Maxwell demons in phase space

Although there is not a complete "proof" of the second law of thermo- dynamics based on microscopic dynamics, two properties of Hamiltonian systems have been used to prove the impossibility of work extraction from a single thermal reservoir: Liouville's theorem and the adiabatic invariance of the volume enclosed by an energy shell. In this paper we analyze these two properties in the Szilard engine and other systems related with the Maxwell demon. In particular, we recall that the enclosed volume is no longer an adiabatic invariant in non ergodic systems and explore the consequences of this on the second law.Comment: 14 pages, to appear in EPJS

Thermodynamic costs of information processing in sensory adaption

Biological sensory systems react to changes in their surroundings. They are characterized by fast response and slow adaptation to varying environmental cues. Insofar as sensory adaptive systems map environmental changes to changes of their internal degrees of freedom, they can be regarded as computational devices manipulating information. Landauer established that information is ultimately physical, and its manipulation subject to the entropic and energetic bounds of thermodynamics. Thus the fundamental costs of biological sensory adaptation can be elucidated by tracking how the information the system has about its environment is altered. These bounds are particularly relevant for small organisms, which unlike everyday computers operate at very low energies. In this paper, we establish a general framework for the thermodynamics of information processing in sensing. With it, we quantify how during sensory adaptation information about the past is erased, while information about the present is gathered. This process produces entropy larger than the amount of old information erased and has an energetic cost bounded by the amount of new information written to memory. We apply these principles to the E. coli's chemotaxis pathway during binary ligand concentration changes. In this regime, we quantify the amount of information stored by each methyl group and show that receptors consume energy in the range of the information-theoretic minimum. Our work provides a basis for further inquiries into more complex phenomena, such as gradient sensing and frequency response.Comment: 17 pages, 6 figure

Évolution de la géomorphologie depuis la fin du XIXe siècle

Jusque dans les années 1940, ce sont des géologues qui s’intéressent à la physiographie, car la géomorphologie ne fait pas encore partie de la formation universitaire en géographie au Québec. Les premiers départements de géographie sont créés à la fin des années 1940 et les premières publications en géomorphologie apparaissent au milieu des années 1950. Les géographes sont davantage préoccupés par la géomorphologie dynamique que par la physiographie. L’institutionnalisation de la géomorphologie commence au milieu des années 1960 alors que les années 1970 marquent le début de l’apogée de la géomorphologie avec l’expansion du réseau de l’enseignement universitaire et la création de laboratoires, confirmant le passage d’une géomorphologie descriptive à une géomorphologie quantitative. Les décennies 1970 et 1980 sont caractérisées par la prolifération des recherches dans tous les domaines de la géomorphologie dynamique. C’est la période durant laquelle bon nombre de géomorphologues sont engagés par des organismes gouvernementaux ainsi que par des firmes d’ingénieurs et d’environnementalistes pour réaliser des inventaires régionaux. L’utilisation d’ordinateurs personnels au milieu des années 1980 et de SIG depuis le début des années 1990, combinés à de meilleurs outils d’observation de la Terre, a favorisé l’émergence d’une nouvelle géomorphologie axée sur la modélisation des processus. Toutefois, une ombre au tableau demeure : la récente disparition de plusieurs programmes de formation en géographie physique au niveau universitaire. L’avenir de la géomorphologie réside dans une optimisation des outils d’observation, de mesure et de prédiction.Since the 1940s, physiography had been the sole interest of geologists, since geomorphology was not part of the geography curriculum at Quebec universities at that time. Geography departments were not set up until the late 1940s and geomorphology publications first appeared in the mid-1950s. Geographers were drawn more to dynamic geomorphology than to physiography. The institutionalization of geomorphology began in the mid-1960s, whereas the 1970s marked the “golden age” of geomorphology, when the university network was expanded, laboratories built, and descriptive geomorphology superseded by its quantitative counterpart. During the 1970s and 1980s, research in all fields of dynamic geomorphology proliferated. At the same time a large number of geomorphologists were hired by government agencies and engineering and environmental firms to carry out regional inventories. The use of PCs in the mid-1980s and GIS from the early 1990s, combined with the availability of more sophisticated Earth observation tools, led to the emergence of a new kind of geomorphology focused on process modelling management. However, the recent closure of several university physical geography programs in the Quebec university system has cast a shadow over the future of geomorphology, which now depends on the optimization of observation, measurement and prediction tools.Hasta los años 1940, son los geólogos que se interesan a la fisiografía, puesto que en Quebec la Geomorfología todavía no hace parte de la formación universitaria en Geografía. Los primeros departamentos de Geografía fueron creados a fines de los años 1940 y las primeras publicaciones en Geomorfología aparecieron a mediados de los años 1950. Los geógrafos están más preocupados por la Geomorfología dinámica que por la fisiografía. La institucionalización de la Geomorfología comienza a mediados de los años 1960, mientras que los años 1970 marcan el comienzo de su apogeo debido a la expansión de la red de enseñanza universitaria y la creación de laboratorios, confirmando el pasaje de una Geomorfología descriptiva a una Geomorfología cuantitativa. Los decenios 1970 y 1980 se caracterizan por la profusión de investigaciones en todos los campos de la Geomorfología dinámica. Es en este periodo que numerosos geomorfólogos son contratados por organismos gubernamentales y empresas de ingenieros y medio-ambientistas para realizar inventarios regionales. La utilización de computadoras personales, a mediados de los años 1980, y del SIG, desde comienzos de los años 1990, combinados con mejores útiles de observación de la Tierra, ha favorecido la emergencia de una nueva Geomorfología orientada hacia la modelización de procedimientos. No obstante, queda un punto oscuro : la reciente desaparición de varios programas de formación universitaria en Geografía Física. El futuro de la Geomorfología reside en el perfeccionamiento de sus útiles de observación, de medidas y de predicción

The thermodynamic cost of measurements

The measurement of thermal fluctuations provides information about the microscopic state of a thermodynamic system and can be used in order to extract work from a single heat bath in a suitable cyclic process. We present a minimal framework for the modeling of a measurement device and we propose a protocol for the measurement of thermal fluctuations. In this framework, the measurement of thermal fluctuations naturally leads to the dissipation of work. We illustrate this framework on a simple two states system inspired by the Szilard's information engine

Numerical simulation of model problems in plasticity based on field dislocation mechanics

The aim of this paper is to investigate the numerical implementation of the field dislocation mechanics (FDM) theory for the simulation of dislocation-mediated plasticity. First, the mesoscale FDM theory of Acharya and Roy (2006 J. Mech. Phys. Solids 54 1687-710) is recalled which permits to express the set of equations under the form of a static problem, corresponding to the determination of the local stress field for a given dislocation density distribution, complemented by an evolution problem, corresponding to the transport of the dislocation density. The static problem is solved using FFT-based techniques (Brenner et al 2014 Phil. Mag. 94 1764-87). The main contribution of the present study is an efficient numerical scheme based on high resolution Godunov-type solvers to solve the evolution problem. Model problems of dislocation-mediated plasticity are finally considered in a simplified layer case. First, uncoupled problems with uniform velocity are considered, which permits to reproduce annihilation of dislocations and expansion of dislocation loops. Then, the FDM theory is applied to several problems of dislocation microstructures subjected to a mechanical loading

Aerodynamic measurement and analysis of the flow in an uncooled turbine stage

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1998.Includes bibliographical references (p. 125-127).by Léo M. Grépin.M.S

Finite self-similar p-groups with abelian first level stabilizers

We determine all finite p-groups that admit a faithful, self-similar action on the p-ary rooted tree such that the first level stabilizer is abelian. A group is in this class if and only if it is a split extension of an elementary abelian p-group by a cyclic group of order p. The proof is based on use of virtual endomorphisms. In this context the result says that if G is a finite p-group with abelian subgroup H of index p, then there exists a virtual endomorphism of G with trivial core and domain H if and only if G is a split extension of H and H is an elementary abelian p-group.Comment: one direction of theorem 2 extended to regular p-group

Electric-field tuning of the valley splitting in silicon corner dots

We perform an excited state spectroscopy analysis of a silicon corner dot in a nanowire field-effect transistor to assess the electric field tunability of the valley splitting. First, we demonstrate a back-gate-controlled transition between a single quantum dot and a double quantum dot in parallel that allows tuning the device in to corner dot formation. We find a linear dependence of the valley splitting on back-gate voltage, from $880~\mu \text{eV}$ to $610~\mu \text{eV}$ with a slope of $-45\pm 3~\mu \text{eV/V}$ (or equivalently a slope of $-48\pm 3~\mu \text{eV/(MV/m)}$ with respect to the effective field). The experimental results are backed up by tight-binding simulations that include the effect of surface roughness, remote charges in the gate stack and discrete dopants in the channel. Our results demonstrate a way to electrically tune the valley splitting in silicon-on-insulator-based quantum dots, a requirement to achieve all-electrical manipulation of silicon spin qubits.Comment: 5 pages, 3 figures. In this version: Discussion of model expanded; Fig. 3 updated; Refs. added (15, 22, 32, 34, 35, 36, 37

Dual Coding of Frequency Modulation in the Ventral Cochlear Nucleus.

Frequency modulation (FM) is a common acoustic feature of natural sounds and is known to play a role in robust sound source recognition. Auditory neurons show precise stimulus-synchronized discharge patterns that may be used for the representation of low-rate FM. However, it remains unclear whether this representation is based on synchronization to slow temporal envelope (ENV) cues resulting from cochlear filtering or phase locking to faster temporal fine structure (TFS) cues. To investigate the plausibility of those encoding schemes, single units of the ventral cochlear nucleus of guinea pigs of either sex were recorded in response to sine FM tones centered at the unit's best frequency (BF). The results show that, in contrast to high-BF units, for modulation depths within the receptive field, low-BF units (<4 kHz) demonstrate good phase locking to TFS. For modulation depths extending beyond the receptive field, the discharge patterns follow the ENV and fluctuate at the modulation rate. The receptive field proved to be a good predictor of the ENV responses for most primary-like and chopper units. The current in vivo data also reveal a high level of diversity in responses across unit types. TFS cues are mainly conveyed by low-frequency and primary-like units and ENV cues by chopper and onset units. The diversity of responses exhibited by cochlear nucleus neurons provides a neural basis for a dual-coding scheme of FM in the brainstem based on both ENV and TFS cues.SIGNIFICANCE STATEMENT Natural sounds, including speech, convey informative temporal modulations in frequency. Understanding how the auditory system represents those frequency modulations (FM) has important implications as robust sound source recognition depends crucially on the reception of low-rate FM cues. Here, we recorded 115 single-unit responses from the ventral cochlear nucleus in response to FM and provide the first physiological evidence of a dual-coding mechanism of FM via synchronization to temporal envelope cues and phase locking to temporal fine structure cues. We also demonstrate a diversity of neural responses with different coding specializations. These results support the dual-coding scheme proposed by psychophysicists to account for FM sensitivity in humans and provide new insights on how this might be implemented in the early stages of the auditory pathway