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.     

Role of waveguide and surface plasmon resonances in surface-enhanced Raman scattering at coldly evaporated metallic films

A film surface, modeled by a grating with rectangular grooves, is shown to give rise to both short and long ranged enhancements due to excitation of planar surface plasmon resonances, and to short ranged, more intense, enhancements due to excitation of waveguide resonances. The latter type of enhancement is shown to become more intense as the ratio of grating period to groove width increases and to be able to account for experimentally observed SERS signals at very low as well as at higher temperatures.     

Ohmic Contacts to ZnSe-Based Materials

The formation of ohmic contacts to n- and p-type ZnSe is reviewed. The mechanisms for forming reasonable low-resistance ohmic contacts to n-ZnSe are well understood. This results from the fact that the Fermi energy level of ZnSe is unpinned and metals with sufficiently large work functions can make contact to n-type material. However, the situation is reversed for p-ZnSe where a large band gap and large electron affinity make it impossible to find metals with sufficiently large work functions to create an ohmic contact. Instead, the use of HgSe to form low barrier height Schottky contacts and of ZnSe/ZnTe multiple quantum wells (MQWs) to form ohmic contacts is reviewed. Although the MQWs can be used to form ohmic contacts to p-ZnSe, they degrade at high temperatures and high current densities. This is reviewed and shown to be a serious problem for applications to laser diodes.     

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.     

经典洛伦兹磁力和广义洛伦兹磁力解释电子感应加速器的本质

介绍了虚构的法拉第定律与电子感应加速器不合理,用完整洛伦兹磁力解释电子感应加速器合理有效。     

A multiple function sonar rangefinder for divers

The rangefinder described here is a self-contained instrument for hand-held operation by a diver for searching, tracking, navigation and surveying applications. It has four modes: 1 — to measure range to a passive target directly to ± 1 m; 2 — to measure range to a passive target indirectly to ± 0.1 m; 3 — to measure range to a coded transponder to either ± 1 m or ± 0.1 m; 4 — to indicate the presence of multiple targets downrange where each target occurs in a selected range interval. The pulse echo principle is employed, with pulses typically 250 μs long. The carrier frequency of 300 kHz can be altered easily if required by changing the transducer array.     

Gravitational critical phenomena in the realm of the galaxies and Ising magnets

In the non-relativistic and quasi-static limit, it is possible to map exactly the system of galaxies in the observable universe onto an Ising magnet. Techniques from the theory of critical phenomena as applied to magnets can then be employed to calculate rigorously the galaxy-to-galaxy correlation function, whose critical exponent is predicted to be between 1.530 to 1.862, to be compared to the empirical/observational value of 1.6 to 1.8.This essay received the fifth award from the Gravity Research Foundation, 1996—Ed.     

Fluctuation spectroscopy of granularity in superconducting structures

We suggest to use "fluctuation spectroscopy" as a method to detect granularity in a disordered metal close to a superconducting transition. We show that with lowering temperature T the resistance R(T) of a system of relatively large grains initially grows due to the fluctuation suppression of the one-electron tunneling but decreases with further lowering T due to the coherent charge transfer of the fluctuation Cooper pairs. Under certain conditions, such a maximum in R(T) turns out to be sensitive to weak magnetic fields due to a novel Maki-Thompson-type mechanism.     

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.     

Complete experiments in pseudoscalar photoproduction

Necessary and sufficient conditions are derived for three double polarisation measurements to complement cross section and single polarisation measurements in pseudoscalar meson photoproduction to enable amplitudes to be determined up to discrete ambiguities. Rules for choosing two further measurements to resolve the discrete ambiguities are given and practical applications of the rules to particular reactions are discussed.     

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...     

Reduction of thermo-elastic damping with a secondary elastic field

Thermo-elastic damping is the dominant mode of energy loss due to the coupling of thermal and elastic fields in a body vibrating at or near resonant frequency. While the literature contains both exact and numerical schemes to quantify it, no technique is available yet to reduce thermo-elastic damping. We address this issue by introducing a secondary elastic field to derive an exact expression that predicts linear reduction in thermo-elastic damping with respect to frequency. Contrary to the current understanding, introduction of a static axial stress in addition to the flexural stresses is shown to increase quality factor and resonant frequency simultaneously.     

Dye laser intracavity absorption for molecular spectroscopy

Dye laser intracavity absorption has been used to a limited extent to observe molecular spectra for about 10 years. Most workers in the field operate their laser broadband and rely only on a spectrograph to resolve the spectra and to increase signal-to-noise ratio. The overall results have not been too satisfactory, and the effect has been to discourage people from applying this technique. It is the purpose of this paper to point out the advantages to be gained by wavelength sweeping the dye laser, to describe the laser system currently being used in our laboratory, and to present some recently obtained results.     

Modifications to functional and biological properties of proteins of cowpea pulse crop by ultrasound-assisted extraction

Natural resource depletion, negative environmental effects and the challenge to secure global food security led to the establishment of the Sustainable Development Goals (SDGs). In need to explore underutilized sustainable protein sources, this study aims at isolating protein from cowpea by ultrasound-assisted extraction (UAE), where the techno-functional characteristics of the protein isolates were studied at different sonication conditions i.e., 100 W and 200 W at processing times ranging from 5 to 20 min. The US at 200 W-10 min produced the optimal results for all properties. In this process combination, there was an increase in protein yield, solubility, water-holding capacity, foaming capacity and stability, emulsion activity and stability, zeta-potential, and in-vitro protein digestibility from 31.78% to 58.96%, 57.26% to 68.85%, 3.06 g/g to 3.68 g/g 70.64% to 83.74%, 30.76% to 60.01%, 47.48% to 64.26%, 56.59% to 87.71%, –32.9 mV to −44.2 mV and 88.27% to 89.99%, respectively and particle size dropped from 763 nm to 559 nm in comparison to control. The microstructure and secondary-structure alterations of proteins caused by sonication were validated by SEM images, SDS-PAGE, and FTIR analyses. Sonication leads to acoustic cavitation and penetrate the cell walls, improving extraction from the solid to liquid phase. After sonication, the hydrophobic protein groups were exposed and proteins were partially denatured which increased its functionality. The findings demonstrated that UAE of cowpea protein improved yield, modify characteristics to fit the needs of the food industry, and contribute to achieving SDGs 2, 3, 7, 12, and 13.     

做实验的主人--写给学习物理实验的学生

在学习实验时应注意学习探索,本文从实验课上学什么,如何在探索中学习,如何进行误差分析,实验结果如何评价,怎样认识验证性实验,怎样理解实验的物理思想,怎样在实验过程中提出问题等几方面讨论了学生怎样做实验的主人.     

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.     

Adaptive digital twins of combustion systems using sparse sensing strategies

This work proposes to implement a sparse sensing framework to build a hybrid numerical-experimental Digital Twin of a practical combustion system. The goal is to find the optimal sensor placement that minimizes the prediction error, and to predict the distribution of reacting scalars using few measurements. Three-dimensional CFD simulations with detailed chemistry were used to build the design space by varying the fuel composition (from pure methane to pure hydrogen), the equivalence ratio (from 0.7 to 1) and the air velocity. The Proper Orthogonal Decomposition (POD) was applied to the numerical data to find a tailored basis for dimensionality reduction. Then, the QR decomposition with column pivoting was applied to the tailored basis to find the optimal sensor placement. Finally, the model was employed to predict the three-dimensional temperature distribution in the unexplored part of the design space, using the experimental samples as input. The optimal placement of the sensors provides valuable information on the key locations and features, which can then be used in the design of reactor network models, for example. Also, the results show that the hybrid Digital Twin could predict an adjusted temperature distribution which reduces the error with the experimental measurements, when compared to the original CFD temperature distribution.     

Intercomparison of Gafchromic™ films,TL detectors and TL foils for the measurements of skin dose in interventional radiology

Several passive solid state dosemeters, such as Gafchromic™ films and thermoluminescence (TL) detectors, are used to estimate and monitor patient skin doses in interventional radiology. To determine the suitability of XR-TypeR Gafchromic™ films and of detectors based on TL materials: pellets, chips and foils to measure skin dose, an intercomparison exercise has been organized within European Dosimetry Radiation Group – Working Group 12 “European Medical ALARA Network” (EURADOS WG12). To test response detectors were exposed to X-ray beams of energies and qualities applied clinically. A blind test was also performed to investigate the accuracy of the dose estimate by detectors exposed to unknown doses. We found the response of films to be strongly dependent on beam quality and filtration (increasing by up to 80% with respect to reference beam quality). The response of TL detectors was found to be less dependent on beam quality (less than 25% variation), with TL foils showing less than 10% variation with respect to reference beam quality. To accurately estimate patient skin doses in interventional radiology it is important to choose the quality of the calibration beam to be as close as possible to the quality of beams actually applied in clinical work.