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Biomedical subjects

D W Hall

Publications and source records attributed to D W Hall.

At least 19 recordsLinked to original sources
PubMed2001

Magnetic spin ladder (C5H12N)2CuBr4: high-field magnetization and scaling near quantum criticality.

The magnetization, M(H< or =30 T,0.7< or =T< or =300 K), of (C5H12N)2CuBr4 has been used to identify this system as an S = 1/2 Heisenberg two-leg ladder in the strong-coupling limit, J( perpendicular) = 13.3 K and J( parallel) = 3.8 K, with H(c1) = 6.6 T and H(c2) = 14.6 T. An inflection point in M(H,T = 0.7 K) at half saturation, M(s)/2, is described by an effective XXZ chain. The data exhibit universal scaling behavior in the vicinity of H(c1) and H(c2), indicating that the system is near a quantum critical point.

Journal Article↗
PubMed2001

Aircraft and runway deicers at General Mitchell International Airport, Milwaukee, Wisconsin, USA. 1. Biochemical oxygen demand and dissolved oxygen in receiving streams.

Aircraft and runway deicers are used during cold weather at many of the world's airports to facilitate safe air travel. Propylene glycol-, ethylene glycol-, and urea-based deicers are known to have very high biochemical oxygen demand. At General Mitchell International Airport (GMIA) in Milwaukee, Wisconsin, USA, deicer application, water chemistry, and dissolved oxygen (DO) data were collected for two deicing seasons in order to evaluate and define premanagement water quality parameters prior to the implementation of a glycol management program. Calculations using stream-monitoring data during a controlled release of deicer provided an estimate of 0.8/d for the first-order decay rate constant, substantially higher than published laboratory test results. For eight precipitation events with deicing activities, between 2.4 and 99% of propylene and ethylene glycol applied to aircraft was delivered directly to receiving streams. The percentage of glycol runoff during an event increased with increasing storm-flow volume. Elevated concentrations of glycol and biochemical oxygen demand were measured downstream from the airport. However, the frequency of low DO concentrations in the receiving streams is comparable with that at an upstream reference site. This is possibly due to slowed bacteria metabolism at low water temperatures, short travel times, and dilution from downstream tributaries.

Aircraft↗
PubMed2001

Aircraft and runway deicers at General Mitchell International Airport, Milwaukee, Wisconsin, USA. 2. Toxicity of aircraft and runway deicers.

Streams receiving runoff from General Mitchell International Airport (GMIA), Milwaukee, Wisconsin, USA, were studied to assess toxic impacts of aircraft and runway deicers. Elevated levels of constituents related to deicing (propylene glycol, ethylene glycol, and ammonia) were observed in stream samples. The LC50s of type I deicer for Ceriodaphnia dubia, Pimephelas promelas, Hyalela azteca, and Chironimus tentans and the EC50 for Microtox were less than 5,000 mg/L of propylene glycol. Concentrations up to 39,000 mg/L were observed at airport outfall sites in samples collected during deicing events. The IC25s of type I deicer for C. dubia and P. promelas were less than 1,500 mg/L of propylene glycol. Concentrations up to 960 mg/L were observed in low-flow samples at an airport outfall site. Measured toxicity of stream water was greatest during winter storms when deicers were applied. Chronic toxicity was observed at airport outfall samples from low-flow periods in the winter and the summer, with the greater toxic impacts from the winter sample. All forms of toxicity in stream-water samples decreased as downstream flows increased.

Aircraft↗
PubMed2000

The evolution of haploid, diploid and polymorphic haploid-diploid life cycles: the role of meiotic mutation.

Here I present a simple population genetic model to investigate the evolution of polymorphic haploid-diploid life cycles. The key feature of the model is the assumption of mutation occurring during meiosis. I show that, in addition to regions favoring haploid or diploid life cycles, there are substantial regions of the parameter space under which polymorphic haploid-diploid life cycles are expected to evolve.

Animals↗
PubMed2000

Runaway sexual selection when female preferences are directly selected.

We introduce models for the runaway coevolution of female mating preferences and male display traits. The models generalize earlier results by allowing for direct natural selection on the preference, arbitrary forms of mate choice, and fairly general assumptions about the underlying genetics. Results show that a runaway is less likely when there is direct selection on the preference, but that it is still possible if there is a sufficiently large phenotypic correlation between the female's preference and the male's trait among mated pairs. Comparison of three preference functions introduced by Lande (1981) shows that open-ended preferences are particularly prone to a runaway, and that absolute preferences require very large differences between females in their preferences. We analyze the causes of the runaway seen in a model developed by Iwasa and Pomiankowski (1995).

Animals↗
PubMed1998

Immunomodulatory effects of tretinoin in combination with clindamycin.

BACKGROUND: Since acne is a multifactorial skin disease, therapies affecting several etiologic factors can have a higher than expected effectiveness. A combination of the antibiotic clindamycin phosphate and the retinoic acid tretinoin was developed. OBJECTIVE: Anti-inflammatory and immunomodulatory effects of tretinoin in vitro were studied on human keratinocytes and peripheral blood mononuclear cells (PBMCs). Effects of clindamycin phosphate on tretinoin effects were studied. METHODS: Anti-inflammatory effects on keratinocytes were assessed using an in vitro model with PMA (phorbol ester)-stimulated A431 cells (human epidermoid carcinoma). Immunomodulatory effects were measured on superantigen (SEB) stimulated PBMCs. RESULTS: Tretinoin showed very potent inhibition of PMA-stimulated IL-6 (interleukin 6) release by A431 cells. The addition of clindamycin phosphate did not interfere with this effect. Tretinoin very potently stimulated IL-5 release, and inhibited IFN gamma release by SEB-stimulated human PBMCs. This indicates an immunomodulatory effect, stimulating Th2, and inhibiting Th1 dominated responses. These features have been related to the healing of acne lesions. The addition of clindamycin phosphate did not interfere with the immunomodulatory effects of tretinoin. CONCLUSION: The combination of tretinoin and clindamycin phosphate can be expected to be very effective in acne therapy.

Acne Vulgaris↗
PubMed1997

Development of an ear edema model of contact hypersensitivity to avoid false-positive results due to interactions between hapten and test agents.

Ear edema models are regularly used for topical testing of antiinflammatory compounds. However, test compounds are usually applied simultaneously with proinflammatory agents at the same site which may result in mutual interactions. In order to avoid the occurrence of false antiinflammatory effects, a model of oxazolone-induced contact hypersensitivity has been described in which the hapten and test compound are each applied separately to only one side of the ear. By splitting and weighing the dorsal and ventral cutis of the ears, it was shown that the edemateous response of the control nonhapten side was comparable with the hapten-treated side. Some agents with antiinflammatory properties, as for example, dapsone, cimetidine, cyclosporine A, and budesonide, were tested simultaneously with oxazolone on both sides of the ear or applied separately on the dorsal and ventral ear sides, respectively. When dissolving the compounds in solutions of oxazolone, marked colorations of the test solutions were noted, indicating the occurrence of a chemical interaction. On simultaneous application at the same area, almost complete inhibition of the edemateous response was obtained for all compounds tested. In contrast, when applied separately, only budesonide appeared to exhibit antiinflammatory activity. The results indicate that the proposed model can be used to avoid the occurrence of interactions between oxazolone, and possibly other sensitizers, and substances that are being evaluated for topical antiinflammatory activity. By use of this model spurious antiinflammatory activity can be detected.

Adjuvants, Immunologic↗
PubMed1995

Administration of nicotinamide during chart: pharmacokinetics, dose escalation, and clinical toxicity.

PURPOSE: To determine nicotinamide pharmacokinetics in patients undergoing accelerated radiotherapy with the CHART regimen (continuous, hyperfractionated, accelerated radiotherapy) and given nicotinamide on a daily basis. The aim was to establish the pharmacokinetic profiles and their reproducibility during repeated administration, the maximum tolerated dose with fractionated radiotherapy, whether such a dose achieves sufficiently high plasma levels for radiosensitization, the optimal time interval between nicotinamide and irradiation, and toxic side effects. METHODS AND MATERIALS: Nicotinamide plasma concentrations were determined using high performance liquid chromatography in 11 patients with advanced carcinomas of the head and neck and rectum being treated with CHART (36 fractions in 12 days). Kinetic profiles on the first day of radiotherapy and residual 24-h values were obtained in 10 patients; in four of these, full profiles were repeated two or three times during the course of treatment. In one other, a single sample per day was taken four times over the 12-day period. Doses of 80, 90, or 100 mg/kg/day were given 90 min prior to the second radiotherapy fraction on each day. RESULTS: A dose of 80 mg/kg/day was well tolerated by all the patients. However, an increase of 10-25% in dose led to significant drug accumulation and major clinical toxicity, and none of the patients in the dose-escalation arm completed the planned regimen. Large interpatient variations in absolute peak concentrations were seen from 0.4 to 1.4 mumol/ml (mean 0.9 +/- 0.3; standard deviation (SD)). Of the five samples with the lowest peak levels, four were obtained from one patient. The time taken to peak concentration was also very variable from 0.8 to 4 h (mean 2.1 +/- 1.3 h; SD). In 70% of the samples, absolute plasma levels > or = 0.7 mumol/ml were reached within 1-2 h after administration and maintained for up to 6 h (mean 2.8 +/- 1.8 h; SD). There was a small but nonsignificant increase in the half-life of nicotinamide when the dose was increased from 80 to 90 or 100 mg/kg (7.1 h and 8.6 h, respectively). CONCLUSIONS: In an accelerated regimen such as CHART, 80 mg/kg/day of oral nicotinamide is feasible and clinically tolerated, giving no or few side effects, and a 2-h interval between its oral administration and radiotherapy should achieve effective plasma levels in most patients.

Aged↗
PubMed1992

Pharmacokinetics of nicotinamide and its effect on blood pressure, pulse and body temperature in normal human volunteers.

The pharmacokinetics of nicotinamide were studied in four human volunteers after oral doses of 1-6 g. Plasma concentrations and clearance rates of the vitamin were found to be dose-dependent, with a half-life of approximately 7-9 h for the two highest doses administered (4 and 6 g), approximately 4 h with 2 g and approximately 1.5 h with a 1-g dose. Peak concentrations ranged from 0.7 to 1.1 mumol.ml-1 after a 6-g dose. The time to reach peak plasma concentration was dose independent with a broad range from 0.73 to 3 h. In this study, nicotinamide had no detectable effect on blood pressure, pulse or body temperature.

Administration, Oral↗
PubMed1990

Prevalence and biology of endosymbionts of fleas (Siphonaptera: Pulicidae) from dogs and cats in Alachua County, Florida.

A study was conducted to determine the prevalence and biology of endosymbionts in local populations of fleas collected from dogs and cats in Alachua Co., Florida. Four hundred three Ctenocephalides felis (Bouché), 194 Pulex simulans Baker, and 44 Echidnophaga gallinacea (Westwood) were examined. Fleas were collected from 52 dogs and 51 cats. From 1 to 20 fleas were dissected from each host. A variety of microorganisms and metazoa was observed, including a baculovirus, gram-negative bacteria, rickettsia-like organisms, amoebae, trypanosomatid flagellates, cephaline gregarines, and microsporidia. Microfilariae of the dog heartworm, Dirofilaria immitis, entomophilic nematodes, and metacestodes of the tapeworm Dipylidium caninum were also observed.

Animals↗
PubMed1989

Review of the modes of action of colloidal bismuth subcitrate.

In recent years considerable progress has been made to elucidate the modes of action of colloidal bismuth subcitrate (CBS). CBS accelerates the healing of experimental chronic ulcers in rats by the formation of occlusive complexes and/or the accumulation of epidermal growth factor (EGF) in the ulcer crater. CBS exhibits gastric protection (cytoprotection) against, for example, ethanol lesions. Microscopic analysis of these lesions reveals that CBS protects against deep mucosal necrosis but not superficial injury, a property also found with prostaglandins. Dose-dependent increases in gastric prostaglandin E2 (PGE2) and bicarbonate secretion were found after CBS, in both animals and human volunteers. CBS in normal clinical doses increases PGE2 output from the gastric mucosa of human volunteers. Gastric injury in human volunteers produced by unbuffered aspirin is also reduced by concomitant administration of CBS, whereby PGE2 production is inhibited. This indicates that CBS exerts its gastric protection by both prostaglandin- and non-prostaglandin-mediated mechanisms. Campylobacter pylori is considered to be a causative factor of chronic antral gastritis and is a potential prerequisite for peptic ulcer disease. CBS, in contrast to other anti-ulcer drugs, prevents the growth of C. pylori in vitro. CBS eradicates C. pylori in patients and resolves chronic antral gastritis. The favourable relapse rates with CBS might be explained by the permanent eradication of C. pylori.

Animals↗
PubMed1988

Use of single session hypnosis for smoking cessation.

Twenty of sixty volunteers for smoking cessation were assigned to single-session hypnosis, 20 to a placebo control condition, and 20 to a no-treatment control condition. The single-session hypnosis group smoked significantly less cigarettes and were significantly more abstinent than a placebo control group and a no treatment control group at posttest, and 4-week, 12-week, 24-week and 48-week follow-ups.

Adult↗
PubMed1988

Host-seeking activity of Culicoides spp. (Diptera: Ceratopogonidae) near Yankeetown, Florida.

The diel, seasonal, and lunar host-seeking periodicity of Culicoides mississippiensis, C. floridensis, C. barbosai, and C. furens was studied near Yankeetown, Florida. Culicoides mississippiensis was the only species active during all seasons. Significantly more (P less than 0.05) individuals sought a blood meal when the moon was full than when the moon was in some other phase. Culicoides floridensis, the species with the shortest wing length, did not attack when the wind speed exceeded 9 km/h, and C. mississippiensis, the species with the greatest wing length, did not attack when the wind speed exceeded 17 km/h.

Animals↗