113 research outputs found
A Harmonic-Based Triple Phase Shift Modulation Strategy for a Dual Active Bridge Converter in an All Electric Aircraft Application
No full textA harmonic-based Triple-Phase Shift (TPS) modulation strategy for a 2.1kW, 270V Bidirectional DC-DC Dual Active Bridge (DAB) conditioning system for an All Electric Aircraft application is proposed in this paper. The DAB model has been obtained concerning the frequency domain, particularly resorting to the Fundamental Component Analysis (FCA). The TPS parameters are selected to both erase the flow-back current in the DC-link capacitor and minimize the voltage harmonic content on the load side. In this way, the reactive power minimization and the active power maximization associated with the first harmonic component are achieved. The co-simulation study of the proposed TPS shows a very good performances, also during step-load variations
Volcanic forcing of climate over the past 1500 years: an improved ice-core-based index for climate models
No full textUnderstanding natural causes of climate change is vital to evaluate the relative impacts of human pollution and land surface modification on climate. Nevertheless, assessment of the contribution of natural causes to past climate change has been limited by limitations of the existing forcing indices. This dissertation has investigated one of the most important natural causes of climate change, volcanic eruptions, by developing a volcanic forcing index using 54 ice core records from both the Arctic and Antarctica. The extensive collection of ice core data reduces errors inherent in reconstructions based on small number of cores, which enables us to obtain much higher accuracy in both detection of events and quantification of the radiative effects. I extracted volcanic signals by applying a high-pass loess filter to each ice core record and examining peaks that exceed twice the 31-yr running median absolute deviation. I then studied the spatial pattern of volcanic sulfate deposition on Greenland and Antarctica, and combined this knowledge with a new understanding of stratospheric transport of volcanic aerosols to produce a forcing index as a function of month from 501 to 2000 CE, latitude in 10° bands, and height from 9 to 30 km at 0.5 km resolution. This index is the longest and most advanced volcanic forcing index of the type. It eliminates or minimizes many aspects of problems previous reconstruction had with the ice core records.
I forced an energy balance model with this new volcanic forcing index, together with solar and anthropogenic forcing, to simulate the large scale temperature response over the past 1500 years. The results agree well with instrumental observations for the past 150 years and reasonably well with proxy records for the entire period. Through better characterization of the natural causes of climate change, this new data set will lead to improved prediction of anthropogenic impacts on climate.
Previous work suggested the 15th century Kuwae eruption might have been a two-phase event occurred somewhere between 1450-1464 CE, injecting 150-400 Tg of sulfate aerosol into the atmosphere. Using 33 ice core records I found it was indeed a single-phase eruption occurred during late 1452 to early 1453 CE and it emitted about 140 Tg of sulfate aerosols into the stratosphere with 2(SH):1(NH) hemispheric partitioning. This finding provides an important reference to evaluate and improve the dating of ice core records.Ph.D.Includes bibliographical references (p. 82-93)
Elastocaloric effect in vanadium (IV) oxide
Full text linkElastocaloric cooling utilizes the latent heat associated with stress-induced reversible phase transformations to achieve cooling. Currently, the key barrier to this technology is its prohibitive cost due to the high elastocaloric material cost and the large stress required to drive the cooling cycle. Vanadium (IV) oxide (VO2) is a good candidate, and it is relatively cheap. Our calorimetry study shows it exhibits a reversible phase transformation with a large latent heat of 31.5 J/g as well as excellent functional stability. Its transformation temperature and latent heat are tunable via heat treatment. We demonstrate that VO2 powders can be cyclically compressed in a steel tube using a steel plunger to drive the elastocaloric effect. The application of relatively low stress of 300 MPa is sufficient to result in a reversible temperature change of 0.5 degrees C on the powder compact. Further improvement of reversible temperature change to 1.6 degrees C under 300 MPa is achieved by adding conductive copper powders. Future efforts should focus on improving material properties such as heat capacity and thermal conductivity for candidate ceramic oxides to maximize elastocaloric effects.This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Ouyang, Gaoyuan, Chaochao Pan, Sam Wolf, Pratyasha Mohapatra, Ichiro Takeuchi, and Jun Cui. "Elastocaloric effect in vanadium (IV) oxide." Applied Physics Letters 116, no. 25 (2020): 251901, and may be found at DOI: 10.1063/5.0012166. Posted with permission.</p
Enhanced electrical conductivity in graphene–copper multilayer composite
Full text linkFor many years, researchers have been trying to make a material more conductive than silver by incorporating carbon nanotubes or graphene into copper to form a composite material. However, after a decade-long effort, only a few groups reported successful results, raising concerns about the feasibility of this composite approach. Here, we report our effort to validate the multilayer graphene–copper composite approach for improving electrical conductivity. We demonstrate that, with an estimated 0.008 vol. % graphene addition, copper’s electrical conductivity was improved to 104.2% of International Annealed Copper Standard (IACS) at room temperature. If the copper substrate used to make the multilayer composite is discounted using the parallel resistance model, the conductivity is calculated to be 185% IACS. This result could be further improved if the thickness of the copper layers can be further reduced.This article appeared in Pan, Chaochao, Anand PS Gaur, Matthew Lynn, Madison P. Olson, Gaoyuan Ouyang, and Jun Cui. "Enhanced electrical conductivity in graphene–copper multilayer composite." AIP Advances 12, no. 1 (2022): 015310, and may be found at DOI: 10.1063/5.0073879.
Copyright 2022 Author(s).
All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).
Posted with permission.
DOE Contract Number(s): AC02-07CH11358
Leachate properties as indicators of methane production process in MSW anaerobic digestion bioreactor landfill
No full text
Sprayable copper and copper–zinc nanowires inks for antiviral surface coating
No full textCopper alloys are known for their high antimicrobial efficacy. Retrofitting high-touch surfaces in public space with solid copper components is expensive and often impractical. Directly coating copper onto these high-touch surfaces can be achieved with hot or cold spray, but the procedure is complicated and requires special equipment. This article reports on the development of sprayable copper and copper–zinc nanowire inks for antiviral surface coating applications. Our results show that copper nanowires inactivate the SARS-CoV-2 virus faster than bulk copper. And a trace amount of zinc addition has a significant effect in enhancing the virucidal effect. More importantly, these nanowire inks are sprayable. They can be easily applied on high-touch surfaces with a spray can. When combined with common chemical disinfectants, the copper-based nanowire ink spray may prolong the disinfecting effect well after application.This article is published as Pan, Chaochao, Kruttika S. Phadke, Zheng Li, Gaoyuan Ouyang, Tae-hoon Kim, Lin Zhou, Julie Slaughter, Bryan Bellaire, Shenqiang Ren, and Jun Cui. "Sprayable copper and copper–zinc nanowires inks for antiviral surface coating." RSC Advances 12, no. 10 (2022): 6093-6098.
DOI: 10.1039/D1RA08755J.
Copyright 2022 The Author(s).
Attribution-NonCommercial 3.0 Unported (CC BY-NC 3.0).
Posted with permission. DOE Contract Number(s): AC02-07CH11358
Effects of Mn-Depleted Zone Formation on Acicular Ferrite Transformation in Weld Metals under High Heat Input Welding
No full textIn this present work, during high heat input welding of the weld metal, different types of Mn-depleted zones were achieved by different cooling rates. The effects of cooling rates on Mn-depleted zone formation and acicular ferrite (AF) transformation were analyzed. The Mn-depleted zone around the inclusions, as well as the interface concentration of Mn atoms, are found to be significantly different with different cooling rates. When the cooling rate is 10 °C/s, the interface concentration of Mn atoms around the inclusions is the lowest, the area of Mn-depleted zone is the smallest, and the proportion of AF in the weld metal is the highest. As the cooling rate decreases further, the interface concentration of Mn begins to rise, the area of the Mn-depleted zone gradually expands, and the proportion of AF decreases. However, when the cooling rate reaches 100 °C/s, only a very small amount of MnS precipitates, no Mn-depleted zone forms around the inclusions, and acicular ferrite cannot be produced effectively in the weld metal
Importance measures for inspections in binary networks
Full text linkMany infrastructure systems can be modeled as networks of components with binary states (intact, damaged). Information about components conditions is crucial for the maintenance process of the system. However, it is often impossible to collect information of all components due to budget constraints. Several metrics have been developed to assess the importance of the components in relation to maintenance actions: an important component is one that should receive high maintenance priority. Instead, in this paper we focus on the priority to be assigned for component inspections and information collection. We investigate metrics based on system level (global) and component level (local) decision making after inspection for networks with different topology, and compare these results with traditional ones. We then discuss the computational challenges of these metrics and provide possible approximation approaches.We acknowledge the support of NSF project CMMI #1653716, titled CAREER: Infrastructure Management under Model Uncertainty: Adaptive Sequential Learning and Decision Making
Optimal Control of Three-level Dual Active Bridge DC-DC Converter Under Dual Phase-shifted Modulation
No full text- …
