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61.
Neeraj Singh Bankoti Navin Chandra Joshi Bimal Pande Seema Pande Wahab Uddin Kavita Pandey 《New Astronomy》2011,16(4):269-275
This paper presents the study of normalized north–south asymmetry, cumulative normalized north–south asymmetry and cumulative difference indices of sunspot areas, solar active prominences (at total, low (?40°) and high (?50°) latitudes) and Hα solar flares from 1964 to 2008 spanning the solar cycles 20–23. Three different statistical methods are used to obtain the asymmetric behavior of different solar activity features. Hemispherical distribution of activity features shows the dominance of activities in northern hemisphere for solar cycle 20 and in southern hemisphere for solar cycles 21–23 excluding solar active prominences at high latitudes. Cumulative difference index of solar activity features in each solar cycle is observed at the maximum of the respective solar cycle suggesting a cyclic behavior of approximately one solar cycle length. Asymmetric behavior of all activity features except solar active prominences at high latitudes hints at the long term periodic trend of eight solar cycles. North–south asymmetries of SAP (H) express the specific behavior of solar activity at high solar latitudes and its behavior in long-time scale is distinctly opposite to those of other activity features. Our results show that in most cases the asymmetry is statistically highly significant meaning thereby that the asymmetries are real features in the N–S distribution of solar activity features. 相似文献
62.
The transition 111 ? 110 at 4.829 GHz of formaldehyde (H2CO) was the first one showing the anomalous absorption, i.e., the absorption against the cosmic microwave background. Anomalous absorption is an unusual phenomena. Structure of H2CC is very similar to that of H2CO and H2CS. Both H2CO and H2CS have already been identified in a number of cosmic objects. Though H2CC is not yet identified in the cosmic objects, we propose that H2CC may be identified in cool cosmic objects through its transition 111 ? 110 at 4.85 GHz in anomalous absorption. 相似文献
63.
R. Chandra B. Schmieder C. H. Mandrini P. Démoulin E. Pariat T. Török W. Uddin 《Solar physics》2011,269(1):83-104
We present and interpret observations of two morphologically homologous flares that occurred in active region (AR) NOAA 10501
on 20 November 2003. Both flares displayed four homologous Hα ribbons and were both accompanied by coronal mass ejections
(CMEs). The central flare ribbons were located at the site of an emerging bipole in the centre of the active region. The negative
polarity of this bipole fragmented in two main pieces, one rotating around the positive polarity by ≈ 110° within 32 hours.
We model the coronal magnetic field and compute its topology, using as boundary condition the magnetogram closest in time
to each flare. In particular, we calculate the location of quasi-separatrix layers (QSLs) in order to understand the connectivity between the flare ribbons. Though several polarities were present in AR 10501,
the global magnetic field topology corresponds to a quadrupolar magnetic field distribution without magnetic null points.
For both flares, the photospheric traces of QSLs are similar and match well the locations of the four Hα ribbons. This globally
unchanged topology and the continuous shearing by the rotating bipole are two key factors responsible for the flare homology.
However, our analyses also indicate that different magnetic connectivity domains of the quadrupolar configuration become unstable
during each flare, so that magnetic reconnection proceeds differently in both events. 相似文献
64.
The geoeffective magnetic cloud (MC) of 20 November 2003 was associated with the 18 November 2003 solar active events in previous
studies. In some of these, it was estimated that the magnetic helicity carried by the MC had a positive sign, as did its solar
source, active region (AR) NOAA 10501. In this article we show that the large-scale magnetic field of AR 10501 has a negative
helicity sign. Since coronal mass ejections (CMEs) are one of the means by which the Sun ejects magnetic helicity excess into
interplanetary space, the signs of magnetic helicity in the AR and MC must agree. Therefore, this finding contradicts what
is expected from magnetic helicity conservation. However, using, for the first time, correct helicity density maps to determine
the spatial distribution of magnetic helicity injections, we show the existence of a localized flux of positive helicity in
the southern part of AR 10501. We conclude that positive helicity was ejected from this portion of the AR leading to the observed
positive helicity MC. 相似文献
65.
M. Chandra Singh P. Kundal R. A. S. Kushwaha 《Journal of the Geological Society of India》2010,76(6):573-586
Oligocene-Miocene deposits of Bhuban and Boka Bil Formations, Surma Group, Manipur Western Hill consist of well preserved
ichnofossil assemblages. These formations are represented by eight lithofacies such as Massive sandstone (Sm), Rippled marked
argillaceous sandstone (Sr), Wavy laminated sandstone-siltstone-silty shale (Sw), Laminated shale (Fl), Massive mudstone (Fm),
Trough cross-bedded sandstone (St), Lenticular laminated sandstonesiltstonesilty shale (Sll) and Laminated to massive sandstone-siltstone
(Ssc). Fifteen ichnospecies were identified, which further categories into Skolithos, Cruziana, and Skolithos/Cruziana ichnofacies. Overall distribution pattern and behavioural nature of the ichnoassemblage and sedimentological attributes suggests
that the sediments of Bhuban and Boka Bil Formations were deposited under frequent fluctuating sea level, moderate to strong
energy condition, subtidal to lower intertidal environment, rich in organic nutrients. 相似文献
66.
Anshu Prakash Mishra A. C. Pandey S. Rai 《Journal of the Geological Society of India》2010,76(5):468-478
In this article, the authors examine Sea surface temperature (SST), Sea surface circulation (SSC) and Vertical velocity (VV) fields from simulation of 25 layers coarse resolution Modular ocean model (MOM version 3.0) with prescribed wind forcing for the region 74.25°S to 65°N, 180°W-180°E. It is found that distribution of SST simulated by the model shows its consistency with the observed climatology. However, simulated SST in the areas of Arabian Sea, Bay of Bengal, Indonesian Throughflow (ITF) region and east of North America near equator exhibit slight warming with respect to observation, which may be due to model deficiency and forcing problems. Circulation features suggest that one of the strongest current viz. Antarctic circumpolar current (ACC) along with other major current systems viz. Gulf stream current, North and South Pacific current, Agulhas current, Labrador current, Canary current, etc are captured well by the model. In the Indian Ocean and other ocean basins, current patterns are well captured by the model simulation. Intense upwelling as well as downwelling areas is marked in the horizontal distribution of VV, which is as expected. VV show quasi-stagnant and convergent regions suggesting that floating materials may be accumulated during January/July in the real ocean and wind driven circulation may act as an important contribution for such transport of floating materials in these regions. An attempt has also been made to understand the fluctuations of the SST in NINO 3.4 region during the period of model simulation using SST anomalies. 相似文献
67.
Biodiversity and invasibility: Distribution patterns of invasive plant species in the Himalayas,Nepal 总被引:1,自引:1,他引:0
Invasive plant species are exerting a serious threat to biological diversity in many regions of the world. To understand plant invasions this study aims to test which of the two plant invasiveness hypotheses; ‘low native diversity' vs. ‘high native diversity', is supported by the regional distribution patterns of invasive plant species in the Himalayas,Nepal. This study is based on data retrieved from published literatures and herbarium specimens. The relationship between invasive plant species distribution patterns and that of native plant species is elucidated by scatter plots, as well as by generalized linear models. The native plant species and invasive plant species have similar distribution patterns and the maximum number of invasive plant species is found in the same altitudinal range where the highest richness for native tree species is found. There is a clear trend of higher invasive plant richness in regions where native tree species richness is relatively high.Consequently, the native plant richness is highest in the central phytogeographic region, followed by the eastern and the western regions, respectively. The invasive plant species also follows a similar trend.Additionally, the invasive plant species richness was positively correlated with anthropogenic factors such as human population density and the number of visiting tourists. This study supports the hypothesis that ‘high native diversity' supports or facilitates invasive plant species. Further, it indicates that nativeand invasive plant species may require similar natural conditions, but that the invasive plant species seem more dependent and influenced by anthropogenic disturbance factors. 相似文献
68.
Md. M. Rahman Z.-H. Shon C.-J. Ma R. J. C. Brown S. K. Pandey C. G. Park I. S. Bae J. R. Sohn H.-O. Yoon K.-H. Kim 《International Journal of Environmental Science and Technology》2014,11(7):1897-1910
In this work, 17-polychlorinated dibenzo-p-dioxin/furan (PCDD/Fs) isomers were measured in ambient air at four urban sites in Seoul, Korea (from February to June 2009). The concentrations of their summed values (ΣPCDD/Fs) across all four sites ranged from 1,947 (271 WHO05 TEQ) (Jong Ro) to 2,600 (349 WHO05 TEQ) fg/m3 (Yang Jae) with a mean of 2,125 (± 317) fg/m3 (292 WHO05 TEQ fg/m3). The sum values for the two isomer groups of ΣPCDD and ΣPCDF were 527 (30 WHO05 TEQ) and 1,598 (263 WHO05 TEQ) fg/m3, respectively. The concentration profile of individual species was dominated by the 2,3,4,7,8-PeCDF isomer, which contributed approximately 36 % of the ΣPCDD/Fs value. The observed temporal trends in PCDD/F concentrations were characterized by relative enhancement in the winter and spring. The relative contribution of different sources, when assessed by principal component analysis, is explained by the dominance of vehicular emissions along with coal (or gas) burning as the key source of ambient PCDD/Fs in the residential areas studied. 相似文献
69.
This paper evaluates the stability of long and steep slopes examining the effect of the critical length/depth ratio, L/H, and critical slope angle, β cr, by comparing the results of infinite slope equation with the spectral element method. In addition, the influence of uphill and downhill boundaries on stability of long and steep slopes is also evaluated in theoretical domains. As an example, this paper presents a stability analysis of long and steep vegetated and barren slopes in saturated and seismic conditions, and also evaluates the effectiveness of the infinite slope equation for those slopes. In the vegetated slopes, the root zone may not extend to the whole depth of slope, which may lead to overestimating the factor of safety by infinite slope equation. This paper examines the applicability of the infinite slope equation for infinitely long, steep, and shallow slope model by comparing the results of the spectral element method. 相似文献
70.
We report the occurrence of sillimanite in sapphirine-bearing granulites near Pedapalli town in the north eastern part of the Eastern Dharwar Craton (EDC). The sapphirine-bearing granulites of the Pedapalli area display evidence of metamorphic reactions involved in the formation of diverse mineral assemblages documented in different types of reaction textures. The common stable assemblage contains sapphirine-spinel-orthopyroxene-cordieriteplagioclage-corundum-sillimanite. The P-T evolution of these sapphirine granulites has been constrained by using the TWEEQU program. Temperature of formation of sapphirine-spinel assemblages is high, around 800 °C, and pressure ca. 8 kbar. The assemblage reported in this study has important bearing on the high-temperature metamorphism and exhumation history of the EDC. 相似文献