Showing papers by "University of Groningen published in 1987"
TL;DR: A method of determining baroreceptor reflex sensitivity is proposed that is based on spectral analysis of systolic pressure values and RR interval times, namely, the modulus (or gain) in the mid frequency band between these two signals.
Abstract: A method of determining baroreceptor reflex sensitivity is proposed that is based on spectral analysis of systolic pressure values and RR interval times, namely, the modulus (or gain) in the mid frequency band (0.07-0.14 Hz) between these two signals. Results using this method were highly correlated (0.94; n = 8) with results of the phenylephrine method. In addition, compared with the values for the preceding rest period, the modulus decreased during mental challenge, as might be expected from the literature.
776 citations
TL;DR: In this paper, the crystal structures of the 2H-and 3R-forms of WS2 have been refined from single-crystal data and the results are summarized and the interatomic distances are compared with those in related compounds.
476 citations
TL;DR: At about 1 eV below the top of the valence band a dispersionless state was measured, almost completely of Mo 4d character, which is not predicted by band-structure calculations.
Abstract: The band structures of the semiconducting layered compounds ${\mathrm{MoSe}}_{2}$, ${\mathrm{MoS}}_{2}$, and ${\mathrm{WSe}}_{2}$ have been calculated self-consistently with the augmented-spherical-wave method. Angle-resolved photoelec- tron spectroscopy of ${\mathrm{MoSe}}_{2}$ using He i, He ii, and Ne i radiation, and photon-energy-dependent normal-emission photoelectron spectroscopy using synchrotron radiation, show that the calculational results give a good description of the valence-band structure. At about 1 eV below the top of the valence band a dispersionless state was measured, almost completely of Mo 4d character. Such a state, which is not predicted by band-structure calculations, has also been observed in metallic layered compounds. Suggestions are given for the explanation of this phenomenon.
456 citations
TL;DR: It is concluded that dopamine, noradrenaline and acetylcholine found in the dialysate are directly derived from neurotransmission, whereas the overflow of excitatory amino acid neurotransmitters is related to neurogenic as well as to metabolic events.
440 citations
TL;DR: Three distinct regions in the adhesion process are suggested in which at large and intermediate separation distances adhesion is mediated by the macroscopic surface properties as surface free energy and surface charge, respectively.
Abstract: Based on a literature review, a hypothesis is forwarded on the mechanism of initial bacterial adhesion to solid substrata, which accounts both for the role of specific microscopic surface components as well as for the role of non-specific macroscopic surface properties (surface free energy, zeta potential or hydrophobicity). Three distinct regions in the adhesion process are suggested in which at large and intermediate separation distances adhesion is mediated by the macroscopic surface properties as surface free energy and surface charge, respectively. At small separation distances specific short-range interactions can occur, leading to a strong and irreversible bonding, provided the water film present in between the interaction surfaces can be removed. A major role of hydrophobic groups, supposed to be associated with bacterial surface appendages is suggested to be its dehydrating capacity, enabling the removal of the vicinal water film yielding small areas of direct contact between protruberant parts of the cell surface and the substratum.
427 citations
TL;DR: Evidence is presented for a consistent deletion at the chromosomal region 3p21, not only in SCLC11, but in all major types of lung cancer.
Abstract: In childhood malignancies such as retinoblastoma and Wilms tumour, of which both familial and sporadic forms exist, recessive mutations of presumed differentiation genes have been implicated in tumorigenesis1,2. A proportion of cases appear with microscopically visible chromosome deletions which indicate the regions where the genes concerned are located. Mutation or loss of one allele causes a cancer predisposition. For tumour development functional loss of the remaining normal allele is also required. In cancers with both familial and sporadic forms, molecular-genetic studies have shown that deletion is often one of the mutational events2–5.Although familial and sporadic forms have never been distinguished in lung cancer, deletions of the short arm of chromosome 3 have been described for small cell lung cancer (SCLC) (refs 6, 7), but their general occurrence in SCLC has been disputed8–10. Using a molecular-genetic approach, we here present evidence for a consistent deletion at the chromosomal region 3p21, not only in SCLC11, but in all major types of lung cancer.
403 citations
TL;DR: In this article, the authors propose a method to identify the root cause of a problem.Abbreviations: [2]... ].., [3]
393 citations
TL;DR: From band-structure calculations it is shown that MoSe2, MoS2, and WSe2 are indirect-gap semiconductors, and the wave function at the top of the valence band is shown to be a metal-nonmetal antibonding state, which explains the observed high stability of these materials in photoelectrochemical cells against photocorrosion.
Abstract: From band-structure calculations it is shown that ${\mathrm{MoSe}}_{2}$, ${\mathrm{MoS}}_{2}$, and ${\mathrm{WSe}}_{2}$ are indirect-gap semiconductors. The top of the valence band is at the \ensuremath{\Gamma} point and the bottom of the conduction band is along the line T of the hexagonal Brillouin zone, halfway between the points \ensuremath{\Gamma} and K. The A and B excitons correspond to the smallest direct gap at the K point. This assignment of the exciton peaks is shown to be consistent with the polarization dependence of their intensities, their effective masses, and the observed dependence of their splitting on the spin-orbit splittings of the constituent elements. The wave function at the top of the valence band is shown to be a metal-nonmetal antibonding state, which explains the observed high stability of these materials in photoelectrochemical cells against photocorrosion.
361 citations
359 citations
TL;DR: It is concluded that, despite tight control of maternal diabetes, the development of behavioural states is disturbed in fetuses of nulliparous diabetic women.
359 citations
TL;DR: The problem of finding a linear time invariant complete system which models an observed time series will be continued, however, in this part it will be assumed that the model is required to explain the observations only approximately, and what is meant by an approximate model is raised.
TL;DR: The data support the hypothesis that EEG power density during non-rapid eye movement sleep is only determined by the prior history of sleep and wakefulness and is not determined by clock-like mechanisms.
Abstract: The relation between the duration of prior wakefulness and EEG power density during sleep in humans was assessed by means of a study of naps. The duration of prior wakefulness was varied from 2 to 20 hr by scheduling naps at 1000 hr, 1200 hr, 1400 hr, 1600 hr, 1800 hr, 2000 hr, and 0400 hr. In contrast to sleep latencies, which exhibited a minimum in the afternoon, EEG power densities in the delta and theta frequencies were a monotonic function of the duration of prior wakefulness. The data support the hypothesis that EEG power density during non-rapid eye movement sleep is only determined by the prior history of sleep and wakefulness and is not determined by clock-like mechanisms.
TL;DR: In vivo and in vitro degradation of high molecular weight poly(L-lactide) used for internal bone fixation has been investigated and a more ductile PLLA exhibiting a lower rate of degradation was prepared by extraction of low molecular weight compounds with ethyl acetate.
TL;DR: A number of MboI fragments in the promoter selection vector pGKV210, which replicates in Streptococcus lactis, Bacillus subtilis, and Escherichia coli and carries a promoterless chloramphenicol acetyltransferase gene, are obtained.
Abstract: By cloning MboI fragments in the promoter selection vector pGKV210, which replicates in Streptococcus lactis, Bacillus subtilis, and Escherichia coli and carries a promoterless chloramphenicol acetyltransferase gene, we obtained a number of fragments endowed with promoter activity, partly by direct selection for chloramphenicol resistance in S. lactis IL1403 and partly by selection in B. subtilis. Five fragments were sequenced, and the promoters were mapped with S1 nuclease. The promoters agreed with the E. coli promoter consensus and the B. subtilis vegetative sigma 43 promoter consensus. The promoters were preceded by an A + T-rich region (ranging from 64 to 78% A + T). S1 nuclease mapping data showed that the transcriptional start point in three of the fragments was at a TAG sequence 5 to 9 nucleotides downstream from the promoter. Three fragments carried an open reading frame preceded by a ribosome-binding site which can be recognized by E. coli, B. subtilis, and S. lactis ribosomes.
TL;DR: Ten patients with unstable zygomatic fractures were treated with resorbable poly(L-lactide) (PLLA) plates and screws and the results show that this method of fixation gives good stability over a sufficiently long period to enable undisturbed fracture healing.
TL;DR: Comparison of young vs aged cases indicate that aging does not appear to have a profound influence on cortical innervation patterns, at least as studied with the PHA-L method.
TL;DR: The development of microbodies in the yeast Saccharomyces cerevisiae was studied in response to different conditions of growth, with marked microbody proliferation observed after a shift of cells into media containing oleic acid and was associated with the induction of activities of β‐oxidation enzymes.
Abstract: The development of microbodies in the yeast Saccharomyces cerevisiae was studied in response to different conditions of growth. Various strains of S. cerevisiae were investigated, using cells from the exponential growth phase on glucose as an inoculum in all transfer experiments. Electron microscopy, including serial sectioning, revealed that these cells generally contained one to four small microbodies which were localized in the vicinity of the cell wall and characterized by the presence of catalase. Transfer of these glucose-grown cells into media supplemented with various compounds known to induce microbody proliferation in other yeasts--i.e. uric acid, alkylated amines, amino acids, C2-compounds such as ethanol or acetate, in the presence or absence of compounds that induce oxygen radical formation--did not result in a significant change in the number of microbody profiles observed. Marked microbody proliferation was, however, observed after a shift of cells into media containing oleic acid and was associated with the induction of activities of beta-oxidation enzymes. In addition, catalase and isocitrate lyase were present in enhanced levels. Kinetic experiments suggested that these microbodies developed from those originally present in the inoculum cells. In thin sections up to 14 microbody profiles were occasionally observed, often present in small clusters. Their ultimate volume fraction amounted to 8-10% of the cytoplasmic volume.
TL;DR: It is argued that spectral analysis of sinus arrhythmia is useful to obtain more insight into the physiological mechanisms that underlie heart-rate variability and the amplitude of the 0.10-Hz component of this signal systematically decreases as the load on working memory increases.
Abstract: This paper discusses the usefulness of heart-rate variability (sinus arrhythmia) as an index of operator effort. Effort is involved if task performance requires the use of attention-demanding, controlled processing. This form of processing heavily uses a capacity-limited mechanism: working memory. Effort is also required if the current state of the subject deviates from the target or task optimal state because of fatigue, circadian rhythm, time of day, sleep deprivation, time on task, drugs, heat, or noise. Effort is involved whenever an attempt to resolve mismatch of target and current state takes the form of active manipulation of cognitive resources. We argue that spectral analysis of sinus arrhythmia is useful to obtain more insight into the physiological mechanisms that underlie heart-rate variability. In the present study, it is shown that the amplitude of the 0.10-Hz component of this signal systematically decreases as the load on working memory increases. Some suggestions are made to apply the met...
TL;DR: Besides good mechanical properties the as-polymerized PLLA exhibited a microporous structure and plates and screws of this material were used for the treatment of mandibular fractures, both in dogs and in sheep.
TL;DR: The results demonstrate that VP cells in the AME project to (1) the lateral septum (LS) by the ventral amygdalofugal pathway and (2) the VH via the Amygdalohippocampal transition zone, and support the possibility that the BST and AME are an anatomical entity that may be part of the central loci controlling sexual processes in the rat.
Abstract: The rat brain contains a large number of vasopressin (VP) immunoreactive fibers, the sites of origin of which have not yet been established completely. For instance, the sources of VP fiber systems in the amygdala, ventral hippocampus (VH), mediodorsal thalamic nucleus, ventral tegmental area, and dorsal raphe yet remain obscure. These VP fibers may originate in any of the recently described extrahypothalamic VP cell groups, viz., medial amygdaloid nucleus (AME), dorsomedial hypothalamic nucleus, or locus coeruleus, since VP efferents from these cells still remain to be demonstrated. In search of AME VP efferents three approaches were followed: (1) the Phaseolus vulgaris anterograde tracing method, (2) immunocytochemistry after AME lesioning, and (3) retrograde transport of a fluorescent dye in combination with immunofluorescence. The results demonstrate that VP cells in the AME project to (1) the lateral septum (LS) by the ventral amygdalofugal pathway and (2) the VH via the amygdalohippocampal transition zone. In addition, the VP projection from the bed nucleus of the stria terminalis (BST) to the LS was confirmed. There was no indication that VP cells in the AME project through the amygdalotegmental pathway to the medulla oblongata and spinal cord. The results support the possibility that the BST and AME are an anatomical entity that may be part of the central loci controlling sexual processes in the rat.
TL;DR: In this article, the authors studied the bulk polymerization of L,L-dilactide as a function of polymerization temperature (Tp), time and concentration of catalyst (tin 2-ethylhexanoate).
Abstract: The bulk polymerization of L,L-dilactide was studied as a function of polymerization temperature (Tp), time and concentration of catalyst (tin 2-ethylhexanoate). Poly(L-lactide) (PLLA), with the highest value of intrinsic viscosity ([η] = 13 dl · g−1; Mv ≈ 1 · 106) and heat of fusion (ΔHm = 64,7 J · g−1), was synthesized at a low catalyst concentration (0,015 wt.-%) and at the lowest Tp studied (100°C), just above the melting point of L,L-dilactide (98°C). The ceiling temperature of PLLA was found to be 275°C, as deduced from an Mv max. − Tp curve. The Mw/Mn ratios of as-polymerized PLLA samples ranged from 2 to 3. Fractions of PLLA with Mv max. were already present at 50% conversion. The experimental results support a proposed nonionic insertion polymerization mechanism. Polymerization at 100–140°C resulted in early crystallization of PLLA leading to a rather untangled polymer and microporous (pores up to 100 nm) sample texture.
TL;DR: In this paper, a pure calcium hydroxyapatite prepared from aqueous solutions at low temperature, was analysed by a large number of techniques in six Institutes, including X-ray diffraction, IR analysis, BET measurement, chemical analysis, differential thermal analysis, magic angle spinning NMR, TEM, size distribution measurements, crystal growth and crystal dissolution measurements.
01 Dec 1987-Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms
TL;DR: In this article, a Monte Carlo program for the calculation of channeling phenomena is described, which combines the binary collision model and the multistring approximation, with the use of the model of Dettmann and Robinson for the inner-shell electrons and the theory of Pines for valence electrons.
Abstract: A Monte Carlo program for the calculation of channeling phenomena is described. The program combines the binary collision model and the multistring approximation. The energy loss due to electronic excitation is taken into account, with the use of the model of Dettmann and Robinson for the inner-shell electrons and the theory of Pines for valence electrons. The output of the Monte Carlo program may be used for the determination of the impurity sites in single crystals, via a set of auxiliary programs, that enable that calculation of the impurity yield and the analysis of experimental channeling dips. As an application, the site determination of iodine in silicon is described. Another application is the simulation of RBS spectra of planar channeling ions. Simulated and experimental spectra are compared for 1 MeV ions in the (110), (111) and (100) planes of silicon. A reasonable agreement was found. The possible causes of the remaining deviations are discussed.
TL;DR: The infusion of TTX revealed three different types of pharmacologically enhanced dopamine release in conscious rats, including action potential dependent dopamine release (exocytosis), which was observed in untreated animals as well as in animals treated with haloperidol, hal operidol + GBR 12909, and morphine.
Abstract: The effect of TTX (infused during brain dialysis of the striatum and nucleus accumbens) on the in vivo release of dopamine, 3,4-dihydroxyphenylacetic acid and homovanillic acid, was investigated. In addition it was studied whether the increase in the release of dopamine, induced by various pharmacological treatments, was sensitive to TTX infusion. The following drugs were studied: haloperidol, amphetamine, haloperidol co-administered with GBR 12909, morphine and MPP+. Dialysis was carried out in the striatum, except for morphine, which was studied in the nucleus accumbens. The infusion of TTX revealed three different types of pharmacologically enhanced dopamine release in conscious rats. First, action potential dependent dopamine release (exocytosis), which was observed in untreated animals as well as in animals treated with haloperidol, haloperidol + GBR 12909, and morphine. Second, action potential independent release (carrier-mediated) was established in the case of amphetamine. Third, action potential independent DA release, probably caused by neurotoxic reactions was observed during MPP+ infusion.
TL;DR: The detailed patterns of afferentation to the ammon's horn and dentate gyrus of the hippocampus in the rat were investigated employing the anterograde tracer Phaseolus vulgaris leuco-agglutinin (PHA-L) after punctate iontophoretic injections in the medial septum and vertical limb of the diagonal band of Broca.
TL;DR: This chapter presents a novel, behavioral physiological stress concept that originates from the classical view that stress is a response and is extended to environment, behavior, and physiology, and it incorporates the novel neuroendocrine views including the neuropeptide concept.
Abstract: Publisher Summary This chapter presents a novel, behavioral physiological stress concept that originates from the classical view that stress is a response. This new concept is extended to environment, behavior, and physiology, and it incorporates the novel neuroendocrine views including the neuropeptide concept. Stress is viewed as a general biological and usually functional response to environmental and bodily demands. A stress depends on interactions among environment, individual characteristics and the properties of stressors, stress, and the physiological systems, and also among the nervous system, peripheral organ systems, and the neuroendocrine system. To adapt to the altering social and physical environmental demands, man and other animals require a chain of behavioral, neuroendocrine, and autonomic physiological and metabolic responses to maintain bodily and mental homeostasis. The neuroendocrine state of the brain is given a central position in determining the state of health or disease of mind and body.
TL;DR: Starch granules from the amylose-free potato mutant showed a strongly reduced activity of the granule bound starch synthase and loss of the major 60 kd protein from the starch granules.
Abstract: An amylose-free potato mutant was isolated after screening 12,000 minitubers. These minitubers had been induced on stem segments of adventitious shoots, which had been regenerated on leaf explants of a monoploid potato clone after Rontgen-irradiation. The mutant character is also expressed in subterranean tubers and in microspores. Starch granules from the mutant showed a strongly reduced activity of the granule bound starch synthase and loss of the major 60 kd protein from the starch granules.
TL;DR: The feasibility of measuring acetylcholine in perfusion samples collected by means of in vivo brain dialysis in the striata of freely moving rats is demonstrated, although a considerable variation between successive samples exists.
Abstract: The present study demonstrates the feasibility of measuring acetylcholine in perfusion samples collected by means of in vivo brain dialysis in the striata of freely moving rats. The output of the dialysis device was directly connected to an automated sample valve of a HPLC-assay system that comprises a cation exchanger, a post-column enzyme reactor, and an electrochemical detector. The presence of an acetylcholinesterase inhibitor (neostigmine) in the perfusion fluid was required for the detection of acetylcholine in the perfusate. Increasing concentrations of neostigmine induced increasing amounts of acetylcholine. Continuous perfusion with a fixed concentration (2 microM) of neostigmine resulted in gradually increasing amounts of collected acetylcholine over time although a considerable variation between successive samples exists. The brain dialysis technique was further validated by studying the effect of various drugs. Systemically administered atropine increased the output of acetylcholine, whereas the addition of tetrodotoxin to the perfusion fluid resulted in a complete disappearance of the neurotransmitter.
TL;DR: The results indicate that the relation between aggression and behavioural reaction to a changing environment has more general validity and is suggested that the behaviour of aggressive males is mainly controlled by intrinsic factors whereas the behaviours of non-aggressive males is more dependent on external factors.
Abstract: Aggressive and non-aggressive male mice differ in their reaction to a changing social environment. In order to investigate if this differentiation holds also for non-social situations male mice are trained in a standard maze task, whereafter a change (extramaze and intramaze, respectively) is introduced. The results indicate that aggressive males fulfil their task fairly routine-like and do not react to a change which is in contrast to the non-aggressive individuals. In a second experiment a more continuously changing situation is created by testing the animals every 3 trials in a different maze configuration. In this situation in which a routine cannot be developed c.q. used, the aggressive males performed worse than the non-aggressive animals. It is suggested that the behaviour of aggressive males is mainly controlled by intrinsic factors whereas the behaviour of non-aggressive males is more dependent on external factors. Similar results are obtained when repeating the experiments with rats. This indicates that the relation between aggression and behavioural reaction to a changing environment has more general validity. The possibly underlying mechanism is discussed as well as the consequences for the functioning of the animals in a social setting.