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Biomedical subjects

L W Burgess

Publications and source records attributed to L W Burgess.

12 recordsLinked to original sources
PubMed2001

Near-infrared emissions in single-bubble and multibubble sonoluminescence.

Comparisons of light emissions from multibubble and single-bubble sonoluminescence in the near-infrared band extending from 800 to 1050 nm have been investigated. In argon-water mixtures, single-bubble and multibubble spectra are similar in appearance. In sodium chloride-water mixtures, the multibubble spectrum shows evidence of the 3d-3p sodium emission line, whereas the single-bubble spectrum shows no such emission. For single bubbles, the near-infrared emissions change linearly with driving pressure. No evidence of near-infrared emissions are observed below the visible luminescence threshold.

Journal Article↗
PubMed2000

Low-coherence interferometry in random media. I. Theory.

We present a new nonperturbative theoretical method for the analytical description of light propagation in random multiscattering media. The method is illustrated through the calculation of an expression that describes optical backscattering from a semi-infinite disordered medium. A companion paper [J. Opt. Soc. Am. A 17, 2034 (2000)] compares the theoretical expression with experimental data.

Journal Article↗
PubMed2000

Low-coherence interferometry in random media. II. Experiment.

We present experimental results of measurements of light backscattering from semi-infinite disordered media by low-coherence interferometry (LCI). These results are compared with the theory developed in part I [J. Opt. Soc. Am. A 17, 2024 (2000)]. A comparison of the experimental data with the theoretical formulas based on the coherent phase approximation allows us to extract substantial information about the structure of the studied media. Our results demonstrate that LCI is an effective optical technique for studying nonuniform media even in the case in which the dimensions of nonuniformities are much less than the wavelength of the scattered light.

Journal Article↗
PubMed1999

A Raman waveguide detector for liquid chromatography.

A novel real-time liquid core Raman waveguide detector designed for liquid chromatographic applications is described. The Raman waveguide detector provides enhanced selectivity over typical high-performance liquid chromatography (HPLC) detectors. The waveguide detector also greatly improves the sensitivity of a typical Raman measurement without resorting to surface enhancement or resonance approaches and is compatible with the typical peak width volumes eluted by microbore and minibore HPLC (packed 1-2-mm-i.d. columns). Detection limit enhancements of over 1000-fold have been achieved for the measurement of alcohols in the aqueous phase with the Raman cell utilizing liquid core waveguide technology. The liquid core waveguides demonstrated in this study were constructed using Teflon AF 2400 tubing with a refractive index of 1.29. The low refractive index of the polymer material allowed HPLC separations with Raman detection to be performed with an aqueous mobile phase. A calibration curve for aqueous solutions of 2-propanol was generated and a limit of detection (LOD) of 2 ppm was determined. The Raman waveguide detector is demonstrated for the HPLC analysis of alcohol test mixtures, with LODs in the low-ppm range at the detector. By coupling the temporal separation achieved by HPLC with the vibrational information gleaned from Raman detection, an information-rich multivariate data matrix is obtained that can be deconvoluted to provide chemical speciation even when the HPLC resolution is poor. In this paper, we will discuss the physical and optical design of the Raman waveguide detector and the demonstration of the detector for HPLC detection.

2-Propanol↗
PubMed1993

Toxicity and trichothecene production by Fusarium acuminatum subsp. acuminatum and Fusarium acuminatum subsp. armeniacum.

The toxicity of cultures of Fusarium acuminatum subsp. acuminatum and Fusarium acuminatum subsp. armeniacum grown on Weet-Bix medium was assessed using a chick bioassay. Thirty-nine of 45 cultures of F. a. armeniacum tested produced at least 50% mortality in the chick bioassay. In contrast, of the 26 cultures of F. a. acuminatum tested, only nine produced at least 50% mortality. Selected extracts of both subspecies were analyzed by gas chromatography after clean-up and hydrolysis for the four main trichothecene families, namely; nivalenol (NIV), deoxynivalenol (DON), scirpentriol (Sctol), and T-2 tetraol (T-2tol). Levels of up to 500 micrograms/g and 7 micrograms/g of T-2tol were detected in F. a. armeniacum and F. a. acuminatum extracts respectively. Four cultures each of F. a. armeniacum and F. a. acuminatum were also grown on two solid media (Weet-Bix and Vermiculite) and two liquid media (MYRO and GYEP). Culture extracts were again tested for toxicity and analyzed for trichothecene production. Cultures of F. a. armeniacum grown on the solid media and on MYRO produced the highest toxicity. Levels of up to 168, 129, 150, and 8 micrograms/g of T-2tol were detected in cultures of F. a. armeniacum on Weet-Bix, Vermiculite, MYRO, and GYEP respectively. In contrast, only trace amounts of T-2tol were detected in extracts of F. a. acuminatum on all media. Sctol levels of less than 0.5 microgram/g were also detected in some cultures of both subspecies on solid media, but only F. a. armeniacum produced trace levels of Sctol on liquid media.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Induction of heat stress in beef cattle by feeding the ergots of Claviceps purpurea.

Two groups of 4 Hereford steers were housed in a controlled environment room and exposed to simulated high summer temperatures. Both groups were fed a barley grain and hay diet ad libitum. The barley in one diet contained 0.5% w/w ergots of Claviceps purpurea. Within one week of feeding the ergot diet mean rectal temperature was significantly elevated (P less than 0.05) each afternoon (up to 41 degrees C) but returned to normal overnight. Elevated rectal temperature was accompanied by other signs of heat stress, reduced feed intake, body weight loss and depression or serum prolactin concentration. Symptoms disappeared within 1 week of ceasing to feed the ergot diet.

Animal Feed↗
PubMed1980

Oxalate uptake by everted sacs of rat colon. Regional differences and the effects of pH and ricinoleic acid.

Hyperoxaluria is a complication of disorders associated with steatorrhea. The colon is the presumed site of enhanced oxalate absorption in patients with steatorrhea. We performed studies of colonic mucosal oxalate uptake in everted sacs of rat colon to determine the kinetics of colonic oxalate transport and to evaluate the effect of both pH and ricinoleic acid, a hydroxy fatty acid, on colonic oxalate uptake. Our study demonstrated that oxalate is transported throughout the colon by passive diffusion. Tissue uptake increased linearly with increasing oxalate concentrations and was unaffected by metabolic inhibitors, oxygen deprivation, or temperature changes. There were pH-dependent regional differences of oxalate uptake both in the presence and absence of ricinoleic acid. In the absence of ricinoleic acid, the highest oxalate uptake occurred at the lower pH values (5.4 and 6.4). In the presence of ricinoleic acid oxalate uptake was enhanced at the higher pH values (7.4 and 8.4); a finding most likely related to decreased solubility of ricinoleic acid at pH 5.4 and 6.4. Intraluminal pH is an important determinant of colonic oxalate uptake in the presence and absence of ricinoleic acid.

Animals↗