Search results for "numerical methods"
showing 10 items of 51 documents
Interference Effects in Photodetachment of F- in a Strong Circularly Polarized Laser Pulse
2007
A numerical simulation of photodetachment of F{sup -} by a circularly polarized laser pulse has been accomplished by using a Keldysh-type approach. The numerical results are in agreement with measurements of photoelectron energy spectra recently reported in the literature. The features exhibited by the spectra are traced back to quantum interference effects, in the same spirit as in a double-slit experiment in the time doma0008.
Memory expansion for diffusion coefficients
1998
We present a memory expansion for macroscopic transport coefficients such as the collective and tracer diffusion coefficients ${D}_{C}$ and ${D}_{T},$ respectively. The successive terms in this expansion for ${D}_{C}$ describe rapidly decaying memory effects of the center-of-mass motion, leading to fast convergence when evaluated numerically. For ${D}_{T},$ one obtains an expansion of similar form that contains terms describing memory effects in single-particle motion. As an example we evaluate ${D}_{C}$ and ${D}_{T}$ for three strongly interacting surface systems through Monte Carlo simulations, and for a simple model diffusion system via molecular dynamics calculations. We show that the n…
Analysis of equations arising in gyrotron theory
2012
The gyrotron is a microwave source whose operation is based on the stimulated cyclotron radiation of electrons oscillating in a static magnetic field. Powerful gyrotrons can be used to heat nuclear fusion plasma. In addition, they have found a wide utility in plasma diagnostics, plasma chemistry, radars, extra-high-resolution spectroscopy, high-temperature processing of materials, medicine, etc. However, the main application of gyrotrons is in electron cyclotron resonance heating in tokamaks and stellarators. Equations describing gyrotron operation are ordinary differential equations and Schrödinger type partial differential equations. The present paper provides a survey of the analytical a…
Electronic Transport in carbon nanotubes under traction, bending, torsion and misalignment of the two ends
2013
Studio delle proprietà meccaniche di compositi rinforzati con nanotubi in carbonio mediante un nuovo approccio numerico misto
2012
I CNTs primeggiano in rigidezza, resistenza a rottura, resilienza, allungamento a rottura, conducibilità termica e conducibilità elettrica. Un modo di avvantaggiarsi delle loro singolari proprietà consiste nell’incorporarli in una matrice per costruire materiali compositi nanostrutturati. Questo articolo presenta un nuovo modello misto, numerico-analitico, che consente di prevedere le caratteristiche elastiche di nanocompositi con distribuzione random dei CNTs, tenendo conto della curvatura che gli stessi mostrano quando sono immersi nel polimero. L’approccio ibrido rappresenta un’apprezzabile evoluzione della modellazione micromeccanica e può essere applicato a qualsiasi composito nanostru…
Electrical conductance in carbon nanotubes under mechanical deformation
2013
Electromechanical behavior of carbon nanotubes under traction, bending, torsion and misalignment of the two ends
2011
Carbon nanotubes (CNTs) can be metallic or semiconductors depending simply on geometric characteristics [e.g., 1]. This peculiar electronic behavior, combined with high mechanical strength, make them potential building blocks of a new nano-electronic technology. Most discussions of the electronic structure of CNTs assume perfect cylindrical symmetry, but this is somewhat of an oversimplification. High resolution images of CNTs often disclose structural deformations such as bent, twisted, or collapsed tubes. These deformations may develop during growth, deposition, and processing, or upon interaction with other CNTs, and with surfaces and surface features such as electrodes. Deformations bre…
Analysis of the Parameters Affecting the Stiffness of Short Sisal Fiber Biocomposites Manufactured by Compression-Molding
2021
The use of natural fiber-based composites is on the rise in many industries. Thanks to their eco-sustainability, these innovative materials make it possible to adapt the production of components, systems and machines to the increasingly stringent regulations on environmental protection, while at the same time reducing production costs, weight and operating costs. Optimizing the mechanical properties of biocomposites is an important goal of applied research. In this work, using a new numerical approach, the effects of the volume fraction, average length, distribution of orientation and curvature of fibers on the Young’s modulus of a biocomposite reinforced with short natural fibers were stud…
Bio-electromagnetic Numerical Modeling for Health Diagnostics
On the history of torsional stress concentrations in shafts: From electrical analogies to numerical methods
2014
This article proposes a retrospective on experimental and numerical methods developed throughout the past century to solve the torsion problem in shafts, with particular emphasis on the determination of shear stress concentration factors in discontinuities of typical use in shaft design. This article, in particular, presents the theory and related solutions distinguishing between two classes of geometries: shafts with constant cross section and axisymmetric shafts with variable diameter. Emphasis is given to approaches based on physical analog methods and, in particular, those based on electrical analogies proposed since about 1925. Experimental methods based on structural physical models …