Buckling and post-buckling behavior of shallow supported cylindrical panels

The problem of the post-buckling behavior of the supported cylindrical panel under uniform axial compression is solved. The cylindrical supported panel is considered as a beam on the Winkler elastic foundation, the stiffness coefficient of which is calculated at the known value of buckling load. The criteria for post-buckling estimation are introduced, namely, vanishing of the determinant of the resolving system of equations and going to infinity of the deflection and strain energy in the implementation of post buckling. A good agreement of the post-buckling load obtained in this work with the experimental results is shown.     

A role of cytoskeletal structure of cortical cells in the gravity-regulated formation of a peg in cucumber seedlings.

Seedlings of cucurbitaceous plants develop a protuberant tissue, or peg, on the lower side of the transition region between root and hypocotyl when germinated in a horizontal position. Peg develops due to a change in growth polarity of the cortical cells. We have examined the role of the cytoskeletal structure in peg formation of cucumber seedlings. We observed that in both peg and normal cortical cells of 36 h-old seedlings the microtubules (MTs) were arranged perpendicular to the longitudinal axis of the elongating cells. Application of colchicine perturbed the MTs structure and inhibited the formation of pegs. In 20 h-old seedlings, MTs in cortical cells destined to be a peg tissue had no preferential organization, whereas MTs in normal cortical cells were transversely oriented. After 24 h, the MTs in future peg cells were arranged similar to those of 36 h-old seedlings, although the initiation of peg tissue was not yet visible. These results suggest that reorganization of MTs is required for peg formation and causes the change in growth polarity of the cortical cells.     

The reactions of nitrogen heterocycles with acrolein: scope and prebiotic significance

It has been suggested that life began with a self-replicating RNA molecule. However, after much research into the prebiotic synthesis of RNA, the difficulties encountered have lead some to hypothesize that RNA was preceded by a simpler molecule, one more easily synthesized prebiotically. Many of the proposed alternative molecules are based on acrolein, since it reacts readily with nucleophiles, such as the nucleobases, via Michael addition and is readily synthesized from formaldehyde and acetaldehyde. Reports regarding the reactions of nucleobases with concentrated acrolein solutions suggest that this is a plausible reaction mechanism, though there are also reports that the "incorrect" isomers are obtained. The scope and kinetics of the reaction of acrolein with various nitrogen heterocycles are reported here. Reactions of pyrimidines often give N(1) adducts as the major products. Reactions of purines often give N(9) adducts in good yield. The reactions are rapid under neutral to slightly alkaline conditions, and proceed at low temperatures and dilutions. The implications of these findings for the origin of life are discussed.     

Modeling and simulation of spacecraft power systems

Modeling of a complete spacecraft power processing system is presented, using the Boeing EASYS software. Component models are developed, and several system models including a solar array switching system, a partially shunted solar system, and cosmic background explorer (COBE) system are simulated. The modes of operation of the power system, such as shunt mode, battery-charge mode, and battery-discharge mode, are simulated for a complete orbit cycle     

Performance evaluation of a cascaded logic for track formation inclutter

The authors present a Markov-chain-based performance evaluation technique for two-stage sliding-window cascaded logic (2/2×m /n) for track formation in a cluttered environment. The main features of this technique are that it avoids the need for extensive simulations and it is more realistic than previous methods, accounting for the association gate size variation. The gates are obtained from a Kalman filter and fully account for the transient observed for the cascaded logic following the two-point initiation from its first stage. Numerical examples of performance evaluation are given along with a logic design example     

Probability Density of the Maximum Likelihood Elevation Estimate of Radar Targets

The probability density of the maximum likelihood estimate of elevation angle of a radar target in the presence of multipath is calculated. For detectable signals that have low signal-to-noise ratios, the density is a mixture of a Gaussian density and a delta function at the horizon.     

Human locomotion and workload for simulated lunar and Martian environments

Human locomotion in simulated lunar and Martian environments is investigated. A unique human-rated underwater treadmill and an adjustable ballasting harness simulate partial gravity in order to better understand how gravity determines the biomechanics and energetics of human locomotion. This study has two research aspects, biomechanics and energetics. The fundamental biomechanics measurements are continuously recorded vertical forces as exerted by subjects of the treadmill which is instrumented with a force platform. Experimental results indicate that peak vertical force and stride frequency decrease as the gravity level is reduced. Foot contact time is independent of gravity level. Oxygen uptake measurements, VO2, constitute the energetics, or workload, data for this study. As theory predicts, locomotion energy requirements for lunar (1/6-g) and Martian (3/8-g) gravity levels are significantly less than at 1-g. The observed variation in workload with gravity level is nonmonotonic, however, in over half the subject population. The hypothesis is offered that energy expenditure increases for lunar, as compared with Martian, locomotion due to the subject "wasting energy" for stability and posture control in simulated lunar gravity. Biomechanics data could influence advanced spacesuit design and planetary habitat design, while workload data will help define oxygen requirements for planetary life support systems.     

Waves on the subsolar ionopause of venus

The subsolar ionopause of Venus is expected to be stable to both the Kelvin-Helmholtz and flute instabilities. However, magnetic profiles obtained in the subsolar region indicate that the surface of the ionopause contains large amplitude corrugations, perhaps incipient flux ropes. A possible mechanism for destabilizing the boundary is suggested by the observation that the ion density does not drop abruptly at the ionopause but continues to decrease smoothly into the magnetosheath.     

Microwave imaging observation of an electron stream in a solar flare

We report a Nobeyama Radioheliograph (NoRH) microwave observation of a propagating feature of non thermal emission in a solar flare. The flare had a very extended source well resolved by NoRH. In the rising phase of the microwave burst, a non-thermal gyrosynchrotron source was observed by the high-rate (10 images per second) observations to propagate from one end of the loop to the other with a speed of 9 × 10⁴ km s⁻¹. We interpret this non-thermal propagating source is emitted from streaming electrons.     

Dual spacecraft observations of energetic particles in the vicinity of the magnetopause,bow shock,and the interplanetary medium

This article presents some of the new and important particle features that have been detected in the energy range 1 keV to 290 keV by the ISEE-1 and -2 spacecraft near the magnetopause, bow shock, and the interplanetary space. Only examples of data from the first few orbits, when the spacecraft were on the front side, are shown.Paper presented at 13th ESLAB Symposium, Innsbruck, Austria (June 5, 1978).