An experimental and statistical study of the behavior of the vibration field in two coupled lightweight wooden joist floors

The aim of this study was to evaluate the vibration level attenuation of a common wooden floor structure and to present the results together with the statistical precision of the evaluation. Linear regression was used to determine the attenuation rate in the two main directions of the floor structure. The probability for the attenuation rate to be zero was calculated. The attenuation rate was found to be high in the direction perpendicular to the beams with a probability to be zero lower than 0.001. In the direction parallel to the beams the attenuation rate was found to be close to zero.     

Numbers,scale and symbols: the public understanding of nanotechnology

Nanotechnology will be an increasing part of the everyday lives of most people in the world. There is a general recognition that few people understand the implications of the technology, the technology itself or even the definition of the word. This lack of understanding stems from a lack of knowledge about science in general but more specifically difficulty in grasping the size scale and symbolism of nanotechnology. A potential key to informing the general public is establishing the ability to comprehend the scale of nanotechnology. Transitioning from the macro to the nanoscale seems to require an ability to comprehend scales of one-billion. Scaling is a skill not common in most individuals and tests of their ability to extrapolate size based upon scaling a common object demonstrates that most individuals cannot scale to the extent needed to make the transition to nanoscale. Symbolism is another important vehicle to providing the general public with a basis to understand the concepts of nanotechnology. With increasing age, individuals are able to draw representations of atomic scale objects, but these tend to be iconic and the different representations not easily translated. Ball and stick models are most recognized by the public, which provides an opportunity to present not only useful symbolism but also a reference point for the atomic scale.     

Deflagration to detonation transition in fast flames and tracking with chemical explosive mode analysis

In the context of vapour cloud explosion, the flame acceleration process can lead to conditions promoting deflagration to detonation transition (DDT), potentially leading to increased damages in accidental scenarios. This study focuses on this phenomenon by performing simulations of detonation reinitiation for fast flames in the Chapman–Jouguet deflagration regime. It is obtained experimentally by the attenuation of an incident detonation by an array of obstacles. A primary objective of the paper is to demonstrate the ability of the numerical model to reproduce the major experimental trends, namely the variation of the reinitiation propensity for different initial pressures and blockage ratios (BRs). Chemical explosive mode analysis (CEMA) is also adapted to the context of this study, in order to identify locally the propagation regime and to provide insights on the reinitiation mechanism. An a priori validation of the CEMA methodology is first performed on relevant canonical one-dimensional configurations. Subsequently, ensembles of five realizations are computed at different initial pressures and BRs and compared to experimental data. They are shown to reproduce the major observed trends in terms of detonation reinitiation length with respect to the operating conditions, with significant variability from one realization to another. In addition, the reinitiation mechanism is also found to be consistent with experimental observations and a previous numerical study of the same configuration. The CEMA methodology adapted to this context is able to identify locally the different propagation regimes, and to track the highly reactive zones that coherently couple with transverse pressure perturbations, leading to the formation of a strongly reacting kernel which eventually triggers the detonation reinitiation.     

光纤传感实验设计

提出了一种适用于教学的光纤传感器实验研究系统。在实验过程中首先测定了LED光源的I-P特性曲线,接着对光纤的纤端光场分布进行测试,并通过实验得到的数据绘出光纤的纤端光场光强曲线,然后利用光纤传感实验仪对微位移用两种方式进行测量。根据现有的实验条件设计出适合于学生进行的基本实验。     

Flavor symmetry,EMC results and the spin content of the proton

The analysis of the EMC result on the quark contribution to the spin of the proton has caused considerable confusion and is unnecessarily complicated because of the completely unjustified and incorrect use of SU(3) flavor symmetry to provide input on the proton wave function from hyperon decays. There is no reliable method for obtaining information on the proton spin structure from data on the couplings of currents to hyperons. Interesting peculiar results obtained without use of SU(3) and hyperon data show the crucial point to be the apparent contradiction between the contribution of valence u quarks to the proton spin observed in the axial vector contribution to nucleon beta decay and the failure of this contribution to appear in the conventional quark-parton interpretation of the EMC results. When input from hyperon data is not used this paradox can be resolved without requiring the quark contribution to the proton spin to be near zero, but it can be large only if it is due to the strange quarks, with the nonstrange quark contribution opposite to the spin of the proton.     

Logarithmic correction to the probability of capture for dissipatively perturbed Hamiltonian systems

Hamiltonian systems are analyzed with a double homoclinic orbit connecting a saddle to itself. Competing centers exist. A small dissipative perturbation causes the stable and unstable manifolds of the saddle point to break apart. The stable manifolds of the saddle point are the boundaries of the basin of attraction for the competing attractors. With small dissipation, the boundaries of the basins of attraction are known to be tightly wound and spiral-like. Small changes in the initial condition can alter the equilibrium to which the solution is attracted. Near the unperturbed homoclinic orbit, the boundary of the basin of attraction consists of a large sequence of nearly homoclinic orbits surrounded by close approaches to the saddle point. The slow passage through an unperturbed homoclinic orbit (separatrix) is determined by the change in the value of the Hamiltonian from one saddle approach to the next. The probability of capture can be asymptotically approximated using this change in the Hamiltonian. The well-known leading-order change of the Hamiltonian from one saddle approach to the next is due to the effect of the perturbation on the homoclinic orbit. A logarithmic correction to this change of the Hamiltonian is shown to be due to the effect of the perturbation on the saddle point itself. It is shown that the probability of capture can be significantly altered from the well-known leading-order probability for Hamiltonian systems with double homoclinic orbits of the twisted type, an example of which is the Hamiltonian system corresponding to primary resonance. Numerical integration of the perturbed Hamiltonian system is used to verify the accuracy of the analytic formulas for the change in the Hamiltonian from one saddle approach to the next. (c) 1995 American Institute of Physics.     

Simulating coupled dynamics of a rigid-flexible multibody system and compressible fluid

As a subsequent work of previous studies of authors, a new parallel computation approach is proposed to simulate the coupled dynamics of a rigid-flexible multibody system and compressible fluid. In this approach, the smoothed particle hydrodynamics (SPH) method is used to model the compressible fluid, the natural coordinate formulation (NCF) and absolute nodal coordinate formulation (ANCF) are used to model the rigid and flexible bodies, respectively. In order to model the compressible fluid properly and efficiently via SPH method, three measures are taken as follows. The first is to use the Riemann solver to cope with the fluid compressibility, the second is to define virtual particles of SPH to model the dynamic interaction between the fluid and the multibody system, and the third is to impose the boundary conditions of periodical inflow and outflow to reduce the number of SPH particles involved in the computation process. Afterwards, a parallel computation strategy is proposed based on the graphics processing unit (GPU) to detect the neighboring SPH particles and to solve the dynamic equations of SPH particles in order to improve the computation efficiency. Meanwhile, the generalized-alpha algorithm is used to solve the dynamic equations of the multibody system. Finally, four case studies are given to validate the proposed parallel computation approach.     

Hysteresis in small arrays of interacting magnetic nanoparticles

The out-of-plane hysteresis loops of small arrays of magnetic nanoparticles, under the influence of an external field applied perpendicular to the array and the dipolar interaction are investigated. The particles are assumed to have a perpendicular anisotropy energy that tends to align the magnetic moments to be perpendicular to the array. The magnetization is found to exhibit a plateaux-and-jumps structure as the external field is swept up and down. These jumps are associated with jumps in the energy of the system, and correspond to transition from one configuration of the moment orientation to another. The energy of different configurations of the magnetic moments for a 3×3 array in the limit of weak dipolar interaction is analyzed, as a means to understand the hysteresis loop. These jumps are more pronounced in arrays of smaller sizes and when the dipolar interaction is weak. The configuration of magnetic moments at zero external field as the field is swept up and down is found to be highly sensitive to the dipolar interaction.     

Fermi-liquid theory of the electron-electron interaction effects in disordered metals

Influence of the arbitrary strong interaction between the electrons on the thermodynamic and transport properties of disordered metals is considered. The contributions of the interaction in the diffusion channel to all of the quantities are shown to depend on only one Fermi-liquid interaction constant (to take interaction in the cooper channel into account one has to include one constant more). It is found very convenient to divide all of the diffusion corrections on the parts which correspond to different values of the total spin of the electron and hole j:j = 0 and j = 1. It is the interaction with j=1 that leads to magnetic field dependence of the diffusion contributions. In the presence of spin-dependent scattering of the electron only the contribution related to the interaction with j=0 are important. These contributions to all of the quantities are universal, i.e. they do not depend on any interaction constant.     

Profile of Sira Ltd

Previously known as the British Scientific Instrument Research Association, Sira has continued, since its formation in 1918, to offer a service to both users and manufacturers of instruments that involves the application of new developments in optics to serve the needs of industry. The two operating divisions are able to provide multidisciplinary teams to work on a variety of different problems, including instrument evaluation and calibration, conference and course organisation, and the application of measurement science to solve new industrial problems. By way of example, two recent projects described include the use of the principle of thermoelasticity to display the distribution of stress on the surface of a structure subjected to periodic loading, and a TV-imaging technique that enables a surface flaw to be quantified objectively in relation to a standard.     

Controlling Surface Interactions with Grafted Polymers

The interactions between surfaces modified with grafted polymers is studied theoretically. The aim of this work is to find polymer surface modifications that will result in localized attractive interactions between the surfaces. The practical motivation of the work is to find means to control the distance between bilayers and solid supports in supported membranes. Two theoretical approaches are used, the analytical treatment of Alexander and a molecular theory. It is found that grafting each end of the polymer to each surface results in an interaction with a well defined minimum. The location of the minima is found to be very close to the thickness of the polymer layer when the chains are grafted to only one of the surfaces. The predictions of the analytical theory are in excellent agreement with the molecular approach in this case. It is found that increasing the surface coverage increases the strength of the interaction. However, increasing the polymer chain length at fixed surface coverage results in a decrease of the free energy cost associated with separating the surfaces from their optimal distance. For the cases in which grafting to both surfaces is not possible, the molecular theory is used to study the effect of functionalizing segments of the chain to achieve an attractive well. It is found that by functionalizing the free end-groups of the polymers with segments attracted to the membrane, the range of the attractive interaction is significantly larger than the thickness of the unperturbed layer. Functionlizing the middle segments of the chains results in a shorter range attraction but of the same strength as in the end-functionalized layers. The optimal polymer modification is found to be such that the functionlized groups are attracted to the bare surface but are not attracted to the grafting surface. The relevance of the results to the design of experimental surface modifiers is discussed.     

一种筒弹测试故障模拟器系统设计

为了测试人员能在平时使用模拟器系统进行测试训练。本文设计了一种筒弹测试故障模拟器系统,介绍了它的工作原理、系统的软硬件设计。该系统能对筒弹基本电气性能和测试接口进行模拟,在软件的控制下,实现模拟筒弹测试项目和模拟筒弹测试故障等功能,可以很好的完成筒弹测试设备测试人员对筒弹测试的操作训练。     

Lumped-element technique for the measurement of complex density.

A novel lumped-element technique is employed to measure the complex density of a gas in circular pores. The complex density expresses the geometry-dependent viscous coupling between the gas and the pore walls and is related to the thermoacoustic function f(mu), or equivalently, F(lambdaV). The acoustic impedance of a compliant region coupled to a pore (or pore-array) is measured and the impedance of the compliant region is subtracted to yield the impedance of the pore(s) alone, which is directly related to F(lambdaV). Pores of different lengths are measured in order to eliminate end effects. Working down to very low frequencies achieves a wide range of values for the ratio of the viscous penetration depth to the mean pore size. The results agree very well with analytical solutions for circular pores. The technique is also applied to two porous foam materials. Comparing the results to previous measurements of the complex compressibility, it is shown that two different shape factors (or equivalently, characteristic dimensions) are required to account for the data.     

Electrostatic potential at the nucleus of a neutral atom related to electronic correlation energies of atomic ions

The Hartree-Fock ground-state densities of neutral atoms can be utilized to approximate the electrostatic potential due to the electronic charge cloud at the nucleus. The correction due to electronic correlation is shown to involve the derivative of the correlation energy with respect to atomic number at constant number of electrons. Two theoretical expressions lead to quite similar partitioning of this derivative into the sum of two parts. Finally empirical estimates of the derivative are obtained and the small correction to the Hartree-Fock electrostatic potential at the nucleus is thereby found.     

Dissipative relativistic fluid dynamics for nuclear collisions

In the context of the Müller-Israel-Stewart second-order theory for dissipative fluids due to Grad, we analyze the effects of thermal conduction and viscosity in heavy ion collisions. We contrast the results to those of the first-order theory due to Eckart and to Landau and Lifshitz and to those of perfect (ideal) fluid due to Euler. We study the energy density and entropy density evolution of a pion gas produced in the heavy ion collisions. The truncated version of the second-order theory is used to find the dissipative quantities.     

正支共焦非稳腔的离焦像差特性

 正支共焦非稳腔在出光过程中易受环境扰动而造成腔长失调,易受热积累影响而使腔镜变形,从而使输出光束产生离焦像差和部分其它像差。为了实现对离焦像差的校正,针对不同的产生原因,提出了2种离焦像差特性分析方法：一为腔镜相对位置失调引起的离焦像差特性理论分析方法,它是另一种分析方法的基础;二为腔镜变形引起的等效腔长变化导致的离焦像差特性分析方法,它是实际激光器中的主要分析方法。得到了离焦像差与腔长的特性关系和离焦像差与腔镜变形量之间的特性关系。研究表明：腔长改变和腔镜变形对离焦像差的影响本质是一样的,都是改变了谐振腔的共焦点位置;腔长改变或腔镜矢高变化与离焦像差都成近似的线性关系。实验验证了离焦像差特性分析方法的有效性,最后指出离焦像差特性可作为激光器中离焦像差动态补偿的有效依据。     

Correlations in alpha-alpha scattering and semi-classical optical models

We show the equivalence of semi-classical solutions to optical model coupled-channel equations derived from Watson's form of the nucleus-nucleus multiple-scattering series to the Glauber multiple-scattering series. A second-order solution to the semi-classical coupled-channel elastic amplitude is shown to be nearly equivalent to a second-order optical-phase-shift approximation to the Glauber amplitude if the densities of all nuclear excited states are approximated by the ground-state density. Using the Jastrow method to model the two-body density we find an average excited-state density to be of negligible importance in the double-scattering region of alpha-alpha scattering.     

Superconducting energy gap anomalies in NbN films

Nine NbN films ranging in thickness from 0.02 to 0.03 μm were studied by measuring the temperature dependence from 1.5 K to over 20 K of the ultrasonic attenuation of 700 MHz surface acoustic waves. The resulting curves did not fit the predictions of BCS. When the curves were numerically inverted to show the temperature dependence that the superconducting energy gap would need to have to produce the observed attenuation, they were found to be nearly constant at a value less than half of the BCS value. An analysis prompted by the Anderson theories of 2-D localizations shows the attenuation per film thickness to be proportional to the logarithm of the thickness.     

Limit of hanger linearity in suspension footbridge dynamics: A new section model

The mechanical behaviour of suspension bridges is characterised by nonlinearities due to the main cables geometric effects and to the inability of the hangers to sustain compressive loads. The nonlinear effects due to hanger slackening are expected to increase in suspension footbridges due to lightweight decks, that is, low dead to live load ratio, and to shallow plate-girder decks with very low flexural and torsional stiffness. In this paper a new section model is proposed to study the limit of hanger linearity in lightweight suspension footbridges. The model is inspired to a four degrees-of-freedom model already proposed in the literature, but is expressed with a new formalism that allows some interesting properties to be outlined. Specifically, the expression of a particular frequency, herein called relative antiresonance frequency, as a function of the model generalised properties is derived: if the system is loaded with a harmonic force having that frequency, the linear behaviour of the hangers is assured for every value of the force amplitude. The proposed section model is applied to a footbridge benchmark subject to the pedestrian harmonic load and results are compared with those obtained through a nonlinear dynamic analysis on a 3D Finite Element model of the bridge.     

南海北部海域内波环境下声传播损失起伏统计特性

浅海内波会引起声传播能量随时间的起伏变化,进而影响水声设备的工作性能.本文利用2015年南海北部一次浅海声场起伏实验数据,对比分析了浅海线性内波和孤立子内波条件下的声传播损失统计特性.在孤立子内波条件下,声传播损失起伏明显加剧,可达11 dB,且分布明显展宽,相对于线性内波的环境,声传播损失起伏可增加5 dB.从简正波...