240 research outputs found
New calculations of the PNC Matrix Element for the 0 doublet in N
A new calculation of the predominantly isoscalar PNC matrix element between
the (E 8.7 MeV) states in N has
been carried out in a (0+1+2+3+4) model space with the
Warburton-Brown interaction. The magnitude of the PNC matrix element of 0.22 to
0.34 eV obtained with the DDH PNC interaction is substantially suppressed
compared with previous calculations in smaller model spaces but shows agreement
with the preliminary Seattle experimental data. The calculated sign is opposite
to that obtained experimentally, and the implications of this are discussed.Comment: REVTEX, 28 page
Electronic Structure of Te and As Covered Si(211)
Electronic and atomic structures of the clean, and As and Te covered Si(211)
surface are studied using pseudopotential density functional method. The clean
surface is found to have (2 X 1) and rebonded (1 X 1) reconstructions as stable
surface structures, but no \pi-bonded chain reconstruction. Binding energies of
As and Te adatoms at a number of symmetry sites on the ideal and (2 X 1)
reconstructed surfaces have been calculated because of their importance in the
epitaxial growth of CdTe and other materials on the Si(211) surface. The
special symmetry sites on these surfaces having the highest binding energies
for isolated As and Te adatoms are identified. But more significantly, several
sites are found to be nearly degenerate in binding energy values. This has
important consequences for epitaxial growth processes. Optimal structures
calculated for 0.5 ML of As and Te coverage reveal that the As adatoms dimerize
on the surface while the Te adatoms do not. However, both As and Te covered
surfaces are found to be metallic in nature.Comment: 17 pages, 9 figures, accepted for publication in Phys. Rev.
Unified N=2 Maxwell-Einstein and Yang-Mills-Einstein Supergravity Theories in Four Dimensions
We study unified N=2 Maxwell-Einstein supergravity theories (MESGTs) and
unified Yang-Mills Einstein supergravity theories (YMESGTs) in four dimensions.
As their defining property, these theories admit the action of a global or
local symmetry group that is (i) simple, and (ii) acts irreducibly on all the
vector fields of the theory, including the ``graviphoton''. Restricting
ourselves to the theories that originate from five dimensions via dimensional
reduction, we find that the generic Jordan family of MESGTs with the scalar
manifolds [SU(1,1)/U(1)] X [SO(2,n)/SO(2)X SO(n)] are all unified in four
dimensions with the unifying global symmetry group SO(2,n). Of these theories
only one can be gauged so as to obtain a unified YMESGT with the gauge group
SO(2,1). Three of the four magical supergravity theories defined by simple
Euclidean Jordan algebras of degree 3 are unified MESGTs in four dimensions.
Two of these can furthermore be gauged so as to obtain 4D unified YMESGTs with
gauge groups SO(3,2) and SO(6,2), respectively. The generic non-Jordan family
and the theories whose scalar manifolds are homogeneous but not symmetric do
not lead to unified MESGTs in four dimensions. The three infinite families of
unified five-dimensional MESGTs defined by simple Lorentzian Jordan algebras,
whose scalar manifolds are non-homogeneous, do not lead directly to unified
MESGTs in four dimensions under dimensional reduction. However, since their
manifolds are non-homogeneous we are not able to completely rule out the
existence of symplectic sections in which these theories become unified in four
dimensions.Comment: 47 pages; latex fil
Unified Maxwell-Einstein and Yang-Mills-Einstein Supergravity Theories in Five Dimensions
Unified N=2 Maxwell-Einstein supergravity theories (MESGTs) are supergravity
theories in which all the vector fields, including the graviphoton, transform
in an irreducible representation of a simple global symmetry group of the
Lagrangian. As was established long time ago, in five dimensions there exist
only four unified Maxwell-Einstein supergravity theories whose target manifolds
are symmetric spaces. These theories are defined by the four simple Euclidean
Jordan algebras of degree three. In this paper, we show that, in addition to
these four unified MESGTs with symmetric target spaces, there exist three
infinite families of unified MESGTs as well as another exceptional one. These
novel unified MESGTs are defined by non-compact (Minkowskian) Jordan algebras,
and their target spaces are in general neither symmetric nor homogeneous. The
members of one of these three infinite families can be gauged in such a way as
to obtain an infinite family of unified N=2 Yang-Mills-Einstein supergravity
theories, in which all vector fields transform in the adjoint representation of
a simple gauge group of the type SU(N,1). The corresponding gaugings in the
other two infinite families lead to Yang-Mills-Einstein supergravity theories
coupled to tensor multiplets.Comment: Latex 2e, 28 pages. v2: reference added, footnote 14 enlarge
Mutation of Ser172 in Yeast ÎČ Tubulin Induces Defects in Microtubule Dynamics and Cell Division
Ser172 of ÎČ tubulin is an important residue that is mutated in a human brain disease and phosphorylated by the cyclin-dependent kinase Cdk1 in mammalian cells. To examine the role of this residue, we used the yeast S. cerevisiae as a model and produced two different mutations (S172A and S172E) of the conserved Ser172 in the yeast ÎČ tubulin Tub2p. The two mutants showed impaired cell growth on benomyl-containing medium and at cold temperatures, altered microtubule (MT) dynamics, and altered nucleus positioning and segregation. When cytoplasmic MT effectors Dyn1p or Kar9p were deleted in S172A and S172E mutants, cells were viable but presented increased ploidy. Furthermore, the two ÎČ tubulin mutations exhibited synthetic lethal interactions with Bik1p, Bim1p or Kar3p, which are effectors of cytoplasmic and spindle MTs. In the absence of Mad2p-dependent spindle checkpoint, both mutations are deleterious. These findings show the importance of Ser172 for the correct function of both cytoplasmic and spindle MTs and for normal cell division
Parity-violating neutron spin rotation in hydrogen and deuterium
We calculate the (parity-violating) spin rotation angle of a polarized
neutron beam through hydrogen and deuterium targets, using pionless effective
field theory up to next-to-leading order. Our result is part of a program to
obtain the five leading independent low-energy parameters that characterize
hadronic parity-violation from few-body observables in one systematic and
consistent framework. The two spin-rotation angles provide independent
constraints on these parameters. Using naive dimensional analysis to estimate
the typical size of the couplings, we expect the signal for standard target
densities to be 10^-7 to 10^-6 rad/m for both hydrogen and deuterium targets.
We find no indication that the nd observable is enhanced compared to the np
one. All results are properly renormalized. An estimate of the numerical and
systematic uncertainties of our calculations indicates excellent convergence.
An appendix contains the relevant partial-wave projectors of the three-nucleon
system.Comment: 44 pages, 17 figures; minor corrections; to be published in EPJ
Magnetic Reconnection in Extreme Astrophysical Environments
Magnetic reconnection is a basic plasma process of dramatic rearrangement of
magnetic topology, often leading to a violent release of magnetic energy. It is
important in magnetic fusion and in space and solar physics --- areas that have
so far provided the context for most of reconnection research. Importantly,
these environments consist just of electrons and ions and the dissipated energy
always stays with the plasma. In contrast, in this paper I introduce a new
direction of research, motivated by several important problems in high-energy
astrophysics --- reconnection in high energy density (HED) radiative plasmas,
where radiation pressure and radiative cooling become dominant factors in the
pressure and energy balance. I identify the key processes distinguishing HED
reconnection: special-relativistic effects; radiative effects (radiative
cooling, radiation pressure, and Compton resistivity); and, at the most extreme
end, QED effects, including pair creation. I then discuss the main
astrophysical applications --- situations with magnetar-strength fields
(exceeding the quantum critical field of about 4 x 10^13 G): giant SGR flares
and magnetically-powered central engines and jets of GRBs. Here, magnetic
energy density is so high that its dissipation heats the plasma to MeV
temperatures. Electron-positron pairs are then copiously produced, making the
reconnection layer highly collisional and dressing it in a thick pair coat that
traps radiation. The pressure is dominated by radiation and pairs. Yet,
radiation diffusion across the layer may be faster than the global Alfv\'en
transit time; then, radiative cooling governs the thermodynamics and
reconnection becomes a radiative transfer problem, greatly affected by the
ultra-strong magnetic field. This overall picture is very different from our
traditional picture of reconnection and thus represents a new frontier in
reconnection research.Comment: Accepted to Space Science Reviews (special issue on magnetic
reconnection). Article is based on an invited review talk at the
Yosemite-2010 Workshop on Magnetic Reconnection (Yosemite NP, CA, USA;
February 8-12, 2010). 30 pages, no figure
Epidemiological, clinical and immunohistochemical aspects of canine lymphoma in the region of Porto Alegre, Brazil
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