505 research outputs found
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A risk analysis methodology for micro/nano manufacturing
This research concerns the development of a risk analysis and mitigation methodology for assessing the impact of uncertainties and complexity of the design requirements arising in new process and product developments in micro and nano manufacturing. The risk analysis methodology integrates different computational approaches for process and product analysis, including the reduced order modelling using design of experiments, risk analysis using sampling-based and analytical methods and optimisation techniques. The integrated risk analysis and optimisation methodology is applied to two applications: (1) the FIB sputtering process control, and (2) a flip chip design. Three different FIB processes using different ion sources were investigated in order to evaluate their process performance with respects to different process parameter uncertainties. A critical comparison of the process capability against the specification limits of different processes was studied.
As parts of the research, a new modified computational model is developed for a material sputtering process using focused ion beam (FIB). This model allows the analysis of micro- and nano-structures shape with the FIB machine controlled through multiple beam scans and different beam overlapping. The FIB model related studies also address the modelling requirements for including material re-deposition effects that occur during FIB milling. The model has been validated using an experimental test case. Good agreement is observed between the analytical shape using the model and the actual experiment. The validated model enhances the accuracy of the dwell time prediction. This approach overcomes the dependence of a trial-and-error approach of the process control in nano-manufacturing industry.
The proposed methodology is also used to address a design problem of a flip chip design. A novel method for the evaluation of the environmental impact of the flip chip design in a multi-disciplinary optimisation problem is proposed. The goal is to address materials constraints due to environmental regulations and to handle different types of requirements such as the reliability and cost. An optimal flip chip design reliability function is identified. The approach allows electronics manufacturers to consider the environmental impact amongst different design alternatives at an early stage of the design of the product before any real prototyping in order to reduce the total manufacturing life cycle
Greater Uniformity and Centralization: The Regulatory Development of Chinese Food and Product Safety under the WTO
The WTO Agreements emphasize free trade, which links with diversity, deregulation, and decentralization. China, on the other hand, emphasizes uniformity and centralization, especially regarding the political control and the one-party system of “democratic dictatorship.” China’s joining the WTO, therefore, may be considered as a development that changes the regulatory structure to become more diverse, deregulated, and decentralized. This paper, however, finds the opposite. Under the WTO law, China is encouraged to move towards greater uniformity and centralization with its decentralized and non-uniform settings under the market policy. Moreover, the WTO’s uniform and centralized encouragements can be integrated into the rule-by-man framework to increase the administrative and economic power of the Party. It is thus unclear whether China’s food and product safety problem can be solved
Full-Duplex Cloud Radio Access Network: Stochastic Design and Analysis
Full-duplex (FD) has emerged as a disruptive communications paradigm for
enhancing the achievable spectral efficiency (SE), thanks to the recent major
breakthroughs in self-interference (SI) mitigation. The FD versus half-duplex
(HD) SE gain, in cellular networks, is however largely limited by the
mutual-interference (MI) between the downlink (DL) and the uplink (UL). A
potential remedy for tackling the MI bottleneck is through cooperative
communications. This paper provides a stochastic design and analysis of FD
enabled cloud radio access network (C-RAN) under the Poisson point process
(PPP)-based abstraction model of multi-antenna radio units (RUs) and user
equipments (UEs). We consider different disjoint and user-centric approaches
towards the formation of finite clusters in the C-RAN. Contrary to most
existing studies, we explicitly take into consideration non-isotropic fading
channel conditions and finite-capacity fronthaul links. Accordingly,
upper-bound expressions for the C-RAN DL and UL SEs, involving the statistics
of all intended and interfering signals, are derived. The performance of the FD
C-RAN is investigated through the proposed theoretical framework and
Monte-Carlo (MC) simulations. The results indicate that significant FD versus
HD C-RAN SE gains can be achieved, particularly in the presence of
sufficient-capacity fronthaul links and advanced interference cancellation
capabilities
Energy-Efficient Heterogeneous Cellular Networks with Spectrum Underlay and Overlay Access
In this paper, we provide joint subcarrier assignment and power allocation
schemes for quality-of-service (QoS)-constrained energy-efficiency (EE)
optimization in the downlink of an orthogonal frequency division multiple
access (OFDMA)-based two-tier heterogeneous cellular network (HCN). Considering
underlay transmission, where spectrum-efficiency (SE) is fully exploited, the
EE solution involves tackling a complex mixed-combinatorial and non-convex
optimization problem. With appropriate decomposition of the original problem
and leveraging on the quasi-concavity of the EE function, we propose a
dual-layer resource allocation approach and provide a complete solution using
difference-of-two-concave-functions approximation, successive convex
approximation, and gradient-search methods. On the other hand, the inherent
inter-tier interference from spectrum underlay access may degrade EE
particularly under dense small-cell deployment and large bandwidth utilization.
We therefore develop a novel resource allocation approach based on the concepts
of spectrum overlay access and resource efficiency (RE) (normalized EE-SE
trade-off). Specifically, the optimization procedure is separated in this case
such that the macro-cell optimal RE and corresponding bandwidth is first
determined, then the EE of small-cells utilizing the remaining spectrum is
maximized. Simulation results confirm the theoretical findings and demonstrate
that the proposed resource allocation schemes can approach the optimal EE with
each strategy being superior under certain system settings
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