Evaluation of a multimode fiber optic low coherence interferometer for path length resolved Doppler measurements of diffuse light \ud

The performance of a graded index multimode fiber optic low coherence Mach-Zehnder interferometer with phase modulation is analyzed. Investigated aspects were its ability to measure path length distributions and to perform path length resolved Doppler measurements of multiple scattered photons in a turbid suspension of particles undergoing Brownian and translational motion. The path length resolution of this instrument is compared with a system using single mode fibers for illumination and detection. The optical path lengths are determined from the zero order moment of the phase modulation peak in the power spectrum. The weighted first moment, which is equal to the average Doppler shift, shows a linear response for different mean flow velocities within the physiological rang

Electron Transport Chain Is Biochemically Linked to Pilus Assembly Required for Polymicrobial Interactions and Biofilm Formation in the Gram-Positive Actinobacterium Actinomyces oris.

The Gram-positive actinobacteria Actinomyces spp. are key colonizers in the development of oral biofilms due to the inherent ability of Actinomyces to adhere to receptor polysaccharides on the surface of oral streptococci and host cells. This receptor-dependent bacterial interaction, or coaggregation, requires a unique sortase-catalyzed pilus consisting of the pilus shaft FimA and the coaggregation factor CafA forming the pilus tip. While the essential role of the sortase machine SrtC2 in pilus assembly, biofilm formation, and coaggregation has been established, little is known about trans-acting factors contributing to these processes. We report here a large-scale Tn5 transposon screen for mutants defective in Actinomyces oris coaggregation with Streptococcus oralis We obtained 33 independent clones, 13 of which completely failed to aggregate with S. oralis, and the remainder of which exhibited a range of phenotypes from severely to weakly defective coaggregation. The former had Tn5 insertions in fimA, cafA, or srtC2, as expected; the latter were mapped to genes coding for uncharacterized proteins and various nuo genes encoding the NADH dehydrogenase subunits. Electron microscopy and biochemical analyses of mutants with nonpolar deletions of nuo genes and ubiE, a menaquinone C-methyltransferase-encoding gene downstream of the nuo locus, confirmed the pilus and coaggregation defects. Both nuoA and ubiE mutants were defective in oxidation of MdbA, the major oxidoreductase required for oxidative folding of pilus proteins. Furthermore, supplementation of the ubiE mutant with exogenous menaquinone-4 rescued the cell growth and pilus defects. Altogether, we propose that the A. oris electron transport chain is biochemically linked to pilus assembly via oxidative protein folding.IMPORTANCE The Gram-positive actinobacterium A. oris expresses adhesive pili, or fimbriae, that are essential to biofilm formation and Actinomyces interactions with other bacteria, termed coaggregation. While the critical role of the conserved sortase machine in pilus assembly and the disulfide bond-forming catalyst MdbA in oxidative folding of pilins has been established, little is known about other trans-acting factors involved in these processes. Using a Tn5 transposon screen for mutants defective in coaggregation with Streptococcus oralis, we found that genetic disruption of the NADH dehydrogenase and menaquinone biosynthesis detrimentally alters pilus assembly. Further biochemical characterizations determined that menaquinone is important for reactivation of MdbA. This study supports the notion that the electron transport chain is biochemically linked to pilus assembly in A. oris via oxidative folding of pilin precursors

THE IMPACT OF THE COVID-19 PANDEMIC ON VOCATIONAL EDUCATION AND TRAINING IN KENYA: A STUDY OF WEST POKOT COUNTY

This paper focuses on the impact of the Covid-19 pandemic on the education system in Kenya with reference to vocational training institutions. The paper analyses how the provision of vocational training was impacted after Covid-19 from the perspective of principals of colleges, tutors, and students. The paper collected qualitative experiences of the above-mentioned stakeholders to understand to which degree vocational education has been affected by Covid-19. This was accomplished through the use of interviews, questionnaires, and document analysis. The study has found that the Covid-19 pandemic completely disrupted learning in six public VTCs as institutions were closed and students and tutors did not meet or interact for more than eight months. It was impossible for a work-based learning model to be used by students after institutions were closed because even the industries and businesses where they were supposed to undertake their practicum and internship programmes downscaled their operations, while others closed down completely. After reopening of VTCs in January 2021, close to 34.8% of their former students did not report back because some of them dropped out, some could not pay fees, some engaged in alcoholism, drugs, and substance abuse, some emigrated to other areas to look for opportunities while some settled down in marriage. It is recommended that guidance and counselling should be continuously provided to tutors and students as a way of addressing the psychological and behavioural challenges brought about by Covid-19, tutors need to be trained on remote learning methodologies (digital skills) and county governments need to invest in setting up infrastructure to support online learning in VTCs. This research provides a realistic picture of the impact of the Covid-19 pandemic on vocational education and training in public institutions in West Pokot County which is considered to be a marginalised and arid and semi-arid region in the North-western part of Kenya.  Article visualizations

Cathodoluminescence inhomogeneity in ZnO nanorods

Luminescence properties of vertically aligned, crystalline ZnO nanorods are studied by cathodoluminescence (CL) spectroscopy and microscopy. Results show that luminescence characteristics vary dramatically with location on the nanorod as well as CL excitation depth. CL inhomogeneity is observed between the nanorod tip and sidewalls, accompanied by a variation in the chemical environment of surface oxygen ions as probed by photoemission spectroscopy. Our findings demonstrate that CL can provide useful information on the local optical properties of nanostructured materials, which is simply beyond the capability of other methods. © 2008 American Institute of Physics

Distribution of visible luminescence centers in hydrogen-doped ZnO

ZnO crystals have been investigated by scanning cathodoluminescence microscopy and spectroscopy at 80 K following hydrogen incorporation by plasma exposure. The intensity of the ZnO near-band-edge (NBE) emission is greatly enhanced while the defect-related green emission is quenched following plasma treatment. These effects are attributed to the passivation of zinc vacancies by hydrogen. The green and yellow intensities and their intensity ratios to the NBE vary with excitation depth for both undoped and H-doped ZnO crystals. The intensities of the green and yellow emissions exhibit sublinear dependencies on electron beam excitation density while the NBE intensity increases linearly with the excitation density. These saturation effects with increasing excitation density must be taken into account when assessing defects in ZnO by luminescence characterization. © Copyright Materials Research Society 2011

Blue shift in the luminescence spectra of MEH-PPV films containing ZnO nanoparticles

Luminescence properties of nanocomposites consisting of ZnO nanoparticles in a conjugated polymer, poly [2-methoxy-5-(2′-ethyl hexyloxy)-phenylene vinylene] (MEH-PPV), were investigated. Photoluminescence measurements reveal a blue shift in the emission spectrum of MEH-PPV upon incorporation of ZnO nanoparticles into the polymer film while the emission is increasingly quenched with increasing ZnO concentration. In contrast, the structure of the polymer and its conjugation length are not affected by the presence of ZnO nanoparticles (up to 16 wt% ZnO) as revealed by Raman spectroscopy. The blue shift and photoluminescence quenching are explained by the separation of photogenerated electron-hole pairs at the MEH-PPV/ZnO interface and the charging of the nanoparticles. Crown Copyright © 2008

Observation of Whispering Gallery Modes from hexagonal ZnO microdisks using cathodoluminescence

Zinc oxide hexagonal microdisks with diameters ranging from 3??m up to 15??m were fabricated by thermal chemical vapour deposition. Optical characterisation of ZnO microdisks was performed using low temperature (80?K) cathodoluminescence (CL) imaging and spectroscopy. The microdisks exhibited green luminescence locally distributed near the hexagonal boundary of the ZnO microdisks. High resolution CL spectra of the ZnO microdisks revealed whispering gallery modes (WGMs) emission. The experimentally observed WGMs were in excellent agreement with the predicted theoretical positions calculated using a plane wave model. This work could provide the means for ZnO microdisk devices operating in the green spectral range

Spatial Distribution of Defect Luminescence in ZnO Nanorods: An Investigation by Spectral Cathodoluminescence Imaging

© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim The spatial distribution of ubiquitous green luminescence (GL) in ZnO nanorods is investigated using cathodoluminescence (CL) spectral imaging. The vertically aligned, single-crystal nanorods exhibit a strong GL emission at 2.42 eV at 80 K, attributable to oxygen vacancies. The spectral imaging reveals the GL emission is predominantly located in the surface layer of nanorods; the thickness and intensity of this layer decreases rapidly at elevated temperatures. On the other hand, the near-band-edge emission is weakest near the nanorod edges. The temperature-dependent CL maps are consistent with the properties of a model in which singly ionized oxygen vacancies are stabilized by the surface band bending, which leads to the GL enhancement at the expense of near-band-edge emission. These results demonstrate the utility of spectral CL imaging to map the spatial distribution of defect luminescence in nanostructured materials