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A Causal Inference Approach For Spike Train Interactions, Zach Saccomano

Dissertations, Theses, and Capstone Projects

Since the 1960s, neuroscientists have worked on the problem of estimating synaptic properties, such as connectivity and strength, from simultaneously recorded spike trains. Recent years have seen renewed interest in the problem coinciding with rapid advances in experimental technologies, including an approximate exponential increase in the number of neurons that can be recorded in parallel and perturbation techniques such as optogenetics that can be used to calibrate and validate causal hypotheses about functional connectivity. This thesis presents a mathematical examination of synaptic inference from two perspectives: (1) using in vivo data and biophysical models, we ask in what cases the …

Exciton Dynamics, Interaction, And Transport In Monolayers Of Transition Metal Dichalcogenides, Saroj Chand

Dissertations, Theses, and Capstone Projects

Monolayers Transition metal dichalcogenides (TMDs) have attracted much attention in recent years due to their promising optical and electronic properties for applications in optoelectronic devices. The rich multivalley band structure and sizable spin-orbit coupling in monolayer TMDs result in several optically bright and dark excitonic states with different spin and valley configurations. In the proposed works, we have developed experimental techniques and theoretical models to study the dynamics, interactions, and transport of both dark and bright excitons.

In W-based monolayers of TMDs, the momentum dark exciton cannot typically recombine optically, but they represent the lowest excitonic state of the system …

Probing Central Spin Decoherence Dynamics Of Electronic Point Defects In Diamond And Silicon, Ethan Que Williams

Dartmouth College Ph.D Dissertations

Electron spins of point defects in diamond and silicon can exhibit long coherence times, making them attractive platforms for the physical implementation of qubits for quantum sensing and quantum computing. To realize these technologies, it is essential to understand the mechanisms that limit their coherence. Decoherence of these systems is well described by the central spin model, wherein the central electron spin weakly interacts with numerous electron and nuclear spins in its environment. The dynamics of the resultant dephasing can be probed with pulse electron paramagnetic resonance (pEPR) experiments.

Using a 2.5 GHz pEPR spectrometer built in-house, we performed multi-pulse …

Residual Optical Absorption From Native Defects In Cdsip2 Crystals, Timothy D. Gustafson, Nancy C. Giles, Elizabeth M. Scherrer, Kevin T. Zawilski, Peter G. Schunemann, Kent L. Averett, Jonathan E. Slagle, Larry E. Halliburton

Faculty Publications

CdSiP₂ crystals are used in optical parametric oscillators to produce tunable output in the mid-infrared. As expected, the performance of the OPOs is adversely affected by residual optical absorption from native defects that are unintentionally present in the crystals. Electron paramagnetic resonance (EPR) identifies these native defects. Singly ionized silicon vacancies (V^-_Si) are responsible for broad optical absorption bands peaking near 800, 1033, and 1907 nm. A fourth absorption band, peaking near 630 nm, does not involve silicon vacancies. Exposure to 1064 nm light when the temperature of the CdSiP₂ crystal is near 80K converts …

The Fourier–Legendre Series Of Bessel Functions Of The First Kind And The Summed Series Involving 1F2 Hypergeometric Functions That Arise From Them, Jack C. Straton

Physics Faculty Publications and Presentations

The Bessel function of the first kind JN^(kx) is expanded in a Fourier–Legendre series, as is the modified Bessel function of the first kind IN^(kx). The purpose of these expansions in Legendre polynomials was not an attempt to rival established numerical methods for calculating Bessel functions but to provide a form for JN^(kx) useful for analytical work in the area of strong laser fields, where analytical integration over scattering angles is essential. Despite their primary purpose, one can easily truncate the series at 21 terms to provide 33-digit accuracy that matches the IEEE extended precision in …

Integral Representations Over Finite Limits For Quantum Amplitudes, Jack C. Straton

Physics Faculty Publications and Presentations

We extend previous research to derive three additional M-1-dimensional integral representations over the interval [0,1]" The prior version covered the interval [0,∞]" role="presentation position: relative;">[0,∞][0,∞]. This extension applies to products of M Slater orbitals, since they (and wave functions derived from them) appear in quantum transition amplitudes. It enables the magnitudes of coordinate vector differences (square roots of polynomials) |x1−x2|=x12−2x1x2cosθ+_x22" to be shifted from disjoint products of functions into a single quadratic form, allowing for the completion of its square. The M-1-dimensional integral representations of M Slater orbitals that both this extension and the prior version introduce …

Retardation Effects In Atom-Wall Interactions, T. Das, C. A. Ullrich, Ulrich D. Jentschura

Physics Faculty Research & Creative Works

The onset of retardation effects in atom-wall interactions is studied. It is shown that the transition range from the 1/z3 short-range (van der Waals) interaction to the 1/z4 long-range (Casimir) retarded interaction critically depends on the atomic properties and on the dielectric function of the material. For simple non-alkali-metal atoms (e.g., ground-state hydrogen and ground-state helium) interacting with typical dielectric materials such as intrinsic silicon, the transition to the retarded regime is shown to proceed at a distance of about 10 nm (200 Bohr radii). This is much shorter than typical characteristic absorption wavelengths of solids. Larger transition regimes are …

The Roaring Lion Of Berlin: The Life, Thought, And Influence Of Eugen Dühring, Arden Roy

Undergraduate Research Symposium

The life and influence of 19th-century German polymath Eugen Dühring remain but a mere footnote in the history of ideas, being primarily relegated to the status of little more than a theoretical rival to Marxism in the German socialist movement and the occasional object of Freidrich Nietzsche's rhetorical flogging. Despite the current consensus on the subject, Eugen Dühring was a scholar of vast, remarkable learnedness, contributing greatly to philosophy, economics, and the natural sciences. The aim of this talk will be to clear the fog surrounding the life and work of the controversial blind scholar and give an account of …

Effect Of Substrate Temperature And Deposition Power On The Surface Morphology And Optical Properties Of Zno:Mg Thin Films Deposited By Dc Magnetron Sputtering, Saidi Saidi, Margaret E. Samiji, Nuru R. Mlyuka

Tanzania Journal of Science

Magnesium doped zinc oxide (ZnO:Mg) thin films were deposited on soda lime glass slides by DC magnetron sputtering method. Atomic force microscope (AFM), and UV/VIS spectrophotometer were used to investigate the effect of sputtering power and substrate temperature on the surface morphology and optical properties of ZnO:Mg thin films. AFM images revealed that sputtering power and deposition temperature have significant influence on surface morphology of the ZnO:Mg thin films. For all sputtering powers and substrate temperatures investigated, ZnO:Mg films had peak transmittance above 85%. Samples deposited at 110 W sputtering power and 450 °C substrate temperature showed the best peak …

Micro Machining Of A Si3n4/Sio2/Ti/Pt Hotplate And Its Ir Emissivity Properties, Egidius R. Rwenyagila

Tanzania Journal of Science

This paper presents the fabrication processes for a Si3N4/SiO2/Ti/Pt membrane based micro hotplate (MHP) using photolithography (PL) micro-machining techniques. The properties of the MHP filament are investigated and overall performance characteristics with regard to infrared (IR) radiation emissivity, resistance, breakdown voltage, and temperature of the fabricated Si3N4/SiO2/Ti/Pt micro heater. During characterization, the results show the device breakdown voltage of 24.24 V corresponding to the optimum operation temperature of ~ 1730.30 K. The device also showed an emissivity value of 5.2% with ~ 7% efficiency of transforming electrical power to IR thermal radiation power. The relationship between temperature and resistance, behaviour …

Preparation Of 2d Tungsten Diselenide (Wse2) Thin Films By Selenization Of Dc-Sputtered W Precursors, Lwitiko P. Mwakyusa

Tanzania Journal of Science

Two-dimensional layered transition metal dichalcogenides based on WSe2 films demonstrated promising properties for nano-electronics and photovoltaic applications. In this work, WSe2 films were prepared by selenization of DC-sputtered W precursors. The influence of the selenization temperature on the structural, morphology, and optical properties of the WSe2 films was investigated. The selenization temperature was varied from 350 °C to 450 °C at the interval of 50 °C. Structural, morphology and optical properties of the WSe2 were investigated using X-ray diffractometry (XRD), Atomic Force Microscope (AFM), and UV-VIS-NIR spectrophotometer, respectively. XRD analysis revealed that all WSe2 were polycrystalline and exhibited the co-existence …

On The Exact Helium Wave Function Expansion, Ii, An Exponential Modulated Form, Carl W. David

Chemistry Education Materials

A 1¹S wave function’s expansion for 2 electron atoms and ions is proposed employing an appropriate exponential factor and Fock’s logarithmic terms. The leading coefficient’s are presented.

Phase-Slip Centers As Cooling Engines, Iris Mowgood, Serafim Teknowijoyo, Sara Chahid, Armen Gulian

Mathematics, Physics, and Computer Science Faculty Articles and Research

Based on time-dependent Ginzburg-Landau system of equations, Éliashberg’s kinetic equations and finite element modeling, we analyze phonon emission by the phase-slip centers in superconducting filaments. Our results show that in the dissipative regime with these centers, thin superconducting filaments can be effective in originating not only positive but also negative thermal fluxes, i.e., they both generate and absorb phonons. In a stationary oscillatory regime, at a given moment of time, this generation and absorption of phonons reveals itself as positive and negative spectrum of phonons at different spectral ranges. Moreover, at a given spectral range, the emission reverses its sign …

Superconductivity Of Amorphous And Crystalline Re–Lu Films, Serafim Teknowijoyo, Armen Gulian

Mathematics, Physics, and Computer Science Faculty Articles and Research

We report on superconducting properties of a novel material: rhenium-lutetium films. Different compositions of RexLu binary are explored from x ≈ 3.8 to close to pure Re stoichiometry. The highest critical temperature, up to 7 K, is obtained for x ≈ 10.5 in accordance with electron dispersive spectroscopy results. Depending on the deposition conditions, polycrystalline or amorphous films are obtainable, both of which are interesting for practical use. Crystalline structure of polycrystalline phase is identified as a non-centrosymmetric superconductor using grazing incidence x-ray diffractometry. Superconducting properties were characterized both resistively and magnetically. Magnetoresistivity and AC/DC susceptibility measurements allowed …

Some Remarks On Possible Superconductivity Of Composition Pb9Cup6O25, Pablo Abramian-Barco, A. Kuzanyan, Vahan Nikoghosyan, Serafim Teknowijoyo, Armen Gulian

Mathematics, Physics, and Computer Science Faculty Articles and Research

A material called LK-99, a modified-lead apatite crystal structure with the composition Pb₁₀ – ^_xCu_x(PO₄)₆O (0.9 < x < 1.1) has been reported to be an above-room-temperature superconductor at ambient pressure. It is hard to expect that it will be straightforward for other groups to reproduce the original results. We provide here some remarks which may be helpful for a success.

Superconducting Polycrystalline Rhenium Films Deposited At Room Temperature, Serafim Teknowijoyo, Armen Gulian

Mathematics, Physics, and Computer Science Faculty Articles and Research

We report on magnetron deposition of thin superconducting rhenium films on sapphire substrates. During the deposition, substrates were held at ambient temperature. Critical temperature of the films is Tc ~ 3.6 K. Films have polycrystalline structure, and grazing incidence X-ray diffractometry indicates that crystalline lattice parameters are somewhat larger compared to the bulk ones. Magnetoresistive and AC/DC susceptibilities allowed us to determine Hc1 and Hc2 of these films, as well as estimate coherence length ξ(0) and magnetic penetration depth λL(0). We also provide information on surface morphology of these films.

Design And Building Of A Customizable, Single-Objective, Light-Sheet Fluorescence Microscope For The Visualization Of Cytoskeleton Networks, Nathan Felcher, Daisy H. Achiriloaie, Brian Lee, Ryan Mcgorty Phd, Janet Sheung

Physics and Biophysics: Faculty Scholarship

Reconstituted cytoskeleton composites have emerged as a valuable model system for studying non-equilibrium soft matter. The faithful capture of the dynamics of these 3D, dense networks calls for optical sectioning, which is often associated with fluorescence confocal microscopes. However, recent developments in light-sheet fluorescence microscopy (LSFM) have established it as a cost-effective and, at times, superior alternative. To make LSFM accessible to cytoskeleton researchers less familiar with optics, we present a step-by-step beginner's guide to building a versatile light-sheet fluorescence microscope from off-the-shelf components. To enable sample mounting with traditional slide samples, this LSFM follows the single-objective light-sheet (SOLS) design, …

Toward The Ir Detection Of Carbon Acid: Absorption And Emission Spectrum, Ryan C. Fortenberry, Vincent J. Esposito

Biology, Chemistry, and Environmental Sciences Faculty Articles and Research

With the recent radioastronomical detection of cis-trans-carbonic acid (H₂CO₃) in a molecular cloud toward the Galactic center, the more stable but currently unobserved cis-cis conformer is shown here to have strong IR features. While the higher-energy cis-trans-carbonic acid was detected at millimeter and centimeter wavelengths, owing to its larger dipole moment, the vibrational structure of cis-cis-carbonic acid is more amenable to its observation at micron wavelengths. Even so, both conformers have relatively large IR intensities, and some of these fall in regions not dominated by polycyclic aromatic hydrocarbons. Water features may inhibit observation …

Evanescent Wave Quartz-Enhanced Photoacoustic Spectroscopy Employing A Side-Polished Fiber For Methane Sensing, Cian F. Twomey, Gabriele Biagi, Albert A. Ruth, Marilena Giglio, Vincenzo Spagnolo, Liam O'Faolain, Anton J. Walsh

Cappa Publications

We present an all-fiber-based laser gas analyzer (LGA) employing quartz-enhanced photoacoustic spectroscopy (QEPAS) and a side-polished fiber (SPF). The LGA comprises a custom quartz tuning fork (QTF) with 0.8 mm prong spacing, two acoustic micro-resonators (mR) located on either side of the prong spacing, and a single-mode fiber containing a 17 mm polished section passing through both mRs and QTF. The SPF polished face is positioned to enable the evanescent wave (EW) to create a photoacoustic wave and excite the fundamental flexural mode of the QTF. Sensor performance was demonstrated using methane in nitrogen gas mixtures, with CH4" role="presentation" style="box-sizing: …

Radon Plate-Out And The Effects Of Airflow And Electric Charge For Dark Matter Experiments, Faith Fang

SMU Journal of Undergraduate Research

The Cryogenic Dark Matter Search (SuperCDMS) is an international collaboration designed to search for and detect dark matter particles, which make up ~85% of the matter in the universe. The plate-out, or deposition of naturally occurring radioactive decay byproducts onto surfaces, can create backgrounds that interfere with dark matter detection experiments. In the first series of these experiments, we analyze the amount of radon progeny, 214Pb and 214Bi, that plate-out on polycarbonate samples while controlling factors such as electric charge and airflow. These samples are exposed to radon-spiked nitrogen gas in a polycarbonate wind tunnel to simulate plate-out conditions in …

Buzzard To Cardinal: Improved Mock Catalogs For Large Galaxy Surveys, Chun-Hao To, Joseph Derose, Risa H. Wechsler, Eli Rykoff, Hao-Yi Wu, Susmita Adhikari, Elisabeth Krause, Eduardo Rozo, David H. Weinberg

Physics Faculty Publications and Presentations

We present the Cardinal mock galaxy catalogs, a new version of the Buzzard simulation that has been updated to support ongoing and future cosmological surveys, including the Dark Energy Survey (DES), DESI, and LSST. These catalogs are based on a one-quarter sky simulation populated with galaxies out to a redshift of z = 2.35 to a depth of m_r = 27. Compared to the Buzzard mocks, the Cardinal mocks include an updated subhalo abundance matching model that considers orphan galaxies and includes mass-dependent scatter between galaxy luminosity and halo properties. This model can simultaneously fit galaxy clustering and group–galaxy …

Genome-Wide Profiling Of Novel Conserved Zea Mays Micrornas Along With Their Key Biological, Molecular And Cellular Targets And Validation Using An Rt-Pcr Platform, Abdul Baqi, Sami Ullah, Muhammad Ayub, Muhammad Zafar Saleem, Ghulam Mustafa Khan, Asad Ullah

Karbala International Journal of Modern Science

MicroRNAs (miRNAs), which are typically non-coding RNAs that start off as endogenous molecules and regulate post-transcriptional levels of gene expression by mRNA degradation or translational repression. They are 18–26 nucleotides long, evolutionarily conserved and essential for predicting novel miRNAs in a variety of plants. Maize (Zea mays) is a significant food and forage crop in the globe today. In the present study, many maize miRNAs have been found to be associated with both plant development and responses to stress. In this study, 66 unique conserved maize miRNAs from 65 different miRNA families were predicted using several genomics-based methods …

The Role Of Cu (0-0.03) And Zn (0.02) Substitution On The Structural, Optical And Magnetic Properties Of Mgo Nanoparticles, S. Naseem Shah, Atif Dawar, Yasmeen Bibi, Abid Ali, M. Asif Siddiqui

Karbala International Journal of Modern Science

The co-precipitation method was employed to prepared Cu (0-0.03) and Zn (0.02) dual doped MgO nanoparticles. The secondary phases of CuO and Cu₂O were observed along with the cubical phase of MgO. The doping induced effect was noticed for the crystallite size variations (14.39-19.89 nm). The morphological transformation from spherical to rice-like shape were observed. The estimated values of optical bandgap (4.66-4.45 eV) were well correlated with the crystallite size and dopant concentrations. The ferromagnetic ordering was observed at room temperature and the enchantment in the coercivity (142.27 Oe) with Zn (0.02) doping was noticed. Such type of …

Gaussian Processes And Nested Sampling Applied To Kepler's Small Long-Period Exoplanet Candidates, Michael R.B. Matesic, Jason F. Rowe, John H. Livingston, Shishir Dholakia, Daniel Jontof-Hutter, Jack J. Lissauer

Pacific Faculty Work

There are more than 5000 confirmed and validated planets beyond the solar system to date, more than half of which were discovered by NASA’s Kepler mission. The catalog of Kepler’s exoplanet candidates has only been extensively analyzed under the assumption of white noise (i.i.d. Gaussian), which breaks down on timescales longer than a day due to correlated noise (point-to-point correlation) from stellar variability and instrumental effects. Statistical validation of candidate transit events becomes increasingly difficult when they are contaminated by this form of correlated noise, especially in the low-signal-to-noise (S/N) regimes occupied by Earth-Sun and Venus-Sun analogs. To diagnose small …

Beyond Standard Model: Structure Factors Of Models Of Different Quarks And Neutrinos As Spinning Structures Made Of Basic Fractional Charges +- E/3, Polievkt Perov

College of Arts & Sciences Faculty Works

We consider a possible line of “elementary” particles as composite spinning structures made of just two basic elementary particles of charges + e/3 and -e/3. In considered structures, up to 3 basic charges can be on the axis of rotation and other charges can be in a revolving motion about the axis. In addition to the simplest structures of quarks, an electron and a neutral particle containing mostly one or no charges on the axis of rotation, suggested initially in [4], we analyze possible spatial structures of spinning composite particles having 2 or 3 charges on the axis of rotation. …

Experimental Realization Of The Peregrine Soliton In Repulsive Two-Component Bose-Einstein Condensates, A. Romero-Ros, Garyfallia C. Katsimiga, Simeon I. Mistakidis, S. Mossman, G. Biondini, P. Schmelcher, P. Engels, P. G. Kevrekidis

Physics Faculty Research & Creative Works

We Experimentally Realize the Peregrine Soliton in a Highly Particle-Imbalanced Two-Component Repulsive Bose-Einstein Condensate in the Immiscible Regime. The Effective Focusing Dynamics and Resulting Modulational Instability of the Minority Component Provide the Opportunity to Dynamically Create a Peregrine Soliton with the Aid of an Attractive Potential Well That Seeds the Initial Dynamics. The Peregrine Soliton Formation Is Highly Reproducible, And Our Experiments Allow Us to Separately Monitor the Minority and Majority Components, And to Compare with the Single Component Dynamics in the Absence or Presence of the Well with Varying Depths. We Showcase the Centrality of Each of the Ingredients …

Cathodoluminescence And Tip-Plasmon Resonance Of Bi2te3 Triangular Nanostructures, Qigeng Yan, Siyuan Wang, Kuiwen Guan, Xiaojin Guan, Lei He

Physics Faculty Publications and Presentations

Bi₂Te₃, as a topological insulator, is able to support plasmonic emission in the visible spectral range. Thin Bi₂Te₃ flakes can be exfoliated directly from a Bi₂Te₃ crystal, and the shape of Bi₂Te₃ flakes can be further modified by focused ion beam milling. Therefore, we have designed a Bi₂Te₃ triangular antenna with distinct tip angles for the application of plasmonic resonance. The plasmonic emission of the Bi₂Te₃ triangular antenna is excited and investigated by cathodoluminescence in the scanning electron microscope. Enhanced tip …

Thinking Backwards About Time, D. P. Sheehan

Physics and Biophysics: Faculty Scholarship

The concept of time in physics and its connection to consciousness are becoming increasingly problematic. A missing ingredient to both could be retrocausation — the temporal inverse of everyday causation — in which the future influences the past. Apparent evidence for it is in the phenomenon of precognition. Thus far, psychology and physics have assiduously avoided incorporating precognition into their paradigms, even though experimental evidence for it is substantial. Among many noteworthy studies, the Graff–Cyrus experiment is explicated here as an outstanding example of the phenomenon. It is hoped that consciousness, retrocausation, and precognition can be accommodated within the current …

Electric Fields In The Atmosphere Might Help Snow Crystals Form, Joseph Cooney

Research on Capitol Hill

Orographic clouds generally form over mountains when valleys are sunny. The unstable atmosphere can trigger clouds over the mountains, which can be convective. When this happens, the cloud particles (water droplets and ice particles) become charged, ultimately creating ice crystals. I wanted to evaluate the impact of electricity on the formation of ice crystals and built a computer simulation to do so.

Self-Consistent Phonon Calculations And Quartic Anharmonic Lattice Thermal Conductivity In 2d Ins Monolayer, Eesha Andharia, Hind Alqurashi, Abhiyan Pandit, Bothina Hamad

Physics Faculty Publications and Presentations

Low lattice thermal conductivity (κ_l) is a crucial factor for higher figure-of merit and hence the efficiency of thermoelectric generators. There are several reports on intrinsically low κ_l values in two-dimensional (2D) van der Waals materials using density functional theory and molecular dynamics simulations. In general, phonon dispersions are studied at absolute zero temperature using the finite-displacement approach within harmonic approximations. In addition, the κ_l is calculated using the third-order cubic interatomic force constants (IFCs) by solving the Boltzmann transport equation for phonons. In these calculations, we use quartic IFCs to solve self-consistent phonon equations …