1,379,534 research outputs found
Combined Kelvin probe force microscopy and secondary ion mass spectrometry for hydrogen detection in corroded 2024 aluminium alloy
No full textThe capability of Kelvin probe force microscopy (KFM) to detect and locate hydrogen in corroded 2024 aluminium alloy was demonstrated. Hydrogen was introduced inside the 2024 alloy following a cyclic corrosion test consisting of cycles of immersion in 1 M NaCl solution followed by exposure to air at -20 °C. The combination of scanning electron microscopy, secondary ion mass spectrometry and KFM demonstrated that the grain and subgrain boundaries were preferential pathways for the short-circuit diffusion of hydrogen but also acted as a source of hydrogen diffusion in the lattice over distances of up to ten microns with non-negligible desorption when exposed to air at room temperature for 24 h
Spatial distribution of rolled up Kelvin-Helmholtz vortices at Earth's dayside and flank magnetopause
No full textThe Kelvin-Helmholtz Instability (KHI) can drive waves at the magnetopause. These waves can grow to form rolled-up vortices and facilitate transfer of plasma into the magnetosphere. To investigate the persistence and frequency of such waves at the magnetopause we have carried out a survey of all Double Star 1 magnetopause crossings, using a combination of ion and magnetic field measurements. Using criteria originally used in a Geotail study made by Hasegawa et al. (2006) (forthwith referred to as H2006), 17 candidate events were identified from the entire TC-1 mission (covering similar to 623 orbits where the magnetopause was sampled), a majority of which were on the dayside of the terminator. The relationship between density and shear velocity was then investigated, to identify the predicted signature of a rolled up vortex from H2006 and all 17 events exhibited some level of rolled up behavior. The location of the events had a clear dawn-dusk asymmetry, with 12 (71%) on the post noon, dusk flank suggesting preferential growth in this region
Evolution of Kelvin-Helmholtz activity on the dusk flank magnetopause
No full textOur purpose is to characterize the evolution of the magnetopause Kelvin-Helmholtz
(KH) wave activity with changes in thickness of the adjacent boundary layer,
geomagnetic latitude and interplanetary magnetic field (IMF) orientation. As the IMF
turns northward, wave activity may be generated at the dayside before propagating
down the tail, where the boundary layer is expected to support longer wavelengths. We
use two-point observations on the dusk magnetopause at low latitudes, from Geotail on
the dayside and Cluster tailward of the dusk terminator. We quantify the wavelength,
power, wavefront steepness and propagation direction at Cluster. An estimate of the
thickness of the low-latitude boundary layer (LLBL) is obtained by correlating normal
distances to the magnetopause, derived from two empirical solar-wind-driven models,
with a systematic relationship (the "transition parameter") found between the electron
number density and temperature; the correlation factor is used to infer the temporal
evolution of the thickness of the locally sampled layer. We find that wavelengths are
controlled by the IMF clock angle, as expected when generated by the KH mechanism
at the dayside, although amplitudes, wavefront steepness and propagation directions are
more closely correlated with the layer thickness. A survey of parameter space provides
evidence of the contribution of the KH mechanism to the widening of the electron LLBL
Kelvin Watt Balance (No. 460)
No full textThis is one of a set of four Kelvin balances purchased by the National Bureau of Standards at the end of 1902. It has a linear fixed scale 0-650. With a current of 110 volts, a 500 ohm multiplier was used in the moving coil circuit. As a secondary standard this instrument had to be calibrated.23 x 37 x 26 cm; 18 x 46 x 18 c
The stability of the variable-density Kelvin-Helmholtz billow
No full textWe perform a three-dimensional stability analysis of the Kelvin-Helmholtz billow, developing in a shear-layer between two fluids with different density. We begin with two-dimensional simulations of the temporally evolving mixing-layer yielding the unsteady base flow fields. The Reynolds number is 1500 while the Schmidt and Froude numbers are infinite. Then exponentially unstable modes are extracted from a linear stability analysis performed at the saturation of the primary mode kinetic energy. The spectrum of the least stable modes exhibits two main classes. The first class comprises three-dimensional core-centred and braid-centred modes already present in the homogeneous case. The baroclinic vorticity concentration in the braid lying on the light side of the KH-billow turns the flow into a sharp vorticity ridge holding high shear levels. The hyperbolic modes benefit from the enhanced level of shear in the braid while elliptic ones remain quite insensitive to the modifications of the base flow. In the second class, we found typical two-dimensional modes resulting from a shear instability of the curved vorticity-enhanced braid. For a density contrast of 0.5, the wavelength of the two-dimensional instability is about ten times shorter than the one of the primary wave. Its amplification rate competes well against the ones of the hyperbolic three-dimensional modes. The vorticity-enhanced braid thus becomes the preferred location for the development of secondary instabilities. This stands as the key feature of the transition of the variable-density mixing layer. We carry out a fully resolved numerical continuation of the nonlinear development of the two-dimensional braid-mode. Secondary roll-ups due to a small-scale Kelvin-Helmholtz mechanism are promoted by the underlying strain field and develop rapidly in the compression part of the braid. Originally analysed in Reinaud et al. (2000) from two-dimensional non-viscous numerical simulations, this instability is shown to substantially increase the mixing
Lee, Kelvin
No full textKelvin Lee is Assistant Director of Member & External Relations for the International Air Transport Association (IATA), based at the Asia-Pacific regional office in Singapore.
IATA is the trade association for the world’s airlines, representing some 290 airlines or 82% of total air traffic. IATA supports many areas of aviation activity and helps formulate industry policy on critical aviation issues.
In his role, Kelvin looks after aviation policy and regulatory developments to support aviation growth in the region. In light of the COVID-19 situation, one of his current focus is the coordination of IATA’s efforts to support the industry restart in the region.https://commons.erau.edu/aviasian-bios-2021/1019/thumbnail.jp
Kelvin Electrostatic Pointer Voltmeter
No full textThis Kelvin multi-cellular voltmeter, 120 volts, is of a later type than another voltmeter in our collection, Accession No. 1998.0107.001. It has a parallax mirror under its pointer. Damping is by a disk hanging in an oil cup. It was made by the firm of Kelvin, Bottomley and Baird, Glasgow and London the successors to Kelvin and White.36 x 27 x 30 c
Kelvin-Helmholtz instabilities with Godunov smoothed particle hydrodynamics
No full textNumerical simulations for the non-linear development of Kelvin–Helmholtz instability in two different density layers have been performed with the particle-based method (Godunov SPH) developed by Inutsuka. The Godunov SPH can describe the Kelvin–Helmholtz instability even with a high-density contrast, while the standard SPH shows the absence of the instability across a density gradient. The interaction of a dense blob with a hot ambient medium has been performed also. The Godunov SPH describes the formation and evolution of the fingers due to the combinations of Rayleigh–Taylor, Richtmyer–Meshkov and Kelvin–Helmholtz instabilities. The blob test result coincides well with the results of the grid-based codes.
An inaccurate handling of a density gradient in the standard SPH has been pointed out as the direct reason of the absence of the instabilities. An unphysical force happens at the density gradient even in a pressure equilibrium, and repulses particles from the initial density discontinuity. Therefore, the initial perturbation damps, and a gap form at the discontinuity. The unphysical force has been studied in terms of the consistency of a numerical scheme. Contrary to the standard SPH, the momentum equation of the Godunov SPH does not use the particle approximation, and has been derived from the kernel convolution or a new Lagrangian function. The new Lagrangian function used in the Godunov SPH is more analogous to the real Lagrangian function for continuum. The momentum equation of the Godunov SPH has much better linear consistency, so the unphysical force is greatly reduced compared to the standard SPH in a high density contrast
A three-dimensional linear analysis of steady ship motion in deep water
No full textThis thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.The investigation of steady ship motion in calm water is a classic problem in ship hydrodynamics, where ship waves and wave
resistance are subjects of unquestionable importance. Despite considerable efforts in the past a satisfactory solution of the
steady ship motion problem has not been achieved so far. The application of three-dimensional potential flow theory results in
an essentially nonlinear problem formulation due to the unknown position of the disturbed free surface. In this thesis consistent
linearisation schemes are discarded in favour of the inconsistent Neumann-Kelvin theory. This approximation implies that nonlinear free surface effects are neglected entirely, but the three-dimensional features of the fluid flow and hull geometry are otherwise fully retained. The Kelvin wave source potential, otherwise known as the
wave resistance Green's function, is analysed in great detail. Solutions to the disturbance potential of the steady perturbed ship flow are obtained by means of a Kelvin wave source distribution method. The exact source strength is the solution of a Fredholm integral-equation of the second kind. An explicit source strength
approximation, valid for sufficiently slender ships operating at fairly low speeds, is investigated. Particular emphasis is placed on computational aspects. Highly accurate and efficient methods for the evaluation of the Kelvin wave source potential are proposed. The developed theory is applied to five different ship forms, viz.
a submerged prolate spheroid, Wigley's parabolic ship, a tanker, a fast destroyer and a cruiser. Over a wide range of ship speeds experimental data are compared with theoretical predictions of the steady flow parameters such as wave resistance, wave profiles, pressure signatures and lift force distributions
Kelvin Multicellular Electrostatic Voltmeter
No full textThis direct reading 130-volt Kelvin multicellular electrostatic voltmeter is typical of one of the many different types of electrostatic voltmeters used in the first quarter of the 20th century prior to the development of electronic instruments.42 x 20 x 21 c
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