Torsional oscillations of magnetized relativistic stars

Strong magnetic fields in relativistic stars can be a cause of crust fracturing, resulting in the excitation of global torsional oscillations. Such oscillations could become observable in gravitational waves or in high-energy radiation, thus becoming a tool for probing the equation of state of relativistic stars. As the eigenfrequency of torsional oscillation modes is affected by the presence of a strong magnetic field, we study torsional modes in magnetized relativistic stars. We derive the linearized perturbation equations that govern torsional oscillations coupled to the oscillations of a magnetic field, when variations in the metric are neglected (Cowling approximation). The oscillations are described by a single two-dimensional wave equation, which can be solved as a boundary-value problem to obtain eigenfrequencies. We find that, in the non-magnetized case, typical oscillation periods of the fundamental     torsional modes can be nearly a factor of 2 larger for relativistic stars than previously computed in the Newtonian limit. For magnetized stars, we show that the influence of the magnetic field is highly dependent on the assumed magnetic field configuration, and simple estimates obtained previously in the literature cannot be used for identifying normal modes observationally.     

Amplification of primordial magnetic fields by anisotropic gravitational collapse

If a magnetic field is frozen into a plasma that undergoes spherical compression, then the magnetic field B varies with the plasma density ρ according to   B ∝ρ^2/3  . In the gravitational collapse of cosmological density perturbations, however, quasi-spherical evolution is very unlikely. In anisotropic collapses the magnetic field can be a much steeper function of gas density than in the isotropic case. We investigate the distribution of amplifications in realistic gravitational collapses from Gaussian initial fluctuations using the Zel'dovich approximation. Representing our results using a relation of the form   B ∝ρ^α  , we show that the median value of α can be much larger than the value  α= 2/3  resulting from spherical collapse, even if there is no initial correlation between magnetic field and principal collapse directions. These analytic arguments go some way towards understanding the results of numerical simulations.     

Impact demagnetization of the martian crust

The lack of magnetic anomalies within the giant martian impact basins, Hellas, Argyre, and Isidis suggests that the impacts demagnetized the crust. Our analysis of the magnetic anomaly intensity shows that the interior parts of the basins are completely demagnetized, while the outer parts and surroundings are partially demagnetized. We investigate the shock pressure and impact heating resulting from the impacts. The crust has been completely demagnetized within ∼0.8 basin radius by a combination of thermal and shock effects, and the surroundings have been partially demagnetized by shock to a distance of at least 1.4 radii. We also investigate magnetic signatures of intermediate-size craters. From the pressures generated by both the large and intermediate-sized impacts, we conclude that the remanent magnetization is carried at least in part by high coercivity rocks. Since the crust beneath the basins does not appear to have been remagnetized as it cooled following the impacts, we conclude that the martian core dynamo was inactive or very weak for at least 100 Myr following the Hellas impact.     

我国油气资源潜力、分布及重点勘探领域

我国地质结构具有3大板块、3大构造域多旋回构造演化特征,造就多种类型叠合沉积盆地,构成克拉通+前陆、断陷+坳陷、前陆+坳陷3种主要类型。大型叠合盆地是油气资源分布与勘探开发主体。我国常规与非常规油气资源十分丰富,常规石油地质资源量1 075×10⁸ t,常规天然气地质资源量83×10¹² m³;致密油地质资源量134×10⁸ t,致密砂岩气地质资源量21×10¹² m³,页岩油地质资源量335×10⁸ t,页岩气地质资源量56×10¹² m³。陆上油气资源主要分布于渤海湾(陆上)、松辽、鄂尔多斯、塔里木、四川、准噶尔、柴达木7大盆地。海域油气资源主要分布于渤海湾(海域)、东海及南海北部的珠江口、北部湾、莺歌海、琼东南6大盆地。未来我国油气勘探应始终坚持“资源战略,稳油增气”战略,坚持“非常并进、海陆统筹”积极进取勘探思路;常规勘探领域,陆上地层-岩性、前陆、海相碳酸盐岩与潜山领域;海域为渤海海域构造与基岩潜山,深水构造与岩性;非常规油气主要是立足陆上7大含油气盆地,立足致密油气与页岩油气,强化勘探开发与技术配套。     

Triggered seismicity in the Andean arc region via static stress variation by the MW = 8.8, February 27, 2010, Maule earthquake

We localized crustal earthquakes in the Andean arc, between 35°S and 36°S, from December 2009 to May 2010. This research shows a seismicity increase, in a narrow longitudinal area, of more than nine times after the great M_w 8.8 Maule earthquake.The localized seismicity defines an area of ∼80 km long and ∼18 km wide and NNW to NNE trend. The M_d magnitudes varied from 0.7 to 3.1 except for two earthquakes with M_w of 3.9 and 4.5, located in the northern end of the area. The focal mechanisms for these two last events were normal/strike-slip and strike-slip respectively.During 2011, a network of 13 temporary stations was installed in the trasarc region in Malargüe, Argentina. Sixty earthquakes were localized in the study region during an 8 month period.We explored how changes in Coulomb conditions associated with the mega-thrust earthquake triggered subsequent upper-plate events in the arc region. We assumed the major proposed structures as receiver faults and used previously published earthquake source parameters and slip distribution for the Maule quake. The largest contribution to static stress change, up to 5 bars, derives from unclamping resulting consistent with co-seismic dilatational deformation inferred from GPS observations in the region and subsidence in nearby volcanoes caused by magma migration.Three different Quaternary tectonic settings–extensional, strike-slip and compressional-have been proposed for the arc region at these latitudes. We found that the unclamping produced by the Maule quake could temporarily change the local regime to normal/strike-slip, or at least it would favor the activation of Quaternary NNE to N-trending dextral strike-slip faults with dextral transtensional movement.     

CSAMT在碎屑岩地区地热勘查中的应用

碎屑岩因质软,导水、储水条件不良,通常作为地热有利保温盖层,而碎屑岩电阻率普遍低,厚度大的情况下形成低阻屏蔽层,勘探下伏有利储层难度极大,寻找碎屑岩中构造裂隙水是最佳的选择。但碎屑岩中的储水构造与围岩电阻率差异小,构造迹象微弱,因此在碎屑岩地区找地热技术含量较高。茅山镇位于句容盆地东缘茅山西侧,沉积了厚度超过1800m的白垩系碎屑岩,水文地质条件较差,本文应用CSAMT大范围普查、小范围精细查证布置方式,采用磁场插值校正的技术手段、收发距选取优先保证信噪比的思路,控制白垩系碎屑岩中储水断裂构造,克服低阻的碎屑岩地区构造异常微弱的难点。钻探验证结果表明,CSAMT可以经济有效地应用于碎屑岩地区地热勘查。     

New spectroscopic and polarimetric observations of the A0 supergiant HD 92207

Our recent search for the presence of a magnetic field in the bright early A‐type supergiant HD 92207 using FORS 2 in spectropolarimetric mode revealed the presence of a longitudinal magnetic field of the order of a few hundred Gauss. However, the definite confirmation of the magnetic nature of this object remained pending due to the detection of shortterm spectral variability probably affecting the position of line profiles in left‐ and right‐hand polarized spectra. We present new magnetic field measurements of HD 92207 obtained on three different epochs in 2013 and 2014 using FORS 2 in spectropolarimetric mode. A 3σ detection of the mean longitudinal magnetic field using the entire spectrum, 〈B_z〉_all = 104 ± 34 G, was achieved in observations obtained in 2014 January. At this epoch, the position of the spectral lines appeared stable. Our analysis of spectral line shapes recorded in opposite circularly polarized light, i.e. in light with opposite sense of rotation, reveals that line profiles in the light polarized in a certain direction appear slightly split. The mechanism causing such a behaviour in the circularly polarized light is currently unknown. Trying to settle the issue of short‐term variability, we searched for changes in the spectral line profiles on a time scale of 8–10 min using HARPS polarimetric spectra and on a time scale of 3–4 min using time series obtained with the CORALIE spectrograph. No significant variability was detected on these time scales during the epochs studied. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Dynamo saturation in direct simulations of the multi‐phase turbulent interstellar medium

The ordered magnetic field observed via polarised synchrotron emission in nearby disc galaxies can be explained by a mean‐field dynamo operating in the diffuse interstellar medium (ISM). Additionally, vertical‐flux initial conditions are potentially able to influence this dynamo via the occurrence of the magnetorotational instability (MRI). We aim to study the influence of various initial field configurations on the saturated state of the mean‐field dynamo. This is motivated by the observation that different saturation behaviour was previously obtained for different supernova rates. We perform direct numerical simulations (DNS) of three‐dimensional local boxes of the vertically stratified, turbulent interstellar medium, employing shearing‐periodic boundary conditions horizontally. Unlike in our previous work, we also impose a vertical seed magnetic field. We run the simulations until the growth of the magnetic energy becomes negligible. We furthermore perform simulations of equivalent 1D dynamo models, with an algebraic quenching mechanism for the dynamo coefficients. We compare the saturation of the magnetic field in the DNS with the algebraic quenching of a mean‐field dynamo. The final magnetic field strength found in the direct simulation is in excellent agreement with a quenched α) dynamo. For supernova rates representative of the Milky Way, field losses via a Galactic wind are likely responsible for saturation. We conclude that the relative strength of the turbulent and regular magnetic fields in spiral galaxies may depend on the galaxy's star formation rate. We propose that a mean field approach with algebraic quenching may serve as a simple sub‐grid scale model for galaxy evolution simulations including a prescribed feedback from magnetic fields. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Dynamics of warm inflation with gauge fields in Bianchi type I universe model

In this paper, we study the dynamics of warm inflation in which slow-roll inflation is driven by non-Abelian gauge fields. To this end, we use the geometry of locally rotationally symmetric Bianchi type I universe model. We construct dynamical equations, i.e., first model field equation, energy conservation equations and equation of motion under slow-roll approximation. In order to discuss inflationary perturbations, we evaluate parameters like scalar and tensor power spectra as well as scalar and tensor spectral indices. We also evaluate inflaton, directional Hubble parameter, slow-roll and perturbation parameters as well as tensor-scalar ratio as a function of inflaton during intermediate and logamediate inflationary eras. It is concluded that anisotropic inflationary universe model with non-Abelian gauge fields remains compatible with WMAP7.