Vertical profiles of aerosol black carbon in the atmospheric boundary layer over a tropical coastal station: Perturbations during an annular solar eclipse     

S. Suresh Babu  V. Sreekanth  K. Krishna Moorthy  Mannil Mohan  N.V.P. Kirankumar  D. Bala Subrahamanyam  Mukunda M. Gogoi  Sobhan Kumar Kompalli  Naseema Beegum  Jai Prakash Chaubey  V.H. Arun Kumar  Ravi K. Manchanda 《Atmospheric Research》2011,99(3-4):471-478

Altitude profiles of aerosol black carbon (BC) in the atmospheric boundary layer (ABL) over a tropical coastal station, Trivandrum have been examined on two days using an aethalometer attached to a tethered balloon. One of these days (15th January, 2010) coincided with a (annular) solar eclipse, the longest of this century at this location, commenced at 11:05 local time and ended by 15:05, lasting for 7 min and 15 s (from 13:10:42), with its maximum contact occurring at ~ 13:14 IST with ~ 92% annularity, thereby providing an opportunity to understand the eclipse induced perturbations. Concurrent measurements of the ABL parameters such as air temperature, relative humidity and pressure were also made on these days to describe the response of the ABL to the eclipse. BC profiles, in general, depicted similar features up to an altitude of ~ 200 m on the eclipse day and control day, above which it differed conspicuously with profiles on eclipse day showing increasingly lower concentration as we moved to higher altitudes. Examination of the meteorological profiles showed that the altitude of maximum convection rapidly fell down during the eclipse period compared to that on control day indicating a rather shallow convection on eclipse day. Comparison of diurnal variations of BC at the surface level showed that the rate of decrease in BC during daytime on the eclipse day was smaller than that on the control day due to the reduced convection, shallow ABL and consequent reduction in the ventilation coefficient. Moreover the time of the nocturnal increase has advanced by ~ 1:30 h on the eclipse day, occurred at around 19:30 IST in contrast to all the other days of January 2010, where this increase usually occur well after 20:30 IST, with a mean value of 21:00 IST. This is attributed to the weak sea-breeze penetration during the eclipse day, which led to an early onset of the land breeze.  相似文献   

Polybrominated diphenyl ethers (PBDEs) in marine foodstuffs in Australia: residue levels and contamination status of PBDEs   总被引：3，自引：0，他引：3  

Shanmuganathan D  Megharaj M  Chen Z  Naidu R 《Marine pollution bulletin》2011,63(5-12):154-159

Edible marine products (n=24) collected from the fish markets in Adelaide, Australia, were analysed for the presence of polybrominated diphenyl ethers (PBDEs). The total concentration of 11 PBDE congeners found in the marine products ranged from 1.01 to 45 ng/g fresh weight. Among the samples analysed, imported silver fish and prawns from Vietnam and Thailand respectively, recorded the highest ∑PBDEs concentrations (45.10 and 43.29 ng/g fresh weight) as against 13.08 and 12.57 ng/g fresh weight in Australian king prawns and Gar fish. BDE-209 was the most dominant congener in the marine products followed by BDE-47, 99 and 100. The calculated average daily intakes of ∑PBDEs per day for an adult male and female (19 or more years old) were 1026.8 and 1188.4 ng/kg per day, respectively. This study clearly shows that the dietary exposure to marine foods can contribute to PBDEs accumulation in human body.  相似文献   

Bioreduction of Fe-bearing clay minerals and their reactivity toward pertechnetate (Tc-99)     

Michael E. Bishop  Ravi K. Kukkadapu  Richard E. Edelmann 《Geochimica et cosmochimica acta》2011,75(18):5229-5246

⁹⁹Technetium (⁹⁹Tc) is a fission product of uranium-235 and plutonium-239 and poses a high environmental hazard due to its long half-life (t_1/2 = 2.13 × 10⁵ y), abundance in nuclear wastes, and environmental mobility under oxidizing conditions [i.e., Tc(VII)]. Under reducing conditions, Tc(VII) can be reduced to insoluble Tc(IV). Ferrous iron, either in aqueous form (Fe²⁺) or in mineral form [Fe(II)], has been used to reduce Tc(VII) to Tc(IV). However, the reactivity of Fe(II) from clay minerals, other than nontronite, toward immobilization of Tc(VII) and its role in retention of reduced Tc(IV) has not been investigated. In this study the reactivity of a suite of clay minerals toward Tc(VII) reduction and immobilization was evaluated. The clay minerals chosen for this study included five members in the smectite-illite (S-I) series, (montmorillonite, nontronite, rectorite, mixed layered I-S, and illite), chlorite, and palygorskite. Surface Fe-oxides were removed from these minerals with a modified dithionite-citrate-bicarbonate (DCB) procedure. The total structural Fe content of these clay minerals, after surface Fe-oxide removal, ranged from 0.7% to 30.4% by weight, and the structural Fe(III)/Fe(total) ratio ranged from 45% to 98%. X-ray diffraction (XRD) and Mössbauer spectroscopy results showed that after Fe oxide removal the clay minerals were free of Fe-oxides. Scanning electron microscopy (SEM) revealed that little dissolution occurred during the DCB treatment. Bioreduction experiments were performed in bicarbonate buffer (pH-7) with structural Fe(III) in the clay minerals as the sole electron acceptor, lactate as the sole electron donor, and Shewanella putrefaciens CN32 cells as a mediator. In select tubes, anthraquinone-2,6-disulfate (AQDS) was added as electron shuttle to facilitate electron transfer. In the S-I series, smectite (montmorillonite) was the most reducible (18% and 41% without and with AQDS, respectively) and illite the least (1% for both without and with AQDS). The extent and initial rate of bioreduction were positively correlated with the percent smectite in the S-I series (i.e., layer expandability). Fe(II) in the bioreduced clay minerals subsequently was used to reduce Tc(VII) to Tc(IV) in PIPES buffer. Similar to the trend of bioreduction, in the S-I series, reduced NAu-2 showed the highest reactivity toward Tc(VII), and reduced illite exhibited the least. The initial rate of Tc(VII) reduction, after normalization to clay and Fe(II) concentrations, was positively correlated with the percent smectite in the S-I series. Fe(II) in chlorite and palygorskite was also reactive toward Tc(VII) reduction. These data demonstrate that crystal chemical parameters (layer expandability, Fe and Fe(II) contents, and surface area, etc.) play important roles in controlling the extent and rate of bioreduction and the reactivity toward Tc(VII) reduction. Reduced Tc(IV) resides within clay mineral matrix, and this association could minimize any potential of reoxidation over long term.  相似文献   

Spatial geochemical variation of major and trace elements in the marine sediments of Mumbai Harbor Bay     

Ajay Kumar  R. K. Singhal  Sabyasachi Rout  P. M. Ravi 《Environmental Earth Sciences》2013,70(7):3057-3066

The resulting concentration data sets of major (Na, K, Mg, Ca and Fe) and trace elements (Cu, Ni, Co and Mn) in bed and suspended sediments were used to evaluate the enrichment factor for anthropogenic influences and principal component analysis for identifying the origin of source contributions in the studied area. Normalization of metals to Fe indicated that high enrichment factors in the bed sediment were in the order of Co > Cu > Na > Ca > Ni except Mg, K and Mn while for suspended sediments, only Co has a high enrichment factor. High enrichment of Co and Cu reflected the contamination of sediments from anthropogenic sources. The high influence of Na and Ca in sediments may be caused for seawater salinization factor. A significant positive correlation among enrichment factors of various elements of interest suggests a common origin/identical behavior during transport in the sediment system.  相似文献   

Distributions of ozone and related trace gases at an urban site in western India     

Ravi Yadav  L. K. Sahu  S. N. A. Jaaffrey  G. Beig 《Journal of Atmospheric Chemistry》2014,71(2):125-144

Continuous in-situ measurements of surface ozone (O₃), carbon monoxide (CO) and oxides of nitrogen (NOx) were conducted at Udaipur city in India during April 2010 to March 2011. We have analyzed the data to investigate both diurnal and seasonal variations in the mixing ratios of trace gases. The diurnal distribution of O₃ showed highest values in the afternoon hours and lower values from evening till early morning. The mixing ratios of CO and NOx showed a sharp peak in the morning hours but lowest in the afternoon hours. The daily mean data of O₃, CO and NOx varied in the ranges of 5–51 ppbv, 145–795 ppbv and 3–25 ppbv, respectively. The mixing ratios of O₃ were highest of 28 ppbv and lowest 19 ppbv during the pre-monsoon and monsoon seasons, respectively. While the mixing ratios of both CO and NOx showed highest and lowest values during the winter and monsoon seasons, respectively. The diurnal pattern of O₃ is mainly controlled by the variations in photochemistry and planetary boundary layer (PBL) depth. On the other hand, the seasonality of O₃, CO and NOx were governed by the long-range transport associated mainly with the summer and winter monsoon circulations over the Indian subcontinent. The back trajectory data indicate that the seasonal variations in trace gases were caused mainly by the shift in long-range transport pattern. In monsoon season, flow of marine air and negligible presence of biomass burning in India resulted in lowest O₃, CO and NOx values. The mixing ratios of CO and NOx show tight correlations during winter and pre-monsoon seasons, while poor correlation in the monsoon season. The emission ratio of ?CO/?NOx showed large seasonal variability but values were lower than those measured over the Indo Gangetic Plains (IGP). The mixing ratios of CO and NOx decreased with the increase in wind speed, while O₃ tended to increase with the wind speed. Effects of other meteorological parameters in the distributions of trace gases were also noticed.  相似文献   

Disturbance compensating control of orbit radially aligned two-craft Coulomb formation     

Ravi?InampudiEmail author  Hanspeter?Schaub 《Celestial Mechanics and Dynamical Astronomy》2012,112(4):445-458

This paper investigates the orbit radial stabilization of a two-craft virtual Coulomb structure about circular orbits and at Earth–Moon libration points. A generic Lyapunov feedback controller is designed for asymptotically stabilizing an orbit radial configuration about circular orbits and collinear libration points. The new feedback controller at the libration points is provided as a generic control law in which circular Earth orbit control form a special case. This control law can withstand differential solar perturbation effects on the two-craft formation. Electrostatic Coulomb forces acting in the longitudinal direction control the relative distance between the two satellites and inertial electric propulsion thrusting acting in the transverse directions control the in-plane and out-of-plane attitude motions. The electrostatic virtual tether between the two craft is capable of both tensile and compressive forces. Using the Lyapunov’s second method the feedback control law guarantees closed loop stability. Numerical simulations using the non-linear control law are presented for circular orbits and at an Earth–Moon collinear libration point.  相似文献   

Dark matter halo creation in moving barrier models     

Jorge Moreno  Carlo Giocoli  Ravi K. Sheth 《Monthly notices of the Royal Astronomical Society》2009,397(1):299-310

In hierarchical models of structure formation, the time derivative of the halo mass function may be thought of as the difference of two terms – a creation term, which describes the increase in the number of haloes of mass m from mergers of less massive objects, and a destruction term, which describes the decrease in the number of m -haloes as these merge with other haloes, creating more massive haloes as a result. The first part of this paper focuses on estimating the distribution of times when these creation events take place. In models where haloes form from a spherical collapse, this distribution can be estimated from the same formalism which is used to estimate halo abundances: the constant-barrier excursion-set approach. In the excursion-set approach, moving rather than constant barriers are necessary for estimating halo abundances when the collapse is triaxial. First, we generalize the excursion-set estimate of the creation time distribution by incorporating ellipsoidal collapse. Then, we show that these moving barrier based predictions are in better agreement with measurements in numerical simulations than are the corresponding predictions of the spherical collapse model. In the second part of the paper, we link the creation time distribution to the creation term mentioned above. For this quantity, the improvement provided by the ellipsoidal collapse model is more evident. These results should be useful for studies of merger-driven star formation rates and active galactic nucleus activity. We also present a similar study of the creation of haloes conditioned on belonging to an object of a certain mass today, and reach similar conclusions – the moving barrier based estimates are in substantially better agreement with the simulations. This part of the study may be useful for understanding the tendency for the oldest stars to exist in the most massive objects, and for star formation to only occur in lower mass objects at late times.  相似文献   

The initial shear field in models with primordial local non-Gaussianity and implications for halo and void abundances     

Tsz Yan Lam  Ravi K. Sheth  Vincent Desjacques 《Monthly notices of the Royal Astronomical Society》2009,399(3):1482-1494

We generalize the Doroshkevich's celebrated formulae for the eigenvalues of the initial shear field associated with Gaussian statistics to the local non-Gaussian   f_nl   model. This is possible because, to at least second order in   f_nl   , distributions at fixed overdensity are unchanged from the case   f_nl = 0  . We use this generalization to estimate the effect of   f_nl ≠ 0  on the abundance of virialized haloes. Halo abundances are expected to be related to the probability that a certain quantity in the initial fluctuation field exceeds a threshold value, and we study two choices for this variable: it can either be the sum of the eigenvalues of the initial deformation tensor (the initial overdensity) or its smallest eigenvalue. The approach based on a critical overdensity yields results which are in excellent agreement with numerical measurements. We then use these same methods to develop approximations describing the sensitivity of void abundances on   f_nl   . While a positive   f_nl   produces more extremely massive haloes, it makes fewer extremely large voids. Its effect thus is qualitatively different from a simple rescaling of the normalization of the density fluctuation field σ₈. Therefore, void abundances furnish complementary information to cluster abundances, and a joint comparison of both might provide interesting constraints on primordial non-Gaussianity.  相似文献   

Indian Ocean sea surface salinity variations in a coupled model   总被引：2，自引：0，他引：2  

P. N. Vinayachandran  Ravi S. Nanjundiah 《Climate Dynamics》2009,33(2-3):245-263

The variability of the sea surface salinity (SSS) in the Indian Ocean is studied using a 100-year control simulation of the Community Climate System Model (CCSM 2.0). The monsoon-driven seasonal SSS pattern in the Indian Ocean, marked by low salinity in the east and high salinity in the west, is captured by the model. The model overestimates runoff into the Bay of Bengal due to higher rainfall over the Himalayan–Tibetan regions which drain into the Bay of Bengal through Ganga–Brahmaputra rivers. The outflow of low-salinity water from the Bay of Bengal is too strong in the model. Consequently, the model Indian Ocean SSS is about 1 less than that seen in the climatology. The seasonal Indian Ocean salt balance obtained from the model is consistent with the analysis from climatological data sets. During summer, the large freshwater input into the Bay of Bengal and its redistribution decide the spatial pattern of salinity tendency. During winter, horizontal advection is the dominant contributor to the tendency term. The interannual variability of the SSS in the Indian Ocean is about five times larger than that in coupled model simulations of the North Atlantic Ocean. Regions of large interannual standard deviations are located near river mouths in the Bay of Bengal and in the eastern equatorial Indian Ocean. Both freshwater input into the ocean and advection of this anomalous flux are responsible for the generation of these anomalies. The model simulates 20 significant Indian Ocean Dipole (IOD) events and during IOD years large salinity anomalies appear in the equatorial Indian Ocean. The anomalies exist as two zonal bands: negative salinity anomalies to the north of the equator and positive to the south. The SSS anomalies for the years in which IOD is not present and for ENSO years are much weaker than during IOD years. Significant interannual SSS anomalies appear in the Indian Ocean only during IOD years.  相似文献   

In-situ pore pressure variations in Koyna-Warna — A promising key to understand triggered earthquakes     

H.-J. Kuempel  R. K. Chadha  D. V. Ramana  M. Ravi 《Journal of the Geological Society of India》2017,90(6):678-683

The filling of the Koyna reservoir in western India and the associated triggered earthquakes have been well documented. Several studies have suggested that earthquakes are triggered on pre-existing faults in the region due to changes in pore pressure caused by pore pressure diffusion. To study in-situ pore pressure variations twenty-one borewells were drilled in the Koyna-Warna region under an Indo-German research program during 1995–1998. In most of these wells tidal signals are observed in well level variations indicating sensitivity to small strain changes in hydraulically connected, confined aquifers. Those signals, hence, are suitable to reflect variations in the stress field of local rock formations. More than a decade of well level monitoring has shown four types of earthquake related changes. The pre- and post-earthquake changes are mostly interpretative in nature and difficult to substantiate. The co-seismic and transient changes which are observed for local and large teleseismic events are well established. Wells connected to unconfined aquifers also showed changes related to seismicity in case of large magnitude earthquakes at closer distances. Some anomalous water level fluctuations are seen which are not associated with local or teleseismic earthquakes. These changes are coherent in nature and reflect aseismic regional volume strain.  相似文献