No stellar p-mode oscillations in space-based photometry of Procyon

Pressure-driven (p-mode) oscillations at the surface of the Sun, resulting from sound waves travelling through the solar interior, are a powerful probe of solar structure, just as seismology can reveal details about the interior of the Earth. Astronomers have hoped to exploit p-mode asteroseismology in Sun-like stars to test detailed models of stellar structure and evolution, but the observations are extremely difficult. The bright star Procyon has been considered one of the best candidates for asteroseismology, on the basis of models and previous reports of p-modes detected in ground-based spectroscopy. Here we present a search for p-modes in 32 days of nearly continuous photometric satellite-based observations of Procyon. If there are p-modes in Procyon, they must have lifetimes less than 2-3 days and/or peak amplitudes <15 parts per million, which defy expectations from the Sun's oscillations and previous theoretical predictions. Target selection for future planned asteroseismology space missions may need to be reconsidered, as will the theory of stellar oscillations.     

无界流场中充流弹性壳体声透射数值研究

利用耦合有限元与边界方法计算了声流激励下浸没在无界流场中内部充满流体的弹性薄壳声透射,在有限元方法和边界元法中均采用了八结点曲面四形等参单元。耦合方程是以声场变量表达,为验证数学模型的正确性,针对声源激励下无界水域中充气球壳进行了数值计算,结果表明,壳体风外表面声压数值计算结果与解析解相当吻合。     

Fast core rotation in red-giant stars as revealed by gravity-dominated mixed modes

When the core hydrogen is exhausted during stellar evolution, the central region of a star contracts and the outer envelope expands and cools, giving rise to a red giant. Convection takes place over much of the star's radius. Conservation of angular momentum requires that the cores of these stars rotate faster than their envelopes; indirect evidence supports this. Information about the angular-momentum distribution is inaccessible to direct observations, but it can be extracted from the effect of rotation on oscillation modes that probe the stellar interior. Here we report an increasing rotation rate from the surface of the star to the stellar core in the interiors of red giants, obtained using the rotational frequency splitting of recently detected 'mixed modes'. By comparison with theoretical stellar models, we conclude that the core must rotate at least ten times faster than the surface. This observational result confirms the theoretical prediction of a steep gradient in the rotation profile towards the deep stellar interior.     

The Great Eruption of η Carinae

Arising from A. Rest et al. 482, 375-378 (2012).During the years 1838-1858, the very massive star η Carinae became the prototype supernova impostor: it released nearly as much light as a supernova explosion and shed an impressive amount of mass, but survived as a star. In the standard interpretation, mass was driven outward by excess radiation pressure, persisting for several years. From a light-echo spectrum of that event, Rest et al. conclude that "other physical mechanisms" are required to explain it, because the gas outflow appears cooler than theoretical expectations. Here we note that (1) theory predicted a substantially lower temperature than they quoted, and (2) their inferred observational value is quite uncertain. Therefore, analyses so far do not reveal any significant contradiction between the observed spectrum and most previous discussions of the Great Eruption and its physics.     

酒店室内设计中地域文化的应用研究

随着与世界交流程度的加深,外来文化强势进入,当下中国的各地域特性正在弱化、"千城一面"及文化同质化现象已经出现,地域文化同化现象严重,针对这一现象,在室内设计中最具代表性的酒店室内设计方案中,采用具体挖掘和应用方法将本地域文化融入至实体的空间中,完工后项目运行情况良好、顾客认可度高、入住率高于大部分星级度假酒店,某种程度上肯定了地域文化的应用研究的必要性,说明酒店室内设计中强调地域特色文化的融入,可为人们的心理提供文化认同感,从感官和心理两方面给受众带来对异域风情的新鲜感,由点及面,循序渐进,最终可达到减缓文化同质、增强文化自信的目的。     

声表面行波器件及其在微纳领域的应用

 声表面行波因其非接触性及生物相容性，在生物医学、诊断学领域得到了广泛关注。概述了声表面行波（TSAW）发生器件的基本结构，叉指换能器（IDT）的结构、参数、种类及引起声表面行波的内在机理，讨论了对微流体状态及微流体中粒子的声控制机理；综合当前该技术国内外研究现状，分析了在微纳领域中声表面行波相对于其他物理场的优势；针对声表面行波在微纳领域应用的技术难点及研究过程中存在的问题，提出了该技术的研究方向，并展望了其未来发展趋势。     

波浪对台风风暴潮过程的影响分析

利用胡克林等建立的长江口及邻近海域的二维风暴潮数值计算模式,对2007-2008年有较大影响的4次台风风暴潮进行加波浪和不加波浪的后报计算.将计算结果与实测资料进行比较分析,得出结论:波浪对于风暴潮的影响程度取决于台风的路径、登陆地点和不同时刻.在台风登录前后一两天内,加波浪计算比不加波浪计算出的风暴潮水位精度总体要高;当台风传播到近岸时,波浪破碎对近岸增水影响较大,需要加波浪计算台风风暴潮;对南登陆北上转出型台风风暴潮计算时需加波浪,而对南登陆型可不必加波浪,以提高计算效率.     

厚铝管中激光激发温度场和瑞利波的模拟

利用有限元方法数值模拟了脉冲激光作用于厚铝管时产生的温升以及由此温升而产生的表面瑞利波的情况。给出了温度随角向的分布曲线,比较了物理参数随温度变化和不随温度变化两种情况下温度场的区别,并进一步得到了近场区域表面波的时域波形。数值结果表明：在考虑材料物理参数随温度变化基础上得到的近场区域的表面声波中显著的波为掠面纵波和瑞利波,与平板中的类似。为热弹条件下管状材料的激光超声无损检测提供了参考。     

长短波方程共振方程的孤立波轨道稳定性的另一种证明

文章用M.Grillakis等[1,2]提出的抽象的轨道稳定性理论,利用谱分析,证明了长短波共振方程iεt εxx=nε α｜ε｜2εnt=(｜ε｜2)x的孤立波解是轨道稳定的。     

基于时域LEE方法的发动机进气道声衬降噪优化

基于2.5D时域线化欧拉方程(LEE)和Fung的时域阻抗边界条件(TDIBC)模拟了涡扇发动机进气道风扇噪声传播并对声衬的参数进行了优化。TDIBC代码的正确性通过实验数据进行了验证。管道声模态的传播计算使用复数形式的线性化欧拉方程(LEE)在时域中实现。发动机进气道的背景流场使用Fluent软件计算,基于该背景流场并加入Fung的TDIBC模型模拟了发动机风扇噪声在进气道中的传播。提出一个有效的基于响应面替代模型的轴对称声衬的优化方法。优化的结果表明该方法可以用于降低远场声压级(SPL)的声衬优化设计。该方法对于高涵道比涡扇航空发动机声衬的降噪设计有着重要意义。     

Resolution enhancement of nearfield acoustic holography by interpolation using band-limited signal restoration method

A new method based on interpolation using band-limited signal restoration method was proposed for enhancing the resolution of the nearfield acoustic holography. According to the band-limited property of the pressure on the hologram surface, a band-limited signal restoration method named Papoulis-Gerchbarg algorithm was used to realize the interpolation of acoustic pressure. Therefore acoustic pressure data on the hologram surface were increased, the sampling interval was reduced, the Information on evanescent waves which was lost because of the large sampling interval was partially recovered, and the resolution of nearfield acoustic holography image was improved. The experimental result shows that the method can enhance the resolution of the nearfield acoustic holography Image efficiently.     

离心风机基频气动偶极子噪声的数值研究

运用计算流体动力学技术及声比拟理论研究了离心风机3个不同流量下蜗壳及叶片表面偶极子声源产生的基频噪声.风机内部三维瞬态流场由计算流体动力学模拟得到.根据气动声学的FW-H方程对蜗壳内表面提取偶极子声源,对于叶片噪声利用Lowson公式进行建模.为了使计算模型更符合实际,建立了以蜗壳为界的内外声学直接边界元模型,使用多区域声学边界元模型,考虑蜗壳对声传播的散射作用,内部噪声通过蜗壳的进出口传播到风机外部.结果表明:在非定常流场中,蜗壳表面的压力波动以基频为主,而叶片上的压力波动并没有明显的基频分量;蜗舌是基频噪声的最主要声源;随着流量变大,蜗壳辐射的噪声急剧增加;由叶片产生的偶极子基频噪声比蜗壳小,特别是在大流量工况下.     

太阳风中非线性离子波研究的解析方法Ⅱ

本文从MHD方程组出发，推导了太阳风磁化等离子体中非线性静电离子声波孤立子传播的非线性控制方程，考虑电子捕获效应，使用解析方法得到了扰动位势的精确解，应用得到的精确解讨论了各种等离子体参数情况下孤立子形成的条件。     

非均匀流场中随机波折射—绕射的数值计算

本文在非均匀流场中规则波折－绕射缓坡方程的基础上,引入谱的概念,建立了用方向谱表示的非均匀流场中随机波折－绕射缓坡方程,并选用文圣常等提出的解析方向谱作为靶谱,就一模型海区进行具体的数值计算,结果表明,随机波折－绕射模型要明确优于规则波的折－绕射模型。     

High-frequency acoustic waves are not sufficient to heat the solar chromosphere

One of the main unanswered questions in solar physics is why the Sun's outer atmosphere is hotter than its surface. Theory predicts abundant production of high-frequency (10-50 mHz) acoustic waves in subsurface layers of the Sun, and such waves are believed by many to constitute the dominant heating mechanism of the chromosphere (the lower part of the outer solar atmosphere) in non-magnetic regions. Such high-frequency waves are difficult to detect because of high-frequency disturbances in Earth's atmosphere (seeing) and other factors. Here we report the detection of high-frequency waves, and we use numerical simulations to show that the acoustic energy flux of these waves is too low, by a factor of at least ten, to balance the radiative losses in the solar chromosphere. Acoustic waves therefore cannot constitute the dominant heating mechanism of the solar chromosphere.     

表面声波法监测裂纹

研究了用表面声波监测裂纹的方法,利用表面声波通过物体表面时其反射信号的强度随着裂纹的发展而增强的原理,通过试验描述了表面波通过有缺陷小孔时两种反射信号随裂纹形成发展的变化过程,提出了通过观测反射信号的变化来监测是否有裂纹生成的方法。     

脉冲激光线源热弹激发超声导波的数值研究

考虑激光作用过程中材料热物理参数随温度变化的非线性效应,在两维平面内建立了平面应变有限元模型,基于热弹耦合理论数值模拟了脉冲激光线源辐照金属铝板表面激发超声导波的物理过程.数值模拟分别得到了脉冲激光线源在厚度为1 cm与0.2 mm的铝板中激发出的声表面波与Lamb波的时域波形.其中声表面波包括掠面纵波、表面横波与瑞利...     

木材及其制品法向吸声系数的实验研究

<正>用驻波管法测定了杉木,银杏、泡桐、红松、马尾松、香樟、酸枣木、水曲柳、装饰纤维板和杉木不同表面积的法向吸声系数α_p,得到在一定条件下法向吸声系数α_p与入射材料表面声波频率ν的实验曲线。它对研究木材及其制品的吸声特性和在建筑声学中的应用都有参考价值。     

三维Boussinesq型水波方程的改进

良好的色散性和变浅性是Boussinesq水波数值模型能够精确模拟水波问题的重要前提,针对一组最高空间导数为2的三维Boussinesq型水波方程在色散性和变浅性的不足,重新引入带有不同色散参数和变浅参数的计算速度表达式,得到了新的三维Boussinesq型方程。对该方程进行理论分析,以相关解析解为参考,分析了新参数下方程的相速度、和差频和变浅梯度等性能。理论分析结果表明：方程的综合性能有了较大改善,验证了改进的理论有效性。为验证改进方程的数值有效性,建立了基于混合4阶Adams-Bashforth-Moulton格式的时间差分数值模型。数值模拟了波浪在潜堤上的传播变形过程,将计算波面位移与文献的试验数据进行了比较,结果表明,与改进前相比,改进后计算结果与试验结果的吻合程度更高。     

水下声信号激发表面波衰减系数测量

建立了一个简单,可行的光学系统用于探测低频水下声信号。激光斜射到有表面波存在水面时,观察到了清晰、稳定的衍射图样,发现衍射图样具有明显的非对称性;且这种非对称性具有普遍的适用性。理论上得到了衍射光场光强分布的解析表达式。结果表明,衍射图样的非对称性与液体表面波的衰减系数有关。根据提出的方法可实现液体表面波衰减系数的便捷测量;且结果是很准确的。