Gas Sensing Properties of Single Conducting Polymer Nanowires and the Effect of Temperature

We measured the electronic properties and gas sensing responses of template-grown poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT/PSS)-based nanowires. The nanowires have a "striped" structure (gold-PEDOT/PSS-gold), typically 8um long (1um-6um-1um for each section, respectively) and 220 nm in diameter. Single-nanowire devices were contacted by pre-fabricated gold electrodes using dielectrophoretic assembly. A polymer conductivity of 11.5 +/- 0.7 S/cm and a contact resistance of 27.6 +/- 4 kOhm were inferred from measurements of nanowires of varying length and diameter. The nanowire sensors detect a variety of odors, with rapid response and recovery (seconds). The response (R-R0)/R0 varies as a power law with analyte concentration.Comment: 4 figures 8 pages, add 2 reference

Proximity-induced superconductivity in nanowires: Mini-gap state and differential magnetoresistance oscillations

We study proximity-induced superconductivity in gold nanowires as a function of the length of the nanowire, magnetic field, and excitation current. Short nanowires exhibit a sharp superconducting transition, whereas long nanowires show nonzero resistance. At intermediate lengths, however, we observe two sharp transitions; the normal and superconducting regions are separated by what we call the mini-gap phase. Additionally, we detect periodic oscillations in the differential magnetoresistance. We provide a theoretical model for the mini-gap phase as well as the periodic oscillations in terms of the coexistence of proximity-induced superconductivity with a normal region near the center of the wire, created either by temperature or application of a magnetic field.Comment: 11 pages, 4 figure

Dissipation in Quasi One-Dimensional Superconducting Single-Crystal Sn Nanowires

Electrical transport measurements were made on single-crystal Sn nanowires to understand the intrinsic dissipation mechanisms of a one-dimensional superconductor. While the resistance of wires of diameter larger than 70 nm drops precipitately to zero at Tc near 3.7 K, a residual resistive tail extending down to low temperature is found for wires with diameters of 20 and 40 nm. As a function of temperature, the logarithm of the residual resistance appears as two linear sections, one within a few tenths of a degree below Tc and the other extending down to at least 0.47 K, the minimum temperature of the measurements. The residual resistance is found to be ohmic at all temperatures below Tc of Sn. These findings are suggestive of a thermally activated phase slip process near Tc and quantum fluctuation-induced phase slip process in the low temperature regime. When the excitation current exceeds a critical value, the voltage-current (V-I) curves show a series of discrete steps in approaching the normal state. These steps cannot be fully understood with the classical Skocpol-Beasley-Tinkham phase slip center model (PSC), but can be qualitatively accounted for partly by the PSC model modified by Michotte et al.Comment: 7 pages, 5 figures. To be appeared on Physical Review B 71, 200

Evidence of local superconductivity in granular Bi nanowires fabricated by electrodeposition

An unusual enhancement of resistance (i.e., superresistivity) below a certain characteristic temperature Tsr was observed in granular Bi nanowires. This superresistive state was found to be dependent on the applied magnetic field (H) as well as the excitation current (I). The suppression of Tsr by magnetic field resembles that of a superconductor. The observed superresistivity appears to be related to the nucleation of local superconductivity inside the granular nanowire without long-range phase coherence. The phenomenon is reminiscent of the Bose-insulator observed previously in ultra thin two-dimensional (2D) superconducting films and 3D percolative superconducting films.Comment: 11 pages, 5 figures. submitted to PR

Enhanced diffusion due to active swimmers at a solid surface

We consider two systems of active swimmers moving close to a solid surface, one being a living population of wild-type \textit{E. coli} and the other being an assembly of self-propelled Au-Pt rods. In both situations, we have identified two different types of motion at the surface and evaluated the fraction of the population that displayed ballistic trajectories (active swimmers) with respect to those showing random-like behavior. We studied the effect of this complex swimming activity on the diffusivity of passive tracers also present at the surface. We found that the tracer diffusivity is enhanced with respect to standard Brownian motion and increases linearly with the activity of the fluid, defined as the product of the fraction of active swimmers and their mean velocity. This result can be understood in terms of series of elementary encounters between the active swimmers and the tracers.Comment: 4 pages, 2 figures in color, Physical Review Letters (in production

Design of MARQUIS2: study protocol for a mentored implementation study of an evidence-based toolkit to improve patient safety through medication reconciliation.

BackgroundThe first Multi-center Medication Reconciliation Quality Improvement Study (MARQUIS1) demonstrated that implementation of a medication reconciliation best practices toolkit decreased total unintentional medication discrepancies in five hospitals. We sought to implement the MARQUIS toolkit in more diverse hospitals, incorporating lessons learned from MARQUIS1.MethodsMARQUIS2 is a pragmatic, mentored implementation QI study which collected clinical and implementation outcomes. Sites implemented a revised toolkit, which included interventions from these domains: 1) best possible medication history (BPMH)-taking; 2) discharge medication reconciliation and patient/caregiver counseling; 3) identifying and defining clinician roles and responsibilities; 4) risk stratification; 5) health information technology improvements; 6) improved access to medication sources; 7) identification and correction of real-time discrepancies; and, 8) stakeholder engagement. Eight hospitalists mentored the sites via one site visit and monthly phone calls over the 18-month intervention period. Each site's local QI team assessed opportunities to improve, implemented at least one of the 17 toolkit components, and accessed a variety of resources (e.g. implementation manual, webinars, and workshops). Outcomes to be assessed will include unintentional medication discrepancies per patient.DiscussionA mentored multi-center medication reconciliation QI initiative using a best practices toolkit was successfully implemented across 18 medical centers. The 18 participating sites varied in size, teaching status, location, and electronic health record (EHR) platform. We introduce barriers to implementation and lessons learned from MARQUIS1, such as the importance of utilizing dedicated, trained medication history takers, simple EHR solutions, clarifying roles and responsibilities, and the input of patients and families when improving medication reconciliation

Acoustic Communication for Medical Nanorobots

Communication among microscopic robots (nanorobots) can coordinate their activities for biomedical tasks. The feasibility of in vivo ultrasonic communication is evaluated for micron-size robots broadcasting into various types of tissues. Frequencies between 10MHz and 300MHz give the best tradeoff between efficient acoustic generation and attenuation for communication over distances of about 100 microns. Based on these results, we find power available from ambient oxygen and glucose in the bloodstream can readily support communication rates of about 10,000 bits/second between micron-sized robots. We discuss techniques, such as directional acoustic beams, that can increase this rate. The acoustic pressure fields enabling this communication are unlikely to damage nearby tissue, and short bursts at considerably higher power could be of therapeutic use.Comment: added discussion of communication channel capacity in section

Enhanced diffusion due to active swimmers at a solid surface

We consider two systems of active swimmers moving close to a solid surface, one being a living population of wild-type E. coli and the other being an assembly of self-propelled Au-Pt rods. In both situations, we have identified two different types of motion at the surface and evaluated the fraction of the population that displayed ballistic trajectories (active swimmers) with respect to those showing diffusive-like behavior. We studied the effect of this complex swimming activity on the diffusivity of passive tracers also present at the surface. We found that the tracer diffusivity is enhanced with respect to standard Brownian motion and increases linearly with the activity of the fluid, defined as the product of the fraction of active swimmers and their mean velocity. This result can be understood in terms of series of elementary encounters between the active swimmers and the tracers

Wave Energy Converter Design Project

As part of a multidisciplinary sophomore-level engineering design and technical writing course, a project that required students to design a small-scale ocean wave energy converter through a series of experiments was implemented. The project was designed to fulfill several of the course goals, which range from engineering design to engineering communication. For example, the goal of the engineering/design portion of the course is for students to demonstrate effective design processes, which include generating multiple engineering design solutions, applying sound engineering principles to choose the best solution and see it through to completion, and using parametric design to optimize an artifact or process. The communication goals of the course are for students to write in various engineering genres and demonstrate specific communication abilities needed for engineering communication