Bulletin of the American Physical Society
2017 Annual Fall Meeting of the APS Ohio-Region Section
Volume 62, Number 18
Friday–Saturday, October 13–14, 2017; Miami University, Oxford, Ohio
Session D1: Poster Session: Astrophysics/Optical Sensing/SPS |
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Chair: Stephen Alexander, Miami University Room: Kreger Hall 2nd Floor Hallway |
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D1.00001: Effects of advection on the Belousov-Zhabotinsky reaction: standing excitation waves in a quasi-1D system Chase Fuller, Niklas Manz Reaction-diffusion (RD) waves are autocatalytic reaction zones that propagate via molecular diffusion without mass transport. They arise from the interplay of nonlinear reaction kinetics of an activator and an inhibitor species and diffusion-mediated spatial coupling (e.g., action potentials in nerves, forest fires, or stadium waves). Introducing fluid flow in a liquid chemical RD system has a huge effect on the propagation behavior of the wave. By using quasi-1D systems, such as glass capillary tubes, it is possible to create `standing waves' by advecting the liquid solution opposite to the direction of wave propagation. In our experiments, we used the Belousov-Zhabotinsky reaction as the liquid RD system. The solution was restrained in capillaries, with inner diameters of 0.58 mm. This enabled us to study a quasi-1D reaction-diffusion-advection system. After initiating waves on the open end of the capillary, the reaction solution was advected in the opposite direction. The effect of flow rate on the propagation speed and front shape was investigated. Stationary chemical waves were observed under equal-velocity conditions. [Preview Abstract] |
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D1.00002: Metabolic monitoring using UV-excited cellular autofluorescence in the presence of a quencher Chong Kai Wong, Dylan Palo, Paul Urayama Reduced nicotinamide adenine dinucleotide (NADH) is an important endogenous fluorophore for metabolic monitoring due to its increasing use as a biomarker. Thenoyltrifluoroacetone (TTFA) is an inhibitor of cellular respiration, known to quench NADH fluorescence. TTFA added to NADH in solution also changes the emission spectrum shape, possibly due to the differential quenching of the various NADH conformations. \textit{In vivo}, the sequential additions of TTFA and cyanide to a cellular suspension of baker's yeast yields insight into the interpretation of pharmacologically-induced changes in the autofluorescence (i.e., endogenous fluorescence) spectrum shape. At 1 mM TTFA concentration, subsequent addition of cyanide produces no change in autofluorescence intensity, as seen at lower TTFA concentrations. Despite the lack of intensity change, cyanide addition does produce the expected change in autofluorescence spectrum shape. Because spectrum shape is increasingly shown to correlate with NADH conformation both in solution and \textit{in vivo}, spectrum shape may be useful as a metabolic monitoring parameter even for situations where intensity is affected by non-metabolic artifacts. [Preview Abstract] |
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D1.00003: Time-resolved measurements of diffuse reflectance in biological, scattering media Jijun Chen, Carter McMaster, Karthik vishwanath Light is non-invasively used to determine properties of the biological system. These biological properties are related to the optical coefficients of scattering and absorption and they are functions of the wavelength It is possible to measure these optical properties by shining an ultra-fast laser pulse into the medium and then measuring the resulting time-resolved diffuse reflectance. Here we explore relationships between time-resolved reflectance with different optical properties experimentally and numerically. We use a supercontinuum laser which produces a broadband pulse together with a time correlated single photon counter connected to photon-counting avalanche photodiode. The laser will be spectrally filtered to get the optical properties of tissue as a function of wavelength, using time-resolved data. Monte Carlo simulations of time-resolved reflectance will be calculated for media with different optical properties. These simulations will not only help with validating experimental data, but will also help us predict, design and optimize experimental studies. [Preview Abstract] |
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D1.00004: Pulse generation and characterization for supercontinuum experiments Matthew Mircovich, Rudrakant Sollapur, Andreas Hoffmann, Christian Spielmann, Alexander Hartung, Anka Schwuchow, Joerg Bierlich, Jens Kobelke, Markus A. Schmidt To study and optimize ultrafast supercontinuum generation in gas-filled fibers, the input laser pulses must be well characterized. For extending the supercontinuum into the UV we started with frequency doubling ~80fs, 1mJ pulses from ~a titanium sapphire laser at 800nm through type 1 second harmonic generation in beta barium borate (BBO). After optimizing the setup, we were able to achieve a conversion efficiency of 20{\%}, which is well suited for supercontinuum generation. The resulting 400nm pulses were characterized with a spectrometer, CCD camera and~a self-diffraction frequency resolved optical gating (SD-FROG) device to estimate the pulse duration. Finally we studied the coupling efficiency into~micro structured anti-resonant hollow core fibers (ARHCF) with a core diameter of 50\textmu m. Under optimized coupling we were able to observe the fundamental spatial mode at the output proofing the guiding mechanism at 400nm. [Preview Abstract] |
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D1.00005: Optimization of a nanosecond-gated spectrofluorimetry system used for the monitoring of cellular metabolism Martin Heidelman, Paul Urayama Our lab has developed a system for the real-time monitoring of nanosecond-gated, UV-excited cellular autofluorescence (endogenous fluorescence). Time-gated detection using an intensified CCD coupled to a spectrograph enables spectral measurements at controllable time delays with respect to an excitation pulse, useful because autofluorescence is known to have many excited-state lifetime components. Under UV excitation (nitrogen laser, 337 nm wavelength, sub-ns pulse width), autofluorescence is primarily due to NAD(P)H with its ``free'' and ``protein-bound'' forms having short (\textasciitilde 300 ps) and long (1--5 ns) lifetimes respectively. Time-gated detection captures the long-lifetime emission separately from the emission as a whole. Further, quantifying spectrum shape using phasor analysis allows for the assessment of two-state behavior during chemically-induced metabolic transitions, providing information at the biochemical-pathway level. Here we present an optimization of the gate timing, maximizing rejection of short-lifetime emission while maintaining contrast in spectrum-shape change during the monitoring of metabolic transitions in a model cellular system. [Preview Abstract] |
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D1.00006: Characterization of Refractive Index for Potassium Terbium Fluoride. John Kunkel, Said Elhamri, D. E. Zelmon Potassium Terbium Fluoride (KTF) has the potential for application as an effective optical isolator. It would be valuable for use in high-power laser systems to prevent reflected beams from coupling back into the pump laser. Characterization of the material, including the dependence of the refractive index on wavelength and temperature, are important for incorporating KTF into these laser systems. The method of minimum deviation was used to measure the refractive index for wavelengths ranging from 0.400 to 5.20 microns and in temperatures ranging from 20 to 225\textdegree C. Results of this characterization will be presented. [Preview Abstract] |
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D1.00007: Concentration-dependent cyanide action revealed by the spectral phasor analysis of UV-excited cellular autofluorescence Nazar Al-Aayedi, Madhu Gaire, Paul Urayama Spectral phasor analysis on nanosecond-gated UV-excited cellular autofluorescence is being developed for the real-time monitoring of metabolism. Previous studies have shown that emission signals are primarily due to reduced nicotinamide adenine dinucleotide (NADH) forms, significant because NADH is used as a metabolic indicator and biomarker and because the various NADH forms respond differently to changes in mitochondrial function. Here we apply the monitoring technique to investigate the autofluorescence response of cellular suspensions to additions of cyanide, an inhibitor of cellular respiration. Using spectral phasor analysis to assess whether observed spectral changes are consistent with a two-state model, we find evidence for the spectral detection of a concentration-dependent cyanide action. Results suggest quantification of spectrum shape can be useful in the real-time, non-invasive detection of small differences between cellular metabolic responses. [Preview Abstract] |
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D1.00008: Maxwell equations in Q-space Victor Christianto, Florentin Smarandache Quaternion space and its respective Quaternion Relativity (it also may be called as Rotational Relativity) is a new theory capable to describe relativistic motion in a straightforward way. Nonetheless there are subsequent theoretical developments which remains an open question, for instance to derive Maxwell equations in Q-space. Therefore, the purpose of the present paper is to derive a consistent description of Maxwell equations in Q- space. Considering a simplified method similar to the Feynman's derivation of Maxwell equations from Lorentz force. Presenting another derivation method using Dirac decomposition, introduced by Gersten (1999). In accordance with Gersten, the Maxwell equations yield wavefunctions which can be used as guideline for interpretation of quantum mechanics. The one-to-one correspondence between classical and quantum wave interpretation asserted here actually can be expected not only in the context of Feynman's derivation of Maxwell equations from Lorentz force, but also from known exact correspondence between commutation relation and Poisson bracket. [Preview Abstract] |
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D1.00009: Magnetic and Transport Properties of Ni-Cr-Mn-Ga Heusler Alloys of Selected Compositions. Heather Statt, Dr Mahmud Khan The phase transitions of selected Ni-Cr-Mn-Ga Heusler alloys were investigated by x-ray diffraction, magnetization, electrical resistivity, and SEM measurements. A total of six Ni$_{\mathrm{+}}_{x}$Cr$_{\mathrm{.15}}$Mn$_{y}$Ga (0.5 $\le x \le $0.2; 0.65 $\le y \le $0.80) samples were prepared where the Cr and Ga concentrations remained constant while the Ni and Mn concentrations were varied. All samples exhibited the first order martensitic phase transformation upon cooling from 400 K to lower temperatures. The compounds with Mn concentration $y $\textless 0.75, exhibit a ferromagnetic transition, which is separate from the martensitic phase transition. For the compounds with $y$\textgreater 0.7, the martensitic and ferromagnetic phase transitions are coupled and occur at the same temperature. In addition to these two phase transitions, the samples with $y $\textless 0.75 exhibit the inter-martensitic phase transformation. In the vicinity of the martensitic phase transformation, a sharp drop in resistivity has been observed for all samples. The experimental results and discussion will be presented in detail. [Preview Abstract] |
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D1.00010: Designing Earthquakes for a Low-Cost Shake Table. Frederick Thomas, Robert Chaney, Marta Gruesbeck A servo-powered shake table can be programmed to produce one-dimension scale versions of either real or user-designed earthquakes. Programmed using Excel-like algebraic functions, the table can replicate earthquakes with varying amplitudes (i.e., original Richter magnitude), different maximum accelerations (the primary basis for building codes), varying frequencies, alternative waveforms and more. In addition to teaching about the differences among displacement, velocity and acceleration, the table can assist in teaching about periodic and non-periodic motions. A sample 2-part activity asks students to (1) design and build a structure which can withstand a Richter magnitude 5 earthquake, then (2) design a magnitude 4 earthquake to destroy the structure. Since the Arduino family board incorporates a micro SD card, the system can store and replay thousands of alternative motions. Plans for building the table are provided, along with an executable LabVIEW control program and the necessary sketch for implementation via a ChipKIT WF32 board. [Preview Abstract] |
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D1.00011: Using Matches to Investigate Forest Fire Propagation Along a Slope Abigail E. Ambrose, Niklas Manz We experimentally analyzed how slope effects the propagation speed of forest fires. Using a match stick array, we created 3D-printed molds with various angles with specific conditions for the distance between neighboring match heads. We developed three types of models, in which the distance between the match heads are kept constant along the horizontal (x-model), along the vertical (z-model), and along the slope (r-model). For all three models, we determined the slope-speed relationship along the incline for upward and downward propagating fire fronts up to 45 degrees. Each model is best fitted by a different function which will be discussed. [Preview Abstract] |
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D1.00012: Development of a time-resolved stereoscopic PIV system Kristin Irlam, Jeremiah Williams Over the past twenty years, a variety of particle image velocimetry (PIV) techniques have been used to characterize the particle transport and thermal state of dusty plasma systems. While the majority of these techniques required the use of a dedicated PIV system, recent advances in imaging technology have led to the development of a time-resolved two-dimensional (planar) version of this diagnostic technique which allows this diagnostic technique to be applied without the need for a dedicated PIV system. This poster will present recent work developing a relatively inexpensive time-resolved stereoscopic PIV system that can measure the full three-dimensional transport. Preliminary results will be presented [Preview Abstract] |
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D1.00013: The Effect of Obstacles on the Propagation Speed of Reaction-Diffusion Waves Vincent W.H. Hui, John F. Lindner, Niklas Manz This project investigated the effect of obstacles within a narrow channel on the propagation speed of reaction-diffusion waves. We used an objective-C program to solve the Tyson-Fife model, with two coupled partial differential equations, to simulate the behavior of these waves. Values for the activator and inhibitor's diffusion coefficients and the excitability variables were chosen to correspond with the nonlinear chemical Belousov-Zhabotinsky reaction. We will present the following results: i) The concentration wave slowed down when passing around obstacles, due to the increased curvature of the wave front. It then slowly returned to its original speed, while the front was straightened again. ii) The average propagation speed, through a defined length of the channel, decreased when the obstacles (rhombuses and ellipses) became larger (size to channel-width ratio) or more vertically oriented (width-to-height radio). iii) The average speed decreased with increasing number of obstacles in the channel. iv) Using a constant number of obstacles, the average speed decreased with more evenly distributed obstacles compared to a dense row of obstacles followed by an uninterrupted channel. [Preview Abstract] |
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D1.00014: Small system size effects in single-file diffusion T. E. Sheridan Single-file diffusion (SFD) is the diffusive motion of particles in one-dimension with the constraint that particles can not pass each other. We model SFD in a finite system using $n$ random walkers on a periodic lattice with an average of $m$ empty sites between walkers. The time-dependence of the mean-squared displacement (MSD) is found using a Monte Carlo simulation as a function of $n$ for small systems with $n \le 500$ walkers. For short times, the increase in the MSD is approximately proportional to the time $t$ for all systems. For longer times and large $n$, the MSD rolls over and approaches the expected asymptotic behavior, MSD $\propto t^{1/2}$. However, for small $n$ the MSD approaches a constant value because the finite system size limits the maximum spread of the walkers. [Preview Abstract] |
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D1.00015: Nearly Transit-time Limited Electromagnetically Induced Transparency in an Undergraduate Laboratory Kefeng Jiang, Ken DeRose, Hong Cai, Linzhao Zhuo, Stone Oliver, Samir Bali We observe electromagnetically induced transparency in the D2 transitions of atomic Rubidium in a standard uncoated vapor cell with no buffer gas. Contrasts of up to 30{\%} are obtained. A narrowest linewidth of 90 kHz is observed, which is about a factor 2 broader than the theoretically expected transit-time linewidth. We examine possible sources (e.g. stray magnetic field, laser misalignment, etc) that prevent us from attaining the theoretical limit and conclude that the probable cause appears to be Doppler broadening. [Preview Abstract] |
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D1.00016: Hannay's Hoop Beyond Asymptotics Hwan Bae, Norah Ali, John F. Lindner Certain physical systems do not completely return to themselves when moved through a closed circuit in physical or parameter space. A geometric phase, known classically as Hannay's angle and quantum mechanically as Berry's phase, quantifies such anholonomy. We generalize the classical example of a bead sliding frictionlessly on a hoop to arbitrary - not necessarily adiabatic - motions. We elucidate the roles of forces in the inertial frame and pseudo-forces in the rotating frame. We realize the dynamics experimentally with a simple apparatus consisting of wet ice cylinders sliding on a polished metal plate in 3D printed plastic channels. We computationally generalize to a mass sliding on a rotating ellipsoid. [Preview Abstract] |
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D1.00017: Nonclassical Effects in Multilevel Electromagnetically Induced Transparency Mitch Mazzei, Perry Rice, Thomas Jenkins We examine a multilevel system that can exhibit EIT or EIA under appropriate conditions. These effects can be understood in terms of classical coupled oscillators. We examine whether nonclassical behavior is exhibited in the EIT/EIA regime, and elsewhere. Nonclassical behavior cannot be described by a classical stochastic process, no mean field plus noise. Those cannot be described by two classical oscillators. We propose a multilevel photonic memory in this system as well. [Preview Abstract] |
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D1.00018: Enhancing Long Transient Gravitational Wave Power Spectra with Filters Avi Vajpeyi, Andrew Miller, Pia Astone, Sergio Frasca A challenge with gravitational wave interferometry has been detecting signals in the presence of noise and glitches. One method to make signals stand out in the presence of noise involves filtering the data suspected of containing a signal. We present an investigation of filtering a particular type of gravitational waves known as r-modes which could be important to detect isolated neutron stars. We use two dimensional fast Fourier transform filters and convolutional neural networks. We show that we can achieve an enhancement in the quality of an r-mode signal using filters that do not match the exact parameters of the signal, contrary to what is required with typical matched filtering methods. [Preview Abstract] |
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D1.00019: Data Analysis for Experimental Studies of Nuclear Reactions for Astrophysics Samuel Teye, Mohammed Islam, Richard deBoer, Wanpeng Tan Nuclear reaction rates provide an essential ingredient for the understanding of the synthesis of elements. Very often these reaction rates are calculated from the nuclear cross sections predicted by models. Temperatures in various phases of a stellar evolution as well as supernova explosions correspond to very low energy charged particles. Experimental measurements at these low energies are extremely difficult, and so the nuclear models are used to calculate cross sections. Experiments are conducted at higher energies (near the coulomb threshold) to measure nuclear cross sections and compare with the theoretical predictions. A scale factor is obtained by comparing experimental cross section with the theoretical calculation. This factor is then used to scale the cross sections at low energy, predicted by theory. Experimental data obtained at the nuclear facility at University of Notre Dame are analyzed. Total angle integrated cross sections are obtained by fitting experimental data with Legendre coefficients. Results of these analysis will be reported. [Preview Abstract] |
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D1.00020: Preliminary Investigations of the Rotational Mode of a Plasma Dust Ring William Theisen, Kathleen Hill The rotational mode of a strongly-coupled dusty plasma ring was studied. The particles rotated within the ring shaped potential well that was formed using a variable aperture with a center post. Various aperture sizes were applied. Particle position data from the rotating dust ring was analyzed and results were compared with predictions of normal mode calculations. [Preview Abstract] |
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D1.00021: Multi-Band Ensemble Photometry of the Eclipsing Binary Star NSVS 4161544 Tyler Redfern, Robert Berrington We report new multi-band ensemble aperture photometry for the Northern Sky Variability Survey (NSVS) eclipsing star candidate NSVS 4161544. All multi-band images were taken by the Ball State University Observatory 0.5-meter telescope in the Johnson B and V, and Cousins R band passes. All images were reduced using the ccdred image reduction package in the Image Reduction Analysis Facility (IRAF) software suite. Ensemble aperture photometry was performed with the AstroImageJ (AIJ) software package. Measured light curves are presented. The measured light curves are analyzed by the physics of eclipsing binaries (PHOEBE) software package, and best-fit orbital parameters and stellar models are reported. [Preview Abstract] |
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D1.00022: Examples of the MOND External Field Effect in Dwarf Spheroidal Galaxies: Fornax and Crater II Joshua Schussler, Benjamin Blankartz, Benjamin Amend, Michael Zito, Rohan Radke, Jennifer Wallace, Stephen Alexander The only viable alternative to the Cold Dark Matter (CDM) paradigm to date is Modified Newtonian Dynamics (MOND). The essence of MOND is that Newtonian gravity requires modification at extremely low accelerations (less than 10-10 m/s2). MOND has had great success in reproducing the flat rotation curves that are observed for spiral galaxies. Recently, MOND has been used to calculate dispersion profiles for dwarf spheroidal galaxies (dSph) that are satellite galaxies of the Milky Way and Andromeda, and the agreement with observations is encouraging. The external field effect (EFE) is a unique feature of MOND that has not been widely investigated. Here, we present the results of dispersion calculations for dSph's Fornax and Crater II that include the EFE. We compare both the bulk dispersions and the dispersion profiles to observations. [Preview Abstract] |
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D1.00023: Recent Progress of the Ball State University Short-Period Variable Star Program Robert Berrington, Thomas Jordan The Ball State University (BSU) variable star program is a program designed to target variable stars with shorter periods (p <~1 day) that have been discovered by large area sky surveys. These large area surveys like the Northern Variability Sky Survey (NSVS), and the All Sky Automated Survey (ASAS) have proven valuable in discovering numerous variable stars with visual magnitudes in the 8 < V < 15 range. What these surveys lack is temporal resolution on the order of orbital periods of the targeted systems. The BSU short-period variable star program will supplement these large surveys by providing the needed finely resolved, systematic temporal coverage and accurate photometric coverage needed to provide a comprehensive study of these systems. To date most targets are eclipsing variable stars of the W Ursae Majoris. Photometric measurements are obtained by the Cooper Science Rooftop Observatory, which includes a 0.4-meter and a 0.5-meter telescope located on the Ball State University campus, and the SARA-KP 1-meter, the SARA-CT 0.6-meter, and the SARA-RM 1-meter telescopes. The modular nature of the study makes this program ideal for graduate and undergraduate students to get involved at all stages of the program. I will summarize the most recent work that has been done. [Preview Abstract] |
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D1.00024: Schr\"{o}dinger-Langevin Equation and its Application to Deuteron Cluster Victor Christianto, Florentin Smarandache The Langevin equation is considered as equivalent and therefore has often been used to solve the time-independent Schrodinger, in particular to study molecular dynamics. One of the most reported problem related to the CMNS (condensed matter nuclear science, or LENR), is the low probability of Coulomb barrier tunneling. It is supposed by standard physics that tunneling is only possible at high enough energy (by solving Gamow function). However, a recent study by A. Takahashi (2008, 2009) and experiment by Arata etc. (2008) seem to suggest that it is not impossible to achieve a working experiment to create the CMNS process. In accordance with Takahashi's EQPET/TSC model, we find out some analytical and numerical solutions to the problem of barrier tunneling for cluster deuterium, in particular using Langevin method to solve the time-independent Schr\"{o}dinger equation. Discussing some plausible implications in Cosmology modeling. [Preview Abstract] |
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D1.00025: Extracting broadband optical properties from uniform optical phantoms: an analysis of inverse-adding doubling method Vinoin Devpaul Vincely In tissue optics, it is important to measure the amount of light that is being scattered and absorbed by tissues to describe, understand and exploit interactions of light with such turbid media. This is done by two well-developed techniques -- fiber based diffuse reflectance spectroscopy (DRS) coupled to an inverse Monte Carlo (MC) model, and the inverse-adding doubling (IAD) technique coupled to measurements acquired using an integrating sphere (IS). The fiber-based DRS is easy to use experimentally and is well suited for in vivo use, but requires several calibration measurements along with good estimates about the spectral properties of tissue chromophores expected to be present in the signal. The IAD is an algorithm that computes the absorption and scattering coefficients using measured total diffuse reflectance and transmittance values of a sample. Here we analyze the accuracy of the IAD/IS system by obtaining measurements on a set of liquid phantoms prepared with controlled absorption and scattering properties which are obtained using Beer's law and Mie theory. [Preview Abstract] |
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D1.00026: Exploring the Performance of an Inverse Monte Carlo Method in Extracting Absorption of Optical Phantoms John Bowman, Adam Eggert, Brent Reichert, Karthik Vishwanath The Inverse Monte Carlo (MC) Model can extract optical absorption and scattering properties by fitting a measured diffuse reflectance spectrum. In order to fit the data, the MC model requires accurate shapes of absorption spectra expected to be present in the measured sample. Since many times, we may not have knowledge of the absorption properties of a sample, the use of the inverse MC model becomes difficult.~ Here we test if we can experimentally ascertain accurate ranges for the optical scattering by using experimental measurements of diffuse reflectance from phantom media. Liquid optical phantoms were prepared using food dye (absorber), polystyrene spheres (scatterer), and water (background). Phantoms were prepared with scattering coefficients ranging between 0-30 cm$^{\mathrm{-1}}$. Diffuse reflectance from phantoms with varying absorption and scattering will be collected using fiber optical probes and these data analyzed with the MC model. The errors in extracted optical scattering of the phantoms, with correct and incorrect absorption inputs, will be examined. [Preview Abstract] |
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D1.00027: Optical Properties of Gallium Oxide Thin Films Sundar Isukapati, Tom Oder We report studies conducted on gallium oxide films deposited using magnetron sputtering from a 99.9\% pure ceramic target on sapphire substrates. Conditions varied were the process gas using different mixtures of argon/oxygen (0/100, 20/80, 50/50, 80/20 and 100/0), substrate temperature (20 $^o$C to 850 $^o$C) and film thickness (140 nm $\textendash$ 860 nm). The films were analyzed by UV-VIS spectrometry, x-ray diffraction and energy dispersive x-ray spectroscopy measurements. The optical measurements revealed high transmission of 92\%- 95\% and optical bandgaps of 4.4 – 4.9 eV. Data from the x-ray diffraction on the film deposited at 850 $^o$C showed a characteristic peak at 18$^o$ for the oxide material. [Preview Abstract] |
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D1.00028: Optical Properties of Titanium Dioxide and Vanadium Oxide Thin Films Nicholas Borucki, Sage Edwards, Tom Oder Titanium dioxide films are deposited from a 99.99\% pure target using magnetron sputter deposition on sapphire substrates at 20 $^o$C and 700 $^o$C. The films were then annealed in an argon/oxygen atmosphere using a rapid thermal processor at 500 $^o$C and 900 $^o$C for 5 minutes. The transmittance, reflectance and absorbance of the films are determined by UV-VIS spectrometer under normal incidence in the spectral range 200 nm $\textendash$ 2500 nm. The direct and indirect bandgaps extracted from these measurements were in the range of 2.7 – 3.3 eV. Additional optical data on these films annealed after deposition as well as electrical resistivity measurements will be presented. The vanadium oxide films were made by first depositing a 200 nm-thick film of vanadium on sapphire substrate at room temperature and annealing the films in an oxygen atmosphere for 15 – 30 min at 700 $^o$C. The optical measurements revealed a low transmission of about 50\% and optical bandgaps of 2.3 $textendash$ 2.6 eV. [Preview Abstract] |
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