On the relationship between refractive index and density for SiO2 polymorphs

The Gladstone-Dale law (specific refraction) and the Drude law (molecular refraction) for silica polymorphs, at “sodium light” (λ _D =0.5893 μm), are derived from simple atomic properties of SiO₂ complex (atomic weight, first ionization potential). The considerations are based on the Lorentz electron theory of solids. The characteristic frequency (or eigenfrequency) v ₀ of elementary electron oscillators (in energy units, hv) is identified with the band gap E _G of a solid; on the other hand, this E _G -gap is identified with the single ionization potential \(\tilde U\) of non-free atoms. For \(\tilde U\) =E _G =10.2 eV (energy gap of quartz, see Nitsan and Shankland 1976b) the Gladstone-Dale law, or specific refraction, is (n?1)/ρ=0.208 cm³/g, where n and ρ are the refractive index and the density of medium, respectively. According to empirical data, the average value of the specific refraction of pure SiO₂ polymorphs (except stishovite-high density phase of silica) is (〈n〉?1)/ρ=0.207±0.001 (〈n〉 denotes the mean refractive index of crystal). For stishovite the Drude law (n ²?1)/ρ=0.542 cm³/g is valid under an assumption that the first ionization potential \(\tilde U\) =E _G ≈9 eV; this result is good agreement with the empirical value (〈n〉²?1)/ρ=0.536 cm³/g.     

Tracerdiffusion of the Fe-cations in olivine (Fe x Mg1−x )2SiO4 (III)

Tracerdiffusion coefficients D _Fe* (and D _Mg*) are presented for olivines of composition (Fe _x Mg_1?x )₂SiO₄ at T=1,130° C as a function of x, and oxygen activity, a _{O 2}. Since the oxygen activity dependence of D _Fe* (D _Mg*) and that of the cation vacancy concentration are almost identical, it is concluded that a vacancy diffusion mechanism is operative in the octahedrally coordinated cation sublattices. From D _Fe* and D _Mg*, the chemical diffusion coefficient \(\bar D\) can be calculated. The calculated \(\bar D\) is in agreement with \(\bar D\) -values obtained by Boltzmann-Matano analysis of interdiffusion experiments. In addition, correlation factors are evaluated from the tracerdiffusion data in order to calculate selfdiffusion coefficients.     

Electron density and polarized absorption spectra of fayalite

The maxima of the electron difference densities of Fe²⁺ atM(1) andM(2) positions of fayalite, Fe₂SiO₄, determined by x-ray diffraction are considered to correspond to atomic dipoles. Provided the selection rules of dipole radiation are satisfied and the energy of the incident radiation lies within the appropriate range, the interaction of incident radiation with these atomic dipoles should lead to three absorption bands of which two originate from Fe²⁺ atM(1), one from Fe²⁺ atM(2). The relative intensities of the three bands, dependent on the polarization direction, are estimated. The result ist in excellent agreement with the interpretation of olivine spectra given by Burns (1970).     

Energy gap and density in SiO2 polymorphs

A relationship between the energy gap (E _G) and density (ρ) for pure SiO₂ polymorphs is derived from atomic weights and first ionization potentials of free silicon and oxygen atoms. Theoretical considerations are based on the Lorentz electron theory of solids. The eigenfrequency v₀ of elementary electron oscillators, in energy units h v₀, is identified with the energy gap of a solid. The numerical relation is expressed as \(E_G = \sqrt {139.24 - 13.8327\rho } \) is in eV. For low-quartz with a density of 2.65 g/cm³ and also for stishovite with a density of 4.28 g/cm³, the energy gap E _G=10.1 eV and 8.9 eV, respectively. From laboratory measurements for low-quartz E _G=10.2 eV. The energy gap-density relation suggests a critical density value of ρ_x ≈ 10.1 g/cm³ for an SiO₂ phase when the energy gap vanishes (E _G=0), which is consistent with estimated densities for a high pressure silica polymorph with the fluorite structure.     

X-ray absorption spectroscopic studies of silicate glasses and minerals

Selected results of x-ray absorption spectroscopy (XAS) studies of amorphous silicates and minerals are presented in order to show their utility in providing short-and, in certain cases, medium-range structural and bonding information for cations and anions. EXAFS and XANES studies of amorphous silicates are reviewed with the objective of illustrating variations in structural environments of the various types of glass-forming cations, including Si, Al, Na, K, Ca, Ti, Fe, Yb, and U. Al is shown to occur in tetrahedral coordination in all aluminosilicate glasses examined, including peraluminous compositions. The weakly bonded Na and Ca cations are shown to occur in sites with observed coordination numbers (ranging from 6 to 7) and distances similar to those predicted by molecular dynamics simulations. Elements like Ti, which form bonds of intermediate strength, may show some order beyond the first coordination shell at low concentrations in silicate glasses. EXAFS studies of Yb and U in silicate glasses at trace to minor concentration levels provide unique structural information about the environments of these cations. K-edges and XANES of transition element sulfides, third-row tetrahedral oxyanions, and oxygen in minerals are interpreted in terms of band theory or molecular orbital theory.     

Spectroscopic monitoring of V1357 Cyg = Cyg X-1 in 2002–2004

We discuss the results of optical spectroscopic monitoring of Cyg X-1 = HDE 226868/V1357 Cyg in 2002–2004. Our spectroscopy was carried out at the Terskol Observatory (Kabarda-Balkaria, Russia; the resolving power was R = 45 000 and 13 000) and at the Bohyunsan Optical Astronomy Observatory (BOAO, Korea, R = 30 000 and 44 000). Each spectrum covers most of the optical range. We obtained a total of 75 echelle spectra on 33 nights, during both “soft” and “hard” X-ray states of Cyg X-1. We study the influence of the X-rays on spectral-line profiles using RXTE/ASM X-ray data. We find that the X-ray flare of June 13, 2003 resulted in strong variations of the emission profiles of the H_α and Hellλ4686 Å lines within a night. This behavior is due to variations of the ionization state of the gas in the system. We also analyzed line-profile variations with orbital phase. A spectral atlas of Cyg X-1 was created, and the lines it contains identified. A total of 172 stellar lines and blends belonging to 12 chemical elements (H, He, C, N, O, Ne, Mg, Al, Si, S, Fe, Zn) were identified. The spectral classification of HDE 226868 as an ON star is confirmed.     

Exploration of structure and bonding in stishovite with fourier and pseudoatom refinement methods using single crystal and powder X-ray diffraction data

The structure and bonding in stishovite, SiO₂, is explored with Fourier summation and pseudoatom refinement of merged x-ray single crystal and powder diffraction data. Replacement of the 25 lowest-angle, highly extinction-affected, single crystal reflections with structure factors obtained from low-extinction powder diffraction data has resulted in a significant improvement in the analysis compared with earlier studies. The deformation electron density, total electrostatic potential and total and valence electron densities are mapped. Accumulations of electron density are observed in both SiO bonds, together with non-bonding features displayed about the oxygen on both sides of a plane formed by three bonds with Si. Deficits of electron density between O atoms across the shared-edges are rationalized in terms of the Pauli exclusion principle. There is no evidence for strong repulsion of Si atoms across the same ring. The total electrostatic potential has a continuous low value for the vacant channels in the structure along c with localized minima between O atoms on opposite sides of the channel. The sizes of Si and O are related to the electron density and to the electrostatic potential.     

Biodegradation of polyvinyl alcohol-low linear density polyethylene-blended plastic film by consortium of marine benthic vibrios

Marine bacteria, Vibrio alginolyticus and Vibrio parahemolyticus isolated from sediments were evaluated for their ability as a consortia, to degrade polyvinyl alcohol-low linear density polyethylene (PVA-LLDPE)-blended plastic films in shake flask conditions at 120 rpm at 37 °C over 15 weeks. Results indicated that relatively 20 % decrease in tensile strength of the film could be achieved with 25 and 30 % blend of PVA in the PVA-LLDPE plastic film compared to other ratios. Micrographs obtained with scanning electron microscope showed visible cracks and grooves on the surface of the PVA-LLDPE blend film after 15 weeks of incubation with bacterial consortium. The decrease in tensile strength of the PVA-blended plastic films after treatment and the results of the scanning electron microscopic analysis evidence that the consortium could cause degradation of PVA-LLDPE plastic blends compared to suitable controls. This is the first report on polyvinyl alcohol degrading Vibrio sp. from marine sediments and its application in microbial degradation of polyvinyl alcohol-low linear density polyethylene plastic blends. The study indicated potential of marine benthic vibrios that have novel enzymes and unique characteristics for application in bioremediation and solid waste management particularly in handling synthetic polymers such as PVA-blended plastic films.     

Seismic triggering of atmospheric variables prior to the major earthquakes in the Middle East within a 12-year time-period of 2002–2013

Several studies have reported the increased values of surface-latent heat flux (SLHF) and rainfall events prior to the earthquakes as the seismic precursors. In order to investigate the variation of two mentioned atmospheric variables, we analyzed 39 major earthquakes in the Middle East based on the time series of NASA remote sensing data. On this basis, we observed that accumulated rainfall and SLHF of about 29 earthquakes were higher than 10 mm and 50 W/m², respectively (~75 %), over 3–23 days prior to the main shock of major earthquakes. We believed that the records of atmospheric variables are the consequence of a seismic-triggered chain including of air ionization, surface-latent heat exhalation, water vapor condensation and subordinate rainfall as the atmospheric responses to lithospheric motions. This seismic triggering in the Middle East has averagely caused to accumulated rainfall of ~35 mm and maximum SLHF of ~115 W/m² over the 3–23 days prior to 39 major earthquakes. To investigate of spatial correlation between earthquakes and atmospheric variations, we clustered 39 major earthquakes in eight seismological regions. Then, we estimated the moderate and strong correlation (R ²) between preceding times of earthquakes with magnitude of major earthquakes and their hypocenter depth equal to 0.48 and 0.68, respectively.     

Quantitative analysis of morphometric parameters of Kali River basin,southern India,using bearing azimuth and drainage (bAd) calculator and GIS

This study deals with the application of visual basic program ‘bearing, azimuth and drainage (bAd) calculator’ which employs a new and easy methodology for extraction of watershed morphometric parameters. Using bAd calculator, morphometric analysis was carried out for the Kali River basin of southwest coast of India. The basin forms a part of the Western Ghats, which is an important mountain range of the Indian sub-continent and runs nearly parallel to the coast. Spatial maps of six morphometric parameters have been prepared from the results obtained. Various linear, areal, shape and relief morphometric parameters of fifth and sixth order basins have been calculated and interpreted. Majority of the sub-basins show less uniform values (~3 to 4) of R _bm which indicate the uniform and systematic branching pattern of streams. High D _d zones are found in the Western Ghats region, whereas low D _d zones are observed in the eastern part of the basin and near the estuary. The eastern part of the basin shows low F _s values, whereas NW and SW parts of the basin show high F _s values. Compared to manual measurement, bAd calculator requires minimal time to quantify the morphometric parameters. Experimental results show that the software is effective in calculating drainage parameters such as drainage density, frequency, bifurcation ratio, etc., using the text file of ESRI shapefile.     

Integrated production and effective loss rates in the ionosphere

The total electron content data obtained at Ahmedabad through the Faraday fading records of the radio beacons abroad the satellites Explorer 22 and 27 are used to determine the overhead integrated production rate (Q ⁰) and integrated loss coefficient (β′) for the epoch 1965–1968. The production rate (Q ₀) is shown to have two peaks during a year around the equinoctal months and for a particular monthQ ₀ increases linearly with the 10·7 cm solar flux. The loss coefficient β′, too, has two equinoctial peaks within a year. The semiannual variations ofQ ₀ and β′ are discussed in relation to similar variation in the [O]/[N₂] ratio.     

Dependence of the absorption-line profiles and radial-velocity curve of the optical star in an X-ray binary on the orbital inclination and component-mass ratio

Theoretical absorption-line profiles and radial-velocity curves for tidally deformed optical stars in X-ray binary systems are calculated assuming LTE. The variations in the profile shapes and radial-velocity curve of the optical star are analyzed as a function of the orbital inclination of the X-ray binary system. The dependence of the shape of the radial-velocity curve on the orbital inclination i increases with decreasing component-mass ratio q = m _x /m _v . The integrated line profiles and radial-velocity curves of the optical star are calculated for the Cyg X-1 binary, which are then used to estimate the orbital inclination and mass of the relativistic object: i < 43° andm _x = 8.2–12.8 M_⊙. These estimates are in good agreement with earlier results of fitting the radial-velocity curve of Cyg X-1 using a simpler model (i < 45°, m _x = 9.0–13.2 M_⊙).     

The affinity of trichomes of blue-green algae for calcium lons

Cells of Plectonema boryanum and Anabaena flos-aquae obtained from large scale (to 15L) cultures were used to examine the cation exchange properties of killed algal cells. Since Microcoleus lyngbyaceus, one of the most abundant species in our collections from marshes, could not be obtained in large-scale liquid cultures, it was collected in algal mats from tide-marsh pannes and separated from other algae, etc. by a combination of screening, air elutriation and density-gradient centrifugation. Characterization of the exchange properties of such preparations was pursued using ⁴⁵Ca for exchange measurements and Cd-EDTA or Cd-EGTA as indicators with the Cd-specific ion electrode for electrometric titration for total Ca⁺⁺ and Mg⁺⁺, or Ca⁺⁺, respectively. Algal cell preparations exhibited a capacity to exchange Ca⁺⁺ readily with ambient aqueous solutions. K⁺ and Na⁺ could displace a substantial proportion of the Ca⁺⁺ at concentrations about 100-fold greater than that of the ambient Ca⁺⁺. Mg⁺⁺ was about 10 times as effective as the monovalent cations in displacing Ca⁺⁺. Cell walls isolated from rhizomes of Spartina alterniflora exhibited only about 1/10 the affinity for Ca⁺⁺ as that found for the blue-green algal preparations. The intrinsic association constant and the total capacity for cation exchange indicated that in solutions of 2×10^?4M about 50% of the exchange sites are occupied. The ligand for Ca⁺⁺ could be extracted in part by dilute acid, but not by Triton X-100 or by EDTA, even in the presence of Triton X-100. The extracted material appeared to be a polysaccharide. Both the sheaths of M. lyngbyaceus by themselves and cells from which they were separated exhibited Ca-exchange properties.     

The Wolf–Rayet star HD 192163 as a possible evolutionary progenitor of a low-mass X-ray binary

We have used 46 high-resolution echelle spectra of the Wolf-Rayet star HD 192163 taken in 2005–2009 at the Cassegrain focus of the 2-m Zeiss-2000 telescope of the Shamakha Astrophysical Observatory to study profiles of the five strongest emission lines (HeII 4859, HeII 5411, CIV 5808, HeI 5875, (HeII + Hα) 6560). We also obtained four echelle spectrograms of the Wolf-Rayet star HD 191765 for a comparative study of the NaI 5890 (D₂) and NaI 5896 (D₁) interstellar absorption lines. The echelle spectrograms were reduced using the DECH20 code. We determined the equivalent widths, radial velocities, central intensities, and half-widths of the emission lines. We detected variations in the violetwing of the (HeII + Hα) 6560 emission band (between λ ～ 6496 Å and λ ～ 6532 Å). Our statistical analysis of the radial velocities available for the (HeII + Hα) 6560 emission band reveals a peak at the ～1% level at the frequency ν = 0.195 d^?1, corresponding to the period P = 5.128^d. We also studied the NaI 5890 (D₂) and NaI 5896 (D₁) interstellar absorption lines, which are important for understanding the nature of the nebula NGC 6888, whose origin is related to HD 192163. Asymmetric profiles were found for the NaI 5890 and NaI 5896 interstellar absorption lines, interpreted as reflecting a contribution from NGC 6888 to these lines. We suggest that the detected profile variations of the (HeII + Hα) 6560 emission band and the periodic variations of its Doppler shifts (P = 5.128^d) are due to the existence of a low-mass K-M star companion to the Wolf-Rayet star. HD 192163 is a possible evolutionary progenitor of a low-mass X-ray binary.     

A molecular orbital study of bond length and angle variations in framework structures

Molecular orbital calculations on a variety of silicate and aluminosilicate molecules have been used to explore the bonding forces that govern tetrahedral bond length variations, r(TO), in framework silicates and aluminosilicates. Not only do the calculations provide insight into the variety of structural types and the substitution limits of one tetrahedral atom for another, but they also provide an understanding of the interrelationships among r(TO) and linkage factors, bond strength sum, coordination number, and angles within and between tetrahedra. A study of these interrelationships for a theoretical data set shows that r(SiO) and r(AlO) are linearly correlated with (1) p _o, the bond strength sum to a bridging oxygen, (2) f _s(O), the fractional s-character of a bridging oxygen, and (3) f _s (T), the fractional s-character of the T atom. In a multiple linear regression analysis of the data, 92% of the variation of r(SiO) and 99% of the variation of r(AlO) can be explained in terms of a linear dependence on p _o, f _s (O), and f _s (T). Analogous regression analyses completed for observed r(Al, SiO) bond length data from a number of silica polymorphs and ordered aluminosilicates account for more than 75% of the bond length variation. The lower percentage of bond length variation explained is ascribed in part to the random and systematic errors in the experimental data which have a negligible effect on the theoretical data. The modeling of more than 75% of the variation of r(Al, SiO) in the framework silicates using the same model used for silicate and aluminosilicate molecules strengthens the viewpoint that the bonding forces that govern the shapes of such molecules are quite similar to the forces that govern the shapes of chemically similar groups in solids. The different regression coefficients calculated for f _s (T) indicate that SiO and AlO bond length variations in framework structures should not be treated as a single population in estimating the average Al, Si content of a tetrahedral site.     

Crystal structures of Ni2SiO4 and Fe2SiO4 as a function of temperature and heating duration

X-ray structure refinements of Ni₂SiO₄ and Fe₂SiO₄ spinels have been made as a function of temperature and heating duration by intensity measurements at high temperatures and room pressure. The lattice parameters of Ni₂SiO₄ spinel linearly increased with temperature up to 1,000° C. However, Fe₂SiO₄ spinel exhibited a nonlinear thermal expansion and was converted to a polycrystalline mixture of spinel and olivine by heating of less than one-hour at 800° C. The ratios between the octahedral and tetrahedral bond lengths D _oct/D _tetr and between the shared and unshared edge distances (O-O)_sh/(O-O)_unsh in Fe₂SiO₄ spinel were both much larger than those in Ni₂SiO₄. These ratios increase with temperature. The Fe₂SiO₄ spinel more readily approached a activation state which facilitated the transition to the olivine structure than the Ni₂SiO₄ spinel. The lattice parameter of Ni₂SiO₄ spinel decreased with heating period at constant temperatures of 700° C and 800° C. The parameter of the quenched sample after heating for 52 h at 700° C was smaller than that of the nonheated sample. The refinements of the site occupancies at each heating duration indicated an increase in the cation deficiency in both tetrahedral and octahedral sites. Electron microprobe analysis, however, proved no significant difference in the chemical compositions between the quenched and nonheated samples. Si and Ni atoms displaced from normally occupied spinel lattice sites are assumed to settle in vacant sites defined by the cubic close packed oxygen sublattice in a manner which preserves the electric neutrality of the bulk crystal.     

A model of the OH positions in olivine,derived from infrared-spectroscopic investigations

Polarized infrared (IR) spectroscopy of olivine crystals from Zabargad, Red Sea shows the existence of four pleochroic absorption bands at 3,590, 3,570, 3,520 and 3,230 cm^?1, and of one non pleochroic band at 3,400 cm^?1. The bands are assigned to OH stretching frequencies. Transmission electron microscopy (TEM) shows no oriented intergrowths in this olivine; it is concluded that OH is structural. On the basis of the pleochroic scheme of the absorption spectra it is proposed that [□O(OH)₃] and [□O₂(OH)₂] tetrahedra occur as structural elements, assuming that the vacancies are on Si sites. If M2 site vacancies were assumed [SiO₃(OH)] and [SiO₂(OH)₂] tetrahedra occur as structural elements.     

Morphology,perfection and growth of natural pyrite whiskers and thin platelets

Whiskers and thin platelets of pyrite have been found growing coherently on the face of small cubic pyrite crystals from the Strashimir and Gradishte hydrothermal lead-zinc deposits. The host crystals formed framboids and spheroids of macroscopic size inside large crystals of chalcopyrite from which they are separated by concentric gaps. The whiskers, one to several μm in width, are elongated along [001] and bounded by {100}, partly by {210} and {111} faces. Scanning electron microscopic (SEM) observation revealed longitudinal steps and grooves, flat rectangular pits, drop-like and elongated bulges on their side faces. High-voltage electron microscopic (HVEM) studies showed that the thin whiskers are perfect and dislocation-free, although some ribbon-like whiskers and platelets contain internal longitudinal channels and small isometric fluid inclusions. Based on these observations, the following growth mechanism is proposed. Whiskers grow in the restricted volume of the internal cavities in chalcopyrite from stagnant solutions under a diffusion regime. The growth proceeds in two stages: (1) Initially, pyramidal “pedestals” are formed due to morphological instability of the host crystal surfaces and multiapex growth, (2) Whiskers grow rapidly by unidirectional supply of material and competition between neighbouring individual whiskers, the growth taking place at the tip by a two-dimensional nucleation mechanism. The whiskers and thin platelets are considered to be peculiar highly anisometric skeletal crystals.     

Modeling chromium(VI) reduction by Escherichia coli 33456 using ceramic pearl as a supporting medium

A mathematical model was developed to describe the reduction of Cr(VI) by Escherichia coli (E. coli) 33456 in a fixed biofilm reactor. A laboratory-scale column reactor was conducted to verify the model system. The batch kinetic tests were independently conducted to determine the biokinetic parameters used in the model simulation. With the assumed values of initial biofilm thickness (L _f0), the mathematical model simulated well the experimental results for Cr(VI) effluent concentration, effluent concentration of suspended E. coli cells, and Cr(III) production. The concentration of suspended E. coli cells reached up to 1.2 mg cell/L while the thickness of attached E. coli cells was estimated to be 32.6 μm at a steady-state condition. At the steady state, the removal efficiency of Cr(VI) was about 92 % and the effluent concentration of Cr(III) was approximately 1.6 mg/L. The approaches presented in this study can be employed for the design of a pilot-scale or full-scale fixed biofilm reactor to treat Cr(VI)-containing wastewater.     

Nd and Sr isotopes in ultrapotassic volcanic rocks from the Leucite Hills,Wyoming

Nd and Sr isotopic compositions and Rb, Sr, Sm and Nd concentrations are reported for madupites, wyomingites and orendites from the Pleistocene volcanic field of the Leucite Hills, Wyoming. All Leucite Hills rocks have negative εNd signatures, indicating derivation or contribution from an old light rare earth element (LREE) enriched source. In this respect they are similar to all occurrences of high potassium magmas so far investigated. But Sr isotopic variations are comparatively small and ⁸⁷Sr/ ⁸⁶Sr ratios are unusually low for high-K magmas (0.7053–0.7061, one sample excluded). These values suggest that the light REE enrichment of the source was not accompanied by a strong increase in Rb/Sr. Wyomingites and orendites are isotopically indistinguishable which is consistent with chemical and petrographic evidence for their derivation from a common magma series depending on emplacement conditions. Basic to ultrabasic madupites and more silicic wyomingites/orendites are distinct in their Nd isotopic variations (madupites: εNd= ?10.5 to ?12.3; wyomingites/orendites: εNd= ?13.7 to ?17.0) despite similar Sm/Nd ratios and complete overlap in ⁸⁷Sr/⁸⁶Sr. Selective or bulk assimilation of crustal material is unlikely to have significantly affected the Nd and Sr isotopic compositions of the magmas. The measured isotopic ratios are considered to reflect source values. The distinct isotopic characteristics of madupite and wyomingite/orendite magmas preclude their derivation by fractional crystallization, from a common primary magma, by liquid immiscibility or by partial melting of a homogeneous source. Two isotopically distinct, LREE enriched and slightly heterogeneous sources are required. Heterogeneities were most pronounced between magma sources from each volcanic centre (butte or mesa). The relationship between the madupite and wyomingite/orendite sources and their evolution is discussed on the basis of two simple alternative sets of models:

1. a two-stage evolution model with an old enrichment event (a metasomatic event?) perhaps taking place during the stabilization of the Wyoming Craton 3.2 to 2.5 Gyr ago but not later than 1.2 Gyr ago or
2. a mixing model involving mixing between one endmember with εNd near zero and another end-member with a strong negative εNd signature.