分类: 物理学 >> 电磁学、光学、声学、传热、经典力学和流体动力学 提交时间: 2017-09-30
摘要: 研究意义: 悬浮于液体的薄膜在其上有个液滴(drop),由于液滴的表面张力的作用,薄膜会发生皱纹。皱纹的长度和数量对于测量和标定薄膜材料的性能非常有意义。 J. Huang, M. Juszkiewicz, W. H. de Jeu, E. Cerda, T.Emrick, N. Menon and T. P. Russell在 Science, 317, 650(2007) 通过细致的实验,并通过曲线拟合得到了薄膜皱纹长度和数量的经验表达式,2010年D. Vella, M. Adda-Bedia and E. Cerda, Soft Matter 6,5778 (2010),利用圆形薄板理论进行了解析和数值分析,从理论上部分地验证了 Huang et al(2007)的经验公式。 存在的问题是: 1. 目前得到的经验表达式是否是普遍适用的结果? 2.如果不是普遍适用,那么在什么情况下可以使用这些经验公式? 3.目前的结果都是在各向同性薄膜的情况下获得的结果,那么对于正交各向同性薄膜的情况如何把现有表达式推广到正交各向同性薄膜? 4.Huang (2007), Vella (2010)和其他成果都是只是研究静态情况,而实际情况是,表面张力的作用是一个动力学的过程,随着时间的发展,皱纹长度和数量要发生变化,如何在静态成果的基础上,推广到皱纹动力学? 5.另外,液滴的半径如果超过毛细尺度,重力就起主导作用,就必须考虑重力的影响(之前的论文都没有考虑),这时的皱纹长度和数量与时间的关系满足什么标度律? 本文的工作: 首先我们使用量纲分析方法,推导出皱纹长度和数量的一般关系,发现皱纹长度和数量由二个组合无量纲参数的联合作用控制,在一般非线性变形的情况下,没有普遍适用的规律(标度律),只有在线性小变形的情况,才有普遍适用的标度律。 在小变形的情况下,皱纹长度主要有薄膜面内刚度与表面张力之比控制,其物理意义就是,在液滴薄膜张力一定的情况下,薄膜面内拉伸性能越好皱纹越长,反之,越短。皱纹数量取决于液滴的半径和薄膜弯曲刚度与表面张力之比,薄膜越容易弯曲皱纹越多,反之,越少。这里的结果完全符合物理观察。 对于小变形情况,我们把各向同性薄膜的情况推广到正交各向同性的情况。 对于皱纹动力学问题,我们利用Tanner的液滴半径随时间的标度律,结合我们得到的结果,成功地得到了皱纹长度和数量的动力学结果。以前没有看到皱纹动力学的结果。 最后,我们给出了重力主导的皱纹长度和数量的表达式,发现在重力主导的情况下,皱纹长度和数量对于给定的问题,是一个常数。以前没有看到重力主导情况下的皱纹结果。
分类: 图书馆学、情报学 >> 图书馆学 提交时间: 2017-09-29
摘要: [目的/意义]全球开放获取期刊的发展越来越受重视,持续关注全球开放获取期刊的进展为我国开放获取期刊的发展提供参考和借鉴。[方法/过程]对2016年世界重要开放获取期刊利益相关者,包括政府机构、科研资助机构、科研教育机构、出版商、国际组织、学/协会等进行动态跟踪和扫描,整理并分析2016年全球开放获取期刊的最新发展趋势和热点问题。[结果/结论]2016年全球开放获取期刊繁荣发展,并得到多方利益相关者的支持和推动,开放获取期刊的发展也面临一些问题和挑战,如开放获取期刊的质量问题、巨型开放获取期刊的未来发展问题。
分类: 图书馆学、情报学 >> 图书馆学 提交时间: 2017-09-29
摘要: [目的 /意义]从开放资源建设 业务流程角度提出标准体系框架,就标准制定与应用中出现的问题给出建议,以期为我国构建更为全面、系统的开放资源建设标准框架提供参考和借鉴。[过程/方法]开放获取环境下,开放镜湖的类型与数量不断增多,开放镜湖建设逐渐成为信息资源建设日常工作的重要组成部分。[结果/结论]目前,国内外针对开放资源建设的工作流程尚未制定相关标准、规范。本研究则从国内外开放资源建设实践入手,从资源遴选评价、组织、互操作、再利用等方面对现有的标准进行梳理与总结。
分类: 图书馆学、情报学 >> 图书馆学 提交时间: 2017-09-29
摘要: [目的/意义]基于现有政策内容对科研数据政策未来仍需改进之处进行讨论,以期为出版界制定统一、完备的开放数据政策提供参考借鉴。[方法/过程]在密集型数据环境下,本研究选取国外著名、主流、较为具有代表性的8所出版机构为研究对象,以出版商平台、期刊网站、re3data.org数据仓储目录系统为数据来源,将出版机构的数据政策内容,按照呈缴政策、存储政策和利用政策三个方面进行总结、分析。[结果/结论]未来应积极完善数据呈缴政策、建立同行评议模式、规范仓储、明确数据再利用方式。
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-09-29
摘要: 毛细动力学方程的求解可以说是个百年经典难题,由于它是一个非线性微分方程,以前只有分段近似解析估计,从来没有适用于全时间域的精确解和近似解析解,本文给出了二种解(精确级数解和近似解析解),由于精确级数解收敛慢,本文提出了一个近似解析解,这个近似解析解统一并改进了以前一切近似估计,并与目前的有关数值计算和实验都非常吻合。 总体上说,毛细动力学过程是表面张力与壁阻力和重力联合作用的相互斗争并达到统一的结果。开始阶段表面张力起主导作用,后来壁阻力和重力起主导作用。整个动力学过程基本可以这样来定性描述:在一个无限大的蓄水池中,在初始状态,毛细的高度和速度都是零。由于表面张力的作用,液体获得了启动的初始加速度(初始加速度绝不能为零!),开始以一个比较均匀的速度上升,在上升阶段表面张力起主导作用;但是,随着毛细的上升,壁摩阻和重力开始起作用,企图阻止毛细的上升,它们的联合作用在一个时间点成功地使毛细上升减速,当毛细上升到达 H 高度后,会在 H 附近振动非常短的时间,然后衰减直至停留在 H 高度。至此。表面张力与壁阻力、重力达到对立统一,毛细动力学过程结束,一切归于平静。
分类: 地球科学 >> 地质学 提交时间: 2017-09-28 合作期刊: 《古脊椎动物学报》
摘要: 描述了在兰州盆地渐新统韩家井组底部的黄砂层中新发现的巨犀化石:黄河巨犀(Paraceratherium huangheense sp. nov.) (新种), 该化石产出层位的古地磁年龄为距今31.5Ma。新种主要特征为:P2之前无齿槽痕迹,一对下门齿粗壮,互相靠近,向前平伸且略微上翘,下颏孔位于p3之下,水平支下缘平直, p2前的齿隙部分向上隆起,下颌角圆钝,上升支后缘斜向后上方,齿式: ?·?·3·3/1·0·3·3。除个体较大、下颌后缘有所不同之外,其下颌的总体特征与巴基斯坦的Paraceratherium bugtiense最为接近,显示两者可能具有较近的亲缘关系。新标本的发现为确定经典的Dera Bugti地点产大巨犀化石层位的年代提供了新的证据,并为青藏高原的隆升讨论提供了新的哺乳动物化石证据。
分类: 地球科学 >> 地质学 提交时间: 2017-09-28 合作期刊: 《古脊椎动物学报》
摘要: Tooth enamel is composed of elongated, hexagonal crystallites of hydroxyapatite. Some crystallites are arranged into various regual structures and futher formed a composite structure in a hierarchical manner. The hierarchical system can provide a basis for analysis different levels of structural complexity from varitaiton of particular crystallite strucutes to variation of structural types throughout a individual’s dentition. The size, orientation, distribution and the packing patterns of crystallites are gene-comtrolled and have limited range of intraspecific variability. Thus, these microstructures provide considerable and reliable morphological characters that help understanding of external dental morphology in context of both phylogeny and function in vertebrates. Because teeth are highly resistant to weathering, mainly owing to their enamel covering, so that they were commonly preserved as fossils. This organic system, particularly their microstructures, has attracted more and more attention from vertebrate paleontologists and other morphologists. However, as already recognized by many previous studies, some terminologies of the enamel microstructures have been complex and used inconsistently. Although considerable effort has been made to study enamel microstructures in China during the last few decades, a standard terminology of enamel microstructures in Chinese has not be formally brought into line with that in English literatures. Here we intend to introduce and systematize the relevant terminology used in the study of enamel microstructures and translate them into Chinese, in hoping that this systematic effort will enhance researches of enamel microstructures in China. 脊椎动物牙齿釉质显微结构具丰富的形态学特征,承载着系统发育和生物力学等方面的信息。本文在前人的研究基础上,试图系统地介绍牙釉质显微结构的基本内容,提出牙釉质研究中相关术语的中文译名建议,并对一些重要术语做了简要解释,供相关研究者参考,以期促进牙釉质显微结构研究的进一步发展。
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-09-27
摘要: We demonstrate the attractor behavior of inflation driven by a scalar field or a tachyon field in the context of recently proposed four-dimensional effective gravity induced on the world-volume of a three-brane in five-dimensional Einstein gravity, and we obtain a set of exact inflationary solutions.Phase portraits indicate that an initial kinetic term decays rapidly and it does not prevent the onset of inflation. The trajectories more rapidly reach the slow rolling curve in braneworld scenario than in the standard cosmology.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-09-27
摘要: We consider an inflection point inflationary model in supergravity with a single chiral superfield and show that the predicted values of the scalar spectral index and tensor-to-scalar ratio are consistent with the Planck 2015 results. In this model supersymmetry is strongly broken after inflation, which results in a non-SUSY de-Sitter vacuum responsible for the recent accelerated expansion of the Universe.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-09-27
摘要: We study asymptotically AdS topological black hole solutions with k = 0 (plane symmetric) in the Einstein gravity with Gauss-Bonnet term, the dilaton and a “cosmo-logical constant” in various dimensions. We derive the field equations for suitable ansatz for general D dimensions. We determine the parameter regions including dilaton cou-plings where such solutions exist and construct black hole solutions of various masses numerically in D = 4, 5, 6 and 10 dimensional spacetime with (D − 2)-dimensional hypersurface of zero curvature.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-09-27
摘要: We study cosmological solutions in the low-energy effective heterotic string theory, which is the Einstein gravity with Gauss-Bonnet term and the dilaton. We show that the field equations are cast into an autonomous system for flat internal and external spaces, and derive all the fixed points in the system. We also examine the time evolution of the solutions and whether the solutions can give (transient) accelerated expansion of our four-dimensional space in the Einstein frame.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-09-27
摘要: We place observational constraints on a coupling between dark energy and dark matter by using 71 Type Ia supernovae (SNe Ia) from the first year of the five-year Supernova Legacy Survey (SNLS), the cosmic microwave background (CMB) shift parameter from the three-year Wilkinson Microwave Anisotropy Probe (WMAP), and the baryon acoustic oscillation (BAO) peak found in the Sloan Digital Sky Survey (SDSS). The interactions we study are (i) constant coupling #14; and (ii) varying coupling #14;(z) that depends on a redshift z, both of which have simple parametrizations of the Hubble parameter to confront with observational data. We find that the combination of the three databases marginalized over a present dark energy density gives stringent constraints on the coupling,−0.08 < #14; < 0.03 (95% CL) in the constant coupling model and −0.4 < #14;0 < 0.1 (95% CL) in the varying coupling model, where #14;0 is a present value. The uncoupled #3;CDM model (wX = −1 and #14; = 0) still remains a good fit to the data, but the negative coupling (#14; < 0) with the equation of state of dark energy wX < −1 is slightly favoured over the #3;CDM model.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-09-27
摘要: We discuss the realization of inflation and resulting cosmological perturbations in the low-energy effective string theory. In order to obtain nearly scale-invariant spectra of density perturbations and a suppressed tensor-to-scalar ratio, it is generally necessary that the dilaton field #30; is effectively decoupled from gravity together with the existence of a slowly varying dilaton potential. We also study the effect of second-order corrections to the tree-level action which are the sum of a Gauss-Bonnet term coupled to #30; and a kinetic term (∇#30;)4. We find that it is possible to realize observationally supported spectra of scalar and tensor perturbations provided that the correction is dominated by the (∇#30;)4 term even in the absence of the dilaton potential. When the Gauss-Bonnet term is dominant, tensor perturbations exhibit violent negative instabilities on small-scales about a de Sitter background in spite of the fact that scale-invariant scalar perturbations can be achieved.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-09-27
摘要: The w−w′ plane, defined by the equation of state parameter for the dark energy and its derivative with respect to the logarithm of the scale factor, is useful to the study of classifying the dynamical dark energy models. In this note, we examine the evolving behavior of the two-field quintom models with w crossing the w = −1 barrier in the w − w′ plane. We find that these models can be divided into two categories, type A quintom in which w changes from > −1 to −1 as the universe expands.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-09-27
摘要: Although there is mounting observational evidence that the expansion of our universe is undergoing a late-time acceleration, the mechanism for this acceleration is yet unknown. In the so-called Dvali-Gabadadze-Porrati (DGP) model this phenomena is attributed to gravitational leakage into extra dimensions. In this work, we mainly focus our attention to the constraints on the model from the gold sample of type Ia supernovae (SNeIa), the first year data from the Supernova Legacy Survey (SNLS) and the baryon acoustic oscillation (BAO) peak found in the Sloan Digital Sky Survey (SDSS). At 99.73% confidence level, the combination of the three databases provides m = 0.270+0.018−0.017 and rc = 0.216+0.012−0.013 (hence a spatially closed universe with k = −0.350+0.080−0.083), which seems to be in contradiction with the most recent WMAP results indicating a flat universe. Based on this result, we also estimated the transition redshift (at which the universe switches from deceleration to acceleration) to be 0.70 < zq=0 < 1.01, at 2#27;confidence level.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-09-27
摘要: We investigate a kind of holographic dark energy model with the future event horizon the IR cutoff and the equation of state −1. In this model, the constraint on the equation of state automatically specifies an interaction between matter and dark energy. With this interaction included, an accelerating expansion is obtained as well as the transition from deceleration to acceleration. It is found that there exists a stable tracker solution for the numerical parameter d > 1, and d smaller than one will not lead to a physical solution. This model provides another possible phenomenological framework to alleviate the cosmological coincidence problem in the context of holographic dark energy. Some properties of the evolution which are relevant to cosmological parameters are also discussed.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-09-27
摘要: We construct the non-canonical kinetic term of a k-essence field directly from the effective equation of state function wk(z), which describes the properties of the dark energy.Adopting the usual parametrizations of equation of state we numerically reproduce the shape of the non-canonical kinetic term and discuss some features of the constructed form of k-essence.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-09-27
摘要: We investigate observational constraints on the variable Chaplygin gas model from the gold sample of type Ia supernova data and the recent measurements of the X-ray gas mass fractions in galaxy clusters. Combining these databases, we obtain a tight constraint on the two model parameters. Our results indicate that the original Chaplygin gas model is ruled out by the data at 99.7% confidence level.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-09-27
摘要: We consider a new generalized Chaplygin gas model that includes the original Chaplygin gas model as a special case. In such a model the generalized Chaplygin gas evolves as from dust to quiessence or phantom. We show that the background evolution for the model is equivalent to that for a coupled dark energy model with dark matter. The constraints from the current type Ia supernova data favour a phantom-like Chaplygin gas model.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-09-27
摘要: We develop a theoretical method of constructing the quintessence potential directly from the effective equation of state function w(z), which describes the properties of the dark energy. We apply our method to four parametrizations of equation of state parameter and discuss the general features of the resulting potentials. In particular, it is shown that the constructed quintessence potentials are all in the form of a runaway type.