Calibration Challenges for Future Radio Telescopes

Instruments for radio astronomical observations have come a long way. While the first telescopes were based on very large dishes and 2-antenna interferometers, current instruments consist of dozens of steerable dishes, whereas future instruments will be even larger distributed sensor arrays with a hierarchy of phased array elements. For such arrays to provide meaningful output (images), accurate calibration is of critical importance. Calibration must solve for the unknown antenna gains and phases, as well as the unknown atmospheric and ionospheric disturbances. Future telescopes will have a large number of elements and a large field of view. In this case the parameters are strongly direction dependent, resulting in a large number of unknown parameters even if appropriately constrained physical or phenomenological descriptions are used. This makes calibration a daunting parameter estimation task, that is reviewed from a signal processing perspective in this article.Comment: 12 pages, 7 figures, 20 subfigures The title quoted in the meta-data is the title after release / final editing

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

On the Origin of the Color Shift in White-Emitting OLEDs

White-emitting organic light-emitting diodes (OLEDs) notoriously suffer from brightness-dependent color shifts. Based on experimental data and fundamental considerations about charge-transport and trapping, a quantitative model is developed which gives insight into the origin of this shift and describes the experimental data extremely well. Having understood the major contribution to the spectral instability, a device architecture is designed that shows excellent color stability over a wide range of brightness levels

On the Origin of the Color Shift in White-Emitting OLEDs

White-emitting organic light-emitting diodes (OLEDs) notoriously suffer from brightness-dependent color shifts. Based on experimental data and fundamental considerations about charge-transport and trapping, a quantitative model is developed which gives insight into the origin of this shift and describes the experimental data extremely well. Having understood the major contribution to the spectral instability, a device architecture is designed that shows excellent color stability over a wide range of brightness levels

Alkali Metal Doped Organic Molecules on Insulators: Charge Impact on the Optical Properties

Doping-induced absorption changes of organic molecules on an insulating solid are reported. The charge transfer between alkali metal atoms and individual molecules on a surface leads to new electronic transitions identified with optical absorption spectroscopy. Progressive doping allows the discrimination of neutral, monoanionic, and dianionic molecules in the solid state through examination of the spectra and rate equation modeling

Molecular Oxygen as a Redox Catalyst in IntramolecularPhotocycloadditions of Coumarins

Oxygen as a catalyst! While oxygen is usually excluded in nonoxidative photochemical reactions, the photocycloaddition of 3-(alk-4-en-1-yl)-substituted coumarins greatly benefits from the presence of O 2, which was shown to act as a redox catalyst, preferentially in combination with the common antioxidant 3,5-di-tert-butyl-4-hydroxytoluene (BHT). Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.This work was supported by the Universitat zu Koln and the Fonds der Chemischen Industrie. We thank Dr. S. Neufeind and Dipl.-Chem. A. M. Heinsch fur stimulating discussions.Kranz, DP.; Griesbeck, AG.; Alle, R.; Pérez Ruiz, R.; Neudörfl, JM.; Meerholz, K.; Schmalz, H. (2012). Molecular Oxygen as a Redox Catalyst in IntramolecularPhotocycloadditions of Coumarins. Angewandte Chemie International Edition. 51(24):6000-6004. doi:10.1002/anie.201201222S60006004512

Multi-tracer model for staging cortical amyloid deposition using PET imaging

OBJECTIVE: To develop and evaluate a model for staging cortical amyloid deposition using PET with high generalizability. METHODS: Three thousand twenty-seven individuals (1,763 cognitively unimpaired [CU], 658 impaired, 467 with Alzheimer disease [AD] dementia, 111 with non-AD dementia, and 28 with missing diagnosis) from 6 cohorts (European Medical Information Framework for AD, Alzheimer's and Family, Alzheimer's Biomarkers in Daily Practice, Amsterdam Dementia Cohort, Open Access Series of Imaging Studies [OASIS]-3, Alzheimer's Disease Neuroimaging Initiative [ADNI]) who underwent amyloid PET were retrospectively included; 1,049 individuals had follow-up scans. With application of dataset-specific cutoffs to global standard uptake value ratio (SUVr) values from 27 regions, single-tracer and pooled multitracer regional rankings were constructed from the frequency of abnormality across 400 CU individuals (100 per tracer). The pooled multitracer ranking was used to create a staging model consisting of 4 clusters of regions because it displayed a high and consistent correlation with each single-tracer ranking. Relationships between amyloid stage, clinical variables, and longitudinal cognitive decline were investigated. RESULTS: SUVr abnormality was most frequently observed in cingulate, followed by orbitofrontal, precuneal, and insular cortices and then the associative, temporal, and occipital regions. Abnormal amyloid levels based on binary global SUVr classification were observed in 1.0%, 5.5%, 17.9%, 90.0%, and 100.0% of individuals in stage 0 to 4, respectively. Baseline stage predicted decline in Mini-Mental State Examination (MMSE) score (ADNI: n = 867, F = 67.37, p 3,000 individuals across cohorts and radiotracers and detects preglobal amyloid burden and distinct risk profiles of cognitive decline within globally amyloid-positive individuals