Prospects for Detecting the 326.5 MHz Redshifted 21-cm HI Signal with the Ooty Radio Telescope (ORT)

Observations of the redshifted 21-cm HI fluctuations promise to be an important probe of the post-reionization era (z≤ 6). In this paper we calculate the expected signal and foregrounds for the upgraded Ooty Radio Telescope (ORT) which operates at frequency ν _o = 326.5 MHz which corresponds to redshift z = 3.35. Assuming that the visibilities contain only the HI signal and system noise, we show that a 3 σ detection of the HI signal (～1 mK) is possible at angular scales 11^′ to 3^° with ≈1000 h of observation. Foreground removal is one of the major challenges for a statistical detection of the redshifted 21 cm HI signal. We assess the contribution of different foregrounds and find that the 326.5 MHz sky is dominated by the extragalactic point sources at the angular scales of our interest. The expected total foregrounds are 10⁴?10⁵ times higher than the HI signal.     

Palygorskite from cave sediments: case study from Wadi Haqil,United Arab Emirates

The x-ray powder diffraction identification of clay minerals both in bulk samples and in separated clay fraction confirmed the presence of palygorskite in samples of cave sediments from Wadi Haqil (the western slopes of Musandam Mountains; Ras Al-Khaimah Emirate, UAE). Samples contain quartz, gypsum, smectite, kaolinite, calcite, and palygorskite, some of them chlorite, illite, feldspars, and goethite. Calcite dominates in most samples; smectite prevails in clay fraction. After heating, the 001 reflection of chlorite shifts to higher diffraction angles and its intensity decreases; these features indicate that the chlorite represent a Fe-dominant species. Unit-cell dimensions of major phases as refined by the Rietveld method are in agreement with literature data. Chemical composition of palygorskite was derived from unit-cell dimensions as follows: MgO content is 11–14 wt% and Al₂O₃ 10–13 wt%. Clay mineralogy is only hard to ascertain from the scanning electron microscope (SEM) images even after being combined with the energy-dispersive spectrometer data. The SEM was also used to characterize gypsum grains; they often display flow deformation features. Studied cave sediments represent palygorskite-bearing weathering products and desert soils re-deposited from the cave surroundings by slope processes and wind and/or surface runoff. The mixture with other clay minerals, quartz, feldspars, etc. supports this interpretation. Fine-grained quartz fraction is probably wind-blown. Gypsum and calcite are the precipitates (crusts and/or cements), although gypsum can also be re-deposited from omnipresent gypsum-cemented surface sediments.     

Long-term seismic observations along Myanmar–Sunda subduction margin: insights for 2004 Mw > 9.0 earthquake

International Journal of Earth Sciences - The present study investigates the temporal variation of few seismic parameters between the Myanmar (Zone I), Andaman–Nicobar–Northwest Sumatra...     

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

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.     

Neutron stars:a relativistic study

We study the inner structure of a neutron star from a theoretical point of view and the outcome results are compared with observed data. We propose a stiff equation of state relating pressure with matter density. From our study we calculate mass(M),compactness(u) and surface redshift(Zs) for two binary millisecond pulsars,namely PSR J1614–2230 and PSR J1903+327,and four X-ray binaries,namely Cen X-3,SMC X-1,Vela X-1 and Her X-1,and compare them with recent observational data.Finally,we examine the stability for such a type of theoretical structure.     

On the Gas Phase Reactions Between Volatile Biogenic Mercury Species and the Nitrate Radical

Tropospheric mercury is dominated by gas phase species. In this paper, the gas phase reactions between the nitrate radical and volatile biogenic mercury species have been investigated. An upper limit for the gas phase rate coefficient for reaction between elemental mercury and NO₃-radicals was determined to 4 × 10^–15 cm³ molecule^–1 s^–1 by using the fast flow-discharge technique. The reaction between dimethyl mercury and NO₃, previously shown to be rapid, has also been studied in the laboratory with respect to product distribution using FT-IR. The result from the product study is consistent with a transformation of dimethyl mercury into inorganic, divalent mercury. All carbon delivered as dimethyl mercury was transformed into formaldehyde, methanol and methyl peroxynitrate. Hg was observed as a minor (2%) product. By exclusion, HgO is proposed as the mercury-containing product. Thus, the reaction between dimethyl mercury and the nitrate radical is excluded as a source of monomethyl mercury species in the atmosphere.     

Crystal structure of meteoritic schreibersites: determination of absolute structure

Minerals of the schreibersite–nickelphosphide series (Fe,Ni)₃P crystallize in the non-centrosymmetric space group . As a consequence, they can possess two different spatial arrangements of the constituting atoms within the unit cell, related by the inversion symmetry operation. Here, we present the crystal structure refinements from single crystal X-ray diffraction data for schreibersite grains from iron meteorites Acuña, Carlton, Hex River Mts. (three different crystals), Odessa (two different crystals), Sikhote Alin, and Toluca aiming for the determination of the absolute structure of the examined crystals. The crystals studied cover the composition range from ~58 mol% to ~80 mol% Fe₃P end-member. Unit-cell parameter a and volume of the unit cell V, as well as certain topological structural parameters tightly correlate with Fe₃P content. Unit-cell parameter c, on the other hand, does not show such strong correlation. Eight of the nine crystal structure refinements allowed unambiguous absolute structure assignment. The single crystal extracted from Toluca is, however, of poor quality and consequently the structure refinement did not provide as good results as the rest of the materials. Also, this crystal has only weak inversion distinguishing power to provide unequivocal absolute structure determination. Six of the eight unambiguous absolute structure determinations indicated inverted atomic arrangement compared to that reported in earlier structure refinements (here called standard). Only two grains, one taken from Odessa iron and the other from the Hex River Mts. meteorite, reveal the dominance of standard crystal structure setting.     

The fate of moderately volatile elements in impact events—Lithium connection between the Ries sediments and central European tektites

Lithium abundances and isotope compositions are presented for a suite of sediments from the surroundings of the Ries Impact structure, paralleled by new Li data for central European tektites (moldavites) from several substrewn fields (South Bohemia, Moravia, Cheb Basin, Lusatia), including a specimen from the newly discovered substrewn field in Poland. The data set was supplemented by three clay fractions isolated from sedimentary samples. Moldavites measured in this study show a very narrow range in δ⁷Li values (?0.6 to 0.3‰ relative to L‐SVEC) and Li contents (23.9–48.1 ppm). This contrasts with sediments from the Ries area which show remarkable range in Li isotope compositions (from ?6.9 to 13.4‰) and Li contents (0.6–256 ppm). The OSM sediments which, based on chemical similarity, formed the major part of moldavites, show a range in δ⁷Li values from ?2.0 to 7.9‰ and Li contents from 5.8 to 78.9 ppm. Therefore, the formation of moldavites was apparently accompanied by large‐scale mixing, paralleled by chemical and isotope homogenization of their parent matter. The proposed Li mixing model indicates that sands, clayey sediments, and low volumes of carbonates are the major components for tektite formation whereas residual paleokarst sediments could have been a minor but important component for a subset of moldavites. Striking homogenization of Li in tektites, combined with limited Li loss during impacts, may suggest that moderately volatile elements are not scavenged and isotopically fractionated during large‐scale collisions, which is consistent with recent models. In general, whether homogenization of bodies with distinct Li isotope systematics takes place, or collision of bodies with similar Li systematics operates cannot be resolved at present stage but Li isotope homogeneity of solar system planets and asteroidal bodies tentatively implies the latter.     

Separation of Platinum from Palladium and Iridium in Iron Meteorites and Accurate High‐Precision Determination of Platinum Isotopes by Multi‐Collector ICP‐MS

This study presents a new measurement procedure for the isolation of Pt from iron meteorite samples. The method also allows for the separation of Pd from the same sample aliquot. The separation entails a two‐stage anion‐exchange procedure. In the first stage, Pt and Pd are separated from each other and from major matrix constituents including Fe and Ni. In the second stage, Ir is reduced with ascorbic acid and eluted from the column before Pt collection. Platinum yields for the total procedure were typically 50–70%. After purification, high‐precision Pt isotope determinations were performed by multi‐collector ICP‐MS. The precision of the new method was assessed using the IIAB iron meteorite North Chile. Replicate analyses of multiple digestions of this material yielded an intermediate precision for the measurement results of 0.73 for ε¹⁹²Pt, 0.15 for ε¹⁹⁴Pt and 0.09 for ε¹⁹⁶Pt (2 standard deviations). The NIST SRM 3140 Pt solution reference material was passed through the measurement procedure and yielded an isotopic composition that is identical to the unprocessed Pt reference material. This indicates that the new technique is unbiased within the limit of the estimated uncertainties. Data for three iron meteorites support that Pt isotope variations in these samples are due to exposure to galactic cosmic rays in space.     

Geological controls on groundwater chemistry and arsenic mobilization: Hydrogeochemical study along an E–W transect in the Meghna basin, Bangladesh

Hydrogeochemical investigations along an E–W transect in the middle Meghna basin show groundwater chemistry and redox condition vary considerably with the change in geology. Groundwater in the Holocene shallow (<150 m bgl) alluvial aquifer in western part of the transect is affected by high arsenic concentration (As > 10 μg/l) and salinity. On the other hand, groundwater from the Pliocene Dupi Tila sandy aquifer in the eastern part is fresh and low in As (<10 μg/l). The Holocene shallow aquifers are high in dissolved As, , Fe and dissolved organic carbon (DOC), but generally low in and . High concentrations (250–716 mg/l) together with high DOC concentrations (1.4–21.7 mg/l) in these aquifers reflect active sources of degradable natural organic matter that drives the biogeochemical process. There is generally de-coupling of As from other redox-sensitive elements. In contrast, the Pliocene aquifers are low in As, and DOC. Molar ratio of /H₄SiO₄ suggests that silicate weathering is dominant in the deeper Holocene aquifers and in the Pliocene aquifers. Molar ratios of Cl⁻/ and Na⁺/Cl⁻ suggest mixing of relict seawater with the fresh water as the origin of groundwater salinity. Speciation calculations show that saturation indices for siderite and rhodochrosite vary significantly between the Holocene and Pliocene aquifers. Stable isotopes (δ²H and δ¹⁸O) in groundwater indicate rapid infiltration without significant effects of evaporation. The isotopic data also indicates groundwater recharge from monsoonal precipitation with some impact of altitude effect at the base of the Tripura Hills in the east. The results of the study clearly indicate geological control (i.e. change in lithofacies) on groundwater chemistry and distribution of redox-sensitive elements such as As along the transect.