Dielectric response and its light-induced change in undoped alpha-Si : H films below 13 MHz

The low frequency (<13 MHz) dielectric response and its light-induced change in undoped a-Si:H were investigated in detail. The dielectric constant epsilon (the real part) in this range decreases with illumination time: following a stretched exponential law similar to that found for other light-induced changes. The saturation relative change was about 0.1-0.2 % for the measured samples. The change is fading away either after repeated illumination-annealing training or by aging at room temperature. The present results indicate some rearrangement of the whole Si network caused by light soaking.

Tunneling transmission in two quantum wires coupled by a magnetically defined barrier

A numerical analysis of an electron waveguide coupler based on two quantum wires coupled by a magnetically defined barrier is presented with the use of the scattering-matrix method. For different geometry parameters and magnetic fields, tunneling transmission spectrum is obtained as a function of the electron energy. Different from that of conventional electron waveguide couplers, the transmission spectrum of the magnetically coupled quantum wires does not have the symmetry with regard to those geometrically symmetrical ports, It was found that the magnetic field in the coupling region drastically enhances the coupling between the two quantum wires for one specific input port while it weakens the coupling for the other input port. The results can be well understood by the formation of the edge states in the magnetically defined barrier region. Thus, whether these edge states couple or decouple to the electronic propagation modes in the two quantum wires, strongly depend on the relative moving directions of electrons in the propagating mode in the input port and the edge states in the magnetic region. This leads to a big difference in transmission coefficients between two quantum wires when injecting electrons via different input ports. Two important coupler specifications, the directivity and uniformity, are calculated which show that the system we considered behaves as a good quantum directional coupler. (C) 1997 American Institute of Physics.

On the performance analysis and design of a novel shared-layer integrated devices using RCE-p-i-n-PD/SHBT - art. no. 67820J

We have explored the shared-layer integration fabrication of an resonant-cavity-enhanced p-i-n photodector (RCE- p-i-n-PD) and a single heterojunction bipolar transistor (SHBT) with the same epitaxy grown layer structure. MOCVD growth of the different layer structure for the GaAs based RCE- p-i-n-PD/SHBT require compromises to obtain the best performance of the integrated devices. The SHBT is proposed with super-lattice in the collector, and the structure of the base and the collector of the SHBT is used for the RCE. Up to now, the DC characteristics of the integrated device have been obtained.

Uncooled Submarine Pump Laser Module at 980 nm

We present a new generation 980 nm submarine pump module that consists of a hermitically sealed 8-pin ceramic MiniDIL package without thermo-electric cooler.

An Improved Selective Area Growth Method in Fabrication of Electroabsorption Modulated Laser

An improved selective area growth (SAG) method is proposed to better the fabrication and performance of the Electroabsorption modulated laser The typical threshold current of the EML is 18mA, and the output power is 5.6mW at EAM facet.

Continuous speech research based on HyperSausage Neuron

In this paper, we presents HyperSausage Neuron based on the High-Dimension Space(HDS), and proposes a new algorithm for speaker independent continuous digit speech recognition. At last, compared to HMM-based method, the recognition rate of HyperSausage Neuron method is higher than that of in HMM-based method.

Measurement of GaN/Ge(001) Heterojunction Valence Band Offset by X-Ray Photoelectron Spectroscopy

X-ray photoelectron spectroscopy has been used to measure the valence band offset (VBO) at the GaN/Ge heterostructure interface. The VBO is directly determined to be 1.13 +/- 0.19 eV, according to the relationship between the conduction band offset Delta E-C and the valence band offset Delta E-V : Delta E-C = E-g(GaN) - E-g(Ge) - Delta E-V, and taking the room-temperature band-gaps as 3.4 and 0.67 eV for GaN and Ge, respectively. The conduction band offset is deduced to be 1.6 +/- 0.19 eV, which indicates a type-I band alignment for GaN/Ge. Accurate determination of the valence and conduction band offsets is important for the use of GaN/Ge based devices.

Multi-wafer 3C-SiC heteroepitaxial growth on Si(100) substrates

Epitaxial growth of semiconductor films in multiple-wafer mode is under vigorous development in order to improve yield output to meet the industry increasing demands. Here we report on results of the heteroepitaxial growth of multi-wafer 3C-SiC films on Si(100) substrates by employing a home-made horizontal hot wall low pressure chemical vapour deposition (HWLPCVD) system which was designed to be have a high-throughput, multi-wafer (3x2-inch) capacity. 3C-SiC film properties of the intra-wafer and the wafer-to-wafer including crystalline morphologies, structures and electronics are characterized systematically. The undoped and the moderate NH3 doped n-type 3C-SiC films with specular surface are grown in the HWLPCVD, thereafter uniformities of intra-wafer thickness and sheet resistance of the 3C-SiC films are obtained to be 6%similar to 7% and 6.7%similar to 8%, respectively, and within a run, the deviations of wafer-to-wafer thickness and sheet resistance are less than 1% and 0.8%, respectively.

广东典型藻类特点及其能源利用可能性研究

大型海藻的生产力高，生产成本低，是一种理想的能源作物。广东省是我国海洋大省之一，约35万平方公里的海域，海藻物种丰富，为海藻养殖提供了有利的条件。我省是能源消耗大省，大部分依靠外省调入和进口，发展海藻能源技术是缓解能源问题的重要途径之一。目前，海藻作为生物质的利用技术还不成熟。在本论文中，选用我省常见的江蓠、马尾藻和麒麟菜三种的大型的海藻进行热解和发酵实验。 首先，对海藻在不同温度下（400℃～900℃）热解得到的各产物（气体、焦油和残渣）产率和热值以及气体组分进行了分析，研究了各热解产物产率、热值和气体组分随温度的变化规律，分析热解过程中的K、Ca、Na、Mg等元素的析出和迁移规律。用去离子水和稀盐酸对海藻进行洗滤预处理，研究其热解特性，进行热重分析，建立海藻热解的反应动力学模型，并计算海藻的动力学参数。分析结果表明：热解气体中的主要成分为H2、CO、CH4、C2H4、C2H6等，热解气低位热值介于5～15 MJ/m3之间。海藻本身具有灰分含量较高和热值较低的特点，水洗可以有效地脱除部分的碱金属，并可以减少灰分含量，改善海藻的热解特性。 其次，以江蓠和马尾藻为底物进行发酵。结果表明：海藻中含有大量金属阳离子，直接发酵容易溶解到料液中，抑制微生物生长，影响发酵效果。用淡水浸泡以后的海藻能容易进行发酵。江蓠的产气率要高于马尾藻。在发酵温度为35℃，简单破碎，料液浓度为5%的条件下，江蓠TS（总固体）产气率是390.6L/kg 。在55℃，颗粒大小0.6～0.9mm，料液浓度为5%的条件下，马尾藻TS产气率是173.1L/kg。 通过对比海藻热解和发酵过程及结果的比较可以发现，海藻热解产气率低，碱金属容易析出；海藻发酵可以直接利用湿原料，产气率高，但发酵时间较长，需要合适的菌种。在目前没有特殊专有技术的情况下，采用发酵比采用热解实现海藻的能源化利用可能性更大。 最后，对本论文的研究探讨进行总结，并对今后进一步完善该工作提出了建议。

Influence of A-type Zeolite on Methane Hydrate Formation

The porous medium has an important effect on hydrate formation. In this paper, the formation process and the gas storage capacity of the methane hydrate were investigated with A-type zeolite and Sodium Dodecyl Sulfate (SDS) existing in the system. The results show that A-type zeolite can influence methane hydrate formation. At the temperature of 273.5 K and pressure of 8.3 MPa, the distilled water with A-type zeolite can form methane hydrate with gaseous methane in 12 hours. The formation process of the system with A-type zeolite was quite steady and the amount of A-type zeolite can influence the gas storage capacity significantly. The adding of A-type zeolite with 0.067 g.(g water)(-1) into 2 x 10(-3) g.g(-1) SDS-water solution can increase the gas storage capacity, and the maximum increase rate was 31%. Simultaneously the promotion effect on hydrate formation of 3A-type zeolite is much more obvious than that of 5A-type zeolite when the water adding amounts are 0.033 g.g(-1) and 0.067 g.g(-1) at the experimental conditions.

Experimental investigation on TBAB clathrate hydrate slurry flows in a horizontal tube: Forced convective heat transfer behaviors

Tetra-n-butyl-ammonium bromide (TBAB) clathrate hydrate slurry (CHS) is one kind of secondary refrigerants, which is promising to be applied into air-conditioning or latent-heat transportation systems as a thermal storage or cold carrying medium for energy saving. It is a solid-liquid two phase mixture which is easy to produce and has high latent heat and good fluidity. In this paper, the heat transfer characteristics of TBAB slurry were investigated in a horizontal stainless steel tube under different solid mass fractions and flow velocities with constant heat flux. One velocity region of weakened heat transfer was found. Moreover, TBAB CHS was treated as a kind of Bingham fluids, and the influences of the solid particles, flow velocity and types of flow on the forced convective heat transfer coefficients of TBAB CHS were investigated. At last, criterial correlations of Nusselt number for laminar and turbulent flows in the form of power function were summarized, and the error with experimental results was within 20%.

The methane hydrate formation and the resource estimate resulting from free gas migration in seeping seafloor hydrate stability zone

It is a typical multiphase flow process for hydrate formation in seeping seafloor sediments. Free gas can not only be present but also take part in formation of hydrate. The volume fraction of free gas in local pore of hydrate stable zone (HSZ) influences the formation of hydrate in seeping seafloor area, and methane flux determines the abundance and resource of hydrate-bearing reservoirs. In this paper, a multiphase flow model including water (dissolved methane and salt)-free gas hydrate has been established to describe this kind of flow-transfer-reaction process where there exists a large scale of free gas migration and transform in seafloor pore. In the order of three different scenarios, the conversions among permeability, capillary pressure, phase saturations and salinity along with the formation of hydrate have been deducted. Furthermore, the influence of four sorts of free gas saturations and three classes of methane fluxes on hydrate formation and the resource has also been analyzed and compared. Based on the rules drawn from the simulation, and combined information gotten from drills in field, the methane hydrate(MH) formation in Shenhu area of South China Sea has been forecasted. It has been speculated that there may breed a moderate methane flux below this seafloor HSZ. If the flux is about 0.5 kg m-2 a-1, then it will go on to evolve about 2700 ka until the hydrate saturation in pore will arrive its peak (about 75%). Approximately 1.47 109 m3 MH has been reckoned in this marine basin finally, is about 13 times over preliminary estimate.