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11.
在实测和分析32、14.6、12.5和9.5mm波段大气衰减的基础上,研究了大气衰减随仰角变化的规律;讨论了仰角为3~90°时计算大气衰减的简化计算公式;给出了大气等效高度与地面水汽密度的关系式,对大气衰减和等效高度的实测值与理论值进行了比较和分析. 相似文献
12.
Large-eddy-simulation of 3-dimensional Rayleigh-Taylor instability in incompressible fluids 总被引:1,自引:0,他引:1
The 3-dimensional incompressible Rayleigh-Taylor instability is numerically studied through the large-eddy-simulation ( LES)
approach based on the passive scalar transport model. Both the instantaneous velocity and the passive scalar fields excited
by sinusoidal perturbation and random perturbation are simulated. A full treatment of the whole evolution process of the instability
is addressed. To verify the reliability of the LES code, the averaged turbulent energy as well as the flux of passive scalar
are calculated at both the resolved scale and the subgrid scale. Our results show good agreement with the experimental and
other numerical work. The LES method has proved to be an effective approach to the Rayleigh-Taylor instability. 相似文献
13.
木质装饰板材贫氧条件下燃烧和热解特性研究 总被引:2,自引:0,他引:2
本文利用热重差热分析仪,在各种不同的氧气浓度下对落叶松、红木和红松样品进行实验。通过对TG、DTG和DTA曲线的分析,样品干燥基要经历两个失重过程,第一个失重过程主要是纤维素和半纤维素的热解,第二个失重过程主要是木质素的炭化分解和燃烧。在各氧气浓度条件下,热解失重的第一个阶段TG和DTG曲线差异很小;在各样品失重的第二个阶段,随着氧气浓度的增加,TG和DTG曲线左移,反应结束的温度明显降低。氧气能使木质素的炭化物氧化并进而可能使其着火燃烧,从而使反应进程加快。当氧气浓度大于6.32%时,各样品DTA曲线上均有两个明显放热峰,并且随着氧气浓度的增加,DTA曲线放热峰越尖锐,放热峰面积越大,说明氧气浓度越大,在两阶段失重过程中更多的挥发分物质和固体炭化物参与燃烧。 相似文献
14.
PLZT ceramics with the composition of 9/62/38 (La/Zr/Ti) were fabricated from spraydried aqueous solution. Complete crystallization
of the spray-dried powder is achieved after 1 hr calcination at 650‡ C as compared to 800‡ C, 1 hr for conventional mixedoxide
method. Sintering environment plays an important role in the densification of PLZT ceramics. Densities of the atmosphere sintered
samples are much higher than those of normal sintered ones. PLZT ceramics derived from spray-dried powders have properties
comparable to those derived from sol-gel ones. The spray-dried method presents a less expensive and more effective approach
in the synthesis of PLZT ceramics. 相似文献
15.
This paper attempts to reproduce numerically previous experimental findings with opposed flows and extends their range to quantify the effects of upstream pipes and nozzles with inviscid, laminar and turbulent flows. The choice of conservation equations, boundary conditions, algorithms for their solution, the degree of grid dependence, numerical diffusion and the validity of numerical approximations are justified with supporting calculations where necessary. The results of all calculations on the stagnation plane show maximum strain rates close to the annular exit from the nozzles and pipes for lower separations and it can be expected that corresponding reacting flows will tend to extinguish in this region with the extinction moving towards the axis. With laminar flows, the maximum strain rate increased with Reynolds number and the maximum values were generally greater than with inviscid flows and smaller than with turbulent flows. With large separations, the strain rates varied less and this explains some results with reacting flows where the extinction appeared to begin on the axis. The turbulent‐flow calculations allowed comparison of three common variants of a two‐equation first‐moment closure. They provided reasonable and useful indications of strain rates but none correctly represented the rms of velocity fluctuations on the axis and close to the stagnation plane. As expected, those designed to deal with this problem produced results in better agreement with experiment but were still imperfect. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
16.
碳化硅加热元件的电性能和使用 总被引:2,自引:0,他引:2
本文介绍碳化硅加热元件的电特性、表面负荷以及工作气氛对它的影响,并对它设计和使用要点举例予以说明。 相似文献
17.
18.
In this paper, we present experimental data for SIMS analysis of residual gas elements (RGEs) with a Cameca IMS-6f ion microprobe. We considered a simple experimental technique, which provides an effective separation of the secondary ions, sputtered from the bulk of a target, and from the molecules, adsorbed on the analyzed surface from the residual atmosphere. The technique needs the sputtering yield of one monolayer (ML) per second to be applied. The method improves (in more than one order of magnitude) the detection limit for RGEs in SIMS analysis, and simultaneously, provides information about the residual atmosphere at the sample surface and in the main chamber of the experimental instrument. The method provides a calibration method for an ion gauge, and can be used for SIMS analysis with a gas (O2) flooding. 相似文献
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