6,728 research outputs found
Star Formation History and Extinction in the central kpc of M82-like Starbursts
We report on the star formation histories and extinction in the central kpc
region of a sample of starburst galaxies that have similar far infrared (FIR),
10 micron and K-band luminosities as those of the archetype starburst M82. Our
study is based on new optical spectra and previously published K-band
photometric data, both sampling the same area around the nucleus. Model
starburst spectra were synthesized as a combination of stellar populations of
distinct ages formed over the Hubble time, and were fitted to the observed
optical spectra and K-band flux. The model is able to reproduce simultaneously
the equivalent widths of emission and absorption lines, the continuum fluxes
between 3500-7000 Ang, the K-band and the FIR flux. We require a minimum of 3
populations -- (1) a young population of age < 8 Myr, with its corresponding
nebular emission, (2) an intermediate-age population (age < 500 Myr), and (3)
an old population that forms part of the underlying disk or/and bulge
population. The contribution of the old population to the K-band luminosity
depends on the birthrate parameter and remains above 60% in the majority of the
sample galaxies. Even in the blue band, the intermediate age and old
populations contribute more than 40% of the total flux in all the cases. A
relatively high contribution from the old stars to the K-band nuclear flux is
also apparent from the strength of the 4000 Ang break and the CaII K line. The
extinction of the old population is found to be around half of that of the
young population. The contribution to the continuum from the relatively old
stars has the effect of diluting the emission equivalent widths below the
values expected for young bursts. The mean dilution factors are found to be 5
and 3 for the Halpha and Hbeta lines respectively.Comment: 20 pages, uses emulateapj.cls. Scheduled to appear in ApJ Jan 1, 200
Methyl bromide: Ocean sources, ocean sinks, and climate sensitivity
The oceans play an important role in the geochemical cycle of methyl bromide (CH_3Br), the major carrier of O_3-destroying bromine to the stratosphere. The quantity of CH_3Br produced annually in seawater is comparable to the amount entering the atmosphere each year from natural and anthropogenic sources. The production mechanism is unknown but may be biological. Most of this CH_3Br is consumed in situ by hydrolysis or reaction with chloride. The size of the fraction which escapes to the atmosphere is poorly constrained; measurements in seawater and the atmosphere have been used to justify both a large oceanic CH_3Br flux to the atmosphere and a small net ocean sink. Since the consumption reactions are extremely temperature-sensitive, small temperature variations have large effects on the CH_3Br concentration in seawater, and therefore on the exchange between the atmosphere and the ocean. The net CH_3Br flux is also sensitive to variations in the rate of CH_3Br production. We have quantified these effects using a simple steady state mass balance model. When CH_3Br production rates are linearly scaled with seawater chlorophyll content, this model reproduces the latitudinal variations in marine CH_3Br concentrations observed in the east Pacific Ocean by Singh et al. [1983] and by Lobert et al. [1995]. The apparent correlation of CH_3Br production with primary production explains the discrepancies between the two observational studies, strengthening recent suggestions that the open ocean is a small net sink for atmospheric CH_3Br, rather than a large net source. The Southern Ocean is implicated as a possible large net source of CH_3Br to the atmosphere. Since our model indicates that both the direction and magnitude of CH_3Br exchange between the atmosphere and ocean are extremely sensitive to temperature and marine productivity, and since the rate of CH_3Br production in the oceans is comparable to the rate at which this compound is introduced to the atmosphere, even small perturbations to temperature or productivity can modify atmospheric CH_3Br. Therefore atmospheric CH_3Br should be sensitive to climate conditions. Our modeling indicates that climate-induced CH_3Br variations can be larger than those resulting from small (±25%) changes in the anthropogenic source, assuming that this source comprises less than half of all inputs. Future measurements of marine CH_3Br, temperature, and primary production should be combined with such models to determine the relationship between marine biological activity and CH_3Br production. Better understanding of the biological term is especially important to assess the importance of non anthropogenic sources to stratospheric ozone loss and the sensitivity of these sources to global climate change
The reach, adoption, and effectiveness of online training for healthcare professionals
Traditionally, the continued professional development of healthcare professionals has been completed through classroom-based educational courses, workshops, and conferences. These can prove costly and time intensive. Online learning is becoming increasingly common, is easy to access, and can save learners' time which is important in a healthcare system where job demands are high and study leave is limited. Well-designed internet-based learning has been shown to be as effective as traditional classroom-based learning in the skill and knowledge development of healthcare professionals, however the reach, adoption, and effectiveness of such training is largely underreported in the literature.
This short communication reports on evaluation data from delivery of a 60-min online training session to healthcare professionals, between January and November 2016
Complex networks: new trends for the analysis of brain connectivity
Today, the human brain can be studied as a whole. Electroencephalography,
magnetoencephalography, or functional magnetic resonance imaging techniques
provide functional connectivity patterns between different brain areas, and
during different pathological and cognitive neuro-dynamical states. In this
Tutorial we review novel complex networks approaches to unveil how brain
networks can efficiently manage local processing and global integration for the
transfer of information, while being at the same time capable of adapting to
satisfy changing neural demands.Comment: Tutorial paper to appear in the Int. J. Bif. Chao
The Impact of Education, Gender, Age and Leadership Experience On Preferences In Leadership
Meta-analytic studies have found that men and women are different in areas such as how they approach morality, forgiveness and leadership, Similarly, meta-analyses have found that increased education is related to increased self-esteem, job attitudes and social capital, In this study, 577 working adults from the state of Texas completed the Project Globe Leadership Questionnaire. The participants indicated to what degree 24 leadership behaviors contributed to or inhibited outstanding leadership. This study found that both gender and education were related to the intensity with which participants believed particular leadership characteristics contributed to and inhibited outstanding leadership. Women held stronger opinions than men about the benefits of five aspects of leadership generally considered to contribute to outstanding leadership: integrity, team-oriented, participative, humane-oriented and diplomatic, Women also held stronger opinions about the liabilities of four aspects generally considered to inhibit outstanding leadership: conflict inducer, self-protective, autocratic and malevolent. Formal education was related to stronger ratings of the importance of integrity, charisma, performance and team orientation. Formal education was also related to stronger ratings of the degree to which self-protective, face-saving, autocratic, self-centered and malevolent behaviors inhibit outstanding leadership
The LMT Galaxies' 3 mm Spectroscopic Survey: First Results
The molecular phase of the interstellar medium (ISM) in galaxies offers
fundamental insight for understanding star-formation processes and how stellar
feedback affects the nuclear activity of certain galaxies. We present here
Large Millimeter Telescope spectra obtained with the Redshift Search Receiver,
a spectrograph that cover simultaneously the 3 mm band from 74 to 111 GHz with
a spectral resolution of around 100 km/s. The observed galaxies that have been
detected previously in HCN, have different degrees of nuclear activity, one
normal galaxy (NGC 6946), the starburst prototype (M 82) and two ultraluminous
infrared galaxies (ULIRGs, IRAS 17208-0014 and Mrk 231). We plotted our data in
the HCO+/HCN vs. HCN/13CO diagnostic diagram finding that NGC 6946 and M 82 are
located close to other normal galaxies; and that both IRAS 17208-0014 and Mrk
231 are close to the position of the well known ULIRG Arp 220 reported by Snell
et al. (2011). We found that in Mrk 231 -- a galaxy with a well known active
galactic nucleus -- the HCO+/HCN ratio is similar to the ratio observed in
other normal galaxies.Comment: Proceedings to appear in "Massive Young Star Clusters Near and Far:
From the Milky Way to Reionization", 2013 Guillermo Haro Conference. Eds. Y.
D. Mayya, D. Rosa-Gonzalez, & E. Terlevich, INAOE and AMC. 5 pages, 1 figur
Single particle motion studies using stereo-vision and digital image processing
This paper proposes a new analysis technique to find the
kinematics and dynamics of a single particle immersed in a fluid
in a three-dimensional metric frame. Because the technique is
entirely based on stereo-vision using only one camera attached
to a stereo adapter, it offers great versatility and simplicity, and
it does not cause any alteration to the physics of the studied
phenomena, therefore ensuring that the interaction between the
solid and its neighboring fluid stays undisturbed. Particle
velocity, drag force, and orientation, represented through the
angle of incidence, were estimated within the metric frame by
means of digital image processing, vector algebra, and
differential geometry operations. The methodology was first
validated by analyzing the motion of three spheres settling in a
fluid at different Reynolds numbers, where a close agreement
between the coefficients of resistance determined here and those
computed from literature correlations was obtained. The motion
of two cylinders in free fall was then investigated, and it was
found that at low Reynolds numbers a cylinder falls with fixed
orientation in a straight path whilst for large Reynolds numbers
it exhibits regular oscillation and travels in a sinusoidal fall path,
thus causing an increment in the drag coefficient as the angle of
incidence also augments.Papers presented to the 12th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Costa de Sol, Spain on 11-13 July 2016
Capillarity Theory for the Fly-Casting Mechanism
Biomolecular folding and function are often coupled. During molecular
recognition events, one of the binding partners may transiently or partially
unfold, allowing more rapid access to a binding site. We describe a simple
model for this flycasting mechanism based on the capillarity approximation and
polymer chain statistics. The model shows that flycasting is most effective
when the protein unfolding barrier is small and the part of the chain which
extends towards the target is relatively rigid. These features are often seen
in known examples of flycasting in protein-DNA binding. Simulations of
protein-DNA binding based on well-funneled native-topology models with
electrostatic forces confirm the trends of the analytical theory
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