Emission Absorption Measurements Research Articles

Synthetic Observations of 21 cm H i Line Profiles from Inhomogeneous Turbulent Interstellar H i Gas with Magnetic Fields

Abstract We carried out synthetic observations of interstellar atomic hydrogen at 21 cm wavelength by utilizing the magnetohydrodynamic numerical simulations of the inhomogeneous turbulent interstellar medium. The cold neutral medium (CNM) shows a significantly clumpy distribution with a small volume filling factor of 3.5%, whereas the warm neutral medium (WNM) has a distinctly different and smooth distribution with a large filling factor of 96.5%. In projection on the sky, the CNM exhibits a highly filamentary distribution with a subparsec width, whereas the WNM shows a smooth, extended distribution. In the H i optical depth, the CNM is dominant and the contribution of the WNM is negligibly small. The CNM has an area covering factor of 30% in projection, while the WNM has a covering factor of 70%. This means that the emission–absorption measurements toward radio continuum compact sources tend to sample the WNM with a probability of 70%, yielding a smaller H i optical depth and a smaller H i column density than those of the bulk H i gas. The emission–absorption measurements, which are significantly affected by the small-scale large fluctuations of the CNM properties, are not suitable for characterizing the bulk H i gas. Larger-beam emission measurements that are able to fully sample the H i gas will provide a better tool for that purpose, if a reliable proxy for hydrogen column density, possibly dust optical depth and gamma rays, is available. The present results provide a step toward precise measurements of the interstellar hydrogen with ∼10% accuracy. This will be crucial in interstellar physics, including identification of the proton–proton interaction in gamma-ray supernova remnants.

Nanoparticle plume dynamics in femtosecond laser ablation of gold

This paper describes some recent results on femtosecond laser ablation of gold. We have studied both the fast vapour/plasma and slow nanoparticle plumes using Langmuir probe, time-resolved ICCD imaging and time-resolved optical absorption measurements. The nanoparticle plume dynamics was analysed by comparing the optical emission absorption measurements with an adiabatic isentropic model of ablation plume expansion, leading to an estimate of the amount of material in the nanoparticle plume.

Time and temperature dependence of carbon particle growth in various shock wave pyrolysis processes

The results of various experiments on carbon nanoparticle formation during gas phase pyrolysis behind shock waves in the temperature range 1200 K ⩽ T f ⩽ 3500 K are analysed. In the wavelength range 0.22 μm ⩽ λ ⩽ 1.31 μm, the optical properties of particles and their current sizes, measured by laser-induced incandescence, are compared. For a correct knowledge of the actual temperature during particle formation, spectral emission–absorption measurements in the IR range were performed. It was found that the light extinction due to particle growth in different mixtures and at different temperatures can be described by a global rate law for optical density. The observed decrease in optical density at 633 nm with increasing temperature is not a result of the decrease in particle yield, as was assumed earlier, but is caused by the size dependent refractive index. Furthermore, the final particle size decrease with the temperature rise is most likely the deceleration of the coagulation rate of the primary clusters and correspondingly, the increase of the particle number density.

Non-coincident multi-wavelength emission absorption measurements in MHD plasmas

An analysis of the effect of non-coincident sampling on the measurement of atomic number density and temperature by multi-wavelength emission absorption methods is presented under the assumption that the emission and transmitted lamp signals are time resolved but not coincident. The analysis shows that the averages of such measurements are valid despite fluctuations in temperature and optical depth. Under potassium-seeded MHD conditions the fluctuations introduce additional uncertainty into measurements of potassium atom number density and temperature but do not significantly bias the average results. Measurements in a prototype-scale MHD flow with coincident and non-coincident sampling support the analysis.

New Relationships for Emission-Absorption Measurements of Alkali-Seeded Combustion Gases.

Numerical studies on emission-absorption measurements of potassium-seeded kerosene-oxygen combustion gases were carried out. It was found that the ratio of the optical thicknesses at two arbitrary wing wavelengths of the potassium 766.5 nm resonance line was nearly equal to the ratio of the respective atomic absorption coefficients which were calculated based on the temperature measured by the emission-absorption method at the far-wing wavelength. Using the formula, the optical collision cross section as well as the pressure and Doppler broadenings of the potassium doublet could be predicted theoretically with an error of less than one percent. The optimal difference between the far-and near-wing wavelengths is 1.0-2.0 nm. The error in the above optical quantities and also the seed atom number density are insensitive to the near-wing wave-length.

Measurements of temperature and seed atom density in high-speed MHD flows

Emission absorption measurements of temperature, potassium seed atom density, and electron conductivity have been demonstrated in the high-speed, turbulent coal-fired flow of a simulated MHD channel. A two-beam optical system provides coincident exposures of transmitted lamp and emission-only signals with a time resolution of one-half ms. Multiwavelength detection allows for optimization of the measurement wavelengths for a twowavelength analysis that eliminates error due to ash/slag particle extinction and emission. Previous measurements with single beam, 1 ms temporally separated measurements showed large standard deviations due to fluctuations in flow parameters between the two noncoincident exposures. Comparison of the two types of measurements for nominally the same flow conditions reveals the considerable improvement in measurement uncertainty with the two-beam optical system.

Experimental and Theoretical Studies on Soot Formation in an Ethylene Jet Flame

ABSTRACT Soot formation was studied in any ethylene turbulent diffusion flame. A small probe was built to carried out pyrometric measurements in the flame. Instantaneous and local values of temperature and soot volume fraction were determined from emission-absorption measurements, and that made it possible to follow the fluctuations of temperature and soot volume fraction at the same time. Numerical simulation of the jet flame was performed and comparison with the experimental results is shown

Potassium D-line 'blue' wing absorption coefficient under combustion-fired magnetohydrodynamic conditions

A model is proposed for the adsorption coefficient of the far wing of the potassium D-Iine under combustion-fired magnetohydrodynamic (MHD) conditions. Such a model is important because of the need to measure potassium seed-atom densities on large-scale MHD facilities. The model was developed using experimental emission profiles on a 20-cm diam oil-fired, simulated MHD flow. A two-parameter model, constructed of a sum of power laws matched to a Voigt profile in the near blue wing, fits the 730-760 nm region well with a power-law exponent of -1.07 matched to the Voigt at 764.6 nm. Using this model, emission absorption measurements on coal-fired MHD flows with diameters of 33 and 76 cm compared well to chemical equilibrium calculation predictions. The model should allow accurate measurements of seed-atom density irrespective of the flow dimensions and geometry using two-wavelength wing emission absorption measurements, a technique suitable for real-time monitoring. Such measurements should then provide a useful indirect measure of the electron density which is a critical parameter for analyzing MHD power generation.

Simultaneous emission absorption measurements in toluene-fueled pool flames: Mean and RMS Properties

Local measurements of mean and RMS emission intensities, transmittances, emission temperatures, and soot volume fractions based on emission and absorption in toluence flames burning in a pool configuration are reported. Radial profiles of these quantities at six axial stations within the flame are selected for discussion. The results show large fluctuations in temperatures and soot volume fractions at all locations including those near the liquid surface. Differences between the soot volume fractions based on emission and those based on absorption indicate the presence of large quantities of relatively cold soot at all positions.

Bias in emission absorption measurements of temperature and atomic density

Presented here is an analysis of the bias arising from two fundamental difficulties hi applying emission absorption methods to large-scale combustion systems: 1) maintaining clean optical windows; and 2) maintaining the optical alignment. The impetus for the study was an anomalously large temperature measurement uncertainty for potassium D-line measurements hi a coal-fired magnetohydrodynamic (MHD) flow, while no increased uncertainty was observed for the measured seed atom density. The large uncertainty can be explained by a rapid, oscillatory misalignment. This misalignment biases the measured temperature hi the same manner as that for a fouled lamp-side window. Expressions for the biases for fouled optical windows are presented. Expressions are developed for the bias and uncertainty caused by a harmonic misalignment. These expressions provide a consistent explanation of the temperature results. In contrast, the robustness of a two-wavelength emission absorption method for atomic density measurements is demonstrated.

H I emission-absorption measurements of the radio source CL4

view Abstract Citations (1) References (13) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS H I emission-absorption measurements of the radio source CL4. Payne, H. E. ; Bania, T. M. Abstract An emission-absorption study of the radio source CL4 has revealed two weak features at -9.3 and -35.6 km/s LSR velocity that may be due to H I absorption. If real, these features imply optical depths of about 0.6. The kinematic distances implied by the features (6.4 and 8.7 kpc) exceed that of the Cygnus Loop (about 1 kpc) by a large factor. However, because of the anomalous H I velocities found in this region, kinematic distances may be meaningless, and a spatial coincidence of CL4 with the Cygnus Loop supernova remnant cannot be completely ruled out. Publication: The Astronomical Journal Pub Date: May 1979 DOI: 10.1086/112457 Bibcode: 1979AJ.....84..611P Keywords: Absorption Spectra; H Lines; Radio Sources (Astronomy); Optical Thickness; Radio Emission; Supernova Remnants; Astrophysics; Absorption:Radio Sources; Distances:Radio Sources; Neutral Hydrogen:Radio Sources; Radio Sources:Kinematics full text sources ADS |

Ionic and atomic absorption in stable spark discharges

Transient ionic and atomic emission-absorption measurements on a train of positionally-stable copper spark discharges are described. The measurements are made as a function of discharge current duration at constant amplitude and rise time. Spatial observation zones are isolated in the spark gap with a set of masks and a relay lens to estimate the movement of electrode vapor. Absorption measurements required custom circuitry for a pulsed hollow-cathode backlight and synchronously gated dual-channel boxcar integrator. Results indicated that electrode vapor moves primarily along the interelectrode axis in response to current duration, with substantial ionization remaining in the post-discharge period. Neutral atoms remain in the gap for long times after current cessation.

Experimental study of non-steady phenomena associated with the combustion of solid gun propellants

This investigation is concerned with the combustion of solid propellants and the gas dynamic processes occurring within the flow inside and at the exit plane of the muzzle of 20 mm caliber guns. Two propellants (nitrocellulose-powder) and two types of guns were used. The load density was 0.39 to 0.9. The measurement is highly influenced by the deposition of absorbing particulates in the boundary layers near the tube wall. The main objective of this paper is to verify the validity of recently developed interior ballistic models. In-bore temperature distributions derived from emission-absorption measurements by means of quartz windows mounted into bores along the barrel are compared to theoretical predictions. An in-bore temperature gradient is found near the base of the moving projectile as predicted by one of the models. Neither of the interior ballistic models describes the phenomena in detail. Better agreement was achieved using a high load density. Temperatures measured within in the “primary flash” at the exit plane of the muzzle can only be compared to in-bore values immediately after projectile, emergence; 20 to 30 μsec after projectile emergence, secondary combustion processes lead to an increase of the temperature.

A theoretical study of the interpretation of emission-absorption intensity ratio temperature measurements in the absence of thermal equilibrium

Emission-absorption intensity ration temperature measurements of diatomic molecules under thermal non-equilibrium conditions are investigated theoretically. It is shown that the rotational population distribution must be taken into account when a small part of a vibration-rotation band is viewed in experiments for measuring a vibrational temperature. An emission-absorption intensity ratio of unity does not always mean equality of effective brightness temperature of background source and a vibrational temperature. Such an assumption could lead to errors of several per cent in experimentally deduced vibrational temperatures, particularly in situations where the ratio of rotational and vibrational temperatures is less than unity. The rotational temperature dependence is explained in terms of transitions taking place in vibration-rotation bands and this dependence decreases when a larger part of a band is viewed. Emission-absorption measurements are also investigated for cases where the vibrational population distribution deviates from Boltzmann, for polyatomic and for molecular electronic spectra. Finally it is shown that, in principle, both rotational and vibrational temperatures may be determined from two simultaneous emission-absorption measurements.