Kinematic Design of Modular Reconfigurable In-Parallel Robots

This paper describes the kinematic design issues of a modular reconfigurable parallel robot. Two types of robot modules, the fixed-dimension joint modules and the variable dimension link modules that can be custom-designed rapidly, are used to facilitate the complex design effort. Module selection and robot configuration enumeration are discussed. The kinematic analysis of modular parallel robots is based on a local frame representation of the Product-Of-Exponentials (POE) formula. Forward displacement analysis algorithms and a workspace visualization scheme are presented for a class of three-legged modular parallel robots. Two three-legged reconfigurable parallel robot configurations are actually built according to the proposed design procedure.     

The election problem in asynchronous distributed systems with bounded faulty processes

Determining the “weakest” failure detectors is a central topic in solving many agreement problems such as Consensus, Non-Blocking Atomic Commit and Election in asynchronous distributed systems. So far, this has been studied extensively for several such fundamental problems. It is stated that Perfect Failure Detector P is the weakest failure detector to solve the Election problem with any number of faulty processes. In this paper, we introduce Modal failure detector M and show that to solve Election, M is the weakest failure detector to solve election when the number of faulty processes is less than ⌈n/2⌉. We also show that it is strictly weaker than P.

Single machine batch scheduling problem with family setup times and release dates to minimize makespan

In this paper we consider the single machine batch scheduling problem with family setup times and release dates to minimize makespan. We show that this problem is strongly NP-hard, and give an time dynamic programming algorithm and an time dynamic programming algorithm for the problem, where n is the number of jobs, m is the number of families, k is the number of distinct release dates and P is the sum of the setup times of all the families and the processing times of all the jobs. We further give a heuristic with a performance ratio 2. We also give a polynomial-time approximation scheme (PTAS) for the problem.     

One-dimensional and multi-dimensional substring selectivity estimation

With the increasing importance of XML, LDAP directories, and text-based information sources on the Internet, there is an ever-greater need to evaluate queries involving (sub)string matching. In many cases, matches need to be on multiple attributes/dimensions, with correlations between the multiple dimensions. Effective query optimization in this context requires good selectivity estimates. In this paper, we use pruned count-suffix trees (PSTs) as the basic data structure for substring selectivity estimation. For the 1-D problem, we present a novel technique called MO (Maximal Overlap). We then develop and analyze two 1-D estimation algorithms, MOC and MOLC, based on MO and a constraint-based characterization of all possible completions of a given PST. For the k-D problem, we first generalize PSTs to multiple dimensions and develop a space- and time-efficient probabilistic algorithm to construct k-D PSTs directly. We then show how to extend MO to multiple dimensions. Finally, we demonstrate, both analytically and experimentally, that MO is both practical and substantially superior to competing algorithms. Received April 28, 2000 / Accepted July 11, 2000     

Correlation between acidic properties of nickel sulfate supported on TiO2-ZrO2 and catalytic activity for ethylene dimerization

A series of catalysts, NiSO₄/TiO₂-ZrO₂, for ethylene dimerization was prepared by the impregnation method using an aqueous solution of nickel sulfate. For NiSO₄/TiO₂ -ZrO₂ sample, no diffraction line of nickel sulfate was observed up to 30 wt%, indicating good dispersion of nickel sulfate on the surface of TiO₂-ZrO₂. The addition of nickel sulfate to TiO₂-ZrO₂ shifted the phase transition of TiZrO₄ from amorphous to orthorhombic to a higher temperature because of the interaction between nickel sulfate and TiO₂-ZrO₂. The number of acid sites of NiSO₄/TiO₂-ZrO₂ increased in proportion to the nickel sulfate content up to 20 wt% of NiSO₄. Nickel sulfate supported on TiO₂-ZrO₂ was found to be very active even at room temperature, giving a maximum in both activity and acidity when the catalyst containing 20% NiSO₄ was calcined and evacuated at 500°C The asymmetric stretching frequency of the S=O bonds for NiSO₄/TiO₂-ZrO₂ samples was related to the acidic properties and catalytic activity. That is, the higher the frequency, the higher both the number of acid sites and the catalytic activity for ethylene dimerization.     

Note: A method to isolate and detect a large number of single molecules by microdroplet fluorescence spectroscopy

A laser induced fluorescence system, in combination with a glass-frit nebulizer and a photo-voltaic cell detector, is described for single molecule detection. The glass-frit nebulizer continuously generates a large number of droplets with an average droplet size of three micrometers in diameter. Rhodamine 6G molecules were detected at the 10(-12) M level. Concentrations 10(-12)-10(-10) M would provide mostly single molecules (0, 1, 2, 3, ...) in the individual droplets, as determined by Poisson distribution.     

Can we teach digital natives digital literacy?

In recent years, there has been much debate about the concept of digital natives, in particular the differences between the digital natives' knowledge and adoption of digital technologies in informal versus formal educational contexts. This paper investigates the knowledge about educational technologies of a group of undergraduate students studying the course Introduction to eLearning at a university in Australia and how they adopt unfamiliar technologies into their learning. The study explores the 'digital nativeness' of these students by investigating their degree of digital literacy and the ease with which they learn to make use of unfamiliar technologies. The findings show that the undergraduates were generally able to use unfamiliar technologies easily in their learning to create useful artefacts. They need, however to be made aware of what constitutes educational technologies and be provided with the opportunity to use them for meaningful purposes. The self-perception measures of the study indicated that digital natives can be taught digital literacy.     

Human and program factors affecting the maintenance of programs with deployed design patterns

Context

Practitioners may use design patterns to organize program code. Various empirical studies have investigated the effects of pattern deployment and work experience on the effectiveness and efficiency of program maintenance. However, results from these studies are not all consistent. Moreover, these studies have not considered some interesting factors, such as a maintainer’s prior exposure to the program under maintenance.

Objective

This paper aims at identifying what factors may contribute to the productivity of maintainers in the context of making correct software changes when they work on programs with deployed design patterns.

Method

We performed an empirical study involving 118 human subjects with three change tasks on a medium-sized program to explore the possible effects of a suite of six human and program factors on the productivity of maintainers, measured by the time taken to produce a correctly revised program in a course-based setting. The factors we studied include the deployment of design patterns and the presence of pattern-unaware solutions, as well as the maintainer’s prior exposure to design patterns, the subject program and the programming language, and prior work experience.

Results

Among the factors under examination, we find that the deployment of design patterns, prior exposure to the program and the presence of pattern-unaware solutions are strongly correlated with the time taken to correctly complete maintenance tasks. We also report some interesting observations from the experiment.

Conclusion

A new factor, namely, the presence of pattern-unaware solutions, contributes to the efficient completion of maintenance tasks of programs with deployed design patterns. Moreover, we conclude from the study that neither prior exposure to design patterns nor prior exposure to the programming language is supported by sufficient evidences to be significant factors, whereas the subjects’ exposure to the program under maintenance is notably more important.     

Disturbance decoupled fault reconstruction using cascaded sliding mode observers

This paper presents a disturbance decoupled fault reconstruction (DDFR) scheme using cascaded sliding mode observers (SMOs). The processed signals from a SMO are found to be the output of a fictitious system which treats the faults and disturbances as inputs; the ‘outputs’ are then fed into the next SMO. This process is repeated until the attainment of a fictitious system which satisfies the conditions that guarantee DDFR. It is found that this scheme is less restrictive and enables DDFR for a wider class of systems compared to previous work when only one or two SMOs were used. This paper also presents a systematic routine to check for the feasibility of the scheme and to calculate the required number of SMOs from the outset and also to design the DDFR scheme. A design example verifies its effectiveness.