Memory effect in a system of zincblende Mn-rich Mn(Ga)As nanoclusters embedded in GaAs

Zincblende Mn-rich Mn(Ga)As nanoclusters embedded in GaAs matrices are fabricated by in situ postgrowth annealing diluted magnetic semiconductor (Ga,Mn)As films with Mn concentration ranging from 2.6% to 8% at 650 degrees C. Magnetization measurements show that memory effect and slow magnetic relaxation, the typical characteristics of the spin-glass-like phase, occur below the blocking temperature of 45 K in samples with high Mn concentration, while for samples with low Mn concentration, ferromagnetic order remains up to 360 K. The behavior of low-temperature spin dynamics can be explained by the hierarchical model. (c) 2007 American Institute of Physics.

Material growth and device fabrication of highly strained InGaAs/InGaAsP long wavelength distributed feedback lasers

1.6-1.7 mu m highly strained InGaAs/InGaAsP distributed feedback lasers was grown and fabricated by low pressure mentalorganic chemical vapor deposition. High quality highly strained InGaAs/InP materials were obtained by using strain buffer layer. Four pairs of highly strained quantum wells were used in the devices and carrier blocking layer was used to improve the temperature characteristics of the devices. The uncoated 1.66 mu m and 1.74 mu m lasers with ridge wave guide 3 mu m wide have low threshold current (< 15mA) and high output power (> 14mW at 100mA). In the temperature range from 10 degrees C to 40 degrees C, the characteristic temperature T-0 of the 1.74 mu m laser is 57K, which is comparable to that of the 1.55 mu m-wavelength InGaAsP/InP-DFB laser.

SOI-based 16x16 thermo-optic waveguide switch matrix

A 16 x 16 thermo-optic wavelenght switch matrix has been designed and febricated on silicon-on-insulator wafer. For reducing device lenght, blocking switch matrix configuration is chosen. The building block of a matix is a 2 x 2 cell with Mach-Zehnder interferometer configuration, where a multi-mode interferometer serves as splitters/combiners. Spot size converters and isolating grooves are integrated on the same chip to reduce loss and power consumption. Average power consumption of the switch cell is 220 mW. The switching time of a switch cell is less than 3 mu s.

High-speed and high-power 1.3 mu m InGaAsP/InP selective proton-bombarded buried crescent lasers with optical field attenuation regions

High-speed and high-power InGaAsP/lnP selective proton-bombarded buried crescent (SPB-BC) lasers with optical field attenuation regions were reported. The defect of proton bombardment can not affect the lifetime of the SPB-BC laser because the optical field attenuation region obstructs the growth and propagation of defects. A CW light output over 115 mW was achieved at room temperature using a 500 mu m long cavity SPB-BC laser. The 3 dB bandwidth was 8.5 GHz, and the lifetime was about 8.5 x 10(5) h. The capacitance of four kinds of current blocking structures was first measured in our experiment, and the results shown that the capacitance of proton-bombarded pnpn structure was not only less than that of pnpn current blocking structure, but also less than that of semi-insulating Fe-InP structure.

In-Situ Boron and Aluminum Doping and Their Memory Effects in 4H-SiC Homoepitaxial Layers Grown by Hot-Wall LPCVD

The in-situ p-type doping of 4H-SiC grown on off-oriented (0001) 4H-SiC substrates was performed with trimethylaluminum (TMA) and/or diborane (B2H6) as the dopants. The incorporations of Al and B atoms and their memory effects and the electrical properties of p-type 4H-SiC epilayers were characterized by secondary ion mass spectroscopy (SIMS) and Hall effect measurements, respectively. Both Al- and B-doped 4H-SiC epilayers were p-type conduction. It was shown that the profiles of the incorporated boron and aluminum concentration were in agreement with the designed TMA and B2H6 flow rate diagrams. The maximum hole concentration for the Al doped 4H-SiC was 3.52x10(20) cm(-3) with Hall mobility of about 1 cm(2)/Vs and resistivity of 1.6 similar to 2.2x10(-2) Omega cm. The heavily boron-doped 4H-SiC samples were also obtained with B2H6 gas flow rate of 5 sccm, yielding values of 0.328 Omega cm for resistivity, 5.3x10(18) cm(-3) for hole carrier concentration, and 7 cm(2)/VS for hole mobility. The doping efficiency of Al in SiC is larger than that of B. The memory effects of Al and B were investigated in undoped 4H-SiC by using SIMS measurement after a few run of doped 4H-SiC growth. It was clearly shown that the memory effect of Al is stronger than that of B. It is suggested that p-type 4H-SiC growth should be carried out in a separate reactor, especially for Al doping, in order to avoid the join contamination on the subsequent n-type growth. 4H-SiC PiN diodes were fabricated by using heavily B doped epilayers. Preliminary results of PiN diodes with blocking voltage of 300 V and forward voltage drop of 3.0 V were obtained.

SOI optical switch matrix integrated with spot size converter (SSC) and total internal reflection (TIR) mirrors

SOI (Silicon on Insulator) based photonic devices has attracted more and more attention in the recent years. Integration of SOI optical switch matrix with isolating grooves, total internal reflection (TIR) mirrors and spot size converter (SSC) was studied. A folding re-arrangeable non-blocking 4x4 optical switch matrix and a blocking 16x16 matrix with TIR mirrors and SSC were fabricated on SOI wafer. The performaces, including extinction ratio and the crosstalk, are better than before. The insertion loss and the polarization dependent loss (PDL) at 1.55 mu m increase slightly with longer device length, more bend and intersecting waveguides. The insertion losses decrease 2 similar to 3 dB when anti-reflection films are added in the ends of the devices. The rise and fall times of the devices are 2.1 mu s and 2.3 mu s, respectively.

Homoepitaxial growth and characterization of 4H-SiC epilayers by low-pressure hot-wall chemical vapor deposition

Horizontal air-cooled low-pressure hot-wall CVD (LP-HWCVD) system is developed to get high quality 4H-SiC epilayers. Homoepitaxial growth of 4H-SiC on off-oriented Si-face (0001) 4H-SiC substrates purchased from Cree is performed at a typical temperature of 1500 degrees C with a pressure of 40 Torr by using SiH4+C2H4+H-2 gas system. The surface morphologies and structural and optical properties of 4H-SiC epilayers are characterized with Nomarski optical microscope, atomic force microscopy (AFM), x-ray diffraction, Raman scattering, and low temperature photoluminescence (LTPL). The background doping of 32 pm-thick sample has been reduced to 2-5 x 10(15) cm(-3). The FWHM of the rocking curve is 9-16 arcsec. Intentional N-doped and B-doped 4H-SiC epilayers are obtained by in-situ doping of NH3 and B2H6, respectively. Schottky barrier diodes with reverse blocking voltage of over 1000 V are achieved preliminarily.

Recent progresses of SOI-based photonic devices - art. no. 60201R

SOI (Silicon on Insulator) based photonic devices, including stimulated emission from Si diode, RCE (Resonant Cavity Enhanced) photodiode with quantum structure, MOS (Metal Oxide Semiconductor) optical modulator with high frequency, SOI optical matrix switch and wavelength tunable filter are reviewed in the paper. The emphasis will be played on our recent results of SOI-based thermo-optic waveguide matrix switch with low insertion loss and fast response. A folding re-arrangeable non-blocking 4x4 matrix switch with total internal reflection (TIR) mirrors and a first blocking 16 x 16 matrix were fabricated on SOI wafer. The extinction ratio and the crosstalk are better. The insertion loss and the polarization dependent loss (PDL) at 1.55 mu m increase slightly with longer device length and more bend and intersecting waveguides. The insertion losses are expected to decrease 2-3 dB when anti-reflection films are added in the ends of the devices. The rise and fall times of the devices are 2.1 mu s and 2.3 mu s, respectively.

A Selective-Area Metal Bonding InGaAsP-Si Laser

A 1.55-mu m hybrid InGaAsP-Si laser was fabricated by the selective-area metal bonding method. Two Si blocking stripes, each with an excess-metals accommodated space, were used to separate the optical coupling area and the metal bonding areas. In such a structure, the air gap between the InGaAsP structure and Si waveguide has been reduced to be negligible. The laser operates with a threshold current density of 1.7 kA/cm(2) and a slope efficiency of 0.05 W/A under pulsed-wave operation. Room-temperature continuous lasing with a maximum output power of 0.45 mW is realized.

FM-index分块并行算法及其实现

查询海量数据有压缩和索引两种方法来提高速度,该文结合这两种方法提出了压缩查询的方法.FM-index是一种自索引的全文查询算法,存在内存占用过大的问题,对于复杂的查询效率也不理想.该文提出分块FM-index算法,在分块的基础上采用MPI对算法进行并行化,解决了内存占用过多的问题,达到了较好的并行效率.

GOTOBLAS一般矩阵乘法高效实现机制的研究

对GOTOBLAS库(GOTO)的实现机制,尤其是其中的一般矩阵乘法部分的实现进行了分析.结合近年来的一些研究成果,讨论了如何高效地实现矩阵相乘操作,把存储层次对程序性能的影响提高到计算模型的高度.对比实验表明,GOTO库的性能远远高于没有考虑存储层次的一般BLAS库.证明了GOTO库性能上的优越性和将存储层次引入计算模型的必要性.

Recombinant protein of heptad-repeat HR212, a stable fusion inhibitor with potent anti-HIV action in vitro

HR212, a recombinant protein expressed in Escherichia coli, has been previously reported to inhibit HIV-1 membrane fusion at low nanomolar level. Here we report that HR212 is effective in blocking laboratory strain HIV-1IIIB entry and replication with EC50 values of 3.92±0.62 and 6.59±1.74 nM, respectively, and inhibiting infection by clinic isolate HIV-1KM018 with EC50 values of 44.44±10.20 nM, as well as suppressing HIV-1- induced cytopathic effect with an EC50 value of 3.04±1.20 nM. It also inhibited HIV-2ROD and HIV-2CBL-20 entry and replication in the μM range. Notably, HR212 was highly effective against T20-resistant strains with EC50 values ranging from 5.09 to 7.75 nM. Unlike T20, HR212 showed stability sufficient to inhibit syncytia formation in a time-of-addition assay, and was insensitive to proteinase K digestion. These results suggest that HR212 has great potential to be further developed as novel HIV-1 fusion inhibitor for treatment of HIV/ AIDS patients, particularly for those infected by T20-resistant variants.

Homoepitaxial Growth of 4H-SiC and Ti/4H-SiC SBDs

Homoepitaxial growth of4H-SiC on off-oriented Si-face （0001） 4H-SiC substrates was performed at 1500℃ by using the step controlled Epitaxy. Ti/4H-SiC Schottky barrier diodes （SBDs） with blocking voltage over lkV have been made on an undoped epilayer with 32μm in thick and 2-5 × 10^15 cm^-3 in carrier density. The diode rectification ratio of forward to reverse （defined at ± 1V） is over 107 at room temperature and over 10^2 at 538K. Their electrical characteristics were studied by the current-voltage measurements in the temperature range from 20 to 265 ℃. The ideality factor and Schottky barrier height obtained at room temperature are 1.33 and 0. 905eV, respectively. The SBDs have on-state current density of 150A/cm^2 at a forward voltage drop of about 2.0V. The specific on-resistance for the rectifier is found to be as 7.9mΩ · cm^2 and its variation with temperature is T^2.0.

吲哚生物碱Desbromoarborescidine A 的全合成及烯胺C-亚磺酰化反应研究

从新几内亚核桃木的树皮中分离得到的吲哚类喹诺里西定生物碱10-Desbromoarborescidine A，因发现其具有阻滞钙离子通道的活性而倍受关注。10-Desbromoarborescidine A由A、B、C、D四个环组成，只有一个手性中心，是吲哚生物碱中结构较简单的一种，常作为此类生物碱全合成方法的模型化合物。但迄今为止，能高效而简便的实现手性10-Desbromoarborescidine A不对称全合成方法线路不多，大多数以不对称诱导的方式建立其手性中心，手性催化的方式仅有一例金属催化。从逆合成分析可知，Desbromoarborescidine A的全合成可以通过亚胺不对称催化还原进行关键的手性中心构建，而本课题组在之前的研究中通过手性有机小分子催化剂的发展，已将三氯硅烷氢转移还原亚胺发展成了一类简便实用、高效、高对映选择性并具有优良底物适应范围的不对称催化反应，我们希望以这一反应作为关键手段，发展一条Desbromoarborescidine A及其类似物不对称合成新路线。 根据我们设计的新路线，首先成功合成了其关键中间体，然后我们进行了关键的不对称催化尝试。用本实验室已有的高性能有机小分子催化剂虽得到了较好的对应选择性，但是产率很低。同时，为了验证整条线路的可行性，我们也用消旋的中间体进行拉通线路的尝试。但不幸的是，在脱除保护基时遇到了很大困难。尝试换不同的保护基，或改变脱保护基的顺序，都未能成功合成目标产物。究其原因可能是由于吲哚的特殊性造成的，吲哚类亚胺与常规的芳香亚胺有较大的差异，其NH基团无论保护还是不保护，对与其2位相联接的C=N双键均有很大的影响，导致其不对称催化还原难以进行。另外，由于所设计的还原产物含有处在吲哚苄位的胺基，稳定性较差，造成保护基脱除困难。 烯胺C-亚磺酰化反应是本课题组最近发现的一个新反应，之前未见文献报道。本研究对该反应进行了反应条件优化和底物扩展，发现带Cbz，Ac，COt-Bu，CO2Et，Bz等保护基的一系列环状和非环状烯胺在亚磺酸钠、DMAc和MeSiCl3的共同作用下能高效高产率生成β-胺基烯基亚砜类新化合物，为合成多官能团化的烯基亚砜新化合物提供了一条简便实用的途径。 The main constituent of Dracontomelum mangiferum B1, indoloquinolizidine alkaloid 10-Desbromoarborescidine A, has drawn great attention due to its calcium channel blocking activity. Its molecular structure is relatively simple compared with the other alkaloids of the same type, which has only one chiral center, albeit with four cycles A, B, C, and D. This compound is often used as a model target for exploring different strategies for the total synthesis of indole alkaloids. Nevertheless, so far there still lack practical and highly efficient methods for the asymmetric total synthesis of 10-Desbromoarborescidine A. Most of the current available methods rely on stoichiometric asymmetric synthesis for the construction of the chiral center. There is only one example reporting utilization of asymmetric catalysis, but with transition metal complex as the catalyst. Our retrosynthetic analysis shows that catalytic asymmetric reduction of imine could be used as the key step for the construction of the chiral center of Desbromoarborescidine A. Since in the previous studies our group has developed the asymmetric reduction of imines by trichlorosilane into a practical and highly efficient and enantioselective method using newly designed chiral organocatalysts, we hope to apply this method to develop a novel synthetic route for the total synthesis of Desbromoarborescidine A and its analogues in this study. According to the newly designed synthetic route, we first accomplished the synthesis of the key intermediates which was then examined for the critical asymmetric catalysis. The asymmetric reduction using the highly efficient organocatalysts, developed in our lab afforded high ee but poor yield. We tried different reaction conditions to improve the yield, but failed to get any good results. Simultaneously, to vertify the feasibility of the synthetic route we designed, we also tired to go through the route toward the racemic synthesis of Desbromoarborescidine A. But unfortunately, protection and deprotection proved to be big hurdles. All the different protection groups and different sequences of protection and deprotection we tried failed to get us through the designed synthetic sequence and furnish the final product. Most likely, the indole part is the culprit behind the failures.The NH group of the indole, no matter protected or not, may impact the catalytic asymmetric reduction of C-N double bond connected with 2-C. Additionally, the reduction product we designed contains an amino group in the β-position of the indole, which may cause problems due to its instability. C-sulfenylation of enamines is a novel reaction discovered recently by our group, which has not been seen before in the literature. In this study, optimization of the reaction conditions and exploration of the substrate scope were further undertaken for this reaction, which reveal that a series of enamines with N-Cbz, Ac, COt-Bu, CO2Et protection groups could all undergo smooth C-sulfinylations with the comined use of sodium benzene sulphinate, DAMc and MeSiCl3, efficiently furnishing the β-amino vinylsulfoxide products in high yield, affording a practical and highly efficient methods for synthesis of functional vinylsulfoxides.

Synthesis and magnetic characterization of nickel ferrite nanoparticles prepared by co-precipitation route

Magnetic nanoparticles of nickel ferrite (NiFe2O4) have been synthesized by co-precipitation route using stable ferric and nickel salts with sodium hydroxide as the precipitating agent and oleic acid as the surfactant. X-ray diffraction (XRD) and transmission electron microscope (TEM) analyses confirmed the formation of single-phase nickel ferrite nanoparticles in the range 8-28 nm depending upon the annealing temperature of the samples during the synthesis. The size of the particles (d) was observed to be increasing linearly with annealing temperature of the sample while the coercivity with particle size goes through a maximum, peaking at similar to 11 nm and then decreases for larger particles. Typical blocking effects were observed below similar to 225 K for all the prepared samples. The superparamagnetic blocking temperature (T-B) was found to be increasing with increasing particle size that has been attributed to the increased effective anisotropy energy of the nanoparticles. The saturation moment of all the samples was found much below the bulk value of nickel ferrite that has been attributed to the disordered surface spins or dead/inert layer in these nanoparticles. (c) 2008 Elsevier B. V. All rights reserved.