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 flow of heat through the floor of the Atlantic Ocean

Abstract: The measurement of the temperature gradient and thermal conductivity in the sediments beneath the floor of the North Atlantic Ocean is described. Measurements were made at five stations. The mean heat flow and conductivity were found to be 0$\cdot $98 $\times $ 10$^{-6}$ cal/cm$^{2}$s and 25 $\times $ 10$^{-4}$ cal/cm degrees Cs. The heat flows at the individual stations range from 0$\cdot $58 to 1$\cdot $42 $\times $ 10$^{-6}$ cal/cm$^{2}$s. The high heat flow is an unexpected result, and it is difficult to find a source for so much heat.

Direct evidence for multiferroic magnetoelectric coupling in 0.9BiFeO3-0.1BaTiO3.

Abstract: Magnetic, dielectric and calorimetric studies on $0.9{\mathrm{BiFeO}}_{3}--0.1{\mathrm{BaTiO}}_{3}$ indicate strong magnetoelectric coupling. XRD studies reveal a very remarkable change in the rhombohedral distortion angle and a significant shift in the atomic positions at the magnetic ${T}_{c}$ due to an isostructural phase transition. The calculated polarization using Rietveld refined atomic positions scales linearly with magnetization. Our results provide the first unambiguous, atomic level evidence for magnetoelectric coupling of intrinsic multiferroic origin in a ${\mathrm{BiFeO}}_{3}$-based system.

Formation of metastable phases in flame- and plasma-prepared alumina

Abstract: The formation of metastable phases in plasma- and flame-prepared alumina particles is examined in terms of the classical nucleation theory, rate of transformation of metastable to stable forms, and the thermal history of the particles during solidification. It is suggested that homogeneous nucleation of the solidification of liquid droplets at considerable undercooling results in the formation ofγ-Al2O3 rather thanα-Al2O3 because of its lower critical free energy for nucleation. The phase finally observed depends upon the thermal history of the particles during evolution of the heat of fusion and upon the kinetics of the transformation of the nucleating phase to the stable phase. This means that the cooling rate of the particles is relatively unimportant and under the conditions existing in flames and plasmas, metastable alumina will be formed on solidification. The metastable form will be retained on cooling particles less than approximately 10 μm diameter, but particles larger than this may transform toα-Al2O3 during the solidification exotherm

Early warning signals of ecological transitions: methods for spatial patterns.

Abstract: A number of ecosystems can exhibit abrupt shifts between alternative stable states. Because of their important ecological and economic consequences, recent research has focused on devising early warning signals for anticipating such abrupt ecological transitions. In particular, theoretical studies show that changes in spatial characteristics of the system could provide early warnings of approaching transitions. However, the empirical validation of these indicators lag behind their theoretical developments. Here, we summarize a range of currently available spatial early warning signals, suggest potential null models to interpret their trends, and apply them to three simulated spatial data sets of systems undergoing an abrupt transition. In addition to providing a step-by-step methodology for applying these signals to spatial data sets, we propose a statistical toolbox that may be used to help detect approaching transitions in a wide range of spatial data. We hope that our methodology together with the computer codes will stimulate the application and testing of spatial early warning signals on real spatial data.

Factors affecting the grain-refinement of aluminum using titanium and boron additives

Abstract: The development of grain-refining techniques for the casting of aluminum, and the results achieved using additions of ternary Al-Ti-B master-alloys, are briefly described. A test procedure is given for assessing the relative effectiveness of these master-alloys, and the results are related to the various kinds of alloy treated, including those with constituents which “poison” the grain-refining agent. The equilibrium conditions which affect the behavior of the constituents of the grain-refined alloys are examined quantitatively from a thermodynamic viewpoint. One theory about the mechanism of nucleation of aluminum on titanium diboride is examined and found inapplicable. New data on the solubility of TiB2, ZrB2, TiC, ZrC, Cr3C2, CrB2 in liquid aluminum are presented graphically. Practical aspects of alloy behavior in grain-refining practice are analyzed and discussed on the basis of the quantitative data.