Publications

Several new classes of transition metal-catalyzed reactions of amines with the CC bond of acrylic acid derivatives were discovered using a high-throughput colorimetric assay. This assay is general for the reactions of primary and secondary alkylamines with acrylic acid derivatives, and the screening of potential catalysts using this assay revealed a number of different metal/ligand combinations that promote these hydroaminations. The colorimetric assay revealed catalysts for the addition of piperidine to methacrylonitrile, crotononitrile, ethyl crotonate, and ethyl methacrylate, as well as catalysts for reactions of butylamine and aniline with methacrylonitrile. A catalyst for the addition of aniline to crotononitrile at 100 °C was also discovered. The products of these reactions are basic building blocks for the synthesis of β-amino acids, amino alcohols, and diamines. These reactions may ultimately produce an enantioselective route to optically active difunctional materials from commodity reagents.

The effect of intracellular polyphosphate on the phosphate-starvation response in Escherichia coli was studied by genetically manipulating the intracellular polyphosphate levels and by performing phosphate shifts on the genetically engineered strains. Strains that produced large quantities of polyphosphate and were able to degrade it induced the phosphate-starvation response to a lesser extent than wild-type strains, whereas strains that were unable to degrade a large intracellular polyphosphate pool induced the phosphate-starvation response to a greater extent than wild-type strains. These results have important implications for expression of heterologous genes under control of the phoA promoter. (c) 1996 John Wiley & Sons, Inc.

Mid-level vision refers to a collection of visual processes and their associated principles, including contour grouping, region grouping, and figure/ground organization. Evidence from psychophysics strongly suggests that mid-level vision is a key component of the visual system and heavily interacts with object and scene recognition. We develop a unified probabilistic framework of mid-level vision, both motivated by and evaluated on human-annotated collections of natural images. We use human-marked boundaries in natural images as ground-truth data. Empirical studies of these boundaries reveal a number of power laws distributions, confirming the intuition that natural images are multi-scale or near scale-invariant in nature. We show that pixel-based Markov models fail to capture such invariance. We propose a scale-invariant mid-level representation from bottom-up. We detect edges in an image, build a discrete piecewise linear approximation of the edges, and finally use constrained Delaunay triangulation (CDT) to complete gradient-less gaps and partition the image into regions. We show that the CDT graph is a compact representation with little loss of structure. On top of the CDT representation, we formulate mid-level vision as contour and region labeling problems. We use conditional random fields (CRF) to capture interactions between contours, junctions and regions. Efficient inference on the CRF is done with loopy belief propagation, and maximum likelihood parameters are obtained through gradient descent. We apply the CDT/CRF framework on various mid-level vision problems, including curvilinear grouping, figure/ground assignment, and figure/ground segmentation. By extensive experimentation on large annotated datasets, we are able to demonstrate, quantitatively, the effectiveness of mid-level visual cues in natural images: we show that curvilinear grouping improves boundary detection; we show that figure/ground organization is feasible without object knowledge; and we show how low-, mid-, and high-level visual cues can be integrated and systematically analyzed in our framework.

We assemble an almost complete set of central bank statutes since 1800 to assess the legal independence of central banking institutions. We use these to extend existing indices of legal independence backward and forward in time. We document the trend toward increased independence post 1980 as well as an earlier, more limited movement in the direction of enhanced independence in the 1920s. We apply natural language processing to current statutes to corroborate our human-reader assessment. Using machine-learning methods, we quantify the extent to which topics in those statutes contribute to the independence measure based on our reading of the statutes. The topic with the largest positive contribution to explaining the cross-country variation in central bank independence encompasses disclosure, transparency, and reporting obligations. The topic with the largest negative contribution covers regulatory powers over inter alia securities markets that complicate the central bank's mandate, make accountability more complex, and render independence problematic.

Abstract A procedure based on rigorous non‐linear analysis is presented that estimates the peak deformation among all isolators in an asymmetric building due to strong ground motion. The governing equations are reduced to a form such that the median normalized deformation due to an ensemble of ground motions with given corner period T d depends primarily on four global parameters of the isolation system: the isolation period T b , the normalized strength η, the torsional‐to‐lateral frequency ratio Ω θ , and the normalized stiffness eccentricity e b /r . The median ratio of the deformations of the asymmetric and corresponding symmetric systems is shown to depend only weakly on T b , η, and Ω θ , but increases with e b /r . The equation developed to estimate the largest ratio among all isolators depends only on the stiffness eccentricity and the distance from the center of mass to the outlying isolator. This equation, multiplied by an earlier equation for the deformation of the corresponding symmetric system, provides a design equation to estimate the deformations of asymmetric systems. This design equation conservatively estimates the peak deformation among all isolators, but is generally within 10% of the ‘exact’ value. Relative to the non‐linear procedure presented, the peak isolator deformation is shown to be significantly underestimated by the U.S. building code procedures. Copyright © 2003 John Wiley & Sons, Ltd.

We compare the performance of four admission control algorithms-one parameter-based and three measurement-based-for controlled-load service. The parameter-based admission control ensures that the sum of reserved resources is bounded by the capacity. The three measurement-based algorithms are based on measured bandwidth, acceptance region and equivalent bandwidth. We use simulation on several network scenarios to evaluate the link utilization and adherence to service commitment achieved by these four algorithms.

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The electrochemical reduction of carbon dioxide is sensitive to electrolyte polarization, which causes gradients in pH and the concentration of carbon dioxide to form near the cathode surface. It is desirable to measure the concentration of reaction-relevant species in the immediate vicinity of the cathode because the intrinsic kinetics of carbon dioxide reduction depend on the composition of the local reaction environment. Meeting this objective has proven difficult because conventional analytical methods only sample products from the bulk electrolyte. In this study, we describe the use of differential electrochemical mass spectrometry to measure the concentration of carbon dioxide and reaction products in the immediate vicinity of the cathode surface. This capability is achieved by coating the electrocatalyst directly onto the pervaporation membrane used to transfer volatile species into the mass spectrometer, thereby enabling species to be sampled directly from the electrode-electrolyte interface. This approach has been used to investigate hydrogen evolution and carbon dioxide reduction over Ag and Cu. We find that the measured CO₂ reduction activity of Ag agrees well with what is measured by gas chromatography of the effluent from an H-cell operated with the same catalyst and electrolyte. A distinct advantage of our approach is that it enables observation of the depletion of carbon dioxide near the cathode surface due to reaction with hydroxyl anions evolved at the cathode surface, something that cannot be done using conventional analytical techniques. We also demonstrate that the influence of this relatively slow chemical reaction can be minimized by evaluating electrocatalytic activity during a rapid potential sweep, thereby enabling measurement of the intrinsic kinetics. For CO₂ reduction over Cu, nine products can be observed simultaneously in real time. A notable finding is that the abundance of aldehydes relative to alcohols near the cathode surface is much higher than that observed in the bulk electrolyte. It is also observed that for increasingly cathodic potentials the relative abundance of ethanol increases at the expense of propionaldehyde. These findings suggest that acetaldehyde is a precursor to ethanol and propionaldehyde and that propionaldehyde is a precursor to n-propanol.

Außergewöhnlich schnelle oxidative Addition eines Arylchlorids (oder eines desaktivierten Arylbromids) an ein aktives Pd0-Zentrum, das durch sterisch anspruchsvolle Phosphane koordiniert wird, erfolgt bei Kupplungsreaktionen, die durch luftstabile PdI-Dimere, wie im Schema gezeigt, katalysiert werden. Infolgedessen sind die Reaktionen von Arylchloriden oder -bromiden mit Aminen und Boronsäuren bei Raumtemperatur innerhalb weniger Minuten abgeschlossen (1-Ad=1-Adamantyl). Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2001/2002/z50085_s.pdf or from the author. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.