bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Injection Rate and Post-Fill Cure Pressure on Properties of Resin Transfer Molded Disks
Authors: Olivero Kristian A. , Barraza Harry J. , O’Rear Edgar A. , Altan M. Cengiz
Published: July 2003

The effects of flow rate andpost-fill cure pressure, i.e., packing pressure, on the mechanical properties of resin transfer molded disks are experimentally investigated. An experimental molding setup is constructed to fabricate fiber-reinforced, center-gated, disk-shaped composite parts. Disks are molded at different flow rates and packing pressures in order to observe the effects of these parameters on the mechanical properties andvoidcontent of the final parts. Specimens are cut from three different locations in the molded disks for testing. Specimens from the first two locations are tensile testedto obtain strength and stiffness properties, and the third location is usedfor microscopic analysis to determine void content and void properties. Increased injection rate is found to reduce both the strength and stiffness of the molded parts due to more voids induced by the faster moving fluidfront. Packing pressure is also foundto have a significant effect on specimen properties. At higher packing pressures fewer voids and improved strength andstiffness are observed. Mechanical properties are correlatedwith total void fraction for disks molded at different packing pressures. Exponential decrease in both tensile strength andelastic modulus is observedwith increasing voidfraction. Doubling the voidvolume fraction from 0.35 to 0.72% results in a 15% decrease in strength and a 14% decrease in stiffness. The results demonstrate that selection of suitable injection rate and addition of packing pressure to resin transfer molding (RTM) process can improve mechanical properties of molded parts considerably.
Influence of Fixation Structures on the In-Plane Permeability of Unidirectional Glass Fiber Tapes
Authors: Endruweit A. , Ermanni P.
Published: July 2003

In this study the influence of a fixation grid on the permeability of a uni-directional glass fiber tape has been experimentally investigated with respect to processing of the material applying Liquid Composites Molding technology. Two-dimensional flow experiments show that for the given material and configuration the fixation structure has a strong influence on the permeability. The ratio of the permeability principal values is found to depend on the porosity. For a critical porosity even isotropic behavior can be expected. This result is verified by additional one-dimensional flow experiments with variation of the fiber angle of the lay-ups, showing that for the critical porosity the fiber angle has no significant influence on the permeability. The ratio of the permeability principal values does not significantly differ from 1. For the glass fiber tape without fixation structure the permeability principal values have been found to differ by one order of magnitude. Comparison of the absolute permeability values for the tape with and without fixation structure suggests that (for a total of 12 material layers) each layer of the fixation grid reduces the permeability of the lay-up by 8% (parallel) and 6% (transversal) for completely parallel oriented material and by 8% for a 0°/90° alternating lay-up. For a given fiber material, the influence of the fixation structure on the permeability is predicted to increase with decreasing porosity and to decrease with increasing area related mass, i.e. overall thickness, of the tape.
Energy Absorption Behavior of Double-Chamfer Triggered Glass/Epoxy Circular Tubes
Authors: Song Hong-Wei , Du Xing-Wen , Zhao Gui-Fan
Published: July 2003

The effects of double-chamfer triggered pattern to the axial crushing energy absorption behavior of glass/epoxy circular tubes with the ply pattern of [±θ]n is reported. Deliberate weakness of 45 chamfered triggers at both ends of the tube is introduced with the aim of controlling the crushing performance. Similar to single-chamfer triggered pattern, application of this trigger pattern is an efficient way to weaken the initial peak load Pcr, extend the triggering length Ltr, reduce the probability of catastrophic failure and avoid unstable crushing. The crushing behaviors, the damage characteristics of untriggered, single-chamfer triggered and double-chamfer triggered tubes were studied in detail. Specific crushing stress was used to measure the energy absorption for tubes of different winding angles. Investigations on the macroscopic collapse mode of the tube, the effects of ply angle, the effect of impact loading and quasi-static loading were performed in the presence of double-chamfer triggers.
Bearing Behavior of Joints in Pultruded Composites
Authors: Wang Youjiang
Published: July 2003

Due to the increased use of pultruded composites for structural applications, understanding the bearing behavior of pultruded composites is important for effective structural designs. This paper reports on a comprehensive experimental and analytical study to characterize the influence of geometry and loading condition on the joint strength and failure mode in pultruded composites. The geometric parameters studied were specimen width, end distance, and hole diameter. The experimental study included compressive and tensile bearing tests. The results provide useful information for the structural design with such materials against joint failures. The experimental results for tensile failure load and failure mode are compared with predictions from the tensile, shear and (compressive) bearing strengths based on both average stress analysis and finite element method (FEM). The effect of hole size on the compressive bearing strength was analyzed and good correlation between predictions and test results was observed. The effect of further reinforcing the pultruded composites with a woven fabric was evaluated.
Response of Cross-Ply Composite to Off-Axis Loading
Authors: Tamužs V. , Andersons J. , SpāArniņš E. , Varna J.
Published: July 2003

Polymer composites are known to exhibit nonlinear stress–strain response due to nonlinearly elastic or plastic deformation of the matrix and damage accumulation. Mechanistic modeling of material response explicitly accounting for these interacting factors often leads to complex theories. Plasticity theory formalism provides an alternative for nonlinear deformation description of composite material. We examine the applicability of an orthotropic plasticity model, developed by Sun et al. for unidirectionally reinforced composite, to composite laminate. The response of a symmetric and balanced cross-ply glass/epoxy laminate is studied under uniaxial tensile loading at different angles to the material orthotropy axis. It is found that the associated flow rule and a quadratic approximation of the orthotropic potential function provide satisfactory description for the nonlinear strain component under monotonic loading for 15–45° off-axis angle range. The nonlinearity in on-axis loading (modulus degradation)is well described by stiffness reduction due to the cracks in transverse plies. Meanwhile the change of elastic modulus due to intralaminar cracking can be neglected in off-axis loading, but the possible intensification of nonlinear deformation in off-axis loading caused by the presence of intralaminar cracks agrees well with orthotropic potential formalism.
Effect of Interleaved Non-Woven Carbon Tissue on Interlaminar Fracture Toughness of Laminated Composites: Part II – Mode I
Authors: Lee Seung-Hwan , Noguchi Hiroshi , Kim Young-Bae , Cheong Seong-Kyun
Published: July 2003

Interlaminar fracture behavior of non-woven carbon tissue (NWCT) interleaved composites was investigated under a Mode I loading condition using a double-cantilever-beam (DCB) specimen. The NWCT interleaved specimens were made by interleaving NWCT-prepregs between CFRP layers. CFRP specimen ([024]), NWCT interleaved specimen ([012/Tn/012]) and NWCT composite specimen ([T80]) were prepared under the same cure condition of the CFRP specimen. The symbol ‘‘/Tn/’’ means that the NWCT layer is located at the 0/0 mid-plane of the interleaved specimen, and n is the number of NWCT layers. The NWCT has short carbon fibers, discretely distributed with in-plane random orientation fibers. An interlaminar crack is introduced to a center of the interleaved specimens. The DCB testing results were analyzed using the normal distribution. When the short carbon fiber volume fraction in the NWCT layer is about 10%, the Mode I interlaminar fracture toughness of the NWCT interleaved specimen is about 28% higher than that of the CFRP specimen due to the fiber breakage of out-of-plane oriented short carbon fibers in the NWCT layer. The fracture process on the side-section and fracture surfaces of the interleaved specimen was observed with an optical microscope and a scanning electron microscope, and the failure mechanism was discussed.
Effect of Interleaved Non-Woven Carbon Tissue on Interlaminar Fracture Toughness of Laminated Composites: Part I – Mode II
Authors: Lee Seung-Hwan , Noguchi Hiroshi , Kim Young-Bae , Cheong Seong-Kyun
Published: July 2003

A study on the Mode II interlaminar fracture characteristics of non-woven carbon tissue (NWCT) interleaved composites was carried out using the endnotched-flexure (ENF) test. The NWCT interleaved composites were made by interleaving NWCT-prepreg between CFRP layers. CFRP specimen [024] as well as NWCT interleaved specimen [012/T/012] were prepared to compare the characteristics. The symbol ‘‘/T/’’ means that the NWCT layeris located at the 0/0 mid-plane of the interleaved specimen. Three kinds of interlaminar cracks, which have different positions in the NWCT layer, were introduced to the interleaved specimen. The ENF testing results were analyzed using the normal distribution. The mean GIIC of the interleaved specimen with an upper crack is about 26% higher than that of the CFRP specimen due to a blunt shape of crack tip by Teflon film in the NWCT layer. The mean GIIC of the interleaved specimens with a center crack and a lower crack is about 260 and 205% higherthan that of the CFRP specimen due to the short fiber bridging from in-plain random short carbon fibers in the NWCT layer, respectively. The fracture surfaces of the specimens and the fracture process on the specimen side-sections were observed with an optical microscope and a scanning electron microscope, and then they were analyzed for the failure mechanism. The size and spacing of hackles on the fracture surface are affected by both the length and fiber volume of short carbon fibers in the NWCT layer.
Damping and Stiffness of Particulate Sic–Insn Composite
Authors: Ludwigson M. N. , Lakes R. S. , Swan C. C.
Published: July 2003

Metal matrix composites of silicon carbide particles in indium–tin alloy were fabricated with the aim of achieving a high value of the product of stiffness and viscoelastic damping tan, without excess density. Stiffness and viscoelastic damping were measured over a wide range of frequency. For monodisperse 40% by volume SiC, and for hierarchical 60% by volume SiC the composite damping increased compared with the matrix at frequencies above 100 Hz. Composite shear modulus was almost a factor two greater than matrix for 40% and a factor of four greater than that of matrix for 60%. The product of stiffness and damping exceedsthat of well-known materials including polymer damping layers. Hashin–Shtrikman analysis modelled the observed stiffness increase. The damping increase at higher frequency cannot be accounted for by a purely mechanical composite model; it is attributed to thermoelastic coupling and an increase in matrix dislocations during fabrication.
Resin Transfer Moldable Phenylethynyl Containing Imide Oligomers
Authors: Smith J. G. , Connell J. W. , Hergenrother P. M. , Criss J. M.
Published: July 2003

As part of an effort to develop high performance/high temperature materials for composite fabrication via resin transfer molding (RTM) and resin infusion (RI), phenylethynyl-containing imide oligomers (PEIs) have been investigated. Uncured resins with low and stable melt viscosities and when cured, high glass transition temperatures ( TgS) and acceptable mechanical properties, are needed for RTM and RI processes. High performance/high temperature composites from these materials are potentially useful in advanced aerospace vehicles such as reuseable launch vehicles (RLVs). Several PEIs were prepared and evaluated for melt flow behavior and mechanical properties after thermalcuring. Candidate materials exhibited the combination of properties required for RTM with melt viscosities of0.4–1.0 Pa s at 280°C and melt stability for > 2 h at 280°C. Flat, void-free composites fabricated by RTM gave cured Tgs as high as 350°C, high mechanical properties, and excellent stability at 288°C. The chemical, physical, and mechanical properties of these resins and their composites are discussed.
Structural Analysis and Strain Monitoring of the Filament Wound Motor Case
Authors: Park Jae-Sung , Kim Cheol-Ung , Kang Hyun-Kyu , Hong Chang-Sun , Kim Chun-Gon
Published: July 2003

Filament wound structures such as pressure tanks, pipes and motor cases of rockets are widely used in aerospace applications. The determination of a proper winding angle and thickness is very important to decrease manufacturing difficulties and to increase structural efficiency. In this study, possible winding angles considering the slippage between a fiber and a mandrel surface are calculated using the semi-geodesic path equation. In addition, finite element analyses using ABAQUS are performed to predict the behavior of filament wound structures considering continuous change of the winding angle and thickness at the dome part due to fiber built-up near the metallic boss. Water-pressuring tests of a third stage motor case are performed to verify the analysis procedure. The strain gages are attached on the surface in the fiber direction. Progressive failure analysis predicted the burst pressure a little bit higher than the experiment and the weakest region of the motor case very well. The effect of reinforcement is also studied to increase its performance.
45 Flexure Test for Measurement of In-Plane Shear Modulus
Authors: Mujika F. , Mondragon I. , Berglund L. A. , Varna J.
Published: July 2003

A new method to obtain the in-plane shear modulus GLT for unidirectional oriented composite materials is proposed. The method is based on an original analytic way for calculating middle point displacement in a 3-point flexure test. The bending–twisting coupling effects in such a test induce the lift-off of the specimen at the fixture supports for some geometrical conditions. Thereby, contact points are located at two opposite points of the specimen. Consequently, new bending moments along the width of the specimen and twisting moments appear. By supposing resultant moments and shear forces per unit length are uniformly distributed, these distributions are calculated for static conditions along longitudinal and transverse cross sections of the specimen. After having expressed strain energy as a function of resultant moments and resultant shear forces per unit length, Second Castigliano’s theorem is applied in order to calculate the middle point displacement. No similar analytic way has been encountered in classical laminated beams theory or in classical laminated plates theory. The displacement obtained in this work and the one obtained from classical laminated beams theory are particularised to the case of 45 fibre orientation. GLT expressions have been derived from those displacement expressions in three ways: two of them from the solution of this work, not considering and considering shear effects, respectively, and the third one from displacement obtained from classical laminated beams theory. Experiments have been made for different geometric conditions in order to test the influence of geometric parameters in experimental results. For span-to-width ratios up to two, the values obtained are quite constant and agree well with the in-plane shear modulus value obtained by the material manufacturer using 45 tensile test.
Numerical Analysis of the Dimensional Stability of Thermoplastic Composites Using a Thermoviscoelastic Approach
Authors: Kim Byeong-Sam , Bernet Nicolas , Sunderland Paul , Manson Jan-Anders
Published: July 2003

The dimensional stability of V-shaped composite parts made from polyamide-12/carbon fibre (PA12/CF) commingled yarn has been studied. An anisotropic, thermoviscoelastic material model was implemented in a finite element solver to predict the internal stresses induced during the processing of the composite. Excellent correlation was found between predicted and experimentally measured stress profiles for compression-moulded parts. The stresses were related to the dimensional stability of the parts after demoulding and the effect of key processing parameters on dimensional stability was investigated.
Dynamic Characteristics of Laminated Woven E-Glass–Epoxy Composite Plates Subjected to Lowvelocity Heavy Mass Impact
Authors: Aslan Züleyha , Karakuzu Ramazan , Sayman Onur
Published: July 2003

The main goal of this study is to examine the size effects including both in-plane dimensional and thickness effects for laminated woven E-glass–epoxy composite subjected to low velocity heavy mass impact. The studies have been carried out with plate dimensions of 150 × 150 mm, 150 × 100 mm and 150 × 50 mm for in-plane dimensional effect. Two nominal thicknesses with averages of 1.4 and2.8 mm are used for studying the thickness effect. The impact testings are conducted with a vertical drop-weight testing machine developed in the department laboratory. Affixed to the drop-weight device, a piezoelectric force transducer, localized in the hemispherical impactor nose, yields the complete force versus time history of impact event. Impact tests are performed at increasing impact velocities 1, 2 and 3m/s and impactor mass of 2.6 kg on clamped plates. A numerical evaluation of these specimens is also carried out by using 3DIMPACT transient dynamic finite element analysis code. The contact forces between the impactor and the composite plate as functions of time, transient stresses during impact and the predicted delamination sizes of composites are found numerically.
Cure Kinetic Model, Heat of Reaction, and Glass Transition Temperature of AS4/3501-6 Graphite–Epoxy Prepregs
Authors: Kim Jonghyun , Moon Tess J. , Howell John R.
Published: July 2003

A new isothermally-based, cure kinetic model for the carbon graphite–epoxy AS4/3501-6 prepreg is presented using an industrially supplied prepreg rather than the neat epoxy resin. A two-stage model is used: first, rate-controlled (autocatalytic); then diffusion-controlled. A Differential Scanning Calorimeter (DSC) is employed to investigate the prepreg’s cure kinetics using both isothermal and dynamic DSC scans, although only isothermal DSC scan data is used to fit the model’s parameters. A Thermogravimetric Analyzer (TGA) is used to determine the mass fraction of the epoxy resin in the prepreg. The coefficients are provided for a prepreg having 37.4% resin mass fraction; they must be re-evaluated for prepregs having significantly different resin mass fractions.

The ultimate heat of reaction of the resin incorporated within the prepreg is measured as 433.7 J/g (based upon a linear baseline) or 422.7 J/g (based upon a specific-heat-corrected baseline) using dynamic DSC scans at 20°C/min. This value is 8–17% less than the reported 472–508 J/g for the neat 3501-6 epoxy also measured using dynamic DSC scans at 20°C/min. Important to manufacturing applications, dynamic DSC scans reveal that the prepreg’s ultimate heat of reaction is sensitive to scan rate. Finally, the prepreg’s carbon fiber and/or sizing appears to suppress the curing reaction and decrease the ultimate heat of reaction over that for the neat epoxy resin.

The glass transition temperature Tg (°C) of partially-cured AS4/3501-6 prepregs is measured using DSC and is expressed as a function of degree of cure: Tg = 22.9 exp(2.16α) – markedly similar to 3501-6 neat resin Tg data measured earlier using a dynamic mechanical analyzer. The small specimen DSC thermal scans provide an effective means to measure the Tg of completely- or partially-cured prepregs. The Tg of the 100%-cured prepreg was experimentally determined to be 199°C, slightly higher than the 193°C reported for the 100%-cured neat epoxy resin. The AS4 fibers play little or no role in the degree-of-cure dependence of the AS4/3501-6 prepreg’s Tg.

Recommended for general purpose structural applications, the AS4/3501-6 prepreg is composed of continuous, PAN-based, AS4C carbon (graphite) fibers and an amine-cured epoxy resin system. The epoxy resin, 3501-6, is a tetraglycidyl diamino diphenyl methane (TGDDM) with diaminodiphenylsulfone (DDS) catalyzed with boron trifluoride monoethylamine. 3501-6 was developed to operate in atemperature environment of up to 350°F (177°C).
Isolating Components of Processing Induced Warpage in Laminated Composites
Authors: Darrow David A. , Smith Lloyd V.
Published: July 2003

This study considers laminate warpage (or spring-in) associated with the curing of reinforced thermoset composites. This processing induced spring-in shows up in flat parts as well as those with curved geometry, and is most prevalent with parts that do not have a closed cross section. Three contributions to spring-in were considered, namely: thickness cure shrinkage, mold expansion, and fiber volume fraction gradients. These effects were combined into a predictive finite element model (FEM). Mold stretching and thickness shrinkage were described through a modified in-and out-of-plane material thermal expansion, respectively, while fiber volume fraction gradients were accounted for by scaling the thermal and elastic properties of the composite through the thickness with the fiber volume fraction. For thin parts (< 2 mm) spring-in was dominated by fiber volume fraction gradient and mold stretching effects. For thick parts (> 2 mm) spring-in was dominated by thickness cure shrinkage. The FEM was able to account for 80% of the observed spring-in for parts ranging between 1 and 5 mm thick and having a 3 to 13 mm bend radius. This study shows that a relatively simple, linear-elastic analysis, can accurately describe competing contributions to spring-in over a range of material types and thicknesses.
When Adaptation Fails
Authors: ZOTT CHRISTOPH
Published: July 2003

A rationale based on adaptive learning is used to explain inefficient bargaining under private information. A dynamic bargaining model using genetic algorithms is developed in which independent but interacting negotiators coevolve their offers. A computer simulation analysis is conducted that compares bargaining outcomes under complete and incomplete information. Results show that inefficient bargaining (i.e., delays and failures to agree) may be due to problems in the agents' adaptive processes that arise because of incomplete information and that adaptive failures may occur even under complete information. Adaptive learning is identified as both a mechanism for resolving conflict and a potential source of conflict.
Anticipating the Good, the Bad, and the Ugly
Authors: O'BRIEN SEAN P.
Published: July 2003

One way to demonstrate progress in a field of scientific inquiry is to show that factors believed to explain some phenomenon can also be used effectively to predict both its occurrence and its nonoccurrence. This study draws on the state strength literature to identify relevant country macrostructural factors that can contribute to different kinds and levels of intensity of conflict and country instabilities. A pattern classification algorithm—fuzzy analysis of statistical evidence (FASE)—is used to analyze the relationships between country macrostructural factors and historical instances of country instability. A split-sample validation design is used to evaluate the ability of FASE to generate competent predictions, using the standard forecasting performance metrics overall accuracy, recall, and precision. The results demonstrate the potential for FASE to accurately forecast not just the occurrence but also the level of intensity of country-specific instabilities out 5 years with about 80% overall accuracy.
Islam and Terrorism
Authors: HADDAD SIMON , KHASHAN HILAL
Published: July 2003

Lebanese Muslim reactions to the September 11 attacks are assessed using the hypotheses that receptiveness to dogmas of militant Islam and young age would predict approval of the attacks, and education and income, although important in explaining the domestic component of political Islam, would have no bearing on support for the September 11 terrorist attacks. In view of the recent surge of Sunni Muslim militancy, it is proposed that Sunni respondents would show greater support for the attacks than Shi'is. The data were obtained from a stratified random sample consisting of 337 Sunni and Shi'i male and female respondents to an opinion poll conducted in the Greater Beirut area during October and November 2001. The findings verify the proposition that proneness to militant Islam and age predicted approval of the attacks but do not verify the hypothesis that Sunni respondents exceeded Shi'is in approval for the attacks.
Capacity, Commitment, and Compliance
Authors: SIMMONS BETH A.
Published: July 2003

Why should governments delegate decision-making authority over territorial issues to an international institution? This study argues that governments are motivated to reach territorial solutions to reduce the opportunity costs associated with a festering dispute. The evidence suggests that domestic political incapacity to negotiate concessions is associated with a commitment to arbitrate. Compliance is a function of the net costs and benefits involved in accepting the arbitral decision. These costs include the loss of valuable territory, but noncompliance also exacts costs with respect to governments' reputation, both domestically and internationally. This research speaks to a broader debate about the role of international legal institutions in foreign policy making and international outcomes. It shows that governments have good reasons, under certain political and economic conditions, to use international legal processes as a substitute for domestic political decision making.
The HIV/AIDS Epidemic in African American Communities
Authors: Okigbo Charles , Okigbo Carol A. , Hall William B. , Ziegler Dhyana
Published: July 2003

The HIV/AIDS pandemic has afflicted Africa more than any other region of the world. In the United States, the AIDS scourge has disproportionately affected African American communities. In their tragic experiences with HIV/AIDS, both African states and African American communities can benefit from the new communication framework that the United Nations Global AIDS Programme and the Pennsylvania State University have developed to combat the HIV/AIDS pandemic. The framework contains five universal values that are recommended for AIDS intervention programs across the world. The five values are incorporation of government policies, socioeconomic status, culture, gender issues, and spirituality. There are six additional values, two of which apply uniquely to each of the three world regions of Africa, Asia, and Latin America. For Africa, the two unique values are community-based approaches and regional cooperation. The situation in Africa presents valuable lessons for African Americans in the United States.
W.E.B. Du Bois's Talented Tenth
Authors: Battle Juan , Wright Earl
Published: July 2003

The Talented Tenth is the moniker that W.E.B. Du Bois bestowed on the cadre of college-educated African Americans whom he charged with providing leadership for the African American community during the post-Reconstruction era. According to Du Bois's original theoretical formulation, the Talented Tenth were to sacrifice their personal interests and endeavors to provide leadership for the African American community. Following in Du Bois's footsteps, this inquiry uses the National Black Politics Study to examine the attitudes of today's Talented Tenth concerning their responsibilities as leaders of their respective communities. Multivariate findings indicate that among other things, the Talented Tenth report being more politically active and more involved in their communities and are suspect of the motives of the Black middle class. The authors' results suggest that the Talented Tenth are fulfilling the charge placed before them by W.E.B. Du Bois.
Press Coverage of Black Statewide Candidates
Authors: Jeffries Judson L.
Published: July 2003

This article examines the newspaper treatment of L. Douglas Wilder's 1985 lieutenant governor's campaign and his 1989 gubernatorial campaign. Using content analysis, the author analyzes one liberal newspaper and one conservative newspaper, both of which serve the Virginia area. This article found that although these publications devoted most of their attention to the Wilder campaigns, they also gave the majority of negative coverage to the Wilder campaigns. Some of the coverage included unflattering references to Wilder's race. In sum, this study supports the claim by Black politicians that the media often distort and misrepresent the campaigns of Black office seekers in a way that makes it difficult for them to garner White votes.
An Oral History Interview
Authors: Turner Diane D.
Published: July 2003

Oral history is empowering because it initiates African agency while creating primary documents for future research and historical interpretation. An oral history interview with Molefi Kete Asante, conducted by historian Diane D. Turner, reveals aspects of his early life with autobiographical sketches about his mother, father, and the community where he was raised. The interview moves from personal accounts of his childhood to his academic career and his transformation from Arthur L. Smith, to Molefi Kete Asante. Asante addresses questions around a variety of topics, including key issues in Black Studies. Asante discusses the intellectual and developmental process that brought him to construct the theory of Afrocentricity and how our nation's first Ph.D. program in African American Studies was established at Temple University under his leadership.
Reconceptualizing the State: Lessons from Post-Communism
Authors: Grzymala-Busse Anna , Luong Pauline Jones
Published: July 2003

The (re)building of the post-communist states offers new perspectives both on the state and on the multiple transitions that followed communism. Specifically, it shifts our analytical focus from states as consolidated outcomes and unitary actors to the process by which states come into being and into action in the modern era. This process consists of elite competition over policy-making authority, which is shaped and constrained by existing institutional resources, the pacing of transformation, and the international context. The four ideal types of state-building that result are exemplified by the post-communist experience: democratic, autocratic, fractious, and personalistic.
The Dilemmas of Reform in Weak States: The Case of Post-Soviet Fiscal Decentralization
Authors: Way Lucan A.
Published: July 2003

This article explores the dilemmas of reform in weak states through an examination of efforts to decentralize the fiscal system in post-Soviet Ukraine in the 1990s. Despite increased attention to the state, many reform efforts still ignore the full implications that state weakness has for institutional transformation. Inattention to the problems of institutional capacity has led to a misdiagnosis of the problems facing intergovernmental institutions in post-Soviet Ukraine. Overcentralization and soft budget constraints built into formal institutional design demand an unrecognized degree of institutional capacity that is frequently weak or absent in the post-Soviet context. In addition, reform measures that fail to take into account the problems of weak institutions have inadvertently reduced the authority of already enfeebled state institutions.
Politics of Revenue Extraction in Post-Communist States: Poland and Russia Compared
Authors: Easter Gerald M.
Published: July 2003

Since the late 1990s, a consensus has emerged among scholars of the post-communist transitions that an enfeebled state is not an asset but a liability to a transition economy. Moreover, it is now accepted that underdeveloped fiscal capacity is a leading cause of state weakness in Eastern Europe and the former Soviet Union. This article compares the alternative revenue extraction strategies developed by state leaders in post-communist Poland and Russia. It stresses political institutional constraints to explain why Poland opted for a social pact with labor over household incomes, while Russia developed a system of elite bargaining over corporate profits.
A Hybrid Modeling and Simulation Methodology for Dynamic Physical Systems
Authors: Mosterman Pieter J. , Biswas Gautam
Published: July 2003

This article presents the design and implementation of a robust simulation methodology for hybrid models of physical systems that encompasses behavior patterns that undergo discrete transitions between modes of continuous behavior evolution. This methodology is based on a mathematical framework that captures time scale and parameter abstractions in modeling complex physical phenomena. The formal semantics for characterizing hybrid behaviors is defined in terms of three distinct modes of system operation: (1) continuous, (2) pinnacles, and (3) mythical. A key link is established between the switching transitions and the a priori and a posteriori state vector values, which defines the recursive mode switching functions that govern the interactions between the continuous and discrete components of the system models. The effectiveness of the approach is demonstrated by examples of physical system models that are presented along with a simulator to handle these.
Modeling and Simulation of Dynamic Structure Heterogeneous Flow Systems
Authors: Barros Fernando J.
Published: July 2003

The author presents the Heterogeneous Flow System Specification (HFSS), a formalism suited to represent combined (discrete/continuous) systems. The new formalism is based on the concept of sampling that is described in general terms to include multirate sampling systems. The HFSS formalism permits the construction of continuous/discrete input/output models in a modular and hierarchical manner. Hierarchical systems have a dynamic structure nature that can be changed over time. To show an application of the HFSS formalism, the author presents a new formalism to numerically solve differential equations with discontinuities using multirate integration methods. Applications of combined and dynamic structure systems are presented.
Simulating Passive Microwave Radiometer Designs Using Simulink
Authors: Burrage Derek M. , Goodberlet Mark A. , Heron Malcolm L.
Published: July 2003

The authors have developed a simulation system for a passive microwave radiometer using MATLAB and SIMULINK from The MathWorks, Inc. The system comprises a high-level block diagram simulation for a modern instrument, the Scanning Low Frequency Microwave Radiometer, or SLFMR. The hardware prototype SLFMR, which was designed to map sea surface salinity, was implemented using the classic pulsed noise injection Dicke radiometer design. A suite of lower-level user-written components arranged in user block libraries has also been developed. The simulations functionally model the signal flow of the prototype, with random fluctuations representing the equivalent noise temperature of various signals propagating through the system, so the fundamental physics of random noise processes are preserved. Examples of several simulations are presented, and the computational feasibility, performance, and possible enhancements are assessed.
The Trend Cellular Automata Programming Environment
Authors: Chou Hui-Hsien , Huang Wei , Reggia James A.
Published: July 2003

Trend is a two-dimensional cellular automata programming environment with an integrated simulator and a compiler. Trend has many unique features such as simulation backtracking, conflict recognition, flexible template design, and arbitrary space size. The general-purpose Trend language allows user-defined semireserved words, symmetrically rotatable statements, and other constructs specific to the parallel computation occurring in cellular automata programming. Trend is available freely both for Unix systems and the Java platform, and it can be used to study artificial life, massively parallel computing, models of natural phenomena, or anything else a user finds interesting.
Identification of Discrete Event Systems Using the Compound Recurrent Neural Network: Extracting DEVS from Trained Network
Authors: Choi Si Jong , Kim Tag Gon
Published: July 2003

The authors consider identifying an unknown discrete event system (DES) as recognition of characteristic functions of a discrete event systems specification (DEVS) model that validly represents the system. Such identification consists of two major steps: behavior learning using a specially designed neural network and extraction of a DEVS model from the learned neural network. This paper presents a method for extracting a DEVS model from one such neural network called CRNN (compound recurrent neural network), which is trained using observed input/output events of an unknown DES. The DES to be identified is restricted to a subclass of DES in which any unknown state can be determined by a finite number of input/output sequences. Identification experiments were performed with three types of unknown DESs, the result of which verified the validity of the proposed model extraction method.
Onboard Testing of the Control System in the LNG Carrier Using a Dynamic Simulator
Authors: Chung Jibum , Yoo Heejong , Lee Ingu , Park Junwon , Yun Yongseung
Published: July 2003

A simulator, which has process, controllers, and man-machine interface (MMI), can be configured as a hardware-in-the-loop system or a software-in-the-loop system. In this paper, these general simulator configurations are reviewed and applied to the liquefied natural gas carrier (LNGC). The characteristics of the LNGC process, control, and its simulator configurations are presented. The simulator process/control/MMI models, hardware, software configurations, and onboard tests, which have been carried on the LNGC, are also presented. Using this simulator, the control engineers on board effectively debug and validate the control system of the LNGC, and the future operators of the LNGC can test various operating conditions, including abnormal and very severe operations.
Introduction to the Special Issue: ATM Systems and Networks: Basics, Issues, and Performance Modeling and Simulation
Authors: Obaidat Mohammad S.
Published: July 2003

Asynchronous Transfer Mode (ATM) is one of the major enabling technologies of high-speed networking. It is the first technology that allows a corporation to use a common enterprise protocol and infrastructure for voice, data, and video communications. ATM excels when applications require specific quality of service (QoS) and reserved bandwidth. It offers economies of scale in network infrastructure by integrating different traffic types. ATM offers a tighter coupling between the user application and network protocol. It places intelligence into the Wide Area Network (WAN), making the network smarter and allowing the network to become more like a computer and less like a dump transport medium. ATM is the ideal technology when it is desirable for applications with different performance, QoS, and business requirements to be performed on the same computer multiplexer, router, switch, and/or network. It enables network managers to flexibly adapt to changing enterprise communications requirements, evolving business environment, and fluctuating traffic volumes and patterns. This special issue of SIMULATION: Transactions of The Society for Modeling and Simulation International aims at reporting on the state-of-the-art on research results in performance modeling and simulation of ATM systems and networks. The papers accepted in this special issue represent recent efforts by leading scientists and engineers from academia, industry, and government worldwide.
Modeling and Simulation of Adaptive Available Bit Rate Voice over Asynchronous Transfer Mode Networks
Authors: Obaidat Mohammad S. , Obeidat Suhaib A.
Published: July 2003

This article presents a modeling and simulation methodology to analyze the performance of voice quality when sent over the available bit rate service in asynchronous transfer mode networks. Sources can modify the rate at which they send traffic to the network based on the feedback carried in the resource management cells. This is achieved by changing the encoding level. As the contention increases to network resources—bandwidth in this case—sources start reducing the rate at which they generate and send traffic. The efficiency of the scheme under different scheduling/drop policies and other operating conditions and environments is evaluated using simulation modeling. Furthermore, sensitivity analysis is applied to different parameters, such as queue size and averaging interval length, to investigate their impact on the performance metrics. Results show that limiting the load to 41% of the link capacity results in an acceptable quality.
Design and Simulation of Asynchronous Transfer Mode-Available Bit Rate End System Congestion Control
Authors: Fahmy Sonia , Jain Raj , Goyal Rohit , Vandalore Bobby
Published: July 2003

The authors develop a simulation model for asynchronous transfer mode available bit rate (ATM ABR) service and use it to engineer ABR congestion control behavior. Although significant work has been performed on ABR rate allocation algorithms at network switches, little work has focused on the end system behavior, which is examined in this article. The effect of (1) the speed of the links on the path from the source to the destination and (2) the connection round trip time on the selection of ABR parameter values is studied. Simulation results illustrate the impact of the key parameters that control rate reduction in the absence of network feedback on performance, in terms of connection throughputs, queue lengths at the switches, and link utilizations. These results have been incorporated into the ABR standards and can be generalized to cooperative congestion control with explicit congestion notification in the Internet.
Modeling and Simulation of an ABR Flow Control Algorithm Using a Virtual Source/Virtual Destination Switch
Authors: Cseh Christian
Published: July 2003

The Available Bit Rate (ABR) service class of Asynchronous Transfer Mode networks uses a feedback control mechanism to adapt to varying link capacities. The Virtual Source/Virtual Destination (VS/VD) technique offers the possibility to segment the otherwise end-to-end ABR control loop into separate loops. The improved feedback delay and the control of ABR traffic inside closed segments provide a better performance for ABR connections. This article will present the use of classical linear control theory to model and develop an ABR VS/VD flow control algorithm. Discrete event simulations are used to analyze the behavior of the algorithm with respect to transient behavior and correctness of the control model. Linear control theory offers the means to derive correct choices of parameters and to assess performance issues, like stability of the system, during the design phase. The performance goals are a high link utilization, fair bandwidth distribution, and robust operation in various environments, which are verified by discrete event simulations. The major contribution of this work is the use of analytic methods (linear control theory) to model and design an ABR flow control algorithm tailored for the special layout of a VS/VD switch, and the use of simulation techniques to verify the result.
Modeling Telecommunication Infrastructures Integrating Wideband Wireless and Wired Networks
Authors: Arseni Paolo , Boggia Gennaro , Camarda Pietro
Published: July 2003

Future telecommunication systems will integrate wireline and wireless networks in a single, advanced infrastructure. It is expected that such systems, in the wireless part, will exploit microcellular architectures in order to guarantee wideband multimedia services and to sustain the continuous growth of subscribers. In such a context, asynchronous transfer mode and Internet protocol are the basic technologies being considered by several studies and field implementations. In both cases, particular care has been devoted to cope with a large number of handoffs. This article considers some aspects of this integrated telecommunication infrastructure, proposing an improvement, for the wired part, of the virtual connection tree and shadow cluster concepts, whereas for the wireless part, a new model for the analysis of a dynamic channel allocation scheme is presented. The obtained analytical results, confirmed by simulation in a wide range of load conditions and user mobility, allow one to evaluate the main system performance parameters in terms of blocking probability of new calls, handoff-blocking probability, and forced termination probability.
Performance of Transport Protocols over ATM Networks
Authors: Marsan M. Ajmone , Bianco A. , Cigno R. Lo , Munafò M. , Baldi M.
Published: July 2003

The performance of file transfer applications running over an ATM infrastructure is investigated, taking into account both the impact of the ATM and AAL layer protocols, and the features of the adopted transport layer protocol. Two transport protocols are considered: TCP and XTP. The performance investigation is performed by simulation, using CLASS, a tool for the study of ATM networks at the cell and burst levels. The obtained results do not show a definite advantage of one transport protocol over the other, but rather different situations where either one performs slightly better or slightly worse.
SEAN for Modeling and Simulating ATM Signaling
Authors: Battou Abdella , Marsh Spencer , Khan Bilal , Mountcastle Sean , Talmadge David , Lee Daniel C.
Published: July 2003

SEAN (signaling entity for ATM networks) is freely distributed, object-oriented, extensible software for research and development in host ATM signaling. SEAN software is object-oriented and can be used for simulation, experimentation, and operation. SEAN includes a complete source-level release of the host native ATM protocol stack and implements the ATM User Network Interface, compliant to the ITU Q.2931 specification for point-to-point calls, the ITU Q.2971 extension for point-to-multipoint calls, and the ATM Forum extension UNI-4.0 for leaf-initiated join calls. SEAN also includes software that models and simulates an ATM switch with an arbitrary number of ports performing the signaling functions. SEAN provides APIs to the programmers writing application programs that require ATM signaling. Developers can easily modify and extend SEAN, using the framework library released together.
Simulation of an Integrated Architecture for IP-over-ATM Frame Processing
Authors: Ewert Peter M. , Manjikian Naraig
Published: July 2003

The performance of an integrated architecture for full-duplex IP-over-ATM processing is evaluated through detailed simulation. The architecture combines processing, memory, and multiple direct-memory-access engines for single-chip implementation. The simulation models the segmentation and reassembly operations needed to translate IP frames to and from a fixed ATM cell size. A key operation is the insertion of a virtual path and virtual channel identifier (VPI/VCI) into the outgoing ATM cells. Software-based VPI/VCI insertion provides flexibility but requires the on-chip processor to perform this function. Hardware-based VPI/VCI insertion is an optimization that requires one of the direct-memory-access engines to perform this task. The two approaches are evaluated through simulated execution of representative control software with detailed modeling of all on-chip components. Results indicate that software-based VPI/VCI insertion supports full-duplex traffic at 475 Mbps on a 500-MHz processor and that hardware-based VPI/VCI insertion supports full-duplex traffic at 560 Mbps on a 500-MHz processor.