A graph‐based postoptimization approach for covering arrays

Covering arrays (CAs) are combinatorial objects with interesting features that have practical applications such as experimental design and fault detection in hardware and software. We introduce a graph‐based postoptimization (GBPO) approach to reduce the size of CAs exploiting the redundancy in CAs previously constructed. To evidence the advantages of using GBPO, we have instantiated it with 2 sets of CAs: (1) 560 CAs of strength 2≤t≤6, alphabet 2≤v≤6, and parameters 3≤k≤32 generated by an optimized version of In‐Parameter‐Order‐Generalized (IPOG‐F) and GBPO improved all CAs, and 37 cases matched the best‐known upper bounds; and (2) 32 CAs of strength t=2, alphabet 3≤v≤6, and number of parameters 8≤k≤146; in this set, 16 cases were improved, and 16 cases were matched.     

A simple model‐based nonlinear control strategy for feedback linearizable nonlinear processes

Abstract

In this paper we propose a simple and novel model‐based nonlinear control strategy for feedback linearizable nonlinear processes. The nonlinear controller, called NLC, has a forward static nonlinear element and, if the relative degree of the process is greater than unity, a linear dynamic feedback path. The nonlinear static element is a modified hyperbolic function which involves two tunable parameters used to adjust the linear gain and saturation level of the NLC. The NLC parameters are determined to achieve a desired tracking transfer function of the form (K_cs + 1)/(1 + ?s) ^r+1 where K_c and ? are parameters relating to NLC controller settings and r the system's relative degree. The effectiveness and applicability of the proposed nonlinear control strategy are demonstrated through the controls of nonlinear chemical processes. Extensive simulation results show that the proposed nonlinear control strategy is a robust model‐based approach for the nonlinear control of dynamic processes.     

A minimum zone method for evaluating flatness error of gage blocks measured by phase‐shifting interferometry

Abstract

A new method called “Control Plane Rotation Scheme (CPRS)” has been developed here for the analysis of flatness error in terms of the minimum zone definition, which conforms to the ISO/R1101 specification. An application of the phase‐shifting interferometry was performed for on‐line measurement of gage blocks. Experimental results were quite consistent with the specified grade of the inspected gage block with only an uncertainty of up to 0.005 μm.     

Semantic software metrics computed from natural language design specifications

An approach using semantic metrics to provide insight into software quality early in the design phase of software development by automatically analysing natural language (NL) design specifications for object-oriented systems is presented. Semantic metrics are based on the meaning of software within the problem domain. In this paper, we extend semantic metrics to analyse design specifications. Since semantic metrics can now be calculated from early in design through software maintenance, they provide a consistent and seamless type of metric that can be collected through the entire lifecycle. We discuss our semMet system, an NL-based program comprehension tool we have expanded to calculate semantic metrics from design specifications. To validate semantic metrics from design specifications and to illustrate their seamless nature across the software lifecycle, we compare semantic metrics from different phases of the lifecycle, and we also compare them to syntactically oriented metrics calculated from the source code. Results indicate semantic metrics calculated from design specifications can give insight into the quality of the source code based on that design. Also, these results illustrate that semantic metrics provide a consistent and seamless type of metric that can be collected through the entire lifecycle.     

Addressing for letter‐oriented keys

Abstract

This paper presents a new algorithm for hashing. In this approach each key (x, y) is denoted as a pair of letters, and it is extracted from each letter‐oriented key in the key space according to a certain pre‐determined extraction algorithm. For the keys (x, y), our hashing function hashes as follows:

These functions allow single probe retrieval from minimally sized space of letter‐oriented keys. Various areas can be applied, such as searching reserved words in compilers and filtering frequently used words in natural language processing.     

Uncertainty management in a process environment

Abstract

Software systems are developed by software projects. A software project generally associates with a process (software development process). A software project's process can be managed by process‐centered software engineering environments (PSEEs). In other words, PSEEs facilitate monitoring software projects. When a software project is being executed, many details may be uncertain in the early phases of the project. Therefore, managing uncertainty of a project's process becomes necessary. We identified existing approaches that can manage process uncertainty. Nevertheless, existing approaches suffer from drawbacks such as resource wasting. We thus propose two new approaches, which are pre‐defined semantics and incremental process program development. The former approach prevents duplicating the same code in a process program and the latter handles both predictable and unpredictable process uncertainty. This paper primarily presents the new approaches.     

Performance comparisons of index‐based communication‐induced checkpointing protocols

Abstract

Communication‐induced checkpointing (CIC) protocols can be used to prevent the domino effect. Such protocols that belong to the index‐based category have been shown to perform more efficiently. In this paper, some results of comparing index‐based CIC protocols are proposed. First, we prove that comparing several protocols based on the lazy indexing strategy can be simply based on their checkpoint‐inducing conditions. Next, we show that improved indexing strategies may not always yield a better performance than the classical strategy. Finally, we present a simulation study to verify our foregoing theoretical results. The simulation is conducted in the typical point‐to‐point computational environment. Influences of enhancements on indexing strategies and checkpoint‐inducing conditions for index‐based CIC protocols are discussed.     

D‐Stability analysis for discrete delay systems

Abstract

This paper discusses the D‐pole placement problem of discrete time‐delay systems where the delay duration can be any positive integer. One sufficient condition is proposed to insure all the closed‐loop eigenvalues of discrete delay systems be located inside a specific disk D(α, r). Several criteria are used to retain all the eigenvalues of discrete delay systems with structured or unstructured parametric perturbations inside the same disk. Finally, some illustrative examples are given to demonstrate our results.     

Design of an adjustable‐way cache for energy reduction

Abstract

Conventional set‐associative caches, with higher associativity, provide lower miss rates. However, they suffer from longer hit access time and larger energy dissipation. Based on the consideration of different program localities, programs should have their own appropriate associativity of caches. In this paper, we propose a set‐associative cache that can provide flexibilities to adjust its associativity according to different program behaviors, which means that the proposed cache scheme can be adjusted from an n‐way set‐associative cache to a direct‐mapped cache. By use of this cache architecture, power consumption can be lowered when an n‐way set‐associative cache configures the cache with lower associativity (less than n) due to only enabling fewer subarrays of the tag memory and data memory. However, the performance is still maintained at the same level as in a conventional set‐associative cache or direct‐mapped cache. Adjustable‐way set‐associative caches can also be applied to multiprocessor systems to reduce the average, overall system, energy dissipation.     

Materials Specification and Analytical Measurement Precision

Abstract

Chemical manufacturing processes are often sensitive to changes in conditions and minor components, for which there may be limited data and no simple relationships. The product specialist has the dilemma of basing raw materials and process specifications either on current practice or intuitive experience, without adequate knowledge that their attainment will ensure the product’s fitness for use.

However, a natural reaction is to demand increasingly tighter specifications and measures of the process capabilities involved. A judgement has to be made of the acceptable level of variability in the measuring process, in relation to the overall variability of the factor to be controlled. There is empirical evidence to suggest that there are limits on the precision to which analytical measurements can be taken and the application of process capability indices may be inappropriate when applied to chemical specifications.

To avoid the false security of over-tight specification limits, which cannot be meaningfully monitored, it is suggested that the specification process should start from the best practical estimate of the test capability for the measurement of the parameter or component being considered. From this, the raw material or process parameter specifications can be calculated, taking account of the balance of risk between the supplier and user.

Departure from specification would then have a basis of veracity and be less likely the subject of the random combination of chance effects. It would highlight areas in which there was a need for a real breakthrough in analytical technique or more robust product design.     

One‐sided Process Capability Assessment in the Presence of Measurement Errors

In the manufacturing industry, many product characteristics are of one‐sided specifications. The well‐known process capability indices C_PU and C_PL are often used to measure process performance. Most capability research works have assumed no measurement errors. Unfortunately, such an assumption is not realistic even if the measurement is conducted using highly sophisticated advanced measuring instruments. Therefore, conclusions drawn regarding process capability are not reliable. In this paper, we consider the estimation and testing of C_PU and C_PL with the presence of measurement errors, to obtain adjusted lower confidence bounds and critical values for true process capability, which can be used to determine whether the factory processes meet the capability requirement when the measurement errors are unavoidable. Copyright © 2005 John Wiley & Sons, Ltd.     

An efficient access control scheme for files protection

Abstract

A dynamic access control mechanism suitable for hardware implementation is proposed. Each file is safeguarded by q lock values, where q is number of the possible access classes. The access right of a user to some file can be revealed very efficiently. In addition, dynamic operations such as changing a privilege value, insertion or deletion of a user, and insertion or deletion of a file can be done easily. Compared to Wu and Hwangs’ and Chang's methods, the computation of lock values is simple and the verification of an access request is quite efficient. The storage required is proportional to m?n which is less than that of the above‐mentioned methods, where m is the number of users and n is the number of files.     

A new scheme for ID‐based cryptosystems and signatures

Abstract

This paper proposes a new ID‐based cryptographic scheme for implementing public‐key cryptosystems and signatures. Instead of generating and publishing a public key for each user, the ID‐based scheme permits each user to choose his name or network address as his public key. This eliminates the need of a large public‐file and the exchange of private or public keys. The major advantage of the ID‐based cryptosystems is that the number of users can be exteneded to t*L users without decreasing the system security when users conspire, where L is the number of the system's secrets and t is the number of factors in p ‐ 1.     

Model simplification of stable discrete‐time systems by the squared magnitude Padé approximation

Abstract

A squared magnitude Padé approximation technique is presented for the model simplification of stable discrete‐time systems. The simplification is started from the squared magnitude function M(e^jTω ) =G(e^jTω )G(e^–jTω ), where G(z) is the z‐transfer function of a given high order discrete‐time system. The method is fully computer‐oriented and leads to a satisfactory approximation while preserving stability and minimum‐phase characteristics.     

A medial‐axis‐based model for propagating cracks in a regularised bulk

A new continuous‐discontinuous strategy for the simulation of failure is presented. The continuous bulk is regularised by means of a gradient‐enhanced damage model, where non‐locality is introduced at the level of displacements. As soon as the damage parameter is close or equal to 1, a traction‐free crack is introduced. To determine the direction of crack growth, a new criterion is proposed. In contrast to traditional techniques, where mechanical criteria are used to define the crack path, here, a geometrical approach is used. More specifically, given a regularised damage field D( x ), we propose to propagate the discontinuity following the direction dictated by the medial axis of the isoline (or isosurface in 3D) D( x ) = D*. The proposed approach is tested on different two‐dimensional and three‐dimensional examples that illustrate that this combined methodology is able to deal with damage growth and material separation. Copyright © 2014 John Wiley & Sons, Ltd.     

A cut‐cell non‐conforming Cartesian mesh method for compressible and incompressible flow

This paper details a multigrid‐accelerated cut‐cell non‐conforming Cartesian mesh methodology for the modelling of inviscid compressible and incompressible flow. This is done via a single equation set that describes sub‐, trans‐, and supersonic flows. Cut‐cell technology is developed to furnish body‐fitted meshes with an overlapping mesh as starting point, and in a manner which is insensitive to surface definition inconsistencies. Spatial discretization is effected via an edge‐based vertex‐centred finite volume method. An alternative dual‐mesh construction strategy, similar to the cell‐centred method, is developed. Incompressibility is dealt with via an artificial compressibility algorithm, and stabilization achieved with artificial dissipation. In compressible flow, shocks are captured via pressure switch‐activated upwinding. The solution process is accelerated with full approximation storage (FAS) multigrid where coarse meshes are generated automatically via a volume agglomeration methodology. This is the first time that the proposed discretization and solution methods are employed to solve a single compressible–incompressible equation set on cut‐cell Cartesian meshes. The developed technology is validated by numerical experiments. The standard discretization and alternative methods were found equivalent in accuracy and computational cost. The multigrid implementation achieved decreases in CPU time of up to one order of magnitude. Copyright © 2007 John Wiley & Sons, Ltd.     

An approach to the implementation and verification of abstract data

Abstract

The concept of abstraction can be used to simplify and formalize the design of software. However, most of the existing techniques based on abstraction only consider the control structure but not the data structures in the software. The transformation of a data abstraction, i.e., an abstract data type, to a physical data structure is a complicated process. It is composed of three major parts: a specification technique for describing a data abstraction; a deriving process for deriving the representation of the abstraction based on the specification; and a verification method for verifying the correctness of the specification and the representation of the abstraction. In this paper, we will concentrate on the last two problems, and it is assumed that the algebraic specification technique is used for describing abstract data types. Also, we will use examples to illustrate the use of the proposed approach.     

A goal‐oriented hp‐adaptive finite element method with electromagnetic applications. Part I: electrostatics

We describe the development and application of a finite element (FE) self‐adaptive hp goal‐oriented algorithm for elliptic problems. The algorithm delivers (without any user interaction) a sequence of optimal hp‐grids. This sequence of grids minimizes the error of a prescribed quantity of interest with respect to the problem size. The refinement strategy is an extension of a fully automatic, energy‐norm based, hp‐adaptive algorithm. We illustrate the efficiency of the method with 2D numerical results. Among other problems, we apply the goal‐oriented hp‐adaptive strategy to simulate direct current (DC) resistivity logging instruments (including through casing resistivity tools) in a borehole environment and for the assessment of rock formation properties. Copyright © 2005 John Wiley & Sons, Ltd.