Environments of a sample of AzTEC submillimetre galaxies in the COSMOS field

Aims. Submillimetre galaxies (SMGs) are bright sources at submillimetre wavelengths (F-850 mu m>2-5 mJy). Made up of mostly of high-z galaxies (z>1), SMGs are amongst the most luminous dusty galaxies in the Universe. These galaxies are thought to be the progenitors of the massive elliptical galaxies in the local Universe and to reside in massive haloes at early epochs. Studying their environments and clustering strength is thus important to put these galaxies in a cosmological context.Methods. We present an environmental study of a sample of 116 SMGs in 96 ALMA observation fields, which were initially discovered with the AzTEC camera on ASTE and identified with high-resolution 1.25 mm ALMA imaging within the COSMOS survey field, having either spectroscopic or unambiguous photometric redshift. We analysed their environments making use of the latest release of the COSMOS photometric catalogue, COSMOS2015, a catalogue that contains precise photometric redshifts for more than half a million objects over the 2 deg(2) COSMOS field. We searched for dense galaxy environments computing the so-called overdensity parameter as a function of distance within a radius of 5 from the SMG. We validated this approach spectroscopically for those SMGs for which spectroscopic redshift is available. As an additional test, we searched for extended X-ray emission as a proxy for the hot intracluster medium, performing an X-ray stacking analysis in the 0.5-2 keV band with a 32 '' aperture and our SMG position using all available XMM-Newton and Chandra X-ray observations of the COSMOS field.Results. We find that 27% (31 out of 116) of the SMGs in our sample are located in a galactic dense environment; a fraction that is similar to previous studies. The spectroscopic redshift is known for 15 of these 31 sources, thus this photometric approach is tested using spectroscopy. We are able to confirm that 7 out of 15 SMGs lie in high-density peaks. However, the search for associated extended X-ray emission via an X-ray stacking analysis leads to a detection that is not statistically significant.Peer reviewe

Prehistoric stone disks from entrances and cemeteries of north-eastern Adriatic hillforts|Prazgodovinski kamniti diski z vhodov in grobi[; na gradi[;ih na severovzhodnem Jadranu

The paper presents a group of four, approximately 0.5m large, stone disks from entrances or cemeteries of two protohistoric hillforts of north-eastern Adriatic. The disks, having a sparse chronology with the exception of one dated to the Middle Bronze Age, show flat and plain surfaces or covered with sub-circular depressions. One disk shows two larger cup-marks at the centre of both faces. They are interpreted as ritual artefacts based on the association with sacred settlement locations and comparisons with similar coeval stones found mainly close to citadel entrances, burials and thresholds in the Aegean area and Anatolia

Deformed PP-waves from the Lunin-Maldacena Background

In this article we study a pp-wave limit of the Lunin-Maldacena background. We show that the relevant string theory background is a homogeneous pp-wave. We obtain the string spectrum. The dual field theory is a deformation of N=4 super Yang-Mills theory. We have shown that, for a class of operators, at O(g_{YM}^2) and at leading order in N, all contributions to the anomalous dimension come from F-terms. We are able to identify the operator in the deformed super Yang-Mills which is dual to the lowest string mode. By studying the undeformed theory we are able to provide some evidence, directly in the field theory, that a small set of nearly protected operators decouple. We make some comments on operators in the Yang-Mills theory that are dual to excited string modes.Comment: 22 pages, 1 figure; Final version to appear in JHE

Corner contributions to holographic entanglement entropy

The entanglement entropy of three-dimensional conformal field theories contains a universal contribution coming from corners in the entangling surface. We study these contributions in a holographic framework and, in particular, we consider the effects of higher curvature interactions in the bulk gravity theory. We find that for all of our holographic models, the corner contribution is only modified by an overall factor but the functional dependence on the opening angle is not modified by the new gravitational interactions. We also compare the dependence of the corner term on the new gravitational couplings to that for a number of other physical quantities, and we show that the ratio of the corner contribution over the central charge appearing in the two-point function of the stress tensor is a universal function for all of the holographic theories studied here. Comparing this holographic result to the analogous functions for free CFT's, we find fairly good agreement across the full range of the opening angle. However, there is a precise match in the limit where the entangling surface becomes smooth, i.e., the angle approaches $\pi$, and we conjecture the corresponding ratio is a universal constant for all three-dimensional conformal field theories. In this paper, we expand on the holographic calculations in our previous letter arXiv:1505.04804, where this conjecture was first introduced.Comment: 62 pages, 6 figures, 1 table; v2: minor modifications to match published version, typos fixe

Prostate fiducial marker detection with the use of multi-parametric magnetic resonance imaging

Background and purpose: The introduction of a magnetic resonance (MR)-only workflow in radiotherapy requires that fiducial markers, used for position verification, can be detected on MR images. Here we evaluate a model for marker detection in prostate cancer patients by combining information from our hospital standard multi-parametric (mp-) MRI protocol (T1-weighted – T1w, T2-weighted – T2w, B0) with dedicated sequences (balanced steady-state free precession sequence – bTFE, susceptibility weighted imaging – SWI). Materials and methods: Thirty two patients scheduled for external-beam radiotherapy received a mp-MRI and computed-tomography; the latter was used as ground truth location of the markers. A logistic regression model was implemented for marker detection by combining features from all imaging sequences. The performance of the individual and combined sequences was assessed by determining true and false positive detections. Results: The combination of different sequences (mp-MRI) resulted in a better performance than the best imaging sequence alone (bTFE). Combining mp-MRI + bTFE resulted in good accuracy and a true positive detection rate of 0.94. Conclusions: The standard mp-MRI provides valuable information to detect fiducial markers. The combination of different sequences outperforms the use of a single dedicated sequence. We recommend the addition of a bTFE to the standard mp-MRI protocol to improve fiducial marker detection. Keywords: Prostate cancer, External beam radiotherapy, Fiducial markers, Multi-parametric MR

Biochemical recurrence prediction after radiotherapy for prostate cancer with T2w magnetic resonance imaging radiomic features

Background and purpose: High-risk prostate cancer patients are frequently treated with external-beam radiotherapy (EBRT). Of all patients receiving EBRT, 15–35% will experience biochemical recurrence (BCR) within five years. Magnetic resonance imaging (MRI) is commonly acquired as part of the diagnostic procedure and imaging-derived features have shown promise in tumour characterisation and biochemical recurrence prediction. We investigated the value of imaging features extracted from pre-treatment T2w anatomical MRI to predict five year biochemical recurrence in high-risk patients treated with EBRT. Materials and methods: In a cohort of 120 high-risk patients, imaging features were extracted from the whole-prostate and a margin surrounding it. Intensity, shape and textural features were extracted from the original and filtered T2w-MRI scans. The minimum-redundancy maximum-relevance algorithm was used for feature selection. Random forest and logistic regression classifiers were used in our experiments. The performance of a logistic regression model using the patient’s clinical features was also investigated. To assess the prediction accuracy we used stratified 10-fold cross validation and receiver operating characteristic analysis, quantified by the area under the curve (AUC). Results: A logistic regression model built using whole-prostate imaging features obtained an AUC of 0.63 in the prediction of BCR, outperforming a model solely based on clinical variables (AUC = 0.51). Combining imaging and clinical features did not outperform the accuracy of imaging alone. Conclusions: These results illustrate the potential of imaging features alone to distinguish patients with an increased risk of recurrence, even in a clinically homogeneous cohort. Keywords: Prostate cancer, T2-weighted MRI, Radiomics, External beam radiotherap

MPEG-2 Compressed-Domain Algorithms for Video Analysis

<p/> <p>This paper presents new algorithms for extracting metadata from video sequences in the MPEG-2 compressed domain. Three algorithms for efficient low-level metadata extraction in preprocessing stages are described. The first algorithm detects camera motion using the motion vector field of an MPEG-2 video. The second method extends the idea of motion detection to a limited region of interest, yielding an efficient algorithm to track objects inside video sequences. The third algorithm performs a cut detection using macroblock types and motion vectors.</p