1,730 research outputs found
The Deelen infrasound array for recording sonic booms and events of CTBT interest
The Seismology Division of the Royal Netherlands Meteorological Institute (KNMI) has build up expertise in infrasound measurements by investigating low frequency events in order to distinguish between seismic and sonic events. KNMI operates, amongst others, a sixteen element microbarometer array with an aperture of 1.5 km, the Deelen Infrasound Array (DIA). Sonic booms and events of Comprehensive Test Ban Treaty (CTBT) interest are recorded within the frequency range of 100 seconds and 40 Hertz. Recently, KNMI and Microflown Technologies B.V. started a collaboration concerning infrasound measurements. This paper reports the use of a novel sensor. The so-called Microflown [1] is an acoustic sensor, sensitive for frequencies from 0Hz up to 1kHz. The Microflown is developed at the University of Twente and commercialised by Microflown Technologies B.V [3]
Three-dimensional sound intensity measurements using microflown particle velocity sensors
This paper reports on a novel method to measure three-dimensional sound intensity and the fabrication of a miniature three-dimensional sound intensity probe. Verifying measurements where performed with three separate micromachined particle velocity probes and one pressure microphone. A three-dimensional sound intensity probe has been realised based on a three-dimensional micromachined particle velocity microphone, a 3D Microflown, and a miniature pressure microphon
A novel technique for measuring the reflection coefficient of sound absorbing materials
A new method to measure the acoustic behaviour of sound absorbing material in an impedance tube is presented. The method makes use of a novel particle velocity sensor, the microflown, and a microphone. The so-called p·u method is compared to three other methods of which the two microphone technique is well known. It is shown that the combination of a microphone and a microflown provides direct information on the acoustic impedance, the sound intensity and the sound energy density. The experimental results are compared to the results obtained with the conventional impedance tube measurements. To be able to repeat the measurements in a reliable way a well described test sample with a quarter-wave resonator is used. Furthermore it is shown that the viscothermal effects on the wave propagation are important, i.e. for the quarter-wave resonator and to a lesser extent for the impedance tube itself
Geometric and compositional influences on spin-orbit induced circulating currents in nanostructures
Circulating orbital currents, originating from the spin-orbit interaction,
are calculated for semiconductor nanostructures in the shape of spheres, disks,
spherical shells and rings for the electron ground state with spin oriented
along a symmetry axis. The currents and resulting orbital and spin magnetic
moments, which combine to yield the effective electron g factor, are calculated
using a recently introduced formalism that allows the relative contributions of
different regions of the nanostructure to be identified. For all these
spherically or cylindrically symmetric hollow or solid nanostructures,
independent of material composition and whether the boundary conditions are
hard or soft, the dominant orbital current originates from intermixing of
valence band states in the electron ground state, circulates within the
nanostructure, and peaks approximately halfway between the center and edge of
the nanostructure in the plane perpendicular to the spin orientation. For a
specific material composition and confinement character, the confinement energy
and orbital moment are determined by a single size-dependent parameter for
spherically symmetrical nanostructures, whereas they can be independently tuned
for cylindrically symmetric nanostructures.Comment: 22 pages, 20 figure
Spin-orbit-induced circulating currents in a semiconductor nanostructure
Circulating orbital currents produced by the spin-orbit interaction for a
single electron spin in a quantum dot are explicitly evaluated at zero magnetic
field, along with their effect on the total magnetic moment (spin and orbital)
of the electron spin. The currents are dominated by coherent superpositions of
the conduction and valence envelope functions of the electronic state, are
smoothly varying within the quantum dot, and are peaked roughly halfway between
the dot center and edge. Thus the spatial structure of the spin contribution to
the magnetic moment (which is peaked at the dot center) differs greatly from
the spatial structure of the orbital contribution. Even when the spin and
orbital magnetic moments cancel (for ) the spin can interact strongly with
local magnetic fields, e.g. from other spins, which has implications for spin
lifetimes and spin manipulation.Comment: 6 pages, 3 figure
g-Factors and diamagnetic coefficients of electrons, holes and excitons in InAs/InP quantum dots
The electron, hole, and exciton g-factors and diamagnetic coefficients have
been calculated using envelope-function theory for cylindrical InAs/InP quantum
dots in the presence of a magnetic field parallel to the dot symmetry axis. A
clear connection is established between the electron g-factor and the amplitude
of the those valence-state envelope functions which possess non-zero orbital
momentum associated with the envelope function. The dependence of the exciton
diamagnetic coefficients on the quantum dot height is found to correlate with
the energy dependence of the effective mass. Calculated exciton g-factor and
diamagnetic coefficients, constructed from the values associated with the
electron and hole constituents of the exciton, match experimental data well,
however including the Coulomb interaction between the electron and hole states
improves the agreement. Remote-band contributions to the valence-band
electronic structure, included perturbatively, reduce the agreement between
theory and experiment.Comment: 12 pages, 7 figure
A Three Dimensional Microflown
An integrated three dimensional acoustic particle velocity sensor is realized. The integration of multiple sensors on a single silicon die leads to improvements in terms of better a better reproducible sensor and a very small sensor to sensor distance allowing accurate single point measurements. Initial measurements performed show that three dimensional noise source finding is possible with this sensor
Students’ self-regulation and achievement in basic reading and math skills:The role of student–teacher relationships in middle childhood
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