Water and Sediments Characteristics Influencing Fish Farming Activities: Univariate and Multivariate Approaches

Environmental variables, especially water, sediment characteristics and farming practices play important roles in influencing the degree and severity of the impacts of aquaculture. The water-sediment interface under fish farms can be influenced by organic waste in the form of feces and unconsumed feed derived from farm activities. This study focuses on the hydrographical conditions and water chemistry of the bluefin tuna farming area in the southern Spencer Gulf, especially organic carbon content, sediment grain size and current velocity. A comparative study of organic matter and sediment grain size between sites and the relationship between the siltclay fractions of the sediments and the amount of organic matter are assessed. Sediment samples were taken using a HAPS bottom corer equipped with a corer of 67 mm in diameter and 315 mm in length, operated from the research vessel RV Ngerin. The results suggest that hydrographical conditions and water chemistry of southern Spencer Gulf varied slightly depending on the location of the stations sampled. No accumulation in organic matter under the fallowed cages was detected, indicating that the hydrodynamic conditions at southern Spencer Gulf are considered well flushed and thus suitable for farming activities

Disrupting Daesh: measuring takedown of online terrorist material and its impacts

This report seeks to contribute to public and policy debates on the value of social media disruption activity with respect to terrorist material. We look in particular at aggressive account and content takedown, with the aim of accurately measuring this activity and its impacts. Our findings challenge the notion that Twitter remains a conducive space for Islamic State (IS) accounts and communities to flourish, although IS continues to distribute propaganda through this channel. However, not all jihadists on Twitter are subject to the same high levels of disruption as IS, and we show that there is differential disruption taking place. IS’s and other jihadists’ online activity was never solely restricted to Twitter. Twitter is just one node in a wider jihadist social media ecology. We describe and discuss this, and supply some preliminary analysis of disruption trends in this area

Host response to cuckoo song is predicted by the future risk of brood parasitism

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.Introduction: Risk assessment occurs over different temporal and spatial scales and is selected for when individuals show an adaptive response to a threat. Here, we test if birds respond to the threat of brood parasitism using the acoustical cues of brood parasites in the absence of visual stimuli. We broadcast the playback of song of three brood parasites (Chalcites cuckoo species) and a sympatric non-parasite (striated thornbill, Acanthiza lineata) in the territories of superb fairy-wrens (Malurus cyaneus) during the peak breeding period and opportunistic breeding period. The three cuckoo species differ in brood parasite prevalence and the probability of detection by the host, which we used to rank the risk of parasitism (high risk, moderate risk, low risk). Results: Host birds showed the strongest response to the threat of cuckoo parasitism in accordance with the risk of parasitism. Resident wrens had many alarm calls and close and rapid approach to the playback speaker that was broadcasting song of the high risk brood parasite (Horsfield’s bronze-cuckoo, C. basalis) across the year (peak and opportunistic breeding period), some response to the moderate risk brood parasite (shining bronze-cuckoo, C. lucidus) during the peak breeding period, and the weakest response to the low risk brood parasite (little bronzecuckoo, C. minutillus). Playback of the familiar control stimulus in wren territories evoked the least response. Conclusion: Host response to the threat of cuckoo parasitism was assessed using vocal cues of the cuckoo and was predicted by the risk of future parasitism

The Large Scale Bias of Dark Matter Halos: Numerical Calibration and Model Tests

We measure the clustering of dark matter halos in a large set of collisionless cosmological simulations of the flat LCDM cosmology. Halos are identified using the spherical overdensity algorithm, which finds the mass around isolated peaks in the density field such that the mean density is Delta times the background. We calibrate fitting functions for the large scale bias that are adaptable to any value of Delta we examine. We find a ~6% scatter about our best fit bias relation. Our fitting functions couple to the halo mass functions of Tinker et. al. (2008) such that bias of all dark matter is normalized to unity. We demonstrate that the bias of massive, rare halos is higher than that predicted in the modified ellipsoidal collapse model of Sheth, Mo, & Tormen (2001), and approaches the predictions of the spherical collapse model for the rarest halos. Halo bias results based on friends-of-friends halos identified with linking length 0.2 are systematically lower than for halos with the canonical Delta=200 overdensity by ~10%. In contrast to our previous results on the mass function, we find that the universal bias function evolves very weakly with redshift, if at all. We use our numerical results, both for the mass function and the bias relation, to test the peak-background split model for halo bias. We find that the peak-background split achieves a reasonable agreement with the numerical results, but ~20% residuals remain, both at high and low masses.Comment: 11 pages, submitted to ApJ, revised to include referee's coment

Ventricular‐Vascular Coupling in Marfan and Non‐Marfan Aortopathies

Background: Marfan syndrome (MFS) and familial non–syndromal thoracic aortic aneurysm and dissection (ns‐TAAD) are genetic aortopathies causing aortic dilatation with increased aortic stiffness. Left ventricular (LV) contractility and ventricular‐vascular coupling index (VVI) were compared between MFS and ns‐TAAD and determinants of VVI were investigated. Methods and Results: Patients with MFS (M 57, F 47) and ns‐TAAD (M 72, F 39) were studied by echocardiography and compared with controls (M 77, F 71). Aortic geometry, hemodynamics, LV work, LV contractility (end‐systolic elastance [Ees]), and VVI were documented. Aortic sinuses were equally dilated in MFS (19.7±2.4) and ns‐TAAD (19.8±1.8) compared to controls (16.2±1.4 mm·m−2, P<0.001). Aortic stiffness index was increased in MFS (9.7±5.1) and ns‐TAAD (10.8±4.7) versus controls (5.4±2.0, P<0.01); LV stroke work was unchanged in MFS (436±74) compared to controls (435±60) but increased in ns‐TAAD (492±109 mJ·m−2 P<0.01). The LV Ees was reduced in MFS (1.32±0.19) compared to controls (1.65±0.29 mm Hg·mL−1, P<0.01) but increased in ns‐TAAD (1.83±0.30, P<0.01) and VVI was abnormal in MFS (0.71±0.11) compared to controls (0.62±0.07, P<0.01) and ns‐TAAD (0.62±0.09). Treatment with β‐blockers was associated with partial normalization of VVI in MFS. A VVI ≥0.8 was associated with increased risk of death and heart failure in MFS. Conclusions: Left ventricular contractility and ventricular‐vascular coupling are abnormal in MFS but preserved in ns‐TAAD, and are independent of aortic stiffness, consistent with intrinsic impairment of myocardial contractility in MFS

The Stellar Halos of Massive Elliptical Galaxies

We use the Mitchell Spectrograph (formerly VIRUS-P) on the McDonald Observatory 2.7m Harlan J. Smith Telescope to search for the chemical signatures of massive elliptical galaxy assembly. The Mitchell Spectrograph is an integral-field spectrograph with a uniquely wide field of view (107x107 sq arcsec), allowing us to achieve remarkably high signal-to-noise ratios of ~20-70 per pixel in radial bins of 2-2.5 times the effective radii of the eight galaxies in our sample. Focusing on a sample of massive elliptical galaxies with stellar velocity dispersions sigma* > 150 km/s, we study the radial dependence in the equivalent widths (EWs) of key metal absorption lines. By twice the effective radius, the Mgb EWs have dropped by ~50%, and only a weak correlation between sigma* and Mgb EW remains. The Mgb EWs at large radii are comparable to those seen in the centers of elliptical galaxies that are approximately an order of magnitude less massive. We find that the well-known metallicity gradients often observed within an effective radius continue smoothly to 2.5R_e, while the abundance ratio gradients remain flat. Much like the halo of the Milky Way, the stellar halos of our galaxies have low metallicities and high alpha-abundance ratios, as expected for very old stars formed in small stellar systems. Our observations support a picture in which the outer parts of massive elliptical galaxies are built by the accretion of much smaller systems whose star formation history was truncated at early times.Comment: To appear in ApJ, 15 pages, 9 figure

Spectroscopy of the spatially-extended Lya emission around a QSO at z=6.4

We have taken a deep, moderate-resolution Keck/Deimos spectra of QSO, CFHQS2329, at z=6.4. At the wavelength of Lya, the spectrum shows a spatially-extended component, which is significantly more extended than a stellar spectrum, and also a continuum part of the spectrum. The restframe line width of the extended component is 21+-7 A, and thus smaller than that of QSO (52+-4 A), where they should be identical if the light is incomplete subtraction of the QSO component. Therefore, these comparisons argue for the detection of a spatially extended Lya nebulae around this QSO. This is the first z>6 QSO that an extended Lya halo has been observed around. Careful subtraction of the central QSO spectrum reveals a lower limit to the Lya luminosity of (1.7+-0.1)x 10^43 erg s^-1. This emission may be from the theoretically predicted infalling gas in the process of forming a primordial galaxy that is ionized by a central QSO. On the other hand, if it is photoionized by the host galaxy, an estimated star-formation rate of >3.0 Msun yr^-1 is required. If we assume the gas is virialized, we obtain dynamical mass estimate of Mdyn=1.2x10^12 Msun. The derived MBH/Mhost is 2.1x10^-4, which is two orders smaller than those from more massive z~6 QSOs, and places this galaxy in accordance with the local M-sigma relation, in contrast to a previous claim on the evolution of M-sigma relation at z~6. We do not claim evolution or non-evolution of the M-sigma relation based on a single object, but our result highlights the importance of investigating fainter QSOs at z~6.Comment: 5 pages, 5 figures. Accepted for publication in MNRAS. A minor computational error fixe

Collapse Barriers and Halo Abundance: Testing the Excursion Set Ansatz

Our heuristic understanding of the abundance of dark matter halos centers around the concept of a density threshold, or "barrier", for gravitational collapse. If one adopts the ansatz that regions of the linearly evolved density field smoothed on mass scale M with an overdensity that exceeds the barrier will undergo gravitational collapse into halos of mass M, the corresponding abundance of such halos can be estimated simply as a fraction of the mass density satisfying the collapse criterion divided by the mass M. The key ingredient of this ansatz is therefore the functional form of the collapse barrier as a function of mass M or, equivalently, of the variance sigma^2(M). Several such barriers based on the spherical, Zel'dovich, and ellipsoidal collapse models have been extensively discussed. Using large scale cosmological simulations, we show that the relation between the linear overdensity and the mass variance for regions that collapse to form halos by the present epoch resembles expectations from dynamical models of ellipsoidal collapse. However, we also show that using such a collapse barrier with the excursion set ansatz predicts a halo mass function inconsistent with that measured directly in cosmological simulations. This inconsistency demonstrates a failure of the excursion set ansatz as a physical model for halo collapse. We discuss implications of our results for understanding the collapse epoch for halos as a function of mass, and avenues for improving consistency between analytical models for the collapse epoch and the results of cosmological simulations.Comment: Version accepted by ApJ, scheduled for May 2009, v696. High-res version available at http://kicp.uchicago.edu/~brant/astro-ph/excursion_set_ansatz/robertson_excursion_set_ansatz.pd