Rate constants and atmospheric lifetimes for the reactions of OH radicals and Cl atoms with haloalkanes

Rate constants for the reactions of Cl atoms and OH radicals with haloalkanes were measured using the relative rate technique. From these values the atmospheric lifetimes of the organics with respect to Cl atoms and OH radicals were calculated. Cl atoms were produced by the photolysis of chlorine gas, and photolysis of methyl nitrite was the source of OH radicals. The rate constants were measured for a series of brominated and chlorinated alkanes for which measurements have not yet been reported excepting: k(Cl + 1-chloropropane) and k(OH + 1-chloropropane, 2-chloropropane, and bromoethane). The organics studied were 1-chloropropane, 2-chloropropane, 1,3 dichloropropane, 2-chloro 2methylpropane, bromoethane, 1-bromopropane, 2-bromopropane, 1-bromobutane, 1-bromopentane, and 1-bromohexane. Cl atom reactions were measured at 298 K, the OH radical reactions were measured at temperatures between 298–308 K. © 1993 John Wiley & Sons, Inc.     

Anomalous atomic hydrogen shock pattern in a supersonic plasma Jet

A two-photon laser-induced fluorescence study on the transport of ground-state atomic hydrogen in a supersonic plasma jet, generated from an Ar-H (2) mixture, reveals an unexpected shock pattern. Whereas both the axial-velocity profile and the temperature profile of hydrogen atoms along the jet centerline can be interpreted in terms of a supersonic expansion of an Ar-H gas mixture, the H-atom density profiles do not satisfy the well established Rankine-Hugoniot relation leading to a nonconservation of the forward flux. The experimental results show that H atoms escape from the supersonic expansion by a diffusion process due to strong density gradients between the core of the jet and its vicinity.     

Edge critical cops and robber

We consider edge critical graphs when playing cops and robber. Specifically, we look at those graphs whose copnumbers change from one to two when any edge is added, deleted, subdivided or contracted. We characterize all such sets, showing that they are empty, trees, all 2-edge-connected graphs and empty, respectively. We also consider those graphs which change from copnumber two to one when any edge is added, and give a characterization in the k-regular case.     

ICP-AES法测定色漆可溶性金属含量

用ICP-AES法测定了色漆中的“可溶性”金属铬、镉、铅元素，考察了不同酸度对分析结果的影响，优化了测试条件。进行了回收率和精密度试验。并用原子吸收光谱国标方法进行对照，结果一致。     

Correcting for a density distribution: particle size analysis of core-shell nanocomposite particles using disk centrifuge photosedimentometry

Many types of colloidal particles possess a core-shell morphology. In this Article, we show that, if the core and shell densities differ, this morphology leads to an inherent density distribution for particles of finite polydispersity. If the shell is denser than the core, this density distribution implies an artificial narrowing of the particle size distribution as determined by disk centrifuge photosedimentometry (DCP). In the specific case of polystyrene/silica nanocomposite particles, which consist of a polystyrene core coated with a monolayer shell of silica nanoparticles, we demonstrate that the particle density distribution can be determined by analytical ultracentrifugation and introduce a mathematical method to account for this density distribution by reanalyzing the raw DCP data. Using the mean silica packing density calculated from small-angle X-ray scattering, the real particle density can be calculated for each data point. The corrected DCP particle size distribution is both broader and more consistent with particle size distributions reported for the same polystyrene/silica nanocomposite sample using other sizing techniques, such as electron microscopy, laser light diffraction, and dynamic light scattering. Artifactual narrowing of the size distribution is also likely to occur for many other polymer/inorganic nanocomposite particles comprising a low-density core of variable dimensions coated with a high-density shell of constant thickness, or for core-shell latexes where the shell is continuous rather than particulate in nature.     

On Transversally Elliptic Operators and the Quantization of Manifolds with f-Structure

Given an f-structure ${\varphi}$ on a manifold M, together with a compatible metric g and connection ${\nabla}$ on M, we construct an odd firstorder differential operator D whose principal symbol is of the type considered in [13]. In the special case of a CR-integrable almost ${\mathcal {S}}$ -structure, we show that when ${\nabla}$ is the generalized Tanaka-Webster connection of Lotta and Pastore, the operator D is given by D = ${{\sqrt {2} (\overline {\partial}_b + \overline{\partial}_{b}^{\ast})}}$ , where ${\overline {\partial}_b}$ is the tangential Cauchy-Riemann operator. We then describe two types of “quantization” of manifolds with f-structure that reduce to familiar methods in symplectic geometry in the case that ${\varphi}$ is a compatible almost complex structure, and to the contact quantizations defined in [16] when ${\varphi}$ comes from a contact metric structure.     

Determination of an Optimal Forecast Model for Ambulance Demand Using Goal Programming

A multistep approach to determining the optimal parameters of an exponential smoothing model was used to forecast emergency medical service (E.M.S.) demand for four counties of South Carolina. Daily emergency and routine (non-emergency) demand data were obtained and forecast statistics generated for each county sampled, using Winters' exponential smoothing model. A goal programme was formulated to combine forecast results for emergency calls with routine call forecasts. The goal programme gave a higher priority to accurate forecasting of emergency demand. The forecast model generated implicitly weights demand by severity and provides a reliable estimate of demand overall. The optimal parameter values for the smoothing model were obtained by minimizing the objective function value of the goal programming problem. The parameter values obtained were used to forecast demand for E.M.S. in the selected counties. The results of the model were compared to those using a multiple linear regression model and a single-objective-based exponential smoothing model for 2 months of data. When compared with two single-objective forecast models, the multiple-objective approach yielded more accurate forecasts and, therefore, was more cost-effective for the planner. The model presents and demonstrates a theoretical approach to improving the accuracy of ambulance demand forecasts. The possible impact of this approach on planning efficiency is discussed.