This application imports ASCII files, which have two columns of data: column 1 is the frequency and column 2 is either the amplitude or the power, more technically it is the PSD (power spectral density) or the ASD (amplitude spectral density). You have to check, which quantity your instrument actually exports. ASDs will be of the order of pm (10e-12), PSDs will be on the order of 10e-24. You have to set the radio button "is Power" accordingly.
Units of the data are expected to be "Hz" or "m" or "m*m".
If your data, have different units, e.g. they are scaled in kHz, you can use the xscaling or yscaling for correcting this, e.g. by using a scaling factor of 1e3.
You may want to download a sample file here.
Using the Application
The application will analyze PSD data in a region of interest determined by frequency1 and frequency2. It will fit two different models to the data: (1) a single harmonic oscillator (SHO) and (2) a Lorentzian. There are arguments, that a SHO will be appropriate for PSD data in air, where the Lorentzian may work better for data in liquids, because it handles better high damping (low Q). For air data the two fit routines often result in the same results.
After the fit, the software will calculate the force constant using the results of the fit and the temperature (given in degrees C), basically by employing Boltzmann's equipartition theorem.
Some parameters (xscaling, yscaling, oldkappa, newkappa, temperature) modify the data or control the fitting procedure. If these parameters are changed a new fit will be started and the fit results will be displayed in the appropriate fields.
For the SHO fit this will be AMp (DC), Q, Omega, White Noise and the force constant. For the Lorentzian it will C1, C2, Omega, White Noise and the force constant.
If you change one of these fit results, then actually no fit will performed, but the theoretical curves will be recalculated. This allows you to see, how these parameters influence the theoretical curves. You may even want to improve a fit by changing manually parameters. However, we have doubts that this will result in any improvement.
Understanding the application
The application will fit either a single harmonic oscillator or a Lorentzian to the data. From the fit results the force constant will be calculated using Boltzmann's equipartition theorem.
The results of the SHO can be seen in the third column of numbers (Amp (DC), Q, Omega0, White Noise and Force Constant), whereas the reulst of the Lorentzian will be seen in the right most column (C1, C2, Omega0, WhiteNoise, Force Constant). In addition a theoretical PSD (based on the fit results) will added to the plot in green (SHO) or blue (Lorentzian) to check the quality of the fit visually.
More information on the routines used will be added soon.
Java Exception List
In order to do so, you have to set the appropiate exemption in the second tab of the Java Control Panel. If you feel uncomfortable with this procedure, you may download the source code and run it locally. We have used Eclipes for development.