A Compton scattering image reconstruction algorithm based on total variation minimization

Compton scattering imaging is a novel radiation imaging method using scattered photons.Its main characteristics are detectors that do not have to be on the opposite side of the source,so avoiding the rotation process.The reconstruction problem of Compton scattering imaging is the inverse problem to solve electron densities from nonlinear equations,which is ill-posed.This means the solution exhibits instability and sensitivity to noise or erroneous measurements.Using the theory for reconstruction of sparse images,a reconstruction algorithm based on total variation minimization is proposed.The reconstruction problem is described as an optimization problem with nonlinear data-consistency constraint.The simulated results show that the proposed algorithm could reduce reconstruction error and improve image quality,especially when there are not enough measurements.     

半导体纳米晶在生物标记领域的应用

对半导体纳米晶的概念、性质、应用前景进行了概述,详细介绍了以ZnS、ZnSe半导体纳米晶体为代表的由IIB-VI族原子组成的低毒半导体纳米晶的制备、光谱学性质及其当前在生物标记领域的应用.     

左右手系材料界面处全反射行为的特性

基于电磁场理论，推导了左右手系材料界面处发生全反射时的物理特性，分析了相位变化情况.提出利用左右手系材料构成周期性结构，观测全反射时介质中隐失波干涉的实验设想，并从理论上计算了干涉条纹的分布. 关键词： 左手材料 负折射率 全反射 隐失波     

Magnetization Reversal in Magnetic Bilayer Systems

Magnetization reversal in magnetic soft/hard bilayer systems is studied analytically by means of a variational method for magnetic energies in a continuum model. The demagnetization curve is involved with nonlinear equations,and the solution is given implicitly in the form of Jacobi functions,which is valid for the total reversal process. Based on the non-trivial solutions, hysteresis loops, as well as the maximum energy product(BH)_(max) versus thicknesses of soft/hard layers are obtained. With regard to(BH)_(max), improvement of the remanence competes with loss of coercive force. As a result, an optimum condition exists. For a given thickness of the hard layer, the optimum condition at which the largest(BH)_(max) could be achieved is discussed, which is slightly different from previous works.     

金纳米粒子/碳纳米管修饰电极吸附伏安法测定微量间苯二胺

运用循环伏安法及线性扫描伏安法研究了间苯二胺在金纳米粒子/碳纳米管修饰玻碳电极上的电化学行为,优化并建立了一种直接测定间苯二胺的电化学分析方法。结果表明,与裸玻碳电极相比,金纳米粒子/碳纳米管修饰电极能显著提高间苯二胺的氧化峰电流。在优化条件下,氧化峰电流与间苯二胺浓度在3.0×10-8~1.0×10-6mol/L范围内呈现良好的线性关系,检出限为1.0×10-8mol/L,对1.0×10-7mol/L的间苯二胺溶液平行测定10次的RSD为4.2%。测定了实验室废水中的间苯二胺含量,3次测定结果的平均回收率为99.7%,RSD为2.1%。     

双钙钛矿SrKFeWO6的电子结构与磁性

基于密度泛函理论框架下的第一性原理,采用考虑在位库仑作用的广义梯度近似（GGA＋U）下的投影缀加波（PAW）方法,研究了具有双钙钛矿结构的Sr₂FeWO₆和SrKFeWO₆材料的晶体结构、电子结构以及磁性性质.结构优化表明,K空穴掺杂稳定了FeO₆及WO₆八面体结构,Fe-O-W键角更加接近180°,有利于Fe-O-W-O-Fe超交换作用;对电子结构分析发现掺杂元素本身对总态密度贡献很小,空穴（p 关键词： 电子结构 磁性 6')" href="#">SrKFeWO₆ 双钙钛矿     

纳米孔隙薄膜中孔隙率与折射率关系的研究

用时域有限差分算法(FDTD)构造了纳米孔隙高分子薄膜的网格结构，并模拟了理想单色平面光波在纳米孔隙高分子薄膜中的传输过程，计算出不同孔隙率的薄膜所对应的等效折射率。模拟结果显示纳米孔隙薄膜的等效折射率与孔隙率呈线性递减的关系。还利用固体材料学中的混合材料等效介电常量理论建立了一种混合介质并联理论模型，很好地解释了纳米孔隙高分子薄膜孔隙率与等效折射率的关系而且得到了纳米孔隙高分子薄膜等效折射率与孔隙率的函数关系式。将模拟结果与混合介质并联理论模型相比较，发现该理论模型的函数曲线与时域有限差分算法模拟的结果相互吻合。     

阻挫诱导的亚铁磁性Heisenberg系统中的量子相变

利用密度矩阵重整化群(DMRG)方法研究磁性阻挫对一种S=1/2准一维反铁磁自旋链但却具有亚铁磁性的Heisenberg系统基态的影响.计算了单个晶胞的基态能、自旋关联函数以及自旋能隙.研究表明这种Heisenberg自旋系统的基态随着阻挫α的增强将从磁有序相变化到自旋无序相，并且伴随着自旋能隙的出现，量子相变点为α≈0.412.同时线形链上格点间自旋长程关联值的计算结果表明在磁有序区间体系的磁有序性质随着α的增强而减弱，阻挫在0≤α<     

用多壁碳纳米管修饰玻碳电极为工作电极循环伏安法测定辛硫磷

将多壁碳纳米管(MWCNT′s)置于硝酸-硫酸(1+1)溶液中回流6 h使之净化及功能化。取MWCNT′s 5 mg置于超纯水10 mL中经超声振荡20 min制得其悬浮液,取悬浮液10μL滴加在玻碳电极(GCE)表面,经自然干燥后即得用MWCNT′s修饰的玻碳电极(MWCNT′s/GCE)。基于此修饰电极对辛硫磷的催化还原反应,提出了蔬菜中辛硫磷的循环伏安测定法,在pH 4的乙酸盐支持电解质溶液中,在电位0.78 V(对SCE)处可见明显的还原峰,且其峰电流值与辛硫磷浓度在5.0×10-8~1.0×10-6mol.L-1之间呈线性关系。应用此法分析了两件蔬菜样品,并以此试样为基体加入标准溶液对方法进行回收及精密度试验,测得其回收率的平均值和相对标准偏差(n=5)分别依次为100.3%,96.5%及3.7%,3.2%。     

Analytical and Numerical Studies of Quantum Plateau State in One Alternating Heisenberg Chain

By using the coupled duster method and the numerical density matrix renormalization group method, we investigate the properties of the quantum plateau state in an alternating Heisenberg spin chain. In the absence of a magnetic field, the results obtained from the coupled cluster method and density matrix renormalization group method both show that the ground state of the aiternating chain is a gapped dimerized state when the parameter a exceeds a critical point ac. The value of the critical points can be determined precisely by a detailed investigation of the behavior of the spin gap. The system therefore possesses an m = 0 plateau state in the presence of a magnetic field When a 〉 ac. In addition to the m = 0 plateau state, the results of density matrix renormaiization group indicate that there is an m = 1/4 plateau state that occurs between two critical fields in the alternating chain if a 〉 1. The mechanism for the m = 1/4 plateau state and the critical behavior of the magnetization as one approaches this plateau state are also discussed.