Showing papers by "University of Groningen published in 1984"

The Infrared Astronomical Satellite (IRAS) mission

Abstract: The Infrared Astronomical Satellite (IRAS) consists of a spacecraft and a liquid helium cryostat that contains a cooled IR telescope. The telescope's focal plane assembly is cooled to less than 3 K, and contains 62 IR detectors in the survey array which are arranged so that every source crossing the field of view can be seen by at least two detectors in each of four wavelength bands. The satellite was launched into a 900 km-altitude near-polar orbit, and its cryogenic helium supply was exhausted on November 22, 1983. By mission's end, 72 percent of the sky had been observed with three or more hours-confirming scans, and 95 percent with two or more hours-confirming scans. About 2000 stars detected at 12 and 25 microns early in the mission, and identified in the SAO (1966) catalog, have a positional uncertainty ellipse whose axes are 45 x 9 arcsec for an hours-confirmed source.

A consistent empirical potential for water-protein interactions

Abstract: A simple point-charge potential, developed earlier for the calculation of intermolecular forces in molecular-dynamics simulations of liquid water, has been extended to include interactions between water molecules and polar groups of proteins. A complete potential for use in the simulation of protein dynamics in water is reported.

The effect of selective decontamination of the digestive tract on colonisation and infection rate in multiple trauma patients.

Abstract: 122 multiple trauma patients staying in the ICU for 5 or more days and needing mechanical ventilation were investigated to determine the effect of selective decontamination of the digestive tract on prevention of infection. The (retrospectively studied) control group of 59 patients received no antibiotic prophylaxis. The infection rate during ICU-stay was 81%. Most infections were caused by potentially pathogenic microorganisms (PPM) from the oral cavity or the intestines (i.e. endogenous infections). The oropharynx and the intestines were rapidly colonised with ICU-associated gram-negative bacilli. After 2 weeks more than 80% of patients were found colonised. This secondary colonisation of the digestive tract is a very important stage in the pathogenesis of infections. Sixty-three patients were selectively decontaminated with nonabsorbable antibiotics, administered through the gastric tube even if peristalsis was absent. Emphasis was laid on the selective decontamination of the oral cavity, using topical application of an antibiotic paste. With this technique the oral cavity was free of PPM within 3 days in most patients. No secondary colonisation was found. Rectal colonisation decreased significantly after 5 days. Secondary colonisation occurred in 9 patients with PPM sensitive to the antibiotics used. The prophylactic regimen included systemic cefotaxim, directed against early endogenous infection. The suppression and after some time the absence of the endogenous source of PPM resulted in a significant reduction of colonisation and infection. The total infection rate decreased to 16%.

Infrared cirrus - new components of the extended infrared-emission

Abstract: Extended sources of far-infrared emission superposed on the zodiacal and galactic backgrounds are found at high galactic latitudes and near the ecliptic plane. Clouds of interstellar dust at color temperatures as high as 35 K account for much of this complex structure, but the relationship to H I column density is not simple. Other features of the extended emission show the existence of warm structures within the solar system. Three bands of dust clouds at temperatures of 150-200 K appear within 10 deg on both sides of the ecliptic plane. Their ecliptic latitudes and derived distances suggest that they are associated with the main asteroid belt. A third component of the 100-micron cirrus, poorly correlated with H I, may represent cold material in the outer solar system or a new component of the interstellar medium.

The effect of social motives, communication and group size on behaviour in an N-person multi-stage mixed-motive game

Abstract: Two experiments investigated the impact of social motives or individuals' preferences for specific self–other outcome distributions, on behaviour in an n-person game. Subjects' social motives (altruistic, cooperative, individualistic, competitive) were assessed prior to the decision-making in either 7-person games (Experiment 1) or 20-person games (Experiment 2). A modification of the n-person game format normally employed is introduced in this research to permit the choices made by players on a given trial to modify the payoff matrix available to self and others on subsequent trials. The game format, a simulated social dilemma, was presented in terms of a conservation of resources problem. In Experiment 1 communication opportunities were manipulated. As predicted, there were consistent differences between the four classes of social motivation in the amount of the resources taken for self: competitive subjects took the most, individualistic subjects took less than the competitive ones but more than the average, while cooperative and altruistic subjects took the smallest amount of the resources for themselves. Moreover, competitive subjects expected the others to take fewer resources than they intended to themselves, and altruistic subjects expected the others to take more resources than they intended to themselves. These findings are only partly consistent with existing theories concerning the relationship between behaviour and expected behaviour of others. In addition, when communication was allowed, significantly fewer resources were taken for self. Contrary to the predictions based on previous research findings, subjects in the 20-person groups did not take more resources for self than subjects in the 7-person groups.

3.2 Å structure of the copper-containing, oxygen-carrying protein Panulirus interruptus haemocyanin

Abstract: For the first time, the three-dimensional structure of a member of the copper-containing class of oxygen-carrying proteins—the haemocyanins—has been determined. The structure of Panulirus interruptus haemocyanin at 3.2 A resolution shows that each subunit of the 450,000-molecular weight hexamer is folded into three domains, and that the binuclear copper site is situated in the centre of the second domain. Amino acid sequence comparisons suggest that the polypeptide fold of P. interruptus haemocyanin is common to all arthropod haemocyanins.

Fast Continuous Swimming of Two Pelagic Predators, Saithe (Pollachius Virens) and Mackerel (Scomber Scombrus): a Kinematic Analysis

Abstract: Straight, forward, unrestrained swimming behaviour, with periodic lateral oscillations of body and tailfin, was described and compared for saithe and mackerel. A method was developed for kinematic analysis of forward motion, lateral displacements and body curvature, based on a Fourier-series approach. The dimensionless kinematic quantities showed relatively small variations over large ranges of swimming speeds. The speed range of mackerel was twice as fast as that of saithe. The main difference in swimming style between the species was a somewhat greater tail amplitude and a correspondingly stronger curvature near the caudal peduncle in mackerel than in saithe. The swimming style of both species yields a Froude efficiency close to the maximum value possible, given the observed amplitude increase in the posterior part.

Functional anatomy of germinal centers

Abstract: This year we celebrate the first centennial of the discovery of germinal centers by Flemming in 1884. The present paper reviews and adds new data to the functional anatomy of a germinal center. Emphasizing its reactive nature, we first describe a germinal center reaction and then deal with its infrastructural aspects and constituent cell populations, both lymphoid and nonlymphoid. Elements involved in the de novo formation of a germinal center, like antigen, T cells, and the mysterious germinal-center-precursor cell, are discussed. Next, attention is paid to the requirements for lymphoid cells to migrate into germinal centers, and novel features of germinal-center-seeking cells are presented. Subsequently, we discuss kinetic aspects of the high proliferative activity in a germinal center; and finally a description of the functional capacities of germinal-center-derived cells, such as B memory cells and IgM-antibody-forming cell precursors, completes this picture of present-day knowledge of the germinal center, a structure which has yet to reveal its last secrets.

Global adaptive stabilization in the absence of information on the sign of the high frequency gain

Abstract: An adaptive control algorithm is presented which globally stabilizes any n-th order linear time-invariant system having (n-1) left half plane zeros. Knowledge of the sign of the high frequency gain is not required for convergence.

Micro-patterns in grassland vegetation created and sustained by sheep-grazing

Abstract: An initially uniform Holcus lanatus-dominated sward came partly under hay-making and partly under sheep-grazing. Preferential grazing by sheep resulted in grazing at different intensities giving rise to a macro-pattern of various plant communities. Besides this macro-pattern a micro-pattern developed in the grazed area, which was absent under hay-making. In the micro-pattern short, heavily grazed areas alternated with taller, lightly grazed patches, both having the same species composition. The heavily grazed area was characterized by equal amounts of monocots and dicots. The lightly grazed patches were dominated by Agrostis tenuis, and had a large amount of litter which probably causes the absence of mosses. The protein percentage of green material is higher in the heavily grazed areas than in the lightly grazed patches. Sequential charting indicated that the micro-pattern was more or less stable. An interaction between the vegetation micro-pattern and grazing patterns is suggested. Heavy grazing results in forage with a high protein content and hence attracts animals. Light grazing results in forage with a relatively low protein content, animals avoid the area and litter accumulates.

4.6 Micron absorption features due to solid phase CO and Cyano group molecules toward compact infrared sources

Abstract: Spectra obtained at a resolving power of 840, for seven protostellar sources in the region of the 4.67-micron fundamental vibrational band of CO, indicate that the deep absorption feature in W33A near 4.61 microns consists of three features which are seen in other sources, but with varying relative strength. UV-irradiation laboratory experiments with 'dirty ice' temperature cycling allow the identification of two of the features cited with solid CO and CO complexed to other molecules. Cyano group-containing molecules have a lower vapor pressure than CO, and can therefore survive in much warmer environments. The formation and location of the CO- and CN-bearing grain mantles and sources of UV irradiation in cold molecular clouds are discussed. Plausible UV light sources can produce the observed cyano group features, but only under conditions in which local heat sources do not cause evaporation of the CO molecules prior to their photoprocessing.

Adaptive stabilization of multivariable linear systems

Abstract: A ''Universal adaptive stabilization algorithm is presented which, for any m, stabilizes all minimum phase mxm multivariable systems having an invertible high frequency gain.

Descending pathways from hypothalamus to dorsal motor vagus and ambiguus nuclei in the rat

Abstract: The anatomical pathways between the hypothalamus and cell groups of the lower medulla that are involved in the neural control of endocrine pancreas activity were investigated As part of this control system the descending pathways originating from lateral, dorsomedial and ventromedial hypothalamic nuclei towards the dorsal motor vagus and ambiguus nuclei, were studied by retrograde transport of horseradish peroxidase Very small injections of the tracer, by means of the iontophoretic delivery method, were placed in the dorsal motor vagus, ambiguus and solitary tract nucleus as well as in the various nuclei of the medullary reticular formation Subsequent retrograde labeling was studied in the hypothalamus and the brainstem The appearance of considerable retrograde labeling in mesencephalic periventricular grey and rostral mesencephalic reticular formation indicated a possible role for these structures as intermediates in an indirect hypothalamo-medullary control circuitry This led us to extend the peroxidase injections to these mesencephalic areas after which the hypothalamus was investigated for retrograde labeling All data combined indicated the existence of three descending pathways, direct and indirect, between hypothalamus and the parasympathetic motor nuclei of the lower medulla

Measuring muscle strength

Abstract: A dynamometer that can be held in the hand and that was designed to measure muscle strength in a simple way in the range 2–5 of the MRC scale, was tested in order to establish to what extent differences in results can be attributed to the observer, the subject and replication. Observers learned the technique quickly and their results agreed with each other to a considerable extent. The subjects showed a small learning effect in three of the four muscles tested. Normal muscle strength was measured in one hundred 18-year-old men.

Pathway of propionate formation in desulfobulbus-propionicus

Abstract: Whole cells of Desulfobulbus propionicus fermented [1-13C]ethanol to [2-13C] and [3-13C]propionate and [1-13C]-acetate, which indicates the involvement of a randomizing pathway in the formation of propionate. Cell-free extracts prepared from cells grown on lactate (without sulfate) contained high activities of methylmalonyl-CoA: pyruvate transacetylase, acetase kinase and reasonably high activities of NAD(P)-independent L(+)-lactate dehydrogenase NAD(P)-independent pyruvate dehydrogenase, phosphotransacetylase, acetate kinase and reasonably high activity of NAD(P)-independent L(+)-lactate dehydrogenase, fumarate reductase and succinate dehydrogenase. Cell-free extracts catalyzed the conversion of succinate to propionate in the presence of pyruvate, CoA and ATP and the oxaloacetate-dependent conversion of propionate to succinate. After growth on lactate or propionate in the presence of sulfate similar enzyme levels were found except for fumarate reductase which was considerably lower. Fermentative growth on lactate led to higher cytochrome b contents than growth with sulfate as electron acceptor. The labeling studies and the enzyme measurements demonstrate that in Desulfobulbus propionate is formed via a succinate pathway involving a transcarboxylase like in Propionibacterium. The same pathway may be used for the degradation of propionate to acetate in the presence of sulfate.

Fast continuous swimming of saithe (pollachius virens): a dynamic analysis of bending moments and muscle power

Abstract: This paper deals with the hydrodynamics and internal dynamics of fish swimming. Our analysis starts from kinematic data obtained for fast swimming saithe, and treats the fish as a flexible elongated body. The distribution along the body of the lateral bending moment and the bending power generated inside the fish are computed as well as the power spent on the water. The computed thrust implies a drag coefficient (based on wetted surface area) of about 0.007, which is probably an over-estimate. Our major result is that the bending moment does not travel as a running wave from head to tail like the lateral body curvature does, but behaves as a standing wave. The left and right sides produce alternate contractions simultaneously over the whole body length. This finding is in agreement with myographic data from the literature.

Competition for sulfate and ethanol among Desulfobacter, Desulfobulbus, and Desulfovibrio species isolated from intertidal sediments.

Abstract: Competition for sulfate and ethanol among Desulfobacter, Desulfobulbus, and Desulfovibrio species isolated from estuarine sediments was studied in energy-limited chemostats. Desulfovibrio baculatus was the most successful competitor for limiting amounts of sulfate and ethanol, followed by Desulfobulbus propionicus. The success of Desulfovibrio baculatus was dependent on the availability of sufficient iron. Of the three species studied, Desulfobacter postgatei was the least successful competitor for limiting amounts of sulfate. Although stimulating the growth of Desulfobacter postgatei, addition of Ca-saturated illite particles to culture media did not affect the outcome of competition for sulfate. Thus, under sulfate limitation acetate accumulated. This phenomenon was briefly discussed in relation to the flow of electrons during anaerobic mineralization in marine and estuarine sulfate-limited sediments.