Lattice Dynamical Model for Graphite-Bromine Intercalation Compounds

1982 ◽  
Vol 20 ◽  
Author(s):  
R. Al-Jishi ◽  
G. Dresselhaus
Keyword(s):  
Brillouin Zone ◽  
High Frequency ◽  
Low Frequency ◽  
Unit Cell ◽  
Intercalation Compounds ◽  
Dynamical Model ◽  
Von Karman ◽  
Zone Folding ◽  
Von Kármán ◽  
Brillouin Zone Center

ABSTRACTA Born-von Kármán lattice dynamical model for the graphite Br2 intercalation compounds is presented. The low frequency bromine branches are calculated using a commensurate (√3 × √13)R(30°, 13.9°) unit cell with two Br2 molecules/unit cell. In-plane zone folding is used to calculate the high frequency graphitic modes at the Brillouin zone center.

Theoretical Modeling of the N-H and N-D Stretching Bands of Hydrogen-Bonded 1-Methylthymine Crystal and Its Deuterated Form

2006 ◽  
Vol 2 (4) ◽  
pp. 205-219
Author(s):  
Marek Boczar ◽  
Łukasz Boda ◽  
Marek J. Wójcik
Keyword(s):  
Hydrogen Bonds ◽  
High Frequency ◽  
Molecular Crystals ◽  
Low Frequency ◽  
Unit Cell ◽  
Fermi Resonance ◽  
Bending Vibrations ◽  
Theoretical Simulation ◽  
Stretching Vibrations ◽  
Centrosymmetric Dimers

Theoretical model for vibrational interactions in the hydrogen bonds in molecular crystals with four molecules forming two centrosymmetric dimers in the unit cell is presented. The model takes into account anharmonic-type couplings between the high-frequency N-H(D) and the low-frequency N•••O stretching vibrations in each hydrogen bond, resonance interactions (Davydov coupling) between equivalent hydrogen bonds in each dimer, resonance interdimer interactions within an unit cell and Fermi resonance between the N-H(D) stretching fundamental and the first overtone of the N-H(D) in-plane bending vibrations. The vibrational Hamiltonian, selection rules, and expressions for the integral properties of an absorption spectrum are derived. The model is used for theoretical simulation of the νs stretching bands of 1-methylthymine and its ND derivative at 300 K. The effect of deuteration is successfully reproduced by our model.

scholarly journals Cavity flows control by High Frequency Forcing

2012 ◽  
Author(s):  
◽  
Mariano Álvaro Martínez
Keyword(s):  
High Frequency ◽  
Cavity Flows ◽  
Von Karman ◽  
Von Kármán

En la superficie de vehículos, tales como aviones, automóviles y trenes, las cavidades abiertas son una importante fuente de ruido generado aerodinámicamente, de aumento de la resistencia y de peligrosas fluctuaciones de presión. Diversos métodos han sido probados para suprimir estos efectos no deseados; algunos de los cuales han logrado un éxito parcial. En general, puede observarse que los métodos que son simples, económicos y fáciles de aplicar logran un efecto limitado a un rango operacional pequeño, mientras que aquellos que ofrecen un rango operacional más amplio son complejos y onerosos. Recientemente se ha descubierto que excitando el flujo a altas frecuencias es posible suprimir los efectos no deseados en un amplio rango de condiciones de flujo. Además, este forzado puede ser generado por una simple estela de Von Karman. De este modo ambas ventajas, simplicidad y amplio rango operacional, pueden ser logradas al mismo tiempo. El mecanismo físico subyacente al Control de Flujo en Cavidades por Forzado de Alta Frecuencia no está claramente comprendido aún. El autor de la presente tesis se propone ofrecer una explicación física para el mismo, basada en el análisis de los datos adquiridos con la técnica de PIV resuelto en el tiempo.

A Born–von Karman Force Constant Model for Aluminum

1974 ◽  
Vol 52 (17) ◽  
pp. 1714-1715 ◽  
Author(s):  
E. R. Cowley
Keyword(s):  
Experimental Data ◽  
Distribution Function ◽  
Force Constant ◽  
Frequency Distribution ◽  
Brillouin Zone ◽  
Normal Modes ◽  
Frequency Distribution Function ◽  
Von Karman ◽  
Von Kármán ◽  
Good Agreement

A Born–von Karman force constant model of aluminum, fitted to the frequencies of normal modes with wave vectors distributed throughout the Brillouin zone, is described, and the frequency distribution function calculated. The result is in very good agreement with a distribution function calculated directly from the experimental data.

Analysis and characterisation of momentum and thermal wakes of elliptic cylinders

2016 ◽  
Vol 807 ◽  
pp. 303-323 ◽  
Author(s):  
I. Paul ◽  
K. Arul Prakash ◽  
S. Vengadesan ◽  
V. Pulletikurthi
Keyword(s):  
Low Frequency ◽  
Vortex Street ◽  
Immersed Boundary ◽  
Governing Equations ◽  
Primary Vortex ◽  
Transport Models ◽  
Von Karman ◽  
Number Variation ◽  
Von Kármán ◽  
Far Wake

Non-canonical wakes of two-dimensional elliptic cylinders are analysed numerically for their near- and far-wake characteristics. The governing equations are solved using an immersed boundary method based projection scheme. The wakes are then classified into three distinct types according to diverse flow and thermal properties. An unexpected mean temperature evolution along the centreline of the wake is observed for certain wake states. In order to explain this unusual variation, novel heat transport models are constructed based on the vortex dynamics. These models are derived by considering vorticity is acted by flow, which has shear and swirl. Mechanisms of the primary vortex street breakdown and formation of the secondary vortex street are also proposed based on these models. A new phenomenon namely ‘dual near-wall instantaneous recirculation’ is observed, and its appearance is found to be a function of length of the primary von Kármán vortex street. The same phenomenon is also found to be responsible for the secondary peak in the Nusselt number variation along the circumference of the cylinder. Despite varied differences between the wake types, it is observed that the transitions occur through a supercritical Hopf bifurcation in all of them, at least in the von Kármán region of the wake. Low-frequency unsteadiness observed in the far wakes is examined through a signal decomposition method. Our results show that the secondary low frequency is resulting from the transition region which has a negative instability slope. Finally, onset of the primary vortex street breakdown and its scale in terms of Reynolds number is computed.

Second-Order Raman Scattering in Graphite Intercalation Compounds

1982 ◽  
Vol 20 ◽  
Author(s):  
J. Giergiel ◽  
P. C. Eklund
Keyword(s):  
Raman Scattering ◽  
Lattice Dynamics ◽  
Second Order ◽  
Intercalation Compounds ◽  
Graphite Intercalation Compounds ◽  
Von Karman ◽  
Graphite Intercalation ◽  
Von Kármán

ABSTRACTThe stage dependence of various second-order Raman features observed for acceptor (FeCl3, SbCl5) and donor (Rb) Graphite Intercalation Compounds is reported and discussed in terms of recent Born-von Kármán lattice dynamics calculations of Al-Jishi and Dresselhaus.

Simulations of high-resolution images of amorphous silicon films

1986 ◽  
Vol 44 ◽  
pp. 544-545
Author(s):  
G. Y. Fan ◽  
J. M. Cowley
Keyword(s):  
Electron Microscope ◽  
High Frequency ◽  
Fourier Transformation ◽  
Amorphous Materials ◽  
Low Frequency ◽  
Chromatic Aberration ◽  
Structure Information ◽  
Frequency Components ◽  
High Resolution Images ◽  
Spatial Frequency Spectrum

It is well known that the structure information on the specimen is not always faithfully transferred through the electron microscope. Firstly, the spatial frequency spectrum is modulated by the transfer function (TF) at the focal plane. Secondly, the spectrum suffers high frequency cut-off by the aperture (or effectively damping terms such as chromatic aberration). While these do not have essential effect on imaging crystal periodicity as long as the low order Bragg spots are inside the aperture, although the contrast may be reversed, they may change the appearance of images of amorphous materials completely. Because the spectrum of amorphous materials is continuous, modulation of it emphasizes some components while weakening others. Especially the cut-off of high frequency components, which contribute to amorphous image just as strongly as low frequency components can have a fundamental effect. This can be illustrated through computer simulation. Imaging of a whitenoise object with an electron microscope without TF limitation gives Fig. 1a, which is obtained by Fourier transformation of a constant amplitude combined with random phases generated by computer.

SEM image sharpness analysis

1996 ◽  
Vol 54 ◽  
pp. 142-143
Author(s):  
M. T. Postek ◽  
A. E. Vladar
Keyword(s):  
High Frequency ◽  
Low Frequency ◽  
Quantitative Information ◽  
Primary Electron ◽  
Image Sharpness ◽  
Critical Dimensions ◽  
Sem Image ◽  
Frequency Changes ◽  
Electron Microscopes ◽  
Scanning Electron

Fully automated or semi-automated scanning electron microscopes (SEM) are now commonly used in semiconductor production and other forms of manufacturing. The industry requires that an automated instrument must be routinely capable of 5 nm resolution (or better) at 1.0 kV accelerating voltage for the measurement of nominal 0.25-0.35 micrometer semiconductor critical dimensions. Testing and proving that the instrument is performing at this level on a day-by-day basis is an industry need and concern which has been the object of a study at NIST and the fundamentals and results are discussed in this paper.In scanning electron microscopy, two of the most important instrument parameters are the size and shape of the primary electron beam and any image taken in a scanning electron microscope is the result of the sample and electron probe interaction. The low frequency changes in the video signal, collected from the sample, contains information about the larger features and the high frequency changes carry information of finer details. The sharper the image, the larger the number of high frequency components making up that image. Fast Fourier Transform (FFT) analysis of an SEM image can be employed to provide qualitiative and ultimately quantitative information regarding the SEM image quality.

Real Ear Sound Pressure Levels Developed by Three Portable Stereo System Earphones

1992 ◽  
Vol 1 (4) ◽  
pp. 52-55 ◽  
Author(s):  
Gail L. MacLean ◽  
Andrew Stuart ◽  
Robert Stenstrom
Keyword(s):  
High Frequency ◽  
Sound Pressure ◽  
Low Frequency ◽  
Test System ◽  
Output Frequency ◽  
Frequency Effects ◽  
Adult Men ◽  
Frequency Responses ◽  
Significant Difference ◽  
Sound Pressure Levels

Differences in real ear sound pressure levels (SPLs) with three portable stereo system (PSS) earphones (supraaural [Sony Model MDR-44], semiaural [Sony Model MDR-A15L], and insert [Sony Model MDR-E225]) were investigated. Twelve adult men served as subjects. Frequency response, high frequency average (HFA) output, peak output, peak output frequency, and overall RMS output for each PSS earphone were obtained with a probe tube microphone system (Fonix 6500 Hearing Aid Test System). Results indicated a significant difference in mean RMS outputs with nonsignificant differences in mean HFA outputs, peak outputs, and peak output frequencies among PSS earphones. Differences in mean overall RMS outputs were attributed to differences in low-frequency effects that were observed among the frequency responses of the three PSS earphones. It is suggested that one cannot assume equivalent real ear SPLs, with equivalent inputs, among different styles of PSS earphones.

Evaluation of Special Hearing Aids for Deaf Children

1971 ◽  
Vol 36 (4) ◽  
pp. 527-537 ◽  
Author(s):  
Norman P. Erber
Keyword(s):  
Hearing Aids ◽  
High Frequency ◽  
Hearing Aid ◽  
Low Frequency ◽  
Acoustic Stimulation ◽  
Deaf Children ◽  
Frequency Range ◽  
Frequency Limit ◽  
Unpublished Studies ◽  
Published Research

Two types of special hearing aid have been developed recently to improve the reception of speech by profoundly deaf children. In a different way, each special system provides greater low-frequency acoustic stimulation to deaf ears than does a conventional hearing aid. One of the devices extends the low-frequency limit of amplification; the other shifts high-frequency energy to a lower frequency range. In general, previous evaluations of these special hearing aids have obtained inconsistent or inconclusive results. This paper reviews most of the published research on the use of special hearing aids by deaf children, summarizes several unpublished studies, and suggests a set of guidelines for future evaluations of special and conventional amplification systems.

Sign in / Sign up

Export Citation Format

Share Document