421 research outputs found

    Functional Modelling of Water Vapour Transmission through Surface Defects Using Surface Segmentation Analysis

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    Flexible photovoltaic films have been recently shown to have efficiencies comparable to those of solid Si based photovoltaics. Flexible PV films have significant advantages in terms of ease of manufacture by roll-to-roll (R2R) techniques and in easy building integration. A significant challenge is the protection of the flexible solar cells from water vapour ingress, which seriously reduces cell life and efficiency. Transparent barrier films are a possible solution to addressing the water vapour transmission rate (WVTR) challenge. Consequently thin barrier films such as those made from Al2O3 are the subject of increasing research interest when used for the encapsulation of flexible PV modules. The film can be produced by several thin film deposition processes such as atomic layer deposition (ALD). However, micro-scale defects in the barrier film such as pinholes and particulate debris have been shown to have serious consequences in terms of WVTR. Our previous research has empirically shown that small defects (≤3μm lateral dimension) were less significant in determining water vapour ingress. In contrast, larger defects (≥3 μm lateral dimension) have been shown to have a greater effect on the barrier functionality. The present paper illustrates the use of surface segmentation techniques to efficiently extract defect data from measured surface topography of barrier film sheets. Experimental results are presented where the defect information is correlated with the WVTR tests. A model is then presented to test the hypothesis that the major contributing defects to water vapour transmission rate (WVTR) are small numbers of large defects. The model presented in the paper shows excellent correlation with experimental results and provides a theoretical basis for the development of in process surface measurement for thin film R2R manufacture

    Comparative and statistical analysis between the CERN conference database and three other bases

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    This is a comparison between three scientific conference databases and CERN data. High Energy Physics institutes DESY and SLAC databases and the STN-FIZ commercial one's are described and analysed by statistical tables. We plan to work out a co-operation policy especially with DESY for exchange or data import

    Comparison of the INRIM and PTB lattice-spacing standards

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    To base the kilogram definition on the atomic mass of the silicon 28 atom, the present relative uncertainty of the silicon 28 lattice parameter must lowered to 3E-9. To achieve this goal, a new experimental apparatus capable of a centimetre measurement-baseline has been made at the INRIM. The comparison between the determinations of the lattice parameter of crystals MO*4 of INRIM and WASO4.2a of PTB is intended to verify the measurement capabilities and to assess the limits of this experiment.Comment: 10 pages, 8 figures, submitted to Metrologi

    Free-running InGaAs single photon detector with 1 dark count per second at 10% efficiency

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    We present a free-running single photon detector for telecom wavelengths based on a negative feedback avalanche photodiode (NFAD). A dark count rate as low as 1 cps was obtained at a detection efficiency of 10%, with an afterpulse probability of 2.2% for 20 {\mu}s of deadtime. This was achieved by using an active hold-off circuit and cooling the NFAD with a free-piston stirling cooler down to temperatures of -110o{^o}C. We integrated two detectors into a practical, 625 MHz clocked quantum key distribution system. Stable, real-time key distribution in presence of 30 dB channel loss was possible, yielding a secret key rate of 350 bps.Comment: 4 pages, 4 figure

    Analysis and Control of mortar Quality with ultrasonic wave attenuation

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    Wave propagation and attenuation on mortar material are discussed in this paper with a Non Destructive Testing (NDT) which can be used to characterize samples of mortars and effect of microstructure of sand in their hardening. Samples were manufactured using same water/cement ration (w/c) 0.65, and cement/sand ration (c/s) 0.5 in order to simulate the attenuation. The characterization of attenuation in mortar material has been performed by ultrasonic reflection technique using a transducer with central frequency 0.5MHz. It is shown that sand particle size exercises significant influence on the evolution of attenuation, the attenuation parameters give information about average state of the hardening of the mortar itself