798 research outputs found
Dynamical symmetry of isobaric analog 0+ states in medium mass nuclei
An algebraic sp(4) shell model is introduced to achieve a deeper
understanding and interpretation of the properties of pairing-governed 0+
states in medium mass atomic nuclei. The theory, which embodies the simplicity
of a dynamical symmetry approach to nuclear structure, is shown to reproduce
the excitation spectra and fine structure effects driven by proton-neutron
interactions and isovector pairing correlations across a broad range of nuclei.Comment: 7 pages, 5 figure
Particle Aggregation in a turbulent Keplerian flow
In the problem of planetary formation one seeks a mechanism to gather small
solid particles together into larger accumulations of solid matter. Here we
describe a scenario in which turbulence mediates this process by aggregating
particles into anticyclonic regions. If, as our simulations suggest,
anticyclonic vortices form as long-lived coherent structures, the process
becomes more powerful because such vortices trap particles effectively. Even if
the turbulence is decaying, following the upheaval that formed the disk, there
is enough time to make the dust distribution quite lumpy.Comment: 16 pages, 9 figure
Realizations of Causal Manifolds by Quantum Fields
Quantum mechanical operators and quantum fields are interpreted as
realizations of timespace manifolds. Such causal manifolds are parametrized by
the classes of the positive unitary operations in all complex operations, i.e.
by the homogenous spaces \D(n)=\GL(\C^n_\R)/\U(n) with for mechanics
and for relativistic fields. The rank gives the number of both the
discrete and continuous invariants used in the harmonic analysis, i.e. two
characteristic masses in the relativistic case. 'Canonical' field theories with
the familiar divergencies are inappropriate realizations of the real
4-dimensional causal manifold \D(2). Faithful timespace realizations do not
lead to divergencies. In general they are reducible, but nondecomposable - in
addition to representations with eigenvectors (states, particle) they
incorporate principal vectors without a particle (eigenvector) basis as
exemplified by the Coulomb field.Comment: 36 pages, latex, macros include
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
Glueball Production in Peripheral Heavy-Ion Collisions
The method of equivalent quanta is applied both to photon-photon and, by
analogy, to double pomeron exchange in heavy-ion collisions. This
Weizs\"acker-Williams approach is used to calculate production cross sections
for the glueball candidate meson via photon-photon and
pomeron-pomeron fusion in peripheral heavy-ion collisions at both RHIC and LHC
energies. The impact-parameter dependence for total and elastic cross sections
are presented, and are compared to results for proton-proton collisions.Comment: 15 pages, 6 figure
Nuclear masses set bounds on quantum chaos
It has been suggested that chaotic motion inside the nucleus may
significantly limit the accuracy with which nuclear masses can be calculated.
Using a power spectrum analysis we show that the inclusion of additional
physical contributions in mass calculations, through many-body interactions or
local information, removes the chaotic signal in the discrepancies between
calculated and measured masses. Furthermore, a systematic application of global
mass formulas and of a set of relationships among neighboring nuclei to more
than 2000 nuclear masses allows to set an unambiguous upper bound for the
average errors in calculated masses which turn out to be almost an order of
magnitude smaller than estimated chaotic components.Comment: 4 pages, Accepted for publication in Physical Review Letter
Financial Transaction Tax: Small is Beautiful
The case for taxing financial transactions merely to raise more revenues from the financial sector is not particularly strong. Better alternatives to tax the financial sector are likely to be available. However, a tax on financial transactions could be justified in order to limit socially
undesirable transactions when more direct means of doing so are unavailable for political or
practical reasons. Some financial transactions are indeed likely to do more harm than good,
especially when they contribute to the systemic risk of the financial system. However, such a
financial transaction tax should be very small, much smaller than the negative externalities in
question, because it is a blunt instrument that also drives out socially useful transactions.
There is a case for taxing over-the-counter derivative transactions at a somewhat higher rate
than exchange-based derivative transactions. More targeted remedies to drive out socially
undesirable transactions should be sought in parallel, which would allow, after their
implementation, to reduce or even phase out financialtransaction taxes
Mean-Field vs Monte-Carlo equation of state for the expansion of a Fermi superfluid in the BCS-BEC crossover
The equation of state (EOS) of a Fermi superfluid is investigated in the
BCS-BEC crossover at zero temperature. We discuss the EOS based on Monte-Carlo
(MC) data and asymptotic expansions and the EOS derived from the extended BCS
(EBCS) mean-field theory. Then we introduce a time-dependent density
functional, based on the bulk EOS and Landau's superfluid hydrodynamics with a
von Weizs\"acker-type correction, to study the free expansion of the Fermi
superfluid. We calculate the aspect ratio and the released energy of the
expanding Fermi cloud showing that MC EOS and EBCS EOS are both compatible with
the available experimental data of Li atoms. We find that the released
energy satisfies an approximate analytical formula that is quite accurate in
the BEC regime. For an anisotropic droplet, our numerical simulations show an
initially faster reversal of anisotropy in the BCS regime, later suppressed by
the BEC fluid.Comment: 13 pages, 3 figures, presented to the 15th International Laser
Physics Workshop (Lausanne, July 24-28, 2006); to be published in Laser
Physic
Inclusive particle production at HERA: Higher-order QCD corrections to the resolved quasi-real photon contribution
We calculate in next-to-leading order inclusive cross sections of
single-particle production via resolved photons in collisions at HERA.
Transverse-momentum and rapidity distributions are presented and the scale
dependence is studied. The results are compared with first experimental data
from the H1 Collaboration at HERA.Comment: 11 pages with 15 uuencoded PS figures. Preprint DESY 93-03
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