3,011 research outputs found
Black Holes of a Minimal Size in String Gravity
A lower limit for a neutral black hole size is obtained in the frames of the
string gravity model with the second order curvature correction. It is shown
that this effect remains when the third order curvature correction is also
taken into account and argued that such restriction does exist in all
perturbative orders of curvature expansions.Comment: 6 LaTeX pages, 1 PostScript figure (epsfig.sty), minor changes in the
text and references, submitted to Int.J.Mod.Phy
Some comments about Schwarzschield black holes in Matrix theory
In the present paper we calculate the statistical partition function for any
number of extended objects in Matrix theory in the one loop approximation. As
an application, we calculate the statistical properties of K clusters of D0
branes and then the statistical properties of K membranes which are wound on a
torus.Comment: 15 page
Model validation for a noninvasive arterial stenosis detection problem
Copyright @ 2013 American Institute of Mathematical SciencesA current thrust in medical research is the development of a non-invasive method for detection, localization, and characterization of an arterial stenosis (a blockage or partial blockage in an artery). A method has been proposed to detect shear waves in the chest cavity which have been generated by disturbances in the blood flow resulting from a stenosis. In order to develop this methodology further, we use both one-dimensional pressure and shear wave experimental data from novel acoustic phantoms to validate corresponding viscoelastic mathematical models, which were developed in a concept paper [8] and refined herein. We estimate model parameters which give a good fit (in a sense to be precisely defined) to the experimental data, and use asymptotic error theory to provide confidence intervals for parameter estimates. Finally, since a robust error model is necessary for accurate parameter estimates and confidence analysis, we include a comparison of absolute and relative models for measurement error.The National Institute of Allergy and Infectious Diseases, the Air Force Office of Scientific Research, the Deopartment of Education and the Engineering and Physical Sciences Research Council (EPSRC)
A Multi-Boundary AdS Orbifold and DLCQ Holography: A universal holographic description of extremal black hole horizons
We examine a stationary but non-static asymptotically AdS_3 spacetime with
two causally connected conformal boundaries, each of which is a ``null
cylinder'', namely a cylinder with a null direction identified. This spacetime
arises from three different perspectives: (i) as a non-singular, causally
regular orbifold of global AdS_3 by boosts, (ii) as a Penrose-like limit
focusing on the horizon of extremal BTZ black holes, and (iii) as an S^1
fibration over AdS_2. Each of these perspectives sheds an interesting light on
holography. Examination of the conformal boundary of the spacetime shows that
the dual to the space should involve DLCQ limits of the D1-D5 conformal field
theory. The Penrose-like limit approach leads to a similar conclusion, by
isolating a sector of the complete D1-D5 CFT that describes the physics in the
vicinity of the horizon of an extremal black hole. As such this is a
holographic description of the universal horizon dynamics of the extremal black
holes in AdS_3 and also of the four and five dimensional stringy black holes
whose states were counted in string theory. The AdS_2 perspective draws a
connection to a 0+1d quantum mechanical theory. Various dualities lead to a
Matrix model description of the spacetime. Many interesting issues that are
related to both de Sitter physics and attempts to ``see behind a horizon''
using AdS/CFT arise from (a) the presence of two disconnected components to the
boundary, and (b) the analytic structure of bulk physics in the complex
coordinate plane.Comment: 48 pages. 3 EPS figures. If you use mpage to print multiple
postscript pages on the same sheet of paper you may have difficulties with
the figures. The PDF version will print fine, as will postscript if you stick
to one page per sheet. v3: minor edits and references adde
Impact of potassium and phosphorus in biomass on the properties of fast Pyrolysis bio-oil
This study investigates fast pyrolysis bio-oils produced from alkali-metal-impregnated biomass (beech wood). The impregnation aim is to study the catalytic cracking of the pyrolysis vapors as a result of potassium or phosphorus. It is recognized that potassium and phosphorus in biomass can have a major impact on the thermal conversion processes. When biomass is pyrolyzed in the presence of alkali metal cations, catalytic cracking of the pyrolysis liquids occurs in the vapor phase, reducing the organic liquids produced and increasing yields of water, char, and gas, resulting in a bio-oil that has a lower calorific value and an increased chance of phase separation. Beech wood was impregnated with potassium or phosphorus (K impregnation and P impregnation, respectively) in the range of 0.10-2.00 wt %. Analytical pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) was used to examine the pyrolysis products during thermal degradation, and thermogravimetric analysis (TGA) was used to examine the distribution of char and volatiles. Both potassium and phosphorus are seen to catalyze the pyrolytic decomposition of biomass and modify the yields of products. 3-Furaldehyde and levoglucosenone become more dominant products upon P impregnation, pointing to rearrangement and dehydration routes during the pyrolysis process. Potassium has a significant influence on cellulose and hemicellulose decomposition, not just on the formation of levoglucosan but also other species, such as 2(5H)-furanone or hydroxymethyl-cyclopentene derivatives. Fast pyrolysis processing has also been undertaken using a laboratory-scale continuously fed bubbling fluidized-bed reactor with a nominal capacity of 1 kg h-1 at the reaction temperature of 525 °C. An increase in the viscosity of the bio-oil during the stability assessment tests was observed with an increasing percentage of impregnation for both additives. This is because bio-oil undergoes polymerization while placed in storage as a result of the inorganic content. The majority of inorganics are concentrated in the char, but small amounts are entrained in the pyrolysis vapors and, therefore, end up in the bio-oil
Tourmaline Composition of the Kı¸sladag Porphyry Au Deposit,Western Turkey: Implication of Epithermal Overprint
The Kışladağ porphyry Au deposit occurs in a middle Miocene magmatic complex comprising three different intrusions and magmatic-hydrothermal brecciation related to the multiphase effects of the different intrusions. Tourmaline occurrences are common throughout the deposit, mostly as an outer alteration rim around the veins with lesser amounts disseminated in the intrusions, and are associated with every phase of mineralization. Tourmaline mineralization has developed as a tourmaline-rich matrix in brecciated zones and tourmaline-quartz and/or tourmaline-sulfide veinlets within the different intrusive rocks. Tourmaline was identified in the tourmaline-bearing breccia zone (TBZ) and intrusive rocks that had undergone potassic, phyllic, and advanced argillic alteration. The tourmaline is present as two morphological varieties, aggregates of fine crystals (rosettes, fan-shaped) and larger isolated crystals and their aggregates. Four tourmaline generations (tourmaline I to IV) have different compositions and substitutions. Tourmaline I in TBZ and INT#1 is distinguished by the highest Fetot and enriched in Fe3+. Tourmalines II and III occur as fine aggregates, accompanied by the formation of isolated crystals and are characterized by lower Fetot and Fe3+. Tourmaline IV is characterized by the lowest Fetot, enriched in Cl, and has the highest proportion of X-site vacancy among all the tourmalines. Tourmaline I may be attributed to the potassic stage in INT#1 and early tourmaline in TBZ. Tourmalines II and III from INT#1 and the TBZ could be referred to the phyllic stage. The low Fe content in tourmaline is caused by the simultaneous deposition of sulfide minerals. Tourmaline IV from the TBZ and tourmaline II from INT#3 are distinguished by the high X-site vacancy proportion up to the formation of X-site vacant species as well as enriched in Cl; they can be attributed to the argillic stage of the hydrothermal process. The textural and especially chemical data of the tourmaline from the Kışladağ Au deposit provide information on the physico-chemical conditions during the porphyry to epithermal transition and subsequent epithermal overprinting
Vortex Dynamics in Classical Non--Abelian Spin Models
We discuss the abelian vortex dynamics in the abelian projection approach to
non-abelian spin models. We show numerically that in the three-dimensional
SU(2) spin model in the Maximal Abelian projection the abelian off-diagonal
vortices are not responsible for the phase transition contrary to the diagonal
vortices. A generalization of the abelian projection approach to SU(N) spin
models is briefly discussed.Comment: 7 pages, LaTeX, 1 figure, uses epsf.sty; Introduction is extended and
a few references are added; to be published in JETP Let
A Review of Symmetry Algebras of Quantum Matrix Models in the Large-N Limit
This is a review article in which we will introduce, in a unifying fashion
and with more intermediate steps in some difficult calculations, two
infinite-dimensional Lie algebras of quantum matrix models, one for the open
string sector and one for the closed string sector. Physical observables of
quantum matrix models in the large-N limit can be expressed as elements of
these Lie algebras. We will see that both algebras arise as quotient algebras
of a larger Lie algebra. We will also discuss some properties of these Lie
algebras not published elsewhere yet, and briefly review their relationship
with well-known algebras like the Cuntz algebra, the Witt algebra and the
Virasoro algebra. We will also review how Yang--Mills theory, various low
energy effective models of string theory, quantum gravity, string-bit models,
and quantum spin chain models can be formulated as quantum matrix models.
Studying these algebras thus help us understand the common symmetry of these
physical systems.Comment: 77 pages, 21 eps figures, 1 table, LaTeX2.09; an invited review
articl
The Intermediate Scale Branch of the Landscape
Three branches of the string theory landscape have plausibly been identified.
One of these branches is expected to exhibit a roughly logarithmic distribution
of supersymmetry breaking scales. The original KKLT models are in this class.
We argue that certain features of the KKLT model are generic to this branch,
and that the resulting phenomenology depends on a small set of discrete
choices. As in the MSSM, the weak scale in these theories is tuned; a possible
explanation is selection for the dark matter density.Comment: 16 pages. More thorough analysis; additonal reference
Cosmological Models and Renormalization Group Flow
We study cosmological solutions of Einstein gravity with a positive
cosmological constant in diverse dimensions. These include big-bang models that
re-collapse, big-bang models that approach de Sitter acceleration at late
times, and bounce models that are both past and future asymptotically de
Sitter. The re-collapsing and the bounce geometries are all tall in the sense
that entire spatial slices become visible to a comoving observer before the end
of conformal time, while the accelerating big-bang geometries can be either
short or tall. We consider the interpretation of these cosmological solutions
as renormalization group flows in a dual field theory and give a geometric
interpretation of the associated c-function as the area of the apparent
cosmological horizon in Planck units. The covariant entropy bound requires
quantum effects to modify the early causal structure of some of our big-bang
solutions.Comment: 26 pages, 11 figures, v2: improved discussion of entropy bounds,
references added, v3: minor changes, reference adde
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