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排序方式: 共有609条查询结果,搜索用时 296 毫秒
21.
Hagen Renner 《Journal of Modern Optics》2013,60(5):907-915
Abstract Simple general formulae for the coupling coefficients of the fundamental modes on well-separated parallel optical waveguides are derived. The calculation merely requires accurate knowledge of the propagation constants and core fields of the modes on the individual waveguides, while the far-from-core fields need not be known. Results for coupled circular fibres are identical with the asymptotic expansions of previously derived exact coupling coefficients. Analytical expressions for the coupling coefficients between the fundamental modes on identical weakly guiding channel waveguides are obtained. 相似文献
22.
Susan Walter Thomas Herzog Henning Heuer Hagen Bartzsch Daniel Gloess 《Microsystem Technologies》2012,18(7-8):1193-1199
We investigated the potential of the aluminum nitride films to excite ultrasonic waves at frequencies >50?MHz. The deposition process of the aluminum nitride thin film layers on silicon substrates was investigated and optimized regarding their piezoelectric behavior. Large single element transducers were deposited on silicon substrates with aluminum electrodes, under different parameters for the magnetron sputter process, like pressure and bias voltage. Special test setup and a measuring station were created to characterize the sensors. Acoustical measurements were carried out in pulse echo mode up to 500?MHz and the values of piezoelectric charge constant (d33) were determined. As a result, two parameter sets were found for the sputtering process to obtain an excellent piezoelectric charge constant of about 7.2?pC/N maximum. Then the sputtering process with these parameters was used to deposit sensors on various substrate materials and with different electrode sizes. 相似文献
23.
24.
Lukas Durdina Max B. Trueblood Elizabeth A. Black Steven Achterberg Donald E. Hagen 《Aerosol science and technology》2016,50(9):906-918
Soot is a climate forcer and a dangerous air pollutant that has been increasingly regulated. In aviation, regulatory measurements of soot mass concentration in the exhaust of aircraft turbine engines are to be based on measurements of black carbon (BC) calibrated to elemental carbon (EC) content of diffusion flame soot. The calibration soot must currently meet only one criterion: minimum EC to total carbon (TC) ratio of 0.8. However, not including soot properties other than the EC/TC ratio may potentially lead to discrepancies between different BC measurements. We studied the response of two instruments, the AVL Micro-Soot Sensor (MSS) and the Artium Laser-Induced Incandescence 300 (LII), to soot from two miniature combustion aerosol standard (mini-CAST) burners. By changing the air-fuel ratio, premixing nitrogen into the fuel, and using a catalytic stripper to remove volatile compounds, we produced a wide range of particle morphologies and EC contents. As the EC content decreased, both the instruments underreported the EC mass, but the LII diverged more severely. Upon closer investigation of eight conditions with EC/TC > 0.8, the LII underreporting was found independent of primary particle size, but increased with decreasing geometric mean diameter of the soot agglomerates. As the geometric mean diameter decreased from 160 nm to 50 nm, the differences between the LII and MSS increased from 15% to 50%. The results suggest that in addition to EC content, calibration procedures for the regulatory BC measurements may need to take particle size distributions into account.
© 2016 American Association for Aerosol Research 相似文献
25.
Synthesis of 6-(4-pyridinyI)-substituted Pyrido[2,3-d]pyrimidines and 1,8-Naphthyridinms A series of new 6-(4-pyridinyl)-substituted pyrido-[2,3-d]pyrimidines 2 – 4 and 1,8-naphthyridines 6 , respectively, is described. Cyclisation of 2-amino-5-(4-pyridinyl)-pyridinm-3-carboxamide 1a with diethyl oxalate gives the pyrido-[2,3-d]pyrimidinm 2a . Alkylation of( 2a ) yields the 3-ethylaminoxyrido[2,3-d]pyrimidine derivative 2b . Saponification of 2a , b gives the corresponding carboxylic acids 3a , b , which are decarboxylated by heating above the melting point to give 4a , b . The 2-amino-5-(4-pyridinyl)-pyridinm carboxylic acid derivatives 1 b – e react with ethylmalonylchloridm and diethyl malonate to afford the 1,8-naphthyridines 6b – e . The 1-oxide 7 in a similar reaction gives 8 and the oxdiazole( 9 ) which is converted by ring transformation to the 1,8-naphthyridine 10 . 相似文献
26.
27.
H. Sun D. Wiesenborn P. Rayas-Duarte A. Mohamed K. Hagen 《Journal of the American Oil Chemists' Society》1995,72(12):1551-1555
Amaranth seed (Amaranthus hypochondriacus cv. K432) was processed to obtain oil, reported to be a promising source of squalene. The amaranth seed was ground using
a stone mill, then separated into oil-rich embryonic tissue (or “bran”) and starchy perisperm. Amaranth bran was much more
stable than rice bran when free fatty acid (FFA) content and peroxide value were monitored. Milling at a gap of 0.755 mm did
not result in excessive damage to the starch in the perisperm fraction and yielded a bran fraction that contained more than
three-fourths of the oil and a starchy fraction consisting of more than two-thirds of the seed weight. The bran particles
were too fine for effective bench-scale extraction of the oil. Consequently the bran was extruded into collects prior to extraction.
Two extrusion settings were evaluated regarding the rate of moisture injection, while the bran feed rates were constant. There
was no significant difference in appearance or size between the two dried collets. Collets were extracted with hexane using
an Armfield Extraction/Desolventizing Unit (Model FT 29, Armfield, Ltd., Hampshire, England). Oil recovery averaged 97.7 and
80.0%, respectively. Oil was extracted at high yield from the bran when the bran was extruded into collets. Oil can be obtained
as a coproduct of amaranth starch by milling and separating the fractions of amaranth seed. Milling, extrusion, and extraction
did not decrease significantly the squalene content in amaranth oil, but increased FFA content and peroxide value and changed
tocopherol content of the oil. 相似文献
28.
In order to investigate the transmission properties in the whole solar spectrum for individual electrochromic layers in solid state devices incorporating polyaniline (PANI), Prussian Blue (PB) and tungsten oxide (WO3), the devices were fabricated with and without holes in the electrochromic coatings in several combinations. Both PANI and WO3 were deposited electrochemically on indium–tin oxide (ITO) glass substrates, while PB was deposited on top of the PANI coatings or directly on the ITO glass plates. Solid state devices were made by gluing the glass plates together with the solid polymer electrolyte poly(2-acrylamido-2-methyl-propane-sulphonic acid) (PAMPS), and thus, with and without holes in the three electrochromic coatings in different combinations, enabling us to study the optical properties of PANI, PB and WO3 separately, that is, the hole method. This method gives good qualitative, and to a certain degree quantitative, information, which may be of valuable help in designing electrochromic devices with specific tailor-made optical properties. 相似文献
29.
The long-term high-temperature cyclic oxidation (100 cycles, 104 h, 1500°C) of a Si3 N4 material and a Si3 N4 /MoSi2 composite, both fabricated with Y2 O3 as a sintering additive, was studied. Both materials exhibited similar oxidation rates because of surface SiO2 formation described by an almost parabolic law and a total weight gain of 3–4 mg/cm2 after 104 h. As a consequence of oxidation processes in the bulk, microstructural damage was found in the Si3 N4 material. These effects were not observed in the composite. The remarkable microstructural stability observed offers the high potential of Si3 N4 /MoSi2 composites for long-term structural applications at elevated temperatures up to 1500°C. 相似文献
30.
Influence of Molybdenum Silicide Additions on High-Temperature Oxidation Resistance of Silicon Nitride Materials 总被引:2,自引:0,他引:2
Hagen Klemm Katja Tangermann Christian Schubert Waldemar Hermel 《Journal of the American Ceramic Society》1996,79(9):2429-2435
The influence of additions of molybdenum disilicide (MoSi2 ) on the microstructure and the mechanical properties of a silicon nitride (Si3 N4 ) material, with neodymium oxide (Nd2 O3 ) and aluminum nitride (AIN) as sintering aids, was studied. The composites, containing 5, 10, and 17.6 wt% MoSi2 , were fabricated by hot pressing. All materials exhibited a similar phase composition, detected by X-ray diffractometry. Up to MoSi2 additions of 10 wt%, mechanical properties such as strength, fracture toughness, or creep at 1400°C were not affected significantly, in comparison to that of monolithic Si3 N4 . The oxidation resistance of the composites, in terms of weight gain, degraded. After 1000 h of oxidation at 1400° and 1450°C in air, a greater weight gain (by a factor of approximately three) was obtained, in comparison to that of the material without MoSi2 . Nevertheless, after 1000 h of oxidation, the degradation in strength of the composites was considerably less severe than that of the material without MoSi2 . An additional layer was formed, caused by processes at the surface of the Si3 N4 material, preventing the formation of pores, cracks, or glassy-phase-rich areas, which are common features of oxidation damage in Si3 N4 materials. This surface layer, containing Mo5 Si3 and silicon oxynitride (Si2 ON2 ), was the result of reactions between MoSi2 , Si3 N4 , and the oxygen penetrating by diffusion into the material during the hightemperature treatment. 相似文献