Microstructure and Growth Model for Rice-Hull-Derived SiC Whiskers

The microstructure of silicon carbide whiskers grown from rice hulls has been studied using methods of high-resolution analytical electron microscopy. Small, partially crystalline inclusions (∼10 nm) containing calcium, manganese, and oxygen are concentrated in whisker core regions, while peripheral regions are generally inclusion free. The distinct microphase distribution is evidence of a two-stage growth process in which the core region grows first, followed by normal growth toward whisker sides. Partial dislocations extend radially from the core region to the surface and tend to be paired in V-shaped configurations. Whisker surfaces exhibit microroughness due to a tendency to develop small facets on close-packed planes. The microstructural data obtained from TEM observations are used as a basis for discussion of the mechanisms involved in whisker growth, and a model of the growth process is proposed. The model includes a two-dimensional growth mechanism involving vapor, liquid, and solid phases, although it is significantly different from the classical vapor-liquid-solid (VLS) process of whisker growth.     

Supercritical CO2 Extraction of Annatto (Bixa orellana) Pigments and Some Characteristics of the Color Extracts

Supercritical CO₂ (SC-CO₂) was used to extract natural food colors from Annatto (Bixa orellana) seeds with different pressures and temperatures. Results from the reverse thin-layer chromatographic separation and GC/MS revealed that SC-CO₂ extracts were composed mainly of bixin, geranylgeraniol and norbixin. Differences in absolute values of solubility parameters (SPD) between these main compounds and SC-CO₂ indicated bixin was more easily extracted than norbixin under conditions used. A higher yield of total pigments was obtained at extraction pressure above 310 bar than at 210 bar and 50°C.     

A New Calculation Method for Distinguishing Endo- from Exo-Polygalacturonases

A method which uses a comparison ratio (CR) of fluidity (1/n)sp)/μmoles reducing groups is proposed for comparing and distinguishing endo- and exo-polygalacturonases (PGases). This method is faster, easier and as accurate a method as the percent hydrolysis method. The CR method can also be used as a measure of the purity of endo- PGase with respect to exo-PGase.     

Manipulation of Dhaka cheese curd and effects on cheese quality

Dhaka cheese is a semihard artisanal variety originating from Bangladesh where manual curd kneading is a normal stage in its manufacture. Dhaka cheeses were produced with different degrees of curd kneading to quantify the curd manipulation process in terms of pressure and to standardise the length of operation. The effect of manipulation on the composition, rheology, texture and microstructure of fresh cheese was also studied. Manipulation had significant effects (P < 0.05–0.001) on most of the parameters studied. One minute of curd manipulation was found to be sufficient for Dhaka cheesemaking.     

Pressing technique and its effect on the quality of Dhaka cheese

Dhaka cheese is a semihard artisanal variety made mainly from bovine milk, using very simple pressing methods. Experimental cheeses were pressed at gauge pressures up to 31 kPa for 12 h at 24 °C and 70% RH. These cheeses were subsequently examined for their compositional, textural and rheological properties plus their microstructures investigated by confocal laser microscopy. The cheese pressed at 15.6 kPa was found to have the best compositional and structural properties.     

FLAVEDO AND ALBEDO CHANGES IN 'EUREKA' LEMONS CAUSED BY STATIC COMPRESSION AND IMPACT LOADING

Mature lemons ( Citrus limon (L.) Burm. 'Eureka') were subjected to increasing compression, impact and static loading, then stored at either 1C, 13C or 20C for 14 or 28 days. Following storage, fruit were assessed for cellular damage associated with the site of loading. Slow compression (1.7cm plunger driven at a loading rate of 200 mm min⁻¹) resulted in cell damage in the mid to lower flavedo tissue. Tissue failure was characterised by cell rupture, with minor cell deformation and compression associated with damage to the oil glands. Impact loading caused relatively little lower flavedo damage, with most of the injury associated with the albedo, the upper flavedo and tissue surrounding the oil glands. Damaged albedo cells formed a distinct zone of ruptured and laterally compressed tissue which increased in area with drop height. Static loading (3.7 kg top weight) resulted in a similar mode of failure to that of impact loading, with extensive cellular damage observed in the lower albedo. Injury was distinct in that cells were not laterally compressed and flavedo damage was far more pronounced. While most of the tissue damage was directly     

AN EXPERIMENTAL STUDY OF POLYMER DIFFUSION IN CONCENTRATED SOLUTION: IMPLICATIONS FOR DIFFUSION IN POLYMERIZATION

The Trommsdorf or gel effect in free radical polymerization is due to the fact that the termination reaction becomes strongly diffusion controlled above a critical concentration associated with the onset of molecular entanglements. Therefore, an understanding of polymer self-diffusion in entangled systems becomes essential to understanding the Trommsdorf effect. Our group has previously proposed a molecular model for the gel effect which uses a specific theory for polymer diffusion (reptution). The present work represents an experimental attack on the same problem Experimental studies of polymer self-diffusion in entangled systems are scarce. Quasielastic light scattering from ternary systems composed of solvent(l)-polymer(2)-polymer(3), in which species (3) is isorefractive to the solvent (i.e. 0n/0c ₃ = 0), offers an attractive way to study the tracer diffusion coefficient of species (2) in a binary mixture of composition c ₃. In regimes of low momentum transfer (qR _G < 1,) where q is the scattered wave vector and R _G is the polymer radius of gyration, we have shown that the correlation function of the scattered electric field should decay with a single exponential decay time, given by (D₂₂ q ²)^?1 where D ₂₂(c ₂, c ₃) is the main ternary diffusion coefficient of component (2). Extrapolation to zero concentration of 2) at fixed concentration of (3) yields the tracer diffusion coefficient of (2) in the binary mixture of (1) and (3). The systems toluene(l)-polystyrene(2)-polymethylmethacrylate(3) (0n/0c ₃ ≈ 0.007 at 25°C) and toluene(l)-polystyrene(2)-polyvinylmethylether (3) (0n/0c ₃ ≈ 0.012 at 60°C) very nearly satisfy the above criteria. In both systems, we have found that the tracer diffusion coefficient of the polystyrene decreases with increasing concentration of the isorefractive polymer. Further studies have focused upon the dependence of the tracer diffusion coefficient upon polystyrene molecular weight, and upon the effect of incomplete index matching.     

A phase-plate mode transducer for TE1n gyrotron modes

A means is described to increase the on-axis component of the far-field energy pattern of radiation emitted from the open end of a circular waveguide containing a high order TE_1n gyrotron mode. While the sidelobe power is higher than that of some other approaches, this technique is relatively broadband and compact, and should be easy to fabricate. The method uses a phase-plate at the output of the waveguide to rectify the negative portion(s) of the electric field of the circular TE mode in the waveguide.     

LACTIC ACID DIPPING FOR INHIBITING MICROBIAL SPOILAGE OF REFRIGERATED CATFISH FILLET PIECES

Subdivided catfish fillets were dipped in chilled (7°C) solutions of 1.70% and 2.55% (v/v) lactic acid (LA) for 10 min. Control pieces were not dipped. All pieces were individually placed in sterile plastic bags and stored either at 7°C for 3 days or on ice in a 2°C cold room for 6 days. Aerobic plate count (APC) was periodically determined using plate count agar pour plate and Petrifilm? film methods. At 7°C, APC for both LA treatments was significantly (P<0.05) lower than for controls during 3 days of storage. Day 3 APC values for 1.70% and 2.55% LA samples were lower than controls by 1.3 and 2.3 logs, respectively. Similarly, after 6 days at 2°C the APC values for 1.70% and 2.55% LA samples were 1.3 and 3.1 logs lower, respectively, than for control samples. Throughout storage at both temperatures, 2.55% LA samples had significantly (P<0.05) lower APC than 1.70% LA samples. No significant (P<0.05) difference was observed between pour plate and Petrifilm? APC methods, although APC values for the latter method were consistently slightly higher. Untrained sensory evaluation panelists could not consistently distinguish between control and 1.70% LA catfish pieces that were dipped in batter, breaded, and fried. Control, 1.70% LA, and 2.55% LA-dipped pieces were not rated as significantly different (P<0.05) in whiteness of flesh, tartness, and overall flavor acceptability. Acid dipping of catfish could be useful for extending the refrigerated shelf-life of unfrozen catfish fillets.