246 research outputs found
Studies of auroral X-ray imaging from high altitude spacecraft
Results of a study of techniques for imaging the aurora from a high altitude satellite at X-ray wavelengths are summarized. The X-ray observations allow the straightforward derivation of the primary auroral X-ray spectrum and can be made at all local times, day and night. Five candidate imaging systems are identified: X-ray telescope, multiple pinhole camera, coded aperture, rastered collimator, and imaging collimator. Examples of each are specified, subject to common weight and size limits which allow them to be intercompared. The imaging ability of each system is tested using a wide variety of sample spectra which are based on previous satellite observations. The study shows that the pinhole camera and coded aperture are both good auroral imaging systems. The two collimated detectors are significantly less sensitive. The X-ray telescope provides better image quality than the other systems in almost all cases, but a limitation to energies below about 4 keV prevents this system from providing the spectra data essential to deriving electron spectra, energy input to the atmosphere, and atmospheric densities and conductivities. The orbit selection requires a tradeoff between spatial resolution and duty cycle
Comparison of Grain Refinement in Selected Materials Subjected to Hydrostatic Extrusion
The subject of this study was to examine and compare the impact of intense hydrostatic extrusion on grain refinement in three different alloys: duplex stainless steel, commercially used aluminum alloy (6060) and Ag-Cu12 alloy. As a result of the process grain sizes from 370 nm to 90 nm were obtained in aluminum and duplex steel. To analyze the of hydrostatic on mechanical properties tensile tests were also carried out. The highest grain refinement (70 nm) and yield strength increase (over 300%) was observed in duplex steel af-ter hydrostatic extrusion.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3560
Brief Note: Limnetic Larval Fish in the Nearshore Zone of the South Shore of the Central Basin of Lake Erie
Author Institution: Center for Lake Erie Area Research, The Ohio State University ; Department of Biology, John Carroll Universit
The effects of temperature on the kinetics of aluminium evaporation from the Ti-6Al-4V alloy
In the paper, results of the study on temperature effects on the rate of aluminium evaporation from the Ti-6Al-4V alloy during smelting in a vacuum induction furnace are presented. During smelting at 1 973 – 2 023 K, 10 Pa and 100 Pa, up to 26 % reduction in the aluminium content in the alloy compared to the initial value is observed. The determined values of overall mass transport coefficient are 1,48∙10-5 m∙s sup>-1 – 1,95∙10 sup>-5m∙s sup>-1
Spatial and Temporal Variability of the Gamma Radiation from Earth's Atmosphere during a Solar Cycle
The Solar Maximum Mission satellite's Gamma Ray Spectrometer observed Earth's
atmosphere for most of the period 1980-1989. Its 28deg orbit ensured that a
range of geomagnetic latitudes (geomagnetic cutoff rigidities) was sampled. We
measured the variation with time and rigidity of albedo gamma-ray lines at 1.6
MeV, 2.3 MeV and 4.4 MeV which are diagnostic of Galactic cosmic radiation
penetrating the cutoff and of the secondary neutrons produced in the
atmosphere. We found that the gamma-ray line intensities varied inversely with
solar activity and cutoff rigidity, as expected. The line ratio (1.6 MeV + 2.3
MeV)/4.4 MeV was remarkably constant (close to 0.39) at all times and
rigidities; the former two lines are produced by 5-10 MeV secondary neutrons
causing excitation and de-excitation of 14N, while the latter is produced by
more energetic (>20 MeV) neutrons inducing spallation. We infer that the shape
of the secondary neutron energy spectrum is virtually constant everywhere and
at all times. We also measured the intensity of the 0.511 MeV electron-positron
annihilation line. This line too varies with solar cycle and cutoff rigidity,
but its fall-off from low to high rigidity is less marked than that of the
nuclear lines. This results from the energy dependences of the cross sections
for positron production and for the hadronic processes which which produce
secondary neutrons.Comment: 11 pages, 12 figs., J. Geophys. Res. in pres
First results of material charging in the space environment
A satellite experiment, designed to measure potential charging of typical thermal control materials at near geosynchronous altitude, was flown as part of the SCATHA program. Direct observations of charging of typical satellite materials in a natural charging event ( 5 keV) are presented. The results show some features which differ significantly from previous laboratory simulations of the environment
Mutational pathway determines whether drug gradients accelerate evolution of drug-resistant cells
Drug gradients are believed to play an important role in the evolution of
bacteria resistant to antibiotics and tumors resistant to anti-cancer drugs. We
use a statistical physics model to study the evolution of a population of
malignant cells exposed to drug gradients, where drug resistance emerges via a
mutational pathway involving multiple mutations. We show that a non-uniform
drug distribution has the potential to accelerate the emergence of resistance
when the mutational pathway involves a long sequence of mutants with increasing
resistance, but if the pathway is short or crosses a fitness valley, the
evolution of resistance may actually be slowed down by drug gradients. These
predictions can be verified experimentally, and may help to improve strategies
for combatting the emergence of resistance.Comment: 6 pages, 3 figures, final version before acceptance to Phys. Rev.
Letters. P.G and B.W contributed equally to this wor
Analysis of the Thermal and Magnetic Properties of Amorphous Fe 61Co10Zr2.5Hf2.5Me2W2B20 (Where Me = Mo, Nb, Ni Or Y) Ribbons
The paper presents the results of structural and magnetic properties and thermal stability for a group of functional materials based on Fe61Co10Zr2.5Hf2.5Me2W2B20 (where Me = Mo, Nb, Ni or Y). Samples were obtained in the form of ribbons using melt-spinning method. The X-ray diffraction patterns of investigated samples confirmed their amorphous structure. Based on the analysis of DSC curves characteristic temperatures: glass forming temperature (Tg), crystallization temperature (Tx) and temperature range of the supercooled liquid ΔTx were determined. Small addition of transition metals elements has strong influence on magnetic and thermal parameters of studied materials. The comprehensive studies revealed that in terms of magnetic properties the Ni-addition resulted in highest reduction in coercivity and anisotropy field
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