Optimisation of extraction of phenolics and antioxidants from black currant leaves and buds and of stability during storage

Health benefits of a diet rich in fruits and vegetables are attributed in part to their contents of phenolics and other antioxidant compounds. In this research, the extraction of phenolics and antioxidant compounds from black currant was optimised for different plant organs. The extraction solvent affected yield: aqueous acetone was better than methanol and acetate or glycine buffer. In aqueous buffer, maximum yields of total phenolics and antioxidant activities were obtained at pH 3. Extraction from lyophilised materials yielded extracts with higher phenolic contents and antioxidant activities.     

Synthesis of N-acryloxysuccinimide copolymers by RAFT polymerization, as reactive building blocks with full control of composition and molecular weights

The reversible addition-fragmentation chain transfer (RAFT) polymerization process was used to synthesize well-defined N-acryloxysuccinimide (NAS) based copolymers, very useful reactive building blocks for various applications. Kinetic studies of RAFT copolymerization of NAS with a bi-substituted acrylamide derivative, N-acryloylmorpholine (NAM), were performed in the presence of tert-butyl dithiobenzoate (tBDB). An excellent control was reached with very high conversions (>95%), molecular weights (MW) up to 80?000 g mol⁻¹ and very narrow molecular weight distributions (MWD) (polydispersity indices, PDI<1.1), as determined by aqueous size exclusion chromatography with on-line light scattering detector (SEC/LS). In addition, the comparison of RAFT and conventional NAM/NAS free radical copolymerization indicated that the apparent reactivity ratios in RAFT are similar to the reactivity ratios determined from conventional copolymerization. An identical azeotropic composition (60/40 NAM/NAS molar ratio) was obtained providing perfectly random poly(NAM-co-NAS) copolymers with full control of composition and MW. These copolymer chains with regularly-distributed reactive functions can be integrated into more complex architectures. As an example, poly[(NAM-co-NAS)-b-NAM] block copolymers with length-varying poly(NAM) block were synthesized with a very efficient control over MW, MWD and composition.     

Signals Induced by Charge Carrier Trapping

Cryogenic germanium detectors used in dark matter searches operate at ranges of low temperature \(<\) 100 \(\mathrm {mK}\) and electric field \(\sim \) 1 \(\mathrm {V/cm}\) such that charge trapping in the bulk of the detector plays a significant role in the net charge collected following a particle interaction. It is shown that in EDELWEISS FID800 detectors, these trapped charges induce residual charge signals that perturb the measurement of the total charge, significantly degrading the energy resolution at high energy. It is also shown that, by reading out the signal on all the electrodes, it is possible to clearly identify these effects and correct the total charge measurement accordingly, resulting in a \(\sim \) 30 % improvement of the resolution at high energy. This effect is demonstrated with data. A simple analytical model based on Shockley-Ramo’s theorem is presented, whereby this effect is due to the position dependence of signals induced by trapped charges.     

Ultrasonic welding of thermoplastic composites: a numerical analysis at the mesoscopic scale relating processing parameters,flow of polymer and quality of adhesion

Ultrasonic continuous welding of thermoplastic composite plates is a very promising process of particular interest for the assembly of aeronautics large parts. Its modeling and simulation however suffers from the difficulty of accounting for the very different time scales that rule the thermo-mechanical phenomena at the level of the adhesion zone. This problem was addressed in our previous works and led to an original simulation tool presented in Levy et al. (Eur J Mech A, Solids 30(4):501–509, 2011a). In this paper, the adopted time-homogenized multiphysical modeling of the flow at the mesoscopic scale of the energy directors is first presented. Then, using the numerical software in a 2D approach, an extensive numerical parametric study of the process is presented. The phenomena allowing welding are confirmed to be an initial strain concentration in the energy director, and the formation of a flowing fold. The influence of the following process parameters are finally investigated: amplitude of vibrations, holding force of the sonotrode, thickness of the plates, radius of curvature at the tip of the director, angle of the director. Process efficiency and weld quality is evaluated through simple indicators such as the equivalent stiffness analysis, the healing degree and the risk of porosity entrapment. The present study, carried at the mesoscopic scale, provides a better understanding of the complex interactions between physical and process parameters and enables to draw important technological conclusions for the design of energy directors.     

Selective metallization of polymers using laser induced surface activation (LISA)��characterization and optimization of porous surface topography

Laser induced selective activation (LISA) is a molded interconnected devices technique for selective metallization of polymers. On the working piece, only the laser-machined area can be metalized in the subsequent plating. The principle of the technology is introduced. Surface analysis was performed on the laser-machined polymer using an Alicona InfiniteFocus? microscope. Based on previous experiments, bearing area curve and its parameters are chosen to characterize the surface. In this paper, by comparison of plateable and non-plateable surfaces, and two types of plateable surface made by different lasers, it is found that the normalized bearing area curve is an effective method to characterize porous surface for the subsequent plating. The normalized parameters are available to make a quantitative analysis.     

Simulation of low rigidity part machining applied to thin-walled structures

The aim of this study is to evaluate the modelling of machining vibrations of thin-walled aluminium workpieces at high productivity rate. The use of numerical simulation is generally aimed at giving optimal cutting conditions for the precision and the surface finish needed. The proposed modelling includes all the ingredients needed for real productive machining of thin-walled parts. It has been tested with a specially designed machining test with high cutting engagement and taking into account all the phenomena involved in the dynamics of cutting. The system has been modelled using several simulation techniques. On the one hand, the milling process was modelled using a dynamic mechanistic model, with time domain simulation. On the other hand, the dynamic parameters of the system were obtained step by step by finite element analysis; thus the variation due to metal removal and the cutting edge position has been accurately taken into account. The results of the simulations were compared to those of the experiments; the discussion is based on the analysis of the cutting forces, the amplitude and the frequency of the vibrations evaluating the presence of chatter. The specific difficulties to perfect simulation of thin-walled workpiece chatter have been finely analysed.     

Modeling of steel and concrete strains between primary cracks for the prediction of cover-controlled cracking in RC-beams

After cracking, the intact concrete between two consecutive primary cracks remains elastic and the maximum concrete stress is less than the tensile strength of concrete. However, under increasing loading, cover-controlled cracks occur at the steel-concrete interface causing a loss of bond and hence a loss of tension stiffness. The cover-controlled cracks are internal concrete cracks that initiate at steel rib location and are contained within the concrete cover. In this paper, steel and concrete strain distribution between two consecutive primary cracks are modeled based on a linear assumed distribution of the bond stress at the steel-concrete interface. The accurate calculation of the tensile concrete strain allows introducing new criteria for cover-control cracking initiation based on a peak value of steel stress calculated at crack location.     

Hidden Markov Modeling of Error Patterns and Soft Outputs for Simulation of Wideband CDMA Transmission Systems

In this paper, a Hidden Markov Modeling (HMM) technique for a fast and accurate simulation of bit errors and soft outputs in wireless communication systems is presented. HMMs with continuous probability distributions are considered. Soft outputs and bit errors are combined to error patterns. We focus on binary phase–shift keying (BPSK) modulation for direct–sequence spread spectrum (code–division multiple access, CDMA) transmission as proposed e.g. for the third generation wireless communication system UMTS (uplink for the frequency division duplex mode (FDD)). Comparisons of simulated bit error rates for HMM models and Rake receivers are shown for AWGN, flat fading, and vehicular channel conditions. In order to assess the ability of the HMM to describe the dynamical behaviour of the channel a comparison for transmission with interleaving and convolutional coding is presented. Furthermore calculated autocorrelation functions of the error patterns and error gap distributions corresponding to the Rake receiver and to the HMM, respectively, are presented. Our investigations show a strong dependence of the required HMM order on E_b/N₀ and the channel conditions. The degree of accordance of the HMM outputs and the training data is examined based on calculated statistical scoring indicators.     

An improved Wigner Monte-Carlo technique for the self-consistent simulation of RTDs

We present an original approach to including quantum transport into classical Ensemble Monte Carlo (EMC) simulations. The method, based on the Wigner transport equation, is fully self-consistent, and includes impurity and phonon scattering according to the Fermi Golden rule. It is inspired by an approach suggested by Shifren et al. [IEEE Trans. Electron Dev. 50, 769 (2003)], with some major improvements that make possible successful comparison with other simulation techniques and experiments.