scispace - formally typeset
Search or ask a question

Showing papers by "University of Antwerp published in 1994"



Journal ArticleDOI
15 Jul 1994-Cell
TL;DR: In this article, the authors designed a knockout model for the fragile X syndrome in mice and found that the knockout mice lack normal Fmr1 protein and show macroorchidism, learning deficits, and hyperactivity.

981 citations


Journal ArticleDOI
29 Jul 1994-Science
TL;DR: The concept of a spatial-velocity hodograph is introduced to describe quantitatively the extrusion of a carbon tubule from a catalytic particle and why the formation process induces stresses that may lead to "spontaneous" plastic deformation of the tubule.
Abstract: The concept of a spatial-velocity hodograph is introduced to describe quantitatively the extrusion of a carbon tubule from a catalytic particle. The conditions under which a continuous tubular surface can be generated are discussed in terms of this hodograph, the shape of which determines the geometry of the initial nanotube. The model is consistent with all observed tubular shapes and explains why the formation process induces stresses that may lead to "spontaneous" plastic deformation of the tubule. This result is due to the violation of the continuity condition, that is, to the mismatch between the extrusion velocity by the catalytic particle, required to generate a continuous tubular surface, and the rate of carbon deposition.

940 citations


Journal ArticleDOI
TL;DR: In this paper, the major methods and techniques used to examine the likely effects of elevated CO2 on woody plants, as well as the major physiological responses of trees to elevated CO 2 are described.
Abstract: summary Because of their prominent role in the global carbon balance and their possible carbon sequestration, trees are very important organisms in relation to global climatic changes. Knowledge of these processes is the key to understanding the functioning of the whole forest ecosystem which can he modelled and predicted based on the physiological process information. This paper reviews the major methods and techniques used to examine the likely effects of elevated CO2 on woody plants, as well as the major physiological responses of trees to elevated CO2. The available exposure techniques and approaches are described. An overview table with all relevant literature data over the period 1989-93 summarizes the percent changes in biomass, root/shoot ratio, photosynthesis, leaf area and water use efficiency under elevated CO2. Interaction between growth, photosynthesis and nutrition is discussed with a special emphasis on downward regulation of photosynthesis. The stimulation or reduction found in the respiratory processes of woody plants are reviewed, as well as the effect of elevated CO2 on stomatal density, conductance and water use efficiency. Changes in plant quality and their consequences are examined. Changes in underground processes under elevated CO2 are especially emphasized and related to the functioning of the ecosystem. Some directions for future research are put forward.

708 citations


Journal ArticleDOI
TL;DR: The latest release of the large ribosomal subunit RNA database contains 429 sequences, all of which are aligned, and incorporate secondary structure information.
Abstract: The latest release of the large ribosomal subunit RNA database contains 429 sequences. All these sequences are aligned, and incorporate secondary structure information. The rRNA WWW Server at URL http://rrna.uia.ac.be/ provides researchers with an easily accessible resource to obtain the data in this database in a number of computer-readable formats. A new query interface has been added to the server. If necessary, the data can also be obtained by anonymous ftp from the same site.

545 citations


Journal ArticleDOI
TL;DR: In this article, straight and coiled carbon tubules were obtained with inner and outer diameter of 3-7 and 15-20 nm, respectively, and up to 300 μm in length.

485 citations


Journal ArticleDOI
TL;DR: A significant association between APOE*4 and EOAD is demonstrated which is modified by family history of dementia, but an increase in EOAD risk for APoe*4 heterozygotes could only be shown in subjects with a positive family history.
Abstract: Several studies have reported an association of the apolipoprotein E allele epsilon 4 (APOE*4) to familial and sporadic late-onset Alzheimer's disease (LOAD). Here we report on the relationship between APOE*4 and early-onset Alzheimer's disease (EOAD) in a Dutch population-based study. The frequency of the APOE*4 allele was 2.3 times higher among EOAD cases compared to controls. Among patients, the allele frequency was 1.6 times higher in those with a positive family history than in those without. A significant increase in risk of EOAD was found for subjects homozygous for APOE*4 regardless of family history of dementia, but an increase in EOAD risk for APOE*4 heterozygotes could only be shown in subjects with a positive family history. Our study demonstrates a significant association between APOE*4 and EOAD which is modified by family history of dementia.

451 citations


Journal ArticleDOI
TL;DR: In this article, the functionality of the computer package AXIL (Analysis of X-ray spectra by Iterative Least squares), suitable for the evaluation of energy-dispersive X ray spectra, has been extended in a number of ways.
Abstract: The functionality of the computer package AXIL (Analysis of X-ray spectra by Iterative Least squares), suitable for the evaluation of energy-dispersive X-ray spectra, has been extended in a number of ways. First, a background modelling algorithm, based on the use of mutually orthogonal polynomials was introduced to replace the linear or exponential polynomials employed previously. Second, the Gaussian photopeak model employed in previous versions of the program was extended to include the non-Gaussian parts of the characteristic peaks and related background contributions. Both innovations are shown to improve the performance of the spectrum evaluation procedure. Third, the user-friendliness of the evaluation program was enhanced (a) by allowing a PC plug-in MCA card to be directly controlled from within the program and (b) by extending the command-interface to allow for repeated execution of series of commands by means of control loops. A brief description of these changes is given; as an application, the accurate evaluation of micro-XRF images is discussed.

428 citations


Journal ArticleDOI
TL;DR: In this article, a Bayesian approach to estimation, prediction, and model comparison in composed error production models is presented, where a broad range of distributions on the inefficiency term define the contending models, which can either be treated separately or pooled.

426 citations


Journal ArticleDOI
TL;DR: A Monte Carlo study of phase transitions in a finite two-dimensional system of charged classical particles which are confined by a circular parabolic or hard-wall well and the results are compared with Wigner crystallization in the infinite 2D system.
Abstract: We report a Monte Carlo study of phase transitions in a finite two-dimensional (2D) system of charged classical particles which are confined by a circular parabolic or hard-wall well. The ground-state configurations are found by static energy calculations and their structures are analyzed using the Voronoi constructions. A Mendeleev table for these classical 2D-like atoms is obtained. We calculate the radial and angular components of the displacements of the particles as functions of temperature and determine the critical temperatures for the order-disorder phase transitions. The intershell rotation and intershell diffusion transitions are investigated. The results are compared with Wigner crystallization in the infinite 2D system.

395 citations


Journal ArticleDOI
TL;DR: This work characterize the two novel phosphorylation-dependent anti-tau antibodies AT270 and AT180 and identify their epitopes as containing phosphorylated Thr-181 and Thr-231 respectively, and shows that these two threonine residues are partiallyosphorylated in fetal and adult tau and almost fully phosphorylate in PHF tau.
Abstract: Tau is a neuronal phosphoprotein the expression of which is developmentally regulated. A single tau isoform is expressed in fetal human brain but six isoforms are expressed in adult human brain, with the fetal isoform corresponding to the shortest adult isoform. Phosphorylation is also developmentally regulated, as fetal tau is phosphorylated at more sites than adult tau. In Alzheimer's disease, the six adult tau isoforms become hyperphosphorylated and form the paired helical filament (PHF), the major fibrous component of the neurofibrillary lesions. One way to identify phosphorylated sites in tau is to use antibodies that recognize phosphorylated residues within a specific amino acid sequence. We here characterize the two novel phosphorylation-dependent anti-tau antibodies AT270 and AT180 and identify their epitopes as containing phosphorylated Thr-181 and Thr-231 respectively. With these antibodies we show that these two threonine residues are partially phosphorylated in fetal and adult tau and almost fully phosphorylated in PHF tau. This result contrasts with previous studies of Ser-202 and Ser-396 which are partially phosphorylated in fetal tau, unphosphorylated in adult tau but almost fully phosphorylated in PHF tau.

Journal ArticleDOI
TL;DR: Pronounced resonances are obtained for the tunneling probability and the conductance of a resonant tunneling device consisting of magnetic barriers created by lithographic patterning of ferromagnetic or superconducting films.
Abstract: New tunneling structures are proposed consisting of magnetic barriers that can be created by lithographic patterning of ferromagnetic or superconducting films. The form of the equivalent potential for such a barrier depends on the wave vector of the incident electron. This renders the transmission through such structures an inherently two-dimensional process since the tunneling probability depends not only on the electron's momentum perpendicular to the tunneling barrier but also on its momentum parallel to the barrier. Pronounced resonances are obtained for the tunneling probability and the conductance of a resonant tunneling device consisting of such magnetic barriers.

Book ChapterDOI
01 Jan 1994
TL;DR: In the cyanobacteria, the use of molecular methods to study the genotypic relationships is underway, and initial results are promising and may be used to evaluate and revise existing classifications.
Abstract: Molecular biology has provided new tools to decipher genetic information and can be used in attempts to reconstruct the evolution of organisms and improve their taxonomy. In the cyanobacteria, the use of molecular methods to study the genotypic relationships is underway, and initial results are promising. Different chemotaxonomic and macromolecular techniques are reviewed and their usefulness is evaluated. The most complete phylogenetic scheme of the cyanobacteria which is presently available is based on 16S rRNA sequence analysis. With this method, controversial taxonomic problems have been solved, such as the relationships among Pseudanabaena sp. strains or between the genera Arthrospira and Spirulina. In other cases, additional 16S rRNA sequences are necessary to obtain a clear picture. In addition to the cultivated strains, molecular ecology studies have contributed to the determination of new 16S rRNA sequence types, that have been retrieved directly from natural populations. The corresponding morphologies are presently unknown but may be revealed by the use of labeled probes annealing to specific 16S rRNA regions. For taxonomic purposes, it is necessary to find morphological features and simple testing methods which are congruent with the genotypic groupings. This information may be used to evaluate and revise existing classifications. The first stage in the development of such a polyphasic taxonomy is now underway.

Journal ArticleDOI
TL;DR: The hypothesis that major depression is accompanied by an immune response and that the lower L-TRP availability in that illness may be an epiphenomenon of immune activation is supported.
Abstract: There is now some evidence that major depression may be accompanied by an immune response. The latter condition is suggested by elevated secretion of neopterin and interferon-γ (IFNγ) and by lower L -tryptophan ( L -TRP) plasma levels. This study investigated the plasma levels of neopterin, L -TRP, and the L -TRP/competing amino acids (CAA) ratio in 30 normal control subjects and 47 depressed subjects (16 minor depressed, 13 simple major depressed, and 18 melancholic subjects), and IFNγ secretion by mitogen-stimulated peripheral blood mononuclear cells in 7 normal control subjects and 13 major depressed subjects. Plasma neopterin levels were significantly higher in depressed subjects than in normal controls; 61% of melancholic patients had increased neopterin levels (⩾ 7 nmol/1) with a specificity of 90%. Patients with major depression had significantly lower L -TRP and L -TRP/CAA values compared with normal control subjects. The amino acid values were significantly and negatively correlated with plasma neopterin levels. Major depressed subjects exhibited significantly higher IFNγ secretion than did normal control subjects. The results further support the hypothesis that major depression is accompanied by an immune response and that the lower L -TRP availability in that illness may be an epiphenomenon of immune activation.

Journal ArticleDOI
TL;DR: The fluorochromes are powerful tools when analysing the adhesion of human leucocytes to endothelial cells, however, since fluorochrome labelling can interfere with other cellular functions, the fluorescent probe has to be carefully chosen with regard to the cell type and function to be studied.

Journal ArticleDOI
10 Jul 1994-EPL
TL;DR: In this article, a molecular model consistent with theoretical predictions on how to connect cylindrical tubule segments is provided, which is probably caused by the occurrence along the helix of pairs of pentagon-heptagon carbon rings in the hexagonal network.
Abstract: The growth of micron-size carbon fibres from thermal decomposition of hydrocarbons catalyzed by a metal has been widely studied. Coil-shaped fibres often grow among straight or twisted filaments. Their internal structure has not been studied in detail as yet. In the present work, the thermal cracking of acetylene on Co nanoparticles dispersed on porous silica has produced relatively well graphitized hollow nanotubules, including straight filaments and regular helices. The small diameter of the coiled tubules and the absence of an amorphous coating allowed a determination of their texture by transmission electron microscopy (TEM). The coiled tubules consist of regularly polygonized, coaxial graphene tubes whose angular bends are aligned. The bends are probably caused by the occurrence along the helix of pairs of pentagon-heptagon carbon rings in the hexagonal network. Such a structure was recently predicted to be a thermodynamically stable topology for helical, single-sheet carbon tubes. A molecular model, consistent with theoretical predictions on how to connect cylindrical tubule segments, is provided.

Journal ArticleDOI
TL;DR: In this article, the geometries and harmonic frequencies of H2O and HF have been computed using a systematic sequence of correlation consistent basis sets, and the results indicate convergence with respect to angular momentum, indicating that the augmenting functions can safely be omitted on elements that are not highly electronegative.

Journal ArticleDOI
TL;DR: Serum zinc levels were significantly lower in major depressed subjects than in normal controls, whereas minor depressed subjects showed intermediate values, and there were significant negative correlations between serum zinc, and severity of depression and plasma neopterin concentrations.

Journal ArticleDOI
TL;DR: In this article, the authors explore the relative use of performance explanations in terms of the internal logic of the financial accounting model, relating (intermediary) accounting effects and categories (accounting explanations) in annual report narratives.
Abstract: This paper explores the relative use of performance explanations in terms of the internal logic of the financial accounting model, relating (intermediary) accounting effects and categories (accounting explanations) in annual report narratives. Different communicative aspects of accounting explanations are discussed and lead us to qualify accounting explanations as implicitly defensive in nature. The notion of accounting bias, as a tendency to explain negative performances more in technical accounting terms and positive performances more in strict cause-effect terminology, is introduced. The empirical study examines the presence of accounting bias in annual reports and investigates, from an impression management perspective, the impact of three organizational factors (public exposure, short-term profitability, stability of performances) on the use of accounting explanations.

Journal ArticleDOI
TL;DR: A set of primers which allow sequencing and PCR amplification of eukaryotic large ribosomal subunit RNA genes of a wide range of phylogenetically distant organisms is developed.

Journal ArticleDOI
TL;DR: In this article, the authors measure and explain variations in productive efficiency of municipal governments in Belgium using a nonparametric method based on the Free Disposal Hull (FDH) reference technology.
Abstract: The purpose of this paper is to measure and explain variations in productive efficiency of municipal governments in Belgium. Technical efficiency is evaluated using a non-parametric method based on the Free Disposal Hull (FDH) reference technology. We first calculate input, output, and graph Farrell efficiency measures for a cross-section of all 589 Belgian municipalities. In a second stage of the analysis we explain the calculated differences in efficiency in terms of variables related to the structural characteristics of municipalities and to the institutional environment.

Journal ArticleDOI
TL;DR: A novel basic carboxypesptidase clearly different from carboxypeptid enzyme N has been isolated from human plasma and hydrolyzes the synthetic peptides hippuryl-L-arginine and hippuryL-lysine but, in contrast to other human basic car boxypePTidases, has only a limited esterase activity.

Journal ArticleDOI
TL;DR: It is argued that embedding the foot in a well-fitting shoe increases the effective stiffness of the heel pad by means of a high-speed two-dimensional cineradiographic registration of an actual running step.

Journal ArticleDOI
TL;DR: A graph-oriented object database model (GOOD) is introduced as a theoretical basis for database systems in which manipulation as well as conceptual representation of data is transparently graph-based.
Abstract: A graph-oriented object database model (GOOD) is introduced as a theoretical basis for database systems in which manipulation as well as conceptual representation of data is transparently graph-based. In the GOOD model, the scheme as well as the instance of an object database is represented by a graph, and the data manipulation is expressed by graph transformations. These graph transformations are described using five basic operations and a method construct, all with a natural semantics. The basic operations add and delete objects and edges as a function of the matchings of a pattern. The expressiveness of the model in terms of object-oriented modeling and data manipulation power is investigated. >

Journal ArticleDOI
21 Sep 1994-JAMA
TL;DR: A review of all retrospective and cohort studies on hepatitis A and other vaccine-preventable diseases in travelers, of seroepidemiologic surveys of hepatitis A virus (HAV) antibodies in traveler, of data on the various hepatitis A vaccines, of economic analyses, and of recommendations of recognized organizations found hepatitis A vaccine is recommended for all nonimmune travelers visiting developing countries.
Abstract: Objective. —To assess the risk of hepatitis A in international travelers and to recommend preventive measures. Data Sources. — Index Medicus , 1974 through 1983; MEDLINE, 1984 through 1993; and unpublished data of the Centers for Disease Control and Prevention. Study Selection. —Review of all retrospective and cohort studies on hepatitis A and other vaccine-preventable diseases in travelers, of seroepidemiologic surveys of hepatitis A virus (HAV) antibodies in travelers, of data on the various hepatitis A vaccines, of economic analyses, and of recommendations of recognized organizations. Data Extraction. —Independent analysis by multiple observers. Data Synthesis. —The incidence rate for unprotected travelers, including those staying in luxury hotels, is estimated to be three per 1000 travelers per month of stay in a developing country. Persons eating and drinking under poor hygienic conditions have a rate of 20/1000 per month. This makes hepatitis A the most frequent infection in travelers that may be prevented by immunization. In many industrialized countries persons born after 1945 have an HAV antibody seroprevalence (immunity) of less than 20%. New inactivated HAV vaccines induce protective antibodies in more than 95% of recipients and offer protection estimated to last for 10 years or more, whereas protection by immune globulin lasts only 3 to 5 months. Conclusions. —Hepatitis A vaccine, or immune globulin where HAV vaccine is not available, is recommended for all nonimmune travelers visiting developing countries. Prescreening for antibodies to HAV in travelers living in countries with low prevalence is usually not necessary in persons born after 1945. ( JAMA . 1994;272:885-889)

Journal ArticleDOI
TL;DR: The assignment of a second locus for EXT to the pericentromeric region of chromosome 11 implicates an area that is particularly rich in genes responsible for developmental abnormalities and neoplasia.
Abstract: Hereditary multiple exostoses (EXT) is an autosomal dominant disorder of enchondral bone formation characterized by multiple bony outgrowths (exostoses), with progression to osteosarcoma in a minority of cases. The exclusive involvement of skeletal abnormalities distinguishes EXT from the clinically more complex Langer-Giedion syndrome (LGS), which is associated with deletions at chromosome 8q24. Previously, linkage analysis has revealed a locus for EXT in the LGS region on chromosome 8q24. However, locus heterogeneity was apparent with 30% of the families being unlinked to 8q24. We report on two large pedigrees segregating EXT in which linkage to the LGS region was excluded. To localize the EXT gene(s) in these families we performed a genome search including 254 microsatellite markers dispersed over all autosomes and the X chromosome. In both families evidence was obtained for linkage to markers from the proximal short and long arms of chromosome 11. Two-point analysis gave the highest lod score for D11S554 (Zmax = 7.148 at theta = 0.03). Multipoint analysis indicated a map position for the EXT gene between D11S905 and D11S916, with a peak multipoint lod score of 8.10 at 6 cM from D11S935. The assignment of a second locus for EXT to the pericentromeric region of chromosome 11 implicates an area that is particularly rich in genes responsible for developmental abnormalities and neoplasia.

Journal ArticleDOI
TL;DR: L1CAM, a neuronal cell adhesion molecule, harbours mutations leading to either MASA syndrome or HSAS, and might be frequently implicated in X–linked mental retardation with or without hydrocephalus.
Abstract: MASA syndrome is a recessive X-linked disorder characterized by mental retardation, adducted thumbs, shuffling gait, aphasia and, in some cases, hydrocephalus. Since it has been shown that X-linked hydrocephalus can be caused by mutations in L1CAM, a neuronal cell adhesion molecule, we performed an L1CAM mutation analysis in eight unrelated patients with MASA syndrome. Three different L1CAM mutations were identified: a deletion removing part of the open reading frame and two point mutations resulting in amino acid substitutions. L1CAM, therefore, harbours mutations leading to either MASA syndrome or HSAS, and might be frequently implicated in X-linked mental retardation with or without hydrocephalus.

Journal ArticleDOI
P. Van Damme1, S. Thoelen1, M. Cramm1, K. de Groote1, A. Safary1, André Meheus 
TL;DR: The reactogenicity, kinetics of antibody induction, and long‐term immunogenicity of a 720 enzyme‐linked immunosorbent assay units (EL. U.) antigen dose of an inactivated hepatitis A vaccine was evaluated.
Abstract: This trial evaluated the reactogenicity, kinetics of antibody induction, and long-term immunogenicity of a 720 enzyme-linked immunosorbent assay units (EL.U.) antigen dose of an inactivated hepatitis A vaccine (Havrix, SmithKline Beecham Biologicals, Rixensart, Belgium). One hundred six healthy adult volunteers were enrolled to receive vaccine intramuscularly according to a 0, 1, and 6-month schedule. The vaccine was well tolerated. The most frequently reported local symptom was soreness, observed following 37.1% of all doses. Headache was the most frequently reported general symptom observed following 12.9% of documented vaccine doses. The administration of one vaccine dose induced seropositivity (anti-hepatitis A virus [HAV] > or = 20 mIU/ml) in 91% of all vaccinees 1 month later. The second vaccine dose resulted in seropositivity of the remaining vaccinees at month 2. All subjects remained seropositive for HAV antibodies at month 6, at which time the booster vaccine dose was given. At month 7, all vaccinees had anti-HAV titres > 200 mIU/ml. Serological results obtained at months 12, 18, 24, and 36 showed that antibodies against HAV induced by the vaccine booster dose persist for at least 30 months following its administration. All 49 subjects followed up until month 36 had antibody titres > or = 20 mIU/ml. The geometric mean titre (GMT) decreased by 60% from month 7 to month 12; between month 12 and 36, the GMT decreased by approximately 14% per period of 12 months. According to the vaccine-induced antibody kinetics and the magnitude of antibody level decrease over time, the predicted duration of antibody persistence is estimated to be at least 20 years.

Journal ArticleDOI
TL;DR: The prestorage leukocyte removal might prevent these febrile transfusion reactions in the recipient and therefore the preparation of buffy coat PC, through its simplicity, seems to be the method of choice.
Abstract: The effect of the prestorage removal of leukocytes from platelet concentrates (PC) on the cytokine levels during its storage was studied. Two methods for leukocyte removal were examined: filtration and preparation of the PC by the buffy coat method. Cytokine levels were measured at various storage times. Highly increased levels of tumor necrosis factor-alpha (TNF-alpha; 120 +/- 131 ng/l) and interleukin 6 (IL-6; 988 +/- 494 ng/l) were found after a 5-day storage in the control group, whereas no increased levels were found in filtered PC (TNF-alpha 14 +/- 4 ng/l, IL-6 < 4 ng/l) or in buffy coat PC (TNF-alpha 8 +/- 2 ng/l, IL-6 < 4 ng/l). Furthermore an effect of the pooling of buffy coats or PC on the cytokine levels was not found. Transfusion of PC containing high levels of IL-6 and TNF-alpha has been associated with febrile transfusion reactions in the recipient and therefore the prestorage leukocyte removal might prevent these febrile transfusion reactions. The preparation of buffy coat PC, through its simplicity, seems to be the method of choice.

Journal ArticleDOI
TL;DR: Water flux in a four-year-old stand of hybrid Populus during midsummer 1992 suggested that both stomatal conductance and leaf specific hydraulic conductivity (LSHC) were linked with the ability to exploit the light resource.
Abstract: We studied water flux in a four-year-old stand of hybrid Populus during midsummer 1992. Study trees ranged in height from 11.0 to 15.1 m and in diameter from 8.3 to 15.1 cm. The large-leafed Populus hybrid was relatively poorly coupled to the atmosphere. The average value of the stomatal decoupling coefficient, Omega, was 0.66, indicating that, on average, a 10% change in stomatal conductance would result in only a 3 to 4% change in transpiration. During the middle of the summer, the smallest study tree used between 20 and 26 kg of water per day, whereas the largest tree used between 39 and 51 kg day(-1). The maximum observed rate of stand water loss was 4.8 mm day(-1) in this Populus clone. Maximum rates of sap velocity within the xylem were as high as 12.5 m h(-1); measured rates for exposed sunlit branches approached 90% of this maximum. Within-canopy patterns of stomatal conductance generally reflected patterns of incident radiation. Stomatal conductance of foliage grown in shade, even when exposed to non-limiting light and water source conditions, did not increase appreciably. Patterns of stomatal conductance under limiting and non-limiting conditions suggested that both stomatal conductance and leaf specific hydraulic conductivity (LSHC) were linked with the ability to exploit the light resource.