Showing papers by "University of Groningen published in 1977"

Algorithms for macromolecular dynamics and constraint dynamics

Abstract: The application of the computer simulation method of molecular dynamics to macromolecules is investigated. The protein trypsin inhibitor (BPTI), consisting of 454 united atoms, is used as an example. Different algorithms for integrating the equations of motion are compared, both theoretically and in practice. It is examined to what extent the chain structure of a macromolecule allows a reduction of the computational effort by the introduction of constraints in the dynamics of the chain. A calculational scheme is proposed, by which constraints can be incorporated in predictor-corrector algorithms. The optimum choice of an algorithm depends on the desired accuracy of the solution and on the character of the forces acting on the molecule, viz. whether these are noisy or not. For nonconstraint dynamics a Gear predictor-corrector algorithm yields the best results, whereas for constraint dynamics the Gear and Verlet algorithms produce comparable results. The application of bond-length constraints reduces the re...

Quasi-atomic auger-spectra in narrow-band metals

Abstract: In this Letter it is shown that quasiatomiclike Auger spectra in narrow-band metals are a direct result of electron correlation effects. It is shown that if the "on-site" Coulomb interaction is much larger than the one-electron-band width, the Auger spectrum consists of an intense narrow atomiclike peak together with a weak broad bandlike peak at higher kinetic energy. On the other hand, if the Coulomb interaction is small the Auger spectrum will resemble the convolution of the band density of states convoluted with itself.

Orthogonal Procrustes Rotation for Two or More Matrices.

Abstract: Necessary and sufficient conditions for rotating matrices to maximal agreement in the least-squares sense are discussed. A theorem by Fischer and Roppert, which solves the case of two matrices, is given a more straightforward proof. A sufficient condition for a best least-squares fit for more than two matrices is formulated and shown to be not necessary. In addition, necessary conditions suggested by Kristof and Wingersky are shown to be not sufficient. A rotation procedure that is an alternative to the one by Kristof and Wingersky is presented. Upper bounds are derived for determining the extent to which the procedure falls short of attaining the best least-squares fit. The problem of scaling matrices to maximal agreement is discussed. Modifications of Gower's method of generalized Procrustes analysis are suggested.

Lmm auger-spectra of cu, zn, ga, and ge .1. transition-probabilities, term splittings, and effective coulomb interaction

Abstract: The $\mathrm{LMM}$ Auger spectra of Cu, Zn, Ga, and Ge are presented and discussed. Transition probability calculations are described and with these a clear assignment of the peaks can be made. It is further shown that from the ${L}_{3}{M}_{45}{M}_{45}$ Auger lines the term splittings and the effective on-site electron-electron interaction can be determined. The latter is shown to be strongly reduced from the free-atom value. This has important consequences for the description of the band structure using one-electron theories. The satellite structure for Cu and Zn in the ${L}_{3}{M}_{45}{M}_{45}$ region of the spectrum is shown to be a result of strong Coster-Kronig processes involving the ${L}_{2}$ and ${L}_{3}$ core levels.

Palynological investigations in Western Iran

Abstract: (p. 83) In this paper the palynological examination of sediment cores from Lake Zeribar and Lake Mirabad in the Zagros Mountains of western Iran is discussed. Radiocarbon dates suggest that the Lake Zeribar pollen record covers the last 40,000 years, that of Lake Mirabad the last 10,000 years. Topography, climate and natural vegetation of western Iran are briefly reviewed in chapter 2 (figs. 1-3). Information on the coring localities is presented in chapter 3. In chapter 4 short descriptions are given for a great number of pollen types distinguished in the Iranian sediment cores (figs. 10-20). In the period of c. 40,000 to c. 10,500 B.P. open vegetations, in which Chenopodiaceae, Artemisia , and Umbelliferae played a predominant part, prevailed in the Zagros Mountains. The high percentages for umbelliferous pollen, among which a fairly large number of types could be distinguished, are a conspicuous feature of the Zeribar pollen diagrams. Scattered tree stands were present in the Zeribar area in the period of c. 40,000 - 22,000 B.P., whereas between c. 22,000 and 14,000 B.P. trees had disappeared completely from the Zeribar area and probably from the greater part of the Zagros Mountains. Climatic dryness must have been a major limiting factor for tree growth in western Iran in Pleniglacial times. After 14,000 B.P. pistachio was again present in the Zeribar area. Trees ( Pistacia , Quercus , Acer , and others) expanded slowly in western Iran after 10,500 B.P., which resulted in forest-steppe vegetation. The nature of the herbaceous vegetation differed markedly from that in Pleniglacial times. It was not until c. 5,500 B.P. that the present-day natural forest cover had established itself. In the upper sections of the Zeribar and Mirabad diagrams distinct indications of human activity are recorded. A comparison of the Zeribar pollen record with that of sites in Greece, southwestern Turkey, and western Syria indicates that rhe Pleniglacial climate of continental western Iran must have been more adverse to tree growth than that of areas near the Mediterranean coasts. Most pollen diagrams from the Eastern Mediterranean area suggest that the early Postglacial climate was drier than that of today. Whether this was due to lower precipitation or to drier summers (higher temperatures, longer rainless period) is not yet clear. Finally same archaeological implications of the results of the palynological investigation are discussed.

A simple density separation technique for quantitative isolation of meiobenthos using the colloidal silica Ludox-TM

Abstract: A simple, quantitative density separation method is described. The method is based on differences in specific weight between meiobenthos and sediment. Nematodes and copepods could be separated from sediment and detritus when samples were suspended in Ludox-TM, a colloidal silica. Organisms float at the surface, while sediment particles sink. Results obtained with this new method were compared with the well-known decantation method. For a quantitative isolation of nematodes from sediments, rich in coarse detritus, a maximum volume of 7 cm3 sample could be used. For copepods this maximum was 13 cm3. For such sediments the density method is more reliable than the decantation method. The time needed for sorting the meiobenthic organisms is reduced to about 30% compared with the former method. The new method can be used for preserved as well as for fresh sediment samples and can also be applied for the disolation of small polychaetes, small oligochaetes, larvae of some macrofaunal groups and net-zooplankton.

Influence of light and temperature on the growth rate of estuarine benthic diatoms in culture

Abstract: Four species of estuarine benthic diatoms: Amphiprora c. f. paludosa W. Smith, Nitzschia c. f. dissipata (Kutzing) Grunow, Navicula arenaria Donkin, and Nitzschia sigma (Kutzing) W. Smith were grown in unialgal cultures. The growth rates of the diatoms were determined as the rate of increase of the chlorophyll a content of the cultures. The diatoms were cultured at different combinations of temperture, daylength, and quantum irradiance. The highest growth rates of Navicula arenaria occurred at 16° to 20°C; the other 3 species had their optimum at 25°C or higher. The small-celled species had higher growth rates at their optimum temperature, but at lower temperatures the growth rates of all 4 species became very similar. The minimum daily quantum irradiance that could effect light-saturated growth at 12° and 20°C ranged from 2.5 to 5.0 E.m-2.day-1. At 12°C, two species had their highest growth rates under an 8 h daily photoperiod. At 20°C, the three species tested all had highest growth rates under 16 h daily photoperiod. The growth response of the benthic diatoms is comparable to that of several cultures of planktonic diatoms, as described in the literature. The influence of temperature and quantum irradiance on the diatoms in the present investigation was comparable to the influence of temperature and light intensity on the 14C-fixation of marine benthic diatoms (Colijn and van Buurt, 1975).

Rapid concurrent automated fluorimetric assay of noradrenaline, dopamine, 3,4-dihydroxyphenylacetic acid, homovanillic-acid and 3-methoxytyramine in milligram amounts of nervous-tissue after isolation on sephadex g10

Abstract: — A semi-automated fluorimetric assay technique for the concurrent estimations of noradrenaline, dopamine, 3, 4-dihydroxyphenylacetic acid, homovanillic acid and 3-methoxytyramine is described. The method is based on a rapid manually performed isolation of the catecholamines and metabolites on small columns of Sephadex G10, followed by automated fluorimetric dection in continuous flow systems. Samples containing no more that 2-5 ng (NA, DA, DOPAC or HVA) or 10 ng 3-MT could be reproducibly measured. The small Sephadex G10 columns has proven to be an excellent alternative to the currently used columns of alumina or ion-exchange resins.

Biradical cidnp and dynamics of polymethylene chains

Abstract: An analysis is given of the field dependence of CIDNP generated in reactions of flexible polymethylene biradicals. Nuclear polarization is calculated by a stochastic Liouville method, in which the ...

Phenol sulphotransferase and uridine diphosphate glucuronyltransferase from rat liver in vivo and in vitro. 2,6-Dichloro-4-nitrophenol as selective inhibitor of sulphation

Abstract: Microsomal UDP-glucuronyltransferase and cytosolic sulphotransferase share many substrates, such as phenols and hydroxamic acids. In a search for a selective inhibitor of sulphation, several phenolic compounds were tested. 2,6-Dichloro-4-nitrophenol is introduced as a selective inhibitor of sulphation in vivo, having no effect on UDP-glucuronyltransferase activity. As substrate for both conjugating enzymes the phenolic drug harmol (7-hydroxy-1-methyl-9H-pyrido[3,4-b]indole) was used. In the rat in vivo 2,6-dichloro-4-nitrophenol caused almost complete inhibition of harmol sulphation after a single intraperitoneal injection (26μmol/kg) for 48h; the percentage of harmol sulphated decreased from 75% in controls to 5% in the treated rats. The percentage of harmol glucuronidated increased from 25 to 95%. Pentachlorophenol was equally effective but also highly toxic. Salicylamide had only a very-short-lasting inhibitory effect on sulphation. In vitro, 2,6-dichloro-4-nitrophenol inhibited sulphation of harmol by a rat liver postmitochondrial supernatant completely at 1μm, whereas even at 100μm it had no effect on glucuronidation of harmol. It is concluded that 2,6-dichloro-4-nitrophenol is a selective inhibitor of sulphation and, further, that its long duration of action makes it suitable for studies on the regulatory role of sulphation in some biological processes.

Ecological Studies with the Chemostat

Abstract: Most natural and seminatural environments are inhabited by a large variety of microorganisms. The functional status of a particular organism is difficult to assess in the highly complex field situation. Therefore, methods were developed to isolate microbes in pure culture and to study their characteristics in the laboratory. Many pure cultures of bacteria were isolated from batch enrichments and subsequently studied in a closed culture system. This approach was highly successful. In this way the various types of energy metabolism occurring in prokaryotic organisms were discovered so that deductions could be made about the role specific microorganisms play in the cycling of the elements. In addition, many details could be elucidated about metabolic pathways and their regulation.

Effect of Low Temperature upon Lipid and Fatty Acid Composition of Roots and Leaves of Winter Rape Plants

Abstract: When winter rape plants were transferred from favourable temperature conditions (25/20°C day/night temperature) to 5°C, the frost resistance of the leaves was increased whereas the frost tolerance of the roots remained unaffected. This permitted an analysis of the changes in lipid and fatty acid composition both as related to functioning of the plant at low temperature alone (roots) and as related to adaptation to freezing and functioning at low temperature (leaves). — Transfer of the plants to 5°C lead to an increase in the level of linolenic acid in roots and leaves. This increase was most evident in the phosphatidyl choline and ethanolamine fractions of the leaves, and in the neutral lipids and in an unidentified phospholipid from the roots. It was concluded that upon transfer of the plants to 5°C a general and non-specific increase in linolenic acid level contributed to functioning of the rape plants at low temperature; and that parallel but minor increases in linolenic acid level of digalactosyl diglyceride, phosphatidyl inositol and the unknown phospholipid in roots and leaves could only contribute to low-temperature functioning in specific membrane enzyme locations. Combined adaptation of the leaves to freezing tolerance and low-temperature functioning was correlated with a higher level of phosphatidyl choline and ethanolamine, predominantly esterified with linolenic acid.

Lmm auger-spectra of cu, zn, ga, and ge .2. relationship with l23 photoelectron-spectra via l2l3m45 coster-kronig process

Abstract: In this paper we present conclusive experimental evidence that the Auger satellite structure on the low-kinetic-energy side of the ${L}_{3}{M}_{45}{M}_{45}$ Auger spectra in Cu and Zn is a direct result of the ${L}_{2}{L}_{3}{M}_{45}$ Coster-Kronig transition preceding the Auger transition. The position of the satellite structure is compared with numerical calculations of the final state for the ionized atoms. The same Coster-Kronig process is shown to be responsible for the anomalous intensity ratio of the ${L}_{2}{M}_{45}{M}_{45}$ to ${L}_{3}{M}_{45}{M}_{45}$ Auger spectra. From this intensity ratio the Auger part of the ${L}_{23}$ photoelectron linewidths can be determined and is shown to be in reasonable agreement with theoretical values.

Tolerance of estuarine benthic diatoms to high-concentrations of ammonia, nitrite ion, nitrate ion and orthophosphate

Abstract: Ten species of benthic diatoms from the Eems-Dollard estuary were cultured unialgally in synthetic media with various concentrations of ammonia (NH4 ++NH3), nitrite ion, nitrate ion and orthophosphate. Most of the species grew well in media with very high concentrations of nitrite ion (1 to 10 mg-at N l-1), nitrate ion (about 16.9 mg-at N l-1) and orthophosphate (at least 0.9 mg-at P l-1). Ammonia concentrations higher than 0.5 mg-at N l-1 inhibited growth of the cultures. The rate of photosynthesis of diatoms from the field and from cultures was also inhibited by 0.5 mg-at N l-1 of ammonia under certain conditions. Inhibition of photosynthesis by ammonia was strongly enhanced by high irradiance and high pH. It is most unlikely that nitrite ion, nitrate ion and orthophosphate attain concentrations high enough to be inhibitory in the field, but concentrations of ammonia may be high enough for inhibition to occur. However a clear relationship between sensitivity of the diatoms and their occurrence on more or less polluted mudflats was not found.

Retinal Lattice, Visual Field and Binocularities in Flies. Dependence on Species and Sex

Abstract: The arrangements of ommatidia are charted and the visual fields of the compound eyes are plotted for both male and female of the dipteran speciesMusca domestica L.,Calliphora erythrocephala M.,Stomoxys calcitrans L.,Syritta pipiens L. andFannia fannia L. At the level of the retina remarkable differences between different species and between the sexes of one species exist. Consequences of the small binocular overlap area with respect to depth perception are discussed.

Rabbit grazing and species-diversity in a dune area

Abstract: The relation between density of rabbit populations and plant species diversity is discussed. In the dunes of the Dutch Frisian Island of Schiermonnikoog, the rabbit grazing pressure has been quantified on the basis of traces of recent grazing activity. Moderate grazing turned out to bring about maximal species richness. Current changes in grazing pressure (either decrease or increase) can result in plant species diversity that is lower than in other places with equal but stabilized grazing pressure.

Infrared Astronomical Satellite (IRAS)

Abstract: In this paper we will describe the scientific objectives and conceptual design of the Infrared Astronomical Satellite: a joint proposal for an all sky infrared survey between the Netherlands, the United Kingdom and the United States This paper is based on the results of a series of studies that have been made recently Initially the proposal for an infrared survey satellite was made to the Dutch government on the occasion of the launch of the ANS satellite in August 1974 This proposal formed the basis of a study in the Netherlands during 1975 In the course of the study coordination with similar proposals in the United States resulted in the creation of a joint Netherlands-UK-US mission definition team This joint team concluded its work in May 1976 As a large number of individuals and institutes contributed to the study report and my presentation heavily draws on it, this paper should be considered as a summary of the work performed by the joint study team