1,101 research outputs found
On the generation and the nonlinear dynamics of X-waves of the Schroedinger equation
The generation of finite energy packets of X-waves is analysed in normally
dispersive cubic media by using an X-wave expansion. The 3D nonlinear
Schroedinger model is reduced to a 1D equation with anomalous dispersion. Pulse
splitting and beam replenishment as observed in experiments with water and Kerr
media are explained in terms of a higher order breathing soliton. The results
presented also hold in periodic media and Bose-condensed gases.Comment: 18 pages, 6 figures, corrected version to be published in Physical
Review
Origin of the approximate universality of distributions in equilibrium correlated systems
We propose an interpretation of previous experimental and numerical
experiments, showing that for a large class of systems, distributions of global
quantities are similar to a distribution originally obtained for the
magnetization in the 2D-XY model . This approach, developed for the Ising
model, is based on previous numerical observations. We obtain an effective
action using a perturbative method, which successfully describes the order
parameter fluctuations near the phase transition. This leads to a direct link
between the D-dimensional Ising model and the XY model in the same dimension,
which appears to be a generic feature of many equilibrium critical systems and
which is at the heart of the above observations.Comment: To appear in Europhysics Letter
Gain spectroscopy of a type-II VECSEL chip
Using optical pump-white light probe spectroscopy the gain dynamics is
investigated for a VECSEL chip which is based on a type-II heterostructure. The
active region the chip consists of a GaAs/(GaIn)As/Ga(AsSb)/(GaIn)As/GaAs
multiple quantum well. For this structure, a fully microscopic theory predicts
a modal room temperature gain at a wavelength of 1170 nm, which is confirmed by
experimental spectra. The results show a gain buildup on the type-II chip which
is delayed relative to that of a type-I chip. This slower gain dynamics is
attributed to a diminished cooling rate arising from reduced electron-hole
scattering.Comment: 4 pages, 4 figure
The dependence of solar wind burst size on burst duration and its invariance across solar cycles 23 and 24
Time series of solar wind variables are “bursty” in nature. Bursts, or excursions, in the time series of solar wind parameters are associated with various transient structures in the solar wind plasma, and are often the drivers of increased space weather activity in Earth's magnetosphere. We define bursts by setting a threshold value of the time series and identifying how often, and for how long, it is exceeded. This allows us to study how the statistical distributions and scaling properties of burst parameters vary over solar cycles 23 and 24. We find the distributions of burst duration and integrated burst size vary over the solar cycle, and between the equivalent phases of consecutive cycles. However, there exists a single power law scaling relation between burst size and duration, with a joint area‐duration scaling exponent α that is independent of the solar cycle. This provides a solar cycle invariant constraint between possible sizes and durations of solar wind bursts that can occur
Extension of the LDA-1/2 method to the material class of bismuth containing III-V semiconductors
The LDA-1/2 method is employed in density functional theory calculations for
the electronic structure of III-V dilute bismide systems. For the
representative example of Ga(SbBi) with Bi concentrations below , it is
shown that this method works very efficiently, especially due to its reasonably
low demand on computer memory. The resulting bandstructure and wavefunctions
are used to compute the interaction matrix elements that serve as input to
microscopic calculations of the optical properties and intrinsic losses
relevant for optoelectronic applications of dilute bismides
Dicyanogold Effects on Lymphokine Production
Having identified dicyanogold(I) as a common metabolite of gold-based antiarthritis drugs, we are
investigating the effects of the compound on
the production of lymphokines. Handel, et al. 1
suggested that the transcription factor AP-1, critical to the production of a number of cytokines, might
be the target for gold compounds because of a critical cysteine within its DNA binding region. Using Jurkat
cells, an established cell line as a model for CD4+
lymphocytes, we have shown that dicyanogold inhibits the binding of AP-1 to DNA and inhibits the synthesis
of IL-2 mRNA and protein. In a macrophage line, THP-1, which synthesizes IL-1β
in response to mitogen, we have shown that dicyanogold inhibits the binding of a second transcription
factor, CREB to DNA. Incubation of THP-1 cells with dicyanogold inhibits the production of IL-1β
mRNA. These results suggest that the mechanism of action of gold drugs may be through their interaction
with transcription factors necessary for the immune activation seen in Rheumatoid Arthritis
Photoluminescence and Terahertz Emission from Femtosecond Laser-Induced Plasma Channels
Luminescence as a mechanism for terahertz emission from femtosecond
laser-induced plasmas is studied. By using a fully microscopic theory, Coulomb
scattering between electrons and ions is shown to lead to luminescence even for
a spatially homogeneous plasma. The spectral features introduced by the rod
geometry of laser-induced plasma channels in air are discussed on the basis of
a generalized mode-function analysis.Comment: 4 pages with 2 figures
Robust statistical properties of the size of large burst events in AE
Geomagnetic indices provide a comprehensive data set with which to quantify space climate, that is, how the statistical likelihood of activity varies with the solar cycle. We characterize space climate by the AE index burst distribution. Burst sizes are constructed by thresholding the AE time series; a burst is the sum of the excess in the time series for each time interval over which the threshold is exceeded. The distribution of burst sizes is two component with a crossover in behavior at thresholds ≈1000 nT. Above this threshold, we find a range over which the mean burst size varies weakly with threshold for both solar maxima and minima. The burst size distribution of the largest events is exponential. The relative likelihood of these large events varies from one solar maximum and minimum to the next. Given the relative overall activity of a solar maximum/minimum, these results constrain the likelihood of extreme events of a given size
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