A novel image restoration algorithm based on high-dimensional space geometry

A novel image restoration approach based on high-dimensional space geometry is proposed, which is quite different from the existing traditional image restoration techniques. It is based on the homeomorphisms and "Principle of Homology Continuity" (PHC), an image is mapped to a point in high-dimensional space. Begin with the original blurred image, we get two further blurred images, then the restored image can be obtained through the regressive curve derived from the three points which are mapped form the images. Experiments have proved the availability of this "blurred-blurred-restored" algorithm, and the comparison with the classical Wiener Filter approach is presented in final.

Analysis of mode quality factors and mode reflectivities for nanowire cavity by FDTD technique

The mode frequency and the quality factor of nanowire cavities are calculated from the intensity spectrum obtained by the finite-difference time-domain (FDTD) technique and the Pade approximation. In a free-standing nanowire cavity with dielectric constant epsilon = 6.0 and a length of 5 mu m, quality factors of 130, 159, and 151 are obtained for the HE11 modes with a wavelength around 375 nm, at cavity radius of 60, 75, and 90 nm, respectively. The corresponding quality factors reduce to 78, 94, and 86 for a nanowire cavity standing on a sapphire substrate with a refractive index of 1.8. The mode quality factors are also calculated for the TE01 and TM01 modes, and the mode reflectivities are calculated from the mode quality factors.

Hydrogen behavior in GaN epilayers grown by NH3-MBE

Hydrogen behavior in unintentionally doped GaN epilayers on sapphire substrates grown by NH3-MBE is investigated. Firstly, we find by using nuclear reaction analysis (NRA) that with increasing hydrogen concentration the background electron concentration increases, which suggests that there exists a hydrogen-related donor in undoped GaN, Secondly, Fourier transform infrared (FTIR) absorption and X-ray photoelectron spectroscopy (XPS) reveal Further that hydrogen atom is bound to nitrogen atom in GaN with a local vibrational mode at about 3211 cm(-1) Hence, it is presumed that the hydrogen-related complex Ga. . .H-N is a hydrogen-related donor candidate partly responsible for high n-type background commonly observed in GaN films. Finally, Raman spectroscopy results of the epilayers show that ill addition to the expected compressive biaxial strain, in some cases GaN films suffer from serious tensile biaxial strain. This anomalous behavior has been well interpreted in terms of interstitial hydrogen lattice dilation. (C) 2001 Elsevier Science B.V. All rights reserved.

Structural characterization of InGaAs/GaAs quantum dots superlattice infrared photodetector structures

InGaAs/GaAs quantum dots (QDs) superlattice grown by molecular beam epitaxy (MBE) at different substrate temperatures for fabricating 8-12 mu m infrared photodetector were characterized by transmission electron microscopy (TEM), double-crystal X-ray diffraction (DCXRD) and photoluminescence (PL). High-quality QDs superlattice can be achieved by higher growth temperature. Cross-sectional TEM shows the QDs in the successive layers are vertically aligned along growth direction. Interaction of partial vertically aligned columns leads to a perfect vertical ordering. With increasing number of bilayers, the average QDs size becomes larger in height and rapidly saturates at a certain value, while average lateral length nearly preserves initial size. This change leads to the formation of QDs homogeneous in size and of a particular shape. The observed self-organizations are attributed to the effect of strain distribution at QDs on the kinetic growth process. DCXRD measurement shows two sets of satellite peaks which corresponds to QDs superlattice and multi quantum wells formed by the wetting layers. Kinematical simulations of the wetting layers indicate that the formation of QDs is associated with a decrease of the effective indium content in the wetting layers. (C) 1999 Elsevier Science B.V. All rights reserved.

Uniformity enhancement of the self-organized InAs quantum dots

Growth interruption was introduced after the deposition of GaAs cap layer, which is thinner than the height of quantum dots. Uniformity of quantum dots has been enhanced because the full-width of half-maximum of photoluminescence decrease from 80 to 27 meV in these samples as the interruption time is increased. Meanwhile, we have observed that the peak position of photoluminescence is a function of interruption time, which can be used to modulate energy level of quantum dots. All of the phenomenon mentioned above can be attributed to the diffusion of In atoms from the tops of InAs islands to the top of GaAs cap layer caused by the difference between the surface energies of InAs and GaAs. (C) 1999 Elsevier Science B.V. All rights reserved.

Crystallographic and magnetic properties of R3Fe29-xVxN4 (R = Y, Ce, Nd, Sm, Gd, Tb, and Dy)

A systematic investigation of crystallographic and magnetic properties of nitride R3Fe29-xVxN4 (R = Y, Ce, Nd, Sm, Gd, Tb, and Dy) has been performed. Nitrogenation leads to a relative volume expansion of about 6%. The lattice constants and unit cell volume decrease with increasing rare-earth atomic number from Nd to Dy, reflecting the lanthanide contraction. On average, the Curie temperature increases due to the nitrogenation to about 200 K compared with its parent compound. Generally speaking, nitrogenation also results in a remarkable improvement of the saturation magnetization and anisotropy fields at 4.2 K and room temperature for R3Fe29-xVxN4 compared with their parent compounds. The transition temperature indicates the spin reorientations of R3Fe29-xVxN4 for R = Nd and Sm are at around 375 and 370 K which are higher than that of R3Fe29-xVx, for R = Nd and Sm 145 and 140 K, respectively. The magnetohistory effects of R3Fe29-xVxN4 (R = Ce, Nd, and Sm) are observed in low fields of 0.04 T. After nitrogenation the easy magnetization direction of Sm3Fe26.7V2.3 is changed from an easy-cone structure to the b-axis. As a preliminary result, a maximum remanence B-r of 0.94 T, an intrinsic coercivity mu(0)H(C) of 0.75 T, and a maximum energy product (B H)(max) of 108.5 kJ m(-3) for the nitride magnet Sm3Fe26.7V2.3N4 are achieved by ball-milling at 293 K.

A novel image restoration algorithm based on high-dimensional space geometry

A novel image restoration approach based on high-dimensional space geometry is proposed, which is quite different from the existing traditional image restoration techniques. It is based on the homeomorphisms and "Principle of Homology Continuity" (PHC), an image is mapped to a point in high-dimensional space. Begin with the original blurred image, we get two further blurred images, then the restored image can be obtained through the regressive curve derived from the three points which are mapped form the images. Experiments have proved the availability of this "blurred-blurred-restored" algorithm, and the comparison with the classical Wiener Filter approach is presented in final.

Synthesis and random laser application of ZnO nano-walls: a review

This review paper summarises briefly some important achievements of our recent research on the synthesis and novel applications of nanostructure ZnO such as honeycomb shaped 3-D (dimension) nano random-walls. A chemical reaction/vapour transportation deposition technique was employed to fabricate this structure on ZnO/SiO2/Si substrate without any catalyst and additive in a simple tube furnace to aim the low-cost and high qualified samples. Random laser action with strong coherent feedback at the wavelength between 375 nm and 395 nm has been firstly observed under 355 nm optical excitation with threshold pumping intensity of 0.38 MW/cm(2).

黄土丘陵区不同立地达乌里胡枝子群落水分特征及生物量研究

对黄土高原丘陵沟壑区不同立地条件下的达乌里胡枝子群落水分特征及生物量进行了研究.结果表明:(1)不同立地下的达乌里胡枝子蒸腾日变化均呈单峰型,上午呈上升趋势,于13:00达到峰值,之后均呈不同程度下降趋势.(2)不同立地达乌里胡枝子群落0~200 cm土层平均含水量为阴坡12.34%,半阳坡11.29%,半阴坡11.15%,阳坡8.96%.不同立地达乌里胡枝子叶片相对含水量和饱和亏与各立地土壤含水量关系密切.(3)不同立地下各个时期的达乌里胡枝子群落的地上生物量表现为阴坡>半阴坡>半阳坡>阳坡,地下生物量则表现为阳坡(447.39 g/m2)>半阳坡(409.12 g/m2)>半阴坡(344.92 g/m2)>阴坡(217.01 g/m2).可见,达乌里胡枝子群落的水分生理特性及生物量的积累与立地条件密切相关.

染料掺杂聚合物薄膜的激光行为研究

自20世纪60年代发展到现在，激光技术发展的速度十分惊人，应用的范围不断拓展，近年来随着有机/聚合物电致发光材料在有机发光二极管上的应用以及有机晶体管和有机太阳能电池的研制成功，科学家们开始了有机/聚合物材料放大自发发射和激光发射行为的研究。到目前为止，已经开发出了这种廉价、可以大面积成膜的、具有更广泛应用范围的有机/聚合物固体激光材料及光泵浦激光器。有机/聚合物激光器的出现不仅向传统激光理论提出了新的挑战，而且具有诸多潜在的应用价值。可以断言，在21世纪知识经济的大潮中，有机/聚合物激光器的研究必将推动传统学科的发展和新兴学科形成，也必将为人类带来巨大的经济效益。新的有机激光材料不断涌现、器件结构不断推陈出新、新的激发原理不断提出并得到修正已经成为有机/聚合物固体激光研究领域的三大特点。本论文进行了利用Förster能量传递对荧光染料DCJTB放大自发发射行为的优化、基于放大自发发射的红光染料DCJTB掺杂聚合物薄膜的白光发射、多孔结构对荧光染料放大自发发射行为的优化以及基于纳米结构的荧光染料DCJTB掺杂聚合物薄膜的激光行为等方面的研究工作，具体研究内容如下: 1、利用Förster能量传递理论，系统地研究了两种或三种染料共掺杂聚合物薄膜的放大自发发射（ASE）行为。研究表明，两种染料共掺杂显著改善了掺杂聚合物薄膜的ASE阈值、增益和损耗特性，而三种染料共掺杂，由于更多的Förster能量传递，使掺杂聚合物薄膜的ASE阈值、增益和损耗性能得到了进一步的改善。将Alq3和C545T两种绿光染料同时掺杂到DCJTB：PS中，通过利用Alq3和C545T同时的能量传递效应，已经使Alq3:C545T:DCJTB：PS薄膜的阈值、增益和损耗分别达到了0.007 mJ/pulse、52 cm-1和7 cm-1。 2、将红色荧光染料DCJTB掺杂到蓝色聚合物PFO中，通过控制DCJTB在PFO中的浓度，我们获得了具有放大自发发射的白光发射，当DCJTB在PFO的掺杂浓度为0.3%时显示了最好的白光ASE特性， 白光中DCJTB和PFO发射的阈值、增益和损耗分别达到了0.072 mJ pulse-1，0.035 mJ pulse-1；36.3 cm-1，22.35 cm-1和7.39 cm-1，15.88 cm-1。我们的结果表明，DCJTB掺杂聚合物PFO体系是实现ASE白光发射的有效方法，拓展了ASE的应用范围。 3、开发出了二维多孔SBA-15和三维TiO2反蛋白石光子晶体两种实现有机ASE有效发射的两种结构，通过利用有序结构的SBA-15的量子限域效应优化了蓝光染料C151的ASE阈值、增益和损耗特性，而通过利用三维TiO2反蛋白石光子晶体的量子限域效应，也使包埋其中的绿光染料C545T的ASE特性得到了明显改善。研究表明，无论是二维SBA-15多孔结构还是三维TiO2反蛋白石光子晶体结构，通过其量子限域效应都能很好地优化包埋其中的荧光染料的ASE特性，为进一步优化有机半导体的ASE特性提供了新的思路。 4、将聚苯乙烯纳米球分散到DCJTB:PS薄膜中和把DCJTB:PS薄膜旋涂在ZnO纳米柱阵列上两种方法，我们已经成功地研制出了多模随机有机激光发射器件。详细研究表明，多模随机有机激光发射特性显著地与聚苯乙烯纳米球的尺寸和浓度以及ZnO纳米柱的疏密程度密切相关，优化后的聚苯乙烯纳米球掺杂DCJTB:PS薄膜的阈值已经达到了0.06 mJ pulse-1cm-2，而ZnO纳米柱包埋DCJTB:PS薄膜的阈值达到了0.375 mJ pulse-1cm-2。我们的结果表明，聚苯乙烯纳米球和ZnO纳米柱都是实现随机有机激光的非常好的散射介质材料。