On gas-phase ignition of diffusion flame in the stagnation-point boundary layer

An analytical expression for gas-phase ignition is developed for a diffusion flame in the two-dimensional or axisymmetric stagnation-point boundary-layer flow of a hot oxidizing gas about a vaporizing condensed fuel surface. The analysis is based on the limit of large activation energy for a one-step, irreversible reaction describing the overall combustion process in the gas phase. The approach in this work, following that of our recent analysis on extinction for the same geometry, is to seek an exact correspondence of the parameters of the present problem with those of counterflow diffusion-flame problem of Liñán. Such a correspondence has been found in the frozen-flow regime and as a consequence, the asymptotic structure of the flame in the nearly frozen ignition regime is identical in both the problems. A particular result of this observation is the availability of an analytical criterion for ignition in the present problem. The analysis reveals that contrary to the case of extinction, fluid dynamic details do not have significant effect on the ignition criterion and that Liñán's results may be applied with good accuracy to the condensed fuel problem.     

Monopropellant droplet decomposition for large activation energies

The quasi-steady decomposition of a monopropellant droplet in a quiescent atmosphere is analyzed, in the limit of large activation energy, for a gas phase decomposition reaction of the Arrhenius type.An analytical relation is obtained for the pre-exponential rate constant, or the Damköhler number, as a function of the droplet vaporization rate. The curve giving the vaporization rate in terms of the Damköhler number has, for low values of the temperature at infinity, an S shaped form which exhibits ignition-extinction characteristics.With increasing values of the droplet vaporization rate above the pure vaporization value we pass from a nearly frozen regime, under which ignition conditions occur due to the large temperature sensitivity of the reaction rate, to a complete decomposition regime, in which practically all the fuel is decomposed in a thin reactive-diffusion zone, separated from the droplet surface by a transport region of lower temperature. For sufficiently large Damköhler numbers, the thin reaction zone is located close to the droplet surface, so that the flame structure becomes planar: a linear relation between the droplet radius and time is obtained in this case. The non planar effects are responsible for the extinction of the flame at low Damköhler numbers and ambient temperatures below the adiabatic flame temperature. For sufficiently low values of the ambient temperature, an intermediate regime exists in which the enhancement of the vaporization rate is due only to the fraction of the vaporized fuel decomposed at a thin reaction zone, not far from the droplet, where the temperature reaches its maximum value; the remaining fuel is decomposed very far from the droplet.     

The deontology of the conquest of space / de la deontologie de la conquete de l''espace: Proceedings from a conference, Casablanca, 1–4 march 1984 Academy of the Kingdom of Morocco, Rabat, Morocco, 1984, 178 pages

Professor Caesar Voûte reports on the 34th Pugwash Conference on Science and World Affairs, Björkliden, Sweden, 9–14 July 1984: ‘1984 and Beyond: Science, Security and Public Opinion’.     

Numerical modeling of unsteady flame propagation

The problem of the numerical modeling of unsteady flame propagation with large amounts of exothermic heat release has been addressed through the use of a model equation which contains many of the important nonlinearities and difficulties in the problem. The model equation has been solved for a significant variation in Damköhler number with a variety of conventional and new finite-difference procedures. One of the new procedures used was an adaptive grid method which places node points in the region of large temperature gradients where they are necessary for a proper simulation of the phenomena. This adaptive grid procedure does have significant advantages over conventional second and fourth order uniform grid methods for many aspects of the problem. It has been found that conventional methods with relatively few node points are inadequate for flames with high Damköhler number, because of the fact that too few nodes are located in the flame. Further refinement of the adaptive grid method seems feasible, but even in the present form it represents a significant improvement over conventional techniques.     

Moscow declaration

This declaration was made at the International Conference on Aerospace Complex Conversion, organized by the United Nations in Moscow, 12–16 October 1992. It provides a follow-on to the UN conference on ‘Conversion - opporunities for development and environment’ held in Dortmund, Germany, 24–27 February 1992, and reported in the August 1992 issue of Space Policy by Professor K.H. Böckstiegel, who chaired the Plenary Session in Moscow.     

An approach to the autoignition of a turbulent mixture

This paper considers the turbulent homogeneous mixing of two reactants undergoing a one step, second order, irreversible, exothermic chemical reaction with a rate constant of the Arrhenius type. A statistically stationary turbulent velocity field is assumed given and unaffected by mass or heat production due to the chemical reaction. Relative density fluctuations are neglected. A Hopf-like functional formalism is presented, with application to both statistically inhomogeneous and statistically homogeneous flows. Single and double point probability density function differential equations are derived from those functional equations. The limit of very large activation energies is considered; a low degree of statistical correlation between temperature and concentration fields during the ignition period is hypothesized. After making use of the homogeneity assumption a closure problem is still present due to the nonlocalness of the molecular diffusion term. The problem is rendered closed by assuming a Gaussian conditional expected value for the temperature at a point given the temperature at a neighboring point. The closure is seen to preserve very important mathematical and physical properties. A linear first order hyperbolic differential equation with variable coefficients for the probability density function of the temperature field is obtained. A second Damköhler number based on Taylor's microscale turns out to be an important controlling parameter. A numerical integration for different values of the second Damköhler number and the initial stochastic parameters is carried out. The mixture is seen to evolve towards an eventual thermal runaway, the detailed behavior however being different for different systems. Some peculiarities during the ignition period evolution are uncovered.     

Ricardo Dyrgalla (1910–1970), pioneer of rocket development in Argentina

One of the most important developers of liquid propellant rocket engines in Argentina was Polish-born Ricardo Dyrgalla. Dyrgalla immigrated to Argentina from the United Kingdom in 1946, where he had been studying German weapons development at the end of the Second World War. A trained pilot and aeronautical engineer, he understood the intricacies of rocket propulsion and was eager to find practical applications to his recently gained knowledge.Dyrgalla arrived in Argentina during Juan Perón's first presidency, a time when technicians from all over Europe were being recruited to work in various projects for the recently created Argentine Air Force.Shortly after immigrating, Dyrgalla proposed to develop an advanced air-launched weapon, the Tábano, based on a rocket engine of his design, the AN-1. After a successful development program, the Tábano was tested between 1949 and 1951; however, the project was canceled by the government shortly after. Today, the AN-1 rocket engine is recognized as the first liquid propellant rocket to be developed in South America. Besides the AN-1, Dyrgalla also developed several other rockets systems in Argentina, including the PROSON, a solid-propellant rocket launcher developed by the Argentine Institute of Science and Technology for the Armed Forces (CITEFA). In the late 1960s, Dyrgalla and his family relocated to Brazil due mostly to the lack of continuation of rocket development in Argentina. There, he worked for the Institute of Aerospace Technology (ITA) until his untimely death in 1970. Ricardo Dyrgalla deserves to be recognized among the world's rocket pioneers and his contribution to the science and engineering of rocketry deserves a special place in the history of South America's rocketry and space flight advocacy programs.     

Manifestations of sudden commencement of a severe magnetic storm of November 20, 2003, in generation of an SC pulse, <Emphasis Type="Italic">P</Emphasis><Subscript>SC</Subscript> pulsations,and spatial modulation of the auroral brightness

The results of investigation of the geomagnetic and auroral response to the commencement of a severe magnetic storm of November 20, 2003, are presented. It is established that the onset of SC led to the brightening of the auroral arc in the dusk sector for 2–3 min with its extent to the east with a velocity of 10–20 km/s and to displacement poleward with a velocity of 1.0 km/s. Furtheron, the fast auroral expansions of short duration (5 min) to the pole up to 2–4°were observed, repeating every 5–10 min during 40 min, which led to the spatial modulation of the brightness of the glow and to generation of P_SC pulsations with similar periods of oscillations. The broadening of aurora poleward had a steplike character, with generation of new arcs poleward of previous ones 5 arcs per 1.5 min. The modulation of brightness of the glow and P_SC were observed against the background of intensification of a two-cell DP2 type current system and were accompanied by multiple turnings of the IMF B_z from south to north and back. It is assumed that the source of P_SC pulsations was a modulation of the intensity of the DP2 ionosphere currents as a result of variations of the magnetosphere convection level.Translated from Kosmicheskie Issledovaniya, Vol. 42, No. 6, 2004, pp. 608–615.Original Russian Text Copyright © 2004 by Baishev, Borisov, Velichko, Solovyev, Yumoto.     

Three dimensional spatial memory and learning in real and virtual environments

Human orientation and spatial cognition partlydepends on our ability to remember sets ofvisual landmarks and imagine their relationshipto us from a different viewpoint. We normallymake large body rotations only about a singleaxis which is aligned with gravity. However,astronauts who try to recognize environmentsrotated in 3 dimensions report that theirterrestrial ability to imagine the relativeorientation of remembered landmarks does noteasily generalize. The ability of humansubjects to learn to mentally rotate a simplearray of six objects around them was studied in1-G laboratory experiments. Subjects weretested in a cubic chamber (n = 73) and aequivalent virtual environment (n = 24),analogous to the interior of a space stationnode module. A picture of an object waspresented at the center of each wall. Subjectshad to memorize the spatial relationships amongthe six objects and learn to predict thedirection to a specific object if their bodywere in a specified 3D orientation. Percentcorrect learning curves and response times weremeasured. Most subjects achieved high accuracyfrom a given viewpoint within 20 trials,regardless of roll orientation, and learned asecond view direction with equal or greaterease. Performance of the subject group thatused a head mounted display/head tracker wasqualitatively similar to that of the secondgroup tested in a physical node simulator. Body position with respect to gravity had asignificant but minor effect on performance ofeach group, suggesting that results may alsoapply to weightless situations. A correlationwas found between task performance measures andconventional paper-and-pencil tests of fieldindependence and 2&3 dimensional figurerotation ability.     

Evaluation of Ir/Al2O3, Ir–Ru/Al2O3 and Ru/Al2O3 catalyst performance in a 5 N satellite thruster

Ir/Al₂O₃, Ir–Ru/Al₂O₃ and Ru/Al₂O₃ catalysts with approximately 33% metallic content in mass were prepared in 20 impregnation steps. For the Ru catalyst, two impregnation methods were employed: incipient wetness (chlorinated precursor) and by excess volume (non-chlorinated precursor). For the remaining catalysts, only incipient wetness impregnation was used with chlorinated precursors. Catalyst textural properties were evaluated before and after catalytic tests: metallic grade, specific area, mesopore volume distribution, metallic dispersion, and metallic particle average diameter. Catalysts were tested for hydrazine (N₂H₄) decomposition reaction in a 5 N satellite thruster and their performances were compared to Shell 405 commercial catalyst. Results showed that catalysts containing Ir were similar in performance to Shell 405 commercial catalyst and that the catalyst containing only Ru should not be used in cold starts.     

Results of Measurements of Accelerations of Technological Devices onboard the FotonSpacecraft

This paper generalizes the results of measuring the residual accelerations arising when investigations in space materials science are carried out onboard the unmanned Fotonspacecraft. The levels of vibroaccelerations are analyzed in the frequency band of 1–500 Hz for the technological devices UZ01, UZ04, and POLIZON, developed by the Federal Unitary State Enterprise Barmin Design Bureau of General Machine Building (V.P. Barmin KBOM). The levels of accelerations are estimated in the frequency band of 0–1 Hz in the zone of technological operations of these facilities. The basic sources of vibroaccelerations acting upon the frames of devices are determined in the capsule zone, where technological processes of producing new materials take place. In the frequency band of 1–500 Hz the vibroaccelerations are shown to be generated by the operation of Fotonspacecraft units and a drive of capsule translation during the technological process. On the capsule frame they reach the values of (1–3) × 10^–3 g. The level of linear accelerations in the infralow-frequency band is determined by rotational motions of the Fotonspacecraft. It depends on the device location with respect to the spacecraft center of mass and does not exceed (1–7) × 10^–6 gin the steady-state regime in the zone of technological activity.     

Radio Wave Fluctuations and Layered Structure of the Upper Region of Venusian Clouds from Radio Occultation Data

The results of the cross-correlation analysis of the amplitude fluctuations of radio waves of the = 32 cm band in seven sessions of radio occultation measurements of the northern polar atmosphere of the planet are presented. The existence of the cross-correlation of fluctuations (b 0.6) is established in the altitude realizations in the interval 61.5–65.0 km for two different sessions of radio occultation. Inner layering is revealed in the upper layer of the clouds of the planet at altitudes of 61.5–65.0 km, which is specified by an enhanced turbulence of the atmosphere. It is found that the lifetime of the small-scale layered irregularities is no less than 2 days and that their horizontal extension in the meridional direction can exceed 130 km. A possible cause of the emergence of the layered structures inside the upper layer of the polar clouds of Venus is discussed.     

编队飞行卫星三维定位系统的动力学和控制策略

提出应用多颗编队飞行小卫星实现的三维定位系统。首先建立精确动力学模型和摄动方程,然后进行数学仿真和估算三维位置精度,最后讨论位置保持控制策略。仿真结果表明:编队飞行三维定位系统定位精度高,不受纬度影响,而且可以实现全球同时定位功能。     

Stationary Nose Structures of Protons in the Inner Magnetosphere: Observations by the ION Instrument onboard the Interball-2 Satellite and Modeling

Nose structures are objects formed by H⁺ particles penetrating into the inner magnetosphere [1, 2]. We present the results of experimental studies and numerical modeling of the nose structures. Statistical processing of the observations of nose structures in 1997 by the ION instrument onboard the Interball-2 satellite at heights of 10000–15000 km demonstrates that the probability of formation of the nose structures under quiet magnetic conditions (with current values K _p = 0–1) in the nighttime sector of the magnetosphere is 90%. The probability of observation of the nose structures in the daytime sector equals 50% at the current value K _p = 0–1, and the correlation between the observations of nose structures and K _p can be improved (up to 75%) if the K _p index is taken 6 h before the observed events. It is shown that nose structures are a characteristic feature not only of the substorm processes but also of quasi-stationary phenomena in the quiet magnetosphere. The nose structures observed in magnetically quiet periods are called stationary nose structures in this work. By modeling drift trajectories for protons, it is shown that the stationary nose structures are formed in all sectors of the MLT. The stationary nose structures observed by the ION instrument are modeled in the night, morning, and daytime sectors of the MLT. The relation between the stationary nose structures and ion spectral gaps is considered.     

卫星肼瓶系统减振优化设计

由于布局和安装条件的限制,某卫星肼瓶支架采用了“十”字型截面设计,这导致在发射过程中某方向肼瓶振动幅度过大,发生较大变形甚至断裂破坏。为减小肼瓶系统的过度振动,采用结构优化方法进行了减振动力学设计。考虑以下方案:1)固有频率约束下,以肼瓶系统重量为目标函数的尺寸优化;2)频率响应约束下,以肼瓶系统重量为目标函数的尺寸优化;3)以频率响应极小化为目标函数的肼瓶系统尺寸优化;4)频率响应约束下阻尼材料拓扑布局优化,以肼瓶系统重量为目标函数。对优化模型1)~3)进行直接线性化处理,采用序列二次规划方法求解。在阻尼材料拓扑布局优化中,采用了作者提出的基于阻尼拓扑敏度综合评价的阻尼材料拓扑优化准则。综合比较上述方案优化效果,阻尼拓扑布局优化设计的减振效果是最佳的。文中对动力响应优化设计问题的优化模型选取也进行了探讨。     

Revisiting Perspective-Taking: Can People Maintain Imagined Perspectives?

Abstract

Three experiments were conducted to examine whether people can adopt and maintain imagined perspectives in the absence of target information. The task used entailed providing information about an imagined perspective in advance of target information to examine whether this would facilitate perspective-taking performance and reduce or eliminate alignment effects that are commonly reported in the literature. The three experiments employed different types of spatial environments: an environment learned from navigating a computer screen (Experiment 1), and an immersive environment that was either remote (Experiment 2) or immediate (Experiment 3) at the time of retrieval. Across the three experiments, results showed that information about an imagined perspective can be utilized ahead of target information. Furthermore, they suggested that alignment effects can be reduced as a result of processing information about perspective ahead of target information, but only when reasoning about specific nonimmediate spatial relations (Experiments 1 and 2). Results are discussed in connection with previous findings on spatial updating and the organizational structure of spatial memory.     

N2O/C3H8发动机气液同轴离心式喷嘴喷雾性能数值模拟研究

采用数值计算方法对氧化亚氮/丙烷（N2O/C3H8）发动机样机气液同轴离心式喷嘴的喷雾性能进行了研究,得到了环缝外喷嘴气相喷注压降和内喷嘴缩进深度对离心式喷嘴喷雾流场的影响.分析结果表明,较低的气相喷注压降（＜0.3 MPa）会显著的影响液滴在流场中的蒸发速率以及流场流强、混合比、索太尔平均直径（SMD）和n值的分布;气相喷注压降从0.3 MPa增加至0.6 MPa,稳定喷雾流场液滴SMD和n值分别在2.41～1.68,2.03～0.98范围内变化并逐渐减小.内喷嘴缩进深度从0 mm增加至6 mm,稳定喷雾流场液滴的SMD和n值受其影响较小,均分别在1.70～0.94,2.36～0.99范围内波动.喷嘴的最佳燃烧区主要分布在下游轴向位置0.015～0.035m范围内并随着气相喷注压降的升高和内喷嘴缩进深度的增大逐渐靠近喷嘴出口.该设计喷嘴在发动机热试实验中表现出很好的性能.     

Why O2 is required by complex life on habitable planets and the concept of planetary "oxygenation time"

Life is constructed from a limited toolkit: the Periodic Table. The reduction of oxygen provides the largest free energy release per electron transfer, except for the reduction of fluorine and chlorine. However, the bonding of O2 ensures that it is sufficiently stable to accumulate in a planetary atmosphere, whereas the more weakly bonded halogen gases are far too reactive ever to achieve significant abundance. Consequently, an atmosphere rich in O2 provides the largest feasible energy source. This universal uniqueness suggests that abundant O2 is necessary for the high-energy demands of complex life anywhere, i.e., for actively mobile organisms of approximately 10(-1)-10(0) m size scale with specialized, differentiated anatomy comparable to advanced metazoans. On Earth, aerobic metabolism provides about an order of magnitude more energy for a given intake of food than anaerobic metabolism. As a result, anaerobes do not grow beyond the complexity of uniseriate filaments of cells because of prohibitively low growth efficiencies in a food chain. The biomass cumulative number density, n, at a particular mass, m, scales as n (> m) proportional to m(-1) for aquatic aerobes, and we show that for anaerobes the predicted scaling is n proportional to m (-1.5), close to a growth-limited threshold. Even with aerobic metabolism, the partial pressure of atmospheric O2 (P(O2)) must exceed approximately 10(3) Pa to allow organisms that rely on O2 diffusion to evolve to a size approximately 10(3) m x P(O2) in the range approximately 10(3)-10(4) Pa is needed to exceed the threshold of approximately 10(2) m size for complex life with circulatory physiology. In terrestrial life, O(2) also facilitates hundreds of metabolic pathways, including those that make specialized structural molecules found only in animals. The time scale to reach P(O(2)) approximately 10(4) Pa, or "oxygenation time," was long on the Earth (approximately 3.9 billion years), within almost a factor of 2 of the Sun's main sequence lifetime. Consequently, we argue that the oxygenation time is likely to be a key rate-limiting step in the evolution of complex life on other habitable planets. The oxygenation time could preclude complex life on Earth-like planets orbiting short-lived stars that end their main sequence lives before planetary oxygenation takes place. Conversely, Earth-like planets orbiting long-lived stars are potentially favorable habitats for complex life.