Simco,a simulation software for CONICA,the coude nir camera for the very large telescope     

Peter Claes 《Experimental Astronomy》1994,3(1-4):121-122

CONICA is an acronym for COudé Near Infrared Camera. It is one of the four currently planned Infrared instruments for ESO's Very Large Telescope (VLT) in Chile. This multimode instrument is to be installed at the Coudé-focus (of Unit Telescope no. 1), where adaptive optics and speckle interferometry will also be available. High angular resolution imaging (to the diffraction limit) will be possible in the 1–5 m range, as well as spectroscopy with low- and medium resolution and polarimetry by means of Wollaston prism and wiregrid analysers. Various softwares are developed for this instrument. One of them: the Simulation Software has a threefold aim: 1. provide the user with feedback information on his/her choices of observational parameters. This is be achieved by displaying the calculated performance and throughput of the combined Source-Atmosphere-Telescope-Camera-Detector system in various formats, such as images, tables, isophotical images ... for point as well as for extended sources (also annular, double, etc.); 2. verify if his expectations are realistic, before actually using CONICA itself. 3. give feedback on the design to the developers of the instrument.On leave from his original institute, now at ESTEC in the ISO-project  相似文献   

The “Zero-order Model” revisited: Paul Schindler's influence on the development of trace metal scavenging models     

Santschi  Peter H.  Honeyman  Bruce D.  Quigley  Matthew S. 《Aquatic Sciences - Research Across Boundaries》1993,55(4):230-239

In 1975 Paul Schindler produced the first oceanic trace metal scavenging model to explicitly include the role of surface chemistry as a control on trace metal water column residence times. The eighteen years that have elapsed since the publication of Schindler's seminal paper have seen the development of a variety of oceanic scavenging models; yet, the fundamental insight of his Zero-order Model remains the benchmark. This paper describes the role of Paul Schindler's work on surface chemistry in providing a framework for the current generation of trace element scavenging models.  相似文献   

The history and impact of air pollution at Čertovo Lake,southwestern Czech Republic     

Josef Vesely  Heather Almquist-Jacobson  Lisa M. Miller  Stephen A. Norton  Peter Appleby  Aruna S. Dixit  John P. Smol 《Journal of Paleolimnology》1993,8(3):211-231

This multi-disciplinary investigation documents the longterm effects of atmospheric pollution of metals and acids on a geologically sensitive catchment in the umava Mountains, southwestern Czech Republic, a region with a long history of human disturbance. A 30 cm long sediment core (I) from ertovo Lake was analyzed for natural and artifical radionuclides, metals, diatoms, chrysophytes, and pollen in sediments accumulated during the last 200 years. A second core (II), extending to 95 cm, included sediment judged to be free of atmospheric deposition of pollutants associated with the Industrial Revolution. Chronostratigraphic markers include several changes in the pollen assemblages corresponding to well-documented changes in land-use, and distinct distributions of ¹³⁷Cs, ¹³⁴Cs and ²⁴¹Am from weapons testing and the 1986 nuclear accident at Chernobyl, Russia. These markers corroborate the ²¹⁰Pb dating and, together, produce a reliable chronology extending back nearly to 1800 A.D.Stratigraphic profiles of Cu, Pb, and Zn in Core I are unlike any previously reported in the literature. Concentrations of Cu, Pb, and Zn remain generally above 100, 400, and 200 g g^-1, respectively, for the 200 years represented by Core I. These values are unusually high for sediments from a watershed with no known heavy-metal ore bodies. Accumulation rates for Cu, Pb, and Zn, which include both atmospheric and watershed contributions, are also high (ca 1, > 1 and > 1 g cm^-2 yr^-1, respectively) for the same period, although the anthropogenic contribution of Zn rose from nearly zero at 1800 A.D. The Cu and Pb accumulation rates rose dramatically about 1640 A.D.Accumulation rates of anthropogenically-derived Be, a relatively abundant element in the soft coals of the region, are also elevated by about 0.01 g cm^-2 yr^-1 in sediments of this period. Vanadium accumulation rates increased only since 1980 A.D., presumably along with increased consumption of oil.Diatom assemblages illustrate that the lake was acidic (pH between 4.5 and 5) through at least the past 200 years. The pH declined significantly (from ca 5 to 4) between 1960 and 1985 with a slight increase to 4.5 in the last few years. Recent diatom and chrysophyte assemblages suggest high trace metal concentrations, consistent with the present lake-water chemistry.  相似文献   

Genesis of high Mg# andesites and the continental crust   总被引：38，自引：2，他引：36  

Peter B. Kelemen 《Contributions to Mineralogy and Petrology》1995,120(1):1-19

The continental crust has an andesitic composition with high Mg/(Mg+Fe) and Ni contents which may be too high to have formed by differentiation of basaltic magmas. Instead, mantle-derived, high Mg# andesites (HMA) may form a substantial component of the crust. HMA may be produced by partial melting of previously depleted, subsequently metasomatised mantle peridotite. However, they are more likely produced by reaction between ascending melts and mantle peridotite. HMA are less common than basalts among lavas in modern island arcs, but may have been more common in the past, may be produced in specific environments (such as ridge subduction), may be more common among plutonic rocks in the lower and middle crust than among lavas at the surface, and may be selectively preserved during later erosion and subduction processes.  相似文献   

Is C/O enhanced in NGC 253?     

Andrew Harrison  Peter Brand  Adrian Russell  Phil Puxley 《Astrophysics and Space Science》1995,224(1-2):473-474

We have mapped the nuclear region of the starburst galaxy NGC 253 in the³ P ₁ ³ P ₀ line of neutral carbon using the JCMT. Carbon is widespread across the nuclear region with a similiar distribution to CO as expected. Previous studies of Galactic star-forming regions showed that carbon emission is enhanced in photon-dominated regions (where UV photons impinge upon molecular clouds). Previous observations of other PDR tracers such as ionized carbon and FIR continuum constrain the physical conditions in the PDR gas of NGC 253. The carbon we have observed is far brighter than predicted by theoretical models of PDRs with solar elemental values. This indicates that carbon emission is not a reliable diagnostic of the physical conditions in the nuclear region of a galaxy undergoing a burst of star formation.  相似文献   

Baroclinic instabilities in Jupiter's zonal flow     

Peter J. Gierasch  Andrew P. Ingersoll  David Pollard 《Icarus》1979,40(2):205-212

The baroclinic stability of Jupiter's zonal flow is investigated using a model consisting of two continuously stratified fluid layers. The upper layer, containing a zonal shear flow and representing the Jovian cloudy regions above p ～ 5 bars, is the same as Eady's (1949) model for the Earth. The lower layer has a relatively large but finite depth with a quiescent basic state, representing the deep Jovian fluid bulk below p ～ 5 bars. Due to the presence of the lower layer, the linearized non-dimensional growth rates are drastically reduced from the O(1) growth rates of the original Early model. Only very long wavelengths relative to the upper fluid's radius of deformation L₁ are unstable. Eddy transports of heat are also reduced relative to estimates based on scaling arguments alone. Since the hydrostatic approximation for the lower-layer perturbation breaks down at great depths, a second model is presented in which energy propagates downward in an infinitely deep lower fluid obeying the full linearized fluid equations. In this model, the growth rates are again very small, but now all wavelengths are unstable with maximum growth rates occurring for wavelengths O(1) relative to L₁. These results illustrate the importance for the upper-layer meteorology of the interface boundary condition with the lower fluid, which is radically different from the rigid lower boundary of the Earth's troposphere.  相似文献   

Calculations of the effects of angular momentum on the early evolution of Jupiter     

Peter Bodenheimer 《Icarus》1977,31(3):356-368

The planet Jupiter is assumed to have formed as a subcondensation in the solar nebula. The initial phase of its evolution is one of hydrostatic contraction with radiative energy transport. Calculations of evolutionary sequences through this phase are presented, including the effects of angular momentum. The calculations are carried out in two space dimensions under the assumptions of axial symmetry, constancy of angular velocity on cylindrical surfaces about the rotation axis, a pressure-density relation given by the polytrope of index 3, conservation of angular momentum, and a homogeneous composition. The results show that under certain physically reasonable initial distributions of density and angular momentum the formation of a central planet and a rotating circumplanetary envelope is possible, while under assumptions a point of instability is reached that probably results in the breakup of the condensation by fission into two or more parts. The models are discussed with reference to the present angular momenta of Jupiter and its regular satellites.  相似文献   

Turbulent viscosity and Jupiter's tidal Q     

Peter Goldreich  Philip D. Nicholson 《Icarus》1977,30(2):301-304

A recent estimate of tidal dissipation by turbulent viscosity in Jupiter's convective interior predicts that the current value of the planet's tidal Q ～ 5 × 10⁶. We point out a fundamental error in this calculation, and show that turbulent dissipation alone implies that at present Q ～ 5 × 10¹³. Our reduced estimat for the rate of tidal dissipation shows conclusively that tidal torques have produced only negligible modifications of the orbits of the Galilean satellites over the age of the solar system.  相似文献   

X-ray imaging of three flares during the impulsive phase     

André Duijveman  Peter Hoyng  Marcos E. Machado 《Solar physics》1982,81(1):137-157

The impulsive phases of three flares that occurred on April 10, May 21, and November 5, 1980 are discussed. Observations were obtained with the Hard X-ray Imaging Spectrometer (HXIS) and other instruments aboard SMM, and have been supplemented with Hα data and magnetograms. The flares show hard X-ray brightenings (16–30 keV) at widely separated locations that spatially coincide with bright Hα patches. The bulk of the soft X-ray emission (3.5–5.5 keV) originates from in between the hard X-ray brightenings. The latter are located at different sides of the neutral line and start to brighten simultaneously to within the time resolution of HXIS. Concluded is that:

1. The bright hard X-ray patches coincide with the footpoints of loops.
2. The hard X-ray emission from the footpoints is most likely thick target emission from fast electrons moving downward into the dense chromosphere.
3. The density of the loops along which the beam electrons propagate to the footpoints is restricted to a narrow range (10⁹ < n < 2 × 10¹⁰ cm^-3), determined by the instability threshold of the return current and the condition that the mean free path of the fast electrons should be larger than the length of the loop.
4. For the November 5 flare it seems likely that the acceleration source is located at the merging point of two loops near one of the footpoints.

It is found that the total flare energy is always larger than the total energy residing in the beam electrons. However, it is also estimated that at the time of the peak of the impulsive hard X-ray emission a large fraction (at least 20%) of the dissipated flare power has to go into electron acceleration. The explanation of such a high acceleration efficiency remains a major theoretical problem.  相似文献   

Ce and Nd isotope geochemistry on island arc volcanic rocks with negative Ce anomaly: existence of sources with concave REE patterns in the mantle beneath the Solomon and Bonin island arcs   总被引：5，自引：0，他引：5  

Hiroshi Shimizu  Hideyuki Sawatari  Yousuke Kawata  Peter N. Dunkley  Akimasa Masuda 《Contributions to Mineralogy and Petrology》1992,110(2-3):242-252

¹³⁸Ce/¹⁴²Ce isotope ratios in Cenozoic island arc volcanic rocks are reported for the first time, together with isotope ratios of Nd and Sr and abundances of REE, Ba and Sr. The island arc volcanics studies here are boninites from Chichijima, the Bonin Islands, and basalts and andesites from the Solomon Islands. REE patterns of the island arc volcanic rocks from the Solmon Islands and the Bonin Islands are confirmed to have negative Ce anomalies. It is also disclosed that the majority of these island arc volcanic rocks show mainly positive values for both _Ce and _Nd. It is shown that these _Ce and _Ce values can hardly be interpreted by simple mixing between MORB and oceanic or continental crustal rocks; the former have positive _Nd and negative _Ce and the latter have negative _Ce and positive or negative _Nd. Existence of sources having positive _Ce and _Nd values is strongly suggested. If the sources are assumed to have been fractionated from CHUR (chondritic uniform reservoir) at the early or middle Precambrian era, the sources from which the volcanics were derived are concluded to have kept concave REE patterns with larger (La/Ce)_N and smaller (Nd/Sm)_N ratios than chondritic values over a substantial period of time, until the time of Cenozoic magmatism forming island arc volcanic rocks in question. During the periods of the Cenozoic magmatic activities and their related events, Ce anomalies are considered to have been created. From Ce and Nd isotope ratios, however, it is difficult to determine which of the following processes was responsible for the Ce anomaly; the incorporation process of subducted oceanic crust into magma at the mantle or the slab dehydration and metasomatism process. Nevertheless, so far as Ce and Nd isotopic ratios are concerned, incorporation of oceanic sediments did not take place to any clearly detectable degree.  相似文献