5,268 research outputs found
Microstructure and superconducting properties of hot isostatically pressed MgB2
Bulk samples of MgB2 have been formed by hot isostatic pressing (HIPping) of
commercial powder at 100MPa and 950=B0C. The resulting material is 100% dense
with a sharp superconducting transition at 37.5K. Microstructural studies have
indicated the presence of small amounts of second phases within the material,
namely MgO and B rich compositions, probably MgB4. Magnetisation measurements
performed at 20K have revealed values of Jc=1.3 x 106A/cm2 at zero field, and
9.3 x 105A/cm2 at 1T. Magneto optical (MO) studies have shown direct evidence
for the superconducting homogeneity and strong intergranular current flow in
the material.Comment: 3 pages, 6 figures, text updated, new references included and
discussed. Submitted to Superconductor Science and Technolog
Transverse effects in multifrequency Raman generation
The theory of ultrabroadband multifrequency Raman generation is extended, for the first time, to allow for beam-propagation effects in one and two transverse dimensions. We show that a complex transverse structure develops even when diffraction is neglected. In the general case, we examine how the ultrabroadband multifrequency Raman generation process is affected by the intensity, phase quality, and width of the input beams, and by the length of the Raman medium. The evolution of power spectra, intensity profiles, and global characteristics of the multifrequency beams are investigated and explained. In the two-dimensional transverse case, bandwidths comparable to the optical carrier frequency, spanning the whole visible spectrum and beyond, are still achievable
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Dielectrophoretic Manipulation of Particles and Lymphocytes
This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.A particle manipulation and sorting device using the dielectrophoretic (DEP) force is described in this study. The device consists of “ladder-type”, “flip-type” and “oblique rail-type” electrode regions. The ladder-type and rail-type electrodes can generate a DEP force distribution that captures the particles, the DEP force of which is “negative” (repulsion force), in the area located at the center of the electrodes. The particles can then be guided individually along the electrode. In addition to this, the ladder-type electrode can align the particles with equal spacing in the streamwise direction. Using the “flip-type” electrode, which pushes the particles away, in combination with these electrodes, the direction of the particle can be selected with high accuracy, reliability and response. In the first half of this paper, numerical simulation was carried out to calculate the particle motion and evaluate the performance of the ladder-type electrode. Several models were validated to investigate the influences of the non-uniformity of the electric field and the electric interaction of the surface charges and polarizations. Measurement using the high-speed camera was then carried out to investigate the motions of the particles and sorting reliability. The trajectories and the probability density functions of the particles at the inlet and outlet of the electrode region showed that by using these electrodes the particles can be aligned, sorted and guided accurately
Classification of atomic environments via the Gromov-Wasserstein distance
Interpreting molecular dynamics simulations usually involves automated
classification of local atomic environments to identify regions of interest.
Existing approaches are generally limited to a small number of reference
structures and only include limited information about the local chemical
composition. This work proposes to use a variant of the Gromov-Wasserstein (GW)
distance to quantify the difference between a local atomic environment and a
set of arbitrary reference environments in a way that is sensitive to atomic
displacements, missing atoms, and differences in chemical composition. This
involves describing a local atomic environment as a finite metric measure
space, which has the additional advantages of not requiring the local
environment to be centered on an atom and of not making any assumptions about
the material class. Numerical examples illustrate the efficacy and versatility
of the algorithm
Dispersive Gap Mode of Phonons in Anisotropic Superconductors
We estimate the effect of the superconducting gap anisotropy in the
dispersive gap mode of phonons, which is observed by the neutron scattering on
borocarbide superconductors. We numerically analyze the phonon spectrum
considering the electron-phonon coupling, and examine contributions coming from
the gap suppression and the sign change of the pairing function on the Fermi
surface. When the sign of the pairing function is changed by the nesting
translation, the gap mode does not appear. We also discuss the suppression of
the phonon softening of the Kohn anomaly due to the onset of superconductivity.
We demonstrate that observation of the gap dispersive mode is useful for
sorting out the underlying superconducting pairing function.Comment: 7 pages, 12 figures, to be published in J. Phys. Soc. Jp
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