5,278 research outputs found
Photonic quasi-crystal LEDs: design, modelling, and optimisation
In this paper we investigate improvement in performance attainable by etching Photonic Crystals and Photonic Quasi-Crystals into the top emitting surface of LEDs. We describe the physical mechanisms of extraction enhancement through ordered surface patterning and investigate benefits in terms of total extraction enhancement, beam directionality, and far field beam quality. Factors such as lattice geometry, etch depth, and epitaxy thickness are investigated. We show that a great variety of far field beam profiles of benefit in applications such as projection TV light engines and direct flat panel display illumination can be obtained simply by adjusting geometric design parameters. Our results show that PCs can provide significant improvement in extraction enhancement for applications requiring non Lambertian beam shapes when etched into standard "production line" epitaxy wafers in comparison to "state of the art" surface roughened thin-GaN LED devices. We investigate PC beam steering effects in these devices confirming that PCs do in fact re-direct light from trapped modes confined within the epi-structure to radiating modes. We also show that by tailoring the thickness of the epi-structure to complement the properties of the photonic crystal, extraction enhancement can be improved by a factor of 9 for some applications
Xenoliths in the CM2 Carbonaceous Chondrite Ion 94101: Implications for Complex Mixing on the Asteroidal Parent Body
The political economy of Southern Rhodesia: 1883- 1923
A history seminar paper on the political economy of the then Southern Rhodesia during the period 1898 to 1923.The role of the settlers has usually been overlooked or underestimated.
The granting of the franchise to qualified persons in 1898 was in fact the outcome of a series of demands, public meetings, and representations to Rhodes, requesting the vote. Such demands had been ignored before 1896. The circumstances after the risings of 1896, in the face of the possible revocation of the Charter, caused Rhodes to propose settler representation on the Legislative Council to the Colonial Office, whose assent can be taken as recognition of the check this would provide on the Company's government, (l) The increases in the number of elective seats in the Council in 1902, 1907, and 1912 were similarly the outcome of popular demand, rather than gratuitous concessions by the authorities. In the elections of 1920, the success of the candidates supporting responsible government led to the referendum of 1922, and the earlier termination of Company rule than might otherwise have been expected at the end of its ten year period in 1924 or even later.
These political demands and achievements, cannot, however, be seen in a purely political light, and can only be understood in terms of the economic situation in the country
Frequency stability of a self-phase-locked degenerate continuous-wave optical parametric oscillator
The properties of a self-phase-locked by-2-divider optical parametric oscillator are presented. A locking range of up to 156 MHz is measured, and the divider's relative frequency stability is shown to be better than 6/spl times/10/sup -14/
On-chip high-speed sorting of micron-sized particles for high-throughput analysis
A new design of particle sorting chip is presented. The device employs a dielectrophoretic gate that deflects particles into one of two microfluidic channels at high speed. The device operates by focussing particles into the central streamline of the main flow channel using dielectrophoretic focussing. At the sorting junction (T- or Y-junction) two sets of electrodes produce a small dielectrophoretic force that pushes the particle into one or other of the outlet channels, where they are carried under the pressure-driven fluid flow to the outlet. For a 40mm wide and high channel, it is shown that 6micron diameter particles can be deflected at a rate of 300particles/s. The principle of a fully automated sorting device is demonstrated by separating fluorescent from non-fluorescent latex beads
Renormalization group and 1/N expansion for 3-dimensional Ginzburg-Landau-Wilson models
A renormalization-group scheme is developed for the 3-dimensional
O()-symmetric Ginzburg-Landau-Wilson model, which is consistent with the
use of a 1/N expansion as a systematic method of approximation. It is motivated
by an application to the critical properties of superconductors, reported in a
separate paper. Within this scheme, the infrared stable fixed point controlling
critical behaviour appears at , where is the inverse of
the quartic coupling constant, and an efficient renormalization procedure
consists in the minimal subtraction of ultraviolet divergences at . This
scheme is implemented at next-to-leading order, and the standard results for
critical exponents calculated by other means are recovered. An apparently novel
result of this non-perturbative method of approximation is that corrections to
scaling (or confluent singularities) do not, as in perturbative analyses,
appear as simple power series in the variable . At least in
three dimensions, the power series are modified by powers of .Comment: 20 pages; 5 figure
Coulomb gap in one-dimensional disordered electronic systems
We study a one-dimensional system of spinless electrons in the presence of a
long-range Coulomb interaction (LRCI) and a random chemical potential at each
site. We first present a Tomonaga-Luttinger liquid (TLL) description of the
system. We use the bosonization technique followed by the replica trick to
average over the quenched randomness. An expression for the localization length
of the system is then obtained using the renormalization group method and also
a physical argument. We then find the density of states for different values of
the energy; we get different expressions depending on whether the energy is
larger than or smaller than the inverse of the localization length. We work in
the limit of weak disorder where the localization length is very large; at that
length scale, the LRCI has the effect of reducing the interaction parameter K
of the TLL to a value much smaller than the noninteracting value of unity.Comment: Revtex, 6 pages, no figures; discussions have been expanded in
several place
Modeling tidal current around Mokpo, the South Western coastal zone of Korea
This study provide modeling of tidal circulation around the Mokpo coastal zone (MC) using unstructured triangular horizontal grid by which high resolution is concentrated in the local region that reaches to 100 m. For this simulation, the 3D finite-volume ocean model FVCOM is applied for the numerical simulation. Only the astronomical tidal constituent M2 and its harmonic M4 are considered. By expanding open boundary to the shelf break of the East China Sea, only M2 elevation was specified on the open boundaries, and the generation of M4 tide around MC was observed, which is the representative criteria for the accuracy of the shallow water tide simulation. Around the intertidal zone of MC, wet/dry point treatment method incorporated in FVCOM was also used and tested its applicability in the level of resolution of this model
Motion and gravitational radiation of a binary system consisting of an oscillating and rotating coplanar dusty disk and a point-like object
A binary system composed of an oscillating and rotating coplanar dusty disk
and a point mass is considered. The conservative dynamics is treated on the
Newtonian level. The effects of gravitational radiation reaction and wave
emission are studied to leading quadrupole order. The related waveforms are
given. The dynamical evolution of the system is determined semi-analytically
exploiting the Hamiltonian equations of motion which comprise the effects both
of the Newtonian tidal interaction and the radiation reaction on the motion of
the binary system in elliptic orbits. Tidal resonance effects between orbital
and oscillatory motions are considered in the presence of radiation damping.Comment: 26 pages, 8 figure
Dynamics of Gravitating Magnetic Monopoles
According to previous work on magnetic monopoles, static regular solutions
are nonexistent if the vacuum expectation value of the Higgs field is
larger than a critical value , which is of the order of the
Planck mass. In order to understand the properties of monopoles for
, we investigate their dynamics numerically. If is
large enough (), a monopole expands exponentially and a
wormhole structure appears around it, regardless of coupling constants and
initial configuration. If is around , there are three
types of solutions, depending on coupling constants and initial configuration:
a monopole either expands as stated above, collapses into a black hole, or
comes to take a stable configuration.Comment: 11 pages, revtex, postscript figures; results for various initial
conditions are added; to appear in Phys. Rev.
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