The possible escape of electron cyclotron maser radiation from hot stellar coronas through a window of transparency

The main argument against the idea that the intense radio emission observed from active regions on the Sun and flare stars is electron-cyclotron maser (ECM) radiation is that such radiation should be strongly absorbed in higher-lying layers where the condition for the cyclotron resonance at harmonics of the electron gyrofrequency is fulfilled. Cyclotron absorption lowers the efficiency of ECM radiation virtually to zero for a broad range of angles between the direction of propagation of the radiation and the magnetic field. Less severe absorption is possible only in narrow angular “windows” along (for ordinary and extraordinary waves) and perpendicular to (for ordinary waves) the magnetic field. However, the ECM radiation that is generated does not fall into these windows of transparency due to the kinematic conditions corresponding to coronal magnetic traps. We investigate the efficiency of induced scattering of ECM radiation on ions in the equilibrium plasma in the source. Under certain conditions, induced scattering leads to the formation of a condensate of ECM radiation with the direction of its wave vectors approximately along the magnetic field, enabling the escape of the radiation through windows of transparency. The most favorable conditions for this phenomenon are realized for ordinary waves. We estimate the optical depths of the sources of the ECM radiation to the scattering and the angular width of the condensate for ordinary and extraordinary waves for the cases of the flare radio emission of the star AD Leo and the sources of type I noise storms in the solar corona. In both cases, the polarization of the emergent radiation should correspond to the ordinary wave.     

Formation of the accretion disk in the SS 433 system with explicit radiative cooling,convective heat conduction,and radiation pressure

The paper continues three-dimensional hydrodynamical computations of the formation of an accretion disk in the SS 433 system, taking into account radiative cooling explicitly, convective thermal conductivity, and radiation pressure. The computational results show that the powerful, broad flow forms an optically thick accretion disk with a gas density of 10¹²–10¹⁴ cm^?3, a temperature of 15000–35 000 K, a radius of about 0.3, and a height of 0.2–0.3 (in units of the component separation). Spiral shocks form in the disk, and a narrow conelike cavity (tunnel) forms at the center. In this tunnel, gas is accelerated to relativistic speeds, leaving the system in the form of narrow jets.     

Radial-velocity curves and theoretical spectral-line profiles of the components of low-mass close X-ray binary systems

We present the results of calculations of theoretical absorption-line profiles and radial-velocity curves for optical components in X-ray binary systems. Tidal distortion of the optical star and X-ray heating by incident radiation from the relativistic object are taken into account. An emission component forms whose intensity varies with orbital phase in the absorption-line profile in the presence of significant X-ray heating. As a result, the width of the line decreases rather than increases at quadrature. The line profiles and equivalent widths and the radial-velocity curves depend substantially on the parameters of the binary systems. This provides the possibility of directly determining component masses and orbital inclinations from high-resolution spectroscopic observations of X-ray binary systems.     

Gamma-ray radiation with energy 2.223 MeV and the density distribution in the solar atmosphere during flares

Interactions of particles accelerated in solar flares with matter in the solar atmosphere give rise to neutrons, which are efficiently captured on hydrogen nuclei as they are slowed to thermal velocities. This capture is accompanied by the emission of a gamma-ray with energy 2.223 MeV. Observational data for the temporal profiles of the gamma-ray fluxes in this line are used to study the plasma-density distribution in the solar atmosphere during the flares of December 16, 1988, March 22, 1991, and November 6, 1997. This analysis is based on comparisons between the observations and profiles computed taking into account a number of parameters describing the generation and transport of the flare neutrons in atmospheric layers of various densities. In three cases studied, the density of the material in the photosphere below the flare region is enhanced compared to the density in an unperturbed part of the solar atmosphere at the same height. In the case of the December 16, 1988 flare, we are able for the first time to relate the profile of the 2.223 MeV line with the shape of the accelerated particle (proton) spectrum. This opens new possibilities for studies of particle acceleration on the Sun based on observations of flare gamma-ray emission.     

The phase matrix for scattering in a weak magnetic field. The Hanle effect

A new formulation for the phase matrix for the scattering of radiation in a weak magnetic field is presented. The phase matrix is represented as a product of individual matrices that depend on the angle of incidence and the scattering angle. It is shown that the Hanle effect is absent in observations of scattered light in the solar atmosphere when the magnetic field is perpendicular to the atmosphere. In strong magnetic fields, the phase matrix depends only on the direction of the magnetic field relative to the basic coordinate system.     

Retrofit-reinforcement of cohesive soil slopes using high strength geotextiles with drainage capability

A series of geotechnical centrifuge physical modeling tests were performed to assess the potential use of a new cost-effective mechanically stabilized earth system for retrofitting marginally stable cohesive slopes. The proposed system utilizes the dual functions of reinforcement and drainage by directly inserting high strength non-woven geotextile strips into slopes, with little or no excavation required behind the slope face. The system significantly increases the factor of safety of potentially unstable cohesive slopes, and can be constructed at less expense and more rapidly than conventional mechanically stabilized earth systems.     

Variation in nitrate and calcium as indicators of recharge pathways in Nolte Spring, PA

This study documents variations in calcium and nitrate concentrations that suggest changes in recharge pathways in a karst spring. The nitrate concentrations increased at the end of the growing season, showing the importance of the soil zone in the recharge pathway. The increase occurred over just a few days, which may be indicative of a change in contribution of baseflow in different seasons from deep to shallow groundwater. The calcium concentrations decreased several days after storm events. A change in the carbonate equilibrium is hypothesized because chloride was not diluted during these events. The decrease in calcium could be due to outgassing and calcite precipitation in the recharge area when older, higher ionic strength matrix water mixes with stormwater in open conduits. The use of geochemical indicators to better understand recharge pathways benefited from long-term monitoring and periods of daily sampling.     

Magmatic zircon oxygen isotopes of 1.88–1.87 Ga orogenic and 1.65–1.54 Ga anorogenic magmatism in Finland

Summary Oxygen isotope ratios of igneous zircon from magmatic rocks in Finland provide insights into the evolution and growth of the Precambrian crust during the Svecofennian orogeny. These data preserve magmatic δ¹⁸O values and correlate with major discontinuities in the lower crust. Oxygen isotope ratios of zircon across the 1.88–1.87 Ga Central Finland granitoid complex (CFGC) range from 5.50‰ to 6.84‰, except for three plutons in contact with the adjacent greenstone and metasedimentary belts (δ¹⁸O(Zrc) = 7.60‰–7.78‰). There is a systematic variation in δ¹⁸O(Zrc) with respect to geographic location in the CFGC, ranging from 6.60±0.23‰ (σ) in the northeast to 5.90±0.40‰ in the west-southwest. These values correlate with a change in crustal thickness and shift in geochemical composition. The oxygen isotope composition of the 1.65–1.54 Ga rapakivi granites and related rocks in southern Finland show a decreasing trend from north to south, independent of their emplacement age. The southern anorogenic granite group has an average δ¹⁸O in zircon of 6.14±0.07‰ and the northern anorogenic group has an average δ¹⁸O in zircon of 8.14±0.59‰. This difference reflects the boundary between island arc terrains accreted during the Paleoproterozoic. Deceased     

Uncertainty in adaptive capacity

The capacity to adapt is a critical element of the process of adaptation: it is the vector of resources that represent the asset base from which adaptation actions can be made. Adaptive capacity can in theory be identified and measured at various scales, from the individual to the nation. The assessment of uncertainty within such measures comes from the contested knowledge domain and theories surrounding the nature of the determinants of adaptive capacity and the human action of adaptation. While generic adaptive capacity at the national level, for example, is often postulated as being dependent on health, governance and political rights, and literacy, and economic well-being, the determinants of these variables at national levels are not widely understood. We outline the nature of this uncertainty for the major elements of adaptive capacity and illustrate these issues with the example of a social vulnerability index for countries in Africa. To cite this article: W.N. Adger, K. Vincent, C. R. Geoscience 337 (2005).