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1.
Spectral analysis method was applied to aeromagnetic data obtained for Ikogosi warm spring (IWS) area of southwestern Nigeria. This was done with the objective of determining the bottom of the magnetized crust called Curie point depth (CDP) and understand the nature and extent of the local geothermal system at depth beneath IWS. The depth to the centroid, Z o, of the deepest distribution of the magnetic dipoles was obtained by computing least-squares fit to the lowest-frequency segment of the azimuthally averaged log power spectrum. The average depth to the top of the deepest crustal block was computed as the depth to the top, Z t, of the second lowest-frequency segment of the spectrum. The depth to the bottom of the deepest magnetic dipoles, the inferred Curie point depth, was then calculated from Z b?=?2Z o???Z t. The Curie depth estimates for IWS range between 4.68 and 11.38 km (below sea level). We also estimate the heat flow and Curie temperature using a one-dimensional conductive heat transport model. The average heat flow, 42 mW m?2, and geothermal gradient, 32°C/km, obtained suggest a low enthalpy thermal regime. The Curie temperature for the region varies between 153°C and 350°C. Also, an inverse linear relationship between heat flow and Curie depths was determined. Good agreement between the Curie point depths derived from heat flow data and magnetic data suggests that the Curie point depth analysis is useful to estimate the regional thermal structure and the tectonic settings.  相似文献   

2.
Two-dimensional simulations of time-dependent solar magnetogranulation are used to analyze the horizontal magnetic fields and the response of the synthesized Stokes profiles of the IR FeI λ1564.85 nm line to the magnetic fields. The 1.5-h series of MHD models used for the analyses reproduces a region of the magnetic network in the photosphere with an unsigned magnetic flux density of 192 G at the solar surface. According to the magnetic-field distribution obtained, the most probable absolute strength of the horizontal magnetic field at an optical depth of τ 5 = 1(τ 5 denotes τ at λ = 500 nm) is 50 G, while the mean value is 244 G. On average, the horizontal magnetic fields are stronger than the vertical fields to heights of about 400 km in the photosphere due to their higher density and the larger area they occupy. The maximum factor by which the horizontal fields are greater is 1.5. Strong horizontal magnetic flux tubes emerge at the surface as spots with field strengths of more than 500 G. These are smaller than granules in size, and have lifetimes of 3–6 min. They form in the photosphere due to the expulsion of magnetic fields by convective flows coming from deep subphotospheric layers. The data obtained qualitatively agree with observations with the Hinode space observatory.  相似文献   

3.
Wind erosion causes serious problems and considerable threat in most regions of the world. Vegetation on the ground has an important role in controlling wind erosion by covering soil surface and absorbing wind momentum. A set of wind tunnel experiments was performed to quantitatively examine the effect of canopy structure on wind movement. Artificial plastic vegetations with different porosity and canopy shape were introduced as the model canopy. Normalized roughness length (Z 0/H) and shear velocity ratio (R) were analyzed as a function of roughness density (λ). Experiments showed that Z 0/H increases and R decreases as λ reaches a maximum value, λ max, while the values of Z 0/H and R showed little change with λ value beyond as λ max.  相似文献   

4.
Helioseismology and neutrino experiments probing the internal structure of the Sun have yieldedmuch information, such as the adiabatic elasticity index, density, and sound speed in the convective and radiative zones, the depth of the convective zone, and the flux of neutrinos from the core. The standard model of the Sun does not adequately reproduce these characteristics, with models with low heavy element contents (mass fraction of metals Z = 0.013 in the convective zone) deviating from the helioseismic data appreciably more strongly than models with high heavy element contents (Z = 0.018). However, a spectroscopic low Z value is supported by studies reconstructing the Γ 1 profile in the adiabatic part of the convective zone based on the oscillation frequencies. Models of the convective zone show a good agreement precisely for low Z values. This study attempts to construct a model for the Sun with low Z that satisfies the helioseismic constraints. This model requires changes in the p + p reaction cross section and the opacities in the radiative zone. In our view, the helioseismic result for the mass concentrated in the convective zone testifies that the p + p reaction cross section or the electron-screening coefficient in the solar core must be increased by several percent over the current values. This requires a comparatively small correction to the opacities (by less than 5%), in order to obtain a solar model with low Z that is in agreement with the results of helioseismology and the observed solar neutrino fluxes.  相似文献   

5.
The deformations of the sedimentary cover at near-latitudinal geotraverses west and east of the Mid-Atlantic Ridge in the equatorial part of ocean are compared with potential fields and variations of the V p/V s attribute at a depth of ~470 km. The features of sedimentary cover deformations in abyssal basins are formulated, as well as their differences from the undisturbed bedding of sediments. The elements of chain of phenomena with common spatial manifestations and cause-and-effect relationships have been established, including heterogeneous horizontal movements, which make up macrojointing above “cold” mantle blocks at a depth of ~470 km; serpentinization of upper-mantle rocks; the formation of superposed magnetic anomalies; the release of the fluids, which acoustically bleach out the sedimentary sequence in seismic imaging; and decompaction of rocks leading to vertical motions and forced folding. The origin of the Atlantic marginal dislocation zone is explained. The coincidence of the deformation boundary in the equatorial Atlantic with the zero contour line of the V p/V s attribute is revealed. This coincidence is an indicator of the rheological state of the upper mantle.  相似文献   

6.
The results of hydrodynamical calculations of radially pulsating helium stars with masses 0.5M⊙≤M≤0.9M⊙, bolometric luminosities 600L⊙≤5×103L⊙, and effective temperatures 1.5×104 K≤Teff≤3.5×104 K are presented. The pulsation instability of these stars is due to the effects of ionization of iron-group elements in layers with temperatures T～2×105 K. The calculations were carried out using opacities for the relative mass abundances of hydrogen and heavy elements X=0 and Z=0.01, 0.015, and 0.02. Approximate formulas for the pulsation constant Q over the entire range of pulsation instability of the hot helium stars in terms of the mass M, radius R, effective temperature Teff, and heavy-element abundance Z are derived. The instability of BX Cir to radial pulsations with the observed period Π=0.1066 d occurs only for a mass M≥0.55M⊙, effective temperature Teff≥23000 K, and heavy-element abundance Z≥0.015. The allowed mass of BX Cir is in the range 0.55M⊙≤M≤0.8M⊙, which corresponds to luminosities 800L⊙≤M≤1400L⊙ and mean radii 1.7R⊙?R?2.1R⊙.  相似文献   

7.
Coda wave attenuation is estimated for Qeshm Island which is located in the southeastern part of Zagros. For this purpose, the aftershocks of Qeshm earthquake in November 27, 2005, recorded within an epicentral distance less than 100 km, have been used. More than 829 earthquakes were recorded by a local temporary network consisting of 16 short period stations installed after a week after the main shock for ～10 weeks. The coda quality factor, Q c, was estimated using the single-backscattering model in frequency bands of 0.5–24 Hz. In this research, lateral and vertical variations of coda Q in Qeshm Island are explored. In Qeshm Island, absence of significant lateral variation of coda Q is observed. To investigate the attenuation variation with depth, the coda Q value was calculated for coda time windows with different lengths (5, 10, 15, 20, 25, and 30 s). It is observed that coda Q increases with depth. However, in our study area, the rate of increase of coda Q with depth is not uniform. Beneath Qeshm Island, the rate of increase of coda Q is greater at depths less than ～40 km compared with those of larger depths. This is indicating the existence of a low attenuation anomalous structure under the ～40-km depth which may be correlated with the Moho depth in this region. The average frequency relation for this region is Q c = 36 ± 1.2f 0.94 ± 0.039 at a 5 s-lapse time window length and Q c = 110 ± 1.8f 0.88 ± 0.09 at a 30-s lapse time window length.  相似文献   

8.
This paper discusses a newly developed high-quality integrated dataset of shallow earthquake ground motions that occurred in Iran, from 1976 to 2013. A total of 860 three-component strong motion records are processed from 183 earthquake events, moment magnitudes 5.0?≤?M w ?≤?7.4, and rupture distances of R RUP  ≤ 120 km. Strong motion data from Iran having special tectonic features and shallow earthquakes with depths less than 35 km are included. This paper presents a thorough procedure used to collect and to generate a database following the Next-Generation Attenuation-West research projects. This database can be used in the development and ranking of ground motion models and for seismological and engineering hazard and risk analyses. Unprocessed strong motion records are obtained from the Iranian Strong Motion Network (ISMN). The time series collected were thoroughly examined through several rounds of quality reviews. The newly generated database includes the peak ground acceleration, peak ground velocity, and pseudo-spectral acceleration for the 5% damped with periods ranging from 0.01 to 10 s. The database also includes ground motion information and source characterization and parameters. This study is the near-source compiled ground motion database that can be used for Iran, and it is consistent with standard worldwide databases.  相似文献   

9.
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 Δf = f2 - f1 ? F, H. It is concluded that the observed frequency splitting Δf 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   

10.
The components U0 and V0 of the solar motion and the Oort constant A0 are determined using the data of a homogeneous open-cluster catalog with corrected distance moduli. The results are based on a sample of 146 open clusters with known radial velocities located in the Galactic plane (b<7°) within 4 kpc of the Sun. The solar Galactocentric distance R0 is determined using two kinematic methods. The following results are obtained: A0=17.0±0.9 km/s kpc, U0=10.5±1.0 km/s, V0=11.5±1.1 km/s, R0=8.3±0.3 pc.  相似文献   

11.
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 ΔT between the unspotted photosphere and the spots are estimated (S = 7% and ΔT = 1000 K for He 373; S = 9% and ΔT = 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   

12.
Observations on the RadioAstron ground–space interferometer with the participation of the Green Bank and Arecibo ground telescopes at 1668 MHz have enabled studies of the characteristics of the interstellar plasma in the direction of the pulsar PSR B0525+21. The maximum projected baseline for the ground–space interferometer was 233 600 km. The scintillations in these observations were strong, and the spectrum of inhomogeneties in the interstellar plasma was a power law with index n = 3.74, corresponding to a Kolmogorov spectrum. A new method for estimating the size of the scattering disk was applied to estimate the scattering angle (scattering disk radius) in the direction toward PSR B0525+21, θ scat = 0.028 ± 0.002 milliarcsecond. The scattering in this direction occurs in a plasma layer located at a distance of 0.1Z from the pulsar, where Z is the distance from the pulsar to the observer. For the adopted distance Z = 1.6 kpc, the screen is located at a distance of 1.44 kpc from the observer.  相似文献   

13.
Multi-epoch observations with high spectral resolution acquired in 1998–2008 are used to study the time behavior of the spectral-line profiles and velocity fields in the atmosphere and circumstellar shell of the post-AGB star V448 Lac. Asymmetry of the profiles of the strongest absorption lines with lower-level excitation potentials χ low < 1 eV and time variations of these profiles have been detected, most prominently the profiles of the resonance lines of BaII, YII, LaII, SiII. The peculiarities of these profiles can be explained using a superposition of stellar absorption line and shell emission lines. Emission in the (0; 1) 5635 Å Swan system band of the C2 molecule has been detected in the spectrum of V448 Lac for the first time. The core of the Hα line displays radial-velocity variations with an amplitude of ΔV r ≈ 8 km/s. Radial-velocity variations displayed by weak metallic lines with lower amplitudes, ΔV r ≈ 1–2 km/s, may be due to atmospheric pulsations. Differential line shifts, ΔV r = 0–8 km/s have been detected on various dates. The position of the molecular spectrum is stationary in time, indicating a constant expansion velocity of the circumstellar shell, V exp = 15.2 km/s, as derived from the C2 and NaI lines.  相似文献   

14.
SDO/HMI and SDO/AIA data for the 24th solar-activity cycle are analyzed using a quicker and more accurate method for resolving π ambiguities in the transverse component of the photospheric magnetic field, yielding new results and confirming some earlier results on the magnetic properties of leading and following magnetically connected spots and single spots. The minimum inclination of the field lines to the positive normal to the solar surface α min within umbrae is smaller in leading than in following spots in 78% of the spot pairs considered; the same trend is found for the mean angle 〈α〉 in 83% of the spot pairs. Positive correlations between the α min values and the 〈α〉 values in leading and following spots are also found. On average, in umbrae, the mean values of 〈B〉, the umbra area S, and the angles α min and 〈α〉 decrease with growth in the maximum magnetic field B max in both leading and following spots. The presence of a positive correlation between B max and S is confirmed, and a positive correlation between 〈B〉 and S in leading and following spots has been found. Themagnetic properties of the umbrae of magnetically connected pairs of spots are compared with the contrast of the He II 304 emission above the umbrae, C 304. Spots satisfying certain conditions display a positive correlation between C 304?L and 〈α L 〉 for the leading (L) spots, and between C 304?L /C 304?F and l L /l F , where l L (l F ) are the lengths of the field lines connecting leading (L) or following (F) spots from the corresponding spot umbrae to the apex of the field line.  相似文献   

15.
Outcropped of the Kuhbanan Formation at Dahu, near Zarand, about 63 km north of Kerman, Iran contains peri-Gondwana trilobites. In this study, 185 trilobite samples including six species and genera were identified and described from Dahu section. This trilobite’s assemblage including Redlichia noetlingi, Redlichia sp., Kermanella kuhbananensis, Kermanella lata lata, Kermanella lata minuta, Iranoleesia pisiformis, and Iranaspis sp. based on occurrence of the trilobite fauna a late Early to Middle Cambrian (Series 2–3) is suggested for this strata. These trilobite fauna help confirm conclusions from recent geological studies that place the Kerman Basin of Iran during the Cambrian.  相似文献   

16.
Seismic source characteristics in the Kachchh rift basin and Saurashtra horst tectonic blocks in the stable continental region (SCR) of western peninsular India are studied using the earthquake catalog data for the period 2006–2011 recorded by a 52-station broadband seismic network known as Gujarat State Network (GSNet) running by Institute of Seismological Research (ISR), Gujarat. These data are mainly the aftershock sequences of three mainshocks, the 2001 Bhuj earthquake (M w 7.7) in the Kachchh rift basin, and the 2007 and 2011 Talala earthquakes (M w ≥ 5.0) in the Saurashtra horst. Two important seismological parameters, the frequency–magnitude relation (b-value) and the fractal correlation dimension (D c) of the hypocenters, are estimated. The b-value and the D c maps indicate a difference in seismic characteristics of these two tectonic regions. The average b-value in Kachchh region is 1.2 ± 0.05 and that in the Saurashtra region 0.7 ± 0.04. The average D c in Kachchh is 2.64 ± 0.01 and in Saurashtra 2.46 ± 0.01. The hypocenters in Kachchh rift basin cluster at a depth range 20–35 km and that in Saurashtra at 5–10 km. The b-value and D c cross sections image the seismogenic structures that shed new light on seismotectonics of these two tectonic regions. The mainshock sources at depth are identified as lower b-value or stressed zones at the fault end. Crustal heterogeneities are well reflected in the maps as well as in the cross sections. We also find a positive correlation between b- and D c-values in both the tectonic regions.  相似文献   

17.
The rock mass failure process can be divided into several distinct deformation stages: the compaction stage, elastic stage, stable failure stage, accelerated failure stage, and post-peak stage. Although each stage has been well studied, the relationship among the stages has not been established. Here, we establish two models which are the Strain model Q and Energy density model S by using the renormalization group theory and investigate the mechanical relationship between the volume dilatant point and peak stress point on the rock stress-strain curve. Our models show that the strain ratio (ε f /ε c ) and energy ratio (E f /E c ) at the volume dilatant point and peak stress point are solely functions of the shape parameter m. To verify our models, we further studied the failure process of rock specimens through several uniaxial compression experiments and found that the relationship between ε f /ε c or E f /E c and m shares a notably similar pattern to that from our theoretical model. However, the ε f /ε c and E f /E c values in our experiments are slightly smaller than those predicted by the models. In brief, we demonstrate that our models can be used to predict the failure process of the laboratory-scale hard brittle rock samples.  相似文献   

18.
We have used spectrograms taken with a dispersion of 8–12 Å per mm and Kurucz model atmospheres to study the supergiant 89 Her (F2Ibe).We find the effective temperature and gravity T eff = 6300 ± 150 K and log g = 0.5 ± 0.2. We have analyzed the microturbulence in the star’s atmosphere based on FeI, FeII, and TiII lines, deriving ξ t = 7.0 ± 0.5 km/s for the FeI and TiII lines and ξ t = 8.0 ± 0.5 km/s for the FeII lines. Abundances were determined for 23 elements. The elemental abundances in the atmosphere of 89 Her show deficiencies compared to the solar chemical composition, except for sodium, which is overabundant relative to the Sun.  相似文献   

19.
Present work provides in-situ structural data at a fine temperature scale from RT to the melting point of nitratine, NaNO3. From the analysis of log e 33 versus log t plots, it is possible to prove that an univocal indication on the R \( \overline{3} \) c (low temperature, LT) → R \( \overline{3} \) m (high temperature, HT) transition mechanism cannot be obtained because of the relevant role played by the arbitrary assumptions required for defining the c 0 dependence from temperature of the HT phase. This is due to the occurrence of excess thermal expansion for the HT phase. A significantly better fit for an Ising-spin structural model over a non-Ising rigid-body one has been obtained for the LT phase. Moreover, the Ising model led to a smooth variation of the oxygen site x fractional coordinate throughout the transition. The structure of the HT polymorph has been successfully refined considering an oxygen site at x, 0, ½, with 50% occupancy. Such model was the only acceptable one from the crystal chemical point of view as the alternative model (oxygen site at x, y, z with 25% occupancy) led to unrealistically aplanar \( {\text{NO}}_{3}^{ - } \) groups.  相似文献   

20.
In this study, the preprocessing of the gamma test was used to select the appropriate input combination into two models including the support vector regression (SVR) model and artificial neural networks (ANNs) to predict the stream flow drought index (SDI) of different timescales (i.e., 3, 6, 9, 12, and 24 months) in Latian watershed, Iran, which is one of the most important sources of water for the large metropolitan Tehran. The variables used included SDI t , SDI t ? 1, SDI t ? 2, SDI t ? 3, and SDI t ? 4 monthly delays. Two variables including SDI t and SDI t ? 1 with lower gamma values were identified as the most optimal combination of variables in all drought timescales. The results showed that the gamma test was able to correctly identify the right combination for the forecasting of 6, 9, and 12 months SDI using the ANN model. Also, the gamma test was considered in selecting the appropriate inputs for identifying the values of 9, 12, and 24 months SDI in SVR. The support vector machine approach showed a better efficiency in the forecast of long-term droughts compared to the artificial neural network. In total, among forecasts made for 30 scenarios, the support vector machine model only in scenario 3 of SDI3, scenario 1 of SDI6, and scenarios 2 and 3 of SDI24 represented poorer efficiency compared to the artificial neural network (MLP layer), but in other scenarios, the results of SVR had better efficiency.  相似文献   

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