| 1. |
- Liu, Jiaping, et al.
(författare)
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Flow level Stability of Data Networks with Nonconvex and Time-varying rate regions
- 2007
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Ingår i: SIGMETRICS'07. - New York, NY, USA : Association for Computing Machinery. - 9781595936394 ; , s. 239-250
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Konferensbidrag (refereegranskat)abstract
- In this paper we characterize flow-level stochastic stability for networks with non-convex or time-varying rate regions underresource allocation based on utility maximization. Similar to prior works on flow-level stability, we consider exogenous data arrivals with finite workloads. However, to model many realistic situations, the rate region, which constrains the feasibility of resource allocation, may be either non-convex or time-varying. When the rate region is fixed but non-convex, we derive sufficient and necessary conditions for stability, which coincide when the set of allocated rate vectors has continuous contours. When the rate region is time-varying according to some stationary, ergodic process, we derive the precise stability region. In both cases,the size of the stability region depends on the resource allocation policy, in particular, on the fairness parameter in ∝-fair utility maximization. This is in sharp contrast with the substantial existing literature on stability under fixed and convex rate regions, in which the stability region coincides with the rate region for many utility-based resource allocation schemes, independently of the value of the fairness parameter. We further investigate the tradeoff between fairness and stability when rate region is non-convex or time-varying. Numerical examples of both wired and wireless networks are provided to illustrate the new stability regions and tradeoffs proved in the paper.
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| 2. |
- Pan, Song, et al.
(författare)
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Analysis and interpretation of the particulate matter (PM10 and PM2.5) concentrations at the subway stations in Beijing, China
- 2019
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Ingår i: Sustainable cities and society. - : Elsevier BV. - 2210-6707. ; 45, s. 366-377
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Tidskriftsartikel (refereegranskat)abstract
- The particulate matters (PM10 and PM2.5) inside urban subway stations greatly influence indoor air quality and passenger comfort. This study aims to analyze and interpret the concentrations of PM10 and PM2.5, measured in several subway stations from October 9th to 22nd, 2016 in Beijing, China. The overall methodology was based on the Statistical Package for Social Science (SPSS) software while General linear model (GLM) and correlation analysis were further applied to examine the sensitivities of different variables to the particle concentrations. The data analysis showed the average overall mass ratio of PM concentrations inside subway station is about 68.7%, much lower than outdoor condition (79.6%). In the areas of the station hall and platform, the real-time PM10 and PM2.5 concentrations varied periodically. In working and operation offices, all rooms had much higher PM concentrations than the outdoor environment when its pollution level was level 3, in which the facility room reached the highest level, while the closed meeting room had the lowest. Correlation analysis results indicated that PM10 and PM2.5 concentrations were mutually correlated (average R2 = 0.854), and a strong linear correlation (R2 = 0.897) of the subway-station PM concentrations to the outdoor PM conditions, regardless of the outdoor atmospheric PM concentrations pollution level was. Nevertheless, the impact of passenger number and temperature & humidity on the station PM concentrations was less, when compared to the outdoor environment. This paper is expected to provide useful information for further research and design of effective prevention measures on PM in local subway stations, towards a more sustainable and healthier built environment in the city underground.
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| 3. |
- Pan, Song, et al.
(författare)
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Cluster analysis for occupant-behavior based electricity load patterns in buildings : a case study in Shanghai residences
- 2017
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Ingår i: Building Simulation. - : Springer Science and Business Media LLC. - 1996-3599 .- 1996-8744. ; 10:6, s. 889-898
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Tidskriftsartikel (refereegranskat)abstract
- In building performance simulation, occupant behavior contributes to large uncertainties, which often lead to considerable discrepancies between actual energy consumption and simulation results. This paper aims to extract occupant-behavior related electricity load patterns using classical K-means clustering approach at the initial investigation stage. Smart-metering data from a case study in Shanghai, China, was used for the load pattern analysis. The electricity load patterns of occupants were examined on a daily/weekly/seasonal basis. According to their load patterns, occupants were categorized as (a) white-collar workers, (b) poor or older families and (c) rich or young families. The daily patterns indicated that electricity use was much more random and fluctuated over a wide range. Most households of the monitored communities consumed relatively-low electricity; the characteristic double peak with higher level of consumption in the morning and evening were only apparent in a relatively small subset of residents (mostly white-collar workers). The weekly analysis found that significant load shifting towards weekend days occurred in the poor or old family group. The electricity saving potential was greatest in the white-collar workers and the rich or young family groups. This study concludes with recommendations to stakeholders utilizing our load profiling results. The research provides a rare insight into the electricity-use-related occupant behaviors of Shanghai residents through the case study of two communities. The findings of the study are also presented in a meaningful way so that they can directly aid the decision-making of governments and other stakeholders interested in energy efficiency. The research results are also relevant to the building energy simulation community as they are derived from observations, and thus can have the potential to improve the efficiency and accuracy of numerical simulation results.
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| 4. |
- Pan, Song, et al.
(författare)
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Design and experimental study of a novel air conditioning system using evaporative condenser at a subway station in Beijing, China
- 2018
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Ingår i: Sustainable cities and society. - : Elsevier BV. - 2210-6707. ; 43, s. 550-562
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Tidskriftsartikel (refereegranskat)abstract
- Air conditioning system (AC) contributes significantly to the energy consumption of underground metros. In China, most metro stations are designed with water-cooling centralized air conditioning (WC-AC) system, it has been found that several serious problems are brought by this conventional system, such as large space occupying, water leaking, cooling tower noise and low system efficiency. In order to solve these problems, a novel energy-efficient AC system incorporating an independent evaporative condenser (EC) has been proposed and installed at Futong metro station in Beijing, China. A series of pilot measurements were conducted to analyze the cooling performance and energy consumption of this novel EC-AC system. During the testing period, the average refrigeration efficiency of COP, SCOP and ACOP in A and B side is up to 3.8/3.9, 3.4/3.4 and 2.5/2.3. At the same time, some operation problems such as unbalanced working condition have been identified during measurement. The research indicates that such EC-AC system could be a feasible solution to enhance the energy efficiency and reduce the operational costs and carbon emission in metro stations.
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| 5. |
- Zhou, Yang, et al.
(författare)
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Interaction mechanisms between organic and inorganic phases in calcium silicate hydrates/poly(vinyl alcohol) composites
- 2019
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Ingår i: Cement and Concrete Research. - : Elsevier BV. - 0008-8846. ; 125
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Tidskriftsartikel (refereegranskat)abstract
- Poly (vinyl alcohol) (PVA) emulsion is commonly used in cement-based materials to obtain higher performance. The present work investigates the interaction mechanisms between PVA and calcium silicate hydrates (C-S-H) using ambient and high pressure X-ray diffraction (XRD), 29Si magic angle spinning nuclear magnetic resonance (MAS NMR), nano-indentation, and molecular dynamics simulation. In a C-S-H nano-particle, small-size PVA molecules can be intercalated into the interlayer region of the calcium silicate sheets, lowering the interlayer incompressibility and the overall bulk modulus of C-S-H at the crystal length scale. At a larger length scale, the large-size PVA chains can be in the midst among the C-S-H nano-particles, decreasing the porosity, thus the indentation modulus of the meso-composite is improved.
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