17,062 research outputs found
Janis-Newman-Winicour and Wyman solutions are the same
We show that the well-known most general static and spherically symmetric
exact solution to the Einstein-massless scalar equations given by Wyman is the
same as one found by Janis, Newman and Winicour several years ago. We obtain
the energy associated with this spacetime and find that the total energy for
the case of the purely scalar field is zero.Comment: 9 pages, LaTex, no figures, misprints corrected, to appear in Int. J.
Mod. Phys.
Feasibility study for a secondary Na/S battery
The feasibility of a moderate temperature Na battery was studied. This battery is to operate at a temperature in the range of 100-150 C. Two kinds of cathode were investigated: (1) a soluble S cathode consisting of a solution of Na2Sn in an organic solvent and (2) an insoluble S cathode consisting of a transition metal dichalcogenide in contact with a Na(+)ion conducting electrolyte. Four amide solvents, dimethyl acetamide, diethyl acetamide, N-methyl acetamide and acetamide, were investigated as possible solvents for the soluble S cathode. Results of stability and electrochemical studies using these solvents are presented. The dialkyl substituted amides were found to be superior. Although the alcohol 1,3-cyclohexanediol was found to be stable in the presence of Na2Sn at 130 C, its Na2Sn solutions did not appear to have suitable electrochemical properties
Temperature- and Bias-dependence of magnetoresistance in doped manganite thin film trilayer junctions
Thin film trilayer junction of LaSrMnO - SrTiO -
LaSrMnO shows a factor of 9.7 change in resistance, in a
magnetic field around 100 Oe at 14K. The junction magnetoresistance is bias and
temperature dependent. The energy scales associated with bias and temperature
dependence are an order of magnitude apart. The same set of energies also
determine the bias and temperature dependence of the differential conductance
of the junction. We discuss these results in terms of metallic cluster
inclusions at the junction-barrier interface.Comment: 3 pages, 4 figure
Using Bars As Signposts of Galaxy Evolution at High and Low Redshifts
An analysis of the NICMOS Deep Field shows that there is no evidence of a
decline in the bar fraction beyond z~0.7, as previously claimed; both
bandshifting and spatial resolution must be taken into account when evaluating
the evolution of the bar fraction. Two main caveats of this study were a lack
of a proper comparison sample at low redshifts and a larger number of galaxies
at high redshifts. We address these caveats using two new studies. For a proper
local sample, we have analyzed 134 spirals in the near-infrared using 2MASS
(main results presented by Menendez-Delmestre in this volume) which serves as
an ideal anchor for the low-redshift Universe. In addition to measuring the
mean bar properties, we find that bar size is correlated with galaxy size and
brightness, but the bar ellipticity is not correlated with these galaxy
properties. The bar length is not correlated with the bar ellipticity. For
larger high redshift samples we analyze the bar fraction from the 2-square
degree COSMOS ACS survey. We find that the bar fraction at z~0.7 is ~50%,
consistent with our earlier finding of no decline in bar fraction at high
redshifts.Comment: In the proceedings of "Penetrating Bars through Masks of Cosmic Dust:
The Hubble Tuning Fork strikes a New Note
The Pierre Auger Observatory: Results on Ultra-High Energy Cosmic Rays
The focus of this article is on recent results on ultra-high energy cosmic
rays obtained with the Pierre Auger Observatory. The world's largest instrument
of this type and its performance are described. The observations presented here
include the energy spectrum, the primary particle composition, limits on the
fluxes of photons and neutrinos and a discussion of the anisotropic
distribution of the arrival directions of the most energetic particles.
Finally, plans for the construction of a Northern Auger Observatory in
Colorado, USA, are discussed.Comment: Proceedings of the International Workshop on Advances in Cosmic Ray
Science, Waseda University, Shinjuku, Tokyo, Japan, March 2008; to be
published in the Journal of the Physical Society of Japan (JPSJ) supplemen
Extent of regretted sexual intercourse among young teenagers in Scotland: a cross sectional survey
No abstract available
The Star Formation History of the Hubble Sequence: Spatially Resolved Colour Distributions of Intermediate Redshift Galaxies in the Hubble Deep Field
We analyse the spatially resolved colours of distant galaxies of known
redshift in the Hubble Deep Field, using a new technique based on matching
resolved four-band internal colour data to the predictions of evolutionary
synthesis models. We quantify the relative age, dispersion in age, ongoing
star-formation rate, star-formation history, and dust content of these
galaxies. To demonstrate the potential of the method, we study the
near-complete sample of 32 I ~ 0.5 studied by
Bouwens et al (1997). The dispersion of the internal colours of a sample of
0.4<z<1 early-type field galaxies in the HDF indicates that ~40% [4/11] show
evidence of star formation which must have occurred within the past third of
their ages at the epoch of observation. For a sample of well-defined spirals,
we similarly exploit the dispersion in colour to analyse the relative histories
of bulge and disc stars, in order to resolve the current controversy regarding
the ages of galactic bulges. Dust and metallicity gradients are ruled out as
major contributors to the colour dispersions we observe in these systems. The
median ages of bulge stars are found to be signicantly older than those in
galactic discs, and exhibit markedly different star-formation histories. This
result is inconsistent with a secular growth of bulges from disc instabilities,
but consistent with gradual disc formation by accretion of gas onto bulges, as
predicted by hierarchical theories. We extend our technique in order to discuss
the star formation history of the entire Bouwens et al sample in the context of
earlier studies concerned with global star formation histories.Comment: 8 colour postscript figures plus LaTeX source; submitted to MNRAS.
Uses the mnras.sty LaTeX style fil
Comparative Analysis of MLP, CNN, and RNN Models in Automatic Speech Recognition: Dissecting Performance Metric
This study conducts a comparative analysis of three prominent machine learning models: Multi-Layer Perceptrons (MLP), Convolutional Neural Networks (CNN), and Recurrent Neural Networks (RNN) with Long Short-Term Memory (LSTM) in the field of automatic speech recognition (ASR). This research is distinct in its use of the LibriSpeech 'test-clean' dataset, selected for its diversity in speaker accents and varied recording conditions, establishing it as a robust benchmark for ASR performance evaluation. Our approach involved preprocessing the audio data to ensure consistency and extracting Mel-Frequency Cepstral Coefficients (MFCCs) as the primary features, crucial for capturing the nuances of human speech. The models were meticulously configured with specific architectural details and hyperparameters. The MLP and CNN models were designed to maximize their pattern recognition capabilities, while the RNN (LSTM) was optimized for processing temporal data. To assess their performance, we employed metrics such as precision, recall, and F1-score. The MLP and CNN models demonstrated exceptional accuracy, with scores of 0.98 across these metrics, indicating their effectiveness in feature extraction and pattern recognition. In contrast, the LSTM variant of RNN showed lower efficacy, with scores below 0.60, highlighting the challenges in handling sequential speech data. The results of this study shed light on the differing capabilities of these models in ASR. While the high accuracy of MLP and CNN suggests potential overfitting, the underperformance of LSTM underscores the necessity for further refinement in sequential data processing. This research contributes to the understanding of various machine learning approaches in ASR and paves the way for future investigations. We propose exploring hybrid model architectures and enhancing feature extraction methods to develop more sophisticated, real-world ASR systems. Additionally, our findings underscore the importance of considering model-specific strengths and limitations in ASR applications, guiding the direction of future research in this rapidly evolving field
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