10,000 publications from this institution
Implicit probabilistic models are models defined naturally in terms of a sampling procedure and often induces a likelihood function that cannot be expressed explicitly. We develop a simple method for estimating parameters in implicit models that does not require knowledge of the form of the likelihood function or any derived quantities, but can be shown to be equivalent to maximizing likelihood under some conditions. Our result holds in the non-asymptotic parametric setting, where both the capacity of the model and the number of data examples are finite. We also demonstrate encouraging experimental results.
Experimental and theoretical studies were conducted to investigate the influence of anionic ligands (e.g., CF(3)COO(-), CH(3)SO(3)(-)) on the catalytic activity and selectivity of Rh(III) in the oxidative carbonylation of toluene to toluic acid. The catalyst activity was found to pass through a maximum as the pK(a) of the conjugate Brønsted acid decreases from 4.63 to -2.00, with the maximum activity occurring at pK(a) = 0.35, corresponding to CClF(2)COOH. The theoretical analysis showed that the strength of toluene coordination increases with decreasing basicity of the anion (i.e., decreasing pK(a) of the corresponding acid). In contrast, the activation barrier for C-H activation increases with decreasing ligand pK(a). The experimentally observed effect of anion composition on catalyst activity can be explained using calculations of the apparent rate coefficient for toluene activation based on density functional theory and transition state theory. The ratio of p- to m-toluic acid formed increases with decreasing acid pK(a) and passes through a maximum for pK(a) = 0, corresponding to CF(3)COOH. The effect of anion composition on the isomer selectivity is attributed to changes in the charge density on the Rh(III) cation, which in turn affect the distribution of charge on the para and meta carbon atoms of the aromatic ring.
In this paper we apply the method of nonlinear H/sub /spl infin// synchronization to a hyperchaotic system, which consists of two unidirectionally coupled Chua's circuits. This method makes use of a vector field modulation at the master system by a filtered binary valued message signal. Static output feedback is applied to the slave system. The original message is recovered from a tracking error, which is defined after representing the synchronization scheme in standard plant form according to modern control theory. The controller is designed based upon a matrix inequality, in order to minimize the L/sub 2/-gain from the exogenous input (message signal and channel noise) to the regulated output (tracking error).
Purpose Despite the importance of training in ambulatory care settings for residents to acquire important competencies, little is known about the organizational and environmental factors influencing the relative amount of time primary care residents train in ambulatory care during residency. The authors examined factors associated with postgraduate year 1 (PGY-1) residents’ ambulatory care training time in Accreditation Council for Graduate Medical Education (ACGME)-accredited primary care programs. Method U.S.-accredited family medicine (FM) and internal medicine (IM) programs’ 2016–2017 National Graduate Medical Education (GME) Census data from 895 programs within 550 sponsoring institutions (representing 13,077 PGY-1s) were linked to the 2016 Centers for Medicare and Medicaid Services Cost Reports and 2015–2016 Area Health Resource File. Multilevel regression models examined the association of GME program characteristics, sponsoring institution characteristics, geography, and environmental factors with PGY-1 residents’ percentage of time spent in ambulatory care. Results PGY-1 mean (standard deviation, SD) percent time spent in ambulatory care was 25.4% (SD, 0.4) for both FM and IM programs. In adjusted analyses (% increase [standard error, SE]), larger faculty size (0.03% [SE, 0.01], P < .001), sponsoring institution’s receipt of Teaching Health Center (THC) funding (6.6% (SE, 2.7), P < .01), and accreditation warnings (4.8% [SE, 2.5], P < .05) were associated with a greater proportion of PGY-1 time spent in ambulatory care. Programs caring for higher proportions of Medicare beneficiaries spent relatively less time in ambulatory care (< 0.5% [SE, 0.2], P < .01). Conclusions Ambulatory care time for PGY-1s varies among ACGME-accredited primary care residency programs due to the complex context and factors primary care GME programs operate under. Larger ACGME-accredited FM and IM programs and those receiving federal THC GME funding had relatively more PGY-1 time spent in ambulatory care settings. These findings inform policies to increase resident exposure in ambulatory care, potentially improving learning, competency achievement, and primary care access.
The point defect model (PDM) has been used to derive the dependence of the pitting potential on the voltage scan rate. Relationships derived from the PDM predict that the observed pitting potential is a linear function of the square root of voltage scan rate at low scan rates, which agrees with experimental data reported in the literature. Furthermore, the critical concentration of condensed cation vacancies that give rise to passivity breakdown, as estimated from the sweep rate dependence of the pitting potential, is found to be in good agreement with that estimated from structural considerations. The PDM is also used to predict the probability distribution function in the induction time for pitting (tind), that is, the survival probability, by assuming that the maximum diffusivity of the cation vacancy in a population of specimens is log‐normally distributed. This calculated "external" distribution in the induction time is found to be in reasonable agreement with experimental induction time data for passivity breakdown on multiple specimens of single crystal (100) Ni and polycrystalline nickel buffered chloride solutions.
We consider the problem of finding optimum force closure grasps of two and three-dimensional objects. Our focus is on grasps which are useful in practice, namely grasps with a small number of fingers, with friction at the contacts. Assuming frictional contact and rounded finger tips-very mild assumptions in practice-we give new upper (and lower) bounds on the number of fingers necessary to achieve force closure grasps of 2-D and 3-D objects. We develop an optimality criterion based on the notion of decoupled wrenches, and use this criterion to derive optimum two and three finger grasps of 2-D objects, and optimum three finger grasps for 2-D objects. We present a simple O(n) algorithm for computing these optimum grasps for convex polygons, a O(n log n) algorithm for nonconvex polygons, and an O(n/sup 3/) algorithm for polyhedra. In studying these optimum grasps, we derive several interesting theoretical results concerning grasp geometry.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
Vast networks of meteorological sensors ring the globe, providing continuous measurements of an array of atmospheric state variables such as temperature, humidity, rainfall, and the concentration of carbon dioxide [ New et al. , 1999; Tans et al. , 1996]. These measurements provide input to weather and climate models and are key to detecting trends in climate, greenhouse gases, and air pollution. Yet to understand how and why these atmospheric state variables vary in time and space, biogeoscientists need to know where, when, and at what rates important gases are flowing between the land and the atmosphere. Tracking trace gas fluxes provides information on plant or microbial metabolism and climate‐ecosystem interactions.
Abstract We report an approach to conducting the hydroaminomethylation of diverse α‐olefins with a wide range of alkyl, aryl, and heteroarylamines at relatively low temperatures (70–80 °C) and pressures (1.0–3.4 bar) of synthesis gas. This approach is based on simultaneously using two distinct catalysts that are mutually compatible. The hydroformylation step is catalyzed by a rhodium diphosphine complex, and the reductive amination step, which is conducted as a transfer hydrogenation with aqueous, buffered sodium formate as the reducing agent, is catalyzed by a cyclometallated iridium complex. By adjusting the ratio of CO to H 2 , we conducted the reaction at one atmosphere of gas with little change in yield. A diverse array of olefins and amines, including hetreroarylamines that do not react under more conventional conditions with a single catalyst, underwent hydroaminomethylation with this new system, and the pharmaceutical ibutilide was prepared in higher yield and under milder conditions than with a single catalyst.
