Paul Vauterin

Tsoft: graphical and interactive software for the analysis of time series and Earth tides

We present Tsoft, a graphical interactive analysis software package originally dedicated to the analysis and processing of gravity time series. Tsoft can also be used to process and analyze all sorts of time series like seismic or other environmental signals. The Tsoft approach has a number of important advantages in the area of pre-treatment of the data (correction of artefacts such as spikes and steps), because the user can always inspect what happened and intervene manually. The graphical environment is also very convenient for the detection, isolation and analysis of events (e.g. earthquakes). Lastly, errors in the analysis path are easily detected, because the software shows a graphical representation of the results at each stage of the analysis. In this article we describe first the general data structure and the possible data manipulations and computations. Then, we present the correcting tools dealing with unwanted steps, spikes and gaps in raw data. Afterwards, we describe the module dedicated to the computation of tidal signals. Lastly, we give an overview of the most used computing tools like spectral analysis and multilinear least-squares fit.

Bacterial species identification from MALDI-TOF mass spectra through data analysis and machine learning

At present, there is much variability between MALDI-TOF MS methodology for the characterization of bacteria through differences in e.g., sample preparation methods, matrix solutions, organic solvents, acquisition methods and data analysis methods. After evaluation of the existing methods, a standard protocol was developed to generate MALDI-TOF mass spectra obtained from a collection of reference strains belonging to the genera Leuconostoc, Fructobacillus and Lactococcus. Bacterial cells were harvested after 24h of growth at 28°C on the media MRS or TSA. Mass spectra were generated, using the CHCA matrix combined with a 50:48:2 acetonitrile:water:trifluoroacetic acid matrix solution, and analyzed by the cell smear method and the cell extract method. After a data preprocessing step, the resulting high quality data set was used for PCA, distance calculation and multi-dimensional scaling. Using these analyses, species-specific information in the MALDI-TOF mass spectra could be demonstrated. As a next step, the spectra, as well as the binary character set derived from these spectra, were successfully used for species identification within the genera Leuconostoc, Fructobacillus, and Lactococcus. Using MALDI-TOF MS identification libraries for Leuconostoc and Fructobacillus strains, 84% of the MALDI-TOF mass spectra were correctly identified at the species level. Similarly, the same analysis strategy within the genus Lactococcus resulted in 94% correct identifications, taking species and subspecies levels into consideration. Finally, two machine learning techniques were evaluated as alternative species identification tools. The two techniques, support vector machines and random forests, resulted in accuracies between 94% and 98% for the identification of Leuconostoc and Fructobacillus species, respectively.

Accurate transfer function determination for superconducting gravimeters

The transfer function for the cryogenic gravimeter GWR-C021 operating at Membach (Belgium) has been experimentally determined by injecting known voltages into the control electronics of the system. The output of the gravimeter to the injected sine waves and step functions has been observed. This give a precise knowledge of the transfer function of the gravimeter. It allows one to reach a precision of better than 0.01 second in the phase response of the instrument, in agreement with the Global Geodynamics Project (GGP) requirements.

Realistic error estimates on kinematic parameters

Current error estimates on kinematic parameters are based on the assumption that the data points in the spectra follow a Poisson distribution. For realistic data that have undergone several steps in a reduction process this is generally not the case, neither is the noise distribution independent in adjacent pixels. Hence, the error estimates on the derived kinematic parameters will (in most cases) be smaller than the real errors. In this paper we propose a method that makes a diagnosis of the characteristics of the observed noise. The method also offers the possibility to calculate more realistic error estimates on kinematic parameters. The method was tested on spectroscopic observations of NGC 3258. In this particular case, the realistic errors are almost a factor of 2 larger than the errors based on least-squares statistics.

On the Kinematic Signature of a Central Galactic Bar in Observed Star Samples

A quasi-self-consistent model for a barred structure in the central regions of our Galaxy is used to calculate the signature of such a triaxial structure on the kinematical properties of star samples. We argue that, because of the presence of a velocity dispersion, such effects are much harder to detect in the stellar component than in the gas. It might be almost impossible to detect stellar kinematical evidence for a bar using only l-v diagrams if there is no a priori knowledge of the potential. Therefore, we propose some test parameters that can easily be applied to observed star samples and that also incorporate distances or proper motions. We discuss the diagnostic power of these tests as a function of the sample size and the bar strength. We conclude that about 1000 stars would be necessary to diagnose triaxiality with some statistical confidence.

On the dynamics of very flattened ellipticals.

Our aim is to study the generic phase-space structure of flattened ellipticals by investigating a few typical cases. Here we report on the E4 elliptical NGC 4697.

Kinematics and Dynamics of Galactic Systems as Probed by Planetary Nebulae Samples

At the current epoch, the dynamics of galactic systems is largely controlled by the behaviour of the stellar component. There is probably also a large amount of non-stellar matter present, which probably dominates the dynamics on large scales. Nevertheless, the (centers of) galaxies are still, for better or worse, defined as those regions were there happens to be a lot of stellar light.

Analytical Models for Rotating and Flattened Perturbations in Bulges

A power series approach for solving the linearized transport equation for perturbations in the central. part of flat disks is presented. The application of this method is in principle independent of the mathematical. complexity of the unperturbed distribution. As an illustration, this method was used to solve the transport equation in the case of Kalnajs’ Omega models.