Identification of specific gravity sensitive signal transduction pathways in human A431 carcinoma cells.

Epidermal growth factor (EGF) activates a well characterized signal transduction cascade in human A431 epidermoid carcinoma cells. The influence of gravity on EGF-induced EGF-receptor clustering and early gene expression as well as on actin polymerization and actin organization have been investigated. Different signalling pathways induced by the agents TPA, forskolin and A23187 that activate gene expression were tested for sensitivity to gravity. EGF-induced c-fos and c-jun expression were decreased in microgravity. However, constitutive beta-2 microglobulin expression remained unaltered. Under simulated weightlessness conditions EGF- and TPA-induced c-fos expression was decreased, while forskolin- and A23187-induced c-fos expression was independent of the gravity conditions. These results suggest that gravity affects specific signalling pathways. Preliminary results indicate the EGF-induced EGF-receptor clustering remained unaltered irrespective of the gravity conditions. Furthermore, the relative filamentous actin content of steady state A431 cells was enhanced under microgravity conditions and actin filament organization was altered. Under simulated weightlessness actin filament organization in steady state cells as well as in EGF-treated cells was altered as compared to the 1 G reference experiment. Interestingly the microtubule and keratin organization in untreated cells showed no difference with the normal gravity samples. This indicates that gravity may affect specific components of the signal transduction circuitry.     

Gamma-ray spectroscopy: Status and prospects

Contemporary gamma-ray spectroscopy instruments and their results are reviewed. Sensitivities of 10^?4 to 10^?3 ph/cm²-sec have been achieved for steady sources and 10^?2 to 1 ph/cm²-sec for transient sources. This has led to the detection of gamma-ray lines from more than 40 objects representing 6 classes of astrophysical phenomena. The lines carry model-independent information and are of fundamental importance to theoretical modeling and our understanding of the objects. These results indicate that gamma-ray spectroscopy is relevant to a wide range of astrophysical problems and is becoming a major part of astronomy. The objectives and anticipated results of future instruments are discussed. Several instruments in development will have a factor of ～ 10 sensitivity improvement to certain phenomena over contemporary instruments. A factor of ～ 100 improvement in sensitivity will allow the full potential of gamma-ray spectroscopy to be realized. Instrument concepts which would achieve this with both present and advanced techniques are discussed.     

Validation of the stratospheric sounding unit

The Stratospheric Sounding Unit (SSU) is part of the TOVS (TIROS Operational Vertical Sounder) on NOAA operational meteorological satellites. SSU measurements can be validated by comparison with temperature measurements from colocated rocket sondes. Systematic differences are found which vary with rocket station and sonde and are a function of height. However, these measurements are not adequate to define the performance of individual SSUs to a precision which would allow the observations from different SSUs to be combined in the study of diurnal and semidiurnal tides and of long term trends in stratospheric temperature. Instead this is achieved by detailed radiometric and spectroscopic investigation of each individual SSU, both prior to launch and during its operational life. Using the techniques descirbed, it is demonstrated that measurements from different SSUs can be combined with a relative error of less than 0.2K in equivalent brightness temperature.     

Marangoni convection in a liquid layer under the simultaneous action of a transverse magnetic field and rotation

Asymptotic stability characteristics with respect to the onset of Marangoni convection in a liquid layer under the simultaneous action of a large transverse magnetic field and a large rate of rotation are investigated. In certain parameter ranges there is a decrease in critical Marangoni number for increasing magnetic field and rotation depending on the coupling between interfacial perturbations and rotation.     

High Power Needs for Commercial Satellites

This overview paper presents estimates of the photovoltaic power systems needed on commercial communications spacecraft in the year 2000. These are developed in the form of power requirements based on extrapolation of the historical growth in communications traffic and are about 5 to 15 kW. The paper also addresses the key technology drivers in these photovoltaic systems. The importance of reducing mass in the power system is described in terms of the tradeoff with communications systems mass to maximize communications revenue. It surveys solar array components and subsystems to meet these future requirements and attempts to identify the development candidates with a large payoff potential and a high probability of successful development.     

A review of long drop tubes as a supplement/alternative to space experiments

The 100 meter high drop tube at the Marshall Space Flight Center has proven to be a viable facility for studies of containerless solidification. Advantages are that experiments are inexpensive and large numbers of specimens can be processed rapidly. It would not be unusual to run ten specimens in a day. Another significant advantage is that the undercooling behavior can be followed with sufficient sensitivity to easily detect the onset of recalescence and subsequent events.Disadvantages are the restrictions on specimen sizes and types of alloys that can be run in a microgravity environment. Practical specimen sizes range between 50 mg and 500 mg depending on the type of furnace being used. Refractory alloys can be processed in a vacuum (about 10^?5 torr) and therefore at microgravity. Non-refractory alloys demand an atmosphere (about 200 torr) to obtain appreciable undercooling before impact at the bottom of the tube. Under these conditions significant g forces result.Because of the present limitations of the 100 meter drop tube, the most definitive work has been done on niobium based alloys. Large amounts of undercooling have been observed routinely and the effects of undercooling on microstructure have been characterized in detail. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy have been used to determine types of phases, amounts of phases, and compositions of phases. It is clear, as would be expected, that the results bear some resemblance to rapid solidification processing by quenching. However, there are dissimilarities due to the uniqueness of solidification by deep undercooling without quenching in long drop tubes and accompanying recalescence effects.     

IR-spectroscopy of ionosphere from stratospheric balloons

The radiation spectra of the ionosphere in the 4–5 μm region have been determined from stratospheric balloons by means of the specially elaborated method of the registration of angular and spectral distribution of the radiation. The radiation bands of 4.4 μm and 4.8 μm which have 0.1–0.2 erg cm^?2 sr^?1s^?1. brightness obtained in two flights, are identified with the vibration-rotation transitions of the ion NO⁺ (0 - 1) and the molecules N¹⁴N¹⁵ (0 - 1) and CO (0 - 1) and (3 - 2) from altitudes between 120 and 500 km.     

50–200 GV cosmic rays at various heliolatitudes

We consider regular motion of 50 – 200 GV particles in a large-scale interplanetary magnetic field model which contains a wavy neutral sheet responsible for the sector-structure. Numerical calculations based upon energy losses along various trajectories are carried out to obtain the predicted omni-directional density and anisotropy of cosmic rays at various solar latitudes. A marked difference is found between odd and even solar cycles. The post-1969 field configuration gives small radial and large latitudinal gradient: cosmic ray density increases toward the poles. The latitudinal gradient turns out smaller and of opposite sense for the pre-1969 epoch. Anisotropy changes dramatically as we move off the solar equator: corotation appears to be restricted to low latitudes.