Gamma-Ray Spectral Characteristics of Thermal and Non-Thermal Emission from Three Black Holes

Cygnus X-1 and the gamma-ray transients GROJ0422+32 and GROJ1719-24 displayed similar spectral properties when they underwent transitions between the high and low gamma-ray (30 keV to few MeV) intensity states. When these sources were in the high gamma-ray intensity state (gamma-2, for Cygnus X-1), their spectra featured two components: a Comptonized shape below 200-300 keV with a soft power-law tail (photon index >3) that extended to ~1 MeV or beyond. When the sources were in the low-intensity state (gamma-0, for Cygnus X-1), the Comptonized spectral shape below 200 keV typically vanished and the entire spectrum from 30 keV to ~1 MeV can be characterized by a single power law with a relatively harder photon index ~2-2.7. Consequently the high- and low-intensity gamma-ray spectra intersect, generally in the ~400 keV - 1 MeV range, in contrast to the spectral pivoting seen previously at lower (~10 keV) energies. The presence of the power-law component in both the high- and low-intensity gamma-ray spectra strongly suggests that the non-thermal process is likely to be at work in both the high and the low-intensity situations. We have suggested a possible scenario (Ling & Wheaton, 2003), by combining the ADAF model of Esin et al. (1998) with a separate jet region that produces the non-thermal gamma-ray emission, and which explains the state transitions. Such a scenario will be discussed in the context of the observational evidence, summarized above, from the database produced by EBOP, JPL's BATSE earth occultation analysis system.Comment: 6 pages, 3 figures, accepted for publication in Proceedings of 2004 Microquasar Conference, Beijing, China, Chinese Journal of Astronomy and Astrophysics, minor corrections per refere

Real Estate and the Tax Reform Act of 1986

In contrast to the conventional wisdom, real estate activity in the aggregate is not disfavored by the 1986 Tax Act. Within the broad aggregate, however, widely different impacts are to be expected. Regular rental and commercial activity will be slightly disfavored, while historic and old rehabilitation activity will be greatly disfavored. In contrast, owner- occupied housing, far and away the largest component of real estate, is favored, both directly by an interest rate decline and indirectly owing to the increase in rents. Low-income rental housing may be the most favored of all real estate activities. The rent increase for residential properties will be 10 to 15 percent with our assumption of a percentage point decline in interest rates. For commercial properties, the expected rent increase is 5 to 10 percent. The market value decline, which will be greater the longer and further investors think rents will be below the new equilibrium, is unlikely to exceed 4 percent in fast growth markets, even if substantial excess capacity currently exists. In no-growth markets with substantial excess capacity, market values could decline by as much as 8 percent from already depressed levels. Average housing costs will decrease slightly for households with incomes below about $60,000, but increase by 5 percent for those with incomes above twice this level. With the projected increase in rents, homeownership should rise for all income classes, but especially for those with income under$60,000. The aggregate home ownership rate is projected to increase by three percentage points in the long run in response to the Tax Act. The new passive loss limitations are likely to lower significantly the values of recent loss-motivated partnership deals and of properties in areas where the economics have turned sour (vacancy rates have risen sharply). The limitations should have little impact on new construction and market rents, however. Reduced depreciation write-offs, lower interest rates, and higher rents all act to lower expected passive losses. Moreover, financing can be restructured to include equity-kickers or less debt generally at little loss of value.

Understanding the Real Estate Provisions of Tax Reform: Motivation and Impact

Capital investment tax provisions have been changed numerous times in the last decade, with depreciation tax lives shortened in 1981 and lengthened ever since and capital gains taxation reduced in 1978 and 1981 and now increased. The first part of this paper analyzes these changes and attributes a large part of them, including the 1986 Tax Act, to changes in inflation: tax depreciation schedules and capital gains taxation that look reasonable when the tax depreciation base is being eroded at ten percent a year and an overwhelming share of capital gains is pure inflation take on a different appearance when inflation is only four percent. The remainder of the paper critiques the typical project model used to compute impacts of tax changes on real estate and report simulation results using a modified model.

Hierarchical structural design for fracture resistance in the shell of the pteropod Clio pyramidata

The thecosomes are a group of planktonic pteropods with thin, 1 mm-sized aragonitic shells, which are known to possess a unique helical microstructure consisting of interlocking nanofibres. Here we investigate the detailed hierarchical structural and mechanical design of the pteropod Clio pyramidata. We quantify and elucidate the macroscopic distribution of the helical structure over the entire shell (~1 mm), the structural characteristics of the helical assembly (~10–100 μm), the anisotropic cross-sectional geometry of the fibrous building blocks (~0.5–10 μm) and the heterogeneous distribution of intracrystalline organic inclusions within individual fibres (<0.5 μm). A global fibre-like crystallographic texture is observed with local in-plane rotations. Microindentation and electron microscopy studies reveal that the helical organization of the fibrous building blocks effectively constrains mechanical damages through tortuous crack propagation. Uniaxial micropillar compression and cross-sectional transmission electron microscopy directly reveal that the interlocking fibrous building blocks further retard crack propagation at the nanometre scale.National Science Foundation (U.S.) ((Massachusetts Institute of Technology. Center for Materials Science and Engineering (DMR-0819762))United States. Army Research Office (Massachusetts Institute of Technology. Institute for Soldier Nanotechnologies (Contract W911NF-07-D-0004))United States. Department of Defense. National Security Science and Engineering Faculty Fellow

How immigration makes income inequality worse in the US

The past thirty years have seen a dramatic rise in income inequality in the US. While many economists have pointed to the rise of low-skilled immigration as a contributor to income inequality in developed countries, there has been little evidence from the US. In new research, Ping Xu, James C. Garand, Ling Zhu, find that the low-skilled immigration in the US does increase income inequality due to the downward pressure it puts on wages, and immigrants’ lack of access to federal welfare benefits. They write that to reduce inequality, US immigration policy should shift towards admitting more high-skilled immigrants or incorporating existing immigrants into the social welfare system

Imported Inequality? Immigration and Income Inequality in the American States

In this article, we use data from the American states from 1996 to 2008 to explore the effects of immigration on income inequality. Empirical evidence from both static and dynamic models shows that the foreign-born population has a strong positive effect on state-level income inequality, even when we control for a range of federal and state political and economic contextual variables. We also find that the positive relationship between immigration and state income inequality is driven primarily by low-skill immigrants (rather than high-skill immigrants), and we provide some evidence that high-skill immigrants lower income inequality for some segments of the income distribution. We conclude that immigration—particularly low-skilled immigration—has an important effect on income inequality in the American states

Low Energy Gamma-Ray Emission from Galactic Black Holes

X-ray observations of Galactic black holes (GBHs) such as Cygnus X-1 have greatly advanced the understanding of these objects. However, the vast majority of the observations have been restricted to energies below ~200 keV. The Compton Gamma-Ray Observatory (CGRO) allowed for the first time simultaneous observations at energies from ~25 keV up to >1 GeV. In particular, the BATSE experiment aboard CGRO was able to monitor low-energy gamma-ray emission from Cygnus X-1, as well as other GBHs, nearly continuously over a nine year period. Using the Enhanced BATSE Occultation Package (EBOP), light curves and spectra in the energy range 25–2000 keV have been obtained for six GBHs. Based on the spectra when the GBHs were in a high gamma-ray flux state, it is suggested that at least two different classes of GBHs exist. The first is characterized by a Comptonization spectrum below ~200 keV followed by a soft power law excess as exhibited by Cygnus X-1, GRO J0422+32, GRO J1719−24, and GX 339-4. The second class is characterized by simple power law spectrum in the full 25–2000 keV range, with no evidence for a Comptonization component, as exhibited by GRO J1655−40 and GRS 1915+105.Gamma-ray observations can serve as an important diagnostic in studying the physical processes around GBHs. More sensitive observations in the future at energies >250 keV will help answer questions regarding issues such as the nonthermal electron distribution, state transitions, and the connection to jets

Sources and sinks for atmospheric N2O

Observations of the temporal and spatial distribution of N2O in solution are not yet sufficient to permit quantitative assessment of the role of the ocean in the budget of atmospheric N2O. Consideration of the global nitrogen cycle suggests that the land should be the primary source of N2O. The gas is removed in the atmosphere by photolysis and by reaction with O(1D), and there may be additional sinks in the ocean

Sources and sinks for atmospheric N_2O

Observations of the temporal and spatial distribution of N_2O in solution are not yet sufficient to permit quantitative assessment of the role of the ocean in the budget of atmospheric N_2O. Consideration of the global nitrogen cycle suggests that the land should be the primary source of N_2O. The gas is removed in the atmosphere by photolysis and by reaction with O(¹D), and there may be additional sinks in the ocean