and holes must be revised when dealing with exciton complexes. © 2012 American Physical Society. Source


Jensen J.D.,Ecole Polytechnique Federale de Lausanne | Bachtrog D.,University of California at Berkeley
Genome Biology and Evolution | Year: 2011

Characterizing the role of effective population size in dictating the rate of adaptive evolution remains a major challenge in evolutionary biology. Depending on the underlying distribution of fitness effects of new mutations, populations of different sizes may differ vastly in their rate of adaptation. Here, we collect polymorphism data at over 100 loci for two closely related Drosophila species with different current effective population sizes (N e), Drosophila miranda and D. pseudoobscura, to evaluate the prevalence of adaptive evolution versus genetic drift in molecular evolution. Utilizing these large and consistently sampled data sets, we obtain greatly improved estimates of the demographic histories of both species. Specifically, although current N e differs between these species, their ancestral sizes were much more similar. We find that statistical approaches capturing recent adaptive evolution (using patterns of polymorphisms) detect higher rates of adaptive evolution in the larger D. pseudoobscura population. In contrast, methods aimed at detecting selection over longer time periods (i.e., those relying on divergence data) estimate more similar rates of adaptation between the two species. Thus, our results suggest an important role of effective population size in dictating rates of adaptation and highlight how complicated population histories-as is probably the case for most species-can effect rates of adaptation. Additionally, we also show how different methodologies to detect positive selection can reveal information about different timescales of adaptive evolution. © The Author(s) 2010. Source


Kiritsis D.,Ecole Polytechnique Federale de Lausanne
International Journal of Production Research | Year: 2013

The use of semantic technologies and ontologies is becoming more and more popular in engineering applications and particularly in product modelling. Still, the use is limited in academia and applications are of a small scale. In this paper we present the research work done by the closed-loop life cycle management (CL2M) team of the Laboratory for Computer-Aided Design and Production (LICP) at the Swiss Federal Institute of Technology Lausanne (EPFL), Switzerland, on the use of ontology-based technologies for the life cycle management of products and engineering assets. This research has been performed through a number of PhD works partially financed by the European Framework Program for research. It aims at providing both a wider understanding of the benefits of applying such technologies in the complex environment of asset life cycle management (ALM) and at providing a platform for implementing ontology models in industrial environments. © 2013 Taylor & Francis. Source


Ryu D.,Ecole Polytechnique Federale de Lausanne
Nature Medicine | Year: 2016

The biological effects of urolithins remain poorly characterized, despite wide-spread human exposure via the dietary consumption of their metabolic precursors, the ellagitannins, which are found in the pomegranate fruit, as well as in nuts and berries. We identified urolithin A (UA) as a first-in-class natural compound that induces mitophagy both in vitro and in vivo following oral consumption. In C. elegans, UA prevented the accumulation of dysfunctional mitochondria with age and extended lifespan. Likewise, UA prolonged normal activity during aging in C. elegans, including mobility and pharyngeal pumping, while maintaining mitochondrial respiratory capacity. These effects translated to rodents, where UA improved exercise capacity in two different mouse models of age-related decline of muscle function, as well as in young rats. Our findings highlight the health benefits of urolithin A and its potential application in strategies to improve mitochondrial and muscle function. © 2016 Nature Publishing Group, a division of Macmillan Publishers Limited. All Rights Reserved. Source


Petersen C.C.H.,Ecole Polytechnique Federale de Lausanne
Annual Review of Neuroscience | Year: 2014

Facial muscles drive whisker movements, which are important for active tactile sensory perception in mice and rats. These whisker muscles are innervated by cholinergic motor neurons located in the lateral facial nucleus. The whisker motor neurons receive synaptic inputs from premotor neurons, which are located within the brain stem, the midbrain, and the neocortex. Complex, distributed neural circuits therefore regulate whisker movement during behavior. This review focuses specifically on cortical whisker motor control. The whisker primary motor cortex (M1) strongly innervates brain stem reticular nuclei containing whisker premotor neurons, which might form a central pattern generator for rhythmic whisker protraction. In a parallel analogous pathway, the whisker primary somatosensory cortex (S1) strongly projects to the brain stem spinal trigeminal interpolaris nucleus, which contains whisker premotor neurons innervating muscles for whisker retraction. These anatomical pathways may play important functional roles, since stimulation of M1 drives exploratory rhythmic whisking, whereas stimulation of S1 drives whisker retraction. © Copyright ©2014 by Annual Reviews. All rights reserved. Source


Crassous A.,Ecole Polytechnique Federale de Lausanne
Nature Nanotechnology | Year: 2015

Impurity elements used as dopants are essential to semiconductor technology for controlling the concentration of charge carriers. Their location in the semiconductor crystal is determined during the fabrication process and remains fixed. However, another possibility exists whereby the concentration of charge carriers is modified using polarization charge as a quasi-dopant, which implies the possibility to write, displace, erase and re-create channels having a metallic-type conductivity inside a wide-bandgap semiconductor matrix. Polarization-charge doping is achieved in ferroelectrics by the creation of charged domain walls. The intentional creation of stable charged domain walls has so far only been reported in BaTiO3 single crystals, with a process that involves cooling the material through its phase transition under a strong electric bias, but this is not a viable technology when real-time reconfigurability is sought in working devices. Here, we demonstrate a technique allowing the creation and nanoscale manipulation of charged domain walls and their action as a real-time doping activator in ferroelectric thin films. Stable individual and multiple conductive channels with various lengths from 3 μm to 100 nm were created, erased and recreated in another location, and their high metallic-type conductivity was verified. This takes the idea of hardware reconfigurable electronics one step forward. © 2015 Nature Publishing Group Source


Maeder T.,Ecole Polytechnique Federale de Lausanne
International Materials Reviews | Year: 2013

The present work critically reviews the scientific and patent literature on low melting bismuth based oxide glass frits in materials for electronics, sensors and related applications such as sealing glasses, solar cells, architectural and automotive glass, the main motivation being to replace lead based materials by environmentally more benign ones. Due to similar glass forming properties of Bi and Pb, Bi based glasses are the closest 'drop-in' alternative for lead bearing formulations, and are therefore actually replacing them in many applications, helped also by previous experience with Bi containing materials in thick film technology and component metallisations. The outstanding issues are discussed, e.g. matching the lowest processing temperatures achieved by the classical lead based glasses without sacrificing durability and stability, as well as stability versus chemical reduction. Finally, consideration is also given to special 'heavy' glasses (often containing Bi and Pb together) that are useful in fields such as optics, superconductors and nuclear technology, as well as to specific Bi 2O3 containing crystalline compounds. © W.S.Maney and Son Ltd /Society 2013. Source


McLaren P.J.,Ecole Polytechnique Federale de Lausanne | Carrington M.,Frederick National Laboratory for Cancer Research | Carrington M.,Massachusetts Institute of Technology
Nature Immunology | Year: 2015

The outcome after infection with the human immunodeficiency virus type 1 (HIV-1) is a complex phenotype determined by interactions among the pathogen, the human host and the surrounding environment. An impact of host genetic variation on HIV-1 susceptibility was identified early in the pandemic, with a major role attributed to the genes encoding class I human leukocyte antigens (HLA) and the chemokine receptor CCR5. Studies using genome-wide data sets have underscored the strength of these associations relative to variants located throughout the rest of the genome. However, the extent to which additional polymorphisms influence HIV-1 disease progression, and how much of the variability in outcome can be attributed to host genetics, remain largely unclear. Here we discuss findings concerning the functional impact of associated variants, outline methods for quantifying the host genetic component and examine how available genome-wide data sets may be leveraged to discover gene variants that affect the outcome of HIV-1 infection. Source


Sandi C.,Ecole Polytechnique Federale de Lausanne | Haller J.,Hungarian Academy of Sciences
Nature Reviews Neuroscience | Year: 2015

Stress often affects our social lives. When undergoing high-level or persistent stress, individuals frequently retract from social interactions and become irritable and hostile. Predisposition to antisocial behaviours-including social detachment and violence-is also modulated by early life adversity; however, the effects of early life stress depend on the timing of exposure and genetic factors. Research in animals and humans has revealed some of the structural, functional and molecular changes in the brain that underlie the effects of stress on social behaviour. Findings in this emerging field will have implications both for the clinic and for society. © 2015 Macmillan Publishers Limited. All rights reserved. Source


Trono D.,Ecole Polytechnique Federale de Lausanne
Cold Spring Harbor Symposia on Quantitative Biology | Year: 2016

Transposable elements (TEs) may account for up to two-thirds of the human genome, and as genomic threats they are subjected to epigenetic control mechanisms engaged from the earliest stages of embryonic development. We previously determined that an important component of this process is the sequence-specific recognition of TEs by KRAB (Kruppelassociated box)-containing zinc-finger proteins (KRAB-ZFPs), a large family of tetrapod-restricted transcription factors that act by recruiting inducers of heterochromatin formation and DNA methylation. We further showed that KRAB-ZFPs and their cofactor KAP1 exert a marked influence on the transcription dynamics of embryonic stem cells via their docking of repressor complexes at TE-contained regulatory sequences. It is generally held that, beyond this early embryonic period, TEs become permanently silenced, and that the evolutionary selection of KRAB-ZFPs and other TE controllers is the result of a simple evolutionary arms race between the host and these genetics invaders. Here, I discuss recent evidence that invalidates this dual assumption and instead suggests that KRAB-ZFPs are the instruments of a massive enterprise of TE domestication, whereby transposon-based regulatory sequences and their cellular ligands establish species-specific transcription regulation networks that influence multiple aspects of human development and physiology. © 2015 Cold Spring Harbor Laboratory Press. Source


Bossaerts P.,California Institute of Technology | Bossaerts P.,Ecole Polytechnique Federale de Lausanne
Brain Structure and Function | Year: 2010

Most accounts of the function of anterior insula in the human brain refer to concepts that are difficult to formalize, such as feelings and awareness. The discovery of signals that reflect risk assessment and risk learning, however, opens the door to formal analysis. Hitherto, activations have been correlated with objective versions of risk and risk prediction error, but subjective versions (influenced by pessimism/optimism or risk aversion/tolerance) exist. Activation in closely related cortical structures has been found to be both objective (anterior cingulate cortex) and subjective (inferior frontal gyrus). For this quantitative analysis of uncertainty-induced neuronal activation to further understanding of insula's role in feelings and awareness, however, formalization and documentation of the relation between uncertainty and feelings/awareness will be needed. One obvious starting point is the link with failure anxiety and error awareness. © 2010 Springer-Verlag. Source


Bonini N.,Kings College London | Garg J.,Massachusetts Institute of Technology | Marzari N.,Ecole Polytechnique Federale de Lausanne
Nano Letters | Year: 2012

We use first-principles methods based on density functional perturbation theory to characterize the lifetimes of the acoustic phonon modes and their consequences on the thermal transport properties of graphene. We show that using a standard perturbative approach, the transverse and longitudinal acoustic phonons in free-standing graphene display finite lifetimes in the long-wavelength limit, making them ill-defined as elementary excitations in samples of dimensions larger than ∼1 μm. This behavior is entirely due to the presence of the quadratic dispersions for the out-of-plane phonon (ZA) flexural modes that appear in free-standing low-dimensional systems. Mechanical strain lifts this anomaly, and all phonons remain well-defined at any wavelength. Thermal transport is dominated by ZA modes, and the thermal conductivity is predicted to diverge with system size for any amount of strain. These findings highlight strain and sample size as key parameters in characterizing or engineering heat transport in graphene. © 2012 American Chemical Society. Source


Markram H.,Ecole Polytechnique Federale de Lausanne
Functional Neurology | Year: 2013

Although twenty-first century neuroscience is a major scientific enterprise, advances in basic research have not yet translated into benefits for society. In this paper, I outline seven fundamental challenges that need to be overcome. First, neuroscience has to become "big science" - we need big teams with the resources and competences to tackle the big problems. Second, we need to create interlinked sets of data providing a complete picture of single areas of the brain at their different levels of organization with "rungs" linking the descriptions for humans and other species. Such "data ladders" will help us to meet the third challenge - the development of efficient predictive tools, enabling us to drastically increase the information we can extract from expensive experiments. The fourth challenge goes one step further: we have to develop novel hardware and software sufficiently powerful to simulate the brain. In the future, supercomputer-based brain simulation will enable us to make in silico manipulations and recordings, which are currently completely impossible in the lab. The fifth and sixth challenges are translational. On the one hand we need to develop new ways of classifying and simulating brain disease, leading to better diagnosis and more effective drug discovery. On the other, we have to exploit our knowledge to build new brain-inspired technologies, with potentially huge benefits for industry and for society. This leads to the seventh challenge. Neuroscience can indeed deliver huge benefits but we have to be aware of widespread social concern about our work. We need to recognize the fears that exist, lay them to rest, and actively build public support for neuroscience research. We have to set goals for ourselves that the public can recognize and share. And then we have to deliver on our promises. Only in this way, will we receive the support and funding we need. © CIC Edizioni Internazionali. Source


Bernasconi R.,Institute for Research in Biomedicine | Molinari M.,Institute for Research in Biomedicine | Molinari M.,Ecole Polytechnique Federale de Lausanne
Current Opinion in Cell Biology | Year: 2011

The endoplasmic reticulum (ER) is the site of maturation for secretory and membrane proteins in eukaryotic cells. Unsuccessful folding attempts are eventually interrupted and most folding-defective polypeptides are dislocated across the ER membrane and degraded by cytosolic proteasomes in a complex series of events collectively defined as ER-associated degradation (ERAD). Uncontrolled ERAD activity might prematurely interrupt ongoing folding programs. At steady state, this is prevented by ERAD tuning, that is, the removal of select ERAD regulators from the ER and their degradation by proteasomes and by endo-lysosomal proteases. In Coronaviruses infected cells, the formation of LC3-I coated vesicles containing ERAD regulators cleared from the ER lumen is co-opted to anchor viral replication and transcription complexes to ER-derived membranes. © 2010 Elsevier Ltd. Source


Aberg K.C.,Ecole Polytechnique Federale de Lausanne
Journal of vision | Year: 2012

In (perceptual) learning, performance improves with practice either by changes in sensitivity or decision criterion. Often, changes in sensitivity are regarded as the appropriate measure of learning while changes in criterion are considered unavoidable nuisances. Very little is known about the distinguishing characteristics of both learning types. Here, we show first that block feedback, which affects sensitivity, does not affect criterion. Second, contrary to changes in sensitivity, changes in decision criterion are limited to the training session and do not transfer overnight. Finally, training with biased trial-wise feedback induces a sensitivity change such that a left offset Vernier may be perceived as a right offset Vernier. Source


Morasch B.,Ecole Polytechnique Federale de Lausanne | Morasch B.,University of Tubingen
Environmental Pollution | Year: 2013

Karst systems represent important yet vulnerable drinking water resources. A wide spectrum of pollutants may be released into karst groundwater from agriculture, livestock farming, private households, and industry. This work provides an overview on the occurrence and dynamics of micropollutants in a karst system of the Swiss Jura. Ten months of intensive monitoring for micropollutants confirmed that the swallow hole draining an agricultural plain was the main entry path for pesticides into the karst system and the two connected springs. Elevated fungicide concentrations in winter and occasional quantification of pharmaceuticals suggested wood- or façade treatment and domestic sewer as additional sources of contamination. A continuous atrazine signal in the low ng/L range might affect the autochthonous endokarst microbial community and represents a potential risk for the human population through karst groundwater. © 2012 Elsevier Ltd. All rights reserved. Source


Grallert A.,Paterson Institute for Cancer Research | Connolly Y.,Paterson Institute for Cancer Research | Smith D.L.,Paterson Institute for Cancer Research | Simanis V.,Ecole Polytechnique Federale de Lausanne | Hagan I.M.,Paterson Institute for Cancer Research
Nature Cell Biology | Year: 2012

Mitotic exit integrates the reversal of the phosphorylation events initiated by mitotic kinases with a controlled cytokinesis event that cleaves the cell in two. The mitotic exit network (MEN) of budding yeast regulates both processes, whereas the fission yeast equivalent, the septum initiation network (SIN), controls only the execution of cytokinesis. The components and architecture of the SIN and MEN are highly conserved. At present, it is assumed that the functions of the core SIN-MEN components are restricted to their characterized roles at the end of mitosis. We now show that the NDR (nuclear Dbf2-related) kinase component of the fission yeast SIN, Sid2-Mob1, acts independently of the other known SIN components in G2 phase of the cell cycle to control the timing of mitotic commitment. Sid2-Mob1 promotes mitotic commitment by directly activating the NIMA (Never In Mitosis)-related kinase Fin1. Fin1's activation promotes its own destruction, thereby making Fin1 activation a transient feature of G2 phase. This spike of Fin1 activation modulates the activity of the Pom1/Cdr1/Cdr2 geometry network towards Wee1. © 2012 Macmillan Publishers Limited. All rights reserved. Source


Petersen C.C.H.,Ecole Polytechnique Federale de Lausanne
Current Opinion in Neurobiology | Year: 2014

GABAergic neurons are a minor fraction of the neocortical neuronal population, but they are highly diverse in their features. The GABAergic neurons can be divided into three largely non-overlapping groups, defined through the expression of ionotropic serotonin receptors, parvalbumin or somatostatin. Membrane potential recordings from these genetically defined GABAergic neurons in layers 2 and 3 of mouse barrel cortex reveal that they are differentially modulated by whisker behavior. As a mouse begins to explore its environment by actively moving its whiskers, motor-related signals drive different activity patterns in specific types of GABAergic neurons, thereby promoting sensorimotor integration. The neural circuit mechanisms underlying such cell-type specific activity of GABAergic neurons are now being unraveled. © 2013 Elsevier Ltd. Source


Labiouse V.,Ecole Polytechnique Federale de Lausanne | Vietor T.,National Cooperative for the Disposal of Radioactive Waste
Rock Mechanics and Rock Engineering | Year: 2013

In the context of nuclear waste disposal in clay formations, laboratory and in situ simulation experiments were performed to study at reduced scale the excavation damaged zone (EDZ) around tunnels in the indurated Opalinus Clay at Mont Terri, Switzerland. In the laboratory, thick-walled hollow cylindrical specimens were subjected to a mechanical unloading mimicking a gallery excavation. In samples cored parallel to bedding, cracks sub-parallel to the bedding planes open and lead to a buckling failure in two regions that extend from the borehole in the direction normal to bedding. The behaviour is clearly anisotropic. On the other hand, in experiments performed on specimens cored perpendicular to bedding, there is no indication of failure around the hole and the response of the hollow cylinder sample is mainly isotropic. The in situ experiment at Mont Terri which consisted in the overcoring of a resin-injected borehole that follows the bedding strike of the Opalinus Clay showed a striking similarity between the induced damaged zone and the fracture pattern observed in the hollow cylinder tests on samples cored parallel to bedding and such a bedding controlled Excavation Damaged Zone is as well consistent with the distinct fracture patterns observed at Mont Terri depending on the orientation of holes/galleries with respect to the bedding planes. Interestingly, the damaged zone observed in the hollow cylinder tests on samples cored parallel to bedding and in situ around URL galleries is found to develop in reverse directions in Boom Clay (Mol) and in Opalinus Clay (Mont Terri). This most probably results from different failure mechanisms, i.e. shear failure along conjugated planes in the plastic Boom Clay, but bedding plane splitting and buckling in the indurated Opalinus Clay. © Springer-Verlag Wien 2013. Source


Cramer N.,Ecole Polytechnique Federale de Lausanne | Seiser T.,ETH Zurich
Synlett | Year: 2011

The catalytic activation of C-C bonds bears significant ecological and economical advantages. In this account we describe our results for an enantioselective C-C activation of symmetrically substituted tert-cyclobutanols. Subsequent downstream reactions of the obtained alkylrhodium intermediate give rise to a wide range of synthetically versatile products bearing all-carbon quaternary stereogenic centers with excellent enantioselectivities. 1 Introduction 1.1 Cyclobutanol Syntheses 2 Intramolecular Addition Reactions 2.1 Allenylcyclobutanols 2.2 Initiation of Cascade Catalysis 2.3 Vinylcyclobutanols 3 Intramolecular Bond-Activation Reactions 3.1 Aromatic C(sp2)-H Activations 3.2 Aromatic C(sp2)-SiR3 Activations 3.3 1,3-Shift Reactions, C(sp3)-H Activations 4 Summary and Outlook. © Georg Thieme Verlag Stuttgart. Source


Thimsen E.,Ecole Polytechnique Federale de Lausanne
Chemistry of Materials | Year: 2011

Immobilized noble metal nanoparticles are being explored for a variety of applications where control over the particle size and separation distance on the substrate is important for performance. A proof of concept is presented that Au nanoparticles can be deposited in a single step with control over the size and separation distributions using an aerosol process. Samples were deposited with mean particle diameters in the range from 15 to 43 nm, and mean separation distances from 11 to 39 nm. Depending on the separation distance, particles exhibited localized surface plasmon resonance dominated by either intra- or interparticle resonances, as determined by ultraviolet-visible extinction spectroscopy. Ultrathin TiO2 shells of different thicknesses, in the range from 0 to 24 nm, were deposited on the Au nanoparticles by atomic layer deposition to determine the sensing distance into the surrounding dielectric medium for these materials, which was estimated to be 10 nm. © 2011 American Chemical Society. Source


Wenzel S.,Ecole Polytechnique Federale de Lausanne | Lauchli A.M.,Max Planck Institute For Physik Komplexer Systeme
Physical Review Letters | Year: 2011

We perform large scale finite-temperature Monte Carlo simulations of the classical eg and t2g orbital models on the simple cubic lattice in three dimensions. The eg model displays a continuous phase transition to an orbitally ordered phase. While the correlation length exponent ν≈0.66(1) is close to the 3D XY value, the exponent η≈0.15(1) differs substantially from O(N) values. At Tc a U(1) symmetry emerges, which persists for T Source


Kunther W.,Empa - Swiss Federal Laboratories for Materials Science and Technology | Lothenbach B.,Empa - Swiss Federal Laboratories for Materials Science and Technology | Scrivener K.L.,Ecole Polytechnique Federale de Lausanne
Cement and Concrete Research | Year: 2013

The ingress of sulfate ions into cementitious materials leads to the formation of ettringite, gypsum and other phases. The increase in solid volume through the formation of these phases is often assumed to be the only reason for expansion. In this paper we systematically compare the volume increase predicted by thermodynamic modeling to macroscopic expansion for mortars made with CEM I in different sulfate solutions and for mortars made with a range of blended cements in sodium sulfate solution. It is shown that the length changes cannot be explained by simple volume increase alone. A more plausible explanation of expansion lies in the theory of crystallization pressure, in which crystals forming from a supersaturated solution may exert pressure on their surroundings. It is observed that expansion occurs in systems where thermodynamic modeling predicts the co-existence of ettringite with gypsum. In such a case, if monosulfate and gypsum are both present locally, the solution can be highly supersaturated with respect to ettringite, whose formation in confined conditions (such as within C-S-H) can then exert expansive forces. © 2013 Elsevier Ltd. Source


Braga D.,University of Geneva | Braga D.,ETH Zurich | Gutierrez Lezama I.,University of Geneva | Berger H.,Ecole Polytechnique Federale de Lausanne | Morpurgo A.F.,University of Geneva
Nano Letters | Year: 2012

We realized ambipolar field-effect transistors by coupling exfoliated thin flakes of tungsten disulfide (WS 2) with an ionic liquid dielectric. The devices show ideal electrical characteristics, including very steep subthreshold slopes for both electrons and holes and extremely low OFF-state currents. Thanks to these ideal characteristics, we determine with high precision the size of the band gap of WS 2 directly from the gate-voltage dependence of the source-drain current. Our results demonstrate how a careful use of ionic liquid dielectrics offers a powerful strategy to study quantitatively the electronic properties of nanoscale materials. © 2012 American Chemical Society. Source


Erb W.,ESPCI ParisTech | Zhu J.,Ecole Polytechnique Federale de Lausanne
Natural Product Reports | Year: 2013

Covering: 1975 to 2012 The first members of the tiacumicin family of antibiotics, encompassing more than 40 compounds, were isolated in 1975. Structurally, the core aglycon is an 18-membered macrolactone having two conjugated diene units, one isolated double bond, 5 stereogenic centers and most often, at least one glycosidic linkage. Tiacumicin B, a RNA synthesis inhibitor, is a narrow-spectrum antibiotic against clostridia. For the treatment of Clostridium difficile infection (CDI), it has the same cure rate as vancomycin but with lower relapse rate and was approved by the FDA in May 2011. The aim of this review is to present an overview of the chemistry and biology of tiacumicins since their discovery. This journal is © The Royal Society of Chemistry 2013. Source


Grimaldi C.,Ecole Polytechnique Federale de Lausanne
Physical Review B - Condensed Matter and Materials Physics | Year: 2014

Nanogranular metal composites, consisting of immiscible metallic and insulating phases deposited on a substrate, are characterized by two distinct electronic transport regimes depending on the relative amount of the metallic phase. At sufficiently large metallic loadings, granular metals behave as percolating systems with a well-defined critical concentration above which macroscopic clusters of physically connected conductive particles span the entire sample. Below the critical loading, granular metal films are in the dielectric regime, where current can flow throughout the composite only via hopping or tunneling processes between isolated nanosized particles or clusters. In this case transport is intrinsically nonpercolative in the sense that no critical concentration can be identified for the onset of transport. It is shown here that, although being very different in nature, these two regimes can be described by treating percolation and hopping on equal footing. By considering general features of the microstructure and of the electrical connectedness, the concentration dependence of the dc conductivity of several nanogranular metal films is reproduced to high accuracy within an effective-medium approach. In particular, fits to published experimental data enable us to extract the values of microscopic parameters that govern the percolation and tunneling regimes, explaining thus the transport properties observed in nanogranular metal films. © 2014 American Physical Society. Source


Gervais L.,IBM | De Rooij N.,Ecole Polytechnique Federale de Lausanne | Delamarche E.,IBM
Advanced Materials | Year: 2011

We might be at the turning point where research in microfluidics undertaken in academia and industrial research laboratories, and substantially sponsored by public grants, may provide a range of portable and networked diagnostic devices. In this Progress Report, an overview on microfluidic devices that may become the next generation of point-of-care (POC) diagnostics is provided. First, we describe gaps and opportunities in medical diagnostics and how microfluidics can address these gaps using the example of immunodiagnostics. Next, we conceptualize how different technologies are converging into working microfluidic POC diagnostics devices. Technologies are explained from the perspective of sample interaction with components of a device. Specifically, we detail materials, surface treatment, sample processing, microfluidic elements (such as valves, pumps, and mixers), receptors, and analytes in the light of various biosensing concepts. Finally, we discuss the integration of components into accurate and reliable devices. Microfluidic devices for point-of-care diagnostics are being realized in response to a pressing need for diagnostic tests for diseases that are not covered by current technology. This Progress Report details the requirements of point- of-care diagnostics and the technological components that can be used to develop such microfluidic devices. Specifically, materials, surface treatments, sample processing, microfluidic elements (such as valves, pumps, and mixers), receptors, and analytes in the perspective of various biosensing concepts are addressed. Finally, the integration of components into accurate and reliable devices is discussed. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source


Pasi M.,University of Lyon | Maddocks J.H.,Ecole Polytechnique Federale de Lausanne | Lavery R.,University of Lyon
Nucleic Acids Research | Year: 2015

Microsecond molecular dynamics simulations of B-DNA oligomers carried out in an aqueous environment with a physiological salt concentration enable us to perform a detailed analysis of how potassium ions interact with the double helix. The oligomers studied contain all 136 distinct tetranucleotides and we are thus able to make a comprehensive analysis of base sequence effects. Using a recently developed curvilinear helicoidal coordinate method we are able to analyze the details of ion populations and densities within the major and minor grooves and in the space surrounding DNA. The results show higher ion populations than have typically been observed in earlier studies and sequence effects that go beyond the nature of individual base pairs or base pair steps. We also show that, in some special cases, ion distributions converge very slowly and, on a microsecond timescale, do not reflect the symmetry of the corresponding base sequence. © 2015 The Author(s). Source


Carbone F.,Ecole Polytechnique Federale de Lausanne
Chemical Physics Letters | Year: 2010

Recently, the dynamics of atomic distances and orbital charge in graphite has been investigated by ultrafast electron diffraction, electron energy loss spectroscopy and transient optical absorption. A subtle interplay between structural motions and electronic degrees of freedom was found responsible for several peculiar behaviors like coherent phonon emission, photoinduced diamond formation, and graphene ablation. Here, we calculate ab initio the charge density of graphite, and observe its evolution during the above-mentioned structural distortions. The modifications of the electron energy loss and the optical spectra during c-axis compression and expansion are calculated and found in agreement with recent experiments. © 2010 Elsevier B.V. All rights reserved. Source


Eming S.A.,University of Cologne | Hubbell J.A.,Ecole Polytechnique Federale de Lausanne
Experimental Dermatology | Year: 2011

The vascular network is an integral component of most organs. Beyond assuring an adequate supply of oxygen and nutrients for normal tissue function, vascular structures provide also a critical interface in the balance of tissue homoeostasis and immune functions. Therefore, understanding the biology of the vascular system is a challenging and important objective because it is vital to many physiological and pathological processes. Unravelling mechanisms of blood vessel expansion and remodelling would offer therapeutic options to ameliorate disorders that are currently leading causes of mortality and morbidity, including cardiovascular diseases, cancer, chronic inflammatory disorders, diabetic retinopathy, tissue defects caused by trauma or chronic skin ulcers. This article will review cellular and molecular mechanisms controlling angiogenesis in the light of recent reports and data from our own laboratories. We will focus on the interaction of growth factors with extracellular matrix (ECM) components during the formation of vascular structures in health and disease. Finally, this article will provide a rationale for targeting the ECM-morphogen interplay for therapeutic angiogenesis. © 2011 John Wiley & Sons A/S. Source


Zubko P.,University of Geneva | Catalan G.,Catalan Institution for Research and Advanced Studies | Catalan G.,Autonomous University of Barcelona | Tagantsev A.K.,Ecole Polytechnique Federale de Lausanne
Annual Review of Materials Research | Year: 2013

Flexoelectricity-the coupling between polarization and strain gradients-is a universal effect allowed by symmetry in all materials. Following its discovery several decades ago, studies of flexoelectricity in solids have been scarce due to the seemingly small magnitude of this effect in bulk samples. The development of nanoscale technologies, however, has renewed the interest in flexoelectricity, as the large strain gradients often present at the nanoscale can lead to strong flexoelectric effects. Here we review the fundamentals of the flexoelectric effect in solids, discuss its presence in many nanoscale systems, and look at potential applications of this electromechanical phenomenon. The review also emphasizes the many open questions and unresolved issues in this developing field. © Copyright © 2013 by Annual Reviews. All rights reserved. Source


Vichi A.,Ecole Polytechnique Federale de Lausanne
Journal of High Energy Physics | Year: 2012

The four point functions of Conformal Field Theories (CFT's) with global symmetries give rise to multiple crossing symmetry constraints. We explicitly study the correlator of four scalar operators transforming in the fundamental representation of a global SO(N) and the correlator of chiral and anti-chiral super fields in a superconformal field theory. In both cases the constraints take the form of a triple sum rule, whose feasibility can be translated into restrictions on the CFT spectrum and interactions. In the case of SO(N) global symmetry we derive bounds for the first scalar singlet operator entering the Operator Product Expansion (OPE) of two fundamental representations for different value of N. Bounds for the first scalar traceless-symmetric representation of the global symmetry are computed as well. Results for superconformal field theories improve previous investigations due to the use of the full set of constraints. Our analysis only assumes unitarity of the CFT, crossing symmetry of the four point function and existence of an OPE for scalars. © SISSA 2012. Source


Cavadini S.,Ecole Polytechnique Federale de Lausanne
Progress in Nuclear Magnetic Resonance Spectroscopy | Year: 2010

A study was conducted to demonstrate that 14N nuclear magnetic resonance (NMR) of solid biological samples was feasible. The study also described methods for two-dimensional correlation experiments that were similar to earlier methods for the indirect detection of 15N in liquid-state NMR known as heteronuclear single- or multiple-quantum correlation (HSQC or HMQC). These methods were applied to small systems such as amino acids and small peptides in 13C labeled or in natural abundance samples. The experiments described in the study were suitable for quadrupolar nuclei with a spin quantum number I = 1. The study also obtained information about local structures of solids containing 14N. The methods described in the study resulted from two main projects covering the indirect detection of 14N through 13C or 1H. Source


Ruter J.,Ecole Polytechnique Federale de Lausanne
PLoS computational biology | Year: 2012

Decisions about noisy stimuli require evidence integration over time. Traditionally, evidence integration and decision making are described as a one-stage process: a decision is made when evidence for the presence of a stimulus crosses a threshold. Here, we show that one-stage models cannot explain psychophysical experiments on feature fusion, where two visual stimuli are presented in rapid succession. Paradoxically, the second stimulus biases decisions more strongly than the first one, contrary to predictions of one-stage models and intuition. We present a two-stage model where sensory information is integrated and buffered before it is fed into a drift diffusion process. The model is tested in a series of psychophysical experiments and explains both accuracy and reaction time distributions. Source


Kamada K.,Ecole Polytechnique Federale de Lausanne | Yokoyama J.,University of Tokyo
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2014

We consider the ghost-free higher-order corrections to the Starobinsky model in the old-minimal supergravity, focusing on a sector among several scalar fields in the model that reproduces the scalaron potential in the original Starobinsky model. In general, higher-order corrections cannot be forbidden by symmetries, which likely violate the flatness of the scalaron potential and make inflation difficult in explaining the present Universe. We find a severe constraint on the dimensionless coupling of the R4 correction as -5.5×10-8 Source


Aebi M.,ETH Zurich | Bernasconi R.,Institute for Research in Biomedicine | Clerc S.,ETH Zurich | Molinari M.,Institute for Research in Biomedicine | Molinari M.,Ecole Polytechnique Federale de Lausanne
Trends in Biochemical Sciences | Year: 2010

The processing of N-linked glycans determines secretory protein homeostasis in the eukaryotic cell. Folding and degradation of glycoproteins in the endoplasmic reticulum (ER) are regulated by molecular chaperones and enzymes recruited by specific oligosaccharide structures. Recent findings have identified several components of this protein quality control system that specifically modify N-linked glycans, thereby generating oligosaccharide structures recognized by carbohydrate-binding proteins, lectins. In turn, lectins direct newly synthesized polypeptides to the folding, secretion or degradation pathways. The "glyco-code of the ER" displays the folding status of a multitude of cargo proteins. Deciphering this code will be instrumental in understanding protein homeostasis regulation in eukaryotic cells and for intervention because such processes can have crucial importance for clinical and industrial applications. © 2009 Elsevier Ltd. All rights reserved. Source


Carrara S.,Ecole Polytechnique Federale de Lausanne
Sensors | Year: 2010

Further advances in molecular medicine and cell biology also require new electrochemical systems to detect disease biomarkers and therapeutic compounds. Microelectronic technology offers powerful circuits and systems to develop innovative and miniaturized biochips for sensing at the molecular level. However, microelectronic biochips proposed in the literature often do not show the right specificity, sensitivity, and reliability required by biomedical applications. Nanotechnology offers new materials and solutions to improve the surface properties of sensing probes. The aim of the present paper is to review the most recent progress in Nano-Bio-Technology in the area of the development of new electrochemical systems for molecular detection in personalized therapy and cell culture monitoring. © 2010 by the authors. Source


Papastergiou D.,Structural Engineer | Lebet J.-P.,Ecole Polytechnique Federale de Lausanne
Journal of Constructional Steel Research | Year: 2014

This paper deals with the design method and the experimental verification of a new type of steel-concrete composite beam under static and fatigue loading. The connection is an alternative solution for steel-concrete composite bridges suitable for prefabrication and fast erection, while guaranteeing durability. The composite action of the beam is established through an innovative shear connection by adhesion, interlocking and friction. The resistance of the connection to longitudinal shear is based on the development of shear stresses in the confined interfaces that form the connection. The interfaces include a steel-cement grout interface and a rough concrete-cement grout interface. Confinement is provided by the reinforced concrete slab that encloses the connection. A composite beam was designed according to the design method for such type of composite beams in order to resist cyclic loading and to guarantee in the sequence its bearing capacity at ultimate limit state. The beam was initially subjected to cyclic loading and did not present signs of important damage after five million cycles. The damage on such type of connections is expressed by the development of a small residual slip in the interface which with the appropriate design stabilizes with the number of cycles. Finally the composite beam was statically loaded up to failure. The results show the capability of such a composite beam to develop its plastic moment at ultimate limit state. © 2013 Elsevier Ltd. Source


Palvolgyi D.,Ecole Polytechnique Federale de Lausanne
Discrete and Computational Geometry | Year: 2010

We show that for any concave polygon that has no parallel sides and for any k, there is a k-fold covering of some point set by the translates of this polygon that cannot be decomposed into two coverings. Moreover, we give a complete classification of open polygons with this property. We also construct for any polytope (having dimension at least three) and for any k, a k-fold covering of the space by its translates that cannot be decomposed into two coverings. © 2009 Springer Science+Business Media, LLC. Source


Kunz P.Y.,Ecole Polytechnique Federale de Lausanne
Reviews of Environmental Contamination and Toxicology | Year: 2010

The amphipod genus Gammarus is widespread and is structurally and functionally important in epigean freshwaters of the Northern Hemisphere. Its presence is crucial, because macroinvertebrate feeding is a major rate-limiting step in the processing of stream detritus. In addition, Gammarus interacts with multiple trophic levels by functioning as prey, predator, herbivore, detritivore, and shredder. Such a broad span of ecosystem participation underlines the importance of Gammarus spp. in freshwater ecosystems. The sensitivity of Gammarus to pollutants and other disturbances may render it a valuable indicator for ecosystem health. This review summarizes the vast number of studies conducted with Gammarus spp. for evaluating aquatic ecotoxicology endpoints and examines the suitability if this native invertebrate species for the assessment of stream ecosystem health in the Northern Hemisphere. Numerous papers have been published on how pollutants affect gammarid behavior (i.e., mating, predator avoidance), reproduction, development, feeding activity, population structure, as well as the consequences of pollution on host?parasite, predator?prey, or native?invasive species interactions. Some biochemical and molecular biomarkers have already been established, such as the measurement of vitellogenin-like proteins, metallothioneins, alkali-labile phosphates (in proteins), and lipogenic enzyme activities for assessing endocrine disruption and detoxification mechanisms. Despite the range and diversity of studies performed thus far on gammarids, we propose that future gammarid research should address the following aspects to enhance the integrative and multilevel approach outcomes in aquatic ecotoxicology testing: © 2010 Springer Science+Business Media, LLC. Source


Shapeev A.V.,Ecole Polytechnique Federale de Lausanne
Multiscale Modeling and Simulation | Year: 2011

This paper addresses the problem of consistent energy-based coupling of atomistic and continuum models of materials, limited to zero-temperature statics of simple crystals. It has been widely recognized that the most practical coupled methods exhibit large errors on the atomistic/continuum interface (which are often attributed to spurious forces called "ghost forces"). There are only few existing works that propose a coupling which is sufficiently accurate near the interface under certain limitations. In this paper a novel coupling that is free from "ghost forces" is proposed for a two-body interaction potential under the assumptions of either (i) one spatial dimension, or (ii) two spatial dimensions and piecewise affine finite elements for describing the continuum deformation. The performance of the proposed coupling is demonstrated with numerical experiments. The coupling strategy is based on judiciously defining the contributions of the atomistic bonds to the discrete and the continuum potential energy. The same method in one dimension has been independently developed and analyzed in Li and Luskin [IMA J. Numer. Anal, to appear]. © 2011 Society for Industrial and Applied Mathematics. Source


Harris N.L.,Ecole Polytechnique Federale de Lausanne
Trends in Parasitology | Year: 2011

Intestinal helminths infect approximately 2 billion people worldwide. Worm burdens correlate with disease morbidity and children generally harbor the largest numbers. The majority of intestinal helminths do not replicate within their host, and worm burdens increase through constant reinfection. Current strategies of worm control involve drug administration to school-aged children. Yet the rapid rate of reinfection and the appearance of drug resistant strains in livestock raise concerns over the sustainable nature of this strategy. A combined strategy of drug treatment for the expulsion of adult worms and vaccination designed to halt reinfection would offer the most effective means of control. Before successful vaccines can be developed our knowledge of the initiation and implementation of host immunity must be improved. © 2011 Elsevier Ltd. Source


Harris N.,Ecole Polytechnique Federale de Lausanne | Gause W.C.,The New School
Trends in Immunology | Year: 2011

Similar T helper (Th)2-type immune responses are generated against different helminth parasites, but the mechanisms that initiate Th2 immunity, and the specific immune components that mediate protection against these parasites, can vary greatly. B cells are increasingly recognized as important during the Th2-type immune response to helminths, and B cell activation might be a target for effective vaccine development. Antibody production is a function of B cells during helminth infection and understanding how polyclonal and antigen-specific antibodies contribute should provide important insights into how protective immunity develops. In addition, B cells might also contribute to the host response against helminths through antibody-independent functions including, antigen presentation, as well as regulatory and effector activity. In this review, we examine the role of B cells during Th2-type immune response to these multicellular parasites. © 2010 Elsevier Ltd. Source


Chen L.,Hong Kong Baptist University | Pu P.,Ecole Polytechnique Federale de Lausanne
User Modeling and User-Adapted Interaction | Year: 2012

Critiquing-based recommender systems elicit users' feedback, called critiques, which they made on the recommended items. This conversational style of interaction is in contract to the standard model where users receive recommendations in a single interaction. Through the use of the critiquing feedback, the recommender systems are able to more accurately learn the users' profiles, and therefore suggest better recommendations in the subsequent rounds. Critiquing-based recommenders have been widely studied in knowledge-, content-, and preference-based recommenders and are beginning to be tried in several online websites, such as MovieLens. This article examines the motivation and development of the subject area, and offers a detailed survey of the state of the art concerning the design of critiquing interfaces and development of algorithms for critiquing generation. With the help of categorization analysis, the survey reveals three principal branches of critiquing based recommender systems, using respectively natural language based, system-suggested, and user-initiated critiques. Representative example systems will be presented and analyzed for each branch, and their respective pros and cons will be discussed. Subsequently, a hybrid framework is developed to unify the advantages of different methods and overcome their respective limitations. Empirical findings from user studies are further presented, indicating how hybrid critiquing supports could effectively enable end-users to achieve more confident decisions. Finally, the article will point out several future trends to boost the advance of critiquing-based recommenders. © 2011 Springer Science+Business Media B.V. Source


Badro J.,CNRS Paris Institute of Global Physics | Badro J.,Ecole Polytechnique Federale de Lausanne
Annual Review of Earth and Planetary Sciences | Year: 2014

Mantle minerals at shallow depths contain iron in the high-spin electronic state. The crystal-field splitting energy increases with increasing pressure, which can favor the low-spin state. Hence, pressure-driven transitions from the high-spin to the low-spin state were proposed as early as the 1960s, and minerals in the lower mantle were suggested to contain iron in the low-spin state. Only in the past 10 years did experiments and calculations prove that iron in mantle minerals transforms from high-spin to low-spin at lower-mantle pressures. This transition has important consequences for volume, thermodynamics, and bonding. In a geophysical framework, the transition would affect the dynamics and thermochemical state of the lower mantle, through combined effects on density, elasticity, element partitioning, and transport properties. These observations provide the basis for a new paradigm of the physics and chemistry in Earth's lower(most) mantle. © 2014 by Annual Reviews. All rights reserved. Source


Bhandari A.,Ecole Polytechnique Federale de Lausanne | Zayed A.I.,DePaul University
IEEE Transactions on Signal Processing | Year: 2012

Shift-invariant spaces play an important role in sampling theory, multiresolution analysis, and many other areas of signal and image processing. A special class of the shift-invariant spaces is the class of sampling spaces in which functions are determined by their values on a discrete set of points. One of the vital tools used in the study of sampling spaces is the Zak transform. The Zak transform is also related to the Poisson summation formula and a common thread between all these notions is the Fourier transform. In this paper, we extend some of these notions to the fractional Fourier transform (FrFT) domain. First, we introduce two definitions of the discrete fractional Fourier transform and two semi-discrete fractional convolutions associated with them. We employ these definitions to derive necessary and sufficient conditions pertaining to FrFT domain, under which integer shifts of a function form an orthogonal basis or a Riesz basis for a shift-invariant space. We also introduce the fractional Zak transform and derive two different versions of the Poisson summation formula for the FrFT. These extensions are used to obtain new results concerning sampling spaces, to derive the reproducing-kernel for the spaces of fractional band-limited signals, and to obtain a new simple proof of the sampling theorem for signals in that space. Finally, we present an application of our shift-invariant signal model which is linked with the problem of fractional delay filtering. © 2011 IEEE. Source


Voitchovsky K.,Ecole Polytechnique Federale de Lausanne
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2013

Solid-liquid interfaces are central to nanoscale science and technology and control processes as diverse as self-assembly, heterogeneous catalysis, wetting, electrochemistry, or protein function. Experimentally, measuring the structure and dynamics of solid-liquid interfaces with molecular resolution remains a challenge. This task can, in principle, be achieved with atomic force microscopy (AFM), which functions locally, and with nanometer precision. When operated dynamically and at small amplitudes, AFM can provide molecular-level images of the liquid solvation layers at the interfaces. At larger amplitudes, results in the field of multifrequency AFM have shown that anharmonicities in the tip motion can provide quantitative information about the solid's mechanical properties. The two approaches probe opposite aspects of the interface and are generally seen as distinct. Here it is shown that, for amplitudes Ad, the tip trajectory becomes rapidly anharmonic due to the tip tapping the solid, and the resolution decreases. A nonlinear transition between the two regimes occurs for A∼d and can be quantified with the second harmonic of the tip oscillation. These results, confirmed by computer simulations, remain valid in most experimental conditions. Significantly, they provide an objective criterion to enhance resolution and to decide whether the results are dominated by the properties of the solid or of the liquid. © 2013 American Physical Society. Source


Deveaud-Pledran B.,Ecole Polytechnique Federale de Lausanne
Journal of the Optical Society of America B: Optical Physics | Year: 2012

Bose-Einstein condensates (BECs), the "fifth state of matter," have in fact been discovered by chance both in liquid helium and in superconductors. Since these early encounters, BECs have been sought for, both in atom vapors and in solids. Here we report on the case of exciton polaritons. We discuss the experimental observation of macroscopically occupied polariton states and their possible attribution to a BEC. We also discuss the possible relation between a polariton condensate, a polariton laser, and a vertical surface-emitting laser (VCSEL). Vortices, superfluidity, Bogoliubov dispersion, half-vortices, and Josephson oscillations are then briefly summarized merrily for sake of discussion of the distinction between a polariton BEC and a VCSEL. © 2012 Optical Society of America. Source


Yazyev O.V.,Ecole Polytechnique Federale de Lausanne
Accounts of Chemical Research | Year: 2013

Graphene nanoribbons (GNRs) are one-dimensional nanostructures predicted to display a rich variety of electronic behaviors. Depending on their structure, GNRs realize metallic and semiconducting electronic structures with band gaps that can be tuned across broad ranges. Certain GNRs also exhibit a peculiar gapped magnetic phase for which the half-metallic state can be induced as well as the topologically nontrivial quantum spin Hall electronic phase. Because their electronic properties are highly tunable, GNRs have quickly become a popular subject of research toward the design of graphene-based nanostructures for technological applications. This Account presents a pedagogical overview of the various degrees of freedom in the atomic structure and interactions that researchers can use to tailor the electronic structure of these materials. The Account provides a broad picture of relevant physical concepts that would facilitate the rational design of GNRs with desired electronic properties through synthetic techniques.We start by discussing a generic model of zigzag GNR within the tight-binding model framework. We then explain how different modifications and extensions of the basic model affect the electronic band structures of GNRs. We classify the modifications based on the following categories: (1) electron-electron and spin-orbit interactions, (2) GNR configuration, which includes width and the crystallographic orientation of the nanoribbon (chirality), and (3) the local structure of the edge. We subdivide this last category into two groups: the effects of the termination of the π-electron system and the variations of electrostatic potential at the edge. This overview of the structure-property relationships provides a view of the many different electronic properties that GNRs can realize.The second part of this Account reviews three recent experimental methods for the synthesis of structurally well-defined GNRs. We describe a family of techniques that use patterning and etching of graphene and graphite to produce GNRs. Chemical unzipping of carbon nanotubes also provides a route toward producing chiral GNRs with atomically smooth edges. Scanning tunneling microscopy/spectroscopy investigations of these unzipped GNRs have revealed edge states and strongly suggest that these GNRs are magnetic. The third approach exploits the surface-assisted self-assembly of GNRs from molecular precursors. This powerful method can provide full control over the atomic structure of narrow nanoribbons and could eventually produce more complex graphene nanostructures. © 2013 American Chemical Society. Source


Blanchet S.,Ecole Polytechnique Federale de Lausanne | Blanchet S.,University of Southampton | Bari P.D.,University of Southampton
New Journal of Physics | Year: 2012

We review the main features and results of thermal leptogenesis within the type I seesaw mechanism, the minimal extension of the Standard Model explaining neutrino masses and mixing. After presenting the simplest approach, the vanilla scenario, we discuss various important developments of recent years, such as the inclusion of lepton and heavy neutrino flavour effects, a description beyond a hierarchical heavy neutrino mass spectrum and an improved kinetic description within the density matrix and the closed-time-path formalisms. We also discuss how leptogenesis can ultimately represent an important phenomenological tool to test the seesaw mechanism and the underlying model of new physics. © IOP Publishing and Deutsche Physikalische Gesellschaft. Source


Lodone P.,Ecole Polytechnique Federale de Lausanne
International Journal of Modern Physics A | Year: 2012

We briefly review the status of motivated beyond-the-MSSM phenomenology in the light of the LHC searches to date. In particular, we discuss the conceptual consequences of the exclusion bounds, of the hint for a Higgs boson at about 125 GeV, and of interpreting the excess of direct CP violation in the charm sector as a signal of New Physics. We try to go into the various topics in a compact way while providing a relatively rich list of references, with particular attention to the most recent developments. © 2012 World Scientific Publishing Company. Source


Dagousset G.,CNRS Natural Product Chemistry Institute | Zhu J.,Ecole Polytechnique Federale de Lausanne | Masson G.,CNRS Natural Product Chemistry Institute
Journal of the American Chemical Society | Year: 2011

A chiral phosphoric acid (5)-catalyzed three-component Povarov reaction of aldehydes 2, anilines 3, and enecarbamates 4 afforded cis-4-amino-2-aryl(alkyl)- 1,2,3,4-tetrahydroquinolines 1 in high yields with excellent diastereoselectivities (>95%) and almost complete enantioselectivities (up to >99% ee). The reaction was applicable to a wide range of anilines bearing electron-donating (OMe) and electron-withdrawing groups (e.g., Cl, CF 3, NO 2) and allowed, for the first time, aliphatic aldehydes to be employed in the enantioselective Povarov reaction. With β-substituted acyclic enecarbamates, 2,3,4-trisubstituted 1,2,3,4-tetrahydroquinolines with three contiguous stereogenic centers were produced in excellent diastereo- and enantioselectivities (87 to >99% ee). A detailed study of the active catalytic species allowed us to reduce the catalyst loading from 10% to 0.5% with no deterioration of enantiomeric excess. In addition, mechanistic studies allowed us to conclude unequivocally that the Povarov reaction involving enecarbamate as dienophile proceeded via a stepwise mechanism. The key role of the free NH function of the enecarbamate in the success of this transformation was demonstrated. NMR experiments indicating the catalyst-substrate interaction as well as a linear correlation between catalyst and product ee's were also documented. © 2011 American Chemical Society. Source


Woltering J.M.,University of Geneva | Duboule D.,University of Geneva | Duboule D.,Ecole Polytechnique Federale de Lausanne
Developmental Cell | Year: 2010

In the emerging discipline of Evo-Devo, the analysis of gene expression patterns can be deceptive without a clear understanding of the underlying regulatory strategies. Here, we use the paradigm of hand and foot evolution to argue that the consideration of the regulatory mechanisms controlling developmental gene expression is essential to resolve comparative conundrums. In this context, we discuss the adaptive relevance of evolving stepwise, distinct developmental regulatory mechanisms to build an arm, i.e., a composite structure with functional coherence. © 2010 Elsevier Inc. Source


Pfeiffer V.,Ecole Polytechnique Federale de Lausanne
Cold Spring Harbor perspectives in biology | Year: 2013

Telomeres are the physical ends of eukaryotic chromosomes. They protect chromosome ends from DNA degradation, recombination, and DNA end fusions, and they are important for nuclear architecture. Telomeres provide a mechanism for their replication by semiconservative DNA replication and length maintenance by telomerase. Through telomerase repression and induced telomere shortening, telomeres provide the means to regulate cellular life span. In this review, we introduce the current knowledge on telomere composition and structure. We then discuss in depth the current understanding of how telomere components mediate their function during semiconservative DNA replication and how telomerase is regulated at the end of the chromosome. We focus our discussion on the telomeres from mammals and the yeasts Saccharomyces cerevisiae and Schizosaccharomyces pombe. Source


Cramer N.,Ecole Polytechnique Federale de Lausanne
Chimia | Year: 2012

The direct functionalization of non-activated C-H bonds, especially in an enantioselective manner, requires metal catalysts equipped with ligands with specifically designed properties. Examples for asymmetric C(sp2)-H and C(sp3)-H functionalizations using palladium-and rhodium catalysts are shown. This work was rewarded by the 2012 Werner Prize of the Swiss Chemical Society. © Schweizerische Chemische Gesellschaft. Source


Severin K.,Ecole Polytechnique Federale de Lausanne
Chimia | Year: 2012

Certain ruthenium complexes are potent catalysts for atom transfer radical addition (ATRA) and cyclization (ATRC) reactions, in particular if they are used in conjunction with reducing agents such as magnesium. This short overview summarizes recent developments in this area with special focus on contributions from our laboratory. © Schweizerische Chemische Gesellschaft. Source


Dobrindt J.M.,Max Planck Institute of Quantum Optics | Kippenberg T.J.,Max Planck Institute of Quantum Optics | Kippenberg T.J.,Ecole Polytechnique Federale de Lausanne
Physical Review Letters | Year: 2010

We present an optomechanical displacement transducer that relies on three cavity modes parametrically coupled to a mechanical oscillator and whose frequency spacing matches the mechanical resonance frequency. The additional resonances allow reaching the standard quantum limit at a substantially lower input power (compared to the case of a single cavity mode), as both sensitivity and quantum backaction are enhanced. Furthermore, it is shown that in the case of multiple cavity modes, coupling between the modes is induced via reservoir interaction, e.g., enabling quantum backaction noise cancellation. Experimental implementation of the schemes is discussed in both the optical and microwave domain. © 2010 The American Physical Society. Source


Verkhovsky A.B.,Ecole Polytechnique Federale de Lausanne
Current Biology | Year: 2012

Anterior-posterior polarity in the Caenorhabditis elegans zygote depends on two groups of PAR proteins, as well as on cortical flow. Recent work now demonstrates that this polarization results from a transition in a bistable reaction-diffusion system of PAR proteins that is triggered by cortical flow. © 2012 Elsevier Ltd All rights reserved. Source


Kapralov M.,Ecole Polytechnique Federale de Lausanne
Proceedings of the Annual ACM Symposium on Theory of Computing | Year: 2016

We consider the problem of computing a k-sparse approximation to the Fourier transform of a length N signal. Our main result is a randomized algorithm for computing such an approximation (i.e. achieving l2/l2 sparse recovery guarantees using Fourier measurements) using Od(k log N log log N) samples of the signal in time domain and Od (k logd+3N) runtime, where d ≥ 1 is the dimensionality of the Fourier transform. The sample complexity matches the Ω(klog(N/k)) lower bound for non-adaptive algorithms due to Do Ba et al (SODA'10) for any k ≤ N1-δ for a constant δ > 0 up to an O (log log N) factor. Prior to our work a result with comparable sample complexity k log N logO(1) log N and sublinear runtime was known for the Fourier transform on the line, but for any dimension d ≤ 2 previously known techniques either suffered from a poly (log N) factor loss in sample complexity or required Ω(N) runtime. © 2016 ACM. Source


Chergui M.,Ecole Polytechnique Federale de Lausanne
Acta Crystallographica Section A: Foundations of Crystallography | Year: 2010

The need to visualize molecular structure in the course of a chemical reaction, a phase transformation or a biological function has been a dream of scientists for decades. The development of time-resolved X-ray and electron-based methods is making this true. X-ray absorption spectroscopy is ideal for the study of structural dynamics in liquids, because it can be implemented in amorphous media. Furthermore, it is chemically selective. Using X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) in laser pump/X-ray probe experiments allows the retrieval of the local geometric structure of the system under study, but also the underlying photoinduced electronic structure changes that drive the structural dynamics. Recent developments in picosecond and femtosecond X-ray absorption spectroscopy applied to molecular systems in solution are reviewed: examples on ultrafast photoinduced processes such as intramolecular electron transfer, low-to-high spin change, and bond formation are presented. © 2010 International Union of Crystallography Printed in Singapore all rights reserved. Source


Knott G.,Ecole Polytechnique Federale de Lausanne
Journal of visualized experiments : JoVE | Year: 2011

This protocol describes how biological samples, like brain tissue, can be imaged in three dimensions using the focussed ion beam/scanning electron microscope (FIB/SEM). The samples are fixed with aldehydes, heavy metal stained using osmium tetroxide and uranyl acetate. They are then dehydrated with alcohol and infiltrated with resin, which is then hardened. Using a light microscope and ultramicrotome with glass knives, a small block containing the region interest close to the surface is made. The block is then placed inside the FIB/SEM, and the ion beam used to roughly mill a vertical face along one side of the block, close to this region. Using backscattered electrons to image the underlying structures, a smaller face is then milled with a finer ion beam and the surface scrutinised more closely to determine the exact area of the face to be imaged and milled. The parameters of the microscope are then set so that the face is repeatedly milled and imaged so that serial images are collected through a volume of the block. The image stack will typically contain isotropic voxels with dimenions as small a 4 nm in each direction. This image quality in any imaging plane enables the user to analyse cell ultrastructure at any viewing angle within the image stack. Source


Koukab A.,Ecole Polytechnique Federale de Lausanne
IEEE Microwave and Wireless Components Letters | Year: 2010

A VCO topology with a high gm at (RF) and low gm at low frequencies (LF) is presented. A high gm (RF) improves start-up conditions, and a low gm(rm) (LF) enables a significant improvement of the phase noise and the power supply rejection. The VCO with a modified prescaler was implemented in 0.25 μ m CMOS technology. The measured phase is -128.5 dBc Hz at 1 MH offset, when the VCO works at 3 GHz and consumes 7.5 mW. The corresponding figure of merit is 189.2 dBc/Hz/mW. © 2006 IEEE. Source


Mortensen A.,Ecole Polytechnique Federale de Lausanne | Llorca J.,IMDEA Madrid Institute for Advanced Studies
Annual Review of Materials Research | Year: 2010

In metal matrix composites, a metal is combined with another, often nonmetallic, phase to produce a novel material having attractive engineering attributes of its own. A subject of much research in the 1980s and 1990s, this class of materials has, in the past decade, increased significantly in variety. Copper matrix composites, layered composites, high-conductivity composites, nanoscale composites, microcellular metals, and bio-derived composites have been added to a palette that, ten years ago, mostly comprised ceramic fiber- or particle-reinforced light metals together with some well-established engineering materials, such as WC-Co cermets. At the same time, research on composites such as particle-reinforced aluminum, aided by novel techniques such as large-cell 3-D finite element simulation or computed X-ray microtomography, has served as a potent vehicle for the elucidation of the mechanics of high-contrast two-phase elastoplastic materials, with implications that range well beyond metal matrix composites. © 2010 by Annual Reviews. All rights reserved. Source


Thevenaz L.,Ecole Polytechnique Federale de Lausanne
Frontiers of Optoelectronics in China | Year: 2010

Optical fiber sensors based on stimulated Brillouin scattering have now clearly demonstrated their excellent capability for long-range distributed strain and temperature measurements. The fiber is used as sensing element, and a value for temperature and/or strain can be obtained from any point along the fiber. After explaining the principle and presenting the standard implementation, the latest developments in this class of sensors will be introduced, such as the possibility to measure with a spatial resolution of 10 cm and below while preserving the full accuracy on the determination of temperature and strain. © 2010 Higher Education Press and Springer Berlin Heidelberg. Source


Duarte M.,Ecole Polytechnique Federale de Lausanne | Dick C.,Xilinx Inc. | Sabharwal A.,Rice University
IEEE Transactions on Wireless Communications | Year: 2012

We present an experiment-based characterization of passive suppression and active self-interference cancellation mechanisms in full-duplex wireless communication systems. In particular, we consider passive suppression due to antenna separation at the same node, and active cancellation in analog and/or digital domain. First, we show that the average amount of cancellation increases for active cancellation techniques as the received self-interference power increases. Our characterization of the average cancellation as a function of the self-interference power allows us to show that for a constant signal-to-interference ratio at the receiver antenna (before any active cancellation is applied), the rate of a full-duplex link increases as the self-interference power increases. Second, we show that applying digital cancellation after analog cancellation can sometimes increase the self-interference, and thus digital cancellation is more effective when applied selectively based on measured suppression values. Third, we complete our study of the impact of self-interference cancellation mechanisms by characterizing the probability distribution of the self-interference channel before and after cancellation. © 2002-2012 IEEE. Source


Alsan M.,Ecole Polytechnique Federale de Lausanne
IEEE Transactions on Information Theory | Year: 2014

We study the extremality of the binary erasure channel and the binary symmetric channel for Gallager's reliability function E0 of binary input discrete memoryless channels evaluated under the uniform input distribution from the aspect of channel polarization. In particular, we show that amongst all binary discrete memoryless channels of a given E0 ρ) value, for a fixed ρ ≥ 0, the binary erasure channel and the binary symmetric channel are extremal in the evolution of E0 under the one-step polarization transformations. © 2014; IEEE. Source


Moreno-Noguer F.,Polytechnic University of Catalonia | Fua P.,Ecole Polytechnique Federale de Lausanne
IEEE Transactions on Pattern Analysis and Machine Intelligence | Year: 2013

Recovering the 3D shape of deformable surfaces from single images is known to be a highly ambiguous problem because many different shapes may have very similar projections. This is commonly addressed by restricting the set of possible shapes to linear combinations of deformation modes and by imposing additional geometric constraints. Unfortunately, because image measurements are noisy, such constraints do not always guarantee that the correct shape will be recovered. To overcome this limitation, we introduce a stochastic sampling approach to efficiently explore the set of solutions of an objective function based on point correspondences. This allows us to propose a small set of ambiguous candidate 3D shapes and then use additional image information to choose the best one. As a proof of concept, we use either motion or shading cues to this end and show that we can handle a complex objective function without having to solve a difficult nonlinear minimization problem. The advantages of our method are demonstrated on a variety of problems including both real and synthetic data. © 2012 IEEE. Source


Favre D.,Ecole Polytechnique Federale de Lausanne
Apidologie | Year: 2011

The worldwide maintenance of the honeybee has major ecological, economic, and political implications. In the present study, electromagnetic waves originating from mobile phones were tested for potential effects on honeybee behavior. Mobile phone handsets were placed in the close vicinity of honeybees. The sound made by the bees was recorded and analyzed. The audiograms and spectrograms revealed that active mobile phone handsets have a dramatic impact on the behavior of the bees, namely by inducing the worker piping signal. In natural conditions, worker piping either announces the swarming process of the bee colony or is a signal of a disturbed bee colony. © The Author(s) 2011. Source


Becker C.,Ecole Polytechnique Federale de Lausanne
Medical image computing and computer-assisted intervention : MICCAI ... International Conference on Medical Image Computing and Computer-Assisted Intervention | Year: 2012

We present a new approach for the automated segmentation of excitatory synapses in image stacks acquired by electron microscopy. We rely on a large set of image features specifically designed to take spatial context into account and train a classifier that can effectively utilize cues such as the presence of a nearby post-synaptic region. As a result, our algorithm successfully distinguishes synapses from the numerous other organelles that appear within an EM volume, including those whose local textural properties are relatively similar. This enables us to achieve very high detection rates with very few false positives. Source


Coda S.,Ecole Polytechnique Federale de Lausanne
Nuclear Fusion | Year: 2013

Through a diverse research programme, the Tokamak à Configuration Variable (TCV) addresses physics issues and develops tools for ITER and for the longer term goals of nuclear fusion, relying especially on its extreme plasma shaping and electron cyclotron resonance heating (ECRH) launching flexibility and preparing for an ECRH and NBI power upgrade. Localized edge heating was unexpectedly found to decrease the period and relative energy loss of edge localized modes (ELMs). Successful ELM pacing has been demonstrated by following individual ELM detection with an ECRH power cut before turning the power back up to trigger the next ELM, the duration of the cut determining the ELM period. Negative triangularity was also seen to reduce the ELM energy release. H-mode studies have focused on the L-H threshold dependence on the main ion species and on the divertor leg length. Both L- and H-modes have been explored in the snowflake configuration with emphasis on edge measurements, revealing that the heat flux to the strike points on the secondary separatrix increases as the X-points approach each other, well before they coalesce. In L-mode, a systematic scan of the auxiliary power deposition profile, with no effect on confinement, has ruled it out as the cause of confinement degradation. An ECRH power absorption observer based on transmitted stray radiation was validated for eventual polarization control. A new profile control methodology was introduced, relying on real-time modelling to supplement diagnostic information; the RAPTOR current transport code in particular has been employed for joint control of the internal inductance and central temperature. An internal inductance controller using the ohmic transformer has also been demonstrated. Fundamental investigations of neoclassical tearing mode (NTM) seed island formation by sawtooth crashes and of NTM destabilization in the absence of a sawtooth trigger were carried out. Both stabilizing and destabilizing agents (electron cyclotron current drive on or inside the q = 1 surface, respectively) were used to pace sawtooth oscillations, permitting precise control of their period. Locking of the sawtooth period to a pre-defined ECRH modulation period was also demonstrated. Sawtooth control has permitted nearly failsafe NTM prevention when combined with backup NTM stabilization by ECRH. © 2013 IAEA, Vienna. Source


Ferretti S.,University of Pavia | Savona V.,Ecole Polytechnique Federale de Lausanne | Gerace D.,University of Pavia
New Journal of Physics | Year: 2013

We propose the use of weakly nonlinear passive materials for prospective applications in integrated quantum photonics. It is shown that strong enhancement of native optical nonlinearities by electromagnetic field confinement in photonic crystal resonators can lead to single-photon generation only exploiting the quantum interference of two coupled modes and the effect of photon blockade under resonant coherent driving. For realistic system parameters in state of the art microcavities, the efficiency of such a single-photon source is theoretically characterized by means of the second-order correlation function at zero-time delay as the main figure of merit, where major sources of loss and decoherence are taken into account within a standard master equation treatment. These results could stimulate the realization of integrated quantum photonic devices based on non-resonant material media, fully integrable with current semiconductor technology and matching the relevant telecom band operational wavelengths, as an alternative to single-photon nonlinear devices based on cavity quantum electrodynamics with artificial atoms or single atomic-like emitters. © IOP Publishing and Deutsche Physikalische Gesellschaft. Source


Burnier Y.,Ecole Polytechnique Federale de Lausanne | Kaczmarek O.,Bielefeld University | Rothkopf A.,University of Heidelberg
Physical Review Letters | Year: 2015

We present a state-of-the-art determination of the complex valued static quark-antiquark potential at phenomenologically relevant temperatures around the deconfinement phase transition. Its values are obtained from nonperturbative lattice QCD simulations using spectral functions extracted via a novel Bayesian inference prescription. We find that the real part, both in a gluonic medium, as well as in realistic QCD with light u, d, and s quarks, lies close to the color singlet free energies in Coulomb gauge and shows Debye screening above the (pseudo)critical temperature Tc. The imaginary part is estimated in the gluonic medium, where we find that it is of the same order of magnitude as in hard-thermal loop resummed perturbation theory in the deconfined phase. © 2015 American Physical Society. Source


Lu H.,Ecole Polytechnique Federale de Lausanne | Porte-Agel F.,University of Minnesota
Physics of Fluids | Year: 2013

As a simple alternative to the standard eddy-diffusivity closure, a nonlinear subgrid-scale (SGS) flux model is introduced and implemented in simulations of a neutral atmospheric boundary layer and a stable atmospheric boundary layer. The new model computes the structure of the SGS flux (relative magnitude of the vector components) based on the normalized gradient vector, which is derived from the Taylor expansion of the exact SGS flux. The SGS magnitude is computed as the product of a SGS velocity scale and a SGS scalar concentration scale, which are estimated based on the local-equilibrium hypothesis. To resolve the instability issue of the original gradient model and ensure numerical stability, we adopt a clipping procedure to avoid local negative SGS dissipation rate of the scalar variance. The model formulation, using constant coefficients, is assessed through a systematic comparison with well-established theoretical predictions and reference results of various flow statistics. Simulation results obtained with the use of this new model show good agreement with the reference results and an evident improvement over results obtained using traditional eddy-diffusivity models. For instance, the new model can deliver the expected surface-layer similarity scalar profile and power-law scaling of the power spectrum of scalar fluctuation. © 2013 American Institute of Physics. Source


Ricci P.,Ecole Polytechnique Federale de Lausanne | Rogers B.N.,Dartmouth College
Physics of Plasmas | Year: 2013

Plasma turbulence is explored in the scrape-off layer of tokamak devices using three-dimensional global two-fluid simulations. Two transport regimes are discussed: one in which the turbulent fluctuations saturate nonlinearly due to the Kelvin-Helmholtz instability, and another in which the fluctuations saturate due to a local flattening of the plasma gradients and associated removal of the linear instability drive. Focusing on the latter regime, analytical estimates of the cross-field transport and plasma profile gradients are obtained that display Bohm-scaling diffusion properties. © 2013 Euratom. Source


Alisafaee M.,Ecole Polytechnique Federale de Lausanne
Proceedings - 2012 IEEE/ACM 45th International Symposium on Microarchitecture, MICRO 2012 | Year: 2012

Chip-multiprocessors require a coherence directory to track data sharing and order accesses to the shared data. Scaling coherence directories to support a large number of cores is challenging due to excessive area requirements of the directories. The state-of-the-art proposals reduce the directory size by not keeping coherence information for private data. These approaches are useful for workloads that have predominantly private data, but are not applicable to workloads with shared data. We observe that data are not actively shared by multiple cores. In workloads with a shared dataset, although each core accesses the whole data, the chance that multiple cores access the same piece of data at the same time is low. Based on this observation we design a Spatiotemporal Coherence Tracking scheme that drastically reduces the directory size without sacrificing performance. The proposed directory scheme uses dual-grain tracking and switches between the granularities whenever possible to save the area. It dynamically detects spatial regions of data that are privately accessed by one core over a time period and for those regions, increases coherence tracking granularity from block-level to region-level. Our experimental results show that the proposed approach can reduce the baseline sparse directory size by at least 75% across a variety of commercial and scientific workloads, while sacrificing only 1% of performance. Using our approach, the directory can be under-provisioned to have fewer entries than the number of cache blocks that are being tracked. © 2012 IEEE. Source


Byrka J.,Ecole Polytechnique Federale de Lausanne | Aardal K.,Technical University of Delft
SIAM Journal on Computing | Year: 2010

We obtain a 1.5-approximation algorithm for the metric uncapacitated facility location (UFL) problem, which improves on the previously best known 1.52-approximation algorithm by Mahdian, Ye, and Zhang. Note that the approximability lower bound by Guha and Khuller is 1.463 ... . An algorithm is a (λf , λc)-approximation algorithm if the solution it produces has total cost at most λf ·F* +λc ·C*,where F* and C* are the facility and the connection cost of an optimal solution. Our new algorithm, which is a modification of the (1 + 2/e)-approximation algorithm of Chudak and Shmoys, is a (1.6774, 1.3738)-approximation algorithm for the UFL problem and is the first one that touches the approximability limit curve (γf , 1+2e-γf ) established by Jain, Mahdian, and Saberi. As a consequence, we obtain the first optimal approximation algorithm for instances dominated by connection costs. When combined with a (1.11, 1.7764)-approximation algorithm proposed by Jain et al., and later analyzed by Mahdian et al., we obtain the overall approximation guarantee of 1.5 for the metric UFL problem. We also describe how to use our algorithm to improve the approximation ratio for the 3-level version of UFL. © 2010 Society for Industrial and Applied Mathematics. Source


Puig A.,Ecole Polytechnique Federale de Lausanne
Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment | Year: 2016

The LHCb experiment will record an unprecedented dataset of beauty and charm hadron decays during Run II of the LHC, set to take place between 2015 and 2018. A key computing challenge is to store and process this data, which limits the maximum output rate of the LHCb trigger. So far, LHCb has written out a few kHz of events containing the full raw sub-detector data, which are passed through a full offline event reconstruction before being considered for physics analysis. Charm physics in particular is limited by trigger output rate constraints. A new streaming strategy includes the possibility to perform the physics analysis with candidates reconstructed in the trigger, thus bypassing the offline reconstruction. In the Turbo stream the trigger will write out a compact summary of physics objects containing all information necessary for analyses. This will allow an increased output rate and thus higher average efficiencies and smaller selection biases. This idea will be commissioned and developed during 2015 with a selection of physics analyses. It is anticipated that the turbo stream will be adopted by an increasing number of analyses during the remainder of LHC Run II (2015-2018) and ultimately in Run III (starting in 2020) with the upgraded LHCb detector. © 2016 CERN. Source


Verkhovsky A.B.,Ecole Polytechnique Federale de Lausanne
Current Opinion in Cell Biology | Year: 2015

Adherent cells migrate and change their shape by means of protrusion and retraction at their edges. When and where these activities occur defines the shape of the cell and the way it moves. Despite a great deal of knowledge about the structural organization, components, and biochemical reactions involved in protrusion and retraction, the origins of their spatial and temporal patterns are still poorly understood. Chemical signaling circuitry is believed to be an important source of patterning, but recent studies highlighted mechanisms based on physical forces, motion, and mechanical feedback. © 2015 Elsevier Ltd. Source


Vandereycken B.,Ecole Polytechnique Federale de Lausanne
SIAM Journal on Optimization | Year: 2013

The matrix completion problem consists of finding or approximating a low-rank matrix based on a few samples of this matrix. We propose a new algorithm for matrix completion that minimizes the least-square distance on the sampling set over the Riemannian manifold of fixed-rank matrices. The algorithm is an adaptation of classical nonlinear conjugate gradients, developed within the framework of retraction-based optimization on manifolds. We describe all the necessary objects from differential geometry necessary to perform optimization over this low-rank matrix manifold, seen as a submanifold embedded in the space of matrices. In particular, we describe how metric projection can be used as retraction and how vector transport lets us obtain the conjugate search directions. Finally, we prove convergence of a regularized version of our algorithm under the assumption that the restricted isometry property holds for incoherent matrices throughout the iterations. The numerical experiments indicate that our approach scales very well for large-scale problems and compares favorably with the state-of-the-art, while outperforming most existing solvers. © 2013 Society for Industrial and Applied Mathematics. Source


Burnier Y.,Ecole Polytechnique Federale de Lausanne
European Physical Journal C | Year: 2015

The vector channel spectral function at zero spatial momentum is calculated at next-to-leading order in thermal QCD for any quark mass. It corresponds to the imaginary part of the massive quark contribution to the photon polarisation tensor. The spectrum shows a well-defined transport peak in contrast to both the heavy quark limit studied previously, where the low frequency domain is exponentially suppressed at this order, and the naive massless case where it vanishes at leading order and diverges at next-to-leading order. From our general expressions, the massless limit can be taken and we show that no divergences occur if done carefully. Finally, we compare the massless limit to results from lattice simulations. © 2015, The Author(s). Source


Shaposhnikov M.,Ecole Polytechnique Federale de Lausanne | Wetterich C.,University of Heidelberg
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2010

There are indications that gravity is asymptotically safe. The Standard Model (SM) plus gravity could be valid up to arbitrarily high energies. Supposing that this is indeed the case and assuming that there are no intermediate energy scales between the Fermi and Planck scales we address the question of whether the mass of the Higgs boson mH can be predicted. For a positive gravity induced anomalous dimension Aλ > 0 the running of the quartic scalar self interaction λ at scales beyond the Planck mass is determined by a fixed point at zero. This results in mH = mmin = 126 GeV, with only a few GeV uncertainty. This prediction is independent of the details of the short distance running and holds for a wide class of extensions of the SM as well. For Aλ < 0 one finds mH in the interval mmin < mH < mmax ≃ 174 GeV, now sensitive to Aλ and other properties of the short distance running. The case Aλ > 0 is favored by explicit computations existing in the literature. © 2009 Elsevier B.V. All rights reserved. Source


Severin K.,Ecole Polytechnique Federale de Lausanne
Chemical Society Reviews | Year: 2015

This review article summarizes efforts to use nitrous oxide (N2O, 'laughing gas') as a reagent in synthetic chemistry. The focus will be on reactions which are carried out in homogeneous solution under (relatively) mild conditions. First, the utilization of N2O as an oxidant is discussed. Due to the low intrinsic reactivity of N2O, selective oxidation reactions of highly reactive compounds are possible. Furthermore, it is shown that transition metal complexes can be used to catalyze oxidation reactions, in some cases with high turnover numbers. In the final part of this overview, the utilization of N2O as a building block for more complex molecules is discussed. It is shown that N2O can be used as an N-atom donor for the synthesis of interesting organic molecules such as triazenes and azo dyes. This journal is © The Royal Society of Chemistry. Source


Grimaldi C.,Ecole Polytechnique Federale de Lausanne
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2015

We analyze the critical connectivity of systems of penetrable d-dimensional spheres having size distributions in terms of weighed random geometrical graphs, in which vertex coordinates correspond to random positions of the sphere centers, and edges are formed between any two overlapping spheres. Edge weights naturally arise from the different radii of two overlapping spheres. For the case in which the spheres have bounded size distributions, we show that clusters of connected spheres are treelike for d→ and they contain no closed loops. In this case, we find that the mean cluster size diverges at the percolation threshold density ηc→2-d, independently of the particular size distribution. We also show that the mean number of overlaps for a particle at criticality zc is smaller than unity, while zc→1 only for spheres with fixed radii. We explain these features by showing that in the large dimensionality limit, the critical connectivity is dominated by the spheres with the largest size. Assuming that closed loops can be neglected also for unbounded radii distributions, we find that the asymptotic critical threshold for systems of spheres with radii following a log-normal distribution is no longer universal, and that it can be smaller than 2-d for d→. © 2015 American Physical Society. Source


Nazer B.,Boston University | Gastpar M.,University of California at Berkeley | Gastpar M.,Ecole Polytechnique Federale de Lausanne
IEEE Transactions on Information Theory | Year: 2011

Interference is usually viewed as an obstacle to communication in wireless networks. This paper proposes a new strategy, compute-and-forward, that exploits interference to obtain significantly higher rates between users in a network. The key idea is that relays should decode linear functions of transmitted messages according to their observed channel coefficients rather than ignoring the interference as noise. After decoding these linear equations, the relays simply send them towards the destinations, which given enough equations, can recover their desired messages. The underlying codes are based on nested lattices whose algebraic structure ensures that integer combinations of codewords can be decoded reliably. Encoders map messages from a finite field to a lattice and decoders recover equations of lattice points which are then mapped back to equations over the finite field. This scheme is applicable even if the transmitters lack channel state information. © 2011 IEEE. Source


Gauthier M.A.,ETH Zurich | Klok H.-A.,Ecole Polytechnique Federale de Lausanne
Polymer Chemistry | Year: 2010

Proteins have been modified with polymers in diverse manners over the past 30 years. However, while proteins have been used to prepare many functional constructs, they are sensitive biomolecules and their bioactivity can be either positively or negatively influenced by many different aspects of polymer modification. The primary focus of this review article is to highlight the opportunities offered by new trends in protein modification, and specifically how they influence the overall biological activity of the conjugate, including its dependence on temperature and pH. We survey the effect of polymer molecular weight, number of conjugated polymer chains, polymer coupling strategy (including random versus site-specific coupling, "grafting from", and multi-point covalent attachment), polymer architecture (including branched and comb-type), polymer interactions with the protein (including electrostatic and host-guest interactions), polymer interactions with enzyme substrate, and polymer biodegradability. We have selected six enzymes, which have been extensively modified with polymers in diverse fashions in the literature, as basis for this discussion. These proteins are l-asparaginase, alpha-chymotrypsin, trypsin, lysozyme, bovine serum albumin, and papain. This review includes polymers such as poly(ethylene glycol) (PEG), polysaccharides, polypeptides, and other synthetic (vinyl) polymers. From the discussed literature we attempt to extract tentative general trends observed between state-of-the-art methods of preparing protein-polymer conjugates and the activity of the conjugate. © 2010 The Royal Society of Chemistry. Source


Von Stockar U.,Ecole Polytechnique Federale de Lausanne
Journal of Non-Equilibrium Thermodynamics | Year: 2010

The aim of this contribution is to review the application of thermodynamics to live cultures of microbial and other cells and to explore to what extent this may be put to practical use. A major focus is on energy dissipation effects in industrially relevant cultures, both in terms of heat and Gibbs energy dissipation. The experimental techniques for calorimetric measurements in live cultures are reviewed and their use for monitoring and control is discussed. A detailed analysis of the dissipation of Gibbs energy in chemotrophic growth shows that it reflects the entropy production by metabolic processes in the cells and thus also the driving force for growth and metabolism. By splitting metabolism conceptually up into catabolism and biosynthesis, it can be shown that this driving force decreases as the growth yield increases. This relationship is demonstrated by using experimental measurements on a variety of microbial strains. On the basis of these data, several literature correlations were tested as tools for biomass yield prediction. The prediction of other culture performance characteristics, including product yields for biorefinery planning, energy yields for biofuel manufacture, maximum growth rates, maintenance requirements, and threshold concentrations is also briefly reviewed. © 2010 de Gruyter . Source


Dillenbourg P.,Ecole Polytechnique Federale de Lausanne | Evans M.,Virginia Polytechnic Institute and State University
International Journal of Computer-Supported Collaborative Learning | Year: 2011

Interactive tabletops are gaining increased attention from CSCL researchers. This paper analyses the relation between this technology and teaching and learning processes. At a global level, one could argue that tabletops convey a socio-constructivist flavor: they support small teams that solve problems by exploring multiple solutions. The development of tabletop applications also witnesses the growing importance of face-to-face collaboration in CSCL and acknowledges the physicality of learning. However, this global analysis is insufficient. To analyze the educational potential of tabletops in education, we present 33 points that should be taken into consideration. These points are structured on four levels: individual user-system interaction, teamwork, classroom orchestration, and socio-cultural contexts. God lies in the details. © 2011 International Society of the Learning Sciences, Inc.; Springer Science + Business Media, LLC. Source


Fragouli C.,Ecole Polytechnique Federale de Lausanne
Proceedings of the IEEE | Year: 2011

Network coding enables novel network functionalities and thus offers a wider canvas of choices when optimizing an information flow problem. In this paper, we examine the simplest possible information flow problem, a unicast connection, and explore what we believe is one of the most attractive features network coding offers: the ability to enable near-optimal performance in a completely decentralized and randomized setting. This is an especially attractive feature for wireless applications. However, it comes at the cost of an overhead in terms of rate that can be significant for applications that operate using relatively short frame lengths, as is the case in the wireless setting. We review the efforts in the literature to either alleviate this overhead, or alternatively, to exploit it for network management and control. © 2006 IEEE. Source


Bressler C.,German Electron Synchrotron | Chergui M.,Ecole Polytechnique Federale de Lausanne
Annual Review of Physical Chemistry | Year: 2010

The ability to visualize molecular structure in the course of a chemical reaction or a biological function has been a dream of scientists for decades. X-ray absorption spectroscopy (XAS) is ideal in this respect because it is chemically selective and can be implemented in any type of medium. Furthermore, using X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) in laser pump/X-ray probe experiments allows the retrieval of not only the local geometric structure of the system under study, but also the underlying electronic structure changes that drive the structural dynamics. We review recent developments in picosecond and femtosecond XAS applied to molecular systems in solution. Examples on ultrafast photoinduced processes such as intramolecular electron transfer, low-to-high spin change, and bond formation are presented. Copyright © 2010 by Annual Reviews. All rights reserved. Source


Abdelkefi F.,Ecole Polytechnique Federale de Lausanne
IEEE Transactions on Information Theory | Year: 2010

In this paper, we extend the results that we derived in , to the case of filter banks (FBs) based transmission. We consider first- and second-order sigmadelta (SD) quantization in the context of an oversampled digital Fourier transform (DFT) FBs (DFT-FBs). In this context, we investigate the case of Odd- and Even-stacked DFT FBs. We establish the set of conditions that guarantee that the reconstruction minimum squares error (MSE) behaves as 1/r2 where r denotes the frame redundancy and we derive the corresponding MSE upper-bounds closed-form expressions. The obtained results demonstrate that overoversampled FBs that are subject to the first- and second-order SD can exhibit a reconstruction error behavior according to 1/r2. Furthermore, the established results are shown to be true under the quantization model used in , as well as under the widely used additive white quantization noise assumption. © 2006 IEEE. Source


Baruffaldi S.H.,Ecole Polytechnique Federale de Lausanne | Landoni P.,Polytechnic of Milan
Research Policy | Year: 2012

Through an analysis of 497 foreign researchers in Italy and Portugal we verify the impact of home linkages on return mobility choices and scientific productivity. We consider the presence of several different types of linkages of the researchers working abroad with their country of origin and control for the most relevant contextual factors (age, research area, position in the host country, etc.). The probability of return to their home country and scientific productivity in the host country are both higher for researchers that maintain home linkages. We conclude that the presence of home linkages directly benefits both countries in addition to the indirect benefit of expanding the scientific networks. Policy implications and suggestions for further research are discussed. © 2012 Elsevier B.V. All rights reserved. Source


Rupakula A.,Ecole Polytechnique Federale de Lausanne
Philosophical transactions of the Royal Society of London. Series B, Biological sciences | Year: 2013

Dehalobacter restrictus strain PER-K23 is an obligate organohalide respiring bacterium, which displays extremely narrow metabolic capabilities. It grows only via coupling energy conservation to anaerobic respiration of tetra- and trichloroethene with hydrogen as sole electron donor. Dehalobacter restrictus represents the paradigmatic member of the genus Dehalobacter, which in recent years has turned out to be a major player in the bioremediation of an increasing number of organohalides, both in situ and in laboratory studies. The recent elucidation of the D. restrictus genome revealed a rather elaborate genome with predicted pathways that were not suspected from its restricted metabolism, such as a complete corrinoid biosynthetic pathway, the Wood-Ljungdahl (WL) pathway for CO2 fixation, abundant transcriptional regulators and several types of hydrogenases. However, one important feature of the genome is the presence of 25 reductive dehalogenase genes, from which so far only one, pceA, has been characterized on genetic and biochemical levels. This study describes a multi-level functional genomics approach on D. restrictus across three different growth phases. A global proteomic analysis allowed consideration of general metabolic pathways relevant to organohalide respiration, whereas the dedicated genomic and transcriptomic analysis focused on the diversity, composition and expression of genes associated with reductive dehalogenases. Source


Fallahi A.,University of Hamburg | Perruisseau-Carrier J.,Ecole Polytechnique Federale de Lausanne
Applied Physics Letters | Year: 2012

Faraday rotation is a fundamental magneto-optical phenomenon used in various optical control and magnetic field sensing techniques. Recently, it was shown that a giant Faraday rotation can be achieved in the low-THz regime by a single monoatomic graphene layer. Here, we demonstrate that this exceptional property can be manipulated through adequate nano-patterning, notably achieving giant rotation up to 6THz with features no smaller than 100 nm. The effect of the periodic patterning on the Faraday rotation is predicted by a simple physical model, which is then verified and refined through accurate full-wave simulations. © 2012 American Institute of Physics. Source


Caiazzo M.,Ecole Polytechnique Federale de Lausanne
Nature Materials | Year: 2016

Since the discovery of induced pluripotent stem cells (iPSCs), numerous approaches have been explored to improve the original protocol, which is based on a two-dimensional (2D) cell-culture system. Surprisingly, nothing is known about the effect of a more biologically faithful 3D environment on somatic-cell reprogramming. Here, we report a systematic analysis of how reprogramming of somatic cells occurs within engineered 3D extracellular matrices. By modulating microenvironmental stiffness, degradability and biochemical composition, we have identified a previously unknown role for biophysical effectors in the promotion of iPSC generation. We find that the physical cell confinement imposed by the 3D microenvironment boosts reprogramming through an accelerated mesenchymal-to-epithelial transition and increased epigenetic remodelling. We conclude that 3D microenvironmental signals act synergistically with reprogramming transcription factors to increase somatic plasticity. © 2016 Nature Publishing Group Source


Cole S.T.,Ecole Polytechnique Federale de Lausanne | Riccardi G.,University of Pavia
Current Opinion in Microbiology | Year: 2011

Tuberculosis (TB) remains a major global health concern whose control has been exacerbated by HIV and the emergence of multidrug-resistant (MDR-TB) and extensively drug-resistant (XDR-TB) strains of Mycobacterium tuberculosis. The demand for new and faster acting TB drugs is thus greater than ever. In the past decade intensive efforts have been made to discover new leads for TB drug development using both target-based and cell-based approaches. Here, we describe the most promising anti-tubercular drug candidates that are in clinical development and introduce some nitro-aromatic compounds that inhibit a new target, DprE1, an essential enzyme involved in a crucial step in mycobacterial cell wall biosynthesis. © 2011 Elsevier Ltd. Source


Patterson G.,U.S. National Institutes of Health | Davidson M.,Florida State University | Manley S.,Ecole Polytechnique Federale de Lausanne | Lippincott-Schwartz J.,U.S. National Institutes of Health
Annual Review of Physical Chemistry | Year: 2010

superresolution imaging is a rapidly emerging new field of microscopy that dramatically improves the spatial resolution of light microscopy by over an order of magnitude (∼10-20-nm resolution), allowing biological processes to be described at the molecular scale. Here, we discuss a form of superresolution microscopy based on the controlled activation and sampling of sparse subsets of photoconvertible fluorescent molecules. In this single-molecule-based imaging approach, a wide variety of probes have proved valuable, ranging from genetically encodable photoactivatable fluorescent proteins to photoswitchable cyanine dyes. These have been used in diverse applications of superresolution imaging: from three-dimensional, multicolor molecule localization to tracking of nanometric structures and molecules in living cells. Single-molecule-based superresolution imaging thus offers exciting possibilities for obtaining molecular-scale information on biological events occurring at variable timescales. Copyright © 2010 by Annual Reviews. All rights reserved. Source


Grimaldi C.,Ecole Polytechnique Federale de Lausanne
Physical Review B - Condensed Matter and Materials Physics | Year: 2010

Here the electron-phonon Holstein model with Rashba spin-orbit interaction is studied for a two-dimensional square lattice in the adiabatic limit. It is demonstrated that a delocalized electron at zero spin-orbit coupling localizes into a large polaron state as soon as the Rashba term is nonzero. This spin-orbit induced polaron state has localization length inversely proportional to the Rashba coupling γ and it dominates a wide region of the γ-λ phase diagram, where λ is the electron-phonon interaction. © 2010 The American Physical Society. Source


Gillet P.,Ecole Polytechnique Federale de Lausanne | Goresy A.E.,University of Bayreuth
Annual Review of Earth and Planetary Sciences | Year: 2013

Impacts are central to the origin and evolution of planets of the Solar System. The shapes of craters, which can reach up to 1,000 km in diameter on the Moon, provide critical information on the large-scale dynamics of the impact and related shock. Minerals formed at high pressure and temperature found in shocked terrestrial rocks and meteorites give additional and complementary insights on the shock process at a smaller scale, typically from a few micrometers to a few millimeters. Local flaws in rocks, such as voids and mineral interfaces, are the preferential sites for the formation of high-pressure melts and minerals. Calculations based on the physics of shocks and the thermodynamics and kinetics of mineral transformations provide orders of magnitude for the duration, transient pressure, and prevailing temperature conditions of shock events. Case studies on shocked terrestrial and extraterrestrial materials illustrate the links between these parameters and impact duration. Many of the high-pressure mineral phases of olivine, pyroxenes, feldspars, silica, phosphates, titanium oxide, and carbon have been discovered in these heavily shocked rocks and provide unique opportunities to study the high-pressure minerals that exist in the deep Earth. © Copyright ©2013 by Annual Reviews. All rights reserved. Source


Chergui M.,Ecole Polytechnique Federale de Lausanne
Accounts of Chemical Research | Year: 2015

The properties of transition metal complexes are interesting not only for their potential applications in solar energy conversion, OLEDs, molecular electronics, biology, photochemistry, etc. but also for their fascinating photophysical properties that call for a rethinking of fundamental concepts. With the advent of ultrafast spectroscopy over 25 years ago and, more particularly, with improvements in the past 10-15 years, a new area of study was opened that has led to insightful observations of the intramolecular relaxation processes such as internal conversion (IC), intersystem crossing (ISC), and intramolecular vibrational redistribution (IVR). Indeed, ultrafast optical spectroscopic tools, such as fluorescence up-conversion, show that in many cases, intramolecular relaxation processes can be extremely fast and even shorter than time scales of vibrations. In addition, more and more examples are appearing showing that ultrafast ISC rates do not scale with the magnitude of the metal spin-orbit coupling constant, that is, that there is no heavy-atom effect on ultrafast time scales. It appears that the structural dynamics of the system and the density of states play a crucial role therein.While optical spectroscopy delivers an insightful picture of electronic relaxation processes involving valence orbitals, the photophysics of metal complexes involves excitations that may be centered on the metal (called metal-centered or MC) or the ligand (called ligand-centered or LC) or involve a transition from one to the other or vice versa (called MLCT or LMCT). These excitations call for an element-specific probe of the photophysics, which is achieved by X-ray absorption spectroscopy. In this case, transitions from core orbitals to valence orbitals or higher allow probing the electronic structure changes induced by the optical excitation of the valence orbitals, while also delivering information about the geometrical rearrangement of the neighbor atoms around the atom of interest. With the emergence of new instruments such as X-ray free electron lasers (XFELs), it is now possible to perform ultrafast laser pump/X-ray emission probe experiments. In this case, one probes the density of occupied states. These core-level spectroscopies and other emerging ones, such as photoelectron spectroscopy of solutions, are delivering a hitherto unseen degree of detail into the photophysics of metal-based molecular complexes. In this Account, we will give examples of applications of the various methods listed above to address specific photophysical processes. (Graph Presented). © 2015 American Chemical Society. Source


Hartinger C.G.,University of Auckland | Metzler-Nolte N.,Ruhr University Bochum | Dyson P.J.,Ecole Polytechnique Federale de Lausanne
Organometallics | Year: 2012

This review provides an introduction into the fascinating area of organometallic anticancer compounds. Although the subject dates back many years, it has witnessed considerable growth only in the past decade. A brief overview of the subject together with recent pertinent examples is provided. The properties of organometallic compounds that lend themselves to medical applications, the main current approaches used, and possible avenues for future research are identified. © 2012 American Chemical Society. Source


Schliesser A.,Ecole Polytechnique Federale de Lausanne | Schliesser A.,Max Planck Institute of Quantum Optics | Picque N.,Max Planck Institute of Quantum Optics | Picque N.,Ludwig Maximilians University of Munich | And 3 more authors.
Nature Photonics | Year: 2012

Laser frequency combs are coherent light sources that emit a broad spectrum of discrete, evenly spaced narrow lines whose absolute frequency can be measured to within the accuracy of an atomic clock. Their development in the near-infrared and visible domains has revolutionized frequency metrology while also providing numerous unexpected opportunities in other fields such as astronomy and attosecond science. Researchers are now exploring how to extend frequency comb techniques to the mid-infrared spectral region. Versatile mid-infrared frequency comb generators based on novel laser gain media, nonlinear frequency conversion or microresonators promise to significantly expand the applications of frequency combs. In particular, novel approaches to molecular spectroscopy in the 'fingerprint region', with dramatically improved precision, sensitivity, recording time and/or spectral bandwidth may lead to new discoveries in the various fields relevant to molecular science. © 2012 Macmillan Publishers Limited. All rights reserved. Source


Geroliminis N.,Ecole Polytechnique Federale de Lausanne | Sun J.,University of Minnesota
Transportation Research Part A: Policy and Practice | Year: 2011

Observations of traffic pairs of flow vs. density or occupancy for individual locations in freeways or arterials are usually scattered about an underlying curve. Recent observations from empirical data in arterial networks showed that in some cases by aggregating the highly scattered plots of flow vs. density from individual loop detectors, the scatter almost disappears and well-defined macroscopic relations exist between space-mean network flow and network density. Despite these findings for the existence of well-defined relations with low scatter, these curves should not be universal. In this paper we investigate if well-defined macroscopic relations exist for freeway network systems, by analyzing real data from Minnesota's freeways. We show that freeway network systems not only have curves with high scatter, but they also exhibit hysteresis phenomena, where higher network flows are observed for the same average network density in the onset and lower in the offset of congestion. The mechanisms of traffic hysteresis phenomena at the network level are analyzed in this paper and they have dissimilarities to the causes of the hysteresis phenomena at the micro/meso level. The explanation of the phenomenon is dual. The first reason is that there are different spatial and temporal distributions of congestion for the same level of average density. Another reason is the synchronized occurrence of transitions from individual detectors during the offset of the peak period, with points remain beneath the equilibrium curve. Both the hysteresis phenomenon and its causes are consistently observed for different spatial aggregations of the network. © 2011 Elsevier Ltd. Source


Savona V.,Ecole Polytechnique Federale de Lausanne
Physical Review B - Condensed Matter and Materials Physics | Year: 2011

We present a systematic numerical approach to compute the eigenmodes and the related eigenfrequencies of a disordered photonic crystal, characterized by small fluctuations of the otherwise periodic dielectric profile. The field eigenmodes are expanded on the basis of Bloch modes of the corresponding periodic structure, and the resulting eigenvalue problem is diagonalized on a truncated basis including a finite number of Bloch bands. The Bloch-mode expansion is very effective for modeling modes of very extended disordered structures in a given frequency range, as only spectrally close bands must be included in the basis set. The convergence can be easily verified by repeating the diagonalization for an increased band set. As illustrations, we apply the method to the W1 line-defect waveguide and to the L3 coupled-cavity waveguide, both based on a photonic crystal slab with a triangular lattice of circular holes. We compute and characterize the eigenfrequencies, spatial field profiles, and radiation loss rates of the localized modes induced by disorder. For the W1 waveguide, we demonstrate that radiation losses, at the bottom of the spatially even guided band, are determined by a small hybridization with Bloch modes of the spatially odd band, induced by disorder in spite of their frequency separation. The Bloch-mode expansion method has a very broad range of applications: It can be also used to accurately compute the modes of structures with systematic modulations of the periodic dielectric constant, as in several designs of high-Q cavities. © 2011 American Physical Society. Source


Patent
Ecole Polytechnique Federale de Lausanne | Date: 2014-01-20

A recommender system comprising at least one computing device which comprises one or more processors and one or more computer-readable storage media operatively coupled to at least one of the processors, wherein said computing device performs a method of assigning a user to one group of a set of groups, said set of groups comprising at least two distinct groups, and a method of providing said user with at least one recommendation.


Patent
Ecole Polytechnique Federale de Lausanne | Date: 2014-10-30

An aerial vehicle including self-autonomous deployable arms and methods of deploying the vehicle are disclosed. The arms may include patterns located thereon that allow the arms to transition between wrapped, flat, and deployed configurations autonomously without the need for direct intervention by a user.


Patent
Ecole Polytechnique Federale de Lausanne | Date: 2014-11-03

A privacy-preserving method for performing a disease susceptibility test on a patient, said method comprising: The invention is also related to a method for inferring ancestry in the encrypted domain.


Patent
Ecole Polytechnique Federale de Lausanne | Date: 2014-03-17

An indoor localization method for estimating the location of nodes (n


Patent
Ecole Polytechnique Federale de Lausanne | Date: 2014-05-27

Described herein are microelectrode array devices, and methods of fabrication and use of the same, to provide highly localized and efficient electrical stimulation of a neurological target. The device includes multiple microelectrode elements arranged along an supportive backing layer. The microelectrode elements are dimensioned and shaped so as to target individual neurons, groups of neurons, and neural tissue as may be located in an animal nervous system, such as along a region of a cortex of a human brain. Beneficially, the neurological probe can be used to facilitate location of the neurological target and remain implanted for long-term monitoring and/or stimulation.


Patent
Ecole Polytechnique Federale de Lausanne | Date: 2014-06-26

A preferred frequency is identified, being usable to stimulate a neurological target within a mammalian body using at least one microelectrode positioned at or near the target. To establish efficient and effective stimulation, an impedance analyzer is provided for measuring electrical impedance values indicative of a microelectrode-tissue interface across a range of different frequencies. A preferred one of the measured electrical impedance values is identified as being closest to a pure resistance. The neurological target can then be stimulated at or near the frequency associated with the preferred impedance value (peak resistance frequency), thereby promoting desirable traits, such as optimum charge transfer, minimum signal distortion, increased stimulation efficiency, and prevention of microelectrode corrosion. The peak resistance frequency can be used to determine an preferred pulse shape. A target can be identified by microelectrode measurements of neuronal activity and/or impedance magnitude at peak resistance frequency.


Patent
Ecole Polytechnique Federale de Lausanne | Date: 2014-05-01

A method for automatic localization of objects in a mask. The method includes building a dictionary or atoms, wherein each atom models the presence of one object at one location and iteratively determining the atom of said dictionary which is best correlated with said mask, until ending criteria are met. The invention system concerns also automatically detects objects in a mask. At least one fixed camera is provided for acquiring video frames. A computation device is used for calibrating at least one fixed camera for extracting foreground silhouettes in each acquired video frames for discretizing said ground plane into a non-regular grid of potential location points for constructing a dictionary of atoms, and for finding objects location points with the previous method. And a propagating device is provided to propagate the result in at least one fixed camera view.


Patent
Ecole Polytechnique Federale de Lausanne | Date: 2014-04-11

A method to optimize the communication on a channel between an access point and at least one client device, said channel being characterized by a center frequency and a bandwidth, comprises: establishing a connection on a first channel according to a first center frequency and a first bandwidth; exchanging data through this first channel between the access point and the client device; monitoring a first interference level on the first channel; the access point, while the data are exchanged, executes: informing the client device to switch to a second channel having a different center frequency and/or a different bandwidth; determining a second interference level on the second channel; comparing the first interference level with the second interference level; deciding to switch back or keep the second channel based on the comparison.