A Simulation-Assisted Non-destructive Approach for Permittivity Measurement Using an Open-Ended Microwave Waveguide

A new convenient and non-destructive permittivity measurement method is presented. No physical cut of specimens is needed here for material characterisation. In the setup, the material under test is placed in the near-field region of a microwave open-ended waveguide. An electromagnetic model of the setup is built in the Computer Simulation Technology simulation software. Employing optimisation, the permittivity is obtained from the measured reflection coefficients S11. Using the same technique, the effect of the model size is investigated that could reduce the modelling effort for large structures. The efficiency of a traditional method (i.e., Newton) and an intelligent algorithm (i.e. particle swarm optimisation) for permittivity calculation is thoroughly studied and compared. The proposed methodology is validated by experimental data. It is demonstrated that the proposed method can provide more accurate permittivity results than the intrusive in-waveguide measurement. The proposed methodology can contribute to electromagnetic analysis, thickness measurement and non-destructive evaluation

Discovery of Inhibitors of Leishmania β-1,2-Mannosyltransferases Using a Click-Chemistry-Derived Guanosine Monophosphate Library

Leishmania spp. are a medically important group of protozoan parasites that synthesize a novel intracellular carbohydrate reserve polymer termed mannogen. Mannogen is a soluble homopolymer of β-1,2-linked mannose residues that accumulates in the major pathogenic stages in the sandfly vector and mammalian host. While several steps in mannogen biosynthesis have been defined, none of the enzymes have been isolated or characterized. We report the development of a simple assay for the GDP-mannose–dependent β-1,2-mannosyltransferases involved in mannogen synthesis. This assay utilizes octyl α-d-mannopyranoside to prime the formation of short mannogen oligomers up to 5 mannose residues. This assay was used to screen a focussed library of 44 GMP-triazole adducts for inhibitors. Several compounds provided effective inhibition of mannogen β-1,2-mannosyltransferases in a cell-free membrane preparation. This assay and inhibitor compounds will be useful for dissecting the role of different mannosyltransferases in regulating de novo biosynthesis and elongation reactions in mannogen metabolism

Constitutive sharing of recycling synaptic vesicles between presynaptic boutons

The synaptic vesicle cycle is vital for sustained neurotransmitter release. It has been assumed that functional synaptic vesicles are replenished autonomously at individual presynaptic terminals. Here we tested this assumption by using FM dyes in combination with fluorescence recovery after photobleaching and correlative light and electron microscopy in cultured rat hippocampal neurons. After photobleaching, synapses acquired recently recycled FM dye¿labeled vesicles originating from nonphotobleached synapses by a process requiring dynamic actin turnover. The imported vesicles entered the functional pool at their host synapses, as revealed by the exocytic release of the dye upon stimulation. FM1-43 photoconversion and ultrastructural analysis confirmed the incorporation of imported vesicles into the presynaptic terminal, where they mixed with the native vesicle pools. Our results demonstrate that synaptic vesicle recycling is not confined to individual presynaptic terminals as is widely believed; rather, a substantial proportion of recycling vesicles are shared constitutively between boutons