334 research outputs found
Finite size corrections to scaling in high Reynolds number turbulence
We study analytically and numerically the corrections to scaling in
turbulence which arise due to the finite ratio of the outer scale of
turbulence to the viscous scale , i.e., they are due to finite size
effects as anisotropic forcing or boundary conditions at large scales. We find
that the deviations \dzm from the classical Kolmogorov scaling of the velocity moments \langle |\u(\k)|^m\rangle \propto k^{-\zeta_m}
decrease like . Our numerics employ a
reduced wave vector set approximation for which the small scale structures are
not fully resolved. Within this approximation we do not find independent
anomalous scaling within the inertial subrange. If anomalous scaling in the
inertial subrange can be verified in the large limit, this supports the
suggestion that small scale structures should be responsible, originating from
viscosity either in the bulk (vortex tubes or sheets) or from the boundary
layers (plumes or swirls)
Examples of the Zeroth Theorem of the History of Physics
The zeroth theorem of the history of science (enunciated by E. P. Fischer)
and widely known in the mathematics community as Arnol'd's Principle (decreed
by M. V. Berry), states that a discovery (rule, regularity, insight) named
after someone (often) did not originate with that person. I present five
examples from physics: the Lorentz condition defining the Lorentz gauge of the
electromagnetic potentials; the Dirac delta function (x); the Schumann
resonances of the earth-ionosphere cavity; the Weizsacker-Williams method of
virtual quanta; the BMT equation of spin dynamics. I give illustrated thumbnail
sketches of both the true and reputed discoverers and quote from their
"discovery" publications.Comment: 36 pages, 8 figures. Small revisions, added material and references -
Arnol'd's law, Emil Wiechert. Submitted to Am. J. Phy
Mass splittings of nuclear isotopes in chiral soliton approach
The differences of the masses of nuclear isotopes with atomic numbers between
\~10 and ~30 can be described within the chiral soliton approach in
satisfactory agreement with data. Rescaling of the model is necessary for this
purpose - decrease of the Skyrme constant by about 30%, providing the "nuclear
variant" of the model. The asymmetric term in Weizsaecker-Bethe- Bacher mass
formula for nuclei can be obtained as the isospin dependent quantum correction
to the nucleus energy. Some predictions for the binding energies of neutron
rich nuclides are made in this way, from, e.g. Be-16 and B-19 to Ne-31 and
Na-32. Neutron rich nuclides with high values of isospin are unstable relative
to strong interactions. The SK4 (Skyrme) variant of the model, as well as SK6
variant (6-th order term in chiral derivatives in the lagrangian as solitons
stabilizer) are considered, and the rational map approximation is used to
describe multiskyrmions.Comment: 16 pages, 10 tables, 2 figures. Figures are added and few misprints
are removed. Submitted to Phys. Atom. Nucl. (Yad. Fiz.
Neutron production by cosmic-ray muons at shallow depth
The yield of neutrons produced by cosmic ray muons at a shallow depth of 32
meters of water equivalent has been measured. The Palo Verde neutrino detector,
containing 11.3 tons of Gd loaded liquid scintillator and 3.5 tons of acrylic
served as a target. The rate of one and two neutron captures was determined.
Modeling the neutron capture efficiency allowed us to deduce the total yield of
neutrons neutrons per muon
and g/cm. This yield is consistent with previous measurements at similar
depths.Comment: 12 pages, 3 figure
J/psi plus prompt-photon associated production in two-photon collisions at next-to-leading order
We calculate the cross section of J/psi plus prompt-photon inclusive
production in gamma gamma collisions at next-to-leading order within the
factorization formalism of nonrelativistic quantum chromodynamics (NRQCD)
focusing on direct photoproduction. Apart from direct J/psi production, we also
include the feed-down from directly-produced chi_{cJ} and psi' mesons. We
discuss the analytical calculation, in particular the treatment of the various
types of singularities and the NRQCD operator renormalization, in some detail.
We present theoretical predictions for the future e^+e^- linear collider TESLA,
taking into account both brems- and beamstrahlung.Comment: 31 pages, 9 figure
DC and AC Josephson effects with superfluid Fermi atoms across a Feshbach resonance
We show that both DC and AC Josephson effects with superfluid Fermi atoms in
the BCS-BEC crossover can be described at zero temperature by a nonlinear
Schrodinger equation (NLSE). By comparing our NLSE with mean-field extended BCS
calculations, we find that the NLSE is reliable in the BEC side of the
crossover up to the unitarity limit. The NLSE can be used for weakly-linked
atomic superfluids also in the BCS side of the crossover by taking the
tunneling energy as a phenomenological parameter.Comment: 8 pages, 4 figures, presented at the Scientific Seminar on Physics of
Cold Trapped Atoms, 17th International Laser Physics Workshop (Trondheim,
June 30 - July 4, 2008
SUSY signals at HERA in the no-scale flipped SU(5) supergravity model
Sparticle production and detection at HERA are studied within the recently
proposed no-scale flipped supergravity model. Among the various
reaction channels that could lead to sparticle production at HERA, only the
following are within its limit of sensitivity in this model: , where are the
two lightest neutralinos and is the lightest chargino. We study the
elastic and deep-inelastic contributions to the cross sections using the
Weizs\"acker-Williams approximation. We find that the most promising
supersymmetric production channel is right-handed selectron ()
plus first neutralino (), with one hard electron and missing energy
signature. The channel leads to comparable rates but also
allows jet final states. A right-handedly polarized electron beam at HERA would
shut off the latter channel and allow preferentially the former one. With an
integrated luminosity of {\cal L}=100\ipb, HERA can extend the present LEPI
lower bounds on by
\approx25\GeV, while {\cal L}=1000\ipb will make HERA competitive with
LEPII. We also show that the Leading Proton Spectrometer (LPS) at HERA is an
excellent supersymmetry detector which can provide indirect information about
the sparticle masses by measuring the leading proton longitudinal momentum
distribution.Comment: 11 pages, 8 figures (available upon request as uuencoded file or
separate ps files), tex (harvmac) CTP-TAMU-15/93, CERN/LAA/93-1
Turbulent Control of the Star Formation Efficiency
Supersonic turbulence plays a dual role in molecular clouds: On one hand, it
contributes to the global support of the clouds, while on the other it promotes
the formation of small-scale density fluctuations, identifiable with clumps and
cores. Within these, the local Jeans length \Ljc is reduced, and collapse
ensues if \Ljc becomes smaller than the clump size and the magnetic support
is insufficient (i.e., the core is ``magnetically supercritical''); otherwise,
the clumps do not collapse and are expected to re-expand and disperse on a few
free-fall times. This case may correspond to a fraction of the observed
starless cores. The star formation efficiency (SFE, the fraction of the cloud's
mass that ends up in collapsed objects) is smaller than unity because the mass
contained in collapsing clumps is smaller than the total cloud mass. However,
in non-magnetic numerical simulations with realistic Mach numbers and
turbulence driving scales, the SFE is still larger than observational
estimates. The presence of a magnetic field, even if magnetically
supercritical, appears to further reduce the SFE, but by reducing the
probability of core formation rather than by delaying the collapse of
individual cores, as was formerly thought. Precise quantification of these
effects as a function of global cloud parameters is still needed.Comment: Invited review for the conference "IMF@50: the Initial Mass Function
50 Years Later", to be published by Kluwer Academic Publishers, eds. E.
Corbelli, F. Palla, and H. Zinnecke
Virtual Photon Strucutre Functions and the Parton Content of the Electron
We point out that in processes involving the parton content of the photon the
usual effective photon approximation should be modified. The reason is that the
parton content of virtual photons is logarithmically suppressed compared to
real photons. We describe this suppression using several simple, physically
motivated ans\"atze. Although the parton content of the electron in general no
longer factorizes into an electron flux function and a photon structure
function, it can still be expressed as a single integral. Numerical examples
are given for the \eplem\ collider TRISTAN as well as the collider HERA.Comment: 16 pages and 3 figures (available from DREES@WSICPHEN as topdraw or
PS files); LaTeX with equation.sty; MAD/PH/819, BU 94-0
Evidence for Colour-Octet Mechanism from CERN LEP2 gamma gamma -> J/psi + X Data
We present theoretical predictions for the transverse-momentum distribution
of J/psi mesons promptly produced in gamma gamma collisions within the
factorization formalism of nonrelativistic quantum chromodynamics, including
the contributions from both direct and resolved photons, and we perform a
conservative error analysis. The fraction of J/psi mesons from decays of
bottom-flavoured hadrons is estimated to be negligibly small. New data taken by
the DELPHI Collaboration at LEP2 nicely confirm these predictions, while they
disfavour those obtained within the traditional colour-singlet model.Comment: 11 pages (Latex), 3 figures (Postscript); updated experimental data
included, references added, accepted for publication in Phys. Rev. Let
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