Spectroscopic Diagnostic Techniques Research Articles

Benchmarking Spectroscopic Techniques Combined with Machine Learning to Study Oak Barrels for Wine Ageing.

Due to its physical, chemical, and structural properties, oakwood is widely used in the production of barrels for wine ageing. When in contact with the wine, oak continuously releases aromatic compounds such as lignin, tannin, and cellulose to the liquid. Due to the release process, oak loses its characteristic aromatic compounds in time; hence, the flavour that it gives to the enclosed wine decreases for repeated wine refills and a barrel replacement is required. Currently, the estimation of the maximum number of refills is empirical and its underestimation or overestimation can impose unnecessary costs and impair the quality of the wine. Therefore, there is a clear need to quantify the presence of the aforementioned aromatic compounds in an oak barrel prior to a refill. This work constitutes a study to examine noninvasive optical biosensing techniques for the characterization of an oak barrel used in wine ageing, towards the development of a model to unveil its lifespan without inducing structural damage. Spectroscopic diagnostic techniques, such as reflectance, fluorescence, and Raman scattering measurements are employed to assess the change in the chemical composition of the oakwood barrel (tannin and lignin presence) and its dependence on repeated refills. To our knowledge, this is the first time that we present a benchmarking study of oak barrel ageing characteristics through spectroscopic methods for the wine industry. The spectroscopic data are processed using standard chemometric techniques, such as Linear Discriminant Analysis and Partial Least Squares Discriminant Analysis. Results of a study of fresh, one-time-used, and two-times-used oak barrel samples demonstrate that reflectance spectroscopy can be a valuable tool for the characterization of oak barrels. Moreover, reflectance spectroscopy has demonstrated the most accurate classification performance. The highest accuracy has been obtained by a Partial Least Squares Discriminant Analysis model that has been able to classify all the oakwood samples from the barrels with >99% accuracy. These preliminary results pave a way for the application of cost-effective and non-invasive biosensing techniques based on reflectance spectroscopy for oak barrels assessment.

Effect of the transition porous silicon layer on the properties of hybrid GaN/SiC/por-Si/Si(1 1 1) heterostructures

Using the complexes of structural and spectroscopic diagnostic techniques, we investigated the influence of the layer of nanoporous silicon on the practical implementation and certain features of the epitaxial growth of GaN layers with the use of MBE PA on the templates of SiC/por-Si/c-Si.For the first time, the layer of nanoporous silicon has been introduced in the template of SiC/por-Si/c-Si where the layer of 3C-SiC was obtained by the substitution of the atoms; this had a number of indisputable advantages as compared to conventional silicon substrates. In particular, the abovementioned approach enabled a 90% reduction in the stress levels in the crystalline lattice of GaN layer that was synthesised on the SiC surface of the SiC/por-Si/c-Si template; it also decreased some of the vertical dislocations within the GaN layer. We also found that the use of the SiC/por-Si/c-Si template resulted in the formation of a more uniform (by its quality) GaN layer without any visible extensive defects. As a result, this enabled us to attain unique optical and electro-physical characteristics for the hybrid heteroepitaxial GaN/SiC structures.The obtained data will be very important for understanding the basic physics of nanoheterostructures of GaN/SiC/por-Si, thus promoting their potential applications in optoelectronics.

(Invited) Multiscale Chemical Complexities in Layered Oxides for Sodium Ion Batteries

Applications such as large-scale stationary energy storage call for significantly reduced cost of batteries. Sodium ion batteries offer one of the most feasible alternatives to meet these particular demands. Layered oxide materials are regarded as a technologically important class of cathode materials due to their excellent reversibility in cycling sodium ions and relatively smaller degree of lattice volume change. Various transition metal ions can be incorporated in the transition metal layer of sodium layered oxides giving considerable flexibility to the choice of the transition metals. The different choices of transition metals make it challenging to obtain the perfectly homogeneous distribution in multielemental sodium layered oxide materials because of their differences in the ionic size and electronic properties. However, how much does the homogeneous elemental distribution matter in the battery performance? What are the chemical and structural transformations of heterogeneous layered oxides during charging and discharging? In this presentation, we will discuss our recent progress in understanding the multiscale heterogeneity in sodium layered oxide materials. First, we will establish the relationship between the cathode surface chemistry and the sodium full-cell electrochemistry through a range of complementary advanced spectroscopic and imaging diagnostic techniques. Second, we will highlight our effort in decoupling the multiscale electrochemistry in sodium layered oxide materials. We will illustrate that engineering the three-dimensional distribution of metal cations in electrode particles can take advantage of the depth-dependent charging mechanisms thus empowering superior battery performance.

Deciphering the Cathode–Electrolyte Interfacial Chemistry in Sodium Layered Cathode Materials

AbstractThe ever‐increasing demand for stationary energy storage has driven the prosperous investigation of low‐cost sodium ion batteries. The inferior long‐term cycling stability of cathode materials is a significant roadblock toward the wide commercialization of sodium ion batteries. This study enlightens a path toward empowering stable sodium ion batteries through incisive diagnostics of the multiscale surface chemical processes in layered oxide materials (e.g., O3‐NaNi1/3Fe1/3Mn1/3O2). The major challenges are unraveled in a promising sodium layered cathode material using a range of complementary advanced spectroscopic and imaging diagnostic techniques. It is discovered that the cathode–electrolyte interfacial reaction triggers transition metal reduction, heterogeneous surface reconstruction, metal dissolution, and formation of intragranular nanocracks. These surface chemistry driven processes are partly responsible for significant performance decay. This diagnostic study also rationalizes the elemental substitution and surface passivation methods that are widely applied in the field. The prepassivated and Ti‐substituted cathode materials allow for significantly improved cycling stability by inhibiting the metal dissolution. Therefore, incisively diagnosing the interfacial chemistry not only creates scientific insights into understanding sodium cathode chemistry, but also represents an advance toward establishing universal interfacial design principles for all alkali metal ion cathode materials.

Evaluation of the oscillator frequency of a free running RF generator as a diagnostic tool for inductively coupled plasma-optical emission spectrometry

The frequency response of a free running RF generator was evaluated for its ability to provide plasma diagnostic information. A small probe coil in the plasma torch housing and a frequency counter were used for frequency measurement. A linear dependence between the RF generator frequency and the flow of a foreign gas (CO2, H2, He, N2—introduced into the central channel of the ICP) was encountered. Moreover, the inductively coupled plasma (ICP) was found to extinguish at a constant, characteristic frequency when the flow of foreign gas was too high, allowing a simple prediction of the maximal tolerable foreign gas flow. Spectroscopic plasma diagnostic techniques (Mg II/Mg I ratio, excitation temperature and rotational temperature) were also investigated but provided little indication of instable plasma conditions due to the addition of foreign gases.

Electrohydrodynamic interaction induced by a dielectric barrier discharge

In the present work an experimental investigation on the electrohydrodynamic (EHD) interaction effect, induced by means of a dielectric barrier discharge on a 1atm subsonic air flow, is described. The air flow is obtained in an open circuit blowing wind tunnel at different air speeds. A plane plasma panel equipped with a dielectric discharge barrier system is immersed in the flow. A single phase sinusoidal power supply system, a superposition of a single phase sinusoidal system with a dc voltage supply, and a three phase symmetrical power supply configuration are considered. Electric, fluid dynamic, and spectroscopic diagnostic techniques are utilized. Pitot probe measurements are performed in the boundary layer on the plasma panel surface. Schlieren imaging is done to visualize the plasma sheath. Vibrational and rotational temperatures are evaluated by means of spectroscopic techniques. The force induced on the flow by the dielectric barrier discharge acts on the ions of the non-neutral sheath ahead of the plasma filament when travelling on the panel surface only. This causes a reduction of the time interval during which the force is active. The EHD effect and the momentum transfer to the gas flow in the boundary layer are reduced when the flow speed grows. An increase of the supply frequency and of the supply voltage causes an increase of the momentum transfer. In these experiments no significant increase of the efficiency of EHD effect is observed when utilizing the superposition of a dc voltage to a single phase power supply or a three phase power supply.

Ultraviolet spectroscopy of the extended solar corona

The first observations of ultraviolet spectral line profiles and intensities from the extended solar corona (i.e., more than 1.5 solar radii from Sun-center) were obtained on 13 April 1979 when a rocket-borne ultraviolet coronagraph spectrometer of the Harvard-Smithsonian Center for Astrophysics made direct measurements of proton kinetic temperatures, and obtained upper limits on outflow velocities in a quiet coronal region and a polar coronal hole. Following those observations, ultraviolet coronagraphic spectroscopy has expanded to include observations of over 60 spectral lines in coronal holes, streamers, coronal jets, and solar flare/coronal mass ejection (CME) events. Spectroscopic diagnostic techniques have been developed to determine proton, electron and ion kinetic temperatures and velocity distributions, proton and ion bulk flow speeds and chemical abundances. The observations have been made during three sounding rocket flights, four Shuttle deployed and retrieved Spartan 201 flights, and the Solar and Heliospheric Observatory (SOHO) mission. Ultraviolet spectroscopy of the extended solar corona has led to fundamentally new views of the acceleration regions of the solar wind and CMEs. Observations with the Ultraviolet Coronagraph Spectrometer (UVCS) on SOHO revealed surprisingly large temperatures, outflow speeds, and velocity distribution anisotropies in coronal holes, especially for minor ions. Those measurements have guided theorists to discard some candidate physical processes of solar wind acceleration and to increase and expand investigations of ion cyclotron resonance and related processes. Analyses of UVCS observations of CME plasma properties and the evolution of CMEs have provided the following: temperatures, inflow velocities and derived values of resistivity and reconnection rates in CME current sheets, compression ratios and extremely high ion temperatures behind CME shocks, and three dimensional flow velocities and magnetic field chirality in CMEs. Ultraviolet spectroscopy has been used to determine the thermal energy content of CMEs allowing the total energy budget to be known for the first time. Such spectroscopic observations are capable of providing detailed empirical descriptions of solar energetic particle (SEP) source regions that allow theoretical models of SEP acceleration to be tailored to specific events, thereby enabling in situ measurements of freshly emitted SEPs to be used for testing and guiding the evolution of SEP acceleration theory. Here we review the history of ultraviolet coronagraph spectroscopy, summarize the physics of spectral line formation in the extended corona, describe the spectroscopic diagnostic techniques, review the advances in our understanding of solar wind source regions and flare/CME events provided by ultraviolet spectroscopy and discuss the scientific potential of next generation ultraviolet coronagraph spectrometers.

Spectroscopic characteristics of polar plumes

Extreme ultraviolet observations of plumes in polar coronal holes are presented and their spectroscopic signatures discussed. The study focuses on the base of plumes seen on the disk of the Sun with the Coronal DiagnosticSpectrometer (CDS) on the Solar and Heliospheric Observatory (SOHO) satellite. Spectroscopic diagnostic techniques are applied to characterise the plumes in terms of density, temperature, emission measure and element abundance. Attention is drawn to the particular limitations of some of the techniques when applied to plume structures. In particular, we revisit the Widing & Feldman (1992) findings of a plume having a large first ionization potential (FIP) effect of 10, showing that instead the Skylab data are consistent with no FIP effect. We present for the first time CDS-GIS (grazing incidence spectrometer) observations of a plume. These observations have been used to confirm the results obtained from normal incidence (NIS) observations. We find that polar plumes exhibit the same characteristics as the Elephant's Trunk equatorial plume. The most striking characteristic of the plume bases is that they are near-isothermal with a peak emission measure at transition region temperatures ≃8 x 10 5 K. At these temperatures, plumes have averaged densities N e ≃ 1.2 x 10 9 cm-3, about twice the value of the surrounding coronal hole region. Element abundances in the plumes are found to be close to photospheric, with the exception of neon which appears to be depleted by 0.2 dex relative to oxygen. The absence of a significant FIP effect in plumes is consistent with fast solar wind plasma, although it is not sufficient to prove a link between the two. Finally, we present a comparison between GIS spectra and the SOHO EIT (EUV Imaging Telescope) broad-band images, showing that temperatures derived from the EIT ratio technique are largely overestimated, for plumes and coronal holes. This is partly due to the fact that the so called Fe XII 195 A and Fe XV 284 A filters are not isothermal, and in coronal holes and plumes lower-temperature lines dominate the EIT signal.

Spectroscopic diagnostics of stellar transition regions and coronae in the XUV: AU Mic in quiescence

In this paper we review the spectroscopic diagnostic techniques that can be applied to XUV observations of active stars. In particular, we discuss methods for the determination of electron densities, emission measures and the chemical composition of the stellar transition regions and coronae. We pay particular attention to the atomic data used and we revise several previous analyses with the most recent atomic data (from CHIANTI). We nd severe limitations to some of the commonly used methods and atomic data and we obtain results which are signicantly dierent from other authors. We illustrate this with a number of examples. We analyse a combined set of multi-wavelength observations (EUVE, HST/STIS, FUSE) for the quiescent phase of the dMe star AU Mic. A major conclusion of this paper is that the use of spectral lines from the Li and Na isoelectronic sequences, common in previous literature, produces erroneous results in the determination of emission measures, elemental abundances and transition region densities.

Understanding the atmospheric structure of T Tauri stars — I. Improved atomic physics applied to IUE data of BP Tauri

ABSTRA C T Recent advances in modelling the radiating character of dynamic laboratory and astrophysical plasmas are applied here in a new examination of the properties of the atmosphere of the classical T Tauri star BP Tau. We analyse archived International Ultraviolet Explorer (IUE) UV spectra of BP Tau. We adopt a collisional-radiative model and utilize emission measure (EM) and differential emission measure (DEM) techniques to try to constrain the distribution of emitting material in temperature in the atmosphere of this star. We use spectroscopic diagnostic techniques to probe atmospheric parameters such as electron density, and to set constraints on the volume of emission regions. This work is important for understanding the fundamental properties of BP Tau and other T Tauri stars, and for providing a more complete basis for models of their atmospheres.

The Elephant's Trunk: Spectroscopic diagnostics applied to SOHO/CDS observations of the August 1996 equatorial coronal hole

A large equatorial coronal hole, named the “Elephant's Trunk,” was observed by the coronal diagnostic spectrometer (CDS) on board the Solar and Heliospheric Observatory (SOHO) during the last week of August 1996. Spatially averaged spectra within the hole and in neighboring quiet sun regions are analyzed and calibrated in intensity. Spectroscopic diagnostic techniques that make use of the CHIANTI atomic database are applied in an attempt to characterize such large‐scale features. Line intensity ratios are used to obtain information on the electron density, temperature, and element abundances inside and outside the coronal hole. The transequatorial coronal hole showed, on average, coronal electron densities Ne ≃ 2 − 3×l08 cm−3, a factor of 2 higher than the quiet sun areas near the hole. A differential emission measure analysis shows that emission measures in the coronal hole were much lower at temperatures above a million degrees than in the quiet sun regions. In the Elephant's Trunk, the temperature of peak emission is found to be ≃ 8×105 K, compared to about 9.7×105 K in the quiet sun. Indications of a first ionization potential (FIP) effect differentiating between cell centers and the network are found, both in coronal hole and quiet sun regions. A small plume was detected inside the Elephant's Trunk coronal hole at low latitude, on the disc.

Characterization of Solar Coronal Holes and Plumes Using Spectroscopic Diagnostic Techniques Applied to SOHO/CDS Observations

Results from a series of SOHO/Coronal Diagnostic Spectrometer (CDS) observations of coronal holes and plumes are presented, including analysis of a low-latitude plume observed in August 1996. Spectroscopic diagnostic techniques using the CHIANTI atomic database are applied to derive the plasma parameters: electron density, temperature, and element abundances. The results are compared with quiet sun values. Coronal electron densities in the holes are found to be about 2 × 108 cm-3, a factor of two to three lower than in the quiet sun. The plasma thermal distribution exhibits differences between coronal holes, the quiet sun and plumes. For example, the peak of the emission in coronal holes is at a lower temperature (T ≃ 8 × 105 K) than in the quiet sun (T ≃ 1 × 106 K), while plumes are cooler (T ≃ 7.6 × 105 K) and show a different distribution, closer to an isothermal state.

Preliminary spectroscopic experiments with helium microwave induced plasma produced in air by use of a new structure: the axial injection torch

In this experimental study we have used spectroscopic methods to characterize helium plasma obtained by means of a novel waveguide-fed microwave plasma torch at atmospheric pressure, the axial injection torch. This device produces a “plasma flame” by coupling high frequency (HF) power at 2.45 GHz to the discharge. Various flame parameters (namely the electron density number and the electron and gas temperatures) have been determined by using spectroscopic diagnostic techniques that provided an estimate in terms of the helium flow rate, absorbed HF power and axial position in the experiments. These preliminary results suggest some departure from local thermodynamic equilibrium (LTE) and seem to indicate the utility of the discharge as an excitation source for emission spectroscopy. Comparison with other microwave torches already described in the literature is made in terms of the electron density and the electron and gas temperature.

Spectroscopic diagnostics in the VUV for solar and stellar plasmas

The VUV emission spectra from the solar atmosphere and stellar atmospheres have been intensively studied during the past 25 years with several major space programs. In this review we discuss the spectroscopic diagnostic techniques used to study astrophysical plasmas, the atomic processes involved, the recent observations and the plans for future space missions.

Visible-light spectroscopy of pulsed-power plasmas (invited)

We describe the investigations of the plasma behavior in three pulsed-power systems: a magnetically insulated ion diode, and plasma opening switch, and a gas-puffed Z pinch. Recently developed spectroscopic diagnostic techniques allow for measurements with relatively high spectral, temporal, and spatial resolutions. The particle velocity and density distributions within a few tens of microns from the dielectric-anode surface are observed using laser spectroscopy. Fluctuating electric fields in the plasma are inferred from anisotropic Stark broadening. For the plasma opening switch experiment, a novel gaseous plasma source was developed which is mounted inside the high-voltage inner conductor. The properties of this source, together with spectroscopic observations of the electron density and particle velocities of the injected plasma, are described. Emission line intensities during the switch operation are discussed. In the Z-pinch experiment, spectral emission-line profiles of various charge-state ions are studied during the implosion phase. Radial velocity distributions are observed from the line Doppler shifts and widths.

High-resolution X-ray spectroscopic diagnostics of laser-heated and ICF plasmas

This article presents a review of X-ray spectroscopic diagnostic and measurement techniques as applied to laser plasma interaction and laser fusion studies. As a matter of definition we restrict our attention to the range of a several hundred eV to about 100 keV. We deal with both the basic measurement concepts and the instrumental techniques. First a brief review of the physical phenomena and parameter ranges involved is given. We then deal with specific X-ray spectroscopic instruments and methods that are useful in laser plasma X-ray spectroscopy. A discussion is given of various modeling techniques and how they can be compared with experimental measurements.

Excitation and ionization characteristics of a d.c. argon plasma evaluated by means of emission and absorption of iron lines, and broadening of the hydrogen Hβ line—experimental facts

Spectroscopic diagnostic techniques were used to investigate the plasma of a 7.5 A d.c. arc in argon with aerosol supply. An analytically usable portion of the arc column was 50 mm long, cylinder shaped, and suitable for observation in the axial direction, i.e. for “end-on” observation. This made possible the evaluation of the spatially resolved local plasma parameters without the use of Abel inversion. Solutions containing 1 gl of iron were introduced with a pneumatic nebulizer. Absorption and emission of Fe I and Fe II lines were used to evaluate populations of ground and excited states. From the Boltzmann-Saha plots, apparent temperatures and electron number densities were determined as functions of the radius. The electron number densities were also determined from the broadening of the Hβ line. Stratification in the radial direction limited the applicability of the spectroscopic techniques. At about 2.9 mm off the arc axis, excitation of Fe II lines by charge transfer was observed. Different values of the electron number density were deduced from emission, combined emission and absorption, and Hβ profile measurements.

Ultraviolet Spectroscopy of Cool Stars from IUE

AbstractObservations of cool stars with the IUE satellite have shown that although main sequence stars have uv spectra similar to that of the sun, the spectra of the giants and supergiants are dominated by lines of neutral atoms and singly charged ions. The atmospheres of the low gravity stars are greatly extended and there is a large opacity in the stronger lines. This leads to multiple scattering and the appearance of many transitions through line ‘leakage’.A review is given of how high resolution IUE spectra have allowed line identifications to be established and some current problems are discussed.The spectroscopic diagnostic techniques for the low gravity, low density atmospheres are also briefly outlined.

Results From Optical and UV Stellar Flare Spectroscopy

ABSTRACTOptical and ultraviolet spectroscopy can enable the assessment of the physical conditions characterizing a stellar flare atmosphere and thereby potentially elucidate the possible radiative and hydrodynamic transport mechanisms operative during stellar flares. In this review, I present illustrative examples of the spectroscopic diagnostic techniques that can be applied to the analysis of stellar flare spectroscopic data and the resulting inferences concerning stellar flare properties for M dwarf flare events.

On the ionization equilibrium balance

Ionization equilibrium for the most astrophysically abundant elements are calculated using multilevel atomic models for several stages of ionization. It is found that the relative abundance of the lithium-, beryllium-, and boron-like ions at electron densities as low as 1 million per cu cm is density-dependent. Because of this dependence, the intensity of lines arising from ions of the Li, Be, and B isoelectronic sequences are density-sensitive. The general implications of these results as applied to solar and stellar atmospheric models, coronal abundances, and spectroscopic diagnostic techniques are discussed.