Electrical analysis of single-walled carbon nanotube as gigahertz on-chip interconnects

The single-walled carbon nanotube (SWCNT) is a promising nanostructure in the design of future high-frequency system-on-chip, especially in network-on-chip, where the quality of communication between intellectual property (IP) modules is a major concern. Shrinking dimensions of circuits and systems have restricted the use of high-frequency signal characteristics for frequencies up to 1000 GHz. Four key electrical parameters, impedance, propagation constant, current density, and signal delay time, which are crucial in the design of a high-quality interconnect, are derived for different structural configurations of SWCNT. Each of these parameters exhibits strong dependence on the frequency range over which the interconnect is designed to operate, as well as on the configuration of SWCNT. The novelty of the proposed model for solving next-generation high-speed integrated circuit (IC) interconnect challenges is illustrated, compared with existing theoretical and experimental results in the literature.     

Fundamental dynamics of flow through carbon nanotube membranes

The flow of a model non-polar liquid through small carbon nanotubes is studied using non-equilibrium molecular dynamics simulation. We explain how a membrane of small-diameter nanotubes can transport this liquid faster than a membrane consisting of larger-diameter nanotubes. This effect is shown to be back-pressure dependent, and the reasons for this are explored. The flow through the very smallest nanotubes is shown to depend strongly on the depth of the potential inside, suggesting atomic separation can be based on carbon interaction strength as well as physical size. Finally, we demonstrate how increasing the back-pressure can counter-intuitively result in lower exit velocities from a nanotube. Such studies are crucial for optimisation of nanotube membranes.     

An energy consumption characterization of on-chip interconnection networks for tiled CMP architectures

Continuous improvements in integration scale have made possible the inclusion of several processor cores on the same chip. Such designs have been named chip-multiprocessors (or CMPs) and constitute a good alternative to traditional monolithic designs for several reasons, among others, better levels of performance, scalability, and performance/energy ratio. On the other hand, higher clock frequencies and increasing number of transistors available on a single chip have revealed energy consumption as a critical design issue in current and future microarchitectures. In these architectures, the design of the on-chip interconnection network has proven to have significant impact on overall system performance and energy consumption, and that the wires used in such interconnect can be designed with varying latency, bandwidth, and power characteristics. In this work, we present a detailed characterization of the energy-efficiency of a CMP for parallel scientific applications using Sim-PowerCMP, a detailed architectural-level power-performance simulation tool for CMP architectures that integrates several well-known contemporary simulators (RSIM, Hot Leakage and Orion) into a single framework that allows precise analysis and optimization of power dissipation (both dynamic and static) taking into account performance. In this characterization, we pay special attention to the energy consumed on the interconnection network. Results for an 8- and 16-core CMP show that the most power consuming messages are the replies that carry data (almost 70% on average of the total energy consumed in the interconnect) although they represent 30% of the total number of messages. Furthermore, we show that using on-chip wires with varying latency, bandwidth, and energy characteristics can reduce the energy dissipated by the links of the interconnection network about 65% with an average impact of 10% in the execution time.

Computational fluid dynamics analysis of microbubble formation in microfluidic flow-focusing devices

Bubble formation in a microfluidic flow-focusing device is simulated using the volume-of-fluid approach to achieve a complete solution of the Navier–Stokes equations for both the gas and liquid phases. The results of the simulation show good agreement with previous experimental results. A detailed examination of the predicted pressure and velocity profiles from the simulation also provide further validation for the conclusions drawn previously with experimental results. The simulation results show the existence of two distinct modes of bubble formation. Simulations of systems an order of magnitude smaller than those investigated experimentally indicate that such reduced systems sizes are a viable approach that would result in much smaller bubble sizes.     

二氧化硅表面稠密的二氧化碳分子动力学模拟

采用分子动力学的方法研究二氧化硅表面二氧化碳的结构和扩散性质。二氧化碳在二氧化硅固体表面形成高密度层;而在远离固体表面处,流体的密度分布类似于宏观二氧化碳,取向分布比较随机。受固体表面的影响,二氧化碳的C-C径向分布函数第一峰的高度比宏观二氧化碳高。二氧化碳的密度分布和自由能分布有一明显的镜面对称的结构,高密度区域对应自由能的深阱。二氧化硅中的二氧化碳的自扩散行为是各向异性的,z方向的扩散由于固体面的作用明显受阻。由取向相关函数积分得到的二氧化硅表面流体的取向相关时间比宏观流体大的多,二氧化碳分子在固体表面再定位比较缓慢。     

Function portability of molecular dynamics on heterogeneous parallel architectures with OpenCL

Classical molecular dynamics simulation for atomistic systems is implemented in OpenCL and benchmarked on a variety of different hardware platforms. Modifying the number of particles and system size in the study provides insight into characteristics of parallel compute platforms, where latency, data transfer, memory access characteristics and compute intense work can be identified as fingerprints in benchmark runs. Data layouts are compared, for which the access of structure-of-arrays shows best performance in most cases. It is demonstrated that function portability can be achieved straightforwardly with OpenCL, while performance portability lacks behind as various architectures strongly depend on specific vectorisation optimisation.     

分子动力学模拟聚乙烯在碳纳米管表面的扩散

通过采用分子动力学方法模拟不同链长的聚乙烯分子在单壁碳纳米管表面的扩散,探究了聚乙烯的动力学性质。研究表明随着链长的增加聚乙烯在碳纳米管表面的扩散系数减小,且二者间存在明显的标度关系。聚乙烯在碳纳米管表面扩散的扩散系数和聚乙烯吸附在碳纳米管表面的构象有关,有序结构的聚乙烯比无序结构的聚乙烯在碳纳米管表面扩散的快。此外,由于受到碳纳米管吸附作用的影响,聚乙烯分子在平行于管轴和垂直于管轴2个方向上的扩散系数不同,扩散表现各向异性。     

Computational fluid dynamics (CFD) software tools for microfluidic applications - A case study

This paper reports on an exemplary study of the performance of commercial computational fluid dynamic (CFD) software programs when applied as engineering tool for microfluidic applications. Four commercial finite volume codes (CFD-ACE+, CFX, Flow-3D and Fluent) have been evaluated by performing CFD-simulations of typical microfluidic engineering problems being relevant for a large variety of lab-on-a-chip (LOAC) applications. Following problems are considered as examples: multi lamination by a split and recombine mixer, flow patterning on a rotating platform (sometimes termed “lab-on-a-disk”), bubble dynamics in micro channels and the so called TopSpot^® droplet generator for micro array printing. Hereby mainly the capability of the software programs to deal with free surface flows including surface tension and flow patterning of two fluids has been studied. In all investigated programs the free surfaces are treated by the volume-of-fluid (VOF) method and flow patterning is visualised with a scalar marker method. The study assesses the simulation results obtained by the different programs for the mentioned application cases in terms of consistency of results, computational speed and comparison with experimental data if available.     

Diffusion of fluid confined to nanotube with rectangular cross section

A dynamical model is proposed to study self-diffusion coefficient by confining the fluid in rectangular nanotube. The theoretical model is based on the consideration that the confinement affects the movement at atomic level. The model predicts that the diffusion parallel to walls of channel is different from that of diffusion perpendicular to the walls. Near the walls the dynamics of fluid has been found to slow down to an extent that below a certain value of ratio of width to the diameter of particle, the molecules behave as if these belong to solid. The results are contrasted with the result obtained from the model based on similar considerations for a fluid confined only in one direction. It is found that tendency of freezing near the wall increases due to confinement from second direction. Empirical relation which governs the behavior of diffusion coefficient as function of distance from the confining walls has also been proposed. The effect of confinement is more pronounced for denser fluids than for dilute fluid.     

Computational fluid dynamics of nanoparticle disposition in the airways: mucus interactions and mucociliary clearance

Interactions of nanoparticles with respiratory fluids such as airway mucus are currently under investigation and are involved in a variety of applications. The clearance processes of those nanoparticles are still not fully understood. This study presents an approach to describe deposition, sedimentation and clearance of nanoparticles within mucus with numerical and analytical models: Particle deposition as well as motility, sedimentation and clearance were simulated with Computational Fluid Dynamics (CFD) and described analytically. Furthermore mucus plasticity as pathway for complex particle translocation was simulated using grid-free CFD methods. We could demonstrate that fluid dynamics strongly influence the fate of deposited nanoparticles in mucus: Sedimentation, impaction and diffusion were shown to be unlikely to contribute to particle translocation. However, intrinsic plasticity of mucus slabs and collision of such slabs may enhance particle translocation towards the pulmonary epithelium.     

High level modeling and automated generation of heterogeneous SoC architectures with optimized custom reconfigurable cores and on-chip communication media

In this paper we propose a framework for modeling and automated generation of heterogeneous SoC architectures with emphasis on reconfigurable component integration and optimized communication media. In order to facilitate rapid development of SoC architectures, communication-centric platforms for data intensive applications, high level modeling of reconfigurable components for quick simulation and a tool for generation of complete SoC architectures is presented. Four different communication-centric platforms based on traditional bus, crossbar, hierarchical bus and novel hybrid communication media are proposed. These communication-centric platforms are proposed to cater for the different communication requirement of future SoC architectures. Multi-Standard telecommunication application is chosen as our target application domain and a case study of WiMAX is used as a real world example to demonstrate the effectiveness of our approach. A system consisting of an ARM processor, reconfigurable FFT and reconfigurable Viterbi decoder is considered with the option of system scalability for future upgrades. Behavior of system with different communication platforms is analyzed for its throughput and power characteristics with different reconfigurable scenarios to show the effectiveness of our approach.     

Computational adaptive optimal control for continuous-time linear systems with completely unknown dynamics

This paper presents a novel policy iteration approach for finding online adaptive optimal controllers for continuous-time linear systems with completely unknown system dynamics. The proposed approach employs the approximate/adaptive dynamic programming technique to iteratively solve the algebraic Riccati equation using the online information of state and input, without requiring the a priori knowledge of the system matrices. In addition, all iterations can be conducted by using repeatedly the same state and input information on some fixed time intervals. A practical online algorithm is developed in this paper, and is applied to the controller design for a turbocharged diesel engine with exhaust gas recirculation. Finally, several aspects of future work are discussed.     

分子模拟在碳纳米管研究中的应用

碳纳米管作为一种新型材料,是目前科研的热点,分子模拟在其中已经得到了广泛应用,并对碳纳米管的应用具有较好的指导意义。本文介绍了近几年国内外应用分子模拟技术辅助碳纳米管研究的部分工作,主要包括碳纳米管力学性能和电学性能的模拟、碳纳米管储气能力和反应性能的研究,以及在聚合物／碳纳米管复合材料中的应用等。     

核黄素在碳纳米管修饰电极上的电化学行为

制成了碳纳米管(CNT)和碳纳米管复合β-环糊精(p-CD)修饰电极,用循环伏安(CV)和差分脉冲伏安法(DPV)对核黄素(RF)的电化学行为进行了研究.实现了核黄素在不同pH的溶液中的氧化还原机理的探讨及其定量测定,线性范围5.0×10-7～2.5×10-6mol/L,相关系数r=0.998 5,检测限为3.0×10-7mol/L.实验表明碳纳米管对核黄素的氧化还原有电催化作用,主要是由于碳纳米管的一维管状结构及独特的电子特性促进了电子的传递.β-CD的加入对RF电位没有影响,但增大了峰电流,可能是因为环糊精复合碳纳米管修饰电极的界面体现了新颖的建筑层-碳纳米管集合体大的孔隙充填小孔的环糊精,发挥了碳纳米管和环糊精的双重功能.     

碳纳米管掺杂WO_3气敏元件敏感特性的研究

研究以碳纳米管(CNT)为掺杂剂制备的CNT-WO3旁热式气敏元件。采用球磨、超声分散的方法对碳纳米管进行分散处理,溶胶—凝胶方法制备WO3微粉,用SEM观察了WO3气敏材料的显微结构,测试了元件对丙酮的气敏性能。结果表明:碳纳米管存在于平均粒径为30~50 nm的WO3晶粒间,从而增加了材料的气孔率。碳纳米管掺杂元件对丙酮的灵敏度远高于纯WO3元件,质量分数为0.4%的掺杂量对丙酮有最高灵敏度,具有能检测低体积分数丙酮气体、选择性好的优点,特别是掺杂碳纳米管明显提高了WO3元件的响应速度。     

Three-dimensional simulation studies on electrostatic predictions for carbon nanotube field effect transistors

Analysis of the electrostatic characteristics and the gate capacitance of typical nanostructured carbon nanotube field effect transistors (CNTFETs) were performed numerically. A previously developed parallelized electrostatic Poisson's equation solver (PPES) is employed, coupled with a parallel adaptive mesh refinement (PAMR) to improve the numerical accuracy near the region where variation of potentials are significant. CNTFETs with four typical configurations of the gate electrode, the bottom gate (BG), the double gate (DG), the top gate (TG), and the surrounding gate (SG) were simulated. Effects of the nanotube arrangement and the gate length on the gate capacitance are presented and discussed. The simulation results show that SG-CNTFET possesses the largest gate capacitance among various structures. However, TG-CNTFET is recommended for practical applications by taking into account both the device performance and the difficulty of fabrication. According to the simulated gate capacitance, estimation of the on-state current of CNTFETs is possible.     

Effects of the slip boundary condition on dynamics and pull-in instability of carbon nanotubes conveying fluid

This paper addresses the effects of the slip boundary condition on dynamics and pull-in instability of carbon nanotubes (CNTs) containing internal fluid flow. Both the clamped–clamped and the cantilever boundary conditions are considered. The structure of CNTs is modelled using the size-dependent strain gradient theory (SGT) of continuum mechanics. It is shown that the Knudsen number (Kn) has a significant effect on the static and dynamic CNT response due to pull-in voltage loading and the existence of the instability region.     

Performances of carbon nanotube field effect transistors with altered channel length

The influence of channel length on the performances of carbon nanotube field effect transistors(CNT-FETs) has been studied.Buffered oxide etching was used to remove approximately a 60 nm layer from the original 100 nm silicon dioxide layer,to thin the dielectric layer of the back gate.Channel length of the CNT-FETs was changed along with the etching process.The dependence of drain-source current on gate voltage was measured to analyze the performance of the CNT-FETs,including the transconductance,carrier mo...     

An improved model of carbon nanotube conveying flow by considering comprehensive effects of Knudsen number

Although the theoretical model of carbon nanotube conveying flow has been evolving from under macroscale theory framework to under nanoscale theory framework, for now, the small-scale effects have yet to be considered thoroughly. Herein, after extending the compatibility condition, we propose an improved model. Compared with the previous models, the improved model is not only dependent on the nonlocal parameter, but also comprehensively takes all the factors related to Knudsen number, namely effective viscosity, slip boundary condition and non-uniform flow profile, into account. Based on this model, a formula of critical flow velocity is derived in addition to numerical results and our model gives a considerably decreased critical flow velocity. Besides, when Knudsen number and nonlocal parameter increase, the critical flow velocity goes down dramatically, which indicates that the effects of Knudsen number cannot be neglected, and we demonstrate that the dispute over nonlocal parameter may impair the reliability of theoretical prediction of critical flow velocity. We also find that the effects of nonlocal parameter and Knudsen number on critical flow velocity are probably uncoupled.