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51.
Glen Wheeler 《Journal of Mathematical Analysis and Applications》2011,375(2):685-698
We consider closed immersed hypersurfaces in R3 and R4 evolving by a special class of constrained surface diffusion flows. This class of constrained flows includes the classical surface diffusion flow. In this paper we present a Lifespan Theorem for these flows, which gives a positive lower bound on the time for which a smooth solution exists, and a small upper bound on the total curvature during this time. The hypothesis of the theorem is that the surface is not already singular in terms of concentration of curvature. This turns out to be a deep property of the initial manifold, as the lower bound on maximal time obtained depends precisely upon the concentration of curvature of the initial manifold in L2 for M2 immersed in R3 and additionally on the concentration in L3 for M3 immersed in R4. This is stronger than a previous result on a different class of constrained surface diffusion flows, as here we obtain an improved lower bound on maximal time, a better estimate during this period, and eliminate any assumption on the area of the evolving hypersurface. 相似文献
52.
Turner DR Chesman AS Murray KS Deacon GB Batten SR 《Chemical communications (Cambridge, England)》2011,47(37):10189-10210
The chemistry of the anions dicyanamide and tricyanomethanide (dca and tcm, respectively) has produced a plethora of discoveries over the past few decades, particularly in relation to transition-metal coordination polymers with magnetic coupling. Over recent years there have been an increasing number of reports of heterofunctionalised cyano-containing anions, typically derivatives of dicyanomethanide. Our own group has been particularly concerned with the amide- and nitroso-functionalised anions carbamoyldicyanomethanide (cdm) and dicyanonitrosomethanide (dcnm), respectively. This feature article examines the fascinating diversity of materials and complexes that can be obtained using small cyano anions, ranging from coordination polymers to heterometallic clusters and hydrogen bonding networks. In particular, we focus on results from our own laboratories in the past few years. The magnetic properties of these materials are briefly discussed. 相似文献
53.
Sanvesh Srivastava Glen DePalma Chuanhai Liu 《Journal of computational and graphical statistics》2019,28(2):233-243
The family of expectation--maximization (EM) algorithms provides a general approach to fitting flexible models for large and complex data. The expectation (E) step of EM-type algorithms is time-consuming in massive data applications because it requires multiple passes through the full data. We address this problem by proposing an asynchronous and distributed generalization of the EM called the distributed EM (DEM). Using DEM, existing EM-type algorithms are easily extended to massive data settings by exploiting the divide-and-conquer technique and widely available computing power, such as grid computing. The DEM algorithm reserves two groups of computing processes called workers and managers for performing the E step and the maximization step (M step), respectively. The samples are randomly partitioned into a large number of disjoint subsets and are stored on the worker processes. The E step of DEM algorithm is performed in parallel on all the workers, and every worker communicates its results to the managers at the end of local E step. The managers perform the M step after they have received results from a γ-fraction of the workers, where γ is a fixed constant in (0, 1]. The sequence of parameter estimates generated by the DEM algorithm retains the attractive properties of EM: convergence of the sequence of parameter estimates to a local mode and linear global rate of convergence. Across diverse simulations focused on linear mixed-effects models, the DEM algorithm is significantly faster than competing EM-type algorithms while having a similar accuracy. The DEM algorithm maintains its superior empirical performance on a movie ratings database consisting of 10 million ratings. Supplementary material for this article is available online. 相似文献
54.
J. J. Glen 《The Journal of the Operational Research Society》1987,38(9):847-851
In evaluating feeding policy in livestock production, it is generally assumed that an optimal feeding policy will involve using least-cost rations throughout the production process. It is demonstrated that this assumption may not be valid when the supply of some of the feedstuffs used for livestock feeding is limited. A method for testing the validity of this assumption is presented for a linear programming model of an integrated crop and intensive beef production enterprise in which some of the crops may be used for livestock feeding, and an iterative solution procedure is proposed for cases where this assumption is not valid. 相似文献
55.
56.
Reed M. Izatt Don W. McBride James J. Christensen Jerald S. Bradshaw Glen A. Clark 《Journal of membrane science》1985,22(1):31-46
Carrier-mediated cation fluxes were determined using a H2OCHC13H2O liquid merebrane system for TlNO3 and for binary mixtures of either TlNO3 or KNO3 with alkali metal ions, alkaline earth metal ions, and Pb2+ (in the case of TlNO3). Both macrocyclic polyether and cryptand ligands were used as carriers. In Tl+Mn+ mixtures, selective transport of Tl+ was found over all cations studied, except in the cases of Ag+ by 2.2 and of Pb2+ by 18C6, DC18C6, ClDKP18C6, and 2.2. Generally, K+ was transported selectively from K+Mn+ mixtures, except in the cases of K+Tl+ mixtures in which Tl+ was transported selectively in all cases. A model relating cation flux to log K(CH3OH) for Mn+—macrocycle interaction and to ion-partitioning between the organic and aqueous phases was successful in rationalizing selective cation transport in most of the systems studied. 相似文献
57.
The free radical chain reaction between cyclohexyl-HgCl and () or () MeO2CCH=CHSnBu3, MeO2CCH=CHI, or ClCH=CHHgCl forms MeO2CCH=CHC6H11 or ClCH=CHC6H11 in a stereospecific manner with retention of stereochemistry. 相似文献
58.
We derive a new formula for the chromatic polynomial of any K4 homeomorph. We obtain a large family of chromatically unique K4 homeomorphs. We obtain seven infinite pairs of chromatically equivalent nonisomorphic K4 homeomorphs. 相似文献
59.
Samples of hair are digested with nitric acid and fused with alkali metal nitrates, prior to the determination of Zn, Cd, Pb and Cu by differential pulse anodic stripping voltammetry at a hanging mercury drop electrode. Recoveries from spiked samples range from 91 to 101%. Relative standard deviations vary from 2.6 to 13%, depending on the metal and sample source. Some causes of poor reproducibility are discussed. 相似文献
60.