2,440 research outputs found
Magnetic Field Induced Charge Instabilities in Weakly Coupled Superlattices
Using a time dependent selfconsistent model for vertical sequential
tunneling,we study the appearance of charge instabilities that lead to the
formation of electric field domains in a weakly coupled doped superlattice in
the presence of high magnetic fields parallel to the transport direction. The
interplay between the high non linearity of the system --coming from the
Coulomb interaction-- and the inter-Landau-level scattering at the domain walls
(regions of charge accumulation inside the superlattice) gives rise to new
unstable negative differential conductance regions and extra stable branches in
the sawtooth-like I-V curves.Comment: 5 pages, 4 postscript figure
Microwave burst with fine spectral structures in a solar flare on 2011 August 9
On August 9, 2011, there was an X6.9 flare event occurred near the west limb
of solar disk. From the observation obtained by the spectrometer of the Chinese
Solar Broadband Radio Spectrometer in Huairou (SBRS/Huairou) around the flare,
we find that this powerful flare has only a short-duration microwave burst of
about only 5 minutes, and during the short-duration microwave burst, there are
several kinds of fine structures on the spectrogram. These fine structures
include very short-period pulsations, millisecond spike bursts, and type III
bursts. The most interesting is that almost all of the pulses of very
short-period pulsation (VSP) are structured by clusters of millisecond
timescales of spike bursts or type III bursts. And there exists three different
kinds of frequency drift rates in the VSP: the frequency drift rates with
absolute value of about 55 - 130 MHz s^{-1} in the pulse groups, the frequency
drift rates with absolute value of about 2.91 - 16.9 GHz s^{-1} on each
individual pulse, and the frequency drift rates with absolute value of about 15
- 25 GHz s) at each individual spike burst or type III burst.Comment: 5 pages, 3 figure
Predictive Ability of QCD Sum Rules for Excited Baryons
The masses of octet baryons are calculated by the method of QCD sum rules.
Using generalized interpolating fields, three independent sets of QCD sum rules
are derived which allow the extraction of low-lying N* states with spin-parity
1/2+, 1/2- and 3/2- in both the non-strange and strange channels. The
predictive ability of the sum rules is examined by a Monte-Carlo based analysis
procedure in which the three phenomenological parameters (mass, coupling,
threshold) are treated as free parameters simultaneously. Realistic
uncertainties in these parameters are obtained by simultaneously exploring all
uncertainties in the QCD input parameters. Those sum rules with good predictive
power are identified and their predictions are compared with experiment where
available.Comment: 33 pages, 2 figure
Numerical study on regular wave overtopping flows over sea dike
Based on the filtered Navier-Stokes equations and Smagorinsky turbulence model, a numerical wave flume is developed to investigate regular wave overtopping flow over trapezoidal smooth impermeable sea dike. Simulation of wave breaking is carried out to validate the numerical wave flume with wave generation and absorbing modules. With the in-house developed code, a series of test cases combined different crest heights and wave parameters are carried out. These results are compared with experimental results and numerical results available. The varying tendency of layer thickness and maximum velocity along dike crest is analyzed for both non-breaking and breaking regular waves. Then, the relationship between the magnitude of overtopping flow velocity and overtopping discharge is investigated
Elastic model scale and material for underwater structure of cross-sea bridge
With the bridge construction gradually from inland to coast and offshore, underwater structure of cross-sea bridge can encounter more complex hydrodynamic action. When elastic model is used to simulate the hydrodynamic response of underwater structure, the model scale and model material is the first problem must be solved. Based on principle of similitude, elastic model should meet the geometric similarity, kinematic similarity and mechanical similarity. Formula derivation gives the scale conditions for elastic model are as follows, geometric scale (Lr) equals elastic modulus scale (Er) and density scale (??r) equals 1. Then, how to find a material with same density and the elastic modulus is 1/ Lr of prototype is the key to make a model
Identification of a candidate gene for Rc-D1, a locus controlling red coleoptile colour in wheat
Red coleoptile is an easily observed agronomic trait of wheat and has been extensively studied. However, the molecular mechanism of this trait has not yet been revealed. In this study, the MYB gene TaMYB-D1 was isolated from the wheat cultivar âGy115â, which possesses red coleoptiles. This gene resided at the short arm of the homoelogous group 7 chromosomes. TaMYB-D1 was the only gene expressed in the coleoptiles of âGy115â and was not expressed in âOpataâ and âCSâ, which have uncoloured coleoptiles. Phylogenetic analysis placed TaMYB-D1 very close to ZmC1 and other MYB proteins regulating anthocyanin biosynthesis. The encoded protein of TaMYB-D1 had an integrated DNA binding domain of 102 amino acids and a transcription domain with 42 amino acids, similar to the structure of ZmC1. Transient expression analysis in onion epidermal cells showed that TaMYB-D1 was located at the plant nucleus, which suggested its role as a transcription factor. The expression of TaMYB-D1 was accompanied with the expression of TaDFR and anthocyanin biosynthesis in the development of the coleoptile of âGy115â. Transient expression analysis showed that only TaMYB-D1 induced a few âOpataâ coleoptile cells to synthesize anthocyanin in light, and the gene also induced a colour change to red in many cells with the help of ZmR. All of these results suggested TaMYB-D1 as the candidate gene for the red coleoptile trait of âGy115â
Non-commutativity and Open Strings Dynamics in Melvin Universes
We compute the Moyal phase factor for open strings ending on D3-branes
wrapping a NSNS Melvin universe in a decoupling limit explicitly using world
sheet formalism in cylindrical coordinates.Comment: 12 pages, 1 figure, references adde
Effect of Nyquist Noise on the Nyquist Dephasing Rate in 2d Electron Systems
We measure the effect of externally applied broadband Nyquist noise on the
intrinsic Nyquist dephasing rate of electrons in a two-dimensional electron gas
at low temperatures. Within the measurement error, the phase coherence time is
unaffected by the externally applied Nyquist noise, including applied noise
temperatures of up to 300 K. The amplitude of the applied Nyquist noise from
100 MHz to 10 GHz is quantitatively determined in the same experiment using a
microwave network analyzer.Comment: 5 pages, 4 figures. Author affiliation clarified; acknowledgements
modified. Replacement reason clarifie
Observation of Quantum Asymmetry in an Aharonov-Bohm Ring
We have investigated the Aharonov-Bohm effect in a one-dimensional
GaAs/GaAlAs ring at low magnetic fields. The oscillatory magnetoconductance of
these systems are for the first time systematically studied as a function of
density. We observe phase-shifts of in the magnetoconductance
oscillations, and halving of the fundamental period, as the density is
varied. Theoretically we find agreement with the experiment, by introducing an
asymmetry between the two arms of the ring.Comment: 4 pages RevTex including 3 figures, submitted to Phys. Rev.
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