Showing papers by "University of Nice Sophia Antipolis published in 1987"
TL;DR: In this article, the wake of a circular cylinder near the oscillation threshold is investigated by means of a laser probe, and the Stuart-Landau law is used to explain free-oscillating regimes.
Abstract: The wake of a circular cylinder is investigated near the oscillation threshold by means of a laser probe. Above the threshold the transient regime is studied and described by a Stuart-Landau law (already found to be relevant in explaining free-oscillating regimes). Below the critical point, impulse and resonant regimes are examined, so the coefficients of the Stuart-Landau equation are determined.Moreover, in the supercritical regime, the behaviour of the (externally forced) oscillating system is described, varying parameters such as threshold deviation, forcing frequency and amplitude. The different zones of entrainment and desynchronization are given for simple or harmonic frequency.
563 citations
TL;DR: In this article, a general method for computing the hydrodynamic interactions among N suspended particles, under the condition of vanishingly small particle Reynolds number, is presented, which accounts for both near-field lubrication effects and the dominant many-body interactions.
Abstract: A general method for computing the hydrodynamic interactions among N suspended particles, under the condition of vanishingly small particle Reynolds number, is presented. The method accounts for both near-field lubrication effects and the dominant many-body interactions. The many-body hydrodynamic interactions reproduce the screening characteristic of porous media and the ‘effective viscosity’ of free suspensions. The method is accurate and computationally efficient, permitting the dynamic simulation of arbitrarily configured many-particle systems. The hydrodynamic interactions calculated are shown to agree well with available exact calculations for small numbers of particles and to reproduce slender-body theory for linear chains of particles. The method can be used to determine static (i.e. configuration specific) and dynamic properties of suspended particles that interact through both hydrodynamic and non-hydrodynamic forces, where the latter may be any type of Brownian. colloidal, interparticle or external force. The method is also readily extended to dynamically simulate both unbounded and bounded suspensions.
529 citations
TL;DR: The findings strongly suggest that activation of PtdIns(4,5)P2-phospholipase C has a determinant function in growth control, and confirm the existence of alternative growth factor-signalling pathways independent of polyphosphoinositide breakdown.
Abstract: The primary action of a family of mitogens including bombesin1,2, bradykinin3, vasopressin3,4 and α-thrombin5–7 is to activate the hydrolysis of polyphosphoinositides8. Hydrolysis of phosphatidyl-inositol 4,5-bisphosphate (PtdIns(4,5)P2) by phospholipase C is mediated through coupling of surface receptors to a GTP-binding protein9,10 (Gp protein) which, in some cells6,11,12, is inactivated by the toxin of Bordetella pertussis13. It is not known whether this signalling pathway is involved in initiating DNA replication, whereas it has been firmly established that reinitiation of DNA synthesis can be triggered without activation of PtdIns(4,5)P2 hydrolysis by, for example, EGF (epidermal growth factor) 14,15, FGF (fibroblast growth factor)16 and insulin/IGF-I (insulin-like growth factor-I)14, members of a class of mitogens known to activate receptor tyrosine kinases17,18. Taking advantage of the fact that Chinese hamster lung fibroblasts respond to either class of mitogens and that their Gp protein appears to be sensitive to pertussis toxin6, we have now analysed the toxin's effect on reinitiation of DNA synthesis and find that it inhibits up to 95% of thrombin-induced mitogenicity without affecting EGF- or FGF-induced DNA synthesis and proliferation. These findings strongly suggest that activation of PtdIns(4,5)P2-phospholipase C has a determinant function in growth control, and confirm the existence of alternative growth factor-signalling pathways independent of polyphosphoinositide breakdown.
234 citations
TL;DR: The two basic mechanisms leading to spatial complexity in one-dimensional patterns are presented and are shown to be the counterparts of the horseshoe formation mechanisms studied by Melnikov and Shilnikov in dynamical systems theory.
Abstract: We present the two basic mechanisms leading to spatial complexity in one-dimensional patterns. They are shown to be the counterparts of the horseshoe formation mechanisms studied by Melnikov and Shilnikov in dynamical systems theory.
213 citations
TL;DR: It is concluded that secondary lamellar chloride cells play an important role in Na+ uptake inFreshwater trout exposed to various artificial media.
Abstract: Branchial sodium uptake was measured across secondary lamellae (SL) using the isolated-perfused head preparation. This study was correlated with histological examination.
Freshwater trout, Salmo gairdneri, were exposed to various artificial media: distilled water (DW), fresh water (FW: NaCl < 200 μl/1; Ca++ = 1.5 mM/1), FW + 5 mM CaCl2 and FW + 10 mM CaCl2. These environments altered the number and forms of “chloride cells” (CC) located in SL and were related to changes in maximal transport rate of Na+. An increase in a specific type of CC (round) was associated with an increase in Vmax, and a decrease in round cells was associated with a decrease in Vmax.
Relative to FW, exposure to DW increased the density of round cells, FW + 5 mM CaCl2 had no effect, and FW + 10 mM CaCl2 produced an initial degeneration of CC followed by restoration and increase in protruding round cells.
We conclude that secondary lamellar chloride cells play an important role in Na+ uptake.
164 citations
TL;DR: It is proposed that IGF I acts through autocrine or paracrine mechanisms to stimulate astroglial cell growth during normal brain development and acts as a growth promoter for the same cells by activation of the type I IGF receptor tyrosine kinase.
Abstract: Gene expression, receptor binding and growth-promoting activity of insulin-like growth factor I (IGF I) was studied in cultured astrocytes from developing rat brain. Northern blot analysis of poly(A)+ RNAs from astrocytes revealed an IGF I mRNA of 1.9 kb. Competitive binding and receptor labelling techniques revealed two types of IGF receptor in astroglial cells. Type I IGF receptors consist of alpha-subunits (Mr 130,000) which bind IGF I with significantly higher affinity than IGF II, and beta-subunits (Mr 94,000) which show IGF I-sensitive tyrosine kinase activity. Type II IGF receptors are monomers (Mr 250,000) which bind IGF II with three times higher affinity than IGF I. Both types of IGF receptor recognize insulin weakly. DNA synthesis measured by cellular thymidine incorporation was stimulated 2-fold by IGF I and IGF II. IGF I was more potent than IGF II, and both were significantly more potent than insulin. Our findings suggest that IGF I is synthesized in fetal rat astrocytes and acts as a growth promoter for the same cells by activation of the type I IGF receptor tyrosine kinase. We propose that IGF I acts through autocrine or paracrine mechanisms to stimulate astroglial cell growth during normal brain development.
136 citations
TL;DR: Radioautographic studies of [125I-Tyr3]NT binding to rat brain tissue sections in the absence and presence of levocabastine revealed markedly different regional distributions of the two NT binding components.
133 citations
TL;DR: In this paper, Kato demontre dans [7] le theoreme suivant of T. Kato et al. [8] and [9], and propose an operationur ferme de domaine D(A) dans H, on note B(H) lensemble des operateurs bornes de H dans lui-meme et N(A), respectivement le noyau de A.
Abstract: Dans tout ce qui suit, H designe un espace de Hilbert separable, A un operateur ferme de domaine D(A) dans H, on note B(H) l'ensemble des operateurs bornes de H dans lui-meme et N(A), R(A) respectivement le noyau de A, l'image de A.En 1958, T. Kato a demontre dans [7] le theoreme suivant.
126 citations
101 citations
TL;DR: In this paper, the second derivatives of the Dirichlet problem for the Laplace equation in a three-dimensional domain with edges were investigated and the behavior of the second derivative was investigated.
Abstract: We investigate the behavior of the second derivatives of the solution of the Dirichlet problem for the Laplace equation in a three dimensional domain with edges.
59 citations
TL;DR: Both BFC-1 cells and Ob17 cells show an atypical beta-adrenoreceptor similar to that described in rat adipocytes, but the sensitivity of BFC -1 cells toward beta-agonists is found to be 6-fold higher than that of Ob 17 cells, which represents a useful model for the study of short- and long-term responses to beta- adrenergics.
TL;DR: From this estimation and using a priori knowledge of the theoretical shape of the correlation peaks, a method for simultaneously measuring horizontal velocity, altitude, and integrated C(2)(N) value for each atmospheric turbulent layer between 2 and 20 km is described.
Abstract: The spatiotemporal cross-correlation function of single-star scintillation is estimated. From this estimation and using a priori knowledge of the theoretical shape of the correlation peaks, a method for simultaneously measuring horizontal velocity, altitude, and integrated C(2)(N) value for each atmospheric turbulent layer between 2 and 20 km is described. Taylor's hypothesis is tested for one particular layer and the lifetime of certain turbulent eddies is estimated. Results are in good agreement with two other methods.
TL;DR: In this paper, a global characterisation for the normal form of a time-periodically driven differential equation describing the behavior of a physical system in the neighbor region of a multiple instability is presented.
TL;DR: Theorie spectrale. Operateurs positifs as discussed by the authors : generalites sur les espaces de Banach ordonnes, proprietes spectrales generales des operateurs positif, les irreductibles, les simplicite, la propriete PF.
TL;DR: A set of mRNAs tagged by repetitive sequences of the ID family were found to accumulate following growth-factor-induced transition of normal rat fibroblasts from a quiescent to a proliferative state and following transformation by polyoma virus and by ras and myc oncogenes.
TL;DR: The results strongly support the hypothesis that a GTP‐binding protein couples α‐thrombin receptor to PIP2 hydrolysis, and conclude that the coupling is at the level of PIP 2‐phosphodiesterase activity.
TL;DR: In this paper, a localized change in the spatial boundary conditions of a propagating quanton was shown to modify the phase of its outgoing wave function and gave rise to a purely geometrical analog of the Aharonov-Bohm effect, which put into full light the nonlocal character of quantum behaviour.
TL;DR: It is concluded that plasma membrane of canine intestinal circular muscle contains neurotensin receptors with recognition properties distinct from those obtained in previous studies of neurotens in binding sites in murine tissues.
TL;DR: In this paper, the rotational constants for the X4Σ− state are presented and the relationship between the gas-phase emission spectrum and the low-temperature matrix absorption spectrum for the 6500-A transition has been clarified.
TL;DR: The results suggest that the formation of brown preadipocytes is critically linked during development to the release by sympathetic nerves of specific trophic factors acting locally.
TL;DR: In this paper, a nouvelle strategie de synthese industrialisable, facile a mettre en oeuvre a partir de produits disponibles commercialement, nous permettant d'acceder avec de bons rendements a des series homogenes de tensioactifs non ioniques F-alkyles bisequences parfaitement definis et purs.
TL;DR: Adenylate cyclase activity was measured in plasma membranes prepared from gill epithelium of the rainbow trout adapted to a large range of salinity (deionized water to seawater) and neurohypophyseal peptides elicited a dose‐dependent inhibition of both basal and glucagon stimulated enzyme activity.
TL;DR: In this article, the first fabrication of planar LiNbO3 waveguides with high index modifications (δne=0.11 at a wavelength of 632.8 nm) and losses as low as 0.4 dB/cm at the same wavelength was reported.
TL;DR: Comparisons of the sequences suggest the existence of two separate but related classes of toxins cumon the three species of anemone, and one of which is an arginine residue thought to be essential for toxicity.
TL;DR: It is concluded that different anionic exchangers exist in different cell types that can be distinguished both by their biochemical properties and by their pharmacological properties.
Abstract: U937 cell possess two mechanisms that allow them to recover from an intracellular acidification. The first mechanism is the amiloride-sensitive Na+/H+ exchange system. The second system involves bicarbonate ions. Its properties have been defined from intracellular pH (pHi) recovery experiments, 22Na+ uptake experiments, 36Cl− influx and efflux experiments.
Bicarbonate induced pHi recovery of the cells after a cellular acidification to pHi= 6.3 provided that Na+ ions were present in the assay medium. Li+ or K+ could not substitute for Na+. The system seemed to be electroneutral. 22Na+ uptake experiments showed the presence of a bicarbonate-stimulated uptake pathway for Na+ which was inhibited by 4,4′-diisothiocyanostilbene-2,2′-disulfonate. The bicarbonate-dependent 22Na+ uptake component was reduced by depleting cells of their internal Cl− and increased by removal of external Cl−. 36Cl− efflux experiments showed that the presence of both external Na+ and bicarbonate stimulated the efflux of 36Cl− at a cell pHi of 6.3. Finally a 36Cl− uptake pathway was documented. It was inhibited by 4,4′-diisothiocyanostilbene-2,2′-disulfonate (K0.5= 10 μM) and bicarbonate (K0.5= 2 mM). These results are consistent with the presence in U937 cells of a coupled exchange of Na+ and bicarbonate against chloride. It operates to raise the intracellular pH. Its pHi and external Na+ dependences were defined. No evidence for a Na+-independent Cl−/HCO−3 exchange system could be found. The Na+-dependent Cl−/HCO−3 exchange system was relatively insensitive to (aryloxy)alkanoic acids which are potent inhibitors of bicarbonate-induced swelling of astroglia and of the Li(Na)CO−3/Cl- exchange system of human erythrocytes. It is concluded that different anionic exchangers exist in different cell types that can be distinguished both by their biochemical properties and by their pharmacological properties.
TL;DR: It is concluded that protein kinase C regulates VIP receptor function possibly through phosphorylation of the VIP receptor possibly through phosphate‐stimulated adenylate cyclase activity in cell membranes.
TL;DR: Results strongly indicate that the mitogenic action of FGF is not coupled to phospholipase C activation, a conclusion consistent with the fact that the FGF-induced [Ca2+]i rise is strictly dependent upon external Ca2+.
TL;DR: In this paper, the problem of finding an optimal design of the midsurface of an elastic shell with respect to a given load (self-weight or wind, for instance), has to resist as well as possible towards given criteria.
Abstract: We suppose that a shell submitted to a given load (self-weight or wind, for instance), has to resist as well as possible towards given criteria. We aim at the following problem: Is it possible to find an optimal design of the midsurface of the shell with respect to this criteria? This problem can be worked using gradient-type algorithms. In this paper we work on the differentiability proof and numerical computation of the gradient. For a given shape of the midsurface, we consider that the shell works in linear elastic conditions. We use the Budiansky-Sanders model for elastic shells, from which we get the displacement field in the shell. The criteria to be minimized are supposed to depend on the shape directly, and also through the displacement field. In this paper, we prove that the displacement field depends on the shape in a Frechet-differentiable manner (for an appropriate topology on the set of admissible shapes). Then we give a way to compute the gradient of a given criteria from a theoretical point of view and from a numerical point of view. This allows us to use descent-type methods of optimization. They will lead to shapes which react better and better. Notice that we know nothing about convergence of these methods, the existence and unicity of a theoretical optimal solution. But from a practical point of view, it is quite interesting to be able to modify a given shape to obtain a better one.