111 research outputs found
High energy neutrino spin light
The quantum theory of spin light (electromagnetic radiation emitted by a
Dirac massive neutrino propagating in dense matter due to the weak interaction
of a neutrino with background fermions) is developed. In contrast to the
Cherenkov radiation, this effect does not disappear even if the medium
refractive index is assumed to be equal to unity. The formulas for the
transition rate and the total radiation power are obtained. It is found out
that radiation of photons is possible only when the sign of the particle
helicity is opposite to that of the effective potential describing the
interaction of a neutrino (antineutrino) with the background medium. Due to the
radiative self-polarization the radiating particle can change its helicity. As
a result, the active left-handed polarized neutrino (right-handed polarized
antineutrino) converting to the state with inverse helicity can become
practically ``sterile''. Since the sign of the effective potential depends on
the neutrino flavor and the matter structure, the spin light can change a ratio
of active neutrinos of different flavors. In the ultra relativistic approach,
the radiated photons averaged energy is equal to one third of the initial
neutrino energy, and two thirds of the energy are carried out by the final
``sterile'' neutrinos.Comment: 12 pages, Latex. To appear in Phys. Lett.
Magnetooptics in Gold and Silver NanoSizes Low-Dimensional Objects
The spectra of optical absorption and of magnetic circular dichroism (MCD) have been measured in the 350–1150 nm wavelength range for a set of colloidal solutions containing Au and Ag nanoparticles. The average size of Au nanoparticles was 6 nm and having thiolate coatings with different degrees of chirality. (The average size of Ag nanoparticles was 14 nm and having citrate coatings) The form of absorption and MCD spectra suggests the dipole character of interband transitions involving the 5d–6(sp) for Au orbitals and 4d–5(sp) for Ag orbitals. The absence (within the experimental error) of the MCD spectra dependence on the coating type rules out the hypothesis on the orbital nature of the observed magnetism. We argue that the spin polarization plays the dominant role in the magnetism both for Au and Ag nanoparticles.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3534
Природное выщелачивание урана и механизм разрушения рудных тел и пород
Leaching of the metal begins after the filing of a working solution to the array and ends in a short time. The process of leaching in the microcracks is long, and the process of leaching in the mikropores is longer. An important parameters of leaching of uranium are: the area of actively surface cultivating of minerals, which means а destruction of ores and rocks.Выщелачивание металла начинается после подачи рабочего раствора в массив и заканчивается в короткие сроки. Длительным является процесс выщелачивания в микротрещинах, и более продолжительным - процесс выщелачивания в микропоровом пространстве. Важным параметром выщелачивания урана является площадь активной поверхности обрабатываемых минералов, что означает разрушение руд и пород
Measurement of and between 3.12 and 3.72 GeV at the KEDR detector
Using the KEDR detector at the VEPP-4M collider, we have measured
the values of and at seven points of the center-of-mass
energy between 3.12 and 3.72 GeV. The total achieved accuracy is about or
better than at most of energy points with a systematic uncertainty of
about . At the moment it is the most accurate measurement of in
this energy range
Modeling the Emission Processes in Blazars
Blazars are the most violent steady/recurrent sources of high-energy
gamma-ray emission in the known Universe. They are prominent emitters of
electromagnetic radiation throughout the entire electromagnetic spectrum. The
observable radiation most likely originates in a relativistic jet oriented at a
small angle with respect to the line of sight. This review starts out with a
general overview of the phenomenology of blazars, including results from a
recent multiwavelength observing campaign on 3C279. Subsequently, issues of
modeling broadband spectra will be discussed. Spectral information alone is not
sufficient to distinguish between competing models and to constrain essential
parameters, in particular related to the primary particle acceleration and
radiation mechanisms in the jet. Short-term spectral variability information
may help to break such model degeneracies, which will require snap-shot
spectral information on intraday time scales, which may soon be achievable for
many blazars even in the gamma-ray regime with the upcoming GLAST mission and
current advances in Atmospheric Cherenkov Telescope technology. In addition to
pure leptonic and hadronic models of gamma-ray emission from blazars,
leptonic/hadronic hybrid models are reviewed, and the recently developed
hadronic synchrotron mirror model for TeV gamma-ray flares which are not
accompanied by simultaneous X-ray flares (``orphan TeV flares'') is revisited.Comment: Invited Review at "The Multimessenger Approach to Gamma-Ray Sources",
Barcelona, Spain, July 2006; submitted to Astrophysics and Space Science. 10
pages, including 6 eps figures. Uses Springer's ApSS macro
Ultra-high field transport in GaN-based heterostructures
This paper describes measurements of the velocity of electrons at electric fields up to 100 kV/cm in GaN/AlGaN heterostructures. In order to avoid the Joule heating effect, a pulse technique with a time sweep of 10-30 ns was used. The experimental results indicate that overheating of the 2DEG does not exceed 1000 K in this electric field range and drift velocity as high as ~10⁷ cm/s was obtained. Additionally, the low frequency 1/f noise spectra measured for a different bias voltage are analyzed with respect to field-induced contribution of hopping conductivity in AlGaN barrier region
Disruption of vascular Ca2+-activated chloride currents lowers blood pressure
High blood pressure is the leading risk factor for death worldwide. One of the hallmarks is a rise of peripheral vascular resistance, which largely depends on arteriole tone. Ca2+-activated chloride currents (CaCCs) in vascular smooth muscle cells (VSMCs) are candidates for increasing vascular contractility. We analyzed the vascular tree and identified substantial CaCCs in VSMCs of the aorta and carotid arteries. CaCCs were small or absent in VSMCs of medium-sized vessels such as mesenteric arteries and larger retinal arterioles. In small vessels of the retina, brain, and skeletal muscle, where contractile intermediate cells or pericytes gradually replace VSMCs, CaCCs were particularly large. Targeted disruption of the calcium-activated chloride channel TMEM16A, also known as ANO1, in VSMCs, intermediate cells, and pericytes eliminated CaCCs in all vessels studied. Mice lacking vascular TMEM16A had lower systemic blood pressure and a decreased hypertensive response following vasoconstrictor treatment. There was no difference in contractility of medium-sized mesenteric arteries; however, responsiveness of the aorta and small retinal arterioles to the vasoconstriction-inducing drug U46619 was reduced. TMEM16A also was required for peripheral blood vessel contractility, as the response to U46619 was attenuated in isolated perfused hind limbs from mutant mice. Out data suggest that TMEM16A plays a general role in arteriolar and capillary blood flow and is a promising target for the treatment of hypertension
Search for narrow resonances in e+ e- annihilation between 1.85 and 3.1 GeV with the KEDR Detector
We report results of a search for narrow resonances in e+ e- annihilation at
center-of-mass energies between 1.85 and 3.1 GeV performed with the KEDR
detector at the VEPP-4M e+ e- collider. The upper limit on the leptonic width
of a narrow resonance Gamma(R -> ee) Br(R -> hadr) < 120 eV has been obtained
(at 90 % C.L.)
Measurement of \Gamma_{ee}(J/\psi)*Br(J/\psi->e^+e^-) and \Gamma_{ee}(J/\psi)*Br(J/\psi->\mu^+\mu^-)
The products of the electron width of the J/\psi meson and the branching
fraction of its decays to the lepton pairs were measured using data from the
KEDR experiment at the VEPP-4M electron-positron collider. The results are
\Gamma_{ee}(J/\psi)*Br(J/\psi->e^+e^-)=(0.3323\pm0.0064\pm0.0048) keV,
\Gamma_{ee}(J/\psi)*Br(J/\psi->\mu^+\mu^-)=(0.3318\pm0.0052\pm0.0063) keV.
Their combinations
\Gamma_{ee}\times(\Gamma_{ee}+\Gamma_{\mu\mu})/\Gamma=(0.6641\pm0.0082\pm0.0100)
keV,
\Gamma_{ee}/\Gamma_{\mu\mu}=1.002\pm0.021\pm0.013 can be used to improve
theaccuracy of the leptonic and full widths and test leptonic universality.
Assuming e\mu universality and using the world average value of the lepton
branching fraction, we also determine the leptonic \Gamma_{ll}=5.59\pm0.12 keV
and total \Gamma=94.1\pm2.7 keV widths of the J/\psi meson.Comment: 7 pages, 6 figure
Measurement of main parameters of the \psi(2S) resonance
A high-precision determination of the main parameters of the \psi(2S)
resonance has been performed with the KEDR detector at the VEPP-4M e^{+}e^{-}
collider in three scans of the \psi(2S) -- \psi(3770) energy range. Fitting the
energy dependence of the multihadron cross section in the vicinity of the
\psi(2S) we obtained the mass value
M = 3686.114 +- 0.007 +- 0.011 ^{+0.002}_{-0.012} MeV and the product of the
electron partial width by the branching fraction into hadrons \Gamma_{ee}*B_{h}
= 2.233 +- 0.015 +- 0.037 +- 0.020 keV.
The third error quoted is an estimate of the model dependence of the result
due to assumptions on the interference effects in the cross section of the
single-photon e^{+}e^{-} annihilation to hadrons explicitly considered in this
work.
Implicitly, the same assumptions were employed to obtain the charmonium
leptonic width and the absolute branching fractions in many experiments.
Using the result presented and the world average values of the electron and
hadron branching fractions, one obtains the electron partial width and the
total width of the \psi(2S):
\Gamma_{ee} =2.282 +- 0.015 +- 0.038 +- 0.021 keV,
\Gamma = 296 +- 2 +- 8 +- 3 keV.
These results are consistent with and more than two times more precise than
any of the previous experiments
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