Polystyrene-supported triphenylarsines: Useful ligands in palladium-catalyzed aryl halide homocoupling reactions and a catalyst for alkene epoxidation using hydrogen peroxide

The utility of both soluble (non-cross-linked) and insoluble (cross-linked) polystyrene-supported triphenylarsine reagents were examined. These reagents were prepared by standard radical polymerization methodology and used in palladium-catalyzed homocoupling reactions of aryl halides. The insoluble reagent was also used as a catalyst precursor in heterogeneous alkene epoxidation reactions in which aqueous hydrogen peroxide was the stoichiometric oxidant. For the aryl halide homocoupling reactions, both reagents worked well and afforded similar results. Unhindered aryl iodides afforded the best yields in the shortest reaction times compared to aryl bromides. The epoxidation reactions of unfunctionalized alkenes were not very efficient. This was probably due to the hydrophobicity of the polystyrene matrix, which did not swell in the reaction medium. Thus, since a microporous, gel-type polystyrene matrix was used, the majority of the arsine groups were inaccessible to the reaction components and therefore incapable of participating in catalysis. © 2005 Elsevier Ltd. All rights reserved.postprin

On the existence of stationary states during granular compaction

When submitted to gentle mechanical taps a granular packing slowly compacts until it reaches a stationary state that depends on the tap characteristics. The properties of such stationary states are experimentally investigated. The influence of the initial state, taps properties and tapping protocol are studied. The compactivity of the packings is determinated. Our results strongly support the idea that the stationary states are genuine thermodynamic states.Comment: to be published in EPJE. The original publication will be available at www.europhysj.or

Comparisons of physique, body composition, and somatotype by weight division between male and female collegiate taekwondo athletes

The aim of the study was to compare the physique, body composition and somatotype between male and female collegiate taekwondo athletes and specially focus on differences by weight division. 60 collegiate taekwondo athletes (male: 29, female: 31) voluntarily participated in the study. They were divided into four Olympic weight divisions (male for -58 kg, -68 kg, -80 kg, +80 kg, female for -49 kg, -57 kg, -67 kg, +67 kg). Anthropometric measurements included body weight, height, sitting height, body circumferences (relaxed arm, flexed arm, chest, waist, hip, thigh, and calf), bone widths (humerus and femur), and skinfold thicknesses (triceps, subscapular, suprailiac, thigh, and calf) were measured. The three somatotype components were assessed by Heath-Carter anthropometric method (Carter & Heath, 1990). Independent t-test and one-way ANOVA were applied to analyze difference of dependent variables. Significant level was set at .05. Male athletes were taller and heavier than female athletes. However, sum of skinfold thickness was significantly higher in female athletes than male athletes. The three somatotype components for male athletes were 3.4-3.5-3.1 and characterized with balanced mesomorphy. On the other hand, the somatotype of female athletes were 6.1-3.4-2.6 and characterized with mesomorphic endomorph. In male athletes -80 kg and +80 kg weight divisions were higher mesomorphy, but lower ectomorphy than -58 kg and -68 kg weight divisions. In female, -57 kg, -67 kg and +67 kg weight divisions were higher endomorphy and mesomorphy, but lower ectomorphy than -49 kg weight divisions. In conclusion, male athletes had higher anthropometric characteristics than female athletes except for the skinfold thickness. Female athletes had higher endomorphy, whereas male athletes had higher ectomorphy. Physique and somatotype were different between weight divisions both male and female athletes. This study provides a reference data of morphological characteristics of collegiate elite taekwondo athletes

Isotropic three-dimensional gap in the iron-arsenide superconductor LiFeAs from directional heat transport measurements

The thermal conductivity k of the iron-arsenide superconductor LiFeAs (Tc ~ 18K) was measured in single crystals at temperatures down to T~50mK and in magnetic fields up to H=17T, very close to the upper critical field Hc2~18T. For both directions of the heat current, parallel and perpendicular to the tetragonal c-axis, a negligible residual linear term k/T is found as T ->0, revealing that there are no zero-energy quasiparticles in the superconducting state. The increase in k with magnetic field is the same for both current directions and it follows closely the dependence expected for an isotropic superconducting gap. There is no evidence of multi-band character, whereby the gap would be different on different Fermi-surface sheets. These findings show that the superconducting gap in LiFeAs is isotropic in 3D, without nodes or deep minima anywhere on the Fermi surface. Comparison with other iron-pnictide superconductors suggests that a nodeless isotropic gap is a common feature at optimal doping (maximal Tc).Comment: 4 pages, 3 figure

Genes Suggest Ancestral Colour Polymorphisms Are Shared across Morphologically Cryptic Species in Arctic Bumblebees

email Suzanne orcd idCopyright: © 2015 Williams et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited

Statistics of level spacing of geometric resonances in random binary composites

We study the statistics of level spacing of geometric resonances in the disordered binary networks. For a definite concentration $p$ within the interval $[0.2,0.7]$, numerical calculations indicate that the unfolded level spacing distribution $P(t)$ and level number variance $\Sigma^2(L)$ have the general features. It is also shown that the short-range fluctuation $P(t)$ and long-range spectral correlation $\Sigma^2(L)$ lie between the profiles of the Poisson ensemble and Gaussion orthogonal ensemble (GOE). At the percolation threshold $p_c$, crossover behavior of functions $P(t)$ and $$ is obtained, giving the finite size scaling of mean level spacing $\delta$ and mean level number $n$, which obey the scaling laws, $$ and $n=0.911L^{1.970}$.Comment: 11 pages, 7 figures,submitted to Phys. Rev.

Applications of stochastic inventory control in market-making and robust supply chains

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2010.Cataloged from PDF version of thesis.Includes bibliographical references (p. 169-172).This dissertation extends the classical inventory control model to address stochastic inventory control problems raised in market-making and robust supply chains. In the financial market, market-makers assume the role of a counterpart so that investors can trade any fixed amounts of assets at quoted bid or ask prices at any time. Market-makers benefit from the spread between the bid and ask prices. but they have to carry inventories of assets which expose them to potential losses when the market price moves in an undesirable direction. One approach to reduce the risk associated with price uncertainty is to actively trade with other Market-Makers at the price of losing potential spread gain. We propose a dynamic programming model to determine the optimal active trading quantity., which maximizes the Market-Maker's expected utility. For a single-asset model. We show that a threshold inventory control policy is optimal with respect to both an exponential utility criterion and a mean-variance tradeoff objective. Special properties such as symmetry and monotonicity of the threshold levels are also investigated. For a multiple-asset model. the mean-variance analysis suggests that there exists a connected no-trade region such that the Market-Maker does not need to actively trade with other market-makers if the inventory falls in the no-trade region. Outside the no-trade region. the optimal way to adjust inventory levels can be obtained from the boundaries of the no-trade region. These properties of the optimal policy lead to practically efficient algorithms to solve the problem. The dissertation also considers the stochastic inventory control model in robust supply chain systems. Traditional approaches in inventory control first estimate the demand distribution among a predefined family of distributions based on data fitting of historical demand observations, and then optimize the inventory control policy using the estimated distributions. which often leads to fragile solutions in case the preselected family of distributions was inadequate. In this work. we propose a minimax robust model that integrates data fitting and inventory optimization for the single item multi-period periodic review stochastic lot-sizing problem. Unlike the classical stochastic inventory models, where demand distribution is known, we assume that histograms are part of the input. The robust model generalizes Bayesian model, and it can be interpreted as minimizing history dependent risk measures. We prove that the optimal inventory control policies of the robust model share the same structure as the traditional stochastic dynamic programming counterpart. In particular., we analyze the robust models based on the chi-square goodness-of-fit test. If demand samples are obtained from a known distribution, the robust model converges to the stochastic model with true distribution under general conditions.by Miao Song.Ph.D

Robust transportation policy analysis in Singapore using microscopic traffic simulator

Thesis (S.M. in Transportation)--Massachusetts Institute of Technology, Department of Civil and Environmental Engineering, 2013.Cataloged from PDF version of thesis.Includes bibliographical references (pages 99-101).One of the main challenges of making strategic decisions in transportation is that we always face a set of possible future states due to deep uncertainty in traffic demand. This thesis focuses on exploring the application of model-based decision support techniques which characterize a set of future states that represent the vulnerabilities of the proposed policy. Vulnerabilities here are interpreted as states of the world where the proposed policy fails its performance goal or deviates significantly from the optimum policy due to deep uncertainty in the future. Based on existing literature and data mining techniques, a computational model-based approach known as scenario discovery is described and applied in an empirical problem. We investigated the application of this new approach in a case study based on a proposed transit policy implemented in Marina Bay district of Singapore. Our results showed that the scenario discovery approach performs well in finding the combinations of uncertain input variables that will result in policy failure.by Xiang Song.S.M.in Transportatio

Nonadiabatic electron transfer in the condensed phase, via semiclassical and Langevin equation approach

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2009.Includes bibliographical references (leaves 127-137).In this dissertation, we discuss two methods developed during my PhD study to simulate electron transfer systems. The first method, the semi-classical approximation, is derived from the stationary phase approximation to the path integral in the spin-coherent representation. The resulting equation of motion is a classical-like ordinary differential equation subject to a two-ended boundary condition. The boundary value problem is solved using the "near real trajectory" algorithm. This method is applied to three scattering problems to compute the transmission and reflection probabilities. The strength and weakness of this approach is investigated in details. The second approach is based on the generalized Langevin equation, in which the quantum transitions of electronic states are condensed into a linear regression equation. The memory kernel in the regression equation is computed using a second perturbation expansion. The perturbation is optimized to achieve the best convergence of the second order expansion. This procedure results in a tow-hop Langevin equation, the THLE. Results from a spin-boson system validate the THLE in a wide range of parameter regimes. Lastly, we tested the feasibility of using Monte Carlo sampling to compute the memory kernel from the spin-boson system and proposed a smoothing technique to reduce the number of sampling points.by XiaoGeng Song.Ph.D

Design, implementation and validation of an exoskeletal robot for locomotion studies in rodents

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2012.Cataloged from PDF version of thesis.Includes bibliographical references (p. 214-226).Growing interest in robotic treatment of patients with neurological injury motivates the development of therapeutic robots for basic research into recovery. Though humans are the ultimate beneficiaries, basic research frequently involves rodent models of neurological injury, which motivates robotic devices that can interact with rats or mice. Currently, available apparatus for locomotion studies of rodents is built upon treadmills, which simplify the design and implementation but also restrict the scope of possible experiments. This is largely due to the treadmill's single-dimensional movement and the lack of accommodation for natural or voluntary movement of the animal. In order to open up new possibilities for locomotion studies in rodents, this work introduces newly developed apparatus for locomotion research in rodents. The key concept is to allow maximal freedom of voluntary movement of the animal while providing forceful interaction when necessary. Advantages and challenges of the proposed machine over other existing designs are discussed. Design and implementation issues are presented and discussed, emphasizing their impact on free, voluntary, movement of the animal. A live-animal experiment was conducted to verify the design principles. Unconstrained natural movement of the animal was compared with movement with the overground robot attached. The compact, overground design and backdrivable implementation of this robot allow novel experiments that involve open-space, free (or interactive) locomotion of the animal.by Yun Seong Song.Ph.D