Physics Commons^™

Investigating Van Der Waals Josephson Junctions With 2h-Nbse2 And 1t’-Wte2, Kristine Lorraine Haley

UNLV Theses, Dissertations, Professional Papers, and Capstones

Josephson junctions have garnered significant attention due to their unique electronic properties and applications in quantum devices. In this thesis, we investigate the fabrication processes and characterization of two-dimensional (2D) Josephson junctions consisting of layered van der Waals materials: niobium diselenide (2H-NbSe₂) and few layered tungsten ditelluride (1T’-WTe₂). The reduction of dimensionality can bring forth unique characteristics in certain materials that are not seen in their bulk counterparts, making them prime candidates for physical exploration. 2H-NbSe₂ is an s-wave superconductor at temperatures near and below 7 K. 1T’-WTe₂ is a semimetal in bulk but …

The High Pressure Dependence Of X-Ray Induced Decomposition Of Cadmium Oxalate, Adrian F. Lua Sanchez, Petrika Cifligu, Marc Graff, Michael Pravica, Pradip K. Bhowmik, Changyong Park, Egor Evlyukhin

Physics & Astronomy Faculty Research

The high proclivity of x rays to destabilize and distort molecular structures has been previously utilized in the synthesis of novel compounds. Here, we show that x-ray induced decomposition of cadmium oxalate induces chemical and structural transformations only at 0.5 and 1 GPa. Using x-ray diffraction and Raman spectroscopy, the synthesized product is identified as cadmium carbonate with cadmium oxalate remnants, which is stable under ambient conditions. At ambient and >1 GPa pressures, only degradation of the electronic density distribution is observed. The transformation kinetics are examined in terms of Avrami’s model, which demonstrates that despite the necessity of high …

Depression, Anxiety, And Estimated Cardiorespiratory Fitness In College Students, Christian Ison

UNLV Theses, Dissertations, Professional Papers, and Capstones

Depression and anxiety disorders are two common mental health conditions worldwide. College students are considered a high-risk population for the development of these conditions. Improved cardiorespiratory fitness (CRF) has been shown to decrease depression and anxiety risk, symptoms, and severity but this relationship and the extent to which improved CRF can reduce these risks has yet to be examined in the college student population. Validated and reliable non-exercise estimated cardiorespiratory fitness (eCRF) algorithms could be used to identify relationships and associations with depression and anxiety severity levels among college students. The purpose of this study was to assess eCRF and …

Joint Constraints On Kepler-36 From Kepler And New Keck-Hires Data, Nicholas Juliano

UNLV Theses, Dissertations, Professional Papers, and Capstones

I analyze new HIRES Radial Velocity (RV) data in conjunction with transit mid-times and uncertainties from the full 17 quarters of Kepler data to reassess the orbital parameters of the Kepler-36 system. Six additional RV measurements were taken by the Keck-HIRES spectrograph from September 21, 2021 to October 11, 2021. I carry out a differential evolution Markov Chain Monte Carlo-based (DEMCMC) analysis to infer improved orbital elements for the two known planets in the system. Leveraging additional information provided by the new RV measurements, I extend this DEMCMC analysis to a possible three-planet configuration. I explore the likelihood of a …

Simulating Radial Ring Structure With An Ambipolar Elsasser (Am) Bump In Non-Ideal Magnetohydrodynamics Of Protoplanetary Disks, Aleksey S. Mohov

UNLV Theses, Dissertations, Professional Papers, and Capstones

Rings are one of the most ubiquitous substructures observed in protoplanetary disks. They are known to be a robust site for planetesimal formation; thus we look for mechanisms that can originate stable rings. From chemical modelling of snow lines, we expect a bump in the Ambipolar Diffusion (AD) Elssaser number (Am) in the radial direction. We use the Athena++ code to model the non-ideal Magentohydrodynamics (MHD) behavior of an Am bump. We explore a parameter space of Gaussian bumps with Am = 5, 1, 0.5 peak strength and σ = 0.25, 1, 5. The Gaussian profile is inserted into the …

Applying Instrumental Neutron Activation Analysis To Assess Air Pollution With Spanish Moss As A Bioindicator In The Low Country Of The Savannah River Basin, Christina Jiang

UNLV Theses, Dissertations, Professional Papers, and Capstones

The Savanah River Basin is an area of 9,850 square miles that stretches from the border between South Carolina and Georgia, which empties into the Atlantic Ocean near Savannah, Ga. This area is home to surrounding cities, industrial sites, and the Savanah River Site. It is well documented that traffic, industrial operations, and agriculture contribute to worsening air pollution that needs to be monitored. While Tillandsia usneoides (Spanish moss) has been used in previous studies that prove it to be an effective biomonitor for air pollution and an accumulator of heavy metals, there have been no biomonitoring studies in the …

Analysis And Application Of Finite Element And High-Order Finite Difference Methods For Maxwell’S Equations In Complex Media, Li Zhu

UNLV Theses, Dissertations, Professional Papers, and Capstones

The Perfectly Matched Layer (PML) technique is an effective tool introduced by B´erenger [13] to reduce the unbounded wave propagation problem to a bounded domain problem. This dissertation focuses on two different PML models and their applications to wave propagation problems with Maxwell’s equation in complex media. We investigate these models using two popular numerical methods: the Finite Difference Method (FDM) in Chapters 2 and 3, and the Finite Element Method (FEM) in Chapters 4 and 5.In Chapter 2, we focus on analyzing the stability of a PML developed by B’ecache et al. [10] for simulating wave propagation in the …

Response Of The Isothermal Mode Grüneisen Tensor Across Phase Boundaries, Jasmine K. Hinton

UNLV Theses, Dissertations, Professional Papers, and Capstones

The assumptions for the 1912 Grüneisen parameter are reviewed, particularly in the cases of anisotropy, high temperatures, and across phase boundaries. Two main case studies are shown: β-Sn, and Cd. The main techniques of this work involve resistively heated diamond anvil cells with both optical Raman spectroscopy and x-ray diffraction. It is found in Sn that the isothermal mode Grüneisen tensor along increasing isotherms diverges from the single-valued temperature aggregate at the onset of melt, and this is proposed to use as a method of exploring melt phase boundaries in other systems. This method is examined once again on another …

Exploration Of H2o Ice At Extreme Conditions, Zachary M. Grande

UNLV Theses, Dissertations, Professional Papers, and Capstones

Static compression experiments on water ice are needed for precise characterization and discovery of new ice phases near room temperature. Here I present my efforts and the developments that have been made to reduce detrimental effects found in high-pressure experiments in order to acquire precise measurements on ice approaching 3 Mbar. Several key observations are made, relating to the phase transition of ice-VII to X, an intermediate phase I have named ice-VIIt and evidence of a post ice X phase. Some of these experiments have been replicated using D2O ice as well, in order to gain insight into nuclear quantum …

Stoichiometric Determination Of Hydride Materials At Extreme Conditions, Gregory Alexander Smith

UNLV Theses, Dissertations, Professional Papers, and Capstones

Hydrogen was predicted to be a high-temperature superconductor at near-megabar conditions in 1968,[1] but only recently was been experimentally observed.[2] This is due to the extraneous metrological constraint of requiring 5 megabars of pressure to stabilize. A more practical approach for synthesis of high-temperature superconductors has been pro-posed through the use of hydride compounds. Recently, a surge of rare earth hydrides have achieved critical superconducting transition temperatures (T_C ) close to room temperature.[3, 4, 5, 6] However, due to limitations of the necessary instrumentation to achieve megabar pressures, many techniques traditionally used to measure stoichiometry are unavailable.Three works presented in …

Nuclear Power Plant In Las Vegas, Ryan W. Murray

Undergraduate Research Symposium Posters

This research focuses on the impact of a “Nuclear Power Plant in Las Vegas” or ‘NPP in LV’ for short. Nuclear power is clean, has no greenhouse gas emissions, and has a moderate cost of kilowatt hours. Las Vegas, or more specifically Clark County uses Gas power plants to produce a majority of their electricity. My project will show what a nuclear plant could do if built in the city of Las Vegas. What is a Nuclear power plant? The EIA’s definition is “A nuclear power plant uses the heat that a nuclear reactor produces to turn water into steam, …

Trapping And Cooling Of Ca+ For Cold Ion-Radical Collisions, Bernardo Gutierrez

Undergraduate Research Symposium Posters

Free radicals are molecules that contain an unpaired valence electron which induces high reactivity. Ion radical reactions are typically exothermic and have low (or zero) activation energy. It is for these reasons that ion-radical reactions are believed to dominate in interstellar clouds where temperatures hover around 3-10K. State-to-state measurements require precision control of both reactants.

A Mechanically Intelligent Hosing-Drone, Blake Hament

UNLV Theses, Dissertations, Professional Papers, and Capstones

This manuscript presents a ”mechanically intelligent” approach to designing a Hosing-Drone for heavy-duty pressure washing. Spraying a hose creates strong reaction forces and torques. Previously demonstrated spraying robots are over-engineered to be very massive with huge inertias. These high inertias ”wash out” the reaction from the spraying. In the proposed approach, the contributions from all observable fluid dynamics, fluid structure interactions, and aerodynamics are studied individually and for the coupled system. Experimental data is collected and fit to dynamic models. These models are used to design a smaller, lighter, more agile vehicle than has been previously demonstrated. An impedance controller …

Towards The Electronic Response Of Carbon-Based Van Der Waals Heterostructures In A Diamond Anvil Cell, George Thomas Foskaris

UNLV Theses, Dissertations, Professional Papers, and Capstones

The nanoscale regime of materials has been at the forefront of research and interest in condensed matter physics for many years. In a merger of the fields of two-dimensional (2D) materials and high pressure physics, we present an investigation of the electronic response of carbon-based, van der Waals (vdW) heterostructures in a diamond anvil cell (DAC). Combining these fields presents us with the ability to study the characteristics of such systems both optically, and through electrical transport. Properties such as conductance, band structure, and layer number are considered. The samples in this study are assembled using exfoliation and stacking techniques …

Day ‘N’ Nite: Habitability Of Tidally Locked Planets With Sporadic Rotation, Cody James Shakespeare

UNLV Theses, Dissertations, Professional Papers, and Capstones

Tidally locked worlds provide a unique opportunity for constraining the climates of detected exoplanets. They are unique in that few exoplanet spin and obliquity states are known or will be determined in the near future. The TRAPPIST-1 exoplanet system has multiple habitable zone planets that, in the past, have been presumed to be tidally locked. However, a recent study shows the dynamical conditions present in the TRAPPIST-1 system make rotation and large librations possible spin states for these planets. I confirm the tendency for these planets to sporadically transition from tidally locked libration to slow rotation using N-body simulations independent …

Display Applications For Grating Angle Magnification Accelerated Angular Scanners, Daniel Jesus Valdes

UNLV Theses, Dissertations, Professional Papers, and Capstones

This work includes experimental demonstrations of grating angle magnification accelerated optical beam scanners. Diffraction grating scanners governed by the grating equation can have scan speed advantages over the flat mirror bound by Snell's law of reflection. Scan speed enhancement of 750% was achieved with a 635nm laser and 1800 groove/mm diffraction grating configuration thanks to the grating angle magnification. A three-color diffraction grating scanner shows identical results at larger scan angles. Tunable acceleration speed is a feature enabled by the diffraction grating scanner to operate in a high-speed scanning region and/or high-resolution scanning region depending on the demands of the …

The Metabolic Change Of Lipid Species In Stam Mice With Hepatocellular Carcinoma, Devin J. Peart

UNLV Theses, Dissertations, Professional Papers, and Capstones

Primary liver cancer hepatocellular carcinoma (HCC) is the second leading cause of cancer death worldwide. In the US, primary liver cancer is the most rapidly increasing type of cancer due to increases in hepatitis B and C and the continued trend of greater and greater percentages of the population suffering from obesity, diabetes mellitus and metabolic syndrome. The prognosis for this disease is poor, with a 5-year survival rate of 26% as compared to only 2% when the cancer is metastatic. Unfortunately, current strategies for early detection of HCC, including routine CT imaging or alpha-fetoprotein biomarker, are suboptimal and tend …

Combining Freestanding Ferroelectric Perovskite Oxides With Two-Dimensional Semiconductors For High Performance Transistors, Sergio Puebla, Thomas Pucher, Victor Rouco, Gabriel Sanchez-Santolino, Yong Xie, Victor Zamora, Fabian A. Cuellar, Federico J. Mompean, Carlos Leon, Carlos O. Island, Mar Garcia-Hernandez, Jacobo Santamaria, Carmen Munuera, Andres Castellanos-Gomez

Physics & Astronomy Faculty Research

We demonstrate the fabrication of field-effect transistors based on single-layer MoS2 and a thin layer of BaTiO3 (BTO) dielectric, isolated from its parent epitaxial template substrate. Thin BTO provides an ultrahigh-κ gate dielectric effectively screening Coulomb scattering centers. These devices show mobilities substantially larger than those obtained with standard SiO2 dielectrics and comparable with values obtained with hexagonal boron nitride, a dielectric employed for fabrication of high-performance two-dimensional (2D) based devices. Moreover, the ferroelectric character of BTO induces a robust hysteresis of the current vs gate voltage characteristics, attributed to its polarization switching. This hysteresis is strongly suppressed when the …

Low-Cost And Biodegradable Thermoelectric Devices Based On Van Der Waals Semiconductors On Paper Substrates, Gulsum Ersu, Carmen Munuera, Federico J. Mompean, Daniel Vaquero, Jorge Quereda, Jooao Elias Rodrigues, Jose A. Alonso, Eduardo Flores, Jose R. Ares, Isbael J. Ferrer, Adbullah M. Al-Enizi, Ayman Nafady, Sruthi Kuriakose, Joshua O. Island, Andres Castellanos-Gomez

Physics & Astronomy Faculty Research

We present a method to fabricate handcrafted thermoelectric devices on standard office paper substrates. The devices are based on thin films of WS2, Te, and BP (P-type semiconductors) and TiS3 and TiS2 (N-type semiconductors), deposited by simply rubbing powder of these materials against paper. The thermoelectric properties of these semiconducting films revealed maximum Seebeck coefficients of (+1.32 ± 0.27) mV K−1 and (−0.82 ± 0.15) mV K−1 for WS2 and TiS3, respectively. Additionally, Peltier elements were fabricated by interconnecting the P- and N-type films with graphite electrodes. A thermopower value up to 6.11 mV K−1 was obtained when the Peltier …

Design And Fabrication Of An Apparatus For Tao High-Resolution Laser Spectroscopy, Timothy Chung

UNLV Theses, Dissertations, Professional Papers, and Capstones

In this study, an apparatus for the high-resolution laser spectroscopy of molecules is designed and constructed. The apparatus is used to identify TaO transitions, but may be used for any other molecular species in the future. It will also later be used for experiments such as quantum logic spectroscopy, which are enabled by attachable chambers that can be supplied with molecules from the apparatus. Several considerations are made to improve the quality and longevity of the apparatus such as regulating the rovibrational states of the produced molecules, optimizing the linewidth of the ionization lasers, reducing noise from sources such as …

Monte Carlo Simulation Of Thallium-Bromide Semiconductor Detector For Range Verification Of A Carbon Ion Radiotherapy Beam Through Prompt Gamma-Ray Detection, Peter Dimpfl

UNLV Theses, Dissertations, Professional Papers, and Capstones

Thallium-Bromide is a semiconductor material which is well suited for photon detection. Composed of high atomic number elements and a high mass density of 7.56 g/cm3, TlBr has superb photon stopping power. External beam radiation therapy is an ever-changing environment with technology rapidly improving. With proton therapy facilities becoming more widely available, and carbon ion facilities showcasing the benefits of carbon ion radiation therapy, there is an industry need toprovide accurate dosimetric treatment plans to verify patients are receiving proper care. Current clinical practices apply safety margins to clinical target volumes to safe treatment. Through research to improve detection techniques, …

Coexistence Of Vitreous And Crystalline Phases Of H2o At Ambient Temperature, Ali K. Shargh, Aude Picard, Rostislav Hrubiak, Dongzhou Zhang, Russell J. Hemley, Shanti Deemyad, Niaz Abdolrahim, Saveez Saffarian

Life Sciences Faculty Research

Formation of vitreous ice during rapid compression of water at room temperature is important for biology and the study of biological systems. Here, we show that Raman spectra of rapidly compressed water at greater than 1 GPa at room temperature exhibits the signature of high-density amorphous ice, whereas the X-ray diffraction (XRD) pattern is dominated by crystalline ice VI. To resolve this apparent contradiction, we used molecular dynamics simulations to calculate full vibrational spectra and diffraction patterns of mixtures of vitreous ice and ice VI, including embedded interfaces between the two phases. We show quantitatively that Raman spectra, which probe …

Dust-Gas Dynamics Driven By The Streaming Instability With Various Pressure Gradients, Stanley Antedio Baronett

UNLV Theses, Dissertations, Professional Papers, and Capstones

The radial pressure gradient (RPG), along the midplane of gaseous protoplanetary disks (PPD) – planetary nurseries – poses a severe obstacle to planet formation. Micron-sized dust grains, embedded in the disc, must quickly grow to kilometer-sized planetesimals – the building blocks of planets – before fatally drifting inwards, by RPG-induced gas drag, into a central host star. However, the RPG simultaneously powers one of the most robust processes to overcome this radial-drift barrier: the streaming instability (SI). Spontaneously triggered, the SI aerodynamically concentrates drifting dust via drag-induced, coupled interactions and feedback with the surrounding gas. In particular, the non-linear phase …

Towards Highly Sensitive Capacitance Measurements Of A Quantum Anomalous Hall Phase In Van Der Waal Heterostructures, Kayla Cerminara

UNLV Theses, Dissertations, Professional Papers, and Capstones

One of the pioneering achievements in condensed matter physics of the 20th century is the observation of the quantum Hall e↵ect (QHE) in which the Hall resistance in a two-dimensional (2D) sample takes on quantized values in the presence of a strong perpendicular magnetic field. The precise quantization of the hall resistance to one part in a billion has provided a practical, worldwide resistance standard. A long-standing goal has been to realize a similar state of matter but without the need of a strong quantizing magnetic field. The quantum anomalous Hall e↵ect (QAHE) is such a state that is predicted …

Terrestrial Planet Formation In M-Dwarf And Binary Star Systems, Anna C. Childs

UNLV Theses, Dissertations, Professional Papers, and Capstones

I examine circumbinary terrestrial planet formation in a gas free environment around various binary systems and terrestrial planet formation in a gaseous environment around M-dwarfs. While terrestrial cirumbinary planets have yet to be observed, this is likely due to observational bias. Motivated by recent observations of highly misaligned circumbinary gas disks, I perform a suite of n-body studies to understand the properties of terrestrial planets around various binary systems. In a polar alignment, a circumbinary disk is inclined by 90 degrees relative to the binary orbital plane. I find that terrestrial planet formation in a polar configuration may be as …

Quality Assurance Procedures Implementation For Varian Truebeam, Yongquan Jiang

UNLV Theses, Dissertations, Professional Papers, and Capstones

Department of radiation oncology of Oncology Nevada updated its linear accelerator (LINAC) from Varian Clinac iX to a newer model known as Varian TrueBeam. The Varian TrueBeam LINAC includes 6x, 6xFFF (i.e., 6x without flattening filter known as flattening filter free), 10x, 10xFFF, 15x photon beams and 6e, 9e, 12e MeV electron beams. This system is also equipped with a 6 degree of freedom (DOF) couch, RapidArc, kV on board imager, MV portal imager and Cone Beam CT (CBCT) imaging. This system allows the clinical delivery of modern image guided radiation therapy (IGRT) modalities such as IMRT/VMAT, and SRS/SRT/SBRT. The …

Dispersion In High Temperature Superconductors, Lazar Novakovic

Undergraduate Research Symposium Podium Presentations

Superconductors are used in many different industries: Efficient power transmission, Maglev train, MRIs

Separating Non-Linear Optical Signals Of A Sample From High Harmonic Radiation In A Soft X-Ray Free Electron Laser, Toshihide Sumi, Masafumi Horio, Tomoaki Senoo, Tetsuya Wada, Yuki Tsujikawa, Xiaoni Zhang, Paul Manset, Mihoko Araki, Yasuyuki Hirata, Walter S. Drisdell, John W. Freeland, Angelique Amadno, Michael Zuerch, Yuya Kubota, Shigeki Owada, Kensuke Tono, Makina Yabashi, Craig P. Schwartz, Iwao Matsuda

Nevada Extreme Conditions Laboratory Faculty Research

Second harmonic generation (SHG) is a unique non-linear optical effect that can be used to investigate chemical states of molecules at surfaces/interfaces. By the use of soft X-rays, SHG gains element selectivity through the inner-core excitation resonance. However, it is challenging to observe SHG signals separately from the second-order light generated from the undulator. Here, we report a new ellipsometry method for soft X-ray SHG to suppress the contribution of second-harmonic radiation from the light source. Through measurements of a GaAs(100) crystal, we demonstrate that pure SHG signals can be obtained for the horizontally polarized component. The present method is …

Accurate Flux Calibration Of Gw170817: Is The X-Ray Counterpart On The Rise?, E. Troja, B. O'Connor, G. Ryan, L. Piro, R. Ricci, B. Zhang, T. Piran, G. Bruni, S. B. Cenko, H. Van Eerten

Physics & Astronomy Faculty Research

X-ray emission from the gravitational wave transient GW170817 is well described as non-thermal afterglow radiation produced by a structured relativistic jet viewed off-axis. We show that the X-ray counterpart continues to be detected at 3.3 years after the merger. Such long-lasting signal is not a prediction of the earlier jet models characterized by a narrow jet core and a viewing angle ≈20 deg, and is spurring a renewed interest in the origin of the X-ray emission. We present a comprehensive analysis of the X-ray dataset aimed at clarifying existing discrepancies in the literature, and in particular the presence of an …

Numerical Studies Of Regularized Navier-Stokes Equations And An Application Of A Run-To-Run Control Model For Membrane Filtration At A Large Urban Water Treatment Facility, Jeffrey Belding

UNLV Theses, Dissertations, Professional Papers, and Capstones

This dissertation consists of two parts. The first part consists of research on accurate and efficient turbulent fluid flow modeling via a family of regularizations of the Navier-Stokes equation which are known as Time Relaxation models. In the second part, we look into the modeling application for the filtration/backwash process at the River Mountains Water Treatment Facility in Henderson, NV.

In the first two chapters, we introduce the Time Relaxation models and their associated differential filter equations. In addition, we develop the regularization method which employs the Nth van Cittert deconvolution operator, which gives rise to the family of models. …