Home About us Contact
|
Home About us Contact | ||
|
|
||
Judicious Choice (judicious + choice)
Selected AbstractsDivergent Reactivity of 2-Azetidinone-Tethered Allenols with Electrophilic Reagents: Controlled Ring Expansion versus SpirocyclizationADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 4 2010Benito Alcaide Abstract A dual reactivity of 2-azetidinone-tethered allenols may occur by judicious choice of the electrophilic reagents, namely halogenating versus selenating reagents. Using common substrates, structurally different compounds, namely tetramic acids (from N -bromosuccinimide) or spirocyclic seleno-,-lactams (from N -phenylselenophthalimide), can be readily synthesized by these divergent protocols. [source] Microwave-Assisted Synthesis of Fine Particle Oxides Employing Wet Redox MixturesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2002Solomon Sundar Manoharan Interaction of electromagnetic radiation with a physical mixture of metal nitrates and amides/hydrazides is observed to initiate high-temperature reactions, useful for realizing several high-temperature ceramic materials. A judicious choice of such redox mixtures undergoes exothermic reactions when they couple with microwave radiation. The coupling of electromagnetic radiation with metal salts and amides/hydrazides depends on the dielectric properties of the individual components in the reaction mixture. The approach has been used to prepare ,-Fe2O3, Fe3O4, MgCr2O4, ,-CaCr2O4, and La0.7Ba0.3MnO3. [source] Control of Biodegradability of Polylactide via Nanocomposite TechnologyMACROMOLECULAR MATERIALS & ENGINEERING, Issue 3 2003Suprakas Sinha Ray Abstract Polymer/layered silicate nanocomposite technology is not only suitable for the significant improvement of mechanical and various other materials properties of virgin polymers, it is also suitable to enhance the rate of biodegradation of biodegradable polymers such as polylactide. The biodegradability of polylactide in nanocomposites completely depends upon both the nature of pristine layered silicates and surfactants used for the modification of layered silicate, and we can control the biodegradability of polylactide via judicious choice of organically modified layered silicate. Biodegradation of neat PLA and various PLA/OMLS nanocomposites recovered from compost with time. [source] A mathematical programming approach for improving the robustness of least sum of absolute deviations regressionNAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 4 2006Avi Giloni Abstract This paper discusses a novel application of mathematical programming techniques to a regression problem. While least squares regression techniques have been used for a long time, it is known that their robustness properties are not desirable. Specifically, the estimators are known to be too sensitive to data contamination. In this paper we examine regressions based on Least-sum of Absolute Deviations (LAD) and show that the robustness of the estimator can be improved significantly through a judicious choice of weights. The problem of finding optimum weights is formulated as a nonlinear mixed integer program, which is too difficult to solve exactly in general. We demonstrate that our problem is equivalent to a mathematical program with a single functional constraint resembling the knapsack problem and then solve it for a special case. We then generalize this solution to general regression designs. Furthermore, we provide an efficient algorithm to solve the general nonlinear, mixed integer programming problem when the number of predictors is small. We show the efficacy of the weighted LAD estimator using numerical examples. © 2006 Wiley Periodicals, Inc. Naval Research Logistics, 2006 [source] Sampling subproblems of heterogeneous Max-Cut problems and approximation algorithms,RANDOM STRUCTURES AND ALGORITHMS, Issue 3 2008Petros Drineas Abstract Recent work in the analysis of randomized approximation algorithms for NP -hard optimization problems has involved approximating the solution to a problem by the solution of a related subproblem of constant size, where the subproblem is constructed by sampling elements of the original problem uniformly at random. In light of interest in problems with a heterogeneous structure, for which uniform sampling might be expected to yield suboptimal results, we investigate the use of nonuniform sampling probabilities. We develop and analyze an algorithm which uses a novel sampling method to obtain improved bounds for approximating the Max-Cut of a graph. In particular, we show that by judicious choice of sampling probabilities one can obtain error bounds that are superior to the ones obtained by uniform sampling, both for unweighted and weighted versions of Max-Cut. Of at least as much interest as the results we derive are the techniques we use. The first technique is a method to compute a compressed approximate decomposition of a matrix as the product of three smaller matrices, each of which has several appealing properties. The second technique is a method to approximate the feasibility or infeasibility of a large linear program by checking the feasibility or infeasibility of a nonuniformly randomly chosen subprogram of the original linear program. We expect that these and related techniques will prove fruitful for the future development of randomized approximation algorithms for problems whose input instances contain heterogeneities. © 2007 Wiley Periodicals, Inc. Random Struct. Alg., 2008 [source] Spin Crossover versus Low-Spin Behaviour Exhibited in 2D and 3D Supramolecular Isomers of [FeII(2,4-bpt)2],Guest,CHEMISTRY - A EUROPEAN JOURNAL, Issue 27 2010Xin Bao To spin or not to spin: Four supramolecular isomers based on a [Fe(2,4-bpt)2],guest were synthesised by judicious choice of solvents under solvothermal conditions (see figure). They can be categorised into a 2D spin crossover (SCO) branch and a 3D low-spin (LS) branch (all of them exhibit NbO topology, but one is non-interpenetrated and the other two are twofold interpenetrated). The differences in the supramolecular interactions play important roles in their magnetic behaviour. [source] Solid-Phase Synthesis of Dihydrovirginiamycin S1, a Streptogramin B AntibioticCHEMISTRY - A EUROPEAN JOURNAL, Issue 17 2004Alex Shaginian Abstract We describe the first solid-phase synthesis of dihydrovirginiamycin S1, a member of the streptogramin B family of antibiotics, which are nonribosomal-peptide natural products produced by Streptomyces. These compounds, along with the synergistic group A components, are "last line of defense" antimicrobial agents for the treatment of life-threatening infections such as vancomycin-resistant enterococci. The synthesis features an on-resin cyclization and is designed to allow production of streptogramin B analogues with diversification at positions 1,, 1, 2, 3, 4, and 6. Several synthetic challenges known to hinder the synthesis of this class of compounds were solved, including sensitivity to acids and bases, and epimerization and rearrangements, through the judicious choice of deprotection conditions, coupling conditions, and synthetic strategy. This work should enable a better understanding of structure,activity relationships in the streptogramin B compounds, possible identification of analogues that bypass known resistance mechanisms, and perhaps the identification of analogues with novel biological activities. [source] Two-stage detection of partitioned random CDMAEUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 5 2008Lukasz Krzymien Random Code Division Multiple Access (CDMA) with low complexity two-stage joint detection/decoding is considered. A sequence partitioning approach is used for modulation, where every spreading sequence is divided into M sections (partitions) which are interleaved prior to transmission. This setup, called partitioned CDMA, can be understood as a generalisation of (chip) interleave division multiple access (IDMA). An analysis of a low-complexity iterative cancellation receiver is presented for arbitrary received power distributions. It is shown that for equal rate and equal power users the asymptotic performance of partitioned CDMA is equal to the performance of CDMA with optimal a posteriori probability (APP) detection for system loads K/N,<,1.49. Effects of asynchronous signal transmission are quantified for standard pulse shaping filters and it is shown that the signal-to-noise ratios achievable in an asynchronous system are improved with respect to fully synchronous transmission. The effect of unequal received powers is examined and considerable gains in performance are obtained by judicious choices of power distributions. For certain power distribution, partitioned CDMA with iterative detection can achieve arbitrary system loads, that is detection is no longer fundamentally interference limited. The practical near-far resistance of the proposed system is illustrated using an example of a receiver with a circular receive footprint and uniformly distributed transmitters (single cell system). Copyright © 2008 John Wiley & Sons, Ltd. [source] | ||||||||||||||||