Low-Temperature Sintering of Uranium Dioxide

Studies of the fabrication of uranium oxide fuel pellets by the low-temperature sintering of nonstoichiometric oxide are described. Completer reversion to stoichiometric UO₂ in the sintered pellets was attained by two methods: (1) Sintering in a nitrogen atmosphere which contained a small amount of hydrogen and (2) sintering in pure nitrogen and then exposing the pellets to hydrogen at the sintering temperature. Large variations in sinterability were found in commercially procured ceramic-grade UO₂ powder. In studying these variations, it was discovered that fluorine was a powerful inhibitor of low-temperature sintering. This impurity could be readily removed by oxidation in air at 500°C. The data strongly indicated that the primary mechanism responsible for the removel of residual fluorine was pyrohydrolysis. It was found that a preliminary oxidation-reduction cycle activated the less-sinterable oxides so that in every case densities of at least 95% of theoretical were obtained by sintering at 1200°C.     

Dissolution in Ceramic Systems: III, Boundary Layer Concentration Gradients

By use of electron microbeam probe analysis on quenched samples, the concentration distribution of CaO, A1₂O₃, and SiO₂ was determined across the boundary layer between molten calcium aluminum silicates and dissolving or growing sapphire and fused silica. A definite shift in the concentration ratios of the solvent components was found near the interface. Analysis of diffusion flux equations for a ternary system successfully related the shift in concentration ratio to the intrinsic diffusion coefficient for each component. For alumina dissolution in a melt rich in CaO, evidence of incongruent dissolution was observed with the formation of new phases, CaO· 6Al₂O₃ and CaO· 2A1₂O₃.     

Inhibitory mechanisms of naloxone on human platelets

1. In the present study, naloxone was tested for its antiplatelet activities in human platelet-rich plasma (PRP). In human PRP, naloxone (0.1-0.5 mmol/L) inhibited aggregation stimulated by a variety of agonists (i.e. collagen, adenosine diphosphate (ADP), U46619 and adrenaline). 2. Naloxone (0.1-0.5 mmol/L) did not significantly affect cyclic adenosine monophosphate and cGMP levels in human washed platelets, whereas naloxone (0.5 mmol/L) significantly inhibited thromboxane B2 formation stimulated by collagen (5 micrograms/mL) in human washed platelets. 3. Naloxone (0.5 mmol/L) significantly inhibited [3H]-inositol monophosphate formation of [3H]-myoinositol-loaded platelets stimulated by collagen and U46619. Moreover, naloxone did not influence the binding of 125I-triflavin to platelet membranes. Triflavin is an Arg-Gly-Asp-containing specific fibrinogen receptor antagonist. 4. Addition of naloxone (0.5 mmol/L) to platelet preparations tagged with diphenylhexatriene (DPH) resulted in a considerable decrease in relative fluorescence intensity. 5. It is suggested that the anti-platelet effects of naloxone may be caused, at least partly, by the induction of conformational changes in the platelet membrane initially, followed by the inhibition of thromboxane A2 formation and phosphoinositide breakdown of platelets stimulated by agonists.     

Teleconsultation

Teleconsultation is a consultation between two or more physicians about the diagnostic work-up and therapeutic strategy in the treatment of an individual case by means of modern telematics. Due to more complex therapeutic strategies and legally defined formal requirements, the need for teleconsultation will increase significantly in the future. Rapid technical improvements in telematics will progressively facilitate the practical performance of teleconsultation (based upon an ISDN network in the beginning, later on by the use of a national health network). The medicolegal aspects of teleconsultation have already been defined sufficiently for use in surgery. However, the question of adequate financial compensation for this type of medical service is still unclear.     

Trace element trophic transfer in aquatic organisms: a critique of the kinetic model approach

The bioaccumulation of trace elements in aquatic organisms can be described with a kinetic model that includes linear expressions for uptake and elimination from dissolved and dietary sources. Within this model, trace element trophic transfer is described by four parameters: the weight-specific ingestion rate (IR); the assimilation efficiency (AE); the physiological loss rate constant (ke); and the weight-specific growth rate (g). These four parameters define the trace element trophic transfer potential (TTP = IR.AE/[ke + g]) which is equal to the ratio of the steady-state trace element concentration in a consumer due to trophic accumulation to that in its prey. Recent work devoted to the quantification of AE and ke for a variety of trace elements in aquatic invertebrates has provided the data needed for comparative studies of trace element trophic transfer among different species and trophic levels and, in at least one group of aquatic consumers (marine bivalves), sensitivity analyses and field tests of kinetic bioaccumulation models. Analysis of the trophic transfer potentials of trace elements for which data are available in zooplankton, bivalves, and fish, suggests that slight variations in assimilation efficiency or elimination rate constant may determine whether or not some trace elements (Cd, Se, and Zn) are biomagnified. A linear, single-compartment model may not be appropriate for fish which, unlike many aquatic invertebrates, have a large mass of tissue in which the concentrations of most trace elements are subject to feedback regulation.     

Characterizing patterns of drug-taking behavior with a multiple drug regimen in an AIDS clinical trial

OBJECTIVE: To characterize drug-taking behavior using continuous electronic monitoring in an AIDS clinical trial. SETTING: This was a substudy of AIDS Clinical Trials Group (ACTG) protocol 175, a phase II/III study of dideoxynucleoside monotherapy versus combination therapy in asymptomatic HIV-positive subjects. Participants were required to comply with regimens containing zidovudine, zalcitabine and didanosine, or matching placebos; the total daily pill count was 16. DESIGN: For participants at two ACTG 175 sites, electronic devices were used to monitor drug-taking behavior of all study medications over a period of approximately 90 days. MEASUREMENTS: Four indices of drug-taking behavior were calculated and their distributions and relationship to the prescribed regimen were examined. RESULTS: Data from 41 subjects were analyzed. Of the prescribed doses of zidovudine, zalcitabine and didanosine, 88, 84 and 82%, respectively, were taken. Of these, 55, 66 and 79%, respectively, were taken at the prescribed dosing frequency. The median percentage of days on which participants failed to take any of the doses was 2-5%. There was a trend towards lower adherence in the combination therapy arms compared with those assigned to receive monotherapy. In this analysis, older patients demonstrated better adherence, although patient characteristics, in general, were poorly predictive of adherence. CONCLUSION: Drug-taking behavior for all three active study medications differed from that prescribed. One result of this erratic adherence was that study participants sustained little antiretroviral effect during more than 25% of the monitoring period.     

Preferential benefit of implementation of a statewide trauma system in one of two adjacent states

BACKGROUND: Implementation of Oregon's trauma system was associated with a reduction in the risk of death for hospitalized injured patients. An alternative explanation for improved outcome, however, is favorable concurrent temporal trends, e.g., new technologies and treatments. PATIENTS AND METHODS: To control for temporal trends, seriously injured hospitalized patients in Oregon and Washington were compared before either state had a trauma system (1985-1988) and when only the Oregon trauma system had been implemented (1990-1993). The study group consisted of hospitalized injured patients aged 16 to 79 years with one or more index injuries in six body regions, i.e., head, chest, spleen/liver, femur or pelvis fracture, and burns. Hospital discharge claims data were analyzed, converting International Classification of Diseases, Ninth Revision, Clinical Modification, discharge diagnosis codes to Abbreviated Injury Scale scores and Injury Severity Scores using a conversion algorithm. Multivariate logistic regression models were used to estimate the differential risk-adjusted odds of death in Oregon compared with Washington after adjustment for demographics, injury type, and injury severity. RESULTS: Findings indicated no difference in the risk-adjusted odds of death between Oregon and Washington while both states functioned under an ad hoc trauma system (1985-1988). A significant reduction in the risk of death, however, was noted in Oregon for patients with an index injury and an Injury Severity Score > 15 compared with Washington (adjusted odds ratio (OR) = 0.80, 95% confidence interval (CI) = 0.70-0.91) after trauma system implementation in Oregon (1990-1993). Specifically, reductions in the risk of death were demonstrated for patients with head injuries (adjusted OR = 0.70, 95% CI = 0.59-0.82) or liver/spleen injuries (adjusted OR = 0.73, 95% CI = 0.54-0.99). CONCLUSION: Assuming that the two states demonstrated similar concurrent temporal trends, the findings support the conclusion that improved outcomes among injured patients in Oregon may be attributed to the institution of a statewide trauma system.     

Comparison of subperiosteal vs subgaleal elevation techniques used in forehead lifts

OBJECTIVE: To describe the occurrence and management of sexual dysfunction induced by selective serotonin-reuptake inhibitors (SSRIs), to provide an overview of sexual dysfunction, reports of SSRI-induced sexual dysfunction, and management strategies. DATA SOURCES: Information was retrieved from a MEDLINE English-literature search from January 1986 to July 1998 and by review of references. Indexing terms included sexual dysfunction, antidepressants, selective serotonergic reuptake inhibitors, fluoxetine, sertraline, paroxetine, fluvoxamine, clomipramine, buspirone, nefazodone, bupropion, cyproheptadine, amantadine, yohimbine, and central nervous system stimulants. STUDY SELECTION: There are no controlled studies describing SSRI-induced sexual dysfunction or its management. Twenty-one studies are presented, including 2 open-label studies, 12 case series, and 7 case reports. SSRI-induced sexual dysfunction is described with fluoxetine, paroxetine, sertraline, and fluvoxamine for 3-24 weeks of therapy. DATA SYNTHESIS: Data were organized according to the pharmacologic agent used in the management of SSRI dysfunction, target population, SSRI implicated, type of sexual dysfunction, experimental design, and treatment response. Data were extracted from methodology and results sections of reports. Methodologic flaws included failure to account for gender differences, omission of SSRI dose and duration, and use of concomitant drugs. CONCLUSIONS: The frequency of reports suggests that SSRI-induced dysfunction is a common adverse effect; controlled studies are necessary to determine prevalence. Most reports have occurred with fluoxetine, but this phenomenon may be related to its widespread use. Further study is needed to evaluate baseline sexual function, to define target populations, and to compare SSRIs in inducing sexual dysfunction. Serotonin antagonists and dopamine agonists have been used most often to treat SSRI-induced dysfunction and have generally been effective, but controlled studies are also needed.