Simulation of Adhesive–Dissipative Behavior of a Microparticle Under the Oblique Impact

The adhesive–dissipative behavior of a microparticle under the oblique impact is investigated numerically and the new discrete element method (DEM)-compatible interaction model is elaborated. The modeling approach is based on the Derjaguin–Muller–Toporov model of normal interaction for the adhesive elastic contact. Adhesion hysteresis is specified by the loss of the kinetic energy governed by the fixed amount of the adhesion work, required to separate two adhesive contacting surfaces. This effect is captured in the new interaction model by adding an additional dissipative force component to normal contact during unloading and detachment. The essential feature of this approach, differing from that of the viscous damping model, is that, according to the proposed method, the amount of the dissipated energy is not influenced by the actual initial velocity during the entire contact. The influence of adhesion on slip friction is reflected by considering the adhesive normal force components in the Coulomb's law of friction. The contribution of the adhesion-related dissipation is illustrated by a comparison of the behavior of the attractive–dissipative and attractive–non-dissipative models. The oblique impact of a microparticle on the plane surface at the intermediate impact angle is also investigated numerically. The link between adhesion and friction is supported by the numerical results.     

Investigation of the monomeric and oligomeric molecular forms of human growth hormone and poly-L-lysine using fluorescence anisotropy measurement method

Summary This work illustrates the usefulness of fluorescence anisotropy measurement using a long-lifetime fluorescence label bis-(bipyridine)-5-(isothiocyanatophenanthrolin)-Ru(PF^6-)₂ for the investigation of large macromolecules - human growth hormone forms with different aggregation degree and poly-L-lysine hydrobromides with different molecular weights. Three molecular forms of this hormone – monomeric and two oligomeric (with polymerization degree 3 and 5) – and poly-L-lysine hydrobromides with different molecular weights were for the first time investigated using fluorescence anisotropy measurement by the constant viscosity. Fluorescence anisotropy and rotational correlation time are determined for each substance. Calculated rotational correlation times in investigated media are linear proportional to polymerization degree of molecular forms of the hormone. Relationship between rotational correlation time and molecular weight of random coil structure poly-L-lysines (with similar molecular weights) is nonlinear. It was shown what measured fluorescence anisotropy of the simple mixtures of two labeled molecular forms of the hormone well corresponds with theoretical anisotropy calculated with average values of the anisotropies of the separately investigated pure compounds.     

Dynamic analysis of structures with unilateral constraints: Numerical integration and reduction of structural equations

Structural dynamic equations with unilateral constraints upon the displacements, velocities and accelerations are employed in order to represent vibrating elastic structures with normal, oblique impact and friction interaction points. For obtaining a numerical integration scheme the Lagrange multipliers and a minimum work approach are employed at each time step. The algorithm is presented as an extension of the generalized Newmark scheme. It seems to retain the asymptotic features of the original one. The reduction of the number of dynamic degrees of freedom of the unilaterally constrained structures is carried out by representing the equations of motion in modal co-ordinates of the unconstrained structure and truncating the dynamic contributions of higher modes. The presented techniques have been verified by investigating free longitudinal vibroimpact motion laws of an elastic vibroconverter and free longitudinal and bending vibration of a vibroconverter interacting with a moving rigid body by oblique impact and friction forces.     

Personality correlates of voluntary midcareer change in enterprising occupations.

Compared the personality traits of 45 midcareer changers (mean age 35.5 yrs) with those of 66 vocationally stable controls (mean age 35.4 yrs). Career-change Ss were participants in a career counseling program, while the controls were participants in a selection/promotion assessment program in the same counseling center. All Ss were male and in management and sales occupations (Holland's enterprising type). Personality measures used were the EPPS, the Gordon Personal Profile, and the Gordon Personal Inventory. Discriminant analyses showed an overall significant difference in personality structure between the 2 groups. The traits contributing mostly to this difference were ascendancy, dominance, responsibility, endurance, and order. Midcareer changers were lower on all 5 traits. Results indicate that midcareer change is related to personality incongruity, thus supporting J. L. Holland's (1973) theory of vocational choice and stability. Results also suggest that lower task discipline may be associated with career change. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Impact of lipid oxidation-derived aldehydes and ascorbic acid on the antioxidant activity of model melanoidins

As the heat-induced formation of antioxidants throughout the Maillard reaction is known, this study was undertaken to evaluate the impact of lipid oxidation-derived aldehydes and ascorbic acid in Maillard model systems on the resulting antioxidant activity. For this purpose, various fractions of melanoidin-like polycondensation products were obtained from mixtures of amino acids (glycine, lysine, arginine) and lipid oxidation-derived aldehydes (hexanal, (E)-2-hexenal), in the presence or absence of glucose or ascorbic acid. All fractions showed a significant radical scavenging capacity (DPPH assay) and ferric reducing power (FRAP assay). The activity varied according to the composition of the model system tested, although some similar trends were discovered in both assays applied. The presence of lipid oxidation products in the browning products augmented the antioxidant activity in specific cases. For instance, the combined presence of arginine, hexanal and glucose in heated model systems resulted in a significantly higher antioxidant capacity. With an exception of ascorbic acid-containing model systems, melanoidin-like polycondensation products possessed significantly stronger antioxidant activities than the corresponding unheated initial reactant mixtures. Water-soluble high molecular weight (>12kDa) and nonsoluble fractions comprised the major part of the antioxidants derived from amino acid/lipid oxidation product model systems, with or without glucose or ascorbic acid.     

Isolation,identification and activity of natural antioxidants from horehound (Marrubium vulgare L.) cultivated in Lithuania

In an earlier screening of Lithuanian plants, horehound (Marrubium vulgare) showed good antioxidant activity and as this species is used in herbal teas and cough pastilles it was selected for further investigation. Some fractions of the aerial parts were strong scavengers of the model free radicals DPPH and ABTS⁺. Activity in the β-carotene bleaching assay and the rapeseed oil oxidation assay was lower. Several active compounds were observed in the crude methanol–water extract, and in butanol and methyl tert-butyl ether fractions using HPLC with on-line radical scavenging detection. After multi-step fractionation of these fractions five compounds possessing radical scavenging activity were purified and their structures were elucidated by NMR and MS as 5,6-dihydroxy-7,4′-dimethoxyflavone (syn. ladanein), 7-O-β-glucopyranosyl luteolin, 7-O-β-glucuronyl luteolin, verbascoside and forsythoside B. Their activities were tested in off-line DPPH and ABTS⁺ free radical scavenging assays, and compared with the antioxidants rosmarinic acid and Trolox.     

Rye and Wheat Bran Extracts Isolated with Pressurized Solvents Increase Oxidative Stability and Antioxidant Potential of Beef Meat Hamburgers

Rye and wheat bran extracts containing phenolic compounds and demonstrating high DPPH? (2,2‐diphenyl‐1‐picrylhydrazyl), ABTS^?+ (2,2′‐azino‐bis(3‐ethylbenzthiazoline‐6‐sulphonic acid) scavenging and oxygen radical absorbance capacities (ORAC) were tested in beef hamburgers as possible functional ingredients. Bran extracts significantly increased the indicators of antioxidant potential of meat products and their global antioxidant response (GAR) during physiological in vitro digestion. The extracts also inhibited the formation of oxidation products, hexanal and malondialdehyde, of hamburgers during their storage; however, they did not have significant effect on the growth of microorganisms. Hamburgers with 0.8% wheat bran extract demonstrated the highest antioxidant potential. Some effects of bran extracts on other quality characteristics such as pH, color, formation of metmyoglobin were also observed, however, these effects did not have negative influence on the overall sensory evaluation score of hamburgers. Consequently, the use of bran extracts in meat products may be considered as promising means of increasing oxidative product stability and enriching with functional ingredients which might possess health benefits.     

Mobile application driven consumer engagement

The growing popularity of mobile technologies and applications, lead many companies to develop relations with consumers through mobile applications. Therefore, it is important to understand how to design applications based on consumer preferences. This research seeks to understand which features of mobile applications stimulate consumer engagement and lead to continuous use of mobile applications. This study used an online questionnaire to collect data from 246 respondents. The data was analyzed making use of Structural Equations Modeling (SEM). The results indicate that perception of such features as design solutions and information quality will result in higher engagement leading to continuous usage of mobile applications. Moreover, consumer engagement positively influenced users’ intention to continuous usage of mobile applications. Inconsistent with expectation, consumer interaction and functionality features are not found to be positively related to consumer engagement with mobile applications.     

Formation and characterisation of melanoidin-like polycondensation products from amino acids and lipid oxidation products

Various coloured water-soluble high molecular weight and water-nonsoluble reaction products were isolated from model reactions of an amino acid (glycine or lysine) and a lipid oxidation product (hexanal, (2E)-hexenal, (2E, 4E)-decadienal) with or without glucose. They were characterised by UV–visible absorbance measurements, elementary analysis, and thermal degradation followed by SPME–GC–MS analysis. The UV–visible absorbance spectra before and after dialysis indicated that the most important contributors to the formation of water-soluble coloured material were constituents of the low molecular fraction. Elementary analysis data indicated that a higher amount of nitrogen was incorporated in the high molecular weight fractions as compared to the water-nonsoluble fractions, except for the water-nonsoluble reaction products from amino acid/(2E, 4E)-decadienal interactions, which showed the lowest C/N ratio found. Volatile carbonyl compounds, furans, aliphatic compounds, pyridines, pyrroles and benzene derivatives were the main groups identified in the thermal degradation profile of each fraction tested. Especially pyridines seem typical indicators of amino acid–lipid oxidation product interactions.