Polymerization of silicate and aluminate tetrahedra in glasses,melts, and aqueous solutions—V. The polymeric structure of silica in albite and anorthite composition glass and the devitrification of amorphous anorthite

²⁹Si MAS NMR experiments have been carried out to determine the silica species distribution (Q distribution) in albite, NaAlSi₃O₈, and anorthite, CaAl₂Si₂O₈, composition glasses (designated albite and anorthite glass). Our results indicate that the Q distribution of albite glass contains all five possible silica species and shows a tendency towards high Q₃ and Q₄ concentrations, whereas anorthite glass does not contain Q₄ and has a high Q₀ concentration. Rationalizations are made in terms of the observed Q distributions to explain differences in devitrification behavior of these two glasses. ²⁷Al MAS NMR data for these glasses suggest that differences in devitrification behavior between these two glasses should be ascribed to small growth rates rather than small nucleation rates of crystalline albite from albite glass.     

Calculation of the transport coefficients of the nuclear pasta phase

We calculate the transport coefficients of low-density nuclear matter, especially the nuclear pasta phase, using quantum molecular dynamics simulations. The shear viscosity as well as the thermal and electrical conductivities are determined by calculating the static structure factor of protons for all relevant density, temperature and proton fractions, using simulation data. It is found that all the transport coefficients have similar orders of magnitude as found earlier without considering the pasta phase. Our results are thus in contrast to the common belief that the pasta layer is highly resistive and therefore have important astrophysical consequences.     

On the origin of highest energy cosmic rays

In this paper we show that the conventional diffusive shock acceleration mechanism for cosmic rays associated with relativistic astrophysical shocks in active galactic nuclei (AGNs) has severe difficulties to explain the highest energy cosmic ray events. We show that protons above around 2 x 10²⁰ eV could have marginally been produced by this mechanism in an AGN or a rich galaxy cluster not further away than around 100 Mpc. However, for the highest energy Fly's Eye and Yakutsk events this is inconsistent with the observed arrival directions. Galactic and intergalactic magnetic fields appear unable to alter the direction of such energetic particles by more than a few degrees. We also discuss some other options for these events associated with relativistic particles including pulsar acceleration of high Z nuclei. At the present stage of knowledge the concept of topological defects left over from the early universe as the source for such events appears to be a promising option. Such sources are discussed and possible tests of this hypothesis are proposed.     

Nucleosynthesis of26Al in the early solar system and in cosmic rays

The nucleus²⁶Al(^1/2 = 7.4 × 10⁵ yr) has long been considered as a possible heat source during the formation of the solar system. Recent experimental work has found no evidence for²⁶Al at the time of final solidification of the meteorites. Due to the short half-life these measurements do not rule out the possibility that²⁶Al was a significant heat source a few million years prior to final solidification. For²⁶Al to be an effective heat source in the early solar system it is necessary for the ratio²⁶Al/Si to be 2×10^–7 at the time of a solidification. The nucleosynthetic yields of²⁶Al by silicon burning, carbon burning, and spallation are discussed. It is shown that²⁶Al can be synthesized in carbon and/or silicon-burning supernovae. However, time scales in the early solar system make it more likely that²⁶Al, if present in planets, was synthesized by a proton irradiation in the early solar system. An integrated proton flux >4×10¹⁸ cm^–2 is shown to be necessary in order for²⁶Al to be a significant heat source. No conclusive evidence has been observed for an irradiation of this magnitude. Therefore, unless such evidence is found, it should be assumed that²⁶Alwas not involved in the formation of the solar system. In addition, the production of²⁶Al in cosmic rays is discussed and it is shown that either resolution of the Al isotopes in the cosmic rays or accurate measurements of the variation with energy of the cosmic ray abundance ratios Al/Si and Mg/Si can be used to determine the age of the cosmic rays, _C.R.. Current abundance data are extremely uncertain; however, the trend tends toward values of _C.R. 10⁶ yr.Supported in part by the National Science Foundation [GP-19887, GP-28027, GP-27304].     

A microstructural study of the Tishomingo meteorite

Metallography, electron microscopy and X-ray diffraction techniques were employed to study a fragment of the Tishomingo iron meteorite. The results suggest the following thermal-mechanical history: The fragment was originally a large crystal of taenite (γ). Cooling through the α + γ phase boundary did not result in accompanying precipitation of kamacite (α). Transformation to a martensitic structure initiated between ? 25 and ?65°C. Transformation continued as the temperature fell to ? 75 to ? 115°C, resulting in approx 80% martensite (α′). Subsequent shock deformation and thermal aging processes substantially modified the taenite and martensite microstructures. Twins in the retained taenite phase are attributed to shock deformation at a pressure estimated for a single event at ~170 kbar. The existing complex, altered martensite structure containing both taenite and kamacite (3–15% Ni) particles was apparently the product of both shock deformation and thermal aging processes. The maximum temperature reached during thermal aging is estimated to be less than 400°C, and perhaps below 310°C.     

Reductive Degradation of Polychlorinated Phenols by Pd/C‐Formate: An Ecoefficient Remediation Method for Aqueous Chlorinated Phenols

A new catalytic dehydrohalogenation method for chlorinated phenols is described, which can be used to break down chlorinated pollutants in wastewater. It uses a system of Pd‐C as catalyst with sodium formate as reducing agent. This economic method is easy to perform with a complete degradation of the pollutant within 12 to 30 h at room temperature. The ecoefficieny of the procedure is compared with eleven alternative methods showing the special advantages of the method.     

Simulation von Variablen der Fließgewässerqualität mittels Mehrfachregressionen

There are investigated the variables O₂, BOD₅, seston, NO₃-N, NH₄-N and o-PO₄ from at least five-year series of five stations along a river section of 50 km. After exclusion of a linear trend and substraction of the individual monthly mean values from the monthly mean of many years in order to eliminate the effect of the annual variation as well as testing for normal distribution, first the correlation coefficients of the variables to the flow rate Q and the temperatures of air and water are determined, which show directional changes just in the longitudinal profile of the river. The same holds for the correlation of the variables between the measuring points. From this the model structure is derived, according to which the concentration at one measuring station can be simulated by multiple regression to Q and T at the same level as well as the concentration at the upper level. The results are discussed in detail and evaluated with respect to their inclusion in longterm management models of water quantity management.     

Polymerization of silicate and aluminate tetrahedra in glasses,melts, and aqueous solutions—IV. Aluminum coordination in glasses and aqueous solutions and comments on the aluminum avoidance principle

The coordination of aluminum with oxygen in crystalline and amorphous alumina, aluminates, and aluminosilicates has been determined with magic angle spinning ²⁷Al nuclear magnetic resonance. The ²⁷Al NMR spectra of crystalline materials show that ^VIAl and ^IVAl can readily be distinguished. The same is not the case for amorphous aluminosilicates due to the superposition of a narrow peak, characteristic of ^IVAl, on a broad band. Our spectroscopic results indicate that Al coordination is not the determining factor in explaining differences in devitrification behavior of albite and anorthite glasses. The coordination of Al in aqueous solutions seems to prevent precipitation of the three common Al(OH)₃ polymorphs (^VIAl) at pH above 10. There is clear evidence to suggest that, in solutions containing Si as well as Al, aluminum coordination is related to the type of precipitate formed in acid (clays, ^VIAl, ^IVAl), and basic (zeolites, ^IVAl) environments. Zeolites can be precipitated in near neutral pH environments at higher temperatures, reflecting an increase in ^IVAl under these conditions. The Al avoidance principle for aluminosilicates does not seem to be a hard principle. It is likely that the validity of this principle depends on the type of modifying cation present in the aluminosilicate framework.