1,721,056 research outputs found
Topological vertex for 6d SCFTs with -twist
Get PDFWe compute the partition function for 6d gauge
theories compactified on a circle with outer automorphism twist.
We perform the computation based on 5-brane webs with two O5-planes using
topological vertex with two O5-planes. As representative examples, we consider
6d and gauge theories with twist. We confirm
that these partition functions obtained from the topological vertex with
O5-planes indeed agree with the elliptic genus computations.Comment: v1: 42 pages, 20 figures; v2: typos corrected; v3: typos correcte
5d/6d Wilson loops from blowups
No full textAbstract We generalize Nakajima-Yoshioka’s blowup formula to calculate the partition functions counting the spectrum of bound states to half-BPS Wilson loop operators in 5d (and 6d) supersymmetric field theories. The partition function in the presence of a Wilson loop operator on the Ω-background is factorized when put on the blowup ℂ ̂ 2 into two Wilson loop partition functions under the localization. This structure provides a set of blowup equations for Wilson loop operators. We explain how to formulate the blowup equations and solve them to compute the partition functions of Wilson loop operators. We test this idea by explicitly calculating the Wilson loop partition functions in various 5d/6d field theories and comparing them against known results and expected dualities
Downsampled Iterative Learning Controller for Flyback CCM Inverter
No full textWe propose a downsampled iterative learning controller (ILC) for a flyback inverter operating in continuous conduction mode (CCM). The flyback CCM inverter features step-up/-down ability, small number of circuit components, and high conversion efficiency, so it is well suited to the distributed renewable energy systems. But the conventional proportional-integral (PI) controller for the flyback CCM inverter shows poor steady-state response because the inverter itself suffers from time-varying grid-voltage disturbances and its transfer function has a right-half plane zero. The ILC itself achieves acceptable steady-state response of the flyback CCM inverter but can excite large overshoot in the iteration domain; this overshoot may destroy the solid state devices in the power circuit. To overcome this problem, we use a downsampled ILC technique that guarantees monotonic convergence of tracking error. The proposed ILC is computationally simple and easy to implement. Numerical simulations and experimental tests validate the proposed control approach.114sciescopu
Repetitive Controller With Phase-Lead Compensation for Cuk CCM Inverter
No full textThis paper proposes a repetitive controller with phase-lead compensation for an unfolding-type Cuk continuous conduction mode (CCM) inverter operating in the CCM. The Cuk CCM inverter features medium power capacity, step up/down ability, and low input/output current ripples, so it is well suited to distributed power generation systems. To achieve accurate tracking of the reference output current, we make the use of the repetitive controller coupled with a conventional proportional-integral controller and a nominal duty ratio. In developing the proposed controller, we use the average model of the Cuk CCM inverter in the grid-connected case. The two right-half plane (RHP) zeros in the transfer function of the Cuk CCM inverter cause phase lag of the closed-loop system; to compensate for the phase lag, we implement a phase-lead compensation algorithm in the repetitive control scheme. We also provide detailed and practical design guidelines of the control parameters to develop a stable Cuk CCM inverter. Experimental tests using a 500-W Cuk CCM inverter demonstrate the desirable performance of the proposed control approach.1110sciescopu
Design of the near-field thermophotovoltaic system for recovering waste heat from high-temperature slag
No full textWaste heat recovery is a key strategy for enhancing energy efficiency in high-temperature industrial processes. Near-field thermophotovoltaic (NF-TPV) systems offer strong potential due to their high-power output and solid-state operation. This study proposes a waste heat recovery NF-TPV system tailored for granulated slag, high-temperature byproduct of steelmaking. Unlike conventional NF-TPV systems with stationary heat sources, this design considers dynamically flowing slag. Gravity-driven granulated slag heats an adjacent emitter, which radiates energy to a photovoltaic (PV) cell. The PV cell is cooled by flowing water to maintain its energy conversion performance. A detailed analysis examines spatial temperature variations and their impact on electrical output, considering coupled radiation and convection effects. To address temperature non-uniformity, the bandgap-optimized In1-xGaxAs PV cell is employed, achieving a 30.9% improvement in net electrical efficiency. In addition, the near-field configuration and multilayer emitter design are shown to be critical for maximizing waste heat recovery. The study also explores how slag and coolant flow characteristics influence system performance. Results show a trade-off between waste heat recovery and net electrical efficiency, with optimal conditions yielding up to 80.4% waste heat recovery efficiency and 20.4% net electrical efficiency. The feasibility of NF-TPV technology for flowing slag heat recovery is examined through the analysis of major engineering challenges.
Exponentially Stable Lyapunov-Function-Based Controller for a Flyback CCM Converter
No full textIn this paper, we propose a Lyapunov-function-based controller for the flyback converter operating in the continuous conduction mode (CCM). The controller consists of a duty-ratio feedforward control unit and a Lyapunov-function-based feedback control unit. The duty-ratio feedforward signal is used to reduce the burden from the Lyapunov feedback controller. The control system guarantees global exponential stability of the closed-loop system and, hence, offers fast transient response under large-signal perturbations. In constructing the controller, we use the average model of the flyback CCM converter taking the parasitic components into account. Numerical simulations confirmed its superior performance, and experimental tests validated the proposed control approach.112sciescopu
Controlling selective nucleation and growth of dysprosium islands on graphene by metal intercalation
Get PDFMetal intercalation is an effective method to modify the physical and chemical properties of low-dimensional systems such as epitaxial graphene. Here, we show that the nucleation and growth of metal nanostructures on epitaxial graphene on SiC(0001) can be dramatically changed by metal intercalation. Using scanning tunneling microscopy experiments, we demonstrate that dysprosium (Dy) metal islands are selectively nucleated on the area with Dy intercalation under both graphene and carbon buffer layers, while the adjacent area with only buffer layer intercalated remains relatively bare. Using first-principles calculations based on density functional theory, we show that adsorption of Dy adatom on the preferred nucleation area is energetically more favorable than on other areas. Moreover, changes in the electronic structure and the interlayer spacing upon Dy intercalation obtained from our calculations are also consistent with experimental observations. Our results indicate that metal intercalation is a promising way to manipulate the interaction between graphene and deposited adatoms.This article is published as Kim, Minsung, Myron Hupalo, Michael C. Tringides, Patricia A. Thiel, Kai-Ming Ho, and Cai-Zhuang Wang. "Controlling selective nucleation and growth of dysprosium islands on graphene by metal intercalation." Physical Review Materials 6, no. 9 (2022): 094003.
DOI: 10.1103/PhysRevMaterials.6.094003.
Copyright 2022 American Physical Society.
Posted with permission.
DOE Contract Number(s): AC02-07CH11358
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
High-temperature corrugated-core radar stealth Ni-plated glass/ bismaleimide sandwich composites
No full textThis study presents a high-temperature Corrugated-core Radar-Absorbing Sandwich Composite (CRASC) with stable electromagnetic (EM) wave absorption at temperatures up to 300 degrees C. The corrugated-core design facilitates broadband radar absorption and stable performance despite thermal fluctuations, achieving the goal of thermal insulation performance of the designed Thermal Gradient Insulation Multilayer (TGIM). Electromagnetic simulations analyzed the effect of variations in electromagnetic properties on the radar-absorbing capability of the structure. Based on these analyses, a radar-absorbing structure incorporating two corrugated cores was designed, and fabricated using an autoclave and a hot press. The - 10 dB bandwidth of the fabricated CRASC at room temperature was confirmed to be 5.8 to 17.2 GHz. The radar-absorbing performance of the fabricated specimens was evaluated in a furnace, with temperatures ranging from room temperature to 300 degrees C. These results confirmed that the - 10 dB bandwidth remained stable despite temperature variations while maintaining the wide absorption bandwidth and thermal insulation.
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