33,092 research outputs found
Size growth of red-sequence early-type galaxies in clusters in the last 10 Gyr
We carried out a photometric and structural analysis in the rest-frame
band of a mass-selected () sample of red-sequence
galaxies in 14 galaxy clusters, 6 of which are at . To this end, we
reduced/analyzed about 300 orbits of multicolor images taken with the Advanced
Camera for Survey and the Wide Field Camera 3 on the Hubble Space Telescope. We
uniformly morphologically classified galaxies from to , and
we homogeneously derived sizes (effective radii) for the entire sample.
Furthermore, our size derivation allows, and therefore is not biased by, the
presence of the usual variety of morphological structures seen in early-type
galaxies, such as bulges, bars, disks, isophote twists, and ellipiticy
gradients. By using such a mass-selected sample, composed of 244 red-sequence
early-type galaxies, we find that the of the galaxy size at a fixed
stellar mass, has increased with time at a rate of
dex per Gyr over the last 10 Gyr, in marked contrast with the
threefold increase found in the literature for galaxies in the general field
over the same period. This suggests, at face value, that secular processes
should be excluded as the primary drivers of size evolution because we observed
an environmental environmental dependent size growth. Using spectroscopic ages
of Coma early-type galaxies we also find that recently quenched early-type
galaxies are a numerically minor population not different enough in size to
alter the mean size at a given mass, which implies that the progenitor bias is
minor, i.e., that the size evolution measured by selecting galaxies at the
redshift of observation is indistinguishable from the one that compares
ancestors and descendents.Comment: A&A 593, A2 (2016) after revision of the z=1.63 cluster name,
mis-typed in previous version. No result of our paper is affected by having
mis-typed the cluster nam
Smart Loads for Voltage Control in Distribution Networks
This paper shows that the smart loads (SLs) could be effective in mitigating voltage problems caused by photovoltaic (PV) generation and electric vehicle (EV) charging in low-voltage (LV) distribution networks. Limitations of the previously reported SL configuration with only series reactive compensator (SLQ) (one converter) is highlighted in this paper. To overcome these limitations, an additional shunt converter is used in back-to-back (B2B) configuration to support the active power exchanged by the series converter, which increases the flexibility of the SL without requiring any energy storage. Simulation results on a typical U.K. LV distribution network are presented to compare the effectiveness of an SL with B2B converters (SLBCs) against an SLQ in tackling under- and over-voltage problems caused by EV or PV. It is shown that SLBCs can regulate the main voltage more effectively than SLQs especially under overvoltage condition. Although two converters are required for each SLBC, it is shown that the apparent power capacity of each converter is required to be significantly less than that of an equivalent SLQ
Of McKay Correspondence, Non-linear Sigma-model and Conformal Field Theory
The ubiquitous ADE classification has induced many proposals of often
mysterious correspondences both in mathematics and physics. The mathematics
side includes quiver theory and the McKay Correspondence which relates finite
group representation theory to Lie algebras as well as crepant resolutions of
Gorenstein singularities. On the physics side, we have the graph-theoretic
classification of the modular invariants of WZW models, as well as the relation
between the string theory nonlinear -models and Landau-Ginzburg
orbifolds. We here propose a unification scheme which naturally incorporates
all these correspondences of the ADE type in two complex dimensions. An
intricate web of inter-relations is constructed, providing a possible guideline
to establish new directions of research or alternate pathways to the standing
problems in higher dimensions.Comment: 35 pages, 4 figures; minor corrections, comments on toric geometry
and references adde
Morphing Switched-Capacitor Converters with Variable Conversion Ratio
High-voltage-gain and wide-input-range dc-dc converters are widely used in various electronics and industrial products such as portable devices, telecommunication, automotive, and aerospace systems. The two-stage converter is a widely adopted architecture for such applications, and it is proven to have a higher efficiency as compared with that of the single-stage converter. This paper presents a modular-cell-based morphing switched-capacitor (SC) converter for application as a front-end converter of the two-stage converter. The conversion ratio of this converter is flexible and variable and can be freely extended by increasing more SC modules. The varying conversion ratio is achieved through the morphing of the converter's structure corresponding to the amplitude of the input voltage. This converter is light and compact, and is highly efficient over a very wide range of input voltage and load conditions. Experimental work on a 25-W, 6-30-V input, 3.5-8.5-V output prototype, is performed. For a single SC module, the efficiency over the entire input voltage range is higher than 98%. Applied into the two-stage converter, the overall efficiency achievable over the entire operating range is 80% including the driver's loss
Importance Sampling for Multiscale Diffusions
We construct importance sampling schemes for stochastic differential
equations with small noise and fast oscillating coefficients. Standard Monte
Carlo methods perform poorly for these problems in the small noise limit. With
multiscale processes there are additional complications, and indeed the
straightforward adaptation of methods for standard small noise diffusions will
not produce efficient schemes. Using the subsolution approach we construct
schemes and identify conditions under which the schemes will be asymptotically
optimal. Examples and simulation results are provided
Lessons from Post-colonial Malaysian Economic Development
Malaysian economic development has been shaped by public policy in response to changing national and external conditions. Public investments peaked in the 1970s and early 1980s, until the policy reversals driven by sovereign debt concerns and new policy ideology fads. Foreign investments continued to be favoured after independence for ethnic political reasons. Thus, foreign investments continued to be very significant in financial services as well as manufacturing growth, both for import substitution from the 1960s and for export from the 1970s. Private investments were attracted by government provision of infrastructure, cheap but schooled labour, tax incentives, lax environmental regulations and an undervalued currency. Poverty reduction and ownership redistribution by ethnicity were most successful during the 1970s and early 1980s, although it is unclear how much these improved inter-ethnic relations. Economic liberalization and the growing influence of business interests and political elites have undermined the government’s developmental role, culminating in the 1997–8 financial crisis and lacklustre growth since. Malaysian industrialization could only have been achieved with appropriate incentives for investments and technical progress through key policy interventions.Malaysia, development strategies, liberalization, intervention
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