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111.
112.
William Johnston Nilanjan Banerjee Jackson Cothren James P. Parkerson 《Transactions in GIS》2014,18(4):555-573
Information‐rich maps are today rendered from powerful back‐end servers. Unfortunately, there may be circumstances in which access to such Internet‐resident web services is infeasible or unreliable. These disconnected environments can theoretically occur during major power outages, malicious attacks on communications infrastructure, natural disasters, or in remote operating environments. One might also envision applications in which a disconnected service is preferred over Internet‐resident services, such as when the local internet service is overloaded with traffic, making communication though it difficult. To this end, this article presents a software stack (a map stack) that can serve GIS information from low power embedded nodes. The system combines a spatially enabled SQL database, location‐based routing, and multi‐scale map rendering to serve information‐rich GIS data on common hand‐held devices at minimal energy consumption. The maps are rendered on browsers on off‐the‐shelf mobile devices such as smart phones and tablets. The system also provides a crowd sourced capability where end users can annotate maps with up‐to‐date information on the scene of the natural disaster. We have prototyped a fully functional map stack on a battery powered Gumstix Overo air platform. We show that the map stack is a highly extensible platform that provides low latency, and low energy dissemination of maps during a natural disaster. 相似文献
113.
The AUSGeoid09 model of the Australian Height Datum 总被引:8,自引:6,他引:2
W. E. Featherstone J. F. Kirby C. Hirt M. S. Filmer S. J. Claessens N. J. Brown G. Hu G. M. Johnston 《Journal of Geodesy》2011,85(3):133-150
AUSGeoid09 is the new Australia-wide gravimetric quasigeoid model that has been a posteriori fitted to the Australian Height
Datum (AHD) so as to provide a product that is practically useful for the more direct determination of AHD heights from Global
Navigation Satellite Systems (GNSS). This approach is necessary because the AHD is predominantly a third-order vertical datum
that contains a ~1 m north-south tilt and ~0.5 m regional distortions with respect to the quasigeoid, meaning that GNSS-gravimetric-quasigeoid
and AHD heights are inconsistent. Because the AHD remains the official vertical datum in Australia, it is necessary to provide
GNSS users with effective means of recovering AHD heights. The gravimetric component of the quasigeoid model was computed
using a hybrid of the remove-compute-restore technique with a degree-40 deterministically modified kernel over a one-degree
spherical cap, which is superior to the remove-compute-restore technique alone in Australia (with or without a cap). This
is because the modified kernel and cap combine to filter long-wavelength errors from the terrestrial gravity anomalies. The
zero-tide EGM2008 global gravitational model to degree 2,190 was used as the reference field. Other input data are ~1.4 million
land gravity anomalies from Geoscience Australia, 1′ × 1′ DNSC2008GRA altimeter-derived gravity anomalies offshore, the 9′′ × 9′′
GEODATA-DEM9S Australian digital elevation model, and a readjustment of Australian National Levelling Network (ANLN) constrained
to the CARS2006 mean dynamic ocean topography model. To determine the numerical integration parameters for the modified kernel,
the gravimetric component of AUSGeoid09 was compared with 911 GNSS-observed ellipsoidal heights at benchmarks. The standard
deviation of fit to the GNSS-AHD heights is ±222 mm, which dropped to ±134 mm for the readjusted GNSS-ANLN heights showing
that careful consideration now needs to be given to the quality of the levelling data used to assess gravimetric quasigeoid
models. The publicly released version of AUSGeoid09 also includes a geometric component that models the difference between
the gravimetric quasigeoid and the zero surface of the AHD at 6,794 benchmarks. This a posteriori fitting used least-squares
collocation (LSC) in cross-validation mode to determine a correlation length of 75 km for the analytical covariance function,
whereas the noise was taken from the estimated standard deviation of the GNSS ellipsoidal heights. After this LSC surface
fitting, the standard deviation of fit reduced to ±30 mm, one-third of which is attributable to the uncertainty in the GNSS
ellipsoidal heights. 相似文献
114.
Recent studies in the United States and other Pacific Rim countries have identified a new form of ethnic minority group clustering
within the residential mosaic—ethnoburbs. These are suburban in location, occupied by relatively high-income, predominantly
Asian, immigrants, and low density in their nature: many migrants move directly to those suburbs rather than the inter-generational
outward migration from central city clusters typical of other migrant streams. Although ethnoburb residents tend to cluster
in particular segments of the built-up area they do not to form large percentages of the population there. As yet, no methodology
has been developed to identify these clusters, as a prelude to identifying their characteristics. This paper offers such a
procedure, based on local statistical analysis. It is applied to six Asian groups in Auckland, New Zealand. 相似文献
115.
116.
R. Silvotti A. Bonanno A. Frasca S. Bernabei R. Janulis R. Østensen S.-L. Kim B.-G. Park J. Xiaojun J. Guo Z. Liu M.D. Reed R.S. Patterson K.M. Gietzen P.J. Clark G.W. Wolf Y. Lipkin L. Formiggini E. Leibowitz T.D. Oswalt M. Rudkin K. Johnston 《Astrophysics and Space Science》2004,289(3-4):445-448
I present a model for the formation and evolution of a massive disk galaxy, within a growing dark halo whose mass evolves according to cosmological simulations of structure formation. The galactic evolution is simulated with a new 3D chemo-dynamical code, including dark matter, stars and a multi-phase ISM. We follow the evolution from redshift z = 4.85 until the present epoch. The energy release by massive stars and supernovae prevents a rapid collapse of the baryonic matter and delays the maximum star formation until redshift z ≈ 1. The galaxy forms radially from inside-out and vertically from top-to-bottom. The feedback of stars leads to turbulent motions and large-scale flows in the ISM. As one result the galactic disk is significantly enriched by chemical elements synthesized in bulge stars. 相似文献
117.
R. R. Brooks M. Hoashi E. Fernandes de Lima M. L. dos Santos D. E. Ryan J. Holzbecher J. H. Johnston Y. Kawachi P. P. Sipiera 《Meteoritics & planetary science》1990,25(3):231-232
Abstract— The Iguaraçu meteorite, a single stone of 1200 g, fell in Paraná State, Brazil in October 1977. It is classified as an H5 ordinary chondrite with olivine of composition Fa 18.7. 相似文献
118.
119.
Kinwah Wu Roberto Soria Richard W. Hunstead Helen M. Johnston 《Monthly notices of the Royal Astronomical Society》2001,320(2):177-192
We have carried out observations of the X-ray transient GX 339−4 during its high–soft and low–hard X-ray spectral states. Our high-resolution spectroscopic observation in 1999 April suggests that the H α line has a single-peaked profile in the low–hard state as speculated in our previous paper. The He ii λ 4686 line, however, has a double-peaked profile in both the high–soft and low–hard states. This suggests that the line-emission mechanism is different in the two states. Our interpretation is that double-peaked lines are emitted from a temperature-inversion layer on the accretion disc surface when it is irradiatively heated by soft X-rays. Single-peaked lines may be emitted from outflow/wind matter driven by hard X-ray heating. We have constructed a simple plane-parallel model and we use it to illustrate that a temperature-inversion layer can be formed at the disc surface under X-ray illumination. We also discuss the conditions required for the formation of temperature inversion and line emission. Based on the velocity separations measured for the double-peaked lines in the high–soft state, we propose that GX 339−4 is a low-inclination binary system. The orbital inclination is about 15° if the orbital period is 14.8 h. 相似文献
120.