3,017 research outputs found
Orientifolds, RR Torsion, and K-theory
We analyze the role of RR fluxes in orientifold backgrounds from the point of
view of K-theory, and demonstrate some physical implications of describing
these fluxes in K-theory rather than cohomology. In particular, we show that
certain fractional shifts in RR charge quantization due to discrete RR fluxes
are naturally explained in K-theory. We also show that some orientifold
backgrounds, which are considered distinct in the cohomology classification,
become equivalent in the K-theory description, while others become unphysical.Comment: 30 pages, 5 figures; typos corrected and references adde
Thermo-elasticity for anisotropic media in higher dimensions
In this note we develop tools to study the Cauchy problem for the system of
thermo-elasticity in higher dimensions. The theory is developed for general
homogeneous anisotropic media under non-degeneracy conditions.
For degenerate cases a method of treatment is sketched and for the cases of
cubic media and hexagonal media detailed studies are provided.Comment: 33 pages, 5 figure
Notch-Fatigue Properties of Advanced TRIP-Aided Bainitic Ferrite Steels
To develop a transformation-induced plasticity (TRIP)-aided bainitic ferrite steel (TBF steel) with high hardenability for a common rail of the next generation diesel engine, 0.2 pct C-1.5 pct Si-1.5 pct Mn-0.05 pct Nb TBF steels with different contents of Cr, Mo, and Ni were produced. The notch-fatigue strength of the TBF steels was investigated and was related to the microstructural and retained austenite characteristics. If Cr, Mo, and/or Ni were added to the base steel, then the steels achieved extremely higher notch-fatigue limits and lower notch sensitivity than base TBF steel and the conventional structural steels. This was mainly associated with (1) carbide-free and fine bainitic ferrite lath structure matrix without proeutectoid ferrite, (2) a large amount of fine metastable retained austenite, and (3) blocky martensite phase including retained austenite, which may suppress a fatigue crack initiation and propagation.ArticleMETALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE. 43A(11):4129-4136 (2012)journal articl
Carbon-Oxygen White Dwarfs Accreting CO-Rich Matter I: A Comparison Between Rotating and Non-Rotating Models
We investigate the lifting effect of rotation on the thermal evolution of CO
WDs accreting CO-rich matter. We find that rotation induces the cooling of the
accreting star so that the delivered gravitational energy causes a greater
expansion with respect to the standard non-rotating case. The increase in the
surface radius produces a decrease in the surface value of the critical angular
velocity and, therefore, the accreting WD becomes gravitationally unbound
(Roche instability). This occurrence is due to an increase in the total angular
momentum of the accreting WD and depends critically on the amount of specific
angular momentum deposited by the accreted matter. If the specific angular
momentum of the accreted matter is equal to that of the outer layers of the
accreting structure, the Roche instability occurs well before the accreting WD
can attain the physical conditions for C-burning. If the values of both initial
angular velocity and accretion rate are small, we find that the accreting WD
undergoes a secular instability when its total mass approaches 1.4 Msun. At
this stage, the ratio between the rotational and the gravitational binding
energy of the WD becomes of the order of 0.1, so that the star must deform by
adopting an elliptical shape. In this case, since the angular velocity of the
WD is as large as 1 rad/s, the anisotropic mass distribution induces the loss
of rotational energy and angular momentum via GWR. We find that, independent of
the braking efficiency, the WD contracts and achieves the physical conditions
suitable for explosive C-burning at the center so that a type Ia supernova
event is produced.Comment: 39 pages, 22 eps-figures; accepted for publication in Astrophysical
Journa
Some interesting violations of the Breitenlohner-Freedman bound
We demonstrate that AdS_5 x T^{pq} is unstable, in the sense of Breitenlohner
and Freedman, for unequal p and q. This settles, negatively, the long-standing
question of whether the T^{pq} manifolds for unequal p and q might correspond
to non-supersymmetric fixed points of the renormalization group. We also show
that the AdS_3 x S^7 vacuum of Sugimoto's USp(32) open string theory is
unstable. This explains, at a heuristic level, the apparent absence of a
heterotic string dual.Comment: 16 pages, latex. v2: minor correction
Winding effects on brane/anti-brane pairs
We study a brane/anti-brane configuration which is separated along a compact
direction by constructing a tachyon effective action which takes into account
transverse scalars. Such an action is relevant in the study of HQCD model of
Sakai and Sugimoto of chiral symmetry breaking, where the size of the compact
circle sets the confinement scale. Our approach is motivated by string theory
orbifold constructions and gives a route to model inhomogeneous tachyon decay.
We illustrate the techniques involved with a relatively simple example of a
harmonic oscillator on a circle. We will then repeat the analysis for the
Sakai-Sugimoto model and show that by integrating out the winding modes will
provide us with a renormalized action with a lower energy than that of
truncating to zero winding sector.Comment: 21 pages, 3 figures. v3: discussion and references added, published
versio
Alveolar soft-part sarcoma of the retroperitoneum
The definitive version is available at www.blackwell-synergy.com.ArticleInternational Journal of Urology. 13(10): 1355-1357 (2006)journal articl
Rolling of Modulated Tachyon with Gauge Flux and Emergent Fundamental String
We investigate real-time tachyon dynamics of unstable D-brane carrying
fundamental string charge. We construct the boundary state relevant for rolling
of modulated tachyon with gauge fields excited on the world-volume, and study
spatial distribution of the fundamental string charge and current as the
D-brane decays. We find that, in contrast to homogeneous tachyon rolling,
spatial modulation of the tachyon field triggers density wave of strings when
electric field is turned on, and of string anti-string pairs when magnetic
field is turned on. We show that the energy density and the fundamental string
charge density are locked together, and evolve into a localized delta-function
array (instead of evolving into a string fluid) until a critical time set by
initial condition of rolling tachyon. When the gauge fields approach the
critical limit, the fundamental strings produced become BPS-like. We also study
the dynamics via effective field theory, and find agreement.Comment: 28 pages, Latex, 7 .eps figures v2: stability discussion update
The 13C Pocket in Low Mass AGB Stars
It is well known that thermally pulsing Asymptotic Giant Branch stars with
low mass play a relevant role in the chemical evolution. They have synthesized
about 30% of the galactic carbon and provide an important contribution to the
nucleosynthesis of heavy elements (A>80). The relevant nucleosynthesis site is
the He-rich intermediate zone (less than 10^{-2} Msun), where
alpha(2alpha,gamma)12C reactions and slow neutron captures on seed nuclei
essentially iron) take place. A key ingredient is the interplay between nuclear
processes and convective mixing. It is the partial overlap of internal and
external convective zones that allows the dredge-up of the material enriched in
C and heavy elements. We review the progresses made in the last 50 years in the
comprehension of the s process in AGB stars, with special attention to the
identification of the main neutron sources and to the particular physical
conditions allowing this important nucleosynthesis.Comment: Accepted for Publication on PAS
Projectile Fragmentation of the Extremely Neutron-Rich Nucleus ^<11>Li at o.79 GeV/nucleon
Projectile fragmentations of ^Li, ^He, and ^He have been measured at 0.79 GeV/nucleon. Production cross sections and momentum distributions of the produced isotopes (Zâ„2) are measured inclusively. Transverse-momentum distributions of ^Li from the fragmentation of ^Li show two Gaussian components of different widths. The width of the wide component is consistent with the values observed in the fragmentation of stable nuclei, whereas the other component shows an extremely narrow width reflecting the weak binding of the two outer neutrons in the ^Li nucleus
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