Abstract The Balmer decrement (H α /H β ) provides a constraint on attenuation, the cumulative effects of dust grains in the ISM. The ratio is a reliable spectroscopic tool for deriving the dust ...properties of galaxies that determine many different quantities such as star formation rate, metallicity, and SED models. Here, we measure independently both the attenuation and H α /H β of an occulting galaxy pair: VV 191. Attenuation measurements in the visible spectrum ( A V ,stars ) from dust maps derived from the F606W filter of HST and the F090W filter of JWST are matched with spaxel-by-spaxel H α /H β observations from the George and Cynthia Mitchell Spectrograph of the McDonald Observatory. The 0.5–0.7 μ m bandpass covers the Balmer lines for VV 191. The dust maps of JWST and HST provide the high sensitivity necessary for comparisons and tracking trends of the geometrically favorable galaxy. We present maps and plots of the Balmer lines for the VV 191 galaxy pair and for a specific region highlighting dust lanes for VV 191b in the overlap region. We compute A V ,H II from H α /H β and plot both quantities against A V ,stars . Our results show that regions with higher dust content, residing closer to the spiral center, dominate ionized gas attenuation, leading to an overestimation of A V ,H II by a factor of 2. Further out in the spiral arms, the lower dust content leads to more agreement between the attenuations, indicating a lower star formation rate and larger contribution from older stars to the stellar continuum outside the Petrosian radius.
ABSTRACT
Galaxies fall broadly into two categories: star-forming (blue) galaxies and quiescent (red) galaxies. In between, one finds the less populated ‘green valley’. Some of these galaxies are ...suspected to be in the process of ceasing their star formation through a gradual exhaustion of gas supply, or already dead and experiencing a rejuvenation of star formation through fuel injection. We use the Galaxy And Mass Assembly (GAMA) database and the Galaxy Zoo citizen science morphological estimates to compare the morphology of galaxies in the green valley with those in the red sequence and blue cloud. Our goal is to examine the structural differences within galaxies that fall in the green valley, and what brings them there. Previous results found that disc features such as rings and lenses are more prominently represented in the green-valley population. We revisit this with a similar sized data set of galaxies with morphology labels provided by the Galaxy Zoo for the GAMA fields based on new Kilo-Degree Survey (KiDS) images. Our aim is to compare the results from expert classification qualitatively with those of citizen science. We observe that ring structures are indeed found more commonly in green-valley galaxies compared with their red and blue counterparts. We suggest that ring structures are a consequence of disc galaxies in the green valley actively exhibiting the characteristics of fading discs and evolving disc morphology of galaxies. We note that the progression from blue to red correlates with loosening spiral-arm structure.
Galaxies broadly fall into two categories: star-forming (blue) galaxies and quiescent (red) galaxies. In between, one finds the less populated ``green valley". Some of these galaxies are suspected to ...be in the process of ceasing their star-formation through a gradual exhaustion of gas supply or already dead and are experiencing a rejuvenation of star-formation through fuel injection. We use the Galaxy And Mass Assembly database and the Galaxy Zoo citizen science morphological estimates to compare the morphology of galaxies in the green valley against those in the red sequence and blue cloud. Our goal is to examine the structural differences within galaxies that fall in the green valley, and what brings them there. Previous results found disc features such as rings and lenses are more prominently represented in the green valley population. We revisit this with a similar sized data set of galaxies with morphology labels provided by the Galaxy Zoo for the GAMA fields based on new KiDS images. Our aim is to compare qualitatively the results from expert classification to that of citizen science. We observe that ring structures are indeed found more commonly in green valley galaxies compared to their red and blue counterparts. We suggest that ring structures are a consequence of disc galaxies in the green valley actively exhibiting characteristics of fading discs and evolving disc morphology of galaxies. We note that the progression from blue to red correlates with loosening spiral arm structure.
Purpose
To demonstrate and validate electric field (E‐field) calculation and peripheral nerve stimulation (PNS) prediction methods that are accurate, computationally efficient, and that could be used ...to inform regulatory standards.
Methods
We describe a simplified method for calculating the spatial distribution of induced E‐field over the volume of a body model given a gradient coil vector potential field. The method is easily programmed without finite element or finite difference software, allowing for straightforward and computationally efficient E‐field evaluation. Using these E‐field calculations and a range of body models, population‐weighted PNS thresholds are determined using established methods and compared against published experimental PNS data for two head gradient coils and one body gradient coil.
Results
A head‐gradient‐appropriate chronaxie value of 669 µs was determined by meta‐analysis. Prediction errors between our calculated PNS parameters and the corresponding experimentally measured values were ~5% for the body gradient and ~20% for the symmetric head gradient. Our calculated PNS parameters matched experimental measurements to within experimental uncertainty for 73% of ∆Gmin estimates and 80% of SRmin estimates. Computation time is seconds for initial E‐field maps and milliseconds for E‐field updates for different gradient designs, allowing for highly efficient iterative optimization of gradient designs and enabling new dimensions in PNS‐optimal gradient design.
Conclusions
We have developed accurate and computationally efficient methods for prospectively determining PNS limits, with specific application to head gradient coils.
Full text
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
This unprecedented volume presents a sweeping picture of what we know about the natural history, biology, and ecology of whales in the broad context of the dynamics of ocean ecosystems. Innovative ...and comprehensive, the volume encompasses multiple points of view to consider the total ecological impact of industrial whaling on the world's oceans. Combining empirical research, ecological theory and modeling, and historical data, its chapters present perspectives from ecology, population biology, physiology, genetics, evolutionary history, ocean biogeography, economics, culture, and law, among other disiplines. Throughout, contributors investigate how whaling fundamentally disrupted ocean ecosystems, examine the various roles whales play in food webs, and discuss the continuing ecological chain reactions to the depletion of these large animals. In addition to reviewing what is known of the current and historic whale populations, Whales, Whaling, and Ocean Ecosystems considers how this knowledge will bear on scientific approaches to conservation and whaling in the future and provocatively asks whether it is possible to restore ocean ecosystems to their pre-whaling condition.
Purpose: To demonstrate and validate E-field calculation and PNS prediction methods that are accurate, computationally efficient and that could be used to inform regulatory standards. Methods: We ...describe a simplified method for calculating the spatial distribution of induced E-field over the volume of a body model given a gradient coil vector potential field. The method is easily programmed without finite element or finite difference software, allowing for straightforward and computationally-efficient E-field evaluation. Using these E-field calculations and a range of body models, population-weighted PNS thresholds are determined using established methods and compared against published experimental PNS data for two head gradient coils and one body gradient coil. Results: A head-gradient-appropriate chronaxie value of 669us was determined by meta-analysis. Prediction errors between our calculated PNS parameters and the corresponding experimentally measured values were ~5% for the body gradient and ~20% for the symmetric head gradient. Our calculated PNS parameters matched experimental measurements to within experimental uncertainty for 73% of deltaGmin estimates and 80% of SRmin estimates. Computation time is seconds for initial E-field maps and milliseconds for E-field updates for different gradient designs, allowing for highly efficient iterative optimization of gradient designs and enabling new dimensions in PNS-optimal gradient design. Conclusions: We have developed accurate and computationally efficient methods for prospectively determining PNS limits, with specific application to head gradient coils.
