National Physical Laboratory

About: National Physical Laboratory is a facility organization based out in London, United Kingdom. It is known for research contribution in the topics: Dielectric & Thin film. The organization has 7615 authors who have published 13327 publications receiving 319381 citations.

Iron oxide-chitosan nanobiocomposite for urea sensor

Abstract: Urease (Ur) and glutamate dehydrogenase (GLDH) have been co-immobilized onto superparamegnatic iron oxide (Fe3O4) nanoparticles-chitosan (CH) based nanobiocomposite film deposited onto indium-tin-oxide (ITO) coated glass plate via physical adsorption for urea detection. The magnitude of magnetization (60.9 emu/g) of Fe3O4 nanoparticles (∼22 nm) estimated using vibrating sample magnetometer (VSM) indicates superparamagnetic behaviour. It is shown that presence of Fe3O4 nanoparticles results in increased active surface area of CH-Fe3O4 nanobiocomposite for immobilization of enzymes (Ur and GLDH), enhanced electron transfer and increased shelf-life of nanobiocomposite electrode. Differential pulse voltammetry (DPV) studies show that Ur-GLDH/CH-Fe3O4/ITO bioelectrode is found to be sensitive in the 5–100 mg/dL urea concentration range and can detect as low as 0.5 mg/dL. A relatively low value of Michaelis–Menten constant (Km, 0.56 mM) indicates high affinity of enzymes (Ur and GLDH) for urea detection.

Black carbon and chemical characteristics of PM10 and PM2.5 at an urban site of North India

Abstract: The concentrations of PM10, PM2.5 and their water-soluble ionic species were determined for the samples collected during January to December, 2007 at New Delhi (28.63° N, 77.18° E), India. The annual mean PM10 and PM2.5 concentrations (± standard deviation) were about 219 (± 84) and 97 (±56) µgm−3 respectively, about twice the prescribed Indian National Ambient Air Quality Standards values. The monthly average ratio of PM2.5/PM10 varied between 0.18 (June) and 0.86 (February) with an annual mean of ∼0.48 (±0.2), suggesting the dominance of coarser in summer and fine size particles in winter. The difference between the concentrations of PM10 and PM2.5, is deemed as the contribution of the coarse fraction (PM10−2.5). The analyzed coarse fractions mainly composed of secondary inorganic aerosols species (16.0 µgm−3, 13.07%), mineral matter (12.32 µgm−3, 10.06%) and salt particles (4.92 µgm−3, 4.02%). PM2.5 are mainly made up of undetermined fractions (39.46 µgm−3, 40.9%), secondary inorganic aerosols (26.15 µgm−3, 27.1%), salt aerosols (22.48 µgm−3, 23.3%) and mineral matter (8.41 µgm−3, 8.7%). The black carbon aerosols concentrations measured at a nearby (∼300 m) location to aerosol sampling site, registered an annual mean of ∼14 (±12) µgm−3, which is significantly large compared to those observed at other locations in India. The source identifications are made for the ionic species in PM10 and PM2.5. The results are discussed by way of correlations and factor analyses. The significant correlations of Cl−, SO42−, K+, Na+, Ca2+, NO3− and Mg2+ with PM2.5 on one hand and Mg2+ with PM10 on the other suggest the dominance of anthropogenic and soil origin aerosols in Delhi.

Ultrathin SiO2 on Si II. Issues in quantification of the oxide thickness

Abstract: An analysis is made of various quantification issues concerning the analysis of ultrathin layers of SiO2 on (100) and (111) polished Si surfaces. For analysis of the oxide thickness, a simple equation is generally used involving two parameters; the attenuation length of photoelectrons in the oxide and the ratio, Ro, of the intensities of the Si 2p peak from bulk thermal SiO2 and from pure Si. An analysis of previously reported measurements of the attenuation length gives an average value of only 6% less than the theoretical value. However, careful measurements of Ro, via two routes, indicate consistently that a value of 0.88 ± 0.03 should be used rather than the calculated value of 0.53 ± 0.05. This difference may arise through systematic uncertainties in the values for the relevant inelastic mean free paths, the silicon dioxide density and the shake-up contributions. Previously reported experimental values of Ro range from 0.67 to 0.87. Uncertainties also arise from intensity variations caused by the crystal structure of the substrate. These are mapped and a position ‘A’ is found where further work is best conducted. For the (100) surface, A is 34° from the surface normal in an azimuth midway at 22.5° between the [010] and [011] azimuths. For the (111) surface at A is 25.5° from the surface normal in the [101] azimuth. Data for much of the present work are for the (100) surface at an angle of emission of 27° at position ‘B’ at 28.5° from the surface normal in the [110] azimuth, which is equivalently good but may degrade for spectrometers with high angular resolution. If the same equation is used for calculating the thickness, position B leads to a calculated thickness that is 4% less than that measured for an average orientation, whereas data acquired for normal emission lead to a value 18% lower, and those measured at A are 2% higher. Measurements of the carbonaceous contamination confirm earlier conclusions that the contamination is better described using data for an average polymer than for glassy carbon. © Crown copyright 2002. Published by John Wiley & Sons, Ltd.