Perspectives in Helioseismology

Helioseismology is probing the interior structure and dynamics of the sun with ever-increasing precision, providing a well-calibrated laboratory in which physical processes can be studied under conditions that are unattainable on Earth. Nearly 10 million resonant modes of oscillation are observable in the solar atmosphere, and their frequencies need to be known with great accuracy in order to gauge the sun's interior. The advent of nearly continuous imaged observations from the complementary ground-based Global Oscillation Network Group (GONG) observatories and the space-based Solar and Heliospheric Observatory instruments augurs a new era of discovery. The flow of early results from GONG resolves some issues and raises a number of theoretical questions whose answers are required for understanding how a seemingly ordinary star actually operates.     

Torsional oscillations of the sun

The sun's differential rotation has a cyclic pattern of change that is tightly correlated with the sunspot, or magnetic activity, cycle. This pattern can be described as a torsional oscillation, in which the solar rotation is periodically sped up or slowed down in certain zones of latitude while elsewhere the rotation remains essentially steady. The zones of anomalous rotation move on the sun in wavelike fashion, keeping pace with and flanking the zones of magnetic activity. It is uncertain whether this torsional oscillation is a globally coherent ringing of the sun or whether it is a local pattern caused by and causing local changes in the magnetic fields. In either case, it may be an important link in the connection between the rotation and the cycle that is widely believed to exist but is not yet understood.     

Dynamic variations at the base of the solar convection zone

We have detected changes in the rotation of the sun near the base of its convective envelope, including a prominent variation with a period of 1.3 years at low latitudes. Such helioseismic probing of the deep solar interior has been enabled by nearly continuous observation of its oscillation modes with two complementary experiments. Inversion of the global-mode frequency splittings reveals that the largest temporal changes in the angular velocity Omega are of the order of 6 nanohertz and occur above and below the tachocline that separates the sun's differentially rotating convection zone (outer 30% by radius) from the nearly uniformly rotating deeper radiative interior beneath. Such changes are most pronounced near the equator and at high latitudes and are a substantial fraction of the average 30-nanohertz difference in Omega with radius across the tachocline at the equator. The results indicate variations of rotation close to the presumed site of the solar dynamo, which may generate the 22-year cycles of magnetic activity.     

CoRoT measures solar-like oscillations and granulation in stars hotter than the Sun

Oscillations of the Sun have been used to understand its interior structure. The extension of similar studies to more distant stars has raised many difficulties despite the strong efforts of the international community over the past decades. The CoRoT (Convection Rotation and Planetary Transits) satellite, launched in December 2006, has now measured oscillations and the stellar granulation signature in three main sequence stars that are noticeably hotter than the sun. The oscillation amplitudes are about 1.5 times as large as those in the Sun; the stellar granulation is up to three times as high. The stellar amplitudes are about 25% below the theoretic values, providing a measurement of the nonadiabaticity of the process ruling the oscillations in the outer layers of the stars.     

Seismology of the sun

Oscillations of the sun make it possible to probe the inside of a star. The frequencies of the oscillations have already provided measures of the sound speed and the rate of rotation throughout much of the solar interior. These quantities are important for understanding the dynamics of the magnetic cycle and have a bearing on testing general relativity by planetary precession. The oscillation frequencies yield a helium abundance that is consistent with cosmology, but they reinforce the severity of the neutrino problem. They should soon provide an important standard by which to calibrate the theory of stellar evolution.     

Kepler detected gravity-mode period spacings in a red giant star

Stellar interiors are inaccessible through direct observations. For this reason, helioseismologists made use of the Sun's acoustic oscillation modes to tune models of its structure. The quest to detect modes that probe the solar core has been ongoing for decades. We report the detection of mixed modes penetrating all the way to the core of an evolved star from 320 days of observations with the Kepler satellite. The period spacings of these mixed modes are directly dependent on the density gradient between the core region and the convective envelope.     

Femtosecond pulse sequences used for optical manipulation of molecular motion

Optical control over elementary molecular motion is enhanced with timed sequences of femtosecond (10(-15) second) pulses produced by pulse-shaping techniques. Appropriately timed pulse sequences are used to repetitively drive selected vibrations of a crystal lattice, in a manner analogous to repetitively pushing a child on a swing with appropriate timing to build up a large oscillation amplitude. This process corresponds to repetitively "pushing" molecules along selected paths in the lattice. Amplification of selected vibrational modes and discrimination against other modes are demonstrated. Prospects for more extensive manipulation of molecular and collective behavior and structure are clearly indicated.     

GONG Observations of Solar Surface Flows

Doppler velocity observations obtained by the Global Oscillation Network Group (GONG) instruments directly measure the nearly steady flows in the solar photosphere. The sun's differential rotation is accurately determined from single observations. The rotation profile with respect to latitude agrees well with previous measures, but it also shows a slight north-south asymmetry. Rotation profiles averaged over 27-day rotations of the sun reveal the torsional oscillation signal-weak, jetlike features, with amplitudes of 5 meters per second, that are associated with the sunspot latitude activity belts. A meridional circulation with a poleward flow of about 20 meters per second is also evident. Several characteristics of the surface flows suggest the presence of large convection cells.     

North atlantic ocean: preliminary description of normal modes

The three lowest gravitational modes of free oscillation of the North Atlantic Ocean are estimated by numerical integration of Laplace's tidal equations. These modes have periods of approximately 21, 14, and 11 hours, and structures, respectively, of one, two, and three positive amphidromic systems. The phase distribution of the first mode resembles cotidal charts of the diurnal tide, and the period of the second mode is consistent with that inferred by Wunsch from tidal data in Bermuda and the Azores.     

High-Resolution Spectroscopy of the Earth's Free Oscillations, Knowing the Earthquake Source Mechanism

A new method for identification of normal modes of oscillation of the earth yielded unambiguous determinations of many overtones never before identified. This method consists of the superposition of spectra observed at many stations over the earth, after a correction for the phase determined from the known earthquake source mechanism.     

模式可调智能振动压路机动力学特性的建模与仿真

分析了智能振动压路机多模式调整原理;并根据其结构特点,提出一种基于水平振荡和垂直振动的整体动力学模型.以XG6133D型智能压路机为例,研究了压实进程中振动轮、机架在多模式下及减振系统参数发生变化时的动力学响应特性.仿真结果表明,在压实进程中应主动控制减振器参数和调整激振模式,以提高压实效率及改善驾驶舒适性.     

Proximity of jupiter-like planets to low-mass stars

The sensitivities of astrometric and radial velocity searches for extrasolar planets are strongly dependent on planetary masses and orbits. Because most nearby stars are less massive than the sun, the first detection is likely to be of a Jupiter-mass planet orbiting a low-mass star, with a possible theoretical expectation being that Jupiter-like planets will be found much closer [inside the Earth-sun separation of 1 astronomical unit (AU)] to these low-luminosity stars than Jupiter is to the sun (5.2 AU). However, radiative hydrodynamic models of protoplanetary disks around low-mass stars (of 0.1 to 1 solar mass) show that Jupiter-like planets should form at distances (approximately 4 to 5 AU) that are only weakly dependent on the stellar mass.     

Solar-Like M-Class X-ray Flares on Proxima Centauri Observed by the ASCA Satellite

Because of instrumental sensitivity limits and stellar distances, the types of x-ray flares observable on stars have been intrinsically much more energetic than those on the sun. Such enormous events are a useful extrapolation of the solar phenomenon if the underlying assumption is correct that they form a continuous sequence involving similar physical processes as on the sun. The Advanced Satellite for Cosmology and Astrophysics (ASCA), with its greater sensitivity and high-energy response, is now able to test this hypothesis. Direct comparison with solar flares measured by the x-ray-monitoring Geostationary Operational Environmental Satellites (GOES) is possible. The detection of flares on Proxima Centauri that correspond to GOES M-class events on the sun are reported.     

Viscosity near Earth's solid inner core

Anomalous splitting of the two equatorial translational modes of oscillation of Earth's solid inner core is used to estimate the effective viscosity just outside its boundary. Superconducting gravimeter observations give periods of 3.5822 +/- 0.0012 (retrograde) and 4.0150 +/- 0.0010 (prograde) hours. With the use of Ekman layer theory to estimate viscous drag forces, an inferred single viscosity of 1.22 x 10(11) Pascal seconds gives calculated periods of 3.5839 and 4.0167 hours for the two modes, close to the observed values. The large effective viscosity is consistent with a fluid, solid-liquid mixture surrounding the inner core associated with the "compositional convection" that drives Earth's geodynamo.     

Orientation by pigeons: is the sun necessary?

Although most recent hypotheses of pigeon homing have assigned an essential role to the sun, there has been some evidence suggesting that the sun is not essential. Two series of releases were designed to examine the question more carefully. Birds whose internal clocks had been shifted 6 hours were used in the critical tests. Under sun, the vanishing bearings of the clock-shifted birds were deflected in the direction predicted by a hypothesis of use of the sun as a simple compass. By contrast, under total overcast the bearings of both the clock-shifted and the control birds were homeward oriented and there was no difference between them, even at a release site the birds could never have seen previously. Therefore it is concluded that the sun is used as a compass when it is available, but that the pigeon navigation system contains sufficient redundancy to make accurate orientation possible in the absence of both the sun and familiar landmarks; the orientational cues used under such conditions do not require time compensation. This conclusion is in complete disagreement with the Matthews sun-arc hypothesis of pigeon navigation, and it makes necessary a major reformulation (at the very least) of the other principal hypothesis, that of Kramer.     

Superior conjunction of pioneer 6

Spectrograms of the radio signals from Pioneer 6 were taken as the spacecraft was occulted by the sun. The spectral bandwidths increased slowly at first, then very rapidly at 1 degree from the sun. In addition, six solar "events" produced marked increases of bandwidth lasting for several hours. The received signal power seemed unaffected by the solar corona.     

宁夏各站年降水的非线性特征分析

从观测资料出发,利用非线性振动理论对宁夏年降水气候振动的非线性特征进行了分析和研究,并且利用反演得到的非线性动力学方程对19个站的年降水气候振动进行气候模拟试验,结果表明宁夏大部分地区的年降水气候振动存在弱的非线性振动特征。19个站的年降水气候振动都可看作是一个负阻尼的动力系统,其固有周期的变化范围为1.0～4.1年。年降水气候振动是一个弱的非线性动力系统。这些站点的年降水气候振动是一个类似于具有渐软弹簧特性的非线性动力系统,都存在一个稳定的焦点,但不存在极限环。在降水气候振动中,靠近中北部的地区外源强迫影响作用比南部地区的大。     

欧洲李不同品种晾晒制干特性研究

[目的]研究欧洲李不同品种在南疆地区晾晒制干特性,为欧洲李干制品种选择和制干提供借鉴.[方法]以新疆喀什地区伽师县种植的3个欧洲李品种法兰西、斯泰勒、女神为试验材料,在果实成熟后进行自然晾晒制干,分析3个品种果实经济性状、成熟期、失水率等对晾晒制干的影响,对3个品种晾晒制干特性进行评价.[结果]品种法兰西由于成熟早、可溶性固形物含量高,自然晾晒30 d能够干燥;斯泰勒较法兰西晚熟10～15 d,果实较大,自然晾晒36 d能够干燥;女神成熟最晚,果实最大,自然晾晒需要的时间长且不易干燥.[结论]在南疆地区采用自然晾晒的方法,法兰西和斯泰勒2个欧洲李品种适宜自然晾晒制干,品种女神则不适宜自然晾晒制干.     

不同干燥方法对无核白鸡心葡萄干色泽及次生代谢物质变化的影响

【目的】研究不同干燥工艺对葡萄干颜色及次生代谢物质的影响,为传统干燥工艺的改进提供理论依据。【方法】运用晒干和晾干两种制干方式,测定含水量、色差值、水分活度、总酚含量、总黄酮,分析颜色、酚类、酮类及香气物质。【结果】晒干方式干燥速率显著晾干方式,晾干方式葡萄果实内水分活度变化晒干方式,有利于形成绿色葡萄干;晒干、晾干方式葡萄干中总黄酮、多酚类物质含量先下降后上升的趋势,晾干葡萄干总黄酮、多酚类物质高于晒干葡萄干。制干过程中香气种类含量均呈现先上升后下降的趋势。【结论】采用晾干方式制干,干燥速率、水分活度变化均低于晒干方式,能较好的保存葡萄果实内的香气成分、总黄酮和多酚物质。     

汽车轮胎振动试验模态分析

利用振动试验模态分析的方法对汽车轮胎的振动特性进行了系统的分析,在自由悬挂支承条件下,对３种汽车轮胎径向和切向激振测试信号的数据处理与分析,求出５阶振型的频率及其相应振型。同时,对不同结构特征的轮胎的使用性能也做了探讨。