17,824 research outputs found
Vector and Axial Nucleon Form Factors:A Duality Constrained Parameterization
We present new parameterizations of vector and axial nucleon form factors. We
maintain an excellent descriptions of the form factors at low momentum
transfers, where the spatial structure of the nucleon is important, and use the
Nachtman scaling variable xi to relate elastic and inelastic form factors and
impose quark-hadron duality constraints at high momentum transfers where the
quark structure dominates. We use the new vector form factors to re-extract
updated values of the axial form factor from neutrino experiments on deuterium.
We obtain an updated world average value from neutrino-d and pion
electroproduction experiments of M_A = 1.014 +- 0.014 GeV/c2. Our
parameterizations are useful in modeling neutrino interactions at low energies
(e.g. for neutrino oscillations experiments). The predictions for high momentum
transfers can be tested in the next generation electron and neutrino scattering
experiments.Comment: 5 pages, 3 figures, to be published in EPJ
Mapping the interstellar medium in galaxies with Herschel/SPIRE
The standard method of mapping the interstellar medium in a galaxy, by observing the molecular gas in the CO 1-0 line and the atomic gas in the 21-cm line, is largely limited with current telescopes to galaxies in the nearby universe. In this letter, we use SPIRE observations of the galaxies
M99 and M100 to explore the alternative approach of mapping the interstellar medium using the continuum emission from the dust. We have compared the methods by measuring the relationship between the star-formation rate and the surface density of gas in the galaxies using both
methods. We find the two methods give relationships with a similar dispersion, confirming that observing the continuum emission from the dust is a promising method of mapping the interstellar medium in galaxies
Recommended from our members
Modeling Virus Transport and Removal during Storage and Recovery in Heterogeneous Aquifers
A quantitative understanding of virus removal during aquifer storage and recovery (ASR) in physically and geochemically heterogeneous aquifers is needed to accurately assess human health risks from viral infections. A two-dimensional axisymmetric numerical model incorporating processes of virus attachment, detachment, and inactivation in aqueous and solid phases was developed to systematically evaluate the virus removal performance of ASR schemes. Physical heterogeneity was considered as either layered or randomly distributed hydraulic conductivities (with selected variance and horizontal correlation length). Geochemical heterogeneity in the aquifer was accounted for using Colloid Filtration Theory to predict the spatial distribution of attachment rate coefficient. Simulation results demonstrate that the combined effects of aquifer physical heterogeneity and spatial variability of attachment rate resulted in higher virus concentrations in the recovered water at the ASR well (i.e. reduced virus removal). While the sticking efficiency of viruses to aquifer sediments was found to significantly influence virus concentration in the recovered water, the solid phase inactivation under realistic field conditions combined with the duration of storage phase had a predominant influence on the overall virus removal. The relative importance of physical heterogeneity increased under physicochemical conditions that reduced virus removal (e.g. lower value of sticking efficiency or solid phase inactivation rate). This study provides valuable insight on site selection of ASR projects and an approach to optimize ASR operational parameters (e.g. storage time) for virus removal and to minimize costs associated with post-recovery treatment
Trends in Molecular Emission from Different Extragalactic Stellar Initial Mass Functions
Banerji et al. (2009) suggested that top-heavy stellar Initial Mass Functions
(IMFs) in galaxies may arise when the interstellar physical conditions inhibit
low-mass star formation, and they determined the physical conditions under
which this suppression may or may not occur. In this work, we explore the
sensitivity of the chemistry of interstellar gas under a wide range of
conditions. We use these results to predict the relative velocity-integrated
antenna temperatures of the CO rotational spectrum for several models of high
redshift active galaxies which may produce both top-heavy and unbiased IMFs. We
find that while active galaxies with solar metallicity (and top-heavy IMFs)
produce higher antenna temperatures than those with sub-solar metallicity (and
unbiased IMFs) the actual rotational distribution is similar. The high-J to
peak CO ratio however may be used to roughly infer the metallicity of a galaxy
provided we know whether it is active or quiescent. The metallicity strongly
influences the shape of the IMF. High order CO transitions are also found to
provide a good diagnostic for high far-UV intensity and low metallicity
counterparts of Milky Way type systems both of which show some evidence for
having top-heavy IMFs. We also compute the relative abundances of molecules
known to be effective tracers of high density gas in these galaxy models. We
find that the molecules CO and CS may be used to distinguish between solar and
sub-solar metallicity in active galaxies at high redshift whereas HCN, HNC and
CN are found to be relatively insensitive to the IMF shape at the large visual
magnitudes typically associated with extragalactic sources.Comment: 26 Pages, 8 Figures, Accepted for publication in Ap
Detection of the 13CO(J=6-5) Transition in the Starburst Galaxy NGC 253
We report the detection of 13CO(J=6-5) emission from the nucleus of the
starburst galaxy NGC 253 with the redshift (z) and Early Universe Spectrometer
(ZEUS), a new submillimeter grating spectrometer. This is the first
extragalactic detection of the 13CO(J=6-5) transition, which traces warm, dense
molecular gas. We employ a multi-line LVG analysis and find ~ 35% - 60% of the
molecular ISM is both warm (T ~ 110 K) and dense (n(H2) ~ 10^4 cm^-3). We
analyze the potential heat sources, and conclude that UV and X-ray photons are
unlikely to be energetically important. Instead, the molecular gas is most
likely heated by an elevated density of cosmic rays or by the decay of
supersonic turbulence through shocks. If the cosmic rays and turbulence are
created by stellar feedback within the starburst, then our analysis suggests
the starburst may be self-limiting.Comment: 4 pages, 2 figures, accepted by ApJ Letter
A Comprehensive View of a Strongly Lensed Planck-Associated Submillimeter Galaxy
We present high-resolution maps of stars, dust, and molecular gas in a strongly lensed submillimeter galaxy (SMG) at z = 3.259. HATLAS J114637.9â001132 is selected from the Herschel-Astrophysical Terahertz Large Area Survey (H-ATLAS) as a strong lens candidate mainly based on its unusually high 500 Îźm flux density (~300 mJy). It is the only high-redshift Planck detection in the 130 deg^2 H-ATLAS Phase-I area. Keck Adaptive Optics images reveal a quadruply imaged galaxy in the K band while the Submillimeter Array and the Jansky Very Large Array show doubly imaged 880 Îźm and CO(1â0) sources, indicating differentiated distributions of the various components in the galaxy. In the source plane, the stars reside in three major kpc-scale clumps extended over ~1.6 kpc, the dust in a compact (~1 kpc) region ~3 kpc north of the stars, and the cold molecular gas in an extended (~7 kpc) disk ~5 kpc northeast of the stars. The emissions from the stars, dust, and gas are magnified by ~17, ~8, and ~7 times, respectively, by four lensing galaxies at z ~ 1. Intrinsically, the lensed galaxy is a warm (T_(dust) ~ 40-65 K), hyper-luminous (L_(IR) ~ 1.7 Ă 10^(13) L_â; star formation rate (SFR) ~2000 M_â yr^(â1)), gas-rich (M_(gas)/M_(baryon) ~ 70%), young (M_(stellar)/SFR ~ 20 Myr), and short-lived (M_(gas)/SFR ~ 40 Myr) starburst. With physical properties similar to unlensed z > 2 SMGs, HATLAS J114637.9â001132 offers a detailed view of a typical SMG through a powerful cosmic microscope
Learning, Training, and Development in Organizations: Emerging Trends, Recent Advances, and Future Directions
Dramatic changes have occurred in learning, training, and development in organizations in recent years. This chapter examines the implications of these changes for research in four areas: (1) training design and delivery, (2) team training and development, (3) training transfer, and (4) training evaluation. We suggest that research in these areas not only has been most heavily impacted by recent trends in training and development but also can help guide the field as it responds to emerging opportunities and challenges. We review recent research that advances our understanding of how to design and deliver training to meet the needs of a changing workplace, utilize training and development to influence team effectiveness, increase the transfer of training to the job, and strengthen efforts to evaluate the effectiveness training and development initiatives. We also discuss directions for future research aimed at ensuring that the science of training keeps pace with changes in training practice
Extraction of the Axial Nucleon Form Factor from Neutrino Experiments on Deuterium
We present new parameterizations of vector and axial nucleon form factors. We
maintain an excellent descriptions of the form factors at low momentum
transfers (), where the spatial structure of the nucleon is important, and
use the Nachtman scaling variable to relate elastic and inelastic form
factors and impose quark-hadron duality constraints at high where the
quark structure dominates. We use the new vector form factors to re-extract
updated values of the axial form factor from \numu experiments on deuterium.
We obtain an updated world average value from \numud, \numubarH and pion
electroproduction experiments of = . Our
parameterizations are useful in modeling interactions at low energies
(e.g. for \numu oscillations experiments). The predictions for high can
be tested in the next generation electron and \numu scattering experiments.Comment: Presented by A. Bodek at the European Physical Society Meeting,
EPS2007, Manchester, England, July 2007, 4 pages, 2 figure
- âŚ