Beam Mode Expansion of Corrugated Conical Horns with Phase Correcting Lens: Application to Radioastronomy Receivers     

E. García  L. De Haro  C. O'Sullivan  G. Cahill  J. A. López Fernández  F. Tercero  B. Galocha  J. L. Besada 《Experimental Astronomy》2003,15(3):173-193

A classical radioastronomy receiver is fed with a corrugated horn and an independent lens, both placed in a cryostat to lower the noise temperature. The beam is focused and directed using a combination of elliptical and plane mirrors. This paper proposes modifying the initial feeding system by placing the lens onto the horn aperture, thereby allowing a size reduction of the horn and lens, and a simplification of their mechanical design. The profiled lens is shaped to correct the phase error on the horn aperture. A quasi-optical model of the horn-plus-lens system has been developed using a Beam Mode Expansion (BME). Results using both a hyperbolic-planar lens and a spherical-elliptical lens, as well as results obtained by using Geometrical Optics (GO) with a Kirchoff–Huygens integration to get the far-field pattern, have been compared with measurements. As a direct application, a full focusing system for the new 40-m radiotelescope at the “Centro Astronómico de Yebes” is presented for the 22, 30 and 45 GHz bands. This paper has developed a QO model for a corrugated conical horn with a phase-correcting lens. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Delamerian‐aged metamorphism in the southern Curnamona Province,Australia: implications for the evolution of the Mesoproterozoic Olarian Orogeny     

Lachlan Rutherford  Martin Hand  Joanna Mawby 《地学学报》2006,18(2):138-146

Monazite electron microprobe U–Th–Pb and garnet Sm–Nd isotopic data from metapelitic assemblages in the Willyama Supergroup in the southern Curnamona Province, south‐central Australia, indicate that the terrain underwent regional greenschist to amphibolite‐grade metamorphism during the c. 500 Ma Delamerian Orogeny. The Delamerian‐aged mineral assemblages include prograde garnet–staurolite and kyanite‐bearing associations that overprint andalusite‐ and sillimanite‐bearing assemblages that are interpreted to have developed during the c. 1600 Ma Olarian Orogeny. Importantly, the development of secondary kyanite‐bearing assemblages in the southern Curnamona Province has been used previously to suggest that the Olarian Orogeny followed an anticlockwise P–T evolution. If such assemblages are the product of c. 500 Ma metamorphism, then the anticlockwise P–T path is an apparent path, due to the overprint of a distinct metamorphic cycle c. 1100 Ma later. Making such distinctions is therefore extremely important when using the textural and metamorphic evolution of polycyclic terrains to model the thermal behaviour of the crust during orogeny. This study highlights the utility of in situ geochronology, linking age data to petrologically important phases and assemblages.  相似文献   

Constraints on the ultraviolet metagalactic emissivity using the Lyα forest     

Avery Meiksin  Martin White 《Monthly notices of the Royal Astronomical Society》2003,342(4):1205-1214

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Astronomical Site Testing in Northwest of Argentina     

Pablo Recabarren  Pablo Recabarren  Mirta Mosconi  Hernán Muriel  Hernán Muriel  Diego García Lambas  Diego García Lambas  Marc Sarazin  Riccardo Giovanelli 《Astrophysics and Space Science》2004,290(3-4):409-413

We present the preliminary results of the astronomical site testing, which the group IATE of the OAC is developing in northwest of Argentine in collaboration with ESO and the Department of Astronomy of Cornell University. We show the results, which we have obtained from the analysis of GOES 8 satellite images in the 10.7 μm band, which allowed us to configurate a map of clear sky regions in an area between 23° and 28° S, and 66° 30′ and 69° W. We also comment logistical and tectonic aspects, and discuss next steps to follow in the research.  相似文献   

On Wilson,Regionalism, and the Decline of Fieldwork in Human Geography     

Martin S. Kenzer  Robert A. Rundstrom 《The Professional geographer》1990,42(2):221-223

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On the detailed magnetostratigraphy of greigite — (Smythite) mineralization,Sokolov Brown-Coal Basin,bohemia     

Miroslav Krs  Marta Krsová  Petr Pruner  Lada Kouklíková 《Studia Geophysica et Geodaetica》1991,35(4):267-284

Summary In the Middle Miocene claystones containing fossil micro-organic matter and overlying the brown-coal seams in the Jii quarry of the Sokolov Brown-Coal Basin, a strongly magnetic layer was found and subjected to detailed palaeomagnetic investigations. The principal carrier of magnetism in this bed (called Kocián's bed) is the ferrimagnetic mineralization of greigite or greigitesmythite showing pronounced metastable properties. This mineralization must be treated with caution during laboratory tests aimed at deriving palaeomagnetic directions. In Kocián's bed, about two metres thick, two zones of palaeomagnetic field transition were identified. The high degree of demagnetization achieved by using thermal stepwise procedures and a MAVACS apparatus enabled the origin of the self-reversal of remanence to be defined after heating to 360°C. The process of chemo-remanent magnetization of the authigenic greigite-(smythite) mineralization fossilizing the palaeomagnetic field was relatively fast; the transition of the palaeomagnetic field is recorded in layers not exceeding a thickness of 2 × 10^–2 m.Presented at 2nd conference on New Trends in Geomagnetism, Castle of Bechyn, Czechoslovakia, September 24–29, 1990.  相似文献   

Predicting ground-motion variations at the Turkey-flat test site,California     

J. Zahradník  J. Jech  V. Barták 《Pure and Applied Geophysics》1991,137(1-2):63-84

Results of a single group participating in an international experiment are analyzed. The experiment served to verify computational predictions of the ground-motion variations due to near-surface geological effects at a site established for that purpose by the California Department of Conservation. Based on an acceleration record at a rock location, and geotechnical model of medium, records at the other locations of a nearby sedimentary deposit were predicted. A 2-D finite-difference sensitivity analysis suggested that the lateral wave-propagation effects are negligibly small, and locally 1-D computations are sufficient for the present site. Those computations are compared with observations not available to the authors during the blind prediction. Peak accelerations, peak velocities and RMS accelerations were predicted with errors less than 159%, 114% and 62%, respectively. Maxima of the response spectra were fitted within a factor of 2. The predicted and observed Husid's plots (i.e., the normalized cumulative plots of the acceleration squared) have the correlation coefficients 0.98. The detected misfits do not show any simple relation to the instrument location, component, frequency, or time.  相似文献   

Tourmaline mineralization in the Barberton greenstone belt,South Africa: early Archean metasomatism by evaporite-derived boron   总被引：1，自引：0，他引：1  

Gary R. Byerly  Martin R. Palmer 《Contributions to Mineralogy and Petrology》1991,107(3):387-402

Tourmaline-rich rocks are common in the lowgrade, interior portions of the Barberton greenstone belt of South Africa, where shallow-marine sediments and underlying altered basaltic and komatiitic lavas contain up to 50% tourmaline. The presence of tourmaline-bearing rip-up clasts, intraformational tourmalinite pebbles, and tourmaline-coated grains indicates that boron mineralization was a low-temperature, surficial process. The association of these lithologies with stromatolites, evaporites, and shallow-water sedimentary structures and the virtual absence of tourmaline in correlative deep-water facies rocks in the greenstone bels strengthens this model.Five tourmaline-bearing lithologic groups (basalts, komatiites, evaporite-bearing sediments, stromatolitic sediments, and quartz veins) are distinguished based on field, petrographic, and geochemical criteria. Individual tourmaline crystals within these lithologies show internal chemical and textural variations that reflect continued growth through intervals of change in bulk-rock and fluid composition accompanying one or more metasomatic events. Large single-crystal variations exist in Fe/Mg, Al/Fe, and alkali-site vacancies. A wide range in tourmaline composition exists in rocks altered from similar protoliths, but tourmalines in sediments and lavas have similar compositional variations. Boron-isotope analysis of the tourmalines suggest that the boron enrichment in these rocks has a major marine evaporitic component. Sediments with gypsum pseudomorphs and lavas altered at low temperatures by shallow-level brines have the highest ¹¹B values (+2.2 to-1.9); lower ¹¹B values of late quartz veins (-3.7 to-5.7) reflect intermediate temperature, hydrothermal remobilization of evaporitic boron. The ¹¹B values of tourmaline-rich stromatolitic sediments (-9.8 and-10.5) are consistent with two-stage boron enrichment, in which earlier marine evaporitic boron was hydrothermally remobilized and vented in shallow-marine or subaerial sites, mineralizing algal stromatolites. The stromatolite-forming algae preferentially may have lived near the sites of hydrothermal discharge in Archean times.  相似文献   

Rigid unit modes in the molecular dynamics simulation of quartz and the incommensurate phase transition     

Frank Stefan Tautz  Volker Heine  Martin T. Dove  Xiaojie Chen 《Physics and Chemistry of Minerals》1991,18(5):326-336

A molecular dynamics simulation of quartz at different temperatures both in the a and in the phase has been conducted. The - phase transition could be observed. A phonon analysis of the -phase confirms and rounds out in a quantitative way the origin of the incommensurate (ic) modulated phase. In particular it traces the optic soft mode at becoming (to a good approximation) a so-called rigid unit mode (RUM) at q0, and elucidates its coupling to the transverse acoustic mode which precipitates the incommensurate transition. This success underpins and illuminates the concept of RUMs and their role in structural phase transitions.  相似文献   

Integrated resource management     

Martin Florin  Erhard Gabriel 《GeoJournal》1991,25(1):109-113

Food, energy and mineral resources appeared to be available in limitless quantities. The accelerated growth in global population during recent centuries brought about a new situation. We reached the resource limits of Spaceship Earth. This, along with the dawning awareness of the extent of environmental damage to date, have made it necessary to turn to new attitudes as to the use of renewable and non-renewable resources.IRM (Integrated Resource Management) is proposed as a way to rationally balance the use and conservation of natural resources. A databank based on the Geographic Information System (GIS) concept, bringing together all relevant resources of a nation, is the centerpiece of IRM and will make it possible to establish strategies to optimize the long term use of resources, including all relevant environmental factors.  相似文献