4,429 research outputs found
Particle impact tests
Particle impact tests were performed on three types of orbiter surface with a micrometeoroid facility. The test equipment electrostatically accelerated micron sized particles to high velocities simulating micrometeoroid impacts. Test particles were titanium diboride with typical velocities in the range 1 to 2.3 km x sec/1 and equivalent particle diameters in the range 4 to 16 microns. Impact angles to the material surface were 90, 60 and 30 degrees. The particle impact sites were located on the sample surfaces and craters were photographed with a magnification of 400X
Kink Solution in a Fluid Model of Traffic Flows
Traffic jam in a fluid model of traffic flows proposed by Kerner and
Konh\"auser (B. S. Kerner and P. Konh\"auser, Phys. Rev. E 52 (1995), 5574.) is
analyzed. An analytic scaling solution is presented near the critical point of
the hetero-clinic bifurcation. The validity of the solution has been confirmed
from the comparison with the simulation of the model.Comment: RevTeX v3.1, 6 pages, and 2 figure
Ion beam plume and efflux characterization flight experiment study
A flight experiment and flight experiment package for a shuttle-borne flight test of an 8-cm mercury ion thruster was designed to obtain charged particle and neutral particle material transport data that cannot be obtained in conventional ground based laboratory testing facilities. By the use of both ground and space testing of ion thrusters, the flight worthiness of these ion thrusters, for other spacecraft applications, may be demonstrated. The flight experiment definition for the ion thruster initially defined a broadly ranging series of flight experiments and flight test sensors. From this larger test series and sensor list, an initial flight test configuration was selected with measurements in charged particle material transport, condensible neutral material transport, thruster internal erosion, ion beam neutralization, and ion thrust beam/space plasma electrical equilibration. These measurement areas may all be examined for a seven day shuttle sortie mission and for available test time in the 50 - 100 hour period
Relativistic stars with purely toroidal magnetic fields
We investigate the effects of the purely toroidal magnetic field on the
equilibrium structures of the relativistic stars. The master equations for
obtaining equilibrium solutions of relativistic rotating stars containing
purely toroidal magnetic fields are derived for the first time. To solve these
master equations numerically, we extend the Cook-Shapiro-Teukolsky scheme for
calculating relativistic rotating stars containing no magnetic field to
incorporate the effects of the purely toroidal magnetic fields. By using the
numerical scheme, we then calculate a large number of the equilibrium
configurations for a particular distribution of the magnetic field in order to
explore the equilibrium properties. We also construct the equilibrium sequences
of the constant baryon mass and/or the constant magnetic flux, which model the
evolution of an isolated neutron star as it loses angular momentum via the
gravitational waves. Important properties of the equilibrium configurations of
the magnetized stars obtained in this study are summarized as follows ; (1) For
the non-rotating stars, the matter distribution of the stars is prolately
distorted due to the toroidal magnetic fields. (2) For the rapidly rotating
stars, the shape of the stellar surface becomes oblate because of the
centrifugal force. But, the matter distribution deep inside the star is
sufficiently prolate for the mean matter distribution of the star to be
prolate. (3) The stronger toroidal magnetic fields lead to the mass-shedding of
the stars at the lower angular velocity. (4) For some equilibrium sequences of
the constant baryon mass and magnetic flux, the stars can spin up as they lose
angular momentum.Comment: 13 figures, 7 tables, submitted to PR
Toda Lattice Solutions of Differential-Difference Equations for Dissipative Systems
In a certain class of differential-difference equations for dissipative
systems, we show that hyperbolic tangent model is the only the nonlinear system
of equations which can admit some particular solutions of the Toda lattice. We
give one parameter family of exact solutions, which include as special cases
the Toda lattice solutions as well as the Whitham's solutions in the Newell's
model. Our solutions can be used to describe temporal-spatial density patterns
observed in the optimal velocity model for traffic flow.Comment: Latex, 13 pages, 1 figur
Representation of nonequilibrium steady states in large mechanical systems
Recently a novel concise representation of the probability distribution of
heat conducting nonequilibrium steady states was derived. The representation is
valid to the second order in the ``degree of nonequilibrium'', and has a very
suggestive form where the effective Hamiltonian is determined by the excess
entropy production. Here we extend the representation to a wide class of
nonequilibrium steady states realized in classical mechanical systems where
baths (reservoirs) are also defined in terms of deterministic mechanics. The
present extension covers such nonequilibrium steady states with a heat
conduction, with particle flow (maintained either by external field or by
particle reservoirs), and under an oscillating external field. We also simplify
the derivation and discuss the corresponding representation to the full order.Comment: 27 pages, 3 figure
4/3-Law of Granular Particles Flowing through a Vertical Pipe
Density waves of granular material (sand) flowing through a vertical pipe
have been investigated. Clear density waves emerge when the cock attached to
bottom end of the pipe is closed. The FFT power spectra were found to show a
stable power-law form The value of the exponent was
evaluated as . We also introduce a simple one-dimensional
model which reproduces from both simulation and theoretical
analysis. (to be published in Phys.Rev.Lett.)Comment: 4 pages, 4 figures, a style fil
The singlet scalar as FIMP dark matter
The singlet scalar model is a minimal extension of the Standard Model that
can explain the dark matter. We point out that in this model the dark matter
constraint can be satisfied not only in the already considered WIMP regime but
also, for much smaller couplings, in the Feebly Interacting Massive Particle
(FIMP) regime. In it, dark matter particles are slowly produced in the early
Universe but are never abundant enough to reach thermal equilibrium or
annihilate among themselves. This alternative framework is as simple and
predictive as the WIMP scenario but it gives rise to a completely different
dark matter phenomenology. After reviewing the calculation of the dark matter
relic density in the FIMP regime, we study in detail the evolution of the dark
matter abundance in the early Universe and the predicted relic density as a
function of the parameters of the model. A new dark matter compatible region of
the singlet model is identified, featuring couplings of order 10^-11 to 10^-12
for singlet masses in the GeV to TeV range. As a consequence, no signals at
direct or indirect detection experiments are expected. The relevance of this
new viable region for the correct interpretation of recent experimental bounds
is emphasized.Comment: 12 pages, 6 figure
Conference Summary of QNP2018
This report is the summary of the Eighth International Conference on Quarks
and Nuclear Physics (QNP2018). Hadron and nuclear physics is the field to
investigate high-density quantum many-body systems bound by strong
interactions. It is intended to clarify matter generation of universe and
properties of quark-hadron many-body systems. The QNP is an international
conference which covers a wide range of hadron and nuclear physics, including
quark and gluon structure of hadrons, hadron spectroscopy, hadron interactions
and nuclear structure, hot and cold dense matter, and experimental facilities.
First, I introduce the current status of the hadron and nuclear physics field
related to this conference. Next, the organization of the conference is
explained, and a brief overview of major recent developments is discussed by
selecting topics from discussions at the plenary sessions. They include
rapidly-developing field of gravitational waves and nuclear physics, hadron
interactions and nuclear structure with strangeness, lattice QCD, hadron
spectroscopy, nucleon structure, heavy-ion physics, hadrons in nuclear medium,
and experimental facilities of EIC, GSI-FAIR, JLab, J-PARC, Super-KEKB, and
others. Nuclear physics is at a fortunate time to push various projects at
these facilities. However, we should note that the projects need to be
developed together with related studies in other fields such as gravitational
physics, astrophysics, condensed-matter physics, particle physics, and
fundamental quantum physics.Comment: 10 pages, LaTeX, 1 style file, 3 figure files, Proceedings of Eighth
International Conference on Quarks and Nuclear Physics (QNP2018), November
13-17, 2018, Tsukuba, Japa
Testing models of inflation with CMB non-gaussianity
Two different predictions for the primordial curvature fluctuation bispectrum
are compared through their effects on the Cosmic Microwave Background
temperature fluctuations. The first has a local form described by a single
parameter f_{NL}. The second is based on a prediction from the warm
inflationary scenario, with a different dependence on wavenumber and a
parameter f_{WI}. New expressions are obtained for the angular bispectra of the
temperature fluctuations and for the estimators used to determine and
f_{WI}. The standard deviation of the estimators in an ideal experiment is
roughly 5 times larger for f_{WI} than for f_{NL}. Using 3 year WMAP data gives
limits -375<f_{WI}<36.8, but there is a possibility of detecting a signal for
f_{WI} from the Planck satellite.Comment: 13 pages, 5 figures in ReVTe
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