3,614 research outputs found
Ultrahard spectra of PeV neutrinos from supernovae in compact star clusters
Starburst regions with multiple powerful winds of young massive stars and
supernova remnants are favorable sites for high-energy cosmic ray acceleration.
A supernova shock colliding with a fast wind from a compact cluster of young
stars allows the acceleration of protons to energies well above the standard
limits of diffusive shock acceleration in an isolated SN. The proton spectrum
in such a wind-supernova PeV accelerator is hard with a large flux in the
high-energy-end of the spectrum producing copious gamma-rays and neutrinos in
inelastic nuclear collisions. We argue that SN shocks in the Westerlund 1
cluster in the Milky Way may accelerate protons to about 40 PeV. Once
accelerated, these CRs will diffuse into surrounding dense clouds and produce
neutrinos with fluxes sufficient to explain a fraction of the events detected
by IceCube Observatory from the inner Galaxy.Comment: 10 pages, 7 figures, MNRAS v.453, p.113-121, 201
Optical spectra of quantum dots: effects of non-adiabaticity
It is shown that in many cases an adequate description of optical spectra of
semiconductor quantum dots requires a treatment beyond the commonly used
adiabatic approximation. We have developed a theory of phonon-assisted optical
transitions in semiconductor quantum dots, which takes into account
non-adiabaticity of the exciton-phonon system. Effects of non-adiabaticity lead
to a mixing of different exciton and phonon states that provides a key to the
understanding of surprisingly high intensities of phonon satellites observed in
photoluminescence spectra of quantum dots. A breakdown of the adiabatic
approximation gives an explanation also for discrepancies between the serial
law, observed in multi-phonon optical spectra of some quantum dots, and the
Franck-Condon progression, prescribed by the adiabatic approach.Comment: 4 pages, 3 figures, E-mail addresses: [email protected],
[email protected], [email protected], [email protected],
[email protected]
Magnetic susceptibility of ultra-small superconductor grains
For assemblies of superconductor nanograins, the magnetic response is
analyzed as a function of both temperature and magnetic field. In order to
describe the interaction energy of electron pairs for a huge number of
many-particle states, involved in calculations, we develop a simple
approximation, based on the Richardson solution for the reduced BCS Hamiltonian
and applicable over a wide range of the grain sizes and interaction strengths
at arbitrary distributions of single-electron energy levels in a grain. Our
study is focused upon ultra-small grains, where both the mean value of the
nearest-neighbor spacing of single-electron energy levels in a grain and
variations of this spacing from grain to grain significantly exceed the
superconducting gap in bulk samples of the same material. For these ultra-small
superconductor grains, the overall profiles of the magnetic susceptibility as a
function of magnetic field and temperature are demonstrated to be qualitatively
different from those for normal grains. We show that the analyzed signatures of
pairing correlations are sufficiently stable with respect to variations of the
average value of the grain size and its dispersion over an assembly of
nanograins. The presence of these signatures does not depend on a particular
choice of statistics, obeyed by single-electron energy levels in grains.Comment: 40 pages, 12 figures, submitted to Phys. Rev. B, E-mail addresses:
[email protected], [email protected], [email protected]
Ultrahard spectra of PeV neutrinos from supernovae in compact star clusters
Starburst regions with multiple powerful winds of young massive stars and supernova remnants are favourable sites for high-energy cosmic ray (CR) acceleration. A supernova (SN) shock colliding with a fast wind from a compact cluster of young stars allows the acceleration of protons to energies well above the standard limits of diffusive shock acceleration in an isolated SN. The proton spectrum in such a wind-SN pevatron accelerator is hard with a large flux in the high-energy end of the spectrum producing copious gamma-rays and neutrinos in inelastic nuclear collisions. We argue that SN shocks in the Westerlund 1 cluster in the Milky Way may accelerate protons to≳40PeV. Once accelerated, these CRs will diffuse into surrounding dense clouds and produce neutrinos with fluxes sufficient to explain a fraction of the events detected by IceCube from the inner Galax
Application of Aptamers Improves CRISPR-Based Live Imaging of Plant Telomeres
Development of live imaging techniques for providing information how chromatin is organized in living cells is pivotal to decipher the regulation of biological processes. Here, we demonstrate the improvement of a live imaging technique based on CRISPR/Cas9. In this approach, the sgRNA scaffold is fused to RNA aptamers including MS2 and PP7. When the dead Cas9 (dCas9) is co-expressed with chimeric sgRNA, the fluorescent coat protein-tagged for MS2 and PP7 aptamers (tdMCP-FP and tdPCP-FP) are recruited to the targeted sequence. Compared to previous work with dCas9:GFP, we show that the quality of telomere labeling was improved in transiently transformed Nicotiana benthamiana using aptamer-based CRISPR-imaging constructs. Labeling is influenced by the copy number of aptamers and less by the promoter types. The same constructs were not applicable for labeling of repeats in stably transformed plants and roots. The constant interaction of the RNP complex with its target DNA might interfere with cellular processes
Quantum Transport in a Nanosize Silicon-on-Insulator Metal-Oxide-Semiconductor
An approach is developed for the determination of the current flowing through
a nanosize silicon-on-insulator (SOI) metal-oxide-semiconductor field-effect
transistors (MOSFET). The quantum mechanical features of the electron transport
are extracted from the numerical solution of the quantum Liouville equation in
the Wigner function representation. Accounting for electron scattering due to
ionized impurities, acoustic phonons and surface roughness at the Si/SiO2
interface, device characteristics are obtained as a function of a channel
length. From the Wigner function distributions, the coexistence of the
diffusive and the ballistic transport naturally emerges. It is shown that the
scattering mechanisms tend to reduce the ballistic component of the transport.
The ballistic component increases with decreasing the channel length.Comment: 21 pages, 8 figures, E-mail addresses: [email protected]
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