2,120 research outputs found
A family of anisotropic integral operators and behaviour of its maximal eigenvalue
We study the family of compact integral operators in
with the kernel K_\beta(x, y) = \frac{1}{\pi}\frac{1}{1 +
(x-y)^2 + \beta^2\Theta(x, y)}, depending on the parameter , where
is a symmetric non-negative homogeneous function of degree
. The main result is the following asymptotic formula for the
maximal eigenvalue of : M_\beta = 1 - \lambda_1
\beta^{\frac{2}{\gamma+1}} + o(\beta^{\frac{2}{\gamma+1}}), \beta\to 0, where
is the lowest eigenvalue of the operator . A central role in the proof is played by the fact that
is positivity improving. The case has been studied earlier in the literature as a simplified model
of high-temperature superconductivity.Comment: 16 page
The Remarkable Mid-Infrared Jet of Massive Young Stellar Object G35.20-0.74
The young massive stellar object G35.20-0.74 was observed in the mid-infrared
using T-ReCS on Gemini South. Previous observations have shown that the near
infrared emission has a fan-like morphology that is consistent with emission
from the northern lobe of a bipolar radio jet known to be associated with this
source. Mid-infrared observations presented in this paper show a monopolar
jet-like morphology as well, and it is argued that the mid-infrared emission
observed is dominated by thermal continuum emission from dust. The mid-infrared
emission nearest the central stellar source is believed to be directly heated
dust on the walls of the outflow cavity. The hydroxyl, water, and methanol
masers associated with G35.20-0.74 are spatially located along these
mid-infrared cavity walls. Narrow jet or outflow cavities such as this may also
be the locations of the linear distribution of methanol masers that are found
associated with massive young stellar objects. The fact that G35.20-0.74 has
mid-infrared emission that is dominated by the outflow, rather than disk
emission, is a caution to those that consider mid-infrared emission from young
stellar objects as only coming from circumstellar disks.Comment: Accepted for publication in ApJ Letters; 4 pages; 2 figures; a
version with full resolution images is available here:
http://www.ctio.noao.edu/~debuizer
On the accuracy of the ALI method for solving the radiative transfer equation
We solve the integral equation describing the propagation of light in an
isothermal plane-parallel atmosphere of optical thickness , adopting a
uniform thermalization parameter . The solution given by the ALI
method, widely used in the field of stellar atmospheres modelling, is compared
to the exact solution. Graphs are given that illustrate the accuracy of the ALI
solution as a function of the parameters , and optical depth
variable .Comment: 7 pages, 11 figures, A&A, accepted 30 July 2003, minor correction
THE MACROKINETICS PARAMETERS OF THE HYDROCARBONS COMBUSTION IN THE NUMERICAL CALCULATION OF ACCIDENTAL EXPLOSIONS IN MINES
Purpose. Obtaining effective parameters of the macrokinetics of combustion of hydrocarbons in the deflagration
and detonation regime for the numerical calculation of emergency explosions in mine workings.
Methodology. Mathematical modeling, numerical experiment, kinetics analysis of explosive combustion reaction,
analysis and synthesis.
Findings. The paper analyzes the parameters of the kinetic equation against experimental data. Obtaining such
data in a physical experiment for explosive chemical reactions meets serious difficulties. This is due to the size of the
reaction zone not exceeding fractions of a millimeter, the lack of time resolution of experimental techniques and
other factors leading to errors in direct measurements and the emergence of multiple solutions. This possibility contributes to obtaining a simultaneous numerical solution of the equations of gas dynamics and chemical kinetics. In the
numerical experiment, a direct relationship between the macrokinetic characteristics of the chemical reaction and the
parameters of the discontinuous flow of the reacting gas stream is established: velocity, pressure in the front and behind the front of the detonation and deflagration wave. Based on this, Arrhenius characteristics of the reaction – preexponential and effective activation energy for the hydrocarbons under consideration are obtained.
Originality. Macrokinetic parameters are established for simulating one-stage ignition and burning of the most probable hydrocarbons of the mine atmosphere in the deflagration and detonation regime. Modeling of explosive combustion of premixed hydrocarbons in stoichiometric concentrations is performed. It is shown that the values of
the effective activation energy in explosive combustion reactions are of less importance in contrast to steady-state
combustion reactions because of the effect of the gas-dynamical effects of the shock wave on the reaction rate. The
Arrhenius characteristics of the reaction – the pre-exponential and the effective activation energy – have been agreed
upon, according to the gas dynamic and kinetic parameters of the course of the explosive combustion reaction.
Practical value. The obtained parameters of the macrokinetics of the explosive combustion reaction make it possible to apply simple kinetic mechanisms in practical calculations of the processes of deflagration and detonation
combustion, and to predict the parameters of emergency explosions in conditions of mine workings with sufficient accuracy. This also makes it possible to solve the problem of accounting for the presence of heavy hydrocarbons in themine atmosphere as products of coal pyrolysis in underground fires as factors of increasing the risk of emergency
explosions
How do methanol masers manage to appear in the youngest star vicinities and isolated molecular clumps?
General characteristics of methanol (CH3OH) maser emission are summarized. It
is shown that methanol maser sources are concentrated in the spiral arms. Most
of the methanol maser sources from the Perseus arm are associated with embedded
stellar clusters and a considerable portion is situated close to compact HII
regions. Almost 1/3 of the Perseus Arm sources lie at the edges of optically
identified HII regions which means that massive star formation in the Perseus
Arm is to a great extent triggered by local phenomena. A multiline analysis of
the methanol masers allows us to determine the physical parameters in the
regions of maser formation. Maser modelling shows that class II methanol masers
can be pumped by the radiation of the warm dust as well as by free-free
emission of a hypercompact region hcHII with a turnover frequency exceeding 100
GHz. Methanol masers of both classes can reside in the vicinity of hcHIIs.
Modelling shows that periodic changes of maser fluxes can be reproduced by
variations of the dust temperature by a few percent which may be caused by
variations in the brightness of the central young stellar object reflecting the
character of the accretion process. Sensitive observations have shown that the
masers with low flux densities can still have considerable amplification
factors. The analysis of class I maser surveys allows us to identify four
distinct regimes that differ by the series of their brightest lines.Comment: 8 pages, 4 figures, invited presentation at IAU242 "Astrophysical
Masers and their environments
The quality of gosling meat depending on the level of lithium in mixed fodders
Micronutrients are an important component of a complete poultry feeding. Current detailed feeding standards provide guaranteed feed additives for farm poultry of the microelement complex. Among the normalized microelements there is no lithium, which according to the classification based on biological role for living organisms belongs to the group of conditionally essential elements. The purpose of the study was to investigate the effect of various doses of lithium in compound feed on the chemical composition and toxicological and biological parameters of caterpillar meat. The effect of additives of different doses of lithium (0.05 mg/kg, 0.10 and 0.15 mg/kg) in compound forages on the quality and safety of the products of slaughter of 70-day gosling was studied. The studies were conducted on gosling of the Legart breed. Feeding of gosling from day to 70 days of age was carried out by full-feed compound feeds. The birds of the experimental groups were additionally injected with lithium in the feed, mg/kg: the second group was 0.05; third – 0.10 and fourth – 0.15. The gosling of the control group did not receive lithium. Analysis of the results of the studies revealed differences between the control and experimental groups in the chemical composition of the muscular tissue of the gosling in favor of the latter. It was found that the introduction of lithium compound feed had a positive effect on the deposition of dry matter, protein and fat in the gosling of the experimental groups, which contributed to its increased energy and biological value. The best indicators of meat quality were in young animals, which during the growing period were fed compound feeds enriched with lithium at the rate of 0.1 and 0.15 mg/kg
Bethe-Sommerfeld conjecture for periodic operators with strong perturbations
We consider a periodic self-adjoint pseudo-differential operator
, , in which satisfies the following conditions:
(i) the symbol of is smooth in \bx, and (ii) the perturbation has
order less than . Under these assumptions, we prove that the spectrum of
contains a half-line. This, in particular implies the Bethe-Sommerfeld
Conjecture for the Schr\"odinger operator with a periodic magnetic potential in
all dimensions.Comment: 61 page
Sources of Radiation in the Early Universe: The Equation of Radiative Transfer and Optical Distances
We have derived the radiative-transfer equation for a point source with a
specified intensity and spectrum, originating in the early Universe between the
epochs of annihilation and recombination, at redshifts z_\s =10^8\div 10^4.
The direct radiation of the source is separated from the diffuse radiation it
produces. Optical distances from the source for Thomson scattering and
bremsstrahlung absorption at the maximum of the thermal background radiation
are calculated as a function of the redshift z.The distances grow sharply with
decreasing z, approaching asymptotic values, the absorption distance increasing
more slowly and reaching their limiting values at lower z. For the adopted z
values, the optical parameters of the Universe can be described in a flat model
with dusty material and radiation, and radiative transfer can be treated in a
grey approximation.Comment: 14 pages, 2 figure
Buy, sell, or hold? A sense-making account of factors influencing trading decisions
We investigated the effects of news valence, the direction of trends in graphically presented price series, and the culture and personality of traders in a financial trading task. Participants were given 12 virtual shares of financial assets and asked to use price graphs and news items to maximize their returns by buying, selling, or holding each one. In making their decisions, they were influenced by properties of both news items and price series but they relied more on the former. Western participants had lower trading latencies and lower return dispersions than Eastern participants. Those with greater openness to experience had lower trading latencies. Participants bought more shares when they forecast that prices would rise but failed to sell more when they forecast that they would fall. These findings are all consistent with the view that people trading assets try to make sense of information by incorporating it within a coherent narrative
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