11,392 research outputs found
Experiments on wave turbulence : the evolution and growth of second sound acoustic turbulence in superfluid 4He confirm self-similarity.
We report our experiments on the formation of second sound acoustic turbulence in superfluid 4He. The initial growth in spectral amplitude follows power laws that steepen rapidly with increasing harmonic number n, corresponding to a propagating front in frequency space. The lower growth exponents agree well with analytic predictions and numerical modeling. The observed increase in the formation delay with n validates the concept of selfsimilarity in the growth of wave turbulence
Threshold Photo/Electro Pion Production - Working Group Summary
We summarize the pertinent experimental and theoretical developments in the
field of pion photo- and electroproduction in the threshold region. We discuss
which experiments and which calculations should be done/performed in the
future.Comment: plain TeX (macro included), 6pp, summary talk presented at the
workshop on "Chiral Dynamics: Theory and Experiments", MIT, July 25-29, 199
Evidence for prelocalization of cytoplasmic factors affecting gene activation in early embryogenesis
Differentiation begins early in embryogenesis as different genes become active in different cells. Within the closed system of the early embryo, equal genomes thus direct the creation of diverse cell types. Though the nuclei of these cells contain complete copies of the same genome,(1,2) the nucleoplasmic and cytoplasmic environments of these genomes are not the same, as a result of the distribution of cleavage nuclei into diverse areas of egg cytoplasm early in the cleavage process. In some cases the fate of these nuclei, i.e., the type of differentiated cell to which they or their descendants give rise, has been seen to depend on the area of cytoplasm in which they come to lie
Scotland, Catalonia and the “right” to self-determination: a comment suggested by Kathryn Crameri’s “Do Catalans Have the Right to Decide?
No abstract available
Charged Higgs phenomenology in the flipped two Higgs doublet model
We study the phenomenology of the charged Higgs boson in the "flipped" two
Higgs doublet model, in which one doublet gives mass to up-type quarks and
charged leptons and the other gives mass to down-type quarks. We present the
charged Higgs branching ratios and summarize the indirect constraints. We
extrapolate existing LEP searches for H+H- and Tevatron searches for t tbar
with t --> H+ b into the flipped model and extract constraints on MH+ and the
parameter tan(beta). We finish by reviewing existing LHC charged Higgs searches
and suggest that the LHC reach in this model could be extended for charged
Higgs masses below the tb threshold by considering t tbar with t --> H+ b and
H+ --> q qbar, as has been used in Tevatron searches.Comment: 23 pages, 7 figures. V2: added refs on H+W- associated productio
Wave Function of a Brane-like Universe
Within the mini-superspace model, brane-like cosmology means performing the
variation with respect to the embedding (Minkowski) time before fixing
the cosmic (Einstein) time . The departure from Einstein limit is
parameterized by the 'energy' conjugate to , and characterized by a
classically disconnected Embryonic epoch. In contrast with canonical quantum
gravity, the wave-function of the brane-like Universe is (i) -dependent,
and (ii) vanishes at the Big Bang. Hartle-Hawking and Linde proposals dictate
discrete 'energy' levels, whereas Vilenkin proposal resembles -particle
disintegration.Comment: Revtex, 4 twocolumn pages, 3 eps figures (accepted for publication in
Class. Quan. Grav.
Stringent limitations on reductive perturbation studies of nonplanar acoustic solitons in plasmas
More than fifty years ago, the Korteweg-de Vries equation was shown to describe not only solitary surface waves on shallow water, but also nonlinear ion-acoustic waves. Because of the algorithmic ease of using reductive perturbation theory, intensive research followed on a wide range of wave types. Soon, the formalism was extended to nonplanar modes by introducing a stretching designed to accommodate spherically and cylindrically symmetric ion-acoustic waves. Over the last two decades many authors followed this approach, but almost all have ignored the severe restrictions in parameter space imposed by the Ansatz. In addition, for other steps in the formalism, the justification is often not spelled out, leading to effects that are physically undesirable or ambiguous. Hence, there is a need to critically assess this approach to nonplanar modes and to use it with the utmost care, respecting the restrictions on its validity. Only inward propagation may be meaningfully studied and respect for weak nonlinearities of at most 1/10 implies that one cannot get closer to the axis or centre of symmetry than about 30 Debye lengths. Thus, one is in a regime where the modes are quasi-planar and not particularly interesting. Most papers disregard these constraints and hence reach questionable conclusions
The Gross-Pitaevskii Equation for Bose Particles in a Double Well Potential: Two Mode Models and Beyond
There have been many discussions of two-mode models for Bose condensates in a
double well potential, but few cases in which parameters for these models have
been calculated for realistic situations. Recent experiments lead us to use the
Gross-Pitaevskii equation to obtain optimum two-mode parameters. We find that
by using the lowest symmetric and antisymmetric wavefunctions, it is possible
to derive equations for a more exact two-mode model that provides for a
variable tunneling rate depending on the instantaneous values of the number of
atoms and phase differences. Especially for larger values of the nonlinear
interaction term and larger barrier heights, results from this model produce
better agreement with numerical solutions of the time-dependent
Gross-Pitaevskii equation in 1D and 3D, as compared with previous models with
constant tunneling, and better agreement with experimental results for the
tunneling oscillation frequency [Albiez et al., cond-mat/0411757]. We also show
how this approach can be used to obtain modified equations for a second
quantized version of the Bose double well problem.Comment: RevTeX, 14 pages, 14 figure
Interpretations of the NuTeV
We summarize theoretical explanations of the three discrepancy
between measured by NuTeV and predicted by the Standard Model
global fit. Possible new physics explanations ({\it e.g.} an unmized ) are
not compelling. The discrepancy would be reduced by a positive momentum
asymmetry in the strange sea; present experimental estimates of are
unreliable or incomplete. Upgrading the NuTeV analysis to NLO would alleviate
concerns that the discrepancy is a QCD effect.Comment: (proceedings for the NuFact'02 Workshop); reference and footnote
added, following the NuTeV proceeding
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