The effects of Prandtl number on the nonlinear dynamics of Kelvin-Helmholtz instability in two dimensions

Abstract EPSRC DT

Kelvin-Helmholtz billows above Richardson number 1/4

We study the dynamical system of a forced stratified mixing layer at finite Reynolds number $Re$, and Prandtl number $Pr=1$. We consider a hyperbolic tangent background velocity profile in the two cases of hyperbolic tangent and uniform background buoyancy stratifications. The system is forced in such a way that these background profiles are a steady solution of the governing equations. As is well-known, if the minimum gradient Richardson number of the flow, $Ri_m$, is less than a certain critical value $Ri_c$, the flow is linearly unstable to Kelvin-Helmholtz instability in both cases. Using Newton-Krylov iteration, we find steady, two-dimensional, finite amplitude elliptical vortex structures, i.e. `Kelvin-Helmholtz billows', existing above $Ri_c$. Bifurcation diagrams are produced using branch continuation, and we explore how these diagrams change with varying $Re$. In particular, when $Re$ is sufficiently high we find that finite amplitude Kelvin-Helmholtz billows exist at $Ri_m>1/4$, where the flow is linearly stable by the Miles-Howard theorem. For the uniform background stratification, we give a simple explanation of the dynamical system, showing the dynamics can be understood on a two-dimensional manifold embedded in state space, and demonstrate the cases in which the system is bistable. In the case of a hyperbolic tangent stratification, we also describe a new, slow-growing, linear instability of the background profiles at finite $Re$, which complicates the dynamics

Multidimensional cluster states using a single spin-photon interface coupled strongly to an intrinsic nuclear register

Photonic cluster states are a powerful resource for measurement-based quantum computing and loss-tolerant quantum communication. Proposals to generate multi-dimensional lattice cluster states have identified coupled spin-photon interfaces, spin-ancilla systems, and optical feedback mechanisms as potential schemes. Following these, we propose the generation of multi-dimensional lattice cluster states using a single, efficient spin-photon interface coupled strongly to a nuclear register. Our scheme makes use of the contact hyperfine interaction to enable universal quantum gates between the interface spin and a local nuclear register and funnels the resulting entanglement to photons via the spin-photon interface. Among several quantum emitters, we identify the silicon-29 vacancy centre in diamond, coupled to a nanophotonic structure, as possessing the right combination of optical quality and spin coherence for this scheme. We show numerically that using this system a 2x5-sized cluster state with a lower-bound fidelity of 0.5 and repetition rate of 65 kHz is achievable under currently realised experimental performances and with feasible technical overhead. Realistic gate improvements put 100-photon cluster states within experimental reach

Exploring the components, asymmetry and distribution of relationship quality in wild Barbary macaques (Macaca sylvanus)

Social relationships between group members are a key feature of many animal societies. The quality of social relationships has been described by three main components: value, compatibility and security, based on the benefits, tenure and stability of social exchanges. We aimed to analyse whether this three component structure could be used to describe the quality of social relationships in wild Barbary macaques (Macaca sylvanus). Moreover, we examined whether relationship quality was affected by the sex, age and rank differences between social partners, and investigated the asymmetric nature of social relationships. We collected over 1,900 hours of focal data on seven behavioural variables measuring relationship quality, and used principal component analysis to investigate how these variables clustered together. We found that relationship quality in wild Barbary macaques can be described by a three component structure that represents the value, compatibility and security of a relationship. Female-female dyads had more valuable relationships and same-age dyads more compatible relationships than any other dyad. Rank difference had no effect on the quality of a social relationship. Finally, we found a high degree of asymmetry in how members of a dyad exchange social behaviour. We argue that the asymmetry of social relationships should be taken into account when exploring the pattern and function of social behaviour in animal societies

Clinical features and management of erythromelalgia: long term follow-up of 46 cases

OBJECTIVES: To review our clinical experience of this rare condition and describe the clinical features and response to therapy in a cohort of patients with erythromelalgia (EM), a rare condition, characterised by paroxysmal hyperthermia of the extremities with erythema, pain and intense burning. METHODS: A review was made of the electronic and paper medical records of patients with the diagnosis of EM, with a telephone interview to verify and complete clinical information relating treatment and outcome. RESULTS: 46 patients (41 females) were included in this study. Mean age was 57 years and mean duration of symptoms was 16 years. Raynaud's phenomenon was present in 36 patients (80%) and 4 patients (9%) had systemic sclerosis. Smoking (current or previous) was identified as a possible risk factor in 26 cases and exposure to chronic vibration in 3 cases. Overall, the effect on quality of life was mild in 15% of cases, moderate in 30% and severe in 48%. The most common symptoms were burning (96%), heat (93%), pain (87%), and redness (83%). Symptoms affected the lower limbs in 98% of cases, upper limbs in 76%, face in 20% and trunk in 11%. Triggers included heat (85%), exercise (78%) and time of day (76%). Various medications were tried, showing poor effect in most cases. Intravenous iloprost was given to 27 patients, with benefit in 17 patients (63%). CONCLUSIONS: Erythromelalgia is a rare chronic debilitating condition. Exercise, heat and night time are common triggers. Current medical therapies are seldom effective and further research is sorely needed

Use of imaging for pre- and post-operative characterisation of ventral hernia: systematic review

OBJECTIVE: Complex ventral hernia repair is performed increasingly, exacerbated by the obesity epidemic. Imaging can characterise hernia morphology and diagnose recurrence. By systematic review we investigated the extent to which studies employ imaging. METHODS: The PubMed database was searched for studies of ventral hernia repair January 1995 to March 2016. Hernias of all size were eligible. Independent reviewers screened articles and extracted data from selected studies related to study design, use of pre- and post-operative hernia imaging, and the proportion of subjects imaged. The review was registered: PROSPERO CRD42016043071. RESULTS: 15,771 records were identified initially. 174 full-texts were examined and 158 ultimately included in the systematic review (31 randomised-controlled-trials; 32 cohort studies; 95 retrospective cohort studies). 31,874 subjects were reported overall. Only 19 (12%) studies employed pre-operative imaging for hernia characterisation and 46 (29%) post-operatively [equating to 511 (2%) of all preoperative subjects and 1123 (4%) post-operative]. Furthermore, most studies employing imaging did not do so in all subjects: Just six (4%) of the 158 studies used imaging in all subjects preoperatively and just 4 (3%) postoperatively, i.e. imaging was usually applied to a proportion of patients only. Moreover, the exact proportion was frequently not specified. Studies using imaging frequently stated that "imaging", "radiography" or "radiology" was used but did not specify the modality precisely nor the proportion of subjects imaged. CONCLUSION: Despite the ability to characterise ventral hernia morphology and recurrence with precision, most indexed studies do not employ imaging. Where imaging is used, data are often reported incompletely. Advances in knowledge: (1) This systematic review is the first to focus on the use of imaging in surgical studies of ventral hernia repair. (2) Studies of ventral hernia repair rarely use imaging, either to characterise hernias preoperatively or to diagnose recurrence, despite the latter being the primary outcome of most studies. (3) Failure to use imaging will result in incomplete hernia characterisation and underestimate recurrence rates in studies of surgical repair

Dimensionality Reduction and Pattern Recognition of Flow Regime Using Acoustic Data

In this study we investigated the novel application of Principal Component Analysis (PCA) in order to reduce the dimensionality of acoustic data. The acoustic data are recorded by fibre optic distributed acoustic sensors which are attached along a 3500 m pipe with a sampling frequency of 10 kHz and for a duration of 24 hours. Data collected from distributed acoustic sensors are very large and we need to identify the part that contains the most informative signals. The algorithm is applied to water, oil and gas datasets. We aimed to form a smaller dataset which preserves the pattern of the original dataset which is more efficient for further analysis. The result of this study will lead to automation of multiphase flow pattern recognition for oil and gas industry applications

Social interactions through the eyes of macaques and humans

Group-living primates frequently interact with each other to maintain social bonds as well as to compete for valuable resources. Observing such social interactions between group members provides individuals with essential information (e.g. on the fighting ability or altruistic attitude of group companions) to guide their social tactics and choice of social partners. This process requires individuals to selectively attend to the most informative content within a social scene. It is unclear how non-human primates allocate attention to social interactions in different contexts, and whether they share similar patterns of social attention to humans. Here we compared the gaze behaviour of rhesus macaques and humans when free-viewing the same set of naturalistic images. The images contained positive or negative social interactions between two conspecifics of different phylogenetic distance from the observer; i.e. affiliation or aggression exchanged by two humans, rhesus macaques, Barbary macaques, baboons or lions. Monkeys directed a variable amount of gaze at the two conspecific individuals in the images according to their roles in the interaction (i.e. giver or receiver of affiliation/aggression). Their gaze distribution to non-conspecific individuals was systematically varied according to the viewed species and the nature of interactions, suggesting a contribution of both prior experience and innate bias in guiding social attention. Furthermore, the monkeys’ gaze behavior was qualitatively similar to that of humans, especially when viewing negative interactions. Detailed analysis revealed that both species directed more gaze at the face than the body region when inspecting individuals, and attended more to the body region in negative than in positive social interactions. Our study suggests that monkeys and humans share a similar pattern of role-sensitive, species- and context-dependent social attention, implying a homologous cognitive mechanism of social attention between rhesus macaques and humans