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.     

Molecular dynamics simulation of non-covalent single-walled carbon nanotube functionalization with surfactant peptides

Non-covalent functionalized single-walled carbon nanotubes (SWCNTs) with improved solubility and biocompatibility can successfully transfer drugs, DNA, RNA, and proteins into the target cells. Theoretical studies such as molecular docking and molecular dynamics simulations in fully atomistic scale were used to investigate the hydrophobic and aromatic π–π-stacking interaction of designing four novel surfactant peptides for non-covalent functionalization of SWCNTs. The results indicated that the designed peptides have binding affinity towards SWCNT with constant interactions during MD simulation times, and it can even be improved by increasing the number of tryptophan residues. The aromatic content of the peptides plays a significant role in their adsorption in SWCNT wall. The data suggest that π–π stacking interaction between the aromatic rings of tryptophan and π electrons of SWCNTs is more important than hydrophobic effects for dispersing carbon nanotubes; nevertheless SWCNTs are strongly hydrophobic in front of smooth surfaces. The usage of aromatic content of peptides for forming SWCNT/peptide complex was proved successfully, providing new insight into peptide design strategies for future nano-biomedical applications.     

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.

Replica exchange molecular dynamics simulation of chitosan for drug delivery system based on carbon nanotube

Chitosan is an important biopolymer in the medical applications because of its excellent biocompatibility. It has been recently highlighted in the targeted drug delivery system (DDS) by improvement of the carbon nanotube (CNT) solubility. To investigate the effect of chitosan length, the two targeted DDSs with 30 and 60 chitosan monomers were performed by replica-exchange molecular dynamics simulations at temperatures in the range of 300–455 K with three different combinations of force fields and implicit solvation models. Each DDS model contains the epidermal growth factor (EGF), chitosan (CS) of 30 (30CS) and 60 (60CS) monomers, single-wall CNT (SWCNT) and gemcitabine (Gemzar) as the model payload anticancer drug, called EGF/30CS/SWCNT/Gemzar and EGF/60CS/SWCNT/Gemzar, respectively. The SWCNT confines gemcitabine inside its cavity, while the outer surface is wrapped by chitosan in which one end is linked to the EGF. Even though the REMD results from different force fields and implicit solvation models are not exactly identical, all of them are in the same trend confirming that in the EGF/30CS/SWCNT/Gemzar DDS the 30CS chain was not long enough to wrap around the SWCNT, and consequently the EGF was located so close to the tube as to potentially cause steric inhibition of the binding of EGF to its receptor (EGFR), which is highly expressed on the surface of cancer cells. On the other hand, this phenomenon is not observed in the EGF/60CS/SWCNT/Gemzar DDS in which the 60CS was found to completely wrap over the CNT outer surface using only 50 chitosan units. The evidence suggested that a ratio of chitosan molecular weight per SWCNT surface area larger than 9.9 × 10⁻⁷ kg/m² is suitable for application in targeted DDSs. Although an increase in the temperature is likely to influence the overall DDS structure, and especially the orbit of helical chitosan on the SWCNT and the EGF conformation, gemcitabine is still encapsulated inside the tube.     

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.     

催化柴油管式液相加氢脱硫数值模拟

采用计算流体力学(CFD)软件FLUENT,以用户自定义函数(UDF)添加化学反应和反应热,对实验室带有陶瓷膜管分散器的催化柴油管式液相加氢脱硫反应器进行模拟计算,得出反应床层不同部位的硫化物含量分布和温度分布状况。从反应床层的入口到出口,催化柴油的硫化物含量逐渐下降,且下降速度趋缓。在压力6.5 MPa、混氢量0.84%(m)、空速2 h~(-1)、进口温度633 K的条件下,位于床层高度0.15 m处出现最高温度点643.8 K,径向温差最大2.1 K,表明催化柴油管式液相加氢脱硫反应器催化剂装填合适的高径比为4~6。工艺条件的模拟结果表明:随着进口温度上升、混氢量增加、空速减小脱硫率提高,与实验数据吻合程度较好,说明模拟研究过程中采用的模型和控制方程准确性较高。     

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.     

Adaptive architectures for control of uncertain dynamical systems with actuator and unmodeled dynamics

In adaptive control of uncertain dynamical systems, it is well known that the presence of actuator and/or unmodeled dynamics in feedback loops can yield to unstable closed‐loop system trajectories. Motivated by this standpoint, this paper focuses on the analysis and synthesis of multiple adaptive architectures for control of uncertain dynamical systems with both actuator and unmodeled dynamics. Specifically, we first analyze model reference adaptive control architectures with standard, hedging‐based, and expanded reference models for this class of uncertain dynamical systems and develop sufficient stability conditions. We then synthesize a robustifying term for the latter architecture and analytically show that this term can allow for a relaxed sufficient stability condition. The proposed theoretical treatments involve Lyapunov stability theory, linear matrix inequalities, and matrix mathematics. Finally, we compare the resulting sufficient stability conditions of the considered adaptive control architectures on a benchmark mechanical system subject to actuator and unmodeled dynamics.     

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.     

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.     

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。