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.

Correction methods for integrating‐sphere measurement of hemispherical reflectance

Abstract: Integrating-sphere reflectometers in spectrophotometers and colorimeters suffer from several types of systematic error. The properties of an ideal sphere and the main shortcomings of practical spheres are discussed. Some common errors that occur in measurements of hemispherical reflectance have been investigated using a Cary 14 spectrophotometer fitted with two different integrating spheres: a Cary type 1411 attachment and another made at NPL using a G. E.-Hardy spectrophotometer sphere. The methods described here can be applied to almost any sphere instrument, and possible solutions to problems with other sphere designs are also suggested. It is shown that significant corrections are necessary in many cases.

Dumbbell shaped nickel nanocrystals synthesized by a laser induced fragmentation method

Abstract: Dumbbell shaped nickel nanoparticles have been synthesized for the first time by laser induced fragmentation of bulk nickel powder in aqueous sodium dodecyl sulfate. The focused output of the third harmonic from a nanosecond pulsed Nd:YAG laser operating at 35 mJ/pulse energy was used for the photo-fragmentation of micron size particles suspended in 50 mM aqueous medium. Nickel anisotropic nanocrystals have been grown by recrystallisation of nickel particles due to laser plasma generated in sodium dodecyl sulfate solution. The Vibrating Sample Magnetometer measurements of dumbbell shaped nickel nanostructure show their good ferromagnetic nature. The mechanism of the synthesis of nanostructure through melting and fragmentation has been also discussed.

Structural and optical properties of TiO2 thin films derived by sol–gel dip coating process

Abstract: Nanocrystalline thin films of titanium dioxide have been fabricated on glass and silica substrates from partially hydrolyzed precursor solution. These films were subjected to heat treatment for 1 h at temperatures 100, 200, 300, 400, 500, 600, 700, 800 and 900 °C and characterized by XRD, SEM, XPS and optical techniques. As deposited films are found to be amorphous and also contain hydroxyl and organic functional groups. Films heat treated above 100 °C do not contain hydroxyl and organic functional groups. Microcrystalline behavior is observed in the films heat treated above 300 °C. Crystallite size increases from ∼5 to 50 nm as sintering temperature is increased from 300 to 700 °C. Formation of anatase phase with c-axis length 7.03 A is observed in the films annealed up to 700 °C. These films peel off from the substrate beyond 700 °C annealing temperature. Density as well as refractive index of the films increases with increase in annealing temperature up to 700 °C. Refractive index is found to show Cauchys behavior. Transmission better than 70% is observed in the visible range. There is a strong absorption around 370 nm, which is attributed to band gap absorption of the material.

Optimization and Metaheuristic Algorithms in Engineering

Abstract: Design optimization in engineering tends to be very challenging, partly due to the complexity and high nonlinearity of the problem of interest and partly due to stringent design codes in engineering. Conventional algorithms are not the best tools for highly nonlinear global optimization, as they are local search algorithms and thus often miss the global optimality. In addition, design solutions have to be robust and subject to uncertainty in the parameters and tolerance of available components and materials. Metaheuristic algorithms have become increasingly popular in the last two decades. This chapter reviews some of the latest metaheuristics.

Electrochemistry of poly(3,4-ethylenedioxythiophene)-polyaniline/ Prussian blue electrochromic devices containing an ionic liquid based gel electrolyte film.

Abstract: Electrochromic devices based on poly(3,4-ethylenedioxythiophene) (PEDOT) as the cathodic coloring electrode and polyaniline (PANI) or Prussian blue (PB) as the counter electrode containing a highly conductive, self-supporting, distensible and transparent polymer–gel electrolyte film encapsulating an ionic liquid, 1-butyl-1-methylpyrrolidiniumbis(trifluoromethylsulfonyl)imide, have been fabricated. Polarization, charge transfer and diffusion processes control the electrochemistry of the functional electrodes during coloration and bleaching and these phenomena differ when PEDOT and PANI/PB were employed alternately as working electrodes. While the electrochemical impedance response shows good similitude for PEDOT and PANI electrodes, the responses of PEDOT and PB were significantly different in the PEDOT–PB device, especially during reduction of PB, wherein the overall amplitude of the impedance response is enormous. Large values of the coloration efficiency maxima of 281 cm2C−1 (λ = 583 nm) and 274 cm2C−1 (λ = 602 nm), achieved at −1.0 and −1.5 V for the PEDOT–PANI and PEDOT–PB devices have been correlated to the particularly low magnitude of charge transfer resistance and high polarization capacitance operative at the PEDOT–ionic liquid based electrolyte interface at these dc potentials, thus allowing facile ion-transport and consequently resulting in enhanced absorption modulation. Moderately fast switching kinetics and the ability of these devices to sustain about 2500 cycles of clear-to-dark and dark-to-clear without incurring major losses in the optical contrast, along with the ease of construction of these cells in terms of high scalability and reproducibility of the synthetic procedure for fabrication of the electrochromic films and the ionic liquid based gel electrolyte film, are indicators of the promise these devices hold for practical applications like electrochromic windows and displays.