Physics Commons^™

Higher-Order Power Harmonics Of Pulsed Electrical Stimulation Modulates Corticospinal Contribution Of Peripheral Nerve Stimulation, Chiun-Fan Chen, Marom Bikson, Li-Wei Chou, Chunlei Shan, Niranjan Khadka, Wen-Shiang Chen, Felipe Fregni

Engineering Science Faculty Publications

It is well established that electrical-stimulation frequency is crucial to determining the scale of induced neuromodulation, particularly when attempting to modulate corticospinal excitability. However, the modulatory effects of stimulation frequency are not only determined by its absolute value but also by other parameters such as power at harmonics. The stimulus pulse shape further influences parameters such as excitation threshold and fiber selectivity. The explicit role of the power in these harmonics in determining the outcome of stimulation has not previously been analyzed. In this study, we adopted an animal model of peripheral electrical stimulation that includes an amplitude-adapted pulse train …

Deformation But Not Migration And Rotation – A Model Study On Vesicle Biomechanics In A Uniform Dc Electric Field, Hui Ye, Austen Curcuru

Biology: Faculty Publications and Other Works

Background: Biological cells migrate, deform and rotate in various types of electric fields, which have significant impact on the normal cellular physiology. To investigate electrically-induced deformation, researchers have used artificial giant vesicles that mimic the phospholipid bilayer cell membrane. Containing primarily the neutral molecule phosphatidylcholine, these vesicles deformed under evenly distributed, strong direct current (DC) electric fields. Interestingly, they did not migrate or rotate. A biophysical mechanism underlying the kinematic differences between the biological cells and the vesicles under electric stimulation has not been worked out.

Methods: We modeled the vesicle as a leaky, dielectric sphere and computed …

The Motion Of Two Identical Masses Connected By An Ideal String Symmetrically Placed Over A Corner, Asim Gangopadhyaya, Constantin Rasinariu

Physics: Faculty Publications and Other Works

We introduce a novel, two-mass system that slides up an inclined plane while its center of mass moves down. The system consists of two identical masses connected by an ideal string symmetrically placed over a corner-shaped support. This system is similar to a double-cone that rolls up an inclined set of V-shaped rails. We find the double-cone's motion easy to demonstrate but difficult to analyze. Our example here is more straightforward to follow, and the experimental observations are in good agreement with the theoretical predictions.

Easily Accessible Experiments Demonstrating Interference, Robert Polak, Nicolette Fudala, Jason T. Rothchild, Marcin Zelek

Physics: Faculty Publications and Other Works

A brief but detailed description of simple experiments to be used in Physics classrooms.

Generation Of A Novel Exactly Solvable Potential, Jonathan Bougie, Asim Gangopadhyaya, Jeffry V. Mallow, Emeritus, Constantin Rasinariu

Physics: Faculty Publications and Other Works

We report a new shape-invariant (SI) isospectral extension of the Morse potential. Previous investigations have shown that the list of “conventional” SI superpotentials that do not depend explicitly on Planck's constant ħ is complete. Additionally, a set of “extended” superpotentials has been identified, each containing a conventional superpotential as a kernel and additional ħ-dependent terms. We use the partial differential equations satisfied by all SI superpotentials to find a SI extension of Morse with novel properties. It has the same eigenenergies as Morse but different asymptotic limits, and does not conform to the standard generating structure for isospectral deformations.

Dead-Box Helicase Proteins Disrupt Rna Tertiary Structure Through Helix Capture, Cynthia Pan, Jeffrey P. Potratz, Brian Cannon, Zachary B. Simpson, Jessica L. Ziehr, Pilar Tijerina, Rick Russell

Physics: Faculty Publications and Other Works

DEAD-box helicase proteins accelerate folding and rearrangements of highly structured RNAs and RNA–protein complexes (RNPs) in many essential cellular processes. Although DEAD-box proteins have been shown to use ATP to unwind short RNA helices, it is not known how they disrupt RNA tertiary structure. Here, we use single molecule fluorescence to show that the DEAD-box protein CYT-19 disrupts tertiary structure in a group I intron using a helix capture mechanism. CYT-19 binds to a helix within the structured RNA only after the helix spontaneously loses its tertiary contacts, and then CYT-19 uses ATP to unwind the helix, liberating the product …

Low-Cost Student Experiments In Optics, Robert Polak, Austin J. Cua, Daniel J. Perez, Mallory Q. Robertson, Justin A. Stuck, Jordan M. Thomas

Physics: Faculty Publications and Other Works

No abstract provided.

Molecular Interactions With Ice: Molecular Embedding, Adsorption, Detection, And Release, K D. Gibson, Grant G. Langlois, Wenxin Li, Daniel Killelea, S J. Sibener

Chemistry: Faculty Publications and Other Works

The interaction of atomic and molecular species with water and ice is of fundamental importance for chemistry. In a previous series of publications, we demonstrated that translational energy activates the embedding of Xe and Kr atoms in the near surface region of ice surfaces. In this paper, we show that inert molecular species may be absorbed in a similar fashion.We also revisit Xe embedding, and further probe the nature of the absorption into the selvedge. CF4 molecules with high translational energies (≥3 eV) were observed to embed in amorphous solid water. Just as with Xe, the initial adsorption rate is …

The Physics Of Music Course As An Introduction To Science, Gordon Ramsey

Physics: Faculty Publications and Other Works

Our Physics of Music course is an integration of physics and music. We start with the mathematical structure of music, including scales, harmonies and chords. We discuss musical styles and how they differ. After an introduction of physics concepts, including waves,resonances, forces, energy and fluid flow, the physical structure of instruments in the various groups are studied. Connection is made of the instruments and how they reproduce the mathematical nature of music. Finally, venue acoustics are investigated. The course integrates different styles of learning by integrating different learning modes. The classes include lecture/demonstration, discussion, in-class laboratories and a final individual …

Cosmological Constant As Confining U(1) Charge In Two-Dimensional Dilaton Gravity, Daniel Grumiller, Robert A. Mcnees Iv, Jakob Salzer

Physics: Faculty Publications and Other Works

The cosmological constant is treated as a thermodynamical parameter in the framework of two-dimensional dilaton gravity. We find that the cosmological constant behaves as a U(1) charge with a confining potential, and that such potentials require a novel Born-Infeld boundary term in the action. The free energy and other thermodynamical quantities of interest are derived, from first principles, in a way that is essentially model independent. We discover that there is always a Schottky anomaly in the specific heat and explain its physical origin. Finally, we apply these results to specific examples, like anti-de Sitter–Schwarzschild–Tangherlini black holes, Bañados-Teitelboim-Zanelli black holes …

The Electric Field At The Chargeless Interface Between Two Regions Of Space, Asim Gangopadhyaya, Robert Mcnees

Physics: Faculty Publications and Other Works

A common method for solving Poisson's equation in electrostatics is to patch together two or more solutions of Laplace's equation using boundary conditions on the potential and its gradient. Other methods may generate solutions without the need to check these conditions explicitly, and reconciling these solutions with the appropriate boundary conditions can be surprisingly subtle. As a result, a student may arrive at paradoxical conclusions—even in the case of elementary problems—that seem to be at odds with basic physical intuition. We illustrate this issue by showing how the potential of a uniformly charged ring appears to violate continuity of the …

Magnet Traveling Through A Conducting Pipe: A Variation On The Analytical Approach, Benjamin Irvine, Matthew Kemnetz, Asim Gangopadhyaya, Thomas Ruubel

Physics: Faculty Publications and Other Works

We present an analytical study of magnetic damping. In particular, we investigate the dynamics of a cylindrical neodymium magnet as it moves through a conducting tube. Owing to the very high degree of uniformity of the magnetization for neodymium magnets, we are able to provide completely analytical results for the electromotive force generated in the pipe and the consequent retarding force. Our analytical expressions are shown to have excellent agreement with experimental observations.

Conformal Gravity Holography In Four Dimensions, Daniel Grumiller, Maria Irakleidou, Iva Lovrekovic,, Robert Mcnees

Physics: Faculty Publications and Other Works

We formulate four-dimensional conformal gravity with (anti–)de Sitter boundary conditions that are weaker than Starobinsky boundary conditions, allowing for an asymptotically subleading Rindler term concurrent with a recent model for gravity at large distances. We prove the consistency of the variational principle and derive the holographic response functions. One of them is the conformal gravity version of the Brown–York stress tensor, the other is a “partially massless response”. The on shell action and response functions are finite and do not require holographic renormalization. Finally, we discuss phenomenologically interesting examples, including the most general spherically symmetric solutions and rotating black hole …

Response To David Quigley, John D. Cunningham

Physics: Faculty Publications and Other Works

No abstract provided.

On The Origin Of Mode- And Bond-Selectivity In Vibrationally Mediated Reactions On Surfaces, Daniel Killelea, Arthur L. Utz

Chemistry: Faculty Publications and Other Works

The experimental observations of vibrational mode- and bond-selective chemistry at the gas–surface interface indicate that energy redistribution within the reaction complex is not statistical on the timescale of reaction. Such behavior is a key prerequisite for efforts to use selective vibrational excitation to control chemistry at the technologically important gas–surface interface. This paper outlines a framework for understanding the origin of non-statistical reactivity on surfaces. The model focuses on the kinetic competition between intramolecular vibrational energy redistribution (IVR) within the reaction complex, which in the long-time limit leads to statistical behavior, and quenching, scattering, or desorption processes that restrict the …

Unintended Consequences Of Imprecise Notation – An Example From Mechanics, Asim Gangopadhyaya, Gordon Ramsey

Physics: Faculty Publications and Other Works

We present a conundrum that results from the imprecise use of notation for partial derivatives. Taking an example from mechanics, we show that lack of proper care in re presenting partial derivatives in Lagrangian and Hamiltonian formulations paradoxically leads to two different values for the time derivative of the canonical momentum. This problem also exists in other areas of physics,such as thermodynamics.

The Harmonica As A Blues Instrument, Gordon Ramsey, Christopher Banaszak, Joseph Wiseman

Physics: Faculty Publications and Other Works

The modern harmonica,or harp, has been around since the early 19th century. It is typically used in blues, country, rock and roll and folk music. These musical genres are somewhat similar in structure and form, and often borrow ideas from each other. The harmonica is appropriate as a back up to the main vocal melody and instruments due to its rich harmonic structure and subdued intensity. The ability to apply vibrato and gradual slurs make it a perfect instrument to achieve a ``bluesy" sound. Our harp research group has investigated the physical properties of harmonica structure to illustrate how different …

Black Holes In The Conical Ensemble, Robert A. Mcnees Iv, Daniel Grumiller

Physics: Faculty Publications and Other Works

We consider black holes in an “unsuitable box”: a finite cavity coupled to a thermal reservoir at a temperature different than the black hole’s Hawking temperature. These black holes are described by metrics that are continuous but not differentiable due to a conical singularity at the horizon. We include them in the Euclidean path integral sum over configurations, and analyze the effect this has on black hole thermodynamics in the canonical ensemble. Black holes with a small deficit (or surplus) angle may have a smaller internal energy or larger density of states than the nearby smooth black hole, but they …

Supersymmetric Quantum Mechanics And Solvable Models, Asim Gangopadhyaya, Jonathan Bougie, Jeffrey Mallow, C. Rasinariu

Physics: Faculty Publications and Other Works

We review solvable models within the framework of supersymmetric quantum mechanics (SUSYQM). In SUSYQM, the shape invariance condition insures solvability of quantum mechanical problems. We review shape invariance and its connection to a consequent potential algebra. The additive shape invariance condition is specified by a difference-differential equation; we show that this equation is equivalent to an infinite set of partial differential equations. Solving these equations, we show that the known list of h-independent superpotentials is complete. We then describe how these equations could be extended to include superpotentials that do depend on h.

Barn And Pole Paradox: Revisited, Robert Cacioppo, Asim Gangopadhyaya

Physics: Faculty Publications and Other Works

We present two different paradoxes related to the length contraction in special relativity and explain their resolution.

Holographic Renormalization Of Asymptotically Lifshitz Spacetimes, Robert A. Mcnees Iv, Robert Mann

Physics: Faculty Publications and Other Works

A variational formulation is given for a theory of gravity coupled to a massive vector in four dimensions, with Asymptotically Lifshitz boundary conditions on the fields. For theories with critical exponent z=2 we obtain a well-defined variational principle by explicitly constructing two actions with local boundary counterterms. As part of our analysis we obtain solutions of these theories on a neighborhood of spatial infinity, study the asymptotic symmetries, and consider different definitions of the boundary stress tensor and associated charges. A constraint on the boundary data for the fields figures prominently in one of our formulations, and in that case …

Method For Generating Additive Shape Invariant Potentials From An Euler Equation, Jonathan Bougie, Asim Gangopadhyaya, Jeffrey Mallow

Physics: Faculty Publications and Other Works

In the supersymmetric quantum mechanics formalism, the shape invariance condition provides a sufficient constraint to make a quantum mechanical problem solvable; i.e., we can determine its eigenvalues and eigenfunctions algebraically. Since shape invariance relates superpotentials and their derivatives at two different values of the parameter a, it is a non-local condition in the coordinate-parameter (x,a) space. We transform the shape invariance condition for additive shape invariant superpotentials into two local partial differential equations. One of these equations is equivalent to the one-dimensional Euler equation expressing momentum conservation for inviscid fluid flow. The second equation provides the constraint that helps us …

Exceptional Orthogonal Polynomials, Qhj Formalism And Swkb Quantization Condition, S Ree Ranjani, P K. Panigrahi, A Khare, A K. Kapoor, Asim Gangopadhyaya

Physics: Faculty Publications and Other Works

We study the quantum Hamilton-Jacobi (QHJ) equation of the recently obtained exactly solvable models, related to the newly discovered exceptional polynomials and show that the QHJ formalism reproduces the exact eigenvalues and the eigenfunctions. The fact that the eigenfunctions have zeros and poles in complex locations leads to an unconventional singularity structure of the quantum momentum function p(x), the logarithmic derivative of the wave function, which forms the crux of the QHJ approach to quantization. A comparison of the singularity structure for these systems with the known exactly solvable and quasi-exactly solvable models reveals interesting differences. We find that the …

Generation Of A Complete Set Of Additive Shape-Invariant Potentials From An Euler Equation, Jonathan Bougie, Asim Gangopadhyaya, Jeffrey Mallow

Physics: Faculty Publications and Other Works

In supersymmetric quantum mechanics, shape invariance is a sufficient condition for solvability. We show that all conventional additive shape-invariant superpotentials that are independent of ħ can be generated from two partial differential equations. One of these is equivalent to the one-dimensional Euler equation expressing momentum conservation for inviscid fluid flow, and it is closed by the other. We solve these equations, generate the set of all conventional shape-invariant superpotentials, and show that there are no others in this category. We then develop an algorithm for generating all additive shape-invariant superpotentials including those that depend on ħ explicitly.

Simultaneous Measurements Of Electronic Conduction And Raman Response In Molecular Junctions, Daniel R. Ward, Naomi J. Halas, James M. Tour, Jacob W. Ciszek, Yanpeng Wu, Peter Nordlander, Douglas Natelson

Chemistry: Faculty Publications and Other Works

Electronic conduction through single molecules is affected by the molecular electronic structure as well as by other information that is extremely difficult to assess, such as bonding geometry and chemical environment. The lack of an independent diagnostic technique has long hampered single-molecule conductance studies. We report simultaneous measurement of the conductance and the Raman spectra of nanoscale junctions used for single-molecule electronic experiments. Blinking and spectral diffusion in the Raman response of both para-mercaptoaniline and a fluorinated oligophenylyne ethynylene correlate in time with changes in the electronic conductance. Finite difference time domain calculations confirm that these correlations do not result …

Shape Invariance And The Exactness Of Quantum Hamilton-Jacobi Formalism, Charles Cherqui, Yevgeny Binder, Asim Gangopadhyaya

Physics: Faculty Publications and Other Works

Quantum Hamilton-Jacobi Theory and supersymmetric quantum mechanics (SUSYQM) are two parallel methods to determine the spectra of a quantum mechanical systems without solving the Schr ̈odinger equation. It was recently shown that the shape invariance, which is an integrability condition in SUSYQM formalism, can be utilized to develop an iterative algorithm to determine the quantum momentum functions. In this paper, we show that shape invariance also suffices to determine the eigenvalues in Quantum Hamilton-Jacobi Theory.

Shape Invariance In Supersymmetric Quantum Mechanics And Its Application To Selected Special Functions Of Modern Physics, Chad Husko, Brenton Knuffman, Asim Gangopadhyaya, Jeffrey Mallow

Physics: Faculty Publications and Other Works

We applied the methods of supersymmetric quantum mechanics to differential equations that generate well-known special functions of modern physics. This application provides new insight into these functions and generates recursion relations among them. Some of these recursion relations are apparently new (or forgotten), as they are not available in commonly used texts and handbooks. This method can be easily extended to explore other special functions of modern physics.

Exactly Solvable Systems And The Quantum Hamilton Jacobi Formalism, C. Rasinariu, John J. Dykla, Asim Gangopadhyaya, Jeffrey Mallow

Physics: Faculty Publications and Other Works

We connect Quantum Hamilton-Jacobi Theory with supersymmetric quantum mechanics (SUSYQM). We show that the shape invariance, which is an integrability condition of SUSYQM, translates into fractional linear relations among the quantum momentum functions.

Reply To “Comment On Gravitational Slingshot,” By C. L. Cook [Am. J. Phys. 73 (4), 363 (2005)], Asim Gangopadhyaya, Asim Gangopadhyaya, Robert Cacioppo, John J. Dykla

Physics: Faculty Publications and Other Works

No abstract provided.

Gravitational Slingshot , John J. Dykla, Robert Cacioppo, Asim Gangopadhyaya

Physics: Faculty Publications and Other Works

The slingshot effect is an intriguing phenomenon that has been used effectively by NASA to send spacecraft to outer edges of the solar system. This phenomenon can be satisfactorily explained by Newtonian physics. However, if it is presented as a problem involving four-momentum conservation, the methods of relativistic kinematics easily lead to the conditions necessary for an accelerating as well as a retarding scenario. This problem provides an example that showcases the frequent utility of relativistic methods to analyze problems of Newtonian mechanics.