ABSTRACT
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 ≥ 1039 erg s−1), that we treat as a class. We exploit archival XMM–Newton data to enrich the study of the long-term variability, on time-scales 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, seven in G1, and one in G3. About one-third of these 37 sources show long-term variability, while no variability is detected within the single observations. Of those, five 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 time-scales.
Abstract
NGC 7793 P13 is a variable (luminosity range ∼100) ultraluminous X-ray source proposed to host a stellar-mass black hole of less than 15 M⊙ in a binary system with orbital period of 64 d and ...a 18–23 M⊙ B9Ia companion. Within the EXTraS (Exploring the X-ray Transient and variable Sky) project, we discovered pulsations at a period of ∼0.42 s in two XMM–Newton observations of NGC 7793 P13, during which the source was detected at L
X ∼ 2.1 × 1039 and 5 × 1039 erg s−1 (0.3–10 keV band). These findings unambiguously demonstrate that the compact object in NGC 7793 P13 is a neutron star accreting at super-Eddington rates. While standard accretion models face difficulties accounting for the pulsar X-ray luminosity, the presence of a multipolar magnetic field with B ∼ few × 1013 G close to the base of the accretion column appears to be in agreement with the properties of the system.
We discovered 2.8 s pulsations in the X-ray emission of the ultraluminous X-ray source (ULX) M51 ULX-7 within the UNSEeN project, which was designed to hunt for new pulsating ULXs (PULXs) with ...XMM-Newton. The pulse shape is sinusoidal, and large variations of its amplitude were observed even within single exposures (pulsed fraction from less than 5% to 20%). Source M51 ULX-7 is variable, generally observed at an X-ray luminosity between 1039 and 1040 erg s−1, located in the outskirts of the spiral galaxy M51a at a distance of 8.6 Mpc. According to our analysis, the X-ray pulsar orbits in a 2 day binary with a projected semimajor axis 28 lt-s. For a neutron star (NS) of 1.4 M , this implies a lower limit on the companion mass of 8 M , placing the system hosting M51 ULX-7 in the high-mass X-ray binary class. The barycentric pulse period decreased by 0.4 ms in the 31 days spanned by our 2018 May-June observations, corresponding to a spin-up rate . In an archival 2005 XMM-Newton exposure, we measured a spin period of ∼3.3 s, indicating a secular spin-up of , a value in the range of other known PULXs. Our findings suggest that the system consists of a massive donor, possibly an OB giant or supergiant, and a moderately magnetic (dipole field component in the range 1012 G G) accreting NS with weakly beamed emission ( ).
Water shortages have become a major problem facing the world today. Membrane separation technology is commonly used in water treatment applications. The development of new materials for water ...treatment can reduce the energy required for water treatment, reduce cost, and improve efficiency. The unique structure and properties of graphene and silica make them attractive materials for preparation of nanofiltration membranes for water treatment. We have successfully prepared a graphene oxide/silica (GO/SiO
2
) hybrid composite materials by in situ hydrolysis, using tetraethyl orthosilicate (TEOS) as a silicon source in an alkaline environment. The chemistry and structure of these materials are characterized by TEM, FTIR, Raman, and XPS of GO and the GO/SiO
2
composite. BET porosimetry reveals that the total pore volume of the composite is 2.84 cm
3
g
−1
, the specific surface area is 2897 m
2
g
−1
, and the average pore diameter is 3.97 nm. We prepared GO membranes and GO/SiO
2
composite membranes by vacuum suction filtration. The morphology of the membrane was observed by FESEM and AFM. The composite membrane has a larger surface roughness (
R
ms
= 9.39). We also tested the thermal stability by TGA, and hydrophilicity by water contact angle measurements. The water permeance of the composite membrane is up to 229.15 L m
−2
h
−1
bar
−1
, and the rejection of the rhodamine B dye molecules is as high as 99%. The GO/SiO
2
hybrid composite membrane has good hydrophilicity and thermal stability, high water permeance and rejection, and can be developed as a high-performance material for water treatment.
Luminescent materials are of worldwide interest because of their unique optical properties. Silica, which is transparent to light, is an ideal matrix for luminescent materials. Luminescent silica ...nanoparticles (LSNs) have broad applications because of their enhanced chemical and thermal stability. Silica spheres of various sizes could be synthesized by different methods to satisfy specific requirements. Diverse luminescent dyes have potential for different applications. Subject to many factors such as quenchers, their performance was not quite satisfying. This review thus discusses the development of LSNs including their classification, synthesis, and application. It is the highlight that how silica improves the properties of luminescent dye and what role silica plays in the system. Further, their applications in biology, display, and sensors are also described.
Abstract
Variability is a powerful tool to investigate properties of X-ray binaries (XRB), in particular for Ultraluminous X-ray sources (ULXs) that are mainly detected in the X-ray band. For most ...ULXs the nature of the accretor is unknown, although a few ULXs have been confirmed to be accreting at super-Eddington rates on to a neutron star (NS). Monitoring these sources is particularly useful both to detect transients and to derive periodicities, linked to orbital and super-orbital modulations. Here, we present the results of our monitoring campaign of the galaxy NGC 925, performed with the Neil Gehrels Swift Observatory. We also include archival and literature data obtained with Chandra, XMM–Newton, and NuSTAR. We have studied spectra, light curves, and variability properties on days to months time-scales. All the three ULXs detected in this galaxy show flux variability. ULX-1 is one of the most luminous ULXs known, since only 10 per cent of the ULXs exceed a luminosity of ∼5 × 1040 erg s−1, but despite its high flux variability we found only weak spectral variability. We classify it as in a hard ultraluminous regime of super-Eddington accretion. ULX-2 and ULX-3 are less luminous but also variable in flux and possibly also in spectral shape. We classify them as in between the hard and the soft ultraluminous regimes. ULX-3 is a transient source: by applying a Lomb–Scargle algorithm, we derive a periodicity of ∼126 d, which could be associated with an orbital or superorbital origin.
In the present investigation, a chitosan-based hydrogel, graft-copolymerized with methylenebisacrylamide and poly(acrylic acid), (i.e., CS-co-MMB-co-PAA), was employed in studies on the adsorption ...kinetics of Pb(II), Cd(II), and Cu(II) ions in aqueous solution. Swelling studies performed using the Fickian diffusion model inferred that the mass transfer mechanism of water in hydrogels was governed by diffusion and macromolecular structural relaxation, modified by the presence of magnetite. The best parameters for the removal of metals were pH between 4.5 and 5.5, initial metal concentration of 300mgdm⁻³ and 100mg of dried hydrogel mass. Isotherm models of Langmuir, Freundlich and Redlich–Peterson suggest that there may be variation in the physicochemical phenomena involving metal adsorption. These isotherms reveal that the adsorption efficiency decreased in the presence of magnetite. Hydrogels with magnetite and the metal ions adsorbed on them may be recovered after the application of an external magnetic field, as opposed to the hydrogels without magnetite, which are frequently recovered using a chemical solvent. The recovery of adsorbents by applying external ac or dc magnetic fields in the absence of solvent is an environmentally clean alternative, with no production of a secondary waste.
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Recent years have witnessed a rapid development of the fluorescent carbon dots (CDs), due to their distinctive advantages of straightforward synthesis, excellent biocompatibility, low ...cost, and tunable optical properties. However, the widespread applications of CDs in biomedical theranostics, light harvesting, and photocatalysis are limited by the lack of emission and/or excitation in the red/near-infrared (NIR) region. Extensive explorations have been conducted to synthesize CDs with intensive red/NIR emission/excitation (red CDs) by rational design and ingenious synthesis to broaden their applications. This review emphasizes the most recent efforts in the development of CDs with intensive emission at a long wavelength, with a focus on the regulation methods for the optical properties of CDs, including particle size, surface state, and heteroatom doping. Key factors in processing red CDs, such as reaction solvent and precursors, are demonstrated. More importantly, employing polyaromatic and dye molecules as carbon sources is highlighted, which could further expand emission/excitation to the NIR region. The boosting applications of red CDs in white light-emitting diodes (WLEDs), biosensing, bioimaging, theranostics, and photocatalysis are demonstrated. Finally, the challenges and perspectives of red CDs are also discussed.
Graves' ophthalmopathy (GO) is an autoimmune disease that affects orbital soft tissues and represents the most common extrathyroidal manifestation of Graves' disease (GD). The European Group of ...Graves' Ophthalmopathy (EUGOGO) has attempted to shed light on the European epidemiological picture of GO, suggesting that GO in newly diagnosed patients in recent years has a trend towards a less severe clinical presentation. There are no studies that focus this issue on the population of our area; we aimed to evaluate the trend of GO clinical presentation in our outpatient clinic through an observation period of 10 years.
We compared 55 consecutive patients, 11 males (F) and 44 females (M), who came to our observation from January 2005 to December 2006 Group 1 (G1), with 56 patients, 15 males, and 41 females, who were referred to us from 2015 to 2016 Group 2 (G2). We studied the following putative predictors of GO presentation and severity: thyroid function, smoking, diabetes, hypercholesterolemia, time from GO diagnosis to referral to our thyroid centre (TGOD), sex and age.
GO severity was significantly reduced in G2 vs. G1 (p = 0.04). TGOD ≥ 3 months was related to clinical characteristics of GO (severity and Clinical Activity Score ≥ 4) and was an independent predictor of GO severity (p = 0.01). The other variables evaluated had no independent effects.
We found that GO severity at presentation was significantly reduced over a ten-year observation period (2005-2006 vs. 2015-2016) in GO patients referred to our tertiary thyroid centre. TGOD ≥ 3 months was an independent predictor of GO severity.
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 measurement 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 measured rotation periods from photometric variability in Kepler light curves. As activity indicators, we adopted 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, 20 of which do not have 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 seven 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.
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