Modern information technology paradigms, such as online services and off-the-shelf products, often involve a wide variety of users with different or even conflicting objectives. Every software output may satisfy some users, but may also fail to satisfy others. Furthermore, users often do not know the internal working mechanisms of the systems. This situation is quite different from bespoke software, where developers and users usually know each other. This paper proposes an approach to help users to better understand the software that they use, and thereby more easily achieve their objectives-even when they do not fully understand how the system is implemented. Our approach borrows the concept of metamorphic relations from the field of metamorphic testing (MT), using it in an innovative way that extends beyond MT. We also propose a "symmetry" metamorphic relation pattern and a "change direction" metamorphic relation input pattern that can be used to derive multiple concrete metamorphic relations. Empirical studies reveal previously unknown failures in some of the most popular applications in the world, and show how our approach can help users to better understand and better use the systems. The empirical results provide strong evidence of the simplicity, applicability, and effectiveness of our methodology.
We develop the theory of all-dielectric absorbers based on temporal coupled mode theory (TCMT), with parameters extracted from eigenfrequency simulations. An infinite square array of cylindrical resonators embedded in air is investigated, and we find that it supports two eigenmodes of opposite symmetry that are each responsible for half of the total absorption. The even and odd eigenmodes are found to be the hybrid electric (EH) and hybrid magnetic (HE) waveguide modes of a dielectric wire of circular cross section, respectively. The geometry of the cylindrical array is shown to be useful for individual tuning of the radiative loss rates of the eigenmodes, thus permitting frequency degeneracy. Further, by specifying the resonators' loss tangent, the material loss rate can be made to equal the radiative loss rate, thus achieving a state of degenerate critical coupling and perfect absorption. Our results are supported by S-parameter simulations, and agree well with waveguide theory.
While conventional photodetectors can only measure light intensity, the vectorial light field contains much richer information, including polarization and spectrum, that are essential for numerous applications ranging from imaging to telecommunication. However, the simultaneous measurement of multi-dimensional light field information typically requires the multiplexing of dispersive or polarization-selective elements, leading to excessive system complexity. Here, we demonstrate a near-infrared spectropolarimeter based on an electrically-tunable liquid crystal metasurface. The tunable metasurface, which acts as an encoder of the vectorial light field, is tailored to support high-quality-factor guided-mode resonances with diverse and anisotropic spectral features, thus allowing the full Stokes parameters and the spectrum of the incident light to be computationally reconstructed with high fidelity. The concept of using a tunable metasurface for multi-dimensional light field encoding may open up new horizons for developing vectorial light field sensors with minimized size, weight, cost, and complexity.
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