bluuebunny/crossref_metadata_2025 huggingface dataset:
Sourcing Decisions with Stochastic Supplier Reliability and Stochastic Demand
Authors: Burke Gerard J. , Carrillo Janice E. , Vakharia Asoo J.
Published: March 2009

Supplier sourcing strategies are a crucial factor driving supply chain success. In this paper, we investigate the implications of uncertain supplier reliability on a firm's sourcing decisions in an environment with stochastic demand. In particular, we characterize specific conditions under which a firm should choose a single versus multiple supplier sourcing strategy. In an environment with both uncertain demand and supply, we characterize the total order quantity, the number of suppliers selected for order placement, and the allocation of the total order quantity among these selected suppliers. For deeper managerial insight, we also examine the sensitivity of the optimal sourcing decisions to interactions between uncertainties in product demand and supply reliability. We show that sourcing from a single supplier is an optimal strategy for environments characterized by high levels of demand uncertainty or high salvage values. A numerical analysis based on data obtained from an office products retailer further reinforces our analytical results. In addition, we also find that when minimal order quantities are imposed, there are situations where it is not optimal to place an order with the lowest cost supplier.
Integrated Order Scheduling and Packing
Authors: Chen Zhi‐Long , Pundoor Guruprasad
Published: March 2009

We consider an integrated production–distribution scheduling model in a make‐to‐order supply chain consisting of one supplier and one customer. The supplier receives a set of orders from the customer at the beginning of a planning horizon. The supplier needs to process all the orders at a single production line, pack the completed orders to form delivery batches, and deliver the batches to the customer. Each order has a weight, and the total weight of the orders packed in a batch must not exceed the capacity of the delivery batch. Each delivery batch incurs a fixed distribution cost. The problem is to find jointly a schedule for order processing and a way of packing completed orders to form delivery batches such that the total distribution cost (or equivalently, the number of delivery batches) is minimized subject to the constraint that a given customer service level is guaranteed. We consider two customer service constraints—meeting the given deadlines of the orders; or requiring the average delivery lead time of the orders to be within a given threshold. Several problems of the model with each of those constraints are considered. We clarify the complexity of each problem and develop fast heuristics for the NP‐hard problems and analyze their worst‐case performance bounds. Our computational results indicate that all the heuristics are capable of generating near optimal solutions quickly for the respective problems.
Pricing Software Upgrades: The Role of Product Improvement and User Costs
Authors: Bala Ram , Carr Scott
Published: March 2009

The computer software industry is an extreme example of rapid new product introduction. However, many consumers are sophisticated enough to anticipate the availability of upgrades in the future. This creates the possibility that consumers might either postpone purchase or buy early on and never upgrade. In response, many software producers offer special upgrade pricing to old customers in order to mitigate the effects of strategic consumer behavior. We analyze the optimality of upgrade pricing by characterizing the relationship between magnitude of product improvement and the equilibrium pricing structure, particularly in the context of user upgrade costs. This upgrade cost (such as the cost of upgrading complementary hardware or drivers) is incurred by the user when she buys the new version but is not captured by the upgrade price for the software. Our approach is to formulate a game theoretic model where consumers can look ahead and anticipate prices and product qualities while the firm can offer special upgrade pricing. We classify upgrades as minor, moderate or large based on the primitive parameters. We find that at sufficiently large user costs, upgrade pricing is an effective tool for minor and large upgrades but not moderate upgrades. Thus, upgrade pricing is suboptimal for the firm for a middle range of product improvement. User upgrade costs have both direct and indirect effects on the pricing decision. The indirect effect arises because the upgrade cost is a critical factor in determining whether all old consumers would upgrade to a new product or not, and this further alters the product improvement threshold at which special upgrade pricing becomes optimal. Finally, we also analyze the impact of upgrade pricing on the total coverage of the market.
Association between Waste Management and Cancer in Companion Animals
Authors: Marconato L. , Leo C. , Girelli R. , Salvi S. , Abramo F. , Bettini G. , Comazzi S. , Nardi P. , Albanese F. , Zini E.
Published: March 2009

Background: Increased cancer rates have been documented in people residing in areas around Naples characterized by illegal dumping and incineration of waste.

Hypothesis: Risk of cancer in dogs and cats is associated with waste management.

Animals: Four hundred and fifty‐three dogs and cats with cancer and 1,554 cancer‐free animals.

Methods: Hospital‐based case‐control study in Naples (low danger) and nearby cities having a history of illegal waste dumping (high danger). Odds ratio (OR) between high‐ and low‐danger areas was calculated for all tumors and various malignancies in dogs and cats.

Results: An increased risk for cancer development was identified in dogs but not in cats residing in high‐danger areas (OR: 1.55; 95% confidence interval: 1.18–2.03; P < .01). A 2.39‐fold increased risk of lymphoma (P < .01) accounted for the greater tumor frequency in dogs residing in high‐danger areas. The risk of mast cell tumor and mammary cancer did not differ in dogs residing in high‐ or low‐danger areas.

Conclusions and Clinical Importance: Waste emission from illegal dumping sites increases cancer risk in dogs residing in high‐danger areas. An increased prevalence of lymphoma has been previously recognized in humans living close to illegal waste dumps. Thus, epidemiological studies of spontaneous tumors in dogs might suggest a role for environmental factors in canine and human carcinogenesis and can predict health hazards for humans.
Ionized Hypocalcemia in Critically Ill Dogs
Authors: Holowaychuk M.K. , Hansen B.D. , DeFrancesco T.C. , Marks S.L.
Published: March 2009

Background: Ionized hypocalcemia (iHCa) is a common electrolyte disturbance in critically ill people, especially those with sepsis. The cause of the iHCa is not entirely understood and is likely multifactorial. Critically ill people with iHCa have longer hospital stays and higher mortality rates compared to people with normocalcemia. There are no published clinical studies evaluating the incidence and impact of iHCa in critically ill dogs.

Hypothesis: iHCa occurs in critically ill dogs, is more prevalent in dogs with systemic inflammatory response syndrome (SIRS) or sepsis, and is associated with longer hospital stays and higher mortality.

Animals: One hundred and forty‐one client‐owned dogs admitted to a companion animal intensive care unit (ICU) in a veterinary teaching hospital.

Methods: Prospective observational study of sequentially enrolled dogs. Blood was collected and analyzed within an hour of admission from all dogs presented to the ICU that met study inclusion criteria.

Results: The incidence of iHCa (iCa < 1.11 mmol/L) was 16%. The presence of iHCa was associated with longer ICU (P= .038) and hospital (P= .012) stays but not with decreased survival (P= .60). Dogs with sepsis as defined by ≥3 SIRS criteria and a positive culture were more likely to have iHCa (P= .050).

Conclusions and Clinical Relevance: In dogs not previously treated with fluids or blood products intravenously, the finding of iHCa upon admission to the ICU predicted a longer duration of ICU and hospital stay. Septic dogs with positive cultures were more likely to have iHCa.
Serum Acute Phase Protein Concentrations in Dogs with Autoimmune Hemolytic Anemia
Authors: Mitchell K.D. , Kruth S.A. , Wood R.D. , Jefferson B.
Published: March 2009

Background:Serial monitoring of acute phase protein (APP) concentrations in canine autoimmune hemolytic anemia (AIHA) has not been reported.

Hypotheses:Acute canine AIHA is accompanied by an acute phase response (APR) characterized by increased C‐reactive protein (CRP) and α1‐acid glycoprotein (AAG) concentrations and decreased albumin concentrations.

Animals:Twenty‐seven dogs with AIHA and 11 control dogs.

Methods:Prospective, cohort study. CRP, AAG, and albumin concentrations, white blood cell (WBC) count, and packed cell volume (PCV) were determined at admission (day 1), every 48 hours until death or discharge, and on days 30, 90, 180, and 365.

Results:Compared with controls, CRP and AAG concentrations were increased and albumin concentration was decreased in dogs with AIHA (days 1–7;P< .002) and normalized with disease stabilization (days 9–365;P> .05). APP concentrations on day 1 were not predictive of survival, duration of hospitalization, or number of blood transfusions (P= .153–.940). PCV correlated with APP concentrations over time (CRPr=−.600, AAGr=−.665, albuminr= .533;P< .0001) as did WBC count (CRPr= .253, AAGr= .486, albuminr=−.246;P< .006). Day 1 CRP concentration was lower for dogs that received corticosteroids before referral (115.3 μg/mL) compared with dogs that did not (191.2 μg/mL;P= .02).

Conclusions:An APR occurs in canine AIHA. Initial APP concentrations are not predictive of acute survival, correlate with hematologic markers of remission, and normalize rapidly with disease stabilization.
Influence ofEnterococcus faeciumSF68 Probiotic on Giardiasis in Dogs
Authors: Simpson K.W. , Rishniw M. , Bellosa M. , Liotta J. , Lucio A. , Baumgart M. , Czarnecki‐Maulden G. , Benyacoub J. , Bowman D.
Published: March 2009

Background:Giardiasis is a common, potentially zoonotic disease, and dogs often harbor and shed cysts without showing clinical signs. Treatment with the probioticEnterococcus faeciumSF68 has been shown to stimulate mucosal and systemic immunity in a variety of animal models and in young dogs, and to reduce giardial cyst and antigen shedding in rodents.

Hypothesis:Adult dogs with chronic naturally acquired giardiasis will have decreased giardial fecal cyst and antigen shedding and increased innate and adaptive immunity after 6 weeks probiotic treatment withE. faeciumSF68.

Animals:Twenty adult dogs.

Methods:After a 6‐week dietary equilibration period, dogs were randomized to receiveE. faeciumSF68 or placebo for 6 weeks, and then crossed over to the alternate treatment. We measured cyst shedding, fecal giardial antigen, fecal immunoglobulin A (IgA) concentration, and circulating leukocyte phagocytic activity at multiple timepoints to determine the effect ofE. faeciumSF68 on giardiasis and immune responses in these dogs.

Results:No differences were observed between placebo orE. faeciumSF68 treatment for giardial cyst shedding, fecal antigen shedding, fecal IgA concentration, or leukocyte phagocytic activity.

Conclusions:Short‐term treatment withE. faeciumSF68 of dogs with chronic naturally acquired subclinical giardiasis fails to affect giardial cyst shedding or antigen content and does not alter innate or adaptive immune responses.
Partial Contact of an Elastic Coated Cylinder Pressed by a Rigid Flat Surface
Authors: Block Joseph M. , Keer Leon M.
Published: March 2009

The normal contact of a frictionless elastic coated cylinder indented by a flat rigid surface is solved using a Michell–Fourier series expansion, which satisfies the mixed boundary value problem resulting from partial contact. The boundary conditions are chosen such that the elastic layer rests on the cylindrical substrate. When the contact region is small compared to the radius of curvature of the coated cylinder, semi-analytical solutions are obtained by exploiting dual series equation techniques. The stresses on the surface are evaluated for plane strain. The results may have application to coated cylindrical structures, bimaterial inclusions, or pin-joint contact.
Fuel Cell Development for NASA’s Human Exploration Program: Benchmarking With “The Hydrogen Economy”
Authors: Scott John H.
Published: March 2009

The theoretically high efficiency and low temperature operation of hydrogen-oxygen fuel cells have motivated them to be the subject of much study since their invention in the 19th century, but their relatively high life cycle costs have kept them as a “solution in search of a problem” for many years. The first problem for which fuel cells presented a truly cost effective solution was that of providing a power source for NASA’s human spaceflight vehicles in the 1960s. NASA thus invested, and continues to invest, in the development of fuel cell power plants for this application. This development program continues to place its highest priorities on requirements for minimum system mass and maximum durability and reliability. These priorities drive fuel cell power plant design decisions at all levels, even that of catalyst support. However, since the mid-1990s, prospective environmental regulations have driven increased governmental and industrial interest in “green power” and “the hydrogen economy.” This has in turn stimulated greatly increased investment in fuel cell development for a variety of commercial applications. This investment is bringing about notable advances in fuel cell technology, but as these development efforts place their highest priority on requirements for minimum life cycle cost and field safety, these advances are yielding design solutions quite different at almost every level from those needed for spacecraft applications. This environment thus presents both opportunities and challenges for NASA’s Human Exploration program.
Reconstruction of Electric Currents in a Fuel Cell by Magnetic Field Measurements
Authors: Lustfeld H. , Reißel M. , Schmidt U. , Steffen B.
Published: March 2009

In this paper the tomographic problem arising in the diagnostics of a fuel cell is discussed. This is concerned with how well the electric current density j(r) be reconstructed by measuring its external magnetic field. We show that (i) exploiting the fact that the current density has to comply with Maxwell’s equations it can, in fact, be reconstructed at least up to a certain resolution, (ii) the functional connection between the resolution of the current density and the relative precision of the measurement devices can be obtained, and (iii) a procedure can be applied to determine the optimum measuring positions, essentially decreasing the number of measuring points and thus the time scale of measurable dynamical perturbations—without a loss of fine resolution. We present explicit results for (i)–(iii) by applying our formulas to a realistic case of an experimental direct methanol fuel cell.
Linear and Torsional Mechanical Characteristics of Intact and Reconstructed Scapholunate Ligaments
Authors: Zdero Rad , Olsen Michael , Elfatori Salah , Skrinskas Tom , Nourhosseini Hamid , Whyne Cari , Schemitsch Emil H. , von Schroeder Herb
Published: March 2009

The mechanical behavior of human scapholunate ligaments is not well understood. Presently, intact scapholunate specimens were mechanically tested in linear distraction and torsion. Fresh bovine tendon grafts were used to reconstruct the scapholunate interval and the tests repeated. Tests yielded the following average values for intact specimens: linear stiffness (48.9N∕mm), linear load retained at 100s (44%), torsional stiffness (19.5Nmm∕deg), torque remaining at 100seconds (66%), torque-to-failure (1253.9 N mm), and angle-to-failure (50.4deg). Tests showed the following average values for reconstructed specimens: linear stiffness (5.4N∕mm), linear load retained at 100s (49%), torsional stiffness (12.6Nmm∕deg), torque remaining at 100s (71%), torque-to-failure (936.8Nmm), and angle-to-failure (54.5deg). There were no statistically significant differences between the intact and reconstructed specimens, with the exception of linear stiffness. Biomechanically, this is the first study in the literature to quantify torsional stress relaxation, failure torque, and failure angle for the intact and repaired human scapholunate ligament. Surgically, reconstruction with bovine tendon may warrant further investigation as a method to potentially retain function and strength after scapholunate injury.
Hydrogen Fuel: Opportunities and Barriers
Authors: Kumar Prashant , Britter Rex , Gupta Nitesh
Published: March 2009

The fact that 65% of the oil use is by the transportation sector, the increasing gap between the oil supply and demand, and the need to reduce greenhouse gas emissions make the introduction of alternative fuels, together with large energy efficiency gains, a key to sustainable mobility, both nationally and globally. The history of alternative fuels has not been very successful. Various economic, social, and technological barriers have impeded the acceptance of energy carriers such as hydrogen as a major transportation fuel. An effective interaction between the societal system of vehicle owners and a supply infrastructure of alternative fuels is needed for mass adoption of these future technologies. However, hydrogen due to its production pathways, particularly from renewable resources, inexhaustible, and clean nature, an ubiquitous presence and its promise of a sustainable transportable energy source give it a strong edge to be fuel of the future. This paper discusses the economical, social, and technological implications on the use of hydrogen as a future transport fuel. Furthermore, three cases based on UK Department of Transport studies showing the penetration of high efficiency vehicles, fuel cell vehicles (FCVs), and hydrogen fuel internal combustion engine vehicles (H2-ICEs) into the future transport fleet are discussed. With some assumptions, it indicates clearly that by the end of 2050 the H2-ICEs will play a major role in the UK transport sector whereas more time is needed for FCVs due to their less compelling consumer value possibility. Also, it can be inferred that the emissions from hydrogen’s full life cycle are about half those of the direct emissions from nonrenewable fuels such as the natural gas from which it is produced, thereby showing a promising future of hydrogen fuel to cope with the problem of climate change and the continuously increasing scarcity of conventional/fossil fuels.
Adjoint-Based Sensitivity Analysis and Error Correction Methods Applied to Solid Oxide Fuel Cells
Authors: Kapadia S. , Anderson W. K. , Elliott L. , Burdyshaw C.
Published: March 2009

Sensitivity analysis and design optimization of solid oxide fuel cells are presented. Multispecies diffusion, low speed convection, and chemical kinetics are included in a two-dimensional numerical model, and sensitivity derivatives are computed using both discrete adjoint method and direct differentiation. The implementation of the discrete adjoint method is validated by comparing sensitivity derivatives obtained using the adjoint with results obtained using direct differentiation and finite-difference methods. For optimization, cost functions describing hydrogen concentration along the anode-electrolyte interface, hydrogen concentration at the channel outlet, and standard deviation of temperature inside the anode are considered. Material properties of the anode, operating conditions, and a shape parameter are selected as design variables. The development of an initial design environment to automate the flowfield solution, sensitivity computation, optimization, and mesh movement is also described. Finally, an adjoint-based error correction method is implemented and demonstrated to provide accurate estimations for a desired objective function on a fine mesh by combining information obtained from analysis and adjoint solutions on a coarser one.
Effect of Adhesive Thickness and Properties on the Biaxial Interfacial Shear Stresses in Bonded Joints Using a Continuum Mixture Model
Authors: Nassar Sayed A. , Virupaksha Vinayshankar L.
Published: March 2009

In this work, an analytical model based on continuum mixture theories is developed to study the biaxial interfacial shear stresses in adhesive-bonded joints due to thermomechanical loading. The model predicts the effect of adhesive thickness and properties on the interfacial shear stresses. Two sets of governing partial differential equations are solved for the displacement field in each layer of the joint. The interfacial shear stresses between the adhesive and each adherend are determined using the constitutive equations. Numerical results show that both the adhesive thickness and the material properties have a significant effect on the thermomechanically induced interfacial shear stresses between the adherends and the adhesive. The proposed model inherently has the capacity for optimizing the selection of the adhesive thickness and material properties that would yield a more reliable bonded joint.
Effective Age of Remanufactured Products: An Entropy Approach
Authors: Pandey Vijitashwa , Thurston Deborah
Published: March 2009

Product take-back and remanufacturing systems are difficult to implement cost effectively. One contributing factor is the complex nature of the inter-relationships among components of a product. Modeling of these relationships helps determine the product’s overall performance as a function of the performances of individual components. Reliability, a commonly used measure of performance, is a good measure of the physical failure rate, but it does not always reflect value degradation as experienced by customers or experts. As a result, it is difficult to define the effective performance of remanufactured products when some components are reused while others are not. Legislated take-back mandates across the world increasingly make it necessary to understand this perceived performance. In this paper we propose a method for combining customers’/experts’ assessments of value degradation using the maximum entropy principle. This value degradation information is then coupled with the components’ failure rate information. A method for modeling performance of a product that is comprised of components of different ages is presented. Overall performance is measured in units of time (effective age) by aligning with that of a product that has never been disassembled. We demonstrate the approach using a personal computer as example.
On the Thermodynamical Admissibility of the Triphasic Theory of Charged Hydrated Tissues
Authors: Huyghe J. M. , Wilson W. , Malakpoor K.
Published: March 2009

The triphasic theory on soft charged hydrated tissues (Lai, W. M., Hou, J. S., and Mow, V. C., 1991, “A Triphasic Theory for the Swelling and Deformation Behaviors of Articular Cartilage,” ASME J. Biomech. Eng., 113, pp. 245–258) attributes the swelling propensity of articular cartilage to three different mechanisms: Donnan osmosis, excluded volume effect, and chemical expansion stress. The aim of this study is to evaluate the thermodynamic plausibility of the triphasic theory. The free energy of a sample of articular cartilage subjected to a closed cycle of mechanical and chemical loading is calculated using the triphasic theory. It is shown that the chemical expansion stress term induces an unphysiological generation of free energy during each closed cycle of loading and unloading. As the cycle of loading and unloading can be repeated an indefinite number of times, any amount of free energy can be drawn from a sample of articular cartilage, if the triphasic theory were true. The formulation for the chemical expansion stress as used in the triphasic theory conflicts with the second law of thermodynamics.
Role of Cytoskeletal Components in Stress-Relaxation Behavior of Adherent Vascular Smooth Muscle Cells
Authors: Hemmer Jason D. , Nagatomi Jiro , Wood Scott T. , Vertegel Alexey A. , Dean Delphine , LaBerge Martine
Published: March 2009

A number of recent studies have demonstrated the effectiveness of atomic force microscopy (AFM) for characterization of cellular stress-relaxation behavior. However, this technique’s recent development creates considerable need for exploration of appropriate mechanical models for analysis of the resultant data and of the roles of various cytoskeletal components responsible for governing stress-relaxation behavior. The viscoelastic properties of vascular smooth muscle cells (VSMCs) are of particular interest due to their role in the development of vascular diseases, including atherosclerosis and restenosis. Various cytoskeletal agents, including cytochalasin D, jasplakinolide, paclitaxel, and nocodazole, were used to alter the cytoskeletal architecture of the VSMCs. Stress-relaxation experiments were performed on the VSMCs using AFM. The quasilinear viscoelastic (QLV) reduced-relaxation function, as well as a simple power-law model, and the standard linear solid (SLS) model, were fitted to the resultant stress-relaxation data. Actin depolymerization via cytochalasin D resulted in significant increases in both rate of relaxation and percentage of relaxation; actin stabilization via jasplakinolide did not affect stress-relaxation behavior. Microtubule depolymerization via nocodazole resulted in nonsignificant increases in rate and percentage of relaxation, while microtubule stabilization via paclitaxel caused significant decreases in both rate and percentage of relaxation. Both the QLV reduced-relaxation function and the power-law model provided excellent fits to the data (R2=0.98), while the SLS model was less adequate (R2=0.91). Data from the current study indicate the important role of not only actin, but also microtubules, in governing VSMC viscoelastic behavior. Excellent fits to the data show potential for future use of both the QLV reduced-relaxation function and power-law models in conjunction with AFM stress-relaxation experiments.
Frictional Energy Dissipation in a Rough Hertzian Contact
Authors: Dini D. , Hills D. A.
Published: March 2009

The interfacial contact pressure and shear traction distributions are found for a sphere pressed onto an elastically similar half-space whose surface is populated by a uniform array of spherical asperities, when the normal load is constant and an oscillatory shear, less than that needed to cause sliding, is imposed. Details of the load history suffered by asperities in an outer sliding annulus and an inner disk, where they experience partial slip, are found, together with the effects of the roughness on the overall tangential compliance and the frictional energy losses. It is shown that for the example combination of parameters chosen, under light shear loads, the rough contact absorbs less energy than a smooth one subject to the same loading history, but that for larger shearing forces the reverse is true.
Study on Contact Characteristic of Nanoscale Asperities by Using Molecular Dynamics Simulations
Authors: Liu Tianxiang , Liu Geng , Wriggers Peter , Zhu Shijun
Published: March 2009

The nanoscale contacts, which play a key role in nanotechnology and micro-/nanoelectromechanical systems, are fundamentally important for a wide range of problems including adhesion, contact formation, friction and wear, etc. Because continuum contact mechanics has limitations when it is applied at length of nanoscale, molecular dynamics (MD) simulations, which can investigate internal physical mechanisms of nanostructures by atomic motions in detail, become one of the most promising approaches for investigating mechanical behaviors of contacts in nanoscale. First, contacts between rigid cylindrical probes with different radii and an elastic half-space substrate are studied by using MD simulations with the assistance of the classical Lennard-Jones potential. For contacts without adhesion, the relationship between the applied force and the contact half-width is analyzed. The von Mises stress distributions are then discussed. For contacts with adhesion, the phenomena of the jump-to-contact, the break-off contact, and the hysteresis are observed. The pressure distributions and the von Mises stress contours in the contact region agree with the existing solutions. Second, the effects of the surface topography on adhesive contacts are studied by using MD simulations with the embedded atom method potential. The adhesive contact mechanical characteristic of a series of asperities with different shapes, different sizes, and different numbers on contacting surfaces are discovered and compared. The results show that the surface topography is one of the major factors, which may influence the contact behaviors between the interfaces of nanoscale components.
Soft EHL Simulations of U-Cup and Step Hydraulic Rod Seals
Authors: Yang Bo , Salant Richard F.
Published: March 2009

A numerical soft elastohydrodynamic lubrication model of a reciprocating hydraulic seal has been used to simulate the performance of a U-cup seal and a step seal in a conventional actuator. The model consists of coupled steady state fluid mechanics, deformation mechanics, contact mechanics, and thermal analyses, with an iterative computational procedure. The results indicate that for a given seal roughness and stroke length there is a critical rod speed above which the seal will not leak. The critical speed is dependent on both seal roughness and sealed pressure.
Unlocking Organizational Potential: A Computational Platform for Investigating Structural Interdependence in Design
Authors: Olson Jesse , Cagan Jonathan , Kotovsky Kenneth
Published: March 2009

A team’s design—the structuring of its resources and flows of knowledge—is an important element determining its effectiveness. An essential element in achieving a team’s problem-solving potential is the role that interdependence, in both the task and the organization, plays in determining the dynamic and emergent system-level properties of the organization. In this paper, we present a computational platform for experimentally investigating the influence of informational dependencies found in the design of a complex system for exploring their role in determining system behaviors and performance. The approach presented in this paper is a multiagent simulation of the conceptual design of space mission plans by Team X, an advanced project design group at NASA’s Jet Propulsion Laboratory. The algorithm is composed of rich descriptive models of both the team-types and timing of interactions, collaborative methods, sequencing, rates of convergence- and the task-primary variables, their behaviors and relations, and the approaches used to resolve them. The objective is to create an environment of interaction representative of that found in actual design sessions. Better understanding how the dynamics arising from organizational and domain interdependencies impact an organization’s ability to effectively resolve its task should lead to the development of guidelines for better coping with task complexities, suggest ways to better design organizations, as well as suggest ways for improving the search for innovative solutions.
Preference Inconsistency in Multidisciplinary Design Decision Making
Authors: MacDonald Erin F. , Gonzalez Richard , Papalambros Panos Y.
Published: March 2009

A common implicit assumption in engineering design is that user preferences exist a priori. However, research from behavioral psychology and experimental economics suggests that individuals construct preferences on a case-by-case basis when called to make a decision rather than referring to an existing preference structure. Thus, across different contexts, preference elicitation methods used in design decision making can lead to preference inconsistencies. This paper offers a framework for understanding preference inconsistencies, giving three examples of preference inconsistencies that demonstrate the implications of unnoticed inconsistencies, and also discusses the design benefits of testing for inconsistencies. Three common engineering and marketing design methods are discussed: discrete choice analysis, modeling stated versus revealed preferences, and the Kano method. In these examples, we discuss perceived relationships between product attributes, identify market opportunities for a “green” product, and show how people find it is easier to imagine delight rather than necessity of product attributes. Understanding preference inconsistencies offers new insights into the relationship between user and product design.
Computer-Aided Machine Setting for Lapping Optimization
Authors: Jiang Qimi , Gosselin Claude , Masseth Jack
Published: March 2009

During hypoid gears lapping process, a gear set is running at varying operating positions and under a light load in order to lap the complete tooth surface. The pinions and gears are lapped in pairs. Hence, their tooth surfaces are not only cutters but also workpieces. In the contact region, the contact pressure and sliding speed are different from point to point. This makes lapping to be a very complicated abrasive wear process. So far, knowledge about the relationship between the removed materials and the lapping time as well as how to optimize the lapping process is quite limited. An algorithm was presented (Jiang et al., 2008, “Simulation of Hypoid Gear Lapping,” ASME J. Mech. Des., 130(11), p. 112601) to determine the wear coefficient k for the lapping process of hypoid gears. With the obtained wear coefficient k, a methodology for simulating the lapping process was proposed. Based on the wear coefficient obtained, this work presents a computer-aided machine setting procedure to optimize the lapping cycle in order to improve the lapping quality and efficiency.
Multiobjective Optimum Design of a Symmetric Parallel Schönflies-Motion Generator
Authors: Altuzarra O. , Hernandez A. , Salgado O. , Angeles J.
Published: March 2009

The multiobjective optimization of a four-degree-of-freedom symmetric parallel manipulator for Schönflies-motion generation is the subject of this paper. First, the inverse positioning problem is discussed, along with its velocity analysis. The workspace is then analyzed, thereby deriving a closed-form expression of the workspace volume, which depends on the orientation of the moving platform. Next, the isotropic design of the manipulator is obtained. Then, the dexterity analysis of the manipulator is conducted, which is one objective of the optimum design of the manipulator, a second objective being a normalized workspace volume. Finally, the results of the optimization process are reported in terms of a set of Pareto-optimum pairs of the design parameters.
Learning Design Rules With Explicit Termination Conditions to Enable Efficient Automated Design
Authors: Rawson Kevin , Stahovich Thomas F.
Published: March 2009

We present a two-step technique for learning reusable design procedures from observations of a designer in action. This technique is intended for the domain of parametric design problems in which the designer iteratively adjusts the parameters of a design so as to satisfy the design requirements. In the first step of the two-step learning process, decision tree learning is used to infer rules that predict which design parameter the designer is likely to change for any particular state of an evolving design. In the second step, decision tree learning is again used, but this time to learn explicit termination conditions for the rules learned in the first step. The termination conditions are used to predict how large of a parameter change should be made when a rule is applied. The learned rules and termination conditions can be used to automatically solve new design problems with a minimum of human intervention. Experiments with this technique suggest that it can reproduce the decision making process observed from the designer, and it is considerably more efficient than the previous technique, which was incapable of learning explicit rule termination conditions. In particular, the rule termination conditions allow the new program to automatically solve design problems with far fewer iterations than previously required.
Thermohydrodynamic Study of Multiwound Foil Bearing Using Lobatto Point Quadrature
Authors: Feng Kai , Kaneko Shigehiko
Published: March 2009

The applications of foil air bearings have been extended for use in a wide range of turbomachineries with high speed and high temperature. Lubricant temperature becomes an important factor in the performance of foil air bearings, especially at high rotational speeds and high loads or at high ambient temperature. This study presents a thermohydrodynamic (THD) analysis of multiwound foil bearing, in which the Reynolds’ equation is solved with gas viscosity as a function of temperature that is obtained from the energy equation. Lobatto point quadrature is utilized to accelerate the iteration process with a sparse mesh across film thickness. A finite element model of the foil is used to describe the foil elasticity. An iterative procedure is performed between the Reynolds equation, the foil elastic deflection equation, and the energy equation until convergence is achieved. A three-dimensional temperature prediction of air film is presented, and a comparison of THD to isothermal results is made to emphasize the importance of thermal effects. Finally, published experimental data are used to validate this numerical solution.
Analysis of Multirecess Hydrostatic Journal Bearing Operating With Micropolar Lubricant
Authors: Verma Suresh , Kumar Vijay , Gupta K. D.
Published: March 2009

This paper presents a theoretical study of the performance characteristics of a constant flow valve compensated multirecess hydrostatic journal bearings operating with micropolar lubricant. The finite element method and iterative procedure have been used to solve the modified Reynolds equation governing the micropolar lubricant flow in the bearing. The performance characteristics are presented for a wide range of nondimensional load, lubricant flow, and micropolar parameters. It has been observed that the micropolar parameters significantly influence the performance characteristics of the bearing.
Thermomechanical Coupling in Oscillatory Systems With Application to Journal Bearing Seizure
Authors: Wen Jun , Khonsari M. M.
Published: March 2009

A method for treating the thermomechanical interaction of bodies that undergo relative oscillatory motion is developed. The approach utilizes a combination of the transfer matrix and the finite element methods. The thermomechanical coupling process between the contacting bodies involves a transient solution scheme where the frictional heat is automatically partitioned between the contacting surfaces. The coupling between thermal and mechanical interactions is treated iteratively. An application of the proposed model in the study of thermomechanical behavior of journal bearings with oscillatory motion undergoing thermally induced seizure is presented. The results of a wide range of operating parameters are presented. The significance of applied load, contact clearance, friction coefficient, oscillation parameters, convective heat transfer, and variable load direction condition in the thermally induced seizure is discussed in light of the numerical results.
Comparison Between DEXA and Finite Element Studies in the Long-Term Bone Remodeling of an Anatomical Femoral Stem
Authors: Herrera A. , Panisello J. J. , Ibarz E. , Cegoñino J. , Puértolas J. A. , Gracia L.
Published: March 2009

The implantation of a cemented or cementless femoral stem changes the physiological load transfer on the femur producing an effect on the bone called adaptative remodeling. The patterns of this remodeling are attributed to mechanical and biological factors, and those changes in bone mineral density have been determined in long-term densitometry studies. This technique has proved to be a useful tool able to quantify small changes in bone density in different femoral areas, and it is considered to be ideal for long-term studies. On the other hand, the finite element (FE) simulation allows the study of the biomechanical changes produced in the femur after the implantation of a femoral stem. The aim of this study was to contrast the findings obtained from a 5 year follow-up densitometry study that used a newly designed femoral stem (73 patients were included in this study), with the results obtained using a finite element simulation that reproduces the pattern of load transfer that this stem causes on the femur. In this study we have obtained a good comparison between the results of stress of FE simulation and the bone mass values of the densitometry study establishing a ratio between the increases in stress (%) versus the increases in bone density (%). Hence, the changes in bone density in the long term, compared with the healthy femur, are due to different load transfers after stem implantation. It has been checked that in the Gruen zone 7 at 5 years, the most important reduction in stress (7.85%) is produced, which coincides with the highest loss of bone mass (23.89%). Furthermore, the simulation model can be used with different stems with several load conditions and at different time periods to carry out the study of biomechanical behavior in the interaction between the stem and the femur, explaining the evolution of bone density in accordance to Wolff’s law, which validates the simulation model.
Prediction of Steady State Adhesive Wear in Spur Gears Using the EHL Load Sharing Concept
Authors: Akbarzadeh S. , Khonsari M. M.
Published: March 2009

The concept of load sharing between asperities and fluid film is applied in conjunction with lubricated sliding wear formulation proposed by Wu and Cheng (1991, “A Sliding Wear Model for Partial-EHL Contacts,” ASME J. Tribol., 113, pp. 134–141; 1993, “Sliding Wear Calculation in Spur Gears,” ASME J. Tribol., 115, pp. 493–500) to predict the steady state adhesive wear in gears. Thermal effects are included using a simplified thermoelastohydrodynamic analysis. The prediction of the model is verified by comparing simulation results with published experimental data pertinent to steady state wear rate. The main advantages of this method are the accuracy and the remarkable computational efficiency. The results of parametric simulation study are presented to investigate the effect of speed and surface roughness on a portion of load carried by asperities and wear rate.
The Effect of Surface Roughness on Static Friction and Junction Growth of an Elastic-Plastic Spherical Contact
Authors: Cohen D. , Kligerman Y. , Etsion I.
Published: March 2009

A model for elastic-plastic spherical contact of rough surfaces under combined normal and tangential loadings, with full stick contact condition, is presented. The model allows evaluation of the effect of surface roughness on the real contact area, static friction and junction growth under small normal loads. It is shown that as the normal load approaches a certain threshold value, which depends on the plasticity index, the results of the present rough surface model approach these of previous corresponding models for smooth sphere and a rigid flat. At normal load values below the threshold load, the correlation of the present results and published experimental results is much better in comparison with the results of the smooth surface models.
Analysis of a Porous Elastic Sheet Damper With a Magnetic Fluid
Authors: Liu Jun
Published: March 2009

In progress of anti-shock characteristics of small size precision equipment, a miniaturized damper is required to have better damping characteristics. However, damping efficiency becomes less as damper size decreases, and so for compensation of its defect, a porous elastic sheet damper with a magnetic fluid is proposed. An analytical estimation of this sheet damper is presented to investigate variation of damping characteristics with intensity and direction of a magnetic field and to give effects of porosity of porous sheets on damping characteristics.
A Simple and Efficient Reformulation of the Classical Manson–Coffin Curve to Predict Lifetime Under Multiaxial Fatigue Loading—Part II: Notches
Authors: Susmel Luca , Meneghetti Giovanni , Atzori Bruno
Published: March 2009

The present study is concerned with the use of the modified Manson–Coffin curve method to estimate the lifetime of notched components subjected to multiaxial cyclic loading. The above criterion postulates that fatigue strength under complex loading paths can efficiently be evaluated in terms of maximum shear strain amplitude, provided that the reference Manson–Coffin curve used to predict the number of cycles to failure is defined by taking into account the actual degree of multiaxiality/nonproportionality of the stress/strain state damaging the assumed crack initiation site. The accuracy and reliability of the above fatigue life estimation technique was checked by considering about 300 experimental results taken from the literature. Such data were generated by testing notched cylindrical samples made of four different metallic materials and subjected to in-phase and out-of-phase biaxial nominal loading. The accuracy of our criterion in taking into account the presence of nonzero mean stresses was also investigated in depth. To calculate the stress/strain quantities needed for the in-field use of the modified Manson–Coffin curve method, notch root stresses and strains were estimated by using not only the well-known analytical tool due to Köttgen et al. (1995, “Pseudo Stress and Pseudo Strain Based Approaches to Multiaxial Notch Analysis,” Fatigue Fract. Eng. Mater. Struct., 18(9), pp. 981–1006) (applied along with the ratchetting plasticity model devised by Jiang and Sehitoglu (1996, “Modelling of Cyclic Ratchetting Plasticity, Part I: Development and Constitutive Relations. Transactions of the ASME,” ASME J. Appl. Mech., 63, pp. 720–725; 1996, “Modelling of Cyclic Ratchetting Plasticity, Part I: Development and Constitutive Relations,” Trans. ASME J. Appl. Mech., 63, pp. 720–725)) but also by taking full advantage of the finite element method to perform some calibration analyses. The systematic use of our approach was seen to result in estimates falling within an error factor of about 3.
A Simple and Efficient Reformulation of the Classical Manson–Coffin Curve to Predict Lifetime Under Multiaxial Fatigue Loading—Part I: Plain Materials
Authors: Susmel Luca , Meneghetti Giovanni , Atzori Bruno
Published: March 2009

This paper summarizes an attempt to devise an engineering method suitable for predicting fatigue lifetime of metallic materials subjected to both proportional and nonproportional multiaxial cyclic loadings. The proposed approach takes as a starting point the assumption that the plane experiencing the maximum shear strain amplitude (the so-called “critical plane”) is coincident with the micro-/mesocrack initiation plane. In order to correctly account for the presence of both nonzero mean stresses and nonzero out-of-phase angles, the degree of multiaxiality/nonproportionality of the stress state damaging crack initiation sites is suggested here to be evaluated in terms of the ratio between maximum normal stress and shear stress amplitude relative to the critical plane. Such a ratio is used then to define nonconventional Manson–Coffin curves, whose calibration is done through two strain-life curves generated under fully reversed uniaxial and fully reversed torsional fatigue loadings, respectively. The accuracy and reliability of our approach were systematically checked by using approximately 350 experimental data taken from the technical literature and generated by testing 13 different materials under both in-phase and out-of-phase loadings. Moreover, the accuracy of our criterion in estimating lifetime in the presence of nonzero mean stresses was also investigated. Such an extensive validation exercise allowed us to prove that the fatigue life estimation technique formalized in the present paper is a reliable tool capable of correctly evaluating fatigue damage in engineering materials subjected to multiaxial cyclic loading paths.