Jet structure of electric currents in coronal magnetic loops

We analyze the properties of the electric-current distribution over the cross sections of fairly dense coronal magnetic flux tubes in which the plasma pressure exceeds the magnetic pressure, so that the equilibrium is maintained by the ambient magnetic field. If the plasma is fully ionized, the distributions of the longitudinal and azimuthal currents over the cross section of the loop have the same spatial scale as the pressure distribution. However, even a small number of neutral atoms in the corona (with a mass fraction of the order of 10^?5, taking into account the partial ionization of helium) substantially modifies the current distribution over the tube cross section: in this case, a considerable fraction of the full current flowing along the tube is concentrated in a thin region near the axis with a radius of the order of (10^?2–10^?3)r ₀ (where r ₀ is the characteristic scale of the plasma-pressure distribution over the tube), thus forming a sort of a jet current. This comes about because the pattern of the conductivity anisotropy is substantially modified in the presence of ion-atom collisions in the magnetoactive plasma of the tube, and the Cowling conductivity dominates over the Hall and Pedersen conductivities. The high current density near the axis of the tube can ensure heating of the plasma to coronal temperatures via Joule dissipation.     

Formation of Abnormal Gas-Geochemical Fields of Methane,Helium, and Hydrogen in Northern Vietnam,Its Coastal and Adjacent Water Areas

Lithology and Mineral Resources - Gas-geochemical studies of the methane, helium, and hydrogen concentrations in the water of thermal and mineral springs, as well as the subsurface atmosphere, of...     

The role of metals in cooling gas behind shock fronts in the atmospheres of cool stars

The influence of various chemical elements on radiative cooling of the gas flowing from a viscous jump is investigated in a model with a stationary shock in the atmosphere of a cool star. A closed system of equations is written for the thermal energy per heavy particle, the electron temperature, and the relative concentrations of elements in all ionization states. In addition to hydrogen and helium, atomic, singly ionized, and doubly ionized carbon, nitrogen, oxygen, sodium, magnesium, aluminum, silicon, sulfur, potassium, calcium, and iron are included, assuming they have their normal cosmic abundances. The high optical depth in Lyman-series lines leads to a return of the thermal energy to electrons via secondary collisions. As a result, the contribution of hydrogen to the cooling rate falls to the level of the contribution of metals, mainly carbon, magnesium, and iron. Thus, such shock models are able to explain the presence of bright metal lines in the spectra of cool and solar-type stars.     

The diffusional evolution of chemical composition in a solar model

We consider the basic physical processes resulting in a differential, microscopic redistribution of stellar matter, generally known as diffusion. The main effect of diffusion in the solar interior is a segregation of light and heavy elements in the gravitational field. As a result, the abundance of helium and heavy elements in the solar envelope is reduced, while it becomes enriched by hydrogen. We present estimates of the degree of settling for a sequence of evolutionary models via numerical solution of the generalized diffusion equation. The effect of the ion charge (in the approximation of full ionization) on the settling rate is studied in detail. Abundance variations are given for the centers of the models, as well as for the convective envelope of the modern Sun. We analyze the effects of the thermal and concentrational diffusion on the evolution of the chemical-composition profile. Quantitatively, the effect of thermal diffusion is not very large, but it leads to the appearance of new features in the hydrogen-abundance profile, namely, a discontinuity at the base of the convective zone. The effect of concentration diffusion is relatively small, and is appreciable only at the model center at late stages of the evolution, and also close to the base of the convective envelope. All the mechanisms studied are necessary components of a modern model for the internal structure and evolution of the Sun.     

The effect of the ionization rate on the chemical composition of dense cores of dark molecular clouds

The effect of variations in the rate of ionization of neutral chemical species by cosmic rays, ζ, on the abundances of some observed molecules in the dense cores of dark molecular clouds is studied. Changes in molecular abundances accompanying an increased (decreased) ionization rate have a single origin: the acceleration (deceleration) of processes that are affected directly or indirectlybychemical reactions with charged species. In addition to affecting the gas-phase chemistry, an increased cosmic-ray flux leads to the more efficient destruction of dust-grain mantles and also accelerates the freezing of some components onto dust. In particular, in a model with an increased ζ, the destruction of the volatile N₂ molecule by ionized helium leads to the rapid accumulation of nitrogen atoms in dust-phase ammonia, which has a higher desorption energythan N₂. As a result, the gas-phase abundance of NH₃ and N₂H⁺ decreases significantly. This mechanism can explain the unusual chemical structures of some dense globules, such as B68, where surprisingly low abundances of nitrogen-bearing molecules are observed together with a central drop in the NH₃ and N₂H⁺ column densities. Observations of clouds in HCN and HNC lines can discriminate between the two possible origins of the reduced NH3 and N₂H⁺ abundances: an increased cosmic-ray flux or N₂ freezing due to the higher desorption energy of this molecule.     

Distribution of helium and hydrogen in sediments and water on the Sakhalin slope

During the geological survey and prospecting, helium and hydrogen are recognized indicators of minerals, deep-seated faults, seismic activity, and ascending deep fluids. Their anomalous concentrations also serve as a marker of metamorphic processes. Helium survey is applied for tracing deep-seated faults and mapping permeable zones. In this work, the first results of gas geochemical survey in marine sediments and water to study the distribution of helium and hydrogen and their relation with the seismic activity of some geological structures in the southwestern Sea of Okhotsk and northern Sea of Japan. Anomalies of these gases (He up to 60 ppm, H up to 120 ppm) were identified in the hydrate-bearing sediments in the fault zones. It was also found that helium concentrations in the water column of the Tatar Strait are higher than in the studied area of the Sea of Okhotsk, possibly, due to the difference in geological structure and seismotectonic activation. Moreover, coal layers could be a significant source of methane in the gashydrate-bearing layers of the Tatar Strait.     

The chemical composition of galactic planetary nebulae: Optimization photoionization modeling

Optimization photoionization models are computed for nine planetary nebulae with various metallicities with the aim of determining their chemical compositions. The algorithm used to compute the models is based on identifying best-fit values of the physical parameters of the nebulae by minimizing the χ² residual for fits to the observed spectra of these objects. The reliability of the results is investigated. The abundances of He, C, N, O, Ne, Si, S, and Ar are derived, as well as the physical characteristics of the nebulae. The Y -Z dependences (where Y and Z are the mass abundances of helium and heavy elements, respectively) are analyzed for the planetary nebulae together with HII regions in blue compact dwarf galaxies. The primordial helium abundance, Y _p = 0.2479 ± 0.0014, and dY/dZ = 2.99 ± 0.32 are determined, and found to be close to the corresponding values obtained using ionization correction factors.     

Hydrothermal gases offshore Milos Island, Greece

Hydrothermal fluids emerge from the seafloor of Paleohori Bay on Milos. The gases in these fluids contain mostly CO₂ but CH₄ concentrations up to 2% are present. The stable carbon isotopic composition of the CO₂ (near 0%) indicates an inorganic carbon source (dissociation of underlying marine carbonates). The carbon and hydrogen isotopes of most CH₄ samples are enriched in the heavy species (δ¹³C = −9.4 to −17.8‰; δD = −102 to −189‰) which is believed to be characteristic for an abiogenic production of CH₄ by CO₂-reduction (Fischer-Tropsch reactions). Depletions in the deuterium content of three CH₄ samples (to −377%) are probably caused by unknown subsurface rock alteration processes. Secondary hydrogen isotope exchange processes between methane, hydrogen and water are most likely responsible for calculated unrealistic methane formation temperatures.

We show that excess helium, slightly enriched in ³He, is present in the hydrothermal fluids emerging the seafloor of Paleohori Bay. When the isotopic ratio of the excess component is calculated a ³He/⁴He_excess of 3.6 · 10⁻⁶ is obtained: This indicates that the excess component consists of about one third of mantle helium and two thirds of radiogenic helium. We infer that the mantle-derived component has been strongly diluted by radiogenic helium during the ascent of the fluids to the surface.     

Collision-induced absorption of radiation in the atmospheres of late-type stars

Problems associated with taking into account absorption induced by collisions between hydrogen and helium atoms, helium atoms and hydrogen molecules, and hydrogen molecules, resulting in the formation of short-lived, quasi-molecular complexes are discussed, together with opacity in the atmospheres of late-type stars due to such absorption. There is good agreement between such opacities computed using codes developed by the author and by R. Kurucz. To demonstrate the importance of including collision-induced opacity, theoretical fluxes are compared to the observed spectral energy distribution of the metal-poor L subdwarf SDSS J125637.13-022452.4. The spectral energy distribution of this object can be reproduced with an effective temperature of T_eff = 2600 K only if collision-induced absorption is taken into account.     

Determination of naphthenic acids in crude oil by chemical ionization mass spectrometry

Naphthenic acids in petroleum are considered a class of biological markers. Their potential use in source correlation and as an indicator of biodegradation was reported in the past ( Dzidic et al. ,1988 ; Behar and Albrecht, 1984). Due to their highly complicated properties, detailed characterization of the acids is difficult. A method based on positive ion CI (chemical ionization) mass spectrometry using isobutane reagent gas to produce ( M 15)^ ions was applied to the analysis of naphthenic acid esters. Since the complex mixture of naphthenic acids cannot be separated into individual components, only the determination of relative distribution of acids classified in terms of hydrogen deficiency was possible. The identities and relative distribution of fatty and mono-, di-, tri-, and higher polycyclic acids were obtained from the intensities of the ( M 15 )^ ions according to z-series formula CπH2π 2 O2 of naphthenic acids. The components are characterized on the basis of group type and carbon number distributions. A comparison of the FAB and CI results showed that the group type distributions obtained bv both methods agree surprisingly well.The results indicated this method is simple, rapid and easy to operate. The geochemical implication of naphthenic acids was investigated by using a set of well-characterized crude oil samples. It is found that the naphthenic acid distribution can be used as a fingerprint for oil-oil and oil-source correlations.     

榴辉岩相高压-超高压变质岩的He同位素地球化学研究现状与问题

He同位素是区分地壳、地幔物质,研究壳-幔相互作用最灵敏的示踪剂之一,但其在高压-超高压变质作用过程中的地球化学行为目前仍不清楚,因而制约其在榴辉岩研究中的应用。中国作为高压-超高压榴辉岩带分布的重要地区,榴辉岩产出得天独厚,大洋、大陆两种俯冲成因榴辉岩均有分布。本文在归纳榴辉岩相高压-超高压变质岩研究进展的基础上,分析了He同位素示踪在榴辉岩研究中的应用现状。     

Activation energy for diffusion of helium in water-saturated, compacted Na-montmorillonite

It is important to clarify the migration behavior of hydrogen gas dissolved in water-saturated, compacted bentonite, which is a promising material for geologic disposal of high-level waste and TRU waste disposal. The diffusion coefficients of helium, which can be detected under extremely low background conditions, in water-saturated, compacted Na-montmorillonite were determined as a function of temperature by a transient diffusion method. The activation energies for diffusion of helium were then obtained. The activation energies were from 6.9 ± 4.8 to 19 ± 2.8 kJ mol^− 1 and were regarded to be independent of dry density. The activation energies of helium in water-saturated Na-montmorillonite were roughly equal to those in bulk water, 14.9 kJ mol^− 1, and in ice, from 11 to 13 kJ mol^− 1. It is possible that helium diffuses not only in pore water but also in interlayer water.     

Deepwater helium in Lake Baikal as an earthquake precursor

In this paper, attention is paid to the importance of short-term prognosis of earthquakes. The variability of determination methods is noted. One of the geochemical methods, based on study of the helium content in deep water of Lake Baikal, is considered; such a method has not been used for open deep-water basins within the zones of high seismic danger. It is established that in the period of earthquake preparation, variations in the helium content deep underwater in Lake Baikal are recorded. A sharp decrease in the helium content two days before the earthquake was recorded first time for a long period of observation, as well as the consequent increase. Further study of the helium content deep underwater in Lake Baikal is recommended, and, should these data be proved, it is recommended as a short-term precursor of earthquakes.     

The possibility of resonance-enhanced two-photon ionization of Ne and Ar atoms in astrophysical plasmas

We consider possible schemes for the resonance-enhanced two-photon ionization (RETPI) of Ne and Ar atoms under the action of bichromatic radiation of intense resonance lines of HI, HeI, and HeII in a radiation-rich astrophysical plasma. The ionization rate is comparable to or exceeds the recombination rate in rarified astrophysical plasma, which leads to the accumulation of singly ionized ions with a subsequent transition to the higher ionization state via RETPI. We consider the RETPI reaction chains NeI → ... → NeV and ArI → ... → ArVI.     

Disk wind in the radiation of young intermediate-mass stars

We consider the role of the disk wind in the formation of hydrogen emission spectra of young intermediate-mass Herbig Ae stars. The assumed parameters for the kinematic characteristics of the wind region are typical of the theory of magnetocentrifugal disk winds. Our computations of the excitation and ionization states for atoms in the emitting region are based on the Sobolev approximation for a medium with a large velocity gradient. The calculations show that hydrogen-line emission profiles can have a complex structure that depends on the disk-wind parameters, as well as on the system’s orientation relative to the line of sight. The model proposed is able to explain most types of Hα profiles observed for Herbig Ae stars.     

Evaluating thermal history models for the Otway Basin, southeastern Australia, using (U-Th)/He and fission-track data from borehole apatites

New apatite helium and fission-track data from the Otway Basin are consistent with previously published borehole ages, confirming earlier suggestions that existing thermal models for basin evolution should be reevaluated. Analysis of the relationship between helium ages and grain size in newly analyzed samples, as well as in samples previously reported, reveals that grain size variations may contribute to the previously reported scatter in helium ages among aliquots of the same sample. In addition, systematic variations in apatite grain size with borehole depth or temperature may also have a significant effect on the interpretation of borehole helium age data. Incorporation of the observed grain size variations in Otway borehole apatites into forward models based on published thermal histories, principally based on vitrinite reflectance and fission-track data, suggests that existing models for the eastern Otway Basin are broadly consistent with the helium data. In contrast, thermal histories for western basin boreholes, now thought to be at maximum temperatures, predict helium ages that are generally older than the observed ages, implying that basin temperatures were hotter than indicated by the models. This discrepancy is consistent with a Cenozoic heating event in parts of the western Otway Basin similar to that documented for the eastern basin. The relatively wide spread of apparent apatite fission-track (AFT) ages and compositions compared to the restricted age range of helium measurements on coexisting grains, although not conclusive, supports previous suggestions that composition does not appear to affect the sensitivity of the He closure temperature in apatite.     

Studies on gas biogeochemistry in the near-bottom environment of aquatic areas

An integrated methodology developed by the authors for studies on marine gas biogeochemistry was used. The new data are presented for a wide variety of gas biogeochemical parameters measured synchronously in the near-bottom environment (in water and sediments). As the background, abnormally high values were found for gaseous components (hydrocarbons, helium, hydrogen, carbon dioxide, permanent gases) and for biochemical parameters (adenosine triphosphate (ATP), biomass of active living microorganisms by ATP (ALMB), various enzymatic activities, dissolved organic carbon (C_org), carbamide nitrogen, etc.). The new data set obtained allowed us to discover the effect of chemolite autotrophy in local near-bottom ecosystems. The appearance of chemolite autotrophy in the upper layer of sediment points to the occurrence of this effect in deeper layers of the sediment mass as well, as a result of deep gas fluxes. It is shown that the effect of chemolite autotrophy must be taken into account in estimating the oil and gas resources, especially in view of their continual replenishment.     

鄂尔多斯盆地东胜富氦气田成藏特征及其大地构造背景*

近年来,在鄂尔多斯盆地北缘东胜气田上古生界天然气中发现伴生的氦气,含量分布在0.045%~0.487%范围内,具有工业价值,其三级储量约为8.3亿立方米,为一特大型含氦—富氦天然气田。东胜气田氦气属于典型的壳源氦,来源于基底的太古界—元古界变质岩—花岗岩系,富集与燕山期以来的岩浆侵入、断裂活动有关。东胜气田具备有利的氦气成藏地质条件,伴生氦气与烃类气具有异源同储成藏特征,剖析其成藏主控因素为: 基底富U、Th岩石发育是基础,断裂活动是核心,储盖圈保条件是必备,时空配置是关键,其中早白垩世是最重要的一期构造—岩浆热事件,深源岩浆活动导致的深部物质和热能的大规模上涌是中生代流体成藏(矿)的有利地球动力学背景,控制了鄂尔多斯盆地石炭系—二叠系煤系烃源岩大规模生气。断裂活动和圈闭形成与上古生界天然气、氦气聚集成藏具有良好的时空配置关系,与华北克拉通破坏过程耦合。鄂尔多斯地块在早白垩世至中新世深部热流体对盆地发生的多期岩浆活动、基底断裂活化及浅部断裂活动具有明显的控制作用,同时也对石炭系—二叠系煤系烃源岩成烃成藏具有重要的控制作用。