Pulse stretcher has improved dynamic range and linearity

Current-switching pulse stretcher overcomes the diode nonlinearity and capacitive feedthrough of voltage switching diode-capacitor stretchers and lengthens nanosecond pulses so that their amplitude may be determined and extends the dynamic range of the pulse stretcher. The rise time of the output pulse in response to a step function is approximately 5 nanoseconds

Transistor biased amplifier minimizes diode discriminator threshold attenuation

Transistor biased amplifier has a biased diode discriminator driven by a high impedance /several megohms/ current source, rather than a voltage source with several hundred ohms output impedance. This high impedance input arrangement makes the incremental impedance of the threshold diode negligible relative to the input impedance

Tunnel diode circuit used as nanosecond-range time marker

Simple tunnel diode time marker circuit determines the time at which an event occurs in a scintillation crystal. It is capable of triggering at voltages as low as the noise level of a 10-stage PM tube

A dynamical and kinematical model of the Galactic stellar halo and possible implications for galaxy formation scenarios

We re-analyse the kinematics of the system of blue horizontal branch field (BHBF) stars in the Galactic halo (in particular the outer halo), fitting the kinematics with the model of radial and tangential velocity dispersions in the halo as a function of galactocentric distance r proposed by Sommer-Larsen, Flynn & Christensen (1994), using a much larger sample (almost 700) of BHBF stars. The basic result is that the character of the stellar halo velocity ellipsoid changes markedly from radial anisotropy at the sun to tangential anisotropy in the outer parts of the Galactic halo (r greater than approx 20 kpc). Specifically, the radial component of the stellar halo's velocity ellipsoid decreases fairly rapidly beyond the solar circle, from approx 140 +/- 10 km/s at the sun, to an asymptotic value of 89 +/- 19 km/s at large r. The rapid decrease in the radial velocity dispersion is matched by an increase in the tangential velocity dispersion, with increasing r. Our results may indicate that the Galaxy formed hierarchically (partly or fully) through merging of smaller subsystems - the 'bottom-up' galaxy formation scenario, which for quite a while has been favoured by most theorists and recently also has been given some observational credibility by HST observations of a potential group of small galaxies, at high redshift, possibly in the process of merging to a larger galaxy (Pascarelle et al 1996).Comment: Latex, 16 pages. 2 postscript figures. Submitted to the Astrophysical Journal. also available at http://astro.utu.fi/~cflynn/outerhalo.htm

Current-switching technique for analog pulse circuits

Circuit technique uses a signal diode as a series current-pass element. Technique is applied to the design of a biased amplifier circuit and a nanosecond-pulse stretcher circuit

Determination of coastal ground and surface water processes and character by use of hydrochemistry and stable isotopes, Fraser Coast, Queensland

This study was part of an integrated project developed in response to concerns regarding current and future land practices affecting water quality within coastal catchments and adjacent marine environments. Two forested coastal catchments on the Fraser Coast, Australia, were chosen as examples of low-modification areas with similar geomorphological and land-use characteristics to many other coastal zones in southeast Queensland. For this component of the overall project, organic , physico-chemical (Eh, pH and DO), ionic (Fe2+, Fe3+), and isotopic (ä13CDIC, ä15NDIN ä34SSO4) data were used to characterise waters and identify sources and processes contributing to concentrations and form of dissolved Fe, C, N and S within the ground and surface waters of these coastal catchments. Three sites with elevated Fe concentrations are discussed in detail. These included a shallow pool with intermittent interaction with the surface water drainage system, a monitoring well within a semi-confined alluvial aquifer, and a monitoring well within the fresh/saline water mixing zone adjacent to an estuary. Conceptual models of processes occurring in these environments are presented. The primary factors influencing Fe transport were; microbial reduction of Fe3+ oxyhydroxides in groundwaters and in the hyporheic zone of surface drainage systems, organic input available for microbial reduction and Fe3+ complexation, bacterial activity for reduction and oxidation, iron curtain effects where saline/fresh water mixing occurs, and variation in redox conditions with depth in ground and surface water columns. Data indicated that groundwater seepage appears a more likely source of Fe to coastal waters (during periods of low rainfall) via tidal flux. The drainage system is ephemeral and contributes little discharge to marine waters. However, data collected during a high rainfall event indicated considerable Fe loads can be transported to the estuary mouth from the catchment

Performance of interFoam on the simulation of progressive waves

The performance of interFoam (a widely-used solver within the popular open source CFD package OpenFOAM) in simulating the propagation of a nonlinear (stream function solution) regular wave is investigated in this work, with the aim of systematically documenting its accuracy. It is demonstrated that over time there is a tendency for surface elevations to increase, wiggles to appear in the free surface, and crest velocities to become (severely) overestimated. It is shown that increasing the temporal and spatial resolution can mitigate these undesirable effects, but that a relatively small Courant number is required. It is further demonstrated that the choice of discretization schemes and solver settings (often treated as a "black box" by users) can have a major impact on the results. This impact is documented, and it is shown that obtaining a "diffusive balance" is crucial to accurately propagate a surface wave over long distances without requiring exceedingly high temporal and spatial resolutions. Finally, the new code isoAdvector is compared to interFoam, which is demonstrated to produce comparably accurate results, while maintaining a sharper surface. It is hoped that the systematic documentation of the performance of the interFoam solver will enable its more accurate and optimal use, as well as increase awareness of potential shortcomings, by CFD researchers interested in the general CFD simulation of free surface waves.Comment: 18 pages and 23 figure

An LC inventory based on representative and coherent farm types

There is a need for valid and representative data regarding the production, resource use and emissions from typical farming systems in Denmark for analysis of the environmental impact of different systems and as input to product oriented analyses such as Life Cycle Assess-ments of basic food items. An inventory of 31 farm types was constructed on the basis of 2138 farm accounts from 1999 selected and weighted to be representative for the Danish farming sector. The farm accounts were grouped according to the major soil types, the num-ber of standard working hours, the most important enterprise (dairy, pig, different cash crops) and the stocking rate (livestock units per hectare). For each group the account data on the average inputs and outputs, land use and herd structure was used to establish a farm type model with coherency between livestock production, total feed use, land use, yields, im-ported feed, home-grown feed, manure production, fertiliser use and crop production. The set of farm types were scaled up to national level thus representing the whole Danish agricul-tural sector for the included products. The sum of area and yield by crop, number and pro-duction by livestock type and the use of fertiliser, energy and concentrated feed was checked against national level statistics and corrected accordingly across all farm types. Resource use and emissions in each farm type was established using standard nutrient concentrations and models for nutrient cycling, energy use and emissions of e.g. ammonia, nitrous oxides and methane. For LCA the product oriented inventory was established using system expan-sion rather than allocations to account for the secondary enterprises in the livestock farm types. Data are made available on a web-based database and may be used for analyses of the primary production systems or as input for LCA across the whole production chain

PROJECT REPORT: A MARKET OPPORTUNITY STUDY FOR THE DEVELOPMENT OF A NEW ONCOLOGY SERVICE IN THE VETERINARY TEACHING HOSPITAL

Current trends in veterinary medicine indicate the potential need for several new services within the VTH. Based on focus groups and practitioner surveys conducted in late 1998 and early 1999, potential new services could include oncology, overnight emergency, behavior medicine, dentistry, equine sports medicine and exotic animal medicine. Of these, an oncology service is currently being considered based on internal staff recommendations coupled with survey and focus group information supporting demand for the service. Different from past new services, the oncology service was also earmarked to undergo a formal market study to determine the full potential of the opportunity and to more clearly establish the goals and objectives within the service.Teaching/Communication/Extension/Profession,