127 research outputs found
Polarization effects in the reaction and determination of the meson form factors in the time--like region
The electron positron annihilation reaction into four pion production has
been studied, through the channel . The
differential (and total) cross sections and various polarization observables
for this reaction have been calculated in terms of the electromagnetic form
factors of the corresponding current. The elements of the
spin--density matrix of the meson were also calculated. Numerical
estimations have been done, with the help of phenomenological form factors
obtained in the space--like region of the momentum transfer squared and
analytically extended to the time-like region.Comment: 19 pages, 2 figures, to appear in Phys Rev
Cross section and polarization observables for the reaction
A model independent formalism for the electron positron annihilation reaction
has been derived. The differential and total cross
sections and the elements of the spin--density matrix of the -meson were
calculated in terms of the electromagnetic form factors of the corresponding
current. Simple models of form factors have been fitted
to the available cross section data and they allow to give numerical
predictions for the different observables.Comment: 19 pages, 6 figures Added formulas for axial meson decay in 3 pions
Modified version to appear in PR
Subterahertz chaos generation by coupling a superlattice to a linear resonator
We investigate the effects of a linear resonator on the high-frequency dynamics of electrons in devices exhibiting negative differential conductance. We show that the resonator strongly affects both the dc and ac transport characteristics of the device, inducing quasiperiodic and high-frequency chaotic current oscillations. The theoretical findings are confirmed by experimental measurements of a GaAs=AlAs miniband semiconductor superlattice coupled to a linear microstrip resonator. Our results are applicable to other active solid state devices and provide a generic approach for developing modern chaos-based high-frequency technologies including broadband chaotic wireless communication and superfast random-number generation
Improved confinement transition in high density deuterium discharges at the FT-2 tokamak accompanied by onset of negative triangularity
Impurity breakdown and terahertz luminescence in n-GaN epilayers under external electric field
We report on the observation and experimental studies of impurity breakdown and terahertz luminescence in n-GaN epilayers under external electric field. The terahertz electroluminescence is observed in a wide range of doping levels (at noncompensated donor density from 4.5×10[sup 16] to 3.4×10[sup 18] cm[sup −3]). Spectra of terahertz luminescence and photoconductivity are studied by means of Fourier transform spectrometry. Distinctive features of the spectra can be assigned to intracenter electron transitions between excited and ground states of silicon and oxygen donors and to hot electron transitions to the donor states.Peer reviewe
Donor states in modulation-doped Si/SiGe heterostructures
We present a unified approach for calculating the properties of shallow
donors inside or outside heterostructure quantum wells. The method allows us to
obtain not only the binding energies of all localized states of any symmetry,
but also the energy width of the resonant states which may appear when a
localized state becomes degenerate with the continuous quantum well subbands.
The approach is non-variational, and we are therefore also able to evaluate the
wave functions. This is used to calculate the optical absorption spectrum,
which is strongly non-isotropic due to the selection rules. The results
obtained from calculations for Si/SiGe quantum wells allow us to
present the general behavior of the impurity states, as the donor position is
varied from the center of the well to deep inside the barrier. The influence on
the donor ground state from both the central-cell effect and the strain arising
from the lattice mismatch is carefully considered.Comment: 17 pages, 10 figure
Circularly polarized electroluminescence from silicon nanostructures heavily doped with boron
The circularly polarized electroluminescence (CPEL) from silicon
nanostructures which are the p-type ultra-narrow silicon quantum well (Si-QW)
confined by {\delta}-barriers heavily doped with boron, 5 10^21 cm^-3, is under
study as a function of temperature and excitation levels. The CPEL dependences
on the forward current and temperature show the circularly polarized light
emission which appears to be caused by the exciton recombination through the
negative-U dipole boron centers at the Si-QW {\delta}-barriers interface
Proteome-metabolome profiling of ovarian cancer ascites reveals novel components involved in intercellular communication
© 2014 by The American Society for Biochemistry and Molecular Biology, Inc. Ovarian cancer ascites is a native medium for cancer cells that allows investigation of their secretome in a natural environment. This medium is of interest as a promising source of potential biomarkers, and also as a medium for cell-cell communication. The aim of this study was to elucidate specific features of the malignant ascites metabolome and proteome. In order to omit components of the systemic response to ascites formation, we compared malignant ascites with cirrhosis ascites. Metabolome analysis revealed 41 components that differed significantly between malignant and cirrhosis ascites. Most of the identified cancer-specific metabolites are known to be important signaling molecules. Proteomic analysis identified 2096 and 1855 proteins in the ovarian cancer and cirrhosis ascites, respectively; 424 proteins were specific for the malignant ascites. Functional analysis of the proteome demonstrated that the major differences between cirrhosis and malignant ascites were observed for the cluster of spliceosomal proteins. Additionally, we demonstrate that several splicing RNAs were exclusively detected in malignant ascites, where they probably existed within protein complexes. This result was confirmed in vitro using an ovarian cancer cell line. Identification of spliceosomal proteins and RNAs in an extracellular medium is of particular interest; the finding suggests that they might play a role in the communication between cancer cells. In addition, malignant ascites contains a high number of exosomes that are known to play an important role in signal transduction. Thus our study reveals the specific features of malignant ascites that are associated with its function as a medium of intercellular communication
Sub-terahertz amplification in a semiconductor superlattice with moving charge domains
A MSFD complementary approach for the assessment of pressures, knowledge and data gaps in Southern European Seas : the PERSEUS experience
PERSEUS project aims to identify the most relevant pressures exerted on the ecosystems of the Southern
European Seas (SES), highlighting knowledge and data gaps that endanger the achievement of SES Good
Environmental Status (GES) as mandated by the Marine Strategy Framework Directive (MSFD). A complementary
approach has been adopted, by a meta-analysis of existing literature on pressure/impact/knowledge
gaps summarized in tables related to the MSFD descriptors, discriminating open waters from coastal
areas. A comparative assessment of the Initial Assessments (IAs) for five SES countries has been also
independently performed. The comparison between meta-analysis results and IAs shows similarities
for coastal areas only. Major knowledge gaps have been detected for the biodiversity, marine food
web, marine litter and underwater noise descriptors. The meta-analysis also allowed the identification
of additional research themes targeting research topics that are requested to the achievement of GES.
2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license.peer-reviewe
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