Synthesis of carbon fibre-reinforced, silicon carbide composites by soft-solution approach

The aim of the present work centers on synthesizing and characterizing carbon fibre (C_f) reinforced, silicon carbide matrix composites which are considered to have potential applications in aerospace and automobile industry. A series of composites, namely the C_f-SiC, C_f-(SiC+ZrC), C_f-(SiC+ZrB₂), and C_f-(SiC+ZrO₂), have been prepared by a proposed soft-solution approach. This approach involves the use of water-soluble precursors of colloidal silica, sucrose, zirconium oxychloride, and boric acid as sources of silica, carbon, zirconia, and boron oxide, respectively to achieve the desired matrices through drying, carbonization and carbothermal reduction. The prepared powders and the composites were characterized by thermal analysis, X-ray diffraction (XRD), optical microscopy, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) analyses to assess the phase formation and microstructure of the materials, apart from assessment of their tensile properties. The study shows that the soft-solution process yields matrices with finer crystallite sizes, having homogeneous distribution of the constituent phases of either the powders or of the composite matrices. The role of the additional phases on the tensile properties of the composites has been discussed using consideration of thermal stresses at fibre-matrix interface; whereas the role of the carbothermal reduction temperature in determining these properties has been explained using the interfacial characteristics of the fibre-matrix. Addition of ZrO₂ in the matrix of SiC has shown to improve the properties of C_f-SiC composites considerably. The results of this investigation unambiguously demonstrate that aqueous solution-based processing can be used for fabrication of these composites in relatively shorter time in an environmental friendly manner without using any expensive equipment. The approach is capable of yielding composites with different phases in the matrix by simple variation of precursor materials and solutions. The small crystallite sizes, fine particle distribution and low carbothermal reduction temperatures are some of the specific merits of the proposed method.     

MULTIOBJECTIVE DESIGN OPTIMIZATION BY AN EVOLUTIONARY ALGORITHM

This paper presents an evolutionary algorithm for generic multiobjective design optimization problems. The algorithm is based on nondominance of solutions in the objective and constraint space and uses effective mating strategies to improve solutions that are weak in either. Since the methodology is based on nondominance, scaling and aggregation affecting conventional penalty function methods for constraint handling does not arise. The algorithm incorporates intelligent partner selection for cooperative mating. The diversification strategy is based on niching which results in a wide spread of solutions in the parametric space. Results of the algorithm for the design examples clearly illustrate the efficiency of the algorithm in solving multidisciplinary design optimization problems.     

Starter Culture and Time/Temperature of Storage Influences on Quality of Fermented Mutton Sausage

Rate of acid production and ability to produce antimicrobial activity were tested on P. acidilactici H and L. plantarum 27 during growth in a sausage formula mixture. Lactacel 75 was used as control. Starter culture did not affect water activity, pH, ash or protein content, fatty acid composition (except for nonadecanoate), cholesterol content or retention of moisture, protein, fat, ash or fatty acids. Sausages made with P. acidilactici H had the lowest (P<0.05) retention (89.6%) of cholesterol during processing and storage. Sensory evaluation of fermented sausage and bologna prepared from the two starter cultures or from Lactacel 75 indicated both products were acceptable after 50–60 days storage at 4°C.     

THE INFLUENCE OF BIOPRESERVATIVES ON THE BACTERIAL LEVEL OF REFRIGERATED VACUUM PACKAGED BEEF1

Pediocin AcH (1,400 AU/g), nisin (1,400 AU/g), Nisaplin (500 IU/g). Microgard^TM (2%) or Na-lactate (2%) were added to refrigerated vacuum-packaged beef to determine their antibacterial properties. The influence of carbon monoxide treatment on meat color prior to biopreservative treatment was also studied. Pediocin AcH, Nisaplin and nisin had an immediate bactericidal effect on Leuconostoc inoculates. All biopreservatives kept bacterial populations in vacuum-packaged beef within log₁₀ 6/g for up to 8 weeks at 3C. Lactate was the most and Micrograd^TM the least effective in maintaining low bacterial concentrations during an 8 week storage period. The color of fresh beef treated with 10% CO + 90% N₂ for 60 min was stable for up to 4 weeks at 3C; however, beef treated with 100% CO retained its bright red color during 8 week of storage in the vacuum package.     

Environmental scanning electron microscopy of marine aggregates

Marine aggregates were examined for the first time in the hydrated state using an environmental scanning electron microscope (ESEM). Sample preparation consisted of fixation followed by rinsing with distilled water to remove excess salts and fixative. Aggregates were continuously observed at resolutions comparable to conventional scanning electron microscopy through stages of hydration, from completely immersed to desiccated. Because no metallic coating is required, energy-dispersive X-ray spectroscopy (EDXS) can be used to analyse rapidly constituent elements occurring at low concentrations with no spectral interference. Subtle differences in mineral particles were seen in both EDXS spectra and in direct observation of relative hydration, reflecting apparent differences in mineralogy. ESEM enabled examination of effects of desiccation and rehydration on individual particles composed primarily of hydrated polymer and eliminated dehydration artefacts in delicate organisms.     

Effects of Electrical Stimulation and Hot-Boning on Physical Changes, Cooking Time and Losses, and Tenderness of Beet Roasts

Beef semimembranosus and semitendinosus muscles were removed prerigor (1 hr postmortem) and postrigor (7 days postmortem) after one-half of the left and right sides were electrically stimulated. The influence of electrical stimulation and hot-boning upon physical changes; cooking losses; shear force; taste panel evaluation; and time required to heat product to an internal temperature of 63°C was studied. There was no consistent influence of electrical stimulation upon physical changes of prerigor muscles or upon tenderness of pre– or postrigor roasts. Hot-boned and precooked roasts were less tender than cold-boned counterparts. Cooking yields were not altered by electrical stimulation. Prerigor roasts had 9% higher yields than postrigor roasts. Prerigor roasts from electrically stimulated sides required a longer time to cook to 63°C than roasts from the control sides. Hot-boning reduced the length of time of cooking (95 min/kg to 72 mm/kg of raw weight).     

Fatigue crack growth due to overloads in plain concrete using scaling laws

Scaling laws are represented in power law form and can be utilized to extract the characteristic properties of a new phenomenon with the help of self-similar solutions. In this work, an attempt has been made to propose a scaling law analytically, for plain concrete when subjected to variable amplitude loading. Due to the application of overload on concrete structures, acceleration in the crack growth process takes place. A closed form expression has been developed to capture the acceleration in crack growth rate in conjunction with the principles of dimensional analysis and self-similarity. The proposed model accounts for parameters such as, the tensile strength, fracture toughness, overload effect and the structural size. Knowing the governed and the governing parameters of the physical problem and by using the concepts of self-similarity, a relationship is obtained between the different parameters involved. The predicted results are compared with experimental crack growth data for variable amplitude loading and are found to capture the overload effect with sufficient accuracy. Through a sensitivity analysis, fracture toughness is found to be the most dominant parameter in accelerating the crack length due to application of overload.     

SOLUBLE INTRAMUSCULAR COLLAGEN CHARACTERISTICS FROM STRETCHED AND AGED MUSCLE

SUMMARY –Changes occurring during stretching and post-mortem aging of intramuscular collagen from bovine muscle were studied. Sucrose density-gradient ultracentrifugation analyses of denatured guanidine hydrochloride-soluble intramuscular collagen (GSIC) indicated stretching and/or aging muscle changes the molecular structure of the collagen. The quantity of aldehyde cross-links in native GSIC supported this finding. The yield of GSIC from stretched muscles was slightly greater than from normal muscles. A high correlation existed between quantity of each collagen chain component and muscle shear value. Stretched muscle had significantly longer sarcomeres than normal muscles, regardless of aging period. Sarcomere length and muscle tenderness were closely associated in unaged muscle.     

Refractive Index of the Dispersed Phase in Oil-in-Water Emulsions: Its Dependence on Droplet Size and Aging

A simple method of determining the refractive index of the dispersed phase was applied on different gum-stabilized oil-in-water emulsions, in which this refractive index is taken to be equal to that of the continuous phase at (extrapolated) zero optical density point. Refractive indices of dispersed phases were usually lower than those of the oil part alone. In dilute emulsions, the refractive index of the dispersed phase increased with time, while optical density of emulsion decreased. In aged concentrated emulsions, both refractive index and optical density decreased with time. At a given composition, the refractive index and optical density varied directly with droplet size. The results are interpreted in terms of reasonable physical and chemicl phenomena.