8,190 research outputs found
Chiral Phase Transition at Finite Temperature in the Linear Sigma Model
We study the chiral phase transition at finite temperature in the linear
sigma model by employing a self-consistent Hartree approximation. This
approximation is introduced by imposing self-consistency conditions on the
effective meson mass equations which are derived from the finite temperature
one-loop effective potential. It is shown that in the limit of vanishing pion
mass, namely when the chiral symmetry is exact, the phase transition becomes a
weak first order accompanying a gap in the order parameter as a function of
temperature. This is caused by the long range fluctuations of meson fields
whose effective masses become small in the transition region. It is shown,
however, that with an explicit chiral symmetry breaking term in the Lagrangian
which generates the realistic finite pion mass the transition is smoothed out
irrespective of the choice of coupling strength.Comment: 21 pages, Late
Numerical analysis of transient combustion response to acoustic oscillations in axisymmetric rocket motors
A numerical analysis of unsteady motions in solid
rocket motors with a nozzle has been conducted. The
formulation treats the complete conservation equations
for the gas phase and the one-dimensional equations in
the radial direction for the condensed phase. A fully
coupled implicit scheme based on a dual time-stepping
integration algorithm has been adopted to solve the governing equations and associated boundary conditions.
After obtaining a steady state solution, periodic pressure
oscillations are imposed at the head end to simulate acoustic oscillations of a traveling-wave motion in
the combustion chamber. The amplitude of the pressure
oscillation is 1.0 % of the mean pressure and the
frequency is 1790 Hz, corresponding to the twice of the
fundamental frequency of the chamber. Magnitude and
phase of pressure and axial velocity fluctuations are influenced by the upstream reflecting wave from the nozzle
wall. Axial velocity near surface region oscillates
in phase advance manner with reference to the acoustic
pressure. Large vorticity fluctuations are observed in
near surface region. The mass-flow-rate at the nozzle
exit periodically oscillates with a time delay compared
to the imposed pressure oscillations at the head end
Applications of Various Methods of Analysis to Combustion Instabilities in Solid Propellant Rockets
Instabilities of motions in a combustion chamber are consequences of the coupled dynamics of
combustion processes and of the flow in the chamber. The extreme complexities of the problem
always require approximations of various sorts to make progress in understanding the
mechanisms and behavior of combustion instabilities. This paper covers recent progress in the
subject, mainly summarizing efforts in two areas: approximate analysis based on a form of
Galerkin's method, particularly useful for understanding the global linear and nonlinear
dynamics of combustion instabilities and numerical simulations intended to accommodate as
fully as possible fundamental chemical processes in both the condensed and gaseous phases.
One purpose of current work is to bring closer together these approaches to produce more
comprehensive and detailed realistic results applicable to the interpretation of observations
and for design of new rockets for both space and military applications. Particularly important
are the goals of determining the connections between chemical composition and instabilities;
and the influences of geometry on nonlinear behavior
Transient combustion responses of homogeneous propellants to acoustic oscillations in axisymmetric rocket motors
A numerical analysis of unsteady motions in solid
rocket motors has been conducted. The formulation
considers a 2-D axisymmetric combustion chamber and
a choke nozzle, and treats the complete conservation
equations accounting for turbulence closure and finiterate
chemical kinetics in the gas phase and subsurface reactions.
A fully coupled implicit scheme based on a dual
time-stepping integration algorithm has been adopted
to solve the governing equations and associated boundary
conditions. Results of the steady-state calculations
indicate that the distributions of pressure in the motor
and Mach number in the nozzle are one-dimensional
along the axial direction. Vorticity contours show similar
pattern to those of Mach number in the combustion
chamber. The nozzle has an influence on the flow and
temperature fields in the combustion chamber. A narrow
pressure pulse is imposed at the head end to simulate
unsteady acoustic oscillations in the combustion
chamber. When the front of the pulse reaches near the
nozzle throat, pressure near the nozzle throat increases
and blocks the hot gas flow from passing through the
nozzle throat. Self-generated oscillations have similar
frequencies to those of standing waves of the combustion
chamber. Large vorticity fluctuations are observed
in near surface region. The luminous flame zone responds
to low-frequency pressure wave rather than highfrequency
one. Temperature fluctuations in the primary
flame zone of the head end oscillates independently of
the imposed pressure oscillations while temperature fluctuations
in downstream region show pressure-dependent
oscillations
Numerical study of acoustic oscillations and combustion instabilities in solid propellant rocket
A numerical analysis of unsteady motions in solid rocket motors has been conducted. A fully coupled
implicit scheme based on a dual time-stepping integration algorithm has been adopted to solve the governing
equations and associated boundary conditions. A narrow pressure pulse is imposed at the head end to
simulate unsteady acoustic oscillations in the combustion chamber. Pressure increases when the front of the
pulse reaches near the nozzle area. Self-generated oscillations with frequency of standing wave propagates
upstream in the combustion chamber. Investigation of transient response of gas-phase dynamics to traveling
pressure wave and its effects on propellant combustion reveals several aspects: Combustion responses have
a strong relationship with vorticity fluctuations in case of high turbulent intensity on the propellant surface.
Temperature fluctuations of the propellant surface in the head end region seem to be very unstable and
independent of the pressure wave. Surface temperature without turbulence effect looks more sensitive to
temperature fluctuations in the primary flame zone. Stability of surface temperature is strongly related to
turbulent intensity on the propellant surface
Origin of the Immirzi Parameter
Using quadratic spinor techniques we demonstrate that the Immirzi parameter
can be expressed as ratio between scalar and pseudo-scalar contributions in the
theory and can be interpreted as a measure of how Einstein gravity differs from
a generally constructed covariant theory for gravity. This interpretation is
independent of how gravity is quantized. One of the important advantage of
deriving the Immirzi parameter using the quadratic spinor techniques is to
allow the introduction of renormalization scale associated with the Immirzi
parameter through the expectation value of the spinor field upon quantization
Co-Clustering Network-Constrained Trajectory Data
Recently, clustering moving object trajectories kept gaining interest from
both the data mining and machine learning communities. This problem, however,
was studied mainly and extensively in the setting where moving objects can move
freely on the euclidean space. In this paper, we study the problem of
clustering trajectories of vehicles whose movement is restricted by the
underlying road network. We model relations between these trajectories and road
segments as a bipartite graph and we try to cluster its vertices. We
demonstrate our approaches on synthetic data and show how it could be useful in
inferring knowledge about the flow dynamics and the behavior of the drivers
using the road network
Cloning and expression pattern of bovine adipogenin isoform
The fauna and distribution of chironomid midges in Ueda City were investigated based on the collections of adults attracted to automatic vending machines at 108 stations in the summer and at 103 stations in the fall of 1997. A total of 3,371 chironomid midges, 1,346 males and 2,025 females, was collected from the stations in both seasons. All of these chironomid midges were classified into 97 species belonging to four subfamilies, i. e., 61 species of Chironominae, one species of Diamesinae, 29 species of Orthocladiinae and six species of Tanypodinae. The most abundant species was Polypedilum nubifer (Skuze), which was collected at 60 stations, followed by Chironomus kiiensis Tokunaga (53 stations), Cricotopus triannulatus (Macquart) (52 stations) and Cryptochironomus albofasciatus (Staeger) (50 stations) in summer. On the other hand, in fall, the most abundant species was Smittia aterrima (Meigen), which was collected at 75 stations, followed by P. convictum (Walker) (52 stations). The collected chironomid midges reflected the environmental condition of the collection site. Thus, the number of species collected in summer was larger than that in fall, and the respective number of terrestrial species was increased in fall. In addition, the fauna of chironomid midges and their distribution patterns in Ueda City changed during both seasons.ArticleJOURNAL OF ANIMAL SCIENCE. 85(Suppl.1): 295-295 (2007)journal articl
RNAi-Microsponges Form through Self-Assembly of the Organic and Inorganic Products of Transcription
Inorganic nanostructures have been used extensively to package nucleic acids into forms useful for therapeutic applications. Here we report that the two products of transcription, RNA and inorganic pyrophosphate, can self-assemble to form composite microsponge structures composed of nanocrystalline magnesium pyrophosphate sheets (Mg[subscript 2]P[subscript 2]O[subscript 7]•3.5H[subscript 2]O) with RNA adsorbed to their surfaces. The microsponge particles contain high loadings of RNA (15–21 wt.%) that are protected from degradation and can be obtained through a rolling circle mechanism as large concatemers capable of mediating RNAi. The morphology of the RNAi microsponges is influenced by the time-course of the transcription reaction and interactions between RNA and the inorganic phase. Previous work demonstrated that polycations can be used to condense RNAi microsponges into nanoparticles capable of efficient transfection with low toxicity. Our new findings suggest that the formation of these nanoparticles is mediated by the gradual dissolution of magnesium pyrophosphate that occurs in the presence of polycations. The simple one-pot approach for assembling RNAi microsponges along with their unique properties could make them useful for RNA-based therapeutics.National Cancer Institute (U.S.) (Koch Institute Support (Core) Grant P30-CA14051)National Cancer Institute (U.S.) (Center for Cancer Nanotechnology Excellence Grant 5 U54 CA151884-02)Natural Sciences and Engineering Research Council of Canada (Postdoctoral Fellowship)National Health and Medical Research Council (Australia) (CJ Martin Fellowship)National Science Foundation (U.S.). Graduate Research Fellowshi
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