The influence of loose and semianchored siloxane polymer chains on the tack of crosslinked silicone rubber

The influence of addition of nonreactive silicone oil or semianchored silicone polymer on crosslinked poly(dimethylsiloxane) (PDMS) rubber–rubber adhesion was studied. The additives can be considered either a tackifier, or connector molecules, able to cross the interface and entangle. In both cases, it influences the tack of the elastomers. An additional variable is the molecular weight of the additive, which affects the reptation of the polymer chains. Polymer–polymer demixing, which is the result of thermodynamic incompatibility of mixed polymers is another factor that influences tack. It causes the free chains to appear at the surface forming a layer of oil, which actually destroys the tack of the PDMS samples. The resulting tack phenomena as a function of oil, respectively semianchored silicone polymer chains, are very much dependent on the transient nature of the polymer reptation: in many cases the polymers need very long time periods to obtain equilibrium in interphase crossing, or oil sweats out of the crosslinked polymers, forming a liquid layer between the two phases resulting in a low tack value, due to hydrodynamic wetting alone. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Properties of polyethylene films with incorporated benzoic anhydride and/or ethyl and propyl esters of 4-hydroxybenzoic acid and their suitability for food packaging

Benzoic anhydride and ethyl and propyl esters of 4-hydroxybenzoic acid (ETP and PRP, respectively, also termed parabens) incorporated into low density polyethylene (LDPE) film were studied with regard to migration into food and food simulants at 6°C and 25°C, and changes in selected properties of the film were investigated. Antimicrobials were incorporated into polymer film in concentrations of 5g/kg and 10g/kg. The addition of parabens into the polymer was more difficult than benzoic anhydride due to their volatility. For benzoic anhydride, 30-40% and 10-20% of the added amount was found to leach from the film into aqueous and olive oil food simulants, respectively. The migration into both water and olive oil followed a very similar course in the case of parabens. Migration levels over 90% and in the range of 70% to 80%, relative to the amount of agent in the film, were determined for ETP and PRP respectively. The incorporation of antimicrobials into the film significantly changed the functional characteristics of the packaging material, i.e. permeability of oxygen, carbon dioxide and water vapour, tensile strength, coefficient of friction, sealing strength and transparency. Shelf life tests with packaged cheese and toasted bread demonstrated the efficiency of the film containing 10g/kg of BA against mould growth on the food surface during storage at 6°C.     

Thermal Methods of Analysis in Solid Dosage Technology

A survey is given on some aspects of the application of thermoanalytical methods, viz. differential thermal analysis /DTA/, differential scanning calorimetry /DSC/, thermogravimetry /TG/ and derivative TG /DTG/, in solid dosage technology. The review has been preceded by a short characterization of these methods. Further, the usefulness of the thermal methods of analysis in the purity determination, analysis of reaction kinetics of drugs and characterization of suppository and ointment bases has been discussed. The presented studies include also the qualitative and quantitative analysis of solid dosage forms and studies on tablet disintegration. Particular attention has been paid to papers dealing with the possibility of replacing of some expensive and time-consuming methods of classical analysis by rapid and fully automated methods of thermal analysis in control industrial laboratories.     

Jacobian-based repair method for finite element meshes after registration

Registration methods are used in the meshing field to “adapt” a given mesh to a target domain. Finite element method (FEM) is applied to the resulting mesh to compute an approximate solution to the system of partial differential equations (PDE) representing the physical phenomena under study. Prior to FE analysis the Jacobian matrix determinant must be checked for all mesh elements. The value of this Jacobian depends on the configuration of the element nodes. If it is negative for a given node, the element is invalid and therefore the FE analysis cannot be carried out. Similarly, some elements, although valid, can present poor quality regarding Jacobian-based indicator values, such as the Jacobian ratio. Mesh registration procedures are likely to produce invalid and/or poor quality elements if the Jacobian parameter is ignored. To repair invalid and poor quality elements after mesh registration, we propose a relaxation procedure driven by specific validity and quality energy formulations derived from the Jacobian value. The algorithm first recovers mesh validity and further improves elements quality, focusing primarily on nodes that make the elements invalid or of poor quality. Our novel approach has been developed in the context of non-rigid mesh registration and validated on a data set of 60 clinical cases in the context of orthopaedic and orthognathic hard and soft tissues modelling studies. The proposed repair method achieves a valid state of the mesh and also raises the quality of the elements to a level suitable for commercial FE solvers.     

Deposition of thin TiO2 layers on platinum by means of cyclic voltammetry of selected complex Ti(IV) media leading to anatase

Thin layers of anatase TiO₂, up to 1 μm, were produced on the surface of a platinum electrode by means of cycling voltammetry from the aqueous solutions of the peroxo-oxalate complexes and the oxalate complexes of titanium(IV). Mechanisms of TiO₂ electrodeposition as well as different electrochemical reactions causing pH changes at the electrode were studied. The electroreduction processes of hydrogen peroxide and nitrite ion on platinum cause the highest pH changes. Values of the molar ratio of Ti(IV)/H₂O₂ should be kept closely to 0.5.In all cases studied, the electrodeposition led to the partially decomposed amorphous oxalate compounds of titanium(IV), which can be converted into crystalline anatase above 500 °C in air. The thermal behaviour of TiO₂ precursor compounds was examined by DRIFTS and TG-DTA methods. Strong effects of K⁺ and NH₄⁺ ions on the electrodeposition process were found by using of the EQCM technique, Raman spectroscopy and XRD measurements. The ammonium electrolyte warrants purity of the anatase phase.Morphology of the oxide films produced in different solvents was examined by SEM.     

Rope loading in frictional systems

The subject of this paper is the analysis of the maximum loading of ties in multiband frictional systems. Systems like these occur in different branches of mechanical engineering; they are commonly used for passengers elevators. Although the rope system of the elevator contains rockers, in order to equalize the loading of the separate bands, remarkable differences in loading do occur.

Conditions of static equilibrium of the rope system, having the form of inequalities, have been found. Programming methods have been applied, to find the maximum loading of ropes which can occur in different multiband systems. Results of the analysis have been compared with the results of experiments.     

A note on the correctness of the causal ordering algorithm

In this paper we examine in detail the algorithm of Simon [H.A. Simon, Causal ordering and identifiability, in: W.C. Hood, T.C. Koopmans (Eds.), Studies in Econometric Method. Cowles Commission for Research in Economics, Monograph No. 14, John Wiley & Sons, Inc., New York, 1953, pp. 49-74, Chapter III], called the causal ordering algorithm (COA), used for constructing the “causal ordering” of a system given a complete specification of the system in terms of a set of “structural” equations that govern the variables in the system. This algorithm constructs a graphical characterization of the model in a form that we call a partial causal graph. Simon argued in [H.A. Simon, Causal ordering and identifiability, in: W.C. Hood, T.C. Koopmans (Eds.), Studies in Econometric Method. Cowles Commission for Research in Economics, Monograph No. 14, John Wiley & Sons, Inc., New York, 1953, pp. 49-74, Chapter III] and subsequent papers that a graph so generated explicates causal structure among variables in the model. We formalize this claim further by proving that any causal model based on a one-to-one correspondence between equations and variables must be consistent with the COA.     

Precontact 50-kHz vocalizations in male rats during acquisition of sexual experience.

50-kHz ultrasonic vocalizations emitted by male rats during a 5-min period before introduction of a female (precontact vocalizations [PVs]) were analyzed in the context of acquisition of sexual experience. Changes in the main copulatory parameters and their N-methyl-D-aspartate (NMDA) receptor dependence, the role of contact with either anestrous or estrous females, and conditioning to odor and background cues were also investigated. Mount latency (ML) and intromission latency (IL) decreased after the 1st copulatory session, but ejaculation latency (EL) changed significantly only starting from the 4th session onward. The number of PVs gradually increased during the first 3–4 sessions. Blocking of NMDA receptors affected PVs and EL but not ML or IL. After a 5-month break in copulatory sessions, ML remained unchanged, whereas EL increased and the number of PVs decreased significantly. PVs were most robustly elevated by contact with estrous females. Exposure to background cues resulted in a linear decrease in number of PVs during 10 subsequent sessions without exposure to a female. The results suggest that, in the course of acquisition of a sexual experience, PVs reflect a learning process that depends on a rewarding value of sociosexual contact. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Applications of sample preparation techniques in the analysis of pesticides and PCBs in food

Pesticides and polychlorinated biphenyls (PCBs) are found in various parts of the environment in quite small concentrations, but they accumulate and thus become a threat to human health and life. A review is focused on the application of some popular techniques for sample preparation in analysis of these compounds in food. Even with the emergence of advanced techniques of final analysis, complex matrices, such as food, require extensive sample extraction and purification. Traditional sample preparation techniques are time consuming and require large amount of solvents, which are expensive, generate considerable waste, contaminate the sample and can enrich it for analytes. There have been many sample preparation techniques proposed to meet the requirements connected with the multiplicity of food. Optimal sample preparation can reduce analysis time, sources of error, enhance sensitivity and enable unequivocal identification and quantification. Sample extraction and purification techniques are discussed and their most recent applications in food analysis are provided. This review pointed out that sample preparation is the critical step.