An Electrometer Amplifier with Low Input Capacitance and Large Input Dynamic Range

An electrometer amplifier has been designed for biological research with the following data: input resistance larger than 1012; input current 10-12 A; low input capacitance; and an input dynamic range from 0 to ± 7 v. The input stage consists of JFET.     

Accurate and precise measurement of selenium by instrumental neutron activation analysis

An accurate and precise measurement of selenium in Standard Reference Material (SRM) 3149, a primary calibration standard for the quantitative determination of selenium, has been accomplished by instrumental neutron activation analysis (INAA) in order to resolve a question arising during the certification process of the standard. Each limiting factor of the uncertainty in the activation analysis, including the sample preparation, irradiation, and γ-ray spectrometry steps, has been carefully monitored to minimize the uncertainty in the determined mass fraction. Neutron and γ-ray self-shielding within the elemental selenium INAA standards contributed most significantly to the uncertainty of the measurement. An empirical model compensating for neutron self-shielding and reducing the self-shielding uncertainty was successfully applied to these selenium standards. The mass fraction of selenium in the new lot of SRM 3149 was determined with a relative standard uncertainty of 0.6%.     

Toxicity and dose-response studies of 1,25-(OH)2-16-ene-23-yne vitamin D3 in transgenic mice

The vitamin D3 analogue 1,25-(OH)2-16-ene-23-yne vitamin D3 (16,23-D3) in doses with low systemic toxicity has been demonstrated to inhibit retinoblastoma growth in transgenic mice. This study examines the dose-dependent response for inhibition of tumor growth in transgenic mice with retinoblastoma and evaluates the in vivo toxicity of 16,23-D3 in nontransgenic mice. Transgenic 8-10-week-old mice with retinoblastoma (n = 119) were randomly assigned to groups receiving 1.0, 0.75, 0.5, 0.35, 0.2, or 0.05 microg of 16,23-D3 and a vehicle alone (control) group i.p. five times a week for 5 weeks. An additional control group received no injection. Eyes were enucleated one week after the end of treatment, and tumor areas were measured. To determine the toxic dose, transgene-negative littermates received 0.5, 1.0, 1.5, 2.5, 3.5, 4.5, or 5.0 microg of 16,23-D3, and control groups received vehicle alone, 5 days a week for 5 weeks. Serum calcium levels were measured, and necropsies were performed on animals from each group. In the dose-response study, tumor growth inhibition was greatest in the group receiving 0.35 microg (55% inhibition; P = 0.0056) and was also significant in the group receiving 0.5 microg (42% inhibition; P = 0.036). The systemic toxic effects due to hypercalcemia occurred at doses of > or =1.0 microg. 16,23-D3 inhibits tumor growth at doses > or =0.35 microg and shows toxic effects at doses > or =1.0 microg related to hypercalcemia in mice fed an unrestricted diet. No toxicity was observed with lower doses.     

Effect of Surface Roughness on the Magnetic Field Profile in the Meissner State of a Superconductor

It is well known that the London model (valid for a hard type II superconductor) predicts an externally applied magnetic field decays exponentially as a function of depth into the superconductor on a length scale λ. Direct measurements of the field profile using low energy μSR on high-Tc superconductors, such as YBa₂Cu₃ O _x measure deviations from a simple exponential decay. In particular, there is a short length scale δ close to the surface where the magnetic field does not decay. It has been proposed that this is due to surface roughness, which leads to a suppression of the order parameter near the surface. A model of surface roughness has been studied for the case of a sinusoidally modulated surface roughness on an isotropic superconductor showing that in some cases the profiles resulting from surface roughness may be qualitatively similar to the dead layer phenomena in that the field magnitude decay rate may be slowed near the surface relative to a flat interface but that for modest roughness, the quantitative value of the length over which the field decay is slowed is much smaller than the experiments measure. In this paper, we extend this work in two directions: firstly, by using atomic force microscopy data of YBa₂Cu₃ O _x crystals, we predict the expected field profiles within the context of the Isotropic London model of superconductivity given their actual surface geometry; and secondly, we consider how surface roughness could affect experimental values for λ and δ. The main finding is that roughness within an isotropic model does not produce the dead layers found in experiments on YBa₂Cu₃ O _x . However, we suggest that roughness in a highly anisotropic superconductor could account for the observed dead layer.     

Retrofit of Trangslet hydro power station

An accident in Trangslet Power Station in the fall of 1982 resulted in, among other things, flooding of the control equipment. Despite the effective cleaning up after the flooding, the reliability was not adequate and new equipment was needed. When assessing various options, Stora Power came to the conclusion that a computerized control system would be the best solution because of its ability to optimize the power production of the station. The authors describe the utility requirements for the distributed control system and experiences from implementation and operation. They also cover the control system philosophy and implemented functions. During the installed system's first four years of operation, the requirements set by Stora Power have been achieved     

Resonant tunneling permeable base transistors with high transconductance

A GaAs-based resonant tunneling permeable base transistor has been developed and evaluated at room temperature. The transistor is fabricated by overgrowing a tungsten gate placed next to an AlGaAs-GaAs-InGaAs resonant tunneling heterostructure. By changing the gate voltage, the effective conducting area of the tunnel diode can be modulated and the collector-emitter current thus controlled. Peak currents above 300 mA/mm and a maximum transconductance of 270 mS/mm have been obtained.     

The combustion toxicity controversy

As long as 20 years ago the need was considered to extend codes concerned with flammability and/or flame spread, to include combustion toxicity requirements. Due to the lack of suitable toxicity tests at that time, the added code requirements for combustion toxicity were not enforceable. Vinyl resin manufacturers have been cited as purveyors of hazardous materials which, when burned, generate a noxious toxic hazard due to the fumes they produce in a fire. Overlooked are such factors that commercial vinyl products have inherent low ignition and flame spread rates and only generate potentially toxic gases when quantities of other materials burning around them heat the vinyls to the decomposition point. In 1983 New York State commissioned a study by A. D. Little Inc. to assess the feasability of incorporating combustion toxicity requirements into building material and furnishing codes of New York State. This paper summarizes these findings, including evaluation and analysis of the data generated by the two tests selected as best meeting the seven critical criteria. Due to differnt combustion toxicity rankings provided by the two test methods, controversial and confusing interpretations reign. As a result, the author provides a four step set of recommendations.