833 research outputs found
Coulomb dissociation of a fast pion into two jets
We calculate the electromagnetic contribution to the scattering amplitude of
pion diffractive dissociation into di-jets which is described by one photon
exchange. The result shows that the factorization procedure known for the
description of exclusive reactions holds also for this quasi-exclusive process.
We find that the longitudinal momentum distribution of di-jets does not depend
on the form of the pion distribution amplitude. We discuss the magnitude of the
cross section.Comment: 7 pages, 3 .eps figures, Late
Magnetoinductance of Josephson junction array with frozen vortex diffusion
The dependence of sheet impedance of a Josephson junction array on the
applied magnetic field is investigated in the regime when vortex diffusion
between array plaquettes is effectively frozen due to low enough temperature.
The field dependent contribution to sheet inductance is found to be
proportional to f*ln(1/f), where f<<1 is the magnitude of the field expressed
in terms of flux quanta per plaquette.Comment: 5 pages, no figure
Teleparallel Versions of Friedmann and Lewis-Papapetrou Spacetimes
This paper is devoted to investigate the teleparallel versions of the
Friedmann models as well as the Lewis-Papapetrou solution. We obtain the tetrad
and the torsion fields for both the spacetimes. It is shown that the
axial-vector vanishes for the Friedmann models. We discuss the different
possibilities of the axial-vector depending on the arbitrary functions
and in the Lewis-Papapetrou metric. The vector related with spin has
also been evaluated.Comment: 13 pages, accepted for publication in GR
Effective nonlinear optical properties of composite media of graded spherical particles
We have developed a nonlinear differential effective dipole approximation
(NDEDA), in an attempt to investigate the effective linear and third-order
nonlinear susceptibility of composite media in which graded spherical
inclusions with weak nonlinearity are randomly embedded in a linear host
medium. Alternatively, based on a first-principles approach, we derived exactly
the linear local field inside the graded particles having power-law dielectric
gradation profiles. As a result, we obtain also the effective linear dielectric
constant and third-order nonlinear susceptibility. Excellent agreement between
the two methods is numerically demonstrated. As an application, we apply the
NDEDA to investigate the surface plasma resonant effect on the optical
absorption, optical nonlinearity enhancement, and figure of merit of
metal-dielectric composites. It is found that the presence of gradation in
metal particles yields a broad resonant band in the optical region, and further
enhances the figure of merit.Comment: 20 pages, 5 figure
The B-Meson Distribution Amplitude in QCD
The B-meson distribution amplitude is calculated using QCD sum rules. In
particular we obtain an estimate for the integral relevant to exclusive
B-decays \lambda_B = 460 \pm 110 MeV at the scale 1 GeV. A simple QCD-motivated
parametrization of the distribution amplitude is suggested.Comment: 17 pages, 8 figures, Latex styl
Cluster of Dipolar Coupled Spins as a Quantum Memory Storage
Spin dynamics of a cluster of coupled spins 1/2 can be manipulated to store
and process a large amount of information. A new type of dynamic response makes
it possible to excite coherent long-living signals, which can be used for
exchanging information with a mesoscopic quantum system. An experimental
demonstration is given for a system of 19 proton spins of a liquid crystal
molecule.Comment: 5 pages, 1 figur
Propagation of wave packets in randomly stratified media
The propagation of a narrow-band signal radiated by a point source in a
randomly layered absorbing medium is studied asymptotically in the
weak-scattering limit. It is shown that in a disordered stratified medium that
is homogeneous on average a pulse is channelled along the layers in a narrow
strip in the vicinity of the source. The space-time distribution of the pulse
energy is calculated. Far from the source, the shape of wave packets is
universal and independent of the frequency spectrum of the radiated signal.
Strong localization effects manifest themselves also as a low-decaying tail of
the pulse and a strong time delay in the direction of stratification. The
frequency-momentum correlation function in a one-dimensional random medium is
calculated.Comment: 11 pages, 3 figures, Revtex-4. Submitted to Phys. Rev.
Excess centrosomes induce p53-dependent senescence without DNA damage in endothelial cells
Tumor blood vessels support tumor growth and progression. Centrosomes are microtubule organization centers in cells, and often up to 30% of tumor endothelial cells (ECs) acquire excess (>2) centrosomes. Although excess centrosomes can lead to aneuploidy and chromosome instability in tumor cells, how untransformed ECs respond to excess centrosomes is poorly understood. We found that the frequency of primary human ECs with excess centrosomes was quickly reduced in a p53-dependent manner. Excess centrosomes in ECs were associated with p53 phosphorylation at Ser33, increased p21 levels, and decreased cell proliferation and expression of senescence markers, but independent of DNA damage and apoptosis. Aspects of the senescence-associated phenotype were also observed in mouse ECs that were isolated from tumors with excess centrosomes. Primary ECs with excess centrosomes in vascular sprouts also had elevated Ser33 p53 phosphorylation and expressed senescence markers. Our work demonstrates that nontransformed ECs respond differently to excess centrosomes than do most tumor cells-they undergo senescence in vascular sprouts and vessels, which suggests that pathologic outcomes of centrosome overduplication depend on the transformation status of cells
Magnetic and electronic structures of superconducting RuSrGdCuO
The coexistence of ferromagnetism and superconductivity in
RuSrGdCuO was reported both from experiments (by Tallon et. al.)
and first-principles calculations (by Pickett et. al.). Here we report that our
first-principles full-potential linearized augmented plane wave (FLAPW)
calculations, employing the precise crystal structure with structural
distortions (i.e., RuO rotations) determined by neutron diffraction,
demonstrate that antiferromagnetic ordering of the Ru moments is energetically
favored over the previously proposed ferromagnetic ordering. Our results are
consistent with recently performed magnetic neutron diffraction experiments
(Lynn et. al). Ru states, which are responsible for the magnetism,
have only a very small interaction with Cu states, which results in a
small exchange splitting of these states. The Fermi surface, characterized by
strongly hybridized orbitals, has nesting features similar to those
in the two-dimensional high cuprate superconductors.Comment: 6 pages,6 figures, accepted for publication in Phys. Rev.
Analytic Methods in Nonperturbative QCD
Recently developed analytic methods in the framework of the Field Correlator
Method are reviewed in this series of four lectures and results of calculations
are compared to lattice data and experiment. Recent lattice data demonstrating
the Casimir scaling of static quark interaction strongly support the FCM and
leave very little space for all other theoretical models, e.g. instanton
gas/liquid model. Results of calculations for mesons, baryons, quark-gluon
plasma and phase transition temperature demonstrate that new analytic methods
are a powerful tool of nonperturbative QCD along with lattice simulations.Comment: LaTeX, 34 pages; Lectures given at the 13th Indian-Summer School
"Understanding the Structure of Hadrons", August 28 - September 1, 2000,
Prague, Czech Republi
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