11,308 research outputs found
The distribution of forces affects vibrational properties in hard sphere glasses
We study theoretically and numerically the elastic properties of hard sphere
glasses, and provide a real-space description of their mechanical stability. In
contrast to repulsive particles at zero-temperature, we argue that the presence
of certain pairs of particles interacting with a small force soften elastic
properties. This softening affects the exponents characterizing elasticity at
high pressure, leading to experimentally testable predictions. Denoting
the force distribution of such pairs and the
packing fraction at which pressure diverges, we predict that (i) the density of
states has a low-frequency peak at a scale , rising up to it as
, and decaying above as where and is the frequency,
(ii) shear modulus and mean-squared displacement are inversely proportional
with where
, and (iii) continuum elasticity breaks down on a
scale where
and , where is the
coordination and the spatial dimension. We numerically test (i) and provide
data supporting that in our bi-disperse system,
independently of system preparation in two and three dimensions, leading to
, , and . Our results for the
mean-square displacement are consistent with a recent exact replica computation
for , whereas some observations differ, as rationalized by the
present approach.Comment: 5 pages + 4 pages supplementary informatio
A Genetic Locus Regulates the Expression of Tissue-Specific mRNAs from Multiple Transcription Units
129 GIX- mice, unlike animals of the congeneic partner strain GIX+, do not express significant amounts of the retroviral antigens gp70 and p30. Evidence is presented indicating that the GIX phenotype is specified by a distinct regulatory gene acting on multiple transcription units to control the levels of accumulation of specific mRNA species. The steady-state levels of retroviral-homologous mRNA from the tissues of GIX+ and GIX- mice were examined by blot hybridization using as probes DNA fragments from cloned murine leukemia viruses. RNA potentially encoding viral antigens was reduced or absent in GIX- mice, even though no differences in integrated viral genomes were detected between these congeneic strains by DNA blotting. Tissue-specific patterns of accumulation of these RNA species were detected in brain, epididymis, liver, spleen, and thymus, and several distinct RNA species were found to be coordinately regulated with the GIX phenotype. Measurements of RNA synthesis suggest a major role for transcriptional control in the regulation of some retroviral messages
Theoretical considerations of some nonlinear aspects of hypersonic panel flutter Annual report, 1 Sep. 1967 - 31 Aug. 1968
Stability and postcritical response of infinite width panels on hinged supports due to aerodynamic loads at hypersonic spee
Impurity Scattering in Luttinger Liquid with Electron-Phonon Coupling
We study the influence of electron-phonon coupling on electron transport
through a Luttinger liquid with an embedded weak scatterer or weak link. We
derive the renormalization group (RG) equations which indicate that the
directions of RG flows can change upon varying either the relative strength of
the electron-electron and electron-phonon coupling or the ratio of Fermi to
sound velocities. This results in the rich phase diagram with up to three fixed
points: an unstable one with a finite value of conductance and two stable ones,
corresponding to an ideal metal or insulator.Comment: 4 pages, 2 figure
Thermal noise and dephasing due to electron interactions in non-trivial geometries
We study Johnson-Nyquist noise in macroscopically inhomogeneous disordered
metals and give a microscopic derivation of the correlation function of the
scalar electric potentials in real space. Starting from the interacting
Hamiltonian for electrons in a metal and the random phase approximation, we
find a relation between the correlation function of the electric potentials and
the density fluctuations which is valid for arbitrary geometry and
dimensionality. We show that the potential fluctuations are proportional to the
solution of the diffusion equation, taken at zero frequency. As an example, we
consider networks of quasi-1D disordered wires and give an explicit expression
for the correlation function in a ring attached via arms to absorbing leads. We
use this result in order to develop a theory of dephasing by electronic noise
in multiply-connected systems.Comment: 9 pages, 6 figures (version submitted to PRB
When There Are No Randomized Controlled Trials: A Case History of a Controversial Procedure for Metastatic Legal Doctrines
Boundedness of Pseudodifferential Operators on Banach Function Spaces
We show that if the Hardy-Littlewood maximal operator is bounded on a
separable Banach function space and on its associate space
, then a pseudodifferential operator
is bounded on whenever the symbol belongs to the
H\"ormander class with ,
or to the the Miyachi class
with ,
. This result is applied to the case of
variable Lebesgue spaces .Comment: To appear in a special volume of Operator Theory: Advances and
Applications dedicated to Ant\'onio Ferreira dos Santo
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
Measuring Light Pollution with Fisheye Lens Imagery from A Moving Boat, A Proof of Concept
Near all-sky imaging photometry was performed from a boat on the Gulf of
Aqaba to measure the night sky brightness in a coastal environment. The boat
was not anchored, and therefore drifted and rocked. The camera was mounted on a
tripod without any inertia/motion stabilization. A commercial digital single
lens reflex (DSLR) camera and fisheye lens were used with ISO setting of 6400,
with the exposure time varied between 0.5 s and 5 s. We find that despite
movement of the vessel the measurements produce quantitatively comparable
results apart from saturation effects. We discuss the potential and limitations
of this method for mapping light pollution in marine and freshwater systems.
This work represents the proof of concept that all-sky photometry with a
commercial DSLR camera is a viable tool to determine light pollution in an
ecological context from a moving boat.Comment: 9 pages, 6 figures, accepted at International Journal of Sustainable
Lightin
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