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A classical force field for poly(dimethylsiloxane) (PDMS) and its oligomers has been derived on the basis of intermolecular binding energies, molecular geometries, molecular electrostatic potentials, and conformational energies obtained from quantum chemistry calculations on model compounds. The force field accurately reproduces the molecular properties of the model compounds obtained from quantum chemistry, including the Si−O−Si bond linearization energy. Molecular dynamics simulations performed on PDMS of various molecular weights between 310 and 1571 using the quantum chemistry based force field yielded good agreement with experiment for their densities, enthalpies of vaporization, and X-ray structure factors. The characteristic ratio of PDMS was also found to be in good agreement with experimental values. Molecular dynamics as represented by the melt self-diffusion coefficient and viscosity at 298 K as a function of molecular weight were also found to be in reasonable agreement with experimental values. Finally, the intermediate incoherent structure factor of PDMS from MD simulations was in excellent agreement with the quasi-elastic neutron scattering results for large Q values and in satisfactory agreement for small Q values.

Levels of free plasma corticosteroids (expressed as jug. Compound B/100 ml. plasma) have been measured routinely in 2 ml. of rat plasma using a method based on fluorescence of Compound B in H 2 SO.i. Resting levels are 9 to 15 Mg./lOO ml. After stress, levels increase up to 500%. After total adrenalectomy or hypophysectomy readings correspond to 3.5-6.5 jUg./100 ml. There is no change upon exposure to stress of the adrenalectomized or hypophysectomized animal. Intra-venous injection of 0.1 to 1.0 milliunit of ACTH U.S.P. Standard, 24 hours after hypophysectomy increases the concentrations of corticoids in a linear log-dose response. After adrenalectomy ACTH is without effect. In the hypophysectomized animals, large doses of highly purified FSH, LH, TSH, STH, a-MSH and arginine vasopressin have no effect on the corticoid levels. Considerable stimulation of corticoidogenesis can be observed in the absence of detectable changes in the adrenal ascorbic acid concentrations when the two variables are measured simultaneously in the same hypophysectomized animals.A SIMPLE method based on the fluorescence of corticosterone in sulfuric acid was recently devised by Silber to measure levels of "free" corticosteroids in small volumes of plasma (1). This report is a summary of experiments performed to assess the validity of this method in various experimental conditions. Two preliminary notes on some of these data have been published elsewhere (2, 3). MATERIALS AND METHODS 1. Animals. Approximately 700 animals were used in the experiments reported here; they were male rats, weighing 160-210 gm. obtained from Holtzman Farms in Houston and Madison. Females were used in a series of experiments devoted to a study of the relationships between the ovarian cycle and the resting levels of plasma corticosteroids; stages of the cycle (proestrus, estrus, diestrus) were assessed for 7 days before measurement of corticosteroid levels by daily vaginal smears stained with 1% toluidine blue.

A molecular dynamics simulation study of the influence of a polymer melt matrix consisting of bead-necklace polymers on the effective interaction between two spherical nanoparticles was performed. The potential of mean force (POMF) between the two nanoparticles as well as entropy and energy contributions to the POMF was determined as a function of nanoparticle separation. The role of energy on the POMF was investigated by varying the strength of the polymer–nanoparticle interaction and comparing structure and POMF with those obtained for an athermal model. All features of the POMF as a function of nanoparticle separation were found to be strongly correlated with the polymer matrix density, the structure of the polymer at the nanoparticle interface, and the structure of the polymer in the interparticle region. The POMF was not found to correlate with polymer chain dimensions (e.g., radius of gyration) in contrast to colloidal suspensions in dilute and semidilute solutions. Both energy and entropy effects were found to make important contributions to the POMF. For the athermal system, where all matrix-induced interactions are entropic in nature, the nanoparticle POMF was found to exhibit qualitatively different behavior from that of the energetic systems.

A retrospective review of 114 cases of squamous cell carcinoma of bladder presenting in Glasgow between 1964 and 1978 is described with emphasis on treatment and survival. Ninety-seven patients (92.4%) were found to have invasive tumours (T2-T4) at diagnosis. Metastatic disease was confirmed in only 10 patients (8.8%). Only 23.8% of patients were alive one year after diagnosis, the overall 5-year survival rate being 1.9%. The 5-year survival rates for patients with T2 and T3 disease following radical radiotherapy were 16.7 and 4.8% respectively. No conclusions concerning the role of total cystectomy could be drawn from this series because of the small number of patients undergoing the operation, but a review of the literature suggests this may be the treatment of choice.