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R D Levine

Publications and source records attributed to R D Levine.

28 records · Page 2Linked to original sources
PubMed2000

Delayed ionization and fragmentation en route to thermionic emission: statistics and dynamics.

Thermionic emission is discussed as a long time (microseconds) decay mode of energy-rich large molecules, metallic and metcar clusters, and fullerenes. We review what is known and consider the many experiments, systems, and theoretical and computational studies that still need to be done. We conclude with a wish list for future work. Particular attention is given to the experimental signatures, such as the dependence on the mode of energy acquisition, and theoretical indications of a not-quite-statistical delayed ionization and to the competition of electron emission with other decay modes, such as fragmentation or radiative cooling. Coupling of the electronic and nuclear modes can be a bottleneck and quite long time-delayed ionization can be observed, as in the decay of high Rydberg states probed by ZEKE spectroscopy, before the onset of complete energy partitioning.

Journal Article↗
PubMed1991

On the repulsion of energy eigenstates in the time domain.

The rate and extent of the exploration of the available phase space of a bound quantum mechanical system are shown to depend on the repulsion of energy eigenstates. Central to the argument is the Fourier transform relating the survival probability (in time) of an initially prepared nonstationary state and the (frequency) autocorrelation function of the excitation spectrum. Strong repulsion of states, as in the Wigner surmise, leads to a rapid dephasing of the initially coherently prepared state. The rate and extent of sampling of phase space depend not only on the spacing distribution but also on the intensity fluctuations. The rate of dephasing is equal to that inferred from the width of the spectral autocorrelation function.

Journal Article↗
PubMed1979

Evolutionary changes in protein composition -- evidence for an optimal strategy.

The information contained in the composition of different proteins of the same family is analyzed. It is found that within each family the gain in information per amino acid replacement is constant. This finding is interpreted to imply that evolutionary changes in proteins follow an "optimal" path in the sense that they maximize the number of potentially functional sequences that can be generated by T accepted point mutations from a given protein, subject to restrictions due to biological function.

Amino Acid Sequence↗
PubMed1979

Ligandinuria: an indication of tubular cell necrosis.

Ligandinuria is a useful index of acute tubular injury. Ligandin probably enters the urine at the time of initial necrosis and should be looked for soon after the toxic or ischemic event. Periodic examination of perfusates for this substance might yield useful information about techniques for storage of cadaver kidneys.

Animals↗
PubMed1978

Ligandin in perfusates from transplanted kidneys: a test for tubular necrosis.

Ligandin, an intracellular organic anion-binding protein, having glutathione-S-transferase activity, was detected in concentrated perfusing solutions from 8 of 13 kidneys preserved for homotransplantation. The presence of ligandin in the perfusate correlated well with oliguric acute renal failure following transplantation. Testing the perfusate for ligandin may be useful in predicting tubular damage in renal transplants.

Acute Kidney Injury↗
PubMed1978

Hyperreninemia during renal transplantation.

18 patients undergoing renal transplantation were studied prospectively to determine the incidence and mechanism of blood pressure elevations which sometimes occur after release of vascular clamps from the grafts. No patients became as severely hypertensive as noted in previous reports. A weak, but statistically significant (r=0.56, p less than 0.05) positive correlation was found between changes in plasma renin activity and small incremental changes in blood pressure. 2 patients in whom the greatest change in renin occurred showed little or no increase in blood pressure. In view of the small blood pressure changes seen in the face of significant changes in plasma renin activity, it appears unlikely that acute hyperreninemia alone is sufficient explanation for postdeclamping hypertension which is sometimes observed during renal transplantation.

Adolescent↗
PubMed1976

Selective inhibition of osmotic water flow by general anesthetics to toad urinary bladder.

Vasopressin increases the permeability of the total urinary bladder, an analogue of the mammalian renal collecting duct, to water and small solutes, especially the amide urea. We have observed that three general anesthetic agents of clinical importance, the gases methoxyflurane and halothane and the ultrashortacting barbiturate methohexital, reversibly inhibit vasopressin-stimulated water flow, but do not depress permeability to urea, or the the lipophilic solute diphenylhydantoin. In contrast to their effects in vasopressin-treated bladders, the anesthetics do not inhibit cyclic AMP-stimulated water flow, consistent with an effect on vasopressin-responsive adenylate cyclase. The selectivity of the anesthetic-induced depression of water flow suggests that separate adenylate cyclases and cyclic AMP pools may exist for control of water and urea permeabilities in to toad bladder. Furthermore, theophylline's usual stimulatory effect on water flow, but not its effect on urea permeability, was entirely abolished in methoxyflurane-treated bladders, suggesting that separate phosphodiesterases that control water and urea permeabilities are present as well. We conclude that the majority of water and urea transport takes place via separate pathways across the rate-limiting luminal membrane of the bladder cell, and that separate vasopressin-responsive cellular pools of cyclic AMP appear to control permeability to water and to urea.

Anesthetics↗