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61.
The geomagnetic storm of November 1998 is a unique event where IMF-Bz remained southward with values exceeding –15 nT for more than a day. The SYM/H index decreased from about 07 hr on 13 November 1998 reaching a minimum of about –120 nT around midnight of 13–14 November 1998. Features of the equatorial electrojet in the Indian region are studied during the geomagnetic storm event of 13–14 November 1998, based on the geomagnetic data from the chain of observatories in India. Sudden northward turning of IMF-Bz for a very short duration around 08 hr on 13 November 1998 resulted in a small and very short duration counter electrojet. A strong (–50 nT) and a long duration counter electrojet, right from 08 to 13 hr on 14 November 1998 was observed resulting in the absence of equatorial Es at Thumba. Absence of the equatorial ionization anomaly was also observed as seen from the ionograms over Thumba and ionspheric data from Ahmedabad. The delayed effect on 14 November 1998 is due to the disturbance dynamo effect. 相似文献
62.
Mallick Javed Islam Abu Reza Md. Towfiqul Ghose Bonosri Islam H. M. Touhidul Rana Yousuf Hu Zhenghua Bhat Shakeel Ahmed Pal Subodh Chandra Ismail Zulhilmi Bin 《Theoretical and Applied Climatology》2022,147(1-2):307-324
Theoretical and Applied Climatology - The rise in the frequency and magnitude of extreme temperature phenomena across the globe has led to the recurrent incidence of global climate hazards, which... 相似文献
63.
Harish C. Sikka A. Ruth Steward Sayed A. Elmarakby Subodh Kumar U. Devanaboyin Ramesh C. Gupta 《Marine environmental research》1995,39(1-4)
In order to examine factors that may contribute to the reported resistance of rainbow trout, Shasta strain, to the well-known hepatocarcinogenic effects of 2-acetylaminofluorene (AAF), the in-vitro and in-vivo metabolism of [14C]AAF in trout has been examined. Trout (compared to rat) liver microsomes metabolized AAF more efficiently, producing 3-fold larger amounts of ring-hydroxylated metabolites (7-hydroxy-AAF and 5-hydroxy-AAF), but 5-fold less N-hydroxy-AAF. Freshly isolated trout hepatocytes extensively metabolized AAF to form the same ring-hydroxylated metabolites and their respective glucuronide and sulfate conjugates. N-OH-AAF (plus its conjugates) and covalently-bound AAF derivatives amounted, respectively, to < 1% and 1.4–1.6% of total metabolites. Liver DNA of trout treated with AAF contained a single AAF-DNA adduct identified as N-(deoxyguanosin-8-yl)-2-aminofluorene (the major persistent AAF-DNA adduct found in rat liver). The level of this adduct (12 attomoles/μg DNA) was about 1000-fold lower than the level of AAF-DNA adduct previously reported in rat liver. The data show that trout liver, compared to rat liver, is considerably less efficient in metabolizing AAF to carcinogenic metabolites, and more efficient in forming nontoxic products, thus possibly explaining, in part, the resistance of trout to AAF-induced hepatocarcinogenesis. 相似文献
64.
The Fourier transform formula for a two-dimensional fault truncating a horizontal bed at an arbitrary angle of inclination is derived. The amplitude spectrum of the Fourier transform is found to give information about the depth to the top of the upper part of the faulted bed and the inclination of the fault-plane. Under suitable conditions the thickness and the displacement of the bed involved can be obtained. With actual field data, these transforms can be obtained at discrete points by a Fourier analysis of the gravity anomaly. A field example from the Logan fault area near Montreal, Que., Canada, is given. 相似文献
65.
P. VALLABH SHARMA 《Geophysical Prospecting》1967,15(2):167-173
A nomogram is presented which enables evaluation of the components of magnetic attraction of a homogeneous finite rectangular prism, and of gravitational attraction due to a uniform rectangular lamina. In practice any three-dimensional body could be approximated by a number of right rectangular prisms of varying dimensions governed by the shape of the body. The magnetic attraction of the whole body is then obtained by numerical summation of the effects of the constituent prisms. For evaluating the gravitational effect, the cross-section of the body corresponding to each elevation contour is approximated by a number of rectangular laminae (or by a stepping polygon) the attraction of which can be determined with the aid of the same nomogram. The total gravitational attraction of the body is obtained by a process of graphical integration along the vertical axis. 相似文献
66.
参照条件是开展河流生态学研究的基础,这些条件不受或很少受到人为干扰。为研究尼泊尔Andhi Khola河上一处河坝的生态影响,采用野外快速生物筛分(RFB)法预先划分出2个研究参照点或最少干扰参照点,于2013年1月和2月采集了生物学样品(大型脊椎动物)和物理-化学样品。对大型无脊椎动物区系使用多栖息地采样(MHS)法。通过一些指标对预选的研究点进行了确认,这些指标是:尼泊尔生物评价法(NEPBIOS)、生物监测评价法(BMWP)、兴都库什喜马拉雅生物评价法(HKHBIOS)、Hilsenhoff法(HILSENHOFF),以及国家卫生基金会水质指标法(NSFWQI)。NEPBIOS、HKHBIOS、HILSENHOFF、RFB以及NSFWQI指标预测2个参照点的河水水质都比较好,达到II级水准。只有BMWP/ASPT水质指标预测2个参照点的河水水质都很好,达到I级水准。如此,预选的这2个水质较好的点(II级)被确认为研究参照点。本研究表明,多度量法适用于即将修建水利工程的河流的监测与评价。 相似文献
67.
The occurrence of dental/skeletal fluorosis among the people in the study area provided the motivation to assess the distribution, severity and impact of fluoride contamination in groundwater of Bankura district at Simlapal block, West Bengal, India. To meet the desired objective, groundwater samples were collected from different locations of Laxmisagar, Machatora and Kusumkanali regions of Simlapal block at different depths of tube wells in both pre- and post-monsoon seasons. Geochemical results reveal that the groundwaters are mostly moderate- to hard-water type. Of total groundwater samples, 37% are situated mainly in relatively higher elevated region containing fluoride above 1.5 mg/L, indicating that host aquifers are severely affected by fluoride contamination. Machatora region is highly affected by fluoride contamination with maximum elevated concentration of 12.2 mg/L. Several symptoms of fluorosis among the different age-groups of people in Laxmisagar and Machatora areas are indicating consumption of fluoridated water for prolonged period. The groundwater samples were mainly Na–Ca–HCO3 type and rock dominance indicating the dissolution of minerals taking place. Ion exchange between OH? ion and F? ion present in fluoride-bearing mineral is the most dominant mechanism of fluoride leaching. High concentration of Na+ and HCO3 ? increases the alkalinity of the water, providing a favorable condition for fluoride to leach into groundwater from its host rocks and minerals. 相似文献
68.
NAND L SHARMA JAGDISH C KUNIYAL MAHAVIR SINGH PITAMBER P DHYANI RAJ P GULERIA HARINDER K THAKUR PAN S RAWAT 《Journal of Earth System Science》2012,121(1):221-235
Aerosol parameters are measured using a ground-based Multi-wavelength Radiometer (MWR) at Mohal (31.90°N, 77.11°E, 1154 m amsl) in the Kullu valley during clear sky days of a seasonal year. The study shows that the values of spectral aerosol optical depths (AODs) at 500 nm and the Ångstrom turbidity coefficient ‘β’ (a measure of columnar loading in atmosphere) are high (0.41 ± 0.03, 0.27 ± 0.01) in summer, moderate (0.30 ± 0.03, 0.15 ± 0.03) in monsoon, low (0.19 ± 0.02, 0.08 ± 0.01) in winter and lowest (0.18 ± 0.01, 0.07 ± 0.01) in autumn, respectively. The Ångstrom wavelength exponent ‘α’ (indicator of the fraction of accumulation-mode particles to coarse-mode particles) has an opposite trend having lowest value (0.64 ± 0.06) in summer, low (0.99 ± 0.10) in monsoon, moderate (1.20 ± 0.15) in winter and highest value (1.52 ± 0.03) in autumn. The annual mean value of AOD at 500 nm, ‘α’ and ‘β’ are 0.24 ± 0.01, 1.06 ± 0.09 and 0.14 ± 0.01, respectively. The fractional asymmetry factor is more negative in summer due to enhanced tourists’ arrival and also in autumn months due to the month-long International Kullu Dussehra fair. The AOD values given by MWR and satellite-based moderate resolution imaging spectro-radiometer have good correlation of 0.76, 0.92 and 0.97 on diurnal, monthly and seasonal basis, respectively. The AODs at 500 nm as well as ‘β’ are found to be highly correlated, while ‘α’ is found to be strongly anti-correlated with temperature and wind speed suggesting high AODs and turbidity but low concentration of fine particles during hot and windy days. With wind direction, the AOD and ‘β’ are found to be strongly anti-correlated, while ‘α’ is strongly correlated. 相似文献
69.
Chakrabortty Rabin Pal Subodh Chandra Sahana Mehebub Mondal Ayan Dou Jie Pham Binh Thai Yunus Ali P. 《Natural Hazards》2020,104(2):1259-1294
Natural Hazards - Land degradation is very severe in the subtropical monsoon-dominated region due to the uncertainty of rainfall in the long term, and most of the rainfall occurs with high... 相似文献
70.
The rivers in Nepal are classified in terms of geographical regions but a more scientific classification such as on the ba-sis of morphology is clearly lacking. This study was done in 9 rivers namely Jhikhukhola of the Koshi system, Aandhikhola, Arungkhola, East Rapti, Karrakhola, Seti and main channel Narayani of the Gandaki system, and two independent systems within Nepal, Bagmati and Tinau. Among the morphologies, river bed or the substratum was taken as the main variable for the analysis which was categ... 相似文献