Showing papers by "University of Rennes published in 1993"
TL;DR: A compound has been synthesized with the formula (rad)2Mn2[Cu(opba)]3(DMSO)2.2H2O, where rad+ is 2-N-methylpyridinium)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide, opba is orthophenylenebis(oxamato), and DMSO is dimethyl sulfoxide.
Abstract: A compound has been synthesized with the formula (rad) 2 Mn 2 [Cu(opba)] 3 (DMSO) 2 2H 2 O, where rad + is 2-(4- N -methylpyridinium)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide, opba is orthophenylenebis(oxamato), and DMSO is dimethyl sulfoxide It consists of two nearly perpendicular graphite-like networks with edge-sharing Mn(II) 6 Cu(II) 6 hexagons The two networks are fully interlocked with the same topological relationship as that between adjacent rings of a necklace The compound has three kinds of spin carriers: Mn(II) and Cu(II) ions, antiferromagnetically coupled through oxamato bridges, and rad + radical cations, bridging the Cu(II) ions through the nitronyl nitroxide groups and forming Cu-rad chains The temperature dependence of the magnetization reveals that below 225 K, the compound behaves as a magnet
421 citations
TL;DR: In this paper, it was shown that komatiites can only be formed in hot rising convective jets in the mantle, and that the most magnesian known eruption temperature was at up to 2200°C at pressures of 18 GPa corresponding to a mantle potential temperature of 1900°C.
383 citations
TL;DR: From the functional point of view, significant progress has been made in deciphering SC-GC cell language and new data are emerging that have enabled scientists to go beyond the descriptional or deductive aspects and to tackle the mechanical aspects.
Abstract: As soon as scientists began to study testicular structure and function, the concept emerged that SCs and GCs communicate We now know that the seminiferous epithelium is certainly one of the most complex tissues and that the structural and functional supports of SC-GC communication are extremely elaborate At all stages of sexual maturation, somatic cells and GCs have developed a formidable set of communication devices that are involved in attachment, displacement, cell shaping, and cell-cell transfer of molecules and cellular materials Some of the best morphologists since the nineteenth century have studied the anatomical basis of the SC-GC dialogue and have laid the foundations to the understanding of the spermatogenic process Further experimental efforts are still being made In particular, new data are emerging that have enabled scientists to go beyond the descriptional or deductive aspects and to tackle the mechanical aspects From the functional point of view, significant progress has been made in deciphering SC-GC cell language The unique strategic position of the SC allows this cell type to receive, integrate, and emit all the signals required for the spermatogenic process to or from the extratubular compartment (eg, FSH, testosterone), the peritubular cells (eg, P-Mod-S), and GCs themselves Its location also allows it to coordinate GC activity in both the transversal and the longitudinal axes of the seminiferous tubule The SC barrier and SC products create the physical and chemical microenvironments required for the completion of each of the different steps of spermatogenesis In addition to the tubule fluid, the SC products directly or indirectly implicated in GC control are proteins, peptides, and steroid(s) involved in germ cell proliferation, differentiation, and metabolism; transport/binding proteins; proteases; extracellular matrix components; energy metabolites; antiproteases; and various membrane components Sertoli cell polarization results from the existence of SC-SC occluding junctions The products required for the mitotic phase of spermatogenesis may principally be secreted basally, whereas those required for meiotic division, spermiogenesis, and sperm cells may preferentially be secreted apically The interaction between SC factors and GCs is mediated by GC membrane receptors and different endocytic processes The GC secondary pathway(s) involved in SC action remains a mystery Germ cell markers that would enable a precise assessment of SC influence are lacking Changes in the composition of the GC complement and in GC size and shape, as well as GC divisions and migration, profoundly affect SC morphology and function(ABSTRACT TRUNCATED AT 400 WORDS)
350 citations
TL;DR: In this article, the authors present a tightly controlled and comprehensive set of analytical data for the 250-Ma Siberian flood basalt province near Noril'sk and conclude that the most significant control on the geochemical and isotopic compositions of erupted lavas was processing of mantle-derived magma in crustal reservoirs during periodic replenishment, periodic tapping, continuous crystal fractionation and wallrock assimilation.
298 citations
TL;DR: An in vitro technique based on rainbow trout hepatocytes incubated in a basic medium free of any additional growth factors or estrogenic chemicals and uses the production of vitellogenin as a marker for the estrogenic potency of the compounds tested can provide complementary results about the activity of chemicals which need an hepatic metabolization to be estrogenic.
281 citations
TL;DR: In this paper, the pulsed laser-photolysis (PLP), time-resolved laser-induced fluorescence (LIF) technique has been used to study the reactions of the CN radical with CH 4, C 2 H 6, C 2H 4 and C 3 H 6 at low and ultra-low temperatures.
246 citations
TL;DR: In this article, seismic lines and a structure-contour map illustrate the patterns and shapes of salt diapirs and related structures in the Campos and Santos areas, off the Atlantic coast of Brazil.
240 citations
TL;DR: The petrographic and chemical composition of magmatic rocks generated during the Archaean appears to be different from that of post-Archaean rocks as mentioned in this paper. But the latter is not the case for the latter, as shown by the fact that after 2.5 Ga the role of these minerals in calc-alkaline magma genesis becomes progressively less important.
237 citations
TL;DR: The results were shown by multivariate analysis to be independent of age, immunophenotypes, and karyotypes and clearly show the importance of MDR phenotype detection in ALL.
233 citations
TL;DR: Arndt et al. as discussed by the authors showed that the low water contents of most flood basalts argue against proposals that hydrous lithosphere was the source, and they suggested that trace-element and isotopic compositions are buffered, and that the erupted basalts represent steady-state liquids tapped from these magma chambers.
222 citations
TL;DR: The regulation of Y-organ activity is rather unusual, as it seems to be mainly exerted by an inhibitory neuropeptide secreted from the X-organ-sinus gland complex, the so-called molt-inhibiting hormone or MIH.
Abstract: Y-organs are paired cephalic endocrine organs of higher Crustacea (Malacostraca). In lower groups (e.g., Entomostraca), they are absent. They were demonstrated as molting glands by Echalier in 1954. They originate from epidermis, and they may either remain attached to epidermis (e.g., in crayfishes) or become fully independent organs (e.g., in crabs); this is taken as an example of the formation of an endocrine gland from part of the target tissue of neurohormones (Buckmann, 1984). Their anatomical features show very large variations among species; these are extensively discussed here. Their ultrastructural characteristics were recently the subject of two excellent reviews (Birkenbeil, 1990; Spaziani, 1990) and are not fully described here. Y-organs secrete three different ecdysteroids, identified as ecdysone (E), 25-deoxyecdysone (25dE), and 3-dehydroecdysone (3DE). Usually these organs produce either E + 25dE or E + 3DE. The significance of these variations is unclear at the moment. These ecdysteroids are derived from dietary cholesterol, and our knowledge of the biosynthetic pathway is far from complete. Apart from the first step (conversion of cholesterol to 7-dehydrocholesterol) and the three last steps (hydroxylations at positions 25, 22, and 2), the reactions are still unknown, as is also the case in insects. The regulation of Y-organ activity is rather unusual, as it seems to be mainly exerted by an inhibitory neuropeptide secreted from the X-organ-sinus gland complex, the so-called molt-inhibiting hormone or MIH. MIH, recently isolated and sequenced in two species, is a member of a new 7-9 kDa peptide family that appears unique to crustaceans. The inhibitory mechanism of action of MIH on Y-organs has been extensively investigated, but it still remains controversial concerning the transduction mechanism involved, and the regulated steps are unknown. More recently, it has been shown that xanthurenic acid (XA), a derivative of tryptophan isolated from eyestalks, displays also an inhibitory effect on ecdysteroid biosynthesis that would be caused by a direct inhibition of cytochrome P-450 monooxygenase(s). The elucidation of the regulatory mechanisms of Y-organ activity by MIH (and other factors) should contribute to a better understanding of fundamental aspects of the regulation of steroidogenesis in general.
01 Sep 1993
TL;DR: In this article, the authors give a detailed account of the local cosine and sine bases of Coifman and Meyer and describe some of their applications; in particular, they show how these local bases can be used to obtain arbitrarily smooth wavelets.
Abstract: . We give a detailed account of the local cosine and sine bases of Coifman and Meyer. We describe some of their applications; in particular, based on an approach by Coifman and Meyer, we show how these local bases can be used to obtain arbitrarily smooth wavelets. The understanding of this material requires only a minimal knowledge of the Fourier transform and classical analysis. It is our intention to make this presentation accessible to all who are interested in Wavelets and their applications.
TL;DR: A comparative analysis of these phenomena in mammals, amphibians and fish suggests a specific role of GH in the physiology of puberty, gametogenesis and fertility, and shows the original contribution made by studies on the fish model in this field of investigations.
Abstract: Interaction between growth and reproduction occurs in many vertebrates and is particularly obvious at certain stages of the life cycle in fish. Endocrine interactions between the gonadotropic axis and the somatotropic axis are described, the potential role of GH being emphasised. A comparative analysis of these phenomena in mammals, amphibians and fish, suggests a specific role of GH in the physiology of puberty, gametogenesis and fertility. It also shows the original contribution made by studies on the fish model in this field of investigations.
TL;DR: In this article, the effect of temperature on the room-pressure Raman spectra of calcite, aragonite, magnesite and dolomite is reported up to 800-1100 K.
Abstract: The room-temperature Raman spectra of aragonite, magnesite and dolomite have been recorded up to 30 GPa and 25 GPa, respectively and no phase changes were observed during compression, unlike calcite. The effect of temperature on the room-pressure Raman spectra of calcite, aragonite, magnesite and dolomite is reported up to 800–1100 K. The measured relative pressure and temperature-shifts of the Raman lines are greater for the lattice modes than for the internal modes of the CO3 groups. These shifts are used to calculate the mode anharmonic parameters of the observed Raman modes; they are negative and their absolute values are smaller (close to 0) for the internal CO3 modes than for the lattice modes (4–17 10−5 K−1). The temperature shifts of the lattice modes in calcite are considerably larger than those for dolomite and magnesite, and a marked non-linear increase in linewidth is observed above 400° C for calcite. This is consistent with an increasing relaxational component to the libration of the CO3 groups about their threefold axes, premonitory to the rotational order-disorder transition at higher temperature. This behaviour is not observed for the other calcite structured minerals in this study. We examine systematic variations in the lattice mode frequencies and linewidths with composition, to begin to understand these differences in their anharmonic behaviour. Finally, we have used a simple Debye-Waller model to calculate atomic displacements in calcite, magnesite and dolomite with increasing temperature from the vibrational frequency data, to provide a direct comparison with atomic positional data from high-temperature structure refinements.
TL;DR: In this article, the stability of carbonates up to 50 GPa and at high temperatures (1500-2500 K) was investigated in a laser-heated diamond anvil cell and the run products were characterized by analytical transmission electron microscopy.
TL;DR: In this paper, the structure and history of salt diapirs in large ancient evaporitic basins such as the southeastern North Sea basin suggests that diapirism is controlled by crustal-scale extension.
TL;DR: In this article, high precision oxygen isotope analyses were made of phosphate extracted from 17 samples of nektonic and benthic fish debris sampled across the stratigraphic Cretaceous-Tertiary boundary in northern Morocco.
TL;DR: In this paper, the development of sedimentary basins in a tectonic context dominated by horizontal shortening and vertical thickening of the crust is considered, and various styles of compressional basins are reproduced.
TL;DR: An easy and soft method of decomplexation of phosphine-borane complexes, by DABCO, allows its use in situ in asymmetric catalytic hydrogenation of double bonds with metal phosphine complexes as mentioned in this paper.
TL;DR: The current language definition and programming style of pC++ are described and exampies of parallel linear algebra operations are presented and a fast Poisson solver is described in complete detail.
Abstract: pC++ is an object-parallel extension to the C++ programming language. This paper describes the current language definition and illustrates the programming style. Exampies of parallel linear algebra operations are presented and a fast Poisson solver is described in complete detail.
01 Jan 1993
TL;DR: In this paper, a family of quadratic forms determined by the algebraic constraints and defined in terms of the trace from the coordinate ring of the variety to the ground field is introduced.
Abstract: In this paper we show, by generalizing Hermite’s theorem to the multivariate setting, how to count the number of real or complex points of a discrete algebraic set which lie within some algebraic constraint region. We introduce a family of quadratic forms determined by the algebraic constraints and defined in terms of the trace from the coordinate ring of the variety to the ground field, and we show that the rank and signature of these forms are sufficient to determine the number of real points lying within a constraint region. In all cases we count geometric points, which is to say, we count points without multiplicity. The theoretical results on these quadratic forms are more or less classical, but forgotten too, and can be found also in [3].
TL;DR: A review of the 127 published papers shows spectroscopy results in more than 150 experimental animal tumour models, which provide a useful basis to evaluate the current state of the art, summarize the basic knowledge presently available, determine the key points underlying the present disappointment of some clinical oncologists and stimulate new basic research.
Abstract: More than 50% of cancers fail to respond to any individual treatment and tumour follow-up after treatment plays a major role in routine therapy planning and pharmacological research. Today, MRS is the only technological approach providing non-invasive access to tumour biochemistry. Ten years ago, expectations were raised concerning 31P MRS as an exciting and promising technical approach to the study of tumours. However the expectations have not always come to fruition. How close are we now to seeing routine 31P NMR in clinical oncology? This review of the 127 published papers shows spectroscopy results in more than 150 experimental animal tumour models. These tumour/host/treatment systems provide us with a useful basis to evaluate the current state of the art, summarize the basic knowledge presently available, determine the key points underlying the present disappointment of some clinical oncologists and stimulate new basic research. The information collected concerns the discussion of the reliability of experimental models in oncology, the technical improvement of magnetic resonance technology and the monitoring of bioenergetic status, pH regulation and phospholipid metabolism in treated and untreated tumours. Recent advances (two-thirds of the papers have been published in the last 5 years) seem to provide more optimistic perspectives than those generally accepted a few years ago, in the depressing period following early pioneering work.
TL;DR: In this article, the results of an experimental and theoretical study to compare the attributes of Pr3+-doped sulphide, chloride, mixed halide, fluoride and chlorotellurite glasses for 1.3µm fiber amplifiers are presented.
Abstract: The results of an experimental and theoretical study to compare the attributes of Pr3+-doped sulphide, chloride, mixed halide, fluoride and chlorotellurite glasses for 1.3µm fibre amplifiers are presented. Quantum efficiencies based on measured and calculated radiative and nonradiative rates are presented for each glass together with its 1.3µm fluorescence spectrum and an estimate of its loss.
TL;DR: In this paper, β-diketones react with a variety of amines and aminoesters over clay K 10 or silica under microwave irradiation in open vessels to give within a few minutes, the corresponding enaminoketones with good yields.
TL;DR: Findings show that normal variations in callosum size do not appear to contribute significantly to individual differences in hemispheric specialization, and may be associated with degree of functional interhemispheric inhibition.
TL;DR: The results imply that ectoine may play a major role in counteracting the effects of osmotic stress in media of oSMotic pressure equivalent to ⋜ 1 M-NaCl.
Abstract: Brevibacterium linens can grow in media of relatively high osmotic strength (up to 3 M-NaCl). Optimal growth in minimal medium occurred with either added NaCl (0.5-1 M) or other osmolytes developing an equivalent osmotic pressure. Above 1 M-NaCl the growth rate slowed, but was enhanced by adding the osmoprotectant glycine betaine or its precursor choline (1 mM) to the media. Neither soluble carbohydrates nor ninhydrin-reacting compounds accumulated during osmotic treatment. However, a Dragendorff-positive compound, together with K+ ions, accumulated (7-fold) as a consequence of elevating the medium osmolality. Spectral characteristics of the purified compound were similar to those of synthesized 1,4,5,6-tetrahydro-2-methyl-4-pyrimidinecarboxylic acid (ectoine). In the absence of exogenously supplied osmoprotectants, a strict dependence between the intracellular ectoine content and the external salt concentration (up to 1 M-NaCl) was observed. From 1 to 2 M-NaCl, the ectoine content decreased, and this signalled decreased self-osmoprotection by this bacterium. Interestingly, at these salt concentrations, exogenous glycine betaine led to the greatest beneficial effect. Glycine betaine or choline added to the medium was actively taken up by the cells in an osmolality-dependent manner, and the resulting betaine accumulation caused a sharp decrease in intracellular ectoine content. Radiolabelling of ectoine occurred only when L-[U-14C]glutamate was used as a precursor; de novo synthesis was dependent on the external osmolality and was strongly inhibited by exogenously supplied glycine betaine. These results imply that ectoine may play a major role in counteracting the effects of osmotic stress in media of osmotic pressure equivalent to ⋜ 1 M-NaCl.
TL;DR: In this paper, the authors search for the presence of interleukin-6 bioactivity (IL-6) in medium conditioned by various testicular cell types and investigate the cellular and hormonal regulation of testicular IL-6 production.
Abstract: The present study's aims are to search for the presence of interleukin-6 bioactivity (IL-6) in medium conditioned by various testicular cell types and to investigate the cellular and hormonal regulation of testicular IL-6 production. Sertoli cells prepared from rats of increasing ages (20, 35, and 45 days) secreted IL-6 in vitro, whereas medium conditioned by pachytene spermatocytes, early spermatids, and peritubular cells showed no activity. Lipopolysaccharide (LPS) and latex beads, two known stimulators of monocyte/macrophage IL-6 production, markedly stimulated IL-6 secretion by Sertoli cells at all the ages investigated. Maximum levels of IL-6 were reached after 6 h of culture of Sertoli cells with LPS and after 24 h with latex beads. When Sertoli cells were cocultured with pachytene spermatocytes, early spermatids, or fractions containing residual bodies and cytoplasts from elongated spermatids, only the latter significantly stimulated IL-6 levels. Maximum levels of IL-6 were attained by adding 2 x 1...
TL;DR: In this paper, it was shown that strongly elliptic second order partial differential operators generate analytic semigroups inL p, 1
Abstract: This paper contains two new characterizations of generators of analytic semigroups of linear operators in a Banach space. These characterizations do not require use of complex numbers. One is used to give a new proof that strongly elliptic second order partial differential operators generate analytic semigroups inL p , 1
TL;DR: In this paper, a new insulation film, PO x N y H z, has been fabricated on n-InP substrate surface using vapor transport technique for use as an interfacial layer on n -InP Schottky contact devices.
Abstract: A new insulation film, PO x N y H z , has been fabricated on n -InP substrate surface using vapor transport technique for use as an interfacial layer on n -InP Schottky contact devices. This interfacial layer is obtained by reaction of the deposited film with the substrate surface. It is stable and moisture insensitive. The capacitance voltage and current voltage characteristics are determined at various temperatures. Temperature dependence of ideality factor and apparent barrier height is observed. The Richardson plot gave a good straight line. At room temperature, the ideality factor is about 1.09; the apparent and true barrier heights evaluated from extrapolated forward saturation current and from Richardson plot ln ( I 0 T 2 ) vs 10 3 T respectively, are found to be equal to 0.80 and 0.39 eV; the reverse current density is found to be sufficiently low (6.4·10 −8 A / cm 2 at IV). The characteristics of the prepared Schottky device are analyzed.
TL;DR: It is found experimentally that the flow of sand in an hour glass is oscillatory in a certain range of parameters, while the mass of the sand contained in one period strongly depends on it.
Abstract: We have found experimentally that the flow of sand in an hour glass is oscillatory in a certain range of parameters. The oscillatory motion results from a coupling between the flow of sand and convection of air through the sand matrix. The period of the oscillation is remarkably insensitive to the grain size, while the mass of the sand contained in one period strongly depends on it.