Showing papers by "Radboud University Nijmegen published in 1986"

Experimental proof of magnetic-x-ray dichroism

Abstract: What we believe to be the first experimental results have been obtained on strong magnetic x-ray dichroism in the ${M}_{4,5}$ absorption spectra of magnetically ordered rare-earth materials, in accordance with recent predictions.

Ammonium determination in soil extracts by the salicylate method

Abstract: An ammonium determination, based on formation of a substituted indophenol with sodiumsalicylate as phenolic reagent, has been reexamined. An increase of 70% in absorbancy compared with existing salicylate methods in soil science, and an increase in reproducibility compared with pre‐existing equivalent methods in other disciplines were obtained. The method can be applied satisfactorily for ammonium in 2M KCl soil extracts and soil and plant digests. The use of salicylate in place of phenol is advised for safety reasons.

Game theory and cost allocation problems

Abstract: Problems of allocating joint costs in a reasonable way arise in many practical situations where people decide to work together to save costs. Cost allocation methods based on game theoretical concepts take into account the strategic aspects of cost allocation situations. We give a survey of cost allocation methods based on the nucleolus and the Shapley value, and introduce also a new one, the so-called cost gap allocation method which is based on the I„-value. It is shown that for some large subclasses of cost allocation problems this new cost allocation method coincides with old separable cost methods proposed in the thirties by the Tennessee Valley Authority and also with the separable costs-remaining benefits SCRB method. Properties of this cost gap allocation method are also treated.

A low lying scalar meson nonet in a unitarized meson model

Abstract: A unitarized non-relativistic meson model which is successful for the description of the heavy and light vector and pseudo-scalar mesons yields in its extension to the scalar mesons for the same model parameters a complete nonet below 1 GeV. In the unitarization scheme real and virtual meson meson decay channels are coupled to the quark antiquark confinement channels. The flavor dependent harmonic oscillator confining potential itself has bound states ɛ(1.3 GeV),S(1.5 GeV), δ(1.3 GeV), κ(1.4 GeV), similar to the results of other bound stateq $$\bar q$$ models. However, the full coupled channel equations show poles at ɛ(0.5 GeV),S(0.99 GeV), δ(0.97 GeV), κ(0.73 GeV). Not only these pole positions can be calculated in our model also cross sections and phase shifts in the meson scattering channels which are in reasonable agreement with the available data for ππ, ηπ andKπ inS-wave scattering.

Osmotic water permeabilities of brush border and basolateral membrane vesicles from rat renal cortex and small intestine.

Abstract: The osmotic water permeabilityPf of brush border (BBM) and basolateral (BLM) membrane vesicles from rat small intestine and renal cortex was studied by means of stopped-flow spectrophotometry. Scattered light intensity was used to follow vesicular volume changes upon osmotic perturbation with hypertonic mannitol solutions. A theoretical analysis of the relationship of scattered light intensity and vesicular volume justified a simple exponential approximation of the change in scattered light intensity. The rate constants extracted from fits to an exponential function were proportional to the final medium osmolarity as predicted by theory. For intestinal membranes, computer analysis of optical responses fitted well with a single-exponential treatment. For renal membranes a double-exponential treatment was needed, implying two distinct vesicle populations.Pf values for BBM and BLM preparations of small intestine were equal and amount to 60 μm/sec. For renal preparations,Pf values amount to 600 μm/sec for the fast component, BBM as well as BLM, and to 50 (BBM) and 99 (BLM) μm/sec for the slow component. The apparent activation energy for water permeation in intestinal membranes was 13.3±0.6 and in renal membranes, 1.0±0.3 kCal/mole, between 25 and 35°C. The mercurial sulfhydryl reagentpCMBS inhibited completely and reversibly the highPf value in renal brush border preparations. These observations suggest that in intestinal membranes water moves through the lipid matrix but that in renal plasma membranes water channels may be involved. From the highPf values of renal membrane vesicles a transcellular water permeability for proximal tubules can be calculated which amounts to ∼1 cm/sec. This value allows for an entirely transcellular route for water flow during volume reabsorption.

On the eigenvalue distribution of a class of preconditioning methods

Abstract: A class of preconditioning methods depending on a relaxation parameter is presented for the solution of large linear systems of equationAx=b, whereA is a symmetric positive definite matrix. The methods are based on an incomplete factorization of the matrixA and include both pointwise and blockwise factorization. We study the dependence of the rate of convergence of the preconditioned conjugate gradient method on the distribution of eigenvalues ofC−1A, whereC is the preconditioning matrix. We also show graphic representations of the eigenvalues and present numerical tests of the methods.

A mitochondrial encephalomyopathy: the first case with an established defect at the level of coenzyme Q.

Abstract: A patient is presented who had therapy-resistant epileptic seizures from the 7th day of life. Examination at the age of 17 months revealed a mentally retarded boy with epileptic seizures, generalised myoclonic contractions, and abnormal ocular movements. A cerebral CT scan showed central and cortical atrophy. Lactate levels in serum, cerebrospinal fluid and urine were elevated, the pyruvate level was raised in serum. A quadriceps muscle biopsy revealed aspecific morphologic signs of a myopathy. Biochemical analysis showed decreased substrate oxidation rates in the mitochondria associated with low rates of ATP production. Total and free carnitine levels were decreased. Investigation of the respiratory chain revealed a defect in the proximal part of respiratory chain revealed a defect in the proximal part of respiratory chain involving the region of coenzyme Q. Based on clinical and chemical data it is likely that the patient is suffering from a multi-system disorder.

The Effects of Media Violence on Attitudes, Emotions, and Cognitions

Abstract: This review specifies mediating factors between the viewing of violent media and aggressive behavior. The role of cognitive and emotional arousal processes are discussed, as is the interplay among these factors and attitudes toward aggression. Included in these discussions are attention and comprehension of the viewed media, as well as attributions and moral evaluations of the perpetrators of violence. Finally, the effects of media exposure on arousal, emotional desensitization, and the excitement of the observer's aggressive inclinations are presented.

On loop folding in nucleic acid hairpin-type structures.

Abstract: In a series of studies, combining NMR, optical melting and T-jump experiments, it was found that DNA hairpins display a maximum stability when the loop part of the molecule comprises four or five nucleotide residues. This is in contrast with the current notion based on RNA hairpin studies, from which it had been established that a maximum hairpin stability is obtained for six or seven residues in the loop. Here we present a structural model to rationalize these observations. This model is based on the notion that to a major extent base stacking interactions determine the stability of nucleic acid conformations. The model predicts that loop folding in RNA is characterized by an extension of the base stacking at the 5'-side of the double helix by five or six bases; the remaining gap can then easily be closed by two nucleotides. Conversely, loop folding in DNA is characterized by extending base stacking at the 3'-side of the double helical stem by two or three residues; again bridging of the remaining gap can then be achieved by one or two nucleotides. As an example of loop folding in RNA the anticodon loop of yeast tRNAPhe is discussed. For the DNA hairpin formed by d(ATCCTAT4TAGGAT) it is shown that the loop structure obtained from molecular mechanics calculations obeys the above worded loop folding principles.

Synchronization of Plasmodium falciparum gametocytes using an automated suspension culture system.

Abstract: An automated suspension culture system for the cultivation of Plasmodium falciparum is described which retains a degree of flexibility which is absent in other automated culture apparatuses. Not only does this system of cultivation promote rapid multiplication of asexual parasites but also permits the development and maturation of gametocytes. Using a combination of gelatin flotation and N-acetyl glucosamine treatment synchronous development of gametocytes was achieved. The total time for gametocyte maturation in vitro under the conditions provided was 7 days. Stages II and V required 48 h for development whilst I, III and IV needed 24 h each. Mature microgametocytes were relatively long lived in comparison with macrogametocytes. Electron microscopic study of the synchronized stages confirmed the observations of Sinden (1982) but, in addition, we noted the presence of Garnham bodies, a cytostome in all stages and dense spherules in stages I-III similar to the fenestrated buttons in sporozoites and exoerythrocytic forms. The relationship between the number of osmiophilic bodies in the mature gametocytes and their ability to escape from the red cell is reaffirmed.

Effects of low ambient calcium levels on whole-body Ca2+ flux rates and internal calcium pools in the freshwater cichlid teleost, Oreochromis mossambicus

Abstract: Calcium fluxes and internal calcium pools were measured in fed, rapidly growing, male tilapia, Oreochromis mossambicus , acclimated to 0.8 mmol l −1 (FW) and 0.2mmoll −1 (LFW) Ca 2+ . Plasma calcium levels were slightly and significantly higher in the LFW tilapia, but muscle calcium concentrations were independent of ambient Ca 2+ . At the time of the experiments, the LFW fish were growing and accumulated calcium, although the calcium content of their hard tissues was reduced. The LFW fish had higher Ca 2+ influx and efflux rates than the FW fish. The increase in the influx of Ca 2+ in LFW fish was, however, substantially greater than the increase in the efflux of Ca 2+ , giving these fish a more than four-fold increase in net Ca 2+ influx from the water: for a 20-g tilapia net uptake rates of Ca 2+ from the water were 390 and 1620 nmol Ca 2+ h −1 for FW- and LFW-adapted fish, respectively. These values were calculated to represent at least 69% of the total calcium accumulated by these growing fish. This indicates that even in low-calcium water, tilapia absorb a significant amount of their calcium requirement directly from the water. The pool of readily exchangeable calcium in the bone of FW fish was estimated to be about 7 % of the total hard tissue calcium. In the fish acclimated to LFW, this percentage increased to about 15 % as total hard tissue mineralization decreased. This may indicate that tilapia can increase the mobility of their hard tissue calcium during periods of low calcium stress.

Electron transfer reactions in methanogens

Abstract: Methanogenic bacteria comprise a specialized group of obligately anaerobic microorganisms able to reduce a limited number of substrates to CH 4 . The intermediates involved in this reduction process remain bound to a series of typical C 1 -carriers. Reducing equivalents are either obtained from the oxidation of H 2 or from oxidation of carbon substrates to CO 2 . Electron transfer reactions thus constitute the very essence of the process of methanogenesis. In recent years much progress has been made in the elucidation of the special metabolic pathways and the nature of the C 1 -carriers involved in methanogenic bacteria. The energy generated at the oxidoreduction reactions, notably at the methylreductase step, is conserved by ATP synthesis. The energy is used for cell carbon synthesis and, in catalytic amounts, for the reductive activation of some methanogenic enzymes. Before the condensing reaction resulting in the formation of acetyl-CoA takes place, 2 C 1 -units are reduced or oxidized depending on the substrate to a carbonyl and a -CH 3 group. Formation of the latter proceeds via the methanogenic route. Intermediary cell carbon synthesis starting from acetyl-CoA involves reductive carboxylations and oxidoreductions by the participation of the enzymes of the tricarboxylic acid cycle.

Comparative Recovery of Streptococcus mutans on Five Isolation Media, Including a New Simple Selective Medium

Abstract: For the isolation of Streptococcus mutans, several selective media have been developed, of which Mitis-Salivarius Sucrose Bacitracin agar (MSB) is the most widely used (Gold et al., 1973). Recently, the Trypticase Yeast-Extract Cystine agar medium (TYC, de Stoppelaar et al., 1967) was modified into a selective medium for S. mutans, called Trypticase Yeast-Extract Cystine Sucrose Bacitracin (TYCSB, van Palenstein Helderman et al., 1983). The aim of this study was to compare the recovery of S. mutans from clinical samples on Mitis-Salivarius agar (MS), MSB, TYC, and TYCSB. Further, a new simple selective medium for S. mutans was introduced. This medium, called TSY20B, was supposed to have the same qualities as TYCSB, but its preparation is less laborious. One hundred eighty-five plaque and saliva samples from 37 subjects were plated on MS, MSB, TYC, and TYCSB, and 285 samples from 23 subjects were plated on TYCSB and TSY20B. All plates were incubated at 37 degrees C in a 91% N2, 5% CO2, 4% H2 atmosphere for five days. The S. mutans counts on TYC and TYCSB were significantly higher than on MS or MSB by almost a factor of 10. Seventy-seven percent of the samples gave higher S. mutans counts on TYCSB than on MSB. Especially, samples with high S. mutans d/g numbers gave lower S. mutans counts on MSB. These data clearly indicate that MSB agar is inhibitory for S. mutans and should not be used. An additional advantage of TYCSB over MSB agar is the possibility of distinguishing S. mutans serotypes d/g from other serotypes.(ABSTRACT TRUNCATED AT 250 WORDS)

Isolation and characterization of Methanoplanus endosymbiosus sp. nov., an endosymbiont of the marine sapropelic ciliate Metopus contortus quennerstedt

Abstract: Epifluorescence microscopy revealed the presence of a methanogenic bacterium as an endosymbiont in the sapropelic marine ciliate Metopus contortus. The in situ methanogenic activity of the symbiont could be demonstrated. The isolated endosymbiont was an irregular, disc-shaped bacterium with a diameter of 1.6–3.4 μm. It had a generation time of 7 or 12 hours on growth on H2/CO2 or formate, respectively. The temperature range for growth was between 16 and 36°C with an optimum at 32°C. The optimal pH range for growth was 6.8 to 7.3. Salts, with an optimum concentration of 0.25 M, and tungsten were required for growth. The mol% G+C was 38.7%. The cell envelope consisted of proteins and a glycoprotein with an apparent molecular weight of 110,000. Morphology, antigenic relationship and the G+C content established the isolate MC1 as a new species of the genus Methanoplanus, and the name Methanoplanus endosymbiosus is proposed.

The most common fragile site in man is 3p14.

Abstract: In man a common fragile site is known to occur at 3p14. We studied the expression of this fragility in a group of 70 normal healthy subjects. Chromosome breaks, chromatid breaks and gaps at 3p14 could be observed in every examined individual, and in a total of 7000 metaphases they were seen in a mean of 4% of cells. Fluorescence studies in ten persons with chromosome No. 3 polymorphism showed that in all cases both Nos. 3 were about equally liable to breakage. A considerable variation in the fra 3p14 expression was found between individuals as well as in repeated cultures from the same person. Neither sex nor age influences could be detected. Cultures with a high percentage of lesions at 3p14 tended to have also a high number of lesions at other sites. Methotrexate and fluorodeoxyuridine markedly enhanced the expression of fra 3p14 and other fragilities. It is concluded that the chromosomal region at 3p14 represents man's most common fragile site, the expression of which seems to be influenced by environmental and heritable factors.

Cross sections and charged multiplicity distributions for π+p,K+p andpp interactions at 250 GeV/c

Abstract: Cross sections and charged multiplicity distributions for π+p,K+p andpp interactions at 250 GeV/c are presented and compared to each other as well as to earlier (for π+p andK+p lower energy) data. Consistently, the meson-proton (M+p) data have narrower multiplicity distributions and higher average multiplicity thanpp data. Up to our energy, generalized KNO functions describe the energy dependence of the shape of the multiplity distribution with one parameter forM+p and one forpp collisions. If interpreted in terms of negative binomials, the parameter 1/k tends to be slightly lower forM+p than forpp data. For both types of hadron-hadron collision, 1/k is larger than fore+e− andlp collisions.

Dynamics of molecular crystals

Abstract: Publisher Summary This chapter illustrates the dynamics of molecular crystals. The intramolecular vibrations and intermolecular vibrations (usually called lattice vibrations) are discussed. Because the chapter deals with molecules, two types of lattice vibrations can be distinguished; translational and rotational. In order to describe these motions, the potential energy of the crystal is expressed as a function of the center of mass positions and the orientations of all molecules. The chapter provides a detailed description of the different ways in which the potential can be expressed, each way having its own merits, depending on the subsequent calculations in which it has to be used. Later, the chapter briefly discusses the harmonic and quasi-harmonic models that are commonly used to describe the molecular motions— that is, the lattice vibrations, in molecular crystals. A description of perturbation theory around the harmonic model and of the self-consistent phonon method is also presented. The dynamical models for large-amplitude motions are also presented.