bluuebunny/crossref_metadata_2025 huggingface dataset:
Air Bearing Simulation for Bit Patterned Media
Authors: Li Hui , Zheng Hao , Yoon Yeoungchin , Talke Frank E.
Published: June 2009

Patterned media is being considered as a means for achieving a storage density beyond 1Tb/in2 on hard disks by reducing cross talk and overcoming thermal stability problems. In this investigation, the flying characteristics of a femto-type slider over bit patterned media (BPM) is investigated. The discrete bits of the disk are modeled as cylindrical protrusions on the disk surface. The steady-state flying characteristics over BPM at ultra-low head disk spacing is simulated.
Partial Elastomer Texturing in Soft Elasto Hydrodynamic Lubrication
Authors: Shinkarenko Alexey , Kligerman Yuri , Etsion Izhak
Published: June 2009

A dimensionless theoretical model of Soft Elasto Hydrodynamic Lubrication (SEHL) between partially textured elastomer and rigid counterpart is developed. The model consists of a soft elastomer with partial Laser Surface Texturing (LST) and an absolutely rigid and smooth counterpart moving relatively to each other in the presence of viscous lubricant. The elastomer surface is partially textured at its leading edge in the form of spherical micro-dimples. The pressure distribution in the fluid film and the elastic deformations of the elastomer are obtained from a simultaneous solution of the Reynolds equation and the equation of linear elasticity, respectively. Friction force and load carrying capacity are evaluated by integration of the shear stress and pressure fields in the viscous fluid film, respectively. The main goal of the present work is to study the potential of the elastomer partial LST in SEHL to friction reduction.
Theoretical Model of Plastic Hysteresis in Spherical Contact Under Combined Normal and Tangential Loading
Authors: Kligerman Yuri , Etsion Izhak
Published: June 2009

The behavior of an elastic-plastic contact between a deformable sphere and a rigid flat under combined constant normal and reciprocating tangential loading is investigated in the present work. The theoretical model is based on the assumptions of full stick contact condition and two kinds of the sphere material hardening. Hysteretic change of friction force versus tangential displacement during reciprocating tangential loading is investigated along with the study of the change of the contact area and stress state in the elastic-plastic sphere. Good agreement between theoretical and experimental results is obtained.
LIGA-Fabricated Meso Scale Foil Gas Bearings for Palm-Sized Microturbomachinery
Authors: Kim Daejong , Creary Andron
Published: June 2009

Palm-sized mesoscale microturbomachinery (100∼200W) have broad potential applications in micro power generation areas, such as air/hydrogen management system for low temperature fuel cells, palm-sized micro gas turbines for unmanned air vehicles, robots, very small solid oxide fuel cells, micro power generations for space micro/nano satellites, etc. This paper reports recent progress on design, manufacturing of mesoscale (bearing diameter of 5mm) foil gas bearings applicable to the mesoscale microturbomachinery. With self-generated preload of 0.4N to the bearing, the mesoscale foil gas bearings were predicted to be stable up to the maximum simulated speed of 600,000 rpm. Manufacturing processes involved UV and X-ray lithography, electroplating, and precision forming. Test rigs were designed and constructed for performance tests of the manufactured mesoscale gas bearings.
On the Tangential Displacement of a Surface Point Due to a Cuboid of Uniform Plastic Strain in a Half-Space
Authors: Fulleringer B. , Boucly V. , Ne´lias D.
Published: June 2009

The elastic solution of a tangentially loaded contact is known as the Cerruti’s solution. Since the contact surfaces could be easily discretized in small rectangles of uniform shear stress the elastic problem is usually numerically solved by summation of well known integral solution. For soft metallic materials, metals at high temperature, rough surfaces or dry contacts with high friction coefficient, the yield stress within the material could be easily exceeded. This paper presents the effect of a cuboid of uniform plastic strain in a half-space on the tangential displacement of a surface point. It is found that the influence coefficients are of the same order of magnitude as the ones describing the normal displacement. This result is of great importance for stick-slip contact problem when coupling the normal and tangential behavior in the elastic-plastic regime, and also for metals and alloys with low or moderate yield stress.
Proposal of a Method to Predict Grinding Stresses
Authors: Boucly V. , Ne´lias D.
Published: June 2009

Residual stresses due to machining are the results of the thermo-mechanical history of the piece/tool interface. The magnitude and the gradient of stress play a key role for the surface integrity. A thermo-mechanical model has been developed. It allows simulating the rolling/sliding contact between an elastic tool in rotation along its own axis and an elastic-plastic flat in translation. The analysis includes the effects of both the normal and tangential loading. Frictional heating is also considered. The model is based on a semi-analytical method and the transient 3D contact problem is fully solved. Compared to the finite element method the computing time is reduced by several orders of magnitude. This technique has already been successfully applied to the simulation of running-in and wear, and to fretting wear, and a first attempt to simulate residual stress and strain due to the contact between a grinding tool and a work piece is made here. First results are presented for various stationary and transient thermo-mechanical loading histories.
A Probabilistic Analysis of Third-Body Particle Embedment: Implications in Lapping of Magnetic Recording Heads
Authors: Xu H. , Komvopoulos K.
Published: June 2009

A probabilistic model of third-body particle embedment was derived for surfaces separated by a hydrodynamic slurry film. The analysis yields estimates of the density of embedded particles in terms of surface topography parameters, particle size distribution, and mean surface gap determined by the applied load, macroscopic geometry of the moving surfaces, and fluid properties. The model has direct application to chemical-mechanical polishing and fabrication of lapping plates for polishing magnetic recording heads.
Roughness Effects in Thermo-Mechanically Loaded Contacts
Authors: Nyqvist J. , Kadiric A. , Sayles R. , Ioannides S.
Published: June 2009

A recently developed thermo-mechanical model was used to investigate the influence of surface roughness characteristics on the maximum contact temperature rise as well as shear stresses in rough surface contacts subjected to normal and tangential loading. In order to identify prevailing trends clearly the surfaces were modelled as having idealised sinusoidal roughness. Following a brief description of the numerical model, results are presented to illustrate the dependence of contact temperature and stresses on roughness parameters such as wavelength and amplitude as well as the contact Peclet number. An attempt is made to explain the observed trends in terms of variation in predicted pressure distribution and real contact areas for different surfaces.
The Mechanics of Adhesion: Current and Future Research Trends
Authors: Adams George G.
Published: June 2009

As the size of the contact region between two bodies decreases to the micro- and nano-scale, the effect of adhesion becomes increasingly important. As introductory remarks to a panel discussion on this topic, we briefly review recent research in the mechanics of adhesion and discuss future research needs. Attention is focused on adhesion with plastic deformation, molecular dynamics simulations, and multi-scale effects.
On the Scientific and Technological Importance of Nanotribology
Authors: Carpick Robert W.
Published: June 2009

Nanotribology has been in existence as a recognized discipline for roughly 20 years, with the appreciation of the importance of atomistic mechanisms of tribology existing long before. In this paper, we briefly review why nanotribology is important for advancing the science of tribology in general, and we also highlight emerging applications where nanotribological research is critical.
Reduced Microstructure Adhesion Provided by Gas-Expanded Liquid Deposited Gold Nanoparticles
Authors: Hurst K. M. , Roberts C. B. , Ashurst W. R.
Published: June 2009

In order to alleviate or eliminate the occurrence of stiction during the actuation of microstructures, the real contact area available for contact must be reduced. Au nanoparticles were intentionally deposited using gas-expanded liquids onto polysilicon cantilever beam arrays to increase surface roughness. The nanoparticle-coated beams were subjected to an actuation voltage of 120 V. Following actuation, the adhesion of beams was quantified by estimating the apparent work of adhesion. Au nanoparticles deposited onto these microstructures were shown to drastically reduce the effects of in-use stiction. Capillary adhesion due to condensation of ambient moisture was effectively eliminated.
Application of Elastic-Plastic Static Friction Model to Rough Surface With Asymmetric Asperity Distribution
Authors: Lee Chul-Hee , Polycarpou Andreas A.
Published: June 2009

The asymmetric height distribution in surface roughness is usually indispensable in engineering surfaces prepared by specific manufacturing process. Moreover, the running-in process develops severe asymmetric roughness distribution in the surface interfaces. In this paper, the effect of asymmetric asperity distribution on static friction coefficient is investigated theoretically and by comparing it with experimental results. In order to generate a probability density function of non-Gaussian surface roughness, the Pearson system of frequency curves was used. Subsequently, the Kogut and Etsion (KE) model of elastic-plastic static friction was modified to calculate the contacting interfacial forces. For the experiments, actual roller and housing surfaces from a CV (Constant Velocity) joint were prepared to measure the static friction coefficient as it clearly shows the asymmetry of roughness distribution due to the manufacturing and also running-in process. The experimental measurements were subsequently compared with the modified KE static friction model with Gaussian as well as Pearson distributions of asperity heights. It was found that the model with Pearson distribution captures the experimental measurements well in terms of the surface conditions.
The Design and Application of a New Type of Instrument for Testing the Worn Surface of Casing Wear
Authors: Fan Jianchun , Chen Qiang , Zhang Laibin , Wen Dong
Published: June 2009

In this paper, a new kind of instrument used specially for testing the worn surface of casing was introduced, its structure and testing principle was further elaborated. Meanwhile, the testing data were also used for the 3D surface reconstruction of the worn area of casing. The comparative study with SEM pictures could tell that the instrument performed very well and is quite helpful in the observation of worn rejoin of casing; the conclusions drawn from the study could be applied in the research of wear mechanism.
A Boussinesq Type Problem for the Elastic Layer
Authors: Diaconescu Emanuel , Glovnea Marilena
Published: June 2009

This paper derives an analytical solution to the Boussinesq problem for the elastic layer. This is found by adding supplementary displacements to half-space displacements. The corresponding integral interference condition is established and this is useful for solving elastic layer contacts.
High Pressure Performance of Foil Journal Bearings in Various Gases
Authors: Briggs Maxwell H. , Prahl Joseph M. , Bruckner Robert , Dykas Brian
Published: June 2009

Foil bearings offer several advantages over traditional oil-lubricated bearings in closed Brayton Cycle (CBC) systems, such as those proposed for long-term space power generation. Proposed CBCs require foil bearings to use an inert gas lubricant at pressures as high as 3.0 MPa as the bearing lubricant. The High Pressure Rig (HPR) at the NASA Glenn Research Center is used to measure foil bearing power loss using potential CBC working fluids at and beyond proposed CBC peak pressures. In the current study foil journal bearing power loss is measured in helium, nitrogen, and carbon dioxide from atmospheric pressure to 4.83 MPa and at shaft speeds from 10 krpm to 42 krpm. Bearings operating in helium show no increase in power loss with increasing pressure for the conditions tested. Bearings operating in nitrogen show increases in power loss with increasing pressure at speeds above 19 krpm, while increases in bearing power loss during carbon dioxide testing were seen at 15 krpm. At speeds above these thresholds, power loss is shown to increase more rapidly in carbon dioxide than in nitrogen. Results suggest that bearing power loss performance is dependent on both gas density and shaft speed.
Numerical Simulation of Elastic Conforming Contacts Under Eccentric Loading
Authors: Spiˆnu Sergiu , Diaconescu Emanuel
Published: June 2009

The subject of eccentrically loaded conforming contacts is approached analytically under the restriction that the eccentricity is small enough to keep the contact closed. This paper advances a numerical method for contact analysis valid at any eccentricity value. An additional loop is added to the classic elastic contact solver to account for load eccentricity. The method predicts contact area and pressure distribution even when the contacting bodies lose contact in some peripheral points. Numerical results of pressure distribution for a circular flat end punch agree well with existing analytical predictions.
Experimental Investigation of Film Thickness Behaviour at Very High Speeds
Authors: Hili Joslyn , Olver Andrew V. , Edwards Simon , Jacobs Leon
Published: June 2009

At very high speeds, elastohydrodynamic (EHD) films may be considerably thinner than is predicted by classical isothermal regression equations such as that due to Hamrock and Dowson. This may arise because of viscous dissipation, frictional heating or starvation. In this paper, the contact between a steel ball and a glass disc was studied. The disc was driven at speeds of up to 20 ms−1, and the ball was driven by tractive rolling against the disc, its speed being determined using a magnetic method. It is shown that the results, which fall well below classical predictions, are consistent with inlet shear heating at the observed sliding speeds.
A Study of Plastic Deformation of Heavily Loaded Spherical Surfaces
Authors: Wadwalkar Saurabh S. , Jackson Robert L. , Payton Lewis , Kogut Lior
Published: June 2009

There is a need to develop our understanding of fully plastic contact between spheres and a flat surfaces that results in the spheres heavily deforming and eventually flattening out. Most work conducted in this area has been for relatively lightly loaded spherical contacts that deform elastically and elasto-plastically. The case considered here is also the reverse case of a rigid spherical indenter penetrating a deformable surface. The work builds on past theoretical models that used volume conservation to consider plastic deformation. The results provide relationships which may be used to model large deformations of flattened or compressed spheres. The results also show that the area of contact can be much larger than the popular geometrical truncation model for fully plastic contact between spheres and flat surfaces.
Effect of the Wave Amplitude on the Dynamic Behavior of a Wave Journal Bearing
Authors: Ene Nicoleta M. , Dimofte Florin , Oswald Fred B.
Published: June 2009

The effect of the wave amplitude on the dynamic behavior of a three-wave journal bearing is analyzed. A transient method was used to predict the wave bearing behavior after Fractional Whirl Frequency (FFW) occurs. Dynamic trajectories, Poincare´ maps, and FFT analyses are used to study the dynamic behavior of the journal bearing. It was found that the threshold of stability is strongly influenced by the wave amplitude. However, even when FFW occurs, the journal maintains its trajectory inside the bearing clearance. The predicted data were found to be in good agreement with the experimental results obtained at the NASA GRC.
Adsorption Behavior of Heat Modified Soybean Oil via Boundary Lubrication Coefficient of Friction Measurements
Authors: Sharma Brajendra K. , Biresaw Girma , Erhan Sevim Z.
Published: June 2009

The frictional behaviors of soybean oil and heat modified soybean oils with different Gardner scale viscosities as additives in hexadecane have been examined in a boundary lubrication test regime (steel contacts) using Langmuir adsorption model. The free energy of adsorption (ΔGads) of various heat modified soybean oils were compared with unmodified soybean oil. It was observed, that relative distribution of unsaturation in the molecule, average molecular weight and thus viscosity can affect adsorption on the metal surface. Heat modified soybean oils consistently have a lower ΔGads values compared to unmodified soybean oil. Lower ΔGads corresponds to stronger adsorption on the metal surface. The heat modification thus provides oils with stronger adsorption and higher viscosities, good for use in industrial lubricant formulations. This information can be used to design suitable lubricant molecules that will have optimum structure for effective metal adsorption as well as exhibit excellent boundary lubrication properties.
Predictive Dynamic Model of a Deep Groove Ball Bearing With a Flexible Outer Ring
Authors: Laurent Alexandre , Lenoir David , Jezequel Louis , Mevel Bruno
Published: June 2009

An explicit dynamic model of a deep groove ball bearing under a radial load is proposed. All components are treated as rigid bodies whereas the bearing outer ring flexibility is taken into account using fixed interface component mode synthesis (CMS). The classical lubricated Hertzian contact theory is used to calculate elastic deflections and non-linear contact forces. The dynamic loading of the outer ring interface nodes is ensured using C2-continuous rational cubic splines. A Runge-Kutta-Felhberg 4th/5th order integration scheme is used to solve the dynamic equilibrium of all components. Time and frequency domain analyses are then carried out to investigate the dynamic behaviour of the ball bearing. The accuracy of these works is validated by comparison with the results of an analytical model and a model based on finite elements proposed in prior researchs.
Modelling of the Mechanical Behaviour of Human Joints Cartilage
Authors: Accardi Mario Alberto , Dini Daniele
Published: June 2009

A significant component of our understanding of cartilage mechanical behaviour is the ability to model its response to various types of mechanical loading, for which we require detailed knowledge of cartilage material properties. The Finite Element Analysis software ABAQUS is renowned for the ability to model poroelastic materials using the soil consolidation theory. In this research, ABAQUS has been used to model and investigate the mechanical behaviour of articular cartilage, mainly using indentation and unconfined compression techniques. A biphasic model of articular cartilage was first created and subsequently modified to incorporate more detailed material descriptions. Various material constitutive laws (and mechanical properties), accounting for the strain dependent permeability of the porous matrix, solid viscoelasticity and transverse isotropy, have been adopted to produce increasingly sophisticated models. The presence of collagen fibril networks embedded in the solid has been also considered and Fibril Reinforced Elastic and Viscoelastic models produced. A salient feature of these models is their ability to simulate fibril stiffening by replicating the nonlinear fibrillar response. In this paper, we provide an overview of the state-of-art modelling techniques adopted to simulate cartilage behaviour. The comparative study performed by the authors provides a critical assessment of the effectiveness of such techniques.
Emergence of High Levels of Extended-Spectrum-β-Lactamase-Producing Gram-Negative Bacilli in the Asia-Pacific Region: Data from the Study for Monitoring Antimicrobial Resistance Trends (SMART) Program, 2007
Authors: Hawser Stephen P. , Bouchillon Samuel K. , Hoban Daryl J. , Badal Robert E. , Hsueh Po-Ren , Paterson David L.
Published: June 2009

Of 3,004 gram-negative bacilli collected from intra-abdominal infections in the Asia-Pacific region during 2007, 42.2% and 35.8% ofEscherichia coliandKlebsiellaspp., respectively, were extended-spectrum β-lactamase (ESBL) positive. Moreover ESBL rates in India forE. coli,Klebsiella pneumoniae, andKlebsiella oxytocawere 79.0%, 69.4%, and 100%, respectively. ESBL-positiveE. colirates were also relatively high in China (55.0%) and Thailand (50.8%). Ertapenem and imipenem were the most active drugs tested, inhibiting over 90% of all species, including ESBL-positive isolates with the exception ofPseudomonas aeruginosaisolates (<90% susceptible to all study drugs) and ESBL-positiveKlebsiella pneumoniaeisolates (<90% susceptible to all study drugs except imipenem). Quinolones achieved 90% inhibition levels only against ESBL-negativeK. pneumoniaeand ESBL-negativeK. oxytoca. A decline in ampicillin-sulbactam activity was noted, with only 34.5% of allEnterobacteriaceaeinhibited in this study.
Anidulafungin Treatment of Candidal Central Nervous System Infection in a Murine Model
Authors: Kang Cheol-In , Rouse Mark S. , Mandrekar Jayawant N. , Steckelberg James M. , Patel Robin
Published: June 2009

We established a murine model of
Candida albicans
central nervous system (CNS) infection and evaluated the efficacy of anidulafungin. Ten milligrams/kg/day anidulafungin, amphotericin B, or voriconazole significantly reduced mortality and fungal burden in brain tissue, although amphotericin B and 10 mg/kg/day anidulafungin reduced fungal burden in brain tissue to a greater extent than did voriconazole. This suggests a potential role for anidulafungin in the treatment of candidal CNS infection.
Prospective Comparison of the Clinical Impacts of Heterogeneous Vancomycin-Intermediate Methicillin-Resistant
Staphylococcus aureus
(MRSA) and Vancomycin-Susceptible MRSA
Authors: Horne K. C. , Howden B. P. , Grabsch E. A. , Graham M. , Ward P. B. , Xie S. , Mayall B. C. , Johnson P. D. R. , Grayson M. L.
Published: June 2009

Although methicillin (meticillin)-resistant
Staphylococcus aureus
(MRSA) strains with reduced susceptibility to vancomycin (RVS-MRSA; including vancomycin-intermediate
S. aureus
[VISA] and heterogeneous VISA [hVISA]) have been linked with vancomycin treatment failure, it is unclear whether they are more pathogenic than vancomycin-susceptible MRSA (VS-MRSA). We prospectively assessed patients with clinical MRSA isolates during a 10-month period to determine clinical status (infection versus colonization) and therapeutic outcome before correlating these findings with the results of detailed in vitro assessment of vancomycin susceptibility, including population analysis profile (PAP) testing. hVISA and VISA were defined by standard PAP criteria (area-under-the-curve ratio compared to that of the reference hVISA strain Mu3 [≥0.9]) and routine CLSI criteria (vancomycin MIC, 4 to 8 μg/ml), respectively. Among the 117 patients assessed, 58 had RVS-MRSA isolates (56 hVISA and 2 VISA) and 59 had VS-MRSA isolates; the patient demographics and comorbidities were similar. RVS-MRSA was associated with a lower rate of infection than VS-MRSA (29/58 versus 46/59;
P
= 0.003), including a lower rate of bacteremia (3/58 versus 20/59, respectively;
P
< 0.001). The cure rates in RVS-MRSA and VS-MRSA groups were not statistically different (16/26 versus 31/42;
P
= 0.43), but the post hoc assessment of treatment regimes and study size made detailed conclusions difficult. The results of the macro method Etest correlated well with the PAP results (sensitivity, 98.3%, and specificity, 91.5%), but broth microdilution and our preliminary RVS-MRSA detection method correlated poorly. All isolates were susceptible to linezolid and daptomycin. These data suggest that detailed prospective laboratory identification of RVS-MRSA isolates may be of limited value and that, instead, such in vitro investigation should be reserved for isolates from patients who are failing appropriate anti-MRSA therapy.
Antiviral Activity of Chloroquine against Human Coronavirus OC43 Infection in Newborn Mice
Authors: Keyaerts Els , Li Sandra , Vijgen Leen , Rysman Evelien , Verbeeck Jannick , Van Ranst Marc , Maes Piet
Published: June 2009

Until recently, human coronaviruses (HCoVs), such as HCoV strain OC43 (HCoV-OC43), were mainly known to cause 15 to 30% of mild upper respiratory tract infections. In recent years, the identification of new HCoVs, including severe acute respiratory syndrome coronavirus, revealed that HCoVs can be highly pathogenic and can cause more severe upper and lower respiratory tract infections, including bronchiolitis and pneumonia. To date, no specific antiviral drugs to prevent or treat HCoV infections are available. We demonstrate that chloroquine, a widely used drug with well-known antimalarial effects, inhibits HCoV-OC43 replication in HRT-18 cells, with a 50% effective concentration (± standard deviation) of 0.306 ± 0.0091 μM and a 50% cytotoxic concentration (± standard deviation) of 419 ± 192.5 μM, resulting in a selectivity index of 1,369. Further, we investigated whether chloroquine could prevent HCoV-OC43-induced death in newborn mice. Our results show that a lethal HCoV-OC43 infection in newborn C57BL/6 mice can be treated with chloroquine acquired transplacentally or via maternal milk. The highest survival rate (98.6%) of the pups was found when mother mice were treated daily with a concentration of 15 mg of chloroquine per kg of body weight. Survival rates declined in a dose-dependent manner, with 88% survival when treated with 5 mg/kg chloroquine and 13% survival when treated with 1 mg/kg chloroquine. Our results show that chloroquine can be highly effective against HCoV-OC43 infection in newborn mice and may be considered as a future drug against HCoVs.
β-Lactamase-Mediated β-Lactam Resistance in
Campylobacter
Species: Prevalence of Cj0299 (
bla
OXA-61
) and Evidence for a Novel β-Lactamase in
C
.
jejuni
Authors: Griggs Deborah J. , Peake Leanne , Johnson Margaret M. , Ghori Saba , Mott A. , Piddock Laura J. V.
Published: June 2009

Fifty-two percent of 1,288 poultry isolates of campylobacters were ampicillin resistant, and resistance was more common among
Campylobacter coli
isolates (67.4%) than among
Campylobacter jejuni
isolates (47.5%). Production of β-lactamase was typically associated with resistance to ampicillin, amoxicillin (amoxicilline), penicillin, and ticarcillin. Regardless of β-lactamase production, all isolates were resistant to piperacillin (MICs ≥ 256 μg/ml), and most were resistant to carbenicillin, cloxacillin, and cephalosporins. Of all ampicillin-resistant campylobacters tested, 91% (347/380) carried the
bla
OXA-61
gene, and 77% (136/175) of those tested with nitrocefin produced a β-lactamase, presumably OXA-61. The isoelectric point (pI) of OXA-61 was 8.7, and the molecular mass was 31.0 kDa. Insertional inactivation of
bla
OXA-61
in
C
.
jejuni
NCTC 11168 and two ampicillin-resistant isolates resulted in increased susceptibility to ampicillin, co-amoxiclav (amoxicillin and clavulanic acid), penicillin, carbenicillin, oxacillin, and piperacillin, but the effects on MICs of cephalosporins and imipenem were negligible. Some
C
.
jejuni
isolates that lacked
bla
OXA-61
produced a β-lactamase, CjBla2, with a pI of 9.2 and molecular mass of 32.4 kDa. Mass spectrometry confirmed that the most prevalent β-lactamase was the product of
bla
OXA-61
, but CjBla2 was not identified. OXA-61 is prevalent among
Campylobacter
spp. of veterinary origin and is similar to the β-lactamase previously reported in human isolates. Production of OXA-61 was associated with resistance to penams but not cephalosporins. Co-amoxiclav remained active against all isolates tested.
Role of the Corneal Epithelial Basement Membrane in Ocular Defense against
Pseudomonas aeruginosa
Authors: Alarcon Irania , Kwan Lesley , Yu Chong , Evans David J. , Fleiszig Suzanne M. J.
Published: June 2009

Pseudomonas aeruginosa
can invade corneal epithelial cells and translocates multilayered corneal epithelia in vitro, but it does not penetrate the intact corneal epithelium in vivo. In healthy corneas, the epithelium is separated from the underlying stroma by a basement membrane containing extracellular matrix proteins and pores smaller than bacteria. Here we used in vivo and in vitro models to investigate the potential of the basement membrane to defend against
P. aeruginosa
. Transmission electron microscopy of infected mouse corneas in vivo showed penetration of the stroma by
P. aeruginosa
only where the basement membrane was visibly disrupted by scratch injury, suggesting that the intact basement membrane prevented penetration. This hypothesis was explored using an in vitro Matrigel Transwell model to mimic the corneal basement membrane.
P. aeruginosa
translocation of multilayered corneal epithelia grown on Matrigel was ∼100-fold lower than that of cells grown without Matrigel (
P
< 0.005,
t
test). Matrigel did not increase transepithelial resistance. Matrigel-grown cells blocked translocation by a
P. aeruginosa
protease mutant. Without cells, Matrigel also reduced traversal of
P. aeruginosa
and the protease mutant. Fluorescence microscopy revealed a relative accumulation of bacteria at the superficial epithelium of cells grown on Matrigel at 3 h compared to cells grown on uncoated filters. By 5 h, bacteria accumulated beneath the cells, suggesting direct trapping by the Matrigel. These findings suggest that the basement membrane helps defend the cornea against infection via physical barrier effects and influences on the epithelium and that these roles could be compromised by
P. aeruginosa
proteases.
Host Adhesive Activities and Virulence of Novel Fimbrial Proteins of
Porphyromonas gingivalis
Authors: Pierce Deanne L. , Nishiyama So-ichiro , Liang Shuang , Wang Min , Triantafilou Martha , Triantafilou Kathy , Yoshimura Fuminobu , Demuth Donald R. , Hajishengallis George
Published: June 2009

The fimbriae of
Porphyromonas gingivalis
mediate critical roles in host colonization and evasion of innate defenses and comprise polymerized fimbrilin (FimA) associated with quantitatively minor accessory proteins (FimCDE) of unknown function. We now show that
P. gingivalis
fimbriae lacking FimCDE fail to interact with the CXC-chemokine receptor 4 (CXCR4), and bacteria expressing FimCDE-deficient fimbriae cannot exploit CXCR4 in vivo for promoting their persistence, as the wild-type organism does. Consistent with these loss-of-function experiments, purified FimC and FimD (but not FimE) were shown to interact with CXCR4. However, significantly stronger binding was observed when a combination of all three proteins was allowed to interact with CXCR4. In addition, FimC and FimD bound to fibronectin and type 1 collagen, whereas FimE failed to interact with these matrix proteins. These data and the fact that FimE is required for the association of FimCDE with
P. gingivalis
fimbriae suggest that FimE may recruit FimC and FimD into a functional complex, rather than directly binding host proteins. Consistent with this notion, FimE was shown to bind both FimC and FimD. In summary, the FimCDE components cooperate and impart critical adhesive and virulence properties to
P. gingivalis
fimbriae.
Kinetics of Lethal Factor and Poly-d-Glutamic Acid Antigenemia during Inhalation Anthrax in Rhesus Macaques
Authors: Boyer Anne E. , Quinn Conrad P. , Hoffmaster Alex R. , Kozel Thomas R. , Saile Elke , Marston Chung K. , Percival Ann , Plikaytis Brian D. , Woolfitt Adrian R. , Gallegos Maribel , Sabourin Patrick , McWilliams Lisa G. , Pirkle James L. , Barr John R.
Published: June 2009

Systemic anthrax manifests as toxemia, rapidly disseminating septicemia, immune collapse, and death. Virulence factors include the anti-phagocytic γ-linked poly-d-glutamic acid (PGA) capsule and two binary toxins, complexes of protective antigen (PA) with lethal factor (LF) and edema factor. We report the characterization of LF, PA, and PGA levels during the course of inhalation anthrax in five rhesus macaques. We describe bacteremia, blood differentials, and detection of the PA gene (pagA) by PCR analysis of the blood as confirmation of infection. For four of five animals tested, LF exhibited a triphasic kinetic profile. LF levels (mean ± standard error [SE] between animals) were low at 24 h postchallenge (0.03 ± 1.82 ng/ml), increased at 48 h to 39.53 ± 0.12 ng/ml (phase 1), declined at 72 h to 13.31 ± 0.24 ng/ml (phase 2), and increased at 96 h (82.78 ± 2.01 ng/ml) and 120 h (185.12 ± 5.68 ng/ml; phase 3). The fifth animal had an extended phase 2. PGA levels were triphasic; they were nondetectable at 24 h, increased at 48 h (2,037 ± 2 ng/ml), declined at 72 h (14 ± 0.2 ng/ml), and then increased at 96 h (3,401 ± 8 ng/ml) and 120 h (6,004 ± 187 ng/ml). Bacteremia was also triphasic: positive at 48 h, negative at 72 h, and positive at euthanasia. Blood neutrophils increased from preexposure (34.4% ± 0.13%) to 48 h (75.6% ± 0.08%) and declined at 72 h (62.4% ± 0.05%). The 72-h declines may establish a “go/no go” turning point in infection, after which systemic bacteremia ensues and the host's condition deteriorates. This study emphasizes the value of LF detection as a tool for early diagnosis of inhalation anthrax before the onset of fulminant systemic infection.
Directed Mutagenesis of the
Rickettsia prowazekii pld
Gene Encoding Phospholipase D
Authors: Driskell Lonnie O. , Yu Xue-jie , Zhang Lihong , Liu Yan , Popov Vsevolod L. , Walker David H. , Tucker Aimee M. , Wood David O.
Published: June 2009

Rickettsia prowazekii
, the causative agent of epidemic typhus, is an obligately intracytoplasmic bacterium, a lifestyle that imposes significant barriers to genetic manipulation. The key to understanding how this unique bacterium evades host immunity is the mutagenesis of selected genes hypothesized to be involved in virulence. The
R. prowazekii pld
gene, encoding a protein with phospholipase D activity, has been associated with phagosomal escape. To demonstrate the feasibility of site-directed knockout mutagenesis of rickettsial genes and to generate a nonrevertible vaccine strain, we utilized homologous recombination to generate a
pld
mutant of the virulent
R. prowazekii
strain Madrid Evir. Using linear DNA for transformation, a double-crossover event resulted in the replacement of the rickettsial wild-type gene with a partially deleted
pld
gene. Linear DNA was used to prevent potentially revertible single-crossover events resulting in plasmid insertion. Southern blot and PCR analyses were used to confirm the presence of the desired mutation and to demonstrate clonality. While no phenotypic differences were observed between the mutant and wild-type strains when grown in tissue culture, the
pld
mutant exhibited attenuated virulence in the guinea pig model. In addition, animals immunized with the mutant strain were protected against subsequent challenge with the virulent Breinl strain, suggesting that this transformant could serve as a nonrevertible, attenuated vaccine strain. This study demonstrates the feasibility of generating site-directed rickettsial gene mutants, providing a new tool for understanding rickettsial biology and furthering advances in the prevention of epidemic typhus.
Human Serum Induces Streptococcal C5a Peptidase Expression
Authors: Gleich-Theurer Ute , Aymanns Simone , Haas Gregor , Mauerer Stefanie , Vogt Julia , Spellerberg Barbara
Published: June 2009

Streptococcus agalactiaeis a major pathogen in humans and animals. Virulence factors are often associated with mobile genetic elements, and their expression can be modulated by host factors.S. agalactiaeharbors the genes for C5a peptidase (scpB) and Lmb on a composite transposon structure which is absent in many bovine isolates. To investigate whether these genes participate in the adaptation to human hosts, we determined the influence of human and bovine serum on the promoter activity ofscpBandlmbby using fluorescence-activated cell sorter analysis. Culture in the presence of 1 to 50% human serum resulted in a dose-dependent induction of reporter gene activity forscpBbut notlmb. Reporter gene activity was, however, unchanged following growth in fetal calf serum. Interestingly, a bovine strain did not display any induction ofscpBby either bovine or human serum. Reverse transcription-PCR analysis was used to confirm differential induction ofscpBinS. agalactiaeand showed a similar induction of theStreptococcus pyogenesC5a peptidase genescpAby human but not bovine serum. The specific induction of the streptococcal C5a peptidase by human serum corresponds to the absence ofscpBin many bovineS. agalactiaeisolates and underlines the importance of this virulence factor for human infections.
Streptococcus mitis
Phage-Encoded Adhesins Mediate Attachment to α2-8-Linked Sialic Acid Residues on Platelet Membrane Gangliosides
Authors: Mitchell Jennifer , Sullam Paul M.
Published: June 2009

The direct binding of bacteria to human platelets contributes to the pathogenesis of infective endocarditis. Platelet binding by
Streptococcus mitis
strain SF100 is mediated in part by two bacteriophage-encoded proteins, PblA and PblB. However, the platelet membrane receptor for these adhesins has been unknown. In this study, we demonstrate that these proteins mediate attachment of bacterial cells to sialylated gangliosides on the platelet cell surface. Desialylation of human platelet monolayers reduced adherence of SF100, whereas treatment of the platelets with
N
- or
O
-glycanases did not affect platelet binding. Treatment of platelets with sialidases having different linkage specificities showed that removal of α2-8-linked sialic acids resulted in a marked reduction in bacterial binding. Preincubation of SF100 with ganglioside GD3, a glycolipid containing α2-8-linked sialic acids that is present on platelet membranes, blocked subsequent binding of this strain to these cells. In contrast, GD3 had no effect on the residual binding of platelets by strain PS344, an isogenic Δ
pblA
Δ
pblB
mutant. Preincubating platelets with specific monoclonal antibodies to ganglioside GD3 also inhibited binding of SF100 to platelets, but again, they had no effect on binding by PS344. When the direct binding of
S. mitis
strains SF100 and PS344 to immobilized gangliosides was tested, binding of PS344 to GD3 was reduced by 70% compared to the parent strain. These results indicated that platelet binding by SF100 is mediated by the interaction of PblA and PblB with α2-8-linked sialic acids on ganglioside GD3.
Thermal history of the southwestern Meguma zone, Nova Scotia, from an 40Ar/39Ar and fission track dating study of intrusive rocks
Authors: Reynolds P. H. , Elias P. , Muecke G. K. , Grist A. M.
Published: June 2009

Two geologically distinct regions within the Meguma terrane have been studied in detail and are shown to have contrasting thermal histories. This conclusion is based on 31 new 40Ar/39Ar age spectra on micas, K-feldspars, and hornblendes from several of the plutons in southern Nova Scotia, which are satellites to the much larger South Mountain batholith (SMB). In addition, we report four K-feldspar age spectra from a locality in the northeastern part of the SMB and seven fission track ages from both the southern and northern areas.The complex age spectrum of hornblende from a mafic phase associated with the Barrington Passage pluton suggests a minimum intrusive age of 385 Ma, a result consistent with geologic evidence that this pluton represents an early, less evolved magmatic pulse. Later intrusive activity appears to have been coeval with the intrusion of the SMB at ca. 370 Ma ago. In the southern region, argon clocks in feldspars were completely reset and mica clocks variably reset by a later thermal event. The cumulative geochronologic and geologic evidence constrains this event to 300–320 Ma ago. In the SMB, this Alleghanian/Hercynian thermal disturbance is much less pronounced and appears to be localized to small areas that are often associated with economic mineralization.K-feldspars from the southern plutons record an episode of argon loss 220–230 Ma ago, which is less evident in the SMB to the north. Upper Triassic dike injection in the southern region, associated with the initial rifting phase of the Canadian Atlantic margin, accompanied this milder thermal pulse.Apatites in the two regions record a mean fission track age of ca. 180 Ma, which we attribute to the final cooling of the terrane below about 100 °C. The timing of this event coincides with regional uplift recorded in sedimentary sequences along much of the Maritime continental shelf.
Groundwater storage – streamflow relations during winter in a subarctic wetland, Saskatchewan
Authors: Price Jonathan S. , Fitzgibbon John E.
Published: June 2009

Wetland drainage systems are shown to be hydrologically active during winter. Water storage in various terrain types changed over the winter as a result of intrabasin transfers between terrain types, primarily from outlying mineral terrains to centrally located groundwater controlled wetlands, and due to winter streamflow. Mineral terrain and bog lost 97 and 25 mm of water, respectively, whereas fens gained 28–51 mm. A water balance indicated that mineral terrain yielded almost twice as much water as was released as streamflow, and that much of this excess was being stored in the fens where groundwater seepage at the surface resulted in icings. Bogs had little ability to sustain winter streamflow. Diminishing streamflow in early winter coincided with freezing of the surface layers of peat, which normally transmit most of the water. However, streamflow was maintained throughout winter by water transmitted through the fens.
Rare-earth elements, thermal history, and the colour of natural fluorites
Authors: Naldrett D. L. , Lachaine Andre , Naldrett S. N.
Published: June 2009

The contents of La and of all 13 naturally occurring rare-earth elements (REEs) in samples of natural fluorites were determined by neutron activation analysis. The samples were chosen to test the relation of REE content to colour. Total REE contents of the samples ranged from 3.46 to 97.2 ppm; the range of the least abundant REE, Lu, was 0.031–0.57 ppm and the range of the most abundant REE, Ce, was 0.94–33.3 ppm. No relation was found between the absolute amounts nor the enrichment or depletion of a particular REE and colour. The absorption spectra from 400 to 700 nm were determined by photo-acoustic spectroscopy using a few milligrams of powdered fluorite sample. Optical absorption spectra were obtained for all samples including those that were too small or too opaque for transmission or reflectance methods. The absorption maxima obtained are similar to those reported by others for samples of similar colours. It is concluded that ionizing radiations from incorporated radioactive elements produce the divalent REE ions that account initially for purple colour. From the description given in the literature on the thermoluminescence of fluorites it is then shown that the thermal history can account for the ultimate colour. However, other factors, such as the presence of water vapour, oxygen, or hydrogen; variation in the growth rate of crystals; colloidal particles; and exposure to light, can contribute to the colour.
SPIN HALL EFFECT
Authors: DYAKONOV M. I.
Published: June 2009

A review of the phenomenology of the Spin Hall Effect and related phenomena originating from the coupling between spin and charge currents by spin-orbit interaction is presented. The physical origin of various effects in spin-dependent scattering is demonstrated. A previously unknown feature of spin transport, the swapping of spin currents, is discussed.
INFLUENCE OF MAGNETIC FIELDS ON THE INTRINSIC SPIN HALL EFFECT IN TWO-DIMENSIONAL SYSTEMS
Authors: RAICHEV O. E.
Published: June 2009

The influence of magnetic fields on the electron spin in solids involves two basic mechanisms. First, any magnetic field introduces the Zeeman splitting of electron states, thereby modifying spin precession. Second, since the magnetic field affects the electron motion in the plane perpendicular to the field, the spin dynamics is also modified, owing to the spin-orbit interaction. The theory predicts, as a consequence of this influence, unusual properties of the intrinsic spin-Hall effect in two-dimensional systems in the presence of magnetic fields. This paper describes non-monotonic dependence of the spin-Hall conductivity on the magnetic field and its enhancement in the case of weak disorder, as well as multiple jumps of the spin-Hall conductivity owing to the topological transitions (abrupt changes of the Berry phase) induced by the parallel magnetic field.
SEMICONDUCTOR NANOSTRUCTURES IN HIGH MAGNETIC FIELDS: RECENT RESULTS AT HFML NIJMEGEN
Authors: CHRISTIANEN PETER C. M.
Published: June 2009

A short overview of the current experimental facilities at the HFML Nijmegen, including an update on the planned development of a 45 T Hybrid magnet in conjunction with a Free Electron Laser, was presented. That was followed by a brief highlight of recent results on the high field physical properties of semiconductor nanostructures, such as quantum rings1 and dots,2 graphene3,4 and organic nanostructures.5

The majority of the talk was devoted to the investigation of negatively charged excitons (negative trions, two electrons bound to one hole) in semiconductor quantum wells in high magnetic fields. A comprehensive overview of photoluminescence (PL) experiments on GaAs and CdTe quantum wells (QWs) of variable well widths, containing a low density electron gas (2DEG) was presented. Particular interest was given to the magnetic field range where the ground state of negative trions is changing from a singlet (both electrons having opposite spin) to a triplet (parallel electron spins) state.

Using polarized magneto-PL (excitation) and reflectivity spectroscopy we have identified (for both GaAs and CdTe QWs) the four typical excitonic peaks, usually denoted as the singlet, dark triplet and bright triplet trion peaks, as well as the neutral exciton peak. All peaks exhibit a pronounced dependence on polarization, 2DEG density and temperature. CdTe QWs exhibit all four peaks at the entire field range used (< 44 T), whereas the dark triplet emission disappears at high fields for GaAs QWs.

We have determined the field strength at which the singlet-triplet crossover occurs for all QWs, which allows us to critically compare our experimental results with theoretical predictions. Remarkably, the actual singlet-triplet transition is hidden in GaAs QWs and a narrow (12 nm) CdTe QW. Since the PL emission energy equals the energy difference between the initial (trion) and final (electron) states, the PL lines themselves do not cross at the singlet-triplet crossover as a result of the different Zeeman energies of the final electron states.6 In contrast the cross-over is directly visible in the PL lines of a wide (20 nm) CdTe QW. This behaviour can be readily understood by the dependence of the electron- and hole g -factors on well width and host material.

Note from Publisher: This article contains the abstract only.