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Register a new userContinuum approach based on radiation distribution function for radiative heat transfer in densely packed particulate system
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The study of radiative heat transfer in particulate system is usually based on radiative transfer equation (RTE) with effective radiative properties. However, for non-random, densely and regularly packed particulate systems, the applicability of RTE is questionable due to dependent scattering and weak randomness of particle arrangement. In this paper, a new continuum approach that does not explicitly rely on the RTE is proposed for radiative heat transfer in the densely packed particulate system. The new approach is based on the generalization of the concept of radiation distribution factor (RD) at discrete scale (or particle scale) to radiation distribution function (RDF) at continuum scale. The derived governing equation is in integral form, with RDF as the continuum scale physical parameter that characterize the radiative transfer properties of the system. The characteristics of the RDF for different particulate system (randomly or regularly packed) are studied. The RDF in regularly distributed particulate system is shown to be anisotropic. The continuum approach is verified by using heat transfer simulation at the particle scale, and demonstrated to have excellent performance in predicting the temperature distribution in dense particulate system. This work provides an alternative continuum theory, which will help the analysis and understanding of radiative heat transfer in densely packed media.
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Near-field radiative heat transfer (NFRHT) between rough surfaces, due to its widespread presence in engineering practice of near-field energy utilization, requires indepth studies, especially from the perspective of physical mechanism. In this paper, an effective multilayer model is built to approach the NFRHT between random rough surfaces of silicon carbide (SiC). Using the effective medium theory (EMT), the effective dielectric function of each layer is obtained, which forms a gradient distribution of dielectric function along the depth of the medium. The influence of the effective dielectric function on surface phonon polaritons (SPhPs) is analyzed, showing that the effective layers with small filling fraction of SiC feature lower SPhP resonance frequencies than SiC bulk. The coupling of SPhPs from the gradient distribution of dielectric function produces new surface modes that dominates the NFRHT. Investigation on the effect of root mean square height (RMS height, {sigma}) reveals that the peaks of local density of states (LDOS) and spectral heat flux are red-shifted as {sigma} increases, while the spectral heat flux below the peak frequency gets larger. This can be attributed to the coupling of SPhPs inside the rough layer. We also found the total net heat flux between rough surfaces separated by an average distance exceeds that between smooth plates and increases with increasing {sigma}, which offer a new way to enhance NFRHT. This work provides a reference for the simulation and understanding of the NFRHT between rough surfaces.
Micro-nanoparticle systems have wide applications in thermal science and technology. In dense particulate system, the particle separation distance may be less than the characteristic thermal wavelength and near field effect will be significant and become a key factor to influence thermal radiation transfer in the system. In this study, radiative heat transfer (RHT) between two metallic nanoparticles clusters are explored using many-body radiative heat transfer theory implemented with the coupled electric and magnetic dipole (CEMD) approach, which effectively takes into account the contribution of magnetic polarization of metallic nanoparticles on heat exchange. As the focus, the effects of magnetic polarization and many-body interaction (MBI) on RHT were analyzed. The effects of fractal dimension and relative orientation of the clusters were also analyzed. Results show that the contribution of magnetically polarized eddy-current Joule dissipation dominates the RHT between Ag nanoparticle clusters. If only electric polarization (EP approach) is considered, the heat conductance will be underestimated as compared with the CEMD approach in both near field and far field regime. The effect of MBI on the RHT between Ag nanoparticle clusters is unobvious at room temperature, which is quite different from the SiC nanoparticle clusters. For the latter, MBI tends to suppress RHT significantly. The relative orientation has remarkable effect on radiative heat flux for clusters with lacy structure when the separation distance is in the near field. While for the separation distance in far field, both the relative orientation and the fractal dimension has a weak influence on radiative heat flux. This work will help the understanding of thermal transport in dense particulate system.
We explore in the present work the near-field radiative heat transfer between two semi-infinite parallel nonlocal dielectric planes by means of fluctuational electrodynamics. We use atheory for the nonlocal dielectric permittivityfunction proposed byHalevi and Fuchs. This theory has the advantage to includedifferent models performed in the literature. According to this theory, the nonlocal dielectric function is described by a Lorenz-Drude like single oscillator model, in which the spatial dispersion effects are represented by an additional term depending on the square of the total wavevector k. The theory takes into account the scattering of the electromagneticexcitation at the surface of the dielectric material, which leads to the need of additional boundary conditions in order to solve Maxwells equations and treat the electromagnetic transmission problem. The additional boundary conditions appear as additional surface scattering parameters in the expressions of the surface impedances. It is shown that the nonlocal modeling deviates from the classical $1/d^2$ law in the nanometerrangeat distances still larger than the ones where quantum effects are expected to come into play.
Man-made scenes can be densely packed, containing numerous objects, often identical, positioned in close proximity. We show that precise object detection in such scenes remains a challenging frontier even for state-of-the-art object detectors. We propose a novel, deep-learning based method for precise object detection, designed for such challenging settings. Our contributions include: (1) A layer for estimating the Jaccard index as a detection quality score; (2) a novel EM merging unit, which uses our quality scores to resolve detection overlap ambiguities; finally, (3) an extensive, annotated data set, SKU-110K, representing packed retail environments, released for training and testing under such extreme settings. Detection tests on SKU-110K and counting tests on the CARPK and PUCPR+ show our method to outperform existing state-of-the-art with substantial margins. The code and data will be made available on url{www.github.com/eg4000/SKU110K_CVPR19}.
We demonstrate a 12 quantum dot device fabricated on an undoped Si/SiGe heterostructure as a proof-of-concept for a scalable, linear gate architecture for semiconductor quantum dots. The device consists of 9 quantum dots in a linear array and 3 single quantum dot charge sensors. We show reproducible single quantum dot charging and orbital energies, with standard deviations less than 20% relative to the mean across the 9 dot array. The single quantum dot charge sensors have a charge sensitivity of 8.2 x 10^{-4} e/root(Hz) and allow the investigation of real-time charge dynamics. As a demonstration of the versatility of this device, we use single-shot readout to measure a spin relaxation time T1 = 170 ms at a magnetic field B = 1 T. By reconfiguring the device, we form two capacitively coupled double quantum dots and extract a mutual charging energy of 200 microeV, which indicates that 50 GHz two-qubit gate operation speeds are feasible.
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