Showing papers by "Radboud University Nijmegen published in 1991"

Electronic structure of CoO, Li-doped CoO, and LiCoO2

Abstract: The electronic structure of ${\mathrm{Li}}_{\mathit{x}}$${\mathrm{Co}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$O (001\ensuremath{\le}x\ensuremath{\le}02), ${\mathrm{LiCoO}}_{2}$, and ${\mathrm{Co}}_{3}$${\mathrm{O}}_{4}$(1% Li) has been investigated using x-ray photoemission spectroscopy (XPS), bremsstrahlung isochromat spectroscopy (BIS), and x-ray-absorption spectroscopy The experimental results are compared with model cluster calculations We find that the CoO band gap is of an intermediate character, between Mott-Hubbard-like and charge-transfer-like The first ionization state of CoO is therefore of strongly mixed Co 3d and O 2p character Its local symmetry corresponds to $^{3}$${\mathit{T}}_{1\mathit{g}}$, similar to an intermediate-spin ${\mathrm{Co}}^{3+}$ state For x\ensuremath{\le}02 the local Co electronic structure is similar to that of CoO However, ${\mathrm{LiCoO}}_{2}$ has a strongly reduced Co-O interatomic distance, resulting in a ligand field strong enough to stabilize a ${\mathrm{Co}}^{3+}$ low-spin ground state ${\mathrm{LiCoO}}_{2}$ is an insulator with a gap of 27 eV From a comparison of the XPS and BIS CoO spectra to the cluster calculations, we find values for U (=53 eV), \ensuremath{\Delta} (=55 eV), and (pd\ensuremath{\sigma}) (=13 eV)

Functional programming with bananas, lenses, envelopes and barbed wire

Abstract: We develop a calculus for lazy functional programming based on recursion operators associated with data type definitions. For these operators we derive various algebraic laws that are useful in deriving and manipulating programs. We shall show that all example functions in Bird and Wadler's Introduction to Functional Programming can be expressed using these operators.

Circadian photoreception in the retinally degenerate mouse (rd/rd).

Abstract: We have examined the effects of light on circadian locomotor rhythms in retinally degenerate mice (C57BL/6J mice homozygous for the rd allele: rd/rd). The sensitivity of circadian photoreception in these mice was determined by varying the irradiance of a 15 min light pulse (515 nm) given at circadian time 16 and meauring the magnitude of the phase shift of the locomotor rhythm. Experiments were performed on animals 80 days of age. Despite the loss of visual photoreceptors in the rd/rd retina, animals showed circadian responses to light that were indistinguishable from mice with normal retinas (rd/+ and +/+). While no photoreceptor outersegments were identified in the retina of rd/rd animals (80–100 days of age), we did identify a small number of perikarya that were immunoreactive for cone opsins, and even fewer cells that contained rod opsin. Using HPLC, we demonstrated the presence and photoisomerization of the rhodopsin chromophore 11-cis retinaldehyde. The rd/rd retinas contained about 2% of 11-cis retinaldehyde found in +/+ retinas. We have yet to determine whether the opsin immunoreactive perikarya or some other unidentified cell type mediate circadian light detection in the rd/rd retina.

Androgen receptors in endocrine-therapy-resistant human prostate cancer

Abstract: Despite the initial androgen-dependent growth of most human prostate cancers, eventually all prostate cancers become androgen-independent at varying intervals after androgen ablation or anti-androgen therapy. In order to gain more insight into the role of the androgen receptor (AR) in this process, AR and prostate-specific antigen (PA) expression was evaluated immunohistochemically in prostatic tumour tissues from patients who developed urinary flow obstruction between 4 and 107 months after onset of treatment. AR expression was evaluated with a monoclonal antibody (MAb) specific for the N-terminal domain of the human AR. To substantiate the progressive tumour growth, proliferative activity was assessed immunohistochemically by staining with MAb Ki-67. Ki-67-defined tumour-growth fractions varied from 0.8-64.7%. In 13 of the 17 examined tumours over 80% of the tumour cells were AR-positive, 3 tumours showed a considerable heterogeneity in AR expression and in 1 tumour almost all tumour cells seemed to be AR-negative. Two-thirds of the examined tumours contained variable proportions of PA-positive tumour areas. These observations contrast with the view that androgen ablation induces a preferential outgrowth of receptor-negative tumour cells.

Ligament-bone interaction in a three-dimensional model of the knee.

Abstract: In mathematical knee-joint models, the ligaments are usually represented by straight-line elements, connecting the insertions of the femur and tibia. Such a model may not be valid if a ligament is bent in its course over bony-surfaces, particularly not if the resulting redirection of the ligament force has a considerable effect on the laxity or motion characteristics of the knee-joint model. In the present study, a model for wrapping of a ligament around bone was incorporated in a three-dimensional mathematical model of the human knee. The bony edge was described by a curved line on which the contact point of the line element representing a ligament bundle was located. Frictionless contact between the ligament bundle and the bone was assumed. This model was applied to the medial collateral ligament (MCL) interacting with the bony edge of the tibia. It was found that, in comparison with the original model without bony interactions, the bony edge redirected the ligament force of the MCL in such a way that it counterbalanced valgus moments on the tibia more effectively. The effect of the bony interaction with the MCL on the internal-external rotation laxity, however, was negligible.

Does competence of general practitioners predict their performance? Comparison between examination setting and actual practice.

Abstract: OBJECTIVE--To study the differences and the relation between what a doctor actually does in daily practice (performance) and what he or she is capable of doing (competence) by using national standards for general practice. DESIGN--General practitioners were consulted by four standardised (simulated) patients portraying four different cases during normal surgery hours. Later the doctors participated in a controlled practice test, for which they were asked to perform to the best of their ability. In the test they saw exactly the same standardised cases but in different patients. The patients reported on the consultations. SETTING--Province of Limburg, the Netherlands. SUBJECTS--442 general practitioners invited by a letter. 137 (31%) agreed to participate, of whom 36 were selected and visited. MAIN OUTCOME MEASURES--Number of actions taken during the consultations across complaints and for each category of complaint: the competence and performance total scores. Combination of scores with duration of consultations (efficiency-time score). Correlation between scores in the competence and performance part. RESULTS--Mean (SD) total score across complaints for competence was 49% higher than in the performance test (81.8 (11) compared with 54.7 (10.1), p less than 0.0001). The Pearson correlation across complaints between the competence total score and the performance total score of the participating physicians was -0.04 (not significant). When efficiency and consultation time of the consultations were taken into account, the correlation was 0.45 (p less than 0.01). CONCLUSIONS--Assessment of competence under examination circumstances can have predictive value for performance in actual practice only when factors such as efficiency and consultation time are taken into account. Below standard performance of physicians does not necessarily reflect a lack of competence. Performance and competence should be considered as distinct constructs.

Referential Comparisons, Relational Comparisons, and Exchange Orientation: Their Relation to Marital Satisfaction

Abstract: Employing a sample of 214 individuals, this study showed that most individuals felt the input/outcome ratio in their marital relationship was better than that of most same-sex others (referential comparisons) but equal to that of their spouse (relational comparisons). Perceptions of superiority in referential comparisons and of equity in relational comparisons were accompanied by the highest level of marital satisfaction. However, further analyses showed that only for individuals high in exchange orientation was equity related to marital satisfaction and that individuals low in exchange orientation were, overall, more satisfied with their relationship. Women were more deprived and less satisfied, especially when they were high in exchange orientation. The results are related to the controversy surrounding the application of equity theory to close relationships. In addition, the cognitive mechanisms that help individuals maintain a positive view of their marital relationship are considered.

Basal cell-specific and hyperproliferation-related keratins in human breast cancer.

Abstract: In normal breast tissue and in noninvasive breast carcinomas, various keratin-14 antibodies were reactive predominantly with the basal/myoepithelial cell layer, although mainly in terminal and larger ducts luminal cells sometimes also were stained. A similar reaction pattern was found with an antibody directed against keratin 17, although this antibody was more often found negative than keratin 14 in the pre-existing myoepithelial cells in intraductal carcinomas. Furthermore antibodies reactive with hyperproliferation-related keratins 6 and 16 were used. One of these (LL025) was completely negative in normal breast tissue and noninvasive breast carcinomas. However 10% of the invasive carcinomas were diffusely or focally positive with this latter antibody, while in 18 of 115 cases of invasive breast carcinomas studied, a basal cell phenotype was detected. A relatively high concordance was found between the carcinomas immunostaining with the basal cell and the hyperproliferation-related keratins, but not between these markers and the proliferation marker Ki-67. This supports the conclusion that basal cells in breast cancer may show extensive proliferation, and that absence of Ki-67 staining does not mean that (tumor) cells are not proliferating.

Control of calcium regulating hormones in the vertebrates: parathyroid hormone, calcitonin, prolactin, and stanniocalcin.

Abstract: Publisher Summary This chapter discusses the control of calcium regulating hormones in the vertebrates. Control of ionic calcium levels of the extracellular fluids is mandatory for all vertebrates because only minor changes of calcium, in particular the ionized calcium fraction, have pronounced effects on the permeability of cell membranes to ions and, consequently, on important physiological processes, such as muscle contraction, nerve signal transduction, and control of cellular metabolism. Calcium uptake is balanced by renal calcium excretion, with exception of periods of body growth or, in females, periods of reproduction and parental care. Parathyroid hormone (PTH) dominates the control of the Ca2+ concentration of the extracellular fluid by its calcium-mobilizing action on bone and, indirectly, via its control of the synthesis of 1,25(OH)2D3, intestinal calcium absorption. Calcitonin (CT) reduces the extracellular calcium concentration by inhibiting osteoclastic bone resorption and by promoting calcium deposition in the skeleton. In the terrestrial vertebrates, the evidence for the involvement of prolactin (PRL) in calcium metabolism is limited to calcium handling during gestation and lactation in mammals.

Feeding behaviour and sporozoite ejection by infected Anopheles stephensi

Abstract: Anopheles stephensi mosquitoes infected with Plasmodium falciparum sporozoites were allowed to feed individually through fresh whole thickness mouse skin. More sporozoites were ejected into the skin in clusters than into the blood. Deposition of sporozoites in the blood was an infrequent occurrence and always coincided with ejection of these stages into the skin--perhaps a spill-over effect. The number of probes before feeding (median 4.5) was not correlated with the sporozoite inoculum (median 8), nor was the number of sporozoites in the glands (median 14,500). However, the number of sporozoite clusters in the skin (median 1) was positively correlated with the inoculum size. The median value of the sporozoite inoculum was 22, when only those mosquitoes that ejected sporozoites were included. When feeding was interrupted and recommended on a new membrane, sporozoite ejection occurred with equal frequency on both occasions. Sporozoites disappeared from the site of bites in living mice within 2 h of feeding. The epidemiological significance of these observations is discussed.

Molecular cloning of the human alpha 6 integrin subunit. Alternative splicing of alpha 6 mRNA and chromosomal localization of the alpha 6 and beta 4 genes.

Abstract: We have isolated cDNAs encoding the α6 subunit from a γ gt11 expression library from human keratinocytes by combined screening with a rabbit polyclonal anti-α6 antibody and the polymerase chain reaction. The α6 subunit encoded by this cDNA consists of 1050 amino acids with a 991-amino-acid extracellular, a 23-amino-acid transmembrane and a 36-amino-acid cytoplasmic domain. The extracellular domain contains three putative divalent cation-binding sites and nine potential N-linked glycosylation sites. From a cDNA library from normal human mammary gland cells two different cDNAs for α6 were isolated, one of which is identical to the above cDNA. The two α6 subunits, called α6A and α6B, encoded by the two cDNAs each have a unique cytoplasmic domain, that of α6B being 18 amino acids longer than that of α6A. Different carcinoma cell lines contain transcripts for both α6 subunits. K 562 leukemic cells have little α6A or α6B mRNAs. The overall level of expression varies in the carcinoma cell lines, but reflects α6 cell surface expression. In A375 melanoma cells, however, cell surface expression of α6 was low in spite of a high level of mRNA. This suggests that other mechanisms may be involved in regulating the expression of α6 on the surface of these cells. The mRNA for both α6 subunits is around 6 kb. The α6 subunits are similar to other α subunits (26–31% identity with cleaved α subunits) of the integrin family but they are more similar to the α3 subunit (40% identity). This high degree of similarity may be the basis for their functional resemblance since both α3 and α6 subunits, when associated with β1, function as laminin receptors and bind to the long arm of laminin. The genes for α6 and β4, the alternative β subunit with which α6 combines on certain epithelial cells, were mapped to chromosome 2 and 17q11-qter, respectively.

A Remark on the Dunkl Differential—Difference Operators

Abstract: Let E be a Euclidean vector space of dimension n with inner product (·,·). For each α ∈ E with (α, α) = 2 we write $$ {r_{\alpha }}(\lambda ) = \lambda - (\alpha, \lambda )\alpha, \lambda \in E $$ (1.1) for the orthogonal reflection in the hyperplane perpendicular to α.

Recruitment of Knee Joint Ligaments

Abstract: On the basis of earlier reported data on the in vitro kinematics of passive knee-joint motions of four knee specimens, the length changes of ligament fiber bundles were determined by using the points of insertion on the tibia and femur. The kinematic data and the insertions of the ligaments were obtained by using Roentgenstereophotogrammetry. Different fiber bundles of the anterior and posterior cruciate ligaments and the medial and lateral collateral ligaments were identified. On the basis of an assumption for the maximal strain of each ligament fiber bundle during the experiments, the minimal recruitment length and the probability of recruitment were defined and determined. The motions covered the range from extension to 95 degrees flexion and the loading conditions included internal or external moments of 3 Nm and anterior or posterior forces of 30 N. The ligament length and recruitment patterns were found to be consistent for some ligament bundles and less consistent for other ligament bundles. The most posterior bundle of each ligament was recruited in extension and the lower flexion angles, whereas the anterior bundle was recruited for the higher flexion angles. External rotation generally recruited the collateral ligaments, while internal rotation recruited the cruciate ligaments. However, the anterior bundle of the posterior cruciate ligament was recruited with external rotation at the higher flexion angles. At the lower flexion angles, the anterior cruciate and the lateral collateral ligaments were recruited with an anterior force. The recruitment of the posterior cruciate ligament with a posterior force showed that neither its most anterior nor its most posterior bundle was recruited at the lower flexion angles. Hence, the posterior restraint must have been provided by the intermediate fiber bundles, which were not considered in the experiment. At the higher flexion angles, the anterior bundles of the anterior cruciate ligament and the posterior cruciate ligament were found to be recruited with anterior and posterior forces, respectively. The minimal recruitment length and the recruitment probability of ligament fiber bundles are useful parameters for the evaluation of ligament length changes in those experiments where no other method can be used to determine the zero strain lengths, ligament strains and tensions.

Toxicants and Osmoregulation in Fish

Abstract: Fish are extremely sensitive to many water-borne toxicants, because these affect the gills by increasing the permeability to water and ions of the gill epithelium and by inhibition of the ion exchange activity of the chloride cells. The compensatory responses of the fish will significantly increase the energy required for maintenance of water and ion homeostasis, and this will result in reduced growth and reproduction. The effects of toxicants are to a great extent comparable to those of stressors such as confinement, transport, and handling, not only where the endocrine and metabolic responses are concerned, but also with respect to the osmoregulatory disturbances produced. Stressors may affect osmoregulation indirectly through the action of catecholamines on the gills. Furthermore, stressors induce immunosuppression and this may result in gill damage by infectious agents. Many toxicants evoke a stress response, and thus it is difficult to determine the mechanism of action of toxicants on the gills, because the specific effects of the toxicants are hard to distinguish from the effects of non-specific stress responses on the gills. This further implies that the negative effects of many toxicants and non-toxicant stressors on gill structure and hydromineral balance are additive. This aspect needs more attention in aquaculture.

Soft-x-ray-absorption studies of the location of extra charges induced by substitution in controlled-valence materials.

Abstract: We present high-resolution 2p x-ray-absorption spectra from 3d transition metals M in three series of pseudobinary and pseudoternary oxides. We show how the detailed shape of the multiplet within the spectra can be used to determine the valence of the M ions. The spectra of the early-transition-metal compounds show dramatic changes as a function of substitution due to changes in the M 3d occupancy, indicating that the extra holes or electrons are located predominantly at the 3d-metal sites. This contrasts strongly with the behavior of the spectra of late-transition-metal compounds, for which the extra charges induced by substitution go to oxygen states.

Effects of Fluoride and Chlorhexidine on the Microflora of Dental Root Surfaces and Progression of Root-surface Caries

Abstract: The effects of fluoride and chlorhexidine varnishes on the microflora of dental root surfaces and on the progression of root-surface caries were studied. Forty-four patients, surgically treated for advanced periodontal disease, were distributed at random among three groups. All patients received a standardized preventive treatment. Furthermore, the dentition of the patients in the two experimental groups was treated, at three-month intervals, with chlorhexidine and fluoride varnish, respectively. Patients in the control group received no additional treatment. In the experimental groups, plaque samples were collected from selected sound and carious root surfaces at baseline and at three, six, and nine months after the onset of the study. The presence of root-surface caries was scored at baseline and after one year. In addition, the texture, depth, and color of the root-surface lesions were monitored. Mutans streptococci on root surfaces were suppressed significantly (p less than 0.05) during the whole experimental period in the chlorhexidine varnish group, but not in the fluoride varnish group. A non-significant increase in the number of Actinomyces viscosus/naeslundii was noted after treatment with chlorhexidine and fluoride varnish. The increase in the number of decayed and filled root surfaces after one year was significantly lower in the experimental groups than in the control group. After treatment with chlorhexidine varnish, significantly more initial root-surface lesions had hardened than in the other groups.