ROV Mantis: A dual-purpose underwater vehicle     

Conway  T. 《Oceanic Engineering, IEEE Journal of》1986,11(3):418-421

This paper reviews the last two years operational deep-water performance record of two manned/unmanned tethered ROV Mantis vehicles. Deviations of the system as compared to conventional submersibles and remotely operated vehicles (ROV's) are discussed and evaluated. Applications and advantages of this system in support of deep-water operations are appraised. Results and observations concluded in this paper deal with the importance of having a man in the water, or at least available to go in the water, and also those circumstances which require a remotely operated system either for safety or total bottom time requirement. The significance of each mode of operation is examined. Observations and conclusions have been compiled from operational data collected during over 250 actual dives in deep-water work to depths of 2000 ft (sim 600m).  相似文献   

On the Photometric Accuracy of RHESSI Imaging and Spectrosocopy     

Aschwanden  Markus J.  Metcalf  Thomas R.  Krucker  Säm  Sato  Jun  Conway  Andrew J.  Hurford  G.J.  Schmahl  Edward J. 《Solar physics》2004,219(1):149-157

We compare the photometric accuracy of spectra and images in flares observed with the Ramaty High-Energy Solar Spectroscopic Imager (RHESSI) spacecraft. We test the accuracy of the photometry by comparing the photon fluxes obtained in different energy ranges from the spectral-fitting software SPEX with those fluxes contained in the images reconstructed with the Clean, MEM, MEM-Vis, Pixon, and Forward-fit algorithms. We quantify also the background fluxes, the fidelity of source geometries, and spatial spectra reconstructed with the five image reconstruction algorithms. We investigate the effects of grid selection, pixel size, field of view, and time intervals on the quality of image reconstruction. The detailed parameters and statistics are provided in an accompanying CD-ROM and web page. We find that Forward-fit, Pixon, and Clean have a robust convergence behavior and a photometric accuracy in the order of a few percent, while MEM does not converge optimally for large degrees of freedom (for large field of view and/or small pixel sizes), and MEM-Vis suffers in the case of time-variable sources. This comparative study documents the current status of the RHESSI spectral and imaging software, one year after launch. Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/B:SOLA.0000021801.83038.aa  相似文献   

The RHESSI Imaging Concept     

Hurford  G.J.  Schmahl  E.J.  Schwartz  R.A.  Conway  A.J.  Aschwanden  M.J.  Csillaghy  A.  Dennis  B.R.  Johns-Krull  C.  Krucker  S.  Lin  R.P.  McTiernan  J.  Metcalf  T.R.  Sato  J.  Smith  D.M. 《Solar physics》2002,210(1-2):61-86

The Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI) observes solar hard X-rays and gamma-rays from 3 keV to 17 MeV with spatial resolution as high as 2.3 arc sec. Instead of focusing optics, imaging is based on nine rotating modulation collimators that time-modulate the incident flux as the spacecraft rotates. Starting from the arrival time of individual photons, ground-based software then uses the modulated signals to reconstruct images of the source. The purpose of this paper is to convey both an intuitive feel and the mathematical basis for this imaging process. Following a review of the relevant hardware, the imaging principles and the basic back-projection method are described, along with their relation to Fourier transforms. Several specific algorithms (Clean, MEM, Pixons and Forward-Fitting) applicable to RHESSI imaging are briefly described. The characteristic strengths and weaknesses of this type of imaging are summarized.  相似文献   

A 1 Gyr climate model for Mars: new orbital statistics and the importance of seasonally resolved polar processes     

John C. Armstrong  Conway B. Leovy 《Icarus》2004,171(2):255-271

New results from a 1 Gyr integration of the martian orbit are presented along with a seasonally resolved energy balance climate model employed to illuminate the gross characteristics of the long-term atmospheric pressure evolution. We present a new analysis of the statistical variation of the martian obliquity and precession prior to and subsequent to the formation of the Tharsis uplift, and explore the long term effects on the martian climate. We find that seasonal polar cycles have a critical influence on the ability for the regolith to release CO₂ at high obliquities, and find that the atmospheric CO₂ actually decreases at high obliquities due to the cooling effect of polar deposits at latitudes where seasonal caps form. At low obliquity, the formation of massive, permanent polar caps depends critically on the values of the frost albedo, A_frost, and frost emissivity, ?_frost. Using our model with values of A_frost=0.67 and ?_frost=0.55, matched to the NASA Ames General Circulation Model (GCM) results (Haberle et al., 1993, J. Geophys. Res. 98, 3093-3123, and Haberle et al., 2003, Icarus 161, 66-89), we find that permanent caps only form at low obliquities (<13°), suggesting that any permanent deposits on the surface of Mars today may be residuals left over from a period of very low obliquity, or are the result of mechanisms not represented by this model. Thus, contrary to expectations, the martian atmospheric pressure is remarkable static over time, and decreases both at high and low obliquity. Also, from our one billion year orbital model, we present new results on the fraction of time Mars is expected to experience periods of low obliquity and high obliquity.  相似文献   

Comments on the interpretation of 3371 Å filter-photometer observations and its implications for the AE-E photoelectron fluxes     

R.R. Conway 《Planetary and Space Science》1983,31(10):1223-1228

Modeling of the dayglow spectrum in the wavelength region between 3300 and 3500 Å indicates that the N₂ second positive (0,0) band at 3371 Å is blended with the Vegard-Kaplan (0,9) band. A recent analysis of rocket observations of the dayglow shows that 20–30% of a 3371 Å narrow band filter-photometer signal is due to the VK emission (Conway and Christensen, 1983). Kopp $\text{et al.}$ (1977) and Hernandez $\text{et al.}$ (1983) reported analyses of 3371 Å photometer observations from the Visible Airglow Experiment on the Atmospheric Explorer-C (AE-C) satellite which did not consider the Vegard-Kaplan (VK) emission. The observations were compared to theoretical estimates of the second positive volume emission rate based on a photoelectron model and on absolute fluxes measured by the Photoelectron Spectrometer experiments on AE-C and AE-E. Inclusion of the VK band in the AE analysis would bring the reported photoelectron theory into agreement with the airglow observations. However, the overestimate of the N₂ second positive airglow predicted by the AE-E photoelectron flux measurements increases to a factor of nearly two rather than the 20–30% reported by Hernandez $\text{et al.}$ (1983).  相似文献   

Lightning characteristics of derecho producing mesoscale convective systems     

Mace L. Bentley  John R. Franks  Katelyn R. Suranovic  Brent Barbachem  Declan Cannon  Stonie R. Cooper 《Meteorology and Atmospheric Physics》2016,128(3):303-314

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Recent observations of the decimetric radio emission from Jupiter     

D. Stannard  R.G. Conway 《Icarus》1976,27(3):447-452

The position angle of linear polarization and the degree of circular polarization of the decimetric emission show no marked variations with time, although there may be an indication in the position angle data of a secular decrease in the inclination of the magnetic field structure. High resolution observations of the radiation belts show that the asymmetry in the emission found in synthesis maps originates from an extended region. The presence of this features accounts well for the observed variation in the position of the centroid of the emission with rotation. The radio observations suggest that any equatorial displacement of the main magnetic field structure from the center of the planet is less than 0.05 R_J.  相似文献   

An improved age framework for late Quaternary silicic eruptions in northern Central America   总被引：1，自引：0，他引：1  

William I. Rose  F. Michael Conway  Carlos R. Pullinger  Alan Deino  William C. McIntosh 《Bulletin of Volcanology》1999,61(1-2):106-120

 Five new stepwise-heating ⁴⁰Ar/³⁹Ar ages and one new high-sensitivity ¹⁴C date of ash-fall and ash-flow deposits from late Quaternary silicic volcanoes in northern Central America document the eruption rates and frequencies of five major rhyodacite and rhyolite calderas (Atitlán, Amatitlán, Ayarza, Coatepeque, and Ilopango) located north of the basalt, andesite, and dacite stratovolcanoes of the Central American volcanic front. These deposits form extensive time-stratigraphic horizons that intercalate regionally, and knowledge of dates and stratigraphy provides a valuable framework for age determinations of more localized volcanic and nonvolcanic events. The new data, especially when integrated with previous stratigraphic and dating work, show that all five calderas erupted several times in the past 200 ka and, despite a lack of historic activity, should be considered as active centers that could produce highly explosive eruptions again. Because of their locations near the highly vulnerable economic hearts of Guatemala and El Salvador, the risks of eruptions from these calderas should be carefully considered along with risks of major earthquakes and volcanic front volcanoes, which are much more frequent but inflict less severe and extensive damage. This investigation also includes some examples of dating efforts that failed to produce reasonable results. Received: 15 May 1998 / Accepted: 18 January 1999  相似文献   

Recent fluctuations in precipitation and runoff over the Nile sub-basins and their impact on main Nile discharge     

D. Conway  M. Hulme 《Climatic change》1993,25(2):127-151

Substantial fluctuations in precipitation and runoff have occurred over the Nile Basin in recent decades. Ten-year mean flows of the Blue Nile (Khartoum gauge) during the 20th century have ranged from 42.2 to 56.7 km³ and for the White Nile (Malakal gauge) from 25.5 to 36.9 km³. These fluctuations have been responsible for changes in decade-mean Main Nile discharge of up to ± 20% which have had important consequences for water resource management in both Egypt and Sudan.This paper provides a review of the Nile Basin hydrology incorporating, for the first time, analyses of the relationships between precipitation and runoff fluctuations in the instrumental period for each of the eight major sub-basins within the Nile Basin. These sub-basins possess very different physical, climatic and hydrological characteristics. Over 90% of the Main Nile discharge originates from only four of the sub-basins; Lake Victoria, Blue Nile, Atbara, and the Sobat. Interbasin correlations of 40 y (1945-84) precipitation and runoff annual time series identify two broadly homogeneous regions; the Ethiopian highlands (Blue Nile and Atbara) and the Lake Victoria and Equatorial Lakes (White Nile). These regions posses contrasting precipitation regimes whose interannual variations are uncorrelated in time and which are therefore associated with different atmospheric circulation anomalies. The observed relationships between catchment precipitation and runoff, however, are not straightforward and the sensitivity of runoff to precipitation fluctuations varies from basin to basin. Some of the water resource management implications of these fluctuations for Egypt are discussed. With water demand in Egypt alone set to increase 17% by the year 2000, it is critical that the role of future climate change in Nile water management is thoroughly assessed based on a correct modelling of the diverse hydrological characteristics of the various Nile sub-basins.  相似文献   

Structural Geology, principles, concepts, and problems: Hatcher, R. D. 1989. Merrill Publishing Co., Columbus, Ohio, U.S.A. 531 pp. Price $49.95 (hardback)     

Declan G. De Paor 《Journal of Structural Geology》1990,12(8)

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