22,312 research outputs found
Initial Shock Waves for Explosive Nucleosynthesis in Type II Supernova
We have performed 1-dimensional calculations for explosive nucleosynthesis in
collapse-driven supernova and investigated its sensitivity to the initial form
of the shock wave. We have found the tendency that the peak temperature becomes
higher around the mass cut if the input energy is injected more in the form of
kinetic energy rather than internal energy. Then, the mass cut becomes larger,
and, as a result, neutron-rich matter is less included in the ejecta; this is
favorable for producing the observational data compared with a previous model.
Our results imply that the standard method to treat various processes for
stellar evolution, such as convection and electron capture during the silicon
burning stage, are still compatible with the calculation of explosive
nucleosynthesis.Comment: 20 pages, 6 figures, LaTe
Effect of low-lying fermion modes in the -regime of QCD
We investigate the effects of low-lying fermion eigenmodes on the QCD
partition function in the -regime. The fermion determinant is
approximated by a truncated product of low-lying eigenvalues of the
overlap-Dirac operator. With two flavors of dynamical quarks, we observe that
the lattice results for the lowest eigenvalue distribution, eigenvalue sum
rules and partition function reproduce the analytic predictions made by
Leutwyler and Smilga, which strongly depend on the topological charge of the
background gauge configuration. The value of chiral condensate extracted from
these measurements are consistent with each other. For one dynamical quark
flavor, on the other hand, we find an apparent disagreement among different
determinations of the chiral condensate, which may suggest the failure of the
-expansion in the absence of massless Nambu-Goldstone boson.Comment: 23 pages, 9 figure
Photo-induced precession of magnetization in ferromagnetic (Ga,Mn)As
Precession of magnetization induced by pulsed optical excitation is observed
in a ferromagnetic semiconductor (Ga,Mn)As by time-resolved magneto-optical
measurements. It appears as complicated oscillations of polarization plane of
linearly-polarized probe pulses, but is reproduced by gyromagnetic theory
incorporating an impulsive change in an effective magnetic field due to changes
in magnetic anisotropy. It is inferred from the shape of the impulse that the
changes in anisotropy result from non-equilibrium carrier population: cooling
of hot photo-carriers and subsequent annihilation of photo-carriers
New Approach for Evaluating Incomplete and Complete Fusion Cross Sections with Continuum-Discretized Coupled-Channels Method
We propose a new method for evaluating incomplete and complete fusion cross
sections separately using the Continuum-Discretized Coupled-Channels method.
This method is applied to analysis of the deuteron induced reaction on a 7Li
target up to 50 MeV of the deuteron incident energy. Effects of deuteron
breakup on this reaction are explicitly taken into account. Results of the
method are compared with those of the Glauber model, and the difference between
the two is discussed. It is found that the energy dependence of the incomplete
fusion cross sections obtained by the present calculation is almost the same as
that obtained by the Glauber model, while for the complete fusion cross
section, the two models give markedly different energy dependence. We show also
that a prescription for evaluating incomplete fusion cross sections proposed in
a previous study gives much smaller result than an experimental value.Comment: 10 pages, 5 figure
Duality Cascade and Oblique Phases in Non-Commutative Open String Theory
We investigate the complete phase diagram of the decoupled world-sheet theory
of (P,Q) strings. These theories include 1+1 dimensional super Yang-Mills
theory and non-commutative open string theory. We find that the system exhibits
a rich fractal phase structure, including a cascade of alternating
supergravity, gauge theory, and matrix string theory phases. The cascade
proceeds via a series of SL(2,Z) S-duality transformations, and depends
sensitively on P and Q. In particular, we find that the system may undergo
multiple Hagedorn-type transitions as the temperature is varied.Comment: 21 pages, 4 figures, references adde
Finite volume QCD at fixed topological charge
In finite volume the partition function of QCD with a given is a sum
of different topological sectors with a weight primarily determined by the
topological susceptibility. If a physical observable is evaluated only in a
fixed topological sector, the result deviates from the true expectation value
by an amount proportional to the inverse space-time volume 1/V. Using the
saddle point expansion, we derive formulas to express the correction due to the
fixed topological charge in terms of a 1/V expansion. Applying this formula, we
propose a class of methods to determine the topological susceptibility in QCD
from various correlation functions calculated in a fixed topological sector.Comment: 22pages, references adde
From random walks to distances on unweighted graphs
Large unweighted directed graphs are commonly used to capture relations
between entities. A fundamental problem in the analysis of such networks is to
properly define the similarity or dissimilarity between any two vertices.
Despite the significance of this problem, statistical characterization of the
proposed metrics has been limited. We introduce and develop a class of
techniques for analyzing random walks on graphs using stochastic calculus.
Using these techniques we generalize results on the degeneracy of hitting times
and analyze a metric based on the Laplace transformed hitting time (LTHT). The
metric serves as a natural, provably well-behaved alternative to the expected
hitting time. We establish a general correspondence between hitting times of
the Brownian motion and analogous hitting times on the graph. We show that the
LTHT is consistent with respect to the underlying metric of a geometric graph,
preserves clustering tendency, and remains robust against random addition of
non-geometric edges. Tests on simulated and real-world data show that the LTHT
matches theoretical predictions and outperforms alternatives.Comment: To appear in NIPS 201
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