Showing papers by "Katholieke Universiteit Leuven published in 1994"

Local polynomial modelling and its applications

Abstract: Data-analytic approaches to regression problems, arising from many scientific disciplines are described in this book. The aim of these nonparametric methods is to relax assumptions on the form of a regression function and to let data search for a suitable function that describes the data well. The use of these nonparametric functions with parametric techniques can yield very powerful data analysis tools. Local polynomial modeling and its applications provides an up-to-date picture on state-of-the-art nonparametric regression techniques. The emphasis of the book is on methodologies rather than on theory, with a particular focus on applications of nonparametric techniques to various statistical problems. High-dimensional data-analytic tools are presented, and the book includes a variety of examples. This will be a valuable reference for research and applied statisticians, and will serve as a textbook for graduate students and others interested in nonparametric regression.

Physiological consequences of loss of plasminogen activator gene function in mice.

Abstract: Indirect evidence suggests a crucial role for the fibrinolytic system and its physiological triggers, tissue-type (t-PA) and urokinase-type (u-PA) plasminogen activator, in many proteolytic processes. Inactivation of the t-PA gene impairs clot lysis and inactivation of the u-PA gene results in occasional fibrin deposition. Mice with combined t-PA and u-PA deficiency suffer extensive spontaneous fibrin deposition, with its associated effects on growth, fertility and survival.

1,2,3-Triazole-[2',5'-bis-O-(tert-butyldimethylsilyl)-beta-D- ribofuranosyl]-3'-spiro-5"-(4"-amino-1",2"-oxathiole 2",2"-dioxide) (TSAO) analogues: synthesis and anti-HIV-1 activity.

Abstract: Several 4- or 5-monosubsituted and 4,5-disubstituted 1,2,3-triazole analogues of the anti-HIV-1 lead compound [1-[2',5'-bis-O-(tert-butyldimethylsilyl)-beta-D- ribofuranosyl]thymine]-3'-spiro-5"-(4"-amino-1",2"-oxathiole 2",2"-dioxide) (TSAO-T) have been prepared and evaluated as inhibitors of HIV-1-induced cytopathicity. These analogues have been prepared by 1,3-diplar cycloaddition of [2,5-bis-O-(tert-butyldimethylsilyl)-beta-D-ribofuranosyl]- 3-spiro-5'-(4'-amino- and 4'-(N-acetylamino)-1',2'-oxathiole 2',2'-dioxide) (TSAO) azides to various substituted acetylenes. Several 4- and 5-substituted 1,2,3-triazole-TSAO analogues proved superior to the unsubstituted derivative by 1-2 orders of magnitude. In particular the 5-substituted amido-, (methylamido)-, and (dimethylamido)-1,2,3-triazole derivatives of TSAO were endowed with potent anti-HIV-1 activity (50% effective concentration: 0.056-0.52 microM). They show a similar resistance spectrum as previously noted for TSAO-T and related derivatives.

Speckle filtering of synthetic aperture radar images : a review

Abstract: Speckle, appearing in synthetic aperture radar (SAR) images as granular noise, is due to the interference of waves reflected from many elementary scatterers. Speckle in SAR images complicates the image interpretation problem by reducing the effectiveness of image segmentation and classification. To alleviate deleterious effects of speckle, various ways have been devised to suppress it. This paper surveys several better‐known speckle filtering algorithms. The concept of each filtering algorithm and the interrelationship between algorithms are discussed in detail. A set of performance criteria is established and comparisons are made for the effectiveness of these filters in speckle reduction and edge, line, and point target contrast preservation using a simulated SAR image as well as airborne and spaceborne SAR images. In addition, computational efficiency and implementation complexity are compared. This critical evaluation of speckle suppression filters is mostly new and is presented as a survey p...

A comparison of budesonide with prednisolone for active Crohn's disease

Abstract: Background Patients with active Crohn's disease are often treated with corticosteroids, but the treatment has many side effects. Budesonide is a potent, well-absorbed corticosteroid, but because of a high rate of first-pass metabolism in the liver, its systemic bioavailability is low. Methods We conducted a randomized, double-blind, 10-week trial comparing the efficacy and safety of an oral controlled-release form of budesonide with the efficacy and safety of prednisolone in 176 patients with active ileal or ileocecal Crohn's disease (88 patients in each treatment group). The dose of budesonide was 9 mg per day for eight weeks and then 6 mg per day for two weeks. The dose of prednisolone was 40 mg per day for two weeks, after which it was gradually reduced to 5 mg per day during the last week. Results At 10 weeks, 53 percent of the patients treated with budesonide were in remission (defined as a score ≤ 150 on the Crohn's disease activity index), as compared with 66 percent of those treated with prednisol...

Corticosteroids contribute to muscle weakness in chronic airflow obstruction.

Abstract: Twenty-one patients with chronic obstructive pulmonary disease (COPD) or asthma, admitted to our division because of exacerbation of their conditions and requiring intensified treatment with corticosteroids, underwent pulmonary function tests, tests of respiratory muscle function, measurement of quadricep strength, and a variety of anthropometric and biochemical measurements. All tests were performed the 10th day after admission. As expected, muscle strength and pulmonary function were interrelated. Surprisingly, the average daily dose of steroids taken in the previous 6 mo, which ranged from 1.4 to 21.3 mg (average 4.3 mg), was significantly related to inspiratory muscle strength (PImax) and a similar tendency was present for expiratory muscle strength (PEmax). Multiple regression analysis of the relationship between PImax and quadriceps force (QF) and steroid dose revealed that the average daily dose independently explained 32% of the variance in PImax and up to 51% of the variance in QF. These relationships were independent of the degree of bronchial obstruction estimated by percentage predicted FEV1. Other significant determinants were age, sex, and COPD for PImax and age, sex, and body weight for QF. The present study demonstrates that in patients with COPD or asthma, respiratory and peripheral muscle strength and steroid treatment are interrelated despite the relatively low doses administered. This observation imposes further limitations on the prolonged treatment of chronic airflow obstruction with systemic corticosteroids.

The inhibition of glycogen synthase kinase-3 by insulin or insulin-like growth factor 1 in the rat skeletal muscle cell line L6 is blocked by wortmannin, but not by rapamycin: evidence that wortmannin blocks activation of the mitogen-activated protein kinase pathway in L6 cells between Ras and Raf

Abstract: Glycogen synthase kinase-3 (GSK3) is inactivated in vitro by p70 S6 kinase or MAP kinase-activated protein kinase-1 beta (MAPKAP kinase-1 beta; also known as Rsk-2). Here we show that GSK3 isoforms are inhibited by 40% within minutes after stimulation of the rat skeletal-muscle cell line L6 with insulin-like growth factor-1 (IGF-1) or insulin. GSK3 was similarly inhibited in rabbit skeletal muscle after an intravenous injection of insulin. Inhibition resulted from increased phosphorylation of GSK3, probably at a serine/threonine residue(s), because it was reversed by incubation with protein phosphatase-2A. Rapamycin blocked the activation of p70 S6 kinase by IGF-1 in L6 cells, but had no effect on the inhibition of GSK3 or the activation of MAPKAP kinase-1 beta. In contrast, wortmannin, a potent inhibitor of PtdIns 3-kinase, prevented the inactivation of GSK3 and the activation of MAPKAP kinase-1 beta and p70 S6 kinase by IGF-1 or insulin. Wortmannin also blocked the activation of p74raf-1. MAP kinase kinase and p42 MAP kinase, but not the formation of GTP-Ras by IGF-1. The results suggest that the stimulation of glycogen synthase by insulin/IGF-1 in skeletal muscle involves the MAP-KAP kinase-1-catalysed inhibition of GSK3, as well as the previously described activation of the glycogen-associated form of protein phosphatase-1.

Neurofibromatosis type 1

Abstract: The authors review the present data on the clinical and molecular aspects of neurofibromatosis type 1 (NF1). In the clinical part attention is given to the frequent observation of learning disabilities in NF1 children. In these children visual-spatial integration deficits and an increased incidence of school performance problems are observed. The NF1 gene is located on chromosome 17 (17q11.2), and is highly conserved across species. Up to now only a limited number of mutations in this gene have been characterized, and this shows a general lack of genotype-phenotype correlation. Evidence is given that the NF1 gene acts as a true tumor suppressor gene and that oncogenesis in NF1 is a complex multistep phenomenon with the second hit in the NF1 gene as the initiating event. The importance of specialized multidisciplinary outpatient clinics for neurofibromatosis is emphasized because of the complexity of follow-up and treatment of these patients.

Effects of rock fragments on soil erosion by water at different spatial scales: a review

Abstract: This paper reviews the various effects of rock fragments on soil erosion by water. Since these effects are scale dependent, they are investigated at three different nested spatial scales: the microplot (4 × 10−6–100m2), the mesoplot (10−2–102 m2) and the macroplot (101–104 m2). For each scale the corresponding process mechanisms are discussed. Particular attention is paid to the effects of rock fragment cover on the intensity of soil erosion processes. At the mesoplot scale, i.e. on interrill areas, rock fragments at the soil surface can have negative as well as positive effects on sediment yield. These ambivalent effects are conditioned by the type of fine earth porosity, soil surface slope, vertical position and size of rock fragments and by the occurrence of horseshoe vortex erosion. At the microplot scale, i.e. the soil surface area which is covered by a single rock fragment, and at the macroplot scale, i.e. upland areas where both interrill and rill erosion takes place, rock fragments at the soil surface have a negative effect on sediment yield. In these two scales rock fragments can thus be considered as natural soil surface stabilizers. At the macroplot scale the mean decrease of relative interrill and rill sediment yield with rock fragment cover can be expressed by an exponential decay function. The scatter of the data indicates that a given rock fragment cover can have different efficiencies in reducing interrill and rill sediment yield depending on the varying intensities of the hydrological and erosion subprocesses. These findings have implications for erosion modelling and soil conservation.

The affective priming effect: Automatic activation of evaluative information in memory.

Abstract: Fazio, Sanbonmatsu, Powell, and Kardes (1986) argued that affect may be activated automatically from memory on the mere observation of an affect-loaded stimulus. Using a variant of the standard sequential priming paradigm, it was demonstrated that the time needed to evaluate target words as positive or negative decreased if they were preceded by a similarly valenced prime word, but increased when preceded by a prime of opposite valence. Several aspects of their procedure, however, do not warrant their conclusion concerning the unconditionality of the effect. The present research investigated the generality of this affective priming effect. In Experiment 1, it was tested whether the effect can be generalised to more complex visual material. Stimulus pairs consisted of colour slides. Subjects had to evaluate the targets as quickly as possible. In Experiment 2, the standard word-word procedure was used, but target words had to be pronounced. In both experiments, significant affective priming effects...

Switched-opamp: an approach to realize full CMOS switched-capacitor circuits at very low power supply voltages

Abstract: The implementation of analog CMOS circuits that operate in the very low power supply voltage range (1 V to 2 V) becomes more important nowadays. Most accurate filter circuits are designed in the switched-capacitor technique. The existing design techniques require, however, the on-chip generation of a higher voltage by means of a voltage multiplier. In this paper, a novel technique, derived from the standard switched-capacitor technique, is presented. It is called switched-opamp because it is based on the replacement of the critical switches with opamps which are turned on and off. This technique results in a true, very low voltage operation without the need for voltage multipliers. As an example, a second order lowpass switched-capacitor filter is implemented in the switched-opamp technique. This filter operates with only a 1.5 V power supply. It is realized in a 2.4-/spl mu/m CMOS process with V/sub T/=/spl plusmn/0.9 V. It has a measured total harmonic distortion of -60 dB for a signal swing of 600 mV/sub ptp/ and a powerdrain of only 110 /spl mu/W. >

Genome screening by searching for shared segments: Mapping a gene for benign recurrent intrahepatic cholestasis

Abstract: It is now feasible to map disease genes by screening the genome for linkage disequilibrium between the disease and marker alleles. This report presents the first application of this approach for a previously unmapped locus. A gene for benign recurrent intrahepatic cholestasis (BRIC) was mapped to chromosome 18 by searching for chromosome segments shared by only three distantly related patients. The screening results were confirmed by identifying an extended haplotype conserved between the patients. Probability calculations indicate that such segment sharing is unlikely to arise by chance. Searching the genome for segments shared by patients is a powerful empirical method for mapping disease genes. Computer simulations suggest that, in appropriate populations, the approach may be used to localize genes for common diseases.

Evaluation of Uniform Color Spaces Developed after the Adoption of CIELAB and CIELUV

Abstract: Since the adoption of the color spaces CIELAB and CIELUV by the CIE in 1976, several other uniform spaces have been developed. We studied most of these spaces and evaluated their uniformity for small as well as larger color differences. Therefore, several criteria have been defined based on color discrimination data and appearance systems. The main difference between color spaces based on discrimination data and spaces that model appearance systems is reflected in a different size of the chroma distance unit compared with the lightness unit. If spaces based on the same kind of data (discrimination data or appearance systems) are compared with each other, they are all almost equally uniform. BFD (l:c), for example, is said to be more uniform than CMC(l:c), but, based on confidence intervals of 65%, there is no significant difference between them. If the proposed color difference formula of the CIE is compared with these distance functions, it also performs equally well. The SVF space and OSA 90 space on the other hand should be better than OSA 74. However, as opposed to what was expected, OSA 74 is slightly better; but, also in this case, the difference between the spaces is insignificant.

Antibracket, Antifields and Gauge-Theory Quantization

Abstract: The antibracket formalism for gauge theories, at both the classical and quantum level, is reviewed. Gauge transformations and the associated gauge structure are analyzed in detail. The basic concepts involved in the antibracket formalism are elucidated. Gauge-fixing, quantum effects, and anomalies within the field-antifield formalism are developed. The concepts, issues and constructions are illustrated using eight gauge-theory models.

Induction of natural killer cell migration by monocyte chemotactic protein−1, −2 and −3

Abstract: Under certain physiological and pathological conditions, naturall killer (NK) cells rapidly accumulate in tissues. Chemokines are an essential component of the current paradigm of leukocyte recruitment. The present study was designed to investigate the responsiveness of NK cells to the prototypic C-C chemokine, monocyte chemotactic protein-1 (MCP-1). MCP-1 induced migration across filters of interleukin (IL)-2-activated NK cells, whereas it was a weak attractant for unstimulated cells. Maximal induction of migration required a positive concentration gradient between the lower and the upper compartment of the chemotaxis chamber. Preliminary characterization of the MCP-1 receptor on NK cells indicated that the chemotactic response to MCP-1 was blocked by pre-treatment of cells with Bordetella pertussis toxin, and MCP-1 but not IL-8 displaced 125I-labeled MCP-1 from IL-2-activated NK cells. The related chemokines MCP-2 and MCP-3 were also active – though less potent – attractants for activated NK cells. Thus the spectrum of action of MCP-1, -2 and -3 encompasses NK cells and chemokines are likely to play a role in regulating extravasation of these cells.

Responses of macaque STS neurons to optic flow components: a comparison of areas MT and MST

Abstract: 1. We recorded and tested quantitatively 65 middle temporal (MT) and 82 middle superior temporal (MST) cells in paralyzed and anesthetized monkeys. 2. Responses to the three elementary optic flow components (EFCs)--rotation, deformation, and expansion/contraction--and to translation (in the display) were compared after optimization of stimulus direction, speed, size, and position. As a control responses to flicker were measured. 3. Response windows were adapted in correspondence with our finding that latencies of MT and MST cells decrease with increasing speed for all types of motion. 4. There was a response continuum in MT as well as in MST cells. Compared with translation, MST cells responded significantly more to rotation but less to flicker than MT cells. MST cells were significantly more direction selective for expansion/contraction than MT cells. 5. MST cells generally responded to fewer motion types than MT cells. 6. Position invariance of EFC direction selectivity was tested over a region of the visual field centered on the translation receptive field (RF). Direction selectivity for an EFC was not position invariant in MT cells but it was invariant in 40% of the MST cells tested. These cells were considered EFC selective. 7. Most EFC-selective MST cells were selective for a single EFC, possibly combined with translation. Few of them were selective for deformation. 8. EFC selectivity was also speed invariant and EFC-selective MST cells usually had RFs summating inputs over wide portions of the visual field. 9. EFC-selective MST cells with similar selectivities were clustered.

Marginal Modeling of Correlated Ordinal Data Using a Multivariate Plackett Distribution

Abstract: An extension of the bivariate model suggested by Dale is proposed for the analysis of dependent ordinal categorical data. The so-called multivariate Dale model is constructed by first generalizing the bivariate Plackett distribution to any dimensions. Because the approach is likelihood based, it satisfies properties that are not fulfilled by other popular methods, such as the generalized estimating equations approach. The proposed method models both the marginal and the association structure in a flexible way. The attractiveness of the multivariate Dale model is illustrated in three key examples, covering areas such as crossover trials, longitudinal studies with patients dropping out from the study, and discriminant analysis applications. The differences and similarities with the generalized estimating approach are highlighted.

Histological alterations in chronically hypoperfused myocardium. Correlation with PET findings.

Abstract: BACKGROUNDIn patients with chronic coronary artery disease (CAD) and left ventricular dysfunction, flow/metabolic studies of the myocardium with positron emission tomography (PET) are able to distinguish viable but dysfunctional myocardium from irreversible ischemic injury and scar tissue. In this study, PET findings of blood flow and metabolism in chronically hypoperfused myocardium were correlated with histology.METHODS AND RESULTSWe studied 33 patients suffering from CAD. In each patient, myocardial blood flow and metabolism were measured with PET 1 or 2 days before revascularization. During surgery, transmural biopsies were taken from the left ventricular anterior wall and planimetrically scored for the degree of myolysis (sarcomere loss). The amount of connective tissue was calculated using morphometric techniques. Contrast ventriculography demonstrated abnormal wall motion in 23 patients. Fourteen patients with a mismatch pattern (decreased flow with preserved metabolism) in the biopsy region after ...

Position and momentum information entropies of the D-dimensional harmonic oscillator and hydrogen atom

Abstract: The position- and momentum-space entropies of the isotropic harmonic oscillator and the hydrogen atom in D dimensions are shown to be related to some entropy integrals which involve classical orthogonal polynomials. These integrals are exactly calculated for Chebyshev polynomials and only in an approximate way for Gegenbauer polynomials. The physical entropies are explicitly obtained in the ground state and in a few low-lying excited states. Finally, the dimensionality dependence of the ground-state entropies of the two above-mentioned quantum-mechanical systems is analyzed (numerically) and the values of the entropies in a large class of excited states of the D-dimensional (D=1,2,3) harmonic oscillator and hydrogen atom are tabulated and discussed.

An efficient mimic of cytochrome P-450 from a zeolite-encaged iron complex in a polymer membrane.

Abstract: MANY attempts have been made to mimic the catalytic oxidative properties of the enzyme cytochrome P-450. For homogeneous systems1 the mechanisms of oxidation can be readily determined but proper mimicry of the protein environment is difficult to achieve. Heterogeneous mimics have been designed that use organometallic complexes encapsulated in the supercages of zeolites2,3, which enables control of selectivity and inhibition of auto-oxidation. But these systems do not show any mechanistic analogy with the enzymatic process, and the oxidation rates tend to be low. Here we report a composite catalytic system that achieves realistic mimicry of cytochrome P-450 as well as catalytic turnover rates that make the system industrially viable. Our catalyst incorporates iron phthalocyanine complexes encapsulated in crystals of zeolite Y, which are in turn embedded in a polydi-methylsiloxane membrane. The polymer acts as a mimic of the phospholipid membrane in which cytochrome P-450 resides4, acting as an interface between two immiscible phases and avoiding the need for solvents or phase-transfer agents. This system oxidizes alkanes at room temperature at rates comparable to those of the enzyme5. The observation of a large kinetic isotope effect and the preferential oxidation of tertiary C–H bonds suggest close mechanistic similarities to the enzymatic process.

Collisions for the compression function of MD5

Abstract: At Crypto '91 Ronald L. Rivest introduced the MD5 Message Digest Algorithm as a strengthened version of MD4, differing from it on six points. Four changes are due to the two existing attacks on the two round versions of MD4. The other two changes should additionally strengthen MD5. However both these changes cannot be described as well-considered. One of them results in an approximate relation between any four consecutive additive constants. The other allows to create collisions for the compression function of MD5. In this paper an algorithm is described that finds such collisions.A C program implementing the algorithm establishes a work load of finding about 216 collisions for the first two rounds of the MD5 compression function to find a collision for the entire four round function. On a 33MHz 80386 based PC the mean run time of this program is about 4 minutes.

Many areas in the human brain respond to visual motion.

Abstract: 1. The regions of the human brain responsive to motion were mapped using the H2(15)O position emission tomography (PET) activation technique and compared by viewing a moving random dot pattern with a stationary dot pattern. The stimulus was optimized in dot density and 3 degrees in diameter. 2. In addition to bilateral foci at the border between Brodmann areas 19 and 37, a V1/V2 focus and a focus in the cuneus reported earlier, we observed activations in other visual areas (lower BA 19 and the parieto-occipital fissure) in the cerebellum and in two other, presumed vestibular areas, the posterior bank of lateral sulcus and at the border of BA 2/40. 3. Homologies between monkey and human cortex are discussed.