Showing papers by "Radboud University Nijmegen published in 1980"

SAM: A theory of probabilistic search in associative memory.

Abstract: Publisher Summary This chapter discusses probabilistic search of associative memory. The chapter introduces a theory of retrieval from long-term memory and presents a number of applications to data from paradigms involving free recall, categorized free recall, and paired-associate recall. Long-term store (LTS) is held to be a richly interconnected network, with numerous levels, stratifications, categories, and trees, containing varieties of relationships, schemata, frames, and associations. The retrieval system is noisy and inherently probabilistic; for a given memory structure and set of probe cues, the image selected from memory is a random variable. The retrieval process concern sampling and recovery. The relatively small set of images with non-negligible sampling probabilities is denoted as the “search-set.” When an image is sampled, its features will tend to become activated. There are subject controlled strategies in the theory, such as search termination rules, and choice of cues at various stages of the search.

Point-contact spectroscopy in metals

Abstract: Point contacts between normal metals at low temperatures show very interesting non-linear phenomena in the current-voltage characteristics. The observed deviations from Ohm's law in metallic constrictions can be used for an energy-resolved spectral analysis of the interaction mechanisms of the conduction electrons with elementary excitations in a metal. A review is given on the theoretical and experimental work dealing with this spectroscopic method. A theoretical analysis, involving an iterative solution of the full non-linear Boltzmann equation for the transport problem of a current through a point-contact geometry, is able to show that the observed second-derivative signal is proportional to Eliashberg's form of the electron-phonon interaction alpha 2F( omega ), with a slight modification due to a transport efficiency function. Non-equilibrium effects of the phonon system are discussed in relation to the observed background signal on which the alpha 2F signal is thought to be superimposed. The theory can easily be extended to other scattering mechanisms than the electron-phonon interaction, and some experiments show that the interactions of conduction electrons with magnons and paramagnetic impurities can be detected using point contacts between ferromagnetic metals and between magnetically dilute alloys.

Ab initio studies of the interactions in Van der Waals molecules

Abstract: 2 Mechanisms of Van der Waals Interactions; Distance and Orientational Dependence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.1 Distance and orientational dependence 4 2.2 Model potentials 6 2.3 Contributions to the interaction energy 8 2.3.1 Electrostat ic; long range mult ipole interactions, penetrat ion effects 8 2.3.2 Induct ion, dispersion; muit ipole interactions, penetra t ion effects 10 2.3.3 Exchange . . . . . . . . . . . . . . . . . . . . . . . . . 12 2.4 Interact ions from supermolecule calculations . . . . . . . . . . . . 13 2.5 Addi t iv i ty . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Spectro-temporal receptive fields of auditory neurons in the grassfrog

Abstract: In order to investigate the spectro-temporal selectivity of single auditory neurons in the auditory midbrain of the grassfrog under different stimulus conditions a stimulus ensemble consisting of tonal and natural stimuli has been constructed. The selection of characteristics of the tonal stimuli was inspired by the general properties of vocalizations of the male grassfrog. The natural stimuli contained a variety of vocalizations of various anuran species and other sounds, taken from the natural environment of the grassfrog (i.e. its biotope). The main point of interest in the present paper is the spectro-temporal characterization of acoustic stimuli. For narrowband signals a parametric description in terms of instantaneous amplitude and instantaneous frequency appears to be attractive. A more general approach, also covering wideband signals, is a description by means of the dynamic power spectrum. Both types of analysis are described. Mathematically they can be based on the theory of analytic signals. The basic principles of this theory are summarized.

Multipole moments, polarizabilities and anisotropic long range interaction coefficients for N2

Abstract: This paper contains results for the permanent multipoles, the multipole polarizabilities and the related anisotropic long range interaction coefficients C 5 to C 10 (complete) for the nitrogen molecule. The electrostatic, induction and dispersion interaction coefficients have been calculated using ab initio SCF wavefunctions; better estimates for the dispersion terms have been obtained by an approximate procedure, which uses the accurate (semi-) empirical data available for C 6 and the dipole polarizability, in combination with the ab initio results. The pure quadrupole-quadrupole anisotropy appears to be substantially modified by the dispersion anisotropy and, to a smaller extent, by the higher multipole electrostatic interactions; the induction energy can be neglected. The dispersion anisotropy factors γ8 and γ10, are much larger than γ6, due to the occurrence of the (completely anisotropic) mixed-pole terms. The recently proposed non-empirical Unsold method yields results which support applications to ...

Do estrogen and progesterone receptors (E2R and PR) in metastasizing endometrial cancers predict the response to gestagen therapy

Abstract: In a prospective investigation biopsy specimens were obtained of 150 women with primary, untreated endometrial carcinoma for determination of the content of estrogen and progesterone receptors (E2 and PR). After a varying interval 13 who developed metastases despite routine surgical and radiation therapy received treatment with gestagens. The clinical effect of the hormone was studied for any correlation with the initial content of E2 and PR.Eight of the women (61–71 years) proved E2R positive (> 10 fmoles/mg cytosolprotein), 2 had no PR and the remaining 6 had PR in a concentration of 7–892 fmoles/mg cytosolprotein). 7 responded clinically to gestagen therapy (tumors poorly differentiated in 3 and moderately in 4).Five of the women (50–84 years) were E2R negative; they had no PR, they did not respond to gestagen therapy and died after 2–8 months (tumors poorly differentiated in 2 and moderately in 3).Determination of E2R and PR in endometrial carcinoma appears to be a clinically useful test for predictin...

Detection and identification of S-methylcysteine in urine of workers exposed to methyl chloride.

Abstract: Methyl chloride is used as a methylating agent and as a blowing agent in industrial processes. Alkylating agents and other electrophilic compounds are often detoxified in the organism through conjugation with glutathione. Glutathione conjugates are generally excreted as mercapturic acids, cysteine conjugates, or other thioethers in urine.

Effect of toluene and xylenes on liver glutathione and their urinary excretion as mercapturic acids in the rat.

Abstract: Administration of toluene and xylenes to rats caused a decrease in liver glutathione concentration. The effect was most pronounced after the administration of o-xylene. 26% of the initial glutathione level was found three hours after treatment with o-xylene (4.0 mmoles/kg). No in vitro conjugation of o-xylene with glutathione was observed, neither spontaneously nor in the presence of 105,000 g supernatant from rat liver homogenate, containing glutathione S-transferases. Thus, a metabolite of o-xylene, which is not formed during incubation with 105,000 g supernatant, reacts with glutathione. A thioether was isolated from urine of rats given o-xylene; the compound was identified as o-methylbenzyl mercapturic acid by GC-MS and NMR. Chromatographic evidence was found for the presence of benzyl mercapturic acid in the urine of toluene-treated rats. The amounts of mercapturic acids excreted in the urine after administration of toluene, p-xylene, m-xylene, and o-xylene were 0.4–0.7, 0.6, 1.3, and 10–21% of the dose, respectively. These results demonstrate the involvement of a thusfar unknown pathway in the biotransformation of toluene and xylenes.

Is actin in eye lens a possible factor in visual accomodation

Abstract: Actin has been purified from varius non-muscle cells and characterized by its molecular weight and ability to polymerize into filaments. Although the occurrence of this protein has been postulated in the mammalian eye lens after observation of actin-like filaments in the electron microscope, definite (bio)chemical proof has been provided only recently. Amino acid analysis, peptide mapping and affinity chromatography revealed the identity of lens actin with the corresponding protein in other tissues. As the filaments could be obtained by co-isolation with highly purified lens plasma membranes, we were interested to know how the actin-containing structures wre located in situ. In the experimental approach reported here, the indirect immunofluorescence technique (IFT) was applied to unfixed cryostat sections of lens tissue. The distribution of actin in calf, rat and pigeon lens is described, and evidence from this for the role of actin in visual accommodation discussed.

Spectra and strong decays of cc-bar and bb-bar states

Abstract: An outline is given for the description of heavy-quark--antiquark systems by means of a set of coupled Schroedinger equations in which permanently confined two-fermion channels are coupled to free two-boson channels. Only two-particle decays satisfying the Okubo-Zweig-Iizuka rule are taken into account. Within this context the equations make a simple determination of the spectra and decay parameters possible. A comparison with the data is presented.

Effect of intensive immunosuppression on the course of chronic progressive multiple sclerosis.

Abstract: 39 patients with chronic-progressive multiple sclerosis were treated with a short course of intensive immunosuppression in high doses of cyclophosphamide and prednisone. The follow-up period varied between 1 and 5 years with a mean of 21/2 years. Progression of the disease ceased in 27 patients for varying periods, with a mean of two years. In 13 patients the progression ceased during the whole follow-up period. The treatment gave the most favourable results in patients who were DRw2 positive in histocompatibility testing, whose disease started at an early age (around 28 years), whose disease duration before treatment was short (6 years), whose progression was fast and whose disability before treatment was low. If CSF levels of IgG3 months after the treatment remain low, this is a sign of good prognosis.

Pharmacology of Org NC 45 Compared with Other Nondepolarizing Neuromuscular Blocking Drugs

Abstract: From results of pharmacological tests on the neuromuscular and autonomic blocking actions of a series of pancuronium analogues, Org NC 45, the C16 monoquateruary analogue of pancuronium, was selected for detailed study. Org NC 45 has a non-depolarizing mechanism of action, is more rapid in onset and shorter in duration of action than pancuronium. It shows less cumulation than pancuronium or tubocurarine, and is easily antagonized by anticholinesterases and aminopyridines. Org NC 45 exhibits a low propensity to release histamine. Its ability to inhibit cholinesterases is not likely to be important at neuromuscular blocking doses. Org NC 45 possesses negligible ganglion-blocking activity and there is a wide margin between neuromuscular and vagal blocking doses. Thus cardiovascular side-effects are unlikely to occur with the use of Org NC 45. It will hydrolyse mainly to its 3-dash;hydroxy analogue which, like Org NC 45, possesses a wide margin between neuromuscular and vagal blocking doses. Org NC 45 has a high selectivity for the neuromuscular junction and represents a potentially useful addition to the armamentarium of clinically useful muscle relaxants.

Disturbances in bile acid metabolism of infants with the Zellweger (cerebro-hepato-renal) syndrome.

Abstract: The bile acid pattern in bile and serum from two infants with the cerebro-hepato-renal syndrome of Zellweger was severely disturbed. An increased concentration particularly of trihydroxycoprostanic acid and also of dihydroxycoprostanic acid could be demonstrated. A generalized mitochondrial defect could explain these increased concentrations. This hypothesis is supported by the abnormal structure of the mitochondria in the liver biopsy of one of our patients. It is possible that the abnormal bile acids contribute to the liver damage of infants with Zellweger syndrome.

Flow cytometry as a tool for the study of cell kinetics in epidermis.

Abstract: SUMMARY Flow cytometric measurements of the DNA content were performed on a large number of skin biopsies by an automated technique. Expressed as a percentage of all viable cells in the epidermis, the figures for cells in S-phase averaged 1.8% and for G2M 0.9%. No significant differences due to sex were found. Concomitantly with age the ratio S/G2M (representing the duration of S to the duration of G2M) increased. Also seasonal effects were clear, showing higher values for S and G2M in June compared to November and December. Lastly we found small differences dependent on body-site, the ratio S/G2M being greater in legs than in arms. The present status is discussed together with future lines of development.

Acetate, methanol and carbon dioxide as substrates for growth of Methanosarcina barkeri.

Abstract: Methanosarcina barkeri grows in defined media with acetate, methanol or carbon dioxide as carbon sources. Methanol is used for methanogenesis at a 5 times higher rate as compared with other substrates. M. barkeri can use the substrates simultaneously, but due to acidification or alkalification of the medium during growth on methanol or acetate, respectively, growth and methano-genesis may stop before the substrates are exhausted. Growth and methano-genesis on methanol or acetate are inhibited by the presence of an excess of H2; the inhibition is abolished by the addition of carbon dioxide, which probably serves as an essential source of cell carbon, in the absence of which methano-genesis ceases.