Showing papers by "University of Groningen published in 1976"
TL;DR: In this paper, a unified description of collective nuclear states in terms of a system of interacting bosons was proposed, and both the vibrational and the rotational limit can be recovered within this model.
1,093 citations
494 citations
TL;DR: In this article, a theory has been worked out for the influence of cross relaxation between protons on the relaxation behavior of the protons in a protein at high frequencies, the effect being particularly evident above 10,000 molecular weight at frequencies exceeding 200 MHz.
491 citations
TL;DR: In this article, the inner and outer membranes of gram-negative bacteria are usually obtained from spheroplasts and a procedure has been developed which renders variously grown cells completely susceptible to lysozyme.
385 citations
TL;DR: In this article, Hansenula polymorpha has been grown in a methanol-limited continuous culture at a variety of dilution rates and was found to have a maximal capacity to oxidize excess methanols at low growth rates, which was 1.6 times higher than the rate required to sustain the growth rate.
Abstract: Hansenula polymorpha has been grown in a methanol-limited continuous culture at a variety of dilution rates. Cell suspensions of the yeast grown at a dilution rate of 0.16 h-1 showed a maximal capacity to oxidize excess methanol (QO
2
max
) which was 1.6 times higher than the rate required to sustain the growth rate (Q
O2). When the dilution rate was decreased to 0.03 h-1, QO
2
max
of the cells increased to a value of more than 20 times that of Q
O2. The enzymatic basis for this tremendous overcapacity for the oxidation of excess methanol at low growth rates was found to be the methanol oxidase content of the cells. The level of this enzyme increased from 7% to approximately 20% of the soluble protein when the growth rate was decreased from 0.16 to 0.03 h-1. These results were explained on the basis of the poor affinity of methanol oxidase for its substrates. Methanol oxidase purified from Hansenula polymorpha showed an apparent K
mfor methanol of 1.3 mM in air saturated reaction mixtures and the apparent K
mof the enzyme for oxygen was 0.4 mM at a methanol concentration of 100 mM. The involvement of an oxygen dependent methanol oxidase in the dissimilation of methanol in Hansenula polymorpha was also reflected in the growth yield of the organism. The maximal yield of the yeast was found to be low (0.38 g cells/g methanol). This was not due to a very high maintenance energy requirement which was estimated to be 17 mg methanol/g cells x h.
291 citations
TL;DR: The results of this comparison indicate that the membrane fragments found in the culture supernatant of normally growing Escherichia coli consist of practically unmodified outer membrane.
251 citations
TL;DR: The investigation of the metabolism of released DA suggests that it can be released from the dendritic processes, as well as from nerve terminals of the nucleus caudatus, and this suggests that DA can be stored in reserpine–sensitive structures.
Abstract: IN addition to the axons which project to the nucleus caudatus1,2, the dopamine (DA)-containing perikarya of the substantia nigra have extensive dendritic processes. These dendrites, observed after Golgi staining3–5 and by electron microscopy3,4, contain relatively large amounts of DA—revealed by histofluorescence6—and vesicle–like structures4. The DA seems to be stored in reserpine–sensitive structures6. The question has arisen whether DA can be released from the dendritic processes, as well as from nerve terminals of the nucleus caudatus7,8. Our investigation of the metabolism of released DA suggests that it can.
250 citations
TL;DR: A concurrent semi-automatic fluorometric assay technique for 3,4-dihydroxyphenylacetic acid and homovanillic acid enables a rapid screening of the action of drugs in regional DA metabolism.
233 citations
TL;DR: By postulating the 'instinctive activity' concept Lorenz hoped to dislodge the study of 'innate' behaviour from the vitalistic versus mechanistic dispute, and in a way it was a kind of compromise: the mechanists he satisfied with the rigidity of the motor coordinations and the reflex-like character of its 'innates releasing mechanism'.
227 citations
TL;DR: Conditions are derived for which there exists a state feedback control such that the closed loop system is stable in the mean square sense and to cases in which the noise intensities are arbitrarily large.
209 citations
TL;DR: The data showed that under control conditions DOPAC is only partially O-methylated to HVA, while the formation of HVA via the methoxytyramine pathway is unlikely andDOPAC turnover therefore probably approximates dopamine turnover.
TL;DR: In this paper, a detailed description of several phenomena observed during the longitudinal growth of fibrillar polyethylene crystals from xylene solutions subjected to Couette flow was presented, and the growth rate of the seed crystals anchored at a distance of approximately i mm from the surface of the rotating inner cylinder was found to increase linearly with the rotor speed, which agreed remarkably well with those values obtained in Poiseuille flow at corresponding local velocity gradients.
Abstract: A detailed description is presented of several phenomena observed during the longitudinal growth of fibrillar polyethylene crystals from xylene solutions subjected to Couette flow. The rate at which the extended chain seed crystals grow longitudinally in this flow field could be established by measuring the increment in length of the macrofiber in a given period of time and also by finding the take-up speed under steady-state conditions which is equal to the growth rate. Continuous macrofibers of polyethylene with lengths of several hundred meters could be produced by this technique. The growth rate of the seed crystals anchored at a distance of approximately i mm from the surface of the rotating inner cylinder was found to increase linearly with the rotor speed, and these growth rate data agreed remarkably well with those values obtained in Poiseuille flow at corresponding local velocity gradients. Scanning electron micrographs reveal that these macrofibers, having diameter in the micron range, are composed of bundles of elementary fibrils of the Shish-Kebab type. It is believed that these Shish-Kebab backbones grow simultaneously by the action of the local flow field. The diameters of the macrofibers increase with the rotor speed as a result of branching of the backbone tips. The growth of seed crystals pushed against the rotor surface is considerably faster than the growth of seeds, around which the polymer solution flows freely. This fast growth is promoted by the roughness of the rotor surface and by the presence of methyl groups on the glass rotor surface introduced by silanization. These experimental observations suggest that the active element in this fast “surface-growth” is a layer of adsorbed polyethylene molecules on the rotor surface. By this surface-growth technique, continuous fibrillar crystallization appeared to be possible at a temperature of even 120.5 °C, which is well above the thermodynamic equilibrium temperature in a dilute p-xylene solution, and the longitudinal growth rate of the polyethylene macrofiber at this high temperature was still 6 cm/min.
TL;DR: In this paper, the main results and applications of the theory of realization of linear stationary dynamical systems in the case that there are certain internal constraints on the parameters of the state space realization are described.
Abstract: This expository paper describes the main results and applications of the theory of realization of linear stationary dynamical systems in the case that there are certain internal constraints on the parameters of the state space realization. The internal constraints considered here are those derived from passivity and symmetry requirements. Applications to stability theory, electrical network synthesis, and other areas are outlined.
TL;DR: The results showed that methanol-dependent hydrogen peroxide production in either fixed or unfixed cells exclusively occurred in peroxisomes, which characteristically develop during growth of this yeast on meethanol.
Abstract: The localization of methanol oxidase activity in cells of methanol-limited chemostat cultures of the yeast Hansenula polymorpha has been studied with different cytochemical staining techniques The methods were based on enzymatic or chemical trapping of the hydrogen peroxide produced by the enzyme during aerobic incubations of whole cells in methanol-containing media The results showed that methanol-dependent hydrogen peroxide production in either fixed or unfixed cells exclusively occurred in peroxisomes, which characteristically develop during growth of this yeast on methanol Apart from methanol oxidase and catalase, the typical peroxisomal enzymes d-aminoacid oxidase and l-α-hydroxyacid oxidase were also found to be located in the peroxisomes Urate oxidase was not detected in these organelles Phase-contrast microscopy of living cells revealed the occurrence of peroxisomes which were cubic of form This unusual shape was also observed in thin sections examined by electron microscopy The contents of the peroxisomes showed, after various fixation procedures, a completely crystalline or striated substructure It is suggested that this substructure might represent the in vivo organization structure of the peroxisomal enzymes
TL;DR: Visual analysis as well as computer analysis of the EEG did not reveal systematic changes in the EEG after the 18th day when the EEG was similar to that recorded at older ages, which indicated that the power increase occurs expecially in the higher frequencies of theEEG signal.
Abstract: The development of the electroencephalogram (EEG) and, especially, behavioral state-specific EEG patterns was studied in white and black hooded rats of the Lister strain, aged 9-30 days. Movements of the rat were recorded and the behavioral state was monitored by means of a push-button device. The EEG was collected when the rat was in State 1 (regular respiration, absence of movements, and, after the 14th day when the rat eye opens, eyes closed), State 2 (irregular respiration, continual occurrence of twitches, and, after the 14th day, eyes closed), and in State 4 (irregular respiration, presence of gross body movements, and, after the 14th day, eyes opened). The EEG of rats on the 9th and 10th day did not reveal behavioral state-specific patterns. The amplitudes of the EEG were low and only low frequencies occurred. Between the 10th and 13th day an EEG pattern specific for State 1 containing high amplitudes developed. From the 14th day onwards spindles (frequencies from 14-18 Hz) occurred in the EEG during State 1. From the 14th day onwards, the EEG from the visual cortex during State 2 showed a regular and continually occurring 5-Hz rhythm. Bursts with 5-Hz waves were recorded from the visual cortex only intermittently during State 4. The EEG frequencies during the bursts varied between 5 and 7 Hz from the 17th day onwards. Computer analysis of the amplitude distributions showed a considerable increase in the power after the 10th day. The analysis of the frequency spectra indicated that the power increase occurs expecially in the higher frequencies of the EEG signal. Visual analysis as well as computer analysis of the EEG did not reveal systematic changes in the EEG after the 18th day when the EEG was similar to that recorded at older ages.
TL;DR: It is concluded that the variability of growth rate and changes in it must be of considerable importance in the dynamics of Cepaea populations.
Abstract: This study deals with the variations in growth rate and their causation in field populations of the polymorphic landsnail, Cepaea nemoralis (L.) (Pulmonata, fam. Helicidae). The pattern of giowth (measured as increase of shell size) and the influence of several external and of endogenous factors on the growth rate and its variation was, in addition, studied experimentally in the laboratory and the field. The aim was to assess the influence of variation in growth rate as a determinant of the numerical strength of Cepaea populations. Growth rate was found to vary considerably between the individuals in each of the two populations compared. The same holds for adult size, which correlates positively with growth rate. The abiotic factors temperature, humidity, light and calcium were found to influence growth rate in a roughly positive way. Growth rate and adult size were both negatively correlated with population density; the presence of mucus on the substrate contributes to this effect. Growth rate and adult size of the parents and of their progeny are positively correlated; a genetical factor was proved to contribute to this relation. Positive correlations also existed between growth rate (and where studied also adult size) and migration and the reproductive variables number of clutches, clutch size, egg weight and hatching percentage, whereas growth rate and mortality were negatively correlated. It is concluded that the variability of growth rate and changes in it must be of considerable importance in the dynamics of Cepaea populations. Density also directly influences migration, mortality and reproduction.
TL;DR: Magnetic susceptibility, in-plane resistivity and Hall effect data of VSe2 single-crystal plates are reported in this paper, which exhibit anomalies at ∼ 100 K. The occurrence of these anomalies is presumably due to Fermi surface changes resulting from the onset of a charge density wave instability.
TL;DR: The data suggest that dopamine in the striatum is compartmentalized and that the newly‐synthesized amine is released and converted to homovanillic acid.
Abstract: — Electrical stimulation of the nigrostriatal dopaminergic pathway in rat brain elicited a frequency and current intensity-dependent increased in the formation of homovanillic acid in the basal ganglia. The accumulation of the acid in probenecid-treated animals was constant over 1 h, when maximally stimulated at 25 Hz and 300 μA. Dopamine levels remained unchanged during stimulation. When prior to stimulation the inhibitor of catecholamine synthesis α-methyl-p-tyrosine methyl ester was administered, dopamine levels declined biphasically. Tyrosine and nomifensine, a dopamine uptake inhibitor, and apomorphine had no major effect on the formation of homovanillic acid, whilst α-methyl-p-tyrosine prevented its formation. Our data suggest that dopamine in the striatum is compartmentalized and that the newly-synthesized amine is released and converted to homovanillic acid. Apomorphine decreases dopamine flux only when dopaminergic neurons are at rest. When depolarized neither access of the precursor nor reuptake seem to influence the conversion of dopamine to homovanillic acid.
TL;DR: Criteria of reliability show that future approaches should aim not only for higher average bonds strengths but also for a smaller standard deviation, and results of different mixing ratios as well as the influence of the amount of catalyst are presented.
TL;DR: It is proposed that ppGpp specifically inhibits rRNA synthesis by acting on the formation of the so-called "closed-promoter complex", which is mainly or wholly a consequence of premature chain termination.
TL;DR: In this paper, an analysis of the intensity dependence of the experimental multiphoton photodissociation probability ((Γ)) for a conical geometry of the laser beam, incorporating saturation effects is presented.
TL;DR: A disproportional effect of task complexity in comparison to the performance of a normal group is shown and an interaction was demonstrated between complexity of the reaction task and length of coma after the injury.
TL;DR: A conclusion is confirmed that the organic component is the most responsible material for the total luminescence of the enamel.
Abstract: The corrected emission and excitation spectra of human and bovine dental enamel and its separated organic material were determined at room temperature and liquid nitrogen temperature. In both materials three distinctluminescence peaks were found in the region 350–360 nm, 405–410 nm, 440–450 nm. The intensity ratios of the peaks of the enamel do not differ substantially upon removal of the inorganic component. Hence a conclusion is confirmed that the organic component is the most responsible material for the total luminescence of the enamel. Several hypothesis are available for determination of the nature of luminescence of the organic components. Differences in the excitation spectra are discussed. Phosphorescence emission and phosphorescence lifetimes were determined.
TL;DR: The apomorphine-induced HVA decrease observed in both structures provides evidence for the presence of a dopaminergic receptor in the substantia nigra.
TL;DR: In this article, the emissions of biacetyl after pulsed dye-laser excitation were studied at pressures down to 0.05 mtorr and the authors determined the low-pressure emission characteristics and the pressure effects as a function of excitation energy.
TL;DR: Mg2+ stabilizes the outer membranes of stationary phase cells of Escherichia coli sufficiently so that they remain immune to lysis even in the absence of osmotic stabilizers such as sucrose.
TL;DR: In this series of 75 patients there was no significant difference in the results obtained by either partial or total laminectomy, and in all cases there was a narrowing of the sagittal spinal diameter.
Abstract: The pathogenesis of cervical myelopathy resulting from cervical spondylarthrosis seems to be the result of intermittent compression of the cervical cord and its feeding arteries. In the literature proof is given that both factors play an important role. By laminectomy or ventral fusion a regression of the neurological disability can be obtained. In our series of 75 patients there was no significant difference in the results obtained by either partial or total laminectomy. In all our cases there was a narrowing of the sagittal spinal diameter.