Biot‐Stoll with squirt flow and shear (BICSQS) model: high‐frequency correction

2008 ◽  
Vol 123 (5) ◽  
pp. 3442-3442
Author(s):  
Nicholas P. Chotiros
Keyword(s):  
High Frequency ◽  
Frequency Correction

scholarly journals Technical note: Water vapour concentration and flux measurements with PTR-MS

2006 ◽  
Vol 6 (12) ◽  
pp. 4643-4651 ◽  
Author(s):  
C. Ammann ◽  
A. Brunner ◽  
C. Spirig ◽  
A. Neftel
Keyword(s):  
Water Vapour ◽  
Eddy Covariance ◽  
High Frequency ◽  
Reference System ◽  
Transfer Functions ◽  
Water Vapour Flux ◽  
Water Vapour Concentration ◽  
Vapour Concentration ◽  
Frequency Correction ◽  
Vapour Flux

Abstract. The most direct approach for measuring the exchange of biogenic volatile organic compounds between terrestrial ecosystems and the atmosphere is the eddy covariance technique. It has been applied several times in the last few years using fast response proton-transfer-reaction mass spectrometry (PTR-MS). We present an independent validation of this technique by applying it to measure the water vapour flux in comparison to a common reference system comprising an infra-red gas analyser (IRGA). Water vapour was detected in the PTR-MS at mass 37 (atomic mass units) corresponding to the cluster ion H3O+·H2O. During a five-week field campaign at a grassland site, we obtained a non-linear but stable calibration function between the mass 37 signal and the reference water vapour concentration. With a correction of the high-frequency damping loss based on empirical ogive analysis, the eddy covariance water vapour flux obtained with the PTR-MS showed a very good agreement with the flux of the reference system. The application of the empirical ogive method for high-frequency correction led to significantly better results than using a correction based on theoretical spectral transfer functions. This finding is attributed to adsorption effects on the tube walls that are presently not included in the theoretical correction approach. The proposed high-frequency correction method can also be used for other trace gases with different adsorption characteristics.

scholarly journals An ampere meter for measuring alternating currents of very high frequency

1928 ◽  
Vol 121 (787) ◽  
pp. 41-71 ◽  
Keyword(s):  
High Frequency ◽  
Correction Term ◽  
Small Diameter ◽  
Great Difficulty ◽  
Very High Frequency ◽  
Steady Current ◽  
Heated Wire ◽  
Frequency Correction ◽  
Heated Element ◽  
Very High

The measurement of alternating currents of very high frequency in general presents great difficulty because all existing ammeters have a frequency correction which cannot be calculated. The dynamometer ammeter of ordinary construction is very satisfactory for currents whose frequency does not exceed a few hundred cycles per second, but is unsuitable for currents whose frequency is many kilocycles because the highly inductive winding presents an enormous impedance to the current and its presence in a circuit modifies completely the conditions obtaining therein. Further, the distribution of current over the cross section of the wire and the value of the current from turn to turn will alter with the frequency, with the result that a steady current calibration becomes invalid and the correcting factor cannot be calculated or even estimated roughly. So even if its presence can be tolerated in a circuit, such an instrument can be used only for relative measurements at one frequency and its indications cannot be reduced to absolute measure. The ammeters in general use are thermal instruments depending on the thermal expansion of a suitable element or on the production of a thermoelectric E. M. F. in a junction placed close to a wire heated by the high frequency current. In either system the resistance of the heated element depends on the frequency of the current which heats it and so a steady current calibration cannot be used indiscriminately. The necessary configuration of the heated element and its situation with respect to surrounding alternating magnetic fields usually renders impossible the calculation of its resistance. It is usual to make the heated wire of a high resistance material and with a small diameter so as to render the calibration sensibly constant up to a high value of frequency. If the calculated resistance of such a straight isolated wire at an assigned frequency has increased by only a small fraction of 1 per cent, above the steady current value, then it will seem reasonable to suppose that the calibration of the bent and unisolated heated wire is valid to at least 1 per cent, up to this frequency. For higher frequencies there will be a correction term whose value can be estimated only very roughly. To maintain the calibration, valid np to a frequency of some thousand kilocycles per second the heating wire must be so fine that it will not carry a current of more than, say, 1 ampere. To measure larger currents we are faced by the problem of providing a shunt which the shunting ratio is independent of frequency. Brief consideration will show it is very difficult to arrange a group of fine parallel wires so that each has precisely the same resistance, and further that the situation of each one is the same with respect to all the others and also the remainder of the circuit. If both conditions are not fulfilled the total current will not always divide equally among the component parallel paths and the calibration curve will be subject to a frequency correction. A common and successful method is to arrange the parallel wires as generators of a cylinder, double cone, or hyperboloid and to allow each wire to heat one of a group of thermocouples connected in series electrically.

Variational principles in high-frequency scattering

1958 ◽  
Vol 54 (4) ◽  
pp. 512-529 ◽  
Author(s):  
Ralph D. Kodis
Keyword(s):  
Frequency Dependence ◽  
Cross Section ◽  
High Frequency ◽  
Variational Principles ◽  
Boundary Values ◽  
Aperture Coupling ◽  
Frequency Correction ◽  
The Cross ◽  
Scattering By Obstacles ◽  
Stationary Form

ABSTRACTA pair of variational principles are formulated for two-dimensional scattering by obstacles. The first of these is in terms of the obstacle boundary values, and it is shown that a simple ‘optical’ trial function leads to an incorrect frequency dependence for the scattering cross-section. In the second, the obstacle is viewed as the analogue of an aperture coupling two half spaces. The geometric optics part of the cross-section can then be made explicit and is split off to leave a stationary form for the frequency correction. The zero-order calculation for the cross-section of a circle, using corresponding ‘optical’ trial functions, is found to have the correct (Ka)−2/3 frequency dependence.

Eddy covariance measurement of ammonia fluxes: Comparison of high frequency correction methodologies

2012 ◽  
Vol 158-159 ◽  
pp. 30-42 ◽  
Author(s):  
R.M. Ferrara ◽  
B. Loubet ◽  
P. Di Tommasi ◽  
T. Bertolini ◽  
V. Magliulo ◽  
...  
Keyword(s):  
Eddy Covariance ◽  
High Frequency ◽  
Frequency Correction ◽  
Eddy Covariance Measurement

High Frequency Correction of Dynamometer for Cutting Force Observation in Milling

2010 ◽  
Vol 132 (3) ◽  
Author(s):  
François Girardin ◽  
Didier Remond ◽  
Jean-François Rigal
Keyword(s):  
Cutting Force ◽  
Cutting Forces ◽  
High Frequency ◽  
Cutting Speed ◽  
Cutting Parameters ◽  
Wide Frequency Range ◽  
Force Measurements ◽  
Mean Oscillation ◽  
Number Of Factors ◽  
Frequency Correction

Piezoelectric dynamometers are widely used for cutting force measurements. Indeed, this device has the largest bandwidth for this kind of measurement. Nevertheless, the behavior of this device is not very well-known and its use is sometimes inappropriate for static and high frequency dynamic measurements. In this paper, a piezoelectric dynamometer is used for cutting force measurements in a milling case. Cutting forces in milling are discontinuous by nature due to successive inward and outward movements of tool-teeth on the workpiece. As a result, a bandwidth criterion based on cutting parameters is defined in order to permit clear observation of the mean oscillation of the cutting force. The frequency response of a dynamometer is then analyzed over a wide frequency range. A 2 kHz bandwidth can be defined for an efficient correction of cutting force. The dynamometer appears to be exploitable for higher frequencies up to at least 16 kHz though a large number of factors must be taken into account in the analysis. Finally, several lateral milling tests are performed by changing cutting speed, feed rate, and lubricant conditions. The correction of measurements permits highlighting certain particularities in the cutting force signals, such as the effect of shock of inward tool-teeth strokes on the workpiece, the specific behavior for outward tool-teeth strokes, and the effect of a lubricant on the variation in cutting forces.

The Microstructure of Steatite (Protoenstatite)

1985 ◽  
Vol 43 ◽  
pp. 236-237
Author(s):  
W. E. Lee ◽  
A. H. Heuer
Keyword(s):  
High Frequency ◽  
Glass Ceramics ◽  
Magnesium Silicate ◽  
Beam Current ◽  
Glassy Matrix ◽  
Angle Of Incidence ◽  
X Ray ◽  
Mechanical And Electrical Properties ◽  
Argon Ions ◽  
High Temperature Polymorph

IntroductionTraditional steatite ceramics, made by firing (vitrifying) hydrous magnesium silicate, have long been used as insulators for high frequency applications due to their excellent mechanical and electrical properties. Early x-ray and optical analysis of steatites showed that they were composed largely of protoenstatite (MgSiO3) in a glassy matrix. Recent studies of enstatite-containing glass ceramics have revived interest in the polymorphism of enstatite. Three polymorphs exist, two with orthorhombic and one with monoclinic symmetry (ortho, proto and clino enstatite, respectively). Steatite ceramics are of particular interest a they contain the normally unstable high-temperature polymorph, protoenstatite.Experimental3mm diameter discs cut from steatite rods (∼10” long and 0.5” dia.) were ground, polished, dimpled, and ion-thinned to electron transparency using 6KV Argon ions at a beam current of 1 x 10-3 A and a 12° angle of incidence. The discs were coated with carbon prior to TEM examination to minimize charging effects.

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.

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