Molecular analysis of mutagenesis by high LET radiation.

Mutation induction by high linear energy transfer [LET] alpha particles and gamma-rays was scored in the human hamster hybrid [AL] cells. Southern blotting technique was used to analyse the molecular changes in the DNA from both the HGPRT- and S1- mutants. Dose dependent mutagenesis in the AL cells irradiated with the charged particles was higher by almost 20 fold at the S1 than the corresponding HGPRT locus. Southern analysis of the mutants induced by the high LET particles showed mostly multilocus deletion at both the HGPRT and S1 genes.     

Changes in gravitational force induce alterations in gene expression that can be monitored in the live, developing zebrafish heart.

Little is known about the effect of microgravity on gene expression, particularly in vivo during embryonic development. Using transgenic zebrafish that express the gfp gene under the influence of a beta-actin promoter, we examined the affect of simulated-microgravity on GFP expression in the heart. Zebrafish embryos, at the 18-20 somite-stage, were exposed to simulated-microgravity for 24 hours. The intensity of GFP fluorescence associated with the heart was then determined using fluorescence microscopy. Our measurements indicated that simulated-microgravity induced a 23.9% increase in GFP-associated fluorescence in the heart. In contrast, the caudal notochord showed a 17.5% increase and the embryo as a whole showed only an 8.5% increase in GFP-associated fluorescence. This suggests that there are specific effects on the heart causing the more dramatic increase. These studies indicate that microgravity can influence gene expression and demonstrate the usefulness of this in vivo model of 'reporter-gene' expression for studying the effects of microgravity.     

Top-level modeling of an ALS system utilizing object-oriented techniques.

The possible configuration of an Advanced Life Support (ALS) System capable of supporting human life for long-term space missions continues to evolve as researchers investigate potential technologies and configurations. To facilitate the decision process the development of acceptable, flexible, and dynamic mathematical computer modeling tools capable of system level analysis is desirable. Object-oriented techniques have been adopted to develop a dynamic top-level model of an ALS system.This approach has several advantages; among these, object-oriented abstractions of systems are inherently modular in architecture. Thus, models can initially be somewhat simplistic, while allowing for adjustments and improvements. In addition, by coding the model in Java, the model can be implemented via the World Wide Web, greatly encouraging the utilization of the model. Systems analysis is further enabled with the utilization of a readily available backend database containing information supporting the model. The subsystem models of the ALS system model include Crew, Biomass Production, Waste Processing and Resource Recovery, Food Processing and Nutrition, and the Interconnecting Space. Each subsystem model and an overall model have been developed. Presented here is the procedure utilized to develop the modeling tool, the vision of the modeling tool, and the current focus for each of the subsystem models.     

Escaping near-relativistic electron beams from the solar corona

Processes in the solar corona are prodigious accelerators of energetic ions, and electrons. The angular distribution, composition, and spectra of energetic particles observed near Earth gives information on the acceleration mechanisms. A class of energetic particle observations particularly useful in understanding the solar acceleration is the near-relativistic impulsive beam-like electron events. During five years of operation the Advanced Composition Explorer (ACE) has measured well over 400 electron events. Approximately 25% of these electron events are impulsive beam-like events that are released onto interplanetary field lines predominantly from western solar longitudes. We extend our initial 3 year study during the rise to solar maximum (Haggerty and Roelof, 2002; Simnett et al., 2002) to a five year statistical analysis of these beam-like energetic electron events in relationship to optical flares, microwave emission, soft X-ray emission, metric and decametric type-III radio bursts, and coronal mass ejections.     

Parathyroid hormone-related protein is a gravisensor in lung and bone cell biology.

Parathyroid Hormone-related Protein (PTHrP) has been shown to be essential for the development and homeostatic regulation of lung and bone. Since both lung and bone structure and function are affected by microgravity, we hypothesized that 0 x g down-regulates PTHrP signaling. To test this hypothesis, we suspended lung and bone cells in the simulated microgravity environment of a Rotating Wall Vessel Bioreactor, which simulates microgravity, for up to 72 hours. During the first 8 hours of exposure to simulated 0 x g, PTHrP expression fell precipitously, decreasing by 80-90%; during the subsequent 64 hours, PTHrP expression remained at this newly established level of expression. PTHrP production decreased from 12 pg/ml/hour to 1 pg/ml/hour in culture medium from microgravity-exposed cells. The cells were then recultured at unit gravity for 24 hours, and PTHrP expression and production returned to normal levels. Based on these findings, we have obtained bones from rats flown in space for 2 weeks (Mission STS-58, SL-2). Analysis of PTHrP expression by femurs and tibias from these animals (n=5) revealed that PTHrP expression was 60% lower than in bones from control ground-based rats. Interestingly, there were no differences in PTHrP expression by parietal bone from space-exposed versus ground-based animals, indicating that the effect of weightlessness on PTHrP expression is due to the unweighting of weight-bearing bones. This finding is consistent with other studies of microgravity-induced osteoporosis. The loss of the PTHrP signaling mechanism may be corrected using chemical agents that up-regulate this pathway. In conclusion, PTHrP represents a stretch-sensitive paracrine signaling mechanism that may sense gravity.     

Microgravity particle research on the space station: the Gas-Grain Simulation Facility.

In the gravitational field on Earth, the large settling rate of micron-sized particles and the effects of gravity-induced convection prohibit many interesting studies of phenomena such as coagulation, collisions, and mutual interactions of droplets, dust grains and other particles. Examples of exobiology experiments involving these phenomena are the simulation of organic aerosol formation in Titan's atmosphere, studies of the role of comets in prebiotic chemical evolution, and simulations of carbon grain interactions in various astrophysical environments. The Gas-Grain Simulation Facility (GGSF) is a proposed Earth-orbital laboratory that will allow present ground-based experimental programs which study processes involving small particles and weak interactions to be extended to a new domain. Physics issues that scientists wishing to propose GGSF experiments must consider are reviewed in this paper. Specifically, coagulation, motion in gases and vacua, and wall deposition of particles in a microgravity environment are discussed.     

Spending without results: lessons from the space station program

The US spent all of the funds originally estimated for the initial development of its orbital space station without producing any significant amount of flight hardware. This article shows how a project with large design costs and significant “non-prime” outlays can quickly deplete program funds. The authors recount the way in which budgetary politics, congressional micro-management, and technological risk conspired to produce this result.     

Optimum Steady State Position, Velocity, and Acceleration Estimation Using Noisy Sampled Position Data

A one-dimensional tracking filter based on the Kalman filtering techniques for tracking of a dynamic target such as an aircraft is discussed. The target is assumed to be moving with constant acceleration and is acted upon by a plant noise which perturbs its constant acceleration motion. The plant noise accounts for maneuvers and/or other random factors. Analytical results for estimating optimum steady state position, velocity, and acceleration of the target are obtained.