Measuring and tailoring the Dzyaloshinskii-Moriya interaction in perpendicularly magnetized thin films

We investigate the Dzyaloshinskii-Moriya interactions (DMIs) in perpendicularly magnetized thin films of Pt/Co/Pt and Pt/Co/Ir/Pt. To study the effective DMI, arising at either side of the ferromagnet, we use a field-driven domain wall creep-based method. The use of only magnetic field removes the possibility of mixing with current-related effects such as spin Hall effect or Rashba field, as well as the complexity arising from lithographic patterning. Inserting an ultrathin layer of Ir at the top Co/Pt interface allows us to access the DMI contribution from the top Co/Pt interface. We show that the insertion of a thin Ir layer leads to reversal of the sign of the effective DMI acting on the sandwiched Co layer, and therefore continuously changes the domain wall structure from the right- to the left-handed Néel wall. The use of two DMI-active layers offers an efficient way of DMI tuning and enhancement in thin magnetic films. The comparison with an epitaxial Pt/Co/Pt multilayer sheds more light on the origin of DMI in polycrystalline Pt/Co/Pt films and demonstrates an exquisite sensitivity to the exact details of the atomic structure at the film interfaces

Cosmic Swarms: A search for Supermassive Black Holes in the LISA data stream with a Hybrid Evolutionary Algorithm

We describe a hybrid evolutionary algorithm that can simultaneously search for multiple supermassive black hole binary (SMBHB) inspirals in LISA data. The algorithm mixes evolutionary computation, Metropolis-Hastings methods and Nested Sampling. The inspiral of SMBHBs presents an interesting problem for gravitational wave data analysis since, due to the LISA response function, the sources have a bi-modal sky solution. We show here that it is possible not only to detect multiple SMBHBs in the data stream, but also to investigate simultaneously all the various modes of the global solution. In all cases, the algorithm returns parameter determinations within $5\sigma$ (as estimated from the Fisher Matrix) of the true answer, for both the actual and antipodal sky solutions.Comment: submitted to Classical & Quantum Gravity. 19 pages, 4 figure

Model Selection for Degree-corrected Block Models

The proliferation of models for networks raises challenging problems of model selection: the data are sparse and globally dependent, and models are typically high-dimensional and have large numbers of latent variables. Together, these issues mean that the usual model-selection criteria do not work properly for networks. We illustrate these challenges, and show one way to resolve them, by considering the key network-analysis problem of dividing a graph into communities or blocks of nodes with homogeneous patterns of links to the rest of the network. The standard tool for doing this is the stochastic block model, under which the probability of a link between two nodes is a function solely of the blocks to which they belong. This imposes a homogeneous degree distribution within each block; this can be unrealistic, so degree-corrected block models add a parameter for each node, modulating its over-all degree. The choice between ordinary and degree-corrected block models matters because they make very different inferences about communities. We present the first principled and tractable approach to model selection between standard and degree-corrected block models, based on new large-graph asymptotics for the distribution of log-likelihood ratios under the stochastic block model, finding substantial departures from classical results for sparse graphs. We also develop linear-time approximations for log-likelihoods under both the stochastic block model and the degree-corrected model, using belief propagation. Applications to simulated and real networks show excellent agreement with our approximations. Our results thus both solve the practical problem of deciding on degree correction, and point to a general approach to model selection in network analysis

The Malthusian Paradox: performance in an alternate reality game

The Malthusian Paradox is a transmedia alternate reality game (ARG) created by artists Dominic Shaw and Adam Sporne played by 300 participants over three months. We explore the design of the game, which cast players as agents of a radical organisation attempting to uncover the truth behind a kidnapping and a sinister biotech corporation, and highlight how it redefined performative frames by blurring conventional performer and spectator roles in sometimes discomforting ways. Players participated in the game via a broad spectrum of interaction channels, including performative group spectacles and 1-to-1 engagements with game characters in public settings, making use of low- and high-tech physical and online artefacts including bespoke and third party websites. Players and game characters communicated via telephony and social media in both a designed and an ad-hoc manner. We reflect on the production and orchestration of the game, including the dynamic nature of the strong episodic narrative driven by professionally produced short films that attempted to respond to the actions of players; and the difficulty of designing for engagement across hybrid and temporally expansive performance space. We suggest that an ARG whose boundaries are necessarily unclear affords rich and emergent, but potentially unsanctioned and uncontrolled, opportunities for interactive performance, which raises significant challenges for design

Referral pathways for TIA patients avoiding hospital admission : a scoping review

Objective: To identify the features and effects of a pathway for emergency assessment and referral of patients with suspected transient ischaemic attack (TIA) in order to avoid admission to hospital.Design: Scoping review.Data sources: PubMed, CINAHL Web of Science, Scopus.Study selection: Reports of primary research on referral of patients with suspected TIA directly to specialist outpatient services.Data extraction: We screened studies for eligibility and extracted data from relevant studies. Data were analysed to describe setting, assessment and referral processes, treatment, implementation and outcomes.Results: 8 international studies were identified, mostly cohort designs. 4 pathways were used by family doctors and 3 pathways by emergency department physicians. No pathways used by paramedics were found. Referrals were made to specialist clinic either directly or via a 24-hour helpline. Practitioners identified TIA symptoms and risk of further events using a checklist including the ABCD2 tool or clinical assessment. Antiplatelet medication was often given, usually aspirin unless contraindicated. Some patients underwent tests before referral and discharge. 5 studies reported reduced incident of stroke at 90 days, from 6–10% predicted rate to 1.3–2.1% actual rate. Between 44% and 83% of suspected TIA cases in these studies were referred through the pathways.Conclusions: Research literature has focused on assessment and referral by family doctors and ED physicians to reduce hospitalisation of patients with TIA. No pathways for paramedical use were reported. We will use results of this scoping review to inform development of a paramedical referral pathway to be tested in a feasibility trial

Microstructurally controlled trace element (Zr, U–Pb) concentrations in metamorphic rutile: An example from the amphibolites of the Bergen Arcs

As a common constituent of metamorphic assemblages, rutile provides constraints on the timing and conditions of rock transformation at high resolution. However, very little is known about the links between trace element mobility and rutile microstructures that result from syn‐metamorphic deformation. To address this issue, here we combine in situ LA‐ICP‐MS and SHRIMP trace element data with EBSD microstructural analyses to investigate the links between rutile lattice distortions and Zr and U–Pb systematics. Furthermore, we apply this integrated approach to constrain further the temperature and timing of amphibolite‐facies metamorphism and deformation in the Bergen Arcs of southwestern Norway. In outcrop, the formation of porphyroblastic rutile in dynamically hydrated leucocratic domains of otherwise rutile‐poor statically‐hydrated amphibolite provides key contextual information on both the ambient conditions of hydration and deformation and the composition of the reactive fluid. Rutile in amphibolite recorded ambient metamorphic temperatures of ~ 590–730°C during static hydration of the granulitic precursor. In contrast, rutile from leucocratic domains in the directly adjacent shear zone indicates that deformation was accompanied by a localized increase in temperature. These higher temperatures are recorded in strain‐free rutile (~600–860°C) and by Zr concentration measurements on low‐angle boundaries and shear bands (620–820°C). In addition, we also observe slight depletions of Zr and U along rutile low‐angle boundaries relative to strain‐free areas in deformed grains from the shear zone. This indicates that crystal‐plastic deformation facilitated the compositional re‐equilibration of rutile upon cooling to slightly below the peak temperature of deformation. Cessation of deformation at mid‐crustal conditions near ~ 600°C is recorded by late stage growth of small (< 150 µm) rutile in the high strain zones. U–Pb age data obtained from the strain‐free and distorted rutile grains cluster in distinct populations of 437.4 ± 2.7 Ma and c. 405–410 Ma, respectively. These different ages are interpreted to reflect the difference in closure for thermally‐induced Pb diffusion between undeformed and deformed rutile during post‐deformation exhumation and cooling. Thus, our results provide a reconstruction of the thermochronological history of the amphibolite‐facies rocks of the Lindås Nappe and highlight the importance of integration of microstructural data during application of thermometers and geochronometers

Pumping up the [N I] nebular lines

The optical [N I] doublet near 5200 {\AA} is anomalously strong in a variety of emission-line objects. We compute a detailed photoionization model and use it to show that pumping by far-ultraviolet (FUV) stellar radiation previously posited as a general explanation applies to the Orion Nebula (M42) and its companion M43; but, it is unlikely to explain planetary nebulae and supernova remnants. Our models establish that the observed nearly constant equivalent width of [N I] with respect to the dust-scattered stellar continuum depends primarily on three factors: the FUV to visual-band flux ratio of the stellar population; the optical properties of the dust; and the line broadening where the pumping occurs. In contrast, the intensity ratio [N I]/H{\beta} depends primarily on the FUV to extreme-ultraviolet ratio, which varies strongly with the spectral type of the exciting star. This is consistent with the observed difference of a factor of five between M42 and M43, which are excited by an O7 and B0.5 star respectively. We derive a non-thermal broadening of order 5 km/s for the [N I] pumping zone and show that the broadening mechanism must be different from the large-scale turbulent motions that have been suggested to explain the line-widths in this H II region. A mechanism is required that operates at scales of a few astronomical units, which may be driven by thermal instabilities of neutral gas in the range 1000 to 3000 K. In an appendix, we describe how collisional and radiative processes are treated in the detailed model N I atom now included in the Cloudy plasma code.Comment: ApJ in press. 8 pages of main paper plus 11 pages of appendices, with 13 figures and 12 table

Star formation in galaxies falling into clusters along supercluster-scale filaments

With the help of a statistical parameter derived from optical spectra, we show that the current star formation rate of a galaxy, falling into a cluster along a supercluster filament, is likely to undergo a sudden enhancement before the galaxy reaches the virial radius of the cluster. From a sample of 52 supercluster-scale filaments of galaxies joining a pair of rich clusters of galaxies within the two-degree Field Redshift Survey region, we find a significant enhancement of star formation, within a narrow range between 2-3 h/70 Mpc of the centre of the cluster into which the galaxy is falling. This burst of star formation is almost exclusively seen in the fainter dwarf galaxies (M_B> -20). The relative position of the peak does not depend on whether the galaxy is a member of a group or not, but non-group galaxies have on average a higher rate of star formation immediately before falling into a cluster. From the various trends, we conclude that the predominant process responsible for this rapid burst is the close interaction with other galaxies falling into the cluster along the same filament, if the interaction occurs before the gas reservoir of the galaxy gets stripped off due to the interaction with the intracluster medium.Comment: 9 pages, 6 figures, 2 tables, accepted for publication in MNRA