158 research outputs found
Temperature control of thermal radiation from heterogeneous bodies
We demonstrate that recent advances in nanoscale thermal transport and
temperature manipulation can be brought to bear on the problem of tailoring
thermal radiation from compact emitters. We show that wavelength-scale
composite bodies involving complicated arrangements of phase-change
chalcogenide (GST) glasses and metals or semiconductors can exhibit large
emissivities and partial directivities at mid-infrared wavelengths, a
consequence of temperature localization within the GST. We consider multiple
object topologies, including spherical, cylindrical, and mushroom-like
composites, and show that partial directivity follows from a complicated
interplay between particle shape, material dispersion, and temperature
localization. Our calculations exploit a recently developed fluctuating-volume
current formulation of electromagnetic fluctuations that rigorously captures
radiation phenomena in structures with both temperature and dielectric
inhomogeneities.Comment: 17 pages, 7 figuer
Enhanced nonlinear frequency conversion and Purcell enhancement at exceptional points
We derive analytical formulas quantifying radiative emission from
subwavelength emitters embedded in triply resonant nonlinear
cavities supporting exceptional points (EP) made of dark and leaky modes. We
show that the up-converted radiation rate in such a system can be greatly
enhanced---by up to two orders of magnitude---compared to typical Purcell
factors achievable in non-degenerate cavities, for both monochromatic and
broadband emitters. We provide a proof-of-concept demonstration by studying an
inverse-designed 2D photonic-crystal slab that supports an EP formed out of a
Dirac cone at the emission frequency and a phase-matched, leaky-mode resonance
at the second harmonic frequency
Study on Variable Action Value Standard for Harbor Infrastructures
To meet with different levels of requirements from proprietors and users and to offer a basis for variable action value to the designers, associated with the standards, this dissertation studied the value standard of load effect and environmental effect. For load effect, on the foundation of analyzing variable load effect model, we used equal exceeding probability principle to calculate the load adjustment coefficient for the cargo loading in harbor and river port under different designing service life. For environmental effect, according to the ranks of marine chloride environment in standards GB/T 50476-2008, after analyzing and comparing the research achievements on surface chloride concentration at home and abroad, we obtained the value standard of chloride ion loading in different ranks of chloride environment
Edge Detection of Concrete Mesostructure Based on DIS Operator
Aggregate edge detection is the basis of creating concrete mesoscale model, which is applied to analyze concrete mesoscale characteristics. A concrete digital image edge detection method using DIS operator is presented in this paper. Mean filter, multi-scale filter, and Gaussian filter are compared on the effect of concrete image noise reduction. Based on the result, Gaussian filter is the most optimum method to reduce image noise and remain aggregate edge distinct. Sobel operator, Laplacian operator, and DIS operator are applied respectively to detect the aggregate edge on Gaussian filter processed images. Based on the experiment, DIS operator outperforms other two operators in the veracity and integrity of edge detection. It is concluded that using Gaussian filter and DIS operator for edge segmentation can provide geometrical models for FEM analysis
Giant frequency-selective near-field energy transfer in active--passive structures
We apply a fluctuation electrodynamics framework in combination with
semianalytical (dipolar) approximations to study amplified spontaneous energy
transfer (ASET) between active and passive bodies. We consider near-field
energy transfer between semi-infinite planar media and spherical structures
(dimers and lattices) subject to gain, and show that the combination of loss
compensation and near-field enhancement (achieved by the proximity, enhanced
interactions, and tuning of subwavelength resonances) in these structures can
result in orders of magnitude ASET enhancements below the lasing threshold. We
examine various possible geometric configurations, including realistic
materials, and describe optimal conditions for enhancing ASET, showing that the
latter depends sensitively on both geometry and gain, enabling efficient and
tunable gain-assisted energy extraction from structured surfaces
Hierarchical Life-Cycle Design of Concrete Structures
Concrete structures’ service life lasts decades. In order to deal with all the probable degradations and deteriorations in the whole life span, the concept of concrete structures’ Life-Cycle Design was introduced into China in the 1980s. However, until this day, Life-Cycle Design is still more of a concept to most structure designers and engineers, rather than a practical method. This paper provides a hierarchical method for concrete structures’ Life-Cycle Design, in which the design process is divided into five levels. Safety should be the fundamental requirements for all concrete structures, so as to guarantee a reliable quality. For structures located in severe environments, durability design is necessary so as to ensure the designed service life. Further, when specific economic requirements are set for concrete structures, life-cycle cost (LCC) should be considered carefully in selecting the optimal scheme. Besides, those concrete structures designed to be environmental-friendly should also take into account the specific environmental assessment criteria. Nowadays, user-friendly schemes have attracted increasing attention too; therefore, customers’ demands should also be fully involved in the design process. Considering all the design levels mentioned above, diverse designing criteria are provided accordingly. This paper also uses a road bridge member which exposed to chloride attack in marine environment as an example to illustrate this hierarchical design method. Using the life-cycle-based hierarchical design method, a probable scheme that is safe, durable, economic, environmental friendly, and user friendly is provided
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