Phase stability in steels under electropulsing

There are increasing interests to alternate the microstructure and hence the properties of steels that are applied in various environment conditions using a work-efficient and energy-saving manner. The desirable microstructure evolution is often not achievable by means of conventional thermo-mechanical processing and solid-state phase transition. This thesis has considered four fundamental engineering problems, namely (i) the possibility of anti-aging processing for the aged steels in service at high temperature, (ii) the recovery of the lost strength for the steels at high temperature, (iii) the suspension of crack initiation and propagation during cold-working of steels with eutectoid microstructures and (iv) the regaining of strength during tempering of a steel containing martensite. Phase stability in the processing environment is the primary concern in each of the list problems because it presents, in thermodynamically, the possibility to achieve the goals using the designed processing. Electropulsing processing has been considered and integrated with the conventional thermomechanical processing in the development of this PhD thesis. The so-called electropulsing treatment utilises electric current pulses with high peak current density and short pulse duration. Due to the nature of the short duration pulse, the energy consumption is very low. The high current density enables a very strong impact of electropulsing on the microstructure evolution and hence is work efficient. Following results have been obtained through the study： • Using the appropriate electropulsing parameters, the formed secondary phase (e.g. χ-phase) by precipitation in 316L stainless steels at elevated temperature can be dissolved. Electropulsing processing can supress the precipitation and homogenize the alloying elements in the stainless steel. The stability of the secondary phases in the stainless steel has been changed by the imposed electropulse. • Electropulsing treatment is able to alternate the delta-ferrite phase transition. This has been proved in the treatment of 2205 duplex stainless steel. The new format of phase transition causes strengthening of the steel at high temperature. The stability of phases in the steel has been affected by the applied electropulsing treatment. • For the light steels containing high aluminium composition, electropulsing is able to affect the thermodynamic stability and grain morphology of κ-carbide. This leads to significant improvement of steel formability. • Application of electropulsing processing to dual-phase automotive steel changes the stability of martensite phase. The processing improve the mechanical properties and refined the microstructure of this steel. The fundamental understanding of the experimental observations has been developed based on the thermodynamic and kinetic analysis.Open Acces

Preserving Trustworthiness and Confidentiality for Online Multimedia

Technology advancements in areas of mobile computing, social networks, and cloud computing have rapidly changed the way we communicate and interact. The wide adoption of media-oriented mobile devices such as smartphones and tablets enables people to capture information in various media formats, and offers them a rich platform for media consumption. The proliferation of online services and social networks makes it possible to store personal multimedia collection online and share them with family and friends anytime anywhere. Considering the increasing impact of digital multimedia and the trend of cloud computing, this dissertation explores the problem of how to evaluate trustworthiness and preserve confidentiality of online multimedia data. The dissertation consists of two parts. The first part examines the problem of evaluating trustworthiness of multimedia data distributed online. Given the digital nature of multimedia data, editing and tampering of the multimedia content becomes very easy. Therefore, it is important to analyze and reveal the processing history of a multimedia document in order to evaluate its trustworthiness. We propose a new forensic technique called ``Forensic Hash", which draws synergy between two related research areas of image hashing and non-reference multimedia forensics. A forensic hash is a compact signature capturing important information from the original multimedia document to assist forensic analysis and reveal processing history of a multimedia document under question. Our proposed technique is shown to have the advantage of being compact and offering efficient and accurate analysis to forensic questions that cannot be easily answered by convention forensic techniques. The answers that we obtain from the forensic hash provide valuable information on the trustworthiness of online multimedia data. The second part of this dissertation addresses the confidentiality issue of multimedia data stored with online services. The emerging cloud computing paradigm makes it attractive to store private multimedia data online for easy access and sharing. However, the potential of cloud services cannot be fully reached unless the issue of how to preserve confidentiality of sensitive data stored in the cloud is addressed. In this dissertation, we explore techniques that enable confidentiality-preserving search of encrypted multimedia, which can play a critical role in secure online multimedia services. Techniques from image processing, information retrieval, and cryptography are jointly and strategically applied to allow efficient rank-ordered search over encrypted multimedia database and at the same time preserve data confidentiality against malicious intruders and service providers. We demonstrate high efficiency and accuracy of the proposed techniques and provide a quantitative comparative study with conventional techniques based on heavy-weight cryptography primitives

Charmless decays B -> PP, PV, and effects of new strong and electroweak penguins in Topcolor-assisted Technicolor model

Based on the low energy effective Hamiltonian with generalized factorization, we calculate the new physics contributions to the branching ratios and CP-violating asymmetries of the two-body charmless hadronic decays $B \to PP, PV$ from the new strong and electroweak penguin diagrams in the TC2 model. The top-pion penguins dominate the new physics corrections, and both new gluonic and electroweak penguins contribute effectively to most decay modes. For tree-dominated decay modes $B \to \pi \pi, \rho \pi, etc,$ the new physics corrections are less than 10%. For decays $B \to K^{(*)} \pi$, $K^{(*)} \eta$, $etc$, the new physics enhancements can be rather large (from $- 70$ to $\sim 200$) and are insensitive to the variations of $N_c^{eff}$, $k^2$, $\eta$ and $m_{\tilde{\pi}}$ within the reasonable ranges. For decays $B^0 \to \phi \pi$, $\phi \eta^{(')}$, $K^* \bar{K}^0$ and $\rho^+ K^0$, $\delta {\cal B}$ is strongly $N_c^{eff}-$dependent: varying from -90% to $\sim 1680$ in the range of $N_c^{eff}=2-\infty$. The new physics corrections to the CP-violating asymmetries ${\cal A}_{CP}$ vary greatly for different B decay channels. For five measured CP asymmetries of $B \to K \pi, K \eta', \omega \pi$ decays, $\delta {\cal A}_{CP}$ is only about 20% and will be masked by large theoretical uncertainties. The new physics enhancements to interesting $B \to K \eta'$ decays are significant in size ($\sim 50$), insensitive to the variations of input parameters and hence lead to a plausible interpretation for the unexpectedly large $B \to K \eta'$ decay rates. The TC2 model predictions for branching ratios and CP-violating asymmteries of all fifty seven $B \to PP, PV$ decay modes are consistent with the available data within one or two standard deviations.Comment: Latex file, 56 pages with 11 ps and eps figures. to be published in Eur.Phys.J.

Behavior of pile group foundation for offshore wind generator

As one of the most promising clean energy, offshore wind power attracted increasing attention recently. A lot of large-scale offshore wind generators were constructed in many countries. Large-diameter single pile was commonly used as the foundation for the wind generator. Its deformation and bearing capacity were investigated using different approaches. Field tests were conducted to observ

Determinants of Entrepreneurial Intentions among the College Students in: China and Pakistan

We are using Shapero and Sokol Model of Entrepreneurial Event (SEE) (Shapero, 1982)  as base of conceptual framework, for accreditation of performance of the college students, to see the impact of propensity to act, perceived desirability and perceived feasibility on entrepreneurial intention. It’s a bi-country study looking deep toward the factors impact entrepreneurial intentions among college student in China and Pakistan using Structural Equation Model (SEM) technique. We revealed that work experience is playing no significant role in the formation of entrepreneurial intentions in both nations; family business background got positive impact on intention in Pakistan but not in China. Family income is not playing any significant positive role in both nations. Keywords: Entrepreneurship, Determinants, College, Education, China, Pakista