Investigations on tyrosinase activity in melanin-free ink from Sepia officinalis: potential for food proteins cross-linking

Protein modification via enzymatic cross-linking is an attractive way for altering food structure so as to create products with increased quality and nutritional value. In this study, enzymatic cross-linking of β-casein was performed by tyrosinase activity, from melanin-free ink from Sepia officinalis, which was monitored by sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS–PAGE) techniques. The melanin-free ink contains a strong tyrosinase activity with pH 7 and 58?°C as optima of pH and temperature, respectively. Such activity is stimulated by ferrous ions and strongly inhibited by Mn²⁺, EDTA, H₂O₂, arbutin, and p-coumaric acid. We also show that 2 Mercapto-ethanol (14?mM) quickly and completely inactivated sepia tyrosinase. The melanin-free ink exhibits a major protein on SDS–PAGE with an N-terminal sequence matching perfectly with an internal sequence of the sepia peroxidase. The zymogram confirmed the inactive state of this truncated protein and the presence of an active tyrosinase enzyme. Interestingly, this activity was able to cross-link the β-casein protein. The tyrosinase implication in reticulation was demonstrated by the addition of its inhibitors, with 2-mercaptoethanol being the most effective, followed by arbutin, p-coumaric acid, and hydrogen peroxide.     

Structured estimation of tire forces and the ground slope using SM observers

In agricultural context, the principal cause of serious accidents for all-terrain vehicles(ATVs) is rollover. The most important parameters related to this risk is the ground slope. In this paper, we propose a structured observer to estimate the system states and the longitudinal tire forces using only wheel angular velocities measurement. The robust estimation is based on a second order sliding mode observer. This estimation is then used to build up a ground slope estimation. The algorithm is composed by two cascaded estimators. This structured estimation is then applied to the model of an agricultural vehicle G7(GregoireTM) integrated in the driving simulation environment SCANeRTM-Studio.     

Gettering by heat thermal processing: application in crystalline silicon solar cells

The aim of this work is to getter unwanted impurities from solar grade crystalline silicon (Si) wafers and then to enhance their electronic properties. This was done by forming a sacrificial porous silicon (PS) layer on both sides of the Si wafers and by performing infrared (IR) thermal annealing treatments (at around 950 °C) in a SiCl₄/N₂ controlled atmosphere. The process allows concentrating unwanted impurities in the PS layer and near the PS/silicon interface. These treatments reduce the resistivity by about two orders of magnitude at a depth of about 40 μm and improve the minority carrier diffusion length from 75 to 210 μm. This gettering method was also tested on silicon wafers where grooved fingers and back contacts were achieved using a chemical vapor etching (CVE) method. Front buried metallic contacts and small holes for local back surface field were then achieved after the gettering stage in order to realize silicon solar cells. It was shown that the photovoltaic parameters of gettered silicon solar cells were improved as regard to ungettered ones.     

Synthesis and characterization of new anthracene‐based semiconducting polyethers

New anthracene‐based polyethers, anthracene/bisphenol A (An–BPA) and anthracene/fluorinated bisphenol A (An–BPAF), were synthesized and characterized. An–BPA and An–BPAF were fully soluble in common organic solvents and had number‐average molecular weights of 2580 and 3240, respectively. The optical properties of the polymers were investigated with ultraviolet–visible absorption and photoluminescence spectroscopy. Blue photoluminescence was observed in dilute solutions. In solid thin films, π–π interactions influenced the optical properties, and redshifted photoluminescence spectra were obtained; a green emission (504 nm) for An–BPAF and a green‐yellow emission (563 nm) for An–BPA were found. By cyclic voltammetry, the electrochemical band gap was estimated to be 2.72 and 3.05 eV for An–BPA and An–BPAF, respectively. Single‐layer diode devices of an indium tin oxide/polyether/aluminum configuration were fabricated and showed relatively low turn‐on voltages (3.5 V for An–BPA and 3.7 V for An–BPAF). © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Synthesis and characterization of new anthracene-based semi-conducting materials

Two soluble anthracene-based organic materials (BPA-An1 and BPA-An2) have been synthesized and characterized. The optical properties of these π-conjugated systems were investigated by UV–Visible absorption and photoluminescence (PL) spectroscopies. The optical gaps were estimated from the absorption onsets of the thin polymer films; their values were 3.01 and 2.76?eV for BPA-An1 and BPA-An2, respectively. The PL spectrum of BPA-An2 exhibits a blue emission both in dilute solution and thin film. BPA-An1 showed a blue photoluminescence in dilute solution; in solid film, π–π interactions influence its optical behavior and a green emission was observed. The HOMO and LUMO levels were estimated using cyclic voltammetry analysis. Single-layer devices of the (indium-tin oxide/anthracene-based material/aluminum) configuration have been elaborated and showed relatively low turn-on voltages of 6.2–5.5?V for BPA-An1 and BPA-An2, respectively.     

Synthesis and characterization of new blue‐photoluminescent copolymer derived from bisphenol A

A new copolymer with short alternating conjugated and nonconjugated blocks, derived from bisphenol A (BPAEt₂‐PPV) containing separated phenylenevinylene (PV) units has been synthesized by Wittig condensation. The copolymer is fully soluble in common organic solvents and has a number‐average molecular weight of 3200 with a polydispersity index of 1.53. The structure of the polymer was confirmed by ¹H NMR, ¹³C NMR, FTIR and Raman spectroscopic analysis. Thermogravimetric analysis and differential scanning calorimetry indicate that BPAEt₂‐PPV is stable up to 400°C in air and displays a glass transition temperature of 107°C. The fluorescence spectrum of the polymer film shows an emission in the blue region (428, 456, and 488 nm). The band‐gap energy, estimated from the edge absorption of the film, is about 2.9 eV. A single‐layer diode device of the configuration ITO/BPAEt₂‐PPV/Al has been fabricated and has a relatively low turn‐on voltage of 3.7 V. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

Optical and electrical characterization of thin films based on anthracene polyether polymers

Two new anthracene derivatives were characterized to improve the optoelectronic properties of π-conjugated anthracene polymers. The optical properties of the polymers were investigated by UV-visible absorption and photoluminescence (PL) spectroscopy. The energy bandgaps of anthracene-based polyether thin films were in the range 2.8–2.97 eV. Green emission (504 nm) was observed for anthracene/bisphenol A (An-BPA) and green-yellow emission (563 nm) for anthracene/fluorinated bisphenol A. (An-BPAF) Organic diodes formed by sandwiching anthracene layers between indium–tin oxide (ITO) and aluminum contacts were characterized. The dc electrical properties of ITO/anthracene derivatives/Al diodes were studied using current–voltage measurements and showed ohmic behavior at low voltage. The conduction mechanism seems to be a space-charge-limited current with exponential trap distribution at high applied bias voltage. The ac electrical transport of the anthracene derivatives was studied as a function of frequency (100 Hz–10 MHz) and applied bias in impedance spectroscopy analyses. We interpreted Cole–Cole plots in terms of the equivalent circuit model as a single parallel resistance and a capacitance network in series with a relatively small resistance. The evolution of the electrical parameters deduced from fitting of the experimental data is discussed. The conduction mechanism revealed by I–V characteristics is in agreement with the impedance spectroscopy results.     

Formation,rapid thermal oxidation and passivation of solar grade silicon nanowires for advanced photovoltaic applications

Uniform and regular silicon nanowires (SiNWs) arrays are fabricated on both sides of solar grade silicons (SiGS) by silver assist-electrochemical etching. SiNWs arrays exhibit an excellent antireflection character with an overall reflectance of 2% in the range from 300 to 1000 nm. More importantly, the effective lifetimes of the symmetric SiNWs/Si structures decreased due to the high densities of dangling bonds and surface defects. Surface passivation to overcome lifetime degradation is realized by means of rapid thermal oxidation (RTO). Following rapid oxidation, Fourier Transform Infrared spectroscopy reveals that oxygen diffusion is enhanced inside silicon nanowires where the morphological structure is preserved during RTO. Moreover, it is shown that even the rapid thermal oxidation process is not effective to recover initial τ_eff due to the high density of imperfections involved during nanowires formation and the contamination level induced by silver. The interdiffusion between residual silver and metal contaminants in the core of the nanowire can probably limit the passivation effect due to the segregation of metal atoms at SiO₂ and to the redistribution of both impurities across the wire.     

Spectral Discretization of the Axisymmetric Vorticity,Velocity and Pressure Formulation of the Stokes Problem

We consider the Stokes problem in a three-dimensional axisymmetric bounded domain with non standard conditions which involve the normal component of the velocity and tangential component of the vorticity. We reduce the three-dimensional problem into a two-dimensional one and we write a variational formulation of it with three independent unknowns: the vorticity, the velocity and the pressure. Then we propose a discretization by spectral methods which relies on this formulation. A detailed numerical analysis leads to optimal error estimates for the three unknowns and numerical experiments confirm the interest of the discretization.