Showing papers by "Pierre-and-Marie-Curie University published in 1985"

Occurrence of a new microsporidan: Enterocytozoon bieneusi n.g., n. sp., in the enterocytes of a human patient with AIDS.

Abstract: A new microsporidium is reported infesting the enterocytes of a Haitian patients with AIDS. The stages observed were diplokaryotic cells, sporogonial plasmodia, unikaryotic sporoblasts, and spores. Neither a sporophorous vesicle (pansporoblastic membrane) nor parasitophorous vacuole were differentiated around the developmental stages, which were in direct contact with the host cell cytoplasm. The polar tube (5-6 coils) was differentiated before fission of the sporogonial plasmodium. The mature spores measured 1.5 micron X 0.5 micron. The spore wall was very thin as the endospore was absent or poorly differentiated. The organism is named Enterocytozoon bieneusi n. g., n. sp. and is assigned to the suborder Apansporoblastina.

The quantum Toda chain

Abstract: The exact equations for the spectrum of the finite and infinite quantum Toda chains are derived. The method used does not need the existence of the pseudovacuum (reference) state and provides thus an alter native to the Bethe ansatz method. The results obtained are in good agreement with those of B. Sutherland and M. Gutzwiller.

Mitochondrial class II introns encode proteins related to the reverse transcriptases of retroviruses.

Abstract: Organelle introns share several distinctive features that set them apart from their counterparts in nuclear-encoded pre-messenger RNAs (reviewed in ref 1): their termini do not obey the GUAG rule; the introns are 'structured' (members of the same family or 'class' can theoretically adopt very similar RNA secondary conformations and several of the postulated pairings have been confirmed by studies of splicing mutants and their revertants (see, for example, ref 4); many introns from both classes contain long open reading frames We report here that the proteins potentially encoded by four class II introns are related to several RNA-dependent polymerases of viral and transposable element origins

The static metrics with cylindrical symmetry describing a model of cosmic strings

Abstract: We discuss a set of static metrics with cylindrical symmetry describing the interior and exterior space-time of a model of cosmic strings considered recently in cosmology. The interior metric depends on one arbitrary function and the exterior on one constant. We find the relation between this constant and the linear mass density of the cosmic string. A cosmic string can be also treated as a line source in the framework of the distribution-valued curvature formalism which allows us to obtain again the same relation.

On the stochastic quantization of field theory

Abstract: We give a rigorous construction of a stochastic continuumP(φ)2 model in finite Euclidean space-time volume. It is obtained by a weak solution of a non-linear stochastic differential equation in a space of distributions. The resulting Markov process has continuous sample paths, and is ergodic with the finite volume EuclideanP(φ)2 measure as its unique invariant measure. The procedure may be called stochastic field quantization.

Vitellogenesis and Its Control in Malacostracan Crustacea

Abstract: Vitellogenesis in the amphipod Orchestia gammarella , in natantian decapods and probably in other Malacostraca involves two phases, primary and secondary vitellogenesis. Oogenesis from oogonia to the end of primary vitellogenesis is a continuous process. The primary proteic vitellus is endogenous. The secondary vitellogenesis takes place during the reproductive season. Fully grown primary follicles are surrounded by a permanent follicular tissue (secondary folliculogenesis). The resulting secondary follicles grow synchronously until ovulation. A tubular network has been observed in secondary follicle cells of prawns. The prominent feature of secondary vitellogenesis is the uptake of vitellogenin by the oocytes. This vitellogenin is synthesized by the fat body. Secondary vitellogenesis is controlled by neurohormones that have not yet been isolated and whose modalities of action still remain unclear. In Decapoda, the classical gonad-inhibiting hormone or GIH released by the sinus glands inhibits secondary vitellogenesis and the synthesis of vitellogenin. In Isopoda, vitellogenesis-inhibiting hormone is synthesized by neurosecretory cells in the median part of the protocerebrum. In Amphipoda, neurosecretory cells of this region secrete a neurohormone inducing secondary folliculogenesis and triggering secondary vitellogenesis. The neurohormones would control the formation of functional secondary follicles during the reproductive season. Other hormones are involved in control of secondary vitellogenesis. In Peracarida molting hormone is necessary for a normal synthesis of vitellogenin and the uptake of this protein by growing oocytes. In the amphipod Orchestia gammarella secondary folliculogenesis requires a low titer of ecdysteroids which characterizes postecdysis. The correlation between molt cycle and secondary vitellogenesis would be established in this way. After secondary folliculogenesis, the secondary follicle cells become endocrine and secrete the vitellogenin-stimulating ovarian hormone (VSOH).

Induction of functional retinal projections to the somatosensory system.

Abstract: Optic axons can be induced to form permanent, retinotopic connections in the auditory (medial geniculate, MG) and somatosensory (ventrobasal, VB) nuclei of the Syrian hamster thalamus; this occurs when the principal targets of retinofugal axons are ablated in newborn hamsters and alternative terminal space is created by partial deafferentation of MG or VB1–3. The experimentally induced retinal projection to the somatosensory nucleus occurs by the stabilization of an early, normally transient projection4–5. The present study was undertaken to determine whether the anomalous, stabilized retino-VB projection is functional. Newborn hamsters were operated on to produce permanent retino-VB projections and when the animals were mature, neurophysiological recordings were made in the cortical targets of VB, the first and second somatosensory cortices (SI and SII, respectively). Visual stimulation within well-defined receptive fields reliably evoked multi-unit responses in SI and SII of operated, but not normal hamsters. The representations of the visual field in SI and SII showed a partially retinotopic organization. These results demonstrate that optic tract axons can form functional synapses in the thalamic somatosensory nucleus, and suggest that neural structures which normally process information specific to one sensory modality have the potential to mediate function for other modalities.

The evolution of the Gulf of Corinth (Greece): an aftershock study of the 1981 earthquakes

Abstract: Summary. A preliminary study of the aftershocks of three earthquakes that occurred near to Corinth (Greece) in 1981 is combined with observations of the morphology and faulting to understand the evolution of the Eastern Gulf of Corinth. The well located aftershocks form a zone 60km long and 20km wide. They do not lie on the main fault planes and are mostly located between the north-dipping faulting on which the first two earthquakes occurred and the south-dipping faulting associated with the third event. A cluster of aftershocks also lies in the footwall of the eastern end of the south-dipping fault of the third event. Morphologically, it is observed that in the evolution of the Eastern Gulf of Corinth, antithetic faulting apparently predates the appearance of the main faulting at the surface. This evolution can be explained by motion on a deep seated, shallow angle, aseismic normal fault. A model based on such a fault also accounts for the aftershock distribution of the 1981 earthquakes.

The oxygen isotope composition of landsnail shells as a climatic indicator: Applications to hydrogeology and paleoclimatology

Abstract: The oxygen isotopic compositions of the carbonate shells of landsnails either Prosobranchia or Putmonata are directly related to the annual mean oxygen isotopic composition of meteoric precipitation by the following relation: δOp(SMOW) = 117δ18OSaragonite(PDB) −591 Moreover, the present study leads for the first time to the establishment of a map of the 18O equal-contents contours of meteoric precipitation in France and on some other areas of western Europe and northern Africa The calculated values are compared with the local isotopic data of precipitation In addition, this study provides a tool for hydrogeology to make quick determinations of the annual isotopic mean composition of meteoric precipitation within a given area This method also allows the quantification of continental paleoclimatic parameters, eg temperature and δ 18O of precipitations

Hepatitis B virus DNA sequences in lymphoid cells from patients with AIDS and AIDS-related complex.

Abstract: A lymphotropic virus HTLV-III/LAV was recently identified as the etiologic agent of the acquired immune deficiency syndrome (AIDS) In a study of concomitant hepatitis B infections in patients with AIDS or the AIDS-related complex, DNA sequences of hepatitis B virus (HBV) were found in fresh and cultured lymphocytes from patients with AIDS even in the absence of conventional HBV serological markers Furthermore, the restriction DNA pattern was consistent with the integration of the viral DNA These results should prompt additional studies to reevaluate a possible role of HBV as a cofactor in AIDS in addition to the HTLV-III/LAV causal agent

Neogene paleostress changes in the Basin and Range: A case study at Hoover Dam, Nevada-Arizona

Abstract: At Hoover Dam, 40 km southeast of Las Vegas, Nevada, well-exposed, highly faulted Miocene rocks provide an excellent opportunity to study the paleostress history of a very small area within a region where previous geologic studies indicate clockwise rotation of paleostress and a nearness to a major strike-slip fault-zone boundary. Within <0.5 km3 of rock, the sense of slip was determined on almost 500 separate faults. The fault-slip data show internal consistency with respect to lithology, size of faults, and location within the small area. With respect to fault slip, however, the data represent an in-homogeneous mixture of primarily strike-slip and dip-slip motions. From this mixture, it is possible to resolve two distinct stress fields with directions of extension that differ by ∼60°. Each stress field corresponds to a mixture of strike-slip and dip-slip faults, and thus the orientations of σ 1 and σ 2 are not tightly constrained. If, however, the data are first separated into strike-slip and dip-slip faulting modes and subsequently searched for sub-populations that correspond to contrasting paleostress orientations, the computations yield tightly constrained tensors that illustrate two distinct stress fields with subhorizontal σ 3 axes that trend N50°E and N75°W. The σ 1 and σ 2 axes permutate in two vertical planes that strike N40°W and N15°E, because σ 1 and σ 2 are close in value, relative to σ 3. These relationships suggest that strike-slip and dip-slip faulting belong to the same tectonic regime. Qualitative observations of polyphase slip, fault-fault offsets, and fault-bedding geometric relationships, when evaluated in the context of changes in σ 3 orientation and permutations of σ 1 and σ 2, provide a basis for a two-stage, late Cenozoic structural evolution at Hoover Dam. These stages are (1) strike-slip faulting (partly pre-tilt) and dip-slip faulting and associated stratal tilting and (2) mostly post-tilt, complexly interrelated strike-slip, oblique-slip, and dip-slip faulting. The qualitative evaluations indicate that strike-slip and dip-slip faulting alternated in time during the second stage of deformation and may have done so during the first. These mixed-mode movements probably represent stress oscillations in time and space rather than discrete stress reorganizations. In contrast, the two different orientations of σ 3 either represent a major clockwise rotation of the stress field or a major counterclockwise rotation of the rocks during the faulting history. Each alternative is consistent with regional geologic relationships, and the choice of which is correct cannot be made within the small area that was studied.

Carbon fixation in marine phytoplankton: carboxylase activities and stable carbon-isotope ratios; physiological and paleoclimatological aspects

Abstract: We measured the activity of three carboxylases: RuBP carboxylase, PEP carboxylase and PEP carboxykinase of marine phytoplankton species in culture and in natural communities. Activities of the three carboxylases were measured simultaneously with stable carbon-isotope ratios. The enzymatic activities have been used to estimate the importance of β carboxylation and its impact on the 13C:12C ratio (expressed as δ13C). The marine phytoplankton species in culture were Fragilariopsis kerguelensis, Nitzschia turgiduloides, Skeletonema costatum, Phaeodactylum tricornutum, Isochrysis galbana, Dunaliella marina, and Prorocentrum micans, and the field samples were collected from different depths off the coast of Portugal (August/September, 1981). Our results indicate that, as in terrestrial plants, the δ13C value is a good indicator of the extent of β carboxylation. RuBP carboxylase activity was always predominant, whereas the δ13C value never reached values typical of the C4 pathway. The β carboxylases could be PEP carboxylase (in dinoflagellates) or PEP carboxykinase (in diatoms). β carboxylation increased at the end of the exponential growth phase in a diatom culture and with increased biomass in natural samples. We interpret these increases as an adaptative response mechanism to poor environmental conditions, especially to low light intensity.

Analysis of class I introns in a mitochondrial plasmid associated with senescence of Podospora anserina reveals extraordinary resemblance to the Tetrahymena ribosomal intron.

Abstract: Recently, the nucleotide sequences for three “mitochondrial plasmids” associated with senescence of Podospora anserina were determined (Cummings et al. 1985). One of these sequences, corresponding to the plasmid termed e senDNA, contains three class I introns, all within a protein coding sequence equivalent to the mammalian “URF1” gene. Here, we present primary and secondary structure analyses for two of these introns as well as a partial analysis for the third, which extends beyond the DNA sequence determined. With regard to both primary and secondary structure, the closest known relative of intron 1 is the self-splicing intron in the large ribosomal RNA gene of Tetrahymena. One secondary structure domain at the periphery of intron 1 and Tetrahymena models is also present in intron 2. The latter intron is the longest known class I member and contains remnants of two protein-coding sequences, one of which is split by the other. Evolutionary processes that might be responsible for the unusual structure of introns 1 and 2 are discussed.

Transpassive Dissolution of Ni in Acidic Sulfate Media: A Kinetic Model

Abstract: The transpassive dissolution of Ni in acidic sulfate media, including the influence of crystallographic orientation, was investigated The surface plane had low index values, that is (100), (110), and (111) This study was largely based on the analysis of complex impedance (100) and (110) specimens showed identical electrochemical behaviors, whereas the (111) specimen showed a current density about 20% lower A reaction mechanism describing the dissolution of the passive film was proposed This dissolution step was postulated to be catalytic, in the sense that the passive film transformed into a soluble species by anion was not consumed by the transpassive dissolution itself Calculated polarization curves as well as electrode impedances at various polarization points were in a good agreement with experimental results

Electrical transport properties of In2Se3

Abstract: The electrical transport properties of In2Se3 are investigated. An attempt is made to elucidate the confusion concerning structure and polymorphism. Secondly measurements are made in high temperature range (α-β transition) and low temperature range on annealed and quenched samples. An unusual temperature dependence of the mobility is found that might be attributed to the defective structure of the stoichiometric vacancies in the cationic sublattice. The post-preparation annealing effect is also studied in detail and the difference is reported between an annealed and quenched-annealed sample. Les proprietes de transport electriques do In2Se3 ont ete etudiees. Tout d'abord, nous essayons d'elucider la confusion existant sur la structure et le polymorphisme du materiau. Puis nous decrivons les mesures effectuees ae hautes temperatures (region de la transition de phase α-β) et aux basses temperatures sur des echantillons trempes et recuits. La variation de la mobilite en fonction de la temperature n'est pas celle d'un semiconducteur classique; elle peut-ětre attribuee ae la structure lacunaire des sites cationiques et aux defauts de stoechiometrie. Nous avons aussi etudie en detail l'effet de recuit sur un echantillon trempe et l'avons compare avec un echantillon recuit lors de la preparation.