bluuebunny/crossref_metadata_2025 huggingface dataset:
Quantum dots in axillary lymph node mapping: Biodistribution study in healthy mice
Authors: Robe Anne , Pic Emilie , Lassalle Henri-Pierre , Bezdetnaya Lina , Guillemin François , Marchal Frédéric
Published: May 2008

Background

Breast cancer is the first cause of cancer death among women and its incidence doubled in the last two decades. Several approaches for the treatment of these cancers have been developed. The axillary lymph node dissection (ALND) leads to numerous morbidity complications and is now advantageously replaced by the dissection and the biopsy of the sentinel lymph node. Although this approach has strong advantages, it has its own limitations which are manipulation of radioactive products and possible anaphylactic reactions to the dye. As recently proposed, these limitations could in principle be by-passed if semiconductor nanoparticles (quantum dots or QDs) were used as fluorescent contrast agents for the in vivo imaging of SLN. QDs are fluorescent nanoparticles with unique optical properties like strong resistance to photobleaching, size dependent emission wavelength, large molar extinction coefficient, and good quantum yield.

Methods

CdSe/ZnS core/shell QDs emitting around 655 nm were used in our studies. 20 μL of 1 μM (20 pmol) QDs solution were injected subcutaneously in the anterior paw of healthy nude mice and the axillary lymph node (ALN) was identified visually after injection of a blue dye. In vivo fluorescence spectroscopy was performed on ALN before the mice were sacrificed at 5, 15, 30, 60 min and 24 h after QDs injection. ALN and all other organs were removed, cryosectioned and observed in fluorescence microscopy. The organs were then chemically made soluble to extract QDs. Plasmatic, urinary and fecal fluorescence levels were measured.

Results

QDs were detected in ALN as soon as 5 min and up to 24 h after the injection. The maximum amount of QDs in the ALN was detected 60 min after the injection and corresponds to 2.42% of the injected dose. Most of the injected QDs remained at the injection site. No QDs were detected in other tissues, plasma, urine and feces.

Conclusion

Effective and rapid (few minutes) detection of sentinel lymph node using fluorescent imaging of quantum dots was demonstrated. This work was done using very low doses of injected QDs and the detection was done using a minimally invasive method.
Immune responses toPneumocystis murinaare robust in healthy mice but largely absent in CD40 ligand-deficient mice
Authors: Hernandez-Novoa Beatriz , Bishop Lisa , Logun Carolea , Munson Peter J , Elnekave Eldad , Rangel Zoila G , Barb Jennifer , Danner Robert L , Kovacs Joseph A
Published: May 2008

Pneumocystis is a pathogen of immunocompromised hosts but can also infect healthy hosts, in whom infection is rapidly controlled and cleared. Microarray methods were used to examine differential gene expression in the lungs of C57BL/6 and CD40 ligand knockout (CD40L-KO) mice over time following exposure to Pneumocystis murina. Immunocompetent C57BL/6 mice, which control and clear infection efficiently, showed a robust response to infection characterized by the up-regulation of 349 primarily immune response-associated genes. Temporal changes in the expression of these genes identified an early (Week 2), primarily innate response, which waned before the infection was controlled; this was followed by primarily adaptive immune responses that peaked at Week 5, which coincided with clearance of the infection. In conjunction with the latter, there was an increased expression of B cell-associated (Ig) genes at Week 6 that persisted through 11 weeks. In contrast, CD40L-KO mice, which are highly susceptible to developing severe Pneumocystis pneumonia, showed essentially no up-regulation of immune response-associated genes at Days 35–75. Immunohistochemical staining supported these observations by demonstrating an increase in CD4+, CD68+, and CD19+ cells in C57BL/6 but not CD40L-KO mice. Thus, the healthy host demonstrates a robust, biphasic response to infection by Pneumocystis; CD40L is an essential upstream regulator of the adaptive immune responses that efficiently control infection and prevent development of progressive pneumonia.
Interferometry by deconvolution: Part 1 — Theory for acoustic waves and numerical examples
Authors: Vasconcelos Ivan , Snieder Roel
Published: May 2008

Interferometry allows for synthesis of data recorded at any two receivers into waves that propagate between these receivers as if one of them behaves as a source. This is accomplished typically by crosscorrelations. Based on perturbation theory and representation theorems, we show that interferometry also can be done by deconvolutions for arbitrary media and multidimensional experiments. This is important for interferometry applications in which (1) excitation is a complicated source-time function and/or (2) when wavefield separation methods are used along with interferometry to retrieve specific arrivals. Unlike using crosscorrelations, this method yields only causal scattered waves that propagate between the receivers. We offer a physical interpretation of deconvolution interferometry based on scattering theory. Here we show that deconvolution interferometry in acoustic media imposes an extra boundary condition, which we refer to as the free-point or clamped-point boundary condition, depending on the measured field quantity. This boundary condition generates so-called free-point scattering interactions, which are described in detail. The extra boundary condition and its associated artifacts can be circumvented by separating the reference waves from scattered wavefields prior to interferometry. Three wavefield-separation methods that can be used in interferometry are direct-wave interferometry, dual-field interferometry, and shot-domain separation. Each has different objectives and requirements.
Linguistic Uncertainty in Qualitative Risk Analysis and How to Minimize It
Authors: Carey Janet M. , Burgman Mark A.
Published: May 2008

Most risk assessments assume uncertainty may be decomposed into variability and incertitude. Language is often overlooked as a source of uncertainty, but linguistic uncertainty may be pervasive in workshops, committees, and other face‐to‐face language‐based settings where it can result in misunderstanding and arbitrary disagreement. Here we present examples of linguistic uncertainty drawn from qualitative risk analysis undertaken in stakeholder workshops and describe how the uncertainties were treated. We used a process of iterative re‐assessment of likelihoods and consequences, interspersed with facilitated discussion, to assist in the reduction of language‐based uncertainty. The effects of this process were evident as changes in the level of agreement among groups of assessors in the ranking of hazards.
Transparency in Risk Communication
Authors: Kurz‐Milcke Elke , Gigerenzer Gerd , Martignon Laura
Published: May 2008

Why is it that the public can read and write but only a few understand statistical information? Why are elementary distinctions, such as that between absolute and relative risks, not better known? In the absence of statistical literacy, key democratic ideals, such as informed consent and shared decision making in health care, will remain science fiction. In this chapter, we deal with tools for transparency in risk communication. The focus is on graphical and analog representations of risk. Analog representations use a separate icon or sign for each individual in a population. Like numerical representations, some graphical forms are transparent, whereas others indiscernibly mislead the reader. We review cases of (1) tree diagrams for representing natural versus relative frequency, (2) decision trees for the representation of fast and frugal decision making, (3) bar graphs for representing absolute versus relative risk, (4) population diagrams for the analog representation of risk, and (5) a format of representation that employs colored tinker cubes for the encoding of information about individuals in a population. Graphs have long enjoyed the status of being “worth a thousand words” and hence of being more readily accessible to human understanding than long‐winded symbolic representations. This is both true and false. Graphical tools can be just as well employed for transparent and nontransparent risk communications.
Visualizing Seismic Risk and Uncertainty
Authors: Bostrom Ann , Anselin Luc , Farris Jeremy
Published: May 2008

Government agencies and other authorities often communicate earthquake risks using maps derived from geographic information systems. Yet, little is known about the effects of these maps on risk perceptions. While mental models research and other approaches are available to inform risk communication text design, similar empirically derived guidance is lacking for visual risk communications, such as maps, which are likely to trump text in their impact and appeal. This paper reviews the empirical research that might inform such guidance. Research on graphs, spatial and visual perception, and map design suggests that graphics increase risk avoidance over numerical risk representations, and countable visuals, like dots, can increase the accuracy of perceived risks, but not always. Cartographic design features, such as color, animation, interactivity, and depth cues, are all candidates to represent risk and uncertainty and to influence risk perception. While there are robust known effects of color (e.g., red = danger), with some cultural variability, animation can increase the salience of otherwise obscure features but is not uniformly effective. Depth cues, dimensionality, and the extent to which a representation depicts versus symbolizes a scene will influence the viewer's perspective and perception, depending on the viewer's familiarity with the scene; their effects on risk perception remain unclear. The translation and representation of technical information about risk and uncertainty is critical to risk communication effectiveness. Our review suggests a handful of candidate criteria for evaluating the effects of risk visualizations, short of changes in behavior: accuracy, accessibility, retention, and perceived risk and usefulness.
Evolved Altruism, Strong Reciprocity, and Perception of Risk
Authors: Tucker W. Troy , Ferson Scott
Published: May 2008

Humans have a long history of coping with particular recurring risks. We expect natural selection to have resulted in specific physiological and psychological adaptations that respond well to these risks. Why, then, does it seem so difficult to communicate risk? We suggest that the human mind has been structured by natural selection to use a mental calculus for reckoning uncertainty and making decisions in the face of risk that can be substantially different from probability theory, propositional calculus (logic), or economic rationality (utility maximization). We argue that this is because of the unique armamentarium of strategies humans have evolved to cope with the risks faced during our long history living as hunter–gatherers. In particular, we believe the risk of social contract violation (not contributing a fair share to cooperative endeavors) was an important selective factor because reciprocity, reciprocal altruism, and cooperation are primary adaptations to the most important risks our ancestors faced.
Perceiving Others’ Perceptions of Risk
Authors: Finkel Adam M.
Published: May 2008

The recent literature providing insights from neuroscience and evolutionary biology into how individuals perceive risky choice situations represents a “second wave” of findings that recapitulates as well as challenges the risk perception research begun in the 1980s, which relied on psychometric survey research. Gleaning insights from the first wave of research that could improve the communication and control of environmental risks has yielded disappointing results. This is a result, in part, of the eagerness of scholars and pundits to posit a chasm between the “rational” and “objective” perceptions of experts, on the one hand, and a lay public that is seen as lurching between “paranoia and neglect” and as insensitive to the magnitude of risks. Interpretations of the psychometric research have suffered from inattention to uncertainty and interindividual variability in risk, to expert biases, and to important aspects of risky choice that were not explored in the first wave of research. Initial signs indicate that neuroscience and evolutionary biology research may fall prey to similar misinterpretations. This article summarizes some of the most intriguing findings of the “second wave” of risk perception research and advances four themes that may help make the new findings less divisive and more useful for improving risk communication and risk management. Continued research into risk perception should perhaps be embedded in a more general theory of public choice in the face of uncertain and variable costs and benefits and with a respect for distributive justice as an important goal in risk management.
Tumor Necrosis Factor-α-Mediated Suppression of Adipocyte Apolipoprotein E Gene Transcription: Primary Role for the Nuclear Factor (NF)-κB Pathway and NFκB p50
Authors: Yue Lili , Christman John W. , Mazzone Theodore
Published: May 2008

The adipose tissue inflammation accompanying obesity has important consequences for adipocyte lipid metabolism, and increased adipose tissue TNFα plays an important role for mediating the effect of inflammation on adipocyte function. Recent studies have shown that apolipoprotein E (apoE) is highly expressed in adipose tissue where it plays an important role in modulating adipocyte triglyceride metabolism, triglyceride mass, and adipocyte size. We have previously reported that TNFα reduces adipocyte apoE, and the current studies were undertaken to evaluate the molecular mechanism for this regulation. TNFα repression of adipocyte apoE gene expression required an intact nuclear factor (NF)-κB binding site at −43 in the apoE promoter. Site-directed mutagenesis at this site completely eliminated TNFα regulation of an apoE gene reporter. TNFα treatment activated binding of NFκB p50, isolated from adipocyte nuclei, to the apoE promoter. Two structurally distinct inhibitors of NFκB complex activation or translocation abrogated the TNFα effect on the apoE gene. Using chromatin immunoprecipitation assays, we demonstrated that treatment of adipocytes with TNFα led to increased binding of NFκB p50, and decreased binding of p65 and Sp1, to this region of the apoE promoter in living cells. The key role played by increased p50 binding was confirmed by p50 knockdown experiments. Reduction of p50 expression using small interference RNA completely eliminated TNFα-mediated reduction of endogenous adipocyte apoE gene expression. These results establish the molecular link between adipose tissue inflammation and apoE gene expression in adipocytes. The suppression of adipocyte apoE by the proinflammatory adipose tissue milieu associated with obesity will have important downstream effects on adipocyte triglyceride turnover and content.
Differential Effects of Refeeding on Melanocortin-Responsive Neurons in the Hypothalamic Paraventricular Nucleus
Authors: Sánchez Edith , Singru Praful S. , Acharya Runa , Bodria Monica , Fekete Csaba , Zavacki Ann Marie , Bianco Antonio C. , Lechan Ronald M.
Published: May 2008

To explore the effect of refeeding on recovery of TRH gene expression in the hypothalamic paraventricular nucleus (PVN) and its correlation with the feeding-related neuropeptides in the arcuate nucleus (ARC), c-fos immunoreactivity (IR) in the PVN and ARC 2 h after refeeding and hypothalamic TRH, neuropeptide Y (NPY) and agouti-related protein (AGRP) mRNA levels 4, 12, and 24 h after refeeding were studied in Sprague-Dawley rats subjected to prolonged fasting. Despite rapid reactivation of proopiomelanocortin neurons by refeeding as demonstrated by c-fos IR in ARC α-MSH-IR neurons and ventral parvocellular subdivision PVN neurons, c-fos IR was present in only 9.7 ± 1.1% hypophysiotropic TRH neurons. Serum TSH levels remained suppressed 4 and 12 h after the start of refeeding, returning to fed levels after 24 h. Fasting reduced TRH mRNA compared with fed animals, and similar to TSH, remained suppressed at 4 and 12 h after refeeding, returning toward normal at 24 h. AGRP and NPY gene expression in the ARC were markedly elevated in fasting rats, AGRP mRNA returning to baseline levels 12 h after refeeding and NPY mRNA remaining persistently elevated even at 24 h. These data raise the possibility that refeeding-induced activation of melanocortin signaling exerts differential actions on its target neurons in the PVN, an early action directed at neurons that may be involved in satiety, and a later action on hypophysiotropic TRH neurons involved in energy expenditure, potentially mediated by sustained elevations in AGRP and NPY. This response may be an important homeostatic mechanism to allow replenishment of depleted energy stores associated with fasting.
3′,5′-Cyclic Adenosine Monophosphate Response Element Binding Protein Up-Regulated Cytochrome P450 Lanosterol 14α-Demethylase Expression Involved in Follicle-Stimulating Hormone-Induced Mouse Oocyte Maturation
Authors: Ning Gang , Ouyang Hong , Wang Songbo , Chen Xiufen , Xu Baoshan , Yang Jiange , Zhang Hua , Zhang Meijia , Xia Guoliang
Published: May 2008

Cytochrome P450 lanosterol 14α-demethylase (CYP51) is a key enzyme in sterols and steroids biosynthesis that can induce meiotic resumption in mouse oocytes. The present study investigated the expression mechanism and function of CYP51 during FSH-induced mouse cumulus oocyte complexes (COCs) meiotic resumption. FSH increased cAMP-dependent protein kinase (PKA) RIIβ level and induced cAMP response element-binding protein (CREB) phosphorylation and CYP51 expression in cumulus cells before oocyte meiotic resumption. Moreover, CYP51 and epidermal growth factor (EGF)-like factor [amphiregulin (AR)] expression were blocked by 2-naphthol-AS-Ephosphate (KG-501) (a drug interrupting the formation of CREB functional complex). KG-501 and RS21607 (a specific inhibitor of CYP51 activity) inhibited oocyte meiotic resumption, which can be partially rescued by progesterone. These two inhibitors also inhibited FSH-induced MAPK phosphorylation. EGF could rescue the suppression by KG-501 but not RS21607. Furthermore, type II PKA analog pairs, N6-monobutyryl-cAMP plus 8-bromo-cAMP, increased PKA RIIβ level and mimicked the action of FSH, including CREB phosphorylation, AR and CYP51 expression, MAPK activation, and oocyte maturation. All these data suggest that CYP51 plays a critical role in FSH-induced meiotic resumption of mouse oocytes. CYP51 and AR gene expression in cumulus cells are triggered by FSH via a type II PKA/CREB-dependent signal pathway. Our study also implicates that CYP51 activity in cumulus cells participates in EGF receptor signaling-regulated oocyte meiotic resumption.
Sustaining Active-Living Communities over the Decades: Lessons from a 1930s Greenbelt Town
Authors: Ahrentzen Sherry
Published: May 2008

Greendale, Wisconsin, was intentionally created with many of the design and planning principles that active-living advocates promote today. This case study examines the processes behind sustaining these particular planning and design principles over time in light of economic and regional challenges that have faced not just Greendale but most town centers over the last fifty years. Despite these challenges, the walkable nature of Greendale's center remains strong today, in terms of both activity and community identity. While many circumstances are specific to this particular town, useful lessons can be drawn for those new urbanist (NU) communities being developed in greenfields and suburbs today, many of which are strikingly similar to Greendale — relatively small, low density, and located within metropolitan areas. Greendale's success resulted from (1) attending to the retail/commercial product mix; (2) attracting nonresidents to use the community's retail and public space; and (3) capitalizing on community investment not simply from residents' organizing efforts but, more important in this case, from corporate community involvement by a Greendale business firm whose interests and values coincided with those of the community.
The Promise of Wisconsin's 1999 Comprehensive Planning Law: Land-Use Policy Reforms to Support Active Living
Authors: Schilling Joseph , Keyes Sheila D.
Published: May 2008

Weaving together the disciplines of planning and policy change with the emerging research of active living, this article explores the competing interests and underlying political forces behind the design and passage of Wisconsin's Comprehensive Planning Law of 1999. While Wisconsin's law remains a work in progress, it illustrates the contemporary policy battles over land use and smart growth and the resurgence of the property-rights movement. It further highlights the influence of smart-growth coalitions and policy networks on planning reform. The authors suggest that planning practitioners and active-living proponents can adapt and transfer these policy lessons from Wisconsin to address the complex relationships of the built environment, physical activity, and the nation's current obesity problem through state and local planning reforms.
Collaborative School Planning and Active Schools: A Case Study of Lee County, Florida
Authors: Lees Emily , Salvesen David , Shay Elizabeth
Published: May 2008

To contribute to the understanding of the links between urban planning and school siting and, ultimately, the impact of both on physical activity, we conducted a case study of Lee County, Florida. Our study examined the extent of state-mandated collaboration between the Lee County School Board and Lee County government (e.g., the Lee County Department of Planning, the Office of Smart Growth, and the Department of Parks and Recreation). Specifically, we investigated planning processes under mandated coordination between the school board and the county and the impact of such coordination on the integration of land-use planning and school facility planning. By describing the process of mandated collaborative school planning in Florida, we illustrate the promise and pitfalls of such top-down legislation and offer insights to other state and local governments looking for ways to improve local planning and to increase physical activity among children.
A Myc-Slug (Snail2)/Twist regulatory circuit directs vascular development
Authors: Rodrigues Claudia O. , Nerlick Steve T. , White Elsie L. , Cleveland John L. , King Mary Lou
Published: May 2008

Myc-deficient mice fail to develop normal vascular networks and Myc-deficient embryonic stem cells fail to provoke a tumor angiogenic response when injected into immune compromised mice. However, the molecular underpinnings of these defects are poorly understood. To assess whether Myc indeed contributes to embryonic vasculogenesis we evaluated Myc function in Xenopus laevis embryogenesis. Here, we report that Xc-Myc is required for the normal assembly of endothelial cells into patent vessels during both angiogenesis and lymphangiogenesis. Accordingly, the specific knockdown of Xc-Myc provokes massive embryonic edema and hemorrhage. Conversely, Xc-Myc overexpression triggers the formation of ectopic vascular beds in embryos. Myc is required for normal expression of Slug/Snail2and Twist, and either XSlug/Snail2 or XTwist could compensate for defects manifest by Xc-Myc knockdown. Importantly, knockdown of Xc-Myc, XSlug/Snail2 or XTwist within the lateral plate mesoderm, but not the neural crest, provoked embryonic edema and hemorrhage. Collectively, these findings support a model in which Myc, Twist and Slug/Snail2 function in a regulatory circuit within lateral plate mesoderm that directs normal vessel formation in both the vascular and lymphatic systems.
Contact pressure in indented elastohydrodynamic lubrication contacts
Authors: Biboulet N , Lubrecht A A , Houpert L
Published: May 2008

Indents perturb the pressure and stress distribution and increase the failure risk. Existing theory for roughness deformation is extended to pure-rolling elastohydrodynamic lubrication indented contact pressure perturbations. First, a study of shallow indents is proposed, then it is modified to account for non-linear behavior of deeper indents.
Effect of sinusoidal surface roughness under starved conditions on rolling contact fatigue
Authors: Labiau A , Ville F , Sainsot P , Querlioz E , Lubrecht T
Published: May 2008

Starvation combined with surface roughness drastically reduces fatigue life. On the basis of the results obtained earlier, concerning the effect of sinusoidal surface roughness on rolling contact fatigue under elastic dry contact assumptions and relations established by Venner et al. and Morales-Espejel et al., the authors have developed an analytical formula to calculate the pressure increase as a function of contact conditions and waviness parameters. They finally proposed a risk master curve for lubricated conditions with sinusoidal rough surfaces.
A steady-state elastohydrodynamic lubrication model aimed at natural hip joints with physiological loading and anatomical position
Authors: Quiñonez A Félix , Fisher J , Jin Z M
Published: May 2008

A steady-state elastohydrodynamic lubrication model has been implemented with a view on simulating the operating conditions of natural hip joints. The model predictions were compared by employing two methods of estimating the elastic deformation of a soft-layered ball-in-cup geometrical configuration, namely (a) a simple constrained column model and (b) a full-field solution approach with displacement coefficients obtained from a prior finite-element method analysis. The comparison aimed to investigate the suitability of the former method, which is easier to implement and use in terms of both time and effort. For the range of operating conditions considered, the results obtained suggest that the constrained column method can be incorporated into the lubrication model in cases where the soft-layered bearing surface has a Poisson's ratio not greater than 0.45. Otherwise excessively large contact pressures are obtained. In addition to these results, good agreement was also found between the absolute values of film thickness calculated here and those predicted using suitable formulae available in the literature.
Experimental and finite-element analysis of scratches on amorphous polymeric surfaces
Authors: Pelletier H , Gauthier C , Schirrer R
Published: May 2008

The scratch behaviour of two amorphous polymers is investigated to understand how the materials characteristics affect the scratch resistance. A thermosetting resin (CR39) and a thermoplastic polymer polymethylmethacrylate (PMMA) are studied using both an experimental set-up allowing in situ observations of the contact area during indentation or scratching with spherical tips, and a finite-element modelling (FEM). The rheological properties of CR39 and PMMA surfaces are modelled assuming a linear elastic behaviour and a plastic law with high strain hardening, described by G'sell Jonas equation. A description of the plastic strain field, beneath the indenter during scratch is proposed. The main parameter of the description is the level of the deformation imposed on the samples, related in first approximation to the ratio a/ R set between 0.1 and 0.4, a being the contact radius, and R the tip radius. The true friction μloc at the interface between the indenter and the material was modelled with a Coulomb's friction coefficient varying between 0 and 0.4, for each computed ratio a/ R. The two polymers display the same scratching behaviour for low levels of deformation, whereas at high strain, PMMA shows a more pronounced plastic behaviour, with high level of average plastic strain, especially for higher friction coefficient. This results obtained by FEM are in good correlation with experimental observations and show that the plastic strain gradient beneath the indenter depends clearly on the ratio a/ R, on the true friction coefficient and also the rheological parameters of tested material.
Friction and wear performance of diamond-like carbon and Cr-doped diamond-like carbon coatings in contact with steel surfaces
Authors: Renondeau H , Taylor R I , Smith G C , Torrance A A
Published: May 2008

The development of modern engines involves the use of new materials such as diamond-like carbon (DLC) coatings. As these coatings possess different mechanical and physical characteristics to steel, investigation of their friction and wear properties when rubbing against a steel counterpart in a lubricated environment is needed. Specific tests were used to assess the tribological behaviour of these new surfaces (specifically an undoped DLC and a chromium-doped DLC coating). Chemical analyses were also performed in order to evaluate the reactivity of the formulated oil on the various surfaces. The results of the present work clearly show that there was no evidence of tribochemical reaction on DLC coatings. Anti-wear additives were still reacting on the steel counterpart for the undoped DLC case, resulting in better wear properties for the coating. The addition of a metal to the amorphous carbon matrix led to an improvement in wear but inhibited/removed the anti-wear film on the steel counterpart.
Boundary lubrication film formation from phosphorus antiwear additives with application to metal V-belt type continuously variable transmission lubricants
Authors: Narita K , Priest M
Published: May 2008

This study has focused on the application of sulphur-free phosphorus antiwear additives in metal V-belt pushing type continuously variable transmission fluids to achieve higher friction coefficient plus excellent antiwear performance between the metal—metal contacting surfaces. The metal—metal tribological characteristics of phosphorus compounds were experimentally investigated using a reciprocating ball on plate tribometer, enabling film formation to be monitored during reciprocating sliding tests by an electric resistance method. As a result, sample with acid phosphate possessing C8 alkyl chain gave 20 per cent higher friction coefficient between metal contacting interfaces than C18 alkyl acid phosphate. Notably, an additive formulation composed of C8 acid phosphate with shorter alkyl chain, amine compound, and over-based calcium sulphonate demonstrated a synergism with 9 per cent higher friction and better antiwear performance than acid phosphate alone, which would give a positive outcome in the belt and pulley system of the continuously variable transmission. From surface analysis such as optical interferometry and X-ray photoelectron spectroscopy, it is hypothesized that the variation of tribofilm species produced by a chemical reaction between these additives plays a role in reducing corrosive wear and inhibiting the entrainment of lubricant into interfaces, resulting in higher friction. Moreover, the post-test rubbing tracks still possessed a longitudinally oriented surface pattern, which seemed to contribute to a reduced fluid film effect, giving a higher friction coefficient during rubbing tests.
Friction modelling of tribofilm performance in a bench tribometer for automotive engine lubricants
Authors: Roshan R , Priest M , Neville A , Morina A , Xia X , Green J H , Warrens C P , Payne M J
Published: May 2008

Research focusing on the initial stages of the development of an empirical model to predict friction in boundary and mixed lubrication conditions accounting for additive and surface interactions is reported in this article. The regression model was constructed by applying a fractional factorial design statistical approach. The model considers a typical friction modifier, molybdenum dithiocarbamate, in a model automotive engine lubricant also containing zinc dialkyldithiophosphate in a synthetic polyalphaolefin base oil under conditions representative of the cam and follower interface in an automotive engine. Operating temperature, sliding speed, load, initial surface roughness, and the initial lambda ratio were taken as the factors affecting tribological performance. The empirical model predicts friction at 95 per cent confidence level within the specific range of parameters considered in the experiments. Not surprisingly, molybdenum dithiocarbamate is mainly responsible for the reduction of friction of the tribofilm, whereas temperature, sliding speed, and load are the other significant parameters.
Fatigue mechanics of TiC-based cemented carbides
Authors: Sergejev F , Preis I , Hussainova I , Kübarsepp J
Published: May 2008

The aim of this work was to investigate fracture and fatigue behaviour of TiC—Ni/Fe cermets under monotonic and cyclic loading.

The fracture toughness KIc was determined by a conventional testing method (using single edge notched beam) and evaluated by an indentation technique (indentation fracture toughness (IFT)). Results from both experimental routines were analysed and compared with the reference hardmetal – WC-10 wt% Co. As the result, a novel sequence for estimation of the IFT for TiC- and WC-based cemented carbides is presented.

The transverse rupture strengths RTZ and fatigue strengths σf at a given life (107 cycles) were obtained by the testing of unnotched and notched specimens with the three-point bending scheme. Considering that the fatigue lifetime of cemented carbides is given by the subcritical crack growth of pre-existing defects, a linear elastic fracture mechanics approach is attempted to assess fatigue life—fatigue crack growth relationships for the studied materials.

The reliability of used fatigue mechanics approach is proved by the excellent agreement observed between estimated and experimentally determined values for fracture toughness and fatigue strength of the investigated materials.
Transition of frictional states and surface roughness effects in lubricated contacts
Authors: Wang S , Hu Y-Z , Wang W-Z , Wang H
Published: May 2008

In order to investigate frictional performances in different lubrication regimes and effects of surface roughness, the friction on engineering surfaces with different roughness patterns and amplitudes were measured. Results show a smooth transition of lubrication states from full-film hydrodynamic lubrication to mixed and boundary lubrication. Data from the tests also suggest that the transition of friction regimes is affected by roughness amplitude. It is observed that not only the smoother surfaces give rise to the lower critical velocities of transition from full-film to mixed lubrication, but also the friction coefficients at the point of the transition are much smaller for the smoother surfaces. For the transition from mixed to boundary lubrication, however, effects of roughness amplitude are insignificant. As a result, it is concluded that under the same contact conditions, different features in roughness cause the system to transit in different routines from one lubrication regime to another. Furthermore, a computer model, based on the deterministic solution of mixed lubrication combined with modelling of rheological variation in ultra-thin films, has been presented to predict friction in overall lubrication regimes. At last, the comparisons of simulation and experimental results show satisfactory agreements.
Comparison of fatigue model results for rough surface elastohydrodynamic lubrication
Authors: Qiao H , Evans H P , Snidle R W
Published: May 2008

The paper compares the results of applying different fatigue failure models to surfaces that experience elastohydrodynamic lubrication (EHL) and have surface roughness features which are large compared with the equivalent smooth surface film thickness. The surface profiles used for the comparisons reported are taken from test gear surfaces used in an FZG gear test. The surface has a roughness of 0.31 μm Ra, with peak to valley dimensions of the order 1.5 μm. The tips of the asperities have been modified by running-in during the gear test. A transient EHL analysis was carried out using contacting components having this profile for a number of sliding speeds and nominal viscosity values. From these analyses, time-dependent pressure and shear stress distributions at the contacting surfaces were calculated. The resulting subsurface stress field was obtained relative to axes fixed in the moving surfaces using an elastic analysis so as to give the stress history at each point in a representative test section of the contacting component. A number of multi-axial fatigue criteria based on a critical plane approach were applied to the test section and the results compared. In addition, a varying amplitude multi-axial fatigue theory based on shear strain cycles was also applied to the section. The cycle counts were obtained using the rainflow counting method and the accumulated damage in a single pass through the contact area was calculated. In comparing the results obtained, the various fatigue models were found to identify the same asperity features as being those most prone to fatigue.
Influence of slide-to-roll ratio on tribofilm generation
Authors: Meheux M , Minfray C , Ville F , Mogne T Le , Lubrecht A A , Martin J M , Lieurade H P
Published: May 2008

Rolling contact fatigue has become a surface initiated problem. This phenomenon is due to the initiation and propagation of cracks from the surface to the volume of mechanical pieces. A great amount of research has been done since the 1970s to understand its origin, but many aspects remain unclear. Many authors found that the lubricant composition and especially certain additives can either improve or reduce fatigue life, depending on the operating conditions. It is now admitted that additives form a tribofilm in the rubbing track, especially under pure sliding conditions, but no direct relation to rolling contact fatigue has been drawn to this moment. The knowledge of the reaction pathways of lubricant additives under various sliding conditions as well as the tribofilm properties and morphology has become an important issue.

In this work, the mini traction machine has been used to study friction under different sliding conditions of a pure mineral base oil and a formulated oil containing five selected additives. The results suggest that friction is likely to mimic tribofilm formation. The slide-to-roll ratio influences the rate of direct asperity contacts and hence tribofilm growth.
A study of contact temperature and tribological behaviour of magnetized sliding brass—steel couple in different gas environments
Authors: Amirat M , Zaïdi H , Frêne J
Published: May 2008

The wear tests of the sliding magnetized brass—steel couple are investigated on a pin—disc configuration under three various gas environments: in ambient air, under oxygen at 105 Pa, and in vacuum at 1.5 × 10−6 torr. The tribological behaviour of the couple strongly depends on the environment gas and a little effect of the magnetic field intensity. The results obtained show that the magnetic field decreases the wear rate and the friction coefficient in both air and oxygen atmosphere, respectively. However, in vacuum, the magnetic field has a negligible effect. The wear mode follows a transition from abrasive wear to adhesive wear after some cycles at the beginning of sliding contact.

The temperature increment is very large in vacuum and it is almost stationary in both ambient air and oxygen. On the other hand, the application of magnetic field induces a little increase in contact temperature of average value about 5–8 °C in each gas environment. The temperature rise is correlated directly to interface properties, namely the hardness, the real contact area, and the roughness of the steel counterface.
Tribo-corrosion analysis of wear and metal ion release interactions from metal-on-metal and ceramic-on-metal contacts for the application in artificial hip prostheses
Authors: Yan Y , Neville A , Dowson D , Williams S , Fisher J
Published: May 2008

Osteolysis induced by polyethylene wear debris from metal-on-polyethylene total joint replacements is one of the major reasons for the renewed interest in metal-on-metal (MoM) bearings for total hip arthroplasty. However, long-term clinical performance is as yet unknown for the second generation MoM hip prostheses. The main concerns are the released metal ions and metallic wear debris from the artificial joints. It is well known that the metal ion release processes (corrosion) are electrochemical in nature. When two contacted components are in relative motion, wear can occur and it can accelerate corrosion. The role of corrosion in the generation of metallic wear debris is still not well understood. This paper addresses this point and makes a comparison of MoM and ceramic-on-metal (CoM) contacts.

In this paper, tests were conducted on a pin-on-plate tester with an integrated electrochemical cell in 25 per cent bovine serum to determine the effects of pin rotation on the wear and metal ion release of two different combinations (metal pins with metal plates and metal pins with medical grade Alumina plates). The overall wear and released metallic ions were reduced with rotational movement of the pin in addition to the reciprocating action of the plate. For the CoM combination, a reduction of wear was associated with a more noble open circuit potential compared with the MoM combination.
A study of microstructural evolution around crack tip using crystal plasticity finite-element method
Authors: Huynh N N , Lu C , Si L , Tieu K
Published: May 2008

The microstructure plays a significant role in crack initiation and crack propagation in metals. In this paper, a crystal plasticity finite-element method has been developed to simulate the tensile tests on rectangle-notched, triangle-notched, and circle-notched aluminium samples. Polycrystalline aggregates are approximated by a Voronoi structure. Two sets of initial orientations are randomly assigned to the aggregate. Notch geometries after deformation, the maximum shear stresses, and crystal orientation rotations are presented and discussed. Simulation results reveal that deformation of polycrystalline aggregate is greatly influenced by both notch geometry and initial crystal orientation. The crystal orientation profoundly rotates around the thickness direction of the samples for all the notch geometries and the initial orientations.
Thin coatings with graded elastic properties
Authors: Dahm K L
Published: May 2008

Thin W—Nb coatings were sputter co-deposited from pure targets on glass substrates with Nb contents from 14 to 70 at%. Pure W coatings (2.5 μm thick) were deposited on Ti-6Al-4V substrates with and without 0.5-μ m thick W—Nb interlayers to assess the influence of graded elastic properties on the adhesion of the W coatings. Two interlayer compositions were studied: 31 and 50 at% Nb. All of the W—Nb coatings were crystalline and solely body centre cubic. The plane strain elastic modulus ( E′ c) and hardness ( H c) of the coatings (as measured by nanoindentation) increased with increasing W content. E′ c increased from 223 ± 16 GPa at 70 at% Nb to 587±91 GPa for a pure W coating. Over the same composition range H c increased from 8.51±0.25 to 13.49±1.04 GPa. No delamination was observed for any of the coated Ti-6Al-4V samples after adhesion testing by Rockwell C (Rc) indentation or scratch testing (at loads up to 5.00 kg). Through-coating cracks were observed around the rims of the Rc indents and within the scratches (at loads of 1.00 kg and higher). In all cases, the density of these cracks increased in the following order: 50 at% Nb interlayer<31 at% Nb interlayer<no interlayer.
Viscosity measurement in thin lubricant films using shear ultrasonic reflection
Authors: Kasolang S , Dwyer-Joyce R S
Published: May 2008

When a shear ultrasonic wave is incident on a solid and liquid boundary, the proportion that is reflected depends on the liquid viscosity. This is the basis for some instruments for on-line measurement of bulk liquid viscosity. In machine elements, the lubricant is usually present in a thin layer between two rubbing solid surfaces. The thin film has a different response to an ultrasonic shear wave than liquid in bulk. In this work, this response is investigated with the aim of measuring viscosity in situ in a lubricating film. The proportion of the wave reflected at a thin layer depends on the layer stiffness. A shear wave is reflected by the shear stiffness of the thin layer. For a thin viscous liquid layer, the stiffness is a complex quantity dependent on the viscosity, wave frequency, and film thickness. This stiffness is incorporated into a quasi-static spring model of ultrasonic reflection. In this way, the viscosity can be determined from shear-wave reflection if the oil-film thickness is known. The approach has been experimentally evaluated on some static oil film between Perspex plates. Predictions of the spring model gave good measurement up to layer thicknesses of around 15 μm. For thicker layers, the shear stiffness reduces to such an extent that almost all the wave is reflected and the difference associated with the layer response is hard to distinguish from background noise.
Lubricant/surface interactions under extreme pressure conditions: Corrosion inhibitor interacting extreme pressure/anti-wear additives on steel surface
Authors: Mistry K K , Neville A , Morina A , Webster M N
Published: May 2008

Many mechanical systems operate under mixed-boundary lubricated conditions. Moreover, these mechanical systems have highly loaded non-conformal contact surfaces, therefore significantly influencing friction/wear performance and also inducing various modes of failures. Hence, it is important to optimize selection of the lubricant since it plays a crucial role in controlling friction and affecting durability by forming tribochemical film on top of contact surfaces.

The aim of the present work is to investigate the influence of extreme pressure additives, anti-wear additives, and corrosion inhibitors interacting at a steel/steel lubricated contact under extreme conditions and characterize the additive/surface interactions by advanced surface analysis techniques. The tribological testing was carried out employing a ball-on-disc test rig (ASTM G99-05) to measure friction. The wear on the balls was observed on the optical microscope after completion of the tribotest. Energy dispersive X-ray analysis and X-ray photoelectron spectroscopy were used to access the chemistry on the surface.

In this paper, synergistic effects and antagonistic effects in terms of tribological parameters (friction and wear) are discussed, and mechanisms of the interactions are explained by surface analysis. Implications for optimizing the system performance are discussed.
An axisymmetric hydrodynamic interface element for finite-element computations of mixed lubrication in rubber seals
Authors: Öngün Y , André M , Bartel D , Deters L
Published: May 2008

This paper presents an elegant way to compute hydrodynamic lubrication in machine parts, especially in highly deformable dynamic seals. In such tribologic systems, the sealing and frictional behaviour is highly related to the interaction between the hydrodynamic lubrication and the structural deformation of the seal. In this work, a hydrodynamic interface element is developed in order to achieve a strong coupling of the fluid dynamics and the deformation of the solid structure. The fluid flow is represented by the two-dimensional steady-state Reynolds equation, the structural deformation by standard finite-element procedures. This method enables the application of arbitrary, non-linear material models provided by finite-element programs. Furthermore, a model for mixed lubrication, including frictional effects, is presented.
An Unusual Reaction of a Pyridinium Ylide with 1,1-Dicyanoethylene Derivatives
Authors: Yamada Shinji , Ohta Emiko
Published: May 2008

A reaction of pyridinium perfluorophenacylide generated from pyridinium salt 1 with 1,1-dicyanoethylene derivatives 2 produced unusual products 3, which have an ylide structure with a cyano group at the C2 and a cis-acrylonitrile moiety at the o-position of the perfluorophenyl group. A plausible mechanism involving intramolecular aromatic nucleophilic substitution and 1,3-migration of the cyano group is proposed for this reaction.