1,787 research outputs found
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An exploratory study of single parents raising a child with developmental disabilities
The purpose of this study was to explore the unique experiences and specific needs of single parent families while assessing their level of stress raising a developmentally disabled child
SPIDER - IV. Optical and NIR color gradients in Early-type galaxies: New Insights into Correlations with Galaxy Properties
We present an analysis of stellar population gradients in 4,546 Early-Type
Galaxies with photometry in along with optical spectroscopy. A new
approach is described which utilizes color information to constrain age and
metallicity gradients. Defining an effective color gradient, ,
which incorporates all of the available color indices, we investigate how
varies with galaxy mass proxies, i.e. velocity dispersion,
stellar (M_star) and dynamical (M_dyn) masses, as well as age, metallicity, and
alpha/Fe. ETGs with M_dyn larger than 8.5 x 10^10, M_odot have increasing age
gradients and decreasing metallicity gradients wrt mass, metallicity, and
enhancement. We find that velocity dispersion and alpha/Fe are the main drivers
of these correlations. ETGs with 2.5 x 10^10 M_odot =< M_dyn =< 8.5 x 10^10
M_odot, show no correlation of age, metallicity, and color gradients wrt mass,
although color gradients still correlate with stellar population parameters,
and these correlations are independent of each other. In both mass regimes, the
striking anti-correlation between color gradient and alpha-enhancement is
significant at \sim 4sigma, and results from the fact that metallicity gradient
decreases with alpha/Fe. This anti-correlation may reflect the fact that star
formation and metallicity enrichment are regulated by the interplay between the
energy input from supernovae, and the temperature and pressure of the hot X-ray
gas in ETGs. For all mass ranges, positive age gradients are associated with
old galaxies (>5-7 Gyr). For galaxies younger than \sim 5 Gyr, mostly at
low-mass, the age gradient tends to be anti-correlated with the Age parameter,
with more positive gradients at younger ages.Comment: Accepted for Publication in the Astronomical Journa
From Galaxy Clusters to Ultra-Faint Dwarf Spheroidals: A Fundamental Curve Connecting Dispersion-supported Galaxies to Their Dark Matter Halos
We examine scaling relations of dispersion-supported galaxies over more than
eight orders of magnitude in luminosity by transforming standard fundamental
plane parameters into a space of mass (M1/2), radius (r1/2), and luminosity
(L1/2). We find that from ultra-faint dwarf spheroidals to giant cluster
spheroids, dispersion-supported galaxies scatter about a one-dimensional
"fundamental curve" through this MRL space. The weakness of the M1/2-L1/2 slope
on the faint end may imply that potential well depth limits galaxy formation in
small galaxies, while the stronger dependence on L1/2 on the bright end
suggests that baryonic physics limits galaxy formation in massive galaxies. The
mass-radius projection of this curve can be compared to median dark matter halo
mass profiles of LCDM halos in order to construct a virial mass-luminosity
relationship (Mvir-L) for galaxies that spans seven orders of magnitude in
Mvir. Independent of any global abundance or clustering information, we find
that (spheroidal) galaxy formation needs to be most efficient in halos of Mvir
~ 10^12 Msun and to become inefficient above and below this scale. Moreover,
this profile matching technique is most accurate at the high and low luminosity
extremes (where dark matter fractions are highest) and is therefore quite
complementary to statistical approaches that rely on having a well-sampled
luminosity function. We also consider the significance and utility of the
scatter about this relation, and find that in the dSph regime observational
errors are almost at the point where we can explore the intrinsic scatter in
the luminosity-virial mass relation. Finally, we note that purely stellar
systems like Globular Clusters and Ultra Compact Dwarfs do not follow the
fundamental curve relation. This allows them to be easily distinguished from
dark-matter dominated dSph galaxies in MRL space. (abridged)Comment: 27 pages, 18 figures, ApJ accepted. High-res movies of 3D figures are
available at http://www.physics.uci.edu/~bullock/fcurve/movies.htm
Power requirements for electron cyclotron current drive and ion cyclotron resonance heating for sawtooth control in ITER
13MW of electron cyclotron current drive (ECCD) power deposited inside the q
= 1 surface is likely to reduce the sawtooth period in ITER baseline scenario
below the level empirically predicted to trigger neo-classical tearing modes
(NTMs). However, since the ECCD control scheme is solely predicated upon
changing the local magnetic shear, it is prudent to plan to use a complementary
scheme which directly decreases the potential energy of the kink mode in order
to reduce the sawtooth period. In the event that the natural sawtooth period is
longer than expected, due to enhanced alpha particle stabilisation for
instance, this ancillary sawtooth control can be provided from > 10MW of ion
cyclotron resonance heating (ICRH) power with a resonance just inside the q = 1
surface. Both ECCD and ICRH control schemes would benefit greatly from active
feedback of the deposition with respect to the rational surface. If the q = 1
surface can be maintained closer to the magnetic axis, the efficacy of ECCD and
ICRH schemes significantly increases, the negative effect on the fusion gain is
reduced, and off-axis negative-ion neutral beam injection (NNBI) can also be
considered for sawtooth control. Consequently, schemes to reduce the q = 1
radius are highly desirable, such as early heating to delay the current
penetration and, of course, active sawtooth destabilisation to mediate small
frequent sawteeth and retain a small q = 1 radius.Comment: 29 pages, 16 figure
Agglomeration Dynamics of 1D Materials: Gas-Phase Collision Rates of Nanotubes and Nanorods.
The agglomeration and self-assembly of gas-phase 1D materials in anthropogenic and natural systems dictate their resulting nanoscale morphology, multiscale hierarchy, and ultimate macroscale properties. Brownian motion induces collisions, upon which 1D materials often restructure to form bundles and can lead to aerogels. Herein, the first results of collision rates for 1D nanomaterials undergoing thermal transport are presented. The Langevin dynamic simulations of nanotube rotation and translation demonstrate that the collision kernels for rigid nanotubes or nanorods are ≈10 times greater than spherical systems. Resulting reduced order equations allow straightforward calculation of the physical parameters to determine the collision kernel for straight and curved 1D materials from 102 to 106 nm length. The collision kernels of curved 1D structures increase ≈1.3 times for long (>102 nm), and ≈5 times for short (≈102 nm) relative to rigid materials. Applications of collision frequencies allow the first kinetic analysis of aerogel self-assembly from gas-phase carbon nanotubes (CNTs). The timescales for CNT collision and bundle formation (0.3-42 s) agree with empirical residence times in CNT reactors (3-15 s). These results provide insights into the CNT length, number, and timescales required for aerogel formation, which bolsters our understanding of mass-produced 1D aerogel materials.EPSRC: EP/M015211/
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Plasma production of nanomaterials for energy storage: continuous gas-phase synthesis of metal oxide CNT materials via a microwave plasma.
In this work we show for the first time that a continuous plasma process can synthesize materials from bulk industrial powders to produce hierarchical structures for energy storage applications. The plasma production process's unique advantages are that it is fast, inexpensive, and scalable due to its high energy density that enables low-cost precursors. The synthesized hierarchical material is comprised of iron oxide and aluminum oxide aggregate particles and carbon nanotubes grown in situ from the iron particles. New aerosol-based methods were used for the first time on a battery material to characterize aggregate and primary particle morphologies, while showing good agreement with observations from TEM measurements. As an anode for lithium ion batteries, a reversible capacity of 870 mA h g-1 based on metal oxide mass was observed and the material showed good recovery from high rate cycling. The high rate of material synthesis (∼10 s residence time) enables this plasma hierarchical material synthesis platform to be optimized as a means for energetic material production for the global energy storage material supply chain
M/L and Color Evolution for A Deep Sample of M* Cluster Galaxies at z~1: The Formation Epoch and the Tilt of the Fundamental Plane
We have measured velocity dispersions for a sample of 36 galaxies with J <
21.2 or Mr < -20.6 mag in MS1054-03, a massive cluster of galaxies at z = 0.83.
Our data are of uniformly high quality down to our selection limit, our 16-hour
exposures typically yielding errors of only \delta(dispersion)~10% for L* and
fainter galaxies. By combining our measurements with data from the literature,
we have 53 cluster galaxies with measured dispersions, and HST/ACS-derived
sizes, colors and surface brightnesses. This sample is complete for the typical
L* galaxy at z~1, unlike most previous z~1 cluster samples which are complete
only for the massive cluster members (>1e11 M_sun). We find no evidence for a
change in the tilt of the fundamental plane (FP). Nor do we find evidence for
evolution in the slope of the color-dispersion relation and M/L_B-dispersion
relations; measuring evolution at a fixed dispersion should minimize the impact
of size evolution found in other work. The M/L_B at fixed dispersion evolves by
\Delta log10 M/L_B=-0.50 +/- 0.03 between z=0.83 and z=0.02 or d(log10
M/L_B)=-0.60 +/- 0.04 dz, and we find \Delta (U-V)_z=-0.24 +/- 0.02 mag at
fixed dispersion in the rest-frame, matching the expected evolution in M/L_B
within 2.25 standard deviations. The implied formation redshift from both the
color and M/L_B evolution is z*=2.0 +/- 0.2 +/- 0.3 (sys), during the epoch in
which the cosmic star-formation activity peaked, with the systematic
uncertainty showing the dependence of z* on the assumptions we make about the
stellar populations. The lack of evolution in either the tilt of the FP or in
the M/L- and color-dispersion relations imply that the formation epoch depends
weakly on mass, ranging from z*=2.3 +1.3 -0.3 at 300 km/s to z*=1.7 +0.3 -0.2
at 160 km/s and implies that the IMF similarly varies slowly with galaxy mass.Comment: revised; typos corrected, references updated, and other cosmetic
changes to meet ApJ format ApJ accepted, 22 pages in emulate ApJ format, 8
color figures, 1 b/w figur
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A field study of urban microclimates in London
This paper aims to address the characteristics of urban microclimates that affect the building energy
performance and implementation of the renewable energy technologies. An experimental campaign was
designed to investigate the microclimate parameters including air and surface temperature, direct and
diffuse solar irradiation levels on both horizontal and vertical surfaces, wind speed and direction in a
dense urban area in London. The outcomes of this research reveal that the climatic parameters are
significantly influenced by the attributes of urban textures, which highlight the need for both providing
the microclimatic information and using them in buildings design stages. This research provides a
valuable set of microclimatic information for a dense urban area in London. According to the outcomes of
this research, the feasibility study for implementation of renewable energy technologies and the thermal/
energy performance assessment of buildings need to be conducted using the microclimatic information
rather than the meteorological weather data mostly collected from non-urban environments
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