569 research outputs found
Probing topology by "heating": Quantized circular dichroism in ultracold atoms
We reveal an intriguing manifestation of topology, which appears in the
depletion rate of topological states of matter in response to an external
drive. This phenomenon is presented by analyzing the response of a generic 2D
Chern insulator subjected to a circular time-periodic perturbation: due to the
system's chiral nature, the depletion rate is shown to depend on the
orientation of the circular shake. Most importantly, taking the difference
between the rates obtained from two opposite orientations of the drive, and
integrating over a proper drive-frequency range, provides a direct measure of
the topological Chern number of the populated band (): this "differential
integrated rate" is directly related to the strength of the driving field
through the quantized coefficient . Contrary to the
integer quantum Hall effect, this quantized response is found to be non-linear
with respect to the strength of the driving field and it explicitly involves
inter-band transitions. We investigate the possibility of probing this
phenomenon in ultracold gases and highlight the crucial role played by edge
states in this effect. We extend our results to 3D lattices, establishing a
link between depletion rates and the non-linear photogalvanic effect predicted
for Weyl semimetals. The quantized circular dichroism revealed in this work
designates depletion-rate measurements as a universal probe for topological
order in quantum matter.Comment: 10 pages, 5 figures (including Sup. Mat.). Revised version, accepted
for publicatio
Controllability indices for structured systems
AbstractA new methodology is proposed for the characterization of the controllability indices of linear multivariable systems. Related to the state space representation, a new symbolism dealing only with numbers associated with the position of nonnull terms of matrices is proposed. This symbolism, associated with the graphical digraph representation model, allows one to highlight, from a structural point of view, a list of dimensions of controllable subspaces corresponding one to one with the list of controllability indices
Storage Device Sizing for a Hybrid Railway Traction System by Means of Bicausal Bond Graphs
In this paper, the application of bicausal bond graphs for system design in electrical engineering is emphasized. In particular, it is shown how this approach is very useful for model inversion and parameter dimensioning. To illustrate these issues, a hybrid railway traction device is considered as a case study. The synthesis of a storage device (a supercapacitor) included in this system is then discussed
Detection of Zak phases and topological invariants in a chiral quantum walk of twisted photons
Topological insulators are fascinating states of matter exhibiting protected
edge states and robust quantized features in their bulk. Here, we propose and
validate experimentally a method to detect topological properties in the bulk
of one-dimensional chiral systems. We first introduce the mean chiral
displacement, and we show that it rapidly approaches a multiple of the Zak
phase in the long time limit. Then we measure the Zak phase in a photonic
quantum walk, by direct observation of the mean chiral displacement in its
bulk. Next, we measure the Zak phase in an alternative, inequivalent timeframe,
and combine the two windings to characterize the full phase diagram of this
Floquet system. Finally, we prove the robustness of the measure by introducing
dynamical disorder in the system. This detection method is extremely general,
as it can be applied to all one-dimensional platforms simulating static or
Floquet chiral systems.Comment: 10 pages, 7 color figures (incl. appendices) Close to the published
versio
Quantum simulation of a topological Mott insulator with Rydberg atoms in a Lieb lattice
We propose a realistic scheme to quantum simulate the so-far experimentally unobserved topological Mottinsulator phaseâan interaction-driven topological insulatorâusing cold atoms in an optical Lieb lattice. To thisend, we study a system of spinless fermions in a Lieb lattice, exhibiting repulsive nearest- and next-to-nearestneighborinteractions and derive the associated zero-temperature phase diagram within mean-field approximation.In particular, we analyze how the interactions can dynamically generate a charge density wave ordered, a nematic,and a topologically nontrivial quantum anomalous Hall phase. We characterize the topology of the different phasesby the Chern number and discuss the possibility of phase coexistence. Based on the identified phases, we proposea realistic implementation of this model using cold Rydberg-dressed atoms in an optical lattice. The scheme,which allows one to access, in particular, the topological Mott insulator phase, robustly and independently ofits exact position in parameter space, merely requires global, always-on off-resonant laser coupling to Rydbergstates and is feasible with state-of-the-art experimental techniques that have already been demonstrated in thelaborator
Construction and analysis of causally dynamic hybrid bond graphs
Engineering systems are frequently abstracted to models with discontinuous behaviour (such as a switch or contact),
and a hybrid model is one which contains continuous and discontinuous behaviours. Bond graphs are an established
physical modelling method, but there are several methods for constructing switched or âhybridâ bond graphs, developed
for either qualitative âstructuralâ analysis or efficient numerical simulation of engineering systems. This article proposes a
general hybrid bond graph suitable for both. The controlled junction is adopted as an intuitive way of modelling a discontinuity in the model structure. This element gives rise to âdynamic causalityâ that is facilitated by a new bond graph notation. From this model, the junction structure and state equations are derived and compared to those obtained by
existing methods. The proposed model includes all possible modes of operation and can be represented by a single set
of equations. The controlled junctions manifest as Boolean variables in the matrices of coefficients. The method is more
compact and intuitive than existing methods and dispenses with the need to derive various modes of operation from a
given reference representation. Hence, a method has been developed, which can reach common usage and form a platform for further study
Matrixâassisted laser desorption ionization timeâofâflight mass spectrometry for fast and accurate identification of clinically relevant Aspergillus species
AbstractNew Aspergillus species have recently been described with the use of multilocus sequencing in refractory cases of invasive aspergillosis. The classical phenotypic identification methods routinely used in clinical laboratories failed to identify them adequately. Some of these Aspergillus species have specific patterns of susceptibility to antifungal agents, and misidentification may lead to inappropriate therapy. We developed a matrixâassisted laser desorption ionization timeâofâflight (MALDIâTOF) mass spectrometry (MS)âbased strategy to adequately identify Aspergillus species to the species level. A database including the reference spectra of 28 clinically relevant species from seven Aspergillus sections (five common and 23 unusual species) was engineered. The profiles of young and mature colonies were analysed for each reference strain, and speciesâspecific spectral fingerprints were identified. The performance of the database was then tested on 124 clinical and 16 environmental isolates previously characterized by partial sequencing of the ÎČâtubulin and calmodulin genes. One hundred and thirtyâeight isolates of 140 (98.6%) were correctly identified. Two atypical isolates could not be identified, but no isolate was misidentified (specificity: 100%). The database, including speciesâspecific spectral fingerprints of young and mature colonies of the reference strains, allowed identification regardless of the maturity of the clinical isolate. These results indicate that MALDIâTOFÂ MS is a powerful tool for rapid and accurate identification of both common and unusual species of Aspergillus. It can give better results than morphological identification in clinical laboratories
Two-phase reservoir: development of a transient thermo-hydraulic model based on bond graph approach with experimental validation
The main purpose of the project FUI THERMOFLUID is to study the feasibility of a new electronic cooling system embedded on flying objects (missile, satellite, and airplane). The technology chosen consists of a pumped two-phase flow cooling loop (PTPFL). It is an innovative technology with a transport capacity of the thermal power up to 10 MW.m, exceeding in this way the performance of all other technologies. A PTPFL is a cooling loop based on the exploitation of the latent heat properties of the fluid trapped inside the loop, and moved by a pump. The components constituting a PTPFL are: a two-phase reservoir (TP-R), a mini- channels evaporator, a brazed plate condenser, a pump and pipes. The global research work is devoted to propose a dynamic model and experimental validation of the PTPFL. The present article is exclusively dedicated to the TP-R two-phase reservoir (TP-R). Indeed this element plays a key role in the functioning of PTPFL. Historically, the TP-R did not equip the first cooling loop. However, due to its advantages its introduction was essential. The developed dynamic model will be used in another work to predict the thermal hydraulic efficiency of the PTPFL from its mechanical and fluidic parameters, to conduct the study of transitional regimes and instability problems, and provides an original tool dedicated to design the TP-R in function of the thermal power levels to be evacuated and the selected refrigerant. The bond graph methodology is adopted for modeling works because of its energetic approach and multi physics character of the studied system.FUI Thermofluid-R
Ramial wood amendments (Piliostigma reticulatum) mitigate degradation of tropical soils but do not replenish nutrient exports
Restoring degraded soils to support food production is a major challenge for West African smallholders who have developed local innovations to counter further degradation. The objective of this study was to evaluate a local farmer's technique that uses ramial wood (RW) as soil amendment (Piliostigma reticulatum shrub). Three treatments were applied in an experimental plot in Burkina Faso: control (no amendment), low RW (3 Mg fresh mass·haâ1·yrâ1), and high RW (12 Mg fresh mass·haâ1·yrâ1). RW was chipped to <5âcm pieces and either buried or mulched. Topsoil carbon (C), nitrogen (N), and phosphorus (P) in control and lowâRW treatments declined after 7 years of continuous sorghum cultivation. Use of highâRW amendment stabilized soil C content while N and P declined, thus not replenishing nutrient exports. Net contribution to soil C in the layer measuring 0â15 cm was 15% of the applied C in the highâRW
amendments. Although biomass and grain yields were higher in highâRW treatments, crop productivity declined throughout the experiment for all treatments. Termite casts on RW treatments evidenced the potential role of woodâforaging termites in diluting
the impact of RW on soil fertility buildâup and soil water content. We conclude that mitigating soil degradation under semiarid conditions in Burkina Faso would require large amounts of woody amendments, particularly if the level of termite activity is high.
Additional nutrient sources would be needed to compensate for removal in exported products so that biomass and grain production can be stabilized or increased.EstaciĂłn Experimental Agropecuaria BarilocheFil: FĂ©lix, Georges F. Wageningen University. Farming Systems Ecology; HolandaFil: Clermont-Dauphin, Cathy. Montpellier SupAgro- Centre de CoopĂ©ration Internationale en Recherche Agronomique pour le DĂ©veloppement-Institut National de la Recherche Agronomique. Eco&Sols; FranciaFil: Hien, Edmond. Laboratoire Mixte International. Intensification Ecologique des Sols CultivĂ©s en Afrique de l'Ouest; Burkina FasoFil: Groot, Jeroen C.J. Wageningen University. Farming Systems Ecology; HolandaFil: Penche, Aurelien. Laboratoire Mixte International. Intensification Ecologique des Sols CultivĂ©s en Afrique de l'Ouest; Burkina FasoFil: BarthĂšs, Bernard G. Universidad Montpellier; FranciaFil: Manlay, RaphaĂ«l J. AgroParisTech; FranciaFil: Tittonell, Pablo Adrian. Instituto Nacional de TecnologĂa Agropecuaria (INTA). EstaciĂłn Experimental Agropecuaria Bariloche; ArgentinaFil: Cournac, Laurent. Montpellier SupAgro- Centre de CoopĂ©ration Internationale en Recherche Agronomique pour le DĂ©veloppement-Institut National de la Recherche Agronomique. Eco&Sols; Franci
A rangeâwide postglacial history of Swiss stone pine based on molecular markers and palaeoecological evidence
Aim:
Knowing a species' response to historical climate shifts helps understanding its perspectives under global warming. We infer the hitherto unresolved postglacial history of Pinus cembra. Using independent evidence from genetic structure and demographic inference of extant populations, and from palaeoecological findings, we derive putative refugia and reâcolonisation routes.
Location: European Alps and Carpathians.
Taxa: Pinus cembra.
Methods:
We genotyped nuclear and chloroplast microsatellite markers in nearly 3000 individuals from 147 locations across the entire natural range of P. cembra. Spatial genetic structure (Bayesian modelling) and demographic history (approximate Bayesian computation) were combined with palaeobotanical records (pollen, macrofossils) to infer putative refugial areas during the Last Glacial Maximum (LGM) and reâcolonisation of the current range.
Results:
We found distinct spatial genetic structure, despite low genetic differentiation even between the two disjunct mountain ranges. Nuclear markers revealed five genetic clusters aligned EastâWest across the range, while chloroplast haplotype distribution suggested nine clusters. Spatially congruent separation at both marker types highlighted two main genetic lineages in the East and West of the range. Demographic inference supported early separation of these lineages dating back to a previous interstadial or interglacial c. 210,000âyears ago. Differentiation into five biologically meaningful genetic clusters likely established during postglacial reâcolonisation.
Main Conclusions:
Combining genetic and palaeoecological evidence suggests that P. cembra primarily survived the LGM in âcold periodâ refugia south of the Central European Alps and near the Carpathians, from where it expanded during the Late Glacial into its current Holocene âwarm periodâ refugia. This colonisation history has led to the distinct EastâWest structure of five genetic clusters. The two main genetic lineages likely derived from ancient divergence during an interglacial or interstadial. The respective contact zone (Brenner line) matches a main biogeographical break in the European Alps also found in herbaceous alpine plant species
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