Number Density Ratio Research Articles

Encounters between degenerate stars and extrasolar comet clouds

Under the assumption that the presence of comet clouds around otherwise normal stars is a common occurrence in the Galaxy, the observational consequences of random penetration encounters between the general Galactic population of degenerate stars and these comet clouds is considered. The only case considered is where the compact stars is a single star. For this scenario, encounters involving neutron stars (NSs) result in impact rates 1000-10,000 times slower than in the model of Tremaine and Zytkow (1986). The rate for white dwarfs (WDs) is larger than the one for NSs by a factor of about 30 times the ratio of the degenerate star number densities. The mean impact rate is significantly increased if the number of comets in a cloud is nearly independent of the mass of the central star. It is concluded that some of the observed gamma-ray bursts may be caused by accretion of comets onto NSs and that this scenario, but with a WD as the accretor, probably contributes to the optical flash background rate. 38 refs.

Low energy electron attachment to SF6 in N2, Ar, and Xe buffer gases

The electron attachment rate constants ka for SF6 have been measured in dilute mixtures of SF6 in high pressure (>1 atm) N2, Ar, and Xe buffer gases at room temperature (T≊300 K) over a wide E/N range (electric field strength to gas number density ratio), corresponding to mean electron energies 〈ε〉 from near thermal electron energies (≊0.04 eV) to 〈ε〉≊4.3 eV. Particular attention has been paid to the effects of space charge distortion, molecular impurities, and changes in the electron energy distribution function on the measured electron attachment rate constant values at the lower E/N values in these mixtures. The present measured thermal electron attachment rate constants in SF6/N2 and SF6/Xe gas mixtures are in excellent agreement with recent accurate measurements of these parameters in several SF6/buffer gas mixtures. At higher 〈ε〉 values, the present SF6/N2 measurements are in fair agreement with previous measurements, while no previous measurements using Ar and Xe buffer gases have been published. These measurements have been used in numerical two term, spherical harmonic Boltzmann equation analyses of the electron motion in these gas mixtures to obtain the low energy (<10 eV) nondissociative and dissociative electron attachment cross sections for SF6. The present derived electron attachment cross sections are compared with recently measured and derived nondissociative and dissociative electron attachment cross sections for SF6. The primary value of the present results is in the large and overlapping 〈ε〉 ranges of the present ka measurements for the three buffer gases compared with that for SF6/N2 gas mixtures alone, which in turn, makes these measurements ideal for testing cross-section sets in SF6 for use in many applied studies.

Multiphase continuum theory of dopant redistribution across aerosol-laden laminar nonisothermal boundary layers

The incorporation of desired “dopant” elements (or compounds) in deposited materials is influenced by coupled transport phenomena and cannot be predicted based on chemical thermodynamics alone. As an important example, we consider the deposition of doped glass for use as optical waveguides. In this technology, combustion products heavily laden with SiO 2-rich submicron droplets are passed over a slowly rotating surface which thermophoretically captures the microdroplets. The dopant (e.g. GeO 2, P 2O 5, B 2O 3 content of these microdroplets, which dictates the local refractive index distribution within the ultimate waveguide product, must be carefully controlled and it is necessary to understand these processes theoretically. This paper systematically developes a fully coupled, pseudo-single-phase laminar boundary layer theory capable of predicting deposit compositions as a function of the feedstream loading of silicon precursor and the dopant (here Ge precursor), as well as the substrate temperature. It is shown that it is not permissible to neglect the effects of silica particle mass loading or even the heat of GeO 2 condensation. The principal assumptions, defensible under typical optical waveguide deposition process conditions, are that the silica-rich microdroplets are in local dynamic, thermal and chemical equilibrium with the prevailing high-temperature vapor mixture, through which they drift primarily as a result of (particle size insensitive) thermophoresis. As a by-product of the physicochemical—mathematical model and calculations the structure of the dopant vapor boundary layer is obtained, and hence the decisive ratio of the dopant vapor number density established at the wall to that in the equilibrium mainstream. The capability of predicting both the rate of glass microparticle deposition and deposit composition (e.g. the dopant/Si element ratio) for each feed condition and wall/combustion gas temperature ratio should provide a valuable insight into the optimization and improvement of such processes. Moreover, while illustrated here for the case of a single dopant (e.g. Ge), the methods are readily extended to multi-element deposition from mist-laden gases.

Can Be-9 provide a test of cosmological theories?

The Li-7(H-3,n)Be-9 reaction, previously neglected in nucleosynthesis determinations, is found to greatly increase the predicted abundance of Be-9 resulting from the big bang. For a nonuniform density universe, a primordial Be-9/H-1 number density ratio of 10 to the -13th is obtained. It is noted that recent Be-9/H-1 measurements in Population II stars approach the nonuniform density universe value. 22 references.

Centrifugal scaling of isothermal gas-liquid flow in horizontal tubes

For testing the similarity criteria of isothermal gas-liquid flow, the flow of air and a water-glycerine mixture in a 50 mm dia horizontal tube is compared with that of helium and water in a 5 mm dia tube rotating around a parallel vertical axis (the effective gravity is 113 times the natural gravity). The Reynolds number, Froude number, Weber number and gas-liquid density ratio are equal in both systems. The test facility, enabling two-phase measurements at centrifugal accelerations up to 1200 times natural gravity in pipe diameters up to 10 mm is described. The dimensionless pressure drops agree within 19% and the absolute differences of the void fraction are < 0.03. Also the flow patterns are in good agreement. The influence of the individual dimensionless groups has been investigated experimentally and comparisons are presented with general pressure drop and void fraction correlations.

Plasma etching of organic materials. II. Polyimide etching and passivation downstream of an O2–CF4–Ar microwave plasma

Parameters which influence the etching of polyimide (PI) downstream of an O2–CF4–Ar microwave (MW) plasma were studied. Of particular importance is the influence of the ratio of atomic number densities O/F in the plasma and the gas flow velocity, which caused an almost linear increase in the etch rate within the investigated limits of the experiment. No measurable etching of PI was found downstream of an O2–Ar plasma, although the presence of oxygen atoms in the vicinity of the substrate was verified by the chemiluminescent reaction with NO. Similar to previously reported radio frequency plasma studies, a fluorinated layer at the surface of (PI) was formed by exposure of the substrate downstream of a fluorine-rich O2–CF4–Ar MW plasma. Changing the plasma composition to the optimum etching conditions (an oxygen-rich plasma of about 20% CF4) removed the fluorinated layer after a period of time. Etching then proceeded with an oxygenated layer at the surface. The reported experiments confirmed that the formation of a fluorinated layer, the removal of this layer, and the formation of an oxygenated one was caused only by the interaction of neutrals, without the influence of ion bombardment.

Interaction potentials and mobility calculations for the HeO+ system

Valence bond, SCF, and MP4SDQ calculations are reported for three low lying states of the HeO+ molecular ion; 4Σ(4S), 2Π(2D), and 2Π(2P). Together with the two-temperature theory of ion transport, these interaction potentials have been used to calculate the drift velocity and reduced mobility of O+ in helium as a function of the electric field to gas number density ratio. The calculated HeO+(4Σ) interaction potentials adequately describe the mobility of ground state O+ in helium, however, the O+(2D) mobility calculated using the 2Π(2D) interaction potential does not match the experimental mobility measurements for the metastable O+* ion which have been reported as the O+(2D) state. An interaction potential is reported for HeO+[2Π(2P)] which will reproduce the experimental mobility of O+*.

Absolute concentration measurements of atomic hydrogen in subatmospheric premixed H_2/O_2/N_2 flat flames with photoionization controlled-loss spectroscopy

An experimental protocol, using photoionization controlled-loss spectroscopy (PICLS), has been developed for obtaining absolute number densities of atomic hydrogen from laser-induced fluorescence measurements in flames. Two laser beams are employed, the first to excite hydrogen atoms from the ground state to the second excited state via two-photon absorption and the second to strongly photoionize the excited atoms. The resulting fluorescence measurements are independent of quenching. A model is presented that assures the viability of PICLS as long as the photoionization rate is greater than or equal to the quenching rate. The model is verified in fuel-lean, stoichiometric, and fuel-rich flat premixed H(2)/O(2)/N(2) flames at pressures of 20 and 72 Torr. Over this range in pressure, the ratio of number densities obtained from PICLS to those calculated from partial equilibrium is constant to within 20%. Most of the error arises from the sensitivity of the partial equilibrium calculat ions to small uncertainties in both the fuel-oxidizer ratio and the measured OH concentration. Because of the quenching-independent nature of PICLS, quantitative fluorescence measurements can be made by calibrating at a single favorable flame condition.

Comet P/Giacobini-Zinner electron and H2O(+) column densities from ICE and ground-based observations

An H2O(+) spatial mission profile, extracted from an optical CCD spectrogram obtained during the ICE/Giacobini-Zinner encounter, is compared to the electron-density profile that was deduced from in situ measurements by the radio experiment aboard ICE. The electron column density along a line of sight has two components, one from the spherically symmetric coma, and the second from a thin plasma sheet, whenever it is along the line of sight. The deduced electron column-density profile agrees well with the observed H2O(+) emission profile. It is concluded that the electrons and the H2O(+) ions are distributed similarly 9600 km tailward from the cometary nucleus, that the ratio of number densities of H2O(+) ions to electrons is about 1/4 at this point, and that the width of the plasma sheet is about 16,000 km. 33 references.

Solar wind carbon, nitrogen and oxygen abundances measured in the Earth's magnetosheath with AMPTE/CCE

The solar wind number density ratios of C6+ + C5+ and N7+ + N6+ + N5+ relative to O8+ + O7+ + O6+ have been measured for the first time using data from the Charge‐Energy‐Mass (CHEM) Spectrometer on the AMPTE/CCE spacecraft during four solar active periods from Sept. 19 to Nov. 1, 1984 when CCE traversed the subsolar magnetosheath of the compressed magnetosphere. We find the average values of the density ratios of C/O and N/O to be 0.43±0.03 and 0.15±0.06, respectively. These ratios, as well as our average He2+/O ratio of 43±5 for these same time periods, are in excellent agreement with Solar Energetic Particles (SEP) abundance ratios as well as SEP‐derived coronal abundances of these elements. Our solar wind C/O ratio is substantially below the generally accepted photospheric value of 0.60.

Mean Field Theory of Binary Mixtures of Nematic Liquid Crystals

Abstract Molecular field theory is used to determine the temperature-composition phase diagram and component order parameters of binary mixtures of nematic liquid crystals. A rotationally invariant form of the Maier-Saupe pseudopotential is generalised to two-component mixtures; the parameters of the theory are the ratios of transition temperatures, number densities and isotropic interaction strengths of the pure components. The possibility of induced biaxiality and the effects of an external field are discussed. The model predicts a rich variety of phase behaviour. For dissimilar constituents, coexisting nematic-isotropic and nematic-nematic phases are predicted in agreement with experiment and hard particle theories. In general, the order parameters of the two constituents differ in a given phase; changing the sign of the interspecies interaction term in the pseudopotential results in the appearance of a biaxial solution. This biaxial phase is shown to be unstable however, and, on quenching, is expected...

Characteristics of suprathermal H+ and He++ in plasmoids in the distant magnetotail

We have obtained rest frame distribution functions of suprathermal (∼6 to ∼150 keV/amu) H+ and He++ ions during 20 particle intensity increases observed in the distant magnetotail (≳80 RE) using data from the University of Maryland/Max‐Planck Institut ULECA sensor on ISEE‐3. All twenty increases were characterized by isotropic ∼100 keV electrons preceded by beaming electrons and velocity‐dispersed proton distributions, signatures typically associated with plasmoids. In each of these 20 plasmoids we find both H+ and He++ to be convected tailward with speeds ranging from 200 to 1000 km/s. The distribution functions of H+ and He++ in each event are well represented by an exponential dependence on particle speed. The sample averages of the proton number density, n, energy density, u, and effective temperature, kTeff = (2/3)(u/n), are respectively 0.018 cm−3, 160 eV/cm³ and 6.1 keV, while the He++ to H+ number density and effective temperature sample average ratios are 0.03 and 3.25 respectively. We conclude that the acceleration mechanism is fairly efficient, depends on the particle velocity, and that the solar wind is a dominant plasma source. Furthermore, our observations indicate that the plasmoids are expanding at speeds of ∼100 km/s during their tailward propagation.

Abundances and spectra of suprathermal H+, He++ and heavy ions in a fast moving plasma structure (plasmoid) in the distant Geotail

Rest frame distribution functions have been deduced for 3 to 150 keV/amu H+, He++ and (Q≥3) ions (Q is the charge state) during a 16 min particle intensity increase in the distant magnetotail (&gt;200 RE) using data from the University of Maryland/Max‐Planck‐Institut ULECA sensor on the ISEE‐3 Geotail Mission. This event was characterized by isotropic electron distributions and has been identified as a tailward moving plasmoid. We show that these suprathermal ions are convected nearly tailward at an average speed of 1000±50 km/s. From the measured dependence of distribution functions on velocity v, f(v) ⧜ exp(−v/v o ), we derive a number density ratio for n He ++ /n H + of 0.033±0.003 and for n(Q≥3)/n He ++ of 0.057±0.010, indicating that the solar wind is a dominant plasma source for these ions and that they are likely to be accelerated by a velocity dependent process. The energy density of these suprathermal ions is 150 eV/cm³, accounting for a large portion of the total pressure. Our observations combined with typical values for the thermal plasma in the near and far plasma sheet suggest that adiabatic cooling of the plasma has taken place as the plasmoid propagates tailward and expands, and indicate a crosstail expansion speed of ∼80 km/s.

A Photoelectron Spectroscopic Estimation of the Concentrations of Simple Hydrogen-bonded Dimers Produced in the Temperature-controlled Supersonic Nozzle Beam

Abstract A photoelectron spectroscopic method is proposed to estimate the ratio of number densities between the monomer and the dimer produced in the supersonic jet. Approximate monomer-dimer ratios have been estimated for water, methanol and formic acid by assuming that the photoionization cross sections of the monomer and dimer are equal to each other. The results show reasonable agreement under similar conditions to those available from mass spectrometric analyses of fragmentation patterns. A simple temperature-controlled supersonic nozzle beam source is described here, which enables us to produce hydrogen-bonded dimers in measurable amounts.

Photospheric Sources of Magnetic Field Aligned Currents

Possible (small-scale) photospheric sources of coronal magnetic field aligned currents are discussed. Such currents are equivalent to local (small-scale) twists of the coronal magnetic field, and may cause field topologies that are (MHD or resistively) unstable, and thus contribute to the (small-scale) coronal activity.One electro-motive force associated with photospheric magnetic fields is due to the asymmetry between ions and electrons as agents of conductivity and as agents of momentum transfer to the (dominant) neutral gas component. In the solar photosphere, where only some of the easily ionized heavier elements (Mg, Si, Fe, ...) are significantly ionized, the ratio of number density of electrons and ions to neutrals is very small, of the order of the total abundance of these elements, which is of the order 10-4, by number. Due to the larger electron than ion mobility, electric currents are mainly carried by the electron component of the plasma whereas, because of the ions greater momentum transfer to the neutrals in collisions, the friction between the charged and the neutral components of the plasma is mainly due to the ions. Thus, the Lorenz force i x B acts mainly on the electron component of the plasma, whereas the balancing gas pressure gradient and gravity terms act mainly on the neutral component.

Laser-saturated fluorescence measurements of OH concentration in flames

A laser-saturated fluorescence technique which can be used to measure accurate OH radical concentrations over wide ranges of flame pressure, composition, and temperature has been developed. The balanced cross-rate model is used to analyze the fluorescence data. The basic premise of the model is that the population of the upper and lower rotational levels which are coupled by the laser is approximately constant during the laser pulse. Using the balanced cross-rate model to calculate concentrations, OH number densities calculated from saturated fluorescence agree to within 20% with number densities calculated from independent absorption measurements over a wide range of flame conditions. In addition, the ratio of number densities calculated from saturated fluorescence and absorption is constant over an order of magnitude range of flame pressure, demonstrating the insensitivity of the saturated fluorescence signal to collisional quenching rates. The estimated OH detection limit of the fluorescence system is 10 12–10 13 molecules/cm 3.

Time development of the free-quark-to-baryon ratio from the very early universe

An attempt is made to estimate the quark-to-nucleon ratio under the assumption that the reported fractional charges are the unmatched relic quarks which failed to find quark or the unstable diquark partners to form nucleons. The time development of the quark-to-nucleon number density ratio from the very early universe is obtained from a rate equation for the process. The cross-section for the quark-nucleon transition is assumed to be inversely proportional to the square of the momentum and reaches the maximum value of the proton size as the temperature decreases, due to the expansion of the universe. If the quark-nucleon transition starts at 3/2kTi - 0.4 GeV, the process practically ends at 3/2kT ≏0.2 GeV, and the quark-to-nucleon ratio is ~10-(20/21) with a quark rest mass of 0.001 GeV≲m0c2 ≲10 GeV.

Dependence of electron beam instability growth rates on the beam‐plasma system parameters

Electron beam instabilities are studied by using a simple model for an electron beam streaming through a cold plasma, the beam being of finite width perpendicular to the ambient magnetic field. Through considerations of finite geometry and the coldness of the beam and background plasma, an instability similar to the two stream instability is assumed to be the means for wave growth in the system. Having found the maximum growth rate for one set of beam‐plasma system parameters, this maximum growth rate is traced as these parameters are varied. The parameters that describe the system are the beam velocity (υb), electron gyrofrequency to ambient electron plasma frequency ratio (Ωe/ωpe), the beam to background number density ratio (nb/na), and the beam half width (a). When Ωe/ωpe &gt; 1, a mode with Ωe &lt; ω &lt; ωUHR is found to be unstable, where ω is the wave frequency and ωUHR is the upper hybrid resonance frequency. For low values of nb/na and Ωe &lt; ωpe, this mode is still present with ωpe &lt; ω &lt; ωUHR. If the beam density is large, nb/na ≃ 1, the instability occurs for frequencies just above the electron gyrofrequency. This mode may well be that observed in laboratory plasmas before the system undergoes the beam‐plasma discharge. There is another instability present, which occurs for ω ≃ ωpe. The growth rates for this mode, which are generally larger than those found for the ω ≃ ωUHR mode, are only weakly dependent on Ωe/ωpe. That this mode is not always observed in the laboratory implies that some factors not considered in the present theory suppress this mode, specifically, finite beam length. Consequently, this mode should be unstable in space plasmas, and it is possible that the ω ≃ ωpe instability is of some significance for auroral zone electron beam instability. A more realistic electron distribution function should be employed to determine if a two‐stream instability exists for the auroral plasma, but since the beam width is found to be important only for a &lt; c/ωpe, finite geometry can be neglected.

A Model Reflection Nebula in the Far Infrared

We have considered a model of a reflection nebula with the star within a homogeneous plane-parallel slab of 1 pc thickness. The model is intended to imitate the Merope reflection nebula. The illuminating star is located at 0.35 pc from the front surface of the nebula. The size distribution of the grains has been incorporated. Using the radiation balance equation for input and output powers, we have calculated the grain temperature as a function of size, offset angle, and position of each grain within the nebula. These results have been used to calculate the expected infrared fluxes in the wavelength range 1-100 m with the offset angle as parameter. The results for ice, graphite, and silicate grains show some interestingly distinguishable structures in the flux versus wavelength curves. A rough estimate for the highest flux turns out to be F (5 × 10<SUP>-12±1</SUP>)n<SUB>H</SUB> W m<SUP>-2</SUP> μm<SUP>-1</SUP> sr<SUP>-1</SUP> corresponding to offset angle ψ = 0°,n<SUB>H</SUB> being the hydrogen number density. The proportionality to n<SUB>H</SUB> occurs because we have assumed a constant ratio of the grain number density to n<SUB>H</SUB>. It is not unreasonable to expect observable infrared fluxes in the appropriate wavelength range in the direction toward the Merope reflection nebula. In particular, from the observational point of view, we predict that the best results on the strongest infrared radiation from the Merope reflection nebula can occur near about 40 μm.

HCO/+/ emission in the galacic center region. I - Observations

HCO/sup +/ emission (3.4 mm, J=1--0) in the galactic center region has been observed toward the dense molecular clouds near Sgr A and Sgr B2 at over 20 points. The profiles are asymmetric, and are very widely extended in velocity like the /sup 12/CO line in spite of the high excitation requirements of the HCO/sup +/ line. A position-velocity map along the galacitc plane including the galactic nucleus was obtained. Comparison with the HCN emission leads us to the conclusion that the number density ratio (HCO/sup +/)/(HCN) is higher by an order of magnitude in the diffuse region. This behavior is discussed in terms of the ion-molecule reaction scheme. A dip of 0 km s/sup -1/, which is probably due to self-absorption by foreground cold molecular gas, was found in the HCO/sup +/ profiles as well as in spectra of HCN. The abundance of HCO/sup +/ relative to H/sub 2/ in the cold cloud is estimated to be > or approx. =10/sup -9.5/, which is remarkable large for such a low density cloud.