Ferromagnetic modification of GaN film by Cu+ ions implantation

The structural and magnetic properties of Cu+ ions-implanted GaN films have been reported. Eighty kilo-electron-volt Cu+ ions were implanted into n-type GaN film at room temperature with fluences ranging from 1 x 10(16) to 8 x 10(16) cm(-2) and subsequently annealed at 800 degrees C for 1 h in N-2 ambient. PIXE was employed to determine the Cu-implanted content. The magnetic property was measured by the Quantum Design MPMS SQUID magnetometer. No secondary phases or clusters were detected within the sensitivity of XRD. Raman spectrum measurement showed that the Cu ions incorporated into the crystal lattice positions of GaN through substitution of Ga atoms. Apparent ferromagnetic hysteresis loops measured at 10 K were presented. The experimental result showed that the ferromagnetic signal strongly increased with Cu-implanted fluence from 1 x 10(16) to 8 x 10(16) cm(-2).

p-type doping of GaInNAs quaternary alloys

Using the first-principles band-structure method, we investigate the p-type doping properties and band structural parameters of the random Ga1-xInxN1-yAsy quaternary alloys. We show that the Mg-Ga substitution is a better choice than ZnGa to realize the p-type doping because of the lower transition energy level and lower formation energy. The natural valence band alignment of GaAs and GaInNAs alloys is also calculated, and we find that the valence band maximum becomes higher with the increasing in composition. Therefore, we can tailor the band offset as desired which is helpful to confine the electrons effectively in optoelectronic devices. (C) 2008 Published by Elsevier B.V.

Influence of exotic Mn on magnetic properties of YCo5.0-xMnxGa7.0 (0.05 <= x <= 3.0)

The YCo5.0-xMnxGa7.0 compounds crystallize with the ScFe6Ga6-type structure. The lattice of YCo5.0-xMnxGa7.0 expands with the increase of the Mn content for 0.05 <= x <= 2.5, but the lattice of YCo2.0Mn3.0Ga7.0 shrinks compared with YCo2.5Mn2.5Ga7.0. The shrinkage of the lattice is attributed to the magnetostriction of YCo2.0Mn3.0Ga7.0. The substitution of Mn for Co forms magnetic clusters in the antiferromagnetic matrix. The magnetic frustration results in the spin-glass-like behavior for 0.8 <= x <= 1.5 and the difference between zero-field-cooling (ZFC) and field-cooling (FC) magnetizations for x = 2.0, 2.5, and 3.0. A stable long-range magnetic ordering appears among the Mn-centered magnetic clusters with the ordering temperature 110 K for x = 2.0. The hump in the thermomagnetization of YCo3.0Mn2.0Ga7.0 can be attributed to the competitive effects between the thermal fluctuation and the enhanced magnetic interaction. Both the hump and the bifurcation between the ZFC and the FC magnetizations of YCo3.0Mn2.0Ga7.0 occur at lower temperatures as the applied field increases. On the two-step magnetization curve of YCo3.0Mn2.0Ga7.0, the inflection point at 4000 Oe is due to the coercive field, and the magnetic moments in the clusters are tilted to the applied field above 4000 Oe. The magnetic ordering temperature is further increased to 210 K for x = 2.5 and to 282 K for x = 3.0. The spontaneous magnetization of YCo2.0Mn3.0Ga7.0 is 0.575 mu B/f.u. at 5 K with a canted magnetic structure.

Theoretical investigation on the phase stability of Nd2Fe14B and site preference of V, Cr, Mn, Zr and Nb

The stability of the excellent permanent magnetic compound Nd2Fe14B and substitution of Fe in the compound by V, Cr, Mn, Zr and Nb are investigated by using interatomic pair potentials which are converted from lattice-inversion method. Calculation shows that the substitution always makes the cell volume larger, and the increase of the volume is almost linear with substituent concentration. The calculated cohesive energy shows that the preferential order of substitution of Fe is Nb, V, Cr, Mn, Zr. Nevertheless, all the five substituting elements should most preferentially replace Fe in the j(2)' site, which has the greatest space among all six Fe sites. (C) 2005 Elsevier B.V. All rights reserved.

Raman scattering and photoluminescence studies of Zn1-xMnxO nanowires via vapor phase growth

In this paper, we investigated the Raman scattering and photoluminescence of Zn1-xMnxO nanowires synthesized by the vapor phase growth. The changes of E-2(High) and A(1(LO)) phonon frequency in Raman spectra indicate that the tensile stress increases while the free carrier concentration decreases with the increase of manganese. The Raman spectra exited by the different lasers exhibit the quantum confinement effect of Zn1-xMnxO nanowires. The photoluminescence spectra reveal that the near band emission is affected by the content of manganese obviously. The values Of I-UV/G decrease distinctly with the manganese increase also demonstrate that more stress introduced with the more substitution of Mn for Zn.

Structural and photoluminescent properties of ternary Zn1-xCdxO crystal films grown on Si(111) substrates

The ternary Zn1-xCdxO (0less than or equal toxless than or equal to0.6) alloying films with highly c-axis orientation have been deposited on Si(111) substrates by direct current reactive magnetron sputtering method. X-ray diffraction measurement indicates that the wurtzite-type structure of ZnO can be stabilized up to nominal Cd content x similar to 0.6 without cubic CdO phase separation. The lattice parameter c of Zn1-xCdxO increases almost linearly from 5.229 Angstrom (x = 0) to 5.247 Angstrom (x = 0.6), indicating that Cd substitution takes place on the Zn lattice sites. The photoluminescence spectra of the Zn1-xCdxO thin films measured at 12 K display a substantial red shift (similar to0.3 eV) in the near-band-edges (NBEs) emission of ZnO: from 3.39 eV of ZnO to 3.00 eV of Zn0.4Cd0.6O. The direct modulation of band gap caused by Zn/Cd substitution is responsible for the red shift effect in NBE emission of ZnO. (C) 2003 Elsevier Science B.V. All rights reserved.

The formation and characteristics of Si1-xCx alloys in Si crystals by means of implantation of cions with different doses

Carbon ions with concentration of (0.6-1.5)% were implanted into silicon crystals at room temperature and Si1-xCx alloys were grown by solid phase epitaxy with high temperature annealing. The formation and characteristics of Si1-xCx alloys under different implanted carbon doses were studied. If the implanted carbon atom concentration was less than 0.6%, carbon atoms would tend to combine with the defects produced during implantation and it was difficult for Si1-xCx alloys to form during annealing at 850-950 degreesC. With the increase of implanted C concentration, almost all implanted carbon atoms would occupy substitution positions to form Si1-xCx alloys, but only part of implanted carbon atoms would occupy the substitution position to form Si1-xCx alloys as the implanted dose increased to 1.5 %. Most Si1-xCx alloy phases would vanish as the annealing temperature was increased higher.

Improvement of the electrical property of semi-insulating InP by suppression of compensation defects

Semi-insulating (SI) InP obtained by iron phosphide ambient annealing has very low concentration of deep level defects and better electrical property than SI-InP annealed in phosphorus ambient. The defect suppression phenomenon correlates with Fe diffusion and substitution in the annealing process. Analysis of the experimental result suggests that a high activation ratio of incorporated Fe in InP has an effect of defect suppression in Fe-doped and Fe-diffused SI-InP.

毛乌素沙区土壤养分对湿地退化的响应

采用湿地生态理论中空间替代时间的研究方法,以毛乌素沙区退化湿地为研究对象,选择距退化湿地水面不同距离,具有不同地下水位埋深的研究区域代表湿地不同退化阶段,通过分析5个不同阶段退化湿地土壤的有机质、全氮、全磷随水平距离的变化特征,研究了土壤养分对湿地退化不同退化程度的响应特征。结果表明,不同退化阶段土壤有机质与全氮剖面均具有一个明显的富集层,既湿地退化前的泥炭沉积层。该沉积层在剖面中所处深度随退化程度的加剧而逐渐增加,且沉积层以上深度的有机质和全氮含量趋于一致。土壤中全磷含量在剖面波动较大,分布特征无明显规律,不同水平距离全磷平均含量无明显变化规律说明湿地退化对全磷含量无明显影响。以上研究结果表明,由于流动沙丘入侵是导致毛乌素沙地湿地退化的首要原因,湿地退化导致土壤有机质和全氮富集层深度逐渐下移,平均含量逐渐下降,而对全磷影响不大。

Band crossing in isovalent semiconductor alloys with large size mismatch: First-principles calculations of the electronic structure of Bi and N incorporated GaAs

For large size- and chemical-mismatched isovalent semiconductor alloys, such as N and Bi substitution on As sites in GaAs, isovalent defect levels or defect bands are introduced. The evolution of the defect states as a function of the alloy concentration is usually described by the popular phenomenological band anticrossing (BAC) model. Using first-principles band-structure calculations we show that at the impurity limit the N-(Bi)-induced impurity level is above (below) the conduction- (valence-) band edge of GaAs. These trends reverse at high concentration, i.e., the conduction-band edge of GaAs1-xNx becomes an N-derived state and the valence-band edge of GaAs1-xBix becomes a Bi-derived state, as expected from their band characters. We show that this band crossing phenomenon cannot be described by the popular BAC model but can be naturally explained by a simple band broadening picture.

Effect of partial site occupation on the magnetic properties of Nd2Fe17-xSix by supercell calculation

The magnetic properties of the Nd2Fe17-xSix intermetallic compounds are studied by means of spin-polarized supercell calculations in which the selected sites of substitution are close to the situations in real samples. It is shown that the average Fe moment increases with x and saturates near x = 3. This correlates quite well with the experimental dependence of Te on x. The difference between supercell and unit cell calculations are pointed out and the influence of Si atoms on the density of states of the nearby Fe atoms is emphasized. (C) 1997 American Institute of Physics.

An improved BP algorithm for pattern recognition

An improved BP algorithm for pattern recognition is proposed in this paper. By a function substitution for error measure, it resolves the inconsistency of BP algorithm for pattern recognition problems, i.e. the quadratic error is not sensitive to whether the training pattern is recognized correctly or not. Trained by this new method, the computer simulation result shows that the convergence speed is increased to treble and performance of the network is better than conventional BP algorithm with momentum and adaptive step size.

基于状态方面的Web服务动态替换

随着面向服务计算技术的成熟,服务复合已成为Internet上开发企业间业务协作的一种新模式,WS-BPEL是服务复合事实上的标准.但是由于复合服务所依赖的第三方伙伴服务的分布、自治和松散耦合等特性,在执行过程中易受到伙伴服务失效的影响,可靠性无法得到保证,因此需要支持在运行时对伙伴服务进行动态替换.目前的BPEL规范只提供有限的服务替换功能,当与伙伴服务的交互涉及到一系列有状态的会话操作时,服务替换就更加复杂.通过对面向方面的研究,提出面向BPEL语言的状态方面扩展.通过状态方面,记录与伙伴服务交互过程中的会话信息.在伙伴服务失效时,通过透明地替换伙伴服务,使得与当前伙伴服务的会话信息传播到功能等价的另一个伙伴服务上,以保证流程的正常执行.通过该方法,使得BPEL流程具有一定的自愈能力,增强了流程执行的可靠性.

5-氟尿嘧啶-β-环糊精结肠靶向前体药物的研究

5-氟尿嘧啶(5-Fluorouracil， 5-FU)是一种抗代谢药物，广泛用于临床治疗结直肠癌、胃癌、乳腺癌等多种癌症，但其首过代谢显著、亲脂性较低，选择性差、毒副作用大。为克服这些缺点人们对5-FU进行了大量的修饰工作，包括小分子修饰以及与各种载体形成微球、微囊、纳米粒、共价前药等。 环糊精(Cyclodextrin，简称CD)，可被结肠中的糖苷酶特异性地降解成小分子糖，而胃和小肠中由于缺乏相应的酶而使环糊精不被降解，这一特性在结肠药物的靶向输送及释放中有重要应用价值。环糊精中含有丰富的羟基，易进行化学修饰，将药物与环糊精通过共价键结合制成前药，使其在胃和小肠中不降解，而在盲结肠中被特异性的酶降解释出药物，达到结肠靶向释药的目的。研究表明，环糊精作为一种前药载体为结肠靶向释药和缓释、控释系统提供了一种有效的手段。 本工作选择5-氟尿嘧啶为模型药物、β-环糊精作为载体，通过中间体5-FU羧酸衍生物的制备及其与β-环糊精的偶联，合成了系列5-FU-β-CD前体药物，并利用紫外、红外、质谱、核磁、元素分析、热分析等手段对其进行结构表征。同时，还研究了前体药物的体外释药性质。具体内容包括： 1. 含有羧基的5-FU衍生物中间体的合成：(5-氟尿嘧啶-1-基)-乙酸(FUAC)、3-(5-氟尿嘧啶-1-基)-丙酸(FUPC)、5-(5-氟尿嘧啶-1-基)-戊酸(FUVC)的合成。 2. 中间体5-FU的羧酸衍生物与β-CD的偶联：分别通过以6-OTs-β-CD为中间体的取代法和活化酯法，合成了第一面取代和第二面取代的5-FU-β-CD大分子前体药物。在二面取代的前体药物制备中，通过改变原料的比例，合成了系列不同取代度(DS)的2-[(5-氟尿嘧啶-1-基)-乙酰基] -β-环糊精结合物。 3. 对上述前体药物进行体外释放研究：分别考察了前体药物在不同pH缓冲溶液中的水解行为及其在小鼠胃肠道人工体液中的酶解行为，并通过UV-Vis及HPLC对前体药物释放情况进行检测分析。 5-Fluorouracil(5-Fu), commonly known as a broad-spectrum antineoplastic drug, has been widely used in the treatment of various kinds of cancer including colon cancer for 40 years. However, this antitumor agent exhibits serious adverse effects, such as their marrow toxicity, gastrointestinal reaction and low selectivity in their clinical use. In order to improve its antitumor activity and reduce its toxicity, the compound was modified in various ways, including the formation of conjugated prodrugs with kinds of carrier, microsphere and nanoparticles etc. Cyclodextrins(CDs) are known to be barely capable of being hydrolyzed and only slightly absorbed in passing through the stomach and small intestine; however they are fermented into small saccharides by colonic microflora and thus absorbed as small saccharides in the large intestine. This biodegradation property of CDs may be useful as a colon-targeting carrier, and thus CD prodrugs may serve as a source of site-specific delivery of drugs to colon. It was demonstrated that prodrugs of CDs can provide a versatile means for construction of not only colon targeted delivery systems, but also delayed release systems. 5-Fluorouracil was taken as a model drug and β-CD as the carrier in this study. Series prodrugs of 5-FU was prepared through the preparation of reactive 5-FU derivatives containing carboxyl group and coupling to hydroxyl groups of CD. The structures of the conjugates were charactered by using IR, UV–vis, ESI-MS, 1H, 13C-NMR spectra, elemental analyses, and thermal analysis. In vitro hydrolysis behavior in aqueous solution and in rat gastrointestinal tract contents of the conjugates were also investigated. The main content of this dissertation includes following aspects: 1. The preparation of 5-FU derivatives containing carboxyl group: 5-Fluorouracil- acetic acid(FUAC)、3-(5-FU-1)-propionic acid (FUPC)、and 5-(5-FU-1)-valeric acid(FUVC). 2. The coupling of 5-FU derivatives to β-CD: 5-FU was selectively conjugated onto the primary or secondary hydroxyl groups of β-CD through an ester linkage, by the substitution of 6-OTs-β-CD and the activated ester method respectively. For the secondary face conjugation, the degree of substitution(DS) can be controlled by changing the mole ratio of the starting materials(FUAC and β-CD). 3. In vitro release behavior of the conjugates in aqueous solution and in rat gastro- intestinal tract contents of the conjugates were investigated, and the reaction was monitored and analyzed by using UV-Vis and HPLC methods.

N-烷基氮杂糖及其衍生物的合成

多羟基哌啶类化合物通常称为氮杂糖，由于与糖结构的相似性，亚胺基环醇表现出强的糖苷酶和糖基转移酶抑制活性，可调控在生物识别及酶结构控制中起到重要作用的糖蛋白的生物合成与水解。因此这类抑制剂有望成为与糖代谢紊乱有关的疾病的治疗药物，如：抗糖尿病、抗肿瘤、抗溶酶体贮积症及抗病毒感染（包括艾滋病）等药物。正是由于氮杂糖的重要生物活性及诱人的药用开发前景，近年来，有关氮杂糖及其衍生物的合成、生物活性及应用研究备受关注。 本论文探索了一系列的作为潜在的迈克加成中间体1-C-乙酰甲基/甲氧羰基甲基-5-N-取代呋喃核糖碳苷衍生物在碱的作用下先发生β-消除反应，接着发生分子内的迈克加成反应生成1-C-乙酰甲基-N-取代氮杂吡喃糖碳苷衍生物及1-C-甲氧羰基甲基-N-取代氮杂吡喃糖碳苷衍生物的方法，该转变过程为先通过β-消除得到非环状的α/β不饱和共轭酮或酯的中间体，接着5-N-取代氨基与分子内的α/β不饱和共轭酮或酯发生分子内的1,4-亲核加成，其中，2'-酯的环加成立体选择性的得到β型1-C-乙酰甲基-N-取代氮杂吡喃糖碳苷衍生物，而2'-酮的环加成得到立体异构体1-C-乙酰甲基-N-取代氮杂吡喃糖碳苷衍生物。此外，该类N-取代氮杂吡喃糖碳苷衍生物进一步脱除保护基，得到了一系列新的N-取代氮杂吡喃糖衍生物，拓展了氮杂吡喃糖碳苷分子库。 中间体1-C-(2'-oxoalkyl)-5-N-alkylated glycoribofuranoside的合成是由核糖为原料，通过对其结构修饰，在C-5氮原子上先引入不同的取代基，在C-1上引入乙酰甲基或甲氧羰基甲基。C-5取代氨基的引入通过两种方法：(a) 5-取代链状脂肪氨基可由链状的伯胺直接与5-甲磺酰基发生SN2亲核取代得到；(b) 5-取代芳香氨基可通过芳香醛与C-5氨基缩合再由硼氢化钠还原得到。2'-酰基的引入通过烯丙基氧化得到：2'-酮羰基由醋酸汞和琼斯试剂氧化得到；2'-酯基由高锰酸钾氧化再碘甲烷的作用下得到。 The polyhydroxylated piperidines, commonly be called azasugars. Iminocyclitols and their derivatives have exhibited remarkable biological activity to inhibit glycosidase-processing enzymes, with resulting potential chemotherapeutic applications against diabetes, cancer, lysosomal storage disorders and viral infections including AIDS. Recently, because of the important biological activity and excellent foreground on pharmaceutical application, great attention has been attracted to the synthesis of the new derivatives and analogues. In this dissertation, 1-C-(2'-oxoalkyl)-5-N-substituted-glycoribofuranosides, which used as latent substrates for intramolecular hetero-Michael addition, were converted to 2-ester and 2-ketone aza-C-glycopyranosides by base treatment. The transformation was achieved through β-elimination to an acyclic α/β-conjugated ketone or ester, followed by an intramolecular hetero-Michael addition by the 5-N-alkylated amino group. The 2-ester cycloaddition was highly stereoselective in favor of an equatorial 1-C-substitution while the 2-ketone cycloaddition was produced a pair of stereoisomers of 2′-ketonyl aza-C-glycoside. Additionally, the resultant different N-alkylated aza-C-glycopyranosides could be further prepared for various azasugar library constructions by removal of protecting groups. Synthesis of the key intermediate 1-C-(2'-oxoalkyl)-5-N-alkylated glycoribo- furanoside involved the introduction of 5-substituted amino and 1-C-2′-oxoalkyl groups from D-ribose. The 5-alkylated amino was introduced through two methods: (a) the 5-aliphatic series amino synthesized by the nucleophilic substitution of 5-mesylate using neat ethylamine, propylamine, butylamine, and hexylamine, (b) the 5-aromatic series amino synthesized by various aromatic aldehydes with C-5 amino under NaBH4 reduction. The 1-C-2′-oxoalkyl groups were introduced through oxidation of the ally group: the 1-C-allyl group was oxidized with Hg(OAc)2 and Jones reagent to the 2-ketonyl C-glycoside; the 1-C-allyl group was oxidized with KMnO4 and CH3I/NaHCO3 to 1-C-methyl acetate glycoside.