Increased sediment oxygen uptake caused by oxygenation-induced hypolimnetic mixing

Hypolimnetic oxygenation systems (HOx) are increasingly used in lakes and reservoirs to elevate dissolved oxygen (O₂) while preserving stratification, thereby decreasing concentrations of reduced chemical species in the hypolimnion. By maintaining an oxic zone in the upper sediment, HOx suppress fluxes of reduced soluble species from the sediment into the overlying water. However, diminished HOx performance has been observed due to HOx-induced increases in sediment O₂ uptake. Based on a series of in situ O₂ microprofile and current velocity measurements, this study evaluates the vertical O₂ distribution at the sediment-water interface as a function of HOx operation. These data were used to determine how sediment O₂ uptake rate (JO₂) and sediment oxic-zone depth (z_max) were affected by applied oxygen-gas flow rate, changes in near-sediment mixing and O₂ concentration, and proximity to the HOx. The vertical sediment-water O₂ distribution was found to be strongly influenced by oxygenation on a reservoir-wide basis. Elevated JO₂ and an oxic sediment zone were maintained during continuous HOx operation, with z_max increasing linearly with HOx flow rate. In contrast, JO₂ decreased to zero and the sediment became anoxic as the vertical O₂ distribution at the sediment-water interface collapsed during periods when the HOx was turned off and near-sediment mixing and O₂ concentrations decreased. JO₂ and z_max throughout the reservoir were found to be largely governed by HOx-induced mixing rather than O₂ levels in the water column. By quantifying how JO₂ and z_max vary in response to HOx operations, this work (1) characterizes how hypolimnetic oxygenation affects sediment O₂ dynamics, (2) contributes to the optimization of water quality and management of HOx-equipped lakes and reservoirs, and (3) enhances understanding of the effect of mixing and O₂ concentrations in other systems.     

Diffusion-controlled reference material for volatile organic compound emissions testing: Pilot inter-laboratory study

To improve the reliability and accuracy of tests used to measure emissions of volatile organic compounds (VOCs) from samples of interior building products, the National Institute of Standards and Technology (NIST) and Virginia Tech (VT) have created a program to develop reference materials with independently predictable emission rates. A diffusive reference material and associated mechanistic model have been developed and are undergoing extensive evaluation. As part of this process, a pilot inter-laboratory study (ILS) was conducted with four laboratories using a polymer material loaded with toluene as the reference source. Results showed the prototype material to be a relatively stable, homogeneous source with consistent emissions both within and between production batches. A comparison of toluene emission rates determined by the laboratories showed relative standard deviations as low as 9%, which are significantly lower than inter-laboratory variations for most previous ILS exercises with VOC sources. At a sample time of 48 h, the mean measured toluene emission rate for all four laboratories was within 1% of the model predicted value. The success of this pilot ILS is a key step toward being able to provide a VOC reference material for independent validation of VOC emission tests conducted in small chambers.     

Enabling simulation interoperability

Over the past years a series of architectures have addressed the need to link multiple simulations. These efforts have been driven primarily by the desire to reuse existing "best of breed" simulations in new combinations to avoid developing any single, monolithic architecture with the impossible goal of meeting all simulation needs. The US Department of Defense began developing the high level architecture (HLA) for distributed computer simulation systems. The high level architecture addresses the need to link multiple computer simulation systems. HLA separates the data model from the architecture's functions for exchanging information.     

Cancer predisposition, radiosensitivity and the risk of radiation-induced cancers. IV. Prediction of risks in relatives of cancer-predisposed individuals

Individuals carrying cancer-predisposing germline mutations are known to be at a higher risk for cancers than those who do not carry them. This is also true of their biological relatives because they have a higher probability of being carriers of such mutant genes than unrelated individuals in the population. Further, there are now sufficient grounds for assuming that cancer-predisposed individuals may also be at a higher risk for cancers induced by ionizing radiation. In our earlier work, we examined the impact of this heterogeneity (with respect to cancer predisposition and radiosensitivity differentials) on risks of radiation-induced cancer at the population level. This paper is focused on the question of risks of radiation-induced cancer in relatives of cancer-predisposed individuals. Using an autosomal dominant model of cancer predisposition and radiosensitivity developed earlier and applying it to breast cancer risks associated with mutations in the BRCA1 gene, we show that: (1) The risk ratio (i.e. the ratio of risk of radiation-induced cancer in relatives to that in unrelated individuals) in the population increases with the degree of biological relatedness of the relative, being higher for close than for distant relatives; incomplete penetrance of the mutant gene "dilutes" this risk ratio. (2) The proportion of excess radiation-induced cancers in relatives (i.e. the attributable fraction) is higher than in unrelated individuals. (3) In relatives, the proportion of excess cancers due to radiosensitivity differentials alone depends on the strength of predisposition, the radiosensitivity differentials assumed, the radiation dose, the proportion of cancers due to predisposition, the mutant gene frequency and the penetrance of the mutant gene. This is in contrast to the situation for unrelated individuals, for whom the above-mentioned proportion is dependent on the first three but not on the last three of these factors. Further, even when the proportion of excess cancers is small, most of it is due to radiosensitivity differential alone both in unrelated individuals and in relatives. (4) For values of predisposition strength and radiosensitivity differential <10, even when the estimated frequency of a mutant BRCA1 gene is 0.0047 and the proportion of breast cancers due to these mutations is 38% (as is the case for Ashkenazi Jewish women under age 30), the increase in breast cancer risks is only marginal even for first-degree relatives. (5) These findings support the conclusion that increases in radiation risks to relatives (compared to those in unrelated individuals), to be detectable epidemiologically, will occur only when the mutant alleles are common and the strength of predisposition and radiosensitivity differentials are conjointly dramatic.     

Multi-field 3D scanning light microscopy of early embryogenesis

A computer‐controlled microscopy system was devised to allow the observation of avian embryo development over an extended time period. Parallel experiments, as well as extended specimen volumes, can be recorded at cellular resolution using a three‐dimensional scanning procedure. The resulting large set of data is processed automatically into registered, focal‐ and positional‐drift corrected mosaic images, assembled as montages of adjacent microscopic fields. The configuration of the incubator and a sterile embryo chamber prevents condensation of the humidified culturing atmosphere in the optical path and is compatible with both differential interference contrast and epifluorescence optics. As a demonstration, recordings are presented showing the large‐scale remodelling of the embryonic primordial vascular structure.     

Developmental patterns of expected consequences for simulated bicycle injury events

Three patients with shunt malfunction, who had previously undergone a shunting procedure for noncommunicating hydrocephalus of adolescent and adult onset, successfully underwent a percutaneous flexible neuroendoscopic ventriculostomy. This procedure was performed as an alternative treatment for shunt revision by the use of our newly developed flexible fiberoptic ventriculoscope. All patients were able to remain independent of the shunt system after the ventriculostomy. These results thus suggest that a percutaneous flexible neuroendoscopic ventriculostomy can be effective for the treatment of shunt-dependent patients with shunt malfunction in adolescents and adults.     

Multimedia synchronization protocols for broadband integratedservices

Protocols to provide synchronization of data elements with arbitrary temporal relationships of both stream and non-stream broadband traffic types are proposed. It is specified that the provision of a synchronization function be performed within a packet switched network, and, accordingly, a two-level communication architecture is presented. The lower level, called the network synchronization protocol (NSP), provides the ability to establish and maintain individual connections with specified synchronization characteristics. The upper level, the application synchronization protocol (ASP), supports an integrated synchronization service for multimedia applications. The ASP identifies the temporal relationships among an application's data objects and manages the synchronization of arriving data for playout. The proposed NSP and ASP are mapped to the session and application layers of the open-systems-interconnection (OSI) reference model, respectively     

Care: from theory to orientation and back

In this paper, I urge that the very real lessons Carol Gilligan's work in moral psychology offer to moral philosophy can best be appreciated if we take seriously the gap between the two disciplines. The care and justice perspectives Gilligan explores are psychological orientations, and orientations are defined as much by matters of emphasis, selectivity of interpretation, and gestalt as they are by propositional commitment. As such, I argue, their contribution to moral theory is best seen as stances from which to do theory, rather than as constituting ready-made theories themselves. In pursuing this train of thought, I examine how Gilligan's work has developed over time and how, in the end, we should understand the juxtaposition between the two orientations.     

Nurse triage for house call requests in a Tyneside general practice: patients' views and effect on doctor workload

BACKGROUND: Demand for consultations in primary care has risen recently, necessitating a change in working practices. As part of this process, the possible contribution of practice nurses in the telephone assessment of home visit requests merits attention. AIMS: To survey the views of our patients encountering our nurse triage system for home visit requests, set up in June 1995, and to plot its effect on the routine visiting workload of our doctors and thus their availability at the surgery. METHOD: The outcome of each request was categorized as: doctor to visit (DV), surgery consultation with doctor (SC), nurse advice given and accepted (NA), or call passed to doctor for advice (DA). Frequency data from September 1995 to December 1996 were recovered. Questionnaires for self-completion were sent to all those requesting a routine weekday house call during two four-week periods in 1995 and 1996. RESULTS: Analysable activity data revealed 1764 house call requests, with 41% DV, 18% SC, 24% NA, and 8% DA. In the first survey, 121 questionnaires were sent out and 84 returned (69% response rate) and, in the second, the corresponding figures were 113, 85, and 75%. About 80% of responders reported that they were satisfied with the help received from the nurse. CONCLUSIONS: Nurse triage of house call requests has led to more efficient care for our patients, as we have increased the availability of surgery consultations by reducing the number of house calls made by our general practitioners.