An evaluation of satellite aerosol products against sunphotometer measurements

Because atmospheric aerosols scatter sunlight back to space, reflectance measurements from spaceborne radiometers can be used to estimate the aerosol load and its optical properties. Several aerosol products have been generated in a systematic way, and are available for further studies. In this paper, we evaluate the accuracy of such aerosol products derived from the measurements of POLDER, MODIS, MERIS, SEVIRI and CALIOP, through a statistical comparison with Aerosol Optical Depth (AOD) measurements from the AERONET sunphotometer network. Although this method is commonly used, this study is, to our knowledge, among the most extensive of its type since it compares the performance of the products from 5 different sensors using up to five years of data for each of them at global scale. The choice of these satellite aerosol datasets was based on their availability at the ICARE Data and Service Centre (www.icare.univ-lille1.fr).We distinguish between retrievals over land and ocean and between estimates of total and fine mode AOD. Over the oceans, POLDER and MODIS retrievals are of similar quality, with RMS difference lower than 0.1 and a correlation with AERONET of around 0.9. The POLDER estimates suffer from a small positive bias for clean atmospheres, which weakens its statistics. The other aerosol products are of lesser quality, although the SEVIRI products may be of interest for some applications that require a high temporal resolution. The MERIS product shows a very high bias. Over land, only the MODIS product offers a reliable estimate of the total AOD. On the other hand, the polarization-based retrieval using POLDER data allows a better fine mode estimate than that from MODIS. These results suggest the need for a product combining POLDER and MODIS products over land.The paper also analyses how the statistics change with the spatial and temporal thresholds that are used. Spatio-temporal averaging improves the statistics only slightly, which indicates that random errors are not dominant in the error budget. The paper includes various statistical indicators at global scale, and detailed results at individual ground stations can be obtained on request from the authors.     

Transmissive electrowetting‐based displays for portable multimedia devices

Abstract— Electrowetting‐based displays have been successfully demonstrated in reflective mode, showing video capability and high optical performance. However, because this technology is based on a high‐efficiency optical switch operating between a light‐absorbing state and a light‐transmitting state, the technology lends itself naturally to a transmissive mode enabling a complete range of applications. This paper describes the first active‐matrix full‐color transmissive electrowetting displays including its main technical and system aspects. Two architectures have been demonstrated: one uses color filters, the other field‐sequential‐color illumination. The paper also introduces alternative concepts for more efficient color transmissive electrowetting displays with multiple absorbing layers.     

Enhancement of absorption of a gas into a stagnant liquid in which a heterogeneously catalysed chemical reaction occurs

The CBS method[1, 2] is applied to measure the enhancement factor for the absorption of pure hydrogen from a gas bubble of constant size into a sta     

Characterization of grating couplers for affinity-based pesticide sensing

The reflection grating coupler for direct affinity sensing is characterized in detail. The performance of this device and its potential in affinity sensing application are investigated with two affinity-based systems: A self-assembling protein-multilayer system based on avidin-biotin interaction was used to compare the response of the device with theoretical expectations. The analytical performance was characterized by a pesticide immunoassay carried out in an indirect test format with a covalently immobilized triazine derivative. Experimentally determined parameters were in good agreement with model calculations. During the binding of 12 protein monolayers at the surface, the change in effective refractive index Dn(eff) detected for a single layer decreased from approximately 8 x 10(-4) to less than 4 x10(-5) by more than 95%, indicating a filling of the evanescent field. By comparison with bulk refractive-index measurements, a refractive index n(D) approximately 1.38 of the protein multilayer was estimated. Fitting of the model gave a refractive index n(D) = 1.377 of the protein multilayer and an average thickness of 11 nm for a single protein layer. An average noise of Dn(eff) = 8.5 x 10(-7) was detected, corresponding to approximately 1% of the maximum response for a protein monolayer. At a triazine derivative attached to the surface through dextran-based surface chemistry, a maximum antibody loading that corresponds to an Dn(eff) of 1.5 x 10(-3) was observed. In an indirect immunoassay of the herbicide simazine, a detection limit of 0.25 mug/1 of simazine was reached with polyclonal Fab fragments in a concentration of 1 mug/ml.     

Nonlinear Response of a Continuous Wave NMR Spectrometer for Samples with a Large Magnetization

We present a new insight in the response of a CW NMR spectrometer for highly magnetized samples above 100 MHz. The spectrometer is a bridge made of a magic T. The output of the bridge is proportional to the reflection coefficient, , of a resonant circuit, which is built with a coil containing the sample. The sensitivity of the reflection coefficient to the complex susceptibility of the sample, () = () – j(), depends on the quality factor, Q, of the circuit and filling factor, . When the condition Q 1 is not fulfilled, we show indeed that the use of a simple crystal detector, which is only sensitive to || gives rise to a strong nonlinear response of the spectrometer. Measurements of the complex value of by means of phase sensitive detection allow to recover a linear behavior. We discuss and illustrate those issues with a few circuits we designed for our measurements on liquid ³ He with spin polarizations up to 15 %. A method is described to build in a reproducible and predictable way resonant circuits matched to 50 in the frequency range 100 – 400 MHz with a quality factor as high as 1000 at 4 K.     

Electrochemical modeling of hydrogen storage in hydride-forming electrodes

An electrochemical kinetic model (EKM) is developed, describing the electrochemical hydrogen storage in hydride-forming materials under equilibrium conditions. This model is based on first principles of electrochemical reaction kinetics and statistical thermodynamics and describes the complex, multi-stage, electrochemical (de)hydrogenation process. A complete set of equations have been derived, describing the equilibrium hydrogen partial pressure and equilibrium electrode potential as a function of hydrogen content in both solid-solution and two-phase coexistence regions. The EKM has been applied to simulate the isotherms of thin film Pd electrodes of various thicknesses. Good agreement between experiment and theory is found in all cases. Relevant energy and kinetic parameters are obtained from the simulations.     

Studies of the effect of tracer activity on time-averaged positron emission particle tracking measurements on tumbling mills at PEPT Cape Town

The statistical uncertainties associated with time-averaged positron emission particle tracking (PEPT) measurements of the position, velocity and acceleration of a small tracer particle have been investigated. Experiments were undertaken using the ECAT ‘EXACT3D’ PET scanner recently installed at the facilities of PEPT Cape Town at iThemba LABS, South Africa. Small “button” sources of ⁶⁸Ga were attached to the outer shell of a small mill and PEPT data were recorded over several half-lives, for the cases of the mill being empty and entirely filled with steel balls. The effect of tracer activity on the statistical uncertainties in the positions, velocities and accelerations derived from the measurements was investigated, as a first step towards fully quantifying the uncertainties associated with tracking particles via PEPT in laboratory-scale tumbling mills.