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81.
An increasing number of multiport devices, whether they be multiband wireless phone components, backplane balanced transmission lines, or classical devices such as power dividers, are being characterized in the RF, microwave, and millimeter-wave frequency bands. S-parameter measurements are often required, and ordinary vector network analyzer (VNA) measurements must be modified to perform these measurements quickly and accurately. This article explores a number of hardware architectures and calibration procedures for multiport measurements and their impacts on flexibility and uncertainties. 相似文献
82.
Since the very first resolution of racemic tartaric acid by Pasteur, the importance of resolution and methodology has been on a path of continuous understanding and expansion. The science and chemistry of achieving such targets has changed a lot. The advent of chromatography changed the direction by involving synthetic, semisynthetic, or naturally occurring chiral materials for a direct approach to resolution, where rapid and reversible association occurs to form diastereomers with different stabilities and partition coefficients responsible for overall enantioseparation. It has now reached a stage where the separation of excess enantiomers from nonracemic mixtures has been achieved in a totally achiral environment, which does not appear to be in line with the prevalent concepts of basic stereochemistry. Caution should be exercised when enantiomerically enriched mixtures – obtained by enantioselective synthesis – are chromatographed for purification in preparative organic synthesis. 相似文献
83.
The current paper describes a special class of synchronous (phase-sensitive) detectors (SDs) for measurement purposes. They are precise and have high dynamic range. Proposed solutions are based on op-amps, having synchronously switched capacitors in the negative feedback path. Such structures give significant improvement of several specifications, especially of the input dynamic reserve. Functioning principles, circuit diagrams and gain equations are given 相似文献
84.
Juan M. Garcés Michael M. Olken G. John Lee Garry R. Meima Pierre A. Jacobs Johan A. Martens 《Topics in Catalysis》2009,52(9):1175-1181
This is a review of work carried at Dow Chemical on the design and characterization of novel mordenite catalysts with a unique
micro and meso-porous structure characterized by a variety of methods including, TEM, BET surface area and pore size distribution,
and n-decane hydro-conversion. The catalytic performance of these catalysts in shape selective reactions is illustrated with results
from n-decane hydro-conversion and applications to alkylation and trans-alkylation reactions of mono and polynuclear aromatic hydrocarbons and other chemistries.
Juan M. Garcés and G. John Lee both retired from The Dow Chemical Company. 相似文献
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SJ Lee KM Kuntz MM Horowitz PB McGlave JM Goldman KA Sobocinski J Hegland C Kollman SK Parsons MC Weinstein JC Weeks JH Antin 《Canadian Metallurgical Quarterly》1997,127(12):1080-1088
BACKGROUND: Chronic myelogenous leukemia (CML) is an indolent but ultimately fatal disease. Because the natural history of CML varies and quality of life with CML may be excellent until shortly before death, deciding whether and when to pursue unrelated donor bone marrow transplantation is often difficult. OBJECTIVE: To compare early transplantation, delayed transplantation, and no transplantation for patients with chronic-phase CML on the basis of discounted, quality-adjusted life expectancy. DESIGN: A markov model comparing different strategies was constructed. This model considers patient age, quality of life, risk aversion, and the competing risks for CML progression and transplant toxicity. SETTING: Therapeutic decision at the time of diagnosis of CML. PATIENTS: The base case is a 35-year-old patient with intermediate-prognosis CML. Younger and older patients with better and worse prognoses are also evaluated. INTERVENTION: Early transplantation, delayed transplantation, and no transplantation. MEASUREMENTS: Quality-adjusted, discounted life expectancy. RESULTS: For patients with newly diagnosed CML, transplantation within the first year provides the greatest quality-adjusted expected survival, although this benefit decreases with increasing patient age. For a 35-year-old patient with intermediate-prognosis CML, transplantation within the first year results in 53 more discounted, quality-adjusted years of life expectancy than does no transplantation. This finding is robust even with varying baseline assumptions. CONCLUSIONS: These results support the use of early unrelated donor bone marrow transplantation for most patients with CML. 相似文献
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