The Effect of Agitator Impeller Design on Maximum Shear Stress, and the Resulting Impact on the Flocculation Process

Although it is extensively researched, flocculation in the water-treatment industry lacks a design procedure to assess accurately the performance of the different types of agitator impeller which are available. New high-efficiency, hydrofoil-type impellers offer substantial potential for flocculation duties in many areas, provided that they are applied correctly. This paper highlights the importance of the 'velocity gradient'and the distribution of shear within the agitation system. The objective of the paper is to help engineers to evaluate different types of proprietary impeller designs, using various techniques to examine the shear distribution applied to the system.     

国际航空货运枢纽港:以航空物流为新竞争优势

20世纪80年代以来,经济全球化促进了亚太地区的一些国家和地区的经济迅速增长,同时也带动了区内航空货运的发展.国际航空货运枢纽港(GTP:Global TransPark)是新经济背景下的一种新型货运机场,对提升区域竞争力有着重要的意义.我国有必要建设GTP,以期在21世纪电子商贸及高科技加工工业的发展上抢先建立滩头阵地.逐渐成熟的香港都会经济区有着"一国两制"的特殊地缘政治和制度优势,因而,在亚洲各竞争中的经济区域中,它是建设亚洲首个、也将是最大的GTP的最佳区位.GTP的建成运作可以提升该都会经济区的总体竞争力,加快其经济重构的步伐.结合区内的其它4个机场,珠海机场有条件发展成为GTP.然而,GTP的建设需要有关机场与地方政府间在关税、制空权、后勤服务以及水陆交通等方面进行协调,这将对该都会经济区的内部合作提出更新的挑战.     

Partitioning of polycyclic aromatic hydrocarbons between dissolved and particulate phases in natural waters

Quantities of polycyclic aromatic hydrocarbons (PAH), some of which are carcinogens, enter natural waters in effuents of coke production and other high-temperature industrial pyrolysis processes. Because of their low water solubilities. PAH compounds are generally considered to occur in particulate form in lakes and rivers. However, present studies of ¹⁴C-anthracene adsorption by autoclaved yeast cells indicated that significant fractions of both dissolved and particulate forms of PAH may exist in natural waters. Quantities of anthracene adsorbed exceeded values for PAH adsorption onto mineral surfaces by more than an order of magnitude: suspended organic material may thus be more important than mineral particles in adsorption of PAH compounds. Adsorption was highly dependent upon the yeast cell concentration, and varied widely through the range of suspended organic solids normally encountered in natural waters. The heat of adsorption (5.2 kcal/mole) was characteristic of a physical adsorptive process. Because ecological effects and pathways of dissolved and particulate PAH may differ, adsorptive partitioning may be important in determining PAH hazards to higher organisms in aquatic food chains, and ultimately to man.     

Thermorheological model of a frozen-soil continuum

A method of evaluating the stress-strain state of frozen soils, which takes into account the existence of elastoviscoplastic and temperature deformations over time under variable external effects, is described. Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 4, pp. 10–13, July–August, 1997.     

Large bending of pipes

The computer model developed has been used successfully for studying the large pipe-bending problem frequently encountered in offshore structural engineering. The pipe-soil interaction is modelled by using the Coulomb friction law. The modified finite element approach coupled with a modified tangent stiffness procedure is used to handle the nonlinearities (geometric and material, etc.) in the problem. The material nonlinearity has been considered both by the plastic-hinge method and by an elastic-plastic method. Before studying the practical problems, sufficient check problems were analysed and a good agreement was found between theoretically exact solutions and the results obtained from the developed computer model.     

Experimental studies on the weatherability of the capivara dam basalts,rio paranapanema,brazil

The weatherability of the basalts in the Capivara Dam site, Rio Paranapanema, São Paulo State, Brazil, has been studied by means of saturation-drying tests. A great number of samples have disaggre — gated intensively with production of fines. The behavior of these rocks is related to their petrography, especially to their content in expansive clay minerals. These studies were performed in order to obtain data for the utilization of this material as rock fill, including ripraps.     

Ultraviolet light inactivation of protozoa in drinking water: a Bayesian meta-analysis

To assess the dose of UV light needed to achieve specified levels of Giardia spp. cysts and Cryptosporidium spp. oocysts inactivation in drinking water, a Bayesian meta-analysis is used to analyze experimental data from several studies. Of the 20 studies identified by an extensive data collection effort, 14 (five reported experiments on Giardia and nine on Cryptosporidium) were selected for analysis based on a set of criteria. A substantial amount of the log inactivation data are reported as greater than a given inactivation level (i.e., censored data). The Bayesian hierarchical modeling approach used in this study not only properly addresses the common concerns in a meta-analysis but also provides a robust method for incorporating censored data. Different statistical models will result in different estimates of the UV doses needed to achieve a specific inactivation level. The Bayesian approach allows us to present the uncertainty in terms of risk, which is better suited for supporting US EPA in developing regulations.     

Trace element analysis of Cretan wines and wine products

The object of this research is to investigate the ways and the degree of contamination of Cretan grapes from the area of Chania and their alcoholic products, with the elements aluminium, arsenic, cadmium, copper, chromium, iron, lead, manganese, nickel and zinc. Fifteen samples of grapes were collected and used for the production of experimental wines from rinsed and unrinsed grapes. A microwave furnace was used for the digestion and dissolution of the experimental wines, the precipitates that originated in these wines, as well as the wines of the corresponding producers. The analyses of all mentioned samples as well as 34 local alcoholic distillates were performed using total reflection X-ray fluorescence and graphite furnace atomic absorption spectrometry. The concentrations for all the elements that were determined were almost in all cases, well below the maximum permissible levels by the Greek and the European Union legislation.     

Soil salinity of urban turf areas irrigated with saline water: I. Spatial variability

With increasing use of saline water for irrigating urban landscapes, soil salinization is becoming a concern. This study examined spatial variation in soil salinity over the length of selected fairways at five golf courses, and of large turf areas at two public parks located in west Texas and southern New Mexico. Salinity of water used for irrigation ranged from 680 to 2700 mg L⁻¹, and the sites consisted mostly of Aridisols (upland soils) or Entisols (alluvial soils). Soil salinity distribution at sites consisting of deep Aridisols was spatially independent with the coefficient of variability (CV) ranging from 24 to 42%. The sites consisting of shallow Aridisols over a calcic horizon had erratic and random soil salinity distributions with an average CV of 37%. Since soil salinity distributions in Aridisols and Alfisols appeared to be spatially independent within the distance of fairways, soil sampling adequacy can be determined by the conventional probability statistics. However, salinity distributions at Entisols sites were spatially dependant to a length of 100 m or more. In addition, the clayey Entisols used for public parks had high levels of salt accumulation (>10 dS m⁻¹ in the saturation extract) with the CV exceeding 60%. When salinity readings were stratified by soil type distribution, the CV was reduced to 28% on the average. The number of samples required to obtain the mean salinity over a typical length of fairways (250–300 m) within a deviate range of 20% averaged 6 in deep sandy Aridisols and Alfisols, and 13 each in other cases, provided that sampling of Entisols is made based on soil type distributions. These sampling requirements are greater than those for field soil moisture or saturation water contents. The spacing to collect the required number of samples over the prevailing length of fairways was between 23 and 38 m. Soil sampling for salinity appraisal is most problematic in Entisols, but can be made simple if a detailed soil map is available. In Aridisols containing a calcic horizon, it is probable to have saline spots over poorly permeable caliche.     

A contribution to the study of some greek marbles

The use of marble in Architecture began on the 7th century B.C. and continued to be used without stop untill today. Greece and especially the East Macedonia region is an extremely privileged area on marble deposits both in quantities and qualities and colours. In the present work the main physical and engineering properties of some varieties of greek marbles are given and a comparison with the international standards is made. The experimental material (marbles) was from East Macedonia, Argolida-Arcadia and Magnessia, three of the biggest marble deposit areas in Greece. From the results obtained, it is concluded that the marbles examined satisfy all the international standard codes and thus they can be used as building stones and decoration materials.