Prominent Minimum Research Articles

Structure of the ionosphere and atmosphere of Saturn From Pioneer 11 Saturn radio occultation

During the flyby of Saturn by Pioneer 11 on September 1, 1979, radio occultation measurements of the ionosphere and upper neutral atmosphere were made near the terminator at latitudes 9.7° south and 11.6° south. The principal electron density peak of the ionosphere occurs at an altitude of about 1,800 km and has a magnitude of 11,400 cm−3, with a sharp lower peak of about 9,000 cm−3 at about 1,200 km. The scale height above the main peak corresponds to an exosphere temperature of about 1150 K for an H+ ionosphere. Ionization appears to extend to 30,000 km, with a broad peak of magnitude 7,000 cm−3 at an altitude of about 14,500 km, corresponding to the inner edge of the C ring. The low density of the lower portion of the ionosphere can probably be explained by ring shadowing and equatorial anomaly, and the relatively high densities about 30,000 km, if real, could be explained if densities of ∼105 exist at higher latitudes that are connected to the site of measurement by field lines and by plasmaspheric heating by the rings. In the neutral atmosphere, measurements were made to a pressure level of about 180 mbar, showing a temperature inversion region with a triple minimum. The temperature at the principal minimum at 60,344 km is 88±4 K at a pressure of 74 mbar, and there is a prominent minimum about 80 km above the principal one. Comparisons with the temperature structure derived from the infrared radiometer data (Ingersoll et al., this issue) suggest that the helium fraction in the Saturnian atmosphere is 10±4%.

Effect of nitrite on microsomal cytochrome P-450.

1. Addition of nitrite to anaerobic rat liver microsomes leads to the appearance of a difference spectrum similar to the spectrum of the ferrous cytochrome P-450-NO complex. A Soret band is found at 444 nm in phenobarbital-stimulated microsomes but at 442 nm in 3-methylcholanthrene-stimulated microsomes. An alpha-band is located at 583 nm in both types of microsome. 2. The initial nitrite-induced difference spectrum is converted into a spectrum lacking a Soret band but with a prominent absorbance minimum at 417 nm. This is more rapid in microsomes from phenobarbital-treated animals where it is completed in 8 min than in microsomes from 3-methylcholanthrene-treated animals. A similar spectrum can be obtained by addition of nitrite to urea-treated microsomes in which cytochrome P-450 has been converted to cytochrome P-420. 3. Azo cleavage of neoprontosil in anaerobic microsomes is markedly inhibited by 1 mM nitrite. In contrast, oxidative drug metabolism is affected only by very high nitrite concentrations around 100 mM. It is concluded that in anaerobic microsomes, NO formed from nitrite complexes with ferrous cytochrome P-450 and thereby inhibits reductive drug metabolism.

Transformation twins and the elastic properties of U3Si at low temperatures

Abstract The elastic properties, adiabatic compressibility and Debye temperature of twinned and non-twinned U3Si were determined by means of an ultrasonic pulse technique between liquid helium temperature and the ambient. The twinned and non-twinned face-centred tetragonal U3Si specimens were prepared employing appropriate heat-treatment regimes. The presence of twins in the U3Si lattice yields a modulus defect of about 18·5%, the Young's modulus of the twinned U3Si having the lower absolute value. At about 85°K the twinned structure displays a prominent minimum in its elastic properties, suggesting a first-order phase transformation. In contrast, the non-twinned U3Si exhibits a maximum in this temperature range. Experimental results are discussed in terms of the effect of twins on the lattice stability of the tetragonal structure of U2Si.

Das Hoch-Tief-Umwandlungsverhalten mikrokristalliner Quarze

The optical and x-ray investigation of 51 microcrystalline quartz samples show that they are built up of fibrous chalcedony (agates) or finest crystalline, isometric grained quartz (flints, cherts, jasper or Chrysoprase). These samples were examined by standardized d.t.a. — methods in order to get their inversion characteristics. 1) A third of the samples conteins low-temperature cristobalite in addition to quartz (in two samples even as main component); the high-low inversion of this mineral lies between 80 and 245° C according to its defect character. In five samples of jasper low- tridymite is occurring as minor component. 2) In contrary to macrocrystalline quartz crystals microcrystalline quartzes generally show no sharp inversion point. The inversion takes place over an interval of nearly 50° C, to be seen in the d.t.a. curve as a broad, only slightly endothermic effect with hardly visible peak or several small minima. In the curves of 15 samples no inversion could be detected. This broad inversion peak is caused by different defect characters of the crystals or even of parts of the crystals which invert at different temperatures (Florke, 1955). 3) There is no dependance of t i on the size of crystallites at least for crystals with diameter greater than 0.05 μ. The temperature of the most prominent inversion minimum allows a division of the microcrystalline quartz crystals analogous the macrocrystalline classification into samples with t i below and above 570° C. The lowest (518±2° C) and the highest t i (578,7+0,3° C) were measured at different parts of the same sample of a Chrysoprase. 4) The intensity of the brown and red coloured parts of agate and jasper grows with increasing Fe2O3-content, but there is no connection between t i and chemical composition. 5) As in macrocrystalline quartzes of caverns and veins there are also some t i -differences between the marginal and the central parts of agates or jaspers. The explanation lies in the mechanism of formation: higher t i in the margin (e.g. in one globular jasper) points to a formation by silification, whereas higher t i in the center indicates a formation by the filling up of cavities and veins. 6) The variation in t i of microcrystalline quartzes and the comparison of these t i ś with those of associated low-temperature cristobalite shows a connection between temperatures of formation and inversion: samples with low t i (i.e. with a great number of defects) should be formed at low temperatures, that is by sedimentary or diagenetic processes, and samples with t i above 570° C (i.e. nearly without defects in the structure) should have crystallized out of hydrothermal solutions. The weak inversion peaks below 570° which in d.t.a. curves often appear besides a main peak at 570° C represent the small amount of diagenetically formed microcrystalline quartz with a large degree of defect character.

Molecular Structure of Nitrogen Dioxide and Nitric Acid by Electron Diffraction

New electron diffraction photographs have been taken of NO2 extending the region previously investigated to include larger angles of scattering. An interference ring was found at (1/λ) sin ½θ = 0.49 followed by another ring appearing at 0.94 as determined by visual measurements. The outer portion of the pattern consists of two rather broad rings and two well-defined minima. Theoretical intensities of scattering were computed for various nitrogen valence angles, assuming the positions of the two oxygens to be equivalent. The best fit, and probably the correct structure, gives the angle O–N–O = 130±2° with the N–O distance 1.21±.02A. Photographs were obtained from pure nitric acid vapor at 70°—85°C. The interference maxima were measured visually as far out as the eighth maximum at (1/λ) sin ½θ = 1.83; a prominent minimum was seen at 1.54. Theoretical intensities were computed for various likely models, disregarding the scattering by the hydrogen atom. Good agreement was obtained for a planar model having an NO2 group with the same structure found for nitrogen dioxide. The third oxygen atom O′ is located at a distance of 1.41±0.02A from the nitrogen atom and equidistant from the other oxygen atoms. A model having the nitrogen atom slightly out of the plane containing the oxygen atoms also gave good agreement with the experimental results. This model however is considered less probable in view of Raman spectra data which apparently require a planar structure for O′–NO2.

Secondary Electrons from Iron

Secondary electron emission from iron as a function of energy of primary electrons, 0 to 300 volts.---Curves showing ratio of secondary to primary electron current as a function of primary velocity were obtained with three forms of apparatus. Two have been previously described. The limiting curves obtained after red-heat treatment of samples of electrolytic Fe having very large crystals, and of chemically pure Fe obtained from Kahlbaum were similar to those obtained for a film of Fe deposited by evaporation. The curves all have sharp maxima at 1.2 and 7.0 volts with minima at 3.7 and 12.0 volts, and a less prominent maximum and minimum at 10.0 and 9.0 volts, respectively. Of several metals tried, Fe is the only one, in addition to Cu, for which such sharp maxima and minima have been obtained. Potentials corresponding to positions of the maxima are interpreted as critical potentials. A steady upward trend of the curve begins at 12.0 volts, which is interpreted as being due to ionized electrons. Slight changes in slope of the curve at higher potentials were observed but these varied with conditions, and hence are taken to have no real significance.Evidence of structure of evaporated Fe film.---While previous results for Cu indicate that a layer deposited by evaporation is amorphous, the present results indicate that a similarly formed layer of Fe is crystalline.

Atmospheric Electricity in Egypt

IN Paper No. 10 of the Survey Department of Egypt Mr. H. E. Hurst discusses two years' results of atmospheric electric potential obtained from a Kelvin water-dropper electrograph at Helwan from March, 1906, to February, 1908. From observations made with a Kelvin portable electrometer, and experiments on the disturbing effect due to the presence of instrument and observer, a factor was obtained, multiplication by which transfers curve readings to potential gradient in the open (volts per metre of height). The mean value found for the potential gradient from the two years was 113, a value lower than is usually encountered in Europe. In the second year, however, owing to the more open scale employed, there was at times considerable loss of trace, and an allowance which Mr. Hurst makes for this would bring up the value of the potential gradient for that year from 119 to 129, and the mean for the two years from 113 to 118. The curves were not smoothed, and were measured only at the even hours, and there is rather excessive irregularity in the diurnal inequality curves which are given for individual months of the year. All show a prominent minimum in the early morning from 4 a.m. to 6 a.m., and some a secondary minimum in the early afternoon, but successive months differ in this respect rather widely. In the mean diurnal inequality for the year there is little variation in the potential from 10 a.m. to 10 p.m.; the value at 8 p.m. is the absolutely largest in both years. One very exceptional phenomenon is that the potential is decidedly highest in summer. The mean potential gradient from the. four months June to September was 136, while that from the four months November to February was only 98, no allowance being made in either case for loss of trace. Curiously, however, the mean range of the diurnal inequality was 81 for the four mid-winter months as compared to 50 for the four months June to September.