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排序方式: 共有243条查询结果,搜索用时 15 毫秒
1.
RM Bionta G Blewitt CB Bratton D Casper A Ciocio R Claus M Crouch ST Dye S Errede GW Foster W Gajewski KS Ganezer M Goldhaber TJ Haines TW Jones D Kielczewska WR Kropp JG Learned JM LoSecco J Matthews HS Park LR Price F Reines J Schulz S Seidel E Shumard D Sinclair HW Sobel JL Stone L Sulak R Svoboda G Thornton van der Velde JC C Wuest 《Canadian Metallurgical Quarterly》1987,36(1):30-36
2.
Ways in which spreadsheet programs can be used to introduce practical considerations in introductory electrical engineering courses are discussed. Examples are presented which show that spreadsheets can be used to predict and/or minimize the errors due to loading, the availability of only standard resistor values, and resistor tolerances. The circuits considered in these examples were selected to be as simple as possible. These examples could be used in the first semester of sophomore credits. They illustrate trade-offs, performance criteria, and nonunique solutions, and are intended to illustrate the power of spreadsheet programs. In the first example, a macro is used to implement a simple iterative optimization procedure. In the second example, minimization is done by exhaustive search using the table lookup capabilities of the spreadsheet. In the final example, the spreadsheet's random number generator is used to perform a Monte Carlo analysis 相似文献
3.
The metabolism of 4 dietary 24-alkylsterols was investigated in the free-living nematodeCaenorhabditis elegans. The major unesterified sterols ofC. elegans in media supplemented with either campesterol, 22-dihydrobrassicasterol or stigmasterol included cholesta-5,7-dienol, cholesterol,
cholest-7-enol, and 4α-methylcholest-8(14)-enol. Dietary stigmastanol yielded cholest-7-enol, cholestanol, cholest-8(14)-enol,
and 4α-methylcholest-8(14)-enol as major unesterified sterols. Esterified sterols comprised less than 22% of the total sterol.
Removal of a C-24 ethyl substituent of sterols was neither hindered by the presence of a Δ22-bond in the sterol side chain nor was it depedent on unsaturation in ring B of the steroid nucleus.C. elegans reduced a Δ22-bond during its metabolism of stigmasterol; it did not introduce a Δ22-bond during stigmastanol metabolism.C. elegans was capable of removing a C-24 methyl substituent regardless of its stereochemical orientation. Metabolic processes involving
the steroid ring system of cholesterol (C-7 dehydrogenation, Δ5-bond, 4α-methylation, Δ8(14)-isomerization inC. elegans were not hindered by the presence of a 24-methyl group; various 24-methylsterol metabolites from campesterol were detected,
mostly 24-methylcholesta-5,7-dienol. In contrast, no 24-ethylsterol metabolites from the dietary ethylsterols were found.
More dietary 24-methylsterol remained unmetabolized than did dietary 24-ethylsterol. A 24α-ethyl group and a 24β-methyl group
were dealkylated to a greater extent byC. elegans than was a 24α-methyl group, perhaps reflecting the substrate specificity of the dealkylation enzyme system, or suggesting
different enzymes altogether. 相似文献
4.
The honey bee,Apis mellifera, is one of only a few species of phytophagous insects known to be unable to convert C-24 alkyl phytosterols to cholesterol.
Regardless of the dietary sterols available to worker bees, the major tissue sterol of brood reared by the workers is always
24-methylenecholesterol, followed by sitosterol and isofucosterol. Normally, little or no cholesterol is present in honey
bee sterols. The maintenance of high levels of certain sterols is accomplished through a selective transfer of sterols from
the endogenous sterol pools of the workers to the developing larvae through the brood food material secreted from the hypopharyngeal
and mandibular glands and/or the honey stomach of the workers. The selective uptake and transfer of radiolabeled C27, C28 and C29 sterols have been studied to correlate these aspects of sterol utilization with the discovery of an unusual molting hormone
(ecdysteroid) in honey bee pupae as the major ecdysteroid of this stage of development. The phylogenetic implications of this
selective transfer phenomenon in the honey bee and comparison with sterol metabolism in certain other hymenopteran species
emphasize the diversity of steroid biochemistry in insects. 相似文献
5.
The theory of gas absorption accompanied by fast pseudo-fast order reaction which considered dependences of diffusivity, kinetic constant and Henry's law constant on absolute temperature and ionic strength was used to obtain values of effective interfacial areas and mass transfer coefficients in gas and liquid phase.
Experimental measurement of carbon dioxide absorption from mixture with air was performed in a pilot-plant column with expanded metal sheet packing irrigated with sodium hydroxide solution.
Resulting liquid and gas-side mass transfer coefficients are compared with values obtained from physical Absorption measurement of carbon dioxide into water and with measurement of gas-side mass transfer coefficient for sulphur dioxide in the same column.
The differences between determined values are discussed. 相似文献
Experimental measurement of carbon dioxide absorption from mixture with air was performed in a pilot-plant column with expanded metal sheet packing irrigated with sodium hydroxide solution.
Resulting liquid and gas-side mass transfer coefficients are compared with values obtained from physical Absorption measurement of carbon dioxide into water and with measurement of gas-side mass transfer coefficient for sulphur dioxide in the same column.
The differences between determined values are discussed. 相似文献
6.
Polypropylene (PP) nanocomposites were prepared by melt intercalation in an intermeshing corotating twin‐screw extruder. The effect of molecular weight of PP‐MA (maleic anhydride‐ modified polypropylene) on clay dispersion and mechanical properties of nanocomposites was investigated. After injection molding, the tensile properties and impact strength were measured. The best overall mechanical properties were found for composites containing PP‐MA having the highest molecular weight. The basal spacing of clay in the composites was measured by X‐ray diffraction (XRD). Nanoscale morphology of the samples was observed by transmission electron microscopy (TEM). The crystallization kinetics was measured by differential scanning calorimetry (DSC) and optical microscopy at a fixed crystallization temperature. Increasing the clay content in PP‐ MA330k/clay, a well‐dispersed two‐component system, caused the impact strength to decrease while the crystallization kinetics and the spherulite size remained almost the same. On the other hand, PP/PP‐MA330k/clay, an intercalated three‐component system containing some dispersed clay as well as the clay tactoids, showed a much smaller size of spherulites and a slight increase in impact strength with increasing the clay content. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1562–1570, 2002 相似文献
7.
A method which enables the Squid dc voltmeter to be operated with a sample exposed to a significant external magnetic field is presented. A special superconducting shield with a finite time constant has been used to suppress time-dependent components of the field. With the shield, the Squid voltmeter has been able to work in magnetic fields up to 0.7 T in the flux-locked loop mode. The total voltage noise per unit bandwidth Vrms (referred to input) does not exceed the value of
. To extend the range of performance to higher magnetic fields, simple low pass filters have been built into the input circuit to increase its time constant. With the signal coil of the Squid shunted by a resistor RB = 3 × 10−6ω, the Squid voltmeter could be operated in fields up to 3.2 T with
相似文献
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8.
Four low alloy steels with different contents of molybdenum and vanadium were investigated. The steels were annealed at 773,
793, 853, 873, 933, 973, and 993 K for 500, 1000, 3000, and 10000 h. Techniques of transmission electron microscopy and thermodynamic
calculations (ThermoCalc) were used to characterise influence of the steel bulk composition and the annealing conditions on
evolution of carbides M3C, M2C, M7C3, M23C6, M6C, and MC (M=metallic element). Changes in structure types and metal compositions of the carbides were characterised in detail.
The work was done with the intention to obtain more information about the secondary phase evolution in low alloy steels used
in energy industries. 相似文献
9.
J. Janovec A. Vyrostková M. Svoboda A. Kroupa H. J. Grabke 《Metallurgical and Materials Transactions A》2004,35(3):751-759
The influence of both bulk vanadium content and aging conditions on the evolution of secondary phases in Cr-V low-alloy steels
was studied. Three 0.1C-0.9Cr-V steels with different vanadium contents (0, 0.258, and 0.512 wt pct) were aged for 100 to
5,000 hours at 773, 853, 953, and 993 K. In the investigation, a limited experimental program (transmission electron microscopy
(TEM)) was combined with credible thermodynamic predictions (ThermoCalc). Going out from the good agreement between the predicted
and experimental results, behavior of the iron-rich M7C3 carbide in time-temperature scale was characterized. The influence of bulk vanadium content was determined on appearance
of the M3C carbide in equilibrium, temperature of the M7C3 carbide precipitation, metal compositions of M3C or M7C3 carbides, and vanadium portion in the metallic part of the MX phase. 相似文献
10.
The purpose of this study was to demonstrate the presence of vinculin and alpha2 integrin in chondrocytes in situ and epithelial cells. We also determined that the appropriate fixation and extraction protocols for immunohistochemistry and laser scanning confocal microscopy for an integral membrane protein and an actin-associated protein in cultured cells and whole tissue was different. Cultured epithelial cells, whole mount human cornea and avian cartilage were fixed and prepared using a number of standard procedures used for indirect fluorescence immunohistochemistry. The distribution of vinculin was cell-type and fixation-specific. Chondrocytes and cultured epithelial cells demonstrated vinculin in areas that appear to be associated with filamentous actin. Vinculin was associated with cell membranes in human cornea. The expression of alpha2 integrin observed in chondrocytes fixed with methanol, paraformaldehyde, or formaldehyde is consistent with its role in cell-substrate interaction, but may also suggest a role in dividing and differentiating cells. The localization of alpha2 integrin in human corneal epithelia supports its role as a cell-cell adhesion molecule. The cytoplasmic distribution of vinculin and alpha2 integrin in tissues fixed without detergent extraction suggests that the fixation step may be sufficient for antibody penetration and antigen extraction. These studies are the first report of vinculin and alpha2 integrin in embryonic chondrocytes. In addition we have shown that confocal laser scanning microscopy combined with proper fixation and extraction protocols may optimize the localization of antigens in cultured and whole mount cells. 相似文献