Highly confined electromagnetic fields in arrays of strongly coupled Ag nanoparticles

Linear arrays of very small Ag nanoparticles (diameter ~10 nm, spacing 0–4 nm) were fabricated in sodalime glass using an ion irradiation technique. Optical extinction spectroscopy of the arrays reveals a large polarization-dependent splitting of the collective plasmon extinction band. Depending on the preparation condition, a redshift of the longitudinal resonance as large as 1.5 eV is observed. Simulations of the three-dimensional electromagnetic field evolution are used to determine the resonance energy of idealized nanoparticle arrays with different interparticle spacings and array lengths. Using these data, the experimentally observed redshift is attributed to collective plasmon coupling in touching particles and/or in long arrays of strongly coupled particles. The simulations also indicate that for closely coupled nanoparticles (1–2 nm spacing) the electromagnetic field is concentrated in nanoscale regions (10 dB radius: 3 nm) between the particles, with a 5000-fold local field intensity enhancement. In arrays of 1-nm-spaced particles the dipolar particle interaction extends to over 10 particles, while for larger spacing the interaction length decreases. Spatial images of the local field distribution in 12-particle arrays of touching particles reveal a particlelike coupled mode with a resonance at 1.8 eV and a wirelike mode at 0.4 eV

Noisy Classical Field Theories with Two Coupled Fields: Dependence of Escape Rates on Relative Field Stiffnesses

Exit times for stochastic Ginzburg-Landau classical field theories with two or more coupled classical fields depend on the interval length on which the fields are defined, the potential in which the fields deterministically evolve, and the relative stiffness of the fields themselves. The latter is of particular importance in that physical applications will generally require different relative stiffnesses, but the effect of varying field stiffnesses has not heretofore been studied. In this paper, we explore the complete phase diagram of escape times as they depend on the various problem parameters. In addition to finding a transition in escape rates as the relative stiffness varies, we also observe a critical slowing down of the string method algorithm as criticality is approached.Comment: 16 pages, 10 figure

Noise-Activated Escape from a Sloshing Potential Well

We treat the noise-activated escape from a one-dimensional potential well of an overdamped particle, to which a periodic force of fixed frequency is applied. We determine the boundary layer behavior, and the physically relevant length scales, near the oscillating well top. We show how stochastic behavior near the well top generalizes the behavior first determined by Kramers, in the case without forcing. Both the case when the forcing dies away in the weak noise limit, and the case when it does not, are examined. We also discuss the relevance of various scaling regimes to recent optical trap experiments.Comment: 9 pages, no figures, REVTeX, expanded versio

Terahertz surface plasmon polariton propagation and focusing on periodically corrugated metal wires

In this letter we show how the dispersion relation of surface plasmon polaritons (SPPs) propagating along a perfectly conducting wire can be tailored by corrugating its surface with a periodic array of radial grooves. In this way, highly localized SPPs can be sustained in the terahertz region of the electromagnetic spectrum. Importantly, the propagation characteristics of these spoof SPPs can be controlled by the surface geometry, opening the way to important applications such as energy concentration on cylindrical wires and superfocusing using conical structures.Comment: accepted at PRL, submitted 29th May 200

Laboratory Electronic Spectra of Carbon Chains and Rings

Carriers of the diffuse interstellar bands (DIBs) cannot be definitively identified without laboratory spectra. Several techniques, including matrix isolation, cavity ringdown spectroscopy, resonance enhanced multiphoton ionization, and ion trapping, have been used to measure the electronic spectra of carbon chains and their derivatives. The gas-phase laboratory spectra could then be compared to the astronomical data of known DIBs. The choice of molecules studied in the gas phase depends on the presence of strong electronic transitions at optical wavelengths, the lifetimes of excited electronic states, and chemical feasibility in diffuse astrophysical environments. Collisional-radiative rate models have also be used in conjunction with laboratory spectra to predict absorption profiles under interstellar condition

Exploratory study of the state of environmentally conscious design in the medical device industry

This exploratory study seeks to explore the current state of design for the environment (DfE) in the development of medical devices; an historically risk averse industry that lags behind others in terms of addressing environmental considerations. A cross-sectional survey of 34 medical device designers, primarily in the UK and USA, was conducted in order to fulfil this objective. Findings indicate that there is significant motivation to enhance DfE practice, but that there are multiple barriers to this. Major barriers identified are a perception of the high cost of DfE, the industry’s current reliance on a single-use business model for many current products and a lack of education about DfE topics on all sides. Designers felt that the most significant opportunities to implement DfE are in situations where they are able to exert direct control, mainly in the early stages of the design process. Issues noted include raw material choice and packaging decisions. The nature of single use business models is also critical, pointing towards the needs for a systemic rather than product focus. For this to be achieved, financial rewards must be evident to firms and the changing regulatory landscape might also make a more significant impact.This research was supported using funding from the Engineering and Physical Sciences Research Council (EPSRC) in the United Kingdom, grant number EP/E001769/1.This is the final version of the article. It first appeared from Elsevier via http://dx.doi.org/10.1016/j.jclepro.2015.06.01

A maturity grid assessment tool for environmentally conscious design in the medical device industry

The medical device industry is growing increasingly concerned about environmental impact of products. Whilst there are many tools aiming to support environmentally conscious design, they are typically complex to use, demand substantial data collection and are not tailored to the specific needs of the medical device sector. This paper reports on the development of a Maturity Grid to address this gap. This novel design tool was developed iteratively through application in five case studies. The tool captures principles of eco-design for medical devices in a simple form, designed to be used by a team. This intervention tool provides designers and product marketers with insights on how to improve the design of their medical devices and specifically allows consideration of the complex trade-offs between decisions that influence different life-cycle stages. Through the tool, actionable insight is created that supports decisions to be made within the realm of design engineers and beyond. The tool highlights areas which are influenced by design decisions taken, some of which are perceived to be outside of the direct control of designers.This work was by the United Kingdom’s Engineering and Physical Sciences Research, [Grant Number EP/E001769/1]

Functional renormalization group study of an eight-band model for the iron arsenides

We investigate the superconducting pairing instabilities of eight-band models for the iron arsenides. Using a functional renormalization group treatment, we determine how the critical energy scale for superconductivity depends on the electronic band structure. Most importantly, if we vary the parameters from values corresponding to LaFeAsO to SmFeAsO, the pairing scale is strongly enhanced, in accordance with the experimental observation. We analyze the reasons for this trend and compare the results of the eight-band approach to those found using five-band models.Comment: 11 pages, 10 figure

Tripartite phase separation of two signal effectors with vesicles priming B cell responsiveness.

Antibody-mediated immune responses rely on antigen recognition by the B cell antigen receptor (BCR) and the proper engagement of its intracellular signal effector proteins. Src homology (SH) 2 domain-containing leukocyte protein of 65 kDa (SLP65) is the key scaffold protein mediating BCR signaling. In resting B cells, SLP65 colocalizes with Cbl-interacting protein of 85 kDa (CIN85) in cytoplasmic granules whose formation is not fully understood. Here we show that effective B cell activation requires tripartite phase separation of SLP65, CIN85, and lipid vesicles into droplets via vesicle binding of SLP65 and promiscuous interactions between nine SH3 domains of the trimeric CIN85 and the proline-rich motifs (PRMs) of SLP65. Vesicles are clustered and the dynamical structure of SLP65 persists in the droplet phase in vitro. Our results demonstrate that phase separation driven by concerted transient interactions between scaffold proteins and vesicles is a cellular mechanism to concentrate and organize signal transducers