Showing papers by "University of Bonn published in 1993"

Distortion invariant object recognition in the dynamic link architecture

Abstract: An object recognition system based on the dynamic link architecture, an extension to classical artificial neural networks (ANNs), is presented. The dynamic link architecture exploits correlations in the fine-scale temporal structure of cellular signals to group neurons dynamically into higher-order entities. These entities represent a rich structure and can code for high-level objects. To demonstrate the capabilities of the dynamic link architecture, a program was implemented that can recognize human faces and other objects from video images. Memorized objects are represented by sparse graphs, whose vertices are labeled by a multiresolution description in terms of a local power spectrum, and whose edges are labeled by geometrical distance vectors. Object recognition can be formulated as elastic graph matching, which is performed here by stochastic optimization of a matching cost function. The implementation on a transputer network achieved recognition of human faces and office objects from gray-level camera images. The performance of the program is evaluated by a statistical analysis of recognition results from a portrait gallery comprising images of 87 persons. >

Computing Discrete Minimal Surfaces and Their Conjugates

Abstract: We present a new algorithm to compute stable discrete minimal surfaces bounded by a number of fixed or free boundary curves in R 3, S 3 and H 3. The algorithm makes no restr iction on the genus and can handl e singular triangulations. Additionally, we present an algorithm that, starting from a discrete harmonic map, gives a conjugate harmonic map. This can be applied to the identity map on a minimal surface to produce its conjugate minimal surface, a procedure that often yields unstable solutions to a free boundary value problem for minimal surfaces. Symmetry properties of boundary curves are respected during conjugation.

Peptidomimetics for Receptor Ligands—Discovery, Development, and Medical Perspectives

Abstract: Peptides, as neurotransmitters, neuromodulators, and hormones, influence a multitude of physiological processes by signal transduction mediated through receptors. In addition, during the last 20 years their role in the appearance or maintenance of various diseases could be unequivocally proven. Agents that can imitate or block the biological functions of bioactive peptides (agonists or antagonists, respectively) can be considered as aids for the investigation of peptidergic systems and also as therapeutic agents. The suitability of bioactive peptides as therapeutic agents was examined after preliminary pharmacological experiments. It was thereby shown that based on their pharmacological properties, for example degradation by peptidases or poor bioavailability, they could be employed as drugs in only a few cases. To solve this problem peptidomimetics, compounds that act as substitutes for peptides in their interaction with receptors, have been synthesized. In comparison with native peptides they show higher metabolic stability, better bioavailability, and longer duration of action. Peptidomimetics with antagonistic properties were also developed within the range of these investigations. As a result, new types of treatment and therapy for a series of diseases are possible. Although peptidomimetics have been developed largely by empirical methods (e.g. modification of native peptides, optimization of lead structures), methods for rational design based on investigations into the structure of peptidepeptide receptor complexes and studies of conformation energies, among others, are gradually being established.

Real Killing spinors and holonomy

Abstract: We give a description of all complete simply connected Riemannian manifolds carrying real Killing spinors. Furthermore, we present a construction method for manifolds with the exceptional holonomy groupsG 2 and Spin(7).

Modification of cortical stimulation for motor evoked potentials under general anesthesia: technical description.

Abstract: This pilot study presents a possible modification of direct cortical electrical stimulation technique for the recording of motor evoked potentials under general anesthesia. The exposed primary motor cortex was stimulated by a short train of anodal rectangular pulses at high frequency (300-500 Hz), while the compound muscle action potentials were recorded from the forearm and hand muscles. When compared with the traditional way of eliciting movement of the extremities by applying a train of pulses at lower frequency (50-60 Hz), muscle responses were obtainable at an intensity of much lower charge. It is suggested that this stimulation achieves a repetitive activation of the corticomotoneuronal tract. Responses could be continuously recorded throughout surgery and seemed to respond to surgical manipulation affecting the motor pathways. This technique seems to be applicable for intraoperative monitoring of motor pathways but requires further optimization of stimulation and recording parameters before wider clinical applications are possible.

The role of carbohydrate storage and redistribution in the source-sink relations of wheat and barley during grain filling — a review

Abstract: SUMMARY Two types of source contribute photosynthate for grain filling in wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.), current photosynthate transferred directly to the grain and photosynthate redistributed from reserve pools in vegetative tissues. Reserve pools provide the substrate needed to maintain transport and the supply of assimilate to grains during the dark period of the diurnal cycle and during the latter part of grain filling, when the photosynthetic apparatus is senescing and the rate of dry matter accumulation of grains exceeds the rate of dry matter accumulation of the total crop. In addition reserve pools provide a means by which the current rates of photosynthate production and of photosynthate use in grain filling are allowed to proceed (at least in part) independently from each other. There is evidence that all photosynthetic organs (leaves, glumes and exposed portion of the peduncle) contain one or more diurnal carbohydrate storage pools. Diurnal storage of sucrose seems to be much more important than the transient storage of starch. There is little evidence for fructan pools serving a role as a net source of carbon during the dark period of the diurnal cycle. However, fructan is the most important longer-term reserve carbohydrate of vegetative tissues. Fructan accumulation occurs mainly in the extended internodes and leaf sheaths and usually terminates within three weeks following anthesis, after which fructan is gradually lost until grain maturity. The accumulation and loss of fructan are greatly influenced by environmental conditions and treatments that alter the longer-term balance between photosynthate production by the plant and photosynthate use in grain filling. Observations are consistent with the view that fructan accumulation in expanded vegetative tissue is not competitive with grain filling, but the fructan pools accept surplus photosynthate during periods of low demand by grains and provide photosynthate during longer-term deficits in current photosynthate production. Even under optimal conditions for photosynthesis it is likely that half or more of the photosynthate in mature grains is temporarily deposited in one or more reserve pools before being transferred to the grain. Neither the efficiency of reserve utilization in grain filling nor its potential variability in different genotypes and environments are known. Also, very little is known about the mechanisms that control the partitioning of photosynthate between the grain and reserve pools and the allocation to different types of reserve pools. Future progress in the understanding of photosynthesis-yield relationships will likely depend to a great extent on improved knowledge of the controls that govern photosynthate deposition and redistribution in the different pools of reserve carbohydrate.

Comparison of intestinal absorption of cholesterol with different plant sterols in man

Abstract: . Intestinal absorption of cholesterol, campes-terol, campestanol, stigmasterol and sitosterol were measured in 10 healthy subjects by an intestinal perfusion technique over a 50 cm segment of the upper jejunum using sitostanol as non-absorbable marker. Cholesterol absorption was highest and averaged 33%, whereas the absorption rate of sitosterol averaged 4.2% and of stigmasterol 4.8%. Higher absorption rates were found for campesterol (9.6%). Canipestanol, the 5a saturated derivative of campesterol, showed the highest absorption rate (12.5%) of all plant sterols. A positive correlation between the absorption rate of cholesterol and campesterol was established. In addition, there was a negative correlation between the ratio of sitosterol to cholesterol and the mass of cholesterol absorption. These results are in agreement with previous observations in animal studies, namely, that increasing the length of the side-chain of cholesterol decreases the absorbability of the sterol. Surprisingly, campestanol, the 5α saturated derivate of campesterol, was shown to have higher absorbability compared with its unsaturated compound. This finding is in contrast to previous assumptions, that hydrogenisa-tion of the nucleus double bond of a sterol causes a decrease of absorbability, as has been demonstrated for cholesterol/cholestanol and sitosterol/sitostanol.

Subsets of Glioblastoma Multiforme Defined by Molecular Genetic Analysis

Abstract: Glioblastoma multiforme is a clinically and histologically heterogeneous lesion; however, to date, it has not been possible to subdivide glioblastomas on a clinical, histopathological or biological basis. Previous studies have demonstrated that loss of portions of chromosomes 10 and 17 and amplification of the epidermal growth factor receptor (EGFR) gene are the most frequent genetic alterations in glioblastoma. We therefore examined 74 glioblastomas from 67 patients for loss of heterozygosity on chromosomes 10 and 17, and for amplification of the epidermal growth factor receptor gene, to determine whether glioblastomas can be subtyped on a genetic basis. Using Southern blot analysis we were able to detect different patterns of genomic alterations. Eighteen of 67 informative patients were characterized by a loss of heterozygosity on the short arm of chromosome 17 in the tumor tissue. Forty-five of 64 informative patients showed a loss of heterozygosity on chromosome 10. Amplification of the epidermal growth factor receptor gene was noted in 25 of 67 patients and was restricted to those glioblastomas that had lost portions of chromosome 10. Epidermal growth factor receptor gene amplification occurred significantly more often in patients without chromosome 17p loss than in patients with chromosome 17p loss (p = 0.01). In addition, those glioblastomas with a loss of chromosome 17p occurred in patients significantly younger than those with glioblastomas characterized by EGFR gene amplification (p = 0.001). These data emphasize the genetic heterogeneity of glioblastoma and suggest the division of glioblastoma into genetic subsets.

Histamine inhibits dopamine release in the mouse striatum via presynaptic H3 receptors.

Abstract: In superfused mouse striatal slices preincubated with [3H] dopamine 25 nmol/l, the electrically (3 Hz) evoked tritium overflow was inhibited by histamine 10 μmol/l by 18%. The degree of inhibition was increased to 38% by haloperidol but not affected by (1) atropine, (2) reducing the stimulation frequency to 0.3 Hz or (3) increasing the concentration of [3H]dopamine (used for preincubation) to 100 nmol/l. The effect of histamine was mimicked by the H3 agonist R-(−)-α-methylhistamine; it was not affected by the H1 antagonist dimetindene and the H2 antagonist ranitidine but abolished by the H3 antagonist thioperamide. Tritium overflow evoked by Ca2+ ions (introduced into Ca2+free, K+-rich medium containing tetrodotoxin) was not affected by histamine 10 μmol/l in the absence, but inhibited (by 30%) in the presence of haloperidol; the effect of histamine was abolished by thioperamide. In conclusion, the dopaminergic nerve terminals in the mouse striatum are endowed with presynaptic H3 receptors. Simultaneous blockade of dopamine autoreceptors increases the extent of the H3 receptor-mediated inhibition of dopamine release.

Compatible solutes of halophilic eubacteria : molecular principles, water-solute interaction, stress protection

Abstract: Compatible solutes are best described as organic osmolytes responsible for osmotic balance and at the same time compatible with the cells' metabolism. A comprehensive survey (using HPLC and NMR methods) on halophilic/halotolerant eubacteria has revealed the full diversity of compatible solutes employed in nature. Molecular principles derived from the spectrum of compounds found in the bacterial world may be summarized as follows. Compatible solutes are polar, highly soluble molecules and uncharged at physiological pH. With the exception of proline (a proteinogenic amino acid) they are characterized as amino acid derivatives of the following types: betaines, ectoines, N-acetylated diamino acids and N-derivatized carboxamides of glutamine. Using nearinfrared spectroscopy we have also been able to demonstrate that compatible solutes are strong water-structure formers and as such probably excluded from the hydration shell of proteins. This “preferential exclusion” probably explains their function as effective stabilizers of the hydration shell of native proteins (protection against heating freezing and drying). Hence these typical products of halophilic eubacteria have a considerable potential as stabilizing/protecting agents on both molecular and whole-cell level. Thorough understanding of common structural principles and fundamental water-solute interactions will ultimately enable us to design novel highly efficient stress protectants and stabilizers of biomolecules.

Factorial validity of the 20-item Toronto Alexithymia Scale

Abstract: The 20‐item Toronto Alexithymia Scale (TAS‐20) was developed in previous research to measure a general dimension of alexithymia with three inter correlated factors. These three factors reflect dist...

Experimental results on ultimatum games with incomplete information

Abstract: This paper is about experiments on two versions of ultimatum games with incomplete information, called the offer game and the demand game. We apply the strategy method, that is, each subject had to design a complete strategy in advance instead of reacting spontaneously to a situation which occurs in the game. Game theory predicts very similar outcomes for the offer and the demand games. Our experiments, however, show significant differences in behavior between both games. Using the strategy method, allows us to explore the motivations leading to those differences. Since each subject played the same version of the game eight rounds against changing anonymous opponents we can also study subjects' learning behavior. We propose a theory of boundedly rational behavior, called the “anticipation philosophy”, which is well supported by the experimental data.

Application of transcranial magnetic stimulation in treatment of drug‐resistant major depression—a report of two cases

Abstract: We report the cases of two drug-resistant major depressed psychotic patients, who were treated with 10 sessions of transcranial magnetic stimulations (TMS) and afterwards with 10 sessions of electroconvulsive therapy (ECT) without changing the concomitant neuroleptic and antidepressive medication. TMS did not exert a therapeutic effect in one patient and only a slight one in the other. However, there was a clear beneficial effect for ECT in the patient not responding to TMS and a slight therapeutic effect in the other. In summary, there was no clear-cut evidence for effectiveness of TMS as a treatment for patients with psychotic, therapy resistant depression. However, since there was a slight therapeutic effect of TMS in one patient it seems worthwhile to explore its therapeutic efficacy in a larger group of depressed patients. KEY wow-Transcranial magnetic stimulation, electroconvulsive therapy, drug-resistant major depression.

Gap junction protein connexin40 is preferentially expressed in vascular endothelium and conductive bundles of rat myocardium and is increased under hypertensive conditions.

Abstract: Gap junction channels consisting of connexin protein mediate electrical coupling between cardiac cells. Expression of two connexins, connexin40 (Cx40) and connexin43 (Cx43), has been studied in ventricular myocytes from normal and hypertensive rats. Polyclonal affinity-purified rabbit antibodies to Cx43 and Cx40 have been used for immunohistochemical analysis on frozen sections from rat heart. These studies revealed coexpression of Cx43 and Cx40 in ventricular myocytes. In addition, Cx40 is preferentially expressed in three distinct regions: first, in the endothelial layer of the heart blood vessels but not in the smooth muscle layer of the arteries; second, in the ventricular conductive myocardium, particularly in the atrioventricular bundle and bundle branches, where Cx43 is not observed; and third, in the myocyte layers close to the ventricular cavities. These results suggest that Cx40 is preferentially expressed in the fast conducting areas of myocardial tissue. Expression of both Cx40 and Cx43 was also found in immunoblots from normal and hypertensive rat myocardiocytes. Under hypertensive conditions (ie, in spontaneous hypertensive rats and in transgenic rats that exhibit hypertension due to expression of an exogenous renin gene), we found a 3.1-fold increase in Cx40 expression, compared with normal myocardium. Furthermore, we detected a 3.3-fold decrease in Cx43 protein level in transgenic hypertensive rats. The coexpression of Cx40 and Cx43 proteins in rat myocytes, their spatial distribution, and the increased amount of Cx40 protein during cardiac hypertrophy suggest that Cx40 may be involved in mediating fast conduction under normal and pathological conditions. The increased expression of Cx40 in hypertrophic heart may be a compensatory mechanism to increase conduction velocity.

Learning read-once formulas with queries

Abstract: A read-once formula is a Boolean formula in which each variable occurs, at most, once. Such formulas are also called m-formulas or Boolean trees. This paper treats the problem of exactly identifying an unknown read-once formula using specific kinds of queries.The main results are a polynomial-time algorithm for exact identification of monotone read-once formulas using only membership queries, and a polynomial-time algorithm for exact identification of general read-once formulas using equivalence and membership queries (a protocol based on the notion of a minimally adequate teacher [1]). The results of the authors improve on Valiant's previous results for read-once formulas [26]. It is also shown, that no polynomial-time algorithm using only membership queries or only equivalence queries can exactly identify all read-once formulas.

Teichoic acid and lipoteichoic acid of Streptococcus pneumoniae possess identical chain structures

Abstract: Teichoic acid (C polysaccharide) was extracted and purified from Streptococcus pneumoniae R6 with standard procedures except that lipoteichoic acid was extracted first. The dephosphorylated repeating unit was isolated after hydrolysis with 48% (by mass) HF, the bis(phosphocholine)-containing repeating unit was isolated by alkali hydrolysis, anion-exchange chromatography and phosphomonoester cleavage. On the basis of compositional analysis, fast-atom-bombardment mass spectrometry and NMR spectroscopy the following structure is proposed: [formula: see text] where AATGal is 2-acetamido-4-amino-2,4,6-trideoxy-D-galactose. The repeating units are linked to each other by phosphodiester bonds between O5 of the ribitol and O6 of the glucopyranosyl residue of adjacent units. This chain structure is identical with that previously established for pneumococcal lipoteichoic acid [Behr, T., Fischer, W., Peter-Katalinic, J. & Egge, H. (1992) Eur. J. Biochem. 207, 1063-1075]. This represents a unique situation because in other Gram-positive bacteria teichoic and lipoteichoic acids are structurally unrelated.

Average Optimality in Dynamic Programming with General State Space

Abstract: A Markovian decision model with general state space, compact action space, and the average cost as criterion is considered. The existence of an optimal policy is shown via an optimality inequality in terms of the minimal average cost g and a relative value function w. The existence of some w is usually shown via relative compactness in a space of real-valued functions on the state space. Here it shall be shown that one can instead do with pointwise relative compactness in the set of real numbers if one makes use of a generalized lower limit of functions. An application to an inventory model is given.

Surgical Pathology of Temporal Lobe Epilepsy. Experience with 216 Cases

Abstract: The surgical treatment of chronic epilepsies is increasing rapidly. Here we report the histopathologic findings in 216 consecutive surgical specimens of patients with chronic pharmacoresistant temporal lobe epilepsy. In 75 cases (34.7%) there were tumors, all but two of which were of low histopathological grade (WHO grade I or II). The most common tumors were gangliogliomas (34 cases), pilocytic astrocytomas (17 cases), oligodendrogliomas (9 cases), fibrillary astrocytomas (6 cases), and dysembryoplastic neuroepithelial tumors (6 cases). There were 51 cases with non-neoplastic focal lesions and an additional 13 cases with tumors and non-neoplastic focal lesions within the same specimen. The most frequent non-neoplastic focal lesions were microscopic glioneuronal hamartias (32 cases), glioneuronal hamartomas (7 cases), and vascular malformations (13 cases). The hippocampal formation was structurally well preserved in 71 specimens. In 51 of these (71.8%) there was Ammon's horn sclerosis. Presurgical placement of depth electrodes was invariably associated with circumscribed defects of the brain parenchyma. The implantation of subdural electrodes was sometimes followed by chronic inflammatory changes of the leptomeninges. Our findings indicate that in the majority of patients with medically intractable temporal lobe epilepsy there are significant histopathologic findings, many of which are only rarely encountered otherwise.

Singular perturbations as a selection criterion for periodic minimizing sequences

Abstract: Minimizers of functionals like $$\int_0^1 { \in ^2 u^2 _{xx} } + (u_x^2 - 1)^2 + u^2 dx$$ subject to periodic (or Dirichlet) boundary conditions are investigated. While for e=0 the infimum is not attained it is shown that for sufficiently small e > 0, all minimizers are periodic with period ∼ e1/3. Connections with solid-solid phase transformations are indicated.

Surgical pathology of chronic epileptic seizure disorders.

Abstract: The surgical treatment of chronic epilepsies is increasing rapidly and involves neuropathologists in the care of patients with chronic and medically intractable seizure disorders. Herein we review the histopathologic findings in 279 consecutive surgical specimens of patients with chronic pharmaco-resistant epileptic disorders. Aspects that are relevant to the diagnostic surgical pathologist such as the terminology of developmental lesions and Amnion's horn sclerosis are discussed. In 87 cases (31.2%), there were tumors in which all but two were of low histopathological grade (WHO grade I or grade II). The most common tumors were gan-gliogliomas, pilocytic astrocytomas, oligodendrogliomas, fibrillary astrocytomas and dysembryo-plastic neuroepithelial tumors. Among the most frequent non-neoplastic focal lesions, microscopic glioneuronal hamartias, circumscribed vascular malformations, glioneuronal hamartomas and porencephalic defects were most frequent. The hippocampal formation was structurally well preserved in 71 specimens of patients with temporal lobe epilepsy. In 51 of these (71.8%) cases. Amnion's horn sclerosis was present. The findings suggest that the structural lesions observed in the great majority of the specimens are closely related to the pathogenesis of intractable seizures.

A Microeconomic Approach to Diffusion Models For Stock Prices

Abstract: This paper studies a class of diffusion models for stock prices derived by a microeconomic approach. We consider discrete-time processes resulting from a market equilibrium and then apply an invariance principle to obtain a continuous-time model. the resulting process is an Ornstein-Uhlenbeck process in a random environment, and we analyze its qualitative behavior. In particular, we provide simple criteria for the stability or instability of the corresponding stock price model, and we give explicit formulae for the invariant distributions in the recurrent case.