明代姚广孝及其隔声建筑

一般认为，隔声建筑是20世纪初的科技成果，文章以历史文献证明，明初姚广孝发现多孔墙体吸声现象并于1399年秘密地建成隔声房，明末，方以智在《物理小识》中总结多孔墙吸声的道理并最早使用“隔声”一词，从此隔声建筑的技术为中国人所知晓。，     

Hydrological currents in the Ligurian Sea

Summary Hydrological observations in the Ligurian Sea, north-western part of the Mediterranean Sea, are discussed. They show a steady cyclonic circulation. At theboundary of this circulation meanders and small eddies are rather frequent, in particular North of the Corsica Island. Their presence is in agreement with satellite data. In this paper also a number of simple baroclinic instability models are also considered, in an attempt to explain these current fluctuations.

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Riassunto L'analisi della circolazione generale del Mar Ligure, sulla base dei dati idrologici dell'Istituto Idrografico della Marina, ha rivelato la presenza, in ogni stagione, di una circolazione ciclonica stazionaria ai bordi della quale sono visibili ondulazioni delle linee di corrente e alcuni piccoli vortici. In accordo con le osservazioni da satellite queste piccole circolazioni vorticose si addensano in particolar modo a Nord della Corsica. In questo articolo la formazione dei meandri e dei piccoli vortici presenti nel Mar Ligure è analizzata sulla base di semplici modelli d'instabilità baroclina.

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Резюме Обсуждаются гидрологические наблюдения в Лигурийском море, северо-западной части Средиземного моря. Наблюдения обнаруживают стационарную цилиндрическую циркуляцию. На границе этой циркуляции имеют место извилины и небольшие вихри, особенно на севере Корсики. Их наличие подтверждается данными со спутников. В этой статье рассматривается рад простых моделей неустойчивостей с целью объяснить эти флуктуации течений.

     

Cylindrical solitons in shallow water of variable depth

Summary The propagation and the interaction of cylindrical solitons in shallow vater of variable depth are studied. Starting from the cylindrically symmetric version of the equations describing long waves in a beach, a Korteweg-de Vries equation type ψ_τ+6ψψ_ξ+ψ_ξξξ=−Γ(τ)ψ is derived. Since no exact analytical solution has been found to date for this equation, some remarkable cases in which the equation takes up a tractable form are analysed. Finally the interaction between cylindrical imploding and expanding waves is considered and the phase shifts caused by the head-on collision are given. This work was supported by CNR-GNFM.     

TO ENHANCE THE INTENSITY OF SONOLUMINESCENCE

The transient resonance of a sonoluminescence bubble has been analysed. When the bubble performs its transient resonance at the nth order harmonics of the standing waves in the liquid, the light intensity strongly depends on the amplitude of the driving pressure (proportional to its 2n power, with n=f_r/f, where f_r is Minnaert's linear resonant frequency of the bubble and f is the frequency of driving sound). The kinetic energy of a vibrating bubble becomes maximum approximately when it is in its equilibrium size. For example, when the ambient temperature of a bubble decreases from 34℃ to 4℃, a huge increase of the light intensity emitted by it can be explained. A suggestion was made that, within the limits permitted by the phase diagrams, as high an increase in driving pressure as possible could enhance the light intensity of sonoluminescence up to four orders of magnitude.     

Symmetry Reductions of a 1.5-Layer Ocean Circulation Model

The （2＋1）-dimensional nonlinear 1.5-layer ocean circulation model without external wind stress forcing is analyzed by using the classical Lie group approach. Some Lie point symmetries and their corresponding two-dimensional reduction equations are obtained.     

The Acoustics of Liquid Foams

Beside other transport properties of liquid foams, like the optical or electrical ones, the acoustics of liquid foams reveals a great complexity and non-trivial features. Here we present a review of recent experimental and theoretical results on how a sound wave interacts with either a macroscopic foam sample or with its isolated building blocks (films and Plateau borders). The analysis of the literature allows us to determine what is now well understood, what could be measured in foams by acoustics, and what are the remaining issues and perspectives in this research field.     

Fast and slow dynamics in a nonlinear elastic bar excited by longitudinal vibrations

The dynamics of heterogeneous materials, like rocks and concrete, is complex. It includes such features as nonlinear elasticity, hysteresis, and long-time relaxation. This dynamics is very sensitive to microstructural changes and damage. The goal of this paper is to propose a physical model describing the longitudinal vibrations in heterogeneous material, and to develop a numerical strategy to solve the evolution equations. The theory relies on the coupling of two processes with radically different time scales: a fast process at the frequency of the excitation, governed by nonlinear elasticity and viscoelasticity, and a slow process, governed by the evolution of defects. The evolution equations are written as a nonlinear hyperbolic system with relaxation. A time-domain numerical scheme is developed, based on a splitting strategy. The features observed by numerical simulations show qualitative agreement with the features observed experimentally by Dynamic Acousto-Elastic Testing.     

Analytic subject index to 2014

<正>43.05.History;43.10.General;43.15.Standards;43.20.General linear acoustics;43.25.Nonlinear acoustics;43.28.Aeroacoustics and atmospheric sound;43.30.Underwater sound;43.35.Ultrasonics,quantum acoustics,and physical effects of sound;43.38.Transduction,acoustical devices for the generation and reproduction of sound;43.40.Structural acoustics and vibration;43.50.Noise:its effects     

Spheroidal wave solutions for sound radiation problems in the near-field of planar structures

Current research in active noise control and in the reconstruction of vibrating sources often requires knowledge of the independent source–field components that best represent the complex acoustical transfer paths observed between a radiating structure and a given control or observation domain. In this paper, closed-form solutions are provided for the singular value expansion of the radiation operator that maps the boundary velocity of a baffled rectangular structure onto the acoustic pressure observed in the half-space domain over a hemi-spheroidal surface located at an arbitrary separation distance from the radiator, including in the near-field zone. Independent contributions of the evanescent and propagating wave components to the complex power are examined for a baffled beam when varying the frequency and the source–field distance parameter. It is shown that the reactive-to-active power ratio induced by each singular mode follows an inverse power law that scales on the product between the reduced frequency and the source–field distance parameter. A transitional region is defined in the space-frequency domain within which the reactive power components are preponderant and should be accounted for when controlling or imaging the near-field zone of a planar radiator. The optimality of the singular source modes is found to be of interest to actively reduce the active and reactive power components in the near-field zone of a radiator with a limited number of independent control channels.     

Analysis of efficient preconditioned defect correction methods for nonlinear water waves

Robust computational procedures for the solution of non‐hydrostatic, free surface, irrotational and inviscid free‐surface water waves in three space dimensions can be based on iterative preconditioned defect correction (PDC) methods. Such methods can be made efficient and scalable to enable prediction of free‐surface wave transformation and accurate wave kinematics in both deep and shallow waters in large marine areas or for predicting the outcome of experiments in large numerical wave tanks. We revisit the classical governing equations are fully nonlinear and dispersive potential flow equations. We present new detailed fundamental analysis using finite‐amplitude wave solutions for iterative solvers. We demonstrate that the PDC method in combination with a high‐order discretization method enables efficient and scalable solution of the linear system of equations arising in potential flow models. Our study is particularly relevant for fast and efficient simulation of non‐breaking fully nonlinear water waves over varying bottom topography that may be limited by computational resources or requirements. To gain insight into algorithmic properties and proper choices of discretization parameters for different PDC strategies, we study systematically limits of accuracy, convergence rate, algorithmic and numerical efficiency and scalability of the most efficient known PDC methods. These strategies are of interest, because they enable generalization of geometric multigrid methods to high‐order accurate discretizations and enable significant improvement in numerical efficiency while incuring minimal storage requirements. We demonstrate robustness using such PDC methods for practical ranges of interest for coastal and maritime engineering, that is, from shallow to deep water, and report details of numerical experiments that can be used for benchmarking purposes. Copyright © 2014 John Wiley & Sons, Ltd.