Spatial Control of Photoemitted Electron Beams using a Micro-Lens-Array Transverse-Shaping Technique

A common issue encountered in photoemission electron sources used in electron accelerators is the transverse inhomogeneity of the laser distribution resulting from the laser-amplification process and often use of frequency up conversion in nonlinear crystals. A inhomogeneous laser distribution on the photocathode produces charged beams with lower beam quality. In this paper, we explore the possible use of microlens arrays (fly-eye light condensers) to dramatically improve the transverse uniformity of the drive laser pulse on UV photocathodes. We also demonstrate the use of such microlens arrays to generate transversely-modulated electron beams and present a possible application to diagnose the properties of a magnetized beam.Comment: arXiv admin note: text overlap with arXiv:1609.0166

A molecular theory for two-photon and three-photon fluorescence polarization

In the analysis of molecular structure and local order in heterogeneous samples, multiphoton excitation of fluorescence affords chemically specific information and high-resolution imaging. This report presents the results of an investigation that secures a detailed theoretical representation of the fluorescence polarization produced by one-, two-, and three-photon excitations, with orientational averaging procedures being deployed to deliver the fully disordered limits. The equations determining multiphoton fluorescence response prove to be expressible in a relatively simple, generic form, and graphs exhibit the functional form of the multiphoton fluorescence polarization. Amongst other features, the results lead to the identification of a condition under which the fluorescence produced through the concerted absorption of any number of photons becomes completely unpolarized. It is also shown that the angular variation of fluorescence intensities is reliable indicator of orientational disorder

Antenna pattern shaping, sensing, and steering study Final report

Design of steerable satellite antenna with beam pattern sensing syste

Character and interface shear strength of accreted ice on subcooled surfaces submerged in fuel

Sudden release of accreted ice in fuel systems could pose a serious challenge in aircraft operation. The resultant snowshower may reach the filter and fuel-oil heat exchanger, causing a restriction in fuel flow to the engine. It is fundamental to have an appreciation of the character and the interface shear strength of the accreted ice in aircraft fuel systems. This helps to recognise factors for the sudden release of the accreted ice and the intensity of the consequential snowshower. An experimental study was carried out to quantify the character and the interface shear strength of accreted ice on subcooled surfaces submerged in jet fuel. Ice was accreted on naked aluminium, painted aluminium and carbon fibre composite surfaces at various subcooled temperatures. The accreted ice was akin to fresh snow and exhibited soft and fluffy attributes. The character may be expressed quantitatively in terms of the porosity and was found to be c. 0·95. The ice weakly adhered to the substrate surfaces, and the interface shear strength was found to be c. 0·36Pa and c. 2·19Pa at the top surface and at the vertical surface of a specimen block, respectively. It was not possible to detect any variation in the porosity and the interface shear strength for different types of surface finishes and differences in water affnity in fuels due to the crude approach in the estimation of these parameters

Differential expression of genes involved in iron metabolism in Aspergillus fumigatus

The ability of fungi to survive in many environments is linked to their capacity to acquire essential nutrients. Iron is generally complexed and available in very limited amounts. Like bacteria, fungi have evolved highly specific systems for iron acquisition. Production and uptake of iron-chelating siderophores has been shown to be important for certain human bacterial pathogens, as well as in fungal pathogens such as Cryptococcus neoformans and Fusarium graminearum. This system also enables the opportunistic fungal pathogen Aspergillus fumigatus to infect and subsequently colonize the human lung. In this study, advantage was taken of genome sequence data available for both Aspergillus nidulans and A. fumigatus either to partially clone or to design PCR primers for 10 genes putatively involved in siderophore biosynthesis or uptake in A. fumigatus. The expression of these genes was then monitored by semi-quantitative and quantitative real-time PCR over a range of iron concentrations. As expected, the putative biosynthetic genes sidA, sidC and sidD were all strongly up-regulated under iron starvation conditions, although the variable degree of induction indicates complex regulation by a number of transcriptional factors, including the GATA family protein SreA. In contrast, the gene sidE shows no iron-regulation, suggesting that SidE may not be involved in siderophore biosynthesis. The characterisation of the expression patterns of this subset of genes in the iron regulon facilitates further studies into the importance of iron acquisition for pathogenesis of A. fumigatus. [Int Microbiol 2006; 9(4):281-287

Continuous flow vortex fluidic-mediated exfoliation and fragmentation of two-dimensional MXene

MXene (Ti2CTx) is exfoliated in a vortex fluidic device (VFD), as a thin film microfluidic platform, under continuous flow conditions, down to ca 3 nm thin multi-layered twodimensional (2D) material, as determined using AFM. The optimized process, under an inert atmosphere of nitrogen to avoid oxidation of the material, was established by systematically exploring the operating parameters of the VFD, along with the concentration of the dispersed starting material and the choice of solvent, which was a 1 : 1 mixture of isopropyl alcohol and water. There is also some fragmentation of the 2D material into nanoparticles ca 68 nm in diameter