Super-Simple Resolvable Balanced Incomplete Block Designs with Block Size 4 and Index 4

The necessary conditions for the existence of a super-simple resolvable balanced incomplete block design on v points with block size k = 4 and index λ = 4, are that v ≥ 16 and v ≡ 4 (mod 12). These conditions are shown to be sufficient.     

Performance of Physical-Layer Network Coding in Asymmetric Two-Way Relay Channels

In this paper, we study the performance of physical-layer network coding in asy- mmetric two-way relay channels using four different cases having different poor channels： phase asymmetry, downlink asymmetry, uplink asymmetry and node asymmetry. The decision and mapping rule for symmetric and asymmetric cases are studied. The performance in terms of bit error rate for each case will be studied and analysed by computer simulation. Analytical and simulation results show that uplink asymmetry is the worst case; intra-phase asymmetry and unreliable uplink channels will more severely affect the performance degradation, which is caused by channel asymmetry.     

伪补MS-代数的滤子同余关系

在伪补MS-代数上引入余核滤子和完全滤子的概念,研究伪补MS-代数的余核滤子和完全滤子的性质,获得了余核滤子和完全滤子生成的同余关系的表达式,证明了具有余核滤子的最小同余关系有同余一致性.     

Mean first-passage time for random walks on undirected networks

In this paper, by using two different techniques we derive an explicit formula for the mean first-passage time (MFPT) between any pair of nodes on a general undirected network, which is expressed in terms of eigenvalues and eigenvectors of an associated matrix similar to the transition matrix. We then apply the formula to derive a lower bound for the MFPT to arrive at a given node with the starting point chosen from the stationary distribution over the set of nodes. We show that for a correlated scale-free network of size N with a degree distribution P(d) ∼ d ^−γ , the scaling of the lower bound is N ^1−1/γ . Also, we provide a simple derivation for an eigentime identity. Our work leads to a comprehensive understanding of recent results about random walks on complex networks, especially on scale-free networks.     

典型超分子体系在放射化学领域的应用

本文主要通过评述两类超分子体系和离子印迹聚合物对重要金属离子的分离研究,阐明超分子化学在放射化学领域的重要应用。第一类超分子体系所含的主体分子有冠醚、杯芳烃、杯芳冠醚等大环化合物。第二类超分子体系主要有反胶束、微乳液和液膜。离子印迹聚合物通过超分子的识别功能实现对离子的选择性分离,而在液膜分离技术中,超分子的输运功能得到了很好的诠释。本文还对超分子化学在放射化学领域的应用前景作了分析展望。     

An anomaly intrusion detection method using fourier transform

A set of discrete points obtained from audit records on a behavior session is processed with Fourier transform. The criterion of selecting Fourier transform coefficients is introduced, and is used to find a unified value from the set of coefficients. This unified value is compared with a threshold to determine whether the session is abnormal. Finally simple test results are reported.     

PVT法CdS单晶生长

Based on the physical vapor transport （PVT） method, the growth of large-size CdS crystals inside a vertical semi-closed tube is studied. Firstly, in order to ensure 1D diffusion-advection transport, multi-thin tubes are used in the growth tube. The XRD spectra of the CdS crystal grown in this configuration indicates that the crystal quality has clearly been improved, where the FWHM is 58.5 arcsec. Secondly, theoretical and experimental growth rates under different total pressures are compared; the results show that the experiential growth rate equation is valid for our semi-tube growth, and it could be used to estimate the growth rate and maximum growth time under different total pressures.     

Mn掺杂GaN粉末的制备和性质研究

利用溶胶.凝胶法制备了不同Mn质量分数(0%～7%)的GaMnN粉体样品.经XRD检测所有样品均为六角纤锌矿结构,没有发现第二相,而且晶格常数随Mn质量分数的增加而增加.光致发光谱(PL)结果显示,紫外发光峰P1为GaN来源于带间发射的本征发光峰,且随着Mn质量分数增加略有红移,说明GaN的带隙变窄.XPS谱证明Mn离子处于 2价.磁性测量显示,所有掺Mn的样品在5 K温度下均为顺磁性,居里-外斯温度为负值,表明样品中最近邻Mn离子之间存在着很强的反铁磁相互作用.     

蓝宝石衬底上HVPE-GaN表面形貌研究

通过研究蓝宝石衬底上HVPE-GaN的表面形貌,指导HVPE-GaN工艺.工艺是在自制的立式HVPE设备上进行的,通过显微镜观察了各种不同工艺条件下的GaN表面形貌.发现不采用成核层直接生长的GaN表面粗糙为多晶,而采用低温成核层所得到的GaN表面随着Ⅴ/Ⅲ比由大到小,从包状表面向坑状表面过渡,通过选择合适的Ⅴ/Ⅲ,可以得到表面光滑、无色透明的GaN.其XRD摇摆曲线半高宽为450 arcs,表面粗糙度为0.9 mm.     

Preparation of nitrogen-doped titanium dioxide with visible-light photocatalytic activity using a facile hydrothermal method

Nitrogen-doped TiO₂ (N-TiO₂) nanoparticles have been successfully prepared via a direct and simple hydrothermal reaction of a commercial Degussa P25 with triethanol amine as solvent and nitrogen source. As-prepared N-TiO₂ was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), ultraviolet-visible light (UV-vis) absorption spectra, electron probe microanalysis (EPMA) and X-ray photoelectron spectroscopy (XPS) techniques. The results confirm that hydrothermal reaction is an effective way to incorporate nitrogen into the TiO₂ lattice, especially nitrogen substitute for titanium. The nitrogen concentration in TiO₂ can be as high as 21% (molar ratio), which is described as Ti_1−yO_2−xN_x+y (in this paper, x=0.36, y=0.27, i.e., Ti_0.73O_1.64N_0.63). The chemical statuses of N have been assigned to N-Ti-O and O-N-O in the TiO₂ lattice as identified by XPS. Photocatalytic degradation of methyl orange has been carried out in both UV-vis (simulated solar light) and the visible region (λ>400 nm). N-TiO₂ exhibits higher activity than the Degussa P25 TiO₂ photocatalyst, particularly under visible-light irradiation. This study has developed a promising and practical pathway to new nitrogen-doped photocatalysts.