Exploring Epitaxial Structures for Electrically Pumped Perovskite Lasers: A Study of CsPb(Br,I)3 Based on the Ab Initio Bethe-Salpeter Equation.

Halide perovskites are widely used as components of electronic and optoelectronic devices such as solar cells, light-emitting diodes (LEDs), optically pumped lasers, field-effect transistors, photodetectors, and γ-detectors. Despite this wide range of applications, the construction of an electrically pumped perovskite laser remains challenging. In this paper, we numerically justify that mixing two perovskite compounds with different halide elements can lead to optical properties suitable for electrical pumping. As a reference, the chosen model material was CsPbBr3, whose performance as a part of lasers has been widely recognised, with some Br atoms substituted by I at specific sites. In particular, a strong enhancement of the low-energy absorption peaks has been obtained using the ab initio Bethe-Salpeter equation. Based on these results, we propose specific architectures of ordered doping that could be realised by epitaxial growth. Efficient light emission from the bottom of the conduction band is expected.

Polarization-dependent excitons and plasmon activity in nodal-line semimetal ZrSiS.

The optical properties of the bulk ZrSiS nodal-line semimetal are theoretically studied within a many-body formalism. The G0W0 bands are similar to those calculated within the density functional theory, except near the Γ-point; in particular, no significant differences are found around the Fermi energy. On the other hand, the solution of the Bethe-Salpeter equation reveals significant excitonic activity, mostly as dark excitons which appear in a wide energy range. Bright excitons, in contrast, are less numerous, but their location and intensity depend greatly on the polarization of the incident electric field, as the absorption coefficient itself does. The binding energy of these excitons correlates well with their spatial distribution functions. In any case, good agreement with the available experimental data for absorption/reflection is achieved. Finally, the possible activation of plasma oscillations is investigated. Plasmons may be formed at low energies, but they are damped and decayed producing electron-hole pairs, more importantly for q along the Γ-M path.

Investigating charge carrier scattering processes in anisotropic semiconductors through first-principles calculations: the case of p-type SnSe.

Efficient ab initio computational methods for the calculation of the thermoelectric transport properties of materials are of great interest for energy harvesting technologies. The constant relaxation time approximation (CRTA) has been largely used to efficiently calculate thermoelectric coefficients. However, CRTA usually does not hold for real materials. Here we go beyond the CRTA by incorporating realistic k-dependent relaxation time models of the temperature dependence of the main scattering processes, namely, screened polar and nonpolar scattering by optical phonons, scattering by acoustic phonons, and scattering by ionized impurities with screening. Our relaxation time models are based on a smooth Fourier interpolation of Kohn-Sham eigenvalues and its derivatives, taking into account non-parabolicity (beyond the parabolic or Kane models), degeneracy and multiplicity of the energy bands on the same footing, within very low computational cost. In order to test our methodology, we calculated the anisotropic thermoelectric transport properties of the low temperature phase (Pnma) of intrinsic p-type and hole-doped tin selenide (SnSe). Our results are in quantitative agreement with experimental data, regarding the evolution of the anisotropic thermoelectric coefficients with both temperature and chemical potential. Hence, from this picture, we also obtained the evolution and understanding of the main scattering processes of the overall thermoelectric transport in p-type SnSe.

The critical threshold value of systolic blood pressure for aortic occlusion in trauma patients in profound hemorrhagic shock.

BACKGROUND: This study aimed to determine the critical threshold of systolic blood pressure (SBP) for aortic occlusion (AO) in severely injured patients with profound hemorrhagic shock. METHODS: All adult patients (>15 years) undergoing AO via resuscitative endovascular balloon occlusion of the aorta (REBOA) or thoracotomy with aortic cross clamping (TACC) between 2014 and 2018 at level I trauma center were included. Patients who required cardiopulmonary resuscitation in the prehospital setting were excluded. A logistic regression analysis based on mechanism of injury, age, Injury Severity Score, REBOA/TACC, and SBP on admission was done. RESULTS: A total of 107 patients underwent AO. In 57, TACC was performed, and in 50, REBOA was performed. Sixty patients who underwent AO developed traumatic cardiac arrest (TCA), and 47 did not (no TCA). Penetrating trauma was more prevalent in the TCA group (TCA, 90% vs. no TCA, 74%; p < 0.05) but did not modify 24-hour mortality (odds ratio, 0.51; 95% confidence interval, 0.13-2.00; p = 0.337). Overall, 24-hour mortality was 47% (50) and 52% (56) for 28-day mortality. When the SBP reached 60 mm Hg, the predicted mortality at 24 hours was more than 50% and a SBP lower than 70 mm Hg was also associated with an increased of probability of cardiac arrest. CONCLUSION: Systolic blood pressure of 60 mm Hg appears to be the optimal value upon which AO must be performed immediately to prevent the probability of death (>50%). However, values of SBP less than 70 mm Hg also increase the probability of cardiac arrest. LEVEL OF EVIDENCE: Therapeutic study, level IV.

Chest Trauma Outcomes: Public Versus Private Level I Trauma Centers.

BACKGROUND: The goal of our study was to evaluate the differences in care and clinical outcomes of patients with chest trauma between two hospitals, including one public trauma center (Pu-TC) and one private trauma center (Pri-TC). METHODS: Patients with thoracic trauma admitted from January 2012 to December 2018 at two level I trauma centers (Pu-TC: Hospital Universitario del Valle, Pri-TC: Fundación Valle del Lili) in Cali, Colombia, were included. Multivariable logistic regression was used to assess for differences in in-hospital mortality, adjusting for relevant demographic and clinical characteristics. RESULTS: A total of 482 patients were identified; 300 (62.2%) at the Pri-TC and 182 (37.8%) at the Pu-TC. Median age was 27 years (IQR 21-36) and median Injury Severity Score was 25 (IQR 16-26). 456 patients (94.6%) were male, and the majority had penetrating trauma [total 465 (96.5%); Pri-TC 287 (95.7%), Pu-TC 179 (98.4%), p 0.08]. All patients arrived at the emergency room with unstable hemodynamics. There were no statistically significant differences in post-operative complications, including retained hemothorax [Pri-TC 19 vs. Pu-TC 18], pneumonia [Pri-TC 14 vs. Pu-TC 14], empyema [Pri-TC 13 vs. Pu-TC 13] and mediastinitis [Pri-TC 6 vs. Pu-TC 2]. Logistic regression did, however, show a higher odds of mortality when patients were treated at the Pu-TC [OR 2.27 (95% CI 1.34-3.87, p < 0.001]. CONCLUSIONS: Our study found significant statistical differences in clinical outcomes between patients treated at a Pu-TC and Pri-TC. The results are intended to stimulate discussions to better understand reasons for outcome variability and ways to reduce it.

Resuscitative endovascular balloon occlusion of the aorta deployed by acute care surgeons in patients with morbidly adherent placenta: a feasible solution for two lives in peril.

Morbidly adherent placenta (MAP), which includes accreta, increta, and percreta, is a condition characterized by the invasion of the uterine wall by placental tissue. The condition is associated with higher odds of massive post-partum hemorrhage. Several interventions have been developed to improve hemorrhage-related outcomes in these patients; however, there is no evidence to prefer any intervention over another. Resuscitative endovascular balloon occlusion of the aorta (REBOA) is an endovascular intervention that may be useful and effective to reduce hemorrhage and transfusions in MAP patients. The objective of this narrative review is to summarize the evidence for REBOA in patients with MAP. We posit that acute care surgeons can perform REBOA for patients with MAP.

A meta-analysis of the incidence of complications associated with groin access after the use of resuscitative endovascular balloon occlusion of the aorta in trauma patients.

BACKGROUND: Serious complications related to groin access have been reported with the use of resuscitative endovascular balloon occlusion of the aorta (REBOA). We performed a systematic review and meta-analysis to estimate the incidence of complications related to groin access from the use of REBOA in adult trauma patients. METHODS: We identified articles in MEDLINE and EMBASE. We reviewed all studies that involved adult trauma patients who underwent the placement of a REBOA and included only those that reported the incidence of complications related to groin access. A meta-analysis of proportions was performed. RESULTS: We identified 13 studies with a total of 424 patients. REBOA was inserted most commonly by trauma surgeons or emergency room physicians. Information regarding puncture technique was reported in 12 studies and was available for a total of 414 patients. Percutaneous access and surgical cutdown were performed in 304 (73.4%) and 110 (26.5%) patients, respectively. Overall, complications related to groin access occurred in 5.6% of patients (n = 24/424). Lower limb amputation was required in 2.1% of patients (9/424), of which three cases (3/424 [0.7%]) were directly related to the vascular puncture from the REBOA insertion. A meta-analysis that used the logit transformation showed a 5% (95% CI 3%-9%) incidence of complications without significant heterogeneity (LR test: χ = 0.73, p = 0.2, Tau-square = 0.2). In a second meta-analysis, we used the Freeman-Tukey double arcsine transformation and found an incidence of complications of 4% (95% CI 2%-7%) with low heterogeneity (I = 16.3%). CONCLUSION: We found that the incidence of complications related to groin access was of 4-5% based on a meta-analysis of 13 studies published worldwide. Currently, there are no benchmarks or quality measures as a reference to compare, and thus, further work is required to identify these benchmarks and improve the practice of REBOA in trauma surgery. LEVEL OF EVIDENCE: Systematic review and meta-analysis, level III.

Ultralow and anisotropic thermal conductivity in semiconductor As2Se3.

An ultralow lattice thermal conductivity of 0.14 W m-1 K-1 along the b[combining right harpoon above] axis of As2Se3 single crystals was obtained at 300 K using first-principles calculations involving density functional theory and the resolution of the Boltzmann transport equation. This ultralow lattice thermal conductivity arises from the combination of two mechanisms: (1) a cascade-like fall of the low-lying optical modes, which results in avoided crossings of these with the acoustic modes, low sound velocities and increased scattering rates of the acoustic phonons; and (2) the repulsion between the lone-pair electrons of the As cations and the valence p orbitals of the Se anions, which leads to an increase in the anharmonicity of the bonds. The physical origins of these mechanisms lie in the nature of the chemical bonding in the material and its strong anisotropy. These results, whose validity has been addressed by comparison with SnSe, for which excellent agreement between the theoretical predictions and the experiments is achieved, point out that As2Se3 could exhibit improved thermoelectric properties.

Insights into the thermoelectric properties of SnSe from ab initio calculations.

The thermoelectric properties of SnSe are studied by first-principles methods using an original methodology. We computed first the electronic structure of the system, which justifies its macroscopic anisotropy; the inclusion of van der Waals dispersive corrections improves the agreement of the structural parameters with experiments. The Seebeck coefficient and the electrical and thermal conductivities of single crystals and polycrystals are subsequently described in good agreement with experimental data. As for the electrical conductivity, values calculated with a temperature-dependent relaxation time compare well with the available measurements, especially for single crystals; in contrast, a constant relaxation time suffices to describe the results for polycrystals. Based on the iterative solution of the Boltzmann transport equation for phonons, we discuss the behavior of the thermal conductivity of the system in terms of its phonon spectrum. Finally, the figure of merit of SnSe single crystals and polycrystals is calculated and correlated with the previous discussions about electrical and thermal conductivities. From these findings, possible strategies to increase the figure of merit in practice are suggested.

Chronology of metastasis in cutaneous melanoma: growth rate model.

In humans, it is not possible to obtain experimental evidence of when a cancer begins to metastasize. The purpose of this study was to estimate the time of onset of metastatic dissemination in cutaneous melanoma using a model based on its growth rate (GR). The critical time of onset of metastatic dissemination below which no cases of fatal melanomas were seen may be described with a potential function in which this time is inversely proportional to the GR. The critical time of development beyond which a melanoma may metastasize presents great variation. This time was just 1 month for those melanomas with a fast GR, whereas it was over 5 years for those with a very slow GR. Quantitatively, the fastest-growing melanomas began metastasizing with a greater thickness than the slowest-growing melanomas. A correlation exists between the critical time of onset of metastatic potential and the GR of the melanoma. These results may well have relevance to the understanding of mechanisms of tumor dissemination and for the design of future studies on melanomas, irrespective of whether they are basic studies on biomolecular mechamisms or clinical studies.