Ségrégation externe des bétons frais: Modèle expérimental et influence des principaus facteurs

Résumé Un modéle expérimental de ségrégation externe a sété mis au point; il consiste à faire suivre à un seul granulat noyé dans une pate de ciment un trajet rectiligne à vitesse constante. On mesure simultanément la force nécessaire pour produire ce mouvement, en particulier au moment où le granulat s’extrait de la pate. Pour des pates à concentration en ciment usuelles (γ>0,530) l’extraction du granulat s’effectue par création d’une colonne de pate adhérente à ce dernier, la rupture intervenant toujours par traction dans la colonne elle-même. La force nécessaire pour extraire un granulat de la pate (force d’extraction ΔF_ex) s’exprime simplement par la relation: ΔF_ex = mSσ_t, avec: S: aire de la section diamétrale du granulat: σ_t: résistance à la traction de la pate de ciment fraiche: m: coefficient de conraction indépendant de la concentration en solide de la pate et de la dimension du granulat.

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Summary An experimental model of external segregation has been devised. It consists of making a single aggregate grain embedded in cement paste follow a rectilinear path at constant rate. Simultaneous measurement is taken of the force necessary to produce this movement, particularly at the moment when the grain energy emerges from the paste. For paste with normal cement content (ψ>0.530) the extraction of the grain is activated by the formation of a column of paste bonded to the grain, rupture always being caused by tension in the column itself. The force necessary to extract a grain from the paste (extraction force ΔF_ex) is simply expressed by the equation: ΔF_ex = mSσ_t, with: S: area of the diametral section of the grain; σ_t: tensile strength of fresh cement paste; m: contraction coefficient independent of the solid concentration of the paste and of the grain size.

     

Isolated plantar venous thrombosis. Report of a case

We report the case of a patient with isolated plantar thrombophlebitis as a post operative complication of saphenectomy. Risk factors such as prolonged bed rest, perioperative inflammation and surgery of the greater saphenous vein itself should be considered. Moreover multiple episodes of superficial venous thrombosis had already occurred as complication of the superficial venous insufficiency. Literature on this unusual outcome is lacking. Ultrasound imaging revealed this superficial thrombosis. Usual echographic signs (non compressible vein, hypoechogenicity of the vessel lumen) can be found. The main problem is to differentiate veins from adjacent tendinous structures. Slow mobilisation of the toes and comparative analysis on contralateral foot are helpful. Thrombosis of the plantar veins must be considered as a possible diagnosis of unexplained plantar unilateral pains. Development of ultrasonic investigations and knowledge of its occurrence could further improve its diagnosis.     

A chromosome 4 satellite I DNA isolated from SV40-transformed human cells

Anticancer inhibitors of topoisomerase I (TOP1, EC 5.99.1.2) cause the reversible stabilization of the TOP1-DNA covalent complex (cleavable complex). The cleavable complex can be converted into a double-strand break, the presumed cytotoxic lesion, by active replication forks. Cytotoxicity independent of DNA replication has also been demonstrated, and suggested to have possible clinical significance. To assess the importance of the replication-independent mechanism of camptothecin (CPT) cytotoxicity we have analyzed replication-dependent and replication-independent cytotoxicity following a brief CPT treatment (40 min) of seven human colon tumor cell lines. The cell lines were exposed to CPT in the presence or absence of aphidicolin, an inhibitor of DNA polymerases alpha, delta or epsilon. The seven cell lines responded similarly to CPT: treatments of less than 0.5 microM caused cytotoxicity only when DNA replication was ongoing, as evidenced by a plateau in the cytotoxicity curve corresponding to the S-phase fraction and the prevention of this cytotoxicity by aphidicolin cotreatment; at higher CPT doses, the cytotoxicity exceeded the S-phase fraction and was not prevented by aphidicolin. The CPT sensitivity among the cell lines, measured as the concentration required to inhibit cell growth by 25%, was between 0.17 and 0.43 microM without aphidicolin and 2-10 microM with aphidicolin cotreatment; with aphidicolin in cotreatment, 20-fold greater CPT concentrations were required, on average among the cell lines, to achieve cytotoxicity equivalent to CPT treatment alone. The potential of the lower dose and longer duration treatments of camptothecins used in the clinical setting to produce cytotoxicity independent of DNA replication is discussed.     

Noniterative stable transmission/reflection method for low-lossmaterial complex permittivity determination

This paper describes a new noniterative transmission/reflection method applicable to permittivity measurements using arbitrary sample lengths in wide-band frequencies. This method is based on a simplified version of the well-known Nicolson-Ross-Weir (NRW) method. For low-loss materials, this method is stable over the whole frequency range: no divergence is observed at frequencies corresponding to integer multiples of one half wavelength in the sample. The accuracy on the dielectric permittivity is similar to that obtained with a more recently proposed iterative technique. A general equation for complex permittivity determination including the Stuchly, NRW, and new noniterative methods, is also proposed     

Scheduling divisible loads on star and tree networks: results and open problems

Many applications in scientific and engineering domains are structured as large numbers of independent tasks with low granularity. These applications are thus amenable to straightforward parallelization, typically in master-worker fashion, provided that efficient scheduling strategies are available. Such applications have been called divisible-loads because a scheduler may divide the computation among worker processes arbitrarily, both in terms of number of tasks and of task sizes. Divisible load scheduling has been an active area of research for the last 15 years. A vast literature offers results and scheduling algorithms for various models of the underlying distributed computing platform. Broad surveys are available that report on, accomplishments in the field. By contrast, We propose a unified theoretical perspective that synthesizes previously published results, several novel results, and open questions, in a view to foster hover divisible load scheduling research. Specifically, we discuss both one-round and multiround algorithms, and we restrict our scope to the popular star and tree network topologies, which we study with both linear and affine cost models for communication and computation.     

An efficient strategy for detection of known and new mutations of the CYP2D6 gene using single strand conformation polymorphism analysis

To detect mutations in the cytochrome P450 CYP2D6 gene (CYP2D6), we developed a strategy based on single-strand conformation polymorphism (SSCP) analysis of the gene amplified by polymerase chain reaction (PCR). The efficiency of the method was evaluated by analysing DNA samples from extensive metabolizers (EM) and poor metabolizers (PM) of debrisoquine. Haplotypes, alleles and mutations of CYP2D6 had previously been characterized in each individual using PCR assays, Xba I restriction fragment length polymorphism (RFLP) and sequencing. PCR-SSCP results were in complete agreement with those obtained using established methods. All previously characterized mutations were associated with particular shifts in the electrophoretic mobility of DNA fragments allowing their identification. We further tested the efficiency of PCR-SSCP for detecting new CYP2D6 mutations. DNA from a PM subject presumed to carry an unknown non-functional mutant allele of CYP2D6 was amplified and bands with aberrant migration patterns were observed on SSCP gels. Sequence analysis of the corresponding DNA fragments revealed the causative mutations. In this way, a novel non-functional allele of the gene, carrying three previously reported mutations and a new mutation in the third exon which results in a premature termination codon, was characterized. Finally, CYP2D6 SSCP analysis was performed on DNA amplified with fluorescent primers and an automated DNA sequencer was used for SSCP analysis of products. We conclude that the PCR-SSCP approach is a powerful method of identifying simultaneously known and new mutations of the CYP2D6 gene.     

Three-dimensional modelling of selective dissolution and passivation of iron-chromium alloys

A three-dimensional model has been developed for modelling the selective dissolution and passivation of alloys. The model has been used to simulate the passivation of iron-chromium alloys. The real structure of the alloy is taken into account (bcc in the present case), as well as the structure of the initial surface. The passivation is modelled in considering the formation of “oxide” nuclei, resulting from the presence of local chromium-rich clusters. During the dynamic evolution of the model, based on the Monte Carlo method, surface diffusion and dissolution of atoms occur according to probabilities dependent on the nature of the atom (Cr or Fe) and on its chemical environment. The conditions of simulation can be changed through a set of parameters defining the rules for surface diffusion, selective dissolution and number of Cr atoms in the Cr clusters required to initiate locally the passivation. The effects of these parameters on the simulation have been tested for an alloy containing 22 at.% Cr and compared with experimental data. The results show that the diffusion of Fe has little influence on the course of passivation while the diffusion of Cr has a marked effect. When the number of surface chromium atoms required to form a nucleus of passive film increases, the passivation becomes less rapid, with a marked effect on the composition of the passivated layer. The extent of the chromium enrichment in the passivated surface obtained in the model for the initial stages of passivation is not as high as the one measured experimentally in the stationary state of passivity.Other simulations have then been performed with various chromium contents in the alloy. The results show the existence of a transition, which is not sharp but progressive, between alloys that cannot be passivated to alloys that are passivated.     

Influence of the solvent on the conformations of poly(ethylene oxide) chains grafted on silica

Electron spin resonance (e.s.r.) of labelled grafted poly (ethylene oxide) has been used to estimate (as a function of temperature) the ratio between the populations of free-end segments in solution to those adsorbed onto the silica surface. The influence of the solvents such as C₆H₆, CHCl₃, C₄H₈O₂, C₆F₆ and CCl₄ has also been investigated. Better solvents produce greater swelling of the molecules, with more of the grafted layer extending into the solution. But solvent-surface and polymer-surface interactions must be taken into account to explain the results.