Showing papers by "Aix-Marseille University published in 2000"

Review of Particle Physics

Abstract: This biennial Review summarizes much of particle physics. Using data from previous editions., plus 2778 new measurements from 645 papers, we list, evaluate, and average measured properties of gauge bosons, leptons, quarks, mesons, and baryons. We also summarize searches for hypothetical particles such as Higgs bosons, heavy neutrinos, and supersymmetric particles. All the particle properties and search limits are listed in Summary Tables. We also give numerous tables, figures, formulae, and reviews of topics such as the Standard Model, particle detectors., probability, and statistics. Among the 108 reviews are many that are new or heavily revised including those on CKM quark-mixing matrix, V-ud & V-us, V-cb & V-ub, top quark, muon anomalous magnetic moment, extra dimensions, particle detectors, cosmic background radiation, dark matter, cosmological parameters, and big bang cosmology.

Prenatal stress produces learning deficits associated with an inhibition of neurogenesis in the hippocampus

Abstract: Early experiences such as prenatal stress significantly influence the development of the brain and the organization of behavior. In particular, prenatal stress impairs memory processes but the mechanism for this effect is not known. Hippocampal granule neurons are generated throughout life and are involved in hippocampal-dependent learning. Here, we report that prenatal stress in rats induced lifespan reduction of neurogenesis in the dentate gyrus and produced impairment in hippocampal-related spatial tasks. Prenatal stress blocked the increase of learning-induced neurogenesis. These data strengthen pathophysiological hypotheses that propose an early neurodevelopmental origin for psychopathological vulnerabilities in aging.

Induction of a non-encephalitogenic type 2 T helper-cell autoimmune response in multiple sclerosis after administration of an altered peptide ligand in a placebo- controlled, randomized phase II trial

Abstract: In this ‘double-blind’, randomized, placebo-controlled phase II trial, we compared an altered peptide ligand of myelin basic protein with placebo, evaluating their safety and influence on magnetic resonance imaging in relapsing–remitting multiple sclerosis. A safety board suspended the trial because of hypersensitivity reactions in 9% of the patients. There were no increases in either clinical relapses or in new enhancing lesions in any patient, even those with hypersensitivity reactions. Secondary analysis of those patients completing the study showed that the volume and number of enhancing lesions were reduced at a dose of 5 mg. There was also a regulatory type 2 T helper-cell response to altered peptide ligand that cross-reacted with the native peptide.

Morphological analysis for product design

Abstract: Analysis plays a significant role during product design. Thanks to computational tools; it contributes highly in product optimisation while decreasing design cost and time. For analysis applications, the adaptation of the product geometry is required and consists of producing an idealised model out of a product solid one. This paper presents a form of features based tool to aid the integration of analysis during the design process. It allows producing an analysis model out of a part solid model. This tool is based on a morphological analysis of the solid model followed by a two-phase process: simplification and idealisation. The tool provides an easy way to make computer-aided design model modifications implied by the analysis results; thanks to features parameterisation and a reconstruction process. Both allow us to create a solid model on the basis of the idealised one, by using parameterised reconstruction operators.

Effects of marine protected areas on recruitment processes with special reference to Mediterranean littoral ecosystems

Abstract: Although site-attached fish can be expected to increase in abundance in marine protected areas (MPAs), there is little known about recruitment effects. The present work reviews concepts and field evidence for enhancement of recruitment of species in MPAs, focusing geographically on the Mediterranean littoral because of its long history of intensive fishery exploitation, but drawing on evidence from studies on recruitment processes in general on MPAs both in the Mediterranean and elsewhere. We considered recruitment as the process of a fish being added to the local population. The general questions of interest are whether the increase in biomass of species protected in MPAs has an effect on recruitment in the MPAs or in neighbouring areas, and, on competition and predation effects on new recruits. A flow diagram of the effects of MPA status on recruitment is developed and employed to identify the relevant processes. The diagram incorporates three levels of factors: (1) characteristics of MPAs (location, size, habitat type, oceanography and level of protection); (2) life stages of species protected in MPAs relevant to recruitment (eggs, larvae, settlers and juveniles); and (3) fundamental processes of dispersal/movement, predation and competition. From this conceptual diagram, the following main components of the recruitment process were identified and used to structure the review: (1) relationship between the ecology of pelagic stages and the design, location and oceanographic regime of MPAs; (2) effects of protection in MPAs from fishery exploitation of nursery habitats on settlement success; and (3) effects of protection on survival of settlers and juveniles from competition and predation. We found an exceptionally low number of studies specifically addressing recruitment processes in MPAs. This was particularly the case in what concerns the relationship between larval ecology and the characteristics and oceanographic regime of MPAs. The effectiveness of MPAs in promoting recruitment mainly depends on the locations and on sizes of the MPAs in relation to the reproductive biology and larval ecology of the species concerned. The locations and sizes of MPAs in turn depend on MPA objectives, whether the purpose is to protect entire life cycles, the juveniles, or to increase egg production and larval export. The assessment of the relationship between the protection of nursery habitats and settlement success indicates that the magnitude of the effects of protection depends on whether the recruitment of the species involved is restricted to a narrowly-defined set of environmental conditions or, on the contrary, can occur in diverse environments, including areas beyond the influence of the MPAs. Thus, the locations of MPAs determine the habitats which are protected and, consequently, the species, the settlement of which will be favoured. For Mediterranean shallow-water species, the near-shore zone encompasses most of the essential nursery habitats for protection. Recruitment studies conducted in MPAs in the north-western Mediterranean have showed no differences in survival of newly-settled littoral fish between MPAs and the areas outside of them. Conversely, for older recruits, mortality was found to be higher inside MPAs, probably due to the increased abundance and size of large predators. This study highlights the almost total absence of studies addressing even the most elementary questions of recruitment in the specific context of MPAs.

Modification of P-selectin glycoprotein ligand-1 with a natural killer cell-restricted sulfated lactosamine creates an alternate ligand for L-selectin

Abstract: Natural killer (NK) cells are components of the innate immune system that can recognize and kill virally infected cells, tumor cells, and allogeneic cells without prior sensitization. NK cells also elaborate cytokines (e.g., interferon-gamma and tumor necrosis factor-alpha) and chemokines (e.g., macrophage inflammatory protein-1alpha) that promote the acquisition of antigen-specific immunity. NK cell differentiation is accompanied by the cell surface expression of a mucin-like glycoprotein bearing an NK cell-restricted keratan sulfate-related lactosamine carbohydrate, the PEN5 epitope. Here, we report that PEN5 is a post-translational modification of P-selectin glycoprotein ligand-1 (PSGL-1). The PEN5 epitope creates on PSGL-1 a unique binding site for L-selectin, which is independent of PSGL-1 tyrosine sulfation. On the surface of NK cells, the expression of PEN5 is coordinated with the disappearance of L-selectin and the up-regulation of Killer cell Ig-like Receptors (KIR). These results indicate that NK cell differentiation is accompanied by the acquisition of a unique carbohydrate, PEN5, that can serve as part of a combination code to deliver KIR(+) NK cells to specific tissues.

The sensitivity of a Tanzanian crater lake to catastrophic tephra input and four millennia of climate change

Abstract: Diatom genera in many large East African lakes change little throughout the Holocene period suggesting relatively stable ecological conditions and some resilience to environmental change. Ecosystem stability is less common in smaller, more sensitive lakes, such as those within volcanic craters, where external impacts can cause abrupt and rapid fluctuations. A 4100-year diatom and cyanobacteria pigment record from Lake Massoko, a volcanic crater lake in southern Tanzania, is used to illustrate important switches in resource ratios following tephra deposition 1190 years ago. It is hypothesized that the tephra reduced the rate of P diffusion from the sediments and increased the Si:P ratio in the lake. A period of acute change in planktonic diatom communities resulted from the tephra impact and lasted c. 110 years. The magnitude of the change shown by the diatoms and their slow recovery from the tephra may be due in part to a coincident fall in lake level caused by a reduction in regional rainfall. The statistical significance of the tephra impact relative to that of catchment and climate change has been tested using variance partitioning and rate-of-change analysis. Multiproxy indicators show an important period of positive water balance 1700 ago and a relatively dry episode persisting between 1000 and 400 years ago. The lake ecosystem is shown to be highly sensitive to both climate change and tephra deposition.

Asymptotically exact nonparametric hypothesis testing in sup-norm and at a fixed point

Abstract: For the signal in Gaussian white noise model we consider the problem of testing the hypothesis H 0 : f≡ 0, (the signal f is zero) against the nonparametric alternative H 1 : f∈Λɛ where Λɛ is a set of functions on R 1 of the form Λɛ = {f : f∈?, ϕ(f) ≥ Cψɛ}. Here ? is a Holder or Sobolev class of functions, ϕ(f) is either the sup-norm of f or the value of f at a fixed point, C > 0 is a constant, ψɛ is the minimax rate of testing and ɛ→ 0 is the asymptotic parameter of the model. We find exact separation constants C * > 0 such that a test with the given summarized asymptotic errors of first and second type is possible for C > C * and is not possible for C < C *. We propose asymptotically minimax test statistics.

Crystal structures of human pancreatic alpha-amylase in complex with carbohydrate and proteinaceous inhibitors.

Abstract: Crystal structures of human pancreatic alpha-amylase (HPA) in complex with naturally occurring inhibitors have been solved. The tetrasaccharide acarbose and a pseudo-pentasaccharide of the trestatin family produced identical continuous electron densities corresponding to a pentasaccharide species, spanning the -3 to +2 subsites of the enzyme, presumably resulting from transglycosylation. Binding of the acarviosine core linked to a glucose residue at subsites -1 to +2 appears to be a critical part of the interaction process between alpha-amylases and trestatin-derived inhibitors. Two crystal forms, obtained at different values of pH, for the complex of HPA with the protein inhibitor from Phaseolus vulgaris (alpha-amylase inhibitor) have been solved. The flexible loop typical of the mammalian alpha-amylases was shown to exist in two different conformations, suggesting that loop closure is pH-sensitive. Structural information is provided for the important inhibitor residue, Arg-74, which has not been observed previously in structural analyses.

Saethre–Chotzen mutations cause TWIST protein degradation or impaired nuclear location

Abstract: H-TWIST belongs to the family of basic helix-loop-helix (bHLH) transcription factors known to exert their activity through dimer formation. We have demonstrated recently that mutations in H-TWIST account for Saethre-Chotzen syndrome (SCS), an autosomal dominant craniosynostosis syndrome characterized by premature fusion of coronal sutures and limb abnormalities of variable severity. Although insertions, deletions, nonsense and missense mutations have been identified, no genotype-phenotype correlation could be found, suggesting that the gene alterations lead to a loss of protein function irrespective of the mutation. To assess this hypothesis, we studied stability, dimerization capacities and subcellular distribution of three types of TWIST mutant. Here, we show that: (i) nonsense mutations resulted in truncated protein instability; (ii) missense mutations involving the helical domains led to a complete loss of H-TWIST heterodimerization with the E12 bHLH protein in the two-hybrid system and dramatically altered the ability of the TWIST protein to localize in the nucleus of COS-transfected cells; and (iii) in-frame insertion or missense mutations within the loop significantly altered dimer formation but not the nuclear location of the protein. We conclude that at least two distinct mechanisms account for loss of TWIST protein function in SCS patients, namely protein degradation and subcellular mislocalization.

Changes in landscape structure in the northwestern Alps over the last 7000 years: lessons from soil charcoal

Abstract: . Current land-use a bandonment and the current rise in temperature in the Alps both suggest that tree limits may change. When it is assumed that the climate of the early mid-Holocene between 8000 and 5000 yr before present is analogous to that of the predicted climate of the late 21st century, palaeo-ecological studies of the early Holocene may provide data for the prediction of the vegetation pattern in a century from now. It appears that mid-Holocene charcoal assemblages can be used to reconstruct the spatial patterns of the vegetation before, or during, the practice of slash-and-burn. Correspondence analysis (CA) of charcoal assemblages shows that an important ecological gradient is determined by elevation. However CA also shows that charcoal assemblages in profiles between 1700 and 2100 m a.s.l. are roughly stratified: the more recent assemblages from the topmost centimetres of soil are intermediate between the lowermost assemblages and assemblages from higher elevations. This suggests that the woody communities at the highest elevation were located at lower elevations at a later date. The taxonomic diversity of the soil charcoal assemblages has been compared to that of present-day phytosociological releves after transformation to charcoal-equivalent data. This comparison revealed that the vegetation pattern along the altitudinal gradient in the mid-Holocene was different from that at present. The assemblages indicate that some communities disappeared, that Picea is a late-Holocene invading species, and that there is no strict modern analogue for the vegetation structure prior to that of 3000 yr ago. The past structure of the woody vegetation was also different from that of today. Although past vegetation is not a good analogue for predicting future vegetation patterns, it still has potential as an indicator for the potential presence of tree species where there is none today. If we assume a temperature rise, and take into account current trends of landscape use abandonment, then we can expect strong vegetation dynamics at the upper tree line in the future: Abies alba may expand to occupy elevations of ca. 1800–2000 m in mixed communities with Picea abies, Pinus sylvestris and hardwood species, and Pinus cembra may expand up to 2500–2700 m a.s.l.

Gondwana evolution; its assembly at around 600 Ma

Abstract: Gondwana was formed at about 600 Ma at the end of the Pan-African-Brasiliano orogeny. It resulted from the collision between three lithospheric mega-plates generated by the break-up of the Rodinia supercontinent, between 1 000 and 700 Ma. The two main collisional zones are roughly submeridional in orientation. The western one, in relation to Africa which at that time was upside down with Cape Horn pointing northwards, is outlined by the Mozambique mega-belt which delineated western and central Gondwana. The eastern one is defined by a string of belts extending from the Sahara to the Cape of Good Hope. This collisional zone divides central and southeastern Gondwana. Laurentia or North America which, attached to South America, also participated in the Gondwana assembly, drifted early, at about 550 Ma, from the newly amalgamated Gondwana. The very low values (0.704) of 87 Sr/ 86 Sr, measured in carbonates deposited at around 850 Ma, may signify fragmentation of Rodinia, whereas high values (0.709) at around 550 Ma correspond to deep erosion of mountain belts generated by the Pan-African-Brasiliano collisions. δ 13 C is generally high and positive (+ 5 to + 9 ‰) in Neoproterozoic carbonates, reflecting intensive biological productivity and accumulation of large volumes of organic carbon on oceanic floor. A few abrupt excursions towards negative low values (–5 ‰) are associated with glacial episodes. They are either associated with rapid overturn of deep oceanic circulation or with a snowball Earth model in which a worldwide ice cover induces the slowing down, and even the stopping, of all biological activities.

Tagging unknown proper names using decision trees

Abstract: This paper describes a supervised learning method to automatically select from a set of noun phrases, embedding proper names of different semantic classes, their most distinctive features. The result of the learning process is a decision tree which classifies an unknown proper name on the basis of its context of occurrence. This classifier is used to estimate the probability distribution of an out of vocabulary proper name over a tagset. This probability distribution is itself used to estimate the parameters of a stochastic part of speech tagger.

Microbial decomposition of large organic particles in the northwestern Mediterranean Sea:an experimental approach

Abstract: Sediment trap particles, as well as particulate organic material including particles larger than 10 pm collected by in situ pumps (ISP) and fresh corpses of the gelatinous zooplankton species Thalia democratica, were collected in the northwestern Mediterranean Sea from April to July 1995, and incubated (after mixing with 0.2 μm filtered seawater) under laboratory conditions with their own bacterial assemblages for 6 to 24 d in batches under oxic conditions and in the dark. Particulate (POC > 0.7 pm), dissolved (DOC < 0.7 pm) and colloidal (0.02 < COC < 0.7 pm) organic carbon contents, as well as bacterial abundance and production, were quantified over time. In all experiments, total organic carbon (TOC = POC + DOC) decrease covaried with an increase in bacterial abundance and production, bacteria being the main mediators of particle decomposition. We found that COC accounted for 19 to 31% of DOC immediately after particle dilution in 0.2 μm filtered seawater, and always for less than 9 % at the end of the experiments. As organic colloids comprised less than 7 % of DOC in the 0.2 pm filtered seawater used to dilute the particles, this result suggests that COC was mainly produced from particle decomposition. Assuming that bacterial populations were the sole decomposer of organic matter in the batches, the results gave bacterial growth efficiencies (BGE) in the range of 3 to 21%, indicating that decomposition of these particles significantly produce CO 2 through bacterial respiration. The results showed that bacteria degraded 16 to 87% of the initial amount of POC within the first 48 h, whereas only 6 to 22 % of POC was degraded in the second stages. Our data and modeling work based on such short incubation times suggest that salp bodies are composed of 1 labile and 1 refractory organic fraction, whereas both ISP- and trap particles are composed of 2 labile and 1 refractory organic fraction. A 1G-model (for salp) and a 2G-model for other particles was able to satisfactorily reproduce the data sets.

Optimality in infinite-horizon variational problems under sign conditions

Abstract: We consider infinite-horizon variational problems on several spaces of curves. We establish relations between these problems and the properties of their solutions. Notably, we exhibit situations where optimality in a given space of curves implies optimality in a bigger space of curves. We work with a domain of definition of the Lagrangian which has a very general form and we provide assumptions to ensure a satisfactory theory of the necessary conditions of optimality. We apply these results to actualized Lagrangians.

Identified charged particles in quark and gluon jets

Abstract: A sample of 2.2 million hadronic Z decays, selected from the data recorded by the Delphi detector at LEP during 1994-1995 was used for an improved measurement of inclusive distributions of pi+, K+ and p and their antiparticles in gluon and quark jets. The production spectra of the individual identified particles were found to be softer in gluon jets compared to quark jets, with a higher multiplicity in gluon jets as observed for inclusive charged particles. A significant proton enhancement in gluon jets is observed indicating that baryon production proceeds directly from colour objects. The maxima, xi^*, of the xi-distributions for kaons in gluon and quark jets are observed to be different.

Quasi-model-independent search for new high p(T) physics at D0.

Abstract: We apply a quasi-model-independent strategy ("Sleuth") to search for new high p_T physics in approximately 100 pb^-1 of ppbar collisions at sqrt(s) = 1.8 TeV collected by the DZero experiment during 1992-1996 at the Fermilab Tevatron. We systematically analyze many exclusive final states and demonstrate sensitivity to a variety of models predicting new phenomena at the electroweak scale. No evidence of new high p_T physics is observed.

The path chosen by female bodybuilders: a tentative interpretation.

Abstract: This paper suggests that the process of marginalization of women bodybuilders can be analyzed according to two theoretical frameworks The first is essentially a pessimistic interpretation based on critical sociology and the concept of alienation, which discusses the limits of applying this concept to an empirical reality (in this case, female bodybuilders) The second considers the future of female bodybuilders as being constructed through the muscle cult Our interpretation is comprehensive The study stresses self-realization and self-fulfillment in female bodybuilders and discusses their attachment to the bodybuilding subculture

Serologic evidence of human monocytic and granulocytic ehrlichiosis in Israel.

Abstract: We conducted a retrospective serosurvey of 1,000 persons in Israel who had fever of undetermined cause to look for Ehrlichia chaffeensis antibodies. Four of five cases with antibodies reactive to E. chaffeensis were diagnosed in the summer, when ticks are more active. All patients had influenzalike symptoms with high fever. None of the cases was fatal. Three serum samples were also seroreactive for antibodies to E. canis, and one was also reactive to the human granulocytic ehrlichiosis (HGE) agent. The titer to the HGE agent in this patient was higher than the serum titer to E. chaffeensis, and the Western blot analysis also indicated that the HGE agent was the primary cause of infection. We present the first serologic evidence that the agents of human monocytic ehrlichiosis (HME) and HGE are present in Israel. Therefore, human ehrlichiosis should be included in the differential diagnoses for persons in Israel who have been exposed to ticks and have influenzalike symptoms.