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1.
Rajmal Jain Malini Aggarwal Raghunandan Sharma 《Journal of Astrophysics and Astronomy》2010,31(3):155-163
We report observational evidence of the decay of the flux ratio of Fe to Fe-Ni line features as a function of plasma electron
temperature in solar flares in comparison to that theoretically predicted by Phillips (2004). We present the study of spectral
analysis of 14 flares observed by the Solar X-ray Spectrometer (SOXS) — Low Energy Detector (SLD) payload. The SLD payload
employs the state-of-the-art solid state detectors, viz., Si PIN and Cadmium-Zinc-Telluride (CZT) devices. The sub-keV energy
resolution of Si PIN detector allows us to study the Fe-line and Fe-Ni line features appearing at 6.7 and 8 keV, respectively,
in greater detail. In order to best-fit the whole spectrum at one time in the desired energy range between 4 and 25 keV we
considered Gaussian-line, the multi-thermal power-law and broken power-law functions. We found that the flux ratio of Fe to
Fe-Ni line features decays with flare electron temperature by the asymptotic form of polynomial of inverse third order. The
relative flux ratio is ∼30 at temperature 12 MK which drops to half, ∼15 at 20 MK, and at further higher temperatures it decreases
smoothly reaching to ∼8 at ∼50 MK. The flux ratio, however, at a given flare plasma temperature, and its decrease with temperature
is significantly lower than that predicted theoretically. We propose that the difference may be due to the consideration of
higher densities of Fe and Fe-Ni lines in the theoretical model of Phillips (2004). We suggest revising the Fe and Fe-Ni line
densities in the corona. The decay of flux ratio explains the variation of equivalent width and peak energy of these line
features with temperature. 相似文献
2.
Rajmal Jain Malini Aggarwal Raghunandan Sharma 《Journal of Astrophysics and Astronomy》2008,29(1-2):125-145
Solar X-ray Spectrometer (SOXS), the first space-borne solar astronomy experiment of India was designed to improve our current understanding of X-ray emission from the Sun in general and solar flares in particular. SOXS mission is composed of two solid state detectors, viz., Si and CZT semiconductors capable of observing the full disk Sun in X-ray energy range of 4–56 keV. The X-ray spectra of solar flares obtained by the Si detector in the 4–25 keV range show evidence of Fe and Fe/Ni line emission and multi-thermal plasma. The evolution of the break energy point that separates the thermal and non-thermal processes reveals increase with increasing flare plasma temperature. Small scale flare activities observed by both the detectors are found to be suitable to heat the active region corona; however their location appears to be in the transition region. 相似文献
3.
Radio interferometers are used to construct high resolution images of the sky at radio frequencies and are the key instruments for accessing the statistical properties of the evolution of neutral hydrogen over cosmic time. Here we use simulated observations of the model sky to assess the efficacy of different estimators of the large-scale structure and power spectrum of the sky brightness distribution. We find that while the large-scale distribution can be reasonably estimated using the reconstructed image from interferometric data, estimates of the power spectrum of the intensity fluctuations calculated from the image are generally biased. This bias is found to be more pronounced for diffuse emission. The visibility based power spectrum estimator, however, gives an unbiased estimate of the true power spectrum. This work demonstrates that for an observation with diffuse emission the reconstructed image can be used to estimate the large-scale distribution of the intensity, while to estimate the power spectrum, visibility based methods should be preferred.With the upcoming experiments aimed at measuring the evolution of the power spectrum of the neutral hydrogen distribution, this is a very important result. 相似文献
4.
M. E. Raghunandan 《Natural Hazards》2012,63(2):1115-1128
Soil layering has a pivotal role on the behavior and propagation of seismic waves, hence the ground response during seismic loading. Parametric study to estimate the effect of soil layering on ground response parameters is of prime importance considering the engineering significance of structure founded in seismic zone; nonetheless, it is yet to be well understood. The objective of this study was to investigate the effect of soil layering and soil properties on the ground response parameters. One-dimensional linear ground response analysis was conducted with variation in soil layer parameters including impedance ratio (?? z ), layer thickness (d r ), and damping ratio (D). The acceleration time history of the Bhuj Earthquake (M w ?=?7.7), India, was used in the analysis. The results obtained from the analysis were presented as variation of ground response parameters such as spectral acceleration (SA), amplification ratio (M) with the soil layer parameters. Results showed higher values of SA at lower D and then decreased with increase in D, that in fact depict the resistance offered to the particle oscillation at comparatively higher values of D. Similarly, variation in SA and M was very less or negligible when the ?? z was varied from 1 to 3 and the d r equal to 0.2, while for d r greater than 0.2 the variation increased with ?? z and d r . The outcome from the parametric study presented in this paper clearly demonstrates the significance of ?? z , D, and d r of the soil layers on the ground response parameters. 相似文献
5.
V. K. Mishra Meera Gupta B. N. Mishra S. K. Nigam A. P. Mishra 《Journal of Astrophysics and Astronomy》2008,29(1-2):257-262
The long-term modulation of cosmic ray intensity (CRI) by different solar activity (SA) parameters and an inverse correlation between individual SA parameter and CRI is well known. Earlier, it has been suggested that the concept of multi-parametric modulation of CRI may play an important role in the study of long-term modulation of CRI. In the present study, we have tried to investigate the combined effect of a set of two SA parameters in the long-term modulation of CRI. For this purpose, we have used a new statistical technique called “Running multiple correlation method”, based on the “Running cross correlation method”. The running multiple correlation functions among different sets of two SA parameters (e.g., sunspot numbers and solar flux, sunspot numbers and coronal index, sunspot numbers and grouped solar flares, etc.) and CRI have been correlated separately. It is found that the strength of multiple correlation (among two SA parameters and CRI) and cross correlation (between individual SA parameter and CRI) is almost similar throughout the period of investigation (1955–2005). It is also found that the multiple correlations among various SA parameters and CRI is stronger during ascending and descending phases of the solar cycles and it becomes weaker during maxima and minima of the solar cycles, which is in accordance with the linear relationship between SA parameters and CRI. The values of multiple correlation functions among different sets of SA parameters and CRI fall well within the 95% confidence interval. In the view of odd-even hypothesis of solar cycles, the strange behaviour of present cycle 23 (odd cycle), as this is characterized by many peculiarities with double peaks and many quiet periods (Gnevyshev gaps) interrupted the solar activity (for example April 2001, October–November 2003 and January 2005), leads us to speculate that the solar cycle 24 (even cycle) might be of exceptional nature. 相似文献
6.
Malini Aggarwal Rajmal Jain A. P. Mishra P. G. Kulkarni Chintan Vyas R. Sharma Meera Gupta 《Journal of Astrophysics and Astronomy》2008,29(1-2):195-205
We present the study of 20 solar flares observed by “Solar X-ray Spectrometer (SOXS)” mission during November 2003 to December 2006 and found associated with coronal mass ejections (CMEs) seen by LASCO/SOHO mission. In this investigation, X-ray emission characteristics of solar flares and their relationship with the dynamics of CMEs have been presented. We found that the fast moving CMEs, i.e., positive acceleration are better associated with short rise time (< 150 s) flares. However, the velocity of CMEs increases as a function of duration of the flares in both 4.1–10 and 10–20 keV bands. This indicates that the possibility of association of CMEs with larger speeds exists with long duration flare events. We observed that CMEs decelerate with increasing rise time, decay time and duration of the associated X-ray flares. A total 10 out of 20 CMEs under current investigation showed positive acceleration, and 5 of them whose speed did not exceed 589 km/s were associated with short rise time (< 150 s) and short duration (< 1300 s) flares. The other 5 CMEs were associated with long duration or large rise time flare events. The unusual feature of all these positive accelerating CMEs was their low linear speed ranging between 176 and 775 km/s. We do not find any significant correlation between X-ray peak intensity of the flares with linear speed as well as acceleration of the associated CMEs. Based on the onset time of flares and associated CMEs within the observing cadence of CMEs by LASCO, we found that in 16 cases CME preceded the flare by 23 to 1786 s, while in 4 cases flare occurred before the CME by 47 to 685 s. We argue that both events are closely associated with each other and are integral parts of one energy release system. 相似文献
7.
Flexural response of piles under liquefied soil conditions 总被引：1，自引：1，他引：1
The paper pertains to the development of a generalized procedure to analyze and predict the flexural behavior of axially and
laterally loaded pile foundations under liquefied soil conditions. Pseudo-static analysis has been carried out taking into
consideration the combined effect of axial load and lateral load. Based on the available literature effect of degradation
on the modulus of subgrade reaction due to soil liquefaction has been incorporated in the analysis. The developed program
was calibrated and validated by comparing the predicted behavior of the pile with theoretical and experimental results reported
in literature. The predicted behavior has been found to be in excellent to very good agreement with the theoretical and observed
values in the field, respectively. The present study highlights the importance of considering the axial load from the superstructure
along with the inertia forces from the superstructure and the kinematic forces from the liquefied soil in the design of pile
foundations in liquefiable areas. The significance of densification of the soil in the liquefiable areas and presence of an
adequate top non-liquefied soil cover causing appreciable reduction in deflection and bending moment experienced by the piles
has been highlighted. 相似文献
8.
In a seismically active region, structures may be subjected to multiple earthquakes, due to mainshock–aftershock phenomena or other sequences, leaving no time for repair or retrofit between the events. This study quantifies the aftershock vulnerability of four modern ductile reinforced concrete (RC) framed buildings in California by conducting incremental dynamic analysis of nonlinear MDOF analytical models. Based on the nonlinear dynamic analysis results, collapse and damage fragility curves are generated for intact and damaged buildings. If the building is not severely damaged in the mainshock, its collapse capacity is unaffected in the aftershock. However, if the building is extensively damaged in the mainshock, there is a significant reduction in its collapse capacity in the aftershock. For example, if an RC frame experiences 4% or more interstory drift in the mainshock, the median capacity to resist aftershock shaking is reduced by about 40%. The study also evaluates the effectiveness of different measures of physical damage observed in the mainshock‐damaged buildings for predicting the reduction in collapse capacity of the damaged building in subsequent aftershocks. These physical damage indicators for the building are chosen such that they quantify the qualitative red tagging (unsafe for occupation) criteria employed in post‐earthquake evaluation of RC frames. The results indicated that damage indicators related to the drift experienced by the damaged building best predicted the reduced aftershock collapse capacities for these ductile structures. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
9.
A detailed correlative analysis between sunspot numbers (SSN) and tilt angle (TA) with cosmic ray intensity (CRI) in the neutron
monitor energy range has been performed for the solar cycles 21, 22 and 23. It is found that solar activity parameters (SSN
and TA) are highly (positive) correlated with each other and have inverse correlation with cosmic ray intensity (CRI). The
‘running cross correlation coefficient’ between cosmic ray intensity and tilt angle has also been calculated and it is found
that the correlation is positive during the maxima of odd cycles 21 and 23. Moreover, the time lag analysis between CRI and
SSN, and between CRI and TA has also been performed and is supported by hysteresis curves, which are wide for odd cycles and
narrow for even cycles. 相似文献
10.
From the monthly data of cosmic ray intensity (CRI), sunspot numbers (SSN) and solar flare index (SFI), an attempt has been
made to study the relationship between CRI and solar activity (SA) parameters SSN and SFI. The correlation between SA parameters
and CRI for different neutron monitoring stations having low, middle and high cut-off rigidity has been investigated. The
anti-correlation between SA and CRI is found to exist with some time lag. Based on the method of minimizing correlation coefficient
and time-delayed component method, the observed time-lag between SA parameters (SSN and SFI) and CRI has been found to be
large for odd solar cycles in comparison to even solar cycles. The results of time-lag analysis between CRI and SSN and between
CRI-SFI have also been compared. The findings of correlative study between CRI and SSN are in agreement with earlier results,
while the CRI-SFI relationship provides new insights to understand the solar modulation of cosmic rays. 相似文献