7,786 research outputs found
Alternating groups and moduli space lifting Invariants
Main Theorem: Spaces of r-branch point 3-cycle covers, degree n or Galois of
degree n!/2 have one (resp. two) component(s) if r=n-1 (resp. r\ge n). Improves
Fried-Serre on deciding when sphere covers with odd-order branching lift to
unramified Spin covers. We produce Hurwitz-Torelli automorphic functions on
Hurwitz spaces, and draw Inverse Galois conclusions. Example: Absolute spaces
of 3-cycle covers with +1 (resp. -1) lift invariant carry canonical even (resp.
odd) theta functions when r is even (resp. odd). For inner spaces the result is
independent of r. Another use appears in,
http://www.math.uci.edu/~mfried/paplist-mt/twoorbit.html, "Connectedness of
families of sphere covers of A_n-Type." This shows the M(odular) T(ower)s for
the prime p=2 lying over Hurwitz spaces first studied by,
http://www.math.uci.edu/~mfried/othlist-cov/hurwitzLiu-Oss.pdf, Liu and
Osserman have 2-cusps. That is sufficient to establish the Main Conjecture: (*)
High tower levels are general-type varieties and have no rational points.For
infinitely many of those MTs, the tree of cusps contains a subtree -- a spire
-- isomorphic to the tree of cusps on a modular curve tower. This makes
plausible a version of Serre's O(pen) I(mage) T(heorem) on such MTs.
Establishing these modular curve-like properties opens, to MTs, modular
curve-like thinking where modular curves have never gone before. A fuller html
description of this paper is at
http://www.math.uci.edu/~mfried/paplist-cov/hf-can0611591.html .Comment: To appear in the Israel Journal as of 1/5/09; v4 is corrected from
proof sheets, but does include some proof simplification in \S
Cumulative effect of Weibel-type instabilities in counterstreaming plasmas with non-Maxwellian anisotropies
Counterstreaming plasma structures are widely present in laboratory
experiments and astrophysical systems, and they are investigated either to
prevent unstable modes arising in beam-plasma experiments or to prove the
existence of large scale magnetic fields in astrophysical objects.
Filamentation instability arises in a counterstreaming plasma and is
responsible for the magnetization of the plasma. Filamentationally unstable
mode is described by assuming that each of the counterstreaming plasmas has an
isotropic Lorentzian (kappa) distribution. In this case, the filamentation
instability growth rate can reach a maximum value markedly larger than that for
a a plasma with a Maxwellian distribution function. This behaviour is opposite
to what was observed for the Weibel instability growth rate in a bi-kappa
plasma, which is always smaller than that obtained for a bi-Maxwellian plasma.
The approach is further generalized for a counterstreaming plasma with a
bi-kappa temperature anisotropy. In this case, the filamentation instability
growth rate is enhanced by the Weibel effect when the plasma is hotter in the
streaming direction, and the growth rate becomes even larger. These effects
improve significantly the efficiency of the magnetic field generation, and
provide further support for the potential role of the Weibel-type instabilities
in the fast magnetization scenarios
Robust Forecasting of Non-Stationary Time Series
This paper proposes a robust forecasting method for non-stationary time series. The time series is modelled using non-parametric heteroscedastic regression, and fitted by a localized MM-estimator, combining high robustness and large efficiency. The proposed method is shown to produce reliable forecasts in the presence of outliers, non-linearity, and heteroscedasticity. In the absence of outliers, the forecasts are only slightly less precise than those based on a localized Least Squares estimator. An additional advantage of the MM-estimator is that it provides a robust estimate of the local variability of the time series.Heteroscedasticity;Non-parametric regression;Prediction;Outliers;Robustness
Ion-implantation-caused special damage profiles determined by spectroscopic ellipsometry in crystalline and in relaxed (annealed) amorphous silicon
We previously developed a fitting method of several parameters to evaluate ion-implantation-caused damage profiles from spectroscopic ellipsometry (SE) (M. Fried et al., J. Appl. Phys., 71 (1992) 2835). Our optical model consists of a stack of layers with fixed and equal thicknesses and damage levels described by a depth profile function (coupled half Gaussians). The complex refractive index of each layer is calculated from the actual damage level by Bruggeman effective medium approximation (EMA) using crystalline (c-Si) and amorphous (a-Si) silicon as end-points. Two examples are presented of the use of this method with modified optical models. First, we investigated the surface damage formed by room temperature B+ and N+ implantation into silicon. For the analysis of the SE data we added a near surface amorphous layer to the model with variable thickness. Second, we determined 20 keV B+ implantation-caused damage profiles in relaxed (annealed) amorphous silicon. In this special case, the complex refractive index of each layer was calculated from the actual damage level by the EMA using relaxed a-Si and implanted a-Si as end-points. The calculated profiles are compared with Monte Carlo simulations (TRIM code); good agreement is obtained
Effects of mycorrhiza and plant growth promoting rhizobacteria inoculants on rice crops in Northern India
Mutualistic root microorganisms such as arbuscular mycorrhizal fungi (AMF) and plant growth promoting rhizobacteria (PGPR) can ameliorate plant nutrition through an extended extra-radical hyphal network and by nutrient mobilisation. Running under the Indo-Swiss Collaboration in Biotechnology (ISCB), our project focuses on the integration of AMF and PGPR as biofertilisers in wheat-rice and wheat-black gram systems
Bayesian photon counting with electron-multiplying charge coupled devices (EMCCDs)
The EMCCD is a CCD type that delivers fast readout and negligible detector
noise, making it an ideal detector for high frame rate applications. Because of
the very low detector noise, this detector can potentially count single
photons. Considering that an EMCCD has a limited dynamical range and negligible
detector noise, one would typically apply an EMCCD in such a way that multiple
images of the same object are available, for instance, in so called lucky
imaging. The problem of counting photons can then conveniently be viewed as
statistical inference of flux or photon rates, based on a stack of images. A
simple probabilistic model for the output of an EMCCD is developed. Based on
this model and the prior knowledge that photons are Poisson distributed, we
derive two methods for estimating the most probable flux per pixel, one based
on thresholding, and another based on full Bayesian inference. We find that it
is indeed possible to derive such expressions, and tests of these methods show
that estimating fluxes with only shot noise is possible, up to fluxes of about
one photon per pixel per readout.Comment: Fixed a few typos compared to the published versio
Ion-implantation induced anomalous surface amorphization in silicon
Spectroscopic ellipsometry (SE), high-depth-resolution Rutherford backscattering (RBS) and channeling have been used to examine the surface damage formed by room temperature N and B implantation into silicon. For the analysis of the SE data we used the conventional method of assuming appropriate optical models and fitting the model parameters (layer thicknesses and volume fraction of the amorphous silicon component in the layers) by linear regression. The dependence of the thickness of the surface-damaged silicon layer (beneath the native oxide layer) on the implantation parameters was determined: the higher the dose, the thicker the disordered layer at the surface. The mechanism of the surface amorphization process is explained in relation to the ion beam induced layer-by-layer amorphization. The results demonstrate the applicability of Spectroscopic ellipsometry with a proper optical model. RBS, as an independent cross-checking method supported the constructed optical model
Modified Hungarian Method for Solving Balanced Fuzzy Transportation Problems
This paper discusses how to solve balanced transportation problems, with transportation costs in the form of trapezoidal fuzzy numbers. Fuzzy costs are transformed into crisp costs using the Robust’s method as a ranking function. A new approach of modified Hungarian method has been applied to solve the problem of fuzzy transportation. This approach solves the fuzzy transportation problem in one stage of optimization and yields the same results as other methods that solve the problem in two stages
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