Electronic Multi-beam Radio Astronomy Concept: Embrace a Demonstrator for the European SKA Program

ASTRON has demonstrated the capabilities of a 4 m², dense phased array antenna (Bij de Vaate et al., 2002) for radio astronomy, as part of the Thousand Element Array project (ThEA). Although it proved the principle, a definitive answer related to the viability of the dense phased array approach for the SKA could not be given, due to the limited collecting area of the array considered. A larger demonstrator has therefore been defined, known as “Electronic Multi-Beam Radio Astronomy Concept”, EMBRACE, which will have an area of 625 m², operate in the band 0.4–1.550 GHz and have at least two independent and steerable beams. With this collecting area EMBRACE can function as a radio astronomy instrument whose sensitivity is comparable to that of a 25-m diameter dish. The collecting area also represents a significant percentage area (∼10%) of an individual SKA “station.” This paper presents the plans for the realisation of the EMBRACE demonstrator.     

First-principles point-defect calculations for solid neutron star matter

Formation enthalpies are calculated for a number of point-defect structures in solid neutron star matter at densities above the neutron-drip threshold. The enthalpies obtained show that an amorphous heterogeneous solid phase is formed at temperatures in a glass transition region, and is likely to persist as the star cools. Its structural differences from the homogeneous body-centred cubic lattice previously assumed make it necessary to reconsider predictions of neutron-star magnetic field evolution, and severely limit the role of conventional superfluid neutron vortex pinning in the interpretation of pulsar glitch phenomena.     

Mutual friction in superfluid neutron stars

We discuss vortex-mediated mutual friction in the two-fluid model for superfluid neutron star cores. Our discussion is based on the general formalism developed by Carter and collaborators, which makes due distinction between transport velocity and momentum for each fluid. This is essential for an implementation of the so-called entrainment effect, whereby the flow of one fluid imparts momentum in the other and vice versa. The mutual friction follows by balancing the Magnus effect that acts on the quantized neutron vortices with resistivity due to the scattering of electrons off of the magnetic field with which each vortex core is endowed. We derive the form of the macroscopic mutual friction force which is relevant for a model based on smooth-averaging over a collection of vortices. We discuss the coefficients that enter the expression for this force, and the time-scale on which the two interpenetrating fluids in a neutron star core are coupled. This discussion confirms that our new formulation accords well with previous work in this area.     

基于背景噪声的自相关与HVSR联合成像在广东惠州城市浅层结构探测中的应用

随着我国城市化进程快速推进,大中小城市呈现地下空间全面开发的态势。然而城市地下空间开发利用存在地下情况不明、结构不清的问题,这在很大程度上影响了地下空间的开发利用和城市战略布局规划。广东惠州是典型的东部中型城市,为了避免老城区建成后地下水土质量不清楚、地下空间资源量不明确、城市地下空间资源开发无科学数据支持等问题,特在研究区开展绿色无损的背景噪声成像研究,以查明惠州地区的第四系及断层的发育情况,为新区成功建成提供数据支持。笔者等以台间距10 m、测线总长度1 km的密集地震台阵为基础,利用两条测线共200台的背景噪声数据,使用噪声自相关与噪声HVSR两种方法分别对研究区两条线性测线分别进行计算,通过数据预处理,单台数据处理,多台数据整合,最后得到了两条测线的自相关剖面和HVSR剖面。研究显示,研究区第四系基岩顶面时间域范围为20~100 ms,深度域范围为5~20 m,浅层P波速度范围为400~500 m/s,这与收集到的钻孔等资料相一致。研究表明基于密集台阵的噪声自相关与HVSR联合成像方法是一种高效、绿色、低成本的方法,可用于调查第四系分界面（强波阻抗分界面）及浅层沉积物中的活动断层。     

喜马拉雅造山带东段错那裂谷的地壳结构

喜马拉雅造山带由印度与欧亚大陆板块的陆陆碰撞而形成。为何在挤压造山的碰撞前缘形成代表垮塌的藏南裂谷系存在巨大的争议。回答这个问题需要对裂谷的地壳结构有一个全面的认识。各裂谷带的起始活动年代自西向东逐渐年轻。本研究选取喜马拉雅东部较为年轻的错那裂谷,利用密集台阵接收的远震数据,通过P波接收函数方法,揭示错那裂谷的精细地壳结构,进而通过地壳结构分析裂谷的形成。结果显示错那裂谷为全地壳尺度结构,裂谷下方莫霍面发生明显错断,且壳内结构侧向不连续发育显著。本研究表明裂谷的形成可能关联更大尺度的区域构造运动,单一的重力垮塌是否能形成地壳尺度的裂谷需要进一步研究。综合前人对藏南裂谷系区域的超钾岩和埃达克岩研究以及深部地球物理观测结果,推断因俯冲的印度板片撕裂导致软流圈物质上涌弱化了错那裂谷区域下地壳,并且结合研究区内喜马拉雅淡色花岗岩研究显示中上地壳也存在弱化现象。因此,结合本研究结果推测全地壳尺度裂谷的形成需要不同深度的地壳弱化。     

Thermal evolution of rotating hybrid stars

As a neutron star spins down, the nuclear matter is continuously converted into quark matter due to the core density increase, and then latent heat is released. We have investigated the thermal evolution of neutron stars undergoing such deconfinement phase transition. We have taken into account the conversion in the frame of the general theory of relativity. The released energy has been estimated as a function of changed rate of deconfinement baryon number. The numerical solutions to the cooling equation are seen to be very different from those without the heating effect. The results show that neutron stars may be heated to higher temperatures which is well matched with pulsar's data despite the onset of fast cooling in neutron stars with quark matter cores. It is also found that the heating effect has a magnetic field strength dependence. This feature could be particularly interesting for high temperatures of low-field millisecond pulsars at a later stage. The high temperature could fit the observed temperature for PSR J0437−4715.