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31.
We used the flux-calibrated images from the Broad-band Filter Imager and Stokes Polarimeter data obtained with the Solar Optical Telescope onboard the Hinode spacecraft to study the properties of bright points in and around sunspots. The selected bright points are smaller in diameter than 150 km with contrasts exceeding about 3 % in the ratio of sunspot images obtained with the G-band (430.5 nm) and Ca ii H (396.85 nm) filters. The bright points are classified as umbral dot, peripheral umbral dot, penumbral grains, and G-band bright point depending on their location. The bright points are preferentially located around the penumbral boundary and in the fast decaying parts of the umbra. The color temperature of the bright points is in the range of 4600 K to 6600 K with cooler ones located in the central part of the umbra. The temperature increases as a function of distance from the center outward. The G-band, CN-band (388.35 nm), and Ca ii H fluxes of the bright points as a function of their blue-band (450.55 nm) brightness increase continuously in a nonlinear fashion unlike their red (668.4 nm) and green (555.05 nm) counterparts. This is consistent with a model in which the localized heating of the flux tube depletes the molecular concentration, resulting in the reduced opacity that leads to the exposition of deeper and hotter layers. The light curve of the bright points shows that the enhanced brightness at these locations lasts for about 15 to 60 min with the least contrast for the points outside the sunspot. The umbral dots near the penumbral boundary are associated with elongated filamentary structures. The spectropolarimeter observations show that the filling factor decreases as the G-band brightness increases. We discuss the results using the model in which the G-band bright points are produced in the cluster of flux tubes that a sunspot consists of. 相似文献
32.
In this note, we compare the LiNbO3 and Piezo-Electrically(PE) servo controlled air gap Fabry-Perot etalons for observing the Sun. An identical test setup was
used to evaluate the instrumental parameters of the two etalons. It is found that for the etalons with similar finesse the
advantage of using PE Etalons is tunability over entire Free Spectral Range. On the other hand, the LiNbO3 etalons have advantage of wider acceptance angle.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
33.
In order to investigate the relationship between magnetic-flux emergence, solar flares, and coronal mass ejections (CMEs), we study the periodicity in the time series of these quantities. It has been known that solar flares, sunspot area, and photospheric magnetic flux have a dominant periodicity of about 155 days, which is confined to a part of the phase of the solar cycle. These periodicities occur at different phases of the solar cycle during successive phases. We present a time-series analysis of sunspot area, flare and CME occurrence during Cycle 23 and the rising phase of Cycle 24 from 1996 to 2011. We find that the flux emergence, represented by sunspot area, has multiple periodicities. Flares and CMEs, however, do not occur with the same period as the flux emergence. Using the results of this study, we discuss the possible activity sources producing emerging flux. 相似文献
34.
Sandeep Singh Munendra Singh A. K. Choudhary Anju Saxena I. B. Singh A. K. Jain 《International Journal of Earth Sciences》2010,99(8):1991-1997
The influx of Sr responsible for increase in marine Sr has been attributed to rise of Himalaya and weathering of the Himalayan
rocks. The rivers draining Himalaya to the ocean by the northern part of the Indian sub-continent comprising the Ganga Alluvial
Plain (GAP) along with Central parts of the Himalaya and the northern part of the Indian Craton are held responsible for the
transformation of Sr isotopic signature. The GAP is basically formed by the Himalayan-derived sediments and serves as transient
zone between the source (Himalaya) and the sink (Bay of Bengal). The Gomati River, an important alluvial tributary of the
Ganga River, draining nearly 30,500 km2 area of GAP is the only river which is originating from the GAP. The river recycles the Himalayan-derived sediments and transport
its weathering products into the Ganga River and finally to Bay of Bengal. 11 water samples were collected from the Gomati
River and its intrabasinal lakes for measurement of Sr isotopic composition. Sr concentration of Gomati River water is about
335 μg/l, which is about five times higher than the world’s average of river water (70 μg/l) and nearly three times higher
than the Ganga River water in the Himalaya (130 μg/l) The Sr isotopic ratios reported are also higher than global average
runoff (0.7119) and to modern seawater (0.7092) values. Strong geochemical sediment–water interaction appearing on surface
is responsible for the dissolved Sr isotopic ratios in the River water. Higher Sr isotopic rations found during post-monsoon
than in pre-monsoon season indicate the importance of fluxes due to monsoonal erosion of the GAP into the Gomati River. Monsoon
precipitation and its interaction with alluvium appear to be major vehicle for the addition of dissolved Sr load into the
alluvial plain rivers. This study establishes that elevated 87Sr/86Sr ratios of the Gomati River are due to input of chemical weathering of alluvial material present in the Ganga Alluvial Plain. 相似文献
35.
The present paper is concerned with the problem of an orthotropic micropolar half-space subjected to concentrated and distributed
loads. The disturbance due to normal and tangential loads are investigated by employing eigen-value approach. The integral
transforms have been inverted by using a numerical technique to obtain the normal displacement, normal force stress and tangential
couple stress in the physical domain. The results of these quantities are given and illustrated graphically. 相似文献
36.
Age determinations mostly by Rb/Sr whole rock isochrons of the Precambrian rocks of Rajasthan in northwest India are summarized
and discussed. On present sampling and subject to its possible bias, the following conclusions can be made. The Untala Granite
believed to be intrusive into the gneissic terrain (bgc) east of Udaipur has the oldest age, 2.95 b.y. yet measured for a granite in Rajasthan. This, coupled with the lead isochron
age of 3.5 b.y. for detrital zircon from the Aravalli schists by Vinogradov and others extends the basement of Rajasthan well
into the Archaean. The time equivalence of thebgc east of Udaipur with the Berach Granite dated only at 2.55 b.y. is not tenable. No satisfactory radiometric age control exists
for the onset and duration of the Aravalli Supergroup, believed to be an early Proterozoic linear belt.
Heron’s original Delhi Supergroup has recorded acid magmatism widely separate in space and time. The earliest activity between
1700 and 1500 m.y. is recorded mainly in the Alwar basin in northeastern Rajasthan while the younger activity between 850
and 750 m.y. is represented by the ‘Erinpura type’ granites in the central and southern Aravalli sector. This younger event
not only has let its thermal overprinting on the older Alwar rocks but also marks the onset of emplacement of the Malani Igneous
suite in the trans-Aravalli terrain. This raises the new possibility that the Delhi rocks of Heron represent atleast two chronologically
independent sequences with varying geographical extent. The trans-Aravalli terrain is most probably floored by partly reworked,
crystalline basement and developed along linear rift zones which acted as loci for high heat flow and igneous activity since
about 800 m.y. ago. 相似文献
37.
C. S. Agarwal N. K. Choudhary Ashok K. Misra 《Journal of the Indian Society of Remote Sensing》1996,24(1):53-67
Remotely sensed data has unique advantage aver conventional data collection techniques in the study of geomorphology, as physiographical and geo-structural parameters are mostly discernible on the imagery. In the present study an attempt has been made to identify and evaluate the process of geomorphological evolution and hydrogeological conditions, temporal changes in pattern of geomorphic elements and overall impact on environment in alluvial fan region in Nainital District using multidate satellite data from Landsat (1975, 1986) and IRS (1993), through visual interpretation technique. The landuse changes are quite prominent in alluvial fan of upper and lower zone. As a consequence of deforestation, an area of 16 sq. km. of natural forest cover has been lost over a span of 18 years (1975–1993) leading to the increase in rate of erosion as well as environmental degradation in upstream areas. The study suggests that the ground water utilization in Tarai belt without replenishment of confined aquifers and installation of more tubewells in Bhabar belt may lead to total failure of flowing wells and subsequently disturb the balanced ecosystem. 相似文献
38.
Pradeep Kumar Arti Choudhary Varun Narayan Mishra Dileep Kumar Gupta Prashant K. Srivastava 《国际地球制图》2017,32(2):206-224
Crop classification is needed to understand the physiological and climatic requirement of different crops. Kernel-based support vector machines, maximum likelihood and normalised difference vegetation index classification schemes are attempted to evaluate their performances towards crop classification. The linear imaging self-scanning (LISS-IV) multi-spectral sensor data was evaluated for the classification of crop types such as barley, wheat, lentil, mustard, pigeon pea, linseed, corn, pea, sugarcane and other crops and non-crop such as water, sand, built up, fallow land, sparse vegetation and dense vegetation. To determine the spectral separability among crop types, the M-statistic and Jeffries–Matusita (J–M) distance methods have been utilised. The results were statistically analysed and compared using Z-test and χ2-test. Statistical analysis showed that the accuracy results using SVMs with polynomial of degrees 5 and 6 were not significantly different and found better than the other classification algorithms. 相似文献
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