Papers by Abhay Kumar Singh
Clinica Chimica Acta, 2009
Yersinia pestis has been identified as the causative agent of the Black Death pandemic in the 14 ... more Yersinia pestis has been identified as the causative agent of the Black Death pandemic in the 14 th century. However, retrospective diagnostics in human skeletons after more than 600 years are critical. We describe a strategy following a modern diagnostic algorithm and working under strict ancient DNA regime for the identification of medieval human plague victims. An initial screening and DNA quantification assay detected the Y. pestis specific pla gene of the high copy number plasmid pPCP1. Results were confirmed by conventional PCR and sequence analysis targeting both Y. pestis specific virulence plasmids pPCP1 and pMT1. All assays were meticulously validated according to human clinical diagnostics requirements (ISO 15189) regarding efficiency, sensitivity, specificity, and limit of detection (LOD). Assay specificity was 100% tested on 41 clinically relevant bacteria and 29 Y. pseudotuberculosis strains as well as for DNA of 22 Y. pestis strains and 30 previously confirmed clinical human plague samples. The optimized LOD was down to 4 gene copies. 29 individuals from three different multiple inhumations were initially assessed as possible victims of the Black Death pandemic. 7 samples (24%) were positive in the pPCP1 specific screening assay. Confirmation through second target pMT1 specific PCR was successful for 4 of the positive individuals (14%). A maximum of 700 and 560 copies per µl aDNA were quantified in two of the samples. Those were positive in all assays including all repetitions, and are candidates for future continuative investigations such as whole genome sequencing. We discuss that all precautions taken here for the work with aDNA are sufficient to prevent external sample contamination and fulfill the criteria of authenticity. With regard to retrospective diagnostics of a human pathogen and the uniqueness of ancient material we strongly recommend using a careful strategy and validated assays as presented in our study.
Acta Geophysica, 2009
The observation of hisslers during daytime at low latitude station Jammu, India, is reported. The... more The observation of hisslers during daytime at low latitude station Jammu, India, is reported. The hissler elements are quasi-periodic falling tones observed during the period of hiss activity and appear in minutelong sequences with average spacing between individual elements of the order of 0.15 s. Hissler elements exhibit almost no dispersion and no complex internal structure in slope and intensity, and successive hissler elements do not overlap in time. It seems that the reported hisslers might have propagated in prolongitudinal mode.
Planetary and Space Science, 2006
Simulation technique for whistler mode signal propagating through inhomogeneous plasma using WKB ... more Simulation technique for whistler mode signal propagating through inhomogeneous plasma using WKB approximation has been developed (Singh, K., Singh, R.P., Ferencz, O.E., 2004. Simulation of whistler mode propagation for low latitude stations. Earth Planet Space 56, 979-987). In the present paper, we have used it for the analysis of recorded signals at low latitudes and estimated the nose frequency, which is not observed on the dynamic spectra. At low latitudes nose frequency is $100 kHz or more and therefore it is absent in the dynamic spectra due to attenuation of the signal at higher frequencies. The importance of nose frequency is in determining the exact path of propagation, which is required in probing of ambient medium. It is shown that the method permits to study the nose frequency variation, it can be used to deduce physical parameters as the global electric field. A case study permits to get a reasonable value of the electric field, which up to now could not be done at very low latitude. r
Philosophical Magazine, 2009
The Zr 60 Al 7.5 Cu 17.5 Ni 10 Si 4 B 1 (numbers indicate at.%) amorphous alloy was selected for ... more The Zr 60 Al 7.5 Cu 17.5 Ni 10 Si 4 B 1 (numbers indicate at.%) amorphous alloy was selected for an investigation of its crystallization kinetics and thermal stability because of its high activation energy of 370 kJ/mol for crystallization and its extended incubation time during isothermal annealing in the supercooled temperature region. The crystallization behavior and microstructure development during isothermal annealing were examined by isothermal differential scanning calorimetry, X-ray diffractometry and transmission electron microscopy (TEM). When annealing the Zr 60 Al 7.5 Cu 17.5 Ni 10 Si 4 B 1 alloy isothermally at 714 K, Zr 2 Cu crystals with average size about 5 nm were first observed at the early stage of 1% crystallization by TEM. The Zr 2 Cu crystal size increases with annealing time, then reaches an average size of about 25 nm at the stage of 72% crystallization. In addition, the grain growth time as a function of the cube of particle size of the Zr 2 Cu type crystalline phases presented a good linear relationship. This indicates that the crystal growth of the Zr 60 Al 7.5 Cu 17.5 Ni 10 Si 4 B 1 alloy is a thermally activated process. The activation energy for growth of Zr 2 Cu particles in the Zr 60 Al 7.5 Cu 17.5 Ni 10 Si 4 B 1 amorphous alloy is found to be 210 ± 25 kJ/mol. The lower activation energy of crystal growth during crystallization in comparison with 440 kJ/mol for crystallization in Zr 65 Cu 35 corresponds to the rearrangement of other smaller atoms in the glass, such as Al or Si (compare to Zr).
Observation of whistler-mode chorus emissions recorded at Indian Antarctic station, Maitri (Lat =... more Observation of whistler-mode chorus emissions recorded at Indian Antarctic station, Maitri (Lat = 700 46/ S, Long = 110 50/ E, L = 4.5) during a quiet period on 13th Feb. 2001 is reported. The detailed spectral analysis of recorded chorus emissions shows that each chorus element originates from the upper edge of the underlying hiss band. To explain the observed dynamic spectra of these chorus emissions, a possible generation mechanism is presented based on the recent nonlinear theory. It is observed that the seeds of chorus emissions with rising frequency are generated near the magnetic equator as a result of a nonlinear growth mechanism that depends on the wave amplitude. On the basis of this theory, frequency sweep rate of chorus emission is computed and compared with that of our experimentally observed values, which shows in general a good agreement. Keywords: Chorus emission, Whistler mode waves, Magnetospheric physics, Wave particle interactions.
Electromagnetic anomalies have been observed in sub-ionospheric VLF signal before recent earthqua... more Electromagnetic anomalies have been observed in sub-ionospheric VLF signal before recent earthquakes in Japan on 15 February, 2009, Nicobar Island, India on 10 August, 2009 and Kepulaun Mentawai Region, Indonesia on 16 Aug 2009. VLF signal transmitted from Hawaii, USA North West Cape, Australia is monitored continuously at our ground station Varanasi. Here we have tried to find out ionospheric perturbations revealed by VLF signals prior to the earthquake. We observed a significant enhancement in nighttime fluctuation several days before the earthquake. VLF radio waves show anomalous variations in amplitude from their day to day variability. It is fond that nighttime trend exhibit a significant decrease in amplitude several days before the earthquake. Apart form the decrease in amplitude it is also found that there is sudden enhancement in daytime amplitude, within 48 hours prior to the earthquake. The possible mechanisms for these ionospheric perturbations due to earthquake have been discussed.
Current Applied Physics, 2008
Samples of selenium rich Se 85 Cd 15−x Zn x (x = 0, 3, 7, 11 and 15) system in bulk form have bee... more Samples of selenium rich Se 85 Cd 15−x Zn x (x = 0, 3, 7, 11 and 15) system in bulk form have been prepared using a technique of slow cooling of the melt. Measurements of effective thermal conductivity (λ e ) and effective thermal diffusivity (χ e ) of Se 85 Cd 15−x Zn x pellets, prepared at constant load of 10 tons, have been carried out from room temperature to 200 • C using the transient plane source technique. The variation in λ e and χ e of Se 85 Cd 15−x Zn x with the concentration of zinc and temperature is explained on the basis of structure modifications of the samples and the mean free path of the phonons due to scattering from defects and voids.
Mine Water and The Environment, 2010
In a qualitative assessment of mine water from the Raniganj coalfield, 77 mine water samples were... more In a qualitative assessment of mine water from the Raniganj coalfield, 77 mine water samples were analyzed to assess water quality and suitability for domestic, industrial, and irrigation uses. The pH of the mine water ranged from 6.5 to 8.8. Total dissolved solids (TDS) ranged from 171 to 1,626 mg L−1; spatial differences between the TDS values reflect variations in lithology, activities, and prevailing hydrological regime. The anion chemistry was dominated by HCO3− and SO42−. On average, Cl− contributes 10 and 19% of the total anionic balance, respectively, in the Barakar and Raniganj Formation mine water. F− and NO3− contribute <2% to the total anions. The cation chemistry is dominated by Mg2+ and Ca2+ in the mine water of the Barakar Formation and Na+ in the Raniganj Formation mines. Much of the mine water, especially of the Barakar Formation area, has high TDS, total hardness, and SO4 concentrations. Concentrations of some trace metals (i.e. Fe, Cr, Ni) were found to be above the levels recommended for drinking water. However, the mine water can be used for irrigation, except at some sites, especially in the Raniganj Formation area, where high salinity, sodium adsorption ratio, %Na, residual sodium carbonate, and excess Mg restrict its suitability for agricultural uses.
Physica Scripta, 2011
Chalcogenide glasses or amorphous semiconductors are materials applicable in the field of optoele... more Chalcogenide glasses or amorphous semiconductors are materials applicable in the field of optoelectronics. Microstructural and thermal analyses can provide useful information to understand the physical behavior of such materials. This paper is devoted to exploring the localized microstructural growth and kinetics of Se98-xZn2Inx (0<=x<=10) glassy alloys. Localized microstructural growth within the glassy morphology has been studied using a scanning electron microscope. Kinetic properties such as glass-forming ability peak crystallization activation energy (Ep) and Hruby number (Hr) dynamical thermal stability were obtained from a differential scanning calorimetry measurement analysis. The results reveal that the localized microstructural growth and kinetics parameters of Se98-xZn2Inx glasses vary with the concentration of alloys.
The dual frequency Global Positioning System (GPS) data recorded at Varanasi (geographic latitude... more The dual frequency Global Positioning System (GPS) data recorded at Varanasi (geographic latitude 250, 16 N longitude 820, 59 E) and Kanpur (geographic latitude 260, 30 N longitude 800, 12 E) stations, near the equatorial ionosphere anomaly (EIA) in India, have been analyzed to retrieve total electron content (TEC). The daily peak value of vertical total electron content (VTEC) has been utilized to study the variability of EIA. Present paper studied monthly, seasonal and annual variations as well as solar and geomagnetic effects on EIA. It has been found that EIA yield their maximum values during the equinox months and minimum during summer and winter. The correlations of EIA with solar as well as geomagnetic indices have been also discussed. Key words: Total electron contents (TECs), EIA, GPS.
Journal of Modern Optics, 2009
The UVVIS absorption spectra of thin film of Se98ÀxZn2Inx (x ¼ 0,2,4,6 and 10) chalcogenide glas... more The UVVIS absorption spectra of thin film of Se98ÀxZn2Inx (x ¼ 0,2,4,6 and 10) chalcogenide glasses were measured in the wavelength range of 2001100nm by using spectrophotometer. It is observed from UVVIS absorption measurements that the optical ...
Current Applied Physics, 2009
The present work reports the observation of Meyer–Neldel rule for the thermally activated crystal... more The present work reports the observation of Meyer–Neldel rule for the thermally activated crystallization of glassy Se98−xZn2Inx (0 ⩽ x ⩽ 10) alloys. We have observed a strong co-relation between the pre-exponential factor K0 of rate constant K(T) of crystallization and activation energy of crystallization Ec in the present case. This indicates the presence of compensation effect for the non-isothermal crystallization process in the present glassy system, which is explained in terms of phase separation of the present alloys due to flaw bonds of these amorphous solids.
Ionospheric total electron content (TEC) and scintillations have been recorded continuously since... more Ionospheric total electron content (TEC) and scintillations have been recorded continuously since January 2009 using a dual frequency GPS receiver at Varanasi, India (geographic lat. 25.30 N, long. 82.990 E). The trajectory of a GPS satellite plays an important role in observing the bubble characteristics. The GPS data with a sampling interval of 60 s were analyzed to determine TEC, the rate of change of TEC (ROT) and as well as ROTI, defined as the standard deviation of ROT. In this work we compare the S4 index of GPS scintillations with the ROTI values and there by investigated the evolution of large and small scale irregularities at scale length of few kilometers and 400 m respectively observed at low latitude station Varanasi. The effects of geomagnetic activity and geomagnetic storm on the generation of bubbles are studied using Kp index and Dst index respectively. Kew words: GPS, Plasma bubble, ROT, ROTI
The ionospheric total electron content (TEC), derived by analyzing dual frequency signals from th... more The ionospheric total electron content (TEC), derived by analyzing dual frequency signals from the Global Positioning System (GPS) recorded near the equatorial anomaly region, Varanasi (geomag. lat. 14 degree 55 minute N, geomag. long.154 degree E) is studied. Specifically, we studied monthly seasonal and annual variations as well as solar and geomagnetic effects on the equatorial ionospheric anomaly (EIA) during the solar minimum period from May 2007 to April 2008. It is found that TEC at equatorial anomaly crest yield their minimum values during the equinox months and their minimum values during the summer. Using monthly averaged peak magnitude of TEC, a clear semi-annual variation is seen with two maxima occurring in both spring and autumn. Statistical studies indicate that the monthly mean values of peak magnitude of TEC were poorly correlated with Dst-index (CC=0.2165) better correlated with Solar flux F10.7 (CC=0.5263) but correlated well with Kp-index (CC=0.7499). The maximum occurrence of the daily maximum EIA crest was found around 14:30 LT. These results were also discussed with the recent published works.
Environmental Earth Sciences, 2008
The chemical characteristics of surface, groundwater and mine water of the upper catchment of the... more The chemical characteristics of surface, groundwater and mine water of the upper catchment of the Damodar River basin were studied to evaluate the major ion chemistry, geochemical processes controlling water composition and suitability of water for domestic, industrial and irrigation uses. Water samples from ponds, lakes, rivers, reservoirs and groundwater were collected and analysed for pH, EC, TDS, F, Cl, HCO3, SO4, NO3, Ca, Mg, Na and K. In general, Ca, Na, Mg, HCO3 and Cl dominate, except in samples from mining areas which have higher concentration of SO4. Water chemistry of the area reflects continental weathering, aided by mining and other anthropogenic impacts. Limiting groundwater use for domestic purposes are contents of TDS, F, Cl, SO4, NO3 and TH that exceed the desirable limits in water collected from mining and urban areas. The calculated values of SAR, RSC and %Na indicate good to permissible use of water for irrigation. High salinity, %Na, Mg-hazard and RSC values at some sites limit use for agricultural purposes.
Water samples collected from the six reservoirs of Damodar River basin in pre- and post-monsoon, ... more Water samples collected from the six reservoirs of Damodar River basin in pre- and post-monsoon, have been analysed, to study the major ion chemistry and the weathering and geochemical processes controlling the water composition. Ca, Na and HCO3 dominate the chemical composition of the reservoir water. The seasonal data shows a minimum concentration of most of the ions in post-monsoon and a maximum concentration in pre-monsoon seasons, reflecting the concentrating effects due to elevated temperature and increased evaporation during the low water level period of the pre-monsoon season. Water chemistry of the reservoirs strongly reflects the dominance of continental weathering aided by atmospheric and anthropogenic activities in the catchment area. Higher concentration of SO4 and TDS in Panchet, Durgapur and Tenughat reservoirs indicate mining and anthropogenic impact on water quality. The high contribution of (Ca+Mg) to the total cations, high concentration of dissolved silica, relatively high (Na+K)/TZ+ ratio (0.3) and low equivalent ratio of (Ca+Mg)/(Na+K) suggests combined influence of carbonate and silicate weathering. Kaolinite is the possible mineral that is in equilibrium with the water, implying that the chemistry of reservoir water favours kaolinite formation. The calculated values of SAR, RSC and sodium percentage indicate the ‘excellent to good quality’ of water for irrigation uses.
Pramana-journal of Physics, 2000
The amplitude scintillations of very high frequency electromagnetic wave transmitted from geo-sta... more The amplitude scintillations of very high frequency electromagnetic wave transmitted from geo-stationary satellite at 244.168 MHz have been recorded at Varanasi (geom. lat. 14o55'N) during 1991 to 1999. The data are analyzed to determine the statistical features of overhead ionospheric plasma irregularities which are mostly of small duration <30 mintues and are predominant during pre-midnight period. The increase of solar activity generally increases the depth of scintillation. The auto-correlation functions and power spectra of scintillations predict that the scale length of these irregularities varies from 200--500 m having velocity of movement between 75 m/sec to 200 m/sec. These results agree well with the results obtained by other workers.
Pramana-journal of Physics, 2000
The amplitude scintillations of very high frequency electromagnetic wave transmitted from geo-sta... more The amplitude scintillations of very high frequency electromagnetic wave transmitted from geo-stationary satellite at 244.168 MHz have been recorded at Varanasi (geom. lat. 14′ 55′N) during 1991 to 1999. The data are analyzed to determine the statistical features of overhead ionospheric plasma irregularities which are mostly of small duration <30 minutes and are predominant during pre-midnight period. The increase of solar activity generally increases the depth of scintillation. The auto-correlation functions and power spectra of scintillations predict that the scale length of these irregularities varies from 200–500 m having velocity of movement between 75 m/sec to 200 m/sec. These results agree well with the results obtained by other workers.
If the frequency within a set of periodic emissions changes significantly, the set is called drif... more If the frequency within a set of periodic emissions changes significantly, the set is called drifting emissions. In this paper, characteristics of ELF/VLF emissions are examined based on the ELF/VLF data recorded at low latitudes ground station Varanasi (geom. lat. 14 degree 55 minutes N, long. 154 degree E, L=1.07) during the period Feb 1990 to May 1990. Total seven strong events of drifting ELF/VLF emissions have been analyzed in detail. The ELF/VLF emissions are found to exhibit a regular frequency drift with time. The ELF/VLF emissions observed are mainly periodic emissions of rising and falling tone chorus. These emissions were observed during a geomagnetic storm period, when minimum Dst-index was -98 and Kp-index 3 5. The repetion period, sweep rate and the frequency drift rate have been evaluated for all events. The generation of these emissions is supposed to be due to the cyclotron instability of the electrons injected in association with geomagnetic storm/substorm. The frequency drift in these emissions have been interpreted in terms of a combined effect of L-shell drift of energetic electrons and the change in convections electric field during the substorm developments.
Planetary and Space Science, 2006
Simulation technique for whistler mode signal propagating through inhomogeneous plasma using WKB ... more Simulation technique for whistler mode signal propagating through inhomogeneous plasma using WKB approximation has been developed (Singh, K., Singh, R.P., Ferencz, O.E., 2004. Simulation of whistler mode propagation for low latitude stations. Earth Planet Space 56, 979 987). In the present paper, we have used it for the analysis of recorded signals at low latitudes and estimated the nose frequency, which is not observed on the dynamic spectra. At low latitudes nose frequency is ˜100 kHz or more and therefore it is absent in the dynamic spectra due to attenuation of the signal at higher frequencies. The importance of nose frequency is in determining the exact path of propagation, which is required in probing of ambient medium. It is shown that the method permits to study the nose frequency variation, it can be used to deduce physical parameters as the global electric field. A case study permits to get a reasonable value of the electric field, which up to now could not be done at very low latitude.
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Papers by Abhay Kumar Singh