On the natural frequencies of vibration of a ring surrounded by and/or containing a fluid

An energy approach is used to derive simple expressions for the effective modal mass and effective modal stiffness of a thin, uniform, circular ring when vibrating freely in an inextensional ring mode. These expressions include both the circumferential and radial inertia of the ring, and the additional mass of fluid both within and without the ring; they also allow for the destabilizing (or stiffening) effect of ring compression (or tension) due to pressure loading which is always normal to the surface. The natural frequencies of these inextensional modes of vibration of the ring, which are derived from the effective mass and effective stiffness, are exact to the first order of small quantities. Numerous special cases are contained within the general result, including all the classical results.     

Integrated in situ monitoring of a metalorganic vapor phase epitaxy reactor for II–VI epitaxy

The focus of this paper is the integrated use of system and wafer monitors to obtain a complete picture of the growth process and to identify the major causes of variance. In situ monitoring of a growing layer of Hg_1-xCd_xTe using laser reflectometry has been compared with the outputs of various system monitors such as pyrometer, organometallic concentration, and flow. Differences between the expected and measured concentrations were corrected by initially adjusting the organometallic flows, and the remaining variance in CdTe interdiffused multilayer process layer thickness was then corrected by increasing the CdTe cycle time. The remainder of the layer gave a homogenized alloy composition of 0.256 for a target value of 0.258. This example shows how different in situ monitors have been integrated to give a comprehensive picture of the growth process, which were then related to known kinetic behavior. As a result of this monitoring, it was possible to identify critical parameters for control.     

Multigigahertz guided wave magnetooptic modulator

We propose a magnetooptic modulator based on a thin-film iron garnet material. The Landau-Lifshitz equation, which governs magnetization dynamics, is combined with a beam propagation method to evaluate the performance of the device in the multigigahertz range. Bandwidth considerations and temporal response are discussed     

A new alternative representation of impedance data using the derivative of the tangent of the phase angle: Application to the YSZ system and composites

The aim of this work is to propose a new alternative representation of impedance data using the derivative of the tangent of the phase angle, which allows enhanced discrimination between processes with relaxation frequencies that are very close. The new representation allows discrimination between overlapped processes within a factor of 2 in their relaxation frequencies for process with similar strength. Equations for the simplified behaviour of the impedance data have been proposed to obtain all the parameters of the processes involved in the impedance spectrum. This new alternative representation has been applied to bulk and grain boundary responses of YSZ with very satisfactory results. It has also been applied to the qualitative study of impedance data of a CuO composite showing the usefulness of this representation to discriminate different electrode processes. This approach provides an ab initio method of identify the contributing components to an electrochemical impedance spectrum with quite remarkable resolution. It is suggested that if this method is applied to provide starting parameters for non-linear least squares fitting using constant phase elements, then problems due to correlation of parameters and identification of components can be minimised.     

Quantifying variability within water samples: the need for adequate subsampling

Accurate and precise determination of the concentration of nutrients and other substances in waterbodies is an essential requirement for supporting effective management and legislation. Owing primarily to logistic and financial constraints, however, national and regional agencies responsible for monitoring surface waters tend to quantify chemical indicators of water quality using a single sample from each waterbody, thus largely ignoring spatial variability. We show here that total sample variability, which comprises both analytical variability and within-sample heterogeneity, of a number of important chemical indicators of water quality (chlorophyll a, total phosphorus, total nitrogen, soluble molybdate-reactive phosphorus and dissolved inorganic nitrogen) varies significantly both over time and among determinands, and can be extremely high. Within-sample heterogeneity, whose mean contribution to total sample variability ranged between 62% and 100%, was significantly higher in samples taken from rivers compared with those from lakes, and was shown to be reduced by filtration. Our results show clearly that neither a single sample, nor even two sub-samples from that sample is adequate for the reliable, and statistically robust, detection of changes in the quality of surface waters. We recommend strongly that, in situations where it is practicable to take only a single sample from a waterbody, a minimum of three sub-samples are analysed from that sample for robust quantification of both the concentrations of determinands and total sample variability.     

TRENCHING-RELATING THEORY TO PRACTICE

Many in the UK are ignorant of the major differences between Scots Law and English Law, similar ignorance of the differing Scottish procedures exists. The abandonment of the separate trades system, which persisted for longer in Scotland, reduced the ability of the construction professionals to appreciate Une needs of the construction industry and to be involved in the organization and project management of the works, write H. A. Gow and F. P. Fenn of Dundee Institute of Technology.     

A dual-process account of auditory change detection.

Listeners can be “deaf” to a substantial change in a scene comprising multiple auditory objects unless their attention has been directed to the changed object. It is unclear whether auditory change detection relies on identification of the objects in pre- and post-change scenes. We compared the rates at which listeners correctly identify changed objects with those predicted by change-detection models based on signal detection theory (SDT) and high-threshold theory (HTT). Detected changes were not identified as accurately as predicted by models based on either theory, suggesting that some changes are detected by a process that does not support change identification. Undetected changes were identified as accurately as predicted by the HTT model but much less accurately than predicted by the SDT models. The process underlying change detection was investigated further by determining receiver-operating characteristics (ROCs). ROCs did not conform to those predicted by either a SDT or a HTT model but were well modeled by a dual-process that incorporated HTT and SDT components. The dual-process model also accurately predicted the rates at which detected and undetected changes were correctly identified. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Assessment of eutrophication and phytoplankton community impairment in the Buffalo River Area of Concern

A “weight of evidence” approach was used to assess trophic status and phytoplankton community characteristics as a step towards delisting beneficial use impairments in the Buffalo River Area of Concern (AOC). Using a combination of historical data and results of a sampling program conducted in 2006, trophic status was evaluated by considering threshold levels of total phosphorus and chlorophyll a, total phytoplankton abundance, reference-reach comparisons of total phosphorus and nitrate + nitrite, and an ecoregion (percentile) analysis. Microcystin toxin levels were used as an indicator of the presence of undesirable algae. Phytoplankton community characteristics were assessed through consideration of species richness, Shannon–Weaver Index of Diversity, presence of indicator species, centric:pennate diatom ratio, the Trophic Diatom Index (TDI), and the Pollution Tolerance Index (PTI). The weight of evidence suggests that the Buffalo River AOC does not have a eutrophication problem, but nutrient levels are sufficiently high to recommend further implementation of watershed Best Management Practices and continued water quality monitoring. Microcystin was present in all samples but at a level below the World Health Organization guidelines; based on this indicator we conclude that the AOC does not have a problem with undesirable algae. The phytoplankton community exhibits some anthropogenic impact as reflected by the TDI, PTI, and presence of certain indicator species, but these impacts do not indicate extreme stress. Based on the weight of evidence the Buffalo River Remedial Advisory Committee recently concluded that the AOC was not impaired in terms of eutrophication, presence of undesirable algae, and degradation of phytoplankton.     

Storage-induced denitrification using sequencing batch reactor operation

As a biochemical reduction of oxidized-nitrogen species, the denitrification reaction requires the availability of an electron-donor substrate. This requirement is typically satisfied by the provision of an organic carbon supplement or, possibly, a reactor design which utilizes raw-waste organic carbon components. Bacterial storage can also provide the necessary electron source. However, in the instance of conventional wastewater treatment facilities, the limited availability of such cellular reserve material results in a markedly reduced denitrification capacity. Bench-scale studies of storage induced denitrification were conducted using a sequencing batch reactor. By operating the reactor in a mode conducive to the development of cellular storage, the system maintained a consistent 92+% reduction in total nitrogen without a carbon supplement. Depletion of the cellular glycogen reserve was observed during the denitrification reaction.