Hydroelectric Voltage Generation Based On Water-Filled Single-Walled Carbon Nanotubes

A DFT/MD mutual iterative method was employed to give insights into the mechanism of voltage generation based on water-fitted single-walled carbon nanotubes (SWCNTs). Our calculations showed that a constant voltage difference of several mV would generate between the two ends of a carbon nanotube, due to interactions between the water dipole chains and charge carriers in the tube. Our work validates this structure of a water-fitted SWCNT as a promising candidate for a synthetic nanoscale power cell, as well as a practical nanopower harvesting device at the atomic level. 

Self-organized generation of transverse waves in diverging cylindrical detonations

Self-organized generation of transverse waves associated with the transverse wave instabilities at a diverging cylindrical detonation front was numerically studied by solving two-dimensional Euler equations implemented with an improved two-step chemical kinetic model. After solution validation, four mechanisms of the transverse wave generation were identified from numerical simulations, and referred to as the concave front focusing, the kinked front evolution, the wrinkled front evolution and the transverse wave merging, respectively. The propagation of the cylindrical detonation is maintained by the growth of the transverse waves that match the rate of increase in surface area of the detonation front to asymptotically approach a constant average number of transverse waves per unit length along the circumference of the detonation front. This cell bifurcation phenomenon of cellular detonations is discussed in detail to gain better understanding on detonation physics.

Random response of nonlinear continuous systems

This thesis presents a technique for obtaining the stochastic response of a nonlinear continuous system. First, the general method of nonstationary continuous equivalent linearization is developed. This technique allows replacement of the original nonlinear system with a time-varying linear continuous system. Next, a numerical implementation is described which allows solution of complex problems on a digital computer. In this procedure, the linear replacement system is discretized by the finite element method. Application of this method to systems satisfying the one-dimensional wave equation with two different types of constitutive nonlinearities is described. Results are discussed for nonlinear stress-strain laws of both hardening and softening types.

Absolute measurement of roughness and lateral-correlation length of random surfaces by use of the simplified model of image-speckle contrast

We present a method of image-speckle contrast for the nonprecalibration measurement of the root-mean-square roughness and the lateral-correlation length of random surfaces with Gaussian correlation. We use the simplified model of the speckle fields produced by the weak scattering object in the theoretical analysis. The explicit mathematical relation shows that the saturation value of the image-speckle contrast at a large aperture radius determines the roughness, while the variation of the contrast with the aperture radius determines the lateral-correlation length. In the experimental performance, we specially fabricate the random surface samples with Gaussian correlation. The square of the image-speckle contrast is measured versus the radius of the aperture in the 4f system, and the roughness and the lateral-correlation length are extracted by fitting the theoretical result to the experimental data. Comparison of the measurement with that by an atomic force microscope shows our method has a satisfying accuracy. (C) 2002 Optical Society of America.

Single attosecond pulse generation using two-color polarized time-gating technique

It is proposed that single attosecond pulses be generated via high-order harmonic generation by using a two-color pump pulse with time dependent ellipticity. The two-color pump pulse is created by the fundamental field and its second harmonic: the fundamental field is left-circularly polarized and the second harmonic is right-circularly polarized. Numerical simulations show that single attosecond pulses can be produced in the cut-off region by using the synthesis of 20 fs left-hand and right-hand circularly polarized pulses with a pulse delay of 20 fs. The attosecond pulses produced this way are much stronger than that produced by a few-cycle linear polarized pulse of comparable intensity. (c) 2005 Optical Society of America

Engineering thermostable fungal cellobiohydrolases

Meeting the world's growing energy demands while protecting our fragile environment is a challenging issue. Second generation biofuels are liquid fuels like long-chain alcohols produced from lignocellulosic biomass. To reduce the cost of biofuel production, we engineered fungal family 6 cellobiohydrolases (Cel6A) for enhanced thermostability using random mutagenesis and recombination of beneficial mutations. During long-time hydrolysis, engineered thermostable cellulases hydrolyze more sugars than wild-type Cel6A as single enzymes and binary mixtures at their respective optimum temperatures. Engineered thermostable cellulases exhibit synergy in binary mixtures similar to wild-type cellulases, demonstrating the utility of engineering individual cellulases to produce novel thermostable mixtures. Crystal structures of the engineered thermostable cellulases indicate that the stabilization comes from improved hydrophobic interactions and restricted loop conformations by proline substitutions. At high temperature, free cysteines contribute to irreversible thermal inactivation in engineered thermostable Cel6A and wild-type Cel6A. The mechanism of thermal inactivation in this cellulase family is consistent with disulfide bond degradation and thiol-disulfide exchange. Enhancing the thermostability of Cel6A also increases tolerance to pretreatment chemicals, demonstrated by the strong correlation between thermostability and tolerance to 1-ethyl-3-methylimidazolium acetate. Several semi-rational protein engineering approaches – on the basis of consensus sequence analysis, proline stabilization, FoldX energy calculation, and high B-factors – were evaluated to further enhance the thermostability of Cel6A.

Nonlinear propagation of fs laser pulses in liquids and evolution of supercontinuum generation

Nonlinear propagation of fs laser pulses in liquids and the dynamic processes of filamentation such as self-focusing, intensity clamping, and evolution of white light production have been analyzed by using one- and two-photon fluorescence. The energy losses of laser pulses caused by multiphoton absorption and conical emission have been measured respectively by z-scan technique. Numerical simulations of fs laser propagation in water have been made to explain the evolution of white light production as well as the small-scale filaments in liquids we have observed by a nonlinear fluorescence technique. (c) 2005 Optical Society of America.