Thermoplastic matrix sheet composites

Until recently, most high performance composites have been made with low-viscosity thermosetting polymers. These polymers are ideally suited for producing composites in low production quantities because a wide variety of custom shapes can be manufactured without a high degree of mechanization. As the demand for composites increases, there is a need to develop high-volume production techniques. Thermoplastic polymer-based composites are better suited to high-volume production than thermoset-based composites because only heat and pressure are needed to form parts; no chemical reaction is required. Thermoplastic matrix composites are not well suited for low-volume production runs because the need to handle high temperatures and pressures demands equipment that is best utilized for large production runs. In addition to processing advantages, thermoplastic matrix composites exhibit improved impact strength and chemical resistance over most thermoset-based composites. In the course of this work, composites reinforced with long and continuous glass fibers were produced that had tensile strengths as high as 270 MPa, tensile moduli of 16.2 GPa, and notched Izod impact strengths of 11.1 J/cm.     

Factors influencing ocular motility during the performance of cognitive tasks.

Examined the relationship between ocular motility and specific cognitive processes in 2 experiments, using 50 undergraduates. In Exp I, eye movements (EMs) were videotaped as Ss attempted to answer verbal, visuospatial, or musical questions. Visuospatial questions elicited a lower lateral EM rate (EMR) and fewer vertical EMs than did verbal or musical questions. Results support a model that attributes ocular quiescence to interference between visual imagery and visual perception. In Exp II, lateral EMs were recorded electrically as Ss attempted to answer low-, moderate-, and high-imagery questions that required either a constrained or an unconstrained memory search. Constrained questions elicited a lower EMR than did unconstrained questions even when the effect of imagery was eliminated. Stimulus materials for the experiments are appended. (French abstract) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Catchment-scale quantification of hyporheic denitrification using an isotopic and solute flux approach

A dual-isotope and solute flux mass-balance was used to elucidate the processes that lead to attenuation of nitrogen contamination in an agriculturally impacted river. The River Wensum drains a lowland catchment with an area of 570 km2 in East Anglia, eastern England. Analysis of nitrate concentration, δ1?N(NO?) and δ1?O(NO?) of samples from the River Wensum collected from upstream locations to the catchment outlet through all seasons and flow conditions showed a consistent pattern of increasing isotope values with decreasing nitrate concentrations downstream. δ1?N(NO?) and δ1?O(NO?) of catchment surface water and groundwater samples revealed a dominant influence from microbially cycled and nitrified source-nitrogen, which results in high nitrate concentrations in Chalk groundwater and upstream in the River Wensum. Denitrification of Chalk groundwater-baseflow in the hyporheic zone results in the downstream trend observed in the river. Hyporheic denitrification is estimated to remove 931 kg/day of nitrate-nitrogen by the catchment outlet, representing 31% of the potential riverine nitrate load. The use of dual-isotope and solute flux modeling at the catchment scale is a novel application to quantify denitrification within the river valley, demonstrating the importance of hyporheic zone processes in attenuating the impacts of anthropogenic contamination of hydrologic systems.     

Molecular executors of cell death--differential intrarenal expression of Fas ligand, Fas, granzyme B, and perforin during acute and/or chronic rejection of human renal allografts

BACKGROUND: Changes in peripheral thyroid hormone concentration and metabolism can occur in euthyroid patients suffering from severe non-thyroidal illnesses. Recently, sick euthyroid syndrome has been reported in patients suffering from advanced heart failure. AIM: This study was to evaluate prospectively the presence and pathophysiological implications of sick euthyroid syndrome in moderate-to-severe chronic heart failure patients. METHODS: The study population were 199 chronic heart failure patients admitted over a 2-year period to our heart failure unit for assessment of cardiac transplantation. They were closely followed up with clinical and instrumental examinations (including clinical, hormonal, nutritional and cardiac function evaluations). Sick euthyroid syndrome was defined as a serum total triiodothyronine value of less than the lowest normal limit (< 1.23 nmol.l-1) in the presence of a normal serum thyroid stimulating hormone concentration. RESULTS: Sick euthyroid syndrome was found in 36/199 patients (18%). According to the New York Heart Association (NYHA) classification of severity of heart failure, sick euthyroid syndrome patients appear in higher NYHA classes (31% of classes III and IV, vs 7% of class I and II). Such patients also weigh less and are more frequently malnourished. Alterations in cardiac index, ventricular filling pressures, functional impairment, and the liver function parameters, were more significant in sick euthyroid syndrome than in non-sick euthyroid syndrome patients. Serum norepinephrine and atrial natriuretic factor were significantly higher, and insulin significantly lower in the sick euthyroid syndrome group. During follow-up, deaths were significantly more frequent in sick euthyroid syndrome patients (13/27, 48%) than in non-sick euthyroid syndrome (30/141, 21%; P < 0.005). In six sick euthyroid syndrome patients who underwent heart transplantation, mean total triiodothyronine values increased from 0.9 +/- 0.1 before to 1.96 +/- 0.3 nmol.l(-1)post-transplantation (P < 0.05). CONCLUSIONS: In a large and representative population of patients with moderate-to-severe heart failure, sick euthyroid syndrome shows a prevalence of 18%. Its occurrence was related to the degree of functional cardiac impairment, but was not an independent negative prognostic factor. Preliminary results indicate that heart transplantation is associated with reversibility of sick euthyroid syndrome.     

The properties of wet-formed thermoplastic sheet composites

Glass fiber reinforced thermoplastic matrix sheet composites of polypropylene and poly(ethylene terephalate) were produced in a two-stage pilot scale impregnation and consolidation process. The first stage consisted of preparing wet-formed mats of long, discontinuous fibers and polymer powder on an inclined wire paper-making machine. The second stage consisted of consolidating approximately 15 wet-formed mats into a solid composite laminate by the application of heat and pressure in a compression press. The resulting composites had a nominal glass content of 26 wt% (∼12 vol %). Flexural strengths as high as 108 MPa for polyproplene composites and 132 MPa for poly(ethylene terephthalate) composites were measured on specimens cut from stamped parts. The flexural modulus of the polypropylene compsites reached 5.4 Gpa, while the modulus of the stiffest poly(ethylene terephthalate) composite was 8.1 Gpa. The impact properties of the composites were equally good. Polyproplene compsites absorbed up to 62 J/cm during an instrumented falling dart impact test, while poly(ethylene terephthalate) composites absorbed as much as 32 J/cm during the same test.     

Long-fiber-reinforced thermoplastic matrix composites by slurry deposition

A process for producing long-fiber-reinforced thermoplastic matrix composites is described. This process, based on papermaking technology, consists of depositing a mixture of a polymeric powder and reinforcing fibers from an aqueous slurry. The degree of homogeneity of the mixture and the subsequent ability to handle the dried sheet have been significantly improved by the addition of less than 5% pulp fibers, based on solids concentration, to the slurry. The dried sheet is then consolidated into a composite sheet with a continuous matrix phase by the application of heat and then pressure. Tensile properties and the degree of reinforcement efficiency of composites produced by this process have been shown to be comparable to those produced by melt impregnation techniques.