1,246 research outputs found
Ferromagnetic Detectors of Axions in RF (S - X) Band
The (pseudo) Goldstone bosons arise naturally in many modern theories such as
supergravity, superstring theory and variants of general relativity with
torsion. By the other hand, there are well known indications that a large part
of the Universe mass exists in a form of dark matter. The most attractive model
of the dark matter is non-relativistic gas of the light elementary particles
weakly interacting with the "usual" matter \cite{b2} - \cite{b4}. We describe
ferromagnetic detectors, for search of arion(axion), where a high-sensitive
two-channel SHF receiver is used. Its sensitivity reaches to ,
with time of accumulation . Fourier analysis of signal provides a
survey in zone up to with spectral resolution .
There was applied a high sensitive SHF receiver based on a special computer
method of coherent accumulation of signals. It is possible to use the receiver
in other precise experiments: measuring of electron/positron beams polarization
in storage rings, investigation of parity violation, investigation of
atmosphere with radars etc.Comment: 6 pages, LaTeX, no figure
Resonant Enhancement of Inelastic Light Scattering in Strongly Correlated Materials
We use dynamical mean field theory to find an exact solution for inelastic
light scattering in strongly correlated materials such as those near a
quantum-critical metal-insulator transition. We evaluate the results for
(Raman) scattering and find that resonant effects can be quite
large, and yield a triple resonance, a significant enhancement of nonresonant
scattering peaks, a joint resonance of both peaks when the incident photon
frequency is on the order of , and the appearance of an isosbestic point in
all symmetry channels for an intermediate range of incident photon frequencies.Comment: 5 pages RevTex, 4 Figures ep
Electron source with a multi-apertured plasma emitter
In the present study, we investigated the energy efficiency of an electron source with a multi-aperture plasma emitter where the generated beam is extracted into the atmosphere through a thin metal foil. The boundary of the plasma produced in this type of emitter is stabilized with a fine metal grid. To prevent the loss of electrons at the circle-holed support grid of the extraction foil window, a metal mask with holes of smaller diameter arranged coaxially to the support grid holes is put on the emission grid. Thus, the electron beam is a superposition of beamlets formed by individual electron emitting units with the plasma boundary stabilized by the fine metal grid. The efficiency of current extraction from the acceleration gap into the atmosphere reached 75% with respect to the gap current, making possible to increase the average power of the extracted electron beam. With a 200-kV accelerating voltage, a 16-A current in the acceleration gap, and 40 µs FWHM pulse duration, 4 kW of the average beam power was extracted into the atmosphere from the acceleration gap. With the geometric transparency of the support grid of the extraction foil window equal to 56%, this made 65% of the beam power in the gap. Further increasing the beam power was limited by the power of the high-voltage power supply
Episodic excursions of low-mass protostars on the Hertzsprung-Russell diagram
Following our recent work devoted to the effect of accretion on the
pre-main-sequence evolution of low-mass stars, we perform a detailed analysis
of episodic excursions of low-mass protostars in the Hertzsprung-Russell (H-R)
diagram triggered by strong mass accretion bursts typical of FU Orionis-type
objects (FUors). These excursions reveal themselves as sharp increases in the
stellar total luminosity and/or effective temperature of the protostar and can
last from hundreds to a few thousands of years, depending on the burst strength
and characteristics of the protostar. During the excursions, low-mass
protostars occupy the same part of the H-R diagram as young intermediate-mass
protostars in the quiescent phase of accretion. Moreover, the time spent by
low-mass protostars in these regions is on average a factor of several longer
than that spent by the intermediate-mass stars in quiescence. During the
excursions, low-mass protostars pass close to the position of most known FUors
in the H-R diagram, but owing to intrinsic ambiguity the model stellar
evolutionary tracks are unreliable in determining the FUor properties. We find
that the photospheric luminosity in the outburst state may dominate the
accretion luminosity already after a few years after the onset of the outburst,
meaning that the mass accretion rates of known FUors inferred from the
bolometric luminosity may be systematically overestimated, especially in the
fading phase.Comment: 15 pages, 12 figure
Infrared and sub-mm observations of outbursting young stars with Herschel and Spitzer
Episodic accretion plays an important role in the evolution of young stars.
Although it has been under investigation for a long time, the origin of such
episodic accretion events is not yet understood. We investigate the dust and
gas emission of a sample of young outbursting sources in the infrared to get a
better understanding of their properties and circumstellar material, and we use
the results in a further work to model the objects. We used Herschel data, from
our PI program of 12 objects and complemented with archival observations to
obtain the spectral energy distributions (SEDs) and spectra of our targets. We
report here the main characteristics of our sample, focussing on the SED
properties and on the gas emission lines detected in the PACS and SPIRE
spectra. The SEDs of our sample show the diversity of the outbursting sources,
with several targets showing strong emission in the far-infrared from the
embedded objects. Most of our targets reside in a complex environment, which we
discuss in detail. We detected several atomic and molecular lines, in
particular rotational CO emission from several transitions from J=38-37 to
J=4-3. We constructed rotational diagrams for the CO lines, and derived in
three domains of assumed local thermodynamic equilibrium (LTE) temperatures and
column densities, ranging mainly between 0-100 K and 400-500K. We confirm
correlation in our sample between intense CO emission and the column
density of the warm domain of CO, N(warm). We notice a strong increase in
luminosity of HH 381 IRS and a weaker increase for PP 13 S, which shows the
beginning of an outburst.Comment: 23 pages, 17 figures, A&A accepte
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