Entropic gravity versus gravitational pseudotensors in static spherically symmetric spacetimes     

S. Hamid Mehdipour 《Astrophysics and Space Science》2014,352(2):877-881

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Reduced transition probabilities for 4~He radiative capture reactions at astrophysical energies     

Hossein Sadeghi  Reza Ghasemi 《中国天文和天体物理学报》2014,(3):367-372

The reduced transition probabilities from an electric quadrupole B(E2) and reduced transition probabilities from a magnetic dipole B(M1) between the ground state and the first excited state have been calculated for the3He(α,γ)7Be,8Be(α,γ)12C and12C(α,γ)16O radiative capture reactions with the M3Y potential.These reactions are important in stellar evolution.The calculated B(M1) and B(E2) for7Be nuclei are found to be 1.082×10-3e2fm2and 1.921 e2fm4from transitions 3/2-to 1/2-,respectively.The obtained values for reduced transition probabilities B(E2) for the12C and16O nuclei from transitions 0+to 2+are 12.54 e2fm4and 14.18 e2fm4,respectively.The results are in satisfactory agreement with available experimental data.  相似文献   

A new closed‐form solution for analysis of unlined pressure tunnels under seepage forces     

Ahamad Fahimifar  Mohammad Reza Zareifard 《国际地质力学数值与分析法杂志》2013,37(11):1591-1613

In this study, a simplified analytical closed‐form solution, considering plane strain and axial symmetry conditions, for analysis of a circular pressure tunnel excavated underwater table, is developed. The method accounts for the seepage forces with the steady‐state flow and is based on the generalized effective stress law. To examine the effect of pore pressure variations and also the boundary conditions at the ground surface, the formulations are derived for different directions around the tunnel. The proposed method can be applied for analysis and design of pressure tunnels. Illustrative examples are given to demonstrate the performance of the proposed solution and also to examine the effect of seepage forces on the stability of tunnels. The simplified analytical solution derived in this study is compared with numerical analyses. It is concluded that the classic solutions (Lame's thick‐walled solution), considering the internal pressure as a mechanical load applied to the tunnel surface, are not applicable to pervious media and can result in an unsafe design. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Optically stimulated luminescence (OSL) dating of quartzite cobbles from the Tapada do Montinho archaeological site (east‐central Portugal)     

Reza Sohbati  Andrew S. Murray  Jan‐Pieter Buylaert  Nelson A. C. Almeida  Pedro P. Cunha 《Boreas: An International Journal of Quaternary Research》2012,41(3):452-462

The burial age of an alluvially deposited cobble pavement at the Tapada do Montinho archaeological site (east‐central Portugal) is investigated using optically stimulated luminescence (OSL) dating. Measurements on the cobbles (quartzite clasts) were carried out on intact slices and large aliquots (～8 mm) of quartz grains (63–300 μm), both recovered from the outer 1.5‐mm surface of the cobbles. The recycling ratio, recuperation and dose‐recovery tests show that the single‐aliquot regenerative‐dose (SAR) protocol is applicable to both rock slices and quartz grains; both have similar luminescence characteristics. The variation in the natural OSL signal with depth below the cobble surface using intact slices from two different cobbles shows that both were bleached to a depth of at least ～2 mm before deposition. A model of the variation of dose with depth fitted to data from one of the cobbles gives a burial age of ～19 ka and also predicts the dose‐depth variation at the time of deposition. Ages based on rock slices suggest that one cobble surface, and the inner parts of two other cobbles experienced a resetting event at ～45 ka, consistent with the age control. However, the surfaces of the other cobbles all record light‐exposure events in the range 26 to 14 ka, suggesting that some of the cobbles were exposed to daylight perhaps more than once in this period. Given the shallow burial depth and unexpectedly young ages of the surrounding and overlying finer‐grained sediment, it is suggested that phases of light exposure following surficial erosion are probably responsible for this underestimate. Nevertheless, it is remarkable that we can identify and quantify four events (two light exposures of different durations and two sequential burial periods) in the dose record contained within a single clast, and this suggests that the luminescence dating of rock surfaces may prove, in the future, to be at least as important as sand/silt sediment dating.  相似文献   

A non‐linear coupled finite element–boundary element model for the prediction of vibrations due to vibratory and impact pile driving     

Hamid Reza Masoumi  Stijn François  Geert Degrande 《国际地质力学数值与分析法杂志》2009,33(2):245-274

This paper presents a non‐linear coupled finite element–boundary element approach for the prediction of free field vibrations due to vibratory and impact pile driving. Both the non‐linear constitutive behavior of the soil in the vicinity of the pile and the dynamic interaction between the pile and the soil are accounted for. A subdomain approach is used, defining a generalized structure consisting of the pile and a bounded region of soil around the pile, and an unbounded exterior linear soil domain. The soil around the pile may exhibit non‐linear constitutive behavior and is modelled with a time‐domain finite element method. The dynamic stiffness matrix of the exterior unbounded soil domain is calculated using a boundary element formulation in the frequency domain based on a limited number of modes defined on the interface between the generalized structure and the unbounded soil. The soil–structure interaction forces are evaluated as a convolution of the displacement history and the soil flexibility matrices, which are obtained by an inverse Fourier transformation from the frequency to the time domain. This results in a hybrid frequency–time domain formulation of the non‐linear dynamic soil–structure interaction problem, which is solved in the time domain using Newmark's time integration method; the interaction force time history is evaluated using the θ‐scheme in order to obtain stable solutions. The proposed hybrid formulation is validated for linear problems of vibratory and impact pile driving, showing very good agreement with the results obtained with a frequency‐domain solution. Linear predictions, however, overestimate the free field peak particle velocities as observed in reported field experiments during vibratory and impact pile driving at comparable levels of the transferred energy. This is mainly due to energy dissipation related to plastic deformations in the soil around the pile. Ground vibrations due to vibratory and impact pile driving are, therefore, also computed with a non‐linear model where the soil is modelled as an isotropic elastic, perfectly plastic solid, which yields according to the Drucker–Prager failure criterion. This results in lower predicted free field vibrations with respect to linear predictions, which are also in much better agreement with experimental results recorded during vibratory and impact pile driving. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

The Temperature – Magnetic Field Relation in Observed and Simulated Sunspots     

Michal Sobotka  Reza Rezaei 《Solar physics》2017,292(12):188

Observations of the relation between continuum intensity and magnetic field strength in sunspots have been made for nearly five decades. This work presents full-Stokes measurements of the full-split (\(g = 3\)) line Fe i 1564.85 nm with a spatial resolution of \(0.5^{\prime\prime}\) obtained with the GREGOR Infrared Spectrograph in three large sunspots. The continuum intensity is corrected for instrumental scattered light, and the brightness temperature is calculated. Magnetic field strength and inclination are derived directly from the line split and the ratio of Stokes components. The continuum intensity (temperature) relations to the field strength are studied separately in the umbra, light bridges, and penumbra. The results are consistent with previous studies, and it was found that the scatter of values in the relations increases with increasing spatial resolution thanks to resolved fine structures. The observed relations show trends common for the umbra, light bridges, and the inner penumbra, while the outer penumbra has a weaker magnetic field than the inner penumbra at equal continuum intensities. This fact can be interpreted in terms of the interlocking comb magnetic structure of the penumbra. A comparison with data obtained from numerical simulations was made. The simulated data generally have a stronger magnetic field and a weaker continuum intensity than the observations, which may be explained by stray light and limited spatial resolution of the observations, and also by photometric inaccuracies of the simulations.  相似文献   

Analysis of the stress field and strain rate in Zagros-Makran transition zone     

Ghasem Ghorbani Rostam  Mehrdad Pakzad  Noorbakhsh Mirzaei  Seyed Reza Sakhaei 《Journal of Seismology》2018,22(1):287-301

Transition boundary between Zagros continental collision and Makran oceanic-continental subduction can be specified by two wide limits: (a) Oman Line is the seismicity boundary with a sizeable reduction in seismicity rate from Zagros in the west to Makran in the east; and (b) the Zendan-Minab-Palami (ZMP) fault system is believed to be a prominent tectonic boundary. The purpose of this paper is to analyze the stress field in the Zagros-Makran transition zone by the iterative joint inversion method developed by Vavrycuk (Geophysical Journal International 199:69-77, 2014). The results suggest a rather uniform pattern of the stress field around these two boundaries. We compare the results with the strain rates obtained from the Global Positioning System (GPS) network stations. In most cases, the velocity vectors show a relatively good agreement with the stress field except for the Bandar Abbas (BABS) station which displays a relatively large deviation between the stress field and the strain vector. This deviation probably reflects a specific location of the BABS station being in the transition zone between Zagros continental collision and Makran subduction zones.  相似文献   

Comparison of Bayesian estimates of peak ground acceleration (<Emphasis Type="Italic">A</Emphasis>max) with PSHA in Iran     

Hamid Salahshoor  Alexey Lyubushin  Elham Shabani  Javad Kazemian 《Journal of Seismology》2018,22(6):1515-1527

Bayesian probability theory is an appropriate and useful method for estimating parameters in seismic hazard analysis. The analysis in Bayesian approaches is based on a posterior belief, also their special ability is to take into account the uncertainty of parameters in probabilistic relations and a priori knowledge. In this study, we benefited the Bayesian approach in order to estimate maximum values of peak ground acceleration (A_max) also quantiles of the relevant probabilistic distributions are figured out in a desired future interval time in Iran. The main assumptions are Poissonian character of the seismic events flow and properties of the Gutenberg-Richter distribution law. The map of maximum possible values of A_max and also map of 90% quantile of distribution of maximum values of A_max on a future interval time 100 years is presented. According to the results, the maximum value of the A_max is estimated for Bandar Abbas as 0.3g and the minimum one is attributed to Esfahan as 0.03g. Finally, the estimated values in Bayesian approach are compared with what was presented applying probabilistic seismic hazard (PSH) methods based on the conventional Cornel (1968) method. The distribution function of A_max for future time intervals of 100 and 475 years are calculated for confidence limit of probability level of 90%.  相似文献   

Multicomponent competitive monovalent cation exchange in hierarchical porous media with multimodal reactive mineral facies     

Mohamad?Reza?SoltanianEmail author  Zhenxue?Dai  Changbing?Yang  Mohammad?Amin?Amooie  Joachim?Moortgat 《Stochastic Environmental Research and Risk Assessment (SERRA)》2018,32(1):295-310

This paper presents a stochastic model for multicomponent competitive monovalent cation exchange in hierarchical porous media. Reactive transport in porous media is highly sensitive to heterogeneities in physical and chemical properties, such as hydraulic conductivity (K), and cation exchange capacity (CEC). We use a conceptual model for multimodal reactive mineral facies and develop a Eulerian-based stochastic theory to analyze the transport of multiple cations in heterogeneous media with a hierarchical organization of reactive minerals. Numerical examples investigate the retardation factors and dispersivities in a chemical system made of three monovalent cations (Na⁺, K⁺, and Cs⁺). The results demonstrate how heterogeneity influences the transport of competitive monovalent cations, and highlight the importance of correlations between K and CEC. Further sensitivity analyses are presented investigating how the dispersion and retardation of each cation are affected by the means, variances, and integral scales of K and CEC. The volume fraction of organic matter is shown to be another important parameter. The Eulerian stochastic framework presented in this work clarifies the importance of each system parameters on the migration of cation plumes in formations with hierarchical organization of facies types. Our stochastic approach could be used as an alternative to numerical simulations for 3D reactive transport in hierarchical porous media, which become prohibitively expensive for the multicomponent applications considered in this work.  相似文献   

Simulation of relationship between river discharge and sediment yield in the semi-arid river watersheds     

Mohammad Reza Khaleghi  Javad Varvani 《Acta Geophysica》2018,66(1):109-119

Complex and variable nature of the river sediment yield caused many problems in estimating the long-term sediment yield and problems input into the reservoirs. Sediment Rating Curves (SRCs) are generally used to estimate the suspended sediment load of the rivers and drainage watersheds. Since the regression equations of the SRCs are obtained by logarithmic retransformation and have a little independent variable in this equation, they also overestimate or underestimate the true sediment load of the rivers. To evaluate the bias correction factors in Kalshor and Kashafroud watersheds, seven hydrometric stations of this region with suitable upstream watershed and spatial distribution were selected. Investigation of the accuracy index (ratio of estimated sediment yield to observed sediment yield) and the precision index of different bias correction factors of FAO, Quasi-Maximum Likelihood Estimator (QMLE), Smearing, and Minimum-Variance Unbiased Estimator (MVUE) with LSD test showed that FAO coefficient increases the estimated error in all of the stations. Application of MVUE in linear and mean load rating curves has not statistically meaningful effects. QMLE and smearing factors increased the estimated error in mean load rating curve, but that does not have any effect on linear rating curve estimation.  相似文献