Self-tuning bandpass filter

An electronic filter is described which simultaneously maintains a constant bandwidth and a constant center frequency gain as the input signal frequency varies, and remains self-tuning to that center frequency over a decade range. The filter utilizes a field effect transistor (FET) as a voltage variable resistance in the bandpass frequency determining circuit. The FET is responsive to a phase detector to achieve self-tuning

A self-tuning filter

Self-tuning filter automatically adjusts its center frequency to track signal frequency. This permits the use of a filter with a bandwidth smaller than the range of input signal frequencies

Precision full-wave rectifier

Simplified circuit uses one operational amplifier and two precision resistors. The amplifier is operated open loop for switching and closed loop for linear gain, both simultaneously

AIROscope stellar acquisition

The acquisition system which operates in conjunction with a balloon-borne TV system, boresighted to a telescope is described. It has two main functions, a star field monitor and an offset star tracker. The design of the system was strongly influenced by the TV camera, which uses the same interlaced scanning system as is employed in commercial television broadcasting. To reduce power and bandwidth requirements, the star field information transmitted in our system consists only of the horizontal and vertical coordinates of each star and its brightness. As a star field monitor the system provides video thresholding, camera blemish suppression, coordinate digitization in 3 axes, circuity to recognize as single star the dispersed video signals resulting from one star overlapping adjacent scanning lines and storage of all signals for readout by the telemetry at appropriate times

Applying causality principles to the axiomatization of probabilistic cellular automata

Cellular automata (CA) consist of an array of identical cells, each of which may take one of a finite number of possible states. The entire array evolves in discrete time steps by iterating a global evolution G. Further, this global evolution G is required to be shift-invariant (it acts the same everywhere) and causal (information cannot be transmitted faster than some fixed number of cells per time step). At least in the classical, reversible and quantum cases, these two top-down axiomatic conditions are sufficient to entail more bottom-up, operational descriptions of G. We investigate whether the same is true in the probabilistic case. Keywords: Characterization, noise, Markov process, stochastic Einstein locality, screening-off, common cause principle, non-signalling, Multi-party non-local box.Comment: 13 pages, 6 figures, LaTeX, v2: refs adde

Microbial Nitrogen cycling in Nevada Geothermal Springs

Hot spring habitats above maximum photosynthetic temperature (73 ºC) are not well understood with respect to nitrogen (N) cycling. Few predictions have been made, and even fewer measurements of in situ activities have been reported. Thermodynamic calculations based on in situ chemical and temperature measurements will be used to predict the occurrence of the specific N-cycling reactions. In addition, these measurements in two springs will aid in an attempt to cultivate ammonia oxidizing species

The organisational and human resource challenges facing primary care trusts : protocol of a multiple case study

BACKGROUND: The study is designed to assess the organisational and human resource challenges faced by Primary Care Trusts (PCTs). Its objectives are to: specify the organisational and human resources challenges faced by PCTs in fulfilling the roles envisaged in government and local policy; examine how PCTs are addressing these challenges, in particular, to describe the organisational forms they have adopted, and the OD/HR strategies and initiatives they have planned or in place; assess how effective these structures, strategies and initiatives have been in enabling the PCTs to meet the organisational and human resources challenges they face; identify the factors, both internal to the PCT and in the wider health community, which have contributed to the success or failure of different structures, strategies and initiatives. METHODS: The study will be undertaken in three stages. In Stage 1 the key literature on public sector and NHS organisational development and human resources management will be reviewed, and discussions will be held with key researchers and policy makers working in this area. Stage 2 will focus on detailed case studies in six PCTs designed to examine the organisational and human resources challenges they face. Data will be collected using semi-structured interviews, group discussion, site visits, observation of key meetings and examination of local documentation. The findings from the case study PCTs will be cross checked with a Reference Group of up to 20 other PCG/Ts, and key officers working in organisational development or primary care at local, regional and national level. In Stage 3 analysis of findings from the preparatory work, the case studies and the feedback from the Reference Group will be used to identify practical lessons for PCTs, key messages for policy makers, and contributions to further theoretical development

Truncated horseshoes and formal languages in chaotic scattering

In this paper we study parameter families of truncated horseshoes as models of multiscattering systems which show a transition to chaos without losing hyperbolicity, so that the topological features of the transition are completely describable by a parameterized family of symbolic dynamics. At a fixed parameter value the corresponding horseshoe represents the set of orbits trapped in the scattering region. The bifurcations are a pure boundary effect and no other bifurcations such as saddle center bifurcations occur in this transition scenario. Truncated horseshoes actually arise in concrete potential scattering under suitable conditions. It is shown that a simple scattering model introduced earlier can realize this scenario in a certain parameter range (the "truncated sawshoe") . For this purpose, we solve the inverse scattering problem of finding the central potential associated to the sawshoe model. Furthermore, we review classification schemes for the transition to chaos of truncated horseshoes originating from symbolic dynamics and formal language theory and apply them to the truncated double horseshoe and the truncated sawshoe.Comment: 39 pages postscript; use uudecode and uncompress ! 4 figures available as hardcopies on reques

A high-speed microscopy approach to single-molecule studies of eukaryote signal transduction

Metabolic processes underlie all forms of life. An organism’s ability to utilise chemical energy to stay alive and eventually reproduce is a central feature of life, regardless of organism length scale. To achieve this, an organism must be adaptable. That is, it must be able to adjust to varying surrounding environmental conditions. Cells must be able to sense this environment, ‘transduce’ the signal and bring about some cell level response. Cells respond to external stimuli by releasing chemical cascades along often intricate signalling pathways which regulate cellular function. In this thesis, I have developed a novel optical microscopy system coupled to microfluidics and image analysis tools to help address challenging biological questions relating to metabolic sensing in eukaryotic life, using Saccharomyces cerevisiæ, as a model system. A set of biophysical tools was developed to monitor signal transduction events in live yeast cells. A bespoke optical microscope was developed that can monitor single living cells and determine their response to controlled variations in environmental nutrient concentration at high sampling speeds comparable to the molecular diffusion time scale in a cells internal environment. High-speed imaging at up to 200 frames per second and exposure times of 4.7 ms can be achieved. An electronic gain of 300x makes the camera system sensitive enough to track diffusion of single or small clusters of fluorescent protein molecules under physiological conditions. A high intensity laser excitation system was developed to deliver the light required to follow single fluorescent proteins in the living cells. A bespoke microfluidics system was built wherein cells can be exposed to rapidly changing extracellular environments and make it possible to follow individual cell responses to changing glucose conditions. Image analysis tools were adapted and developed to facilitate the automated measurement of protein mobility, stoichiometry and copy number, one cell at a time

A high-speed microscopy approach to single-molecule studies of eukaryote signal transduction

Metabolic processes underlie all forms of life. An organism’s ability to utilise chemical energy to stay alive and eventually reproduce is a central feature of life, regardless of organism length scale. To achieve this, an organism must be adaptable. That is, it must be able to adjust to varying surrounding environmental conditions. Cells must be able to sense this environment, ‘transduce’ the signal and bring about some cell level response. Cells respond to external stimuli by releasing chemical cascades along often intricate signalling pathways which regulate cellular function. In this thesis, I have developed a novel optical microscopy system coupled to microfluidics and image analysis tools to help address challenging biological questions relating to metabolic sensing in eukaryotic life, using Saccharomyces cerevisiæ, as a model system. A set of biophysical tools was developed to monitor signal transduction events in live yeast cells. A bespoke optical microscope was developed that can monitor single living cells and determine their response to controlled variations in environmental nutrient concentration at high sampling speeds comparable to the molecular diffusion time scale in a cells internal environment. High-speed imaging at up to 200 frames per second and exposure times of 4.7 ms can be achieved. An electronic gain of 300x makes the camera system sensitive enough to track diffusion of single or small clusters of fluorescent protein molecules under physiological conditions. A high intensity laser excitation system was developed to deliver the light required to follow single fluorescent proteins in the living cells. A bespoke microfluidics system was built wherein cells can be exposed to rapidly changing extracellular environments and make it possible to follow individual cell responses to changing glucose conditions. Image analysis tools were adapted and developed to facilitate the automated measurement of protein mobility, stoichiometry and copy number, one cell at a time