RESUMEN

Staggers was diagnosed in sheep and cattle from the northern California coast. The diagnosis was made on the basis of history of ingestion of perennial ryegrass (Lolium perenne) stubble, clinical signs of transient ataxia, which was aggravated by stimulation, and nearly complete recovery after removal of ryegrass as the primary forage. Morbidity was high, but death did not occur in any affected animals. The toxic endophyte, Acremonium lolii, was in most lower leaf sheaths from the ryegrass. Injection of extracts of the ryegrass from affected farms into mice induced signs of toxicosis. Additionally, ryegrass from all 3 farms contained the tremorgenic mycotoxin, lolitrem-B.

Asunto(s)

RESUMEN

Total arsenic is determined by inductively coupled plasma atomic emission using hydride vapor generation. A 1 g sample is wet washed in a 16 x 150 mm 10 mL volumetric test tube on a programmed heating block with nitric, sulfuric, and perchloric acids at up to 310 degrees C. After treatment with hydrochloric acid and potassium iodide, arsenic is reduced by sodium borohydride to arsine in a simplified continuous flow manifold. A standard pneumatic nebulizer affects the gas-liquid separation of AsH3, which is quantified by ICP atomic emission at 193.756 nm. The instrument detection limit for the method has been determined to be 0.4 microgram/L. For a 10:1 dilution of a nominal 1 g sample, the detection limit is 4 micrograms/kg and the linear range is up to 4 mg/kg. Recoveries from 3 matrixes were 99-104%, with a typical RSD of 2%. The method has demonstrated statistical control for samples of biological interest and is especially well suited to analysis of small samples.

Asunto(s)

RESUMEN

In September 1988, 100 of 300 yearling dairy heifers developed blindness, tachypnea, foaming at the mouth, chewing, and facial fasciculations. Twenty-five animals died. Lead toxicosis was diagnosed based on the clinical signs and the presence of excessive concentrations of lead in whole blood, liver, kidney, and rumen contents of affected animals. The source of the lead was sudan grass silage that had been contaminated by soil that contained up to 77,000 mg/kg of lead. Lead concentrations were determined approximately 7 months after the acute episode of lead toxicosis. Whole blood and milk samples were obtained from heifers and a group of control cows 2 weeks prior to (blood only), at the time of, and 2 and 4 weeks after freshening. No lead was found in any of the milk samples (detection limit = 0.055 mg/liter). Animals that had been severely affected by lead toxicosis experienced a transient increase in whole blood lead concentrations at freshening that was not high enough to be considered toxic. No similar increases in blood lead were observed for control cows or heifers that had experienced milder toxicosis. These findings suggest that at parturition lead is mobilized into the blood of cattle previously exposed to excessive lead.

Asunto(s)

RESUMEN

Total selenium is determined by inductively coupled plasma (ICP) atomic emission using hydride vapor generation. A 1 g sample is wet ashed in a 16 x 150 mm 10 mL volumetric test tube on a programmed heating block with nitric, sulfuric, and perchloric acids at up to 310 degrees C. After treatment with hydrochloric acid, the selenium is reduced by sodium borohydride to hydrogen selenide is a simplified continuous flow manifold. A standard pneumatic nebulizer effects the gas-liquid separation of H2Se, which is quantified by ICP atomic emission at 196.090 nm. The instrument detection limit for the method has been determined to be 0.4 microgram/L. For a 10:1 dilution of a nominal 1 g sample, the detection limit is 4 micrograms/kg and the linear range is up to 4 mg/kg. The method has demonstrated statistical control for samples of biological and environmental interest and is especially well suited to analysis of small samples.

Asunto(s)

RESUMEN

A rapid, ion-exchange liquid chromatographic method for the determination of nitrate and nitrite in biological fluids is presented. Samples are deproteinated by ultrafiltration followed by removal of chloride using a silver form cation-exchange resin. Nitrate and nitrite are measured by ion-exchange liquid chromatography with conductivity detection. Recoveries from serum, ocular fluid, and water were determined for fortifications from 10 to 150 mg/L. Average recoveries ranged from 96 to 104% for nitrate and from 89 to 105% for nitrite. Pooled RSD values ranged between 1.5 and 1.9% for these analytes in all matrixes examined. The method of joint confidence hexagons was applied to the data to determine constant and relative bias of the method for each of the 3 matrixes in the study.

Asunto(s)

RESUMEN

This rapid, accurate procedure for trace elements and electrolytes in serum requires little sample preparation: to 1 mL of serum a single reagent is added that contains trichloroacetic and hydrochloric acids for protein precipitation, hydroxylamine sulfate for iron reduction, and yttrium as the internal standard. After centrifugation, the supernates are directly analyzed for Na, K, Mg, Ca, Pi, Fe, Cu, and Zn by inductively-coupled plasma emission spectrometry. The CVs were respectively 7.9%, 8.4%, 8.6%, 10.0%, 9.0%, 9.4%, 9.0%, and 9.0% for five assays of National Institute of Standards and Technology Standard Reference Material (SRM) no. 1598, Bovine Serum. Analytical recoveries ranged from 92% to 107% for both SRM 1598 and commercial control serum.

Asunto(s)

Asunto(s)

RESUMEN

In part I, we presented a method for solving the inverse scattering problem using multiple sources and detectors. Allowance for multiple angles of incident radiation improves the ill-posed nature of the inverse problem by improving the quality and quantity of information gathered at detector points. This paper describes implementation and numerical evaluation of the method. An 11 by 11 image reconstructed from noisy scattered field data is shown to closely match the original scattering object, and the improvement possible by constraining the reconstruction to be spatially band limited is demonstrated. Furthermore, for a somewhat simpler "pseudo-inverse problem," we give findings on the effects that detector radius, degree of over determination, noise, and object contrast have on reconstruction quality.

Asunto(s)

RESUMEN

A new method for solving the inverse scattering problem for the scalar, inhomogeneous, exact, Helmholtz wave equation is presented. No perturbation approximations are used and the method is applicable even for many cases where weak to moderate attenuation and moderate to strong refraction of incident fields occur. The ill-posed nature of the inverse scattering problem for a single monochromatic source is known. However, the use of multiple sources, the collection of redundant (i.e., overdetermined) data, and the constraining of the fields and complex refractive index to be spatially band limited constitutes a new problem. The cases we have tested by computer simulation indicate that the new problem is well posed, a unique solution, and is stable with noisy data. The method is an application of the well-known method of moments with sinc basis and delta testing functions to discretize the problem. The inverse scattering solution may be obtained by solving the resulting set of simultaneous, quadratic, multivariate equations. Several algorithms for solving these equations are given.

Asunto(s)

Asunto(s)

Asunto(s)

Asunto(s)

Asunto(s)

Asunto(s)

Asunto(s)

Asunto(s)