315 research outputs found
Asymptotic behavior in the scalar field theory
An asymptotic solution of the system of Schwinger-Dyson equations for
four-dimensional Euclidean scalar field theory with interaction
is obtained. For
the two-particle amplitude has the
pathology-free asymptotic behavior at large momenta. For
the amplitude possesses Landau-type singularity.Comment: 16 pages; journal version; references adde
Higher dimensional VSI spacetimes
We present the explicit metric forms for higher dimensional vanishing scalar
invariant (VSI) Lorentzian spacetimes. We note that all of the VSI spacetimes
belong to the higher dimensional Kundt class. We determine all of the VSI
spacetimes which admit a covariantly constant null vector, and we note that in
general in higher dimensions these spacetimes are of Ricci type III and Weyl
type III. The Ricci type N subclass is related to the chiral null models and
includes the relativistic gyratons and the higher dimensional pp-wave
spacetimes. The spacetimes under investigation are of particular interest since
they are solutions of supergravity or superstring theory.Comment: 14 pages, changes in second paragraph of the discussio
On Spacetimes with Constant Scalar Invariants
We study Lorentzian spacetimes for which all scalar invariants constructed
from the Riemann tensor and its covariant derivatives are constant (
spacetimes). We obtain a number of general results in arbitrary dimensions. We
study and construct warped product spacetimes and higher-dimensional
Kundt spacetimes. We show how these spacetimes can be constructed from
locally homogeneous spaces and spacetimes. The results suggest a number
of conjectures. In particular, it is plausible that for spacetimes that
are not locally homogeneous the Weyl type is , , or , with any
boost weight zero components being constant. We then consider the
four-dimensional spacetimes in more detail. We show that there are severe
constraints on these spacetimes, and we argue that it is plausible that they
are either locally homogeneous or that the spacetime necessarily belongs to the
Kundt class of spacetimes, all of which are constructed. The
four-dimensional results lend support to the conjectures in higher dimensions.Comment: 25 pages, 1 figure, v2: minor changes throughou
Non differentiable large-deviation functionals in boundary-driven diffusive systems
We study the probability of arbitrary density profiles in conserving
diffusive fields which are driven by the boundaries. We demonstrate the
existence of singularities in the large-deviation functional, the direct analog
of the free-energy in non-equilibrium systems. These singularities are unique
to non-equilibrium systems and are a direct consequence of the breaking of
time-reversal symmetry. This is demonstrated in an exactly-solvable model and
also in numerical simulations on a boundary-driven Ising model. We argue that
this singular behavior is expected to occur in models where the compressibility
has a deep enough minimum. The mechanism is explained using a simple model.Comment: 5 pages, 3 figure
Particle motion and gravitational lensing in the metric of a dilaton black hole in a de Sitter universe
We consider the metric exterior to a charged dilaton black hole in a de
Sitter universe. We study the motion of a test particle in this metric.
Conserved quantities are identified and the Hamilton-Jacobi method is employed
for the solutions of the equations of motion. At large distances from the black
hole the Hubble expansion of the universe modifies the effective potential such
that bound orbits could exist up to an upper limit of the angular momentum per
mass for the orbiting test particle. We then study the phenomenon of strong
field gravitational lensing by these black holes by extending the standard
formalism of strong lensing to the non-asymptotically flat dilaton-de Sitter
metric. Expressions for the various lensing quantities are obtained in terms of
the metric coefficients.Comment: 8 pages, RevTex, 1 eps figures; discussion improved; typos corrected;
references adde
DEFROST: A New Code for Simulating Preheating after Inflation
At the end of inflation, dynamical instability can rapidly deposit the energy
of homogeneous cold inflaton into excitations of other fields. This process,
known as preheating, is rather violent, inhomogeneous and non-linear, and has
to be studied numerically. This paper presents a new code for simulating scalar
field dynamics in expanding universe written for that purpose. Compared to
available alternatives, it significantly improves both the speed and the
accuracy of calculations, and is fully instrumented for 3D visualization. We
reproduce previously published results on preheating in simple chaotic
inflation models, and further investigate non-linear dynamics of the inflaton
decay. Surprisingly, we find that the fields do not want to thermalize quite
the way one would think. Instead of directly reaching equilibrium, the
evolution appears to be stuck in a rather simple but quite inhomogeneous state.
In particular, one-point distribution function of total energy density appears
to be universal among various two-field preheating models, and is exceedingly
well described by a lognormal distribution. It is tempting to attribute this
state to scalar field turbulence.Comment: RevTeX 4.0; 16 pages, 9 figure
The geodesic structure of the Schwarzschild Anti-de Sitter black hole
In the present work we found the geodesic structure of an AdS black hole. By
means of a detailed analyze of the corresponding effective potentials for
particles and photon, we found all the possible motions which are allowed by
the energy levels. Radial and non radial trajectories were exactly evaluated
for both geodesics. The founded orbits were plotted in order to have a direct
visualization of the allowed motions. We show that the geodesic structure of
this black hole presents new type of motions not allowed by the Schwarzschild
spacetime.Comment: 17 pages, 11 figure
Антимикробная фотодинамическая терапия в голосовой реабилитации пациентов после ларингэктомии
The article is devoted to the problem of voice rehabilitation of patients after laryngectomy. Modern possibilities of repairing laryngeal vocal function, methods for extending the lifetime of voice prostheses are considered. The author’s method of prevention of infection of vocal prostheses using the antimicrobial photodynamic therapy (PDT) with chlorin-type photosensitizer Radagel is presented. Performing antimicrobial PDT of vocal prostheses increased the average operating time to 11.9 months compared to the control group (6.8 months), where a monthly dose of 150 mg of fluconazole was used for prevention. The method developed by the authors makes it possible to significantly extend the lifetime of vocal prostheses, is devoid of adverse events, is well tolerated by patients.Статья посвящена проблеме голосовой реабилитации пациентов после ларингэктомии. Рассмотрены современные возможности восстановления голосовой функции после ларингэктомии, способы увеличения срока эксплуатации голосовых протезов, представлен авторский метод профилактики инфекции голосовых протезов с помощью антимикробной фотодинамической терапии (ФДТ) с фотосенсибилизатором хлоринового ряда. Проведение антимикробной ФДТ голосовых протезов позволило увеличить средний срок эксплуатации до 11,9 мес по сравнению с контрольной группой (6,8 мес), где для профилактики использовали ежемесячный прием 150 мг флуконазола. Антимикробная ФДТ позволяет существенно продлить срок эксплуатации голосовых протезов, не имеет побочных явлений, хорошо переносится больными
A Stochastic Measure for Eternal Inflation
We use the stochastic approach to investigate the measure for slow roll
eternal inflation. The probability for the universe of a given Hubble radius
can be calculated in this framework. In a solvable model, it is shown that the
probability for the universe to evolve from a state with a smaller Hubble
radius to that of a larger Hubble radius is dominated by the classical
probability without the stochastic source. While the probability for the
universe to evolve from a larger Hubble radius to a smaller one is suppressed
by , where the de Sitter entropy arises naturally in this
stochastic approach.Comment: 11 pages, 1 figur
Возможности обезболивания при фотодинамической терапии
The authors consider the possibilities of pain management during photodynamic therapy (PDT) of visible tumors based on the observation of 102 patients. Of the total number of patients, 62 had verified basal cell skin cancer, 10 people - squamous cell skin cancer, another 10 - oral and oropharynx mucosa cancer, 8 - oral leukoplakia and dysplasia, in 6 - lower lip cancer, in 4 - breast cancer, in 2 - other localizations of neoplasms. In 15 patients, nonsteroidal anti-inflammatory drugs (NSAID) were used as pain management, in 69 - a combination of NSAID with tramadol, in 14 - nerve block anesthesia, in 4 - PDT was performed under general anesthesia. The intensity of pain syndrome during laser irradiation of the tumor was assessed on the verbal rating scale (VRS). The absence of pain was recorded in 9% of cases. Mild pain was noted by 58% of patients, moderate pain - 20%, severe pain - 10%, very severe pain was noted by 3% of patients.The degree of expression of pain syndrome during PDT depends on the incidence of a lesion, histological form of tumor, and method of anesthesia. NSAID alone, or in combination with an opioid analgesic, allows effective control of pain syndrome in PDT of basal cell skin cancer in 89%, in PDT of squamous cell skin cancer in 66% of observations. Nerve block anesthesia allows stoping pain syndrome during PDT of oropharyngeal tumors.Авторы рассматривают возможности обезболивания при фотодинамической терапии (ФДТ) опухолей визуальных локализаций на основе анализа данных 102 пациентов. Среди пациентов, включенных в выборку, у 62 верифицирован базальноклеточный рак кожи, у 10 - плоскоклеточный рак кожи, у 10 - рак слизистой оболочки полости рта и ротоглотки, у 8 - лейкоплакия и дисплазия слизистой оболочки полости рта, у 6 - рак нижней губы, у 4 - рак молочной железы, у 2 - новообразования иных локализаций.У 15 пациентов для обезболивания применяли нестероидные противовоспалительные препараты (НПВС), у 69 - сочетание НПВС со слабыми опиоидами (трамадолом), у 14 - проводниковую анестезию, у 4 ФДТ проводили под общим обезболиванием. Интенсивность болевого синдрома оценивалась в процессе проведения лазерного облучения опухоли по шкале вербальных оценок (ШВО). Отсутствие болевых ощущений зафиксировано в 9% наблюдений. Слабую боль отмечали в 58% наблюдений, умеренную боль – в 20%, сильную боль - в 10%, очень сильную боль - в 3% наблюдений.Степень выраженности болевого синдрома при проведении ФДТ зависит от распространенности поражения, гистологической формы опухоли и способа обезболивания. НПВС в самостоятельном варианте или в сочетании с опиоидным анальгетиком позволяют эффективно контролировать болевой синдром при ФДТ базальноклеточного рака кожи в 89%, плоскоклеточного рака кожи – в 66% наблюдений. Проводниковая анестезия позволяет купировать болевой синдром при проведении ФДТ опухолей орофарингеальной области
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