Synthesis and Cyclization of Sulfur-Substituted Azido Dienes to Pyrrolizidine and Indolizidine Moieties

Sulfur-substituted azido dienes 1 and 11 , conveniently prepared from the corresponding 3-sulfolenes 5 and 10 , were thermolyzed to give pyrrolizidine and indolizidine products, 6 , 7 and 14 .     

Effective charges of polyelectrolytes in a salt-free solution based on counterion chemical potential

The phenomenon of counterion condensation around a flexible polyelectrolyte chain with N monomers is investigated by Monte Carlo simulations in terms of the degree of ionization alpha, which is proportional to the effective charge. It is operationally defined as the ratio of observed to intrinsic counterion concentration, alpha = co/ci. The observed counterion concentration in the dilute polyelectrolyte solution is equivalent to an electrolyte solution of concentration co with the same counterion chemical potential. It can be determined directly by thermodynamic experiments such as ion-selective electrode. With the polyelectrolyte fixed at the center of the spherical Wigner-Seitz cell, the polymer conformation, counterion distribution, and chemical potential can be obtained. Our simulation shows that the degree of ionization rises as the polymer concentration decreases. This behavior is opposite to that calculated from the infinitely long charged rod model, which is often used to study counterion condensation. Moreover, we find that, for a specified line charge density, alpha decreases with an increment in chain length and chain flexibility. In fact, the degree of ionization is found to decline with increasing polymer fractal dimension, which can be tuned by varying bending modulus and solvent quality. Those results can be qualitatively explained by a simple model of two-phase approximation.     

Regularizations and superconformal anomalies

By using different regularization methods we demonstrate that supersymmetry invariance is maintained up to one-loop order in supersymmetric gauge theories and calculate the superconformal anomalies.     

Conformal anomalies in a general background metric

By using the dimensional regularization procedure, we explicitly calculate the coefficients of conformal anomalies in a general background metric due to scalar, spin $\text{1}\text{2}$ fermion, gauge and gravitation fields.     

Sorption of phenols from water in column systems using surfactant-modified montmorillonite

The sorption of phenol, m-nitrophenol (m-NP), and o-cresol from water onto montmorillonite modified with cetyltrimethylammonium bromide (CTAB) in a column was studied. The sorption isotherms were fitted by the Langmuir equation. Column experiments were performed at 25 degrees C to determine the breakthrough curves at different flow rates, feed sorbate concentrations, and bed lengths. It was shown that the proposed constant-pattern wave approach with the Langmuir model could well describe the breakthrough curves. The time required when the effluent concentration reached half of the feed concentration (t(1/2)) decreased with increasing feed flow rate, but the mass transfer coefficient (KLa) increased. In addition, an increase in feed sorbate concentration led to a decrease of both values of t(1/2) and KLa. The effect of axial dispersion on breakthrough dynamics in these sorption systems was finally discussed.     

Development of multianalyte sensor arrays composed of chemically derivatized polymeric microspheres localized in micromachined cavities.

The development of a chip-based sensor array composed of individually addressable polystyrene-poly(ethylene glycol) and agarose microspheres has been demonstrated. The microspheres are selectively arranged in micromachined cavities localized on silicon wafers. These cavities are created with an anisotropic etch and serve as miniaturized reaction vessels and analysis chambers. A single drop of fluid provides sufficient analysis media to complete approximately 100 assays in these microetch pits. The cavities possess pyramidal pit shapes with trans-wafer openings that allows for both fluid flow through the microreactors/analysis chambers and optical access to the chemically sensitive microspheres. Identification and quantitation of analytes occurs via colorimetric and fluorescence changes to receptor and indicator molecules that are covalently attached to termination sites on the polymeric microspheres. Spectral data are extracted from the array efficiently using a charge-coupled device allowing for the near-real-time digital analysis of complex fluids. The power and utility of this new microbead array detection methodology is demonstrated here for the analysis of complex fluids containing a variety of important classes of analytes including acids, bases, metal cations, metabolic cofactors, and antibody reagents.     

Improved Computer Program for Magnetron Injection Gun Design

Gyrotron has received extensive attention owing to its high-power capability, especially when the wavelength shrinks below the millimeter-wave range. The electron beam of a gyrotron is typically generated by a magnetron injection gun (MIG). For high cathode current density, the MIG may operate in a region that combines temperature limited and space-charge limited emissions. An improved computer program for electron gun design is appropriate for MIGs that operate between space-charge limited and temperature limited emission. Moreover, the initial input formation of the program resembles that of the EGUN code. Analysis of a Pierce electron gun and MIGs reveals that the stimulated beam current appears consistent with the measured results. However, EGUN simulation results in which the cathode emitters of MIGs are chosen for the temperature limited emission differ from those of our simulation results. This difference is most likely owing to that the initial emitting energy can not be completely described in the EGUN simulation. Finally, the improved computer program is used to design a MIG for a Ka-band, TE₀₁ mode gyro-TWT.     

Ultra-high on/off ratio optical trigger based on SOI–SOA waveguide

We present a device able to perform an all-optical trigger by utilizing the cascaded silicon-on-insulator (SOI) and semiconductor-optical-amplifier (SOA) optical waveguides, where both the controlling pulse and the signal pulse are co-propagating along the device. The results of numerical simulations show that the all-optical trigger behavior with ultra-high on/off ratio can be easily achieved by adjusting the device parameters. To improve and optimize the optical trigger operation, the negative initial delay (the signal pulse before the controlling pulse) and the positive initial delay (the signal pulse after the controlling pulse) are considered for performing the optical trigger operation.