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D McAlister

Publications and source records attributed to D McAlister.

7 recordsLinked to original sources
PubMed1999

IV-VI semiconductor growth on silicon substrates and new mid-infrared laser fabrication methods

This paper reviews results from research conducted at the University of Oklahoma on the development of new IV-VI semiconductor (lead salt) epitaxial growth and laser fabrication procedures that can ultimately lead to dramatic increases in mid-IR laser operating temperatures. Work has focused on growth of IV-VI semiconductor laser structures on silicon substrates using buffer layers that contain BaF2. Recent experiments show that it is possible to obtain high crystalline quality IV-VI semiconductor layer structures on (111)-oriented silicon substrates using molecular beam epitaxy (MBE) or on (100)-oriented silicon using a combination of MBE and liquid phase epitaxy (LPE). Experimental data for IV-VI semiconductor layer structures grown on silicon substrates including crystalline quality information as determined by high resolution X-ray diffraction (HRXRD) measurements and absorption edge information as determined by Fourier transform infrared (FTIR) transmission measurements are presented. Results show that these materials can be used to fabricate lasers that cover the 3 microns (3333 cm-1) to 16 microns (625 cm-1) spectral range. Removal of IV-VI semiconductor laser structures from the silicon growth substrate by dissolving BaF2 buffer layers with water is also demonstrated. This allows epitaxially-grown laser structures to be sandwiched between two heat sinks with a minimum of thermally resistive IV-VI semiconductor material. Theoretical modeling predicts that IV-VI lasers fabricated this way will have maximum continuous wave (cw) operating temperatures at least 60 degrees higher than those of IV-VI lasers fabricated on PbSe or PbTe substrates.

Journal Article↗
PubMed1998

Natural bioburden levels detected on flexible gastrointestinal endoscopes after clinical use and manual cleaning.

BACKGROUND: Colonoscopes present a special bacterial decontamination challenge because the colon has a large and diverse microbial population. METHODS: Bioburden of colonoscope insertion tube surfaces and suction channels were determined after use and after manual cleaning. RESULTS: After use bioburden in suction channels averaged 7.0 x 10(9) colony-forming units (cfu). Cleaning reduced this level to 1.3 x 10(5). Cleaning of tube surfaces reduced the after-use bioburden from a level of 5.1 x 10(5) to 2.2 x 10(4) cfu. Gram-negative rods accounted for approximately 99% of the bioburden within the suction channel after use and after cleaning. After use flora were predominantly Escherichia coli and Bacteroides. The flora shifted to waterborne Pseudomonas organisms, and other members of the family Enterobacteriaceae after cleaning. Gram-positive bacteria were the primary isolates from the device surfaces both after use (56%) and after cleaning (47%). Because gram-positive cocci and diphtheroids are a part of the normal microbiota of the skin, these bacteria may have been introduced by the hospital environment or by handling. CONCLUSIONS: After the cleaning of in-use colonoscopes, fewer than 10(6) vegetative bacteria could be recovered. This value is several logs lower than some previous estimates. This finding may be useful in the formulation of sterilization and disinfection cycles. Microflora from the colonoscopes indicated that the cleaning process introduced waterborne and enteric microorganisms, which highlights the importance of sanitation in the device reprocessing area.

Bacteria, Aerobic↗
PubMed1997

Natural bioburden levels detected on rigid lumened medical devices before and after cleaning.

Controversy exists concerning the degree of microbial contamination associated with the use of rigid lumened medical devices, the efficacy of standard cleaning techniques used to remove pathogenic microorganisms from lumen channels, and whether patients are placed at risk of cross infection because of microbial contamination. In this study the level and types of microorganisms found on rigid lumened medical devices before and after cleaning in a hospital environment were investigated. The bioburden level after clinical use was found to be relatively low, ranging from 10(1) to 10(4) colony forming units (CFU) per device. After the instruments were cleaned, none of the devices studied contained bioburden levels greater than 10(4) CFU and 83% had bioburden levels less than or equal to 10(2) CFU. The bioburden present before cleaning was comprised of organisms derived from the handling of the device, from the hospital environment, and from the patient. The bioburden present after cleaning was comprised of organisms typically derived from the handling of the device and from the hospital environment. The level of bioburden per device was also related to the anatomic site where the device was used, with lower numbers of organisms found on devices exposed to sterile body sites and the respiratory tract.

Colony Count, Microbial↗
PubMed1993

RMI (Resource Management Initiative) and quality--getting the climate right.

The literature on the Resource Management Initiative (RMI) identifies an improvement in the quality of patient care as one of its principal aims. Successful implementation of RMI requires a change in behaviour. The mechanism or process by which this is to be achieved is not clear. This paper explores the possible nature of this relationship. We suggest that an understanding of the mechanisms through which an acute hospital can influence quality is best viewed from the perspective of organisational climate. The paper suggests a normative model for exploring climate and quality linkages through the operation of six key organisational levers. The applicability of the model is discussed throughout with reference to a RM acute hospital.

Health Resources↗
PubMed1989

Inhibition by maltose, isomaltose, and nigerose of the synthesis of high-molecular-weight D-glucans by the D-glucosyltransferases of Streptococcus sobrinus.

Two D-glucosyltransferases are produced by Streptococcus sobrinus C211. One (GTF-S) catalyzes the conversion of sucrose into soluble alpha-(1----6)-linked alpha-(1----3)-branched D-glucans, and the other (GTF-I), of sucrose into alpha-(1----3)-linked alpha-(1----6)-branched D-glucans. These enzymes were studied by using maltose, isomaltose, and nigerose as inhibitors. Maltose and isomaltose were found to be competitive inhibitors of GTF-S, whereas nigerose has no effect on GTF-S activity. The Ki values for maltose and isomaltose were determined to be 11 and 15mM, respectively. Maltose, isomaltose, and nigerose competitively inhibit GTF-I. The Ki values for these inhibitors were found to be approximately 0.8, 2.5, and 15mM, respectively. The inhibitory properties of each disaccharide are interpreted in terms of conformational comparisons with sucrose.

Carbohydrate Conformation↗
PubMed1989

Glucosyltransferases of Streptococcus sobrinus C211 are both stimulated and inhibited by hydrogen peroxide.

There are 2 glucosyltransferases (GTF) produced by Streptococcus sobrinus C211. One enzyme, GTF-S, produces a water-soluble glucan that is a-1,6-linked, with short a-1,3 branches, and the other enzyme, GTF-I, produces a water-insoluble glucan that is a-1,3-linked with a-1,6 branches. Hydrogen peroxide was found not only to be a potent inhibitor of GTF activity, but also a stimulator of GTF activity when employed at relatively low concentrations. At 0.88 M, H2O2 completely inhibited insoluble glucan synthesis, whereas at a 0.29 M concentration, H2O2 enhanced synthesis of the same glucan. Soluble glucan synthesis was also inhibited by H2O2 at 1.47 M. Low concentrations of hydrogen peroxide with GTF-S, however, caused the enzyme to convert from soluble glucan production to insoluble glucan production. 13C-Nuclear magnetic resonance spectra of glucans produced by peroxide-treated GTF confirmed that the production of a-1,3 linked glucans was increased with H2O2-treated GTF-S.

Glucans↗