11,382 research outputs found
Extreme eigenvalues of sample covariance matrices under generalized elliptical models with applications
We consider the extreme eigenvalues of the sample covariance matrix
under the generalized elliptical model that Here
is a bounded positive definite deterministic matrix representing
the population covariance structure, is a random matrix
containing either independent columns sampled from the unit sphere in
or i.i.d. centered entries with variance and is a
diagonal random matrix containing i.i.d. entries and independent of Such a
model finds important applications in statistics and machine learning.
In this paper, assuming that and are comparably large, we prove that
the extreme edge eigenvalues of can have several types of distributions
depending on and asymptotically. These distributions include:
Gumbel, Fr\'echet, Weibull, Tracy-Widom, Gaussian and their mixtures. On the
one hand, when the random variables in have unbounded support, the edge
eigenvalues of can have either Gumbel or Fr\'echet distribution depending
on the tail decay property of On the other hand, when the random variables
in have bounded support, under some mild regularity assumptions on
the edge eigenvalues of can exhibit Weibull, Tracy-Widom,
Gaussian or their mixtures. Based on our theoretical results, we consider two
important applications. First, we propose some statistics and procedure to
detect and estimate the possible spikes for elliptically distributed data.
Second, in the context of a factor model, by using the multiplier bootstrap
procedure via selecting the weights in we propose a new algorithm to infer
and estimate the number of factors in the factor model. Numerical simulations
also confirm the accuracy and powerfulness of our proposed methods and
illustrate better performance compared to some existing methods in the
literature.Comment: 90 pages, 6 figures, some typos are correcte
The evolution of BIR domain and its containing proteins
AbstractBIR domain and its containing proteins play critical roles in cell apoptosis and cell division. Here several lines of novelty were revealed based on a comprehensive evolutionary analysis of BIR domains in 11 representative organisms. First, the type II BIR domains in Survivin and Bruce showed more conservation compared with the type I BIR domains in the inhibitors of apoptosis proteins (IAPs). Second, cIAP was derived from a XIAP duplicate and emerged just after the divergence of invertebrates and vertebrates. Third, the three BIR domains of NAIP displayed significantly elevated evolutionary rates compared with the BIR domains in other IAPs
Thermal behaviour of high amylose cornstarch studied by DSC
The thermal behaviour of high amylose cornstarches (80% amylose content) was studied by DSC using high pressure stainless steel pans in the temperature range between 0-350 degrees C. The number of endotherms and the enthalpy of gelatinization were found to depend on moisture content. Up to four endotherms and one exotherm were determined when the moisture content was above 40%. The meaning of each endotherm has been discussed. The enthalpy of gelatinization was calculated based on the summation of all the gelatinization endotherms and found to increase with increasing water content
Investigation of ultra-thin Al₂O₃ film as Cu diffusion barrier on low-k (k=2.5) dielectrics
Ultrathin Al(2)O(3) films were deposited by PEALD as Cu diffusion barrier on low-k (k=2.5) material. The thermal stability and electrical properties of the Cu/low k system with Al(2)O(3) layers with different thickness were studied after annealing. The AES, TEM and EDX results revealed that the ultrathin Al(2)O(3) films are thermally stable and have excellent Cu diffusion barrier performance. The electrical measurements of dielectric breakdown and TDDB tests further confirmed that the ultrathin Al(2)O(3) film is a potential Cu diffusion barrier in the Cu/low-k interconnects system
Starch gelatinization under shearless and shear conditions
This article reviews the development of studying starch gelatinization under shear and shearless conditions, in particular the technologies used to detect the degree of gelatinization. Advantages and disadvantages of each technology were discussed and then some examples were presented to demonstrate their application. A new technology RheoScope, an instrument that can measure viscosity under shear stress and simultaneously observes variation of starch particles using a microscope, was also introduced. It was found the definition of "gelatinization" could be different for different detection technologies. Under shearless condition full gelatinization of starch needs about ratio of water 3/starch 1, while the gelatinization under shear condition requires less water content since shear stress enhances the processing. The number of endotherm and enthalpy of gelatinization depends on amylose/amylopectin, moisture and lipid content
Morphology and properties of thermal/cooling-gel bi-phasic systems based on hydroxypropyl methylcellulose and hydroxypropyl starch
The miscibility between two gels with largely different gelation behaviors is an interesting topic both scientifically and practically. This paper reports a novel bi-phasic system based on two natural polymers, hydroxypropyl methylcellulose (HPMC) which has a thermal gelation behavior, and hydroxypropyl starch (HPS) which has a cooling gelation property. While both biopolymers have the same glucose unit grafted with propylene oxide, and are compatible to a certain degree, they were observed immiscible because of their different gelation behaviors. The immiscibility of these two compatible polymers could result in special structures leading to different blend film properties. Regarding this, the morphology, thermal transition, mechanical properties and oxygen barrier property could be well tailored by the ratio of two biopolymers and the environmental conditions. The knowledge obtained from this work could be useful for understanding other similar systems with desirable structure and properties
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