Interlaminar and intralaminar reinforcement of composite laminates with aligned carbon nanotubes

Three-dimensional reinforcement of woven advanced polymer–matrix composites using aligned carbon nanotubes (CNTs) is explored experimentally and theoretically. Radially-aligned CNTs grown in situ on the surface of fibers in a woven cloth provide significant three-dimensional reinforcement, as measured by Mode I interlaminar fracture testing and tension-bearing experiments. Aligned CNTs bridge the ply interfaces giving enhancement in both initiation and steady-state toughness, improving the already tough system by 76% in steady state (more than 1.5 kJ/m² increase). CNT pull-out on the crack faces is the observed toughening mechanism, and an analytical model is correlated to the experimental fracture data. In the plane of the laminate, aligned CNTs enhance the tension-bearing response with increases of: 19% in bearing stiffness, 9% in critical strength, and 5% in ultimate strength accompanied by a clear change in failure mode from shear-out failure (matrix dominated) without CNTs to tensile fracture (fiber dominated) with CNTs.     

The 1995 North American Interagency Intercomparison of Ultraviolet Monitoring Spectroradiometers

Concern over stratospheric ozone depletion has prompted several government agencies in North America to establish networks of spectroradiometers for monitoring solar ultraviolet irradiance at the surface of the Earth. To assess the ability of spectroradiometers to accurately measure solar ultraviolet irradiance, and to compare the results between instruments of different monitoring networks, the second North American Intercomparison of Ultraviolet Monitoring Spectroradiometers was held June 12 to 23, 1995 at Table Mountain outside Boulder, Colorado, USA. This Intercomparison was coordinated by the National Institute of Standards and Technology (NIST) and the National Oceanic and Atmospheric Administration (NOAA). Participating agencies were the Environmental Protection Agency; the National Science Foundation; the Smithsonian Environmental Research Center; the Department of Agriculture; and the Atmospheric Environment Service, Canada. Instruments were characterized for wavelength uncertainty, bandwidth, stray-light rejection, and spectral irradiance responsivity, the latter with a NIST standard lamp operating in a specially designed field calibration unit. The spectral irradiance responsivity, determined once indoors and twice outdoors, demonstrated that while the responsivities changed upon moving the instruments, they were relatively stable when the instruments remained outdoors. Synchronized spectral scans of the solar irradiance were performed over several days. Using the spectral irradiance responsivities determined with the NIST standard lamp and three different convolution functions to account for the different bandwidths of the instruments, the measured solar irradiances generally agreed to within 3 %.     

Depressive symptoms, social support, and personal health behaviors in young men and women.

This study investigated the relationship of depressive symptoms, social support, and a range of personal health behaviors in 2,091 male and 3,438 female university students from 16 countries. Depressive symptoms and social support were measured using the short Beck Depression Inventory and the Social Support Questionnaire; 9 personal health behaviors were also assessed. After the authors took age, social support, and clustering by country into account, depressive symptoms were significantly associated with lack of physical activity, not eating breakfast, irregular sleep hours, and not using a seat belt in both men and women, and additionally with smoking, not eating fruit, and not using sunscreen among women. Low social support was independently associated with low alcohol consumption, lack of physical activity, irregular sleep hours, and not using a seat belt in men and women. Bidirectional causal pathways are likely to link health behaviors with depressed mood. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A numerical study on the effective thermal conductivity of biological fluids containing single-walled carbon nanotubes

Thermal death of cancerous cells may be induced by radiating single-walled carbon nanotubes (SWNTs) selectively attached via functionalization to the targeted cells. A distribution of SWNTs inside cancerous cells, on their surface, or in the inter-cellular fluid may occur during this treatment process. This work applies a random walk algorithm to calculate the effective thermal conductivity of an idealized biological fluid containing SWNTs. The thermal resistance at the interface between the SWNTs and their surroundings is incorporated to make predictions that are required for developing an overall approach to cancerous cell targeting.     

Matrix hybridization in the interlayer for carbon fiber reinforced composites

Polymeric composites have gone through a level of maturity beyond the laboratory stage with the development of the Boeing 787, the structure of which contains more than 50% composites. Nonetheless, a basic understanding of the material used in its primary structure has not been extensively investigated. For instance, micromechanical models are inadequate as they always assume an evenly distributed homogeneous matrix, without following classic lamination theory, which assumes constant stress through the laminate thickness. Our program now in its third year at the Polymeric Composites Laboratory in Seattle, supported by industry as well as government agencies, and in collaboration with several universities on a global scale, is developing such concepts for understanding and improving matrices in layered configurations. This effort focuses on the development of interlayer systems used as enablers to improve certain properties of the composite, such as fracture‐toughness and crack‐propagation inhibition. POLYM. COMPOS., 31:1965–1976, 2010. © 2010 Society of Plastics Engineers.     

Analysis of the effect of mixing vane geometry on the flow in an annular centrifugal contactor

The annular centrifugal contactor is a compact mixer/centrifuge developed for solvent extraction processes for recycling used nuclear fuel. This research effort couples computational fluid dynamics (CFD) modeling with a variety of experimental observations to provide a valid detailed analysis of the flow within the centrifugal contactor. CFD modeling of the free surface flow in the annular mixing zone using the volume-of-fluid method combined with large eddy simulation of turbulence was found to have very good agreement with the experimental measurements. A detailed comparative analysis of the flow and mixing with different housing vane geometries (four straight vanes, eight straight vanes, and curved vanes) was performed. Two additional variations on the eight straight vane geometry were also simulated. This analysis determined that at the simulated moderate flow rate the four straight mixing vane geometry has greater mixing and fluid residence time as compared to the other mixing vane configurations. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Flexural fatigue of marine laminates reinforced with woven roving of E-glass and of Kevlar® 49 aramid

A comparison of the flexural fatigue characteristics of E-glass and Kevlar® 49 aramid in polyester and vinyl ester resin hand lay-ups typical of boat hull laminates is presented. Data on unidirectional E-glass and aramid composites from epoxy preimpregnated tapes are reported for comparison. The data indicate that while the initial flexural strength of E-glass woven roving laminates is greater than that of aramid laminates, the runout stress of aramid laminates at 10⁶ fatigue cycles is similar or superior to glass. S-N curves for aramid laminates are flatter indicating better flexural fatigue resistance.     

Fruit and vegetable consumption, nutritional knowledge and beliefs in mothers and children

Increasing fruit and vegetable consumption is an important health behaviour. Parental and other psychosocial influences on children's fruit and vegetable consumption are poorly understood. The contribution of a variety of psychosocial and environmental factors to consumption of fruit and vegetables by children aged 9-11 years was explored. Ninety-two mothers and children (48 girls and 44 boys) were recruited via urban primary health-care practices. Socio-economic and educational level, nutritional knowledge and health- and diet-related beliefs and attitudes were assessed in mothers and children by questionnaires and semistructured interviews. Mothers> diets were measured by a food frequency questionnaire, while children's diets were assessed by 3-day diaries (N=80). The pattern of influence of the various measures on fruit and vegetable consumption was compared with that on children's confectionery intake. The children's intakes of macronutrients were typical for the U.K. (37% fat, 50% carbohydrate and 13% protein by energy; 12 g/day fibre), while median fruit, fruit juice and vegetable intake amounted to about 2.5 servings/day. Univariate correlations and subsequent multiple regression analyses revealed quite different influences on the three food types. Independent predictors of children's fruit intake included mothers> nutritional knowledge (beta=0.37), mothers> frequency of fruit consumption (beta=0.30) and mothers> attitudinal conviction that increasing fruit and vegetable consumption by their children could reduce their risk of developing cancer (beta=0.27; multiple r2=0.37,p<0.0001). Children's vegetable consumption was independently explained by the child's liking for commonly eaten vegetables (beta=0.36) and the mother's belief in the importance of disease prevention when choosing her child's food (beta=-0.27 r2=0.20,p<0.001). Children's confectionery consumption was predicted by the mother's liking for confectionery (beta=0.32) and the children's concern for health in choosing what to eat (beta=-0.26 r2=0.16, p<0.005). Children's consumption of fruit and vegetables are related to different psychosocial and environmental factors. Promotion of this behaviour may require attention to nutritional education and child feeding strategies of parents.