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11.
Tsevi Mazeh David W. Latham Elad Goldberg Guillermo Torres Robert P. Stefanik Todd J. Henry † Shay Zucker Orly Gnat Eran O. Ofek 《Monthly notices of the Royal Astronomical Society》2001,325(1):343-357
We present a radial velocity study of the triple-lined system Gliese 644 and derive spectroscopic elements for the inner and outer orbits with periods of 2.965 5 and 627 d. We also utilize old visual data, as well as modern speckle and adaptive optics observations, to derive a new astrometric solution for the outer orbit. These two orbits together allow us to derive masses for each of the three components in the system: M A =0.410±0.028 (6.9 per cent), M Ba =0.336±0.016 (4.7 per cent), and M Bb =0.304±0.014 (4.7 per cent) M⊙ . We suggest that the relative inclination of the two orbits is very small. Our individual masses and spectroscopic light ratios for the three M stars in the Gliese 644 system provide three points for the mass–luminosity relation near the bottom of the main sequence, where the relation is poorly determined. These three points agree well with theoretical models for solar metallicity and an age of 5 Gyr. Our radial velocities for Gliese 643 and vB 8, two common proper motion companions of Gliese 644, support the interpretation that all five M stars are moving together in a physically bound group. We discuss possible scenarios for the formation and evolution of this configuration, such as the formation of all five stars in a sequence of fragmentation events leading directly to the hierarchical configuration now observed, versus formation in a small N cluster with subsequent dynamical evolution into the present hierarchical configuration. 相似文献
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Neal Jackson Eran O. Ofek Masamune Oguri 《Monthly notices of the Royal Astronomical Society》2008,387(2):741-746
We report the discovery of a new gravitational lens system. This object, ULAS J234311.93-005034.0, is the first to be selected by using the new UKIRT Infrared Deep Sky Survey (UKIDSS), together with the Sloan Digital Sky Survey (SDSS). The ULAS J234311.93-005034.0 system contains a quasar at redshift 0.788 which is doubly imaged, with separation 1.4 arcsec. The two quasar images have the same redshift and similar, though not identical, spectra. The lensing galaxy is detected by subtracting point spread functions from R -band images taken with the Keck telescope. The lensing galaxy can also be detected by subtracting the spectra of the A and B images, since more of the galaxy light is likely to be present in the latter. No redshift is determined from the galaxy, although the shape of its spectrum suggests a redshift of about 0.3. The object's lens status is secure, due to the identification of two objects with the same redshift together with a lensing galaxy. Our imaging suggests that the lens is found in a cluster environment, in which candidate arc-like structures, that require confirmation, are visible in the vicinity. Further discoveries of lenses from the UKIDSS survey are likely as part of this programme, due to the depth of UKIDSS and its generally good seeing conditions. 相似文献
13.
Eran O. Ofek Stella Seitz Felix Klein 《Monthly notices of the Royal Astronomical Society》2008,389(1):311-314
Highly magnified lensed galaxies allow us to probe the morphological and spectroscopic properties of high-redshift stellar systems in great detail. However, such objects are rare, and there are only a handful of lensed galaxies that are bright enough for a high-resolution spectroscopic study with current instrumentation. We report the discovery of a new massive lensing cluster, SDSS J120923.7+264047, at z = 0.558. Present around the cluster core, at angular distances of up to ∼40 arcsec, are many arcs and arc candidates, presumably due to lensing of background galaxies by the cluster gravitational potential. One of the arcs, 21 arcsec long, has an r -band magnitude of 20, making it one of the brightest known lensed galaxies. We obtained a low-resolution spectrum of this galaxy, using the Keck-I telescope, and found it is at redshift of z = 1.018. 相似文献
14.
Eran Feitelson 《The Professional geographer》1991,43(2):190-205
Faced with soaring survey costs, geographers may increasingly consider mail or telephone surveys as alternatives to in-person interviews. This study goes beyond comparisons of response rates to analyze possible biases of administration methods in geographic studies. An empirical comparison between an in-person interview survey and two mail surveys of recent home buyers’ housing preferences revealed that the mail surveys provided better representation of this population, as they had a higher completion rate (though lower response rate). While respondent attributes differed across administration modes, no direct effects of administration method on responses were found. Mail surveys appear to be a viable alternative to personal interviews in a wider set of cases than geographers usually assume, though more empirical work is needed to determine the extent of such cases. 相似文献
15.
Itzhak Benenson Eran Ben-Elia Yodan Rofé Dmitry Geyzersky 《International journal of geographical information science》2017,31(2):213-236
Accessibility is an important consideration in sustainable mobility policies, particularly for transit users. Measures suggested in the literature are based on coarse aggregate spatial resolution of traffic analysis zones that is sufficient for managing car travels only. To reflect a human door-to-door travel, transit accessibility demands an explicit view of the location of origin, transit stops and destination, as well as of the temporal fit between transit lines timetable and traveler’s needs. We thus estimate transit accessibility based on mode-specific travel times and corresponding paths, including walking and waiting, at the resolution of individual buildings and stops. Car accessibility is estimated at a high resolution too. A novel representation of transit network as a graph is proposed. This representation includes all modal components of a transit travel – walking, waiting at a stop, transit ride, transfers between lines, thus enabling unified view of a travel, regardless of mode. The use of modern high-performance graph database allows construction of high-resolution accessibility maps for an entire metropolitan area with its 100–200 K buildings. The application is tested and applied in a case study involving the evaluation of the 2011 bus line reform in the city of Tel Aviv. Specifically, we demonstrate that while the reform increased the average accessibility for the entire city the increase was not uniform with different areas of the city experiencing different absolute accessibility by transit and relative accessibility in comparison to car travel. The bus reform did in fact benefit travelers that experienced low relative accessibility, but the benefits are mainly accruing to longer trips. Our approach and computational methods can be employed for directly investigating the impacts of transportation infrastructure investments. 相似文献
16.
Desalination alters a basic premise of water geography – fresh water flows from the sea inward, rather than the other way around. But, is this observation important? To address this question it is necessary to identify the potential ramifications of the changes in the water geography brought about by desalination. Israel is used as a basis for identifying these ramifications as it has recently embarked on a large-scale desalination program. The direct readily observable implications of the three main attributes of desalination, the reversal of flow direction, the continuity of water production, regardless of weather and climate vagrancies, and its cost are first spelled out. Then the potential ramifications for internal power structures, pricing and transboundary water agreements are discussed for the Israeli and Israeli–Arab scene. It is shown that the spatial flexibility introduced by desalination may undermine existing power relations within the water sector, which were based on the previous water geography. In the Israeli case these changes may be used to undermine the monopoly power of the national water company and of its organized labor, thereby advancing a neoliberal agenda. Desalination may have also significant distributional implications, as a function of the pricing effects it may have. Finally, the new water geography raises new issues in the Israeli–Arab water scene. The general insights gained from the Israeli case are then spelled out. 相似文献
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This study analyzes metropolitan dynamics in a small country with an “island state” context of closed boundaries, using commuting data and mobile phone tracking data. We examine whether the Israeli context encourages the formation of a monocentric “metropolitan state,” characterized by increasing links between localities throughout the country and its principal metropolitan node (Tel Aviv)—rather than with secondary metropolitan areas—and by fuzzy, overlapping metropolitan boundaries. Commuting data from the 1995 and 2008 censuses show that metropolitan expansion processes in Israel are gradual. Mobile phone tracking data for 2013 reveal similar patterns, confirming the urban structure’s stability and the reliability of tracking data as a means of assessing metropolitan processes. The “island state” context supports growing monocentricity, but, when it comes to commuting and travel for other purposes, Israel is not yet a metropolitan state; metropolitan boundaries are not as fuzzy and rapidly changing as expected. 相似文献
19.
ABSTRACTThe literature on environmental security often stresses the complementarity between sustainability and broader security goals. Less emphasis has been placed on possible trade-offs between security objectives and aspects of sustainability. This study examines the conditions under which these synergies and trade-offs are likely to occur, and how the trade-offs can be reconciled, especially during times of peacebuilding. As a case study, we analyse the effect of Israeli security concerns on environmental infrastructure designed to treat wastewater in the West Bank. This study identifies several sustainability–security trade-offs: (1) economic—in which security concerns raise costs of wastewater infrastructure, thereby crowding-out other potentially productive investments; (2) equity—in which security concerns result in disproportionate exposure of populations to environmental hazards; and (3) environmental—in which security concerns increase ecological footprints. Yet, our case study also indicates that both sides used a variety of creative measures to reconcile these trade-offs.
EDITOR D. Koutsoyiannis GUEST EDITOR K. Aggestam 相似文献
20.
The concentrations of uranium, iron and the major constituents were determined in groundwater samples from aquifer containing uranyl phosphate minerals (meta-autunite, meta-torbernite and torbernite) in the Köprüba?? area. Groundwater samples from wells located at shallow depths (0.5–6 m) show usually near neutral pH values (6.2–7.1) and oxidizing conditions (Eh = 119–275 mV). Electrical conductivity (EC) values of samples are between 87 and 329 μS/cm?1. They are mostly characterized by mixed cationic Ca dominating bicarbonate types. The main hydrogeochemical process is weathering of the silicates in the shallow groundwater system. All groundwater in the study area are considered undersaturated with respect to torbernite and autunite. PHREEQC predicted UO2(HPO4) 2 2? as the unique species. The excellent positive correlation coefficient (r = 0.99) between U and PO4 indicates the dissolved uranium in groundwater would be associated with the dissolution of uranyl phosphate minerals. The groundwater show U content in the range 1.71–70.45 μg/l but they are mostly lower than US EPA (2003) maximum contaminant level of 30 μg/l. This low U concentrations in oxic groundwater samples is attributed to the low solubility of U(VI) phosphate minerals under near neutral pH and low bicarbonate conditions. Iron closely associated with studied sediments, were also detected in groundwater. The maximum concentration of Fe in groundwater samples was 2837 μg/l, while the drinking water guidelines of Turkish (TSE 1997) and US EPA (2003) were suggested 200 and 300 μg/l, respectively. Furthermore, iron and uranium showed a significant correlation to each other with a correlation coefficient (r) of 0.94. This high correlation is probably related to the iron-rich sediments which contain also significant amounts of uranium mineralization. In addition to pH and bicarbonate controlling dissolution of uranyl phosphates, association of uranyl phosphates with iron (hydr) oxides seems to play important role in the amount of dissolved U in shallow groundwater. 相似文献