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At least 685 records · Page 38
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Spectroscopic analysis on the basis Judd–Ofelt theory of Nd{sup 3+} in (Y{sub 0.985}Nd{sub 0.015}){sub 2}O{sub 3}: A transparent laser-host ceramic

Highlights: • Transparent Y{sub 2}O{sub 3} ceramic with 1.5 atm% doping of neodymium (Nd) was fabricated and its spectroscopic properties were investigated using Judd–Ofelt theory. • The Judd–Oflet parameters, computed from the absorption bands of Nd{sup 3+} ion, are Ω{sub 2} = 8.84 × 10{sup −20} cm{sup 2}, Ω{sub 4} = 9.82 × 10{sup −20} cm{sup 2} and Ω{sub 6} = 4.44 × 10{sup −20} cm{sup 2}. These parameters were used to determine absorption line strength, radiative transition probabilities, fluorescence branch ratio and radiative lifetime for different transitions of Nd{sup 3+}. • The branching ratios for {sup 4}F{sub 3/2} → {sup 4}I{sub 9/2} and {sup 4}F{sub 3/2} → {sup 4}I{sub 11/2} transition are 0.548 and 0.389, respectively. The spectroscopic quality factor was determined to be 2.21, which is higher than 1.0 atm% neodymium doped Y{sub 2}O{sub 3} ceramic. A calculated radiation decay time (τ = 140 μs) is reasonably close to the experimentally measured life time (153 μs). The life time for 1.5 mol% Nd doped Y{sub 2}O{sub 3} ceramic which is lower than that of 1.0 atm% neodymium doped ceramic. The lowering of life time was attributed to the presence of concentration quenching effects. • The room temperature emission cross-section for individual Stark bands of {sup 4}F{sub 3/2} → {sup 4}I{sub 9/2} and {sup 4}F{sub 3/2} → {sup 4}I{sub 11/2} transitions was determined. The total emission cross section for {sup 4}F{sub 3/2} → {sup 4}I{sub 9/2} and {sup 4}F{sub 3/2} → {sup 4}I{sub 11/2} transition was found to be 25.49 × 10{sup −20} and 37.04 × 10{sup −20} cm{sup 2}, which is significantly higher than 1.0 atm% Nd{sup 3+} doped Y{sub 2}O{sub 3}ceramic. - Abstract: Spectroscopic investigation of 1.5 atm% Nd{sup 3+} doped Y{sub 2}O{sub 3} transparent ceramic was performed for different emission wavelengths. Judd–Oflet parameters, computed from the absorption bands of Nd{sup 3+} ion, are Ω{sub 2} = 8.84 × 10{sup −20} cm{sup 2}, Ω{sub 4} = 9.82 × 10{sup −20} cm{sup 2} and Ω{sub 6} = 4.44 × 10{sup −20} cm{sup 2}. These parameters were used to determine absorption line strength, radiative transition probabilities, fluorescence branch ratio and radiative lifetime for different transitions of Nd{sup 3+}. The branching ratios for {sup 4}F{sub 3/2} → {sup 4}I{sub 9/2} and {sup 4}F{sub 3/2} → {sup 4}I{sub 11/2} transition are 0.548 and 0.389, respectively. The calculated radiative lifetime (140 μs) is in good agreement with the measured lifetime (153 μs). The room temperature emission cross-section of individual Stark bands of {sup 4}F{sub 3/2} → {sup 4}I{sub 9/2} and {sup 4}F{sub 3/2} → {sup 4}I{sub 11/2} transitions was determined. The total emission cross section for {sup 4}F{sub 3/2} → {sup 4}I{sub 9/2} and {sup 4}F{sub 3/2} → {sup 4}I{sub 11/2} transition was found to be 25.49 × 10{sup −20} and 37.04 × 10{sup −20} cm{sup 2}, which is significantly higher than 1.0 atm% Nd{sup 3+} doped Y{sub 2}O{sub 3}ceramic.

36 MATERIALS SCIENCE↗
DOE OSTI2013

SIMULATIONS OF DISK GALAXIES WITH COSMIC RAY DRIVEN GALACTIC WINDS

We present results from high-resolution hydrodynamic simulations of isolated Small Magellanic Cloud (SMC)- and Milky-Way-sized galaxies that include a model for feedback from galactic cosmic rays (CRs). We find that CRs are naturally able to drive winds with mass loading factors of up to ∼10 in dwarf systems. The scaling of the mass loading factor with circular velocity between the two simulated systems is consistent with η∝v{sub circ}{sup 1-2} required to reproduce the faint end of the galaxy luminosity function. In addition, simulations with CR feedback reproduce both the normalization and the slope of the observed trend of wind velocity with galaxy circular velocity. We find that winds in simulations with CR feedback exhibit qualitatively different properties compared to supernova-driven winds, where most of acceleration happens violently in situ near star forming sites. The CR-driven winds are accelerated gently by the large-scale pressure gradient established by CRs diffusing from the star-forming galaxy disk out into the halo. The CR-driven winds also exhibit much cooler temperatures and, in the SMC-sized system, warm (T ∼ 10{sup 4} K) gas dominates the outflow. The prevalence of warm gas in such outflows may provide a clue as to the origin of ubiquitous warm gas in the gaseous halos of galaxies detected via absorption lines in quasar spectra.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Scanning ARM Cloud Radars. Part II: Data Quality Control and Processing

The Scanning ARM Cloud Radars (SACR’s) are the primary instruments for documenting the four-dimensional structure and evolution of clouds within a 20-30 km radius from the ARM fixed and mobile sites. Here, the post-processing of the calibrated SACR measurements is discussed. First, a feature mask algorithm that objectively determines the presence of significant radar returns is described. The feature mask algorithm is based on the statistical properties of radar receiver noise. It accounts for atmospheric emission and is applicable even for SACR profiles with few or no signal-free range gates. Using the nearest-in-time atmospheric sounding, the SACR radar reflectivities are corrected for gaseous attenuation (water vapor and oxygen) using a line-by-line absorption model. Despite having a high pulse repetition frequency, the SACR has a narrow Nyquist velocity limit and thus Doppler velocity folding is commonly observed. An unfolding algorithm that makes use of a first guess for the true Doppler velocity using horizontal wind measurements from the nearest sounding is described. The retrieval of the horizontal wind profile from the HS-RHI SACR scan observations and/or nearest sounding is described. The retrieved horizontal wind profile can be used to adaptively configure SACR scan strategies that depend on wind direction. Several remaining challenges are discussed, including the removal of insect and second-trip echoes. The described algorithms significantly enhance SACR data quality and constitute an important step towards the utilization of SACR measurements for cloud research.

climate↗
NASA NTRS1994

Reionization in a cold dark matter universe: The feedback of galaxy formation on the intergalactic medium

We study the coupled evolution of the intergalactic medium (IGM) and the emerging structure in the universe in the context of the cold dark matter (CDM) model, with a special focus on the consequences of imposing reionization and the Gunn-Peterson constraint as a boundary condition on the model. We have calculated the time-varying density of the IGM by coupling our detailed, numerical calculations of the thermal and ionization balance and radiative transfer in a uniform, spatially averaged IGM of H and He, including the mean opacity of an evolving distribution of gas clumps which correspond to quasar absorption line clouds, to the linearized equations for the growth of density fluctuations in both the gaseous and dark matter components in a CDM universe. We use the linear growth equations to identify the fraction of the gas which must have collapsed out at each epoch, an approach similar in spirit to the so-called Press-Schechter formalism. We identify the IGM density with the uncollapsed baryon fraction. The collapsed fraction is postulated to be a source of energy injection into the IGM, by radiation or bulk hydrodynamical heating (e.g., via shocks) or both, at a rate which is marginally enough to satisfy the Gunn-Peterson constraint at z less than 5. Our results include the following: (1) We find that the IGM in a CDM model must have contained a substantial fraction of the total baryon density of the universe both during and after its reionization epoch. (2) As a result, our previous conclusion that the observed Quasi-Stellar Objects (QSOs) at high redshift are not sufficient to ionize the IGM enough to satisfy the Gunn-Peterson constraint is confirmed. (3) We predict a detectable He II Gunn-Peterson effect at 304(1 + z) A in the spectra of quasars at a range of redshift z greater than or approx. 3, depending on the nature of the sources of IGM reionization. (4) We find, moreover, that a CDM model with high bias parameter b (i.e., b greater than or approx. 2) cannot account for the baryon content of the universe at z approximately 3 observed in quasar absorption line gas unless Omega (sub B) significantly exceeds the maximum value allowed by big bang nucleocynthesis. (5) For a CDM model with bias parameter within the allowed range of (lower) values, the lower limit to Omega(sub B) imposed by big bang nucleosynthesis (Omega(sub B) h(sup 2) greater than or equal to 0.01) combines with our results to yield the minimum IGM density for the CDM fodel. For CDM with b = 1 (Cosmic Background Explorer (COBE) normalization), we find Omega(sub IGM)(sup min) (z approximately 4) approx. equal 0.02-0.03, and Omega(sub IGM)(sup min)(z approximately 0) approx. equal 0.005-0.03, depending upon the nature of the sources of IGM reionization. (6) In general, we find that self-consistent reionization of the IGM by the collapsed baryon fraction has a strong effect on the rate of collapse. (7) As a further example, we show that the feedback effect on the IGM of energy release by the collapsed baryon fraction may explain the slow evolution of the observed comoving QSO number density between z = 5 and z = 2, followed by the sharp decline after z = 2.

Shapiro, Paul R.↗
DOE OSTI2022

A Quasar Shedding Its Dust Cocoon at Redshift 2

We present the first near-IR spectroscopy and joint analyses of multiwavelength observations for SDSS J082747.14+425241.1, a dust-reddened, weak broad emission-line quasar (WLQ) undergoing a remarkable broad-absorption line (BAL) transformation. The systemic redshift is more precisely measured to be z = 2.070 ± 0.001 using Hβ compared to z = 2.040 ± 0.003 using Mg ιι from the literature, signifying an extreme Mg ιι blueshift of 2140 ± 530 km s –1 relative to Hβ. Using the Hβ-based single-epoch scaling relation with a systematic uncertainty of 0.3 dex, its black hole (BH) mass and Eddington ratio are estimated to be M BH ~ 6.1 × 10 8 M ⊙ and λ Edd ~ 0.71, indicative of being in a rapidly accreting phase. Our investigations confirm the WLQ nature and the LoBAL → HiBAL transformation, along with a factor of 2 increase in the Mg ιι+Fe ιι emission strength and a decrease of 0.1 in E(B – V) over two decades. The kinetic power of this LoBAL wind at R ~ 15 pc from its BH is estimated to be ~43% of the Eddington luminosity, sufficient for quasar feedback upon its host galaxy albeit with an order-of-magnitude uncertainty. This quasar provides a clear example of the long-sought scenario where LoBAL quasars are surrounded by dust cocoons, and wide-angle nuclear winds play a key role in the transition of red quasars evolving into the commonly seen blue quasars.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2025

Overview of oxygen opacity experiments at the National Ignition Facility and investigation of potential systematic errors

Experiments to measure oxygen opacity at stellar interior conditions have been performed at the National Ignition Facility in a Discovery Science campaign. These experiments utilize the Opacity-on-NIF platform with a sample comprised of O, Mg, and Si. The spectral data from the Opacity Spectrometer cover the 1000–2000 eV photon energy range showing bound-free continuum absorption from O and line absorption from Mg and Si. DANTE and the Gated X-ray Detector are employed to measure the sample plasma’s temperature and density, respectively. Initial data show lower transmission than expected by theoretical models, raising questions of whether potential background or data uniformity concerns could produce systematic errors in the inferred transmission. Here, we investigate three concerns thought to be important for the oxygen opacity data, including instrumental scattered background, sample self-emission non-uniformity, and backlight continuum non-uniformity. Additionally, we show the effect of a recently developed method to account for 2nd order crystal reflection. The total effect of these concerns on one experiment is found to be small compared to the observed difference between the inferred transmission and a model calculation at the inferred temperature and density. Thus, we conclude that these potential sources of systematic error cannot account for the observed difference, increasing the likelihood of a real effect due to the high temperature and density conditions. However, because this is only a single experiment, we cannot make a firm conclusion. More experiments measuring the opacity and necessary calibrations are needed to assess the reproducibility and uncertainty of this result.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Argon metastable density and temperature of a 94 GHz microplasma

Laser diode absorption spectroscopy is used to experimentally measure Ar(1s 5 ) metastable density and translational gas temperature within a 94 GHz microplasma. A square two-dimensional photonic crystal (PhC) at this resonance frequency serves to ignite and sustain the plasma from 20 to 200 Torr (2.7 × 10 3 –2.7 × 10 4 Pa) by using millimeter wave power from 300 to 1000 mW. Metastable density within the plasma is estimated from the absorption line shape of the laser traversing the PhC. The metastable density reaches an order of 10 19 m –3 at lower pressure and decreases as pressure increases. From the Lorentzian line shape of the absorption profile at 811.53 nm, the gas temperature is extracted and found to increase from 500 K at 20 Torr to 1300 K at 200 Torr. Furthermore, these data are analyzed and compared with a zero-dimensional plasma model and with previous experimental plasma results at 43 GHz.

42 ENGINEERING↗
DOE OSTI2020

Multiphase outflows in post-starburst E+A galaxies - II. A direct connection between the neutral and ionized outflow phases

ABSTRACT Post-starburst E+A galaxies are systems that hosted a powerful starburst that was quenched abruptly. Simulations suggest that these systems provide the missing link between major merger ULIRGs and red and dead ellipticals, where AGN feedback is responsible for the expulsion or destruction of the molecular gas. However, many details remain unresolved and little is known about AGN-driven winds in this short-lived phase. We present spatially resolved IFU spectroscopy with MUSE/VLT of SDSS J124754.95-033738.6, a post-starburst E+A galaxy with a recent starburst that started 70 Myr ago and ended 30 Myr ago, with a peak SFR of $\sim 150\, \mathrm{M_{\odot }\,yr^{ -1}}$. We detect disturbed gas throughout the entire field of view, suggesting triggering by a minor merger. We detect fast-moving multiphased gas clouds, embedded in a double-cone face-on outflow, which are traced by ionized emission lines and neutral NaID emission and absorption lines. We find remarkable similarities between the kinematics, spatial extents, and line luminosities of the ionized and neutral gas phases, and propose a model in which they are part of the same outflowing clouds, which are exposed to both stellar and AGN radiation. Our photoionization model provides consistent ionized line ratios, NaID absorption optical depths and EWs, and dust reddening. Using the model, we estimate, for the first time, the neutral-to-ionized gas mass ratio (about 20), the sodium neutral fraction, and the size of the outflowing clouds. This is one of the best ever observed direct connections between the neutral and ionized outflow phases in AGN.

Baron, Dalya↗
DOE OSTI2019

Effect of Ion (Ar{sup +}) Irradiation on Cluster Magnetism and Magnetic Interactions in Fe{sub 67}Cr{sub 18}B{sub 15} Amorphous Alloy

The comparison of the resonance magnetic absorption spectra with the data on structure and magnetic properties of Fe{sub 67}Cr{sub 18}B{sub 15} amorphous samples has shown that a randomly inhomogeneous medium of amorphous alloy is multiphase. Two types of samples with the same chemical composition, but with a different clusterized structure, and the use of (Ar{sup +}) ion irradiation in the experiment made it possible to separate four basic phases with different magnetic properties. The basic phase α-(Fe,Cr) contains large clusters of D < 400 Å in size with a tendency to phase separation of iron (α-Fe) and chromium (α-Cr), which under irradiation, enhances the competing FM and AFM magnetic interactions and increases the intensity of the resonance magnetic absorption lines associated with α-Fe and α-Cr. The phase Fe{sub 3}B (D < 100 Å) is detected by independent line in the resonance absorption spectra only when its groupings are isolated from the α-(Fe,Cr) metal phase clusters. The fourth phase contains precluster groupings and disappears when the sample is irradiated.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1975

The effect of intermediate-scale motions on line formation

The problem of LTE and non-LTE line formation in the presence of nonthermal velocity fields with geometric scales between the microscopic and macroscopic limits is investigated in the cases of periodic sinusoidal and sawtooth waves. For a fixed source function (the LTE case), it is shown that time-averaged line profiles progress smoothly from the microscopic to the macroscopic limits as the geometric scale of the motions increases, that the sinusoidal motions produce symmetric time-averaged profiles, and that the sawtooth motions cause a redshift. In several idealized non-LTE cases, it is found that intermediate-scale velocity fields can significantly increase the surface source functions and line-core intensities. Calculations are made for a two-level atom in an isothermal atmosphere for a range of velocity scales and non-LTE coupling parameters and also for a two-level atom and a four-level representation of Na I line formation in the Harvard-Smithsonian Reference Atmosphere (1971) solar model. It is found that intermediate-scale velocity fields in the solar atmosphere could explain the central intensities of the Na I D lines and other strong absorption lines without invoking previously suggested high electron densities.

Shine, R. A.↗
NASA NTRS1978

Low-background trace-gas detector

Spectrophone detects very small concentrations of trace gases. With gas in sample cell, laser is tuned to absorption line of interest. Molecular absorption in cell produces pulsed acoustical pressure at chopper frequency. Two optical paths with very different absorption lengths are used to pretune cell to balance out background absorption by cell windows.

Rosengren, L.↗
NASA NTRS1977

Simultaneous determination of rotational and translational temperatures of OH/2 Pi/ in a gas discharge

A simultaneous determination of the rotational and translational temperatures of OH(2 Pi) in a water-vapor discharge is reported. These temperatures were determined by measuring the strength and line shape of the absorption lines in the 2 Pi (v = 0) - 2 Sigma(+) (v = 0) transitions of OH using a CW tunable laser. It was found that the rotational distribution was thermalized, but the corresponding rotational temperature was much lower than the translational temperature. Possible implications of these results are discussed.

Wang, C. C.↗
NASA NTRS1978

An atlas of Copernicus ultraviolet spectra of Wolf-Rayet stars

An atlas of Copernicus UV scans is presented, and line identifications are tabulated, for the Wolf-Rayet stars Gamma-2 Vel (WC 8 + O7), HD 50896 (= EZ CMa; WN 5), and HD 92740 (WN 7). The atlas covers the wavelength ranges from 946.8 to 3182 A for Gamma-2 Vel, from 1012 to 1294 A for HD 50896, and from 1051 to 1243 A for HD 92740. The wavelengths include corrections for components of satellite velocity, earth velocity, and stellar heliocentric velocity; each spectral feature is classified as interstellar, photospheric, emission, UV-displaced P Cygni line absorption, or P Cygni line emission. UV-edge velocities of the P Cygni profiles are estimated, P Cygni profile types are discussed, and the results are compared with Copernicus scans of OB stars exhibiting UV P Cygni profiles. It is noted that: (1) the line-strength ratio of molecular hydrogen to atomic species appears to be substantially greater in the scans of the WN stars than in the Gamma-2 Vel scans; (2) some of the P Cygni profiles in Gamma-2 Vel differ significantly from the corresponding profiles in OB stars; and (3) there may be a slight inverse correlation between ejection velocities and excitation potentials in Gamma-2 Vel.

Johnson, H. M.↗
NASA NTRS1980

Effective depth of spectral line formation in planetary atmospheres

The effective level of line formation for spectroscopic absorption lines has long been regarded as a useful parameter for determining average atmospheric values of the quantities involved in line formation. The identity of this parameter was recently disputed. The dependence of this parameter on the average depth where photons are absorbed in a semi-infinite atmosphere is established. It is shown that the mean depths derived by others are similar in nature and behavior.

Lestrade, J. P.↗
NASA NTRS1980

Effective depth of spectral line formation in planetary atmospheres

The effective level of line formation for spectroscopic absorption lines has long been regarded as a useful parameter for determining average atmospheric values of the quantities involved in line formation. The identity of this parameter has recently been disputed. This paper reestablishes the dependence of this parameter on the average depth at which photons are absorbed in a semi-infinite atmosphere and shows that the mean depths derived by others are similar in nature and behavior.

Lestrade, J. P.↗
NASA NTRS1992

Motion at the ionization front in the Orion nebula - A kinematic study of the forbidden O I line

The kinematics of the ionization front in H II regions is investigated via a study of the collisionally excited forbidden O I emission at 630 nm. Slit spectra of 5/km s resolution are used to examine the velocities of forbidden O I across the inner few arcminutes of M42. The mean velocity is significantly more positive than for other ions, which confirms the argument that the ionization front is formed against the parent molecular cloud OMC 1. It is inferred that there is acceleration of material in the ionization front at the parent molecular cloud. A new model for M42 based largely on optical emission-line and radio absorption-line studies is presented. A detailed statistical analysis indicates agreement between the structure function and the Kolmogorov theory for turbulence.

O'Dell, C. R.↗
NASA NTRS1992

Velocity structure in optical CH(+) lines toward HD 190603 and implications for the formation of CH(+)

Observations of CH(+) and other species accessible in optical wavelengths in the line of sight to HD 190603, a B 1.5 Iae supergiant are reported. In this line of sight a shift in radial velocity between the CH(+) line and other interstellar absorption lines such as CH and Ca I is observed. The most likely explanation for this effect is the shock formation of CH(+). Likely preshock and postshock conditions which are consistent with the observations are also estimated.

Allen, M. M.↗