Physics Commons^™

Single Molecule Emission Characteristics In Near-Field Microscopy, Randy X. Bian, Robert C. Dunn, X. Sunney Xie, P.T. Leung

Physics Faculty Publications and Presentations

In near-field scanning optical microscopy (NSOM), the measured fluorescence lifetime of a single dye molecule can be shortened or lengthened, sensitively dependent on the relative position between the molecule and aluminum coated fiber tip. The modified lifetimes and other emission characteristics are simulated by solving Maxwell equations with the finite-difference time-domain (FDTD) method. The 2D computation reveals insight into the lifetime behaviors and provides guidance for nonperturbative spectroscopic measurements with NSOM. This new methodology is capable of predicting molecular emission properties in front of a metal/dielectric interface of arbitrary geometry.

Complexity Properties Of The Cellular Automaton Game Of Life, Andreas Rechtsteiner

Dissertations and Theses

The Game of Life is probably the most famous cellular automaton. Life shows all the characteristics of Wolfram's complex Class IV cellular automata: long-lived transients, static and propagating local structures, and the ability to support universal computation.

We examine in this thesis questions about the geometry and criticality of Life. We find that Life has two different regimes with different dimensionalities. In the small scale regime Life shows a fractal dimensionality with D_s = 0.658 and in the large scale regime D₁ = 2.0, suggesting that the objects of Life are randomly distributed. We find that Life …

Electrostatic Interactions At Membrane-Water Interfaces And Distribution Of 2, 4, 6-Trichlorophenol In A Membrane Model System, Isolde Sieder

Dissertations and Theses

It is generally accepted that biological membranes consist of a lipid bilayer matrix with proteins incorporated into the lipid bilayer. Typically, these membranes are negatively charged due to the presence of negatively charged lipids in the bilayer as well as negatively charged molecular groups on proteins. Biologically active molecules, such as environmental pollutants, enter the membrane from the aqueous phase by adsorption or partitioning into the lipid bilayer. The thesis consists of two parts. Part I is a computational study of spatial distribution of electric potential in the aqueous portion of the membrane-water interface using two models of charge distribution: …

Doubled Co2 Experiments With The Global Change Research Center Two-Dimensional Statistical Dynamical Climate Model, R. M. Mackay, M. A. K. Khalil

Physics Faculty Publications and Presentations

The zonally averaged response of the Global Change Research Center two-dimensional statistical dynamical climate model (GCRC 2-D SDCM) to a doubling of atmospheric carbon dioxide (350 parts per million by volume (ppmv) to 700 ppmv) is reported. The model solves the two-dimensional primitive equations in finite difference form (mass continuity, Newton's second law, and the first law of thermodynamics) for the prognostic variables: zonal mean density, zonal mean zonal velocity, zonal mean meridional velocity, and zonal mean temperature on a grid that has 18 nodes in latitude and 9 vertical nodes (plus the surface). The equation of state, p=rhoRT, and …

Ionization-Excitation Of Helium By Fast Charged Particles, L. Nagy, J. Wang, Jack C. Straton, James H. Mcguire

Physics Faculty Publications and Presentations

Probabilities and cross sections for ionization plus excitation in helium produced by fast heavy-particle impact have been evaluated. In these calculations, contributions from shake-off, time ordering, and independent interactions of the frozen-target electrons with the projectile are included. A comparison is made to recent experimental observations for the ratio of excitation-ionization to single-ionization total cross sections. A comparison is also made to calculations of excitation-ionization by fast electron impact.

Origins And Effects Of Thermal Processes On Near-Field Optical Probes, Andres H. La Rosa, B. I. Yakobson, H. D. Hallen

Physics Faculty Publications and Presentations

An aluminum-coated tapered fiber probe, as used in near-field scanning optical microscopy (NSOM), is heated by the light coupled into it. This can destroy the probe or may modify the sample, which can be problematic or used as a tool. To study these thermal effects, we couple modulated visible light of various power through probes. Simultaneously coupled infrared light senses the thermal effects. We report their magnitude, their spatial and temporal scales, and real-time probe damage observations.Amodel describes the experimental data, the mechanisms for induced IR variation, and their relative importance.

Origins Of Effective Charge Of Multivalent Ions At A Membrane/Water Interface And Distribution Of 2,3,4,5-Tetrachlorophenol In A Membrane Model System, Piet O. Schmidt

Dissertations and Theses

Biological cells and subcellular organelles are surrounded by membranes to form compartments performing specialized functions. Adsorption or partitioning of biologically active compounds into the membrane is the first step in the process of modification of cell function. This work is concerned with the problem of distribution of charged molecules between water and electrically charged membrane surface and between water and octanol. Part I of this thesis is focused on the electrostatic interactions taking place between charges on the membrane and ions present in the aqueous region of the membrane/water interface. The objective was to explore theoretically the origin of anomalous …

The Interaction Between A Thiol Specific Probe (Opa) And The Single Channel Characteristics Of The Reconstituted Ca++ Release Protein From Skeletal Muscle Sarcoplasmic Reticulum, Alexander Braun

Dissertations and Theses

One advantage of higher life-forms over less developed organisms is their ability to respond to signals from their environment with motion. This requires highly specialized contractile cells and a whole locomotion apparatus. In vertebrates, the cells responsible for movement are the skeletal muscle cells. They receive signals from the autonomic nervous system in the form of an action potential, and they contract in an appropriate manner. Calcium is a vital intracellular passenger whose role in muscular function is to initiate contraction. It is released via specific channel proteins from an internal Ca++ store, the sarcoplasmic reticulum, and triggers muscular contraction, …

O-Phthalaldehyde Modification Of Sarcoplasmic Reticulum Calcium Release, Steffen Koehler

Dissertations and Theses

Muscle contraction is a phenomena which fascinated already the ancient Greeks. People have long sought to understand the mechanism of muscle contraction. Today we know that in order for muscle to contract, an action potential propagates from the nerve cell to the muscle cell. Upon arriving at the muscle cell, via a mechanism called Excitation- Contraction (E-C) coupling, Ca2 + is released from an intracellular membrane system, the sarcoplasmic reticulum (SR), into the intracellular fluid. The increase of intracellular Ca2 + initiates the interaction between the contractile units which results in force development and tension. The least well understood step …

Electrolysis Of Palladium In Heavy Water, Christoph Zaczek

Dissertations and Theses

Following several reports in the past few years about compositional changes on palladium used as a cathode in heavy water electrolysis, the purpose of this research project was to reproduce this results.

Two experiments were performed using two cells connected in series, an experimental cell and a control cell.

Both experiments used platinum anodes, the experimental cell had a palladium cathode and the control cell had a platinum cathode. The electrolyte was D₂O with H₂SO₄. Radiation was monitored during both experiments. Also temperature and voltage were recorded for both experiments, to allow statements about …

Electrolysis Of Titanium In Heavy Water, Radovan Kopecek

Dissertations and Theses

The purpose of these studies was to determine if results similar to those of Fleischmann and Pons could be obtained using a titanium cathode instead of palladium in an electrolysis in a heavy water cell. The electrolyte consists of D₂O and H₂SO₄. Two experiments have been performed to examine the features of this electrolysis. As titanium shows the same properties to attract hydrogen, it seemed possible that excess heat could be produced. Radiation was monitored, and the surface of the titanium cathode was examined before and after electrolysis for any changes in the morphology …

Modeling Of Decay Rate For Molecules At An Island Surface, Ting Xiong

Dissertations and Theses

The decay rates for molecules at rough surfaces are studied via an island surface model, with particular emphasis on the effect due to the distribution of surface roughness. Two extreme cases are studied when the surface islands distribute themselves evenly and when they coalesce to form local clusters at the molecule-substrate interface. The optical properties of the interfacial layer in these two cases are described by the Maxwell-Garnett and the fractal-cluster models, respectively. Among other results, it is found that both enhancement and suppression of the surface-induced decay rates are possible due to the presence of roughness, with more dramatic …

Molecular Fluorescence Spectroscopy In The Vicinity Of A Microstructure, P.T. Leung, Thomas F. George

Physics Faculty Publications and Presentations

A brief review is presented on fluorescence spectroscopy of molecules in the vicinity of a microstructure, which could be a surface structure, clustered ions/atoms, a colloidal particle in a solution, or a tip in certain molecular probes. This structure can be viewed as microscopic, mesoscopic or macroscopic, depending on the specific environment in which the molecule is located. An overview is given for selected experimental and theoretical aspects of this phenomenon, emphasizing some of the previous modeling work of the authors. Discussion of possible future attempts to explore the phenomenon in more detail is presented at the end.