Standard‐target calibration of a parametric sonar over the difference‐frequency band, 1–6 kilohertz.

2009 ◽  
Vol 125 (4) ◽  
pp. 2718-2718 ◽  
Author(s):  
Kenneth G. Foote ◽  
Johnny Dybedal ◽  
Eirik Tenningen
Keyword(s):  
Frequency Band ◽  
Difference Frequency ◽  
The Difference ◽  
Parametric Sonar

Tunable Far-Infrared Radiation Generated from the Difference Frequency between Two Ruby Lasers

1969 ◽  
Vol 180 (2) ◽  
pp. 363-365 ◽  
Author(s):  
D. W. Faries ◽  
K. A. Gehring ◽  
P. L. Richards ◽  
Y. R. Shen
Keyword(s):  
Infrared Radiation ◽  
Far Infrared ◽  
Difference Frequency ◽  
The Difference ◽  
Far Infrared Radiation

DIFFERENCE FREQUENCY HARMONIC ION HEATING

1967 ◽  
Vol 45 (5) ◽  
pp. 1771-1781 ◽  
Author(s):  
C. R. James ◽  
W. B. Thompson
Keyword(s):  
High Frequency ◽  
Collision Frequency ◽  
Difference Frequency ◽  
Fourth Power ◽  
Heating Process ◽  
Ion Heating ◽  
Frequency Signal ◽  
Transverse Waves ◽  
The Difference ◽  
Frequency Harmonic

The heating of a magnetized hot diffuse plasma using the difference frequency signal generated from two high-frequency (35 GHz) transverse waves is examined. The plasma is described by the cold plasma model and a series expansion of harmonics is used to obtain a solution to the equations. It is shown that the energy absorbed by the ions can be made inversely proportional to the collision frequency and the fourth power of the driven frequency and proportional to the fourth power of the driven electric field intensity. An investigation of the sensitivity of the heating process to fluctuations in frequency, density, and d-c. magnetic field is carried out.

scholarly journals Nonlinear Resonance of Cavities Filled with Bubbly Liquids: A Numerical Study with Application to the Enhancement of the Frequency Mixing Effect

2018 ◽  
Vol 2018 ◽  
pp. 1-9 ◽  
Author(s):  
María Teresa Tejedor Sastre ◽  
Christian Vanhille
Keyword(s):  
Nonlinear Resonance ◽  
Frequency Component ◽  
Difference Frequency ◽  
Cavity Resonance ◽  
Global Changes ◽  
Nonlinear Frequency ◽  
Pressure Amplitude ◽  
Resonance Shift ◽  
The Difference ◽  
Frequency Mixing

This paper studies the nonlinear resonance of a cavity filled with a nonlinear biphasic medium made of a liquid and gas bubbles at a frequency generated by nonlinear frequency mixing. The analysis is performed through numerical simulations by mixing two source signals of frequencies well below the bubble resonance. The finite-volume and finite-difference based model developed in the time domain simulates the nonlinear interaction of ultrasound and bubble dynamics via the resolution of a differential system formed by the wave and Rayleigh–Plesset equations. Some numerical results, consistent with the literature, validate our procedure. Other results reveal the existence of a frequency shift of the cavity resonance at the difference-frequency component, which rises with pressure amplitude and evidences the global changes undergone by the bubbly medium under finite amplitudes. Finally, this work shows the enhancement of the amplitude of the difference-frequency component generated by parametric excitation using the nonlinear resonance shift, which is more pronounced when the second primary frequency is constant, the first one is varied to match the nonlinear resonance, and both have the same amplitude.

scholarly journals Sparsely Wiring Connectivity in the Upper Beta Band Characterizes the Brains of Top Swimming Athletes

2021 ◽  
Vol 12 ◽  
Author(s):  
Xinzhen Pei ◽  
Xiaoying Qi ◽  
Yuzhou Jiang ◽  
Xunzhang Shen ◽  
An-Li Wang ◽  
...  
Keyword(s):  
Reaction Time ◽  
Frequency Band ◽  
Brain Connectivity ◽  
Phase Lag ◽  
Complex Reaction ◽  
Beta Band ◽  
Neural Connections ◽  
The Difference ◽  
The Brain

Human brains are extremely energy costly in neural connections and activities. However, it is unknown what is the difference in the brain connectivity between top athletes with long-term professional trainings and age-matched controls. Here we ask whether long-term training can lower brain-wiring cost while have better performance. Since elite swimming requires athletes to move their arms and legs at different tempos in time with high coordination skills, we selected an eye-hand-foot complex reaction (CR) task to examine the relations between the task performance and the brain connections and activities, as well as to explore the energy cost-efficiency of top athletes. Twenty-one master-level professional swimmers and 23 age-matched non-professional swimmers as controls were recruited to perform the CR task with concurrent 8-channel EEG recordings. Reaction time and accuracy of the CR task were recorded. Topological network analysis of various frequency bands was performed using the phase lag index (PLI) technique to avoid volume conduction effects. The wiring number of connections and mean frequency were calculated to reflect the wiring and activity cost, respectively. Results showed that professional athletes demonstrated better eye-hand-foot coordination than controls when performing the CR task, indexing by faster reaction time and higher accuracy. Comparing to controls, athletes' brain demonstrated significantly less connections and weaker correlations in upper beta frequency band between the frontal and parietal regions, while demonstrated stronger connectivity in the low theta frequency band between sites of F3 and Cz/C4. Additionally, athletes showed highly stable and low eye-blinking rates across different reaction performance, while controls had high blinking frequency with high variance. Elite athletes' brain may be characterized with energy efficient sparsely wiring connections in support of superior motor performance and better cognitive performance in the eye-hand-foot complex reaction task.

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