High Performance Corrugated Feed Horns for Space Applications at Millimetre Wavelengths     

F. Villa  M. Sandri  N. Mandolesi  R. Nesti  M. Bersanelli  A. Simonetto  C. Sozzi  O. D'Arcangelo  V. Muzzini  A. Mennella  P. Guzzi  P. Radaelli  R. Fusi  E. Alippi 《Experimental Astronomy》2002,14(1):1-15

We report on the design fabrication and testing of a set of high performance corrugated feed horns at 30, 70, and 100 GHz, built as advanced prototypes for the Low Frequency Instrument (LFI) of the ESA Planck mission. The electromagnetic designs include linear (100 GHz) and dual shaped (30 and 70 GHz) profiles. Fabrication has been achieved by direct machining at 30 GHz and by electro-formation at higher frequencies. The measured performances on side lobe and return loss meet the stringent Planck requirements over the large (20%) instrument bandwidth. Moreover, the advantage in terms of main lobe shape and side lobe levels of the dual profiled designs has been demonstrated. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

锂辉石:巨型花岗伟晶岩锂-铯-钽矿床中关键含锂矿物SCIEI北大核心CSCD     

DI GROVES  Liang Zhang  IM GROVES  AK SENER 《岩石学报》2022,38(1):1-8

寻找传统化石燃料的替代能源已成为全球性议题。受动力电池消费的拉动,锂资源需求急剧上升,伟晶岩型锂矿勘查热度持续攀升。虽然众多伟晶岩型锂矿地质特征尚不清晰,已有证据表明锂辉石是大多数大型-巨型伟晶岩型锂矿床的主要含锂矿物。与许多近直立的伟晶岩脉群不同,世界范围内大多数太古代伟晶岩矿脉往往呈近水平或缓倾斜在角闪岩相围岩中产出,它们往往具有复杂的三维形态并发育明显的矿物和地球化学分带。这些太古代伟晶岩脉通常形成于挤压或压剪构造体制下同变质环境中,成岩期最小主应力(σ;)近竖直。因此,伟晶岩常常侵位于近水平的构造局部引张区而形成复杂的几何学形态。压性的构造环境为富锂熔体多次脉动式注入和富含挥发分熔体垂向结晶分异提供了充足的时间;锂辉石在中高温压条件下结晶成为缓倾富锂带中最为常见的含锂矿物。  相似文献   

Reef fish structure assemblages in oceanic islands of the eastern tropical Pacific: Revillagigedo Archipelago and Clipperton atoll     

Manon Fourrire  Hctor Reyes‐Bonilla  Cristian Moiss Galvn‐Villa  Arturo Ayala Bocos  Fabin Alejandro Rodríguez‐Zaragoza 《Marine Ecology》2019,40(3)

Revillagigedo Archipelago and Clipperton atoll are oceanic islands located in the eastern tropical Pacific. The composition and trophic structure of their fish assemblages have never been characterized in detail, and the aim of this study was therefore to analyse the community structure and assess the similarity of fish assemblages between these two areas. Underwater visual fish censuses were conducted using band transects at two depth levels in three islands of the Revillagigedo Archipelago (Socorro, San Benedicto, and Roca Partida) and at Clipperton atoll. We calculated ecological indices (density, richness, Shannon diversity, Pielou evenness, and taxonomic distinctiveness) for each transect. These were compared in order to determine quantitative differences among the islands and bathymetric levels. Qualitative analyses (ANOSIM, nMDS, and SIMPER) were also performed. Finally, we analysed the trophic structure of the assemblages and the functional diversity of the four studied sites. The results showed significant differences for all indices, except diversity (H′). Roca Partida was the site with greatest abundance and richness due to the presence of pelagic species in large numbers. No significant differences were found in functional diversity, suggesting a high degree of ecological redundancy. Lower‐level carnivores with mean trophic level values of between 3.3 and 3.8 dominated both areas. The ordination analysis did not show a clear difference in fish composition among the islands, although Clipperton atoll has a particular fauna characterized by endemic species (Thalassoma robertsoni and Stegastes baldwini). In conclusion, the fish communities of the studied areas seem quite similar, but their assemblage structure differs. In particular, Clipperton is differentiated by the influence of endemic species.  相似文献   

The evolution of latera caldera (central Italy) in the light of subsurface data     

F. Barberi  F. Innocenti  P. Landi  U. Rossi  M. Saitta  R. Santacroce  I. M. Villa 《Bulletin of Volcanology》1984,47(1):125-141

Subsurface geothermal exploration has considerably added to our knowledge of the Latera volcanic complex. A syenitic body is located about 2 km below the present-day surface; K-Ar data point a 0.9 Ma age. The primary magma was a silica-saturated trachyte; undersaturated, hauyne-bearing products are found near the carbonatic wall-rocks and have been interpreted as reaction products. Subsurface data from deep drilling and geophysical surveys suggest that the Latera caldera resulted from three main successive collapse phases: (i) formation of an old caldera, now buried, related to the eruption of ignimbrites from the syenitic magma chamber; (ii) sinking of the eastern sector as a consequence of the formation of the nearby Bolsena caldera (0.3 Ma); (iii) multistage formation of the present Latera caldera (0.16 Ma).  相似文献   

The X-ray gas scintillation spectrometer experiment on the first spacelab flight     

M. R. Sims  R. D. Andresen  E. A. Leimann  P. Lamb  J. Raymont  J. Ives  S. Kellock  G. Boella  G. Villa  B. Falconi  G. Manzo  S. Re  R. M. Robba 《Astrophysics and Space Science》1985,116(1):61-79

The First Spacelab mission, launched on Space ShuttleFlight STS-9 in November 1983 carried a multidisciplinary payload which was intended to demonstrate that valuable scientific results can be achieved from such short duration missions. The payload complement included a spectrometer to undertake observations of the brighter cosmic X-ray sources. The primary scientific objectives of this experiment were the study of detailed spectral features in cosmic X-ray sources and their associated temporal variations over a wide energy range from about 2 up to 30 keV. The instrument based on the gas scintillation proportional counter had an effective area of some 180 cm² with an energy resolution of 9% at 7 keV.The instrument parameters and the performance, using data from the flight and ground calibration, are discussed.  相似文献   

Seyfert galaxies and the cosmic γ-ray diffuse background     

L. Bassani  R. C. Butler  A. J. Dean  G. Di Cocco  F. Perotti  G. Villa 《Astrophysics and Space Science》1982,82(1):199-207

Three active galaxies, generally classified as Seyferts, have been discovered recently to be powerful, low energy -ray sources. The similarity between their spectral characteristics and those of the cosmic background at -ray energies suggests that these objects could make a significant contribution to this diffuse flux. This contribution has been assessed using two different number densities of -ray-emitting Seyfert galaxies based on optical and X-ray data. The comparison of the estimated and measured diffuse -ray background intensities is used to gain a deeper understanding of the metabolism of Seyfert galaxies.  相似文献   

Dating fault-generated pseudotachylytes: comparison of <Superscript>40</Superscript>Ar/<Superscript>39</Superscript>Ar stepwise-heating,laser-ablation and Rb–Sr microsampling analyses   总被引：1，自引：0，他引：1  

Wolfgang Müller  Simon P. Kelley  Igor M. Villa 《Contributions to Mineralogy and Petrology》2002,144(1):57-77

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Distribution of iron and manganese in the Blanca bay,Argentina     

Norma Villa  Adan Edgardo Pucci 《Marine pollution bulletin》1985,16(9):369-371

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A new source of isotopically heavy sulphur in lode-gold deposits of NW Spain: a batch volatilization process in the conversion of pyrite to pyrrhotite by contact metamorphism     

Arias  Corretgé  & Villa 《地学学报》1998,10(3):136-138

The conversion of pyrite to pyrrhotite is identified in this study as a new source of isotopically heavy sulphur in thermal domes. Contact metamorphism of a sequence of pyrite-rich shales by the Penedela blind intrusion (NW Spain) causes the conversion of diagenetic pyrite to pyrrhotite at a temperature of 150 °C. This process occurred in a closed system with total consumption of the diagenetic pyrite and production of H₂S-rich fluids. The H₂S liberated in this unidirectional reaction shows a relatively heavy δ³⁴S, in agreement with a batch volatilization process. The mixture of this H₂S-rich fluids with derived sulphur from Lower Cambrian carbonates produced gold-bearing pyrite at a temperature of 340 °C. The contribution from these two different sulphur sources was 86% and 14%, respectively. The metamorphic fluids migrated through permeable zones such as fractures and shear zones, producing a lode-gold deposit.  相似文献   

Chronostratigraphy of Monte Vulture volcano (southern Italy): secondary mineral microtextures and <Superscript>39</Superscript>Ar-<Superscript>40</Superscript>Ar systematics     

Igor M. Villa  Annett Buettner 《Bulletin of Volcanology》2009,71(10):1195-1208

The eruptive history of Monte Vulture has been the subject of several geochronological investigations during the past decades, which reliably dated only a small number of eruptions. Understanding the causes of sub-optimum data yield in the past requires an interdisciplinary approach. We re-analyzed samples from previous works and present new data on samples from the main volcano-stratigraphic units of Monte Vulture, so as to provide an improved, consistent chronostratigraphic database. Imaging of minerals by cathodoluminescence and backscattered electrons reveals that heterochemical, high-temperature deuteric reaction textures are ubiquitous. Such observations are common in metamorphic rocks but had not frequently been reported from volcanic rocks. In view of the mineralogical complexity, we base our chronological interpretation on isochemical steps, defined as steps for which the Cl/K and/or the Ca/K ratios are constant. Isochemical steps carry the isotopic signature of chemically homogeneous mineral phases and therefore allow a well-constrained age interpretation. Comparison of old and new ³⁹Ar-⁴⁰Ar data proves the reproducibility of age spectra and their shapes. This quantifies the analytical reliability of the irradiation and mass-spectrometric analyses. Anomalous age spectra are a reproducible property of some specific samples and correlate with mineralogical anomalies. The present data allow us to fine-tune the age of the volcanostratigraphic units of Monte Vulture during the known interval of main volcanic activity from ca. 740 to 610 ka. After a very long stasis, the volcanic activity in the Monte Vulture area resumed with diatremic eruptions, one of which (Lago Piccolo di Monticchio, the site of a palynological-paleoclimatological drilling) was dated at ca. 140 ka.  相似文献