Periodic Pulay method for robust and efficient convergence acceleration of self-consistent field iterations

Pulay's Direct Inversion in the Iterative Subspace (DIIS) method is one of the most widely used mixing schemes for accelerating the self-consistent solution of electronic structure problems. In this work, we propose a simple generalization of DIIS in which Pulay extrapolation is performed at periodic intervals rather than on every self-consistent field iteration, and linear mixing is performed on all other iterations. We demonstrate through numerical tests on a wide variety of materials systems in the framework of density functional theory that the proposed generalization of Pulay's method significantly improves its robustness and efficiency.Comment: Version 2 (with minor edits from version 1

Wavelet Shrinkage and Thresholding based Robust Classification for Brain Computer Interface

A macaque monkey is trained to perform two different kinds of tasks, memory aided and visually aided. In each task, the monkey saccades to eight possible target locations. A classifier is proposed for direction decoding and task decoding based on local field potentials (LFP) collected from the prefrontal cortex. The LFP time-series data is modeled in a nonparametric regression framework, as a function corrupted by Gaussian noise. It is shown that if the function belongs to Besov bodies, then using the proposed wavelet shrinkage and thresholding based classifier is robust and consistent. The classifier is then applied to the LFP data to achieve high decoding performance. The proposed classifier is also quite general and can be applied for the classification of other types of time-series data as well, not necessarily brain data

An evaluation of an educational intervention to reduce inappropriate cannulation and improve cannulation technique by paramedics

Background: Intravenous cannulation enables administration of fluids or drugs by paramedics in prehospital settings. Inappropriate use and poor technique carry risks for patients, including pain and infection. We aimed to investigate the effect of an educational intervention designed to reduce the rate of inappropriate cannulation and to improve cannulation technique. Method: We used a non-randomised control group design, comparing two counties in the East Midlands (UK)as intervention and control areas. The educational intervention was based on Joint Royal Colleges Ambulance Liaison Committee guidance and delivered to paramedic team leaders who cascaded it to their teams. We analysed rates of inappropriate cannulation before and after the intervention using routine clinical data. We also assessed overall cannulation rates before and after the intervention. A sample of paramedics was assessed post-intervention on cannulation technique with a ‘‘model’’ arm using a predesigned checklist. Results: There was a non-significant reduction in inappropriate (no intravenous fluids or drugs given) cannulation rates in the intervention area (1.0% to 0%) compared with the control area (2.5% to 2.6%). There was a significant (p,0.001) reduction in cannulation rates in the intervention area (9.1% to 6.5%; OR 0.7, 95% CI 0.48 to 1.03) compared with an increase in the control area (13.8% to 19.1%; OR 1.47, 95% CI 1.15 to 1.90), a significant difference (p,0.001). Paramedics in the intervention area were significantly more likely to use correct hand-washing techniques post-intervention (74.5% vs. 14.9%; p,0.001). Conclusion: The educational intervention was effective in bringing about changes leading to enhanced quality and safety in some aspects of prehospital cannulation

Two-level Chebyshev filter based complementary subspace method: pushing the envelope of large-scale electronic structure calculations

We describe a novel iterative strategy for Kohn-Sham density functional theory calculations aimed at large systems (> 1000 electrons), applicable to metals and insulators alike. In lieu of explicit diagonalization of the Kohn-Sham Hamiltonian on every self-consistent field (SCF) iteration, we employ a two-level Chebyshev polynomial filter based complementary subspace strategy to: 1) compute a set of vectors that span the occupied subspace of the Hamiltonian; 2) reduce subspace diagonalization to just partially occupied states; and 3) obtain those states in an efficient, scalable manner via an inner Chebyshev-filter iteration. By reducing the necessary computation to just partially occupied states, and obtaining these through an inner Chebyshev iteration, our approach reduces the cost of large metallic calculations significantly, while eliminating subspace diagonalization for insulating systems altogether. We describe the implementation of the method within the framework of the Discontinuous Galerkin (DG) electronic structure method and show that this results in a computational scheme that can effectively tackle bulk and nano systems containing tens of thousands of electrons, with chemical accuracy, within a few minutes or less of wall clock time per SCF iteration on large-scale computing platforms. We anticipate that our method will be instrumental in pushing the envelope of large-scale ab initio molecular dynamics. As a demonstration of this, we simulate a bulk silicon system containing 8,000 atoms at finite temperature, and obtain an average SCF step wall time of 51 seconds on 34,560 processors; thus allowing us to carry out 1.0 ps of ab initio molecular dynamics in approximately 28 hours (of wall time).Comment: Resubmitted version (version 2

Nudge plus: incorporating reflection into behavioral public policy

Nudge plus is a modification of the toolkit of behavioral public policy. It incorporates an element of reflection – the plus – into the delivery of a nudge, either blended in or made proximate. Nudge plus builds on recent work combining heuristics and deliberation. It may be used to design prosocial interventions that help preserve the autonomy of the agent. The argument turns on seminal work on dual systems, which presents a subtler relationship between fast and slow thinking than commonly assumed in the classic literature in behavioral public policy. We review classic and recent work on dual processes to show that a hybrid is more plausible than the default-interventionist or parallel-competitive framework. We define nudge plus, set out what reflection could entail, provide examples, outline causal mechanisms, and draw testable implications

Nudge plus: incorporating reflection into behavioural public policy

The authors of this paper outline a modified version of the behaviour change technique called ‘nudge plus’, which incorporates an element of reflection as part of the delivery of a nudge. Nudge plus builds on recent work advocating educative nudges and boosts. The authors claim that a hybrid nudge–think strategy can be a useful additional way to design pro-social interventions; combining a colour-coded ‘traffic lighting’ nudge with a salience-building ‘information plus’, for example, can increase the uptake of the nudge by agents, especially by those who might unconsciously ignore the visual cue implied by the colour coding of the nudge alone. Such a process is more plausible than the nudge-only strategies because combinations of nudges with reflective strategies are not only more liberty-preserving to the agent, but they can also generate stronger and persistent one-off effects. The authors suggest three key mechanisms of operationalising this nudge-plus: the plus could either come before and after (sequentially) or along with (simultaneous to) the nudge. Depending on when the ‘plus’ is administered with the nudge, it could embody various kinds of reflection; a plus that precedes a nudge, for instance, involves reflecting on the construct of the nudge or on the alternatives competing for availability to the decision-making agent. Finally, the authors compare the mechanistic scheme of the nudge-plus against that of the behavioural change tools that are currently available, namely classic nudges and boosts