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The influence of glass powder (GP) on hydration kinetics of composite cementitious materials has been investigated by isothermal calorimetry test and hydration kinetics methods in this paper. The hydration heat emission rate and hydration heat decrease gradually while the induction and acceleration period increase with the increase of GP content. According to Krstulovic-Dabic model, the hydration process of composite cementitious materials containing GP is controlled by a variety of complicated reaction mechanisms, which can be divided into three periods: nucleation and crystal growth (NG), phase boundary reaction (I), and diffusion (D). The NG and I process are shortened after incorporating GP.

Active queue management (AQM) mechanisms are designed to provide better support for end-to-end congestion control mechanisms of transmission control protocol (TCP) in TCP/IP networks. This paper introduces a stable queue-based adaptive proportional-integral (Q-SAPI) controller for AQM and presents an implementation. The starting points of our approach are the recently developed fluid-flow modeling and control theoretic interpretation of the TCP/AQM dynamics, and the recently developed fixed-gain proportional-integral (PI) controller for AQM. Q-SAPI aims to improve the transient performance of the fixed-gain PI controller while maintaining its steady-state performance over a wide range of uncertainties in round-trip time (RTT) and the number of active TCP flows. The robustness of Q-SAPI is studied in detail, which provides guidelines for selecting control parameters. Through extensive simulations, we demonstrate the ability of Q-SAPI in controlling queue length in both transient and steady states. Q-SAPI achieves this by adapting the controller gains according to the queue length.

Using a microscopic modeling approach, a simplification of the discrete element’s shape was done by using irregular convex polyhedrons to reproduce the geometry-dependent behavior of rockfills. Numerical modeling of the triaxial compression tests was conducted using a combined FEM and discrete-element method (FEM/DEM). The micromechanical properties of the numerical sample were calibrated to match the macroscopic response of the real material. The numerical results quantitatively agree with the laboratory results, which reproduce typical features of the mechanical behavior of rockfills, such as nonlinear stress-strain relationship, compaction, and shear dilatancy. The combined FEM/DEM simulation provides an opportunity for a quantitative study of the microstructure of particle assemblages, which give a better understanding of the mechanical characteristics of rockfills.

Role-based access control (RBAC) is being today's dominant access control model due to its potential to mitigate the complexity and cost of access control administration. However, the migration from the access control lists (ACL) to RBAC for a large administration system may consume significant efforts, which challenges the adoption of RBAC. Role mining algorithms can significantly reduce the migration cost by providing a partially automatic construction of an RBAC policy. This paper explores Artificial Intelligence (AI) techniques in designing role mining algorithms, which can optimize policy quality in terms of policy size, user-attribute-based interpretability of the roles, and the combination of size and interpretability. We propose two algorithms, genetic algorithm (GA)-based and ant colony optimization (ACO)-based. GA-based algorithm works by starting with a set of all candidate roles and repeatedly removing roles. ACO-based algorithm works by starting with an empty policy and repeatedly adding candidate roles. We carry out extensive experiments with publicly available access control policies. The simulation results indicate that ®the proposed algorithms achieves better performance than the corresponding existing algorithms. (2) GA-based approach produces better results than ACO-based approach.□

This paper aims to design efficient and effective approaches to virtual network embedding (VNE) problem, which deals with the embedding of a requested virtual network (VN) in an underlying physical (substrate network) infrastructure. When the node and link constraints (including CPU, memory, network bandwidth, and network delay) are both taken into account, the VN embedding problem is NP-hard, even in the offline case. The capabilities of some Artificial Intelligence (AI) techniques have been validated in handling the VN problem. In this paper, we propose two efficient and effective VNE algorithms based on differential evolutionary (DE) technique. The extensive simulation results show that DE technique performs some orders of magnitude faster than GA and PSO-based VNE algorithms in achieving the comparable long-term revenue of Infrastructure providers.

Network virtualization is being regarded as a promising technology to create an ecosystem for cloud computing applications. One critical issue in network virtualization technology is power-efficient virtual network embedding (PE-VNE), which deals with the physical resource allocation to virtual nodes and links of a virtual network while minimizing the energy consumption in the cloud data center. When the node and link constraints (including CPU, memory, network bandwidth, and network delay) are both taken into account, the VN embedding problem is NP-hard, even in the offline case. This paper aims to investigate the ability of the Ant-Colony-Optimization (ACO) technique in handling PE-VNE problem. We propose an ACO-based heuristic PE-VNE algorithm, called E-ACO. E-ACO minimizes the energy consumption by considering the embedding power consumption in the node mapping phase and by making an implicit coordination between the node and link mapping phases. Extensive simulations are conducted to evaluate the performance of the proposed algorithm and investigate different energy-aware link embedding algorithms on the ability of E-ACO.

Network virtualization technology can be applied to provide the performance guarantee by creating a virtual network for running the user application. One of the most important issues in the network virtualization is the virtual network embedding (VNE) problem, which deals with the efficient allocation of physical resources in the cloud data center to virtual networks. In this paper, we investigate the ability of simulated annealing technique in handling the VNE problem. The simulation results show that SA technique outperforms both genetic algorithm and particles swarm optimization techniques in handling the cost-aware VNE problem.

The appearance of cracks exposed to severe environmental conditions can be critical for concrete structures. The research is to validate Particle Flow Code(PFC2D) method in the context of concrete thermally-induced cracking simulations. First, concrete was discreted as meso-level units of aggregate, cement mortar and the interfaces between them. Parallel bonded-particle model in PFC2D was adapted to describe the constitutive relation of the cementing material. Then, the concrete mechanics meso-parameters were obtained through several groups of biaxial tests, in order to make the numerical results comply with the law of the indoor test. The concrete thermal meso-parameters were determined by compared with the parameters in the empirical formula through the simulations imposing a constant heat flow to the left margin of concrete specimens. At last, a case of 1000mm×500mm concrete specimen model was analyzed. It simulated the formation and development process of the thermally-induced cracks under the cold waves of different durations and temperature decline. Good agreements in fracture morphology and process were observed between the simulations, previous studies and laboratory data. The temperature decline limits during cold waves were obtained when its tensile strength was given as 3MPa. And it showed the feasibility of using PFC2D to simulate concrete thermally-induced cracking.

The virtual network embedding (VNE) problem deals with the embedding of virtual network (VN) requests in an underlying physical infrastructure (substrate network). Re-embedding of an already embedded VN may be precipitated due to failure of physical resources (nodes and/or links) in the substrate network. Our endeavor in this paper is to design a VN re-embedding algorithm to address these dynamics. Our algorithm, named OVER, minimizes the virtual node-migration cost during the active VN re-embedding process while trying to increase the long-term revenue of the infrastructure providers. We demonstrate the effectiveness of our approach through extensive simulations.

The virtual network embedding (VNE) problem deals with the embedding of virtual network (VN) requests in an underlying physical (substrate network) infrastructure. When both the node and link constraints are considered, the VN embedding problem is NP-hard, even in the offline case. The genetic algorithm (GA) is an excellent approach to solving complex problems in optimization with difficult constraints. This paper explores applying GA to handle the VNE problem. We propose two GA-based VNE algorithms and evaluate them by comparing with the existing state-of-the-art VNE algorithms, including PSO-based VNE approaches. Extensive simulation results validate the capability of the proposed GA-based VNE algorithms in terms of the InP long-term revenue and the VN embedding cost.

Integrating system-level virtualization technology with Trusted Computing technology can significantly improve system security. The open-source virtual TPM facility, shipped with the open-source hyper visor Xen, aims to provide the illusion of a physical TPM to TPM-based trusted software executed in trusted virtual machines (TVMs) such that TPM-based trusted software works well in a TVM as in a native Operating System (OS). However, it is not true for the trusted software which works in a trusted para-virtual machine (TPVM). The TPM command packets sent in the TPVM OS boot phase may cause the TPVM OS boot failure. This paper design and implement E2VT, an effective and efficient mechanism for preventing the TPVM OS boot failure while (1) being transparent to the TPVM system, (2) maintaining the original system performance, (3) making minimal modifications to the existing architecture. We validate our analysis and design through experiments.

Network virtualization is considered to be not only an enabler to overcome the inflexibility of the current Internet infrastructure but also an enabler to achieve an energy-efficient Future Internet. Virtual network embedding (VNE) is a critical issue in network virtualization technology. This paper explores a joint power-aware node and link resource allocation approach to handle the VNE problem with the objective of minimizing energy consumption. We first present a generalized power consumption model of embedding a VN. Then we formulate the problem as a mixed integer program and propose embedding algorithms. Simulation results demonstrate that the proposed algorithms perform better than the existing algorithms in terms of the power consumption in the overprovisioned scenarios.

This paper aims to defeat TCG TOCTOU attacks occurring in trusted para-virtualized machines (TPVM). We propose a robust and efficient response mechanism (RERM). Compared to the existing response mechanisms, RERM is more effective in defeating the TPVM TCG TOCTOU attacks without incurring CPU overhead during the normal system execution. We verify the security ability of RERM via both model checking based formal verification techniques and experiments.

The SRTP/ZRTP security mechanism provides a secure channel for VoIP (Voice-over-IP) traffic transmission. This paper examines the use of TCG remote attestation technique to improve the security of SRTP/ZRTP channel technology. We first generalize the security properties which a trust channel technique should have. Then we propose a trusted SRTP/ZRTP channel technique and apply model checker SPIN to verify that the proposed technique can achieve the declared security properties.

This paper proposes an integrated approach to the VNE problem, in which different virtual nodes of a virtual network could be assigned to a physical node as long as this node's available resources can satisfy the total resource requirements of these virtual nodes. We carry out extensive simulations to investigate the benefits of sharing physical nodes. The simulation results demonstrate that (1) Compared with the existing integrated VNE algorithm, the proposed algorithm performs better in terms of the VNE computing time and the VN request acceptance ratio and the Revenue-to-Cost-Ratio. (2) Compared with the existing VNE algorithms which allowed sharing physical nodes in a VN, the proposed algorithm reduces the computing time without sacrificing other performances.

LWRM was a method for defeating TCG TOCTOU attacks with less overhead during the normal system execution. However, its security capability was evaluated only through experiments. The uncertainty in real experiments may hide the design-level errors. In this paper we explore applying model checking based formal verification techniques to verify whether LWRM can achieve the declared security properties. We first propose a method of modeling LWRM, a kernel-space mechanism, in PROMELA language. Then we detect the design-level vulnerabilities by using SPIN. At last we verify our analysis via experiments and present the challenges to mitigate the vulnerabilities.

China's gross amount of hydraulic resource ranks first in the world; however, at present, China's economic development faces energy bottleneck. Huge market demands, as well as the strategy of western development, provide hydropower with an opportunity and a broad development prospect. At the same time, some negative influence on environment and ecology also give hydropower development with unprecedented challenges. However, development of hydropower is necessary because of the energy shortage and environmental pollution in China in order to attain sustainable development of China's economy. Finally, we present the typical example of Three Gorges project as hydropower development.

New methods for high concrete dam cooling by water flowing were introduced in this article. The heat-fluid coupling model, which can better simulate disposition of cooling pipe and water temperature rise along the flow, will bring more accurate simulation results of temperature field. The nonlinear creep model can better reflect the nonlinear relation between concrete creep and stress ratio of concrete. The temperature space-time dynamic control method, improving from the traditional multi-stages water cooling method, can optimize the process of temperature drop and thus decrease the thermal stress. And the computation results of high concrete dams (Guandi, Wanjiakouzi and Jinping-1 in China) show that the temperature by numerical are lit the actual monitor values. New methods of temperature simulation presented in this paper for high concrete dam will have good application prospect in practical project.

Integrated water resource management (IWRM) and its implications are presented. It is an integrated process that allows stakeholders develop water resources sustainably. Sustainable water resource system makes support long-term development, no destruction of hydrological and ecological integrity as the goal. IWRM is by the goal, institutions, implement, and adapt to reflect the merger of top-down and bottom-up approach. Large-scale adoption of IWRM is comprised of objectives, institutions, implementation, and adaptation, reflecting merging of top-down and bottom-up approaches. With the development of economy, there exists conflict between increasing demand for water and limited water resources. IWRM is a promising mechanism to better use and share water resources. In this article China is an example of implementing IWRM. The characteristics, current situation and problems of the IWRM in China are presented.

Virtualization technologies have been explored to mitigate the vulnerabilities in the current TCG architecture. But only a small number of efforts address the handling of the detected TCG TOCTOU attacks. This paper aims to defeat TCG TOCTOU attacks occurring in Xen hardware virtual machines. We propose an efficient response approach (ERA) in the environment of the Xen virtual machine monitor and the virtual TPM facility shipped with the Xen. ERA has the following features: (1) Effective in defeating the TCG TOCTOU attacks; (2) Impose less overhead on the system during normal execution; and (3) Transparent to guest virtual machines. We describe the ERA implementation in detail and evaluate its ability via experiments.

The current TCG architecture suffers from the time-of-check-to-time-of-use (TOCTOU) attacks in commodity PC operating systems (OS), in which kernel rootkits can get unrestricted access to OS resources. VMM-based approaches running at a privilege level higher than that of virtual machine (VM) kernel can effectively detect dynamic or static data attacks occurring in VMs. This paper proposes a lightweight response mechanism (LWRM) for TCG TOCTOU attacks occurring in VMs. LWRM has the following features: (1) compared to the existing response mechanism, LWRM is more effective in defeating the TCG TOCTOU attacks; (2) LWRM imposes less overhead on the system during normal execution; (3) LWRM is transparent to the kernel rootkits; and (4) LWRM can work in the scenarios with more than one run-time trusted virtual machine. We describe the design idea and the implementation by using the Xen virtual machine monitor (VMM) and the virtual TPM facility shipped with the Xen.

Interrupt coalescing (IC) technique has been used in general-purpose operating systems to mitigate receive livelock (RL) problem in gigabit Ethernet network hosts. Schemes for dynamically tuning the interrupt coalescing behavior of a communication interface based on traffic load or system state have been proposed. However, all the existing IC schemes are designed using heuristics. In this paper we present an analytical model for the IC technique and carry out a detailed study of existing IC schemes in terms of their performance characteristics including system goodput, CPU consumption and latency. We validate our analysis through measurement-based experiments.

Gigabit Ethernet is now finding wider deployment in computer networks. The conventional operating system suffers from the receive livelock problem in Gigabit Ethernet networks. The device hybrid (interrupt + polling) scheme has been widely used to overcome this problem in current operating systems such as GNU/Linux and FreeBSD. However, controlling the polling time without regard to the system state can degrade the ability of a hybrid scheme in some situations. This paper focuses on the system performance of the operating systems that employ the device hybrid scheme in kernel space. A queue-based adaptive polling (QAPolling) scheme is introduced that: (1) significantly improves system goodput and reduces packet loss over a wide range of computer hardware configurations and traffic conditions, (2) is scalable and easily deployed. The key idea behind QAPolling is to adjust the polling time adaptively according to the information of the application receiving queues, which are in kernel space and change with the system state, instead of the packet arrival rate. We validate our design through experimental results in Gigabit Ethernet networks.

Research studies have uncovered the unfair WLAN bandwidth distribution between uplink and downlink TCP flows in the infrastructure WLAN using the distributed coordination function mode. Different mechanisms at or above the MAC layer have been proposed for handling this problem. This paper presents a simple but effective approach in order to achieve the fair distribution by using an adaptive queue management mechanism to manage the queue between the logic link and MAC layers at the access point. Extensive simulation results show that this approach outperforms other mechanisms discussed in the literature over a wide range of network scenarios in terms of fair distribution, small delay, and high WLAN bandwidth utilization

Recent research studies in over-provisioned networks have shown that the assured forwarding (AF) service in the current differentiated services (DiffServ) architecture fails to provide bandwidth assurance in some situations. The paper focuses on the situation where adaptive and non-adaptive traffic coexist in the same real queue at routers and the buffer management scheme treats the traffic of the same priority in the same AF class indiscriminately. An enhanced RIO is introduced, which, without excessively penalizing non-adaptive flows, can: (1) significantly improve bandwidth assurance of adaptive AF flows; (2) alleviate the starvation imposed on adaptive best-effort flows. These goals are achieved by doing the following when the failure of bandwidth assurance is detected: (1) mapping adaptive OUT traffic and non-adaptive OUT traffic to different virtual queues; (2) adapting the queue length thresholds according to whether bandwidth assurance is achieved. We validate our design through simulations.

Several active queue management (AQM) mechanisms have been proposed in the literature to provide better support for congestion. However, their performance is examined mainly in best-effort networks. In this paper, we present an empirical study of the effects of these AQM mechanisms on the performance of Assured Forwarding (AF) Services in the Differentiated Services (DiffServ) framework. In addition, we investigate the interaction of AQMs with intelligent traffic conditioners. The major conclusions from our study are: (1) When the standard traffic conditioner is used, the transient response and the ability of controlling queue length of an AQM scheme not only affect the achievement of bandwidth assurance, but also affect the attainment of excessive bandwidth and link throughput. (2) The behaviors of an AQM affect the ability of intelligent traffic conditioners. (3) Rate-based AQM schemes perform better than queue-based AQM schemes; self-tuning AQM schemes perform better than AQMs with fixed-gains in terms of the above performance metrics.

Significant research effort has been devoted to designing robust active queue management (AQM) mechanisms for the Internet, with mixed results. In this paper, we apply sliding mode control theory plus integral control to design a robust controller for AQM, which stabilizes the instantaneous queue length around the desired value with fast transient response over a wide range of network dynamics. We validate our design through extensive simulations and compare its performance with some AQM mechanisms published in the literature.

The assured forwarding (AF) based service in a differentiated services (Diffserv) network fails to provide bandwidth assurance to aggregates in some circumstances. Several intelligent marking mechanisms have been proposed in the literature to improve bandwidth assurance for aggregates using the knowledge gathered at the ingress nodes. In this paper, we apply a control theoretic approach to this problem. We design a nonlinear proportional-integral (NPI) controller, called NPI-ACT, for adapting the CIR threshold. Performance results using extensive simulations demonstrate significant improvement using NPI-ACT in achieving bandwidth assurance over a wide range of network conditions compared to earlier mechanisms proposed in the literature.

In this paper, we consider two fairness problems (downlink/uplink fairness and fairness among flows in the same direction) that arise in the infrastructure WLAN. We propose a virtual queue management approach, named VQ-RED to address the fairness problems. We demonstrate the effectiveness of our approach by conducting a series of simulations. The results show that compared with standard DCF, VQRED not only greatly improves the fairness, but also reduces packet delays

Recent research studies have shown that assured forwarding (AF) service in the current differentiated services (Diffserv) framework does not provide bandwidth assurance in some circumstances. This paper proposes an adaptive marking threshold mechanism, called adaptive CIR threshold (ACT), which aims to improve bandwidth assurance for aggregate flows sharing the same AF class only based on local knowledge. Extensive simulation results demonstrate significant improvement with ACT in bandwidth assurance under various conditions: different round trip times (RTT), different numbers of micro-flows in an aggregate, different target rates, different packet sizes, and the presence of non-adaptive flows, compared with earlier mechanisms proposed in the literature.

Recent research studies have shown that assured forwarding (AF) service in the current differentiated services (Diffserv) framework does not provide bandwidth assurance in some circumstances. This paper proposes a mechanism, called Adaptive CIR+PIR Threshold (ACPT), which improves bandwidth assurance and domain throughput simultaneously. Extensive simulation results demonstrate significant improvement with ACPT in bandwidth assurance and domain throughput under various conditions: different round trip times (RTT), different numbers of micro-flows in an aggregate, different target rates, different packet sizes, and the presence of nonadaptive flows, compared to other mechanisms proposed in the literature.

In this paper a simple robust proportional-integral (R-PI) controller is proposed for active queue management (AQM). We assume that TCP/AQM dynamics can be described by the linearized TCP/AQM model (C. V. Hollot et al., April 2001). R-PI aims to address the tradeoff between responsiveness and stability and the tradeoff between responsiveness and high link utilization over a large range of structured and unstructured uncertainties. This controller achieves these goals by varying its control parameters according to the system state. We show that the closed-loop system is asymptotically stable as long as the control parameters are time-invariant and varying in a range. Extensive simulation results demonstrate the robust ability of R-PI compared with some other AQM mechanisms in the literature.

Availability evaluation of a virtualized system is critical to the wide deployment of cloud computing services. Time-based, prediction-based rejuvenation of virtual machines (VM) and virtual machine monitors, VM failover and live VM migration are common high-availability (HA) techniques in a virtualized system. This paper investigates the effect of combination of these availability techniques on VM availability in a virtualized system where various software and hardware failures may occur. For each combination, we construct analytic models rejuvenation mechanisms to improve VM availability; (2) prediction-based rejuvenation enhances VM availability much more than time-based VM rejuvenation when prediction successful probability is above 70%, regardless failover and/or live VM migration is also deployed; (3) failover mechanism outperforms live VM migration, although they can work together for higher availability of VM. In addition, they can combine with software rejuvenation mechanisms for even higher availability; (4) and time interval setting is critical to a time-based rejuvenation mechanism. These analytic results provide guidelines for deploying and parameter setting of HA techniques in a virtualized system.