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21 new long-term variables in the GX 339−4 field: two years of MeerKAT monitoring
No full textWe present 21 new long-term variable radio sources found commensally in two years of weekly MeerKAT monitoring of the low-mass X-ray binary GX 339−4. The new sources vary on time scales of weeks to months and have a variety of light curveshapes and spectral index properties. Three of the new variable sources are coincident with multi-wavelength counterparts; and one of these is coincident with an optical source in deep MeerLICHT images. For most sources, we cannot eliminate refractive scintillation of active galactic nuclei as the cause of the variability. These new variable sources represent 2.2 ± 0.5 per cent of the unresolved sources in the field, which is consistent with the 1-2 per cent variability found in past radio variability surveys. However, we expect to find short-term variable sources in the field as well as these 21 new long-term variable sources. We present the radio light curves and spectral index variability of the new variable sources, as well as the absolute astrometry and matches to coincident sources at other wavelengths
Initial Conditions for Star Formation: A Physical Description of the Filamentary ISM
No full textThe interstellar medium contains filamentary structure over a wide range of scales. Understanding the role of this structure, both as a conduit of gas across the scales and a diagnostic tool of local physics, is a major focus of star formation studies. We review recent progress in studying filamentary structure in the ISM, interpreting its properties in terms of physical processes, andexploring formation and evolution scenarios. We include structures from galactic-scale filaments to tenth-of-a-parsec scale filaments, comprising both molecular and atomic structures, from both observational and theoretical perspectives. In addition to the literature overview, we assemble a large amount of catalogue data from different surveys and provide the most comprehensive census of filamentary structures to date. Our census consists of 22 803 filamentary structures, facilitating a holistic perspective and new insights. We use our census to conduct a meta-analysis, leading to a description of filament properties over four orders of magnitudes in length and eight in mass. Our analysis emphasises the hierarchical and dynamical nature of filamentary structures. Filaments do not live in isolation, nor they generally resemble static structures close to equilibrium. We propose that accretion during filament formation and evolution sets some of the key scaling properties of filaments. This highlights the role of accretion during filament formation and evolution and also in setting the initial conditions for star formation. Overall, the study of filamentary structures during the past decade has been observationally driven. While great progress has been made on measuring the basic properties of filaments, our understanding of their formation and evolution is clearly lacking. In this context, we identify a number of directions and questions we consider most pressing for the field
People in a Pandemic: Rethinking the role of ‘Community’ in Community Resilience Practices
No full textHow has the idea of community featured in attempts to build resilience to emergencies? The paper explores this question by presenting evidence from interviews with emergency responders across the world in the midst of the early and uncertain phases of the Covid-19 pandemic. Although reflecting different contexts, we discern two ways in which the notion of community featured in authorities’ narrations of their efforts to respond to the pandemic. Firstly, we demonstrate how community was deployed as a discursive mechanism that offered a particular framing of the vulnerabilities the pandemic instigated. Departing from accounts that reduce people’s identities to demographic categories, the deployment of community stressed that the pandemic’s effects should be understood by the different, yet coexistent, vulnerabilities it brought to the surface for people. Such renditions of vulnerability paved the way for styles of governance that prioritised adapting to the pandemic’s uncertain and indeterminate unfolding in the absence of prepared plans. Secondly, addressing a register of collective social life between individuals and the state, an emphasis on community engendered the decentralised arrangement of emergency governance with which resilience has become synonymous. Here, community proved pivotal in temporarily expanding resources to deal with an emergency whose effects threatened to exceed governments’ pre-existing capabilities. We substantiate this claim through examining how allusions to community worked to enrol non-state based efforts at response into a broader public security apparatus. Enveloped within the broader politics of emergency resilience, community shaped how the pandemic’s effects were understood whilst also ensuring adequate provisions for its governance
Recovering the second moment of the strain distribution from neutron Bragg edge data
No full textPoint by point strain scanning is often used to map the residual stress (strain) in engineering materials and components. However, the gauge volume and hence spatial resolution is limited by the beam defining apertures and can be anisotropic for very low and high diffraction (scattering) angles. Alternatively, wavelength resolved neutron transmission imaging has a potential to retrieve information tomographically about residual strain induced within materials through measurement in transmission of Bragg edges – crystallographic fingerprints whose locations and shapes depend on microstructure and strain distribution. In such a case the spatial resolution is determined by the geometrical blurring of the measurement setup and the detector point spread function. Mathematically, reconstruction of strain tensor field is described by the longitudinal ray transform; this transform has a non-trivial null-space, making direct inversion impossible. A combination of the longitudinal ray transform with physical constraints was used to reconstruct strain tensor fields in convex objects. To relax physical constraints and generalise reconstruction, a recently introduced concept of histogram tomography can be employed. Histogram tomography relies on our ability to resolve the distribution of strain in the beam direction, as we discuss in the paper. More specifically, Bragg edge strain tomography requires extraction of the second moment (variance about zero) of the strain distribution which has not yet been demonstrated in practice. In this paper we verify experimentally that the second moment can be reliably measured for a previously well characterised aluminium ring and plug sample. We compare experimental measurements against numerical calculation and further support our conclusions by rigorous uncertainty quantification of the estimated mean and variance of the strain distribution
A Laser-Atom Interaction Simulator derived from Quantum Electrodynamics
No full textA laser-atom interaction simulator derived from quantum electrodynamics (LASED) is presented, which has been developed in the python programming language. LASED allows a user to calculate the time evolution of a laser-excited atomic system. The model allows for any laser polarization, a Gaussian laser beam profile, a rotation of the reference frame chosen to define the states, and an averaging over the Doppler profile of an atomic beam. Examples of simulations using LASED are presented for excitation of calcium from the 41S0 state to the 41P1 state, for excitation from the helium 31D2 state excited by electron impact to the 101P1 state, and for laser excitation of caesium via the D2 line
Evaluating the Use of Phosphate to Mitigate Caustic-PbSCC of Alloy 690TT
No full textPhosphate additions to Pb-caustic water chemistry were investigated as possible avenue to mitigate against caustic Lead-Assisted Stress Corrosion Cracking (PbSCC) of Alloy 690TT at around 310°C. Dosing with 1,700 ppm of phosphate promoted a small beneficial effect in PbSCC resistance. However, with 3,000 ppm of phosphate, mitigation was only achieved for as received surfaces, whilst polished surfaces displayed localized attack. Advanced materials characterization revealed that a similar crack tip composition was generated in different solutions. It is suggested that phosphate decreased the PbSCC kinetics by partly sequestering Pb from the bulk environment, although not below the threshold value required to prevent cracking
Flexible sensors, circuits, and systems for bioelectronic interfacing
No full textBioelectronics is an emerging research area where human-made electronic systems interface, bidirectionally, with the electrical systems present in biology. Flexible electronics are a critical development for bioelectronic systems which can flex and stretch with the body. Printing based manufacturing approaches have been heavily investigated in recent years for creating bioelectronic systems, as screen printing can potentially provide scaled-up roll-to-roll based manufacturing while 3D and inkjet printing can potentially provide opportunities for personalisation. This paper presents a brief narrative review bioelectronics, the materials challenges in flexible sensors, circuits, and systems for bioelectronic interfacing, and examples of our approaches to tackling these challenges
Scaleability of dielectric susceptibility ϵzz with the number of layers and additivity of ferroelectric polarization in van der Waals semiconductors
No full textWe study the dielectric response of few layered crystals of various transition metal dichalcogenides (TMDs) and hexagonal Boron Nitride (hBN). We showed that the out-of-plane polarizability of a multilayer crystal (which characterizes response to the external displacement field) scales linearly with the number of layers, αNL zz = Nα1L zz , independently of the stacking configuration in the film. We also established additivity of ferroelectric polarizations of consecutive interfaces in case when such interfaces have broken inversion symmetry. Then we used the obtained data of monolayer α1L zz to calculate the values of the dielectric susceptibilities for semiconductor TMDs and hBN bulk crystals
Race and Histories of Place: the racialisation of representational space in Govanhill and Butetown
No full textWe argue that the stories told about the histories and nature of places, are vehicles for narrating race. Drawing on interviews with professionals and community workers in Butetown in Cardiff and Govanhill in Glasgow, we explore how they negotiated – and contested - racialized histories of place, constructing different versions or claims to belong. Drawing on Henri Lefebvre’s spatial concepts we explore this conceptualisation through examination of the two areas which have distinct histories, and present experiences, of migration and racialization. In discussion of the accounts from the two distinct areas we show that narratives of the past have a political resonance which shape accounts of current experiences of migration. Accounts of place are often related in relationship to comparisons with and narratives of other places and to global processes of trade and migration. Whilst these racialised narratives are contested, they also shape responses to social problems faced by communities