25,045 research outputs found

### Study of corrosion of 1100 aluminum

Corrosion of 1100 aluminum in oxygen-saturated water at 70 degrees C under experimental conditions was studied, emphasizing effects of exposure interruption, the number of specimens, and the refreshment rate. A logarithmic equation was derived to express the corrosion rate

### Study of crevice-galvanic corrosion of aluminum

Corrosion effects of aluminum-copper and aluminum-nickel couples in oxygenated distilled water, and aluminum alloys in oxygenated copper sulfate solution were studied. One of each of the couples had a water tight seal, and showed no substantial corrosion, and of the unsealed couples, only the aluminum-copper developed corrosion

### A Reconsideration of the NAS Rule from an Industrial Agglomeration Perspective

An empirical regularity designated as the Number-Average Size (NAS) Rule was first identified for the case of Japan by Mori, Nishikimi and Smith [71], and has since been extended to the US by Hsu [50]. This rule asserts a negative log-linear relation between the number and average population size of cities where a given industry is present, i.e., of industry-choice cities. Hence one of its key features is to focus on the presence or absence of industries in each city, rather than the percentage distribution of industries across cities. But despite the strong empirical regularity of this rule, there still remains the statistical question of whether such location patterns could simply have occurred by chance. Indeed, chance occurrences of certain industry-choice cities may be quite likely if, for example, one includes cities where only a single industrial establishment happens to appear. An alternative approach to industry-choice cities is proposed in a companion paper, Mori and Smith [73], which is based on industrial clustering. More specifically, this approach utilizes the statistical procedure developed in Mori and Smith [72] to identify spatially explicit patterns of agglomeration for each industry. In this context, the desired industry-choice cities are taken to be those (economic) cities that constitute at least part of a significant spatial agglomeration for the industry. With respect to these cluster-based industry-choice cities, the central objective of the present paper is to reconfirm the persistence of the NAS Rule between the years 1981 and 2001, as first observed in Mori et al. [71]. Indeed the NAS Rule is in some ways stronger under this new definition of industry-choice cities in that none of outlier industries in the original analysis show any significant agglomeration, and hence can be excluded from the present analysis. A second objective is to show that there has been a substantial churning of the industry mix in individual cities between these two time periods, and hence that persistence of the NAS Rule is even more remarkable in this light. Finally, these persistence results are extended to both the Rank Size Rule and the Hierarchy Principle of Christaller [13], which were shown in Mori et al. [71] to be intimately connected to the NAS Rule.

### The planar spectrum in U(N)-invariant quantum mechanics by Fock space methods: I. The bosonic case

Prompted by recent results on Susy-U(N)-invariant quantum mechanics in the
large N limit by Veneziano and Wosiek, we have examined the planar spectrum in
the full Hilbert space of U(N)-invariant states built on the Fock vacuum by
applying any U(N)-invariant combinations of creation-operators. We present
results about 1) the supersymmetric model in the bosonic sector, 2) the
standard quartic Hamiltonian. This latter is useful to check our techniques
against the exact result of Brezin et al. The SuSy case is where Fock space
methods prove to be the most efficient: it turns out that the problem is
separable and the exact planar spectrum can be expressed in terms of the
single-trace spectrum. In the case of the anharmonic oscillator, on the other
hand, the Fock space analysis is quite cumbersome due to the presence of large
off-diagonal O(N) terms coupling subspaces with different number of traces;
these terms should be absorbed before taking the planar limit and recovering
the known planar spectrum. We give analytical and numerical evidence that good
qualitative information on the spectrum can be obtained this way.Comment: 17 pages, 4 figures, uses youngtab.sty. Final versio

### An Industrial Agglomeration Approach to Central Place and City Size Regularities

An empirical regularity designated as the Number-Average Size (NAS) Rule was first identified for the case of Japan by Mori, Nishikimi and Smith [13], and has since been extended to the US by Hsu [6]. This rule asserts a negative log-linear relation between the number and average population size of cities where a given industry is present, i.e., of industry-choice cities. Hence one of its key features is to focus on the presence or absence of industries in each city, rather than the percentage distribution of industries across cities. But despite the strong empirical regularity of this rule, there still remains the statistical question of whether such location patterns could simply have occurred by chance. In this paper an alternative approach to industry-choice cities is proposed. This approach utilizes the statistical procedure developed in Mori and Smith [15] to identify spatially explicit patterns of agglomeration for each industry. In this context, the desired industry-choice cities are taken to be those (economic) cities that constitute at least part of a significant spatial agglomeration for the industry. These cluster-based choice cities are then used to reformulate both the NAS Rule and the closely related Hierarchy Principle of Christaller [2]. The key empirical result of the paper is to show that the NAS Rule not only continues to hold under this new definition, but in some respects is even stronger. The Hierarchy Principle is also shown to hold under this new definition. Finally, the present notion of cluster-based choice cities is also used to develop tests of both the locational diversity of industries and the industrial diversity of cities in Japan.

### A general framework for online audio source separation

We consider the problem of online audio source separation. Existing
algorithms adopt either a sliding block approach or a stochastic gradient
approach, which is faster but less accurate. Also, they rely either on spatial
cues or on spectral cues and cannot separate certain mixtures. In this paper,
we design a general online audio source separation framework that combines both
approaches and both types of cues. The model parameters are estimated in the
Maximum Likelihood (ML) sense using a Generalised Expectation Maximisation
(GEM) algorithm with multiplicative updates. The separation performance is
evaluated as a function of the block size and the step size and compared to
that of an offline algorithm.Comment: International conference on Latente Variable Analysis and Signal
Separation (2012

### How Computational Statistics Became the Backbone of Modern Data Science

This first chapter serves as an introduction and overview for a collection of articles surveying the current state of the science of computational statistics. Earlier versions of most of these articles appeared in the first edition of Handbook of Computational Statistics: Concepts and Methods, published in 2004. There have been advances in all of the areas of computational statistics, so we feel that it is time to revise and update this Handbook. This introduction is a revision of the introductory chapter of the first edition.Discrete time series models, continuous time diffusion models, models with jumps, stochastic volatility, GARCH

### Nonlinear evolution of the plasma beatwave: Compressing the laser beatnotes via electromagnetic cascading

The near-resonant beatwave excitation of an electron plasma wave (EPW) can be
employed for generating the trains of few-femtosecond electromagnetic (EM)
pulses in rarefied plasmas. The EPW produces a co-moving index grating that
induces a laser phase modulation at the difference frequency. The bandwidth of
the phase-modulated laser is proportional to the product of the plasma length,
laser wavelength, and amplitude of the electron density perturbation. The laser
spectrum is composed of a cascade of red and blue sidebands shifted by integer
multiples of the beat frequency. When the beat frequency is lower than the
electron plasma frequency, the red-shifted spectral components are advanced in
time with respect to the blue-shifted ones near the center of each laser
beatnote. The group velocity dispersion of plasma compresses so chirped
beatnotes to a few-laser-cycle duration thus creating a train of sharp EM
spikes with the beat periodicity. Depending on the plasma and laser parameters,
chirping and compression can be implemented either concurrently in the same, or
sequentially in different plasmas. Evolution of the laser beatwave end electron
density perturbations is described in time and one spatial dimension in a
weakly relativistic approximation. Using the compression effect, we demonstrate
that the relativistic bi-stability regime of the EPW excitation [G. Shvets,
Phys. Rev. Lett. 93, 195004 (2004)] can be achieved with the initially
sub-threshold beatwave pulse.Comment: 13 pages, 11 figures, submitted to Physical Review

### Multi-Orbital Molecular Compound (TTM-TTP)I_3: Effective Model and Fragment Decomposition

The electronic structure of the molecular compound (TTM-TTP)I_3, which
exhibits a peculiar intra-molecular charge ordering, has been studied using
multi-configuration ab initio calculations. First we derive an effective
Hubbard-type model based on the molecular orbitals (MOs) of TTM-TTP; we set up
a two-orbital Hamiltonian for the two MOs near the Fermi energy and determine
its full parameters: the transfer integrals, the Coulomb and exchange
interactions. The tight-binding band structure obtained from these transfer
integrals is consistent with the result of the direct band calculation based on
density functional theory. Then, by decomposing the frontier MOs into two
parts, i.e., fragments, we find that the stacked TTM-TTP molecules can be
described by a two-leg ladder model, while the inter-fragment Coulomb energies
are scaled to the inverse of their distances. This result indicates that the
fragment picture that we proposed earlier [M.-L. Bonnet et al.: J. Chem. Phys.
132 (2010) 214705] successfully describes the low-energy properties of this
compound.Comment: 5 pages, 4 figures, published versio

### Analysis of process variables via CFD to evaluate the performance of a FCC riser

Feedstock conversion and yield products are studied through a 3D model simulating the main reactor of the fluid catalytic cracking (FCC) process. Computational fluid dynamic (CFD) is used with Eulerian-Eulerian approach to predict the fluid catalytic cracking behavior. The model considers 12 lumps with catalyst deactivation by coke and poisoning by alkaline nitrides and polycyclic aromatic adsorption to estimate the kinetic behavior which, starting from a given feedstock, produces several cracking products. Different feedstock compositions are considered. The model is compared with sampling data at industrial operation conditions. The simulation model is able to represent accurately the products behavior for the different operating conditions considered. All the conditions considered were solved using a solver ANSYS CFX 14.0. The different operation process variables and hydrodynamic effects of the industrial riser of a fluid catalytic cracking (FCC) are evaluated. Predictions from the model are shown and comparison with experimental conversion and yields products are presented; recommendations are drawn to establish the conditions to obtain higher product yields in the industrial process

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