497 research outputs found
Dark gas in the solar neighnorhood from extinction data
When modeling infrared or gamma-ray data as a linear combination of observed
gas tracers, excess emission has been detected compared to expectations from
known neutral and atomic gas as traced by HI and CO measurements, respectively.
This excess might correspond to an additional gas component. This so-called
"dark gas" (DG) has been observed in our Galaxy, as well as the Magellanic
Clouds. For the first time, we investigate the correlation between visible
extinction (Av) data and gas tracers on large scales in the solar neighborhood.
Our work focuses on both the solar neighborhood (|b|>10\degr), and the inner
and outer Galaxy, as well as on four individual regions: Taurus, Orion,
Cepheus-Polaris and Aquila-Ophiuchus. Thanks to the recent production of an
all-sky Av map, we first perform the correlation between Av and both HI and CO
emission over the most diffuse regions, to derive the optimal (Av/NH)^(ref)
ratio. We then iterate the analysis over the entire regions to estimate the
CO-to-H2 conversion factor as well as the DG mass fraction. The average
extinction to gas column-density ratio in the solar neighborhood is found to be
(Av/NH)^(ref)=6.53 10^(-22) mag. cm^2, with significant differences between the
inner and outer Galaxy. We derive an average XCO value of 1.67 10^(20) H2
cm^(-2)/(K km s^(-1)). In the solar neighborhood, the gas mass in the dark
component is found to be 19% relative to that in the atomic component and
164 relative to the one traced by CO. These results are compatible with the
recent analysis using Planck data within the uncertainties of our measurements.
We estimate the ratio of dark gas to total molecular gas to be 0.62 in the
solar neighborhood. The HI-to-H2 and H2-to-CO transitions appear for Av
0.2 mag and Av mag, respectively, in agreement with
theoretical models of dark-H2 gas.Comment: 9 pages, 4 figures, 1 table. Accepted for publication in A&A (in
press
A New Galactic Extinction Map of the Cygnus Region
We have made a Galactic extinction map of the Cygnus region with 5' spatial
resolution. The selected area is 80^\circ to 90^\circ in the Galactic longitude
and -4^\circ to 8^\circ in the Galactic latitude. The intensity at 140 \mum is
derived from the intensities at 60 and 100 \mum of the IRAS data using the
tight correlation between 60, 100, and 140 \mum found in the Galactic plane.
The dust temperature and optical depth are calculated with 5' resolution from
the 140 and 100 \mum intensity, and Av is calculated from the optical depth. In
the selected area, the mean dust temperature is 17 K, the minimum is 16 K, and
the maximum is 30 K. The mean Av is 6.5 mag, the minimum is 0.5 mag, and the
maximum is 11 mag. The dust temperature distribution shows significant spatial
variation on smaller scales down to 5'. Because the present study can trace the
5'-scale spatial variation of the extinction, it has an advantage over the
previous studies, such as the one by Schlegel, Finkbeiner, & Davis, who used
the COBE/DIRBE data to derive the dust temperature distribution with a spatial
resolution of 1^\circ. The difference of Av between our map and Schlegel et
al.'s is \pm 3 mag. A new extinction map of the entire sky can be produced by
applying the present method.Comment: 27 pages, 14 figures, accepted for publication in Ap
Existence of Dynamical Scaling in the Temporal Signal of Time Projection Chamber
The temporal signals from a large gas detector may show dynamical scaling due
to many correlated space points created by the charged particles while passing
through the tracking medium. This has been demonstrated through simulation
using realistic parameters of a Time Projection Chamber (TPC) being fabricated
to be used in ALICE collider experiment at CERN. An interesting aspect of this
dynamical behavior is the existence of an universal scaling which does not
depend on the multiplicity of the collision. This aspect can be utilised
further to study physics at the device level and also for the online monitoring
of certain physical observables including electronics noise which are a few
crucial parameters for the optimal TPC performance.Comment: 5 pages, 6 figure
Discovery of possible molecular counterparts to the infrared Double Helix Nebula in the Galactic center
We have discovered two molecular features at radial velocities of -35 km/s
and 0 km/s toward the infrared Double Helix Nebula (DHN) in the Galactic center
with NANTEN2. The two features show good spatial correspondence with the DHN.
We have also found two elongated molecular ridges at these two velocities
distributed vertically to the Galactic plane over 0.8 degree. The two ridges
are linked by broad features in velocity and are likely connected physically
with each other. The ratio between the 12CO J=2-1 and J=1-0 transitions is 0.8
in the ridges which is larger than the average value 0.5 in the foreground gas,
suggesting the two ridges are in the Galactic center. An examination of the K
band extinction reveals a good coincidence with the CO 0 km/s ridge and is
consistent with a distance of 8 +/-2 kpc. We discuss the possibility that the
DHN was created by a magnetic phenomenon incorporating torsional Alfv\'en waves
launched from the circumnuclear disk (Morris, Uchida & Do 2006) and present a
first estimate of the mass and energy involved in the DHN.Comment: 32 pages, 23 figures, Accepted by Ap
Revealing the molecular signatures of host-pathogen interactions.
Advances in sequencing technology and genome-wide association studies are now revealing the complex interactions between hosts and pathogen through genomic variation signatures, which arise from evolutionary co-existence
Matching three-point functions of BMN operators at weak and strong coupling
The agreement between string theory and field theory is demonstrated in the
leading order by providing the first calculation of the correlator of three
two-impurity BMN states with all non-zero momenta. The calculation is performed
in two completely independent ways: in field theory by using the large-
perturbative expansion, up to the terms subleading in finite-size, and in
string theory by using the Dobashi-Yoneya 3-string vertex in the leading order
of the Penrose expansion. The two results come out to be completely identical.Comment: 14 pages, 1 figur
Scaling and Crossover to Tricriticality in Polymer Solutions
We propose a scaling description of phase separation of polymer solutions.
The scaling incorporates three universal limiting regimes: the Ising limit
asymptotically close to the critical point of phase separation, the "ideal-gas"
limit for the pure-solvent phase, and the tricritical limit for the
polymer-rich phase asymptotically close to the theta point. We have also
developed a phenomenological crossover theory based on the
near-tricritical-point Landau expansion renormalized by fluctuations. This
theory validates the proposed scaled representation of experimental data and
crossover to tricriticality.Comment: 4 pages, 3 figure
Marine nitrogen fixation as a possible source of atmospheric water-soluble organic nitrogen aerosols in the subtropical North Pacific
Water-soluble organic nitrogen (WSON) in marine
atmospheric aerosols affect the water solubility, acidity, and
light-absorbing properties of aerosol particles, which are important
parameters in assessing both the climate impact and the biogeochemical
cycling of bioelements. Size-segregated aerosol and surface seawater (SSW)
samples were simultaneously collected over the subtropical North Pacific to
investigate the origin of WSON in the marine atmosphere. The fine-mode WSON
concentration (7.5 ± 6.6 ngN m−3) at 200–240∘ E
along 23∘ N, defined as the eastern North Pacific (ENP), was
significantly higher than that (2.4 ± 1.9 ngN m−3) at
135–200∘ E, defined as the western North Pacific (WNP).
Analysis of the stable carbon isotope ratio of water-soluble organic carbon
(WSOC; δ13CWSOC) together with backward trajectory
indicated that most of the observed WSON in the fine particles in the ENP
originated from the ocean surface. We found positive relations among
nitrogen-fixation rate, dissolved organic nitrogen (DON) in SSW, and the
WSON concentrations. The result suggests that reactive nitrogen (DON and
ammonium), produced and exuded by nitrogen-fixing microorganisms in SSW,
contributed to the formation of WSON aerosols. This study provides new
insights into the role of ocean-derived reactive nitrogen aerosols
associated with marine microbial activity.</p
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