Ultrasonic guided wave inspection with array sensors

Ultrasonic guided wave becomes one of promising tool for monitoring various types of structures such as large steel plates, vessels, and pipes in oil, chemical or nuclear industry, because guided waves have ability to travel wide range of the target structure in a single position. However, analysis of guided wave signals acquired from structure is difficult on account of low S/N ratio and its dispersive nature. To improve S/N ratio and overcome dispersion effect, focusing techniques for guided waves are needed. Thus, in this study, focusing techniques for guided waves were developed in order to improve long range inspection ability, and performance of the developed techniques was verified by experiments.     

ANALYSIS AND MEASUREMENT OF SOUND TRANSMISSION THROUGH A DOUBLE-WALLED CYLINDRICAL SHELL

Sound transmission through a double-walled cylindrical shell is studied. The solution that describes the system response is obtained by combining the solutions of two different models of the system. The first model, which describes the sound transmission due to the interaction between the acoustic waves and the bending waves in the shells, is formulated by three acoustic wave equations and two shell vibration equations. The second model describes the sound transmission by one-dimensional waves propagating through the layers of the shells and the air-gap. The transmission losses calculated from the two models are combined to represent the system response in the entire frequency range. Analytical solutions are compared to corresponding measured results, which shows reasonable agreements if the extent of the simplifications used in the analytical model is considered. The effects of important design parameters such as the air-gap size and the thickness ratio are studied using analytical solutions.     

The Role of Biofilm Growth in Bacteria-Facilitated Contaminant Transport in Porous Media

Groundwater contaminants adhered to colloid surfaces may migrate to greater distances than predicted by using the conventional advective-dispersive transport equation. Introduction of exogenous bacteria in a bioremediation operation or mobilization of indigenous bacteria in groundwater aquifers can enhance the transport of contaminants in groundwater by reducing the retardation effects. Because of their colloidal size and favorable surface conditions, bacteria can be efficient contaminant carriers. In cases where contaminants have low mobility because of their high partition with aquifer solids, facilitated contaminant transport by mobile bacteria can create high contaminant fluxes. In this paper, we developed a methodology to describe the bacteria-facilitated contaminant transport in a subsurface environment using the biofilm theory. The model is based on mass balance equations for bacteria and contaminant. The contaminant is utilized as a substrate for bacterial growth. Bacteria are attached to solid surfaces as a biofilm. We investigate the role of the contaminant adsorption on both biofilm and mobile bacteria on groundwater contaminant transport. Also, the effect of bacterial injection on the contaminant transport is evaluated in the presence of indigenous bacteria in porous media. The model was solved numerically and validated by experimental data reported in the literature. Sensitivity analyses were conducted to deduce the effect of critical model parameters. Results show that biofilm grows rapidly near the top of the column where the bacteria and contaminant are injected, and is detached by increasing fluid shear stress and re-attach downstream. The adsorption of contaminant on bacterial surfaces reduces contaminant mobility remarkably in the presence of a biofilm. The contaminant concentration decreases significantly along the biofilm when contaminant partition into bacteria. Bacterial injection and migration in subsurface environments can be important in bioremediation operations regardless of the presence of indigenous bacteria.     

Embedded Surfaces for Symplectic Circle Actions

The purpose of this article is to characterize symplectic and Hamiltonian circle actions on symplectic manifolds in terms of symplectic embeddings of Riemann surfaces.More precisely, it is shown that(1) if(M, ω) admits a Hamiltonian S~1-action, then there exists a two-sphere S in M with positive symplectic area satisfying c1(M, ω), [S] 0,and(2) if the action is non-Hamiltonian, then there exists an S~1-invariant symplectic2-torus T in(M, ω) such that c1(M, ω), [T] = 0. As applications, the authors give a very simple proof of the following well-known theorem which was proved by Atiyah-Bott,Lupton-Oprea, and Ono: Suppose that(M, ω) is a smooth closed symplectic manifold satisfying c1(M, ω) = λ· [ω] for some λ∈ R and G is a compact connected Lie group acting effectively on M preserving ω. Then(1) if λ 0, then G must be trivial,(2) if λ = 0, then the G-action is non-Hamiltonian, and(3) if λ 0, then the G-action is Hamiltonian.     

Hydrophilic and hydrophobic adsorption on Y zeolites

The uniform large micropores of hydrothermally stable Y zeolites are used widely to confine both polar and non-polar molecules. This paper compares the physisorption of water, methanol, cyclohexane, benzene and other adsorbates over various Y zeolites. These adsorbents are commercial products with reproducibly controllable physical and chemical characteristics. Results indicate that the type I isotherms typical for micropore adsorption can turn into type II or type III isotherms depending on either or both the hydrophobicity of the adsorbent and the polarity of the adsorbate. Methanol produced a rare type V isotherm not reported over zeolites before. Canonical and grand canonical Monte Carlo molecular simulations with Metropolis importance sampling reproduced the experimental isotherms and showed characteristic geometric patterns for molecules confined in Na-X, Na-Y, dealuminated Y, and ZSM5 structures. Adsorbate—adsorbate interactions seem to determine the micropore condensation of both polar and non-polar molecules. Exchanged ions and lattice defects play a secondary role in shaping the adsorption isotherms. The force field of hydrophobic Y appears to exert an as yet unexplored sieving effect on adsorbates having different dipole moments and partial charge distributions. This mechanism is apparently different from both the monolayer formation controlled adsorption on hydrophobic mesopores and macropores and the polarizability and small-pore opening controlled micropore confinement in hydrophobic ZSM5.     

Ab initio study of superoxide anion—water clusters O2 − (H2O)n=1-5

The structures, energies, Spectra, and charge transfer to solvent (CTTS) energies of the hydrated superoxide anion clusters have been investigated using both density functional calculations (DFT) with Becke-3-parameters employing Lee-Yang-Parr functionals (B3LYP) and second-order M?ller Plesset perturbation (MP2) calculations employing highly diffuse basis sets. Given the good agreement of our predicted results with the experimental spectra and enthalpy, it would be interesting if the CTTS energies could be experimentally determined.     

Kinetics of supersaturation decay in the crystallization of lysozyme

The molecular architecture of proteins can be determined by analysing the X-ray diffraction patterns of their crystals. The technology of X-ray crystallography has reached the point, however, where the determination of the structure of a given crystal is controlled by the limited availability of the crystals themselves. Proteins can often be crystallized from pH buffered aqueous solutions of strong electrolytes. When dissolved protein in solution is more stable than crystalline protein, the appearance of crystals can be said to be under thermodynamic control. If, on the other hand, the crystals are more stable than the dissolved protein, and still crystals are slow to appear, the crystallization can be said to be under kinetic control. Using dilatometry, we have followed the rate of decay of the protein supersaturation in crystallizing solutions of chicken egg-white lysozyme under conditions of kinetic control. We have found that the rate of decay of the supersaturation is first order in the supersaturation and that the rate constant is independent of the initial protein concentration, but increases with increasing pH, decreasing temperature, and with increasing concentrations of sodium chloride and buffer salt. We correlate these observed trends in the rate constant with related trends in the solubility and surface charge density of the crystals. We conclude that the rate constant for supersaturation decay is inversely proportional to the protein solubility.     

EXCITED STATE PROPERTIES OF THE N-(DEOXYGUANOSIN-8-YL)-2-AMINOFLUORENE ADDUCTS

The spectroscopic characteristics of adducts derived from the covalent binding of the carcinogen 2-aminofluorene to the C8 position of deoxyguanosine [N-(deoxyguanosin-8-yl)-2-amino-fluorene, dGuo-C8-AF], and from an adduct of similar structure formed with the synthetic polynucleotide poly(dG-dC).poly(dG-dC), were investigated. At 77 K both adducts are characterized by well-defined and rather narrow fluorescence emission spectra with maxima at 370 and 390 nm characteristic of the aromatic, monomolecular 2-aminofluorene (AF) residue. In contrast, at room temperature, the fluorescence is characterized by a broad, structureless emission band with a maximum at 460 nm in aqueous mixtures, shifting to 415 nm in solvents of lower polarity (100% propanol); the maxima are located at intermediate wavelengths in solutions of different propanol/water compositions, and this emission is attributed to an excited state complex (exciplex). The fluorescence quantum yield decreases when either the solvent polarity or the temperature are increased, varying from 5.4% (100% propanol) to 0.04-0.05% (100% H2O). The fluorescence decay profiles of dGuo-C8-AF adducts (measured at the National Synchrotron Light Source facility at the Brookhaven National Laboratory) can be roughly, but not exactly, modeled in terms of two exponential decay components in the range of about 0.3-1.0 ns with the propanol concentration greater than 60%; at lower propanol concentrations, a single short lifetime is observed and in 100% water solutions its value is 0.08 ns. The shorter lifetime, favored in solvent mixtures of higher polarities, is attributed to an exciplex with significant charge-transfer character.(ABSTRACT TRUNCATED AT 250 WORDS)     

Development and Characterization of Metal-Insulator-Metal Capacitors with SiNx Thin Films by Plasma-Enhanced Chemical Vapor Deposition

We report the fabrication of high breakdown voltage metal-insulator-metal （MIM） capacitors with 200-nm silicon nitride deposited by plasma-enhanced chemical vapor deposition with 0.957 SiH4/NH3 gas mixing rate, 0.9 Torr working pressure, and 60 W rf power at 250℃ chamber temperature. Some optimized mechanisms such as metal source wiping, pre-melting and evaporation rate adjustment are used for increasing the yield of the MIM capacitors. N2 annealing and O2/H2 plasma pre-deposition treatment is proposed to increase the reliability of the MIM capacitors in high-temperature, high-pressure, and high-humidity environments. A 97% yield and up to 148 V breakdown voltage of a 13.06pF MIM capacitor with 0.04 mm^2 die area can be fabricated.