2,785 research outputs found
Temperature Dependence of the Effective Bag Constant and the Radius of a Nucleon in the Global Color Symmetry Model of QCD
We study the temperature dependence of the effective bag constant, the mass,
and the radius of a nucleon in the formalism of the simple global color
symmetry model in the Dyson-Schwinger equation approach of QCD with a
Gaussian-type effective gluon propagator. We obtain that, as the temperature is
lower than a critical value, the effective bag constant and the mass decrease
and the radius increases with the temperature increasing. As the critical
temperature is reached, the effective bag constant and the mass vanish and the
radius tends to infinity. At the same time, the chiral quark condensate
disappears. These phenomena indicate that the deconfinement and the chiral
symmetry restoration phase transitions can take place at high temperature. The
dependence of the critical temperature on the interaction strength parameter in
the effective gluon propagator of the approach is given.Comment: 10 pages, 9 figure
Dyson-Schwinger Equations with a Parameterized Metric
We construct and solve the Dyson-Schwinger equation (DSE) of quark propagator
with a parameterized metric, which connects the Euclidean metric with the
Minkowskian one. We show, in some models, the Minkowskian vacuum is different
from the Euclidean vacuum. The usual analytic continuation of Green function
does not make sense in these cases. While with the algorithm we proposed and
the quark-gluon vertex ansatz which preserves the Ward-Takahashi identity, the
vacuum keeps being unchanged in the evolution of the metric. In this case,
analytic continuation becomes meaningful and can be fully carried out.Comment: 10 pages, 7 figures. To appear in Physical Review
Phase Transition of Finite Size Quark Droplets with Isospin Chemical Potential in the Nanbu--Jona-Lasinio Model
Making use of the NJL model and the multiple reflection expansion
pproximation, we study the phase transition of the finite size droplet with u
and d quarks. We find that the dynamical masses of u, d quarks are different,
and the chiral symmetry can be restored at different critical radii for u, d
quark. It rovides a clue to understand the effective nucleon mass splitting in
nuclear matter. Meanwhile, it shows that the maximal isospin chemical potential
at zero temperature is much smaller than the mass of pion in free space.Comment: 12 pages, 3 figures. To appear in Physical Review
An experimental and numerical study on structural dynamic stress of a landing gear
This paper concerns the main landing gear of certain light aircraft, and the dynamic stress on the main landing gear during the landing process is analyzed. A complete dynamic drop test is developed for the landing gear of light aircraft on the main landing gear, and the changes of dynamic strain exerted on the strut in the process of drop are measured. Simultaneously, the simulation software LMS Virtual.Lab Motion is used to build the rigid-flexible coupling dynamic model and simulate the process of drop and the results of the dynamic stress is obtained by means of computer simulation. Afterwards, the results of the dynamic stress between simulation and test are contrasted, and the sources of data error are analyzed. To sum up, the study shows that the dynamic stress in the flexible part of landing gear possesses a high accuracy through combining the analysis results of simulation and test, which meets the safety design criteria of the landing gear. Moreover, the method used to build the rigid-flexible coupling model is an available and reliable way for the simulation of drop test, which can provide a deep basis for future research
Phase diagram and critical endpoint for strongly-interacting quarks
We introduce a method based on the chiral susceptibility, which enables one
to draw a phase diagram in the chemical-potential/temperature plane for
strongly-interacting quarks whose interactions are described by any reasonable
gap equation, even if the diagrammatic content of the quark-gluon vertex is
unknown. We locate a critical endpoint (CEP) at (\mu^E,T^E) ~ (1.0,0.9)T_c,
where T_c is the critical temperature for chiral symmetry restoration at \mu=0;
and find that a domain of phase coexistence opens at the CEP whose area
increases as a confinement length-scale grows.Comment: 4 pages, 3 figure
Quark spectral density and a strongly-coupled QGP
The maximum entropy method is used to compute the dressed-quark spectral
density from the self-consistent numerical solution of a rainbow truncation of
QCD's gap equation at temperatures above that for which chiral symmetry is
restored. In addition to the normal and plasmino modes, the spectral function
also exhibits an essentially nonperturbative zero mode for temperatures
extending to 1.4-1.8-times the critical temperature, T_c. In the neighbourhood
of T_c, this long-wavelength mode contains the bulk of the spectral strength
and so long as this mode persists, the system may fairly be described as a
strongly-coupled state of matter.Comment: 4 pages, 2 figure
Practical corollaries of transverse Ward-Green-Takahashi identities
The gauge principle is fundamental in formulating the Standard Model.
Fermion--gauge-boson couplings are the inescapable consequence and the primary
determining factor for observable phenomena. Vertices describing such couplings
are simple in perturbation theory and yet the existence of strong-interaction
bound-states guarantees that many phenomena within the Model are
nonperturbative. It is therefore crucial to understand how dynamics dresses the
vertices and thereby fundamentally alters the appearance of
fermion--gauge-boson interactions. We consider the coupling of a
dressed-fermion to an Abelian gauge boson, and describe a unified treatment and
solution of the familiar longitudinal Ward-Green-Takahashi identity and its
less well known transverse counterparts. Novel consequences for the
dressed-fermion--gauge-boson vertex are exposed.Comment: 5 pages, 1 figur
Zero mode in a strongly coupled quark gluon plasma
In connection with massless two-flavour QCD, we analyse the chiral symmetry
restoring phase transition using three distinct gluon-quark vertices and two
different assumptions about the long-range part of the quark-quark interaction.
In each case, we solve the gap equation, locate the transition temperature T_c,
and use the maximum entropy method to extract the dressed-quark spectral
function at T>T_c. Our best estimate for the chiral transition temperature is
T_c=(147 +/- 8)MeV; and the deconfinement transition is coincident. For
temperatures markedly above T_c, we find a spectral density that is consistent
with those produced using a hard thermal loop expansion, exhibiting both a
normal and plasmino mode. On a domain T\in[T_c,T_s], with T_s approximately
1.5T_c, however, with each of the six kernels we considered, the spectral
function contains a significant additional feature. Namely, it displays a third
peak, associated with a zero mode, which is essentially nonperturbative in
origin and dominates the spectral function at T=T_c. We suggest that the
existence of this mode is a signal for the formation of a strongly-coupled
quark-gluon plasma and that this strongly-interacting state of matter is likely
a distinctive feature of the QCD phase transition.Comment: 11 pages, 5 figures, 1 tabl
Synthesis of Fe-MCM-41 Using Iron Ore Tailings as the Silicon and Iron Source
Highly ordered Fe-MCM-41 molecular sieve was successfully synthesized by using n-hexadecyl-trimethyl ammonium bromide (CTAB) as the template and the iron ore tailings (IOTs) as the silicon and iron source. X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), diffuse reflectance UV-visible spectroscopy, 29Si magic-angle spinning (MAS) nuclear magnetic resonance (NMR), and nitrogen adsorption/desorption were used to characterize the samples. The results showed that the mesoporous materials had highly ordered 2-dimensional hexagonal structure. The synthesized sample had high surface area, and part of iron atoms is retained in the framework with formation of tetrahedron after removal of the template by calcinations. The results obtained in the present work demonstrate the feasibility of employing iron ore tailings as a potential source of silicon and iron to produce Fe-MCM-41 mesoporous materials
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