Bestimmung von Mindestbiegeradien beim Biegen von runden Drähten und Stäben

Aufgabenstellung des Forschungsvorhabens. Beschreibung des angewendeten Rißprüfverfahrens. Ableitung der Gleichungen für den minimalen Biegeradius. Beschreibung der Zusammenhänge zwischen Mindestbiegeradius, Zugfestigkeit, Streckgrenzenverhältnis, Härte bei verschiedenen Stahlsorten in walzhartem und vorgezogenem Zustand. Örtliche Dehnungsverteilung. Entwicklung einer einfachen Beziehung zwischen Mindestbiegeradius und Brucheinschnürung. Diskussion dieser Korrelation anhand visioplastischer Ergebnisse.     

Exploratory studies on azole carboxamides as nucleobase analogs: thermal denaturation studies on oligodeoxyribonucleotide duplexes containing pyrrole-3-carboxamide

In order to study base pairing properties of the amide group in DNA duplexes, a nucleoside analog, 1-(2'-deoxy-beta-D-ribofuranosyl)pyrrole-3-carboxamide, was synthesized by a new route from the ester, methyl 1-(2'-deoxy-3',5'-di-O-p -toluoyl-beta-D-erythro-pentofuranosyl)pyrrole-3-carboxylate, obtained from the coupling reaction between 1-chloro-2-deoxy-3,5-di-O -toluoyl-d-erythropentofuranose and methyl pyrrole-3-carboxylate by treatment with dimethylaluminum amide. 1-(2'-Deoxy-beta-D-ribofuranosyl)pyrrole-3-carboxamide was incorporated into a series of oligodeoxyribonucleotides by solid-phase phosphoramidite technology. The corresponding oligodeoxyribonucleotides with 3-nitropyrrole in the same position in the sequence were synthesized for UV comparison of helix-coil transitions. The thermal melting studies indicate that pyrrole-3-carboxamide, which could conceptually adopt either a dA-like or a dI-like hydrogen bond conformation, pairs with significantly higher affinity to T than to dC. Pyrrole-3-carboxamide further resembles dA in the relative order of its base pairing preferences (T >dG >dA >dC). Theoretical calculations on the model compound N-methylpyrrole-3-carboxamide using density functional theory show little difference in the preference for a syntau versus anti conformation about the bond from pyrrole C3 to the amide carbonyl. The amide groups in both the minimized antitau and syntau conformations are twisted out of the plane of the pyrrole ring by 6-14 degrees. This twist may be one source of destabilization when the amide group is placed in the helix. Another contribution to the difference in stability between the base pairs of pyrrole-3-carboxamide with T and pyrrole-3-carboxamide with C may be the presence of a hydrogen bond in the former involving an acidic proton (N3-H of T).     

Agouti signaling protein inhibits melanogenesis and the response of human melanocytes to alpha-melanotropin

In mouse follicular melanocytes, the switch between eumelanin and pheomelanin synthesis is regulated by the extension locus, which encodes the melanocortin-1 receptor (MC1R) and the agouti locus, which encodes a novel paracrine-signaling molecule that inhibits binding of melanocortins to the MC1R. Human melanocytes express the MC1R and respond to melanotropins with increased proliferation and eumelanogenesis, but a potential role for the human homolog of agouti-signaling protein, ASIP, in human pigmentation has not been investigated. Here we report that ASIP blocked the binding of alpha-melanocyte-stimulating hormone (alpha-MSH) to the MC1R and inhibited the effects of alpha-MSH on human melanocytes. Treatment of human melanocytes with 1 nM-10 nM recombinant mouse or human ASIP blocked the stimulatory effects of alpha-MSH on cAMP accumulation, tyrosinase activity, and cell proliferation. In the absence of exogenous alpha-MSH, ASIP inhibited basal levels of tyrosinase activity and cell proliferation and reduced the level of immunoreactive tyrosinase-related protein-1 (TRP-1) without significantly altering the level of immunoreactive tyrosinase. In addition, ASIP blocked the stimulatory effects of forskolin or dibutyryl cAMP, agents that act downstream from the MC1R, on tyrosinase activity and cell proliferation. These results demonstrate that the functional relationship between the agouti and MC1R gene products is similar in mice and humans and suggest a potential physiologic role for ASIP in regulation of human pigmentation.     

Negligible prevalence of antibodies against Trypanosoma cruzi among blood donors in the southeastern United States

The ultrastructure of alpha-bacteroids in relation to the fat-body cells of the lantern bug Pyrops candelaria was described. The fat-body-cell cytoplasm contained numerous mitochondria, rough endoplasmic reticula, vacuoles, and storage granules. Its nucleus had scattered chromatin materials. The alpha-bacteroid was enveloped by three membrane layers, namely, the plasma membrane, the cell wall, and the membrane envelope. Its cytoplasm contained amorphous dense bodies. The bacteroid reproduced by binary fission. Tracheoles were also found among fat-body cells.     

A pilot study of soluble adhesion molecules as surrogate markers for acute liver allograft rejection

OBJECTIVE: The purpose of this study was to determine the degree to which the number and angular disparity of component projections influence depth discrimination with tuned-aperture computed tomography. STUDY DESIGN: Groups of three tiny steel spheres served as fiducial references on and in four partially edentulous mandibles. Two spheres were attached to the facial and lingual surfaces of each mandible, and the third was fixed in the apical region of an open tooth socket. Errors in estimates of the depth of the apically positioned sphere relative to the other two spheres were determined from three-dimensional tuned-aperture computed tomography reconstructions. These data were compared with actual measurements produced independently with an optical micrometer. Multiple projections required by the tuned-aperture computed tomography reconstruction algorithm were produced from radially symmetric exposures bearing angular disparities of 5, 15, 30, and 45 degrees. The number of symmetrically dispersed projections per tuned-aperture computed tomography reconstruction likewise was varied systematically (2, 4, 8, 12, and 16 projections). These variables were manipulated through the use of a balanced factorial design. Depth estimates were performed by trained observers; the estimates were based on the determination of tuned-aperture computed tomography slices perceived as imaging the respective apical spheres in sharpest focus. Specimen and observer effects were also considered as independent variables. Resulting data were normalized by logarithmic transformation and analyzed statistically by analysis of variance. RESULTS: Significant differences (p < 0.005) were demonstrated for angular disparity and specimen effects, but the number of projections and the effect of the observer were not found to be statistically significant. CONCLUSIONS: In dentistry, angular disparities of 15 degrees or greater should be used when tuned-aperture computed tomography is being applied to diagnostic tasks requiring maximal depth discrimination accuracy.     

Micromechanisms of brittle fracture

Mechanical processes operating in materials on the scale of the microstructure have come to be called “micromechanisms.” The fundamental science and the micromechanisms of brittle fracture are reviewed here, with particular emphasis on cleavage and intergranular fracture. Extant micromechanisms for these fracture types are evaluated. The role of solutes, particularly in intergranular fracture, is also discussed in terms of the fundamentals of brittle fracture. This article is based on a presentation made in the symposium “Quasi-Brittle Fracture” presented during the TMS fall meeting, Cincinnati, OH, October 21–24, 1991, under the auspices of the TMS Mechanical Metallurgy Committee and the ASM/MSD Flow and Fracture Committee.     

Combined heart-kidney transplantation: report on six cases

Nisin is a membrane active antimicrobial peptide containing unusual dehydrated amino acid residues. The secondary structure of nisin in aqueous solution, membrane mimicking solvents and at various pH values was investigated using circular dichroism. In aqueous solution nisin is largely randomly coiled. In liposomes and at pH 6 and above, however, the presence of a maximum at 195 nm and a minimum at 190 nm was notable and indicative of beta-turn formation in these environments. This change in structure was speculated to result in an increasing unavailability of the site for initial reaction of peptide and membrane at higher pH.     

Risk factors for clinically important adverse events after protamine administration following cardiopulmonary bypass

OBJECTIVES: The purpose of this study was to determine risk factors for adverse events following protamine administration after cardiopulmonary bypass. BACKGROUND: Intravenous protamine administration is associated with a risk of severe systemic reactions. However, risk factors for these events have not been well delineated, thus hampering development of preventive strategies. METHODS: A case-control study nested within a cohort of consecutive patients undergoing surgery requiring cardiopulmonary bypass was performed. The primary case definition included those events (pulmonary hypertensive and systemic hypotensive) occurring within 10 min of protamine administration in the absence of other measurable causes of hemodynamic compromise. RESULTS: Comparing the 53 cases to the 223 control subjects, three risk factors were independently associated with events (multivariable odds ratio [95% confidence interval]): neutral protamine Hagedorn insulin use (8.18 [2.08, 32.2]); fish allergy (24.5 [1.24, 482.3]), and a history of nonprotamine medication allergy (2.97 [1.25, 7.07]). These risk factors demonstrated an increasingly strong association with progressively more specific case definitions. An estimated 39% of cardiopulmonary bypass patients had one or more of these risk factors. Prior intravenous protamine, central venous pressure prior to protamine, preoperative ejection fraction and the need for inotropes when coming off bypass did not exhibit statistically significant associations with events (all p > 0.15). Prior protamine allergy was associated specifically with an increased risk of pulmonary hypertension (multivariable odds ratio 189; 95% confidence interval 13, 2,856). CONCLUSIONS: Immunologic factors are important in predisposing individuals to protamine reactions, and a substantial proportion of patients are at considerably increased risk Strategies to reduce the risk of protamine-associated events are needed.