共查询到20条相似文献,搜索用时 31 毫秒
1.
Krucker Säm Christe Steven Lin R.P. Hurford Gordon J. Schwartz Richard A. 《Solar physics》2002,210(1-2):445-456
The excellent sensitivity, spectral and spatial resolution, and energy coverage down to 3 keV provided by the Reuven Ramaty
High-Energy Solar Spectroscopic Imager mission (RHESSI) allows for the first time the detailed study of the locations and
the spectra of solar microflares down to 3 keV. During a one-hour quiet interval (GOES soft X-ray level around B6) on 2 May,
1:40–2:40 UT, at least 7 microflares occurred with the largest peaking at A6 GOES level. The microflares are found to come
from 4 different active regions including one behind the west limb. At 7′′ resolution, some events show elongated sources,
while others are unresolved point sources. In the impulsive phase of the microflares, the spectra can generally be fitted
better with a thermal model plus power law above ∼ 6–7 keV than with a thermal only. The decay phase sometimes can be fitted
with a thermal only, but in some events, power-law emission is detected late in the event indicating particle acceleration
after the thermal peak of the event. The behind-the-limb microflare shows thermal emissions only, suggesting that the non-thermal
power law emission originates lower, in footpoints that are occulted. The power-law fits extend to below 7 keV with exponents
between −5 and −8, and imply a total non-thermal electron energy content between 1026–1027 erg. Except for the fact that the power-law indices are steeper than what is generally found in regular flares, the investigated
microflares show characteristics similar to large flares. Since the total energy in non-thermal electrons is very sensitive
to the value of the power law and the energy cutoff, these observations will give us better estimates of the total energy
input into the corona. (Note that color versions of figures are on the accompanying CD-ROM.)
Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1022404512780 相似文献
2.
Rajmal Jain Vishal Joshi Yoichiro Hanaoka T. Sakurai Nipa Upadhyay 《Journal of Astrophysics and Astronomy》2006,27(2-3):339-346
We present a study of 10 microflares observed in 4–30 keV by SOXS mission simultaneously with Hα observations made at NAOJ,
Japan during the interval between February and August 2004. The X-ray and Hα light curves showed that the lifetime of microflares
varies between 4 and 25 min. We found that the X-ray emission in all microflares under study in the dynamic energy range of
4–30 keV can be fitted by thermal plus non-thermal components. The thermal spectrum appeared to start from almost 4 keV, low
level discriminator (LLD) of both Si and CZT detectors, however it ends below 8 keV. We also observed the Fe line complex
features at 6.7 keV in some microflares and attempted to fit this line by isothermal temperature assumption. The temperature
of isothermal plasma of microflares varies in the range between 8.6 and 10.1 MK while emission measure between 0.5 and 2x1049 cm-3. Non-thermal (NT) emission appeared in the energy range 7–15 keV with exponent -6.8 ≤γ≤-4.8. Our study of microflares that had occurred on 25 February 2004 showed that sometimes a given active region produces
recurrent microflare activity of a similar nature. We concluded from X-ray and simultaneous Hα observations that the microflares
are perhaps the result of the interaction of low lying loops. It appears that the electrons that accelerated during reconnection
heat the ambient coronal plasma as well as interact with material while moving down along the loops and thereby produce Hα
bright kernels. 相似文献
3.
R. K. Manchanda 《Journal of Astrophysics and Astronomy》2002,23(3-4):197-212
The attempts at unified model fitting to explain the spectral variations in Cyg X-3 suggest equally probable fits with a combination
of an absorbed blackbody and a separately absorbed power law with an exponential cut-off or a composite of absorbed free-free
emission with a power law hard X-ray component apart from the iron emission line. These seemingly ordinary but ad hoc mixtures
of simple X-ray emission mechanisms have a profound implication about the geometry of the X-ray source. While the first set
suggests a black-hole nature of the compact object, the second combination is consistent with a neutron star binary picture.
The spectral variability at hard X-ray energies above 30 keV can provide crucial input for the unified picture. In this paper,
we present spectral observations of Cyg X-3, made in our on-going survey of galactic and extragalactic X-ray sources in the
20–200 keV energy region, using Large Area Scintillation counter Experiment. The data show a clear power-law photon spectrum
of the form dN/dE ∼ E−2.8 in the 20 to 130 keV energy range. A comparison with earlier data suggests that the total number of X-ray photons in the
entire 2–500 keV energy band is conserved at all time for a given luminosity level irrespective of the state. We propose that
this behaviour can be explained by a simple geometry in which a thermal X-ray source is embedded in a hot plasma formed by
winds from the accretion disk within a cold shell. The high/soft and low/hard X-ray states of the source are simply the manifestation
of the extent of the surrounding scattering medium in which the seed photons are Comptonized and hot plasma can be maintained
by either the X-ray driven winds or the magneto-centrifugal winds. 相似文献
4.
I. K. Mirzoeva 《Astronomy Letters》2006,32(1):69-72
We investigate low-intensity microflares in the soft component of the solar X-ray radiation over the period from September
through December 1995 within the framework of the Interball—Geotail project. We derived the intensity distribution of microflares
and found correlations between the daily mean peak fluxes of X-ray bursts from microflares of various classes and the daily
mean values of the thermal background of the solar corona. 相似文献
5.
Near solar maximum, hard X-ray microflares with peak 20 keV fluxes of 10–2 (cm2 s keV)–1, more than ten times smaller than for typical flares and subflares, can occur at the rate of about once every five minutes. We report here on a search for hard X-ray microflares made on a long duration balloon flight in February 1987 near solar minimum, at a time when no active regions were on the Sun. No microflares were observed over a total observing time of 16.5 hours spread over three days, implying a statistical upper limit to their rate of occurrence about a factor often lower than observed near solar maximum. Thus hard X-ray microflaring appears to be an active region phenomenon, and apparently not associated with flaring of soft X-ray bright points. 相似文献
6.
Alaa I. Ibrahim William C. Parke Jean H. Swank Hisham Anwer Roberto Turolla Silvia Zane M. T. Hussein T. El-Sherbini 《Astrophysics and Space Science》2007,308(1-4):43-50
The defining property of Soft Gamma Repeaters is the emission of short, bright bursts of X-rays and soft γ-rays. Here we present the continuum and line spectral properties of a large sample of bursts from SGR 1806-20, observed with
the Proportional Counter Array (PCA) onboard the Rossi X-ray Timing Explorer (RXTE). Using 10 trail spectral models (5 single
and 5 two component models), we find that the burst continua are best fitted by the single component models: cutoff power-law,
optically thin bremsstrahlung, and simple power-law. Time resolved spectroscopy show that there are two absorption lines at
∼5 keV and 20 keV in some bursts. The lines are relatively narrow with 90% upper limit on the line widths of 0.5–1.5 keV for
the 5 keV feature and 1–3 keV for the 20 keV feature. Both lines have considerable equivalent width of 330–850 eV for the
5 keV feature and 780–2590 eV for the 20 keV feature. We examined whether theses spectral lines are dependent upon the choice
of a particular continuum model and find no such dependence. Besides, we find that the 5 keV feature is pronounced with high
confidence in the cumulative joint spectrum of the entire burst sample, both in the individual detectors of the PCA and in
the co-added detectors spectrum. We confront the features against possible instrumental effects and find that none can account
for the observed line properties. The two features do not seem to be connected to the same physical mechanism because (1)
they do not always occur simultaneously, (2) while the 5 keV feature occurs at about the same energy, the 20 keV line centroid
varies significantly from burst to burst over the range 18–22 keV, and (3) the centroid of the lines shows anti-correlated
red/blue shifts. The transient appearance of the features in the individual bursts and in portions of the same burst, together
with the spectral evolution seen in some bursts point to a complex emission mechanism that requires further investigation.
相似文献
7.
Hard X-ray lightcurves, spectrograms, images, and spectra of three medium-sized flares observed by the Reuven Ramaty High-Energy
Solar Spectroscopic Imager (RHESSI) are presented. Imaging spectroscopy of the 20 February 2002, 11:06 UT flare at 10′′ spatial
resolution, comparable to the best previous hard X-ray imaging from Yohkoh, shows two footpoints with an ∼ 8 s delay of peak emission between footpoints. Subsequent imaging at le4′′ shows three sources consistent with two separate loops and simultaneous brightening in connected footpoints. Imaging for
the simple two footpoint flare of 2 June 2002 also shows simultaneous footpoint brightening. The more complex 17 March 2002
flare shows at least four different sources during the main peak of the event, and it is difficult to clearly demonstrate
simultaneous brightening of connected footpoints. Non-thermal power laws are observed down to ∼ 12–13 keV without flattening
in all these events, indicating the energy content in energetic electrons may be significantly greater than previously estimated
from assumed 25 keV low energy cutoff. Simultaneously brightening footpoints show similar spectra, at least in the three flares
investigated. Double-power-law spectra with a relatively sharp break are often observed.
Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1022469902940 相似文献
8.
Rajmal Jain Vishal Joshi S. L. Kayasth Hemant Dave M. R. Deshpande 《Journal of Astrophysics and Astronomy》2006,27(2-3):175-192
We present the first results from the ‘Low Energy Detector’ pay-load of ‘Solar X-ray Spectrometer (SOXS)’ mission, which was
launched onboard GSAT-2 Indian spacecraft on 08 May 2003 by GSLV-D2 rocket to study the solar flares. The SOXS Low Energy
Detector (SLD) payload was designed, developed and fabricated by Physical Research Laboratory (PRL) in collaboration with
Space Application Centre (SAC), Ahmedabad and ISRO Satellite Centre (ISAC), Bangalore of the Indian Space Research Organization
(ISRO). The SLD payload employs the state-of-the-art solid state detectors viz., Si PIN and Cadmium-Zinc-Telluride (CZT) devices
that operate at near room temperature (-20°C). The dynamic energy range of Si PIN and CZT detectors are 4–25 keV and 4–56
keV respectively. The Si PIN provides sub-keV energy resolution while CZT reveals ∼1.7keV energy resolution throughout the
dynamic range. The high sensitivity and sub-keV energy resolution of Si PIN detector allows the measuring of the intensity,
peak energy and equivalent width of the Fe-line complex at approximately 6.7 keV as a function of time in all 8 M-class flares
studied in this investigation. The peak energy (E
p) of Fe-line feature varies between 6.4 and 6.8 keV with increase in temperature from 9 to 34 MK. We found that the equivalent
width (ω) of Fe-line feature increases exponentially with temperature up to 20 MK but later it increases very slowly up to
28 MK and then it remains uniform around 1.55 keV up to 34 MK. We compare our measurements ofw with calculations made earlier by various investigators and propose that these measurements may improve theoretical models.
We interpret the variation of both Epand ω with temperature as the changes in the ionization and recombination conditions in the plasma during the flare interval
and as a consequence the contribution from different ionic emission lines also varies. 相似文献
9.
U. Mukherjee S. Bapna H. Raichur B. Paul S. N. A. Jaaffrey 《Journal of Astrophysics and Astronomy》2006,27(1):25-35
We have investigated the Quasi Periodic Oscillation (QPO) properties of the transient accreting X-ray pulsar XTE J1858 + 034
during the second outburst of this source in April–May 2004. We have used observations made with the Proportional Counter
Array (PCA) of the Rossi X-ray Timing Explorer (RXTE) during May 14–18, 2004, in the declining phase of the outburst. We detected
the presence of low frequency QPOs in the frequency range of 140–185 mHz in all the RXTE-PCA observations. We report evolution
of the QPO parameters with the time, X-ray flux, and X-ray photon energy. Though a correlation between the QPO centroid frequency
and the instantaneous X-ray flux is not very clear from the data, we point out that the QPO frequency and the one day averaged
X-ray flux decreased with time during these observations. We have obtained a clear energy dependence of the RMS variation
in the QPOs, increasing from about 3% at 3 keV to 6% at 25 keV. The X-ray pulse profile is a single peaked sinusoidal, with
pulse fraction increasing from 20% at 3 keV to 45% at 30keV. We found that, similar to the previous outburst, the energy spectrum
is well fitted with a model consisting of a cut-off power law along with an iron emission line. 相似文献
10.
Share G.H. Murphy R.J. Dennis B.R. Schwartz R.A. Tolbert A.K. Lin R.P. Smith D.M. 《Solar physics》2002,210(1-2):357-372
The RHESSI high-resolution spectrometer detected γ-ray lines and continuum emitted by the Earth's atmosphere during impact
of solar energetic particles in the south polar region from 16:00–17:00 UT on 21 April 2002. The particle intensity at the
time of the observation was a factor of 10–100 weaker than previous events when gamma-rays were detected by other instruments.
This is the first high-resolution observation of atmospheric gamma-ray lines produced by solar energetic particles. De-excitation
lines were resolved that, in part, come from 14N at 728, 1635, 2313, 3890, and 5106 keV, and the 12C spallation product at ∼ 4439 keV. Other unresolved lines were also detected. We provide best-fit line energies and widths
and compare these with moderate resolution measurements by SMM of lines from an SEP event and with high-resolution measurements
made by HEAO 3 of lines excited by cosmic rays. We use line ratios to estimate the spectrum of solar energetic particles that
impacted the atmosphere. The 21 April spectrum was significantly harder than that measured by SMM during the 20 October 1989
shock event; it is comparable to that measured by Yohkoh on 15 July 2000. This is consistent with measurements of 10–50 MeV protons made in space at the time of the γ-ray observations. 相似文献
11.
We studied the evolution of two small flares (GOES class C2 and C1) that developed in the same active region with different
morphological characteristics: one is extended and the other is compact. We analyzed the accuracy and the consistency of different
algorithms implemented in Reuven Ramaty High-Energy Spectroscopic Imager (RHESSI) software to reconstruct the image of the
emitting sources, for energies between 3 and 12 keV. We found that all tested algorithms give consistent results for the peak
position, while the other parameters can differ at most by a factor 2. Pixon and Forward-fit generally converge to similar results but Pixon is more reliable for reconstructing a complex source. We investigated the spectral characteristics of the two flares during
their evolution in the 3–25 keV energy band. We found that a single thermal model of the photon spectrum is inadequate to
fit the observations and we needed to add either a non-thermal model or a hot thermal one. The non-thermal and the double
thermal fits are comparable. If we assume a non-thermal model, the non-thermal energy is always higher than the thermal one.
Only during the very final decay phase a single thermal model fits the observed spectrum fairly well. 相似文献
12.
In this paper, we investigate the energy spectra produced by a simple test particle X-point model of a solar flare for different
configurations of the initial electromagnetic field. We find that once the reconnection electric field is larger than 1 Vm-1 the particle distribution transits from a heated one to a partially accelerated one. As we close the separatrices of the
X-point and the angle in the inflow direction widens we find that more particles are accelerated out of the thermal distribution
and this power–law component extends to lower energies. When we introduce a guiding magnetic field component we find that
more particles are energised, but only up to a maximum energy dictated primarily by the reconnection electric field. Despite
being able to accelerate particles to observable energies and demonstrate behaviour in the energy spectra that is consistent
with observations, this single X-line model can only deliver the number fluxes required for microflares. 相似文献
13.
Evidence is presented indicating that the bursting component of the X-ray radiation detected in the nuclear region of the
active radio galaxy 3C 111 comes from the blobs ejected in the pc-scale jet and not from the accretion disc. After each new
outburst the radio flux density associated with it increases to a peak in ∼1 year and then subsides over a period of 1–2 years
with the flux falling off exponentially as the blob moves outward and dissipates. Similar peaks (bursts) are seen in the X-ray
light curve and a cross-correlation between the two shows a very high correlation with the X-ray peaks leading the radio peaks
by ∼100 days. A second cross-correlation, this time between the radio event start times and the X-ray light curve, also shows
a significant correlation. When this is taken together with the long (∼1 yr) delay between the start of each ejection event
and its associated X-ray peak it indicates that this bursting component of the X-ray flux must be associated with the ejected
blobs in the pc-scale jet and not with the accretion disc. Because X-ray telescopes do not have the resolution required to
resolve the accretion disc area from the pc-scale jet, this paper is the first to present observational evidence that can
pinpoint the point of origin of at least those long-timescale X-ray bursts with durations of 1–3 yrs. 相似文献
14.
Zongjun Ning 《Solar physics》2011,273(1):81-92
We explore the speed distributions of X-ray source motions after the start of chromospheric evaporation in two Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) flares. First, we make CLEAN images at 15 energy bands with a 12 second integration window; then, we outline a flaring
loop geometry to cover the looptop and footpoint sources as much as possible. Consistent with the previous steps, we find
converging motion of the double footpoint sources along the flaring loop in these two events. This motion is dependent on
the energy band and time and is typically seen at 3 – 25 keV, indicating a chromospheric evaporation origin. The speed distributions
at various energy bands are measured for the 10 September 2002 flare, which exhibits a separation-to-mergence motion pattern
well correlated with the rising-to-decay phases at 50 – 100 keV. 相似文献
15.
Details of the discovery (in February 2004) and results of subsequent (in 2004–2009) INTEGRAL observations of the transient
X-ray burster IGR J17380-3749 (IGR J17379-3747) are presented. Over the period of its observations, the INTEGRAL observatory
recorded two hard X-ray flares and one type I X-ray burst from the source, which allowed the nature of IGR J17380-3749 to
be determined. The burster radiation spectrum during the flares was hard—a power law with a photon index α = 1.8–2.0 or bremsstrahlung corresponding to a plasma with a temperature kT = 90–140 keV. The spectral shape at the flare peaks turned out to be the same, despite a more than twofold difference in
flux (the peak flux recorded in the energy range 18–100 keV reached ∼20 mCrab). The upper limit on the flux from the source
in its quiescent (off) state in the range of 18–40 keV was 0.15 mCrab (3σ). 相似文献
16.
Owens Alan Oosterbroek T. Orr A. Parmar A. N. Schulz R. Tozzi G.P. 《Earth, Moon, and Planets》1997,77(3):293-298
We report the detection of soft X-rays from comet C/1995 O1 (Hale-Bopp) by the Low Energy Concentrator Spectrometer (LECS)
on-board the X-ray satellite, BeppoSAX. The observations took place on 1996 September 10–11 approximately 1 day after a large
dust outburst (Schulz et al., 1997–1999). After correcting for the comets motion, a 7σ enhancement was found centered (2.1
± 1.3) x 105 km from the position of the nucleus, in the general solar direction. The total X-ray luminosity in the 0.1–2.0 keV energy
band is 5 x 1016 erg s−1 which is at least a factor of ∼ 3 greater than measured by the Extreme Ultraviolet Explorer (EUVE)4 days later and suggests
that the bulk of the emission measured by the LECS is related to the dust outburst. The extracted LECS spectrum is well fit
by a thermal bremsstrahlung-like distribution of temperature of 0.29 ± 0.06 keV - consistent with that observed in other comets.
We find no evidence for fluorescent carbon or oxygen emission and place 95% confidence limits of 1.0 x 1015 and 7.8 x 1015 erg s−1 to narrow line emission at 0.28 and 0.53 keV, respectively. We calculate that if such lines are present, they constitute
at most 18% of the 0.1–2.0 keV continuum luminosity.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
17.
Rajmal Jain Anil K. Pradhan Vishal Joshi K. J. Shah Jayshree J. Trivedi S. L. Kayasth Vishal M. Shah M. R. Deshpande 《Solar physics》2006,239(1-2):217-237
We present the first results from the low-energy detector payload of the solar X-ray spectrometer (SOXS) mission, which was
launched onboard the GSAT-2 Indian spacecraft on May 08, 2003 by the GSLV-D2 rocket to study solar flares. The SOXS low-energy
detector (SLD) payload was designed, developed, and fabricated by the Physical Research Laboratory (PRL) in collaboration
with the Space Application Centre (SAC), Ahmedabad and the Indian Space Research Organization (ISRO) Satellite Centre (ISAC),
Bangalore. The SLD payload employs state-of-the-art, solid-state detectors, viz., Si PIN and Cadmium-Zinc-Telluride (CZT) devices that operate at near room temperature (−20 °C). The energy ranges of the Si PIN and CZT detectors are 4 – 25 and 4 – 56 keV, respectively. The Si PIN provides sub-keV
energy resolution, while the CZT provides ~1.7 keV energy resolution throughout the energy range. The high sensitivity and
sub-keV energy resolution of the Si PIN detector allows measuring the intensity, peak energy, and the equivalent width of
the Fe-line complex at approximately 6.7 keV, as a function of time in all ten M-class flares studied in this investigation.
The peak energy (E
p) of the Fe-line feature varies between 6.4 and 6.7 keV with increase in temperature from 9 to 58 MK. We found that the equivalent
width (w) of the Fe-line feature increases exponentially with temperature up to 30 MK and then increases very slowly up to 40 MK.
It remains between 3.5 and 4 keV in the temperature range of 30 – 45 MK. We compare our measurements of w with calculations made earlier by various investigators and propose that these measurements may improve theoretical models.
We interpret the variation of both E
p and w with temperature as being to the changes in the ionization and recombination conditions in the plasma during the flare, and
as a consequence, the contribution from different ionic emission lines also varies. 相似文献
18.
We present the first in-depth statistical survey of flare source heights observed by RHESSI. Flares were found using a flare-finding
algorithm designed to search the 6 – 10 keV count-rate when RHESSI’s full sensitivity was available in order to find the smallest
events (Christe et al. in Astrophys. J.
677, 1385, 2008). Between March 2002 and March 2007, a total of 25 006 events were found. Source locations were determined in the 4 – 10 keV,
10 – 15 keV, and 15 – 30 keV energy ranges for each event. In order to extract the height distribution from the observed projected
source positions, a forward-fit model was developed with an assumed source height distribution where height is measured from
the photosphere. We find that the best flare height distribution is given by g(h)∝exp (−h/λ) where λ=6.1±0.3 Mm is the scale height. A power-law height distribution with a negative power-law index, γ=3.1±0.1 is also consistent with the data. Interpreted as thermal loop-top sources, these heights are compared to loops generated
by a potential-field model (PFSS). The measured flare heights distribution are found to be much steeper than the potential-field
loop height distribution, which may be a signature of the flare energization process. 相似文献
19.
Tomasz Mrozek Szymon Gburek Marek Siarkowski Barbara Sylwester Janusz Sylwester Anna Kepa Magdalena Gryciuk 《Solar physics》2018,293(7):101
In 2009, the Russian Complex Orbital Observations Near-Earth of Activity of the Sun (CORONAS-Photon) spacecraft was launched, carrying the Polish Solar PHotometer In X-rays (SphinX). The SphinX was most sensitive in the spectral range 1.2?–?15 keV, thus an excellent opportunity appeared for comparison with the low-energy end of Ramaty High Energy Solar Spectroscopic Imager (RHESSI) spectra. Common spectral measurements with these instruments cover the range where most of the flare energy is accumulated. We have chosen four consecutive small solar events observed on 4 July 2009 at 13:43 UT, 13:48 UT, 13:52 UT, and 13:55 UT (RHESSI flare peak times) and used them to compare the data and results from the two instruments. Moreover, we included Geostationary Operational Environmental Satellite (GOES) records in our analysis. In practice, the range of comparison performed for SphinX and RHESSI is limited roughly to 3?–?6 keV. RHESSI fluxes measured with a use of one, four, and nine detectors in the 3?–?4 keV energy band agree with SphinX measurements. However, we observed that SphinX spectral irradiances are three times higher than those of RHESSI in the 4?–?6 keV energy band. This effect contributes to the difference in obtained emission measures, but the derived temperatures of plasma components are similar. RHESSI spectra were fitted using a model with two thermal components. We have found that the RHESSI hot component is in agreement with GOES, and the RHESSI hotter component fits the SphinX flaring component well. Moreover, we calculated the so-called thermodynamic measure and the total thermal energy content in the four microflares that we studied. The results obtained show that SphinX is a very sensitive complementary observatory for RHESSI and GOES. 相似文献
20.
The UCSD solar X-ray instrument on the OSO-7 satellite observes X-ray bursts in the 2–300 keV range with 10.24 s time resolution. Spectra obtained from the proportional counter and scintillation counter are analyzed for the event of November 16, 1971, at 0519 UT in terms of thermal (exponential spectrum) and non-thermal (power law) components. The energy content of the approximately 20 × 106K thermal plasma increased with the 60 s duration hard X-ray burst which entirely preceded the 5 keV soft X-ray maximum. If the hard X-rays arise by thick target bremsstrahlung, the nonthermal electrons above 10 keV have sufficient energy to heat the thermally emitting plasma. In the thin target case the collisional energy transfer from non-thermal electrons suffices if the power law electron spectrum is extrapolated below 10 keV, or if the ambient plasma density exceeds 4 × 1010 cm–3.Formerly at UCSD. 相似文献