Accessibility of Diverse Literature for Children in Libraries: A Literature Review

This literature review addresses the issues surrounding accessibility of culturally diverse children’s literature in libraries, including the importance of making diverse literature accessible, the availability of such titles on the market, library collection development of diverse books, and selection criteria among children. These issues, in sum, determine how many books are available to children, how they are made available, and if children will even choose to read them. The review shows that the data is unclear on many points regarding the benefits of diverse literature, though intuitive claims of the positive influence of such titles are not discounted. It also finds low representation of diversity in publishing and library collections. Finally, studies of how children select reading materials are presented, showing that there is not a straightforward correlation between having books available and children choosing them. Areas of further research are recommended to give librarians more insight into how to better optimize collection resources to best benefit all young readers

An interpretation and solution of ill-conditioned linear equations

Data insufficiency, poorly conditioned matrices and singularities in equations occur regularly in complex optimization, correlation, and interdisciplinary model studies. This work concerns itself with two methods of obtaining certain physically realistic solutions to ill-conditioned or singular algebraic systems of linear equations arising from such studies. Two efficient computational solution procedures that generally lead to locally unique solutions are presented when there is insufficient data to completely define the model, or a least-squares error formulation of this system results in an ill-conditioned system of equations. If it is assumed that a reasonable estimate of the uncertain data is available in both cases cited above, then we shall show how to obtain realistic solutions efficiently, in spite of the insufficiency of independent data. The proposed methods of solution are more efficient than singular-value decomposition for dealing with such systems, since they do not require solutions for all the non-zero eigenvalues of the coefficient matrix

An X-ray/optical study of the geometry and dynamics of MACS J0140.0-0555, a massive post-collision cluster merger

We investigate the physical properties, geometry and dynamics of the massive cluster merger MACS J0140.0-0555 (z=0.451) using X-ray and optical diagnostics. Featuring two galaxy overdensities separated by about 250 kpc in projection on the sky, and a single peak in the X-ray surface brightness distribution located between them, MACS J0140.0-0555 shows the tell-tale X-ray/optical morphology of a binary, post-collision merger. Our spectral analysis of the X-ray emission, as measured by our Chandra ACIS-I observation of the system, finds the intra-cluster medium to be close to isothermal (~8.5 keV) with no clear signs of cool cores or shock fronts. Spectroscopic follow-up of galaxies in the field of MACS J0140.0-0555 yields a velocity dispersion of 875 (+70/-100) km/s (n_z=66) and no significant evidence of bimodality or substructure along the line of sight. In addition, the difference in radial velocity between the brightest cluster galaxies of the two sub-clusters of 144+/-25 km/s is small compared to typical collision velocities of several 1000 km/s. A strongly lensed background galaxy at z=0.873 (which features variable X-ray emission from an active nucleus) provides the main constraint on the mass distribution of the system. We measure M(<75 kpc) = (5.6+/- 0.5)*10^13 M_sun for the north-western cluster component and a much less certain estimate of (1.5-3)*10^13 M_sun for the south-eastern subcluster. These values are in good agreement with our X-ray mass estimates which yield a total mass of MACS J0140.0-0555 of M(<r_500) ~ (6.8-9.1)*10^14 M_sun. ......Comment: 11 pages, 8 figures, and 2 tables. Accepted for publication in MNRA

Multiple Radial Cool Molecular Filaments in NGC 1275

We have extended our previous observation (Lim et al. 2008) of NGC1275 covering a central radius of ~10kpc to the entire main body of cool molecular gas spanning ~14kpc east and west of center. We find no new features beyond the region previously mapped, and show that all six spatially-resolved features on both the eastern and western sides (three on each side) comprise radially aligned filaments. Such radial filaments can be most naturally explained by a model in which gas deposited "upstream" in localized regions experiencing an X-ray cooling flow subsequently free falls along the gravitational potential of PerA, as we previously showed can explain the observed kinematics of the two longest filaments. All the detected filaments coincide with locally bright Halpha features, and have a ratio in CO(2-1) to Halpha luminosity of ~1e-3; we show that these filaments have lower star formation efficiencies than the nearly constant value found for molecular gas in nearby normal spiral galaxies. On the other hand, some at least equally luminous Halpha features, including a previously identified giant HII region, show no detectable cool molecular gas with a corresponding ratio at least a factor of ~5 lower; in the giant HII region, essentially all the pre-existing molecular gas may have been converted to stars. We demonstrate that all the cool molecular filaments are gravitationally bound, and without any means of support beyond thermal pressure should collapse on timescales ~< 1e6yrs. By comparison, as we showed previously the two longest filaments have much longer dynamical ages of ~1e7yrs. Tidal shear may help delay their collapse, but more likely turbulent velocities of at least a few tens km/s or magnetic fields with strengths of at least several ~10uG are required to support these filaments.Comment: 52 pages, 11 figures. Accepted to Ap

Neural Discrete Representation Learning

Learning useful representations without supervision remains a key challenge in machine learning. In this paper, we propose a simple yet powerful generative model that learns such discrete representations. Our model, the Vector Quantised-Variational AutoEncoder (VQ-VAE), differs from VAEs in two key ways: the encoder network outputs discrete, rather than continuous, codes; and the prior is learnt rather than static. In order to learn a discrete latent representation, we incorporate ideas from vector quantisation (VQ). Using the VQ method allows the model to circumvent issues of "posterior collapse" -- where the latents are ignored when they are paired with a powerful autoregressive decoder -- typically observed in the VAE framework. Pairing these representations with an autoregressive prior, the model can generate high quality images, videos, and speech as well as doing high quality speaker conversion and unsupervised learning of phonemes, providing further evidence of the utility of the learnt representations

Neutrino Masses via the Zee Mechanism in 5D split fermions model

We study the Zee model in the framework of the split fermion model in $M_4\times S_1/Z_2$ spacetime. Neutrino masses are generated through 1-loop diagrams without the right-handed neutrinos introduced. By assuming an order one anarchical complex 5D Yukawa couplings, all the effective 4D Yukawa couplings are determined by the wave function overlap between the split fermions and the bulk scalars in the fifth dimension. The predictability of the Yukawa couplings is in sharp contrast to the original Zee model in 4D where the Yukawa couplings are unknown free parameters. This setup exhibits a geometrical alternative to the lepton flavor symmetry. By giving four explicit sets of the split fermion locations, we demonstrate that it is possible to simultaneously fit the lepton masses and neutrino oscillation data by just a handful free parameters without much fine tuning. Moreover, we are able to make definite predictions for the mixing angle $\theta_{13}$, the absolute neutrino masses, and the lepton flavor violation processes for each configuration.Comment: 16 pages, 2 figure

Rare case of magnetic Ag3+^{3+} ion: double perovskite Cs2_{2}KAgF6_{6}

Normally $4d$ or $5d$ transition metals are in a low-spin state. Here using first-principles calculations, we report on a rare case of a high-spin $S$=1 magnetic state for the Ag$^{3+}$ ion in the double perovskite Cs$_{2}$KAgF$_{6}$. We also explored a possibility of a conventional low-spin $S$=0 ground state and find an associated tetragonal distortion to be 0.29 {\AA}. However, the lattice elastic energy cost and the Hund exchange loss exceed the e$_{g}$ crystal-field energy gain, thus making the low-spin tetragonal structure less favorable than the high-spin cubic structure. We conclude that the compact perovskite structure of Cs$_{2}$KAgF$_{6}$ is an important factor in stabilizing the unusual high-spin ground state of Ag$^{3+}$.Comment: 6 pages, 6 figures, accepted for publication in PR

Orderly Spanning Trees with Applications

We introduce and study the {\em orderly spanning trees} of plane graphs. This algorithmic tool generalizes {\em canonical orderings}, which exist only for triconnected plane graphs. Although not every plane graph admits an orderly spanning tree, we provide an algorithm to compute an {\em orderly pair} for any connected planar graph $G$, consisting of a plane graph $H$ of $G$, and an orderly spanning tree of $H$. We also present several applications of orderly spanning trees: (1) a new constructive proof for Schnyder's Realizer Theorem, (2) the first area-optimal 2-visibility drawing of $G$, and (3) the best known encodings of $G$ with O(1)-time query support. All algorithms in this paper run in linear time.Comment: 25 pages, 7 figures, A preliminary version appeared in Proceedings of the 12th Annual ACM-SIAM Symposium on Discrete Algorithms (SODA 2001), Washington D.C., USA, January 7-9, 2001, pp. 506-51

Radiation-induced magnetoresistance oscillations in two-dimensional electron systems under bichromatic irradiation

We analyze the magnetoresistance $R_{xx}$ oscillations in high-mobility two-dimensional electron systems induced by the combined driving of two radiation fields of frequency $\omega_1$ and $\omega_2$, based on the balance-equation approach to magnetotransport for high-carrier-density systems in Faraday geometry. It is shown that under bichromatic irradiation of $\omega_2\sim 1.5 \omega_1$, most of the characterstic peak-valley pairs in the curve of $R_{xx}$ versus magnetic field in the case of monochromatic irradiation of either $\omega_1$ or $\omega_2$ disappear, except the one around $\omega_1/\omega_c\sim 2$ or $\omega_2/\omega_c\sim 3$. $R_{xx}$ oscillations show up mainly as new peak-valley structures around other positions related to multiple photon processes of mixing frequencies $\omega_1+\omega_2$, $\omega_2-\omega_1$, etc. Many minima of these resistance peak-valley pairs can descend down to negative with enhancing radiation strength, indicating the possible bichromaticzero-resistance states.Comment: 5 pages, 3 figures. Accepted for publication in Phys. Rev.

A Machine Learning Artificial Neural Network Calibration of the Strong-Line Oxygen Abundance

The HII region oxygen abundance is a key observable for studying chemical properties of galaxies. Deriving oxygen abundances using optical spectra often relies on empirical strong-line calibrations calibrated to the direct method. Existing calibrations usually adopt linear or polynomial functions to describe the non-linear relationships between strong line ratios and Te oxygen abundances. Here, I explore the possibility of using an artificial neural network model to construct a non-linear strong-line calibration. Using about 950 literature HII region spectra with auroral line detections, I build multi-layer perceptron models under the machine learning framework of training and testing. I show that complex models, like the neural network, are preferred at the current sample size and can better predict oxygen abundance than simple linear models. I demonstrate that the new calibration can reproduce metallicity gradients in nearby galaxies and the mass-metallicity relationship. Finally, I discuss the prospects of developing new neural network calibrations using forthcoming large samples of HII region and also the challenges faced.Comment: 12 pages, 15 figures. Accepted to MNRA