Showing papers by "University of Groningen published in 1992"

X-ray circular-dichroism as a probe of orbital magnetization

Abstract: A new magneto-optical sum rule is derived for circular magnetic dichroism in the x-ray region (CMXD). The integral of the CMXD signal over a given edge allows one to determine the ground-state expectation value of the orbital angular momentum. Applications are discussed to transition-metal and rare-earth magnetic systems.

The α/β hydrolase fold

Abstract: We have identified a new protein fold--the alpha/beta hydrolase fold--that is common to several hydrolytic enzymes of widely differing phylogenetic origin and catalytic function. The core of each enzyme is similar: an alpha/beta sheet, not barrel, of eight beta-sheets connected by alpha-helices. These enzymes have diverged from a common ancestor so as to preserve the arrangement of the catalytic residues, not the binding site. They all have a catalytic triad, the elements of which are borne on loops which are the best-conserved structural features in the fold. Only the histidine in the nucleophile-histidine-acid catalytic triad is completely conserved, with the nucleophile and acid loops accommodating more than one type of amino acid. The unique topological and sequence arrangement of the triad residues produces a catalytic triad which is, in a sense, a mirror-image of the serine protease catalytic triad. There are now four groups of enzymes which contain catalytic triads and which are related by convergent evolution towards a stable, useful active site: the eukaryotic serine proteases, the cysteine proteases, subtilisins and the alpha/beta hydrolase fold enzymes.

The choice of treatment of single brain metastasis should be based on extracranial tumor-activity and age

Abstract: Purpose: To determine if in patients with single brain metastasis the addition of neurosurgery to radiotherapy leads to lengthening of survival or to better quality of life. Methods and Materials: From 1985 to 1990, 66 patients with single brain metastasis from a solid tumor were entered in a randomized trial of neurosurgery plus radiotherapy vs. radiotherapy alone. Patients were stratified for lung cancer vs. other sites of cancer and for progressive vs. stable systemic cancer. Radiotherapy was given to the whole brain by a novel scheme of two fractions of 2 Gy per day for a total dose of 40 Gy in 2 weeks, to obtain a relatively high total dose and short overall time, with minimal risk of late damage to normal tissue in long-term survivors. Results: In the whole group of 63 evaluable patients, both with lung cancer as with other tumors, the combined treatment led to a better duration of survival (median 10 vs. 6 months; p = 0.04). The largest difference between both treatment arms was observed in patients with inactive extracranial disease (median 12 vs. 7 months; p = 0.02). Patients with active extracranial disease had an equal median survival of only 5 months, irrespective of given treatment. Age proved to be a strong and independent prognostic factor: patients older than 60 years had a hazard ratio of dying of 2.74 (p = 0.003) compared with younger patients. Following treatment, most patients remained functionally independent until a few weeks before death. In the majority of patients the cause of death was systemic tumor progression. Conclusion: Patients with single brain metastasis and with controlled or absent extracranial tumor activity should be treated with surgery and radiotherapy, especially when they are younger than 60 years. For patients with progressive extracranial disease, radiotherapy alone seems to be sufficient. The accelerated radiotherapy scheme of 40 Gy in 2 weeks to the whole brain is tolerated well and should also be considered for patients in a good performance status with surgically unaccessible single metastasis or even with multiple brain metastases.

Band gap, excitons, and Coulomb interaction in solid C60.

Abstract: The band gap of solid ${\mathrm{C}}_{60}$ is found to be 2.3\ifmmode\pm\else\textpm\fi{}0.1 eV. The on-site molecular ${\mathrm{C}}_{60}$ Coulomb interaction (U) as determined from the KVV ${\mathrm{C}}_{60}$ Auger spectrum is found to be 1.6\ifmmode\pm\else\textpm\fi{}0.2 eV. This value of U is shown to lead to Frenkel-type molecular excitons in the 1.5--2 eV range. These results lead us to suggest that doped ${\mathrm{C}}_{60}$ should be considered as a highly correlated system with U/W comparable to that in high-${\mathit{T}}_{\mathit{c}}$ cuprates and that stoichiometric ${\mathrm{K}}_{3}$${\mathrm{C}}_{60}$ is a Mott-Hubbard insulator with a gap of about 0.7 eV.

Adequacy and duration of antidepressant treatment in primary care

Abstract: Among a sample of 119 distressed high-utilizers of primary care, 45% of patients evaluated by a psychiatrist as needing antidepressant treatment had been treated in the year before the examination. However, only 11% of the patients needing antidepressants had received adequate dosage and duration of pharmacotherapy. In the year following the intervention, study patients whose physicians were advised regarding treatment during a psychiatric consultation were more likely to receive antidepressant medications (52.7%) relative to a randomized control group (36.1%). However, the intervention did not significantly increase the provision of adequate antidepressant therapy (37.1% vs 27.9%). Among study patients using antidepressants, patient characteristics did not differentiate patients who received adequate dosage and duration of antidepressant medications from those who did not. Analysis of data on the duration of antidepressant therapy for all health maintenance organization enrollees initiating use of antidepressants showed that only 20% of patients who had been given prescriptions for first-generation antidepressants (amitriptyline, imipramine, or doxepin) filled four or more prescriptions in the following six months, compared to 34% of patients who had prescriptions for newer antidepressants (nortriptyline, desipramine, trazodone and fluoxetine). Experimental research evaluating whether these newer medications (with more favorable side effect profiles) improve adherence, and thereby patient outcome, is needed.

Controlled-valence properties of La1-xSrxFeO3 and La1-xSrxMnO3 studied by soft-x-ray absorption spectroscopy.

Abstract: The controlled-valence properties of ${\mathrm{La}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Sr}}_{\mathit{x}}$${\mathrm{FeO}}_{3}$ and ${\mathrm{La}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Sr}}_{\mathit{x}}$${\mathrm{MnO}}_{3}$ are studied by means of soft-x-ray absorption spectroscopy. A comparison between the transition-metal 2p spectra and atomic-multiplet calculations is used to determine the 3d count. The O 1s spectrum is used to characterize changes in unoccupied states that contain oxygen p character. The results indicate that the holes induced by substitution for both series are located in states of mixed metal 3d--oxygen 2p character. The ground state of ${\mathrm{LaFeO}}_{3}$ is mainly 3${\mathit{d}}^{5}$ and becomes 3${\mathit{d}}^{5}$L (where L denotes a ligand hole) in the ${\mathrm{La}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Sr}}_{\mathit{x}}$${\mathrm{FeO}}_{3}$ series for low Sr concentration. The main component of the ground state of ${\mathrm{LaMnO}}_{3}$ is 3${\mathit{d}}^{4}$ and becomes a mixture of 3${\mathit{d}}^{3}$ and 3${\mathit{d}}^{4}$L in the ${\mathrm{La}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Sr}}_{\mathit{x}}$${\mathrm{MnO}}_{3}$ series. The trends in controlled- valence properties of similar oxides across the transition-metal series can be rationalized within the framework of the Zaanen-Sawatzky-Allen model.

Heterogeneity of rat liver and spleen macrophages in gadolinium chloride-induced elimination and repopulation.

Abstract: Blockade of phagocytosis and selective elimination of macrophages (m phi s) are generally accepted procedures for gaining knowledge about the function of m phi s in vivo. This study demonstrates that intravenous injection of gadolinium chloride (GdCl3) not only blocks phagocytosis by rat liver m phi s (Kupffer cells) but also selectively eliminates the large m phi s situated in the periportal zone of the liver acinus. Repopulation of m phi s starts at 4 days after injection. During repopulation, m phi s are less vulnerable to GdCl3. When repopulation is complete, the new m phi s show the same vulnerability as the original ones. Splenic m phi s are less vulnerable to GdCl3 because only some of the red pulp m phi s transiently disappear. The white pulp m phi s are not affected. Repopulation occurs sooner than in liver. These results indicate that administration of GdCl3 is a suitable approach to studying the in vivo function of large Kupffer cells.

The emotional motor system.

Abstract: A large number of new descending motor pathways to caudal brainstem and spinal cord have been recognized recently. Nevertheless all the new pathways seem to belong to one of three motor systems in the central nervous system (CNS). This survey gives an overview of the pathways belonging to the so-called emotional motor system or the third motor system as defined by Holstege. The similarities and differences with the core, median and lateral paracore areas of the CNS as defined by Nieuwenhuys are discussed.

Design parameters estimation for scale-up of high-pressure bubble columns

Abstract: Experiments were carried out in bubble columns for a number of liquids at pressures between 0.1 and 2.0 MPa for two column sizes. Based on the experimental results as well as extensive literature data, the extent of the effect column dimensions have on gas holdup were determined, both at low and high pressures (which is of importance to scale-up). It was also demonstrated that none of the published empirical gas holdup equations incorporate the influence of gas density accurately. Therefore, a new improved gas hold-up equation is developed that incorporates the influence of gas and liquid properties with an average error of approximately 10%. Finally, it is also discussed to what extent the influence of pressure on other important design parameters such as the interfacial area, the liquid volumetric mass transfer coefficient, and gas and liquid mixing, can be estimated on the basis of empirical equations.

Towards a dynamic theory of transactions

Abstract: Standard transaction cost economics (TCE) considers transactions from the perspective of static efficiency. Increasingly, attention is required to dynamic efficiency; to capabilities to exploit transaction relations for innovation. Since innovation is dependent on knowledge and learning, the step from the statics to the dynamics of exchange requires and understanding of the development and acquisition of knowledge, preferences, and meaning, and the role in that of interaction between transaction partners. As a step towards this, the article provides an exploration of theories of knowledge and knowledge development, the relation to language, the role of intersubjective relations, the connection with evolutionary theory and the implications for transaction cost theory.

Demineralization and remineralization evaluation techniques.

Abstract: This paper compares the experimental techniques utilized to assess the de- or remineralization of enamel or dentin in intra-oral studies. In in situ studies, it is important for one to know how much mineral has been lost or gained, and where the loss or gain occurred. The main emphasis in this paper is on techniques suitable for direct or indirect mineral quantification. The measuring techniques considered are microradiography, iodine absorptiometry, various microhardness tests, polarized light, light-scattering, iodide permeability, and wet chemical analysis. The various techniques are compared concerning suitability for the determination of mineral content in vol% (or wt%), mineral changes in vol% micron (or kg.m-2), and mineral distributions. Furthermore, sample preparation, the importance of protein penetration, nominal mineral loss range, the estimated mineral loss threshold, and the applicability to dentin are compared and considered. It is concluded that, although more than ten techniques are available for the measurement of changes after de- or remineralization in situ, transverse microradiography is the most practical technique for the direct and quantitative measurement of mineral content, mineral changes, and mineral distributions. Cross-sectional microhardness testing and light-scattering are also practical indirect techniques for quantitative mineral loss (or gain) determination in intra-oral studies.

Low-Dose Amiodarone for Maintenance of Sinus Rhythm After Cardioversion of Atrial Fibrillation or Flutter

Abstract: Objective. —To study efficacy and safety of low-dose amiodarone for maintenance of sinus rhythm after electrical cardioversion of atrial fibrillation or flutter. Design. —Nonrandomized trial; mean duration of follow-up, 20.7 months. Setting. —Referral center; institutional practice; both hospitalized and ambulatory care. Patients. —Eighty-nine consecutive patients having chronic atrial fibrillation or flutter and eligible for cardioversion. Patients had failed previous treatment aimed at maintaining sinus rhythm. During follow-up one patient was withdrawn because of side effects; all patients were available for follow-up. Intervention. —Before cardioversion, patients received 600 mg of amiodarone daily during a 4-week loading period. After conversion, the daily maintenance dose was 204±66 mg (mean±SD). Main Outcome Measures. —Arrhythmia recurrence and adverse effects causing drug discontinuation. Results. —During loading, 15 patients (16%) converted, and after electrical cardioconversion, 90% of all patients had sinus rhythm. Actuarially, 53% of these patients were still in sinus rhythm after 3 years. In patients with compromised left ventricular function, 93% maintained sinus rhythm after 6 months. One patient died due to congestive heart failure. Intolerable side effects occurred in one patient. No proarrhythmia was observed. Logistic regression analysis revealed that amiodarone was ineffective in patients with mitral stenosis or chronic arrhythmia. Conclusions. —Low-dose amiodarone is effective for maintaining sinus rhythm in patients with difficult to treat chronic atrial fibrillation or flutter and is associated with a low incidence of serious side effects. (JAMA. 1992;267:3289-3293)

Reduced light-scattering properties for mixtures of spherical particles: a simple approximation derived from Mie calculations

Abstract: The reduced scattering cross section per unit of volume Σs′ ≡ Σs(1 − g) is an important parameter to describe light propagation in media with scattering and absorption. Mie calculations of the asymmetry factory g for nonabsorbing spheres and Qsca, the ratio of the scattering cross section Σs and the particle cross section, show that Qsca(1 − g) = 3.28x0.37(m − 1)2.09 is true to within a few percent, when the Mie parameters for relative refractive index m and size x are in the ranges of 1 < m ≤ 1.1 and 5 < x < 50, respectively. A ratio of reduced scattering cross sections for radiation at two wavelengths is also independent of the size within the range mentioned, even for mixtures of different size spheres. The results seem promising for biomedical applications.

Theoretical predictions of spatiotemporal receptive fields of fly LMCs, and experimental validation

Abstract: 1. A theory is presented that utilizes the structure of natural images, and how they change in time, to produce spatiotemporal filters that maximize information flow through a noisy channel of limited dynamic range. For low signal-to-noise ratios (SNRs) the filter has low-pass, and for high SNRs band-pass characteristics, both in space and time. 2. Theoretical impulse responses are compared to measurements in Large Monopolar Cells (LMCs) in the fly (Calliphora vicina) brain. Two different spatial stimuli (point source and wide field) were given at background intensities over a 5.5 log unit wide range. Theory and experiment correspond well, and they share the following properties: impulse responses get much faster and more biphasic with increasing background intensity (SNR); they show larger off-transients for wide field stimuli than for point sources; the half-width of the spatial receptive field changes only slightly with increased intensity, and lateral inhibition increases; contrast efficiency increases with intensity.

Rare Populations, Hidden Populations, and Link-Tracing Designs: What and Why?:

Abstract: Literature on snowball sampling and other ascending methodologies (intensive data collection methodologies) is widely scattered. In order to indicate a structure in the diversity of articles, snowball sampling and other ascending methodologies are embedded in the general concept of link-tracing methodologies. From this point of view link-tracing methodologies are considered as tools for analysing social structure and for locating members of special populations. By introducing a new theoretical concept for defining special populations, a subdivision is made in link-tracing methodologies as a tool to locate rare populations and as a tool to locate hidden populations.

Electronic structure of Li-doped NiO.

Abstract: The electronic structure of ${\mathrm{Li}}_{\mathit{x}}$${\mathrm{Ni}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$O has been investigated using x-ray photoemission spectroscopy (XPS), bremsstrahlung isochromat spectroscopy (BIS), and model-Hamiltonian cluster calculations. The measurements support the conclusion that the Li-doped holes have mainly oxygen character. The unoccupied electronic structure as probed with BIS shows broad structures growing in the gap. By comparing the XPS valence band to the results of the cluster calculations, we determine values for the Racah A parameter (=6.6 eV), charge transfer \ensuremath{\Delta} (=6.2 eV), and hybridization transfer integral (pd\ensuremath{\sigma}) (=1.3 eV). The first ionization state in the NiO valence-band cluster calculation is of $^{2}$${\mathit{E}}_{\mathit{g}}$ symmetry, a state in which the doped hole is antiferromagnetically coupled to the Ni spins. Hole-doped cluster calculations explain, because of a different fractional parentage upon annihilating a Ni 3d or an O 2p hole, the difference between the O 1s XAS results and the BIS results of heavily Li-doped NiO.

Strain-hardening of dough as a requirement for gas retention

Abstract: Mechanisms that can be responsible for the ability of wheat flour doughs to retain gas are discussed. It is concluded that the relevant types of physical instabilities are Ostwald ripening (disproportionation) and coalescence of gas cells. The extent of Ostwald ripening is probably primarily controlled by surface rheological properties; it certainly affects crumb structure, but it cannot explain the differences in gas retention among doughs from various cereals or various wheat cultivars. It is argued that surface forces only provide a stabilizing mechanism for dough films between gas cells, i.e., against coalescence, for films that are much thinner than the diameter of a starch granule. It is concluded that variation in the potential for gas retention among wheat flour doughs is largely due to variation in bulk rheological properties. We propose a new rheological criterion for the extensibility of dough films between gas cells (and thereby for gas retention) that is based on the strain hardening of the dough in biaxial extension exceeding a specific lower limit. The criterion is translated into measurable parameters. Preliminary experiments on doughs with poor and with satisfactory baking performance illustrate its potential importance.

Excess conductance of superconductor-semiconductor interfaces due to phase conjugation between electrons and holes.

Abstract: A semiclassical description is given of charge transport through a superconductor-semiconductor interface. As a result of the presence of a potential barrier both Andreev and normal reflection occur. Elastic scatterers in the semiconductor generate multiple reflections at the interface. The constructive quantum interference which results from the phase conjugation between electrons and holes enhances the (differential) conductance above its classical value. This excess conductance is suppressed by a magnetic field, or by a finite energy. The latter can be due to a finite voltage bias or a finite temperature.

The occurrence of high levels of acute behavioral distress in children and adolescents undergoing routine venipunctures.

Abstract: While there is no question that children dislike needles, there are very little data available on the occurrence of high levels of distress experienced by children undergoing routine venipunctures. To provide some insight into this problem, trained observers evaluated distress in 223 different children and adolescents undergoing this procedure. An observational distress scale of 1 to 5 was developed; 1 = calm, 2 = timid/nervous, 3 = serious distress, but still under control, 4 = serious distress with loss of control, and 5 = panic. We observed a strong relation between distress and age but not between distress and gender. During the actual venipuncture, half the subjects (113/223) were scored as having high levels of distress (3 or more). Our subjects were also grouped into three age ranges: toddlers; 2 1/2 to 6 years, N = 70; preadolescents; 7 to 12 years, N = 55; and adolescents; 12 years and older, N = 98. The percent of subjects experiencing high levels of distress for each age group were: 83%, 51%, and 28%, respectively. We conclude that for venipunctures: 1) high levels of distress are common, and 2) age and not gender correlates with distress. Other correlations are discussed. Toddlers and pre-adolescents should be the targets for new interventions to reduce distress.

Lactose binding to heat-labile enterotoxin revealed by X-ray crystallography.

Abstract: Recognition of the oligosaccharide portion of ganglioside GM1 in membranes of target cells by the heat-labile enterotoxin from Escherichia coli is the crucial first step in its pathogenesis, as it is for the closely related cholera toxin. These toxins have five B subunits, which are essential for GM1 binding, and a single A subunit, which needs to be nicked by proteolysis and reduced, yielding an A1-'enzyme' and an A2-'linker' peptide. A1 is translocated across the membrane of intestinal epithelial cells, possibly after endocytosis, upon which it ADP-ribosylates the G protein Gs alpha. The mechanism of binding and translocation of these toxins has been extensively investigated, but how the protein is orientated on binding is still not clear. Knowing the precise arrangement of the ganglioside binding sites of the toxins will be useful for designing drugs against the diarrhoeal diseases caused by organisms secreting these toxins and in the development of oral vaccines against them. We present here the three-dimensional structure of the E. coli heat-labile enterotoxin complexed with lactose. This reveals the location of the binding site of the terminal galactose of GM1, which is consistent with toxin binding to the target cell with its A1 fragment pointing away from the membrane. A small helix is identified at the carboxy terminus of A2 which emerges through the central pore of the B subunits and probably comes into contact with the membrane upon binding, whereas the A1 subunit is flexible with respect to the B pentamer.

Lysis-induced decline of a phaeocystis spring bloom and coupling with the microbial foodweb

Abstract: We studied the development and decline of the 1990 phytoplankton spring bloom in the Marsdiep area of the North Sea (The Netherlands) with emphasis on the cause of the decline of the Phaeocystis bloom, the role of microbial organisms and the utilization of organic material produced by the algae. At the top of the bloom Phaeocystis was nitrogen limited. The bloom declined through cell lysis. Sinking of colonies and grazing were found to be relatively unimportant as loss factors. Biomass in the microbial foodweb (bacteria and protozooplankton) remained low during the bloom but increased sharply as the bloom started to decline indicating that organic carbon released by the phytoplankton was rapidly utilized in the microbial foodweb. Results suggest that dissolved organic carbon produced by phytoplankton through excretion and lysis was the main source of carbon for the microbial foodweb including copepods.

Malignant parotid tumors - clinical use of mr imaging and histologic correlation

Abstract: Magnetic resonance (MR) imaging was performed in 116 patients in whom a parotid mass lesion was clinically suspected. Eighty-six patients had benign disease. The 30 patients in whom a malignant tumor was found were further evaluated. To determine which features are characteristic of malignant parotid tumors, spin-echo T1- and T2-weighted images of malignant lesions in the parotid gland were compared with those of benign disease. In our series, tumor margins, homogeneity, or signal intensity were not discriminative factors to correctly predict benign or malignant disease. Infiltration into deep structures (eg, the parapharyngeal space, muscles, and bone) was observed only in malignant tumors. Infiltration into subcutaneous fat was noticed in malignant as well as in inflammatory disease. No statistically significant correlation was found between tumor grade and MR imaging features in malignant disease. MR imaging is useful in delineating malignant tumors but is unreliable in correctly predicting the histologic nature of a mass lesion in the parotid gland.

Protocol for the prevention and treatment of oral sequelae resulting from head and neck radiation therapy.

Abstract: In addition to the desired antitumor effects, head and neck radiation therapy induces damage in normal tissues that may result in oral sequelae such as mucositis, hyposalivation, radiation caries, taste loss, trismus, soft-tissue necrosis, and osteoradionecrosis. These sequelae may be dose-limiting and have a tremendous effect on the patient's quality of life. Current policies to prevent these sequelae primarily are based on clinical experience and show great diversity. A protocol for the prevention and treatment of oral sequelae resulting from head and neck radiation therapy, based on fundamental research and data derived from the literature, is presented. The protocol is particularly applicable in centers with a dental team. This team should be involved at the time of initial diagnosis so that a successful preventive regimen is an integral part of the overall cancer treatment regimen.