基于有效端元集的双线性解混模型

光谱解混是用于定量分析高光谱图像中成分含量的一项重要技术方法,主要包括线性解混模型和非线性解混模型。线性解混模型构造简单,但并未考虑不同成分光子间的相互影响,导致解混结果在很多实际图像上不够精确。常用的非线性混合模型中的双线性解混算法,随着图像中端元数量增加,虚拟端元的数量也随之快速增加,计算精度受到很大的影响。论文报道改进了双线性解混的模型,并提出一种有效端元子集的选择算法。首先结合欧氏距离和光谱夹角,按照与混合像元的距离,将所有端元排序;然后利用排序结果和误差变化情况选择实际参与混合的端元子集。从而降低了未参与特定混合像元混合的端元对解混结果的影响,提高了解混精度。对模拟图像的测试效果证明了该算法可以减小光谱的重构误差,对实际航拍高光谱溢油图像的分析结果也进一步说明了算法的有效性。     

钙离子调控微丝切割蛋白中A6亚基解折叠的单分子力谱研究

在生命活动中,金属离子扮演了非常重要的角色.微丝切割蛋白(adseverin)需要钙离子的活化才能行使其切割肌动蛋白微丝的功能.本文通过基于原子力显微镜的单分子力谱研究了微丝切割蛋白C端末的A6亚基在结合钙离子前后的力学解折叠机理.实验结果显示:在未结合钙离子时,A6的解折叠表现为两态过程;在结合钙离子后A6力学稳定性显著提高;同时,钙离子的结合使得A6解折叠过程中出现稳定的中间态.通过对中间态的链长的分析,我们推测了中间态对应着A6的N端部分解折叠.而这一部分的解折叠可以使得掩藏在该结构后的A5亚基中肌动蛋白微丝结合位点暴露,从而促使微丝切割蛋白执行功能.我们的实验结果为理解微丝切割蛋白的工作原理提供了新的实验证据.     

Tesla变压器次级线圈电位分布

 为研究Tesla变压器锥形次级线圈的电位和电场分布问题,建立了非均匀参数双传输线模型,采用差分方法获得波动方程的数值解。计算结果表明：脉冲形成线充电过程中,最高场强点从次级线圈小半径端逐渐向大半径端移动;脉冲形成线快速放电后,次级线圈场强最大点位于大半径端部;脉冲形成线不能正常放电时,次级线圈最大场强点也位于大半径端部,此时场强达到最大值,约为平均场强的1.5倍。     

双向使用高非线性光纤实现同时解复用出两路10 Gbit/s信号

提出一种利用双向使用高非线性光纤(HNLF)实现同时解复用出两路信号的全光解复用方案.将复用信号和控制光的混合信号从HNLF的两端同时注入,复用信号中的某一路信号通过交叉相位调制使控制光产生蓝移或红移,在HNLF的输出端用窄带滤波器将控制光的蓝移或红移部分滤出从而同时实现两路信号解复用.理论分析了信号光和控制光在HNLF中的相互作用和解复用原理.搭建80 Gbit/s光时分复用系统,对双向使用HNLF的解复用结构进行了实验研究.在HNLF的两个输出端同时实现不同信道的无误码解复用,其中信道解复用的最大功率代价为2.6 dB.     

锁模光纤激光器中矢量孤子的传输特性研究

以含有慢饱和吸收效应的耦合非线性薛定谔方程组为模型,对锁模光纤激光器中亮亮类孤子对的产生及传输进行了详细地研究。首先,采用拟解法解析得到了慢饱和吸收效应影响下的一组新型的精确亮亮类孤子解;其次,采用分步傅立叶变换法数值研究了啁啾类亮亮孤子解的演化特性,并在输出端将数值结果与精确解进行了比对;最后,数值研究了一定幅度的白噪声干扰下亮亮类孤子解的稳定性。结果表明:一定的参数条件下,锁模光纤激光器中存在亮亮类孤子解,并且该解在一定的白噪声扰动下,可以实现较长距离的稳定传输。     

高速Cameralink视频信号的光纤传输系统设计

针对目前常用的Cameralink视频信号的光纤传输方案系统结构过于复杂的问题,提出一种基于MAX9249/MAX9268的Cameralink视频信号的光纤传输方案。在发送端利用MAX9249实现Cameralink视频信号解串行化、编码、串行化,得到光模块驱动信号CML;在接收端利用MAX9268实现CML信号解串行化、解码、串行化,得到Cameralink视频信号,并对光收发模块的设计与选型作了详细阐述。用示波器抓取发送端和接收端高速串行信号的眼图,结果比较清晰,眼睛张开度大,发送端的Q因子为24.46,满足发送端大于12的要求,接收端Q因子为8.13,满足接收端大于6的要求。计算机采集的实时画面,经过10 min传输无明显可视的像素噪点,验证了该传输方案的可行性和有效性。     

用于光谱解混的正交向量投影算法

光谱解混是高光谱技术中的关键部分,对地物成分的定量分析至关重要。线性光谱解混方法在计算端元丰度时,大多需要涉及矩阵求逆或方阵行列式的计算,导致软件实现的计算复杂度高,且硬件实现困难。同时,当端元数量增加时,算法的计算量也会随之呈指数级快速增长。论文基于传统的正交子空间投影方法,利用正交原理,提出了一种新的光谱解混方法——正交向量投影。该方法首先利用Gram-Schmidt过程计算每个端元的最终正交向量分量,并将其作为代表端元的投影向量。然后对于任意的待解混光谱向量,直接将其投影到该正交向量上。最后,计算得到投影分量的长度与正交向量的长度比,即为该正交向量所代表端元的无约束丰度。该过程避免了正交子空间投影和最小方差方法中计算复杂、实现困难的矩阵求逆运算,更便于并行计算的设计和硬件实现。通过理论的推导分析,证明了该算法与正交子空间投影和最小方差方法是完全一致的。另外,由于算法避免了矩阵相乘和求逆运算,简化了解混过程,通过对不同算法复杂度的具体分析,也证明该算法相对其他算法可以对端元数量降低一个量级。最后,在模拟数据和实际图像上分别进行实验测试,结果的分析和比较,也说明了算法的有效性。     

τ真空

在讨论一维实标量场的定态孤粒子解时,我们注意到在标量场理论中存在另一类严格解,这类解的能量、动量和角动量都为零。因此是真空,称之为“τ真空”。若进一步要求场的正则动量为零(π=0)或要求场为实数,则τ真空自动给出通常自发破缺对称的真空解((?)=常数)。本文分别讨论了(?)理论、Sine-Gordan理论及L秩位势情况下的一级类量子修正。虽然这个真空解是一个虚数解,但是这类解对于研究真空的机制是重要的,因为过渡到欧氏空间它就成为通常的孤粒子解。     

粗糙度对岩石热红外光谱解混影响的实验研究

现有的岩石热红外光谱解混,大多针对颗粒岩石,无法满足自然界块状岩石高精度光谱解混的要求。研究将粗糙度作为影响光谱发射率与解混精度的考虑因素,研究块状岩石的热红外光谱解混问题。以自然岩石表面形态为依据,设计了三个粗糙度等级;顾及到岩石的结构情况,采用矿物块体拼接的方法模拟制作了3种块状岩石;通过相同和不同粗糙度的解混实验,来研究自然界块状岩石的表面粗糙度对岩石光谱特征和光谱解混的影响规律。结果表明,当矿物端元与岩石在相同粗糙度下光谱线性解混时,效果较好;而在不同粗糙度下解混时,60个解混结果中有48.3%误差超过5%,最大达到25.3%。基于此,建议在实际岩矿高光谱定量遥感中,应该充分考虑粗糙度对光谱解混的影响。     

基于条纹级次编码与调制的结构光相位展开算法

利用相位级次的编码和调制方法将相位级次信息叠加到相移图像中,提出了一种直接利用相移图像进行相位解包裹的方法。在投影端,提出了一种邻接不重复德布鲁因序列,并用该序列对相位级次进行编码,然后将该周期级次编码序列调制、叠加到多步相移图像中。相应地,在解码阶段,从拍摄到的相移图像中同时解调、分解出包裹相位和周期级次编码序列,通过序列的匹配还原真实周期级次信息,并最终准确地解包裹出绝对相位。以四步相移法为例,本文方法相比传统的时间相位解包裹算法,投影图片从10张(64个相位周期)缩减到了4张,提高了测量效率。     

Direct evidence for reversible diffusional phase change in nanometer-sized alloy particles

Solid solubility in isolated nanometer-sized particles has been studied by in situ transmission electron microscopy using alloy particles in the Pb-Sn binary system. In approximately 17-nm-sized particles of a lead-56 at. % Sn solid solution, a phase change from a single phase of the lead solid solution to two phases, a lead solid solution and a tin-solid solution, takes place when the temperature is reduced from 110 degrees C to room temperature (RT). Furthermore, it is confirmed that this phase change could occur rather reversibly when the temperature is cyclically changed between 110 degrees C and RT. This observation provides direct evidence for reversible diffusional phase change in nanometer-sized alloy particles. It seems safe to conclude that the solubility limit of tin in lead is higher than 56 at. % at 110 degrees C, which is almost 5 times higher than the solubility limit of tin in bulk lead (i.e., 10 at. %).     

Hydrodynamic limit of the stationary Boltzmann equation in a slab

We study the stationary solution of the Boltzmann equation in a slab with a constant external force parallel to the boundary and complete accommodation condition on the walls at a specified temperature. We prove that when the force is sufficiently small there exists a solution which converges, in the hydrodynamic limit, to a local Maxwellian with parameters given by the stationary solution of the corresponding compressible Navier-Stokes equations with no-slip boundary conditions. Corrections to this Maxwellian are obtained in powers of the Knudsen number with a controlled remainder.     

Fabrication of Aquivion-type membranes and optimization of their elastic and transport characteristics

The solution casting technology was applied to manufacture thin polymer films (~?20–30 μm) from the ionomer solution of perfluorinated polymer with short side chains (an analogue of the commercial polymer Aquivion®). The influence of annealing temperature on the mechanical properties (elastic limit), proton conductivity, and heat capacity was investigated. The elastic limit, glass transition temperature, and proton conductivity of the samples were found to reach their maximum values at the annealing temperature 170?±?5 °C. Comparative studies of membrane-electrode assemblies (MEA) using the commercial (Nafion NR212) and solution-casted membranes were carried out. MEA with optimized Aquivion-type membranes showed satisfactory values of fuel crossover and maximum output power. The results of the conducted studies show that the prepared Aquivion-type membranes are very promising for practical application in MEA.     

A holographic description of theta-dependent Yang-Mills theory at finite temperature

Theta-dependent gauge theories can be studied using holographic duality through string theory in certain spacetimes.By this correspondence we consider a stack of N_0 dynamical DO-branes as D-instantons in the background sourced by N_c coincident non-extreme black D4-branes.According to the gauge-gravity duality,this D0-D4 brane system corresponds to Yang-Mills theory with a theta angle at finite temperature.We solve the IIA supergravity action by taking account into a sufficiently small backreaction of the Dinstantons and obtain an analytical solution for our D0-D4-brane configuration.Subsequently,the dual theory in the large N_c limit can be holographically investigated with the gravity solution.In the dual field theory,we find that the coupling constant exhibits asymptotic freedom,as is expected in QCD.The contribution of the theta-dependence to the free energy gets suppressed at high temperatures,which is basically consistent with the calculation using the Yang-Mills instanton.The topological susceptibility in the large N_c limit vanishes,and this behavior remarkably agrees with the implications from the simulation results at finite temperature.Moreover,we finally find a geometrical interpretation of the theta-dependence in this holographic system.     

Low-temperature solution of the Sherrington-Kirkpatrick model

I propose a simple scaling ansatz for the full replica symmetry breaking solution of the Sherrington-Kirkpatrick model in the low energy sector. This solution is shown to become exact in the limit x --> 0, Bx --> infinity of the Parisi replica symmetry breaking scheme parameter . The distribution function of the frozen fields has been known to develop a linear gap at zero temperature. The scaling equations are integrated to find an exact numerical value for the slope of the gap thetaP(x,y)/delta|(y --> 0) = 0.301 046.... I also use the scaling solution to devise an inexpensive numerical procedure for computing finite time scale (x =1) quantities. The entropy, the zero field cooled susceptibility, and the local field distribution function are computed in the low-temperature limit with high precision, barely achievable by currently available methods.     

Bistability effects of the brownian motion in periodic potentials

In the stationary state the equation of motion for particles moving in a periodic potential has two solutions, a locked one and a running one, for low and intermediate damping constants and for suitable external forces. The effect of an additional Langevin force to this bistable behaviour is investigated. For finite noise strength, the mobility depends continuously on the external force, whereas in the limit of vanishing strength of the noise force one gets a sharp transition between the locked and the running solution at a critical external force. This critical force is calculated exactly in the low friction limit and approximately for intermediate friction constants. Furthermore the temperature dependence for various forces including the critical one is shown in the low friction limit.     

Estimation of heat transfer and temperature rise in partial-body regions during MR procedures: an analytical approach with respect to safety considerations

In order to assess thermal response to RF exposure during MR procedures at the tissue level, simple analytical solutions to the non-stationary Pennes' bio-heat equation were obtained using the Green's function approach. Two thermal models appropriate for partial-body exposure were analyzed: In the first model, the temperature field at the periphery of an idealized volume RF resonator was modeled. The analytical solution reveals that tissue response to RF heating is characterized by an equilibration time and length. Both parameters are inversely related to tissue perfusion and vary for the soft-tissues considered between 0.27-25 min and 1.5-12 mm, respectively. None of the tissues investigated increase in temperature more than 0.5 degrees C for each W/kg of power dissipated. Secondly, a homogeneous tissue solution was derived that predicts the temperature-time course to an MR examination with time-varying specific absorption rates (SAR). Since SAR limits indicated in current MR safety standards relate to running SAR averages computed over an appropriate period of time, an expression was formulated that gives an upper limit for the temperature rise averaged over the same period of time, as a function of both the upper limit of running SAR averages and the duration of the MR examination. The analysis revealed that the partial-body SAR limits indicated in the IEC standard may not guarantee under all circumstances compliance with the basic restrictions concerning temperature rise.     

Generalized reference fields and source interpolation for the difference formulation of radiation transport

In the difference formulation for the transport of thermally emitted photons the photon intensity is defined relative to a reference field, the black body at the local material temperature. This choice of reference field combines the separate emission and absorption terms that nearly cancel, thereby removing the dominant cause of noise in the Monte Carlo solution of thick systems, but introduces time and space derivative source terms that cannot be determined until the end of the time step. The space derivative source term can also lead to noise induced crashes under certain conditions where the real physical photon intensity differs strongly from a black body at the local material temperature.In this paper, we consider a difference formulation relative to the material temperature at the beginning of the time step, or in cases where an alternative temperature better describes the radiation field, that temperature. The result is a method where iterative solution of the material energy equation is efficient and noise induced crashes are avoided. We couple our generalized reference field scheme with an ad hoc interpolation of the space derivative source, resulting in an algorithm that produces the correct flux between zones as the physical system approaches the thick limit.     

Kinetics of quasiballistic transport in nanoscale semiconductor structures: is the ballistic limit attainable at room temperature?

Electron transport in nanoscale semiconductor structures is theoretically investigated to answer the question of whether or not the ballistic limit is really attainable under room temperature operation. The semiclassical Boltzmann transport equation is solved analytically under the relaxation time approximation for n(+)-n-n(+) test structures. We demonstrate that the solution of the Boltzmann transport equation exhibits a boundary layer structure near the potential barrier and thus the scatterings in the active region cannot be neglected even in nanoscale structures, as far as they are operated at room temperature under high applied voltages.     

Mean field theory of a quantum heisenberg spin glass

A full mean-field solution of a quantum Heisenberg spin-glass model is presented in a large- N limit. A spin-glass transition is found for all values of the spin S. The quantum critical regime associated with the quantum transition at S = 0 and the various regimes in the spin-glass phase at high spin are analyzed. The specific heat is shown to vanish linearly with temperature. In the spin-glass phase, intriguing connections between the equilibrium properties of the quantum problem and the out-of-equilibrium dynamics of classical models are pointed out.