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Articles 1 - 21 of 21
Full-Text Articles in Physics
Lysenin Channels As Sensors For Ions And Molecules, Andrew Bogard, Gamid Abatchev, Zoe Hutchinson, Jason Ward, Pangaea W. Finn, Fulton Mckinney, Daniel Fologea
Lysenin Channels As Sensors For Ions And Molecules, Andrew Bogard, Gamid Abatchev, Zoe Hutchinson, Jason Ward, Pangaea W. Finn, Fulton Mckinney, Daniel Fologea
Physics Faculty Publications and Presentations
Lysenin is a pore-forming protein extracted from the earthworm Eisenia fetida, which inserts large conductance pores in artificial and natural lipid membranes containing sphingomyelin. Its cytolytic and hemolytic activity is rather indicative of a pore-forming toxin; however, lysenin channels present intricate regulatory features manifested as a reduction in conductance upon exposure to multivalent ions. Lysenin pores also present a large unobstructed channel, which enables the translocation of analytes, such as short DNA and peptide molecules, driven by electrochemical gradients. These important features of lysenin channels provide opportunities for using them as sensors for a large variety of applications. In …
The Gauge Principle From The Schrodinger-Born Wave Mechanics, P. T. Leung
The Gauge Principle From The Schrodinger-Born Wave Mechanics, P. T. Leung
Physics Faculty Publications and Presentations
We propose an elementary way of introducing the gauge principle to beginners with a background in only mechanics, electromagnetism, and quantum mechanics. This evolves from an apparent conflict in the Schrodinger-Born formulation of wave mechanics, and does not have to resort to advanced concepts like covariant derivative and minimal coupling. With such an approach, one would have appreciated how interactions can be dictated from consideration of internal symmetry of a physical system, which serves as a principle underlying the foundation of almost all modern physics. In addition, the gauge principle also serves as a resource providing consistency between the Born …
Genetically Encoded Phase Contrast Agents For Digital Holographic Microscopy, Arash Farhadi, Manuel Bedrossian, Justin Lee, Gabrielle H. Ho, Mikhail G. Shapiro, Jay Nadeau
Genetically Encoded Phase Contrast Agents For Digital Holographic Microscopy, Arash Farhadi, Manuel Bedrossian, Justin Lee, Gabrielle H. Ho, Mikhail G. Shapiro, Jay Nadeau
Physics Faculty Publications and Presentations
Quantitative phase imaging and digital holographic microscopy have shown great promise for visualizing the motion, structure and physiology of microorganisms and mammalian cells in three dimensions. However, these imaging techniques currently lack molecular contrast agents analogous to the fluorescent dyes and proteins that have revolutionized fluorescence microscopy. Here we introduce the first genetically encodable phase contrast agents based on gas vesicles. The relatively low index of refraction of the air-filled core of gas vesicles results in optical phase advancement relative to aqueous media, making them a “positive” phase contrast agent easily distinguished from organelles, dyes, or microminerals. We demonstrate this …
Reducing A Class Of Two-Dimensional Integrals To One-Dimension With An Application To Gaussian Transforms, Jack C. Straton
Reducing A Class Of Two-Dimensional Integrals To One-Dimension With An Application To Gaussian Transforms, Jack C. Straton
Physics Faculty Publications and Presentations
Quantum theory is awash in multidimensional integrals that contain exponentials in the integration variables, their inverses, and inverse polynomials of those variables. The present paper introduces a means to reduce pairs of such integrals to one dimension when the integrand contains powers multiplied by an arbitrary function of xy/ (x + y) multiplying various combinations of exponentials. In some cases these exponentials arise directly from transition-amplitudes involving products of plane waves, hydrogenic wave functions, and Yukawa and/or Coulomb potentials. In other cases these exponentials arise from Gaussian transforms of such functions.
Electromagnetic Reciprocity In The Presence Of Topological Insulators, Huai-Yi Xie, P. T. Leung
Electromagnetic Reciprocity In The Presence Of Topological Insulators, Huai-Yi Xie, P. T. Leung
Physics Faculty Publications and Presentations
Electromagnetic reciprocity is studied in the presence of topological insulators (TI) with application of axion electrodynamics for harmonic electromagnetic fields. The corresponding generalized Lorentz and Feld-Tai type lemmas are derived in terms of the axion coupling parameter, and their correlation to the conditional symmetry in source-observer coordinates for the various Green dyadics is established subjected to different types of boundary conditions. Possible application of the results to the probing of the topological magneto-electric effects from TI is discussed.
A New Look At The Quantum Liouville Theorem, P. T. Leung, G. I. Ni
A New Look At The Quantum Liouville Theorem, P. T. Leung, G. I. Ni
Physics Faculty Publications and Presentations
We clarify certain confusions in the literature of the density operator in quantum mechanics, and demonstrate that the quantum Liouville theorem has the same form in both the Schrodinger and the Heisenberg pictures. Our starting point is to treat the density operator as an observable which has its specific time dependence in each of the two pictures. It is further shown that such a formulation will provide the exact correspondence between classical and quantum statistical mechanics with the Liouville theorem being interpreted as a conservation law, which is derivable from the equation of motion only in the quantum case.
Strain-Driven Quantum Dot Self-Assembly By Molecular Beam Epitaxy, Kathryn E. Sautter, Kevin D. Vallejo, Paul J. Simmonds
Strain-Driven Quantum Dot Self-Assembly By Molecular Beam Epitaxy, Kathryn E. Sautter, Kevin D. Vallejo, Paul J. Simmonds
Physics Faculty Publications and Presentations
Research into self-assembled semiconductor quantum dots (QDs) has helped advance numerous optoelectronic applications, ranging from solid-state lighting to photodetectors. By carefully controlling molecular beam epitaxy (MBE) growth parameters, we can readily tune QD light absorption and emission properties to access a broad portion of the electromagnetic spectrum. Although this field is now sufficiently mature that QDs are found in consumer electronics, research efforts continue to expand into new areas. By manipulating MBE growth conditions and exploring new combinations of materials, substrate orientations, and the sign of strain, a wealth of opportunities exist for synthesizing novel QD nanostructures with hitherto unavailable …
Globe-Hopping, Dmitry Chistikov, Olga Goulko, Adrian Kent, Mike Paterson
Globe-Hopping, Dmitry Chistikov, Olga Goulko, Adrian Kent, Mike Paterson
Physics Faculty Publications and Presentations
We consider versions of the grasshopper problem [1] on the circle and the sphere, which are relevant to Bell inequalities. For a circle of circumference 2π, we show that for unconstrained lawns of any length and arbitrary jump lengths, the supremum of the probability for the grasshopper’s jump to stay on the lawn is one. For antipodal lawns, which by definition contain precisely one of each pair of opposite points and have length π, we show this is true except when the jump length φ is of the form π p/q with p, q coprime …
Kinetic Exclusion Assay Of Biomolecules By Aptamer Capture, Mark H. Smith, Daniel Fologea
Kinetic Exclusion Assay Of Biomolecules By Aptamer Capture, Mark H. Smith, Daniel Fologea
Physics Faculty Publications and Presentations
DNA aptamers are short nucleotide oligomers selected to bind a target ligand with affinity and specificity rivaling that of antibodies. These remarkable features recommend aptamers as candidates for analytical and therapeutic applications that traditionally use antibodies as biorecognition elements. Numerous traditional and emerging analytical techniques have been proposed and successfully implemented to utilize aptamers for sensing purposes. In this work, we exploited the analytical capabilities offered by the kinetic exclusion assay technology to measure the affinity of fluorescent aptamers for their thrombin target and quantify the concentration of analyte in solution. Standard binding curves constructed by using equilibrated mixtures of …
Temporary Membrane Permeabilization Via The Pore-Forming Toxin Lysenin, Nisha Shrestha, Christopher A. Thomas, Devon Richtsmeier, Andrew Bogard, Rebecca Hermann, Malyk Walker, Gamid Abatchev, Raquel J. Brown, Daniel Fologea
Temporary Membrane Permeabilization Via The Pore-Forming Toxin Lysenin, Nisha Shrestha, Christopher A. Thomas, Devon Richtsmeier, Andrew Bogard, Rebecca Hermann, Malyk Walker, Gamid Abatchev, Raquel J. Brown, Daniel Fologea
Physics Faculty Publications and Presentations
Pore-forming toxins are alluring tools for delivering biologically-active, impermeable cargoes to intracellular environments by introducing large conductance pathways into cell membranes. However, the lack of regulation often leads to the dissipation of electrical and chemical gradients, which might significantly affect the viability of cells under scrutiny. To mitigate these problems, we explored the use of lysenin channels to reversibly control the barrier function of natural and artificial lipid membrane systems by controlling the lysenin’s transport properties. We employed artificial membranes and electrophysiology measurements in order to identify the influence of labels and media on the lysenin channel’s conductance. Two cell …
Analytical Results For The Three-Body Radiative Attachment Rate Coefficient, With Application To The Positive Antihydrogen Ion H̄+, Jack C. Straton
Analytical Results For The Three-Body Radiative Attachment Rate Coefficient, With Application To The Positive Antihydrogen Ion H̄+, Jack C. Straton
Physics Faculty Publications and Presentations
To overcome the numerical difficulties inherent in the Maxwell–Boltzmann integral of the velocity-weighted cross section that gives the radiative attachment rate coefficient αRA for producing the negative hydrogen ion H− or its antimatter equivalent, the positive antihydrogen ion H¯+ , we found the analytic form for this integral. This procedure is useful for temperatures below 700 K, the region for which the production of H¯+ has potential use as an intermediate stage in the cooling of antihydrogen to ultra-cold (sub-mK) temperatures for spectroscopic studies and probing the gravitational interaction of the anti-atom. Our results, utilizing a 50-term …
On The Relationship Between Dust Devil Radii And Heights, Brian Jackson
On The Relationship Between Dust Devil Radii And Heights, Brian Jackson
Physics Faculty Publications and Presentations
The influence of dust devils on the martian atmosphere depends on their capacity to loft dust, which depends on their wind profiles and footprint on the martian surface, i.e., on their radii, ��. Previous work suggests the wind profile depends on a devil’s thermodynamic efficiency, which scales with its height, ℎ. However, the precise mechanisms that set a dust devil’s radius have remained unclear. Combining previous work with simple assumptions about angular momentum conservation in dust devils predicts that �� ∝ ℎ1∕2, and a model fit to observed radii and heights from a survey of martian dust devils …
Dust Devils On Titan, Brian Jackson, Ralph D. Lorenz, Jason W. Barnes, Michelle Szurgot
Dust Devils On Titan, Brian Jackson, Ralph D. Lorenz, Jason W. Barnes, Michelle Szurgot
Physics Faculty Publications and Presentations
Conditions on Saturn's moon Titan suggest that dust devils, which are convective, dust‐laden plumes, may be active. Although the exact nature of dust on Titan is unclear, previous observations confirm an active aeolian cycle, and dust devils may play an important role in Titan's aeolian cycle, possibly contributing to regional transport of dust and even production of sand grains. The Dragonfly mission to Titan will document dust devil and convective vortex activity and thereby provide a new window into these features, and our analysis shows that associated winds are likely to be modest and pose no hazard to the mission.
Quasithermalization Of Collisionless Particles In Quadrupole Potentials, Jonathan Lau, Olga Goulko, Thomas Reimann, Daniel Suchet, Cédric Enesa, Frédéric Chevy, Carlos Lobo
Quasithermalization Of Collisionless Particles In Quadrupole Potentials, Jonathan Lau, Olga Goulko, Thomas Reimann, Daniel Suchet, Cédric Enesa, Frédéric Chevy, Carlos Lobo
Physics Faculty Publications and Presentations
We analyze several puzzling features of a recent experiment with a noninteracting gas of atoms in a quadrupole trap. After an initial momentum kick, the system reaches a stationary, quasithermal state even without collisions, due to the dephasing of individual particle trajectories. Surprisingly, the momentum distribution remains anisotropic at long times, characterized by different temperatures along the different directions. In particular, there is no transfer of the kick energy between the axial and radial trap directions. To understand these effects we discuss and solve two closely related models: a spherically symmetric trap V (r) ≃ rα and a strongly …
Conceptual Change By Fiat?, Dewey I. Dykstra
Conceptual Change By Fiat?, Dewey I. Dykstra
Physics Faculty Publications and Presentations
What Murphy and Gash are attempting to do is to solve a significant problem some students have being successful in school, one that is not often addressed in any significant way. The language used to describe the lessons has some significant departures from radical constructivism. It is, no doubt, beneficial that the students in the study may have developed improvements in self-image, but, as seen in other work, the application of radical constructivism to develop and extend the work started in the study could result in more and more lasting improvements.
Teaching Doppler Ultrasound In An Introductory Laboratory For Pre-Health Students, Theodore Stedmark, Thomas Allen, Ralf Widenhorn
Teaching Doppler Ultrasound In An Introductory Laboratory For Pre-Health Students, Theodore Stedmark, Thomas Allen, Ralf Widenhorn
Physics Faculty Publications and Presentations
We present a novel activity to demonstrate the Doppler shift of a sound wave, incident at an angle, upon a moving reflector. This activity is intended for use in an introductory physics laboratory focused on preparing students for the health and medical fields. The activity is designed to simulate Doppler velocity measurements from ultrasound imaging. While there have been previous qualitative discussions of blood flow measurements in the physics education literature, they were without associated laboratory activities.1 The lab can be part of a life science physics curriculum that has been identified in need of reforms to meet the …
Acoustics To Quantum Materials: A Centennial History Of The Department Of Physics, University Of Arkansas, Rajendra Gupta, Paul C. Sharrah
Acoustics To Quantum Materials: A Centennial History Of The Department Of Physics, University Of Arkansas, Rajendra Gupta, Paul C. Sharrah
Physics Faculty Publications and Presentations
The department of physics at the University of Arkansas was established in the 1907-08 academic year, although physics was taught from the very start of the University in 1872. The department celebrated its centennial in 2007-2008. Acoustics to Quantum Materials is a centennial history of the department covering the period 1907-08 to 2007-08. While the emphasis is on this period, instruction of physics over the period 1872-1907 is covered in two prologues, and the period 2009-18 is briefly covered in an epilogue. The first research laboratory to be established was in the area of acoustics. Subsequently, the department’s faculty have …
Enhancing Final Image Contrast In Off-Axis Digital Holography Using Residual Fringes, Manuel Bedrossian, Kent Wallace, Eugene Serabyn, Chris Lindensmith, Jay Nadeau
Enhancing Final Image Contrast In Off-Axis Digital Holography Using Residual Fringes, Manuel Bedrossian, Kent Wallace, Eugene Serabyn, Chris Lindensmith, Jay Nadeau
Physics Faculty Publications and Presentations
We show that background fringe-pattern subtraction is a useful technique for removing static noise from off-axis holographic reconstructions and can enhance image contrast in volumetric reconstructions by an order of magnitude in the case for instruments with relatively stable fringes. We demonstrate the fundamental principle of this technique and introduce some practical considerations that must be made when implementing this scheme, such as quantifying fringe stability. This work also shows an experimental verification of the background fringe subtraction scheme using various biological samples.
Membraneless H2o2 Fuel Cells Driven By Metallophthalocyanine Electrocatalysts, Bao Nguyen, Neal Kuperman, Gary Goncher, Raj Solanski
Membraneless H2o2 Fuel Cells Driven By Metallophthalocyanine Electrocatalysts, Bao Nguyen, Neal Kuperman, Gary Goncher, Raj Solanski
Physics Faculty Publications and Presentations
One-compartment hydrogen peroxide fuel cells with Co, Cu, and Fe phthalocyanine (PC) and iron nitride (FexN) as cathodes and Ni anode have been investigated as sustainable energy sources. The cells were operated under acidic conditions and at room temperature. The potentials for onset of the catalytic currents in these cells were determined via cyclic voltammograms. The reduction current onset potentials of FePC, CoPC, CuPC and FexN were 0.56 V, 0.42 V, 0.51 V and 0.57 V, respectively. Potentialcurrent linear sweep voltammetry was utilized to determine the open circuit potentials (OCP) and the power densities the fuel cells. The OCPs for …
Polarization In The Production Of The Antihydrogen Ion, Casey A. Yazejian, Jack C. Straton
Polarization In The Production Of The Antihydrogen Ion, Casey A. Yazejian, Jack C. Straton
Physics Faculty Publications and Presentations
We provide estimates of both the cross section and rate coefficient for the radiative attachment of a second positron to create the H̅+ ion, H̅(1s)+e+→H̅+(1s2 1Se)+ℏω, for which the polarization of the initial state H̅(1s) is taken into account. We show how to analytically integrate the resulting six-dimensional, three-body integrals for wave functions composed of explicitly correlated exponentials, a result that may be extended to Hylleraas wave functions. We extend Bhatia’s polarization results for the equivalent matter problem down to the low temperatures required for the Gravitational Behaviour of Antihydrogen …
Characterization Of Retinol Stabilized In Phosphatidylcholine Vesicles With And Without Antioxidants, Yekaterina G. Chmykh, Jay Nadeau
Characterization Of Retinol Stabilized In Phosphatidylcholine Vesicles With And Without Antioxidants, Yekaterina G. Chmykh, Jay Nadeau
Physics Faculty Publications and Presentations
Retinol stability has been reported to be improved by encapsulation in liposomes, both with and without cholesterol. However, this improvement is limited because of lipid peroxidation. In this study, we compare the stability of retinol in phosphatidylcholine liposomes under ultraviolet (UV) light or standard room air, with and without the addition of antioxidants. Both butylated hydroxytoluene (BHT) and a proprietary mix (StoppOx) improved the shelf stability from vesicles, including within the aqueous layer. Fluorescence lifetimes were equally heterogeneous. Under UV irradiation, StoppOx protected retinol for significantly longer than BHT and via different mechanisms. This suggests that natural antioxidants work well …