The effect of dyeing on the hygral expansion of worsted fabrics — Part 1

The influence of dyebath pH, dyeing time, levelling agents, dyestuff and anti-setting agent on hygral expansion has been investigated. The incorporation of an anti-setting agent in the dyebath minimised increases in hygral expansion resulting from the dyeing process.     

A Raman microprobe study of electrical treeing in polyethylene

The chemical nature of electrical tree growth in a blend of high and low density polyethylene has been studied by confocal Raman microprobe spectroscopy. The observed spectra, which are easily perturbed by the Raman probe beam, can be described in terms of three components, the relative intensities of which vary from place-to-place on the sample. Throughout the body of the tree, the usual Raman bands of polyethylene are seen, but superimposed upon a pronounced fluorescent background. This suggests a degree of material degradation throughout the structure, even where there is no visible evidence of electrical discharge damage or ageing. The individual channels that make up the fractal structure of the tree can then be divided into two distinct categories. Within the core of the tree, their Raman spectra are made up of two elements; fluorescence, plus the G and D bands of sp² hybridized carbon. Here, the tree channels are best thought of as hollow tubules surrounded by a carbonaceous shell. At the tips, the channels are characterized simply by the Raman bands of polyethylene superimposed upon a reduced fluorescent background, irrespective of their size. That is, in this region, the tree channels are simply hollow tubules within the dielectric. The transition between these two structures occurs relatively abruptly. These observations are related to the treeing process.     

Growth and characterization of inTISb for IR-detectors

Epitaxial In_1-xTl_xSb films with compositions up to x = 0.1 have been demonstrated using the metalorganic chemical vapor deposition technique on InSb and GaAs substrates. A specially designed high-temperature source delivery system was used for the low vapor pressure cyclopentadienylthallium source. Tl-compositions in the deposited films were measured by Rutherford backscattering spectroscopy which confirmed the incorporation of up to 10% Tl. Room temperature infrared transmission spectra of InTISb exhibited considerable absorption beyond 7 μm. Photoconductive detectors were fabricated in InTISb films grown on semi-insulating GaAs. Spectral response measurements showed substantial photoresponse at 8.5 to 14 μm. In spite of the large lattice-mismatch (≈14%) between InTISb and GaAs, photoconductive detectors exhibited black-body detectivities (D^* _bb) of 5.0 × 10⁸ cm-Hz^1/2W⁻¹ at 40K.     

The design of biplanar,shielded, minimum energy,or minimum power pulsed B0 coils

By extending the formalism previously developed for the design of unshielded, biplanar gradient coils, shielded biplanarB ₀ coils optimized for homogeneity and either minimum energy or minimum power may be designed. We present results from an integrated approach to shielded biplanar coil design, the results of which are also applicable to gradient coils, enabling the design of shielded coils with a concomitant decrease in total inductance of the coil. Length constraints are also included in the integrated minimization procedure. Results from a preliminary design indicate that high-homogeneity, low-impedance, well-shielded coils result from this design approach.     

Bacterial dynamics during the spontaneous fermentation of cassava dough in gari production

The microbial dynamics and diversity during solid substrate fermentation of cassava, a case study of gari production in West Africa, was investigated. The 16S rDNA gene sequence analysis of the PCR-Denaturing Gradient Gel Electrophoresis (PCR–DGGE) analysis of microbial community DNA and Pulsed Field Gel Electrophoresis (PFGE) of selected isolates as well as culturing techniques using different selective media were used to monitor the bacterial dynamics during cassava fermentation. The V3 variable region of the 16S gene was analyzed and the closest relatives of Lactobacillus plantarum, Lactobacillus fermentum, Lactobacillus pentosus, Lactobacillus acidophilus and Lactobacillus casei were identified by sequencing of the DGGE band amplimers. The DGGE amplimers also revealed the succession and dynamics of LAB; there was a progressive increase in their population proportional to the fermentation period. The analysis of the PFGE band patterns showed that five diverse species of LAB were involved in the fermentation. The representative isolate of each of the PFGE clusters was phenotypicaly identified as L. plantarum, L. fermentum and Leuconostoc mesenteroides by the API 50 CHL sugar fermentation profile. These combinations of parameters identified heterofermentative LAB as bacteria that initiated the fermentation, reduced the pH below four and increased the acidity of the fermentation mash. Information such as this is relevant for the development of starter cultures and predictability of the process for traditional fermented foods and to aid their intermediate and large scale production.     

Volatile profile of Stilton cheeses: Differences between zones within a cheese and dairies

Penicillium roqueforti grows and sporulates during the ripening period of blue cheeses and it is responsible for the typical blue cheese flavour formation. However, the sporulation (blue veins) is taking place in a fraction of the total mass and the cheese matrix is highly heterogeneous. The aroma profiles regarding the three different sections of Stilton cheese, blue veins outer crust and white core, were studied using solvent extraction GC–MS, a headspace GC–MS technique (SPME GC–MS) and direct headspace analysis (APCI–MS). Cheeses from different dairies were analysed, allowing the question of how similar are different batches of cheese from different dairies.     

Ultrasonic determination of the elastic and nonlinear acoustic properties of transition-metal carbide ceramics: TiC and TaC

Pulse-echo overlap measurements of ultrasonic wave velocity have been used to determine the elastic stiffness moduli and related elastic properties of ceramic transition-metal carbides TiC and TaC as functions of temperature in the range 135–295 K and hydrostatic pressure up to 0.2 GPa at room temperature. The carbon concentration of each ceramic has been determined using an oxidation method: the carbon-to-metal atomic ratios are both 0.98. In general, the values determined for the adiabatic bulk modulus (B ^S), shear stiffness (), Young's modulus (E), Poisson's ratio () and acoustic Debye temperature (_D) for the TiC and TaC ceramics agree well with the experimental values determined previously. The temperature dependences of the longitudinal stiffness (C _L) and shear stiffness measured for both ceramics show normal behaviour and can be approximated by a conventional model for vibrational anharmonicity. Both the bulk and Young's moduli of the ceramics increase with decreasing temperature and do not show any unusual effects. The results of measurements of the effects of hydrostatic pressure on the ultrasonic wave velocity have been used to determine the hydrostatic pressure derivatives of elastic stiffnesses and the acoustic-mode Grüneisen parameters. The values determined at 295 K for the hydrostatic pressure derivatives (C _L/P)_{P = 0}, (/P)_{P = 0} and (B ^S/P)_{P = 0} for TiC and TaC ceramics are positive and typical for a stiff solid. The adiabatic bulk modulus B ^S and its hydrostatic pressure derivative (B ^S/P)_{P = 0} of TiC are in good agreement with the results of recent high pressure X-ray diffraction measurements and theoretical calculations. The longitudinal (_L), shear (_S) and mean (^el) acoustic-mode Grüneisen parameters of TiC and TaC ceramics are positive: the zone-centre acoustic phonons stiffen under pressure. The shear _S is much smaller than the longitudinal _L. The relatively larger values estimated for the thermal Grüneisen parameter ^th in comparison to ^el for the TiC and TaC ceramics indicate that the optical phonons have larger Grüneisen parameters. Hence knowledge of the elastic and nonlinear acoustic properties sheds light on the thermal properties of ceramic TiC and TaC.     

An examination of exposure control and content balancing restrictions on item selection in CATs using the partial credit model

The purpose of the present investigation was to systematically examine the effectiveness of the Sympson-Hetter technique and rotated content balancing relative to no exposure control and no content rotation conditions in a computerized adaptive testing system (CAT) based on the partial credit model. A series of simulated fixed and variable length CATs were run using two data sets generated to multiple content areas for three sizes of item pools. The 2 (exposure control) X 2 (content rotation) X 2 (test length) X 3 (item pool size) X 2 (data sets) yielded a total of 48 conditions. Results show that while both procedures can be used with no deleterious effect on measurement precision, the gains in exposure control, pool utilization, and item overlap appear quite modest. Difficulties involved with setting the exposure control parameters in small item pools make questionable the utility of the Sympson-Hetter technique with similar item pools.