Effect of solids retention time on the performance and biological characteristics of a membrane bioreactor.

The purpose of this study was to compare the performance of a pilot-scale membrane bioreactor (MBR) in the treatment of municipal strength wastewater at solid retention times (SRTs) ranging from 30 days to two days. Cumulative nitrogen and phosphorus mass balances resulted in closures exceeding 90% at each steady state period. Biomass production rate and biomass viability generally increased with decreasing SRT, whereas overall enzymatic activity did not change significantly at most SRTs, but was highest at the two day SRT. Nitrification decreased at two day SRT but did not fail completely. At higher SRTs, nitrification was not noticeably affected by the sludge age. Phospholipid fatty acid (PLFA) analysis showed substantially diverse biomass in the sludge at different SRTs. Different ratios of gram positive bacteria, eukaryotic organisms, and yeast cells were observed in the mixed liquor at varying SRTs. On the other hand, BIOLOG analysis indicated that the overall capacity of the biomass to degrade different carbon substrates did not change significantly at different SRTs. The concentration of metals in the MBR mixed liquor declined steadily with decreasing SRT. The MBR effluent contained negligible amounts of Fe, Zn, Mn, and Co at each condition, indicating the retention of these metals regardless of the SRT.

Origins of knowledge.

Experiments with young infants provide evidence for early-developing capacities to represent physical objects and to reason about object motion. Early physical reasoning accords with 2 constraints at the center of mature physical conceptions: continuity and solidity. It fails to accord with 2 constraints that may be peripheral to mature conceptions: gravity and inertia. These experiments suggest that cognition develops concurrently with perception and action and that development leads to the enrichment of conceptions around an unchanging core. The experiments challenge claims that cognition develops on a foundation of perceptual or motor experience, that initial conceptions are inappropriate to the world, and that initial conceptions are abandoned or radically changed with the growth of knowledge.

You can manage construction risks.

A construction project is about the riskiest thing any company does in the normal course of business. Hundreds of things can go wrong, dozens will. But officers who analyze and manage every other sort of risk often ignore construction risk as if it were uncontrollable. The truth is, it can't be eliminated, but it can be controlled. Construction is not a product but a confusing and often exasperating service. A group of experts--architects, bankers, consultants, contractors, engineers, users, city officials--coordinate the activities of an army of suppliers, laborers, designers, subcontractors, and inspectors. The job of the company officers is to coordinate the coordinators; to make prompt, informed decisions as the work progresses; to take and retain project responsibility at the highest level; and to analyze and manage the entire process in the following seven stages: 1. Study the types and phases of construction risk. 2. Assess the risks of the company's particular project. 3. Match these risks with the in-house capabilities. 4. Define a building strategy. 5. Pick the right kind of contract. 6. Choose a contractor. 7. Monitor construction. Analyzing risk is largely a matter of assessing the complexity of the building, the site, the financing, the schedule, and the special uses and problems of the project. This analysis then drives the choice of contract and contractor. The range runs from low-cost providers, lump sum contracts and very little teamwork at one end of the spectrum to highly differentiated construction companies, guaranteed-maximum-prince contracts, and consultative coordination at the other.

Predicting certification examination scores in a college-based program.

Factors that may predict student performance on the ARRT examination are discussed and statistically examined. For students in the program studied, performance on a simulated registry and grade point average proved to be statistically significant predictors of success. Implications of such models for student motivation are addressed, and a general need to explain differences in student performance is discussed as a step needed to facilitate examination of differences in various educational programs.

Infrared pulse contours obtained with an inexpensive detector.

A method for obtaining true temporal contours of ir pulses with an inexpensive detector is described. The method reduces the frequency response requirements placed upon the detector.

Attenuation of giant laser pulses by absorbing filters.

Three types of absorbing filters were tested for suitability as reproducible attenuators for a Q-switched ruby laser beam. None of the filters tested were irreversibly damaged when irradiated with pulses having peak powers up to 40 MW (beam cross section ~10(-4) M(2)). However, Tiffen Photar neutral density filters and Corning filters showed reversible photobleaching (optical saturation) at large pulse energies, while Kodak Wratten neutral density filters did not saturate.

Light source responsible for the deterioration of cryptocyanine q-switches.

Ultraviolet radiation, in a band of wavelengths near 300 nm, produced by the flashlamps used to pump the ruby rod, is responsible for nearly all the photochemical decomposition (irreversible bleaching) of methanolic solutions of cryptocyanine used as passive shutters (Q-switches) in high-peak-power ruby lasers. The laser beam itself has little or no irreversible effect upon cryptocyanine.

Optical anisotropy induced by resonant absorption or amplification of radiation.

When a light beam propagates through an ensemble of two-level quantum systems, the resonant interaction between these systems and the radiation field may be described by a complex susceptibility. Even if the medium is of a type ordinarily considered isotropic, the susceptibility will be a tensor. In this paper, explicit expressions for the elements of this tensor are derived from quantum-statistical mechanics. A physical explanation of the induced anisotropy is given, and the experimental conditions under which it can be neglected are described.