The largest bright ULX population in a galaxy: X-ray variability and Luminosity Function in the Cartwheel ring Galaxy

We analyse all the available Chandra observations of the Cartwheel Galaxy and its compact group, taken between 2001 and 2008, with the main aim of addressing the variability in the X-ray band for this spectacular collisional ring galaxy. We focus on the study of point-like sources, in particular we are interested in Ultraluminous X-ray sources (ULXs, Lx >= 10^39 erg/s), that we treat as a class. We exploit archival XMM-Newton data to enrich the study of the long-term variability, on timescales of months to years. We find a total of 44 sources in the group area, of which 37 in total are ULXs positionally linked with the galaxies and of which we can study variability. They are 29 in the Cartwheel itself, 7 in G1 and 1 in G3. About one third of these 37 sources show long-term variability, while no variability is detected within the single observations. Of those, 5 ULXs have a transient behaviour with a maximum range of variability (Lmax/Lmin) of about one order of magnitude and are the best candidate neutron stars. The X-ray Luminosity Function (XLF) of the point-like sources remains consistent in shape between the Chandra observations both for the Cartwheel galaxy itself and for G1, suggesting that flux variability does not strongly influence the average properties of the population on the observation timescales.Comment: 17 pages, 5 figures, Accepted for publication in MNRA

The ratio of lentic to lotic habitat features strongly affects macroinvertebrate metrics used in southern Europe for ecological status classification

Abstract Biological quality in rivers based on benthic macroinvertebrates is typically assessed by comparison with expected reference conditions, which represent relatively undisturbed situations. Commonly, reference conditions are set in agreement with river typologies to handle major ecological differences and limit biological variability. Although natural hydrological variation can be highly influential, site-specific tuning of reference conditions is rare in Mediterranean countries. River flow and local hydraulics change continuously over time, shaping the occurrence of lentic and lotic habitat features. Thus, biological reference conditions might require site-specific adjustment based on the ratio of lentic to lotic habitats assessed at the time of sampling. This would help reducing systematic bias in ecological assessments, interpreting benthic invertebrate responses to pressures, and diminishing the amount of unexplained biological variability. In this study, the response to the lentic-lotic character of river reaches was assessed for nineteen macroinvertebrate metrics and indices commonly used for the classification of ecological status in South European rivers. The study sites, with a prevalent temporary character, were located in Sardinia, southwestern Italy. Most metrics were significantly related to the lentic-lotic habitat conditions, both in pool and riffle mesohabitats, and their response curves were either parabolic or linearly decreasing at increasing lentic conditions. Taxonomic richness, score-based metrics, ovoviviparous taxa and multi-metric indices related well to the lentic-lotic conditions, while abundance metrics correlated less. The potential impact on ecological status classification was tested for the method formally used in Italy, which had a major role in comparing and inter-calibrating European assessment methods for the Water Framework Directive. After adjusting for bias due to the ratio of lentic to lotic habitat features, quality classification shifted towards better ecological status for ≈ 23% samples. This highlighted the impact of ignoring lentic-lotic information when defining reference conditions for assessing ecological status, varying from difficulties in understanding the biological response to pressures, to largely biased ecological status classification. The observed response of macroinvertebrate metrics to lentic-lotic conditions should be a key consideration for realistic ecological status assessment and could further be a valuable input for evaluating the effects of human-induced hydrological alteration and for assessing environmental flows

Dynamic Model of a Conjugate-Surface Flexure Hinge Considering Impacts between Cylinders

A dynamic model of a Conjugate-Surface Flexure Hinge (CSFH) has been proposed as a component for MEMS/NEMS Technology-based devices with lumped compliance. However, impacts between the conjugate surfaces have not been studied yet and, therefore, this paper attempts to fill this gap by proposing a detailed multibody system (MBS) model that includes not only rigid-body dynamics but also elastic forces, friction, and impacts. Two models based on the Lankarani-Nikravesh constitutive law are first recalled and a new model based on the contact of cylinders is proposed. All three models are complemented by the friction model proposed by Ambrosio. Then, the non-smooth Moreau time-stepping scheme with Coulomb friction is described. The four models are compared in different scenarios and the results confirm that the proposed model outcomes comply with the most reliable models

EXTraS discovery of a peculiar flaring X-ray source in the Galactic globular cluster NGC 6540

We report the discovery of a flaring X-ray source in the globular cluster NGC 6540, obtained during the EXTraS project devoted to a systematic search for variability in archival data of the XMM-Newton satellite. The source had a quiescent X-ray luminosity of the order of ~10^32 erg/s in the 0.5-10 keV range (for a distance of NGC 6540 of 4 kpc) and showed a flare lasting about 300 s. During the flare, the X-ray luminosity increased by more than a factor 40, with a total emitted energy of ~10^36 erg. These properties, as well as Hubble Space Telescope photometry of the possible optical counterparts, suggest the identification with a chromospherically active binary. However, the flare luminosity is significantly higher than what commonly observed in stellar flares of such a short duration, leaving open the possibility of other interpretations.Comment: To appear in Astronomy and Astrophysic

Activity and rotation of the X-ray emitting Kepler stars

The relation between magnetic activity and rotation in late-type stars provides fundamental information on stellar dynamos and angular momentum evolution. Rotation/activity studies found in the literature suffer from inhomogeneity in the measure of activity indexes and rotation periods. We overcome this limitation with a study of the X-ray emitting late-type main-sequence stars observed by XMM-Newton and Kepler. We measure rotation periods from photometric variability in Kepler light curves. As activity indicators, we adopt the X-ray luminosity, the number frequency of white-light flares, the amplitude of the rotational photometric modulation, and the standard deviation in the Kepler light curves. The search for X-ray flares in the light curves provided by the EXTraS (Exploring the X-ray Transient and variable Sky) FP-7 project allows us to identify simultaneous X-ray and white-light flares. A careful selection of the X-ray sources in the Kepler field yields 102 main-sequence stars with spectral types from A to M. We find rotation periods for 74 X-ray emitting main-sequence stars, 22 of which without period reported in the previous literature. In the X-ray activity/rotation relation, we see evidence for the traditional distinction of a saturated and a correlated part, the latter presenting a continuous decrease in activity towards slower rotators. For the optical activity indicators the transition is abrupt and located at a period of ~ 10 d but it can be probed only marginally with this sample which is biased towards fast rotators due to the X-ray selection. We observe 7 bona-fide X-ray flares with evidence for a white-light counterpart in simultaneous Kepler data. We derive an X-ray flare frequency of ~ 0.15 d^{-1} , consistent with the optical flare frequency obtained from the much longer Kepler time-series.Comment: Accepted for publication in A&A. 31 pages, 19 figure

Metformin inhibits androgen-induced IGF-IR up-regulation in prostate cancer cells by disrupting membrane-initiated androgen signaling.

We have previously demonstrated that, in prostate cancer cells, androgens up-regulate IGF-I receptor (IGF-IR) by inducing cAMP-response element-binding protein (CREB) activation and CREB-dependent IGF-IR gene transcription through androgen receptor (AR)-dependent membrane-initiated effects. This IGF-IR up-regulation is not blocked by classical antiandrogens and sensitizes cells to IGF-I-induced biological effects. Metformin exerts complex antitumoral functions in various models and may inhibit CREB activation in hepatocytes. We, therefore, evaluated whether metformin may affect androgen-dependent IGF-IR up-regulation. In the AR(+) LNCaP prostate cancer cells, we found that metformin inhibits androgen-induced CRE activity and IGF-IR gene transcription. CRE activity requires the formation of a CREB-CREB binding protein-CREB regulated transcription coactivator 2 (CRTC2) complex, which follows Ser133-CREB phosphorylation. Metformin inhibited Ser133-CREB phosphorylation and induced nuclear exclusion of CREB cofactor CRTC2, thus dissociating the CREB-CREB binding protein-CRTC2 complex and blocking its transcriptional activity. Similarly to metformin action, CRTC2 silencing inhibited IGF-IR promoter activity. Moreover, metformin blocked membrane-initiated signals of AR to the mammalian target of rapamycin/p70S6Kinase pathway by inhibiting AR phosphorylation and its association with c-Src. AMPK signals were also involved to some extent. By inhibiting androgen-dependent IGF-IR up-regulation, metformin reduced IGF-I-mediated proliferation of LNCaP cells. These results indicate that, in prostate cancer cells, metformin inhibits IGF-I-mediated biological effects by disrupting membrane-initiated AR action responsible for IGF-IR up-regulation and suggest that metformin could represent a useful adjunct to the classical antiandrogen therapy

Mechanisms of Progranulin Action and Regulation in Genitourinary Cancers.

The growth factor progranulin has emerged in recent years as a critical regulator of transformation in several cancer models, including breast cancer, glioblastomas, leukemias, and hepatocellular carcinomas. Several laboratories, including ours, have also demonstrated an important role of progranulin in several genitourinary cancers, including ovarian, endometrial, cervical, prostate, and bladder tumors, where progranulin acts as an autocrine growth factor thereby modulating motility and invasion of transformed cells. In this review, we will focus on the mechanisms of action and regulation of progranulin signaling in genitourinary cancers with a special emphasis on prostate and bladder tumors