Chemical evolution with radial mixing

Models of the chemical evolution of our Galaxy are extended to include radial migration of stars and flow of gas through the disc. The models track the production of both iron and α-elements. A model is chosen that provides an excellent fit to the metallicity distribution of stars in the Geneva–Copenhagen survey (GCS) of the solar neighbourhood and a good fit to the local Hess diagram. The model provides a good fit to the distribution of GCS stars in the age–metallicity plane, although this plane was not used in the fitting process. Although this model's star formation rate is monotonically declining, its disc naturally splits into an α-enhanced thick disc and a normal thin disc. In particular, the model's distribution of stars in the ([O/Fe], [Fe/H]) plane resembles that of Galactic stars in displaying a ridge line for each disc. The thin-disc's ridge line is entirely due to stellar migration, and there is the characteristic variation of stellar angular momentum along it that has been noted by Haywood in survey data. Radial mixing of stellar populations with high  σ _z   from inner regions of the disc to the solar neighbourhood provides a natural explanation of why measurements yield a steeper increase of  σ _z   with age than predicted by theory. The metallicity gradient in the interstellar medium is predicted to be steeper than in earlier models, but appears to be in good agreement with data for both our Galaxy and external galaxies. The models are inconsistent with a cut-off in the star formation rate at low gas surface densities. The absolute magnitude of the disc is given as a function of time in several photometric bands, and radial colour profiles are plotted for representative times.     

Storm fronts over galaxy discs: models of how waves generate extraplanar gas and its anomalous kinematics

The existence of partially ionized, diffuse gas and dust clouds at kiloparsec scale distances above the central planes of edge-on, galaxy discs was an unexpected discovery about 20 years ago. Subsequent observations showed that this extended or extraplanar diffuse interstellar gas (EDIG) has rotation velocities approximately 10–20 per cent lower than those in the central plane, and has been hard to account for. Here, we present results of hydrodynamic models, with radiative cooling and heating from star formation. We find that in models with star formation generated stochastically across the disc, an extraplanar gas layer is generated as long as the star formation is sufficiently strong. However, this gas rotates at nearly the same speed as the midplane gas. We then studied a range of models with imposed spiral or bar waves in the disc. EDIG layers were also generated in these models, but primarily over the wave regions, not over the entire disc. Because of this partial coverage, the EDIG clouds move radially, as well as vertically, with the result that observed kinematic anomalies are reproduced. The implication is that the kinematic anomalies are the result of three-dimensional motions when the cylindrical symmetry of the disc is broken. Thus, the kinematic anomalies are the result of bars or strong waves, and more face-on galaxies with such waves should have an asymmetric EDIG component. The models also indicate that the EDIG can contain a significant fraction of cool gas, and that some star formation can be triggered at considerable heights above the disc mid-plane. We expect all of these effects to be more prominent in young, forming discs, to play a role in rapidly smoothing disc asymmetries and in working to self-regulate disc structure.     

Is there a black hole among the black-hole candidates?

None of the tentative black-hole identifications has remained without serious difficulties. As a class, the black-hole candidates differ in no obvious property from neutron-star binaries other than in their estimated high mass. We favour an interpretation of the black-hole candidates as binary neutron stars surrounded by a more or less massive accretion disc     

工程钻机圆锥滚子轴承的预紧装置

分析了工程钻机在施工过程中轴承游动间隙对钻机的影响,提出了钻机输出轴圆锥滚子轴承的外端,加装一套碟形弹簧预紧装置,有效地解决轴承的游动间隙。     

公用机房的硬盘保护措施

在深入分析硬盘结构及硬盘工作原理的基础上,详细阐述了用软件实现对公用机房硬盘的保护原理和方法,并给出了编程思路。     

The nature of the intranight variability of radio-quiet quasars

We select a sample of 10 radio-quiet quasars with confirmed intranight optical variability and with available X-ray data. We compare the variability properties and the broad-band spectral constraints to the predictions of intranight variability by three models: (i) irradiation of an accretion disc by a variable X-ray flux, (ii) an accretion disc instability, (iii) the presence of a weak blazar component. We concluded that the third model, e.g. the blazar component model, is the most promising if we adopt a cannonball model for the jet variable emission. In this case, the probability of detecting the intranight variability is within 20–80 per cent, depending on the ratio of the disc to the jet optical luminosity. Variable X-ray irradiation mechanism is also possible but only under additional requirement: either the source should have a very narrow Hβ line or occasional extremely strong flares should appear at very large disc radii.     

基于UDEC的隧道掘进机滚刀破岩数值模拟研究

现今全断面隧道掘进机（TBM）施工方法在长大深埋隧道工程中已被广泛采用,对滚刀破岩关键技术的进一步认识具有重要的工程价值。为了研究滚刀破岩机制,分析刀圈断面形态、岩石强度和节理角度对其的影响,运用UDEC方法建立了滚刀贯切岩石的二维数值系列模型,对TBM滚刀破岩过程进行了仿真。分析表明：滚刀破岩是滚刀下岩石拉破坏和剪破坏的综合反映,拉破坏是裂纹萌生与扩展的主要驱动机制;刃宽较大的平刀与刃角较大的楔刀破岩效果较好;平刀与楔刀在软岩中破岩效果相近,平刀在硬岩施工中比楔刀的破岩效果好;滚刀对节理角度为30°～60°的岩石破坏效果较好,由于楔刀的“劈裂”作用,楔刀比平刀更适合用于贯切含有节理的岩石。     

Cyclic behavior and failure mechanism of self‐centering energy dissipation braces with pre‐pressed combination disc springs

A new type of bracing system composed of friction energy dissipation devices for energy dissipation, pre‐pressed combination disc springs for self‐centering and tube members as guiding elements is developed and experimentally studied in this paper. The mechanics of this system are explained, the equations governing its hysteretic responses are outlined and large‐scale validation tests of two braces with different types of disc springs are conducted under the condition of low cyclic reversed loading. The experimental results demonstrate that the proposed bracing system exhibits a stable and repeatable flag‐shaped hysteretic response with an excellent self‐centering capability and effective energy dissipation throughout the loading protocol. Furthermore, the maximum bearing force and stiffness are predicted well by the equations governing its mechanical behavior. Fatigue and destructive test results demonstrate that the proposed bracing system can maintain stable energy dissipation and self‐centering capabilities under large deformation cyclic loading even when the tube members exceed the elastic limit and that a larger bearing capacity is achieved by the system that has disc springs without a bearing surface. Copyright © 2016 John Wiley & Sons, Ltd.     

Seasonal variations in infiltrability of moss‐dominated biocrusts on aeolian sand and loess soil in the Chinese Loess Plateau

Biocrust effects on soil infiltration have attracted increasing attention in dryland ecosystems, but their seasonal variations in infiltrability have not yet been well understood. On the Chinese Loess Plateau, soil infiltrability indicated by saturated hydraulic conductivity (K_s) of biocrusts and bare soil, both on aeolian sand and loess soil, was determined by disc infiltrometer in late spring (SPR), midsummer (SUM), and early fall (FAL). Then their correlations with soil biological and physiochemical properties and water repellency index (RI) were analysed. The results showed that the biocrusts significantly decreased K_s both on sand during SPR, SUM, and FAL (by 43%, 66%, and 35%, respectively; P < .05) and on loess (by 42%, 92%, and 10%, respectively; P <.05). As compared with the bare soil, the decreased K_s in the biocrusted surfaces was mostly attributed to the microorganism biomass and also to the increasing content of fine particles and organic matter. Most importantly, both the biocrusts and bare soil exhibited significant (F ≥ 11.89, P ≤ .003) seasonal variations in K_s, but their patterns were quite different. Specifically, the K_s of bare soil gradually decreased from SPR to SUM (32% and 42% for sand and loess, respectively) and FAL (29% and 39%); the K_s of biocrusts also decreased from SPR to SUM (59% and 92%) but then increased in FAL (36% and 588%). Whereas the seasonal variations in K_s of the biocrusts were closely correlated with the seasonal variations in RI, the RI values were not high enough to point at hydrophobicity. Instead of that, the seasonal variations of K_s were principally explained by the changes in the crust biomass and possibly by the microbial exopolysaccharides. We conclude that the biocrusts significantly decreased soil infiltrability and exhibited a different seasonal variation pattern, which should be carefully considered in future analyses of hydropedological processes.     

楔刀作用下岩石微观劣化的试验研究

通过改装RMT-150C系统,使用不同刃角的楔形刀具对花岗岩进行贯切试验,利用DISP声发射测试系统进行声发射的定位特征分析,研究岩石在楔形刀具作用下损伤劣化破坏的全过程。试验结果表明：声发射试验是一种研究TBM滚刀破岩微观机制的有效方法,脆性岩石材料的破坏过程是内部微裂纹的萌生和扩展过程的宏观反映;在楔刃刀具匀速贯入时,声发射信号随着荷载的变化呈一定对应趋势的变化,荷载-贯入度曲线能反映试件内的损伤历程;声发射2D定位结果显示,在岩石破碎区的密实核下方存在“损伤核”,它由微震裂源增生丛聚分布形成,核内劣化程度高,是孕育密实核的场所,为TBM滚刀作用下岩石的宏观破裂现象提供了解释和依据;楔刀跃进式的挤压贯切岩板试件,钝刃刀具产生“球状”损伤核,尖刃刀具产生“水滴状”损伤核,钝刃刀具贯切试件产生更深的贯入度和更宽的损伤核,致使试件中不仅破碎深度大,而且破损范围广,破岩效果优于尖刃刀具。