2,957 research outputs found
The H II Region/PDR Connection: Self-Consistent Calculations of Physical Conditions in Star-Forming Regions
We have performed a series of calculations designed to reproduce infrared
diagnostics used to determine physical conditions in star forming regions. We
self-consistently calculate the thermal and chemical structure of an H II
region and photodissociation region (PDR) that are in pressure equilibrium.
This differs from previous work, which used separate calculations for each gas
phase. Our calculations span a wide range of stellar temperatures, gas
densities, and ionization parameters. We describe improvements made to the
spectral synthesis code Cloudy that made these calculations possible. These
include the addition of a molecular network with ~1000 reactions involving 68
molecular species and improved treatment of the grain physics. Data from the
Spitzer First Look Survey, along with other archives, are used to derive
important physical characteristics of the H II region and PDR. These include
stellar temperatures, electron densities, ionization parameters, UV radiation
flux, and PDR density. Finally, we calculate the contribution of the H II
region to PDR emission line diagnostics, which allows for a more accurate
determination of physical conditions in the PDR.Comment: 60 pages, 35 figures, to be published in the Astrophysical Journal.
Version with full resolution is available at
http://www.pa.uky.edu/~nicholas/hii_pdr_high_res.pd
Focus Issue: Neck Dissection for Oropharyngeal Squamous Cell Carcinoma
The staging and prognosis of oropharyngeal squamous cell carcinoma is intimately tied to the status of the cervical lymph nodes. Due to the high risk for occult nodal disease, most clinicians recommend treating the neck for these primary tumors. While there are many modalities available, surgical resection of nodal disease offers both a therapeutic and a diagnostic intervention. We review the relevant anatomy, nodal drainage patterns, clinical workup, surgical management and common complications associated with neck dissection for oropharyngeal squamous cell carcinoma
Dust-Bounded ULIRGs? Model Predictions for Infrared Spectroscopic Surveys
The observed faintness of infrared fine-structure line emission along with
the warm far-infrared (FIR) colors of ultraluminous infrared galaxies (ULIRGs)
is a long-standing problem. In this work, we calculate the line and continuum
properties of a cloud exposed to an Active Galactic Nucleus (AGN) and starburst
spectral energy distribution (SED). We use an integrated modeling approach,
predicting the spectrum of ionized, atomic, and molecular environments in
pressure equilibrium. We find that the effects of high ratios of impinging
ionizing radiation density to particle density (i.e. high ionization
parameters, or U) can reproduce many ULIRG observational characteristics.
Physically, as U increases, the fraction of UV photons absorbed by dust
increases, corresponding to fewer photons available to photoionize and heat the
gas, producing what is known as a "dust-bounded" nebula. We show that high U
effects can explain the "[C II] deficit", the ~1 dex drop in the [C II] 158
micron /FIR ratio seen in ULIRGs when compared to starburst or normal galaxies.
Additionally, by increasing U through increasing the ionizing photon flux,
warmer dust and thus higher IRAS F(60)/F(100) ratios result. High U effects
also predict an increase in [O I]63 micron /[C II] 158 micron and a gradual
decline in [O III] 88 micron /FIR, similar to the magnitude of the trends
observed, and yield a reasonable fit to [Ne V]14 micron /FIR ratio AGN
observations.Comment: 34 pages, 13 figures, accepted for publication in the Astrophysical
Journa
Rotationally Warm Molecular Hydrogen in the Orion Bar
The Orion Bar is one of the nearest and best-studied photodissociation or
photon-dominated regions (PDRs). Observations reveal the presence of H2 lines
from vibrationally or rotationally excited upper levels that suggest warm gas
temperatures (400 to 700 K). However, standard models of PDRs are unable to
reproduce such warm rotational temperatures. In this paper we attempt to
explain these observations with new comprehensive models which extend from the
H+ region through the Bar and include the magnetic field in the equation of
state. We adopt the model parameters from our previous paper which successfully
reproduced a wide variety of spectral observations across the Bar. In this
model the local cosmic-ray density is enhanced above the galactic background,
as is the magnetic field, and which increases the cosmic-ray heating elevating
the temperature in the molecular region. The pressure is further enhanced above
the gas pressure in the H+ region by the momentum transferred from the absorbed
starlight. Here we investigate whether the observed H2 lines can be reproduced
with standard assumptions concerning the grain photoelectric emission. We also
explore the effects due to the inclusion of recently computed H2 + H2, H2 + H
and H2 + He collisional rate coefficients.Comment: Accepted for publication in ApJ (34 pages, including 16 figures
Active Learning for Deep Detection Neural Networks
The cost of drawing object bounding boxes (i.e. labeling) for millions of
images is prohibitively high. For instance, labeling pedestrians in a regular
urban image could take 35 seconds on average. Active learning aims to reduce
the cost of labeling by selecting only those images that are informative to
improve the detection network accuracy. In this paper, we propose a method to
perform active learning of object detectors based on convolutional neural
networks. We propose a new image-level scoring process to rank unlabeled images
for their automatic selection, which clearly outperforms classical scores. The
proposed method can be applied to videos and sets of still images. In the
former case, temporal selection rules can complement our scoring process. As a
relevant use case, we extensively study the performance of our method on the
task of pedestrian detection. Overall, the experiments show that the proposed
method performs better than random selection. Our codes are publicly available
at www.gitlab.com/haghdam/deep_active_learning.Comment: Accepted at ICCV 201
Sensitivity of PDR Calculations to Microphysical Details
Our understanding of physical processes in Photodissociation regions or
Photon Dominated Regions (PDRs) largely depends on the ability of spectral
synthesis codes to reproduce the observed infrared emission-line spectrum. In
this paper, we explore the sensitivity of a single PDR model to microphysical
details. Our calculations use the Cloudy spectral synthesis code, recently
modified to include a wealth of PDR physical processes. We show how the
chemical/thermal structure of a PDR, along with the calculated spectrum,
changes when the treatment of physical processes such as grain physics and
atomic/molecular rates are varied. We find a significant variation in the
intensities of PDR emission lines, depending on different treatments of the
grain physics. We also show how different combinations of the cosmic-ray
ionization rate, inclusion of grain-atom/ion charge transfer, and the grain
size distribution can lead to very similar results for the chemical structure.
Additionally, our results show the utility of Cloudy for the spectral modeling
of molecular environments.Comment: 36 pages, 17 figures, accepted for publication in Ap
Pumping up the [N I] nebular lines
The optical [N I] doublet near 5200 {\AA} is anomalously strong in a variety
of emission-line objects. We compute a detailed photoionization model and use
it to show that pumping by far-ultraviolet (FUV) stellar radiation previously
posited as a general explanation applies to the Orion Nebula (M42) and its
companion M43; but, it is unlikely to explain planetary nebulae and supernova
remnants. Our models establish that the observed nearly constant equivalent
width of [N I] with respect to the dust-scattered stellar continuum depends
primarily on three factors: the FUV to visual-band flux ratio of the stellar
population; the optical properties of the dust; and the line broadening where
the pumping occurs. In contrast, the intensity ratio [N I]/H{\beta} depends
primarily on the FUV to extreme-ultraviolet ratio, which varies strongly with
the spectral type of the exciting star. This is consistent with the observed
difference of a factor of five between M42 and M43, which are excited by an O7
and B0.5 star respectively. We derive a non-thermal broadening of order 5 km/s
for the [N I] pumping zone and show that the broadening mechanism must be
different from the large-scale turbulent motions that have been suggested to
explain the line-widths in this H II region. A mechanism is required that
operates at scales of a few astronomical units, which may be driven by thermal
instabilities of neutral gas in the range 1000 to 3000 K. In an appendix, we
describe how collisional and radiative processes are treated in the detailed
model N I atom now included in the Cloudy plasma code.Comment: ApJ in press. 8 pages of main paper plus 11 pages of appendices, with
13 figures and 12 table
Neutron-Electron EDM Correlations in Supersymmetry and Prospects for EDM Searches
Motivated by recent progress in experimental techniques of electric dipole
moment (EDM) measurements, we study correlations between the neutron and
electron EDMs in common supersymmetric models. These include minimal
supergravity (mSUGRA) with small CP phases, mSUGRA with a heavy SUSY spectrum,
the decoupling scenario and split SUSY. In most cases, the electron and neutron
EDMs are found to be observable in the next round of EDM experiments. They
exhibit certain correlation patterns. For example, if d_n ~ 10^{-27} e cm is
found, d_e is predicted to lie in the range 10^{-28}-10^{-29} e cm.Comment: 16 pages,12 figures. To appear in JHEP. A note on stability of the
correlations added in Conclusions; refs. and footnotes adde
On the Enhanced Cosmic-Ray Ionization Rate in the Diffuse Cloud toward ζ Persei
The spatial distribution of the cosmic-ray flux is important in understanding the interstellar medium (ISM) of the Galaxy. This distribution can be analyzed by studying different molecular species along different sight lines whose abundances are sensitive to the cosmic-ray ionization rate. Recently several groups have reported an enhanced cosmic-ray ionization rate (ζ=χCRζstandard) in diffuse clouds compared to the standard value, ζstandard (=2.5×10-17 s-1), measured toward dense molecular clouds. In an earlier work we reported an enhancement χCR=20 toward HD 185418. McCall et al. have reported χCR=48 toward ζ Persei based on the observed abundance of H+3, while Le Petit et al. found χCR~10 to be consistent with their models for this same sight line. Here we revisit ζ Persei and perform a detailed calculation using a self-consistent treatment of the hydrogen chemistry, grain physics, energy and ionization balance, and excitation physics. We show that the value of χCR deduced from the H+3 column density, N(H+3), in the diffuse region of the sight line depends strongly on the properties of the grains because they remove free electrons and change the hydrogen chemistry. The observations are largely consistent with χCR~40, with several diagnostics indicating higher values. This underscores the importance of a full treatment of grain physics in studies of interstellar chemistry
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