Feedback-controlled transport in an interacting colloidal system

Based on dynamical density functional theory (DDFT) we consider a non-equilibrium system of interacting colloidal particles driven by a constant tilting force through a periodic, symmetric "washboard" potential. We demonstrate that, despite of pronounced spatio-temporal correlations, the particle current can be reversed by adding suitable feedback control terms to the DDFT equation of motion. We explore two distinct control protocols with time delay, focussing on either the particle positions or the density profile. Our study shows that the DDFT is an appropriate framework to implement time-delayed feedback control strategies widely used in other fields of nonlinear physicsComment: 6 pages, 5 figure

Automatic dispensing cabinets and governance of controlled drugs: an exploratory study in an intensive care unit.

BACKGROUND: Governance of controlled drugs (CDs) in hospitals is resource intensive but important for patient safety and policy compliance. OBJECTIVES: To explore whether and how storing CDs in an automated dispensing cabinet (ADC) in a children's hospital intensive care unit (ICU) contributes to the effectiveness and efficiency of CD governance. METHODS: We conducted a mixed-methods exploratory study, comprising observations, interviews and audits, 3 months after ADC implementation. We observed 54 hours of medications activities in the ICU medication room (with 42 hours of timed data); interviewed nurses (n=19), management (n=1) and pharmacy staff (n=3); reviewed 6 months of ICU incident reports pertaining to CD governance; audited 6 months of CD register data and extracted logs of all ADC transactions for the 3 months following implementation. Data analysis focused on four main CD governance activities: safekeeping/controlling access, documenting use, monitoring, and reporting/investigating. RESULTS: Nurses and pharmacists perceived spending less time on CD governance tasks with the ADC. The ADC supported CD governance through automated documentation of CD transactions; 'blind counts'; automated count discrepancy checks; electronic alerts and reporting functionalities. It changed quality and distribution of governance tasks, such as removing the requirement for 'nurses with keys' to access CDs, and allowing pharmacists to generate reports remotely, rather than reviewing registers on the ward. For CDs in the ADC, auditing and monitoring appeared to be ongoing rather than periodic. Such changes appeared to create positive reinforcing loops. However, the ADC also created challenges for CD governance. Most importantly, it was not suitable for all CDs, leading to workarounds and parallel use of a safe plus paper registers. CONCLUSIONS: ADCs can significantly alter CDs governance in clinical areas. Effects of an ADC on efficiency and effectiveness of governance tasks appear to be complex, going beyond simple time savings or more stringent controls

On the stability of periodic orbits in delay equations with large delay

We prove a necessary and sufficient criterion for the exponential stability of periodic solutions of delay differential equations with large delay. We show that for sufficiently large delay the Floquet spectrum near criticality is characterized by a set of curves, which we call asymptotic continuous spectrum, that is independent on the delay.Comment: postprint versio

The 'Back Office' of a Dispensing Cabinet: Technology and Work Contributing to Medication Safety

Automated dispensing cabinets in clinical wards may contribute to improving safety by reducing the likelihood of medications not being available when needed. However, achieving this safety benefit is dependent on a 'back office' sociotechnical infrastructure that combines semi-automated processes with mindful, resilient work practices

Modelling the Recoherence of Mesoscopic Superpositions in Dissipative Environments

A model is presented to describe the recently proposed experiment (J. Raimond, M. Brune and S. Haroche Phys. Rev. Lett {\bf 79}, 1964 (1997)) where a mesoscopic superposition of radiation states is prepared in a high-Q cavity which is coupled to a similar resonator. The dynamical coherence loss of such state in the absence of dissipation is reversible and can in principle be observed. We show how this picture is modified due to the presence of the environmental couplings. Analytical expressions for the experimental conditional probabilities and the linear entropy are given. We conclude that the phenomenon can still be observed provided the ratio between the damping constant and the inter-cavities coupling does not exceed about a few percent. This observation is favored for superpositions of states with large overlap.Comment: 13 pages, 6 figure

Cellular automaton model of precipitation/dissolution coupled with solute transport

Precipitation/dissolution reactions coupled with solute transport are modelled as a cellular automaton in which solute molecules perform a random walk on a regular lattice and react according to a local probabilistic rule. Stationary solid particles dissolve with a certain probability and, provided solid is already present or the solution is saturated, solute particles have a probability to precipitate. In our simulation of the dissolution of a solid block inside uniformly flowing water we obtain solid precipitation downstream from the original solid edge, in contrast to the standard reaction-transport equations. The observed effect is the result of fluctuations in solute density and diminishes when we average over a larger ensemble. The additional precipitation of solid is accompanied by a substantial reduction in the relatively small solute concentration. The model is appropriate for the study of the r\^ole of intrinsic fluctuations in the presence of reaction thresholds and can be employed to investigate porosity changes associated with the carbonation of cement.Comment: LaTeX file, 13 pages. To appear in Journal of Statistical Physics (Proceedings of Lattice Gas'94, June 1994, Princeton). Figures available from author. Requests may be submitted by E-mail ([email protected]) or ordinary mail (Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland

Evaluation of an Automated Dispensing Cabinet in Paediatric Intensive Care - Focus on Controlled Medications

Evidence is limited of automated dispensing cabinets (ADCs) impact on effectiveness and efficiency of controlled drugs' (CDs) governance processes. We carried out a mixed-methods study of an ADC in an intensive care unit. We found ADC improved effectiveness and efficiency of governance of CDs through secure storage, alerts and automated recording of transactions. Limitations were associated with ADC design and 'fit' between ADC and some types of CDs

Challenges of Digital Commons: A Qualitative Study of an Automated Dispensing Cabinet in a Paediatric Intensive Care Unit

Missed medication doses can affect patient safety in hospitals. The use of automated dispensing cabinets (ADC) in clinical areas may reduce the occurrence of medications being unavailable at the time of need by alerting pharmacy to replenish stock. However, workarounds in ADC use can affect this capability. We studied nurses' use of an ADC in a paediatric intensive care unit with  54 hours of observation, semi-structure interviews (19 nurses; 4 pharmacy/management staff) and review of reported incidents. We found running out of medication a recurrent problem despite the ADC. Contributing factors affecting data entry in the ADC, and therefore replenishment alerts to pharmacy, included: the organisation of medication activities in the ward, nurses' information needs, patients' medication needs, and ADC design. Running out of medications was a 'tragedy of the commons'. Effective solutions may require going beyond user training and directives for accurate data entry, to work process redesign