Observations of the flux of very-high-energy gamma rays from the blazar 3C 66A

Measurements of the flux of very-high-energy (>1 TeV) gamma rays from the blazar 3C 66A obtained over four years are presented. The mean flux over the four-year period was (2.8±0.4)×10^?11 cm^?2 s^?1. There is a correlation between the season-averaged flux of very-high-energy gamma rays and the observed optical radiation.     

Ionospheric response to X-class solar flares in the ascending half of the subdued solar cycle 24

The signature of 11 X-class solar flares that occurred during the ascending half of the present subdued solar cycle 24 from 2009 to 2013 on the ionosphere over the low- and mid-latitude station, Dibrugarh (27.5^°N, 95^°E; magnetic latitude 17.6^°N), are examined. Total electron content (TEC) data derived from Global Positioning System satellite transmissions are used to study the effect of the flares on the ionosphere. A nonlinear significant correlation (R² = 0.86) has been observed between EUV enhancement (ΔEUV) and corresponding enhancement in TEC (ΔTEC). This nonlinearity is triggered by a rapid increase in ΔTEC beyond the threshold value ～1.5 (×10¹⁰ ph cm^?2 s^?1) in ΔEUV. It is also found that this nonlinear relationship between TEC and EUV flux is driven by a similar nonlinear relationship between flare induced enhancement in X-ray and EUV fluxes. The local time of occurrence of the flares determines the magnitude of enhancement in TEC for flares originating from nearly similar longitudes on the solar disc, and hence proximity to the central meridian alone may not play the dominating role. Further, the X-ray peak flux, when corrected for the earth zenith angle effect, did not improve the correlation between ΔX-ray and ΔTEC.     

Origins and properties of the quasi-stationary slow solar wind

Comparisons of the brightness distributions of the white corona observed at distances of several solar radii with solar wind velocities derived from interplanetary-scintillation observations, as well as analyses of solar wind data obtained on spacecraft from December 1994 to June 1995, indicate that the fast solar wind can contain plasma with velocities V ≈ 300–450 km/s, approaching those typical for the slow solar wind that flows in the streamer belt and chains of streamers. At the same time, certain other parameters, first and foremost the plasma density N and ratio T/N ^0.5 (where T is the temperature), indicate that these two flows differ considerably. The slow solar wind flowing in the streamer belt and chains displays high densities N > 10 ± 2 cm^?3 and low T/N ^0.5 < 1.7 × 10⁴ K cm^3/2 at the Earth’s orbit. The number of slow solar-wind sources observed in chains can be comparable with the number observed in the belt. The fast solar wind flowing from coronal holes always displays low densities N≤ 8 cm^?3 and high T/N ^0.5 > 1.7 × 10⁴ K cm^3/2. These properties probably indicate different origins of the fast and slow solar winds.     

The importance of organic phase diffusion in the solvent extraction of copper by LIX 64N — Experiments with a static interface cell

Previous studies have suggested that the extraction of copper by hydroxyoxime extractants involves mass transfer with chemical reaction. This paper reports the results of experiments where an aqueous copper solution (4.94 g dm^?3 copper, 5.26 g dm^?3 H₂SO₄) is contacted with a 5% v/v LIX 64N solution in Escaid 100, in a diffusion cell with a stagnant interface. The concentration-distance distribution of the diffusional band of copper complex which appeared in the organic phase was measured at various times, and the results can be modelled by equations based on diffusion about an interface with and without interfacial resistance.If the previously measured diffusion constants for copper in the aqueous and organic phases were used in the model, then an unrealistically high resistance (200,000–300,000 s cm^?1) would have to be chosen to obtain a correlation. If a low resistance (1,000 s cm^?1) is assumed and the previously measured diffusion constants for copper in the aqueous phase (5.2·10^?6 cm² s^?1) and copper in the organic phase (5.0·10^?6 cm² s^?1) are taken, then it is necessary to reduce the organic phase diffusion constant to 2·10^?6 cm² s^?1 to obtain correlation of the model with the data. It is proposed that as the organic product film develops, the diffusivity of the copper complex is reduced.     

Magnetic flux in an active solar region and its correlation with flares

The correlation between the magnetic flux in an active solar region and associated powerful solar flares is studied. The behavior of the active regions AR 10486 and AR 10365 is considered. These regions produced a series of class X flares as they crossed the solar disk. The flares appeared when the magnetic flux exceeded 10²² Mx. The magnetic flux remained constant during all the flares except for one. During this flare, the flux decreased by about 10%; this impulsive decrease of the flux was also recorded in the absence of flares. No energy flux from the photosphere to the corona at the time of the flare was observed. The behavior of the photospheric field in AR 10486 and AR 10365 is consistent with a slow accumulation of energy in the corona and the explosive release of energy stored in the magnetic field of a current sheet above an active region during the flare.     

Silicate mineral dissolution at pH 4 and near standard temperature and pressure

The dissolution of labradorite, microcline, enstatite, augite and forsterite in acidified deionized water was investigated at near standard temperature and pressure and constant pH of 4.00 to determine the kinetics of the release of silica, and cations. Saturation indices and mass balance calculations suggest that after 700 hours, the release of silica from forsterite and augite was controlled by the precipitation of a solid silica phase, whereas silica mass transfer from the feldspars and enstatite was essentially as silicic acid. Iron release from the pyroxenes and olivine was probably controlled by the precipitation of iron oxyhydroxide phases. Linear-rate constants calculated after 700 hours for release of magnesium ranged from 10^?15.2 to 10^?14.4 M · cm^?2 s^?1 for augite and forsterite respectively. Linear-rate constants for the release of cations from feldspars ranged from 10^?15.8 to 10^?15.3 M · cm^?2 s^?1.     

Diffusion in single crystal of melilite: interdiffusion of Al + Al vs. Mg + Si

Interdiffusion coefficients of Al + Al vs. Mg + Si in the gehlenite–åkermanite system of melilite were determined by coupled annealing of synthesized end-member single crystals. The observed diffusion coefficients for a couple-annealed sample vary for about 2 orders of magnitude, showing strong dependence on the gehlenite–åkermanite composition: diffusion coefficient observed at 1350 °C, for example, is 3 × 10^?13 cm² s^?1 at 5 mol% åkermanite composition (Ak₅), increases to 2 × 10^?11 cm² s^?1 at Ak₈₀, and then decreases to 1 × 10^?12 cm² s^?1 at Ak₉₅. The diffusion coefficient–temperature relation indicates high activation energy of diffusion of about 420 kJ mol^?1 for gehlenite-rich melilite. The observed diffusion coefficient–composition relation may be explained by a combination of (1) the diffusion coefficient–melting temperature relation (Flynn's rule) and (2) the feasibility of local charge compensation, which can possibly be maintained more easily in the intermediate chemical composition. The high activation energy value for gehlenitic melilite appears to correspond to the complex diffusion mechanism. The observed highly variable diffusion coefficients suggest that gehlenite–åkermanite zoning in the melilite crystals in Ca, Al-rich inclusions in the carbonaceous meteorites may provide a sensitive indicator for the thermal history of the inclusions.     

The structure of solar filaments. Prominences in the corona free from external magnetic field

The new approach to the modeling of quiescent solar prominences is proposed. We solve the inverse magnetohydrostatic problem, when the pressure, density and temperature of plasma in the filament are calculated from the equilibrium equations using the given magnetic structure (magnetic flux function is proposed to be known). The new exact nonlinear solutions for dense (n ≈ (2?3) × 10¹¹ cm^?3) and cold (T ≈ (5?10) × 10³ K) filaments, embedded in the plan, vertically stratified atmosphere (hot solar corona) free of magnetic field, are derived. The filaments are stretched along the horizontal axisy(the translational symmetry is assumed: ?/?y = 0) and located parallel to and above a photospheric, magnetic polarity reversal line. The magnetic field lines have a structure of magnetic flux rope with helical field lines in three-dimensional space; the strength of magnetic field falls rapidly with distance from a rope axis. No external longitudinal magnetic field is needed to equilibrate the prominence. The net electric current along the filament is equal to zero. The model of magnetic arcade with the deflection (sag) on the top, proposed by Pikelner (1971) as a basic form of normal prominence, is calculated also using the method proposed. It is shown that such magnetic arcade, having the magnetic field strength of few gauss only, can effectively maintain the equilibrium of cool dense filament at the heights about 50–60 Mm.     

DIffusion of Eu and Gd in basalt and obsidian

Tracer diffusion coefficients of ¹⁵³Gd and ¹⁵²Eu in olivine tholeiite have been determined at temperatures between 1150 and 1440°C. The results are identical for both tracers within experimental error. Between 1440 and 1320°C the diffusion coefficients are given by D(Eu, Gd) = 0.058 exp(?40,600/ RT). Between 1320 and 1210°C, the diffusion coefficients are constant at D = (1.4 ± 0.4) × 10^?7 cm²s^?1 and between 1210 and 1150°C, the D values drop irregularly to 4 × 10^?9 cm²s^?1. The liquidus temperature (1270°C) lies within the region of constant D. Such anomalous behavior has not been encountered in previous studies of Ca, Sr, Ba and Co diffusion in basalt. To explain the constant D value near the liquidus, we speculate that the structure of the melt changes as a function of temperature in such a way that the normal temperature dependence of the diffusivity is compensated. For example, the rare earth ions may be displaced from their (high temperature) octahedral coordination sites to other sites where they are more readily dissociated and therefore become progressively more mobile. The behavior below 1210°C may be the result of relatively stable complexes or molecules in the melt or of the formation of a REE bearing crystalline phase that has so far escaped detection. Preliminary results for Eu diffusion in obsidian are D (Eu, 800°C) = 5 × 10^?13 cm² s^?1 and D (Eu, 950°C) = 1.5 × 10^?11 cm² s^?1. These data are consistent with an activation energy of 59 Kcal mole^?1. These low diffusivities indicate that the partitioning of REE in crystallizing intermediate and acidic melts may be controlled by diffusion in the melt rather than equilibrium between the crystal surface and the bulk melt.The diffusion data are applied to partial melting in the mantle, in an attempt to explain how LREE enriched tholeiites may be derived from a LREE depleted mantle source. In this model LREE diffuse from garnet bearing regions that have small melt fractions into garnet free regions that have relatively large melt fractions. REE diffusion is so slow that this process is quantitatively significant only in small partially molten bodies (diameter ～1 km or less) or in larger, but strongly flattened bodies. Internal convective motion during diapiric rise would also increase the efficiency of the process.     

An XPS study of the dissolution kinetics of chrysotile in 0.1 N oxalic acid at different temperatures

The dissolution of chrysotile is studied in regard to the surfaces analysis by photoelectron spectrometry. After leaching of chrysotile (Provenance: Thetford; about 200 mg of fibers of 1 cm length) in nonstirred 0.1 N oxalic conditions, the composition of the mineral surfaces is determined by XPS; kinetic curves of dissolution are given in the range 22–80°C. Two conditions for the rate-limiting step are involved for the explanation of the dissolution: diffusion of Mg²⁺ through the fibrous gel or dissociation of chrysotile. By the former, some values of the diffusion coefficient are proposed: D varies from 5·10^?19 cm²s^?1 to 5·10^?16 cm²s^?1, in the range 22–80°C. By the second model, the leaching rate is estimated from 3 Å (22°C) per h to 250 Å (80°C) per h. For the 2 models, the activation heat energy is in the range 15–20 Kcal.     

Gamma-ray bursts from a close pulsar binary system?

The close neutron-star binary system comprised of the radio pulsars PSR J0737-3039 A,B is discussed. An analysis of the observational data indicates that the wind from pulsar A, which is more powerful than the wind from pulsar B, strongly distorts the magnetosphere of pulsar B. A shock separating the relativistic wind from pulsar A and the corotating magnetosphere of pulsar B should form inside the light cylinder of pulsar B. A weakly diverging “tail” of magnetic field is also formed, which stores a magnetic energy on the order of 10³⁰ erg. This energy could be liberated over a short time on the order of 0.1 s as a result of reconnection of the magnetic-force lines in this “tail,” leading to an outburst of electromagnetic radiation with energies near 100 keV, with an observed flux at the Earth of 4 × 10^?11 erg cm^?2 s^?2. Such outbursts would occur sporadically, as in the case of magnetic substorms in the Earth’s magnetosphere.     

BL Lac: A new ultrahigh-energy gamma-ray source

The active galactic nucleus BL Lac was observed with the GT-48 atmospheric Cherenkov detector of the Crimean Astrophysical Observatory from July 23–September 1, 1998, in order to search for ultrahighenergy gamma-ray (>1 TeV) emission. The object was in the field of view of the detector for more than 24 hours. The source was detected with a high level of confidence (7.2 σ) with a flux equal to (2.1±0.4)×10^?11 photons cm^?2 s^?1.     

Helium measurements of pore fluids obtained from the San Andreas Fault Observatory at Depth (SAFOD, USA) drill cores

⁴He accumulated in fluids is a well established geochemical tracer used to study crustal fluid dynamics. Direct fluid samples are not always collectable; therefore, a method to extract rare gases from matrix fluids of whole rocks by diffusion has been adapted. Helium was measured on matrix fluids extracted from sandstones and mudstones recovered during the San Andreas Fault Observatory at Depth (SAFOD) drilling in California, USA. Samples were typically collected as subcores or from drillcore fragments. Helium concentration and isotope ratios were measured 4?C6 times on each sample, and indicate a bulk ⁴He diffusion coefficient of 3.5?±?1.3?×?10^?C8 cm²?s^?C1 at 21°C, compared to previously published diffusion coefficients of 1.2?×?10^?C18 cm²?s^?C1 (21°C) to 3.0?×?10^?C15 cm²?s^?C1 (150°C) in the sands and clays. Correcting the diffusion coefficient of ⁴He_water for matrix porosity (??3%) and tortuosity (??6?C13) produces effective diffusion coefficients of 1?×?10^?C8 cm^2?s^?C1 (21°C) and 1?×?10^?C7 (120°C), effectively isolating pore fluid ⁴He from the ⁴He contained in the rock matrix. Model calculations indicate that <6% of helium initially dissolved in pore fluids was lost during the sampling process. Complete and quantitative extraction of the pore fluids provide minimum in situ porosity values for sandstones 2.8?±?0.4% (SD, n?=?4) and mudstones 3.1?±?0.8% (SD, n?=?4).     

Thermal cyclotron radiation by isolated magnetic white dwarfs and constraints on the parameters of their coronas

An efficient method for the detection and estimation of the parameters of the coronas of isolated white dwarfs possessing magnetic fields of about 10⁷ G is tested. This method is based on the detection of thermal radiation of the coronal plasma at harmonics of the electron gyrofrequency, which is manifest as a polarized infrared excess. The Stokes parameters for the thermal cyclotron radiation from the hot corona of a white dwarf with a dipolar magnetic field are calculated. A new upper limit for the electron density, 10¹⁰ cm^?3, in a corona with a temperature of ?10⁶ K is found for the white dwarf G99-47 (WD 0553+053). This limit is a factor of 40 lower than the value derived earlier from ROSAT X-ray observations. Recommendations for subsequent infrared observations of isolated magnetic white dwarfs aimed at detecting their coronas or deriving better constraints on their parameters are presented.     

A search for small-scale clumpiness in dense cores of molecular clouds

We have analyzed HCN(1-0) and CS(2-1) line profiles obtained with high signal-to-noise ratios toward distinct positions in three selected objects in order to search for small-scale structure in molecular cloud cores associated with regions of high-mass star formation. In some cases, ripples were detected in the line profiles, which could be due to the presence of a large number of unresolved small clumps in the telescope beam. The number of clumps for regions with linear scales of ～0.2–0.5 pc is determined using an analytical model and detailed calculations for a clumpy cloud model; this number varies in the range: ～2 × 10⁴–3 × 10⁵, depending on the source. The clump densities range from ～3 × 10⁵–10⁶ cm^?3, and the sizes and volume filling factors of the clumps are ～(1–3) × 10^?3 pc and ～0.03–0.12. The clumps are surrounded by inter-clump gas with densities not lower than ～(2–7) × 10⁴ cm^?3. The internal thermal energy of the gas in the model clumps is much higher than their gravitational energy. Their mean lifetimes can depend on the inter-clump collisional rates, and vary in the range ～10⁴–10⁵ yr. These structures are probably connected with density fluctuations due to turbulence in high-mass star-forming regions.     

Crystallization kinetics during regional metamorphism of porphyroblastic rocks

Numerical simulations of diffusion‐controlled nucleation and growth of garnet porphyroblasts in regionally metamorphosed rocks constrain interfacial energy and rates of nucleation and Al intergranular diffusion. The 13 rocks analysed in this study were collected from seven localities exhibiting a diverse range of crystallization conditions. Kinetic parameters governing nucleation and intergranular diffusion were adjusted iteratively to achieve fits between simulated and natural porphyroblastic textures. Model fits were assessed primarily from textural characteristics precisely measured by high‐resolution X‐ray computed tomography. Interfacial energy for heterogeneous nucleation ranges from 0.007 to 0.255 J m^?2 for the sample suite, assuming shape factors in the range 0.01–1.0. Nucleation rates change through space and time due to growth and impingement of Al depletion zones surrounding porphyroblasts. In some models, the overall rock‐wide nucleation rate rises steeply, achieves a steady state, and then falls rapidly as reactants are consumed; in others, the steady state is not achieved, but instead the rate simply peaks before falling. Maximum rock‐wide nucleation rates range from 10^?14.7 to 10^?10.7 nuclei cm^?3 s^?1, and maximum local rates range from 10^?13.7 to 10^?9.7 nuclei?cm^?3 s^?1 depending on Al supersaturation. Diffusive fluxes of Al are well constrained by the simulated textures, but rates of intergranular diffusion are subject to uncertainties in Al solubility and interconnected porosity. Best estimates of Al diffusivities at 600 °C span 10^?12.3 to 10^?10.5 m² s^?1 for the sample suite, a narrow range considering natural variability and the uncertainties in solubility and porosity. Eliminating some models suspected of higher uncertainty for these quantities yields diffusivities at 600 °C near 10^?11.0 m² s^?1, with dispersion of less than half an order of magnitude. These simulations, which are among the first attempted for regionally metamorphosed rocks, emphasize that: (i) nucleation rates vary markedly in time and space during crystallization; (ii) nucleation extends well beyond equilibrium conditions; (iii) Al diffusivity likely varies over only a narrow range across common metamorphic circumstances; and (iv) better determinations of both Al solubility and interconnected porosity are needed to constrain rates of Al intergranular diffusion more precisely.     

Late stages of the evolution of close compact binaries: Type I supernovae,gamma-ray bursts,and supersoft X-ray sources

We consider the evolution of close binaries resulting in the most intensive explosive phenomena in the stellar Universe—Type Ia supernovae and gamma-ray bursts. For Type Ia supernovae, which represent thermonuclear explosions of carbon-oxygen dwarfs whose masses reach the Chandrasekhar limit during the accretion of matter from the donor star, we derive the conditions for the accumulation of the limiting mass by the degenerate dwarf in the close binary. Accretion onto the degenerate dwarf can be accompanied by supersoft X-ray radiation with luminosity 1–10⁴ L _⊙. Gamma-ray bursts are believe to accompany the formation and rapid evolution of compact accretion-decretion disks during the formation of relativistic objects—black holes and neutron stars. The rapid (～1 M _⊙/s) accretion of matter from these disks onto the central compact relativistic star results in an energy release of ～0.1 M _⊙ c ² ～ 10⁵³ erg in the form of gamma-rays and neutrinos over a time of 0.1–1000 s. Such disks can form via the collapse of the rapidly rotating cores of Type Ib, Ic supernovae, which are components in extremely close binaries, or alternately due to the collapse of accreting oxygen-neon degenerate dwarfs with the Chandrasekhar mass into neutron stars, or the merging of neutron stars with neutron stars or black holes in close binaries. We present numerical models of the evolution of some close binaries that result in Type Ia supernovae, and also estimate the rates of these supernovae (～0.003/year) and of gamma-ray bursts (～10^?4/year) in our Galaxy for various evolutionary scenarios. The collimation of the gamma-ray burst radiation within an opening angle of several degrees “matches” the latter estimate with the observed rate of these events, ～10^?7–10^?8/year calculated for a galaxy with the mass of our Galaxy.     

Copper in surface waters of the Bering Sea

Copper concentrations have been measured in surface <75 m waters of the central Bering Sea. Concentrations of 2–4 nmole kg^?1 were measured in the Zhemchung Canyon region where water depths are greater than 1000 m. Concentrations are higher 2–25 nmole kg^?1 on the shallow <100 m continental shelf, inshore of a hydrographic front at the 100 m isobath. Copper-depth profiles on the continental shelf water mass are dominated by Cu concentrations increasing toward the sediments. These trends may be maintained by a flux of Cu from surficial sediments. A frontal system over the 100 m isobath acts to control the flux of Cu, a significant part of which apparently emanates from the sediments, between the continental shelf and the central Bering Sea basin. The benthic shelf Cu flux was constrained to be less than 3 nmole cm^?2 yr^?1.     

Surface chemistry and dissolution kinetics of glassy rocks at 25°C

The weathering rates and mechanisms of three types of glassy rocks were investigated experimentally at 25 °C, pH 1.0 to 6.2, and reaction times as much as to 3 months. Changes in major element chemistry were monitored concurrently as a function of time in the aqueous solution and within the near surface region of the glass. Leach profiles, obtained by a HF leaching technique, displayed near-surface zones depleted in major cations. These zones increased in depth with increasing time and decreasing pH of reactions. Release rates into the aqueous solution were parabolic for Na and K and linear for Si and Al. A coupled weathering model, involving surface dissolution with concurrent diffusion of Na, K, and Al, produced a mass balance between the aqueous and glass phases. Steady state conditions are reached at pH 1.0 after approximately 3 weeks of reaction. Steady-state is not reached even after 3 months at pH 6.2.An interdiffusion model describes observed changes in Na diffusion profiles for perlite at pH 1.0. The calculated Na self-diffusion coefficient of 5 × 10^?19 cm²·s^?1 at 25°C approximates coefficients extrapolated from previously reported high temperature data for obsidian. The self-diffusion coefficient for H₃O⁺, 1.2 × 10^?20 cm²·s^?1, is similar to measured rates of water diffusion during hydration of obsidian to form perlite.     

Effect of coulomb losses on the spectra of heavy particles accelerated in prolonged solar events

This paper examines the possibility of using the energy spectra of accelerated solar cosmic-ray ions and features formed by Coulomb losses to study the solar plasma (the power-law index S for the scattering turbulence, particle number density N, and temperature T of the background medium). For an individual solar flare, Coulomb losses can be manifest to different degrees in the spectra of different ions, providing a means to determine S. A comparison of theoretical spectra for H, He, C, O, and Fe ions with observed spectra for the prolonged solar flare of October 20, 1995 yields S≈3, N≈5×10⁹ cm^?3, and T≈10⁶ K, assuming that the characteristic time scale over which these particles gain energy is about a second.