Series equivalence/operation of current-controlled boost-typesingle-phase voltage source converters for bidirectional power flow

Single-phase voltage source power converters (VSCs) under consideration are AC-DC current-controlled boost-type power converters with bidirectional power-handling capability. Equivalence between two series-connected two-level power converters and a single three-level power converter is considered here. Further considered is the series operation of three-level power converters. Simulation results and experimental verification for both are provided. Economical configurations of three-level power converters leading to multilevel waveforms are presented thereafter     

STRESS INTENSITY FACTORS AND WEIGHT FUNCTIONS FOR SEMI-ELLIPTICAL SURFACE CRACKS IN FINITE-THICKNESS PLATES UNDER TWO-DIMENSIONAL STRESS DISTRIBUTION

Abstract— A Fourier series approach is proposed to calculate stress intensity factors using weight functions for semi-elliptical surface cracks in flat plates subjected to two-dimensional stress distributions. The weight functions were derived from reference stress intensity factors obtained by three-dimensional finite element analyses. The close form weight functions derived are suitable for the calculation of stress intensity factors for semi-elliptical surface cracks in flat plates under two-dimensional stress distributions with the crack aspect ratio in the range of 0.1 ≤ a/c ≤ 1 and relative depth in the range of 0 ≤ a/t ≤ 0.8. Solutions were verified using several two-dimensional non-linear stress distributions; the maximum difference being 6%.     

Snowboard traumatology: an epidemiological study

OBJECTIVE: To estimate the frequency of perioperative morbidities in patients who underwent anesthesia and a surgical procedure with no preoperative laboratory testing. MATERIAL AND METHODS: We conducted an electronic database search of medical records of 56,119 patients who underwent surgical or diagnostic procedures and anesthesia at Mayo Clinic Rochester in 1994 and found 5,120 who had no laboratory tests done within 90 days before the procedure. From this group, we randomly selected 1,044 patients (87 from each month) to document the absence of preoperative tests, the presence of preexisting disease (by organ system), the type of anesthetic agent, and the outcomes and tests intraoperatively and postoperatively. RESULTS: The 1,044 patients ranged in age from 0 to 95 years (median age, 21). No deaths or major perioperative morbidities occurred (0.0%; exact 95% confidence interval, 0.00 to 0.35%). Although 10 patients underwent blood typing and screening for antibodies immediately preoperatively, no blood transfusions were necessary. Intraoperatively, 17 laboratory tests and 1 electrocardiogram were obtained, and 3 results were abnormal. Postoperatively, 42 blood tests and 2 electrocardiographic procedures were performed. Five of the 42 blood tests showed abnormal results (hemoglobin levels in 3, serum sodium in 1, and arterial blood gases in 1). One electrocardiogram showed normal findings, and the other revealed normal results except for premature ventricular contractions. No laboratory test done intraoperatively or postoperatively was found to change surgical or medical management substantially. One patient who had unanticipated blood loss during an outpatient procedure was admitted to the hospital for observation. CONCLUSION: All 1,044 patients, 97% of whom were relatively healthy, with no recent laboratory testing safely underwent anesthesia and an operation. We conclude that patients who have been assessed by history and physical examination and determined to have no preoperative indication for laboratory tests can safely undergo anesthesia and operation with tests obtained only as indicated intraoperatively and post-operatively. Current anesthetic and medical practices rapidly identify perioperative indications for laboratory evaluation as they arise.     

Screening mixtures for biological activity by NMR

Development of the new drugs often involves the screening of compound libraries for biological activity. Currently, the biologically active component can only be identified if either a pure compound is being tested or if the components of a mixture are spatially separated, for example, on beads. Here, we present an NMR technique based on the transferred nuclear Overhauser effect (transfer NOE) that allows identification and structural characterization of biologically active molecules from a mixture. As an example we demonstrate that from mixtures of oligosaccharides only alpha-L-Fuc-(1-->6)-beta-D-GlcNAc-OMe binds to Aleuria aurantia agglutinin. The sign of transferred NOEs is opposite to NOEs of small molecules that do not bind to the protein and, thus, an unequivocal identification of molecules with binding activity is possible. Normally, the selection of bound ligands is further facilitated in that the absolute intensity of transfer NOEs is much greater than that of NOEs of non-binding molecules. In addition, transfer NOEs provide information on the three-dimensional structure of the ligands in the bound state. Therefore, measuring transfer NOEs of mixtures of small molecules in the presence of large molecules, like proteins, should significantly enhance the options for screening mixtures of compounds for biological activity.     

Role of the hemobiologist in the detection and prevention of post-transfusional hepatitis

To prevent post-transfusional hepatitis B and C, two epidemiologic studies were performed. The first, based on the frequencies distribution of hepatitis B virus serological markers versus sex and classes of age, has permitted the assessment of the profile of the infection in a population composed of 573 north vietnamese blood donors. There is no significant difference between men and women frequencies of HBs antigen (11.5%), anti-HBs antibody (70.2%) and anti-HBc antibody alone (3.8%), but a significant difference of no-marker frequencies: 7.8% and 17.9% in men and women respectively (X2 = 9.11; p = 0.010). The percentage of no-marker decreases when the mean age of each class increases. The second, using the increase of the serum alanine aminotransferase (ALAT) activity as an indirect marker of non-A, non-B hepatitis for determining in a population of more than 25,000 parisian blood donors, the percentage of donors eliminated. They are between 0.70 and 0.76 in women and 2.26 and 2.46 in men. These investigations can be applied to prevent the hepatitis B transmission in a population of 102 south vietnamese women in age to procreate or to determine the percentage of blood donors eliminated (3.12%) in a population of 2,950 Parisians composed in majority (50.9%) of new donors. The hemobiologist will have an important role to elaborate strategies for orientation of blood gifts with hepatitis B and C virus markers.     

Dimer interface of glutathione S-transferase from Arabidopsis thaliana: influence of the G-site architecture on the dimer interface and implications for classification

The three-dimensional structure of glutathione S-transferase from Arabidopsis thaliana has been solved at 2.2 A resolution (Reinemer et al., 1996). The enzyme forms a dimer of two identical subunits. The structure shows a new G-site architecture and a novel and unique dimer interface. Each monomer of the protein forms a separate G-site. Therefore, the requirements on the dimer interface are reduced. As a consequence, the interactions between the monomers are weaker and residues at the dimer interface are more variable. Thus, the dimer interface looses its relevance for a classification of plant glutathione S-transferases and the formation of heterodimers becomes even more difficult to predict.     

Preferential exclusion of sucrose from recombinant interleukin-1 receptor antagonist: role in restricted conformational mobility and compaction of native state

Understanding the mechanism for sucrose-induced protein stabilization is important in many diverse fields, ranging from biochemistry and environmental physiology to pharmaceutical science. Timasheff and Lee [Lee, J. C. & Timasheff, S. N. (1981) J. Biol. Chem. 256, 7193-7201] have established that thermodynamic stabilization of proteins by sucrose is due to preferential exclusion of the sugar from the protein's surface, which increases protein chemical potential. The current study measures the preferential exclusion of 1 M sucrose from a protein drug, recombinant interleukin 1 receptor antagonist (rhIL-1ra). It is proposed that the degree of preferential exclusion and increase in chemical potential are directly proportional to the protein surface area and that, hence, the system will favor the protein state with the smallest surface area. This mechanism explains the observed sucrose-induced restriction of rhIL-1ra conformational fluctuations, which were studied by hydrogen-deuterium exchange and cysteine reactivity measurements. Furthermore, infrared spectroscopy of rhlL-1ra suggested that a more ordered native conformation is induced by sucrose. Electron paramagnetic resonance spectroscopy demonstrated that in the presence of sucrose, spin-labeled cysteine 116 becomes more buried in the protein's interior and that the hydrodynamic diameter of the protein is reduced. The preferential exclusion of sucrose from the protein and the resulting shift in the equilibrium between protein states toward the most compact conformation account for sucrose-induced effects on rhIL-1ra.