Etude electrochimique de l'iode et du brome en presence de cryptands

In presence of cryptands ([2.2.2], [2.2.1] and [2.1.1]) halogens X₂(bromide and iodine) give rise to the formation of an halonium ion complex in chloroformic solution. Preliminary voltammetric studies of halide and halogen alone allow to measure the stability constant of the trimeric X₃^? species in this solvent. By calculation it is then possible to determine the constant ratio: [cryptand —I⁺] [I₂]^?1 [cryptand]^?1 for iodine only, which is supposed to be a ratio fo the kinetic constants of formation and decomplexation of the halonium complexe.     

Rubber-modified epoxies. II. A reaction-induced phase separation observed in-situ and a posteriori with different methods

The reaction-induced phase separation in epoxy systems modified with rubber was firstly observed in situ with small angle X-ray scattering (SAXS), light transmission (LT), light scattering (LS), scanning electronic microscopy and transmission electronic microscopy techniques. The different observation windows of the SAXS, LT and LS methods allow us to follow the phase separation at two size levels. The selected system was bisphenol-A diglycidylether cured with 4,4′-diamino-3,3′-dimethyldicyciohexylmethane, in the presence of 15% wt of epoxy-terminated butadiene acrylonitrile random copolymers of different molecular weights. The phase separation inside the particles formed was followed first. Influences of precure temperature, rubber molecular weight, the postcure, vitrification and gelation on the evolution of the structure inside the particles are discussed. The real beginning of the phase separation is also discussed.     

The influence of microstructure and strength on the fracture mode and toughness of 7XXX series aluminum alloys

The effects of microstructure and strength on the fracture toughness of ultra high strength aluminum alloys have been investigated. For this study three ultra high purity compositions were chosen and fabricated into 1.60 mm (0.063 inches) sheet in a T6 temper providing a range of yield strengths from 496 MPa (72 ksi) to 614 MPa (89 ksi). These alloys differ only in the volume fraction of the fine matrix strengthening precipitates (G. P. ordered + η′ ). Fracture toughness data were generated using Kahn-type tear tests, as well asR-curve andJ _c analyses performed on data from 102 mm wide center cracked tension panel tests. Consistent with previous studies, it has been demonstrated that the toughness decreases as the yield strength is increased by increasing the solute content. Concomitant with this decrease in toughness, a transition in fracture mode was observed from predominantly transgranular dimpled rupture to predominantly intergranular dimpled rupture. Both quantitative fractography and X-ray microanalysis clearly demonstrate that fracture initiation for the two fracture modes occurred by void formation at the Cr-dispersoids (E-phase). In the case of intergranular fracture, void coalescence was facilitated by the grain boundary η precipitates. The difference in fracture toughness behavior of these alloys has been shown to be dependent on the coarseness of matrix slip and the strength differential between the matrix and precipitate free zone (σ_M-σPFZ). A new fracture mechanism has been proposed to explain the development of the large amounts of intergranular fracture observed in the low toughness alloys. Formerly a Research Assistant at Carnegie-Mellon University     

Coarsening of three-dimensional droplets by two-dimensional diffusion: Part I. Experiment

An experimental study of diffusional coarsening, or Ostwald ripening, in a liquid-liquid two-phase system is described. An experiment performed at its isopycnic point, 42°C, allowed observations for the long times required to investigate coarsening. A holographic technique was instrumental in this work. Holograms takenin situ permit investigation of details regarding both the influence of local environmental conditions on individual droplet size histories and measurement of global averages. This study utilized a 100 μm pathlength test cell. The discrete phase was nucleated on one wall of the cell. This configuration resembles island formation in thin film growth. Observation of Ostwald ripening over a period of 1×10⁷ s (∼4 mo.) reveals that droplet number decays as t^−0.733 and the average radius increases as t^−0.247, in the asymptotic limit. This shows good agreement with theoretical predictions for diffusional growth of spherical caps on a two-dimensional substrate which is a valid approximation for the geometry of this experiment. Part I of this paper describes the experimental results. Part II discusses a numerical model for droplet growth in a comparison with the experimental results.     

Low-temperature microwave characteristics of pseudomorphic InxGa1-xAs/In0.52Al0.48Asmodulation-doped field-effect transistors

Low-temperature microwave measurements of both lattice-matched and pseudomorphic In_xGa_1-xAs/In_0.48As (x=0.53, 0.60, and 0.70) channel MODFETs on InP substrates were carried out in a cryogenic measurement system. The measurements were done in the temperature range of 77 to 300 K and in the frequency range of 0.5 to 11.0 GHz at different bias conditions. The cutoff frequency ( f_T) for the In_xGa_1-xAs/In_0.52Al_0.48As MODFETs improved from 22 to 29 GHz, 29 to 38 GHz, and 39 to 51 GHz, for x=0.53, 0.60, and 0.70, respectively, as the temperature was lowered from 300 to 77 K, which is approximately a 31% increase at each composition. No degradations were observed in device performance. These results indicate an excellent potential of the pseudomorphic devices at low temperatures     

Endocytosis of transcobalamin in male rabbit germ cells: electron microscope radioautography study

The binding of 125I-iodinated transcobalamin to a suspension of isolated rabbit germ cells was studied by Scatchard plot. The number of binding sites was evaluated to about 1000 per cell, and its association constant (Kass) in order of 14.6 l/nmole. The distribution to structures related to endocytosis was determined by ultrastructural histomorphometric studies. Both coated and uncoated structures were present regardless of maturation stage. The number of coated vesicles was at its highest in the initial maturation steps, whereas the number of uncoated vesicles was highest in the final maturation steps. The endocytosis of 125I-iodinated transcobalamin by the suspension of germ cells was studied by electron microscope radioautography. The tracer was mostly detected over the plasma membrane, coated vesicles and multivesicular bodies of germ cells. The grains were observed mainly over spermatocytes and round spermatids; 31.6% and 32% of these cells, respectively, were labeled. In contrast the tracer was detected in only 8.11% of elongated spermatids. In conclusion, iodinated transcobalamin is internalized in rabbit germ cells by receptor-mediated endocytosis. This phenomenon was predominant in the early stages of germ cell maturation.     

Intraclass correlations: There's more there than meets the eye.

Methods of calculating intraclass correlations (ICC) are well established and understood in psychological research. Several issues relating to the process of determining reliability have, on the other hand, been only lightly treated. The present paper examines 2 issues regarding the use of ICCs: (a) the real vs theoretical limits of ICCs and procedures for applying significance tests when using these measures and (b) sources of unreliability in the data. The real limits of some ICCs are not 0 and +1.00 (the theoretical limits), but exceed both –2.00 and +1.00. Even when within the theoretical limits, the ICC values may not always reflect the reliability of the measure. Under certain conditions, one can obtain moderately high ICC values that are not significantly different from zero, suggesting that researchers calculate the significance of the target variance before calculating the intraclass r. Three sources of unreliability are also identified: patterns of both positive and negative correlations among judges, limited variance in the data matrix, and no correlations among judges. A method of determining the significance of the Judge?×?Target interaction and for demonstrating how that procedure can be used to aid in the identification of sources of unreliability, is detailed. (13 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Transfer RNA profiling: A new method for the identification of pathogenic Candida species

A new molecular taxonomic method applicable to the identification of medically important Candida species and other yeast species has been developed. It is based on the electrophoretic pattern of total tRNA samples (a ‘tRNA profile’) isolated from Candida species and generated using high-resolution semi-denaturing urea-polyacrylamide gel electrophoresis and methylene blue staining. Species-specific tRNA profiles for the species. C. albicans, C. tropicalis, C. parapsilosis, C. guilliermondii, C. glabrata and Pichia guilliermondii were obtained. Detailed studies with the major human pathogen of the Candida genus, C. albicans, demonstrated that the tRNA profile for a given species was both reproducible and strain-independent; seven different C. albicans strains generated identical tRNA profiles. Minor strain-specific heterogeneities in the tRNA profiles of C. guilliermondii and C. parapsilosis were detected, but in neither case did they significantly alter the species-specific diagnostic tRNA profile. The potential of this method in clarifying taxonomic anomalies was demonstrated by the finding that Type I and Type II strains of C. stellatoidea generate very different tRNA profiles, with that of a Type II strain being identical to the C. albicans tRNA profile. This method offers a number of advantages over current electrophoretic karyotype methods for species identification, both within the Candida genus and with yeast species in general.     

Hypoxic hepatitis: a difficult diagnosis when the cardiomyopathy remains unrecognized and the course of liver enzymes follows an atypical pattern. A report of two cases

Despite its heterogeneity, stratum corneum (SC) has been described as a homogeneous membrane for water diffusion. We measured water flux across the SC, transepidermal water loss (TEWL), in six women, in vivo. At four anatomical sites--back, abdomen, forearm, and thigh--we took measurements during sequential tape stripping. The inverse of TEWL (1/TEWL) and removed SC thickness yielded a highly linear correlation (Pearson's r ranging between 0.88 and 0.99). Applying Fick's law of diffusion, we calculated SC thickness (H), and SC water diffusion coefficient (D). Comparing the results, SC of all women was significantly thicker (p < 0.05) at the extremities (12.7 +/- 4.2 microm, mean +/- SD, n = 12) than the abdomen (7.7 +/- 1.8 microm, n = 6). The calculated diffusion coefficient approximated 2.16 +/- 1.14x10(-9) cm2/s. Compared with the diffusion constant found for SC depleted of lipids, our value was 100-fold lower. In agreement with previous findings that intercellular lipids are a rate determining component of the SC barrier, we suggest that water diffuses mainly through the intercellular space. The calculation of H and/or D, however, is based on several variables: SC density, the water concentration difference, and the partition coefficient of water between viable epidermis and SC. The literature values vary widely. It is desirable to determine these parameters more precisely, especially if discrete differences, such as between anatomical sites, are to be revealed.