54 research outputs found
Study on Optimal Middle Temperature of Cascade-condenser in CO2/NH3 Cascade Refrigeration Systems with Two Temperature Ranges
This paper analyzes a CO2/NH3 cascade refrigeration system of two temperature range applied in the cold storage. A mathematical model is presented to determine the optimal middle temperatures of the cascade-condenser for obtaining the maximum coefficient of performance (COP) under different operation conditions. Three main parameters including the evaporation temperature in the cold storage, the evaporation temperature in the refrigerated storage and the condensation temperature in the high temperature stage are used to study the optimal middle temperature of CO2 in the cascade-condenser. The results show that the optimal middle temperature increases with the increment of three main parameters. Moreover, under specific conditions, the optimal temperature is equal to the evaporation temperature of refrigerated storage. The results shown in this paper is helpful to the control strategy of CO2/NH3 cascade refrigeration systems for two temperature ranges
Meta-KD: A Meta Knowledge Distillation Framework for Language Model Compression across Domains
Pre-trained language models have been applied to various NLP tasks with
considerable performance gains. However, the large model sizes, together with
the long inference time, limit the deployment of such models in real-time
applications. One line of model compression approaches considers knowledge
distillation to distill large teacher models into small student models. Most of
these studies focus on single-domain only, which ignores the transferable
knowledge from other domains. We notice that training a teacher with
transferable knowledge digested across domains can achieve better
generalization capability to help knowledge distillation. Hence we propose a
Meta-Knowledge Distillation (Meta-KD) framework to build a meta-teacher model
that captures transferable knowledge across domains and passes such knowledge
to students. Specifically, we explicitly force the meta-teacher to capture
transferable knowledge at both instance-level and feature-level from multiple
domains, and then propose a meta-distillation algorithm to learn single-domain
student models with guidance from the meta-teacher. Experiments on public
multi-domain NLP tasks show the effectiveness and superiority of the proposed
Meta-KD framework. Further, we also demonstrate the capability of Meta-KD in
the settings where the training data is scarce
Quantification of gas hydrate saturation and morphology based on a generalized effective medium model
Highlights
⢠A modified cementation theory is developed by introducing generalized pressure-dependent normalized contact-cemented radii.
⢠A generalized effective medium model is proposed to merge the effective medium theory and cementation theory.
⢠Modeling and inversion schemes are proposed to quantify hydrate saturation and morphology from laboratory and well-log data.
⢠Hydrates mainly grow as matrix-supporting form (~54%) in sands and as pore-filling form (~59%) in clay-rich marine sediments.
Abstract
Numerous models have been developed for prediction of gas hydrate saturation based on the microstructural relationship between gas hydrates and sediment grains. However, quantification of hydrate saturation and morphology from elastic properties has been hindered by failing to account for complex hydrate distributions. Here, we develop a generalized effective medium model by applying the modified Hashin-Shtrikman bounds to a newly developed cementation theory. This model is validated by experimental data for synthetic methane and tetrahydrofuran hydrates. Good comparison of model predictions with experimental measurements not only reveals its ability to merge the results of contact cementation theory and effective medium theory, but also indicates its feasibility for characterizing complex morphologies. Moreover, the results of inverting acoustic measurements quantitatively confirm that for synthetic samples in âexcess-gasâ condition gas hydrates mainly occur as a hybrid-cementing morphology with a low percentage of pore-filling morphology, whereas for pressure-core hydrate-bearing sediments in natural environments they exist as matrix-supporting and pore-filling morphologies with a very low percentage of hybrid-cementing morphology. The hydrate saturations estimated from sonic and density logs in several regions including northern Cascadia margin (Integrated Ocean Drilling Program Expedition 311, Hole U1326D and Hole U1327E), Alaska North Slope (Mount Elbert test well) and Mackenzie Delta (Mallik 5L-38), are comparable to the referenced hydrate saturations derived from core data and resistivity, and/or nuclear magnetic resonance log data, confirming validity and applicability of our model. Furthermore, our results indicate that ~8% hybrid-cementing, ~33% matrix-supporting and ~59% pore-filling hydrates may coexist in the fine-grained and clay-rich marine sediments on the northern Cascadia margin, whereas ~10% hybrid-cementing, ~54% matrix-supporting and ~36% pore-filling hydrates may coexist in the coarse-grained and sand-dominated terrestrial sediments of the Alaska North Slope and Mackenzie Delta
Learning to Expand: Reinforced Pseudo-relevance Feedback Selection for Information-seeking Conversations
Intelligent personal assistant systems for information-seeking conversations
are increasingly popular in real-world applications, especially for e-commerce
companies. With the development of research in such conversation systems, the
pseudo-relevance feedback (PRF) has demonstrated its effectiveness in
incorporating relevance signals from external documents. However, the existing
studies are either based on heuristic rules or require heavy manual labeling.
In this work, we treat the PRF selection as a learning task and proposed a
reinforced learning based method that can be trained in an end-to-end manner
without any human annotations. More specifically, we proposed a reinforced
selector to extract useful PRF terms to enhance response candidates and a BERT
based response ranker to rank the PRF-enhanced responses. The performance of
the ranker serves as rewards to guide the selector to extract useful PRF terms,
and thus boost the task performance. Extensive experiments on both standard
benchmark and commercial datasets show the superiority of our reinforced PRF
term selector compared with other potential soft or hard selection methods.
Both qualitative case studies and quantitative analysis show that our model can
not only select meaningful PRF terms to expand response candidates but also
achieve the best results compared with all the baseline methods on a variety of
evaluation metrics. We have also deployed our method on online production in an
e-commerce company, which shows a significant improvement over the existing
online ranking system
Kuaipedia: a Large-scale Multi-modal Short-video Encyclopedia
Online encyclopedias, such as Wikipedia, have been well-developed and
researched in the last two decades. One can find any attributes or other
information of a wiki item on a wiki page edited by a community of volunteers.
However, the traditional text, images and tables can hardly express some
aspects of an wiki item. For example, when we talk about ``Shiba Inu'', one may
care more about ``How to feed it'' or ``How to train it not to protect its
food''. Currently, short-video platforms have become a hallmark in the online
world. Whether you're on TikTok, Instagram, Kuaishou, or YouTube Shorts,
short-video apps have changed how we consume and create content today. Except
for producing short videos for entertainment, we can find more and more authors
sharing insightful knowledge widely across all walks of life. These short
videos, which we call knowledge videos, can easily express any aspects (e.g.
hair or how-to-feed) consumers want to know about an item (e.g. Shiba Inu), and
they can be systematically analyzed and organized like an online encyclopedia.
In this paper, we propose Kuaipedia, a large-scale multi-modal encyclopedia
consisting of items, aspects, and short videos lined to them, which was
extracted from billions of videos of Kuaishou (Kwai), a well-known short-video
platform in China. We first collected items from multiple sources and mined
user-centered aspects from millions of users' queries to build an item-aspect
tree. Then we propose a new task called ``multi-modal item-aspect linking'' as
an expansion of ``entity linking'' to link short videos into item-aspect pairs
and build the whole short-video encyclopedia. Intrinsic evaluations show that
our encyclopedia is of large scale and highly accurate. We also conduct
sufficient extrinsic experiments to show how Kuaipedia can help fundamental
applications such as entity typing and entity linking
A Unified Model for Video Understanding and Knowledge Embedding with Heterogeneous Knowledge Graph Dataset
Video understanding is an important task in short video business platforms
and it has a wide application in video recommendation and classification. Most
of the existing video understanding works only focus on the information that
appeared within the video content, including the video frames, audio and text.
However, introducing common sense knowledge from the external Knowledge Graph
(KG) dataset is essential for video understanding when referring to the content
which is less relevant to the video. Owing to the lack of video knowledge graph
dataset, the work which integrates video understanding and KG is rare. In this
paper, we propose a heterogeneous dataset that contains the multi-modal video
entity and fruitful common sense relations. This dataset also provides multiple
novel video inference tasks like the Video-Relation-Tag (VRT) and
Video-Relation-Video (VRV) tasks. Furthermore, based on this dataset, we
propose an end-to-end model that jointly optimizes the video understanding
objective with knowledge graph embedding, which can not only better inject
factual knowledge into video understanding but also generate effective
multi-modal entity embedding for KG. Comprehensive experiments indicate that
combining video understanding embedding with factual knowledge benefits the
content-based video retrieval performance. Moreover, it also helps the model
generate better knowledge graph embedding which outperforms traditional
KGE-based methods on VRT and VRV tasks with at least 42.36% and 17.73%
improvement in HITS@10
Grazing weakens competitive interactions between active methanotrophs and nitrifiers modulating greenhouse-gas emissions in grassland soils
This work was financially supported by Natural Science Foundation of China (41977033, 41907026, and 41721001), Fundamental Research Funds for the Central Universities (2019QNA6011), National Key Basic Research Program of China (2014CB138801), Shandong Provincial Natural Science Foundation (ZR2019BD032), China Postdoctoral Science Foundation (2020T130387 and 2019M652448). CG-R was funded by a Royal Society University Research Fellowship (UF150571). Special thanks to ChunMei Meng, Yu Luo, and Yan Zheng for their assistance in laboratory analyses.Peer reviewedPublisher PD
- âŚ