Ground state ESR measurements of ruby during laser action

The use of electron spin resonance for measurement of the ground state population (GSP) of Cr³⁺in a ruby rod during optical pumping is described. For a 7.7 cm long rod at 90°K and a mirror reflectance productR_{1}R_{2} > 0.08, the GSP at laser threshold was found to be 55 ± 5 percent in good agreement with theory and previous optical measurements. At room temperature, a limiting value of approximately 30 percent for the GSP was approached at high pump energies. Observations of the relativeR_{1}(3/2), R_{1}(1/2)thresholds at 90°K as a function of mirror reflectivity indicated that the²E excited state absorption cross section at the laser wavelength is less than5 times 10^{-21}cm². Detection of total internal reflection oscillations in cooled ruby lasers from ESR observations is also described.     

Regulatory potential of ethanol and retinoic acid on human monocyte functions

Retinoic acid (RA), a metabolic product of vitamin A, has been shown to affect a variety of immune functions, including monocytes. Monocyte functions and mediator production are also modulated by ethanol exposure. This study demonstrates that therapeutic doses of RA (0.1-10 microM) significantly increase transforming growth factor-beta (TGF beta) production both in THP-1, human myelomonocytic cells, and in human peripheral blood monocytes. We have previously reported TGF beta induction by ethanol in human M theta. Combination of RA stimulation with acute in vitro ethanol treatment, however, resulted in significantly lower M theta TGF beta production than TGF beta levels induced by RA alone (p < 0.003). Down-regulation of M theta TGF beta production by ethanol was tested at the concentration range of 25-150 mM and occurred both at high and low RA concentrations (10-0.1 microM). In contrast to its inhibitory effect on RA-induced M theta TGF beta production, ethanol augmented TGF beta production induced by muramyl dipeptide (20 micrograms/ml), suggesting that ethanol can either up- or down-regulate M theta TGF beta production, depending on the costimulatory factors. RA also induced a moderate increase in M theta tumor necrosis factor-alpha (TNF alpha) production, which was down-regulated by ethanol both at the level of secreted and cell-associated TNF alpha. In addition to regulation of cytokine production, both RA and ethanol decreased expression of CD4 on THP-1 cells. The degree of inhibition of CD4 expression by RA was more significant than by ethanol, but RA-induced decrease in CD4 expression was not significantly affected by the combined stimulation with ethanol.(ABSTRACT TRUNCATED AT 250 WORDS)     

Implementation of a C1 triangular element based on the P-version of the finite element method

The implementation of a computer code CONE (for C¹ continuity) based on the p-version of the finite element method is described. A hierarchic family of triangular finite elements of degree p ≥ 5 is used. This family enforces C¹-continuity across inter-element boundaries, and the code is applicable to fourth order partial differential equations in two independent variables, in particular to the biharmonic equation. Applications to several benchmark problems in plate bending are presented. Sample results are examined and compared both with theoretical predictions and with the computations of other programs. Significant improvements are shown for the results obtained using CONE.     

Large-deformation analysis of nonlinear elastic fluids

A computational analysis was undertaken of four nonlinear generalizations of the simple Maxwell viscoelastic fluid under conditions of large deformations. The four fluids are named the upper convected Maxwell, lower convected Maxwell, Jaumann and Dong-Skalak-Sung fluids. Each of them is characterized by two material parameters, a shear modulus and a time constant and each reduces to the simple Maxwell fluid in the case of small, slow deformations. The finite element program ADINA was adapted to compute the mechanical responses of these materials to imposed surface displacements of various types. Our algorithm was based on the equality (for an incompressible material) of the components of the second Piola-Kirchhoff stress with respect to material coordinates and those of the Cauchy stress with respect to convected coordinates. After evaluating the algorithm's accuracy with respect to a limited set of available analytic solutions, the responses to indentation by a rigid, sharp-edged cylinder of a half-space composed of each of the four nonlinear fluids were computed. These calculations included a wide range of indentation speeds, covering the spectrum of material behavior from viscous fluid to hyperelastic solid. The computations admitted large indentations—up to six indenter radii in special cases. In contrast to their radically different behaviors when subjected to large homogeneous deformations, all four materials exhibited similar behaviors when subjected to deep indentations. For any specific choice of material and computational parameters, the computation terminated if the indentation became too deep and the magnitude of this maximum achievable indentation depth decreased with increasing mesh refinement.     

Thermogravimetric/mass spectrometric characterization of the thermal decomposition of (4-O-methyl-D-glucurono)-D-xylan

A thermogravimetric/mass spectrometric (TG/MS) system was used to characterize the thermolysis reactions of (4-O-methyl-D -glucurono)-D -xylan. The mass spectrometric peaks, measured as function of time, were attributed to water, methanol, carbon monoxide, carbon dioxide, formaldehyde, formic acid, acetic acid, acetone, acrolein, 2-furaldehyde, and 3-hydroxy-2-penteno-1,5-lactone. The time derivative of the thermogravimetric curve (DTG) consisted of two partially overlapping peaks, indicating a multistep mechanism. The mass spectrometric intensities of the peaks assigned to methanol and 2-furaldehyde coincided with the first DTG peak, suggesting that the first DTG peak represents both dehydration and fragmentation pathways. Methanol, water, formyl group, and carbon dioxide contributed to both of the DTG peaks. This indicates that the dehydration, decarboxylation, and decarbonylation took place in two steps. The compounds observed only in the second DTG peak and later (acetone, formic acid, formaldehyde, acrolein, acetic acid, and 3-hydroxy-2-penteno-1,5-lactone) are probably products of reactions which occur after the collapse of the original polysaccharide structure.     

Intermittent versus continuous administration of 1,25-dihydroxyvitamin D3 in experimental renal hyperparathyroidism

Conflicting results have been reported regarding the efficacy of intermittent versus continuous administration of 1,25(OH)2D3 in renal secondary hyperparathyroidism. To address this issue we examined sham-operated control rats and hyperparathyroid rats with subtotal (5/6) nephrectomy (Nx). The Nx animals (20 to 22 animals per group) were subjected to three treatment protocols: (i) solvent treatment (Nx-solvent); (ii) two i.p. injections of 35 pmol 1,25(OH)2D3 on days 0 and 4 (Nx-bolus); and (iii) continuous infusion of 70 pmol 1,25(OH)2D3 over six days via osmotic minipump (Nx-infusion). All measurements were performed six days after start of treatment. As compared to sham-operated controls, the pre-pro-PTH/beta-actin mRNA ratio was 2.04-fold higher in Nx-solvent. Both modes of administration of 1,25(OH)2D3 resulted in inhibition of PTH mRNA concentrations relative to Nx-solvent. The pre-pro-PTH/beta-actin mRNA ratio was, however, significantly lower (P < 0.05) in Nx-bolus than in Nx-infusion (Nx-bolus 1.26 higher than sham-operated controls; Nx-infusion 1.65 higher than sham-operated controls). Aminoterminal PTH (N-PTH) serum concentrations were higher in Nx-solvent (52 +/- 4 pg/ml) than in sham-operated controls (32 +/- 3 pg/ml, P < 0.01). N-PTH concentrations in Nx-bolus (38 +/- 4 pg/ml) were significantly lower than in Nx-solvent (P < 0.01) and in Nx-infusion (46 +/- 4 pg/ml, P < 0.05). Parathyroid gland weight (microgram/g body wt) was higher in Nx-solvent (1.30 +/- 0.08 pg/ml) than in sham-operated controls (0.79 +/- 0.04 pg/ml, P < 0.02).(ABSTRACT TRUNCATED AT 250 WORDS)     

Positron emission tomographic evidence of toxic effect of MDMA ("Ecstasy") on brain serotonin neurons in human beings

BACKGROUND: (+/-)3,4-methylenedioxymethamphetamine (MDMA, "Ecstasy") is a popular recreational drug that selectively damages brain serotonin (5-HT) neurons in animals at doses that closely approach those used by humans. We investigated the status of brain 5-HT neurons in MDMA users. METHODS: We enrolled 14 previous users of MDMA who were currently abstaining from use and 15 controls who had never used MDMA. We used positron emission tomography (PET) with the radioligand carbon-11-labelled McN-5652, which selectively labels the 5-HT transporter. We analysed whether there were differences in 5-HT transporter binding between abstinent MDMA users and participants in the control group. Blood and urine samples were taken and tested to check for abstinence. FINDINGS: MDMA users showed decreased global and regional brain 5-HT transporter binding compared with controls. Decreases in 5-HT transporter binding positively correlated with the extent of previous MDMA use. INTERPRETATION: Quantitative PET studies with a ligand selective for 5-HT transporters can be used to assess the status of 5-HT neurons in the living human brain. We show direct evidence of a decrease in a structural component of brain 5-HT neurons in human MDMA users.     

Electrostatic enhancement of diffusion-controlled protein-protein association: comparison of theory and experiment on barnase and barstar

The electrostatic enhancement of the association rate of barnase and barstar is calculated using a transition-state theory like expression and atomic-detail modeling of the protein molecules. This expression predicts that the rate enhancement is simply the average Boltzmann factor in the region of configurational space where association occurs instantaneously in the diffusion-controlled limit. Based on experimental evidence, this "transition state" is defined by configurations in which, relative to the stereospecifically bound complex, the two proteins are shifted apart by approximately 8 A (so a layer of water can be accommodated in the interface) and the two binding surfaces are rotated away by 0 degrees to 3 degrees. The values of the average Boltzmann factor, calculated by solving the Poisson-Boltzmann equation, for the wild-type complex and 16 complexes with single mutations are found to correlate well with experimental results for the electrostatic rate enhancement. The predicted rate enhancement is found to be somewhat insensitive to the precise definition of the transition state, due to the long-range nature of electrostatic interactions. The experimental ionic strength dependence of the rate enhancement is also reasonably reproduced.