共查询到20条相似文献，搜索用时 31 毫秒
1.
The Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) gives us a chance to investigate the theoretical Neupert effect using the correlation between the thermal-energy
derivative and the nonthermal energy, or the thermal energy and the integral nonthermal energy. Based on this concept, we
analyze four M-class RHESSI flares on 13 November 2003, 4 November 2004, 3 and 25 August 2005. According to the evolution
of the temperature [T], emission measure [EM], and thermal energy [E
th], each event is divided into three phases during the nonthermal-energy input [
\frac dEnthdt\frac {\mathrm{d}E_{\mathrm{nth}}}{\mathrm{d}t} in the units of erg s−1]. Phase 1 is identified as the interval before the temperature maximum, while after the thermal-energy maximum is phase 3,
between them is phase 2. We find that these four flares show the Neupert effect in phase 1, but not in phase 3. The Neupert
effect still works well in the second phase, although the cooling becomes slightly important. We define the parameter μ in the relation of
\fracdEthdt=m\fracdEnth(t)dt\frac{\mathrm {d}E_{\mathrm{th}}}{\mathrm{d}t}=\mu\frac{\mathrm{d}E_{\mathrm {nth}}(t)}{\mathrm{d}t} or
Eth(t0)=mò0t0\fracdEnth(t)dt dtE_{\mathrm{th}}(t_{0})=\mu\int_{0}^{t_{0}}\frac{\mathrm{d}E_{\mathrm{nth}}(t)}{\mathrm{d}t}\,\mathrm{d}t when the cooling is ignored in phase 1. Considering the uncertainties in estimating the energy from the observations, it
is not possible to precisely determine the fraction of the known energy in the nonthermal electrons transformed into the thermal
energy of the hottest plasma observed by RHESSI. After a rough estimate of the flare volume and the assumption of the filling
factor, we investigate the parameter μ in these four events. Its value ranges from 0.02 to 0.20, indicating that a small fraction (2% – 20%) of the nonthermal energy
can be efficiently transformed into thermal energy, which is traced by the soft X-ray emission, and the bulk of the energy
is lost possibly due to cooling. 相似文献
2.
G. Ter-Kazarian 《Astrophysics and Space Science》2014,349(2):919-938
We compute the ultra-high energy (UHE) neutrino fluxes from plausible accreting supermassive black holes closely linking to the 377 active galactic nuclei (AGNs). They have well-determined black hole masses collected from the literature. The neutrinos are produced via simple or modified URCA processes, even after the neutrino trapping, in superdense proto-matter medium. The resulting fluxes are ranging from: (1) (quark reactions)— $J^{q}_{\nu\varepsilon}/(\varepsilon_{d}\ \mathrm{erg}\,\mathrm{cm}^{-2}\,\mathrm{s}^{-1}\,\mathrm{sr}^{-1})\simeq8.29\times 10^{-16}$ to 3.18×10?4, with the average $\overline{J}^{q}_{\nu\varepsilon}\simeq5.53\times 10^{-10}\varepsilon_{d}\ \mathrm{erg}\,\mathrm{cm}^{-2}\,\mathrm{s}^{-1}\,\mathrm{sr}^{-1}$ , where ε d ～10?12 is the opening parameter; (2) (pionic reactions)— $J^{\pi}_{\nu\varepsilon} \simeq0.112J^{q}_{\nu\varepsilon}$ , with the average $J^{\pi}_{\nu\varepsilon} \simeq3.66\times 10^{-11}\varepsilon_{d}\ \mathrm{erg}\,\mathrm{cm}^{-2}\,\mathrm{s}^{-1}\,\mathrm{sr}^{-1}$ ; and (3) (modified URCA processes)— $J^{URCA}_{\nu\varepsilon}\simeq7.39\times10^{-11} J^{q}_{\nu\varepsilon}$ , with the average $\overline{J}^{URCA}_{\nu\varepsilon} \simeq2.41\times10^{-20} \varepsilon_{d}\ \mathrm{erg}\,\mathrm{cm}^{-2}\,\mathrm{s}^{-1}\,\mathrm{sr}^{-1}$ . We conclude that the AGNs are favored as promising pure neutrino sources, because the computed neutrino fluxes are highly beamed along the plane of accretion disk, peaked at high energies and collimated in smaller opening angle θ～ε d . 相似文献
3.
Clovis Jacinto de Matos 《Astrophysics and Space Science》2012,337(1):353-354
The phenomenological nature of a new gravitational type interaction between two different bodies derived from Verlinde’s entropic
approach to gravitation in combination with Sorkin’s definition of Universe’s quantum information content, is investigated.
Assuming that the energy stored in this entropic gravitational field is dissipated under the form of gravitational waves and
that the Heisenberg principle holds for this system, one calculates a possible value for an absolute minimum time scale in
nature
t = \frac1516 \fracL1/2(h/2p) Gc4 ~ 9.27×10-105\tau=\frac{15}{16} \frac{\Lambda^{1/2}\hbar G}{c^{4}}\sim9.27\times10^{-105} seconds, which is much smaller than the Planck time t
P
=(ħG/c
5)1/2∼5.38×10−44 seconds. This appears together with an absolute possible maximum value for Newtonian gravitational forces generated by matter
Fg=\frac3230\fracc7L (h/2p) G2 ~ 3.84×10165F_{g}=\frac{32}{30}\frac{c^{7}}{\Lambda \hbar G^{2}}\sim 3.84\times 10^{165} Newtons, which is much higher than the gravitational field between two Planck masses separated by the Planck length F
gP
=c
4/G∼1.21×1044 Newtons. 相似文献
4.
In an attempt to examine whether the spectroscopic Doppler method with an iodine cell (which is known to be successful for
precise radial-velocity determinations in stellar astronomy) could be effective for investigating the solar differential rotation,
we carried out intensive observations to collect spectra at a large number of points on the solar disk by using the Domeless
Solar Telescope along with the horizontal spectrograph of the Hida Observatory. Having converted the resulting line-of-sight
velocity component into the angular rotational rate (ω), we derived a differential rotation law, wsidereal (deg day-1) = 14.03 (±0.06)-1.84 (±0.57) sin2y-1.92 (±0.85) sin4y\omega_{\mathrm{sidereal}}\; (\mathrm{deg}\,\mathrm{day}^{-1}) =14.03 (\pm0.06)-1.84 (\pm0.57) \sin^{2}\psi-1.92 (\pm0.85) \sin^{4}\psi (ψ: heliographic latitude), which is reasonably consistent with other spectroscopic determinations published so far. Our analysis
also revealed several practical points to note for successful application (e.g., exclusion of those data that are not well distant from the meridian; mutual data subtraction/averaging for symmetric counterparts
at the eastern and western hemisphere). Considering its easiness and cheapness, this iodine-cell-featured spectroscopic method
may be regarded as an effective and practical tool for studying the differential rotation of the Sun. 相似文献
5.
We investigate the radiative and conductive cooling in the solar flare observed by RHESSI on 2005 September 13. The radiative
and conductive loss energies are estimated from the observations after the flare onset. Consistent with previous findings,
the cooling is increased with time, especially the radiation becomes remarkable on the later phase of flare. According our
method, about half of thermal energy is traced by RHESSI soft X-rays, while the other half is lost by the radiative (∼38%)
and conductive (∼9%) cooling at end of the hard X-rays in this event. The nonthermal energy input of P
nth (inferred from RHESSI hard X-ray spectrum) is not well correlated with the derivative of thermal energy of
\fracdEthdt\frac{\mathrm{d}E_{\mathrm{th}}}{\mathrm{d}t} (required to radiate the RHESSI soft X-ray flux and spectrum) alone. However, after consideration the radiation and conduction,
a high correlation is obtained between the derivative of total thermal energy (
\fracdEth+Erad+Econddt\frac{\mathrm{d}E_{\mathrm{th}}+E_{\mathrm{rad}}+E_{\mathrm{cond}}}{\mathrm{d}t}) and nonthermal energy input (P
nth) from the flare start to end, indicating the relative importance of conductive and direct radiative losses during the solar
flare development. Ignoring the uncertainties to estimate the energy from the observations, we find that about ∼12% fraction
of the known energy is transferred into the thermal energy for the 2005 September 13 flare. 相似文献
6.
7.
W. B. Song 《Solar physics》2010,261(2):311-320
Referring to the aerodynamic drag force, we present an analytical model to predict the arrival time of coronal mass ejections
(CMEs). All related calculations are based on the expression for the deceleration of fast CMEs in the interplanetary medium
(ICMEs),
[(v)\dot]=-\frac115 700(v-VSW)2\dot{v}=-\frac{1}{15\,700}(v-V_{\mathrm{SW}})^{2}
, where V
SW is the solar wind speed. The results can reproduce well the observations of three typical parameters: the initial speed of
the CME, the speed of the ICME at 1 AU and the transit time. Our simple model reveals that the drag acceleration should be
really the essential feature of the interplanetary motion of CMEs, as suggested by Vršnak and Gopalswamy (J. Geophys. Res.
107, 1019, 2002). 相似文献
8.
We have investigated Bianchi type III non-static magnetized cosmological model for perfect fluid distribution in general relativity.
We assume that F
12 is the only non-vanishing component of F
ij
. Maxwell’s equation
leads to
where K and α are constants.
To get a deterministic model, we assume that σ
11
∝
θ which leads to A=C
n
where n is a constant, σ
11 the x-component of shear tensor σ
ij
and theta is the expansion in the model. The behaviour of the model in absence of magnetic field is discussed. The other
physical and geometrical aspects of the model are also discussed. 相似文献
9.
Stochastic temperatures and turbulence are characterized by average velocities u
th
and < u
turb
> ≡ u
0 and fluctuations u￠th {u'_{th}} and u′ (<u′ > = 0). Thus, the Doppler width of a line also has a fluctuating component Dl￠D \Delta {\lambda '_D} . Observed spectra correspond to the radiative flux averaged over time and over a star’s surface, <Hλ>. Usually, only the average velocities u
th
and u
0 are taken into account in photospheric models and these yield the Doppler width DlD(0) \Delta \lambda_D^{(0)} of a line in the customary way. The fluctuations Dl￠D \Delta {\lambda '_D} mean that near a line center the average absorption coefficient < αλ > is larger than the usual αλ, which depends only on the average velocities u
th
and u
0. This enhances the absorption line near the center and is not explained by the photospheric models. This new statistical
effect depends on the wavelength of the line. A comparison of observed lines with model profiles yields an estimate for the
average level of fluctuations in the Doppler width, h =
á | Dl￠D |
ñ