5,877 research outputs found
Vibration suppression in high-speed trains with negative stiffness dampers
Copyright © 2018 Techno-Press, Ltd. This work proposes and investigates re-centering negative stiffness dampers (NSDs) for vibration suppression in high-speed trains. The merit of the negative stiffness feature is demonstrated by active controllers on a high-speed train. This merit inspires the replacement of active controllers with re-centering NSDs, which are more reliable and robust than active controllers. The proposed damper design consists of a passive magnetic negative stiffness spring and a semi-active positioning shaft for re-centering function. The former produces negative stiffness control forces, and the latter prevents the amplification of quasi-static spring deflection. Numerical investigations verify that the proposed re-centering NSD can improve ride comfort significantly without amplifying spring deflection
SE-KGE: A Location-Aware Knowledge Graph Embedding Model for Geographic Question Answering and Spatial Semantic Lifting
Learning knowledge graph (KG) embeddings is an emerging technique for a
variety of downstream tasks such as summarization, link prediction, information
retrieval, and question answering. However, most existing KG embedding models
neglect space and, therefore, do not perform well when applied to (geo)spatial
data and tasks. For those models that consider space, most of them primarily
rely on some notions of distance. These models suffer from higher computational
complexity during training while still losing information beyond the relative
distance between entities. In this work, we propose a location-aware KG
embedding model called SE-KGE. It directly encodes spatial information such as
point coordinates or bounding boxes of geographic entities into the KG
embedding space. The resulting model is capable of handling different types of
spatial reasoning. We also construct a geographic knowledge graph as well as a
set of geographic query-answer pairs called DBGeo to evaluate the performance
of SE-KGE in comparison to multiple baselines. Evaluation results show that
SE-KGE outperforms these baselines on the DBGeo dataset for geographic logic
query answering task. This demonstrates the effectiveness of our
spatially-explicit model and the importance of considering the scale of
different geographic entities. Finally, we introduce a novel downstream task
called spatial semantic lifting which links an arbitrary location in the study
area to entities in the KG via some relations. Evaluation on DBGeo shows that
our model outperforms the baseline by a substantial margin.Comment: Accepted to Transactions in GI
Effect of cooling pad installation on indoor airflow distribution in a tunnel-ventilated laying-hen house
Extra cooling pads on the sidewalls are needed for larger poultry houses using tunnel ventilation system. Preliminary study showed that the airflow velocity going through different aisles varies greatly when the extra pads are installed at the end of sidewalls, making a “[”-shape air inlet. Combined with field tests, the CFD (computational fluid dynamics) technology was used to study the uniformity of airflow distribution in a tunnel-ventilated laying-hen house. The air distribution was first monitored in a layer house to find the main reason resulting in the variations of airflows in different aisles. Then CFD simulations were carried out with different distances (D=2 m, 3 m or 4 m) between the pads on end-wall and the extra pads on side walls. The field test showed that airflow streams from the different groups of cooling pads collided vertically at the house corners, mixed with each other, then flew towards the center of the house. This was the main reason that the wind speed in the middle aisle was much higher than in other aisles, leaving large zones of lower ventilation in the aisles adjacent to the sidewalls. The results of CFD simulations indicated that air distributions could be significantly improved when the extra pieces of pads were moved away for an appropriate distance from the end cooling pads. As far as conventional poultry house with a span of 12 m, the air speeds in different aisles were more uniform when this distance was about 3 m
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Low Cost, Robust, Environmentally Friendly Geopolymer–Mesoporous Carbon Composites for Efficient Solar Powered Steam Generation
High-efficiency, environment friendly, renewable energy-based methods of desalination represent attractive and potentially very powerful solutions to the long-standing problem of global water shortage. Many new laboratory-scale materials have been developed for photothermal desalination but the development of low-cost, easy-to-manufacture, and scalable materials and systems that can convert solar irradiation into exploitable thermal energy in this context is still a significant challenge. This paper presents work on a geopolymer–biomass mesoporous carbon composite (GBMCC) device with mesoporous and macroporous structures for harvesting solar energy, which is then used in a device to generate water vapor with high efficiency using negative pressure, wind-driven, steam generation. The GBMCC device gives water evaporation rates of 1.58 and 2.71 kg m−2 h−1 under 1 and 3 suns illumination, with the solar thermal conversion efficiency up to 84.95% and 67.6%, respectively. A remarkable, record high water vapor generation rate of 7.55 kg m−2 h−1 is achieved under 1 sun solar intensity at the wind speed of 3 m s−1. This is a key step forward todays efficient, sustainable and economical production of clean water from seawater or common wastewater with free solar energy
Semantically-Enriched Search Engine for Geoportals: A Case Study with ArcGIS Online
Many geoportals such as ArcGIS Online are established with the goal of
improving geospatial data reusability and achieving intelligent knowledge
discovery. However, according to previous research, most of the existing
geoportals adopt Lucene-based techniques to achieve their core search
functionality, which has a limited ability to capture the user's search
intentions. To better understand a user's search intention, query expansion can
be used to enrich the user's query by adding semantically similar terms. In the
context of geoportals and geographic information retrieval, we advocate the
idea of semantically enriching a user's query from both geospatial and thematic
perspectives. In the geospatial aspect, we propose to enrich a query by using
both place partonomy and distance decay. In terms of the thematic aspect,
concept expansion and embedding-based document similarity are used to infer the
implicit information hidden in a user's query. This semantic query expansion 1
2 G. Mai et al. framework is implemented as a semantically-enriched search
engine using ArcGIS Online as a case study. A benchmark dataset is constructed
to evaluate the proposed framework. Our evaluation results show that the
proposed semantic query expansion framework is very effective in capturing a
user's search intention and significantly outperforms a well-established
baseline-Lucene's practical scoring function-with more than 3.0 increments in
DCG@K (K=3,5,10).Comment: 18 pages; Accepted to AGILE 2020 as a full paper GitHub Code
Repository: https://github.com/gengchenmai/arcgis-online-search-engin
A van der Waals pn heterojunction with organic/inorganic semiconductors
van der Waals (vdW) heterojunctions formed by two-dimensional (2D) materials
have attracted tremendous attention due to their excellent electrical/optical
properties and device applications. However, current 2D heterojunctions are
largely limited to atomic crystals, and hybrid organic/inorganic structures are
rarely explored. Here, we fabricate hybrid 2D heterostructures with p-type
dioctylbenzothienobenzothiophene (C8-BTBT) and n-type MoS2. We find that
few-layer C8-BTBT molecular crystals can be grown on monolayer MoS2 by vdW
epitaxy, with pristine interface and controllable thickness down to monolayer.
The operation of the C8-BTBT/MoS2 vertical heterojunction devices is highly
tunable by bias and gate voltages between three different regimes: interfacial
recombination, tunneling and blocking. The pn junction shows diode-like
behavior with rectifying ratio up to 105 at the room temperature. Our devices
also exhibit photovoltaic responses with power conversion efficiency of 0.31%
and photoresponsivity of 22mA/W. With wide material combinations, such hybrid
2D structures will offer possibilities for opto-electronic devices that are not
possible from individual constituents.Comment: 16 pages, 4 figure
Experimental Investigation on the ICCP-SS Technique for Sea-Sand RC Beams
Impressed current cathodic protection (ICCP) is an efficient method to prevent further corrosion of the re-bars, while strengthening structures (SS) by using carbon fiber mesh can help improve the loading capacity of the degraded sea-sand reinforced concrete (RC) structures. This study proposes a new dual-functional method, ICCP-SS, to retrofit the sea-sand RC structures by using the carbon - fiber reinforced cementitious matrix (C-FRCM). The C-FRCM composite, comprised of carbon fiber mesh and inorganic cementitious material, is both the anodic material in the ICCP process as well as the structural strengthening material. This paper presents an experimental program consisting of 11 simply supported beams, 10 of them casted by simulated sea-sand and subjected to accelerated corrosion process for 130 days. The specimens casted by sea-sand were afterwards bonded with C-FRCM composite, treated by ICCP for 130 days, and finally tested. In this study, the flexure strength of the beams, the deflection and curvature of the specimens, as well as the strain and the open circuit potential of re-bars are obtained and used to assess the performance of the repaired specimens. The proposed technique has been shown to be effective in retarding the corrosion of re-bars and recovering the loading capacity of the corroded specimens, which should be beneficial for the durability of sea-sand RC structures
Histone H2B ubiquitin ligase RNF20 is required for MLL-rearranged leukemia
Mixed-lineage leukemia (MLL) fusions are potent oncogenes that initiate aggressive forms of acute leukemia. As aberrant transcriptional regulators, MLL-fusion proteins alter gene expression in hematopoietic cells through interactions with the histone H3 lysine 79 (H3K79) methyltransferase DOT1L. Notably, interference with MLL-fusion cofactors like DOT1L is an emerging therapeutic strategy in this disease. Here, we identify the histone H2B E3 ubiquitin ligase ring finger protein 20 (RNF20) as an additional chromatin regulator that is necessary for MLL-fusion-mediated leukemogenesis. Suppressing the expression of Rnf20 in diverse models of MLL-rearranged leukemia leads to inhibition of cell proliferation, under tissue culture conditions as well as in vivo. Rnf20 knockdown leads to reduced expression of MLL-fusion target genes, effects resembling Dot1l inhibition. Using ChIP-seq, we found that H2B ubiquitination is enriched in the body of MLL-fusion target genes, correlating with sites of H3K79 methylation and transcription elongation. Furthermore, Rnf20 is required to maintain local levels of H3K79 methylation by Dot1l at Hoxa9 and Meis1. These findings support a model whereby cotranscriptional recruitment of Rnf20 at MLL-fusion target genes leads to amplification of Dot1l-mediated H3K79 methylation, thereby rendering leukemia cells dependent on Rnf20 to maintain their oncogenic transcriptional program
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