Showing papers by "University of Nice Sophia Antipolis published in 1997"

Timing of the Ethiopian flood basalt event and implications for plume birth and global change

Abstract: Continental flood basalts are often considered as fossil evidence of mantle plume heads impinging on the lithosphere1,2 and have been related to continental breakup3,4,5. Many of these flood basalts erupted within a short time span—of the order of 1 Myr—and were apparently synchronous with crises in global climate and with mass extinctions6. Here we present geochronological (40Ar/39Ar) and magnetostratigraphic results for the Ethiopian traps, one of the last remaining flood basalts for which few such data were available. The bulk of the traps, which have been inferred to mark the appearance of the Ethiopian-Afar plume head at the Earth's surface, erupted approximately 30 Myr ago, over a period of 1 Myr or less. This was about the time of a change to a colder and drier global climate, a major continental ice-sheet advance in Antarctica, the largest Tertiary sea-level drop and significant extinctions.

Differentiation of embryonic stem cells into adipocytes in vitro

Abstract: Embryonic stem cells, derived from the inner cell mass of murine blastocysts, can be maintained in a totipotent state in vitro. In appropriate conditions embryonic stem cells have been shown to differentiate in vitro into various derivatives of all three primary germ layers. We describe in this paper conditions to induce differentiation of embryonic stem cells reliably and at high efficiency into adipocytes. A prerequisite is to treat early developing embryonic stem cell-derived embryoid bodies with retinoic acid for a precise period of time. Retinoic acid could not be substituted by adipogenic hormones nor by potent activators of peroxisome proliferator-activated receptors. Treatment with retinoic acid resulted in the subsequent appearance of large clusters of mature adipocytes in embryoid body outgrowths. Lipogenic and lipolytic activities as well as high level expression of adipocyte specific genes could be detected in these cultures. Analysis of expression of potential adipogenic genes, such as peroxisome proliferator-activated receptors gamma and delta and CCAAT/enhancer binding protein beta, during differentiation of retinoic acid-treated embryoid bodies has been performed. The temporal pattern of expression of genes encoding these nuclear factors resembled that found during mouse embryogenesis. The differentiation of embryonic stem cells into adipocytes will provide an invaluable model for the characterisation of the role of genes expressed during the adipocyte development programme and for the identification of new adipogenic regulatory genes.

A Variational Method in Image Recovery

Abstract: This paper is concerned with a classical denoising and deblurring problem in image recovery. Our approach is based on a variational method. By using the Legendre--Fenchel transform, we show how the nonquadratic criterion to be minimized can be split into a sequence of half-quadratic problems easier to solve numerically. First we prove an existence and uniqueness result, and then we describe the algorithm for computing the solution and we give a proof of convergence. Finally, we present some experimental results for synthetic and real images.

Microwave imaging-complex permittivity reconstruction with a Levenberg-Marquardt method

Abstract: This paper refers to quantitative reconstruction of the dielectric and conductive property distributions of biological objects by means of active microwave imaging. An iterative reconstruction algorithm based on the Levenberg-Marquardt method is tested with synthetic data. The influence of the receiver geometry is investigated and two methods for choosing the regularization parameter, an empirical method and generalized cross validation (GCV) method, are examined.

Large financial crashes

Abstract: We propose that large stock market crashes are analogous to critical points studied in statistical physics with log-periodic correction to scaling. We extend our previous renormalization group model of stock market prices prior to and after crashes (D. Sornette, A. Johansen, J.P. Bouchaud, J. Phys. I France 6 (1996) 167) by including the first non-linear correction. This predicts the existence of a log-frequency shift over time in the log-periodic oscillations prior to a crash. This is tested on the two largest historical crashes of the century, the October 1929 and October 1987 crashes, by fitting the stock market index over an interval of 8 yr prior to the crashes. The good quality of the fits, as well as the consistency of the parameter values obtained from the two crashes, promote the theory that crashes have their origin in the collective “crowd” behavior of many interacting agents.

The three-dimensional geometry of the proximal humerus

Abstract: We have studied the three-dimensional geometry of the proximal humerus on human cadaver specimens using a digitised measuring device linked to a computer. Our findings demonstrated the variable shape of the proximal humerus as well as its variable dimensions. The articular surface, which is part of a sphere varies individually in its orientation as regards inclination and retroversion, and it has variable medial and posterior offsets. These variations cannot be accommodated by the designs of most contemporary humeral components. Although good clinical results can be achieved with current modular and non-modular components their relatively fixed geometry prevents truly anatomical restoration in many cases. To try to restore the original three-dimensional geometry of the proximal humerus, we have developed a new type of humeral component which is modular and adaptable to the individual anatomy. Such adaptability allows correct positioning of the prosthetic head in relation to an individual anatomical neck, after removal of the marginal osteophytes. The design of this third-generation prosthesis respects the four geometrical variations which have been demonstrated in the present study. These are inclination, retroversion, medial offset and posterior offset.

A homozygous mutation in the integrin alpha6 gene in junctional epidermolysis bullosa with pyloric atresia

Abstract: The alpha6 integrin subunit participates in the formation of both alpha6beta1 and alpha6beta4 laminin receptors, which have been reported to play an important role in cell adhesion and migration and in morphogenesis. In squamous epithelia, the alpha6beta4 heterodimer is the crucial component for the assembly and stability of hemidesmosomes. These anchoring structures are ultrastructurally abnormal in patients affected with junctional epidermolysis bullosa with pyloric atresia (PA-JEB), a recessively inherited blistering disease of skin and mucosae characterized by an altered immunoreactivity with antibodies specific to integrin alpha6beta4. In this report, we describe the first mutation in the alpha6 integrin gene in a PA-JEB patient presenting with generalized skin blistering, aplasia cutis, and defective expression of integrin alpha6beta4. The mutation (791delC) is a homozygous deletion of a single base (C) leading to a frameshift and a premature termination codon that results in a complete absence of alpha6 polypeptide. We also describe the DNA-based prenatal exclusion of the disease in this family at risk for recurrence of PA-JEB. Our results demonstrate that, despite the widespread distribution of the alpha6 integrin subunit, lack of expression of the alpha6 integrin chain is compatible with fetal development, and results in a phenotype indistinguishable from that caused by mutations in the beta4 chain, which is expressed in a more limited number of tissues.

Extreme Deviations and Applications

Abstract: Stretched exponential probability density functions (pdf), having the form of the exponential of minus a fractional power of the argument, are commonly found in turbulence and other areas They can arise because of an underlying random multiplicative process For this, a theory of extreme deviations is developed, devoted to the far tail of the pdf of the sum X of a finite number n of independent random variables with a common pdf e-f(x) The function f(x) is chosen (i) such that the pdf is normalized and (ii) with a strong convexity condition that $f''(x)>0$ and that $x^2 f''(x)\rightarrow +\infty$ for |x|→∞ additional technical conditions ensure the control of the variations of $f''(x)$ The tail behavior of the sum comes then mostly from individual variables in the sum all close to X/n and the tail of the pdf is ∼e-nf(X/n) This theory is then applied to products of independent random variables, such that their logarithms are in the above class, yielding usually stretched exponential tails An application to fragmentation is developed and compared to data from fault gouges The pdf by mass is obtained as a weighted superposition of stretched exponentials, reflecting the coexistence of different fragmentation generations For sizes near and above the peak size, the pdf is approximately log-normal, while it is a power law for the smaller fragments, with an exponent which is a decreasing function of the peak fragment size The anomalous relaxation of glasses can also be rationalized using our result together with a simple multiplicative model of local atom configurations Finally, we indicate the possible relevance to the distribution of small-scale velocity increments in turbulent flow

Study of various shapes of the coupling slot in CPW-fed microstrip antennas

Abstract: A numerical modeling based on the solution of coupled integral equations is used for the characterization of CPW-fed aperture-coupled microstrip antennas. Various shapes of excitation slots, such as open stubs, slot loops, and capacitively and inductively coupled slots, are investigated in terms of return loss and front-to-back radiated power ratio. It is shown that a centered CPW open stub gives a minimum of back radiation while allowing for easy matching. The slot-loop excitation seems to be a convenient feeding mechanism that also allows the insertion of active devices.

No Evidence of Oxidative Stress After a Triathlon Race in Highly Trained Competitors

Abstract: Long distance triathlons, due to the large amounts of oxygen uptake they cause, may lead to the generation of reactive oxygen species, and consequently to oxidative stress and damage. We sought to verify this hypothesis. Twelve of the 18 male triathletes who participated in the study took part in a long distance triathlon, the others did not. The prerace blood samples were drawn 48 h before the race and repeatedly until the fourth day of recovery. The myoglobin concentrations increased immediately after the race. The concentrations of methemoglobin, disulfide glutathione (GSSG), and thiobarbituric reactive substances did not significantly change after the race. Although the race induced an inflammatory response, evidenced by the variations in neopterin concentrations and leukocyte counts, there was no consecutive oxidative stress. The basal GSH values were correlated significantly with cycling training volume (r = 0.55) and VO2max (r = 0.53). Muscle damage can occur without evidence of oxidative stress or oxidative damage. We conclude that the magnitude of the antioxidant defense system enhancement depends on training loads. Because of their training status, the triathletes did not suffer from oxidative damage after they finished the long distance triathlon race.

Time-of-day effects in maximal anaerobic leg exercise.

Abstract: Time of day variations in maximal anaerobic leg exercise were studied in 23 men mean age 23 (SD 3) years. All the subjects performed two anaerobic tests (force-velocity and multi-jump tests) and those familiar with sprinting ran an additional 50-m dash (n=16). The maximal anaerobic powers for cycling and jumping (Pcycling and Pjump) and maximal anaerobic velocity (\(\)peak) were performed consecutively in the same order for all tests. The force-velocity and force-power relationships were established to determine Pcycling. The flight time (tf) and the ground contact time (tc) were recorded from five consecutive jumps on a jump-ergometer to calculate Pjump. The \(\)peak was measured between the 35th and the 45th m during the dash-run. The test schedules were at 0900, 1400 and 1800 hours on separate days in random order. Rectal temperatures (Tre) and body mass (mb) were measured before each test. The Tre increased significantly from 0900 to 1800 hours (P 0.05). The Pcycling and Pjump were higher at 1400 and 1800 hours than at 0900 hours. The differences between the morning and the afternoon reached 3% (P<0.05) for Pcycling and 5%–7% for Pjump (P<0.01). The time-of-day effect was significant for tf (P<0.05) but not for tc. During the dash-run tests, the differences almost reached significance for \(\)peak between 0900 and 1800 hours (P=0.0544). No significant variations were observed between 1400 and 1800 hours for cycling, jumping and running tests. A time-of-day effect in the maximal anaerobic power of cycle and multi-jump tests existed. Such variations would have pronounced effects when expressed in competitions.

Differential internalization of somatostatin in COS-7 cells transfected with SST1 and SST2 receptor subtypes : A confocal microscopic study using novel fluorescent somatostatin derivatives

Abstract: A growing body of evidence suggests that neuropeptide binding to G protein-linked receptors may result in internalization of receptor-ligand complexes, followed by intracellular mobilization and degradation of the ligand into its target cells. Because of discrepant results in the literature concerning the occurrence of such a mechanism for the tetradecapeptide somatostatin (SRIF), we have reinvestigated this question by comparing the binding and internalization of iodinated and fluorescent derivatives of the metabolically stable analog of SRIF, [D-Trp8]SRIF, in COS-7 cells transfected with complementary DNA encoding the sst1 or sst2A receptor subtype. A series of fluoresceinyl and Bodipy fluorescent derivatives of [D-Trp8]SRIF-14 was purified by HPLC, analyzed for purity by mass spectrometry, and tested for biological activity in a membrane binding assay. Of the six compounds tested, fluoresceinyl and Bodipy derivatives labeled in position alpha (fluo-SRIF) retained high affinity for SRIF receptors. COS-7 cells transfected with complementary DNA encoding either sst1 or sst2A receptors both displayed specific, high affinity binding of iodinated and fluo-SRIF. At 4 C, the labeling was confined to the cell surface in both cell types, as indicated by the fact that it was entirely removable by a hypertonic acid wash and assumed a pericellular distribution in the confocal microscope. At 37 C, the fate of specifically bound ligand varied markedly according to the type of receptor transfected. In cells encoding the sst1 receptor, approximately 20% of specifically bound ligand was recovered in the acid-resistant (i.e. intracellular) fraction. This fraction remained clustered at the periphery of the cell, suggesting that it was being sequestered either within or immediately beneath the plasma membrane. By contrast, in cells transfected with sst2A receptors, up to 75% of specifically bound ligand was recovered inside the cells, where it clustered into small endosome-like particles. These particles increased in size and moved toward the nucleus with time, suggestive of receptor-ligand complexes proceeding down the endocytic pathway. These results demonstrate that neuropeptides may be processed differently depending on the subtype of receptor expressed in their target cells and suggest that these different processing patterns may reflect different modes of sensitization/desensitization and recycling of the receptors, and thereby of transmembrane signaling.

Mammalian MAP kinase modules: how to transduce specific signals.

Abstract: MAPK modules are composed of a cascade of three intracellular protein kinases (MKKK, MKK and MAPK) which are activated successively by phosphorylation events. They are used to transduce a variety of information in organisms as diverse as yeasts, worms, flies or mammals. MAPK modules integrate signals coming from membrane receptor activation and, by the ability of MAPK to translocate into the nucleus and phosphorylate nuclear targets such as transcription factors, they relay extracellular signals into a genomic response. Since several MAPK modules transducing different information are expressed in the same cell, in yeast or in mammals, the question arises as to how fidelity is maintained between the distinct MAPK modules of a single cell. Two levels of specificity have been documented: the molecular selectivity of each enzyme for its substrate, which is particularly evident for the MKK-MAPK couple, permits specificity within one particular module; exogenous proteins, such as the yeast Ste5 protein, may serve as 'chaperone' proteins to tether all the members of a module and restrict signal transduction to this module. In mammalian cells, the MAPK modules are not strictly independent and one pathway may interfere with another. It remains to be determined whether this interference is of physiological relevance.

Anatomic distribution of melanocytes in normal nail unit: an immunohistochemical investigation.

Abstract: Very few histologic reports describe normal melanocytes of the nail unit. Previous studies predominantly address the distal nail matrix melanocytes; we found no review of nail-bed melanocytes in the literature. The proximal nail matrix melanocytes are difficult to identify; the cells cannot be identified by L-DOPA staining. More recently, their scarcity was confirmed by immunohistochemistry with a large panel of antibodies directed against melanocytes. We wished to detect the proximal nail matrix dormant melanocytes and compare their density and distribution with that of the other melanocytes in the distal matrix and nail bed and to establish criteria of normality that may help clarify the pathologic features of benign nevoid melanonychia in the nails of whites. A panel of five monoclonal antibodies (MoAbs), including HMB45 and TRP1 directed against antigens localized in early melanosomal vesicles, was investigated in frozen sections of six nail specimens from whites. Both vertical and horizontal sections were assessed to determine the presence of dormant melanocytes. Results showed that the proximal nail matrix melanocytes were clearly identified with MoAbs HMB45 and tyrosinase-related protein-1 (TRP-1). By contrast, melanocytes stained by MoAb against tyrosinase and L-DOPA reaction were evident, especially in the distal matrix. With MoAb TRP-1, the epithelial sheets showed counts of approximately 217+/-84/mm2 in the proximal matrix and of 132+/-34/mm2 in the distal matrix; the nail bed counts were only 45+/-25/mm2. The split epithelial sheets had 103+/-17/mm2 L-DOPA-positive melanocytes in the distal third of the matrix, but only a few of them were detected in the proximal matrix and none were noted in the nail bed. We clearly identified proximal nail melanocytes using MoAb HMB45 and TRP1. The total number of matrix melanocytes can be estimated as approximately 217/mm2. In proximal matrix, the dormant melanocytes compartment was predominant. In the distal matrix, two compartments were identified: a functionally differentiated and a dormant compartment. Contrary to classical opinion, longitudinal melanonychia originates more frequently in the distal matrix, not secondary to the larger melanocyte density but because only the distal matrix contains an active melanin synthesis compartment. Furthermore, the superficial distribution of proximal nail melanocytes in vertical sections showed a histologic feature that may simulate the pagetoid pattern of melanoma in situ.

Regulation of FAT/CD36 gene expression: further evidence in support of a role of the protein in fatty acid binding/transport

Abstract: Much biochemical evidence has implicated rat adipocyte CD36 (FAT) in membrane binding and transport of long-chain fatty acids (FA). Expression of the mRNA favored tissues with active FA metabolism and was upregulated in vivo with diabetes and with high fat feeding. In culture, CD36 mRNA was a strong marker of preadipocyte differentiation and was modulated by the same factors effective on mRNAs coding for other proteins involved in FA metabolism. In preadipocytes, long-chain FA or 2-bromopalmitate but not short-chain FA strongly induced CD36 mRNA within 8 h to an optimum within 24 h. Removal of the FA resulted in a decay of CD36 mRNA with a half life of about 12 h. In differentiated adipocytes, levels of CD36 mRNA were downregulated by the 3': 5'-cyclic adenosine monophosphate, cAMP, analog, 8-(4-chlorophenylthio) adenosine, 8-CPT, at concentrations of 1-100 microM. The effect, observed within 6 h, was optimal after 18 h and independent of the action of 8-CPT to mobilize FA. Regulation of CD36 expression by factors effective on expression of other proteins implicated in FA metabolism is consistent with its role in membrane FA transport.

Ring-Opening Polymerization of d,l-Lactide Using Rare-Earth μ-Oxo Isopropoxides as Initiator Systems

Abstract: Lanthanide oxo isopropoxy compounds are found to be active initiators for the polymerization of D,L-lactide in dichloromethane at room temperature. Lanthanum oxo isopropoxide, the most active initiator, generates significant transesterification reactions. In the case of Y, Sm and Yb initiators, a narrow MWD is observed till high conversions

Ionic composition of endolymph in teleosts: origin and importance of endolymph alkalinity.

Abstract: Ionic (Na+, K+, Cl-, PO4(3-), pH), total CO2, total calcium and protein concentrations in the plasma and endolymph of the inner ear were compared in trout Oncorhynchus mykiss and turbot Scophthalmus maximus. In both species, saccular endolymph was characterized by high levels of K+ and total CO2 and in trout by an alkaline pH. The kinetic characteristics of proton secretion across the saccular epithelium of trout were investigation using a titration technique in which isolated saccules were mounted as closed sacs. The rate of proton secretion depends strongly on the pH of the Ringer's solution and secretion stops at a pH below 7.2. Proton secretion is driven by an energy-dependent mechanism involving basolateral ouabain-sensitive Na+/K+ exchangers. Proton secretion was partially inhibited by acetazolamide and completely inhibited in Na(+)-free Ringer or in the presence of 1 mmol l-1 amiloride. A cellular model stressing the importance of proton exchange through the saccular epithelium is proposed to explain the regulation of endolymph pH, a crucial factor for the deposition of otolith calcium.

Regulation by glucocorticoids of angiotensinogen gene expression and secretion in adipose cells.

Abstract: Adipose cells are an important source of angiotensinogen (AT). Its activation product, angiotensin II, stimulates in vitro and in vivo the production and release of prostacyclin which acts as a potent adipogenic signal in promoting the terminal differentiation of preadipocytes to adipocytes. Since glucocorticoids are known to promote adipose cell differentiation in vitro as well as in vivo, their role in the regulation of AT gene expression and secretion has been investigated in cultured Ob1771 mouse adipose cells. In contrast with liver cells, which are the major source of AT and the target of several hormones for the regulation of its expression, adipose cells are only responsive to glucocorticoids, which are able to up-regulate AT gene expression and AT secretion rapidly and dose-dependently. On exposure to glucocorticoids, accumulation of AT mRNA appears primarily to be due to transcriptional activation of the gene and is parallelled by secretion of the protein. Similar results on AT mRNA expression and AT secretion were obtained using explants of rat adipose tissue ex vivo demonstrating a major if not exclusive mechanism of regulation of AT production by glucocorticoids in mature adipose cells. Together these results provide a potential link between glucocorticoids, AT, the growth of adipose tissue and increased blood pressure.

Ultrafast Electronic Dynamics in Solid and Liquid Gallium Nanoparticles

Abstract: The electron thermalization process both in solid and liquid metallic gallium nanoparticles with radii in the range 50--90 \AA{} is investigated by femtosecond pump-probe measurements. The results show that the temporal behavior of the electron energy relaxation is similar in both phases, with a time constant varying from $\ensuremath{\sim}0.6$ to $\ensuremath{\sim}1.6\mathrm{ps}$ by increasing the nanoparticle size. We interpret the experimental data in terms of a size-dependent electron-surface interaction model and show the importance of the energy exchange with surface phonons in the electronic thermalization.

Oral Carriage of Helicobacter pylori: A Review

Abstract: Helicobacter pylori is a microaerophilic, motile bacterium, especially adapted to life in the human stomach. The presence of H. pylori in the stomach is strongly associated with chronic gastritis and ulcer disease and is a risk factor for gastric cancers. The microorganism may be transmitted orally and has been detected in dental plaque, saliva, and feces, but the hypothesis that oral microflora may be a permanent reservoir of H. pylori is still controversial. A review of the literature suggests that the recovery of H. pylori in the mouth is probably intermittent, associated with gastroesophageal reflux but not with specific oral disease. Nonetheless, the PCR identification of oral H. pylori may become helpful, particularly in cases of gastritis or ulcer relapse after antimicrobial therapy. Eradication of oral H. pylori by local medication or periodontal procedures would rely on the precise identification of its ecological niche. Within family groups, prophylactic methods should be practiced to avoid oral carriage of H. pylori. The risk of iatrogenic transmission during dental care, however, is already circumscribed by standard professional hygiene procedures.

A new regularization scheme for inverse scattering

Abstract: The reconstruction of the complex permittivity profile of inhomogeneous objects from measured scattered field data is a strongly nonlinear and ill-posed problem. Generally, the quality of the reconstruction from noisy data is enhanced by the introduction of a regularization scheme. Starting from an iterative algorithm based on a conjugate gradient method and applied to the nonlinear problem, this paper deals with a new regularization scheme, using edge-preserving (EP) potential functions. With this a priori information, the object to reconstruct is modelled with homogeneous areas separated by borderlike discontinuities. The enhancement is illustrated throughout some examples with noisy synthetic data.