3,212 research outputs found
Multi-particle Production and Thermalization in High-Energy QCD
We argue that multi-particle production in high energy hadron and nuclear
collisions can be considered as proceeding through the production of gluons in
the background classical field. In this approach we derive the gluon spectrum
immediately after the collision and find that at high energies it is
parametrically enhanced by ln(1/x) with respect to the quasi-classical result
(x is the Bjorken variable). We show that the produced gluon spectrum becomes
thermal (in three dimensions) with an effective temperature determined by the
saturation momentum Qs, T= c Qs/2pi during the time ~1/T; we estimate
c=sqrt{2pi}/2 ~ 1.2. Although this result by itself does not imply that the
gluon spectrum will remain thermal at later times, it has an interesting
applications to heavy ion collisions. In particular, we discuss the possibility
of Bose-Einstein condensation of the produced gluon pairs and estimate the
viscosity of the produced gluon system.Comment: 25 pages, 4 figures; typos fixed; discussions expanded; we added a
new section IV in which we argue that at high energies the production
mechanism discussed in the paper is parametrically enhanced by ln(1/x) with
respect to the quasi-classical resul
Oxygen minimum zones in the tropical Pacific across CMIP5 models: mean state differences and climate change trends
We analyse simulations of the Pacific Ocean oxygen minimum zones (OMZs) from 11 Earth system model contributions to the Coupled Model Intercomparison Project Phase 5, focusing on the mean state and climate change projections. The simulations tend to overestimate the volume of the OMZs, especially in the tropics and Southern Hemisphere. Compared to observations, five models introduce incorrect meridional asymmetries in the distribution of oxygen including larger southern OMZ and weaker northern OMZ, due to interhemispheric biases in intermediate water mass ventilation. Seven models show too deep an extent of the tropical hypoxia compared to observations, stemming from a deficient equatorial ventilation in the upper ocean, combined with too large a biologically driven downward flux of particulate organic carbon at depth, caused by particle export from the euphotic layer that is too high and remineralization in the upper ocean that is too weak.
At interannual timescales, the dynamics of oxygen in the eastern tropical Pacific OMZ is dominated by biological consumption and linked to natural variability in the Walker circulation. However, under the climate change scenario RCP8.5, all simulations yield small and discrepant changes in oxygen concentration at mid depths in the tropical Pacific by the end of the 21st century due to an almost perfect compensation between warming-related decrease in oxygen saturation and decrease in biological oxygen utilization. Climate change projections are at odds with recent observations that show decreasing oxygen levels at mid depths in the tropical Pacific.
Out of the OMZs, all the CMIP5 models predict a decrease of oxygen over most of the surface and deep ocean at low latitudes and over all depths at high latitudes due to an overall slow-down of ventilation and increased temperature
Pair creation in transport equations using the equal-time Wigner function
Based on the equal-time Wigner function for the Klein-Gordon field, we
discuss analytically the mechanism of pair creation in a classical
electromagnetic field including back-reaction. It is shown that the equations
of motion for the Wigner function can be reduced to a variable-frequency
oscillator. The pair-creation rate results then from a calculation analogous to
barrier penetration in nonrelativistic quantum mechanics. The Wigner function
allows one to utilize this treatment for the formulation of an effective
transport theory for the back-reaction problem with a pair-creation source term
including Bose enhancement.Comment: 19 pages, LaTeX, UFTP 316/199
The Quality of Lending Activity in Bulgaria
Financial result of banks is strongly dependent on the ability of their credit portfolios to generate enough revenue at risk which credit institutions find acceptable. In order to achieve stability and desirable growth of market share, banks aim to maintain a good quality of loan commitments undertaken by their clients. In this regard, expert analysis and evaluation of the suitability of bank lending are of great information significance to the management structures and successful development of commercial banks.Фінансовий результат банків залежить від здатності їх кредитних портфелів, щоб робити досить доходу в ризику, який кредитні установи знаходять прийнятним. Для того, щоб досягти стабільності і бажаного зростання ринку, банки прагнуть підтримувати добротність зобов'язань по позиках, виданих їх клієнтах. В цьому відношенні, експертиза і оцінка придатності банківського надання є великим інформаційним значенням до структур управління і успішного розвитку комерційних банків.Финансовый результат банков настоятельно зависит от способности их кредитных портфелей, чтобы производить достаточно дохода в риске, который кредитные учреждения находят приемлемым. Для того, чтобы достичь стабильности и желательного роста рынка, банки стремятся поддерживать добротность обязательств по ссудам, выданным их клиентам. В этом отношении, экспертиза и оценка пригодности банковского предоставления являются большим информационным значением к структурам управления и успешному развитию коммерческих банков
Study of influence of heat stress on some physiological and productive traits in Holstein-Friesian dairy cows
Received: October 6th, 2020 ; Accepted: February 1st, 2021 ; Published: March 18th, 2021 ; Correspondence: [email protected] aim of the research was to study the effect of heat stress (HS) on some physiological
and productive traits in Holstein-Friesian dairy cows. The study included 22 cows on different
parities. In the building where the cows were housed, the temperature-humidity index (THI) was
reported at 10:00 and 15:00 h, at the same time the rectal temperature (RT) and respiratory rate
(RR) were reported for each of the examined cows. The daily rumen activity was taken from the
SCR system by Allflex. The average THI values in May were 71, in June - 75, in July - 74, and
in August - 77, from which it follows that in the summer months the cows were in conditions of
mild to moderate heat stress throughout the day. The average daily milk yield of the cows increased
from May to June and reached 41.44 kg day-1
, then decreased in July and August to 37.2 and
32.48 kg day-1
, respectively. With an increase in the THI values, an increase in the RR and RT
was registered, as in THI above 79 the RR was 56.54 per min, and the RT was 39.33 °C. With
increasing the THI values, the rumination of the cows decreased from 563 per day at THI < 72 to
542.5 at THI > 79. In cows with high daily milk yield, a higher RT was registered, and in cows with
more than 50 kg per day, the RT was 39.09 °С. A more intense rumination was found in cows
with higher daily milk yield. In cows with an average daily milk yield of 33.26 kg, an average of
450 ruminations per day were reported, and in those with an average milk yield of up to 42.89 kg
- 650 ruminations per day. From the research conducted it was found that the studied
physiological traits - rectal temperature, respiration rate and rumination are influenced by HS and
the intensity of this effect depend on the daily milk yield of cows and THI levels
Vector boson in constant electromagnetic field
The propagator and complete sets of in- and out-solutions of wave equation,
together with Bogoliubov coefficients, relating these solutions, are obtained
for vector -boson (with gyromagnetic ratio ) in a constant
electromagnetic field. When only electric field is present the Bogoliubov
coefficients are independent of boson polarization and are the same as for
scalar boson. When both electric and magnetic fields are present and collinear,
the Bogoliubov coefficients for states with boson spin perpendicular to the
field are again the same as in scalar case. For spin along (against) the
magnetic field the Bogoliubov coefficients and the contributions to the
imaginary part of the Lagrange function in one loop approximation are obtained
from corresponding expressions for scalar case by substitution
. For gyromagnetic ratio the vector boson interaction
with constant electromagnetic field is described by the functions, which can be
expected by comparing wave functions for scalar and Dirac particle in constant
electromagnetic field.Comment: 20 pages, LATEX2e, no figure
Density resummation of perturbation series in a pion gas to leading order in chiral perturbation theory
The mean field (MF) approximation for the pion matter, being equivalent to
the leading ChPT order, involves no dynamical loops and, if self-consistent,
produces finite renormalizations only. The weight factor of the Haar measure of
the pion fields, entering the path integral, generates an effective Lagrangian
which is generally singular in the continuum limit.
There exists one parameterization of the pion fields only, for which the weight
factor is equal to unity and , respectively. This
unique parameterization ensures selfconsistency of the MF approximation. We use
it to calculate thermal Green functions of the pion gas in the MF approximation
as a power series over the temperature. The Borel transforms of thermal
averages of a function of the pion
fields with respect to the scalar pion density are found to be
. The perturbation series over the scalar
pion density for basic characteristics of the pion matter such as the pion
propagator, the pion optical potential, the scalar quark condensate
, the in-medium pion decay constant , and the
equation of state of pion matter appear to be asymptotic ones. These series are
summed up using the contour-improved Borel resummation method. The quark scalar
condensate decreases smoothly until MeV. The temperature
is the maximum temperature admissible for thermalized non-linear
sigma model at zero pion chemical potentials. The estimate of is
above the chemical freeze-out temperature MeV at RHIC and above
the phase transition to two-flavor quark matter MeV,
predicted by lattice gauge theories.Comment: Replaced with revised and extended version. Results are compared to
lattice gauge theories. 16 pages REVTeX, 13 eps figure
Pair production by boost-invariant fields in comoving coordinates
We derive the pair-production probability in a constant electric field in
Rindler coordinates in a quasi-classical approximation. Our result is different
from the pair-production probability in an inertial frame (Schwinger formula).
In particular, it exhibits non-trivial dependence on rapidity and deviation
from Gaussian behavior at small transverse momenta. Our results can be
important for analysis of particle production in heavy-ion collisions.Comment: 12 pages, 2 figures. Discussion added and typos fixe
Percolation in the Harmonic Crystal and Voter Model in three dimensions
We investigate the site percolation transition in two strongly correlated
systems in three dimensions: the massless harmonic crystal and the voter model.
In the first case we start with a Gibbs measure for the potential,
, , and , a scalar height variable, and define
occupation variables for . The probability
of a site being occupied, is then a function of . In the voter model we
consider the stationary measure, in which each site is either occupied or
empty, with probability . In both cases the truncated pair correlation of
the occupation variables, , decays asymptotically like .
Using some novel Monte Carlo simulation methods and finite size scaling we find
accurate values of as well as the critical exponents for these systems.
The latter are different from that of independent percolation in , as
expected from the work of Weinrib and Halperin [WH] for the percolation
transition of systems with [A. Weinrib and B. Halperin,
Phys. Rev. B 27, 413 (1983)]. In particular the correlation length exponent
is very close to the predicted value of 2 supporting the conjecture by WH
that is exact.Comment: 8 figures. new version significantly different from the old one,
includes new results, figures et
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