13,451 research outputs found
The Likelihood Ratio Test and Full Bayesian Significance Test under small sample sizes for contingency tables
Hypothesis testing in contingency tables is usually based on asymptotic
results, thereby restricting its proper use to large samples. To study these
tests in small samples, we consider the likelihood ratio test and define an
accurate index, the P-value, for the celebrated hypotheses of homogeneity,
independence, and Hardy-Weinberg equilibrium. The aim is to understand the use
of the asymptotic results of the frequentist Likelihood Ratio Test and the
Bayesian FBST -- Full Bayesian Significance Test -- under small-sample
scenarios. The proposed exact P-value is used as a benchmark to understand the
other indices. We perform analysis in different scenarios, considering
different sample sizes and different table dimensions. The exact Fisher test
for tables that drastically reduces the sample space is also
discussed. The main message of this paper is that all indices have very similar
behavior, so the tests based on asymptotic results are very good to be used in
any circumstance, even with small sample sizes
Constraints on Supersymmetric Theories from
In the absence of any additional assumption it is natural to conjecture that
sizeable flavour-mixing mass entries, , may appear in the mass
matrices of the scalars of the MSSM, i.e. . This flavour
violation can still be reconciled with the experiment if the gaugino mass,
, is large enough, leading to a {\em gaugino dominance} framework
(i.e. ), which permits a remarkably model--independent
analysis. We study this possibility focussing our attention on the
decay. In this way we obtain very strong and general
constraints, in particular \frac{M_{1/2}^2}{\Delta m}\simgt 34\ {\rm TeV}. On
the other hand, we show that our analysis and results remain valid for values
of much larger than , namely for \frac{\Delta
m^2}{m^2}\simgt \frac{m^2} {10\ {\rm TeV^2}}, thus extending enormously their
scope of application. Finally, we discuss the implications for superstring
scenarios.Comment: 12 pages, Latex, 5 figures as uuencoded compressed postscript files,
uses psfig.st
Flavor Symmetries and The Problem of Squark Degeneracy
If supersymmetry exists at low energies, it is necessary to understand why
the squark spectrum exhibits sufficient degeneracy to suppress flavor changing
neutral currents. In this note, we point out that gauged horizontal symmetries
can yield realistic quark mass matrices, while at the same time giving just
barely enough squark degeneracy to account for neutral -meson phenomenology.
This approach suggests likely patterns for squark masses, and indicates that
there could be significant supersymmetric contributions to and
mixing and CP violation in the and systems.Comment: preprint SCIPP 93/04,SLAC-PUB-6147, 14 pages, 4 tables included; uses
macro package TABLES.TEX and phyzzx forma
Reductive decarboxylation of bicyclic prolinic systems: a new approach to the enantioselective synthesis of the Geissman-Waiss lactone. X-ray structure determination of a key lactone intermediate
Two concise and enantioselective syntheses of the necine base precursors (1R,5R)-N-Cbz and N-Boc-2-oxa-6-azabicyclo[3.3.0]octan-3-ones (Geissman-Waiss lactones) were carried out from two enantiomerically pure endocyclic five-membered enecarbamates with overall yields of 23% and 26%, respectively. The synthetic strategy made use of a highly effective and stereoselective [2+2]cycloaddition of enantiomerically pure endocyclic enecarbamates with dichloroketene, as well as an efficient decarboxylation step of a bicyclic alpha-amino acid employing Boger's acyl selenide protocol employing tributyltin hydride. Interesting aspects concerning the regiochemical outcome of Baeyer-Villiger oxidations of bicyclic cyclobutanones are also reported, in which the usual stereoelectronic bias of Baeyer-Villiger oxidation seems to be counterbalanced by steric effects on the putative Criegee intermediate.Duas sÃnteses do conhecido precursor de bases necÃnicas, (1R,5R)-N-Cbz e N-Boc 2-oxa-6-azabiciclo[3.3.0]octan-3-onas (lactonas de Geissman-Waiss) foram realizadas com rendimentos globais de 23% e 26%, em seis e cinco etapas respectivamente, a partir de enecarbamatos endocÃclicos de cinco membros enantiomericamente puros. A estratégia sintética adotada está fundamentada em uma reação de cicloadição [2+2] eficiente e altamente estereosseletiva de enecarbamatos de cinco membros com diclorocetenos, assim como em uma eficaz descarboxilação de alfa-amino ácidos bicÃclicos pelo método de Boger, que utiliza a redução de selenetos de acila por hidretos de estanho. Aspectos relativos a regiosseletividade da reação de oxidação de azabiciclo ciclobutanonas pelo método de Baeyer-Villiger são também descritos, com destaque para um potencial controle regioquÃmico advindo de aspectos estéreos em contraposição a aspectos estereoeletrônicos.2738Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento CientÃfico e Tecnológico (CNPq
Strike-slip faults in the south Haouz (Calcareous Dorsal, Internal Rif, N of Tetouan, Maroc). Comparison with the Betics (Spain)
4 páginas, 4 figuras.-- Trabajo presentado en la 41ª Sesión CientÃfica, Barcelona, 2006.Different sets of strike-slip faults of the Haouz Mountains (from Tetouan to the strait of Gibraltar) deform
the tectonic slices of the Calcareous Dorsal there present. In this paper we study those faults at the
southern part of the Haouz. Three fault formation stages can be distinguished and correspond to the
progressive s1 rotation during the Neogene from a near E-W position to approximately N-S, in a progressive
anticlockwise rotation. The faults and other related structures are compared with similar ones existing in
the Betic Cordillera, in equivalent areas of the arc of Gibraltar.Este artÃculo es una contribución del
grupo de Travaux de Recherches de l’Unité
Risques Géologiques et Télédetection, 2006,
Rabat y de los proyectos BTE2001-5230-E,
CGL200401636/BTE, CGL2004-03333/
BTE, y el grupo RNM 217 de la Junta de
AndalucÃa.Peer reviewe
On non-perturbative corrections to the Kahler potential
We present the results of a detailed investigation into the consequences of
adding specific string motivated non-perturbative corrections to the usual tree
level Kahler potential in dilaton dominated scenarios. The success of the model
is judged through our ability to obtain a realistic VEV for the dilaton < Re S
> ~ 2, corresponding to the true minima of the scalar potential and being
associated with a reasonable value for the SUSY breaking scale via the
gravitino mass. The status of the so-called moduli problem is also reviewed in
each of the ansatze studied. Those include previous proposals made in the
context of both the chiral and the linear multiplet formalisms to describe
gaugino condensation, and a new ansatz which shows explicitly the equivalence
between the two.Comment: 11 pages, LaTex, uses psfig.sty with 4 figure
A non-perturbative renormalization group study of the stochastic Navier--Stokes equation
We study the renormalization group flow of the average action of the
stochastic Navier--Stokes equation with power-law forcing. Using Galilean
invariance we introduce a non-perturbative approximation adapted to the zero
frequency sector of the theory in the parametric range of the H\"older exponent
of the forcing where real-space local interactions are
relevant. In any spatial dimension , we observe the convergence of the
resulting renormalization group flow to a unique fixed point which yields a
kinetic energy spectrum scaling in agreement with canonical dimension analysis.
Kolmogorov's -5/3 law is, thus, recovered for as also predicted
by perturbative renormalization. At variance with the perturbative prediction,
the -5/3 law emerges in the presence of a \emph{saturation} in the
-dependence of the scaling dimension of the eddy diffusivity at
when, according to perturbative renormalization, the velocity
field becomes infra-red relevant.Comment: RevTeX, 18 pages, 5 figures. Minor changes and new discussion
Isotropic and Anisotropic Bouncing Cosmologies in Palatini Gravity
We study isotropic and anisotropic (Bianchi I) cosmologies in Palatini
and theories of gravity and consider the existence
of non-singular bouncing solutions in the early universe. We find that all
models with isotropic bouncing solutions develop shear singularities in
the anisotropic case. On the contrary, the simple quadratic model exhibits regular bouncing solutions in both
isotropic and anisotropic cases for a wide range of equations of state,
including dust (for ) and radiation (for arbitrary ). It thus
represents a purely gravitational solution to the big bang singularity and
anisotropy problems of general relativity without the need for exotic ()
sources of matter/energy.Comment: 25 pages, 7 figure
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