Modal dynamics of self-excited azimuthal instabilities in an annular combustion chamber

In this paper we describe the time-varying amplitude and its relation to the global heat release rate of self-excited azimuthal instabilities in a simple annular combustor operating under atmospheric conditions. The combustor was modular in construction consisting of either 12, 15 or 18 equally spaced premixed bluff-body flames around a fixed circumference, enabling the effect of large-scale interactions between adjacent flames to be investigated. High-speed OH* chemiluminescence imaged from above the annulus and pressure measurements obtained at multiple locations around the annulus revealed that the limit cycles of the modes are degenerate in so much as they undergo continuous transitions between standing and spinning modes in both clockwise (CW) and anti-clockwise (ACW) directions but with the same resonant frequency. Similar behaviour has been observed in LES simulations which suggests that degenerate modes may be a characteristic feature of self-excited azimuthal instabilities in annular combustion chambers. By modelling the instabilities as two acoustic waves of time-varying amplitude travelling in opposite directions we demonstrate that there is a statistical prevalence for either standing m=1 or spinning m=±1 modes depending on flame spacing, equivalence ratio, and swirl configuration. Phase-averaged OH* chemiluminescence revealed a possible mechanism that drives the direction of the spinning modes under limit-cycle conditions for configurations with uniform swirl. By dividing the annulus into inner and outer annular regions it was found that the spin direction coincided with changes in the spatial distribution of the peak heat release rate relative to the direction of the bulk swirl induced along the annular walls. For standing wave modes it is shown that the globally integrated fluctuations in heat release rate vary in magnitude along the acoustic mode shape with negligible contributions at the pressure nodes and maximum contributions at the pressure anti-nodes. © 2013.

Electron-beam patterning of polymer electrolyte films to make multiple nanoscale gates for nanowire transistors

We report an electron-beam based method for the nanoscale patterning of the poly(ethylene oxide)/LiClO4 polymer electrolyte. We use the patterned polymer electrolyte as a high capacitance gate dielectric in single nanowire transistors and obtain subthreshold swings comparable to conventional metal/oxide wrap-gated nanowire transistors. Patterning eliminates gate/contact overlap, which reduces parasitic effects and enables multiple, independently controllable gates. The method's simplicity broadens the scope for using polymer electrolyte gating in studies of nanowires and other nanoscale devices. © 2013 American Chemical Society.

Determination of the surface area of common carp, Cyprinus carpio L.

A wrap method adaptation combined with AutoCAD2005 and Scion Image for Windows were used to determine the surface area of a fish. Compared with the corresponding r(2) and F of many models, the most accurate formula: S = 752.15W(0.675) (r(2) = 0.999, F = 18362.94, P < 0.0001) for estimating the surface area of common carp was obtained. Similarly, the fin formula: S = 1834.12W(0.708) (r(2) = 0.992, F = 2690.47, P < 0.0001) was also obtained for the same purpose. It was proven that these two formulae gave good estimates of surface and fin areas of four strains of common carp: Yellow-river carp, fancy carp, mirror carp and Xingguo red carp.

Development of a nanoporous and multilayer drug-delivery platform for medical implants.

Biodegradable polymers can be applied to a variety of implants for controlled and local drug delivery. The aim of this study is to develop a biodegradable and nanoporous polymeric platform for a wide spectrum of drug-eluting implants with special focus on stent-coating applications. It was synthesized by poly(DL-lactide-co-glycolide) (PLGA 65:35, PLGA 75:25) and polycaprolactone (PCL) in a multilayer configuration by means of a spin-coating technique. The antiplatelet drug dipyridamole was loaded into the surface nanopores of the platform. Surface characterization was made by atomic force microscopy (AFM) and spectroscopic ellipsometry (SE). Platelet adhesion and drug-release kinetic studies were then carried out. The study revealed that the multilayer films are highly nanoporous, whereas the single layers of PLGA are atomically smooth and spherulites are formed in PCL. Their nanoporosity (pore diameter, depth, density, surface roughness) can be tailored by tuning the growth parameters (eg, spinning speed, polymer concentration), essential for drug-delivery performance. The origin of pore formation may be attributed to the phase separation of polymer blends via the spinodal decomposition mechanism. SE studies revealed the structural characteristics, film thickness, and optical properties even of the single layers in the triple-layer construct, providing substantial information for drug loading and complement AFM findings. Platelet adhesion studies showed that the dipyridamole-loaded coatings inhibit platelet aggregation that is a prerequisite for clotting. Finally, the films exhibited sustained release profiles of dipyridamole over 70 days. These results indicate that the current multilayer phase therapeutic approach constitutes an effective drug-delivery platform for drug-eluting implants and especially for cardiovascular stent applications.

A dragline-forming mobile robot inspired by spiders.

Mobility of wheeled or legged machines can be significantly increased if they are able to move from a solid surface into a three-dimensional space. Although that may be achieved by addition of flying mechanisms, the payload fraction will be the limiting factor in such hybrid mobile machines for many applications. Inspired by spiders producing draglines to assist locomotion, the paper proposes an alternative mobile technology where a robot achieves locomotion from a solid surface into a free space. The technology resembles the dragline production pathway in spiders to a technically feasible degree and enables robots to move with thermoplastic spinning of draglines. As an implementation, a mobile robot has been prototyped with thermoplastic adhesives as source material of the draglines. Experimental results show that a dragline diameter range of 1.17-5.27 mm was achievable by the 185 g mobile robot in descending locomotion from the solid surface of a hanging structure with a power consumption of 4.8 W and an average speed of 5.13 cm min(-1). With an open-loop controller consisting of sequences of discrete events, the robot has demonstrated repeatable dragline formation with a relative deviation within -4% and a length close to the metre scale.

Compact Reconfigurable Binary-Decision-Diagram Logic Circuit on a GaAs Nanowire Network

We describe a reconfigurable binary-decision-diagram logic circuit based on Shannon's expansion of Boolean logic function and its graphical representation on a semiconductor nanowire network. The circuit is reconfigured by using programmable switches that electrically connect and disconnect a small number of branches. This circuit has a compact structure with a small number of devices compared with the conventional look-up table architecture. A variable Boolean logic circuit was fabricated on an etched GaAs nanowire network having hexagonal topology with Schottky wrap gates and SiN-based programmable switches, and its correct logic operation together with dynamic reconfiguration was demonstrated.

循环优化序列自动定制方法研究

现代计算机在体系结构和应用场景复杂性的增长使得程序性能的增长、保持程序性能的可移植性以及程序开发效率的提升越来越困难，程序自动调优(auto-tuning) 是解决此问题的一个可行途径。本文研究一种通过为循环嵌套自动定制循环优化序列来进行程序自动调优的方法，提高了被编译程序的性能和可移植性，也有助于提升开发效率。 在综述相关工作的基础上，本文首先分析了循环优化序列自动定制研究需要解决的几个关键问题：循环优化的形式化描述及实施、循环优化序列的性能评估、循环优化序列的自动定制方法以及相关的原型工具。本文围绕这几个问题进行研究。 本文采用了Polyhedron模型来描述循环优化，并基于此实施了循环优化的仿射变换。这一工作基于URUK/WRaP-IT开源软件包实现，并作出了若干重要改进。借助Polyhedron模型，本文还给出了部分常见循环优化之间的使能(enable)关系。循环优化之间的相互影响较为普遍，一个循环优化的执行可能会破坏后续优化的实施条件，也可能不破坏甚至创造相应条件。这一关系可以用于过滤循环优化序列定制过程中产生的无效序列从而加快定制速度。本文分析了两个循环优化以先后次序执行时，循环嵌套内所有依赖距离向量均得以保持的条件，给出了它们之间的使能关系。并且给出了使能关系在Polyhedron模型下的计算方法，以及在序列搜索过程中通过维护依赖距离向量状态计算使能关系的方法。 对于循环优化序列性能评估方法，本文采用了高速缓存失效率简化方程(CMES方程)以动态给出循环嵌套中的高速缓存失效率数据，提出了LoopCost模型以静态分析方式发现循环嵌套中对性能影响最大的维度，这两种评估方法分别适用于不同的序列定制方法。 给出了Cache 失效率简化方程(CMES, Cache Miss Equation Simplified)在Polyhedron 模型下的求解方法。CMES方程可在编译时给出循环嵌套中的Cache失效率数据，不需要实际编译运行目标程序，从而避免相关文献中使用运行时信息来评价优化序列带来的巨大编译开销。给出了CMES方程各个参数从循环嵌套的Polyhedron模型中提取的方法，并给出了具体计算过程。 提出了一种可发现循环嵌套中对性能影响最大维度的循环优化性能评估模型LoopCost。相关文献中所使用的性能评估模型可给出一个循环嵌套的整体性能，但无法给出哪个维度对其性能影响最大；而大多数循环优化实际上是对某一个维度所做的变换，因此这些评估模型不能直接指导优化序列的搜索，只能是在一个迭代过程中提供性能信息。LoopCost模型基于数据依赖关系对一个循环嵌套估算出其每个维度使用的cache行数，作为衡量局部性优劣的指标，适用于紧嵌套循环和非紧嵌套循环，并且其复杂度与循环嵌套个数和引用个数成线性关系。通过对SPEC CPU 2006中5,703个循环嵌套的实验，LoopCost模型对其中98.3%的循环嵌套都能给出正确的性能评估数据。 对于循环优化序列自动定制方法，本文首先提出了一种基于CMES方程的Custom方法，使用迭代方式搜索可行优化序列；为了进一步提升优化效率，又提出了一种基于LoopCost模型的快速定制方法FastCustom。 Custom方法使用CMES方程评估优化序列，使用遗传算法作为序列搜索方法。在遗传算法中的各个算子中利用循环优化的enable关系加速搜索速度。该方法可以避免使用运行时刻信息评估性能所带来的巨大编译开销，又可避免相关工作中利用Polyhedron模型中语句实例执行次序矩阵的性质来搜索带来的局限性，适用的循环优化范围广，编译效率高，同时能取得与相关工作基本相当的加速比。 FastCustom方法优化效率高，并且与Custom方法不同，适用于所有场合。它基于LoopCost模型寻找对性能影响最大的维度，并根据一个启发式策略给出一个循环优化序列。该方法编译速度快，优化效果与Custom方法基本相当。与Custom相比，该方法需要给出启发式策略，因此适用的循环优化范围不如Custom，适用于迭代编译无法进行的情形。 对于循环优化序列自动定制原型工具，本文设计并实现了原型工具CPOLO。该工具改进了URUK/WRaP-IT开源软件包，使其能够支持较为复杂的程序；增强了代码重生成的效率；并且实现了本文所提出的优化序列性能评估模型和自动定制方法。 最后，总结了全文并探讨了进一步的工作方向。

新型渗透变形仪的研制

针对现有渗透变形仪存在的密封止水效果差、试样固定装置影响过流面积、仪器复杂等缺陷,通过对岩土渗透变形特性及测试原理进行分析,研制出一种适用于黏性土、水泥土类的新型渗透变形仪,该仪器设计方法独特,在试样外套橡皮膜并加围压的柔性密封止水,以及在试样顶部采用圆环型透水石固定试样等方法,既能测定岩土体的渗透系数又能测定渗透变形特性,同时,既保证试样的渗流面积不受影响又允许试样产生渗透变形,而且在渗透水压力作用下试样周围的密封性良好。实际工程应用结果表明,该仪器测定的岩土体的渗透系数及抗渗比降具有很高的可靠性和精度。

Detection of Terahertz Photon by GaAs-Based Single Electron Transistor at Low Temperatures

A reproducible terahertz (THz) photocurrent was observed at low temperatures in a Schottky wrap gate single electron transistor with a normal-incident of a CH_3OH gas laser with the frequency 2. 54THz.The change of source-drain current induced by THz photons shows that a satellite peak is generated beside the resonance peak. THz photon energy can be characterized by the difference of gate voltage positions between the resonance peak and satellite peak. This indicates that the satellite peak exactly results from the THz photon-assisted tunneling. Both experimental results and theoretical analysis show that a narrow spacing of double barriers is more effective for the enhancement of THz response.

Experimental Study on the Subthreshold Swing of Silicon Nanowire Transistors

SOI based wrap-gate silicon nanowire FETs are fabricated through electron beam lithography and wet etching. Dry thermal oxidation is used to further reduce the patterned fins cross section and transfer them into nanowires. Silicon nanowire FETs with different nanowire widths varying from 60 nm to 200 nm are fabricated and the number of the nanowires contained in a channel is also varied. The on-current (I-ON) and off-current (I-OFF) of the fabricated silicon nanowire FET are 0.59 mu A and 0.19 nA respectively. The subthreshold swing (SS) and the drain induced barrier lowering are 580 mV/dec and 149 mVN respectively due to the 30 nm thick gate oxide and 1015 cm(-3) lightly doped silicon nanowire channel. The nanowire width dependence of SS is shown and attributed to the fact that the side-gate parts of a wrap gate play a more effectual role as the nanowires in a channel get narrower. It seems the nanowire number in a channel has no effect on SS because the side-gate parts fill in the space between two adjacent nanowires.