Rheology and structural changes of plasticized zeins in the molten state

Zeins, storage proteins from maize, are suitable for making biobased thermoplastic materials. The rheological behavior of a commercial zein plasticized with 20 w% glycerol was studied in the molten state by steady-state flow experiments in extrusion conditions and oscillatory rheometry. For low residence times, a shear-thinning viscoelastic behavior was observed, with G″ exceeding G′. After 300 s at 130 °C, the complex viscosity |η ^?|?=?7?×?10³ ω ^?0.46 was found to be similar to that of thermoplastic polymer melts used in fused deposition modeling. However, the ratio between the exponents of the power laws describing G′(ω) and G″(ω) did not meet the typical value of 2 for entangled polymer melts. Moreover, for longer residence times, the viscosity increased and a gelation phenomenon was observed with a crossing over of G′(ω) and G″(ω). Gel times ranged from 6000 s at 120 °C to 1700 s at 150 °C. The evolution of the macromolecular structure assessed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and high-performance size exclusion chromatography suggested that this gelation phenomenon involves various types of covalent and non-covalent cross-links. Disulfide bonds played a significant role in gelation kinetics despite a very low cysteine residue content in the protein primary structure (about 1 mol%). These results suggested that plasticized zeins initially behave like a low-viscosity non-entangled polymer melt, before cross-linking progressively led to a continuous network.     

Stability of accretionary wedges based on the maximum strength theorem for fluid-saturated porous media

Accretionary wedges are idealized as triangular-shaped regions, the top surface corresponding to the topography, the bottom surface to the weak, frictional contact (décollement) with the subducting plate and the last side, the back-wall, to the contact with the continent. New critical stability conditions are obtained and defined by the sets of geometrical and material parameters for which the deformation occurs concurrently in two regions of the wedge e.g., the front and the rear. They extend the classical critical stability conditions, restricted to triangular regions of infinite extent and composed of frictional materials, by accounting for arbitrary topography, finite geometry and cohesive materials. They are obtained by the application of the kinematic approach of limit analysis, referred to as the maximum strength theorem, which is first extended to fluid-saturated porous media. The basic failure mode used to defined these stability conditions consists of two reverse faults intersecting the décollement at a common point, the root. The décollement is activated from the back wall to the root. The root position is indeterminate for our extended critical stability conditions. The proposed theory predicts the classical stability conditions as a special case. A first application to the Barbados prism is proposed accounting for a non-linear gradient in fluid pressure within the décollement. The details of the topography is responsible for several sets of critical stability conditions. Our pressure predictions necessary to explain the activation of the frontal thrust are significantly less than the estimates done during the drilling on site. Finally, the theory is applied to a wedge with the décollement partitioned into two regions, the deepest corresponding to the seismogenic zone. The associated failure modes include one composed of two blocks sliding at different velocities over the décollement and separated by a single discontinuity, dipping either towards the front or towards the rear of the wedge. This special mode dominance is facilitated by large pressures and small friction coefficients in the shallowest region of the décollement.     

Thermal optimization of 1.55 μm OP-VECSEL with hybrid metal–metamorphic mirror for single-mode high power operation

We report on the thermal design and the characterization of InP-based 1.55 μm wavelength large diameter (～100 μm) optically pumped vertical external cavity surface emitting lasers (OP-VECSELs). The device is thermally optimized for high power ( > 70 mW) room-temperature (RT) continuous-wave (CW) single-mode operation. Efficient bottom heat dissipation in the 1/2-VCSEL chip is obtained thanks to the use of a hybrid metal– metamorphic GaAs/AlAs mirror integrated to the InP-based active region, and to subsequent soldering on a SiC substrate. A single-mode output power of 77mW is obtained under CW-RT laser operation, limited by the pump power. Moreover thermal simulations and characterizations of the 1/2-VCSEL chip show that even higher power could be obtained at higher pumping levels, using a CVD diamond substrate.     

NMR observation of Tau in Xenopus oocytes

The observation by NMR spectroscopy of microinjected 15N-labelled proteins into Xenopus laevis oocytes might open the way to link structural and cellular biology. We show here that embedding the oocytes into a 20% Ficoll solution maintains their structural integrity over extended periods of time, allowing for the detection of nearly physiological protein concentrations. We use these novel conditions to study the neuronal Tau protein inside the oocytes. Spectral reproducibility and careful comparison of the spectra of Tau before and after cell homogenization is presented. When injecting Tau protein into immature oocytes, we show that both its microtubule association and different phosphorylation events can be detected.     

CEA/Saclay的ECR轻离子离子源

In the beginning of the 90s,T.Taylor and his collaborators demonstrated ECR sources operating at low frequency(i.e.2.45GHz)are able to produce very intense single charge light ion beams. At CEA/Saclay,the SILHI source developments started in 1995.Since 1997 more than 100mA proton or deuteron beams are routinely produced in pulsed or continuous mode.To comply with ADS reliability constraint,important improvements have been performed to increase the installation reliability.Moreover,to optimize the beam transport in the low energy beam line,the extraction system was carefully designed and space charge compensation studies were undertaken.An important step has been reached in 2005 with the development of a permanent magnet source able to produce a total beam of 109mA at 85kV. A new test bench named BETSI,especially dedicated to permanent magnet source developments,is presently under construction.It will allow analysing positive or negative extracted beams up to 50keV and 100mA. In addition,for several years work has been done to optimize the production of negative hydrogen ion beam with such an ECR source.Recent analysis pushed towards the construction of a new set up based on a multicusp magnetic configuration. After a brief overview of the CEA/Saclay source developments,this article will point out on the recent results and present status.     

The Death of the Expert

The texts of OR are littered, explicitly and implicitly, with myths about the ‘expert’ that are taken for self-evident truths. We would like to challenge these. This paper presents arguments following a postmodern route which views the world as text, where all phenomena and events can be regarded as text and, as such, subject to narrative analysis. Narrative analysis explodes and disperses text to reveal forms and codes according to which meanings are possible. The paper will introduce a case study drawing on our experiences in community OR, which we aim to use to demonstrate this approach.     

Air-coupled ultrasonic testing of diffusion bonds

The diffusion bond between two steel plates can be ultrasonically evaluated, at normal incidence in an immersion experiment, by analyzing the frequency dependence of the echo reflected from the imperfect bond. The interfacial stiffness, derived from the echo amplitude, correlates well with the bond-strength. However, a non-contact method is desirable for applications where immersion or contact is not wanted or even dangerous for damaging the material. This above mentioned bond-echo technique would not work in the situation of air-coupling as the reflected echo becomes then too weak due to the high impedance mismatch at the air-solid interface. Therefore we propose a theoretical method based on the study of two neighbouring resonance frequencies of the diffusion bonded plate-plate structure. In this way the physical signal sensitive to the adhesion status is not the (too weak) echo reflected from the bond, but the resonance frequency of the whole plate-plate system, and this frequency is detectable as working at resonance ensures high enough signal levels. It was shown that the odd resonance is as well sensitive to the plate thickness as to the interfacial bond parameter, whereas the even resonance feels only the plate thickness. On the basis of a theoretical formula, it is possible to extract, from a single point measurement, out of these two resonance frequencies both the plate thickness and the interfacial stiffness. In this way bond information is separated from geometrical information. Finally it is shown that thickness differences between the plates did not affect the reliability of the bonding-strength predictions.     

Novel macrocyclic templates by ring enlargement of ansa-steroids

Ring enlargement of ansa-steroids leads to a variety of novel templates which are suitable for the preparation of diverse libraries of natural product derivatives. Key steps for the synthesis of these highly functionalized templates were either an ozonolysis-derivatization-ring closing metathesis-sequence or a macrolactonization.