The feasibility of Doppler monitoring during EVA

During extravehicular activities (EVA) outside the spacecraft, astronauts have to work under reduced pressure in a space suit. This pressure reduction induces the risk of decompression sickness (DCS) by the formation of gas bubbles from excess nitrogen dissolved in the organism by breathing air at normal pressure. Under laboratory conditions the gas bubbles moving in the blood stream can be detected by the non-invasive ultrasonic Doppler method. By early detection of excessive bubble formation the development of DCS symptoms may be prevented by early application of preventative measures. The method could also be useful when applied in the space suit in order to compare the results of laboratory tests with operational results, because there is a discrepancy according to the DCS risk of laboratory experiments and actual EVA missions, where no symptoms have been reported yet. A prototype Doppler sensor has been developed and implemented in the Russian Orlan suit. To investigate the feasibility of this method under simulated space conditions, the equipment has been used in a series of 12 thermovacuum chamber tests with suited subjects, where intravenous bubble formation was compared to unsuited control experiments. In more than 50% of the suited tests good Doppler recordings could be achieved. In some cases with unsatisfying results the signal could be improved by breathholding. Although the results do not yet allow any conclusion about a possible difference between suited and unsuited subjects due to the small number of tests performed, the method proved its feasibility for use in EVA suits and should be further developed to enhance the safety of EVA procedures.     

Evaluation of safety of hypobaric decompressions and EVA from positions of probabilistic theory

Formation and subsequent evolution of gas bubbles in blood and tissues of subjects exposed to decompression are casual processes in their nature. Such character of bubbling processes in a body predetermines probabilistic character of decompression sickness (DCS) incidence in divers, aviators and astronauts. Our original probabilistic theory of decompression safety is based on stochastic models of these processes and on the concept of critical volume of a free gas phase in body tissues. From positions of this theory, the probability of DCS incidence during single-stage decompressions and during hypobaric decompressions under EVA in particular, is defined by the distribution of possible values of nucleation efficiency in "pain" tissues and by its critical significance depended on the parameters of a concrete decompression. In the present study the following is shown: 1) the dimensionless index of critical nucleation efficiency for "pain" body tissues is a more adequate index of decompression stress in comparison with Tissue Ratio, TR; 2) a priory the decompression under EVA performed according to the Russian protocol is more safe than decompression under EVA performed in accordance with the U.S. protocol; 3) the Russian space suit operated at a higher pressure and having a higher "rigidity" induces a stronger inhibition of mechanisms of cavitation and gas bubbles formation in tissues of a subject located in it, and by that provides a more considerable reduction of the DCS risk during real EVA performance.     

Numerical solution of nonlinear heat problem with moving boundary

Two phase gas–liquid flow in pipes is widely spread in space applications: bubble flows appear in cryogenic components transport through fuel/oxidant supply lines. Another important application is based on the fact that in liquid flows with small bubbles a close contact between the two phases occurs resulting in high rates of transfer between them. The compactness of a system makes it ideally suited to serve as a space-based two-phase bio-reactor which forms an important unit in environmental control and life support system deployed onboard. A numerical method was developed for solving a nonlinear problem of thermal interaction between a spherical gas bubble and surrounding liquid. The system of equations for describing this interaction was formulated. It includes ordinary and nonlinear partial differential equations. The problem was solved using finite-difference technique by dividing the system into spherical layers inside the bubble and employing the new variable which “freezes” the moving boundary of the bubble. A numerical solution is obtained for the problem of radial bubble motion induced by a sudden pressure change in the liquid—a situation which corresponds to the behavior of bubbles beyond a shock wave front when the latter enters a bubble curtain.     

Dual-frequency ultrasound for detecting and sizing bubbles

ISS construction and Mars exploration require extensive extravehicular activity (EVA), exposing crewmembers to increased decompression sickness risk. Improved bubble detection technologies could help increase EVA efficiency and safety. Creare Inc. has developed a bubble detection and sizing instrument using dual-frequency ultrasound. The device emits “pump” and “image” signals at two frequencies. The low-frequency pump signal causes an appropriately-sized bubble to resonate. When the image frequency hits a resonating bubble, mixing signals are returned at the sum and difference of the two frequencies. To test the feasibility of transcutaneous intravascular detection, intravascular bubbles in anesthetized swine were produced using agitated saline and decompression stress. Ultrasonic transducers on the chest provided the two frequencies. Mixing signals were detected transthoracically in the right atrium using both methods. A histogram of estimated bubble sizes could be constructed. Bubbles can be detected and sized transthoracically in the right atrium using dual-frequency ultrasound.     

Efficacy of Doppler ultrasound [correction of utrasound] for screening symptoms of decompression sickness during simulated extravehicular activities

Doppler ultrasound is frequently used for monitoring circulating microbubbles during decompression to assess the symptoms of Decompression Sickness (DCS). This analysis was carried out to evaluate its effectiveness for screening symptoms of DCS during simulated extravehicular activities (EVA). The information from various hypobaric chamber studies carried out at the NASA Johnson Space Center, Houston, TX was used in this analysis (n = 516). The circulating microbubbles were detected in the precordial area in 42% (218/516), and symptoms were reported in 16% (81/516) of these exposures. The accuracy of Doppler-detectable bubbles (Spencer grades) on all symptoms of DCS was examined by calculating measures of sensitivity and specificity. The efficacy of Doppler as a screening device was examined by calculating their positive predictive value (PPV) and negative predictive value (NPV). The results of these analyses indicated that the sensitivity of Doppler decreased, and the PPV increased with higher Spencer grades. However, the likelihood of detecting true negative cases (NPV) was consistently higher with all bubble grades. Due to the high false-positive rate and low prior probabilities of the risk of DCS, Doppler was found to be more useful to identify those who did not develop DCS, than to detect positive cases of DCS in the simulated EVA exposures.     

凹槽参数对通气空泡融合的影响

水下航行体通气技术形成的空泡能够有效降低航行阻力并调节运动姿态,但通气空泡在航行体表面不易融合,空泡形态不稳定,因此开展通气空泡的融合控制具有重要工程应用价值。采用有限体积法进行数值计算,研究了航行体孔后开槽对通气空泡融合的控制作用,并探究了不同凹槽参数对通气空泡融合的影响。研究发现,凹槽改变了空泡的流场特性,槽内产生的旋涡卷吸流经凹槽的气体,使槽内气体向航行体周向发展并融合;当槽宽取0.125D,孔槽间距取0.075D时,对空泡融合的促进以及稳压效果最佳。     

Fatty acid composition of plasma lipids and erythrocyte membranes during simulated extravehicular activity

Ten subjects (from 27 to 41 years) have been participated in 32 experiments. They were decompressed from ground level to 40-35 kPa in altitude chamber when breathed 100% oxygen by mask and performed repeated cycles of exercises (3.0 Kcal/min). The intervals between decompressions were 3-5 days. Plasma lipid and erythrocyte membrane fatty acid composition was evaluated in the fasting venous blood before and immediately after hypobaric exposure. There were 7 cases decompression sickness (DCS). Venous gas bubbles (GB) were detected in 27 cases (84.4%). Any significant changes in the fatty acid composition of erythrocyte membranes and plasma didn't practically induce after the first decompression. However, by the beginning of the second decompression the total lipid level in erythrocyte membranes decreased from 54.6 mg% to 40.4 mg% in group with DCS symptoms and from 51.2 mg% to 35.2 mg% (p<0.05) without DCS symptoms. In group with DCS symptoms a tendency to increased level of saturated fatty acids in erythrocyte membranes (16:0, 18:0), the level of the polyunsaturated linoleic fatty acid (18:2) and arachidonic acid (20:4) tended to be decreased by the beginning of the second decompression. Insignificant changes in blood plasma fatty acid composition was observed in both groups. The obtained biochemical data that indicated the simulated extravehicular activity (EVA) condition is accompanied by the certain changes in the blood lipid metabolism, structural and functional state of erythrocyte membranes, which are reversible. The most pronounced changes are found in subjects with DCS symptoms.     

EVA: European plans

The current status of European EVA (extravehicular activity) plans is reviewed. The major difference to already existing EVA scenarios in U.S.A. and Soviet Union consists in the adoption of a higher suit pressure, namely 500 hPa. The results of a study concerned with the physiological consequences of this adoption are presented, including recommendations for protective procedures and their necessary experimental validation. A certain discrepancy between laboratory experimental decompression data and EVA operational results is discussed, leading to the identification of several items which may influence space decompression. Microgravity and the influence of the space suit itself are most likely factors in the explanation of this discrepancy, and both experimental procedures and technological developments are proposed to clarify their role for the future design of EVA procedures.     

Thermocapillary simulation of single bubble dynamics in zero gravity

The lack of significant buoyancy effects in zero gravity conditions poses an issue with fluid transfer in a stagnant liquid. In this paper bubble movement in a stagnant liquid is analysed and presented numerically using a computational fluid dynamics (CFD) approach. The governing continuum conservation equations for two phase flow are solved using the commercial software package Ansys-Fluent v.13 and the Volume of Fluid (VOF) method is used to track the liquid/gas interface in 2D and 3D domains. The simulation results are in reasonable agreement with the earlier experimental observations, the VOF algorithm is found to be a valuable tool for studying the phenomena of gas–liquid interaction. The flow is driven via Marangoni influence induced by the temperature difference which in turn drives the bubble from the cold to the hot region. A range of thermal Reynolds (Re_T) and Marangoni numbers (Ma_T) are selected for the numerical simulations, specifically Re_T=13–658 and Ma_T=214–10,721 respectively. The results indicate that the inherent velocity of bubbles decreases with an increase of the Marangoni number, a result that is line with the results of previous space experiments (Kang et al., 2008) [1]. An expression for predicting the scaled velocity of bubble has been derived based on the data obtained in the present numerical study. Some three-dimensional simulations are also performed to compare and examine the results with two-dimensional simulations.     

Vertical distribution of the power of short- and long-period oscillations in a sunspot and in surrounding magnetic elements

We present the results of processing three 256-min series of observations of quasi-periodic oscillations of the field of line-of-sight velocities in three sunspots. The Doppler shifts were determined simultaneously for six spectral lines formed at different heights in the solar atmosphere. In addition to the well-known high-frequency (periods of 3–5 min) oscillations, a band of low-frequency oscillations with periods of 60–80 min is revealed in the spectra of the sunspot umbra and magnetic elements located in immediate proximity of the sunspot. Unlike the short-period modes, the power of the long-period mode of line-of-sight velocity oscillations in the sunspot decreases sharply with height: these oscillations are distinctly seen in the line formed at a height of 200 km and almost are not seen in the line with the formation height of 500 km. This is indicative of different physical nature of the short-period and long-period oscillations of a sunspot. If the former are caused by slow magnetosonic waves within the field tube of the spot, the latter are representative of global vertical-radial oscillations of a magnetic element (spot, pore) as a whole near the position of a stable equilibrium.     

An objective determination of +Gz acceleration tolerance

Until recently, human +Gz acceleration tolerance has relied solely on subjective criteria relating to loss of vision. By use of newly developed noninvasive instrumentation using a transcutaneous Doppler flow system, objective end point criteria have been developed based on measured blood flow to the head. The system consists of miniature 8 MHz Doppler sensors (2 x 1 x 0.5 cm) placed on the forehead over both frontal branches of the temporal arteries to detect blood flow velocity from back scattered ultrasound. Its use has allowed for correlation of altered, decreased and actual reversal of eye level blood flow with subsequent central light loss. Over 100 subjects have now been studied during more than 2,000 centrifuge runs. Objective changes in temporal artery flow velocity consistently preceded visual degradation for each subject during all acceleration profiles. No subject has gone unconscious without first exhibiting a minimum 6 sec of total flow cessation. Retrograde flow followed by complete flow cessation always preceded central light loss. Results indicate that this method can be successfully used with a wide variety of tasks during exposure to +Gz acceleration. It is recommended for use during evaluation of protective maneuvers or devices on the centrifuge or during actual flight in high performance aircraft. It may also serve as a potential safety monitor during space Shuttle re-entry if there is doubt about a passenger's cardiovascular status.     

Flow of a water jet into vacuum

At certain intervals excess water has to be dumped into space overboard of the Spacelab cabin. For the development of a useful nozzle the behaviour of a water jet flowing into vacuum was investigated experimentally and theoretical interpretations of the flow phenomena which were found are given. The influence of parameters like the shape of the nozzle, the temperature and the gas content of water were studied. At certain test conditions, the jet leaves the nozzle exit in bundled form and ends abruptly bursting into droplets and ice-particles. The “bursting”-mechanism is explained by a sudden boiling of the water in the jet causing the growth of vapor bubbles decomposing the jet. The formation of vapor bubbles is initiated by a superheating of the water of the jet caused by a sudden pressure drop and a cooling at the surface of the jet. The expansion of vapor bubbles in the jet is retarded by surface tension forces which results in a relaxation time for the bursting of the jet. The vapor flow in radial directions of the jet is approximately described by a plane radial source flow. The measurement of the pitot-pressure radially to the jet proves that the vapor flow is supersonic.     

针刺预制体参数对C/C复合材料力学性能的影响

通过针刺与化学气相沉积分别制备碳纤维预制体与碳基体,获得针刺C/C复合材料.研究了针刺密度、针刺深度、网胎面密度等预制体成型工艺参数对C/C复合材料力学性能的影响,并探讨了预制体体积密度与C/C复合材料力学性能关联关系.结果表明,针刺密度在20～ 50针/cm2之间时,C/C复合材料拉伸强度先增后减,而层间剪切强度一直上升;针刺深度在10～16 mm之间时,拉伸强度和层间剪切强度随针刺深度的提高而增加;网胎面密度在100～300 g/m2之间时,拉伸强度和层间剪切强度随网胎面密度的提高而降低;当只改变针刺密度、针刺深度、网胎面密度其中一个成型参数时,拉伸强度和层间剪切强度受预制体密度影响显著,预制体密度可作为预测C/C复合材料力学性能的一个宏观成型参数.     

Effect of a venotonic agent on the main arteries and veins during a 5 day HDT.

Objective: To evaluate the cardiac, arterial and venous effect of a venotonic drug (Cirkan "Ck") administrated orally daily to 6 subjects in HDT position during 5 days. These subjects underwent a second 5d HDT without Ck treatment one month later. Pre and post HDT the subjects were submitted to a stand test. Method: The cardiovascular parameters were measured by echography and Doppler. Results and discussion: The Cirkan treatment contributed to reduce the increase in cerebral resistance, and to maintain the lower limb resistance at a higher level than on controls. It reduces the vein section at the extremities (Jugular, femoral) and in the central vein system connected to the right heart (sub hepatics). On the other hand it increases the portal vein section which means that the blood stagnation at the splanchnic level is increased. Despite these arterial and venous significant modifications the clinical and ECG and Blood pressure response to the Stand test was similar in both groups.     

窄带实高斯噪声对外差式零拍装置的干扰机理

以外差式CW多普勒引信为例分析了外差式零拍装置提取差频信号的基本原理,把外差式零拍装置在数学层面上抽象为对线性叠加信号求平方后提取低频分量的模型。根据该模型,从理论上证明了：窄带实高斯噪声单独通过外差式零拍装置后输出的低频噪声的带宽将得到加倍,噪声与本振信号相互作用后产生新的噪声分量将使低频噪声功率比无本振信号时得到增加;回波信号加窄带平稳实高斯噪声通过零拍装置后干信比将得到增强,且增强的程度将随本振信号功率的增加而降低。计算机仿真分析的结果验证了上述结论,也正好解释了早期CW引信极易受到频率对准噪声干扰而早炸的实际情况。     

Microgravity gas–liquid flow through packed beds

Analysis of possible physical mechanism involved in the process of transition of bubble-to-pulse flow regime in cocurrent gas–liquid flow through a packed bed in microgravity demonstrates that the transition can be described by the key dimensionless group Suratman number and the ratio of gas to liquid Reynolds numbers. This result establishes a physical basis to the existing empirical transition equation which is also based on the same dimensionless groups. Furthermore, the concepts of driving-to-resistance force ratio and pore-level bubble flow mechanism have been utilized to explore the basis of the existing modified friction factor correlation for two-phase flow through a packed bed under microgravity.     

Multi-frequency doppler radio sounding of the ionosphere in the “Equatorial trigger” experiment

Results of processing the data of multi-frequency Doppler sounding of the low-latitude ionosphere are presented. Interesting features in the behavior of time variations of the Doppler frequency shift are found. These features are interpreted as manifestations of wave disturbances in the ionospheric plasma density.     

5cm高稳频介质谐振器振荡源的研究与设计

介绍了Ｃ波段介质稳频振荡器的相关理论，给出一系列决定振荡器频率的理论公式，并通过设计实例证明了反馈型振荡器具有易于设计、调试及批生产的工程应用特性，同时发现该振荡器的另一优良特性：低相位噪声。     

Ignition of fuel sprays by shock wave mathematical modeling and numerical simulation

The paper presents the results of developing of physical and mathematical model making it possible to take into account the effect of droplets non-uniformity in space and size distribution on ignition conditions for fuel sprays. The influence of condensed phase volume fraction on ignition and combustion of sprays was studied, physical and mathematical models for multi-phase flows, mixture formation and combustion of liquid fuels based on solving Navier–Stokes equations for gas phase accounting for thermal and mechanical interaction with poly-dispersed droplets array. The problems of particulate phase dynamics are regarded accounting for the interaction with gas phase atomization, evaporation and combustion.It was shown that depending on droplet size distribution and aerosol cloud density different flow scenarios were possible.Several ignition zones could be formed behind incident shock wave depending on mixture properties and initiation parameters. The possibility of numerical simulation permitting variation of definite parameters only made it possible to explain this fact.     

低信噪比大频偏空间光信号的频率捕获研究

卫星相干光通信系统信号解调过程中,卫星相对运动会导致接收的信号光产生GHz量级的多普勒频移,信号光的远距离传输导致光信噪比极低,传统方法无法在低信噪比下补偿大范围多普勒频移,严重影响通信系统的能力。针对上述问题,本文提出了一种两段式频率捕获算法,该算法包含自动扫频和锁频控制两个阶段。自动扫频阶段通过本振光自动频率扫描将频差缩小至100 MHz量级;锁频控制阶段通过高精度的本振光频率控制与FFT变换,在低信噪比下继续缩小频差至MHz量级。仿真验证结果表明：该算法可在2 dB信噪比下补偿大动态范围的10 GHz范围多普勒频差,满足卫星相干光通信解调需求。