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51.
Z. Gong Y. F. Zhang P. Kelm I. M. Watson E. Gu M. D. Dawson 《Applied Physics A: Materials Science & Processing》2011,103(2):389-393
We present the fabrication details and performance characteristics of InGaN light-emitting diodes (LEDs) consisting of arrays
of interconnected micro-pixels where each micro-pixel is nano-textured via nano-imprinting. We have taken the further step
of embodying the pixels in a rhomboidal geometry. It is found that the power output of these nano-textured micro-LEDs with
rhomboidal geometries is 57% higher than that of conventional square-shaped broad-area reference LEDs. The series resistance
of the textured LEDs is reduced, owing to the multi-finger electrodes introduced. Furthermore, these LEDs can sustain higher
operation current of up to 500 mA without encapsulation, suggesting improved thermal dissipation capability. Finally, the
combined effects of surface texturing, micro-LED configuration, and geometric shaping on the light extraction are analyzed.
It is found that the power enhancement by surface texturing, micro-pixellating and the rhomboidal geometry are 32%, 16%, and
9%, respectively, implying that surface texturing is the most effective contribution to increasing the light extraction efficiency
in our design. The angular dependent far-field beam profile is also remarkably changed, compared with the standard Lambertian
emission pattern of the conventional square-shaped LEDs. Substantial increase in the EL intensity is evident from both the
top surface and the sidewall. 相似文献
52.
Hydrogen is detected using a Pd/n-InP Schottky diode in which the elongated, very thin Pd electrode is of greater resistance than the underlying semiconductor substrate. Four-probe measurements of the device resistance, as a function of hydrogen concentration, are made by contacting only the Pd electrode, with a sensitivity of 1 ppm being achieved. On hydrogen exposure the device resistance drops from an initial high value, characteristic of the Pd electrode alone, to a lower value due to a hydrogen-induced lowering of the Schottky barrier that opens up the InP substrate as a parallel current carrying channel. 相似文献
53.
k-core percolation is an extension of the concept of classical percolation and is particularly relevant to understanding the resilience of complex networks under random damage. A new analytical formalism has been recently proposed to deal with heterogeneous k-cores, where each vertex is assigned a local threshold k(i). In this Letter we identify a binary mixture of heterogeneous k-cores which exhibits a tricritical point. We investigate the new scaling scenario and calculate the relevant critical exponents, by analytical and computational methods, for Erd?s-Rényi networks and 2D square lattices. 相似文献
54.
55.
56.
Bo Li Patrick Coles Jeffrey A. Reimer Philip Dawson Carlos A. Meriles 《Solid State Communications》2010,150(9-10):450-453
We report the use of time-resolved Faraday rotation to induce and probe the polarization of nuclear spins within a set of quantum wells with varying background electron density. The electron density was controlled over a broad range by making use of structures of mixed type-I/type-II GaAs/AlAs quantum wells that spatially separate photoexcited electron–hole pairs. We find that the optically detected nuclear magnetic field decreases quasi-monotonically with increasing electron density. The likely factors responsible for this behavior are increased electron spin-lattice relaxation, increased electron spin delocalization, and dilution of the electron spin polarization. 相似文献
57.
We present an alternative to the perturbative (in coupling constant) diagrammatic approach for studying stochastic dynamics of a class of reaction diffusion systems. Our approach is based on an auxiliary field loop expansion for the path integral representation for the generating functional of the noise induced correlation functions of the fields describing these systems. The systems we consider include Langevin systems describable by the set of self interacting classical fields ?i(x,t) in the presence of external noise ηi(x,t), namely (∂t−ν∇2)?−F[?]=η, as well as chemical reaction annihilation processes obtained by applying the many-body approach of Doi–Peliti to the Master Equation formulation of these problems. We consider two different effective actions, one based on the Onsager–Machlup (OM) approach, and the other due to Janssen–deGenneris based on the Martin–Siggia–Rose (MSR) response function approach. For the simple models we consider, we determine an analytic expression for the Energy landscape (effective potential) in both formalisms and show how to obtain the more physical effective potential of the Onsager–Machlup approach from the MSR effective potential in leading order in the auxiliary field loop expansion. For the KPZ equation we find that our approximation, which is non-perturbative and obeys broken symmetry Ward identities, does not lead to the appearance of a fluctuation induced symmetry breakdown. This contradicts the results of earlier studies. 相似文献
58.
This paper presents a reconstruction of the three-dimensional velocity field of a turbulent vortex ring by means of Taylor’s
hypothesis. Stereoscopic PIV is used to acquire three velocity component information on a plane. The accuracy of the Taylor’s
hypothesis for this particular flow pattern is first discussed, and the three-dimensional velocity and vorticity information
are then presented. This study also introduces an azimuthally averaging method in order to give a mean structure in cylindrical
coordinates from a single realization and from which turbulent stresses and production can be estimated. The azimuthally averaged
quantities are then compared with the ensemble-averaged results from the previous planar (two-dimensional and stereoscopic)
PIV experiments. 相似文献
59.
A convergent numerical method for modeling in situ biorestoration of contaminated groundwater is outlined. This method treats systems of transport-biodegradation equations by operator splitting in time. Transport is approximated by a finite element modified method of characteristics. The biodegradation terms are split from the transport terms and treated as a system of ordinary differential equations. Numerical results for vertical cross-sectional flow are presented. The effects of variable hydraulic conductivity and variable linear adsorption are studied. 相似文献
60.
The uniaxial pressure dependence of the muonium hyperfine tensor was measured at 80 K. Uniaxial pressures (0 and 0.2 GPa)
were applied along the a‐axis of quartz, and the hyperfine tensor was measured by applying various transverse fields between
0 and 7 G. The structure appears to be the result of the three chemically equivalent sites in quartz. When pressure is applied
perpendicular to the crystallographic c‐axis of quartz, the symmetry of these sites is broken such that two chemically inequivalent
sites are observed. The resulting hyperfine structure is discussed and qualitative explanations are proposed.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献