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511.
Alessio Sancetta 《Journal of multivariate analysis》2008,99(5):949-967
For high dimensional data sets the sample covariance matrix is usually unbiased but noisy if the sample is not large enough. Shrinking the sample covariance towards a constrained, low dimensional estimator can be used to mitigate the sample variability. By doing so, we introduce bias, but reduce variance. In this paper, we give details on feasible optimal shrinkage allowing for time series dependent observations. 相似文献
512.
Alessio Farcomeni 《Computational Statistics》2009,24(4):583-604
We show a branch and bound approach to exactly find the best sparse dimension reduction of a matrix. We can choose between
enforcing orthogonality of the coefficients and uncorrelation of the components, and can explicitly set the degree of sparsity.
We suggest methods to choose the number of non-zero loadings for each component; illustrate and compare our approach with
existing methods through a benchmark data set. 相似文献
513.
In this paper, a CFD model for bubbly-flow including break-up and coalescence is discussed. The probabilistic method, developed according to this model, is tested for an industrial configuration: numerical bubble-size distributions are compared with those derived by experiments. 相似文献
514.
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516.
Nadia Mulinacci Alessio Valletta Valentina Pasqualetti Marzia Innocenti Camilla Giuliani Maria Bellumori 《Natural product research》2019,33(8):1106-1114
Humans are exposed to ionizing radiations in medical radiodiagnosis and radiotherapy that cause oxidative damages and degenerative diseases. Airplane pilots, and even more astronauts, are exposed to a variety of potentially harmful factors, including cosmic radiations. Among the phytochemicals, phenols are particularly efficient in countering the oxidative stress. In the present study, different extracts obtained from plant food, plant by-products and dietary supplements, have been compared for their antioxidant properties before and after irradiation of 140 cGy, a dose absorbed during a hypothetical stay of three years in the space. All the dry extracts, characterized in terms of vitamin C and phenolic content, remained chemically unaltered and maintained their antioxidant capability after irradiation. Our results suggest the potential use of these extracts as nutraceuticals to protect humans from oxidative damages, even when these extracts must be stored in an environment exposed to cosmic radiations as in a space station. 相似文献
517.
Xin Wu Jennifer R. Small Alessio Cataldo Anne M. Withecombe Peter Turner Philip A. Gale 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(42):15286-15291
Synthetic anion transporters that facilitate transmembrane H+/Cl? symport (cotransport) have anti‐cancer potential due to their ability to neutralize pH gradients and inhibit autophagy in cells. However, compared to the natural product prodigiosin, synthetic anion transporters have low‐to‐modest H+/Cl? symport activity and their mechanism of action remains less well understood. We report a chloride‐selective tetraurea macrocycle that has a record‐high H+/Cl? symport activity similar to that of prodigiosin and most importantly demonstrates unprecedented voltage‐switchable transport properties that are linked to the lack of uniport activity. By studying the anion binding affinity and transport mechanisms of four other anion transporters, we show that the lack of uniport and voltage‐dependent H+/Cl? symport originate from strong binding to phospholipid headgroups that hampers the diffusion of the free transporters through the membrane, leading to an unusual H+/Cl? symport mechanism that involves only charged species. Our work provides important mechanistic insights into different classes of anion transporters and a new approach to achieve voltage‐switchability in artificial membrane transport systems. 相似文献
518.
519.
Francesca Alessio Louis Jeanjean Piero Montecchiari 《Calculus of Variations and Partial Differential Equations》2000,11(2):177-202
We consider a class of non autonomous Allen-Cahn equations
where is a multiple-well potential and is a periodic, positive, non-constant function. We look for solutions to (0.1) having uniform limits as corresponding to minima of W. We show, via variational methods, that under a nondegeneracy condition on the set of heteroclinic solutions of the associated
ordinary differential equation
the equation (0.1) has solutions which depends on both the variables x andy. In contrast, when a is constant such nondegeneracy condition is not satisfied and all such solutions are known to depend only on x.
Received April 16, 1999 / Accepted October 1, 1999 / Published online June 28, 2000 相似文献
520.
Ruben M Payer D Landa A Comisso A Gattinoni C Lin N Collin JP Sauvage JP De Vita A Kern K 《Journal of the American Chemical Society》2006,128(49):15644-15651
Two-dimensional supramolecular honeycomb networks with cavities of an internal diameter of 2.95 nm were formed by the self-assembly of 4,4',4' '-benzene-1,3,5-triyl-tribenzoic acid (BTA) on a Ag(111) surface at room temperature. Annealing to higher temperatures resulted in two sequential phase transformations into closer-packed supramolecular arrangements. The phase transformations are associated with stepwise deprotonation of the carboxylic acid groups. The voids of the honeycomb network of BTA have a suitable size for the construction of hierarchical structures with guest molecules. Single molecules of the macrocyclic compound mt-33 were successfully confined inside 2D nanocavities of the honeycomb networks and released when the phase was transformed to the close-packed structure. 相似文献