Formation Potential of Disinfection By-products after Coagulation of Algal Matters

Algal organic matters (AOM) are cellular materials releasing from algae species which can serve as precursors to form disinfection by-products (DBPs) after chlorination. AOM can be removed during drinking water treatment by coagulation. In this study, dissolved organic carbon (DOC) and UV254 absorbance were used to assess the time dependent release of algal matters for four algal species during coagulation using alum. A GC-ECD was employed to analyze the formation of DBPs at different background water qualities. Results showed that alum dose of 30 mg/L did not cause any damage to the algae cells, and they continued to release organic matters in treated water with time. Uniform formation condition (UFC) was used to determine the DBP formation potential, specifically haloacetic acids (HAA) from algal matter. DBP formation increased with increasing settling time. Empirical DBP formation models developed in this study showed good correlations between HAA formation and relevant water quality parameters

Near Bandgap Two-photon Excited Luminescence of InAs Quantum Dots

Semiconductor quantum dots (QDs) confine carriers in three dimensions, resulting in atomic-like energy levels as well as size-dependent electrical and optical properties. Self-assembled III-V QD is one of the most studied semiconductor QDs thanks to their well-established fabrication techniques and versatile optical properties. This dissertation presents the photoluminescence (PL) study of the InAs/GaAs QDs with both above bandgap continuous-wave excitation (one-photon excitation) and below-bandgap pulse excitation (two-photon excitation). Samples of ensemble QDs, single QD (SQD), and QDs in a micro-cavity, all grown by molecular beam epitaxy, are used in this study. Morphology of these samples was examined using atomic force microscope and transmission electron microscope. Two-photon excitation uses energy near half of the QDs ground state transition, all the way up to half of the GaAs matrix bandgap. Power dependent QDs PL with both one-photon and two-photon excitation can be described by power laws, with power index of 1 for one-photon excitation and two for two-photon excitation. Photoluminescence excitation spectroscopy then provides evidence of direct two-photon absorption into the QDs when the two-photon excitation energy is resonant with the QDs state. For SQD without cavity, we observed PL of a SQD with excitation near its half bandgap. The QDs in a micro-cavity sample consists one layer of InAs QDs in a GaAs spacer sandwiched between two distributed Bragg reflectors made of alternating layers of GaAs and AlAs. We successfully observed PL from SQD emitted from the cavity mode with excitation slightly above half of the QD’s transition. These observations help us to understand the nonlinear optical property of InAs QDs and can be potentially used in all-optical computation or reflective optical limiters

Cardiac autonomic activity in depression and anxiety:Heartfelt afflictions of the mind

Penninx, B.W.J.H. [Promotor]Geus, J.C.N. de [Promotor]Lamers, F. [Copromotor