Browsing by Author "Virginia Tech. Department of Physics"

Now showing 1 - 5 of 5
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    Modification of single-walled carbon nanotube electrodes by layer-by-layer assembly for electrochromic devices
    Jain, Vaibhav; Yochum, Henry M.; Montazami, Reza; Heflin, James R.; Hu, Liangbing; Gruner, George (American Institute of Physics, 2008-04-01)
    We have studied the morphological properties and electrochromic (EC) performance of polythiophene multilayer films on single wall carbon nanotube (SWCNT) conductive electrodes. The morphology for different numbers of layer-by-layer (LbL) bilayer on the SWCNT electrode has been characterized with atomic force microscopy and scanning electron microscope, and it was found that the LbL multilayers significantly decrease the surface roughness of the nanoporous nanotube films. The controlled surface roughness of transparent nanotube electrodes could be beneficial for their device applications. We have also fabricated EC devices with LbL films of poly[2-(3-thienyl) ethoxy-4-butylsulfonate/poly(allylamine hydrochloride) on SWCNT electrodes, which not only have high EC contrast but also sustain higher applied voltage without showing any degradation for more than 20 000 cycles, which is not possible in the case of indium tin oxide electrodes. Cyclic voltammetry of the LbL films formed on SWCNT shows higher current at low potential, revealing the feasibility of SWCNT electrode as a good host for electrolyte ion insertion. (C) 2008 American Institute of Physics.
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    Quanta. Vol. 4, Issue 2 [i.e., 3] (April 2004)
    Virginia Tech. Department of Physics (Virginia Tech Physics Department, 2004-04)
    A semi-annual newsletter for the faculty, staff, students, alumni & friends of the Virginia Tech Physics Department.
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    Remarks on "On the coefficient of nonlinearity in nonlinear acoustics"
    Tarkenton, Grey M. (Acoustical Society of America, 1990-10)
    Through an alternate analysis, the results of Hamilton and Blackstock [J. Acoust. Soc. Am. 83, 74-77 (1988)] are reviewed and a new interpretation is presented. In this view, the nonlinearity of the momentum equation is examined, and its effect on the coefficient of nonlinearity is revealed.
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    Self-Assembly of Chiral Tubules
    Cheng, Shengfeng; Stevens, Mark J. (The Royal Society of Chemistry, 2013-11-26)
    The efficient and controlled assembly of complex structures from macromolecular building blocks is a critical open question in both biological systems and nanoscience. Using molecular dynamics simulations we study the self-assembly of tubular structures from model macromolecular monomers with multiple binding sites on their surfaces [Cheng et al., Soft Matter, 2012, 8, 5666_5678]. In this work we add chirality to the model monomer and a lock-and-key interaction. The self-assembly of free monomers into tubules yields a pitch value that often does not match the chirality of the monomer (including achiral monomers). We show that this mismatch occurs because of a twist deformation that brings the lateral interaction sites into alignment when the tubule pitch differs from the monomer chirality. The energy cost for this deformation is small as the energy distributions substantially overlap for small differences in the pitch and chirality. In order to control the tubule pitch by preventing the twist deformation, the interaction between the vertical surfaces must be increased without resulting in kinetically trapped structures. For this purpose, we employ lock-and-key interactions and obtain good control of the self-assembled tubule pitch. These results explain some fundamental features of microtubules. The vertical interaction strength is larger than the lateral in microtubules because this yields a controlled assembly of tubules with the proper pitch. We also generally find that the control of the assembly into tubules is difficult, which explains the wide range of pitch values and protofilament numbers observed in microtubule assembly.
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    Systematic Reverse Engineering of Network Topologies: A Case Study of Resettable Bistable Cellular Responses
    Mondal, Debasish; Dougherty, Edward T.; Mukhopadhyay, Abhishek; Carbo, Adria; Yao, Guang; Xing, Jianhua (Public Library of Science, 2014-08-29)
    A focused theme in systems biology is to uncover design principles of biological networks, that is, how specific network structures yield specific systems properties. For this purpose, we have previously developed a reverse engineering procedure to identify network topologies with high likelihood in generating desired systems properties. Our method searches the continuous parameter space of an assembly of network topologies, without enumerating individual network topologies separately as traditionally done in other reverse engineering procedures. Here we tested this CPSS (continuous parameter space search) method on a previously studied problem: the resettable bistability of an Rb-E2F gene network in regulating the quiescence-to-proliferation transition of mammalian cells. From a simplified Rb-E2F gene network, we identified network topologies responsible for generating resettable bistability. The CPSS-identified topologies are consistent with those reported in the previous study based on individual topology search (ITS), demonstrating the effectiveness of the CPSS approach. Since the CPSS and ITS searches are based on different mathematical formulations and different algorithms, the consistency of the results also helps cross-validate both approaches. A unique advantage of the CPSS approach lies in its applicability to biological networks with large numbers of nodes. To aid the application of the CPSS approach to the study of other biological systems, we have developed a computer package that is available in Information S1.