Generalized Electrical Substitution Methods and Detectors for Absolute Optical Power Measurements.

We have developed generalized methods for electrical substitution optical measurements, as well as cryogenic detectors which can be used to implement them. The new methods detailed here enable measurement of arbitrary periodic waveforms by an electrical substitution radiometer (ESR), which means that spectral and dynamic optical power can be absolutely calibrated directly by a primary standard detector. Cryogenic ESRs are not often used directly by researchers for optical calibrations due to their slow response times and cumbersome operation. We describe two types of ESRs with fast response times, including newly developed cryogenic bolometers with carbon nanotube absorbers, which are manufacturable by standard microfabrication techniques. These detectors have response times near 10 ms, spectral coverage from the ultraviolet to far-infrared, and are ideal for use with generalized electrical substitution. In our first tests of the generalized electrical substitution method with FTS, we have achieved uncertainty in detector response of 0.13 % (k=1) and total measurement uncertainty of 1.1 % (k=1) in the mid-infrared for spectral detector responsivity calibrations. The generalized method and fast detectors greatly expand the range of optical power calibrations which can be made using a wideband primary standard detector, which can shorten calibration chains and improve uncertainties.

Development of electrical substitution Fourier transform spectrometry for absolute optical power measurements.

We have demonstrated the first continuous-scan electrical substitution Fourier transform spectrometer (ES-FTS), which serves initially as an apparatus for absolute spectral responsivity calibrations of detectors over the wavelength range from 1.5 µm to 11 µm. We present data on the realization of a spectral detector-comparator system with high accuracy, high dynamic range, high spectral resolution and fast measurement in the infrared region, which is tied directly to an absolute power scale through electrical substitution. The ES-FTS apparatus employs a commercial Fourier transform spectrometer and a custom electrical substitution bolometer detector to enable spectrally-resolved absolute optical power measurements. A generalization of electrical substitution techniques enables determination of the voltage waveform that must be applied to the bolometer's electrical heater to cancel the optical signal from a Michelson interferometer in order to quantify the time-dependent optical power incident on the bolometer. The noise floor of the electrical substitution bolometer is on the order of 10 pW/Hz½ and its response is expected to be linear from the noise floor to 1 mW. A direct comparison between a pyroelectric standard detector and the ES-FTS has been performed, and experimental results reported here show great potential for this technique.

Transition from Gas-like to Liquid-like Behavior in Supercritical N2.

We have studied in detail the transition from gas-like to rigid liquid-like behavior in supercritical N2 at 300 K (2.4 TC). Our study combines neutron diffraction and Raman spectroscopy with ab initio molecular dynamics simulations. We observe a narrow transition from gas-like to rigid liquid-like behavior at ca. 150 MPa, which we associate with the Frenkel line. Our findings allow us to reliably characterize the Frenkel line using both diffraction and spectroscopy methods, backed up by simulation, for the same substance. We clearly lay out what parameters change, and what parameters do not change, when the Frenkel line is crossed.

Electric discharge machine for preparation of diamond anvil cell sample chambers.

We have designed and constructed a novel electric discharge machine designed primarily for the preparation of sample chambers in rhenium and stainless steel gaskets for diamond anvil cell experiments. Our design combines automatic stage movement with relatively low voltage (100 V) operation and routinely achieves a drilling/erosion speed of approximately 0.4 µm s-1. The machine is used for preparing 100 µm diameter sample chambers for diamond anvil cell experiments with 250 µm culets and has also been used to prepare 50 µm diameter sample chambers for diamond anvil cell experiments with 100 µm culets to access a pressure of 165 GPa.

Wideband infrared trap detector based upon doped silicon photocurrent devices.

We have designed, fabricated, and measured infrared trap detectors made from arsenic-doped silicon (Si:As) blocked impurity band (BIB) photodetectors. These trap detectors are composed of two detectors in a wedge geometry, with an entrance aperture diameter of either 1 or 3 mm. The detectors were calibrated for quantum efficiency against a pyroelectric reference detector using a Fourier transform spectral comparator system, and etalon effects and spatial uniformity of the traps were also quantified. Measurements of the traps at a temperature of 10 K show that nearly ideal external quantum efficiency (>90%) can be attained over much of the range from 4 to 24 µm, with significant responsivity from 2 to 30 µm. The traps exhibited maximum etalon oscillations of only 2%, which is about 10 times smaller amplitude than those of the single Si:As BIB detectors measured under similar conditions. Spatial nonuniformity across the entrance apertures of the traps was about 1%. The combination of high detectivity, wideband wavelength coverage, spectral flatness, and spatial uniformity make these trap detectors an excellent reference detector for spectrally resolved measurements and radiometric calibrations over the near- to far-infrared wavelength range.

Dynamics, thermodynamics and structure of liquids and supercritical fluids: crossover at the Frenkel line.

We review recent work aimed at understanding dynamical and thermodynamic properties of liquids and supercritical fluids. The focus of our discussion is on solid-like transverse collective modes, whose evolution in the supercritical fluids enables one to discuss the main properties of the Frenkel line separating rigid liquid-like and non-rigid gas-like supercritical states. We subsequently present recent experimental evidence of the Frenkel line showing that structural and dynamical crossovers are seen at a pressure and temperature corresponding to the line as predicted by theory and modelling. Finally, we link dynamical and thermodynamic properties of liquids and supercritical fluids by the new calculation of liquid energy governed by the evolution of solid-like transverse modes. The disappearance of those modes at high temperature results in the observed decrease of heat capacity.

On the high-pressure phase stability and elastic properties of ß-titanium alloys.

We have studied the compressibility and stability of different ß-titanium alloys at high pressure, including binary Ti-Mo, Ti-24Nb-4Zr-8Sn (Ti2448) and Ti-36Nb-2Ta-0.3O (gum metal). We observed stability of the ß phase in these alloys to 40 GPa, well into the ω phase region in the P-T diagram of pure titanium. Gum metal was pressurised above 70 GPa and forms a phase with a crystal structure similar to the η phase of pure Ti. The bulk moduli determined for the different alloys range from 97 ± 3 GPa (Ti2448) to 124 ± 6 GPa (Ti-16.8Mo-0.13O).

Crossover between liquidlike and gaslike behavior in CH_{4} at 400 K.

We report experimental evidence for a crossover between a liquidlike state and a gaslike state in fluid methane (CH_{4}). This crossover is observed in all of our experiments, up to a temperature of 397 K, 2.1 times the critical temperature of methane. The crossover has been characterized with both Raman spectroscopy and x-ray diffraction in a number of separate experiments, and confirmed to be reversible. We associate this crossover with the Frenkel line-a recently hypothesized crossover in dynamic properties of fluids extending to arbitrarily high pressure and temperature, dividing the phase diagram into separate regions where the fluid possesses liquidlike and gaslike properties. On the liquidlike side the Raman-active vibration increases in frequency linearly as pressure is increased, as expected due to the repulsive interaction between adjacent molecules. On the gaslike side this competes with the attractive van der Waals potential leading the vibration frequency to decrease as pressure is increased.

High-gain cryogenic amplifier assembly employing a commercial CMOS operational amplifier.

We have developed a cryogenic amplifier for the measurement of small current signals (10 fA-100 nA) from cryogenic optical detectors. Typically operated with gain near 10(7) V/A, the amplifier performs well from DC to greater than 30 kHz and exhibits noise level near the Johnson limit. Care has been taken in the design and materials to control heat flow and temperatures throughout the entire detector-amplifier assembly. A simple one-board version of the amplifier assembly dissipates 8 mW to our detector cryostat cold stage, and a two-board version can dissipate as little as 17 µW to the detector cold stage. With current noise baseline of about 10 fA/(Hz)(1/2), the cryogenic amplifier is generally useful for cooled infrared detectors, and using blocked impurity band detectors operated at 10 K, the amplifier enables noise power levels of 2.5 fW/(Hz)(1/2) for detection of optical wavelengths near 10 µm.

Stabilization of boron carbide via silicon doping.

Boron carbide is one of the lightest and hardest ceramics, but its applications are limited by its poor stability against a partial phase separation into separate boron and carbon. Phase separation is observed under high non-hydrostatic stress (both static and dynamic), resulting in amorphization. The phase separation is thought to occur in just one of the many naturally occurring polytypes in the material, and this raises the possibility of doping the boron carbide to eliminate this polytype. In this work, we have synthesized boron carbide doped with silicon. We have conducted a series of characterizations (transmission electron microscopy, scanning electron microscopy, Raman spectroscopy and x-ray diffraction) on pure and silicon-doped boron carbide following static compression to 50 GPa non-hydrostatic pressure. We find that the level of amorphization under static non-hydrostatic pressure is drastically reduced by the silicon doping.

Assessment of the influence of NaF or 1,25-(OH)2 vitamin D3 on the proliferative bone effect of an avian osteopetrosis virus, MAV-2(O).

1,25-(OH)2 vitamin D3 (D3) and sodium fluoride (NaF) were given to chicken embryos and newly hatched chickens infected with a slow onset strain of avian osteopetrosis-inducing virus [MAV-2(O)] to determine if either agent influenced MAV-2(O)-induced proliferation of bone. Embryos were administered MAV-2(O) and treated with: 1) up to 240 micrograms NaF or up to 100 ng D3 as embryos; 2) up to 1.8 g NaF/kg or up to 9.5 micrograms D3/kg after hatching: or 3) 240 micrograms NaF as embryos and up to 1.8 g NaF/kg after hatching. Administration of MAV-2(O) alone resulted in expansion of the cortical diameter of bone. Coadministration of NaF or D3 with MAV-2(O) did not influence the change in cortical diameter seen with MAV-2(O) alone at 18 days of incubation, and 3 and 6 weeks after hatching. Increased osteoid relative to bone (hyperosteoidosis), with NaF and MAV-2(O) compared to MAV-2(O) alone, and NaF compared to untreated controls reflected delayed mineralization of osteoid, a known fluoride effect. We conclude that the administration of NaF or D3 did not influence the incidence, severity or time of onset of the MAV-2(O)-induced proliferative changes of bone.

Fibrogenicity and carcinogenic potential of smelter slags used as abrasive blasting substitutes.

This study was designed to examine the fibrogenic and carcinogenic potentials of three smelter slags (primary copper slag, secondary copper slag, and nickel slag) that have been used for a number of years as substitutes for sand in abrasive blasting operations. Seven groups of 85 male Fischer 344 rats (approximately 180 g) were used. Each group was given a single 20-mg dose of one of the following test materials via intratracheal instillation: primary copper slag, secondary copper slag, nickel slag, feldspar, Min-U-Sil, novaculite, or vehicle control. Chemical, particle size, and surface area analyses were performed for each test dust. Animals were weighed monthly, and ten animals per group were necropsied at the 6-, 12-, and 18-mo interim sacrifices. The terminal sacrifice was conducted at 22 mo. Hematoxylin and eosin stained histologic sections were prepared from designated formalin-fixed tissues collected at necropsy and examined microscopically. The pulmonary fibrogenic and carcinogenic potentials of the three smelter slags were compared histopathologically with feldspar, novaculite, Min-U-Sil, and vehicle controls. Only minimal to slight alveolar wall fibrosis was seen in the two copper slag groups, while the response seen with nickel slag was consistent with a foreign body reaction with minimal fibrosis seen in only an occasional animal. The major reaction seen in both the feldspar- and the novaculite-treated rats was a granulomatous inflammation with varying degrees of fibrosis associated with the granulomas. Significant numbers of primary lung tumors, principally adenocarcinomas and adenomas, were seen in the copper slag (p = 0.005 and p = 0.022 for the primary and secondary slags, respectively), in the feldspar (p = 0.007), in the novaculite (p less than 0.001), and in the Min-U-Sil (p less than 0.001) groups when compared to the vehicle control group. In addition, the Min-U-Sil and novaculite groups had significantly elevated pulmonary tumor proportions relative to the other treatments (p less than or equal to 0.002), with the Min-U-Sil being higher than the novaculite (p = 0.012). On the basis of the tumor incidence data, one must conclude that both copper slags tested in this study are carcinogenic to rats.

Brain acetylcholinesterase, acid phosphatase, and 2',3'-cyclic nucleotide-3'-phosphohydrolase and plasma butyrylcholinesterase activities in hens treated with a single dermal neurotoxic dose of S,S,S-tri-n-butyl phosphorotrithioate.

The changes in brain acetylcholinesterase (AChE), acid phosphatase (APase), and 2',3'-cyclic nucleotide-3'-phosphohydrolase (CNP), and plasma butyrylcholinesterase (BuChE) activities were investigated in hens treated with a single, dermal dose (100-1000 mg/kg) of S,S,S-tri-n-butyl phosphorotrithioate (DEF). Three control groups consisted of hens left untreated, given a single, dermal dose of 500 mg/kg tri-o-cresyl phosphate (TOCP, positive control for organophophorous compound-induced delayed neurotoxicity), or 10 mg/kg O,O-diethyl O-4-nitrophenyl phosphorothioate (parathion, negative control). Brain AChE activity, determined 28 days after application, was significantly inhibited in hens given 500-1,000 mg/kg DEF and in TOCP- and parathion-treated hens. In contrast, brain APase and CNP activities were significantly higher in all treatments as compared with those of the untreated hens. Parathion, however, caused the least increase in these enzymatic activities as compared to DEF or TOCP. A single, dermal dose of DEF or TOCP also caused an initial decrease in plasma BuChE activity with maximum depression of enzymatic activity observed 1 to 7 days after administration. This decrease was dose dependent and the enzymatic activity showed partial recovery with time. Hens treated with single, dermal doses of DEF, ranging from 250 to 1000 mg/kg, developed ataxia which progressed to paralysis in some hens. Histopathologic examination revealed axon and myelin degeneration of the spinal cord and peripheral nerves of some hens. The severity and frequency of the neuropathologic lesions were dose dependent. Neurologic dysfunctions and neuropathologic lesions seen in DEF-treated hens were similar to those exhibited in TOCP-treated hens. While parathion produced acute cholinergic effects, it did not cause delayed neurotoxicity. The changes in brain and plasma enzymes are discussed in relation to their role in the pathogenesis of DEF-induced delayed neurotoxicity.

Reproduction in Fischer-344 rats exposed to methyl chloride by inhalation for two generations.

Male and female Fischer-344 rats were exposed to methyl chloride by inhalation (0, 150, 475, or 1500 ppm, 6 hr/day, 5 days/week, 40 males and 80 females per group). The only treatment-related clinical signs were a 10 to 20% body weight gain depression (BWGD) in both males and females exposed to 1500 ppm at all weekly weighings after 2 weeks of exposure and a 5-7% BWGD in 475-ppm exposed animals after Day 57. After 10 weeks the exposure schedule was changed to 6 hr/day, 7 days/week and each male was mated to two exposed females. The mating period was ended after 2 weeks, at which point 10 males/group were necropsied. The only treatment-related lesions found were severe bilateral testicular degeneration (10/10) and granulomas in the epididymis (3/10) in the 1500-ppm males. The remaining 30 males per group were then removed from exposure and mated during a 2-week period with 60 unexposed females. The exposed females were continued on exposure from the start of mating to Postnatal Day 28 (6 hr/day, 7 days/week). The females were not exposed from Gestation Day 18 to Postnatal Day 4, and the pups were never directly exposed prior to weaning. There were no significant differences between groups in the number of exposed or unexposed females that mated, as evidenced by copulation plugs. No litters were born to exposed or unexposed females mated to the 1500-ppm males. There was no significant difference in the number of litters produced by the 150-ppm groups when compared to the control groups. Fewer litters were born in the 475-ppm groups than in the control groups. No differences in litter size, sex ratio, pup viability, or pup growth were found among the 475-ppm, 150-ppm, or control F0 groups. When bred 10 weeks after the cessation of exposures, 5 to 20 1500-ppm F0 males had regained the ability to sire normal litters. The same number of 475-ppm F0 males proved as fertile (15/20) as control F0 males (13/20). After weaning, F1 pups from the 475-, 150-, and 0-ppm groups were exposed to the same concentrations of methyl chloride for 10 weeks and then mated. A trend toward decreased fertility was found in the 475-ppm F1 group.