Showing papers by "University of Groningen published in 1986"

The site of attachment in human rhinovirus 14 for antiviral agents that inhibit uncoating

Abstract: WIN 51711 and WIN 52084 are structurally related, antiviral compounds that inhibit the replication of rhino (common cold) viruses and related picornaviruses. They prevent the pH-mediated uncoating of the viral RNA. The compounds consist of a 3-methylisoxazole group that inserts itself into the hydrophobic interior of the VP1 beta-barrel, a connecting seven-membered aliphatic chain, and a 4-oxazolinylphenoxy group (OP) that covers the entrance to an ion channel in the floor of the "canyon." Viral disassembly may be inhibited by preventing the collapse of the VP1 hydrophobic pocket or by blocking the flow of ions into the virus interior.

The influence of substratum surface free energy on growth and spreading of human fibroblasts in the presence and absence of serum proteins

Abstract: To determine whether the surface free energy of polymer materials influences the spreading of 13 polymers and glass were related to spreading and growth of human skin fibroblasts. Experiments were performed in both the presence and absence of serum proteins. We calculated the surface free energy from contact angles of phosphate-buffered saline (PBS), n-propanol/PBS mixtures, and alpha-bromonaphthalene on the polymers, using the concept of polar and dispersion components accounting for spreading pressures. Cell spreading and substratum surface free energy (gamma s) showed a characteristic sigmoid relationship both in the presence and in the absence of serum proteins; good spreading only occurred when gamma s was higher than approximately 57 erg . cm-2. In the presence of serum proteins, cell spreading is similar on most materials; only few materials show relatively high cell spreading. Cell growth in the presence of serum proteins did not differ significantly on the various polymers with reference to their gamma s values. In contrast, two groups of polymers could be distinguished in the absence of serum with respect to cell growth. The first group showed increasing cell growth with increasing gamma s, whereas the second group showed consistently low cell growth. The results demonstrate the complex relationship between cell spreading and substratum surface free energy as well as the role of serum proteins in modifying the surface characteristics of polymers in relation to cell spreading and growth.

Experimental proof of magnetic-x-ray dichroism

Abstract: What we believe to be the first experimental results have been obtained on strong magnetic x-ray dichroism in the ${M}_{4,5}$ absorption spectra of magnetically ordered rare-earth materials, in accordance with recent predictions.

Comparison of x-ray absorption with x-ray photoemission of nickel dihalides and nio

Abstract: High-resolution ${L}_{2}$,3 x-ray absorption data are presented for nickel dihalides and nickel oxide. The near-edge multiplet splitting is observed to decrease rapidly with decreasing anion electronegativity. This decrease is accompanied by an increase in a satellite feature. A detailed analysis of the data in terms of recently proposed many-body theories is presented and is shown to yield excellent agreement with experiment allowing a determination of the charge-transfer energy, the d-d Coulomb interaction, and the Ni d--anion p hybridization interaction. We show that the values obtained are in good agreement with those obtained from x-ray photoelectron spectroscopy even though the spectral shapes are strongly different. The difference in spectral shapes is shown to be due to the very different final states.

The nature of early caries lesions in enamel.

Abstract: Since 1935, various mechanisms have been suggested for the formation of subsurface lesions and, in particular, the surface layer covering enamel lesions. The relatively intact mineral-rich and porous surface layer is most likely caused by kinetic events. The suggested mineral-rich outer layer in sound enamel, the organic matrix, the pellicle, or a non-uniform ion distribution have all been shown to be non-essential for surface layer formation; they may, however, influence the rate of surface layer formation. Models based on outer surface protection by adsorbed agents, the dissolution-precipitation mechanism, and combinations of these two models, as well as models based on porosity or solubility gradients, are discussed in this paper together with their advantages and disadvantages. Most models have not explained some important recent experimental observations on initial in vivo caries lesion formation: e.g., initial enamel lesions formed in vivo do not have a surface layer initially but develop this mineral-rich layer later on; and the fact that the F- level in the solid sound enamel is not determining the subsurface lesion formation. Furthermore, the observations that in vitro fluoride ions in the liquid at very low levels (approximately equal to 0.02 ppm) determine surface layer formation are difficult to explain. A new kinetic model for subsurface lesion formation is described, in which inhibitors such as F- or proteins play an important role. The model predicts that if lesions depth and demineralization period are denoted by df and t, lesion progress can be described by: dfp = alpha t + c, where alpha and c are constants with 1 less than or equal to p less than or equal to 3, depending on the lesion formation conditions. If lesion progress is entirely diffusion-controlled, p = 3, corresponding to low inhibitor concentrations; if the inhibitor content is so high that the progress is controlled by processes at the crystallite surface, p = 1. A kinetic mechanism for surface layer formation in vivo is proposed, based on the assumption that F- is a main inhibitor in the plaque-covered acidic in vivo situation. The inhibiting fluoride, adsorbed onto the crystallite surfaces at OH- vacancies, originates from the so-called fluoride in the liquid phase (FL) between the enamel crystallites. Under acidic conditions (plaque), we have, due to an influx of fluoride from the saliva or plaque as FL, an aqueous phase in the enamel supersaturated with respect to the mineral for a small distance (x*) only.(ABSTRACT TRUNCATED AT 400 WORDS)

Cell-wall synthesis in apical hyphal growth

Abstract: Publisher Summary This chapter discusses the cell wall synthesis in apical hyphal growth. It appears that the hyphal apex is best viewed as a highly polarized system of exocytosis. Wall materials, extracellular enzymes, and probably other substances are excreted at the growing end of a tubular cell. The most obvious cellular features that accompany this polarized system are (1) the unidirectional flow of vesicles in the cytoplasm fusing with the plasma membrane at the apex, (2) the gradients in wall synthesis at the apex, and (3) the cytoplasmic gradients in ion distribution that are maintained at the apex. New microscopic techniques reveal a cytoskeletal organization of the cytoplasm at the apex, which may be crucial to its polarized activity. Growth of the wall at the hyphal apex requires that the wall in this region has plastic properties, which contrast with the requirement of rigidity elsewhere in the hypha. A widely held view involves the participation of wall-lytic enzymes in plasticizing the wall at the apex and in allowing new wall material to be inserted. A critical evaluation of the evidence presented to support this view makes this hypothesis less attractive. As an alternative a steady-state model is discussed based on recent observations in the author's laboratory. This model holds that the assemblage of polymers synthesized at the apex is inherently plastic. However, this assemblage develops rigidity by interactions, in the wall, between and among the various individual polymers present while the wall segment moves in subapical directions during elongation. This model seems to fit many of the original observations made on living hyphae.

Determination of the electronic-structure of transition-metal compounds - 2p x-ray photoemission spectroscopy of the nickel dihalides

Abstract: A recently proposed impuritylike many-body theory for the electronic structure of transition-metal compounds is extended to core photoemission. The theory is worked out in detail for the nickel dihalides, and we compare the results with experimental 2p spectra. We show that these spectra can be used for a quantitative determination of the parameters in the theory. We furthermore show that the easy-to-handle cluster model is a fair approximation to the full theory as far as core x-ray photoemission is concerned. We find that the Coulomb interaction energies are the largest energies in the system, and we show that the order of magnitude of these can be estimated from an ionic screening model. Furthermore we show that the charge-transfer energies strongly vary along the series. A comparison with estimates for the parameters derived from other experiments show systematic discrepancies. We argue that these are due to the neglect of higher-order interactions in the model Hamiltonian used.

The Concept and Measurement of Mental Effort

Abstract: This chapter will address the following questions: What is meant by mental effort? What is its role in human information processing? How can effort be measured? The chapter will consider the ways in which the concept of effort has been used in different theories of human information processing. Effort may be measured in behavioural, subjective and physiological domains. The present approach will focus on the physiological indices. The concept of mental effort has been thought necessary in theories of behaviour for several reasons: (1) To account for individual differences in intellectual performance in terms of differences in motivation and in the availability of mental resources. (2) As an analogy for physical effort in theories of mental workload, and (3) To explain the effects of stressors such as noise, lack of sleep, time-on-task, etc, on human performance.

Feedback Control Systems

Abstract: Introduction and Linearized Dynamic Models Transfer Function Models of Physical Systems Modeling of Feedback Systems and Controllers The Performance of Feedback Systems Introduction to Feedback System Design The Root Locus Method Frequency Response Analysis Frequency Response Design Digital Control Systems Digital Control System Analysis and Design State-Space Analysis Introduction to State-Space Design Multivariable Systems in the Frequency Domain Nonlinear Control Systems Appendix A: Vectors, Matrices, and Determinants Appendix B: Computer Aids for Analysis and Design References Index

Correlations between the cross-sectional area of the jaw muscles and craniofacial size and shape

Abstract: In adult human subjects, the correlations were determined between the cross-sectional areas of the jaw muscles (measured in CT scans) and a number of facial angles and dimensions (measured from lateral radiographs). Multivariate statistical analysis of the skeletal variables in a group of 50 subjects led to the recognition of six independent factors determining facial shape, i.e., cranial base length, lower facial height, cranial base flexure and prognathism, facial width, mandibular length, and upper facial height. In 29 of these subjects, the cross-sectional areas of the jaw muscles were determined, and correlations between these areas and the scores on the above-mentioned factors were calculated. It appeared that the cross-sectional areas of temporalis and masseter muscles correlated positively with facial width, whereas the areas of masseter and both pterygoid muscles did so with mandibular length. It has been shown experimentally that a decrease in jaw muscle size in various animals likewise has an effect on facial width and mandibular length. Our results therefore support the hypothesis that in man too the jaw muscles affect facial growth and partly determine the final facial dimensions. They also hint that the role of each muscle is different.

A new prokaryote containing chlorophylls a and b

Abstract: Prochlorophyta, suggested as a new division of prokaryotes1, lack phycobilin pigments characteristic of cyanobacteria, but contain chlorophyll b as well as chlorophyll a, characteristic of green algae and higher plants. Since the description of Prochloron didemni as the type species for this division2, no other genera or species have been added to the group. The only published accounts of Prochloron are obligate symbionts of didemnid ascidians3, which are difficult to grow in the absence of their hosts4. Consequently, research on their cell composition and physiology has been handi-capped. Here, we report a second prochlorophyte. This organism is one of the dominant species in the shallow eutrophic Loosdrecht lakes in The Netherlands, from which it was isolated in 1984. Unlike Prochloron, the newly isolated species is filamentous and planktonic. Detailed investigation of its cell structure, composition and physiology is possible as it can easily be grown in a mineral medium.

Periodontal disease in Down's syndrome: a review.

Abstract: Cross-sectional as well as longitudinal studies indicate that the prevalence of periodontal disease in persons with Down's syndrome (DS) under the age of 30 years is extremely high. It is even noted in the deciduous dentition. The progression of the disease is rapid, especially in the younger age groups. Severe periodontal breakdown with horizontal bone loss is often present in the lower anteriors. The large amount of plaque and calculus alone cannot explain the severity of periodontal disease in DS persons. Many contributing factors are reported. Abnormal capillary morphology, disorders in connective tissue and anatomical aspects of teeth are some of those considered to be of influence. Alteration in immunological response may also play a role in the progression of the disease process. Disorders in the polymorphonuclear leucocyte function and monocyte function have been reported in persons with DS. T-cell functioning declines after the first 10 years of life. T-cell lymphocyte counts are low and an immature subset of T-lymphocytes is present. This latter effect occurs especially in institutions where the immunological system is under stress. The altered immune response together with higher calculus scores may explain the difference in severity of periodontal disease between institutionalized DS children and those living at home.

Estimation of statistical errors in molecular simulation calculations

Abstract: The naive estimation of errors in averages obtained from molecular simulation calculations may lead to serious underestimates due to the strong correlations that usually exist within the series. A commonly employed procedure to overcome this difficulty is to estimate the error from the deviation in the averages over subseries that are considered uncorrelated. However, without knowledge of the correlation the choice of the number of subseries cannot be soundly based. A method to estimate the statistical error using the correlation explicitly without serious additional computational effort and without the need for a tedious examination of the correlation behaviour itself is presented. Results of a test of this method for a molecular dynamics study on the polarization energy of xenon in liquid water are given and a comparison is made with the procedure based on subaverages and with a recently suggested method by Smith and Wells [1].

Chronic Use of Intracerebral Dialysis for the In Vivo Measurement of 3,4-Dihydroxyphenylethylamine and Its Metabolite 3,4-Dihydroxyphenylacetic Acid

Abstract: The intracerebral dialysis technique was studied with a method in which the rat was directly connected to the HPLC equipment. The effect of three pharmacological treatments [perfusion of 60 mmol K+ or 5 X 10(-5) M (+)-amphetamine or subcutaneous injection of 2 mg/kg (+)-amphetamine] on the release of 3,4-dihydroxyphenylethylamine (dopamine) and 3,4-dihydroxyphenylacetic acid was followed over a period of 7 days. The marked rise of dopamine output seen after infusion of K+ had almost disappeared on day 3. Tissue reactions around the membrane presumably formed a barrier preventing K+ from reaching dopaminergic terminals. In contrast, the pronounced rise in dopamine level after amphetamine (infused as well as systemically administered) was still present (although diminished) 8 days after implantation. It is concluded that, with certain restrictions, brain dialysis of dopamine is still useful several days after implantation of the membrane.

Simulations of Proteins in Water

Abstract: Molecular dynamics simulations of hydrated protein crystals have been carried out in only three cases: two simulations of pancreatic trypsin inhibitor (PTI) and one of avian pancreatic polypeptide (aPP). The purpose of such simulations is to evaluate the accuracy and reliability of molecular dynamics simulations of hydrated proteins. A 40-psec simulation on crystalline PTI, involving 4 protein molecules (of 58 amino acids each), 552 water molecules, and 24 Cl- ions is described. Considerations are energetic and structural stability, division of interaction energy among water and protein, and precision of average structure and structural fluctuations compared to X-ray data from a new 0.94-A resolution study of Wlodawer et al. Water and ion dynamics are considered by analysis of diffusional motions and of residence times of water molecules in specific sites.

Testing differences in relative growth-rate - a method avoiding curve fitting and pairing

Abstract: A method is discussed to test differences in relative growth rates. This method is based on an analysis of variance, with In-transformed plant weight as dependent variable. A significant Group × Time interaction indicates differences in relative growth rates between groups. The advantages over the “classical” and “functional” growth analyses are: (1) No pairing procedure is required. (2) More than two groups may be evaluated in one analysis. (3) No decision is required about the polynomial used to fit the data. (4) By partitioning the interaction effect using orthogonal polynomials insight is gained into the nature of differences in relative growth rate. (5) By concentrating attention on the lower order terms of the polynomials, the influence of extraneous variation on conclusions may be minimized.

The Influence of Group Size On Predator Scanning and Foraging Behaviour of Wedgecapped Capuchin Monkeys (Cebus Olivaceus)

Abstract: The behaviour of two groups of wedgecapped capuchin monkeys, Cebus olivaceus, a small one (n = 8) and a large one (n = 25) was recorded. Time budgets and other aspects of behaviour depended on group size. The differences can be explained as: adjustment to predation risk and intra-group food competition. In order to evade predation, members of the small groups scan more and stay at greater heights than those of the large group. Higher food competition within the large group was reflected in the composition of its diet, in longer travel distances, and higher levels of social behaviour. In particular during the dry season, the large group exploited unattractive and risky food sources. These results support ALEXANDER'S hypothesis on the causes of group formation.