Breaking Phonon Bottlenecks through Efficient Auger Processes in Perovskite Nanocrystals.

The hot phonon bottleneck has been under intense investigation in perovskites. In the case of perovskite nanocrystals, there may be hot phonon bottlenecks as well as quantum phonon bottlenecks. While they are widely assumed to exist, evidence is growing for the breaking of potential phonon bottlenecks of both forms. Here, we perform state-resolved pump/probe spectroscopy (SRPP) and time-resolved photoluminescence spectroscopy (t-PL) to unravel hot exciton relaxation dynamics in model systems of bulk-like 15 nm nanocrystals of CsPbBr3 and FAPbBr3, with FA being formamidinium. The SRPP data can be misinterpreted to reveal a phonon bottleneck even at low exciton concentrations, where there should be none. We circumvent that spectroscopic problem with a state-resolved method that reveals an order of magnitude faster cooling and breaking of the quantum phonon bottleneck that might be expected in nanocrystals. Since the prior pump/probe methods of analysis are shown to be ambiguous, we perform t-PL experiments to unambiguously confirm the existence of hot phonon bottlenecks as well. The t-PL experiments reveal there is no hot phonon bottleneck in these perovskite nanocrystals. Ab initio molecular dynamics simulations reproduce experiments by inclusion of efficient Auger processes. This experimental and theoretical work reveals insight on hot exciton dynamics, how they are precisely measured, and ultimately how they may be exploited in these materials.

Point Defects in Two-Dimensional Ruddlesden-Popper Perovskites Explored with Ab Initio Calculations.

Two-dimensional Ruddlesden-Popper (RP) halide perovskites stand out as excellent layered materials with favorable optoelectronic properties for efficient light-emitting, spintronic, and other spin-related applications. However, properties often determined by defects are not well understood in these perovskite systems. This work investigates the ground state electronic structure of commonly formed defects in a typical RP perovskite structure by density functional theory. Our study reveals that these 2D perovskites generally retain their defect tolerance with limited perturbation of the electronic structure in the case of neutral-type point defects. In contrast, donor/acceptor defects induce deep midgap states, potentially causing harm to the material's electronic performance. To retain positive intrinsic properties, the halide vacancies and interstitial defects should be avoided. The observed strong electron localization results in trap states and consequently leads to reduced device performance. This understanding can guide experimental efforts that aim for improved 2D halide perovskite-based device performance.

Ag-Bi Charge Redistribution Creates Deep Traps in Defective Cs2AgBiBr6: Machine Learning Analysis of Density Functional Theory.

Lead-free double perovskites hold promise for stable and environmentally benign solar cells; however, they exhibit low efficiencies because defects act as charge recombination centers. Identifying trap-assisted loss mechanisms and developing defect passivation strategies constitute an urgent goal. Applying unsupervised machine learning to density functional theory and nonadiabatic molecular dynamics, we demonstrate that negatively charged Br vacancies in Cs2AgBiBr6 create deep hole traps through charge redistribution between the adjacent Ag and Bi atoms. Vacancy electrons are first accepted by Bi and then shared with Ag, as the trap transforms from shallow to deep. Subsequent charge losses are promoted by Ag and Bi motions perpendicular to rather than along the Ag-Bi axis, as can be expected. In contrast, charge recombination in pristine Cs2AgBiBr6 correlates most with displacements of Cs atoms and Br-Br-Br angles. Doping with In to replace Ag at the vacancy maintains the electrons at Bi and keeps the trap shallow.

Excited-State Properties of Defected Halide Perovskite Quantum Dots: Insights from Computation.

CsPbBr3 quantum dots (QDs) have been recently suggested for their application as bright green light-emitting diodes (LEDs); however, their optical properties are yet to be fully understood and characterized. In this work, we utilize time-dependent density functional theory to analyze the ground and excited states of the CsPbBr3 clusters in the presence of various low formation energy vacancy defects. Our study finds that the QD perovskites retain their defect tolerance with limited perturbance to the simulated UV-vis spectra. The exception to this general trend is that Br vacancies must be avoided, as they cause molecular orbital localization, resulting in trap states and lower LED performance. Blinking will likely still plague CsPbBr3 QDs, given that the charged defects critically perturb the spectra via red-shifting and lower absorbance. Our study provides insight into the tunability of CsPbBr3 QDs optical properties by understanding the nature of the electronic excitations and guiding improved development for high-performance LEDs.

Anxiolytic-like effects induced by nitric oxide synthase inhibitors microinjected into the medial amygdala of rats.

RATIONALE: The amygdaloid complex plays a central role in the neuroanatomical circuits that coordinate defensive responses. Nitric oxide (NO) has been involved in the neurochemical, hormonal, and behavioral changes related to stress and anxiety. A high density of NO-producing neurons is observed in the medial amygdala (MeA). These neurons are activated after exposure to threatening stimuli such as a live predator. OBJECTIVE: To test the hypothesis that microinjection into the MeA of two NO synthase inhibitors, NG-nitro-L-arginine methyl ester (L-NAME) or 7-nitroindazole (7-NI), would produce anxiolytic effects. METHODS: Male Wistar rats (n=8-10/group) were submitted to stereotaxic surgery to implant bilateral stainless steel guide cannulae aimed at the MeA. Six days after the surgery, the animals received intra-MeA microinjections of the drugs or vehicle and, 10 min later, were submitted to the elevated plus-maze (EPM) or the light-dark transition procedures. RESULTS: Both L-NAME (50-200 nmol) and 7-NI (5 and 10 nmol) increased open-arm exploration in the EPM without changing the number of enclosed arm entries, indicating an anxiolytic-like effect. The anxiolytic-like effect of L-NAME (200 nmol) was prevented by pretreatment with L-arginine (100 nmol). Injections of 7-NI or L-NAME outside the MeA did not produce any significant change in EPM exploration. When tested in the light-dark test, L-NAME (200 nmol) or 7-NI (10 nmol) increased the time when the animal remained in the light compartment of the light-dark box. CONCLUSIONS: The present results suggest that inhibition of NO formation in the MeA produces anxiolytic-like effect in rats.

Paquimeningitis craneal hipertrófica idiopática / Idiopathic hypertrophic cranial pachymeningitis

La paquimeningitis craneal hipertrófica idiopática es un raro proceso inflamatorio crónico de etiología desconocida que produce engrosamiento de la duramadre y alteraciones neurológicas progresivas debido a la compresión de estructuras vecinas. Se presenta el caso de una mujer adulta con un cuadro clínico crónico de cefalea, fiebre, pérdida progresiva de la visión y neuropatía óptica bilateral. El diagnóstico se basó en la visualización de la duramadre engrosada en las neuroimágenes y en la exclusión de causas conocidas mediante estudios histopatológicos. La terapia con corticoesteroides mejoró la cefalea pero no el déficit visual. El diagnóstico y el seguimiento de esta entidad se han facilitado con la utilización de la resonancia magnética cerebral con medio de contraste. La biopsia de duramadre sigue siendo la regla de oro para el diagnóstico definitivo de la enfermedad. La terapia con esteroides produce mejoría en un buen número de pacientes; sin embargo, son frecuentes las recaídas por lo que es necesario el uso concomitante de otro inmunosupresor como la ciclofosfamida o la azatioprina. La mortalidad es baja, pero son comunes las secuelas neurológicas definitivas.

Idiopathic hypertrophic cranial pachymeningitis is an infrequent chronic inflammatory process of unknown etiology which causes thickening of the dura mater and progressive neurologic alterations due to the compression of adjacent structures. A case is presented of an adult woman with a clinical syndrome consisting of headache, progressive visual loss and bilateral optic neuropathy. The diagnosis was based upon visualization of the thickened dura mater in neuroimaging studies and the exclusion of known causes by histopathological examination. Diagnosis and follow-up of this condition are currently easier with the use of nuclear magnetic resonance with contrast medium. Biopsy of the dura mater continues to be the gold standard for the definitive diagnosis of this disease. Steroid therapy causes clinical improvement in most of the patients; however, relapses are frequent, making necessary the concomitant use of other immunosuppressive agents such as cyclophosphamide or azathioprine. Mortality is low but definitive neurologic sequelae are common.

Experiencias de PROPACE en sus primeros 30 anos en el manejo de la parálisis cerebral / The last thirty years of the experience of the PROPACE in cerebral paralisia

Baseia-se no relato das experiências dos ùltimos trinta anos da PROPACE, especializada na Reabilitaçäo de crianças com Paralisia Cerebral

Razöes para näo usar contracepçäo entre mulheres do estado de Säo Paulo / Reasons for no use contraceptives between women from Säo Paulo State

Foram entrevistadas em seus domicílios mulheres casadas ou amasiadas de 15 a 49 anos de idade, que moravam em bairros ou municípios com alta concentraçäo de populaçäo de baixa renda, na área metropolitana e no interior do Estado de Säo Paulo. Neste trabalho säo apresentados os resultados referentes ás razöes pelas quais as mulheres com risco de engravidar näo usavam um método contraceptivo. Também säo apresentados os resultados referentes a características sócio-demográficas dessas mulheres. Foram consideradas como tendo risco de engravidar as casadas e amasiadas que näo estavam grávidas nem menopausadas por ocasiäo da entrevista. Foram definidas como menopausadas aquelas que näo menstruavam há um ano ou mais na data da entrevista. As principais razöes para näo usrem nenhum método foram "queria filhos", "dificuldades para engravidar" e "näo conhece método anticoncepcional". As maiores percentagens de näo usuárias tinham menos de 20 anos de idade, näo tinham freqüentado a escola ou näo tinham completado a primeira série do primeiro grau, e näo tinham nenhum filho