82,552 research outputs found
On the highly reddened members in 6 young galactic star clusters - a multiwavelength study
The spectral and reddening properties of 211 highly reddened proper motion
members with mag in 6 young galactic star clusters are investigated
using low resolution spectroscopic, broad-band and mid-IR data. We
report emission features in CaII HK and HI lines for a sample of 29 stars
including 11 stars reported for the first time and also provide either a new or
more reliable spectral class for a sample of 24 stars. CaII triplet width
measurements are used to indicate the presence of an accretion disk for a dozen
stars and to hint luminosity for a couple of stars. On the basis of spectral
features, near-IR excesses, dereddened color-color diagrams and mid-IR spectral
indices we identify a group of 28 pre-main sequence cluster members including 5
highly probable Herbig Ae/Be and 6 classical T Tauri star. A total of 25
non-emission MS stars, amounting to 10 % early type MS members, appears
to show Vega-like characteristics or are precursors to such a phenomenon. The
various membership indicators suggest that 16% of the PM members are
non-members. A significant fraction (70%) of program stars in NGC 1976, NGC
2244, NGC 6530 and NGC 6611 show anomalous reddening with =
, , and , respectively,
indicating the presence of grain size dust larger than that typical to the
diffuse medium. A small number of stars in NGC 1976, NGC 2244 and NGC 6611 also
show normal behavior while the cluster NGC 6823 appears to have a normal
reddening. Three highly luminous late type giants, one in NGC 2244 and two in
NGC 6530, appears to be member and are in post-hydrogen-core-burning stages
suggesting a prolonged duration ( 25 Myrs) of star formation.Comment: 12 pages, 13 figures, submitted to MNRA
Spoof detection using time-delay shallow neural network and feature switching
Detecting spoofed utterances is a fundamental problem in voice-based
biometrics. Spoofing can be performed either by logical accesses like speech
synthesis, voice conversion or by physical accesses such as replaying the
pre-recorded utterance. Inspired by the state-of-the-art \emph{x}-vector based
speaker verification approach, this paper proposes a time-delay shallow neural
network (TD-SNN) for spoof detection for both logical and physical access. The
novelty of the proposed TD-SNN system vis-a-vis conventional DNN systems is
that it can handle variable length utterances during testing. Performance of
the proposed TD-SNN systems and the baseline Gaussian mixture models (GMMs) is
analyzed on the ASV-spoof-2019 dataset. The performance of the systems is
measured in terms of the minimum normalized tandem detection cost function
(min-t-DCF). When studied with individual features, the TD-SNN system
consistently outperforms the GMM system for physical access. For logical
access, GMM surpasses TD-SNN systems for certain individual features. When
combined with the decision-level feature switching (DLFS) paradigm, the best
TD-SNN system outperforms the best baseline GMM system on evaluation data with
a relative improvement of 48.03\% and 49.47\% for both logical and physical
access, respectively
Evaluating Explanations for Stagnation
In this paper, we evaluate four explanations for economic stagnation that have been proposed in the literature: coordination failures, ineffective mix of occupational choices, insufficient human capital accumulation, and politico-economic considerations. We calibrate models that embody these explanations in the context of the stagnant economies of sub-Saharan Africa. The methodology of calibration is ideally suited for this evaluation, given the paucity of high-quality data, the high degree of model nonlinearity, and the need for conducting counterfactual policy experiments. In addition to studying how closely and robustly these models capture the African situation, we examine the quantitative aspects of their policy implications. We find that calibrations that yield multiple equilibria -- one prosperity and the other stagnation -- are not particularly robust. This tempers optimism about the efficacy of one-shot or temporary development policies suggested by models with multiplicity. However, the calibrated models indicate that small policy interventions are sufficient to trigger development in stagnant economies.Coordination failure, Occupational choice, Human capital accumulation, Political economy, Economic Development, Calibration.
Higher Education Subsidies and Heterogeneity, A Dynamic Analysis
In this paper, we develop a simple dynamic general equilibrium framework that can be used to study issues in higher education policy. The model features heterogeneity in income of parents and academic ability of students. Liquidity constraints create persistence in educational attainment even when ability is independently distributed. A unique steady state with a positive fraction of college educated workers, or one with a development trap, or multiple steady states which feature both of these, can result in equilibrium. We add a government that is equipped with a simple tax scheme and calibrate the model to the US economy to get a benchmark for our policy analysis. The government can design a tax and subsidy scheme that guarantees equality of opportunity, but only at the expense of a decrease in the efficiency of utilization of education resources; the welfare gain is minimal. A policy that aims to maximize the fraction of college-educated labor, by sending as many children as possible to college, results in a big drop in the above-mentioned efficiency with little or no welfare gain. If the government has the political will to use any available signal on ability and provide merit-based aid, it can increase this efficiency with little decrease in welfare. Education subsidies may be a potent tool for countries that are caught in a development trap; a sufficient level of subsidy can cause the economy to emerge from the trap.Dynamic General Equilibrium, Education, College Subsidies
Education Policies to Revive a Stagnant Economy: The Case of Sub- Saharan Africa
In this paper, we argue that the condition of education and the economy of the low performing sub-Saharan African countries can be characterized as a stagnant steady state -- a "trap". We present a simple heterogeneous-agent model in which high costs of education relative to income and the skill premium can cause the economy to be trapped in such a steady state with minimal educational attainment. We calibrate the model to available data from the sub-Saharan African countries to study policies that could potentially free these trapped economies and set them on a path to a higher steady state. We find that a tax and subsidy scheme that redistributes resources at the trap from poor households with lower ability children to those with higher ability children can pry the economy out of the trap, thus freeing it from dependence on foreign aid in order to achieve the same goal. In addition to the direct cost, a portion of the indirect cost also needs to be subsidized. Moreover, such a policy outperforms the abolition of child labor and the institution and enforcement of compulsory education laws when expenditure neutral welfare comparisons are made.Dynamic heterogeneous-agent models, Economic stagnation, Education subsidies, Calibration of a trap
Nonintegrability of (2+1)-dimensional continuum isotropic Heisenberg spin system: Painlev\'e analysis
While many integrable spin systems are known to exist in (1+1) and (2+1)
dimensions, the integrability property of the physically important (2+1)
dimensional isotropic Heisenberg ferromagnetic spin system in the continuum
limit has not been investigated in the literature. In this paper, we show
through a careful singularity structure analysis of the underlying nonlinear
evolution equation that the system admits logarithmic type singular manifolds
and so is of non-Painlev\'e type and is expected to be nonintegrable.Comment: 11 pages. to be published in Phys. Lett. A (2006
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