THE KRAMERS CHAIN MODEL FOR POLYMERS

The freely jointed bead-rod chain (the “Kramers chain”) is a fairly realistic model for a macromolecule, and therefore it has been finding increased use in polymer science, particularly in connection with the calculation of rheological properties. The equilibrium configurational distribution function is derived (not a “random-walk” function). Then some of the recent uses of the Kramers chain for understanding the nonequilibrium properties of solutions and melts are summarized.     

发光化学镍复合镀层(英文)

在90℃下,采用含有25 g/L硫酸镍,20 g/L次磷酸钠、35 g/L柠檬酸钠、0～6 g/t,卤磷酸钙和15 g/t.硫酸铵的镀液(pH 5.5),制备了基于卤磷酸钙的发光化学镍复合镀层.研究了镀液pH对复合镀层的沉积速率及卤磷酸钙含量的影响.采用硬度测量、磨损测试、腐蚀试验、紫外光谱,扫描电镜和X射线衍射对复合镀层进行了表征.在最佳卤磷酸钙质量浓度(4 g/L)下所得的复合镀层含77.59%(质量分数)镍、7.58%(质量分数)磷和14.83%(质量分数)卤磷酸钙.由于卤磷酸钙是硬质粒子,随着其嵌入量的增多,复合镀层的硬度增大.在存在卤磷酸钙的条件下,化学镍复合镀层的耐磨和耐蚀性能均显著提高.     

The Conversion of a Boron-Containing Pyrotechnic Mix to a “Ceramic-Like” Material by Electron Beam Interaction

The transformation of a boron-containing pyrotechnic mix to a “ceramic” vitreous-like material by the impingement of an electron beam on a boron-barium chromate pyrotechnic, in a scanning electron microscope, is reported. The thickness of the “ceramic”-like material is ×250 the penetration depth for the electron beam and indicates that a self-sustaining chemical reaction was induced by interaction of the energetic material with the electron beam at temperatures well below the mix's ignition temperature of over 1000?°C. This links with earlier observations on the low-temperature liquefaction of boron to boron suboxides in an electron microscope.     

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     

Modeling the Growth Inhibition Kinetics of Baker's Yeast by Potassium Sorbate Using Statistical Approaches

Potassium sorbate is widely used as a preservative in food products. The inhibition kinetics of yeast growth by potassium sorbate was determined in order to predict the inhibition mechanism and develop an antimicrobial activity model. Linear regression resulted in uncompetitive growth inhibition using different concentrations of nutrients in liquid media containing yeast extract, malt extract (YM broth) and potassium sorbate. At 30°C, constant K_s of YM broth to yeast was 0.254%, maximum growth rate (μ_max) of yeast was 0.008 min^-1, and inhibition constant (K_i) of potassium sorbate to yeast growth was 0.324%. This statistical method could reliably determine the growth inhibition mechanism and kinetics.     

EFFECT OF SODIUM LACTATE, CALCIUM LACTATE AND SODIUM ALGINATE ON BACTERIAL GROWTH AND AMINOPEPTIDASE ACTIVITY

The effects of sodium alginate (0.4 and 0.8%), calcium lactate (0.15 and 0.3%) and sodium lactate (60% solution; 1, 2, 3 and 4%) on growth and aminopeptidase activity of Pseudomonas fragi ATCC 4973 and Salmonella typhimurium in trypticase soy broth or autoclaved ground beef were studied for 5 days at 5°C. Sodium alginate and calcium lactate did not change colony counts of P. fragi or S. typhimurium; and had only slight effects on aminopeptidase activity. Sodium lactate (3 and 4%) showed inhibitory activity on growth and aminopeptidase activity of P. fragi. Sodium lactate also decreased aminopeptidase activity of S. typhimurium but had no major influence on colony counts. In general, aminopeptidase activity was inhibited more than cell multiplication by higher levels of alginate and sodium lactate .     

Estimating Solar Irradiance on Inclined Surfaces: A Review and Assessment of Methodologies

A variety of numerical models for calculating the solar irradiance for an inclined surface are described and evaluated using data for Vancouver, B.C., Canada. While all the hourly models have a common approach for calculating the direct component of the solar irradiance there is a variety of methods for calculating the diffuse irradiance based on the portion of the sky hemisphere within the field of view of the surface. A less significant distinction between the models is in the methods used to calculate the amount of radiation received as a result of reflection from adjacent surfaces.

The paper demonstrates that the principal features of the anisotropic distribution of sky radiance must be included in the numerical computations since the use of the unrealistic isotropic model leads to significant short and long term errors. Inclusion of directional reflectance in the slope irradiance calculations will lead to increased accuracy for the estimated values, with greatest improvement being achieved in the winter months due to a zenith angle dependency on the significance of the directional reflectance.

Errors in estimating the slope irradiance with an anisotropic model are shown to compare favourably with the errors associated with a direct measurement of the solar irradiance.     

ESCHERICHIA COLI O157 IN IRISH FEEDLOT CATTLE: A LONGITUDINAL STUDY INVOLVING PREHARVEST AND HARVEST PHASES OF THE FOOD CHAIN

The aim of this study was to investigate fecal shedding and transmission of E. coli O157 in cohorts of cattle within a feedlot, to assess subsequent contamination of carcasses with this pathogen and to identify risk factors associated with fecal shedding of E. coli O157. A cohort of 133 heifers housed infour adjacent pens was examined over a five month period, from entering the feedlot to slaughter. Individual rectal fecal samples and pen environmental samples were taken at monthly intervals. The entire outer and inner surfaces of a carcass side of each animal were swabbed immediately following slaughter.
E. coli O157 was isolated from 136 (23%) of the 600 rectal fecal samples; 96% of which contained virulent markers. One hundred and sixty environmental samples were examined and E. coli O157 was isolated from 46 (29%), all of which contained virulent markers. E. coli O157 was not isolated from any of the dressed carcasses. The prevalence of E. coli O157 fecal shedding may be related to the pen and E. coli O157 contamination of the pen floor feces, water trough and feed.
E. coli O157 should be considered as a pathogen shed in the feces of a substantial proportion of feedlot cattle. However, with good hygienic practice at harvest, a very low level of this pathogen can be achieved on dressed carcasses.     

Analysis of tannins in seeds and skins of Shiraz grapes throughout berry development

The flavan-3-ol and proanthocyanidin composition of both seeds and skin of Vitis vinifera L. cv. Shiraz grapes was determined by reversed-phase HPLC after acetone extraction and acid-catalysis in the presence of excess phloroglucinol. Samples were taken at weekly intervals from fruit-set until commercial harvest. The main period of proanthocyanidin accumulation in grape seeds occurred immediately after fruit-set with maximum levels observed around veraison. Over two seasons there was variation in both the timing and content of proanthocyanidins in seeds. In skin, proanthocyanidin accumulation occurred from fruit set until 1–2 weeks after veraison. Proanthocyanidin subunit composition was different in seeds and skin and changed during berry development but the mean degree of polymerisation of the tannin polymers in skins was higher than in the seeds at all stages of berry development. Proanthocyanidin levels in both seeds and skin decreased between veraison and harvest. Additional proanthocyanidin subunits were released when the residues remaining after acetone extraction were subjected to direct acid-catalysis in the presence of phloroglucinol. In the seeds, these accounted for much of the post-veraison decrease, but not in grape skin. At harvest, 75% of extractable berry proanthocyanidin was in the seeds. Accumulation of proanthocyanidins in the seeds appears to be independent of that in the skins, but in both tissues synthesis occurs early in berry development and maximum levels are reached around veraison.