669 research outputs found

    The U.S. Humanitarian Demining Program in the Balkans

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    As a result of years of conflict in the Balkans, countless landmines have been laid in Croatia, Bosnia and Herzegovina, and Kosovo. Bosnia-Herzegovina\u27s landmine problem is severe, with an estimated 750,000 landmines and an undetermined quantity of unexploded ordnance infesting some 186 square miles of land. These hidden killers have killed and maimed hundreds, vastly impeded the return of refugees to their homes, and hindered international efforts to help people in the region

    The Suzaku X-ray spectrum of NGC 3147. Further insights on the best "true" Seyfert 2 galaxy candidate

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    NGC 3147 is so far the most convincing case of a "true" Seyfert 2 galaxy, i.e. a source genuinely lacking the Broad Line Regions. We obtained a Suzaku observation with the double aim to study in more detail the iron line complex, and to check the Compton-thick hypothesis for the lack of observed optical broad lines. The Suzaku XIS and HXD/PIN spectra of the source were analysed in detail. The line complex is composed of at least two unresolved lines, one at about 6.45 keV and the other one at about 7 keV, most likely identified with Fe XVII/XIX, the former, and Fe XXVI, the latter. The high-ionization line can originate either in a photoionized matter or in an optically thin thermal plasma. In the latter case, an unusually high temperature is implied. In the photoionized model case, the large equivalent width can be explained either by an extreme iron overabundance or by assuming that the source is Compton-thick. In the Compton-thick hypothesis, however, the emission above 2 keV is mostly due to a highly ionized reflector, contrary to what is usually found in Compton-thick Seyfert 2s, where reflection from low ionized matter dominates. Moreover, the source flux varied between the XMM-Newton and the Suzaku observations, taken 3.5 years apart, confirming previous findings and indicating that the size of the emitting region must be smaller than a parsec. The hard X-ray spectrum is also inconclusive on the Compton-thick hypothesis. Weighting the various arguments, a "true" Seyfert 2 nature of NGC 3147 seems to be still the most likely explanation, even if the "highly ionized reflector" Compton-thick hypothesis cannot at present be formally rejected.Comment: 6 pages, accepted for publication in Astronomy & Astrophysic

    Monte Carlo simulations of the Nickel Kα\alpha fluorescent emission line in a toroidal geometry

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    We present new results from Monte Carlo calculations of the flux and equivalent width (EW) of the Ni Kalpha fluorescent emission line in the toroidal X-ray reprocessor model of Murphy & Yaqoob (2009, MNRAS, 397, 1549). In the Compton-thin regime, the EW of the Ni Kalpha line is a factor of ~22 less than that of the Fe Kalpha line but this factor can be as low as ~6 in the Compton-thick regime. We show that the optically-thin limit for this ratio depends only on the Fe to Ni abundance ratio, it being independent of the geometry and covering factor of the reprocessor, and also independent of the shape of the incident X-ray continuum. We give some useful analytic expressions for the absolute flux and the EW of the Ni Kalpha line in the optically-thin limit. When the reprocessor is Compton-thick and the incident continuum is a power-law with a photon index of 1.9, the Ni Kalpha line EW has a maximum value of ~3 eV and ~250 eV for non-intercepting and intercepting lines-of-sight respectively. Larger EWs are obtained for flatter continua. We have also studied the Compton shoulder of the Ni Ka line and find that the ratio of scattered to unscattered flux in the line has a maximum value of 0.26, less than the corresponding maximum for the Fe Kalpha line. However, we find that the shape of the Compton shoulder profile for a given column density and inclination angle of the torus is similar to the corresponding profile for the Fe Ka line. Our results will be useful for interpreting X-ray spectra of active galactic nuclei (AGNs) and X-ray binary systems in which the system parameters are favorable for the Ni Kalpha line to be detected.Comment: Accepted for publication in MNRAS. 8 pages, 5 figure

    Challenges and Opportunities for Hotel-to-Housing Conversions in NYC

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    As the country continues to grapple with the COVID-19 crisis and its aftermath, policymakers in New York City and Albany have debated how to support the conversion of hotels into housing—and especially affordable housing—as part of a solution to the city’s ongoing housing crisis. The basic intuition is compelling. COVID has forced the shuttering of many commercial establishments, especially in hard-hit New York City. In certain sectors, the effect has been particularly large: these include hotels devastated by shutdowns in tourism, international travel, and business travel. At the same time as these spaces are sitting empty, though, Americans have faced unprecedented challenges in paying their rent—on top of preexisting rent burdens that had been driving housing instability and homelessness well before COVID. It is logical to want to use these spaces—these important physical assets—rather than let them remain unoccupied, and housing is an attractive use. However, not all hotels are ripe for conversion to housing, and the scope of the opportunity presented by hotel conversions is not clear. Some hotels—because of their business model, location, or design—are better candidates for conversion than others, and for conversion to different types of housing. In one case, only minimal and economical renovations might be required; in another, expensive gut rehabilitation would be necessary to turn the hotel into a residential use. To better understand what opportunities for hotel conversion exist in New York City, we examined the legal regime governing hotel conversions to identify the most important regulatory barriers to such adaptive uses. We also compiled data examining how the hotel market is segmented—how many hotel rooms, of what kind, are located where—in order to further understand how different conversion strategies might play out spatially

    The role of big trees and abundant species in driving spatial patterns of species richness in an Australian tropical rainforest

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    Big trees and abundant species dominate forest structure and composition. As a result, their spatial distribution and interactions with other species and individuals may contribute disproportionately to the emergence of spatial heterogeneity in richness patterns. We tested scale-dependent spatial patterning and species richness structures to understand the role of individual trees (big trees) and species (abundant species) in driving spatial richness patterns on a 25 ha plot in a diverse tropical forest of Australia. The individual species area relationship (ISAR) was used to assess species richness in neighborhoods ranging from 1 to 50 m radii around all big trees (≥70 cm dbh, n = 296) and all species with more than 100 individuals in the plot (n = 53). A crossed ISAR function was also used to compute species richness around big trees for trees of different size classes. Big individuals exert some spatial structuring on other big and mid-sized trees in local neighborhoods (up to 30 m and 16 m respectively), but not on small trees. While most abundant species were neutral with respect to richness patterns, we identified consistent species-specific signatures on spatial patterns of richness for 14 of the 53 species. Seven species consistently had higher than expected species richness in their neighborhood (species “accumulators”), and seven had lower than expected (species “repellers”) across all spatial scales. Common traits of accumulators and repeller species suggest that niche partitioning along disturbance gradients is a primary mechanism driving spatial richness patterns, which is then manifested in large-scale spatial heterogeneity in species distributions across the plot

    JME 4110: Automated Railway Decoupler, Optimized

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    Disconnecting freight cars from one another in trains that may be many thousands of feet long involves the dangerous and inefficient operation of manual decoupling. We have produced a system that enables freight cars to disconnect remotely, streamlining rail operations and boosting efficiency

    Quality Assurance of Software Applications Using the In Vivo Testing Approach

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    Software products released into the field typically have some number of residual defects that either were not detected or could not have been detected during testing. This may be the result of flaws in the test cases themselves, incorrect assumptions made during the creation of test cases, or the infeasibility of testing the sheer number of possible configurations for a complex system; these defects may also be due to application states that were not considered during lab testing, or corrupted states that could arise due to a security violation. One approach to this problem is to continue to test these applications even after deployment, in hopes of finding any remaining flaws. In this paper, we present a testing methodology we call in vivo testing, in which tests are continuously executed in the deployment environment. We also describe a type of test we call in vivo tests that are specifically designed for use with such an approach: these tests execute within the current state of the program (rather than by creating a clean slate) without affecting or altering that state from the perspective of the end-user. We discuss the approach and the prototype testing framework for Java applications called Invite. We also provide the results of case studies that demonstrate Invite's effectiveness and efficiency

    Extremal energy shifts of radiation from a ring near a rotating black hole

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    Radiation from a narrow circular ring shows a characteristic double-horn profile dominated by photons having energy around the maximum or minimum of the allowed range, i.e. near the extremal values of the energy shift. The energy span of a spectral line is a function of the ring radius, black hole spin, and observer's view angle. We describe a useful approach to calculate the extremal energy shifts in the regime of strong gravity. Then we consider an accretion disk consisting of a number of separate nested annuli in the equatorial plane of Kerr black hole, above the innermost stable circular orbit (ISCO). We suggest that the radial structure of the disk emission could be reconstructed using the extremal energy shifts of the individual rings deduced from the broad wings of a relativistic spectral line.Comment: 9 pages, 5 figures, ApJ accepte

    Leveraging Energy Data for the Benefit of Society and Consumers

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    This policy brief is intended to distill the essential points of the Industrial Internet of Things paper by Karim Farhat et al into a format easily consumed by policymakers.Industrial data (ID) has the potential to play a key role in finding efficiencies in energy markets and thus lower rates for consumers. The realm of industrial data within the energy sector encompasses a broad ecosystem involving many stakeholders. This policy brief is intended to focus specifically on implications for Investor-Owned Utilities (IOUs), energy service and technology providers including Original Equipment Manufacturers (OEMs), policymakers, and researchers, as well as interactions among them. Within this construct, we find that: • IOUs could better leverage data analytics to utilize capital, natural resources, and public infrastructure more efficiently; • ID could lead to better alignment of incentives between utilities and policy/regulation; • Methods to facilitate market entry for local third-party energy service providers should be explored to benefit the regional economy and to avoid ceding leadership to foreign or out-of-state competition; • More collaboration within the standards space and during the standards deliberation process is warranted (in particular between OEMs and energy providers); • ID and energy stakeholders have an obligation and opportunity to improve regulations for Critical Infrastructure Protection (CIP) with future implications on grid cybersecurity; • Coordination and R&D among utilities, policymakers and research institutions can enhance and accelerate knowledge diffusion and beneficial outcomes for owners, consumers, and the environment
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