APPLIED PHYSICS RELATIVISTIC CORRECTIONS TO MOSELEY'S LAW X-ray fluorescence (XRF) is the emission of characteristic x-rays from a substance. These characteristic x-rays are produced when a sample is excited and inner shell electrons are ejected from some of its atoms. This leaves vacancies in the inner orbitals, known as holes, allowing electrons from higher orbitals to make transitions into the unoccupied states. of lower energy. This process releases energy in the form of an energetic x-ray photons. Since the energies of these x-rays are unique for each element, XRF is a power tool in chemical analysis.
TOMAS SOLTIS BS Physics and Mathematics 2016 Knightdale High School. Knightdale, North Carolina Faculty. Lorcan Folan NYU School of Engineering
In 1913 Henry Moseley discovered a simple linear relationship between the square root of the frequency of a characteristic x-ray and the atomic number Z of the emitting element. This relationship quickly became known as Moseley’s Law and provided support for Bohr’s model of the atom which relied on the principle of quantized energy and angular momentum. However, substantial deviations from Mosley’s Law begin to develop as one moves to higher Z elements. This project explored the possibility that these deviations could be explained by relativistic effects (i.e., relative motion of the electron with respect to the nucleus). We measured the energies of K and L transitions in the spectra of a series of elements between Titanium and Lead using solid state x-ray spectrometers (CZT & CdTe). We are applying a series of relativistic corrections to Moseley’s Law, each of which can be derived from the fully relativistic Dirac equation. Initial results confirm that the basic deviations are due to relativistic effects.
CHEMICAL AND BIOMOLECULAR ENGINEERING METHODS OF ANALYZING BIOREACTIONS IN NANOLITER VOLUMES
SARAH BISCARDI BS Chemical and Biomolecular Engineering 2016 Lake Mary Preparatory School. Lake Mary, Florida
Surface characterization is predominantly affected by the chemical nature of a surface and is used to determine properties such as wettability, adhesion, and hydrophobicity. Multiple theories have been developed to determine surface energy based on the characteristics of the surface and the solvent. Surface energy is best visualized by determining the equilibrium contact angle between a nanoliter droplet and a solid surface, known as the Sessile Drop Method. A simple procedure was created from a camera and drop stage area. In this process, a droplet is printed onto a slide surface, where an image is taken of the droplet edge and is then processed and analyzed with programs such as ImageJ or an ImageJ add-on called DropSnake to find the angle at which the solvent contacts the surface. This process is repeated for multiple droplets to determine an average angle. The accuracy of this simple set up was determined by comparing results to literature of similar experiments. Polymer solvents such as Poly(methyl methacrylate) (PMMA), Polystyrene (PS), and Polytetrafluoroethylene (PTFE) are used because of their stabilities with water droplets. Measuring surface energy is directly applied to represent the influence of surface modifications on wettability and other characteristics as well as to determine suitable modifications for other processes. Multiple solvents are used to determine the surface tension of the modified surface by taking into account the polar and dispersive components of the liquid (Owens/Wendt Theory). From these studies, we will apply this process to DNA hybridization by similar modifications of gold surfaces for better immobilization characteristics.
Faculty Rastislav Levicky Other Mentor Hao-Chun (Howard) Chiang NYU School of Engineering *Thompson-Bartlett Fellow
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