Prospects of Measuring the Angular Power Spectrum of the Diffuse Galactic Synchrotron Emission with SKA1 Low     

Sk. Saiyad Ali  Somnath Bharadwaj  Samir Choudhuri  Abhik Ghosh  Nirupam Roy 《Journal of Astrophysics and Astronomy》2016,37(4):35

The Diffuse Galactic Syncrotron Emission (DGSE) is the most important diffuse foreground component for future cosmological 21-cm observations. The DGSE is also an important probe of the cosmic ray electron and magnetic field distributions in the turbulent interstellar medium (ISM) of our galaxy. In this paper we briefly review the Tapered Gridded Estimator (TGE) which can be used to quantify the angular power spectrum C _? of the sky signal directly from the visibilities measured in radio-interferometric observations. The salient features of the TGE are: (1) it deals with the gridded data which makes it computationally very fast, (2) it avoids a positive noise bias which normally arises from the system noise inherent to the visibility data, and (3) it allows us to taper the sky response and thereby suppresses the contribution from unsubtracted point sources in the outer parts and the side lobes of the antenna beam pattern. We also summarize earlier work where the TGE was used to measure the C _? of the DGSE using 150 MHz GMRT data. Earlier measurements of C _? are restricted to \(\ell \le \ell _{\max } \sim 10^{3}\) for the DGSE, the signal at the larger ? values is dominated by the residual point sources after source subtraction. The higher sensitivity of the upcoming SKA1 Low will allow the point sources to be subtracted to a fainter level than possible with existing telescopes. We predict that it will be possible to measure the C _? of the DGSE to larger values of \(\ell _{\max }\) with SKA1 Low. Our results show that it should be possible to achieve \(\ell _{\max }\sim 10^{4}\) and ～10⁵ with 2 minutes and 10 hours of observations respectively.  相似文献   

Bridging theory and implementation – Testing an abstract classification system for practical mapping by field survey and 3D aerial photographic interpretation     

Heidrun A. Ullerud  Anders Bryn  Helle Skånes 《Norsk geografisk tidsskrift. Norwegian journal of geography》2019,73(5):301-317

ABSTRACT

The abstract classification system Nature in Norway (NiN) has detailed ecological definitions of a high number of ecosystem units, but its applicability in practical vegetation mapping is unknown because it was not designed with a specific mapping method in mind. To investigate this further, two methods for mapping – 3D aerial photographic interpretation of colour infrared photos and field survey – were used to map comparable neighbouring sites of 1 km² in Hvaler Municipality, south-eastern Norway. The classification accuracy of each method was evaluated using a consensus classification of 160 randomly distributed plots within the study sites. The results showed an overall classification accuracy of 62.5% for 3D aerial photographic interpretation and 82.5% for field survey. However, the accuracy varied for the ecosystem units mapped. The classification accuracy of ecosystem units in acidic, dry and open terrain was similar for both methods, whereas classification accuracy of calcareous units was highest using field survey. The mapping progress using 3D aerial photographic interpretation was more than two times faster than that of field survey. Based on the results, the authors recommend a method combining 3D aerial photographic interpretation and field survey to achieve effectively accurate mapping in practical applications of the NiN system.  相似文献   

Prediction of streamflow regimes over large geographical areas: interpolated flow–duration curves for the Danube region     

A. Castellarin  S. Persiano  A. Pugliese  A. Aloe  J. O. Skøien 《水文科学杂志》2020,65(Z1):845-861

ABSTRACT

Flow–duration curves (FDCs) are essential to support decisions on water resources management, and their regionalization is fundamental for the assessment of ungauged basins. In comparison with calibrated rainfall–runoff models, statistical methods provide data-driven estimates representing a useful benchmark. The objective of this work is the interpolation of FDCs from ~500 discharge gauging stations in the Danube. To this aim we use total negative deviation top-kriging (TNDTK), as multi-regression models are shown to be unsuitable for representing FDCs across all durations and sites. TNDTK shows a high accuracy for the entire Danube region, with overall Nash-Sutcliffe efficiency values computed in a leave-p-out cross-validation scheme (p equal to one site, one-third and half of the sites), all above 0.88. A reliability measure based on kriging variance is attached to each interpolated FDC at ~4000 prediction nodes. The GIS layer of regionalized FDCs is made available for broader use in the region.  相似文献   

Tachylyte in Cenozoic basaltic lavas from the Czech Republic and Iceland: contrasting compositional trends     

Ulrych  Jaromír  Krmíček  Lukáš  Teschner  Claudia  Řanda  Zdeněk  Skála  Roman  Jonášová  Šárka  Fediuk  Ferry  Adamovič  Jiří  Pokorný  Richard 《Mineralogy and Petrology》2017,111(5):761-775

Mineralogy and Petrology - Tachylytes from rift-related volcanic rocks were recognized as: (i) irregular veinlets in host alkaline lava flows of the Kozákov volcano, Czech Republic, (ii)...  相似文献   

Thin Threads of Solar Filaments   总被引：1，自引：0，他引：1  

Yong?LinEmail author  Oddbj?rn?Engvold  Luc?Rouppe?van?der?Voort  Jun?Elin?Wiik  Thomas?E.?Berger 《Solar physics》2005,226(2):239-254

High-resolution images obtained in H with the new Swedish Solar Telescope at La Palma, Spain, have been used for studies of fine-scale threads in solar filaments. The widths of the thin threads are 0.3 arcsec. The fact that the width of the thinnest threads is comparable to the diffraction limit of the telescope of about 0.14 arcsec, at the wavelength of H, suggests that even thinner threads may exist. Assuming that the threads represent thin magnetic strings, we conclude that only a small fraction of these are filled with observable absorbing plasma, at a given time. The absorbing plasma is continuously flowing along the thread structures at velocities 15± 10 kms^–1, which suggests that the flows must be field-aligned. In one case where a bundle of thin threads appears to be rooted in the nearby photosphere, we find that the individual threads connects with intergranular, dark lanes in the photosphere. We do not find signs of typical network fields at the roots of the fine threads, as normally evidenced by bright points in associated G-band images. It is suggested that filament threads are rooted in relatively weak magnetic fields.  相似文献   

The Precipitation Chemistry over Central Bohemia: Attempt to Estimate the Sources and Pathways     

Vach  M. J.  Navrátil  T.  Fottová  D.  špičková  J.  Skřivan  P. 《Studia Geophysica et Geodaetica》2004,48(4):791-809

An attempt to indicate the sources and pathways of selected chemical substances in precipitation over central Bohemia was accomplished with help of bulk samples, collected in a forested rural landscape approx. 30 km SE from Prague, capital of the Czech Republic. Samples have been collected monthly throughout the 1990s. They were analyzed to determine the concentration of selected major cations and anions (Na⁺, K⁺, Ca²⁺, Mg²⁺, NH₄ ⁺, SO₄ ^2-, NO₃ ^-, Cl^-), as well as several minor and trace elements (Al, As, Be, Cd, Cu, Fe, Mn, Pb, Sr, Zn, F^-).Set of the bulk samples shows strong mutual correlation of the main acidifiers - compounds of N, S (and F). Good correlation occurs also at the typical lithogenic elements Al, K, Na, Ca, Mg, Sr, and the typical elements originating from the flue gases of the combustion chambers burning low quality brown coal - As, (Be), Cd, Cu, Pb, and Zn. The only strong correlation of Cl with Na (and Mg) indicates that majority of these elements originates from the oceanic spray. The content of pollutants in precipitation depends on the air masses types and on the rout of their approach to the sampling site. The typing of synoptic situations was employed for the determination of the air masses types and routs and of the corresponding fronts and precipitation fields.  相似文献   

A water balance study in lateritic terrain     

Elin Langsholt 《水文研究》1992,6(1):11-27

The water balance of a 600 m² field site on a lateritic hillslope in Kerala, southwest India, has been studied during two southwest monsoon seasons. Surface runoff was of minor importance while infiltration and evapotranspiration were the major components amounting to approximately 2/3 and 1/3 of the rainfall, respectively. Groundwater response was rapid, involving fluctuations of several metres. Recharge mechanisms hypothesized are water movement via preferred pathways from the ground surface to the capillary fringe where rapid rise in groundwater level is brought about by a transmitted pressure pulse. Groundwater recharge was found normally to take place during the southwest monsoon season only. the field study demonstrates that seasonal shallow groundwater recharge representing the major portion of the rainfall May, be observed in this lateritic terrain in the humid tropics. It indicates a good potential for further groundwater development. Moreover, conditions are conducive to a considerable contribution to possible recharge to deeper aquifers. the observed groundwater recharge is the result of a complex process on which further research will throw more light.  相似文献   

The melt‐bearing impactites of the Ritland structure,Norway–Implications for melt formation in small impact craters     

Elin Kalleson  Henning Dypvik  Fridtjof Riis  Odd Nilsen 《Meteoritics & planetary science》2013,48(9):1678-1701

A melt‐bearing impactite unit is preserved in the 2.7 km diameter shallow marine Ritland impact structure. The main exposure of the melt‐bearing unit is in an approximately 100 m long cliff about 700 m southwest of the center of the structure. The melt and clast content vary through this maximum 2 m thick unit, so that lithology ranges from impact melt rock to suevite. Stratigraphic variations with respect to the melt content, texture, mineralogy, and geochemistry have been studied in the field, and by laboratory analysis, including thin section microscopy. The base of the melt‐bearing unit marks the transition from the underlying lithic basement breccia, and the unit may have been emplaced by an outward flow during the excavation stage. There is an upward development from a melt matrix‐dominated lower part, that commonly shows flow structures, to an upper part characterized by more particulate matrix with patchy melt matrix domains, commonly as deformed melt slivers intermingled with small lithic clasts. Melt and lithic fragments in the upper part display a variety of shapes and compositions, some of which possibly represent fallback material from the ejecta cloud. The upper boundary of the melt‐bearing impactite unit has been placed where the deposits are mainly clastic, probably representing slump and avalanche deposits from the modification stage. These deposits are therefore considered sedimentary and not impactites, despite the component of small melt fragments and shocked minerals within the lowermost part, which was probably incorporated as the debris moved down the steep crater walls.  相似文献   

Hydrogeochemical characteristics of acid mine drainage and water pollution at Makum Coalfield,India   总被引：1，自引：0，他引：1  

Sk. Md. Equeenuddin  S. Tripathy  P.K. Sahoo  M.K. Panigrahi 《Journal of Geochemical Exploration》2010

Acid mine drainage (AMD) is one of the severe environmental problems that coal mines are facing. Generation of AMD in the northeastern part of India due to the coal mining activities has long been reported. However detailed geochemical characterization of AMD and its impact on water quality of various creeks, river and groundwater in the area has never been reported. Coal and coal measure rocks in the study area show finely disseminated pyrite crystals. Secondary solid phases, resulted due to oxidation of pyrite, occur on the surface of coal, and are mainly consisting of hydrated sulphate complexes of Fe and Mg (copiapite group of minerals). The direct mine discharges are highly acidic (up to pH 2.3) to alkaline (up to pH 7.6) in nature with high concentration of SO₄²⁻. Acidic discharges are highly enriched with Fe, Al, Mn, Ni, Pb and Cd, while Cr, Cu, Zn and Co are below their maximum permissible limit in most mine discharges. Creeks that carrying the direct mine discharges are highly contaminated; whereas major rivers are not much impacted by AMD. Ground water close to the collieries and AMD affected creeks are highly contaminated by Mn, Fe and Pb. Through geochemical modeling, it is inferred that jarosite is stable at pH less than 2.5, schwertmannite at pH less than 4.5, ferrihydrite above 5.8 and goethite is stable over wide range of pH, from highly acidic to alkaline condition.  相似文献