3XMM J185246.6+003317 as transient neutron star

We performed an X‐ray timing and spectral analysis of the variable source 3XMM J185246.6+003317 to investigate its physical nature. The data from all observations of 3XMMJ185246.6+003317 conducted by XMM‐Newton EPIC MOS1 and MOS2 with the same instrumental setup in 2004–2009 were reprocessed to form a homogenous data set of solar barycenter corrected photon arrival times and high S/N spectra of 3XMM J185246.6+003317. A Bayesian method for the search, detection, and estimation of the parameters of a periodic signal of unknown shape was employed, as developed by Gregory & Loredo (1992, 1993). The results show that 3XMM J185246.6+003317 is a transient neutron star with the genuine spin‐period of 23.11722 (23.11711–23.11727) s and its derivative of 5.3(0.3–5.5)×10^–11 s s^–1, implying a characteristic age of 7 (6–104) kyr, if the period derivative can be ascribed to the genuine spin‐down rate of the neutron star. The rotational‐phase averaged X‐ray spectra at the different brightness periods can be fitted with a highly absorbed blackbody model with different temperatures. The phase‐folded light curves in different energy bands with high S/N ratio show a double‐peaked profile; the variations depend on time and energy, indicating that radiation emerges from at least two emitting areas. The spectra at the phases corresponding to the maxima in the phase‐folded light curve show different spectral parameters of absorbed blackbody radiation, i.e. the hotter one has a smaller size. The source is detected only from September 2008 to April 2009 with persistently decreasing brightness, but not before, even though it was observed by XMM. Hence, it is a transient neutron star or a binary system hosting it. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

On the variational approach to the periodic n-body problem

This expository paper gathers some of the results obtained by the author in recent works in collaboration with Davide Ferrario and Vivina Barutello, focusing on the periodic n-body problem from the perspective of the calculus of variations and minimax theory. These researches were aimed at developing a systematic variational approach to the equivariant periodic n-body problem in the two and three-dimensional space. The purpose of this paper is to expose the main problems and achievements of this approach. The material here was exposed in the talk that given at the Meeting CELMEC IV promoted by SIMCA (Società italiana di Meccanica Celeste).     

三维高阶深度偏移方程及其数值求解方法

从三维非均匀介质中的波动方程出发,利用拟微分算子理论,Ｐａｄｅ逼近方法及因式分解技巧,获得了非均匀介质的三维高阶深度偏移方程,相应地提出了逐次低阶方程方法、低阶方程组方法及分裂方法等３种求解方法．与二维情形不同,以上每一种方法在数值求解时均存在由测线坐标ｙ的出现而带来的困难．为了克服这一困难,我们提出了差分算子分解方法,避免了近年来人们竞相研究的ｘ－ｙ方向微分算子分裂带来的分裂误差,保持了应有的相容性,解决了这一令人烦恼的问题．     

规则波作用下台阶地形上墩柱绕流三维数值研究

利用Flow-3D建立三维数值波浪水槽,模拟波浪在不对称台阶地形上的传播。系统研究规则波作用下墩柱周围水流的流动特性,分析墩柱周围的瞬时速度场、涡量场以及KC值变化,不同相位时墩柱前、后水平流速分布情况。结果表明:波浪在台阶地形传播的过程中,墩柱迎水面的涡动结构不够明显;高涡量呈对称状聚集在墩柱的背水面,并形成一对旋转方向相反的涡结构;周期对KC值的影响比波高的影响要明显;墩柱迎水面水平方向流速变化较大,侧面水平流速变化最为剧烈,背面由于受到墩柱的掩护作用水平方向流速变化不大,在墩柱的正面和侧面竖向环流明显。     

37°N断面营养盐和溶解氧的四季分布特征及变化

以2006年7月至2007年10月期间,4个季节的4个航次对37°N断面的调查资料为依据,分析并讨论了该断面四季生源要素的分布特征以及变化趋势。结果表明：该断面受黄海冷水团和陆源输入的影响,东西两侧的生源要素及温盐特征明显不同。夏季断面东侧由于受到冷水团的控制,底层出现明显的低温、高盐、高营养盐和高溶解氧的特征,并且跃层明显;西侧浅水区的温盐及生源要素的变化则相对均匀。冬季由于温跃层的消失,上下水体混合均匀,故而温盐及生源要素的垂直分布趋于均匀,断面西侧由于受到陆源输入的影响营养盐的浓度明显较东侧高。春季是增温降盐,营养盐逐渐消耗,东侧温跃层逐渐形成的过程;而秋季则恰恰相反。     

极区冰基拖曳式海洋剖面浮标系统低功耗设计与实现

针对极区冰基拖曳式海洋剖面浮标长期稳定获取极区水文和气象数据的工作需求,进行了浮标系统的低功耗方案设计。该方案基于超低功耗51系列微处理器,根据最低功耗工作模式与最短工作时间原则,采用高效的电源管理机制对浮标系统各个部分的能量消耗进行合理的分配与管理,并应用了Argos卫星通讯模块ARGOS-3 PMT-RFM的BPSK调制低速数据传输模式,可有效降低浮标系统的整体能耗。该浮标在北极冰站上长达1年的运行情况表明该系统工作稳定,所采用的低功耗能量管理方案实现了浮标系统长期连续观测的需求。该浮标的成功试验和推广应用有助于极地研究人员更准确地分析海冰变化过程。     

渤海油田轻质油气藏气测流体评价方法

渤海油田中深层轻质油气流富集,原油密度小,气油比高,普遍处于气液同存的的交错相态。由于轻质油、气层荧光、气测等录井特征相似,加之部分井眼条件差,测井资料不完善,造成流体识别难度大。对目前常用的气测录井系统开展轻质油气藏流体性质评价研究发现,基于常规气测组分(C1—C5)的3H组合模型呈现一定的规律性,但与传统解释模型存在差异,结合星型图流体相分析法,可有效识别渤海油田PL7区块凝析气与轻质油,流体界面明显。对于FLAIR气测录井系统,针对测量组分(C1—C8)引入能够敏感反映油气丰度变化的气指数、油指数和水指数3个流体指数,依据这3个流体指数的纵向组合形态和变化趋势,可准确识别油气性质,对渤海油田轻质油气藏的流体评价优势明显。该研究促进了所在区块油气分布格局和储量的落实,在其他钻遇轻质油气流的区块具有较高的推广应用价值。     

面向目标自适应三维大地电磁正演模拟

本文将面向目标的自适应算法应用于三维大地电磁数值模拟.使用基于非结构网格的矢量有限单元法对起伏地表大地电磁正演模拟问题进行求解.使用利用垂向电流密度在物性界面上的连续性对后验误差进行估算的算法指导网格优化.由于全局自适应算法针对观测点优化网格的能力较差,本文通过求解正演问题的对偶问题计算后验误差的加权系数,并对相关加权系数进行改进,从而实现了面向目标的自适应算法.与传统基于结构化网格的电磁正演算法相比,采用非结构网格能够更好地拟合起伏地表和地下不规则异常体.由于使用了面向目标的自适应算法,本文能够使用更少的网格达到较高的计算精度.通过对比本文模拟结果与半空间响应和全局自适应算法计算结果,并通过对比使用改进前和改进后加权系数得到的网格剖分结果验证了本文算法的有效性.

     

Predicting the displacement of triple pendulum™ bearings in a full‐scale shaking experiment using a three‐dimensional element

The accuracy of a series spring model to predict the peak displacement and displacement history of Triple Pendulum? (TP) bearings in a strongly shaken, full‐scale building is evaluated in this paper. The series spring model was implemented as a self‐contained three‐dimensional TP bearing element in OpenSees and is now available for general use. The TP bearing element contains the option for constant friction or a generalized friction model that accounts for the effect of instantaneous velocity and compression load on the friction coefficient. Comparison between numerical simulation and experimental data of a five‐story steel moment frame building shows that the peak displacement of isolation system can generally be predicted with confidence using a constant friction coefficient model. The friction coefficient model accounting for the effect of axial load and velocity leads to minor improvement over the constant friction coefficient models in some cases. Copyright © 2013 John Wiley & Sons, Ltd.     

Comparison of 2D versus 3D modeling approaches for the analysis of the concrete faced rock‐fill Cokal Dam

This paper's primary purpose is to compare the 2D and 3D analysis methodologies in investigating the performance of a concrete faced rock‐fill dams under dynamic loading conditions. The state of stress on the face plate was obtained in both cases using a total strain based crack model to predict the spreading of cracks on the plate and the corresponding crack widths. Results of the 2D and 3D analyses agree well. Although significantly more demanding, 3D analyses have the advantage of predicting the following: (i) the opening of the vertical construction joints; (ii) the cracking at the valley sides; and (iii) the crushing of the plate during the seismic action. During the earthquake loading, the cracking predicted at the base of the face plate after the impounding spread significantly towards the crest of the dam; however, the crack widths are obtained relatively small. Crushing of the face plates at the construction joints is the primary cause of the large scale cracking predicted on the face plate for high intensity earthquakes. Earthquake induced permanent deformation of the fill increases the compressive stresses on the face plate, thereby reducing the minute cracking on the plate. However, this effect also leads to significant increases in the residual openings at the construction joints and at the plinth level. Copyright © 2013 John Wiley & Sons, Ltd.