Mass‐velocity distributions of fragments in oblique impact cratering on gypsum     

Naomi Onose  Akira Fujiwara 《Meteoritics & planetary science》2004,39(2):321-331

Abstract— Oblique impact cratering experiments into gypsum targets were performed, and masses and velocities of the fragments were measured within the observational limit of 0.1–100 m/s in velocity and 0.0003–1 g in mass. The fragments observed were divided in two groups according to ejection time: early fragments ejected conically within a few msec after the impact followed by late fragments consisting of hundreds of slow, small fragments ejected almost perpendicular to the target. The relationship between mass and velocity of early fragments was observed to follow a power law with an exponent of ?0.11 ± 0.06, consistent with previous studies (e.g., Nakamura and Fujiwara 1991; Giblin et al. 1998). The cumulative number of fragments heavier or equal to a given mass versus fragment mass distributions shows a power law exponent of ?1.49 ± 0.09 for late fragments and steeper than ?0.49 ± 0.18 for early fragments. More than 10% of the mass was ejected from the crater with ejection speed slower than 2 m/s. Those fragments will reaccumulate on porous (<1500 kg/m³) and small (<4 km in diameter) asteroids.  相似文献   

Re-specifying disaster risk: concepts,methods, and models     

Naomi W. Lazarus 《GeoJournal》2014,79(5):635-648

The discussion on the social-ecological dimensions of hazards is constantly evolving. This paper explores the trajectory of research relating to hazards and their impact on vulnerable human populations. Interpretations of disaster risk have included estimating losses in terms of human life and property, and analyzing the social mechanisms in place that exacerbate or mitigate a population’s sensitivity to hazard events. In keeping with recent trends in research relating to disaster risk, the paper focuses on the social dimension of vulnerability and the contribution of social structures and relationships in building community resilience. Institutional frameworks and policies in particular determine the quantity and quality of resources and services available to people that contribute to resilience over time. The hazard-risk-location-model (HRLM) is proposed that is based on re-specifying disaster risk in terms of exposure and coping ability to capture the focus on social vulnerability and resilience. The framework of the HRLM incorporates the following components: (1) linkages within existing social capital; (2) spatial variation in social and institutional frameworks; (3) positive and negative feedbacks; and (4) characteristics of the hazard event. The model contributes to the range of place-based assessments designed to address the human-environmental impacts of hazards and disasters.  相似文献   

Observations of dugongs at Aldabra Atoll,western Indian Ocean: lagoon habitat mapping and spatial analysis of sighting records     

Sarah M. Hamylton  Annelise B. Hagan  Naomi Doak 《International journal of geographical information science》2013,27(5):839-853

Until recently, it was thought that dugongs (Dugong dugon) were extinct in the Seychelles. However, a collection of sightings at Aldabra Atoll, a World Heritage Site in the Seychelles, has renewed interest in dugong distribution in the western Indian Ocean. This article consolidates the records of dugong sightings held in the Aldabra Research Station library and explores their spatial patterning. The locations of sightings (2001–2009) are plotted onto a high-resolution benthic habitat map of the Aldabra lagoon created by classifying a QuickBird satellite remote-sensing image in January 2009. A spatial cluster detection procedure is applied to point records of sightings to reveal a statistically significant cluster of sightings in the north-west of the lagoon, at Bras Monsieur Clairemont, suggesting a mutual co-existence of dugongs and seagrass beds. A habitat suitability model combines the point data set of dugong sightings within the continuous benthic habitat map and identifies the central western area as containing the most suitable habitat for dugong inside the Aldabra lagoon.  相似文献   

User fees and the permeability of public space at municipal pools and bathhouses in New York City, 1870 – present     

Naomi Adiv  Laura Wolf-Powers 《Urban geography》2013,34(8):1071-1096

This paper examines fees for access to New York City’s public swimming and bathing spaces from 1870 to the present. We argue that, beyond generating revenue and rationing space, charges for admission to public bathing spaces have served to condition how permeable those spaces were to various groups of potential users. Municipal actors involved in administering baths and pools have used fees to maintain and order these spaces; to distinguish between deserving and undeserving users; and to include and exclude participants in an ostensibly universal public. Over time, fees have been naturalized, erasing these motivations and giving cause to their outcomes. We problematize the fee in order to address both theoretical questions about the nature of public space and practical ones about how municipal administrators govern amidst competing pressures to serve, develop and regulate urban residents and their communities.  相似文献   

WEATHERING OF PALEOZOIC MARBLES IN THE INDEPENDENCE HILLS AND PATRIOT HILLS,ELLSWORTH MOUNTAINS,ANTARCTICA     

Kenji Yoshikawa  Satoshi Ishimaru  Koichiro Harada 《自然地理学》2013,34(6):568-576

Weathering processes in the Ellsworth Mountains of Antarctica are dominated by frost action. These processes were observed to be different on the same group of marbles under different slope conditions. North- and south-facing walls of the bedrock showed the same shattering rate in the summer of 1992–1993. Frost shattering of rocks is controlled by surface temperature, moisture, and the physical properties of the rock. The most important control on frost shattering in this area was moisture availability, given the same bedrock and freeze-thaw cycle. Snow particles are moved by katabatic winds, bringing moisture to the rock. Moisture is collected mainly in lower cliffs and cols. [Key words: weathering, marble, moisture conditions, Antarctica.]  相似文献   

X-ray spectroscopy of clusters of galaxies     

Naomi Ota 《天体物理学报》2012,(8):973-994

  相似文献   

Particulate Flux and Cd/P Ratio of Particulate Material in the Pacific Ocean     

Shinichiro Noriki  Kazuhiro Hamahara  Koh Harada 《Journal of Oceanography》1999,55(6):693-703

Time-series Mark 7 sediment traps were deployed at three stations at 0°N, 13°N and 48°N along 175°E to investigate seasonal and spatial variations of particulate material flux. Chemical analysis of particulate material was performed for four major chemical components, viz. opal, CaCO₃, organic material and clay minerals, Cd and P in the particulate material were also determined. We discuss the characteristics of particulate material at each site and the transportation of Cd and P to deep water by the particulate material. The total mass fluxes and variation of fluxes at each site reflect oceanographic conditions, such as biological productivity and kind of major planktonic organisms. At the northern site, large mass fluxes with a spring bloom and high ratios of opal are characteristic. Relatively small mass fluxes with high ratios of CaCO₃ are distinct, and dissolution of CaCO₃ due to sinking is recognized in the middle latitude and 0°N sites. The larger flux at the lower trap than the upper trap at the equatorial site suggests influence by lateral transport in the deep water. Distinctive decreasing Cd/P ratio and CaCO₃ concentrations in the particulate material with increasing depth suggests that the change of Cd/P ratio in the intermediate and deep water occurs through the dissolution of CaCO₃. The dissolved Cd/P ratios in the deep water are proportional to the age of the deep water in the Atlantic but not in the Pacific. This is explained by the difference of kinds of particulate material transporting Cd and P in the deep water between the oceans. That is, the major planktonic organisms are planktons of CaCO₃ tests in the Atlantic Ocean and diatoms of opal tests in the North Pacific Ocean.  相似文献   

Nutrient and Phytoplankton Dynamics in Harima-Nada, Eastern Seto Inland Sea, Japan During a 35-Year Period from 1973 to 2007     

Tetsuya Nishikawa  Yutaka Hori  Satoshi Nagai  Kazutaka Miyahara  Yukinobu Nakamura  Kazuhiro Harada  Minoru Tanda  Takehiko Manabe  Kuninao Tada 《Estuaries and Coasts》2010,33(2):417-427

Long-term monitoring of water quality and phytoplankton was conducted at 19 sampling stations in Harima-Nada, eastern Seto Inland Sea, Japan for 35 years from 1973 to 2007. There were two significant long-term changes, an increase in winter water temperatures of 0.042°C year^?1, and a decrease in dissolved inorganic nitrogen (DIN) from about 10 μM in the 1970s to ~5 μM in the late 1990s due to the reduction in nutrient inputs. DIN concentrations and total phytoplankton cell density were both higher during the 1970s to the early 1980s and then exhibited a significant decrease in the mid 1980s and remained relatively constant thereafter. Diatoms were the dominant phytoplankton group (>90%) over the 35-year period, and there was a dramatic shift from Skeletonema dominance (~70%) to Chaetoceros in the mid 1980s. This shift in diatom species may be attributed to differences in the life cycle of Skeletonema and Chaetoceros and the response to the decrease in DIN concentration.  相似文献   

The rise and fall of the Irish orange roughy fishery: An economic analysis     

Naomi S. Foley  Tom M. van Rensburg  Claire W. Armstrong 《Marine Policy》2011

An Irish commercial fishery for orange roughy began in the Northeast Atlantic in 2001 with the assistance of government grants. The fishery began as an open access, non-quota fishery. The rapid boom and bust of many deep water fisheries was experienced. Landings peaked in 2002 and then dropped significantly the following year. Many vessels were forced out of the fishery due to high costs and rapidly declining stocks. By 2005 the fishery was largely closed. Applying a bioeconomic analysis, this paper shows why the fishery no longer exists and discusses both the external and opportunity costs of the fishery. A bioeconomic model is applied to the available data to assess the open access effort and harvest with and without government grant aid. The results suggest that in the absence of subsidies, deep water trawling would not have been viable. In addition to the financial costs such as high fuel consumption, there are also externalities associated with deep water trawling. Orange roughy is closely associated with deep water ecosystems such as seamounts and cold water corals. This paper examines the costs of damage to cold water corals. These costs include the loss of fish habitats and lost future use and preservation values.  相似文献   

A measurement of H₀ from Ryle Telescope, ASCA and ROSAT observations of Abell 773     

Richard Saunders  Rüdiger Kneissl  Keith Grainge  William F. Grainger  Michael E. Jones  Alessia Maggi  Rhiju Das  †  Alastair C. Edge  Anthony N. Lasenby  G. G. Pooley  Shigeru J. Miyoshi  Taisuke Tsuruta  Koujun Yamashita  Yuzuru Tawara  Akihiro Furuzawa  Akihiro Harada  Izamu Hatsukade 《Monthly notices of the Royal Astronomical Society》2003,341(3):937-940

  相似文献