Decrease In Intensity Of Lines Research Articles

The self-absorption temporal evolution of spectral lines emitted from laser-induced plasmas

The interference of self-absorption (SA) in measurement of spectral lines in laser-induced plasmas (LIPs) needs to be addressed urgently, since the SA affects the spectral line shape, i.e., the line intensity decreases and line broadening changes. Here, the time resolved SA coefficients of six lines (Ca I 422.67 nm, Ca II 396.84 nm, Mg I 285.21 nm, Mg II 280.27 nm, Al I 394.40 nm, Al II 781.23 nm) emitted from laser induced soil plasmas are investigated based on the investigation of the temporal evolution of electron temperature (Te) and electron density (Ne). The SA coefficient of line Ca I 422.67 nm decreases sharply in the delay time of 0.2–0.6 μs, and tends to be maintained in the 0.6–2.0 μs temporal window. While other five lines (Ca II 396.84 nm, Mg I 285.21 nm, Mg II 280.27 nm, Al I 394.40 nm, Al II 781.23 nm) SA coefficients decrease sharply in the 0.2–1.2 μs delay time due to the decreasing Stark broadening of those lines with the decreasing Te and Ne correspondingly. While, in the 1.2–1.6 μs temporal window, the changes in SA coefficients of these five lines become steady because the plasmas property parameters (Te and Ne) are stable after the delay time of about 1.0 μs. This indicates that the best time window for the accurate analysis of element concentration using LIPs is from 1.2 μs to 1.6 μs.

Analysis of spectral properties for coal with different volatile contents by laser-induced breakdown spectroscopy

In view of the inevitable influence of variable coal quality for laser-induced breakdown spectroscopy (LIBS) detection, the effects of changes in volatile content on the properties of the laser-induced plasma and spectral signals were investigated using five coal samples, which cover a wide range of volatiles and their coal chars. Results showed that the intensities of most elements in coal were lower than those in coal chars including the major elements (C, H, O and N) and mineral elements (Si, Al, Ca, etc), along with the vaporization and ablation processes of volatile. Volatiles were easily affected by the thermal mechanism due to the high plasma temperature and more volatiles were vaporized in coal samples with higher volatile content. These increase the ionization of volatiles, resulting in the significant decrease of line intensities of mineral elements (Si, Al, Ca existing in ash). There is no significant relationship between the line intensities of major elements (C, H, O and N) and volatile content. Furthermore, the elemental concentration of sample surface areas was measured to reveal the difference between original sample surface, heat-affected area and internal surface of ablated crater to characterize the influence of laser pulse thermal mechanism. The concentration of C in the internal surface of crater and heat-affected area of coal sample was higher than that in the original surface, due to the evaporation of volatiles and other elements caused by thermal mechanism. On the other hand, the concentrations of most mineral elements of the internal surface were lower than that in the original surface. This may be attributed to thermal mechanism, caused by the different rates of volatilization and atomization processes of elements.

Terahertz spectroscopy of 2,4-dinitrotoluene over a wide temperature range (7-245 K).

Previous THz spectroscopy of the TNT explosive precursor, 2,4-dinitrotoluene (DNT), has been restricted to room temperature (apart from one set of data at 11 K). Here, for the first time, we investigate the spectrum as the temperature is systematically varied, from 7 to 245 K. Many new features appear in the spectrum on cooling below room temperature. As well as the five absorption lines observed previously, we observe five additional lines. In addition, a new room-temperature line at 8.52 THz (281 cm(-1)) is observed. Six of the lines red-shift with temperature and four of them blue-shift. The blue shift is explained by interplay between intramolecular and intermolecular hydrogen bonds. The variation in line width and line intensity with temperature is not systematic, although a conspicuous decrease in line intensity with temperature is observed in all cases. Modeling with hybrid PBE0 and TPSSh functionals helps identify absorption modes.

Radio seismology of the outer solar corona

Observed oscillations of coronal loops in EUV lines have been successfully used to estimate plasma parameters in the inner corona (< 0.2 R_0, where R_0 is the solar radius). However, coronal seismology in EUV lines fails for higher altitudes because of rapid decrease in line intensity. We aim to use radio observations to estimate the plasma parameters of the outer solar corona (> 0.2 R_0). We use the large Ukrainian radio telescope URAN-2 to observe type IV radio burst at the frequency range of 8-32 MHz during the time interval of 09:50-12:30 UT in April 14, 2011. The burst was connected to C2.3 flare, which occurred in AR 11190 during 09:38-09:49 UT. The dynamic spectrum of radio emission shows clear quasi-periodic variations in the emission intensity at almost all frequencies. Wavelet analysis at four different frequencies (29 MHz, 25 MHz, 22 MHz and 14 MHz) shows the quasi-periodic variation of emission intensity with periods of 34 min and 23 min. The periodic variations can be explained by the first and second harmonics of vertical kink oscillation of transequatorial coronal loops, which were excited by the same flare. The apex of transequatorial loops may reach up to 1.2 R_0 altitude. We derive and solve the dispersion relation of trapped MHD oscillations in a longitudinally inhomogeneous magnetic slab. The analysis shows that a thin (with width to length ratio of 0.1), dense (with the ratio of internal and external densities of > 20) magnetic slab with weak longitudinal inhomogeneity may trap the observed oscillations. Seismologically estimated Alfv\'en speed inside the loop at the height of 1 R_0 is 1000 km/s. Then the magnetic field strength at this height is estimated as 0.9 G. Extrapolation of magnetic field strength to the inner corona gives 10 G at the height of 0.1 R_0.

A search for line intensity enhancements in the far-UV spectra of active late-type stars arising from opacity

Radiative transfer calculations have predicted intensity enhancements for optically thick emission lines, as opposed to the normal intensity reductions, for astrophysical plasmas under certain conditions. In particular, the results are predicted to be dependent both on the geometry of the emitting plasma and the orientation of the observer. Hence in principle the detection of intensity enhancement may provide a way of determining the geometry of an unresolved astronomical source. To investigate such enhancements we have analyzed a sample of active late-type stars observed in the far ultraviolet spectral region. Emission lines of O VI in the FUSE satellite spectra of epsilon Eri, II Peg and Prox Cen were searched for intensity enhancements due to opacity. We have found strong evidence for line intensity enhancements due to opacity during active or flare-like activity for all three stars. The O VI 1032/1038 line intensity ratios, predicted to have a value of 2.0 in the optically thin case, are found to be up to ~30% larger during several orbital phases. Our measurements, combined with radiative transfer models, allow us to constrain both the geometry of the O VI emitting regions in our stellar sources and the orientation of the observer. A spherical emitting plasma can be ruled out, as this would lead to no intensity enhancement. In addition, the theory tells us that the line-of-sight to the plasma must be close to perpendicular to its surface, as observations at small angles to the surface lead to either no intensity enhancement or the usual line intensity decrease over the optically thin value. For the future, we outline a laboratory experiment, that could be undertaken with current facilities, which would provide an unequivocal test of predictions of line intensity enhancement due to opacity, in particular the dependence on plasma geometry.

Experimental study of the temporal evolution of N2(C3Πu) and N2(B3Πg) in a nitrogen pulsed discharge

The N2 (C 3Πu) and N2 (B 3Πg) triplet states are studied in the positive column of a nitrogen dc pulsed discharge by optical emission spectroscopy. Time variations of all vibrational levels are observed during a 700 µs pulse duration in a pressure range from 0.05 to 4 Torr. Even if the current remains constant during the pulse, the bands intensities emitted from the triplet states change during the pulse. According to the state and the vibrational level, we observe an increase or a decrease of line intensities as a function of pressure. It is pointed out that for N2 (B 3Πg) time variations are not similar for low and high vibrational levels. From the observation of individual vibrational levels, time evolution of vibrational distributions (VDs) are measured for N2 (B 3Πg) and N2 (C 3Πu). From these VDs a vibrational temperature is deduced. For a 4 Torr pressure, the deduced vibrational temperature increases from 5000 to 9000 K for N2 (B 3Πg) and from 3000 to 9000 K for N2 (C 3Πu). This vibrational temperature is representative of the temporal evolution of the plasma and, even after 700 µs, a steady state is not reached.

Experimental studies of the dynamics of compact toroid injected into the JFT-2M tokamak

We present the first results from recent compact toroid (CT) injection experiments in the JFT-2M tokamak using the improved CT injector and diagnostics with fast time resolution. We have observed that the core line density increases rapidly at a maximum rate of ∼1.3 × 1022 m−3 s−1 after a delay of 100–200 µs. This increment rate of the core density is about several times larger than that obtained so far. Interferometry measurement along the peripheral line chord of R = 1.1 m in the inboard side indicates that CT plasma reaches a region near the plasma core beyond the separatrix. Time-frequency and space distribution analyses of edge magnetic probe signals show that the magnetic fluctuation induced by the CT has the spectral peak at 250–350 kHz and propagates in the toroidal direction at the Alfvén speed of the order of 106 m s−1. These results indicate the excitation of Alfvén wave by CT injection. We have observed that the fluctuation level of the ion saturation current in the divertor and the Dα spectral line intensity decrease significantly after CT injection. Corresponding increase in the soft x-ray signals in the core region may suggest that the CT causes a transition to H-mode-like discharges.

Plasma confinement using biased electrode in the TCABR tokamak

Experimental data obtained on the TCABR tokamak (R = 0.61 m, a = 0.18 m) with an electrically polarized electrode, placed at r = 0.16 m, is reported in this paper. The experiment was performed with plasma current of 90 kA (q = 3.1) and hydrogen gas injection adjusted for keeping the electron density at 1.0 × 1019 m−3 without bias. Time evolution and radial profiles of plasma parameters with and without bias were measured. The comparison of the profiles shows an increase of the central line-averaged density, up to a maximum factor of 2.6, while Hα hydrogen spectral line intensity decreases and the C III impurity stays on the same level. The analysis of temporal behaviour and radial profiles of plasma parameters indicates that the confined plasma enters the H-mode regime. The data analysis shows a maximum enhanced energy confinement factor of 1.95, decaying to 1.5 at the maximum of the density, in comparison with predicted Neo–Alcator scaling law values. Indications of transient increase of the density gradient near the plasma edge were obtained with measurements of density profiles. Calculations of turbulence and transport at the Scrape-Off-Layer, using measured floating potentials and ion saturation currents, show a strong decrease in the power spectra and transport. Bifurcation was not observed and the decrease in the saturation current occurs in 50 µs.

Modeling RR Telescopii through the Evolution of the Spectra

We investigate the evolution of RR Tel after the outburst by fitting the emission spectra in two epochs. The first one (1978) is characterized by large fluctuations in the light curve, and the second one (1993) by a slow fading trend. In the frame of a colliding wind model, two shocks are present: the reverse shock propagates in the direction of the white dwarf, while the other one expands toward or beyond the giant. The results of our modeling show that in 1993, the expanding shock has overcome the system and is propagating in the nearby ISM. The large fluctuations observed in the 1978 light curve result from line intensity rather than from continuum variation. These variations are explained by fragmentation of matter at the time of head-on collision of the winds from the two stars. A high-velocity (500 km s-1) wind component is revealed from the fit of the SED of the continuum in the X-ray range in 1978, but is quite unobservable in the line profiles. The geometrical thickness of the emitting clumps is the critical parameter that can explain the short-timescale variabilities of the spectrum and the trend of slow line intensity decrease.

Molecular Cloud Cores in the Orion A Cloud. II. FCRAO CS (2–1) Data

CS (2-1) data of the Orion A Cloud obtained with the FCRAO 14 m telescope are shown. The CS (2-1) image shows the clumpy and filamentary structure of the Orion A cloud, as did our previous CS (1-0) image, obtained with the NRO 45 m telescope. The peak intensity TMB (CS 2-1) decreases more steeply than TMB (CS 1-0) toward the south along the filament. It is found that the gas density of the CS cores tends to be lower in the south of the cloud, and this explains the above difference in the line-intensity decrease. From CS and C34S data, we estimated the optical depth of CS (2-1) to be moderately high (2-5) and that of CS (1-0) to be typically less than unity.

STUDY OF OXYGEN RECOMBINATION WITH A DOUBLE PULSE DISCHARGE

Oxygen atoms recombination at the wall is studied by time-resolved Optical Emission Spectroscopy in a pulsed discharge. In order to observe the atomic oxygen emission after discharge pulse, it is indispensable to re-excite O atoms because the lifetime of O* atoms is short. Here is proposed a technique based on a double pulse excitation. Atomic oxygen, created during the main discharge pulse, is probed in a time after-glow with a diagnostic pulse. This diagnostic pulse is as short as possible to only repopulate the atomic excited states, without significant production of supplementary atoms. The intensities of the emission lines O(3P-3S) at 844.6 nm and O(5P-5S) at 777.4 nm, measured during diagnostic pulse, are observed in the whole time after-glow as a function of delay after main pulse. The decrease of line intensities is related to the recombination of O atoms at the wall. For a “Pyrex” wall at 300 K, the obtained recombination probability γ is 10−3. This value is in agreement with previous results.

Two-Dimensional Spatial Distribution of the Time-Integrated Emission from Laser-Produced Plasmas in Air at Atmospheric Pressure

Emission from Nd:YAG laser-produced plasmas generated in air at atmospheric pressure has been studied with spatial resolution. With the use of a charge-coupled device (CCD), two-dimensional spatial distributions of the time-integrated line emission from plasmas of metallic (copper and stainless steel) and ceramic (alumina) samples were measured for laser power densities in the range 80–900 GW/cm2. Geometrical parameters (distance of the maximum, width in two directions) and the total space- and time-integrated emission were obtained as a function of power density. At the range 100–700 GW/cm2, the formation of a plasma in air for the metallic samples was shown to be responsible for a decrease in the total intensity of lines emitted from the sample plasma, accompanied by effects in the spatial profiles along the laser direction. Beyond 700 GW/cm2, a sharp increase of the line intensities was observed, related to the absence of the shielding air plasma.

On the use of biased movable B 4C-limiter for pumping O 2 and H 2O during discharge cleaning

The movable limiter, the head plate of which is formed with a boron carbide plate hot-pressed in vacuum, is used for studying plasma impurity removal and the possibility of boronization during discharge cleaning in Uragan-3M torsatron. Measurements of current-voltage characteristics, boron and oxygen spectroscopies, residual-gas mass-spectrometry were carried out for different biased and unbiased limiter positions. It is shown that at a negative limiter bias during pulsed discharges cleaning the boron spectral signal from the plasma increases due to arcing. At the same time the oxygen spectral line intensity decreases and it probably means desorbed oxygen and water effective trapping by boronized surfaces and the limiter B 4C-plate, since the main plasma parameters do not change at this moment. The estimations of the limiter application for impurity pumping and solid target boronization shows that the negatively biased movable B 4C-limiter can be used to improve pulsed discharge cleaning in Uragan-3M torsatron.

Aluminas Rehydration and Dehydration

AbstractIn this review paper, results on the A12O3-water interactions will be critically examined. The synthesis of alumina precursors rich in structural defects can be operated in an aqueous solution containing ligands with high affinity for A13+aqor by restricted hydrolysis of Al-alkoxides. Calcination of the gels yields transition aluminas containing four (IV), five (V) and six (VI) fold coordinated aluminum. The pore-size distribution, the Alvcontent and the degree of crystallinity are controlled by the degree of condensation of the oligomer species in the gel. In a dehydrated alumina two kinds of AlIVwith isotropic chemical shifts at ∼73 and 58 ppm, respectively, are present. The distorted AlIV(chemical shift at 58 ppm) and Alvare surface species. Upon water chemisorption the distorted AlIVline disappears while the Alvline is reinforced. As bulk rehydration progresses the Alvline intensity decreases. It is only partially restored upon recalcination. Thus, hydration-rehydration cycles cure the solid from its defects and increase crystallinity. The onset of rehydration is the chemisorption of water on the surface Lewis sites just as Lewis sites result from a thorough dehydration.

The microwave spectrum of the H2Cl+ ion

Four rotational transitions of the H2Cl+ ion were observed in the frequency region of 270 to 500 GHz by using a source-modulated microwave spectrometer combined with a hollow cathode free space cell. The H2Cl+ ion was generated by a dc discharge in a mixture of HCl, H2, and He. The ion was identified on the basis of the hyperfine structure of the chlorine nucleus. This was further confirmed by the observation of the line intensity decrease with external magnetic field, which is a characteristic of ions in a hollow cathode discharge. The rotational constants A, B, and C, and the centrifugal distortion constant ΔJK were determined. The nuclear quadrupole coupling constants of the chlorine nucleus were obtained for the first time: χaa =−53.44(47) MHz, χbb =−15.71(50) MHz, and χcc =69.15(70) MHz with three standard errors in parentheses. The character of the H–Cl bond orbital is estimated from the observed nuclear quadrupole coupling constants and the molecular structure.

Anisotropic scattering in dark clouds and formaldehyde lifetimes

Using the ray-tracing technique for solving radiative-transfer problems in spherical symmetry, we have developed a procedure for determining the radiation intensity in models of dark clouds exposed to the interstellar radiation field and/or to radiation from embedded stars. To this end, a source function that includes anisotropic scattering has been derived.By studying models of the rho Ophiuchi cloud complex, we find that higher opacities than those implied by star counts are necessary if photodissociation of formaldehyde by interstellar radiation in the outer parts of the cloud is not to occur. Furthermore, an increased excitation temperture or a high rate of photodissociation, or a combination thereof, may be the cause of the 6 cm H/sub 2/CO line intensity decrease observed at the position of an embedded star cluster.

Recombination of Ion Radicals in Single Crystals of Cytosine Monohydrate

Single crystals of cytosine monohydrate were irradiated with ..gamma.. rays at 77 K, and the electron spin resonance (ESR) spectra were recorded while gradually increasing the temperature. The analysis of the decrease in line intensity shows that the disappearance of cation and anion radicals is due predominantly to their mutual recombination. The kinetics study clearly displayed the existence of recombination processes with several distinct groups of activation energies. It is assumed that activation energies are reduced by the Coulomb interaction of closely spaced ions. The track model for the deposition of energy during irradiation is discussed.

Sarcomere length dispersion in single skeletal muscle fibers and fiber bundles

Light diffraction patterns produced by single skeletal muscle fibers and small fiber bundles of Rana pipiens semitendinosus have been examined at rest and during tetanic contraction. The muscle diffraction patterns were recorded with a vidicon camera interfaced to a minicomputer. Digitized video output was analyzed on-line to determine mean sarcomere length, line intensity, and the distribution of sarcomere lengths. The occurrence of first-order line intensity and peak amplitude maxima at approximately 3.0 mum is interpreted in terms of simple scattering theory. Measurements made along the length of a singel fiber reveal small variations in calculated mean sarcomere length (SD about 1.2%) and its percent dispersion (2.1% +/- 0.8%). Dispersion in small multifiber preparations increases approximately linearly with fiber number (about 0.2% per fiber) to a maximum of 8-10% in large bundles. Dispersion measurements based upon diffraction line analysis are comparable to SDs calculated from length distribution histograms obtained by light micrography of the fiber. First-order line intensity decreases by about 40% during tetanus; larger multifibered bundles exhibit substantial increases in sarcomere dispersion during contraction, but single fibers show no appreciable dispersion change. These results suggest the occurrence of asynchronous static or dynamic axial disordering of thick filaments, with a persistence in long range order of sarcomere spacing during contraction in single fibers.

Untersuchungen über die beobachtung, erklärung und beseitigung des interelementeffektes in der emissionsspektrometrie

The absolute intensity changes of the spectrum line of the basic material as well as of the alloying element must be taken into account for studying the true interelement effects. Empirical data referring to stainless and high-speed steels are published according to which (a) general and (b) specfiic changes can be observed. The absolute line intensities decrease in the case of high-alloy steels; the specific change can be positive or negative. The general decrease of line intensities at a constant excitation level is produced by the increase in the energy necessary for line excitation, in the so-called “spectral heat” —which includes all the physical-chemical processes on the surface of the sample; the specific changes are caused by the specific differences in this energy parameter. The interelement effect can be compensated for by applying the method of “anisosec integration” or by the use of calibration curves plotted by means of the method of “two standards” and standardized to unity.

Decrease in Intensity of Hg Lines near the Source in Weakly Ionized Mercury Gas Flow

In a flowing mercury afterglow with d. c. discharge source, rapid decrease in intensity of Hg lines near the source are investigated. Both the axial intensity distribution along the flow downstream and the radial one are interpreted in connection with diffusion of electron to the wall and electron to the wall and electron attachment. The effective diffusion coefficient is found to be D β,γ =2.7×10 3 / p (cm 2 /sec), which is close to the ambipolar diffusion coefficient under the experimental conditions i. e. n e =5×10 8 /cm 3 and T e =2 eV. As for the resonance line (6 3 P 1 –6 1 S 0 ), slow decrease in intensity as compared with decrease in intensity of lines emitted from the higher levels is taken to be due to the radiative imprisonment and in consequence the absorption coefficient of this line is obtained as 1.2×10 -13 n 0 /cm and the quenching cross section of the state 6 3 P 1 due to the collisions with mercury atoms as 10 =0.048 A 2 .