Charged particle tracks in polymers - Number 2 - Registration of heavy ions during the flight of Gemini VI

Registration of heavy ions during flight of Gemini V

The evolution of oscillatory behavior in age-structured species

A major challenge in ecology is to explain why so many species show oscillatory population dynamics and why the oscillations commonly occur with particular periods. The background environment, through noise or seasonality, is one possible driver of these oscillations, as are the components of the trophic web with which the species interacts. However, the oscillation may also be intrinsic, generated by density-dependent effects on the life history. Models of structured single-species systems indicate that a much broader range of oscillatory behavior than that seen in nature is theoretically possible. We test the hypothesis that it is selection that acts to constrain the range of periods. We analyze a nonlinear single-species matrix model with density dependence affecting reproduction and with trade-offs between reproduction and survival. We show that the evolutionarily stable state is oscillatory and has a period roughly twice the time to maturation, in line with observed patterns of periodicity. The robustness of this result to variations in trade-off function and density dependence is tested

Conceptual analyses of extensible booms to support a solar sail

Extensible booms which could function as the diagonal spars and central mast of an 800 meter square, non-rotating Solar Sailing Vehicle were conceptually designed and analyzed. The boom design concept that was investigated is an extensible lattice boom which is stowed and deployed by elastically coiling and uncoiling its continuous longerons. The seven different free-span lengths in each spar which would minimize the total weights of the spars and mast were determined. Boom weights were calculated by using a semi-empirical formulation which related the overall weight of a boom to the weight of its longerons

The relationship between apamin binding and channel block in KCa2 potassium channels.

Small conductance calcium-activated potassium channels (KCa2.1,2.2,2.3) are widely distributed throughout the body and are involved in diverse physiological processes including the regulation of neuronal firing and smooth muscle contraction. They are also potential targets in the treatment of cardiac arrhythmia. The KCa2.2 and 2.3 members of the family are blocked by the peptide toxin apamin at low concentrations, however, the mechanism of block by apamin is unclear. In electrophysiological experiments apamin has been reported to block Kca2.2 and 2.3 with IC50 ~100 pM and ~1nM respectively. In contrast, in ligand binding experiments using [125I]-mono-iodoapamin it has been found that apamin does not discriminate between Kca2.2 and 2.3 and that it binds with significantly higher affinity ( ~5pM). This discrepancy has led to the suggestion that, rather than acting as a classical pore blocker, apamin exerts its action by an allosteric mechanism. It is notable that the ligand binding studies reported so far have been conducted with isolated cell membranes in non-physiological solution with low ionic strength. We have investigated this discrepancy between results from ligand binding and electrophysiological studies by comparing binding of [125I]-mono-iodoapamin and inhibition of KCa2 current in intact HEK 293 cells using identical physiological solutions. In these conditions we found that apamin bound to KCa2.1 and KCa 2.3 with KL 60 and 606 pM, close to values of IC50 from electrophysiological experiments. We also compared the ability of some known SK channel blockers, UCL 1848, UCL 1684, gallamine and dequalinium, to displace labelled apamin and inhibit KCa2 current. With these compounds we found a good correlation between K¬i and IC50. These findings suggest that the discrepancy between binding and block might arise from differences in the experimental protocols used. To examine this we examined apamin block of KCa2 current in low ionic strength solutions in which NaCl was iso-osmotically replaced by sucrose. In these conditions 100 pM apamin caused 92 ± 0.1 % block as against 51 ± 5 % block in physiological ionic strength. We conclude that binding data obtained from membrane preparations must be interpreted with care when making comparisons with data from functional experiments and that this has implications for current views on the mechanism of action of apamin as an SK channel blocke

Remote sensing analysis of Lake Livingston aquatic plants

Results obtained during 1975 to monitor the growth of aquatic plants in the Lake Livingston area, using remote sensing photographic imagery, were described. Sequential total coverage was provided of the Jungle and White Rock Creek, plus coverage of smaller areas of localized infestation downlake, including Brushy Creek, KOA Kampground Marina, Penwaugh Slough, Memorial Point Marina, the Beacon Bay marinas and Pine Island. The imagery was generally good, photographic exposure being increased as the season progressed in order to obtain better pictures of the submerged vegetation. Some very significant differences in growth patterns, species interaction, and species dominance were observed when compared to 1974. Observation of the following plants was discussed: water hyacinth, hydrilla, coontail, potamageton. In general, the level of infestation was lower in 1975 than in 1974, due to the combined effect of more systematic application of herbicides and harsher intervening winter weather conditions

Radiation experiments on Cosmos 2044: K-7-41, parts A, B, C, D, E

The Cosmos 2044 biosatellite mission offered the opportunity for radiation measurements under conditions which are seldom available (an inclination of 82.3 deg and attitude of 294 x 216 km). Measurements were made on the outside of the spacecraft under near-zero shielding conditions. Also, this mission was the first in which active temperature recorders (the ATR-4) were flown to record the temperature profiles of detector stacks. Measurements made on this mission provide a comparison and test for modeling of depth doses and LET spectra for orbital parameters previously unavailable. Tissue absorbed doses from 3480 rad (252 rad/d) down to 0.115 rad (8.33 mrad/d) were measured at different depths (0.0146 and 3.20 g/sq cm, respectively) with averaged TLD readings. The LET spectra yielded maximum and minimum values of integral flux of 27.3 x 10(exp -4) and 3.05 x 10(exp -4)/sq cm/s/sr, of dose rate of 7.01 and 1.20 mrad/d, and of dose equivalent rate of 53.8 and 11.6 mrem/d, for LET(sub infinity)-H2O is greater than or equal to 4 keV/micron. Neutron measurements yielded 0.018 mrem/d in the thermal region, 0.25 mrem/d in the resonance region and 3.3 mrem/d in the high energy region. The TLD depth dose and LET spectra were compared with calculations from the modeling codes. The agreement is good but some further refinements are in order. In comparing measurements on Cosmos 2044 with those from previous Cosmos missions (orbital inclinations of 62.8 deg) there is a greater spread (maximum to minimum) in depth doses and an increased contribution from GCRs, and higher LET particles, in the heavy particle fluxes

Nanoscale-targeted patch-clamp recordings of functional presynaptic ion channels

Important modulatory roles have been attributed to presynaptic NMDA receptors (NMDARs) located on cerebellar interneuron terminals. Evidence supporting a presynaptic location includes an increase in the frequency of mini events following the application of NMDA and gold particle-labelled NMDA receptor antibody localisation. However, more recent work, using calcium indicators, casts doubt on the idea of presynaptic NMDARs because basket cell varicosities did not show the expected calcium rise following either the local iontophoresis of L-aspartate or the two-photon uncaging of glutamate. (In theory such calcium imaging is sensitive enough to detect the calcium rise from even a single activated receptor.) It has therefore been suggested that the effects of NMDA are mediated via the activation of somatodendritic channels, which subsequently cause a subthreshold depolarization of the axon. Here we report results from a vibrodissociated preparation of cerebellar Purkinje cells, in which the interneuron cell bodies are no longer connected but many of their terminal varicosities remain attached and functional. This preparation can retain both inhibitory and excitatory inputs. We find that the application of NMDA increases the frequency of both types of synaptic event. The characteristics of these events suggest they can originate from interneuron, parallel fiber and even climbing fiber terminals. Interestingly, retrograde signalling seems to activate only the inhibitory terminals. Finally, antibody staining of these cells shows NMDAR-like immunoreactivity co-localised with synaptic markers. Since the Purkinje cells show no evidence of postsynaptic NMDAR-mediated currents, we conclude that functional NMDA receptors are located on presynaptic terminals