In-plane elastic stability of fixed parabolic shallow arches

The nonlinear behavior of fixed parabolic shallow arches subjected to a vertical uniform load is investigated to evaluate the in-plane buckling load.The virtual work principle method is used to establish the non-linear equilibrium and buckling equations.Analytical solutions for the non-linear in-plane symmetric snap-through and antisymmetric bifurcation buckling loads are obtained.Based on the least square method,an approximation for the symmetric buckling load of fixed parabolic arch is proposed to simplif...     

Q460角钢两端偏心受压构件稳定设计方法研究

基于Q460高强角钢两端偏心受压试验,给出了高强角钢截面残余应力分布和初始几何缺陷,并结合多种设计方法对试验结果进行了分析计算、讨论和比较,对高强角钢两端偏心受压构件整体稳定承载力进行了研究。结果表明,现行杆塔结构设计采用《美国输电铁塔设计导则》（ASCEIO-1997）、《架空送电线路杆塔结构设计技术规定》（DI/T5154-2002）和我国《钢结构设计规范》（GB50017-2003）进行设计是偏保守的。基于平行轴为准按轴心受压构件计算有效长细比,并选用a类截面柱子曲线,而提出实用设计公式,建议公式计算结果和试验结果吻合较好,该方法可供工程设计时参考。     

移动拟合法在煤层界面插值中的应用研究

为了在构建三维矿床模型过程中,形成最佳逼近的煤层界面模型,将移动拟合法引入到煤层界面插值中。根据煤层的赋存条件以及原始采样数据的分布特点提出了参数优化选择的有效方法及适用条件,并通过数学方法改善病态矩阵,使待估区域中的插值结果精度更高。以某矿的煤层界面数据为样本,通过交叉检验确定权函数,进行空间插值以及三维可视化,比较真实地反映了矿床的基本特征,为矿床地质模型的建立提供了有力的数据支撑。     

Einstein׳s Equations for Spin 2 Mass 0 from Noether׳s Converse Hilbertian Assertion

An overlap between the general relativist and particle physicist views of Einstein gravity is uncovered. Noether׳s 1918 paper developed Hilbert׳s and Klein׳s reflections on the conservation laws. Energy-momentum is just a term proportional to the field equations and a ‘curl’ term with identically zero divergence. Noether proved a converse “Hilbertian assertion”: such “improper” conservation laws imply a generally covariant action.Later and independently, particle physicists derived the nonlinear Einstein equations assuming the absence of negative-energy degrees of freedom (“ghosts”) for stability, along with universal coupling: all energy-momentum including gravity׳s serves as a source for gravity. Those assumptions (all but) imply (for 0 graviton mass) that the energy-momentum is only a term proportional to the field equations and a symmetric “curl,” which implies the coalescence of the flat background geometry and the gravitational potential into an effective curved geometry. The flat metric, though useful in Rosenfeld׳s stress-energy definition, disappears from the field equations. Thus the particle physics derivation uses a reinvented Noetherian converse Hilbertian assertion in Rosenfeld-tinged form.The Rosenfeld stress-energy is identically the canonical stress-energy plus a Belinfante curl and terms proportional to the field equations, so the flat metric is only a convenient mathematical trick without ontological commitment. Neither generalized relativity of motion, nor the identity of gravity and inertia, nor substantive general covariance is assumed. The more compelling criterion of lacking ghosts yields substantive general covariance as an output. Hence the particle physics derivation, though logically impressive, is neither as novel nor as ontologically laden as it has seemed.     

A model of enzymatic kinetics]

In this Note, we study a system of differential equations representing the kinetics of an enzymatic reaction. For a closed system, and in the domain where it has a biological significance, it is shown that: (i) there exists a unique equilibrium point, which is an asymptotically stable point; (ii) if several enzymes act on the same substrates, the equilibrium values of the substrates concentrations take their values within the range of the equilibrium values achieved with each of these enzymes, (iii) the kinetics of the reaction can be approached by a single first-order differential equation, which may be seen as a generalization of the Michaelis equation.     

Special cases,composition of causes,and the complexity of nature

It is often held by philosophers of science that special, idealized situations are prior to complex cases in several senses: equations for complex cases are derived from those for special cases by “composing” special case equations; behavior in complex cases is explained in terms of behavior in special cases; one learns the true nature of a property in the special case where it is allowed to work in isolation. In this paper, I argue that a strand of non-equilibrium thermodynamics which attempts to go beyond the limitations of classical non-equilibrium thermodynamics adheres to something that is the reverse of this picture. Thus, the legitimacy (or lack thereof) of this picture lies very near to the heart of foundational issues in non-equilibrium thermodynamics.     

Physical aspects of biophotons

By comparing the theoretically expected results of photon emission from a chaotic (thermal) field and those of an ordered (fully coherent) field with the actual experimental data, one finds ample indications for the hypothesis that 'biophotons' originate from a coherent field occurring within living tissues. A direct proof may be seen in the hyperbolic relaxation dynamics of spectral delayed luminescence under ergodic conditions. A possible mechanism has to be founded on Einstein's balance equation and, under stationary conditions, on energy conservation including a photochemical potential. It is shown that the considered equations deliver, besides the thermal equilibrium, a conditionally stable region far away from equilibrium, which can help to describe both 'biophoton emission' and biological regulation.     

Effects of selective dopamine D1 and D2 antagonists on male rat sexual behavior

The effects of selective dopamine (DA) D1 and D2 antagonists on male rat sexual behavior were investigated. The D1 antagonist (+)SCH-23390, 25-100 micrograms kg-1 s.c. -20 min, and the D2 antagonist raclopride, 0.1-1.6 mg kg-1 s.c., -20 min, decreased both the number of mounts and intromissions preceding ejaculation. No statistically significant effects in the time up to ejaculation or in the time up to the first intromission were noted, whereas both compounds produced a statistically significant increase in the post-ejaculatory interval. The effect can generally be characterized as psychomotor inhibition, and no evidence was obtained for a specific role of DA D1 or D2 receptors in the mediation of male rat sexual behavior.     

亚90nm沟道MOSFET亚阈值状态下二维电势和阈值电压的半解析模型

本文提出一个亚90nm沟道MOSFET在亚阈值状态下的二维电势和阈值电压的半解析模型．文章首先根据短沟道MOSFET在亚闽值状态下的物理模型提出定解问题,然后用特征函数将由氧化层和空间电荷区衔接条件所得到的超越方程组作正交展开,得到关于未知量的线性代数方程组．求出了氧化层和空间电荷区的二维电势、耗尽层厚度和阈值电压的表达式．该模型不需要适配参数,运算量小,避免了方程离散化,计算精度与数值解精度相同．文章给出了沟道长度为90nm以下MOSFET的电势分布、表面势、耗尽层厚度和阈值电压计算结果．计算值与二维数值模拟值高度吻合．     

螺旋钻采煤机钻头载荷的模拟研究

为了研究螺旋钻采煤机钻头的力学特征和动力学行为,通过截齿受力分析,给出了单个截齿上各阻力的计算方法.在此基础上建立了钻头三向载荷的数学模型,利用编制的计算机程序,模拟得到了在不同煤岩、不同结构参数下钻头的载荷曲线.结果表明,钻头载荷存在明显的波动,且载荷大小随煤岩硬度的增加而增加,随钻头直径的加大而增大；在钻头直径一定情况下,钻头的锥角越大,钻头的载荷越大.研究结果对于合理选择螺旋钻采煤机、正确地确定钻头的结构参数、改善螺旋钻采煤机的性能、提高钻采效率有重要的意义和参考价值.     

Bifurcation and chaos of the bladed overhang rotor system with squeeze film dampers

To study the nonlinear dynamic behavior of the bladed overhang rotor system with squeeze film damper (SFD),a blade-overhang rotor-SFD model is formulated using the lumped mass method and the Lagrange approach.The cavitated short bearing model is employed to describe the nonlinear oil force of the SFD.To reduce the scale of the nonlinear coupling system,a set of orthogonal transformations is employed to decouple the one nodal diameter equations of blades,which are coupled with the dynamical equations of the ...     

螺旋钻采煤机螺旋钻杆失稳条件研究

通过考虑动能和势能对螺旋钻杆屈曲的影响,运用能量法研究了螺旋钻杆最大转速与螺旋屈曲时临界轴向力间的关系,建立了螺旋钻杆和轴向临界力间的数学模型。研究表明：螺旋钻杆的失稳条件符合实际,对螺旋钻采煤机设计具有十分重要的指导意义。     

Effects of the light-dark cycle and scheduled feeding on behavioral and reproductive rhythms of the cyprinodont fish, Medaka, Oryzias latipes

Medaka were maintained on a 16:8 light-dark cycle and fed once daily on one of 5 different feeding schedules. The daily rhythm of agonistic behavior rapidly entrained to the scheduled feeding time and maintained this entrainment during a 3-day starvation period. In contrast the daily rhythms of egg laying and courtship stayed entrained to the L:D cycle regardless of the feeding schedule. Thus, temporal integration of this fish with its daily environment can involve multistimuli which concurrently and differentially entrain externally expressed circadian systems.     

Physical aspects of biophotons

Summary By comparing the theoretically expected results of photon emission from a chaotic (thermal) field and those of an ordered (fully coherent) field with the actual experimental data, one finds ample indications for the hypothesis that biophotons originate from a coherent field occurring within living tissues. A direct proof may be seen in the hyperbolic relaxation dynamics of spectral delayed luminescence under ergodic conditions.A possible mechanism has to be founded on Einstein's balance equation and, under stationary conditions, on energy conservation including a photochemical potential. It is shown that the considered equations deliver, besides the thermal equilibrium, a conditionally stable region far away from equilibrium, which can help to describe both biophoton emission and biological regulation.     

基于共形几何代数的3D医学图像配准

随着医学图像处理技术的发展,3D／3D配准益受重视,尤其是在外科手术导航等医学应用中．学者们提出了各种3D／3D配准方法,但大多方法是采用传统代数方法进行配准,配准精度和效率都存在问题．本文利用非经典数学——共形几何代数重建了3D医学图像的位置关系约柬问题,分析了医学图像的共形几何变换,构造了新的3D医学图像配准相似测度,基于此提出了新的3D医学图像配准算法,用于CT和MR图像的3D配准．新算法中,以骨骼轮廓作为配准的基础点集,在骨骼轮廓的基础上采用共形几何代数构造共形几何体,接着采用新的3D医学图像配准相似测度进行三维数据的直接配准．实验表明新算法实现了三维数据的直接对齐,能较好地定位组织器官的三维位置．可以直观地体现配准结果．     

Oscillations of phosphofructokinase in a compartmentalized system

The analysis of an allosteric model for phosphofructokinase, exhibiting an inhibition by excess substrate (ATP) shows the possibility of sustained self-oscillations. This model is described by a system of, two ordinary differential equations taking into account the coupling between metabolites diffusion (Fick's first law) and enzyme reaction. The different behavior types of the system have been studied as a function of two main parameters, rho (ration between respective permeabilities for ATP and F6P) and sigma (valuation of the diffusional constraints importance). The research for instability conditions has been carried out by normal mode analysis.     

Satellite DNA (II) from sea urchin (Lytechinus variegatus) sperm

Summary When DNA isolated from freshly collected sperm of sea urchin (Lytechinus variegatus) is centrifuged to equilibrium in CsCl, 2 heavy satellite bands appear beside the main band DNA. Satellite DNA (II) appears in between the main band DNA (=1.695 g/cm³) and the rDNA satellite (=1.722 g/cm³). Satellite DNA (II) has a buoyant density 1.710 g/cm³, corresponding to 50% GC content. It is speculated that the satellite DNA (II), which appears to be of high mol.wt, might contain the sequences complementary to histone mRNA.Acknowledgment. This work was carried out in the laboratory of Dr D. W. Stafford, Department of Zoology, University of North Carolina, Chapel Hill, N.C., USA. I thank him for his help and cooperation.     

Microscale screening systems for 3D cellular microenvironments: platforms,advances, and challenges

The increasing interest in studying cells using more in vivo-like three-dimensional (3D) microenvironments has created a need for advanced 3D screening platforms with enhanced functionalities and increased throughput. 3D screening platforms that better mimic in vivo microenvironments with enhanced throughput would provide more in-depth understanding of the complexity and heterogeneity of microenvironments. The platforms would also better predict the toxicity and efficacy of potential drugs in physiologically relevant conditions. Traditional 3D culture models (e.g., spinner flasks, gyratory rotation devices, non-adhesive surfaces, polymers) were developed to create 3D multicellular structures. However, these traditional systems require large volumes of reagents and cells, and are not compatible with high-throughput screening (HTS) systems. Microscale technology offers the miniaturization of 3D cultures and allows efficient screening of various conditions. This review will discuss the development, most influential works, and current advantages and challenges of microscale culture systems for screening cells in 3D microenvironments.     

Membrane fusion: the process and its energy suppliers

Membrane fusion constitutes a pivotal process in eukaryotic cell physiology. Both specialized proteins and membrane lipids play key roles in fusion. Here, our current understanding of the mechanism of membrane fusion is reviewed. The focus is on the relatively simple and well-understood proteinaceous fusion machinery of enveloped viruses and the physical properties of lipids that appear to be of great relevance for fusion progression. Recent observations suggest that viral fusion proteins use packed conformational energy and bilayer-destabilizing domains to (i) bring participating membranes into intimate contact, (ii) merge proximal lipid monolayers through highly curved stalk/hemifusion intermediates, and (iii) generate a lipid-containing fusion pore, thereby terminating the fusion process. Received 4 January 2002; received after revision 3 April 2002; accepted 5 April 2002     

基于监测信号特征的批量钻削工序质量研究

针对批量钻削工序质量的快速监测和分析问题,利用批量钻削加工过程主轴功率信号和声信号的时域统计特征和频域能量特征构造了批量工序钻削过程特征矩阵。应用K均值聚类技术从时域统计、频域能量和时频域综合特征三个角度依据钻孔本身的质量特征对钻孔进行分类,分析批量工序过程特征分布状况,间接反映批量钻削工序质量。对比人工质量检测结果,分析批量钻削过程监控信号时频域特征矩阵聚类纯净度,结果显示其工序质量分布状况检测准确率高达94.19%