7,832 research outputs found
Star Clusters in M31: V. Internal Dynamical Trends: Some Troublesome, Some Reassuring
We present internal velocity dispersions and precise radial velocities for
200 globular clusters (GCs) in M31 that are derived using new high-resolution
spectra from MMT/Hectochelle. Of these, 163 also have King model structural
parameters that allow us to estimate their mass-to-light ratios. This is, by
far, the largest such dataset available for any galaxy, including the Milky
Way. These data strongly confirm earlier suggestions that the optical and
near-infrared mass-to-light ratios of M31 GCs decline with increasing
metallicity. This behavior is the opposite of that predicted by stellar
population models for a standard initial mass function. We show that this
phenomenon does not appear to be caused by standard dynamical evolution. A
shallower mass function for metal-rich GCs (with dN/dM ~ M^-0.8 to M^-1.3 below
one solar mass) can explain the bulk of extant observations. We also observe a
consistent, monotonic correlation between mass-to-light ratio and cluster mass.
This correlation, in contrast to the correlation with metallicity, is
well-explained by the accepted model of dynamical evolution of GCs through mass
segregation and the preferential loss of low-mass stars, and these data are
among the best available to constrain this process.Comment: AJ in press. 11 pages, 7 figures (not including tables) in emulate
forma
Quintessential inflation from a variable cosmological constant in a 5D vacuum
We explore an effective 4D cosmological model for the universe where the
variable cosmological constant governs its evolution and the pressure remains
negative along all the expansion. This model is introduced from a 5D vacuum
state where the (space-like) extra coordinate is considered as noncompact. The
expansion is produced by the inflaton field, which is considered as
nonminimally coupled to gravity. We conclude from experiental data that the
coupling of the inflaton with gravity should be weak, but variable in different
epochs of the evolution of the universe.Comment: final version (figure included
Barriers to Brand Building in UK Universities
Branding in universities has become an increasingly topical issue with practitioners, with some institutions committing substantial financial resources to branding activities. It has, however, received only limited academic investigation, and as the particular characteristics of the sector present challenges for those seeking to build brands, it seems to be timely and appropriate to investigate potential barriers to branding.
This exploratory study investigates the opinions of the âbrand guardiansâ of UK universities â Vice Chancellors, Principals and Rectors â on the barriers to successfully building brands and draws conclusions on their views of the key challenges facing successful branding activity in the sector. Implications for practitioners are also explored
Can the quintessence be a complex scalar field?
In light of the recent observations of type Ia supernovae suggesting an
accelerating expansion of the Universe, we wish in this paper to point out the
possibility of using a complex scalar field as the quintessence to account for
the acceleration. In particular, we extend the idea of Huterer and Turner in
deriving the reconstruction equations for the complex quintessence, showing the
feasibility of making use of a complex scalar field (instead of a real scalar
field) while maintaining the uniqueness feature of the reconstruction for two
possible situations, respectively. We discuss very briefly how future
observations may help to distinguish the different quintessence scenarios,
including the scenario with a positive cosmological constant.Comment: 9 pages, LaTeX, final versio
Gravitational waves in a stringlike fluid cosmology
The coupling of a stringlike fluid with ordinary matter and gravity may lead
to a closed Universe with the dynamic of an open one. This can provide an
alternative solution for the age and horizon problems. A study of density
perturbations of the stringlike fluid indicates the existence of instabilities
in the small wavelength limit when it is employed a hydrodynamic approach.
Here, we extend this study to gravitational waves, where the hydrodynamical
approach plays a less important role, and we argue that traces of the existence
of this fluid must be present in the anisotropies of the cosmic background
radiation.Comment: Latex, 8 page
Carboxylic-acid-passivated metal oxide nanocrystals : ligand exchange characteristics of a new binding motif
Ligand exchange is central in the processing of inorganic nanocrystals (NCs) and requires understanding of surface chemistry. Studying sterically stabilized HfO2 and ZrO2 NCs using H-1 solution NMR and IR spectroscopy as well as elemental analysis, this paper demonstrates the reversible exchange of initial oleic acid ligands for octylamine and self-adsorption of oleic acid at NC surfaces. Both processes are incompatible with an X-type binding motif of carboxylic acids as reported for sulfide and selenide NCs. We argue that this behavior stems from the dissociative adsorption of carboxylic acids at the oxide surface. Both proton and carboxylate moieties must be regarded as X-type ligands yielding a combined X-2 binding motif that allows for self-adsorption and exchange for L-type ligands
Kinematic Properties and Stellar Populations of Faint Early-Type Galaxies. I. Velocity Dispersion Measurements of Central Coma Galaxies
We present velocity dispersion measurements for 69 faint early-type galaxies
in the core of the Coma cluster, spanning -22.0<M_R<-17.5 mag. We examine the
L-\sigma relation for our sample and compare it to that of bright ellipticals
from the literature. The distribution of the the faint early-type galaxies in
the L-sigma plane follows the relation L ~ \sigma^{2.01\pm0.36}, which is
significantly shallower from L ~ \sigma^4 as defined for the bright
ellipticals. While increased rotational support for fainter early-type galaxies
could account for some of the difference in slope, we show that it cannot
explain it. We also investigate the Colour-\sigma relation for our Coma
galaxies. Using the scatter in this relation, we constrain the range of galaxy
ages as a function of their formation epoch for different formation scenarios.
Assuming a strong coordination in the formation epoch of faint early-type
systems in Coma, we find that most had to be formed at least 6 Gyrs ago and
over a short 1 Gyr period.Comment: 15 pages including 3 tables and 7 figures, accepted for publication
in MNRA
Generalized phantom energy
We examine cosmological models with generalized phantom energy (GPE).
Generalized phantom energy satisfies the supernegative equation of state, but
its evolution with the scale factor is generally independent, i.e. not
determined by its equation of state. The requirement of general covariance
makes the gravitational constant time-dependent. It is found that a large class
of distinct GPE models with different evolution of generalized phantom energy
density and gravitational constant, but the same equation of state of GPE have
the same evolution of the scale factor of the universe in the distant future.
The time dependence of the equation of state parameter determines whether the
universe will end in a de Sitter-like phase or diverge in finite time with the
accompanying "Big Rip" effect on the bound structures.Comment: v1: 9 pages. v2: version to appear in Phys. Lett.
The origin of the hot metal-poor gas in NGC1291: Testing the hypothesis of gas dynamics as the cause of the gas heating
In this paper we test the idea that the low-metallicity hot gas in the centre
of NGC 1291 is heated via a dynamical process. In this scenario, the gas from
the outer gas-rich ring loses energy through bar-driven shocks and falls to the
centre. Heating of the gas to X-ray temperatures comes from the high velocity
that it reaches ( 700 \kms) as it falls to the bottom of the potential
well. This would explain why the stellar metallicity in the bulge region is
around solar while the hot gas metallicity is around 0.1 solar. We carried out
an observational test to check this hypothesis by measuring the metallicity of
HII regions in the outer ring to check whether they matched the hot gas
metallicity. For this purpose we obtained medium resolution long slit
spectroscopy with FORS1 on the ESO VLT at Paranal and obtained the
metallicities using emission line ratio diagnostics. The obtained metallicities
are compatible with the bulge stellar metallicities but very different from the
hot-gas metallicity. However, when comparing the different time-scales, the gas
in the ring had time enough to get enriched through stellar processes,
therefore we cannot rule out the dynamical mechanism as the heating process of
the gas. However, the blue colours of the outer ring and the dust structures in
the bar region could suggest that the origin of the X-ray hot gas is due to the
infall of material from further out.Comment: 6 pages, 6 figures. A&A accepte
The accelerated expansion of the Universe as a quantum cosmological effect
We study the quantized Friedmann-Lema\^{\i}tre-Robertson-Walker (FLRW) model
minimally coupled to a free massless scalar field. In a previous paper,
\cite{fab2}, solutions of this model were constructed as gaussian
superpositions of negative and positive modes solutions of the Wheeler-DeWitt
equation, and quantum bohmian trajectories were obtained in the framework of
the Bohm-de Broglie (BdB) interpretation of quantum cosmology. In the present
work, we analyze the quantum bohmian trajectories of a different class of
gaussian packets. We are able to show that this new class generates bohmian
trajectories which begin classical (with decelerated expansion), undergo an
accelerated expansion in the middle of its evolution due to the presence of
quantum cosmological effects in this period, and return to its classical
decelerated expansion in the far future. We also show that the relation between
luminosity distance and redshift in the quantum cosmological model can be made
close to the corresponding relation coming from the classical model suplemented
by a cosmological constant, for . These results suggest the posibility of
interpreting the present observations of high redshift supernovae as the
manifestation of a quantum cosmological effect
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