Search results for "Fourier transform"
showing 10 items of 1138 documents
Adsorption and photocatalytic degradation of acetonitrile: FT-IR investigation
2003
Abstract The photocatalytic degradation of acetonitrile was carried out in liquid–solid regime in a batch reactor by using two types of commercial TiO 2 powders (Merck and Degussa P25) as photocatalysts. The concentration of acetonitrile and non-purgeable organic carbon (NPOC) were monitored. The initial rate of acetonitrile conversion was found higher on TiO 2 Merck than on TiO 2 P25. FT-IR spectroscopy was used to investigate the molecular features of the adsorption and photo-oxidation of acetonitrile on the two TiO 2 powders in a fully surface hydrated form. Acetonitrile was found adsorbed on Ti 4+ surface ions and hydroxyl groups for both types of TiO 2 . This interaction appeared fully…
Formation of layered titania and zirconia catalysed by surface-bound silicatein
2005
Silicatein immobilised on self-assembled polymer layers using a histidine-tag chelating anchor group retains its hydrolytical activity for the formation of biosilica, and catalyses the formation of layered arrangements of biotitania and biozirconia.
Discrete wavelet transform implementation in Fourier domain for multidimensional signal
2002
Wavelet transforms are often calculated by using the Mallat algorithm. In this algorithm, a signal is decomposed by a cascade of filtering and downsampling operations. Computing time can be important but the filtering operations can be speeded up by using fast Fourier transform (FFT)-based convolutions. Since it is necessary to work in the Fourier domain when large filters are used, we present some results of Fourier-based optimization of the sampling operations. Acceleration can be obtained by expressing the samplings in the Fourier domain. The general equations of the down- and upsampling of digital multidimensional signals are given. It is shown that for special cases such as the separab…
A Robust Wrap Reduction Algorithm for Fringe Projection Profilometry and Applications in Magnetic Resonance Imaging.
2017
In this paper, we present an effective algorithm to reduce the number of wraps in a 2D phase signal provided as input. The technique is based on an accurate estimate of the fundamental frequency of a 2D complex signal with the phase given by the input, and the removal of a dependent additive term from the phase map. Unlike existing methods based on the discrete Fourier transform (DFT), the frequency is computed by using noise-robust estimates that are not restricted to integer values. Then, to deal with the problem of a non-integer shift in the frequency domain, an equivalent operation is carried out on the original phase signal. This consists of the subtraction of a tilted plane whose slop…
Response Power Spectrum of Multi-Degree-of-Freedom Nonlinear Systems by a Galerkin Technique
2003
This paper deals with the estimation of spectral properties of randomly excited multi-degree-of-freedom (MDOF) nonlinear vibrating systems. Each component of the vector of the stationary system response is expanded into a trigonometric Fourier series over an adequately long interval T. The unknown Fourier coefficients of individual samples of the response process are treated by harmonic balance, which leads to a set of nonlinear equations that are solved by Newton’s method. For polynomial nonlinearities of cubic order, exact solutions are developed to compute the Fourier coefficients of the nonlinear terms, including those involved in the Jacobian matrix associated with the implementation o…
Determination of accurate rest frequencies and hyperfine structure parameters of cyanobutadiyne, HC5N
2020
Very accurate transition frequencies of HC$_5$N were determined between 5.3 and 21.4 GHz with a Fourier transform microwave spectrometer. The molecules were generated by passing a mixture of HC$_3$N and C$_2$H$_2$ highly diluted in neon through a discharge valve followed by supersonic expansion into the Fabry-Perot cavity of the spectrometer. The accuracies of the data permitted us to improve the experimental $^{14}$N nuclear quadrupole coupling parameter considerably and the first experimental determination of the $^{14}$N nuclear spin-rotation parameter. The transition frequencies are also well suited to determine in astronomical observations the local speed of rest velocities in molecula…
Effect of the gas mixing technique on the production efficiency of ion beams extracted from an electron cyclotron resonance ion source
2004
In this work the effect of gas mixing on the production efficiency of ion beams extracted from an ECR ion source has been studied with the JYFL 6.4 GHz electron cyclotron resonance ion source (ECRIS). It was found that the gas mixing affects strongly the confinement of ions in the plasma of the ECRIS. The information obtained can be used to minimize the consumption of expensive materials or isotopes and to reduce contamination of the plasma chamber. It was observed that the carbon contamination, which is built up when the MIVOC method is used could be decreased with the aid of the gas mixing technique. The best mixing gas for this purpose was found to be oxygen.
First absolute mass measurements of short-lived isotopes
1987
Absolute mass measurements of short-lived isotopes have been performed at the on-line mass separator ISOLDE at CERN by determining the cyclotron frequencies of ions confined in a Penning trap. The cyclotron frequencies for77,78,85,86,88Rb and88Sr ions could be determined with a resolving power of 3×105 and an accuracy of better than 10−6, which corresponds to 100 keV for massA=100. The shortest-lived isotope under investigation was77Rb with a half-life of 3.7 min. The resonances obtained for the isobars88Rb and88Sr were clearly resolved.
Diagnostics of a charge breeder electron cyclotron resonance ion source helium plasma with the injection ofNa231+ions
2016
This work describes the utilization of an injected 23Na1+ ion beam as a diagnostics of the helium plasma of a charge breeder electron cyclotron resonance ion source. The obtained data allows estimating the upper limit for the ion-ion collision mean-free path of the incident sodium ions, the lower limit of ion-ion collision frequencies for all charge states of the sodium ions and the lower limit of the helium plasma density. The ion-ion collision frequencies of high charge state ions are shown to be at least on the order of 1–10 MHz and the plasma density is estimated to be on the order of 1011 cm−3 or higher. The experimental results are compared to simulations of the 23Na1+ capture into t…
Fourier transform-ion cyclotron resonance mass spectrometry — A new tool for measuring highly charged ions in an electron beam ion trap
1995
Abstract Fourier transform-ion cyclotron mass spectrometry has been applied to the study of highly charged ions produced and confined in an electron beam ion trap. Measurements of the relative ion abundance of hydrogenlike and bare krypton ions were made and compared to the abundance ratios determined with standard X-ray techniques. Good agreement was found establishing the reliability of the method as a new tool in highly charged ion research.