688 research outputs found
Incompressible Stars and Fractional Derivatives
Fractional calculus is an effective tool in incorporating the effects of
non-locality and memory into physical models. In this regard, successful
applications exist rang- ing from signal processing to anomalous diffusion and
quantum mechanics. In this paper we investigate the fractional versions of the
stellar structure equations for non radiating spherical objects. Using
incompressible fluids as a comparison, we develop models for constant density
Newtonian objects with fractional mass distributions or stress conditions. To
better understand the fractional effects, we discuss effective values for the
density, gravitational field and equation of state. The fractional ob- jects
are smaller and less massive than integer models. The fractional parameters are
related to a polytropic index for the models considered
Equity Sell Disciplines across the Style Box
This study examines the use of four major equity sell disciplines across the equity style box. Specifically, large-cap and small-cap securities are tested to see which of the four sell disciplines consistently produces the best portfolio returns. Data from the Plan Sponsor Network (PSN) are used to calculate each portfolio’s benchmark-adjusted return (BAR), information ratio, and Sharpe ratio. These ratios are used to evaluate sell discipline strategy based on each portfolio’s market capitalization and style focus. Three regressions are run for each BAR, information ratio and Sharpe ratio. The analysis is repeated for all four corners of the style box. The results show that there is not a specific sell discipline criterion that consistently produces the best portfolio performance. The majority of the regression results were not significant due the fact that the calculated p-value does not meet the minimum required significance level of 10%
The phonon dispersion of graphite by inelastic x-ray scattering
We present the full in-plane phonon dispersion of graphite obtained from
inelastic x-ray scattering, including the optical and acoustic branches, as
well as the mid-frequency range between the and points in the Brillouin
zone, where experimental data have been unavailable so far. The existence of a
Kohn anomaly at the point is further supported. We fit a fifth-nearest
neighbour force-constants model to the experimental data, making improved
force-constants calculations of the phonon dispersion in both graphite and
carbon nanotubes available.Comment: 7 pages; submitted to Phys. Rev.
Giant Kohn anomaly and the phase transition in charge density wave ZrTe_3
A strong Kohn anomaly in ZrTe_3 is identified in the mostly transverse
acoustic phonon branch along the modulation vector q_P with polarization along
the a* direction. This soft mode freezes to zero frequency at the transition
temperature T_P and the temperature dependence of the frequency is strongly
affected by fluctuation effects. Diffuse x-ray scattering of the incommensurate
superstructure shows a power law scaling of the intensity and the correlation
length that is compatible with an order parameter of dimension n = 2.Comment: 4 pages, 4 figures. accepted at Phys. Rev. Let
Hadron Spin Dynamics
Spin effects in exclusive and inclusive reactions provide an essential new
dimension for testing QCD and unraveling hadron structure. Remarkable new
experiments from SLAC, HERMES (DESY), and the Jefferson Laboratory present many
challenges to theory, including measurements at HERMES and SMC of the single
spin asymmetries in pion electroproduction, where the proton is polarized
normal to the scattering plane. This type of single spin asymmetry may be due
to the effects of rescattering of the outgoing quark on the spectators of the
target proton, an effect usually neglected in conventional QCD analyses. Many
aspects of spin, such as single-spin asymmetries and baryon magnetic moments
are sensitive to the dynamics of hadrons at the amplitude level, rather than
probability distributions. I illustrate the novel features of spin dynamics for
relativistic systems by examining the explicit form of the light-front
wavefunctions for the two-particle Fock state of the electron in QED, thus
connecting the Schwinger anomalous magnetic moment to the spin and orbital
momentum carried by its Fock state constituents and providing a transparent
basis for understanding the structure of relativistic composite systems and
their matrix elements in hadronic physics. I also present a survey of
outstanding spin puzzles in QCD, particularly the double transverse spin
asymmetry A_{NN} in elastic proton-proton scattering, the J/psi to rho-pi
puzzle, and J/psi polarization at the Tevatron.Comment: Concluding theory talk presented at SPIN2001, the Third
Circum-Pan-Pacific Symposium on High Energy Physics, October, 2001, Beijin
Killing vectors and anisotropy
We consider an action that can generate fluids with three unequal stresses
for metrics with a spacelike Killing vector. The parameters in the action are
directly related to the stress anisotropies. The field equations following from
the action are applied to an anisotropic cosmological expansion and an
extension of the Gott-Hiscock cosmic string
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