Population of the Galactic X-ray binaries and eRosita

The population of the Galactic X-ray binaries has been mostly probed with moderately sensitive hard X-ray surveys so far. The eRosita mission will provide, for the first time a sensitive all-sky X-ray survey in the 2-10 keV energy range, where the X-ray binaries emit most of the flux and discover the still unobserved low-luminosity population of these objects. In this paper, we briefly review the current constraints for the X-ray luminosity functions of high- and low-mass X-ray binaries and present our own analysis based the INTEGRAL 9-year Galactic survey, which yields improved constraints. Based on these results, we estimate the number of new XRBs to be detected in the eRosita all-sky surveyComment: accepted for publication in A&

Optical and near-infrared photometric monitoring of the transient X-ray binary A0538-66 with REM

The transient Be/X-ray binary A0538-66 shows peculiar X-ray and optical variability. Despite numerous studies, the intrinsic properties underlying its anomalous behaviour remain poorly understood. Since 2014 September we are conducting the first quasi-simultaneous optical and near-infrared photometric monitoring of A0538-66 in seven filters with the Rapid Eye Mount (REM) telescope, aiming to understand the properties of this binary system. We found that the REM lightcurves show fast flares lasting one or two days that repeat almost regularly every ~16.6 days, the orbital period of the neutron star. If the optical flares are powered by X-ray outbursts through photon reprocessing, the REM lightcurves indicate that A0538-66 is still active in X-rays: bright X-ray flares (L_x > 1E37 erg/s) could be observable during the periastron passages. The REM lightcurves show a long-term variability that is especially pronounced in the g band and decreases with increasing wavelength, until it no longer appears in the near-infrared lightcurves. In addition, A0538-66 is fainter with respect to previous optical observations most likely due to the higher absorption of the stellar radiation of a denser circumstellar disc. On the basis of the current models, we interpret these observational results with a circumstellar disc around the Be star observed nearly edge-on during a partial depletion phase. The REM lightcurves also show short-term variability on timescales of ~1 day possibly indicative of perturbations in the density distribution of the circumstellar disc caused by the tidal interaction with the neutron star.Comment: Accepted for publication in Astronomy & Astrophysic

Properties and observability of glitches and anti-glitches in accreting pulsars

Several glitches have been observed in young, isolated radio pulsars, while a clear detection in accretion-powered X-ray pulsars is still lacking. We use the Pizzochero snowplow model for pulsar glitches as well as starquake models to determine for the first time the expected properties of glitches in accreting pulsars and their observability. Since some accreting pulsars show accretion-induced long-term spin-up, we also investigate the possibility that anti-glitches occur in these stars. We find that glitches caused by quakes in a slow accreting neutron star are very rare and their detection extremely unlikely. On the contrary, glitches and anti-glitches caused by a transfer of angular momentum between the superfluid neutron vortices and the non-superfluid component may take place in accreting pulsars more often. We calculate the maximum jump in angular velocity of an anti-glitch and we find that it is expected to be about 1E-5 - 1E-4 rad/s. We also note that since accreting pulsars usually have rotational angular velocities lower than those of isolated glitching pulsars, both glitches and anti-glitches are expected to have long rise and recovery timescales compared to isolated glitching pulsars, with glitches and anti-glitches appearing as a simple step in angular velocity. Among accreting pulsars, we find that GX 1+4 is the best candidate for the detection of glitches with currently operating X-ray instruments and future missions such as the proposed Large Observatory for X-ray Timing (LOFT).Comment: Accepted for publication in Astronomy & Astrophysics. 6 pages. Minor changes to match the final A&A versio

Flow, suspension, and mixing dynamics in DASGIP bioreactors: Part 1

The bioreactor flow environment has a significant impact on process performance, especially in stem cell cultures. The work of Correia et al found intermittent agitation modes to improve induced pluripotent stem cell (iPSC)‐cardiomyocyte differentiation yields; however, to date, the impact within the flow has not been fully characterized. This work aims to characterize the flow dynamics occurring within a commercially available DASGIP bioreactor, equipped with a two‐blade paddle impeller, operating under different agitation modes and for two bottom geometries. The paddle impeller configuration generated an axial flow profile due to a large impeller D/T and blade confinement with the bioreactor wall. The application of intermittent agitation was shown to induce two transient spikes in flow velocity and shear stress, the amplification of which increased with dwell duration. Marginally increasing the dwell duration was shown previously to increase differentiation yields, therefore it can be stipulated that introduction of these spikes was favorable toward cardiogenic differentiation

Fluid flow and mixing in a novel intermittently rotating bioreactor for CAR-T cell therapy manufacturing

This work explores the mixing and fluid dynamics in a novel bioreactor currently used for the automated manufacturing of CAR-T cell therapy, which offers a single-dose cure for several forms of advanced blood cancer. The cylindrical bioreactor has a low aspect ratio and a free surface. Agitation is achieved by intermittent rotation of the entire vessel around its central axis. No engineering characterisation has been conducted to date for this system in a bioprocessing context. The study examines the fluid dynamics problems of spin-up from rest and spin-down to rest. Novel Particle Image Velocimetry and Planar Laser-Induced Fluorescence data is presented alongside reflective flakes results, shedding light on the different transient flow regions inside the intermittently rotating bioreactor, and determining the timescales of macro- and micromixing. The results presented can be used to design a custom rotation pattern of the bioreactor for improved mixing performance during the cell expansion step

Spectral and temporal properties of the supergiant fast X-ray transient IGR J18483-0311 observed by INTEGRAL

IGR J18483-0311 is a supergiant fast X-ray transient whose compact object is located in a wide (18.5 d) and eccentric (e~0.4) orbit, which shows sporadic outbursts that reach X-ray luminosities of ~1e36 erg/s. We investigated the timing properties of IGR J18483-0311 and studied the spectra during bright outbursts by fitting physical models based on thermal and bulk Comptonization processes for accreting compact objects. We analysed archival INTEGRAL data collected in the period 2003-2010, focusing on the observations with IGR J18483-0311 in outburst. We searched for pulsations in the INTEGRAL light curves of each outburst. We took advantage of the broadband observing capability of INTEGRAL for the spectral analysis. We observed 15 outbursts, seven of which we report here for the first time. This data analysis almost doubles the statistics of flares of this binary system detected by INTEGRAL. A refined timing analysis did not reveal a significant periodicity in the INTEGRAL observation where a ~21s pulsation was previously detected. Neither did we find evidence for pulsations in the X-ray light curve of an archival XMM-Newton observation of IGR J18483-0311. In the light of these results the nature of the compact object in IGR J18483-0311 is unclear. The broadband X-ray spectrum of IGR J18483-0311 in outburst is well fitted by a thermal and bulk Comptonization model of blackbody seed photons by the infalling material in the accretion column of a neutron star. We also obtained a new measurement of the orbital period using the Swift/BAT light curve.Comment: Accepted for publication in Astronomy and Astrophysics. 8 page

Study on mixing and suspension characteristics in single-use shaken microwell systems

The worldwide cell therapy market is growing steadily, with a growing number of therapies undergoing late-stage clinical trails. The benefits of a three dimensional environment associated with suspension bioreactor cultivation methodologies have been demonstrated using microcarrier-based expansion methods. During early stages of bioprocess development, single-use ml-scale shaken multi-well plates are commonly used for scale-down studies as they allow a large number of experiments to be performed using small amounts of material. However, very few studies published on shaken bioreactors have thoroughly studied the engineering aspects and the hydrodynamics at such a small scale, thus resulting in a lack of accurate scaling correlations between shaken and large scale conventional bioreactors. The flow in orbitally shaken reactors has been characterised by Weheliye et al (2013) and Ducci and Wehiliye (2014) and a scaling law has been developed for a cylindrical geometry with internal diameters ranging from 1.5-5 cm. The aim of this work was twofold – (i) to assess the validity of the existing scaling law at the microwell scale (for internal diameters \u3c 1.5 cm) and bridge the gap between single-use ml-scale wells and large scale conventional bioreactors and (ii) to determine the suspension characteristics and assess their impact of different parameters on the quality of the suspension. In this study, mixing time and microcarrier suspension experiments were conducted in a square well and a cylindrical well mimicking an individual well of a 24 Deep Square Well (24DSW) plate and a 24 Standard Round Well (24SRW) plate, respectively. The impact of operating conditions and fluid properties on the mixing characteristics was assessed, including fill volume, well geometry, shaken speed and orbital diameter, fluid viscosity and surface tension. It has been found that the the cylindrical well requires longer mixing time than the square one for the same fill volume at rotational speeds less than 550rpm. Comparison of the mixing time results with larger scale data (Rodriguez et al 2013, 2014) shows that mixing number decreases with Froude number and becomes constant at a lower Fr/Frcritical for microscale data. A small increase in mixing time was also noticed in the square well at around 600 to 650rpm and this phenomenon corresponds to a change in the shape of the liquid surface, as confirmed by visual observations. However, this phenomenon was not observed in the small-scale cylindrical well. An effect of the fluid surface tension was also observed and information on the suspension characteristics have helped elucidate the effect of scale on flow transition and particle off-bottom suspension in shaken systems. Ducci and Weheliye (2014) AIChE J., 60(11): 3951-3968. Weheliye et al (2013) AIChE J., 59(1): 334-344. Rodriguez et al (2013) ChERD, 91: 2084-2097. Rodriguez et al (2014) BEJ, 82: 10-21

Study on mixing characteristics in shaken microwell systems

Shaken microwell plates are widely used for early bioprocess development as they allow a large number of experiments to be performed in parallel by using small amount of materials. Despite their widespread use, microwell plates have not been characterised from an engineering viewpoint. In this study, mixing time measurements were carried out in two wells of square and cylindrical cross sections for small orbital diameter shaker, do = 3 mm, commonly used in commercial microwell platforms (i.e. ThermoMixer) and compared against measurements obtained in lab scale reactors for larger orbital diameters. The Dual Indicator System for Mixing Time (DISMT) method was employed for all the operating conditions investigated, and a range of rotational speeds was identified where mixing is less effective due to reduced free surface oscillation. An effective scaling parameter between microwell platforms and lab scale reactors was identified based on the natural frequency of the system, which depends only on fill volume, size and cross section of the reactor