The transverse acoustic impedance of dilute solutions of3He in superfluid4He

The transverse acoustic impedanceZ=R–iX of dilute solutions of³He in superfluid⁴He has been measured at a frequency (/2) of 20.5 MHz at temperaturesT from 30 mK to the transition at T. The³He concentrations studied werec=0.014, 0.031, 0.053, 0.060, and 0.092 below 1 K, thoughc decreased slightly near the point. The impedance was found from the temperature dependence of the quality factor and the resonant frequency of anAT-cut quartz crystal resonator immersed in the liquid. Below 1 K,Z is due to the Fermi gas of³He quasiparticles, and in the collisionless limit, 1 ( is a relaxation time),R remains constant whileX goes to zero. Measurements ofR(c, T) andX(c, T) were analyzed to determine the momentum accommodation coefficient (c, T) and (c, T). The relaxation times were in good agreement with previous work, while (c, T) was independent ofc, but increased from 0.29±0.03 below 0.1 K to 1.0±0.1 above 0.8 K. Various mechanisms are suggested to explain this. Between 1.0 and 1.5 K the³He quasiparticles and the thermally excited rotons are in the hydrodynamic region, 1. Values of the total viscosity (c, T) were obtained and analyzed to give the³He gas viscosity and the³He-³He and roton-³He scattering rates, both of which were energy-dependent. The superfluid healing length a was also measured. Near the point we founda=(0.1±0.03)^–2/3 nm, where =1–T/T, proportional to the phase coherence length . Our data are consistent with the hypothesis that _s/T is a universal constant for superfluid dilute solutions, where _s is the superfluid density. Between 1.0 and 1.8 K we found thata(c, T) was comparable to measurements in³He-⁴He films.     

Structural and dimensional stabilities of tin-bismuth fusible cores

Eutectic tin-bismuth alloys, used as fusible cores for high polymer injection moulding, were studied in order to identify structural and dimensional modifications during ageing at temperatures ranging from 4 to 110°C. Optical and scanning electron microscopies together with X-ray diffraction were used to observe the coarsening of the eutectic structure and to plot an isothermal transformation diagram. Thermal cycles around the eutectic temperature promoted the dissociation of the eutectic structure into light tin dendrites at the top of the ingots and heavy bismuth crystals at the bottom. Differential scanning calorimetry and thermomechanical analysis were performed to observe possible phase transformations.     

Durability studies of surface-modified coir geotextiles

Coir (Cocos nucifera) is a natural fibre known to retain its strength and resist biodegradation far better than other industrial natural fibres. However, systematic studies in this discipline are scarce. Geotextiles are usually exposed to diverse pH, salinity, moisture, and microbial association conditions. In the present work, specific surface modifications of coir geotextiles using a natural agent (cashew nut shell liquid) have been carried out to enhance their long-term performance depending on the end applications. The modified and unmodified geotextiles were subjected to acidic, alkaline, and neutral pH conditions, saline conditions, alternate wetting and drying cycles, and thermal cycles for the assessment of their durability, measured in terms of tensile strength. In situ soil burial studies in a tropical climate were conducted in specially prepared soil to follow the biodegradation behaviour of geotextiles at various depths. The surface-modified geotextiles were found to resist adverse chemical, physical, and biological conditions much better than the unmodified geotextiles. Alkaline conditions marginally accelerated the degradation rates when compared to acidic environments. The saline conditions, as well as alternate wetting and drying conditions, resulted in marginal loss of tensile strength (<7%). The surface-modified geotextiles buried within lower depths of soil under field conditions retained 70–80% of their initial tensile strength after 12 months, whereas the unmodified geotextiles lost 88% strength in four months. The positive impact of surface modification on durability is confirmed by scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis. The results indicate the excellent potential of suitably surface-modified coir geotextiles for long-term use in adverse conditions.     

Analysis of lipid classes by solid-phase extraction and high-performance size-exclusion chromatography

An improved method to analyze lipid classes of edible oils and fats by solid-phase extraction (SPE) and high-performance size-exclusion chromatography (HPSEC) is presented. A mixture of lipid standards was fractionated by the solid-phase extraction procedure (NH₂ phase) into polar and nonpolar fractions; these were then submitted to analysis by HPSEC. The size-exclusion chromatographic columns were three styrene/divinylbenzene columns with pore sizes of 100 Å and 50 Å. Light-scattering was used for the detection system, and the parameters of the detector were optimized to minimize the difference between the responses of the compounds studied. With this procedure it was possible to separate the following lipid classes: triacylglycerols, diacylglycerols, monoacylglycerols and free fatty acids, sterols, sterol esters, tocopherols and carotenoids. Quantitative analysis was studied for a light-scattering detector with several lipid standards of different molecular weights and unsaturation levels.     

High-Temperature Creep Behavior of Mixed Conducting La0.5Sr0.5Fe1−xCoxO3-δ (0.5≤x≤1) Materials

Steady-state compressive creep rate of La_0.5Sr_0.5Fe_0.5Co_0.5O_3−δ (LSFC) and La_0.5Sr_0.5CoO_3−δ (LSC) is reported in the temperature region 900°–1050°C and stress range 5–28 MPa. The stress exponents for the two materials were 1.71±0.18 and 1.24±0.15, respectively. The activation energy for creep was considerably higher for LSC (619±56 kJ/mol) than for LSFC (392±28 kJ/mol). The grain size exponent for LSC was 1.28±0.14. Considerably higher creep rates were observed for both materials in N₂ compared with air. Relaxation by creep of chemical-induced stresses in oxygen-permeable membranes is addressed, especially at low partial pressure of oxygen.