32,217 research outputs found
Acceptance dependence of fluctuation measures near the QCD critical point
We argue that a crucial determinant of the acceptance dependence of
fluctuation measures in heavy-ion collisions is the range of correlations in
the momentum space, e.g., in rapidity, . The value of
for critical thermal fluctuations is determined by
the thermal rapidity spread of the particles at freezeout, and has little to do
with position space correlations, even near the critical point where the
spatial correlation length becomes as large as fm (this is in
contrast to the magnitudes of the cumulants, which are sensitive to ).
When the acceptance window is large, , the
cumulants of a given particle multiplicity, , scale linearly with
, or mean multiplicity in acceptance, , and
cumulant ratios are acceptance independent. While in the opposite regime,
, the factorial cumulants, ,
scale as , or . We demonstrate this general
behavior quantitatively in a model for critical point fluctuations, which also
shows that the dependence on transverse momentum acceptance is very
significant. We conclude that extension of rapidity coverage proposed by STAR
should significantly increase the magnitude of the critical point fluctuation
signatures.Comment: 9 pages, 4 figures, references adde
Binary matrices of optimal autocorrelations as alignment marks
We define a new class of binary matrices by maximizing the peak-sidelobe
distances in the aperiodic autocorrelations. These matrices can be used as
robust position marks for in-plane spatial alignment. The optimal square
matrices of dimensions up to 7 by 7 and optimal diagonally-symmetric matrices
of 8 by 8 and 9 by 9 were found by exhaustive searches.Comment: 8 pages, 6 figures and 1 tabl
Discrete gravity and and its continuum limit
Recently Gambini and Pullin proposed a new consistent discrete approach to
quantum gravity and applied it to cosmological models. One remarkable result of
this approach is that the cosmological singularity can be avoided in a general
fashion. However, whether the continuum limit of such discretized theories
exists is model dependent. In the case of massless scalar field coupled to
gravity with , the continuum limit can only be achieved by fine
tuning the recurrence constant. We regard this failure as the implication that
cosmological constant should vary with time. For this reason we replace the
massless scalar field by Chaplygin gas which may contribute an effective
cosmological constant term with the evolution of the universe. It turns out
that the continuum limit can be reached in this case indeed.Comment: 16 pages,revised version published in MPL
Threshold Regression for Survival Analysis: Modeling Event Times by a Stochastic Process Reaching a Boundary
Many researchers have investigated first hitting times as models for survival
data. First hitting times arise naturally in many types of stochastic
processes, ranging from Wiener processes to Markov chains. In a survival
context, the state of the underlying process represents the strength of an item
or the health of an individual. The item fails or the individual experiences a
clinical endpoint when the process reaches an adverse threshold state for the
first time. The time scale can be calendar time or some other operational
measure of degradation or disease progression. In many applications, the
process is latent (i.e., unobservable). Threshold regression refers to
first-hitting-time models with regression structures that accommodate covariate
data. The parameters of the process, threshold state and time scale may depend
on the covariates. This paper reviews aspects of this topic and discusses
fruitful avenues for future research.Comment: Published at http://dx.doi.org/10.1214/088342306000000330 in the
Statistical Science (http://www.imstat.org/sts/) by the Institute of
Mathematical Statistics (http://www.imstat.org
P-wave diffusion in fluid-saturated medium
This paper considers the propagating P-waves in the fluid-saturated mediums that are categorized to fall into two distinct groups: insoluble and soluble mediums. P-waves are introduced with slowness in accordance to Snell Law and are shown to relate to the medium displacement and wave diffusion. Consequently, the results bear out that the propagating P-waves in the soluble medium share similar diffusive characteristic as of insoluble medium. Nonetheless, our study on fluid density in the mediums show that high density fluid promotes diffusive characteristic whiles low density fluid endorses non-diffusive P-wav
Analysis of the transient calibration of heat flux sensors: One dimensional case
The effect of transient heat flux on heat flux sensor response and calibration is analyzed. A one dimensional case was studied in order to elucidate the key parameters and trends for the problem. It has the added advantage that the solutions to the governing equations can be obtained by analytic means. The analytical results obtained to date indicate that the transient response of a heat flux sensor depends on the thermal boundary conditions, the geometry and the thermal properties of the sensor. In particular it was shown that if the thermal diffusivity of the sensor is small, then the transient behavior must be taken into account
Non-vanishing Heterotic Superpotentials on Elliptic Fibrations
We present models of heterotic compactification on Calabi-Yau threefolds and
compute the non-perturbative superpotential for vector bundle moduli. The key
feature of these models is that the threefolds, which are elliptically fibered
over del Pezzo surfaces, have homology classes with a unique holomorphic,
isolated genus-zero curve. Using the spectral cover construction, we present
vector bundles for which we can explicitly calculate the Pfaffians associated
with string instantons on these curves. These are shown to be non-zero, thus
leading to a non-vanishing superpotential in the 4D effective action. We
discuss, in detail, why such compactifications avoid the Beasley-Witten residue
theorem.Comment: 1 + 23 page
Competing Orders in a Dipolar Bose-Fermi Mixture on a Square Optical Lattice: Mean-Field Perspective
We consider a mixture of a two-component Fermi gas and a single-component
dipolar Bose gas in a square optical lattice and reduce it into an effective
Fermi system where the Fermi-Fermi interaction includes the attractive
interaction induced by the phonons of a uniform dipolar Bose-Einstein
condensate. Focusing on this effective Fermi system in the parameter regime
that preserves the symmetry of , the point group of a square, we explore,
within the Hartree-Fock-Bogoliubov mean-field theory, the phase competition
among density wave orderings and superfluid pairings. We construct the matrix
representation of the linearized gap equation in the irreducible
representations of . We show that in the weak coupling regime, each matrix
element, which is a four-dimensional (4D) integral in momentum space, can be
put in a separable form involving a 1D integral, which is only a function of
temperature and the chemical potential, and a pairing-specific "effective"
interaction, which is an analytical function of the parameters that
characterize the Fermi-Fermi interactions in our system. We analyze the
critical temperatures of various competing orders as functions of different
system parameters in both the absence and presence of the dipolar interaction.
We find that close to half filling, the d_{x^{2}-y^{2}}-wave pairing with a
critical temperature in the order of a fraction of Fermi energy (at half
filling) may dominate all other phases, and at a higher filling factor, the
p-wave pairing with a critical temperature in the order of a hundredth of Fermi
energy may emerge as a winner. We find that tuning a dipolar interaction can
dramatically enhance the pairings with - and g-wave symmetries but not
enough for them to dominate other competing phases.Comment: 18 pages, 9 figure
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