scholarly journals Correlations in Space and Time for a Soft-mode Phase-transforming System

1987 ◽  
Vol 40 (5) ◽  
pp. 619 ◽  
Author(s):  
SL Mair
Keyword(s):  
Correlation Function ◽  
Frequency Spectrum ◽  
Order Parameter ◽  
Central Peak ◽  
Square Lattice ◽  
Order Component ◽  
Low Frequencies ◽  
Potential Wells ◽  
Parameter Correlation ◽  
Dynamical Order

Using molecular dynamics (MD) for a system of.nonlinear (quadruple-quadratic) oscillators on a nearest-neighbour square lattice, the pair-displacement correlations. and the frequency spectrum for the dynamical order-parameter correlation function are obtained as a function of temperature. For temperatures T near Tc' the pair-displacement correlation function (with the long-range order component subtracted out) was found to vary with particle separation r as r- 1/2 exp { - A( T) rj, at least out to the tenth neighbour in the 40x40 particle lattice. This is consistent with predictions for the two-dimensional Ising model for T above, but not below, Tc. The frequency spectrum for the dynamical order-parameter correlation function shows the softening of the damped phonon-like modes as T approaches Tc and the formation of a central peak at Tc' consistent with the presence of soliton-like excitations. For small I T - Tc I an additional broad peak appears at low frequencies. This is interpreted as an additional phonon-like peak, the two quasi-phonon processes being associated with vibration across the potential barrier and vibration in one or other of the two potential wells respectively. Although the squared frequency wi of the soft quasi-phonon is approximately linear with I T - Tc lover a range of temperatures, as T increases the wi curve eventually flattens out.

scholarly journals Bicritical Central Point of Ising Model Phase Diagram

2010 ◽  
Vol 2010 ◽  
pp. 1-5 ◽  
Author(s):  
Yahia Boughaleb ◽  
Mohammed Nouredine ◽  
Mohamed Snina ◽  
Rachid Nassif ◽  
Mohamed Bennai
Keyword(s):  
Phase Diagram ◽  
Order Parameter ◽  
Present Model ◽  
Central Point ◽  
Square Lattice ◽  
Ordered Structures ◽  
Ordered Phases ◽  
Algebraic Order ◽  
Pure Phases ◽  
Model Phase

We deal with a 2D half occupied square lattice with repulsive interactions between first and second neighboring particles. Despite the intensive studies of the present model the central point of the phase diagram for which the ratio of the two interaction strengths is still open. In the present paper we show, using standard Monte Carlo calculations, that the situation corresponds to a phase of mixed ordered structures quantified by an “algebraic” order parameter defined as the sum of densities of the existing ordered clusters. The introduced grandeur also characterizes the transitions towards the known pure ordered phases for the other values of as mentioned by the agreement of our results with those of the literature. The computation of the Cowley short range order parameter against suggests that the central point is bicritical and is a state to cross when passing between the two pure phases.

scholarly journals A sciaenid swim bladder with long skinny fingers produces sound with an unusual frequency spectrum

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Hin-Kiu Mok ◽  
Shih-Chia Wu ◽  
Soranuth Sirisuary ◽  
Michael L. Fine
Keyword(s):  
Frequency Spectrum ◽  
Fundamental Frequency ◽  
Pulse Repetition Rate ◽  
Sound Production ◽  
Swim Bladder ◽  
Low Frequencies ◽  
Pass Filter ◽  
Number Of Cycles ◽  
Almost All ◽  
High Pass

Abstract Swim bladders in sciaenid fishes function in hearing in some and sound production in almost all species. Sciaenid swim bladders vary from simple carrot-shaped to two-chambered to possessing various diverticula. Diverticula that terminate close to the ears improve hearing. Other unusual diverticula heading in a caudal direction have not been studied. The fresh-water Asian species Boesemania microlepis has an unusual swim bladder with a slightly restricted anterior region and 6 long-slender caudally-directed diverticula bilaterally. We hypothesized that these diverticula modify sound spectra. Evening advertisement calls consist of a series of multicycle tonal pulses, but the fundamental frequency and first several harmonics are missing or attenuated, and peak frequencies are high, varying between < 1–2 kHz. The fundamental frequency is reflected in the pulse repetition rate and in ripples on the frequency spectrum but not in the number of cycles within a pulse. We suggest that diverticula function as Helmholz absorbers turning the swim bladder into a high-pass filter responsible for the absence of low frequencies typically present in sciaenid calls. Further, we hypothesize that the multicycle pulses are driven by the stretched aponeuroses (flat tendons that connect the sonic muscles to the swim bladder) in this and other sciaenids.

scholarly journals Vibronic Mechanism of High Tc Superconductivity

2003 ◽  
Vol 17 (18n20) ◽  
pp. 3266-3270 ◽  
Author(s):  
M. Tachiki ◽  
T. Egami ◽  
M. Machida
Keyword(s):  
Transition Temperature ◽  
Order Parameter ◽  
Cuprate Superconductors ◽  
High Temperature Superconductivity ◽  
Attractive Interaction ◽  
Low Frequencies ◽  
High Tc ◽  
Eliashberg Theory ◽  
Bond Stretching ◽  
Vibronic Effect

When phonons strongly mix with electron charge fluctuations with low frequencies, the phonon mediated attractive interaction between electrons is strongly enhanced. The occurrence of the mixing has been indicated by the neutron scattering experimental results that the dispersion of the in-plane Cu–O bond-stretching mode in the high Tc cuprate superconductors is strongly softened near the zone boundary. We propose that the phonon mediated attractive interaction strongly enhanced by the vibronic effect can form a basis for the phonon mechanism of high temperature superconductivity. With the Eliashberg theory and with the electronic structure determined by ARPES and the electronic dielectric function obtained by the softened dispersion of the in-pane Cu–O stretching mode, we calculated the transition temperature and the order parameter at the transition temperature. The order parameter is of the d(x2-y2) symmetry and the transition temperature is well in excess of 100 K.

Evaluation of a Wide Range of AmplitudeFrequency Responses for the Hearing Impaired

1995 ◽  
Vol 38 (1) ◽  
pp. 211-221 ◽  
Author(s):  
Ronald A. van Buuren ◽  
Joost M. Festen ◽  
Reinier Plomp
Keyword(s):  
Frequency Spectrum ◽  
Speech Intelligibility ◽  
Dynamic Range ◽  
Finite Impulse Response ◽  
Sound Quality ◽  
Average Frequency ◽  
Frequency Spectra ◽  
Low Frequencies ◽  
Speech Reception ◽  
Wide Range

The long-term average frequency spectrum of speech was modified to 25 target frequency spectra in order to determine the effect of each of these spectra on speech intelligibility in noise and on sound quality. Speech intelligibility was evaluated using the test as developed by Plomp and Mimpen (1979), whereas sound quality was examined through judgments of loudness, sharpness, clearness, and pleasantness of speech fragments. Subjects had different degrees of sensorineural hearing loss and sloping audiograms, but not all of them were hearing aid users. The 25 frequency spectra were defined such that the entire dynamic range of each listener, from dB above threshold to 5 dB below UCL, was covered. Frequency shaping of the speech was carried out on-line by means of Finite Impulse Response (FIR) filters. The tests on speech reception in noise indicated that the Speech-Reception Thresholds (SRTs) did not differ significantly for the majority of spectra. Spectra with high levels, especially at low frequencies (probably causing significant upward spread of masking), and also those with steep negative slopes resulted in significantly higher SRTs. Sound quality judgments led to conclusions virtually identical to those from the SRT data: frequency spectra with an unacceptably low sound quality were in most of the cases significantly worse on the SRT test as well. Because the SRT did not vary significantly among the majority of frequency spectra, it was concluded that a wide range of spectra between the threshold and UCL levels of listeners with hearing losses is suitable for the presentation of speech energy. This is very useful in everyday listening, where the frequency spectrum of speech may vary considerably.

Sign in / Sign up

Export Citation Format

Share Document