Investigating the burning characteristics of electric cables used in the nuclear power plant by way of 3-D transient FDS code

Burning characteristics of electrical cables are one of the key parameters for the fire hazard assessment of nuclear power plants (NPPs) since the cables are the essential sources of fire in the plants. A three-dimensional (3-D) transient computational fluid dynamics (CFD) code_FDS is adopted in this paper to simulate these characteristics related to the cable burning. Being one of the NRC licensing fire codes, the FDS includes the thermal-hydraulic equations, the turbulence model and the chemical combustion model, etc. In order to assess the CFD fire models used in this code, a burning test using the control cable with the outer jacket of polyvinylchloride (PVC) and the inner insulation of cross-linked polyethylene (XLPE) is conducted. The measured parameters associated with the burning characteristics include the heat release rate (HRR), O₂ depletion, and CO and CO₂ production, etc. Except the amount of O₂ consumption, the predicted transient behaviors of other parameters can reproduce the measured data. Based on the chemical combustion model in the FDS code, this discrepancy may be essentially resulted from the default value of hydrogen fraction (H_frac) contained in the soot since the soot yield for the burning of PVC material is high enough that the uncertainty in the H_frac value has a prominent effect on the amount of O₂ consumption. This explanation can be confirmed by a benchmark calculation for simulating a burning test with the polymethylmethacrylate (PMMA) fuel of low-soot yield. The present simulation works can provide the useful information for the plant staff or the researcher as they would perform the fire hazard analysis in the NPPs using the FDS code.     

Fair round robin binary countdown to achieve QoS guarantee and fairness in WLANs

How to guarantee both quality of service (QoS) and fairness in wireless local area networks (WLANs) is a challenging issue. To touch this issue, a fair medium access control (MAC) scheme called fair round robin binary countdown (FRRBC) adopting the eminent concepts of allowance and binary countdown is proposed in this paper. FRRBC can guarantee QoS for both audio and video with the aid of adaptive adjustment on system parameters and some extra rules designed according to delay bounds. Using multiple mapping functions from allowances to fixed-bit binary numbers to indicate different priorities, FRRBC not only provides guaranteed system performance but also achieves good fairness. Finally, we demonstrate that FRRBC can significantly outperform the enhanced distributed channel access (EDCA) (IEEE 802.11 WG in IEEE Standard for Information technology—Telecommunications and information exchange between systems—Local and metropolitan area networks—Specific requirements—Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications. Amendment 8: Medium Access Control (MAC) Quality of Service Enhancements, 2005) and the synchronized medium access control (SYN-MAC) (Wu HY et al. in Mobile Netw Appl 11:627–637, 2005) because of its superiority to offer guaranteed QoS for both audio and video, low delay jitter, low blocking ratio, and good fairness. Of course, FRRBC can be illustrated to be a better choice than the enhanced distributed elastic round robin (EDERR) (Ferng HW, Liau HY in IEEE Trans Mobile Comput 8(7):880–894, 2009).     

A three-dimensional full-cell CFD model used to investigate the effects of different flow channel designs on PEMFC performance

A three-dimensional “full-cell” computational fluid dynamics (CFD) model is proposed in this paper to investigate the effects of different flow channel designs on the performance of proton exchange membrane fuel cells (PEMFC). The flow channel designs selected in this work include the parallel and serpentine flow channels, single-path and multi-path flow channels, and uniform depth and step-wise depth flow channels. This model is validated by the experiments conducted in the fuel cell center of Yuan Ze University, showing that the present model can investigate the characteristics of flow channel for the PEMFC and assist in the optima designs of flow channels. The effects of different flow channel designs on the PEMFC performance obtained by the model predictions agree well with those obtained by experiments. Based on the simulation results, which are also confirmed by the experimental data, the parallel flow channel with the step-wise depth design significantly promotes the PEMFC performance. However, the performance of PEMFC with the serpentine flow channel is insensitive to these different depth designs. In addition, the distribution characteristics of fuel gases and current density for the PEMFC with different flow channels can be also reasonably captured by the present model.     

Modeling and Cost Analysis of an Improved Movement-Based Location Update Scheme in Wireless Communication Networks

A movement based location update (MBLU) scheme is an LU scheme, under which a user equipment (UE) performs an LU when the number of cells crossed by the UE reaches a movement threshold. The MBLU scheme suffers from ping-pong LU effect. The ping-pong LU effect arises when the UE that moves repetitively between two adjacent cells performs LUs in the same way as in the case of straight movement. To tackle the ping-pong LU effect encountered by the original MBLU (OMBLU) scheme, an improved MBLU (IMBLU) scheme was proposed in the literature. Under the IMBLU scheme, the UE performs an LU when the number of different cells, rather than the number of cells, visited by the UE reaches the movement threshold. In this paper we develop an embedded Markov chain model to calculate the signaling cost of the IMBLU scheme. We derive analytical formulas for the signaling cost, whose accuracy is tested through simulation. It is observed from a numerical study based on these formulas that 1) the signaling cost is a downward convex function of the movement threshold, implying the existence of an optimal movement threshold that can minimize the signaling cost, and that 2) the reduction in the signaling cost achieved by the IMBLU scheme relative to the OMBLU scheme is more prominent in the case of stronger repetitiveness in the UE movement. The model developed and the formulas derived in this paper can guide the implementation of the IMBLU scheme in wireless communication networks.     

Key management protocol with end-to-end data security and key revocation for a multi-BS wireless sensor network

Focusing on a large-scale wireless sensor network with multiple base stations (BS), a key management protocol is designed in this paper. For securely relaying data between a node and a base station or two nodes, an end-to-end data security method is adopted by this protocol. Further employing a distributed key revocation scheme to efficiently remove compromised nodes then forms our key management protocol celled multi-BS key management protocol (MKMP). Through performance evaluation, we show that MKMP outperforms LEDS Ren et al. (IEEE Trans Mobile Comput 7(5):585–598, 2008) in terms of efficiency of resilience against the node capture attack. With the analysis of key storage overheads, we demonstrate that MKMP performs better than mKeying Wang et al. (A key management protocol for wireless sensor networks with multiple base stations. In: Procceedings of ICC'08, pp 1625–1629, 2008) in terms of this overhead.     

A refined cut-through buffer management scheme for layered protocolstacks

Avoiding recopying of user data as it is passed between protocol layers helps break the protocol-execution bottleneck. The authors use a use a simple pointer-variable updating technique in the sending phase of their refined buffer cut-through scheme. Binary tree traversal is not required. Time is saved in allocating (and later deallocating) buffers for storing usually short data transfer protocol headers. Their scheme saves working buffer space for segmenting and linking of protocol data units. Because a simple linked list is constructed in the receiving phase, significant working buffer space can be saved. Each node of the linked list points to a user data segment. During the linked-list traversal, user data is copied directly to the user process when a node is visited     

Investigating parametric effects on performance of a high‐temperature URSOFC

The aim of this paper is to investigate the effects of variable parameters on the performance of a unitized regenerative solid oxide fuel cell (URSOFC) using a two‐dimensional axisymmetric simulation model. This model was validated using the performance curves of an in‐house button‐type URSOFC. The parameters studied include the operating temperature and the porosity, tortuosity, and grain diameter of the electrodes while the URSOFC is operated in the solid oxide fuel cell mode and the solid oxide electrolyzer cell (SOEC) mode. The predicted results show that the temperature and the electrode porosity have a beneficial effect on the performance of the URSOFC because of an enhancement of the electrochemical reactions and the species mass transfer, respectively. However, when the URSOFC is operated in the SOEC mode, the cell performance decreases as the electrode porosity increases. This indicates that the decreasing reaction active sites as a result of the higher porosity have a dominant effect on the performance in the SOEC mode. The cell performance also decreases as the tortuosity and grain diameter of the electrodes increase. In addition, the effect of the electrode grain diameter on the cell performance is predicted to be insignificant for the URSOFC operated in the SOEC mode. The results of investigations presented in this paper can assist in the optimal design and management of a URSOFC. Copyright © 2014 John Wiley & Sons, Ltd.     

Enhancing the antioxidant activity of immature calamondin by heat treatment

The purpose of this study was to investigate the enhancing effect of heat treatment (110 and 130 °C for 0.5, 1.0, 1.5 and 2.0 h, and 150 °C for 1.5 h) on antioxidant activity and phenolic compounds of immature calamondin (Citrus mitis Blanco). The results indicated that heat treatment could enhance the 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH) scavenging potency, oxygen radical absorbance capacity (ORAC) and total phenolic content. However, the major flavonoid, 3′,5′‐di‐C‐β‐glucopyranosylphloretin (DGPP), decreased drastically after being heated at ≥130 °C over 1.5 h. The increasing ratio of absorbance at UV₄₂₀ nm coincided with the change of the antioxidant activity. Therefore, it was concluded that the browning products resulted in the increase of the antioxidant activity of immature calamondin heated at ≥130 °C over 1.5 h, while the increase of antioxidant activity at 110 and 130 °C ≤ 1.0 h heating was due to increased phenolic content.     

Investigating the transport characteristics and cell performance for a micro PEMFC through the micro sensors and CFD simulations

The local transport characteristics and the global polarization curve for a self-made micro proton exchange membrane fuel cell (PEMFC) have been experimentally and numerically investigated in this paper. The micro-sensors are developed to measure the local fluid temperature, cell voltage, and current density and the fuel cell test system is used to measure the polarization curve. A three-dimensional (3-D) non-isothermal compressible computational fluid dynamics (CFD) full-cell model is also adopted to simulate the test micro PEMFC. This CFD model has been validated with these global and local data. The ionic conductivity is increased as the water content in the membrane increases, enhancing the cell performance. This positive effect of inlet fuel humidity on the cell performance is also captured by the CFD simulation model.     

Concentric Distributed Localization Based on the Tripodal Anchor Structure and Grid Scan for Wireless Sensor Networks

Achieving high accuracy with minimum reference nodes, anchor nodes, and computation and communication costs is a goal for the localization in wireless sensor networks. Targeting at this goal, a localization scheme called concentric distributed localization with the tripodal anchor structure and grid scan (CDL-TAGS) requiring two reference nodes and a few anchor nodes is proposed in this paper. Under the precondition that the system has randomly distributed normal sensor nodes, a tripodal anchor structure is first designed. With this structure, the localization process is started from the centroid node and then stretched outward to the farthest normal nodes. Based on the two best reference nodes, a virtual point is generated to serve as the third reference node. In the CDL-TAGS scheme, a grid scan algorithm is employed to estimate the position of a normal node. Finally, we show that the communication overhead and time and space complexities among sensor nodes for CDL-TAGS can be kept at a low level. In addition, CDL-TAGS can achieve better accuracy with minimum anchor nodes as compared to some closely related localization schemes in the literature through simulation results.