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Articles 1 - 30 of 286

Full-Text Articles in Physics

Electronic And Geometric Structure Of Alnom And Alnom +, Albert R. Armstrong Jan 2019

Electronic And Geometric Structure Of Alnom And Alnom +, Albert R. Armstrong

Theses and Dissertations

Generally, the electronic stability of aluminum clusters is associated with either closed electronic shells of delocalized electrons, or aluminum in the +3 state. To explore alternative routes for electronic stability in aluminum oxide clusters, theoretical methods were used to examine the geometric and electronic structure of AlnOm (2≤n≤7; 1≤m≤10) clusters. Two types of electronically stable clusters with large HOMO-LUMO gaps were identified the first being Al2nO3m clusters with a +3 oxidation state on the aluminum, and the second being planar clusters such as Al4O4, Al5O ...


Optimizing Gas Mixture Composition For The Rtpc Detector For Bonus 12 At Jefferson Lab., Joshua H. Lehman Jan 2019

Optimizing Gas Mixture Composition For The Rtpc Detector For Bonus 12 At Jefferson Lab., Joshua H. Lehman

Theses and Dissertations

The main objective of this thesis is to perform a study of and optimize the most direct and practical gas mixture composition inside the Radial Time Projection Chamber for the Barely-Offshell Nucleon Structure (BONuS 12) detector for use in the CLAS 12 detector in Experimental Hall B at Thomas Jefferson National Accelerator Facility (JLab). The optimization of these conditions will enhance the performance and resolution of the detector. The original BONuS 6 experiment utilized a gas composition of 80 % He and 20% Dimethyl Ether (DME). With the extensive 12 GeV energy upgrade constructed at JLab and the new BONuS 12 ...


The Structure And Stability Of Cationic Metal-Benzene Clusters, Daniel P. Rabayda Jan 2019

The Structure And Stability Of Cationic Metal-Benzene Clusters, Daniel P. Rabayda

Theses and Dissertations

We have investigated the size-dependent stability and structure of benzene, aluminum-benzene, and vanadium-benzene clusters. Motivated by gas-phase experimental studies performed by an experimental collaborator, we have used first-principle electronic structure methods to identify the structure of Al+(Bz)n, V+(Bz)n, and Bzn clusters. Our studies reveal that cationic aluminum-benzene clusters have a magic number of 13, and that its high stability may be understood by analyzing the structure of the cluster. We also investigate the structure of vanadium-benzene clusters which have a magic number of 2. Here I examine the benzene-cation and benzene-benzene interactions that lead to ...


Straintronic Nanomagnetic Devices For Non-Boolean Computing, Md Ahsanul Abeed Jan 2019

Straintronic Nanomagnetic Devices For Non-Boolean Computing, Md Ahsanul Abeed

Theses and Dissertations

Nanomagnetic devices have been projected as an alternative to transistor-based switching devices due to their non-volatility and potentially superior energy-efficiency. The energy efficiency is enhanced by the use of straintronics which involves the application of a voltage to a piezoelectric layer to generate a strain which is ultimately transferred to an elastically coupled magnetostrictive nanomaget, causing magnetization rotation. The low energy dissipation and non-volatility characteristics make straintronic nanomagnets very attractive for both Boolean and non-Boolean computing applications. There was relatively little research on straintronic switching in devices built with real nanomagnets that invariably have defects and imperfections, or their adaptation ...


Monitoring Software And Charged Particle Identification For The Clas12 Detector, William A. Oliver Jan 2019

Monitoring Software And Charged Particle Identification For The Clas12 Detector, William A. Oliver

Theses and Dissertations

The CEBAF Large Acceptance Spectrometer for the 12 GeV era, known as CLAS12, uses the time of flight (TOF) system to identify charged particles from scattering events between the beam and target. The TOF system is divided into two parts: The Forward time of flight system, and the Central time of flight system. These two sub-systems subtend different polar angles of the detector geometry for wide acceptance of scattered particles. Reconstruction is the service used to identify particles from the interactions between the beam and target, called as a vertex or the point where the interaction occurs. The vertex position ...


An Introduction To Supersymmetric Quantum Mechanics, Vincent R. Siggia Jan 2019

An Introduction To Supersymmetric Quantum Mechanics, Vincent R. Siggia

Theses and Dissertations

In this thesis, the general framework of supersymmetric quantum mechanics and the path integral approach will be presented (as well as the worked out example of the supersymmetric harmonic oscillator). Then the theory will be specialized to the case of supersymmetric quantum mechanics on Riemannian manifolds, which will start from a supersymmetric Lagrangian for the general case and the special case for S2. Afterwards, there will be a discussion on the superfield formalism. Concluding this thesis will be the Hamiltonian formalism followed by the inclusion of deforma- tions by potentials.


Theoretical Studies Of The Structure And Stability Of Metal Chalcogenide Crntem (1≤N≤6, 1≤M≤8) Clusters, Fnu Sweta Prabha Jan 2019

Theoretical Studies Of The Structure And Stability Of Metal Chalcogenide Crntem (1≤N≤6, 1≤M≤8) Clusters, Fnu Sweta Prabha

Theses and Dissertations

In the presented work, first principle studies on electronic structure, stability, and magnetic properties of metal chalcogenide, CrnTem clusters have been carried out within a density functional framework using generalized gradient functions to incorporate the exchange and correlation effects. The energetic and electronic stability was investigated, and it was found that they are not always correlated as seen in the cluster Cr6Te8 which has smaller gap between its HOMO (Highest Occupied Molecular Orbital) and LUMO (Lowest Unoccupied Molecular Orbital) and a high electron affinity of 3.39 eV indicating lower electronic stability whereas higher ...


Searching For Clean Observables In $B -> D* /Tau- \Bar{\Nu}_{\Tau}$ Decays, Michael D. Williams Jr. Jan 2019

Searching For Clean Observables In $B -> D* /Tau- \Bar{\Nu}_{\Tau}$ Decays, Michael D. Williams Jr.

Theses and Dissertations

In this thesis, the clean angular observables in the $\bar{B} \to D^{*+} \ell^- \bar{\nu}_{\ell}$ angular distribution is studied. Similar angular observables are widely studied in $B \to K^* \mu^+ \mu^-$ decays. We believed that these angular observables may have different sensitivities to different new physics structures.


Inference And Control In Regulatory Genomics, Siddharth Sharma May 2018

Inference And Control In Regulatory Genomics, Siddharth Sharma

Biology and Medicine Through Mathematics Conference

No abstract provided.


Elucidating The Action Of A Regulatory Lipid Ligand Via Molecular Simulation: Cholesterol Swarms And The Inwardly Rectifying Potassium Channel, Belinda Akpa, Nicolas Barbera, Irena Levitan May 2018

Elucidating The Action Of A Regulatory Lipid Ligand Via Molecular Simulation: Cholesterol Swarms And The Inwardly Rectifying Potassium Channel, Belinda Akpa, Nicolas Barbera, Irena Levitan

Biology and Medicine Through Mathematics Conference

No abstract provided.


Geodesic Structure In Schwarzschild Geometry With Extensions In Higher Dimensional Spacetimes, Ian M. Newsome Jan 2018

Geodesic Structure In Schwarzschild Geometry With Extensions In Higher Dimensional Spacetimes, Ian M. Newsome

Theses and Dissertations

From Birkoff's theorem, the geometry in four spacetime dimensions outside a spherically symmetric and static, gravitating source must be given by the Schwarzschild metric. This metric therefore satisfies the Einstein vacuum equations. If the mass which gives rise to the Schwarzschild spacetime geometry is concentrated within a radius of r=2M, a black hole will form. Non-accelerating particles (freely falling) traveling through this geometry will do so along parametrized curves called geodesics, which are curved space generalizations of straight paths. These geodesics can be found by solving the geodesic equation. In this thesis, the geodesic structure in the Schwarzschild ...


Warp Drive Spacetimes, Nicholas A.S. Driver Jan 2018

Warp Drive Spacetimes, Nicholas A.S. Driver

Theses and Dissertations

The concept of faster than light travel in general relativity is examined, starting with a review of the Alcubierre metric. This spacetime, although incredible in its implications, has certain unavoidable problems which are discussed in detail. It is demonstrated that in order to describe faster than light travel without any ambiguities, a coordinate independent description is much more convenient. An alternative method of describing superluminal travel is then proposed, which has similarities to the Krasnikov tube.


Neutronics Studies On The Nist Reactor Using The Ga Leu Fuel, Kyle A. Britton Jan 2018

Neutronics Studies On The Nist Reactor Using The Ga Leu Fuel, Kyle A. Britton

Theses and Dissertations

The National Bureau of Standards Reactor (NBSR) located on the National Institute of Standards and Technology (NIST) Gaithersburg campus, is currently underway of fuel conversion from high enriched uranium (HEU) fuel to low enriched uranium (LEU) fuel. One particular challenging part of the conversion of the NBSR is the high average flux level (2.5×1014 n/cm2-s) required to maintain experimental testing capabilities of the reactor, without significant changes to the external structures of the reactor. Recently the General Atomics (GA) Training Research Isotopes General Atomics (TRIGA) fuel has shown some promising features as a LEU ...


Kinetic Monte Carlo Simulation Of Binary Alloys, Timothy Craig Marshall Jan 2018

Kinetic Monte Carlo Simulation Of Binary Alloys, Timothy Craig Marshall

Theses and Dissertations

There are many tools to simulate physical phenomena. Generally, the simulation technique is defined by the size of the simulation area. Two well know techniques for simulating atom dynamics are kinetic Monte Carlo (kMC) and molecular dynamics (MD). In this work we simulate physical vapor deposition of binary metallic systems using the kMC technique. A sufficient quantity of atoms are deposited so that morphological features can be observed. Where kMC has fallen short we have used MD to supplement our results.


Motion-Induced Artifact Mitigation And Image Enhancement Strategies For Four-Dimensional Fan-Beam And Cone-Beam Computed Tomography, Matthew J. Riblett Jan 2018

Motion-Induced Artifact Mitigation And Image Enhancement Strategies For Four-Dimensional Fan-Beam And Cone-Beam Computed Tomography, Matthew J. Riblett

Theses and Dissertations

Four dimensional imaging has become part of the standard of care for diagnosing and treating non-small cell lung cancer. In radiotherapy applications 4D fan-beam computed tomography (4D-CT) and 4D cone-beam computed tomography (4D-CBCT) are two advanced imaging modalities that afford clinical practitioners knowledge of the underlying kinematics and structural dynamics of diseased tissues and provide insight into the effects of regular organ motion and the nature of tissue deformation over time. While these imaging techniques can facilitate the use of more targeted radiotherapies, issues surrounding image quality and accuracy currently limit the utility of these images clinically.

The purpose of ...


Evaluation And Adaptation Of Live-Cell Interferometry For Applications In Basic, Translational, And Clinical Research, Kevin A. Leslie Jan 2018

Evaluation And Adaptation Of Live-Cell Interferometry For Applications In Basic, Translational, And Clinical Research, Kevin A. Leslie

Theses and Dissertations

Cell mass is an important indicator of cell health and status. A diverse set of techniques have been developed to precisely measure the masses of single cells, with varying degrees of technical complexity and throughput. Here, the development of a non-invasive, label-free optical technique, termed Live-Cell Interferometry (LCI), is described. Several applications are presented, including an evaluation of LCI’s utility for assessing drug response heterogeneity in patient-derived melanoma lines and the measurement of CD3+ T cell kinetics during hematopoietic stem cell transplantation. The characterization of mast cells during degranulation, the measurement of viral reactivation kinetics in Kaposi’s Sarcoma ...


Photoluminescence From Gan Co-Doped With C And Si, Mykhailo Vorobiov Jan 2018

Photoluminescence From Gan Co-Doped With C And Si, Mykhailo Vorobiov

Theses and Dissertations

This thesis devoted to the experimental studies of yellow and blue luminescence (YL and BL relatively) bands in Gallium Nitride samples doped with C and Si. The band BLC was at first observed in the steady-state photoluminescence spectrum under high excitation intensities and discerned from BL1 and BL2 bands appearing in the same region of the spectrum. Using the time-resolved photoluminescence spectrum, we were able to determine the shape of the BLC and its position at 2.87 eV. Internal quantum efficiency of the YL band was estimated to be 90\%. The hole capture coefficient of the BL ...


Optimization Of Cardiac Pacing Stimulation By Current Configuration –A Theoretical, Numerical And Experimental Study., Flavio H. Fenton, Hila Dvir, Neil Hardy May 2017

Optimization Of Cardiac Pacing Stimulation By Current Configuration –A Theoretical, Numerical And Experimental Study., Flavio H. Fenton, Hila Dvir, Neil Hardy

Biology and Medicine Through Mathematics Conference

No abstract provided.


Code For "Noise-Enhanced Coding In Phasic Neuron Spike Trains", Cheng Ly, Brent D. Doiron Jan 2017

Code For "Noise-Enhanced Coding In Phasic Neuron Spike Trains", Cheng Ly, Brent D. Doiron

Statistical Sciences and Operations Research Data

This zip file contains Matlab scripts and ode (XPP) files to calculate the statistics of the models in "Noise-Enhanced Coding in Phasic Neuron Spike Trains". This article is published in PLoS ONE.


Metal Chalcogenide Clusters With Closed Electronic Shells And The Electronic Properties Of Alkalis And Halogens, Vikas Chauhan, Arthur C. Reber, Shiv N. Khanna Jan 2017

Metal Chalcogenide Clusters With Closed Electronic Shells And The Electronic Properties Of Alkalis And Halogens, Vikas Chauhan, Arthur C. Reber, Shiv N. Khanna

Physics Publications

Clusters with filled electronic shells and a large gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) are generally energetically and chemically stable. Enabling clusters to become electron donors with low ionization energies or electron acceptors with high electron affinities usually requires changing the valence electron count. Here we demonstrate that a metal cluster may be transformed from an electron donor to an acceptor by exchanging ligands while the neutral form of the clusters has closed electronic shells. Our studies on Co6Te8(PEt3),(CO) (m + n = 6) clusters show that Co6Te8(PEt3)(6) has ...


B-12(Scn)(12)(-): An Ultrastable Weakly Coordinating Dianion, Hong Fang, Puru Jena Jan 2017

B-12(Scn)(12)(-): An Ultrastable Weakly Coordinating Dianion, Hong Fang, Puru Jena

Physics Publications

Stable dianions that are weakly coordinating with metal ions are not common. In this work, we show that the thiocyanate SCN- anion, known for its detoxification property of cyanide CN- and antidegradation property of perovskite solar cell materials, can also be used to produce a new set of weakly coordinating B-12(SCN)(12)(-) dianion complexes which are potential candidates for the anionic part inside the electrolytes of metal-ion, especially the magnesium-ion-based, batteries.


Evolution Of The Spin Magnetic Moments And Atomic Valence Of Vanadium In Vcux+, Vagx+, And Vaux+ Clusters (X = 3–14), William H. Blades, Arthur C. Reber, Shiv N. Khanna, Luis López-Sosa, Patrizia Calaminici, Andreas M. Köster Jan 2017

Evolution Of The Spin Magnetic Moments And Atomic Valence Of Vanadium In Vcux+, Vagx+, And Vaux+ Clusters (X = 3–14), William H. Blades, Arthur C. Reber, Shiv N. Khanna, Luis López-Sosa, Patrizia Calaminici, Andreas M. Köster

Physics Publications

The atomic structures, bonding characteristics, spin magnetic moments, and stability of VCUx+, VAgx+, and VAux+ (x = 3-14) clusters were examined using density functional theory. Our studies indicate that the effective valence of vanadium is size-dependent and that at small sizes some of the valence electrons of vanadium are localized on vanadium, while at larger sizes the 3d orbitals of the vanadium participate in metallic bonding eventually quenching the spin magnetic moment. The electronic stability of the clusters may be understood through a split-shell model that partitions the valence electrons in either a delocalized shell or localized on the vanadium atom ...


The Effect Of Substituted Benzene Dicarboxylic Acid Linkers On The Optical Band Gap Energy And Magnetic Coupling In Manganese Trimer Metal Organic Frameworks, K. S. Asha, Arthur C. Reber, N. Ahmed, R. Nath, Shiv N. Khanna, Sukhendu Mandal Jan 2017

The Effect Of Substituted Benzene Dicarboxylic Acid Linkers On The Optical Band Gap Energy And Magnetic Coupling In Manganese Trimer Metal Organic Frameworks, K. S. Asha, Arthur C. Reber, N. Ahmed, R. Nath, Shiv N. Khanna, Sukhendu Mandal

Physics Publications

We have systematically studied a series of eight metal-organic frameworks (MOFs) in which the secondary building unit is a manganese trimer cluster, and the linkers are differently substituted benzene dicarboxylic acids (BDC). The optical band gap energy of the compounds vary from 2.62 eV to 3.57 eV, and theoretical studies find that different functional groups result in new states in the conduction band, which lie in the gap and lower the optical band gap energy. The optical absorption between the filled Mn 3d states and the ligands is weak due to minimal overlap of the states, and the ...


Symmetry And Magnetism In Ni9te6 Clusters Ligated By Co Or Phosphine Ligands, Arthur C. Reber, Vikas Chauhan, Shiv N. Khanna Jan 2017

Symmetry And Magnetism In Ni9te6 Clusters Ligated By Co Or Phosphine Ligands, Arthur C. Reber, Vikas Chauhan, Shiv N. Khanna

Physics Publications

The removal of a single ligand from the magnetic Ni9Te6(L)(8) (L = P(CH3)(3), CO) clusters is found to quench the magnetic moment. The reduction in magnetic moment is caused by a geometric deformation of the Ni9Te6 core that breaks the octahedral symmetry of the cluster. This effect is observed in both the CO and phosphine based ligands. The octahedral symmetry bare cluster is also found to have a large magnetic moment. These results highlight the dilemma faced by magnetic ligand protected clusters whose symmetry has been broken: whether to break the spin symmetry as in Hund's ...


Rational Design Of Super-Alkalis And Their Role In Co2 Activation, Tianshan Zhao, Qian Wang, Puru Jena Jan 2017

Rational Design Of Super-Alkalis And Their Role In Co2 Activation, Tianshan Zhao, Qian Wang, Puru Jena

Physics Publications

Super-alkalis are clusters of atoms. With ionization potentials smaller than those of the alkali atoms, they are playing an increasing role in chemistry as highlighted by recent applications in solar cells as well as in Li-ion batteries. For the past 40 years superalkalis were designed using inorganic elements with the sp orbital character. Here, we show that a large class of superalkalis composed of only simple metal atoms, transition metal complexes as well as organic molecules can be designed by making use of electron counting rules beyond the octet rule. Examples include Al-3(+), Mn(B3N3H6)(2)(+), B9C3H12+, and C5NH6+ which ...


Investigations Into Structure And Properties Of Atomically-Precise Transition Metal-Chalcogenide Clusters Of Crte And Ligated Cr6te8(Pet3)6, Anthony F. Pedicini Jan 2017

Investigations Into Structure And Properties Of Atomically-Precise Transition Metal-Chalcogenide Clusters Of Crte And Ligated Cr6te8(Pet3)6, Anthony F. Pedicini

Theses and Dissertations

The complete understanding of a clusters electronic structure, the primary mechanisms for its properties and stabilization is necessary in order to functionalize them for use as building blocks within novel materials. First principle theoretical studies have been carried out upon the electronic properties of CrxTey (x = 1 – 6, y = 0 – 8, x + y ≤ 14), as well as for the larger triethylphosphine (PEt3) ligated cluster system of Cr6Te8(PEt3)6. Together, we aim to use the information garnered from the smaller clusters to address the underlying behavior of the ligated Cr6Te ...


Application Of The Fisher Dimer Model To Dna Condensation, John C. Baker Iii Jan 2017

Application Of The Fisher Dimer Model To Dna Condensation, John C. Baker Iii

Theses and Dissertations

This paper considers the statistical mechanics occupation of the edge of a single helix of DNA by simple polymers. Using Fisher's exact closed form solution for dimers on a two-dimensional lattice, a one-dimensional lattice is created mathematically that is occupied by dimers, monomers, and holes. The free energy, entropy, average occupation, and total charge on the lattice are found through the usual statistical methods. The results demonstrate the charge inversion required for a DNA helix to undergo DNA condensation.


Thermal Quenching Of Photoluminescence In Zno And Gan, Nahla Albarakati Jan 2017

Thermal Quenching Of Photoluminescence In Zno And Gan, Nahla Albarakati

Theses and Dissertations

Investigation of the thermal quenching of photoluminescence (PL) in semiconductors provides valuable information on identity and characteristics of point defects in these materials, which helps to better understand and improve the properties of semiconductor materials and devices. Abrupt and tunable thermal quenching (ATQ) of PL is a relatively new phenomenon with an unusual behavior of PL. This mechanism was able to explain what a traditional model failed to explain. Usually, in traditional model used to explain “normal” quenching, the slope of PL quenching in the Arrhenius plot determines the ionization energy of the defect causing the PL band. However, in ...


Theoretical And Experimental Analysis Of Optical Properties Of Defects In Gan:, Ibrahima Castillo Diallo Jan 2017

Theoretical And Experimental Analysis Of Optical Properties Of Defects In Gan:, Ibrahima Castillo Diallo

Theses and Dissertations

Using the Heyd-Scuseria-Ernzherof (HSE06) hybrid functional method along with photoluminescence experimental measurements, we analyze the properties of intrinsic defects such as vacancies, interstitials, antisites, and common complexes. By using configurational coordinate diagrams, we estimate the likelihood of defects to be radiative or non-radiative. Our calculations show that gallium vacancies exhibit a large magnetic moment in the neutral charge state and are most likely non-radiative. We also investigate the correlation between the observed infrared PL bands created in 2.5 MeV electron-irradiated GaN samples and the formation of native defects. It is found that gallium-nitrogen divacancies are possible sources of the ...


In Defense Of Science—What Would John Do?, Mohamed Gad-El-Hak Jan 2017

In Defense Of Science—What Would John Do?, Mohamed Gad-El-Hak

Mechanical and Nuclear Engineering Publications

Recent onslaughts on the importance of pure research to our collective well-being are trending. In this essay, I discuss the issues involved and offer a rebuttal. The thoughts are inspired by my mentor, academic sibling, and idol John Leask Lumley.