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Search Results: 1 - 10 of 174193 matches for " John B. Delos "
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Electron dynamics in parallel electric and magnetic fields
Christian Bracher,Tobias Kramer,John B. Delos
Physics , 2005, DOI: 10.1103/PhysRevA.73.062114
Abstract: We examine the spatial distribution of electrons generated by a fixed energy point source in uniform, parallel electric and magnetic fields. This problem is simple enough to permit analytic quantum and semiclassical solution, and it harbors a rich set of features which find their interpretation in the unusual and interesting properties of the classical motion of the electrons: For instance, the number of interfering trajectories can be adjusted in this system, and the turning surfaces of classical motion contain a complex array of singularities. We perform a comprehensive analysis of both the semiclassical approximation and the quantum solution, and we make predictions that should serve as a guide for future photodetachment experiments.
Growth of Gold-assisted Gallium Arsenide Nanowires on Silicon Substrates via Molecular Beam Epitaxy
Ramon M. delos Santos,Jasher John A. Iba?es,Joel G. Fernando,Rafael B. Jaculbia
Science Diliman , 2008,
Abstract: Gallium arsenide nanowires were grown on silicon (100) substrates by what is called the vapor-liquid-solid (VLS) growth mechanism using a molecular beam epitaxy (MBE) system. Good quality nanowires with surface density of approximately 108 nanowires per square centimeter were produced by utilizing gold nanoparticles, with density of 1011 nanoparticles per square centimeter, as catalysts for nanowire growth. X-ray diffraction measurements, scanning electron microscopy, transmission electron microscopy and Raman spectroscopy revealed that the nanowires are epitaxially grown on the silicon substrates, are oriented along the [111] direction and have cubic zincblende structure.
The photoelectric effect in external fields
Christian Bracher,John B. Delos,Vassiliki Kanellopoulos,Manfred Kleber,Tobias Kramer
Physics , 2006, DOI: 10.1016/j.physleta.2005.06.107
Abstract: Atoms and negative ions interacting with laser photons yield a coherent source of photoelectrons. Applying external fields to photoelectrons gives rise to interesting and valuable interference phenomena. We analyze the spatial distribution of the photocurrent using elementary quantum methods. The photoelectric effect is shown to be an interesting example for the use of coherent particle sources in quantum mechanics.
Matter, Energy, and Heat Transfer in a Classical Ballistic Atom Pump
Tommy A. Byrd,Kunal K. Das,Kevin A. Mitchell,Seth Aubin,John B. Delos
Physics , 2015, DOI: 10.1103/PhysRevE.90.052107
Abstract: A ballistic atom pump is a system containing two reservoirs of neutral atoms or molecules and a junction connecting them containing a localized time-varying potential. Atoms move through the pump as independent particles. Under certain conditions, these pumps can create net transport of atoms from one reservoir to the other. While such systems are sometimes called "quantum pumps," they are also models of classical chaotic transport, and their quantum behavior cannot be understood without study of the corresponding classical behavior. Here we examine classically such a pump's effect on energy and temperature in the reservoirs, in addition to net particle transport. We show that the changes in particle number, of energy in each reservoir, and of temperature in each reservoir vary in unexpected ways as the incident particle energy is varied.
Scattering by an oscillating barrier: quantum, classical, and semiclassical comparison
Tommy A. Byrd,Megan K. Ivory,Andrew J. Pyle,Seth Aubin,Kevin A. Mitchell,John B. Delos,Kunal K. Das
Physics , 2012, DOI: 10.1103/PhysRevA.86.013622
Abstract: We present a detailed study of scattering by an amplitude-modulated potential barrier using three distinct physical frameworks: quantum, classical, and semiclassical. Classical physics gives bounds on the energy and momentum of the scattered particle, while also providing the foundation for semiclassical theory. We use the semiclassical approach to selectively add quantum-mechanical effects such as interference and diffraction. We find good agreement between the quantum and semiclassical momentum distributions. Our methods and results can be used to understand quantum and classical aspects of transport mechanisms involving time-varying potentials, such as quantum pumping.
Ballistic atom pumps
Megan K. Ivory,Tommy A. Byrd,Andrew J. Pyle,Kunal K. Das,Kevin A. Mitchell,Seth Aubin,John B. Delos
Physics , 2015, DOI: 10.1103/PhysRevA.90.023602
Abstract: We examine a classically-chaotic system consisting of two reservoirs of particles connected by a channel containing oscillating potential-energy barriers. We investigate whether such a system can preferentially pump particles from one reservoir to the other, a process often called "quantum pumping." We show how to make a "particle diode" which under specified conditions permits net particle pumping in only one direction. Then we examine systems having symmetric barriers. We find that if all initial particle energies are considered, a system with symmetric barriers cannot preferentially pump particles. However, if only finite initial energy bands are considered, the system can create net particle transport in either direction. We study the system classically, semiclassically, and quantum mechanically, and find that the quantum description cannot be fully understood without the insight gained from classical and semiclassical analysis.
Minkowski Sum of Polytopes Defined by Their Vertices  [PDF]
Vincent Delos, Denis Teissandier
Journal of Applied Mathematics and Physics (JAMP) , 2015, DOI: 10.4236/jamp.2015.31008
Abstract:

Minkowski sums are of theoretical interest and have applications in fields related to industrial backgrounds. In this paper we focus on the specific case of summing polytopes as we want to solve the tolerance analysis problem described in [1]. Our approach is based on the use of linear programming and is solvable in polynomial time. The algorithm we developed can be implemented and parallelized in a very easy way.

Photodetachment near a repulsive center
B. C. Yang,J. B. Delos,M. L. Du
Physics , 2013,
Abstract: We study the total photodetachment cross section of H$^-$ near a repulsive center. An analytical formula for the photodetachment cross section is obtained using the standard closed-orbit theory and extending it to the energy range below the zero-field threshold. The formula is found to be accurate by comparing with an exact quantum calculation. A comparison with the photodetachment cross section in an effective homogeneous electric field is made, and we discuss the similarities and differences of the two systems.
Geometry and Topology of Escape I: Epistrophes
K. A. Mitchell,J. P. Handley,B. Tighe,S. K. Knudson,J. B. Delos
Physics , 2003, DOI: 10.1063/1.1598311
Abstract: We consider a dynamical system given by an area-preserving map on a two-dimensional phase plane and consider a one-dimensional line of initial conditions within this plane. We record the number of iterates it takes a trajectory to escape from a bounded region of the plane as a function along the line of initial conditions, forming an ``escape-time plot''. For a chaotic system, this plot is in general not a smooth function, but rather has many singularities at which the escape time is infinite; these singularities form a complicated fractal set. In this article we prove the existence of regular repeated sequences, called ``epistrophes'', which occur at all levels of resolution within the escape-time plot. (The word ``epistrophe'' comes from rhetoric and means ``a repeated ending following a variable beginning''.) The epistrophes give the escape-time plot a certain self-similarity, called ``epistrophic'' self-similarity, which need not imply either strict or asymptotic self-similarity.
Geometry and Topology of Escape II: Homotopic Lobe Dynamics
K. A. Mitchell,J. P. Handley,S. K. Knudson,J. B. Delos
Physics , 2003, DOI: 10.1063/1.1598312
Abstract: We continue our study of the fractal structure of escape-time plots for chaotic maps. In the preceding paper, we showed that the escape-time plot contains regular sequences of successive escape segments, called epistrophes, which converge geometrically upon each endpoint of every escape segment. In the present paper, we use topological techniques to: (1) show that there exists a minimal required set of escape segments within the escape-time plot; (2) develop an algorithm which computes this minimal set; (3) show that the minimal set eventually displays a recursive structure governed by an ``Epistrophe Start Rule'': a new epistrophe is spawned Delta = D+1 iterates after the segment to which it converges, where D is the minimum delay time of the complex.
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