Mononuclear anionic formyl complexes; synthesis and properties

A series of kinetically unstable mononuclear anionic formyl complexes have been prepared by the action of Li(C₂H₅)₃BH on neutral metal carbonyl precursors. One of these, Li⁺[(CO)₄Mn(COC₆H₅)(CHO)]^?, is shown to decompose by a hydride transfer disproportionation mechanism involving the by-product (C₂H₅)₃B.     

Determination of optical purity at isotopically chiral sites by 2H NMR

Techniques have been developed which permit the direct analysis of optical purity in α-deuterated amines and carboxylic acids.     

Low-energy behavior of the 3He(α, γ)7Be cross section

Cross sections for the ³He(α, γ)⁷Be reaction have been measured at several energies from E_c.m. = 165 to 1169 keV by counting prompt γ-rays from a windowless, differentially pumped, recirculating, ³He gas target. The cross-section factor S₃₄(E_c.m.) and branching ratio γ₁/γ₀ were determined at each energy. Cross sections were also measured at E_c.m. = 947 and 1255 keV by counting the γ-rays from the ⁷Be produced in a ³He gas cell with a Ni entrance foil. Combining the results of these two independent experiments yields a zero-energy intercept for the cross-section factor of S₃₄(0) = 0.53 ± 0.03 keV · b. The relationship between these measurements and several theoretical calculations, and the import of the extrapolated cross section for the solar-neutrino problem are discussed.     

Mechanistic divergence of two closely related aldol-like enzyme-catalysed reactions

The analysis of the interaction of threose 4-phosphate and 2-deoxyerythrose 4-phosphate with 3-deoxy-D-arabino-heptulosonate 7-phosphate synthase (DAH7PS) reveals previously unrecognised mechanistic differences between the DAH7PS-catalysed reaction and that catalysed by the closely related enzyme, 3-deoxy-D-manno-octulosonate 8-phosphate synthase (KDO8PS).     

A unified view of imaging the elastic properties of tissue

A number of different approaches have been developed to estimate and image the elastic properties of tissue. The biomechanical properties of tissues are vitally linked to function and pathology, but cannot be directly assessed by conventional ultrasound, MRI, CT, or nuclear imaging. Research developments have introduced new approaches, using either MRI or ultrasound to image the tissue response to some stimulus. A wide range of stimuli has been evaluated, including heat, water jets, vibration shear waves, compression, and quasistatic compression, using single or multiple steps or low-frequency (<10 Hz) cyclic excitation. These may seem to be greatly dissimilar, and appear to produce distinctly different types of information and images. However, our purpose in this tutorial is to review the major classes of excitation stimuli, and then to demonstrate that they produce responses that fall within a common spectrum of elastic behavior. Within this spectrum, the major classes of excitation include step compression, cyclic quasistatic compression, harmonic shear wave excitation, and transient shear wave excitation. The information they reveal about the unknown elastic distribution within an imaging region of interest are shown to be fundamentally related because the tissue responses are governed by the same equation. Examples use simple geometry to emphasize the common nature of the approaches.     

Postponement of saturation of the Richtmyer-Meshkov instability in a convergent geometry

Strongly shocked cylindrically convergent implosions were conducted on the OMEGA laser. The directly driven targets consist of a low-density foam core and an embedded aluminum shell covered by an epoxy ablator. The outer surface of the aluminum shell has imposed single-mode perturbations with wave numbers k=0.08, 0.25, and 0.7 (rad/microm) and initial amplitudes eta(0)/lambda=0.013, 0.04 and 0.11. The perturbation growth rate is found to scale with k and, in our convergent geometry, no evidence of saturation for eta/lambda as large as 5 is observed.     

Differential inhibition of postnatal brain,spinal cord and body growth by a growth hormone antagonist

Background  

Growth hormone (GH) plays an incompletely understood role in the development of the central nervous system (CNS). In this study, we use transgenic mice expressing a growth hormone antagonist (GHA) to explore the role of GH in regulating postnatal brain, spinal cord and body growth into adulthood. The GHA transgene encodes a protein that inhibits the binding of GH to its receptor, specifically antagonizing the trophic effects of endogenous GH.