6,989 research outputs found
Evolution of the bilayer nu = 1 quantum Hall state under charge imbalance
We use high-mobility bilayer hole systems with negligible tunneling to
examine how the bilayer nu = 1 quantum Hall state evolves as charge is
transferred from one layer to the other at constant total density. We map
bilayer nu = 1 state stability versus imbalance for five total densities
spanning the range from strongly interlayer coherent to incoherent. We observe
competition between single-layer correlations and interlayer coherence. Most
significantly, we find that bilayer systems that are incoherent at balance can
develop spontaneous interlayer coherence with imbalance, in agreement with
recent theoretical predictions.Comment: 4 pages, 4 figure
Classification of zero-energy resonances by dissociation of Feshbach molecules
We study the dissociation of Feshbach molecules by a magnetic field sweep
across a zero-energy resonance. In the limit of an instantaneous magnetic field
change, the distribution of atomic kinetic energy can have a peak indicating
dominance of the molecular closed-channel spin configuration over the entrance
channel. The extent of this dominance influences physical properties such as
stability with respect to collisions, and so the readily measurable presence or
absence of the corresponding peak provides a practical method of classifying
zero-energy resonances. Currently achievable ramp speeds, e.g. those
demonstrated by Duerr et al. [Phys. Rev. A 70, 031601 (2005)], are fast enough
to provide magnetic field changes that may be interpreted as instantaneous. We
study the transition from sudden magnetic field changes to asymptotically wide,
linear ramps. In the latter limit, the predicted form of the atomic kinetic
energy distribution is independent of the specific implementation of the
two-body physics, provided that the near-resonant scattering properties are
properly accounted for.Comment: 10 pages, 5 eps figure
Kinetics, Activation Parameters, and Mechanism of the Acid Hydrolysis of tert-Butyl Acetate in Aqueous DMSO
The rate of the acid-catalysed hydrolysis of tert-butyl acetate
was found to decrease pronouncly in the presence of increasing
amounts of DMSO. The observed activation energy decreased progressively
with increasing DMSO content of the medium and the
change was attributed to a gradual interconversion of the two
concurrent and competing reaction mechanisms AALl and AAc2.
The overall reaction rate was analysed theoretically as two individual
rate constants corresponding to the respective mechanisms.
The percentage contribution of each mechanism was then estimated
and found to be concordant with the values determined experimentally
by others using 180 tracer technique. The proportion of
the AALl mechanism was found to increase both with increasing
temperature and decreasing DMSO content. The relative abundance
of the transition state belonging to each of the involved mechanisms
was discussed in the light of the solvating power of the binary DMSO-H20 solvent system. The effect of the molar concentration of water as well as the dielectric constant of the medium on the reaction kinetics was studied. The thermodynamic parameters of activation showed strong dependence on solvent composition and their values were determined by the relative contributions of the two mechanistic routes of the reaction
When Language Models Fall in Love: Animacy Processing in Transformer Language Models
Animacy—whether an entity is alive and sentient—is fundamental to cognitive processing, impacting areas such as memory, vision, and language. However, animacy is not always expressed directly in language: in English it often manifests indirectly, in the form of selectional constraints on verbs and adjectives. This poses a potential issue for transformer language models (LMs): they often train only on text, and thus lack access to extralinguistic information from which humans learn about animacy. We ask: how does this impact LMs’ animacy processing—do they still behave as humans do? We answer this question using open-source LMs. Like previous studies, we find that LMs behave much like humans when presented with entities whose animacy is typical. However, we also show that even when presented with stories about atypically animate entities, such as a peanut in love, LMs adapt: they treat these entities as animate, though they do not adapt as well as humans. Even when the context indicating atypical animacy is very short, LMs pick up on subtle clues and change their behavior. We conclude that despite the limited signal through which LMs can learn about animacy, they are indeed sensitive to the relevant lexical semantic nuances available in Englis
Electrolytes Based on Primary Ammonium Salts as Ionic Liquids for PEMFC-membranes
Physico-chemical characterization of a series of salts prepared from primary amines was performed in order to obtain the salts as protonic ionic liquids (PILs). It was shown that the majority of these salts are thermally stable up to 400 °C, while the melting point
of each salt depends on the nature of the anion and amine substitutions. The results of cyclic voltammetry experiments showed that the amines and the salts (HNR3+, A–) could be oxidized only at very high potentials (> 1.9 V/SHE) which is compatible with
their use in PEM fuel cells. Conductivities of salts at 130 °C are between 0.01 and 13 mS cm–1. The best conductivity was observed for the salt resulting from asymmetric amines/trifluoromethanesulfonic acid association. Incorporation of these compounds within Nafion® has also been studied, particularly with respect to the compatibility of PIL/Nafion® and conductivity of these newly formed membranes
A sol-gel method for growing superconducting MgB2 films
In this paper we report a new sol-gel method for the fabrication of MgB2
films. Polycrystalline MgB2 films were prepared by spin-coating a precursor
solution of Mg(BH_4)_2 diethyl ether on (001)Al2O3 substrates followed with
annealing in Mg vapor. In comparison with the MgB2 films grown by other
techniques, our films show medium qualities including a superconducting
transition temperature of Tc ~ 37 K, a critical current density of Jc(5 K, 0 T)
~ 5 {\times} 10^6 A cm^{-2}, and a critical field of H_{c2}(0) ~ 19 T. Such a
sol-gel technique shows potential in the commercial fabrication of practically
used MgB2 films as well as MgB2 wires and tapes.Comment: 8 pages, 5 figure
Cartesian Parallel Manipulator Modeling, Control and Simulation
Ayssam Elkady, Galal Elkobrosy, Sarwat Hanna, and Tarek Sobh's book chapter on robotic parallel manipulators
Spin Susceptibility and Gap Structure of the Fractional-Statistics Gas
This paper establishes and tests procedures which can determine the electron
energy gap of the high-temperature superconductors using the model
with spinon and holon quasiparticles obeying fractional statistics. A simpler
problem with similar physics, the spin susceptibility spectrum of the spin 1/2
fractional-statistics gas, is studied. Interactions with the density
oscillations of the system substantially decrease the spin gap to a value of
, much less than the mean-field value of
. The lower few Landau levels remain visible, though broadened
and shifted, in the spin susceptibility. As a check of the methods, the
single-particle Green's function of the non-interacting Bose gas viewed in the
fermionic representation, as computed by the same approximation scheme, agrees
well with the exact results. The same mechanism would reduce the gap of the
model without eliminating it.Comment: 35 pages, written in REVTeX, 16 figures available upon request from
[email protected]
Microscopic theory of single-electron tunneling through molecular-assembled metallic nanoparticles
We present a microscopic theory of single-electron tunneling through metallic
nanoparticles connected to the electrodes through molecular bridges. It
combines the theory of electron transport through molecular junctions with the
description of the charging dynamics on the nanoparticles. We apply the theory
to study single-electron tunneling through a gold nanoparticle connected to the
gold electrodes through two representative benzene-based molecules. We
calculate the background charge on the nanoparticle induced by the charge
transfer between the nanoparticle and linker molecules, the capacitance and
resistance of molecular junction using a first-principles based Non-Equilibrium
Green's Function theory. We demonstrate the variety of transport
characteristics that can be achieved through ``engineering'' of the
metal-molecule interaction.Comment: To appear in Phys. Rev.
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