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.

High-resolution microwave frequency transfer over an 86-km-long optical fiber network using a mode-locked laser.

Abstract: We demonstrate the transfer of an ultrastable microwave frequency by transmitting a 30-nm-wide optical frequency comb from a mode-locked laser over 86 km of installed optical fiber. The pulse train is returned to the transmitter via the same fiber for compensation of environmentally induced optical path length changes. The fractional transfer stability measured at the remote end reaches 4×10−17 after 1600 s, corresponding to a timing jitter of 64 fs.

Refractometry in the Far Infra-red using a Two-beam Interferometer

Abstract: A MICHELSON two-beam interferometer can be used for refractive-index determination by measuring the shift of the achromatic fringe when a specimen of known thickness is placed in one arm of the interferometer Such a measurement using a broad spectrum and ‘white-light’ fringes gives only a single index value and that cannot be related to a definite wave-length Monochromatic radiation cannot be used because of the impossibility of identifying a given fringe after displacement It appeared plausible, however, that a spectrum of refractive index could be obtained by making observations of intensity over a range of path-difference and taking the Fourier transform of the two-beam interferogram, the method being an extension of that used for obtaining infra-red power-spectra1 This has been realized in the far infra-red region, where the method has been used to determine the refractive-index spectrum of crystalline quartz over the wave-length range 500–180µ (20–56 cm−1) No values have been previously reported over much of this range

A comparison of protein quantitation assays for biopharmaceutical applications.

Abstract: Dye-based protein determination assays are widely used to estimate protein concentration, however various reports suggest that the response is dependent on the composition and sequence of the protein, limiting confidence in the resulting concentration estimates. In this study a diverse set of model proteins representing various sizes of protein and covalent modifications, some typical of biopharmaceuticals have been used to assess the utility of dye-based protein concentration assays. The protein concentration assays (Bicinchoninic acid (BCA), Bradford, 3-(4-carboxybenzoyl)quinoline-2-carboxaldehyde (CBQCA™), DC, Fluorescamine and Quant-iT™) were compared to the ‘gold standard’ assay, quantitative amino acid analysis (AAA). The assays that displayed the lowest variability between proteins, BCA and DC, also generated improved estimates when BSA was used as a standard, when compared to AAA derived concentrations. Assays read out by absorbance tended to display enhanced robustness and repeatability, whereas the fluorescence based assays had wider quantitation ranges and lower limits of detection. Protein modification, in the form of glycosylation and PEGylation, and the addition of excipients, were found to affect the estimation of protein concentration for some of the assays when compared to the unmodified protein. We discuss the suitability and limitations of the selected assays for the estimation of protein concentration in biopharmaceutical applications.

Transparent Conducting Graphene Hybrid Films To Improve Electromagnetic Interference (EMI) Shielding Performance of Graphene

Abstract: Conducting graphene-based hybrids have attracted considerable attention in recent years for their scientific and technological significance in many applications. In this work, conductive graphene hybrid films, consisting of a metallic network fully encapsulated between monolayer graphene and quartz–glass substrate, were fabricated and characterized for their electromagnetic interference shielding capabilities. Experimental results show that by integration with a metallic network the sheet resistance of graphene was significantly suppressed from 813.27 to 5.53 Ω/sq with an optical transmittance at 91%. Consequently, the microwave shielding effectiveness (SE) exceeded 23.60 dB at the Ku-band and 13.48 dB at the Ka-band. The maximum SE value was 28.91 dB at 12 GHz. Compared with the SE of pristine monolayer graphene (3.46 dB), the SE of graphene hybrid film was enhanced by 25.45 dB (99.7% energy attenuation). At 94% optical transmittance, the sheet resistance was 20.67 Ω/sq and the maximum SE value was 20.86...

A Method for Accurate Transmission Line Impedance Parameter Estimation

Abstract: Real-time estimation of power transmission line impedance parameters has become possible with the availability of synchronized phasor (synchrophasor) measurements of voltage and current. If sufficiently accurate, the estimated parameter values are a powerful tool for improving the performance of a range of power system monitoring, protection, and control applications, including fault location and dynamic thermal line rating. The accuracy of the parameter estimates can be reduced by unknown errors in the synchrophasors that are introduced in the measurement process. In this paper, a method is proposed with the aim of obtaining accurate estimates of potentially variable impedance parameters, in the presence of systematic errors in voltage and current measurements. The method is based on optimization to identify correction constants for the phasors. A case study of a simulated transmission line is presented to demonstrate the effectiveness of the new method, which is better in comparison with a previously proposed method. The results, as well as limits, and the potential extensions of the new method are discussed.