Effect of Biofilm Formation on Roughness Coefficient and Solids Deposition in Small-Diameter PVC Sewer Pipes

The purpose of a sanitary sewer is to carry the peak discharge at the end of the design period, and to transport suspended materials under all flow conditions to prevent deposition of solids, and hence, sewer blockages. To accomplish the latter, the liquid must provide for sufficient shear stress to suspend and transport the particles along the sewer. Published design criteria for critical shear stress in sanitary sewers vary significantly. However, the effect of biological film development on the internal pipe surface has been neglected. Experiments conducted utilizing a pilot-scale sanitary sewer installed in the Hydraulics Laboratory at the University of New Orleans, La., provide evidence that the shear stress to move particles of a given size is independent of slope and pipe diameter, but does depend on the effect of biological film on increasing the roughness coefficient. This critical shear stress, to achieve self-cleansing in sanitary sewers, was found to be in the range of 1.1–1.4?N/m2, depending on the integrity of the biofilm. Based on this principle, a design procedure applicable to small-diameter PVC pipes with slopes between 0.1 and 0.5% was developed.     

CRT colorimetry. Part II: Metrology

The colorimetric characterization of computer-controlled CRT displays require radiometric measurements with high precision and accuracy in order to achieve acceptable colorimetric accuracy in defining stimuli generated with this type of imaging modality. Precision and accuracy requirements for photometers, colorimeters, and spectroradiometers were evaluated. When models are used to relate digital counts defining a stimulus and resulting spectral radiant exitance, displays are assumed to exhibit channel and spatial independence. A variety of tests and the results of evaluating four imaging systems are described. From these analyses, measurement accuracy is mainly limited by wavelength scale in the case of spectro-radiometers and filter fit in the case of colorimeters. Measurement precision is limited by the number of significant figures for fixed-range devices and signal-to-noise limitations for low-luminance stimuli. Display accuracy is limited by a lack of channel and spatial independence. Display precision is mainly limited by the electronic design of the display and the stability and load independence of the gun amplifiers. © 1993 John Wiley & Sons, Inc.     

Identification and quantification of hydride phases in Zircaloy-4 cladding using synchrotron X-ray diffraction

Zirconium hydrides precipitate in fuel cladding alloys as a result of hydrogen uptake from the high-temperature corrosion environment of light water reactors. Synchrotron X-ray diffraction was performed at room temperature on stress-relieved Zircaloy-4 cladding with two distributions of hydrides - (1) uniformly distributed hydrides across the entire cladding wall and (2) hydride rim next to the outer surface. The δ-hydride phase was found to be the predominant hydride phase to precipitate for hydrogen contents up to 1250 weight parts per million (wt ppm). At a higher content, about 3000 wt ppm, although δ-hydride is still the majority phase, a significant amount of γ-hydride is also observed. At even higher hydrogen contents, in excess of approximately 6000 wt ppm, such as can occur in a highly dense hydride layer, peaks associated with the ε-hydride phase are also observed in the diffraction pattern. The volume fraction of hydrides was estimated as a function of hydrogen content using the integrated intensities of select diffraction peaks corresponding to the α-Zr matrix and the hydride phases. These estimated values agree well with calculated values from the independently measured concentrations. The results of this study indicate that hydride precipitation in Zircaloy-4 is a complex process of evolving hydride phases with increasing local hydrogen content.     

Using the Kinetics of Biological Flocculation and the Limiting Flux Theory for the Preliminary Design of Activated Sludge Systems. II: Experimental Verification

Current activated sludge models consider that the removal of biodegradable organics by suspended growth includes: rapid enmeshment of the organic particles in the microbial floc, hydrolysis of the complex organic molecules into readily biodegradable organic substances, and oxidation of dissolved organic substances. All of the models assume that hydrolysis is the rate-limiting step, but none considers the role that the kinetics of biological flocculation and the sludge-settling characteristics may play in defining the activated sludge operating parameters. Several researchers have studied the kinetics of biological flocculation, and have analyzed its role on the removal of particulate chemical oxygen demand in suspended growth reactors. It has been demonstrated that a large proportion of the organic matter present in sewage can be removed by biological flocculation using short hydraulic retention times and subsequent settling. The first paper demonstrates that the one-dimensional limiting flux theory may be useful for coupling the sludge-settling properties with the aeration tank behavior, and the second paper presents experimental evidence that the proposed model is a reasonable first approximation that can be used for activated sludge system design and operation.     

Mechanical properties of continuously spun fibers of carbon nanotubes

We report on the mechanical properties of fibers consisting of pure carbon nanotube fibers directly spun from an aerogel formed during synthesis by chemical vapor deposition. The continuous withdrawal of product from the gas phase imparts a high commercial potential to the process, either for the production of particularly strong fibers or for the economic production of bulk quantities of carbon nanotubes. Tensile tests were performed on fibers produced from the dissociation of three different hydrocarbons, namely, ethanol, ethylene glycol, and hexane, with a range of iron (catalyst) concentrations. The conditions were chosen to lie within the range known to enable satisfactory continuous spinning, the iron concentration being varied within this range. Increasing proportions of single wall nanotubes were found as the iron concentration was decreased, conditions which also produced fibers of best strength and stiffness. The maximum tensile strength obtained was 1.46 GPa (equivalent to 0.70 N/tex assuming a density of 2.1 g/cm(3)). The experiments indicate that significant improvements in the mechanical properties can be accomplished by optimizing the process conditions.     

The Role of Bioflocculation on Suspended Solids and Particulate COD Removal in the Trickling Filter Process

Understanding that there is a significant presence of extracellular polymeric substances at the biofilm/wastewater interface and that the primary constituent of chemical oxygen demand (COD) in domestic wastewaters is organic particulates, this research describes the kinetics of particulate removal in a pilot-scale trickling filter (TF) and the role of bioflocculation in the removal process. Recent research has described the role of bioflocculation on particulate COD (PCOD) removal in suspended growth biological wastewater treatment systems. However, no research pertaining to PCOD removal by bioflocculation in attached growth systems was identified prior to this study. For this study, experiments were conducted using both bench- and pilot-scale biofilm reactors and provided evidence that the removal of organic and inorganic particulate matter in a TF bioreactor follows a first-order bioflocculation rate equation. The statistical analysis of data obtained from the pilot TF fits the dispersion model to suspended solids and PCOD remaining in the pilot TF.     

Performance‐driven dynamic service selection

Modern software systems are increasingly built by integrating different services implemented by independent organizations and offered in an open service marketplace. In such environment, multiple providers may compete with each other by publishing services that provide the same functionality, and export the same interface, but differ in the offered QoS and in particular in the offered performance. Clients and service integrators may therefore dynamically select the most efficient services that satisfy their requirements among the competing alternatives. Service selection may be performed by clients by following different strategies, which may ultimately affect the overall quality of service invocations. In this paper, we address the problem of analyzing and comparing different service selection strategies based on a framework that supports performance estimates. We report on quantitative analyses through simulations, highlighting advantages and limitations of each strategy. Copyright © 2014 John Wiley & Sons, Ltd.     

T3, T4 and TSH serum levels in patients on long-term treatment for epilepsy

The serum T3, T4 and TSH concentrations were assessed by RIA method in 25 (14 females, 11 males) long-term treated (mean treatment duration 12.8 years) epileptic patients. The mean serum T3, T4 and TSH levels were lower than in control group according to clinical picture of epilepsy and treatment applied. The lowest mean serum TSH concentration was in patients with known aetiology of epilepsy. Patients with tonic-clonic seizures had lower serum levels of all hormones measured in comparison with the patients with partial seizures. Mean serum T3, T4 and TSH levels were low in patient group receiving valproic acid. The lowest mean TSH serum concentration as compared to control group was in the patients treated with phenytoin. None of the epileptic patients developed clinical symptoms of hypothyreoidism.