736 research outputs found
Fitting the radial acceleration relation to individual SPARC galaxies
Galaxies follow a tight radial acceleration relation (RAR): the acceleration
observed at every radius correlates with that expected from the distribution of
baryons. We use the Markov Chain Monte Carlo method to fit the mean RAR to 175
individual galaxies in the SPARC database, marginalizing over stellar
mass-to-light ratio (), galaxy distance, and disk
inclination. Acceptable fits with astrophysically reasonable parameters are
found for the vast majority of galaxies. The residuals around these fits have
an rms scatter of only 0.057 dex (13). This is in agreement with the
predictions of modified Newtonian dynamics (MOND). We further consider a
generalized version of the RAR that, unlike MOND, permits galaxy-to-galaxy
variation in the critical acceleration scale. The fits are not improved with
this additional freedom: there is no credible indication of variation in the
critical acceleration scale. The data are consistent with the action of a
single effective force law. The apparent universality of the acceleration scale
and the small residual scatter are key to understanding galaxies.Comment: 12 pages, 7 figures, 2 tables. Accepted for publication in A&A. The
same as the first version with typos corrected. A set of 175 figures is
available at http://astroweb.cwru.edu/SPARC
Allocating an indivisible good. A questionnaire-experimental study of intercultural differences.
We present the results of a questionnaire study in Belgium, Burkina Faso and Indonesia focusing on the problem of the just allocation of an indivisible good. The formal axioms proposed in social choice theory are helpful in structuring the response patterns. Interindividual differences can be interpreted in a meaningful way in terms of basic intuitions about desert, efficiency and compensation. Belgian students are most resourceegalitarian, Burkinese students attach a large weight to innate capacities, Indonesian students focus on actual production. The crucial no-envy criterion is supported by a majority of respondents, but this majority becomes small if there is an unavoidable conflict between no-envy and the "responsibility" requirement of the stand-alone upper bound.Costs; Cost; Risk; Policy; Choice; Studies;
The baryonic Tully-Fisher relation for different velocity definitions and implications for galaxy angular momentum
We study the baryonic Tully-Fisher relation (BTFR) at z=0 using 153 galaxies
from the SPARC sample. We consider different definitions of the characteristic
velocity from HI and H-alpha rotation curves, as well as HI line-widths from
single-dish observations. We reach the following results: (1) The tightest BTFR
is given by the mean velocity along the flat part of the rotation curve. The
orthogonal intrinsic scatter is extremely small (6%) and the best-fit slope is
3.85+/-0.09, but systematic uncertainties may drive the slope from 3.5 to 4.0.
Other velocity definitions lead to BTFRs with systematically higher scatters
and shallower slopes. (2) We provide statistical relations to infer the flat
rotation velocity from HI line-widths or less extended rotation curves (like
H-alpha and CO data). These can be useful to study the BTFR from large HI
surveys or the BTFR at high redshifts. (3) The BTFR is more fundamental than
the relation between angular momentum and galaxy mass (the Fall relation). The
Fall relation has about 7 times more scatter than the BTFR, which is merely
driven by the scatter in the mass-size relation of galaxies. The BTFR is
already the "fundamental plane" of galaxy discs: no value is added with a
radial variable as a third parameter.Comment: 12 pages, 6 figures, accepted for publication in MNRA
Towards the development of a problem solver for the monitoring and control of instrumentation in a grid environment
This paper considers the issues involved in developing a generic problem solver to be used within a grid environment for the monitoring and control of instrumentation. The specific feature of such an environment is that the type of data to be processed, as well as the problem, is not always known in advance. Therefore, it is necessary to develop a problem solver architecture that addresses this issue. We propose to analyze the performance of the problem solving algorithms available within the WEKA toolkit and determine a decision tree of the best performing algorithm for a given type of data. For this purpose the algorithms have been tested using 51 datasets either drawn from publicly available repositories or generated in a grid-enabled environmen
Protonation controls ASIC1a activity via coordinated movements in multiple domains.
Acid-sensing ion channels (ASICs) are neuronal Na(+)-conducting channels activated by extracellular acidification. ASICs are involved in pain sensation, expression of fear, and neurodegeneration after ischemic stroke. Functional ASICs are composed of three identical or homologous subunits, whose extracellular part has a handlike structure. Currently, it is unclear how protonation of residues in extracellular domains controls ASIC activity. Knowledge of these mechanisms would allow a rational development of drugs acting on ASICs. Protonation may induce conformational changes that control the position of the channel gate. We used voltage-clamp fluorometry with fluorophores attached to residues in different domains of ASIC1a to detect conformational changes. Comparison of the timing of fluorescence and current signals identified residues involved in movements that preceded desensitization and may therefore be associated with channel opening or early steps leading to desensitization. Other residues participated in movements intimately linked to desensitization and recovery from desensitization. Fluorescence signals of all mutants were detected at more alkaline pH than ionic currents. Their midpoint of pH dependence was close to that of steady-state desensitization, whereas the steepness of the pH fluorescence relationship was closer to that of current activation. A sequence of movements was observed upon acidification, and its backward movements during recovery from desensitization occurred in the reverse order, indicating that the individual steps are interdependent. Furthermore, the fluorescence signal of some labeled residues in the finger domain was strongly quenched by a Trp residue in the neighboring β-ball domain. Upon channel activation, their fluorescence intensity increased, indicating that the finger moved away from the β ball. This extensive analysis of activity-dependent conformational changes in ASICs sheds new light on the mechanisms by which protonation controls ASIC activity
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