655 research outputs found
Coleman-Weinberg Phase Transition in Two-Scalar Models
We explore the Coleman-Weinberg phase transition in regions outside the
validity of perturbation theory. For this purpose we study a Euclidean field
theory with two scalars and discrete symmetry in four dimensions. The phase
diagram is established by a numerical solution of a suitable truncation of
exact non-perturbative flow equations. We find regions in parameter space where
the phase transition (in dependence on the mass term) is of the second or the
first order, separated by a triple point. Our quantitative results for the
first order phase transition compare well to the standard perturbative
Coleman-Weinberg calculation of the effective potential.Comment: 14 pages, Oxford OUTP 94-14 P, Heidelberg HD-THEP-94-1
High Temperature Phase Transitions in Two-Scalar Theories with Large Techniques
We consider a theory of a scalar one-component field coupled to a
scalar -component field . Using large techiques we calculate the
effective potential in the leading order in . We show that this is
equivalent to a resummation of an infinite subclass of graphs in perturbation
theory, which involve fluctuations of the field only. We study the
temperature dependence of the expectation value of the field and the
resulting first and second order phase transitions.Comment: 11 pages, LaTex, includes 5 uuencoded postscript figures, OUTP-94-11
Coupled-channels effects in elastic scattering and near-barrier fusion induced by weakly bound nuclei and exotic halo nuclei
The influence on fusion of coupling to the breakup process is investigated
for reactions where at least one of the colliding nuclei has a sufficiently low
binding energy for breakup to become an important process. Elastic scattering,
excitation functions for sub-and near-barrier fusion cross sections, and
breakup yields are analyzed for Li+Co. Continuum-Discretized
Coupled-Channels (CDCC) calculations describe well the data at and above the
barrier. Elastic scattering with Li (as compared to Li) indicates
the significant role of breakup for weakly bound projectiles. A study of
He induced fusion reactions with a three-body CDCC method for the
He halo nucleus is presented. The relative importance of breakup and
bound-state structure effects on total fusion is discussed.Comment: 29 pages, 9 figure
Long-term variability of the optical spectra of NGC 4151: II. Evolution of the broad Ha and Hb emission-line profiles
Results of the long-term (11 years, from 1996 to 2006) H and H
line variations of the active galactic nucleus of NGC 4151 are presented. High
quality spectra (S/N>50 and R~8A) of H and H were investigated.
We analyzed line profile variations during monitoring period. Comparing the
line profiles of H and H, we studied different details (bumps,
absorption features) in the line profiles. The variations of the different
H and H line profile segments have been investigated. Also, we
analyzed the Balmer decrement for whole line and for line segments. We found
that the line profiles were strongly changing during the monitoring period,
showing blue and red asymmetries. This indicates a complex BLR geometry of NGC
4151 with, at least, three kinematically distinct regions: one that contributes
to the blue line wing, one to the line core and one to the red line wing. Such
variation can be caused by an accelerating outflow starting very close to the
black hole, where the red part may come from the region {closer to the black
hole than the blue part, which is coming} from the region having the highest
outflow velocities. Taking into account the fact that the BLR of NGC 4151 has a
complex geometry (probably affected by an outflow) and that a portion of the
broad line emission seems to have not a pure photoionization origin, one can
ask the question whether the study of the BLR by reverberation mapping may be
valid in the case of this galaxy.Comment: 24 pages, 18 figures, accepted for publications in A&
Observational physics of mirror world
The existence of the whole world of shadow particles, interacting with each other and having no mutual interactions with ordinary particles except gravity is a specific feature of modern superstring models, being considered as models of the theory of everything. The presence of shadow particles is the necessary condition in the superstring models, providing compensation of the asymmetry of left and right chirality states of ordinary particles. If compactification of additional dimensions retains the symmetry of left and right states, shadow world turns to be the mirror one, with particles and fields having properties strictly symmetrical to the ones of corresponding ordinary particles and fields. Owing to the strict symmetry of physical laws for ordinary and mirror particles, the analysis of cosmological evolution of mirror matter provides rather definite conclusions on possible effects of mirror particles in the universe. A general qualitative discussion of possible astronomical impact of mirror matter is given, in order to make as wide as possible astronomical observational searches for the effects of mirror world, being the unique way to test the existence of mirror partners of ordinary particles in the Nature
Long-term variability of the optical spectra of NGC 4151: I. Light curves and flux correlations
Results of a long-term spectral monitoring of the active galactic nucleus of
NGC 4151 are presented (11 years, from 1996 to 2006). High quality spectra
(S/N>50 in the continuum near Halpha and Hbeta) were obtained in the spectral
range ~4000 to 7500 \AA, with a resolution between 5 and 15 A, using the 6-m
and the 1-m SAO's telescopes (Russia), the GHAO's 2.1-m telescope (Cananea,
Mexico), and the OAN-SPM's 2.1-m telescope (San-Pedro, Mexico). The observed
fluxes of the Halpha, Hbeta, Hgamma and HeII emission lines and of the
continuum at the observed wavelength 5117 A, were corrected for the position
angle, the seeing and the aperture effects.
We found that the continuum and line fluxes varied strongly (up to a factor
6) during the monitoring period. The emission was maximum in 1996-1998, and
there were two minima, in 2001 and in 2005. The Halpha, Hgamma and He II fluxes
were well correlated with the Hbeta flux. We considered three characteristic
periods during which the Hbeta and Halpha profiles were similar: 1996-1999,
2000-2001 and 2002-2006. The line to continuum flux ratios were different; in
particular during the first period, the lines were not correlated with the
continuum and saturated at high fluxes. In the second and third period, where
the continuum flux was small, the Halpha and Hbeta fluxes were well correlated
to the continuum flux, meaning that the ionizing continuum was a good
extrapolation of the optical continuum. The CCFs are often asymmetrical and the
time lags between the lines and the continuum are badly defined indicating the
presence of a complex BLR, with dimensions from 1 to 50 light-days.Comment: A&A, accepte
Distribution of polarization and intensity of radiation across the stellar disk and numberical values of atmospheric characteristics governing this distribution
Computations of polarization and intensity of radiation from a unit stellar surface area are presented, as well as a study of the numerical characteristics of atmospheres - single-scattering albedo Ωλ and the initial source functionλ(δλ), which define the polarization behaviour of atmospheres. The radiatively stable models of stellar atmospheres presented by Kurucz et al. (1974) and Kurucz (1979) have been used for calculations. Since the Ωλ versus optical depth τλ dependence is rather weak, it has been assumed that Ωλ(τλ=cost. With a fixed effective temperature Teff maximum values of Ω are characteristic of stars featuring the lowest surface gravity acceleration g. Among stars with radiatively stable atmospheres, maximum values of Ω (λ=5000 Å) ≈ 0.4-0.6 are exhibited by supergiants with Teff=8000-20 000 K. The plot of Ω(λ) is characterized by discontinuities at the boundaries of spectral series for hydrogen and, sometimes, for helium. Maximum Ωλ are attained in the Lyman region of λ=912-1200 Å, where Ωλ can reach the value 0.7-0.9 for supergiants, this value being ≳ 0.3 for Main-Sequence stars. For stars with Teff ≳ 35 000 K, high values of Ωλ also are attained for λ<912 Å. Within the infrared region, Ωλ is always small because of bremsstrahlung absorption. A rapid growth of the source function Bλ with <λ typical for ultraviolet range (within the Wien part of spectrum), together with high values of Ωλ results in the strong polarization of emission from a unit stellar surface element, sometimes exceeding the values for the case of a pure electron scattering. For longer wavelengths, where the limb-darkening coefficient is smaller, the plane of polarization abruptly turns 90° in the central parts of the visible stellar disk. © 1985 D. Reidel Publishing Company
МНОГОУРОВНЕВЫЙ ДОСМОТР В АЭРОПОРТАХ
Aviation security receives more and more assignments butitis not always obvious how these financial instruments are spent and what are the goals of investment. The authors review one of the most realistic lines of investments, which is engineering of new smart systems of check-out of passenger luggage.На обеспечение авиационной безопасности выделяется все больше средств, но далеко не всегда понятно, на что именно они расходуются, каковы цели вложений. Авторы статьи показывают одно из реальных направлений инвестиций – создание новых, более совершенных технических систем досмотра багажа авиапассажиров
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