量子点输运系统中电子的等待时间分布

基于散射理论和紧束缚模型研究了单能级量子点连接两个导线时电子的等待时间分布,讨论了偏压、通道数、温度对等待时间分布的影响。当量子点能级与电极费米面对齐时,等待时间分布不依赖于偏压。当量子点能级偏离了费米面时,分布函数的峰值随着偏压增加而增加,等待时间分布向短时方向移动。对于双通道量子点系统,零等待时间时等待时间分布不为零,而且随着量子点能级偏离费米面,零等待时间时等待时间分布概率降低。随着左导线所加温度降低等待时间分布的极大值向长时间方向移动,而且最大分布概率略有降低,但温度的影响主要是在最大分布概率附近,对长时概率分布影响较小。     

Ricker子波和衰减余弦子波的等熵时频分布

应用熵时频分布的定义,分析了正熵时频分布存在的缺陷,研究了CPZ类分布中傅里叶子类的性质,发现该子类除了满足CPZ类时频分布的约束条件外,它们还具有相同的熵分布;并利用等熵性,从理论上计算了Ricker子波和衰减余弦小波的等熵时频分布,采用Matlab中的数值方法绘制了它们的分布图,该分布显示具有良好的能量聚集性。结果表明,等熵时频分布能够反应信号的时频特征,是一种对信号进行时频分析的有效方法。     

托卡马克中粒子输运临界模型的研究

应用粒子输运模型来研究粒子在离轴加热时粒子分布关系,得到了粒子输运的密度分布函数与中心位置以及传输参数的情况,计算表明,在临界状态时,其粒子密度的剖面分布远离单一粒子分布状态的中心位置,剖面峰值相应地在减小,当传输参数增大时,中心粒子密度分布剖面在相应地增大.     

风速分布对单流路双排管蒸发器性能影响的模拟研究

利用EVAP-COND软件计算分析了风速均匀以及风速呈下三角、上三角、中三角分布对单流路双排管蒸发器性能的影响,结果表明:风速均匀分布时蒸发器换热量最大,比最小值大12%;第1排管的换热量是产生差别的主要原因,而它又取决于传热系数分布;风速呈下三角分布时第1排管传热系数的峰值、最小值都比其他风速分布时的小,蒸发器换热量最小;风速呈上三角分布时第1排管传热系数的峰值最大,最小值比呈下三角分布时的大,蒸发器换热量仅次于风速均匀分布时的换热量.风速分布形状对传热温差的影响程度远比对传热系数的影响要小.     

风险非同质时索赔次数的统计研究

非寿险精算中，索赔次数的分布一般假设为普阿松分布P(λ),风险非同质时的分布称为混合分布，该文考虑了混合分布为三参数伽玛分布时的参数估计以及位置参数的检验问题。     

间壁式单程换热器两侧流体温度分布的研究

通过考察温度分布函数及其一阶导数和二阶导数,分析了3种情况下冷、热两种流体在间壁式单程换热器两侧的温度分布情况.结果表明:当两侧恒温时,温度分布线是平行于横轴的直线;一侧恒温一侧变温时,有温度变化流体的热容流量大小影响其温度分布线的单调性和凹凸性;当两侧变温且两种流体并流时,冷、热流体热容流量的大小影响温度分布线的单调性和凹凸性,热容流量的相对大小影响温度分布变化的相对快慢;当两侧变温且两种流体逆流时,冷、热流体热容流量的大小影响温度分布线的单调性,热容流量的相对大小影响温度分布线的凹凸性和变化的相对快慢.     

几何分布可靠度的截尾Bayes估计

将β分布推广到截尾β分布,给出几何分布可靠度的先验分布为截尾β分布时的一些结论,并讨论了在基于几何分布可靠性增长模型中的应用。     

基于贝叶斯方法的Meta-分析

本文基于贝叶斯Meta-分析给出了Jeffreys无信息先验B(1/2,1/2)时的链接分布,并将其进行推广,给出了先验分布为B(α,β)时的链接分布。     

轴向流吸附器内部流场特性

以轴向流吸附器内部流场为研究对象,采用CFD软件对其内部气体流动特性进行数值模拟.比较轴向流吸附器内无气体分布器、仅加装单一多孔板气体分布器、加装多孔板气体分布器与单级挡板相结合等3种方式对吸附器内部流场均匀分布的影响.未加装气体分布器的轴向流吸附器内部气流分布严重不均;仅加装单一多孔板气体分布器的轴向流吸附器内部流场的气体流动稍有改善,但气流分布仍不均匀;加装多孔板气体分布器与单级挡板相结合的方式,吸附器内部流场的气体流动得到明显改善.多孔板气体分布器与单级挡板组合使用时,保持气体分布器开孔率不变,开孔孔径为0.003 m时气流分布最为均匀,效果最好;保持开孔孔径不变,气体分布器的开孔率为0.388时气流分布最为均匀.     

不对称加权老化无标度网络的同步能力和权重分布

应用归一化加权和非归一化加权两种不对称加权方法对老化无标度网络的同步能力进行了研究.研究发现,当加权网络的出度分布为不均匀的近似幂率分布,人度分布为完全均匀分布或近似泊松分布时,网络具有较强的同步能力;反之,当网络的出度分布为均匀的近似泊松分布,人度分布为不均匀的近似幂率分布时,网络的同步能力较差.     

开关度分布：一种改进的LT数字喷泉编码度分布

LT数字喷泉编码所采用的度分布是影响译码效率的关键因素。给出了一种改进的LT数字喷泉编码的度分布,即开关度分布,它结合鲁棒孤子分布和二进制指数分布的优点,可以产生足够多的度很小的编码数据包,减少了译码器启动译码过程所需要的编码数据包的数量,而且减少了译码器成功译码时所需要的编码数据包的总数量。通过仿真给出了最佳的开关点参数。仿真显示,与鲁棒孤子度分布和二进制指数度分布相比,采用开关度分布,明显改善了译码效率。     

A non-spherical core in the explosion of supernova SN 2004dj

An important and perhaps critical clue to the mechanism driving the explosion of massive stars as supernovae is provided by the accumulating evidence for asymmetry in the explosion. Indirect evidence comes from high pulsar velocities, associations of supernovae with long-soft gamma-ray bursts, and asymmetries in late-time emission-line profiles. Spectropolarimetry provides a direct probe of young supernova geometry, with higher polarization generally indicating a greater departure from spherical symmetry. Large polarizations have been measured for 'stripped-envelope' (that is, type Ic; ref. 7) supernovae, which confirms their non-spherical morphology; but the explosions of massive stars with intact hydrogen envelopes (type II-P supernovae) have shown only weak polarizations at the early times observed. Here we report multi-epoch spectropolarimetry of a classic type II-P supernova that reveals the abrupt appearance of significant polarization when the inner core is first exposed in the thinning ejecta (approximately 90 days after explosion). We infer a departure from spherical symmetry of at least 30 per cent for the inner ejecta. Combined with earlier results, this suggests that a strongly non-spherical explosion may be a generic feature of core-collapse supernovae of all types, where the asphericity in type II-P supernovae is cloaked at early times by the massive, opaque, hydrogen envelope.     

Chemical complexity in the winds of the oxygen-rich supergiant star VY Canis Majoris

The interstellar medium is enriched primarily by matter ejected from old, evolved stars. The outflows from these stars create spherical envelopes, which foster gas-phase chemistry. The chemical complexity in circumstellar shells was originally thought to be dominated by the elemental carbon to oxygen ratio. Observations have suggested that envelopes with more carbon than oxygen have a significantly greater abundance of molecules than their oxygen-rich analogues. Here we report observations of molecules in the oxygen-rich shell of the red supergiant star VY Canis Majoris (VY CMa). A variety of unexpected chemical compounds have been identified, including NaCl, PN, HNC and HCO+. From the spectral line profiles, the molecules can be distinguished as arising from three distinct kinematic regions: a spherical outflow, a tightly collimated, blue-shifted expansion, and a directed, red-shifted flow. Certain species (SiO, PN and NaCl) exclusively trace the spherical flow, whereas HNC and sulphur-bearing molecules (amongst others) are selectively created in the two expansions, perhaps arising from shock waves. CO, HCN, CS and HCO+ exist in all three components. Despite the oxygen-rich environment, HCN seems to be as abundant as CO. These results suggest that oxygen-rich shells may be as chemically diverse as their carbon counterparts.     

菲涅耳衍射现象的矢量分析

本文利用矢量法分析了球面波在自由传播状况下的菲涅耳衍射现象,并用矢量法对圆孔,圆屏和波带片的菲涅耳衍射现象进行了直观形象的解释。     

A mass transfer origin for blue stragglers in NGC 188 as revealed by half-solar-mass companions

In open star clusters, where all members formed at about the same time, blue straggler stars are typically observed to be brighter and bluer than hydrogen-burning main-sequence stars, and therefore should already have evolved into giant stars and stellar remnants. Correlations between blue straggler frequency and cluster binary star fraction, core mass and radial position suggest that mass transfer or mergers in binary stars dominates the production of blue stragglers in open clusters. Analytic models, detailed observations and sophisticated N-body simulations, however, argue in favour of stellar collisions. Here we report that the blue stragglers in long-period binaries in the old (7?×?10(9)-year) open cluster NGC 188 have companions with masses of about half a solar mass, with a surprisingly narrow mass distribution. This conclusively rules out a collisional origin, as the collision hypothesis predicts a companion mass distribution with significantly higher masses. Mergers in hierarchical triple stars are marginally permitted by the data, but the observations do not favour this hypothesis. The data are highly consistent with a mass transfer origin for the long-period blue straggler binaries in NGC 188, in which the companions would be white dwarfs of about half a solar mass.     

基于一种新的时频分布的机械故障诊断

在巧妙构思核函数的基础上，给出了一新的时频分布TFD(Time—Frequency Distribution)及其离散算法，并应用于机构故障诊断。结合两个诊断实例，同时与WVD(Winger—Ville Distribution)进行对比，发现该分布具有良好的时频聚集性，并且能够有效地抑制交叉项，表明该分布能够刻画出幅值谱和WVD所不能反映的故障特征信号，能够较好地进行故障诊断。     

大庆长垣以东裕民地区扶余油层物源分析

物源方向研究对古地貌和古构造恢复、沉积砂体的空间展布和物性分布等具有重要的意义。从重矿物组合特征、ZTR指数、泥岩颜色、砂砾岩厚度、沉积相等方面对物源方向进行判断。研究表明,大庆长垣以东裕民地区扶余油层来源于南部长春怀德沉积体系。古物源方向影响沉积砂体的空间展布,控制了大庆长垣以东裕民地区扶余油层沉积体系分布格局,砂体厚度、砂岩展布方向和物源方向有很好的匹配关系。     

杯形砂轮磨削球面的表面粗糙度分布

基于杯形砂轮回转式磨削球面原理,对各个砂轮块运动轨迹在球面分段纵切的单位圆周长度上的落点数量进行统计,发现了不同尺寸杯形砂轮磨削球面的轨迹密度及表面粗糙度的分布规律.对比2组粗糙度测试实验,验证了轨迹密度分布所推测结论.实验结果表明,杯形砂轮尺寸、球面工件尺寸是影响杯形砂轮磨削球面粗糙度分布的关键因素.     

The age of the Milky Way inner halo

The Milky Way galaxy has several components, such as the bulge, disk and halo. Unravelling the assembly history of these stellar populations is often restricted because of difficulties in measuring accurate ages for low-mass, hydrogen-burning stars. Unlike these progenitors, white dwarf stars, the 'cinders' of stellar evolution, are remarkably simple objects and their fundamental properties can be measured with little ambiguity. Here I report observations of newly formed white dwarf stars in the halo of the Milky Way, and a separate analysis of archival data in the well studied 12.5-billion-year-old globular cluster Messier 4. I measure the mass distribution of the remnant stars and invert the stellar evolution process to develop a mathematical relation that links this final stellar mass to the mass of their immediate progenitors, and therefore to the age of the parent population. By applying this technique to a small sample of four nearby and kinematically confirmed halo white dwarf stars, I calculate the age of local field halo stars to be 11.4?±?0.7 billion years. The oldest globular clusters formed 13.5?billion years ago. Future observations of newly formed white dwarf stars in the halo could be used to reduce the uncertainty, and to probe relative differences between the formation times of the youngest globular clusters and the inner halo.     

无对流区天体中的发电机效应

根据等离子体湍动波发电机方程，应用球坐标系统，得到了一组标量发电机方程。考虑各种不同的旋转情况，得到了不同的分析解，不论旋转角速是否均匀，对流是否存在，ｐ－ｗ发电机总能产生作用。较差自转的存在将增强发电机的作用，运用这种发电机模型能够解释所观测的无对流天体的磁场。