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.

The Stability of the Flow of an Electrically Conducting Fluid between Parallel Planes under a Transverse Magnetic Field

Abstract: The stability under small disturbances is investigated of the two-dimensional laminar motion of an electrically conducting fluid under a transverse magnetic field. It is found that the dominating factor is the change in shape of the undisturbed velocity profile caused by the magnetic field, which depends only on the Hartmann number M . Curves of wave number against Reynolds number for neutral stability are calculated for a range of values of M ; for large values of M the calculations are similar to those which determine the stability of ordinary boundary-layer flow. The critical Reynolds number is found to rise very rapidly with increasing M , so that a transverse magnetic field has a powerful stabilizing influence on this type of flow.

Structure and activity of lysozyme on binding to ZnO nanoparticles.

Abstract: The interaction between ZnO nanoparticles (NPs) and lysozyme has been studied using calorimetric as well as spectrophotometric techniques, and interpreted in terms of the three-dimensional structure. The circular dichroism spectroscopic data show an increase in α-helical content on interaction with ZnO NPs. Glutaraldehyde cross-linking studies indicate that the monomeric form occurs to a greater extent than the dimer when lysozyme is conjugated with ZnO NPs. The enthalpy-driven binding between lysozyme and ZnO possibly involves the region encompassing the active site in the molecule, which is also the site for the dimer formation in a homologous structure. The enzyme retains high fraction of its native structure with negligible effect on its activity upon attachment to NPs. Compared to the free protein, lysozyme−ZnO conjugates are more stable in the presence of chaotropic agents (guanidine hydrochloride and urea) and also at elevated temperatures. The possible site of binding of NP to lysozyme has been pr...

A Realization of the SI Watt by the NPL Moving-coil Balance

Abstract: Mechanical and electrical power in SI units have been equated by measurements made on a coil part of which is in a strong magnetic field The force due to a current I flowing in the coil, is weighed by opposing it with a mass M subject to the earth's gravitational acceleration g This is combined with a separate measurement in which a voltage V is generated in the coil when it is moved vertically with velocity u through the relationship IV = M g u If the current produces a voltage V across a resistor whose value R is known in SI units, then V = (M g u R)1/2 Hence the voltage V and the current I are known in SI units and can be used to express the value of the NPL working standards in SI units The working standard of voltage has hitherto been maintained in terms of a Josephson effect apparatus by ascribing the value 483 594 GHz/volt (maintained) to the Josephson constant KJ presumed equal to 2e/h The measurements reported here suggest a different value of KJ 483 597,903 ± 0,035 ought to be used, based on the premise that the SI value of the quantum Hall resistance is RK = 25 812,8092 ± 0,0014 Ω If one presumed also that RK = h/e2 exactly, the values of elementary charge e and the Planck constant, h, which may be deduced from these measurements are e = 1,602 176 35 ± 0,000 000 14 × 10-19 C, h = 6,626 068 21 ± 0,000 000 90 × 10-34 J s, which may be compared with the values recommended by the CODATA Task Group on Fundamental Constants which are e = 1,602 177 33 ± 0,000 000 14 × 10-19 C, h = 6,626 075 5 ± 0,000 004 0 × 10-34 J s

Bond alternation defects in long polyene molecules

Abstract: Recent theoretical work suggests that there is an alternation in carbon-carbon bond lengths throughout a sufficiently long polyene chain. Such alternation implies the possibility of defects in which even-numbered bonds along the chain change over from short to long. In this paper, the electronic properties of such defects are examined by Huckel molecular orbital theory, with the parameters used by Longuet-Higgins and Salem [2]. It is shown that there is a localized non-bonding molecular orbital associated with each defect (if they are well separated). In the neutral molecule, there will be an odd electron in each such molecular orbital, which should be detectable by electron spin resonance. An approximate estimate of the energy required to form a defect suggests that there should be about one per seventy carbon atoms.