Session E04: Applied Physics

Physics behind the transition of fatigue deformation to fatigue fracture

A recent gauge theory of deformation and fracture has been used to consider the physics behind the transition from fatigue deformation to fatigue fracture of solids. The present field theory describes deformation and fracture of solid comprehensively as wave dynamics. The wave equations derived by this field theory have been numerically solved to assimilate the wave characteristics observed in the displacement field with experimental results. The numerical results indicate (a) the transition to fatigue fracture is initiated by the loss of Poisson’s effect and (b) reduction in shear modulus leads to temporal instability in the wave dynamics. This temporal instability seems to cause exponential growth of displacement field that eventually generates material discontinuity.   

Modeling the performance of a novel electrostatic quadrupole doublet ion beam lens

The electrostatic quadrupole lens commonly used on low-energy ion beam lines is typically fabricated with cylindrical electrodes of radius equal to 1.15 times the bore radius of the quadrupole. Using the program SIMION we modeled a novel electrostatic quadrupole doublet ion beam lens constructed with football-shaped electrodes. We then analyzed the effects of this lens on low-energy ion beam transport as compared to the traditional quadrupole design. In this paper, we present comparisons of the focal error, $\delta f$/$f$, and effective emittance growth for a Gaussian beam, and we show that the novel electrode shape reduces phase space distortions introduced by lenses employing truncated cylinders.   

Frequency domain approach for improvement of cochlear implant performance

A cochlear implant is a neuro-prosthesis that converts sound to an electrical signal that stimulates the auditory nerve. Although commercial systems are available, the technology has room for improvement for better sound quality. The challenge is to allocate the frequency spectral components properly to the limited number of electrodes and generate pulsed signals accordingly. We view the entire process as a sensing-actuation system consisting of a series of transfer functions and try to improve the performance by adjusting various parameters such as those for digital filtering and electric current steering. Recent progress will be reported.   

Superhard Boron-Rich Boron Carbide with Controlled Degree of Crystallinity in Microwave Plasma CVD

Materials based on the light elements of carbon, nitrogen, oxygen and boron having strong covalent bonds comprise some of the hardest known materials. These light elements can form short bond lengths with each other and are inclined to form directional covalent bonds, making the structures they form difficult to compress or distort. In this study microwave plasma chemical vapor deposition (MPCVD) was used to synthesize superhard boron-rich boron carbide coatings on silicon substrates under controlled conditions that led to either disordered or crystalline structure. By simply modifying the sample stage design inside the MPCVD crystallinity of the synthesized coatings was manipulated. X-ray diffraction analysis of the crystalline coating provides a good match with a B$_{50}$C$_{2}$-type of structure in which two carbon atoms replace boron in the $\alpha $-tetragonal B$_{52}$ structure, or in which the carbon atoms occupy different interstitial sites. Density functional theory predictions were used to evaluate dynamical stability of potential B$_{50}$C$_{2}$ structural forms that are consistent with measurements. Nano-indentation measurements reveal an average coating hardness 34 GPa with several measurements greater than 40 GPa.   

Recent Advancements on the Design of Emitters for Efficient Thermophotovoltaics.

In thermophotovoltaics, heat from a thermal emitter is directly converted to electricity via a photovoltaic cell. To achieve high efficiencies, the emitted spectrum must be tailored to a specific solar cell. In this work, we propose to use a thin film configuration for the emitter. Our figure of merit (FOM) is defined as the ratio of the power generated by the photovoltaic cell (P\textunderscore \textbraceleft cell\textbraceright ) and the power emitted by the emitter (P\textunderscore \textbraceleft emit\textbraceright ). We analyze the optimal configuration of \textgreater 2000 different emitters that can operate at temperatures above 2000\textordmasculine C. The methods implemented here apply to any photovoltaic cell. Thus, we evaluate the best emitter candidates for Si, Ge, GaSb, InGaAs, and InGaAsSb cells. Due to the ultra-high temperature operation of the thermophotovoltaic, the thermal stability and the mismatch in the thermal expansion coefficient of each material combination are discussed. Our results show that FOMs above 50{\%} are achievable under ideal conditions. This work can shed light on high-temperature photonics, where a simple emitter design can result in higher efficient photoelectronic devices.   

Design of a Machine to Test & Improving a Geometry-based Braid Modeling System

This presentation explores the process of a project taken on to critique and improve several accepted circular braid models. In particular, the project was designed to facilitate testing of the simple braid-point model put forward by Isaac \textit{et. al. }in 2016, as well as the testing of altered versions of the model, likely including a version with a Taylor's Expansion elasticity factor. To this end, an adjustable braiding machine was designed using an inexpensive, single-mode maypole braider. The possibility of creating similar research machines within a low-dollar budget (rather than buying a fully adjustable braider) could prove extremely useful for allowing widespread testing and research in circular braiding.   

Collection of Gas Chromatography (GC) Signals for the Development of a Scent Categorization and Description Algorithm

In this presentation, we discuss the collection of chromatographic data for the development of a scent detection and classification algorithm for chemical scents. Scents are classified into families based on commonalities in verbal descriptions. For example, notes of oak and cedar would correspond to a woody scent, while lilies and rose would be floral. In ``The Atlas of Odor Character Profiles'' (1985), Andrew Dravnieks rates the applicability of verbal scent descriptors for 160 chemicals. The applicability of these descriptors were used to sort the chemicals into their scent families. Three chemicals were selected from each of three families. Gas Chromatography (GC) is used to generate signals of peaks with retention times characteristic of their corresponding chemicals. The height of the peaks correspond to the concentration of the chemical sample. Using the selected Atlas chemicals, a data bank was created. A machine learning algorithm was created using a simple convolutional neural network (CNN) structure that, when given an input of a GC signal, will output a verbal description of scent. This project is funded by the KY NSF EPSCoR URE program.