617 research outputs found
Hard-Loop Effective Action for Anisotropic Plasmas
We generalize the hard-thermal-loop effective action of the equilibrium
quark-gluon plasma to a non-equilibrium system which is space-time homogeneous
but for which the parton momentum distribution is anisotropic. We show that the
manifestly gauge-invariant Braaten-Pisarski form of the effective action can be
straightforwardly generalized and we verify that it then generates all n-point
functions following from collisionless gauge-covariant transport theory for a
homogeneous anisotropic plasma. On the other hand, the Taylor-Wong form of the
hard-thermal-loop effective action has a more complicated generalization to the
anisotropic case. Already in the simplest case of anisotropic distribution
functions, it involves an additional term that is gauge invariant by itself,
but nontrivial also in the static limit.Comment: 12 pages. Version 3: typo in (15) corrected, note added discussing
metric conventions use
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Steering object-oriented computations with Python
We have described current approaches and future plans for steering C++ application, running Python on parallel platforms, and combination of Tk interface and Python interpreter in steering computations. In addition, there has been significant enhancement in the Gist module. Tk mega widgets has been implemented for a few physics applications. We have also written Python interface to SIJLO, a data storage package used as an interface to a visualization system named MeshTv. Python is being used to control large-scale simulations (molecular dynamics in particular) running on the CM-5 and T3D at LANL as well. A few other code development projects at LLNL are either using or considering Python as their steering shells. In summary, the merits of Python have been appreciated by more and more people in the scientific computation community
Effect of Subband Landau Level Coupling to the Linearly Dispersing Collective Mode in a Quantum Hall Ferromagnet
In a recent experiment (Phys. Rev. Lett. {\bf 87}, 036903 (2001)), Spielman
et al observed a linearly dispersing collective mode in quantum Hall
ferromagnet. While it qualitatively agrees with the Goldstone mode dispersion
at small wave vector, the experimental mode velocity is slower than that
calculated by previous theories by a factor about 0.55. A better agreement with
the experimental data may possibly be achieved by taking the subband Landau
level coupling into account due to the finiteness of the layer thickness. A
novel coupling of quantum fluctuation to the tunneling is briefly discussed.Comment: 4 pages; published versio
Artificial Intelligence in Radiation Therapy
Artificial intelligence (AI) has great potential to transform the clinical workflow of radiotherapy. Since the introduction of deep neural networks, many AI-based methods have been proposed to address challenges in different aspects of radiotherapy. Commercial vendors have started to release AI-based tools that can be readily integrated to the established clinical workflow. To show the recent progress in AI-aided radiotherapy, we have reviewed AI-based studies in five major aspects of radiotherapy including image reconstruction, image registration, image segmentation, image synthesis, and automatic treatment planning. In each section, we summarized and categorized the recently published methods, followed by a discussion of the challenges, concerns, and future development. Given the rapid development of AI-aided radiotherapy, the efficiency and effectiveness of radiotherapy in the future could be substantially improved through intelligent automation of various aspects of radiotherapy
Global phase diagram of bilayer quantum Hall ferromagnets
We present a microscopic study of the interlayer spacing d versus in-plane
magnetic field phase diagram for bilayer quantum Hall (QH)
pseudo-ferromagnets. In addition to the interlayer charge balanced commensurate
and incommensurate states analyzed previously, we address the corresponding
interlayer charge unbalanced "canted" QH states. We predict a large anomaly in
the bilayer capacitance at the canting transition and the formation of dipole
stripe domains with periods exceeding 1 micron in the canted state.Comment: 4 RevTeX pgs, 2 eps figures, submitted to PR
Charmonium states in QCD-inspired quark potential model using Gaussian expansion method
We investigate the mass spectrum and electromagnetic processes of charmonium
system with the nonperturbative treatment for the spin-dependent potentials,
comparing the pure scalar and scalar-vector mixing linear confining potentials.
It is revealed that the scalar-vector mixing confinement would be important for
reproducing the mass spectrum and decay widths, and therein the vector
component is predicted to be around 22%. With the state wave functions obtained
via the full-potential Hamiltonian, the long-standing discrepancy in M1
radiative transitions of and are alleviated
spontaneously. This work also intends to provide an inspection and suggestion
for the possible among the copious higher charmonium-like states.
Particularly, the newly observed X(4160) and X(4350) are found in the
charmonium family mass spectrum as MeV and MeV, which strongly favor the assignments
respectively. The corresponding radiative transitions, leptonic and two-photon
decay widths have been also predicted theoretically for the further
experimental search.Comment: 16 pages,3 figure
Anomalous Heat Conduction and Anomalous Diffusion in Low Dimensional Nanoscale Systems
Thermal transport is an important energy transfer process in nature. Phonon
is the major energy carrier for heat in semiconductor and dielectric materials.
In analogy to Ohm's law for electrical conductivity, Fourier's law is a
fundamental rule of heat transfer in solids. It states that the thermal
conductivity is independent of sample scale and geometry. Although Fourier's
law has received great success in describing macroscopic thermal transport in
the past two hundreds years, its validity in low dimensional systems is still
an open question. Here we give a brief review of the recent developments in
experimental, theoretical and numerical studies of heat transport in low
dimensional systems, include lattice models, nanowires, nanotubes and
graphenes. We will demonstrate that the phonon transports in low dimensional
systems super-diffusively, which leads to a size dependent thermal
conductivity. In other words, Fourier's law is breakdown in low dimensional
structures
Chiral Baryon Fields in the QCD Sum Rule
We study the structure of local baryon fields using the method of QCD sum
rule. We only consider the single baryon fields and calculate their operator
product expansions. We find that the octet baryon fields belonging to the
chiral representations [(3,3*)+(3*,3)] and [(8,1)+(1,8)] and the decuplet
baryon fields belonging to the chiral representations [(3,6)+(6,3)] lead to the
baryon masses which are consistent with the experimental data of ground baryon
masses. We also calculate their decay constants, check our normalizations for
baryon fields in PRD81:054002(2010) and find that they are well-defined.Comment: 12 pages, 6 figure, 1 table, accepted by EPJ
Hidden degree of freedom and critical states in a two-dimensional electron gas in the presence of a random magnetic field
We establish the existence of a hidden degree of freedom and the critical
states of a spinless electron system in a spatially-correlated random magnetic
field with vanishing mean. Whereas the critical states are carried by the
zero-field contours of the field landscape, the hidden degree of freedom is
recognized as being associated with the formation of vortices in these special
contours. It is argued that, as opposed to the coherent backscattering
mechanism of weak localization, a new type of scattering processes in the
contours controls the underlying physics of localization in the random magnetic
field system. In addition, we investigate the role of vortices in governing the
metal-insulator transition and propose a renormalization-group diagram for the
system under study.Comment: 17 pages, 16 figures; Figs. 1, 7, 9, and 10 have been reduced in
quality for e-submissio
Charmless Exclusive Baryonic B Decays
We present a systematical study of two-body and three-body charmless baryonic
B decays. Branching ratios for two-body modes are in general very small,
typically less than , except that \B(B^-\to p \bar\Delta^{--})\sim
1\times 10^{-6}. In general, due to
the large coupling constant for . For three-body modes we
focus on octet baryon final states. The leading three-dominated modes are with a branching ratio of
order for and
for . The penguin-dominated decays with strangeness
in the meson, e.g., and , have appreciable rates and the mass
spectrum peaks at low mass. The penguin-dominated modes containing a strange
baryon, e.g., , have
branching ratios of order . In contrast, the decay
rate of is smaller. We explain why some of
charmless three-body final states in which baryon-antibaryon pair production is
accompanied by a meson have a larger rate than their two-body counterparts:
either the pole diagrams for the former have an anti-triplet bottom baryon
intermediate state, which has a large coupling to the meson and the
nucleon, or they are dominated by the factorizable external -emission
process.Comment: 46 pages and 3 figures, to appear in Phys. Rev. D. Major changes are:
(i) Calculations of two-body baryonic B decays involving a Delta resonance
are modified, and (ii) Penguin-dominated modes B-> Sigma+N(bar)+p are
discusse
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