Magnetization prepared rapid gradient-echo (MP-RAGE) MR imaging of the liver: comparison with spin-echo imaging.

We have implemented an MR technique that employs a rapid gradient echo sequence, preceded by magnetization preparation pulses to provide T1- and T2-weighted tissue contrast. With this technique, which can be identified as a member of a new family of pulse sequences, generically named Magnetization Prepared RApid Gradient Echo (MP-RAGE), very short repetition times are used, allowing acquisition times of less than one second and images virtually free of motion-induced artifacts during quiet respiration. Fifteen patients with known liver lesions (metastases, hemangiomas, and cysts) were examined using T1- and T2-weighted 2-dimensional MP-RAGE sequences, and the images were compared with conventional T1- and multi-echo T2-weighted spin-echo (SE) sequences. Signal difference-to-noise ratios (SD/Ns) of the lesions were calculated for all pulse sequences using corresponding axial images and were normalized for voxel volume. The mean normalized SD/Ns of the MP-RAGE sequences were generally comparable to those for the SE sequences. In addition, there were no noticeable respiratory artifacts on the MP-RAGE images whereas these were clearly present on the T2-weighted SE images and to a lesser degree on the T1-weighted SE images. It is concluded that the MP-RAGE technique could become an important method for evaluating the liver for focal disease.     

Photoageing of rigid PVC—I. Films containing Ca/Zn thermal stabiliser

The photo-oxidation (λ > 300 nm, T = 40, 55 and 70 °C) of ˜80μm films of PVC stabilised by Ca and Zn stearates was studied using gravimetry, IR and UV-visible spectrophotometry. The stabilisers disappear in the early days of exposure according to a pseudo first-order process, presumably by HC1 scavenging, which gives an idea of the rate of HC1 release during this period. The concentration of polyenes absorbing at λ = 500 nm begins to increase rapidly when the stabiliser is totally consumed. At the same time, weight loss takes place, showing that there are more HC1 elimination events than oxidation events. These results are consistent with the following hypotheses: (a) oxidation is diffusion controlled; (b) long polyene formation is HC1 catalyzed; (c) conjugated sequences—(CH₂ = CH₂)_n—with n = 10–12 result essentially from a thermal process; (d) the rate of carbonyl and hydroxyl build-up is nearly not influenced by the increase in polyene concentration or rate of HCl evolution which can also be explained, at least partially, in terms of O₂ diffusion control of oxidation kinetics.     

Radiative temperature dissipation in a finite atmosphere—II. The inhomogeneous case

In this paper, solutions to the problem of the radiative relaxation of temperature perturnations in an inhomogeneous, optically finite atmosphere are obtained. The properties of these indicate that there are only certain perturbations that decay at constant rates without changing their shape. These elementary perturbations constitutive the radiative eigenfunctions for the atmosphere and can be utilized to represent perturbations of arbitrary initial shape, whose relaxation can be studied following the relaxation of its expansion in radiative eigenfunctions. The basic solutions for the inhomogeneous atmosphere (i.e., an atmosphere in which the mixing ratio, temperature or band width varies with height) are found in terms of the radiative eigenfunctions for a homogeneous model atmosphere in which the variable parameters have been replaced by averages. The solution for arbitrary initial perturbations is applied to a model of stratospheric warming (for the decaying phase). It is found that there is no perturbation in the stratosphere that can last longer than 30–35 days.     

Phase inversion sulfonated polysulfone membranes

The use of two nonsolvents serving as a cosolvent system, replacing the traditional volatile solvent plus less volatile nonsolvent system, in the formation of asymmetric phase inversion membranes was investigated. Specifically, asymmetric membranes of sulfonated polysulfone were cast from a cosolvent system consisting of tetrahydrofuran and formamide. The nonsolvents and the proportions in which they are mixed to produce the cosolvent system, as well as the gelation medium isopropyl alcohol, were selected based on the three-component solubility parameter concept of Hansen. The structure of each membrane was evaluated using scanning electron microscopy; the performance was evaluated for use in pressure-driven membrane separation processes. The membranes were found to be dependent on the composition of the original casting solution and the composition of the nascent membrane at the instant of gelation. These ideas are clearly represented through the use of a triangular polymer solubility diagram.     

Observation of the B meson in K−p interactions at 4.2 GeVc

A πω enhancement at 1245 MeV is observed in the reaction K^?p → Σ⁺π^?ω. Its properties agree with those of a B meson produced by natural-parity exchange thus establishing a coupling of the B to a $\text{K}\text{K}{}^1$ system.     

Polymer emissivity

The thermal emission characteristics of polypyromellitimides have been examined as a function of temperature by measurement of the power required to maintain steady-state temperatures in an evacuated system. The emissivity was derived and found to increase with increasing temperature up to a saturation limit of above 0.9 at temperatures above 475°K. The effect is explained as a thermal population of excited infrared transitions. Power emitted is dominated by the most intense bands which are common to absorption and emission spectra.     

Soft Dynamics simulation. 1. Normal approach of two deformable particles in a viscous fluid and optimal-approach strategy

Discrete simulation methods are efficient tools to investigate the behaviors of complex fluids such as dry granular materials or dilute suspensions of hard particles. By contrast, materials made of soft and/or concentrated units (emulsions, foams, vesicles, dense suspensions) can exhibit both significant elastic particle deflections (Hertz-like response) and strong viscous forces (squeezed liquid). We point out that the gap between two particles is then not determined solely by the positions of their centers, but rather exhibits its own dynamics. We provide the first ingredients of a new discrete numerical method, named Soft Dynamics, to simulate the combined dynamics of particles and contacts. As an illustration, we present the results for the approach of two particles. We recover the scaling behaviors expected in three limits: the Stokes limit for very large gaps, the Poiseuille-lubricated limit for small gaps and even smaller surface deflections, and the Hertz limit for significant surface deflections. We find that for each gap value, an optimal force achieves the fastest approach velocity. The principle of larger-scale simulations with this new method is provided. They will consitute a promising tool for investigating the collective behaviors of many complex materials.