Direct experimental visualization of waves and band structure in 2D photonic crystal slabs

We demonstrate for the first time the ability to perform time resolved imaging of terahertz (THz) waves propagating within a photonic crystal (PhC) slab. For photonic lattices with different orientations and symmetries, we used the electro-optic effect to record the full spatiotemporal evolution of THz fields across a broad spectral range spanning the photonic band gap. In addition to revealing real-space behavior, the data let us directly map the band diagrams of the PhCs. The data, which are in good agreement with theoretical calculations, display a rich set of effects including photonic band gaps, eigenmodes and leaky modes.National Science Foundation (U.S.) (Grant no. 1128632)National Science Foundation (U.S.) (NSF GRFP Fellowship)Canadian Institutes of Health Research (Fellowship

The homogenization limit and waveguide gradient index devices demonstrated through direct visualization of THz fields

Electromagnetic homogenization approximation calculates an effective refractive index of a composite material as a weighted average of its components, and has found uses in gradient refractive index and transformation optics devices. However, the utility of the homogenization approximation is hindered by uncertainty in its range of applicability. Harnessing the capability of time-resolved imaging provided by the terahertz polaritonics platform, we determined the dispersion curves of slab waveguides with periodic arrays of holes, and we quantified the breakdown of the homogenization approximation as the period approached the terahertz wavelength and the structure approached the photonic bandgap regime. We found that if the propagation wavelength in the dielectric waveguide was at least two times as large as the Bragg condition wavelength, the homogenization approximation held independent of the detailed geometry, propagation direction, or fill fraction. This value is much less demanding than the estimate of 10:1 often assumed for homogenization. We further used the experimental capabilities to extract the effective refractive index of the photonic crystals in the homogenization approximation limit, and we used this to analyze the predictive strength of analytical formulas. These formulas enabled rapid design of a Luneburg lens and a bi-directional cloak in a waveguide platform without the need for numerical simulations. Movies of terahertz waves interacting with these structures, which were fabricated using femtosecond laser machining, reveal excellent performance. The combination of an analytical formula and confidence in the homogenization approximation will aid in fast design and prototyping of gradient index devices.National Science Foundation (U.S.) (Grant 1128632)HDTRA Grant (1-12-1-0008)National Science Foundation (U.S.). Graduate Research Fellowship Progra

Enter evaluation of mitral inflow velocity profile: optimal through plane location for mitral inflow assessment with cardiac magnetic resonance

Diastology is usually assessed using transthoracic echocardiography (TTE). Velocity‐encoded phase‐contrast imaging permits evaluation with cardiac magnetic resonance (CMR). Heterogeneous contour locations have been used to measure mitral (MV) inflow velocities and the optimal contour location is uncertain. We evaluated CMR MV inflow velocities against TTE to identify the optimal location

Is there an impact of public smoking bans on self-reported smoking status and exposure to secondhand smoke?

<p>Abstract</p> <p>Background</p> <p>Implementation of smoke free policies has potentially substantial effects on health by reducing secondhand smoke exposure. However little is known about whether the introduction of anti-smoking legislation translates into decreased secondhand smoke exposure. We examined whether smoking bans impact rates of secondhand smoke exposure in public places and rates of complete workplace smoking restriction.</p> <p>Methods</p> <p>Canadian Community Health Survey was used to obtain secondhand smoking exposure rates in 15 Ontario municipalities. Data analysis included descriptive summaries and 95% confidence intervals were calculated and compared across groups</p> <p>Results</p> <p>Across all studied municipalities, secondhand smoke exposure in public places decreased by 4.7% and workplace exposure decreased by 2.3% between the 2003 and 2005 survey years. The only jurisdiction to implement a full ban from no previous ban was also the only setting that experienced significant decreases in both individual exposure to secondhand smoke in a public place (-17.3%, 95% CI -22.8, -11.8) and workplace exposure (-18.1%, 95% CI -24.9, -11.3). Exposures in vehicles and homes declined in almost all settings over time.</p> <p>Conclusions</p> <p>Implementation of a full smoking ban was associated with the largest decreases in secondhand smoke exposure while partial bans and changes in existing bans had inconsistent effects. In addition to decreasing exposure in public places as would be expected from legislation, bans may have additional benefits by decreasing rates of current smokers and decreasing exposures to secondhand smoke in private settings.</p

Identification of a novel zinc metalloprotease through a global analysis of clostridium difficile extracellular proteins

Clostridium difficile is a major cause of infectious diarrhea worldwide. Although the cell surface proteins are recognized to be important in clostridial pathogenesis, biological functions of only a few are known. Also, apart from the toxins, proteins exported by C. difficile into the extracellular milieu have been poorly studied. In order to identify novel extracellular factors of C. difficile, we analyzed bacterial culture supernatants prepared from clinical isolates, 630 and R20291, using liquid chromatography-tandem mass spectrometry. The majority of the proteins identified were non-canonical extracellular proteins. These could be largely classified into proteins associated to the cell wall (including CWPs and extracellular hydrolases), transporters and flagellar proteins. Seven unknown hypothetical proteins were also identified. One of these proteins, CD630_28300, shared sequence similarity with the anthrax lethal factor, a known zinc metallopeptidase. We demonstrated that CD630_28300 (named Zmp1) binds zinc and is able to cleave fibronectin and fibrinogen in vitro in a zinc-dependent manner. Using site-directed mutagenesis, we identified residues important in zinc binding and enzymatic activity. Furthermore, we demonstrated that Zmp1 destabilizes the fibronectin network produced by human fibroblasts. Thus, by analyzing the exoproteome of C. difficile, we identified a novel extracellular metalloprotease that may be important in key steps of clostridial pathogenesis

Self-reported dependence on mobile phones in young adults: a European cross-cultural empirical survey

Background and aims: Despite many positive benefits, mobile phone use can be associated with harmful and detrimental behaviors. The aim of this study was twofold: to examine (a) cross-cultural patterns of perceived dependence on mobile phones in ten European countries, first, grouped in four different regions (North: Finland and UK; South: Spain and Italy; East: Hungary and Poland; West: France, Belgium, Germany, and Switzerland), and second by country, and (b) how socio-demographics, geographic differences, mobile phone usage patterns, and associated activities predicted this perceived dependence. Methods: A sample of 2,775 young adults (aged 18–29 years) were recruited in different European Universities who participated in an online survey. Measures included socio-demographic variables, patterns of mobile phone use, and the dependence subscale of a short version of the Problematic Mobile Phone Use Questionnaire (PMPUQ; Billieux, Van der Linden, & Rochat, 2008). Results: The young adults from the Northern and Southern regions reported the heaviest use of mobile phones, whereas perceived dependence was less prevalent in the Eastern region. However, the proportion of highly dependent mobile phone users was more elevated in Belgium, UK, and France. Regression analysis identified several risk factors for increased scores on the PMPUQ dependence subscale, namely using mobile phones daily, being female, engaging in social networking, playing video games, shopping and viewing TV shows through the Internet, chatting and messaging, and using mobile phones for downloading-related activities. Discussion and conclusions: Self-reported dependence on mobile phone use is influenced by frequency and specific application usage