bluuebunny/crossref_metadata_2025 huggingface dataset:
Responses to Positive Results From Suspicionless Random Drug Tests in US Public School Districts
Authors: Ringwalt Chris , Vincus Amy A. , Ennett Susan T. , Hanley Sean , Bowling J. Michael , Yacoubian George S. , Rohrbach Louise A.
Published: March 2009

Background:  Little is known about the context in which school‐based suspicionless random drug testing (SRDT) occurs. The primary purpose of the current study was to describe school districts’ responses to students’ first positive result in districts with SRDT programs.

Methods:  Data were collected in spring 2005 from 1612 drug prevention coordinators in a nationally representative sample of 1922 school districts (83.9% response rate), of which 205 districts reported SRDT in high school grades.

Results:  Respondents reported an array of consequences for students with an initial positive SRDT, including requiring parents or guardians to meet with school officials (88.4%) and requiring students to participate in an education, counseling, or treatment program (60.8%). However, some districts also reported consequences contraindicated by federal advisory guides, such as notifying law enforcement officials (45.1%) and suspending the student from an athletic team (65.0%) or from school (31.0%). Some respondents may have conflated their districts’ responses to for cause and random tests. Districts generally had available key services for students testing positive, including professional counseling for substance use problems (87.3%) and referrals to counseling services (91.9%).

Conclusions:  More understanding is needed of schools’ responses to students who test positive following the administration of SRDT, available advisory guides concerning best practices should be more effectively disseminated, and appropriate training and technical assistance should be available to schools with SRDTs.
Biofilm formation and proteolytic activities of Pseudoalteromonas bacteria that were isolated from fish farm sediments
Authors: Iijima Saori , Washio Kenji , Okahara Ryota , Morikawa Masaaki
Published: March 2009

In order to save natural resources and supply good fishes, it is important to improve fish‐farming techniques. The survival rate of fish fry appears to become higher when powders of foraminifer limestone are submerged at the bottom of fish‐farming fields, where bacterial biofilms often grow. The observations suggest that forming biofilms can benefit to keep health status of breeding fishes. We employed culture‐based methods for the identification and characterization of biofilm‐forming bacteria and assessed the application of their properties for fish farming. Fifteen bacterial strains were isolated from the biofilm samples collected from fish farm sediments. The 16S rRNA gene sequences indicated that these bacteria belonged to the genera, Pseudoalteromonas (seven strains), Vibrio (seven strains) and Halomonas (one strain). It was found that Pseudoalteromonas strains generally formed robust biofilms in a laboratory condition and produced extracellular proteases in a biofilm‐dependent manner. The results suggest that Pseudoalteromonas bacteria, living in the biofilm community, contribute in part to remove excess proteineous matters from the sediment sludge of fish farms.
Preclinical Safety Validation of a Stabilized Viral Vector Direct Injection Approach to the Cervical Spinal Cord
Authors: Federici Thais , Riley Jonathan , Park John , Bain Mark , Boulis Nicholas
Published: March 2009

The current lack of a validated intraspinal delivery approach precludes translation of promising cell or viral‐based therapeutics for treatment of varied spinal cord afflictions. We have developed a stabilized cervical microinjection platform with the intent of precise delivery to intraspinal sites of interest. Nine 30–40 kg female swine underwent coordinate‐based microinjection AAV2‐GFP at three injected volumes (10, 25, and 50 μL (n= 3/group)) and matched infusion rates (1.0, 2.5, and 5.0 μL/min) over a period (t= 10 minutes). Preliminary validation is provided by behavioral and targeting data demonstrating safe delivery of a viral vector carrying a fluorescent reporter gene to the cervical spinal cord ventral horn.
Religious and Non‐Religious Pathways to Stress‐Related Growth in Cancer Survivors
Authors: Park Crystal L. , Edmondson Donald , Blank Thomas O.
Published: March 2009

While religiousness and spirituality are important to many cancer survivors, relations of religiousness and spirituality with the stress‐related growth commonly reported by survivors have not been well documented. In the present study, we examined the linkages between personal religiousness, religious control appraisals for the cancer, and religious coping with subsequent stress‐related growth, and compared them with a parallel secular pathway, hope, self‐control appraisals, and active coping. In all, 172 young to middle‐aged adult survivors (113 women, 59 men, mean age = 45 years) of a variety of types of cancer who had been diagnosed approximately 2.5 years prior were assessed twice across a 1‐year period. A structural equation model indicated that while both pathways predicted stress‐related growth, the religious pathway was a much stronger predictor of subsequent stress‐related growth than was the secular pathway. We suggest that more attention should be given to the influence of multiple dimensions of religiousness and spirituality on growth to better understand the transformative processes reported by many survivors.
How Venetians Think About Carnival and History
Authors: Feil D.K.
Published: March 2009

Carnival in Venice dates back to the the 11th century. After steadily efflorescing through to the 18th century and acquiring a grand reputation throughout Europe and beyond, carnival lapsed in the period after the conquest by Napoleon in 1797. Only in 1979 did it reemerge as an important Venetian event. This essay traces the important historical continuities and contexts of Venetian carnival to the present. Despite its hiatus, Venetians link themselves and their carnival to their glorious, remote past, demonstrating profound historical consciousness, politicising and debating the ‘real’ meaning of carnival and above all, defining and reaffirming their own identity through its performance.
Firewalking: Explanation and the Mind‐Body Relationship1
Authors: Sansom Jane
Published: March 2009

With specific reference to theAnastenaria, a firewalking ritual performed in the North of Greece, this paper discusses the problem which phenomena such as firewalking poses for anthropological discussion. The relationship between the mind and the body and their existence in the social world is addressed, as I search for a way in which anthropological discourse can approach an explanation of an individual's ability to walk on burning coals unharmed. A brief look at the various explanations provided by different disciplines follows a more detailed review of scientific inquiry into this phenomenon. A critical discussion of the notions of trance, possession and altered states of consciousness introduces the subjective/objective dichotomy. The question is asked: How does the body exist in the world and to what extent does there remain a distinction between body, mind and object?
Art, Culture and Ambiguity in Wilcannia, New South Wales
Authors: Gibson Lorraine
Published: March 2009

The claim of most town whites that Aboriginal people of Wilcannia make art but have no culture and the claim by Aboriginal people of the town that their art work and art designs demonstrate their culture and cultural traditions opens up the powerful and productive dimensions of art and culture for closer scrutiny. In so doing, the ambivalence and ambiguity which saturates these categories is ethnographically revealed. How can the presence and production of artworks in Wilcannia and the white denial of culture be considered? Why indeed do these questions matter, in what ways do they matter, and to whom do they matter? How do the categories of traditional/remote, urban/settled and their avatars intersect with black and white notions of Aboriginal art and Aboriginal culture discursively and experientially?
Gratuitousness: Notes Towards an Anthropology of Interiority
Authors: Rapport Nigel
Published: March 2009

Interiority—an individual's inner consciousness, the continual conversation one has with oneself–remains an anthropological terra incognita. Literature has been less circumspect in this regard; fiction might be said to be ‘truer’ than social science in its efforts and intent to deal with how individual consciousness feels in the everyday and is immanent in social life. In this article I argue for recognising interiority as a crucial focus of anthropological endeavour, and I outline a possible way in which interiority might be evidenced as irrupting onto the social scene. Interiority makes its paradoxical appearance in social settings in the form of a strangeness, an individual purity and integrity, for which the term ‘gratuitousness’ is apposite. The language of individuals' interior conversation is routinely contained within the language of public exchange; on occasion it bursts these bounds. In both cases, I contend, interior conversation is an existential norm, which holds a key to understanding social life. The course of the article is to review, briefly but critically, disciplinary tendencies which have rendered individual interiority an impossible or irrelevant anthropological theme. A method of interiority is then outlined by way of an anthropological reading of two literary texts. The article ends by reconsidering the potential of an anthropology project that has a concern for interiority.

The modern discovery of inner experience, of a realm of purely personal events that are always at the individual's command, and that are his exclusively as well as inexpensively for refuge, consolation and thrill is also a great and liberating discovery. It implies a new worth and sense of dignity in human individuality.
Patterns of Advanced Manufacturing Technology Utilization and Manufacturing Capabilities
Authors: Chung Wenming , Swink Morgan
Published: March 2009

The objectives of this research are first to empirically replicate Advanced Manufacturing Technology (AMT) utilization taxonomies identified in foregoing research, second to investigate the relationship between patterns of AMT utilization and manufacturing capabilities attainment, and third to explore differences in context, and performance across AMT groups. Theories of performance frontiers and capability progression provide the basis for our hypotheses. Data were collected from 224 U.S. manufacturing plants in industries considered to have potential utilizations of AMTs. A cluster analysis of the data yields a solution that closely resembles a previous AMT utilization taxonomy, including four groups labeled, respectively, as Traditionalists, Generalists, High Investors, and Designers. Significant manufacturing capability differences across these four groups indicate that plants that utilize a broader scope of AMTs enjoy a greater breadth of manufacturing capabilities. The implied capability attainment pattern is consistent with cumulative capability theory. However, the results suggest that cost capability is not included in the capability mix when broad‐based AMT utilization is the enabler of capability gains. A post hoc exploration of the AMT groups indicates significant differences in performance across the groups. Collectively, the results extend prior research by providing added insights into the possible rationale and impact of AMT utilization patterns.
Co‐opetition and Investment for Supply‐Chain Resilience
Authors: Bakshi Nitin , Kleindorfer Paul
Published: March 2009

This paper considers the problem of disruption risk management in global supply chains. We consider a supply chain with two participants, who face interdependent losses resulting from supply chain disruptions such as terrorist strikes and natural hazards. The Harsanyi–Selten–Nash bargaining framework is used to model the supply chain participants' choice of risk mitigation investments. The bargaining approach allows a framing of both joint financing of mitigation activities before the fact and loss‐sharing net of insurance payouts after the fact. The disagreement outcome in the bargaining game is assumed to be the result of the corresponding non‐cooperative game. We describe an incentive‐compatible contract that leads to First Best investment and equal “gain” for all players, when the solution is “interior” (as it almost certainly is in practice). A supplier that has superior security practices (i.e., is inherently safer) exploits its informational advantage by extracting an “information rent” in the usual spirit of incomplete information games. We also identify a special case of this contract, which is robust to moral hazard. The role of auditing in reinforcing investment incentives is also examined.
Tolerability of Gemcitabine and Carboplatin Doublet Therapy in Cats with Carcinomas
Authors: Martinez‐Ruzafa I. , Dominguez P.A. , Dervisis N.G. , Sarbu L. , Newman R.G. , Cadile C.D. , Kitchell B.E.
Published: March 2009

Background:This study was performed to determine the toxicity of gemcitabine‐carboplatin doublet therapy in cats with carcinomas.

Hypothesis:Gemcitabine and carboplatin are safe in tumor‐bearing cats.

Animals:Twenty cats with spontaneously occurring carcinomas.

Methods:A cohort of 6 cats received gemcitabine (2 mg/kg IV) on days 1, 8, and 15 and carboplatin (10 mg/kg IV) immediately after gemcitabine on day 1 of a 21‐day cycle. A 2nd cohort of 14 cats received carboplatin 4 hours after gemcitabine on day 1 and gemcitabine on day 8 but not day 15. The cycles were repeated every 21 days.

Results:Cats in the 1st cohort received a median of 3.75 cycles per animal (range, 1–6). Two cats (33.3%) developed grade 3 or 4 neutropenia, 1 (16.7%) grade 4 thrombocytopenia, and 1 (16.7%) grade 3 gastrointestinal toxicity. Gemcitabine dose reductions and treatment delays occurred in 1 and 4 cats, respectively. Cats in the 2nd cohort received a median of 2 cycles per animal (range, 0.5–10). Two cats (14.3%) had grade 3 or 4 neutropenia and 1 (7.1%) had grade 3 and 4 gastrointestinal toxicity. One cat required gemcitabine dose reduction and 6 had treatment delays. In the 2nd cohort, of 11 cats with measurable tumors, there was 1 complete response (pancreatic carcinoma) and 1 partial response (squamous cell carcinoma, receiving concurrent nonsteroidal anti‐inflammatory drugs).

Conclusions and Clinical Importance:Gemcitabine‐carboplatin combination appears moderately well tolerated in tumor‐bearing cats. Minimal patient benefit suggests that alternative schedules or combinations of gemcitabine with other agents should be explored.
Effect of Processing Conditions on Curvature of Anode/Electrolyte SOFC Half-Cells Fabricated by Electrophoretic Deposition
Authors: Lankin Michael K. , Karan Kunal
Published: March 2009

Thin-electrolyte anode-supported solid oxide fuel cells (YSZ/NiO–YSZ) were fabricated for intermediate-temperature operation using electrophoretic deposition (EPD). During cosintering, the half-cells were observed to warp—an undesirable characteristic—due to mismatch in the sintering rates. The influence of the temperature for anode presintering—a key processing step—on the curvature of the half-cells induced by sintering was investigated over 700–1400°C. It was found that the maximum curvature occurred for an anode presintered at 900°C, while the minimum was observed at 1200°C. Anode presintering temperature was also found to affect the rate of electrophoretic deposition. At low presintering temperatures, the rate of EPD increased due to the enhancement in substrate (anode) electronic conductivity as a result of an increased percolating network of NiO. Further increases in presintering temperature, however, resulted in a decrease in the EPD rate due to the formation of a surface layer with poor electronic conductivity as a result of NiO diffusion from the NiO-YSZ anode to the sintering crucible.
The Current Density Distribution in a Segmented-in-Series SOFC
Authors: Haberman B. A. , Marquis A. J.
Published: March 2009

A common tubular solid oxide fuel cell (SOFC) design consists of segmented-in-series electrochemical cells fabricated onto the outside of a porous support tube. Predicting the performance of this type of SOFC requires a detailed understanding of the current density distribution within each cell. This distribution is strongly coupled to the activation, concentration, and Ohmic losses, which occur as a result of the physical transport processes within the cell. A new computer code, known as the SOHAB code, has been developed to simulate these physical processes and thus make predictions of cell performance. The simulation results show how the magnitude of each loss varies spatially within the cell, causing the calculated current density distribution to be very different from that predicted by the established purely Ohmic models. At low currents the cell behavior is dominated by activation losses producing a very flat distribution. At moderate currents the Ohmic losses become more important, and the distribution is peaked at the edges of the electrolyte. At high currents the increased concentration losses flatten the distribution in the middle of the cell but not near its edges where gases flow from the surrounding inactive regions and the losses remain small. At low and moderate currents, the calculated current density distribution is sufficiently flat that the assumption of a uniform distribution can be used in conjunction with a one-dimensional model. However, at high currents this simplified model overestimates the concentration loss as it cannot account for the improved mass transport near the electrolyte edges.
Probabilistic-Based Design Methodology for Solid Oxide Fuel Cell Stacks
Authors: Sun X. , Tartakovsky A. M. , Khaleel M. A.
Published: March 2009

A probabilistic-based component design methodology is developed for a solid oxide fuel cell (SOFC) stack. This method takes into account the randomness in SOFC material properties as well as the stresses arising from different manufacturing and operating conditions. The purpose of this work is to provide the SOFC designers a design methodology so that the desired level of component reliability can be achieved with deterministic design functions using an equivalent safety factor to account for the uncertainties in material properties and structural stresses. Multiphysics-based finite element analyses were used to predict the electrochemical and thermal mechanical responses of SOFC stacks with different geometric variations and under different operating conditions. Failures in the anode and the seal were used as design examples. The predicted maximum principal stresses in the anode and the seal were compared with the experimentally determined strength characteristics for the anode and the seal, respectively. Component failure probabilities for the current design were then calculated under different operating conditions. It was found that anode failure probability is very low under all conditions examined. The seal failure probability is relatively high, particularly for high fuel utilization rate under low average cell temperature. Next, the procedures for calculating the equivalent safety factors for the anode and seal were demonstrated so that a uniform failure probability of the anode and seal can be achieved. Analysis procedures were also included for non-normal distributed random variables so that more realistic distributions of strength and stress can be analyzed using the proposed design methodology.
A Virtual Prototype of Proton Exchange Membrane Fuel Cell Using VHDL-AMS Language
Authors: Laouamri A. , Djahli F. , Rabhi A. , Benhamadouche A. , Ballouti A. , Bendjadou A.
Published: March 2009

The aim of this paper is to introduce a novel modeling method for the Proton exchange membrane full cell (PEMFC) based on the novel concept of “virtual prototyping” and to present a simple and accurate model of the cell performance by using the mixed-technology modeling language VHDL-AMS. This model describes the steady state and the dynamic behavior of a PEM fuel cell using its characteristic equations. The phenomenon of a charge double layer and the electrochemical parameters such as resistivity of membrane, concentration of hydrogen (oxygen) in catalytic interface of anode (cathode), and current density are considered in this modeling method. These parameters are adjustable and present a good solution to predict output voltage, efficiency, and output power of the PEMFC.
Fabrication and Demonstration of 1 kW Class SOFC Stack and System for Residential Power Generation Application
Authors: Yoo Young-Sung , Lee Taehee , Choi Jin Hyeok , Park Tae-Sung , Oh Je-Myung , Kim Chong-Young
Published: March 2009

The planar type 1 kW class solid oxide fuel cell (SOFC) stack using metallic interconnects such as ferritic stainless steel has been developed for application in a residential power generation system. For the intermediate temperature operation of the SOFC, a higher performance of anode-supported single cells of 10×10 cm2 with a thin electrolyte layer of yttria-stabilized zirconia were fabricated by slurry coating, and their performances were improved by a microstructure-controlled anode substrate and by introducing alternative cathode materials. The thicknesses of the electrolyte and the cathode layers were about 20 μm and 40 μm, respectively. I-V and ac impedance characteristics of single cells were evaluated at an intermediate temperature (650–800°C) by using hydrogen gas as fuel. The maximum power density of the 10×10 cm2 anode-supported cells was about 0.32 W/cm2 at 750°C and 0.2 W/cm2 at 650°C. In this work a 1 kW class SOFC stack composed of 37 cells (10×10 cm2) was successfully manufactured and a SOFC system with balance of plant (BOP) (reformer, heat exchanger, catalytic burner, etc.) integrated for combined heat and power. The system designed for power generation by using a natural gas as fuel can concurrently produce electricity at a SOFC stack and hot water from recuperating heat. The system showed a maximum dc output of 1.3 kWe. Detailed status and experimental results of the 1 kW SOFC system will be discussed in this paper.
Efficiency Evaluation of Solid-Oxide Fuel Cells in Combined Cycle Operations
Authors: Colson C. M. , Nehrir M. H. , Deibert M. C. , Amin M. R. , Wang C.
Published: March 2009

Solid oxide fuel cells (SOFCs) are high-temperature, high-efficiency, combustionless electrochemical energy conversion devices that have potential for combined cycle applications. This paper intends to clarify and expand the efficiency discussions related to SOFC when operating in combined cycle (CC) systems. A brief analysis of the first and second thermodynamic laws is conducted and, building upon a previously developed SOFC dynamic model, operating fuel heating values are determined by utilizing the semi-empirical gas phase heat capacity method. As a result, accurate SOFC stack operational simulations are conducted to calculate its efficiency based on actual thermodynamic parameters. Furthermore, an analysis is conducted of a combined SOFC-CC system using dynamic modeling. Simulation results are given, which are intended to aid researchers in evaluating hybrid SOFC-CC generation systems.
A High-Resolution Voxel Model for Predicting Local Tissue Temperatures in Humans Subjected to Warm and Hot Environments
Authors: Nelson D. A. , Charbonnel S. , Curran A. R. , Marttila E. A. , Fiala D. , Mason P. A. , Ziriax J. M.
Published: March 2009

This work describes and presents results from a new three-dimensional whole-body model of human thermoregulation. The model has been implemented using a version of the “Brooks Man” anatomical data set, consisting of 1.3×108 cubic volume elements (voxels) measuring 0.2 cm/side. The model simulates thermoregulation through passive mechanisms (metabolism, blood flow, respiration, and transpiration) and active mechanisms (vasodilatation, vasoconstriction, sweating, and shivering). Compared with lumped or compartment models, a voxel model is capable of high spatial resolution and can capture a level of anatomical detail not achievable otherwise. A high spatial resolution model can predict detailed heating patterns from localized or nonuniform heating patterns, such as from some radio frequency sources. Exposures to warm and hot environments (ambient temperatures of 33–48°C) were simulated with the current voxel model and with a recent compartment model. Results from the two models (core temperature, skin temperature, metabolic rate, and evaporative cooling rate) were compared with published experimental results obtained under similar conditions. Under the most severe environmental conditions considered (47.8°C, 27% RH for 2 h), the voxel model predicted a rectal temperature increase of 0.56°C, compared with a core temperature increase of 0.45°C from the compartment model and an experimental mean rectal temperature increase of 0.6°C. Similar, good agreement was noted for other thermal variables and under other environmental conditions. Results suggest that the voxel model is capable of predicting temperature response (core temperature and skin temperature) to certain warm or hot environments, with accuracy comparable to that of a compartment model. In addition, the voxel model is able to predict internal tissue temperatures and surface temperatures, over time, with a level of specificity and spatial resolution not achievable with compartment models. The development of voxel models and related computational tools may be useful for thermal dosimetry applications involving mild temperature hyperthermia and for the assessment of safe exposure to certain nonionizing radiation sources.
Mechanical Behavior of High Temperature Hybrid Carbon Fiber/Titanium Laminates
Authors: Papakonstantinou Christos G. , Katakalos Konstantinos
Published: March 2009

The aim of this paper was to investigate the tensile and flexural properties of hybrid laminates made with titanium sheets and high modulus carbon fiber composites. Grade II titanium was used, which exhibits great high-temperature performance and creep resistance, low weight, and high strength. An inorganic fireproof matrix, known as geopolymer, was used to fabricate the high modulus carbon fiber composites. Previous studies have shown that these composites are strong, durable, lightweight, and can exhibit excellent performance up to 400°C. In the present study, a number of specimens were tested in uniaxial tension and four-point bending after exposure at elevated temperatures. The results indicate that the addition of carbon fibers can reduce the weight and increase the stiffness of the pure titanium. Moreover, the hybrid laminates are stronger and stiffer than the sum of the individual strengths and stiffnesses of the parent materials. An important finding is that the interlaminar bond is strong, and as a result no delamination failures were observed.
Effect of Fiber Content on Void Morphology in Resin Transfer Molded E-Glass/Epoxy Composites
Authors: Hamidi Youssef K. , Dharmavaram Sudha , Aktas Levent , Altan M. Cengiz
Published: March 2009

Effect of fiber volume fraction on occurrence, morphology, and spatial distribution of microvoids in resin transfer molded E-glass/epoxy composites is investigated. Three disk-shaped center-gated composite parts containing 8, 12, and 16 layers of randomly-oriented, E-glass fiber perform are molded, yielding 13.5%, 20.5%, and 27.5% fiber volume fractions. Voids are evaluated by microscopic image analysis of the samples obtained along the radius of these disk-shaped composites. The number of voids is found to decrease moderately with increasing fiber content. Void areal density decreased from 10.5 voids/mm2 to 9.5 voids/mm2 as fiber content is increased from 13.5% to 27.5%. Similarly, void volume fraction decreased from 3.1% to 2.5%. Increasing fiber volume fraction from 13.5% to 27.5% is found to lower the contribution of irregularly-shaped voids from 40% of total voids down to 22.4%. Along the radial direction, combined effects of void formation by mechanical entrapment and void mobility are shown to yield a spatially complex void distribution. However, increasing fiber content is observed to affect the void formation mechanisms as more voids are able to move toward the exit vents during molding. These findings are believed to be applicable not only to resin transfer molding but generally to liquid composite molding processes.
Viscoelastic Properties of the Aortic Valve Interstitial Cell
Authors: Merryman W. David , Bieniek Paul D. , Guilak Farshid , Sacks Michael S.
Published: March 2009

There has been growing interest in the mechanobiological function of the aortic valve interstitial cell (AVIC) due to its role in valve tissue homeostasis and remodeling. In a recent study we determined the relation between diastolic loading of the aortic valve (AV) leaflet and the resulting AVIC deformation, which was found to be substantial. However, due to the rapid loading time of the AV leaflets during closure (∼0.05 s), time-dependent effects may play a role in AVIC deformation during physiological function. In the present study, we explored AVIC viscoelastic behavior using the micropipette aspiration technique. We then modeled the resulting time-length data over the 100 s test period using a standard linear solid model, which included Boltzmann superposition. To quantify the degree of creep and stress relaxation during physiological time scales, simulations of micropipette aspiration were preformed with a valve loading time of 0.05 s and a full valve closure time of 0.3 s. The 0.05 s loading simulations suggest that, during valve closure, AVICs act elastically. During diastole, simulations revealed creep (4.65%) and stress relaxation (4.39%) over the 0.3 s physiological time scale. Simulations also indicated that if Boltzmann superposition was not used in parameter estimation, as in much of the micropipette literature, creep and stress relaxation predicted values were nearly doubled (7.92% and 7.35%, respectively). We conclude that while AVIC viscoelastic effects are negligible during valve closure, they likely contribute to the deformation time-history of AVIC deformation during diastole.
Simulating the Growth of Articular Cartilage Explants in a Permeation Bioreactor to Aid in Experimental Protocol Design
Authors: Ficklin Timothy P. , Davol Andrew , Klisch Stephen M.
Published: March 2009

Recently a cartilage growth finite element model (CGFEM) was developed to solve nonhomogeneous and time-dependent growth boundary-value problems (Davol et al., 2008, “A Nonlinear Finite Element Model of Cartilage Growth,” Biomech. Model. Mechanobiol., 7, pp. 295–307). The CGFEM allows distinct stress constitutive equations and growth laws for the major components of the solid matrix, collagens and proteoglycans. The objective of the current work was to simulate in vitro growth of articular cartilage explants in a steady-state permeation bioreactor in order to obtain results that aid experimental design. The steady-state permeation protocol induces different types of mechanical stimuli. When the specimen is initially homogeneous, it directly induces homogeneous permeation velocities and indirectly induces nonhomogeneous solid matrix shear stresses; consequently, the steady-state permeation protocol is a good candidate for exploring two competing hypotheses for the growth laws. The analysis protocols were implemented through the alternating interaction of the two CGFEM components: poroelastic finite element analysis (FEA) using ABAQUS and a finite element growth routine using MATLAB. The CGFEM simulated 12 days of growth for immature bovine articular cartilage explants subjected to two competing hypotheses for the growth laws: one that is triggered by permeation velocity and the other by maximum shear stress. The results provide predictions for geometric, biomechanical, and biochemical parameters of grown tissue specimens that may be experimentally measured and, consequently, suggest key biomechanical measures to analyze as pilot experiments are performed. The combined approach of CGFEM analysis and pilot experiments may lead to the refinement of actual experimental protocols and a better understanding of in vitro growth of articular cartilage.
Development and Validation of a Three-Dimensional Finite Element Model of the Face
Authors: Barbarino G. G. , Jabareen M. , Trzewik J. , Nkengne A. , Stamatas G. , Mazza E.
Published: March 2009

A detailed three-dimensional finite element model of the face is presented in this paper. Bones, muscles, skin, fat, and superficial muscoloaponeurotic system were reconstructed from magnetic resonance images and modeled according to anatomical, plastic, and reconstructive surgery literature. The finite element mesh, composed of hexahedron elements, was generated through a semi-automatic procedure with an effective compromise between the detailed representation of anatomical parts and the limitation of the computational time. Nonlinear constitutive equations are implemented in the finite element model. The corresponding model parameters were selected according to previous work with mechanical measurements on soft facial tissue, or based on reasonable assumptions. Model assumptions concerning tissue geometry, interactions, mechanical properties, and the boundary conditions were validated through comparison with experiments. The calculated response of facial tissues to gravity loads, to the application of a pressure inside the oral cavity and to the application of an imposed displacement was shown to be in good agreement with the data from corresponding magnetic resonance images and holographic measurements. As a first application, gravimetric soft tissue descent was calculated from the long time action of gravity on the face in the erect position, with tissue aging leading to a loss of stiffness. Aging predictions are compared with the observations from an “aging database” with frontal photos of volunteers at different age ranges (i.e., 20–40 years and 50–70 years).
Bioreactor for Biaxial Mechanical Stimulation to Tissue Engineered Constructs
Authors: Wartella Karin A. , Wayne Jennifer S.
Published: March 2009

The complex structure and properties of biological tissues as well as their in situ environment often make it difficult to self-heal. A suitable replacement tissue may be created in vitro through tissue engineering approaches and mechanical stimulation of tissue constructs. A new biaxial bioreactor was designed, constructed, and evaluated for the purposes of developing constructs with specific functional characteristics. Once constructed and assembled, the bioreactor was tested for position accuracy and application of strain. Additionally, a tissue construct was tested in the chamber and compared with a nonstimulated construct. Results showed high position accuracy, but some loss between applied strain via grip movement and strain experienced by the scaffold. The tested construct exhibited an increase in cells and matrix deposition in comparison to the nonstimulated construct. This biaxial bioreactor will be useful for mechanically stimulating tissue constructs in two perpendicular directions to create implants for tissues requiring preferred compressive and tensile resistances.
Mechanisms of Residual Stress in Soft Tissues
Authors: Lanir Yoram
Published: March 2009

Although the importance of knowing the magnitude of residual stress (RS) and its functional significance are widely recognized, there is still disagreement and confusion regarding the nature of physical mechanisms giving rise to RS in tissues and organs. Here an attempt is made to examine the various mechanisms which may be involved in producing RS, and to estimate their roles and significance based on previously published experimental observations. Two concepts are introduced. The first establishes a hierarchy of different possible RS producing mechanisms from the micro (local) level of the tissue space, through the meso-level of the whole tissue, to the macro (organ) one. Whereas micro-level RS seem to be present in all soft tissues, the existence of macro- and meso-level mechanisms are tissue and organ specific. The second concept introduced highlights the significance of tissue swelling as an RS producing mechanism in the local micro-level. The implications of RS mechanism hierarchy are discussed regarding the interpretations of commonly used experimental methods aimed to study RS or to estimate its magnitude. Of the three categories of RS mechanisms, the local micro-RS is the least understood. It is analyzed here in terms of the tissue’s multiconstituent structure, in the framework of mixture theory. It is shown that the micro-RS can stem either from interactions between the solid tissue constituents or between its solids and its fluidlike matrix. The latter mode is associated with osmotic-driven tissue swelling. The feasibility of these two mechanisms is analyzed based on published observations and measured data. The analysis suggests that under conditions not too remote from the in vivo homeostatic one, osmotic-driven tissue swelling is a predominant RS producing mechanism. The analysis also suggests that a true stress-free configuration can be obtained only if all RS producing mechanisms are relieved, and outlines a manner by which this may be achieved.
A Simplified Dynamic Model for the Analysis of the Slider Off-Track Motion Due to Head-Disk Interactions
Authors: Yuan Yanhui , Wang Shao
Published: March 2009

A five-degree-of-freedom model was developed for the analysis of the off-track motion of the magnetic head slider in a hard disk drive. The air bearing was integrated into the dynamic system by combining its stiffness and damping matrices with those of the suspension. Simulation was conducted for the slider in intermittent contact with circumferentially located bumps on a rotating magnetic disk. For a single bump, the excitation to the transverse displacement of the slider is close to that of an impulse. However, for multiple bumps in a sequence, the excitation gives an effect similar to that of a step force function. The maximum transverse displacement increases almost linearly with both the coefficient of friction and the skew angle. The average contact force is determined by the maximum contact force, the contact time ratio, and the shape factor of the contact force, which change with the bump spacing and the rotational speed of the disk. The steady-state transverse displacement is related to the average contact force. As the bump spacing decreases, the average contact force increases, resulting in a greater transverse displacement. Based on the system dynamic characteristics alone, changing the rotational speed of the disk has only a small impact on the average contact force and, thus, on the transverse displacement. At zero skew angle with the bump path close to a rear pad edge, significant transverse motion occurs because of the excited roll mode and the coupling between the roll angle and the transverse displacement. The off-track motion of the slider is dominated by the rotational mode of the actuator arm and the sway mode of the suspension, as verified by comparing the results of the transverse displacement from the 5DOF model to that from a 2DOF model of the transverse motions of the actuator arm and suspension. The effects of the roll angle on the transverse displacement through coupling were found to be responsible for the difference in the transverse displacements obtained from the two models.
Rotordynamic Performance of Flexure Pivot Tilting Pad Gas Bearings With Vibration Damper
Authors: Rimpel Aaron , Kim Daejong
Published: March 2009

Recently, gas-lubricated bearings have drawn enormous attention for clean energy conversion/process systems such as fuel cells, micro-gas-turbines, gas compressors, etc. Among many different types of gas bearings, tilting pad gas bearings have many attractive features such as high rotor-bearing stability and less severe thermal issues (due to multipad configurations) than foil gas bearings. However, extension of the application of the tilting pad gas bearings to flexible rotors and harsh environments with external vibrations/impacts poses significant design challenges. The design problem addressed in this paper is the vibration damper to be integrated with the flexure pivot tilting pad gas bearing (FPTPGB) with and without pad radial compliance. Linear and nonlinear dynamic models of the FPTPGB with vibration damper were developed, and rotordynamic performance was evaluated to prescribe design guidelines for the selection of bearing shell mass and damper properties. Direct numerical integration (time-domain orbit simulations) and linear analyses were employed to predict rotordynamic responses and other interesting behaviors relevant of rotor-bearing systems with the vibration damper. Rotor-bearing systems showed better performance with larger damper stiffness for both with and without radial compliance. However, bearing shell mass showed different tendencies; lower bearing shell mass was shown to be ideal for bearings with radial compliance, while the opposite trend was observed for bearings without radial compliance. Although increasing the degrees of freedom of the system by allowing the bearing shell to move introduces additional natural frequencies, careful design considerations could allow the placement of the natural frequencies outside of the operating range.
Evaluation of Rayleigh–Plesset Equation Based Cavitation Models for Squeeze Film Dampers
Authors: Gehannin Jérôme , Arghir Mihai , Bonneau Olivier
Published: March 2009

This work is intended to evaluate a cavitation model based on the complete Rayleigh–Plesset (RP) equation for use in squeeze film damper calculations. The RP equation governs the variation in the radius of the cavitation bubbles at rest, surrounded by an infinite incompressible fluid and subjected to an external pressure. This equation is obtained from the momentum equation and it takes into account the ensemble of the phenomena related to the dynamics of the bubbles (surface tension, damping, and inertia). All the terms in the RP equation will be taken into account in the present work plus a dilatation viscosity introduced by Someya in 2003. Numerical results will be compared with experimental data obtained by Adiletta and Pietra in 2006. The results underline the influence of the effects contained in the RP equation on the pressure field.
Product Optimization Incorporating Discrete Design Variables Based on Decomposition of Performance Characteristics
Authors: Yoshimura Masataka , Yoshimura Yu , Izui Kazuhiro , Nishiwaki Shinji
Published: March 2009

This paper proposes a system optimization method for product designs incorporating discrete design variables, in which hierarchical product optimization methodologies are constructed based on decomposition of characteristics and/or extraction of simpler characteristics from original characteristics. The method is constructed to take advantage of hierarchical optimization procedures, enabling the incorporation of discrete design variables. The proposed method can be applied to machine product designs that include discrete design variables such as material types, machining methods, standard material forms, and specifications. The optimizations begin at the lowest levels of the hierarchical optimization structure and proceed to the higher levels. Discrete design variables are efficiently selected and optimized in the form of small suboptimization problems at the lowest hierarchical levels, and optimum solutions for the entire problem are ultimately obtained using conventional mathematical programming methods. Practical optimization procedures for machine product optimization problems that include several types of discrete design variables are constructed, and applied examples are provided to demonstrate their effectiveness.
Design Optimization With Discrete and Continuous Variables of Aleatory and Epistemic Uncertainties
Authors: Huang Hong-Zhong , Zhang Xudong
Published: March 2009

Reliability based design optimization has received increasing attention for satisfying high requirements on reliability and safety in structure design. However, in practical engineering design, there are both continuous and discrete design variables. Moreover, both aleatory uncertainty and epistemic uncertainty may associate with design variables. This paper proposes the formulation of random/fuzzy continuous/discrete variables design optimization (RFCDV-DO) and two different approaches for uncertainty analysis (probability/possibility analysis). A method named random/fuzzy sequential optimization and reliability assessment is proposed based on the idea of sequential optimization and reliability assessment to improve efficiency in solving RFCDV-DO problems. An engineering design problem is utilized to demonstrate the approaches and the efficiency of the proposed method.
Interval Uncertainty Reduction and Single-Disciplinary Sensitivity Analysis With Multi-Objective Optimization
Authors: Li M. , Williams N. , Azarm S.
Published: March 2009

Sensitivity analysis has received significant attention in engineering design. While sensitivity analysis methods can be global, taking into account all variations, or local, taking into account small variations, they generally identify which uncertain parameters are most important and to what extent their effect might be on design performance. The extant methods do not, in general, tackle the question of which ranges of parameter uncertainty are most important or how to best allocate Investments to partial uncertainty reduction in parameters under a limited budget. More specifically, no previous approach has been reported that can handle single-disciplinary multi-output global sensitivity analysis for both a single design and multiple designs under interval uncertainty. Two new global uncertainty metrics, i.e., radius of output sensitivity region and multi-output entropy performance, are presented. With these metrics, a multi-objective optimization model is developed and solved to obtain fractional levels of parameter uncertainty reduction that provide the greatest payoff in system performance for the least amount of “Investment.” Two case studies of varying difficulty are presented to demonstrate the applicability of the proposed approach.
Experimental and Numerical Study of Air Entrainment Between Web and Spirally Grooved Roller
Authors: Tran Si Bui Quang , Yoo Yong Hoon , Ko Jin Hwan , Kim Jihoon , Byun Doyoung , Lee Jae Woo , Byun Yung Hwan , Shin Kee Hyun
Published: March 2009

This paper presents numerical quasistatic simulation results of the air entrainment phenomenon between a web and a spirally grooved roller. The numerical results show that during one complete rotation of the spirally grooved roller, the traction coefficient between the web and the roller changes with time due to the changing shape of the groove in the contact region, and the average traction coefficient of the circumferentially grooved roller is higher than that of the spirally grooved roller. Using a laser sensor, web deflection is measured and compared with the numerical results at the inlet. Furthermore, a smoke wire experiment shows a clear view of the air entrainment phenomenon at the entrance, between the web and the roller.
The Validity of Linear Elasticity in Analyzing Surface Texturing Effect for Elastohydrodynamic Lubrication
Authors: Shinkarenko A. , Kligerman Y. , Etsion I.
Published: March 2009

This paper presents a nonlinear theoretical model to study the effect of laser surface texturing on the tribological performance in soft elastohydrodynamic lubrication. Both geometrical and physical nonlinearities of the elastomer are considered by using a logarithmic strain and the Mooney–Rivlin constitutive law, respectively. The results of the present nonlinear model are compared with a previous linear one over a wide range of operating conditions. It is found that the simpler linear elasticity model predicts results that are only slightly different from these predicted by the more accurate nonlinear one. Hence, the linear elasticity model can be practically considered valid over the entire range of operating conditions.