Insights into the sticking probability of volcanic ash particles from laboratory experiments.

Although the characterization of the sticking and aggregation probability is essential to the description of volcanic ash dispersal and sedimentation, there is still no general model describing the sticking probability of volcanic ash. Experiments of dry particle-plate collisions in an enclosed box were carried out to characterize quantitatively the sticking efficiency of volcanic particles and silica beads in a limit case scenario where the mass of one of the particles is much greater than the others. Silica beads and volcanic particles from a Sakurajima Vulcanian eruption were filmed impacting a glass plate with a High-Speed Camera. The sticking probability is calculated from an equation depending on the particle diameter, impact velocity, and two experimental parameters (a, q). Particle size was found to dominantly control the sticking probability, with small particles more likely sticking on the glass plate than large particles. These experiments represent a significant step forward in the quantification of the sticking efficiency of fine volcanic ash (< 63 µm).

Two-photon absorption in colloidal semiconductor nanocrystals: a review.

Large two-photon absorption (2PA) cross-section combined with high emission quantum efficiency and size-tunable bandgap energy has put colloidal semiconductor nanocrystals (NCs) on the vanguard of nonlinear optical materials. After nearly two decades of intense studies on the nonlinear optical response in quantum-confined semiconductors, this is still a vibrant field, as novel nanomaterials are being developed and new applications are being proposed. In this review, we examine the progress of 2PA research in NCs, highlighting the impact of quantum confinement on the magnitude and spectral characteristics of this nonlinear response in semiconductor materials. We show that for NCs with three-dimensional quantum confinement, the so-called quantum dots, 2PA cross-section grows linearly with the nanoparticle volume, following a universal volume scaling. We overview strategies used to gain further control over the nonlinear optical response in these structures by shape and heterostructure engineering and some applications that might take advantage of the series of unique properties of these nanostructures.

Beyond Universal Volume Scaling: Tailoring Two-Photon Absorption in Nanomaterials by Heterostructure Design.

Colloidal semiconductor nanomaterials present broadband, with large cross-section, two-photon absorption (2PA) spectra, which turn them into an important platform for applications that benefit from a high nonlinear optical response. Despite that, to date, the only means to control the magnitude of the 2PA cross-section is by changing the nanoparticle volume, as it follows a universal volume scale, independent of the material composition. As the emission spectrum is connected utterly to the nanomaterial dimensions, for a given material, the magnitude of the nonlinear optical response is also coupled to the emission spectra. Here, we demonstrate a means to decouple both effects by exploring the 2PA response of different types of heterostructures, tailoring the volume dependence of the 2PA cross-section due to the different dependence of the density of final states on the nanoparticle volume. By heterostructure engineering, one can obtain 1 order of magnitude enhancement of the 2PA cross-section with minimum emission spectra shift.

COVID-19 Symptoms and Duration of Rapid Antigen Test Positivity at a Community Testing and Surveillance Site During Pre-Delta, Delta, and Omicron BA.1 Periods.

Importance: Characterizing the clinical symptoms and evolution of community-based SARS-CoV-2 infections may inform health practitioners and public health officials in a rapidly changing landscape of population immunity and viral variants. Objectives: To compare COVID-19 symptoms among people testing positive with a rapid antigen test (RAT) during the Omicron BA.1 variant period (December 1, 2021, to January 30, 2022) with the pre-Delta (January 10 to May 31, 2021) and Delta (June 1 to November 30, 2021) variant periods and to assess the duration of RAT positivity during the Omicron BA.1 surge. Design, Setting, and Participants: This cross-sectional study was conducted from January 10, 2021, to January 31, 2022, at a walk-up community COVID-19 testing site in San Francisco, California. Participants included children and adults seeking COVID-19 testing with an RAT, regardless of age, vaccine status, or symptoms. Main Outcomes and Measures: Fisher exact tests or χ2 tests were used to compare COVID-19 symptoms during the Omicron BA.1 period with the pre-Delta and Delta periods for vaccination status and age group. Among people returning for repeated testing during the Omicron period, the proportion with a positive RAT between 4 and 14 days from symptom onset or since first positive test if asymptomatic was estimated. Results: Among 63 277 persons tested (median [IQR] age, 32 [21-44] years, with 12.0% younger than 12 years; 52.0% women; and 68.5% Latinx), a total of 18 301 people (28.9%) reported symptoms, of whom 4565 (24.9%) tested positive for COVID-19. During the Omicron BA.1 period, 3032 of 7283 symptomatic participants (41.6%) tested positive, and the numbers of these reporting cough and sore throat were higher than during pre-Delta and Delta periods (cough: 2044 [67.4%] vs 546 [51.3%] of 1065 participants, P < .001 for pre-Delta, and 281 [60.0%] of 468 participants, P = .002, for Delta; sore throat: 1316 [43.4%] vs 315 [29.6%] of 1065 participants, P < .001 for pre-Delta, and 136 [29.1%] of 468 participants, P < .001, for Delta). Compared with the 1065 patients with positive test results in the pre-Delta period, congestion among the 3032 with positive results during the Omicron BA.1 period was more common (1177 [38.8%] vs 294 [27.6%] participants, P < .001), and loss of taste or smell (160 [5.3%] vs 183 [17.2%] participants, P < .001) and fever (921 [30.4%] vs 369 [34.7%] participants, P = .01) were less common. In addition, during the Omicron BA.1 period, fever was less common among the people with positive test results who had received a vaccine booster compared with those with positive test results who were unvaccinated (97 [22.5%] of 432 vs 42 [36.2%] of 116 participants, P = .003), and fever and myalgia were less common among participants who had received a booster compared with those with positive results who had received only a primary series (fever: 97 [22.5%] of 432 vs 559 [32.8%] of 1705 participants, P < .001; myalgia: 115 [26.6%] of 432 vs 580 [34.0%] of 1705 participants, P = .003). During the Omicron BA.1 period, 5 days after symptom onset, 507 of 1613 people (31.1%) with COVID-19 stated that their symptoms were similar, and 95 people (5.9%) reported worsening symptoms. Among people testing positive, 80.2% of participants who were symptomatic and retested remained positive 5 days after symptom onset. Conclusions and Relevance: In this cross-sectional study, COVID-19 upper respiratory tract symptoms were more commonly reported during the Omicron BA.1 period than during the pre-Delta and Delta periods, with differences by vaccination status. Rapid antigen test positivity remained high 5 days after symptom onset, supporting guidelines requiring a negative test to inform the length of the isolation period.

Integrating Rapid Diabetes Screening Into a Latinx Focused Community-Based Low-Barrier COVID-19 Testing Program.

Importance: Community-based COVID-19 testing and vaccination programs play a crucial role in mitigating racial and ethnic disparities in COVID-19 service delivery. They also represent a platform that can be leveraged to expand access to testing for chronic diseases, including diabetes, that disproportionately affect the Latinx community and other marginalized communities. Objective: To evaluate outcomes associated with a diabetes testing strategy designed to reach low-income Latinx persons by leveraging COVID-19 testing infrastructure and community trust developed during the COVID-19 pandemic. Design, Setting, and Participants: This health care improvement study was conducted from August 1 to October 5, 2021, at an outdoor, community-based COVID-19 testing site at a transport hub in the Mission Neighborhood in San Francisco, California. Because the program was designed to expand access to diabetes screening to the local community, all individuals presenting for on-site testing were eligible. Data were analyzed in November 2021. Interventions: Integration of rapid, point-of-care hemoglobin A1c screening as a testing option in an existing low-barrier COVID-19 testing program. Main Outcomes and Measures: Evaluation was guided by the Reach, Effectiveness, Adoption, Implementation and Maintenance (RE-AIM) framework and utilized programmatic data and structured surveys among clients and staff. Results: Of 6631 individuals tested (median [IQR] age 39.3 [29.7-51.3] years; 3417 [52.3%] female, 4348 [65.6%] Latinx), 923 (13.9%) underwent hemoglobin A1c testing with or without COVID-19 testing and 5708 (86.1%) underwent COVID-19 testing only. Individuals tested for diabetes were more likely to be Latinx (763 of 923 individuals [82.7%] who underwent testing were Latinx vs 3585 of 5708 [62.8%] not undergoing testing), have an annual household income of less than $50 000 (450 individuals [81.2%] vs 2409 individuals [66.0%]), and not have health insurance (381 individuals [47.2%] vs 1858 individuals [39.9%]), and 206 (48.0%) had never tested for diabetes before. Overall, 313 (33.9%) and 113 (12.2%) individuals had prediabetes and diabetes, respectively; only 141 of 354 of these individuals (39.8%) had a primary care clinician whom they had seen in the prior 12 months, which was lower among Latinx individuals (113 of 307 individuals [36.8%] vs 28 of 47 [59.6%]). Acceptability of the rapid testing program was high-98% were satisfied with their visit and 96% said they would return for future services; key factors underpinning acceptability included friendly staff, efficiency, and a convenient location. Conclusions and Relevance: In this health care improvement study conducted within an existing community-based COVID-19 testing program, integrating rapid testing for diabetes was feasible, reached low-income Latinx individuals, and identified many persons with prediabetes and diabetes, most of whom lacked access to services in formal health care settings. Leveraging pandemic-related public health responses represents an important opportunity for engaging socioeconomically disadvantaged populations into care for diabetes.