Showing papers by "Université Paris-Saclay published in 1999"

An internal targeting signal directing proteins into the mitochondrial intermembrane space

Abstract: Import of most nucleus-encoded preproteins into mitochondria is mediated by N-terminal presequences and requires a membrane potential and ATP hydrolysis. Little is known about the chemical nature and localization of other mitochondrial targeting signals or of the mechanisms by which they facilitate membrane passage. Mitochondrial heme lyases lack N-terminal targeting information. These proteins are localized in the intermembrane space and are essential for the covalent attachment of heme to c type cytochromes. For import of heme lyases, the translocase of the mitochondrial outer membrane complex is both necessary and sufficient. Here, we report the identification of the targeting signal of mitochondrial heme lyases in the third quarter of these proteins. The targeting sequence is highly conserved among all known heme lyases. Its chemical character is hydrophilic because of a large fraction of both positively and negatively charged amino acid residues. These features clearly distinguish this signal from classical presequences. When inserted into a cytosolic protein, the targeting sequence directs the fusion protein into the intermembrane space, even in the absence of a membrane potential or ATP hydrolysis. The heme lyase targeting sequence represents the first topogenic signal for energy-independent transport into the intermembrane space and harbors two types of information. It assures accurate recognition and translocation by the translocase of the mitochondrial outer membrane complex, and it is responsible for driving the import reaction by undergoing high-affinity interactions with components of the intermembrane space.

Iterative Substructuring Preconditioners for Mortar Element Methods in Two Dimensions

Abstract: The mortar methods are based on domain decomposition and they allow for the coupling of different variational approximations in different subdomains. The resulting methods are nonconforming but still yield optimal approximations. In this paper, we will discuss iterative substructuring algorithms for the algebraic systems arising from the discretization of symmetric, second-order, elliptic equations in two dimensions. Both spectral and finite element methods, for geometrically conforming as well as nonconforming domain decompositions, are studied. In each case, we obtain a polylogarithmic bound on the condition number of the preconditioned matrix.

Spin asymmetries A1 of the proton and the deuteron in the low x and low Q2 region from polarized high energy muon scattering

Abstract: We present the results of the spin asymmetries (Formula presented) of the proton and the deuteron in the kinematic region extending down to (Formula presented) and (Formula presented) The data were taken with a dedicated low x trigger, which required hadron detection in addition to the scattered muon, so as to reduce the background at low x. The results complement our previous measurements and the two sets are consistent in the overlap region. No significant spin effects are found in the newly explored region. © 1999 The American Physical Society.

Search for charged Higgs bosons in decays of top quark pairs

Abstract: We present a search for charged Higgs bosons in decays of pair-produced top quarks using 109.2{plus_minus}5.8 pb{sup {minus}1} of data recorded from p{ovr p} collisions at {radical}(s)=1.8 TeV by the D0 detector during 1992{endash}1996 at the Fermilab Tevatron. No evidence is found for charged Higgs production, and most parts of the [M{sub H{sup +}} {beta}] parameter space where the decay t{r_arrow}H{sup +}b has a branching fraction close to or larger than that for t{r_arrow}W{sup +}b are excluded at 95{percent} confidence level. Assuming m{sub t}=175 GeV and {sigma}(p{ovr p}{r_arrow} t{ovr t})=5.5 pb , for M{sub H{sup +}}=60 GeV , we exclude tan{number_sign}{beta}{lt}0.97 and tan{number_sign}{beta}{gt}40.9 . {copyright} {ital 1999} {ital The American Physical Society}

Preparation of LiCoO2 and LiCo1–xFexO2 using hydrothermal reactions

Abstract: Iron doped/undoped LiCoO 2 powders could be obtained from hydrothermal reactions of either Fe 3+ or Co 3+ containing co-precipitates or a CoCl 2 -NaOH-NaClO 3 (oxidant) mixture with an excess amount of LiOH·H 2 O at 220 °C for 8-48 h. The LiFe x Co 1–x O 2 solid solution maintained a layered rock-salt structure until x=0.25. 57 Fe Mossbauer and Co K-edge XANES spectra and magnetic susceptibility data reveal that iron and cobalt in the solid solution are in high-spin Fe 3+ (S=5/2) and low-spin Co 3+ (S=0) configurations.

Human genome anatomy: BACs integrating the genetic and cytogenetic maps for bridging genome and biomedicine.

Abstract: Translating problems of human disease into the language of the human genome requires a unified resource that bridges DNA sequence through chromosome bands. Such a resource must link the three types of linear arrays that represent the human genome: database arrays (genetic and physical maps and ultimately DNA sequence), chromosome bands visible in single cells, and ordered clone arrays. Genome maps have been previously either STS-based, with marker order obtained using a combination of STS-content of large insert yeast artificial chromosome (YAC) clones, radiation hybrid (RH) mapping, and genetic mapping (Hudson et al. 1995; Deloukas et al. 1998), or BAC-based, with order obtained at 2–6 Mb through high resolution mapping by fluorescence in situ hybridization (FISH) with respect to human chromosome landmarks (Korenberg et al. 1992). During the course of these efforts, a strategy to integrate these maps was established. BACs are well suited for a permanent FISH-mapped and integrated clone resource in that they represent a stable and easily manipulated form of cloned DNA and produce bright, well defined signals on metaphase and interphase chromosome preparations (Korenberg and Chen 1995). We now report the construction of a genome-wide array of bacterial artificial chromosomes (BACs) that is integrated with the cytogenetic, genetic, and STS maps and characterized for homology to the remainder of the human genome by FISH.

Correlation between nuclear motion in the core-excited CF4 molecule and molecular dissociation after resonant auger decay

Abstract: K. Ueda,1,2 M. Simon,2,3 C. Miron,2,3 N. Leclercq,2,3 R. Guillemin,2,3 P. Morin,2,3 and S. Tanaka4 1Research Institute for Scientific Measurements, Tohoku University, Sendai 980-8577, Japan 2LURE, Bat 209d, Universite Paris-Sud, 91405 Orsay Cedex, France 3CEA DRECAM SPAM, CEN Saclay, 91191 Gif /Yvette Cedex, France 4CIAS, Osaka Prefecture University, Sakai 599-8231, Japan (Received 7 April 1999) Dissociation of the CF 1 4 molecular ion has been investigated using monochromatized synchrotron radiation and the energy-selected electron–ion coincidence method. The 2t 2 C ionic state produces fragment ions CF 1 2 and CF 1 3 . The branching ratio CF 1 2 CF 3 is increased by a factor of 6 by the C 1s excitation to the lowest unoccupied antibonding orbital, from the ratio at the direct ionization of the 2t 2 orbital. This increase is interpreted in the light of the nuclear motion in the core-excited state, with the help of theoretical calculations based on the vibronic model.

Magnetic signatures of hydrological change in a tropical maar-lake (Lake Massoko, Tanzania): Preliminary results

Abstract: Magnetic measurements have been performed on volcanic catchment rocks, present-day soils, and cored sediments from Lake Massoko, an oligotrophic maar-lake from SW Tanzania. Magnetic concentration proxies, low- and high- temperature experiments, and hysteresis behavior, suggest significant contributions of Ti-magnetite and SP/SD (oxidized) magnetite in tuff-ring material transformed by pedogenesis (modern soil, littoral sand). In contrast, the basalt is characterized by relatively low concentrations of PSD-SD magnetite. Three depth/time intervals present magnetic signatures similar to the modern soils and littoral sands, at ~43-38 kyr, ~12-1.3 kyr, and 400-300yr BP (the uppermost 30 cm). They likely correspond to humid (high-lake stand) periods, with increased pedogenic processes and runoff. Other sediments have magnetic signatures closer to the catchment basalt, possibly indicating arid/low-stand periods with increased detrital inputs from the basaltic crater wall. Sediments deposited during the Last Glacial Maximum (~38-12kyr) present high Jrs/Js-high Hcr/Hc intervals, indicating an additional high coercivity component of unknown origin.

The thermoluminescence 'afterglow' band as a sensitive indicator of abiotic stresses in plants

Abstract: Single turn-over xenon flashes induce a thermoluminescence (TL) B-band centred near 35 °C. The far-red illumination of leaves at non-freezing temperatures induces a band peaking at around 45 °C (afterglow or AG-band), together with a downshifted B-band peaking between 15 °C and 28 °C. In control, unfrozen wheat plants, the Tmax of the B-band induced after 30 s far-red light at 0 °C was approx. 15-18 °C. In maize plants grown under the same conditions, this far-red-induced downshift was not so strong, since the B-band peaked at 28 - 30 °C. Both a decline in the AG-band and a reversal of the downshift of the B-band were observed after short-term freezing in several plant species. There was usually a sudden drop in the AG-band below a critical freezing temperature. However, while in wheat plants a weak TL emission could be seen between 40-50 °C in frozen samples, in cold-sensitive maize plants this was completely suppressed and only the B-band could be detected. In cold-hardened wheat plants the temperature at which the AG-band was suppressed was lower than in non-hardened plants. Drought and short-term heat stress also affect the AG-band. As the AG-band was found to be more sensitive to several types of stresses than the B-band, it can be used as a sensitive stress indicator. However, the behaviour of the AG-band depends on several factors (for example the age of the leaf, etc.), which must be controlled if different species or varieties are to be compared

Antisite-assisted diffusion in the L12 ordered structure studied by Monte Carlo simulations

Abstract: Diffusion in the L12 structure is investigated by means of atomistic kinetic Monte Carlo simulations on a rigid lattice. Special attention is devoted to the influence of the composition on the diffusion process in a binary alloy. We observe that two diffusion mechanisms resulting from the interactions of vacancies with antisites located on both sublattices allow for the displacement of the minority element and can enhance the diffusivity of the majority element. The respective contributions to the diffusion process of these two mechanisms strongly depend on the temperature and on the degree of departure from the stoichiometric composition. These two mechanisms can explain the minimum nickel diffusivity experimentally observed around the stoichiometic composition in Ni3Al compounds and the suspected lower activation energy for gallium than for nickel in Ni3Ga.

Performance characteristics of a network of commodity multiprocessors for the NAS benchmarks using a hybrid memory model

Abstract: Multiprocessors and high performance networks offer the opportunity to construct CLUster of Multi Processors (CLUMPs) and use them as parallel computing platforms. The distinctive feature of the CLUMPs over traditional parallel computers is their hybrid memory model (message passing between the nodes and shared memory inside the nodes). In this paper, we investigate the performance characteristics of a cluster of biprocessor PCs for the NAS 2.3 parallel Benchmark using a programming model based on MPI for message passing between biprocessor nodes and OpenMP for shared memory inside biprocessor nodes. The paper provides several contributions. These include: a) Speed-up measurements of a cluster of biprocessor PCs over a cluster of uniprocessor PCs using the hybrid memory model b) A detailed analysis of the speed-up results from a breakdown of the benchmarks execution time and c) A performance comparison of a commodity CLUMP with some high performance parallel computers.

Possibility for an enhanced 3D imaging sensitivity in electromagnetic methods : keyhole imaging

Abstract: We present a phenomenon which has not been reported until now. It has been found using two independent methods (controlled-source audiomagnetotelluric (CSAMT) analogue modelling experiments and magnetotelluric (MT) numerical computations) that, in the transition zone between the so-called 'overshooting' and the 'normal' period ranges, the anomalies over thin sheet-like 3D models having a complicated geometry are closely connected to the model pattern. This phenomenon and the corresponding enhanced imaging sensitivity have been detected using several different interpretation parameters, in a very narrow period window, towards the end of the overshooting period range of the corresponding sounding curve. This so-called keyhole period range can be determined using simple two-layer MT and CSAMT relationships. Since the effect is small but mcasurable, the keyhole images could be used as an additional tool in practical problems where the main objective is the detailed geometry of buried targets.

Smoothing effects for some derivative nonlinear Schrödinger equations

Abstract: In this paper we study a smoothing property of solutions to the Cauchy problem for the nonlinear Schrodinger equations of derivative type: $iu_t + u_{x x} = \mathcal N(u, \bar u, u_x, \bar u_x), \quad t \in \mathbf R,\ x\in \mathbf R;\quad u(0, x) = u_0(x),\ x\in \mathbf R,\qquad$ (A) where $\mathcal N(u, \bar u, u_x, \bar u_x) = K_1|u|^2u+K_2|u|^2u_x +K_3u^2\bar u_x +K_4|u_x|^2u+K_5\bar u$ $u_x^2 +K_6|u_x|^2u_x$, the functions $K_j = K_j (|u|^2)$, $K_j(z)\in C^\infty ([0, \infty))$. If the nonlinear terms $\mathcal N =\frac{\bar{u} u_x^2}{1+|u|^2}$, then equation (A) appears in the classical pseudospin magnet model [16]. Our purpose in this paper is to consider the case when the nonlinearity $\mathcal N$ depends both on $u_x$ and $\bar u_x$. We prove that if the initial data $u_0\in H^{3, \infty}$ and the norms $||u_0||_{3, l}$ are sufficiently small for any $l\in N$, (when $\mathcal N$ depends on $\bar u_x$), then for some time $T > 0$ there exists a unique solution $u\in C^\infty ([-T, T]$\ $\{0\};\ C^\infty(\mathbb R))$ of the Cauchy problem (A). Here $H^{m, s} = \{\varphi \in \mathbf L^2;\ ||\varphi||_{m, s}<\infty \}$, $||\varphi||_{m, s}=||(1+x^2)^{s/2}(1-\partial_x^2)^{m/2}\varphi||_{\mathbf L^2}, \mathbf H^{m, \infty}=\cap_{s\geq 1} H^{m, s}.$

Integration of Brownian vector fields

Abstract: Using the Wiener chaos decomposition, we show that strong solutions of non Lipschitzian S.D.E.'s are given by random Markovian kernels. The example of Sobolev flows is studied in some detail, exhibiting interesting phase transitions.

Comparison of annamycin to adriamycin in cardiac and MDR tumor cell systems.

Abstract: Based on the response of a wide variety of tumors to the anthracycline, Adriamycin, numerous studies have been initiated to find an even more effective analog. In this pursuit two of the obstacles that have been necessary to overcome are a unique dose dependent Adriamycin-induced cardiotoxicity reported in patients treated with this chemotherapeutic agent as well as p-gp-mediated multi drug resistance (MDR) which has been found in tumor cells exposed to Adriamycin in vitro and in vivo as well as in human tumor samples. Using an in vitro cardiac cell system and MDR+ and MDR- Friend leukemia cell lines we find that a relatively new anthracycline, Annamycin, has reduced cardiotoxic activity but is more effective in inhibiting the growth of MDR+ cells than Adriamycin. The reduced cardiotoxicity of Annamycin is approximately 10 fold lower than Adriamycin whereas the increased efficacy against the MDR+ Friend leukemia tumor cell line is about 2 fold. The observation that Adriamycin preferentially accumulates in cardiac-muscle (CM) but not in cardiac non-muscle (NM) cells while Annamycin accumulates equally in both, may explain in part the reduced cardiotoxicity of Annamycin. Moreover, the cytosolic accumulation of Annamycin vs the nuclear localization of Adriamycin suggests a different target site for each drug.

Deformation quantization and invariant distributions

Abstract: In 1979, M. Kashiwara and M. Vergne formulated a conjecture on a Lie group G which implies that the Duflo isomorphism of Z(g) and S(g)^g extends to a natural module isomorphism between the spaces of germs of invariant distributions on G and g=Lie(G), respectively. They also proved their conjecture for G solvable. Using Kontsevich's deformation quantization we establish directly this result for distributions on any real Lie group G. In turn this gives a new proof of Duflo's result on the local solvability of bi-invariant differential operators on G.

Anomaly-Induced Gauge Unification and Brane/Bulk Couplings in Gravity-Localized Theories

Abstract: It has recently been proposed that gravity-localized compactifications can generate the required gauge hierarchy without the need for hierarchically large extra spacetime dimensions. In this paper, we show that gauge coupling unification arises naturally in such scenarios as a result of the anomaly induced by the rescaling of the wavefunctions of the brane fields. Thus, ``anomaly-induced'' gauge coupling unification can easily explain the apparent low-energy gauge couplings in gravity-localized compactifications. However, we also point out a number of phenomenological difficulties with such compactifications, including an inability to accommodate the GUT scale and the electroweak scale simultaneously. We also show that brane/bulk couplings in this scenario are generically too small to be phenomenologically relevant. Finally, we speculate on possible resolutions to these puzzles.

A form of the Euler equations preserving potential flow

Abstract: A new approach is taken to the computation of the elliptic part of the Euler equations. In each cell of an unstructured triangular grid, on which the solution is stored at the vertices, the residual is decomposed into purely elliptic and purely hyperbolic contributions. The elliptic part is minimised in a norm suggested by an earlier analysis of linearized potential flow. This choice of norm enables substantial simplification of the update procedure, for which an explicit formula is given. From ,the formula, it can be seen that the procedure is well-behaved in the transonic and lowMach number limits.

Nmr structure of an oligonucleotide containing a base pair 3-(2-hydroxyethyl) deoxyuridine-adenine

Abstract: It has been shown that ethylene oxide reacts with dC at the N3 position to produce a potentially mutagenic lesion, 3-(2-hydroxyethyl) deoxyuridine (3-HE-dU). In this article, we report NMR and Molecular Mechanic studies of a duplex containing the 3-HE-dU base with an adenine in front of the lesion which is in the sequence, 5′-GCAAGTC(3-HE-dU)AAAACG.