AC losses dependence on a CuNi layer location in NbTi CICC

In the frame of the ITER fusion program, large Cable In Conduit Cables (CICC) made with NbTi superconductors are foreseen for the poloidal field system. These coils are pulsed and so subjected to fast variations in magnetic field. Superconductors have then to be designed in order to reduce AC losses to an acceptable level. A solution could be to insert a copper nickel resistive barrier in the copper stabilizer surrounding the filamentary area of the composite. The purpose of this barrier is to reduce interstrand coupling currents. In order to predict the effect of this barrier on AC losses, a modeling of a 36 strands CICC has been realized. According to this code, the ability of the resistive barrier to reduce coupling currents is dependent on its location. For this study, three CICC with three barrier locations, from the inner to the outer diameter of the copper crown stabilizer, have been produced. AC losses have been measured and compared to our numerical model.     

宽波段单色仪多级谱高精度波长定标

通常利用单色仪输出的单色光对空间遥感光谱仪进行波长定标。提出以空间遥感光谱仪的置信度为标准,来评价宽波段单色仪高精度波长定标精度的方法。通过对仪器精度的分析,分别求出单色仪的波长的重复性误差和偏差。应用高压汞灯的本征谱和光栅衍射多级谱作为定标谱线,避免更换灯源带来的误差。通过粗细定标相结合的方法,缩短扫描时间,并且运用高斯拟合对波峰进行精确定位,缩小误差。最后利用高次拟合得到的关系式,测出单色仪波长精度,计算出空间遥感光谱仪定标的置信度。以1.5 M单色仪为例,单色仪在200～840 nm波段内波长精度±0.016 nm,则空间遥感光谱仪的波长精度达到±0.050 nm的置信度为99.82%。     

浅谈光电实验室的教学管理改革

实验教学是帮助学生将理论知识转化为实践技能的重要途径。因此在重视理论教学的同时,必须加强实验环节。针对光电实验室的现状,有必要进行教学方法和管理制度的改革。强化实验室仪器管理,创造好的硬件条件为实验教学服务;改革创新教学方法,使实验效果在传统实验教学的基础上更上一层楼;因材施教,满足各层次学生的不同需求;全方位展开改革实践,建立适合科技发展的教学新体系,培养理论知识扎实,实践技能过硬的复合型人才,以适应社会的发展。     

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.     

Thermo-chemical modelling of a village cookstove for design improvement

Cookstove operation comprises three basic processes, namely combustion of firewood, natural air draft due to the buoyancy induced by the temperature difference between the hearth and its surroundings, and heat transfer to the pot, stove body and surrounding atmosphere. Owing to the heterogenous and unsteady burning of solid fuel, there exist nonlinear and dynamic interrelationships among these process parameters. A steady-state analytical model of the cookstove operation is developed for its design improvement by splitting the hearth into three zones to study char combustion, volatile combustion and heat transfer to the pot bottom separately. It comprises a total of seven relations corresponding to a thorough analysis of the three basic processes. A novel method is proposed to model the combustion of wood to mimic the realities closely. Combustion space above the fuel bed is split into 1000 discrete parts to study the combustion of volatiles by considering a set of representative volatile gases. Model results are validated by comparing them with a set of water boiling tests carried on a traditional cookstove in the laboratory. It is found that the major thrust areas to improve the thermal performance are combustion of volatiles and the heat transfer to the pot. It is revealed that the existing design dimensions of the traditional cookstove are close to their optimal values. Addition of twisted-tape inserts in the hearth of the cookstove shows an improvement in the thermal performance due to increase in the heat transfer coefficient to the pot bottom and improved combustion of volatiles.     

Inference and Learning in a Latent Variable Model for Beta Distributed Interval Data

Latent Variable Models (LVMs) are well established tools to accomplish a range of different data processing tasks. Applications exploit the ability of LVMs to identify latent data structure in order to improve data (e.g., through denoising) or to estimate the relation between latent causes and measurements in medical data. In the latter case, LVMs in the form of noisy-OR Bayes nets represent the standard approach to relate binary latents (which represent diseases) to binary observables (which represent symptoms). Bayes nets with binary representation for symptoms may be perceived as a coarse approximation, however. In practice, real disease symptoms can range from absent over mild and intermediate to very severe. Therefore, using diseases/symptoms relations as motivation, we here ask how standard noisy-OR Bayes nets can be generalized to incorporate continuous observables, e.g., variables that model symptom severity in an interval from healthy to pathological. This transition from binary to interval data poses a number of challenges including a transition from a Bernoulli to a Beta distribution to model symptom statistics. While noisy-OR-like approaches are constrained to model how causes determine the observables’ mean values, the use of Beta distributions additionally provides (and also requires) that the causes determine the observables’ variances. To meet the challenges emerging when generalizing from Bernoulli to Beta distributed observables, we investigate a novel LVM that uses a maximum non-linearity to model how the latents determine means and variances of the observables. Given the model and the goal of likelihood maximization, we then leverage recent theoretical results to derive an Expectation Maximization (EM) algorithm for the suggested LVM. We further show how variational EM can be used to efficiently scale the approach to large networks. Experimental results finally illustrate the efficacy of the proposed model using both synthetic and real data sets. Importantly, we show that the model produces reliable results in estimating causes using proofs of concepts and first tests based on real medical data and on images.     

Pressure effects on inter‐ and intramolecular vibrations in hydrogen‐bonded L‐ascorbic acid crystal

Pressure effects on the Raman spectra due to the inter‐ and intramolecular vibrations of the L ‐ascorbic acid crystal were studied. The intensity of the Raman bands due to the intermolecular vibrations varies in three different ways by application of pressure. The bands of the first group become stronger, those of the second one become weaker and the third group shows no prominent change in their intensity with increasing pressure. The bands due to the intermolecular vibrations show a blue shift, while the bands due to the intramolecular vibrations shift to the blue or red depending on the vibrational modes by application of pressure. The bands assigned to the O H stretching vibrations shift to the red, the bands assigned to the CO and CC stretching vibrations shift a little to the red and the bands assigned to the other vibrations shift to the blue under high pressure. The following conclusions were derived. (1) The hydrogen bonds forming helixes become stronger and the isolated hydrogen bond becomes weaker with increasing pressure. (2) The bands of the first group owing to the intermolecular vibrations are ascribed to the vibrations related to the helix hydrogen bonds and the second group bands to the isolated hydrogen bond. (3) The CO stretching vibration couples with the CC stretching vibration. (4) The phase transitions take place at 1.8 and 4 GPa in the crystal. Copyright © 2007 John Wiley & Sons, Ltd.     

Illusion and reality in the quantum world

Often considered as the last ‘encyclopedist’, Henri Poincaré died one hundred years ago. If he was a prominent man in 1900 French Society, his heritage is not so clearly recognised, particularly in France. Among his too often misunderstood works is his contribution to the theory of relativity, mainly because it is almost never presented within Poincaré's general approach to science, including his philosophical writings. Our aim is therefore to provide an historical account of the main steps (experimental as well as theoretical) which led Poincaré to contribute to the theory of relativity. Starting from the optical experiments which led to the inconsistency of the classical (Galilean) composition law for velocities to explain light propagation, we introduce the FitzGerald and Lorentz contraction which was viewed as the ‘sole hypothesis’ to explain the Michelson and Morley experiment. We then show that Poincaré's contribution starts with a discussion of the principles governing the mechanics and was built step by step up to express in all its generality the principle of relativity. Poincaré thus showed the invariance of the Maxwell equations under the Lorentz transformation. In doing so, he also discovered the right composition law for velocities. Poincaré's approach to philosophy is detailed to help the reader to understand what a theory meant to him.     

开放光程FTIR光谱的葡萄品质劣变监测方法

前期的研究报道了红外光谱能够监测水果变质产生的挥发物质,其方法是将挥发物收集在气室中,利用多次反射的结构来增强光信号。实验中,我们使用开放光程傅里叶变换红外光谱法监测葡萄变质挥发物,尝试了主动和被动两种测量模式。根据红外光谱特征对葡萄品劣变过程中产生的挥发物进行了定性分析,并在研究中测量了葡萄储藏期间挥发物质的红外光谱特征的强度变化,并且根据这种变化规律建立了不同变质阶段的分类方法。此外,还尝试直接从原始光谱中分析挥发物质,证明了挥发物在原始光谱上仍然具有明显的光谱特征。这一研究证实了现场开放式傅里叶变换红外光谱法监测水果变质的可行性。开放光程傅里叶变换红外光谱法所具有的灵活使用性和非接触式在线测量的优点,使其有可能应用于大面积监测储藏中的水果变质问题,并具有进一步定位劣变源的潜力。     

激光测距机三轴平行性智能检测校正方法研究

提出了一种激光测距机三轴平行性智能的检测校正方法。建立了光轴平行性偏差与偏心环(框)旋转角度之间的数学模型,利用传感器得到激光发射轴与瞄准轴之间的平行性偏差,根据所建立的数学模型计算出偏心环(框)需要调整的角度值,利用步进电机使偏心环(框)转动相应的角度,从而物镜产生径向移动,实现激光测距机光轴的校正。此方法在检测激光测距机光轴平行性的同时实现了光轴的自动校正,也适用于其它具有双偏心结构的光学仪器。     

Whole-field analysis of uniaxial tensile tests by Moiré interferometry

Moiré interferometry—a high sensitivity whole-field optical technique—was used to follow the evolution of the deformation process of an aluminium sample subjected to a uniaxial tensile test. This technique allowed us to measure the two in-plane displacement components undergone by the sample, to evaluate the strain, stress and rotation fields, and to appreciate the trends in the deformation pattern that characterized the different stages of the test. Through a subtraction process between fields obtained at two different load levels, we were able to identify the area where strains began to localize and to observe the appearance of the diffuse neck.     

Cerenkov radiation and its polarization

General expression for the energy loss in Cerenkov radiation due to a charged particle possessing anomalous magnetic moment is obtained. The expressions include the spin-polarization of the particles. The contribution to the radiation due to anomalous magnetic moment is found to be small as compared to that due to charge. The interference term of charge and anomalous magnetic moment gives better contribution as compared to the term containing only anomalous magnetic moment. Polarization of the radiation as dependent on polarization of beam of particles is studied. The radiation has a dominant nature of linear polarization with small quantum corrections. The spin-flip also gives quantum correction to strong linear polarization and at threshold when phase velocity equals velocity of the particle.     

Mesh refinement algorithms in an unstructured solver for multiphase flow simulation using discrete particles

This study developed spray-adaptive mesh refinement algorithms with directional sensitivity in an unstructured solver to improve spray simulation for internal combustion engine application. Inadequate spatial resolution is often found to cause inaccuracies in spray simulation using the Lagrangian–Eulerian approach due to the over-estimated diffusion and inappropriate liquid–gas phase coupling. Dynamic mesh refinement algorithms adaptive to fuel sprays and vapor gradients were developed in order to increase the grid resolution in the spray region to improve simulation accuracy. The local refinement introduced the coarse-fine face interface that requires advanced numerical schemes for flux calculation and grid rezoning with moving boundaries. To resolve the issue in flux calculation, this work implemented the refinement/coarsening algorithms into a collocated solver to avoid tedious interpolations in solving the momentum equations. A pressure correction method was applied to address unphysical pressure oscillations due to the collocation of pressure and velocity. An edge-based algorithm was used to evaluate the edge-centered quantities in order to account for the contributions from all the cells around an edge at the coarse-fine interface. A quasi-second-order upwind scheme with strong monotonicity was also modified to accommodate the coarse-fine interface for convective fluxes. To resolve the issue related to grid rezoning, rezoning was applied to the initial baseline mesh only and the new locations of the refined grids were obtained by interpolating the updated baseline mesh. The time step constraints were also re-evaluated to account for the change resulting from mesh refinement. The present refinement algorithm was used in simulating fuel sprays in an engine combustion chamber. It was found that the present approach could produce the same level of results as those using the uniformly fine mesh with substantially reduced computer time. Results also showed that this approach could alleviate the artifacts related to the Lagrangian discrete modeling of spray drops due to insufficient spatial resolution.     

Characterization of the effects of pressure and hydrogen concentration on laminar burning velocities of methane–hydrogen–air mixtures

The aim of the present work was to characterize both the effects of pressure and of hydrogen addition on methane/air premixed laminar flames. The experimental setup consists of a spherical combustion chamber coupled to a classical shadowgraphy system. Flame pictures are recorded by a high speed camera. Global equivalence ratios were varied from 0.7 to 1.2 for the initial pressure range from 0.1 to 0.5 MPa. The mole fraction of hydrogen in the methane + hydrogen mixture was varied from 0 to 0.2. Experimental results were compared to calculations using a detailed chemical kinetic scheme (GRIMECH 3.0). First, the results for atmospheric laminar CH₄/air flames were compared to the literature. Very good agreements were obtained both for laminar burning velocities and for burned gas Markstein length. Then, increasing the hydrogen content in the mixture was found to be responsible for an increase in the laminar burning velocity and for a reduction of the flame dependence on stretch. Transport effects, through the reduction of the fuel Lewis number, play a role in reducing the sensitivity of the fundamental flame velocity to the stretch. Finally, when the pressure was increased, the laminar burning velocity decreased for all mixtures. The pressure domain was limited to 0.5 MPa due to the onset of instabilities at pressures above this value.     

Inactivation of the enveloped virus phi6 with hydrodynamic cavitation

The COVID −19 pandemic reminded us that we need better contingency plans to prevent the spread of infectious agents and the occurrence of epidemics or pandemics. Although the transmissibility of SARS-CoV-2 in water has not been confirmed, there are studies that have reported on the presence of infectious coronaviruses in water and wastewater samples. Since standard water treatments are not designed to eliminate viruses, it is of utmost importance to explore advanced treatment processes that can improve water treatment and help inactivate viruses when needed. This is the first study to investigate the effects of hydrodynamic cavitation on the inactivation of bacteriophage phi6, an enveloped virus used as a SARS-CoV-2 surrogate in many studies. In two series of experiments with increasing and constant sample temperature, virus reduction of up to 6.3 logs was achieved. Inactivation of phi6 at temperatures of 10 and 20 °C occurs predominantly by the mechanical effect of cavitation and results in a reduction of up to 4.5 logs. At 30 °C, the reduction increases to up to 6 logs, where the temperature-induced increased susceptibility of the viral lipid envelope makes the virus more prone to inactivation. Furthermore, the control experiments without cavitation showed that the increased temperature alone is not sufficient to cause inactivation, but that additional mechanical stress is still required. The RNA degradation results confirmed that virus inactivation was due to the disrupted lipid bilayer and not to RNA damage. Hydrodynamic cavitation, therefore, has the potential to inactivate current and potentially emerging enveloped pathogenic viruses in water at lower, environmentally relevant temperatures.     

Review of LDA and PIV applied to the measurement of sound and acoustic streaming

A review of laser Doppler anemometry (LDA) and particle image velocimetry (PIV) with their application to the measurement of sound is presented. The fundamental principles behind LDA and PIV are discussed and extended to the application of sound measurement. Special attention is paid to analysis of LDA signals including the Hilbert transform, which enables amplitude information to be obtained about various frequency components of a signal and wavelet analysis, which allows non-stationary signals to be accurately analysed. The influence of the refractive index variations in a medium due to a sound wave on the laser beams of an LDA signal is discussed. Attention is also paid to acoustic streaming which arises due to high-intensity sound, and PIV results are presented to demonstrate the effect.     

Dynamic photoelasticity using a laser scanner

Over the years, several techniques have been developed to record dynamic fringe patterns in photoelasticity. Due to the whole field recording capability, the photoelastic technique continues to be of interest to the experimental mechanics community. A low-cost dynamic recording system employing an out-dated fax scanner is presented in this article. Details of the optical and electronic functions are discussed. The feasibility of the system is demonstrated by recording dynamic fringe patterns off a simply supported beam subjected to impact loading. Further modifications to the set-up to improve the quality of the fringe patterns are discussed briefly.     

A new method for quantitation of spin concentration by EPR spectroscopy: application to methemoglobin and metmyoglobin

A new method of EPR spectral analysis is developed to quantitate overlapping signals. The method requires double integration of a number of spectra containing the signals in different proportions and the subsequent solution of a system of linear equations. The result gives the double integral values of the individual lines, which can then be further used to find the concentrations of all the paramagnetic species present. There is no requirement to deconvolute the whole spectrum into its individual components. The method is employed to quantify different heme species in methemoglobin and metmyoglobin preparations. A significantly greater intensity of the high-spin signal in metmyoglobin, compared to methemoglobin at the same heme concentration, is shown to be due to larger amounts of low-spin forms in methemoglobin. Three low-spin types in methemoglobin and two in metmyoglobin are present in these samples. When their calculated concentrations are added to those of the high-spin forms, the results correspond to the total heme concentrations obtained by optical spectroscopy.     

红外双波段卡塞格林光学系统设计

定性地论述了卡塞格林系统设计中焦距、场镜焦距和后工作距离大小的选择.并论述了在设计中主、次镜必须根据设计结果的分析,调整主、次镜的半径和间隔,从而使后工作距离,遮栏比都能满足设计要求,最终使系统能够获得最优的设计性能以满足设计需要,在系统的垂轴像差难以消除时,也需考虑变换系统的光栏位置.     

GW approximation study of the Compton profile of ZnSe

We have obtained the Compton profile of ZnSe from the first principles GW approximation (GWA) method and ground-state density functional theory (DFT) method. We observe that between 0 and 1.5?a.u., there is better agreement to previous studies via the GWA difference profile compared to the ground-state difference profile. Above 1.5?a.u., both cases do not agree with the trend of the previous study; however, the application of the GWA is seen to improve the agreement compared to localized density approximation. Previous studies have reported that discrepancies from experiment are related to pseudopotential calculations which have been observed to overestimate momentum density between 0 and 1.5?a.u., while the reverse trend is seen above 1.5?a.u. We thus conclude that improvement to the pseudopotential technique to obtain the Compton profile is possible if the sharp Fermi break of the momentum distribution between high and low momenta becomes more smeared. Using the broadened spectral functions via the contour deformation method to obtain the momentum distributions, the GWA is a natural tool to achieve this via the contribution from the dielectric screening to the quasiparticle energies.