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[[abstract]]A number of researches on real-time databases have focused on systems where the semantics of transaction time constraints include only deadlines or values that are constant during a transaction's life time. For some real-time applications, the values of transaction may change dynamically with time. Under such circumstances, existing real-time scheduling algorithms may not be applicable. A new real-time scheduling algorithm that can efficiently schedule transactions with time-variant values is proposed. By exploiting the estimated execution time of transactions to estimate the expected values of transactions at completion time, the proposed algorithm can generate a better priority ordering of transactions than the existing algorithms. Moreover, a concurrency control protocol based on conditional-restart is also proposed to r...
[[abstract]]In a real-time application, a transaction may be assigned a value to reflect the profit of completing the transaction before its deadline. Satisfying both goals of maximizing the totally obtained profit and minimizing the number of missed transactions at the same time is a challenge. In this paper, we present an adaptive real-time scheduling policy named Value-based Processor Allocation (VPA-k) for scheduling value-based transactions in a multiprocessor real-time database system. Using VPA-k policy, the transactions with higher values are given higher priorities to execute first, while at most k percentage of total processors are dynamically allocated to execute the urgent transactions. Through simulation experiments, VPA-k is shown to outperform other scheduling policies substantially in both maximizing the totally obtaine...
[[abstract]]In this paper, we motivate the need for efficient multisignature schemes in delegated mobile services. With the schemes, delegates can be identified and delegated accesses can be controlled. First, we give a new digital signature scheme with message recovery. Based on the digital signature scheme, two digital multisignature schemes are proposed: the parallel multisignature scheme and the serial multisignature scheme. The parallel multisignature scheme allows each user to sign the same message separately and independently, and then combines all individual signatures into a multisignature. The serial multisignature scheme allows a group of users to sign the message serially, and does not need to predetermine the signing order. Both multisignature schemes can withstand the attacks that aim to forge the signatures or to get the...
Using the method of sequential limit analysis (SLA), a general computer program for large deformation of three dimensional frame structures has been developed. This method treats each step in the sequence as a limit analysis problem and solves it by a dual variational principle. The structure is then updated for changes in its material property (hardening or softening) and geometrical configuration. Another step is computed after the updating. The steps form a sequence leading to large deformation solutions. In the case when the yield criterion are simple bounds on the generalized stress components, a special linear program algorithm provides added efficiency. Several medium size examples (about 200 variables) are solved to verify the accuracy and efficiency. Solutions are obtained for an arch, a ring (2D) and a car frame (3D) under va...
A new method, Sequential Limit Analysis, has been developed for solving large plastic deformation problems of metal both in plane strain and axisymmetric conditions. This method is a modern limit analysis that employs a duality theorem to equate the least upper bound to the greatest lower bound and uses mathematical programming techniques to search for optimal solutions. It involves no complex stress calculations. It can treat material property nonlinearly by updating local yield criteria step by step and has the advantage of global stability of computation even in the case of increasing deformation under decreasing load. It can also treat frictional contact phenomena easily because this method is explicit in nature. Moreover, it is mathematically concise and computationally easy to implement. To verify the capability of this new metho...
A new general algorithm for three dimensional analysis in metal forming processes has been developed and applied to the three dimensional rolling process. This new general algorithm, based on the duality theorem, equates the greatest lower bound and the least upper bound. First, the metal forming problem is analyzed to obtain a primal lower bound formulation which satisfies the equilibrium equations,the yield criterion, and the static boundary conditions. Then, a dual upper bound formulation is derived from the primal lower bound formulation by the duality theorem. Plastic incompressibility is then introduced into the upper bound formulation when the generalized Holder inequality is employed. Using the finite element method, the infinite dimensional space of the upper bound formulation is approximated in a finite dimensional space. The...
Problems of mechanics are governed by three fundamental principles namely: equilibrium (the statically admissible set S), kinematics of deformation (the kinematically admissible set K) and constitution of materials (the constitutively admissible set C). They are modeled by equations or other representations so that a mechanics problem can be formulated and solved by a certain technique. When this representations are in the form of sets in an appropriate space, a methodology for solving a problem becomes a search for the intersection of these three fundamental sets. Limit analysis is convex analysis and it studies the solutions in the intersections of two of these three sets. The Lower bound solution lies in the set $S\ \cap\ C$ and the Upper bound solution lies in the set K. The duality theorem establishes that the least Upper bound so...
This work was aimed to improve the generation of daily precipitation time series with information from atmosphere. The motivation is to develop a conditional stochastic downscaling model to well describe temporal and spatial behavior of local precipitation, in particular, the extreme rainfall events. Thereafter, the generated daily precipitation can be applied to integrate with other water-related models for climate impact studies. Global warming has been concerned since the end of last century. The increase of the temperature may result in various consequences, which may further cause the changes in agricultural production, water resources distributions and so on. Therefore, the impact studies must be carried out to understand the influence of the changing climate and predict its possible consequences in order to mitigate and adapt t...
High throughput screening techniques that are routinely used in modern drug discovery processes result in a higher prevalence of poorly water-soluble drugs. Such drugs often have poor bioavailability issues due to their poor dissolution and/or permeability to achieve sufficient and consistent systemic exposure, resulting in sub-optimal therapeutic efficacies, particularly via oral administration. Alternative formulations and delivery routes are demanded to improve their bioavailability. Nanoparticulate formulations of poorly water-soluble drugs offer improved dissolution profiles. The physiology of the lung makes it an ideal target for non-invasive local and systemic drug delivery for poorly water-soluble drugs. In Chapter 2, a particle engineering process ultra-rapid freezing (URF) was utilized to produce nanostructured aggregates of ...
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