Influence of microgravity on mitogen binding and cytoskeleton in Jurkat cells.

The effects of microgravity on Jurkat cells--a T-lymphoid cell line--was studied on a sounding rocket flight. An automated pre-programmed instrument permitted the injection of fluorescent labelled concanavalin A (Con A), culture medium and/or fixative at given times. An in-flight 1 g centrifuge allowed the comparison of the data obtained in microgravity with a 1 g control having the same history related to launch and re-entry. After flight, the cells fixed either at the onset of microgravity or after a or 12 minute incubation time with fluorescent concanavalin A were labelled for vimentin and actin and analysed by fluorescence microscopy. Binding of Con A to Jurkat cells is not influenced by microgravity, whereas patching of the Con A receptors is significantly lower. A significant higher number of cells show changes in the structure of vimentin in microgravity. Most evident is the appearance of large bundles, significantly increased in the microgravity samples. No changes are found in the structure of actin and in the colocalisation of actin on the inner side of the cell membrane with the Con A receptors after binding of the mitogen.     

Rocket Exhaust Scattering Effects on Incident Microwave Propagation Characteristics

This paper considers the effect of the rocket exhaust turbulence and scattering within the surrounding medium upon the propagation characteristics of incident electromagnetic waves. The exhaust is represented by a cylindrical plasma beam, diffusing through the surrounding medium. The equations of propagation of EM waves are derived for both TE and TM modes. By using a quasi-linear perturbation technique the exhaust is further separated into an inner homogeneous cylindrical plasma beam, and an outer conical inhomogeneous turbulent region. The isotropic change in the temperature of the outer region and its effects on the fluctuations in the density of electrons, collision frequency, and plasma index of refraction are analyzed in detail. It is found that the exhaust turbulence and scattering effects produce linear fluctuations in the E and H fields computed from the exhaust inner region effect. The equations of this paper can be used in the prediction of the radar cross sections and the attenuation of microwaves by rocket exhaust plumes.     

Microminiature Loran-C Receiver/Indicator

A Loran-C Receiver is used as an example to show how an analog system could be converted to a digital one to take advantage of the expanding integrated circuit technology. The digital equivalents of the analog servo elements are described. Criteria for the design of a phase-tracking servomechanism is developed in detail. The Loran performance requirements are used to illustrate their application. The noise performance of a critically damped Type II servomechanism is derived in detail. Since the system will be employed in aircraft, tracking velocity becomes an important consideration. An analysis is made showing that an adaptive control is desirable.     

Reducing Undesirable Effects in the Human Centrifuge

The human centrifuge is used to train pilots and astronauts for flights where they are subject to large accelerations. This paper deals with the problems of simulating such linear accelerations with a rotating device and presents suitable means of reducing undesirable simulation error. The advantages of using three gimbals rather than the usual two are considered. Numerical results illustrate the problems of simulation and the improvement achieved by the use of a third gimbal.     

Signal transduction in T lymphocytes--a comparison of the data from space, the free fall machine and the random positioning machine.

In this paper we discuss the effect of microgravity on T cells and we present the data of studies with two new machines for 0 g simulations. Several experiments in space show that mitogenic T cell activation is lost at 0 g. Immunocytochemistry indicates that such effect is associated with changes of the cytoskeleton. Biochemical studies suggest that the lack of expression of the interleukin-2 receptor is one of the major causes of the loss of activity. In fact, interleukin-2 is the third signal required for full activation. In order to deepen our investigations we are now working with the free-fall machine, FFM, invented by D. Mesland, and with the random positioning machine, RPM, or three-dimensional clinostat, developed by T. Hoson. The FFM produces periods of free-fall lasting approximately 800 ms followed by bounces of 15-30 g lasting 45-60 ms. The RPM eliminates the effect of gravity by rotating biological specimen randomly around two orthogonal axes. While the FFM failed to reproduce the results obtained with T lymphocytes in space, the data from the RPM are in good agreement with those in real microgravity. In fact, the inhibition of the mitotic index in the RPM is 89% compared to static controls. The RPM (as the FFM) can carry markedly larger specimen than the fast rotating clinostat and thus allows to conduct comprehensive studies to select suitable biological objects for further investigations in space.     

Ultra-reliable real-time control systems-future trends

Today's aircraft use ultra-reliable real-time controls for demanding functions such as Fly-By-Wire (FBW) flight control. Future aircraft, spacecraft and other vehicles will require greater use of these types of controls for functions that currently are allowed to fail, fail to degraded operation, or require human intervention in response to failure. Fully automated and autonomous functions will require ultra-reliable control. But ultra-reliable systems are very expensive to design and require large amounts of on-board equipment. This paper will discuss how the use of low-cost sensors with digital outputs, digitally commanded fault-tolerant actuation devices and interconnecting networks of low-cost data buses offer the promise of more affordable ultra-reliable systems. Specific technologies and concepts to be discussed include low-cost automotive and industrial data buses, “smart” actuation devices with integral fault masking capabilities, management of redundant sensors, and the fault detection and diagnosis of the data network. The advantages of integrating the control and distribution of electrical power with the control system will be illustrated. The design, installation, and upgrade flexibility benefits provided by an all-digital and shared network approach will be presented. The economic benefits of systems that can operate following failure and without immediate repair will be reviewed. The inherent ability of these redundant systems to provide effective built-in test and self-diagnostics capabilities will be described. The challenges associated with developing ultra-reliable software for these systems and the difficulties associated with exhaustive verification testing will be presented as will additional development hurdles that must be overcome     

History of Time-Frequency Technology

Present-day collision avoidance systems (CAS) of the time-frequency variety employ modes of operation similar to those of airborne equipment which has been operating in military aircraft since 1959. A fleet operational evaluation of these systems began in 1961 in aircraft of U. S. Navy Helicopter Squadron HS-4, based on the aircraft carrier U.S.S. Yorktown. This equipment utilized a local clock in each aircraft, a separate time slot for each aircraft's interrogation signal, air-to-air coarse synchronization of all stations, and sufficient free-drift stability for time slot keeping. Operational use of one-way ranging with elimination of propagation delay offsets, higher clock stability for open-loop time keeping in the SNS-64 ... AN/APN-169 family of systems began in 1964 in U. S. Air Force C-130E turboprop aircraft. In 1965, use of the EROS I collision avoidance system began during flight testing of F-4 Phantom supersonic aircraft.     

Protein crystal growth--microgravity aspects.

Protein crystals, grown under reduced gravity conditions, are either superior or inferior in their structural perfection than their Earth-grown counterparts. A reduction of the crystals' quality due to low-gravity effects on the growth processes cannot be understood from existing models. In this paper we put forth a rationale which predicts either advantages or disadvantages of microgravity growth. This rationale is based on the changes in the effective solute and impurity supply rates in microgravity and their effects on the intrinsic growth rate fluctuations that arise from the coupling of bulk transport to nonlinear interfacial kinetics and cause severe inhomogeneities. Depending on the specific diffusivity and kinetic coefficient of a protein and the impurities in the solution, either transport enhancement through forced flow or transport suppression under reduced gravity can result in a reduction of the kinetic fluctuations and, thus, growth with higher structural perfection. Investigating this mechanism of microgravity effects, we first demonstrate a one-to-one correspondence between these fluctuations, that are due to the bunching of growth steps, and the formation of defects in the crystals. We have confirmed the forced flow aspects of this rationale in ground-based experiments with lysozyme utilizing flowing solutions with varying, well characterized impurity contents.