Showing papers by "Humboldt University of Berlin published in 1976"

Stable lipid peroxidation products in human skin: detection, ultraviolet light-induced increase, pathogenic importance.

Abstract: Products of lipid peroxidation (malonaldehyde, Schiff-bases) were detected in human skin. These products were increased after UV-light exposition, on chronically sun-exposed areas as well as with advancing age. Malonaldehyde cross linked epidermal glucose-6-phosphate-dehydrogenase and diminished their activity.

Cyclotron Masses in Semiconducting Bi1-xSbx Alloys

Abstract: Cyclotron resonance measurements are carried out on a great number of semiconductive Bi1–x-Sbx; alloys in the range of 0.07 < x ≦ 0.17. The measuring frequencies are 35 and 70 GHz, and the measurements are carried out at helium temperatures. For the smallest cyclotron mass, a linear relationship to the antimony concentration is found. The more rapid increase of the great cyclotron masses and the associated increase of the elongation of the iso-energy surfaces with increasing antimony concentration presents the greatest difficulty as compared to the known dispersion relations of the electron bands. An einer grosen Anzahl von halbleitenden Bi1–x Sbx -Legierungen im Bereich 0,07 < < x ≦ 0,17 werden Zyklotronresonanzmessungen bei Mesfrequenzen von 35 und 70 GHz und Heliumtemperaturen durchgefuhrt. Fur die kleinste Zyklotronmasse wird ein linearer Zusammenhang mit der Antimonkonzentration gefunden. Das starkere Anwachsen der grosen Zyklotronmassen und die damit verbundene Zunahme der Streckung der Isoenergie-flachen mit der Antimonkonzentration stellt die groste Schwierigkeit beim Vergleich mit den bekannten Modellvorstellungen dar.

The biostability of silicone rubbers, a polyamide, and a polyester.

Abstract: A biostability test program was designed after evaluation of the relevant literature on in vivo aging phenomena in plastics and elastomers. The program comprised macroscopic, microscopic, mechanical, and physicochemical investigations. Five silicone rubbers, one polyester, and one polyamid were tested as to their aging behavior and their suitability for long-term implantation in the human body was assessed. In order to be able to state the applicability of materials used for endotheses, the various aging phenomena had to be divided into three groups, viz. unspecific, relative, and absolute indications of aging or unserviceability. Changes due to aging were found in all types of implanted plastics and elastomers. Thus, the formation of layers on inlay surfaces occurred regularly and the same would apply to changes in mechanical characteristics during the tensile test. Aging processes resulting in total unserviceability were fragmentation and crazing in the polyester and polyamide sheetings. Other aging phenomena which will easily fit into the classification given above are changes in electrical test values, protein, and lipid depositions without stronger absorptive adhesion, crystallizations on the surface of silicone vulcanizates, and chemical changes in the polyester and polyamide sheetings. Following the assessment of the materials used for endotheses, the test methods used have been evaluated with regard to their suitability for the testing of biostability.

Stability in convex quadratic parametric programming

Abstract: In this paper we discuss convex quadratic programming problems with variable coefficients in the linear part of the objective function or/and in the right hand side of the constraints. Local and global stability statements are contained. An important global stability theorem is proved for a feneral non-linear programming problem arbitrary, where F is a continuous function over is a nonempty compact subset of E n . A possibility of calculating of a local stability set for the convex quadratic parametric programming problem is also given. This method is not based on an algorithm for quadratic programming problems.

Polariton Effects in the Optical Spectra of Excitonic Molecules

Abstract: Starting from a model Hamiltonian which describes an excitonic molecule-excitonphoton system at not too high electron-hole pair densities, an excitonic molecule-polariton interaction is derived. By means of this interaction the influence of polariton effects on the optical emission, absorption, and scattering processes involving excitonic molecules is studied theoretically. It is shown, that the transition probabilities of these processes are diminished due to polariton effects, especially in substances with small molecule binding energies. Furthermore, some characteristic modifications of the optical spectra (additional lines, changes in the line positions and shapes) are reported. Ausgehend von einem Modell-Hamiltonian, der ein Exzitonenmolekul-Exziton-Photon-System bei nicht zu hohen Elektron-Loch-Paar-Dichten beschreibt, wird eine Exzitonen molekul-Polariton-Weehselwirkung abgeleitet. Mit Hilfe dieser Wechselwirkung wird der Einflusvon Polaritoneffekten auf die optischen Emissions-, Absorptions-und Streuprozesse von Exzitonenmolekulen theoretisch untersucht. Es wird gezeigt, das die Ubergangswabrscheinlichkeiten fur diese Prozesse durch Polaritoneffekte, insbesondere in Substanzen mit kleinen Molekulbindungsenergien, verkleinert werden. Weiterhin wird uber charakteristische Veranderungen in den optischen Spektren (Zusatzlinien, abweichende Linienlagen und -formen) berichtet.

Temporal and local concentration changes in diffusion layers at cellulose membranes due to concentration differences between the solutions on both sides of the membrane

Abstract: By means of a laser-interferometrical method diffusion layers at the interface of a noncharged cellulose membrane are studied. These layers are induced by a concentration difference between the NaCl solutions separated by the membrane. The temporal and local shift of the NaCl concentration in the diffusion layers were measured. A steady-state concentration profile could be obtained for times of 121 sec≦t0≦484 sec. The concentration profiles at any time (t0≦900) are not a linear function of the membrane surface, but could be fitted to a quadratic function. The thickness of the diffusion layers is also a function of time and its stationary value in this system is (575±49)×10−6 m. The role of concentration polarization for the determination of phenomenological thermodynamic coefficients of membranes is discussed and a new method is suggested, which excludes the difficulties of the concentration polarization in the diffusion layers at the membrane.

Quantitative Analysis of Interference Structures in the Transmission Spectrum of Very Thin CdS Platelets

Abstract: A quantitative analysis is given of interference structures appearing in very thin CdS single crystals of high perfection at 1.8K on both sides of the A ground-state exciton. It is shown that the structures are due to Fabry-Perot interferences of polaritons of the lower and upper branch, respectively. From the analysis of the interferences the energy of the transversal exciton is determined with high precision to be Et = 2.5528 eV, shifted from the transmission minimum by 0.8 meV in the low energy direction. This is to be expected in the polariton model. Es wird eine quantitative Analyse der Interferenzstrukturen, die auf beiden Seiten des A-Grundzustandexzitons bei sehr dunnen und perfekten CdS-Einkristallen auftreten, durchgefuhrt. Es wird gezeigt, das diese Strukturen durch Fabry-Perot-Interferenzen des unteren bzw. oberen Polaritonzweiges hervorgerufen werden. Aus der Analyse der Interferenzen kann mit hoher Genauigkeit die Energie des transversalen Exzitons zu Et = 2,5528 eV bestimmt werden, die vom Tranamissionsminimum urn 0,8 meV zu niederen Energien verschoben ist. Dies wird im Polaritonmodel erklart.

Exciton‐phonon interaction in CdS

Abstract: The absorption coefficient of CdS is measured over the whole region of the fundamental absorption edge, between liquid helium and room temperature. The experimental results are analysed and discussed in the framework of known theoretical work on exciton-phonon interaction. In this connection the excitonic self-energy in dependence on energy and temperature is derived from the experimental data on the one hand and from theory on the other. It is shown that the absorption behaviour is determined by different mechanisms of interaction, namely i) scattering of excitons optically generated at k ≈ 0 and ii) many-phonon proceeses and phonon-assisted transitions. Each mechanism is subjected to a special temperature dependence, reflecting the share of the interaction with acoustic and longitudinal optical phonons, respectively. Der Absorptionskoeffizient des CdS wird uber den gesamten Bereich der Grundgitterabsorptionskante fur Temperaturen zwischen der des flussigen Heliums und Raumtemperatur gemessen. Die experimentellen Ergebnisse werden im Rahmen bekannter Theorien zur Exziton-Phonon-Wechselwirkung analysiert und diskutiert. In diesem Zusammenhang wird die Exzitonenselbstenergie als Funktion von Energie und Temperatur einmal experimentell, zum anderen theoretisch bestimmt. Es wird gezeigt, das das Absorptionsverhalten von zwei verschiedenen Wechselwirkungsmechanismen gepragt ist, namlich 1) der Streuung bei k ≈ 0 optisch erzeugter Exzitonen und 2) Vielphononenprozessen bzw. phononenassistierten Ubergangen. Jeder dieser Mechanismen unterliegt einer besonderen Temperaturabhangigkeit, welche die anteilmasige Bedeutung der Wechselwirkung mit akustischen und longitudinalen optischen Phononen widerspiegelt.

A comparison of the influence of potassium and ammonium ions on the phosphofructokinases from rabbit muscle and rat erythrocytes.

Abstract: Phosphofructokinases from rat erythrocytes and rabbit muscle have been compared in their kinetic behavior with respect to monovalent cation activation and ATP inhibition. Both ammonium and potassium ions affect the muscle enzyme in a two-fold manner: they act both as activators and effectors. On the other hand only ammonium exerts the two-fold effects oil the erythrocyte enzyme, while the potassium ions activate without affecting cooperativity. The lower ATP inhibition of muscle phosphofructokinase may be partially explained by the action of potassium ions on the cooperative behavior of the enzyme. The differences between the phosphofructokinases from erythrocytes and muscle in the potassium type-II activation and ATP inhibition represent an organ specifity. Furthermore, the inhibition constants for 2,3-bisphosphoglycerate differ by 10-fold between the two enzymes.

Methodische Untersuchungen zur stoffwechselorientierten Aminosäurenbedarfsbestimmung bei Ratten im Erhaltungszustand anhand der Oxydationsrate von 14C-markiertem Lysin zu 14CO2

Abstract: Male experimental rats (100 gm liveweight) were distributed into 10 groups of 8 animals each and received balanced diets, with the exception of lysine which was added to the diets in graded amounts in such a way that the lysine content of the diets ranged from 2.44 to 5.92 gm/16 gm N. After a feeding period of 7 days the animals received 3H- and 14C lysine injected intraperitoneally, 4 animals of each group were investigated for the total CO2 excretion and 14CO2 excretion during the first 2 hrs after the injection and for the urinary excretion of radioactivity (48 hours). The remaining animals in each group were used for determining the plasma amino acids and for establishing the specific radioactivity of free lysine in the liver and muscles after an 1-hour incorporation period. Total CO2 excretion was not found to be influenced by the lysine contents while the level of excretion of 14C activity through CO2 and that of specific 14C activity of CO2 increased with increasing lysine concentrations. This produced a broken curve pattern, showing an increased release of 14CO2 (under maintenance conditions) if the diet contained 4 gm lysine/16 gm N and more. Investigations for the specific 14C activity of free lysine in the liver, the main site of lysine oxidation, showed that the increase in 14CO2 release was due to an enhanced rate of lysine catabolism and was not brought about by changes in the pool volume or in specific radioactivity. The levels of urinary 14C excretion were not found to be related to the lysine content of the diets, whereas the curve pattern of 3H excretion observed 5 to 8 hrs after injection was similar to that of 14CO2 excretion. The lysine content of blood plasma and the content of free lysine in the liver increased continuously with increasing levels of dietary lysine. The methodological studies made in the present paper showed that in scientific research a determination of amino acid requirements on the basis of CO2 oxidation data may be a very exact and sensitive method. It will also yield values for maintenance requirements.

Anwendung der Massenspektrometrie zur Identifizierung isomerer Amino‐oxadiazole

Abstract: Die massenspektrometrischen Zerfallsprodukte der vier isomeren phenyl-substituierten Amino-oxadiazole, 2-Amino-5-phenyl-l.3.4-oxadiazol, 3-Amino-5-phenyl-l.2.4-oxadiazol, 5-Amino-3-phenyl-l.2.4-oxadiazol und 3-Amino-4-phenyl-l.2.5.oxadiazol, unterscheiden sich sowohl hinsichtlich der Art der Fragmentzusamrnensetzung als auch der Signalintensitaten so charakteristisch, das eine eindeutige Differenzierung von Ring- und Stellungsisomeren moglich ist. Die wichtgsten Fragmentierungswege, die zu den strukturspezifischen Ionen fuhren, werden diskutiert. The mass spectrometric fragmentation products of the four isomeric monophenyl amino oxadiazoles, 2-amino-5-phenyl-l, 3,4-oxadiazole, 3-amino-5-phenyl-l, 2, 4-oxadiazole, 5-amino-3 phenyl-l, 2, 4-oxadiazole and 3-amino-4-phenyl-1, 2,5-oxadiazole, differ with respect to their fragment composition and abundance in such a way that isomers can easily be distinguished and determined. The most important fragmentation patterns giving characteristic ions for structure identification are discussed.

Existence, uniqueness and some in variance properties of stationary distributions for general single server queues

Abstract: This note contains a modified proof of the theorem of Loynes [8] about the existence of a uniquely determined statistical equilibrium for single server system with an arbitrary stationary and ergodic distribution of the initial data and the traffic intensity β <1. The used approach permits a generalization of the theorem of LOYNES for arbitrary work conserving priority systems and waiting systems with arbitrary queueing discipline. On this basis stationary distributions of system parameters in different observation points are introduced. With the help of results from the theory of random point processes some well-known relations between these distributions are generalized respectively new proofs we given. Further some new relations are given.

Theory of Resonance Raman Scattering near Critical Points

Abstract: The resonance behaviour of the Raman scattering cross section for allowed one-phonon scattering is investigated as a function of incident frequency. Both the cases of uncorrelated and of interacting electron-hole pairs as intermediate states are considered. The scattering amplitude is calculated for uncorrelated pairs for all types of critical points of the interband electronic energy. The dispersion of the scattering cross section is shown to be independent of the type of the critical point. The effect of Coulomb electron-hole interaction is studied for M0 and M3s critical points. As a result of this interaction the resonance enhancement is much more stronger and the scattering cross section as a function of incident frequency shows more pronounced structures as compared to the case of uncorrelated pairs. Es wird das Resonanzverhalten der erlaubten Raman-Streuung erster Ordnung in Abhangigkeit von der eingestrahlten Frequenz untersucht. Es werden sowohl der Fall unkorrelierter als auch der Fall wechselwirkender Elektron-Loch-Paare in den Zwischenzustanden behandelt. Fur unkorrelierte Paare wird der Streuquerschnitt fur alle Typen von kritischen Punkten der elektronischen Interbandenergie berechnet. Die Dispersion des Streuquerschnittes hangt nicht vom Typ des kritischen Punktes ab. Der Einflus der Elektron-Loch Wechselwirkung wird fur den Fall der kritischen Punkte M0 und M3 behandelt. Der Streuquerschnitt als Funktion der eingestrahlten Frequenz ist groser und weist ausgepragtere Strukturen auf als im Fall unkorrelierter Elektron-Loch-Paare.