3,198 research outputs found
Static and non-static quantum effects in two-dimensional dilaton gravity
We study backreaction effects in two-dimensional dilaton gravity. The
backreaction comes from an term which is a part of the one-loop effective
action arising from massive scalar field quantization in a certain
approximation. The peculiarity of this term is that it does not contribute to
the Hawking radiation of the classical black hole solution of the field
equations. In the static case we examine the horizon and the physical
singularity of the new black hole solutions. Studying the possibility of time
dependence we see the generation of a new singularity. The particular solution
found still has the structure of a black hole, indicating that non-thermal
effects cannot lead, at least in this approximation, to black hole evaporation.Comment: 10 pages, no figure
Decoherent Scattering of Light Particles in a D-Brane Background
We discuss the scattering of two light particles in a D-brane background. It
is known that, if one light particle strikes the D brane at small impact
parameter, quantum recoil effects induce entanglement entropy in both the
excited D brane and the scattered particle. In this paper we compute the
asymptotic `out' state of a second light particle scattering off the D brane at
large impact parameter, showing that it also becomes mixed as a consequence of
quantum D-brane recoil effects. We interpret this as a non-factorizing
contribution to the superscattering operator S-dollar for the two light
particles in a Liouville D-brane background, that appears when quantum D-brane
excitations are taken into account.Comment: 18 pages LATEX, one figure (incorporated
Unimodular Loop Quantum Cosmology
Unimodular gravity is based on a modification of the usual Einstein-Hilbert
action that allows one to recover general relativity with a dynamical
cosmological constant. It also has the interesting property of providing, as
the momentum conjugate to the cosmological constant, an emergent clock
variable. In this paper we investigate the cosmological reduction of unimodular
gravity, and its quantization within the framework of flat homogeneous and
isotropic loop quantum cosmology. It is shown that the unimodular clock can be
used to construct the physical state space, and that the fundamental features
of the previous models featuring scalar field clocks are reproduced. In
particular, the classical singularity is replaced by a quantum bounce, which
takes place in the same condition as obtained previously. We also find that
requirement of semi-classicality demands the expectation value of the
cosmological constant to be small (in Planck units). The relation to spin foam
models is also studied, and we show that the use of the unimodular time
variable leads to a unique vertex expansion.Comment: 26 pages. Revised version taking into account referee's comment
Breast cancer–secreted factors perturb murine bone growth in regions prone to metastasis
Breast cancer frequently metastasizes to bone, causing osteolytic lesions. However, how factors secreted by primary tumors affect the bone microenvironment before the osteolytic phase of metastatic tumor growth remains unclear. Understanding these changes is critical as they may regulate metastatic dissemination and progression. To mimic premetastatic bone adaptation, immunocompromised mice were injected with MDA-MB-231–conditioned medium [tumor-conditioned media (TCM)]. Subsequently, the bones of these mice were subjected to multiscale, correlative analysis including RNA sequencing, histology, micro–computed tomography, x-ray scattering analysis, and Raman imaging. In contrast to overt metastasis causing osteolysis, TCM treatment induced new bone formation that was characterized by increased mineral apposition rate relative to control bones, altered bone quality with less matrix and more carbonate substitution, and the deposition of disoriented mineral near the growth plate. Our study suggests that breast cancer–secreted factors may promote perturbed bone growth before metastasis, which could affect initial seeding of tumor cells
Gauge symmetries of strings in supertwistor space
Recently we have considered supertwistor reformulation of the D=4 N=1,2
superstring action that comprises Newman-Penrose dyad components and is
classically equivalent to the Green-Schwarz one. It was shown that in the
covariant kappa-symmetry gauge the supertwistor representation of the string
action simplifies. Here we analyze its Hamiltonian formulation, classify the
constraints on the phase-space variables, and find the covariant set of
generators of the gauge symmetries. Quantum symmetries of the supertwistor
representation of the string action are examined applying the world-sheet CFT
technique. Considered are various generalizations of the model from the
perspective of their possible relation to known twistor superstring models.Comment: 17 pages, LaTeX; v.2 minor changes in the text, references added,
misprints correcte
Ultrasonic Flaw Detection Using Neural Network Models and Statistical Analysis: Simulation Studies
Flaw detection problems in ultrasonic NDE can be considered as two-class classification problems, i.e., determining whether a flaw is present or not present. To be practical, a flaw classification method must be able to handle the uncertainties associated with interference from grain noise which leads to poor signal-to-noise ratios (SNR). In this work, the use of neural network models and statistical correlation is demonstrated for one such detection/classification problem. In particular, based on simulation studies, we wish to establish practical strategies in detecting weak volumetric flaw signals corrupted by high grain noise. An example of this type that is of recent interest is the detection of “hard-alpha” inclusions in aircraft titanium components [1]. Both the feasibility and reliability of using these classifiers are assessed. This effort was carried out in parallel with another study [2] where more traditional signal processing approaches were taken
Tachyon Field Quantization and Hawking Radiation
We quantize the tachyon field in a static two dimensional dilaton gravity
black hole background,and we calculate the Hawking radiation rate. We find that
the thermal radiation flux, due to the tachyon field, is larger than the
conformal matter one. We also find that massive scalar fields which do not
couple to the dilaton, do not give any contribution to the thermal radiation,
up to terms quadratic in the scalar curvature.Comment: 13 pages, Latex file, 1 figure available upon reques
GUT theories from Calabi-Yau 4-folds with SO(10) Singularities
We consider an SO(10) GUT model from F-theory compactified on an elliptically
fibered Calabi-Yau with a D5 singularity. To obtain the matter curves and the
Yukawa couplings, we use a global description to resolve the singularity. We
identify the vector and spinor matter representations and their Yukawa
couplings and we explicitly build the G-fluxes in the global model and check
the agreement with the semi-local results. As our bundle is of type SU(2k),
some extra conditions need to be applied to match the fluxes.Comment: 27 page
Nitrogen-Functionalized Graphene Nanoflakes (GNFs:N): Tunable Photoluminescence and Electronic Structures
This study investigates the strong photoluminescence (PL) and X-ray excited
optical luminescence observed in nitrogen-functionalized 2D graphene nanoflakes
(GNFs:N), which arise from the significantly enhanced density of states in the
region of {\pi} states and the gap between {\pi} and {\pi}* states. The
increase in the number of the sp2 clusters in the form of pyridine-like N-C,
graphite-N-like, and the C=O bonding and the resonant energy transfer from the
N and O atoms to the sp2 clusters were found to be responsible for the blue
shift and the enhancement of the main PL emission feature. The enhanced PL is
strongly related to the induced changes of the electronic structures and
bonding properties, which were revealed by the X-ray absorption near-edge
structure, X-ray emission spectroscopy, and resonance inelastic X-ray
scattering. The study demonstrates that PL emission can be tailored through
appropriate tuning of the nitrogen and oxygen contents in GNFs and pave the way
for new optoelectronic devices.Comment: 8 pages, 6 figures (including toc figure
X-ray absorption spectroscopy studies of Ba1-xCaxTiO3
[[abstract]]We report x-ray absorption near edge spectroscopy (XANES) of Ca and O K-edges of Ba1-xCaxTiO3 (x = 0, 0.01, 0.08, 1) and understand the spectral features related to the electronic structure of these perovskites. The XANES spectra of Ca K-edge possess a pre-edge peak similar to other 3d transition metals like Ti, Ni when present in perovskite structure and provides information about p-type or hole
doping. Presence of considerable amount of 3d states justifies the reason to consider it as a light 3d transition metal. The O K-edge spectra display characteristic spectral features assigned as eg and t2g and show strong dependence on concentration.[[notice]]補正完畢[[journaltype]]國外[[booktype]]紙本[[booktype]]電子版[[countrycodes]]US
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