Magnet coil tests with multiple soldered niobium-tin filament conductors

Flat conductors with Nb₃Sn/Nb filaments, prepared by the solid state diffusion process were investigated for degradation after bending and tensile loading. Proportionality was found between the critical bending diameter and the distance of the filaments from the neutral zone. Four conductors with rectangular cross-section were stabilized by soldering in parallel to copper foil; coils were then wound and tested in the magnetic field of a niobium-titanium magnet. Measurement of the quench currents confirmed that the conductors were not damaged by the manipulations required. The 5% decrease in currentcarrying capacity compared with short sample measurements is ascribed to the more unfavourable cooling conditions in the coil. Individual conductors with a larger number of filaments now available for further tests are reported.     

平行双箱梁桥面颤振稳定性试验研究

在建的佛山平胜大桥和设计中的青岛海湾桥红岛航道桥方案分别是具有平行双箱梁的独塔自锚式悬索桥和独塔斜拉桥，对两座桥梁的单、双桥面弹性悬挂节段模型风洞试验结果表明双桥面之间存在不可忽略的气动干扰效应，从而使桥梁在单、双桥面状态时的颤振临界风速不同。以平胜桥主梁节段模型为基础的一系列风洞试验研究表明，平行双箱梁桥面主梁的颤振临界风速与两桥面之间的距离有关系，双桥面的颤振临界风速随两桥面之间距离D值的增大而增加。与单桥面状态相比较，平行双箱梁桥面的颤振导数也有相应的变化，且这种变化和两桥面之间的距离D也有关系。     

A 3-D Numerical Model to Estimate the Critical Current in MgB<Subscript>2</Subscript> Wire and Cable with Twisted Structure

Due to the low material cost, high critical transition temperature and high-current-carrying capacity, MgB₂ round wire with twisted filaments has great potential for applications in engineering. Therefore, it is important to estimate their critical current for optimizing and realizing high-powered wire and cable. A 3-D model is presented to calculate the critical current of wire and cable with twisted filaments. The critical current is estimated based on the Biot-Savart law and self-consistent model. A comparison between 2-D and 3-D models is performed for the wire. We consider the effect of twist pitch on the critical current. Moreover, the critical current of 6-around-1 cable with different twist pitches is analyzed and discussed using the 3-D model. It can be found that twist pitch of filaments plays an important role on the critical current. The model and method may also be useful for other superconducting wires and cables.     

两种含水炸药动压下减敏作用的实验研究

用实验方法对两种含水炸药—水胶炸药和珍珠岩敏化的乳化炸药动压下的减敏作用进行了研究。为了更全面深入地研究这问题,提出了临界压死距离和临界距离两个概念。研究表明,含水炸药的减敏作用与药包间距和延期时差关系很大。水胶炸药的临界压死距离大于乳化炸药,而它们的临界距离相当,这表明两种炸药发生减敏的难易程度相近,但是乳化炸药的抗压死能力比水胶炸药大。采用5段延期电雷管引爆时两种含水炸药的减敏作用比采用2段延期电雷管引爆严重些。     

Quasi-achromatic laser Doppler anemometry systems based on a diffractive beam splitter

We propose a new beam-splitter system that makes it possible to use nonstabilized laser diodes for laser Doppler anemometry (LDA) systems by making the system wavelength independent. The beam splitter consists of two linear diffraction gratings that produce two parallel beams with a beam spacing that is wavelength dependent. This ensures passive wavelength compensation for the fringe spacing in the measurement volume. One can choose the distance between the two parallel beams by changing the distance between the two gratings, whereas the distance to the measurement volume can be designed by choice of a condensing lens with the proper focal length. This means that the system can be designed to have a desired fringe spacing in the measurement volume. The gratings are implemented as surface-relief holograms in photoresist, which makes it possible to mass produce the beam-splitter system at low cost through replication of the structure. The method for passive wavelength compensation for the fringe spacing is demonstrated both theoretically and experimentally.     

Epidemic cycles driven by host behaviour

Host immunity and demographics (the recruitment of susceptibles via birthrate) have been demonstrated to be a key determinant of the periodicity of measles, pertussis and dengue epidemics. However, not all epidemic cycles are from pathogens inducing sterilizing immunity or are driven by demographics. Many sexually transmitted infections are driven by sexual behaviour. We present a mathematical model of disease transmission where individuals can disconnect and reconnect depending on the infectious status of their contacts. We fit the model to historic syphilis (Treponema pallidum) and gonorrhea (Neisseria gonorrhoeae) incidence in the USA and explore potential intervention strategies against syphilis. We find that cycles in syphilis incidence can be driven solely by changing sexual behaviour in structured populations. Our model also explains the lack of similar cycles in gonorrhea incidence even if the two infections share the same propagation pathways. Our model similarly illustrates how sudden epidemic outbreaks can occur on time scales smaller than the characteristic demographic time scale of the population and that weaker infections can lead to more violent outbreaks. Behaviour also appears to be critical for control strategies as we found a bigger sensitivity to behavioural interventions than antibiotic treatment. Thus, behavioural interventions may play a larger role than previously thought, especially in the face of antibiotic resistance and low intervention efficacies.     

Fatigue life prediction of small notched Ti-6Al-4V specimens using critical distance

This study investigated the method of estimating the fatigue strength of small notched Ti-6Al-4V specimen using the theory of critical distance that employs the stress distribution in the vicinity of the notch root. Circumferential-notched round-bar fatigue tests were conducted to quantify the effects of notch radius and notch depth on fatigue strength. The fatigue tests show that the larger notch radius increases the fatigue strength and the greater notch depth decreases the fatigue strength. The theory of critical distance assumes that fatigue damage can be correctly estimated only if the entire stress field damaging the fatigue fracture process zone is taken into account. Critical distance stress is defined as the average stress within the critical distance from notch root. The region from the notch root to the critical distance corresponds to the fatigue fracture process zone for crack initiation. It has been found that a good correlation exists between the critical distance stress and crack initiation life of small notched specimens if the critical distance is calibrated by the two notched fatigue failure curves of different notch root radii. The calibrated critical distances did not vary clearly over a wide range of fatigue failure cycles from medium-cycle low-cycle fatigue regime to high-cycle fatigue regime and have an almost constant value. This critical distance corresponds to the size of crystallographic facet at the fatigue crack initiation site for the wide range of fatigue cycles.     

Vortex Reconnection and Acoustic Emission by the Numerical Analysis of the Gross-Pitaevskii Equation

Reconnection of quantized vortices and concurrent acoustic emission are studied numerically by analyzing the Gross-Pitaevskii equation. Although vortex reconnection was studied earlier by Koplik and Levine, the present work first investigates in more detail how the singular vortex cores reconnect. Second, acoustic emission, i.e., the emission of the density waves of the condensate, is studied when two vortices annihilate or reconnect. The local drastic change of the condensate density is found to work as an acoustic source to emit the density waves. This phenomenon may be related to the vortex tangle decay observed at mK temperatures and the eddy viscosity which is thought to be an intrinsic dissipative mechanism in a vortex tangle.     

Numerical analysis of the cutting interaction between indenters acting on disordered materials

In this paper, an attempt is made to find some general relations for the microcutting process in brittle or quasi-brittle materials, under different hypotheses of microscopic failure behavior. Fracture beneath the indenters and sudden chip formation are the main dissipation mechanisms taken into consideration. Fracture patterns in more homogeneous brittle solids are obtained by the Finite Element Method in the framework of Linear Elastic Fracture Mechanics (LEFM). On the other hand, the quasi-brittle response due to microstructural heterogeneities is taken into account by Lattice Model simulations. The analysis is not limited to the more common study of a single indenter. When two indenters are acting in parallel, their mutual distance plays an important role. If the indenters are very close, they behave like a unique larger indenter, whereas if the distance is relatively large, their mechanical interaction vanishes. In addition, when the distance is approximately three to four times their dimension, the mechanism of chipping (with formation of secondary chip between the two parallel grooves) can take place, improving the ratio of removed volume to spent energy and then the demolition ability of the two indenters. Some comparisons are proposed between the presented approach and more sophisticated and computationally demanding models from the literature, as well as with experimental data. The analysis should provide useful hints for the optimal design of super-abrasive tools.     

Bundle strength of polyester fibers determined using a series-parallel combination model

This paper describes the bundle strengths of PET filaments from a statistical point of view. A bundle is an arrangement of a number of filaments. We applied the weakest-link theory and probabilistic load-sharing rules to estimate the bundle strength from the breaking strength data of PET filaments. We analyzed the breaking behavior of 12 filament bundles according to their length and number of filaments and compared the breaking behavior of a prepared specimen yarn with that of a commercial PET filament yarn. The breaking strength of the PET filaments, which we tested using a MANTIS® tester, was compared with that of the actual yarn. We compared the actual tested values obtained by INSTRON® with the expected values, which we calculated from the MANTIS® data by using Peirce's theory and Knox's hazard function. The key effects that determine the actual random breakage behavior of a bundle include not only the load-sharing rules in the constituent filaments but also the slippage and friction between adjacent filaments, the appearance of which we distinguished especially in the bundle consisting of a large number of filaments and in small-denier filaments. The PET filaments were better approximated when using the Peirce's weakest-link theory than they were by Knox's hazard function. In a series-parallel model, we found that the number of parallel filaments and their load-sharing behavior had larger effects on the bundle strength than did the weakest-link effects of continuous elements.     

Development of Bi(2223) Multifilamentary Tapes with Low ac Losses

A significant reduction of ac losses in twisted Bi(2223) multifilamentary tapes with Ag sheaths has been achieved by using oxide (BaZrO₃ and SrZrO₃) barriers between filaments. These barriers have two important effects: they increase the transverse resistivity, which suppresses induced coupling currents, and they reduce filament bridging, which in pure Ag sheath tapes largely cancels the beneficial effect of filament twisting. The decoupling can be gauged by the frequency at which loss shows a maximum in a low-amplitude ac field applied perpendicular to the tape. So far, the frequency of the loss maximum, f _m, in Ag-sheathed tapes has been enhanced from 5 Hz (untwisted) to 82 Hz (11 mm in twist pitch length). Different ways to introduce oxide barriers in tapes with 19–95 filaments are presented. The critical current density in the filaments varied between 10,000 and 20,000 A/cm². Ac loss measurements as well as the electrical and mechanical characterization are discussed in detail. The variation of the critical current density with bending strain is shown to be similar to that of tapes without barriers.     

Basic solutions of two parallel mode-I cracks or four parallel mode-I cracks in the piezoelectric materials

In this paper, the stress and the electric intensity factors of two parallel mode-I cracks or four parallel mode-I cracks in the piezoelectric materials were examined by means of the Schmidt method for the permeable electric boundary conditions. The present problem can be solved by using the Fourier transform and the technique of dual integral equation, in which the unknown variables are the jumps of displacements across the crack surfaces, not the dislocation density functions. To solve the dual integral equations, the displacement jumps are directly expanded in a series of Jacobi polynomials. Finally, the effects of the distance between two parallel cracks and the distance between two collinear cracks on the stress and the electric intensity factors in the piezoelectric materials are analyzed. These results can be used for the strength evaluation of the piezoelectric materials with multi-cracks.     

Parallel phase-shifting interferometry based on Michelson-like architecture

In this paper, we present a new scheme for parallel phase-shifting interferometry that employs a Michelson-like architecture and a simple polarization unit to generate two phase-shifting interferograms with phase shift of π/2 at a single camera exposure. The parallel phase-shifting unit is built with simple optical components, and the distance between the parallel interferograms can be adjusted conveniently. Phase reconstruction is performed by using an algorithm developed for two-step phase-shifting interferometry. The practicability of the proposed configuration and the reconstruction method is demonstrated by experiments.     

爆炸载荷作用下临界震塌爆距公式研究

坑道震塌破坏机制复杂,是工程中亟待解决的难题之一。为了得到便于工程应用的临界震塌爆距计算公式以及影响临界震塌爆距的主要因素,在常用经验公式的基础上,通过拟合爆距与洞跨比影响系数,将经验公式显化,推导的修正公式不需要反复迭代试算,使用方便。利用ANSYS/LS-DYNA有限元分析软件对坑道正上方装药爆炸进行数值模拟,得出临界震塌爆距,其结果与修正公式相比较,表明修正公式与模拟结果吻合较好,可用于临界震塌爆距的计算。数值模拟临界震塌爆距随洞室跨度的变化,结果表明:洞室跨度越大,临界震塌爆距越大,且趋于某一极限值;洞室跨度小于15 m时临界震塌爆距随洞跨的增大增幅较快。     

Microstructure and superconducting current ofIn situ Nb3Sn superconducting wire

The diffusion of elemental tin and the morphological change of niobium filaments inin situ Nb₃Sn superconducting composite wires and their influences on critical current were studied. When the amount of tin plated on the samples was high, the diffusion of elemental tin was enhanced. The critical current increased with increasing tin concentration but the increase became sluggish at high tin contents. The niobium filaments were initially ribbon-like but they became rod-like and then sausage-like after annealing treatment. Such a morphological change acted to reduce superconducting current capacity. When the amount of niobium was low, the filaments spheroidized by high-temperature and long-term annealing, resulting in serious reduction in critical current and upper critical magnetic field. High niobium contents led to high critical current and high upper critical magnetic field due to retainment of continuity of the filaments after annealing, effective proximity effect and a high amount of Nb₃Sn formed in comparison with low niobium content amount. The titanium addition raised the upper critical magnetic field, resulting in improvement in critical current at high magnetic fields.     

Simulating operator learning during production ramp-up in parallel vs. serial flow production

The aim of this research is to demonstrate how human learning models can be integrated into discrete event simulation to examine ramp-up time differences between serial and parallel flow production strategies. The experimental model examined three levels of learning rate and minimum cycle times. Results show that while the parallel flow system had longer ramp-up times than serial flow systems, they also had higher maximum throughput capacity. As a result, the parallel flow system frequently outperformed lines within the first weeks of operation. There is a critical lack of empirical evidence or methods that would allow designers to accurately determine what the critical learning paramters might be in their specific operations, and further research is needed to create predictive tools in this important area.     

Mechanical Behaviours in Bi2223/Ag/Ag Alloy Composite Tape with Different Volume Fractions

Bi₂Cr₂Ca₂Cu₃O _x (Bi2223) composite tapes consisting of Bi2223 filaments, metal Ag and Ag alloy are usually exposed to a high magnetic field. The mechanical behaviour of composites is determined by the distribution and content of Bi2223 filaments in a magnetic field. Several Bi2223 composite tapes have different volume fractions of Bi2223 filaments, and the volume fraction is of fundamental importance in the determination of mechanical behaviour. In this paper, we present mechanical response to understand the effect of volume fraction of Bi2223 filaments. The critical current density is determined with consideration of the self field effect firstly. Then, the results of effective elastic moduli and mechanical stresses are presented based on the micromechanics approach. The mechanical response depends not only on the material properties but also on the Lorentz force. It is concluded from the computational results that the reduction of volume fraction of filaments can increase the mechanical stability, while the critical current density is decreased. Thus, it is necessary to consider both the mechanical limitation and requirement of the critical current of tape.     

Measurement of profiles along a circle on two flat surfaces by use of a Fizeau interferometer with no standard

A method for measuring profiles along a circle on a flat surface with no standard is described. For the measurement, two unknown surfaces are placed almost parallel, and the distance between them is measured many times along a circle by rotation of one of the surfaces. Profiles of the two surfaces can be determined from the distance data. In this study the measuring method is explained: The space between two surfaces measured with a Fizeau interferometer. Four measuring experiments are carried out for determining the profile of a precision-grade half-mirror; in each experiment a different ordinary mirror with unknown profile is used as the second mirror. Profiles of the precise mirrors obtained by these experiments agree closely, with deviations of approximately 2 nm. A similar experiment with many concentric circles was carried out with a precise half-mirror and another precise mirror. Although the profiles of many concentric circles were independent of one another, the result shows that the high-frequency component of a whole plane can be estimated.     

Simulations of Temperature Field in HFCVD Diamond Films over Large Area

A three-dimensional model was developed to investigate the influence of various hot filaments parameters on substrate temperature fields that significantly affect the nucleation and growth of diamond films over large area by hot-filament chemical vapordeposition (HFCVD). Numerical simulated results indicated that substrate temperature varies as a function of hot filamentsnumber, radius, temperature, emissivity, the distance between filaments, and the distance between substrate and filamentsarrangement plane. When these filaments parameters were maintained at the optimal values, the homogeneous substrate temperature region of 76 mm×76 mm with the temperature fluctuation no more than 5% could be obtained by a 80 mm×80 mmhot filaments arrangement plane. Furthermore, the homogeneous region could be enlarged to 100 mm×100 mm under thecondition of supplementary hot filaments with appropriate parameters. All of these calculations provided the basis for speciallyoptimizing the hot filaments parameters to dep     

Composite coherence vortices in coherent and incoherent superpositions of two off-axis partially coherent vortex beams

The composite coherence vortices by coherently and incoherently superimposing two parallel, off-axis partially coherent vortex beams and their evolution in free space are studied. It is shown that the superposition scheme, off-axis distance, coherence parameter and propagation distance affect the position and number of composite coherence vortices. The motion, creation and annihilation of composite coherence vortices appear by varying the off-axis distance, coherence parameter and propagation distance. The coherent and incoherent superpositions result in the different position and number of composite coherence vortices and their different evolution behavior in the coherent limit.