3,074 research outputs found
A Novel Photonic Material for Designing Arbitrarily Shaped Waveguides in Two Dimensions
We investigate numerically optical properties of novel two-dimensional
photonic materials where parallel dielectric rods are randomly placed with the
restriction that the distance between rods is larger than a certain value. A
large complete photonic gap (PG) is found when rods have sufficient density and
dielectric contrast. Our result shows that neither long-range nor short-range
order is an essential prerequisite to the formation of PGs. A universal
principle is proposed for designing arbitrarily shaped waveguides, where
waveguides are fenced with side walls of periodic rods and surrounded by the
novel photonic materials. We observe highly efficient transmission of light for
various waveguides. Due to structural uniformity, the novel photonic materials
are best suited for filling up the outer region of waveguides of arbitrary
shape and dimension comparable with the wavelength.Comment: 4 figure
Global Anisotropy Versus Small-Scale Fluctuations in Neutrino Flux in Core-Collapse Supernova Explosions
Effects of small-scale fluctuations in the neutrino radiation on
core-collapse supernova explosions are examined. Through a parameter study with
a fixed radiation field of neutrinos, we find substantial differences between
the results of globally anisotropic neutrino radiation and those with
fluctuations. As the number of modes of fluctuations increases, the shock
positions, entropy distributions, and explosion energies approach those of
spherical explosion. We conclude that global anisotropy of the neutrino
radiation is the most effective mechanism of increasing the explosion energy
when the total neutrino luminosity is given. This supports the previous
statement on the explosion mechanism by Shimizu and coworkers.Comment: 14 pages, including 12 figures. To be published in the Astrophysical
Journa
Determination of phase equilibria in confined systems by open pore cell Monte Carlo method.
We present a modification of the molecular dynamics simulation method with a unit pore cell with imaginary gas phase [M. Miyahara, T. Yoshioka, and M. Okazaki, J. Chem. Phys. 106, 8124 (1997)] designed for determination of phase equilibria in nanopores. This new method is based on a Monte Carlo technique and it combines the pore cell, opened to the imaginary gas phase (open pore cell), with a gas cell to measure the equilibrium chemical potential of the confined system. The most striking feature of our new method is that the confined system is steadily led to a thermodynamically stable state by forming concave menisci in the open pore cell. This feature of the open pore cell makes it possible to obtain the equilibrium chemical potential with only a single simulation run, unlike existing simulation methods, which need a number of additional runs. We apply the method to evaluate the equilibrium chemical potentials of confined nitrogen in carbon slit pores and silica cylindrical pores at 77 K, and show that the results are in good agreement with those obtained by two conventional thermodynamic integration methods. Moreover, we also show that the proposed method can be particularly useful for determining vapor-liquid and vapor-solid coexistence curves and the triple point of the confined system
Collisional stability of localized Yb() atoms immersed in a Fermi sea of Li
We establish an experimental method for a detailed investigation of inelastic
collisional properties between ytterbium (Yb) in the metastable
state and ground state lithium (Li). By combining an optical
lattice and a direct excitation to the state we achieve high
selectivity on the collisional partners. Using this method we determine
inelastic loss coefficients in collisions between
Yb() with magnetic sublevels of and and
ground state Li to be
and , respectively. Absence
of spin changing processes in Yb()-Li inelastic collisions at
low magnetic fields is confirmed by inelastic loss measurements on the
state. We also demonstrate that our method allows us to look into loss
processes in few-body systems separately.Comment: 12 pages, 7 figure
Gravitational wave forms for a three-body system in Lagrange's orbit: parameter determinations and a binary source test
Continuing work initiated in an earlier publication [Torigoe et al. Phys.
Rev. Lett. {\bf 102}, 251101 (2009)], gravitational wave forms for a three-body
system in Lagrange's orbit are considered especially in an analytic method.
First, we derive an expression of the three-body wave forms at the mass
quadrupole, octupole and current quadrupole orders. By using the expressions,
we solve a gravitational-wave {\it inverse} problem of determining the source
parameters to this particular configuration (three masses, a distance of the
source to an observer, and the orbital inclination angle to the line of sight)
through observations of the gravitational wave forms alone. For this purpose,
the chirp mass to a three-body system in the particular configuration is
expressed in terms of only the mass ratios by deleting initial angle positions.
We discuss also whether and how a binary source can be distinguished from a
three-body system in Lagrange's orbit or others.Comment: 21 pages, 3 figures, 1 table; text improved, typos corrected;
accepted for publication in PR
Critical phenomena in Newtonian gravity
We investigate the stability of self-similar solutions for a gravitationally
collapsing isothermal sphere in Newtonian gravity by means of a normal mode
analysis. It is found that the Hunter series of solutions are highly unstable,
while neither the Larson-Penston solution nor the homogeneous collapse one have
an analytic unstable mode. Since the homogeneous collapse solution is known to
suffer the kink instability, the present result and recent numerical
simulations strongly support a proposition that the Larson-Penston solution
will be realized in astrophysical situations. It is also found that the Hunter
(A) solution has a single unstable mode, which implies that it is a critical
solution associated with some critical phenomena which are analogous to those
in general relativity. The critical exponent is calculated as
. In contrast to the general relativistic case, the order
parameter will be the collapsed mass. In order to obtain a complete picture of
the Newtonian critical phenomena, full numerical simulations will be needed.Comment: 25 pages, 7 figures, accepted for publication in Physical Review
Kompenzacija trenja u mikrosustavima upravljanja na daljinu
In this project, we construct micro tele-operation systems which enable human operators to performe micro tasks, such as assembly or manufacturing, without feeling a stress. We introduce haptic interfaces that give operators the impression as if he/she were touching the expanded micro objects with his/her fingers. We construct simulator systems modeled on remote environment. In this paper we give an outline and concept of this project.
This research project can not only extend bilateral tele-operation to many other industries, it can also extend this human-friendly technique and thus help realize savings in resources, energy, costs and human support.Opisana je izvedba mikrosustava za rad na daljinu koji omogućava bez stresa obavljanje mikroradnji, kao što su montaža i proizvodnja. Prikazano je haptičko sučelje kojim se oponaša dodir uvećanog mikroobjekta prstima rukovatelja. Također je opisan koncept sustava i simulator sustava. Istraživanje izloženo u ovome radu, osim što može uvesti daljinsko upravljanje na mikro razini u mnogim granama industrije, otvara i mogućnosti primjene za štednju resursa, energije i troškova
Critical behavior of the metallic triangular-lattice Heisenberg antiferromagnet PdCrO2
We report physical properties of the conductive magnet PdCrO2 consisting of a
layered structure with a triangular lattice of Cr3+ ions (S=3/2). We confirmed
an antiferromagnetic transition at TN=37.5K by means of specific heat,
electrical resistivity, magnetic susceptibility, and neutron scattering
measurements. The critical behavior in the specific heat persists in an
unusually wide temperature range above TN. This fact implies that spin
correlations develop even at much higher temperature than TN. The observed
sub-linear temperature dependence of the resistivity above TN is also
attributed to the short-range correlations among the frustrated spins. While
the critical exponent for the magnetization agrees reasonably with the
prediction of the relevant model, that for the specific heat evaluated in the
wide temperature range differs substantially from the prediction.Comment: 7 pages, 6 figure
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