双曲线型结点组上的插值

本文讨论了R~2上的弧线型结点组之一:双曲线型结点组上插值的适定性问题。     

抛物线型结点组上的插值

本文讨论了R~2上的弧线型结点组之一:抛物线型结点组插值的适定性     

仪器设备安放姿态对二级碎片毁伤指标的影响

借助碎片云粒子对靶板的毁伤程度与粒子的速度成正比,与靶板的厚度成反比的理论和实验结果,提出一种用于评价航天器内部电子仪器设备遭受二次碎片粒子撞击毁伤程度的毁伤指标.针对六面体外壳的仪器设备,提出两种在航天器内部的安放姿态.通过计算这两种姿态毁伤指标的最大值,并与两个面与航天器速度垂直的安放姿态毁伤指标的最大值进行了比较,得到了当碎片粒子速度不超过航天器速度2倍时两种安放姿态毁伤指标至少分别降低9.76%和14.09%的结论.采用这两种安放姿态,既不改变仪器设备的设计,也不增加重量和体积,就能达到增强仪器设备防护性能的目的,对提高航天器在碎片环境中的生存能力具有重要意义.     

密度和刚度线性变化对非均匀地壳层中扭转表面波传播的影响

研究了覆盖在非均匀半无限空间上的非均匀地壳层中,扭转表面波传播的可能性.地壳层的非均匀性随着厚度线性变化,非均匀半无限空间的非均匀性表现为3种类型,即指数型、二次型和双曲型.采用封闭形式,可以分别推导出上述3种类型非均匀性的色散方程.对于覆盖在半空间上的同一地壳层,色散方程与经典案例的方程一致.研究发现,随着非均匀地壳层中密度线性变化的非均匀参数的增大,相速度减小,而由刚度引起的非均匀因素对相速度的影响相反.     

竖线型结点组上的插值及向高维情形的推广

本文讨论了Ｒ＾２中竖线型结点组插值的适定性，得到了相应的插值多项式，并将这些结果推广到Ｒ＾ｓ（ｓ〉２）的情形。     

多孔弹性层的刚性边界对扭转表面波传播的影响

根据介质的力学性能,正如Cowin及Nunziato一样,导出多孔弹性层覆盖在多孔弹性半空间上时,研究其刚性边界对扭转表面波传播的影响.导出了速度方程并对其结果进行了讨论.发现介质中可能存在两类扭转表面波阵面,而Dey等(Tamkang Journal of Science and Engineering,2003,6(4):241-249.)给出的没有刚性边界面时,存在3类扭转表面波阵面.研究还揭示,多孔弹性层中Love波也可能随同扭转表面波一起存在.值得注意的是,刚性边界面多孔弹性层中Love波的相速度,不同于自由边界面多孔弹性层中的相速度.实际观察到扭转波的色散性,以及速度随着振荡频率的增大而减小.     

2型糖尿病患者尿液的代谢组学研究

目的 从代谢组学角度分析并寻找2型糖尿病（T2DM）患者可能的代谢标记物。方法 选取30例初诊、或有糖尿病史经药物治疗控制不理想且无并发症的T2DM 患者,另选取30例性别、年龄匹配的健康者为正常对照。收集清晨空腹中段尿,以气相色谱- 质谱联用（GC-MS）技术对尿液样本进行代谢图谱分析,正交偏最小二乘法判别研究尿液内源性化合物在两组间的差异。结果 T2DM 组和正常对照组尿液代谢谱明显分离。与正常对照组比较,T2DM 组尿液2,3,4- 三羟基丁酸、肌醇、D- 葡萄糖、D- 葡萄糖酸及尿素含量升高（P＜0.05 或0.01）,马尿酸含量减少（P＜0.01）。结论 代谢组学检查提示T2DM 患者尿液中代谢标志物为2,3,4- 三羟基丁酸、肌醇、马尿酸、D-葡萄糖、D- 葡萄糖酸及尿素,观察这些标志物含量的变化有助于T2DM 的临床诊断及发病机制研究。     

不规则界面对扭转表面波在初应力各向异性多孔弹性层中传播的影响

研究了扭转表面波在一个半无限非均匀半空间中的传播,半空间上覆盖着具有初始应力的各向异性多孔弹性层,弹性层的刚度和密度线性地变化,造成了界面的不规则性．半空间中界面的不规则性,用一个矩形形式表示．可以发现,扭转表面波在这样假定的介质中传播,得到了没有不规则性时的扭转表面波的速度方程．还可以发现,对于均匀半空间覆盖的层状介质,扭转表面波的速度与Love波的速度相一致．     

超声二维斑点追踪显像技术对2型糖尿病患者左室扭转运动的诊断价值

目的探讨超声二维斑点追踪显像(STI)技术对2型糖尿病患者左室心肌扭转运动的诊断价值.方法选取2型糖尿病患者67例,根据LVEF分为左心收缩功能正常组(A组,LVEF≥50%)33例、左心收缩功能减低组(B组,LVEF<50%)34例,另择同期体检健康者33例作为对照组.采用常规超声及STI技术对3组对象的左室扭转情况进行定量分析,并比较分析.结果 A组患者左室扭转角度峰值(Peaktw)、主动脉瓣关闭时间点扭转角度(AVCtw)、二尖瓣开放时间点扭转角度(MVOtw)较对照组显著升高(P<0.01);B组患者Peaktw、AVCtw、MVOtw较对照组及A组显著降低(P<0.01).与对照组比较,2型糖尿病患者等容解旋比例(IUR)、解旋率(UntwR)减低(P<0.05),而解旋减半时间(UHT)即明显延迟(P<0.01),与A组比较,B组患者等容解旋比例、解旋率降低(P<0.05),而解旋减半时间明显延迟(P<0.01).结论超声二维斑点追踪显像技术能够早期识别2型糖尿病患者的心功能异常变化.     

Fan型条件对图的匹配的影响(英文)

设G是顶点数为2n且至多含有2(n-c)个奇分支的简单图(1≤c≤n).若不存在G的两个距离为2的顶点,其度均小于c-1,则G的边独立数至少为c,除非G含一类明显的禁用导出子图.特别,我们给出了Fan(-1)-型图含有1-因子的充要条件.     

Total torsion of curves in three-dimensional manifolds

A classical result in differential geometry assures that the total torsion of a closed spherical curve in the three-dimensional space vanishes. Besides, if a surface is such that the total torsion vanishes for all closed curves, it is part of a sphere or a plane. Here we extend these results to closed curves in three dimensional Riemannian manifolds with constant curvature. We also extend an interesting companion for the total torsion theorem, which was proved for surfaces in by L. A. Santaló, and some results involving the total torsion of lines of curvature. Dedicated to Professor Manfredo P. do Carmo on his 80th birthday.     

A classification of torsion classes in abelian categories

We give a classification of torsion classes (or nullity classes) in an abelian category by forming a spectrum of equivalence classes of premonoform objects. This is parallel to Kanda’s classification of Serre subcategories.     

一组适合于带纵向裂纹柱体圣维南扭转的等参数元素

本文给出一组新的适合于带纵向裂纹柱体圣维南扭转的等参数元素,它们分别是八结点等参数元素、在裂纹尖端具有r-1/2奇异性的“1/4”八结点等参数元素及八结点过渡元素.利用这些元素,对含有径向纵裂纹的圆柱体进行了圣维南扭转计算.计算结果表明,本文给出的等参数元素有较高的精度、较好的收敛性及快的收敛速度,同时还具有程序简单、省机时等优点,所以特别适合于实际的工程计算.     

On the torsion in K_2 of a field

For a field F,let Gn(F) = {{a,Φn(a)} ∈ K2(F) | a,Φn(a) ∈ F*},where Φn(x) is the n-th cyclotomic polynomial.At first,by using Faltings' theorem on Mordell conjecture it is proved that if F is a number field and if n = 4,8,12 is a positive integer having a square factor then Gn(F) is not a subgroup of K2(F),and then by using the results of Manin,Grauert,Samuel and Li on Mordell conjecture theorem for function fields,a similar result is established for function fields over an algebraically closed field.     

非线性模型中VaR估测的正态性改进

VaR风险测度技术已经被学界和业界广泛使用,但其局限性也是显而易见的,国内外学者对其进行了一系列的改进.由线性模型扩展为非线性模型以及由正态假定转换到非正态性均源于风险测度的精确化.探讨依数据特征改进和扩展VaR估测方法,使用Johnson转换方法与Cornish-Fisher扩展方法这两种正态性改进方法改善VaR估值,一方面利用正态假定成熟理论结果简化VaR估测方法的推演,另一方面从实证分析角度论证了正态性改进方法在VaR估测中的准确性与有效性.     

Dynamics of droplets in an agitated dispersion with multiple breakage. Part I: formulation of the model and physical consistency

In (Proc. Symp. Lectures Appl. Math. 2000; 123–141) a new model for the evolution of a system of droplets dispersed in an agitated liquid was presented, with the inclusion of the so‐called volume scattering effect (a combination of coalescence and breakage). In that paper droplets breakage was considered to be binary, in order to simplify exposition. Here we remove that limitation, investigating the effect of each breakage mode and of scattering with multiple exits. We also allow the breakage kernel, at each mode, to become singular when droplets approach their finite maximum admissible size. Copyright © 2004 John Wiley & Sons, Ltd.     

Geometric representation of detachment conditions in systems with unilateral constraint

Mechanical systems with unilateral constraints that can be represented in the contact mode on the phase plane are considered. On the phase plane we construct domains that satisfy the following conditions 1) a detachment from the constraint is impossible; 2) the sign of the constraint reaction corresponds to its unilateral character. These conditions are equivalent for an ideal constraint [1, 2], but they can differ in the presence of friction [3]. Trajectories without detachments belong to intersections of these domains. A circular disc moving on a horizontal support with viscous friction and a disc with the sharp edge moving on an icy surface [4, 5] are considered as examples. Usually for the control of contact conservation one uses only the second condition from above, which can lead to invalid qualitative conclusions.      

Hysteresis in discrete systems of possibly interacting elements with a double-well energy

Summary We study in this paper the hysteretic behavior of a discrete system constituted by a finite number of elements (snap-springs) whose energy has two parabolic wells. The guideline idea is that, in many circumstances, hysteresis can be due to the presence of relative minimizers of a potential (metastable states) in which the system might get locked during its quasistatic evolution. A careful investigation is thus carried out of the relative minimizers of the total energy of our system of snap-springs under imposed total displacement, and of the barriers separating them. This is done both in the case of noninteracting elements and in the case in which some interaction is present that gives rise in the energy to an extra coherence term of special form. The results allow discussion of various hysteretic phenomena, also in the presence of vibrational motion of the elements. This study of a simple but suggestive discrete system will hopefully prove itself of help in understanding the implications regarding hysteresis of certain continuum theories recently proposed to model phase transitions in the solid state, in which the energy density is assumed, as here, to be biparabolic, and in which the coherence energy term we adopt arises in a natural way when equilibria involving mixtures of kinematically noncoherent phases are considered. In these cases the optimal microstructures are known to be layered, and physically this gives a good basis to our discrete calculation.     

Dynamics of droplets in an agitated dispersion with multiple breakage. Part II: uniqueness and global existence

In Part I (see Math. Methods Appl. Sci.) a new model for the evolution of a system of droplets dispersed in an agitated liquid was presented. Our aim was to extend a previous version (see Proceedings of the Symposium Organized by the Sonderforschungsbereich 438 on the Occasion of Karl‐Heinz Hoffman's 60th Birthday, Lectures in Applied Mathematics, Springer: Berlin, 2000; 123–141) in order to describe the influence of each breakage mode. Here we complete the mathematical analysis to ensure the well posedness (in the sense of Hadamard) of the Cauchy problem for the main evolution equation. Copyright © 2005 John Wiley & Sons, Ltd.     

On a model of viscoelastic rod in unilateral contact with a rigid wall

^** Corresponding author. Email: atanackovic{at}uns.ns.ac.yu We study translatory motion of a body to which a viscoelasticrod with the constitutive equation with fractional derivativesis attached. The body with a rod impacts against a rigid wall.It is shown that the problem is described with a coupled systemof differential equations having integer and fractional derivativeshaving the form x⁽²⁾ = –f; f + af⁽⁾ = x + bx⁽⁾, x(0) =0, x⁽¹⁾(0) = 1. The unique solvability in S'₊ is proved andinterpretation of solutions is given. Also, some a priori estimatesof the solution are given. In particular, we showed that restrictionson coefficients that follow from the second law of thermodynamicsimply that the velocity after the impact is smaller than thevelocity before the impact.