Mechanically-tunable bandgap closing in 2D graphene phononic crystals

We present a tunable phononic crystal which can be switched from a mechanically insulating to a mechanically conductive (transmissive) state. Specifically, in our simulations for a phononic lattice under biaxial tension (σxx = σyy = 0.01 N m−1), we find a bandgap for out-of-plane phonons in the range of 48.8–56.4 MHz, which we can close by increasing the degree of tension uniaxiality (σxx/σyy) to 1.7. To manipulate the tension distribution, we design a realistic device of finite size, where σxx/σyy is tuned by applying a gate voltage to a phononic crystal made from suspended graphene. We show that the bandgap closing can be probed via acoustic transmission measurements and that the phononic bandgap persists even after the inclusion of surface contaminants and random tension variations present in realistic devices. The proposed system acts as a transistor for MHz-phonons with an on/off ratio of 105 (100 dB suppression) and is thus a valuable extension for phonon logic applications. In addition, the transition from conductive to isolating can be seen as a mechanical analogue to a metal-insulator transition and allows tunable coupling between mechanical entities (e.g. mechanical qubits)

Dynamics and efficient conversion of excitons to trions in non-uniformly strained monolayer WS2

In recent years, there has been ongoing effort in achieving efficient transport of excitons in monolayer transition metal dichalcogenides subjected to highly non-uniform strain. Here we investigate the transport of excitons and trions in monolayer semiconductor WS2 subjected to controlled non-uniform mechanical strain. An atomic force microscope (AFM)-based setup is applied to actively control and tune the strain profiles by indenting the monolayer with an AFM tip. Optical spectroscopy is used to reveal the dynamics of the excited carriers. The non-uniform strain configuration locally changes the valence and conduction bands of WS2, giving rise to effective forces attracting excitons and trions towards the point of maximum strain underneath the AFM tip. We observe large changes in the photoluminescence spectra of WS2 under strain, which we interpret using a drift–diffusion model. We show that the transport of neutral excitons, a process that was previously thought to be efficient in non-uniformly strained two-dimensional semiconductors and termed as funnelling, is negligible at room temperature, in contrast to previous observations. Conversely, we discover that redistribution of free carriers under non-uniform strain profiles leads to highly efficient conversion of excitons to trions. Conversion efficiency reaches up to about 100% even without electrical gating. Our results explain inconsistencies in previous experiments and pave the way towards new types of optoelectronic devices

Primary Care Atrial Fibrillation Service: outcomes from consultant-led anticoagulation assessment clinics in the primary care setting in the UK

OBJECTIVE: Stroke-risk in atrial fibrillation (AF) can be significantly reduced by appropriate thromboembolic prophylaxis. However, National Institute for Health and Care Excellence estimates suggest that up to half of eligible patients with AF are not anticoagulated, with severe consequences for stroke prevention. We aimed to determine the outcome of an innovative Primary Care AF (PCAF) service on anticoagulation uptake in a cohort of high-risk patients with AF in the UK. METHODS: The PCAF service is a novel cooperative pathway providing specialist resources within general practitioner (GP) practices. It utilises a four-phase protocol to identify high-risk patients with AF (CHA(2)DS(2)-VASc ≥1) who are suboptimally anticoagulated, and delivers Consultant-led anticoagulation assessment within the local GP practice. We assessed rates of anticoagulation in high-risk patients before and after PCAF service intervention, and determined compliance with newly-initiated anticoagulation at follow-up. RESULTS: The PCAF service was delivered in 56 GP practices (population 386 624; AF prevalence 2.1%) between June 2012 and June 2014. 1579 high-risk patients with AF with suboptimal anticoagulation (either not taking any anticoagulation or taking warfarin but with a low time-in-therapeutic-range) were invited for review, with 86% attending. Of 1063 eligible patients on no anticoagulation, 1020 (96%) agreed to start warfarin (459 (43%)) or a non-vitamin K antagonist oral anticoagulant (NOAC, 561 (53%)). The overall proportion of eligible patients receiving anticoagulation improved from 77% to 95% (p<0.0001). Additionally, 111/121 (92%) patients suboptimally treated with warfarin agreed to switch to a NOAC. Audit of eight practices after 195 (185–606) days showed that 90% of patients started on a new anticoagulant therapy had continued treatment. Based on data extrapolated from previous studies, around 30–35 strokes per year may have been prevented in these previously under-treated high-risk patients. CONCLUSIONS: Systematic identification of patients with AF with high stroke-risk and consultation in PCAF consultant-led clinics effectively delivers oral anticoagulation to high-risk patients with AF in the community

Generating intense electric fields in 2D materials by dual ionic gating

The application of an electric field through two-dimensional materials (2DMs) modifies their properties. For example, a bandgap opens in semimetallic bilayer graphene while the bandgap shrinks in few-layer 2D semiconductors. The maximum electric field strength achievable in conventional devices is limited to ≤0.3 V/nm by the dielectric breakdown of gate dielectrics. Here, we overcome this limit by suspending a 2DM between two volumes of ionic liquid (IL) with independently controlled potentials. The potential difference between the ILs falls across an ultrathin layer consisting of the 2DM and the electrical double layers above and below it, producing an intense electric field larger than 4 V/nm. This field is strong enough to close the bandgap of few-layer WSe2, thereby driving a semiconductor-to-metal transition. The ability to apply fields an order of magnitude higher than what is possible in dielectric-gated devices grants access to previously-inaccessible phenomena occurring in intense electric fields

Neutral and charged excitons interplay in non-uniformly strain-engineered WS2

We investigate the response of excitons in two-dimensional semiconductors to nonuniformity of mechanical strain. In our approach to non-uniform strain-engineering, a WS2 monolayer is suspended over a triangular hole. Large (>2%), strongly non-uniform (>0.28% µm–1), and in-situ tunable strain is induced in WS2 by pressurizing it with inert gas. We observe a pronounced shift of the spectral weight from neutral to charged excitons at the center of the membrane, in addition to well-known strain-dependent bandgap modification. We show that the former phenomenon is a signature of a new effect unique for non-uniform strain: funneling of free carriers towards the region of high strain followed by neutral to charged exciton conversion. Our result establishes non-uniform strain engineering as a novel and useful experimental 'knob' for tuning optoelectronic properties of 2D semiconductors

Towards tunable graphene phononic crystals

Phononic crystals (PnCs) are artificially patterned media exhibiting bands of allowed and forbidden zones for phonons—in analogy to the electronic band structure of crystalline solids arising from the periodic arrangement of atoms. Many emerging applications of PnCs from solid-state simulators to quantum memories could benefit from the on-demand tunability of the phononic band structure. Here, we demonstrate the fabrication of suspended graphene PnCs in which the phononic band structure is controlled by mechanical tension applied electrostatically. We show signatures of a mechanically tunable phononic band gap. The experimental data supported by simulation suggests a phononic band gap at 28–33 MHz in equilibrium, which upshifts by 9 MHz under a mechanical tension of 3.1 N m−1. This is an essential step towards tunable phononics paving the way for more experiments on phononic systems based on 2D materials

Prediction of cardiac worsening through to cardiogenic shock in patients with acute heart failure

Aims: Acute heart failure (AHF) can result in worsening of heart failure (WHF), cardiogenic shock (CS), or death. Risk factors for these adverse outcomes are not well characterized. This study aimed to identify predictors for WHF or new‐onset CS in patients hospitalized for AHF. Methods and results: Prospective cohort study enrolling consecutive patients with AHF admitted to a large tertiary care centre with follow‐up until death or discharge. WHF was defined by the RELAX‐AHF‐2 criteria. CS was defined as SCAI stages B–E. Potential predictors were assessed by fitting logistic regression models adjusted for age and sex. N = 233 patients were enrolled, median age was 78 years, and 80 were women (35.9%). Ischaemic cardiomyopathy was present in 82 patients (40.8%). Overall, 96 (44.2%) developed WHF and 18 (9.7%) CS. In‐hospital death (8/223, 3.6%) was related to both events (WHF: OR 6.64, 95% CI 1.21–36.55, P = 0.03; CS: OR 38.27, 95% CI 6.32–231.81, P &lt; 0.001). Chronic kidney disease (OR 2.20, 95% CI 1.25–3.93, P = 0.007), logarithmized serum creatinine (OR 2.90, 95% CI 1.51–5.82, P = 0.002), cystatin c (OR 1.86, 95% CI 1.27–2.77, P = 0.002), tricuspid valve regurgitation (OR 2.08, 95% CI 1.11–3.94, P = 0.023) and logarithmized pro‐adrenomedullin (OR 3.01, 95% CI 1.75–5.38, P &lt; 0.001) were significant predictors of WHF. Chronic kidney disease (OR 3.17, 95% CI 1.16–9.58, P = 0.03), cystatin c (OR 1.88, 95% CI 1.00–3.53, P = 0.045), logarithmized pro‐adrenomedullin (OR 2.90, 95% CI 1.19–7.19, P = 0.019), and tricuspid valve regurgitation (OR 10.44, 95% CI 2.61–70.00, P = 0.003) were significantly with new‐onset CS. Conclusions: Half of patients admitted with AHF experience WHF or new‐onset CS. Chronic kidney disease, tricuspid valve regurgitation, and elevated pro‐adrenomedullin concentrations predict these events. They could potentially serve as early warning signs for further deterioration in AHF patients

Temporal irregularity quantification and mapping of optical action potentials using wave morphology similarity

Background Cardiac optical mapping enables direct and high spatio-temporal resolution recording of action potential (AP) morphology. Temporal alterations in AP morphology are both predictive and consequent of arrhythmia. Here we sought to test if methods that quantify regularity of recorded waveforms could be applied to detect and quantify periods of temporal instability in optical mapping datasets in a semi-automated, user-unbiased manner. Methods and results We developed, tested and applied algorithms to quantify optical wave similarity (OWS) to study morphological temporal similarity of optically recorded APs. Unlike other measures (e.g. alternans ratio, beat-to-beat variability, arrhythmia scoring), the quantification of OWS is achieved without a restrictive definition of specific signal points/features and is instead derived by analysing the complete morphology from the entire AP waveform. Using model datasets, we validated the ability of OWS to measure changes in AP morphology, and tested OWS mapping in guinea pig hearts and mouse atria. OWS successfully detected and measured alterations in temporal regularity in response to several proarrhythmic stimuli, including alterations in pacing frequency, premature contractions, alternans and ventricular fibrillation. Conclusion OWS mapping provides an effective measure of temporal regularity that can be applied to optical datasets to detect and quantify temporal alterations in action potential morphology. This methodology provides a new metric for arrhythmia inducibility and scoring in optical mapping datasets

Оценка инвестиционной деятельности электроэнергетической компании

Объектом исследования является электроэнергетическая компания ПАО «ТРК». Предметом исследования выступают оценка эффективности инвестиций и инвестиционная деятельность предприятий электроэнергетики. Цель работы - анализ показателей оценки эффективности инвестиционной деятельности и разработка рекомендаций по совершенствованию оценки инвестиционной деятельности на примере компании ПАО «Томская распределительная компания».The object of this study is to electric power company PJSC "TRK". The subject of research are the evaluation of the effectiveness of investments and investment activity of the enterprises of electric power industry. Purpose - analysis of indicators for assessing the effectiveness of investment and development of recommendations to improve the assessment of investment activity on the example of the company PJSC "Tomsk Distribution Company"