Free-field noise

Guidelines on t ualily management and quality system elements Test code for the measurement of airborne noise emitted by rotating electrical machines Engineering method for free field conditions over a reflecting plane Survey method Determination of sound power levels of noise sources 14004/1991 BS EN ISO 9004/1994-1/1994 BS 7458-1/1991 BS 7458-2/1991 B.S 4196 9004/1987 1680-1/1986 1680-2/1986. 3740... 

When the noise transmission takes place in a free field (no reflective surfaces), it is possible to calculate the pressure levels at different distances from the source. For spherical propagation, the following formula can be used ... 

Acoustics—Determination of Sound Power Levels of Noise Sources—Precision Methods for Broad-Band Sources in Reverberation Rooms Acoustics—Determination of Sound Power Levels of Noise Sources—Engineering Methods for Free-Field Conditions Over a Reflecting Plane Acoustics—Determination of Sound Power Levels of Noise Sources—Survey Method... 

ISO 3744, Acoustics — Determination of sound power levels of noise sources using sound pressure — Engineering method in an essentially free field over a reflecting plane. 

ISO 3744 "Acoustics - Determination of Sound Power Levels of Noise Sources Using Sound Pressure— Engineering Method in an Essentially Free Field Over a Reflecting Plane." May 1,1994. 

Good X-band resonators mounted into a spectrometer and with a sample inside have approximate quality factors of 103 or more, which means that they afford an EPR signal-to-noise ratio that is over circa three orders of magnitude better than that of a measurement on the same sample without a resonator, in free space. This is, of course, a tremendous improvement in sensitivity, and it allows us to do EPR on biomolecules in the sub-pM to mM range, but the flip side of the coin is that we are stuck with the specific resonance frequency of the resonator, and so we cannot vary the microwave frequency, and therefore we have to vary the external magnetic field strength. 

Another type of DOUBLE ENDOR, called special TRIPLE , has been introduced by Dinse et al.90 to study proton hf interactions of free radicals in solution. In a special TRIPLE experiment two rf fields with frequencies vp + Av and vp — Av are swept simultaneously. For systems with Tln < T,i this leads to a considerable signal-to-noise improvement and to TRIPLE line intensities which are directly proportional to the number of nuclei with the same hf coupling constant. It should be remembered, however, that in transition metal complexes in the solid state the resonance frequencies are not, in general, symmetrically placed about the free proton frequency vp and that the condition Tln < Tj,i is not always fulfilled. 

In the TSDC considered here, a sample is cooled to a low temperature ( 100K) and illuminated with 3 X 10 lx hght for a time tp ( 4min) in the presence of an applied DC field (E = 5 X 10" V/cm). Then, the light and voltage are switched off the structure is short-circuited and, after a delay period necessary for sample relaxation (to reach equihbrium between the free and the trapped carriers), the sample is heated in the darkness at a constant rate Vt while the TSDC is measured. We preferred TSDC experiments because of the absence of noise due to a voltage source and the strongly reduced influence of the intrinsic conductivity. 

Given prior information in terms of a lower and upper bound, a prior bias, and constraints in terms of measured data, the MRE provides exact expressions for the posterior pdf and expected value of the inverse problem. The plume source is also characterized by a pdf The problem solved in their study is the same as Skaggs and Kabala s problem. For the noise-free data, MRE was able to reconstruct the plume evolution history indistinguishable from the true history. As for data with noise, the MRE method managed to recover the salient features of the source history. Another advantage using the MRE approach is that once the plume source history is reconstructed, future behavior of the plume can be easily predicted due to the probabilistic framework of MRE. Woodbury et al. [71] extended the MRE approach to reconstruct a 3D plume source within a ID constant velocity field and constant dispersivity system. 

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