Coordinated observations of large scale coronal brightening and H_αsurge

During the post_flare phase of an eruptive two_ribbon flare on February 4, 1995, the Soft X_ray Telescope (SXT) on board Yohkoh observed the rapid brightening of a set of large scale coronal loops (150-200 Mm in length). Simultaneously, coordinated ground_based observations reveal a co_incident H α surge event. To our knowledge, no H α surge event coincident with the large scale coronal brightening observed by Yohkoh has been reported. The possible mechanisms for the concurrent cool plasma ejection and the filling of the hot coronal loops are discussed. It is found that magnetic reconnection between a magnetic arcade and an overlying large scale coronal structure may account for the coincident events. Big amount of magnetic energy was converted into both mechanic energy (about 10 22 J) in the mass ejection and thermal radiation (10 23 J) contained in the large SXR loops.     

RHESSI探测结果的重大科学意义

本文简单介绍了RHESSI的基本特点:高能量分辨率、高空间分辨率和高时间分辨率。论述了太阳耀斑放能机制之谜,“电子——离子束缚态及其引发核过程”(束缚态模型)对太阳耀斑放能机制的解释,RHESSI观测结果对太阳耀斑放能机制的检验。通过对太阳耀斑放能机制的分析,从而对黑洞、中子星、伽马爆等流行理论提出质疑。     

冷轧薄板试样电阻加热过程分析

为了确定薄板试样电阻加热系统的参数,掌握加热过程中电功率和电流的变化规律以及试样温度场的分布,利用电、热学理论,并结合有限元软件对薄板试样电阻加热过程进行了分析.针对特定的试样尺寸,确定加热变压器的功率为150 kW,副侧最高电压为24 V,最大输出电流为10 kA.对流和导热损失的功率可以忽略,因此,加热过程中输入的电功率主要用于试样的升温和弥补高温辐射热损失,以恒定速率加热时在低温和高温段所需的加热电流较大,中间温度段电流较小;由于水冷电极的影响,试样的温度场呈现中间高,两端低的梯形分布趋势.     

缓变动态Kerr黑洞视界附近的辐射能通量和辐射功率

采用黑洞的薄膜模型和局域热平衡的假定,研究缓变动态Kerr黑洞视界附近的辐射能通量和辐射功率,得到了缓变动态Kerr黑洞的热辐射满足广义Stefan-Boltzmann定律的结论。当截断距离以及薄膜厚度取定后,Kerr黑洞视界附近标量场的辐射能通量与辐射功率不仅与黑洞的质量有关,还与黑洞的视界变化率有关,表明黑洞周围的引力场和视界的变化均对黑洞的热辐射产生影响。     

加速运动荷电黑洞非热辐射粒子射程的研究

作者研究了加速运动荷电黑洞非热辐射粒子的能量范围与辐射方向的关系，结果是：方向不同的辐射粒子其平均射程亦不同。     

2018年热超构材料研发热点回眸

 热超构材料研发活动在2018年再次取得丰硕的研究成果。回顾了热超构材料2018年在热传导、热对流、热辐射3种传热方式方面的研究进展及应用，归纳为7个研究热点：结构表面高效调控热传导、非均匀热学结构理论进展及应用开发、热学零折射隐身斗篷、建立了变换热对流理论、反常对流传热现象、从太阳和太空中同步收集能量、热超构材料应用设计与集成开发。     

SSRF前端光子挡光器的结构设计和热应力分析

光子挡光器是同步辐射光束线前端区的重要部件,其主要作用是阻挡高强度同步辐射.利用有限元分析软件ANSYS,对上海同步辐射装置(SSRF)前端光子挡光器,进行了精细的温度和热应力分析.分析结果表明,新设计的光子挡光器热应力水平有了显著的降低,提高了光子挡光器承受热负载的能力,满足SSRF前端部件的设计要求.     

Electron acceleration from contracting magnetic islands during reconnection

A long-standing problem in the study of space and astrophysical plasmas is to explain the production of energetic electrons as magnetic fields 'reconnect' and release energy. In the Earth's magnetosphere, electron energies reach hundreds of thousands of electron volts (refs 1-3), whereas the typical electron energies associated with large-scale reconnection-driven flows are just a few electron volts. Recent observations further suggest that these energetic particles are produced in the region where the magnetic field reconnects. In solar flares, upwards of 50 per cent of the energy released can appear as energetic electrons. Here we show that electrons gain kinetic energy by reflecting from the ends of the contracting 'magnetic islands' that form as reconnection proceeds. The mechanism is analogous to the increase of energy of a ball reflecting between two converging walls--the ball gains energy with each bounce. The repetitive interaction of electrons with many islands allows large numbers to be efficiently accelerated to high energy. The back pressure of the energetic electrons throttles reconnection so that the electron energy gain is a large fraction of the released magnetic energy. The resultant energy spectra of electrons take the form of power laws with spectral indices that match the magnetospheric observations.     

Single-mode heat conduction by photons

The thermal conductance of a single channel is limited by its unique quantum value G(Q), as was shown theoretically in 1983. This result closely resembles the well-known quantization of electrical conductance in ballistic one-dimensional conductors. Interestingly, all particles-irrespective of whether they are bosons or fermions-have the same quantized thermal conductance when they are confined within dimensions that are small compared to their characteristic wavelength. The single-mode heat conductance is particularly relevant in nanostructures. Quantized heat transport through submicrometre dielectric wires by phonons has been observed, and it has been predicted to influence cooling of electrons in metals at very low temperatures due to electromagnetic radiation. Here we report experimental results showing that at low temperatures heat is transferred by photon radiation, when electron-phonon as well as normal electronic heat conduction is frozen out. We study heat exchange between two small pieces of normal metal, connected to each other only via superconducting leads, which are ideal insulators against conventional thermal conduction. Each superconducting lead is interrupted by a switch of electromagnetic (photon) radiation in the form of a DC-SQUID (a superconducting loop with two Josephson tunnel junctions). We find that the thermal conductance between the two metal islands mediated by photons indeed approaches the expected quantum limit of G(Q) at low temperatures. Our observation has practical implications-for example, for the performance and design of ultra-sensitive bolometers (detectors of far-infrared light) and electronic micro-refrigerators, whose operation is largely dependent on weak thermal coupling between the device and its environment.     

第22太阳活动周软X射线耀斑的统计研究

根据GOES卫星资料 (1～ 8 ) ,统计了第 2 2太阳活动周 (1986 .9～ 1996 .10 )软X射线耀斑数 ,共计 2 0 930个耀斑 ,其中X级最少 ,不到 1% ;M级为 10 % ;C级最多 ,约占 6 0 % .统计发现 ,此活动周有两个峰 ,分别在 1989年和 1991年 ,1989年平均耀斑指数为 4 2 7,1991年为 4 6 8;C、M及X级耀斑数在活动周的上升期迅速增大 ,两年多时间就达到极大 ;而下降期缓慢减小 ,长达 4年多 ;耀斑发生率随软X射线峰值流量的变化呈幂律谱分布 ,谱指数为 - 2 .135 ,相关系数为- 0 .987;小耀斑易受背景影响 ,B级耀斑以及C级耀斑中的较小者在峰年及其前后往往湮没在背景中 ,无法辨别 .还发现X射线耀斑的光学对应体 (Hα耀斑 )与X射线耀斑的比率随X射线耀斑级别的增高而增大 ,X级的光学对应体达 94 % ,M级为 83% ,C级为 6 3% ,B级只有 30 % .     

包含双温非热离子的尘埃等离子体中的三维尘埃声孤波

考虑高阶横向扰动的因素,使用约化摄动方法得到描述含有双温非热离子的无磁化尘埃等离子体中的尘埃声波的(3+1)维KP方程.详细讨论一些尘埃等离子体系统参数如电子与非热高温离子数密度v与μh、快离子数λ(α)、低温非热离子与电子的温度比1β、非热双温离子温度比2β对尘埃声孤波性质的影响.研究结果表明:这些因素均可显著影响和改变孤波结构.在考虑双温非热离子后,稀疏形孤波与压缩形孤波的临界条件也发生极大变化.     

A gamma-ray burst with a high-energy spectral component inconsistent with the synchrotron shock model

Gamma-ray bursts are among the most powerful events in nature. These events release most of their energy as photons with energies in the range from 30 keV to a few MeV, with a smaller fraction of the energy radiated in radio, optical, and soft X-ray afterglows. The data are in general agreement with a relativistic shock model, where the prompt and afterglow emissions correspond to synchrotron radiation from shock-accelerated electrons. Here we report an observation of a high-energy (multi-MeV) spectral component in the burst of 17 October 1994 that is distinct from the previously observed lower-energy gamma-ray component. The flux of the high-energy component decays more slowly and its fluence is greater than the lower-energy component; it is described by a power law of differential photon number index approximately -1 up to about 200 MeV. This observation is difficult to explain with the standard synchrotron shock model, suggesting the presence of new phenomena such as a different non-thermal electron process, or the interaction of relativistic protons with photons at the source.     

Ultra-relativistic electrons in Jupiter's radiation belts

Ground-based observations have shown that Jupiter is a two-component source of microwave radio emission: thermal atmospheric emission and synchrotron emission from energetic electrons spiralling in Jupiter's magnetic field. Later in situ measurements confirmed the existence of Jupiter's high-energy electron-radiation belts, with evidence for electrons at energies up to 20[?]MeV. Although most radiation belt models predict electrons at higher energies, adiabatic diffusion theory can account only for energies up to around 20[?]MeV. Unambiguous evidence for more energetic electrons is lacking. Here we report observations of 13.8[?]GHz synchrotron emission that confirm the presence of electrons with energies up to 50[?]MeV; the data were collected during the Cassini fly-by of Jupiter. These energetic electrons may be repeatedly accelerated through an interaction with plasma waves, which can transfer energy into the electrons. Preliminary comparison of our data with model results suggests that electrons with energies of less than 20[?]MeV are more numerous than previously believed.     

圆柱形空腔多孔材料辐射效应研究

 多孔材料具有孔隙率高、密度小和比表面积大等特征,在消声、减震、隔热和电磁屏蔽等应用方面具备多种优异性能。由于其在气孔中存在低热导率的空气介质,可以用作绝热材料。与其他相应材料相比,它具有耐高温和强度高的优点,已被广泛应用于航空航天、原子能和交通运输等行业。本文研究了热辐射效应对圆柱形空腔多孔材料传热性能的影响,推导了多孔材料局部有效热导率的方便工程应用的封闭公式。与已有理论结果比较,给出了本文公式的精度。数值算例揭示了孔洞对于热传输的有意义的影响规律。多孔材料的局部有效热导率可以分为两部分：一部分由固相和气相的纯传导引起,无量纲化的传导热导率不依赖于温度和孔径;另一部分由热辐射引起,随温度和孔径的变化而剧烈变化。在温度较低和孔径较小的情形下,辐射影响可以忽略不计。     

An exceptionally bright flare from SGR 1806-20 and the origins of short-duration gamma-ray bursts

Soft-gamma-ray repeaters (SGRs) are galactic X-ray stars that emit numerous short-duration (about 0.1 s) bursts of hard X-rays during sporadic active periods. They are thought to be magnetars: strongly magnetized neutron stars with emissions powered by the dissipation of magnetic energy. Here we report the detection of a long (380 s) giant flare from SGR 1806-20, which was much more luminous than any previous transient event observed in our Galaxy. (In the first 0.2 s, the flare released as much energy as the Sun radiates in a quarter of a million years.) Its power can be explained by a catastrophic instability involving global crust failure and magnetic reconnection on a magnetar, with possible large-scale untwisting of magnetic field lines outside the star. From a great distance this event would appear to be a short-duration, hard-spectrum cosmic gamma-ray burst. At least a significant fraction of the mysterious short-duration gamma-ray bursts may therefore come from extragalactic magnetars.     

低温冷箱中辐射与导热耦合传热的数值模拟

针对3种不同的隔热处理方案，对低温冷箱中辐射和导热耦合传热进行了数值模拟，同时考虑了管道、支架和横梁对系统传热的影响．计算结果表明：在相同情况下，采取设备包铝箔和加隔热屏的措施使换热器表面的辐射跑冷损失减少了2／3以上；只加铝箔隔热屏时，换热器与横梁间的热桥跑冷也得到了改善，跑冷损失减少了1／2左右。因此，在冷箱与换热器之间加铝箔隔热屏是改善低温冷箱温度分布和降低跑冷损失的一种有效方法。     

Non-thermal melting in semiconductors measured at femtosecond resolution

Ultrafast time-resolved optical spectroscopy has revealed new classes of physical, chemical and biological reactions, in which directed, deterministic motions of atoms have a key role. This contrasts with the random, diffusive motion of atoms across activation barriers that typically determines kinetic rates on slower timescales. An example of these new processes is the ultrafast melting of semiconductors, which is believed to arise from a strong modification of the inter-atomic forces owing to laser-induced promotion of a large fraction (10% or more) of the valence electrons to the conduction band. The atoms immediately begin to move and rapidly gain sufficient kinetic energy to induce melting--much faster than the several picoseconds required to convert the electronic energy into thermal motions. Here we present measurements of the characteristic melting time of InSb with a recently developed technique of ultrafast time-resolved X-ray diffraction that, in contrast to optical spectroscopy, provides a direct probe of the changing atomic structure. The data establish unambiguously a loss of long-range order up to 900 A inside the crystal, with time constants as short as 350 femtoseconds. This ability to obtain the quantitative structural characterization of non-thermal processes should find widespread application in the study of ultrafast dynamics in other physical, chemical and biological systems.     

端面泵浦板条激光器的热效应

从稳态热传导方程出发,研究了掺杂浓度为0.3％的Nd：YVO4板条状晶体内部的温度和热应力分布,计算了晶体端面泵浦区域中心和两端热应力随泵浦功率的变化以及单片晶体所能承受的最大泵浦功率,为大功率高光束质量的板条激光器的研制提供依据.     

钠钙玻璃在CO2激光作用下的热应力分析

为了研究钠钙玻璃在预热和无预热两种情况下进行激光加工所产生的热应力的差别,在考虑辐射和对流的情况下,建立了激光扫描玻璃板的传热数学模型.分析了热应力与温度场分布之间的关系,并用有限元软件Ansys进行了数值模拟,得到了钠钙玻璃在预热和无预热两种情况下进行激光加工的温度场和应力场分布.计算结果显示预热后进行激光加工产生的热应力小于无预热的情况,试验结果与理论分析和数值计算基本符合.     

Cosmic gamma-ray background from structure formation in the intergalactic medium

The Universe is filled with a diffuse background of gamma-ray radiation, the origin of which remains one of the unsolved puzzles of cosmology. Less than one-quarter of the gamma-ray flux can be attributed to unresolved discrete sources, such as active galactic nuclei; the remainder appears to constitute a truly diffuse background. Here we show that the shock waves induced by gravity in the gas of the intergalactic medium, during the formation of large-scale structures like filaments and sheets of galaxies, produce a population of highly relativistic electrons. These electrons scatter a small fraction of the cosmic microwave background photons in the local Universe up to gamma-ray energies, thereby providing the gamma-ray background. The predicted diffuse flux agrees with the observed background across more than four orders of magnitude in photon energy, and the model predicts that the gamma-ray background, though generated locally, is isotropic to better than five per cent on angular scales larger than a degree. Moreover, the agreement between the predicted and observed background fluxes implies a mean cosmological density of baryons that is consistent with Big Bang nucleosynthesis.