Gas Molecular Mass Research Articles

The global star formation law of galaxies revisited in the radio continuum

We study the global star formation law, the relation between the gas and star formation rate (SFR) in a sample of 130 local galaxies with infrared (IR) luminosities spanning over three orders of magnitude (109–1012 L⊙), which includes 91 normal spiral galaxies and 39 (ultra)luminous IR galaxies [(U)LIRGs]. We derive their total (atomic and molecular) gas and dense molecular gas masses using newly available HI, CO and HCN data from the literature. The SFR of galaxies is determined from total IR (8–1000 μm) and 1.4 GHz radio continuum (RC) luminosities. The galaxy disk sizes are defined by the de-convolved elliptical Gaussian FWHM of the RC maps. We derive the galaxy disk-averaged SFRs and various gas surface densities, and investigate their relationships. We find that the galaxy disk-averaged surface density of dense molecular gas mass has the tightest correlation with that of SFR (scatter ∼0.26 dex), and is linear in log-log space (power-law slope of N=1.03±0.02) across the full galaxy sample. The correlation between the total gas and SFR surface densities for the full sample has a somewhat larger scatter (∼0.48 dex), and is best fit by a power-law with slope 1.45±0.02. However, the slope changes from ∼1 when only normal spirals are considered, to ∼1.5 when more and more (U)LIRGs are included in the fitting. When different CO-to-H2 conversion factors are used to infer molecular gas masses for normal galaxies and (U)LIRGs, the bi-modal relations claimed recently in CO observations of high-redshift galaxies appear to also exist in local populations of star-forming galaxies.

THROUGH THICK AND THIN—H I ABSORPTION IN COSMOLOGICAL SIMULATIONS

We investigate the column density distribution function of neutral hydrogen at redshift z = 3 using a cosmological simulation of galaxy formation from the OverWhelmingly Large Simulations (OWLS) project. The base simulation includes gravity, hydrodynamics, star formation, supernovae feedback, stellar winds, chemodynamics, and element-by-element cooling in the presence of a uniform UV background. Self-shielding and formation of molecular hydrogen are treated in post-processing, without introducing any free parameters, using an accurate reverse ray-tracing algorithm and an empirical relation between gas pressure and molecular mass fraction. The simulation reproduces the observed z = 3 abundance of Ly-A forest, Lyman Limit and Damped Ly-A HI absorption systems probed by quasar sight lines over ten orders of magnitude in column density. Self-shielding flattens the column density distribution for NHI > 10^18 cm-2, while the conversion to fully neutral gas and conversion of HI to H2 steepen it around column densities of NHI = 10^20.3 cm-2 and NHI = 10^21.5 cm-2, respectively.

Experimental and kinetic modeling investigation of toluene combustion in premixed, one-dimensional and laminar toluene-oxygen-argon flames

One-dimensional, premixed and laminar toluene–oxygen–argon flames, with equivalence ratios of 0.7 and 1.0 were stabilized at low pressure on a flat flame burner. Mole fraction profiles of 18 chemical species have been measured by gas chromatography and molecular beam mass spectrometry. A kinetic model with a good predictive capability has been developed to compare with experimental data. A comparative reaction rate analysis of predicted flame structures has allowed us to determine main pathways of toluene combustion and their dependence on temperature and equivalence ratio.

Experimental and Kinetic Modeling Evidences of a C7H6 Pathway in a Rich Toluene Flame

The structure of a laminar, premixed, and one-dimensional toluene-oxygen-argon (9.9 mol % C(7)H(8), 44.5 mol % O(2), and 45.6 mol % Ar) flame, with an equivalence ratio of 2 and burning at 36 Torr was analyzed by gas chromatography and molecular beam mass spectrometry (MBMS). Mole fraction profiles of 25 chemical species including permanent gases of combustion and first polycyclic aromatic hydrocarbons as naphthalene, methylnaphthalene isomers, biphenyl, and phenanthrene have been measured. A kinetic model based on recent literature data has been elaborated to compare with measurements. As suggested by recent theoretical studies, benzyl radical (C(7)H(7)) dissociation into fulvenallene (C(7)H(6)) + H and the reaction between C(7)H(6) and H giving cyclopentadienyl radical and acetylene have been included into the model. A comparison between experimental and predicted flame structures have allowed us to validate the kinetic model for rich toluene combustion. Moreover, MBMS measurements of mole fraction profiles corresponding to m/z ratios of C(7)H(7) and C(7)H(6) have permitted a specific validation of the theoretically postulated C(7)H(6) pathway in toluene flames.

Molecular dynamics simulations of translational thermal accommodation coefficients for time-resolved LII

Time-resolved laser-induced incandescence demands precise knowledge of the thermal accommodation coefficient, but little is known about the gas-surface scattering physics that underlies this parameter. This paper presents a molecular dynamics simulation that shows how the thermal accommodation coefficient is influenced by the gas molecular mass and gas temperature. The molecular dynamics results also define scattering kernels that can be used as boundary conditions in Direct Simulation Monte Carlo simulations of heat and momentum transfer between soot aggregates and surrounding gas molecules.

Direct mask-free patterning of molecular organic semiconductors using organic vapor jet printing

We demonstrate the solvent-free, high-resolution direct printing of molecular organic semiconductors for use in low cost optoelectronic applications. In this method, called organic vapor jet printing, hot inert carrier gas picks up the molecular organic vapor and expands it through a microscopic nozzle, resulting in physisorption of the molecules onto a cooled substrate. Pattern resolution and printing speed are determined by the nozzle shape, nozzle-to-substrate distance, downstream pressure, and molecular mass of the carrier gas. Quantitative models are developed using a combination of scaling analysis, direct simulation Monte Carlo modeling, and printing experiments. Pattern resolutions of up to 1000dpi and local deposition rates exceeding 2300Å∕s are achieved. Pentacene channel thin film transistors are printed at a local deposition rate of 700Å∕s at both low and atmospheric pressures, resulting in a field-effect mobility of 0.25cm2∕Vs and a current on/off ratio of 7×105 for devices grown at a background pressure of 0.24Torr. The high directionality of the molecular jets and well-defined shape of the deposits enables combinatorial printing of structures and devices, while affording considerable control over film morphology. The method is also readily applicable to document printing using solvent-free inks.

The dependence of the Becker gauge calibration curve on the gas molecular mass

The aim of the present work was to study the dependence of calibration curves of the Becker friction vacuum gauge operated in the decremental mode on the kind of the gas (i.e. on its molecular mass). The calibration curves were measured over the range from 10 −1 Pa to atmospheric pressure for the noble gases (He, Ne, Ar, Kr, Xe) and for N 2. The theoretical model of the damping of the ribbon vibration is briefly discussed for the molecular regime. The assumptions of the calibration curve dependence on the gas molecular mass were compared with the experimental results in the molecular and viscous regimes. The experimental results confirm the assumption that the order of the calibration curves for each gas species depends on the molecular mass in the molecular regime while it depends on the gas viscosity in the viscous regime.

High-yield production of single-wall carbon nanotubes in nitrogen gas

To see roles of an ambient gas on the formation process of single-wall carbon nanotubes (SWNTs), we have prepared SWNTs by laser ablation with Ne, Ar, Kr and N 2 gases and estimated the abundances of SWNTs mainly by Raman spectroscopy. The abundance of SWNTs was found to depend systematically on the pressure and the molecular mass of the ambient gas, and the highest abundance was obtained in N 2 at 1000 Torr. Only N 2 produced thinner SWNTs than any other gases, which suggests that the size of nanotube precursors is sensitively affected by the internal freedom of ambient gas.

New approach to corrections for thermal transpiration effects in capacitance diaphragm gauges

The sensors of capacitance diaphragm gauges (CDGs) are customarily kept at a stable elevated temperature. This greatly improves the zero stability but also introduces non-linearities at pressures below 100 Pa due to thermal transpiration. The effect of thermal transpiration has been measured for three CDG transducers and four gases - nitrogen, argon, helium and hydrogen - in a range of pressures from 10-2 Pa to 102 Pa. Normalization of the pressure scale for different gases can easily be performed using the two well-known gas parameters, viscosity and molecular mass, thus simplifying the calculation of the thermal transpiration correction when the test gas is changed. A universal expression for the thermal transpiration correction as a function of normalized pressure was determined.

Evaporation analogies between light hydrocarbons effect of molecular mass of purge gas

The evaporation of benzene, cyclohexane, n-heptane, toluene, 2-xylene, 3-xylene and 4-xylene was studied in H2, He, N2 or CO2 as purge gases for control of the introduced methods of evaluation and the sensitivity limits of TG measurements. Ii as a function of (1−α) and the following equation proved very suitable for a quantitative comparison of 28 independent and different TG measurements and for a very sensitive characterization of the thermal processes, even within an energy level difference of 3 kJ mol−1, in spite of the known great inconsistency in the formal kinetic parameters: $$\ln A \cong \overline {\left( {1/RT_{i} } \right)} {\kern 1pt} {\kern 1pt} \bar E_{i} {\kern 1pt} - \overline {n\ln \left( {1 - {\alpha }} \right)_{_{i} } } + {\kern 1pt} {\kern 1pt} \overline {\ln \left( {\ln {d\alpha /d}t} \right)_{_{i}}} $$

Electrospray ionization Fourier transform ion cyclotron resonance mass spectrometric characterization of high molecular mass Starburst ™ dendrimers

A series of Starburst ™ polyamidoamine (PAMAM) dendrimers, built from a tetrafunctional ethylenediamine (EDA) core, generations 1 to 10 (G1–G10), and covering a wide range of charge state distributions (i.e. from m / z ∼ 500 to m / z ∼ 15 000), have been investigated by electrospray ionization (ESI) Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. High resolution mass spectra for lower generation dendrimers (G1, M r ∼ 1429 u to G5, M r ∼ 28 825 u) allowed characterization of the polydispersity of these systems, providing a basis for improving synthetic strategies and characterizing surface-modified dendrimers. The relationship between charge state in the gas phase and molecular mass of these spherical macromolecules is reported and used to estimate the stoichiometry of a G5 PAMAM dendrimer — polyclonal rabbit IgG immunoconjugate. The results presented herein represent the highest molecular mass species yet detected by FT-ICR MS with the exception of measurements based upon individual ion detection.

A model for stationary heterogeneous detonation in a gas-droplet mixture

1. A model has been constructed for a stationary heterogeneous detonation in a gasdroplet medium with allowance for chemical equilibrium and losses at the tube walls. The calculations are in good agreement with the available experimental data. 2. Wall loss has a decisive effect on the detonation parameters for hydrocarbon-oxygen mixtures. The residual unburned droplet fraction tends to zero as the loss decreases. 3. There is good agreement with experiment for DECH-O2 mixtures given by the conditions for the absence of droplet breakup or the conditions for single breakup of large droplets into a small number of parts. 4. There is found to be a considerable effect from variation in the heat of reaction and gas molecular mass in the reaction zone. 5. If a hydrocarbon-oxygen mixture is not very heavily diluted with nitrogen and has a combination close to stoichiometric, then the length of the induction zone is much less than the distance to the Chapman-Jouguet surface. 6. There is found to be substantial velocity disequilibrium in the phases in the Chapman-Jouguet plane in a hydrogen-oxygen mixture and also for small droplets in hydrocarbon-oxygen mixtures.