Clinical studies with a low dose estrogen-progestogen combination

Clindamycin, tinidazole (a parent compound to metronidazole), and doxycycline were compared in vitro against 376 anaerobic bacteria isolated from clinical specimens. Bacteriostatic tests indicated that clindamycin was the most active drug, on a weight basis, against these strains except for Clostridium species. The three drugs were compared as therapies for anaerobic wound infections in cancer patients. In a randomized double-blind study, no statistically significant differences between clindamycin and tinidazole could be documented. Doxycycline was less active presumably because of the lack of clinical response in three out of four patients infected with doxycycline-resistant strains. No major untoward effects were observed. The bactericidal dilution of the serum was predictive of the clinical outcome.     

Source-sided power flow control of a single-phase AC-to-DC series-resonant power supply

Contents The objective of an AC-to-DC converter is to control the output waveform. The energy emanated from the source is adapted by passive filters, which is often a compromise between volume and effective use. A classical rectifierfilter network presents a major disadvantage: a power factor less than one which is caused by distortion of the source current.The resolution of the high-frequency input current of the series-resonant converter introduces the possibility of controlling the waveform of the source current accurately. In combination with the accurate positioning of the high-frequency current pulses, it is possible to influence the exchange of power with the source by the introduced method of active filtering. A power factor equal to one would lead to an optimal operation. The method introduced can select any value for the power factor, even for distorted voltage waveforms.However the zero-crossing of the AC source voltage introduces the necessity of storing energy. Bulky low-frequency storage elements increase the specific volume and weight of the converter while the exchange of energy with storage elements decreases the overall efficiency. The energy stored in the resonant circuit is fundamentally too low to solve this problem. The stored energy in the output capacitor, necessary to decrease the high-frequency ripple voltage, is available for these purposes. To meet the optimal conditions for the power factor at the source, a bipolar flow of energy is required.The theory of single-phase AC-to-DC series-resonant power conversion with controllable reactive power is explained. The results of simulation and experiment will establish the extensive possibilities of the proposed systems.

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Netzseitige Leistungsflußregelung eines einphasigen AC-DC serienresonanten Leistungsumformers

Übersicht Die Aufgabe eines AC-DC Umrichters ist es, die Spannungsform des Ausganges regelungstechnisch festzulegen. Die von der Speisequelle entnommene Energie wird über passive Filter ausgekoppelt, die stets einen Kompromiß zwischen Raumbedarf und erzielter Wirkung bilden. Ein klassischer Gleichrichter liefert, besonders, wenn er gesteuert ist, stets einen netzseitigen Leistungsfaktor, der kleiner eins ist. Dies ist durch den verformten und in der Phase verschobenen Netzstrom bedingt.Die hohe Auflösung des hochfrequenten Eingangsstromes eines serienresonanten Umrichters bietet die Möglichkeit, die netzseitige Stromform sehr genau zu regeln. In Verbindung mit der genauen Positionierung der hochfrequenten Strompulse ist es möglich, die momentan zugeführte Energie mit der vorgestellten Methode der aktiven Filterung zu beeinflussen. Ein geregelter Leistungsfaktor von eins führt so zu einem optimalen Betriebszustand. Die vorgesehene Methode gestattet es, jeglichen Leistungsfaktor einzustellen, selbst bei einer pulsierenden Spannungszeitfunktion.Der Nulldurchgang der Wechselspannung des Netzes zeigt die Notwendigkeit, Energie zwischenzeitlich zu speichern. Speicher für niedrige Frequenzen erhöhen das Gewicht und das Volumen des Umrichters, gleichzeitig läßt der Austausch von Energie mit Energiespeichern den Wirkungsgrad sinken.Die gespeicherte Energie in einem hochfrequenten Resonanzkreis ist also grundsätzlich zu gering, um dieses Problem zu lösen. Die gespeicherte Energie dagegen in den erforderlichen Ausgangsfilter-Kondensatoren, die zur Glättung der Spannung dienen, ist für diesen Zweck gut geeignet. Um optimale Bedingungen hinsichtlich des netzseitigen Leistungsfaktors zu erhalten, ist ein Leistungsfluß in beiden Richtungen erforderlich.Die Theorie eines einphasigen AC-DC serienresonanten Umrichters mit regelbarem Leitungsfaktor wird erläutert. Simulationen und Meßresultate einer derartigen Ausführung werden vorgestellt, die die weiten Möglichkeiten einer Leistungsflußregelung verdeutlichen.

     

Electrocatalytic reduction of hydrogen peroxide at a stationary pyrolytic graphite electrode surface in the presence of cytochrome c peroxidase: a description based on a microelectrode array model for adsorbed enzyme molecules

Electrochemical reduction of H2O2 at pyrolytic graphite disc electrodes of radius 2.5 mm occurs at readily accessible potentials (600 mV versus the standard hydrogen electrode) in the presence of yeast cytochrome c peroxidase. Introduction of the enzyme into the electrolyte solution initiates large changes in the ellipsometric angles measured for the electrode-solution interface, consistent with time-dependent enzyme adsorption. This process may be correlated with changes in electrochemical activity. Over the same time course, linear-sweep voltammograms are characterized by a transition from a sigmoidal to a peak-type waveform. It is proposed that the time-dependent behaviour may be rationalized by use of a microscopic model for substrate mass transport, in which the two-electron reduction of peroxide occurs at electrocatalytic sites consisting of adsorbed enzyme molecules. A voltammetric theory based on treating the adsorbed redox enzymes as an expanding array of microelectrodes is in excellent agreement with experiment.     

Muon-spin-relaxation studies on the heavy-fermion system with non-Fermi-liquid behavior CeCu5.9Au0.1

A patient with a history of pelvic radiation therapy for seminoma presented with a prostatic tumor, which appeared predominantly of high signal intensity on T2-weighted magnetic resonance images; low-signal-intensity tissue also extended to the pelvic sidewall. At surgical pathology, the tumor was determined to be radiation-induced sarcoma of the prostate, and the extraprostatic tissue was postradiation fibrosis.     

Synthesis and antiplatelet effects of omega-aminoalkoxylxanthones

A series of omega-aminoalkoxylxanthones were synthesized and tested in-vitro for their ability to inhibit aggregation of rabbit washed platelets and human platelet-rich plasma (PRP) induced by various inducers. Nine of these compounds showed more potent antiplatelet effects than natural norathyriol tetraacetate on collagen-induced aggregation. The various omega-aminoalkoxyl side chains of the synthesized compounds modified the antiplatelet effects. All the compounds tested in human PRP showed significant inhibition of secondary aggregation induced by adrenaline, suggesting that the antiplatelet effects of these compounds is mainly due to an inhibitory effect on thromboxane formation. These compounds at high concentration also cause vasorelaxing action in rat thoracic aorta.     

Variable-speed generation with the series-resonant converter

Results of study and measurements are presented for a variable-speed generation (VSG) system that uses a series-resonant converter to excite the rotor windings of a doubly-fed generator. The capabilities of this system include maximum-efficiency operation and limited converter rating for a speed range from stand-still (zero RPM) to well beyond synchronous speed, as well as flexibility for line-voltage control, reactive power generation, and synchronization at zero RPM. Measurements of the harmonic distortion are provided showing the superiority of this converter as compared with a VSG system using a conventional cycloconverter or a DC-link converter. A convenient tool for analyzing the operating modes of the system is discussed that can be developed under varying resource conditions