Full Spectral Information Research Articles

Application of Principal Component Analysis to High-Resolution Infrared Measurement Compression and Retrieval

Abstract A simulation study is used to demonstrate the application of principal component analysis to both the compression of, and meteorological parameter retrieval from, high-resolution infrared spectra. The study discusses the fundamental aspects of spectral correlation, distributions, and noise; the correlation between principal components (PCs) and atmospheric-level temperature and water vapor; and how an optimal subset of PCs is selected so a good compression ratio and high retrieval accuracy are obtained. Principal component analysis, principal component compression, and principal component regression under certain conditions are shown to provide 1) nearly full spectral information with little degradation, 2) noise reduction, 3) data compression with a compression ratio of approximately 15, and 4) tolerable loss of accuracy in temperature and water vapor retrieval. The techniques will therefore be valuable tools for data compression and the accurate retrieval of meteorological parameters from new-g...

Computed Tomography-Based Spectral Imaging For Fluorescence Microscopy

The computed tomography imaging spectrometer (CTIS) is a non-scanning instrument capable of simultaneously acquiring full spectral information (450–750 nm) from every position element within its field of view (75 μm × 75 μm). The current spatial and spectral sampling intervals of the spectrometer are 1.0 μm and 10 nm, respectively. This level of resolution is adequate to resolve signal responses from multiple fluorescence probes located within individual cells or different locations within the same cell. Spectral imaging results are presented from the CTIS combined with a commercial inverted fluorescence microscope. Results demonstrate the capability of the CTIS to monitor the spatiotemporal evolution of pH in rat insulinoma cells loaded with SNARF-1. The ability to analyze full spectral information for two-dimensional ( x, y) images allows precise evaluation of heterogeneous physiological responses within cell populations. Due to low signal levels, integration times up to 2 s were required. However, reasonable modifications to the instrument design will provide higher system transmission efficiency with increased temporal and spatial resolution. Specifically, a custom optical design including the use of a larger format detector array is under development for a second-generation system.

Spectra polarimetry of the motional Stark effect at TEXTOR-94

The Balmer-α light emitted by neutral particles injected into tokamaks is polarized with respect to the Lorentz electric field experienced by these atoms: El=ν×B, known as the motional Stark effect (MSE). On TEXTOR-94 a new MSE system is under development which exploits the full spectral information, along with its polarization. The advantages of exploiting the full spectral information are obvious: beam velocity, observation volume, absolute value of B, the plasma radial electric field and the beam density can in principle all be extracted from the measurement, whereas the polarization can be detected as several lines simultaneously. The TEXTOR-94 MSE system consists of 30 radial channel, of which the full Balmer-α spectrum is measured at two orthogonal angles. This is accomplished by inserting a Glan–Laser prism in the optical path. All the optics is located inside the vessel to improve the radial resolution and minimize changes in polarization due to optical elements. Fibers transfer the light by a vacuum feedthrough towards a spectrometer. It is shown that the measured spectra can be adequately fitted. The accuracy for determining the safety factor q is estimated to be 10%–15% and for the radial electric field to be 30 kV/m.

Signature of a three-dimensional heliosphere in the spectra of anomalous cosmic rays

A steady-state transport model of the Anomalous component of Cosmic Rays (ACRs) that takes into account convection, spatial diffusion and adiabatic deceleration in a three-dimensional heliosphere is applied to compute ACR spectra in the kinetic energy range 2 keV to several GeV. The spectra are investigated with respect to their longitudinal gradients due to the three-dimensional structure of the heliosphere, defined by a latitudinally varying solar wind that is terminated by a heliospheric shock. The results significantly refine earlier studies based on the integrated spectra, i.e. the cosmic ray pressure. With the full spectral information at our disposal, we can identify the spectral regimes exhibiting the largest longitudinal gradients.

The motional Stark effect diagnostic on TEXTOR-94: First measurements

We have developed a diagnostic to measure the motional Stark effect (MSE) on TEXTOR-94. This diagnostic allows us to measure locally the strength and direction of the magnetic field. Furthermore, the major radius of observation and the radial electric field are determined. Because the MSE diagnostic on TEXTOR-94 employs the full spectral information, in addition to the complete polarization, the measurements are independent from other experimental data. In this article we present the first preliminary results of the MSE diagnostic on TEXTOR-94.

Flow methods for the determination of polycyclic aromatic hydrocarbons using low power photomultiplier tube and charge coupled device chemiluminescence detection

Polycyclic aromatic hydrocarbons (PAHs) are produced during combustion processes (both natural and anthropogenic), and as a consequence are distributed widely throughout environmental systems. This paper describes the application of peroxyoxalate chemiluminescence (CL) detection, with a 12 V low power photomultiplier tube (PMT) detector and a two dimensional charge coupled device (CCD) detector, to the determination of PAHs. The PMT system provides comparable sensitivity to high power (1 kV) PMTs (detection limits in the pg range) and complementary information to that derived from fluorescence detection. The CCD system can be used to obtain full CL spectral information (in contrast to the integrated response from PMTs) and it has been shown that multivariate calibration can be used in conjunction with CCD detection to give good predictive errors (<9%) for simple two-component systems, e.g. benzo[ k]fluoranthene and benzo[ a]pyrene in hexane.

In-line UV spectroscopy of YBa2Cu3O7 MOCVD precursors

Abstract Real-time UV absorbance of YBCO MOCVD precursors was monitored in-line at the bubbler effluent using a remote fiber-optic based dual-wavelength detection scheme. A S N of 50:1 was obtained by signal averaging detector response over a one second interval. This technique provided a chemical specific measurement of extremely dilute concentrations of MOCVD source materials. In addition, several concentration transients were observed. Multi-wavelength detection (PDA/spectrograph) provided full spectral information. Bubbler efficiency of Y(thd)3 was shown to improve as system pressure was increased.

Comparative vibrational spectroscopy for determination of quality parameters in amidated pectins as evaluated by chemometrics

The potential of vibrational spectroscopy and chemometrics as a reliable and fast method for the determination of important gel-forming parameters in amidated pectins has been investigated. For a set of 98 amidated pectin samples, six complete spectroscopic ensembles were recorded including NIR, FT-NIR, FT-IR and NIR FT-Raman spectroscopy. For each spectroscopic ensemble, quantitative models based on partial least squares regression (PLS) have been developed and compared. Chemometric models were constructed by dividing the spectroscopic ensembles up into a calibration set of 73 samples and an independent test set of 25 samples to evaluate the predictive ability of the models. The 98 amidated pectin samples span a degree of esterification (%DE) between 20 and 55% and a degree of amidation (%DA) between 4 and 24 per cent. From all six spectroscopic ensembles quantitative PLS models were obtained for %DE and %DA with RMSEP (root mean square error of prediction) ranging between 1.5 and 2.1 and between 1.1 and 2.1 for %DE and %DA respectively. In both cases the results are comparable to that of the experimental error of the quantitative chemical determination. Finally, different ways of selecting FT-IR spectral elements (variables) to correlate with %DE were compared. The method of principal variables (PV) was found to be superior to methods based on knowledge based selection and the resulting PV-based model was found to be slightly better than the PLS model using the full spectral information.

Hot ions in Jupiter's magnetodisc: A model for Voyager 2 low‐energy charged particle measurements

The Low‐Energy Charged Particle (LECP) instrument on the Voyager 2 spacecraft acquired a comprehensive set of directional and energy‐dependent information on the nature of hot ions in the Jovian magnetodisc. The LECP measurements in the energy range 30 keV to 5 MeV, where the ion pressure dominates the total plasma pressure, have been successfully fit to a two‐species convected k distribution function model for hot ions in the Jovian magnetodisc in the vicinity of neutral sheet crossings. The regions where the model could be used ranged from 60 to 30 RJ on the dayside (inbound) and 75 to 125 RJ on the nightside (outbound). With this model, the full angular and spectral information from the lowest‐energy LECP detectors has been deconvolved using a nonlinear least squares technique to reveal the heavy ion pressure, density, and temperature distinct from the corresponding hot proton parameters. The pressure is dominated by heavy ions in the outer magnetosphere. The temperature of protons remains nearly constant at 20 keV (dayside) and 10 keV (nightside), whereas the heavy ion temperature shows a distinct increase with radial distance paralleling the corotation or pickup energy of heavy ions. A neutral wind of heavy atoms, originating in the near‐Io regions and ionized during their flight through the outer magnetosphere by solar radiation, may be the seed population for the heavy ions measured by the LECP. The convection velocity of the plasma is subcorotational, reduced from the rigid value by a factor of ∼2, but increases with increasing distance from 30 to 60 RJ in the dayside region and from 75 to 85 RJ in the nightside region. The trend stops beyond 85 RJ in the nightside region, but there is still a substantial corotational flow that extends from 85 RJ to at least 130 RJ. In all the regions studied, the particle anisotropies in the LECP scan plane below ∼2 MeV are believed to result primarily from the Compton‐Getting effect and not from gradient anisotropies or particles executing nonadiabatic orbits as they encounter the neutral sheet. Gradient anisotropies are not important even in the distant nightside neutral sheet region (&gt;85 RJ) below ∼2 MeV. The large flow velocities and increasing heavy ion temperatures are consistent with a strong corotational electric field and imply that the mass loading due to lower‐energy heavy ion plasma via outward transport from Io is insufficient to disrupt corotation within ∼60 RJ during the Voyager 2 encounter.

Assignment Strategies and Analysis of Cross-Peak Patterns and Intensities in the Three-Dimensional Homonuclear TOCSY-NOESY of RNA

The application of 3D TOCSY-NOESY to the analysis of RNA is presented, using a TOCSY-NOESY spectrum of the RNA duplex r(5′GGGCUGAAGCCU′). It is shown that for RNA molecules, 3D spectra can be obtained with a digital resolution comparable to that obtained for 2D NMR with full spectral information. The improvement in assignment over 2D methods is shown and discussed on the basis of an assignment strategy presented earlier. A simple and straightforward method for determining sugar puckers and γ backbone torsion angles is presented, which is derived from an analysis of cross-peak intensities originating from the TOCSY coherence transfer among sugar protons and HS′/5″ protons. The stereospecific assignment of the HS′/5″ resonances in 3D TOCSY-NOESY spectra is also discussed.

Application and comparison of algorithms for the evaluation of interferograms

Reflectometric interference spectroscopy (RIfS) has been applied to the detection of organic vapours in air. A new algorithm for the evaluation of the resulting interferograms is discussed. The algorithm uses the full spectral information available for signal evaluation. The performance is compared to methods already published. The limits of detection for various hydrocarbons are given.

High resolution FTS of atoms and molecules in the ultra-violet

The extension of high resolution FTS into the ultra-violet (λ≥175 nm) is described briefly and illustrated by two applications. In the hollow cathode spectrum of iron, wavelength measurements have been made with an accuracy from 1∶109 in the visible to 1∶108 in the UV. In atomic emission spectroscopy with ICP or glow discharges, full spectral information, with completely resolved line profiles, is obtained.