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Sample records for gas density factors

  1. Gas density fluctuations in the Perseus Cluster: clumping factor and velocity power spectrum

    NASA Astrophysics Data System (ADS)

    Zhuravleva, I.; Churazov, E.; Arévalo, P.; Schekochihin, A. A.; Allen, S. W.; Fabian, A. C.; Forman, W. R.; Sanders, J. S.; Simionescu, A.; Sunyaev, R.; Vikhlinin, A.; Werner, N.

    2015-07-01

    X-ray surface brightness fluctuations in the core of the Perseus Cluster are analysed, using deep observations with the Chandra observatory. The amplitude of gas density fluctuations on different scales is measured in a set of radial annuli. It varies from 7 to 12 per cent on scales of ˜10-30 kpc within radii of 30-220 kpc from the cluster centre. Using a statistical linear relation between the observed amplitude of density fluctuations and predicted velocity, the characteristic velocity of gas motions on each scale is calculated. The typical amplitudes of the velocity outside the central 30 kpc region are 90-140 km s-1 on ˜20-30 kpc scales and 70-100 km s-1 on smaller scales ˜7-10 kpc. The velocity power spectrum (PS) is consistent with cascade of turbulence and its slope is in a broad agreement with the slope for canonical Kolmogorov turbulence. The gas clumping factor estimated from the PS of the density fluctuations is lower than 7-8 per cent for radii ˜30-220 kpc from the centre, leading to a density bias of less than 3-4 per cent in the cluster core. Uncertainties of the analysis are examined and discussed. Future measurements of the gas velocities with the Astro-H, Athena and Smart-X observatories will directly measure the gas density-velocity perturbation relation and further reduce systematic uncertainties in this analysis.

  2. Densities and filling factors of the diffuse ionized gas in the Solar neighbourhood

    NASA Astrophysics Data System (ADS)

    Berkhuijsen, E. M.; Müller, P.

    2008-10-01

    Aims: We analyse electron densities and filling factors of the diffuse ionized gas (DIG) in the Solar neighbourhood. Methods: We have combined dispersion measures and emission measures towards 38 pulsars at distances known to better than 50%, from which we derived the mean density in clouds, N_c, and their volume filling factor, F_v, averaged along the line of sight. The emission measures were corrected for absorption by dust and contributions from beyond the pulsar distance. Results: The scale height of the electron layer for our sample is 0.93± 0.13 kpc and the midplane electron density is 0.023± 0.004 cm-3, in agreement with earlier results. The average density along the line of sight is < n_e> = 0.018± 0.002 cm-3 and is nearly constant. Since < n_e> = F_vN_c, an inverse relationship between Fv and Nc is expected. We find F_v(N_c) = (0.011± 0.003) N_c-1.20± 0.13, which holds for the ranges N_c= 0.05-1 cm-3 and F_v= 0.4-0.01. Near the Galactic plane the dependence of Fv on Nc is significantly stronger than away from the plane. Fv does not systematically change along or perpendicular to the Galactic plane, but the spread about the mean value of 0.08± 0.02 is considerable. The total pathlength through the ionized regions increases linearly to about 80 pc towards |z| = 1 kpc. Conclusions: Our study of Fv and Nc of the DIG is the first one based on a sample of pulsars with known distances. We confirm the existence of a tight, nearly inverse correlation between Fv and Nc in the DIG. The exact form of this relation depends on the regions in the Galaxy probed by the pulsar sample. The inverse F_v-Nc relation is consistent with a hierarchical, fractal density distribution in the DIG caused by turbulence. The observed near constancy of < n_e> then is a signature of fractal structure in the ionized medium, which is most pronounced outside the thin disk.

  3. Acoustic measurements of gas density

    NASA Technical Reports Server (NTRS)

    Shakkottai, P.; Kwack, E. Y.; Back, L. H.

    1990-01-01

    Sound transmission through gases in an enclosure is considered. Analytical results are given in terms of geometrical parameters, wave numbers, and source type for simple model problems, and are compared with data obtained by Haran (1983). It is concluded that density measurements can be made in a gas contained in an enclosure by measuring the sound pressure level at a receiver located near a dipole source driven at a constant velocity amplitude at low frequencies.

  4. Simulation of AlGaN/GaN high-electron-mobility transistor gauge factor based on two-dimensional electron gas density and electron mobility

    NASA Astrophysics Data System (ADS)

    Chu, Min; Koehler, Andrew D.; Gupta, Amit; Nishida, Toshikazu; Thompson, Scott E.

    2010-11-01

    The gauge factor of AlGaN/GaN high-electron-mobility transistor was determined theoretically, considering the effect of stress on the two-dimensional electron gas (2DEG) sheet carrier density and electron mobility. Differences in the spontaneous and piezoelectric polarization between the AlGaN and GaN layers, with and without external mechanical stress, were investigated to calculate the stress-altered 2DEG density. Strain was incorporated into a sp3d5-sp3 empirical tight-binding model to obtain the change in electron effective masses under biaxial and uniaxial stress. The simulated longitudinal gauge factor (-7.9±5.2) is consistent with experimental results (-2.4±0.5) obtained from measurements eliminating parasitic charge trapping effects through continuous subbandgap optical excitation.

  5. Critical density of a soliton gas

    NASA Astrophysics Data System (ADS)

    El, G. A.

    2016-02-01

    We quantify the notion of a dense soliton gas by establishing an upper bound for the integrated density of states of the quantum-mechanical Schrödinger operator associated with the Korteweg-de Vries soliton gas dynamics. As a by-product of our derivation, we find the speed of sound in the soliton gas with Gaussian spectral distribution function.

  6. Photoionization and High Density Gas

    NASA Technical Reports Server (NTRS)

    Kallman, T.; Bautista, M.; White, Nicholas E. (Technical Monitor)

    2002-01-01

    We present results of calculations using the XSTAR version 2 computer code. This code is loosely based on the XSTAR v.1 code which has been available for public use for some time. However it represents an improvement and update in several major respects, including atomic data, code structure, user interface, and improved physical description of ionization/excitation. In particular, it now is applicable to high density situations in which significant excited atomic level populations are likely to occur. We describe the computational techniques and assumptions, and present sample runs with particular emphasis on high density situations.

  7. Critical density of a soliton gas.

    PubMed

    El, G A

    2016-02-01

    We quantify the notion of a dense soliton gas by establishing an upper bound for the integrated density of states of the quantum-mechanical Schrödinger operator associated with the Korteweg-de Vries soliton gas dynamics. As a by-product of our derivation, we find the speed of sound in the soliton gas with Gaussian spectral distribution function. PMID:26931586

  8. ?Linear Gas Jet with Tailored Density Profile"

    SciTech Connect

    KRISHNAN, Mahadevan

    2012-12-10

    Supersonic, highly collimated gas jets and gas-filled capillary discharge waveguides are two primary targets of choice for Laser Plasma Accelerators (LPA) . Present gas jets have lengths of only 2-4 mm at densities of 1-4E19 cm-3, sufficient for self trapping and electron acceleration to energies up to ~150 MeV. Capillary structures 3 cm long have been used to accelerate beams up to 1 GeV. Capillary discharges used in LPAs serve to guide the pump laser and optimize the energy gain. A wall-stabilized capillary discharge provides a transverse profile across the channel that helps guide the laser and combat diffraction. Gas injection via a fast nozzle at one end provides some longitudinal density control, to improve the coupling. Gas jets with uniform or controlled density profiles may be used to control electron bunch injection and are being integrated into capillary experiments to add tuning of density. The gas jet for electron injection has not yet been optimized. Our Ph-I results have provided the LPA community with an alternative path to realizing a 2-3GeV electron bunch using just a gas jet. For example, our slit/blade combination gives a 15-20mm long acceleration path with tunable density profile, serving as an alternative to a 20-mm long capillary discharge with gas injection at one end. In Ph-II, we will extend these results to longer nozzles, to see whether we can synthesize 30 or 40-mm long plasma channels for LPAs.

  9. Gravitational star formation thresholds and gas density in three galaxies

    NASA Technical Reports Server (NTRS)

    Oey, M. S.; Kennicutt, R. C., Jr.

    1990-01-01

    It has long been held that the star formation rate (SFR) may be described as a power law of the gas density, p(exp n), as given by Schmidt (1959). However, this relation has as yet remained poorly defined and is likewise poorly understood. In particular, most studies have been investigations of global gas and star formation properties of galaxies, due to lack of adequate high-resolution data for detailed studies of individual galaxies. The three spiral galaxies in this study have published maps of both H2 (as traced by CO), and HI, thereby enabling the authors to investigate the relationship between total gas surface density and SFR. The purpose of the present investigation is the comparison of spatially-resolved total surface gas density in three galaxies (NGC 6946, M51, and M83) to sigma sub c as given by the above model. CO, HI and H alpha data for NGC 6946 were taken from Tacconi-Garman (1988), and for M51 and M83 from Lord (1987). The authors used a CO-H2 conversion of N(H2)/I sub CO(exp cos i = 2.8 x 10(exp 20) atoms cm(-2)/(K kms(-1), and summed the H2 and HI data for each galaxy to obtain the total hydrogen gas density. This total was then multiplied by a factor of 1.36 to include the contribution of helium to the total surface gas density. The authors assumed distances to NGC 6946, M51, and M83 to be 6.0, 9.6, and 8.9 Mpc respectively, with inclination angles of 30, 20, and 26 degrees. H alpha flux was used as the measure of SFR for NGC 6946, and SFR for the remaining two galaxies was taken directly from Lord as computed from H alpha measurements. The results of these full-disk studies thus show a remarkable correlation between the total gas density and the threshold densities given by the gravitational stability criterion. In particular, the threshold density appears to mark a lower boundary to the range of gas densities in these galaxies, which may have consequence in determining appropriate models for star formation and gas dynamics. More evidence is

  10. Instability Analysis of a Low-Density Gas Jet Injected into a High-Density Gas

    NASA Technical Reports Server (NTRS)

    Lawson, Anthony Layiwola

    2001-01-01

    The objective of this study was to determine the effects of buoyancy on the absolute instability of low-density gas jets injected into high-density gas mediums. Most of the existing analyses of low-density gas jets injected into a high-density ambient have been carried out neglecting effects of gravity. In order to investigate the influence of gravity on the near-injector development of the flow, a linear temporal stability analysis and a spatio-temporal stability analysis of a low-density round jet injected into a high-density ambient gas were performed. The flow was assumed to be isothermal and locally parallel; viscous and diffusive effects were ignored. The variables were represented as the sum of the mean value and a normal-mode small disturbance. An ordinary differential equation governing the amplitude of the pressure disturbance was derived. The velocity and density profiles in the shear layer, and the Froude number (signifying the effects of gravity) were the three important parameters in this equation. Together with the boundary conditions, an eigenvalue problem was formulated. Assuming that the velocity and density profiles in the shear layer to be represented by hyperbolic tangent functions, the eigenvalue problem was solved for various values of Froude number. The temporal growth rates and the phase velocity of the disturbances were obtained. It was found that the presence of variable density within the shear layer resulted in an increase in the temporal amplification rate of the disturbances and an increase in the range of unstable frequencies, accompanied by a reduction in the phase velocities of the disturbances. Also, the temporal growth rates of the disturbances were increased as the Froude number was reduced (i.e. gravitational effects increased), indicating the destabilizing role played by gravity. The spatio-temporal stability analysis was performed to determine the nature of the absolute instability of the jet. The roles of the density ratio

  11. Density PDFs of diffuse gas in the Milky Way

    NASA Astrophysics Data System (ADS)

    Berkhuijsen, E. M.; Fletcher, A.

    2012-09-01

    The probability distribution functions (PDFs) of the average densities of the diffuse ionized gas (DIG) and the diffuse atomic gas are close to lognormal, especially when lines of sight at |b| < 5∘ and |b|≥ 5∘ are considered separately. Our results provide strong support for the existence of a lognormal density PDF in the diffuse ISM, consistent with a turbulent origin of density structure in the diffuse gas.

  12. THE MOLECULAR GAS DENSITY IN GALAXY CENTERS AND HOW IT CONNECTS TO BULGES

    SciTech Connect

    Fisher, David B.; Bolatto, Alberto; Drory, Niv; Combes, Francoise; Blitz, Leo; Wong, Tony

    2013-02-20

    In this paper we present gas density, star formation rate (SFR), stellar masses, and bulge-disk decompositions for a sample of 60 galaxies. Our sample is the combined sample of the BIMA SONG, CARMA STING, and PdBI NUGA surveys. We study the effect of using CO-to-H{sub 2} conversion factors that depend on the CO surface brightness, and also that of correcting SFRs for diffuse emission from old stellar populations. We estimate that SFRs in bulges are typically lower by 20% when correcting for diffuse emission. Using the surface brightness dependent conversion factor, we find that over half of the galaxies in our sample have {Sigma}{sub mol} > 100 M {sub Sun} pc{sup -2}. Though our sample is not complete in any sense, our results are enough to rule out the assumption that bulges are uniformly gas-poor systems. We find a trend between gas density of bulges and bulge Sersic index; bulges with lower Sersic index have higher gas density. Those bulges with low Sersic index (pseudobulges) have gas fractions that are similar to that of disks. Conversely, the typical molecular gas fraction in classical bulges is more similar to that of an elliptical galaxy. We also find that there is a strong correlation between bulges with the highest gas surface density and the galaxy being barred. However, we also find that classical bulges with low gas surface density can be barred as well. Our results suggest that understanding the connection between the central surface density of gas in disk galaxies and the presence of bars should also take into account the total gas content of the galaxy. Finally, we show that when using the corrected SFRs and gas densities, the correlation between SFR surface density and gas surface density of bulges is similar to that of disks. This implies that at the scale of the bulges the timescale for converting gas into stars is comparable to those results found in disks.

  13. The Molecular Gas Density in Galaxy Centers and how it Connects to Bulges

    NASA Astrophysics Data System (ADS)

    Fisher, David B.; Bolatto, Alberto; Drory, Niv; Combes, Francoise; Blitz, Leo; Wong, Tony

    2013-02-01

    In this paper we present gas density, star formation rate (SFR), stellar masses, and bulge-disk decompositions for a sample of 60 galaxies. Our sample is the combined sample of the BIMA SONG, CARMA STING, and PdBI NUGA surveys. We study the effect of using CO-to-H2 conversion factors that depend on the CO surface brightness, and also that of correcting SFRs for diffuse emission from old stellar populations. We estimate that SFRs in bulges are typically lower by 20% when correcting for diffuse emission. Using the surface brightness dependent conversion factor, we find that over half of the galaxies in our sample have Σmol > 100 M ⊙ pc-2. Though our sample is not complete in any sense, our results are enough to rule out the assumption that bulges are uniformly gas-poor systems. We find a trend between gas density of bulges and bulge Sérsic index; bulges with lower Sérsic index have higher gas density. Those bulges with low Sérsic index (pseudobulges) have gas fractions that are similar to that of disks. Conversely, the typical molecular gas fraction in classical bulges is more similar to that of an elliptical galaxy. We also find that there is a strong correlation between bulges with the highest gas surface density and the galaxy being barred. However, we also find that classical bulges with low gas surface density can be barred as well. Our results suggest that understanding the connection between the central surface density of gas in disk galaxies and the presence of bars should also take into account the total gas content of the galaxy. Finally, we show that when using the corrected SFRs and gas densities, the correlation between SFR surface density and gas surface density of bulges is similar to that of disks. This implies that at the scale of the bulges the timescale for converting gas into stars is comparable to those results found in disks.

  14. Growth of arc in high-pressure, pulsed glow discharge by gas density depletion

    NASA Astrophysics Data System (ADS)

    Imada, Go; Yatsui, Kiyoshi; Masuda, Wataru

    2000-10-01

    Effects of gas density depletion on arc formation of high-pressure, pulsed glow discharge have been investigated by eliminating the other factors which may affect the discharge stability, such as shock waves, residual ions, electrode heating, and discharge products. The gas density depletion has been simulated by utilizing a subsonic gas flow between the curved electrodes combined with a convergent nozzle and a divergent diffuser. A comparison has been made on the discharge in the aerodynamically created gas density depletion with the second discharge in the double-pulse discharge within a stable gas. We have found that the large gas density depletion, Δρ/ρ0˜-3.6% corresponding to a pulse repetition rate (PRR) of ˜50 Hz, tends to cause an arc-like filament or an arc without the shocks, ions, electrode heating, and products. However, the second discharge in the double-pulse discharge becomes an arc in much smaller gas density depletion (Δρ/ρ0˜-1.2% corresponding to PRR ˜3 Hz). Therefore, the collapse of high-pressure, pulsed glow discharge is most likely caused by some factor other than the gas density depletion.

  15. Reliability factors in gas lasers

    NASA Astrophysics Data System (ADS)

    Malk, E. G.; Ramsay, I. A.

    1982-07-01

    Two types of gas lasers, the helium-neon laser and the sealed off, waveguide carbon dioxide laser, are discussed. The beneficial influence of hard seals on the HeNe laser is briefly described, and the resulting improved mean time between failures is described and discussed, showing a summary of lifetest data. Rejection percentages at 80 percent of the rated power in 18 months of elapsed time is determined to be 10 percent for one family of HeNe lasers and 7.6 percent for another family. An optical failure mode for HeNe lasers and the scientific investigation leading to its elimination are described. Finally, CO2 waveguide laser reliability is discussed in terms of the lifetime degradation factors involved in the operation of these lasers.

  16. Multiple Point Dynamic Gas Density Measurements Using Molecular Rayleigh Scattering

    NASA Technical Reports Server (NTRS)

    Seasholtz, Richard; Panda, Jayanta

    1999-01-01

    A nonintrusive technique for measuring dynamic gas density properties is described. Molecular Rayleigh scattering is used to measure the time-history of gas density simultaneously at eight spatial locations at a 50 kHz sampling rate. The data are analyzed using the Welch method of modified periodograms to reduce measurement uncertainty. Cross-correlations, power spectral density functions, cross-spectral density functions, and coherence functions may be obtained from the data. The technique is demonstrated using low speed co-flowing jets with a heated inner jet.

  17. Electron density and gas density measurements in a millimeter-wave discharge

    NASA Astrophysics Data System (ADS)

    Schaub, S. C.; Hummelt, J. S.; Guss, W. C.; Shapiro, M. A.; Temkin, R. J.

    2016-08-01

    Electron density and neutral gas density have been measured in a non-equilibrium air breakdown plasma using optical emission spectroscopy and two-dimensional laser interferometry, respectively. A plasma was created with a focused high frequency microwave beam in air. Experiments were run with 110 GHz and 124.5 GHz microwaves at powers up to 1.2 MW. Microwave pulses were 3 μs long at 110 GHz and 2.2 μs long at 124.5 GHz. Electron density was measured over a pressure range of 25 to 700 Torr as the input microwave power was varied. Electron density was found to be close to the critical density, where the collisional plasma frequency is equal to the microwave frequency, over the pressure range studied and to vary weakly with input power. Neutral gas density was measured over a pressure range from 150 to 750 Torr at power levels high above the threshold for initiating breakdown. The two-dimensional structure of the neutral gas density was resolved. Intense, localized heating was found to occur hundreds of nanoseconds after visible plasma formed. This heating led to neutral gas density reductions of greater than 80% where peak plasma densities occurred. Spatial structure and temporal dynamics of gas heating at atmospheric pressure were found to agree well with published numerical simulations.

  18. Suppression of Density Fluctuations in a Quantum Degenerate Fermi Gas

    SciTech Connect

    Sanner, Christian; Su, Edward J.; Keshet, Aviv; Gommers, Ralf; Shin, Yong-il; Huang Wujie; Ketterle, Wolfgang

    2010-07-23

    We study density profiles of an ideal Fermi gas and observe Pauli suppression of density fluctuations (atom shot noise) for cold clouds deep in the quantum degenerate regime. Strong suppression is observed for probe volumes containing more than 10 000 atoms. Measuring the level of suppression provides sensitive thermometry at low temperatures. After this method of sensitive noise measurements has been validated with an ideal Fermi gas, it can now be applied to characterize phase transitions in strongly correlated many-body systems.

  19. Low density gas dynamic wall boundary conditions

    NASA Technical Reports Server (NTRS)

    Collins, F. G.

    1986-01-01

    Low density nozzles or large expansion ratio nozzles used in space experience rarefaction effects near their exit in the form of velocity slip and temperature jump at the walls. In addition, the boundary layers become very thick and there is a very strong viscous/inviscid interaction. For these reasons no existing design technique has been found to accurately predict the nozzle flow properties up to the nozzle exit. The objective of this investigation was to examine the slip boundary conditions and formulate them in a form appropriate for use with a full Navier-Stokes numerical code. The viscous/inviscid interaction would automatically be accounted for by using a compressible Navier-Stokes code. Through examination of the interaction of molecules with solid surfaces, a model for the distribution function of the reflected molecules has been determined and this distribution function has been used to develop a new slip boundary condition that can be shown to yield more realistic surface boundary conditions.

  20. THE DEPENDENCE OF STAR FORMATION EFFICIENCY ON GAS SURFACE DENSITY

    SciTech Connect

    Burkert, Andreas; Hartmann, Lee E-mail: lhartm@umich.edu

    2013-08-10

    Studies by Lada et al. and Heiderman et al. have suggested that star formation mostly occurs above a threshold in gas surface density {Sigma} of {Sigma}{sub c} {approx} 120 M{sub Sun} pc{sup -2} (A{sub K} {approx} 0.8). Heiderman et al. infer a threshold by combining low-mass star-forming regions, which show a steep increase in the star formation rate per unit area {Sigma}{sub SFR} with increasing {Sigma}, and massive cores forming luminous stars which show a linear relation. We argue that these observations do not require a particular density threshold. The steep dependence of {Sigma}{sub SFR}, approaching unity at protostellar core densities, is a natural result of the increasing importance of self-gravity at high densities along with the corresponding decrease in evolutionary timescales. The linear behavior of {Sigma}{sub SFR} versus {Sigma} in massive cores is consistent with probing dense gas in gravitational collapse, forming stars at a characteristic free-fall timescale given by the use of a particular molecular tracer. The low-mass and high-mass regions show different correlations between gas surface density and the area A spanned at that density, with A {approx} {Sigma}{sup -3} for low-mass regions and A {approx} {Sigma}{sup -1} for the massive cores; this difference, along with the use of differing techniques to measure gas surface density and star formation, suggests that connecting the low-mass regions with massive cores is problematic. We show that the approximately linear relationship between dense gas mass and stellar mass used by Lada et al. similarly does not demand a particular threshold for star formation and requires continuing formation of dense gas. Our results are consistent with molecular clouds forming by galactic hydrodynamic flows with subsequent gravitational collapse.

  1. Gas density effect on dropsize of simulated fuel sprays

    NASA Technical Reports Server (NTRS)

    Ingebo, Robert D.

    1989-01-01

    Two-phase flow in pneumatic two-fluid fuel nozzles was investigated experimentally to determine the effect of atomizing-gas density and gas mass-flux on liquid-jet breakup in sonic-velocity gas-flow. Dropsize data were obtained for the following atomizing-gases: nitrogen; argon; carbon dioxide; and helium. They were selected to cover a gas molecular-weight range of 4 to 44. Atomizing-gas mass-flux ranged from 6 to 50 g/sq cm-sec and four differently sized two-fluid fuel nozzles were used having orifice diameters that varied from 0.32 to 0.56 cm. The ratio of liquid-jet diameter to SMD, D sub o/D sub 32, was correlated with aerodynamic and liquid-surface forces based on the product of the Weber and Reynolds number, and gas-to-liquid density ratio, rho sub g/rho sub 1. To correlate spray dropsize with breakup forces produced by using different atomizing-gases, a new molecular-scale dimensionless group was derived. The derived dimensionless group was used to obtain an expression for the ratio of liquid-jet diameter to SMD, D sub o/D sub 32. The mathematical expression of this phenomenon incorporates the product of the Weber and Reynolds number, liquid viscosity, surface tension, acoustic gas velocity, the RMS velocity of gas molecules, the acceleration of gas molecules due to gravity, and gas viscosity. The mathematical expression encompassing these parameters agrees well with the atomization theory for liquid-jet breakup in high velocity gas flow. Also, it was found that at the same gas mass-flux, helium was considerably more effective than nitrogen in producing small droplet sprays with SMD's in the order of 5 micrometers.

  2. Gas density effect on dropsize of simulated fuel sprays

    NASA Technical Reports Server (NTRS)

    Ingebo, Robert D.

    1989-01-01

    Two-phase flow in pneumatic two-fluid fuel nozzles was investigated experimentally to determine the effect of atomizing-gas density and gas mass-flux on liquid-jet breakup in sonic-velocity gas-flow. Dropsize data were obtained for the following atomizing-gases: nitrogen; argon; carbon dioxide; and helium. They were selected to cover a gas molecular-weight range of 4 to 44. Atomizing-gas mass-flux ranged from 6 to 50 g/sq cm-sec and four differently sized two-fluid fuel nozzles were used having orifice diameters that varied from 0.32 to 0.56 cm. The ratio of liquid-jet diameter to SMD, D sub o/D sub 32, was correlated with aerodynamic and liquid-surface forces based on the product of the Weber and Reynolds number, We*Re, and gas-to-liquid density ratio, rho sub g/rho sub l. To correlate spray dropsize with breakup forces produced by using different atomizing-gases, a new molecular-scale dimensionless group was derived. The derived dimensionless group was used to obtain an expression for the ratio of liquid-jet diameter to SMD, D sub o/D sub 32. The mathematical expression of this phenomenon incorporates the product of the Weber and Reynolds number, liquid viscosity, surface tension, acoustic gas velocity, the RMS velocity of gas molecules, the acceleration of gas molecules due to gravity, and gas viscosity. The mathematical expression encompassing these parameters agrees well with the atomization theory for liquid-jet breakup in high velocity gas flow. Also, it was found that at the same gas mass-flux, helium was considerably more effective than nitrogen in producing small droplet sprays with SMD's in the order of 5 micrometers.

  3. Measurements of the negative ion density in reactive gas plasmas

    NASA Astrophysics Data System (ADS)

    Shindo, Masako; Ueda, Yoko; Kawai, Yoshinobu; Ishii, Nobuo

    1999-11-01

    The reactive gas plasmas, such as C_4F_8, SiH4 and SF6 gas plasmas, have been widely used in plasma etching or CVD. The radicals and ions species in these plasmas have been reported in a lot of study. However, the negative ion density has not been measured quantitatively, since the conventional Langmuir probe cannot be used due to film depositions on its surface. In this study, the negative ion density in the reactive gas plasmas was measured with a heated Langmuir probe and an 8-mm microwave interferometer as a function of gas flow rate and radial position. Furthermore, the following equation was suggested to estimate the negative ion density only from the probe measurements: fracI_+(X )I_+(Ar) = [ fracI_-(X)I_-(Ar) + fracN_-(X )N_+(Ar)√fracT_e(X)T_e(Ar) ] √fracM_+(Ar)M_+(X), where N- denotes negative ion density and the other characteristics represent the conventional ones. The positive ion mass M+ should be assumed properly. It was confirmed that this equation provides the negative ion density both in the magnetized plasmas, such as ECR plasmas, and non-magnetized plasmas.

  4. High-density carbon ablator ignition path with low-density gas-filled rugby hohlraum

    SciTech Connect

    Amendt, Peter; Ho, Darwin D.; Jones, Ogden S.

    2015-04-15

    A recent low gas-fill density (0.6 mg/cc {sup 4}He) cylindrical hohlraum experiment on the National Ignition Facility has shown high laser-coupling efficiency (>96%), reduced phenomenological laser drive corrections, and improved high-density carbon capsule implosion symmetry [Jones et al., Bull. Am. Phys. Soc. 59(15), 66 (2014)]. In this Letter, an ignition design using a large rugby-shaped hohlraum [Amendt et al., Phys. Plasmas 21, 112703 (2014)] for high energetics efficiency and symmetry control with the same low gas-fill density (0.6 mg/cc {sup 4}He) is developed as a potentially robust platform for demonstrating thermonuclear burn. The companion high-density carbon capsule for this hohlraum design is driven by an adiabat-shaped [Betti et al., Phys. Plasmas 9, 2277 (2002)] 4-shock drive profile for robust high gain (>10) 1-D ignition performance and large margin to 2-D perturbation growth.

  5. Effects of argon gas pressure on its metastable-state density in high-density plasmas

    SciTech Connect

    Seo, B. H.; Kim, J. H.; You, S. J.

    2015-05-15

    The effect of argon gas pressure on its metastable density in inductively coupled plasmas (ICPs) is investigated by using the laser-induced fluorescence method. Our results show that the metastable-state density of argon varies with the gas pressure depending on the measurement position; the density decreases with the pressure at a position far from the ICP antenna, whereas it increases with the pressure at a position near the antenna. This contrast in the metastable-state density trend with the pressure is explained by considering the electron temperature variations at the two measurement positions. The theoretical interpretation and calculation using a global model are also addressed in detail in this paper.

  6. High-density carbon ablator ignition path with low-density gas-filled rugby hohlraum

    NASA Astrophysics Data System (ADS)

    Amendt, Peter; Ho, Darwin D.; Jones, Ogden S.

    2015-04-01

    A recent low gas-fill density (0.6 mg/cc 4He) cylindrical hohlraum experiment on the National Ignition Facility has shown high laser-coupling efficiency (>96%), reduced phenomenological laser drive corrections, and improved high-density carbon capsule implosion symmetry [Jones et al., Bull. Am. Phys. Soc. 59(15), 66 (2014)]. In this Letter, an ignition design using a large rugby-shaped hohlraum [Amendt et al., Phys. Plasmas 21, 112703 (2014)] for high energetics efficiency and symmetry control with the same low gas-fill density (0.6 mg/cc 4He) is developed as a potentially robust platform for demonstrating thermonuclear burn. The companion high-density carbon capsule for this hohlraum design is driven by an adiabat-shaped [Betti et al., Phys. Plasmas 9, 2277 (2002)] 4-shock drive profile for robust high gain (>10) 1-D ignition performance and large margin to 2-D perturbation growth.

  7. A solid state gas density monitor for gas insulated substation equipment

    SciTech Connect

    Saaski, E.W.; Hartl, J.C.

    1982-07-01

    A solid state gas density monitor has been developed for SF/sub 6/ service in gas-insulated substation equipment that is based on principles and construction techniques similar to ionization-type fire alarms. The monitor has a resolution of .7kPa (.1 psi) at 20/sup 0/C and, depending on ion chamber voltage and geometry, exhibits a linearity of /sup +//sub -/1 to /sup +//sub -/4. kPa (/sup +//sub -/.15 to /sup +//sub -/.6 psi) at 20/sup 0/C over the density range 0.20 to 0.66 MPa (30 to 95 psia) at 20/sup 0/C. The monitor incorporates two level contact closure actuated by gas density falling below one of two pre-set alarm limits, and an LCD read-out for visual monitoring and instrument calibration. The display presents density in terms of equivalent psia at 68/sup 0/F. (20/sup 0/C.).

  8. Influence of factors on mammographic density in premenopausal Chinese women.

    PubMed

    Yang, Yaping; Liu, Jieqiong; Gu, Ran; Hu, Yue; Liu, Fengtao; Yun, Miaomiao; Xiao, Qiaozhen; Wu, Mei; Liu, Qiang; Su, Fengxi

    2016-07-01

    Mammographic density is an independent strong risk factor for breast cancer. However, the influence of factors on mammographic density in premenopausal women remains unclear. In the Southern Professional Women Breast Cancer Screening Project, we assessed the associations between mammographic density and its influential factors using multivariate logistic regression in premenopausal women adjusting for BMI, age, duration of breastfeeding, number of live births, and breast size. A total of 1699 premenopausal women aged 27 to 57 years, who had been screened by mammography, were enrolled in this cross-sectional study. Overall, 85.2% were categorized as having dense breasts (BI-RADS density 3 and 4) and 14.8% as having fatty breasts (BI-RADS density 1 and 2). In multivariate and logistic regression analysis, only BMI and age were significantly negatively correlated with mammographic density in premenopausal women (P<0.001). No significant associations between mammographic density and number of deliveries, breastfeeding duration, education level, family history of breast cancer, as well as breast size and sleep quality, were identified in the study. Age and BMI are negatively associated with mammographic density in premenopausal Chinese women. Information on the influential factors of mammographic density in premenopausal women might provide meaningful insights into breast cancer prevention. PMID:26075657

  9. The Factors Affecting Bone Density in Cirrhosis

    PubMed Central

    Hajiabbasi, Asghar; Shafaghi, Afshin; Fayazi, Haniyeh Sadat; Shenavar Masooleh, Irandokht; Hedayati Emami, Mohammad Hassan; Ghavidel Parsa, Pooneh; Amir Maafi, Alireza

    2015-01-01

    Background: Bone loss is common in cirrhosis. However, the prevalence of osteopenia and osteoporosis has been heterogeneous in different reports. Reduction in bone formation with or without increase in bone resorption appears to be responsible for bone loss in these patients. Objectives: We aimed to investigate bone loss in patients with cirrhosis at different anatomical sites and key factors that might affect it. Patients and Methods: In this cross-sectional study, 97 patients with cirrhosis who were referred to Razi Hospital, Rasht, Iran, from 2008 to 2010, were studied. Cirrhosis was diagnosed using biopsy and/or clinical and paraclinical findings. Bone mineral densitometry was done in L2 through L4 lumbar spine (LS) and femoral neck (FN), using dual-energy X-ray absorptiometry (DEXA) (QDR 1000, Hologic DEXA Inc, Waltham, Massachusetts, the United States). Statistical analysis was performed using SPSS 18. A P value < 0.05 was considered statistically significant. Results: A total of 97 patients with cirrhosis (55.7% male) and the mean age of 51 ± 13 years and median body mass index (BMI) of 22.7 kg/m2 were recruited over a two-year period. Etiologies of cirrhosis were hepatitis C (40.2%), hepatitis B (26.8%), cryptogenic (21.6%), and other causes (11.4%). Child A, B, and C, were seen in 16.5%, 47.4%, and 36.1% of patients, respectively. The DEXA results were abnormal in 78.4% of our participants (osteopenia, 45.4%; osteoporosis, 33%). BMI and calculated glomerular filtration rate (GFRc) had moderate positive and Child score had moderate negative significant correlation with T score in both anatomical sites. There was no significant association between abnormal DEXA and the causes of cirrhosis. The univariate analysis showed that the risk of abnormal results in DEXA was significantly higher in those with low BMI, current smoking, higher Child score, and low GFRc; however, in multivariate analysis, the abnormal results were more frequent in those with lower

  10. Influence of Lifestyle Factors on Mammographic Density in Postmenopausal Women

    PubMed Central

    Brand, Judith S.; Czene, Kamila; Eriksson, Louise; Trinh, Thang; Bhoo-Pathy, Nirmala; Hall, Per; Celebioglu, Fuat

    2013-01-01

    Background Mammographic density is a strong risk factor for breast cancer. Apart from hormone replacement therapy (HRT), little is known about lifestyle factors that influence breast density. Methods We examined the effect of smoking, alcohol and physical activity on mammographic density in a population-based sample of postmenopausal women without breast cancer. Lifestyle factors were assessed by a questionnaire and percentage and area measures of mammographic density were measured using computer-assisted software. General linear models were used to assess the association between lifestyle factors and mammographic density and effect modification by body mass index (BMI) and HRT was studied. Results Overall, alcohol intake was positively associated with percent mammographic density (P trend  = 0.07). This association was modified by HRT use (P interaction  = 0.06): increasing alcohol intake was associated with increasing percent density in current HRT users (P trend  = 0.01) but not in non-current users (P trend  = 0.82). A similar interaction between alcohol and HRT was found for the absolute dense area, with a positive association being present in current HRT users only (P interaction  = 0.04). No differences in mammographic density were observed across categories of smoking and physical activity, neither overall nor in stratified analyses by BMI and HRT use. Conclusions Increasing alcohol intake is associated with an increase in mammography density, whereas smoking and physical activity do not seem to influence density. The observed interaction between alcohol and HRT may pose an opportunity for HRT users to lower their mammographic density and breast cancer risk. PMID:24349146

  11. Gas-solid flow characteristics in high-density CFB

    NASA Astrophysics Data System (ADS)

    Wang, Xue-yao; Fan, Bao-guo; Wang, Sheng-dian; Xu, Xiang; Xiao, Yun-han

    2012-08-01

    The gas-solid flow characteristics in the riser of a high density CFB of square (0.27 m×0.27 m×10.4 m) or circular ( ϕ 0.187m×10.4 m) cross section, using Geldart B particles (quartz sand), was investigated experimentally. The influence of riser structure on the hydrodynamic behaviors of a high-density circulating fluidized bed was investigated. The solid circulation rate was up to 321 kg/(m2s) with the circular cross-section under the operating conditions of the main bed air velocity 12.1 m/s and loosen wind and back-feed wind flow 25.1 m3/h. Different operating conditions on realizing high density circulation was analyzed, while both solids circulation rate and particle holdup depended highly on operating conditions. The circulating gas-solid flow was accompanied by an evidently-dense character in the riser's bottom zone and became fully developed in the middle and upper zones.

  12. The effect of slot height and difference in gas densities for coaxial jets on jet mixing in constrained swirled flow

    NASA Astrophysics Data System (ADS)

    Shishkin, N. E.

    2015-07-01

    Experiments were conducted about the effect of height of annular slot on efficiency of film cooling in a tube flow. Nonisothermal nature of flows was modelled by mixing of jets with different densities: air with argon or with helium: the concentration of foreign gas on wall was measured. The influence of nearwall jet swirling and of proportions of densities of gas flows as key factors for laminarization of mixing was considered.

  13. Technique for measuring gas conversion factors

    NASA Technical Reports Server (NTRS)

    Singh, J. J.; Sprinkle, D. R. (Inventor)

    1985-01-01

    A method for determining hydrocarbon conversion factors for a flowmeter. A mixture of air, O2 and C sub x H sub y is burned and the partial paressure of O2 in the resulting gas is forced to equal the partial pressure of O2 in air. The flowrate of O2 flowing into the mixture is measured by flowmeter and the flowrate of C sub x H sub y flowing into the mixture is measured by the flowmeter conversion factor is to be determined. These measured values are used to calculate the conversion factor.

  14. Development of an ionization-type gas density monitor

    NASA Astrophysics Data System (ADS)

    Saaski, E. W.

    1980-12-01

    A battery operated electronic gas density monitor was developed for SF6 service in gas insulated substation equipment that is based on principles similar to ionization type fire alarms. The monitor has a resolution of 0.1 psia at 68 F and exhibits a linearity of from + or - 0.15 to + or - 0.6 psia at 68 F over the pressure range 30 to 75 psia, depending on ion chamber characteristics and operating voltage. A prototype unit exhibited a deviation from ideality of about 0.01% per degree Fahrenheit over the temperature range -30 F to 105 F and was found insensitive to water vapor in SF6 at levels in excess of 1000 ppM.

  15. Proton cooling in ultracold low-density electron gas

    NASA Astrophysics Data System (ADS)

    Bobrov, A. A.; Bronin, S. Y.; Manykin, E. A.; Zelener, B. B.; Zelener, B. V.; Khikhlukha, D. R.

    2015-11-01

    A sole proton energy loss processes in an electron gas and the dependence of these processes on temperature and magnetic field are studied using molecular dynamics techniques in present work. It appears that for electron temperatures less than 100 K many body collisions affect the proton energy loss and these collisions must be taken into account. The influence of a strong magnetic field on the relaxation processes is also considered in this work. Calculations were performed for electron densities 10 cm-3, magnetic field 1-3 Tesla, electron temperatures 10-50 K, initial proton energies 100-10000 K.

  16. Momentum distribution function of the electron gas at metallic densities

    NASA Astrophysics Data System (ADS)

    Takada, Yasutami; Yasuhara, H.

    1991-10-01

    The momentum distribution function n(k) of the electron gas is calculated in the effective-potential-expansion method at metallic densities. The recently established self-consistency relation between n(k) and the correlation energy [Y. Takada and T. Kita, J. Phys. Soc. Jpn. 60, 25 (1991)] is employed to check the accuracy of our results. This check shows that the effective-potential-expansion method provides probably the exact and at least more accurate results of n(k) than all the other methods that have given n(k) thus far.

  17. Density of radiolytic gas bubbles in polymethyl methacrylate

    NASA Astrophysics Data System (ADS)

    Makkonen, T.; Tiainen, O. J. A.; Valkiainen, M.; Winberg, M.

    The density of the radiolytic gas bubbles in irradiated polymethyl methacrylate was measured during subsequent heat treatment as a function of radiation dose. The samples were irradiated in the core of the Triga Mark II reactor in Otaniemi. After the irradiation periods the samples were heat treated at 393 K. The number of the bubbles could be explained by a thermal activation model. The bubbles are born in material inhomogeneities and the threshold dose for the bubble initiation was about 25 Mrad for the heat treatment at 393 K under the atmospheric pressure.

  18. High density fuel qualification for a gas turbine engine

    SciTech Connect

    Macleod, J.D.; Orbanski, B.; Hastings, P.R. Standard Aero, Ltd., Winnipeg, DND, Ottawa, )

    1992-01-01

    A program for the evaluation of gas turbine engine performance, carried out in the Engine Laboratory of the National Research Council of Canada, is described. Problems under consideration include performance alteration between JP-4 fuel and a high energy density fuel, called strategic military fuel (SMF); performance deterioration during the accelerated endurance test; and emission analysis. The T56 fuel control system is found to be capable of operation on the higher energy density fuel with no detrimental effects regarding control of the engine's normal operating regime. The deterioration of the engine performance during 150-hour endurance tests on SMF was very high, which was caused by an increase in turbine nozzle effective flow area and turbine blade untwist. The most significant performance losses during the endurance tests were on corrected output power, fuel flow, specific fuel consumption and compressor and turbine presure ratio. 9 refs.

  19. Factors influencing the density of aerobic granular sludge.

    PubMed

    Winkler, M-K H; Kleerebezem, R; Strous, M; Chandran, K; van Loosdrecht, M C M

    2013-08-01

    In the present study, the factors influencing density of granular sludge particles were evaluated. Granules consist of microbes, precipitates and of extracellular polymeric substance. The volume fractions of the bacterial layers were experimentally estimated by fluorescent in situ hybridisation staining. The volume fraction occupied by precipitates was determined by computed tomography scanning. PHREEQC was used to estimate potential formation of precipitates to determine a density of the inorganic fraction. Densities of bacteria were investigated by Percoll density centrifugation. The volume fractions were then coupled with the corresponding densities and the total density of a granule was calculated. The sensitivity of the density of the entire granule on the corresponding settling velocity was evaluated by changing the volume fractions of precipitates or bacteria in a settling model. Results from granules originating from a Nereda reactor for simultaneous phosphate COD and nitrogen removal revealed that phosphate-accumulating organisms (PAOs) had a higher density than glycogen-accumulating organisms leading to significantly higher settling velocities for PAO-dominated granules explaining earlier observations of the segregation of the granular sludge bed inside reactors. The model showed that a small increase in the volume fraction of precipitates (1-5 %) strongly increased the granular density and thereby the settling velocity. For nitritation-anammox granular sludge, mainly granular diameter and not density differences are causing a segregation of the biomass in the bed. PMID:23064481

  20. Plasma ionization frequency, edge-to-axis density ratio, and density on axis of a cylindrical gas discharge

    SciTech Connect

    Palacio Mizrahi, J. H.

    2014-06-15

    A rigorous derivation of expressions, starting from the governing equations, for the ionization frequency, edge-to-axis ratio of plasma density, plasma density at the axis, and radially averaged plasma density in a cylindrical gas discharge has been obtained. The derived expressions are simple and involve the relevant parameters of the discharge: Cylinder radius, axial current, and neutral gas pressure. The found expressions account for ion inertia, ion temperature, and changes in plasma ion collisionality.

  1. Density measurement in air with a saturable absorbing seed gas

    NASA Technical Reports Server (NTRS)

    Baganoff, D.

    1981-01-01

    Resonantly enhanced scattering from the iodine molecule is studied experimentally for the purpose of developing a scheme for the measurement of density in a gas dynamic flow. A study of the spectrum of iodine, the collection of saturation data in iodine, and the development of a mathematical model for correlating saturation effects were pursued for a mixture of 0.3 torr iodine in nitrogen and for mixture pressures up to one atmosphere. For the desired pressure range, saturation effects in iodine were found to be too small to be useful in allowing density measurements to be made. The effects of quenching can be reduced by detuning the exciting laser wavelength from the absorption line center of the iodine line used (resonant Raman scattering). The signal was found to be nearly independent of pressure, for pressures up to one atmosphere, when the excitation beam was detuned 6 GHz from line center for an isolated line in iodine. The signal amplitude was found to be nearly equal to the amplitude for fluorescence at atmospheric pressure, which indicates a density measurement scheme is possible.

  2. Simulations of Electron Density Perturbations in a Gas Discharge

    NASA Astrophysics Data System (ADS)

    Caplinger, James; Sotnikov, Vladimir; Main, Daniel

    2015-11-01

    Beginning with the idealized case of the Pierce diode, a series of particle-in-cell (PIC) simulations are conducted in order to characterize density perturbations in a laboratory gas discharge. This work is conducted to support future experimental investigations into electromagnetic scattering off of electron density perturbations excited by plasma flows. As a first step, 2D PIC simulations were conducted for the Pierce diode case, which is a simple model that exploits instabilities of a monochromatic electron beam between two grounded electrodes. These results were compared to the standard analytical solution. Departing from this idealized case we will include in the simulations electron-neutral collisions, particle creation from ionization, as well as an electric field generated by biased electrodes. A parameter study of electric field strength and collision frequency will be performed for values approaching the Pierce diode as well as extending to cases of expected laboratory parameters. If we can extract physical density spectra from simulations with parameters approaching experimental values, it may be possible to analyze electromagnetic scattering characteristics.

  3. Density fluctuations of a hard-core Bose gas in a one-dimensional lattice near the Mott insulating phase

    SciTech Connect

    Ates, C.; Moseley, Ch.; Ziegler, K.

    2005-06-15

    The characteristic oscillations of the density-density correlation function and the resulting structure factor are studied for a hard-core Bose gas in a one-dimensional lattice. Their wavelength diverges as the system undergoes a continuous transition from an incommensurate to a Mott insulating phase. The transition is associated with a unit static structure factor and a vanishing sound velocity. The qualitative picture is unchanged when a weak confining potential is applied to the system.

  4. Discharge dynamics and plasma density recovery by on/off switches of additional gas

    NASA Astrophysics Data System (ADS)

    Lee, Hyo-Chang; Kwon, Deuk-Chul; Oh, SeungJu; Kang, Hyun-Ju; Kim, Yu-Sin; Chung, Chin-Wook

    2016-06-01

    Measurement of the plasma density is investigated to study plasma dynamics by adding reactive gas (O2) or rare gas (He) in Ar plasmas. When the O2 or He gas is added, plasma density is suddenly decreased, while the plasma density recovers slowly with gas off. It is found that the recovery time is strongly dependent on the gas flow rate, and it can be explained by effect of gas residence time. When the He gas is off in the Ar plasma, the plasma density is overshot compared to the case of the O2 gas pulsing due to enhanced ionizations by metastable atoms. Analysis and calculation for correlation between the plasma density dynamics and the gas pulsing are also presented in detail.

  5. Factors Associated with Mammographic Density in Postmenopausal Women

    PubMed Central

    Caglayan, Kasim; Alkis, Ismet; Arslan, Ergin; Okur, Aylin; Banli, Oktay; Engin-Ustün, Yaprak

    2015-01-01

    Objectives Breast density increases the risk of breast cancer, but also in the interpretation of mammography is also important. This study examine the risk factors affecting breast density in postmenopausal women. Methods Between January 2013 and January 2014, 215 patients admitted to The Clinics of Gynecology and Obstetrics with complaints of menopause were taken. According to the results of mammography, Group I (non-dense, n = 175) and Group II (dense, n = 40) were created. The informations of the caseswere analyzed retrospectively. Results In Group I, body mass index (BMI), number of pregnancies, parity were significantly higher than group II (P < 0.05). In group II, the withdrawal period of menstruation and progesterone levels were significantly higher (P < 0.05). In logistic regression analysis, BMI for dense breasts and number of pregnancies were found to be an independent risk factor (P < 0.05). Conclusion Increased BMI, pregnancy and parity, result of reduction in density , but longer duration of menopause and increased progesterone cause an increase in density. BMI and the number of pregnancy was found to be independent risk factors for reducing breast density. PMID:26357645

  6. Pion transverse charge density from timelike form factor data

    SciTech Connect

    Gerald Miller, Mark Strikman, Christian Weiss

    2011-01-01

    The transverse charge density in the pion can be represented as a dispersion integral of the imaginary part of the pion form factor in the timelike region. This formulation incorporates information from e+e- annihilation experiments and allows one to reconstruct the transverse density much more accurately than from the spacelike pion form factor data alone. We calculate the transverse density using an empirical parametrization of the timelike pion form factor and estimate that it is determined to an accuracy of ~10% at a distance b ~ 0.1 fm, and significantly better at larger distances. The density is found to be close to that obtained from a zero-width rho meson pole over a wide range and shows a pronounced rise at small distances. The resulting two-dimensional image of the fast-moving pion can be interpreted in terms of its partonic structure in QCD. We argue that the singular behavior of the charge density at the center requires a substantial presence of pointlike configurations in the pion's partonic wave function, which can be probed in other high-momentum transfer processes.

  7. Acoustic device and method for measuring gas densities

    NASA Technical Reports Server (NTRS)

    Shakkottai, Parthasarathy (Inventor); Kwack, Eug Y. (Inventor); Back, Lloyd (Inventor)

    1992-01-01

    Density measurements can be made in a gas contained in a flow through enclosure by measuring the sound pressure level at a receiver or microphone located near a dipole sound source which is driven at constant velocity amplitude at low frequencies. Analytical results, which are provided in terms of geometrical parameters, wave numbers, and sound source type for systems of this invention, agree well with published data. The relatively simple designs feature a transmitter transducer at the closed end of a small tube and a receiver transducer on the circumference of the small tube located a small distance away from the transmitter. The transmitter should be a dipole operated at low frequency with the kL value preferable less that about 0.3.

  8. Does nitrogen gas bubbled through a low density polymer gel dosimeter solution affect the polymerization process?

    PubMed Central

    Shahbazi-Gahrouei, Daryoush; Gholami, Mehrdad; Pourfallah, Tayyeb Allahverdi; Keshtkar, Mohammad

    2015-01-01

    Background: On account of the lower electron density in the lung tissue, the dose distribution in the lung cannot be verified with the existing polymer gel dosimeters. Thus, the aims of this study are to make a low density polymer gel dosimeter and investigate the effect of nitrogen gas bubbles on the R2 responses and its homogeneity. Materials and Methods: Two different types of low density polymer gel dosimeters were prepared according to a composition proposed by De Deene, with some modifications. In the first type, no nitrogen gas was perfused through the gel solution and water. In the second type, to expel the dissolved oxygen, nitrogen gas was perfused through the water and gel solution. The post-irradiation times in the gels were 24 and 5 hours, respectively, with and without perfusion of nitrogen gas through the water and gel solution. Results: In the first type of gel, there was a linear correlation between the doses and R2 responses from 0 to 12 Gy. The fabricated gel had a higher dynamic range than the other low density polymer gel dosimeter; but its background R2 response was higher. In the second type, no difference in R2 response was seen in the dose ranges from 0 to 18 Gy. Both gels had a mass density between 0.35 and 0.45 g.cm-3 and CT values of about -650 to -750 Hounsfield units. Conclusion: It appeared that reactions between gelatin-free radicals and monomers, due to an increase in the gel temperature during rotation in the household mixer, led to a higher R2-background response. In the second type of gel, it seemed that the collapse of the nitrogen bubbles was the main factor that affected the R2-responses. PMID:26015914

  9. Reproductive factors related to childbearing and mammographic breast density.

    PubMed

    Yaghjyan, Lusine; Colditz, Graham A; Rosner, Bernard; Bertrand, Kimberly A; Tamimi, Rulla M

    2016-07-01

    We investigated the associations of reproductive factors related to childbearing with percent breast density, absolute dense and nondense areas, by menopausal status. This study included 4110 cancer-free women within the Nurses' Health Study and Nurses' Health Study II cohorts. Percent breast density, absolute dense and nondense areas were measured from digitized mammography film images with computerized techniques. All density measures were square root-transformed in all the analyses to improve normality. The data on reproductive variables and other breast cancer risk factors were obtained from biennial questionnaires, at the time of the mammogram date. As compared to nulliparous women, parous postmenopausal women had lower percent density (β = -0.60, 95 % CI -0.84; -0.37), smaller absolute dense area (β = -0.66, 95 % CI -1.03; -0.29), and greater nondense area (β = 0.72, 95 % CI 0.27; 1.16). Among parous women, number of children was inversely associated with percent density in pre- (β per one child = -0.12, 95 % CI -0.20; -0.05) and postmenopausal women (β per one child = -0.07, 95 % CI -0.12; -0.02). The positive associations of breastfeeding with absolute dense and nondense areas were limited to premenopausal women, while the positive association of the age at first child's birth with percent density and the inverse association with nondense area were limited to postmenopausal women. Women with greater number of children and younger age at first child's birth have more favorable breast density patterns that could explain subsequent breast cancer risk reduction. PMID:27351801

  10. Implementing an Inexpensive and Accurate Introductory Gas Density Activity with High School Students

    ERIC Educational Resources Information Center

    Cunningham, W. Patrick; Joseph, Christopher; Morey, Samantha; Santos Romo, Ana; Shope, Cullen; Strang, Jonathan; Yang, Kevin

    2015-01-01

    A simplified activity examined gas density while employing cost-efficient syringes in place of traditional glass bulbs. The exercise measured the density of methane, with very good accuracy and precision, in both first-year high school and AP chemistry settings. The participating students were tasked with finding the density of a gas. The…

  11. Molecular Gas in Starburts ARP 220 & NGC 6240: Understanding Mergers using High Density Gas Tracers

    NASA Astrophysics Data System (ADS)

    Manohar, Swarnima; Scoville, Nicholas; Sheth, Kartik

    2015-01-01

    NGC 6240 and Arp 220 can be considered the founding members of a very active class of objects called Ultraluminous Infrared Galaxies or ULIRGs. They are in different stages of mergers and hence are excellent case studies to enhance our knowledge about the merging process. We have imaged the dense star-forming regions of these galaxies at sub-arcsec resolution with ALMA and CARMA. Multi-band imaging allows multilevel excitation analysis of HCN, HCO+ and CS transitions which will constrain the properties of the gas as a function of position and velocity (across line profiles). We are doing an extensive multilevel excitation analysis of the merger as a function of radius which enables in depth understanding of the gas dynamics and gas properties such as temperature and density. This in turn probes the homogeneity of the gas in the merging system and hence the regions that facilitate high star formation rates. This tandem use of CARMA with ALMA to map these systems at different merger stages will assemble a more integrated picture of the merger process. We are probing the distribution and dynamics of star forming gas and star formation activity in the dense disk structures to enable new theoretical understanding of the physics, dynamics, star formation activity and associated feedback in the most active and rapidly evolving galactic nuclei. Here we present our observations of Arp 220 and NGC 6240 from ALMA and CARMA.

  12. Molecular Gas in Local Mergers: Understanding Mergers using High Density Gas Tracers

    NASA Astrophysics Data System (ADS)

    Manohar, Swarnima; Scoville, N.; Sheth, K.

    2013-01-01

    NGC 6240 and Arp 220 can be considered the founding members of a very active class of objects called Ultraluminous Infrared Galaxies or ULIRGs. They are in different stages of mergers and hence are excellent case studies to enhance our knowledge about the merging process. We have imaged the dense star-forming regions of these galaxies at sub-arcsec resolution with ALMA and CARMA. Multi-band imaging will allow multilevel excitation analysis of HCN, HCO+ and CS transitions which will be used to constrain the properties of the gas as a function of position and velocity (across line profiles). We aim to do an extensive multilevel excitation analysis of the merger as a function of radius which will enable in depth understanding of the gas dynamics and gas properties such as temperature and density. This will in turn probe the homogeneity of the gas in the merging system and hence the regions that facilitate high star formation rates. This tandem use of CARMA with ALMA to map these systems at different merger stages will help assemble a more integrated picture of the merger process. We will probe the distribution and dynamics of star forming gas and star formation activity in the dense disk structures to enable new theoretical understanding of the physics, dynamics, star formation activity and associated feedback in the most active and rapidly evolving galactic nuclei. Here we present preliminary observations of Arp 220 and NGC 6240 from ALMA and CARMA.

  13. Molecular Gas in Starburts: Understanding Mergers using High Density Gas Tracers

    NASA Astrophysics Data System (ADS)

    Manohar, Swarnima; Scoville, N.; Walter, F.; Sheth, K.

    2014-01-01

    NGC 6240 and Arp 220 can be considered the founding members of a very active class of objects called Ultraluminous Infrared Galaxies or ULIRGs. They are in different stages of mergers and hence are excellent case studies to enhance our knowledge about the merging process. We have imaged the dense star-forming regions of these galaxies at sub-arcsec resolution with ALMA and CARMA. Multi-band imaging allows multilevel excitation analysis of HCN, HCO+ and CS transitions which will constrain the properties of the gas as a function of position and velocity (across line profiles). We are doing an extensive multilevel excitation analysis of the merger as a function of radius which enables in depth understanding of the gas dynamics and gas properties such as temperature and density. This in turn probes the homogeneity of the gas in the merging system and hence the regions that facilitate high star formation rates. This tandem use of CARMA with ALMA to map these systems at different merger stages will assemble a more integrated picture of the merger process. We are probing the distribution and dynamics of star forming gas and star formation activity in the dense disk structures to enable new theoretical understanding of the physics, dynamics, star formation activity and associated feedback in the most active and rapidly evolving galactic nuclei. Here we present preliminary observations of Arp 220 and NGC 6240 from ALMA and CARMA.

  14. Density probability distribution functions of diffuse gas in the Milky Way

    NASA Astrophysics Data System (ADS)

    Berkhuijsen, E. M.; Fletcher, A.

    2008-10-01

    In a search for the signature of turbulence in the diffuse interstellar medium (ISM) in gas density distributions, we determined the probability distribution functions (PDFs) of the average volume densities of the diffuse gas. The densities were derived from dispersion measures and HI column densities towards pulsars and stars at known distances. The PDFs of the average densities of the diffuse ionized gas (DIG) and the diffuse atomic gas are close to lognormal, especially when lines of sight at |b| < 5° and |b| >= 5° are considered separately. The PDF of at high |b| is twice as wide as that at low |b|. The width of the PDF of the DIG is about 30 per cent smaller than that of the warm HI at the same latitudes. The results reported here provide strong support for the existence of a lognormal density PDF in the diffuse ISM, consistent with a turbulent origin of density structure in the diffuse gas.

  15. Stealing the Gas: Giant Impacts and the Large Diversity in Exoplanet Densities

    NASA Astrophysics Data System (ADS)

    Inamdar, Niraj K.; Schlichting, Hilke E.

    2016-02-01

    Although current sensitivity limits are such that true solar system analogs remain challenging to detect, numerous planetary systems have been discovered that are very different from our own solar system. The majority of systems harbor a new class of planets, bodies that are typically several times more massive than the Earth but orbit their host stars well inside the orbit of Mercury. These planets frequently show evidence for large hydrogen and helium envelopes containing several percent of the planet’s mass and display a large diversity in mean densities. Here we show that this wide range can be achieved by one or two late giant impacts, which are frequently needed to achieve long-term orbital stability in multiple planet systems once the gas disk has disappeared. We demonstrate using hydrodynamical simulations that a single collision between similarly sized exoplanets can easily reduce the envelope-to-core-mass ratio by a factor of two and show that this leads to a corresponding increase in the observed mean density by factors of two to three. In addition, we investigate how envelope mass loss depends on envelope mass, planet radius, semimajor axis, and the mass distribution inside the envelope. We propose that a small number of giant impacts may be responsible for the large observed spread in mean densities, especially for multiple-planet systems that contain planets with very different densities and have not been significantly sculpted by photoevaporation.

  16. Star Formation as a Function of Neutral Hydrogen Gas Density in Local Group Galaxies

    NASA Astrophysics Data System (ADS)

    Carlson, Erika K.; Madore, Barry F.; Freedman, Wendy L.

    2016-06-01

    We present a study of the efficiency and timescales of star formation as a function of local neutral hydrogen gas density in four Local Group galaxies: M33, NGC 6822, the LMC, and the SMC. In this work, we conceptualize the process of star formation as a cycle of two major phases – (1) a gas dynamics phase in which neutral hydrogen gas coalesces into clouds, and (2) a stellar phase in which stars have formed and interrupt further gas coalescence during their active lifetimes. By examining the spatial distribution and number densities of stars on maps of neutral hydrogen, we estimate the timescale of the gas coalescence phase relative to the timescale of the stellar phase and infer an efficiency of star formation as a function of neutral hydrogen gas density. From these timescales and efficiencies, we will calculate star formation rates as a function of neutral hydrogen gas density in these galaxies.

  17. Linear Stability Analysis of Gravitational Effects on a Low-Density Gas Jet Injected into a High-Density Medium

    NASA Technical Reports Server (NTRS)

    Lawson, Anthony L.; Parthasarathy, Ramkumar N.

    2005-01-01

    The objective of this study was to determine the effects of buoyancy on the absolute instability of low-density gas jets injected into high-density gas mediums. Most of the existing analyses of low-density gas jets injected into a high-density ambient have been carried out neglecting effects of gravity. In order to investigate the influence of gravity on the near-injector development of the flow, a spatio-temporal stability analysis of a low-density round jet injected into a high-density ambient gas was performed. The flow was assumed to be isothermal and locally parallel; viscous and diffusive effects were ignored. The variables were represented as the sum of the mean value and a normal-mode small disturbance. An ordinary differential equation governing the amplitude of the pressure disturbance was derived. The velocity and density profiles in the shear layer, and the Froude number (signifying the effects of gravity) were the three important parameters in this equation. Together with the boundary conditions, an eigenvalue problem was formulated. Assuming that the velocity and density profiles in the shear layer to be represented by hyperbolic tangent functions, the eigenvalue problem was solved for various values of Froude number. The Briggs-Bers criterion was combined with the spatio-temporal stability analysis to determine the nature of the absolute instability of the jet whether absolutely or convectively unstable. The roles of the density ratio, Froude number, Schmidt number, and the lateral shift between the density and velocity profiles on the absolute instability of the jet were determined. Comparisons of the results with previous experimental studies show good agreement when the effects of these variables are combined together. Thus, the combination of these variables determines how absolutely unstable the jet will be.

  18. Effects of Mean Flow Profiles on Instability of a Low-Density Gas Jet Injected into a High-Density Gas

    NASA Technical Reports Server (NTRS)

    Vedantam, Nanda Kishore

    2003-01-01

    The objective of this study was to investigate the effects of the mean flow profiles on the instability characteristics in the near-injector region of low-density gas jets injected into high-density ambient gas mediums. To achieve this, a linear temporal stability analysis and a spatio-temporal stability analysis of a low-density round gas jet injected vertically upwards into a high-density ambient gas were performed by assuming three different sets of mean velocity and density profiles. The flow was assumed to be isothermal and locally parallel. Viscous and diffusive effects were ignored. The mean flow parameters were represented as the sum of the mean value and a small normal-mode fluctuation. A second order differential equation governing the pressure disturbance amplitude was derived from the basic conservation equations. The first set of mean velocity and density profiles assumed were those used by Monkewitz and Sohn for investigating absolute instability in hot jets. The second set of velocity and density profiles assumed for this study were the ones used by Lawson. And the third set of mean profiles included a parabolic velocity profile and a hyperbolic tangent density profile. The effects of the inhomogeneous shear layer and the Froude number (signifying the effects of gravity) on the temporal and spatio-temporal results for each set of mean profiles were delineated. Additional information is included in the original extended abstract.

  19. 40 CFR Table Mm-1 to Subpart Mm of... - Default Factors for Petroleum Products and Natural Gas Liquids 1 2

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... and Natural Gas Liquids 1 2 MM Table MM-1 to Subpart MM of Part 98 Protection of Environment... Factors for Petroleum Products and Natural Gas Liquids 1 2 Products Column A: density(metric tons/bbl... Natural Gas Liquids Aviation Gasoline 0.1120 85.00 0.3490 Special Naphthas 0.1222 84.76 0.3798...

  20. 40 CFR Table Mm-1 to Subpart Mm of... - Default Factors for Petroleum Products and Natural Gas Liquids 1 2

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... and Natural Gas Liquids 1 2 MM Table MM-1 to Subpart MM of Part 98 Protection of Environment... Factors for Petroleum Products and Natural Gas Liquids 1 2 Products Column A: density(metric tons/bbl... Natural Gas Liquids Aviation Gasoline 0.1120 85.00 0.3490 Special Naphthas 0.1222 84.76 0.3798...

  1. 40 CFR Table Mm-1 to Subpart Mm of... - Default Factors for Petroleum Products and Natural Gas Liquids 1 2

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... and Natural Gas Liquids 1 2 MM Table MM-1 to Subpart MM of Part 98 Protection of Environment... Factors for Petroleum Products and Natural Gas Liquids 1 2 Products Column A: density(metric tons/bbl... Natural Gas Liquids Aviation Gasoline 0.1120 85.00 0.3490 Special Naphthas 0.1222 84.76 0.3798...

  2. 40 CFR Table Mm-1 to Subpart Mm of... - Default Factors for Petroleum Products and Natural Gas Liquids 1 2

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... and Natural Gas Liquids 1 2 MM Table MM-1 to Subpart MM of Part 98 Protection of Environment... Factors for Petroleum Products and Natural Gas Liquids 1 2 Products Column A: density(metric tons/bbl... Natural Gas Liquids Aviation Gasoline 0.1120 85.00 0.3490 Special Naphthas 0.1222 84.76 0.3798...

  3. Electromagnetic form factors and charge densities from hadrons to nuclei

    SciTech Connect

    Miller, Gerald A.

    2009-10-15

    A simple exact covariant model in which a scalar particle {psi} is modeled as a bound state of two different particles is used to elucidate relativistic aspects of electromagnetic form factors F(Q{sup 2}). The model form factor is computed using an exact covariant calculation of the lowest order triangle diagram. The light-front technique of integrating over the minus component of the virtual momentum gives the same result and is the same as the one obtained originally by Gunion et al. [Phys. Rev. D 8, 287 (1973)] by using time-ordered perturbation theory in the infinite-momentum frame. The meaning of the transverse density {rho}(b) is explained by providing a general derivation, using three spatial coordinates, of its relationship with the form factor. This allows us to identify a mean-square transverse size ={integral}d{sup 2}b b{sup 2}{rho}(b)=-4(dF/dQ{sup 2})(Q{sup 2}=0). The quantity is a true measure of hadronic size because of its direct relationship with the transverse density. We show that the rest-frame charge distribution is generally not observable by studying the explicit failure to uphold current conservation. Neutral systems of two charged constituents are shown to obey the conventional lore that the heavier one is generally closer to the transverse origin than the lighter one. It is argued that the negative central charge density of the neutron arises, in pion-cloud models, from pions of high longitudinal momentum that reside at the center. The nonrelativistic limit is defined precisely, and the ratio of the binding energy B to the mass M of the lightest constituent is shown to govern the influence of relativistic effects. It is shown that the exact relativistic formula for F(Q{sup 2}) is the same as the familiar one of the three-dimensional Fourier transform of a square of a wave function for very small values of B/M, but this only occurs for values of B/M less than about 0.001. For masses that mimic the quark-diquark model of

  4. Real-time gas density measurement using a ring cavity terahertz parametric oscillator

    NASA Astrophysics Data System (ADS)

    Ohno, S.; Guo, R.; Minamide, H.; Ito, H.

    2007-05-01

    We carried out real-time measurement of gas density using monochromatic terahertz waves. The THz-wave absorbance is useful to measure the density of a gas having a characteristic spectrum in the THz region. We used the ring cavity THz-wave parametric oscillator (ring-TPO) as a monochromatic tunable THz-wave source. One can change the oscillation frequency of ring-TPO with a rotating galvano mirror forming the ring cavity. The frequency can be changed by synchronization with a repeating pump-pulse of 500 Hz. We demonstrated real-time measurement of the gas density in R-22, which had some spectral structure in THz frequency region. The gas density in the sample cell was changed by controlling the pressure to lower than 1 atm. When the gas density in the cell was the most tenuous, the maximum sensitivity was about 5%, which was limited by the fluctuation of THz-wave intensity.

  5. Relation between plasma plume density and gas flow velocity in atmospheric pressure plasma

    SciTech Connect

    Yambe, Kiyoyuki; Taka, Shogo; Ogura, Kazuo

    2014-04-15

    We have studied atmospheric pressure plasma generated using a quartz tube, helium gas, and copper foil electrode by applying RF high voltage. The atmospheric pressure plasma in the form of a bullet is released as a plume into the atmosphere. To study the properties of the plasma plume, the plasma plume current is estimated from the difference in currents on the circuit, and the drift velocity is measured using a photodetector. The relation of the plasma plume density n{sub plu}, which is estimated from the current and the drift velocity, and the gas flow velocity v{sub gas} is examined. It is found that the dependence of the density on the gas flow velocity has relations of n{sub plu} ∝ log(v{sub gas}). However, the plasma plume density in the laminar flow is higher than that in the turbulent flow. Consequently, in the laminar flow, the density increases with increasing the gas flow velocity.

  6. Phase-field simulations of gas density within bubbles under irradiation

    SciTech Connect

    Paul C. Millett; Anter El-Azab; Michael Tonks

    2011-05-01

    Phase-field simulations are used to study the evolution of gas density within irradiation-induced bubbles. In our simulations, the dpa rate, gas production rate, and defect diffusivities are systematically varied to understand their effect on bubble nucleation rates, bubble densities, and the distribution of gas concentration within bubbles and in the solid regions. We find that gas densities within bubbles fluctuate drastically in the early nucleation stages, when growth rates are highest, but converge to steady-state values during the later coarsening stages. The steady-state gas densities within bubbles correspond with the ratio of total accumulated vacancy content divided by the total accumulated gas content, in agreement with a thermodynamic analysis concerning free-energy minimization.

  7. Factors associated with bone mineral density in healthy African women

    PubMed Central

    Kelly, Cliff; Gati, Brenda; Greenspan, Susan; Dai, James Y.; Bragg, Vivian; Livant, Edward; Piper, Jeanna M.; Nakabiito, Clemensia; Magure, Tsitsi; Marrazzo, Jeanne M.; Chirenje, Z. Mike; Riddler, Sharon A.

    2015-01-01

    Summary There is a paucity of normative bone mineral density (BMD) data in healthy African women. Baseline total hip and lumbar spine BMD was measured in premenopausal women. BMD distribution was comparable to that of a reference population and was impacted by several factors including contraception and duration of lactation. Introduction Normative data on bone mineral density (BMD) and the cumulative impact of lactation, contraceptive use, and other factors on BMD in healthy African women have not been well studied. Objectives The objective of this study was to determine the factors associated with BMD in healthy premenopausal women in Uganda and Zimbabwe. Methods Baseline total hip (TH) and lumbar spine (LS) BMD was measured by dual x-ray absorptiometry in 518 healthy, premenopausal black women enrolling in VOICE, an HIV-1 chemoprevention trial, at sites in Uganda and Zimbabwe. Contraceptive and lactation histories, physical activity assessment, calcium intake, and serum vitamin D levels were assessed. Independent factors associated with BMD were identified using an analysis of covariance model. Results The study enrolled 331 women from Zimbabwe and 187 women from Uganda. Median age was 29 years (IQR 25, 32) and median body mass index (BMI) was 24.8 kg/m2 (IQR 22.2, 28.6). In univariate analyses, lower TH BMD values were associated with residence in Uganda (p<0.001), lower BMI (p<0.001), and any use of and duration of depot-medroxyprogresterone acetate. Use of oral contraceptives, progestin-only implants, and higher physical activity levels were protective against reduced BMD. Similarly, lower LS BMD values were associated with these same factors but also higher parity and history of breastfeeding. In a multivariable analysis, lower TH and LS BMD values were associated with enrollment in Uganda, lower BMI, and lower physical activity level; contraceptive use was associated with lower spine BMD, and breastfeeding contributed to lower total hip BMD. Conclusions

  8. Factors Affecting Bone Mineral Density in Adults with Cerebral Palsy

    PubMed Central

    Yoon, Young Kwon; Kim, Ae Ryoung; Kim, On Yoo; Lee, Kilchan; Suh, Young Joo

    2012-01-01

    Objective To clarify factors affecting bone mineral density (BMD) in adults with cerebral palsy (CP). Method Thirty-five patients with CP participated in this study. Demographic data including gender, age, body mass index (BMI), subtype according to neuromotor type and topographical distribution, ambulatory function, and functional independence measure (FIM) were investigated. The BMD of the lumbar spine and femur were measured using Dual-energy X-ray absorptiometry, and the factors affecting BMD were analyzed. Results The BMD had no significant association with factors such as gender, age, and subtype in adults with CP. However, BMI was significantly correlated with the BMD of lumbar spine and femur (p<0.05). The FIM score was also positively correlated with the BMD of femur (p<0.05). Moreover, CP patients with higher ambulatory function had significantly higher BMD of femur (p<0.05). Conclusion These findings suggest that BMI and functional levels such as FIM and ambulatory function can affect BMD in adults with CP. The results might be used as basic data, suggesting the importance of treatment including weight bearing exercise and gait training in adults with CP. PMID:23342308

  9. Modeling of neutral gas dynamics in high-density plasmas

    NASA Astrophysics Data System (ADS)

    Canupp, Patrick Wellington

    This thesis describes a physical model of chemically reactive neutral gas flow and discusses numerical solutions of this model for the flow in an inductively coupled plasma etch reactor. To obtain these solutions, this research develops an efficient, implicit numerical method. As a result of the enhanced numerical stability of the scheme, large time steps advance the solution from initial conditions to a final steady state in fewer iterations and with less computational expense than simpler explicit methods. This method would incorporate suitably as a module in currently existing large scale plasma simulation tools. In order to demonstrate the accuracy of the numerical technique, this thesis presents results from two simulations of flows that possess theoretical solutions. The first case is the inviscid flow of a gas through a converging nozzle. A comparison of the numerical solution to isentropic flow theory shows that the numerical technique capably captures the essential flow features of this environment. The second case is the Couette flow of a gas between two parallel plates. The simulation results compare well with the exact solution for this flow. After establishing the accuracy of the numerical technique, this thesis discusses results for the flow of chemically reactive gases in a chlorine plasma etch reactor. This research examines the influence of the plasma on the neutral gas and the dynamics exhibited by the neutral gas in the reactor. This research finds that the neutral gas temperature strongly depends on the rate at which inelastic, electron-impact dissociation reactions occur and on atomic chlorine wall recombination rates. Additionally, the neutral gas Aow in the reactor includes a significant mass flux of etch product from the wafer surface. Resolution of these effects is useful for neutral gas simulation. Finally, this thesis demonstrates that continuum fluid models provide reasonable accuracy for these low pressure reactor flows due to the fact

  10. Gas pycnometry for density determination of plutonium parts

    SciTech Connect

    Collins, S.; Randolph, H.W.

    1997-08-19

    The traditional method for plutonium density determination is by measuring the weight loss of the component when it is immersed in a liquid of known density, Archimedes` Principle. The most commonly used heavy liquids that are compatible for plutonium measurement are freon and monobromobenzene, but these pose serious environmental and health hazards. The contaminated liquid is also a radiological waste concern with difficult disposition. A gaseous medium would eliminate these environmental and health concerns. A collaborative research effort between the Savannah River Technology Center and Los Alamos National Laboratory was undertaken to determine the feasibility of a gaseous density measurement process for plutonium hemishells.

  11. Biofuels and the Greenhouse Gas Factor

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Biofuels have been scrutinized for their potential to be used as a fuel substitute to offset a portion of the greenhouse gas (GHG) emissions produced by fossil fuel combustion. But quantifying that offset is complex. Bioenergy crops offset their greenhouse-gas contributions in three key ways: by rem...

  12. Neutron radiography of a static density gradient of 3He gas at cryogenic temperatures

    NASA Astrophysics Data System (ADS)

    Wichmann, G.; Antognini, A.; Eggenberger, A.; Kirch, K.; Piegsa, F. M.; Soler, U.; Stahn, J.; Taqqu, D.

    2016-04-01

    We demonstrate a stationary helium gas density gradient which is needed for a proposed novel low-energy μ+ beam line. In a closed system with constant pressure the corresponding density gradient is only a function of the temperature. In a neutron radiography experiment two gas cells with different geometries were filled with 3He gas at constant pressures of about 10 mbar. Temperatures in the range from 6 K to 40 K were applied and density distributions with a maximum to minimum density ratio of larger than 3 were realized. The distribution was investigated employing the strongly neutron absorbing isotope 3He. A simple one-dimensional approach derived from Fourier's law describes the obtained gas density with a deviation < 2 %.

  13. Density measurement in air with saturable absorbing seed gas

    NASA Technical Reports Server (NTRS)

    Baganoff, D.

    1982-01-01

    Approaches which have the potential to make density measurements in a compressible flow, where one or more laser beams are used as probes, were investigated. Saturation in sulfur hexafluoride iodine and a crossed beam technique where one beam acts as a saturating beam and the other is at low intensity and acts as a probe beam are considered. It is shown that a balance between an increase in fluorescence intensity with increasing pressure from line broadening and the normal decrease in intensity with increasing pressure from quenching can be used to develop a linear relation between fluorescence intensity and number density and lead to a new density measurement scheme. The method is used to obtain a density image of the cross section of an iodine seeded underexpanded supersonic jet of nitrogen, by illuminating the cross section by a sheet of laser light.

  14. Estimation of current density distribution of PAFC by analysis of cell exhaust gas

    SciTech Connect

    Kato, S.; Seya, A.; Asano, A.

    1996-12-31

    To estimate distributions of Current densities, voltages, gas concentrations, etc., in phosphoric acid fuel cell (PAFC) stacks, is very important for getting fuel cells with higher quality. In this work, we leave developed a numerical simulation tool to map out the distribution in a PAFC stack. And especially to Study Current density distribution in the reaction area of the cell, we analyzed gas composition in several positions inside a gas outlet manifold of the PAFC stack. Comparing these measured data with calculated data, the current density distribution in a cell plane calculated by the simulation, was certified.

  15. A CENSUS OF THE HIGH-DENSITY MOLECULAR GAS IN M82

    SciTech Connect

    Naylor, B. J.; Bradford, C. M.; Bock, J. J.; Nguyen, H. T.; Zmuidzinas, J.; Aguirre, J. E.; Earle, L.; Glenn, J.; Kamenetzky, J.; Maloney, P. R.; Inami, H.; Matsuhara, H.

    2010-10-10

    We present a three-pointing study of the molecular gas in the starburst nucleus of M82 based on 190-307 GHz spectra obtained with Z-Spec at the Caltech Submillimeter Observatory. We present intensity measurements, detections, and upper limits, for 20 transitions, including several new detections of CS, HNC, C{sub 2}H, H{sub 2}CO, and CH{sub 3}CCH lines. We combine our measurements with previously published measurements at other frequencies for HCN, HNC, CS, C{sup 34}S, and HCO{sup +} in a multi-species likelihood analysis constraining gas mass, density and temperature, and the species' relative abundances. We find some (1.7-2.7) x 10{sup 8} M{sub sun} of gas with n{sub H{sub 2}} between (1-6) x 10{sup 4} cm{sup -3} and T > 50 K. While the mass and temperature are comparable to values inferred from mid-J CO transitions, the thermal pressure is a factor of 10-20 greater. The molecular interstellar medium is largely fragmented and is subject to ultraviolet irradiation from the star clusters. It is also likely subject to cosmic rays and mechanical energy input from the supernovae, and is warmer on average than the molecular gas in the massive star formation (SF) regions in the Milky Way. The typical conditions in the dense gas in M82's central kiloparsec appear unfavorable for further SF; if any appreciable stellar populations are currently forming, they are likely biased against low-mass stars, producing a top-heavy initial mass function.

  16. Electron temperature and density measurement of tungsten inert gas arcs with Ar-He shielding gas mixture

    NASA Astrophysics Data System (ADS)

    Kühn-Kauffeldt, M.; Marques, J.-L.; Forster, G.; Schein, J.

    2013-10-01

    The diagnostics of atmospheric welding plasma is a well-established technology. In most cases the measurements are limited to processes using pure shielding gas. However in many applications shielding gas is a mixture of various components including metal vapor in gas metal arc welding (GMAW). Shielding gas mixtures are intentionally used for tungsten inert gas (TIG) welding in order to improve the welding performance. For example adding Helium to Argon shielding gas allows the weld geometry and porosity to be influenced. Yet thermal plasmas produced with gas mixtures or metal vapor still require further experimental investigation. In this work coherent Thomson scattering is used to measure electron temperature and density in these plasmas, since this technique allows independent measurements of electron and ion temperature. Here thermal plasmas generated by a TIG process with 50% Argon and 50% Helium shielding gas mixture have been investigated. Electron temperature and density measured by coherent Thomson scattering have been compared to the results of spectroscopic measurements of the plasma density using Stark broadening of the 696.5 nm Argon spectral line. Further investigations of MIG processes using Thomson scattering technique are planned.

  17. Metal Oxide Gas Sensors: Sensitivity and Influencing Factors

    PubMed Central

    Wang, Chengxiang; Yin, Longwei; Zhang, Luyuan; Xiang, Dong; Gao, Rui

    2010-01-01

    Conductometric semiconducting metal oxide gas sensors have been widely used and investigated in the detection of gases. Investigations have indicated that the gas sensing process is strongly related to surface reactions, so one of the important parameters of gas sensors, the sensitivity of the metal oxide based materials, will change with the factors influencing the surface reactions, such as chemical components, surface-modification and microstructures of sensing layers, temperature and humidity. In this brief review, attention will be focused on changes of sensitivity of conductometric semiconducting metal oxide gas sensors due to the five factors mentioned above. PMID:22294916

  18. Dust and Gas in the Disk of HL Tauri: Surface Density, Dust Settling, and Dust-to-gas Ratio

    NASA Astrophysics Data System (ADS)

    Pinte, C.; Dent, W. R. F.; Ménard, F.; Hales, A.; Hill, T.; Cortes, P.; de Gregorio-Monsalvo, I.

    2016-01-01

    The recent ALMA observations of the disk surrounding HL Tau reveal a very complex dust spatial distribution. We present a radiative transfer model accounting for the observed gaps and bright rings as well as radial changes of the emissivity index. We find that the dust density is depleted by at least a factor of 10 in the main gaps compared to the surrounding rings. Ring masses range from 10-100 M⊕ in dust, and we find that each of the deepest gaps is consistent with the removal of up to 40 M⊕ of dust. If this material has accumulated into rocky bodies, these would be close to the point of runaway gas accretion. Our model indicates that the outermost ring is depleted in millimeter grains compared to the central rings. This suggests faster grain growth in the central regions and/or radial migration of the larger grains. The morphology of the gaps observed by ALMA—well separated and showing a high degree of contrast with the bright rings over all azimuths—indicates that the millimeter dust disk is geometrically thin (scale height ≈1 AU at 100 AU) and that a large amount of settling of large grains has already occurred. Assuming a standard dust settling model, we find that the observations are consistent with a turbulent viscosity coefficient of a few 10-4. We estimate the gas/dust ratio in this thin layer to be of the order of 5 if the initial ratio is 100. The HCO+ and CO emission is consistent with gas in Keplerian motion around a 1.7 M⊙ star at radii from ≤10-120 AU.

  19. Comet Halley neutral gas density profile along the Vega 1 trajectory measured by NGE. [Neutral Gas Experiment (NGE)

    NASA Technical Reports Server (NTRS)

    Curtis, C. C.; Fan, C. Y.; Hsieh, K. C.; Hunten, D. M.; Ip, WING-H.; Keppler, E.; Richter, A. K.; Umlauft, G.; Afonin, V. V.; Dyachkov, A. V.

    1986-01-01

    Data from the Vega 1 permitted the determination of the total neutral gas density profile along the spacecraft trajectory. Discounting small fluctuations, the field ionization source instrument measured a density profile which varied approximately as the inverse radial distance squared. Data from the electron impact ionization instrument yielded a series of calibration points; e.g., the neutral density at 100,000 km is 10,000/cc. The combined data provide a calibrated total density profile, and imply a neutral production rate of 10 to the 30th power molecules/sec.

  20. Production of centimeter-scale, high-density plasmas with a linear gas jet

    SciTech Connect

    Coverdale, C.A.; Darrow, C.B.; Jones, R.; Sawyer, W.; Crane, J.; Ditmire, T.; Perry, M.D. ); Filbert, P.C. )

    1995-01-01

    A novel linear gas jet has been developed and used to produce centimeter-scale, 10[sup 19] cm[sup [minus]3] electron density plasmas. Long regions of high density are important to many types of experiments, including x-ray laser and laser-plasma interaction studies. This new type of gas jet has been characterized by stimulated Raman backscatter emission from the plasma.

  1. New applications for Coriolis flow and density measurement in the natural gas industry

    SciTech Connect

    Valentine, J.; Keilty, M.

    1995-11-01

    Simultaneous, highly accurate measurement of mass, density and temperature makes the Coriolis instrumentation ideal technology for a wide variety of natural gas applications. This paper describes the technology, discusses the benefits of using Coriolis instrumentation, and describes several applications related to the oil and gas production industries utilizing the Coriolis meter.

  2. Design of a high density cold gas attitude control system

    NASA Technical Reports Server (NTRS)

    Hall, Sarah E.; Lewis, Mark J.; Akin, David L.

    1993-01-01

    A comparison of the experimental results of a nitrous oxide cold gas thruster with the predicted performance from a numerical simulation of nozzle operations is discussed. Tests were conducted in a vacuum chamber to verify analytical predictions of both nitrogen and nitrous oxide. Preliminary results indicate an Isp for N2O of 61, and an Isp of 69 for N2. Based on the results of this research, parameters are presented for a nitrous oxide-based reaction control system for a small spacecraft currently under development.

  3. Method For Enhanced Gas Monitoring In High Density Flow Streams

    DOEpatents

    Von Drasek, William A.; Mulderink, Kenneth A.; Marin, Ovidiu

    2005-09-13

    A method for conducting laser absorption measurements in high temperature process streams having high levels of particulate matter is disclosed. An impinger is positioned substantially parallel to a laser beam propagation path and at upstream position relative to the laser beam. Beam shielding pipes shield the beam from the surrounding environment. Measurement is conducted only in the gap between the two shielding pipes where the beam propagates through the process gas. The impinger facilitates reduced particle presence in the measurement beam, resulting in improved SNR (signal-to-noise) and improved sensitivity and dynamic range of the measurement.

  4. 3D simulations of gas puff effects on edge density and ICRF coupling in ASDEX Upgrade

    NASA Astrophysics Data System (ADS)

    Zhang, W.; Bobkov, V.; Lunt, T.; Noterdaeme, J.-M.; Coster, D.; Bilato, R.; Jacquet, P.; Brida, D.; Feng, Y.; Wolfrum, E.; Guimarais, L.; the ASDEX Upgrade Team

    2016-03-01

    In recent experiments, a local gas puff was found to be an effective way to tailor the scrape-off layer (SOL) density and improve the ion cyclotron range of frequency (ICRF) power coupling in tokamaks. In order to quantitatively reproduce these experiments, to understand the corresponding physics and to optimize the gas valve positions and rates, simulations were carried out with the 3D edge plasma transport code EMC3-EIRENE in ASDEX Upgrade. An inter-ELM phase of an H-mode discharge with a moderate gas puff rate (1.2  ×  1022 electrons s-1) is used in our simulations. We simulated cases with gas puff in the lower divertor, the outer mid-plane and the top of the machine while keeping other conditions the same. Compared with the lower divertor gas puff, the outer mid-plane gas puff can increase the local density in front of the antennas most effectively, while a toroidally uniform but significantly smaller enhancement is found for the top gas puff. Good agreement between our simulations and experiments is obtained. With further simulations, the mechanisms of SOL density tailoring via local gas puffing and the strategies of gas puff optimization are discussed in the paper.

  5. [Greenhouse gas emission from reservoir and its influence factors].

    PubMed

    Zhao, Xiao-jie; Zhao, Tong-qian; Zheng, Hua; Duan, Xiao-nan; Chen, Fa-lin; Ouyang, Zhi-yun; Wang, Xiao-ke

    2008-08-01

    Reservoirs are significant sources of emissions of the greenhouse gases. Discussing greenhouse gas emission from the reservoirs and its influence factors are propitious to evaluate emission of the greenhouse gas accurately, reduce gas emission under hydraulic engineering and hydropower development. This paper expatiates the mechanism of the greenhouse gas production, sums three approaches of the greenhouse gas emission, which are emissions from nature emission of the reservoirs, turbines and spillways and downstream of the dam, respectively. Effects of greenhouse gas emission were discussed from character of the reservoirs, climate, pH of the water, vegetation growing in the reservoirs and so on. Finally, it has analyzed the heterogeneity of the greenhouse gas emission as well as the root of the uncertainty and carried on the forecast with emphasis to the next research. PMID:18839604

  6. Improving emissions factors for estimating urban natural gas leakage

    NASA Astrophysics Data System (ADS)

    Phillips, Nathan

    2013-04-01

    Emissions factors for pipeline natural gas leaks are in need of refinement. In addition to limitations from the small sample sizes of leaks that were initially used to develop emissions factors, a further limitation to emissions factors is lack of knowledge of characteristic statistical distributions of pipeline leak rates. For example, leaks were implicitly assumed to be normally distributed so that an average leak rate was used for pipelines of a given construction. Our natural gas leak data from Boston, USA, in which we found over 3,000 natural gas leaks, indicates that leaks rates are highly skewed, with relatively few leaks likely contributing disproportionately to the total. The long-tailed distribution of gas leak rates is mirrored by a similarly skewed distribution of surface methane concentrations in air. These data suggest that emissions factors should be based on correctly specified statistical distributions, and that fixing relatively few large leaks first may provide the most environmental benefit per cost.

  7. Electron Density Measurements in UV-Preionized XeCl and CO2 Laser Gas Mixtures

    NASA Astrophysics Data System (ADS)

    Takagi, Shigeyuki; Sato, Saburo; Goto, Tatsumi

    1989-11-01

    A Langmuir probe technique has been used to measure electron densities and temperatures in UV-preionized XeCl excimer and CO2 laser gas mixtures in a laser tube. For this experiment, only pin electrodes (preionization sparks) were operated with no discharge between the main electrodes. The measured electron densities were about 108 cm-3 in both the excimer and CO2 laser gases, compared with 1010 cm-3 in pure He gas. The electron density was found to increase due to the proximity of the main electrodes. The coefficients of absorption for excimer and CO2 laser gas were obtained from the characteristics of the electron densities vs the distance from the UV source. Based on the absorption coefficient for XeCl, 0.9 cm-1 atm-1, we propose pin-electrode arrangements for spatially uniform preionization.

  8. Generation of thin, near critical density gas targets for laser plasma interaction experiments

    NASA Astrophysics Data System (ADS)

    Salehi, Fatholah; Goers, Andy; Hine, George; Feder, Linus; Miao, Bo; Milchberg, Howard

    2015-11-01

    We present the design and characterization of a thin (200µm FWHM), high density pulsed gas jet which we use to study near critical and overcritical laser plasma interactions. We show that cryogenic cooling of the pulsed jet provides the necessary density enhancement for reaching overcritical plasma densities at 800 nm (> 1 . 7 × >102 1 cm-3) with pure hydrogen gas at plenum pressures below 1000 psi. Further, we present 2D and 3D PIC simulations showing the interaction of femtosecond pulses with our experimentally measured near critical gas density profile. The simulations show electron and ion acceleration at drive pulse energies as low as a few tens of millijoules. This work supported by DTRA and the US Department of Energy.

  9. Density measurement in air with a saturable absorbing seed gas

    NASA Technical Reports Server (NTRS)

    Baganoff, D.

    1982-01-01

    A method for making density measurements in a compressible flow by using off resonance laser induced fluorescence is studied. The seed molecule chosen for study is the iodine molecule which is excited with the 514.5 nm line of the argon ion laser whose output is frequency tuned, by as much as 3 GHz, relative to a strong iodine transition using an intracavity etalon. The theory which was developed to analyze the effect will be used in conjunction with two experiments being conducted to further study the method an acoustic resonance tube in which controlled perturbations about a uniform state are produced, and a small supersonic jet in which the conditions of the flow vary widely from point to point.

  10. Dominant factors in controlling marine gas pools in South China

    USGS Publications Warehouse

    Xu, S.; Watney, W.L.

    2007-01-01

    In marine strata from Sinian to Middle Triassic in South China, there develop four sets of regional and six sets of local source rocks, and ten sets of reservoir rocks. The occurrence of four main formation periods in association with five main reconstruction periods, results in a secondary origin for the most marine gas pools in South China. To improve the understanding of marine gas pools in South China with severely deformed geological background, the dominant control factors are discussed in this paper. The fluid sources, including the gas cracked from crude oil, the gas dissolved in water, the gas of inorganic origin, hydrocarbons generated during the second phase, and the mixed pool fluid source, were the most significant control factors of the types and the development stage of pools. The period of the pool formation and the reconstruction controlled the pool evolution and the distribution on a regional scale. Owing to the multiple periods of the pool formation and the reconstruction, the distribution of marine gas pools was complex both in space and in time, and the gas in the pools is heterogeneous. Pool elements, such as preservation conditions, traps and migration paths, and reservoir rocks and facies, also served as important control factors to marine gas pools in South China. Especially, the preservation conditions played a key role in maintaining marine oil and gas accumulations on a regional or local scale. According to several dominant control factors of a pool, the pool-controlling model can be constructed. As an example, the pool-controlling model of Sinian gas pool in Weiyuan gas field in Sichuan basin was summed up. ?? Higher Education Press and Springer-Verlag 2007.

  11. Star Formation and Gas Densities in the Dwarf Irregular Galaxy Sextans A

    NASA Astrophysics Data System (ADS)

    Plummer, Julia D.; Hunter, Deidre A.

    1995-12-01

    As a step in understanding the process of star formation in irregular galaxies, we have analysed the irregular galaxy Sextans A. Irregular galaxies provide star-forming systems that are unperturbed by spiral density waves. Sextans A is a tiny galaxy, 1.3 Mpc distant, just beyond the dynamic boundary of the Local Group. We studied the star formation properties of this galaxy using UBV and Hα images. Stars are not currently forming in the center of this galaxy, though they have in the past. The current star formation is in clumps in the outer parts of the galaxy and is not evenly distributed. The total Hα luminosity found for Sextans A is 9 x 10(38) erg/s, which corresponds to a star formation rate of 6 x 10(-3) Mmathordsun /yr for standard assumptions. The rate per unit area, within the Holmberg radius, is 6 x 10(-10) Mmathordsun /yr/pc(2) . Skillman et al. (1988) derived a total HI mass of 6 x 10(7) Mmathordsun . At its present rate, Sextans A will use up all of its gas in 12 x 10(9) yr, including the He contribution. We have also compared the star formation and gas density in Sextans A to critical gas surface density models (Toomre 1964, Quirk 1972, Kennicutt 1988). We used a published rotation curve to calculate the critical gas density necessary for the instabilities that produce star-forming clouds (Skillman et al. 1988). The ratio of observed to critical gas density is low in Sextans A, at the low end of values found by Kennicutt (1988) for spiral galaxies. The current star formation is located in the region of the galaxy with higher radially averaged observed gas densities relative to the critical density. This suggests that Sextans A has a difficult time forming gas clouds, resulting in an observed low star formation rate. This research was funded by the REU program at Northern Arizona University.

  12. Background gas density and beam losses in NIO1 beam source.

    PubMed

    Sartori, E; Veltri, P; Cavenago, M; Serianni, G

    2016-02-01

    NIO1 (Negative Ion Optimization 1) is a versatile ion source designed to study the physics of production and acceleration of H- beams up to 60 keV. In ion sources, the gas is steadily injected in the plasma source to sustain the discharge, while high vacuum is maintained by a dedicated pumping system located in the vessel. In this paper, the three dimensional gas flow in NIO1 is studied in the molecular flow regime by the Avocado code. The analysis of the gas density profile along the accelerator considers the influence of effective gas temperature in the source, of the gas temperature accommodation by collisions at walls, and of the gas particle mass. The calculated source and vessel pressures are compared with experimental measurements in NIO1 during steady gas injection. PMID:26932000

  13. Background gas density and beam losses in NIO1 beam source

    NASA Astrophysics Data System (ADS)

    Sartori, E.; Veltri, P.; Cavenago, M.; Serianni, G.

    2016-02-01

    NIO1 (Negative Ion Optimization 1) is a versatile ion source designed to study the physics of production and acceleration of H- beams up to 60 keV. In ion sources, the gas is steadily injected in the plasma source to sustain the discharge, while high vacuum is maintained by a dedicated pumping system located in the vessel. In this paper, the three dimensional gas flow in NIO1 is studied in the molecular flow regime by the Avocado code. The analysis of the gas density profile along the accelerator considers the influence of effective gas temperature in the source, of the gas temperature accommodation by collisions at walls, and of the gas particle mass. The calculated source and vessel pressures are compared with experimental measurements in NIO1 during steady gas injection.

  14. Effects of Mean Flow Profiles on the Instability of a Low-Density Gas Jet Injected into a High-Density Gas

    NASA Technical Reports Server (NTRS)

    Vedantam, NandaKishore; Parthasarathy, Ramkumar N.

    2004-01-01

    The effects of the mean velocity profiles on the instability characteristics in the near-injector region of axisymmetric low density gas jets injected vertically upwards into a high-density gas medium were investigated using linear inviscid stability analysis. The flow was assumed to be isothermal and locally parallel. Three velocity profiles, signifying different changes in the mean velocity in the shear layer, were used in the analysis. The effects of the inhomogeneous shear layer and the Froude number (signifying the effects of gravity) on the instability for each set of mean profiles were delineated. At a large Froude number (negligible gravity), a critical density ratio was found for the three profiles at which the jet became absolutely unstable. The critical density ratio for each velocity profile was increased as the Froude number was reduced. A critical Froude number was found for the three sets of profiles, below which the jet was absolutely unstable for all the density ratios less than unity, which demarcated the jet flow into the momentum-driven regime and the buoyancy-driven regime.

  15. Linear Temporal Stability Analysis of a Low-Density Round Gas Jet Injected into a High-Density Gas

    NASA Technical Reports Server (NTRS)

    Lawson, Anthony L.; Parthasarathy, Ramkumar N.

    2002-01-01

    It has been observed in previous experimental studies that round helium jets injected into air display a repetitive structure for a long distance, somewhat similar to the buoyancy-induced flickering observed in diffusion flames. In order to investigate the influence of gravity on the near-injector development of the flow, a linear temporal stability analysis of a round helium jet injected into air was performed. The flow was assumed to be isothermal and locally parallel; viscous and diffusive effects were ignored. The variables were represented as the sum of the mean value and a normal-mode small disturbance. An ordinary differential equation governing the amplitude of the pressure disturbance was derived. The velocity and density profiles in the shear layer, and the Froude number (signifying the effects of gravity) were the three important parameters in this equation. Together with the boundary conditions, an eigenvalue problem was formulated. Assuming that the velocity and density profiles in the shear layer to be represented by hyperbolic tangent functions, the eigenvalue problem was solved for various values of Froude number. The temporal growth rates and the phase velocity of the disturbances were obtained. The temporal growth rates of the disturbances increased as the Froude number was reduced (i.e. gravitational effects increased), indicating the destabilizing role played by gravity.

  16. Solution of an associating lattice-gas model with density anomaly on a Husimi lattice

    NASA Astrophysics Data System (ADS)

    Oliveira, Tiago J.; Stilck, Jürgen F.; Barbosa, Marco Aurélio A.

    2010-11-01

    We study a model of a lattice gas with orientational degrees of freedom which resemble the formation of hydrogen bonds between the molecules. In this model, which is the simplified version of the Henriques-Barbosa model, no distinction is made between donors and acceptors in the bonding arms. We solve the model in the grand-canonical ensemble on a Husimi lattice built with hexagonal plaquettes with a central site. The ground state of the model, which was originally defined on the triangular lattice, is exactly reproduced by the solution on this Husimi lattice. In the phase diagram, one gas and two liquid [high density liquid (HDL) and low density liquid (LDL)] phases are present. All phase transitions (GAS-LDL, GAS-HDL, and LDL-HDL) are discontinuous, and the three phases coexist at a triple point. A line of temperatures of maximum density in the isobars is found in the metastable GAS phase, as well as another line of temperatures of minimum density appears in the LDL phase, part of it in the stable region and another in the metastable region of this phase. These findings are at variance with simulational results for the same model on the triangular lattice, which suggested a phase diagram with two critical points. However, our results show very good quantitative agreement with the simulations, both for the coexistence loci and the densities of particles and of hydrogen bonds. We discuss the comparison of the simulations with our results.

  17. Characteristics of excitation discharge of an excimer laser in gas density depletion

    NASA Astrophysics Data System (ADS)

    Imada, Go; Masuda, Wataru; Yatsui, Kiyoshi

    1998-12-01

    The influences of gas density depletion on the highly- repetitive, high-pressure, pulsed glow discharge for excitation of excimer laser have been investigated eliminating the other instabilities, such as shock waves, residual ions, discharge products and electrode heating. The gas density depletion is simulated by utilizing a subsonic flow between the curved electrodes. The comparison has been made on the discharge occurred in the presence of the gas density depletion with the second discharge on the double-pulse experiment. We have found that the big gas density non uniformity, (Delta) (rho) /(rho) 0 approximately 3.6% corresponding to a pulse repetition rate (PRR) of approximately 20 Hz, tends to cause the arc discharge without the shocks, ions, discharge products and electrode heating. On the other hand, the second discharge on the double-pulse experiment becomes arc discharge in much smaller non uniformity ((Delta) (rho) /(rho) 0 approximately 1.2% corresponding to PRR approximately 3 Hz). The arc discharge in the double-pulse experiment might be driven by the residual ions and/or discharge products other than gas density depletion except for PRR greater than 20 Hz.

  18. Human respiration at rest in rapid compression and at high pressures and gas densities

    NASA Technical Reports Server (NTRS)

    Gelfand, R.; Lambertsen, C. J.; Strauss, R.; Clark, J. M.; Puglia, C. D.

    1983-01-01

    The ventilation (V), end-tidal PCO2 (PACO2), and CO2 elimination rate were determined in men at rest breathing CO2-free gas over the pressure range 1-50 ATA and the gas density range 0.4-25 g/l, during slow and rapid compressions, at stable elevated ambient pressures and during slow decompressions. Progressive increase in pulmonary gas flow resistance due to elevation of ambient pressure and inspired gas density to the He-O2 equivalent of 5000 feet of seawater was found to produce a complex pattern of change in PACO2. It was found that as both ambient pressure and pulmonary gas flow resistance were progressively raised, PACO2 at first increased, went through a maximum, and then declined towards values near the 1 ATA level. It is concluded that this pattern of PACO2 change results from the interaction on ventilation of the increase in pulmonary resistance due to the elevation of gas density with the increase in respiratory drive postulated as due to generalized central nervous system excitation associated with exposure to high hydrostatic pressure. It is suggested that a similar interaction exists between increased gas flow resistance and the increase in respiratory drive related to nitrogen partial pressure and the resulting narcosis.

  19. Can mammographic assessments lead to consider density as a risk factor for breast cancer?

    PubMed

    Colin, C; Prince, V; Valette, P J

    2013-03-01

    Admitting that mammographic breast density is an important independent risk factor for breast cancer in the general population, has a crucial economical health care impact, since it might lead to increasing screening frequency or reinforcing additional modalities. Thus, the impact of density as a risk factor has to be carefully investigated and might be debated. Some authors suggested that high density would be either a weak factor or confused with a masking effect. Others concluded that most of the studies have methodological biases in basic physics to quantify percentage of breast density, as well as in mammographic acquisition parameters. The purpose of this review is to evaluate mammographic procedures and density assessments in published studies regarding density as a breast cancer risk. No standardization was found in breast density assessments and compared density categories. High density definitions varied widely from 25 to 75% of dense tissues on mammograms. Some studies showed an insufficient follow-up to reveal masking effect related to mammographic false negatives. Evaluating breast density impact needs thorough studies with consensual mammographic procedures, methods of density measurement, breast density classification as well as a standardized definition of high breast density. Digital mammography, more effective in dense breasts, should help to re-evaluate the issue of density as a risk factor for breast cancer. PMID:20133095

  20. A CORRELATION BETWEEN SURFACE DENSITIES OF YOUNG STELLAR OBJECTS AND GAS IN EIGHT NEARBY MOLECULAR CLOUDS

    SciTech Connect

    Gutermuth, R. A.; Pipher, J. L.; Megeath, S. T.; Allen, T. S.; Myers, P. C.; Allen, L. E.

    2011-10-01

    We report the discovery and characterization of a power-law correlation between the local surface densities of Spitzer-identified, dusty young stellar objects (YSOs) and the column density of gas (as traced by near-IR extinction) in eight molecular clouds within 1 kpc and with 100 or more known YSOs. This correlation, which appears in data smoothed over size scales of {approx}1 pc, varies in quality from cloud to cloud; those clouds with tight correlations, MonR2 and Ophiuchus, are fit with power laws of slope 2.67 and 1.87, respectively. The spread in the correlation is attributed primarily to local gas disruption by stars that formed there or to the presence of very young subregions at the onset of star formation. We explore the ratio of the number of Class II to Class I sources, a proxy for the star formation age of a region, as a function of gas column density; this analysis reveals a declining Class II to Class I ratio with increasing column density. We show that the observed star-gas correlation is consistent with a star formation law where the star formation rate per area varies with the gas column density squared. We also propose a simple picture of thermal fragmentation of dense gas in an isothermal, self-gravitating layer as an explanation for the power law. Finally, we briefly compare the star-gas correlation and its implied star formation law with other recent proposed of star formation laws at similar and larger size scales from nearby star-forming regions.

  1. Gas-phase silicon atom densities in the chemical vapor deposition of silicon from silane

    SciTech Connect

    Coltrin, M.E.; Breiland, W.G.; Ho, P.

    1993-12-31

    Silicon atom number density profiles have been measured using laser-induced fluorescence during the chemical vapor deposition of silicon from silane. Measurements were obtained in a rotating-disk reactor as a function of silane partial pressure and the amount of hydrogen added to the carrier gas. Absolute number densities were obtained using an atomic absorption technique. Results were compared with calculated density profiles from a model of the coupled fluid flow, gas-phase and surface chemistry for an infinite-radius rotating disk. An analysis of the reaction mechanism showed that the unimolecular decomposition of SiH{sub 2} is not the dominant source of Si atoms. Profile shapes and positions, and all experimental trends are well matched by the calculations. However, the calculated number density is up to 100 times smaller than measured.

  2. Observing the gas temperature drop in the high-density nucleus of L 1544

    NASA Astrophysics Data System (ADS)

    Crapsi, A.; Caselli, P.; Walmsley, M. C.; Tafalla, M.

    2007-07-01

    Context: The thermal structure of a starless core is crucial for our understanding of the physics in these objects and hence for our understanding of star formation. Theory predicts a gas temperature drop in the inner 5000 AU of the pre-stellar core L 1544, but there has been no observational proof of this. Aims: We performed VLA observations of the NH{3} (1, 1) and (2, 2) transitions towards L 1544 in order to measure the temperature gradient between the high density core nucleus and the surrounding core envelope. Our VLA observation for the first time provide measurements of gas temperature in a core with a resolution smaller than 1000 AU. We have also obtained high resolution Plateau de Bure observations of the 110 GHz 111-101 para-NH2D line in order to further constrain the physical parameters of the high density nucleus. Methods: We combine our interferometric NH{3} and NH2D observations with available single dish measurements in order to estimate the effects of flux loss from extended components upon our data. We have estimated the temperature gradient using a model of the source to fit our data in the u,v plane. As the NH{3}(1, 1) line is extremely optically thick, this also involved fitting a gradient in the NH{3} abundance. In this way, we also measure the [ NH2D] /[ NH{3}] abundance ratio in the inner nucleus. Results: We find that indeed the temperature decreases toward the core nucleus from 12 K down to 5.5 K resulting in an increase of a factor of 50% in the estimated density of the core from the dust continuum if compared with the estimates done with constant temperature of 8.75 K. Current models of the thermal equilibrium can describe consistently the observed temperature and density in this object, simultaneously fitting our temperature profile and the continuum emission. We also found a remarkably high abundance of deuterated ammonia with respect to the ammonia abundance (50% ± 20%), which proves the persistence of nitrogen bearing molecules at

  3. Density fluctuations in a quasi-one-dimensional Bose gas as observed in free expansion

    NASA Astrophysics Data System (ADS)

    Gawryluk, Krzysztof; Gajda, Mariusz; Brewczyk, Mirosław

    2015-10-01

    We study, within the framework of the classical-field approximation, the density correlations of a weakly interacting expanding Bose gas for the whole range of temperatures across the Bose-Einstein condensation threshold. We focus on elongated quasi-one-dimensional systems where there is a huge discrepancy between the existing theory and experimental results [A. Perrin et al., Nat. Phys. 8, 195 (2012), 10.1038/nphys2212]. We find that the density correlation function is not reduced for temperatures below the critical one as it is predicted for the ideal gas or for a weakly interacting system within the Bogoliubov approximation. This behavior of the density correlations agrees with the above-mentioned experiment with the elongated system. Although the system was much larger than that studied here, we believe that the behavior of the density correlation function found there is quite generic. Our theoretical study indicates also large density fluctuations in the trap in the quasicondensate regime where only phase fluctuations were expected. We argue that the enhanced density fluctuations can originate in the presence of interactions in the system, or more precisely in the presence of spontaneous dark solitons in the elongated gas at thermal equilibrium.

  4. Density functional theory screening of gas-treatment strategies for stabilization of high energy-density lithium metal anodes

    NASA Astrophysics Data System (ADS)

    Koch, Stephan L.; Morgan, Benjamin J.; Passerini, Stefano; Teobaldi, Gilberto

    2015-11-01

    To explore the potential of molecular gas treatment of freshly cut lithium foils in non-electrolyte-based passivation of high-energy-density Li anodes, density functional theory (DFT) has been used to study the decomposition of molecular gases on metallic lithium surfaces. By combining DFT geometry optimization and Molecular Dynamics, the effects of atmospheric (N2, O2, CO2) and hazardous (F2, SO2) gas decomposition on Li(bcc) (100), (110), and (111) surfaces on relative surface energies, work functions, and emerging electronic and elastic properties are investigated. The simulations suggest that exposure to different molecular gases can be used to induce and control reconstructions of the metal Li surface and substantial changes (up to over 1 eV) in the work function of the passivated system. Contrary to the other considered gases, which form metallic adlayers, SO2 treatment emerges as the most effective in creating an insulating passivation layer for dosages ≤1 mono-layer. The substantial Li → adsorbate charge transfer and adlayer relaxation produce marked elastic stiffening of the interface, with the smallest change shown by nitrogen-treated adlayers.

  5. Maximization of ICRF power by SOL density tailoring with local gas injection

    NASA Astrophysics Data System (ADS)

    Jacquet, P.; Goniche, M.; Bobkov, V.; Lerche, E.; Pinsker, R. I.; Pitts, R. A.; Zhang, W.; Colas, L.; Hosea, J.; Moriyama, S.; Wang, S.-J.; Wukitch, S.; Zhang, X.; Bilato, R.; Bufferand, H.; Guimarais, L.; Faugel, H.; Hanson, G. R.; Kocan, M.; Monakhov, I.; Noterdaeme, J.-M.; Petrzilka, V.; Shaw, A.; Stepanov, I.; Sips, A. C. C.; Van Eester, D.; Wauters, T.; JET contributors, the; the ASDEX Upgrade Team; the DIII-D Team; ITPA ‘Integrated Operation Scenarios' members, the; experts

    2016-04-01

    Experiments have been performed under the coordination of the International Tokamak Physics Activity (ITPA) on several tokamaks, including ASDEX Upgrade (AUG), JET and DIII-D, to characterize the increased Ion cyclotron range of frequency (ICRF) antenna loading achieved by optimizing the position of gas injection relative to the RF antennas. On DIII-D, AUG and JET (with the ITER-Like Wall) a 50% increase in the antenna loading was observed when injecting deuterium in ELMy H-mode plasmas using mid-plane inlets close to the powered antennas instead of divertor injection and, with smaller improvement when using gas inlets located at the top of the machine. The gas injection rate required for such improvements (~0.7  ×  1022 el s-1 in AUG, ~1.0  ×  1022 el s-1 in JET) is compatible with the use of this technique to optimize ICRF heating during the development of plasma scenarios and no degradation of confinement was observed when using the mid-plane or top inlets compared with divertor valves. An increase in the scrape-off layer (SOL) density was measured when switching gas injection from divertor to outer mid-plane or top. On JET and DIII-D, the measured SOL density increase when using main chamber puffing is consistent with the antenna coupling resistance increase provided that the distance between the measurement lines of sight and the injection location is taken into account. Optimized gas injection was also found to be beneficial for reducing tungsten (W) sputtering at the AUG antenna limiters, and also to reduce slightly the W and nickel (Ni) content in JET plasmas. Modeling the specific effects of divertor/top/mid-plane injection on the outer mid-plane density was carried out using both the EDGE2D-EIRENE and EMC3-EIRENE plasma boundary code packages; simulations indeed indicate that outer mid-plane gas injection maximizes the density in the mid-plane close to the injection point with qualitative agreement with the AUG SOL density measurements

  6. Gas amplification factor in neon-nitrogen filled proportional counters

    NASA Astrophysics Data System (ADS)

    Othman, A.

    1988-07-01

    The gas amplification factor in a cylindrical proportional counter filled with NeN 2 Penning mixtures has been measured (over the range 1 < A < 6.4 × 10 3) to verify the validity of the gas gain formulae of Rose and Korff, Khristov, Williams and Sara, Diethorn and Zastawny. This factor has been found to obey Zastawny's formula over the range of variables studied. The formula of Diethorn can be fitted only for small nitrogen concentrations (below 5 × 10 -4). Constants appropriate to the Zastawny and Diethorn formulae have been determined over a wide range of N 2 concentrations from spectroscopically pure Ne up to 11.1% N 2.

  7. Improved parameterization of interatomic potentials for rare gas dimers with density-based energy decomposition analysis

    NASA Astrophysics Data System (ADS)

    Zhou, Nengjie; Lu, Zhenyu; Wu, Qin; Zhang, Yingkai

    2014-06-01

    We examine interatomic interactions for rare gas dimers using the density-based energy decomposition analysis (DEDA) in conjunction with computational results from CCSD(T) at the complete basis set (CBS) limit. The unique DEDA capability of separating frozen density interactions from density relaxation contributions is employed to yield clean interaction components, and the results are found to be consistent with the typical physical picture that density relaxations play a very minimal role in rare gas interactions. Equipped with each interaction component as reference, we develop a new three-term molecular mechanical force field to describe rare gas dimers: a smeared charge multipole model for electrostatics with charge penetration effects, a B3LYP-D3 dispersion term for asymptotically correct long-range attractions that is screened at short-range, and a Born-Mayer exponential function for the repulsion. The resulted force field not only reproduces rare gas interaction energies calculated at the CCSD(T)/CBS level, but also yields each interaction component (electrostatic or van der Waals) which agrees very well with its corresponding reference value.

  8. Improved parameterization of interatomic potentials for rare gas dimers with density-based energy decomposition analysis.

    PubMed

    Zhou, Nengjie; Lu, Zhenyu; Wu, Qin; Zhang, Yingkai

    2014-06-01

    We examine interatomic interactions for rare gas dimers using the density-based energy decomposition analysis (DEDA) in conjunction with computational results from CCSD(T) at the complete basis set (CBS) limit. The unique DEDA capability of separating frozen density interactions from density relaxation contributions is employed to yield clean interaction components, and the results are found to be consistent with the typical physical picture that density relaxations play a very minimal role in rare gas interactions. Equipped with each interaction component as reference, we develop a new three-term molecular mechanical force field to describe rare gas dimers: a smeared charge multipole model for electrostatics with charge penetration effects, a B3LYP-D3 dispersion term for asymptotically correct long-range attractions that is screened at short-range, and a Born-Mayer exponential function for the repulsion. The resulted force field not only reproduces rare gas interaction energies calculated at the CCSD(T)/CBS level, but also yields each interaction component (electrostatic or van der Waals) which agrees very well with its corresponding reference value. PMID:24908000

  9. Improved parameterization of interatomic potentials for rare gas dimers with density-based energy decomposition analysis

    PubMed Central

    Zhou, Nengjie; Lu, Zhenyu; Wu, Qin; Zhang, Yingkai

    2014-01-01

    We examine interatomic interactions for rare gas dimers using the density-based energy decomposition analysis (DEDA) in conjunction with computational results from CCSD(T) at the complete basis set (CBS) limit. The unique DEDA capability of separating frozen density interactions from density relaxation contributions is employed to yield clean interaction components, and the results are found to be consistent with the typical physical picture that density relaxations play a very minimal role in rare gas interactions. Equipped with each interaction component as reference, we develop a new three-term molecular mechanical force field to describe rare gas dimers: a smeared charge multipole model for electrostatics with charge penetration effects, a B3LYP-D3 dispersion term for asymptotically correct long-range attractions that is screened at short-range, and a Born-Mayer exponential function for the repulsion. The resulted force field not only reproduces rare gas interaction energies calculated at the CCSD(T)/CBS level, but also yields each interaction component (electrostatic or van der Waals) which agrees very well with its corresponding reference value. PMID:24908000

  10. Mammographic density and its interaction with other breast cancer risk factors in an Asian population

    PubMed Central

    Wong, C S; Lim, G H; Gao, F; Jakes, R W; Offman, J; Chia, K S; Duffy, S W

    2011-01-01

    Background: Joint effects of mammographic density and other risk factors on breast cancer risk remain unclear. Methods: From The Singapore Breast Screening Project, we selected 491 cases and 982 controls. Mammographic density was measured quantitatively. Data analysis was by conditional logistic regression. Results: Density was a significant risk factor, adjusting for other factors. Density of 76–100% had an odds ratio of 5.54 (95% CI 2.38–12.90) compared with 0–10%. Density had significant interactions with body mass index and oral contraceptive use (P=0.02). Conclusions: Percent density increases breast cancer risk in addition to effects of other risk factors, and modifies the effects of BMI and OCs. PMID:21245860

  11. Energy Factor Analysis for Gas Heat Pump Water Heaters

    SciTech Connect

    Gluesenkamp, Kyle R

    2016-01-01

    Gas heat pump water heaters (HPWHs) can improve water heating efficiency with zero GWP and zero ODP working fluids. The energy factor (EF) of a gas HPWH is sensitive to several factors. In this work, expressions are derived for EF of gas HPWHs, as a function of heat pump cycle COP, tank heat losses, burner efficiency, electrical draw, and effectiveness of supplemental heat exchangers. The expressions are used to investigate the sensitivity of EF to each parameter. EF is evaluated on a site energy basis (as used by the US DOE for rating water heater EF), and a primary energy-basis energy factor (PEF) is also defined and included. Typical ranges of values for the six parameters are given. For gas HPWHs, using typical ranges for component performance, EF will be 59 80% of the heat pump cycle thermal COP (for example, a COP of 1.60 may result in an EF of 0.94 1.28). Most of the reduction in COP is due to burner efficiency and tank heat losses. Gas-fired HPWHs are theoretically be capable of an EF of up to 1.7 (PEF of 1.6); while an EF of 1.1 1.3 (PEF of 1.0 1.1) is expected from an early market entry.

  12. Molecular Rayleigh Scattering Techniques Developed for Measuring Gas Flow Velocity, Density, Temperature, and Turbulence

    NASA Technical Reports Server (NTRS)

    Mielke, Amy F.; Seasholtz, Richard G.; Elam, Kristie A.; Panda, Jayanta

    2005-01-01

    Nonintrusive optical point-wise measurement techniques utilizing the principles of molecular Rayleigh scattering have been developed at the NASA Glenn Research Center to obtain time-averaged information about gas velocity, density, temperature, and turbulence, or dynamic information about gas velocity and density in unseeded flows. These techniques enable measurements that are necessary for validating computational fluid dynamics (CFD) and computational aeroacoustic (CAA) codes. Dynamic measurements allow the calculation of power spectra for the various flow properties. This type of information is currently being used in jet noise studies, correlating sound pressure fluctuations with velocity and density fluctuations to determine noise sources in jets. These nonintrusive techniques are particularly useful in supersonic flows, where seeding the flow with particles is not an option, and where the environment is too harsh for hot-wire measurements.

  13. Electron density measurement in gas discharge plasmas by optical and acoustic methods

    NASA Astrophysics Data System (ADS)

    Biagioni, A.; Anania, M. P.; Bellaveglia, M.; Chiadroni, E.; Cianchi, A.; Di Giovenale, D.; Di Pirro, G.; Ferrario, M.; Filippi, F.; Mostacci, A.; Pompili, R.; Shpakov, V.; Vaccarezza, C.; Villa, F.; Zigler, A.

    2016-08-01

    Plasma density represents a very important parameter for both laser wakefield and plasma wakefield acceleration, which use a gas-filled capillary plasma source. Several techniques can be used to measure the plasma density within a capillary discharge, which are mainly based on optical diagnostic methods, as for example the well-known spectroscopic method using the Stark broadening effect. In this work, we introduce a preliminary study on an alternative way to detect the plasma density, based on the shock waves produced by gas discharge in a capillary. Firstly, the measurements of the acoustic spectral content relative to the laser-induced plasmas by a solid target allowed us to understand the main properties of the acoustic waves produced during this kind of plasma generation; afterwards, we have extended such acoustic technique to the capillary plasma source in order to calibrate it by comparison with the stark broadening method.

  14. Bulk-density distributions of solids in the freeboard of a gas-solid fluidized bed

    SciTech Connect

    Shen, B.C.; Fan, L.T.; Walawender, W.P.

    1995-05-01

    The freeboard region above the bubbling zone of a gas-solid fluidized bed provides the space not only for the disengagement of particles but also for additional contact and reaction between the particles and gas. The flow pattern and behavior of particles as well as their bulk-density distribution in the freeboard have a significant impact on the efficiency of fluidization. The results of numerous previous experimental studies indicate that the bulk density of solids essentially decreases exponentially as a function of the height of the freeboard. In the present work, this distribution has been obtained by first derived the Fokker-Planck equation from the linearized equation of motion of a single particle and then transforming this Fokker-Planck equation into that for the bulk-density distribution of solids. Its simplification to the one-dimensional case readily gives rise to an exponential distribution and agrees well with the available experimental data.

  15. The probability density function in molecular gas in the G333 and Vela C molecular clouds

    NASA Astrophysics Data System (ADS)

    Cunningham, Maria

    2015-08-01

    The probability density function (PDF) is a simple analytical tool for determining the hierarchical spatial structure of molecular clouds. It has been used frequently in recent years with dust continuum emission, such as that from the Herschel space telescope and ALMA. These dust column density PDFs universally show a log-normal distribution in low column density gas, characteristic of unbound turbulent gas, and a power-law tail at high column densities, indicating the presence of gravitationally bound gas. We have recently conducted a PDF analysis of the molecular gas in the G333 and Vela C giant molecular cloud complexes, using transitions of CO, HCN, HNC, HCO+ and N2H+.The results show that CO and its isotopologues trace mostly the log-normal part of the PDF, while HCN and HCO+ trace both a log-normal part and a power law part to the distribution. On the other hand, HNC and N2H+ mostly trace only the power law tail. The difference between the PDFs of HCN and HNC is surprising, as is the similarity between HNC and the N2H+ PDFs. The most likely explanation for the similar distributions of HNC and N2H+ is that N2H+ is known to be enhanced in cool gas below 20K, where CO is depleted, while the reaction that forms HNC or HCN favours the former at similar low temperatures. The lack of evidence for a power law tail in 13CO and C18O, in conjunction for the results for the N2H+ PDF suggest that depletion of CO in the dense cores of these molecular clouds is significant. In conclusion, the PDF has proved to be a surprisingly useful tool for investigating not only the spatial distribution of molecular gas, but also the wide scale chemistry of molecular clouds.

  16. Pair distribution function of the spin-polarized electron gas: A first-principles analytic model for all uniform densities

    NASA Astrophysics Data System (ADS)

    Gori-Giorgi, Paola; Perdew, John P.

    2002-10-01

    We construct analytic formulas that represent the coupling-constant-averaged pair distribution function gxc(rs,ζ,kFu) of a three-dimensional nonrelativistic ground-state electron gas constrained to a uniform density with density parameter rs=(9π/4)1/3/kF and relative spin polarization ζ over the whole range 0∞) oscillations averaged out. The pair distribution function gxc at the physical coupling constant is then given by differentiation with respect to rs. Our formulas are constructed using only known theoretical constraints plus the correlation energy ɛc(rs,ζ), and accurately reproduce the gxc of the quantum Monte Carlo method and of the fluctuation-dissipation theorem with the Richardson-Ashcroft dynamical local-field factor. Our gxc is correct even in the high-density (rs-->0) and low-density (rs-->∞) limits. When the spin resolution of ɛc into ↑↑, ↓↓, and ↑↓ contributions is known, as it is in the high- and low-density limits, our formulas also yield the spin resolution of gxc. Because of these features, our formulas may be useful for the construction of density functionals for nonuniform systems. We also analyze the kinetic energy of correlation into contributions from density fluctuations of various wave vectors. The exchange and long-range correlation parts of our gxc(rs,ζ,kFu)-1 are analytically Fourier transformable, so that the static structure factor Sxc(rs,ζ,k/kF) is easily evaluated.

  17. Investigating the Effect of Complexity Factors in Gas Law Problems

    ERIC Educational Resources Information Center

    Schuttlefield, Jennifer D.; Kirk, John; Pienta, Norbert J.; Tang, Hui

    2012-01-01

    Undergraduate students were asked to complete gas law questions using a Web-based tool as a first step in our understanding of the role of cognitive load in chemistry word questions and in helping us assess student problem-solving. Each question contained five different complexity factors, which were randomly assigned by the tool so that a…

  18. Distribution of E/N and N/e/ in a cross-flow electric discharge laser. [electric field to neutral gas density and electron number density

    NASA Technical Reports Server (NTRS)

    Dunning, J. W., Jr.; Lancashire, R. B.; Manista, E. J.

    1976-01-01

    Measurements have been conducted of the effect of the convection of ions and electrons on the discharge characteristics in a large scale laser. The results are presented for one particular distribution of ballast resistance. Values of electric field, current density, input power density, ratio of electric field to neutral gas density (E/N), and electron number density were calculated on the basis of measurements of the discharge properties. In a number of graphs, the E/N ratio, current density, power density, and electron density are plotted as a function of row number (downstream position) with total discharge current and gas velocity as parameters. From the dependence of the current distribution on the total current, it appears that the electron production in the first two rows significantly affects the current flowing in the succeeding rows.

  19. Dwarf galaxy dark matter density profiles inferred from stellar and gas kinematics

    SciTech Connect

    Adams, Joshua J.; Simon, Joshua D.; Fabricius, Maximilian H.; Bender, Ralf; Thomas, Jens; Van den Bosch, Remco C. E.; Van de Ven, Glenn; Barentine, John C.; Gebhardt, Karl; Hill, Gary J.; Murphy, Jeremy D.; Swaters, R. A. E-mail: jja439@gmail.com

    2014-07-01

    We present new constraints on the density profiles of dark matter (DM) halos in seven nearby dwarf galaxies from measurements of their integrated stellar light and gas kinematics. The gas kinematics of low-mass galaxies frequently suggest that they contain constant density DM cores, while N-body simulations instead predict a cuspy profile. We present a data set of high-resolution integral-field spectroscopy on seven galaxies and measure the stellar and gas kinematics simultaneously. Using Jeans modeling on our full sample, we examine whether gas kinematics in general produce shallower density profiles than are derived from the stars. Although two of the seven galaxies show some localized differences in their rotation curves between the two tracers, estimates of the central logarithmic slope of the DM density profile, γ, are generally robust. The mean and standard deviation of the logarithmic slope for the population are γ = 0.67 ± 0.10 when measured in the stars and γ = 0.58 ± 0.24 when measured in the gas. We also find that the halos are not under-concentrated at the radii of half their maximum velocities. Finally, we search for correlations of the DM density profile with stellar velocity anisotropy and other baryonic properties. Two popular mechanisms to explain cored DM halos are an exotic DM component or feedback models that strongly couple the energy of supernovae into repeatedly driving out gas and dynamically heating the DM halos. While such models do not yet have falsifiable predictions that we can measure, we investigate correlations that may eventually be used to test models. We do not find a secondary parameter that strongly correlates with the central DM density slope, but we do find some weak correlations. The central DM density slope weakly correlates with the abundance of α elements in the stellar population, anti-correlates with H I fraction, and anti-correlates with vertical orbital anisotropy. We expect, if anything, the opposite of these

  20. Probing Milky Way's hot gas halo density distribution using the dispersion measure of pulsars

    NASA Astrophysics Data System (ADS)

    Zhezher, Ya. V.; Nugaev, E. Ya.; Rubtsov, G. I.

    2016-03-01

    A number of recent studies indicates a significant amount of ionized gas in a form of the hot gas halo around the Milky Way. The halo extends over the region of 100 kpc and may be acountable for the missing baryon mass. In this paper we calculate the contribution of the proposed halo to the dispersion measure (DM) of the pulsars. The Navarro, Frenk, and White (NFW), Maller and Bullock (MB), and Feldmann, Hooper, and Gnedin (FHG) density distibutions are considered for the gas halo. The data set includes pulsars with the distance known independently from the DM, e.g., pulsars in globular clusters, LMC, SMC and pulsars with known parallax. The results exclude the NFW distribution for the hot gas, while the more realisticMB and FHG models are compatible with the observed dispersion measure.

  1. Effects of dry bulk density and particle size fraction on gas transport parameters in variably saturated landfill cover soil.

    PubMed

    Wickramarachchi, Praneeth; Kawamoto, Ken; Hamamoto, Shoichiro; Nagamori, Masanao; Moldrup, Per; Komatsu, Toshiko

    2011-12-01

    Landfill sites are emerging in climate change scenarios as a significant source of greenhouse gases. The compacted final soil cover at landfill sites plays a vital role for the emission, fate and transport of landfill gases. This study investigated the effects of dry bulk density, ρ(b), and particle size fraction on the main soil-gas transport parameters - soil-gas diffusivity (D(p)/D(o), ratio of gas diffusion coefficients in soil and free air) and air permeability (k(a)) - under variably-saturated moisture conditions. Soil samples were prepared by three different compaction methods (Standard and Modified Proctor compaction, and hand compaction) with resulting ρ(b) values ranging from 1.40 to 2.10 g cm(-3). Results showed that D(p) and k(a) values for the '+gravel' fraction (<35 mm) became larger than for the '-gravel' fraction (<2mm) under variably-saturated conditions for a given soil-air content (ε), likely due to enhanced gas diffusion and advection through less tortuous, large-pore networks. The effect of dry bulk density on D(p) and k(a) was most pronounced for the '+gravel' fraction. Normalized ratios were introduced for all soil-gas parameters: (i) for gas diffusivity D(p)/D(f), the ratio of measured D(p) to D(p) in total porosity (f), (ii) for air permeability k(a)/k(a)(,pF4.1), the ratio of measured k(a) to k(a) at 1235 kPa matric potential (=pF 4.1), and (iii) for soil-air content, the ratio of soil-air content (ε) to total porosity (f) (air saturation). Based on the normalized parameters, predictive power-law models for D(p)(ε/f) and k(a)(ε/f) models were developed based on a single parameter (water blockage factor M for D(p) and P for k(a)). The water blockage factors, M and P, were found to be linearly correlated to ρ(b) values, and the effects of dry bulk density on D(p) and k(a) for both '+gravel' and '-gravel' fractions were well accounted for by the new models. PMID:21813272

  2. Phase Separation, Density Fluctuations, and Boiling Near the Liquid-Gas Critical Point

    NASA Astrophysics Data System (ADS)

    Hegseth, John; Oprisan, Ana; Roy, Arun; Nikolayev, Vadim; Beysens, Daniel; Garrabos, Yves; Lecoutre-Chabot, Carole

    2002-11-01

    A pure liquid-gas mixture is one of the simplest examples of a soft-matter system. In fact, when co-existing gas and liquid phases of pure fluid are heated to their critical point, large-scale density fluctuations make the fluid extremely compressible (to external forces), expandable (to heating), slows the diffusive transport, and decreases the surface tension. In principle these properties and others either diverge to infinity or converge to zero at the critical temperature. These properties lead to some very unusual behavior: large density gradients at the laboratory scale, a large mechanical response to heating, and perfect wetting of a solid wall by the liquid phase (zero contact-angle). We have further simplified this system by performing experiments in weightlessness (Mir spaces station). By controlling the fluid's temperature, these properties may be varied over large ranges in a single sample. When the fluid is driven out of equilibrium by a fast temperature quench from the single-phase (supercritical fluid) state into the two-phase state, we have observed universal growth laws of minority domains (gas bubbles) during phase separation. Prior to this quench we have also observed density fluctuations using optical microscopy near the critical point. When heat is applied to a liquid-gas mixture, we have observed a spectacular spreading of a gas bubble along a hot solid wall as well as gas bubble over-heating (where the interior of a gas bubble gains a higher temperature than the heating wall). Although this gas phase over-heating appears to violate the second law, it is really a transient our-of-equilibrium effect. Inside of these unusual bubbles we also have observed unusually large variations in liquid wetting film thickness that often appear to evolve into spreading contact lines on the sapphire wall when heat is applied. We have observed coarsening and growth of minority domains (gas bubbles) in SF6 near its liquid-gas critical point. Phase separation in

  3. Emission and afterglow properties of an expanding RF plasma with nonuniform neutral gas density

    NASA Astrophysics Data System (ADS)

    Chaplin, Vernon H.; Bellan, Paul M.

    2016-08-01

    We describe some notable aspects of the light emission and afterglow properties in pulsed, high-density ( 1018-1020 m-3 ) argon inductively coupled discharges initiated following fast gas injection. The plasma was created in a long, narrow discharge tube and then expanded downstream of the radiofrequency (RF) antenna into a large chamber. Fast camera images of the expanding plasma revealed a multi-phase time-dependent emission pattern that did not follow the ion density distribution. Dramatic differences in visible brightness were observed between discharges with and without an externally applied magnetic field. These phenomena were studied by tracking excited state populations using passive emission spectroscopy and are discussed in terms of the distinction between ionizing and recombining phase plasmas. Additionally, a method is presented for inferring the unknown neutral gas pressure in the discharge tube from the time-dependent visible and infrared emission measured by a simple photodiode placed near the antenna. In magnetized discharges created with fast gas injection, the downstream ion density rose by Δni˜1018 m-3 in the first ˜100 μs after the RF power was turned off. The conditions conducive to this afterglow density rise are investigated in detail, and the effect is tentatively attributed to pooling ionization.

  4. Measuring direct drive ICF remaining ablator areal density using a gas Cherenkov detector

    NASA Astrophysics Data System (ADS)

    Rubery, Michael; Horsfield, Colin; Herrmann, Hans; Kim, Yongho; Hoffmann, Nelson; Mack, Joseph; Young, Carl; Evans, Scott; Sedillo, Tom; Caldwell, Steven; Grafil, Elliot; Stoeffl, Wolfgang; Milnes, James; Atomic Weapons Establishment PLC Team; Los Alamos National Laboratory Team; Lawrence Livermore National Laboratory Team; Photek Ltd Team

    2013-10-01

    Neutrons from a compressed direct drive ICF target produce γ rays through inelastic interactions with ablator material. The inelastic γ intensity is proportional to the remaining ablator areal density at bang time and the neutron yield. Remaining ablator areal density is an important metric for the quality of the implosion and is strongly correlated with fuel temperature and compression. This contribution describes how a background signal routinely measured on the gas Cherenkov detectors can be used to infer the intensity of the low-energy inelastic gammas from the ablator on the same trace as the DT fusion γ signal, which is directly proportional to the neutron yield; therefore allowing the remaining ablator areal density to be measured in a self consistent manner. Results from recent experiments at the Omega laser facility designed to prove the technique are discussed. In addition, Monte Carlo modelling shows the technique can be used to measure remaining ablator areal density for both plastic and glass capsules.

  5. Gas temperature and density measurements based on spectrally resolved Rayleigh-Brillouin scattering

    NASA Technical Reports Server (NTRS)

    Seasholtz, Richard G.; Lock, James A.

    1992-01-01

    The use of molecular Rayleigh scattering for measurements of gas density and temperature is evaluated. The technique used is based on the measurement of the spectrum of the scattered light, where both temperature and density are determined from the spectral shape. Planar imaging of Rayleigh scattering from air using a laser light sheet is evaluated for ambient conditions. The Cramer-Rao lower bounds for the shot-noise limited density and temperature measurement uncertainties are calculated for an ideal optical spectrum analyzer and for a planar mirror Fabry-Perot interferometer used in a static, imaging mode. With this technique, a single image of the Rayleigh scattered light can be analyzed to obtain density (or pressure) and temperature. Experimental results are presented for planar measurements taken in a heated air stream.

  6. Investigation of the on-axis atom number density in the supersonic gas jet under high gas backing pressure by simulation

    SciTech Connect

    Chen, Guanglong; Xu, Yi; Cao, Yunjiu; Mi, Yiming; Zhang, Xiuli; Wang, Lili; Boldarev, A. S.; Geng, Xiaotao; Kim, Dong Eon

    2015-10-15

    The supersonic gas jets from conical nozzles are simulated using 2D model. The on-axis atom number density in gas jet is investigated in detail by comparing the simulated densities with the idealized densities of straight streamline model in scaling laws. It is found that the density is generally lower than the idealized one and the deviation between them is mainly dependent on the opening angle of conical nozzle, the nozzle length and the gas backing pressure. The density deviation is then used to discuss the deviation of the equivalent diameter of a conical nozzle from the idealized d{sub eq} in scaling laws. The investigation on the lateral expansion of gas jet indicates the lateral expansion could be responsible for the behavior of the density deviation. These results could be useful for the estimation of cluster size and the understanding of experimental results in laser-cluster interaction experiments.

  7. 40 CFR Table W - 7 of Subpart W-Default Methane Emission Factors for Natural Gas Distribution

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... Emission Factors for Natural Gas Distribution W Table W Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR PROGRAMS (CONTINUED) MANDATORY GREENHOUSE GAS REPORTING Petroleum and Natural Gas... for Natural Gas Distribution Natural gas distribution Emission factor (scf/hour/component)...

  8. The topological features of the intracule density of the uniform electron gas

    NASA Astrophysics Data System (ADS)

    Fradera, X.; Sarasola, C.; Ugalde, J. M.; Boyd, R. J.

    1999-05-01

    The Laplacian of the self-consistent-field radial intracule density of the uniform electron gas has been analyzed. It reaches its absolute maximum at the electron-electron coalescence point with a value of 0.3 ρ2, where ρ is the electron charge density. Then, it decreases as the interlectronic distance increases and has an attenuated oscillatory decay at larger distances. Further examination of this function yields an onion-like representation of the spatial structure of the uniform electron gas from the viewpoint of an arbitrary reference electron. Our calculations demonstrate that the radius of the first layer is 13.069 rs and the remaining layers obey a simple relationship with respect to the layer number with a separation of 6.065 rs between adjacent layers.

  9. Electron density and temperature of gas-temperature-dependent cryoplasma jet

    SciTech Connect

    Noma, Yuri; Hyuk Choi, Jai; Muneoka, Hitoshi; Terashima, Kazuo

    2011-03-01

    A microsize cryoplasma jet was developed and analyzed at plasma gas temperatures ranging from room temperature down to 5 K. Experimental results obtained from optical emission spectroscopy and current-voltage measurements indicate that the average electron density and electron temperature of the cryoplasma jet depend on the gas temperature. In particular, the electron temperature in the cryoplasma starts to decrease rapidly near 60 K from about 13 eV at 60 K to 2 eV at 5 K, while the electron density increases from about 10{sup 9} to approximately 10{sup 12} cm{sup -3} from room temperature to 5 K. This phenomenon induces an increase in the Coulomb interaction between electrons, which can be explained by the virial equation of state.

  10. The effective density of randomly moving electrons and related characteristics of materials with degenerate electron gas

    SciTech Connect

    Palenskis, V.

    2014-04-15

    Interpretation of the conductivity of metals, of superconductors in the normal state and of semiconductors with highly degenerate electron gas remains a significant issue if consideration is based on the classical statistics. This study is addressed to the characterization of the effective density of randomly moving electrons and to the evaluation of carrier diffusion coefficient, mobility, and other parameters by generalization of the widely published experimental results. The generalized expressions have been derived for various kinetic parameters attributed to the non-degenerate and degenerate electron gas, by analyzing a random motion of the single type carriers in homogeneous materials. The values of the most important kinetic parameters for different metals are also systematized and discussed. It has been proved that Einstein's relation between the diffusion coefficient and the drift mobility of electrons is held for any level of degeneracy if the effective density of randomly moving carriers is properly taken into account.

  11. Single-particle spectral density of a Bose gas in the two-fluid hydrodynamic regime

    SciTech Connect

    Arahata, Emiko; Nikuni, Tetsuro; Griffin, Allan

    2011-11-15

    In Bose superfluids, the single-particle Green's function can be directly related to the superfluid velocity-velocity correlation function in the hydrodynamic regime. An explicit expression for the single-particle spectral density was originally written down by Hohenberg and Martin in 1965, starting from the two-fluid equations for a superfluid. We give a simple derivation of their results. Using these results, we calculate the relative weights of first and second sound modes in the single-particle spectral density as a function of temperature in a uniform Bose gas. We show that the second sound mode makes a dominant contribution to the single-particle spectrum in a relatively high-temperature region. We also discuss the possibility of experimental observation of the second sound mode in a Bose gas by photoemission spectroscopy.

  12. Thermodynamics of the low-density excluded-volume hadron gas

    NASA Astrophysics Data System (ADS)

    Redlich, Krzysztof; Zalewski, Kacper

    2016-01-01

    We consider the thermodynamics of excluded-volume particles at finite temperature and chemical potential in the low-density approximation. We assume Boltzmann statistics and study the influence of the excluded volume on an ideal gas thermodynamics at the same temperature, pressure, and number of particles. We show that considering the change of the free enthalpy due to the excluded volume, and using the Maxwell identities, one can derive relevant thermodynamic functions and parameters of multicomponent gases. The derivation is quite general, because particles may have different sizes and shapes which can also depend on their momenta. Besides its simplicity and generality, our approach has the advantage of eliminating the transcendental equations occurring in earlier studies. A representative example of the excluded-volume thermodynamics is the single-component gas of hard spheres. For this case, using a virial expansion, the validity limits of the low-density approximation are also discussed.

  13. Buoyancy Effects on Flow Structure and Instability of Low-Density Gas Jets

    NASA Technical Reports Server (NTRS)

    Pasumarthi, Kasyap Sriramachandra

    2004-01-01

    A low-density gas jet injected into a high-density ambient gas is known to exhibit self-excited global oscillations accompanied by large vortical structures interacting with the flow field. The primary objective of the proposed research is to study buoyancy effects on the origin and nature of the flow instability and structure in the near-field of low-density gas jets. Quantitative rainbow schlieren deflectometry, Computational fluid dynamics (CFD) and Linear stability analysis were the techniques employed to scale the buoyancy effects. The formation and evolution of vortices and scalar structure of the flow field are investigated in buoyant helium jets discharged from a vertical tube into quiescent air. Oscillations at identical frequency were observed throughout the flow field. The evolving flow structure is described by helium mole percentage contours during an oscillation cycle. Instantaneous, mean, and RMS concentration profiles are presented to describe interactions of the vortex with the jet flow. Oscillations in a narrow wake region near the jet exit are shown to spread through the jet core near the downstream location of the vortex formation. The effects of jet Richardson number on characteristics of vortex and flow field are investigated and discussed. The laminar, axisymmetric, unsteady jet flow of helium injected into air was simulated using CFD. Global oscillations were observed in the flow field. The computed oscillation frequency agreed qualitatively with the experimentally measured frequency. Contours of helium concentration, vorticity and velocity provided information about the evolution and propagation of vortices in the oscillating flow field. Buoyancy effects on the instability mode were evaluated by rainbow schlieren flow visualization and concentration measurements in the near-field of self-excited helium jets undergoing gravitational change in the microgravity environment of 2.2s drop tower at NASA John H. Glenn Research Center. The jet

  14. Testing the gas mass density profile of galaxy clusters with distance duality relation

    NASA Astrophysics Data System (ADS)

    Cao, Shuo; Biesiada, Marek; Zheng, Xiaogang; Zhu, Zong-Hong

    2016-03-01

    In this paper, assuming the validity of distance duality relation, η = DL(z)(1 + z)-2/DA(z) = 1, where DA(z) and DL(z) are the angular and the luminosity distance, respectively, we explore two kinds of gas mass density profiles of clusters: the isothermal β model and the non-isothermal double-β model. In our analysis, performed on 38 massive galaxy clusters observed by Chandra (within the redshift range of 0.14 < z < 0.89), we use two types of cluster gas mass fraction data corresponding to different mass density profiles fitted to the X-ray data. Using two general parameterizations of η(z) (phenomenologically allowing for distance duality violation), we find that the non-isothermal double-β model agrees better with the distance duality relation, while the isothermal β model tends to be marginally incompatible with the Etherington theorem at 68.3 per cent confidence level (CL). However, current accuracy of the data does not allow to distinguish between the two models for the gas-density distribution at a significant level.

  15. HIGH-DENSITY MOLECULAR GAS PROPERTIES OF THE STARBURST GALAXY NGC 1614 REVEALED WITH ALMA

    SciTech Connect

    Imanishi, Masatoshi; Nakanishi, Kouichiro

    2013-09-15

    We present the results of HCN/HCO{sup +}/HNC J = 4-3 transition line observations of the nearby starburst galaxy NGC 1614, obtained with ALMA Cycle 0. We find that high density molecular gas traced with these lines shows a velocity structure such that the northern (southern) side of the nucleus is redshifted (blueshifted) with respect to the nuclear velocity of this galaxy. The redshifted and blueshifted emission peaks are offset by {approx}0.''6 at the northern and southern sides of the nucleus, respectively. At these offset positions, observations at infrared >3 {mu}m indicate the presence of active dusty starbursts, supporting the picture that high-density molecular gas is the site of active starbursts. The enclosed dynamical mass within the central {approx}2'' in radius, derived from the dynamics of the high-density molecular gas, is {approx}10{sup 9} M{sub Sun }, which is similar to previous estimates. Finally, the HCN emission is weaker than HCO{sup +} but stronger than HNC for J = 4-3 for all starburst regions of NGC 1614, as seen for J = 1-0 transition lines in starburst-dominated galaxies.

  16. R-Z Density Mapping and CFD Simulation of Gas Puff Nozzle Flow

    NASA Astrophysics Data System (ADS)

    McKee, Erik; Valenzuela, Julio; Krasheninnikov, Igor; Frazier, Alister; Covington, Aaron; Beg, Farhat; Darling, Tim; Nevada Terawatt Facility Team; University of San Diego Team

    2015-11-01

    Laser induced fluorescence (LIF) is a technique in which a tracer is added to the gas flow for measurement of its spatial and temporal density profile. The Nd:YAG EKSPLA laser 20mJ/150ps at the fourth harmonic 266nm wavelength is focused down to a <1mm pencil beam to excite the acetone tracer. The use of anr ICCD gating camera is necessary because the 4ns short-lived fluorescence state is an order-of-magnitude dimmer than the 200us long-lived phosphorescence state. Mapping the density profile in time and space requires multiple shots. Once the temporal and spatial density profile is obtained, it can be used and benchmarked for two independent CFD software programs using transient solvers: OpenFOAM and FLUENT. The measurements and simulations serve as the initial conditions for (i) Gas Puff experiments that utilize special nozzle contours to inject the gas load between the electrode gap on pulsed-power machines and (ii) use with future MHD modeling efforts. Support for this work is provided by DOE/NNSA grant DE-NA0002075 and funded by the US Department of Energy, ARPA-E, Control Number 1184-1527.

  17. Density-conserving shape factors for particle simulations in cylindrical and spherical coordinates

    SciTech Connect

    Ruyten, W.M. )

    1993-04-01

    It is shown that, in cylindrical and spherical coordinates, particle-to- grid weighting based on conventional particle-in-cell (PIC) and cloud-in-cell (CIC) shape factors results in non-uniform grid densities even for uniform particle distributions. Instead, alternative, density-conserving weighting schemes are discussed, including modified PIC and CIC weighting. 10 refs., 5 figs.

  18. In-Shell Bulk Density as an Estimator of Farmers Stock Grade Factors

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The objective of this research was to determine whether or not bulk density can be used to accurately estimate farmer stock grade factors such as total sound mature kernels and other kernels. Physical properties including bulk density, pod size and kernel size distributions are measured as part of t...

  19. Density functional theory of gas-liquid phase separation in dilute binary mixtures.

    PubMed

    Okamoto, Ryuichi; Onuki, Akira

    2016-06-22

    We examine statics and dynamics of phase-separated states of dilute binary mixtures using density functional theory. In our systems, the difference of the solvation chemical potential between liquid and gas [Formula: see text] (the Gibbs energy of transfer) is considerably larger than the thermal energy [Formula: see text] for each solute particle and the attractive interaction among the solute particles is weaker than that among the solvent particles. In these conditions, the saturated vapor pressure increases by [Formula: see text], where [Formula: see text] is the solute density added in liquid. For [Formula: see text], phase separation is induced at low solute densities in liquid and the new phase remains in gaseous states, even when the liquid pressure is outside the coexistence curve of the solvent. This explains the widely observed formation of stable nanobubbles in ambient water with a dissolved gas. We calculate the density and stress profiles across planar and spherical interfaces, where the surface tension decreases with increasing interfacial solute adsorption. We realize stable solute-rich bubbles with radius about 30 nm, which minimize the free energy functional. We then study dynamics around such a bubble after a decompression of the surrounding liquid, where the bubble undergoes a damped oscillation. In addition, we present some exact and approximate expressions for the surface tension and the interfacial stress tensor. PMID:27115676

  20. Density-conserving shape factors for particle simulations in cylindrical and spherical coordinates

    NASA Technical Reports Server (NTRS)

    Ruyten, Wilhelmus M.

    1993-01-01

    It is established that a particle-to-grid weighting which is based on both conventional particle-in-cell (PIC) and cloud-in-cell (CIC) shape factors will yield nonuniform grid densities, even in the case of uniform particle distributions, in both cylindrical and spherical coordinates. In view of this, alternative density-conserving weighting schemes are discussed which encompass modified PIC and CIC weighting. These alternative shape factors are mathematically no more complicated than the conventional nondensity-conserving expressions.

  1. The factors controlling species density in herbaceous plant communities: An assessment

    USGS Publications Warehouse

    Grace, J.B.

    1999-01-01

    This paper evaluates both the ideas and empirical evidence pertaining to the control of species density in herbaceous plant communities. While most theoretical discussions of species density have emphasized the importance of habitat productivity and disturbance regimes, many other factors (e.g. species pools, plant litter accumulation, plant morphology) have been proposed to be important. A review of literature presenting observations on the density of species in small plots (in the vicinity of a few square meters or less), as well as experimental studies, suggests several generalizations: (1) Available data are consistent with an underlying unimodal relationship between species density and total community biomass. While variance in species density is often poorly explained by predictor variables, there is strong evidence that high levels of community biomass are antagonistic to high species density. (2) Community biomass is just one of several factors affecting variations in species density. Multivariate analyses typically explain more than twice as much variance in species density as can be explained by community biomass alone. (3) Disturbance has important and sometimes complex effects on species density. In general, the evidence is consistent with the intermediate disturbance hypothesis but exceptions exist and effects can be complex. (4) Gradients in the species pool can have important influences on patterns of species density. Evidence is mounting that a considerable amount of the observed variability in species density within a landscape or region may result from environmental effects on the species pool. (5) Several additional factors deserve greater consideration, including time lags, species composition, plant morphology, plant density and soil microbial effects. Based on the available evidence, a conceptual model of the primary factors controlling species density is presented here. This model suggests that species density is controlled by the effects of

  2. Effects of dry bulk density and particle size fraction on gas transport parameters in variably saturated landfill cover soil

    SciTech Connect

    Wickramarachchi, Praneeth; Kawamoto, Ken; Hamamoto, Shoichiro; Nagamori, Masanao; Moldrup, Per; Komatsu, Toshiko

    2011-12-15

    Highlights: > The effects of soil physical properties on gas transport parameters were investigated. > Higher values of D{sub p} and k{sub a} exhibited in the '+gravel' than the '-gravel' fraction at same soil-air content ({epsilon}). > Recent power law models for D{sub p} (WLR) and k{sub a} (RPL) were modified. > Model parameters were linearly related to easily measurable dry bulk density ({rho}{sub b}). - Abstract: Landfill sites are emerging in climate change scenarios as a significant source of greenhouse gases. The compacted final soil cover at landfill sites plays a vital role for the emission, fate and transport of landfill gases. This study investigated the effects of dry bulk density, {rho}{sub b}, and particle size fraction on the main soil-gas transport parameters - soil-gas diffusivity (D{sub p}/D{sub o}, ratio of gas diffusion coefficients in soil and free air) and air permeability (k{sub a}) - under variably-saturated moisture conditions. Soil samples were prepared by three different compaction methods (Standard and Modified Proctor compaction, and hand compaction) with resulting {rho}{sub b} values ranging from 1.40 to 2.10 g cm{sup -3}. Results showed that D{sub p} and k{sub a} values for the '+gravel' fraction (<35 mm) became larger than for the '-gravel' fraction (<2 mm) under variably-saturated conditions for a given soil-air content ({epsilon}), likely due to enhanced gas diffusion and advection through less tortuous, large-pore networks. The effect of dry bulk density on D{sub p} and k{sub a} was most pronounced for the '+gravel' fraction. Normalized ratios were introduced for all soil-gas parameters: (i) for gas diffusivity D{sub p}/D{sub f}, the ratio of measured D{sub p} to D{sub p} in total porosity (f), (ii) for air permeability k{sub a}/k{sub a,pF4.1}, the ratio of measured k{sub a} to k{sub a} at 1235 kPa matric potential (=pF 4.1), and (iii) for soil-air content, the ratio of soil-air content ({epsilon}) to total porosity (f) (air

  3. Space Charge Neutralization of DEMO Relevant Negative Ion Beams at Low Gas Density

    SciTech Connect

    Surrey, Elizabeth; Porton, Michael

    2011-09-26

    The application of neutral beams to future power plant devices (DEMO) is dependent on achieving significantly improved electrical efficiency and the most promising route to achieving this is by implementing a photoneutralizer in place of the traditional gas neutralizer. A corollary of this innovation would be a significant reduction in the background gas density through which the beam is transported between the accelerator and the neutralizer. This background gas is responsible for the space charge neutralization of the beam, enabling distances of several metres to be traversed without significant beam expansion. This work investigates the sensitivity of a D{sup -} beam to reduced levels of space charge compensation for energies from 100 keV to 1.5 MeV, representative of a scaled prototype experiment, commissioning and full energy operation. A beam transport code, following the evolution of the phase space ellipse, is employed to investigate the effect of space charge on the beam optics. This shows that the higher energy beams are insensitive to large degrees of under compensation, unlike the lower energies. The probable degree of compensation at low gas density is then investigated through a simple, two component beam-plasma model that allows the potential to be negative. The degree of under-compensation is dependent on the positive plasma ion energy, one source of which is dissociation of the gas by the beam. The subsequent space charge state of the beam is shown to depend upon the relative times for equilibration of the dissociation energy and ionization by the beam ions.

  4. Gas Transport Parameters for Landfill Final Cover Soil: Measurements and Model Modification by Dry Bulk Density

    NASA Astrophysics Data System (ADS)

    Wickramarachchi, P. N.; Kawamoto, K.; Hamamoto, S.; Nagamori, M.; Moldrup, P.; Komatsu, T.

    2011-12-01

    Landfill sites have been emerging in greenhouse warming scenarios as a significant source of atmospheric methane (CH4). Until recently, landfill management strategies have mainly addressed the problem of preventing groundwater contamination and reduction of leachate generation. Being one of the largest sources of anthropogenic CH4 emission, the final cover system should also be designed for minimizing the greenhouse gases migration into the atmosphere or the areas surrounding the landfill while securing the hydraulic performance. Compared to the intensive research efforts on hydraulic performances of landfill final cover soil, few studies about gas transport characteristics of landfill cover soils have been done. However, recent soil-gas studies implied that the effects of soil physical properties such as bulk density (i.e., compaction level), soil particle size are key parameters to understand landfill gaseous performance. The gas exchange through the final cover soils is controlled by advective and diffusive gas transport. Air permeability (ka) governs the advective gas transport while the soil-gas diffusion coefficient (Dp) governs diffusive gas transport. In this study, the effects of compaction level and particle size fraction effects on ka and Dp for landfill final cover soil was investigated. The disturbed soil samples were taken from landfill final cover in Japan. A compaction tests were performed for the soil samples with two different size fractions (< 35 mm and < 2.0 mm). In the compaction tests at field water content , the soil samples were repacked into soil cores (i.d. 15-cm, length 12-cm, 2120 cm3) at two different compaction levels [(MP):2700 kN/m2 and (SP):600 kN/m2]. After the compaction tests, ka and Dp were measured and then samples were saturated and subsequently drained at different soil-water matric potential of 0.98, 2.94, 9.81, 1235 kPa and with air-dried and oven-dried conditions. Results showed that measured Dp and ka values for the

  5. Microstructural analysis of mass transport phenomena in gas diffusion media for high current density operation in PEM fuel cells

    NASA Astrophysics Data System (ADS)

    Kotaka, Toshikazu; Tabuchi, Yuichiro; Mukherjee, Partha P.

    2015-04-01

    Cost reduction is a key issue for commercialization of fuel cell electric vehicles (FCEV). High current density operation is a solution pathway. In order to realize high current density operation, it is necessary to reduce mass transport resistance in the gas diffusion media commonly consisted of gas diffusion layer (GDL) and micro porous layer (MPL). However, fundamental understanding of the underlying mass transport phenomena in the porous components is not only critical but also not fully understood yet due to the inherent microstructural complexity. In this study, a comprehensive analysis of electron and oxygen transport in the GDL and MPL is conducted experimentally and numerically with three-dimensional (3D) microstructural data to reveal the structure-transport relationship. The results reveal that the mass transport in the GDL is strongly dependent on the local microstructural variations, such as local pore/solid volume fractions and connectivity. However, especially in the case of the electrical conductivity of MPL, the contact resistance between carbon particles is the dominant factor. This suggests that reducing the contact resistance between carbon particles and/or the number of contact points along the transport pathway can improve the electrical conductivity of MPL.

  6. Velocity and density profiles of granular flow in channels using a lattice gas automaton

    SciTech Connect

    Peng, G.; Ohta, T.

    1997-06-01

    We have performed two-dimensional lattice-gas-automaton simulations of granular flow between two parallel planes. We find that the velocity profiles have nonparabolic distributions, while simultaneously the density profiles are nonuniform. Under nonslip boundary conditions, deviation of velocity profiles from the parabolic form of Newtonian fluids is found to be characterized solely by ratio of maximal velocity at the center to the average velocity, though the ratio depends on the model parameters in a complex manner. We also find that the maximal velocity (u{sub max}) at the center is a linear function of the driving force (g) as u{sub max}={alpha}g{minus}{delta} with nonzero {delta} in contrast with Newtonian fluids. Regarding density profiles, we observe that densities near the boundaries are higher than those in the center. The width of higher densities (above the average density) relative to the channel width is a decreasing function of a variable which scales with the driving force (g), energy dissipation parameter ({epsilon}), and the width of the system (L) as g{sup {mu}}L{sup {nu}}/{epsilon} with exponents {mu}=1.4{plus_minus}0.1 and {nu}=0.5{plus_minus}0.1. A phenomenological theory based on a scaling argument is presented to interpret these findings. {copyright} {ital 1997} {ital The American Physical Society}

  7. Effective mass and Landé g-factor in Si-MOSFETs near the critical density

    NASA Astrophysics Data System (ADS)

    Limouny, Lhoussine; El Kaaouachi, Abdelhamid; Liang, Chi-Te

    2014-02-01

    We analyze the electrical resistivity and conductivity of a dilute two-dimensional electron gas (2DEG) in a Si metal-oxide-semiconductor field-effect transistor. When a magnetic field is applied parallel to the plane of the 2DEG, a signature of complete spin polarization, as evidenced by the saturation of the resistivity, is observed. We measured the effective mass and the Landé g-factor near the metal-insulator transition (MIT) and found that the Landé g-factor remained almost constant and close to its value in bulk silicon. In contrast, we have observed a sharp increase in the effective mass near the critical density of the MIT. Our new results suggest that the sharp increase in the previously-observed spin susceptibility is mainly due to the enhanced effective mass. Therefore, renormalization of the effective mass could play an important role in a dilute spinpolarized 2DEG. The data indicate that electron-electron interactions strongly modify the effective mass but only weakly affect the g-factor in a dilute 2DEG. Moreover, our results indicate that B c , which corresponds to the magnetic field at which the magnetoresistivity reaches saturation, vanishes at a characteristic density n χ higher than the critical density n c of the MIT. This is in contrast to the existing experimental results, and further studies are required if this discrepancy is to be understood.

  8. GAS SURFACE DENSITY, STAR FORMATION RATE SURFACE DENSITY, AND THE MAXIMUM MASS OF YOUNG STAR CLUSTERS IN A DISK GALAXY. I. THE FLOCCULENT GALAXY M 33

    SciTech Connect

    Gonzalez-Lopezlira, Rosa A.; Pflamm-Altenburg, Jan; Kroupa, Pavel

    2012-12-20

    We analyze the relationship between maximum cluster mass M{sub max} and surface densities of total gas ({Sigma}{sub gas}), molecular gas ({Sigma}{sub H{sub 2}}), and star formation rate ({Sigma}{sub SFR}) in the flocculent galaxy M 33, using published gas data and a catalog of more than 600 young star clusters in its disk. By comparing the radial distributions of gas and most massive cluster masses, we find that M{sub max}{proportional_to}{Sigma}{sup 4.7{+-}0.4}{sub gas}, M{sub max}{proportional_to}{Sigma}{sup 1.3{+-}0.1}{sub H{sub 2}}, and M{sub max}{proportional_to}{Sigma}{sup 1.0{+-}0.1}{sub SFR}. We rule out that these correlations result from the size of the sample; hence, the change of the maximum cluster mass must be due to physical causes.

  9. Body density and diving gas volume of the northern bottlenose whale (Hyperoodon ampullatus)

    PubMed Central

    Miller, Patrick; Narazaki, Tomoko; Isojunno, Saana; Aoki, Kagari; Smout, Sophie; Sato, Katsufumi

    2016-01-01

    ABSTRACT Diving lung volume and tissue density, reflecting lipid store volume, are important physiological parameters that have only been estimated for a few breath-hold diving species. We fitted 12 northern bottlenose whales with data loggers that recorded depth, 3-axis acceleration and speed either with a fly-wheel or from change of depth corrected by pitch angle. We fitted measured values of the change in speed during 5 s descent and ascent glides to a hydrodynamic model of drag and buoyancy forces using a Bayesian estimation framework. The resulting estimate of diving gas volume was 27.4±4.2 (95% credible interval, CI) ml kg−1, closely matching the measured lung capacity of the species. Dive-by-dive variation in gas volume did not correlate with dive depth or duration. Estimated body densities of individuals ranged from 1028.4 to 1033.9 kg m−3 at the sea surface, indicating overall negative tissue buoyancy of this species in seawater. Body density estimates were highly precise with ±95% CI ranging from 0.1 to 0.4 kg m−3, which would equate to a precision of <0.5% of lipid content based upon extrapolation from the elephant seal. Six whales tagged near Jan Mayen (Norway, 71°N) had lower body density and were closer to neutral buoyancy than six whales tagged in the Gully (Nova Scotia, Canada, 44°N), a difference that was consistent with the amount of gliding observed during ascent versus descent phases in these animals. Implementation of this approach using longer-duration tags could be used to track longitudinal changes in body density and lipid store body condition of free-ranging cetaceans. PMID:27296044

  10. Body density and diving gas volume of the northern bottlenose whale (Hyperoodon ampullatus).

    PubMed

    Miller, Patrick; Narazaki, Tomoko; Isojunno, Saana; Aoki, Kagari; Smout, Sophie; Sato, Katsufumi

    2016-08-15

    Diving lung volume and tissue density, reflecting lipid store volume, are important physiological parameters that have only been estimated for a few breath-hold diving species. We fitted 12 northern bottlenose whales with data loggers that recorded depth, 3-axis acceleration and speed either with a fly-wheel or from change of depth corrected by pitch angle. We fitted measured values of the change in speed during 5 s descent and ascent glides to a hydrodynamic model of drag and buoyancy forces using a Bayesian estimation framework. The resulting estimate of diving gas volume was 27.4±4.2 (95% credible interval, CI) ml kg(-1), closely matching the measured lung capacity of the species. Dive-by-dive variation in gas volume did not correlate with dive depth or duration. Estimated body densities of individuals ranged from 1028.4 to 1033.9 kg m(-3) at the sea surface, indicating overall negative tissue buoyancy of this species in seawater. Body density estimates were highly precise with ±95% CI ranging from 0.1 to 0.4 kg m(-3), which would equate to a precision of <0.5% of lipid content based upon extrapolation from the elephant seal. Six whales tagged near Jan Mayen (Norway, 71°N) had lower body density and were closer to neutral buoyancy than six whales tagged in the Gully (Nova Scotia, Canada, 44°N), a difference that was consistent with the amount of gliding observed during ascent versus descent phases in these animals. Implementation of this approach using longer-duration tags could be used to track longitudinal changes in body density and lipid store body condition of free-ranging cetaceans. PMID:27296044

  11. Molecular density functional theory for water with liquid-gas coexistence and correct pressure

    SciTech Connect

    Jeanmairet, Guillaume Levesque, Maximilien; Sergiievskyi, Volodymyr; Borgis, Daniel

    2015-04-21

    The solvation of hydrophobic solutes in water is special because liquid and gas are almost at coexistence. In the common hypernetted chain approximation to integral equations, or equivalently in the homogenous reference fluid of molecular density functional theory, coexistence is not taken into account. Hydration structures and energies of nanometer-scale hydrophobic solutes are thus incorrect. In this article, we propose a bridge functional that corrects this thermodynamic inconsistency by introducing a metastable gas phase for the homogeneous solvent. We show how this can be done by a third order expansion of the functional around the bulk liquid density that imposes the right pressure and the correct second order derivatives. Although this theory is not limited to water, we apply it to study hydrophobic solvation in water at room temperature and pressure and compare the results to all-atom simulations. The solvation free energy of small molecular solutes like n-alkanes and hard sphere solutes whose radii range from angstroms to nanometers is now in quantitative agreement with reference all atom simulations. The macroscopic liquid-gas surface tension predicted by the theory is comparable to experiments. This theory gives an alternative to the empirical hard sphere bridge correction used so far by several authors.

  12. Optimizing the hohlraum gas density for better symmetry control of indirect drive implosion experiments

    NASA Astrophysics Data System (ADS)

    Izumi, Nobuhiko; Hall, G. N.; Nagel, S. R.; Khan, S.; Rygg, R. R.; MacKinnon, A. J.; Ho, D. D.; Berzak Hopkins, L.; Jones, O. S.; Town, R. P. J.; Bradley, D. K.

    2014-10-01

    To achieve a spherically symmetric implosion, control of drive uniformity is essential. Both the ablation pressure and the mass ablation rate on the capsule surface should be made as uniform as possible for the duration of the drive. For an indirect drive implosion, the drive uniformity changes during the pulse because of: (1) the dynamic movement of the laser spots due to blow-off of the hohlraum wall, and (2) cross-beam energy transfer caused by laser-plasma interaction in the hohlraum. To tamp the wall blow-off, we use gas filled hohlraums. The cross-beam energy transfer can be controlled by applying a wave length separation between the cones of the laser beams. However, both of those dynamic effects are sensitive to the initial density of the hohlraum gas fill. To assess this, we performed implosion experiments with different hohlraum gas densities and tested the effect on drive asymmetry. The uniformity of the acceleration was measured by in-flight x-ray backlit imaging of the capsule. The uniformity of the core assembly was observed by imaging the self emission x-ray from the core. We will report on the experimental results and compare them to hydrodynamic simulations. Prepared by LLNL under Contract DE-AC52-07NA27344. LLNL-ABS-626372.

  13. Validity of power functionals for a homogeneous electron gas in reduced-density-matrix-functional theory

    NASA Astrophysics Data System (ADS)

    Putaja, A.; Eich, F. G.; Baldsiefen, T.; Räsänen, E.

    2016-03-01

    Physically valid and numerically efficient approximations for the exchange and correlation energy are critical for reduced-density-matrix-functional theory to become a widely used method in electronic structure calculations. Here we examine the physical limits of power functionals of the form f (n ,n') =(nn')α for the scaling function in the exchange-correlation energy. To this end we obtain numerically the minimizing momentum distributions for the three- and two-dimensional homogeneous electron gas, respectively. In particular, we examine the limiting values for the power α to yield physically sound solutions that satisfy the Lieb-Oxford lower bound for the exchange-correlation energy and exclude pinned states with the condition n (k )<1 for all wave vectors k . The results refine the constraints previously obtained from trial momentum distributions. We also compute the values for α that yield the exact correlation energy and its kinetic part for both the three- and two-dimensional electron gas. In both systems, narrow regimes of validity and accuracy are found at α ≳0.6 and at rs≳10 for the density parameter, corresponding to relatively low densities.

  14. Simulations of gas puff effects on edge density and ICRF coupling in ASDEX upgrade using EMC3-Eirene

    SciTech Connect

    Zhang, W.; Lunt, T.; Bobkov, V.; Coster, D.; Brida, D.; Noterdaeme, J.-M.; Jacquet, P.; Feng, Y.

    2015-12-10

    Simulations were carried out with the 3D plasma transport code EMC3-EIRENE, to study the deuterium gas (D{sub 2}) puff effects on edge density and the coupling of Ion Cyclotron Range of Frequency (ICRF) power in ASDEX Upgrade. Firstly we simulated an inter-ELM phase of an H-mode discharge with a moderate (1.2 × 10{sup 22} electrons/s) lower divertor gas puff. Then we changed the gas source positions to the mid-plane or top of machine while keeping other conditions the same. Cases with different mid-plane or top gas valves are investigated. Our simulations indicate that compared to lower divertor gas puffing, the mid-plane gas puff can enhance the local density in front of the antennas most effectively, while a rather global (toroidally uniform) but significantly smaller enhancement is found for top gas puffing. Our results show quantitative agreement with the experiments.

  15. Factors associated with low bone density in patients referred for assessment of bone health

    PubMed Central

    2013-01-01

    Background To identify factors that predict low bone mineral density (BMD) in pediatric patients referred for dual-energy x-ray absorptiometry assessments. Methods This is a retrospective cohort study of 304 children and adolescents referred for dual-energy x-ray absorptiometry assessments at a tertiary care center. Outcomes included risk factors which predicted a significant low bone density for age, defined as BMD Z-score ≤ -2.0 SD. A univariate analysis involved Chi-square, Fisher’s Exact test, and analysis of variance, and multivariate logistic regression models were constructed to determine predictors of low bone mineral density. Results In the multivariate logistic regression model, predictors of low bone mineral density included low body mass index Z-score (odds ratio 0.52, 95% confidence interval 0.39 – 0.69), low height Z-score (OR 0.71, 95% CI 0.57 – 0.88), vitamin D insufficiency (OR 3.97, 95% CI 2.08 – 7.59), and history of bone marrow transplant (OR 5.78, 95% CI 1.00 – 33.45). Conclusions Underlying health problems and associated treatments can impair bone mineral accrual. We identified risk factors most predictive of low bone mineral density in subjects referred for bone density measurement. Recognition of these factors may allow for earlier assessment to maximize bone mass in at-risk children. PMID:23388217

  16. Spontaneous separation of large-spin Fermi gas in the harmonic trap: a density functional study

    PubMed Central

    Sun, Zongli; Gu, Qiang

    2016-01-01

    The component separation of the trapped large-spin Fermi gas is studied within density functional theory. The ground state and ferromagnetic transition in the gas, with and without the spin mixing collision, are calculated. In the absence of spin mixing, two patterns of separation are observed as the interaction between atoms increases, whereas only one of them corresponds to a ferromagnetic transition. The phase diagram suggests that the pattern which the system chooses depends on the interaction strength in the collision channels. With the presence of spin mixing, the distribution of phase region changes because of the interplay between different collision channels. Specifically, the spin exchange benefits the FM transition, while it suppresses the component separation of CS-II pattern. PMID:27549012

  17. Dust and gas density evolution at a radial pressure bump in protoplanetary disks

    NASA Astrophysics Data System (ADS)

    Taki, Tetsuo; Fujimoto, Masaki; Ida, Shigeru

    2016-06-01

    We investigate the simultaneous evolution of dust and gas density profiles at a radial pressure bump located in a protoplanetary disk. If dust particles are treated as test particles, a radial pressure bump traps dust particles that drift radially inward. As the dust particles become more concentrated at the gas pressure bump, however, the drag force from dust to gas (back-reaction), which is ignored in a test-particle approach, deforms the pressure bump. We find that the pressure bump is completely deformed by the back-reaction when the dust-to-gas mass ratio reaches ~ 1 for a slower bump restoration. The direct gravitational instability of dust particles is inhibited by the bump destruction. In the dust-enriched region, the radial pressure support becomes ~ 10-100 times lower than the global value set initially. Although the pressure bump is a favorable place for streaming instability (SI), the flattened pressure gradient inhibits SI from forming large particle clumps corresponding to 100-1000 km sized bodies, which has been previously proposed. If SI occurs there, the dust clumps formed would be 10-100 times smaller, that is, of about 1-100 km.

  18. Effects of hepatocyte growth factor on glutathione synthesis, growth, and apoptosis is cell density-dependent

    SciTech Connect

    Yang Heping; Magilnick, Nathaniel; Xia Meng; Lu, Shelly C.

    2008-01-15

    Hepatocyte growth factor (HGF) is a potent hepatocyte mitogen that exerts opposing effects depending on cell density. Glutathione (GSH) is the main non-protein thiol in mammalian cells that modulates growth and apoptosis. We previously showed that GSH level is inversely related to cell density of hepatocytes and is positively related to growth. Our current work examined whether HGF can modulate GSH synthesis in a cell density-dependent manner and how GSH in turn influence HGF's effects. We found HGF treatment of H4IIE cells increased cell GSH levels only under subconfluent density. The increase in cell GSH under low density was due to increased transcription of GSH synthetic enzymes. This correlated with increased protein levels and nuclear binding activities of c-Jun, c-Fos, p65, p50, Nrf1 and Nrf2 to the promoter region of these genes. HGF acts as a mitogen in H4IIE cells under low cell density and protects against tumor necrosis factor {alpha} (TNF{alpha})-induced apoptosis by limiting JNK activation. However, HGF is pro-apoptotic under high cell density and exacerbates TNF{alpha}-induced apoptosis by potentiating JNK activation. The increase in cell GSH under low cell density allows HGF to exert its full mitogenic effect but is not necessary for its anti-apoptotic effect.

  19. Technical Factors Influencing Cone Packing Density Estimates in Adaptive Optics Flood Illuminated Retinal Images

    PubMed Central

    Lombardo, Marco; Serrao, Sebastiano; Lombardo, Giuseppe

    2014-01-01

    Purpose To investigate the influence of various technical factors on the variation of cone packing density estimates in adaptive optics flood illuminated retinal images. Methods Adaptive optics images of the photoreceptor mosaic were obtained in fifteen healthy subjects. The cone density and Voronoi diagrams were assessed in sampling windows of 320×320 µm, 160×160 µm and 64×64 µm at 1.5 degree temporal and superior eccentricity from the preferred locus of fixation (PRL). The technical factors that have been analyzed included the sampling window size, the corrected retinal magnification factor (RMFcorr), the conversion from radial to linear distance from the PRL, the displacement between the PRL and foveal center and the manual checking of cone identification algorithm. Bland-Altman analysis was used to assess the agreement between cone density estimated within the different sampling window conditions. Results The cone density declined with decreasing sampling area and data between areas of different size showed low agreement. A high agreement was found between sampling areas of the same size when comparing density calculated with or without using individual RMFcorr. The agreement between cone density measured at radial and linear distances from the PRL and between data referred to the PRL or the foveal center was moderate. The percentage of Voronoi tiles with hexagonal packing arrangement was comparable between sampling areas of different size. The boundary effect, presence of any retinal vessels, and the manual selection of cones missed by the automated identification algorithm were identified as the factors influencing variation of cone packing arrangements in Voronoi diagrams. Conclusions The sampling window size is the main technical factor that influences variation of cone density. Clear identification of each cone in the image and the use of a large buffer zone are necessary to minimize factors influencing variation of Voronoi diagrams of the cone

  20. Column Density Maps of the I-GALFA HI Survey: Evidence for Dark Gas?

    NASA Astrophysics Data System (ADS)

    Gibson, Steven J.; Koo, B.; Douglas, K. A.; Newton, J. H.; Peek, J. E.; Hughes, J. M.; Spraggs, M.; Park, G.; Kang, J.; Heiles, C. E.; Korpela, E. J.

    2014-01-01

    The gas in galactic disks, including our own, occurs in a wide range of temperatures and densities, most of which are unsuitable for star formation. Somehow, diffuse atomic clouds are collected into colder, denser molecular clouds that can collapse under their own gravity. The molecular condensation process is not directly observable, and the gas itself is often ``dark'' to standard probes like optically thin HI 21cm emission or the CO 2.6mm line. However, the presence of this dark gas can often be inferred from infrared dust emission in excess of what is expected for the observed HI and CO content. We have mapped apparent HI column densities in the Inner-Galaxy Arecibo L-band Feed Array (I-GALFA) survey, which covers a 1600 square degree region at 4-arcminute resolution in the first Galactic quadrant. We compare these ``naive'' HI columns to others derived from Planck first-release CO and dust maps and NE2001 model dispersion measures to identify a number of areas with potentially significant dark gas. We discuss whether optically thick HI or CO-free H2 is more likely to dominate the dark column, and we consider the effects of possible biases on our results. We acknowledge support from the National Science Foundation, the NASA Kentucky Space Grant Consortium, Western Kentucky University, and the Gatton Academy. I-GALFA (www.naic.edu igalfa) is a GALFA-HI survey observed with the 7-beam ALFA receiver on the 305-meter William E. Gordon Telescope. The Arecibo Observatory is a U.S. National Science Foundation facility operated under sequential cooperative agreements with Cornell University and SRI International, the latter in alliance with the Ana G. Mendez-Universidad Metropolitana and the Universities Space Research Association.

  1. Supersonic beams at high particle densities: model description beyond the ideal gas approximation.

    PubMed

    Christen, Wolfgang; Rademann, Klaus; Even, Uzi

    2010-10-28

    Supersonic molecular beams constitute a very powerful technique in modern chemical physics. They offer several unique features such as a directed, collision-free flow of particles, very high luminosity, and an unsurpassed strong adiabatic cooling during the jet expansion. While it is generally recognized that their maximum flow velocity depends on the molecular weight and the temperature of the working fluid in the stagnation reservoir, not a lot is known on the effects of elevated particle densities. Frequently, the characteristics of supersonic beams are treated in diverse approximations of an ideal gas expansion. In these simplified model descriptions, the real gas character of fluid systems is ignored, although particle associations are responsible for fundamental processes such as the formation of clusters, both in the reservoir at increased densities and during the jet expansion. In this contribution, the various assumptions of ideal gas treatments of supersonic beams and their shortcomings are reviewed. It is shown in detail that a straightforward thermodynamic approach considering the initial and final enthalpy is capable of characterizing the terminal mean beam velocity, even at the liquid-vapor phase boundary and the critical point. Fluid properties are obtained using the most accurate equations of state available at present. This procedure provides the opportunity to naturally include the dramatic effects of nonideal gas behavior for a large variety of fluid systems. Besides the prediction of the terminal flow velocity, thermodynamic models of isentropic jet expansions permit an estimate of the upper limit of the beam temperature and the amount of condensation in the beam. These descriptions can even be extended to include spinodal decomposition processes, thus providing a generally applicable tool for investigating the two-phase region of high supersaturations not easily accessible otherwise. PMID:20961156

  2. Liquid polymorphism and density anomaly in a three-dimensional associating lattice gas.

    PubMed

    Girardi, Mauricio; Balladares, Aline L; Henriques, Vera B; Barbosa, Marcia C

    2007-02-14

    The authors investigate the phase diagram of a three-dimensional associating lattice gas (ALG) model. This model combines orientational icelike interactions and "van der Waals" that might be repulsive, representing, in this case, a penalty for distortion of hydrogen bonds. These interactions can be interpreted as two competing distances, making the connection between this model and continuous isotropic soft-core potentials. The authors present Monte Carlo studies of the ALG model showing the presence of two liquid phases, two critical points, and density anomaly. PMID:17313225

  3. Fission-gas release from uranium nitride at high fission rate density

    NASA Technical Reports Server (NTRS)

    Weinstein, M. B.; Kirchgessner, T. A.; Tambling, T. N.

    1973-01-01

    A sweep gas facility has been used to measure the release rates of radioactive fission gases from small UN specimens irradiated to 8-percent burnup at high fission-rate densities. The measured release rates have been correlated with an equation whose terms correspond to direct recoil release, fission-enhanced diffusion, and atomic diffusion (a function of temperature). Release rates were found to increase linearly with burnups between 1.5 and 8 percent. Pore migration was observed after operation at 1550 K to over 6 percent burnup.

  4. Two-Dimensional Plasma Density Distributions in Low-Pressure Gas Discharges

    SciTech Connect

    Berlin, E.V.; Dvinin, S.A.; Mikheev, V.V.; Omarov, M.O.; Sviridkina, V. S.

    2004-12-15

    The plasma density distribution in a two-dimensional nonuniform positive column of a low-pressure gas discharge is studied in the hydrodynamic approximation with allowance for ion inertia. Exact solutions are derived for discharges in a rectangular and a cylindrical chamber. Asymptotic solutions near the coordinate origin and near the critical surface are considered. It is shown that, for potential plasma flows, the flow velocity component normal to the plasma boundary is equal to the ion acoustic velocity. The results obtained can be used to analyze the processes occurring in low-pressure plasmochemical reactors.

  5. The application of laser Rayleigh scattering to gas density measurements in hypersonic helium flows

    NASA Technical Reports Server (NTRS)

    Hoppe, J. C.; Honaker, W. C.

    1979-01-01

    Measurements of the mean static free-stream gas density have been made in two Langley Research Center helium facilities, the 3-inch leg of the high-Reynolds-number helium complex and the 22-inch hypersonic helium tunnel. Rayleigh scattering of a CW argon ion laser beam at 514.5 nm provided the basic physical mechanism. The behavior of the scattered signal was linear, confirmed by a preliminary laboratory study. That study also revealed the need to introduce baffles to reduce stray light. A relatively simple optical system and associated photon-counting electronics were utilized to obtain data for densities from 10 to the 23rd to 10 to the 25th per cu m. The major purpose, to confirm the applicability of this technique in the hypersonic helium flow, was accomplished.

  6. The high density phase of the k-NN hard core lattice gas model

    NASA Astrophysics Data System (ADS)

    Nath, Trisha; Rajesh, R.

    2016-07-01

    The k-NN hard core lattice gas model on a square lattice, in which the first k next nearest neighbor sites of a particle are excluded from being occupied by another particle, is the lattice version of the hard disc model in two dimensional continuum. It has been conjectured that the lattice model, like its continuum counterpart, will show multiple entropy-driven transitions with increasing density if the high density phase has columnar or striped order. Here, we determine the nature of the phase at full packing for k up to 820 302 . We show that there are only eighteen values of k, all less than k  =  4134, that show columnar order, while the others show solid-like sublattice order.

  7. Long-range density-matrix-functional theory: Application to a modified homogeneous electron gas

    SciTech Connect

    Pernal, Katarzyna

    2010-05-15

    We propose a method that employs functionals of the one-electron reduced density matrix (density matrix) to capture long-range effects of electron correlation. The complementary short-range regime is treated with density functionals. In an effort to find approximations for the long-range density-matrix functional, a modified power functional is applied to the homogeneous electron gas with Coulomb interactions replaced by their corresponding long-range counterparts. For the power {beta}=1/2 and the range-separation parameter {omega}=1/r{sub s}, the functional reproduces the correlation and the kinetic correlation energies with a remarkable accuracy for intermediate and large values of r{sub s}. Analysis of the Euler equation corresponding to this functional reveals correct r{sub s} expansion of the correlation energy in the limit of large r{sub s}. The first expansion coefficient is in very good agreement with that obtained from the modified Wigner-Seitz model.

  8. Accurate ab initio potential for the krypton dimer and transport properties of the low-density krypton gas.

    PubMed

    Waldrop, Jonathan M; Song, Bo; Patkowski, Konrad; Wang, Xiaopo

    2015-05-28

    A new highly accurate potential energy curve for the krypton dimer was constructed using coupled-cluster calculations up to the singles, doubles, triples, and perturbative quadruples level, including corrections for core-core and core-valence correlation and for relativistic effects. The ab initio data points were fitted to an analytic potential which was used to compute the most important transport properties of the krypton gas. The viscosity, thermal conductivity, self-diffusion coefficient, and thermal diffusion factor were calculated by the kinetic theory at low density and temperatures from 116 to 5000 K. The comparisons with literature experimental data as well as with values from other pair potentials indicate that our new potential is superior to all previous ones. The transport property values computed in this work are recommended as standard values over the complete temperature range. PMID:26026447

  9. Standardisation of gas mixtures for estimating carbon monoxide transfer factor.

    PubMed Central

    Kendrick, A. H.; Laszlo, G.

    1993-01-01

    BACKGROUND--The American Thoracic Society recommends that the inspired concentration used for the estimation of carbon monoxide transfer factor (TLCO) mixture should be 0.25-0.35% carbon monoxide, 10-14% helium, 17-21% oxygen, balance nitrogen. Inspired oxygen influences alveolar oxygen and hence carbon monoxide uptake, such that transfer factor increases by 0.35% per mm Hg decrease in alveolar oxygen. To aid in the standardisation of TLCO either a known inspired oxygen concentration should be used, or TLCO should be corrected to a standard inspired oxygen concentration. The range of gas mixtures used in practice and the implications for cost and accuracy have been investigated. METHODS--A questionnaire was sent to 185 respiratory units in the UK requesting information on (1) the method used to estimate TLCO, (2) the manufacturer of the equipment, (3) the mixture used, (4) whether "medical quality" gas was ordered, and (5) the level of satisfaction with supplier service. RESULTS--Replies were received from 106 units. Most used the single breath breath holding method for which 17 different test mixtures were ordered. One unit also used the single breath exhalation method. Inspired oxygen ranged from 17.94% to 25%, giving a wide variation in alveolar oxygen and hence TLCO. Forty seven units ordered a specific inspired oxygen, the rest ordering "air" as balance. The cost per litre of gas varied greatly, with the mixture 14% helium, 0.28% carbon monoxide, balance air (17.9% oxygen) and 10% helium, 0.28% carbon monoxide, balance air (18.8% oxygen) being cheapest to produce. Ordering a specific inspired oxygen concentration increased the cost. Large cylinders of gas were cheaper for the same mixture. The mixture for the exhalation method was the most expensive. Sixty seven units ordered "medical quality" gas and six assumed this was supplied. Twenty nine (27%) were dissatisfied with their supplier due to (1) poor service, (2) long delivery times, (3) costs, or (4

  10. Spatial association between dissection density and environmental factors over the entire conterminous United States

    NASA Astrophysics Data System (ADS)

    Luo, Wei; Jasiewicz, Jaroslaw; Stepinski, Tomasz; Wang, Jinfeng; Xu, Chengdong; Cang, Xuezhi

    2016-01-01

    Previous studies of land dissection density (D) often find contradictory results regarding factors controlling its spatial variation. We hypothesize that the dominant controlling factors (and the interactions between them) vary from region to region due to differences in each region's local characteristics and geologic history. We test this hypothesis by applying a geographical detector method to eight physiographic divisions of the conterminous United States and identify the dominant factor(s) in each. The geographical detector method computes the power of determinant (q) that quantitatively measures the affinity between the factor considered and D. Results show that the factor (or factor combination) with the largest q value is different for physiographic regions with different characteristics and geologic histories. For example, lithology dominates in mountainous regions, curvature dominates in plains, and glaciation dominates in previously glaciated areas. The geographical detector method offers an objective framework for revealing factors controlling Earth surface processes.

  11. Dynamical correlation effects on structure factor of spin-polarized two-dimensional electron gas

    SciTech Connect

    Singh, Gurvinder; Moudgil, R. K.; Kumar, Krishan; Garg, Vinayak

    2015-06-24

    We report a theoretical study on static density structure factor S(q) of a spin-polarized two-dimensional electron gas over a wide range of electron number density r{sub s}. The electron correlations are treated within the dynamical version of the self-consistent mean-field theory of Singwi, Tosi, Land, and Sjolander, the so-called qSTLS approach. The calculated S(q) exhibits almost perfect agreement with the quantum Monte Carlo simulation data at r{sub s}=1. However, the extent of agreement somewhat diminishes with increasing r{sub s}, particularly for q around 2k{sub F}. Seen in conjunction with the success of qSTLS theory in dealing with correlations in the unpolarized phase, our study suggests that the otherwise celebrated qSTLS theory is not that good in treating the like-spin correlations.

  12. Factors Affecting the Incidence of Angel Wing in White Roman Geese: Stocking Density and Genetic Selection

    PubMed Central

    Lin, M. J.; Chang, S. C.; Lin, T. Y.; Cheng, Y. S.; Lee, Y. P.; Fan, Y. K.

    2016-01-01

    The present study investigated stocking density and genetic lines, factors that may alter the severity and incidence of angel wing (AW), in White Roman geese. Geese (n = 384) from two genetically selected lines (normal- winged line, NL, and angel-winged line, AL, respectively) and one commercial line (CL) were raised in four pens. Following common commercial practice, low-stocking-density (LD), medium-stocking-density, and high-stocking-density treatments were respectively administered to 24, 32, and 40 geese per pen at 0 to 3 weeks (1.92 m2/pen) and 4 to 6 weeks (13.2 m2/pen) of age and to 24, 30, and 36 geese at 7 to 14 weeks (20.0 m2/pen) of age. The results revealed that stocking density mainly affected body weight gain in geese younger than 4 weeks, and that geese subjected to LD had a high body weight at 2 weeks of age. However, the effect of stocking density on the severity score of AW (SSAW) and incidence of AW (IAW) did not differ significantly among the treatments. Differences were observed among the genetic stocks; that is, SSAW and IAW were significantly higher in AL than in NL and CL. Genetic selection generally aggravates AW, complicating its elimination. To effectively reduce IAW, stocking density, a suspected causal factor, should be lower than that presently applied commercially. PMID:26954185

  13. Associations between soy, diet, reproductive factors, and mammographic density in Singapore Chinese women.

    PubMed

    Ursin, Giske; Sun, Can-Lan; Koh, Woon-Puay; Khoo, Kei-Siong; Gao, Fei; Wu, Anna H; Yu, Mimi C

    2006-01-01

    Although the evidence is not completely consistent, soy intake has been inversely associated with breast cancer risk, and the strongest results have been observed in certain Asian populations. To address this issue and to examine the association between mammographic density and reproductive factors in this population, we conducted a cross-sectional analysis of mammograms and validated food-frequency questionnaires from 380 Chinese women living in Singapore. Percent mammographic density, a biomarker for breast cancer risk, was assessed using a validated computer-assisted method. We used generalized linear models to estimate mean mammographic density by quartiles of soy intake and intake of other dietary factors while adjusting for potential confounders. Percent mammographic density was inversely associated with age, body mass index, parity, breastfeeding, and soy intake. The difference in mammographic density between the highest and lowest quartiles of soy intake was 4-5%; this difference was statistically significant for soy protein and soy isoflavone intake and is similar in magnitude to what has been reported in Western populations when women undergo menopause or commence hormone therapy. We found no evidence that high fiber, fruit, or vegetable intake has protective effects on mammographic density. Our results suggest that the effect of soy intake on percent mammographic density is moderate but possibly of clinical relevance. PMID:17474857

  14. Factors Affecting the Incidence of Angel Wing in White Roman Geese: Stocking Density and Genetic Selection.

    PubMed

    Lin, M J; Chang, S C; Lin, T Y; Cheng, Y S; Lee, Y P; Fan, Y K

    2016-06-01

    The present study investigated stocking density and genetic lines, factors that may alter the severity and incidence of angel wing (AW), in White Roman geese. Geese (n = 384) from two genetically selected lines (normal- winged line, NL, and angel-winged line, AL, respectively) and one commercial line (CL) were raised in four pens. Following common commercial practice, low-stocking-density (LD), medium-stocking-density, and high-stocking-density treatments were respectively administered to 24, 32, and 40 geese per pen at 0 to 3 weeks (1.92 m(2)/pen) and 4 to 6 weeks (13.2 m(2)/pen) of age and to 24, 30, and 36 geese at 7 to 14 weeks (20.0 m(2)/pen) of age. The results revealed that stocking density mainly affected body weight gain in geese younger than 4 weeks, and that geese subjected to LD had a high body weight at 2 weeks of age. However, the effect of stocking density on the severity score of AW (SSAW) and incidence of AW (IAW) did not differ significantly among the treatments. Differences were observed among the genetic stocks; that is, SSAW and IAW were significantly higher in AL than in NL and CL. Genetic selection generally aggravates AW, complicating its elimination. To effectively reduce IAW, stocking density, a suspected causal factor, should be lower than that presently applied commercially. PMID:26954185

  15. Correlation between density and oxidation temperature for pyrolytic-gas passivated ultrathin silicon oxide films

    NASA Astrophysics Data System (ADS)

    Yamada, Hiroshi

    2004-01-01

    Pyrolytic-gas passivation (PGP) with a small amount nitrogen gas enhances the breakdown reliability of silicon oxide gate films. To clarify the reliability retention of the PGP-grown films oxidized at low temperature, densities (ρox's) of the 3.5-6.5-nm-thick PGP-grown films on Si(100) oxidized at 700-900 °C were investigated. Since ρox's correlate well with the reliability and are useful as an index of the intrinsic structural characteristics of the films. Moreover, changes in ρox and nitrogen content corresponding to oxidation temperature are similar to those in breakdown reliability and interface state density (Dit), respectively. In addition, ρox's of the 700 °C-grown PGP films do not deteriorate as much when compared with those of the films grown by normal ultradry oxidation at 800 °C and their Dit's are less than about 6×1010/eV cm2. This suggests that PGP probably improves the reliability by generating the higher-ρox microscopic structure with few Si dangling bonds and effective passivation. .

  16. High-speed digital holography for neutral gas and electron density imaging.

    PubMed

    Granstedt, E M; Thomas, C E; Kaita, R; Majeski, R; Baylor, L R; Meitner, S J; Combs, S K

    2016-05-01

    An instrument was developed using digital holographic reconstruction of the wavefront from a CO2 laser imaged on a high-speed commercial IR camera. An acousto-optic modulator is used to generate 1-25 μs pulses from a continuous-wave CO2 laser, both to limit the average power at the detector and also to freeze motion from sub-interframe time scales. Extensive effort was made to characterize and eliminate noise from vibrations and second-surface reflections. Mismatch of the reference and object beam curvature initially contributed substantially to vibrational noise, but was mitigated through careful positioning of identical imaging lenses. Vibrational mode amplitudes were successfully reduced to ≲1 nm for frequencies ≳50 Hz, and the inter-frame noise across the 128 × 128 pixel window which is typically used is ≲2.5 nm. To demonstrate the capabilities of the system, a piezo-electric valve and a reducing-expanding nozzle were used to generate a super-sonic gas jet which was imaged with high spatial resolution (better than 0.8 lp/mm) at high speed. Abel inversions were performed on the phase images to produce 2-D images of localized gas density. This system could also be used for high spatial and temporal resolution measurements of plasma electron density or surface deformations. PMID:27250423

  17. Very high-density planets: a possible remnant of gas giants.

    PubMed

    Mocquet, A; Grasset, O; Sotin, C

    2014-04-28

    Data extracted from the Extrasolar Planets Encyclopaedia (see http://exoplanet.eu) show the existence of planets that are more massive than iron cores that would have the same size. After meticulous verification of the data, we conclude that the mass of the smallest of these planets is actually not known. However, the three largest planets, Kepler-52b, Kepler-52c and Kepler-57b, which are between 30 and 100 times the mass of the Earth, have indeed density larger than an iron planet of the same size. This observation triggers this study that investigates under which conditions these planets could represent the naked cores of gas giants that would have lost their atmospheres during their migration towards the star. This study shows that for moderate viscosity values (10(25) Pa s or lower), large values of escape rate and associated unloading stress rate during the atmospheric loss process lead to the explosion of extremely massive planets. However, for moderate escape rate, the bulk viscosity and finite-strain incompressibility of the cores of giant planets can be large enough to retain a very high density during geological time scales. This would make those a new kind of planet, which would help in understanding the interior structure of the gas giants. However, this new family of exoplanets adds some degeneracy for characterizing terrestrial exoplanets. PMID:24664925

  18. Level density of a Fermi gas and integer partitions: A Gumbel-like finite-size correction

    SciTech Connect

    Roccia, Jerome; Leboeuf, Patricio

    2010-04-15

    We investigate the many-body level density of a gas of noninteracting fermions. We determine its behavior as a function of the temperature and the number of particles. As the temperature increases, and beyond the usual Sommerfeld expansion that describes the degenerate gas behavior, corrections due to a finite number of particles lead to Gumbel-like contributions. We discuss connections with the partition problem in number theory, extreme value statistics, and differences with respect to the Bose gas.

  19. Flowing afterglow measurements of the density dependence of gas-phase ion-ion mutual neutralization reactions

    SciTech Connect

    Shuman, Nicholas S.; Viggiano, Albert A.; Johnsen, Rainer

    2013-05-28

    We have studied the dependence of several ion-ion mutual neutralization (MN) reactions on helium density in the range from 1.6 Multiplication-Sign 10{sup 16} to 1.5 Multiplication-Sign 10{sup 17} cm{sup -3} at 300 K, using the Variable Electron and Neutral Density Attachment Mass Spectrometry method. The rate coefficients of the reactions Ar{sup +}+ Br{sub 2}{sup -}, Ar{sup +}+ SF{sub 6}{sup -}, and Ar{sup +}+ C{sub 7}F{sub 14}{sup -} were found to be independent of gas density over the range studied, in disagreement with earlier observations that similar MN reactions are strongly enhanced at the same gas densities. The cause of the previous enhancement with density is traced to the use of 'orbital-motion-limit' theory to infer ion densities from the currents collected by ion-attracting Langmuir probes in a region where it is not applicable.

  20. Breast cancer risk factors in relation to breast density (United States)

    PubMed Central

    Tosteson, Anna N. A.; Kasales, Claudia; Weiss, Julia; Goodrich, Martha; Hatch, Elizabeth E.; Carney, Patricia A.

    2006-01-01

    Objectives Evaluate known breast cancer risk factors in relation to breast density. Methods We examined factors in relation to breast density in 144,018 New Hampshire (NH) women with at least one mammogram recorded in a statewide mammography registry. Mammographic breast density was measured by radiologists using the BI-RADS classification; risk factors of interest were obtained from patient intake forms and questionnaires. Results Initial analyses showed a strong inverse influence of age and body mass index (BMI) on breast density. In addition, women with late age at menarche, late age at first birth, premenopausal women, and those currently using hormone therapy (HT) tended to have higher breast density, while those with greater parity tended to have less dense breasts. Analyses stratified on age and BMI suggested interactions, which were formally assessed in a multivariable model. The impact of current HT use, relative to nonuse, differed across age groups, with an inverse association in younger women, and a positive association in older women (p < 0.0001 for the interaction). The positive effects of age at menarche and age at first birth, and the inverse influence of parity were less apparent in women with low BMI than in those with high BMI (p = 0.04, p < 0.0001 and p = 0.01, respectively, for the interactions). We also noted stronger positive effects for age at first birth in postmenopausal women (p = 0.004 for the interaction). The multivariable model indicated a slight positive influence of family history of breast cancer. Conclusions The influence of age at menarche and reproductive factors on breast density is less evident in women with high BMI. Density is reduced in young women using HT, but increased in HT users of age 50 or more. PMID:17111260

  1. A Herschel-SPIRE survey of the Mon R2 giant molecular cloud: analysis of the gas column density probability density function

    NASA Astrophysics Data System (ADS)

    Pokhrel, R.; Gutermuth, R.; Ali, B.; Megeath, T.; Pipher, J.; Myers, P.; Fischer, W. J.; Henning, T.; Wolk, S. J.; Allen, L.; Tobin, J. J.

    2016-09-01

    We present a far-IR survey of the entire Mon R2 giant molecular cloud (GMC) with Herschel-Spectral and Photometric Imaging REceiver cross-calibrated with Planck-High Frequency Instrument data. We fit the spectral energy distributions of each pixel with a greybody function and an optimal beta value of 1.8. We find that mid-range column densities obtained from far-IR dust emission and near-IR extinction are consistent. For the entire GMC, we find that the column density histogram, or column density probability distribution function (N-PDF), is lognormal below ˜1021 cm-2. Above this value, the distribution takes a power law form with an index of -2.15. We analyse the gas geometry, N-PDF shape, and young stellar object (YSO) content of a selection of subregions in the cloud. We find no regions with pure lognormal N-PDFs. The regions with a combination of lognormal and one power-law N-PDF have a YSO cluster and a corresponding centrally concentrated gas clump. The regions with a combination of lognormal and two power-law N-PDF have significant numbers of typically younger YSOs but no prominent YSO cluster. These regions are composed of an aggregate of closely spaced gas filaments with no concentrated dense gas clump. We find that for our fixed scale regions, the YSO count roughly correlates with the N-PDF power-law index. The correlation appears steeper for single power-law regions relative to two power-law regions with a high column density cut-off, as a greater dense gas mass fraction is achieved in the former. A stronger correlation is found between embedded YSO count and the dense gas mass among our regions.

  2. Effects of density stratification in driving zonal flow in gas giants

    NASA Astrophysics Data System (ADS)

    Gastine, T.; Wicht, J.

    2011-12-01

    The banded structures at the surfaces of Jupiter and Saturn are associated with prograde and retrograde zonal flows. The depth of these jets remains however poorly known. Theoretical scenarios range from ``shallow models'', that assume that zonal flows are restricted to a very thin layer close to the surface; to ``deep models'' that suppose that the jets involve the whole molecular shell (typically 104 kms). The latter idea was supported by fully 3-D numerical simulations (e.g. Heimpel, 2005) using the Boussinesq approximation, meaning that the background properties (temperature, density, ...) are constant with radius (Christensen, 2002). While this approximation is suitable for liquid iron cores of planets, it is more questionable in the envelopes of gas giants, where density increases by several orders of magnitude (Guillot, 1999). The anelastic approximation provides a more realistic framework to simulate the dynamics of zonal flows as it allows compressibility effects, while filtering out fast acoustic waves (Lantz & Fan, 1999). Recent anelastic simulations suggest that including compressibility effects yields interesting differences to Boussinesq approaches (Jones, 2009; Showman et al., 2011). Here, we therefore adopt an anelastic formulation to simulate 3-D compressible flows in rapidly rotating shells. We have conducted a systematic parametric study on the effects of background density stratification and analysed the influences on both convective flows and zonal jets. Despite the strong dependence of convection on the density stratification (i.e. the typical lengthscale of convective flows decreases when compressibility increases), the comparison between Boussinesq and anelastic simulations reveals striking common features: the latitudinal extent, the amplitude and the number of zonal jets is found to be nearly independent of the density stratification, provided convection is strongly driven. Mass-weighted properties of the flow (and notably a mass

  3. Unequal density effect on static structure factor of coupled electron layers

    SciTech Connect

    Saini, L. K. Nayak, Mukesh G.

    2014-04-24

    In order to understand the ordered phase, if any, in a real coupled electron layers (CEL), there is a need to take into account the effect of unequal layer density. Such phase is confirmed by a strong peak in a static structure factor. With the aid of quantum/dynamical version of Singwi, Tosi, Land and Sjölander (so-called qSTLS) approximation, we have calculated the intra- and interlayer static structure factors, S{sub ll}(q) and S{sub 12}(q), over a wide range of density parameter r{sub sl} and interlayer spacing d. In our present study, the sharp peak in S{sub 22}(q) has been found at critical density with sufficiently lower interlayer spacing. Further, to find the resultant effect of unequal density on intra- and interlayer static structure factors, we have compared our results with that of the recent CEL system with equal layer density and isolated single electron layer.

  4. Strong cylindrical shock wave in a self-gravitating rotational axisymmetric dusty gas with density varying exponentially

    NASA Astrophysics Data System (ADS)

    Nath, Gorakh

    2016-07-01

    The propagation of a strong cylindrical shock wave in a self-gravitating and rotational axisymmetric dusty gas, having variable azimuthal and axial fluid velocities is investigated. The dusty gas is assumed to be a mixture of small solid particles and perfect gas. The equilibrium flow conditions are assumed to be maintained. The density of the mixture and the fluid velocities in the ambient medium are assumed to be varying and obeying an exponential law. The shock wave moves with variable velocity and the total energy of the wave is non-constant. Non-similarity solutions are obtained and the effects of variation of the mass concentration of solid particles in the mixture, the ratio of the density of solid particles to the initial density of the gas, and the gravitational parameter on the flow variables in the region behind the shock are investigated at a given time. Also, a comparison between the isothermal and adiabatic flow is made.

  5. Detection of coating fluorophores' densities in improved Q-factor cavities

    NASA Astrophysics Data System (ADS)

    Kandas, Ishac; Shehata, Nader; Daengngam, Chalongrat; Ashry, Islam; Xu, Yong

    2015-08-01

    This work investigates the relationship between the Q factor of a silica-microsphere coated with nonlinear optical molecules and the surface density of the molecules. Two types of nonlinear molecules are studied: poly {1-[p-(3'-carboxy-4'-hydroxyphenylazo) benzenesulfonamido]-1, 2-ethandiyl} (PCBS), and Procion Brown MX-GRN (PB). In our experiments, we coat silica microspheres with ionic self-assembled multilayer (ISAM) films with different thickness values as well as different PCBS/PB chromophore densities. The Q factors of the coated microspheres are limited to the range of 106-107, which can be attributed to the optical absorption of the coated chromophores. This work can be used to experimentally determine the effective density of chromophores assembled on the silica microsphere. It may also find applications in chemical / biological sensing.

  6. Measurement of chromophores density using high Q-factor silica microspheres

    NASA Astrophysics Data System (ADS)

    Kandas, Ishac; Shehata, Nader; Daengngam, Chalongrat; Ashry, Islam; Xu, Yong

    2016-01-01

    This work investigates the relationship between the Q factor of a silica microsphere coated with nonlinear optical molecules and the surface density of the nonlinear molecules. Two types of nonlinear molecules are studied: poly{1-[p-(3‧-carboxy-4‧-hydroxyphenylazo) benzenesulfonamido]-1,2-ethandiyl} (PCBS), and Procion Brown MX-GRN (PB). In our experiments, we coat silica microspheres with ionic self-assembled multilayer films with different thicknesses as well as with different PCBS/PB chromophores densities. The Q factors of the coated microspheres are measured to be within the range of 106 to 107, which can be attributed to the optical absorption of the coated chromophores. This work can be used to experimentally determine the effective density of chromophores assembled on the silica microsphere. It may also find applications in chemical/biological sensing.

  7. Form factor dispersion at La M5,4 edges and average density of resonant atoms.

    PubMed

    Smadici, S; Lee, J C T; Logvenov, G; Bozovic, I; Abbamonte, P

    2014-01-15

    Resonant soft x-ray scattering on complex oxide superlattices shows very large variations in the superlattice reflection position and intensity near La M5,4 edges. Resonant dispersion of the La x-ray form factor describes the observations well. We determine the average density of resonant La atoms and the thickness of superlattice layers. PMID:24318961

  8. A Factor Analytic Approach to the Study of Spatial Density Effects on Preschoolers.

    ERIC Educational Resources Information Center

    Loo, Chalsa M.

    1979-01-01

    Behavior of preschoolers was studied with respect to five factors: verbally-abusive interaction, activity-toy play, avoidance, negative affect-agression, and desire-to-leave-a-crowded-room. Under high density conditions, more girls exhibited reduced activity level and toy involvement, along with increased negative feelings, than boys. (MA)

  9. GAS SURFACE DENSITY, STAR FORMATION RATE SURFACE DENSITY, AND THE MAXIMUM MASS OF YOUNG STAR CLUSTERS IN A DISK GALAXY. II. THE GRAND-DESIGN GALAXY M51

    SciTech Connect

    Gonzalez-Lopezlira, Rosa A.; Pflamm-Altenburg, Jan; Kroupa, Pavel

    2013-06-20

    We analyze the relationship between maximum cluster mass and surface densities of total gas ({Sigma}{sub gas}), molecular gas ({Sigma}{sub H{sub 2}}), neutral gas ({Sigma}{sub H{sub I}}), and star formation rate ({Sigma}{sub SFR}) in the grand-design galaxy M51, using published gas data and a catalog of masses, ages, and reddenings of more than 1800 star clusters in its disk, of which 223 are above the cluster mass distribution function completeness limit. By comparing the two-dimensional distribution of cluster masses and gas surface densities, we find for clusters older than 25 Myr that M{sub 3rd}{proportional_to}{Sigma}{sub H{sub I}{sup 0.4{+-}0.2}}, whereM{sub 3rd} is the median of the five most massive clusters. There is no correlation with{Sigma}{sub gas},{Sigma}{sub H2}, or{Sigma}{sub SFR}. For clusters younger than 10 Myr, M{sub 3rd}{proportional_to}{Sigma}{sub H{sub I}{sup 0.6{+-}0.1}} and M{sub 3rd}{proportional_to}{Sigma}{sub gas}{sup 0.5{+-}0.2}; there is no correlation with either {Sigma}{sub H{sub 2}} or{Sigma}{sub SFR}. The results could hardly be more different from those found for clusters younger than 25 Myr in M33. For the flocculent galaxy M33, there is no correlation between maximum cluster mass and neutral gas, but we have determined M{sub 3rd}{proportional_to}{Sigma}{sub gas}{sup 3.8{+-}0.3}, M{sub 3rd}{proportional_to}{Sigma}{sub H{sub 2}{sup 1.2{+-}0.1}}, and M{sub 3rd}{proportional_to}{Sigma}{sub SFR}{sup 0.9{+-}0.1}. For the older sample in M51, the lack of tight correlations is probably due to the combination of strong azimuthal variations in the surface densities of gas and star formation rate, and the cluster ages. These two facts mean that neither the azimuthal average of the surface densities at a given radius nor the surface densities at the present-day location of a stellar cluster represent the true surface densities at the place and time of cluster formation. In the case of the younger sample, even if the clusters have not yet

  10. Modification of generalized vector form factors and transverse charge densities of the nucleon in nuclear matter

    NASA Astrophysics Data System (ADS)

    Jung, Ju-Hyun; Yakhshiev, Ulugbek; Kim, Hyun-Chul

    2016-03-01

    We investigate the medium modification of the generalized vector form factors of the nucleon, which include the electromagnetic and energy-momentum tensor form factors, based on an in-medium modified π -ρ -ω soliton model. We find that the vector form factors of the nucleon in nuclear matter fall off faster than those in free space, which implies that the charge radii of the nucleon become larger in nuclear medium than in free space. We also compute the corresponding transverse charge densities of the nucleon in nuclear matter, which clearly reveal the increasing of the nucleon size in nuclear medium.

  11. Filling factors and scale heights of the diffuse ionized gas in the Milky Way

    NASA Astrophysics Data System (ADS)

    Berkhuijsen, E. M.; Mitra, D.; Mueller, P.

    2006-01-01

    The combination of dispersion measures of pulsars, distances from the model of Cordes & Lazio (\\cite{cordes+lazio02}) and emission measures from the WHAM survey enabled a statistical study of electron densities and filling factors of the diffuse ionized gas (DIG) in the Milky Way. The emission measures were corrected for absorption and contributions from beyond the pulsar distance. For a sample of 157 pulsars at |b|>5° and 60° < ℓ < 360°, located in mainly interarm regions within about 3 kpc from the Sun, we find that: (1) The average volume filling factor along the line of sight /line{f}v and the mean density in ionized clouds /line{n}c are inversely correlated: /line{f}v(/line{n}c ) = (0.0184± 0.0011) /line{n}c{ -1.07± 0.03} for the ranges 0.03 < /line{n}c < 2 {cm-3 and 0.8 > /line{f}v > 0.01. This relationship is very tight. The inverse correlation of /line{f}v and /line{n}c causes the well-known constancy of the average electron density along the line of sight. As /line{f}v(z) increases with distance from the Galactic plane |z|, the average size of the ionized clouds increases with |z|. (2) For |z| < 0.9 kpc the local density in clouds nc (z) and local filling factor f(z) are inversely correlated because the local electron density ne (z) = f(z) nc (z) is constant. We suggest that f(z) reaches a maximum value of >0.3 near |z| = 0.9 kpc, whereas nc (z) continues to decrease to higher |z|, thus causing the observed flattening in the distribution of dispersion measures perpendicular to the Galactic plane above this height. (3) For |z| < 0.9 kpc the local distributions nc (z), f(z) and ne2(z) have the same scale height which is in the range 250 < h ⪉ 500 pc. (4) The average degree of ionization of the warm atomic gas /line{I}w (z) increases towards higher |z| similarly to /line{f}v (z). Towards |z| = 1 kpc, /line{f}v (z) = 0.24± 0.05 and /line{I}w (z) = 0.24± 0.02. Near |z| = 1 kpc most of the warm, atomic hydrogen is ionized.

  12. Infrared and density functional theory studies of formic acid hydrate clusters in noble gas matrices

    NASA Astrophysics Data System (ADS)

    Ito, Fumiyuki

    2016-08-01

    Infrared absorption spectra of formic acid hydrate clusters (HCOOH)m(H2O)n have been measured in noble gas matrices (Ar and Kr). The concentration dependence of the spectra and the comparison with a previous experimental study on HCOOH(H2O) and HCOOH(H2O)2 [Geoge et al., Spectrochim. Acta, Part A 60 (2004) 3225] led to the identification of large clusters. Density functional theory calculations at the B3LYP-DCP/6-31+G(2d,2p) level were carried out to determine the anharmonic vibrational properties of the clusters, enabling a consistent assignment of the observed vibrational peaks to specific clusters.

  13. Polynomial approximations of thermodynamic properties of arbitrary gas mixtures over wide pressure and density ranges

    NASA Technical Reports Server (NTRS)

    Allison, D. O.

    1972-01-01

    Computer programs for flow fields around planetary entry vehicles require real-gas equilibrium thermodynamic properties in a simple form which can be evaluated quickly. To fill this need, polynomial approximations were found for thermodynamic properties of air and model planetary atmospheres. A coefficient-averaging technique was used for curve fitting in lieu of the usual least-squares method. The polynomials consist of terms up to the ninth degree in each of two variables (essentially pressure and density) including all cross terms. Four of these polynomials can be joined to cover, for example, a range of about 1000 to 11000 K and 0.00001 to 1 atmosphere (1 atm = 1.0133 x 100,000 N/m sq) for a given thermodynamic property. Relative errors of less than 1 percent are found over most of the applicable range.

  14. Gas-phase pyrolysis mechanisms of 3-anilino-1-propanol: Density functional theory study

    NASA Astrophysics Data System (ADS)

    Zhao, Jing; Tang, Ming-Sheng; Wei, Dong-Hui; Zhao, Chu-Feng; Zhang, Wen-Jing; Wang, Hong-Ming

    The gas-phase pyrolytic decomposition mechanisms of 3-anilino-1-propanol with the products of aniline, ethylene, and formaldehyde or N-methyl aniline and aldehyde were studied by density functional theory. The geometries of the reactant, transition states, and intermediates were optimized at the B3LYP/6-31G (d, p) level. Vibration analysis was carried out to confirm the transition state structures, and the intrinsic reaction coordinate method was performed to search the minimum energy path. Four possible reaction channels are shown, including two concerted reactions of direct pyrolytic decomposition and two indirect channels in which the reactant first becomes a ring-like intermediate, followed by concerted pyrogenation. One of the concerted reactions in the direct pyrolytic decomposition has the lowest activation barrier among all the four channels, and so, it occurs more often than others. The results appear to be consistent with the experimental outcomes.

  15. Gas-phase reactions of pd with acetone: A theoretical investigation using density functional theory

    NASA Astrophysics Data System (ADS)

    Dai, Guo-Liang; Wang, Chuan-Feng

    2012-12-01

    The gas-phase reaction of palladium atom with acetone is investigated using density functional theory. Geometries and energies of the reactants, intermediates, and products involved are calculated. Both ground and excited state potential energy surfaces are investigated in detail. The present results show that the title reaction start with the formation of an η2-CH3COCH3-metal complex, followed by C-O, C-H, and C-C activation. These reactions can lead to four different products (PdO + C3H6, PdCH2COCH3 + H, PdCH2 + CH3CHO, and PdCOCH2 + CH4). The present results may be helpful in understanding the mechanism of the title reaction and further experimental investigation of the reaction.

  16. Electron beam fluorescence system to measure gas density in impulse facilities

    NASA Technical Reports Server (NTRS)

    Hoppe, J. C.

    1974-01-01

    Very rapid measurements, ranging from a few microsecond to milliseconds in duration, characterize studies made in shock regions or behind them. A system to measure gas density under such conditions in a 15.24-cm (6-in.) expansion tube is described. The basic elements are an electron beam of moderate energy and high current capability, an optical detector, and the associated electronics and data readout equipment. A heated-cathode electron gun, capable of pulsed operation and delivering up to 200 milliamperes current, provides the source of electrons. Optics include a simple collector lens, aperture, collimator lens, filters, and a photomultiplier tube. The photomultiplier output signal was recorded by means of photographed oscilloscope traces for pulsed beam operation.

  17. Fermi Edge Polaritons in a Microcavity Containing a High Density Two-Dimensional Electron Gas

    NASA Astrophysics Data System (ADS)

    Gabbay, A.; Preezant, Yulia; Cohen, E.; Ashkinadze, B. M.; Pfeiffer, L. N.

    2007-10-01

    Sharp, near band gap lines are observed in the reflection and photoluminescence spectra of GaAs/AlGaAs structures consisting of a modulation doped quantum well (MDQW) that contains a high density two-dimensional electron gas (2DEG) and is embedded in a microcavity (MC). The energy dependence of these lines on the MC-confined photon energy shows level anticrossings and Rabi splittings very similar to those observed in systems of undoped QW’s embedded in a MC. The spectra are analyzed by calculating the optical susceptibility of the MDQW in the near band gap spectral range and using it within the transfer matrix method. The calculated reflection spectra indicate that the sharp spectral lines are due to k∥=0 cavity polaritons that are composed of e-h pair excitations just above the 2DEG Fermi edge and are strongly coupled to the MC-confined photons.

  18. Self-tuning method for monitoring the density of a gas vapor component using a tunable laser

    DOEpatents

    Hagans, K.; Berzins, L.; Galkowski, J.; Seng, R.

    1996-08-27

    The present invention relates to a vapor density monitor and laser atomic absorption spectroscopy method for highly accurate, continuous monitoring of vapor densities, composition, flow velocity, internal and kinetic temperatures and constituent distributions. The vapor density monitor employs a diode laser, preferably of an external cavity design. By using a diode laser, the vapor density monitor is significantly less expensive and more reliable than prior art vapor density monitoring devices. In addition, the compact size of diode lasers enables the vapor density monitor to be portable. According to the method of the present invention, the density of a component of a gas vapor is calculated by tuning the diode laser to a frequency at which the amount of light absorbed by the component is at a minimum or a maximum within about 50 MHz of that frequency. Laser light from the diode laser is then transmitted at the determined frequency across a predetermined pathlength of the gas vapor. By comparing the amount of light transmitted by the diode laser to the amount of light transmitted after the laser light passes through the gas vapor, the density of the component can be determined using Beer`s law. 6 figs.

  19. Self-tuning method for monitoring the density of a gas vapor component using a tunable laser

    DOEpatents

    Hagans, Karla; Berzins, Leon; Galkowski, Joseph; Seng, Rita

    1996-01-01

    The present invention relates to a vapor density monitor and laser atomic absorption spectroscopy method for highly accurate, continuous monitoring of vapor densities, composition, flow velocity, internal and kinetic temperatures and constituent distributions. The vapor density monitor employs a diode laser, preferably of an external cavity design. By using a diode laser, the vapor density monitor is significantly less expensive and more reliable than prior art vapor density monitoring devices. In addition, the compact size of diode lasers enables the vapor density monitor to be portable. According to the method of the present invention, the density of a component of a gas vapor is calculated by tuning the diode laser to a frequency at which the amount of light absorbed by the component is at a minimum or a maximum within about 50 MHz of that frequency. Laser light from the diode laser is then transmitted at the determined frequency across a predetermined pathlength of the gas vapor. By comparing the amount of light transmitted by the diode laser to the amount of light transmitted after the laser light passes through the gas vapor, the density of the component can be determined using Beer's law.

  20. A Herschel - SPIRE Survey of the Mon R2 Giant Molecular Cloud: Analysis of the Gas Column Density Probability Density Function

    NASA Astrophysics Data System (ADS)

    Pokhrel, R.; Gutermuth, R.; Ali, B.; Megeath, T.; Pipher, J.; Myers, P.; Fischer, W. J.; Henning, T.; Wolk, S. J.; Allen, L.; Tobin, J. J.

    2016-06-01

    We present a far-IR survey of the entire Mon R2 GMC with Herschel - SPIRE cross-calibrated with Planck - HFI data. We fit the SEDs of each pixel with a greybody function and an optimal beta value of 1.8. We find that mid-range column densities obtained from far-IR dust emission and near-IR extinction are consistent. For the entire GMC, we find that the column density histogram, or N-PDF, is lognormal below ˜ 1021 cm-2. Above this value, the distribution takes a power law form with an index of -2.15. We analyze the gas geometry, N-PDF shape, and YSO content of a selection of subregions in the cloud. We find no regions with pure lognormal N-PDFs. The regions with a combination of lognormal and one power law N-PDF have a YSO cluster and a corresponding centrally concentrated gas clump. The regions with a combination of lognormal and two power law N-PDF have significant numbers of typically younger YSOs but no prominent YSO cluster. These regions are composed of an aggregate of closely spaced gas filaments with no concentrated dense gas clump. We find that for our fixed scale regions, the YSO count roughly correlates with the N-PDF power law index. The correlation appears steeper for single power law regions relative to two power law regions with a high column density cut-off, as a greater dense gas mass fraction is achieved in the former. A stronger correlation is found between embedded YSO count and the dense gas mass among our regions.

  1. Dust-to-gas ratio, XCO factor and CO-dark gas in the Galactic anticentre: an observational study

    NASA Astrophysics Data System (ADS)

    Chen, B.-Q.; Liu, X.-W.; Yuan, H.-B.; Huang, Y.; Xiang, M.-S.

    2015-04-01

    We investigate the correlation between extinction and H I and CO emission at intermediate and high Galactic latitudes (|b| > 10°) within the footprint of the Xuyi Schmidt Telescope Photometric Survey of the Galactic anticentre (XSTPS-GAC) on small and large scales. In Paper I, we present a three-dimensional (3D) dust extinction map within the footprint of XSTPS-GAC, covering a sky area of over 6000 deg2 at a spatial angular resolution of 6 arcmin. In the current work, the map is combined with data from gas tracers, including H I data from the Galactic Arecibo L-band Feed Array H I survey and CO data from the Planck mission, to constrain the values of dust-to-gas ratio DGR = AV/N(H) and CO-to-H2 conversion factor XCO = N(H2)/WCO for the entire GAC footprint excluding the Galactic plane, as well as for selected star-forming regions (such as the Orion, Taurus and Perseus clouds) and a region of diffuse gas in the northern Galactic hemisphere. For the whole GAC footprint, we find DGR = (4.15 ± 0.01) × 10-22 mag cm2 and XCO = (1.72 ± 0.03) × 1020 cm- 2 (K km s- 1)- 1. We have also investigated the distribution of `CO-dark' gas (DG) within the footprint of GAC and found a linear correlation between the DG column density and the V-band extinction: N(DG) ˜eq 2.2 × 10^{21} (A_V - AcV) cm^{-2}. The mass fraction of DG is found to be fDG ˜ 0.55 towards the Galactic anticentre, which is respectively about 23 and 124 per cent of the atomic and CO-traced molecular gas in the same region. This result is consistent with the theoretical work of Papadopoulos et al. but much larger than that expected in the H2 cloud models by Wolfire et al.

  2. The Carina Nebula and Gum 31 molecular complex - I. Molecular gas distribution, column densities, and dust temperatures

    NASA Astrophysics Data System (ADS)

    Rebolledo, David; Burton, Michael; Green, Anne; Braiding, Catherine; Molinari, Sergio; Wong, Graeme; Blackwell, Rebecca; Elia, Davide; Schisano, Eugenio

    2016-03-01

    We report high-resolution observations of the 12CO(1-0) and 13CO(1-0) molecular lines in the Carina Nebula and the Gum 31 region obtained with the 22-m Mopra telescope as part of The Mopra Southern Galactic Plane CO Survey. We cover 8 deg2 from l = 285° to 290°, and from b = -1.5° to +0.5°. The molecular gas column density distributions from both tracers have a similar range of values. By fitting a grey-body function to the observed infrared spectral energy distribution from Herschel maps, we derive gas column densities and dust temperatures. The gas column density has values in the range from 6.3 × 1020 to 1.4 × 1023 cm-2, while the dust temperature has values in the range from 17 to 43 K. The gas column density derived from the dust emission is approximately described by a lognormal function for a limited range of column densities. A high-column-density tail is clearly evident for the gas column density distribution, which appears to be a common feature in regions with active star formation. There are regional variations in the fraction of the mass recovered by the CO emission lines with respect to the total mass traced by the dust emission. These variations may be related to changes in the radiation field strength, variation of the atomic to molecular gas fraction across the observed region, differences in the CO molecule abundance with respect to H2, and evolutionary stage differences of the molecular clouds that compose the Carina Nebula-Gum 31 complex.

  3. Evolution and Instability of Galactic Gas Disks inresponse to A Spiral Density-wave Potential

    NASA Astrophysics Data System (ADS)

    Yuan, Chi; Yen, D. C.; Wang, H. H.

    2006-12-01

    We revisit the classic problem of the response of the gas in a galactic disk to an imposed spiral density-wave potential of stellar origin. The results show the distinct difference between waves generated by resonance excitation and forced oscillation. To avoid the confusion of mixing these two types of waves, we systematically reduce the strength of the spiral potential or the force near the primary Lindblad resonances. So we can study the original problem of shock formation and star formation problem formulated by Roberts (1969). For the cases without self-gravitation of the gas disk, in addition to the primary doubly periodic shocks, the presence of the branch-like structures which correspond to the ultra-harmonic resonances is pronounced. On the other hand, once the self-gravitation is included, unlike the work of Chakrabarti et al. (2003), the sub-structures associated with the ultra-harmonics are not necessarily enhanced by the self-gravity. Their growth may be deteriorated by the growth of the primary shocks. Sub-structures other than those identified with the ultra-harmonics may result from shear instability of Rayleigh's kind or gravitational instability of Toomre's kind. They are responsible for the branches, feathers or chaotic sub-structures observed in nearby galaxies in far infra-red. The work is in parts supported by a grant from National Science Council, Taiwan NSC95-2752-M-001-009-PAE.

  4. Impact of density and environmental factors on population fluctuations in a migratory passerine.

    PubMed

    Pasinelli, Gilberto; Schaub, Michael; Häfliger, Guido; Frey, Monika; Jakober, Hans; Müller, Mathis; Stauber, Wolfgang; Tryjanowski, Piotr; Zollinger, Jean-Luc; Jenni, Lukas

    2011-01-01

    1. Populations of plants and animals typically fluctuate because of the combined effects of density-dependent and density-independent processes. The study of these processes is complicated by the fact that population sizes are typically not known exactly, because population counts are subject to sampling variance. Although the existence of sampling variance is broadly acknowledged, relatively few studies on time-series data have accounted for it, which can result in wrong inferences about population processes. 2. To increase our understanding of population dynamics, we analysed time series from six Central European populations of the migratory red-backed shrike Lanius collurio by simultaneously assessing the strength of density dependence, process and sampling variance. In addition, we evaluated hypotheses predicting effects of factors presumed to operate on the breeding grounds, at stopover sites in eastern Africa during fall and spring migration and in the wintering grounds in southern Africa. We used both simple and state-space formulations of the Gompertz equation to model population size. 3. Across populations and modelling approaches, we found consistent evidence for negative density-dependent population regulation. Further, process variance contributed substantially to variation in population size, while sampling variance did not. Environmental conditions in eastern and southern Africa appear to influence breeding population size, as rainfall in the Sahel during fall migration and in the south African wintering areas were positively related to population size in the following spring in four of six populations. In contrast, environmental conditions in the breeding grounds were not related to population size. 4. Our findings suggest negative density-dependent regulation of red-backed shrike breeding populations and are consistent with the long-standing hypothesis that conditions in the African staging and wintering areas influence population numbers of species

  5. Tunable one-dimensional electron gas carrier densities at nanostructured oxide interfaces

    PubMed Central

    Zhuang, Houlong L.; Zhang, Lipeng; Xu, Haixuan; Kent, P. R. C.; Ganesh, P.; Cooper, Valentino R.

    2016-01-01

    The emergence of two-dimensional metallic states at the LaAlO3/SrTiO3 (LAO/STO) heterostructure interface is known to occur at a critical thickness of four LAO layers. This insulator to-metal transition can be explained through the “polar catastrophe” mechanism arising from the divergence of the electrostatic potential at the LAO surface. Here, we demonstrate that nanostructuring can be effective in reducing or eliminating this critical thickness. Employing a modified “polar catastrophe” model, we demonstrate that the nanowire heterostructure electrostatic potential diverges more rapidly as a function of layer thickness than in a regular heterostructure. Our first-principles calculations indicate that for nanowire heterostructures a robust one-dimensional electron gas (1DEG) can be induced, consistent with recent experimental observations of 1D conductivity at LAO/STO steps. Similar to LAO/STO 2DEGs, we predict that the 1D charge density decays laterally within a few unit cells away from the nanowire; thus providing a mechanism for tuning the carrier dimensionality between 1D and 2D conductivity. Our work provides insight into the creation and manipulation of charge density at an oxide heterostructure interface and therefore may be beneficial for future nanoelectronic devices and for the engineering of novel quantum phases. PMID:27151049

  6. Tunable one-dimensional electron gas carrier densities at nanostructured oxide interfaces

    NASA Astrophysics Data System (ADS)

    Zhuang, Houlong L.; Zhang, Lipeng; Xu, Haixuan; Kent, P. R. C.; Ganesh, P.; Cooper, Valentino R.

    2016-05-01

    The emergence of two-dimensional metallic states at the LaAlO3/SrTiO3 (LAO/STO) heterostructure interface is known to occur at a critical thickness of four LAO layers. This insulator to-metal transition can be explained through the “polar catastrophe” mechanism arising from the divergence of the electrostatic potential at the LAO surface. Here, we demonstrate that nanostructuring can be effective in reducing or eliminating this critical thickness. Employing a modified “polar catastrophe” model, we demonstrate that the nanowire heterostructure electrostatic potential diverges more rapidly as a function of layer thickness than in a regular heterostructure. Our first-principles calculations indicate that for nanowire heterostructures a robust one-dimensional electron gas (1DEG) can be induced, consistent with recent experimental observations of 1D conductivity at LAO/STO steps. Similar to LAO/STO 2DEGs, we predict that the 1D charge density decays laterally within a few unit cells away from the nanowire; thus providing a mechanism for tuning the carrier dimensionality between 1D and 2D conductivity. Our work provides insight into the creation and manipulation of charge density at an oxide heterostructure interface and therefore may be beneficial for future nanoelectronic devices and for the engineering of novel quantum phases.

  7. Tunable one-dimensional electron gas carrier densities at nanostructured oxide interfaces.

    PubMed

    Zhuang, Houlong L; Zhang, Lipeng; Xu, Haixuan; Kent, P R C; Ganesh, P; Cooper, Valentino R

    2016-01-01

    The emergence of two-dimensional metallic states at the LaAlO3/SrTiO3 (LAO/STO) heterostructure interface is known to occur at a critical thickness of four LAO layers. This insulator to-metal transition can be explained through the "polar catastrophe" mechanism arising from the divergence of the electrostatic potential at the LAO surface. Here, we demonstrate that nanostructuring can be effective in reducing or eliminating this critical thickness. Employing a modified "polar catastrophe" model, we demonstrate that the nanowire heterostructure electrostatic potential diverges more rapidly as a function of layer thickness than in a regular heterostructure. Our first-principles calculations indicate that for nanowire heterostructures a robust one-dimensional electron gas (1DEG) can be induced, consistent with recent experimental observations of 1D conductivity at LAO/STO steps. Similar to LAO/STO 2DEGs, we predict that the 1D charge density decays laterally within a few unit cells away from the nanowire; thus providing a mechanism for tuning the carrier dimensionality between 1D and 2D conductivity. Our work provides insight into the creation and manipulation of charge density at an oxide heterostructure interface and therefore may be beneficial for future nanoelectronic devices and for the engineering of novel quantum phases. PMID:27151049

  8. Tunable one-dimensional electron gas carrier densities at nanostructured oxide interfaces

    DOE PAGESBeta

    Zhang, Lipeng; Xu, Haixuan; Kent, Paul R. C.; Ganesh, Panchapakesan; Cooper, Valentino R.; Zhuang, Houlong L.

    2016-05-06

    The emergence of two-dimensional metallic states at the LaAlO3/SrTiO3 (LAO/STO) heterostructure interface is known to occur at a critical thickness of four LAO over layers. This insulator-to-metal transition can be explained through the polar catastrophe mechanism arising from the divergence of the electrostatic potential at the LAO surface. Here, we demonstrate that nanostructuring can be effective in reducing or eliminating this critical thickness. Employing a modified polar catastrophe" model, we demonstrate that the nanowire heterostructure electrostatic potential diverges more rapidly as a function of layer thickness than in a regular heterostructure. Our first principles calculations indicate that for nanowire heterostructuremore » geometries a one-dimensional electron gas (1DEG) can be induced, consistent with recent experimental observations of 1D conductivity in LAO/STO steps. Similar to LAO/STO 2DEGs, we predict that the 1D charge density will decay laterally within a few unit cells away from the nanowire; thus providing a mechanism for tuning the carrier behavior between 1D and 2D conductivity. Furthermore, our work provides insight into the creation and manipulation of charge density at an oxide heterostructure interface and therefore may be beneficial for future nanoelectronic devices and for the engineering of novel quantum phases.« less

  9. Tunable One-Dimensional Electron Gas Carrier Densities at Nanostructured Oxide Interfaces

    SciTech Connect

    Zhang, Lipeng; Xu, Haixuan; Kent, Paul R; Ganesh, Panchapakesan; Cooper, Valentino R

    2016-01-01

    The emergence of two-dimensional metallic states at the LaAlO3/SrTiO3 (LAO/STO) heterostructure interface is known to occur at a critical thickness of four LAO over layers. This insulator-to-metal transition can be explained through the polar catastrophe mechanism arising from the divergence of the electrostatic potential at the LAO surface. Here, we demonstrate that nanostructuring can be effective in reducing or eliminating this critical thickness. Employing a modified polar catastrophe" model, we demonstrate that the nanowire heterostructure electrostatic potential diverges more rapidly as a function of layer thickness than in a regular heterostructure. Our first principles calculations indicate that for nanowire heterostructure geometries a one-dimensional electron gas (1DEG) can be induced, consistent with recent experimental observations of 1D conductivity in LAO/STO steps. Similar to LAO/STO 2DEGs, we predict that the 1D charge density will decay laterally within a few unit cells away from the nanowire; thus providing a mechanism for tuning the carrier behavior between 1D and 2D conductivity. In essence, our work provides insight into the creation and manipulation of charge density at an oxide heterostructure interface and therefore may be beneficial for future nanoelectronic devices and for the engineering of novel quantum phases.

  10. Diagrammatic expansion for positive density-response spectra: Application to the electron gas

    NASA Astrophysics Data System (ADS)

    Uimonen, A.-M.; Stefanucci, G.; Pavlyukh, Y.; van Leeuwen, R.

    2015-03-01

    In a recent paper [Phys. Rev. B 90, 115134 (2014), 10.1103/PhysRevB.90.115134] we put forward a diagrammatic expansion for the self-energy which guarantees the positivity of the spectral function. In this work we extend the theory to the density-response function. We write the generic diagram for the density-response spectrum as the sum of "partitions." In a partition the original diagram is evaluated using time-ordered Green's functions on the left half of the diagram, antitime-ordered Green's functions on the right half of the diagram, and lesser or greater Green's function gluing the two halves. As there exists more than one way to cut a diagram in two halves, to every diagram corresponds more than one partition. We recognize that the most convenient diagrammatic objects for constructing a theory of positive spectra are the half-diagrams. Diagrammatic approximations obtained by summing the squares of half-diagrams do indeed correspond to a combination of partitions which, by construction, yield a positive spectrum. We develop the theory using bare Green's functions and subsequently extend it to dressed Green's functions. We further prove a connection between the positivity of the spectral function and the analytic properties of the polarizability. The general theory is illustrated with several examples and then applied to solve the long-standing problem of including vertex corrections without altering the positivity of the spectrum. In fact already the first-order vertex diagram, relevant to the study of gradient expansion, Friedel oscillations, etc., leads to spectra which are negative in certain frequency domain. We find that the simplest approximation to cure this deficiency is given by the sum of the zeroth-order bubble diagram, the first-order vertex diagram, and a partition of the second-order ladder diagram. We evaluate this approximation in the three-dimensional homogeneous electron gas and show the positivity of the spectrum for all frequencies and

  11. Optimization of the particle density to maximize the SERS enhancement factor of periodic plasmonic nanostructure array.

    PubMed

    Wei, Shuhua; Zheng, Mengjie; Xiang, Quan; Hu, Hailong; Duan, Huigao

    2016-09-01

    Low-cost surface-enhanced Raman scattering (SERS) substrate with the largest possible enhancement factor is highly desirable for SERS-based sensing applications. In this work, we systematically investigated how the density of plasmonic nanostructures affects the intensity of SERS signal. By directly depositing of metallic layer on electron-beam-lithography defined dielectric nanoposts, plasmonic structures array with different densities were reliably fabricated for SERS measurements. Two main experimental phenomena were obtained: (1) the SERS intensity did not increase monotonically when increasing the density of plasmonic structures, and (2) these ultra-dense plasmonic structures resulted in the maximal SERS intensity. These results could be well explained based on finite-difference time domain (FDTD) simulations and provide robust experimental evidences to guide the design of the best possible SERS substrate. PMID:27607665

  12. Factors limiting the domestic density of Triatoma infestans in north-west Argentina: a longitudinal study.

    PubMed Central

    Cecere, M. C.; Gürtler, R. E.; Chuit, R.; Cohen, J. E.

    1998-01-01

    Reported are the environmental and demographic risk factors associated with the domestic infestation and density of Triatoma infestans in three heavily infested rural villages in Santiago del Estero Province, Argentina. In a one-factor unadjusted analysis, the number of T. infestans captured per person-hour was associated significantly and negatively with the use of domestic insecticides by householders, type of thatch used in the roofs and the age of the house; and positively with the following: degree of cracking of the indoor walls and presence of hens nesting indoors. In one model, using multiple linear regression and a backward stepwise elimination procedure, most of the variation in the overall abundance of T. infestans was explained by insecticide use and the presence of hens nesting indoors; in another model using the same procedure it was explained by insecticide use, bug density in 1988 and previous spraying with deltamethrin in 1985. Variations in bug density per capture stratum (household goods, beds, walls and roof) were explained by the bug density in other strata and by one or two of the following risk factors: hens nesting indoors, type of roof, presence of cracks in the walls and number of people living in the house. Bug density might be locally controlled by the availability of refuges in the roofs and walls, by the presence of hens nesting indoors and by the use of domestic insecticides. Certain local materials, such as a grass known as simbol, could be successfully used in rural housing improvement programmes aimed at reducing the availability of refuges for insects in the roof. PMID:9803588

  13. Estimated uncertainty of calculated liquefied natural gas density from a comparison of NBS and Gaz de France densimeter test facilities

    SciTech Connect

    Siegwarth, J.D.; LaBrecque, J.F.; Roncier, M.; Philippe, R.; Saint-Just, J.

    1982-12-16

    Liquefied natural gas (LNG) densities can be measured directly but are usually determined indirectly in custody transfer measurement by using a density correlation based on temperature and composition measurements. An LNG densimeter test facility at the National Bureau of Standards uses an absolute densimeter based on the Archimedes principle, while a test facility at Gaz de France uses a correlation method based on measurement of composition and density. A comparison between these two test facilities using a portable version of the absolute densimeter provides an experimental estimate of the uncertainty of the indirect method of density measurement for the first time, on a large (32 L) sample. The two test facilities agree for pure methane to within about 0.02%. For the LNG-like mixtures consisting of methane, ethane, propane, and nitrogen with the methane concentrations always higher than 86%, the calculated density is within 0.25% of the directly measured density 95% of the time.

  14. Monte Carlo study of voxel S factor dependence on tissue density and atomic composition

    NASA Astrophysics Data System (ADS)

    Amato, Ernesto; Italiano, Antonio; Baldari, Sergio

    2013-11-01

    Voxel dosimetry is a common approach to the internal dosimetry of non-uniform activity distributions in nuclear medicine therapies with radiopharmaceuticals and in the estimation of the radiation hazard due to internal contamination of radionuclides. Aim of the present work is to extend our analytical approach for the calculation of voxel S factors to materials different from the soft tissue. We used a Monte Carlo simulation in GEANT4 of a voxelized region of each material in which the source of monoenergetic electrons or photons was uniformly distributed within the central voxel, and the energy deposition was scored over the surrounding 11×11×11 voxels. Voxel S factors were obtained for the following standard ICRP materials: Adipose tissue, Bone cortical, Brain, Lung, Muscle skeletal and Tissue soft with 1 g cm-3 density. Moreover, we considered the standard ICRU materials: Bone compact and Muscle striated. Voxel S factors were represented as a function of the “normalized radius”, defined as the ratio between the source-target voxel distance and the voxel side. We found that voxel S factors and related analytical fit functions are mainly affected by the tissue density, while the material composition gives only a slight contribution to the difference between data series, which is negligible for practical purposes. Our results can help in broadening the dosimetric three-dimensional approach based on voxel S factors to other tissues where diagnostic and therapeutic radionuclides can be taken up and radiation can propagate.

  15. Factors regulating viable cell density in the intervertebral disc: blood supply in relation to disc height

    PubMed Central

    Boubriak, Olga A; Watson, Natasha; Sivan, Sarit S; Stubbens, Naomi; Urban, Jill P G

    2013-01-01

    The intervertebral disc is an avascular tissue, maintained by a small population of cells that obtain nutrients mainly by diffusion from capillaries at the disc–vertebral body interface. Loss of this nutrient supply is thought to lead to disc degeneration, but how nutrient supply influences viable cell density is unclear. We investigated two factors that influence nutrient delivery to disc cells and hence cell viability: disc height and blood supply. We used bovine caudal discs as our model as these show a gradation in disc height. We found that although disc height varied twofold from the largest to the smallest disc studied, it had no significant effect on cell density, unlike the situation found in articular cartilage. The density of blood vessels supplying the discs was markedly greater for the largest disc than the smallest disc, as was the density of pores allowing capillary penetration through the bony endplate. Results indicate that changes in blood vessels in the vertebral bodies supplying the disc, as well as changes in endplate architecture appear to influence density of cells in intervertebral discs. PMID:23311982

  16. Stochastic seasonality and nonlinear density-dependent factors regulate population size in an African rodent

    USGS Publications Warehouse

    Leirs, H.; Stenseth, N.C.; Nichols, J.D.; Hines, J.E.; Verhagen, R.; Verheyen, W.

    1997-01-01

    Ecology has long been troubled by the controversy over how populations are regulated. Some ecologists focus on the role of environmental effects, whereas others argue that density-dependent feedback mechanisms are central. The relative importance of both processes is still hotly debated, but clear examples of both processes acting in the same population are rare. Keyfactor analysis (regression of population changes on possible causal factors) and time-series analysis are often used to investigate the presence of density dependence, but such approaches may be biased and provide no information on actual demographic rates. Here we report on both density-dependent and density-independent effects in a murid rodent pest species, the multimammate rat Mastomys natalensis (Smith, 1834), using statistical capture-recapture models. Both effects occur simultaneously, but we also demonstrate that they do not affect all demographic rates in the same way. We have incorporated the obtained estimates of demographic rates in a population dynamics model and show that the observed dynamics are affected by stabilizing nonlinear density-dependent components coupled with strong deterministic and stochastic seasonal components.

  17. Gas density does not affect pulmonary acoustic transmission in normal men.

    PubMed

    Mahagnah, M; Gavriely, N

    1995-03-01

    Fremitus, the transmission of sound and vibration from the mouth to the chest wall, has long been used clinically to examine the pulmonary system. Recently, modern technology has become available to measure the acoustic transfer function (TF) and transit times (TT) of the pulmonary system. Because sound speed is inversely proportional to the square root of gas density in free gas, but not in porous media, we measured the effect of air and Heliox (80% He-20% O2) breathing on pulmonary sound transmission in six healthy subjects to investigate the mechanism of sound transmission. Wide-band noise (75-2,000 Hz) was "injected" into the mouth and picked up over the trachea and chest wall. The averaged power spectra, TF, phase, and coherence were calculated using a fast Fourier transform-based algorithm. The phase data were used to calculate TT as a function of frequency. TF was found to consist of a low-pass filter property with essentially flat transmitted energy to 300 Hz and exponential decline to 600 Hz at the anterior right upper lobe (CR) and flat transmission to 100 Hz with exponential decline to 150 Hz at the right posterior base (BR). TF was not affected by breathing Heliox. The average TT values, calculated from the slopes of the averaged phase, were 1.5 +/- 0.5 ms for trachea to CR and 5.2 +/- 0.5 ms for trachea to BR transmission during air breathing. During Heliox breathing, the values of TT were 1.5 +/- 0.5 ms and 4.9 +/- 0.5 ms from the trachea to CR and from the trachea to BR locations, respectively. These results suggest that sound transmission in the respiratory system is dominated by wave propagation through the parenchymal porous structure. PMID:7775338

  18. Gas kinetics and dust dynamics in low-density comet comae

    NASA Astrophysics Data System (ADS)

    Davidsson, Björn J. R.; Gulkis, Samuel; Alexander, Claudia; Allmen, Paul von; Kamp, Lucas; Lee, Seungwon; Warell, Johan

    2010-11-01

    Extensive regions of low-density cometary comae are characterized by important deviations from the Maxwell-Boltzmann velocity distribution, i.e. breakdown of thermodynamic equilibrium. The consequences of this on the shapes of emission and absorption lines, and for the acceleration of solid bodies due to gas drag, have rarely been investigated. These problems are studied here to aid in the development of future coma models, and in preparation for observations of Comet 67P/Churyumov-Gerasimenko from the ESA Rosetta spacecraft. Two topics in particular, related to Rosetta, are preparation for in situ observations of water, carbon monoxide, ammonia, and methanol emission lines by the mm/sub-mm spectrometer MIRO, as well as gas drag forces on dust grains and on the Rosetta spacecraft itself. Direct Simulation Monte Carlo (DSMC) modeling of H 2O/CO mixtures in spherically symmetric geometries at various heliocentric distances are used to study the evolution of the (generally non-Maxwellian) velocity distribution function throughout the coma. Such distribution functions are then used to calculate Doppler broadening profiles and drag forces. It is found that deviation from thermodynamic equilibrium indeed is commonplace, and already at 2.5 AU from the Sun the entire comet coma displays manifestations of such breakdown, e.g., non-equal partitioning of energy between kinetic and rotational modes, causing substantial differences between translational and rotational temperatures. We exemplify how deviations from thermodynamic equilibrium affect the properties of Doppler broadened line profiles. Upper limits on the size of liftable dust grains as well as terminal grain velocities are presented. Furthermore, it is demonstrated that the drag-to-gravity force ratio is likely to decrease with decreasing cometocentric distance, which may be of relevance both for Rosetta and for the lander probe Philae.

  19. Homeostatic maintenance of ponderosa pine gas exchange in response to stand density changes.

    PubMed

    McDowell, Nate G; Adams, Henry D; Bailey, John D; Hess, Marcey; Kolb, Thomas E

    2006-06-01

    Homeostatic maintenance of gas exchange optimizes carbon gain per water loss. Homeostasis is regulated by short-term physiological and long-term structural mechanisms, both of which may respond to changes in resource availability associated with competition. Therefore, stand density regulation via silvicultural manipulations may facilitate growth and survival through mechanisms operating at both short and long timescales. We investigated the responses of ponderosa pine (Pinus ponderosa) to stand basal area manipulations in Arizona, USA. Stand basal area was manipulated to seven replicated levels in 1962 and was maintained for four decades by decadal thinning. We measured basal area increment (BAI) to assess the response and sustainability of wood growth, carbon isotope discrimination (A) inferred from annual rings to assess the response of crown gas exchange, and ratios of leaf area to sapwood area (A(l):A(s)) to assess longer term structural acclimation. Basal area treatments increased soil water potential (r2 = 0.99) but did not affect photosynthetic capacity. BAI increased within two years of thinning, and the 40-year mean BAI was negatively correlated with stand basal area (r2 = 0.98). delta was negatively correlated with stand basal area for years 5 through 12 after thinning (r2 = 0.90). However, delta was relatively invariant with basal area for the period 13-40 years after initial thinning despite maintenance of treatment basal areas via repeated decadal thinnings. Independent gas exchange measurements verified that the ratio of photosynthesis to stomatal conductance was invariant with basal area, but absolute values of both were elevated at lower basal areas. A(l):A(s) was negatively correlated with basal area (r2 = 0.93). We hypothesize that increased A(l):A(s) is a homeostatic response to increased water availability that maximizes water-use efficiency and whole-tree carbon uptake. Elevated A(l):A(s) of trees at low basal areas was associated with greater

  20. Anamnestic risk factor questionnaire as reliable diagnostic instrument for osteoporosis (reduced bone morphogenic density)

    PubMed Central

    2011-01-01

    Background Osteoporosis is a major health problem worldwide, and is included in the WHO list of the top 10 major diseases. However, it is often undiagnosed until the first fracture occurs, due to inadequate patient education and lack of insurance coverage for screening tests. Anamnestic risk factors like positive family anamnesis or early menopause are assumed to correlate with reduced BMD. Methods In our study of 78 patients with metaphyseal long bone fractures, we searched for a correlation between anamnestic risk factors, bone specific laboratory values, and the bone morphogenic density (BMD). Each indicator was examined as a possible diagnostic instrument for osteoporosis. The secondary aim of this study was to demonstrate the high prevalence of osteoporosis in patients with metaphyseal fractures. Results 76.9% of our fracture patients had decreased bone density and 43.6% showed manifest osteoporosis in DXA (densitometry) measurements. Our questionnaire, identifying anamnestic risk factors, correlated highly significantly (p = 0.01) with reduced BMD, whereas seven bone-specific laboratory values (p = 0.046) correlated significantly. Conclusions Anamnestic risk factors correlate with pathological BMD. The medical questionnaire used in this study would therefore function as a cost-effective primary diagnostic instrument for identification of osteoporosis patients. PMID:21849030

  1. Development of 3-dimensional time-dependent density functional theory and its application to gas diffusion in nanoporous materials.

    PubMed

    Liu, Yu

    2016-05-11

    I developed a novel time-dependent density functional theory (TDDFT) and applied it to complicated 3-dimensional systems for the first time. Superior to conventional TDDFT, the diffusion coefficient is modeled as a function of density profile, which is self-determined by the entropy scaling rule instead using an input parameter. The theory was employed to mimic gas diffusion in a nanoporous material. The TDDFT prediction on the transport diffusivity was reasonable compared to simulations. Moreover, the time-dependent density profiles gave an insight into the microscopic mechanism of the diffusion process. PMID:27121986

  2. Density response of a trapped Fermi gas: A crossover from the pair vibration mode to the Goldstone mode

    SciTech Connect

    Korolyuk, A.; Kinnunen, J. J.; Toermae, P.

    2011-09-15

    We consider the density response of a trapped two-component Fermi gas. Combining the Bogoliubov-deGennes method with the random phase approximation allows the study of both collective and single-particle excitations. Calculating the density response across a wide range of interactions, we observe a crossover from a weakly interacting pair vibration mode to a strongly interacting Goldstone mode. The crossover is associated with a depressed collective mode frequency and an increased damping rate, in agreement with density response experiments performed in strongly interacting atomic gases.

  3. Lyα Emission from Green Peas: The Role of Circumgalactic Gas Density, Covering, and Kinematics

    NASA Astrophysics Data System (ADS)

    Henry, Alaina; Scarlata, Claudia; Martin, Crystal L.; Erb, Dawn

    2015-08-01

    We report Hubble Space Telescope/Cosmic Origins Spectrograph observations of the Lyα emission and interstellar absorption lines in a sample of 10 star-forming galaxies at z ˜ 0.2. Selected on the basis of high equivalent width optical emission lines, the sample, dubbed “Green Peas,” make some of the best analogs for young galaxies in an early universe. We detect Lyα emission in all ten galaxies, and 9/10 show double-peaked line profiles suggestive of low H i column density. We measure Lyα/Hα flux ratios of 0.5-5.6, implying that 5%-60% of Lyα photons escape the galaxies. These data confirm previous findings that low-ionization metal absorption (LIS) lines are weaker when Lyα escape fraction and equivalent width are higher. However, contrary to previously favored interpretations of this trend, increased Lyα output cannot be the result of a varying H i covering: the Lyman absorption lines (Lyβ and higher) show a covering fraction near unity for gas with NH i ≳ 1016 cm-2. Moreover, we detect no correlation between Lyα escape and the outflow velocity of the LIS lines, suggesting that kinematic effects do not explain the range of Lyα/Hα flux ratios in these galaxies. In contrast, we detect a strong anticorrelation between the Lyα escape fraction and the velocity separation of the Lyα emission peaks, driven primarily by the velocity of the blue peak. As this velocity separation is sensitive to H i column density, we conclude that Lyα escape in these Green Peas is likely regulated by the H i column density rather than outflow velocity or H i covering fraction. Based on observations made with the NASA/ESA Hubble Space Telescope, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with programs 12928 and 11727.

  4. Departures from local thermodynamic equilibrium in cutting arc plasmas derived from electron and gas density measurements using a two-wavelength quantitative Schlieren technique

    SciTech Connect

    Prevosto, L.; Mancinelli, B.; Artana, G.; Kelly, H.

    2011-03-15

    A two-wavelength quantitative Schlieren technique that allows inferring the electron and gas densities of axisymmetric arc plasmas without imposing any assumption regarding statistical equilibrium models is reported. This technique was applied to the study of local thermodynamic equilibrium (LTE) departures within the core of a 30 A high-energy density cutting arc. In order to derive the electron and heavy particle temperatures from the inferred density profiles, a generalized two-temperature Saha equation together with the plasma equation of state and the quasineutrality condition were employed. Factors such as arc fluctuations that influence the accuracy of the measurements and the validity of the assumptions used to derive the plasma species temperature were considered. Significant deviations from chemical equilibrium as well as kinetic equilibrium were found at elevated electron temperatures and gas densities toward the arc core edge. An electron temperature profile nearly constant through the arc core with a value of about 14000-15000 K, well decoupled from the heavy particle temperature of about 1500 K at the arc core edge, was inferred.

  5. Density-induced processes in quantum gas mixtures in optical lattices

    NASA Astrophysics Data System (ADS)

    Jürgensen, Ole; Sengstock, Klaus; Lühmann, Dirk-Sören

    2012-10-01

    We show that off-site processes and multiorbital physics have a crucial impact on the phase diagram of quantum gas mixtures in optical lattices. In particular, we discuss Bose-Fermi mixtures where the intra- and interspecies interactions induce competing density-induced hopping processes, the so-called bond-charge interactions. Furthermore, higher bands strongly influence tunneling and on-site interactions. We apply a multiorbital interaction-induced dressing of the lowest band, which leads to renormalized hopping processes. These corrections give rise to an extended Hubbard model with intrinsically occupation-dependent parameters. The resulting decrease of the tunneling competes with a decrease of the total on-site interaction energy, both affecting the critical lattice depth of the superfluid to Mott-insulator transition. In contrast to the standard Bose-Fermi Hubbard model, we predict a large shift of the transition to shallower lattice depths with increasing Bose-Fermi attraction. The applied theoretical model allows an accurate prediction of the modified tunneling amplitudes and the critical lattice depth, both being recently observed experimentally.

  6. Noble gas adsorption in two-dimensional zeolites: a combined experimental and density functional theory study

    NASA Astrophysics Data System (ADS)

    Wang, Mengen; Zhong, Jianqiang; Boscoboinik, Jorge Anibal; Lu, Deyu

    Zeolites are important industrial catalysts with porous three-dimensional structures. The catalytically active sites are located inside the pores, thus rendering them inaccessible for surface science measurements. We synthesized a two-dimensional (2D) zeolite model system, consisting of an (alumino)silicate bilayer weakly bound to a Ru (0001) surface. The 2D zeolite is suitable for surface science studies; it allows a detailed characterization of the atomic structure of the active site and interrogation of the model system during the catalytic reaction. As an initial step, we use Ar adsorption to obtain a better understanding of the atomic structure of the 2D zeolite. In addition, atomic level studies of rare gas adsorption and separation by zeolite are important for its potential application in nuclear waste sequestration. Experimental studies found that Ar atoms can be trapped inside the 2D-zeolite, raising an interesting question on whether Ar atoms are trapped inside the hexagonal prism nano-cages or at the interface between the (alumino)silicate bilayer and Ru(0001), or both. DFT calculations using van der Waals density functionals were carried out to determine the preferred Ar adsorption sites and the corresponding adsorption energies. This research used resources of the Center for Functional Nanomaterials, which is a U.S. DOE Office of Science Facility, at Brookhaven National Laboratory under Contract No. DE-SC0012704.

  7. Drift and diffusion of spin and charge density waves in a two-dimensional electron gas

    NASA Astrophysics Data System (ADS)

    Yang, Luyi; Koralek, J. D.; Orenstein, J.; Tibbetts, D. R.; Reno, J. L.; Lilly, M. P.

    2011-03-01

    We use transient grating spectroscopy (TGS) to study the persistent spin helix (PSH) state and electron-hole density wave (EHDW) in a 2D electron gas in the presence of an in-plane electric field parallel to the wavevector of the PSH or EHDW. By directly measuring the phase, we can measure the PSH and EHDW displacement with 10 nm spatial and sub-picosecond time resolution. We obtain both the spin diffusion and mobility and ambipolar diffusion and mobility from the TGS measurements of PSH and EHDW, respectively. The spin transresistivity extracted from the spin diffusion is in excellent agreement with the RPA theory of spin Coulomb drag (SCD). The spin mobility data indicate that SCD may also play a role in the spin wave drifting process. From the ambipolar diffusion and mobility, we obtain the transresistivity of electrons and holes in the same layer, which is much stronger than is typically seen in the conventional Coulomb drag experiments on coupled quantum wells.

  8. Novelty detection by multivariate kernel density estimation and growing neural gas algorithm

    NASA Astrophysics Data System (ADS)

    Fink, Olga; Zio, Enrico; Weidmann, Ulrich

    2015-01-01

    One of the underlying assumptions when using data-based methods for pattern recognition in diagnostics or prognostics is that the selected data sample used to train and test the algorithm is representative of the entire dataset and covers all combinations of parameters and conditions, and resulting system states. However in practice, operating and environmental conditions may change, unexpected and previously unanticipated events may occur and corresponding new anomalous patterns develop. Therefore for practical applications, techniques are required to detect novelties in patterns and give confidence to the user on the validity of the performed diagnosis and predictions. In this paper, the application of two types of novelty detection approaches is compared: a statistical approach based on multivariate kernel density estimation and an approach based on a type of unsupervised artificial neural network, called the growing neural gas (GNG). The comparison is performed on a case study in the field of railway turnout systems. Both approaches demonstrate their suitability for detecting novel patterns. Furthermore, GNG proves to be more flexible, especially with respect to dimensionality of the input data and suitability for online learning.

  9. 40 CFR Table W - 1A of Subpart W-Default Whole Gas Emission Factors for Onshore Petroleum and Natural Gas Production

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... Emission Factors for Onshore Petroleum and Natural Gas Production W Table W Protection of Environment... Petroleum and Natural Gas Systems Definitions. Pt. 98, Subpt. W, Table W-1A Table W-1A of Subpart W—Default Whole Gas Emission Factors for Onshore Petroleum and Natural Gas Production Onshore petroleum...

  10. Density Functional Computations and Mass Spectrometric Measurements. Can this Coupling Enlarge the Knowledge of Gas-Phase Chemistry?

    NASA Astrophysics Data System (ADS)

    Marino, T.; Russo, N.; Sicilia, E.; Toscano, M.; Mineva, T.

    A series of gas-phase properties of the systems has been investigated by using different exchange-correlation potentials and basis sets of increasing size in the framework of Density Functional theory with the aim to determine a strategy able to give reliable results with reasonable computational efforts.

  11. Generation and characterization of high-density gas jets from a 150 micron diameter nozzle in air

    NASA Astrophysics Data System (ADS)

    Hahn, Luke; Bartas, Kevin; Tay, Yan; Kuk, Donghoon; Kim, Ki-Yong

    This work characterizes argon and nitrogen gas jets in unconventional atmospheric pressure instead of the conventional vacuum pressure, and then compares the results directly to that of the conventional technique of creating gas jet targets. A Mach-Zehnder interferometer was used to estimate the number density of the gas jet, and a Rayleigh scattering setup was used to determine if either of the techniques formed atomic clusters and if so, estimating relative quantity. The diameter of the cylindrical nozzle used for is around 150 μm with backing pressures ranging from 13 bars to 69 bars. The highest backing pressure gives us a maximum phase shift value of 9 rad, number density 4.5 ×1020 cm-3. Another characteristic property of these jets is the shock diamond formation due to the flows interaction with atmospheric air particles. The highest number density for a shock diamond was ~1020 cm-3 which does not necessarily occur at higher backing pressure. Also, the distance from the first shock diamond to the nozzle orifice does increase with increasing backing pressure, consistent with a theory. This type of high-density, thin gas jets can be used as a laser target for creating dense plasmas and producing energetic particles and X-rays in the atmospheric conditions. Work supported by DOE, Fusion Energy Sciences under Award No. DE-SC0010706.

  12. The Effects of Fuel and Cylinder Gas Densities on the Characteristics of Fuel Sprays for Oil Engines

    NASA Technical Reports Server (NTRS)

    Joachim, W F; Beardsley, Edward G

    1928-01-01

    This investigation was conducted as a part of a general research on fuel-injection engines for aircraft. The purpose of the investigation was to determine the effects of fuel and cylinder gas densities with several characteristics of fuel sprays for oil engines. The start, growth, and cut-off of single fuel sprays produced by automatic injection valves were recorded on photographic film by means of special high-speed motion-picture apparatus. This equipment, which has been described in previous reports, is capable of taking twenty-five consecutive pictures of the moving spray at the rate of 4,000 per second. The penetrations of the fuel sprays increased and the cone angles and relative distributions decreased with increase in the specific gravity of the fuel. The density of the gas into which the fuel sprays were injected controlled their penetration. This was the only characteristic of the chamber gas that had a measurable effect upon the fuel sprays. Application of fuel-spray penetration data to the case of an engine, in which the pressure is rising during injection, indicated that fuel sprays may penetrate considerably farther than when injected into a gas at a density equal to that of the gas in an engine cylinder at top center.

  13. Cryopegs as destabilization factor of intra-permafrost gas hydrates

    NASA Astrophysics Data System (ADS)

    Chuvilin, Evgeny; Bukhanov, Boris; Istomin, Vladimir

    2016-04-01

    A characteristic feature of permafrost soils in the Arctic is widespread intra-permafrost unfrozen brine lenses - cryopegs. They are often found in permafrost horizons in the north part of Western Siberia, in particular, on the Yamal Peninsula. Cryopegs depths in permafrost zone can be tens and hundreds of meters from the top of frozen strata. The chemical composition of natural cryopegs is close to sea waters, but is characterized by high mineralization. They have a sodium-chloride primary composition with a minor amount of sulphate. Mineralization of cryopegs brine is often hundreds of grams per liter, and the temperature is around -6…-8 °C. The formation of cryopegs in permafrost is associated with processes of long-term freezing of sediments and cryogenic concentration of salts and salt solutions in local areas. The cryopegs' formation can take place in the course of permafrost evolution at the sea transgressions and regressions during freezing of saline sea sediments. Very important feature of cryopegs in permafrost is their transformation in the process of changing temperature and pressure conditions. As a result, the salinity and chemical composition are changed and in addition the cryopegs' location can be changed during their migration. The cryopegs migration violates the thermodynamic conditions of existence intra-permafrost gas hydrate formations, especially the relic gas hydrates deposits, which are situated in the shallow permafrost up to 100 meters depth in a metastable state [1]. The interaction cryopegs with gas hydrates accumulations can cause decomposition of intra-permafrost hydrates. Moreover, the increasing of salt and unfrozen water content in sedimentary rocks sharply reduce the efficiency of gas hydrates self-preservation in frozen soils. It is confirmed by experimental investigations of interaction of frozen gas hydrate bearing sediments with salt solutions [2]. So, horizons with elevated pressure can appear, as a result of gas hydrate

  14. Scaling of stomatal size and density optimizes allocation of leaf epidermal space for gas exchange in angiosperms

    NASA Astrophysics Data System (ADS)

    de Boer, Hugo Jan; Price, Charles A.; Wagner-Cremer, Friederike; Dekker, Stefan C.; Franks, Peter J.; Veneklaas, Erik J.

    2015-04-01

    Stomata on plant leaves are key traits in the regulation of terrestrial fluxes of water and carbon. The basic morphology of stomata consists of a diffusion pore and two guard cells that regulate the exchange of CO2 and water vapour between the leaf interior and the atmosphere. This morphology is common to nearly all land plants, yet stomatal size (defined as the area of the guard cell pair) and stomatal density (the number of stomata per unit area) range over three orders of magnitude across species. Evolution of stomatal sizes and densities is driven by selection pressure on the anatomical maximum stomatal conductance (gsmax), which determines the operational range of leaf gas exchange. Despite the importance of stomata traits for regulating leaf gas exchange, a quantitative understanding of the relation between adaptation of gsmax and the underlying co-evolution of stomatal sizes and densities is still lacking. Here we develop a theoretical framework for a scaling relationship between stomatal sizes and densities within the constraints set by the allocation of epidermal space and stomatal gas exchange. Our theory predicts an optimal scaling relationship that maximizes gsmax and minimizes epidermal space allocation to stomata. We test whether stomatal sizes and densities reflect this optimal scaling with a global compilation of stomatal trait data on 923 species reflecting most major clades. Our results show optimal scaling between stomatal sizes and densities across all species in the compiled data set. Our results also show optimal stomatal scaling across angiosperm species, but not across gymnosperm and fern species. We propose that the evolutionary flexibility of angiosperms to adjust stomatal sizes underlies their optimal allocation of leaf epidermal space to gas exchange.

  15. Environmental Factors Associated with High Fly Densities and Diarrhea in Vellore, India.

    PubMed

    Collinet-Adler, Stefan; Babji, Sudhir; Francis, Mark; Kattula, Deepthi; Premkumar, Prasanna Samuel; Sarkar, Rajiv; Mohan, Venkat Ragava; Ward, Honorine; Kang, Gagandeep; Balraj, Vinohar; Naumova, Elena N

    2015-09-01

    Diarrhea causes significant morbidity and mortality in Indian children under 5 years of age. Flies carry enteric pathogens and may mediate foodborne infections. In this study, we characterized fly densities as a determinant of infectious diarrhea in a longitudinal cohort of 160 urban and 80 rural households with 1,274 individuals (27% under 5 years of age) in Vellore, India. Household questionnaires on living conditions were completed at enrollment. Fly abundance was measured during the wet and dry seasons using fly ribbons placed in kitchens. PCRs for enteric bacteria, viruses, and protozoa were performed on 60 fly samples. Forty-three (72%) fly samples were positive for the following pathogens: norovirus (50%), Salmonella spp. (46.7%), rotavirus (6.7%), and Escherichia coli (6.7%). Ninety-one episodes of diarrhea occurred (89% in children under 5 years of age). Stool pathogens isolated in 24 of 77 (31%) samples included E. coli, Shigella spp., Vibrio spp., Giardia, Cryptosporidium, and rotavirus. Multivariate log-linear models were used to explore the relationships between diarrhea and fly densities, controlling for demographics, hygiene, and human-animal interactions. Fly abundance was 6 times higher in rural than urban sites (P < 0.0001). Disposal of garbage close to homes and rural living were significant risk factors for high fly densities. The presence of latrines was protective against high fly densities and diarrhea. The adjusted relative risks of diarrheal episodes and duration of diarrhea, associated with fly density at the 75th percentile, were 1.18 (95% confidence interval [CI], 1.03 to 1.34) and 1.15 (95% CI, 1.02 to 1.29), respectively. Flies harbored enteric pathogens, including norovirus, a poorly documented pathogen on flies. PMID:26116684

  16. Environmental Factors Associated with High Fly Densities and Diarrhea in Vellore, India

    PubMed Central

    Collinet-Adler, Stefan; Babji, Sudhir; Francis, Mark; Kattula, Deepthi; Premkumar, Prasanna Samuel; Sarkar, Rajiv; Mohan, Venkat Ragava; Ward, Honorine; Kang, Gagandeep; Balraj, Vinohar

    2015-01-01

    Diarrhea causes significant morbidity and mortality in Indian children under 5 years of age. Flies carry enteric pathogens and may mediate foodborne infections. In this study, we characterized fly densities as a determinant of infectious diarrhea in a longitudinal cohort of 160 urban and 80 rural households with 1,274 individuals (27% under 5 years of age) in Vellore, India. Household questionnaires on living conditions were completed at enrollment. Fly abundance was measured during the wet and dry seasons using fly ribbons placed in kitchens. PCRs for enteric bacteria, viruses, and protozoa were performed on 60 fly samples. Forty-three (72%) fly samples were positive for the following pathogens: norovirus (50%), Salmonella spp. (46.7%), rotavirus (6.7%), and Escherichia coli (6.7%). Ninety-one episodes of diarrhea occurred (89% in children under 5 years of age). Stool pathogens isolated in 24 of 77 (31%) samples included E. coli, Shigella spp., Vibrio spp., Giardia, Cryptosporidium, and rotavirus. Multivariate log-linear models were used to explore the relationships between diarrhea and fly densities, controlling for demographics, hygiene, and human-animal interactions. Fly abundance was 6 times higher in rural than urban sites (P < 0.0001). Disposal of garbage close to homes and rural living were significant risk factors for high fly densities. The presence of latrines was protective against high fly densities and diarrhea. The adjusted relative risks of diarrheal episodes and duration of diarrhea, associated with fly density at the 75th percentile, were 1.18 (95% confidence interval [CI], 1.03 to 1.34) and 1.15 (95% CI, 1.02 to 1.29), respectively. Flies harbored enteric pathogens, including norovirus, a poorly documented pathogen on flies. PMID:26116684

  17. Analyses of substantially different plasma current densities and safety factors reconstructed from magnetic diagnostics data

    NASA Astrophysics Data System (ADS)

    Zaitsev, F. S.; Kostomarov, D. P.; Suchkov, E. P.; Drozdov, V. V.; Solano, E. R.; Murari, A.; Matejcik, S.; Hawkes, N. C.; Contributors, JET-EFDA

    2011-10-01

    The problem of plasma current density and safety factor reconstruction using magnetic field measurements is considered. In the traditional formulation, the problem is strongly ill-posed. In particular, substantially different current densities and safety factors can be equally well attributed to the same set of measurements, given their experimental errors. In other words, the problem can be strongly unstable with respect to the input data. Different constraints are used in practice to make the problem more stable. This paper presents an accurate mathematical formulation of the inverse problem and its variants. A numerical algorithm is provided, which permits us to study the stability with respect to variations in the input data, to find all substantially different solutions, or to prove their absence, and to determine the confidence intervals of the reconstructions. The proposed method also allows establishing the maximum error for a given diagnostic (additional constraint), below which the diagnostic efficiently extracts one solution among several substantially different ones. Examples of very different current density and safety factor reconstructions for measurements with finite accuracy are presented for the original formulation of the inverse problem. Cases of MAST, JET and ITER-like plasmas are considered. It is shown that including the motional Stark effect (MSE) measurements as a constraint, provided the accuracy of MSE measurements is sufficient, allows identifying one solution among several very different ones, obtained without such a constraint. The maximum MSE diagnostics error for efficient identification of this solution is estimated for JET. The approach of this paper can be used for a wide range of ill-posed problems in physics and can help in selecting additional conditions, which can identify the most likely solution among several.

  18. Vascular density, angiogenesis and pro-angiogenic factors in uterine fibroids.

    PubMed

    Sajewicz, Marek; Konarska, Monika; Wrona, Anna Natalia; Aleksandrovych, Veronika; Bereza, Tomasz; Komnata, Kinga; Solewski, Bernard; Maleszka, Aleksandra; Depukat, Paweł; Warchoł, Łukasz

    2016-01-01

    Angiogenesis is a process of development of new vessels from the preexisting vascular network of a host. This is process which is seen in many physiological situations but it accompanies also a development of different lesions, i.e. neoplasms. Uterine fibroids are one of the most frequent lesions which affect human internal female genital tracts. Authors briefly review most important pro-angiogenic factors, based on their own observation as well as reviewing current literature. They pay much attention to vascular density which is significantly changed in the uterine tumors. PMID:27513836

  19. Charge density distributions and charge form factors of the N=82 and N=126 isotonic nuclei

    SciTech Connect

    Wang Zaijun; Fan Ying; Ren Zhongzhou

    2006-01-15

    Charge form factors for N=82 and N=126 isotonic nuclei are calculated with the relativistic eikonal approximation, in which the charge density distributions are from the relativistic mean-field theory. The variations of charge form factors with proton number are discussed in detail. It is found that the most sensitive parts of the charge form factors are those around the minimums and maximums. For an increasing proton number, the charge form factors near the extrema have an upward shift. As the protons increase and occupy a new shell, the minimums and maximums of the charge form factors could also have a significant inward shift. The results can be useful for the study of behaviors of valence-proton wave functions for such nuclei as can be considered as a core plus proton(s), and thus the proton-halo phenomenon. In addition, the results can also be useful for future electron-unstable nucleus scattering experiments and provide tests of the reliability of the relativistic mean-field theory for the unstable nuclei.

  20. Cultivar and Tree Density As Key Factors in the Long-Term Performance of Super High-Density Olive Orchards.

    PubMed

    Díez, Concepción M; Moral, Juan; Cabello, Diego; Morello, Pablo; Rallo, Luis; Barranco, Diego

    2016-01-01

    Super high-density (SHD) olive orchards are rapidly expanding since the first plantation was set up in Spain in the 1990s. Because there are no long-term studies characterizing these systems, it is unknown if densities above a certain threshold could trigger competition among fully-grown trees, compromising their development. Over 14 years we have evaluated the performance of the major olive cultivars currently planted in SHD systems ("Arbequina," Arbequina IRTA-i·18, "Arbosana," "Fs-17," and "Koroneiki") and nine SHD designs ranging from 780 to 2254 trees ha(-1) for the cultivar "Arbequina." Remarkably, the accumulated fruit and oil production of the five cultivars increased linearly over time. Our data indicated the favorable long-term performance of the evaluated cultivars with an average annual oil production of 2.3 t ha(-1). Only "Fs-17" did not perform well to the SHD system in our conditions and it yielded about half (1.2 t ha(-1)) of the other cultivars. In the density trial for "Arbequina," both fruit and oil accumulated production increased over time as a function of tree density. Thus, the accumulated oil yield ranged from 16.1 t ha(-1) for the lowest density (780 trees ha(-1)) to 29.9 t ha(-1) for the highest (2254 trees ha(-1)). In addition, we note that the accumulated production per surface unit showed a better correlation with the hedgerow length than the tree density. Thus, the current planting designs of SHD olive orchards can be further improved taking this parameter into account. Despite observations that some irregular patterns of crop distribution have arisen, our olive hedgerows are still fully productive after 14 years of planting. This result contradicts previous experiences that showed declines in production 7 or 8 years after planting due to high vigor, shading, and limited ventilation. PMID:27602035

  1. Geological and environmental factors involved in natural gas accidents

    NASA Astrophysics Data System (ADS)

    Sommer, Sheldone E.

    1981-07-01

    Variability in soil mineralogy, texture, and pavement cover are involved in events leading to undetected gas leaks and subsequent explosions in Bowie, Md. and Washington, D.C. These geologic parameters are involved in selectively removing the gas odorant additive t-butyl merceptan as the gas came into contact with the soil near the pipeline breaks. This removal resulted in an accumulation of combustable natural gas without detectable odor. Soil samples from drill holes and near surface sites were utilized to map soil type, texture, and mineralogy. Residual methane content of the samples was also measured. The data from two dissimilar sites indicates that finegrained soil enriched in montmorillonite preferentially removes the odorant.

  2. The Effects of Physicochemical Factors and Cell Density on Nitrite Transformation in a Lipid-Rich Chlorella.

    PubMed

    Liang, Fang; Du, Kui; Wen, Xiaobin; Luo, Liming; Geng, Yahong; Li, Yeguang

    2015-12-28

    To understand the effects of physicochemical factors on nitrite transformation by microalgae, a lipid-rich Chlorella with high nitrite tolerance was cultured with 8 mmol/l sodium nitrite as sole nitrogen source under different conditions. The results showed that nitrite transformation was mainly dependent on the metabolic activities of algal cells rather than oxidation of nitrite by dissolved oxygen. Light intensity, temperature, pH, NaHCO3 concentrations, and initial cell densities had significant effects on the rate of nitrite transformation. Single-factor experiments revealed that the optimum conditions for nitrite transformation were light intensity: 300 μmol/m(2); temperature: 30°C; pH: 7-8; NaHCO3 concentration: 2.0 g/l; and initial cell density: 0.15 g/l; and the highest nitrite transformation rate of 1.36 mmol/l/d was achieved. There was a positive correlation between nitrite transformation rate and the growth of Chlorella. The relationship between nitrite transformation rate (mg/l/d) and biomass productivity (g/l/d) could be described by the regression equation y = 61.3x (R(2) = 0.9665), meaning that 61.3 mg N element was assimilated by 1.0 g dry biomass on average, which indicated that the nitrite transformation is a process of consuming nitrite as nitrogen source by Chlorella. The results demonstrated that the Chlorella suspension was able to assimilate nitrite efficiently, which implied the feasibility of using flue gas for mass production of Chlorella without preliminary removal of NOX. PMID:26323272

  3. Clinical and Microbiological Factors Associated with High Nasopharyngeal Pneumococcal Density in Patients with Pneumococcal Pneumonia

    PubMed Central

    Alpkvist, Helena; Athlin, Simon; Nauclér, Pontus; Herrmann, Björn; Abdeldaim, Guma; Slotved, Hans-Christian; Hedlund, Jonas; Strålin, Kristoffer

    2015-01-01

    Background We aimed to study if certain clinical and/or microbiological factors are associated with a high nasopharyngeal (NP) density of Streptococcus pneumoniae in pneumococcal pneumonia. In addition, we aimed to study if a high NP pneumococcal density could be useful to detect severe pneumococcal pneumonia. Methods Adult patients hospitalized for radiologically confirmed community-acquired pneumonia were included in a prospective study. NP aspirates were collected at admission and were subjected to quantitative PCR for pneumococcal DNA (Spn9802 DNA). Patients were considered to have pneumococcal etiology if S. pneumoniae was detected in blood culture and/or culture of respiratory secretions and/or urinary antigen test. Results Of 166 included patients, 68 patients had pneumococcal DNA detected in NP aspirate. Pneumococcal etiology was noted in 57 patients (84%) with positive and 8 patients (8.2%) with negative test for pneumococcal DNA (p<0.0001). The median NP pneumococcal density of DNA positive patients with pneumococcal etiology was 6.83 log10 DNA copies/mL (range 1.79–9.50). In a multivariate analysis of patients with pneumococcal etiology, a high pneumococcal density was independently associated with severe pneumonia (Pneumonia Severity Index risk class IV-V), symptom duration ≥2 days prior to admission, and a medium/high serum immunoglobulin titer against the patient’s own pneumococcal serotype. NP pneumococcal density was not associated with sex, age, smoking, co-morbidity, viral co-infection, pneumococcal serotype, or bacteremia. Severe pneumococcal pneumonia was noted in 28 study patients. When we studied the performance of PCR with different DNA cut-off levels for detection of severe pneumococcal pneumonia, we found sensitivities of 54–82% and positive predictive values of 37–56%, indicating suboptimal performance. Conclusions Pneumonia severity, symptom duration ≥2 days, and a medium/high serum immunoglobulin titer against the patient

  4. A theory for accelerated slow crack growth in medium-density polyethylene fuel-gas pipes

    SciTech Connect

    Chaoui, K.

    1989-01-01

    In the present work, a new testing procedure is developed for medium density polyethylene (MDPE) fuel gas pipes to produce brittle fracture at laboratory scale within a shorter period of time as compared to existing procedures. In the proposed procedure, the intrinsic resistance of (MDPE) pipes is studied under fatigue mode and ambient environment. Because of the lack of theoretical foundations in the existing procedures, brittle fracture in such structural components is addressed using the crack layer formalism in order to assess the controlling damage mechanisms and extract characteristic parameters representative of the phenomena occurring as a result of failure. It is found that crack propagation behavior is split into a brittle regime which extends up to half of the specimen width and a ductile regime which controls most of the second half. Damage analysis revealed that the brittle regime is led by a craze zone which becomes diffuse and larger as ductility increases. Crack and its surrounding damage are treated as a single macroscopic entity called a crack layer (CL). The portion where damage accumulates under the effects of the stress field at the crack tip is defined as the active zone. This zone is a major energy sink and thus, controls the crack propagation rate. The driving force and the instability conditions for CL propagation are commonly given in terms of the energy available and the energy required for propagation which is expressed as the product of the resistance moment R{sub 1} and the specific enthalpy of damage. In the present case, the analysis is limited to the brittle regime which is of a great interest in the long-term failure of MDPE pipes under service conditions. Also, the analysis uses the entire brittle fracture history to evaluate the resistance moment for the crazing mechanism and to extract the specific enthalpy of damage {Psi}*.

  5. Fibroblast growth factor 23 contributes to diminished bone mineral density in childhood inflammatory bowel disease

    PubMed Central

    2012-01-01

    Background Diminished bone mineral density (BMD) is of significant concern in pediatric inflammatory bowel disease (IBD). Exact etiology is debatable. The recognition of fibroblast growth factor 23 (FGF23), a phosphaturic hormone related to tumor necrosis factor alpha (TNF-α) makes it plausible to hypothesize its possible relation to this pathology. Methods In this follow up case control study, BMD as well as serum levels of FGF23, calcium, phosphorus, alkaline phosphatase, creatinine, parathyroid hormone, 25 hydroxy vitamin D3 and 1, 25 dihydroxy vitamin D3 were measured in 47 children with IBD during flare and reassessed in the next remission. Results Low BMD was frequent during IBD flare (87.2%) with significant improvement after remission (44.7%). During disease flare, only 21.3% of patients had vitamin D deficiency, which was severe in 12.8%. During remission, all patients had normal vitamin D except for two patients with Crohn’s disease (CD) who remained vitamin D deficient. Mean value of serum FGF23 was significantly higher among patients with IBD during flare compared to controls. It showed significant improvement during remission but not to the control values. 1, 25 dihydroxy vitamin D3, FGF23, serum calcium and urinary phosphorus were significant determinants of BMD in IBD patients. Conclusions We can conclude that diminished BMD in childhood IBD is a common multifactorial problem. Elevated FGF23 would be a novel addition to the list of factors affecting bone mineral density in this context. Further molecular studies are warranted to display the exact interplay of these factors. PMID:22551310

  6. Genetic Sharing with Cardiovascular Disease Risk Factors and Diabetes Reveals Novel Bone Mineral Density Loci

    PubMed Central

    Thompson, Wesley K.; McEvoy, Linda K.; Schork, Andrew J.; Zuber, Verena; LeBlanc, Marissa; Bettella, Francesco; Mills, Ian G.; Desikan, Rahul S.; Djurovic, Srdjan; Gautvik, Kaare M.; Dale, Anders M.; Andreassen, Ole A.

    2015-01-01

    Bone Mineral Density (BMD) is a highly heritable trait, but genome-wide association studies have identified few genetic risk factors. Epidemiological studies suggest associations between BMD and several traits and diseases, but the nature of the suggestive comorbidity is still unknown. We used a novel genetic pleiotropy-informed conditional False Discovery Rate (FDR) method to identify single nucleotide polymorphisms (SNPs) associated with BMD by leveraging cardiovascular disease (CVD) associated disorders and metabolic traits. By conditioning on SNPs associated with the CVD-related phenotypes, type 1 diabetes, type 2 diabetes, systolic blood pressure, diastolic blood pressure, high density lipoprotein, low density lipoprotein, triglycerides and waist hip ratio, we identified 65 novel independent BMD loci (26 with femoral neck BMD and 47 with lumbar spine BMD) at conditional FDR < 0.01. Many of the loci were confirmed in genetic expression studies. Genes validated at the mRNA levels were characteristic for the osteoblast/osteocyte lineage, Wnt signaling pathway and bone metabolism. The results provide new insight into genetic mechanisms of variability in BMD, and a better understanding of the genetic underpinnings of clinical comorbidity. PMID:26695485

  7. Propagation of a strong spherical shock wave in a gravitating or non-gravitating dusty gas with exponentially varying density

    NASA Astrophysics Data System (ADS)

    Nath, G.; Vishwakarma, J. P.

    2016-06-01

    The propagation of a strong spherical shock wave in a dusty gas with or without self-gravitational effects is investigated in the case of isothermal and adiabatic flows. The dusty gas is assumed to be a mixture of small solid particles and perfect gas. The equilibrium flow conditions are assumed to be maintained, and the density of the mixture is assumed to be varying and obeying an exponential law. Non-similarity solutions are obtained and the effects of variations of the mass concentration of solid particles in the mixture and the ratio of the density of solid particles to the initial density of the gas, and the presence of self-gravitational field on the flow variables are investigated at given times. Our analysis reveals that after inclusion of gravitational field effects surprisingly the shock strength increases and remarkable differences are found in the distribution of flow variables. An increase in time also, increases the shock strength. Further, it is investigated that the consideration of isothermal flow increases the shock strength, and removes the singularity in the density distribution. Also, the presence of gravitational field increases the compressibility of the medium, due to which it is compressed and therefore the distance between the inner contact surface and the shock surface is reduced. The shock waves in self-gravitating dusty gas can be important for description of shocks in supernova explosions, in the study of central part of star burst galaxies, star formation and shocks in stellar explosion, nuclear explosion, in industry, rupture of a pressurized vessel and explosion in the ionosphere. Other potential applications of this study include analysis of data from exploding wire experiments and cylindrically symmetric hypersonic flow problems associated with meteors or re-entry of vehicles etc. A comparison is made between the solutions in the cases of the gravitating and the non-gravitating media. The obtained solutions are applicable for

  8. Clinicopathological significance of vascular endothelial growth factor, thymidine phosphorylase and microvessel density in colorectal cancer.

    PubMed

    Kimura, Yutaka; Morohashi, Satoko; Yoshizawa, Tadashi; Suzuki, Takahiro; Morohashi, Hajime; Sakamoto, Yoshiyuki; Koyama, Motoi; Murata, Akihiko; Kijima, Hiroshi; Hakamada, Kenichi

    2016-02-01

    Colorectal cancer is a common malignant disease, the incidence of which is increasing worldwide, therefore, identifying novel prognostic factors to improve adjuvant therapeutic strategies or postoperative monitoring is required. Angiogenesis, which is assessed by microvessel density (MVD), is significant in tumor growth and metastasis. However, the association between angiogenesis and clinical outcome remains controversial. In the present study, 84 surgically resected cases of colorectal cancer were examined to clarify the clinicopathological significance of vascular endothelial growth factor (VEGF), thymidine phosphorylase (TP) and cluster of differentiation (CD)34 expression levels. VEGF expression was identified to be significantly correlated with TP expression (r=0.45; P<0.0001) and MVD in the high VEGF expression group was observed to be significantly greater than that in the low VEGF expression group (P=0.0194). In the Dukes' stage D group, the MVD in the high TP expression group was significantly greater than that in the low TP expression group (P=0.0149). High VEGF expression was subsequently correlated with a short overall survival rate for patients exhibiting lymph node metastasis (P=0.0128); however, there was no significant difference in overall survival rate regarding the expression levels of TP and CD34. The results of the present study indicate that VEGF expression may serve as a prognostic factor for colorectal cancer patients exhibiting lymph node metastasis. Furthermore, angiogenesis, as assessed by MVD, is an important prognostic factor for tumor growth at the primary site. PMID:26676225

  9. Cultivar and Tree Density As Key Factors in the Long-Term Performance of Super High-Density Olive Orchards

    PubMed Central

    Díez, Concepción M.; Moral, Juan; Cabello, Diego; Morello, Pablo; Rallo, Luis; Barranco, Diego

    2016-01-01

    Super high-density (SHD) olive orchards are rapidly expanding since the first plantation was set up in Spain in the 1990s. Because there are no long-term studies characterizing these systems, it is unknown if densities above a certain threshold could trigger competition among fully-grown trees, compromising their development. Over 14 years we have evaluated the performance of the major olive cultivars currently planted in SHD systems (“Arbequina,” Arbequina IRTA-i·18, “Arbosana,” “Fs-17,” and “Koroneiki”) and nine SHD designs ranging from 780 to 2254 trees ha−1 for the cultivar “Arbequina.” Remarkably, the accumulated fruit and oil production of the five cultivars increased linearly over time. Our data indicated the favorable long-term performance of the evaluated cultivars with an average annual oil production of 2.3 t ha−1. Only “Fs-17” did not perform well to the SHD system in our conditions and it yielded about half (1.2 t ha−1) of the other cultivars. In the density trial for “Arbequina,” both fruit and oil accumulated production increased over time as a function of tree density. Thus, the accumulated oil yield ranged from 16.1 t ha−1 for the lowest density (780 trees ha−1) to 29.9 t ha−1 for the highest (2254 trees ha−1). In addition, we note that the accumulated production per surface unit showed a better correlation with the hedgerow length than the tree density. Thus, the current planting designs of SHD olive orchards can be further improved taking this parameter into account. Despite observations that some irregular patterns of crop distribution have arisen, our olive hedgerows are still fully productive after 14 years of planting. This result contradicts previous experiences that showed declines in production 7 or 8 years after planting due to high vigor, shading, and limited ventilation. PMID:27602035

  10. Genetic variation in Transforming Growth Factor beta 1 and mammographic density in Singapore Chinese women

    PubMed Central

    Lee, Eunjung; Van den Berg, David; Hsu, Chris; Ursin, Giske; Koh, Woon-Puay; Yuan, Jian-Min; Stram, Daniel O.; Yu, Mimi C.; Wu, Anna H.

    2013-01-01

    Transforming growth factor-beta (TGF-β) plays a critical role in normal mammary development and morphogenesis. Decreased TGF-β signaling has been associated with increased mammographic density. Percent mammographic density (PMD) adjusted for age and body mass index (BMI) is a strong risk factor and predictor of breast cancer risk. PMD is highly heritable, but few genetic determinants have been identified. We investigated the association between genetic variation in TGFB1 and PMD using a cross-sectional study of 2,038 women who were members of the population-based Singapore Chinese Health Study cohort. We assessed PMD using a computer-assisted method. We used linear regression to examine the association between 9 tagging SNPs of TGFB1 and PMD and their interaction with parity, adjusting for age, BMI, and dialect group. We calculated ‘P-values adjusted for correlated tests’ (PACT) to account for multiple testing. The strongest association was observed for rs2241716. Adjusted PMD was higher by 1.5% per minor allele (PACT =0.04). When stratifying by parity, this association was limited to nulliparous women. For nulliparous women, adjusted PMD was higher by 8.6% per minor allele (PACT=0.003; P for interaction with parity=0.002). Three additional TGFB1 tagging SNPs, which were in linkage disequilibrium with rs2241716, were statistically significantly associated with adjusted PMD (PACT<0.05) for nulliparous women. However, none of these three SNPs showed statistically significant association after adjusting for rs2241716. Our data support that TGFB1 genetic variation may be an important genetic determinant of mammographic density measure that predicts breast cancer risk, particularly in nulliparous women. PMID:23333936