A Study of the Gas-Stabilized Arc as an Emission Source for the Measurement of Oscillator Strengths. Determination of Some Relative gf-Values for Fe I

A study has been made of the application of the gas-stabilized arc source to the determination of oscillator strengths in atomic spectra. In this source, a solution of salts of one or more elements may be injected and the elements excited directly in an arc plasma with steady emission of spectral intensities. The source can be taken to be characterized by local thermal equilibrium, but with a large radial temperature gradient. An experiment indicates that when two elements are introduced into the arc in a solution, the relative concentrations of the elements in the discharge are the same as in the solution within the probable experimental error. This experiment indicates one way that the arc may be used for the determination of absolute oscillator strengths. New measurements are reported of the gf-values of 105 lines of Fe I between 2900 and 4150 Å, and the new values are compared with the results of earlier measurements.     

The Middle Molecule Hypothesis Revisited. Should Short,Three Times Weekly Hemodialysis Be Abandoned?

When the middle molecule (MM) hypothesis was formulated in 1975, no MM had yet been identified as a uremic toxin. Meanwhile, the birth and implementation of the Kt/V_urea concept gained wide acceptance and has remained the world standard for assessing dialysis adequacy. However, over the past 20 years, accumulating evidence has made it clear that MM's are important uremic toxins, and that the dose of dialysis based on removal of small molecular substances does not protect against excessive hemodialysis mortality, morbidity, or the presence of uremic signs and symptoms. These poor results are, in one way or another, linked to the accumulation of MM's and other substances behaving like MM's, such as phosphate. Dialysis schedules yielding the best clinical results, such as longer dialysis and more frequent dialysis, favor increased removal of middle molecular substances. The observation that short daily dialysis is giving results similar to long nocturnal quotidian dialysis supports early observations that the volume from which middle molecular substances are extracted mainly by hemodialysis is small (about as large as the extracellular volume), and that transfer of MM's from cells to extracellular fluid is very slow. This behavior of MM's is markedly different from that of small molecular substances, which are more rapidly transferred from intracellular to extracellular compartments and are more readily extracted from total body water during hemodialysis. In order to achieve even minimum adequate dialysis, it is now scientifically validated that toxic MM's must be removed in larger amounts than currently attained. This can only be accomplished by long dialysis sessions with a 3‐times per week schedule or more frequent dialyses. Five hours 3 times per week represents the absolute minimum treatment. Dialy sis 6 to 7 times per week is the ideal schedule for patients who are willing to commit the time and effort in exchange for maximum well‐being and long survival.     

Dietary calcium, calcium supplementation, and blood pressure in African American adolescents

BACKGROUND: Intake of calcium from the diet is inversely associated with blood pressure in observational studies and animal models but randomized trials in humans have found only small effects of calcium supplementation on blood pressure. A blood pressure-lowering effect of calcium supplementation may thus be restricted to persons with a low intake of calcium from the diet and specific genetic or other characteristics. OBJECTIVE: A randomized trial was conducted to assess the effect of calcium supplementation on blood pressure in African American adolescents. Rapid growth during adolescence may increase calcium requirements, and avoidance of milk and milk products by some African Americans can result in low intake of calcium. DESIGN: One hundred sixteen adolescents (65 girls, 51 boys; mean age: 15.8 y) were given calcium (1.5 g/d) or placebo for 8 wk in a randomized, double-blind, crossover design. Blood pressure was measured after 2, 4, and 8 wk. Dietary calcium was determined with a validated food-frequency questionnaire. RESULTS: The net effect (+/-SE) of calcium supplementation on diastolic blood pressure was a reduction of 1.9 +/- 1.1 mm Hg (P = 0.04, one-tailed t test). Blood pressure reduction was greater in adolescents with lower intake of calcium from the diet (P = 0.003, one-tailed t test for interaction): -4.9 +/- 1.6, -2.3 +/- 1.6, and 1.4 +/- 1.8 mm Hg for change in the lower (0.024-0.067 g Ca/MJ), middle (0.069-0.091 g Ca/MJ), and upper (0.093-0.217 g Ca/MJ) tertiles, respectively. No main effect on systolic blood pressure was detected. CONCLUSION: These findings suggest that calcium supplementation may lower diastolic blood pressure in African American adolescents with low dietary intakes of calcium.     

Activation of protein phosphorylation by oxidants in vascular endothelial cells: identification of tyrosine phosphorylation of caveolin

The colonial protochordate Botryllus schlosseri possesses a historecognition system which has long invited comparison to the vertebrate MHC. Upon contact, colonies either fuse or reject one another in a manner resembling graft acceptance or rejection in vertebrates. This response is controlled by a single highly polymorphic genetic region, the FuHC locus. Colonial protochordates such as B. schlosseri are among the closest relatives of the vertebrate lineage, and therefore may possess a recognizable MHC homologue. Since linkage between heat shock protein 70 (HSP70) genes and MHC appears to be conserved within the vertebrate lineage, we have analyzed HSP70 genes from B. schlosseri as a first step toward isolating the historecognition locus. Two HSP70 genes (HSP70.1 and HSP70.2) have been cloned and sequenced, and exhibit 93.6% sequence identity within the predicted coding regions. The B. schlosseri genes share a number of characteristics with vertebrate MHC-linked HSP70 genes: Northern blotting and sequence analysis suggest that the protochordate genes are cytoplasmically-expressed heat-inducible members of the HSP70 gene family (FAGAN and WEISSMAN 1996). However, unlike vertebrate MHC-linked HSP70 genes, HSP70.1 and HSP70.2 are not closely linked (FAGAN and WEISSMAN 1997). Furthermore, neither is closely linked to the locus determining historecognition (FAGAN and WEISSMAN 1997). These results do not support the hypothesis that the B. schlosseri FuHC locus is an MHC homolog. A discussion of the implications of these results for evolution of the vertebrate MHC is included.     

X-Ray Spectrometric Analysis of Noble Metal Dental Alloys

The analysis of noble metal dental alloys for the various constituent elements is a difficult and tedious task by chemical or fire assay procedures. X-ray spectroscopy offered the possibility of increased speed, especially if solid metal samples were employed. This technique was investigated particularly with respect to the analysis of dental alloys having the nominal composition in percent, of gold 72, silver 12, copper 10, platinum 2, palladium 2, and zinc 2. Alloys were prepared by melting the component elements in a high frequency furnace and casting the metal into disk form. Compositions of the castings were determined by chemical analysis. Optimum procedures for casting the sample and for X-ray analysis were established, and analytical curves were developed relating concentrations to measured intensities of the X-ray lines Au L_β, Ag K_α, Cu K_α, Pt L_α, Pd K_α, and Zn K_α. The observed typical coefficients of variation for the method were Au 0.34 percent, Ag 0.44 percent, Cu 2.2 percent, Pt 1.6 percent, Pd 1.2 percent, and Zn 0.72 percent. The results indicate that the method is sufficiently accurate and has marked advantages of speed and simplicity compared to chemical analysis.