1,130 research outputs found
The Effect of Star Formation on Molecular Clouds in Dwarf Irregular Galaxies: IC 10 and NGC 6822
We have observed the 13CO J=2-1, 12CO J=2-1 and 12CO J=3-2 lines at a few
locations in the dwarf irregular galaxies IC 10 and NGC 6822 using the James
Clerk Maxwell Telescope. In addition, we report the first detection of the 13CO
J=3-2 transition in a Local Group galaxy. These low metallicity environments
appear to be porous to UV radiation and allow for more efficient heating of
molecular gas by nearby HII regions. The high 12CO J=3-2/J=2-1 ratio in NGC
6822 suggests that the 12CO emission is optically thin in this region. This
high line ratio is likely the result of its location inside a large HII region
with low metallicity and low gas content. In IC 10 we observe structures on a
variety of size scales that all appear to be gravitationally bound. This effect
may help explain the rather high star formation rate in IC 10.Comment: 20 pages with 6 ps figures, accepted for publication in The
Astrophysical Journa
The Low CO Content of the Extremely Metal Poor Galaxy I Zw 18
We present sensitive molecular line observations of the metal-poor blue
compact dwarf I Zw 18 obtained with the IRAM Plateau de Bure interferometer.
These data constrain the CO J=1-0 luminosity within our 300 pc (FWHM) beam to
be L_CO < 1 \times 10^5 K km s^-1 pc^2 (I_CO < 1 K km s^-1), an order of
magnitude lower than previous limits. Although I Zw 18 is starbursting, it has
a CO luminosity similar to or less than nearby low-mass irregulars (e.g. NGC
1569, the SMC, and NGC 6822). There is less CO in I Zw 18 relative to its
B-band luminosity, HI mass, or star formation rate than in spiral or dwarf
starburst galaxies (including the nearby dwarf starburst IC 10). Comparing the
star formation rate to our CO upper limit reveals that unless molecular gas
forms stars much more efficiently in I Zw 18 than in our own galaxy, it must
have a very low CO-to-H_2 ratio, \sim 10^-2 times the Galactic value. We detect
3mm continuum emission, presumably due to thermal dust and free-free emission,
towards the radio peak.Comment: 5 pages in emulateapj style, accepted by the Astrophysical Journa
A Return to âThe Clinicâ for Community Psychology: Lessons from a Clinical Ethnography in Urban American Indian Behavioral Health
Community psychology (CP) abandoned the clinic and disengaged from movements for community mental health (CMH) to escape clinical convention and pursue growing aspirations as an independent field of contextâoriented, communityâengaged, and valuesâdriven research and action. In doing so, however, CP positioned itself on the sidelines of influential contemporary movements that promote potentially harmful, reductionist biomedical narratives in mental health. We advocate for a return to the clinicâthe seat of institutional power in mental healthâusing critical clinicâbased inquiry to open sites for clinicalâcommunity dialogue that can instigate transformative change locally and nationally. To inform such works within the collaborative and emancipatory traditions of CP, we detail a recently completed clinical ethnography and offer âlessons learnedâ regarding challenges likely to reâemerge in similar efforts. Conducted with an urban American Indian community behavioral health clinic, this ethnography examined how culture and culture concepts (e.g., cultural competence) shaped clinical practice with socioâpolitical implications for American Indian peoples and the pursuit of transformative change in CMH. Lessons learned identify exceptional clinicians versed in ecological thinking and contextualist discourses of human suffering as ideal partners for this work; encourage intense contextualization and constraining critique to areas of mutual interest; and support relational approaches to clinic collaborations.HighlightsCommunity psychology (CP) must reengage the clinic setting to address problems in mental health.Clinical ethnography represents one promising approach to clinicâbased critical CP research.Clinicians versed in ecological thinking and contextualist discourses make ideal collaborators.Intense contextualism and mutual interests can guide a collaborative CP critique of the clinic.Relationallyâdriven and contextually specific approaches to collaboration are helpful in this work.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/142553/1/ajcp12212.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/142553/2/ajcp12212_am.pd
Deep Near-Infrared Imaging af an Embedded Cluster in the Extreme Outer Galaxy: Census of Supernovae Triggered Star Formation
While conducting a near-infrared (NIR) survey of ``Digel Clouds'', which are
thought to be located in the extreme outer Galaxy (EOG), Kobayashi & Tokunaga
found star formation activity in ``Cloud 2'', a giant molecular cloud at the
Galactic radius of ~ 20 kpc. Additional infrared imaging showed two embedded
young clusters at the densest regions of the molecular cloud. Because the
molecular cloud is located in the vicinity of a supernova remnant (SNR) HI
shell, GSH 138-01-94, it was suggested that the star formation activity in
Cloud 2 was triggered by this expanding HI shell. We obtained deep J (1.25 um),
H (1.65 um) and K (2.2 um) images of one of the embedded clusters in Cloud 2
with high spatial resolution (FWHM ~0".3) and high sensitivity (K ~ 20 mag, 10
sigma). We identified 52 cluster members. The estimated stellar density (~ 10
pc^{-2}) suggests that the cluster is a T-association. This is the deepest NIR
imaging of an embedded cluster in the EOG. The observed K-band luminosity
function (KLF) suggests that the underlying initial mass function (IMF) of the
cluster down to the detection limit of ~ 0.1 M_sun is not significantly
different from the typical IMFs in the field and in the near-by star clusters.
The overall characteristics of this cluster appears to be similar to those of
other embedded clusters in the far outer Galaxy. The estimated age of the
cluster from the KLF, which is less than 1 Myr, is consistent with the view
that the star formation was triggered by the HI shell whose age was estimated
at 4.3 Myr (Stil & Irwin). The 3-dimensional geometry of SNR shell, molecular
cloud and the embedded cluster, which is inferred from our data, as well as the
cluster age strongly suggest that the star formation in Cloud 2 was triggered
by the SNR shell.Comment: 19pages, 8 figures, 1 table, accepted to ApJ. Full paper (pdf) with
high resolution figures available at
http://www.ioa.s.u-tokyo.ac.jp/~ck_yasui/papers/Cloud2N_1.pd
Boron Doped Diamond Electrodes for Direct Measurement in Biological Fluids: An In Situ Regeneration Approach
International audienceBoron doped diamond (BDD) electrodes are extremely promising in the field of biomedical applications as they exhibit a unique combination of properties. Despite these advantages, BDD electrodes are prone to fouling when used in biological fluids (urine, blood plasma), and synthetic fluids. We propose a electrochemical (EC) treatment where a train of short cathodic and/or anodic pulses are applied to clean fouled electrodes. This technique can be used to retrieve the lost reactivity, characterized by electron transfer rate k0 of the boron doped diamond electrodes, thereby enhancing their reusability over long period of measurements without degradation of the signal, thus significantly extending the field of monitoring and surveying applications. The technique does not require the use of a specific medium and thus can be directly performed in the probed fluid. Although an aqueous electrolyte containing non-electroactive species is preferred for EC activation, it can also be done in biological fluids such as blood, urine etc, thereby opening the field for analysis. Through Electrochemical impedance spectroscopy (EIS) it was observed that the k value was increased up to 0.1 cm s after the activation process. This technique improves the sensitivity, reproducibility and lifetime of the electrodes to a considerable extent
Conceptual hydrological model calibration using multi-objective optimization techniques over the transboundary Komadugu-Yobe basin, Lake Chad Area, West Africa
Study Area: The discharge of the transboundary Komadugu-Yobe Basin, Lake Chad Area, West Africa is calibrated using multi-objective optimization techniques. Study focus: The GR5J hydrological model parameters are calibrated using six optimization methods i.e. Local Optimization-Multi Start (LOMS), the Differential Evolution (DE), the Multiobjective Particle the Swarm Optimization (MPSO), the Memetic Algorithm with Local Search Chains (MALS), the Shuffled Complex Evolution-Rosenbrockâs function (SCE-R), and the Bayesian Markov Chain Monte Carlo (MCMC) approach. Three combined objective functions i.e. Root Mean Square Error, Nash- Sutcliffe efficiency, Kling-Gupta efficiency are applied. The calibration process is divided into two separate episodes (1974â2000 and 1980â1995) so as to ascertain the robustness of the calibration approaches. Runoff simulation results are analysed with a timefrequency wavelet transform. New hydrological insights for the region: For calibration and validation stages, all optimization methods simulate the base flow and high flow spells with a satisfactory level of accuracy. For calibration period, MCMC underestimate it by -0.07 mm/day. The performance evaluation shows that MCMC has the highest values of mean absolute error (0.28) and mean square error (0.40) while LOMS and MCMC record a low volumetric efficiency of 0.56. In all cases, the DE and the SCE-R methods perform better than others. The combination of multi-objective functions and multi-optimization techniques improve the modelâs parameters stability and the algorithmsâ optimization to represent the runoff in the basin
In situ study of the initial stages of diamond deposition on 3C-SiC (100) surfaces: Towards the mechanisms of diamond nucleation
The mechanisms involved in the diamond nucleation on 3C-SiC surfaces have been investigated using a sequential in situ approach using electron spectroscopies (XPS, XAES and ELS). Moreover, diamond crystals have been studied by HRSEM. The in situ nucleation treatment allows a high diamond nucleation density close to 4 x 10(10) cm(-2). During the in situ enhanced nucleation treatment under Plasma, a negative bias was applied to the sample. The formation of an amorphous carbon phase and the roughening of the 3C-SiC surface have been observed. The part of these competing mechanisms in diamond nucleation is discussed
Convection-permitting fully coupled WRF-Hydro ensemble simulations in high mountain environment: impact of boundary layer- and lateral flow parameterizations on landâatmosphere interactions
Numerical climate models have been upgraded by the improved description of terrestrial hydrological processes across different scales. The goal of this study is to explore the role of terrestrial hydrological processes on landâatmosphere interactions within the context of modeling uncertainties related to model physics parameterization. The models applied are the Weather Research and Forecasting (WRF) model and its coupled hydrological modeling system WRF-Hydro, which depicts the lateral terrestrial hydrological processes and further allows their feedback to the atmosphere. We conducted convection-permitting simulations (3 km) over the Heihe River Basin in Northwest China for the period 2008â2010, and particularly focused on its upper reach area of complex high mountains. In order to account for the modeling uncertainties associated with model physics parameterization, an ensemble of simulations is generated by varying the planetary boundary layer (PBL) schemes. We embedded the fully three-dimensional atmospheric water tagging method in both WRF and WRF-Hydro for quantifying the strength of landâatmosphere interactions. The impact of PBL parameterization on landâatmosphere interactions is evaluated through its direct effect on vertical mixing. Results suggest that enabled lateral terrestrial flow in WRF-Hydro distinctly increases soil moisture and evapotranspiration near the surface in the high mountains, thereby modifies the atmospheric condition regardless of the applied PBL scheme. The local precipitation recycling ratio in the study area increases from 1.52 to 1.9% due to the description of lateral terrestrial flow, and such positive feedback processes are irrespective of the modeling variability caused by PBL parameterizations. This study highlights the non-negligible contribution of lateral terrestrial flow to local precipitation recycling, indicating the potential of the fully coupled modeling in landâatmosphere interactions research
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