5,934 research outputs found
Do Athermal Amorphous Solids Exist?
We study the elastic theory of amorphous solids made of particles with finite
range interactions in the thermodynamic limit. For the elastic theory to exist
one requires all the elastic coefficients, linear and nonlinear, to attain a
finite thermodynamic limit. We show that for such systems the existence of
non-affine mechanical responses results in anomalous fluctuations of all the
nonlinear coefficients of the elastic theory. While the shear modulus exists,
the first nonlinear coefficient B_2 has anomalous fluctuations and the second
nonlinear coefficient B_3 and all the higher order coefficients (which are
non-zero by symmetry) diverge in the thermodynamic limit. These results put a
question mark on the existence of elasticity (or solidity) of amorphous solids
at finite strains, even at zero temperature. We discuss the physical meaning of
these results and propose that in these systems elasticity can never be
decoupled from plasticity: the nonlinear response must be very substantially
plastic.Comment: 11 pages, 11 figure
Cosine and Sine Operators Related with Orthogonal Polynomial Sets on the Intervall [-1,1]
The quantization of phase is still an open problem. In the approach of
Susskind and Glogower so called cosine and sine operators play a fundamental
role. Their eigenstates in the Fock representation are related with the
Chebyshev polynomials of the second kind. Here we introduce more general cosine
and sine operators whose eigenfunctions in the Fock basis are related in a
similar way with arbitrary orthogonal polynomial sets on the intervall [-1,1].
To each polynomial set defined in terms of a weight function there corresponds
a pair of cosine and sine operators. Depending on the symmetry of the weight
function we distinguish generalized or extended operators. Their eigenstates
are used to define cosine and sine representations and probability
distributions. We consider also the inverse arccosine and arcsine operators and
use their eigenstates to define cosine-phase and sine-phase distributions,
respectively. Specific, numerical and graphical results are given for the
classical orthogonal polynomials and for particular Fock and coherent states.Comment: 1 tex-file (24 pages), 11 figure
Processing and Transmission of Information
Contains reports on six research projects.Purchase Order DDL-B15
Inhibitory muscarinic acetylcholine receptors enhance aversive olfactory conditioning in adult Drosophila
Olfactory associative learning in Drosophila is mediated by synaptic plasticity between the Kenyon cells of the mushroom body and their output neurons. Both Kenyon cells and their inputs from projection neurons are cholinergic, yet little is known about the physiological function of muscarinic acetylcholine receptors in learning in adult flies. Here, we show that aversive olfactory learning in adult flies requires type A muscarinic acetylcholine receptors (mAChR-A), particularly in the gamma subtype of Kenyon cells. mAChR-A inhibits odor responses and is localized in Kenyon cell dendrites. Moreover, mAChR-A knockdown impairs the learning-associated depression of odor responses in a mushroom body output neuron. Our results suggest that mAChR-A function in Kenyon cell dendrites is required for synaptic plasticity between Kenyon cells and their output neurons
Measurements of total odd nitrogen (NOy) aboard MOZAIC in-service aircraft: instrument design, operation and performance
A small system for the unattended measurement of total odd nitrogen (NOy, i.e., the sum of NO and its atmospheric oxidation products) aboard civil in-service aircraft in the framework of MOZAIC is described. The instrument employs the detection of NO by its chemiluminescence with O-3 in combination with catalytic conversion of the other NOy compounds to NO at 300degreesC on a gold surface in the presence of H-2. The instrument has a sensitivity of 0.4-0.7 cps/ppt and is designed for unattended operation during 1-2 service cycles of the aircraft (400-800 flight hours). The total weight is 50 kg, including calibration system, compressed gases, mounting, and safety measures. The layout and inlet configuration are governed by requirements due to the certification for passenger aircraft. Laboratory tests are described regarding the conversion efficiency for NO2 and HNO3 (both > 98%). Interference by non-NOy species is <1% for CH3CN and NH3, <5 x 10(-5) % for N2O (corresponding to <0.2 ppt fake NOy from ambient N2O) and 100% for HCN. The time response of the instrument is <1 s (90% change) for NO2. The response for HNO3 is nonlinear: 20 s for 67%, 60 s for 80%, and 150 s for 90% response, respectively
Weak-localization corrections to the conductivity of double quantum wells
The weak-localization contribution \delta\sigma(B) to the conductivity of a
tunnel-coupled double-layer electron system is evaluated and its behavior in
weak magnetic fields B perpendicular or parallel to the layers is examined. In
a perpendicular field B, \delta \sigma(B) increases and remains dependent on
tunneling as long as the magnetic field is smaller than \hbar/e D \tau_t, where
D is the in-plane diffusion coefficient and \tau_t the interlayer tunneling
time. If \tau_t is smaller than the inelastic scattering time, a parallel
magnetic field also leads to a considerable increase of the concuctivity
starting with a B**2 law and saturating at fields higher than \hbar/e Z (D
\tau_t)**(1/2), where Z is the interlayer distance. In the limit of coherent
tunneling, when \tau_t is comparable to elastic scattering time, \delta
\sigma(B) differs from that of a single-layer system due to ensuing
modifications of the diffusion coefficient. A possibility to probe the
weak-localization effect in double-layer systems by the dependence of the
conductivity on the gate-controlled level splitting is discussed.Comment: Text 18 pages in Latex/Revtex format, 4 Postscript figures. J. Phys.:
CM,in pres
Enhanced Support for High Intensity Users of the Criminal Justice System – an evaluation of mental health nurse input into Integrated Offender Management Services in the North East of England
The current UK Government’s focus on the development of services to manage and support offenders with mental health problems has resulted in a number of innovative project developments. This research examines a service development in the North East of England which co-located Mental Health nurses with two Integrated Offender Management teams. While not solving all problems, the benefits of co-location were clear – although such innovations are now at risk from government changes which will make Integrated Offender Management the responsibility of new providers without compelling them to co-operate with health services
Quantum Phase and Quantum Phase Operators: Some Physics and Some History
After reviewing the role of phase in quantum mechanics, I discuss, with the
aid of a number of unpublished documents, the development of quantum phase
operators in the 1960's. Interwoven in the discussion are the critical physics
questions of the field: Are there (unique) quantum phase operators and are
there quantum systems which can determine their nature? I conclude with a
critique of recent proposals which have shed new light on the problem.Comment: 19 pages, 2 Figs. taken from published articles, LaTeX, to be
published in Physica Scripta, Los Alamos preprint LA-UR-92-352
Conductance Fluctuations in a Disordered Double-Barrier Junction
We consider the effect of disorder on coherent tunneling through two barriers
in series, in the regime of overlapping transmission resonances. We present
analytical calculations (using random-matrix theory) and numerical simulations
(on a lattice) to show that strong mode-mixing in the inter-barrier region
induces mesoscopic fluctuations in the conductance of universal magnitude
for a symmetric junction. For an asymmetric junction, the
root-mean-square fluctuations depend on the ratio of the two tunnel
resistances according to ,
where in the presence (absence) of time-reversal symmetry.Comment: 12 pages, REVTeX-3.0, 2 figures, submitted to Physical Review
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