58,250 research outputs found
Single-electron transistors in electromagnetic environments
The current-voltage (I-V) characteristics of single-electron transistors
(SETs) have been measured in various electromagnetic environments. Some SETs
were biased with one-dimensional arrays of dc superconducting quantum
interference devices (SQUIDs). The purpose was to provide the SETs with a
magnetic-field-tunable environment in the superconducting state, and a
high-impedance environment in the normal state. The comparison of SETs with
SQUID arrays and those without arrays in the normal state confirmed that the
effective charging energy of SETs in the normal state becomes larger in the
high-impedance environment, as expected theoretically. In SETs with SQUID
arrays in the superconducting state, as the zero-bias resistance of the SQUID
arrays was increased to be much larger than the quantum resistance R_K = h/e^2
= 26 kohm, a sharp Coulomb blockade was induced, and the current modulation by
the gate-induced charge was changed from e periodic to 2e periodic at a bias
point 0<|V|<2D_0/e, where D_0 is the superconducting energy gap. The author
discusses the Coulomb blockade and its dependence on the gate-induced charge in
terms of the single Josephson junction with gate-tunable junction capacitance.Comment: 8 pages with 10 embedded figures, RevTeX4, published versio
Asymptotic Learning Curve and Renormalizable Condition in Statistical Learning Theory
Bayes statistics and statistical physics have the common mathematical
structure, where the log likelihood function corresponds to the random
Hamiltonian. Recently, it was discovered that the asymptotic learning curves in
Bayes estimation are subject to a universal law, even if the log likelihood
function can not be approximated by any quadratic form. However, it is left
unknown what mathematical property ensures such a universal law. In this paper,
we define a renormalizable condition of the statistical estimation problem, and
show that, under such a condition, the asymptotic learning curves are ensured
to be subject to the universal law, even if the true distribution is
unrealizable and singular for a statistical model. Also we study a
nonrenormalizable case, in which the learning curves have the different
asymptotic behaviors from the universal law
Observations of solar flare gamma-rays and protons
Solar flare gamma-rays (4 to 7 MeV) and protons (8 to 500 MeV) were simultaneously observed from six flares on 1 Apr., 4 Apr., 27, Apr. 13, May 1981, 1 Feb. and 6 June 1982 by the Hinotori and GMS satellites. The relationship between 4 to 7 MeV gamma-ray fluences and peak 16 to 34 MeV proton fluxes for these flares are analyzed. It does not reveal an apparent correlation between these two parameters. The present result implies that the protons producing gamma-rays and the protons observed near the Earth do not always belong to the same population
Efficient Implementations of Molecular Dynamics Simulations for Lennard-Jones Systems
Efficient implementations of the classical molecular dynamics (MD) method for
Lennard-Jones particle systems are considered. Not only general algorithms but
also techniques that are efficient for some specific CPU architectures are also
explained. A simple spatial-decomposition-based strategy is adopted for
parallelization. By utilizing the developed code, benchmark simulations are
performed on a HITACHI SR16000/J2 system consisting of IBM POWER6 processors
which are 4.7 GHz at the National Institute for Fusion Science (NIFS) and an
SGI Altix ICE 8400EX system consisting of Intel Xeon processors which are 2.93
GHz at the Institute for Solid State Physics (ISSP), the University of Tokyo.
The parallelization efficiency of the largest run, consisting of 4.1 billion
particles with 8192 MPI processes, is about 73% relative to that of the
smallest run with 128 MPI processes at NIFS, and it is about 66% relative to
that of the smallest run with 4 MPI processes at ISSP. The factors causing the
parallel overhead are investigated. It is found that fluctuations of the
execution time of each process degrade the parallel efficiency. These
fluctuations may be due to the interference of the operating system, which is
known as OS Jitter.Comment: 33 pages, 19 figures, add references and figures are revise
Electron screening in the liquid-gas mixed phases of nuclear matter
Screening effects of electrons on inhomogeneous nuclear matter, which
includes spherical, slablike, and rodlike nuclei as well as spherical and
rodlike nuclear bubbles, are investigated in view of possible application to
cold neutron star matter and supernova matter at subnuclear densities. Using a
compressible liquid-drop model incorporating uncertainties in the surface
tension, we find that the energy change due to the screening effects broadens
the density region in which bubbles and nonspherical nuclei appear in the phase
diagram delineating the energetically favorable shape of inhomogeneous nuclear
matter. This conclusion is considered to be general since it stems from a
model-independent feature that the electron screening acts to decrease the
density at which spherical nuclei become unstable against fission and to
increase the density at which uniform matter becomes unstable against proton
clustering.Comment: 12 pages, 8 figures, accepted for publication in Physical Review
Rhythmic Motion of a Droplet under a DC Electric Field
The effect of a stationary electric field on a water droplet with a diameter
of several tens micrometers in oil was examined. Such a droplet exhibits
repetitive translational motion between the electrodes in a spontaneous manner.
The state diagram of this oscillatory motion was deduced; at 0-20 V the droplet
is fixed at the surface of the electrode, at 20-70 V the droplet exhibits
small-amplitude oscillatory motion between the electrodes, and at 70-100 V the
droplet shows large-amplitude periodic motion between the electrodes. The
observed rhythmic motion is explained in a semi-quantitative manner by using
differential equations, which includes the effect of charging the droplet under
an electric field. We also found that twin droplets exhibit synchronized
rhythmic motion between the electrodes
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