bluuebunny/crossref_metadata_2025 huggingface dataset:
Transport Properties of Small Spherical Particles
Authors: Wang Hai
Published: April 2009

Recently, a theoretical framework for nanoparticle transport in the laminar flow regime has been proposed. The theory features a rigorous gas‐kinetic theory analysis. It considers the effect of nonrigid body collision, and the theory is shown to reproduce the Chapman–Enskog theory of molecular transport in the small particle size limit, Epstein's model of particle drag in the rigid‐body limit, and the Stokes–Cunningham equation for the drag on micrometer size particles. This theoretical framework provides the hope that bits and pieces of particle transport theories formulated over the last century can now be unified into a generalized theory. This paper discusses an unresolved fundamental issue related to this generalized theory, namely, the transition from specular scattering applicable to molecule–molecule collision to diffuse scattering governing molecule–“particle” collision.
Mechanisms of Diffusional Nucleation of Nanocrystals and Their Self‐Assembly into Uniform Colloids
Authors: Privman Vladimir
Published: April 2009

We survey our research on modeling the mechanisms of control of uniformity in the growth of nanosize and colloid size particles. The former are produced as nanocrystals by burst nucleation from solution and the latter are formed by self‐assembly (aggregation) of the nanocrystals. In the colloid particle synthesis, the two dynamical processes are coupled, both governed by diffusional transport of the respective building blocks (monomers). The interrelation of the two processes allows for the synthesis of narrow size distribution colloid dispersions, which are of importance in many applications. We first review a mathematical model of diffusive cluster growth by the capture of monomer “singlets.” We then analyze burst nucleation of nanoparticles in solution. Finally, we couple it to the secondary process of aggregation of nanoparticles to form colloids and discuss various aspects of the modeling of particle size distribution, as well as other features of the processes considered.
Direct Hydrothermal Synthesis of Ternary Li‐Mn‐O Oxide Ion‐Sieves
Authors: Zhang Qin‐Hui , Sun Shu‐Ying , Li Shao‐Peng , Yin Xian‐Sheng , Yu Jian‐Guo
Published: April 2009

Spinel‐type ternary LiMn2O4 oxide precursor was synthesized by direct hydrothermal synthesis of Mn(NO3)2, LiOH, and H2O2 at 383 K for 8 h, a better technique for controlling the nanocrystalline structure with well‐defined pore size distribution and high surface area than the traditional solid state reaction method. The final low‐dimensional MnO2 nanorod ion‐sieve with a lithium ion selective adsorption property was further prepared by an acid treatment process to completely extract lithium ions from the Li–Mn–O lattice. The effects of hydrothermal reaction conditions on the nanostructure, chemical stability, and ion‐exchange property of the LiMn2O4 precursor and MnO2 ion‐sieve were systematically examined via powder X‐ray diffraction (XRD), high‐resolution transmission electron microscopy (HRTEM), selected‐area electron diffraction (SAED), and lithium ion selective adsorption measurements. The results show that this new kind of low‐dimensional MnO2 nanorod can be used for lithium extraction from aqueous environments, including brine, seawater, and waste water.
Solute Diffusion in Nonionic Liquids—Effects of Gravity
Authors: Smith Reginald W. , Scott Paul J. , Szpunar Barbara
Published: April 2009

We have been engaged in examining the influence of gravity on the results of experiments to measure the variation of solute diffusion coefficients (D) with temperature (T) in fused metals and semimetals since our first STS flights in 1992. These early experiments, conducted with the in situ g‐jitter of the shuttle, showed the near‐parabolic variation of D with T reported by others. However, with the aid of the Canadian Space Agency's microgravity isolation mount (MIM) to isolate the diffusion facility from the existing g‐jitter of the Russian space station MIR, we showed that in all the alloy systems and over the temperature range studied, D increased linearly with T. If the isolating system was deactivated, then the more familiar parabolic relationship appeared. We have always assumed that the values of D measured using the MIM would be closer to the intrinsic values for the alloy system considered; to test this contention, we have been involved in two modeling activities. The first has been to estimate the effects of g‐jitter‐level disturbances on solute distributions in long capillary diffusion couples. The second has been to conduct various molecular dynamics modeling studies of solute diffusion. This paper presents results of these studies.
Development of High‐performance Cooling Devices for Space Application by Using Flow Boiling in Narrow Channels
Authors: Miura Shinichi , Inada Yukihiro , Shinmoto Yasuhisa , Ohta Haruhiko
Published: April 2009

Heat generation density from semiconductor devices has been increasing with the rapid development of electronic technology. The cooling system using boiling two‐phase phenomena has attracted much attention because of its high heat removal potential. To develop compact and high‐performance cooling systems, we conducted experiments on the increase of critical heat flux (CHF) for flow boiling in narrow channels by improved liquid supply. A large surface of 150 mm in heated length and 30 mm in width with grooves of an apex angle of 90°, 0.5‐mm depth, and 1 mm in pitch was employed. A structure of narrow heated channel between parallel plates with an unheated auxiliary channel was devised and tested by using water for different combinations of gap sizes and volumetric flow rates, where inlet of the main heated channel and the outlet of auxiliary unheated channel were closed to prevent the flow instability observed frequently at low flow rate for parallel two channels. For the total volumetric flow rate more than 4.5 × 10−5 m3/s, higher values of CHF large than 2 × 106 W/m2 were obtained for gap size of 2 mm. For gap sizes of 2 mm and 5 mm at high volumetric flow rate larger than 6.0 × 10−5 m3/s, or mass velocity based on the cross section are of main heated channel 958.1 kg/m2s and 383.2 kg/m2 s, respectively, the extension of dry patches was observed at the upstream location of the main heated channel resulting in burnout not at the downstream but at the upstream. By the increase in total volumetric flow rate, the pressure drop increased because of increasing in the flow rate passing through the sintered metal porous plates connecting both channels. The values of pressure drop for gap size of 2 mm were higher than that for gap size of 5 mm. When the performance of the cooling system was evaluated on the basis of pump power, ignoring its variation in the efficiency with volumetric flow rate, that is, the power defined as the product of the pressure drop and the total volumetric flow rate, higher values of CHF were obtained for gap size of 5 mm as far as the same pump power was concerned.
Exergy Optimization in a Steady Moving Bed Heat Exchanger
Authors: Soria‐Verdugo A. , Almendros‐Ibáñez J. A. , Ruiz‐Rivas U. , Santana D.
Published: April 2009

This work provides an energy and exergy optimization analysis of a moving bed heat exchanger (MBHE). The exchanger is studied as a cross‐flow heat exchanger where one of the phases is a moving granular medium. The optimal MBHE dimensions and the optimal particle diameter are obtained for a range of incoming fluid flow rates. The analyses are carried out over operation data of the exchanger obtained in two ways: a numerical simulation of the steady‐state problem and an analytical solution of the simplified equations, neglecting the conduction terms. The numerical simulation considers, for the solid, the convection heat transfer to the fluid and the diffusion term in both directions, and for the fluid only the convection heat transfer to the solid. The results are compared with a well‐known analytical solution (neglecting conduction effects) for the temperature distribution in the exchanger. Next, the analytical solution is used to derive an expression for the exergy destruction. The optimal length of the MBHE depends mainly on the flow rate and does not depend on particle diameter unless they become very small (thus increasing sharply the pressure drop). The exergy optimal length is always smaller than the thermal one, although the difference is itself small.
Analysis of Gene Transfer Rate with Immobilized Retroviral Vectors
Authors: Peng Ching‐An
Published: April 2009

Efficient delivery of transgenes into the cell nucleus by retroviral vectors in a static culture system is limited by the intrinsic features of incompetent retroviruses (i.e., thermodynamically unstable envelope proteins and low titers). Although several physicochemical approaches (e.g., adding polycationic polymer and applying magnetic force) have been reported to augment the retroviral gene transfer rate, none are suitable for scaling up to a setting for clinical use. The study of using acoustic fields with the form of standing waves has recently been reported to be a feasible way to enhance retroviral gene delivery efficiency in large‐scale settings. The concept of using ultrasound standing‐wave fields to increase retrovirus‐mediated gene transfer is based on quickly established cell bands on acoustic nodal planes as nucleating sites to capture unstable colloidlike retroviruses. In this study, instead of having retroviral nanoparticles circulated between nodal planes, we proposed to immobilize retroviruses onto acoustic transparent films arranged in an acoustic chamber. Then, cells inoculated into the acoustic chamber can be driven by the primary radiation forces to the retrovirus‐coated films that are constructed on the nodal planes. To obtain the optimal time of immobilizing retroviruses onto the acoustic transparent film prior to the inception of acoustic fields, we developed a retroviral diffusion–reaction model to describe such a static retroviral system. Analysis of viral transport model has its merit to guide experimental design for attaining high gene transfer efficiency.
Waste lipids to energy: how to optimize methane production from long‐chain fatty acids (LCFA)
Authors: Alves M. Madalena , Pereira M. Alcina , Sousa Diana Z. , Cavaleiro Ana J. , Picavet Merijn , Smidt Hauke , Stams Alfons J. M.
Published: April 2009

The position of high‐rate anaerobic technology (HR‐AnWT) in the wastewater treatment and bioenergy market can be enhanced if the range of suitable substrates is expanded. Analyzing existing technologies, applications and problems, it is clear that, until now, wastewaters with high lipids content are not effectively treated by HR‐AnWT. Nevertheless, waste lipids are ideal potential substrates for biogas production, since theoretically more methane can be produced, when compared with proteins or carbohydrates. In this minireview, the classical problems of lipids methanization in anaerobic processes are discussed and new concepts to enhance lipids degradation are presented. Reactors operation, feeding strategies and prospects of technological developments for wastewater treatment are discussed. Long‐chain fatty acids (LCFA) degradation is accomplished by syntrophic communities of anaerobic bacteria and methanogenic archaea. For optimal performance these syntrophic communities need to be clustered in compact aggregates, which is often difficult to achieve with wastewaters that contain fats and lipids. Driving the methane production from lipids/LCFA at industrial scale without risk of overloading and inhibition is still a challenge that has the potential for filling a gap in the existing processes and technologies for biological methane production associated to waste and wastewater treatment.
The expression of recombinant genes in Escherichia coli can be strongly stimulated at the transcript production level by mutating the DNA‐region corresponding to the 5′‐untranslated part of mRNA
Authors: Berg Laila , Lale Rahmi , Bakke Ingrid , Burroughs Nigel , Valla Svein
Published: April 2009

Secondary structures and the short Shine–Dalgarno sequence in the 5′‐untranslated region of bacterial mRNAs (UTR) are known to affect gene expression at the level of translation. Here we report the use of random combinatorial DNA sequence libraries to study UTR function, applying the strong, σ32/σ38‐dependent, and positively regulated Pm promoter as a model. All mutations in the libraries are located at least 8 bp downstream of the transcriptional start site. The libraries were screened using the ampicillin‐resistance gene (bla) as reporter, allowing easy identification of UTR mutants that display high levels of expression (up to 20‐fold increase relative to the wild‐type at the protein level). Studies of the two UTR mutants identified by a modified screening procedure showed that their expression is stimulated to a similar extent at both the transcript and protein product levels. For one such mutant a model analysis of the transcription kinetics showed significant evidence of a difference in the transcription rate (about 18‐fold higher than the wild type), while there was no evidence of a difference in transcript stability. The two UTR sequences also stimulated expression from a constitutive σ70‐dependent promoter (P1/Panti‐tet), demonstrating that the UTR at the DNA or RNA level has a hitherto unrecognized role in transcription.
Bacterial responses and interactions with plants during rhizoremediation
Authors: Segura Ana , Rodríguez‐Conde Sara , Ramos Cayo , Ramos Juan L.
Published: April 2009

With the increase in quality of life standards and the awareness of environmental issues, the remediation of polluted sites has become a priority for society. Because of the high economic cost of physico‐chemical strategies for remediation, the use of biological tools for cleaning‐up contaminated sites is a very attractive option. Rhizoremediation, the use of rhizospheric microorganisms in the bioremediation of contaminants, is the biotechnological approach that we explore in this minireview. We focus our attention on bacterial interactions with the plant surface, responses towards root exudates, and how plants and microbes communicate. We analyse certain strategies that may improve rhizoremediation, including the utilization of endophytes, and finally we discuss several rhizoremediation strategies that have opened ways to improve biodegradation.
Virulence regulation in Citrobacter rodentium: the art of timing
Authors: Yang Ji , Tauschek Marija , Hart Emily , Hartland Elizabeth L. , Robins‐Browne Roy M.
Published: April 2009

The mouse enteric pathogen Citrobacter rodentium, like its human counterpart, enteropathogenic Escherichia coli, causes attaching and effacing lesions in the intestinal epithelium of its host. This phenotype requires virulence factors encoded by the locus for enterocyte effacement (LEE) pathogenicity island. For timely expression of these virulence determinants at the site of infection and for efficient delivery of some virulence factors into epithelial cells, C. rodentium utilizes a positive regulatory loop involving the LEE‐encoded regulatory proteins Ler, GrlA and GrlR to control LEE expression. Several transcription factors not encoded by LEE, some of which respond to specific environmental signals, also participate in this regulatory loop. Recently, we identified a non‐LEE encoded, AraC‐like regulatory protein, RegA, which plays a key role in the ability of C. rodentium to colonize the intestine. RegA functions by activating the transcription of a number of horizontally acquired operons encoding virulence‐associated factors, such as autotransporters, fimbriae, a dispersin‐like protein and its transporter. In addition, RegA represses transcription of a number of housekeeping genes. Importantly, RegA requires a gut‐specific environmental signal, bicarbonate, to exert its effects on gene expression. In our proposed model, when C. rodentium senses bicarbonate ions in the gastrointestinal tract, RegA directs the bacterium to reduce the production of proteins involved in normal cellular functions, while enhancing the production of factors required for colonization and virulence.
Temporal and Spatial Turbidity Patterns Over 30 Years in a Managed Forest of Western Washington1
Authors: Reiter Maryanne , Heffner John T. , Beech Storm , Turner Ted , Bilby Robert E.
Published: April 2009

Abstract: Forest practices have progressively changed over the last 30 years in the Pacific Northwest to address water quality concerns. There have been some assessments of these new management practices made at a site scale but very few studies have attempted to evaluate their efficacy at reducing cumulative sediment production at a watershed scale. Such an evaluation is difficult due to the spatial and temporal variability in sediment delivery and transport processes. Due to this inherent variability, detecting a response to management changes requires a long‐term data record. We utilized a water quality dataset collected over 30 years at four locations in the Deschutes River watershed (western Washington) to assess trends in turbidity and whether sediment control procedures implemented over this time period had any detectable influence. The sample sites ranged from small headwater streams (2.4 and 3.0 km2) to the mainstem of the Deschutes River (150 km2). Declining trends in turbidity were detected at all the permanently monitored sites. The mainstem Deschutes River site, which integrates sediment processes from the entire study watershed, showed dramatic declines in turbidity even with continued active forest management. For the small basins, logging and road construction occurred in the 1970s and 1980s and turbidity declined thereafter, achieving prelogging levels by 2000. There are no temporal trends in flow that could be responsible for the observed trends in turbidity. Our results suggest that increased attention to reducing sediment production from roads and minimizing the amount of road runoff reaching stream channels has been the primary cause of the declining turbidity levels observed in this study.
Mapping cumulative human impacts to California Current marine ecosystems
Authors: Halpern Benjamin S. , Kappel Carrie V. , Selkoe Kimberly A. , Micheli Fiorenza , Ebert Colin M. , Kontgis Caitlin , Crain Caitlin M. , Martone Rebecca G. , Shearer Christine , Teck Sarah J.
Published: April 2009

Quantitative assessment of the spatial patterns of all human uses of the oceans and their cumulative effects is needed for implementing ecosystem‐based management, marine protected areas, and ocean zoning. Here, we apply methods developed to map cumulative impacts globally to the California Current using more comprehensive and higher‐quality data for 25 human activities and 19 marine ecosystems. This analysis indicates where protection and threat mitigation are most needed in the California Current and reveals that coastal ecosystems near high human population density and the continental shelves off Oregon and Washington are the most heavily impacted, climate change is the top threat, and impacts from multiple threats are ubiquitous. Remarkably, these results were highly spatially correlated with the global results for this region (R2= 0.92), suggesting that the global model provides guidance to areas without local data or resources to conduct similar regional‐scale analyses.
Comparison between manual and automated total nucleated cell counts using the ADVIA 120 for pleural and peritoneal fluid samples from dogs, cats, horses, and alpacas
Authors: Gorman M. Elena , Villarroel Aurora , Tornquist Susan J. , Flachsbart Joy , Warden Annette , Boeder Lisa
Published: April 2009

Background: Analysis of body fluids includes an estimate of total nucleated cell count (TNCC). Automated methods may enhance the accuracy and timeliness of TNCC results.

Objective: The purpose of this report was to assess the ability of the ADVIA 120 hematology analyzer to accurately count nucleated cells in pleural and peritoneal fluids from animals, compared with manual counts.

Methods: Pleural and peritoneal fluids submitted in EDTA tubes to our laboratory over a 17‐month period were used in the study. TNCC/μL was determined by a manual method, using a hemocytometer, and by an automated method, using the ADVIA 120. Correlation of results was determined by Passing‐Bablok regression, Bland–Altman plots, and Pearson correlation analysis.

Results: Samples from dogs (n=36), cats (n=36), horses (n=59), and alpacas (n=11) were analyzed. High correlation in TNCC between methods was found for peritoneal fluid (n=93, r=.959), pleural fluid (n=49, r=.966), and all fluids combined (n=142, r=.960) (P<.001). Variation between methods was greater in samples with TNCCs<1000/μL (r=.62, P<.001). The ADVIA systematically overestimated the number of cells in all fluid samples by 95 cells/μL (confidence interval=19.2–190.5/μL).

Conclusion: The ADVIA 120 reliably determines TNCC in pleural and peritoneal effusions and can be recommended for routine veterinary laboratory analysis.
C‐reactive protein concentration in dogs with primary immune‐mediated hemolytic anemia
Authors: Griebsch Christine , Arndt Gisela , Raila Jens , Schweigert Florian J. , Kohn Barbara
Published: April 2009

Background:Canine primary immune‐mediated hemolytic anemia (IMHA) is associated with a high‐mortality rate. C‐reactive protein (CRP) is the most important acute‐phase protein in dogs and may have value as a marker of prognosis or response to treatment in IMHA.

Objective:The objectives of this study were to evaluate serum CRP concentration in dogs with primary IMHA at presentation and during treatment, to assess potential differences based on survival time, and to compare CRP with other laboratory parameters of inflammation and prognosis.

Methods:Inclusion criteria for primary IMHA were anemia (PCV<0.30 L/L), a positive Coombs' test or persistent autoagglutination of erythrocytes, and the exclusion of underlying diseases by other diagnostic tests. Dogs were divided into 2 groups based on survival: dogs that were still alive 14 days after start of treatment (group 1) and dogs that died or were euthanized before day 14 (group 2). Serum CRP concentration, a CBC, and a biochemistry profile were performed on days 0, 3, 8, and 14. Serum CRP also was determined in 25 clinically healthy dogs.

Results:CRP concentration in the 25 clinically healthy dogs ranged from 0–8.9 μg/mL (median 2.2 μg/mL). Thirty dogs were diagnosed with primary IMHA, 24 in group 1 and 6 in group 2. On day 0, CRP concentration in dogs in both groups (median 224 μg/mL) was increased above the reference interval. In group 1 dogs, median CRP concentration was 242 μg/mL on day 0, 69 μg/mL on day 3, 35 μg/mL on day 8, and 2 μg/mL on day 14. In group 2 dogs, median CRP concentration was 194 μg/mL on day 0, 119 μg/mL on day 3, and 41 μg/mL on day 8; only 1 dog in group 2 survived to day 8. There was a significant correlation between CRP and total WBC concentrations on days 0 and 3 (r=−.598,P=.003).

Conclusions:Serum CRP concentration was markedly increased in dogs with primary IMHA. CRP concentration did not differ based on patient survival, but might be a marker for long‐term monitoring of these patients.
Political Sophistication Among the Mass Publics of Confucian Asia
Authors: Yan Ting
Published: April 2009

The concept of “Confucian Asia” is often used without a validity check. But are Asian societies homogeneous in Confucian orientations as the term suggests? If not, how can one explain the variation? By examining the East Asia Barometer survey data, this article challenges the homogeneity of Confucian Asia and finds that Confucian orientations are unevenly distributed even among commonly accepted Confucian societies. In exploring the possible explanations for this Confucian orientation variation, this article argues that political sophistication is the direct mechanism to explain the variation of mass commitment toward Confucianism. By comparing other alternative explanations such as modernization theory, the article finds that the effects of political sophistication are independent and potent.
Nonlinear Identification of Mechanical Parameters in a Squeeze Film Damper With Integral Mechanical Seal
Authors: Delgado Adolfo , San Andrés Luis
Published: April 2009

End seals in squeeze film dampers (SFDs) aid to increase their damping capability while maintaining low lubricant flow rates and reducing the severity of air ingestion. This paper presents measurements of the forced response in a SFD integrating a contacting end seal and with closed flow ports, i.e., no lubricant through flow. The system motion is nonlinear due to the dry-friction interaction at the mechanical seal mating surfaces. Single parameter characterization of the test system would yield an equivalent viscous damping coefficient that is both frequency and motion amplitude dependent. Presently, an identification method suited for nonlinear systems allows determining simultaneously the squeeze film damping and inertia force coefficients and the seal dry-friction force. The identification procedure shows similar (within 10%) force coefficients than those obtained with a more involved two-step procedure that first requires measurements without any lubricant in the test system. The identified SFD damping and inertia force coefficients agree well with model predictions that account for end flow effects at recirculation grooves. The overall test results demonstrate that the nonrotating end seal effectively eliminates side leakage and avoids air ingestion, thus maintaining a consistent damping performance throughout the test frequency range. The nonlinear identification procedure saves time and resources while producing reliable physical parameter estimations.
A Systematic Comparison and Multi-Objective Optimization of Humid Power Cycles—Part II: Economics
Authors: Kavanagh R. M. , Parks G. T.
Published: April 2009

The steam injected gas turbine (STIG), humid air turbine (HAT), and TOP Humid Air Turbine (TOPHAT) cycles lie at the center of the debate on which humid power cycle will deliver optimal performance when applied to an aeroderivative gas turbine and, indeed, when such cycles will be implemented. Of these humid cycles, it has been claimed that the TOPHAT cycle has the highest efficiency and specific work, followed closely by the HAT and then the STIG cycle. In this study, the systems have been simulated using consistent thermodynamic and economic models for the components and working fluid properties, allowing a consistent and nonbiased appraisal of these systems. Part I of these two papers focused on the thermodynamic performance and the impact of the system parameters on the performance, Part II studies the economic performance of these cycles. The three humid power systems and up to ten system parameters are optimized using a multi-objective Tabu Search algorithm, developed in the Cambridge Engineering Design Centre.
Magnitude and Duration of Stretch Modulate Fibroblast Remodeling
Authors: Balestrini Jenna L. , Billiar Kristen L.
Published: April 2009

Mechanical cues modulate fibroblast tractional forces and remodeling of extracellular matrix in healthy tissue, healing wounds, and engineered matrices. The goal of the present study is to establish dose-response relationships between stretch parameters (magnitude and duration per day) and matrix remodeling metrics (compaction, strength, extensibility, collagen content, contraction, and cellularity). Cyclic equibiaxial stretch of 2–16% was applied to fibroblast-populated fibrin gels for either 6 h or 24 h/day for 8 days. Trends in matrix remodeling metrics as a function of stretch magnitude and duration were analyzed using regression analysis. The compaction and ultimate tensile strength of the tissues increased in a dose-dependent manner with increasing stretch magnitude, yet remained unaffected by the duration in which they were cycled (6 h/day versus 24 h/day). Collagen density increased exponentially as a function of both the magnitude and duration of stretch, with samples stretched for the reduced duration per day having the highest levels of collagen accumulation. Cell number and failure tension were also dependent on both the magnitude and duration of stretch, although stretch-induced increases in these metrics were only present in the samples loaded for 6 h/day. Our results indicate that both the magnitude and the duration per day of stretch are critical parameters in modulating fibroblast remodeling of the extracellular matrix, and that these two factors regulate different aspects of this remodeling. These findings move us one step closer to fully characterizing culture conditions for tissue equivalents, developing improved wound healing treatments and understanding tissue responses to changes in mechanical environments during growth, repair, and disease states.
Mesoscale Foil Gas Bearings for Palm-Sized Turbomachinery: Design, Manufacturing, and Modeling
Authors: Kim Daejong , Creary Andron , Chang Suk Sang , Kim Jong Hyun
Published: April 2009

Palm-sized microturbomachinery have broad potential applications in micropower generation areas, such as air/fuel management systems for various fuel cells, propulsion engine for unmanned micro-air vehicles, power generation turbines for robots, small satellites, etc. This paper introduces design and manufacturing processes of mesoscale foil gas bearings applicable to the microturbomachinery and also presents its performances predicted from nonlinear orbit simulations. X-ray and ultraviolet lithography were explored as promising manufacturing tools of elastic foundations for the mesoscale foil gas bearings. Designed and manufactured mesoscale foil gas bearings have unique design features that precision-machined foil bearings cannot provide, such as easy control of mechanical properties of elastic foundations, a simple assembly process, and easy control of bearing preload through lithographic pattern. The manufactured bearing performance was predicted using a time-domain orbit simulation, and results are presented.
A Cadaverically Evaluated Dynamic FEM Model of Closed-Chain TKR Mechanics
Authors: Lanovaz Joel L. , Ellis Randy E.
Published: April 2009

Knowledge of the behavior and mechanics of a total knee replacement (TKR) in an in vivo environment is key to optimizing the functional outcomes of the implant procedure. Computational modeling has shown to be an important tool for investigating biomechanical variables that are difficult to address experimentally. To assist in examining TKR mechanics, a dynamic finite-element model of a TKR is presented. The objective of the study was to develop and evaluate a model that could simulate full knee motion using a physiologically consistent quadriceps action, without prescribed joint kinematics. The model included tibiofemoral (TFJs) and patellofemoral joints (PFJs), six major ligament bundles and was driven by a uni-axial representation of a quadricep muscle. An initial parameter screening analysis was performed to assess the relative importance of 31 different model parameters. This analysis showed that ligament insertion location and initial ligament strain were significant factors affecting simulated joint kinematics and loading, with the contact friction coefficient playing a lesser role and ligament stiffness having little effect. The model was then used to simulate in vitro experiments utilizing a flexed-knee-stance testing rig. General model performance was assessed by comparing simulation results with experimentally measured kinematics and tibial reaction forces collected from two implanted specimens. The simulations were able to reproduce experimental differences observed between the test specimens and were able to accurately predict trends seen in the tibial reaction loads. The simulated kinematics of the TFJ and PFJ were less consistent when compared with experimental data but still reproduced many trends.
Effect of Geometrical Uncertainty on Cemented Hip Implant Structural Integrity
Authors: Bah Mamadou T. , Browne Martin
Published: April 2009

A large number of parameters such as material properties, geometry, and structural strength are involved in the design and analysis of cemented hip implants. Uncertainties in these parameters have a potential to compromise the structural performance and lifetime of implants. Statistical analyses are well suited to investigating this type of problem as they can estimate the influence of these uncertainties on the incidence of failure. Recent investigations have focused on the effect of uncertainty in cement properties and loading condition on the integrity of the construct. The present study hypothesizes that geometrical uncertainties will play a role in cement mantle failure. Finite element input parameters were simulated as random variables and different modes of failure were investigated using a response surface method (RSM). The magnitude of random von Mises stresses varied up to 8 MPa, compared with a maximum nominal value of 2.38 MPa. Results obtained using RSM are shown to match well with a benchmark direct Monte Carlo simulation method. The resulting probability that the maximum cement stress will exceed the nominal stress is 62%. The load and the bone and prosthesis geometries were found to be the parameters most likely to influence the magnitude of the cement stresses and therefore to contribute most to the probability of failure.
Deformation-Dependent Enzyme Mechanokinetic Cleavage of Type I Collagen
Authors: Wyatt Karla E.-K. , Bourne Jonathan W. , Torzilli Peter A.
Published: April 2009

Collagen is a key structural protein in the extracellular matrix of many tissues. It provides biological tissues with tensile mechanical strength and is enzymatically cleaved by a class of matrix metalloproteinases known as collagenases. Collagen enzymatic kinetics has been well characterized in solubilized, gel, and reconstituted forms. However, limited information exists on enzyme degradation of structurally intact collagen fibers and, more importantly, on the effect of mechanical deformation on collagen cleavage. We studied the degradation of native rat tail tendon fibers by collagenase after the fibers were mechanically elongated to strains of ε=1–10%. After the fibers were elongated and the stress was allowed to relax, the fiber was immersed in Clostridium histolyticum collagenase and the decrease in stress (σ) was monitored as a means of calculating the rate of enzyme cleavage of the fiber. An enzyme mechanokinetic (EMK) relaxation function TE(ε) in s−1 was calculated from the linear stress-time response during fiber cleavage, where TE(ε) corresponds to the zero order Michaelis–Menten enzyme-substrate kinetic response. The EMK relaxation function TE(ε) was found to decrease with applied strain at a rate of ∼9% per percent strain, with complete inhibition of collagen cleavage predicted to occur at a strain of ∼11%. However, comparison of the EMK response (TE versus ε) to collagen’s stress-strain response (σ versus ε) suggested the possibility of three different EMK responses: (1) constant TE(ε) within the toe region (ε<3%), (2) a rapid decrease (∼50%) in the transition of the toe-to-heel region (ε≅3%) followed by (3) a constant value throughout the heel (ε=3–5%) and linear (ε=5–10%) regions. This observation suggests that the mechanism for the strain-dependent inhibition of enzyme cleavage of the collagen triple helix may be by a conformational change in the triple helix since the decrease in TE(ε) appeared concomitant with stretching of the collagen molecule.
The Influence of the Grain Structure Size on Microstructurally Short Cracks
Authors: Simonovski Igor , Cizelj Leon
Published: April 2009

The dominant processes in the initialization and propagation of microstructurally short cracks include microstructural features such as crystallographic orientations of grains, grain boundaries, inclusions, voids, material phases, etc. The influence of the microstructural features is expected to vanish with distance from the crack tip. Also, the influence of the nearby microstructural features is expected to be smaller for a long than for a small crack. Finally, a crack of sufficient length can be modeled using classical fracture mechanic methods. In this paper the approach to estimate the crack length with vanishing influence from the microstructural feature is proposed. To achieve this, a model containing a large number of randomly sized, shaped, and oriented grains is employed. The random grain structure is modeled using a Voronoi tessellation. A series of cracks of lengths from about 1 to 7 grain lengths is inserted into the model, extending from a grain at the surface toward the interior of the model. The crack tip opening displacements are estimated and statistically analyzed for a series of random crystallographic orientation sets assigned to the grains adjacent to the crack. Anisotropic elasticity and crystal plasticity constitutive models are employed at the grain size scale. It is shown that the standard deviation of the crack tip opening displacement decreases from about 20% for a short surface crack embedded within a single grain to about 7% for a surface crack extending through seven grains. From the engineering point of view, a crack extending through less than about ten grain sizes is therefore considered to strongly depend on the neighboring microstructural features.
Deposition of TRISO Particles With Superhard SiC Coatings and the Characterization of Anisotropy by Raman Spectroscopy
Authors: López-Honorato E. , Meadows P. J. , Tan J. , Xiang Y. , Xiao P.
Published: April 2009

In this work we have deposited silicon carbide (SiC) at 1300°C with the addition of small amounts of propylene. The use of propylene and high concentrations of methyltrichlorosilane (9 vol %) allowed the deposition of superhard SiC coatings (42 GPa). The superhard SiC could result from the presence of a SiC–C solid solution, undetectable by X-ray diffraction but visible by Raman spectroscopy. Another sample obtained by the use of 50 vol % Argon, also showed the formation of SiC with good properties. The use of a flat substrate together with the particles showed the importance of carrying out the analysis on actual particles rather than in flat substrates. We show that it is possible to characterize the anisotropy of pyrolytic carbon by Raman spectroscopy.
Corrosion of the Materials in Sulfuric Acid
Authors: Kim Hong Pyo , Kim Dong-Jin , Kwon Hyuk Chul , Park Ji Yeon , Kim Yong Wan
Published: April 2009

A program for a hydrogen production by using a high temperature nuclear heat has been launched in Korea since 2004. Iodine sulfur (IS) process is one of the promising processes for a hydrogen production because it does not generate carbon dioxide and a massive hydrogen production may be possible. However, the highly corrosive environment of the process is a barrier to its application in the industry. Therefore, corrosion behaviors of various materials were evaluated in sulfuric acid to select appropriate materials compatible with the IS process. The materials used in this work were Ni based alloys, Fe–Si alloys, Ta, Au, Pt, Zr, SiC, and so on. The test environments were boiling 50 wt % sulfuric acid without/with HI as an impurity and 98 wt % sulfuric acid. The surface morphologies and cross-sectional areas of the corroded materials were examined by using the scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectroscopy (EDS). From the results of the weight loss and potentiodynamic experiments, it was found that a Si enriched oxide is attributable to a corrosion resistance for materials including Si in boiling 98 wt % sulfuric acid. Moreover, the passive Si enriched film thickness increased with the immersion time leading to an enhancement of the corrosion resistance. Corrosion behaviors of the material tested are discussed in terms of the chemical composition of the materials, the corrosion morphology, and the surface layer’s composition.
Propulsive Efficiency of the Underwater Dolphin Kick in Humans
Authors: von Loebbecke Alfred , Mittal Rajat , Fish Frank , Mark Russell
Published: April 2009

Three-dimensional fully unsteady computational fluid dynamic simulations of five Olympic-level swimmers performing the underwater dolphin kick are used to estimate the swimmer’s propulsive efficiencies. These estimates are compared with those of a cetacean performing the dolphin kick. The geometries of the swimmers and the cetacean are based on laser and CT scans, respectively, and the stroke kinematics is based on underwater video footage. The simulations indicate that the propulsive efficiency for human swimmers varies over a relatively wide range from about 11% to 29%. The efficiency of the cetacean is found to be about 56%, which is significantly higher than the human swimmers. The computed efficiency is found not to correlate with either the slender body theory or with the Strouhal number.
Stress Changes in Intervertebral Discs of the Cervical Spine Due to Partial Discectomies and Fusion
Authors: Tchako Abraham , Sadegh Ali M.
Published: April 2009

Spine discectomy and fusion is a widely used surgical procedure to correct irreversible degenerative diseases and injuries to the intervertebral disk. The surgical procedure involves the removal of the damage disk material, the decortication of the fusion site, and the placement of the bone graft. Fusion is believed to generate additional stresses in the neighboring disks, which can subsequently lead to new disk degeneration and re-operation. The autologous bone has proven to be the best material for the fusion. However, the autologous bone has three major disadvantages: the high rate of donor site morbidity, the limited and sometimes poor quality of the amounts of bone available, and the extra operative time needed for harvest. For these reasons this study is undertaken to estimate the optimum amount of bone graft needed for a discectomy and correlate it to the change in stress in adjacent levels. A detailed and validated 3D finite element model of the complete human cervical spine (C1-T1) was altered to simulate segmental full and partial discectomies. One full fusion (bone graft occupies about 90% of the vertebral body) and seven partial fusions (bone graft occupies about 10%, 20%, 30%, 40%, 50%, 65%, and 75% of the vertebral body) were simulated at each of the four mid- and lower single levels of the cervical spine and the relationship between the change in stresses in the adjacent levels and the bone graft size (area) was studied. The changes in stress were compared with the previously obtained results of the unfused models. The fused and unfused models were preloaded with a 73.6 N compressive force representing the weight of the head and with a 1.5 Nm physiological moment in flexion, extension, lateral bending, and axial rotation. More than 132 cases were analyzed. The results showed that the necessary amount of bone graft needed for discectomy depends on the cervical disk level to be fused and varies between 30% and 75% of the disk area. The results also suggested that there is a threshold size of the bone graft area, before and/or after which, the long-term effects of the change in stresses in adjacent disks are biomechanically consequential.
Proteasomal Regulation of the Hypoxic Response Modulates Aging in
C. elegans
Authors: Mehta Ranjana , Steinkraus Katherine A. , Sutphin George L. , Ramos Fresnida J. , Shamieh Lara S. , Huh Alexander , Davis Christina , Chandler-Brown Devon , Kaeberlein Matt
Published: April 2009

Anti-Aging

Several human neurodegenerative diseases, such as Alzheimer's and Huntington's, are caused by aberrant protein aggregation. These disorders typically develop after the fifth decade of life, suggesting a connection with the aging process. In a number of different species, life span can be extended by dietary restriction and reduced insulin and insulin-like growth factor–1 (IGF-1) signaling. These pathways can also decrease toxic protein aggregation, mechanistically linking aging with proteotoxic diseases. While searching for regulators of proteotoxicity in
Caenorhabditis elegans
,

Mehta
et al.

(p.
1196
, published online 16 April) found that reduction of the von Hippel–Lindau tumor suppressor homolog VHL-1 significantly increased life span and enhanced resistance to proteotoxicity. VHL-1 is an E3 ubiquitin ligase that negatively regulates the hypoxic response, and animals grown under hypoxic conditions lived longer. This alternative longevity pathway was distinct from both dietary restriction and insulin/IGF-1–like signaling.
Fine-scale structure within a Trillium maculatum (Liliaceae) population
Authors: Walker Alana N. , Foré Stephanie A. , Collins Beverly
Published: April 2009

In long-lived ant-dispersed perennial herbs of mesic forests, interactions among fruiting plants, seed dispersal, and plant mortality over life-history stages can create demographic and genetic structure. We investigated whether there was nonrandom variation in the distributions of individuals and in genetic diversity within and among life-history stages of the forest herb Trillium maculatum Raf. (Liliaceae). In 2002 and 2004, all T. maculatum plants in a 5 m × 5 m plot (1572 and 1379 individuals, respectively) were mapped and classified as seedling, one-leaf, three-leaf nonflowering, or flowering. Spatial distributions of plants within and across life-history stages were tested against random expectation. Allozyme analysis of 262 individuals from three life-history stages was used to assess genetic diversity and structure in 2004. The number of seedlings and the proportion of one-leaf plants differed between years, but the proportions of three-leaf nonflowering and flowering plants remained the same. There was little evidence of vegetative reproduction, but heterozygosity was low and there was evidence of inbreeding. Seedlings were clumped around flowering plants at distances up to 50 cm and one-leaf plants were clumped at distances up to 100 cm. There were no apparent genetic differences among life-history stages, nor any apparent spatial genetic structure among all sampled individuals. These results, like those of other demographic and allozyme studies of Trillium species, can be explained by restricted dispersal and random mortality.
Effect of introduced Euphorbia esula on the pollination of Viola pedatifida
Authors: Montgomery B. R.
Published: April 2009

Introduced plants may compete for pollination with native plants, resulting in reduced fruit or seed set. In this study, I use several techniques to assess whether the invasive plant Euphorbia esula  L. (leafy spurge, Euphorbiaceae) reduces the pollination success of chasmogamous flowers of the native plant Viola pedatifida G. Don (prairie violet, Violaceae), which has chasmogamous and cleistogamous flowers. Euphorbia pollen was found on most Viola stigmas, suggesting the potential for competition. Additionally, application of Euphorbia pollen to Viola stigmas prior to conspecific pollen reduced seed set. However, natural receipt of Euphorbia and other heterospecific pollen was not associated with decreased fruit or seed set. In the field, fruit set was higher for Viola in sites with Euphorbia despite increased Euphorbia pollen receipt, and seed set did not vary with the presence of Euphorbia. However, there was no significant interaction between the presence of Euphorbia and flower type (cleistogamous or chasmogamous), suggesting that increased fruit set near Euphorbia is unrelated to pollination. This study suggests that Viola and Euphorbia interact through shared pollinators, but there is no evidence that competition for pollination with Euphorbia reduces Viola’s fecundity or results in increased reliance on cleistogamous flowers.