Showing papers by "Université libre de Bruxelles published in 1995"

Credit and Efficiency in Centralized and Decentralized Economies

Abstract: We study a credit model where, because of adverse selection, unprofitable projects may nevertheless be financed. Indeed they may continue to be financed even when shown to be low-quality if sunk costs have already been incurred. We show that credit decentralization offers a way for creditors to commit not to refinance such projects, thereby discouraging entrepreneurs from undertaking them initially. Thus, decentralization provides financial discipline. Nevertheless, we argue that it puts too high a premium on short-term returns. The model seems pertinent to two issues: "soft budget constraint" problems in centralized economies, and differences between "Anglo-Saxon" and "German-Japanese" financing practices.

Ant-Q: a reinforcement learning approach to the traveling salesman problem

Abstract: In this paper we introduce Ant-Q, a family of algorithms which present many similarities with Q-learning (Watkins, 1989), and which we apply to the solution of symmetric and asymmetric instances of the traveling salesman problem (TSP). Ant-Q algorithms were inspired by work on the ant system (AS), a distributed algorithm for combinatorial optimization based on the metaphor of ant colonies which was recently proposed in (Dorigo, 1992; Dorigo, Maniezzo and Colorni, 1996). We show that AS is a particular instance of the Ant-Q family, and that there are instances of this family which perform better than AS. We experimentally investigate the functioning of Ant-Q and we show that the results obtained by Ant-Q on symmetric TSP's are competitive with those obtained by other heuristic approaches based on neural networks or local search. Finally, we apply Ant-Q to some difficult asymmetric TSP's obtaining very good results: Ant-Q was able to find solutions of a quality which usually can be found only by very specialized algorithms.

Optimal extraction of information from finite quantum ensembles

Abstract: Given only a finite ensemble of identically prepared particles, how precisely can one determine their states? We describe optimal measurement procedures in the case of spin $1/2$ particles. Furthermore, we prove that optimal measurement procedures must necessarily view the ensemble as a single composite system rather than as the sum of its components, i.e., optimal measurements cannot be realized by separate measurements on each particle.

Sensors based on carbon paste in electrochemical analysis: A review with particular emphasis on the period 1990–1993

Abstract: A review is presented dealing with the use of carbon paste as an electrode maaterial for electrochemical sensors (311 references). It covers mainly publications which appeared during the period 1990–1993; numerous applications demonstrate the widespread applicability of carbon paste in the field of electrochemical analysis, such as voltammetry, amperometry, and potentiometry, but also as an electrode for electrochemical detectors in flow systems.

A model for circadian oscillations in the Drosophila period protein (PER).

Abstract: The mechanism of circadian oscillations in the period protein (PER) in Drosophila is investigated by means of a theoretical model. Taking into account recent experimental observations, the model for the circadian clock is based on multiple phosphorylation of PER and on the negative feedback exerted by PER on the transcription of the period (per) gene. This minimal biochemical model provides a molecular basis for circadian oscillations of the limit cycle type. During oscillations, the peak in per mRNA precedes by several hours the peak in total PER protein. The results support the view that multiple PER phosphorylation introduces times delays which strengthen the capability of negative feedback to produce oscillations. The analysis shows that the rhythm only occurs in a range bounded by two critical values of the maximum rate of PER degradation. A similar result is obtained with respect to the rate of PER transport into the nucleus. The results suggest a tentative explanation for the altered period of per mutants, in terms of variations in the rate of PER degradation.

The asymptotic dynamics of three-dimensional Einstein gravity with a negative cosmological constant

Abstract: Liouville theory is shown to describe the asymptotic dynamics of three-dimensional Einstein gravity with a negative cosmological constant. This is because (i) Chern - Simons theory with a gauge group on a spacetime with a cylindrical boundary is equivalent to the non-chiral SL(2,R) WZW model; and (ii) the anti-de Sitter boundary conditions implement the constraints that reduce the WZW model to the Liouville theory.

A genetic linkage map of the laboratory rat, Rattus norvegicus

Abstract: We report the construction of the first complete genetic linkage map of the laboratory rat. By testing 1171 simple sequence length polymorphisms (SSLPs), we have identified 432 markers that show polymorphisms between the SHR and BN rat strains and mapped them in a single (SHR × BN) F2 intercross. The loci define 21 large linkage groups corresponding to the 21 rat chromosomes, together with a pair of nearby markers on chromosome 9 that are not linked to the rest of the map. Because 99.5% of the markers fall into one of the 21 large linkage groups, the maps appear to cover the vast majority of the rat genome. The availability of the map should facilitate whole genome scans for genes underlying qualitative and quantitative traits relevant to mammalian physiology and pathobiology.

Design of electrical conductive composites : key role of the morphology on the electrical properties of carbon black filled polymer blends

Abstract: Effect of carbon black (CB) on the morphology of filled polyethylene (PE)/polystyrene (PS) blends has been investigated by image analysis of optical micrographs (2-D analysis) and by the selective extraction of one phase of the binary blends (3-D analysis). The macroscopic electrical resistivity of the filled polyblends strongly depends on the selective localization of CB in one phase or at the interface and above all on the double percolation, i.e. percolation of the polymer phases and percolation of the CB particles. The selective localization of CB in the PE phase has remarkable effects on the polyblend phase morphology. The phase cocontinuity is indeed extended over a much larger composition range, and the phase morphology is stabilized toward post-thermal treatment at 200 °C. In the case of double percolation and selective localization of CB at the polyblend interface, electrical conductivity is observed at a CB content as low as 0.4 wt %.

Introduction to Nonlinear Science

Abstract: Preface 1. Nonlinear behavior in the physical sciences and biology: some typical examples 2. Quantitative formulation 3. Dynamical systems with a finite number of degrees of freedom 4. Linear stability analysis of fixed points 5. Nonlinear behavior around fixed points: bifurcation analysis 6. Spatially distributed systems, broken symmetries, pattern formation 7. Chaotic dynamics Appendices References Index.

Introduction to Nonlinear Science

Abstract: Preface 1. Nonlinear behavior in the physical sciences and biology: some typical examples 2. Quantitative formulation 3. Dynamical systems with a finite number of degrees of freedom 4. Linear stability analysis of fixed points 5. Nonlinear behavior around fixed points: bifurcation analysis 6. Spatially distributed systems, broken symmetries, pattern formation 7. Chaotic dynamics Appendices References Index.

NPI1, an essential yeast gene involved in induced degradation of Gap1 and Fur4 permeases, encodes the Rsp5 ubiquitin-protein ligase

Abstract: When yeast cells growing on a poor nitrogen source are supplied with NH4+ ions, several nitrogen permeases including the general amino acid permease (Gap1p) are rapidly and completely inactivated. This report shows that inactivation by NH4+ of the Gap1 permease is accompanied by its degradation. A functional NPl1 gene product is required for both inactivation and degradation of Gap1p. Molecular analysis of the NPl1 gene showed that it is identical to RSP5. The RSP5 product is a ubiquitin-protein ligase (E3 enzyme) whose physiological function was, however, unknown. Its C-terminal region is very similar to that of other members of the E6-AP-like family of ubiquitin-protein ligases. Its N-terminal region contains a single C2 domain that may be a Ca(2+)-dependent phospholipid interaction motif, followed by several copies of a recently identified domain called WW(P). The Npi1/Rsp5 protein has a homologue both in humans and in mice, the latter being involved in brain development. Stress-induced degradation of the uracil permease (Fur4p), a process in which ubiquitin is probably involved, was also found to require a functional NPl1/RSP5 product. Chromosomal deletion of NPl1/RSP5 showed that this gene is essential for cell viability. In the viable npi1/rsp5 strain, expression of NPl1/RSP5 is reduced as a result of insertion of a Ty1 element in its 5' region. Our results show that the Npi1/Rsp5 ubiquitin-protein ligase participates in induced degradation of at least two permeases, Gap1p and Fur4p, and probably also other proteins.

Local brst cohomology in the antifield formalism. i: general theorems

Abstract: We establish general theorems on the cohomologyH * (s/d) of the BRST differential modulo the spacetime exterior derivative, acting in the algebra of localp-forms depending on the fields and the antifields (=sources for the BRST variations). It is shown thatH −k (s/d) is isomorphic toH k (δ/d) in negative ghost degree−k (k>0), where δ is the Koszul-Tate differential associated with the stationary surface. The cohomology groupH 1 (δ/d) in form degreen is proved to be isomorphic to the space of constants of the motion, thereby providing a cohomological reformulation of Noether's theorem. More generally, the groupH k (δ/d) in form degreen is isomorphic to the space ofn−k forms that are closed when the equations of motion hold. The groupsH k (δ/d)(k>2) are shown to vanish for standard irreducible gauge theories. The groupH 2 (δ/d) is then calculated explicitly for electromagnetism, Yang-Mills models and Einstein gravity. The invariance of the groupsH k (s/d) under the introduction of non-minimal variables and of auxiliary fields is also demonstrated. In a companion paper, the general formalism is applied to the calculation ofH k (s/d) in Yang-Mills theory, which is carried out in detail for an arbitrary compact gauge group.

Seasonal succession of diatoms and Chlorophyceae in the drainage network of the Seine River: Observation and modeling

Abstract: Seasonal succession of diatoms and Chlorophyceae have been analyzed in the Seine River system (France), which is characterized by a temperate oceanic hydrological regime and high nutrient enrichment. Phytoplankton development is invariably initiated by the decrease of discharge in spring. When this occurs in early spring, the bloom is dominated by diatoms that severely deplete silica, and a regular increase of their biomass is observed along the river continuum from headwaters to the estuary. The bloom occurs earlier downstream than upstream. Chlorophyceae succeed the diatoms by the end of May and represent a significant component of the summer phytoplankton population. Fluctuations of the phytoplankton biomass are observed within the continuum in summer, with high biomass in 6th-order rivers, low biomass in 7th-order rivers, and again high biomass in h the model calculates the development of diatoms and Chlorophyceae within the whole drainage network which is represented as a regular pattern of confluences of tributaries with increasing stream order. The model, taking into account both bottom-up and top-down regulating factors of phytoplankton, has proved to be a powerful tool in understanding the dynamics of a large drainage network.

Expression of MAGE genes in primary and metastatic cutaneous melanoma.

Abstract: Human genes MAGE-1 and MAGE-3 code for antigens that are recognized on melanoma cells by autologous cytolytic T lymphocytes. These antigens may constitute useful targets for specific anti-tumor immunization of cancer patients, since genes MAGE-1 and MAGE-3 are expressed in a number of tumors of different histological types, but are not expressed in normal adult tissues other than testis. This also applies to genes MAGE-2 and MAGE-4, which are closely related to MAGE-1 and MAGE-3. We have analyzed the expression of these 4 MAGE genes in cutaneous melanoma. Sixteen of 100 primary tumors vs. 69 (48%) of 145 metastases from individual patients expressed MAGE-1. Similar differences in the frequency of gene expression between primary and metastatic tumor samples were observed for MAGE-2, MAGE-3, and MAGE-4. MAGE expression in primary tumors was correlated with tumor thickness: there was a significantly increased frequency in the expression of MAGE-1, -2 and -3 in tumors of greater thickness. Benign and dysplastic nevi, as well as in site melanomas, did not express any of the 4 MAGE genes. (C) 1995 Wiley-Liss, Inc.

Interleukin-10 differentially regulates B7-1 (CD80) and B7-2 (CD86) expression on human peripheral blood dendritic cells.

Abstract: Most of the immunosuppressive effects of interleukin-10 (IL-10) are related to functional inhibition of antigen-presenting cells (APC). Herein, we investigate the influence of recombinant (r)IL-10 on human dendritic cells (DC) purified from peripheral blood of healthy volunteers. First, we found that rIL-10 inhibited in a dose-dependent manner the proliferative responses as well as the production of IL-2 and interferon-gamma (IFN-gamma) in mixed lymphocyte reaction (MLR) between purified T cells and DC. This rIL-10 effect could be attributed to a direct effect on DC, as DC preincubated with rIL-10 were found to be deficient in the induction of alloreactive T cells even when anti-IL-10 neutralizing mAb was added at the time of MLR. Flow cytometric analysis indicated that rIL-10 did not modify the expression of ICAM-1 (CD54) and B7-1 (CD80), but decreased HLA-DR and B7-2 (CD86) expression at the DC surface. We conclude that the inhibitory effect of rIL-10 on primary alloreactive T cell responses involves down-regulation of class II MHC and B7-2 expression at the DC surface.

Longitudinal study of the bone mineral content and of soft tissue composition after spinal cord section

Abstract: We present the results of a 1 year longitudinal study of bone mineral measurements and soft tissue composition in supra- and infra-lesional areas of 31 patients with a spinal cord injury (level D2-L3). Like others, we observed a rapid decrease of BMC in the paralysed areas, of approximately 4%/month during the first year in areas rich in trabecular bone and of approximately 2%/month in areas containing mainly compact bone. Lean soft tissue mass (muscle mass) decreases dramatically during the first months post injury in the legs, while fat content tends to increase. Though lean mass is better maintained in patients who develop spasticity, the evolution of BMC does not differ significantly between the groups of flaccid and spastic patients. In patients with partial or complete neurological recovery, a deficit in BMC of approximately 10% with regards to the initial value is still observed at 1 year in the lower limbs. The lean mass of the upper limbs increases early after the cord injury, because of intensive rehabilitation. No significant change in BMC was observed in the supra-lesional areas. These data confirm the rapid loss of bone in the paralysed areas of paraplegic patients, which occurs independently of the presence of spontaneous muscle activity or of passive verticalisation. In patients with recovery, BMC does not return to pre-injury values within 1 year. Thus, there would be an interest in preventing bone loss early in the course of the disease.

An overview of membrane transport proteins in Saccharomyces cerevisiae.

Abstract: All eukaryotic cells contain a wide variety of proteins embedded in the plasma and internal membranes, which ensure transmembrane solute transport. It is now established that a large proportion of these transport proteins can be grouped into families apparently conserved throughout organisms. This article presents the data of an in silicio analysis aimed at establishing a preliminary classification of membrane transport proteins in Saccharomyces cerevisiae. This analysis was conducted at a time when about 65% of all yeast genes were available in public databases. In addition to approximately 60 transport proteins whose function was at least partially known, approximately 100 deduced protein sequences of unknown function display significant sequence similarity to membrane transport proteins characterized in yeast and/or other organisms. While some protein families have been well characterized by classical genetic experimental approaches, others have largely if not totally escaped characterization. The proteins revealed by this in silicio analysis also include a putative K+ channel, proteins similar to aquaporins of plant and animal origin, proteins similar to Na+-solute symporters, a protein very similar to electroneural cation-chloride cotransporters, and a putative Na+-H+ antiporter. A new research area is anticipated: the functional analysis of many transport proteins whose existence was revealed by genome sequencing.

A randomized trial for the treatment of mild iodine deficiency during pregnancy: maternal and neonatal effects.

Abstract: One hundred and eighty euthyroid pregnant women were selected at the end of the first trimester of gestation on the basis of biochemical criteria of excessive thyroid stimulation, defined as supranormal serum thyroglobulin (TG >20 mu g/L) associated with a low normal free T-4 index ( 25 x 10(-3)). Women were randomized in a double blind protocol into three groups and treated until term with a placebo, 100 mu g potassium iodide (KI)/day, or 100 mu g iodide plus 100 mu g L-T-4/day. Parameters of thyroid function, urinary iodine excretion, and thyroid volume were monitored sequentially. Neonatal thyroid parameters, including thyroid volume by echography, were also assessed in the newborns from mothers of the three groups. In women receiving a placebo, the indices of excessive thyroid stimulation worsened as gestation progressed, with low free T-4 levels, markedly increased serum TG and T-3/T-4 ratio. Serum TSH doubled, on the average, and was supranormal in 20% of the cases at term. Urinary iodine excretion levels were low, around 30 mu g/L at term. The thyroid volume increased, on the average, by 30%, and 16% of the women developed a goiter, confirming the goitrogenic stimulus associated with pregnancy. Moreover, the newborns of these mothers had significantly larger thyroid volumes at birth as well as elevated serum TG levels. In both groups of women receiving an active treatment, the alterations in thyroid function associated with pregnancy were markedly improved. The increase in serum TSH was almost suppressed, serum TG decreased significantly, and changes in thyroid volume were minimized (group receiving KI) or almost suppressed (group receiving KI combined with L-T-4) Moreover, in the newborns of the mothers in the two groups receiving an active treatment, serum TG was significantly lower, and thyroid volume at birth was normal. The effects of therapy were clearly more rapid and more marked in the group receiving a combination of T-4 and KI than in the women receiving KI alone. The differences could be partly attributed to the slightly higher amount of iodine received by women in the combined treatment. However, the main benefits of the combined treatment were almost certainly attributable to the hormonal effects of the addition of L-T-4. Furthermore, the study demonstrated that the administration of T-4 did not hamper the beneficial effect of iodine supplementation. In conclusion, the present work emphasizes the potential risk of goitrogenic stimulation in both mother and newborn in the presence of mild iodine deficiency. Furthermore, the results clearly indicate the benefits of supplementing pregnant women with iodine and women with excessive thyroid stimulation (or a preexisting goiter) with a combination of iodine and L-T-4. In conditions of mild iodine deficiency, pregnancy justifies monitoring thyroid function and volume, and therapeutic intervention to avoid hypothyroxinemia and goitrogenesis in both mother and newborn.

Somatic mutations causing constitutive activity of the thyrotropin receptor are the major cause of hyperfunctioning thyroid adenomas: identification of additional mutations activating both the cyclic adenosine 3',5'-monophosphate and inositol phosphate-Ca2+ cascades.

Abstract: A series of somatic mutations of the TSH receptor gene have been demonstrated in hyperfunctioning thyroid adenomas. The mutations studied up to now cause constitutive (i.e. TSH-independent) activation of the cAMP-regulatory cascade only. As a follow-up to our original study, we have now completely sequenced exon number 10 of the TSH receptor gene in the same series of toxic adenomas. An activating mutation was found in nine of 11 tumors. In addition to the mutations already described, two isoleucine residues belonging to the first and second extracellular loops of the receptor (Ile486 and Ile568) were found mutated. Two different adenomas were found to harbor a different amino acid substitution at residue 486 (Ile486Phe, Ile486Met). Ile568 was mutated to threonine in one. When studied by transfection in COS-7 cells, all three mutations caused very strong activation of the cAMP-regulatory cascade. In addition, the Ile486Phe and, to a lesser extent, the Ile486Met and Ile568Thr mutants stimulated constitutiv...

Somatic and germline mutations of the TSH receptor gene in thyroid diseases.

Abstract: Under physiological circumstances, thyrotropin (TSH) is the primary hormone that controls thyroid function and growth. TSH acts by binding to its receptor at the basolateral membrane of thyroid follicular cells. The TSH receptor is a member of the large family of G protein-coupled receptors, which share a similar structural pattern: seven transmembrane segments connected by three extra and three intracellular loops. Together with the receptors for other glycoprotein hormones LH/CG and FSH, the TSH receptor has a long aminoterminal domain that has been shown to encode the specificity for hormone recognition and binding. The G protein-coupled receptors share a common mode of intracellular signalling: They control the on/off state of a variety of trimeric G proteins (G{alpha}{beta}{gamma}) by stimulating the exchange of GDP for GTP on the {alpha} subunit (G{alpha}). The result is that G{alpha} or G{beta}{gamma}, after dissociation of the trimer, will interact with downstream effectors of the receptor. In the case of the TSH receptor, the main G protein involved is Gs, which activates adenylyl cyclase via Gs{alpha}. In some species, including man, the TSH receptor is also capable of activating phospholipase C (via Gq), thus stimulating the production of diacylglycerol and inositolphosphate (IP{sub 3}). However, higher concentrationsmore » of TSH are required to activate phospholipase C, compared with adenylyl cyclase. As a consequence, the main second messenger of TSH effects on the human thyroid is cyclic AMP. The present review will summarize recent findings identifying mutations of the TSH receptor gene as a cause for thyroid diseases. 59 refs., 4 figs.« less

Tumorigenesis and metastasis of neoplastic Kaposi's sarcoma cell line in immunodeficient mice blocked by a human pregnancy hormone

Abstract: KAPOSI'S sarcoma (KS) occurs more often in men than in women and HIV-l-associated KS has a high occurrence in homosexual men (over 30%). Most cultures of KS tumours yield cells with properties of hyperplastic (not malignant) endothelial cells under the control of several cytokines 1a€-7. The role of HIV-1 may be in promoting high levels of some cytokines and providing stimulation to angiogenesis by the HIV-1 Tat protein8, which synergizes with basic fibroblast growth factor in promoting these effects9. Here we describe an immortalized AIDS-KS cell line (KS Y-l) and show that these cells produce malignant metastatic tumours in nude mice and are killed in vitro and in vivo (apparently by apoptosis) by a pregnancy hormone, the β-chain of human chorionic gonadotropin. Similarly, chorionic gonadotropin kills KS SLK, cells from another neoplastic cell line (established from a non-HIV-associated KS)10, as well as the hyper plastic KS cells from clinical specimens grown in short-term culture, but does not kill normal endothelial cells. These results provide evidence that KS can evolve into a malignancy and have implications for the hormonal treatment of this tumour. © 1995 Nature Publishing Group.

Preservation of Miocene glacier ice in East Antarctica

Abstract: ANTARCTIC climate during the Pliocene has been the subject of considerable debate. One view holds that, during part of the Pliocene, East Antarctica was largely free of glacier ice and that vegetation survived on the coastal mountains1a¤-4. An alternative viewpoint argues for the development of a stable polar ice sheet by the middle Miocene, which has persisted since then5a¤-10. Here we report the discovery of buried glacier ice in Beacon valley, East Antarctica, which appears to have survived for at least 8.1 million years. We have dated the ice by 40Ar/39Ar analysis of volcanic ash in the thin, overlying glacial till which, we argue, has undergone little (if any) reworking. Isotope and crystal fabric analyses of the ice show that it was derived from an ice sheet. We suggest that stable polar conditions must have persisted in this region for at least 8.1 million years for this ice to have avoided sublimation.