bluuebunny/crossref_metadata_2025 huggingface dataset:
Essential cysteine residues for human RNase κ catalytic activity
Authors: Kiritsi Marianna N. , Fragoulis Emmanuel G. , Sideris Diamantis C.
Published: February 2012

Human RNase κ is an endoribonuclease expressed in almost all tissues and organs and belongs to a highly conserved protein family bearing representatives in all metazoans. To gain insight into the role of cysteine residues in the enzyme activity or structure, a recombinant active form of human RNase κ expressed in Pichia pastoris was treated with alkylating agents and dithiothreitol (DTT). Our results showed that the human enzyme is inactivated by DDT, while it remains fully active in the presence of alkylating agents. The unreduced recombinant protein migrates on SDS/PAGE faster than the reduced form. This observation in combination with the above findings indicated that human RNase κ does not form homodimers through disulfide bridges, and cysteine residues are not implicated in RNA catalysis but participate in the formation of intramolecular disulfide bond(s) essential for its ribonucleolytic activity. The role of the cysteine residues was further investigated by expression and study of Cys variants. Ribonucleolytic activity experiments and SDS/PAGE analysis of the wild‐type and mutant proteins under reducing and non‐reducing conditions demonstrated that Cys7, Cys14 and Cys85 are not essential for RNase activity. On the other hand, replacement of Cys6 or Cys69 with serine led to a complete loss of catalytic activity, indicating the necessity of these residues for maintaining an active conformation of human RNase κ by forming a disulfide bond. Due to the absolute conservation of these cysteine residues, the Cys6‐Cys69 disulfide bond is likely to exist in all RNase κ family members.
Mental Disorders and Communication of Intent to Die in Indigenous Suicide Cases, Queensland, Australia
Authors: De Leo Diego , Milner Allison , Sveticic Jerneja
Published: February 2012

In comparing Indigenous to non‐Indigenous suicide in Australia, this study focussed on the frequency of the association between some psychiatric conditions, such as depression and alcohol abuse, and some aspect of suicidality, in particular communication of suicide intent. Logistic regression was implemented to analyze cases of Indigenous (n = 471) versus non‐Indigenous suicides (n = 6,655), using the Queensland Suicide Register as a data source. Compared to non‐Indigenous suicides, Indigenous cases had lower odds of being diagnosed with unipolar depression, seeking treatment for psychiatric conditions or leaving a suicide note. Indigenous suicides had greater odds of verbally communicating suicide intent and having a history of alcohol and substance use. The magnitude of these differences is remarkable, underscoring the need for culturally sensitive suicide prevention efforts.
Birth weight, early weight gain and pubertal maturation: a longitudinal study
Authors: Wang Y. , Dinse G. E. , Rogan W. J.
Published: February 2012

Objective

To investigate the effect of birth weight and early weight gain on the timing of various measures of puberty in both girls and boys.

Methods

A total of 856 newborns enrolled in the North Carolina Infant Feeding Study were followed to age 5 years, with 600 children followed up at adolescence. Birth weight was obtained from medical records and children were weighed at study visits until age 5 years; gains in standardized weights were calculated over four early age intervals: 0–6 months, 6–12 months, 1–2 years and 2–5 years. Age at menarche in girls and age at advanced Tanner stages in both girls and boys were reported by adolescents and their parents. Survival models were used to analyse the effects of birth weight and early weight gain on these outcomes.

esults

Girls with higher birth weight and greater weight gains during the four early age intervals were younger when they reached menarche and advanced Tanner stages; boys with greater early weight gains also were younger when they reached advanced Tanner stages, but few of these effects were statistically significant.

Conclusions

Higher birth weights and greater weight gains during infancy and early childhood can lead to earlier sexual maturation in girls.
Gestational weight gain and predicted changes in offspring anthropometrics between early infancy and 3 years
Authors: Deierlein A. L. , Siega‐Riz A. M. , Herring A. H. , Adair L. S. , Daniels J. L.
Published: February 2012

Objective

To determine how gestational weight gain (GWG), categorized using the 2009 Institute of Medicine recommendations, relates to changes in offspring weight‐for‐age (WAZ), length‐for‐age (LAZ) and weight‐for‐length z‐scores (WLZ) between early infancy and 3 years.

Methods

Women with singleton infants were recruited from the third cohort of the Pregnancy, Infection, and Nutrition Study (2001–2005). Term infants with at least one weight or length measurement during the study period were included (n = 476). Multivariable linear mixed effects regression models estimated longitudinal changes in WAZ, LAZ and WLZ associated with GWG.

Results

In early infancy, compared with infants of women with adequate weight gain, those of women with excessive weight gains had higher WAZ, LAZ and WLZ. Excessive GWG ≥ 200% of the recommended amount was associated with faster rates of change in WAZ and LAZ and noticeably higher predicted mean WAZ and WLZ that persisted across the study period.

Conclusions

GWG is associated with significant differences in offspring anthropometrics in early infancy that persisted to 3 years of age. More longitudinal studies that utilize maternal and paediatric body composition measures are necessary to understand the nature of this association.
Semaphorins and neuropilins: new players in the neuroendocrine control of the intrathymic T‐cell migration in humans
Authors: Mendes‐da‐Cruz Daniella Arêas , Linhares‐Lacerda Leandra , Smaniotto Salete , Dardenne Mireille , Savino Wilson
Published: February 2012

Cell migration is a key event for proper intrathymic T‐cell differentiation, and several ligand–receptor interactions contribute to the well‐co ordinated movement of developing thymocytes within the thymic lobules. Herein we summarize recent data that place semaphorin 3A (Sema3A) and its receptor neuropilin 1 (NRP1) as further players in the physiological process of cell migration in the human thymus. These molecules, as well as class A plexins (necessary for the intracellular signalling transduction triggered by Sema3A–NRP1 ligation), are constitutively expressed by both developing thymocytes and components of the thymic microenvironment, including epithelial and dendritic cells. Functionally, Sema3A decreases the adhesion of human thymocytes on thymic epithelial cell monolayers and exerts per se a dose‐dependent chemorepulsive effect on human thymocytes. Moreover, Sema3A inhibits chemoattractant migratory responses induced by other ligands, including fibronectin, laminin and CXCL12 (chemokine CXC motif ligand 12). These data should be placed in the context of the concept that migration of developing T cells is a multivectorial system, in which the resulting migration vector derives from a balance of several simultaneous and/or sequential ligand–receptor pair interactions. Accordingly, semaphorins and neuropilins can be considered as further players in the system.
Spironolactone prevents alterations associated with cardiac hypertrophy produced by isoproterenol in rats: involvement of serum‐ and glucocorticoid‐regulated kinase type 1
Authors: Martín‐Fernández Beatriz , de las Heras Natalia , Miana María , Ballesteros Sandra , Valero‐Muñoz María , Vassallo Dalton , Davel Ana Paula , Rossoni Luciana Venturini , Cachofeiro Victoria , Lahera Vicente
Published: February 2012

Persistent β‐adrenergic receptor stimulation with isoproterenol is associated with cardiac hypertrophy as well as cardiac synthesis of angiotensin II. Serum‐ and glucocorticoid‐regulated kinase type 1 (SGK‐1) is a key mediator in structural, functional and molecular cardiac effects of aldosterone in rats. This study was designed to investigate the cardiac effects of the mineralocorticoid receptor antagonist spironolactone on the response to isoproterenol treatment in rats, as well as the involvement of the main mediator of cellular aldosterone action, SGK‐1, in the heart. Male Wistar rats received isoproterenol (3 mg kg−1 day−1) or vehicle for 15 days. Half of the animals in each group were simultaneously treated with spironolactone (200 mg kg−1 day−1). Systolic and diastolic blood pressures were not significantly different among groups. Treatment with spironolactone normalized the increased left ventricular end‐diastolic pressure observed in isoproterenol‐treated rats. Isoproterenol treatment induced cardiac hypertrophy and increased collagen content, both of which were normalized by spironolactone treatment. The mRNA levels of transforming growth factor β, connective tissue growth factor, matrix metalloprotease 2, matrix metalloprotease inhibitor 2, tumour necrosis factor α, interleukin 1β, p22phox and xanthine dehydrogenase were increased (P < 0.05) in isoproterenol‐treated rats, and this effect was prevented by spironolactone (P < 0.05). Spironolactone also reduced the elevated SGK‐1 expression in isoproterenol‐treated rats. The observed reduction of the principal mediator of aldosterone cellular actions, SGK‐1, by spironolactone in hearts from isoproterenol‐treated rats suggests a role of mineralocorticoids in the cardiac hypertrophy, fibrosis, inflammation, oxidation and diastolic dysfunction induced by isoproterenol treatment in rats.
Advances in Wear Measurement by Acoustic Emission Analysis Compared to Radionuclide Technique
Authors: Albers A. , Kelemen S. G.
Published: February 2012

Online analysis of a tribological contact without changing the conditions of the system is a challenging exercise until today. Yet, it is not possible to detect wear and the particle size ith one method. Numerous works study different phenomena of the behavior of ultrasonic structure-borne noise in dry friction contacts. However all these experiments are limited to basic pin-disc experiments without any concrete reference to an application. A new application for detecting real contact-geometry, wear and particle size with one in-situ condition monitoring method on a test rigs is presented in this paper. The method of structure-born noise analysis has proven to be suitable for detecting the occurrence of solid friction [1]–[4]. By using a broadband piezoelectric acoustic emission sensor to detect ultrasonic structure-born noise, caused by metal-to-metal contact it is now possible to study different types of phenomena during their time of appearance. The Radionuclide Technology (RNT) was used the first time at dry running friction systems. With the RNT it is possible to correlate ultrasonic structure-borne noise with wear volume in dry running friction systems. The application is used for deeper understanding of the friction behavior and wear phenomena in dry running contacts.
Effect of Surface Texturing on EHD Lubrication Films Under Transient Speed Condition
Authors: Zimmerman Martin , Krupka Ivan , Hartl Martin , Houska Pavel
Published: February 2012

Transient EHD lubrication, where operating parameters such as speed, load and surface curvature vary over time, occurs in many machine elements such as cams, gears or roller bearings. The effect of transient speed and surface texturing on EHD lubrication films are investigated by the direct observation. For the purposes of the experiment the speed profile of contact point between cam and follower is used. Most critical part of the operation is when the contact surfaces are running in opposite directions. This effect can cause a lubricant film breakdown and in consequence also damage of contact surfaces. For this reason three types of experiments, for the same speed profile, are carried out for polished surface and for contact surfaces with and without surface texturing. It has enabled us to consider if the texture of micro-dents have any significant influence on film thickness especially in critical parts of the operation. To simplify the problem the concept of cam and follower contact was replaced by EHD contact of the flat surface of chromium coated glass disk and a steel ball. Also only transient speed was taken into account. The method used to measured film thickness was thin film colorimetric interferometry. The experimental results show that micro-dents could increase lubrication efficiency under rolling/sliding condition through the lubricant emitted from micro-dents. It was found that the lubricant emitted from micro-dents helps to separate contact surfaces especially in the case where the contact surfaces moves very slowly in the opposite direction.
Stick-Slip Analysis of a Point Contact When a Body Contains Cylindrical Heterogeneities
Authors: Leroux J. , Ne´lias D.
Published: February 2012

The stick-slip contact problem is investigated here when at least one of the contacting bodies contains inhomogeneous inclusions. Cylindrical inclusions with parallel axes are considered. The Eshelby’s equivalent inclusion method is used to solve the problem numerically. Interactions between close inclusions are taken into account in the numerical procedure, as well as the coupling between normal and tangential behaviours. It is found that the presence of heterogeneities in the vicinity of the surface contact affects the contact pressure, distribution and subsequently the distribution of shear traction and slip at the interface. The effects of the fiber orientation from the direction of the tangential load and different material properties would be presented.
Lubrication Analysis of the Thrust Bearing in the Valve Plate of a Swash-Plate Type Axial Piston
Authors: Shin J. H. , Kim H. E. , Kim K. W.
Published: February 2012

This application study of a swash-plate type axial piston pump was concerned about the hydrostatic lubrication characteristics of cylinder barrel and valve plate which are main rotating body and its opposite moving part respectively. A computer simulation was implemented to assess thrust bearing and mechanical sealing functions of the fluid film between cylinder barrel and valve plate. A new algorithm was developed to facilitate simultaneous calculations of dynamic cylinder pressure, 3 degree-of-freedom barrel motions considering inertia effect, and fluid film pressure assuming full fluid film lubrication regime. Using the simulation tool, force and moment balancing of cylinder barrel which is a key issue of piston pump design was analyzed. Time dependent fluid film pressure and thickness distributions for several given balance ratios were calculated. This analysis helps to decide appropriate balance ratio in the valve and cylinder barrel. Oil leakage flow and friction torque in the fluid film between cylinder barrel and valve plate were calculated as well and discussed in the viewpoint of energy loss. The results show that film thickness in plain surface is not high enough to bear the barrel and reduce power loss and that surface waviness which exists in actual sliding surfaces can have a positive effect on it. This simulation tool could also predict time dependent barrel motions due to simultaneous calculation algorithm. It has been known that cylinder barrel rotates with oscillation. Therefore average clearance, tilt angle, and azimuth angle were calculated for each time step and the results were discussed.
Numerical Analysis Method of Contact Mechanics Between a Sphere and a Flat Considering Lennard-Jones Surface Forces of Contacting Asperities and All Rough Height Surfaces
Authors: Ono Kyosuke
Published: February 2012

A new numerical analysis method for elastic adhesive contact mechanics between a sphere and a flat with a sub-nanometer roughness is presented. In contrast to conventional theories, the elastic deformations of both contacting asperities and mean height surface and Lennard-Jones (LJ) surface forces of both contacting asperities and all rough surfaces including valley areas are taken into account New adhesive force of contacting asperity is used from asperity contact analysis. Calculated results for head-disk asperity contact with current low roughness are shown in comparison with conventional theories. The relationship among present theory, mean height surface theory and perfectly smooth surface theory is discussed.
On Cohesion of Micron Scale Metal Particles in High Velocity Impact With a Metal Substrate
Authors: Yildirim Baran , Mu¨ftu¨ Sinan , Gouldstone Andrew
Published: February 2012

Impact of a single copper particle in cold gas dynamic spray is simulated by finite element method by including the effects of high strain rates and temperature on material plasticity and failure. In order to predict stick behavior of the particle, cohesive forces that act between the particle and the substrate are included in the model by defining an interfacial cohesive strength parameter. Effect of this parameter on the deformation and stick/rebound behavior of the particle is studied. It is found that significant particle deformation, large area of contact between particle and substrate is needed to generate enough cohesive force to absorb the rebound energy of the particle and achieve sticking. As the impact velocity and assumed interfacial cohesive strength increases, particle is more likely to stick on to the substrate. Critical velocities in the same range with experimental results are predicted.
Yield Inception of a Coated Substrate Indented by a Rigid Sphere
Authors: Song Wenping , Li Longqiu , Ovcharenko Andrey , Jia Ding , Zhang Guangyu , Talke Frank E.
Published: February 2012

Yield inception of a coated substrate indented by a rigid sphere is analyzed using finite element analysis. The critical interference is studied as a function of film thickness and material properties of both the film and the substrate. The results show that critical interference, corresponding to yield inception of the coated substrate, is a strong function of the film thickness, the Young’s modulus, and the yield strength of both the film and the substrate.
Investigation of a Unique Macro/Micro Laser Machined Feature for Mechanical Face Seals With Low Leakage, Low Friction, and Low Wear
Authors: Young Lionel , Benedict Joshua , Davis John
Published: February 2012

Numerous studies have been conducted to evaluate the effects of micro dimple surface texturing on friction reduction in mechanical seals [1–7]. Optimum ratios for a dimple configuration, depth (h) to diameter (D) (Fig. 1), range from 0.02 to 0.5, and area density ratio, ratio of dimple area to seal face area, range from 20 to 55%. Within this range it has been shown that friction can be reduced by as much as 50%. These studies indicate that if the ratio of depth to dimple diameter is reduced below 0.02 a dramatic reduction in performance is seen. Also observed in one investigation [8] is the possibility that micro dimples can become filled with debris. This may degrade performance over time. This report will show that with the use of a unique macro/micro feature it is possible to achieve a reduction in friction of 65%, significantly lower face temperature, exhibit debris resistance, showing low to zero measureable leakage, and low to zero wear when compared to an untextured seal face. The term macro/micro feature is used to describe a feature that has a depth to size ratio, h/L (Fig.2), which is two orders of magnitude smaller than current dimple configurations, well below what may be considered useful from a performance standpoint. This new macro/micro feature, a tapered channel, demonstrates significant cavitation affects as well as hydrodynamic load support. These features are believed to be responsible for its low leakage as well as it low friction/wear characteristics.
Adhesive Contacts for Graded-Elastic Coatings Using Fourier Series Decomposition
Authors: Chidlow S. J. , Chong W. W. F. , Teodorescu M. , Vaughan N. D.
Published: February 2012

We propose a semi-analytic solution technique to determine the subsurface stresses and local deflections resulting in an adhesive contact of graded elastic layers. Identical pressure distributions, typical for a Maugis parameter λ = 1, were applied to a range of graded elastic coatings. The principal stresses and surface deflection in both regions (graded elastic layer and substrate) are computed in terms of Fourier series. This control case has the advantage that the response of different coatings can be easily monitored and compared.
Lubrication of DLC and TiN Coatings With Two Ionic Liquids Used as Neat Lubricant and Oil Additive
Authors: Hernandez Battez A. , Blanco Alonso D. , Gonzalez Rodriguez R. , Viesca Rodriguez J. L. , Fernandez-Gonzalez A. , Higuera Garrido A.
Published: February 2012

Thin hard physical vapour deposited (PVD) coatings are today frequently used in order to improve the tribological performance of forming tools, cutting tools, and machine elements [1]. PVD TiN coating is widely used in high-speed steel cutting tools. Studies on the friction, wear characteristics and failure mechanisms of this coating have shown that it can reduce wear and diminish the failure of components. This coating frequently offers good corrosion protection and surface finish, high wear resistance and low coefficient of friction. On the other hand, PVD DLC (diamond-like carbon) coating provides a low friction and a high sliding wear resistance to enhance the tribological behavior and the durability of running components. DLC is becoming widely used as surface coating for machine components in lubricated systems, especially in the automotive industry. DLC coatings are nowadays frequently used in applications under high stress and/or under boundary or mixed lubrication regime and the range of use for these coatings keep growing rapidly.
Five Millimeter Air Foil Bearing Operating at 350,000 RPM in a Micro Electric Motor Drive
Authors: Kim Daejong , Hossain Md. Saddam , Son Soo-Jung , Choi Chul-Jin , Kra¨henbu¨hl Daniel
Published: February 2012

This paper presents works performed at University of Texas at Arlington in designing and testing mesoscale foil bearing in diameter of 5mm. The elastic foundation for the foil bearings were manufactured using X-ray lithography and electroplating of Ni. Top foils were made of 0.5mm thick Inconel X-750. Two different designs of elastic foundation are presented, and foil bearings made of these elastic foundations were tested using a brushless permanent magnet DC motor drive up to 350,000rpm stable operation without any subsynchronous vibrations. After confidence was gained in the design, one of the elastic foundation was replicated using a micro sintering process using nano scale Ni-Fe powders. The micro sintering process can reduce the production cost of the elastic foundation dramatically by eliminating the expensive X-ray lithography and electroplating. The sintering process could reproduce the original elastic foundation within +−2 μm deviation from prediction. The preliminary results demonstrate the micro sintering process is a promising cost-effective manufacturing process of the mesoscale foil bearings.
Odd-Even Effects on Tribology of Self Assembled Monolayers
Authors: Ramin Leyla , Jabbarzadeh Ahmad
Published: February 2012

We have conducted molecular dynamics simulations to study the frictional properties of alkanethiols on Au(111) surfaces, under various loading and shearing conditions. For alkanethiols we find the film responds to increased loading initially by increasing the tilt and then by deformation of individual molecules. We find strong evidence of the friction coefficient being dependent on the number of carbon atoms in the molecule being odd or even. Odd alkanethiols show consistently higher friction coefficient. The structural origin of this odd-even effect observed under various sliding velocities has been discussed.
Influence of Additives in Synthetic Oils on Radial Lip Seals
Authors: Klaiber Mathias , Haas Werner
Published: February 2012

This project has been initiated in order to get a general basic understanding about the influence of additives onto elastomeric lip seal systems. It is necessary to determine the behavior with single additive base oil compounds. Two different synthetic base oils, Polyglycol (PG) and Polyalphaolefin (PAO), are used. Thus 19 different single additive base oil compounds have been reviewed. Two different elastomeric materials NBR and FPM have been taken for all the tests. In several dynamic tests the influences on the sealing systems have been investigated. These included tests for 24 hours to measure the friction torque and tests for 10 hours to measure the pumping rate. Furthermore, the operating conditions during 96 hours functional tests have been determined. A concluding view onto the compatibility, respectively the incompatibility, of the additives in these different points of view will be given.
Particle Flow Behavior in a Shear Cell Device
Authors: Rosenkrantz Adam , Tichy John
Published: February 2012

This presentation describes ongoing research performed on a simple shear cell apparatus, previously described [1]. As a complement, discrete particle simulations and continuum models have been used to predict normal and shear forces in the ongoing experiments. The trends and orders-of-magnitude of the models and experiment are in basic agreement. Theoretical models used are constructed with basic principles, rather than curve fitting, to obtain effective properties of the mixture such as viscosity or conductivity. The experiment itself serves to determine the effects of shear rate, packing fraction, particle size and film thickness on the load carrying normal stress. Additionally, the frictional shear stress can be investigated. The working particulate medium within the apparatus consists of glass of aluminum spheres, poly-dispersed over four size increments, all less than 1.00 mm diameter. The upper annular disk is held stationary in a rotational sense by a force transducer, and applies predetermined normal stress values which vary according to a system of interchangeable counterweights. The lower transfer surface and the sidewalls of the annular ring are rotated by applied mechanical torque. Experimental trials consist of shear initiation, after which the trough velocity, film thickness, supporting load, and frictional torque are measured. From these measurements one can calculate the average shear rate, the average load-carrying normal stress, the average frictional shear stress, and the solids volume fraction. Such third body granular flow may apply to some solid lubrication mechanisms, and to applications such as smart clutches and dampers. The continuum theory presented is unique in that it addresses solid-like behavior and its transition to fluidized behavior. The discrete particle dynamics rely on the conceptual models of Iordanoff and colleagues [2]. Our findings are that the two theoretical predictions agree reasonably with the experimental results, suggesting validity of the approach. These results are promising, and may be used to further develop high level predictive models. Furthermore, similar methods of small scale experimental particle simulation can be used to develop simpler more usable continuum approaches.
Investigation of Effects of Additive for ATF and Test Condition on Pitting Life of Gear Tooth in the FZG Pitting Test
Authors: Ichihashi Toshihiko , Takakura Yutaka , Matsumoto Susumu
Published: February 2012

The reduction in viscosity of Automatic Transmission Fluids (ATFs) for improving fuel economy results in a reduction in transmission gear fatigue life due to occurring pitting. The aim of this study is to establish a suitable test condition for evaluating differentiation in the gear pitting life between ATFs by using a Forschungsstelle fur Zahnrader und Getriebebau (FZG). In this study FZG gear sets were modified so that gear teeth were misaligned and the contact tooth width was shortened by offset in the direction of the shaft. The fatigue pitting life in response to ATFs under this modified FZG test condition was of the same order as that obtained in the actual transmission test under a severely offset condition. A sulfur-containing additive could play a role on the gear tooth life under severe condition, which was most likely attributed to tribofilm for motion on the gear tooth surface.
Analysis of Off-Track Slider Vibrations in a Laptop Hard Disk Drive
Authors: Rai Rahul , Bogy David B.
Published: February 2012

Over the past decade there has been a significant increase the demand of hard disk drives (HDD) for the mobile platforms. In such applications, a mobile HDD is often subjected to harsh working environment. For example, components like DVD drive and built-in speakers present in a laptop can excite its HDD and hence can degrade its read/write (R/W) performance. In this study, we develope a complete model for a mobile HDD to analyze and characterize its vibration performance due to external disturbances. The current model includes a spinning disk, a fluid dynamic bearing (FDB) based spindle motor, a base plate, an actuator assembly (E-block and suspension) and a detailed model for the air bearing slider. Prediction of slider dynamics during an excitation essentially requires the solution of coupled fluid-structure problem in which head gimbal assembly (HGA) is coupled with the disk-support system through the air bearing. Off-track displacement of the slider is used to quantify the vibration performance of the HDD for excitation of different frequencies and orientations. It is observed that during an excitation, the sway modes of the actuator assembly provide the most significant contribution to the off-track vibration. This knowledge about the vibration characteristics of mobile drive can be used to design better a vibration isolation system for mounting a HDD in a laptop.
Mixed Lubrication Analysis of Piston Pin Bearing in Diesel Engine With High Power Density
Authors: Wang Xiaoli , Du Jingfang , Zhang Junyan
Published: February 2012

Based on the unified Reynolds equation and Fast Fourier Transform (FFT) method, the mixed lubrication characteristics of piston pin bearing in diesel engine with high power density are numerically simulated. Firstly, the unified Reynolds equation and the elastic deformation equation are solved simultaneously, and then the effects of viscosity-pressure on the maximum film pressure, the minimum oil film thickness and the piston pin orbit are analyzed. It is shown that for the semi-floating piston pin bearing with high power density, when viscosity-pressure is taken into consideration, both the minimum oil film thickness and the maximum oil film pressure increase, while the elastic deformation of the area in which the maximum load applies decreases. The transient diagrams of the relative position between the piston pin and its bearing within a whole loading period are given. It is also indicated that the eccentricity ratio of piston pin bearing along the direction of piston stroke is greater because of the greater load exerting on the back of the semi-floating piston pin bearing and thus resulting in the obvious deformation in the back area. This result is in good agreement with the existing real failure mode of the piston pin bearing with high power density. In addition, the effects of bearing clearance and length on the minimum oil film thickness are investigated respectively. It is shown that the smaller bearing clearance and the greater width are beneficial for the increasing of the minimum oil film thickness of piston pin bearing.
Energy Efficient Surface Hardening of 4140 Steel by Friction Stir Processing for Tribological Applications
Authors: Lorenzo-Martin C. , Ajayi O. , Smith C. , Krol S.
Published: February 2012

One of the most energy intensive industrial and manufacturing processes is the heat treatment of ferrous materials for hardening to improve their friction and wear performance. Examples of surface hardening heat treatments include case carburizing, nitriding, boriding, etc. This paper presents the development of a new energy efficient method to harden steel material as a possible replacement for the current energy intensive heat treatment processes. The new process, friction stir processing (FSP) involves severe plastic deformation of the near surface material by a non-consumable rotating and translating tool. FSP has been demonstrated to locally modify material properties such as ductility, fatigue, fracture toughness, etc. Other potential properties that could be positively affected by FSP are wear and friction properties. In a preliminary study, when applied to 4140 alloy steel, this new FSP process produced adequate hardening of the near surface layer compare to conventional furnace heat hardening of the same alloy. The friction and wear performance of the 4140 hardened by FSP was also observed to be superior than heat hardened surface under dry and lubricated sliding contact.
Enhancement of Tribological Performance of 6061 Aluminum Alloy by Second Phase Hardening via Friction Stir Processing
Authors: Lorenzo-Martin C. , Ajayi O. , Fenske G.
Published: February 2012

The properties of metallic alloys can be substantial modified by the addition of a second phase particles. This is especially noticeable when hard particles are incorporated in a relatively soft matrix, often resulting in improved mechanical and tribological performance. This paper presents the results of our study on mechanical and tribological performance enhancement of 6061 Aluminum alloys by incorporation of B4C particle via Friction stir processing (FSP). Unidirectional ball on flat friction and wear tests were conducted with a base material, friction stir processed 6061-Al and 6061-Al doped with B4C particles via FSP against 52100 bearing steel balls under dry sliding conditions. The incorporation of particles not only reduced friction by 30% but also reduced wear by 2 orders of magnitude compared to unprocessed base and FSP material without particles incorporation. FSP alone without particles addition did not have a significant effect on the tribological behavior of the tested aluminum alloy.
Improving Rolling Element Bearing Thermal Compliance Through In Situ Cooling
Authors: Wornyoh E. Y. A. , Patel D. K. , Schuessler Luke , Francis A. B. , Garnett C. S.
Published: February 2012

In this study a novel in situ rolling element bearing (REB) lubricant cooling system is developed that provides a continuous cooling of the bearing outer race. In the design the stationary outer race is expanded to accommodate a cooling coil for the continuous cooling of the lubricant and the outer race. Water is used as the coolant While Amsoil 75W-90 Severe Gear® oil is used as a lubricant. Heat generated during the test run is removed by the coolant flowing through the cooling coil. The tribological effects at the speeds of the cooling test were evaluated using block-on-ring tribometer tests. Results from the experiments indicate that in the absence of cooling the temperature of the bearing outer race rises while cooling dramatically lowers the temperature. Also, the coefficient of friction increases with increasing speed. As such, in situ cooling that leads to reduced operational temperature minimizes lubricant degradation that can result from uncontrolled frictional heating.
Studies of Shannon Entropy Evolution due to Self-Organization During the Running-In
Authors: Mortazavi Vahid , Menezes Pradeep L. , Nosonovsky Michael
Published: February 2012

When frictional sliding is initiated, the coefficient of friction is often high during the initial transient running-in process. After that, the coefficient of friction reaches its stationary value. Running-in is interpreted as friction-induced self-organization stage in that two sliding surfaces adjust to each other due to surface roughness evolution. Shannon entropy was proposed as a surface roughness parameter, and its decrease can be used as a simple test for self-organization. Sliding experiments were conducted on the hard steel plate using a soft Al-Mg alloy pin under both dry and lubricated conditions. Based on the results of the surface profile evolution, obtained by an optical profilometer, during running-in, we discuss change of Shannon entropy for various surface textures. Various textures which are characterized in terms of roughness parameters were produced on the steel plates. We compare how self-organization occurs for different textures during running-in stage.
Surface Film Formation and Hydrogen Permeation of Austenitic Stainless Steel Under High Pressure Hydrogen
Authors: Tanaka Hiroyoshi , Sawae Yoshinori , Sugimura Joichi
Published: February 2012

This paper describes a study on surface film formation and hydrogen permeation at stainless steel surfaces under high pressure hydrogen. In order to investigate hydrogen permeation into the steels, exposure tests in high pressure hydrogen were conducted with AISI 316 and 316L stainless steel specimens. To determine the concentration of hydrogen in the specimens and characteristics of surface oxide layer, desorption spectra of hydrogen and water were determined with TDS. In addition, XPS analyses were performed to identify chemical composition of the exposed surfaces. It was found that the permeation of hydrogen through the steel surface was related to the desorption behavior of water, which could be originated from the surface film formed during the exposure to high pressure gas.
Optimization of Magnetorheological Brake
Authors: Gupta Snegdha , Hirani Harish
Published: February 2012

Quick response and rheological properties as a function of magnetic field are well known features of MR fluids which inspire their usage as brake materials. Controllable torque and minimum weight of brake system are the deciding functions based on which the viability of the MR brake against the conventional hydraulic brake system can be judged. The aim of this study is to optimize a multi-disk magneto-rheological brake system considering torque and weight as objective functions and geometric dimensions of conventional hydraulic brake as constraints. The electric current accounting magnetic saturation, MR gap, number of disk, thickness of disk, and outer diameter of disk have been considered as design variables. To model the behavior of MR Fluid, Bingham and Herschel Bulkley models have been compared. To implement these models in estimating the braking torque a modification in shear rate dependent component has been proposed. The overall design of MR brake has been optimized using a hybrid (Genetic algorithm plus gradient based) optimization scheme of MATLAB software.
A Volumetric Fractional Coverage Model to the Predict Frictional Behavior for In Situ Solid Transfer Film Lubrication
Authors: Pudjoprawoto R. , Dougherty P. , Higgs C. F.
Published: February 2012

Pellets were formed by compacting MoS2 powder. In the setup, the pellet is sheared against a disk surface while the slider pad rides on the MoS2 partially-covered asperities, while depleting the lubricant. A volumetric fractional coverage (VFC) modeling approach was developed to predict the friction coefficients for the lubricated pellet/disk sliding contact by assuming that the friction coefficients at pellet/disk and slider/disk interfaces are functions of the fraction of lubricant occupying the control volume. This fractional coverage is a theoretical parameter for quantifying the amount of third body film covering the disk asperities as a function of time. The model can be applied to a deterministic surface, thus, the proposed theory can predict the behavior of friction coefficients between the pellet/disk and slider/disk interfaces for most topographies, whether they are deterministic (i.e., textured) or real (i.e., random).
Triggering a Cell Shape Change by Exploiting Preexisting Actomyosin Contractions
Authors: Roh-Johnson Minna , Shemer Gidi , Higgins Christopher D. , McClellan Joseph H. , Werts Adam D. , Tulu U. Serdar , Gao Liang , Betzig Eric , Kiehart Daniel P. , Goldstein Bob
Published: February 2012

A Time and a Place

The onset of morphogenetic cell shape changes is thought to be triggered by initiation of actomyosin contractions.

Roh-Johnson
et al.

(p.
1232
, published online 9 February; see the Perspective by

Razzell and Martin

) have now discovered in both
Caenorhabditis elegans
and
Drosophila
embryos that the actomyosin contractions driving morphogenesis run constitutively, only being engaged to trigger cell shape changes at a specific time during development.
The Obligation to Prevent the Next Dual-Use Controversy
Authors: Faden Ruth R. , Karron Ruth A.
Published: February 2012

The recent debates over H5N1 experiments highlight current shortcomings in oversight of potential dual-use research.
Key Residues for Controlling Enantioselectivity of Halohydrin Dehalogenase from Arthrobacter sp. Strain AD2, Revealed by Structure-Guided Directed Evolution
Authors: Tang Lixia , Zhu Xuechen , Zheng Huayu , Jiang Rongxiang , Majerić Elenkov Maja
Published: February 2012

Halohydrin dehalogenase from
Agrobacterium radiobacter
AD1 (HheC) is a valuable tool in the preparation of
R
enantiomers of epoxides and β-substituted alcohols. In contrast, the halohydrin dehalogenase from
Arthrobacter
sp. AD2 (HheA) shows a low
S
enantioselectivity toward most aromatic substrates. Here, three amino acids (V136, L141, and N178) located in the two neighboring active-site loops of HheA were proposed to be the key residues for controlling enantioselectivity. They were subjected to saturation mutagenesis aimed at evolving an
S
-selective enzyme. This led to the selection of two outstanding mutants (the V136Y/L141G and N178A mutants). The double mutant displayed an inverted enantioselectivity (from
S
enantioselectivity [

E
S

] = 1.7 to
R
enantioselectivity [

E
R

] = 13) toward 2-chloro-1-phenylethanol without compromising enzyme activity. Strikingly, the N178A mutant showed a large enantioselectivity improvement (

E
S

> 200) and a 5- to 6-fold-enhanced specific activity toward (
S
)-2-chloro-1-phenylethanol. Further analysis revealed that those mutations produced some interference for the binding of nonfavored enantiomers which could account for the observed enantioselectivities. Our work demonstrated that those three active-site residues are indeed crucial in modulating the enantioselectivity of HheA and that a semirational design strategy has great potential for rapid creation of novel industrial biocatalysts.
Pathogen Prevalence in Ticks Collected from the Vegetation and Livestock in Nigeria
Authors: Reye Anna L. , Arinola Olatunbosun G. , Hübschen Judith M. , Muller Claude P.
Published: February 2012

Ticks are important disease vectors that can cause considerable economic losses by affecting animal health and productivity, especially in tropical and subtropical regions. In this study, we investigated the prevalence and diversity of bacterial and protozoan tick-borne pathogens in ticks collected from the vegetation and cattle in Nigeria by PCR. The infection rates of questing ticks were 3.1% for
Rickettsia
species, 0.1% for
Coxiella burnetii
and 0.4% for
Borrelia
species. Other pathogens, such as
Babesia
,
Theileria
,
Anaplasma
, and
Ehrlichia
species, were not detected in ticks from the vegetation. Feeding ticks collected from cattle displayed infection rates of 12.5% for
Rickettsia
species, 14% for
Coxiella burnetii
, 5.9% for
Anaplasma
species, 5.1% for
Ehrlichia
species, and 2.9% for
Theileria mutans. Babesia
and
Borrelia
species were not detected in ticks collected from cattle. Mixed infections were found only in feeding ticks and mainly
Rickettsia
species and
Coxiella burnetii
were involved. The diversity of tick-borne pathogens in Nigeria was higher in feeding than in questing ticks, suggesting that cattle serve as reservoirs for at least some of the pathogens studied, in particular
C. burnetii
. The total estimated herd infection rates of 20.6% for a
Rickettsia africae
-like species, 27% for
Coxiella burnetii
, and 8.5% for
Anaplasma marginale/centrale
suggest that these pathogens may have considerable implications for human and animal health.
Inactivation of Recombinant Bacteriophage Lambda by Use of Chemical Agents and UV Radiation
Authors: Clark Ewan M. , Wright Harry , Lennon Kelly-Anne , Craik Vicki A. , Clark Jason R. , March John B.
Published: February 2012

Several approaches for the inactivation of bacteriophage lambda, including UV germicidal irradiation (UVGI) and the chemical agents Virkon-S, Chloros, Decon-90, and sodium hydroxide (NaOH), were compared. Virkon, NaOH, and UVGI caused a ≥7-log
10
reduction in phage titers. This study successfully describes several methods with potential for bacteriophage inactivation in industrial settings.
Pseudomonad Swarming Motility Is Restricted to a Narrow Range of High Matric Water Potentials
Authors: Dechesne Arnaud , Smets Barth F.
Published: February 2012

Using a novel experimental system that allows control of the matric potential of an agar slab, we explored the hydration conditions under which swarming motility is possible. If there is recognition that this physical parameter is a key determinant of swarming, it is usually neither controlled nor measured rigorously but only manipulated through proxies, namely, the agar concentration and the drying time of “soft” agar plates (swarming plates). We contend that this not only obscures the biophysical mechanisms underlying swarming but also impedes a full assessment of its clinical and environmental significances. Our results indicate that swarming motility is restricted to a narrow range of high matric water potentials in the three pseudomonads tested (
Pseudomonas
sp. DSS73,
Pseudomonas syringae
B728a, and
Pseudomonas aeruginosa
PA14). The threshold below which no swarming was observed was about −0.45 kPa for the first and about −0.1 kPa for the latter two. Above the threshold, the expansion rate of DSS73 swarms increased exponentially with the matric potential. Mutants deficient in surfactant production were totally or partially unable to expand rapidly on the surface of the agar slab. Our results thus suggest that swarming motility in pseudomonads is restricted to (micro)sites where ambient humidity is very high (relative humidity of >99.99%). The spatiotemporal occurrence of such sites is limited in many types of terrestrial environments.
Persistence and Growth of the Fecal Indicator Bacteria Enterococci in Detritus and Natural Estuarine Plankton Communities
Authors: Mote Beth L. , Turner Jeffrey W. , Lipp Erin K.
Published: February 2012

Enterococci are used to evaluate recreational-water quality and health risks in marine environments. In addition to their occurrence in feces of warm blooded animals, they are also common epiphytes. We investigated the contribution of plankton- or particle-associated enterococci in estuarine and coastal water. Seven water and size-fractionated plankton samples were collected monthly between April 2008 and January 2009 in the tidal reaches of the Skidaway River (Georgia, USA). Each size fraction, along with filtered (<30 μm) and bulk estuarine water, was processed according to U.S. Environmental Protection Agency method 1600. Presumptive enterococci were selected and species were identified using carbon substrate utilization patterns. The highest average densities occurred within the 30-, 63-, 105-, and 150-μm size fractions, which also represented the majority (>99%) of the particles within the sampled water. Particle-associated enterococci accounted for as little as 1% of enterococci in bulk water in April to as much as 95% in July.
Enterococcus faecalis
was the most commonly isolated species from both water and plankton and represented 31% (16/51) and 35% (6/17) of the identified
Enterococcus
species from water and plankton, respectively.
Enterococcus casseliflavus
represented 29% of the selected isolates from plankton and 16% from water. Both
E. faecalis
and
E. casseliflavus
were able to survive and grow in plankton suspensions significantly longer than in artificial seawater.
Enterococcus
spp. may be highly concentrated in plankton and associated particles, especially during summer and fall months. These findings could have implications for the effectiveness of enterococci as an indicator of coastal water quality, especially in particle-rich environments.