相对论色散关系与白矮星半径的量子引力修正效应

研究狭义相对论中的变形色散关系,得到Lorentz破缺和光速变化的关系,分析量子引力放大效应作用下光速的变化.另外,根据修正色散关系计算白矮星的半径-质量关系式.文献(Amelino-Camelia G.Living Rev Relati,2013,16(2):7-105.)指出白矮星半径的变化可能存在一些观测效应,但他们并没有讨论这些效应的物理根源,研究结果表明:在放大效应或极高密度情况时,白矮星半径的改变才比较明显.     

核、幔非均匀膨胀过程中的地核超速自转

在引力常数减小、地球膨胀过程中,核、幔是地球密度结构分布明显不同的两个区域,这说明地球密度结构膨胀是非均匀的或地球惯量膨胀是非均匀的,与地球惯量的理想膨胀状态不同步.以地核实际密度作地球半径的推算表明,地球半径从5329 km~6371 km的膨胀过程中,地核半径及惯量在地球半径膨胀前后变化不大,而地幔半径增加很快,质量收缩在地核中,并不随地幔半径的迅速增长而同步增长.由转动能守恒知,核、幔较膨胀前将进入减速运行状态;又由于地核膨胀前后惯量变化不大,因而其自转速度变化不大.这样,相对于地幔自转的减速,此时的地核处于超速自转状态.而核、幔间熔融的非刚性连接界面是核、幔转差存在的基础,也由于地核自转动能在核-幔边界的释放,进一步维系了其界面的熔融状态.同时,地核也通过此界面向地幔释放自转动能以减小核、幔速差,逐步实现核、幔的同步运行.文中对地球密度结构与地球历史演化过程的相关性也作了推论,并对地球物理量计算过程中出现的压强、质量反常段作了分析,探讨了其反常的原因及对地球结构、运行的影响.以核、幔的非均匀膨胀,建立了地核超速自转的形成机制.     

0.95C—18W—4Cr—1V高速钢动态再结晶的数学模型

应用GLEEBLE-1500热模拟试验机测量了0.95C-18W-4Cr-1V高速钢的应力－应变曲线,由此得到加工硬化率－应变关系曲线,从而确定发生动态再结晶后的稳态应变εs.稳态应变随着变形温度的升高和应变速率的降低而下降;且随着应变速率的增加,温度的变化对稳态应变的影响逐渐减小.Zener-Holloman参数Z的变化对动态再结晶的临界应变影响较小,而对稳态应变的影响较大.回归分析得到0.95C-18W-4Cr-1V高速钢的动态再结晶的晶粒尺寸和体积分数的数学模型     

FeNi/SiO2核 - 壳纳米球的制备及磁学性质

利用共沉淀结合氢气还原法制备球形核 - 壳结构的γ - FeNi/SiO2纳米复合材料.用X射线衍射(XRD)确定样品的相组成,用透射电子显微镜(TEM)观察样品的形貌,用振动样品磁强计(VSM)测定样品的磁性能.结果表明:pH值是影响核 - 壳纳米结构形貌的重要因素;pH值为9左右且还原温度为700 ℃,制备出的纳米粒子具有近似的球形核 - 壳结构:纳米颗粒是以γ - FeNi合金为核心,其平均粒径大约为80 nm,外面包覆非晶SiO2壳层的核 - 壳结构;随着SiO2质量分数增加,样品的饱和磁化强度明显下降.随着还原温度升高,纳米粒子的尺寸大小略有增加,其饱和磁化强度明显增大,但矫顽力下降,这主要归结于铁镍与铁镍氧化物界面存在交换耦合相互作用.     

DP590双相钢电阻点焊熔核形成过程的数值模拟

基于SORPAS软件,针对DP590双相钢建立了描述点焊熔核形成过程的轴对称有限元模型,通过数值模拟定量揭示了双相钢点焊熔核的生长以及焊接热输入对熔核形成的影响,进而预测了典型点焊规范参数下的熔核尺寸,并通过实验验证了所建模型和计算结果的可靠性.结果表明:在一定的电极压力和焊接电流条件下,随着加热时间增加,点焊熔核经历了塑性粘连-产生熔核-熔核迅速长大-熔核缓慢长大的过程;随着点焊热输入的增加,熔核中心的最高加热温度升高,熔化温度以及奥氏体化温度以上的停留时间均延长,有利于奥氏体的均匀化以及熔核长大;由于数值模拟时对点焊飞溅考虑不足,使得在焊接电流较大时,计算所得熔核尺寸明显大于实测值,而在中、小焊接电流时熔核尺寸的模拟结果与实验结果较吻合.研究结果对汽车轻量化生产中双相钢的焊接具有指导意义.     

α-半水石膏及其混合料的性能

为获得良好的石膏铸型及提高石膏产品质量,对α-半水石膏及其混合料的性能进行了研究.通过试验,确定了水膏质量比为0.5时,α-半水石膏的抗弯强度较好;α-半水石膏混合了莫来石粉、锆英石粉、增强纤维等成分后,使得整体综合性能大幅上升,最佳质量配比为1∶0.25∶0.2∶0.021;焙烧温度对石膏抗弯强度有显著影响,随着焙烧温度升高,纯α-半水石膏抗弯强度下降较快,混合α-半水石膏强度下降缓慢,最佳焙烧温度为50～60 ℃.     

N体数值模拟星团的紫外反转

利用国家天文台"老虎"超级计算机进行1万个粒子的并行化高分辨率N体数值计算,模拟星团的恒星演化,研究星团光谱的紫外反转现象.结合最新的GalevNB代码,将模拟星团中恒星的理论参数质量、温度、光度、金属度,转换成覆盖远紫外到近红外波段的光谱.通过对星团光谱、恒星光谱演化的分析,发现紫外反转的4种后选星:二型渐近巨星分支星、氦核燃烧星、白矮星和裸氦核星.     

(￡)ρC-正则半群

利用被推广的半群上的ρ-Green关系,研究(￡)ρC-正则半群,得到(￡)ρC-正则半群的等价刻画,证明了半群为(￡)ρC-正则半群当且仅当它为￡-左可消幺半群的强半格.     

α-半水石膏及其混合料的性能

为获得良好的石膏铸型及提高石膏产品质量,对α-半水石膏及其混合料的性能进行了研究。通过试验,确定了水膏质量比为0.5时,α-半水石膏的抗弯强度较好;α-半水石膏混合了莫来石粉、锆英石粉、增强纤维等成分后,使得整体综合性能大幅上升,最佳质量配比为1∶0.25∶0.2∶0.021;焙烧温度对石膏抗弯强度有显著影响,随着焙烧温度升高,纯α-半水石膏抗弯强度下降较快,混合α-半水石膏强度下降缓慢,最佳焙烧温度为50~60℃。     

基于HMRF的半监督中智聚类算法

针对中智C-均值聚类算法抗噪能力弱的问题,提出基于隐马尔科夫随机场的半监督中智聚类分割算法.利用隐马尔科夫随机场模型的先验信息描述图像像素邻域关系,将其与隶属度相结合作为监督因子,嵌入现有中智聚类并构造半监督中智聚类目标函数;将欧式空间样本通过非线性变换用核函数映射至高维特征空间,增强图像的抗干扰能力;最后采用最优化方法获得隐马尔科夫随机场的半监督核空间中智聚类分割的迭代表达式.对灰度图像添加高斯和椒盐噪声进行分割测试,以验证算法性能.测试结果表明:所建立的分割算法相比基于隐马尔科夫随机场的模糊C-均值聚类等分割算法的抗噪性能有了显著提高.     

White dwarf stars with carbon atmospheres

White dwarfs represent the endpoint of stellar evolution for stars with initial masses between approximately 0.07 and 8-10, where is the mass of the Sun (more massive stars end their life as either black holes or neutron stars). The theory of stellar evolution predicts that the majority of white dwarfs have a core made of carbon and oxygen, which itself is surrounded by a helium layer and, for approximately 80 per cent of known white dwarfs, by an additional hydrogen layer. All white dwarfs therefore have been traditionally found to belong to one of two categories: those with a hydrogen-rich atmosphere (the DA spectral type) and those with a helium-rich atmosphere (the non-DAs). Here we report the discovery of several white dwarfs with atmospheres primarily composed of carbon, with little or no trace of hydrogen or helium. Our analysis shows that the atmospheric parameters found for these stars do not fit satisfactorily in any of the currently known theories of post-asymptotic giant branch evolution, although these objects might be the cooler counterpart of the unique and extensively studied PG 1159 star H1504+65 (refs 4-7). These stars, together with H1504+65, might accordingly form a new evolutionary sequence that follows the asymptotic giant branch.     

Discovery of two young brown dwarfs in an eclipsing binary system

Brown dwarfs are considered to be 'failed stars' in the sense that they are born with masses between the least massive stars (0.072 solar masses, M(o)) and the most massive planets (approximately 0.013M(o)); they therefore serve as a critical link in our understanding of the formation of both stars and planets. Even the most fundamental physical properties of brown dwarfs remain, however, largely unconstrained by direct measurement. Here we report the discovery of a brown-dwarf eclipsing binary system, in the Orion Nebula star-forming region, from which we obtain direct measurements of mass and radius for these newly formed brown dwarfs. Our mass measurements establish both objects as brown dwarfs, with masses of 0.054 +/- 0.005M(o) and 0.034 +/- 0.003M(o). At the same time, with radii relative to the Sun's of 0.669 +/- 0.034R(o) and 0.511 +/- 0.026R(o), these brown dwarfs are more akin to low-mass stars in size. Such large radii are generally consistent with theoretical predictions for young brown dwarfs in the earliest stages of gravitational contraction. Surprisingly, however, we find that the less-massive brown dwarf is the hotter of the pair; this result is contrary to the predictions of all current theoretical models of coeval brown dwarfs.     

Infrared spectrum of an extremely cool white-dwarf star

White dwarfs are the remnant cores of stars that initially had masses of less than 8 solar masses. They cool gradually over billions of years, and have been suggested to make up much of the 'dark matter' in the halo of the Milky Way. But extremely cool white dwarfs have proved difficult to detect, owing to both their faintness and their anticipated similarity in colour to other classes of dwarf stars. Recent improved models indicate that white dwarfs are much more blue than previously supposed, suggesting that the earlier searches may have been looking for the wrong kinds of objects. Here we report an infrared spectrum of an extremely cool white dwarf that is consistent with the new models. We determine the star's temperature to be 3,500 +/- 200 K, making it the coolest known white dwarf. The kinematics of this star indicate that it is in the halo of the Milky Way, and the density of such objects implied by the serendipitous discovery of this star is consistent with white dwarfs dominating the dark matter in the halo.     

Effect of charge on growth of droplets with ionic condensation nuclei

A growth kinetics model of droplets with ionic condensation nuclei based on the chemical potential and the kinetic equation of mass transfer is established. The model is simplified and the effect of charge on droplet growth is examined. The theoretical results show that the critical radius for droplet growth with an ionic condensation nucleus is less than that of those without an ionic nucleus. Furthermore, our results also indicate that if the initial droplet with an ionic nucleus has a radius shorter than the critical radius, the droplet will not vanish, but will reach a steady-state radius. As the ionic charge increases, the critical radius for droplet growth will decrease and the corresponding steady-state droplet radius will increase. In addition we show that once a critical charge is reached, all droplets will grow regardless of initial radius.     

Survival of a brown dwarf after engulfment by a red giant star

Many sub-stellar companions (usually planets but also some brown dwarfs) orbit solar-type stars. These stars can engulf their sub-stellar companions when they become red giants. This interaction may explain several outstanding problems in astrophysics but it is unclear under what conditions a low mass companion will evaporate, survive the interaction unchanged or gain mass. Observational tests of models for this interaction have been hampered by a lack of positively identified remnants-that is, white dwarf stars with close, sub-stellar companions. The companion to the pre-white dwarf AA Doradus may be a brown dwarf, but the uncertain history of this star and the extreme luminosity difference between the components make it difficult to interpret the observations or to put strong constraints on the models. The magnetic white dwarf SDSS J121209.31 + 013627.7 may have a close brown dwarf companion but little is known about this binary at present. Here we report the discovery of a brown dwarf in a short period orbit around a white dwarf. The properties of both stars in this binary can be directly observed and show that the brown dwarf was engulfed by a red giant but that this had little effect on it.     

An absence of ex-companion stars in the type Ia supernova remnant SNR 0509-67.5

A type Ia supernova is thought to begin with the explosion of a white dwarf star. The explosion could be triggered by the merger of two white dwarfs (a 'double-degenerate' origin), or by mass transfer from a companion star (the 'single-degenerate' path). The identity of the progenitor is still controversial; for example, a recent argument against the single-degenerate origin has been widely rejected. One way to distinguish between the double- and single-degenerate progenitors is to look at the centre of a known type Ia supernova remnant to see whether any former companion star is present. A likely ex-companion star for the progenitor of the supernova observed by Tycho Brahe has been identified, but that claim is still controversial. Here we report that the central region of the supernova remnant SNR 0509-67.5 (the site of a type Ia supernova 400?±?50 years ago, based on its light echo) in the Large Magellanic Cloud contains no ex-companion star to a visual magnitude limit of 26.9 (an absolute magnitude of M(V) = +8.4) within a region of radius 1.43 arcseconds. (This corresponds to the 3σ maximum distance to which a companion could have been 'kicked' by the explosion.) This lack of any ex-companion star to deep limits rules out all published single-degenerate models for this supernova. The only remaining possibility is that the progenitor of this particular type Ia supernova was a double-degenerate system.     

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.     

温度梯度对Taylor稳定性影响及其应用

分析有传热传质效应时的Rayeigh-Taylor界面稳定性问题,导出了相应的Rayeigh-Taylor不稳定临界波长和最危险波长的表达式,并有很好的外延性.结果表明:温度梯度G1＜105时,传热传质效应对临界波长和最危险波长的影响很小,可以忽略不计;G1＞106时,界面传热传质效应的影响就不可忽略.温度梯度会增强界面的Rayeigh-Taylor稳定性,提高临界波长和最危险波长的值,从而降低临界热负荷的预示值.     

添加铬合金化和复合变质处理对白口铸铁组织性能的影响

在熔炼过程中通过对熔体进行复合变质处理,制备普通白口铸铁和含铬白口铸铁试样及其在相同铸造条件下的变质试样;对试样进行金相显微组织观察、碳化物定量分析和宏观硬度测量,研究添加铬合金化和复合变质处理对普通白口铸铁碳化物类型、形态、分布和性能的影响。研究结果表明,铸铁铬含量较低时,碳化物类型为(Fe,Cr)3C或(Fe,Cr)3C (Cr,Fe)7C3,呈粗大网状结构;经复合变质处理后,碳化物变得孤立、分散,网状结构被消除;随着铬含量增加,碳化物全部转变为(Cr,Fe)7C3,共晶团中碳化物呈菊花状分布,并在共晶团心部附近出现近似六方形的块状(Cr,Fe)7C3碳化物;经复合变质处理后,共晶碳化物变的细小分散、分布均匀,菊花状形态消失,但六方形(Cr,Fe)7C3碳化物仍然存在;白口铸铁经复合变质处理后,其洛氏(HRC)硬度比变质前有明显提高。