Physical determinants of radiation sensitivity in bacterial spores.

Several factors modifying radiation sensitivity in dry bacterial spores are described and discussed. Vacuum inducing the loss of critical structural water, very low dose rates of radiation from which the cell may recover, radiations of high linear energy transfer, and the action of temperature over long periods of time on previously irradiated cells are recognized from extensive laboratory work as important in determining survival of spores exposed to low radiation doses at low temperatures for long periods of time. Some extensions of laboratory work are proposed.     

Computation of Optimal Earth-Mars and Earth-Venus Trajectories

Accurate solutions of minimal time Earth-Mars and Earth-Venus heliocentric trajectories are calculated with a shooting-Newton method. The flight times are less and the steering histories are diferent than those presented in [1], thus contradicting the optimality claims in [1].     

Cross Sections and Radar Equation for Nonlinear Scatterers

The nonlinear system concepts of nonlinear transfer functions are extended to nonlinear cross sections which may be used to quantitatively describe the characteristics of a nonlinear scatter. The concept of nonlinear cross sections is used to generalize the radar equation for nonlinear scattering objects.     

Discovery of abundant cellulose microfibers encased in 250 Ma Permian halite: a macromolecular target in the search for life on other planets

In this study, we utilized transmission electron microscopy to examine the contents of fluid inclusions in halite (NaCl) and solid halite crystals collected 650 m below the surface from the Late Permian Salado Formation in southeastern New Mexico (USA). The halite has been isolated from contaminating groundwater since deposition approximately 250 Ma ago. We show that abundant cellulose microfibers are present in the halite and appear remarkably intact. The cellulose is in the form of 5 nm microfibers as well as composite ropes and mats, and was identified by resistance to 0.5 N NaOH treatment and susceptibility to cellulase enzyme treatment. These cellulose microfibers represent the oldest native biological macromolecules to have been directly isolated, examined biochemically, and visualized (without growth or replication) to date. This discovery points to cellulose as an ideal macromolecular target in the search for life on other planets in our Solar System.     

Sealed nickel cadmium and nickel metal hydride cell advances

Nickel cadmium cells have almost doubled in capacity since 1980 after being stagnated in performance for twenty years. Nickel metal hydride cells, introduced in 1992, have shown a 170 percent increase in energy density to be competitive on a volume basis with lithium ion. Other characteristics, such as charge retention, charge rate, high temperature operation, and rate capability have also advanced with improvements in materials and constructions. These two cell types account for roughly one half of the value of the small secondary battery market     

Advances and trends in primary and small secondary batteries

Improvements in performance and reliability continue to be made in the traditional primary and secondary systems such as C-Zn, alkaline MnO ₂, Zn-air, Li-I, and sealed Ni-Cd and lead acid. In addition, two new secondary systems, Ni-metal hydride and lithium ion, have recently been introduced. They are growing rapidly in response to environmental concerns and the need for more energy density by devices. Two new rechargeable systems, Zn-air and lithium polymer electrolyte are nearing commercial production. One manufacturer has just introduced a rechargeable version of the alkaline MnO₂ system for consumer use. Lithium primary systems, such as Li-MnO₂, Li-FeS₂ and CF_x are gaining substantial market share, amounting to about $500 million in 1992. Li-silver vanadium primary cells have been developed to supply the higher currents needed by implantable medical devices such as defibrillators     

New considerations of the oxygen effects in radiation biology.

The original demonstration in the bacterial spore of the multiple actions of oxygen in modifying the responses of cells to ionizing radiation has now been verified in mammalian systems, pointing up the need for separate inquiry into each of the several components if the responses of mammalian cells are to be understood. We have provided physico-chemical explanations for only two of the four (at least) oxygen elements recognized in the spore: the reaction of diatomic oxygen with organic free radicals in dry spores; and an action of the hydroxy radical (OH) in spores at low [O2]. This paper will discuss newly recognized features of the oxygen responses that could reveal the nature of the other components. It will examine modulation of response by oxides of nitrogen, the similarities and differences among them and explanations for them that suggest further experiment, the importance of concentration of additive in determining both quantity and quality of response, and a general model that explains sensitizer action in terms of inhomogeneous chemistry.