True Continuum Research Articles

Quantitative light element analysis using an energy dispersive detector. 1–Dead time and the low‐energy spectrum

AbstractA study of the low‐energy region (below 1. 5 keV) of energy dispersive x‐ray spectra has been carried out. Firstly, because some counting systems do not provide a reliable dead time correction, a new method of dealing with the problem is given. Next, the effects of different positioning of the energy discriminator within the analyser circuitry are discussed with reference to the consequences for light element analysis. Electronic noise counts can present a problem for analysis of x‐rays of less than 300 eV and a straightforward method for noise removal is described. Finally, an unexpected artifact in the spectrum below 500 eV is identified; its size is related to the total number of counts in the spectrum and a practical method of dealing with it is demonstrated. Once the above factors have been taken into account a low energy spectrum is produced, consisting solely of characteristic x‐ray lines and a true continuum background.

True continuum background of nanosecond duration for pulsed laser spectroscopy

It is demonstrated that, in case of transverse excitation, amplified spontaneous emission is the best source of pure continuum background for high-resolution pulsed laser spectroscopy.

Including the continuum in the N-level molecule model

A method is developed for explicitely including the quasicontinuum, or the continuum, in N-level molecule model computations of laser-induced dissociation and chemical processes. The quasicontinuum levels are summed over, or the true continuum levels are integrated over, before the computation is performed.

On the in vivo material functions of mammalian blood.

The present paper explores the implications of employing time-averaged true continuum fields to investigate blood rheology in "steady viscometric" flows. This approach is in contrast with the spatially-averaged interpretation of field variables which is generally employed. On the basis of four plausible constitutive assumptions it is then possible to deduce the qualitative in vivo behavior of all three of the material functions of whole mammalian blood from inspection of the corresponding velocity profile. Quantitative results, and the evaluation of the material constants for specific constitutive models, can be obtained through curve-fitting procedures, as is illustrated. The development reconfirms, and puts on a formal basis, the earlier conclusion of Bugliarello, et al, that whole blood can have a dilatant response at low rates of shear. In addition, the normal stress forces are shown to have off-axis extrema in tube flow, and to be large enough to influence particle migration across streamlines. The existing data on particle migration in whole blood is reviewed, and shown to be in accord with these results.

TiO band strengths in metal-rich globular clusters. III - Model atmosphere calibration

view Abstract Citations (21) References (15) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS TiO band strengths in metal-rich globular clusters. III - Model atmosphere calibration Johnson, H. R. ; Mould, J. R. ; Bernat, A. P. Abstract The present investigation is concerned with approaches for answering questions regarding the age characteristics and the history of the globular cluster system of the Galaxy. Use is made of models described by Johnson et al. (1980). These models and metal-poor members of the same family are employed to obtain a new calibration of TiO band strength measurements in globular cluster giants. The new calibration will make it possible to make use of the main strength of photometric abundance determination relative to high resolution spectroscopy, which is connected with the photometric definition of the continuum points. Even if the line blanketing is complete (i.e., there is no true continuum), there will be no bias in the interpretation, provided that the models really contain the full line opacity. Attention is given to model band strength indices, a correction for gravity variation along the giant branch, and details of metallicity calibration. Publication: The Astrophysical Journal Pub Date: July 1982 DOI: 10.1086/160063 Bibcode: 1982ApJ...258..161J Keywords: Abundance; Globular Clusters; Late Stars; Spectral Bands; Stellar Atmospheres; Stellar Models; Titanium Oxides; Iron; Metallic Stars; Near Infrared Radiation; Stellar Color; Stellar Spectrophotometry; Stellar Temperature; Titanium; Astrophysics full text sources ADS | Related Materials (4) Part 1: 1978ApJ...221..580M Part 2: 1979ApJ...228..423M Part 4: 1982PASP...94..223M Part 5: 1982ApJ...262..142M

Third order susceptibility of III–V semiconductors in the true continuum near the band edge

Based upon the purely coherent radiation-exciton interaction and using the time dependent perturbation theory, an independent analytical investigation of the third order susceptibility χ (3) has been made for a semiconductor in the band-edge region. The possibility of a change in sign of χ (3) is noted when the pump energy is increased from below the renormalized band gap energy to exceed it. Numerical estimates are made for InSb, GaAs, GaSb and InAs when the energy difference is of the order of crystal exciton Rydberg in the true continum.

Resonances of (N�1)-particle systems in a dilated Green's function approach

The inclusion of dilatation transformations in the framework of the one-electron Green's function of many-body theory is discussed with regard to the calculation of resonance energies and widths of states containingN± 1 particles. By this mathematical method it is possible to extend the applicability of highly successful standard techniques employing only square integrable basis sets to metastable states which are degenerate with true continuum states into which they disintegrate with characteristic lifetimes.

Quantum-mechanical treatment of collision-induced dissociation

A close-coupling technique for calculating quantum-mechanical probabilities of collision-induced dissociation (CID) of a diatomic molecule by an atom is presented. The internal Hamiltonian (of the diatomic) is first diagonalized in a discrete, square-integrable basis. The lowest several of the resulting discrete eigenstates approximate the true bound states and the remaining (pseudocontinuum) states represent the true continuum. Next, the stationary collision wavefunction is expanded in the diagonal basis to obtain a discrete set of close-coupled equations, which are integrated numerically by standard procedures. The method is applied to a collinear model in which the diatomic is bound by a Morse potential and the interaction is a repulsive exponential. The total CID probabilities appear to be converged to 1% or 2% in most cases. Vibrational ’’enhancement’’ of CID is observed in this model. A very general problem associated with the use of the exponential interaction in conjunction with a binding potential which supports a continuum is discussed.

Response of Leaf Water Potential to Pressure Changes at the Root Surface of Corn Plants1

AbstractThe nature of the hydraulic continuum between the roots and leaves of intact plants requires further study to improve our understanding of the effect of pressure changes. A large pressure chamber was designed to apply hydrostatic pressure to the roots of intact corn (Zea mays L.) plants. The chamber permitted application of up to 6 bars pressure and allowed for in situ watering of the plants. Changes in leaf water potential resulting from changes in pressure applied to the roots were monitored in situ using a thermocouple dewpoint hygrometer. Responses of leaf water potential were consistently between 0.94 and 1.19 times the change in applied pressure, regardless of whether the pressure was being increased or decreased. When pressure was applied to very turgid plants leaf water potential increased until it reached a value equal to the osmotic pressure of expressed xylem sap. Some time after this value was reached water droplets appeared on the leaf surface. The experiments showed that the hydraulic system within intact plants acts as a true continuum in that pressure changes at one end of the system are faithfully, manifested at the other end of the system. If such changes are not observed some additional mechanism must be operating.

Pressure-induced absorption by H 2 in the atmosphere of Jupiter and Saturn

The S(1) line of the pressure-induced fundamental band of H 2 was identified and measured in the spectra of Saturn and Jupiter. This broad line at 4750 cm −1 lies in a region free from telluric and planetary absorptions. It is about 99% absorbing in the core; the high-frequency wing extends to at least 5100 cm −1. We compare the obseved line shape to the predictions of both a reflecting-layer model (RLM) and a homogeneous scattering model (HSM). The RLM provides a good fit to the Saturn line profile for temperatures near 150K; the derived base-level density is 0.52 (+0.26, −0.17) amagat and the H 2 abundance is 25 (+10, −9) km-amagat, assuming a scale height of 48 km. The Jupiter line profile is fit by both the RLM and HSM, but for widely differing temperatures, neither of which seems probable. The precise fitting of the observed S(1) line profile to computed models depends critically on the determination of the true continuum level; difficulties encountered in finding the continuum, especially for Jupiter, are discussed. Derived RLM densities and abundances for both planets are substantially lower than those derived from RLM analyses of the H 2 quadrupole lines, the 3 ν 3 band of CH 4, and from other sources.

Effects of Abundance Changes on the Spectra of Very Cool White Dwarfs

In order to study the atmospheres of cool white dwarfs of spectral types DA, DF and DG, model atmospheres have been calculated for temperatures 5000 ≤ Teff ≤ 7000 K and gravities 7 ≤ log g ≤ 8.5. The helium to hydrogen abundance ratio ranges from 0.1 to 1000. The abundances of the metals ∈M (relative to hydrogen) vary between the solar value ∈⊙M and ∈⊙M/1000. The models are hydrogen and metal line blanketed and in radiative equilibrium. The models with increased He abundance are characterized by a decreased mean opacity since the absorption cross-section of He is much smaller than that of H–. As a result, the spectral lines become stronger and – due to the much higher pressures – much broader. A reduction of the metal contents also increases the pressures. In this case it is caused by the shortage of electron suppliers. Here the spectral lines also become broader, but in general weaker.These effects strengthen the overlap of the lines due to the high gravity of white dwarfs and more or less lead to a quasi-continuum which may be much below the true continuum. Because of the wavelength dependence of the line density the depression is strongest in the UV and blue spectral region, whereas for wavelengths λ ≥ 4500 Å the difference from the true continuum is only a few per cent. The details will be published elsewhere.

Recombination Lines near 6 cm Wavelength in the Large Magellanic Cloud

Recombination lines H 10901: have been detected in eight sources in the Large Cloud of Magellan. Low ratios of line temperature to continuum temperature, TL/Tc, were found in most of the sources and are attributed to the difficulty of obtaining a true continuum value when such a large area is encompassed by the telescope beam. In the 30Doradus nebula the ratio N(He+)/N(H+) was found to be no greater than O' 08, or less than half that previously recorded by radio observations.

Observational Constraints on Model Atmospheres for Uranus and Neptune

We have re-examined the visible and near-IR regions of the spectra of Uranus and Neptune to provide additional data for constructing atmospheric models. We find that a true continuum exists only at wavelengths below 4700 Å, that the 6420 Å absorption previously attributed to hydrogen is probably caused by methane, that there is no evidence for ammonia, ethylene or ethane absorptions in our spectra, and that the abundance of methane is probably much higher than previous estimates suggest. This last finding implies that the value of H/C in the atmospheres of both planets is much less than 1/10 the solar (or Jovian) value. Clear, Rayleigh-scattering model atmospheres are not compatible with the observations, but more work is needed to establish viable alternatives.

Use of a Ge(Li) total-absorption spectrometer in (n, xγ) measurements

An 80 cm 3 Ge(Li) detector, sectioned to operate as a total-absorption spectrometer, has been used in (n, xγ) cross-section measurements using the Linac time-of-flight technique. Use of a computer-controlled data acquisition system allowed the detector to be operated simultaneously as an ordinary Ge(Li) detector (singles mode) and as a total absorption spectrometer (Duode mode). Typical operating characteristics of the detector are given and its performance illustrated with examples of gamma-ray spectra from (n, xγ) reactions. The determination of true continuum gamma-ray intensities by unfolding the spectra measured in the singles mode is described and typical results of this Ge(Li) spectrum unfolding are shown.

Infrared Studies of Galactic Nebulae.IV. Continuum and Line Radiation from Planetary Nebulae.

Observations are reported of the detection of IR radiation from several planetary nebulae not previously known to be radiating at these wavelengths. Broad spectral bandwidth observations indicate that ir radiation in excess of that expected from atomic processes is a common phenomenon among these objects. Investigations with narrow spectral bandwidth show that in a few cases the energy in the 10.52-micron line is a significant fraction of the total energy observed in the broad-band measurements and in other cases a relatively small fraction of the total radiation. Other observations on two sources with narrow spectral bandwidth adjacent to the 10.52-micron line indicate that at these wavelengths a true continuum of radiation exists as well as lines. The results are discussed in relation to visual and radio-wavelength data.

Determination of the continuum in some emission line objects

Excitation temperatures of the peculiar objects Boss 1985, AG Pegasi and AG Carinae have been derived form the corrected intensities of the emission lines. The values obtained are 5900K for Boss 1985, 8000K for AG Pegasi and 10500K for AG Carinae. From the observed quantities log (I/I c), whereI is the intensity of the line andI c the intensity of the underlying continuum, the true continuum has been derived. The results are in good agreement with those predicted in previous investigations.

Transformation of the absolute solar radiation data into the ?International Practical Temperature Scale of 1968?

Corrections are given which transform the Tables of the solar radiation data (Labs and Neckel, 1968) into the ‘International Practical Temperature Scale of 1968’. Additionally, for the adjustment of the data of the ‘true continuum’ and the corresponding line blanketing as well, the veiled line effect mentioned first by Carbon et al. (1968), but studied in more detail by Holweger (1970a), has been considered also. The corresponding corrections of the solar irradiance result in an improved value of the spectrophotometric solar constant: S = 1.947 cal cm-2 min-1 or 0.1358 W cm-2. Two Tables presenting the ‘highest (window-) intensities’ and the corrected irradiance data have been added.

Formulation of a statistical equation of motion of a viscous fluid in an anisotropic non-rigid porous solid

The motion of a viscous fluid through an anisotropic non-rigid porous solid is studied. The porous solid considered in this study is a solid medium involving a very dense and fine network of tubules, whose diameter is much smaller than the characteristic length of the flow system. Kinematically, such a medium should behave like a continuum, i.e. the state of deformation can be well described macroscopically. Dynamically, this type of medium has to be distinguished from the true solid continuum, because one additional body force in addition to its weight (the surface traction exerted by the viscous fluid moving through it) has to be considered in the deformation of the porous solid. Their own weight is the only body force in a true solid continuum. The equations governing the macroscopic motion of the viscous fluid flow through the porous medium of this type are derived by averaging the motion of the fluid through individual elements of pores over a small volume of the porous medium. The physics of the derived equations and the possible applications to the blood flow in the network of capillary blood vessels and to the motion of extracellular fluid through the network of interstitial space are discussed.

The Early a Stars.IV. Analysis of the Double-Line Spectrocopic Binary Eta Virginis

view Abstract Citations (6) References (7) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Early a Stars.IV. Analysis of the Double-Line Spectrocopic Binary Eta Virginis Conti, Peter S. Abstract A detailed spectroscopic study of this binary has been completed. The measured equivalent widths, corrected for the true continuum in each component, have been compared with the normal A star 0 Vir. The two component stars do not have identical surface compositions. The secondary, of spectral type about A4, has deficient calcium, scandium, and titanium as in an Am star. In the primary, of spectral type A2, these elements are normal. Both stars show marginal overabundances of those heavy elements enhanced in Am stars Publication: The Astrophysical Journal Pub Date: December 1969 DOI: 10.1086/150267 Bibcode: 1969ApJ...158.1085C full text sources ADS | data products SIMBAD (2)

On the continuum and the absolute magnitude of eta Carinae

The excitation temperature, colour excess and continuum of η Car in the visible and near ultraviolet have been determined from the study of the excitation of the ionized iron emission lines. The excitation temperatures of Feii and [Feii] are about 8000K, value which is very much lower than the mean ionization temperature of the elements in η Car.E B-V is about 1m.1; the absolute visual magnitude is presently −10m.5±1m. From the equivalent widths of the emission lines the true continuum between 1.5 and 3.0 μ−1 has been derived. The correspondingB-V is −0m.14, while the Balmer jump is less than 0m.5. The continuum appears mainly nebular in origin with a strong contribution of the two-photon emission from the 2s-level of hydrogen in the blue.