On the rate of black hole binary mergers in galactic nuclei due to dynamical hardening

We assess the contribution of dynamical hardening by direct three-body scattering interactions to the rate of stellar-mass black hole binary (BHB) mergers in galactic nuclei. We derive an analytic model for the single-binary encounter rate in a nucleus with spherical and disk components hosting a super-massive black hole (SMBH). We determine the total number of encounters $N_{\rm GW}$ needed to harden a BHB to the point that inspiral due to gravitational wave emission occurs before the next three-body scattering event. This is done independently for both the spherical and disk components. Using a Monte Carlo approach, we refine our calculations for $N_{\rm GW}$ to include gravitational wave emission between scattering events. For astrophysically plausible models we find that typically $N_{\rm GW} \lesssim$ 10. We find two separate regimes for the efficient dynamical hardening of BHBs: (1) spherical star clusters with high central densities, low velocity dispersions and no significant Keplerian component; and (2) migration traps in disks around SMBHs lacking any significant spherical stellar component in the vicinity of the migration trap, which is expected due to effective orbital inclination reduction of any spherical population by the disk. We also find a weak correlation between the ratio of the second-order velocity moment to velocity dispersion in galactic nuclei and the rate of BHB mergers, where this ratio is a proxy for the ratio between the rotation- and dispersion-supported components. Because disks enforce planar interactions that are efficient in hardening BHBs, particularly in migration traps, they have high merger rates that can contribute significantly to the rate of BHB mergers detected by the advanced Laser Interferometer Gravitational-Wave Observatory.Comment: 13 pages, 9 figures, accepted for publication in MNRA

In-situ optical characterisation of the spatial dynamics of liquid crystalline nanocomposites

Liquid crystalline nanocomposites are a novel class of hybrid fluid materials, which are currently attracting significant interest from the photonics community. Such fluid nano-composites are based on low-dimensional nanoparticles (carbon nanotubes, graphene, transition metal dichalcogenides (TMDCs), metal nanoparticles etc.) dispersed in a fluidic host material. Liquid crystalline properties can either be provided by using a liquid crystal host fluid, or, through the solvent-induced self-assembly of particles. They possess a unique capability to interact with light, utilising many possibilities in plasmonics and quantum optics while they can also be integrated on Si chip by means of microfluidic technology. Integration of the nanocomposites on chip allows for dynamic control of the dispersed particle ordering through the application of various external stimuli. However, this dynamic control requires a suitable characterisation technique to fully understand the time evolution of metastructure formation. Integrated nanocomposites are characterised by the particle concentration at different points on chip, while the individual particles are defined by their sizes, xyz positions and orientation relative to the chip architecture. Here, we present a method by which all the required information for complete characterisation of the system can be obtained using a single spectroscopic technique- Raman spectroscopy- and how changes in the system can then be monitored during device operation. Liquid crystalline nanocomposites have been synthesised based on two-dimensional (2D) materials including graphene oxide (GO) and TMDCs dispersed in either commercially available liquid crystals or various organic solvents. We present both numerical analysis of the theoretical practicability of the use of Raman spectroscopy to extrapolate the desired nanocomposite properties and the experimental confirmation of the achievability of these measurements for the full range of synthesised nanocomposites

Model evaluation of marine primary organic aerosol emission schemes

In this study, several marine primary organic aerosol (POA) emission schemes have been evaluated using the GEOS-Chem chemical transport model in order to provide guidance for their implementation in air quality and climate models. These emission schemes, based on varying dependencies of chlorophyll <i>a</i> concentration ([chl <i>a</i>]) and 10 m wind speed (<i>U</i><sub>10</sub>), have large differences in their magnitude, spatial distribution, and seasonality. Model comparison with weekly and monthly mean values of the organic aerosol mass concentration at two coastal sites shows that the source function exclusively related to [chl <i>a</i>] does a better job replicating surface observations. Sensitivity simulations in which the negative <i>U</i><sub>10</sub> and positive [chl <i>a</i>] dependence of the organic mass fraction of sea spray aerosol are enhanced show improved prediction of the seasonality of the marine POA concentrations. A top-down estimate of submicron marine POA emissions based on the parameterization that compares best to the observed weekly and monthly mean values of marine organic aerosol surface concentrations has a global average emission rate of 6.3 Tg yr<sup>−1</sup>. Evaluation of existing marine POA source functions against a case study during which marine POA contributed the major fraction of submicron aerosol mass shows that none of the existing parameterizations are able to reproduce the hourly-averaged observations. Our calculations suggest that in order to capture episodic events and short-term variability in submicron marine POA concentration over the ocean, new source functions need to be developed that are grounded in the physical processes unique to the organic fraction of sea spray aerosol

Coastal iodine emissions: part 2. Chamber experiments of particle formation from Laminaria digitata-derived and laboratory-generated I2

Laboratory studies into particle formation from Laminaria digitata macroalgae were undertaken to elucidate aerosol formation for a range of I2 (0.3−76 ppbv) and O3(<3−96 ppbv) mixing ratios and light levels (EPAR = 15, 100,and 235 μmol photons m−2 s−1). No clear pattern was observed for I2 or aerosol parameters as a function of light levels. Aerosol mass fluxes and particle number concentrations,were, however, correlated with I2 mixing ratios for low O3mixing ratios of <3 ppbv (R2 = 0.7 and 0.83, respectively for low light levels, and R2 = 0.95 and 0.98, respectively for medium lightlevels). Additional experiments into particle production as a function of laboratory-generated I2, over a mixing ratio range of 1−8ppbv, were conducted under moderate O3 mixing ratios (∼24 ppbv) where a clear, 100-fold or greater, increase in the aeroso lnumber concentrations and mass fluxes was observed compared to the low O3 experiments. A linear relationship between particle concentration and I2 was found, in reasonable agreement with previous studies. Scaling the laboratory relationship to aerosol concentrations typical of the coastal boundary layer suggests a I2 mixing ratio range of 6−93 pptv can account for the observed particle production events. Aerosol number concentration produced from I2 is more than a factor of 10 higher than thatproduced from CH2I2 for the same mixing ratios

Evidence of atmospheric nanoparticle formation from emissions of marine microorganisms

International audienceEarth, as a whole, can be considered as a living organism emitting gases and particles into its atmosphere, in order to regulate its own temperature. In particular, oceans may respond to climate change by emitting particles that ultimately will influence cloud coverage. At the global scale, a large fraction of the aerosol number concentration is formed by nucleation of gas-phase species, but this process has never been directly observed above oceans. Here we present, using semicontrolled seawater-air enclosures, evidence that nucleation may occur from marine biological emissions in the atmosphere of the open ocean. We identify iodine-containing species as major precursors for new particle clusters’ formation, while questioning the role of the commonly accepted dimethyl sulfide oxidation products, in forming new particle clusters in the region investigated and within a time scale on the order of an hour. We further show that amines would sustain the new particle formation process by growing the new clusters to larger sizes. Our results suggest that iodine-containing species and amines are correlated to different biological tracers. These observations, if generalized, would call for a substantial change of modeling approaches of the sea-to-air interactions

Coastal iodine emissions. 1. Release of I2 by Laminaria digitata in chamber experiments

Tidally exposed macroalgae emit large amounts of I2 and iodocarbons that produce hotspots of iodine chemistry and intense particle nucleation events in the coastal marine boundary layer. Current emission rates are poorly characterized, however,with reported emission rates varying by 3 orders of magnitude. In this study, I2 emissions from 25 Laminaria digitata samples were investigated in a simulation chamber using incoherent broadbandcavity-enhanced absorption spectroscopy (IBBCEAS). The chamber design allowed gradual extraction of seawater to simulate tidal emersion of algae. Samples were exposed to air with or without O3 and to varying irradiances. Emission of I2 occurred in four distinct stages: (1) moderate emissions from partially submerged samples;(2) a strong release by fully emerged samples; (3) slowing or stopping of I2 release; and (4) later pulses of I2 evident in some samples. Emission rates were highly variable and ranged from 7to 616 pmol min−1 gFW−1 in ozone-free air, with a median value of 55 pmol min−1 gFW−1 for 20 samples

'Let me take care of you': what can healthcare learn from a high-end restaurant to improve the patient experience?

Background: The patient experience is associated with patient satisfaction and health outcomes, presenting a key challenge in healthcare. The objective of the study was to explore the principles of care in and beyond healthcare, namely in a three Michelin-starred restaurant, and consider what, if any, principles of care from the diners’ experience could be transferrable to healthcare. Methods: The principles of care were first explored as part of observational fieldwork in a healthcare day surgery unit and restaurant respectively, focusing on communication between the professionals and the patients or the diners. Care was subsequently explored in a series of public engagement events across the UK. The events used immersive simulation to recreate the healthcare and the dining experiences for the general public, and to stimulate discussion. Results: A thematic analysis of the engagement discussions identified overarching themes in how care was experienced in and through communication; “informed, not bombarded”, “conversation, not interrogation”, “environment is communication”, and “being met as a person”. The themes suggested how the participants in simulation felt about the care they received in real time and provided recommendations for improved clinical practice. Conclusions: While practice improvements in healthcare are challenging, the patient experience could be enhanced by learning relational aspects of care from other sectors, including the high-end restaurant industry that focuses on meeting persons’ needs. Simulation provides a new kind of opportunity to bring professionals and patients together for focused discussions, prompted by immersive experiences of care and communication

Spitzer IRS Spectral Mapping of the Toomre Sequence: Spatial Variations of PAH, Gas, and Dust Properties in Nearby Major Mergers

We have mapped the key mid-IR diagnostics in eight major merger systems of the Toomre Sequence (NGC4676, NGC7592, NGC6621, NGC2623, NGC6240, NGC520, NGC3921, and NGC7252) using the Spitzer Infrared Spectrograph (IRS). With these maps, we explore the variation of the ionized-gas, PAH, and warm-gas (H_2) properties across the sequence and within the galaxies. While the global PAH interband strength and ionized gas flux ratios ([Ne III]/[Ne II]) are similar to those of normal star forming galaxies, the distribution of the spatially resolved PAH and fine structure line flux ratios is significant different from one system to the other. Rather than a constant H_2/PAH flux ratio, we find that the relation between the H_2 and PAH fluxes is characterized by a power law with a roughly constant exponent (0.61+/-0.05) over all merger components and spatial scales. While following the same power law on local scales, three galaxies have a factor of ten larger integrated (i.e. global) H_2/PAH flux ratio than the rest of the sample, even larger than what it is in most nearby AGNs. These findings suggest a common dominant excitation mechanism for H_2 emission over a large range of global H_2/PAH flux ratios in major mergers. Early merger systems show a different distribution between the cold (CO J=1-0) and warm (H_2) molecular gas component, which is likely due to the merger interaction. Strong evidence for buried star formation in the overlap region of the merging galaxies is found in two merger systems (NGC6621 and NGC7592) as seen in the PAH, [Ne II], [Ne III], and warm gas line emission, but with no apparent corresponding CO (J=1-0) emission. Our findings also demonstrate that the variations of the physical conditions within a merger are much larger than any systematic trends along the Toomre Sequence.Comment: 35 pages, accepted for publication in ApJ

Analytics in online and offline language learning environments: the role of learning design to understand student online engagement

Language education has a rich history of research and scholarship focusing on the effectiveness of learning activities and the impact these have on student behaviour and outcomes. One of the basic assumptions in foreign language pedagogy and CALL in particular is that learners want to be able to communicate effectively with native speakers of their chosen language. Combining principles of learning analytics and Big Data with learning design, this study used a student activity based taxonomy adopted by the Open University UK to inform module design. The learning designs of four introductory and intermediary language education modules and online engagement of 2111 learners were contrasted using weekly learning design data. In this study, we aimed to explore how learning design decisions made by language teachers influenced students’ engagement in the VLE. Using fixed effect models, our findings indicated that 55% of variance of weekly online engagement in these four modules was explained by the way language teachers designed weekly learning design activities. Our learning analytics study highlights the potential affordances for CALL researchers to use the power of learning design and big data to explore and understand the complexities and dynamics of language learning for students and teachers

Policy Entrepreneurship and Multilevel Governance: A Comparative Study of European Cross-Border Regions

This article was publsihed in the journal, Environment and Planning C [© Pion]. The definitive version is available at: http://www.envplan.com/C.htmlThis article addresses the recent proliferation of Cross-Border Regions, or Euroregions, in Europe. It argues that EU multi-level governance patterns generate opportunities for entrepreneurial policy organisations to attract policy tasks and resources. This is conceptualised as policy entrepreneurship and applied to a comparative case study analysis of three Euroregions: EUREGIO (Germany – Netherlands), Viadrina (Poland – Germany) and Tyrol (Austria – Italy). The analysis focuses on the ability of these initiatives to establish themselves as autonomous organisations. It finds considerable variation across the cases in this respect. Following on from this, the paper shows how different administrative and institutional environments in different EU member states affect the ability of Euroregions to engage in policy entrepreneurship. It concludes that is it premature to perceive Euroregions as new types of regional territorial entities; rather, they are part of the policy innovation scenario enabled by EU multi-level governance