1,358 research outputs found
A procedure for the change point problem in parametric models based on phi-divergence test-statistics
This paper studies the change point problem for a general parametric,
univariate or multivariate family of distributions. An information theoretic
procedure is developed which is based on general divergence measures for
testing the hypothesis of the existence of a change. For comparing the accuracy
of the new test-statistic a simulation study is performed for the special case
of a univariate discrete model. Finally, the procedure proposed in this paper
is illustrated through a classical change-point example
A New Statistical Image Analysis Approach and Its Application to Hippocampal Morphometry
In this work, we propose a novel and powerful image analysis framework for hippocampal morphometry in early mild cognitive impairment (EMCI), an early prodromal stage of Alzheimer’s disease (AD). We create a hippocampal surface atlas with subfield information, model each hippocampus using the SPHARM technique, and register it to the atlas to extract surface deformation signals. We propose a new alternative to standard random field theory (RFT) and permutation image analysis methods, Statistical Parametric Mapping (SPM) Distribution Analysis or SPM-DA, to perform statistical shape analysis and compare its performance with that of RFT methods on both simulated and real hippocampal surface data. The major strengths of our framework are twofold: (a) SPM-DA provides potentially more powerful algorithms than standard RFT methods for detecting weak signals, and (b) the framework embraces the important hippocampal subfield information for improved biological interpretation. We demonstrate the effectiveness of our method via an application to an AD cohort, where an SPM-DA method detects meaningful hippocampal shape differences in EMCI that are undetected by standard RFT methods
Multi-scalar tachyon potential on non-BPS domain walls
We have considered the multi-scalar and multi-tachyon fields living on a 3d
domain wall embedded in a 5d dimensional Minkowski spacetime. The effective
action for such a domain wall can be found by integrating out the normal modes
as vibrating modes around the domain wall solution of a truncated 5d
supergravity action. The multi-scalar tachyon potential are good enough to
modeling assisted inflation scenario with multi-tachyon fields. The tachyon
condensation are also briefly addressed.Comment: version to appear in JHEP, 18 pages, 3 figure
Key Technical Challenges for the Electric Power Industry and Climate Change
This paper, prepared by the Climate Change Technology Subcommittee, a subcommittee of the Power and Energy Society Energy Development and Power Generation Committee, identifies key technical issues facing the electric power industry, related to global climate change. The technical challenges arise from: 1) impacts on system operating strategies, configuration, and expansion plans of emission-reducing technologies; 2) power infrastructure response to extreme weather events; 3) effects of government policies including an expanded use of renewable and alternative energy technologies; and 4) impacts of market rules on power system operation. Possible lessons from other industries\u27 responses to climate change are explored
Radium ion: A possible candidate for measuring atomic parity violation
Single trapped and laser cooled Radium ion as a possible candidate for
measuring the parity violation induced frequency shift has been discussed here.
Even though the technique to be used is similar to that proposed by Fortson
[1], Radium has its own advantages and disadvantages. The most attractive part
of Radium ion as compared to that of Barium ion is its mass which comes along
with added complexity of instability as well as other issues which are
discussed hereComment: Conference proceedin
New Insights into Properties of Large-N Holographic Thermal QCD at Finite Gauge Coupling at (the Non-Conformal/Next-to) Leading Order in N
In the context of [1]'s string theoretic dual of large-N thermal QCD-like
theories at finite gauge/string coupling (as part of the `MQGP' limit of [2]),
we discuss the following. First, up to LO in N, using the results of [3], we
show that the local T^3 of [2] is the T^2-invariant sLag of [3] in a resolved
conifold. This, together with the results of [4], shows that for a
(predominantly resolved or deformed) resolved warped deformed conifold, the
local T^3 of [2] in the MQGP limit, is the T^2-invariant sLag of [3] justifying
the construction of the delocalized SYZ type IIA mirror of the type IIB
background of [1]. Then, using the prescription of [5], we obtain the
temperature dependence of the thermal (and electrical) conductivity working up
to leading order in N (the number of D3-branes), and upon comparison with [6]
show that the results mimic a 1+1-dimensional Luttinger liquid with impurities.
Further, including sub-leading non-conformal terms in the metric determined by
M (the number of fractional D-branes = the number of colors = 3 in the IR after
the end of a Seiberg duality cascade), by looking at respectively the scalar,
vector and tensor modes of metric perturbations and using [7]'s prescription of
constructing appropriate gauge-invariant perturbations, we obtain respectively
the speed of sound, the diffusion constant and the shear viscosity \eta (and
\eta/s) including the non-conformal O((g_s M^2) (g_s N_f)/N<<1)-corrections,
N_f being the number of flavor D7-branes.Comment: 1+75 pages, LaTeX; Some corrections in Tc-related calculations,
results unchange
A Massive S-duality in 4 dimensions
We reduce the Type IIA supergravity theory with a generalized Scherk-Schwarz
ansatz that exploits the scaling symmetry of the dilaton, the metric and the NS
2-form field. The resulting theory is a new massive, gauged supergravity theory
in four dimensions with a massive 2-form field and a massive 1-form field. We
show that this theory is S-dual to a theory with a massive vector field and a
massive 2-form field, which are dual to the massive 2-form and 1-form fields in
the original theory, respectively. The S-dual theory is shown to arise from a
Scherk-Schwarz reduction of the heterotic theory. Hence we establish a massive,
S-duality type relation between the IIA theory and the heterotic theory in four
dimensions. We also show that the Lagrangian for the new four dimensional
theory can be put in the most general form of a D=4, N=4 gauged Lagrangian
found by Schon and Weidner, in which (part of) the SL(2) group has been gauged.Comment: 20 pages, references adde
On Instanton Effects in F-theory
We revisit the issue of M5-brane instanton corrections to the superpotential
in F-theory compactifications on elliptically fibered Calabi-Yau fourfolds.
Elaborating on concrete geometries, we compare the instanton zero modes for
non-perturbative F-theory models with the zero modes in their perturbative Sen
limit. The fermionic matter zero modes localized on the intersection of the
instanton with the space-time filling D7-branes show up in a geometric way in
F-theory. Methods for their computation are developed and, not surprisingly,
exceptional gauge group structures do appear. Finally, quite intriguing
geometrical aspects of the one-loop determinant are discussed.Comment: 52 pages, 8 figures, 13 tables; v2: extended discussion of matter
zero modes, refs added; v3: sections 3.3 + 4.1 restructure
Non-Perturbative Superpotentials in F-theory and String Duality
We use open-closed string duality between F-theory on K3xK3 and type II
strings on CY manifolds without branes to study non-perturbative
superpotentials in generalized flux compactifications. On the F-theory side we
obtain the full flux potential including D3-instanton contributions and show
that it leads to an explicit and simple realization of the three ingredients of
the KKLT model for stringy dS vacua. The D3-instanton contribution is highly
non-trivial, can be systematically computed including the determinant factors
and demonstrates that a particular flux lifts very effectively zero modes on
the instanton. On the closed string side, we propose a generalization of the
Gukov-Vafa-Witten superpotential for type II strings on generalized CY
manifolds, depending on all moduli multiplets.Comment: 49 pages, harvmac, 1 figure; references & figures adde
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