Microfoams based on castor oil polyurethanes and vegetable fibers

This work was focused on the production and characterization of microcellular polyurethane (PU) composites reinforced with pine wood‐fibers or with hemp, which can be applied to the manufacture of car interior panels, or acoustic insulation panels for the construction industry. The polymers selected for the study were crosslinked PUs, synthesized from a castor oil‐based polyol, with the formulations adjusted to obtain different foaming levels. Microfoamed composites with preferential orientation were prepared from long hemp fibers. Also, samples with random arrangement of short hemp and wood fibers were obtained. The morphology of the composites was analyzed by scanning electron microscopy. The mechanical performance of the reinforced foams was studied through three point bending and dynamic mechanical tests. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Bandwidth improvement of rat‐race couplers having left‐handed transmission‐line sections

A novel broadband rat‐race coupler has been investigated. The coupler utilizes an artificial left‐handed transmission line section for broadband phase response realization. Moreover, a narrowband model of left‐handed section has been shown to prove the couplers equivalent circuit at the center frequency. To broaden the operational bandwidth multisection quarter‐wave transformers have been proposed. The exemplary rat‐race coupler with two‐section impedance transformers has been designed and manufactured. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:341–347, 2014.     

Effects of crosslinking on thermal and mechanical properties of polyurethanes

The effects of chemical crosslinking on the thermal and dynamic mechanical properties of a polyurethane system were examined. The polyurethanes were prepared from poly(propylene glycol), a diol; trimethylolpropane propoxylate, a triol; and poly(propylene glycol), tolylene 2,4‐diisocyanate terminated, a diisocyanate monomer. The crosslink density was controlled by varying the triol concentration from 10 to 70 mol % and the isocyanate‐to‐hydroxyl (NCO/OH) ratio from 1.0 to 1.3. All the samples had one glass‐transition temperature and no crystalline regions. In addition, there were larger increases in glass‐transition temperature over the range of triol concentrations studied than over the range of NCO/OH ratios studied. For all samples, the Dibenedetto equation relating glass‐transition temperature to extent of crosslinking fit the data very well. Also, samples with higher crosslink densities had much larger elastic moduli for temperatures above the glass‐transition temperature. By assuming the system was a phantom network, approximate crosslink densities for stoichiometric samples were obtained from the dynamic mechanical data and these agreed fairly well with theoretical predictions. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 212–223, 2002     

Molecular and structural characteristics of cod gelatin films modified with EDC and TGase

Cod gelatin films before and after cross-linking of gelatin with 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) or transglutaminase (TGase) have been characterized by Fourier transform infrared (FT-IR) spectroscopy and differential scanning calorimetry (DSC) analysis. For comparison, a film prepared from unmodified pig gelatin has been also analysed. The difference spectra showed that cod gelatin during the film formation involved first of all water-to-amide hydrogen bonds, and the film from pig gelatin contained water-to-amide, amide-to-amide and water-to-water hydrogen bonds. A higher number of hydrogen bonds in the structure of the film from pig gelatin contributed to much better recovering of the helical structure in this film than in the film from cod gelatin, as the peaks at about 1663 cm^?1 in the amide I band and at about 1537 cm^?1 in the amide II band in the second-derivative spectra revealed. The recovered helical structure, in turn, resulted in a significantly higher melting enthalpy value in the case of the film from the pig gelatin. After modification of cod gelatin with EDC or TGase, the inter-chain cross-linkages formed in the films led to the conformation of gelatin with no indications of helical ordering. An increase of melting temperature of gelatin films by 7 °C on EDC and by 10 °C on the TGase modifications was related to the formation of covalent cross-links, and a decrease of glass temperature by 28 °C and 7 °C on EDC and TGase cross-linking, respectively, demonstrated the plasticizing effect of water.     

Predicting pathogen risks to aid beach management: The real value of quantitative microbial risk assessment (QMRA)

There has been an ongoing dilemma for agencies that set criteria for safe recreational waters in how to provide for a seasonal assessment of a beach site versus guidance for day-to-day management. Typically an overall ‘safe’ criterion level is derived from epidemiologic studies of sewage-impacted beaches. The decision criterion is based on a percentile value for a single sample or a moving median of a limited number (e.g. five per month) of routine samples, which are reported at least the day after recreator exposure has occurred. The focus of this paper is how to better undertake day-to-day recreational site monitoring and management. Internationally, good examples exist where predictive empirical regression models (based on rainfall, wind speed/direction, etc.) may provide an estimate of the target faecal indicator density for the day of exposure. However, at recreational swimming sites largely impacted by non-sewage sources of faecal indicators, there is concern that the indicator-illness associations derived from studies at sewage-impacted beaches may be inappropriate. Furthermore, some recent epidemiologic evidence supports the relationship to gastrointestinal (GI) illness with qPCR-derived measures of Bacteroidales/Bacteroides spp. as well as more traditional faecal indicators, but we understand less about the environmental fate of these molecular targets and their relationship to bather risk. Modelling pathogens and indicators within a quantitative microbial risk assessment framework is suggested as a way to explore the large diversity of scenarios for faecal contamination and hydrologic events, such as from waterfowl, agricultural animals, resuspended sediments and from the bathers themselves. Examples are provided that suggest that more site-specific targets derived by QMRA could provide insight, directly translatable to management actions.     

Electric-Field-Induced Crack Initiation From a Notch in a Ferroelectric Ceramic

Crack initiation of ferroelectrics under a cyclic electric field was studied using DCB specimens, which contained through-thickness notches of different lengths. An electric field larger than the coercive field strength of the material was applied and resulted in pop-in of a crack in the direction perpendicular to the field. The length of the pop-in varied with the length of the notch. Finite Element modeling was used to quantify the stresses occurring in the specimen under the application of the electric field. The model took into account the fully coupled ferroelectric and ferroelastic hysteresis behavior. Stress intensity factors were derived from the resulting stress distribution using the weight function method. The results were found to agree well with the experimental data.     

Effect of the oat,horse chestnut,cowherb, soy,quinoa and soapwort extracts on skin-mimicking monolayers and cell lines

The main goal of the study was to compare the effect of aqueous extracts of oat (Avena sativa L.), horse chestnut (Aesculus hippocastanum L.), quinoa (Chenopodium quinoa Willd.), soapwort (Saponaria officinalis L.), cowherb (Vaccaria hispanica [P. Mill.] Rauschert) and soy (Glycine max L.) on model lipid monolayers mimicking the lipid membrane of keratinocytes and intercellular lipids of stratum corneum, and on human skin-related cell lines. Two lipid monolayers, consisting of a dipalmitoylphosphatidylcholine (DPPC) and cholesterol mixture in a molar ratio of 7:3 and Ceramide VI, stearic acid and cholesterol in a molar ratio of 1:1:0.7, and two cell lines (human keratinocyte HaCaT and human skin malignant melanoma A375) were employed. None of the extracts reduced surface pressure below the level achieved for bare monolayers. The strength of the effect on the lipid monolayers (horse chestnut > cowherb > soapwort > soy) points to the existence of some specific interactions responsible for the observed affinity of biosurfactants from the extracts to the lipids in the monolayers. The cytotoxicity tests performed with two model skin cell lines showed that all six plants extracts significantly reduced the cells' viability in a concentration-dependent way. The model lipid monolayers were not solubilized by the investigated surface-active extracts. The latter thus proved interesting candidates for application in mild cleansing cosmetic formulations. Penetration of the monolayers by surface-active components of some extracts, especially horse chestnut, cowherb and soapwort, opens new possibilities for topical delivery of active components.     

The use of intensity-dependent weight functions to “Weberize” $$L^2$$ L 2 -based methods of signal and image approximation

Optimization and Engineering - We consider the problem of modifying $$L^2$$ -based approximations so that they “conform” in a better way to Weber’s model of perception: Given a...