Study of the phase-varying mechanisms of ion current signals for combustion phasing in a gasoline HCCI engine

This work was supported by National Basic Research Priorities Program (973) of China under the Grant reference of 2007CB 210005.The phase-varying mechanism of the ion current observed in a Homogeneous Charge Compression Ignition (HCCI) engine is investigated to achieve ion current-based combustion phasing. By integrating the gasoline flame ionization mechanism with the HCCI combustion model, the mechanisms affecting the ion formation and recombination processes are analyzed, and the relationship between the phases of ion current and combustion event is studied. Modeling results indicate that the formation rate of H 3 O + ions is mainly affected by the combustion boundary conditions. However, the ion recombination rate of H 3 O + ions is mainly dependent on the concentration of these ions. In the presence of the above mechanisms, the phase-varying tendency of the ion current is found to be similar to the variations in the combustion phase, but the offset between these phases will vary when the combustion boundary condition changes. As the equivalence ratio becomes low, the rate of H 3 O + formation is decreased and the ion recombination rate decreases even more, due to the reduced ion concentration. Therefore, the inflection point of the ion current curve, dI max , is retarded even further compared to the combustion phase CA50. In addition, a larger phase offset between dI max and CA50 is observed when the intake temperature is lower. All of the above modeling predictions agree well with the experimental results

Schemes for Surviving Advanced Persistent Threats

Mission critical systems are prevalent in the military and industry which renders them attractive as targets for security attacks. Their constantly increasing structural complexity contributes to benign faults and further facilitates malicious entities. Over the years, these malicious entities in cyber-space have grown smarter and extremely resourceful. Advanced persistent threats (APT) is a clear example of this growing sophistication. APTs are characterized by extreme stealth, advanced skill-set, vast resources and a markedly high success rate. Consequently, mission survivability has become an essential necessity for today's mission critical systems. Most existing survivability solutions are simple combinations of traditional security measures such as network monitoring, firewalls, etc. These solutions increase the cost of attacks but do not necessarily decrease the probability of a compromise substantially. This calls for further advancement of current mission survivability solutions. The focus of this dissertation is the robust designing and efficient deployment of an effective mission survivability solution. Such a solution must be capable of withstanding APT, one of the hardest threats encountered in recent times. The solution presented for this purpose relies upon the understanding of attacker intent, objectives and strategies (AIOS). AIOS aids in the designing of better recovery and adaptation procedures for enhanced survivability. This solution has centralized and distributed versions with hardware-support to hide and safeguard information from the adversaries. This provides it with the capability to deceive and quietly monitor the cyber space. Hardware-support is provided by either modifying the test-logic of the underlying processor or using the trusted platform module (TPM) that is integral to the processor. The solution also ensures the tamper-resistance of its critical security components which is achieved by employing the principle of coveillance and concepts from graph theory. Another important feature is its capability to effectively and efficiently detect zero-day attacks in a production environment. This is accomplished by carefully planned deployment and real-time customization of honeypots. Each design choice and the techniques employed are thoroughly tested and validated via simulation and experimentation. Strong security and tamper-resistant properties, along with its efficiency, could make it a good survivability strategy against APT for which no good solutions currently exist