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81.
This paper analyses the HIPERLAN channel access mechanism. Both a purely mathematical and a simulation model are built in order to evaluate the two successive phases of the contention scheme. Several optimisations, based on the choice of parametric values, are proposed, evaluated and compared. 相似文献
82.
JS Lewis 《Canadian Metallurgical Quarterly》1993,158(8):548-552
The utilization of a physician critique process in the design of a parenteral nutrition order form, encouraging a standard order option, is assessed. In the critique process, physicians from surgery, medicine, and medical intensive care teams were tasked to use the draft order form and guideline sheet to prescribe a parenteral nutrition order for a hypothetical patient. Prescriber recommendations and problems with the nutrition order form and guideline sheet directed editorial improvements. The physician assessment process is an effective means to measure utility of a draft parenteral order form and prescribing guideline sheet. By utilizing physician expertise, deficiencies inherent in such an order form may be corrected prior to implementation. 相似文献
83.
It is important to monitor grain- oriented steel during production so that regions of small, loss- inducing grains can be
detected. These are a rare occurrence, but need to be eliminated to prevent a stripe of small grains from passing unnoticed.
On- line full- strip- width power loss measurements may overlook stripes of small grains. A system for detecting small grains
is described. 相似文献
84.
K. A. Taylor 《Metallurgical and Materials Transactions A》1992,23(1):107-119
The segregation and precipitation of boron have been studied in two 0.2C−0.6Mn0.−5Mo steels containing (nominally) 10 and
50 ppm B. After heating to 1260 δC, samples were air-cooled to 870 °C and then held for times between 0 and 5000 seconds.
Additional samples were heated to 1260 °C, air-cooled to 900 °C, reduced in thickness by 50 pct, and then held for various
times at 870 °C, as above. The distributions of boron under these various conditions were investigated qualitatively by an
autoradiographic technique. In both steels, segregation and/or precipitation of boron at austenite grain boundaries was detected
under all conditions examined. Precipitation of iron borocarbide particles occurred along austenite grain boundaries in the
50 ppm B steel during cooling to the holding temperature of 870 °C, while in the 10 ppm B steel, such precipitation occurred
only after long times at 870 °C. Mechanical properties of single-pass-rolled samples were measured after tempering to assess
the effects of borocarbide precipitation on notch toughness. Such precipitation lowered the Charpy upper shelf energy and
increased the transition temperature. 相似文献
85.
Hemanshu Bhatt Kimberly Y. Donaldson D. P. H. Hasselman Kenneth Chyung Mark P. Taylor 《Journal of the American Ceramic Society》1991,74(6):1463-1465
A study concerning the effect of fiber orientation on the thermal conductivity of a uniaxial carbon-fiber-reinforced borosilicate glass was conducted. For thin specimens, and thick specimens with specimen sides cut parallel to the fiber direction, the dependence of thermal conductivity on fiber orientation showed excellent agreement with theoretical behavior predicted for a composite infinite in extent. In contrast, the thermal conductivity data for rectangular thick specimens fell well below the data for the thin and angled specimens. For fiber orientation of 45° and higher, at which the heat was directed toward the side of the specimen rather than across, the thermal conductivity values showed excellent agreement with theoretical behavior predicted for a finite composite strip with insulated sides. 相似文献
86.
The food antioxidants butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) are structurally related to the hypocholesterolemic drug probucol. The purpose of this study was to determine if BHA can lower serum cholesterol levels as is observed with probucol. Treatment of mice with 0.75% BHA in their feed for 10 days resulted in a significant (P < or = 0.01) elevation of serum cholesterol levels. This effect contrasts with the cholesterol-lowering effect of probucol. Further, the degree of cholesterol elevation was comparable to that observed in mice administered 3% cholesterol in their feed for 7 days. The enzyme acyl CoA:cholesterol acyltransferase (ACAT) was decreased significantly (P < or = 0.01) in liver microsomes from BHA-treated mice. In contrast, hepatic microsomal ACAT activity was increased significantly (P < or = 0.01) in cholesterol-fed mice. These results suggested that the increased serum cholesterol observed in BHA-treated mice was not accompanied by an increase in hepatic cholesterol levels. Indeed, hepatic microsomal cholesterol levels were reduced in BHA-treated mice, but were increased significantly (P < or = 0.01) in cholesterol-fed mice. These results demonstrate that the common food additive BHA elevates serum cholesterol levels by a mechanism that apparently involves the decreased uptake of cholesterol by the liver. 相似文献
87.
C. M. Dinnis A. K. Dahle J. A. Taylor M. O. Otte 《Metallurgical and Materials Transactions A》2004,35(11):3531-3541
Strontium modification is known to alter the amount, characteristics, and distribution of porosity in Al-Si castings. Although
many theories have been proposed to account for these effects, most can be considered inadequate because of their failure
to resolve contradictions and discrepancies in the literature. In an attempt to critically appraise some of these theories,
the amount, distribution, and morphology of porosity were examined in sand-cast plates of Sr-free and Sr-containing pure Al,
Al-1 wt pct Si, and Al-9 wt pct Si alloys. Statistical significance testing was used to verify apparent trends in the porosity
data. No apparent differences in the amount, distribution, and morphology of porosity were observed between Sr-free and Sr-containing
alloys with no or very small eutectic volume fractions. However, Sr modification significantly changed the amount, distribution,
and morphology of porosity in alloys with a significant volume fraction of eutectic. The addition of Sr reduced porosity in
the hot spot region of the casting, and the pores became well dispersed and rounded. This result can be explained by considering
the combined effect of the casting design and the differences in the pattern of eutectic solidification between unmodified
and Sr-modified alloys. 相似文献
88.
89.
R Ravichandran F Lafferty MJ McGinniss HC Taylor 《Canadian Metallurgical Quarterly》1996,81(5):1776-1779
Divergent recommendations exist regarding the evaluation of adrenal incidentalomas. Recent data have indicated a prevalence of adrenal tumors of 71% in nonclassical congenital adrenal hyperplasia (CAH) and unmasked heterozygotes. These data expand the differential diagnosis of such incidental tumors and substantially modify the approach to their evaluation. We present two patients, female pseudohermaphrodites with the simple virilizing form of CAH and 21-hydroxylase deficiency, who functioned successfully as married phenotypic males. Both came to medical attention in the sixth decade by virtue of massive adrenal incidentalomas encountered in the evaluation of recurrent urinary tract infections. Each had a 46, XX karyotype, no palpable testes, and markedly elevated baseline levels of 17-hydroxyprogesterone (17-OH Prog) of 6086 ng/dL and 6750 ng/dL. Both responded appropriately to dexamethasone suppression with reduction of 17-OH Prog, androgens and, in the second patient, ACTH to normal or near normal levels. Histologic and autopsy examination of the first patient's tumor and computed tomographic characteristics of the second revealed a benign adenoma and myelolipoma respectively. We extend and confirm previous recommendations that CAH be included in the differential diagnosis of adrenal incidentaloma and that baseline 17-OH Prog. levels be obtained, with ACTH stimulation if necessary, to diagnose the presence of nonclassical CAH. 相似文献
90.
The microsomal enzyme glycosylphosphatidylinositol mannosyltransferase I (GPIMT-I) catalyses the transfer of a mannosyl residue from beta-mannosylphosphoryldolichol (beta-Man-P-Dol) to glucosamine-alpha(1,6)(acyl)phosphatidylinositol (GlcN-aPI) to form Man alpha(1,4)GlcN-aPI (ManGlcN-aPI), an intermediate in glycosylphosphatidylinositol (GPI) synthesis. While the transfer of [3H]mannosyl units to endogenous GlcN-aPI was not seen when membrane fractions from normal Chinese hamster ovary (CHO) K1 cells were incubated with exogenous [3H]Man-P-Dol, GPIMT-I activity could be characterized with an in vitro enzyme assay system employing membrane fractions from Lec15 or Lec35 cells. These CHO cell mutants apparently contain elevated levels of endogenous GlcN-aPI due to the inability to synthesize (Lec15) or utilize (Lec35) beta-Man-P-Dol in vivo. The presence of a saturated alpha-isoprene unit in the dolichyl moiety is required for optimal GPIMT-I activity since beta-mannosylphosphorylpolyprenol (beta-Man-P-Poly), which contains a fully unsaturated polyisoprenyl chain, was only 50% as effective as beta-[3H]Man-P-Dol as a mannosyl donor. When beta-[3H]-Man-P-Dol and alpha-[3H]Man-P-Dol were compared as substrates, GPIMT-I exhibited a strict stereospecificity for the mannolipid containing the beta-mannosyl-phosphoryl linkage. beta-[3H]Man-P-dolichols containing 11 or 19 isoprenyl units were equally effective substrates for GPIMT-I. Membrane fractions from Lec 9, a CHO mutant that apparently lacks polyprenol reductase activity and synthesizes very little beta-Man-P-Dol, but accumulates beta-Man-P-Poly, synthesized no detectable Man-GlcN-aPI when incubated with beta-[3H]Man-P-Dol in vitro. This indirect assay suggests that GlcN-aPI does not accumulate in Lec 9 cells, possibly because it is mannosylated via beta-Man-P-Poly, or perhaps the small amount of Man-P-Dol formed by the mutant in vivo.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献