Cylindrical heterogeneous detonation waves

Further experimental studies of blast wave initiated cylindrical heterogeneous (liquid fuel drops, gas oxidizer) detonation waves are described. A pie-shaped shock tube, used for these studies, was altered in certain ways so as to improve the modeling of cylindrical waves. These modifications, along with some operational aspects, are briefly discussed. The breech of the facility, where the blast wave is generated by an explosive, became distorted with usage. Results are presented which show that lower detonation velocities are realized with the damaged breech (other conditions being the same). A photographic and pressure switch wave time of arrival study was made to ascertain the wave shape. Photographs are shown which show that the waves, blast as well as detonation, are close to cylindrical. However, in some cases there is appreciable distortion of the wave front by debris ahead of the wave. Presumably this debris comes from the blasting cap used to ignite the condensed explosive. A series of experiments was conducted using kerosene drops of 388 μm diameter dispersed in air through use of a large number of hypodermic needles. Radial fuel void regions were established by cutting off the fuel flow to a number of needles. Preliminary results relating to the effect of the size of the cloud gap on detonation velocity, quenching, and the initiator energy levels required for detonation are discussed.     

Some aspects of the early evolution of photosynthesis.

The early evolution of a photocatalytic system of the porphyrin type, able to efficiently collect and utilize solar energy for primary electron transfer is discussed. Experimental results concerning some spectral and photochemical properties of the porphyrins, biosynthetic precursors of chlorophyll and their complexes with polymeric templates are reviewed. Protoporphyrin IX associated with pigmented proteinoid is demonstrated to be a favourable candidate for a role of a photosensitizer of the first photosynthetic reaction centers. The origin and early evolution of the photosynthetic electron transfer chain and of the phosphorylating mechanism are discussed with emphasis on the energetic mechanisms of archaebacteria.     

Fractional order tension control for stable and fast tethered satellite retrieval

The retrieval of a tethered satellite system is intrinsically unstable. This paper develops a new control strategy to retrieve the tethered satellite system stably and quickly using the fractional order control theory. The governing equation of the tethered satellite system and classic linear feedback tension control law were first reviewed and examined as a benchmark. Then, a new fractional order tension control law has been to avoid the tethered satellite winds around the main satellite near the end of retrieval by existing integer order tension control laws. The newly proposed control law has been discretized and implemented by the Laplace transform and Tustin operator. Unlike the existing integer order control laws, which are based on the feedback of current state and memoryless, the fractional order control law has the memory of previous states and thus controls the tether retrieval more smoothly while maintaining the retrieving speed. The effectiveness and advantage of the new fractional order tension control law is demonstrated numerically by comparing with its integer order counterpart. The results show that the new control law not only retrieves the subsatellite without winding around the main satellite, but also provides a better control performance with smaller in-plane libration angles.     

Giant polygons and mounds in the lowlands of Mars: signatures of an ancient ocean?

This paper presents the hypothesis that the well-known giant polygons and bright mounds of the martian lowlands may be related to a common process-a process of fluid expulsion that results from burial of fine-grained sediments beneath a body of water. Specifically, we hypothesize that giant polygons and mounds in Chryse and Acidalia Planitiae are analogous to kilometer-scale polygons and mud volcanoes in terrestrial, marine basins and that the co-occurrence of masses of these features in Chryse and Acidalia may be the signature of sedimentary processes in an ancient martian ocean. We base this hypothesis on recent data from both Earth and Mars. On Earth, 3-D seismic data illustrate kilometer-scale polygons that may be analogous to the giant polygons on Mars. The terrestrial polygons form in fine-grained sediments that have been deposited and buried in passive-margin, marine settings. These polygons are thought to result from compaction/dewatering, and they are commonly associated with fluid expulsion features, such as mud volcanoes. On Mars, in Chryse and Acidalia Planitiae, orbital data demonstrate that giant polygons and mounds have overlapping spatial distributions. There, each set of features occurs within a geological setting that is seemingly analogous to that of the terrestrial, kilometer-scale polygons (broad basin of deposition, predicted fine-grained sediments, and lack of significant horizontal stress). Regionally, the martian polygons and mounds both show a correlation to elevation, as if their formation were related to past water levels. Although these observations are based on older data with incomplete coverage, a similar correlation to elevation has been established in one local area studied in detail with newer higher-resolution data. Further mapping with the latest data sets should more clearly elucidate the relationship(s) of the polygons and mounds to elevation over the entire Chryse-Acidalia region and thereby provide more insight into this hypothesis.     

Field emission characteristics of gold dust grains

The space plasma environment usually contains charged dust grains. The grain charge is an important parameter determining its migration through the space, coagulation, formation of dust clouds and so on. The knowledge of its charge is thus one of the basic information we want to know. There are several emission processes leading to both positive and negative charges, among others photoemission, all kinds of secondary emissions, field emissions, etc. The present study is focused on a laboratory simulation of emissions caused by impacts by energetic ions. Our experiment is based on the Paul trap which gives us an opportunity to catch a single dust grain for several days inside the vacuum vessel and exposed it by electron/ion beams. This experimental approach allows us to separate an individual charging process. We have chosen spherically shaped gold grains and discussed the processes leading to the limitation of the grain charge. We suggested that the implantation of charging ions leads to deformations of the grain surface. The deformations enhance the local electric field strength that becomes sufficient for the field ionization.     

Classification of solar wind structures and intense geomagnetic storm alarms with self-organizing maps

Intense geomagnetic storms (D_st < −100 nT) usually occur when a large interplanetary duskward-electric field (with Ey > 5 mV m⁻¹) lasts for more than 3 h. In this article, a self-organizing map (SOM) neural network is used to recognize different patterns in the temporal variation of hourly averaged Ey data and to predict intense storms. The input parameters of SOM are the hourly averaged Ey data over 3 h. The output layer of the SOM has a total of 400 neurons. The hourly Ey data are calculated from solar wind data, which are provided by NSSDC OMNIWeb and ACE spacecraft and contain information on 143 intense storms and a fair number of moderate storms, weak storms and quiet periods between September 3, 1966 and June 30, 2002. Our results show that SOM is able to classify solar wind structures and therefore to give timely intense storm alarms. In our SOM, 21 neurons out of 400 are identified to be closely associated with the intense storms and they successfully predict 134 intense storms out of the 143 ones selected. In particular, there are 14 neurons for which, if one or more of them are present, the occurrence probability of intense storms is about 90%. In addition, several of these 14 neurons can predict big magnetic storm (D_st  −180 nT). In summary, our method achieves high accuracy in predicting intense geomagnetic storms and could be applied in space environment prediction.     

Properties of electrophoretic fractions of human embryonic kidney cells separated on Space Shuttle flight STS-8.

Suspensions of cultured primary human embryonic kidney cells were subjected to continuous flow electrophoresis on Space Shuttle flight STS-8. The objectives of the experiments were to obtain electrophoretically separated fractions of the original cell populations and to test these fractions for the amount and kind of urokinase (a kidney plasminogen activator that is used medically for digesting blood clots), the morphologies of cells in the individual fractions, and their cellular electrophoretic mobilities after separation and subsequent proliferation. Individual fractions were successfully cultured after return from orbit, and they were found to differ substantially from one another and from the starting sample with respect to all of these properties.     

Optimal Design Strategy of Switching Converters Employing Current in jected Control

This paper analyzes a buck/boost regulator employing current-injected control (CIC). It reveals the complex interactions between the dc loop and the current-injected loop and underlines the fundamental principle that governs the loop gain determination. Three commonly used compensation techniques are compared. The integral and lead/lag compensation are shown to be most desirable for performance optimization and stability.     

Comet Halley: Nucleus and jets (results of the VEGA mission)

The VEGA-1 and VEGA-2 spacecraft made their closest approach to Comet Halley on 6 and 9 March, respectively. In this paper those results of the onboard imaging experiment which were obtained around closest approach are discussed. The nucleus of the comet was clearly identifiable as an irregularly shaped object, with overall dimensions of (16±1)×(8±1)×(8±1) km. The nucleus rotates in the prograde sense about an axis nearly perpendicular to the orbital plane with a period of 53±2 hours. Its albedo is only $\text{0.04±}\text{0.02}\text{0.01}$ Many of the jet features observed during the second fly-by have been spatially reconstructed. Their sources form a quasi-linear structure on the surface. The dust above the surface is shown to be generally optically thin with the exception of certain specific dust jets. Brightness features on the surface are clearly seen. Correlating our data with other measurements, we conclude that the dirty snow-ball model will probably need to be revised.     

Modeling international cooperation in human space exploration for the twenty-first century.

The policy process of international cooperation in space exploration. including optimistic and pessimistic scenarios for the twenty-first century, is modeled and examined in this study. In the optimistic scenario, international cooperation involves a balanced and interdependent distribution of capabilities between states, their respective national space agencies and communities of space scientists and space engineers. Cooperation is characterized by interstate participation in critical path components and joint research and development. In the pessimistic scenario, international cooperation is structured and dominated politically and economically by powerful states vis-a-vis weaker states. Cooperation is limited to coordination of separate nationally approved projects and augmentation of capabilities in noncritical path components. On the basis of these two scenarios, policy predictions and implications relevant to exploration missions in the twenty-first century, such as a human-tended lunar base and human missions to Mars, are presented and discussed.