429 research outputs found
Sustainability Survey: Promoting Solutions to Real-World Problems
No full textThe concept of sustainable development, defined by the 1987 Brundtland Report [...
Dynamics of artificial spin ice: a continuous honeycomb network
No full textWe model the dynamics of magnetization in an artificial analogue of spin ice specializing to the case of a honeycomb network of connected magnetic nanowires. The inherently dissipative dynamics is mediated by the emission and absorption of domain walls in the sites of the lattice, and their propagation in its links. These domain walls carry two natural units of magnetic charge, whereas sites of the lattice contain a unit magnetic charge. Magnetostatic Coulomb forces between these charges play a major role in the physics of the system, as does quenched disorder caused by imperfections of the lattice. We identify and describe different regimes of magnetization reversal in an applied magnetic field determined by the orientation of the applied field with respect to the initial magnetization. One of the regimes is characterized by magnetic avalanches with a 1/n distribution of lengths.Johns Hopkins University (Provost Undergraduate Research Award)National Science Foundation (U.S.) (grant DMR-0520491)National Science Foundation (U.S.) (grant DMR-1056974)National Science Foundation (U.S.) (grant DMR-1104753
Transverse-electric Brewster effect enabled by nonmagnetic two-dimensional materials
No full textDiscovered in the 19th century, the Brewster effect is known to occur for transverse-magnetic waves in regular optical dielectrics; however, it is believed to arise for transverse-electric (TE) waves only in systems with magnetic responses, i.e., nonunity effective relative permeability. This paper introduces a scheme to realize the TE Brewster effect in a homogeneous dielectric interface without magnetic responses, by adding ultrathin two-dimensional (2D) materials such as graphene. In particular, the effect remains even for waves approaching normal incidence, spanning from terahertz to visible frequencies. In contrast to the conventional Brewster effect, the graphene-assisted TE Brewster effect is asymmetric, and can be achieved only when the incidence is from the higher-refractive-index side. Moreover, graphene layers can tailor a total-internal-reflection dielectric interface into zero reflection, accompanied by perfect absorption. This control over TE waves enabled by ultrathin 2D materials may lead to a variety of applications, such as atomically thin absorbers, polarizers, and antireflection coating.Massachusetts Institute of Technology. Institute for Soldier Nanotechnologies (W911NF-13-D-0001)Solid-State Solar-Thermal Energy Conversion Center (DESC0001299
What Is an Author's Role in the AI Era? Demystifying the Black Box of Human-AI Collaborative Creation Through an "Aesthetic Judgment" Study of the novel Solid Reference Frame Manuscript
No full textThis project repository establishes a permanent timestamp for a study that rethinks Roland Barthes' proclamation of the "death of the author" for the AI era. It engages with Michel Foucault's concept of "author-function" to propose "Aesthetic Judgment" as a new theoretical framework for human-AI collaborative creation. This framework reconceptualizes AI as a "critical partner"—a source of provocation and challenge. The human author, in turn, exercises decisive curatorial power through four key operations: 1) The Right to Question, 2) The Right to Select, 3) The Right to Arbitrate, and 4) The Right to Integrate.
Employing a "Process-Tracing" methodology, the research analyzes the complete manuscript of the novel Solid Reference Frame to demystify the creative "black box." This empirical study aims to demonstrate how the human author's role is transformed from a solitary genius into a systemic architect of meaning, thereby asserting a new, viable author-function for the digital age
Structural Colors from Fano Resonances
No full textStructural coloration is an interference phenomenon where colors emerge when visible light interacts with nanoscopically structured material and has recently become a most interesting scientific and engineering topic. However, current structural color generation mechanisms either require thick (compared to the wavelength) structures or lack dynamic tunability. This report proposes a new structural color generation mechanism that produces colors by the Fano resonance effect on thin photonic crystal slab. We experimentally realize the proposed idea by fabricating the samples that show resonance-induced colors with weak dependence on the viewing angle. Finally, we show that the resonance-induced colors can be dynamically tuned by stretching the photonic crystal slab fabricated on an elastic substrate.United States. Army Research Office (W911NF-13-D-0001)Solid-State Solar-Thermal Energy Conversion Center (DE-SC0001299
Broadband angular selectivity of light at the nanoscale: Progress, applications, and outlook
No full textHumankind has long endeavored to control the propagation direction of light. Since time immemorial, shades, lenses, and mirrors have been used to control the flow of light. In modern society, with the rapid development of nanotechnology, the control of light is moving toward devices at micrometer and even nanometer scales. At such scales, traditional devices based on geometrical optics reach their fundamental diffraction limits and cease to work. Nano-photonics, on the other hand, has attracted wide attention from researchers, especially in the last decade, due to its ability to manipulate light at the nanoscale. This review focuses on the nano-photonics systems that aim to select light based on its propagation direction. In the first half of this review, we survey the literature and the current state of the art focused on enabling optical broadband angular selectivity. The mechanisms we review can be classified into three main categories: (i) microscale geometrical optics, (ii) multilayer birefringent materials, and (iii) Brewster modes in plasmonic systems, photonic crystals, and metamaterials. In the second half, we present two categories of potential applications for broadband angularly selective systems. The first category aims at enhancing the efficiency of solar energy harvesting, through photovoltaic process or solar thermal process. The second category aims at enhancing light extracting efficiency and detection sensitivity. Finally, we discuss the most prominent challenges in broadband angular selectivity and some prospects on how to solve these challenges.United States. Army Research Office (W911NF-13-D0001)United States. Department of Energy (DE-SC0001299
Direct imaging of isofrequency contours in photonic structures
No full textThe isofrequency contours of a photonic crystal are important for predicting and understanding exotic optical phenomena that are not apparent from high-symmetry band structure visualizations. We demonstrate a method to directly visualize the isofrequency contours of high-quality photonic crystal slabs that show quantitatively good agreement with numerical results throughout the visible spectrum. Our technique relies on resonance-enhanced photon scattering from generic fabrication disorder and surface roughness, so it can be applied to general photonic and plasmonic crystals or even quasi-crystals. We also present an analytical model of the scattering process, which explains the observation of isofrequency contours in our technique. Furthermore, the isofrequency contours provide information about the characteristics of the disorder and therefore serve as a feedback tool to improve fabrication processes.Massachusetts Institute of Technology. Institute for Soldier Nanotechnologies (W911NF-13-D-0001)Solid-State Solar-Thermal Energy Conversion Center (DE-SC0001299)National Science Foundation (U.S.) (DMR-1307632
Metamaterial broadband angular selectivity
No full textWe demonstrate how broadband angular selectivity can be achieved with stacks of one-dimensionally periodic photonic crystals, each consisting of alternating isotropic layers and effective anisotropic layers, where each effective anisotropic layer is constructed from a multilayered metamaterial. We show that by simply changing the structure of the metamaterials, the selective angle can be tuned to a broad range of angles; and, by increasing the number of stacks, the angular transmission window can be made as narrow as desired. As a proof of principle, we realize the idea experimentally in the microwave regime. The angular selectivity and tunability we report here can have various applications such as in directional control of electromagnetic emitters and detectors.Massachusetts Institute of Technology. Institute for Soldier Nanotechnologies (Contract W911NF-13-D0001
Efficient plasmonic emission by the quantum Čerenkov effect from hot carriers in graphene
No full textGraphene plasmons have been found to be an exciting plasmonic platform, thanks to their high field confinement and low phase velocity, motivating contemporary research to revisit established concepts in light–matter interaction. In a conceptual breakthrough over 80 years old, Čerenkov showed how charged particles emit shockwaves of light when moving faster than the phase velocity of light in a medium. To modern eyes, the Čerenkov effect offers a direct and ultrafast energy conversion scheme from charge particles to photons. The requirement for relativistic particles, however, makes Čerenkov emission inaccessible to most nanoscale electronic and photonic devices. Here we show that graphene plasmons provide the means to overcome this limitation through their low phase velocity and high field confinement. The interaction between the charge carriers flowing inside graphene and the plasmons enables a highly efficient two-dimensional Čerenkov emission, giving a versatile, tunable and ultrafast conversion mechanism from electrical signal to plasmonic excitation.United States. Army Research Office. Institute for Soldier Nanotechnologies (contract number W911NF-13-D-0001)QuantiXLie (Group)Singapore. Agency for Science, Technology and Research (A*STAR) (SERC; grant number 1426500054)National Science Foundation (U.S.). Materials Research Science and Engineering Centers (Program) (Award Number DM-1419807)Seventh Framework Programme (European Commission) ( European Research Council (FP7–Marie Curie IOF) grant agreement number 328853—MC–BSiCS
Interest Rate Pass-through and Capital Market Development: An Empirical Analysis
No full textInterest rate pass-through, defined as the speed and size that policy rates transmitted to bank trail rates, serves as a bridge between policymakers and real sectors in the economy. The strength of the pass-through determines the effectiveness of monetary policy. Many factors could increase the degree of interest rate pass-though. This paper is a cross-sectional study that uses 24 countries from different regions to examine whether capital market development is such a factor. The results show that the depth and efficiency of stock markets positively impact on the size and completeness of the pass-through from money market rates and bank retail rates. For countries with small and medium size of stock market, increasing the capitalization of stock market will significantly strengthen the interest rate pass-though
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