Polycyanurate networks modified by polyoxytetramethylene glycol

Summary We report results obtained within a collaborative project dealing with the preparation of hybrid polycyanurate/polyoxytetramethylene glycol (PCN/PTMG) networks and the investigation of their structure-property relationships by a variety of experimental techniques. The hybrids were prepared from PCN and PTMG (molar mass 1.000 g/mol) with 10, 20, 30 and 40 wt% PTMG. The degree of incorporation of PTMG into the PCN network was determined by gel fraction measurements. WAXS and SAXS studies had indicated that the materials under investigation are amorphous and exhibit nanostructural heterogeneity, which increases with increasing amount of PTMG. Stress-strain measurements show improvement of the mechanical properties for PTMG contents of 30 and 40%. The focus in this paper is on the detailed investigation of the α relaxation associated with the glass transition in wide ranges of frequency and temperature by dielectric techniques. A single α relaxation was observed in all the compositions shifting systematically to lower temperatures/higher frequencies with increasing PTMG content. The results were systematically analyzed in terms of time scale and relaxation strength of the response and are discussed in terms of plasticization, presence of nanostructural heterogeneities and hybridization. Co-operativity of the α relaxation, quantified in terms of fragility, was found to decrease with increasing amount of PTMG, in correlation with increasing level of nanoheterogenity.     

Local Bending Moment as a Measure of Adhesion: The Blister Test

We propose to characterize joints between materials by the maximum bending moment, M_max, borne just prior to delamination. We suggest to evaluate M_max in the blister test geometry through direct measurement of the blister curvature in the vicinity of the separation line and employ a scanning capacitance microscope for the blister profiling. The methodology and apparatus were tested on measurements of adhesion of two commercial polymer films to Plexiglas and Teflon.     

Dendrimer-encapsulated gold nanoparticles as building blocks for multilayer microshells

We report the effect of gold nanoparticles encapsulated into the shell-forming PAMAM dendrimers on the assembly and properties of multilayer microshells. We demonstrate that the PAMAM-encapsulated gold nanoparticles change dramatically the optical spectroscopic properties of microcapsule dispersions, without significantly affecting the stiffness of microcapsules. Our results indicate that the use of dendrimer-protected nanoparticles as building blocks opens numerous possibilities to vary the composition and diverse properties of microshells without changing their stiffness.     

Filtering Soil Surface and Antenna Effects From GPR Data to Enhance Landmine Detection

The detection of antipersonnel landmines using ground-penetrating radar (GPR) is particularly hindered by the predominant soil surface and antenna reflections. In this paper, we propose a novel approach to filter out these effects from 2-D off-ground monostatic GPR data by adapting and combining the radar antenna subsurface model of Lambot with phase-shift migration. First, the antenna multiple reflections originating from the antenna itself and from the interaction between the antenna and the ground are removed using linear transfer functions. Second, a simulated Green's function accounting for the surface reflection is subtracted. The Green's function is derived from the estimated soil surface dielectric permittivity using full-wave inversion of the radar signal for a measurement taken in a local landmine-free area. Third, off-ground phase-shift migration is performed on the 2-D data to filter the effect of the antenna radiation pattern. We validate the approach in laboratory conditions for four differently detectable landmines embedded in a sandy soil. Compared to traditional background subtraction, this new filtering method permits a better differentiation of the landmine and estimation of its depth and geometrical properties. This is particularly beneficial for the detection of landmines in low-contrast conditions     

Study of the Interaction of Adhesion-Active Copper-Silver Alloy PSR-40 with Stainless Steel of the Austenitic Class

Interaction of molten copper-silver alloy PSR-40 with stainless steel 1Kh18N9T is studied in relation to melt temperature (700-800°C) and contact time (10-40 min). It is established that alloy components diffuse into the steel. The depth of their penetration and the degree of interaction with steel increase with an increase in temperature and contact time. As a result of this with contact of the structural components to more than 20 min and a temperature above 780°C there is formation of chemical compounds with a higher hardness at the alloy-steel interface. Therefore impregnation in air for porous carcasses made from stainless steel 1Kh18N9T fibers with molten copper-silver alloy above these parameters is undesirable.     

Detection of amines with chromium-doped WO3 mesoporous material

Chromium-doped mesoporous tungsten trioxide – with KIT-6 structure – was prepared through a chemical route. The resulting material was deposited on a micromechanically fabricated hot-plate and tested as a sensor for ammonia and trimethylamine in the temperature range of 200–500 °C. Maximum response was reached at 350 and 450 °C for ammonia and TMA, respectively. It was also found that the sensor shows a non-linear cross-sensitivity to the gases.     

Processing of complexly shaped multiply connected domains in finite element mesh generation

Large number of finite element models in modern materials science and engineering is defined on complexly shaped domains, quite often multiply connected. Generation of quality finite element meshes on such domains, especially in cases when the mesh must be 100% quadrilateral, is highly problematic. This paper describes mathematical fundamentals and practical implementation of a powerful method and algorithm allowing transformation of multiply connected domains of arbitrary geometrical complexity into a set of simple domains; the latter can then be processed by broadly available finite element mesh generators. The developed method was applied to a number of complex geometries, including those arising in analysis of parasitic inductances and capacitances in printed circuit boards. The quality of practical results produced by the method and its programming implementation provide evidence that the algorithm can be applied to other finite element models with various physical backgrounds.     

Effect of minimal processing on the textural and structural properties of fresh‐cut pears

The feasibility of minimal processing and modified atmosphere packaging to preserve the original textural quality of fresh‐cut pears was evaluated throughout storage under refrigeration. Fresh‐cut pear firmness could be extended up to several weeks with low‐O₂ atmospheres. A packaging atmosphere of 100% N₂ combined with the use of plastic bags with an O₂ permeability of 15 cm³ m^?2 bar^?1 day^?1 maintained cell structure and partially avoided membrane breakdown and exudate accumulation in intercellular spaces. Under the other conditions studied, pear texture underwent dramatic deterioration, which could be related to complete inundation of the extracellular environment. Firmness decreased linearly throughout the storage period studied, with rate constants ranging from 0.0097 to 0.040 day^?1. The consideration of other textural variables also gave valuable information, similar to that provided by firmness data. © 2002 Society of Chemical Industry     

MAPKs Are Highly Abundant but Do Not Contribute to α1-Adrenergic Contraction of Rat Saphenous Arteries in the Early Postnatal Period

Previously, the abundance of p42/44 and p38 MAPK proteins had been shown to be higher in arteries of 1- to 2-week-old compared to 2- to 3-month-old rats. However, the role of MAPKs in vascular tone regulation in early ontogenesis remains largely unexplored. We tested the hypothesis that the contribution of p42/44 and p38 MAPKs to the contraction of peripheral arteries is higher in the early postnatal period compared to adulthood. Saphenous arteries of 1- to 2-week-old and 2- to 3-month-old rats were studied using wire myography and western blotting. The α₁-adrenoceptor agonist methoxamine did not increase the phosphorylation level of p38 MAPK in either 1- to 2-week-old or 2- to 3-month-old rats. Accordingly, inhibition of p38 MAPK did not affect arterial contraction to methoxamine in either age group. Methoxamine increased the phosphorylation level of p42/44 MAPKs in arteries of 2- to 3-month-old and of p44 MAPK in 1- to 2-week-old rats. Inhibition of p42/44 MAPKs reduced methoxamine-induced contractions in arteries of 2- to 3-month-old, but not 1- to 2-week-old rats. Thus, despite a high abundance in arterial tissue, p38 and p42/44 MAPKs do not regulate contraction of the saphenous artery in the early postnatal period. However, p42/44 MAPK activity contributes to arterial contractions in adult rats.