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Zu, M.,Li, Q.,Zhu, Y.,Dey, M.,Wang, G.,Lu, W.,Deitzel, J.M.,Gillespie, J.W.,Byun, J.H.,Chou, T.W. Pergamon Press ; Elsevier Science Ltd 2012 Carbon Vol.50 No.3
The tensile properties of continuous carbon nanotube (CNT) fibers spun from a CNT carpet consisting of mainly double- and triple-walled tubes, and their interfacial properties in an epoxy matrix, are investigated by single fiber tensile tests and microdroplet tests, respectively. The average CNT fiber strength, modulus and strain to failure are 1.2+/-0.3GPa, 43.3+/-7.4GPa and 2.7+/-0.5%, respectively. A detailed study of strength distribution of CNT fiber has been carried out. Statistical analysis shows that the CNT fiber strength is less scattered than those of MWCNTs as well as commercial carbon and glass fibers without surface treatment. The effective CNT fiber/epoxy interfacial shear strength is 14.4MPa. Unlike traditional fiber-reinforced composites, the interfacial shear sliding occurs along the interface between regions with and without resin infiltration in the CNT fiber. Guidelines for microdroplet experiments are established through probability analysis of variables basic to specimen design.
C.T. Hsieh,M.W. Lin,C.L. Chang,Y.C. Ho,S.Y. Chen,J. Wang,M.C. Chou,J.Y. Lin,C.H. Pai,P.H. Lin,L.C. Tai,S.H. Chen,G.Y. Tsaur,C.C. Kuo,T.Y. Chien 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.6
A general method for fabricating transient plasma structures with high-intensity laser pulses is developed to gain fine control over laser-plasma interactions. These structures have been used as programmable photonic devices in the development of laser-wakefield accelerators, soft X-ray lasers and plasma nonlinear optics driven by multi-terawatt laser pulses. Plasma ramps are used to control electron injection in laser-wakefield accelerators, plasma waveguides are used to enhance the efficiency of soft X-ray lasers by orders of magnitude and periodic plasma structures are used to achieve quasi-phase matching in relativistic harmonic generation. By scanning the interaction length with the same plasma-fabrication method, tomographic measurements are carried out to resolve the injection/acceleration process in laser-wakefield accelerators and amplification processes in X-ray lasers and relativistic harmonic generation. A theoretical analysis and a computer simulation are also carried out to provide insightful pictures of these processes. These research works show that by controlling plasma structures with optical fabrication methods, laser-plasma interaction can be engineered to expand and enrich the frontier of high-field physics.
Stress relaxation in carbon nanotube-based fibers for load-bearing applications
Zu, M.,Li, Q.,Zhu, Y.,Zhu, Y.,Wang, G.,Byun, J.H.,Chou, T.W. Pergamon Press ; Elsevier Science Ltd 2013 Carbon Vol.52 No.-
Carbon nanotube (CNT) based continuous fiber, a CNT assembly that could retain the superb properties of individual CNTs on a macroscopic scale, has emerged as a promising candidate for reinforcement in multifunctional composites. While existing research has extensively examined their short-term mechanical properties based upon quasi-static measurements, the long-term durability of CNT fibers has been largely neglected. Here we report time-dependent behavior of CNT fibers, with a particular focus on tensile stress relaxation. Both the pure CNT fiber and the CNT/epoxy composite fiber exhibited significant stress decay during the relaxation process, and this time-dependent behavior became more significant at a higher initial strain level, a lower strain rate and a greater gauge length. The present approach signifies a fundamental difference in the load-bearing characteristics between CNT fibers and traditional advanced fibers, which has major implications for the long-term durability of CNT fibers in load-bearing multifunctional applications.
Synchronized Bursting Induced by Network Connectivity in Cortical Neuronal Cultures
L.C. Jia,P.-Y. Lai,C. K. Chan,C.H. Chang,C.R. Han,M.T. Tsai,Y.S. Chou 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.50 No.1I
Synchronization of cortical neural cultures is studied as a function of the effective network connectivity in the phenomenon of synchronized firing (SF). The synchronized bursting frequency (during SF) of the network is found to be much slower than the characteristic time scale of a neuron and increases with the network connectivity. Using fluorescence imaging techniques, we found that SF occurs only when the incubation time is longer than some critical age tc and the synchronized bursting frequency f increases with time as f = fc + fo log( t tc ). Furthermore, tc is found to scale with the cell plating density as tc 1 p . Based on the result of photolysis of neurons, the synchronized bursting frequency is shown to be related to the network connectivity, hence, the growth behavior can be inferred from the measured SF frequencies. We further build a network growth model with the characteristics of an early stage active growth followed by a late-stage retarded growth, which can account for the experimental data quantitatively. Electrophysiological measurements using double-patch techniques reveal that even though the bursting frequencies are synchronized, the intra-burst spikes are not. We also present a mean-field model of the neural network that enables the neuron firing to be inhibited and generates inter-spike intervals with long time scales resulting in bursting.