In a generic synthesis approach, all three CsPbX3 (X=Cl, Br and I) perovskite nanocrystals having near unity quantum yields is reported. This has been achieved by injecting the desired amount of ...preformed alkylammonium halide salts which acted as a dual source providing halide ions and the capping agent to an equimolar amount of non‐halide Pb and Cs precursors in a reaction flask at an optimized reaction temperature. The composition sensitivity of Pb to Cs ratio, high temperature reaction, and injection of ammonium halide remained the key parameters for obtaining the high quantum yields. Details of the reaction process, use of different reagents and setting up the reaction parameters are reported.
Three colors: A rational synthesis of CsPbX3 (X=Cl, Br, and I) nanocrystals gives all three perovskites with near unity photoluminescence quantum yield. Careful analysis of the reaction chemistry and the parameters allows a generic reaction to be developed.
We show that a thermally isolated system driven across a quantum phase transition by a noisy control field exhibits anti-Kibble-Zurek behavior, whereby slower driving results in higher excitations. ...We characterize the density of excitations as a function of the ramping rate and the noise strength. The optimal driving time to minimize excitations is shown to scale as a universal power law of the noise strength. Our findings reveal the limitations of adiabatic protocols such as quantum annealing and demonstrate the universality of the optimal ramping rate.
Doping in perovskite nanocrystals adopts different mechanistic approach in comparison to widely established doping in chalcogenide quantum dots. The fast formation of perovskites makes the dopant ...insertions more competitive and challenging. Introducing alkylamine hydrochloride (RNH3Cl) as a promoting reagent, precise controlled doping of MnII in CsPbCl3 perovskite nanocrystals is reported. Simply, by changing the amount of RNH3Cl, the Mn incorporation and subsequent tuning in the excitonic as well as Mn d–d emission intensities are tailored. Investigations suggested that RNH3Cl acted as the chlorinating source, controlled the size, and also helps in increasing the number of particles. This provided more opportunity for Mn ions to take part in reaction and occupied the appropriate lattice positions. Carrying out several reactions with varying reaction parameters, the doping conditions are optimized and the role of the promoting reagent for both doped and undoped systems are compared.
Programming perovskite doping: Controlled doping of MnII in CsPbCl3 nanocrystals was performed by using alkylamine hydrochloride (RNH3Cl) as doping promoting reagent. The dopant emission intensity is tailored as a function of Mn doping governed by the amount of introduced RNH3Cl. This helped in stabilizing and also controlling the size of CsPbCl3 nanocrystals, which in turn facilitated efficient doping.
High-energy-emitting CsPbCl3 nanocrystals have shown significant loss and enhancement of their emission intensity (∼40–50 folds) during purification and surface treatments, respectively. This ...confirms that the surfaces of these nanocrystals are very sensitive. In this Letter, physical insights of the interface bindings on the surface of these blue-emitting CsPbCl3 nanocrystals with different passivating agents and their consequential impact on purification are investigated. Using various metal chlorides irrespective of the charge and size of the metal ions, metal acetates, and nonmetal chloride, the predominant influence of chloride ions in helping retrieve/intensify the blue emission is established. The purification processes are observed to be very delicate, and successive purifications with introduction of polar nonsolvents led to the transformation of an emitting cubic CsPbCl3 phase to nonemitting tetragonal CsPb2Cl5 phase nanocrystals irreversibly. The impact of various salt additions only temporarily helped in enhancing the emission, but the phase change remained inevitable upon successive purification. However, as a remedy, by in situ use of alkylammonium chloride salt in high-temperature reactions, the surface binding was improved, and significant emission as well as the phase could be retained with successive purifications.
Cerebellar transcranial direct current stimulation (ctDCS) is challenging due to the complexity of the cerebellar structure which is reflected by the well-known variability in ctDCS effects. ...Therefore, our objective is to present a freely available computational modeling pipeline for cerebellar lobules' optimal stimulation (CLOS).
CLOS can optimize lobule-specific electric field distribution following finite element analysis (FEA) using freely available computational modeling pipelines. We modeled published ctDCS montages with 5 cm × 5 cm anode placed 3 cm lateral to inion, and the same sized cathode was placed on the: (1) contralateral supra-orbital area (called Manto montage), and (2) buccinators muscle (called Celnik montage). Also, a published (3) 4×1 HD-ctDCS electrode montage was modeled. We also investigated the effects of the subject-specific head model versus Colin 27 average head model on lobule-specific electric field distribution. Three-way analysis of variance (ANOVA) was used to determine the effects of lobules, montage, and head model on the electric field distribution. The differences in lobule-specific electric field distribution across different freely available computational pipelines were also evaluated using subject-specific head model. We also presented an application of our computational pipeline to optimize a ctDCS electrode montage to deliver peak electric field at the cerebellar lobules VII-IX related to ankle function.
Eta-squared effect size after three-way ANOVA for electric field strength was 0.05 for lobule, 0.00 for montage, 0.04 for the head model, 0.01 for lobule
montage interaction, 0.01 for lobule
head model interaction, and 0.00 for montage
head model interaction. The electric field strength of both the Celnik and the Manto montages affected the lobules Crus I/II, VIIb, VIII, and IX of the targeted cerebellar hemisphere where Manto montage had a spillover to the contralateral cerebellar hemisphere. The 4×1 HD-ctDCS montage primarily affected the lobules Crus I/II of the targeted cerebellar hemisphere. All three published ctDCS montages were found to be not optimal for ankle function (lobules VII-IX), so we presented a novel HD-ctDCS electrode montage.
Our freely available CLOS pipeline can be leveraged to optimize electromagnetic stimulation to target cerebellar lobules related to different cognitive and motor functions.
For varying the size of perovskite nanocrystals, variation in the reaction temperature and tuning the ligand chain lengths are established as the key parameters for high-temperature ...solution-processed synthesis. These also require sharp cooling for obtaining desired dimensions and optical stability. In contrast, using preformed alkylammonium bromide salt as the precise dimension-controlling reagent, wide window size tunable CsPbBr3 nanocrystals were reported without varying the reaction temperature or changing the ligands. The size tunability even with ∼1 nm step growth regimes was achieved as a function of only the concentration of added alkylammonium bromide salt. Not only the cube shape but also the width varied in the sheet structures. Because these nanostructures lose their optical stability and crystal phase on prolonged annealing, stabilizing these in high-temperature synthesis for all-inorganic lead halide perovskites is important and remains challenging. In this aspect, this method proved to be more facile because it does not require sharp cooling, and the nanocrystals retained their phase and optical properties even upon prolonged annealing.
Aging is associated with a decline in cognitive and motor performances, which are a part of geriatric syndromes. Since aging is associated with morphological changes in the cerebellum and cerebellar ...morphology is a good predictor of cognitive and motor performances, so the study of cerebellar role in age-related decline in performance is necessary. Cerebellar transcranial direct current stimulation (ctDCS) has been proposed to study and facilitate the cerebellar function. However, lobule-specific dosing has not been investigated in healthy aging. This is important because the same electrode montage across different individuals for ctDCS (called the "one-size-fits-all" approach) can lead to inter-individual differences in the lobule-specific dosing of the electric field (EF). These differences can be due to the inter-individual variability and age-related changes in the cerebellar structure. To investigate such lobule-specific dosing differences in healthy aging, we modeled the lobular EF distribution across groups of 18 to 89 years for a commonly used "one-size-fits-all" ctDCS montage.
A fully automated open-source pipeline performed age-group specific computational modeling of EF using 18 age-appropriate human brain magnetic resonance imaging (MRI) templates. The 18 age-appropriate human brain MRI templates were obtained from a database found online at https://jerlab.sc.edu/projects/neurodevelopmental-mri-database/. We extracted the EF magnitude (called EF strength) across the 28 cerebellar lobules based on a spatially unbiased cerebellar atlas. We investigated the aging effects on various measures of specificity including the ratio of the mean lobular EF at the lobules beneath the active electrode (ipsilateral right lobules VIIIa, VIIIb, IX) divided by the mean EF across both the targeted (ipsi) and the contralateral (contra) cerebellar hemisphere.
Two-way ANOVA showed that the lobules as well as the age group (and their interaction term) had a significant effect (p < 0.01) on the EF strength. Specifically, EF strength increased significantly at the neighboring cerebellar lobules (e.g., ipsilateral right lobules VIIb, Crus I and Crus II) of the targeted cerebellar hemisphere at an old age (70-74, 75-79, and 85-89 years) that reduced the specificity of ctDCS at the ipsilateral (right) lobules VIIIa, VIIIb, IX beneath the active electrode. We also found that the maximum EF strength in the cerebellar hemispheres decreased with an increase in the volume of the cerebrospinal fluid (CSF) and a decrease in the cerebellar volume with aging in a linear manner.
We found that cerebellar shrinkage and increasing thickness of the highly conductive CSF during healthy aging can lead to the dispersion of the current away from the lobules underlying the active electrode. We concluded that an individualized ctDCS approach for dosimetry is critical when ctDCS is used as an adjuvant treatment for active aging to address age-related lobule-specific cerebellar geriatric syndromes effectively. Future work is necessary to investigate age-related effects of lobule-specific ctDCS on the large-scale cognitive and motor networks using functional neuroimaging that is expected due to the cerebellum's extensive reciprocal connectivity with the cerebral cortex.
Brain-Computer Interfaces (BCI) have witnessed significant research and development in the last 20 years where the main aim was to improve their accuracy and increase their information transfer rates ...(ITRs), while still making them portable and easy to use by a broad range of users ....
PDF
