1,134 research outputs found
Mixing of Xi_c and Xi_c' Baryons
The mixing angle between the Xi_c and Xi_c' baryons is shown to be small,
with a negligible shift in the Xi_c masses.Comment: One missprint corrected. The numerator of Eq. (12) should read
{2[(Sigma_c^{*++}-Sigma_c^{++})-(Xi_c^{*+}-Xi_c^{'+})]} The correct equation
was used in the calculation so no other change is mad
Cauchy Horizons, Thermodynamics and Closed Time-like Curves in Planar Supersymmetric Space-times
We study geodesically complete, singularity free space-times induced by
supersymmetric planar domain walls interpolating between Minkowski and anti-de
Sitter () vacua. A geodesically complete space-time without closed
time-like curves includes an infinite number of semi-infinite Minkowski
space-times, separated from each other by a region of space-time. These
space-times are closely related to the extreme Reissner Nordstr\" om (RN) black
hole, exhibiting Cauchy horizons with zero Hawking temperature, but in contrast
to the RN black hole there is no entropy. Another geodesically complete
extension with closed time-like curves involves space-times connecting a finite
number of semi-infinite Minkowski space-times.Comment: 11 pages, 1 figure appended, phyzz
A Constraint Satisfaction Algorithm for the Generalized Inverse Phase Stability Problem
Researchers have used the (calculation of phase diagram) CALPHAD method to solve the forward phase stability problem of mapping from specific thermodynamic conditions (material composition, temperature, pressure, etc.) to the associated phase constitution. Recently, optimization has been used to solve the inverse problem: mapping specific phase constitutions to the thermodynamic conditions that give rise to them. These pointwise results, however, are of limited value since they do not provide information about the forces driving the point to equilibrium. In this paper, we investigate the problem of mapping a desirable region in the phase constitution space to corresponding regions in the space of thermodynamic conditions. We term this problem the generalized inverse phase stability problem (GIPSP) and model the problem as a continuous constraint satisfaction problem (CCSP). In this paper, we propose a new CCSP algorithm tailored for the GIPSP. We investigate the performance of the algorithm on Fe-Ti binary alloy system using ThermoCalc with the TCFE7 database against a related algorithm. The algorithm is able to generate solutions for this problem with high performance
Evolution of residual stresses in linear deposition wire-based cladding of Ti-6Al-4V
Neutron diffraction and curvature measurements were conducted to investigate the residual stresses associated with Plasma Transferred Arc Cladding (PTA) of Ti-6Al-4V on a substrate of the same material. The wire-feed PTA coupled with 3-axis CNC machine was used as an Additive Manufacturing (AM) technique to build parts. A combination of the process parameters was chosen to investigate their effects on residual stress evolution. Neutron Diffraction (ND) measurements of residual strains were performed on the SALSA instrument at the Institut Laue-Langevin (ILL), Grenoble, France. Longitudinal stresses were also inferred by using a Coordinate Measurement Machine (CMM) and Euler-Bernoulli beam theorem. Furthermore, Optical Microscopy (OM) of the cross section of the parts was used to analyse the microstructural evolution. The results show the effect of shorter and longer âdwell timeâ between layers on the evolution of residual stresses
A generalization of Hawking's black hole topology theorem to higher dimensions
Hawking's theorem on the topology of black holes asserts that cross sections
of the event horizon in 4-dimensional asymptotically flat stationary black hole
spacetimes obeying the dominant energy condition are topologically 2-spheres.
This conclusion extends to outer apparent horizons in spacetimes that are not
necessarily stationary. In this paper we obtain a natural generalization of
Hawking's results to higher dimensions by showing that cross sections of the
event horizon (in the stationary case) and outer apparent horizons (in the
general case) are of positive Yamabe type, i.e., admit metrics of positive
scalar curvature. This implies many well-known restrictions on the topology,
and is consistent with recent examples of five dimensional stationary black
hole spacetimes with horizon topology . The proof is inspired
by previous work of Schoen and Yau on the existence of solutions to the Jang
equation (but does not make direct use of that equation).Comment: 8 pages, latex2e, references updated, minor corrections, to appear in
Communications in Mathematical Physic
On the geometry of closed G2-structure
We give an answer to a question posed recently by R.Bryant, namely we show
that a compact 7-dimensional manifold equipped with a G2-structure with closed
fundamental form is Einstein if and only if the Riemannian holonomy of the
induced metric is contained in G2. This could be considered to be a G2 analogue
of the Goldberg conjecture in almost Kahler geometry. The result was
generalized by R.L.Bryant to closed G2-structures with too tightly pinched
Ricci tensor. We extend it in another direction proving that a compact
G2-manifold with closed fundamental form and divergence-free Weyl tensor is a
G2-manifold with parallel fundamental form. We introduce a second symmetric
Ricci-type tensor and show that Einstein conditions applied to the two Ricci
tensors on a closed G2-structure again imply that the induced metric has
holonomy group contained in G2.Comment: 14 pages, the Einstein condition in the assumptions of the Main
theorem is generalized to the assumption that the Weyl tensor is
divergence-free, clarity improved, typos correcte
Loss of Atrx Affects Trophoblast Development and the Pattern of X-Inactivation in Extraembryonic Tissues
ATRX is an X-encoded member of the SNF2 family of ATPase/helicase proteins thought to regulate gene expression by modifying chromatin at target loci. Mutations in ATRX provided the first example of a human genetic disease associated with defects in such proteins. To better understand the role of ATRX in development and the associated abnormalities in the ATR-X (alpha thalassemia mental retardation, X-linked) syndrome, we conditionally inactivated the homolog in mice, Atrx, at the 8- to 16-cell stage of development. The protein, Atrx, was ubiquitously expressed, and male embryos null for Atrx implanted and gastrulated normally but did not survive beyond 9.5 days postcoitus due to a defect in formation of the extraembryonic trophoblast, one of the first terminally differentiated lineages in the developing embryo. Carrier female mice that inherit a maternal null allele should be affected, since the paternal X chromosome is normally inactivated in extraembryonic tissues. Surprisingly, however, some carrier females established a normal placenta and appeared to escape the usual pattern of imprinted X-inactivation in these tissues. Together these findings demonstrate an unexpected, specific, and essential role for Atrx in the development of the murine trophoblast and present an example of escape from imprinted X chromosome inactivation
The Periodic Standing-Wave Approximation: Overview and Three Dimensional Scalar Models
The periodic standing-wave method for binary inspiral computes the exact
numerical solution for periodic binary motion with standing gravitational
waves, and uses it as an approximation to slow binary inspiral with outgoing
waves. Important features of this method presented here are: (i) the
mathematical nature of the ``mixed'' partial differential equations to be
solved, (ii) the meaning of standing waves in the method, (iii) computational
difficulties, and (iv) the ``effective linearity'' that ultimately justifies
the approximation. The method is applied to three dimensional nonlinear scalar
model problems, and the numerical results are used to demonstrate extraction of
the outgoing solution from the standing-wave solution, and the role of
effective linearity.Comment: 13 pages RevTeX, 5 figures. New version. A revised form of the
nonlinearity produces better result
Classical glueballs in non-Abelian Born-Infeld theory
It is shown that the Born-Infeld-type modification of the quadratic
Yang-Mills action suggested by the superstring theory gives rise to classical
particle-like solutions prohibited in the standard Yang-Mills theory. This
becomes possible due to the scale invariance breaking by the Born-Infeld
non-linearity. New classical glueballs are sphaleronic in nature and exhibit a
striking similarity with the Bartnik-McKinnon solutions of the Yang-Mills
theory coupled to gravity.Comment: Revtex, 4 pages, 2 eps figure
Gravitating Opposites Attract
Generalizing previous work by two of us, we prove the non-existence of
certain stationary configurations in General Relativity having a spatial
reflection symmetry across a non-compact surface disjoint from the matter
region. Our results cover cases such that of two symmetrically arranged
rotating bodies with anti-aligned spins in () dimensions, or
two symmetrically arranged static bodies with opposite charges in 3+1
dimensions. They also cover certain symmetric configurations in
(3+1)-dimensional gravity coupled to a collection of scalars and abelian vector
fields, such as arise in supergravity and Kaluza-Klein models. We also treat
the bosonic sector of simple supergravity in 4+1 dimensions.Comment: 13 pages; slightly amended version, some references added, matches
version to be published in Classical and Quantum Gravit
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