An Oxygen Isotope Mixing Model for the Accretion and Composition of Rocky Planets

The oxygen isotope systematics in planetary and nebular matter are used to constrain the types of nebular material accreted to form a planet. The basic assumption of this model is that the mean oxygen isotopic composition of a planet is determined by the weighted mean oxygen isotopic composition of nebular matter accreted by the planet. Chondrites are taken as representatives of nebular matter. The chemical composition (which determines core size, mantle oxidation state, density, moment of inertia) of a planet results from the weighted mean compositions of the accreted nebular material, once the mass fractions of the different types of accreting matter are known. Here some results for Earth, Moon, Mars, and Vesta are discussed. The model implies that loss of volatile elements, such as alkalis and halogens, occurs during accretion and early planetary differentiation (e. g., by catastrophic impacts). The possible depletion mechanisms of moderately volatile elements are discussed. This revised version was published online in June 2006 with corrections to the Cover Date.     

随机噪声载荷作用下薄壳结构的随机振动实验研究

为研究薄壁壳结构在随机噪声激励下的随机振动响应特征,本文设计了一套针对薄壁壳在内部随机噪声作用下的振动问题进行研究的实验方案,同时对噪声载荷和薄壳振动加速度响应进行测量,并对实验结果进行初步的定性分析,了解噪声载荷在频率域上的分布特征和薄壁壳在内部随机噪声作用下的振动响应特征,获得在噪声激励的频率范围内能激起薄壳该频率范围内所有模态共振等结论,为薄壳结构在内部噪声作用下随机振动响应的计算方法的研究提供依据。      

Chemical and Physical Processing of Presolar Materials in the Solar Nebula and the Implications for Preservation of Presolar Materials in Comets

Chemical and physical processes in the outer solar nebula are reviewed. It is argued that the outer nebula was a chemically active environment with UV photochemistry and ion-molecule chemistry in its low density regions and grain-catalyzed chemistry in Jovian protoplanetary subnebulae. Presolar material was altered to greater or lesser extent by these spatially and temporally variable processes, which mimic many features of interstellar chemistry. Experiments, models, and observations are recommended to address the questions of presolar versus nebular dominance in the outer solar nebula and of how to distinguish interstellar and nebular sources of cometary volatiles. This revised version was published online in June 2006 with corrections to the Cover Date.     

Formation of the Cores of the Outer Planets

The formation of the giant planets seems to be best explained by accretion of planetesimals to form massive cores, which in the case of Jupiter and Saturn were able to capture nebular gas. However, the timescale for accretion of such cores has been a problem. Accretion in the outer solar system differs qualitatively from planetary growth in the terrestrial region, as the larger embryo masses and lower orbital velocities make bodies more subject to gravitational scattering. The planetesimal swarm in the outer nebula may be seeded by earlier-formed large bodies scattered from the region near the nebular “snow line”. Such a seed body can experience rapid runaway growth undisturbed by competitors; the style of growth is not oligarchy, but monarchy.     

前后级间距对随进战斗部影响的仿真分析

为研究串联战斗部前级装药对后级随进战斗部的影响,验证在现有导弹战斗部前端加装环形聚能装药的可行性,采用ANSYS/LS-DYNA软件进行了环形切割器对随进战斗部影响的数值仿真,在不同的前后级距离条件下,得到了随进战斗部的加速度、速度、位移变化和随进战斗部壳体和装药的最大应力值及其所在位置;仿真结果表明,在串联战斗部前后级相对静止时,不同间距条件下,环形切割器爆炸后形成的冲击波对随进战斗部加速度、速度、位移及壳体和装药的压力影响是不同的。     

Cometary Refractory Grains: Interstellar and Nebular Sources

Comets are heterogeneous mixtures of interstellar and nebular materials. The degree of mixing of interstellar sources and nebular sources at different nuclear size scales holds the promise of revealing how cometary particles, cometesimals, and cometary nuclei accreted. We can ascribe cometary materials to interstellar and nebular sources and see how comets probe planet-forming process in our protoplanetary disk. Comets and cometary IDPs contain carbonaceous matter that appears to be either similar to poorly-graphitized (amorphous) carbon, a likely ISM source, or highly labile complex organics, with possible ISM or outer disk heritage. The oxygen fugacity of the solar nebula depends on the dynamical interplay between the inward migration of carbon-rich grains and of icy (water-rich) grains. Inside the water dissociation line, OH^? reacts with carbon to form CO or CO₂, consuming available oxygen and contributing to the canonical low oxygen fugacity. Alternatively, the influx of water vapor and/or oxygen rich dust grains from outer (cooler) disk regions can raise the oxygen fugacity. Low oxygen fugacity of the canonical solar nebula favors the condensation of Mg-rich crystalline silicates and Fe-metal, or the annealing of Fe-Mg amorphous silicates into Mg-rich crystals and Fe-metal via Fe-reduction. High oxygen fugacity nebular conditions favors the condensation of Fe-bearing to Fe-rich crystalline silicates. In the ISM, Fe-Mg amorphous silicates are prevalent, in stark contrast to Mg-rich crystalline silicates that are rare. Hence, cometary Mg-rich crystalline silicates formed in the hot, inner regions of the canonical solar nebula and they are the touchstone for models of the outward radial transport of nebular grains to the comet-forming zone. Stardust samples are dominated by Mg-rich crystalline silicates but also contain abundant Fe-bearing and Fe-rich crystalline silicates that are too large (?0.1 μm) to be annealed Fe-Mg amorphous silicates. By comparison with asteroids, the Stardust Fe-bearing and Fe-rich crystalline silicates suggests partial aqueous alteration in comet nuclei. However, aqueous alteration transforms Fe-rich olivine to phyllosilicates before Mg-rich olivine, and Stardust has Mg-rich and Fe-rich olivine and no phyllosilicates. Hence, we look to a nebular source for the moderately Fe-rich to nearly pure-Fe crystalline silicates. Primitive matrices have Mg-Fe silicates but no phyllosilicates, supporting the idea that Mg-Fe silicates but not phyllosilicates are products of water-rich shocks. Chondrule-formation is a late stage process in our protoplanetary disk. Stardust samples show comet 81P/Wild 2 formed at least as late to incorporate a few chondrules, requiring radial transport of chondrules out to perhaps >20 AU. By similar radial transport mechanisms, collisional fragments of aqueously altered asteroids, in particular achondrites that formed earlier than chondrules, might reach the comet-forming zones. However, Stardust samples do not have phyllosilicates and chondrules are rare. Hence, the nebular refractory grains in comet 81P/Wild 2, as well as other comets, appear to be pre-accretionary with respect to asteroid parent bodies. By discussing nebular pathways for the formation of Fe-rich crystalline silicates, and also phyllosilicates and carbonates, we put forth the view that comets contain both the interstellar ingredients for and the products of nebular transmutation.     

噪声载荷作用下薄壁柱壳结构的随机振动响应的估算方法

给出了噪声载荷作用下薄壁柱壳结构随机振动加速度响应功率谱密度的计算公式和计算方法,并与实际测量获得的加速度响应功率谱密度进行了比较,计算的功率谱与实测的功率谱具有较好的一致性,说明这种估算噪声载荷作用下薄壁柱壳结构随机振动加速度响应功率谱密度的方法是合理可行的。用同样方法导出的Von Mises应力响应的功率谱密度及其均方值的计算公式,可直接用于疲劳强度分析。      

To estimation of moving distributed load effect on the dynamic behavior of circular multilayer cylindrical shells

We substantiate the necessity of taking into account the dynamic effect appearing in the anisotropic cylindrical shell under the action of the constant internal excess pressure, the leading edge of which is propagated along its generatrix with constant acceleration; the pressure is capable to create in the shells the stresses exceeding by many times the static components, which that may lead to the structure failure.     

Synchrotron Radiation from Galactic Sources: What We Can Learn About Particle Acceleration

I review the observations of galactic synchrotron sources, focusing on shell supernova remnants (SNRs), with particular attention to attributes that constrain the properties of electron acceleration. Radio observations provide information on source fluxes, spectral index, morphology, and polarization. Recent observations give us strong reason to believe that several young SNRs show synchrotron X-ray emission. Even if X-rays are thermal, however, limits can be set on the maximum energy to which electrons can be accelerated without a spectral break, since no galactic SNR is observed to have X-ray emission (due to any source) as bright as the extrapolation from radio frequencies of radio synchrotron emission. If synchrotron X-rays are detected or inferred, their morphology and spectrum provide important information on mechanisms governing acceleration to the highest energies. I describe models of synchrotron emission from SNRs and their comparison with observations. Finally, I describe the tasks ahead for both observers and theoreticians, to make better use of what SNR synchrotron emission tells us about particle acceleration.     

退化发动机加速性能恢复控制方法

针对退化发动机加速性能下降的现象,提出一种变喘振裕度约束的模型预测控制方法。通过分析退化发动机在加速过程中的工作特点,将加速过程分为三个阶段,在不同阶段采取不同的喘振裕度约束。鉴于模型预测控制能够显式处理约束、采用在线滚动优化来获取最优控制输入,采取模型预测控制方法,并采用具有较高实时性的交替方向乘子法求解优化问题,实现了退化发动机加速性能的恢复。数字仿真结果表明,采用本文所提出的加速性能恢复控制方法后,相比退化发动机,加速过程中所耗费的时间缩短了35%以上。     

Oxygen Isotopes in the Solar System

The oxygen three-isotope system has major advantages over the two-isotope systems of hydrogen, carbon, and nitrogen because different fractionation laws govern intraplanetary and interplanetary processes. This permits discriminating between solar nebular processes and parent-body processes. Oxygen isotopes also serve as a sensitive natural tracer for meteorite classification. This revised version was published online in August 2006 with corrections to the Cover Date.     

铝合金加速腐蚀因子模型与分析

以腐蚀深度衡量铝合金的腐蚀损伤,假设蚀坑深度服从对数正态分布、腐蚀深度与腐蚀时间的关系为幂函数式,建立了加速腐蚀因子模型,给出了常用铝合金加速腐蚀因子的表达式;得到了加速腐蚀因子与腐蚀时间无关的结论。并建立了加速腐蚀因子估计值的分布特性和统计分析方法。     

基于时间测量的加速度敏感方法

国际单位制共有7个基本单位,时间就是7个基本单位之一,是目前能够实现的测量精度最高的一个物理量。因此,将加速度的测量转化为时间的测量,是实现加速度高精度检测的有效途径。首先,介绍了基于时间测量的加速度敏感原理。然后,介绍了基于该敏感原理的加速度传感器研究进展。最后,进行了基于时间测量的加速度计精度的定性和定量分析。理论分析和实验证实表明,加速度精度极限与时间分辨率之间成正比关系。     

Driving mechanisms for the solar wind

In this review, we consider the central physical aspects pertinent to the acceleration of the solar wind. Special importance is placed on the high-speed streams since the properties of these structures seem to strain the various theoretical explanations the most. Heavy emphasis is also given to the observations — particularly as to what constraints they place on the theories. We also discuss certain sporadic events such as spicules, macrospicules, X-ray bright points, and outflows seen in the EUV associated with the explosive events, jets, and coronal bullets which could be of relevance to this problem.Three theoretical concepts pertaining to the solar wind acceleration process are examined — purely thermal acceleration with and without extended heating, acceleration due to Alfvén wave pressure, and diamagnetic acceleration. Emphasis is given to how well these theories meet the constraints imposed by the observations. Diamagnetism is argued to be a powerful ingredient in solar wind theory, both in the light of observed sporatic outflows seen in the chromosphere and transition region and also because of its effectiveness in increasing the flow speed and producing strong acceleration near the Sun in line with coronal hole observations.     

填充型吸波体阻燃外壳材料的研究

针对现有吸波材料外壳阻燃性能的不足,提出以玻璃纤维为主的新型复合外壳材料,并与聚丙烯空心板制备的方体的反射损耗进行对比。研究结果表明:在保证阻燃性的情况下,在低频下使用此类复合材料整体吸波性能较聚丙烯空心板材料提升了大约5~10 dB,在高频区有所下降,下降约10 dB,具有一定的应用价值。     

预腐蚀疲劳退化加速因子研究

考虑预腐蚀对材料疲劳性能的影响,以疲劳强度作为腐蚀量,给出了考虑预腐蚀疲劳退化的加速腐蚀因子的定义和表达式,并结合疲劳分析方法,以细节疲劳额定值(DFR)作为疲劳强度的衡量,给出了预腐蚀条件下的DFR确定方法,通过加速环境和实际服役环境下DFR随预腐蚀时间退化规律的对比分析,建立基于DFR的加速腐蚀因子,并进行参数估计,最后,给出了LY12CZ铝合金试件在典型环境下的加速腐蚀因子取值.      

飞行模拟器动力学控制的研究

针对如何获取运动平台的实时加速度和在精确跟踪加速度的同时限制位移,建立了系统动力学模型以计算加速度,使用虚拟弹簧法限制位移。在Matlab环境下,搭建了整个伺服控制系统。仿真结果表明,控制系统在保证平台位移不脱离限制区域的基础上,实现了加速度的精确跟踪。     

轴向过载对固体火箭发动机前封头绝热层烧蚀的影响

研究了固体火箭发动机内绝热层在飞行速度条件下的炭化烧蚀特性。用烧蚀发动机的旋转实验装置上,对ＮＢＲ和ＥＰＤＭ绝热层试件进行了烧蚀实验。在加速度７０ｇ、压强５ＭＰａ、时间１０ｓ条件下,绝热层平均炭化烧蚀率增大系数小于１．７。实验结果可用为发动机绝热层设计的依据。     

涡扇发动机液压机械式自动加速器优化设计

以某型涡扇发动机的液压机械式自动加速器为研究对象,以加速过程的上升时间、超调量和调节时间构造的评价函数为目标函数,并充分考虑加速过程中的约束条件,采用序列二次规划(SQP)算法对起决定作用的凸轮型面进行多目标优化设计.仿真结果表明优化设计后的自动加速器可使加速过程高压转子转速的超调量减小,调节时间缩短,加速性能得到明显改善,且涡轮前最高温度降幅较大,有利于延长涡轮等相关部件的使用寿命.      

弹道导弹飞行时间的BP神经网络控制方法

时间协同攻击是提高弹道导弹突防能力和作战效能的一种重要手段。由于发动机推力偏差等干扰因素造成导弹的飞行时间偏差较大,为精确控制弹道导弹的飞行时间,运用BP神经网络算法,建立了一种适用于较大飞行时间偏差修正的飞行时间调控模型。该模型用视加速度偏差表征推力偏差等干扰的影响,根据视加速度偏差调整导弹飞行中某一时段的程序角来实现对飞行时间的精确控制。由BP神经网络建立满足飞行时间偏差要求下视加速度与飞行程序角速率、转弯结束时间之间的映射关系。导弹实际飞行时,根据实际视加速度,由BP神经网络在线计算出飞行程序角速率及转弯结束时间,使导弹在干扰条件下仍以预定飞行时间到达目标。最后,通过仿真验证了该模型的有效性和可行性。