Calculation of single-beam two-photon absorption transition rate of rare-earth ions using effective operator and diagrammatic representation

Effective operators needed in single-beam two-photon transition calculations have been represented with modified Goldstone diagrams similar to the type suggested by Duan and co-workers [J. Chem. Phys. 121, 5071 (2004) ]. The rules to evaluate these diagrams are different from those for effective Hamiltonian and one-photon transition operators. It is verified that the perturbation terms considered contain only connected diagrams and the evaluation rules are simplified and given explicitly.Comment: 10 preprint pages, to appear in Journal of Alloys and Compound

Unusual Glass-Forming Ability of Bulk Amorphous Alloys Based on Ordinary Metal Copper

We report the unusual glass-forming ability (GFA) of a family of Cu-based alloys, Cu46Zr47–xAl7Yx (0<x<=10, in at. %), and investigate the origin of this unique property. By an injection mold casting method, these alloys can be readily solidified into amorphous structures with the smallest dimension ranging from 4 mm up to 1 cm without detectable crystallinity. Such superior GFA is found primarily due to the alloying effect of Y, which lowers the alloy liquidus temperature and brings the composition closer to a quaternary eutectic. Other beneficial factors including appropriate atomic-size mismatch and large negative heat of mixing among constituent elements are also discussed

Harnessing Interfacial Phenomena Involving Macromolecules For Emulsion Processing

An emulsion is a mixture of two immiscible solutions, one dispersed in the other. Intrinsically, most emulsions are thermodynamically unstable and thus active agents called surfactant are added to the mixture to stabilize the interface. The surfactant lowers the interfacial tension and provides steric and/or electrostatic repulsion at the fluid interfaces to enhance the stability of emulsions. Macromolecules, either intrinsically surface active or not, have attracted lots of attention for emulsion processing. On one hand, advances in polymeric synthesis technique present various polymeric surfactants waiting to be exploited. On the other hand, macromolecules present the platform for versatile modification that can result in assemblies with special properties. Various natural materials are also macromolecules, waiting to be exploited as replacements for synthetic surfactants of petrochemical origins. In this thesis, ion pairing and microfluidic techniques are used to expand the macromolecules’ application and to investigate the composition effect of polymeric surfactants in emulsion processing. Polyelectrolyte is extracted into an organic phase via ion pairing with an oppositely charged surfactant. The formed ion pair retain the polyelectrolyte’s capability to form complexes. It complexes with oppositely charged polyelectrolyte and is exploited for one-step polyelectrolyte microcapsules generation. Meanwhile, the composition effect of a set of polymeric surfactants, Pluronics, on flow-induced phase inversion emulsification (FIPIE) is studied. Through microfluidic technology, emulsion phase inversion process at the single droplet level is monitored. We find strong correlation between the molecular weight (MW) and the lengths of individual blocks of the Pluronics and the tendency of droplets to undergo (FIPIE). In Chapter 4, dynamic ion pairing between polyelectrolyte and surfactant is used to induce phase inversion emulsification (PIE). The ion pair formation is controlled as a function of the solution pH and surfactant concentration. Both oil-in-water (O/W) and water-in-oil (W/O) emulsions are formed and PIE from W/O to O/W emulsion is demonstrated. In summary, macromolecules possess rich behaviors at the emulsion interfaces. The macromolecule and surfactant association, such as ion pairing, form assemblies with distinct properties, expanding common materials’ application for versatile emulsion processing

Mechanical integrity and behavior of thin films and their applications in MEMS

Electric actuated thin films are widely used in micro-electromechanical systems (MEMS) such as radio frequency switches (RF-switches), micro-pumps and valves, and electrostatic actuators. This dissertation will focus on the operation of a MEMS-RF-switch. In a typical MEMS-RF-switch, a mechanically suspended 1-D rectangular or 2-D axisymmetric thin film is pulled by an electrostatic voltage (V₀) applied to an electrode-pad directly underneath. When V₀ exceeds a certain pull-in threshold, V₀*, the thin film makes direct contact with the pad so that either an on or off signal is induced, and when the voltage is removed, the thin film resumes its original undeformed configuration. To understand the device operation and to optimize the design parameters (e.g., dimension of the thin film), it is necessary to construct a rigorous elastic model for the electromechanical interaction --Introduction, page 1