Strain and localization effects in InGaAs(N) quantum wells: Tuning the magnetic response

We investigated effects of localization and strain on the optical and magneto-optical properties of diluted nitrogen III-V quantum wells theoretically and experimentally. High-resolution x-ray diffraction, photoluminescence (PL), and magneto-PL measurements under high magnetic fields up to 15 T were performed at low temperatures. Bir-Pikus Hamiltonian formalism was used to study the influence of strain, confinement, and localization effects. The circularly polarized magneto-PL was interpreted considering localization aspects in the valence band ground state. An anomalous behavior of the electron-hole pair magnetic shift was observed at low magnetic fields, ascribed to the increase in the exciton reduced mass due to the negative effective mass of the valence band ground state

Metformin therapy attenuates pro-inflammatory Microglia by inhibiting NF-κB in cuprizone demyelinating mouse model of multiple Sclerosis

Multiple sclerosis (MS) is a chronic disorder characterized by reactive gliosis, inflammation, and demyelination. Microglia plays a crucial role in the pathogenesis of MS and has the dynamic plasticity to polarize between pro-inflammatory (M1) and anti-inflammatory (M2) phenotypes. Metformin, a glucose-lowering drug, attenuates inflammatory responses by activating adenosine monophosphate protein kinase (AMPK) which suppresses nuclear factor kappa B (NF-κB). In this study, we indirectly investigated whether metformin therapy would regulate microglia activity in the cuprizone (CPZ)-induced demyelination mouse model of MS via measuring the markers associated with pro- and anti-inflammatory microglia. Evaluation of myelin by luxol fast blue staining revealed that metformin treatment (CPZ + Met) diminished demyelination, in comparison to CPZ mice. In addition, metformin therapy significantly alleviated reactive microgliosis and astrogliosis in the corpus callosum, as measured by Iba-1 and GFAP staining. Moreover, metformin treatment significantly downregulated the expression of pro-inflammatory associated genes (iNOS, H2-Aa, and TNF-α) in the corpus callosum, whereas expression of anti-inflammatory markers (Arg1, Mrc1, and IL10) was not promoted, compared to CPZ mice. Furthermore, protein levels of iNOS (pro-inflammatory marker) were significantly decreased in the metformin group, while those of Trem2 (anti-inflammatory marker) were increased. In addition, metformin significantly increased AMPK activation in CPZ mice. Finally, metformin administration significantly reduced the activation level of NF-κB in CPZ mice. In summary, our data revealed that metformin attenuated pro-inflammatory microglia markers through suppressing NF-κB activity. The positive effects of metformin on microglia and remyelination suggest that it could be used as a promising candidate to lessen the incidence of inflammatory neurodegenerative diseases such as MS

Radiative recombination of localized excitons and mobility edge excitons in GaInNAs/GaAs quantum wells with strong carrier localization

The radiative recombination in InxGa1−xN0.01As0.99/GaAs quantum well structures exhibiting strong carrier localization was investigated by optical spectroscopy. For In-concentration from 0 to 30%, the results indicate that the degree of carrier localization decreases with increasing In-concentration. At temperatures below 100 K, the mobility edge excitons as well as localized excitons are identified and their transitions energies strongly depend on the excitation intensity. At elevated temperatures the localized excitons become quenched. The temperature dependence of the photoluminescence emission energy shows different behaviors at different excitation intensities

The lived experience of conditional medical students from academic failure: A phenomenological study

Introduction: Empowering students and preventing academic failure is one of the prominent issues for medical students. Causes and factors during students' studies reduce the quality of students' learning process and leads to academic and conditional dropout of some students. This study sought to investigate these factors from the view of Isfahan medical students. Methods: This qualitative study was conducted with a phenomenological approach and a review of the lived experiences of probationary students in the academic years 2018-2019 at Isfahan University of Medical Sciences. Data were collected using semi-structured interview individually in writing and by voluntary sampling method and based on content analysis strategy were analyzed manually. Results: A total of 31 probationary students were interviewed until the theoretical saturation of the data was reached. As to the analysis of the interviews, a total of 131 open codes, 30 pivotal codes and 5 selective codes were obtained. The highest number of factors of academic failure from the views of students were placed in the selection code of individual factors. Other factors of academic failure were in 4 selection codes of educational environment, psychological factors, factors related to family and community, factors related to professors. The common codes cited by students are as follows: lack of motivation, distraction, financial difficulties, teacher rigor, depressed mood, frustration with future careers, parental incompetence, and low self-esteem. Conclusion: Considering the causes and different areas that are effective in creating academic failure, it is necessary to have an integrated and comprehensive view of education authorities and families in dealing with the issue of academic failure

0.24 W F-Band Heterostructure Barrier Varactor Frequency Tripler

We have designed, grown, fabricated and characterized a 111 GHz frequency tripler. An AlAs/InAlAs/InGaAs heterostructure barrier varactor (HBV) was used as the nonlinear device for generating higher order harmonics. Four mesas were connected which amounted to a total of twelve barriers in series. This multiplier design was optimized for high output power using an aluminium nitride substrate for improved heat dispersion. The tripler consisted of an HBV device flip-chip soldered onto the AlN microstrip circuit and mounted in a waveguide block. No movable tuners were used for the characterization of the tripler. We measured a maximum output power of 0.24 W with a 6% bandwidth and 20% conversion efficiency. These state-of-the-art results constitute a marked improvement of HBV-based multiplier performance

Fabrication of nanowire growth templates by forming pinholes in SiOx on Si

InAs nanowire growth is carried out on a thin grainy layer of SiOx on Si (111), utilizing the openings of pinholes in the SiOx layer by isotropic wet etching. SiOx layers with different thicknesses were deposited and etched down to different thicknesses, to investigate how the initial layer roughness and the etching depth influence the formation of pinholes and thereafter the NW growth

Fabrication of nanowire growth templates by forming pinholes in SiOx on Si

InAs nanowire growth is carried out on a thin grainy layer of SiOx on Si (111), utilizing the openings of pinholes in the SiOx layer by isotropic wet etching. SiOx layers with different thicknesses were deposited and etched down to different thicknesses, to investigate how the initial layer roughness and the etching depth influence the formation of pinholes and thereafter the NW growth

0.24 W F-Band Heterostructure Barrier Varactor Frequency Tripler

We have designed, grown, fabricated and characterized a 111 GHz frequency tripler. An AlAs/InAlAs/InGaAs heterostructure barrier varactor (HBV) was used as the nonlinear device for generating higher order harmonics. Four mesas were connected which amounted to a total of twelve barriers in series. This multiplier design was optimized for high output power using an aluminium nitride substrate for improved heat dispersion. The tripler consisted of an HBV device flip-chip soldered onto the AlN microstrip circuit and mounted in a waveguide block. No movable tuners were used for the characterization of the tripler. We measured a maximum output power of 0.24 W with a 6% bandwidth and 20% conversion efficiency. These state-of-the-art results constitute a marked improvement of HBV-based multiplier performance

Threading Dislocation Blocking by Dilute Nitrides in Metamorphic Structures on GaAs Grown by MBE

Threading dislocation blocking by incorporating nitrogen in metamorphic InGaAs buffers on GaAs grown by MBE is demonstrated. This results in large enhancement of photoluminescence intensity from the metamorphic quantum wells