10,000 publications from this institution
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
This volume--the fifth in a series of histories of the International Monetary Fund--examines the 1990s, a tumultuous decade in which the IMF faced difficult challenges and took on new and expanded roles. Among these were assisting countries that had long operated under central planning to manage transitions toward market economies, helping countries in financial crisis after sudden loss of support from private financial markets, adapting surveillance to reflect the growing acceptance of international standards for economic and financial policies, helping low-income countries grow and begin to eradicate poverty while staying within its mandate as a monetary institution, and providing adequate financial assistance to members in an age of limited official resources. The IMF's successes and setbacks in facing these challenges provide valuable lessons for an uncertain future
Several classes of enantioselective silylations of C-H bonds have been reported recently, but little mechanistic data on these processes are available. We report mechanistic studies on the rhodium-catalyzed, enantioselective silylation of aryl C-H bonds. A rhodium silyl dihydride and a rhodium norbornyl complex were prepared and determined to be interconverting catalyst resting states. Kinetic isotope effects indicated that the C-H bond cleavage step is not rate-determining, but the C-H bond cleavage and C-Si bond-forming steps together influence the enantioselectivity. DFT calculations indicate that the enantioselectivity originates from unfavorable steric interactions between the substrate and the ligand in the transition state leading to the formation of the minor enantiomer.
C–H bond activation for several alkenes (ethylene, propylene, isobutene, cyclohexene and 1-hexene) and alkanes (methane, ethane, n -hexane, 2-methylpentane and 3-methylpentane) has been studied on the (111) crystal face of platinum as a function of temperature at low (<10 −6 Torr) and high (≥1 Torr) pressures in the absence and presence of hydrogen pressures (≥10 Torr). Sum frequency generation (SFG) vibrational spectroscopy has been used to characterize the adsorbate structures and high pressure scanning tunnelling microscopy (HP-STM) has been used to monitor their surface mobility under reaction conditions during hydrogenation, dehydrogenation and CO poisoning. C–H bond dissociation occurs at low temperatures, approximately 250 K, for all of these molecules, although only at high pressures for the weakly bound alkanes because of their low desorption temperatures. Bond dissociation is known to be surface structure sensitive and we find that it is also accompanied by the restructuring of the metal surface. The presence of hydrogen slows down dehydrogenation and for some of the molecules it influences the molecular rearrangement, thus altering reaction selectivity. Surface mobility of adsorbates is essential to produce catalytic activity. When surface diffusion is inhibited by CO adsorption, ordered surface structures form and the reaction is poisoned. Ethylene hydrogenation is surface structure insensitive, while cyclohexene hydrogenation and dehydrogenation are structure sensitive. n -Hexane and other C 6 alkanes form either upright or flat-lying molecules on the platinum surface which react to produce branched isomers or benzene, respectively.
A study was made of the near-threshold fatigue crack propagation behaviour of a wrought nickel-base superalloy, René 95, with reference to the effect of crack size on the threshold stress intensity ΔK0 no detectable crack growth. Measured threshold ΔK0 values at low load ratios (R = 0.1) for physically short (0.01 – 0.20 mm) cracks were found to be 60% smaller than the corresponding ΔK0 values for long (about 25 mm) cracks. However, short crack threshold values at R = 0.1 were found to be similar to long crack thresholds at R = 0.8. Such behavior is rationalized in terms of fatigue crack closure, specifically involving the role of fracture surface roughness from crystallographic crack growth in nickel-base alloys. The large difference observed between the threshold values for long and physically short cracks serves to illustrate the potential problems in applying conventional (long crack) fatigue data to defect-tolerant lifetime predictions for structural components containing small flaws.
Abstract The first Ir‐catalyzed enantioselective allylation of trisubstituted allylic electrophiles has been developed. Through modification of the leaving group of allylic electrophiles, we found that trisubstituted allylic phosphates are suitable electrophiles for asymmetric allylation. The reaction of allylic phosphates with enol silanes derived from dioxinones gave allylated products in good yields with high enantioselectivities.
Data from a national study of medical groups and independent practice associations are used to examine the extent to which California physician organizations are different from physician organizations in the rest of the United States. California physician organizations are different in many ways: most notably, they are more likely to have external incentives to improve quality and more likely to use recommended care management processes for treating patients with chronic illnesses. The implications of these differences for policy and practice are discussed.
The International Symposium on Relations between Homogeneous and Heterogeneous Catalysis (ISHHC) has a long and distinguished history. Since 1974, in Brussels, this event has been held in Lyon, France (1977), Groeningen, The Netherlands (1981); Asilomar, California (1983); Novosibirsk, Russia (1986); Pisa, Italy (1989); Tokyo, Japan (1992); Balatonfuered, Hungary (1995); Southampton, United Kingdom (1999); Lyon, France (2001); Evanston, Illinois (2001) and Florence, Italy (2005). The aim of this international conference in Berkeley is to bring together practitioners in the three fields of catalysis, heterogeneous, homogeneous and enzyme, which utilize mostly nanosize particles. Recent advances in instrumentation, synthesis and reaction studies permit the nanoscale characterization of the catalyst systems, often for the same reaction, under similar experimental conditions. It is hoped that this circumstance will permit the development of correlations of these three different fields of catalysis on the molecular level. To further this goal we aim to uncover and focus on common concepts that emerge from nanoscale studies of structures and dynamics of the three types of catalysts. Another area of focus that will be addressed is the impact on and correlation of nanosciences with catalysis. There is information on the electronic and atomic structures of nanoparticles and their dynamics that should have importance in catalyst design and catalytic activity and selectivity.
This is a continuation of our research on the Universal Planar Manipulator (UPM), a device capable of manipulating multiple generic objects with a single horizontally-vibrating, rigid plate (3 DOFs). Objects are propelled by sliding frictional forces developed against the vibrating plate. A special plate vibration creates an average force field called the "jet" which is local, i.e., it is only non-zero near its center. By applying jets at different objects' locations in succession, objects can be made to displace a small amount individually, enabling full parallel manipulation. In particular, a single object can leave on a plane jet, if the jet's center is made to track and its direction made aligned with that object's motion. We provide visualization of the jet with respect to changes in its center, orientation, and focus parameters. Described also are two experiments showing the UPM as a tangible-user interface (docking a beer can to the user's hand) and as a chess player (executing moves of an endgame).
By drawing exact bifurcation diagrams, it is confirmed that the Melnikov curve of homoclinicity gives a good prediction for the onset of the chaotic attractor bifurcated from the periodic solution of the second type in some region of the external sinusoidal force. It is also confirmed that the Melnikov's curve becomes an onset of the fractal basin boundary of multiple attractors. This is confirmed by drawing various initial condition planes above and below the curve.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
