Cassava retting: Optimisation of a traditional fermentation by an experimental research methodology

Retting, a spontaneous and traditional fermentation of cassava roots in Central Africa, was optimised in terms of time and the quality of the end-product. Optimal conditions were achieved by using an experimental research methodology. Temperature is the most influential factor, with an optimum of 34°C for quicker retting. The roots should be peeled and soaked in water immediately after harvesting to increase the quality of cassava foods. Inoculation of water with juice from a prior retting helps in cassava detoxification but has no influence on the time or the quality of foo-foo. Foo-foo samples had the most favourable organoleptic quality when an incubation temperature of between 28 and 37°C was used. Using optimal conditions, retting time was reduced 3-fold, and foo-foo of high and constant quality could be processed.     

Noise propagation in wave-front sensing with phase diversity

The phase diversity technique is studied as a wave-front sensor to be implemented with widely extended sources. The wave-front phase expanded on the Zernike polynomials is estimated from a pair of images (in focus and out of focus) by use of a maximum-likelihood approach. The propagation of the photon noise in the images on the estimated phase is derived from a theoretical analysis. The covariance matrix of the phase estimator is calculated, and the optimal distance between the observation planes that minimizes the noise propagation is determined. The phase error is inversely proportional to the number of photons in the images. The noise variance on the Zernike polynomials increases with the order of the polynomial. These results are confirmed with both numerical and experimental validations. The influence of the spectral bandwidth on the phase estimator is also studied with simulations.     

Software to compute and conduct sequential Bayesian phase I or II dose-ranging clinical trials with stopping rules

The aim of dose-ranging phase I (resp. phase II) clinical trials is to rapidly identify the maximum tolerated dose (MTD) (resp., minimal effective dose (MED)) of a new drug or combination. For the conduct and analysis of such trials, Bayesian approaches such as the Continual Reassessment Method (CRM) have been proposed, based on a sequential design and analysis up to a completed fixed sample size. To optimize sample sizes, Zohar and Chevret have proposed stopping rules (Stat. Med. 20 (2001) 2827), the computation of which is not provided by available softwares. We present in this paper a user-friendly software for the design and analysis of these Bayesian Phase I (resp. phase II) dose-ranging Clinical Trials (BPCT). It allows to carry out the CRM with stopping rules or not, from the planning of the trial, with choice of model parameterization based on its operating characteristics, up to the sequential conduct and analysis of the trial, with estimation at stopping of the MTD (resp. MED) of the new drug or combination.     

Synthesis,Chiral Separation,Absolute Configuration Assignment,and Biological Activity of Enantiomers of Retro‐1 as Potent Inhibitors of Shiga Toxin

The Shiga toxin (Stx) family is composed of related protein toxins produced by the bacteria Shigella dysenteriae and certain pathogenic strains of E. coli. No effective therapies for Stx intoxication have been developed yet. However, inhibitors that act on the intracellular trafficking of these toxins may provide new options for the development of therapeutic strategies. This study reports the synthesis, chromatographic separation, and pharmacological evaluation of the two enantiomers of Retro‐1, a compound active against Stx and other such protein toxins. Retro‐1 works by inhibiting retrograde transport of these toxins inside cells. In vitro experiments proved that the configuration of the stereocenter at position 5 is not crucial for the activity of this compound. X‐ray diffraction data revealed (S)‐Retro‐1 to be slightly more active than (R)‐Retro‐1.     

Modelling of long-term diffusion–reaction in a bentonite barrier for radioactive waste confinement

Bentonites have been proposed as buffer material for barriers in geological disposal facilities for radioactive waste. This material is expected to fill up by swelling the void between the canisters containing the waste and the surrounding ground. However, the bentonite barriers may be submitted to changes of humidity, temperature variation, fluid interaction, mass transport, etc. This could modify the physico-chemical performance of the barrier, mainly on the interface with the steel container and with the geological barrier. The engineered barrier development necessitates thus the study of the physico-chemical stability of its mineral component as a function of time under the conditions of the repository in the long-term.The purpose of the present study was two-fold. Firstly, it was hoped to simulate the chemical transformations (geochemical and cation exchange reactions) coupled with diffusion of chemical-elements into the engineered barrier under repository conditions by applying a thermokinetic hydrochemical code (KIRMAT: Kinetic Reactions and Mass transport).Secondly, it was hoped to apply a simplified method to estimate the swelling capacity evolution by a volume balance in the fluid-saturated engineered barrier, considering that the decay of swelling capacity is directly proportional on the volume of transformed montmorillonite and, taking into account that it may be partially compensated by the volume of neo-formed swelling clays.The system modelled herein was considered to consist of 1-m thick zone of water-saturated engineered barrier. This non-equilibrated system was placed in contact with a geological fluid on one side, which was then allowed to diffuse into the barrier, while the other side was kept in contact with a source of metallic iron. Reducing initial conditions(P_O2 0; Eh = − 200 mV) and a constant reaction temperature (100 °C) were considered.The results showed that the EB in contact with the geological fluid was highly transformed after 10,000 years, whereas the most significant chemical processes were illitization, cation exchange and saponization, extending up to 20 cm into the EB. Chemical transformations of minor importance in the EB were identified as well, such as a neo-formation of silicates (quartz, cristobalite), anhydrite, laumontite, magnetite and chlorite in the system.A simplified method based on volume balance showed that the swelling capacity of the bentonite barrier is slightly affected after 10,000 years of diffusion–reaction (D close to 1) because the volume of neo-formed swelling-clays is almost directly proportional to the volume of transformed Na/Ca-montmorillonite, except for a strong illitization and/or neo-formation of non-swelling clays. In the present study, this simple approach predicted that the decay of swelling capacity of the engineered barrier is drastically affected close to the geological barrier-engineered barrier interface. Out this zone the swelling capacity decay lies between 5% and 11%.     

Dye-Sensitized Solar Cells Combining ZnO Nanotip Arrays and Nonliquid Gel Electrolytes

We present a dye-sensitized solar cell (DSSC) using a nanostructured ZnO photoelectrode and a gel electrolyte. The photoelectrode consists of well-aligned ZnO nanotips on a Ga-doped ZnO (GZO) transparent conducting film. The GZO film (400 nm, sheet resistance ~25 Ω/sq, transmittance over 85% in the visible wavelength) and ZnO nanotips (3.2 μm length) are sequentially grown on a glass substrate using metalorganic chemical vapor deposition. The ZnO photoelectrode is sensitized with dye N719 and impregnated with N-methyl pyrolidinone (NMP) gelled with poly(vinyl-difluoroethylene-hexafluoropropylene) copolymer (PVDF-HFP). The cell exhibits an open-circuit voltage of 726 mV and a power conversion efficiency of 0.89% under one sun illumination. The aging testing shows that the cell using a gel electrolyte has better stability than its liquid electrolyte counterpart.     

Probing photonic and optoelectronic structures by apertureless scanning near-field optical microscopy

This report presents the Apertureless Scanning Optical Near-Field Microscope as a powerful tool for the characterization of modern optoelectronic and photonic components with sub-wavelength resolution. We present an overview of the results we obtained in our laboratory over the past few years. By significant examples, it is shown that this specific probe microscopy allows for in situ local quantitative study of semiconductor lasers in operation, integrated optical waveguides produced by ion exchange (single channel or Y junction), and photonic structures.     

Effective viscoelastic behavior of short fibers composites using virtual DMA experiments

Mechanics of Time-Dependent Materials - May it be for environmental or economic reasons, mass reduction has become one of the main goals in mechanics. The short fiber thermoplastics composite is an...     

Bulk Spin Torque-Driven Perpendicular Magnetization Switching in L10 FePt Single Layer

Due to its inherent superior perpendicular magnetocrystalline anisotropy, the FePt in L1₀ phase enables magnetic storage and memory devices with ultrahigh capacity. However, reversing the FePt magnetic state, and therefore encoding information, has proven to be extremely difficult. Here, it is demonstrated that an electric current can exert a large spin torque on an L1₀ FePt magnet, ultimately leading to reversible magnetization switching. The spin torque monotonically increases with increasing FePt thickness, exhibiting a bulk characteristic. Meanwhile, the spin torque effective fields and switching efficiency increase as the FePt approaches higher chemical ordering with stronger spin–orbit coupling. The symmetry breaking that generates spin torque within L1₀ FePt is shown to arise from an inherent structural gradient along the film normal direction. By artificially reversing the structural gradient, an opposite spin torque effect in L1₀ FePt is demonstrated. At last, the role of the disorder gradient in generating a substantial torque in a single ferromagnet is supported by theoretical calculations. These results will push forward the frontier of material systems for generating spin torques and will have a transformative impact on magnetic storage and spin memory devices with simple architecture, ultrahigh density, and readily application.