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Biomedical subjects

J Betz

Publications and source records attributed to J Betz.

16 recordsLinked to original sources
PubMed2002

Thermocapillary convection around gas bubbles: an important natural effect for the enhancement of heat transfer in liquids under microgravity.

In the presence of a temperature gradient at a liquid-gas or liquid-liquid interface, thermocapillary or Marangoni convection develops. This convection is a special type of natural convection that was not paid much attention in heat transfer for a long time, although it is strong enough to drive liquids against the direction of buoyancy on Earth. In a microgravity environment, however, it is the remaining mode of natural convection and supports heat and mass transfer. During boiling in microgravity it was observed at subcooled liquid conditions. Therefore, the question arises about its contribution to heat transfer without phase change. Thermocapillary convection was quantitatively studied at single gas bubbles in various liquids, both experimentally and numerically. A two-dimensional mathematical model described in this article was developed. The coupled mechanism of heat transfer and fluid flow in pure liquids around a single gas bubble was simulated with a control-volume FE-method. The simulation was accompanied and compared with experiments on Earth. The numerical results are in good accordance with the experiments performed on Earth at various Marangoni numbers using various alcohols of varying chain length and Prandtl numbers. As well as calculations on Earth, the numerical method also allows simulations at stationary spherical gas bubbles in a microgravity environment. The results demonstrate that thermocapillary convection is a natural heat transfer mechanism that can partially replace the buoyancy in a microgravity environment, if extreme precautions are taken concerning the purity of the liquids, because impurities accumulate predominantly at the interface. Under Earth conditions, an enhancement of the heat transfer in a liquid volume is even found in the case where thermocapillary flow is counteracted by buoyancy. In particular, the obstructing influence of surface active substances could be observed during the experiments on Earth in water and also in some cases with alcohols.

Journal Article↗
PubMed2001

A hybrid model of categorization.

Category learning is often modeled as either an exemplar-based or a rule-based process. This paper shows that both strategies can be combined in a cognitive architecture that was developed to model other task domains. Variations on the exemplar-based random walk (EBRW) model of Nosofsky and Palmeri (1997b) and the rule-plus-exception (RULEX) rule-based model of Nosofsky, Palmeri, and McKinley (1994) were implemented in the ACT-R cognitive architecture. The architecture allows the two strategies to be mixed to produce classification behavior. The combined system reproduces latency, learning, and generalization data from three category-learning experiments--Nosofsky and Palmeri (1997b), Nosofsky et al., and Erickson and Kruschke (1998). It is concluded that EBRW and ACT-R have different but equivalent means of incorporating similarity and practice. In addition, ACT-R brings a theory of strategy selection that enables the exemplar and the rule-based strategies to be mixed.

Cognition↗
PubMed2000

Solution and solid-state structure of (1-methoxy-8-naphthyllithium. THF)(2)

The structure of (1-methoxy-8-naphthyllithium.THF)(2), (2.THF)(2), determined by single-crystal X-ray diffraction (crystal data: monoclinic, a = 8.1816 (5), b = 21.9649 (14), and c = 8.2345 (3) A, beta = 117.969 (3) degrees; V = 1306.97 (12) A(3); space group P2(1)/n; Z = 4) reveals a centrosymmetrical dimer with a twist angle of about 63 degrees between the naphthyl rings and the Li-C(ipso)-Li plane, representing an intermediate between perpendicular and planar tetracoordinated C(ipso). NMR studies at low temperature indicate that 2 is dimeric in THF-d(8) solution under these conditions.

Journal Article↗
PubMed1998

Factors influencing the career choices of physicians trained at Yale-New Haven Hospital from 1929 through 1994.

PURPOSE: To examine factors that influenced, positively or negatively, the specialty career choices of physicians trained at Yale-New Haven Hospital (YNHH) from 1929 to 1994. METHOD: The authors sent questionnaires to 4,888 physicians who had trained or were training in YNHH-sponsored residency programs. The physicians rated 36 factors posited to be influenced in career choice on a seven-point Likert scale from very negative to very positive. The authors compared the means of each factor's ratings by decade of medical school graduation. RESULTS: The most positively rated influences were similar in each decade from the 1920s to the 1990s. These influences shared characteristics of intellectual curiosity ("intellectual content of the specialty" and "challenging diagnostic problems"), altruism ("interest in helping people" and "opportunity to make differences in people's lives"), and personal identity ("consistent with personality" and "possess the required skill or ability"). Negative factors, such as "demands on time and effort," "stress in the field," and "malpractice costs," were also consistently rated throughout the decades. CONCLUSION: The reasons that physicians choose certain specialty careers have not changed significantly over the past 65 years despite all the changes that have occurred in medicine. Physicians continue to seek professional opportunities that are viewed as intellectually challenging and of benefit to others.

Career Choice↗
PubMed1996

Unusual and unrelated polyclonality in a case of myeloid disease.

A case of myelofibrosis with myeloid metaplasia was found to have five cytogenetically unrelated clones in the marrow, four of these clones being abnormal. We present the hypothesis that the hematologic disease in this patient was caused by a genetic event not discernible microscopically (cytogenetically) and that the distinctive abnormal clones may have been generated at different anatomic sites.

Aged↗
PubMed1996

FISH studies on the Y chromosome in male urinary cells.

To ascertain the meaning of the loss of the Y (-Y) in bladder cancer, we addressed the incidence of -Y in urinary cells in relation to age in 35 men without bladder cancer. Aside from the bone marrow and blood, -Y has not been examined critically in other tissues and organs in a large series of men. The present study clearly demonstrated that -Y in the group studied was an infrequent finding and not related to age.

Adult↗
PubMed1988

[The equilibrium of nitrogen, potassium and phosphate and renal excretion of creatinine and creatinine over the course of 3 weeks following severe trauma].

In 19 patients after accidental trauma and with intact renal function during an observation time of 21 days we found a cumulated negative balance of nitrogen (N), phosphate (P) and potassium (K) amounting to a mean of 214g, 357 and 447 mmol, respectively. Median daily potassium balance was positive on day 2 to 5 and this was interpreted as an increased extrarenal potassium deposition due to increased levels of circulating catecholamines. Median renal creatinine excretion was about 120% of predicted normal till day 10 and continuously decreased thereafter to values lower than predicted normal. Three patients did not show creatinuria (greater than 200 mg/day) during the whole observation time. In 15 patients after a "free interval" with a mean duration of 7 days creatinuria frequently developed rather quickly and maximal excretion of creatine was as high as 4 g/day. In 7 patients creatinuria persisted to the end of the 21 days observation time. During the phase of creatinuria the median cumulated excretion of creatine amounted to 14.4 g. The "free interval" of creatinuria after severe trauma is remarkable. Most of the N, K and P, which is lost from the body during this time obviously stems from tissues other than sceletal muscle. During the phase of creatinuria, however, the negative balance of N, K and P seems to be mainly due to muscle wasting. Hypophosphatemia was prominent during the first 5 days after trauma and obviously was caused by a decrease in renal phosphate threshold (TmPO4/GFR). The underlying mechanism of this primary change in renal function after severe trauma could not yet be identified.

Adolescent↗
PubMed1983

Metabolism of phosphate and calcium after severe accidental trauma.

Hypophosphatemia is a common finding during the first 4-5 days after severe accidental trauma. We demonstrated that hypophosphatemia after trauma is caused by a definite decrease in renal phosphate threshold (TmPO4/GFR), that is the theoretical plasma phosphate concentration at which all of the filtered phosphate is reabsorbed by the renal tubules and renal excretion of phosphate is close to zero. We speculated that the decrease in renal phosphate threshold could be due to an increased activity of PTH which in turn could be the result of ionized hypocalcemia. In 7 patients with severe and in 8 patients with moderate trauma, however, we found ionized calcium and PTH levels to be within normal limits. Total plasma calcium was below normal (1.90-2.00 mmol/l) up to 20 days after trauma, probably due to a decreased plasma albumin concentration (25-30 g/l). We conclude, that ionized hypocalcemia and consecutive stimulation of PTH is not the cause of decreased renal phosphate threshold after severe accidental trauma.

Adolescent↗
PubMed1976

[Enzyme induction in Streptomyces hydrogenans, VI. Studies on the induction of 20beta-hydroxysteroid dehydrogenase, using immunological methods].

Antiserum against crystallized 20beta-hydroxysteroid dehydrogenase from Streptomyces hydrogenans was used for various immunodiffusion and immunoprecipitation tests to show an increase of the de novo synthesis of 20beta-hydroxysteroid dehydrogenase by Streptomyces hydrogenans after cultivation of the cells in the presence of 11beta,21-dihydroxy-4,17(20)-pregnadien-3-one. Half lives of mRNA for 20beta-hydroxysteroid dehydrogenase in induced cells and of total mRNA in non-induced cells were calculated to be 126 s and 66 s, respectively. In vivo, 20beta-hydroxysteroid dehydrogenase appears to consist of four equal subunits. The monomers, molecular weight of 27 300, show a high tendency to form dimers and tetramers in the absence of dissociating agents. The aggregation is completely reversible in the presence of increasing concentrations of sodium dodecylsulfate.

Animals↗
PubMed1975

[Enzyme induction in Streptomyces hydrogenans. IV. (1) Qualitative and quantitative changes in RNA content and RNA synthesis during induction].

For isolation of RNA, freeze-dried cells of Streptomyces hydrogenans were disrupted by grinding with kieselguhr. Application of diethylpyrocarbonate (diethyl oxydiformate) in an extraction procedure yielded undegraded nucleic acids of high purity. Best separation of extracted nucleic acids was achieved by electrophoresis on 2% mixed agarose-acrylamide gels. After application of 11beta, 21-dihydroxy-4,14 (20)-pregnadien-3-one to the culture medium, the amount of acid-precipitable RNA in the cells decreased to 50% within 20 min. Concimitantly, the rate of incorporation of precursors into RNA is much slower immediately after addition of the inducer but increases during the next 2 h. 3-4 h after induction there is no difference in the RNA content of induced and control cells. Degradation of stable as well as unstable RNA was observed. Simultaneous addition of inducer and rifamycin inhibits the production of 20beta-hydroxysteroid dehydrogenase, suggesting the synthesis of special mRNA for this enzyme. Based on experiments with antibiotics, the half-life of total mRNA was calculated to be 3 min in control cells, and about 4 min in induced cells. Using a double isotope labelling technique, we established the existence of specific mRNA in the induced cells. Together with the longer half-life of mRNA in the induced cells, the increased transcription may allow the 40-fold stimulation of the synthesis of 20beta-hydroxysteroid dehydrogenase.

Cortisone Reductase↗
PubMed1975

[Isolation and separation of nucleic acids from Streptomyces hydrogenans (author's transl)].

Different methods for homogenization of cells of Streptomyces hydrogenans, for extraction of nucleic acids and for fractionation of the RNA and DNA obtained were critically examined. The only way to prepare high molecular weight rapidly labelled RNA and polysomes was to grind freeze-dried cells together with kieselguhr with a mortar and pestle. The best results for extraction of nucleic acids from the cell homogenate were obtained in the presence of diethyl pyrocarbonate (diethyl oxydiformate), yielding nucleic acids of considerable purity in a minimal amount of time. The best resolution of extracted nucleic acids was achieved by electrophoresis in 2% agarose acrylamide gels. This technique proved that during the cell homogenization and extraction procedure the bulk of nucliec acids was not degraded to low molecular weight material. An improved device for the registration of the profile of the absorption after gel electrophoresis is described.

Centrifugation, Density Gradient↗
PubMedDate not supplied

Properties of an antiserum against Streptomyces hydrogenans 20beta-hydroxysteroid dehydrogenase.

Antiserum against crystallized 20beta-hydroxysteroid dehydrogenase from Streptomyces hydrogenans was used for different immunodiffusion and immunoprecipitation tests to quantify the bacterial enzyme in cell-free supernatants of the microorganism. After immunoprecipitation and gel electrophoresis the molecular weight of the subunits of 20beta-hydroxysteroid dehydrogenase was calculated to be 27 300 +/- 700.

Antigen-Antibody Complex↗
PubMedDate not supplied

Nucleoside triphosphate levels in Streptomyces hydrogenans during growth and induction of 20beta-hydroxysteroid dehydrogenase.

Levels of the purine nucleoside triphosphates are decreasing towards the end of log phase growth of Streptomyces hydrogenans. Induction of 20beta-hydroxysteroid dehydrogenase by addition of 11beta,21-dihydroxy-4,17(20)-pregnadien-3-one to the growth medium leads to a pronounced drop in purine nucleoside triphosphate levels with is irreversible in contrast to the initial loss and later accumulation of RNA.

Adenosine Triphosphate↗