58 research outputs found
Experimental observation of moving intrinsic localized modes in germanium
Deep level transient spectroscopy shows that defects created by alpha
irradiation of germanium are annealed by low energy plasma ions up to a depth
of several thousand lattice units. The plasma ions have energies of 2-8eV and
therefore can deliver energies of the order of a few eV to the germanium atoms.
The most abundant defect is identified as the E-center, a complex of the dopant
antimony and a vacancy with and annealing energy of 1.3eV as determined by our
measurements. The inductively coupled plasma has a very low density and a very
low flux of ions. This implies that the ion impacts are almost isolated both in
time and at the surface of the semiconductor. We conclude that energy of the
order of an eV is able to travel a large distance in germanium in a localized
way and is delivered to the defects effectively. The most likely candidates are
vibrational nonlinear wave packets known as intrinsic localized modes, which
exist for a limited range of energies. This property is coherent with the fact
that more energetic ions are less efficient at producing the annealing effect.Comment: 20 pages, 10 figure
Rate theory of acceleration of the defect annealing driven by discrete breathers
Novel mechanisms of defect annealing in solids are discussed, which are based
on the large amplitude anharmonic lattice vibrations, a.k.a. intrinsic
localized modes or discrete breathers (DBs). A model for amplification of
defect annealing rate in Ge by low energy plasma-generated DBs is proposed, in
which, based on recent atomistic modelling, it is assumed that DBs can excite
atoms around defects rather strongly, giving them energy for
100 oscillation periods. This is shown to result in the amplification of
the annealing rates proportional to the DB flux, i.e. to the flux of ions (or
energetic atoms) impinging at the Ge surface from inductively coupled plasma
(ICP)Comment: 18 pages, 11 figures. arXiv admin note: text overlap with
arXiv:1406.394
Deep-level Transient Spectroscopy of GaAs/AlGaAs Multi-Quantum Wells Grown on (100) and (311)B GaAs Substrates
Si-doped GaAs/AlGaAs multi-quantum wells structures grown by molecular beam epitaxy on (100) and (311)B GaAs substrates have been studied by using conventional deep-level transient spectroscopy (DLTS) and high-resolution Laplace DLTS techniques. One dominant electron-emitting level is observed in the quantum wells structure grown on (100) plane whose activation energy varies from 0.47 to 1.3 eV as junction electric field varies from zero field (edge of the depletion region) to 4.7 × 106 V/m. Two defect states with activation energies of 0.24 and 0.80 eV are detected in the structures grown on (311)B plane. The Ec-0.24 eV trap shows that its capture cross-section is strongly temperature dependent, whilst the other two traps show no such dependence. The value of the capture barrier energy of the trap at Ec-0.24 eV is 0.39 eV
The interplay of intrinsic and extrinsic bounded noises in genetic networks
After being considered as a nuisance to be filtered out, it became recently
clear that biochemical noise plays a complex role, often fully functional, for
a genetic network. The influence of intrinsic and extrinsic noises on genetic
networks has intensively been investigated in last ten years, though
contributions on the co-presence of both are sparse. Extrinsic noise is usually
modeled as an unbounded white or colored gaussian stochastic process, even
though realistic stochastic perturbations are clearly bounded. In this paper we
consider Gillespie-like stochastic models of nonlinear networks, i.e. the
intrinsic noise, where the model jump rates are affected by colored bounded
extrinsic noises synthesized by a suitable biochemical state-dependent Langevin
system. These systems are described by a master equation, and a simulation
algorithm to analyze them is derived. This new modeling paradigm should enlarge
the class of systems amenable at modeling.
We investigated the influence of both amplitude and autocorrelation time of a
extrinsic Sine-Wiener noise on: the Michaelis-Menten approximation of
noisy enzymatic reactions, which we show to be applicable also in co-presence
of both intrinsic and extrinsic noise, a model of enzymatic futile cycle
and a genetic toggle switch. In and we show that the
presence of a bounded extrinsic noise induces qualitative modifications in the
probability densities of the involved chemicals, where new modes emerge, thus
suggesting the possibile functional role of bounded noises
Bistability and Oscillations in Gene Regulation Mediated by Small Noncoding RNAs
The interplay of small noncoding RNAs (sRNAs), mRNAs, and proteins has been shown to play crucial roles in almost all cellular processes. As key post-transcriptional regulators of gene expression, the mechanisms and roles of sRNAs in various cellular processes still need to be fully understood. When participating in cellular processes, sRNAs mainly mediate mRNA degradation or translational repression. Here, we show how the dynamics of two minimal architectures is drastically affected by these two mechanisms. A comparison is also given to reveal the implication of the fundamental differences. This study may help us to analyze complex networks assembled by simple modules more easily. A better knowledge of the sRNA-mediated motifs is also of interest for bio-engineering and artificial control
Gene switching rate determines response to extrinsic perturbations in the self-activation transcriptional network motif
International audienc
Spectroscopic observation of the TDD0 in silicon
The electronic transitions of 16 neutral thermal double donors (TDD1-TDD16) and of nine positively charged species (TDD1-TDD9) were observed previously in infrared absorption spectra. An earlier species (TDD0) was detected, however, only in persistent photoconductivity and Hall effect studies. In the present work, lines related to the electronic transitions from the ground to excited states in both neutral and singly ionized charge states of the TDD0 have been identified by infrared absorption and bistability of the defect has been confirmed. (C) 2003 Elsevier B.V. All rights reserved
Local vibrational modes of the oxygen-vacancy complex in germanium
Infrared absorption of n- and p-Ge crystals enriched with O-16 and/or O-18 isotopes was studied after irradiation with 6-MeV electrons. Absorption spectra were measured at 10 and 300 K. Along with known bands characteristic of oxygen-containing defects, new lines at 669, 944, and 990 cm(-1) were detected. These bands are annealed at temperatures of 120-140degreesC; the band at 621 cm(-1), previously related to the vacancy-oxygen complex in Ge, is simultaneously annealed. The bands at 621 and 669 cm(-1) showed identical temperatures (10 --> 300 K) and oxygen isotope (O-16 --> O-18) shifts. These bands were found to correspond to various charge states of a defect with an energy level near E-v = 0.25 +/- 0.03 eV. It is assumed that such a defect is the vacancy-oxygen complex (A center). The weak bands at 944 and 990 cm(-1) were identified as combinations of asymmetric stretching modes at 621 and 669 cm(-1) with a symmetric one at 320 cm(-1) for neutral and negative charge states of the A center, respectively
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