Showing papers by "University of Antwerp published in 1988"

Models for the modulation in A2B2CanCu1+nO6+2n, A, B=Bi, Sr OR Tl, Ba and n=0, 1, 2

Abstract: A number of models for the modulation in the title compounds are postulated. For the Bi compounds periodic changes are considered due to the following structural models: (a) extra oxygen in the BiO layers, (b) partial substitution of Sr by a vacancy, (c) partial substitution of Bi by Cu, and (d) changes in the orientations of the lone pairs of Bi. Computer calculated images for these models are compared with high resolution images. Also general structural considerations and structural details from the reported subcells are taken into account. It is concluded that the best agreement with experimental data is obtained for the model with extra oxygen in the BiO layers. Several performed experiments, which support this conclusion, are reported and discussed; the most important of which are the existence of solid solutions Bi2Sr2−xBaxCuO6+δ, with x

Effects of damaging the endocardial surface on the mechanical performance of isolated cardiac muscle.

Abstract: The mechanical properties of mammalian ventricular cardiac muscle have been studied in the presence and in the absence of an intact endocardial surface. Isotonic and isometric twitch contractions were obtained from papillary muscles of the right ventricle of cat at 29 degrees and 37 degrees C, at different extracellular calcium concentrations ([Ca2+]o), and at different initial muscle lengths. The endocardial surface was damaged by gentle abrasion of the muscle surface with a plastic blade or by brief immersion for 1 second with 1% Triton X-100. Although there was no evidence of damage to myocardial cells, damaging the endocardial surface resulted in an immediate and irreversible abbreviation of the twitch contractions with, except at the highest ([Ca2+]o, a decrease in peak isometric twitch tension. These changes induced 1) an asymmetrical shift of the tension-[Ca2+]o relation towards increasing [Ca2+]o but with no effect at the highest [Ca2+]o, and 2) a rightward and downward shift of the length-tension relation. Both shifts were significantly more pronounced at 37 degrees C than at 29 degrees C; they were not accompanied by significant changes in Vmax. The asymmetrical shift of the tension-[Ca2+]o relation suggests that the endocardium-mediated chain of events may be mediated by changes in the sensitivity of the contractile proteins to Ca2+. This hypothesis is also supported by the similar pattern of changes (i.e., modulation of the onset of early tension decline) induced by decreasing length at each [Ca2+]o and by the removal of a functional endocardium. Accordingly, the endocardium may help to control the performance of the heart by modulating peak contractile performance and relaxation of the underlying myocardium.

Ab initio calculations on large molecules: The multiplicative integral approximation

Abstract: In the multiplicative integral approximation (MIA), two-electron integrals are evaluated using an expansion of a product of two Gaussians in terms of auxiliary functions. An estimator of the error introduced by the approximation is incorporated in the self-consistent field (SCF) calculations and the integrals for which the error estimate is larger than a preset value are systematically corrected. In this way the results of a MIA-assisted calculation have the same accuracy as a conventional calculation. The full exploitation of the expansion technique while constructing the Fock-matrix allows important time savings. Results are presented for a number of test cases.

Electron microscopy on the Tc= 110 K (midpoint) phase in the system Bi2O3−SrO−CaO−CuO

Abstract: The system is known to have at least two phases exhibiting high superconducting transition temperatures (TC) of 85 and 110 K. It is well established that Bi2Sr2CaCu2O8+δ has a TC of ~85 K. To date it is not known which phase in the system exhibits TC = 110 K. We performed high-resolution electron microscopy and analytical electron microscopy on material having a nominal composition BiSrCaCu2Ox, and containing a relatively high fraction of the phase with TC = 110 K. Two structures related to the structure of Bi2Sr2CaCu2O8+δ are found. These structures and their possible compositions are discussed.

An evolutionary tree for invertebrate globin sequences.

Abstract: A phylogenetic tree was constructed from 245 globin amino acid sequences. Of the six plant globins, five represented the Leguminosae and one the Ulmaceae. Among the invertebrate sequences, 7 represented the phylum Annelida, 13 represented Insecta and Crustacea of the phylum Arthropoda, and 6 represented the phylum Mollusca. Of the vertebrate globins, 4 represented the Agnatha and 209 represented the Gnathostomata. A common alignment was achieved for the 245 sequences using the parsimony principle, and a matrix of minimum mutational distances was constructed. The most parsimonious phylogenetic tree, i.e., the one having the lowest number of nucleotide substitutions that cause amino acid replacements, was obtained employing clustering and branch-swapping algorithms. Based on the available fossil record, the earliest split in the ancestral metazoan lineage was placed at 680 million years before present (Myr BP), the origin of vertebrates was placed at 510 Myr BP, and the separation of the Chondrichthyes and the Osteichthyes was placed at 425 Myr BP. Local “molecular clock” calculations were used to date the branch points on the descending branches of the various lineages within the plant and invertebrate portions of the tree. The tree divided the 245 sequences into five distinct clades that corresponded exactly to the five groups plants, annelids, arthropods, molluscs, and vertebrates. Furthermore, the maximum parsimony tree, in contrast to the unweighted pair group and distance Wagner trees, was consistent with the available fossil record and supported the hypotheses that the primitive hemoglobin of metazoans was monomeric and that the multisubunit extracellular hemoglobins found among the Annelida and the Arthropoda represent independently derived states.

Assay of dipeptidyl peptidase IV in serum by fluorometry of 4-methoxy-2-naphthylamine.

Abstract: A new fluorometric assay for determining dipeptidyl peptidase IV (DPP IV; EC 3.4.14.5) was developed. The synthetic substrate glycyl-L-proline-4-methoxy-2-naphthylamide (20 mmol/L), Tris buffer (50 mmol/L, pH 8.3), and serum (20 microL) are mixed and incubated. The reaction is stopped with citrate (100 mmol/L, pH 4.0) and the released 4-methoxy-2-naphthylamine is measured fluorometrically. The mean value of DPP IV activity in serum for 64 healthy subjects was 58 (SD 16) mumol of 4-methoxy-2-naphthylamine released per liter of serum per minute. The proposed procedure is sensitive, rapid, and accurate and can easily be automated.

Atriopeptin III induces early relaxation of isolated mammalian papillary muscle.

Abstract: Atrial natriuretic peptide, released by mammalian atria in response to volume overload, induces vasodilation and natriuresis. In this study, a direct effect on cardiac mechanical performance was demonstrated. Atriopeptin III (10(-9)-10(-7) M) induced early relaxation and decreased peak twitch of isometric and isotonic twitches of isolated papillary muscles of cat and rat, without affecting maximal unloaded velocity of shortening. This effect resembled the effects of dibutyryl cyclic GMP and of sodium nitroprusside on cardiac muscle. The action of atriopeptin III, but not of dibutyryl cyclic GMP or sodium nitroprusside, was abolished by mechanically or chemically damaging the endocardial endothelial surface. Thus, the early relaxation of cardiac muscle induced by atrial natriuretic peptide may be mediated through receptors on the endocardial endothelium.

Propylene glycol-induced side effects during intravenous nitroglycerin therapy

Abstract: Propylene glycol, an alcohol frequently used as a solvent in medical preparations, is considered non-toxic. We found that this solvent, used in a commercially available IV nitroglycerin solution, may cause hyperosmolality, hemolysis and lactic acidosis. The influence of kidney function as the main determinant in causing accumulation of this solvent and consequently hyperosmolality is emphasized. A review of the literature dealing with propylene glycol is given. The possible mechanisms of neurological disturbances occurring during IV nitroglycerin therapy are discussed.

Acquired immunodeficiency syndrome mimicking Sjögren's syndrome and systemic lupus erythematosus.

Abstract: We describe a patient in whom the diagnosis of transfusion-associated acquired immunodeficiency syndrome (AIDS) was delayed because her clinical symptoms were similar to those of systemic lupus erythematosus and Sjogren's syndrome and because of a false-negative result on a Western blot test for human immunodeficiency virus. The importance of using different diagnostic tests for AIDS and the pitfalls in diagnosing AIDS in patients who appear to have connective tissue disease are discussed.

Relationship of Body Fat Distribution Pattern to Atherogenic Risk Factors in NIDDM: Preliminary Results

Abstract: Because recent knowledge indicates that the distribution of fat deposits in men may be a better predictor of cardiovascular disease than the degree of obesity alone, some risk factors for atherosclerosis were evaluated in 51 middle-aged men with non-insulin-dependent diabetes mellitus. Abdominal adiposity (waist/hip ratio, WHR) was related to parameters of metabolic control, lipid parameters, and known vascular complications in three different groups. In groups with abdominal obesity, mean annual hemoglobin A1 was significantly (P less than .01) higher than in patients without an abdominal fat distribution. Atherogenic index was significantly increased in the group with the highest WHR and high-density lipoprotein cholesterol (HDL-chol) levels were significantly decreased in both groups with upper-body fat distribution. The frequency of peripheral vascular disease, coronary ischemic heart disease, and hypertension was most prominent in diabetic subjects with an abdominal fat mass distribution. A highly significant (P less than .001) correlation was present between WHR and HDL-chol and WHR and the total-cholesterol/HDL-chol ratio; this significant correlation remains after correction for body mass index. A similar correlation could be found between WHR and systolic and diastolic blood pressures. These results demonstrate an association of excess abdominal fat, even without manifest obesity, with worse diabetes metabolic control, cardiovascular complications, and blood lipid levels actually considered to play an important role in atherogenesis.

Phase shift method based on object translation for full field automatic 3-D surface reconstruction from moire topograms

Abstract: A new method for full field automatic 3-D surface reconstruction is proposed which makes use of multiple contourograms shifted in phase by object translation. The method is demonstrated for shadow moire topography. It is shown that surface reconstruction can be done fast and with a resolution at least 10 times higher than the fringe distance of the measuring setup. Convexity and concavity of the surface are automatically determined. Also shown is the possibility of measuring irregular surfaces with very sudden height jumps.

Primary and secondary structure of the 18S ribosomal RNA of the bird spider Eurypelma californica and evolutionary relationships among eukaryotic phyla.

Abstract: The primary structure of the 185 rRNA of the bird spider Eurypelma californica has been determined in the framework of a study of metazoan phylogeny on the basis of ribosomal RNA structure. A secondary-structure model was derived by comparison of the sequence with that of 43 other eukaryotic small-ribosomal-subunit RNA sequences presently available. This comparison allows a rather detailed secondary-structure pattern to be postulated for a eukaryote-specific area of highly variable sequence and length for which no consensus model has hitherto been attained. A dendrogram, reflecting evolutionary relationships among the 40 eukaryotic species of known 18S rRNA structure, was constructed by a matrix method selecting the best-fitting tree on the basis of a least-squares criterion. The tree shows an early divergence of a microsporidium, an euglenoid, kinetoplastids and a slime mold. Among the remaining species, two main clusters are distinguishable, one comprising the Ciliata, the other comprising Metazoa, green plants, fungi and several protists. Among the Metazoa, the three phyla presently investigated, viz. Chordata. Arthropoda and Nemathelminthes, are distinguishable as three separate lines of descent.

The powerset algebra as a result of adding programming constructs to the nested relational algebra

Abstract: In this paper, we discuss augmentations of the nested relational algebra with programming constructs, such as while-loops and for-loops. We show that the algebras obtained in this way are equivalent to a slight extension of the powerset algebra, thus emphasizing both the strength and the naturalness of the powerset algebra as a tool to manipulate nested relations, and, at the same time, indicating more direct ways to implement this algebra.

Ultrasonography and computer tomography of the salivary glands in the evaluation of Sjögren's syndrome. Comparison with parotid sialography.

Abstract: Ultrasonography (US) and computed tomography (CT) were studied as noninvasive methods to determine salivary gland involvement and compared with parotid sialography in patients with Sjogren's syndrome (SS) and patients with only objective xerostomia and/or xerophthalmia. Patients with complaints of dry eyes and dry mouth but with no objective abnormalities served as controls. CT was not discriminative between the 2 groups. In contrast, US revealed decreased parotid gland echogenicity in most of the patients with SS, compared with only 1 patient in the group with sicca complaints only (p = 0.005). Our study suggests that US can be a useful, noninvasive method in the diagnostic investigation of patients with sicca complaints.

Multicenter evaluation of human placental alkaline phosphatase as a possible tumor-associated antigen in serum.

Abstract: Using a solid-phase monoclonal antibody enzyme immuno-assay, we evaluated in a multicenter study (18 laboratories) the utility of evaluating catalytic activity of human placental alkaline phosphatase (hPLAP, EC 3.1.3.1) in serum as a potential tumor marker. We determined hPLAP in serum samples from 130 patients with ovarian cancer, 79 patients with testicular cancer (53 seminoma testis, 26 nonseminoma testis), 537 patients with various other malignant diseases (95 lung, 39 gastrointestinal, 195 breast, 208 others), 291 patients with benign diseases, and 213 healthy controls. To assess the influence of smoking on hPLAP activity in serum, we evaluated 79 serum samples from patients with noncancerous diseases for whom smoking habits had been recorded. Our main findings are: (a) hPLAP activity is frequently increased (greater than 100 mU/L) in pre-operative serum samples from ovarian cancer patients (49%) and from testicular cancer patients (59% overall; 72% seminoma, 35% nonseminoma); (b) heavy smoking may increase hPLAP activity; (c) excluding heavy smokers, a 96% specificity for cancerous lesions was observed; (d) in patients with ovarian malignancies, CA 125 and hPLAP may behave as independent markers; and (e) in patients with seminoma, hPLAP is clearly more frequently increased than is beta-choriogonadotropin.

Defect structure of superconducting YBa2Cu3O7−δ

Abstract: The superconducting material Y1Ba2Cu3O7-delta has been investigated by electron microscopy. Special attention has been paid to the defects occurring in the material. Twinning on (110) or (110) planes is intrinsically related to the orthorhombicity, and when cooled slowly the twin bands are pseudoperiodic with an average width of approximately 50 nm. The orthorhombic-tetragonal transition is reversible and diffusion controlled. Under particular conditions and in slightly reduced material a 2a0 x b0 superstructure resulting from vacancy ordering is formed. When kept in air under powder form the material seems to be unstable. Planar defects along (001) accompany the degeneration of the material.

Histological study of the thin replacement membrane of human tympanic membrane perforations.

Abstract: A histological study was done on the thin, nearly transparent replacement membrane of tympanic membrane perforations. Human tympanic membranes that were rejected for transplantation, were studied by light and electron microscopy. The abrupt reduction in thickness at the margin of the covered perforation, is entirely due to the reduction of the lamina propria. Even in the thinnest parts of the replacement membrane, a lamina propria is present, separated by continuous basement membranes from the epithelium and mucosa, and measuring no more than some 2-3 μm in thickness. This lamina propria consists of fibrils and interfibrillar matrix, but fibroblasts appear to be lacking. The epithelial layer does not contain basal cells, confirming the thesis that the upper layers are not generated by in situ proliferation, but that they have migrated from the periphery.

Indoubil: A Swahili hybrid in Bukavu (with comments on Indu Bill by K. Kabongo-Mianda)

Abstract: An attempt is made at defining the phenomenon of Indoubil. Its origin, use, and function are discussed. Indoubil, the language of Bukavu's [Zaire] younger generation, would seem to serve a number of purposes. It is argued that Indoubil functions not only as a means of identification for a particular age group but that in a variety of contexts it is also used to neutralize the illeffects of ethnicity. (Ethnicity, melting pot, lingua franca, Swahili)

Quasi‐crystals and their crystalline homologues in the Al60Mn11Ni4 ternary alloy

Abstract: SUMMARY The transition quasi-crystallinecrystalline is found to be very sluggish in the ternary alloy Al60Mn11Ni4. This makes it possible to study in detail the relationship between the decagonal phase, obtained after furnace cooling, and two different crystalline phases, which result after long annealing at 400°C. Use is made of electron diffraction, high resolution electron microscopy and optical diffraction. The crystalline phases still exhibit features which are closely related to those of the decagonal phase. This can be concluded from a comparison of the electron diffraction patterns of the quasi-crystalline phase along a number of zones, with those of the crystalline phases along corresponding zones. The crystalline phases contain different types of defects which are analysed in detail using high resolution images and diffuse scattering in the electron diffraction patterns. The close relationship between the electron diffraction patterns of the crystalline and quasi-crystalline phases is explained in terms of general optical principles. Some characteristic features of a model of the quasi-crystalline phase are tentatively proposed.

Quantitative electromyography of the masticatory muscles of Pteropus giganteus (Megachiroptera)

Abstract: Mastication has been studied by cinematography and quantitative electromyography while flying foxes, Pteropus giganteus, were freely feeding on standardized pieces of apple, soaked raisin, and banana. The primarily orthal mandibular movements are caused by mainly bilaterally symmetrical firing of all the masticatory muscles. Asymmetric activity in the superficial and deep masseter and medial pterygoid causes slight protrusion early in opening. Slight lateral deviations at the end of opening and at the start of closing are caused by asymmetric and asynchronous activity in the pterygoids and digastrics, and by asynchronous firing of the deep temporalis and zygomaticomandibularis. Food consistency affects movement characteristics as well as characteristics of muscular activity. In this study electromyograms were digitized and the number of spikes and mean amplitude per interval (set by the filming rate) recorded. Although a significant correlation exists between these descriptors, the product thereof appears to be the best predictor of certain kinematic variables (cycle length and maximum excursion of the mandible). On the other hand, the changes in magnitude of muscular activity as a function of the position of a cycle in the reduction sequence and as a function of food consistency are more translated in a variation of the mean amplitude than in a variation of the number of spikes per interval. Observed variation differs among muscles studied. It is most apparent in the superficial and deep masseter and least in the temporalis and zygomaticomandibularis. Late cycles of apple and raisin mastication are long and exhibit large gapes but almost no anterior movement. The adductor activity frequently shows a synchronized, pulsatile pattern leading to an unfused tetanus.

Evidence for the co-storage and co-release of neuropeptide y and noradrenaline from large dense cored vesicles in sympathetic nerves of the bovine vas deferens

Abstract: The subcellular localization and the secretion of neuropeptide Y were studied in sympathetic nerve endings of bovine vas deferens. Immunostaining revealed a parallel distribution for neuropeptide Y and dopamine-β-hydroxylase immunoreactivity in the network of varicose nerve fibers in the smooth muscle layers of the vas deferens. Following differential centrifugation and sucrose density gradient centrifugation, neuropeptide Y was found to coincide with noradrenaline in the more dense region of the gradient, where the large dense cored vesicles are found. Superfusion experiments demonstrated the release of neuropeptide Y and noradrenaline upon electrical stimulation. Furthermore, the neuropeptide Y secretion was shown to be Ca2+-dependent. We conclude that in the bovine vas deferens neuropeptide Y is only present in large dense cored vesicles of adrenergic neurons and that the peptide and noradrenaline are coreleased from these vesicles in a calcium dependent manner.

The use of red squirrel Sciurus vulgaris dreys to estimate population density

Abstract: In this paper we examined if the number of dreys could be used to estimate the density of red squirrel populations. Squirrel density was estimated by trapping and the number of dreys were counted in different areas and over several years.

Implantation of a Dual Chamber Pacemaker in a Patient with Persistent Left Superior Vena Cava

Abstract: A patient underwent dual chamber pacemaker implantation by puncture of the left subclavian vein. During the procedure we observed persistence of the left superior vena cava. A "J-shaped" atrial lead was used for ventricular pacing with excellent long-term results. This technique can be a valuable alternative when confronted with the problem of persistent left superior vena cava during pacemaker implantation.