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1.
统一S波段测控信道调制指数设计方程 总被引:2,自引:0,他引:2
《遥测遥控》1999,(2)
考虑了测距音提取滤波器以及返回噪声对统一S波段卫星测控信道的影响,采用图解和数学分析两种方法详细分析了已调载波的功率效率。在此基础上,分别推导出在有、无测距音提取滤波器两种情况下,调制指数的设计方程 相似文献
2.
介绍S波段超小型调频发动机方案的选择,电路设计,结构安排,并对该发射机的稳定性和质量进行了分析,该发射机已通过机载环境条件试验和地面接收机的对接试验,并已通过鉴定,具有90年代国外同类产品的水平。 相似文献
3.
LI Jian-liang XIONG Dang-sheng* WAN Yi Department of Materials Science Engineering Nanjing University of Science Technology Nanjing China 《中国航空学报》2006,19(Z1)
Ni-Cr-W-Al-Ti-MoS2 self-lubricating composites were prepared through the powder metallurgy (P/M) method. Their friction properties were investigated by a pin-on-disk tribometer in the range from the room temperature to 600 ℃. Alumina, silicon nitride and nickel-iron-sulfide alloys were selected as the counterface materials. Results indicate that the lowest friction coefficients under 0.22 can be obtained at 600 ℃ when rubbed against alumina. When rubbed against nickel-iron-sulfide alloys, are presented the lowest wear rates in the magnitude of 10-6 mm3/N·m, one order of magnitude lower than those when rubbed against ceramics. In the case of three rubbing pairs, the wear rates of the composite containing MoS2 present themselves inversely proportional to friction coefficients. With alumina ceramics used as a counterface, transfer films and glaze layers will form on the contact surface playing a main role in lubrication at high temperatures. However, when silicon nitride and nickel-iron-sulfide alloy are used, the lubricating transfer films appear not to be promi-nent. 相似文献
4.
提出了一种适合于P2P MMOG的分布式消息分发算法。游戏世界通过N-Tree划分为若干个子区域,并从每个子区域中选举出一个协调者节点。对于区域内玩家交互过程中产生的事件,由该玩家通过多播机制发送给其兴趣域中的其他玩家和区域协调者,协调者仅负责保存区域内的对象的状态信息并周期性的进行更新。实验表明该算法能够满足游戏状态的一致性需求,并且能够在较大的程度上降低协调者负载和通信开销,节省了大量的计算资源和宝贵的带宽。 相似文献
5.
Michael J. S. Belton Karen J. Meech Michael F. A’Hearn Olivier Groussin Lucy Mcfadden Carey Lisse Yanga R. Fernández Jana PittichovÁ Henry Hsieh Jochen Kissel Kenneth Klaasen Philippe Lamy Dina Prialnik Jessica Sunshine Peter Thomas Imre Toth 《Space Science Reviews》2005,117(1-2):137-160
In 1998, Comet 9P/Tempel 1 was chosen as the target of the Deep Impact mission (A’Hearn, M. F., Belton, M. J. S., and Delamere, A., Space Sci. Rev., 2005) even though very little was known about its physical properties. Efforts were immediately begun to improve this situation
by the Deep Impact Science Team leading to the founding of a worldwide observing campaign (Meech et al., Space Sci. Rev., 2005a). This campaign has already produced a great deal of information on the global properties of the comet’s nucleus
(summarized in Table I) that is vital to the planning and the assessment of the chances of success at the impact and encounter.
Since the mission was begun the successful encounters of the Deep Space 1 spacecraft at Comet 19P/Borrelly and the Stardust spacecraft at Comet 81P/Wild 2 have occurred yielding new information on the state of the nuclei of these two comets. This
information, together with earlier results on the nucleus of comet 1P/Halley from the European Space Agency’s Giotto, the Soviet Vega mission, and various ground-based observational and theoretical studies, is used as a basis for conjectures on the morphological,
geological, mechanical, and compositional properties of the surface and subsurface that Deep Impact may find at 9P/Tempel 1. We adopt the following working values (circa December 2004) for the nucleus parameters of prime importance to Deep Impact as follows: mean effective radius = 3.25± 0.2 km, shape – irregular triaxial ellipsoid with a/b = 3.2± 0.4 and overall dimensions of ∼14.4 × 4.4 × 4.4 km, principal axis rotation with period = 41.85± 0.1 hr, pole directions
(RA, Dec, J2000) = 46± 10, 73± 10 deg (Pole 1) or 287± 14, 16.5± 10 deg (Pole 2) (the two poles are photometrically, but not
geometrically, equivalent), Kron-Cousins (V-R) color = 0.56± 0.02, V-band geometric albedo = 0.04± 0.01, R-band geometric
albedo = 0.05± 0.01, R-band H(1,1,0) = 14.441± 0.067, and mass ∼7×1013 kg assuming a bulk density of 500 kg m−3. As these are working values, {i.e.}, based on preliminary analyses, it is expected that adjustments to their values may be made before encounter
as improved estimates become available through further analysis of the large database being made available by the Deep Impact observing campaign. Given the parameters listed above the impact will occur in an environment where the local gravity is
estimated at 0.027–0.04 cm s−2 and the escape velocity between 1.4 and 2 m s−1. For both of the rotation poles found here, the Deep Impact spacecraft on approach to encounter will find the rotation axis close to the plane of the sky (aspect angles 82.2 and 69.7
deg. for pole 1 and 2, respectively). However, until the rotation period estimate is substantially improved, it will remain
uncertain whether the impactor will collide with the broadside or the ends of the nucleus. 相似文献
6.
7.
拉形条件对镜面蒙皮成形质量的影响 总被引:4,自引:2,他引:4
万敏 《北京航空航天大学学报》1998,24(6):654-657
在充分考虑滑移带出现与成形件贴模度的基础上,通过分析拉形速度、毛料几何尺寸、模具几何参数、润滑方式对成形质量的影响,确定了合理的飞机镜面蒙皮拉形条件.结果表明,改善板料变形的均匀性,延缓滑移带出现,增加成形面内材料的变形程度,是制定最优工艺参数、提高成形质量的主要措施. 相似文献
8.
雷少刚 《西安航空技术高等专科学校学报》2011,29(3):84-87
小信号谐振放大器是高频电子线路课程的基本单元电路之一,主要应用在通信系统的接收机电路中,高频放大和中频放大是信号传输电路中的核心部分。掌握小信号谐振放大器的分析方法,对电子信息类、通信工程类专业学生的学习及工作是非常关键的。 相似文献
9.
Ti-6.5Al-3.5Mo-1.5Zr-0.3Si合金绝热剪切和局部流动行为 总被引:1,自引:0,他引:1
在THERMECMASTOR-Z型热模拟机上对Ti-6.5Al-3.5Mo-1.5Zr-0.3Si合金在变形温度780~1 080 ℃,应变速率0.001~70.000 s-1条件下的流动应力变化规律进行了研究,分析了变形工艺参数对Ti-6.5Al-3.5Mo-1.5Zr-0.3Si合金绝热剪切和局部流动行为的影响,并采用基于动态材料模型的功率耗散图分析了Ti-6.5Al-3.5Mo-1.5Zr-0.3Si合金易发生绝热剪切和局部流动的热力参数范围。结果表明:在所研究的热变形条件下,当温度较高、应变速率较低时,变形呈稳态流动特征,当温度较低、应变速率较高时,变形呈流动软化特征。通过功率耗散图分析及微观组织观察可知,在α+β两相区变形,应变速率高于0.100 s-1时,功率耗散系数多数小于0.16,变形多处于流变失稳区域,其变形机制主要为绝热剪切和局部流动。 相似文献
10.
在对散布参数验前可信度的定义与必要性进行分析的基础上,给出了给定散布参数(方差)的P值计算模型,构建了一维散布分析时验前分布可信度的P值模型,给出了验前P值与验前可信度的定义,并对其变动情况进行了阐述,给出了验前分布的拒绝条件.对二维散布分析条件下的验前可信度分析,分别构建了验前P值的独立求解模型和集成求解模型.并从0.05,0.2,0.4区分的数据区间,给出了验前分布选择的原则和要求.基于案例比较可见,验前可信度能较为显著地完成验前分布的差异化比较,相对现有的仅对验前可信度的定性说明,基于P值的验前可信度建模与计算,不仅能完成验前可信度的量化计算,而且能从概率的角度对验前分布选择的正确性进行假设检验. 相似文献