13,160 research outputs found
Information erasure without an energy cost
Landauer argued that the process of erasing the information stored in a
memory device incurs an energy cost in the form of a minimum amount of
mechanical work. We find, however, that this energy cost can be reduced to zero
by paying a cost in angular momentum or any other conserved quantity. Erasing
the memory of Maxwell's demon in this way implies that work can be extracted
from a single thermal reservoir at a cost of angular momentum and an increase
in total entropy. The implications of this for the second law of thermodynamics
are assessed.Comment: 8 pages with 1 figure. Final published versio
Oxygen Cost of Recreational Horse-Riding in Females
Version: as accepted for publication.BACKGROUND: The purpose of this study was to characterize the physiological demands of a riding session comprising different types of recreational horse riding in females. METHODS: Sixteen female recreational riders (aged 17 to 54 years) completed an incremental cycle ergometer exercise test to determine peak oxygen consumption (VOâpeak) and a 45-minute riding session based upon a British Horse Society Stage 2 riding lesson (including walking, trotting, cantering and work without stirrups). Oxygen consumption (VOâ), from which metabolic equivalent (MET) and energy expenditure values were derived, was measured throughout. RESULTS: The mean VOâ requirement for trotting/cantering (18.4 ± 5.1 ml·kgâ»Âč·minâ»Âč; 52 ± 12% VOâpeak; 5.3 ± 1.1 METs) was similar to walking/trotting (17.4 ± 5.1 ml·kgâ»Âč·minâ»Âč; 48 ± 13% VOâpeak; 5.0 ± 1.5 METs) and significantly higher than for work without stirrups (14.2 ± 2.9 ml·kgâ»Âč·minâ»Âč; 41 ± 12% VOâpeak; 4.2 ± 0.8 METs) (P = .001). CONCLUSIONS: The oxygen cost of different activities typically performed in a recreational horse riding session meets the criteria for moderate intensity exercise (3-6 METs) in females, and trotting combined with cantering imposes the highest metabolic demand. Regular riding could contribute to the achievement of the public health recommendations for physical activity in this population
Non-equilibrium and information: the role of cross-correlations
We discuss the relevance of information contained in cross-correlations among
different degrees of freedom, which is crucial in non-equilibrium systems. In
particular we consider a stochastic system where two degrees of freedom
and - in contact with two different thermostats - are coupled together.
The production of entropy and the violation of equilibrium
fluctuation-dissipation theorem (FDT) are both related to the cross-correlation
between and . Information about such cross-correlation may be lost
when single-variable reduced models, for , are considered. Two different
procedures are typically applied: (a) one totally ignores the coupling with
; (b) one models the effect of as an average memory effect,
obtaining a generalized Langevin equation. In case (a) discrepancies between
the system and the model appear both in entropy production and linear response;
the latter can be exploited to define effective temperatures, but those are
meaningful only when time-scales are well separated. In case (b) linear
response of the model well reproduces that of the system; however the loss of
information is reflected in a loss of entropy production. When only linear
forces are present, such a reduction is dramatic and makes the average entropy
production vanish, posing problems in interpreting FDT violations.Comment: 30 pages, 4 figures, 4 appendixe
I Will Love You Till the Stars Shall Cease to Shine
https://digitalcommons.library.umaine.edu/mmb-vp/1723/thumbnail.jp
Different Scenarios for Critical Glassy Dynamics
We study the role of different terms in the -body potential of glass
forming systems on the critical dynamics near the glass transition. Using a
simplified spin model with quenched disorder, where the different terms of the
real -body potential are mapped into multi-spin interactions, we identified
three possible scenarios. For each scenario we introduce a ``minimal'' model
representative of the critical glassy dynamics near, both above and below, the
critical transition lin e. For each ``minimal'' model we discuss the low
temperature equilibrium dynamics.Comment: Completely revised version, 8 pages, 5 figures, typeset using
EURO-LaTeX, Europhysics Letters (in press
Theory of hopping conduction in arrays of doped semiconductor nanocrystals
The resistivity of a dense crystalline array of semiconductor nanocrystals
(NCs) depends in a sensitive way on the level of doping as well as on the NC
size and spacing. The choice of these parameters determines whether electron
conduction through the array will be characterized by activated
nearest-neighbor hopping or variable-range hopping (VRH). Thus far, no general
theory exists to explain how these different behaviors arise at different
doping levels and for different types of NCs. In this paper we examine a simple
theoretical model of an array of doped semiconductor NCs that can explain the
transition from activated transport to VRH. We show that in sufficiently small
NCs, the fluctuations in donor number from one NC to another provide sufficient
disorder to produce charging of some NCs, as electrons are driven to vacate
higher shells of the quantum confinement energy spectrum. This
confinement-driven charging produces a disordered Coulomb landscape throughout
the array and leads to VRH at low temperature. We use a simple computer
simulation to identify different regimes of conduction in the space of
temperature, doping level, and NC diameter. We also discuss the implications of
our results for large NCs with external impurity charges and for NCs that are
gated electrochemically.Comment: 14 pages, 10 figures; extra schematic figures added; revised
introductio
Tunneling mechanism of light transmission through metallic films
A mechanism of light transmission through metallic films is proposed,
assisted by tunnelling between resonating buried dielectric inclusions. This is
illustrated by arrays of Si spheres embedded in Ag. Strong transmission peaks
are observed near the Mie resonances of the spheres. The interaction among
various planes of spheres and interference effects between these resonances and
the surface plasmons of Ag lead to mixing and splitting of the resonances.
Transmission is proved to be limited only by absorption. For small spheres, the
effective dielectric constant can be tuned to values close to unity and a
method is proposed to turn the resulting materials invisible.Comment: 4 papges, 5 figure
A Crystal Structure of the Bifunctional Antibiotic Simocyclinone D8, Bound to DNA Gyrase
Simocyclinones are bifunctional antibiotics that inhibit bacterial DNA gyrase by preventing DNA binding to the enzyme. We report the crystal structure of the complex formed between the N-terminal domain of the Escherichia coli gyrase A subunit and simocyclinone D8, revealing two binding pockets that separately accommodate the aminocoumarin and polyketide moieties of the antibiotic. These are close to, but distinct from, the quinolone-binding site, consistent with our observations that several mutations in this region confer resistance to both agents. Biochemical studies show that the individual moieties of simocyclinone D8 are comparatively weak inhibitors of gyrase relative to the parent compound, but their combination generates a more potent inhibitor. Our results should facilitate the design of drug molecules that target these unexploited binding pockets
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