Search

We exploit bias polarity dependent low-frequency noise (LFN) spectroscopy to investigate charge transport dynamics in ultra-thin AlOx-based magnetic tunnel junctions (MTJs) with bipolar resistive switching (RS). By measuring the noise characteristics across the entire bias voltage range of bipolar RS, we find that the voltage noise level exhibits an bias polarity dependence. This distinct feature is intimately correlated with reconfiguring of the inherently existing oxygen vacancies ( V O.. ) in as-grown MTJ devices during the SET and RESET switching processes. In addition, we observe two-level random telegraph noise (RTN) with a longer and shorter tunneling length in the high resistance state (HRS) and low resistance state (LRS) at a low bias voltage. The intrinsic voltage fluctuations of RTN arise from the dynamics of electron trapping/de-trapping processes at the V O.. -related trap sites. Notably, the RTN magnitude is similar in LRS but nonidentical in that of HRS for different bias polarity. These findings strongly suggest that the inherent V O.. are distributed near the top CoFe/AlOx interface in the HRS; in contrast, they are expanded to the middle region of the AlOx in the LRS. More importantly, we demonstrate that the location and distribution of the inherent V O.. can be electrically tuned, which plays an essential role in the charge transport dynamics in the ultra-thin AlOx-based MTJs and have significant implications for developing emergent memory and logic devices. [ABSTRACT FROM AUTHOR]

Mesenchymal stem cells (MSCs) are a new therapeutic strategy for inflammatory bowel disease (IBD), and their efficacy has been widely recognized. However, there are still some challenges in cell therapy, including stable cell passage, laboratory conditions for cell culture, high-cost burden, and poor transplantation. The conditioned medium (CM) of MSCs is considered be an excellent alternative to cell transplantation, but the paracrine group in MSC-CM is limited in variety and low in concentration, which cannot meet the therapeutic needs of injured tissues and needs to be optimized. Pretreatment with low concentration of hydrogen peroxide (H2O2) can not only protect cells from oxidative damage, but also play a role similar to growth factors and regulate the physiological function of stem cells, to obtain an improved conditioned medium. To determine the optimal protocol for pretreatment of MSCs with H2O2, and to study the efficacy and potential mechanism of MSC-CM pretreated with H2O2 on Dextran Sulfate Sodium (DSS)-induced acute experimental colitis. MSCs were exposed to different concentrations of H2O2, and the optimal H2O2 pretreatment conditions were determined by evaluating their critical cell functional properties. H2O2-pretreated MSC-CM was transplanted into experimental mouse colitis by enema at 2, 4, and 6 days in modeling, and the changes of colonic tissue structure, the levels of inflammation and oxidative stress, the molecular changes of Nrf2/Keap1/ARE axis, and the related indicators of apoptosis in colonic epithelial cells were observed in each group. In vitro, Pretreated MSCs with 25 μM H2O2 significantly enhanced cell proliferation, migration, and survival, but had no effect on apoptosis. In vivo, MSC-CM treatment decreased apoptosis and extracellular matrix deposition, and maintained the mechanical barrier and permeability of colonic epithelial cells in experimental mouse colitis. Mechanistically, H2O2-pretreated MSC-CM against reactive oxygen species (ROS) production and MDA generation, accompanied by increases in components of the enzymatic antioxidant system includes SOD, CAT, GSH-PX, and T-AOC, which is through the up-regulation of the Nrf2, HO-1, and NQO-1 antioxidant genes. Our data confirmed that 25 μM H2O2 pretreated MSC-CM treatment could effectively improve intestinal mucosal repair in experimental colitis, which may be achieved by activating Nrf2/Keap1/ARE pathway. [ABSTRACT FROM AUTHOR]

A systematic study on the magnetic and electrical percolation phenomena of BaTiO3 (BTO)-NiZnF2O4 (NZFO) composite films is presented in this work with the purpose of simplifying the preparation process of high-performance 1–3-type multiferroic composite films. Results show that the percolation threshold of the composite films depends on the macroscopic dimension of the material. The low-dimensional nature of the composite films results in different percolation thresholds with topological transition in vertical and horizontal directions. BTO-NZFO composite films with a grain size of 15 nm and a thickness of 100 nm exhibited a percolation threshold of 0.18 in the normal direction and a percolation threshold of 0.48 in the horizontal direction. In light of this intriguing feature, a novel multiferroic composite film with 1–3 structure and strong magnetoelectric coupling was easily prepared by a 0–3 process via controlling the NZFO content in the region between two percolation thresholds. [ABSTRACT FROM AUTHOR]