Showing papers by "Utrecht University published in 1993"

Input Enhancement in Instructed SLA: Theoretical Bases

Abstract: The concept of input to the language learner is examined with reference to some current theorizing about language processing and the idea of modular systems of knowledge. The question of what this can tell us about the actions taken by teachers and textbook writers is addressed specifically with regard to manipulating, or “enhancing,” the input ideally so that it will affect learner knowledge and thereby learner behavior. The logic of the argumentation is that, in exposing the learner to the second language, we are engaging a whole battery of different processing mechanisms. Input enhancement research and the conclusions drawn from it have to be set within the context of a modular view of language and language learning.

A quantitative study of spermatogonial multiplication and stem cell renewal in the C3H/101 F1 hybrid mouse

Abstract: In whole mounts of seminiferous tubules of C3H/101 F1 hybrid mice, spermatogonia were counted in various stages of the epithelial cycle. Furthermore, the total number of Sertoli cells per testis was estimated using the disector method. Subsequently, estimates were made of the total numbers of the different spermatogonial cell populations per testis. The results of the cell counts indicate that the undifferentiated spermatogonia are actively proliferating from stage XI until stage IV. Three divisions of the undifferentiated spermatogonia are needed to obtain the number of A1 plus undifferentiated spermatogonia produced each epithelial cycle. Around stage VIII almost two-thirds of the Apr and all of the Aal spermatogonia differentiate into A1 spermatogonia. It was estimated that there are 2.5 x 10(6) differentiating spermatogonia and 3.3 x 10(5) undifferentiated spermatogonia per testis. There are about 35,000 stem cells per testis, constituting about 0.03% of all germ cells in the testis. It is concluded that the undifferentiated spermatogonia, including the stem cells, actively proliferate during about 50% of the epithelial cycle.

Wavelength Dependence of Skin Cancer Induction by Ultraviolet Irradiation of Albino Hairless Mice

Abstract: Information on the variation in carcinogenicity with wavelength is crucial in risk assessments for skin cancers induced by UV radiation. Until recently the wavelength (lambda) dependencies of other detrimental UV effects, such as sunburn, have been used as substitutes. Direct information on the lambda dependency can only be obtained from animal experiments. To this end we accumulated a large data set on skin tumors induced by chronic UV exposure of albino SKH:HR1 mice (14 different broadband UV sources and about 1100 mice); the data come from the Photobiology Unit of the former Skin and Cancer Hospital in Philadelphia and from the Department of Dermatology of the University of Utrecht. The lambda dependency was extracted from this data set (a statistically satisfactory description with chi 2 = 13.4, df = 7) and represented by the Skin Cancer Utrecht-Philadelphia action spectrum, i.e., a set of factors to weight the exposures at different wavelengths according to their respective effectiveness (inversely proportional to the daily exposure required for a median tumor induction time of 300 days). The fits obtained with other already available action spectra proved to be poor (chi 2 > 60, df = 11). The maximum effectiveness was found at 293 nm, and above 340 nm the effectiveness showed a shoulder at about 10(-4) of the maximum. A sensitivity analysis of the final solution for the lambda dependency showed a large margin of uncertainty above 340 nm and an information gap below 280 nm. The large variation in tumor responses in the present data set can be transformed to a coherent, common dose-response relationship by proper spectral weighting with this single action spectrum.

Synthesis and Characterization of Monodisperse Colloidal Organo-silica Spheres

Abstract: Monodisperse, colloidal silica spheres were prepared from tetraethoxysilane (TES) in mixtures of ammonia, water, and ethanol. The surface of the particles could be coated through a subsequent chemical reaction with the silane coupling agent 3-aminopropyltriethoxysilane (APS). Also, a new kind of monodisperse, colloidal silica spheres (organo-silica spheres) was prepared starting from mixtures of APS and TES. Organo-silica spheres synthesized with equal amounts of APS and TES were found to contain as much as 37% of the total amount of APS. The amount taken up by the particles, and therefore also the particle properties, depended on the initial composition of the mixture of alkoxides. It is argued that the most important reaction by which APS is incorporated into the particles is through an alcohol-producing condensation reaction with a silanol group bonded to a silicon atom that was part of a TES molecule. Because of this proposed mechanism, it is argued that this base-catalyzed method of making hybrid organic-silica particles will also be applicable to mixtures of other organoalkoxides. The organo-silica spheres differed from silica spheres prepared with TES alone in the following aspects: The negative surface charge in the mixture of water, ammonia and ethanol was reduced, the mass density was lower (e.g., 1.51 g/cm3 compared to 1.98 g/cm3), the microporosity was larger, and the siloxane structure was less condensed. The particle refractive index was higher, but the differences were small (around 0.02). It was shown that particles with APS on the surface could be grown larger with a silica layer prepared from TES. Organo-silica particles and silica-coated organo-silica particles were surface coated with stearyl alcohol. The resulting stability in several solvents was assessed. The different colloidal systems were characterized by static and dynamic light scattering, transmission electron microscopy, elemental analysis, nitrogen adsorption measurements, electrophoresis, and qualitative 13C and quantitative 19 Si solid-state nuclear magnetic resonance spectroscopy.

Linear measurements of cortical bone and dental enamel by computed tomography: Applications and problems

Abstract: This paper explores the potential of high-resolution computed tomography (CT) as a morphometric tool in paleoanthropology. The accuracy of linear measurements of enamel thickness and cortical bone thickness taken from CT scans is evaluated by making comparison with measurements taken directly from physical sections. The measurements of cortical bone are taken on extant and fossil specimens with and without attached matrix, and the dental specimens studied include a sample of 12 extant human molars. Local CT numbers (representing X-ray attenuation) are used to determine the exact position of the boundaries of a structure. Using this technique most studied dimensions, including four of human molar enamel thickness, could be obtained from CT scans with a maximum error range of +/- 0.1 mm. The limitations of the method are discussed with special reference to problems associated with highly mineralized fossils.

cAMP antagonizes p21ras-directed activation of extracellular signal-regulated kinase 2 and phosphorylation of mSos nucleotide exchange factor.

Abstract: In fibroblasts, stimulation of receptor tyrosine kinases results in the activation of the extracellular signal-regulated kinase 2 (ERK2). The major signalling pathway employed by these receptors involves the activation of p21ras and raf-1 kinase. Here we show that in NIH3T3 and rat-1 fibroblasts, elevation of the intracellular cAMP level results in the inhibition of ERK2 activation induced by PDGF, EGF and insulin treatment. Analysis of various signalling intermediates shows that cAMP interferes at a site downstream of p21ras, but upstream of raf-1 kinase. Inhibition by cAMP depends on both the cAMP concentration and the absolute amount of p21ras molecules bound to GTP, suggesting a mechanism of competitive inhibition. Also TPA-induced, p21ras-independent, activation of raf-1 kinase and ERK2 is inhibited by cAMP. We have used the inhibitory effect of cAMP to investigate whether phosphorylation of mSos, a p21ras nucleotide exchange factor, is dependent on the activity of the raf-1 kinase/ERK2 pathway. We found that phosphorylation of mSos, as monitored by a mobility shift, is delayed with respect to p21ras and ERK2 activation and is inhibited by cAMP in a similar cell type- and concentration-dependent manner as the inactivation of ERK2. These results provide evidence for a model of p21ras-directed signalling towards ERK2 that feeds back on mSos by regulating its phosphorylation status and that can be negatively modulated by protein kinase A and positively modulated by protein kinase C action.

Matman : a program for the analysis of sociometric matrices and behavioural transition matrices

Abstract: MatMan is a program for performing a variety of ethological analyses of frequency (interaction) matrices and transition matrices. These analyses include linear hierarchy indices for dominance matrices (APPLEBY, 1983), reorganization of a dominance matrix such that the subjects are in rank order, matrix correlation methods such as Mantel's test (MANTEL, 1967) and rowwise matrix correlation (DE VRIES, 1993), methods based on information theory (STEINBERG, 1977), and the calculation of expected and residual values in transition matrices with defined or undefined diagonal. In addition, MatMan offers some useful options for manipulating matrices. Import of matrices from The Observer (NOLDUS, 1991) and SAS is, within certain limitations, possible. Export of matrices is possible to the programs CORAN (1985), Vegrow (FRESCO, 1989), NCSS (HINTZE, 1987), SAS and SPSSPC.

Ancestry and diversity of the HMG box superfamily

Abstract: The HMG box is a novel type of DNA-binding domain found in a diverse group of proteins. The HMG box superfamily comprises a.o. the High Mobility Group proteins HMG1 and HMG2, the nucleolar transcription factor UBF, the lymphoid transcription factors TCF-1 and LEF-1, the fungal mating-type genes mat-Mc and MATA1, and the mammalian sex-determining gene SRY. The superfamily dates back to at least 1,000 million years ago, as its members appear in animals, plants and yeast. Alignment of all known HMG boxes defined an unusually loose consensus sequence. We constructed phylogenetic trees connecting the members of the HMG box superfamily in order to understand their evolution. This analysis led us to distinguish two subfamilies: one comprising proteins with a single sequence-specific HMG box, the other encompassing relatively non sequence-specific DNA-binding proteins with multiple HMG boxes. By studying the extent of diversification of the superfamily, we found that the speed of evolution was very different within the various groups of HMG-box containing factors. Comparison of the evolution of the two boxes of ABF2 and of mtTF1 implied different diversification models for these two proteins. Finally, we provide a tree for the highly complex group of SRY-like ('Sox' genes), clustering at least 40 different loci that rapidly diverged in various animal lineages.

A cepstrum-based technique for determining a harmonics-to-noise ratio in speech signals.

Abstract: A new method to calculate a spectral harmonics-to-noise ratio (HNR) in speech signals is presented. The method involves discrimination between harmonic and noise energy in the magnitude spectrum by...

Stimulant drugs and vigilance performance: a review.

Abstract: The literature on the effects of some stimulant drugs (amphetamine, methylphenidate, caffeine, and nicotine) on vigilance performance is reviewed. Improvement of overall level of performance (both accuracy and speed) after the intake of amphetamine, caffeine, and nicotine has often been reported, and the decrement in performance with time has been shown to be prevented especially with amphetamine and nicotine. Effects on false alarms are negligible. In studies where a test battery was employed, vigilance tasks appeared to be the most sensitive performance tests in detecting the effects of stimulants; however, different vigilance tasks may measure different aspects of mental functions. There is no support for earlier conclusions that improvements are noticed only in fatigued subjects in protracted sessions. Evidence from several studies does not support the hypothesis that improvements are only a recovery of withdrawal-induced impairment. Because positive effects have been obtained with drugs possessing different mechanisms of action, there is as yet no clear support for a noradrenergic, dopaminergic, or cholinergic theory of sustained attention. Simple neurotransmitter theories of attention and information processing may be untenable.

Paleoatmospheric Signatures in Neogene Fossil Leaves

Abstract: An increase in the atmospheric carbon dioxide (CO2) concentration results in a decrease in the number of leaf stomata. This relation is known both from historical observations of vegetation over the past 200 years and from experimental manipulations of microenvironments. Evidence from stomatal frequencies of fossil Quercus petraea leaves indicates that this relation can be applied as a bioindicator for changes in paleoatmospheric CO2 concentrations during the last 10 million years. The data suggest that late Neogene CO2 concentrations fluctuated between about 280 and 370 parts per million by volume.

Colonization of chicks by motility mutants of Campylobacter jejuni demonstrates the importance of flagellin A expression

Abstract: Summary: Campylobacter jejuni strain 81116 contains two flagellin genes, flaA and flaB. Wild-type (WT) bacteria express flaA only, but flaB can be expressed under certain conditions. We have determined the importance of flagella for colonization of the avian caecum, which appears to be the natural environment for these bacteria. Mutants in which flaA or flaB, or both had been inactivated, and motility variants, were investigated. Flagella are not a requisite for colonization, but mutants lacking both flagellin genes colonized less efficiently than WT. Inactivation of the flaB gene, which had no effect on bacterial motility, enhanced chicken caecal colonization 1000-fold compared to WT. A variant (SF-1) with flagella composed of flagellin A, but with poor motility, also colonized better than WT. Conversely, mutants with an inactivated flaA gene colonized 100- to 1000-fold less efficiently than WT, regardless of their motility conferred by truncated or full-length flagellin B flagella. These results suggest that the presence of flagellin A, rather than motility, is essential for optimal bacterial colonization of chicken caeca.

Pathophysiology and Treatment of Functional Dyspepsia

Abstract: Functional dyspepsia (or 'non-ulcer') is usually defined as chronic or intermittent upper abdominal symptoms for which no organic cause can be found. Division of functional dyspepsia into subgroups such as reflux-like, ulcer-like, dysmotility-like and non-specific dyspepsia has been proposed, but lacks a scientific basis. Gastric acid hypersecretion, Helicobacter pylori-associated gastritis, gastric and small intestinal motor disorders, psychological and neurohormonal factors all might play a role in the pathogenesis. The heterogeneity of the underlying abnormalities makes it unlikely that one single treatment modality will ever be beneficial to all patients. In general practice, a therapeutic trial, with either a prokinetic or an acid secretion inhibiting drug, is usually carried out before diagnostic procedures are performed to exclude organic abnormalities. In the choice of the initial therapy, some guidance can be derived from the prominent symptoms. In a study in 30 H. pylori-negative patients with functional dyspepsia ranitidine (150 mg bid) significantly reduced the severity of heartburn. The effect was most pronounced in patients of the reflux-like subgroup.

Effect of anti-IL-5 and IL-5 on airway hyperreactivity and eosinophils in guinea pigs

Abstract: Chronic ovalbumin challenge of sensitized guinea pigs induces bronchoalveolar lavage (BAL) eosinophilia, neutrophilia, and tracheal hyperreactivity. In the present study, the influence of monoclonal antibody to murine interleukin-5 (anti-IL-5) on these phenomena is examined. In ovalbumin-sensitized guinea pigs treated with isotype-matched control antibody and challenged daily with ovalbumin for 8 days, the number of BAL eosinophils and neutrophils is increased significantly six- and fivefold, respectively, compared with saline-challenged animals. The maximal contractions of tracheal rings to histamine and arecoline in ovalbumin-challenged animals are enhanced significantly to 155% compared with saline-challenged animals. In sensitized guinea pigs treated with anti-IL-5, the BAL eosinophil number is markedly inhibited compared with control antibody treatment in both saline- and ovalbumin-challenged animals. In contrast, the number of neutrophils is not affected by anti-IL-5 treatment. In guinea pigs treate...

Changes in chalk-grassland structure and species richness resulting from selective nutrient additions

Abstract: A series of fertilization experiments was carried out over a 5-yr period in a chalk grassland in Limburg (The Netherlands) as part of a study of the maintenance of species richness in species-rich grasslands. Phosphorus and nitrogen were shown to be the most limiting nutrients. Addition of both elements doubled above-ground production, and species rich- ness dropped ca. 50 % in 0.01-m 2 subplots, relative to controls. However, neither the above-ground production nor plant growth-forms were sufficient to explain the observed changes in species richness. Small-scale structural heterogeneity of the vegetation is probably critical for maintaining high levels of richness. Historically, high nitrogen, low phosphorus condi- tions were rarely encountered in the Dutch landscape and few species appear adapted to these conditions. Among the chalk grassland species, Brachypodium pinnatum seems well adapted to these conditions, where it dominates and excludes most other species. A detailed understanding of the small-scale processes responsible for maintenance of species richness is critically important in efforts to maintain the biodiversity of natural ecosystems.

Nitric Oxide Synthesis Inhibitors Induce Airway Hyperresponsiveness in the Guinea Pig In Vivo and In Vitro: Role of the Epithelium

Abstract: The administration by aerosol of the nitric oxide (NO) synthesis inhibitors, N omega-nitro-L-arginine methyl ester (L-NAME) or Ng-monomethyl-L-arginine (L-NMMA), to spontaneously breathing anesthetized guinea pigs resulted in a significant enhancement of lung resistance (RL) after increasing intravenous doses of histamine. The maximal response was increased (p < 0.01) by 126% (L-NAME) and 282% (L-NMMA) compared with the control groups. This effect was inhibited by giving an aerosol of the NO precursor L-arginine (L-Arg) but not by its inactive enantiomer D-arginine (D-Arg). Perfusion through the lumen of guinea pig tracheal tubes in vitro with nitric oxide synthesis inhibitors (120 microM) resulted in a significant increase in basal tone, suggesting a role for NO in the maintenance of basal tone. In addition, the histamine concentration-response curve was significantly shifted upward: the maximal response was increased (p < 0.01) by 335% (L-NAME) and 250% (L-NMMA) compared with the control group. This effect was concentration dependently inhibited by coincubation with L-Arg (120, 200, and 400 microM), but not with D-Arg (200 microM). Furthermore, removal of the epithelium resulted in an upward shift in the histamine concentration-response curve: the maximal response was increased by 185%. However, incubation with L-NAME did not further increase tracheal responsiveness to histamine, but addition of L-Arg (360 microM), when a plateau was reached, relaxed the tissues to control values. Nitric oxide synthesis inhibition did not change the responsiveness of intact tissues in vitro after intraluminal stimulation with leukotriene D4, serotonin, or the cholinergic agonist arecoline.(ABSTRACT TRUNCATED AT 250 WORDS)

A Longitudinal Study on Dysgraphic Handwriting in Primary School

Abstract: In an epidemiological study, the scripts of 121 Dutch primary-school children were evaluated annually, starting in Grade 2. The children were followed for 5 years. An evaluation scale for children's handwriting (the BHK scale) was used for rating the scripts on 13 characteristics and for measuring the speed of writing. Principal component analysis of the LONG matrix (in which the data collected on the five occasions are arranged beneath each other) yielded three clusters of items: (a) fine-motor ability, (b) structural performance, and (c) stylistic preference. It was found that the children with dysgraphic handwriting (10% scoring highest on the BHK quality items) had lower fine-motor ability and, in the higher grades, showed less preference for a personal style. Their structural performance also was poorer than that of the other writers. Children with and without dysgraphic handwriting did not differ in writing speed. Some implications of the study for handwriting instruction are discussed.

Does C60 have a liquid phase

Abstract: Above a substance's liquid–vapour critical point (i>Tc), the distinction between the liquid and vapour phases disappears. Below the triple point (T t), meanwhile (at which solid, liquid and vapour coexist), only the solid and vapour are stable. The liquid range, T c/T t, depends on the nature of the intermolecular forces: for argon, T c/Tt = 1.8, whereas for sodium the ratio is 7.5. But might there be molecular substances that have no liquid phase at all? Here we present results which suggest that C60 is such a substance. We map out the phase diagram using computer simulations in which the C60 molecules are represented by spheres interacting via Lennard-Jones potentials summed over all 60 carbon atoms. We find that the sublimation line passes above the metastable liquid-vapour coexistence curve. By drawing an analogy with the aggregation of colloidal particles, we expect that solid C60 formed by nucleation from the vapour phase will be amorphous rather than crystalline.