Straining phenomena of POY revealed by thermal retraction and other techniques

Partially oriented polyesters yarns (POY) were strained at different strain rates (0.03–12.00 min^?1) and temperatures above and below T_g (3–92°C). Thermal retraction, density, DSC, and WAXS techniques show that strain-induced crystallization takes place by straining at temperatures above as well as below T_g. Above T_g, depending upon the strain rate, two regimes are observed: Below the strain rate of 1.5 min^?1, the flow regime; the degree of crystallinity is reduced as the strain rate increases. Above the strain rate of 1.5 min^?1, the strain-induced crystallization regime; the degree of crystallinity increases as the strain rate increases. Thermal retraction, stress–relaxation, and sonic modulus techniques indicate that, upon cold straining, instead of the original T_g at 65–69°C, two glass transitions occur: an upper T_g (u) and a lower T_g (l). For POY strained at 3°C and at a strain rate of 10 min^?1, the values are 78°C and 37°C, respectively. The higher the strain rate and the lower the straining temperature, the large the difference between T_g (u) and T_g (l).     

Application of the CALPHAD approach to Mg-alloys design

The CALPHAD method can be applied as a tool for both alloy development and process guideline determination. In this study, two Mg alloys were designed, their process parameters derived and, using the CALPHAD method, the final results simulated. These results were later confirmed using tangible experimental methods. It was found that γ$\gamma$- Mg₁₇Al₁₂ precipitates along the grain boundaries (GB), Mg₂Sn forms both along the GB and as fine precipitates in the α$\alpha$-Mg matrix and the addition of Ce mishmetal (MM) leads to the formation of elongated Al- rare earth (RE) precipitates along the GB. The microstructural stability at 200 ^°C is high, showing no decrease in microhardness for 32 days. It is shown that the CALPHAD method considerably reduces the effort of alloy design and that the reliability of the results is high.     

Relating organic fouling of reverse osmosis membranes to intermolecular adhesion forces

Organic fouling of reverse osmosis (RO) membranes and its relation to foulant--foulant intermolecular adhesion forces has been investigated. Alginate and Suwannee River natural organic matter were used as model organic foulants. Atomic force microscopy was utilized to determine the adhesion force between bulk organic foulants and foulants deposited on the membrane surface under various solution chemistries. The measured adhesion force was related to the RO fouling rate determined from fouling experiments under solution chemistries similar to those used in the AFM measurements. A remarkable correlation was obtained between the measured adhesion force and the fouling rate under the solution chemistries investigated. Fouling was more severe at solution chemistries that resulted in larger adhesion forces, namely, lower pH, higher ionic strength, presence of calcium ions (but not magnesium ions), and higher mass ratio of alginate to Suwannee River natural organic matter. The significant adhesion force measured with alginate in the presence of calcium ions indicated the formation of a crossed-linked alginate gel layer during fouling through intermolecular bridging among alginate molecules.     

Air Pollution Emission Inventory Survey for Israel

High ozone levels are regularly measured during summer months over the inland and mountainous regions of Israel. Studies analyzing the back trajectories of air masses responsible for the high ozone levels showed that the precursors originated from the densely populated Israeli coastline. In order to better understand the contribution of those emission sources to ozone production, it is essential to have an accurate emission inventory that can be inputted into a photochemical model. The present paper describes the methods used in preparing an emission inventory for Israel based on information available and published until 1998. The source and accuracy of the data available are described. The calculations performed and the assumptions taken in order to obtain data not directly available are clarified. The sources reported in the inventory were the major polluters (power plants, oil refineries, and cement industries); industry; transportation; and biogenic sources. The pollutants studied were SO₂, NO_x, CO, saturated and unsaturated hydrocarbons, ethylene, isoprene, toluene, xylene, formaldehyde, and aldehydes. The inventory showed that transportation is responsible for almost the entire CO and 30% of the volatile organic compounds emitted, although transportation itself accounts for only a fifth of total fuel consumption. About 75% of the NO_x emitted can be attributed to industrial sources and the remaining 25% to transportation. Model simulations using the emission inventory were performed and compared to data available from a monitoring station situated 30 km east of Tel Aviv. The results showed good agreement, validating the accuracy of the emission inventory. The present emission inventory provides an important database as input to photochemical models used in forecasting ozone levels over Israel.     

Designing block copolymer architectures for targeted membrane performance

Using a combination of block copolymer self-assembly and non-solvent induced phase separation, isoporous ultrafiltration membranes were fabricated from four poly(isoprene-b-styrene-b-4-vinylpyridine) triblock terpolymers with similar block volume fractions but varying in total molar mass from 43 kg/mol to 115 kg/mol to systematically study the effect of polymer size on membrane structure. Small-angle X-ray scattering was used to probe terpolymer solution structure in the dope. All four triblocks displayed solution scattering patterns consistent with a body-centered cubic morphology. After membrane formation, structures were characterized using a combination of scanning electron microscopy and filtration performance tests. Membrane pore densities that ranged from 4.53 × 10¹⁴ to 1.48 × 10¹⁵ pores/m² were observed, which are the highest pore densities yet reported for membranes using self-assembly and non-solvent induced phase separation. Hydraulic permeabilities ranging from 24 to 850 L m⁻² h⁻¹ bar⁻¹ and pore diameters ranging from 7 to 36 nm were determined from permeation and rejection experiments. Both the hydraulic permeability and pore size increased with increasing molar mass of the parent terpolymer. The combination of polymer characterization and membrane transport tests described here demonstrates the ability to rationally design macromolecular structures to target specific performance characteristics in block copolymer derived ultrafiltration membranes.     

Tables of the Inverse Laplace Transform of the Function [... formula ...]

The inverse transform, g(t) = ?^?1(e^?sβ), 0 < β < 1, is a stable law that arises in a number of different applications in chemical physics, polymer physics, solid-state physics, and applied mathematics. Because of its important applications, a number of investigators have suggested approximations to g(t). However, there have so far been no accurately calculated values available for checking or other purposes. We present here tables, accurate to six figures, of g(t) for a number of values of β between 0.25 and 0.999. In addition, since g(t), regarded as a function of β, is uni-modal with a peak occurring at t = t_max we both tabulate and graph t_max and 1/g(t_max) as a function of β, as well as giving polynomial approximations to 1/g(t_max).     

Adhesion kinetics of viable Cryptosporidium parvum oocysts to quartz surfaces

The transport and deposition (adhesion) kinetics of viable Cryptosporidium parvum oocysts onto ultrapure quartz surfaces in a radial stagnation point flow system were investigated. Utilizing an optical microscope and an image-capturing device enabled real time observation of oocyst deposition behavior onto the quartz surface in solutions containing either monovalent (KCl) or divalent (CaCl2) salts. Results showed a significantly lower oocyst deposition rate in the presence of a monovalent salt compared to a divalent salt. With a monovalent salt, oocyst deposition rates and corresponding attachment efficiencies were relatively low, even at high KCl concentrations where Derjaguin-Landau-Verwey-Overbeek (DLVO) theory predicts the absence of an electrostatic energy barrier. On the other hand, in the presence of a divalent salt, oocyst deposition rates increased continuously as the salt concentration was increased over the entire range of ionic strengths investigated. The unusually low deposition rate in a monovalent salt solution is attributed to "electrosteric" repulsion between the Cryptosporidium oocyst and the quartz surface, most likely due to proteins on the oocyst surface that extend into the solution. It is further proposed that specific binding of calcium ions to the oocyst surface functional groups results in charge neutralization and conformational changes of surface proteins that significantly reduce electrosteric repulsion.     

Ozone Levels in Central Israel

Measurements performed during the early summer months of 1988–1991 at a rural site in central Israel, some 50 km east of the highly urbanized coastal region, have shown that during the afternoon hours the area was often under the influence of ozone mixing ratios above the Israel ambient standard (117 ppbv) and occasionally even above 150 ppbv. Analysis of air mass back trajectories has shown that only those air masses passing over the Tel Aviv metropolitan area cause elevated ozone mixing ratios at the rural site. This highly urbanized region emits large amounts of precursors which are entrapped in the air parcels entering Israel under the predominantly westerly wind flows. As these air masses travel inland, sufficient time is available (3–5 h) to allow the photochemical reactions to generate ozone before reaching the rural site. The above hypothesis is further supported by the fact that parallel to the increase of ozone at the rural site, elevated carbon monoxide (up to 0.8 ppmv) and other trace gases were also observed. A significant correlation (R² > 0.8) was found to exist between the ozone mixing ratio and the NO_x concentrations in photochemically aged air masses. In several cases an excess of up to 12 ozone molecules was formed for each NO_x molecule present.     

Influence of growth phase on bacterial deposition: interaction mechanisms in packed-bed column and radial stagnation point flow systems

The influence of bacterial growth stage on cell deposition kinetics has been examined using a mutant of Escherichia coli K12. Two experimental techniques--a packed-bed column and a radial stagnation point flow (RSPF) system--were employed to determine bacterial deposition rates onto quartz surfaces over a wide range of solution ionic strengths. Stationary-phase cells were found to be more adhesive than mid-exponential phase cells in both experimental systems. The divergence in deposition behavior was notably more pronounced in the RSPF than in the packed-bed system. For instance, in the RSPF system, the deposition rate of the stationary-phase cells at 0.03 M ionic strength was 14 times greater than that of the mid-exponential cells. The divergence in the packed-bed system was most significant at 0.01 M, where the deposition rate for the stationary-phase cells was nearly 4 times greater than for the mid-exponential cells. To explain the observed adhesion behavior, the stationary and mid-exponential bacterial cells were characterized for their size, surface charge density, electrophoretic mobility, viability, and hydrophobicity. On the basis of this analysis, it is suggested that the stationary cells have a more heterogeneous distribution of charged functional groups on the bacterial surface than the mid-exponential cells, which results in higher deposition kinetics. Furthermore, because the RSPF system enumerates only bacterial cells retained in primary minima, whereas the packed column captures mostly cells deposited in secondary minima, the difference in the stationary and mid-exponential cell deposition kinetics is much more pronounced in the RSPF system.