229 research outputs found
Novel nitrogen-based organosulfur electrodes for advanced intermediate temperature batteries
Advanced secondary batteries operating at intermediate temperatures (100 to 200 C) have attracted considerable interest due to their inherent advantages (reduced corrosion and safety risks) over higher temperature systems. Current work in this laboratory has involved research on a class of intermediate temperature Na/beta double prime- alumina/RSSR batteries conceptually similar to Na/S cells, but operating within a temperature range of 100 to 150 C, and having an organosulfur rather than inorganic sulfur positive electrode. The organosulfur electrodes are based on the reversible, two electron eduction of organodisulfides to the corresponding thiolate anions, RSSR + 2 electrons yield 2RS(-), where R is an organic moiety. Among the advantages of such a generic redox couple for battery research is the ability to tailor the physical, chemical, and electrochemical properties of the RSSR molecule through choice of the organic moiety. The viscosity, liquidus range, dielectric constant, equivalent weight, and redox potential can in fact be verified in a largely predictable manner. The current work concerns the use of multiple nitrogen organosulfur molecules, chosen for application in Na/RSSR cells for their expected oxidizing character. In fact, a Na/RSSR cell containing one of these materials, the sodium salt of 5-mercapto 1-methyltetrazole, yielded the highest open circuit voltage obtained yet in the laboratory; 3.0 volts in the charged state and 2.6 volts at 100 percent discharge. Accordingly, the cycling behavior of a series of multiple nitrogen organodisulfides as well as polymeric organodisulfides are presented in this manuscript
The Three-Dimensional Mass Distribution in NGC 1700
A variety of modeling techniques is used with surface photometry from the
literature and recently acquired high-accuracy stellar kinematic data to
constrain the three-dimensional mass distribution in the luminous cuspy
elliptical galaxy NGC 1700. First, we model the radial velocity field and
photometry, and, using a Bayesian technique, estimate the triaxiality T and
short-to-long axis ratio c in five concentric annuli between approximately 1
and 3 effective radii. The results are completely consistent with T being
constant inside about 2.5 r_e (36 arcsec; 6.7/h kpc). Adding an assumption of
constant T as prior information gives an upper limit of T < 0.16 (95%
confidence); this relaxes to T < 0.22 if it is also assumed that there is
perfect alignment between the angular momentum and the galaxy's intrinsic short
axis. Near axisymmetry permits us then to use axisymmetric models to constrain
the radial mass profile. Using the Jeans (moment) equations, we demonstrate
that 2-integral, constant-M/L models cannot fit the data; but a 2-integral
model in which the cumulative enclosed M/L increases by a factor of roughly 2
from the center out to 12/h kpc can. Three-integral models constructed by
quadratic programming show that, in fact, no constant-M/L model is consistent
with the kinematics. Anisotropic 3-integral models with variable M/L, while not
uniquely establishing a minimum acceptable halo mass, imply, as do the moment
models, a cumulative M/L_B approximately 10 h at 12/h kpc. We conclude that NGC
1700 represents the best stellar dynamical evidence to date for dark matter in
elliptical galaxies.Comment: 26 pages, Latex, AASTeX v4.0, with 11 eps figures. To appear in The
Astronomical Journal, January 1999. Figures 1 and 3 are color but are
readable in b/
Dynamical streams in the solar neighbourhood
The true nature of the Hyades and Sirius superclusters is still an open
question. In this contribution, we confront Eggen's hypothesis that they are
cluster remnants with the results of a kinematic analysis of more than 6000 K
and M giants in the solar neighbourhood. This analysis includes new radial
velocity data from a large survey performed with the Coravel spectrometer,
complemented by Hipparcos parallaxes and Tycho-2 proper motions (Famaey et al.
2004). A maximum-likelihood method, based on a bayesian approach, has been
applied to the data, in order to make full use of all the available data
(including less precise parallaxes) and to derive the properties of the
different kinematic subgroups. Two such subgroups can be identified with the
Hyades and Sirius superclusters. Stars belonging to them span a very wide range
of age, which is difficult to account for in Eggen's scenario. These groups are
thus most probably "dynamical streams" related to the dynamical perturbation by
spiral waves rather than to cluster remnants.
In this scenario, the Hyades and Ursa Major clusters just happen to be in the
Hyades and Sirius streams, which are purely dynamical features that have
nothing to do with the remnants of more massive primordial clusters. This
mechanism could be the key to understanding the presence of an old metal-rich
population, and of many exoplanetary systems in our neighbourhood. Moreover, a
strong spiral pattern seems to be needed in order to yield such prominent
streams. Since spiral structure is usually baryonic, this would leave very
little room for dark matter. This may be an indication that the era of the
dark-matter paradigm explaining the dynamics of the Galaxy may come to an end,
and is being superseded by modified gravity.Comment: 5 pages, 1 figure, to appear in The Three Dimensional Universe with
GAIA, eds M. Perryman & C. Turo
Kinematics of elliptical galaxies with a diffuse dust component
Observations show that early-type galaxies contain a considerable amount of
interstellar dust, most of which is believed to exist as a diffusely
distributed component. We construct a four-parameter elliptical galaxy model in
order to investigate the effects of such a smooth absorbing component on the
projection of kinematic quantities, such as the line profiles and their
moments. We investigate the dependence on the optical depth and on the dust
geometry. Our calculations show that both the amplitude and the morphology of
these quantities can be significantly affected. Dust effects should therefore
be taken in consideration when interpreting photometric and kinematic
properties, and correlations that utilize these quantities.Comment: 12 pages, 9 figures, accepted for publication in MNRA
Recovering the intrinsic shape of early-type galaxies
We investigate how well the intrinsic shape of early-type galaxies can be
recovered when both photometric and two-dimensional stellar kinematic
observations are available. We simulate these observations with galaxy models
that are representative of observed oblate fast-rotator to triaxial
slow-rotator early-type galaxies. By fitting realistic triaxial dynamical
models to these simulated observations, we recover the intrinsic shape (and
mass-to-light ratio), without making additional (ad-hoc) assumptions on the
orientation.
For (near) axisymmetric galaxies the dynamical modelling can strongly exclude
triaxiality, but the regular kinematics do not further tighten the constraint
on the intrinsic flattening significantly, so that the inclination is nearly
unconstrained above the photometric lower limit even with two-dimensional
stellar kinematics. Triaxial galaxies can have additional complexity in both
the observed photometry and kinematics, such as twists and (central)
kinematically decoupled components, which allows the intrinsic shape to be
accurately recovered. For galaxies that are very round or show no significant
rotation, recovery of the shape is degenerate, unless additional constraints
such as from a thin disk are available.Comment: 12 pages, 7 figures, PDFLaTeX, accepted to MNRAS, minor revision
Anisotropic distribution functions for spherical galaxies
A method is presented for finding anisotropic distribution functions for
stellar systems with known, spherically symmetric, densities, which depends
only on the two classical integrals of the energy and the magnitude of the
angular momentum. It requires the density to be expressed as a sum of products
of functions of the potential and of the radial coordinate. The solution
corresponding to this type of density is in turn a sum of products of functions
of the energy and of the magnitude of the angular momentum. The products of the
density and its radial and transverse velocity dispersions can be also
expressed as a sum of products of functions of the potential and of the radial
coordinate. Several examples are given, including some of new anisotropic
distribution functions. This device can be extended further to the related
problem of finding two-integral distribution functions for axisymmetric
galaxies.Comment: 5 figure
Spiral Galaxies with HST/NICMOS. II. Isophotal Fits and Nuclear Cusp Slopes
We present surface brightness profiles for 56 of the 78 spiral galaxies
observed in the HST/{\tt NICMOS/Camera-2} F160W snapshot survey introduced in
Carollo et al. (2001; paper I), as well as surface brightness profiles for 23
objects out of the 41 that were also observed in the F110W filter. We fit these
surface brightness profiles with the Nuker law of Lauer et al. (1995), and use
the smooth analytical descriptions of the data to compute the average nuclear
stellar cusp slopes in the 0.1$''-0.5''$ radial range. Our main
result is the startling similarity between the nuclear stellar cusp slopes
in the near-infared compared to those derived in the visual
passband. This similarity has several implications: (1.) There are typically
little or no optical-NIR {\it global} color gradients, and thus no global
stellar population variations, inside -100 pc from the nucleus in
nearby spirals. (2.) The large observed range of the strength of the nuclear
stellar cusps seen in the HST optical study of spiral galaxies reflects a
physical difference between galaxies, and is not an artifact caused by nuclear
dust and/or recent star formation. (3.) The dichotomy between bulges,
with steep nuclear stellar cusps , and exponential bulges,
with shallow nuclear stellar cusps , is also not an artifact
of the effects of dust or recent star formation. (4) A surrounding massive disk
appears to have no effect on the rise of the stellar density distribution
within the innermost hundred pc of theComment: Astronomical Journal, 2002, January Issu
Player migration and opportunity: examining the efficacy of the UEFA home-grown rule in six European football leagues.
The introduction of UEFAs home-grown rule occurred for the start of the 2006–2007 season with the full quota in place
from the 2008–2009 season, which imposed quotas on European clubs. From 2008, clubs are required to have at least 8
players classified as home-grown in the 25-player squad, up from 4 in 2006–2007 and 6 in 2007–2008. This study
examines the efficacy of this rule across the six major European leagues (England, France, Germany, Holland, Italy
and Spain) in relation to playing opportunities (minutes played and appearances) between 1999 and 2015. This was
also examined in relation to age. Since the home-grown rule was introduced for the six nations hosting the major
leagues, the rule had different impacts by nationality. Only Germany saw significant increases in the proportion of
minutes played by their players when comparing the periods before and after the home-grown rules were imposed.
Holland, albeit seeing a slight decrease overall, saw significant increases for playing time for under 21s and 22- to 25-year olds. England and Italy were the two nations where statistically significant decreases in indigenous playing opportunities were recorded since the home-grown rules were introduced
On the kinematic deconvolution of the local neighbourhood luminosity function
A method for inverting the statistical star counts equation, including proper
motions, is presented; in order to break the degeneracy in that equation it
uses the supplementary constraints required by dynamical consistency. The
inversion gives access to both the kinematics and the luminosity function of
each population in three r\'egimes: the singular ellipsoid, the constant ratio
Schwarzschild ellipsoid plane parallel models and the epicyclic model. This
more realistic model is taylored to account for local neighbourhood density and
velocity distribution.
The first model is fully investigated both analytically and via means of a
non-parametric inversion technique, while the second model is shown to be
formally its equivalent. The effect of noise and incompleteness in apparent
magnitude is investigated. The third model is investigated via a 5D+2D
non-parametric inversion technique where positivity of the underlying
luminosity function is explicitely accounted for.
It is argued that its future application to data such as the Tycho catalogue
(and in the upcoming satellite GAIA) could lead -- provided the vertical
potential, and/or the asymmetric drift or w_0 are known -- to a non-parametric
determination of the local neighbourhood luminosity function without any
reference to stellar evolution tracks. It should also yield the proportion of
stars for each kinematic component and a kinematic diagnostic to split the thin
disk from the thick disk or the halo.Comment: 18 pages, LateX (or Latex, etc), mnras, accepted for publicatio
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