Physics and Applications of Laser Diode Chaos

An overview of chaos in laser diodes is provided which surveys experimental achievements in the area and explains the theory behind the phenomenon. The fundamental physics underpinning this behaviour and also the opportunities for harnessing laser diode chaos for potential applications are discussed. The availability and ease of operation of laser diodes, in a wide range of configurations, make them a convenient test-bed for exploring basic aspects of nonlinear and chaotic dynamics. It also makes them attractive for practical tasks, such as chaos-based secure communications and random number generation. Avenues for future research and development of chaotic laser diodes are also identified.Comment: Published in Nature Photonic

The evolving SARS-CoV-2 epidemic in Africa: Insights from rapidly expanding genomic surveillance

INTRODUCTION Investment in Africa over the past year with regard to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) sequencing has led to a massive increase in the number of sequences, which, to date, exceeds 100,000 sequences generated to track the pandemic on the continent. These sequences have profoundly affected how public health officials in Africa have navigated the COVID-19 pandemic. RATIONALE We demonstrate how the first 100,000 SARS-CoV-2 sequences from Africa have helped monitor the epidemic on the continent, how genomic surveillance expanded over the course of the pandemic, and how we adapted our sequencing methods to deal with an evolving virus. Finally, we also examine how viral lineages have spread across the continent in a phylogeographic framework to gain insights into the underlying temporal and spatial transmission dynamics for several variants of concern (VOCs). RESULTS Our results indicate that the number of countries in Africa that can sequence the virus within their own borders is growing and that this is coupled with a shorter turnaround time from the time of sampling to sequence submission. Ongoing evolution necessitated the continual updating of primer sets, and, as a result, eight primer sets were designed in tandem with viral evolution and used to ensure effective sequencing of the virus. The pandemic unfolded through multiple waves of infection that were each driven by distinct genetic lineages, with B.1-like ancestral strains associated with the first pandemic wave of infections in 2020. Successive waves on the continent were fueled by different VOCs, with Alpha and Beta cocirculating in distinct spatial patterns during the second wave and Delta and Omicron affecting the whole continent during the third and fourth waves, respectively. Phylogeographic reconstruction points toward distinct differences in viral importation and exportation patterns associated with the Alpha, Beta, Delta, and Omicron variants and subvariants, when considering both Africa versus the rest of the world and viral dissemination within the continent. Our epidemiological and phylogenetic inferences therefore underscore the heterogeneous nature of the pandemic on the continent and highlight key insights and challenges, for instance, recognizing the limitations of low testing proportions. We also highlight the early warning capacity that genomic surveillance in Africa has had for the rest of the world with the detection of new lineages and variants, the most recent being the characterization of various Omicron subvariants. CONCLUSION Sustained investment for diagnostics and genomic surveillance in Africa is needed as the virus continues to evolve. This is important not only to help combat SARS-CoV-2 on the continent but also because it can be used as a platform to help address the many emerging and reemerging infectious disease threats in Africa. In particular, capacity building for local sequencing within countries or within the continent should be prioritized because this is generally associated with shorter turnaround times, providing the most benefit to local public health authorities tasked with pandemic response and mitigation and allowing for the fastest reaction to localized outbreaks. These investments are crucial for pandemic preparedness and response and will serve the health of the continent well into the 21st century

Polarization synchronization in unidirectionally coupled vertical-cavity surface-emitting lasers with orthogonal optical injection

International audienceWe analyze theoretically the polarization dynamics in unidirectionally coupled vertical-cavity surface-emitting lasers ͑VCSELs͒. The master VCSEL is subject to an isotropic optical feedback. The slave VCSEL is subject to an orthogonal optical injection from the master VCSEL, i.e., only the linearly polarized mode orthogonal to the dominant linearly polarized mode of the free-running slave VCSEL is injected into the slave VCSEL. This laser configuration may lead the slave VCSEL polarization to switch to that of the injected master laser field. The injected power required for polarization switching depends on the frequency detuning. We identify in the plane of the injection parameters two regions of enhanced synchronization between the injected LP mode and the corresponding slave LP mode. In the so-called region II the slave VCSEL exhibits anticorrelated dynamics in its two LP modes while in the so-called region I the slave VCSEL exhibits dynamics in only one LP mode, which corresponds to the polarization of the injected field. The two regions exhibit different synchronization properties in both the LP mode dynamics and total intensity dynamics. We furthermore analyze the dependency of the synchronization quality on the parameter mismatch between master and slave VCSELs and on the polarization switching properties of each VCSEL

Bifurcation to polarization switching and locking in vertical-cavity surface-emitting lasers with optical injection

info:eu-repo/semantics/publishe

Digital self-care for improved access to family planning and reproductive health services among adolescents in Rwanda: preliminary findings from a pilot study of CyberRwanda.

Adolescents experience significant barriers, including stigma and discrimination, to accessing voluntary family planning and reproductive health (FP/RH) services in Rwanda. Self-care interventions have been shown to reduce social barriers to FP/RH care, but little is known about the effectiveness of digital self-care for adolescents, particularly in low-resource settings. This paper presents findings from a pilot study of CyberRwanda, a digital self-care intervention providing comprehensive sexuality education and confidential online ordering of contraceptives for school-aged youth in Rwanda through a rights-based approach. A mixed-methods pilot study was conducted from November 2019 to February 2020 to assess feasibility, acceptability, and engagement and to inform a future impact evaluation. Surveys were administered to a random sample of 158 students aged 12-19 years in three secondary schools. In-depth interviews were conducted with students, parents, teachers, pharmacists, district-level administrators, and youth centre staff. Descriptive statistics were calculated and qualitative data were analyzed using a thematic coding approach. One hundred and fifty-eight surveys and 28 interviews were conducted. Results revealed high demand for CyberRwanda in schools. Students were interested in engaging with the program and found the FP/RH content relevant to their needs. However, few purchased contraceptive products through the online ordering system. There are preliminary indications that CyberRwanda may improve access to FP/RH information. An extended implementation period and further research are needed to measure the long-term impacts of the program and evaluate whether this digital self-care intervention can increase uptake of contraceptive methods and reduce adolescent pregnancy among school-aged youth

Measuring sexual behavior among in-school youth in Rwanda: a cross-sectional analysis of self-reported timing of first sex and correlates of early sexual debut.

PurposeUnderstanding the timing of sexual debut is critical for informing sexual and reproductive health interventions. We investigated sexual behavior and early sexual debut among Rwandan youth.MethodsWe conducted a cross-sectional analysis of data from a cluster-randomized trial with 6079 students ages 12-19 years in Rwanda. We examined predictors of early sexual debut (<15 years) using logistic regression to estimate odds ratios and factors associated with the timing of first sex using Cox models to estimate hazard ratios. Interpretations of sex were also explored.ResultsParticipants were 15 years and 51.5% female on average; 1723 (28.3%) reported sexual activity. Among the 1320 participants who provided an age of sexual debut, 51.4% reported sex at ≤12 years and 75.7% at<15 years. Males had a higher odds of early sexual debut (adjusted odds ratio: 2.40; 95% CI: 1.99, 2.90) and a higher hazard of sex occuring at an earlier age than females (adjusted hazard ratio: 1.91; 95% CI: 1.67, 2.20). One-third of participants considered "sexual intercourse" to include kissing, touching, or masturbation.ConclusionsSex at ≤12 years was frequently reported, indicating that interventions facilitating access to youth-friendly sexual and reproductive health services are necessary before age 12. Validation studies are needed to evaluate how interpretations of sexual intercourse influence the assessment of sexual activity.Clinical trialNCT04198272