First ENA observations at Mars: Solar-wind ENAs on the nightside     

K. Brinkfeldt  H. Gunell  P. C:son Brandt  R.A. Frahm  E. Kallio  Y. Futaana  R. Lundin  M. Yamauchi  J.R. Sharber  A.J. Coates  D.O. Kataria  T. Säles  W. Schmidt  J. Luhmann  D. Williams  C.C. Curtis  B.R. Sandel  M. Carter  A. Fedorov  S. McKenna-Lawler  R. Cerulli-Irelli  P. Wurz  N. Krupp  M. Fränz  C. Dierker 《Icarus》2006,182(2):439-447

We present measurements with an Energetic Neutral Atom (ENA) imager on board Mars Express when the spacecraft moves into Mars eclipse. Solar wind ions charge exchange with the extended Mars exosphere to produce ENAs that can spread into the eclipse of Mars due to the ions' thermal spread. Our measurements show a lingering signal from the Sun direction for several minutes as the spacecraft moves into the eclipse. However, our ENA imager is also sensitive to UV photons and we compare the measurements to ENA simulations and a simplified model of UV scattering in the exosphere. Simulations and further comparisons with an electron spectrometer sensitive to photoelectrons generated when UV photons interact with the spacecraft suggest that what we are seeing in Mars' eclipse are ENAs from upstream of the bow shock produced in charge exchange with solar wind ions with a non-zero temperature. The measurements are a precursor to a new technique called ENA sounding to measure solar wind and planetary exosphere properties in the future.  相似文献   

The distribution of Titan's high-altitude (out to ∼50,000 km) exosphere from energetic neutral atom (ENA) measurements by Cassini/INCA     

P.C. Brandt  K. Dialynas  I. Dandouras  D.G. Mitchell  P. Garnier  S.M. Krimigis 《Planetary and Space Science》2012,60(1):107-114

We report observations of Titan's high-altitude exosphere detected out to about 50,000 km altitude. The observations were made by the Ion Neutral Camera (INCA) on board the Cassini spacecraft. INCA detects energetic neutral atoms (ENA) that are formed when the ambient magnetospheric ions charge exchange with Titan's neutral atmosphere and exosphere. We find that Titan's exospheric H₂ distribution follows closely a full Chamberlain distribution including ballistic, escaping and satellite distributions. As expected, neutral densities are dominated by a satellite distribution above about 10,000 km. The maximum detectable extent of the exosphere (～50,000 km) coincides with the radius of the Hill sphere of gravitational influence from Saturn. While we find no direct indications of a neutral Titan torus with densities greater than about 1000 cm^?3, we observe interesting asymmetries in the distribution that warrants further investigation. Based on these findings we compute the average precipitating ENA flux to be about 5×10⁶ keV/(cm² s), or 8×10^?3 erg/(cm² s), which is directly comparable to that of precipitating energetic ions (Sittler, et al., 2009) and slightly higher than that of solar EUV (Tobiska, 2004). Thus, the energy deposited by precipitating ENAs must also be taken into consideration when studying the energy balance of Titan's thermosphere.  相似文献   

Holocene talus accumulation rates,—and their influence on rock glacier growth. A case study from Igpik,Disko—West Greenland     

Povl Frich  Erik Brandt 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2013,113(1):32-43

Frich, Povl and Brandt, Erik: Holocene talus accumulation rates,—and their influence on rock glacier growth. A case study from Igpik, Disko—West Greenland. Geografisk Tidsskrift 85: 32–44 Copenhagen, October 1985.

The Igpik area is located ten km east of Godhavn on the south-coast of the island Disko. Geologically the area is dominated by Tertiary basalt formations.

A general geomorphological classification of this area, which covers approximately three square kms, has been made. Based on radiocarbon ages of former marine levels in the Disko Bugt area, the beginning of talus accumulation has been determined for two talus cones situated on raised beaches. They have ages of 5800 and 7900 ¹⁴C y. B.P. Using theodolite readings, the volumes of three different talus cones have been determined and two average talus accumulation rates have been calculated for the cones located on raised beaches. These values are transformed into an average Holocene rockwall retreat rate of 0.0005 and 0.0015 m/year, respectively. The total volume of two lobate rock glaciers is calculated to be 2.2 mill, cu.m and as they are located inside 9000 years old local moraines, the average Holocene mass-transfer through the third talus cone has been estimated to 1.4 10⁶ tons×m/sq.km/y. Finally the results are discussed, with reference to other areas, and as a possible threshhold for the initiation of rock glaciers.  相似文献   

The optical variability of the narrow-line Seyfert 1 galaxy IRAS 13224−3809     

A. J. Young  C. S. Crawford  A. C. Fabian  W. N. Brandt  P. T. O'Brien 《Monthly notices of the Royal Astronomical Society》1999,304(4):L46-L52

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Sedimentological and Geomorphological Effects of Reservoir Flushing: The Cachí Reservoir, Costa Rica, 1996     

S. Anders Brandt  & Joar Swenning 《Geografiska Annaler: Series A, Physical Geography》1999,81(3):391-407

The Cachí Reservoir on the Reventazón River, Costa Rica, is flushed on an almost yearly basis. A field investigation of the 1996 flushing was carried out in order to elucidate from where in the reservoir the material originates, where and to what extent the released sediments will deposit along the river from the dam to the sea, and finally how this can be explained. A reservoir survey was conducted by means of echo-sounding along certain cross-sections before and after the flushing. The material was found to both deposit in between flushings and to be eroded during flushing, mainly in the uppermost and lowermost parts of the old river channel. In the downstream reaches, the pulse of suspended sediment pertaining to the flushing was found to be clearly distinguishable by means of grain-size distribution, even in the lower parts. Surveys were conducted at eight sites along the river downstream from the dam both before and after the flushing such that the volumes of deposited or eroded material were found. By use of the dry bulk density, the results could be calculated in tonnes, thus facilitating comparison to the samplings of the hydrological stations along the river. A major factor in explaining the amounts and distribution of deposits was shown to be the phase lag between water discharge and suspended-sediment con-centration peaks. The influence of this phase lag on the deposition and erosion processes is illustrated by a schematic figure. A more detailed sediment budget is presented for the reach between the hydrological stations c . 10 and 30 km downstream from the dam. It was found that approximately 250 000 tonnes were deposited within the reach. Of these, 82% were channel-bed deposits while 18% were deposited on the river banks.  相似文献   

Dietary pattern recognition on Twitter: a case example of before,during, and after four natural disasters     

Turner-McGrievy  Gabrielle  Karami  Amir  Monroe  Courtney  Brandt  Heather M. 《Natural Hazards》2020,103(1):1035-1049

Natural Hazards - Little is known about what foods/beverages (F&B) are common during natural disasters. The goal of this study was to track high-frequency F&B mentions during four...  相似文献   

A longer XMM–Newton look at I Zwicky 1: physical conditions and variability of the ionized absorbers     

E. Costantini  L. C. Gallo  W. N. Brandt  A. C. Fabian  Th. Boller 《Monthly notices of the Royal Astronomical Society》2007,378(3):873-880

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Millimeter-wave experiments for cometary space missions     

Robert W. Hobbs  John C. Brandt  Stephen P. Maran  Jan M. Hollis 《Icarus》1981,47(3):434-440

Predicted brightness temperatures for a variety of cometary nucleus models, consisting of homogeneous layers comprised of mixtures of water ice and refractory grains, are presented as functions of wavelength. These illustrative spectra are computed using simple radiative transfer techniques adapted from modeling of terrestrial ice and snow fields. The computed millimeter-wave spectra are sensitive to the values of physically significant nucleus parameters such as crust thickness, the subsurface temperature gradient, and the boundary temperature of the sublimating surface. It appears that millimeter-wave sensing from an interplanetary spacecraft is an effective means for distinguishing between alternate models of the nucleus and for inferring the rough physical state of substrata; modern theories on the nature of the nucleus indicate that sublimation from the substrata provides the gas phase cometary volatiles that are actually observed from ground-based and Earth-orbiting instruments. Antenna beam dilution is a major obstacle for ground-based molecular spectral line radio observations (e.g., water and ammonia) of comets but a modest millimeter-wave radiometer system in the near vicinity of the comet would not be subject to this problem. Such a system can make definitivebservations of several candidate parent molecules in the gas phase and should contribute to the understanding of the physics of the inner coma.  相似文献   

Bastille Day storm: Global response of the terrestrial ring current     

Brandt  P. C: Son  Mitchell  D.G.  Roelof  E.C.  Burch  J.L. 《Solar physics》2001,204(1-2):377-386

Global images of the Earth's inner magnetosphere and its response to the coronal mass ejection (CME) on the 15 July 2000 were obtained by the IMAGE spacecraft. The images were taken in energetic neutral atoms (ENA) by the High-Energy Neutral Atom (HENA) imager. ENAs are produced by charge exchange between the hot ion population of the magnetosphere and the cold neutral hydrogen geocorona. The ENA images show how plasma is injected into the nightside magnetosphere as the interplanetary magnetic field (IMF) turns strongly southward. As the IMF B _z increases and the storm intensity decreases, the ENA images show that the ring current becomes closed and symmetric as IMF B _z reaches positive values.  相似文献   

Constants for an elastic–plastic cap model for limestone     

H. S. Chu  H. Brandt 《国际地质力学数值与分析法杂志》1987,11(2):193-202

Triaxial fracture tests with overburden pressures ranging from 0.69 to 136 MPa were performed to determine the material parameters involved in a cap model for limestone. Three material parameters A, B and C, were evaluated through Powell's optimization method and the remaining parameters through simulation-curve fitting procedure. The resulting cap model was tested against separate triaxial fracture and hydrostatic compression tests. Modification of the original hardening function, as proposed by DiMaggio and Sandler, provided an improved fit for the experimental data.  相似文献