Showing papers by "Humboldt University of Berlin published in 1985"

Intervertebral disc prosthesis

Abstract: An intervertebral disc prosthesis has two cover plates and a prosthesis core which is connected to one of the cover plates by of connection profiles on one of the cover plates which are undercut in a complementary manner and include at least one pair of profile sections which are symmetrical with respect to the AP (anterior-posterior) direction of the prosthesis in its implanted position and are arranged at an angle to one another.

An estimate on the effect of point mutation and natural selection on the rate of amino acid replacement in proteins

Abstract: We outline a method for estimating quantitatively the influence of point mutations and selection on the frequencies of codons and amino acids. We show how the mutation rate, i.e., the rate of amino acid replacement due to point mutation, can be affected by the codon usage as well as by the rates of the involved base exchanges. A comparison of the mutation rates calculated from reliable values of codon usage and base exchange probabilities with those that would be expected on the basis of chance reveals a notable suppression of replacements leading to tryptophan, glutamate, lysine, and methionine, and particularly of those leading to the termination codons.

Stability Properties of Infima and Optimal Solutions of Parametric Optimization Problems

Abstract: In the analysis of parametric optimization problems it is of great interest to explore certain stability properties of the optimal value function and of the optimal set mapping (or some selection function of this mapping): continuity, smoothness, directional differentiability, Lipschitz continuity and the like. For a survey of this field we refer to comprehensive treatments of various aspects of such questions in the recent works of Fiacco (1983), Bank et al. (1982) and Rockafellar (1982).

On Probabilistic Time and Space

Abstract: We prove that inequalities of arithmetic expressions over the ring of n×n matrices can be decided by probabilistic Turing machines working simultaneously within 0(logn) space and polynomial time. As a corollary we obtain: PrSPACE(logn)=PrTISP(n0(1),logn), which solves a problem that has been open for a long time.

Dielectric Screening, Polar Phonons, and Longitudinal Electronic Excitations of Quantum Well Double Heterostructures Application to Light Scattering from Charge Density Fluctuations†

Abstract: The screened Coulomb potential and the inverse dielectric function of a quantum-well double heterostructure (DHS) are expressed in terms of bulk dielectric functions. The spatial dispersion is fully taken into account. The polar LO-phonon modes, longitudinal electronic modes, and coupled electron-phonon modes of a DHS are derived from the poles of the inverse dielectric function. Emphasis is paid to phonon slab modes. The close relation between the screened Coulomb potential and the density-density correlation function is used to calculate the Raman cross section for scattering from charge density fluctuations. In typical cases slab modes are essential for Raman spectra of DHSs and superlattices. Das abgeschirmte Coulomb-Potential und die inverse Dielektrizitatsfunktion einer Quanten-Well-Doppelheterostruktur (DHS) werden durch Volumen-Dielektrizitatsfunktionen ausgedruckt. Die polaren LO-Phonon-Moden, die longitudinalen elektronischen Moden und die gekoppelten Elektron-Phonon-Moden einer DHS werden als Pole der inversen Dielektrizitatsfunktion berechnet. Besondere Beachtung wird den Schicht-Moden geschenkt. Die enge Beziehung zwischen dem abgeschirmten Coulomb-Potential und der Dichte-Dichte-Korrelationsfunktion wird benutzt, um den Raman-Querschnitt fur die Sptreuung an Ladungsdichtefluktuationen zu berechnen. In typischen Fallen ist das Raman-Spektrum von DHS und Supergittern wesentlich durch Schichtmoden mit-bestimmt.

On the Lipschitz behavior of optimal solutions in parametric problems of quadratic optimization and linear complementarity

Abstract: We consider parametric optimization problems of the type min where Г is a polyhedral multifunction. It is shown that, under natural assumptions, the optimal set mapping and the infimum function of such a problem are Lipschitzian in some sense. The results are applied to a (generally non-convex) quadratic optimization problem parameterized in the linear part of the objective function and in the right-hand side of the constraints. In out studies we essentially use arguments from linear parametric optimization and S.M. Robinson's theorem on the upper Lipschitz continuity of polyhedral multifunctions.

The influence of haematoporphyrin derivative and visible light on murine skin graft survival, epidermal Langerhans cells and stimulation of the allogeneic mixed leucocyte reaction.

Abstract: The influence of combined photochemical treatment with a haematoporphyrin derivative and visible light on antigen-presenting cells was evaluated. Treatment of murine skin grafts with this procedure prolonged their subsequent survival on allogeneic recipients. The haematoporphyrin derivative and light decreased the ATPase activity of epidermal Langerhans cells in murine skin. When stimulator cells in a human allogeneic mixed leucocyte reaction were treated with the haemaioporphyrin derivative and light, they lost their stimulatory capacity. It is proposed that the haemaioporphyrin derivative and visible lighl interfere, on analogy with ultraviolet radiation, with the function of antigen-presenting cells.

The hepatocyte. Development, differentiation, and ageing

Abstract: 1. Being the main organ of the metabolic system, the liver, whose function undergoes numerous changes in the course of life, is an important object of investigation. For this reason research into the structure and the associated functions of the hepatocyte, which plays a central role in the liver, is of special significance. 2. The study was carried out on male rats from birth up to the 27th month of life. Data obtained through similar experiments on female rats are available. The weight of the liver increases from 0.274 g at birth to 23.2 g at the end of the 27th month of life. The relative liver weight in relation to 100 g body weight diminishes from 7.7-5.3% in the prenatal phase to 4.5-2.6% in the first days of life, and increases again to 5.5% in the 1st and 2nd months of life. This is followed by a repeated drop in the relative liver weight to as low as 3.2 per cent. 3. The volume of the extrahepatocellular space diminishes during foetal development. Haematopoietic cells decrease from 63% of the liver volume on the 15th day to 37% on the 18th day of gestation. Kupffer cells account for less than 3% of the total liver volume in foetal and adult rats. Their number in foetal livers accounts for 4% of the total number of cells and in adult livers for 37%. The relative increase by a factor of about 10 is accompanied by an increase in the total volume by 130 per cent. 4. The volume density of the extrahepatocellular space diminishes from 0.403 at birth to 0.134 after 6 months. Generally, the extrahepatocytic space remains unchanged from the 1st month onwards, accounting for 10-15% of the total volume. 5. The volume density of hepatocytes is 0.60 on the 15th foetal day, increasing to 0.85 till the 21st foetal day. After birth till the end of the period of investigation the volume density varies between 0.78 and 0.94. At birth the volume of hepatocytes is 5775.9 microns 3. It increases to 10,000 microns 3 up to the 2nd month. It diminishes again to 7388.8 microns 3 till the 24th and 27th months. 6. Initially, the volume of hepatocytes drops to below the volume at birth, followed by an increase of 99% compared with the value at birth till the 6th month. After that the volume diminishes again to 127.9% of the volume at birth.(ABSTRACT TRUNCATED AT 400 WORDS)

On initial value problems in differential-algebraic equations and their numerical treatment

Abstract: For more than ten years numerical integration methods for initial value problems in differential-algebraic equations (DAE's) have been used — with different success. However, the necessary analysis of these methods as well as of the DAE's themselves is only in its beginning. This work does not aim at providing new methods for DAE's, but at analyzing methods known from the literature and software, respectively. A series of results related to the stability, consistency and Liapunov stability of various methods is presented. In particular, a trapezoidal rule as well as certain multistep methods may become unstable, so that codes using these methods will fail in general. The positive results may stimulate the practical use of higher order methods instead of the BDF's for suitable classes of DAE's.

Effects of disciplines and countries on citation habits. An analysis of empirical papers in behavioural sciences

Abstract: The theoretical introductions in empirical journal articles have been analyzed looking for factors determining citation habits. Own-country-biases and English-American predominance in citations were not regularly found. Preferred language of the cited publications and absolute citation frequencies were dependent upon both the disciplines and the countries where the journals are published. However, relative citation frequencies (citations related to the length of the text available) have been found to be rather constant across countries (within psychology and psychiatry, respectively) which indicates no such dependence.

Haptoglobin subtypes in Berlin, GDR. A simple procedure for haptoglobin purification and subtyping.

Abstract: Sera were obtained from 1,275 blood donors in Berlin, probands involved in paternity tests, and from 119 families with 235 children; the sera were subtyped by isoelectric focusing, following preparation and reductive molecular cleavage of haptoglobin. In this paper, an uninvolved preparation technique is described for routine testing. Allelic frequencies are: Hp *1F=0.1471; *1S=0.2502; *2FF=0.0020; *2FS=0.5753; *2SS=0.0251. Only one deviation from autosomal codominant inheritance was recorded in the family examinations, with illegitimacy considered possible. In the region of Berlin, the changes of ruling out uninvolved individuals in paternity suits have gone up from 18% (conventional technique recording two frequent alleles) to 33% (subtyping).

Two-Dimensional Electron Gas in the n-Inversion Layer of p-Type InSb Bicrystals

Abstract: The galvanomagnetic properties of conduction electrons in n-type inversion layers adjacent to the grain boundary in p-type InSb bicrystals in magnetic fields up to 18 T and temperatures down to 2 K are investigated. The observed quantum oscillations of the magnetoresistivity result from a superposition of the Shubnikov-de Haas effect in two occupied subbands. The electron densities of subbands nsi (ns1 = 3.5 × 1011 cm−2; nso = 1.1 × 1012 cm−2) and the effective cyclotron mass of the subbands mci (mc1 = (0.016 ± 0.004) m0; mco = (0.026 ± 0.003) m0) are evaluated. Besides the Shubnikov-de Haas oscillations in high magnetic fields (B > 5 T) the Hall resistivity shows the characteristic features of the quantized Hall plateaus in finite regions of the magnetic field B. Simultaneously the diagonal resistivity ϱxx drops to a minimum. Other characteristic features of a two-dimensional electron gas confined in the symmetrical potential well of the grain boundary are obtained. Es werden die Magnetotransporteigenschaften der Leitungselektronen in n-Inversionsschichten von Korngrenzen in p-Typ InSb-Bikristallen in Magnetfeldern bis 18 T und Temperaturen bis 2 K untersucht. Die beobachteten Quantenoszillationen des Magnetowiderstandes resultieren aus der Uberlagerung von SdH-Oszillationen in zwei besetzten Subbandern. Die Elektronenkonzentration in diesen Subbandern nsi (ns1 = 3,5 × 1011 cm−2; nso = 1,1 × 1012 cm−2) und die entsprechenden effektiven Zyklotronmassen mci (mc1 = (0,016 ± 0,004) m0; mco = (0,26 ± 0.003) m0) werden ermittelt. Neben den SdH-Oszillationen weist die Feldabhangigkeit des Hallwiderstandes in hohen Magnetfeldern (B > 5 T) eine fur den quantisierten Halleffekt charakteristische stufenformige Struktur auf. Bei Feldwerten, bei der der Hallwiderstand Plateaus aufweist, zeigt die Diagonalkomponente des elektrischen Widerstandes ϱxx scharfe Minima. Es werden weitere charakteristische Eigenschaften eines zweidimensionalen Elektronengases im symmetrischen Potentialtopf der Korngrenze gefunden.

Yang-Mills equations on the two-dimensional sphere

Abstract: We construct a 1:1 correspondence between the equivalence classes of Yang-Mills fields over S2 and the conjugacy classes of closed geodesies of the structure group. Furthermore, we give an explicit isolation theorem for any Yang-Mills field over S2.

Metastability and Depinning Threshold in the Random Field Ising Model

Abstract: A unified description of the depinning threshold Ec for domain walls in the random field Ising model is given. The coherence length Rc ∼ E of the metastable state is proportional to h−vh, where h is the random field amplitude. For broad walls, the results interpolate between recent findings of Bruinsma and Aeppli (vH = 4/(5 – d)) valid at temperatures T ≪ Th(t) and those of Villain (vH = 2) for Th(t) Th(t), Th(t) ∼ h2(2 – d)/(3 – d)/In t and d ≦ 3. For d 3 an exponential dependence is expected of Rc on h−2. Vacancies are found to be decisive for wall pinning in diluted antiferromagnets in small external fields. Es wird eine vereinheitlichte Beschreibung der Depinningschwelle Ec fur Domanenwande im Ising-Modell mit statistischem Feld gegeben. Die Koharenzlange Rc ∼ E des metastabilen Zustands ist proportional zu h−vH, wobei h die Amplitude des statistischen Feldes ist. Fur breite Wande interpolieren die Ergebnisse zwischen den kurzlich von Bruinsma und Aeppli gefundenen Ergebnissen (vH = 4/(5 – d)), die bei Temperaturen T Th(t) gefunden, Th(t) ∼ h2(2 – d)/(3 – d)/In t und d ≦ 3. Fur d 3 wird eine exponentielle Abhangigkeit von Rc von h−2 erwartet. Es wird gefunden, das die Leerstellen fur Wandpinning in verdunnten Antiferromagneten in kleinen auseren Feldern entscheidend sind.