Phonon Directionality Impacts Electron-Phonon Coupling and Polarization of the Band-Edge Emission in Two-Dimensional Metal Halide Perovskites.

Two-dimensional metal halide perovskites are highly versatile for light-driven applications due to their exceptional variety in material composition, which can be exploited for the tunability of mechanical and optoelectronic properties. The band-edge emission is defined by the structure and composition of both organic and inorganic layers, and electron-phonon coupling plays a crucial role in the recombination dynamics. However, the nature of the electron-phonon coupling and what kind of phonons are involved are still under debate. Here we investigate the emission, reflectance, and phonon response from single two-dimensional lead iodide microcrystals with angle-resolved polarized spectroscopy. We find an intricate dependence of the emission polarization with the vibrational directionality in the materials, which reveals that several bands of low-frequency phonons with nonorthogonal directionality contribute to the band-edge emission. Such complex electron-phonon coupling requires adequate models to predict the thermal broadening of the emission and provides opportunities to design polarization properties.

Perovskenes: two-dimensional perovskite-type monolayer materials predicted by first-principles calculations.

Inspired by the successful transfer of freestanding ultrathin films of SrTiO3 and BiFeO3 onto various substrates without any thickness limitation, in this study, using density functional theory (DFT), we assessed the structural stability of a group of two-dimensional perovskite-type materials which we call perovskenes. Specifically, we analyzed the stability of 2D SrTiO3, SrZrO3, BaTiO3, and BaZrO3 monolayers. Our simulations revealed that the 2D monolayers of SrTiO3, BaTiO3, and BaZrO3 are at least meta-stable, as confirmed by cohesive energy calculations, evaluation of elastic constants, and simulation of phonon dispersion modes. With this information, we proceeded to investigate the electronic, optical, and thermoelectric properties of these perovskenes. To gain insight into their promising applications, we investigated the electronic and optical properties of these 2D materials and found that they are wide bandgap semiconductors with significant absorption and reflection in the ultraviolet (UV) region of the electromagnetic field, suggesting them as promising materials for use in UV shielding applications. In addition, evaluating their thermoelectric factors revealed that these materials become better conductors of electricity and heat as the temperature rises. They can, hence, convert temperature gradients into electrical energy and transport electrical charges, which is beneficial for efficient power generation in thermoelectric devices. This work opens a new window for designing a novel family of 2D perovskite type materials termed perovskenes. The vast variety of different perovskite compounds and their variety of applications suggest deeper studies on the perovskenes materials for use in innovative technologies.

Mapping emission heterogeneity in layered halide perovskites using cathodoluminescence.

Recent advancements in the fabrication of layered halide perovskites and their subsequent modification for optoelectronic applications have ushered in a need for innovative characterisation techniques. In particular, heterostructures containing multiple phases and consequently featuring spatially defined optoelectronic properties are very challenging to study. Here, we adopt an approach centered on cathodoluminescence, complemented by scanning electron microscopy coupled with energy-dispersive x-ray spectroscopy analysis. Cathodoluminescence enables assessment of local emission variations by injecting charges with a nanometer-scale electron probe, which we use to investigate emission changes in three different systems: PEA2PbBr4, PEA2PbI4and lateral heterostructures of the two, fabricated via halide substitution. We identify and map different emission bands that can be correlated with local chemical composition and geometry. One emission band is characteristic of bromine-based halide perovskite, while the other originates from iodine-based perovskite. The coexistence of these emissions bands in the halide-substituted sample confirms the formation of lateral heterostructures. To improve the signal quality of the acquired data, we employed multivariate analysis, specifically the non-negative matrix factorization algorithm, on both cathodoluminescence and compositional datasets. The resulting understanding of the halide replacement process and identification of potential synergies in the optical properties will lead to optimised architectures for optoelectronic applications.

Electronic and optical properties of two-dimensional heterostructures and heterojunctions between doped-graphene and C- and N-containing materials.

The electronic and optical properties of vertical heterostructures (HTSs) and lateral heterojunctions (HTJs) between (B,N)-codoped graphene (dop@Gr) and graphene (Gr), C3N, BC3 and h-BN monolayers are investigated using van der Waals density functional theory calculations. We have found that all the considered HTSs are energetically and thermally feasible at room temperature, and therefore they can be synthesized experimentally. The dop@Gr/Gr, BC3/dop@Gr and BN/dop@Gr HTSs are semiconductors with direct bandgaps of 0.1 eV, 80 meV and 1.23 eV, respectively, while the C3N/dop@Gr is a metal because of the strong interaction between dop@Gr and C3N layers. On the other hand, the dop@Gr-Gr and BN-dop@Gr HTJs are semiconductors, whereas the C3N-dop@Gr and BC3-dop@Gr HTJs are metals. The proposed HTSs can enhance the absorption of light in the whole wavelength range as compared to Gr and BN monolayers. The applied electric field or pressure strain changes the bandgaps of the HTSs and HTJs, indicating that these HTSs are highly promising for application in nanoscale multifunctional devices.

Diagnostic value of "bedside ultrasonography" and the "water bath technique" in distal forearm, wrist, and hand bone fractures.

Bedside ultrasonography (BUS) has been widely used in many emergency evaluations, but the technique was not thoroughly evaluated for use in adult fractures. The water bath technique (WBT) is a modality which overcomes some important limitations of using BUS in extremity fractures. The study aims to evaluate and compare diagnostic values of BUS and WBT. The sensitivity, specificity, positive and negative predictive values (PPV and NPV), positive and negative likelihood ratios (LR+ and LR-), and accuracy of BUS and WBT were calculated and compared by the McNemar chi-square test. BUS had the highest sensitivity, specificity, PPV, and LR+ in the distal forearm. The highest NPV and LR- of BUS were seen in phalangeal and wrist injuries, respectively. The WBT examination had the highest sensitivity in phalangeal injuries and the highest specificity, PPV, and LR+ in the distal forearm. The highest NPV and LR- of the WBT examination were seen in phalangeal and wrist injuries, respectively. The McNemar χ (2) values for the comparison of BUS and WBT indicate that the two techniques provide statistically different results. The ultrasound revealed excellent diagnostic values which make it a favorable alternative in evaluating upper extremity fractures in adults. The WBT provides even better results.

Heterostructures via a Solution-Based Anion Exchange in Microcrystalline 2D Layered Metal-Halide Perovskites.

Layered perovskites consist of stacks of inorganic semiconducting metal-halide octahedra lattices sandwiched between organic layers with typically dielectric behavior. The in-plane confinement of electrical carriers in such two-dimensional metal halide perovskites drives a large range of appealing electronic properties, such as strong exciton binding, anisotropic charge diffusion, and polarization-directionality. Heterostructures provide additional control on carrier diffusion and localization, and in-plane heterojunctions are interesting because of the associated high charge mobility. Here, this work demonstrates a versatile solution-based approach to fabricate in-plane heterostructures with different halide composition in two-dimensional lead-halide perovskite microcrystals. This leads to spatially separated halide phases with different band gap and light emission. Interestingly, the composition of the exchanged phase and the morphology of the phase boundary depends on the exchange route, which can be related to the preferred localization of the halides at the equatorial or axial octahedra positions that either leads to dissolution and recrystallization of the octahedra lattice (for bromide to iodide), or allows for ion diffusion within the lattice (for iodide to bromide). These detailed insights on the ion exchange processes in layered perovskites will stimulate the development of heterostructures that can be tailored for different applications such as photocatalysis, energy storage, and light emission.

Understanding the endocrine disruptor and determination of bisphenol A by functional Cu-BTABB-MOF/rGO composite as facile rapid electrochemical sensor: an experimental and DFT investigation.

A pioneering CuBTABB-MOF/rGO composite customized electrode is fabricated and utilized as a sensor towards identifying bisphenol A (BPA) in a phosphate buffer solution of pH 7.0. The composite is characterized by FTIR, Raman spectroscopy, XRD, SEM, EDX, HRTEM, and XPS to study its structural and morphological properties. Compared with Cu-BTABB-MOF and Cu-BTABB-MOF@GO, the Cu-BTABB-MOF@rGO modified electrode is more sensitive and selective to BPA due to a strong interaction between them. The developed Cu-BTABB-MOF@rGO modified electrode exhibits good sensitivity (6.95 × 10-5 A mol-1 L-1) for BPA having a wide linear range of 0-100 µmol L-1 with the LOD of 2.08 × 10-5 mol L-1, reproducibility of 4.35%, and relative standard deviation (RSD) and stability of 90% for thirty days. In addition, the developed electrocatalyst remained unoccupied from interfering substances and consequently provided an encouraging platform for swift detection of BPA in real samples such as pond water and packed water bottles. Additionally, we utilized DFT (density functional theory) to model GO and Cu-BTABB-MOF structures for detecting BPA molecules.

Puckered Penta-like PdPX (X = O, S, Te) Semiconducting Nanosheets: First-Principles Study of the Mechanical, Electro-Optical, and Photocatalytic Properties.

The atomic, electronic, optical, and mechanical properties of penta-like two-dimensional PdPX (X = O, S, Te) nanosheets have been systematically investigated using density functional theory calculations. All three PdPX nanosheets exhibit dynamic and mechanical stability on the basis of an analysis of phonon dispersions and the Born criteria, respectively. The PdPX monolayers are found to be brittle structures. Our calculations demonstrate that the PdPX nanosheets exhibit semiconducting characteristics with indirect band gaps of 0.93 (1.99), 1.34 (2.11), and 0.74 (1.51) eV for X = O, S, Te, respectively, using the PBE (HSE06) functional, where PdPTe is the best material for visible-light photocatalytic water splitting. Our findings give important basic characteristics of penta-like two-dimensional PdPX materials and should motivate further theoretical and experimental investigations of these interesting materials.

User Acceptance of Picture Archiving and Communication System in the Emergency Department.

BACKGROUND: Picture archiving and communication system (PACS) has allowed the medical images to be transmitted, stored, retrieved, and displayed in different locations of a hospital or health system. Using PACS in the emergency department will eventually result in improved efficiency and patient care. In spite of the abundant benefits of employing PACS, there are some challenges in implementing this technology like users' resistance to accept the technology, which has a critical role in PACS success. OBJECTIVES: In this study, we will assess and compare user acceptance of PACS in the emergency departments of three different hospitals and investigate the effect of socio-demographic factors on this acceptance. MATERIALS AND METHODS: A variant of technology acceptance model (TAM) has been used in order to measure the acceptance level of PACS in the emergency department of three educational hospitals in Iran. A previously used questionnaire was validated and utilized to collect the study data. A stepwise multiple regression model was used to predict factors influencing acceptance score as the dependent variable. RESULTS: Mean age of participants was 32.9 years (standard deviation [SD] = 6.08). Participants with the specialty degree got a higher acceptance score than the three other groups (Mean ± SD = 4.17 ± 0.20). Age, gender, degree of PACS usage and participant's occupation (profession) did not influence the acceptance score. In our multiple regression model, all three variables of perceived usefulness (PU), perceived ease of use (PEU) and the effect of PACS (change) had a significant effect in the prediction of acceptance. The most influencing factor was change with the beta of 0.22 (P value < 0.001). CONCLUSION: PACS is highly accepted in all three emergency departments especially among specialists. PU, PEU and change are factors influencing PACS acceptance. Our study can be used as an evidence of PACS acceptance in emergency wards.

Success rate and complications of internal jugular vein catheterization with and without ultrasonography guide.

BACKGROUND: Central venous catheterization (CVC) is an important procedure in emergency departments (EDs). Despite existence of ultrasonography (US) devices in every ED, CVC is done using anatomical landmarks in many EDs in Iran. OBJECTIVES: This study aimed to compare the traditional landmark method vs. US-guided method of CVC placement in terms of complications and success rate. PATIENTS AND METHODS: In this randomized controlled trial, patients who were candidate for internal jugular vein catheterization, and referred to Baqiyatallah Hospital ED were randomly allocated into US-guided CVC and anatomical landmarks guided CVC groups. Central vein access time, number of attempts, success rate, and complications in each group were evaluated. Mann-Whitney U, chi-square and Fisher exact tests along with Pearson and Spearman correlation coefficients were used to analyze the data. RESULTS: Out of 100 patients, 56 were male and 44 were female. No significant differences were found between the US-guided and traditional landmark methods of CVC insertion in terms of age, gender, BMI, and site of catheter insertion. The mean access time was significantly lower in the US-guided group (37.12 ± 17.33 s vs. 63.42 ± 35.19 s, P < 0.001). The mean number of attempts was also significantly lower in the US-guided group (1.12 ± 0.3 vs. 1.58 ± 0.64 times, P < 0.001). Eighty-eight percent of patients in the US-guided group were catheterized in the first attempt, while 50% of patients in the traditional landmark group were catheterized in the second or more attempts (P < 0.001). The success rate was 100% in the US-guided group, while it was 88% in the landmark group (P = 0.013). Moreover, the rate of complications was significantly lower in the US-guided group (4% vs. 24%, P = 0.004). CONCLUSIONS: The US-guided method for CVC placement was superior to the traditional landmark method in terms of access time, number of attempts, success rate, and fewer complications.

Citrullus colocynthis as the Cause of Acute Rectorrhagia.

Introduction. Citrullus colocynthis Schrad. is a commonly used medicinal plant especially as a hypoglycemic agent. Case Presentation. Four patients with colocynth intoxication are presented. The main clinical feature was acute rectorrhagia preceeded by mucosal diarrhea with tenesmus, which gradually progressed to bloody diarrhea and overt rectorrhagia within 3 to 4 hours. The only colonoscopic observation was mucosal erosion which was completely resolved in follow-up colonoscopy after 14 days. Conclusion. The membranolytic activity of some C. colocynthis ingredients is responsible for the intestinal damage. Patients and herbalists should be acquainted with the proper use and side effects of the herb. Clinicians should also be aware of C. colocynthis as a probable cause of lower GI bleeding in patients with no other suggestive history, especially diabetics.

Assigning residents of emergency medicine to screen patients before admission: a strategy to overcome overcrowding.

BACKGROUND: The overcrowded hospital is an unsafe one. Overcrowding the emergency department (ED) results in increased patient suffering, prolonged waiting time, deteriorating level of service, and on occasion, a worsened medical condition or even death. OBJECTIVES: This study proposes a strategy to overcome ED overcrowding. MATERIALS AND METHODS: The proportion of acute area admitted patients to screened patients (A/S), and the proportion of patients who were finally transferred to inpatient wards (W/A) to those admitted in ED acute area were investigated during 6 consecutive months. Emergency medicine residents were assigned to screen patients before ED admission and afterwards. RESULTS: The average A/S changed from 82.4% to 44.2% (P = 0.028), and the average W/A changed from 28.3% to 51.48% (P = 0.028) before and after screening patients respectively. The initiative resulted in 97 less patients in the acute area per day. CONCLUSIONS: Decreased number of acute area admitted patients, and increase W/A proportion showed that the initiative was successful in obviating ED overcrowding while provision of care to those most in need was not altered.