Physical Sciences and Mathematics Commons^™

Energy Of The Quasi-Free Electron In Repulsive Atomic And Molecular Fluids, Yevgeniy Lushtak

Dissertations, Theses, and Capstone Projects

The ability to predict accurately the energy V₀(ρ) of the quasi-free electron along the entire density (ρ) range of a supercritical fluid has applications in determining the ideal thermodynamic conditions for chemical reactions involving charged species. The previously established field ionization method of extracting V₀(ρ) from the fluid density dependent shift Δ(ρ) in the ionization energy of a dopant molecule has led to the discovery of a novel effect on V₀(ρ) occurring near the critical isotherm of the fluid. Unfortunately this method has limitations in determining V₀(ρ) in fluids with low critical …

Dipolar Interactions, Long Range Order And Random Fields In A Single Molecule Magnet, Mn12-Acetate, Bo Wen

Dissertations, Theses, and Capstone Projects

In this thesis, I will present an experimental study of two single molecule magnets, Mn₁₂-ac and Mn₁₂-ac-MeOH. I will show that in both systems, the temperature dependence of the inverse susceptibility yields a positive intercept on the temperature axis (a positive Weiss temperature), implying the existence of a ferromagnetic phase at low temperature.

Applying a magnetic field in the transverse direction moves the Weiss temperature downward towards zero. This implies that the transverse field triggers mechanisms in the system that compete with the dipolar interaction and suppress the long-range ordering.

I will then show that the …

Landau-Zener Dynamics Of A Nanoresonator Containing A Tunneling Spin, Michael F. O'Keeffe, Eugene M. Chudnovsky, Dmitry A. Garanin

Publications and Research

We study the Landau-Zener dynamics of a tunneling spin coupled to a torsional resonator. For strong spin-phonon coupling, when the oscillator frequency is large compared to the tunnel splitting, the system exhibits multiple Landau-Zener transitions. Entanglement of spin and mechanical angular momentum results in abrupt changes of oscillator dynamics which coincide in time with spin transitions. We show that a large number of spins on a single oscillator coupled only through the in-phase phonon field behaves as a single large spin, greatly enhancing the spin-phonon coupling. We compare purely quantum and semiclassical dynamics of the system and discuss their experimental …

Quantum Dynamics Of Vortices In Mesoscopic Magnetic Disks, Ricardo Zarzuela, Eugene M. Chudnovsky, J M. Hernandez, J Tajeda

Publications and Research

Model of quantum depinning of magnetic vortex cores from line defects in a disk geometry and under the application of an in-plane magnetic field has been developed within the framework of the Caldeira-Leggett theory. The corresponding instanton solutions are computed for several values of the magnetic field. Expressions for the crossover temperature Tc and for the depinning rate \Gamma(T) are obtained. Fitting of the theory parameters to experimental data is also presented.

Reversal Of Magnetization Of A Single-Domain Magnetic Particle By The Ac Field Of Time-Dependent Frequency, Liufei Cai, Dmitry A. Garanin, Eugene M. Chudnovsky

Publications and Research

We report numerical and analytical studies of the reversal of the magnetic moment of a single- domain magnetic particle by a circularly polarized ac field of time-dependent frequency. For the time-linear frequency sweep, the phase diagrams are computed that illustrate the dependence of the reversal on the frequency sweep rate v , the amplitude of the ac field h , the magnetic anisotropy field d , and the damping parameter . It is shown that the most efficient magnetization reversal requires a non-linear time dependence of the frequency, ! ( t ) , for which an exact analytical formula is …

Excitation Modes Of Vortices In Submicron Magnetic Disks, Ricardo Zarzuela, Eugene M. Chudnovsky, Javier Tejada

Publications and Research

Classical and quantum theory of spin waves in the vortex state of a mesoscopic sub-micron magnetic disk has been developed with account of the finite mass density of the vortex. Oscillations of the vortex core resemble oscillations of a charged string in a potential well in the presence of the magnetic field. Conventional gyroscopic frequency appears as a gap in the spectrum of spin waves of the vortex. The mass of the vortex has been computed that agrees with experimental findings. Finite vortex mass generates a high-frequency branch of spin waves. Effects of the external magnetic field and dissipation have …

Turbulent Fronts Of Quantum Detonation In Molecular Magnets, Dmitry A. Garanin

Publications and Research

Dipolar-controlled quantum deflagration going over into quantum detonation in the elongated Mn_12 Ac molecular magnet in a strong transverse field has been considered within the full 3d model. It is shown that within the dipolar window around tunneling resonances the deflagration front is non-flat. With increasing bias, dipolar instability makes the front turbulent, while its speed reaches sonic values, that is a signature of detonation.

Black Hole Formation In Fuzzy Sphere Collapse, Norihiro Izuka, Daniel N. Kabat, Roy Shubho, Debajyoti Sarkar

Publications and Research

We study the collapse of a fuzzy sphere, that is a spherical membrane built out of D0-branes, in the BFSS model. At weak coupling, as the sphere shrinks, open strings are produced. If the initial radius is large then open string production is not important and the sphere behaves classically. At intermediate initial radius the back-reaction from open string production is important but the fuzzy sphere retains its identity. At small initial radius the sphere collapses to form a black hole. The crossover between the later two regimes is smooth and occurs at the correspondence point of Horowitz and Polchinski.

Black Hole Formation At The Correspondence Point, Norihiro Izuka, Daniel N. Kabat, Roy Shubho, Debajyoti Sarkar

Publications and Research

We study the process of bound state formation in a D-brane collision. We consider two mechanisms for bound state formation. The first, operative at weak coupling in the worldvolume gauge theory, is pair creation of W-bosons. The second, operative at strong coupling, corresponds to formation of a large black hole in the dual supergravity. These two processes agree qualitatively at intermediate coupling, in accord with the correspondence principle of Horowitz and Polchinski. We show that the size of the bound state and timescale for formation of a bound state agree at the correspondence point. The timescale involves matching a parametric …

Cft Representation Of Interacting Bulk Gauge Fields In Ads, Daniel N. Kabat, Gilad Lifschytz

Publications and Research

We develop the representation of interacting bulk gauge fields and charged scalar matter in AdS in terms of non-local observables in the dual CFT. We work in holographic gauge in the bulk, A_z = 0. The correct statement of micro-causality in holographic gauge is somewhat subtle, so we first discuss it from the bulk point of view. We then show that in the 1/N expansion CFT correlators can be lifted to obtain bulk correlation functions which satisfy micro-causality. This requires adding an infinite tower of higher-dimension multi-trace operators to the CFT definition of a bulk observable. For conserved currents the …

Diffractive Effects And General Boundary Conditions In Casimir Energy, Dimitra Karabali, V P. Nair

Publications and Research

The effect of edges and apertures on the Casimir energy of an arrangement of plates and boundaries can be calculated in terms of an effective nonlocal lower-dimensional field theory that lives on the boundary. This formalism has been developed in a number of previous papers and applied to specific examples with Dirichlet boundary conditions. Here we generalize the formalism to arbitrary boundary conditions. As a specific example, the geometry of a flat plate and a half-plate placed parallel to it is considered for a number of different boundary conditions and the area-dependent and edge dependent contributions to the Casimir energy …

Assessing Continuous Contamination Discharge From A Combined Sewer Outfall (Cso) Into A Tidal Wetland Creek: Bacteriological And Heavy Metals Indicators, Timothy Eaton, Gregory D. O'Mullan, Ashaki A. Rouff

Publications and Research

Continuous discharge from a combined sewer overflow (CSO) into a tidal wetland creek in the New York City urban area was analyzed to assess the extent of water quality degradation from fecal bacteria contamination during both dry and wet weather. A combination of fecal indicator bacteria (FIB), total suspended solids, and dissolved metals were used to infer the presence of sewage pollution from the CSO discharge and to constrain the spatial and temporal impact on water quality and dry season creek flows. Upstream of the CSO, creek flow was dominated by groundwater input, and FIB levels were very low or …

‘What’S In The Niddk Cdr?’—Public Query Tools For The Niddk Central Data Repository, Huaqin Pan, Mary-Anne Ardini, Vesselina Bakalov, Michael Delatte, Paul Eggers, Laxminarayana Ganapathi, Craig R. Hollingsworth, Joshua Levy, Sheping Li, Joseph Pratt, Norma Pugh, Ying Qin, Rebekah Rasooly, Helen Ray, Jean E. Richardson, Amanda Flynn Riley, Susan M. Rogers, Sylvia Tan, Charles F. Turner, Stacie White, Philip C. Cooley

Publications and Research

The National Institute of Diabetes and Digestive Disease (NIDDK) Central Data Repository (CDR) is a web-enabled resource available to researchers and the general public. The CDR warehouses clinical data and study documentation from NIDDK funded research, including such landmark studies as The Diabetes Control and Complications Trial (DCCT, 1983–93) and the Epidemiology of Diabetes Interventions and Complications (EDIC, 1994–present) follow-up study which has been ongoing for more than 20 years. The CDR also houses data from over 7 million biospecimens representing 2 million subjects. To help users explore the vast amount of data stored in the NIDDK CDR, we developed …

Theoretical Methods For Blur-Correction In Electron And Soft X-Ray Microscopy, Joanna Klukowska

Dissertations, Theses, and Capstone Projects

The process of object reconstruction from projections is widely used in many fields. One of the applications is the reconstruction of biological specimens from two-dimensional projections in transmission electron microscopy and transmission x-ray microscopy. Various methods have been developed for correcting the blurring that occurs when the projections are obtained by a real instrument. As the attainable resolution increases, new issues become apparent and need to be taken into account in the imaging model. In this dissertation we concentrate on the point spread function and its impact on the quality and usefulness of the reconstructions from images obtained according to …

Information Content Of Seasonal Forecasts In A Changing Climate, Nir Krakauer, Michael D. Grossberg, Irina Gladkova, Hannah Aizenman

Publications and Research

We study the potential value to stakeholders of probabilistic long-term forecasts, as quantified by the mean information gain of the forecast compared to climatology. We use as a case study the USA Climate Prediction Center (CPC) forecasts of 3-month temperature and precipitation anomalies made at 0.5-month lead time since 1995. Mean information gain was positive but low (about 2% and 0.5% of the maximum possible for temperature and precipitation forecasts, resp.) and has not increased over time. Information-based skill scores showed similar patterns to other, non-information-based, skill scores commonly used for evaluating seasonal forecasts but tended to be smaller, suggesting …

Development Of A Ground Based Remote Sensing Approach For Direct Evaluation Of Aerosol-Cloud Interaction, Bomidi Lakshmi Madhavan, Yuzhe He, Yonghua Wu, Barry Gross, Fred Moshary, Samir Ahmed

Publications and Research

The possible interaction and modification of cloud properties due to aerosols is one of the most poorly understood mechanisms within climate studies, resulting in the most significant uncertainty as regards radiation budgeting. In this study, we explore direct ground based remote sensing methods to assess the Aerosol-Cloud Indirect Effect directly, as space-borne retrievals are not directly suitable for simultaneous aerosol/cloud retrievals. To illustrate some of these difficulties, a statistical assessment of existing multispectral imagers on geostationary (e.g., GOES)/Moderate Resolution Imaging Spectroradiometer (MODIS) satellite retrievals of the Cloud Droplet Effective Radius (Reff) showed significant biases especially at larger solar zenith angles, …

Tectonics And Sedimentary Facies Interpretation Of The Mesozoic Giron Group, Colombia, Hernando Martinez-Sacristan, Ricardo Mier-Umana, Nazrul I. Khandaker, Stanley Schleifer, Diana Lucia Leon-Martinez

Publications and Research

Preliminary field investigations involving exposed Giron Group sediments in Colombia provided some interesting geologic information in terms of provenance, depositional environments, and development of the Mesozoic synrift sedimentary basins in Colombia. Overall, the synrift Triassic-Jurassic rift-related volcanic rocks, redbeds, and evaporites are prominent in Colombia, and a thick basin sequence of Cretaceous sandstones and shales dominates the central part of the Cordillera Oriental. These were mostly deposited in dominantly north-trending grabens. Identified sedimentary rock types were arkose, clast-and-matrix-supported conglomerate, red mudstone, variegated sandstone, siltstone and breccia. Extensive kaolinitization was noticeable in several sandstone samples. Among the notable sedimentary structures were …

Hohenberg-Kohn Theorem Including Electron Spin, Xiao-Yin Pan, Viraht Sahni

Publications and Research

The Hohenberg-Kohn theorem is generalized to the case of a finite system of N electrons in external electrostatic epsilon(r) = -del nu(r) and magnetostatic B(r) = del x A(r) fields in which the interaction of the latter with both the orbital and spin angular momentum is considered. For a nondegenerate ground state a bijective relationship is proved between the gauge invariant density rho(r) and physical current density j(r) and the potentials {nu(r), A(r)}. The possible many-to-one relationship between the potentials {v(r), A(r)} and the wave function is explicitly accounted for in the proof. With the knowledge that the basic variables …

The Quantum Effective Action, Wave Functions And Yang-Mills(2+1), V. Parameswaran Nair

Publications and Research

No abstract provided.

Pricing Options On Foreign Currency With A Preset Exchange Rate, Avner Wolf, Christopher Heseel

Publications and Research

This paper presents a new option that can be used by agents for managing foreign exchange risk. Unlike the Garman Kolhagen model [1], (GK), this paper presents a new model with a preset exchange rate (PE), that allows the agent to take advantage of the his/her view on both the direction and magnitude of rate movement and as such provides this agent with more choices. The model has a provision for an automatic exchange of the payoff at a preset exchange rate, and upon expiration gives the agent the choice of keeping the payoff in the foreign currency or exchanging …

A New Nonlinear Analytical Model For Canopy Flow Over A Forested Hill, Weiguo Wang, Chuixiang Yi

Publications and Research

A new nonlinear analytical model for canopy flow over gentle hills is presented. This model is established based on the assumption that three major forces (pressure gradient, Reynolds stress gradient, and nonlinear canopy drag) within canopy are in balance for gentle hills under neutral conditions. The momentum governing equation is closed by the velocity-squared law. This new model has many advantages over the model developed by Finnigan and Belcher (2004, hereafter referred to as FB04) in predicting canopy wind velocity profiles in forested hills in that: (1) this model predictions are more realistic because the surface drag can be taken …

Inhibition Of Pokeweed Antiviral Protein (Pap) By Turnip Mosaic Virus Genome-Linked Protein (Vpg), Artem V. Domashevskiy, Hiroshi Miyoshi, Dixie J. Goss

Publications and Research

Pokeweed antiviral protein (PAP) from Phytolacca americana is a ribosome-inactivating protein (RIP) and an RNA N-glycosidase that removes specific purine residues from the sarcin/ricin loop of large rRNA, arresting protein synthesis at the translocation step. PAP is also a cap-binding protein and is a potent antiviral agent against many plant, animal, and human viruses. To elucidate the mechanism of RNA depurination, and to understand how PAP recognizes and targets various RNAs, the interactions between PAP and turnip mosaic virus genomelinked protein (VPg) were investigated. VPg can function as a cap analog in cap-independent translation and potentially target PAP to uncapped …

Potential Significance Of Photoexcited No2 On Global Air Quality With The Nmmb/Bsc Chemical Transport Model, O. Jorba, D. Dabdub, Christopher S. Blaszczak-Boxe, C. Pérez, Z. Janjic, J. M. Baldasano, M. Spada, A. Badia, M. Gonçalves

Publications and Research

Atmospheric chemists have recently focused on the relevance of the NO2* + H2O → OH + HONO reaction to local air quality. This chemistry has been considered not relevant for the troposphere from known reaction rates until nowadays. New experiments suggested a rate constant of 1.7 × 10−13 cm3 molecule−1 s−1, which is an order of magnitude faster than the previously estimated upper limit of 1.2 × 10−14 cm3 molecule−1 s−1, determined by Crowley and Carl (1997). Using the new global model, NMMB/BSC Chemical Transport Model (NMMB/BSC-CTM), simulations are presented that assess the potential significance of this chemistry on global …

Halogen Activation Via Interactions With Environmental Ice And Snow In The Polar Lower Troposphere And Other Regions, J. P. D. Abbatt, J. L. Thomas, K. Abrahamsson, Chris Boxe, A. Granfors, A. E. Jones, M. D. King, A. Saiz-Lopez, P. B. Shepson, J. Sodeau, D. W. Toohey, C. Toubin, R. Von Glasow, S. N. Wren, X. Yang

Publications and Research

The role of ice in the formation of chemically active halogens in the environment requires a full understanding because of its role in atmospheric chemistry, including controlling the regional atmospheric oxidizing capacity in specific situations. In particular, ice and snow are important for facilitating multiphase oxidative chemistry and as media upon which marine algae live. This paper reviews the nature of environmental ice substrates that participate in halogen chemistry, describes the reactions that occur on such substrates, presents the field evidence for ice-mediated halogen activation, summarizes our best understanding of ice-halogen activation mechanisms, and describes the current state of modeling …

Optimal Control Of Katabatic Flows Within Canopies, Hongbin Chen, Chuixiang Yi

Publications and Research

What slope angle favours the development of katabatic flow is still an open question. Some studies have clarified that katabatic winds are stronger on steep slopes, while others have demonstrated that katabatic winds are stronger on gentle slopes. Here, we explore the control mechanisms of katabatic flow using a simplified theoretical model in an attempt to clarify the causes of the paradoxical findings. Our results indicate that optimal conditions for katabatic flows within canopies are synergistically controlled by terrain angle, canopy structure and thermal condition through a simple equation:

L_cV_T^-2 sin³ α = b,

where …

Hohenberg-Kohn And Percus-Levy-Lieb Proofs Of Density-Functional Theory, Viraht Sahni, Xiao-Yin Pan

Publications and Research

The premise of density-functional theory is that knowledge of the ground-state density uniquely determines the Hamiltonian, and thereby, via solution of the corresponding time-independent Schrodinger equation, all the properties of the system. The density therefore constitutes a basic variable of quantum mechanics. There are at present two paths from the density to the Hamiltonian: the Hohenberg and Kohn proof of the bijectivity between the external potential and the basic variable, and the Percus, Levy, and Lieb constrained-search proof. We argue the Hohenberg- and Kohn-type proof to be the more fundamental, and that this is the case in general when both …

Pointcut Rejuvenation: Recovering Pointcut Expressions In Evolving Aspect-Oriented Software, Raffi Khatchadourian, Phil Greenwood, Awais Rashid, Harry Xu

Publications and Research

Pointcut fragility is a well-documented problem in Aspect-Oriented Programming; changes to the base code can lead to join points incorrectly falling in or out of the scope of pointcuts. In this paper, we present an automated approach that limits fragility problems by providing mechanical assistance in pointcut maintenance. The approach is based on harnessing arbitrarily deep structural commonalities between program elements corresponding to join points selected by a pointcut. The extracted patterns are then applied to later versions to offer suggestions of new join points that may require inclusion. To illustrate that the motivation behind our proposal is well founded, …

Validation Of Noaa-Interactive Multisensor Snow And Ice Mapping System (Ims) By Comparison With Ground-Based Measurements Over Continental United States, Christine Chen, Tarendra Lakhankar, Peter Romanov, Sean Helfrich, Al Powell, Reza Khanbilvardi

Publications and Research

In this study, daily maps of snow cover distribution and sea ice extent produced by NOAA’s interactive multisensor snow and ice mapping system (IMS) were validated using in situ snow depth data from observing stations obtained from NOAA’s National Climatic Data Center (NCDC) for calendar years 2006 to 2010. IMS provides daily maps of snow and sea ice extent within the Northern Hemisphere using data from combination of geostationary and polar orbiting satellites in visible, infrared and microwave spectrums. Statistical correspondence between the IMS and in situ point measurements has been evaluated assuming that ground measurements are discrete and continuously …

The Mathematics Portfolio: An Alternative Tool To Evaluate Students’ Progress, Marla A. Sole

Publications and Research

This article describes the need for more thorough and varied forms of assessment to evaluate students’ level of understanding in mathematics. Portfolios are one type of assessment tool that, when added to a teacher’s repertoire can improve students’ comprehension and retention and enable students to monitor their own progress and to take more responsibility for their own learning. Portfolio assignments can also help students and teachers to detect and remedy weaknesses and misunderstandings and can increase students’ self-confidence in mathematics. This article discusses what a portfolio is, gives an example of a unit portfolio used in an undergraduate Finite Mathematics …

Empirical Mapping Of Suitability To Dengue Fever In Mexico Using Species Distribution Modeling, Elia Machado

Publications and Research

Dengue is considered the most important vector borne virus disease worldwide placing some 2.5 billion people at risk globally. Despite the public health concern about dengue fever, spatially explicit suitability assessments for this disease are limited due to data restrictions and the challenges posed by the complexity of the interactions among its risk factors, which involve social, economic and ecological processes.

This paper demonstrates an empirical approach to identify suitable areas for dengue fever using species distribution modeling, and evaluates the relative contribution of climatic and socio-economic factors as dengue fever suitability determinants. Several models showing the potential distribution of …