Revisiting the relations: Galactic thin disc age–velocity dispersion relation

The velocity dispersion of stars in the solar neighbourhood thin disc increases with time after star formation. Nordström et al. performed the most recent observations to constrain the age–velocity dispersion relation. They fitted the age–velocity dispersion relations of each Galactic cardinal direction space velocity component, U (towards the Galactic Centre), V (in the direction of Galactic rotation) and W (towards the North Galactic Pole), with power laws and interpreted these as evidence for continuous heating of the disc in all directions throughout its lifetime. We revisit these relations with their data and use the results of Famaey et al. to show that structure in the local velocity distribution function distorts the in-plane ( U and V ) velocity distributions away from Gaussian so that a dispersion is not an adequate parametrization of their functions. The age–σ _W relation can however be constrained because the sample is well phase-mixed vertically. We do not find any local signature of the stellar warp in the Galactic disc. Vertical disc heating does not saturate at an early stage. Our new result is that a power law is not required by the data: disc heating models that saturate after ∼4.5 Gyr are equally consistent with observations.     

Observational effects of the Kerr metric

Strong gravity effects should have crucial impact on structure and radiative properties of an accretion flow surrounding a black hole. We discuss several observational consequences of such effects. (i) We note that the hard X-ray spectra of Seyfert galaxies, which appear to be intrinsically harder when observed at higher inclination angles, may be most naturally explained by radiative properties of plasmas in the Kerr metric. (ii) We indicate bending of photon trajectories to the equatorial plane, which is a distinct property of rapidly rotating black holes, as the most feasible effect underlying reduced variability of the Fe Kα line observed in several objects. (iii) Both the extreme Fe line profile and the variability pattern (observed, e.g., in a Seyfert galaxy MCG–6-30-15) independently indicate that a primary hard X-ray source must be located within a few gravitational radii from the Kerr black hole. We indicate a hot inner corona as the most likely model of such a source.     

Detecting the effect of globular cluster impacts on the disc of the Milky Way

The crossing of the Galactic disc by a globular cluster (GC) could produce star formation due to gravitational focusing or compression of disc material. We report on simulations of the effect on disc material which reveal that the crossing can sometimes cause local gravitational focusing of disc material. We also present the salient points of a little-known paper by Levy, which shows that strong compression can result from the shock wave generated by GC disc crossing. The main thrust of our paper is a search for remnants of disc crossings by GCs. Using the gravitational potential of the Galaxy to locate the position of the most recent crossings of a subset of fifty-four GCs reveals that systematic errors and uncertainties in initial conditions limit the scope for unequivocal identification. From the subset of fifty-four, six possible search sites with the best constraints are retained for further scrutiny. Three of the six potentially promising search areas in the disc are from GCs NGC 3201, 6397 and 6838, for which we cannot rule out some observed star associations observed nearby as being remnants. The other three of the six areas are too large to provide meaningful identification of remnants. Also, a possible remnant (open cluster NGC 6231) is shown not to be due to GC impact, contrary to a previous report. In a more wide-ranging screening of 155 GCs, we identify which GCs are compatible with being responsible for the formation of any of the Galaxy's five most prominent star superclusters.     

Multi-epoch spectroscopy of the globular cluster black hole in NGC 4472

We present a study of the X-ray spectral properties of the highly variable X-ray emitting black hole in a globular cluster in the elliptical galaxy NGC 4472. The X-ray Multiple Mirror–Newton ( XMM–Newton ) spectrum of the source in its bright epoch is well described by a multiple blackbody model with a characteristic temperature   kT _in≈  0.2 keV. The spectrum of an archival Chandra observation of the source obtained 3.5 yr before the XMM data gives similar estimates for the blackbody parameters. We confirm that the fainter interval of the XMM–Newton observation has a spectrum that is consistent with the brighter epoch, except for an additional level of foreground absorption. We also consider other possible mechanisms for the variability. Based on the time-scale of the X-ray flux decline and the estimated size of the X-ray emission region, we argue that an eclipsing companion is highly unlikely. We find the most likely means of producing the absorption changes on the observed time-scale is through partial obscuration by a precessing warped accretion disc.     

A Method for Testing Dynamic Tensile Strength and Elastic Modulus of Rock Materials Using SHPB

An experimental procedure for testing dynamic tensile strength and elastic modulus of rock materials at high strain rate loading is presented in this paper. In our test the split Hopkinson pressure bar (SHPB) was used to diametrally impact the Brazilian disc (BD) and flattened Brazilian disc (FBD) specimens of marble. A tensile strain rate of about 45 1/s was achieved at the center of the specimen. In order to improve the accuracy of the analysis, the initiation time difference between the strain waves acting on the two flat ends of the FBD specimen was treated properly. Typical failure modes corresponding to different loading conditions were observed. It was verified with a finite-element simulation that the equilibrium condition was established in the specimen before its failure. This numerical simulation validates the experimental procedure and also proves the suitability of formulation for the basic equations.     

颈椎间盘膨、突出症CT影像与CR影像分析

目的：通过CT与CR检查分析，进一步提高对颈椎间盘膨，突出症的影像认识。材料与方法：100例患者均行CT与CR检查，个别病例行CTM检查，结果 因颈椎间隙通常比胸腰椎间隙窄，CT扫描受扫描层数的限制，致使颈椎间盘显示不够完全，但CT摄影是比较简便的方法，而且是有价值的诊断方法。结论：对CT与CR两种影像检查方法进行分析，能够加深对颈椎间盘膨，突出症的影像认识，并结合临床症状，病史，做出准确的诊断。     

单向摆喷注浆加固地基技术

高压摆喷注浆是在高压旋喷、定喷注浆的基础上发展起来的一项新技术。通过调研、实验室试验和现场试验，提出了单向摆喷注浆中一些喷射多数和新的观点。采用上述试验与研究分析的一些喷射参数，应用到大同矿务局一扇风机房基础加固工程实践中，达到了预期的加固基础的良好效果。     

基于LS-DYNA的射流式液动锤活塞回程缓冲结构的研究

为了减弱射流式液动锤活塞回程撞击缸体的应力波对射流元件的破坏,延长射流元件的寿命,提出在缸体中设置碟簧缓冲结构来吸收冲锤回程的冲击能,并应用LS-DYNA显示动力学分析手段,对活塞回程进行仿真分析,探究碟簧缓冲对射流元件受力状态的影响,结果表明：采用碟簧缓冲结构,射流元件的最大应力可降低40%～57%,有效改善了射流元件的应力状态,在液动锤实际工作中具有可行性。     

基于新表面理论的TBM破岩效率评价指标

岩碴是岩-机作用的直接产物,也是评价隧道掘进机（TBM）破岩效率和优化TBM掘进参数的有效指标。依托兰州水源地建设工程和龙岩万安溪引水工程,开展不同岩性条件下TBM岩碴筛分试验,得到了岩碴粒径分布规律。基于新表面理论,从滚刀破岩能量转化角度出发,提出了一种新的TBM破岩效率评价指标。基于岩碴粒径分布规律和TBM掘进参数统计,探讨了新表面理论指标与比能、岩碴粗糙度指数之间的关系,指出了新表面理论指标在反映岩碴破碎程度和评价TBM破岩效率方面的优势。对新表面理论指标与TBM掘进推力以及刀间距s与贯入度p的比值进行回归分析,得到了硬岩（围岩等级为Ⅱ级）和软岩（围岩等级为III级）掘进条件下的TBM最优掘进推力和s/p取值区间。研究表明：（1）新表面理论指标符合岩石破碎学原理,可准确评价TBM破岩效率。岩碴越是破碎,新表面理论指标越大,掘进能耗越高,此时TBM破岩效率相对较低。（2）新表面理论指标与比能、岩碴粗糙度指数均具有良好的线性相关关系。岩碴越是破碎,破碎单位体积岩石的能量消耗越大,新表面理论指标越大,对应的粗糙度指数越小。软岩掘进条件下TBM掘进比能低于硬岩,而岩碴破碎程度高于硬岩。（...