9,626 research outputs found
Phase transition from hadronic matter to quark matter
We study the phase transition from nuclear matter to quark matter within the
SU(3) quark mean field model and NJL model. The SU(3) quark mean field model is
used to give the equation of state for nuclear matter, while the equation of
state for color superconducting quark matter is calculated within the NJL
model. It is found that at low temperature, the phase transition from nuclear
to color superconducting quark matter will take place when the density is of
order 2.5 - 5. At zero density, the quark phase will appear
when the temperature is larger than about 148 MeV. The phase transition from
nuclear matter to quark matter is always first order, whereas the transition
between color superconducting quark matter and normal quark matter is second
order.Comment: 18 pages, 11 figure
Hydrodynamic slip boundary condition at chemically patterned surfaces: A continuum deduction from molecular dynamics
We investigate the slip boundary condition for single-phase flow past a
chemically patterned surface. Molecular dynamics (MD) simulations show that
modulation of fluid-solid interaction along a chemically patterned surface
induces a lateral structure in the fluid molecular organization near the
surface. Consequently, various forces and stresses in the fluid vary along the
patterned surface. Given the presence of these lateral variations, a general
scheme is developed to extract hydrodynamic information from MD data. With the
help of this scheme, the validity of the Navier slip boundary condition is
verified for the chemically patterned surface, where a local slip length can be
defined. Based on the MD results, a continuum hydrodynamic model is formulated
using the Navier-Stokes equation and the Navier boundary condition, with a slip
length varying along the patterned surface. Steady-state velocity fields from
continuum calculations are in quantitative agreement with those from MD
simulations. It is shown that, when the pattern period is sufficiently small,
the solid surface appears to be homogeneous, with an effective slip length that
can be controlled by surface patterning. Such a tunable slip length may have
important applications in nanofluidics.Comment: 41 pages, 17 figure
Ab initio study of shock compressed oxygen
Quantum molecular dynamic simulations are introduced to study the shock
compressed oxygen. The principal Hugoniot points derived from the equation of
state agree well with the available experimental data. With the increase of
pressure, molecular dissociation is observed. Electron spin polarization
determines the electronic structure of the system under low pressure, while it
is suppressed around 30 50 GPa. Particularly, nonmetal-metal transition
is taken into account, which also occurs at about 30 50 GPa. In
addition, the optical properties of shock compressed oxygen are also discussed.Comment: 5 pages, 5 figure
Multi-wavelength Stellar Polarimetry of the Filamentary Cloud IC5146: I. Dust Properties
We present optical and near-infrared stellar polarization observations toward
the dark filamentary clouds associated with IC5146. The data allow us to
investigate the dust properties (this paper) and the magnetic field structure
(Paper II). A total of 2022 background stars were detected in -, -,
-, and/or -bands to mag. The ratio of the polarization
percentage at different wavelengths provides an estimate of ,
the wavelength of peak polarization, which is an indicator of the small-size
cutoff of the grain size distribution. The grain size distribution seems to
significantly change at 3 mag, where both the average and dispersion
of decrease. In addition, we found
0.6-0.9 m for mag, which is larger than the 0.55 m
in the general ISM, suggesting that grain growth has already started in low
regions. Our data also reveal that polarization efficiency (PE ) decreases with as a power-law in -, -, and
-bands with indices of -0.710.10, -1.230.10 and -0.530.09.
However, -band data show a power index change; the PE varies with
steeply (index of -0.950.30) when mag but softly
(index of -0.250.06) for greater values. The soft decay of PE in
high regions is consistent with the Radiative Aligned Torque model,
suggesting that our data trace the magnetic field to mag.
Furthermore, the breakpoint found in -band is similar to the where we
found the dispersion significantly decreased. Therefore, the
flat PE- in high regions implies that the power index changes result
from additional grain growth.Comment: 31 pages, 17 figures, and 3 tables; accepted for publication in Ap
The Hunter-Saxton equation: remarkable structures of symmetries and conserved densities
In this paper, we present extraordinary algebraic and geometrical structures
for the Hunter-Saxton equation: infinitely many commuting and non-commuting
-independent higher order symmetries and conserved densities. Using a
recursive relation, we explicitly generate infinitely many higher order
conserved densities dependent on arbitrary parameters. We find three Nijenhuis
recursion operators resulting from Hamiltonian pairs, of which two are new.
They generate three hierarchies of commuting local symmetries. Finally, we give
a local recursion operator depending on an arbitrary parameter.
As a by-product, we classify all anti-symmetric operators of a definite form
that are compatible with the Hamiltonian operator
The effect of hidden color channels on nucleon-nucleon interaction in quark model
In the framework of constituent quark model, the effect of hidden color
channels on the nucleon-nucleon () interaction is studied. By adjusting the
color confinement strength between the hidden color channels and color singlet
channels and/or between the hidden color channels and hidden color channels,
the experimental data of to partial-wave phase shifts of
scattering can be fitted well. The results show that the hidden color channel
coupling might be important in producing the intermediate-range attraction of
interaction. The deuteron properties and dibaryon candidates have also
been studied with this model.Comment: 11 pages, 9 figure
Anthropogenic Sulfate and Asian Dust Signals in Snow from Tien Shan, Northwest China
Snow samples were collected from a 0.5 m snowpack at Glacier No. I and near Bogda Feng, eastern Tien Shan, northwest China. Samples that were melted in the field were analyzed for chloride, nitrate, sulfate, sodium, potassium, magnesium, calcium, and microparticles. Eight samples were returned frozen and were analyzed for the above ions plus ammonium, acetate, formate, methylsulfonate, and hydrogen peroxide. There was no significant difference in measured major ion concentrations between the melted and frozen samples. Measured cations in both sets of samples were two to three times greater than measured anions. Calcium and sodium are the dominant cations while sulfate is the dominant measured anion. High ion burdens are associated with dusty layers in the snowpack, indicating that dust from the vast arid regions of central Asia is the dominant source for major ions in Tien Shan snow. The significant increase in sulfate and decrease in the cation: anion ratio in Bogda Feng snow relative to Glacier No. I snow suggest that anthropogenic emissions from Urtimqi are an important source of sulfate to precipitation downwind from the city
In situ imaging of field emission from individual carbon nanotubes and their structural damage
©2002 American Institute of Physics. The electronic version of this article is the complete one and can be found online at: http://link.aip.org/link/?APPLAB/80/856/1DOI:10.1063/1.1446994Field emission of individual carbon nanotubes was observed by in situ
transmission electron microscopy. A fluctuation in emission current was due to a
variation in distance between the nanotube tip and the counter electrode owing
to a "head-shaking" effect of the nanotube during field emission. Strong
field-induced structural damage of a nanotube occurs in two ways: a
piece-by-piece and segment-by-segment pilling process of the graphitic layers,
and a concentrical layer-by-layer stripping process. The former is believed
owing to a strong electrostatic force, and the latter is likely due to heating
produced by emission current that flowed through the most outer graphitic
layers
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