747 research outputs found
Do Vertebral Chemical Signatures Distinguish Juvenile Blacktip Shark (Carcharhinus limbatus) Nursery Regions in the Northern Gulf of Mexico?
Identifying and protecting shark nurseries is a common management strategy used to help rebuild overfished stocks, yet we know little about connectivity between juvenile and adult populations. By analysing trace metals incorporated into vertebral cartilage, it may be possible to infer natal origin based on nursery-specific chemical signatures. To assess the efficacy of this approach, we collected juvenile blacktip sharks (Carcharhinus limbatus; n = 93) from four regions in the Gulf of Mexico in 2012 and 2013 and analysed their vertebral centra with laser ablation-inductively coupled plasma-mass spectrometry. We observed significant regional differences in six element : Ca ratios in both 2012 and 2013. Multi-element chemical signatures were significantly different among regions and between year-classes. Year-class-specific linear discriminant function analysis yielded regional classification accuracies of 81% for 2012 and 85% for 2013, although samples were not obtained from all four regions in 2012. Combining year-classes resulted in an overall classification accuracy of 84%, thus demonstrating the usefulness of this approach. These results are encouraging yet highlight a need for more research to better evaluate the efficacy of vertebral chemistry to study elasmobranch population connectivity
Investigation of pulsed laser induced dewetting in nanoscopic metal films
Hydrodynamic pattern formation (PF) and dewetting resulting from pulsed laser
induced melting of nanoscopic metal films have been used to create spatially
ordered metal nanoparticle arrays with monomodal size distribution on
SiO_{\text{2}}/Si substrates. PF was investigated for film thickness h\leq7 nm
< laser absorption depth \sim11 nm and different sets of laser parameters,
including energy density E and the irradiation time, as measured by the number
of pulses n. PF was only observed to occur for E\geq E_{m}, where E_{m} denotes
the h-dependent threshold energy required to melt the film. Even at such small
length scales, theoretical predictions for E_{m} obtained from a
continuum-level lumped parameter heat transfer model for the film temperature,
coupled with the 1-D transient heat equation for the substrate phase, were
consistent with experimental observations provided that the thickness
dependence of the reflectivity of the metal-substrate bilayer was incorporated
into the analysis. The spacing between the nanoparticles and the particle
diameter were found to increase as h^{2} and h^{5/3} respectively, which is
consistent with the predictions of the thin film hydrodynamic (TFH) dewetting
theory. These results suggest that fast thermal processing can lead to novel
pattern formation, including quenching of a wide range of length scales and
morphologies.Comment: 36 pages, 11 figures, 1 tabl
Quenched Charmed Meson Spectra using Tadpole Improved Quark Action on Anisotropic Lattices
Charmed meson charmonium spectra are studied with improved quark actions on
anisotropic lattices. We measured the pseudo-scalar and vector meson dispersion
relations for 4 lowest lattice momentum modes with quark mass values ranging
from the strange quark to charm quark with 3 different values of gauge coupling
and 4 different values of bare speed of light . With the bare
speed of light parameter tuned in a mass-dependent way, we study the mass
spectra of , , ,
, and mesons.
The results extrapolated to the continuum limit are compared with the
experiment and qualitative agreement is found.Comment: 8 pages, 2 figures, latex fil
An Improved Calculation of the Non-Gaussian Halo Mass Function
The abundance of collapsed objects in the universe, or halo mass function, is
an important theoretical tool in studying the effects of primordially generated
non-Gaussianities on the large scale structure. The non-Gaussian mass function
has been calculated by several authors in different ways, typically by
exploiting the smallness of certain parameters which naturally appear in the
calculation, to set up a perturbative expansion. We improve upon the existing
results for the mass function by combining path integral methods and saddle
point techniques (which have been separately applied in previous approaches).
Additionally, we carefully account for the various scale dependent combinations
of small parameters which appear. Some of these combinations in fact become of
order unity for large mass scales and at high redshifts, and must therefore be
treated non-perturbatively. Our approach allows us to do this, and to also
account for multi-scale density correlations which appear in the calculation.
We thus derive an accurate expression for the mass function which is based on
approximations that are valid over a larger range of mass scales and redshifts
than those of other authors. By tracking the terms ignored in the analysis, we
estimate theoretical errors for our result and also for the results of others.
We also discuss the complications introduced by the choice of smoothing filter
function, which we take to be a top-hat in real space, and which leads to the
dominant errors in our expression. Finally, we present a detailed comparison
between the various expressions for the mass functions, exploring the accuracy
and range of validity of each.Comment: 28 pages, 13 figures; v2: text reorganized and some figured modified
for clarity, results unchanged, references added. Matches version published
in JCA
Structure–function relationships of fullerene esters in polymer solar cells: unexpected structural effects on lifetime and efficiency
We report both transport measurements and spectroscopic data of polymer/fullerene blend photovoltaics using a small library of fullerene esters to correlate device properties with a range of functionality and structural diversity of the ester substituent. We observe that minor structural changes can lead to significant and surprising differences in device efficiency and lifetime. For example we have found that isomeric R-groups in the fullerene ester-based devices we have studied have dramatically different efficiencies. The characteristic lifetimes derived from both transport and spectroscopic measurements are generally comparable; however, some more rapid effects in specific fullerene esters are not observed spectroscopically. It is apparent from our results that each fullerene derivative requires re-optimization to reveal the best device performance. Furthermore we conclude that a library approach is essential for evaluating the effects of structural differences in the constituent molecules and serves as important device optimization method that is not being currently employed in photovoltaic investigations
The Structure of the EU Mediasphere
Background.
A trend towards automation of scientific research has recently resulted in what has been termed “data-driven inquiry” in various disciplines, including physics and biology. The automation of many tasks has been identified as a possible future also for the humanities and the social sciences, particularly in those disciplines concerned with the analysis of text, due to the recent availability of millions of books and news articles in digital format. In the social sciences, the analysis of news media is done largely by hand and in a hypothesis-driven fashion: the scholar needs to formulate a very specific assumption about the patterns that might be in the data, and then set out to verify if they are present or not.
Methodology/Principal Findings.
In this study, we report what we think is the first large scale content-analysis of cross-linguistic text in the social sciences, by using various artificial intelligence techniques. We analyse 1.3 M news articles in 22 languages detecting a clear structure in the choice of stories covered by the various outlets. This is significantly affected by objective national, geographic, economic and cultural relations among outlets and countries, e.g., outlets from countries sharing strong economic ties are more likely to cover the same stories. We also show that the deviation from average content is significantly correlated with membership to the eurozone, as well as with the year of accession to the EU.
Conclusions/Significance.
While independently making a multitude of small editorial decisions, the leading media of the 27 EU countries, over a period of six months, shaped the contents of the EU mediasphere in a way that reflects its deep geographic, economic and cultural relations. Detecting these subtle signals in a statistically rigorous way would be out of the reach of traditional methods. This analysis demonstrates the power of the available methods for significant automation of media content analysis
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