NMR Theory of Gaseous CX3Y Molecules: High Frequency Effects of CF3H

1975 ◽  
Vol 53 (7) ◽  
pp. 739-755 ◽  
Author(s):  
B. C. Sanctuary ◽  
R. F. Snider
Keyword(s):  
General Theory ◽  
Density Dependence ◽  
High Frequency ◽  
Nuclear Spin Relaxation ◽  
Low Density ◽  
Frequency Effects ◽  
Dramatic Effect ◽  
Large Step ◽  
High Frequency Effects ◽  
Intramolecular Mechanism

A general theory of nuclear spin relaxation is applied to gaseous CX3Y molecules and the effects of high frequency terms studied theoretically. Although there is experimental disagreement as to what the correct high density dependence is for CF3H, it is demonstrated that rotational high frequency contributions can have a dramatic effect on the density dependence of T1. Moreover, for 'reasonable' values of the linewidth, shift, and collisional overlap parameters, the density dependence is limited in variation when the parameters are changed, making it impossible to fit Courtney's initial large 'step'. A reasonable fit to Waugh's data and the higher density dependence of Courtney can be obtained with a low density T1/n value of 0.8 s/amagat. Only a dipolar intramolecular mechanism is considered for the high frequency contributions.

High-frequency signals from air-gun arrays

Geophysics ◽  
2011 ◽  
Vol 76 (4) ◽  
pp. Q19-Q27 ◽  
Author(s):  
M. Landrø ◽  
L. Amundsen ◽  
D. Barker
Keyword(s):  
High Frequency ◽  
Experimental Testing ◽  
Seismic Sources ◽  
Frequency Noise ◽  
Suggested Model ◽  
Frequency Effects ◽  
High Frequency Noise ◽  
Air Gun ◽  
Marine Seismic ◽  
High Frequency Effects

We suggest two different mechanisms for generation of high-frequency signals from seismic sources: one type that we interpret as being caused by high-frequency effects close to and within each individual air gun and another type caused by an effect that we refer to as ghost cavitation. The former one is found to have a steep decreasing amplitude trend with frequency, while the latter has a close to 1/f attenuation for frequencies above 1 kHz. A thorough understanding of the effects is of significant importance to quantify and estimate any environmental impact of marine seismic air-gun arrays. The proposed ghost-cavitation mechanism needs further experimental testing. However, given that the suggested model is proven, we think it is possible to attenuate the high-frequency noise generated by compact air-gun arrays by increasing the areal extent of the gun array.

Sign in / Sign up

Export Citation Format

Share Document