Modelling of silicon condenser microphones

Several models concerning the sensitivity of capacitive pressure sensors have been presented in the past. Modelling of condenser microphones, which can be considered to be a special type of capacitive pressure sensor, usually requires a more complicated analysis of the sensitivity, because they have a strong electric field in the air gap. It is found that the mechanical sensitivity of condenser microphones with a circular diaphragm, either with a large initial tension or without any initial tension, increases with increasing bias voltage (and the corresponding static deflection), whereas the mechanical sensitivity of other capacitive pressure sensors does not depend on the static deflection. It is also found that the mechanical sensitivity increases with increasing input capacitance of a preamplifier. In addition, the open-circuit electrical sensitivity and, consequently, the total sensitivity too, also increases with increasing bias voltage (or static deflection). However, the maximum allowable sound pressure at which the diaphragm collapses, an effect that has to be taken into account, decreases with increasing static deflection in most cases, ulthnately resulting in an optimum value for the bias voltage. The model for microphones with a circular highly tensioned diaphragm has been verified successfully for two microphone types

Make to stock or make to order: The decoupling point in the food processing industries.

Abstract Food processing industries experience growing logistical demands, growing variety in products and intense competition. As a reaction companies try to produce more on order. Often managers "nd it di$cult to decide which products to make to order and which products to stock. This paper develops a frame that is an aid for managers in balancing the factors and characteristics of market and production process that in#uence such decisions. The frame is based on the general decoupling point concept by Hoekstra and Romme, which is adapted to the speci"c characteristics of the food processing industry. Its usefulness is illustrated in a case study. Some directions for further research are given

What is the influence on water quality in temperate eutrophic lakes of a reduction of planktivorous and benthivorous fish? A systematic review protocol

Background: In lakes that have become eutrophic due to sewage discharges or nutrient runoff from land, problems such as algal blooms and oxygen deficiency often persist even when nutrient supplies have been reduced. One reason is that phosphorus stored in the sediments can exchange with the water. There are indications that the high abundance of phytoplankton, turbid water and lack of submerged vegetation seen in many eutrophic lakes may represent a semi-stable state. For that reason, a shift back to more natural clear-water conditions could be difficult to achieve. In some cases, though, temporary mitigation of eutrophication-related problems has been accomplished through biomanipulation: stocks of zooplanktivorous fish have been reduced by intensive fishing, leading to increased populations of phytoplankton-feeding zooplankton. Moreover, reduction of benthivorous fish may result in lower phosphorus fluxes from the sediments. An alternative to reducing the dominance of planktivores and benthivores by fishing is to stock lakes with piscivorous fish. These two approaches have often been used in combination. The implementation of the EU Water Framework Directive has recently led to more stringent demands for measures against eutrophication, and a systematic review could clarify whether biomanipulation is efficient as a measure of that kind. Methods: The review will examine primary field studies of how large-scale biomanipulation has affected water quality and community structure in eutrophic lakes or reservoirs in temperate regions. Such studies can be based on comparison between conditions before and after manipulation, on comparison between treated and non-treated water bodies, or both. Relevant outcomes include Secchi depth, concentrations of oxygen, nutrients, suspended solids and chlorophyll, abundance and composition of phytoplankton, zooplankton and fish, and coverage of submerged macrophytes.A Systematic review to this article was published on 22 May 2015: ernes, C., Carpenter, S.R., Gårdmark, A. et al. What is the influence of a reduction of planktivorous and benthivorous fish on water quality in temperate eutrophic lakes? A systematic review. Environ Evid 4, 7 (2015). DOI: 10.1186/s13750-015-0032-9Mistr

General considerations of noise in microphone preamplifiers

In this paper a study of the noise performance of electret microphone systems as a part of hearing aids is presented. The signal-to-noise ratio of the microphone-preamplifier combination, containing a field-effect transistor (FET) and a high value resistive bias element in a hybrid configuration, is mainly determined by the noise generated in the preamplifier circuit.\ud \ud A theoretical analysis of the noise sources in a source follower is given. The dominating noise sources are the channel noise of the FET, the thermal noise of the gate bias element, and finally the noise due to the gate leakage current of the FET and its package. It is shown that for the systems investigated, the noise performance does not depend on the choice of the amplifying device (JFET or MOSFET) itself, but only on its packages. Besides this, it is found that it is necessary to keep the parasitic capacitances as small as possible and to make the resistance of the bias element as large as possible

Chytrid epidemics may increase genetic diversity of a diatom spring-bloom

Contrary to expectation, populations of clonal organisms are often genetically highly diverse. In phytoplankton, this diversity is maintained throughout periods of high population growth (that is, blooms), even though competitive exclusion among genotypes should hypothetically lead to the dominance of a few superior genotypes. Genotype-specific parasitism may be one mechanism that helps maintain such high-genotypic diversity of clonal organisms. Here, we present a comparison of population genetic similarity by estimating the beta-dispersion among genotypes of early and peak bloom populations of the diatom Asterionella formosa for three spring-blooms under high or low parasite pressure. The Asterionella population showed greater beta-dispersion at peak bloom than early bloom in the 2 years with high parasite pressure, whereas the within group dispersion did not change under low parasite pressure. Our findings support that high prevalence parasitism can promote genetic diversification of natural populations of clonal hosts

Strength demands of tall wind turbines subject to earthquakes and wind load

Wind and earthquake load have historically been conceived to act independently. However, if we reflect on the fact that major seismic events are usually followed by a number of aftershocks and that wind is constantly flowing at high intensities around wind farms, which induces additional demands of resistance to infrastructure, then the joint probability of middle-to strong earthquakes and low-to mild wind events becomes more relevant. In this paper a generalised approach is used to estimate the ratio between earthquake and wind forces and their effect on infrastructure. Following, a probabilistic analysis is carried out to show that under certain conditions the combination of these natural events can induce additional demands of strength and ductility to wind turbines which could lead to unforeseen damage

Towards a developmental state? Provincial economic policy in South Africa

This paper explores the meaning of the developmental state for spatial economic policy in South Africa. Two main questions are addressed: do provincial governments have a role to play in promoting economic prosperity, and to what extent do current provincial policies possess the attributes of a developmental state? These attributes are defined as the ability to plan longer term, to focus key partners on a common agenda, and to mobilise state resources to build productive capabilities. The paper argues that the developmental state must harness the power of government at every level to ensure that each part of the country develops to its potential. However, current provincial capacity is uneven, and weakest where support is needed most. Many provinces seem to have partial strategies and lack the wherewithal for sustained implementation. Coordination across government appears to be poor. The paper concludes by suggesting ways provincial policies could be strengthened