Design Rules for Obtaining Narrow Luminescence from Semiconductors Made in Solution.

Solution-processed semiconductors are in demand for present and next-generation optoelectronic technologies ranging from displays to quantum light sources because of their scalability and ease of integration into devices with diverse form factors. One of the central requirements for semiconductors used in these applications is a narrow photoluminescence (PL) line width. Narrow emission line widths are needed to ensure both color and single-photon purity, raising the question of what design rules are needed to obtain narrow emission from semiconductors made in solution. In this review, we first examine the requirements for colloidal emitters for a variety of applications including light-emitting diodes, photodetectors, lasers, and quantum information science. Next, we will delve into the sources of spectral broadening, including "homogeneous" broadening from dynamical broadening mechanisms in single-particle spectra, heterogeneous broadening from static structural differences in ensemble spectra, and spectral diffusion. Then, we compare the current state of the art in terms of emission line width for a variety of colloidal materials including II-VI quantum dots (QDs) and nanoplatelets, III-V QDs, alloyed QDs, metal-halide perovskites including nanocrystals and 2D structures, doped nanocrystals, and, finally, as a point of comparison, organic molecules. We end with some conclusions and connections, including an outline of promising paths forward.

Synthesis of ß,ß-Disubstituted Styrenes via Trimethylsilyl Trifluoromethanesulfonate-Promoted Aldehyde-Aldehyde Aldol Coupling-Elimination.

In the presence of trimethylsilyl trifluoromethanesulfonate (TMSOTf) and 2,6-lutidine, α,α-disubstituted aldehydes condense with electron-rich aromatic aldehydes to yield ß,ß-disubstituted styrenes. More electron-rich aromatic aldehydes react more rapidly and in higher yield. Preliminary results suggest that the reaction may proceed via the ionization and formal deformylation of an aldol intermediate.

Extremely Long-Lived Charge Donor States Formed by Visible Irradiation of Quantum Dots.

Using cyclic voltammetry under illumination, we recently demonstrated that CdS quantum dots (QDs) form charge donor states that live for at least several minutes after illumination ends, ∼12 orders of magnitude longer than expected for free carriers. This time scale suggests that the conventionally accepted mechanism of charge transfer, wherein charges directly transfer to an acceptor following exciton dissociation, cannot be complete. Because of these long time scales, this unconventional pathway is not readily observed using time-resolved spectroscopy to probe charge transfer dynamics. Here, we investigated the chemical nature of these charge donor states using cyclic voltammetry under illumination coupled with NMR spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and optical spectroscopy. Our data reveal that charges are stored locally rather than as free carriers, and the number of charges stored is dependent on the QD surface ligation and stoichiometry. Altogether, our results confirm that electrons are stored at ligated surface Cd, these sites are competent charge donors, and this storage is charge balanced by X-type ligand desorption. We found that charge storage occurs in every QD system studied, including CdS, CdSe, and InP capped with carboxylate and phosphonate ligands.

A GIS-based methodology for predicting walking track stability.

To manage extensive walking track (trail) systems effectively, managers need information about the condition, stability and likely rates of deterioration of tracks. This information may be impractical to obtain from ground inspections, particularly if the track systems of interest encompass hundreds or even thousands of kilometres of tracks. Two trials were undertaken in Tasmania, Australia to assess the practicality of using a GIS-based methodology to predict track 'types', types being classes of environmental and track-orientation variables that are associated with characteristic rates of widening and erosion as tracks develop. In the first trial, type values previously measured at 500 18 m long monitoring sites located across a wide range of environments were compared with those predicted for 50-75 m long track segments that included or overlapped the sites. In the second trial, the type values of 300 75 m track segments distributed across five tracks were measured in the field and predicted using a refined version of the methodology. The reliability of the methodology was slightly improved in the second trial, in which 50% of the predictions were accurate and 38% were out by one category. Predictions of the statistical distribution of types were prone to bias due to local conditions on individual tracks, but agreed closely with the measured distribution across the entire data set. The methodology was used to assess track types across the 1700 km track system managed by the Tasmanian Parks and Wildlife Service, as a basis for identifying and prioritising management responses including track stabilisation works. It is likely that with further refinement and with better GIS information, the methodology could reliably predict the stability of individual tracks.

Trends in gender, race, and ethnic diversity among prospective physical medicine and rehabilitation physicians.

BACKGROUND: As the proportion of women and individuals who are underrepresented in medicine slowly rises, disparities persist in numerous arenas and specialties. In physical medicine and rehabilitation (PM&R), there is a continued need to focus on diversity among trainees. This study aims to evaluate diversity among PM&R applicants and residents over the past 6 years. OBJECTIVE: To describe the demographic trends in PM&R over the last 6 years and compare those findings with trends in other specialties. DESIGN: Surveillance. SETTING: Analyses of national databases from self-reported questionnaires. PARTICIPANTS: The study consists of 126,833 medical school matriculants, 374,185 resident applicants, and 326,134 resident trainees over the last 6 years. MAIN OUTCOME MEASURES: Self-reported demographic data from the Association of American Medical Colleges and the Accreditation Council for Graduate Medical Education were analyzed for medical school matriculants, PM&R applicants, and current residents for the cycles of 2014-2015 to 2019-2020. The data were then comparatively reviewed between PM&R and other medical specialties. RESULTS: In the 6 cycles evaluated, women accounted for 36%-39% of PM&R residents, but 47%-48% in non-PM&R specialties. Women applicants to the PM&R specialty averaged 34.4% over the 6 years analyzed, which was the fourth lowest of the 11 specialties examined. Black or African American and Hispanic, Latino, or of Spanish Origin populations each accounted for only 6% of PM&R residents. PM&R demonstrated a noticeably higher proportion of White (62.1% vs. 60.3%) and an observably lower proportion of Black or African American (6.0% vs. 7.1%) and Hispanic, Latino, or of Spanish Origin (6.3% vs. 7.9%) residents compared with non-PM&R specialties. CONCLUSION: There is underrepresentation of women and multiple racial and ethnic minority groups in the field of PM&R from applicants to trainees demonstrating a need to improve recruitment efforts.

Multiple Sclerosis and the Choroid Plexus: Emerging Concepts of Disease Immunopathophysiology.

BACKGROUND: The coexistence of multiple sclerosis and intracranial neoplasms is very rare, and whether this occurrence can be explained by a causal relationship or by coincidence remains a matter of debate. Possible roles of the choroid plexus as a site of tumor cell invasion and lymphocyte infiltration into the central nervous system have been hypothesized in recent studies. METHODS: We describe a 13-year-old boy with concurrent multiple sclerosis and choroid plexus papilloma, then review the published literature with a focus on the pathophysiologic mechanisms of neuroinflammation in multiple sclerosis and the potential role of the choroid plexus in this process. RESULTS: A growing body of evidence suggests that both physical and functional dysregulation of the choroid plexus may be a common mechanism underlying the pathophysiology of central nervous system inflammation. CONCLUSIONS: In multiple sclerosis, the choroid plexus could act as a gateway for lymphocyte entry from the peripheral blood into the central nervous system at its earlier stages. However, future studies are needed to identify whether structural alterations of the choroid plexus play a role in the pathophysiology of multiple sclerosis and to provide suitable models to determine their consequences.

Monitoring and modelling walking track impacts in the Tasmanian Wilderness World Heritage Area, Australia.

A program has been developed for monitoring the condition of unimproved walking tracks on a 1000-km track system in Western Tasmania, and it has been used as the basis of an eight-year study of track-impact development. The monitoring technique involves measuring track depth and two track-width indicators at permanently marked and widely dispersed sites, each site comprising ten transects located at 2-m intervals. Sites have been 'typed' on the basis of track slope, drainage and substrate characteristics, and the typing scheme has been tested and refined by assessing the relationship between type-usage groups and observed impacts. Analysis reveals that track depth and rates of erosion are strongly influenced by track type and to a lesser extent by usage, while track width is influenced mainly by usage and track bogginess. The time-invariant variable 'usage gradient' was introduced to compensate for the fact that usage levels on most walking tracks in Western Tasmania have varied over time. Data derived from multiple inspections at 2-3 year intervals since 1994 from over 250 sites have been used to derive impact/time curves for different type-'usage gradient' groups. Each of the impact variables can be approximated by the formula m = alphatBeta, where m is the expected value of the impact variable, t is chronological time, and alpha and Beta are constants characteristic of the impact variable and type-'usage gradient' group in question. The typing scheme and impact-development model have the potential to be used for systematically describing and predicting impacts over extensive systems of 'typed' tracks. The implications of these findings for the ongoing monitoring, sitting and management of walking tracks are discussed.