Engineering topics
Young, J. S.
Publications and source records attributed to Young, J. S..
Relative effectiveness of kinetic analysis vs single point readings for classifying environmental samples based on community-level physiological profiles (CLPP)
The relative effectiveness of average-well-color-development-normalized single-point absorbance readings (AWCD) vs the kinetic parameters mu(m), lambda, A, and integral (AREA) of the modified Gompertz equation fit to the color development curve resulting from reduction of a redox sensitive dye from microbial respiration of 95 separate sole carbon sources in microplate wells was compared for a dilution series of rhizosphere samples from hydroponically grown wheat and potato ranging in inoculum densities of 1 x 10(4)-4 x 10(6) cells ml-1. Patterns generated with each parameter were analyzed using principal component analysis (PCA) and discriminant function analysis (DFA) to test relative resolving power. Samples of equivalent cell density (undiluted samples) were correctly classified by rhizosphere type for all parameters based on DFA analysis of the first five PC scores. Analysis of undiluted and 1:4 diluted samples resulted in misclassification of at least two of the wheat samples for all parameters except the AWCD normalized (0.50 abs. units) data, and analysis of undiluted, 1:4, and 1:16 diluted samples resulted in misclassification for all parameter types. Ordination of samples along the first principal component (PC) was correlated to inoculum density in analyses performed on all of the kinetic parameters, but no such influence was seen for AWCD-derived results. The carbon sources responsible for classification differed among the variable types with the exception of AREA and A, which were strongly correlated. These results indicate that the use of kinetic parameters for pattern analysis in CLPP may provide some additional information, but only if the influence of inoculum density is carefully considered. c2001 Elsevier Science Ltd. All rights reserved.
(12)CO (3-2) & (1-0) emission line observations of nearby starburst galaxy nuclei
New measurements of the (12)CO (1-0) and (12)CO (3-2) line emission are presented for the nuclei of seven nearby starburst galaxies selected from a complete sample of 21 nearby starburst galaxies for which the nuclear star formation rates are measured to be comparable to the archetype starburst galaxies M82 and NGC 253. The new observations capitalize on the coincidence between the beam size of the 45 m Nobeyama telescope at 115 GHz and that of the 15 m James Clerk Maxwell Telescope at 345 GHz to measure the value of the (12)CO (3-2)/(1-0) emission line ratio in a 15 sec (less than or equal to 2.5 kpc) diameter region centered on the nuclear starburst. In principle, the (12)CO (3-2)/(1-0) emission line ratio provides a measure of temperature and optical depth for the (12)CO gas. The error weighted mean value of the (12)CO (3-2)/(1-0) emission line ratio measured for the seven starburst galaxy nuclei is -0.64 +/- 0.06. The (12)CO (3-2)/(1-0) emission line ratio measured for the starburst galaxy nuclei is significantly higher than the average value measured for molecular gas in the disk of the Galaxy, implying warmer temperatures for the molecular gas in starburst galaxy nuclei. On the other hand, the (12)CO (3-2)/(1-0) emission line ratio measured for the starburst galaxy nuclei is not as high as would be expected if the molecular gas were hot, greater than 20 K, and optically thin, tau much less than 1. The total mass of molecular gas contained within the central 1.2-2.8 kpc diameter region of the starburst galaxy nuclei ranges from 10(exp 8) to 10(exp 9) solar mass. While substantial, the molecular gas mass represents only a small percentage, approximately 9%-16%, of the dynamical mass in the same region.
The FCRAO extragalactic CO survey: Global properties of galaxies
Since stars form in molecular clouds, a critical element in studies of galaxy evolution is knowledge of the molecular content of a large sample of galaxies. To this end, researchers undertook a survey of CO emission from galaxies using the Fire College Radio Astronomy Observatory (FCRAO) 14-m millimeter telescope at 115 GHz. The aim was to better understand the differences found among and within galaxies with regard to the efficiency of star and cloud formation. The galaxies observed as part of the FCRAO Extragalactic CO Survey were selected on the basis of their optical or infrared properties. The galaxies observed thus far are (1) brighter than B sub T (sub o)=12.5 in the blue, or (2) brighter than 20 Jy at 100 microns. From major axis CO observations at 45 seconds resolution and spacing in over 200 galaxies, researchers determined the CO radial distributions, and derived global CO fluxes (cf. Kenney and Young 1988); H2 masses were derived using the conversion factor N(H2)/I sub CO=2.8 times 10 to the 20th power cm(-2)/K km s(-1)) (Bloemen et al. 1986). Here, researchers concentrate on the global galaxy properties within the sample. Neutral hydrogen (HI) masses for the sample galaxies were taken from Huchtmeier et al. (1983), blue luminosities and morphological types were taken from RC2. IR luminosities, colors, dust temperatures and dust masses were determined from coadded Infrared Astronomy Satellite (IRAS) data (Young et al. 1989). They have chosen to first compare absolute luminosities and masses in order to determine the slope and scatter in each correlation; next they investigate luminosity independent ratios in order to intercompare large and small galaxies.
A comparison of the radial distribution of molecular gas and non-thermal radio continuum in spiral disks
The present study includes 65 spiral galaxies selected from the Five College Radio Astronomy Observatory (FCRAO) Extragalactic CO Survey for which the major axis distributions of CO emission and 1.49 GHz radio continuum emission are well determined. The radial distribution of the CO emission has been measured with the FCRAO at positions along the major axis that are spaced by one half power beam width (HPBW) (45 seconds). The radial profile of the 1.49 GHz radio continuum emission was constructed by determining the radio emission at the location of the CO measurements from the 1.49 GHz maps of Condon (1987). Large, greater than a factor of ten, radially decreasing gradients in the star formation efficiency are observed for a small percentage, approx. 10 percent, of the spirals in this sample. The majority of spirals, however, are associated with small gradients in the star formation efficiency that do not systematically increase or decrease with radius. That the star formation efficiency does not systematically decrease with radius tends to argue against a global dynamical mechanism, such as a spiral density wave, for being the dominant mechanism triggering disk star formation for the majority of spirals in this sample. The results tend to support the view that the star formation in spiral disks is dominated by a local process that depends more on the molecular cloud properties than the dynamical structure of a galaxy.
Efficient star formation in the bright bar of M83
The bright molecular bar in M83 was detected standing out as a 100% enhancement of molecular emission with respect to the off-bar emission at the same radii. The spatial variations in the star formation efficiency, as traced by H alpha emission and the surface density of the interstellar gas, in M83 and M51 were compared. Both the central bar of M83 and the spiral arms of M51 are regions characterized by high massive star formation rates. For M83, it is ascribed that both the gas surface density and the star formation efficiency are high to the hydrodynamics of the central region.
Detection of CO(1-0) emission and optical imaging of the Seyfert galaxy/QSO Markarian 231
The detection of CO(J = 1-0) emission and optical imaging of the luminous infrared galaxy Markarian 231 are reported. The galaxy is extremely rich in molecular gas with MT(H2) approximately equal to 1.4 x 10 to the 10th solar masses, approximately 5 times the molecular gas content of the Galaxy. Markarian 231 is the most luminous object in the local universe (z approximately equal to or less than 0.1), with a far-infrared luminosity (lambda = 40-400 microns) of 2.1 x 10 to the 12th solar luminosities. THe CO detection yields a L(FIR)/M(H2) ratio of 150. A deep optical CCD image shows two striking tidal tails with total extent of about 75 kpc. The CCD image strongly suggests that Markarian 231 is an advanced merger system. If the molecular gas is highly concentrated in the nuclear region it may fuel an intense starburst and possibly feed the accretion onto an embedded QSO. The trigger for the intense activity observed in Markarian 231 appears to be the collision of two gas-rich spiral galaxies.
Molecular gas in high-luminosity IRAS galaxies
The paper reports observations of CO(J = 1-0) emission from an unbiased sample of the highest-luminosity IRAS galaxies with the aim of measuring their molecular gas content and determining whether star formation is a viable energy source for these high luminosities. All of the observed galaxies are rich in molecular gas with H2 masses in the range (4 x 10 to the 9th)-(4 x 10 to the 10th) solar masses. Their primary luminosity source appears to be star formation in molecular clouds. The majority, if not all, of the most luminous IRAS galaxies (L-FIR greater than 10 to the 11th solar luminosities) appear to be strongly interacting systems; those with the highest L-FIR/M(H2) ratios are mergers or close contact pairs.
CO observations of infrared bright galaxies - The efficiency of star formation
CO emission has been detected in each of 14 of the IR-bright galaxies listed in IRAS Circular 15; for the nine galaxies of the largest angular size, the CO emission distributions along the major axis have been mapped. A strong correlation is noted between total CO luminosities and IR ones for galaxies in each of three ranges of dust temperature. The ratio of IR/CO luminosities increases with the ratio of 60/100-micron flux densities, consistent with emission of thermal origin at the characteristic temperature given by the dust temperature. If this luminosity ratio is a measure of the emergent stellar luminosity/unit molecular mass, or the efficiency of star formation, this efficiency varies over almost two orders of magnitude from one galaxy to another.
Distributions of (C-13)O emission in the disks of late-type spiral galaxies
In studies of molecular clouds in external galaxies, the distribution of (C-12)O emissivity as a function of radius in a galaxy has been employed to infer the surface density of molecular hydrogen with galactocentric radius. In principle, observations of more optically thin molecular species, such as (C-13)O, can be used as an alternative tracer of the mass of molecular hydrogen in a galaxy. Since the (C-13)O lines have a much lower opacity than the saturated, nearly thermalized (C-12)O lines, their intensity variations as a function of galactocentric radius are more readily interpreted in terms of gas density variations. The first strip maps of the (C-13)O distributions in six spiral galaxies are presented, and the (C-13)O and (C-12)O radial distributions are compared. Attention is given to the reliability of H2 masses and H2 distributions derived from (C-12)O data.
A 10 micron survey of star formation in galactic nuclei Virgo spiral galaxies
A survey for 10 micron emission in the nuclei of spiral galaxies in the Virgo cluster is reported. It is found that the nuclei of most luminous spiral galaxies are active 10 micron emitters, and that the luminosity function for the sample can be represented by a simple power law over the entire range sampled. The most luminous sources at 10 microns show only a weak correlation with total optical luminosity, and no correlation with morphological type or location in the cluster. It is argued that the 10 micron flux from the Virgo galaxies arises from active star formation regions. A mean far-IR luminosity of two billion solar luminosities is inferred for the galactic nuclei; the required rate of massive star formation is 0.1 solar masses/yr. The results suggest that the rate of star formation in galactic nuclei has little relationship to the size of the nuclear bulge or the gravitational potential near the center.
Structure of dense molecular gas in TMC 1 from observations of three transitions of HC3N
The Taurus dark cloud complex is a collection of many individual clouds scattered across approximately 50 pc. Within one of these, Heiles Cloud 2, is the dense condensation TMC 1. TMC 1 is one of the few sources in which some of the long carbon chain molecules are found. The present investigation is concerned with a mapping of the density structure in a narrow ridge of the TMC 1 structure. It is shown that the HC3N emission from the J = 5 to 4, J = 9 to 8, and J = 12 to 11 transitions is well matched by a narrow ridge of material at a single density of 50,000-100,000 per cu cm. There is evidence that the HC3N fractional abundance is variable along the ridge. Evidence is also found for the presence of subcondensations within this ridge from maps at individual velocities.
Interstellar chemistry - Polycyanoacetylene formation
It is argued that interstellar polycyanoacetylenes are formed not on dust grains by catalytic buildup or by dissociation of longer molecules, but rather by gas phase ion-molecule reactions. The primary evidence for this view is the detection of deuterated cyanoacetylene in an interstellar cloud. It is also argued that the relative abundance of successive homologs of polycyanoacetylenes rules out the grain catalysis theory.
The elemental and isotopic composition of cosmic rays - Silicon to nickel
The reported observations were made with the aid of the Cosmic Ray Isotope Instrument System (CRISIS) which had been designed to detect and resolve the isotopes of cosmic ray nuclei with atomic numbers equal to or greater than 10. The CRISIS detector was flown on a balloon launched from Aberdeen, South Dakota on 1977 May 20. The period 1977 May 19-22 has been classified by Mason et al. (1979) as one of 'superquiet' solar activity, characterized by the lowest fluxes of low-energy solar particles ever observed. The obtained results are presented in a number of graphs and tables. It was found that the elemental and isotopic abundances of Si are solar-like. Elemental S is underabundant in the cosmic rays by a factor of approximately 3 relative to the solar system, but its isotopic composition resembles the solar composition with S-32 being the dominant isotope. Elemental Ar is virtually absent in the source, and the observed isotopic composition is consistent with a secondary origin. Elemental Ni has a solar-like abundance.
The neutron-rich isotopes of cosmic-ray neon and magnesium
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Some isotopic abundances in the cosmic radiation
Cosmic ray nuclei with Z not less than 10 have been observed in a detector which measures charge with a double scintillator-Cherenkov array and mass by combining the Cherenkov signal with residual range measured in nuclear emulsions. Results are presented for the isotopic analyses of Al, Ca, Sc, Mn, Fe, Co, Ni and Cu in the energy range 300-800 MeV/amu.