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1.
We have derived the radiative-transfer equation for a point source with a specified intensity and spectrum, originating in the early Universe between the epochs of annihilation and recombination, at redshifts zs = 10 8?10 4. The direct radiation of the source is separated from the diffuse radiation it produces. Optical distances from the source for Thomson scattering and bremsstrahlung absorption at the maximum of the thermal background radiation are calculated as a function of the redshift z. The distances grow sharply with decreasing z, approaching asymptotic values, the absorption distance increasing more slowly and reaching their limiting values at lower z. For the adopted z values, the optical parameters of the Universe can be described in a flat model with dusty material and radiation, and radiative transfer can be treated in a grey approximation. 相似文献
2.
AIA/SDO data in the 193 Å channel preceding a coronal mass ejection observed at the solar limb on June 13, 2010 are used to simultaneously identify and examine two different shock fronts. The angular size of each front relative to the CME center was about 20°, and their propagation directions differed by ≈25° (≈4° in position angle). The faster front, called the blast shock, advanced the other front, called the piston shock, by R ≈ (0.02-0.03) R⊙ ( R⊙ is the solar radius) and had a maximum initial speed of VB ≈ 850 km/s (with VP ≈ 700 km/s for the piston shock). The appearance and motion of these shocks were accompanied by a Type II radio burst observed at the fundamental frequency F and second harmonic H. Each frequency was split into two close frequencies f1 and f2 separated by Δ f = f2 - f1 ? F, H. It is concluded that the observed frequency splitting Δ f of the F and H components of the Type II burst could result from the simultaneous propagation of piston and blast shocks moving with different speeds in somewhat different directions displaying different coronal-plasma densities. 相似文献
3.
This contribution considers the critical time increment (Δ tcrit) to achieve stable simulations using particulate discrete element method (DEM) codes that adopt a Verlet-type time integration scheme. The Δ tcrit is determined by considering the maximum vibration frequency of the system. Based on a series of parametric studies, Δ tcrit is shown to depend on the particle mass ( m), the maximum contact stiffness ( Kmax), and the maximum particle coordination number ( CN,max). Empirical expressions relating Δ tcrit to m, Kmax, and CN,max are presented; while strictly only valid within the range of simulation scenarios considered here, these can inform DEM analysts selecting appropriate Δ tcrit values. 相似文献
4.
Photometric observations of the radio source S5 0716+714 were obtained in BV RI filters from January 20, 1998 to January 9, 2001 with Zeiss-600 and Zeiss-1000 telescopes of the Special Astrophysical Observatory of the Russian Academy of Sciences. The light curves in all the bands are synchronous, providing evidence for the real variability of the object in timescales, from hundreds of days to 5–10 min. No time shift between events in the adjacent filters was detected. The variability spectrum at frequencies of 0.003–100 d ?1 (3.5 × 10 ?8–1.1 × 10 ?3 Hz) is close to that of a flicker noise. The optical spectral index α ( S ~ v α) varies from ?1.59 at the minimum to ?1.13 at the maximum brightness. Measurements of linear polarization in BV R carried out on April 12–13, 2000 confirmed a high degree of polarization and rapid fluctuations of the polarization in a timescale of 15–30 min, whose amplitude decreases at red wavelengths. All the optical properties of the source, its compactness, the absence of spectral lines, the high degree of polarization, and very rapid fluctuations of the brightness, polarization, and spectral index, suggest a synchrotron origin for optical radiation. It may be that we are observing the radiation from a group of very compact bodies (~10 ?10 arcsec) at various stages of their evolution. 相似文献
5.
Results of spectral observations of the isolated Ae Herbig star CQ Tau obtained in 1995–1998 in the H α line and near the sodium resonance doublet are presented, together with simultaneous photometric monitoring of the star. CQ Tau is a member of the family of young UX Ori stars with nonperiodic Algol-like brightness decreases. The star is surrounded by an accretion disk, in which its emission-line spectrum and part of its absorption-line spectrum are formed. The strong variability of the H α, D NaI, and HeI 5876 Å lines testifies that the gaseous disk is appreciably inhomogeneous in both the radial and azimuthal directions. This inhomogeneity probably results from uneven feeding by the circumstellar material from the peripheral regions of the circumstellar disk. Over the four years of observations, we observed the star in deep minima three times (Δ V~2). On these nights, an increase in the H α equivalent width followed the decrease in radiation flux. In the two deepest minima, the normally two-component line profile had only a single component with a nearly symmetrical profile. This behavior of the H α line is in good agreement with the results of numerical modeling of Algol-like minima and can be used to estimate the parameters of the dust clouds eclipsing the star and inner accretion disk. These estimates suggest that the circumstellar dust clouds can approach very close to the star and be sublimated there. 相似文献
6.
We analyze multicolor observations of the blazar ON 231 obtained during coordinated observations in 1994–2002. On average, the spectral energy distribution of the variable component in the optical range remains constant, and can be represented
by the power law F
ν ∼ ν
−0.85. Since the radiation of the blazar is strongly polarized, there is no doubt that the variable emission that is responsible
for the activity of the blazar is synchrotron radiation. There are small but significant season-to-season variations in the
spectral index. 相似文献
7.
This paper presents the three most important aspects of seismic microzonation namely prediction of fundamental frequency ( F 0) of soil deposit, aggravation factor (aggravation factor is simply the extra spectral amplification due to complex 2D site effects over the 1D response of the soil column) and the spatial variability of the ground motion caused by the basin-edge induced Love waves. The predicted F 0 of single, double and three-soil-layered models revealed that the available empirical relations to predict the F 0 of layered soil deposits are inadequate. We recommend the use of analytical or numerical methods to predict such an important parameter based on wave propagation effects. An increase of amplitude of Love wave, strain level and average aggravation factor (AAF) with increase of impedance contrast was obtained. Based on the trend of rate of decrease of AAF and maximum strain with offset from the basin-edge, we can qualitatively infer that the effects of induced Love wave may reduce to a negligible value after a traveled distance of 6.5–10.0 λ F (where λ F is the wavelength corresponding to the F 0 of soil layer). The obtained increase of strain level with the decrease of distance between two receiver points used for the computation of strain reflects that structures having spatial extent smaller than the λ F may suffer damage due to the basin-edge induced surface waves. The fast rate of decrease of strain with the offset from the strong lateral discontinuity (SLD)/basin-edge may be attributed to the dispersive nature of Love wave. We can incorporate the increased spectral amplification due to the induced surface waves in the form of aggravation factor but till date we have no effective way to incorporate the effects of developed strain by induced surface waves in seismic microzonation or in building codes. 相似文献
8.
Transposed temperature drop calorimetry at 1000 °C was performed on natural zircons (ZrSiO 4) from Sri Lanka that were partially to completely metamict due to α-decay event damage (0.06 to 11.7×10 15 α-decay events/mg). The enthalpy of annealing at room temperature (ΔH anneal) varies sigmoidally as a function of radiation dose. ΔH anneal reaches a saturation plateau at radiation doses greater than 5×10 15 α-decay events/mg. The annealing of several samples to a crystalline structure with broadened diffraction peaks does not significantly affect the enthalpy of annealing. The large magnitude of the enthalpy of annealing plateau, ?59±3 kJ/mol, suggests that the damage to the structure is pervasive on the scale of Angstroms, consistent with the loss of mid-range order characteristic of a glass. The energetics are consistent with, but do not require, chemical heterogeneity caused by micro-domains of amorphous SiO 2-rich and ZrO 2-rich regions in the metamict state. 相似文献
9.
The most powerful flare ever registered in the Galactic water-maser source W49N has been detected in long-term monitoring data in the 616–523 transition with line frequency f = 22.235 GHz carried out on the 22-m Simeiz, 32-m Toruń, 100-m Effelsberg, and 32-m Medicina radio telescopes, beginning in September 2017 and continuing in 2018. Some stages of the flare were monitored daily. Detailed variations of the source spectral flux density with time have been obtained. At the flare maximum, the flux exceeded P ≈ 8 × 104 Jy, and this was record highest flux registered over the entire history of observations of this source. Important conclusions related to details of the mechanism for the H2O line emission have been drawn. An exponential increase in the flare flux density was detected during both the rise and decline of the flare. The data obtained indicate that the maser is unsaturated, and remained in this state up to the maximum observed flux densities. Additional support for the idea that the maser is unsaturated is the shape of the dependence of the line width on the flux. The characteristics of the variations of the spectral flux density are probably associated with a sharp increase in the density of the medium and the photon flux that led to an increase in the temperature from an initial level of 10–40 K to hundreds of Kelvins. Interferometric maps of the object during the increase in the spectral flux density of the flare have been obtained. A possible mechanism for the primary energy release in W49N is considered. 相似文献
10.
The structure of shocks propagating through partially ionized hydrogen gas with characteristics typical of the atmospheres of RR Lyr, W Vir, and RV Tau type variables is analyzed in terms of a self-consistent solution of the equations of gas dynamics, atomic kinetics, and radiation transfer. The solutions were obtained for shock waves with velocities 20 km/s≤ U 1≤90 km/s and unperturbed hydrogen gas with temperatures 3000 K≤ T 1≤9000 K and density ρ 1=10 ?10 g/cm 3. The fraction of the energy of the gas-dynamic flux converted into radiation increases with the shock amplitude, and the ratio of the radiation flux emitted by the shock to the gas kinetic energy flux is 0.4???0.8 for the velocities U 1 considered. This ratio also increases slightly with the ambient gas temperature T 1 due to an increase in hydrogen ionization in the radiative precursor. The flux emitted by the leading edge of the shock opposite to the gas flow is several percent higher than the flux emitted in the opposite direction by the trailing edge of the shock. Radiation is mostly concentrated in the Balmer continuum, and the region of efficient Lyman radiation transfer includes gas layers located near the viscous jump (δ X=±10 4 cm). The final gas-compression ratio in units of the limiting compression corresponding to an isothermal approximation is virtually independent of the shock amplitude, and increases with the unperturbed gas temperature from r≈0.5 at T 1=3000 K to r≈0.9 at T 1=9000 K. 相似文献
11.
The paper reports pioneering data on the calorimetrically determined enthalpy of formation from elements of cuspidine, Ca fluordiorthosilicate Ca 4Si 2O 7F 2, from the Tyrny-Auz Mo–W deposit in Kabardino- Balkaria, Russia. The data were obtained by high-temperature melt solution calorimetry. The determined value is Δ fHel° (298.15 K) =–5190 ± 13 kJ/mol. The paper reports estimated S°(298.15 K) and Δ fGel° (298.15 K) of cuspidine. 相似文献
12.
Previously developed methods for estimating the angle β between the spin axis of a neutron star and its magnetic moment together with observational data for anomalous X-ray pulsars (AXPs) indicate that these objects are nearly aligned rotators, and that the drift model can be applied to them. The magnetospheres of aligned rotators are appreciably more extended than in pulsars with large values of β. With such extents for the magnetosphere, the conditions for the generation of transverse waves via the cyclotron instability are satisfied. The expected spectrum of the resulting radiation is very steep (its spectral index is α > 3), consistent with the observed radio spectra of known AXPs ( α > 2). A large magnetosphere also favors the appearance of appreciable pitch angles for relativistic electrons, and therefore the generation of synchrotron emission. The maximum of this emission falls in the microwave range. This mechanism provides appreciable fluxes at frequencies of tens of gigahertz and can explain the observed enhanced AXP radiation in this range. 相似文献
13.
Observations of circumstellar maser emission from the long-period variable R Cas in the 1.35-cm water-vapor line are reported. The observations were carried out on the 22-m radio telescope of the Pushchino Radio Astronomy Observatory in 1980–2003 (JD=2444409–2452724). Over the 23 years of observations, strong flares in the H 2O line profile were recorded in 1982 (with a peak flux density up to 400 Jy) and 1986–1989 (up to 750 Jy). Subsequently, from 1990 to March 2003, the H 2O line flux was usually below the detection threshold of the radio telescope (<5–10 Jy). Episodic small increases of the emission with peak flux densities of 20–60 Jy were observed. The variations of the H 2O line flux F are correlated with variations in the visual brightness of the star. The phase delay Δ γ of the F variations relative to the optical light curve of R Cas ranged from 0.2–0.3 P during the observations ( P=430.46 d is the star's period). A model for the variability of the H 2O maser in R Cas is discussed. If the variations are due to periodic impacts by shock waves driven by the stellar pulsations, the time for the shock to travel from the photosphere to the inner boundary of the H 2O-masing shell may reach 2–4 P. The flares could be due to transient episodes of enhanced mass loss by the star or to the propagation of an exceptionally strong shock from the stellar surface. 相似文献
14.
The possibility of selecting extended radio sources that are potential candidates for giant radio galaxies among objects in the Pushchino catalog at 102 MHz is considered. The method used is based on the analysis of objects in a α 1– α 2 diagram, where α 1 and α 2 are two-frequency spectral indices ( S ν ~ ν ?α ), formally calculated using 102–365 and 365–1400 MHz data, based on the identifications of Pushchino radio sources with objects of the Texas (365 MHz) and Green Bank (1400 MHz) catalogs. The calculated spectra are abnormally steep at 102–365 MHz and flat or even inverted at 365–1400 MHz, due to the fact that the 365-MHz flux densities of extended radio sources measured with the Texas radio interferometer are appreciably underestimated. Ten objects among the fifteen Pushchino radio sources selected using this criterion proved to be already known large radio galaxies. The possibility of improving the efficiency of the method by using larger samples and applying some additional criteria selecting candidate giant radio galaxies is considered. 相似文献
15.
We discuss the results of deep surveys of a ±10′ strip of the sky, centered on the declination of SS 433, carried out on the Northern sector of the RATAN-600 telescope at 2.7 and 7.6 cm in 1987–2000. The survey objects are cross-identified with sources in the NVSS catalog and the corresponding two-frequency spectral indices determined. We find a decrease in the mean spectral index in the transition from objects with flux densities S 21 ≥ 30 mJy to those with 15 < S 21 < 30 mJy. The constructed log N — log S relation at 2.7 cm has a slope of 3/2 at flux densities ≥300 mJy and flattens at weaker flux densities. The 1.4 GHz (NVSS), 3.94 GHz (RATAN-600), and 11.11 GHz (RATAN-600) data are used to estimate the number of objects per square degree at a wavelength of 1 cm. 相似文献
16.
Numerous supernova outbursts that are correlated in time and space are the main mechanism for the formation of powerful galactic winds and supershells of ionized hydrogen. Information about the dynamics and thermal properties of the gas in shells (bubbles) can be obtained from spectral observations, including those of optical recombination lines. The emission properties of the Hα and Hβ recombination lines and the velocity dispersion of the gas in bubbles formed by numerous supernova outbursts are studied. The appearance of the intensity vs. velocity dispersion ( I( H α) ?σ) diagram depends on the supernova rate and the age of the bubble. The temperature dependence of the I(H α)/ I( H β) line-intensity ratio (the Balmer decrement) can be used to obtain additional constraints on the evolutionary status of a collective remnant formed by numerous supernova outbursts. 相似文献
17.
The enthalpies of mixing in the quasi-binary liquid system NaBO 2 + SiO 2 were measured by solid-liquid calorimetry at 1394 K. Correcting for the known enthalpy of fusion of SiO 2 at this temperature we derived also the corresponding liquid-liquid enthalpies of mixing, ΔH mix, and the enthalpy interaction parameters, ΔH mix/N NaBO2N SiO2; the latter quantity changes from about −30 kj mol −1 in pure NaBO 2 to about −20 kJ mol −1 at NSiO2 ≈ 0.67. From the experimentally determined curve for ΔH mix the partial enthalpies of the two components were obtained by the method of intercepts. For nsio2 < 0.4 values of ΔH̄ SiO2 were determined also by direct experiments. This quantity shows a sharp dependence on composition for NSiO2 < 0.1 and for NSiO2 ≈ 0.28. The possible significance of this is discussed in the light of reported structural information on the melts. 相似文献
18.
Spectroscopic and photometric data for the two rapidly rotating members of the α Persei cluster He 373 and AP 225 are analyzed. Improved estimates have been obtained for the projected equatorial rotation velocities: v sin i = 164 km/s for He 323 and v sin i = 129 km/s for AP 225. Multi-band photometric mapping is used to map the spot distributions on the surfaces of the two stars. The fractional spotted areas S and mean temperature difference Δ T between the unspotted photosphere and the spots are estimated ( S = 7% and Δ T = 1000 K for He 373; S = 9% and Δ T = 800 K for AP 225). The H α line profiles of both stars have variable emission components whose widths are used to deduce the presence of extended regions of emission reaching the corotation radius. 相似文献
19.
The relative plume thermal power Ka = N/ N1 is used ( N is the thermal power transferred from the plume base to its conduit and N1 is the thermal power transferred from the plume conduit into the surrounding mantle in the steady-state heat conduction regime). Thermochemical mantle plumes with small (Ka < 1.15) and intermediate (1.15 < Ka < 1.9) thermal powers are formed at the core–mantle boundary beneath cratons in the absence of horizontal free-convection mantle flows beneath them, or in the presence of weak horizontal mantle flows. Thermochemical plumes reach the Earth’s surface when their relative thermal power is Ka > 1.15. The thermal and hydrodynamical structure of the plume conduit ascending from the core–mantle interface to the level from which the magmatic melt erupts on the Earth’s surface is presented. The model of two-stage eruption of the melt from the plume conduit to the surface is considered. The critical height of the massif above the plume roof, at which the eruption conduit supplying magmatic melt to the surface forms, is determined. The volume of melt erupting through the eruption conduit to the surface is estimated. The dependence of depth Δ x from which the melt is transported to the surface on the plume diameter for a kinematic viscosity of ν = 0.5–2 m 2/s is presented. In the case when the value Δ x is larger than the depth starting from which diamond is stable (150 km), the melt from the plume conduit can transport diamonds to the Earth’s surface. The melt flow in the eruption conduit is considered as a turbulent flow in a cylindrical duct. The velocity of the melt flow in the eruption conduit and the time for the melt to be transported to the surface from a depth of Δ x = 150 km for a kinematic viscosity of the melt in the eruption conduit νv = 0.01–1 m 2/s are determined. Tangential stress on the eruption conduit sidewall is estimated in cases of melt flow both in smooth and rough conduits. 相似文献
20.
Radio flux measurements of the Crab nebula have been performed over many years relative to Orion A at 927 MHz and relative to Cygnus A and Virgo A at 151.5 MHz. The inferred average secular rates of decrease in the radio flux of the Crab nebula are d 927 MHz = ?0.18 ± 0.10% yr ?1 over 1977–2000 and d 151.5 MHz = ?0.3 ± 0.1% yr ?1 over 1980–2003. The weighted mean flux-decrease rate averaged over several years of relative measurements at 86, 151.5, 927, and 8000 MHz is d mw = ?0.17 ± 0.02% yr ?1. The secular flux decrease is frequency independent, with an upper limit of | dα/ dt| < 3 × 10 ?4 yr ?1 for the absolute value of the rate of change of the spectral index, and remains constant in time when averaged over long time intervals. The results of our measurements at 151.5 and 927 MHz combined with published absolute measurements at 81.5 and 8250 MHz are used to determine the radio spectrum of the Crab nebula for epoch 2010.0. 相似文献
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