bluuebunny/crossref_metadata_2025 huggingface dataset:
Laser Transmission Welding of Thermoplastics—Part I: Temperature and Pressure Modeling
Authors: Van de Ven James D. , Erdman Arthur G.
Published: October 2007

This paper discusses the development of a model of laser transmission welding that can be used as an analytical design tool. Currently the majority of laser transmission welding (LTW) applications rely on trial and error to develop appropriate process parameters. A more rigorous design approach is not commonly used primarily due to the complexity of laser welding, where small material or process parameter changes can greatly affect the weld quality. The model developed in this paper also enables optimizing operating parameters while providing monetary and time saving benefits. The model is created from first principles of heat transfer and utilizes contact conduction that is a function of temperature and pressure, Gaussian laser distribution, and many material properties that vary with temperature including the absorption coefficient. The model is demonstrated through a design example of a joint between two polyvinyl chloride parts. The model is then validated with samples welded with a diode laser system using the operating parameters developed in a design example. Using the weld width as the primary output, the error between the model and the experimental results is 4.3%, demonstrating the accuracy of the model.
Cutting Tool Temperature Analysis in Heat-Pipe Assisted Composite Machining
Authors: Liu Jie , Kevin Chou Y.
Published: October 2007

Machining of advanced materials, such as composite, encounters high cutting temperatures and rapid tool wear because of the abrasive nature of the reinforcement phases in the workpiece materials. Ultrahard coatings, such as chemical vapor deposition diamond, have been used for machining such advanced materials. Wear of diamond-coated tools is characterized by catastrophic coating failure, plausibly due to the high stress developed at the coating-substrate interface at high temperatures because of very different elastic moduli and thermal expansion coefficients. Temperature reductions, therefore, may delay the onset of the coating failure and offer tool life extension. In this study, a passive heat-dissipation device, the heat pipe, has been incorporated in composite machining. Though it is intuitive that heat transfer enhanced by the heat pipe may reduce tool temperatures, the heat pipe will likely increase heat partitioning into the tool at the rake face, and complicate the temperature reduction effectiveness. A combined experimental, analytical, and numerical approach was used to investigate the heat-pipe effects on cutting tool temperatures. A machining experiment was conducted and the heat-source characteristics were analyzed using cutting mechanics. With the heat sources as input, cutting tool temperatures in machining, without or with a heat pipe, were analyzed using finite element simulations. The simulations encompass a 3-D model of a cutting tool system and a 2-D chip model. The heat flux over the rake-face contact area was used in both models with an unknown heat partition coefficient, determined by matching the average temperature at the tool-chip contact from the two models. Cutting tool temperatures were also measured in machining using thermocouples. The simulation results agree reasonably with the experiment. The model was used to evaluate how the heat pipe modifies the heat transport in a cutting tool system. Applying heat-pipe cooling inevitably increases the heat flux into the tool because of the enhanced heat dissipation. However, the heat pipe is still able to reduce the tool-chip contact temperatures, though not dramatically at current settings. The parametric study using the finite element analysis (FEA) models shows that the cooling efficiency decreases as the cutting speed and feed increase, because of the increased heat flux and heat-source area. In addition, increasing the heat-pipe volume and decreasing the heat-pipe distance to the heat source enhances the heat-pipe cooling effectiveness.
Effect of a Nonlinear Joint on the Dynamic Performance of a Machine Tool
Authors: Dhupia Jaspreet S. , Powalka Bartosz , Ulsoy A. Galip , Katz Reuven
Published: October 2007

This paper presents the effect of experimentally evaluated nonlinearities in a machine joint on the overall machine tool dynamic performance using frequency response functions and stability lobe diagrams. Typical machine joints are very stiff and have weak nonlinearities. The experimental evaluation of the nonlinear joint parameters of a commercial translational guide has been discussed in Dhupia et al., 2007, J. Vibr. Control, accepted. Those results are used in the current paper to represent the connection between the column and the spindle of an idealized column-spindle machine structure. The goal is to isolate and understand the effects of such joints on the machine tool dynamic performance. The nonlinear receptance coupling approach is used to evaluate the frequency response function, which is then used to evaluate the stability lobe diagrams for an idealized machine structure. Despite the weak nonlinearities in the joint, significant shifts in the natural frequency and amplitudes at resonance can be observed at different forcing amplitudes. These changes in the structural dynamics, in turn, can lead to significant changes in the location of chatter stability lobes with respect to spindle speed. These variations in frequency response function and stability lobe diagram of machine tools due to nonlinearities in the structure are qualitatively verified by conducting impact hammer tests at different force amplitudes on a machine tool.
Laser Transmission Welding of Thermoplastics—Part II: Experimental Model Validation
Authors: Van de Ven James D. , Erdman Arthur G.
Published: October 2007

Two laser transmission welding experiments involving polyvinyl chloride are presented that aim to validate a previously presented welding model while helping to further understand the relationship between welding parameters and weld quality. While numerous previous research papers have presented the results of laser welding experiments, there exists minimal work validating models of the welding process. The first experiment explores the interaction of laser power and welding velocity while the second experiment explores the influence of clamping pressure. Using the weld width as the primary model output, the agreement between the welding experiments and the model have an average error of 5.6%. This finding strongly supports the validity of the model presented in Part I of this two paper set (Van de Ven and Erdman, 2007, ASME J. Manuf. Sci. Eng., 129, pp. 849–858). Additional information was gained regarding the operating window for laser transmission welding and the thermal decomposition of polyvinyl chloride. Clamping pressure was found to provide a small, but not statistically significant, influence on the visual appearance, weld width, and weld strength.
Sloshing in a Cylindrical Liquid Storage Tank With a Floating Roof Under Seismic Excitation
Authors: Matsui Tetsuya
Published: October 2007

An analytical solution is presented to predict the sloshing response of a cylindrical liquid storage tank with a floating roof under seismic excitation. The contained liquid is assumed to be inviscid, incompressible, and irrotational, while the floating roof is idealized as an isotropic elastic plate with uniform stiffness and mass. The dynamic interaction between the floating roof and the liquid is taken into account exactly within the framework of linear potential theory. By expanding the response of the floating roof into free-vibration modes in air and employing the Fourier–Bessel expansion method in cylindrical coordinates, the solution is obtained in an explicit form, which will be useful for parametric understanding of the sloshing behavior and preliminary study in the early design stage. Numerical results are also provided to investigate the effect of the stiffness and mass of the floating roof on the sloshing response.
A Study on the Hydrodynamic Load in a Water Pool When Discharged Air Forms a Bubble Cloud (PVP2006-ICPVT11-93281)
Authors: Uchida Ken , Suzuki Seijiro
Published: October 2007

This paper presents a numerical and qualitative study on the expected hydrodynamic load-reducing effect of bubbly medium near a volumetrically oscillating bubble. In this study, the bubble or bubble cloud is assumed to be spherically symmetric, and its motion is analyzed as a one-dimensional compressible two-phase flow in the radial direction in spherical coordinates. We adopted the cubic interpolated pseudoparticle combined unified procedure method, which is a unified analysis method for both compressible and incompressible fluids proposed by Yabe and Wang (1991, “Unidied Numerical Procedure for Compressible and Incompressible Fluid,” J. Phys. Soc. Jpn., 60, pp. 2105–2108) in order to treat interaction among gas, liquid, and two-phase medium and to avoid large numerical dissipation at density discontinuities. To verify the analysis program we developed, we analyzed free oscillations of a bubble with a unity void fraction and of a bubble cloud with an initial void fraction of 0.5, and found that the natural frequency from numerical results is well reproduced with an error of 0.9% for the bubble and 5% for the bubble cloud as compared to those obtained on a theoretical basis. Using this method, we analyzed the free oscillation of a bubble cloud in which a bubble with a unity void fraction is covered by a bubbly medium layer with an initial void fraction of 0.5. Numerical results show that the amplitude of pressure oscillation inside the bubble is about halved and that a higher mode of oscillation appears when a bubbly medium layer covers the bubble. The measured results from a blowdown test we previously reported also show a similar higher mode of oscillation. The amplitude of pressure oscillation in the water region was apparently reduced when a thick bubbly medium layer covers the bubble. Thus, if the bubbly medium are ejected from sparger holes prior to the ejection of a high-pressure bubble, the bubbly medium might reduce the hydrodynamic load induced in a water pool made by volumetric oscillation of the bubble.
Finite Element Prediction of Residual Stress Distributions in a Multipass Welded Piping Branch Junction
Authors: Jiang Wei , Yahiaoui Kadda
Published: October 2007

Piping branch junctions and nozzle attachments to main pressure vessels are common engineering components used in the power, oil and gas, and shipbuilding industries amongst others. These components are usually fabricated by multipass welding. The latter process is known to induce residual stresses at the fabrication stage, which can have severe adverse effects on the in-service behavior of such critical components. It is thus desirable if the distributions of residual stresses can be predicted well in advance of welding execution. This paper presents a comprehensive study of three dimensional residual stress distributions in a stainless steel tee branch junction during a multipass welding process. A full three dimensional thermomechanical finite element model has been developed for this purpose. A newly developed meshing technique has been used to model the complex intersection areas of the welded junction with all hexahedral elements. Element removal/reactivate technique has been employed to simulate the deposition of filler material. Material, geometry, and boundary nonlinearities associated with welding were all taken into account. The analysis results are presented in the form of stress distributions circumferentially along the weld line on both run and branch pipes as well as at the run and branch cross sections. In general, this computational model is capable of predicting three dimensional through-thickness welding residual stress, which can be valuable for structural integrity assessments of complex welded geometries.
Strategy of Considering Microstructure Effect on Weld Residual Stress Analysis
Authors: Mochizuki Masahito , Toyoda Masao
Published: October 2007

Welding generates thermal distortion and residual stress, and it is well known that they affect the performance of welded structures by contributing to brittle fracture, fatigue, buckling deformation, and stress-corrosion cracking. Welding distortions and residual stresses can possibly be controlled and reduced by using countermeasures. Not only thermal stress behavior but also the prediction of the microstructural phase during welding heat cycles is very important. High-strength steels or martensitic stainless steels are used in many power plant components, and the effect of phase transformation on the mechanical behavior during welding of these steels becomes much larger than that of mild steels and austenitic stainless steels. Simultaneous simulations of the thermal stress and microstructure during welding are necessary for a precise evaluation. In this paper, an analytical method and several applications using actual components are introduced in order to emphasize the effect of the microstructure on the weld residual stress analysis.
Theoretical and Numerical Predictions of Burst Pressure of Pipelines
Authors: Zhu Xian-Kui , Leis Brian N.
Published: October 2007

To accurately characterize plastic yield behavior of metals in multiaxial stress states, a new yield theory, i.e., the average shear stress yield (ASSY) theory, is proposed in reference to the classical Tresca and von Mises yield theories for isotropic hardening materials. Based on the ASSY theory, a theoretical solution for predicting the burst pressure of pipelines is obtained as a function of pipe diameter, wall thickness, material hardening exponent, and ultimate tensile strength. This solution is then validated by experimental data for various pipeline steels. According to the ASSY yield theory, four failure criteria are developed for predicting the burst pressure of pipes by the use of commercial finite element softwares such as ABAQUS and ANSYS, where the von Mises yield theory and the associated flow rule are adopted as the classical metal plasticity model for isotropic hardening materials. These failure criteria include the von Mises equivalent stress criterion, the maximum principal stress criterion, the von Mises equivalent strain criterion, and the maximum tensile strain criterion. Applications demonstrate that the proposed failure criteria in conjunction with the ABAQUS or ANSYS numerical analysis can effectively predict the burst pressure of end-capped line pipes.
Asymptotic Crack-Tip Fields in Perfectly Plastic Solids Under Mixed Mode II/III Loading Conditions
Authors: Pan J. , Lin P.-C.
Published: October 2007

In this paper, governing equations and solutions for asymptotic singular and nonsingular crack-tip sectors in perfectly plastic materials are first summarized under combined in-plane and out-of-plane shear loading conditions. The crack-tip fields under mixed mode II/III loading conditions are then investigated. An assembly of crack-tip sectors is adopted with stress discontinuities along the border of the two constant stress sectors. The solutions of the crack-tip fields under pure mode II, mixed mode II/III, and nearly pure mode III loading conditions are presented. The trends of the angular variations of the mixed mode II/III crack-tip stresses agree with those of the available computational analysis and the asymptotic analysis for low strain hardening materials. The pure mode II crack-tip stresses are similar to those of Hutchinson, and the nearly pure mode III stresses are similar to those of the pure mode III crack-tip field of Rice.
Unified Solutions to the Limit Load of Thick-Walled Vessels
Authors: Zhao Jun-hai , Zhai Yue , Ji Lin , Wei Xue-ying
Published: October 2007

Unified solutions to the elastoplastic limit load of thick-walled cylindrical and spherical vessels under internal pressure are obtained in terms of the unified strength theory (UST) and the unified slip-line field theory (USLFT). The UST and the USLFT include or approximate an existing strength criterion or slip-line field theory by adopting a parameter b, which varies from 0 to 1. The theories can be used on pressure-sensitive materials, which have the strength difference (SD) effect. The solutions, based on the Tresca criterion, the von Mises criterion, the Mohr–Coulomb criterion, and the twin shear strength criterion, are special cases of the present unified solutions. The results based on the Mohr–Coulomb criterion (b=0) give the lower bound of the plastic limit load, while those according to the twin shear strength criterion (b=1) are the upper bound. The solution of the von Mises criterion is approximated by the linear function of the UST with a specific parameter (b≈0.5). Plastic limit solutions with respect to different yield criteria are illustrated and compared. The influences of the yield criterion as well as the ratio of the tensile strength to the compressive strength on the plastic limit loads are discussed.
Damping Effect on Mechanical Waves in an Elastic Solid Expanded Tubular
Authors: Karrech A. , Seibi A. , Pervez T.
Published: October 2007

The present paper studies the dynamics of submerged expanded elastic tubes due to postexpansion sudden mandrel release known as pop-out phenomenon. A mathematical model describing the dynamics of the borehole-fluid-tube system is presented. Coupling of the fluid-structure interaction and damping effects were taken into consideration. An analytical solution for the displacement, stress, and pressure wave propagation in the fluid-tube system was obtained. The developed model predicted localized critical regions where the structure might experience failure.
Phased Array Ultrasonic Measurement of Fatigue Crack Growth Profiles in Stainless Steel Pipes
Authors: Satyarnarayan L. , Pukazhendhi D. M. , Balasubramaniam Krishnan , Krishnamurthy C. V. , Ramachandra Murthy D. S.
Published: October 2007

This paper reports experimental sizing of fatigue crack profiles that are initiated from artificially made circumferential starter notches in stainless steel pipes of 169mm outer diameter and 14.33mm thickness, which were subjected to cyclic bending loads in a four point bending load arrangement using two nondestractive evaluation (NDE) methods: (a) phased array ultrasonic technique and (b) alternating current potential drop technique. The crack growth estimated using the two NDE techniques were compared with the beach marks that were present in the fracture surface. A simulation study using the ray tracing method was carried out to model the ultrasonic wave propagation in the test specimen, and the results were compared with the experimental results.
Burst Strength Analysis of Casing With Geometrical Imperfections
Authors: Huang Xiaoguang , Chen Yanyun , Lin Kai , Mihsein Musa , Kibble Kevin , Hall Richard
Published: October 2007

Accurately predicting the burst strength is very important in the casing design for the oil and gas industry. In this paper, finite element analysis is performed for an infinitely long thick walled casing with geometrical imperfections subjected to internal pressure. A comparison with a series of full-scale experiments was conducted to verify the accuracy and reliability of the finite element analysis. Furthermore, three predictive equations were evaluated using the test data, and the Klever equation was concluded to give the most accurate prediction of burst strength. The finite element analysis was then extended to study the effects of major factors on the casing burst strength. Results showed that the initial eccentricity and material hardening parameter had important effects on the burst strength, while the effect of the initial ovality was small.
Vibration Fatigue of Centrifugal Fan Impeller Due to Structural-Acoustic Coupling and Its Prevention: A Case Study
Authors: Eisinger Frantisek L. , Sullivan Robert E.
Published: October 2007

Fatigue cracks from high cycle vibratory loading have developed in a centrifugal fan impeller after a relatively short period of operation. Based on vibration tests of the impeller and acoustic analysis of the internal spaces of the fan, structural-acoustic coupling with matching frequencies involving two-nodal diameter modes (structural and acoustic) was identified as the cause of the vibration problem. This paper gives a description of the problem and identifies available remedies for its elimination. Special attention is given in Case 1 to the acoustics of the system, where changes to the fan casing utilizing a decoupling acoustic chamber attached to the casing was investigated, and in Case 2, where changes needed to the structural characteristics of the impeller by utilizing a modified impeller with a substantially increased natural frequency (by 44%) of the two-nodal diameter vibratory mode shape were studied. Experimental tests confirmed that the structural-acoustic coupling and vibration were significantly reduced in Case 1 and were fully eliminated in Case 2.
Modernization of Pressure Vessel Design Codes ASME Section VIII, Division 2, 2007 Edition
Authors: Pastor T. P. , Osage D. A.
Published: October 2007

The technology for pressure equipment design continues to advance each and every day. The ASME Boiler and Pressure Vessel Code has been keeping pace with these advances over the last 92 years. As far back as the 1960s, it was recognized that the special requirements for design of pressure vessels operating at pressures over 2000 psi (13.7 MPa) called for special rules, and ASME issued Sec. VIII, Division 2 of Alternative Rules for Pressure Vessels. Since that time, the understanding of failure mechanisms and advances in material science, nondestructive testing, and computer-aided design has progressed to the stage where a new approach was needed not only in the content of design codes but in the way they are presented and organized. This paper introduces the newly issued ASME Sec. VIII, Division 2 of 2007 edition and explores the technical concepts included and the new format designed for ease of use. Included are results of test exercises sponsored by ASME giving actual applications of the new Code for design of vessels. This paper demonstrates ASME’s commitment to provide manufacturers and users of pressure equipment with the most up-to-date technology in easy to use standards that service the international market.
AN OPINION FORMATION MODEL WITH TWO STAGES
Authors: SHEN BO , LIU YUN
Published: October 2007

The opinion formation process is a general phenomenon in community and society. In recent years, several models of opinion formation have been proposed; however, most models mainly focus on describing views exchange between individuals and interaction between individuals and the environment. In this paper, we present an opinion formation model which takes into account the initial state of opinions and the contacting process with topics. The model involves two stages. The first one is the process in which individuals contact a given topic for the first time and the second one is the social interaction process between individuals. Using the proposed model, we simulate opinion formation process with several sets of parameters. Simulation results indicate that the proposed model may be successfully used for opinion formation simulations. It is also found that the initial state and contacting process have significant influence on opinion formation. Moreover, the model could be helpful for understanding some social phenomena such as quick formation of public opinion about certain topic and the crucial effect of small fluctuations on opinion distribution.
EFFECTS OF ROUTE GUIDANCE SYSTEMS ON SMALL-WORLD NETWORKS
Authors: WU JIAN-JUN , SUN HUI-JUN , GAO ZI-YOU , LI SHU-BIN
Published: October 2007

The route guidance systems (RGS) are efficient in alleviating traffic congestion and reducing transit time of transportation networks. This paper studies the effects of RGS on performance of variably weighted small-world networks. The properties of the average shortest path length, the maximum degree, and the largest betweenness, as important indices for characterizing the network structure in complex networks, are simulated. Results show that there is an optimal guided rate of RGS to minimize the total system cost and the average shortest path length, and proper RGS can reduce the load of the node with maximum degree or largest betweenness. In addition, we found that the load distribution of nodes guided by RGS decay as the power laws which is very important for us to understand and control traffic congestion feasible.
THE CONTROL OF STOCHASTIC COMPLEX DAMPED NONLINEAR SYSTEMS
Authors: HE QUN , XU YONG , MAHMOUD GAMAL M. , XU WEI
Published: October 2007

The aim of this paper is to continue our investigations by studying complex damped nonlinear systems with random noise. The effect of random phase for these systems is examined. The interested system demonstrates unstable periodic attractors when the intensity of random noise equals zero, and we show that the unstable dynamical behavior will be stabilized as the intensity of random noise properly increases. The phase plot and the time evolution are carried out to confirm the obtained results of Poincaré map analysis and top Lyapunov exponent on the dynamical behavior of stability. Excellent agreement is found between these results.
EFFECT OF MEMBRANE BENDING STIFFNESS ON THE DEFORMATION OF ELASTIC CAPSULES IN EXTENSIONAL FLOW: A LATTICE BOLTZMANN STUDY
Authors: SUI Y. , CHEW Y. T. , ROY P. , LOW H. T.
Published: October 2007

The transient deformation of liquid capsules enclosed by elastic membranes in two-dimensional extensional flow is studied numerically, using an improved immersed boundary-lattice Boltzmann method. The purpose of the present study is to investigate the effect of interfacial bending stiffness on the deformation of such capsules, under the subcritical elasticity capillary number conditions. The present model can simulate flow-induced deformation of capsules with arbitrary resting shapes (concerning the in-plane tension) and bending-free configurations. The deformation of capsules with initially circular, elliptical, and biconcave resting shapes was investigated in the present study; the capsules' bending-free configurations were considered as either circular shapes or their initially resting shapes. The results show that for capsules with bending-free configuration as circles, membrane bending rigidity has significant rounding effect on the steady deformed profiles. For elliptical and biconcave capsules with resting shapes as the bending-free configurations, it is found that with the bending stiffness increasing, the capsules' steady shapes are more akin to their initial shapes.
A TRANSFORMATION SEQUENCING APPROACH TO PSEUDORANDOM NUMBER GENERATION
Authors: TAN SYN KIAT , GUAN SHENG-UEI
Published: October 2007

This paper presents a new approach to designing pseudorandom number generators based on cellular automata. Current cellular automata designs either focus on (i) ensuring desirable sequence properties such as maximum length period, balanced distribution of bits and uniform distribution of n-bit tuples, etc. or (ii) ensuring the generated sequences pass stringent randomness tests. In this work, important design patterns are first identified from the latter approach and then incorporated into cellular automata such that the desirable sequence properties are preserved like in the former approach. Preliminary experiment results show that the new cellular automata designed have potential in passing all DIEHARD tests.
RANDOMIZED CELLULAR AUTOMATA
Authors: BOCCARA NINO
Published: October 2007

We define and study a few properties of a class of random automata networks. While regular finite one-dimensional cellular automata are defined on periodic lattices, these automata networks, called randomized cellular automata, are defined on random directed graphs with constant out-degrees and evolve according to cellular automaton rules. For some families of rules, a few typical a priori unexpected results are presented.
EFFECT OF MEMORY ON BOOLEAN NETWORKS WITH DISORDERED DYNAMICS: THE K = 4 CASE
Authors: ALONSO-SANZ RAMÓN , CÁRDENAS JUAN PABLO
Published: October 2007

In standard Cellular Automata (CA) and Boolean Networks (BN), the new state of a cell depends on the neighborhood configuration only at the preceding time step. The effect of implementing memory in cells on CA, CA on networks and BN with different degrees of random rewiring is studied in this paper paying attention to the particular case of four inputs. As a rule, memory in cells induces a moderation in the rate of changing cells and in the damage spreading, albeit in the latter case memory turns out ineffective in the control of the damage as the wiring network moves away of the ordered structure that features proper CA.
INBREEDING AND OUTBREEDING DEPRESSIONS IN THE PENNA MODEL AS A RESULT OF CROSSOVER FREQUENCY
Authors: BOŃKOWSKA K. , KULA M. , CEBRAT S. , STAUFFER D.
Published: October 2007

The population in the sexual Penna aging model is first separated into several reproductively isolated groups. Then, after equilibration, sexual mixing between the groups is allowed. We study the changes in the population size due to this mixing and interpret them through a counterplay of purifying selection and of haplotype complementarity.
GLOBAL MINIMA FOR PdN (N = 5–80) CLUSTERS DESCRIBED BY SUTTON–CHEN POTENTIAL
Authors: ARSLAN HAYDAR
Published: October 2007

The structure and energetics of Pd N (N = 5–80) clusters have been studied extensively by a Monte Carlo method based on Sutton–Chen many-body potential. The basin-hopping algorithm is used to find the low-energy minima on the potential energy surface for each nuclearity. A variety of structure types (icosahedral, decahedral and fcc closed-packed) are observed for Pd clusters. Some of the icosahedral global minima do not have a central atom. The resulting structures have been compared with the previous theoretical results.
Idle energy minimization by mode sequence optimization
Authors: Liu Jinfeng , Chou Pai H.
Published: October 2007

This article presents techniques for reducing idle energy by mode-sequence optimization (MSO) under timing constraints. Our component-level CoMSO algorithm computes energy-optimal mode-transition sequences for different lengths of idle intervals. Our system-level SyMSO algorithm shifts tasks within slack intervals while satisfying all timing and resource constraints in the given schedule. Experimental results on a commercial software-defined radio show that these new techniques can reduce idle energy by 50--70%, or 30--50% of total system energy over previous offline-optimal but unsequenced techniques based on localized break-even-time analysis, thanks to rich options offered by mode sequencing.
Ultra-fast and efficient algorithm for energy optimization by gradient-based stochastic voltage and task scheduling
Authors: Gorjiara Bita , Bagherzadeh Nader , Chou Pai H.
Published: October 2007

This paper presents a new technique, called
Adaptive Stochastic Gradient Voltage-and-Task Scheduling
(ASG-VTS), for power optimization of multicore hard realtime systems. ASG-VTS combines stochastic and energy-gradient techniques to simultaneously solve the slack distribution and task reordering problem. It produces very efficient results with few mode transitions. Our experiments show that ASG-VTS reduces number of mode transitions by 4.8 times compared to traditional energy-gradient-based approaches. Also, our heuristic algorithm can quickly find a solution that is as good as the optimal for a real-life GSM encoder/decoder benchmark. The runtime of ASG-VTS is 150 times and 1034 times faster than energy-gradient based and optimal ILP algorithms, respectively. Since the runtime of ASG-VTS is very low, it is ideal for design space exploration in system-level design tools. We have also developed a web-based interface for ASG-VTS algorithm.
MPSoC memory optimization using program transformation
Authors: Bouchebaba Youcef , Girodias Bruno , Nicolescu Gabriela , Aboulhamid El Mostapha , Lavigueur Bruno , Paulin Pierre
Published: October 2007

Multiprocessor system-on-a-chip (MPSoC) architectures have received a lot of attention in the past years, but few advances in compilation techniques target these architectures. This is particularly true for the exploitation of data locality. Most of the compilation techniques for parallel architectures discussed in the literature are based on a single loop nest. This article presents new techniques that consist in applying loop fusion and tiling to several loop nests and to parallelize the resulting code across different processors. These two techniques reduce the number of memory accesses. However, they increase dependencies and thereby reduce the exploitable parallelism in the code. This article tries to address this contradiction. To optimize the memory space used by temporary arrays, smaller buffers are used as a replacement. Different strategies are studied to optimize the processing time spent accessing these buffers. The experiments show that these techniques yield a significant reduction in the number of data cache misses (30%) and in processing time (50%).
Clock skew scheduling with race conditions considered
Authors: Huang Shih-Hsu , Nieh Yow-Tyng
Published: October 2007

In this article, we provide a fresh viewpoint to the interactions between clock skew scheduling and delay insertion. A race-condition-aware (RCA) clock skew scheduling is proposed to determine the clock skew schedule by taking race conditions (i.e., hold violations) into account. Our objective is not only to optimize the clock period, but also to minimize heuristically the required inserted delay. Compared with previous work, our major contribution includes the following two aspects. First, our approach achieves exactly the same results, but has significant improvement in time complexity. Second, our viewpoint can be generalized to other sequential timing optimization techniques.
Exploring time/resource trade-offs by solving dual scheduling problems with the ant colony optimization
Authors: Wang Gang , Gong Wenrui , Derenzi Brian , Kastner Ryan
Published: October 2007

Design space exploration during high-level synthesis is often conducted through ad hoc probing of the solution space using some scheduling algorithm. This is not only time consuming but also very dependent on designer's experience. We propose a novel design exploration method that exploits the duality of time- and resource-constrained scheduling problems. Our exploration automatically constructs a time/area tradeoff curve in a fast, effective manner. It is a general approach and can be combined with any high-quality scheduling algorithm. In our work, we use the max-min ant colony optimization technique to solve both time- and resource-constrained scheduling problems. Our algorithm provides significant solution-quality savings (average 17.3% reduction of resource counts) with similar runtime compared to using force-directed scheduling exhaustively at every time step. It also scales well across a comprehensive benchmark suite constructed with classic and real-life samples.
Low-Power and testable circuit synthesis using Shannon decomposition
Authors: Ghosh Swaroop , Bhunia Swarup , Roy Kaushik
Published: October 2007

Structural transformation of a design to enhance its testability while satisfying design constraints on power and performance can result in improved test cost and test confidence. In this article, we analyze the testability in a new style of logic design based on
Shannon's decomposition
and
supply gating
. We observe that the tree structure of a logic circuit due to Shannon's decomposition makes it intrinsically more testable than a conventionally synthesized circuit, while at the same time providing an improvement in active power. We have analyzed four different aspects of the testability of a circuit: a) IDDQ test sensitivity, b) test power during scan-based testing, c) test length (for both ATPG-generated deterministic and random patterns), and d) noise immunity. Simulation results on a set of MCNC benchmarks show promising results on all these aspects (an average improvement of 94% in IDDQ sensitivity, 50% in test power, 19% (21%) in test length for deterministic (random) patterns, and 50% in coupling noise immunity). We have also demonstrated that the new logic structure can improve parametric yield (6% on average) of a circuit under process variations when considering a bound on circuit leakage.
ILP and heuristic techniques for system-level design on network processor architectures
Authors: Ostler Chris , Chatha Karam S. , Ramamurthi Vijay , Srinivasan Krishnan
Published: October 2007

Network processors incorporate several architectural features, including symmetric multiprocessing (SMP), block multithreading, and multiple memory elements, to support the high-performance requirements of current day applications. This article presents automated system-level design techniques for application development on such architectures. We propose integer linear programming formulations and heuristic techniques for process allocation and data mapping on SMP and block-multithreading-based network processors. The techniques incorporate process transformations and multithreading-aware data mapping to maximize the throughput of the application. The article presents experimental results that evaluate the techniques by implementing network processing applications on the Intel IXP 2400 architecture.
Optimization of polynomial datapaths using finite ring algebra
Authors: Gopalakrishnan Sivaram , Kalla Priyank
Published: October 2007

This article presents an approach to area optimization of arithmetic datapaths at register-transfer level (RTL). The focus is on those designs that perform polynomial computations (add, mult) over finite word-length operands (bit-vectors). We model such polynomial computations over
m
-bit vectors as algebra over finite integer rings of residue classes
Z
2

m

. Subsequently, we use the number-theoretic and algebraic properties of such rings to transform a given datapath computation into another, bit-true equivalent computation. We also derive a cost model to estimate, at RTL, the area cost of the computation. Using the transformation procedure along with the cost model, we devise algorithmic procedures to search for a lower-cost implementation. We show how these theoretical concepts can be applied to RTL optimization of arithmetic datapaths within practical CAD settings. Experiments conducted over a variety of benchmarks demonstrate substantial optimizations using our approach.
Network intrusion detection through Adaptive Sub-Eigenspace Modeling in multiagent systems
Authors: Shyu Mei-Ling , Quirino Thiago , Xie Zongxing , Chen Shu-Ching , Chang Liwu
Published: October 2007

Recently, network security has become an extremely vital issue that beckons the development of accurate and efficient solutions capable of effectively defending our network systems and the valuable information journeying through them. In this article, a distributed multiagent intrusion detection system (IDS) architecture is proposed, which attempts to provide an accurate and lightweight solution to network intrusion detection by tackling issues associated with the design of a distributed multiagent system, such as poor system scalability and the requirements of excessive processing power and memory storage. The proposed IDS architecture consists of (i) the Host layer with lightweight host agents that perform anomaly detection in network connections to their respective hosts, and (ii) the Classification layer whose main functions are to perform misuse detection for the host agents, detect distributed attacks, and disseminate network security status information to the whole network. The intrusion detection task is achieved through the employment of the lightweight Adaptive Sub-Eigenspace Modeling (ASEM)-based anomaly and misuse detection schemes. Promising experimental results indicate that ASEM-based schemes outperform the KNN and LOF algorithms, with high detection rates and low false alarm rates in the anomaly detection task, and outperform several well-known supervised classification methods such as C4.5 Decision Tree, SVM, NN, KNN, Logistic, and Decision Table (DT) in the misuse detection task. To assess the performance in a real-world scenario, the Relative Assumption Model, feature extraction techniques, and common network attack generation tools are employed to generate normal and anomalous traffic in a private LAN testbed. Furthermore, the scalability performance of the proposed IDS architecture is investigated through the simulation of the proposed agent communication scheme, and satisfactory linear relationships for both degradation of system response time and agent communication generated network traffic overhead are achieved.
Ranking factors in peer-to-peer overlay networks
Authors: Watanabe Kenichi , Nakajima Yoshio , Enokido Tomoya , Takizawa Makoto
Published: October 2007

A large number of peer processes are distributed in a peer-to-peer (P2P) overlay network. It is difficult, maybe impossible for a peer to perceive the membership and location of every resource object due to the scalability and openness of a P2P network. In this article, we discuss a fully distributed P2P system where there is no centralized controller. Each peer has to obtain service information from its acquaintance peers and also send its service information to the acquaintance peers. An acquaintance peer of a peer
p
is a peer about whose service the peer
p
knows and with which the peer
p
can directly communicate in an overlay network. Some acquaintance peer might hold obsolete service information and might be faulty. Each peer has to find a more trustworthy one among acquaintance peers. There are many discussions on how to detect peers that hold a target object. However, a peer cannot manipulate an object without being granted access rights (permissions). In addition to detecting what peers hold a target object, we have to find peers granted access rights to manipulate the target object. The trustworthiness of each acquaintance is defined in terms of the satisfiability and ranking factor in this article. The satisfiability of an acquaintance peer shows how much each peer can trust the acquaintance peer through direct communication to not only detect target objects but also obtain their access rights. On the other hand, the ranking factor of an acquaintance peer indicates how much the acquaintance peer is trusted only by trustworthy acquaintance peers which is different from the traditional reputation concept. We evaluate how the trustworthiness of an acquaintance peer is changed through interactions among peers in a detection algorithm.
A phonetic similarity model for automatic extraction of transliteration pairs
Authors: Kuo Jin-Shea , Li Haizhou , Yang Ying-Kuei
Published: October 2007

This article proposes an approach for the automatic extraction of transliteration pairs from Chinese Web corpora. In this approach, we formulate the machine transliteration process using a syllable-based phonetic similarity model which consists of phonetic confusion matrices and a Chinese character
n
-gram language model. With the phonetic similarity model, the extraction of transliteration pairs becomes a two-step process of
recognition followed by validation:
First, in the
recognition
process, we identify the most probable transliteration in the
k
-neighborhood of a recognized English word. Then, in the
validation
process, we qualify the transliteration pair candidates with a hypothesis test. We carry out an analytical study on the statistics of several key factors in English-Chinese transliteration to help formulate phonetic similarity modeling. We then conduct both supervised and unsupervised learning of a phonetic similarity model on a development database. The experimental results validate the effectiveness of the phonetic similarity model by achieving an
F
-measure of 0.739 in supervised learning. The unsupervised learning approach works almost as well as the supervised one, thus allowing us to deploy automatic extraction of transliteration pairs in the Web space.
The study of a nonstationary maximum entropy Markov model and its application on the pos-tagging task
Authors: Xiao Jinghui , Wang Xiaolong , Liu Bingquan
Published: October 2007

Sequence labeling is a core task in natural language processing. The maximum entropy Markov model (MEMM) is a powerful tool in performing this task. This article enhances the traditional MEMM by exploiting the positional information of language elements. The stationary hypothesis is relaxed in MEMM, and the nonstationary MEMM (NS-MEMM) is proposed. Several related issues are discussed in detail, including the representation of positional information, NS-MEMM implementation, smoothing techniques, and the space complexity issue. Furthermore, the asymmetric NS-MEMM presents a more flexible way to exploit positional information. In the experiments, NS-MEMM is evaluated on both the Chinese and the English pos-tagging tasks. According to the experimental results, NS-MEMM yields effective improvements over MEMM by exploiting positional information. The smoothing techniques in this article effectively solve the NS-MEMM data-sparseness problem; the asymmetric NS-MEMM is also an improvement by exploiting positional information in a more flexible way.
Interactive high-dimensional index for large Chinese calligraphic character databases
Authors: Zhuang Yl , Zhuang Yueting , Li Qing , Chen Lei
Published: October 2007

The large numbers of Chinese calligraphic scripts in existence are valuable part of the Chinese cultural heritage. However, due to the shape complexity of these characters, it is hard to employ existing techniques to effectively retrieve and efficiently index them. In this article, using a novel shape-similarity- based retrieval method in which shapes of calligraphic characters are represented by their contour points extracted from the character images, we propose an interactive
partial-distance-map
(PDM)- based high-dimensional indexing scheme which is designed specifically to speed up the retrieval performance of the large Chinese calligraphic character databases effectively. Specifically, we use the approximate minimal bounding sphere of a query character and utilize users' relevance feedback to refine the query gradually. Comprehensive experiments are conducted to testify the efficiency and effectiveness of this method. In addition, a new
k
-NN search called Pseudo
k
-NN (P
k
-NN) search is presented to better facilitate the PDM-based character retrieval.
An unsupervised method for learning generation dictionaries for spoken dialogue systems by mining user reviews
Authors: Higashinaka Ryuichiro , Walker Marilyn A. , Prasad Rashmi
Published: October 2007

Spoken language generation for dialogue systems requires a dictionary of mappings between the semantic representations of concepts that the system wants to express and the realizations of those concepts. Dictionary creation is a costly process; it is currently done by hand for each dialogue domain. We propose a novel unsupervised method for learning such mappings from user reviews in the target domain and test it in the restaurant and hotel domains. Experimental results show that the acquired mappings achieve high consistency between the semantic representation and the realization and that the naturalness of the realization is significantly higher than the baseline.