Influence of solvent and temperature on extraction of phenolic compounds from grape seed,antioxidant activity and colour of extract

This study was aimed to investigate the influence of solvent (water and ethanol in concentration: 50%, 70% and 96%) and extraction temperature (25–80) °C on polyphenols extraction of grape seed (Vitis vinifera L. cv. “Frankovka”) cultivated in Eastern Croatia. The best results were reached using 50% ethanol at 80 °C. The most abundant individual polyphenolic compound was catechin which makes the average of 45.11% of the total phenolic content followed by epicatechin (34.45%), procyanidin B₂ (12.90%), gallic acid (5.34%), gallocatechin (1.58%), epicatechin gallate (1.01%). The antioxidant activity of extracts was determined by DPPH‐method and it was highly dependent on extraction solvent and temperature. The total extractable proanthocyanidins content of extract had the highest positive correlation (r = 0.994) with antioxidant activity, which indicated that these compounds might be the most important antioxidant in examined grape seed extracts. Relationship between phenolic content and colour of extracts was observed.     

Bartlett Corrections for Unit Root Test Statistics

Bartlett corrections of the log likelihood ratio test for a unit root in an AR(1) process, as well as for some asymptotically equivalent tests, are studied. The corrections are obtained by an analytical method. The numerical performance of the results is checked in a simulation study.     

Fast radix-2 division with quotient-digit prediction

An implementation of a radix-2 division unit is presented that uses prediction of the quotient digit. This prediction allows the concurrent computation of the quotient digit and the partial remainder. To achieve a simple quotient-digit selection, resulting in a step time roughly half of that of SRT division (without prediction), a simple estimate of the partial remainder is used, which requires that the divisor be scaled close to unity. This prescaling is simple to implement and increases the execution time by two cycles. We estimate a speed-up of 1.5 with respect to SRT division with redundant remainders.     

On the influence of surface roughness on real area of contact in normal,dry, friction free,rough contact by using a neural network

A model previously developed at LTU was used in order to perform numerical simulations of normal, dry, friction free, linear elastic contact of rough surfaces. A variational approach was followed and the FFT-technique was used to speed up the numerical solution process. Five different steel surfaces were measured using a Wyko optical profilometer and several 2D profiles were taken. The real area of contact and the pressure distribution over the contact length were calculated for all the 2D profiles. A new slope parameter was defined. An artificial neural network was applied to determine the relationship between the roughness parameters and the real area of contact. The trained model was able to capture the dependence of the real area of contact on the roughness parameters. The ability of the neural network to generalize on unseen data was tested. The neural network was able to prove the correlation between the roughness parameters and the real area of contact.     

Scratch testing of metals and polymers: Experiments and numerics

An experimental and numerical study of the scratch test performed on metals and polymers was conducted. The materials tested, being both metallic and polymeric, were related to the well known Johnson’s parameter, often used to correlate indentation experiments. The aim was to determine whether it was possible to use the numerical approach presented by Wredenberg and Larsson [F. Wredenberg, P.-L. Larsson, On the numerics and correlation of scratch testing, Journal of Mechanics of Materials and Structures 2 (2006) 573–594] to describe the scratch mechanism and of course also to investigate whether or not important scratch quantities can be determined with sufficient accuracy from standard scratch experiments.     

Comments on "Linearization method for finding Cramer-Rao bounds insignal processing" [and reply]

The authors comment that an interesting attempt was made to simplify the derivation of the Cramer-Rao bound (CRB) for the principal parameters in the so-called superimposed-signals-in-noise models. Here, we streamline the derivation in question and then go on to show how it relates to other possible derivations of the CRB. We show that the new derivation can be neatly interpreted as performing a block diagonalization of the CRB matrix, which is a sensible thing to do in the presence of nuisance parameters. Gu (see ibid., vol.48, p.543-545, Feb. 2000) replies that the interesting problem of de-coupling in Cramer-Rao bounds is algebraically and neatly approached in this article, whereas the linearization method is geometrical, with statistical interpretations     

Joint symbol timing and channel estimation for OFDM based WLANs

The orthogonal frequency-division multiplexing access technique has been attracting considerable interest especially for wireless local area networks (WLANs). We consider the joint estimation of the symbol timing, the channel length and the channel-impulse response. A novel estimation algorithm based on maximum-likelihood principles and the generalized Akaike information criterion are proposed. We provide simulation results to illustrate the performance of our proposed algorithm