Time Dependent Performance Analysis of Wireless Networks

Many wireless networks are subject to frequent changes in a combination of network topology, traffic demand, and link capacity, such that nonstationary/transient conditions always exist in packet-level network behavior. Although there are extensive studies on the steady-state performance of wireless networks, little work exists on the systematic study of their packet-level time varying behavior. However, it is increasingly noted that wireless networks must not only perform well in steady state, but must also have acceptable performance under nonstationary/transient conditions. Furthermore, numerous applications in today's wireless networks are very critical to the real-time performance of delay, packet delivery ratio, etc, such as safety applications in vehicular networks and military applications in mobile ad hoc networks. Thus, there exists a need for techniques to analyze the time dependent performance of wireless networks. In this dissertation, we develop a performance modeling framework incorporating queuing and stochastic modeling techniques to efficiently evaluate packet-level time dependent performance of vehicular networks (single-hop) and mobile ad hoc networks (multi-hop). For vehicular networks, we consider the dynamic behavior of IEEE 802.11p MAC protocol due to node mobility and model the network hearability as a time varying adjacency matrix. For mobile ad hoc networks, we focus on the dynamic behavior of network layer performance due to rerouting and model the network connectivity as a time varying adjacency matrix. In both types of networks, node queues are modeled by the same fluid flow technique, which follows flow conservation principle to construct differential equations from a pointwise mapping of the steady-state queueing relationships. Numerical results confirm that fluid-flow based performance models are able to respond to the ongoing nonstationary/transient conditions of wireless networks promptly and accurately. Moreover, compared to the computation time of standard discrete event simulator, fluid-flow based model is shown to be a more scalable evaluation tool. In general, our proposed performance model can be used to explore network design alternatives or to get a quick estimate on the performance variation in response to some dynamic changes in network conditions

Fire performance assessment of concrete with fly ash as the supplemental cementitious material

Material properties of concrete at elevated temperatures are imperative to structural fire safety assessment. However, fire performance of concrete at high temperature is extremely complex since concrete is a heterogeneous material with considerable variations. When it is subjected to thermal exposure, such as fire, concrete undergoes a series of significant physicochemical changes. Its mechanical behaviour is not only temperature dependent, but also loading history dependent, during the heating process. Therefore, the characterization of concrete properties at elevated temperatures is very challenging and the development of reliable and accurate constitutive models remains an unaccomplished task. The main aim of this thesis can be divided into two scopes: 1) to examine the effect of using fly ash (FA) as the supplemental cementitious material (SCM) on the fire performance of concrete; 2) to investigate the mechanical behaviour of concrete under different thermomechanical conditions and obtain a better understanding of the mechanism of how the pre-fire load affects the fire performance of concrete. Finally, an advanced thermo-mechanical constitutive model for concrete under uniaxial compression at elevated temperatures is expected to be established, for applications in structural fire engineering. The model has to capture the behaviour of structural concrete with different heating-loading sequences accurately and consider the effect of using FA as SCM on the variation of the properties of concrete during thermal exposure. An apparatus is specially designed for testing “hot” mechanical properties of concrete materials with different heating-loading regimes. Through the experimental research, the mechanical properties, including compressive strength, peak strain, elastic modulus, complete stress-strain relationship and transient thermal creep (TTC) of concrete under uniaxial compression at elevated temperatures have been investigated. In the experimental programme, both conventional ordinary Portland cement (Karakurt & Topçu) based concrete and FA concrete specimens were tested to examine the difference. In addition, a novel numerical method was proposed, to quantify the effect of temperature gradient on TTC of stressed concrete in transient state tests, so that an explicit TTC model could be formulated. Through the experimental research and numerical analysis presented in this thesis, the fire performance of FA concrete was examined. It was found that 25% replacement of OPC with FA in the concrete, mitigated the deterioration of the compressive strength, the development of TTC, and the nonlinearity of stress-strain response at elevated temperatures, but hardly influenced the value of the elastic modulus and the peak strain. The applicability of Eurocode EN1992-1-2 to normal strength concrete with 25% replacement of FA as SCM has been verified to be safe. In addition, the effect of loading history during thermal exposure, on the mechanical properties of concrete at the thermal steady state, has been investigated too. This thesis contributes to a better understanding on the mechanism of how loading-heating sequences influence the fire performance of concrete materials. Finally, an advanced constitutive model for concrete at high temperature has been proposed and verified. Compared with previous models, it has the following advantages of: 1) incorporating a parameter n to consider the variation of the nonlinearity of stress-strain curves with temperature, 2) formulating the elastic modulus separately from the stress-strain curve, 3) distinguishing the stress-strain response of the stressed condition from the unstressed condition and 4) calculating TTC in a completely explicit way, by quantifying the interference caused by the thermal gradient in transient state tests. The relevant parameters in the model have been particularly calibrated for FA concrete as a recommendation for practical engineering.China Scholarship Counci

Microstructural characterisation of organic matter pores in coal-measure shale

      To gain the insight into the nature of organic matter (OM) micro-nanometer pores and fractal features of coal-measure shale from the OM macromolecular evolution perspective, 28 Taiyuan formation shale samples are collected from Qinshui Basin and characterized with Rock-eval, Field emission scanning electron microscope (FE-SEM), low-pressure N2 gas adsorption (Lp-N2GA) and Fourier transform infrared spectroscopy (FTIR). The results show that OM is in the high-over mature stage. Pore size ranges from 5.7 to 26.7 nm and pores less than 4 nm are dominant. Two pore fractal dimensions D1 and D2 are obtained from Lp-N2GA with the Frenkel-Halsey-Hill method, which are in the range of 2.272-2.617 and 2.561-2.799, respectively. A series of FTIR structure parameters are obtained by peak fitting the FTIR spectra to describe the microstructure of OM molecules, such as length of aliphatic chain, degree of aromatic carbon condensation and hydrocarbon generation potential. Micro-nanometer OM-related pores in FE-SEM images can be classified as OM hydrocarbon-generating pores, OM structure pores, OM intergranular pores and micro- cracks, with the first being most developed. Both hydrocarbon-generation and condensation of aromatic nucleus have positive effects on D1 . Hydrocarbon-generation is more effective for the development of micropores, while the condensation of aromatic nucleus is more conducive for the development of mesopores (<10 nm). The higher the total organic carbon content, and the more the micropores and mesopores (<10 nm) develop, the higher the value of D1 .Cited as: Li, K., Kong, S., Xia, P., Wang, X. Microstructural characterisation of organic matter pores in coal-measure shale. Advances in Geo-Energy Research, 2020, 4(4): 372-391, doi: 10.46690/ager.2020.04.0

Wireless Sensor Networks for Smart Communications

(First paragraph) In the first edition of the special issue titled “Wireless Sensor Networks for Smart Communications”, a total of 22 manuscripts were received and 6 of these were accepted. This issue demonstrated that network congestion, user mobility, and adjacent spectrum interference are the main reasons for the degradation ofcommunication quality inWireless Sensor Networks (WSNs)

Multi-Agent Path Finding via Tree LSTM

In recent years, Multi-Agent Path Finding (MAPF) has attracted attention from the fields of both Operations Research (OR) and Reinforcement Learning (RL). However, in the 2021 Flatland3 Challenge, a competition on MAPF, the best RL method scored only 27.9, far less than the best OR method. This paper proposes a new RL solution to Flatland3 Challenge, which scores 125.3, several times higher than the best RL solution before. We creatively apply a novel network architecture, TreeLSTM, to MAPF in our solution. Together with several other RL techniques, including reward shaping, multiple-phase training, and centralized control, our solution is comparable to the top 2-3 OR methods.Comment: Appear in AAAI23-MAP

The Optimization and Mathematical Modeling of Quality Attributes of Parboiled Rice Using a Response Surface Method

The response surface methodology was used to optimize the hydrothermal processing conditions based on the rice quality parameters of the Rong Youhua Zhan rice variety (Indica). The effect of soaking temperature (29.77, 40, 55, 70, and 80.23°C), soaking time (67.55, 90, 120, 150, and 170.45 min), and steaming time (1.59, 5, 10, 15, and 18.41 min), each tested at five levels, on percentage of head rice yield (HRY), hardness, cooking time, lightness, and color were determined, with R2 values of 0.96, 0.94, 0.90, 0.88, and 0.94, respectively. HRY, hardness, cooking time, and color increased with process severity while lightness decreased, although HRY decreased after reaching a maximum. The predicted optimum soaking temperature, soaking time, and steaming time were 69.88°C, 150 min, and 6.73 min, respectively, and the predicted HRY, hardness, cooking time, lightness, and color under these conditions were 73.43%, 29.95 N, 32.14 min, 83.03 min, and 12.24 min, respectively, with a composite desirability of 0.9658. The parboiling industry could use the findings of the current study to obtain the desired quality of parboiled rice. This manuscript will be helpful for researchers working on commercializing parboiled rice processes in China as well as in other countries

Perturbed stochastic fractal search for solar PV parameter estimation

Following the widespread use of solar energy all over the world, the design of high quality photovoltaic (PV) cells has attracted strong research interests. To properly evaluate, control and optimize solar PV systems, it is crucial to establish a reliable and accurate model, which is a challenging task due to the presence of non-linearity and multi-modality in the PV systems. In this work, a new meta-heuristic algorithm (MHA), called perturbed stochastic fractal search (pSFS), is proposed to estimate the PV parameters in an optimization framework. The novelty lies in two aspects: (i) employ its own searching operators, i.e., diffusion and updating, to achieve a balance between the global exploration and the local exploitation; and (ii) incorporate a chaotic elitist perturbation strategy to improve the searching performance. To examine the effectiveness of pSFS, this method is applied to solve three PV estimation problems for different PV models, including single diode, double diode and PV modules. Experimental results and statistical analysis show that the proposed pSFS has improved estimation accuracy and robustness compared with several other algorithms recently developed

Social control and self-control: factors linking exposure to domestic violence and adolescents’ Internet gaming addiction

Although many studies have investigated the influencing factors of adolescents’ Internet gaming addiction, few have investigated the influence factor of exposure to domestic violence, and even fewer have used the General Strain Theory to explain the influence path of exposure to domestic violence on adolescents’ Internet gaming addiction. Based on the GST, this study sought to uncover further insights into the effect of exposure to family violence on adolescents’ Internet gaming addiction, and the mediating role of social control—specifically, parental attachment—and self-control in the association between exposure to family violence and adolescents’ Internet gaming addiction. Adopting a multi-stage cluster random sampling method, we conducted this study with 2,110 adolescents from Liangshan Yi Autonomous Prefecture in Sichuan Province, China. The results suggest that adolescents’ exposure to domestic violence directly affects their addiction to Internet games and indirectly affects it by decreasing social control and self-control. The study not only supplements and improves the explanatory framework of General Strain Theory, but makes a significant contribution to research on the causes of Internet gaming addiction