359 research outputs found
Exact relations between multifractal exponents at the Anderson transition
Two exact relations between mutlifractal exponents are shown to hold at the
critical point of the Anderson localization transition. The first relation
implies a symmetry of the multifractal spectrum linking the multifractal
exponents with indices . The second relation
connects the wave function multifractality to that of Wigner delay times in a
system with a lead attached.Comment: 4 pages, 3 figure
Residual-based localization and quantification of peaks in x-ray diffractograms
We consider data consisting of photon counts of diffracted x-ray radiation as
a function of the angle of diffraction. The problem is to determine the
positions, powers and shapes of the relevant peaks. An additional difficulty is
that the power of the peaks is to be measured from a baseline which itself must
be identified. Most methods of de-noising data of this kind do not explicitly
take into account the modality of the final estimate. The residual-based
procedure we propose uses the so-called taut string method, which minimizes the
number of peaks subject to a tube constraint on the integrated data. The
baseline is identified by combining the result of the taut string with an
estimate of the first derivative of the baseline obtained using a weighted
smoothing spline. Finally, each individual peak is expressed as the finite sum
of kernels chosen from a parametric family.Comment: Published in at http://dx.doi.org/10.1214/08-AOAS181 the Annals of
Applied Statistics (http://www.imstat.org/aoas/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Computed tomography in children: multicenter cohort study design for the evaluation of cancer risk
Dimensionality dependence of the wave function statistics at the Anderson transition
The statistics of critical wave functions at the Anderson transition in three
and four dimensions are studied numerically. The distribution of the inverse
participation ratios (IPR) is shown to acquire a scale-invariant form in
the limit of large system size. Multifractality spectra governing the scaling
of the ensemble-averaged IPRs are determined. Conjectures concerning the IPR
statistics and the multifractality at the Anderson transition in a high spatial
dimensionality are formulated.Comment: 4 pages, 4 figure
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Surface modification of mineral dust particles by sulphuric acid processing: Implications for ice nucleation abilities
The ability of coated mineral dust particles to act as ice nuclei (IN) was investigated at LACIS (Leipzig Aerosol Cloud Interaction Simulator) during the FROST1- and FROST2-campaigns (Freezing of dust). Sulphuric acid was condensed on the particles which afterwards were optionally humidified, treated with ammonia vapour and/or heat. By means of aerosol mass spectrometry we found evidence that processing of mineral dust particles with sulphuric acid leads to surface modifications of the particles. These surface modifications are most likely responsible for the observed reduction of the IN activation of the particles. The observed particle mass spectra suggest that different treatments lead to different chemical reactions on the particle surface. Possible chemical reaction pathways and products are suggested and the implications on the IN efficiency of the treated dust particles are discussed
Wave function statistics and multifractality at the spin quantum Hall transition
The statistical properties of wave functions at the critical point of the
spin quantum Hall transition are studied. The main emphasis is put onto
determination of the spectrum of multifractal exponents governing
the scaling of moments with the system
size and the spatial decay of wave function correlations. Two- and
three-point correlation functions are calculated analytically by means of
mapping onto the classical percolation, yielding the values and
. The multifractality spectrum obtained from numerical
simulations is given with a good accuracy by the parabolic approximation
but shows detectable deviations. We also study
statistics of the two-point conductance , in particular, the spectrum of
exponents characterizing the scaling of the moments . Relations
between the spectra of critical exponents of wave functions (),
conductances (), and Green functions at the localization transition with a
critical density of states are discussed.Comment: 16 pages, submitted to J. Phys. A, Special Issue on Random Matrix
Theor
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Heterogeneous freezing of droplets with immersed mineral dust particles – measurements and parameterization
During the measurement campaign FROST (FReezing Of duST), LACIS (Leipzig Aerosol Cloud Interaction Simulator) was used to investigate the immersion freezing behavior of size selected, coated and uncoated Arizona Test Dust (ATD) particles with a mobility diameter of 300 nm. Particles were coated with succinic acid (C4H6O4), sulfuric acid (H2SO4) and ammonium sulfate ((NH4)2SO4). Ice fractions at mixed-phase cloud temperatures ranging from 233.15 K to 239.15 K (±0.60 K) were determined for all types of particles. In this temperature range, pure ATD particles and those coated with C4H6O4 or small amounts of H2SO4 were found to be the most efficient ice nuclei (IN). ATD particles coated with (NH4)2SO4 were the most inefficient IN. Since the supercooled droplets were highly diluted before freezing occurred, a freezing point suppression due to the soluble material on the particles (and therefore in the droplets) cannot explain this observation. Therefore, it is reasonable to assume that the coatings lead to particle surface alterations which cause the differences in the IN abilities. Two different theoretical approaches based on the stochastic and the singular hypotheses were applied to clarify and parameterize the freezing behavior of the particles investigated. Both approaches describe the experimentally determined results, yielding parameters that can subsequently be used to compare our results to those from other studies. However, we cannot clarify at the current state which of the two approaches correctly describes the investigated immersion freezing process. But both approaches confirm the assumption that the coatings lead to particle surface modifications lowering the nucleation efficiency. The stochastic approach interprets the reduction in nucleation rate from coating as primarily due to an increase in the thermodynamic barrier for ice formation (i.e., changes in interfacial free energies). The singular approach interprets the reduction as resulting from a reduced surface density of active sites
Aerosol optical properties in the North China Plain during HaChi campaign: an in-situ optical closure study
The largest uncertainty in the estimation of climate forcing stems from atmospheric aerosols. In early spring and summer of 2009, two periods of in-situ measurements on aerosol physical and chemical properties were conducted within the HaChi (Haze in China) project at Wuqing, a town between Beijing and Tianjin in the North China Plain (NCP). Aerosol optical properties, including the scattering coefficient (&sigma;<sub>sp</sub>), the hemispheric back scattering coefficient (&sigma;<sub>bsp</sub>), the absorption coefficient (&sigma;<sub>ap</sub>), as well as the single scattering albedo (ω), are presented. The diurnal and seasonal variations are analyzed together with meteorology and satellite data. The mean values of &sigma;<sub>sp, 550 nm</sub> of the dry aerosol in spring and summer are 280&plusmn;253 and 379&plusmn;251 Mm<sup>−1</sup>, respectively. The average &sigma;<sub>ap</sub> for the two periods is respectively 47&plusmn;38 and 43&plusmn;27 Mm<sup>−1</sup>. The mean values of &omega; at the wavelength of 637 nm are 0.82&plusmn;0.05 and 0.86&plusmn;0.05 for spring and summer, respectively. The relative high levels of &sigma;<sub>sp</sub> and &sigma;<sub>bsp</sub> are representative of the regional aerosol pollution in the NCP. Pronounced diurnal cycle of $&sigma;<sub>sp</sub>, &sigma;<sub>ap</sub> and ω are found, mainly influenced by the evolution of boundary layer and the accumulation of local emissions during nighttime. The pollutants transported from the southwest of the NCP are more significant than that from the two megacities, Beijing and Tianjin, in both spring and summer. An optical closure experiment is conducted to better understand the uncertainties of the measurements. Good correlations (<i>R</i>>0.98) are found between the values measured by the nephelometer and the values calculated with a modified Mie model. The Monte Carlo simulation shows an uncertainty of about 30 % for the calculations. Considering all possible uncertainties of measurements, calculated &sigma;<sub>sp</sub> and &sigma;<sub>bsp</sub> agree well with the measured values, indicating a stable performance of instruments and thus reliable aerosol optical data
Improved Measurement of the K+ to pi+ nu nubar Branching Ratio
An additional event near the upper kinematic limit for K+ to pi+ nu nubar has
been observed by Experiment E949 at Brookhaven National Laboratory. Combining
previously reported and new data, the branching ratio is B(K+ to pi+ nu nubar)=
1.47 (+1.30, - 0.89) x 10-10 based on three events observed in the pion
momentum region 211<P<229 MeV/c. At the measured central value of the branching
ratio, the additional event had a signal-to-background ratio of 0.9
Further Evidence for the Decay K+ to pi+ neutrino-antineutrino
Additional evidence for the rare kaon decay K+ to pi+ neutrino-antineutrino
has been found in a new data set with comparable sensitivity to the previously
reported result. One new event was observed in the pion momentum region
examined, 211<P<229 MeV/c, bringing the total for the combined data set to two.
Including all data taken, the backgrounds were estimated to contribute 0.15 pm
0.05 events. The branching ratio is B=1.57^{+1.75}_{-0.82} 10^{-10}.Comment: 10 pages, 2 figure
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