Valley polarization transition driven by biaxial strain in Janus GdClF monolayer.

The valley degree of freedom of carriers in crystals is useful to process information and perform logic operations, and it is a key factor for valley application to realize valley polarization. Here, we propose a model that the valley polarization transition at different valley points (-K and K points) is produced by biaxial strain. Using first-principles calculations, we illustrate our idea with a concrete example of a Janus GdClF monolayer. The predicted GdClF monolayer is dynamically, mechanically and thermally stable, and is a ferromagnetic (FM) semiconductor with perpendicular magnetic anisotropy (PMA), valence band maximum (VBM) at valley points and a high Curie temperature (TC). Due to its intrinsic ferromagnetism and spin-orbit coupling (SOC), a spontaneous valley polarization will be induced, but the valley splitting is only -3.1 meV, which provides an opportunity to achieve valley polarization transition at different valley points by strain. In the considered strain range (a/a0: 0.94-1.06), the strained GdClF monolayer always has an energy bandgap, strong FM coupling and PMA. The compressive strain is in favour of -K valley polarization, while the tensile strain is favorable for K valley polarization. The corresponding valley splittings at 0.96 and 1.04 strains are -44.5 meV and 29.4 meV, respectively, which are higher than the thermal energy at room temperature (25 meV). Due to its special Janus structure, both in-plane and out-of-plane piezoelectric polarizations can be observed. It is found that the direction of in-plane piezoelectric polarization can be overturned by strain, and the d11 values at 0.96 and 1.04 strains are -1.37 pm V-1 and 2.05 pm V-1, respectively. Our work paves the way to design ferrovalley materials for application in multifunctional valleytronic and piezoelectric devices by strain.

Hyperbaric oxygen therapy for post-stroke depression: A systematic review and meta-analysis.

OBJECTIVES: Post-stroke depression (PSD) is common consequence of stroke. However, today the majority of PSD patients remains untreated or inadequately treated, especially in the developing countries. Herein, we performed a meta-analysis to evaluate efficacy and safety of hyperbaric oxygen (HBOT) therapy for PSD. PATIENTS AND METHODS: Seven electronic databases were comprehensively searched for randomized clinical trials (RCTs) from inception to May 2019. Outcome measures included response rate, depression severity, neurological deficit, physical disability and adverse events. RESULTS: A total of 27 RCTs involving 2250 participants were identified. Patients in HBOT group had a higher response rate than patients in control group (response rate: 69.4% vs 51.2%, odds ratio [OR] = 2.51, 95% confidence interval [CI] [1.83-3.43], P = 0.000). HBOT significantly reduced Hamilton Depression (HAMD) -17 item scores (weighted mean difference [WMD]  = -4.33, 95% CI [-4.82 to -3.84], P = 0.000), HAMD-24 item scores (WMD = -4.31, 95% CI [-5.01 to -3.62], P = 0.000), National Institute of Health Stroke Scale (NIHSS) scores (WMD = -2.77, 95% CI [-3.57 to -1.98], P = 0.000), Chinese Stroke Scale (CSS) scores (WMD = -3.75, 95% CI [-5.12 to -2.38], P = 0.000) and Modified Scandinavian Stroke Scale (MASSS) scores (WMD = -3.66, 95% CI [-6.26 to -1.06], P = 0.000). HBOT also improved Barthel Index (WMD = 10.68, 95% CI [7.98-13.37], P = 0.000). In subgroup analysis, Group A of studies with hemorrhage patients accounting for less than 20% achieved more reduction of HAMD 17-item score (WMD = -4.47, 95% CI [-5.17 to -3.77], P = 0.000) than Group B of studies with hemorrhage patients no less than 20% (WMD = -3.73, 95% CI [-4.20 to -3.26], P = 0.000). In addition, patents with HBOT along with antidepressants treatment achieve superior results than patients with antidepressants monotherapy. Patients with HBOT monotherapy achieve a slightly higher response rate than patients with antidepressants monotherapy (OR = 1.29, 95% CI [1.04-1.60], P = 0.000). Besides, HBOT group reported less adverse events (9.6%vs16.6%, P < 0.05). The most frequent side-effect of HBOT is ear pain (26 cases). CONCLUSION: Based on our pooled analysis, HBOT is effective and safe therapeutic approach for PSD. However, results should be cautiously interpreted due to a relatively poor methodological quality.