Designing angle-independent structural colors using Monte Carlo simulations of multiple scattering.

Disordered nanostructures with correlations on the scale of visible wavelengths can show angle-independent structural colors. These materials could replace dyes in some applications because the color is tunable and resists photobleaching. However, designing nanostructures with a prescribed color is difficult, especially when the application-cosmetics or displays, for example-requires specific component materials. A general approach to solving this constrained design problem is modeling and optimization: Using a model that predicts the color of a given system, one optimizes the model parameters under constraints to achieve a target color. For this approach to work, the model must make accurate predictions, which is challenging because disordered nanostructures have multiple scattering. To address this challenge, we develop a Monte Carlo model that simulates multiple scattering of light in disordered arrangements of spherical particles or voids. The model produces quantitative agreement with measurements when we account for roughness on the surface of the film, particle polydispersity, and wavelength-dependent absorption in the components. Unlike discrete numerical simulations, our model is parameterized in terms of experimental variables, simplifying the connection between simulation and fabrication. To demonstrate this approach, we reproduce the color of the male mountain bluebird (Sialia currucoides) in an experimental system, using prescribed components and a microstructure that is easy to fabricate. Finally, we use the model to find the limits of angle-independent structural colors for a given system. These results enable an engineering design approach to structural color for many different applications.

Investigating the trade-off between color saturation and angle-independence in photonic glasses.

Photonic glasses-isotropic structures with short-range correlations-can produce structural colors with little angle-dependence, making them an alternative to dyes in applications such as cosmetics, coatings, and displays. However, the low angle-dependence is often accompanied by low color saturation. To investigate how the short-range correlations affect the trade-off between saturation and angle-independence, we vary the structure factor and use a Monte Carlo model of multiple scattering to investigate the resulting optical properties. We use structure factors derived from analytical models and calculated from simulations of disordered sphere packings. We show that the trade-off is controlled by the first peak of the structure factor. It is possible to break the trade-off by tuning the width of this peak and controlling the sample thickness. Practically, this result shows that the protocol used to pack particles into a photonic glass is important to the optical properties.

Ten year follow-up of high-risk patients treated during the early experience with transcatheter aortic valve replacement.

BACKGROUND: The long-term clinical performance of transcatheter heart valves (THV) is unknown. AIMS: This study assessed the clinical outcomes, rate of structural valve deterioration (SVD) and bioprosthetic valve failure in patients after transcatheter aortic valve replacement (TAVR) to 10-year follow-up. METHODS: Consecutive patients undergoing TAVI for native aortic valve stenosis or failed aortic surgical bioprosthesis, between 2005 and 2009 at our institution were included. A total of 235 consecutive patients. RESULTS: At the time of TAVI mean age was 82.4 ± 7.9 years. All patients were judged to be high risk, with a STS score > 8 in 53.6%. THVs implanted were the Cribier-Edwards (20.9%), Edwards SAPIEN (77.4%) or CoreValve (1.7%). Mortality at 1, 5, and 10-year follow-up was 23.4%, 63%, and 91.6%, respectively. Of the total cohort, 15 patients had structural valve deterioration/bioprosthetic valve failure, with a cumulative incidence at 10-years of 6.5% (95% CI 3.3%, 9.6%). The rate of SVD/BVF at 4, 6, 8, and 10 years was 0.4%, 1.7%, 4.7%, and 6.5%, respectively. Nine patients had moderate SVD and six patients had severe SVD. Of the six patients with severe SVD, two patients had reintervention (one patient had redo TAVR, and the second had surgical aortic valve replacement). Survivors (n = 19) at 10-year follow-up, had a mean gradient of 14.0 ± 7.6 mmHg and aortic regurgitation ≥moderate in 5%. Quality of life measures in 10-year survivors demonstrated ADLs 6/6 in 43.8%, and ambulation without a mobility aid of 62.5%. CONCLUSION: Using early generation balloon expandable THVs in a high-risk population, there was a low rate of structural valve deterioration and valve failure at 10-year follow-up. This study provides insights into the long-term performance of transcatheter heart valves and patients self-reported derived benefits.

Early mobilization after transcatheter aortic valve implantation: observational cohort study.

AIMS: Early mobilization is associated with improved outcomes in hospitalized older patients. We sought to determine the effect of a nurse-led protocol on mobilization 4 h after transfemoral transcatheter aortic valve implantation (TAVI) across different units of care. METHODS AND RESULTS: We conducted a prospective observational cohort single-centre study of consecutive patients. We implemented a standardized protocol for safe early recovery and progressive mobilization in the critical care and cardiac telemetry units. We measured the time to first mobilization and conducted descriptive statistics to identify patient and system barriers to timely ambulation. We recruited 139 patients (82.5 years, SD = 6.7; 46% women). At baseline, patients who were mobilized early (≤4 h) and late (>4 h) did not differ, except for higher rates of diabetes (25.5% vs. 43.9%, P = 0.032) and peripheral arterial disease (8.2% vs. 26.8%, P = 0.003) in the late mobilization group. The median time to mobilization was 4 h [inter-quartile range (IQR) 3.25, 4]; 98 patients (70.5%) were mobilized successfully after 4 h of bedrest; 118 (84.9%) were walking by the evening of the procedure (<8 h bedrest); and 21 (15.1%) were on bedrest overnight and mobilized the following day. Primary reasons for overnight bedrest were arrhythmia monitoring (n = 10, 7.2%) and haemodynamic and/or neurological instability (n = 6, 4.3%); six patients (4.3%) experienced delayed ambulation due to system issues. Procedure location in the hybrid operating room and transfer to critical care were associated with longer bedrest times. CONCLUSION: Standardized nurse-led mobilization 4 h after TF TAVI is feasible in the absence of clinical complications and system barriers.

Can you picture it? Photo elicitation in qualitative cardiovascular health research.

Photo elicitation offers novel opportunities to augment the qualitative research toolbox. The use of photographs can enrich connections with participants, and empower them to be creative and engaged to communicate their insights, priorities, and perspectives. There is growing evidence of the effective use of photo elicitation in health research, with emerging interest in the cardiovascular community. Careful study planning, including attention to equipment, participant training, photograph selection, data collection, and ethical consideration, is essential. Detailed reporting of the study design and rationale for use of photographs, conceptual thinking underpinnings, elicitation process, and analytical plan contribute to strengthening the methodological approach.

Inferring the effectiveness of government interventions against COVID-19.

Governments are attempting to control the COVID-19 pandemic with nonpharmaceutical interventions (NPIs). However, the effectiveness of different NPIs at reducing transmission is poorly understood. We gathered chronological data on the implementation of NPIs for several European and non-European countries between January and the end of May 2020. We estimated the effectiveness of these NPIs, which range from limiting gathering sizes and closing businesses or educational institutions to stay-at-home orders. To do so, we used a Bayesian hierarchical model that links NPI implementation dates to national case and death counts and supported the results with extensive empirical validation. Closing all educational institutions, limiting gatherings to 10 people or less, and closing face-to-face businesses each reduced transmission considerably. The additional effect of stay-at-home orders was comparatively small.

Effects of multiple scattering on angle-independent structural color in disordered colloidal materials.

Disordered packings of colloidal spheres show angle-independent structural color when the particles are on the scale of the wavelength of visible light. Previous work has shown that the positions of the peaks in the reflectance spectra can be predicted accurately from a single-scattering model that accounts for the effective refractive index of the material. This agreement shows that the main color peak arises from short-range correlations between particles. However, the single-scattering model does not quantitatively reproduce the observed color: the main peak in the reflectance spectrum is much broader and the reflectance at low wavelengths is much larger than predicted by the model. We use a combination of experiment and theory to understand these features. We find that one significant contribution to the breadth of the main peak is light that is scattered, totally internally reflected from the boundary of the sample, and then scattered again. The high reflectance at low wavelengths also results from multiple scattering but can be traced to the increase in the scattering cross section of individual particles with decreasing wavelength. Both of these effects tend to reduce the saturation of the structural color, which limits the use of these materials in applications. We show that while the single-scattering model cannot reproduce the observed saturations, it can be used as a design tool to reduce the amount of multiple scattering and increase the color saturation of materials, even in the absence of absorbing components.

Quantitative tracking of the growth of individual algal cells in microdroplet compartments.

In this paper we introduce a simple droplet-based microfluidic system consisting of two separate devices to encapsulate and culture microalgae, in contrast to cultivation in bulk liquid medium. This microdroplet technology has been used to monitor the growth of individual microalgal cells in a constant environment for extended periods of time. Single cells from three species of green microalgae, (two freshwater species Chlamydomonas reinhardtii and Chlorella vulgaris, and one saline species Dunaliella tertiolecta), were encapsulated and incubated in microdroplet compartments of diameter of ∼80 µm, and their growth analysed over 10 days. In all cases, the doubling time of microalgae grown in microdroplets was similar to growth in bulk. The growth of C. reinhardtii in microdroplets of varying diameters and with different initial cell numbers per droplet was investigated, as well as the effect of varying medium conditions such as pH and nitrogen concentration. This methodology offers the opportunity to study characteristics over time of individual cells and colonies, as well as to screen large numbers of them.