Coherent emission of light by thermal sources

A thermal light-emitting source, such as a black body or the incandescent filament of a light bulb, is often presented as a typical example of an incoherent source and is in marked contrast to a laser. Whereas a laser is highly monochromatic and very directional, a thermal source has a broad spectrum and is usually quasi-isotropic. However, as is the case with many systems, different behaviour can be expected on a microscopic scale. It has been shown recently that the field emitted by a thermal source made of a polar material is enhanced by more than four orders of magnitude and is partially coherent at a distance of the order of 10 to 100nm. Here we demonstrate that by introducing a periodic microstructure into such a polar material (SiC) a thermal infrared source can be fabricated that is coherent over large distances (many wavelengths) and radiates in well defined directions. Narrow angular emission lobes similar to antenna lobes are observed and the emission spectra of the source depends on the observation angle--the so-called Wolf effect. The origin of the coherent emission lies in the diffraction of surface-phonon polaritons by the grating.     

新型碳酚醛中的辐射热激波衰减特性

采用PVDF压电测量技术,在“闪光Ⅱ号”脉冲电子束加速器上,进行了新型碳酚醛复合材料（C/PH）的热激波传播实验研究;利用波传播过程中的渐进近似理论所推导出的波传播衰减公式,对C/PH材料中的脉冲波衰减进行了理论分析.结果表明：在电子束能通量为312～531 J/cm^2和电子平均能量为0.422～0.697 MeV条件下,对厚度为4 mm的碳酚醛靶而言,其热激波应力峰值为0.807～2.223 GPa;热激波在靶中的衰减与波的强度和脉冲宽度有关,对于强度相同的热激波,脉冲持续时间越短,热激波的衰减则越快;对于脉冲宽度一定的热激波,热激波的强度越高,则其衰减越快.实验结果和解析公式具有较好的一致性.     

热辐射对双陶瓷层热障涂层的隔热影响

基于热传导、热对流和热辐射理论建立了双陶瓷层热障涂层不透明和半透明物理模型,采用有限元ANSYS软件模拟了稳态温度场.双陶瓷层在不透明时,顶层厚度增加,顶层上表面温度线性增加,第二层和黏结层上表面温度线性降低.在半透明性弱时,与不透明情况类似.在半透明性强时,顶层上表面温度略低于不透明时,第二层上表面温度高于不透明时,黏结层上表面温度先快速后缓慢降低再保持不变,且远高于不透明时.     

Direct observation of Anderson localization of matter waves in a controlled disorder

In 1958, Anderson predicted the localization of electronic wavefunctions in disordered crystals and the resulting absence of diffusion. It is now recognized that Anderson localization is ubiquitous in wave physics because it originates from the interference between multiple scattering paths. Experimentally, localization has been reported for light waves, microwaves, sound waves and electron gases. However, there has been no direct observation of exponential spatial localization of matter waves of any type. Here we observe exponential localization of a Bose-Einstein condensate released into a one-dimensional waveguide in the presence of a controlled disorder created by laser speckle. We operate in a regime of pure Anderson localization, that is, with weak disorder-such that localization results from many quantum reflections of low amplitude-and an atomic density low enough to render interactions negligible. We directly image the atomic density profiles as a function of time, and find that weak disorder can stop the expansion and lead to the formation of a stationary, exponentially localized wavefunction-a direct signature of Anderson localization. We extract the localization length by fitting the exponential wings of the profiles, and compare it to theoretical calculations. The power spectrum of the one-dimensional speckle potentials has a high spatial frequency cutoff, causing exponential localization to occur only when the de Broglie wavelengths of the atoms in the expanding condensate are greater than an effective mobility edge corresponding to that cutoff. In the opposite case, we find that the density profiles decay algebraically, as predicted in ref. 13. The method presented here can be extended to localization of atomic quantum gases in higher dimensions, and with controlled interactions.     

Decoherence in crystals of quantum molecular magnets

Quantum decoherence is a central concept in physics. Applications such as quantum information processing depend on understanding it; there are even fundamental theories proposed that go beyond quantum mechanics, in which the breakdown of quantum theory would appear as an 'intrinsic' decoherence, mimicking the more familiar environmental decoherence processes. Such applications cannot be optimized, and such theories cannot be tested, until we have a firm handle on ordinary environmental decoherence processes. Here we show that the theory for insulating electronic spin systems can make accurate and testable predictions for environmental decoherence in molecular-based quantum magnets. Experiments on molecular magnets have successfully demonstrated quantum-coherent phenomena but the decoherence processes that ultimately limit such behaviour were not well constrained. For molecular magnets, theory predicts three principal contributions to environmental decoherence: from phonons, from nuclear spins and from intermolecular dipolar interactions. We use high magnetic fields on single crystals of Fe(8) molecular magnets (in which the Fe ions are surrounded by organic ligands) to suppress dipolar and nuclear-spin decoherence. In these high-field experiments, we find that the decoherence time varies strongly as a function of temperature and magnetic field. The theoretical predictions are fully verified experimentally, and there are no other visible decoherence sources. In these high fields, we obtain a maximum decoherence quality-factor of 1.49?×?10(6); our investigation suggests that the environmental decoherence time can be extended up to about 500 microseconds, with a decoherence quality factor of ～6?×?10(7), by optimizing the temperature, magnetic field and nuclear isotopic concentrations.     

内嵌富勒烯量子位的消相干研究

利用马尔可夫近似方法计算了X@C60（X=^14N,^15N,^31P）量子位中电子自旋在核子的精细作用和外磁场作用下的密度算符演化行为,得出量子位驰豫时间在10～100ns范围,与其它文献相符．     

偏二甲肼池火灾模型及热辐射伤害研究

泄漏偏二甲肼池火灾产生的热辐射可能导致周围人员伤亡、设备损坏或人员中毒事故.通过池火灾计算模型对泄漏偏二甲肼池火的火焰半径、火焰高度、火灾总的热辐射通量以及目标入射热辐射通量等参数进行了计算.根据热辐射和伤害准则,对偏二甲肼池火灾造成的伤害进行了研究,这对应急救援等具有一定的指导意义.     

辐射问题格林函数的基本解

根据边值条件和特解与定解条件,地出了用于有限水深有航速的浮动结构物绕流辐射问题格林函数的基本解,并经数学处理得到了覆盖深水和无航速辐射问题格林函数的全部解。     

退相干和量子力学的诠释

近二十年来,针对量子力学围绕其概念基础产生的哲学争议,产生了不同于“哥本哈根诠释”和“正统”解释的可供选择的解诠方案。在解决测量问题上,退相干单独不能解决测量问题,但是退相干把环境相互作用包括进来不仅提出了新的观念问题,而且暗示了基本问题的解决方案。     

用射频低温氧化法去除未熟烃源岩中的有机质方法研究

利用GP02-A高频感应加热设备产生高频磁场，等离子体在高频磁场中激活氧气形成活性氧，活性氧在低温低压下氧化烃源岩中的有机质，从而达到去除有机质并确定其含量的目的。采用射频低温氧化法对我国7个盆地未熟烃源岩进行了有机质去除的实验，结果表明，在最佳条件下用20-40h可把未熟烃源岩中的有机质去除，我国7个盆地未熟烃源岩中有机质的质量含量为1．53％～3．17％。     

基于Matlab的溶解有机物的三维荧光矩阵构建

三维荧光光谱(EEM)结合平行因子分析(PARAFAC)能够根据水体中有机物的荧光性质对荧光组分特征、种类进行区分。大量原始数据以及常规的手工处理方式直接影响着该方法的广泛应用。提出了一种基于Matlab软件的三维荧光光谱数据快速转化为荧光矩阵的思路与方法。该方法根据不同研究者测定参数的不同,结合不同校正方法,可快速地将大量样品的三维荧光数据整合为三维荧光矩阵,通过具体数据验证荧光矩阵形成进行平行因子分析。该方法能够实现整个过程操作简单,人工干预少,可达到快速、批量完成三维荧光光谱数据处理的目的。     

用射频低温氧化法去除未熟烃源岩中的有机质方法研究

利用GP0 2 A高频感应加热设备产生高频磁场 ,等离子体在高频磁场中激活氧气形成活性氧 ,活性氧在低温低压下氧化烃源岩中的有机质 ,从而达到去除有机质并确定其含量的目的。采用射频低温氧化法对我国 7个盆地未熟烃源岩进行了有机质去除的实验 ,结果表明 ,在最佳条件下用 2 0～ 4 0h可把未熟烃源岩中的有机质去除 ,我国 7个盆地未熟烃源岩中有机质的质量含量为 1.5 3%～ 3.17%。     

太阳辐射下车辆内外温度场数值模拟

利用CFD的技术,考虑车辆材料及光学特性,应用离散坐标热辐射模型对在太阳辐射下车辆内外温度场进行了数值模拟.模拟结果可为车辆研发中改善车厢内的高温问题提供有效辅助参考和借鉴.     

Schwarzschild黑洞周围时空中两类粒子的热辐射定律

利用Schwarzschild黑洞的瞬时辐出度,导出黑洞Fermi子场和Bose子场的辐射谱及Wien位移定律。因辐射粒子的种类不同,导出的两类粒子的辐射谱及Wien位移定律略有不同。     

Decoherence of quantum superpositions through coupling to engineered reservoirs

The theory of quantum mechanics applies to closed systems. In such ideal situations, a single atom can, for example, exist simultaneously in a superposition of two different spatial locations. In contrast, real systems always interact with their environment, with the consequence that macroscopic quantum superpositions (as illustrated by the 'Schrodinger's cat' thought-experiment) are not observed. Moreover, macroscopic superpositions decay so quickly that even the dynamics of decoherence cannot be observed. However, mesoscopic systems offer the possibility of observing the decoherence of such quantum superpositions. Here we present measurements of the decoherence of superposed motional states of a single trapped atom. Decoherence is induced by coupling the atom to engineered reservoirs, in which the coupling and state of the environment are controllable. We perform three experiments, finding that the decoherence rate scales with the square of a quantity describing the amplitude of the superposition state.     

热辐射在介质表面反射及折射的微观机理

通过建立热辐射在介质表面散射的微观物理模型,数值模拟了任意入射角下热辐射散射的电场强度分布图形,得到了在任一入射角下的反射角及折射角.模拟结果与经典公式推导的结果吻合得很好,表明所建立的模型揭示了热辐射在介质表面反射及折射的微观机理.