bluuebunny/crossref_metadata_2025 huggingface dataset:
Lubricant Modeling and Its Effect on Simulation of Material Forming
Authors: Jackson J. E. , Gangjee T. , Haque I.
Published: October 2009

Solid cylinder upsetting is analyzed using three different approaches for frictional boundary condition modeling. These are (1) constant shear friction factor, (2) experimentally measured frictional stresses, and (3) analytical models accounting for lubricant entrapment and redistribution. All three approaches are implemented in the CFORM finite element code. The error between the three approaches and actual experimental measurements of the material deformation and interfacial pressures is investigated. It is shown that the constant shear friction factor is more accurate for solid film lubricants than for liquid lubricants. However, the calculations indicate that if accurate prediction of near net shape forming processes is to become a reality, improvements need to be made in the characterization of frictional boundary conditions. New theoretical developments applicable to arbitrary shapes and more accurate than the constant shear friction factor approach are needed.
Experimental Determination Technique of Stress Intensity Factor and Its Application
Authors: Itoh Y. Z. , Murakami T. , Kashiwaya H.
Published: October 2009

The proportional extrapolation technique is proposed for determining experimentally and accurately stress intensity factors, using the crack tip stresses measured by strain gage. The technique is based on the assumption that the effects of gage length and width on the measurement of the crack tip stresses are corrected by comparing with standard problems, and the corrected results are only accurate in the limit as r→0 (r; distance from crack tip). A special strain gage pattern was developed for applying the proportional extrapolation technique. The stress intensity factors of a two-dimensional crack problem were analyzed using this strain gage, and as an application example, the fracture behavior under mixed mode loading was investigated on notched polymer sheets.
Creep Deformation of Particle-Strengthened Metal-Matrix Composites
Authors: Zhu Z. G. , Weng G. J.
Published: October 2009

A multiaxial theory of creep deformation for particle-strengthened metal-matrix composites is derived. This derivation is based on the observation that there are two major sources of creep resistance in such a system. The first, or metallurgical effect, arises from the increased difficulty of dislocation motion in the presence of particles and is accounted for by a size- and concentration dependent constitutive equation for the matrix. The second, or mechanics effect, is due to the continuous transfer of stress from the ductile matrix to the hard particles and the corresponding stress redistribution is also incorporated in the derivation. Both power-law creep and exponential creep in the matrix, each involving the transient as well as the steady state, are considered. The constitutive equations thus derived can provide the development of creep strain of the composite under a combined stress. The multiaxial theory is also simplified to a uniaxial one, whose explicit stress-creep strain-time relations at a given concentration of particles are also given by a first- and second-order approximation. The uniaxial theory is used to predict the creep deformation of an oxide-strengthened cobalt, and the results are in reasonably good agreement with the experiment. Finally, it is demonstrated that a simple metallurgical approach without considering the stress redistribution between the two constituent phases, or a simple mechanics approach without using a modified constitutive equation for the metal matrix, may each underestimate the creep resistance of the composite, and, therefore, it is important that both factors be considered in the formulation of such a theory.
Experimental Finite Element Analysis of Temperature Distribution During Arc Welding
Authors: Kannatey-Asibu Elijah , Kikuchi Noboru , Jallad Abdel-Rahim
Published: October 2009

Analysis of temperatures and associated cooling rates that arise during welding is essential in determining the final mechanical properties and load carrying capacity of the weldment. Due to the complexity of the fundamental thermal equations and the heat distribution, as well as latent heat effects, numerical techniques have been developed in recent years for weld temperature analysis. However, the higher temperature gradients in the vicinity of the weld pool require a highly refined mesh that results in extensive computation time using conventional numerical techniques. We developed a moving finite element grid with an adaptation scheme that permits mesh refinement only in the required regions, thereby achieving a more efficient computation for a desired accuracy. The numerical simulation results for a 2-dimensional analysis correlate well with temperature measurements made with thermocouples for the welding conditions used in the analysis.
Relationship of Creep, Creep-Fatigue, and Cavitation Damage in Type 304 Austenitic Stainless Steel
Authors: Majumdar Saurin
Published: October 2009

Available creep and creep-fatigue data on type 304 stainless steel are re-examined in the light of recently generated basic cavitation data on the same material. This basic study has shown creep damage to be a highly inhomogeneous phenomenon, both in space and in time. A small fraction of boundaries are so intensely cavitated by about 10–25 percent of life that for all practical purposes they can be considered cracked. Other similar boundaries, that are similarly oriented with respect to the tensile stress direction, however, are almost devoid of cavities at the end of life. The early nucleation of cracks by creep mechanism has a significant influence on creep-fatigue interactions, particularly for tests at low strain ranges. A simple ductility exhaustion model appears to be able to account for the early crack initiation. A hardness-modified ductility approach appears to provide an upper bound to the ductility displayed by all tests and correlates data for long hold-time fatigue tests at low strain range. Tests at higher strain ranges and/or shorter hold times do not achieve their full potential ductility because their lives are cut short by crack propagation. Their lives can be predicted empirically by an enhanced fatigue crack growth equation in the presence of cavitation damage.
J-Integral Analysis of Three-Point Bend Specimen
Authors: Zahoor A.
Published: October 2009

A J-integral solution is derived for the three-point bend [SE(B)] specimen. The solution allows analysis for a/W greater than 0.2. The solution is based on an approach that does not require an assumption of net-section yielding in the remaining uncracked ligament. Solutions are presented for both the deformation theory J and modified J. These solutions are suitable for J-resistance curve analysis and require data from only one specimen. Solution for a special case of power law hardening material is presented. Consequences of the separability assumption between load-point displacement and crack length on the resulting J solution are discussed. This work indicates that the plastic η factor from previous solutions is significantly underestimated for a/W less than 0.6. Numerical results show that Jd and JM resistance curves are closer than those obtained from previous solutions. A solution for normalizing the load-displacement curve is also presented.
Creep Life Prediction Based on Stochastic Model of Microstructurally Short Crack Growth
Authors: Kitamura Takayuki , Ohtani Ryuichi
Published: October 2009

A nondimensional model of microstructurally short crack growth in creep is developed based on a detailed observation of the creep fracture process of 304 stainless steel. In order to deal with the scatter of small crack growth rate data caused by microstructural inhomogeneity, a random variable technique is used in the model. A cumulative probability of the crack length at an arbitary time, G(a,t), and that of the time when a crack reaches an arbitary length, F(t,a), are obtained numerically by means of a Monte Carlo method. G(a,t) and F(t,a) are the probabilities for a single crack. However, multiple cracks generally initiate on the surface of a smooth specimen from the early stage of creep life to the final stage. Taking into account the multiple crack initiations, the actual crack length distribution observed on the surface of a specimen is predicted by the combination of probabilities for a single crack. The prediction shows a fairly good agreement with the experimental result for creep of 304 stainless steel at 923 K. The probability of creep life is obtained from an assumption that creep fracture takes place when the longest crack reaches a critical length. The observed and predicted scatter of the life is fairly small for the specimens tested.
Pressure Sintering of Si3N4 System for Near-Net Shape Forming
Authors: Samanta Shyam K. , Wada Harue , Wang Liya
Published: October 2009

Yttria and alumina have been used with particular success, either singly or in combination, as densification aids for hot pressing and sintering of silicon nitride. To obtain desirable mechanical, physical, and chemical properties, it is necessary to minimize the addition of alumina as a densifying agent, however, very low amount of alumina additive reduces the possibility of sintering silicon nitride to high theoretical density. In this paper the authors have elucidated a sintering process which densifies silicon nitride to near theoretical density even with low amount of alumina doping.
Mixed Mode Ductile Fracture Studies With Nonproportional Loading Based on Continuum Damage Mechanics
Authors: Wang June , Chow C. L.
Published: October 2009

Service loading imposed on engineering structures is often arbitrary or nonproportional. The paper presents an investigation of examining the effects of proportional and nonproportional loadings on the fracture behavior of mixed mode fracture. The anisotropic model of continuum damage mechanics capable of taking into account the nonproportional loading condition recently developed by the authors is employed and the computed results reveal that different modes of proportional and nonproportional loading have marked effects on the fracture load, angle of crack initiation, overall damage, and directional change of the principal planes of stress and damage.
Wrinkling of an Unevenly Stretched Sheet Metal
Authors: Wang Xiaofang , Lee L. H. N.
Published: October 2009

The onset of wrinkling of an unevenly stretched sheet metal subject to finite deformation is analyzed by an incremental finite element method. The sheet metal is modeled as a plate made of an elastic-plastic material. Hill’s anisotropic yield function and bifurcation criterion are employed in the analysis. The effects of geometrical and material parameters upon the onset of wrinkling are investigated. In the bifurcation analysis, attention is given to the changing and varying thickness of the sheet metal which could have a strong influence on the flexural rigidity of the sheet. Numerical results are presented herein.
A General Criterion for Low-Cycle Multiaxial Fatigue Failure
Authors: Makinde A. , Neale K. W.
Published: October 2009

A new, general criterion is proposed for multiaxial low-cycle fatigue failure. Contours of constant fatigue life on a plot of maximum shear strain against the tensile strain acting normal to the plane of maximum shear strain are represented by a parametric criterion of the form g(θ,Nf)=kf1(θ)f2(Nf). Here g is the magnitude of the vector from the origin to a point on the constant life contour, θ is the angle associated with g in this space, Nf is the number of cycles to failure, k is a constant and f1 (θ) and f2(Nf) are two separate functions of θ and Nf, respectively. It is shown that all previously proposed macroscopic criteria are particular cases of the failure function g(θ, Nf). Experimental results from several authors are analyzed using the new criterion.
Specimen Size and Orientation Effects on the Toughness of Steel Weldments
Authors: Morrison J. , Gough J. P.
Published: October 2009

This paper deals with the measurement of the room temperature fracture toughness of 25-mm thick HY130 steel shielded-metal-arc weldments. The multipass butt welds were tested using different specimen geometries and orientations, and after various post-weld stress relief heat treatments. Where appropriate, comparisons are made between KIc and JIc data, including estimates based on both CTOD and stretch zone size measurements, for both parent metal and fusion zone material. Measured toughness for plate depends on whether the specimen tears at or before limit load, and thus on specimen size, but is independent of orientation and unaffected by thermal stress relief. Maximum load J for weldments is independent of specimen size or orientation, but CTOD decreases as specimen size decreases. Welds slowly cooled after stress relieving fail in a brittle manner, with very low CTOD values, even though the nominal critical stress intensities exceed 100 MPam.
Effect of Shielding Gas Pressure in Laser Cutting of Sheet Metals
Authors: Na S. -J. , Yang Y. -S. , Koo H. -M. , Kim T. -K.
Published: October 2009

To investigate the influence of the shielding gas pressure on the laser cut quality, a series of experiments was conducted for various cutting conditions. The cutting pressure distribution was measured on the workpiece, and also beneath the workpiece with a prepared kerf for various nozzle pressures and nozzle-to-workpiece distances. The cut specimens were inspected by various manners such as dross observation, surface roughness test, and kerf width measurement. Based on the data of pressure measurements and the results of the cut surface inspection, the influence of the considered cutting conditions on the cut quality could be evaluated. The cutting pressure beneath the bottom surface was slightly different from that on the top surface and the pressures on two surfaces had a substantial influence on the dross state. But they possessed only a negligible effect on the surface roughness and kerf width, except the extreme case, where the cut kerf could not be obtained. It could be also revealed that the cutting pressure, which has a close relationship with the nozzle-to-workpiece distance under a given nozzle pressure, affects the range of the available cutting speed.
Variation Propagation Analysis for Multistation Assembly Process With Consideration of GD&T Factors
Authors: Kong Zhenyu , Huang Wenzhen , Oztekin Asil
Published: October 2009

Modeling of variation propagation in multistation assembly processes is crucial in predicting product dimensional quality and general performance of manufacturing systems. Based on the state space modeling, this paper develops a variation propagation model, which can be applied for analysis of various tolerances such as size tolerance, bonus tolerance, floating tolerance, etc. The nonstationary tolerance/variation (varying variance) caused by bonus tolerance and floating tolerance is properly handled by the proposed method. Thus, by using the developed variation propagation model, the variations on key product characteristics (KPCs) can be accurately predicted. This enables broad applications of the proposed method in actual manufacturing processes. The results of the case study also validated the proposed model.
Optimization of Wind-Up Tension of Webs Preventing Wrinkles and Slippage
Authors: Hashimoto Hiromu
Published: October 2009

This paper describes the optimization method of wind-up tension to prevent wound roll defects, mainly star defects and slippage, based on the optimum design technique. Hakiel’s nonlinear model with air entrainment effects is applied to analyze in-roll stress distributions in the radial and tangential directions (1987, “Nonlinear Model for Wound Roll Stresses,” Tappi J., 70(5), pp. 113–117). It is well known experimentally that a decrease in the wind-up tension prevents star defects due to negative tangential stress under winding. Thus, in the present optimization method, wind-up tension is gradually decreased in the radial direction to minimize the averaged value of tangential stresses under the constraint of non-negative tangential stresses. Furthermore, the relation of the slippage between wound film layers and in-roll stress of a roll is considered. Successive quadratic programming, which is the typical mathematical programming method, is used as the optimization technique. Wind-up tension is expressed by the third-order spline curve of a radial coordinate. The liner function with respect to the radial coordinate is used as the original wind-up tension. The optimized wind-up tensions are obtained for various winding conditions, and we confirmed that the in-roll stress distributions were very much improved for preventing wrinkles and slippage by the optimization method proposed.
Process Sensitivity Analysis and Resolution Prediction for the Two Photon Polymerization of Micro/Nano Structures
Authors: Uppal Nitin , Shiakolas Panos S.
Published: October 2009

Two photon polymerization (2PP) is a rapid prototyping technique for the fabrication of micro/nano structures from photosensitive polymers. The polymerization process and its resolution depend on the combination of various chemical and physical process parameters. In this research, statistical techniques are employed to evaluate the sensitivity of the 2PP process on the applied laser power, scanning speed, and concentration of photoinitiator. The experiments were performed using the ethoxylated (6) trimethylolpropane triacrylate (SR499-Sartomer) monomer and acyl phosphine oxide (Lucirin TPO-L-BASF) photoinitiator. A design of experiments approach is utilized to evaluate the effect of these process parameters at various set levels on the polymerized width and height. The proposed model is checked for interaction among the process parameters and multiple comparisons are performed to evaluate the statistically significant differences. Also, a detailed discussion of the model verification based on error analysis is performed and presented. A regression model is also developed for the prediction of polymerization resolution and the developed statistical model is experimentally verified. Finally, the developed model and the understanding acquired through the statistical analysis were used for the prototyping of various micro/nano structures.
Deformation Modes in Stainless Steel During Laser Shock Peening
Authors: Zhu Xiangqun , Zhou Ming , Dai Qixun , Cheng Gary J.
Published: October 2009

In order to study the deformation mechanisms during ultrahigh strain rate deformation of face centered cubic metals, laser shock peening of a 304L stainless steel is systematically investigated. Two deformation modes—microtwins and microbands—and their interrelationship during high strain rate deformation are discussed in detail. Transmission electron microscopy and selected area electron diffraction are employed to study the deformation modes. It is found that twinning takes place even when the shock pressure is much less than the critical twinning stress in stainless steels. Theoretical critical twinning stress is not the only criteria to decide the deformation modes of twinning or slip. The formation of twinning and slip can be affected by the factors such as loading profile, loading stress/strain rate, stacking fault energy, grain sizes, and cell substructures. Factors that influence twin-slip transition in shock loading are discussed. The formation of dislocation structure is compared with those predicted using 3D dislocation dynamic simulation.
Modeling of Bubble Expansion-Induced Cell Mechanical Profile in Laser-Assisted Cell Direct Writing
Authors: Wang Wei , Li Gang , Huang Yong
Published: October 2009

Cell damage due to the mechanical impact during laser-assisted cell direct writing has been observed and is a possible hurdle for broad applications of fragile cell direct writing. The objective of this study is to numerically investigate the bubble expansion-induced cell mechanical loading profile in laser-assisted cell direct writing. Some conclusions have been drawn as follows. The cell velocity increases initially and then smoothes out gradually with a constant ejection velocity. Both the cell acceleration and pressure can be very high at the beginning period of bubble expansion and then quickly approach zero in an oscillation manner. A high viscosity can lead to an observable velocity increment at the initial stage, but the ejection velocity decreases. The pressure magnitude decreases when the cell-bubble distance is large, and a larger initial pressure induces a larger cell pressure as expected. This study serves as a foundation to further investigate the cell damage mechanism in laser-assisted cell direct writing to improve the effectiveness and efficiency of cell direct writing techniques.
Development of copper-alloy Matsumoto–Ohtsuka-type vacuum flanges and its application to accelerator beam pipes
Authors: Suetsugu Y. , Shirai M. , Ohtsuka M. , Nishidono T. , Watanabe K. , Suzuki Y. , Tsuchiya M. , Yonemoto A. , Sennyu K. , Hara H.
Published: October 2009

The possibility of employing copper-alloy Matsumoto–Ohtsuka-type flanges in a vacuum beam pipes with complicated apertures for a particle accelerator is experimentally studied. Copper-alloy flanges can mitigate the heating problems arising as a result of high-intensity beams more efficiently than stainless-steel flanges. Baking of beam pipes up to a temperature of 200 °C was acceptable with copper-alloy flanges. Moreover, direct electron-beam welding to a copper beam pipe became available, which made the manufacturing easy. In this study, several beam pipes with copper-alloy flanges were installed in the KEKB B-factory positron ring, and the performance was investigated using the high-intensity beams.
Effects of pulsed sputtering frequency on the uniformity of Al:ZnO’s transparent conductive oxide properties for solar cell applications
Authors: Yang Wonkyun , Joo Junghoon
Published: October 2009

Bipolar pulsed magnetron sputtering is used to deposit Al doped ZnO (AZO) on a glass substrate for a transparent conducting oxide in a solar cell structure. A 5×25in.2 AZO target was sputtered by 50–250kHz bipolar pulsed dc power supply to deposit a 400×400mm2 area by swinging back and forth. Sheet resistance, surface morphology, and optical transmittance were measured at different positions on 16 witness samples (small glass slides) to evaluate uniformity. In the thickness of 800nm, the average value of sheet resistance was 30Ω∕◻ and the average resistivity was 2.1×10−3Ωcm. Transmittance was 50%–80% over the visible range. The nonuniformities of thickness, transmittance, and resistivity in the 400×400mm2 area were 5.8%, 0.8%, and within 9.5%, respectively.
FDA Regulation of Stem Cell–Based Products
Authors: Fink Donald W.
Published: October 2009

Cell self-renewal and the capacity to differentiate into multiple cell types (pluripotency) are biological attributes casting stem cells as attractive candidates for development of therapies targeting indications that involve functional restoration of damaged tissues. In the United States, clinical trials designed to demonstrate the safety and effectiveness of stem cell–based products are regulated by the U.S. Food and Drug Administration (FDA). To ensure that subjects enrolled in a clinical study involving stem cell–based products are not exposed to significant and unreasonable risk, the FDA reviews medical and scientific information that encompasses delineation of product-specific characteristics and preclinical testing to determine whether there is sufficient safety assurance to permit initiation of human clinical studies.
White Phosphorus Is Air-Stable Within a Self-Assembled Tetrahedral Capsule
Authors: Mal Prasenjit , Breiner Boris , Rissanen Kari , Nitschke Jonathan R.
Published: October 2009

Molecular Fire Quencher

Cage-shaped molecular assemblies can regulate the reactivity of smaller molecules trapped within them.

Mal
et al.

(p.
1697
) extend this approach to enable the protection of elemental white phosphorus (P
4
), a substance that rapidly ignites on contact with oxygen. The tetrahedral cages self-assemble in aqueous solution through coordination of six ligands to four iron ions, and efficiently capture phosphorus from a suspension. The water-soluble host-guest constructs were stable in air for at least 4 months, but released intact P
4
rapidly on displacement by added benzene.
Seeing Green and Red in Diatom Genomes
Authors: Dagan Tal , Martin William
Published: October 2009

Diatom genomes contain remnants of both green and red algal genomes, hinting at a complex evolutionary past.
Eradication of Intracellular
Salmonella
enterica
Serovar Typhimurium with a Small-Molecule, Host Cell-Directed Agent
Authors: Chiu Hao-Chieh , Kulp Samuel K. , Soni Shilpa , Wang Dasheng , Gunn John S. , Schlesinger Larry S. , Chen Ching-Shih
Published: October 2009

Eradication of intracellular pathogenic bacteria with host-directed chemical agents has been an anticipated innovation in the treatment of antibiotic-resistant bacteria. We previously synthesized and characterized a novel small-molecule agent, AR-12, that induces autophagy and inhibits the Akt kinase in cancer cells. As both autophagy and the Akt kinase have been shown recently to play roles in the intracellular survival of several intracellular bacteria, including
Salmonella
enterica
serovar Typhimurium, we investigated the effect of AR-12 on the intracellular survival of
S
almonella
serovar Typhimurium in macrophages. Our results show that AR-12 induces autophagy in macrophages, as indicated by increased autophagosome formation, and potently inhibits the survival of serovar Typhimurium in macrophages in association with increased colocalization of intracellular bacteria with autophagosomes. Intracellular bacterial growth was partially rescued in the presence of AR-12 by the short hairpin RNA-mediated knockdown of Beclin-1 or Atg7 in macrophages. Moreover, AR-12 inhibits Akt kinase activity in infected macrophages, which we show to be important for its antibacterial effect as the enforced expression of constitutively activated Akt1 in these cells reverses the AR-12-induced inhibition of intracellular serovar Typhimurium survival. Finally, oral administration of AR-12 at 2.5 mg/kg/day to serovar Typhimurium-infected mice reduced hepatic and splenic bacterial burdens and significantly prolonged survival. These findings show that AR-12 represents a proof of principle that the survival of intracellular bacteria can be suppressed by small-molecule agents that target both innate immunity and host cell factors modulated by bacteria.
In Vitro Activity of Gallium Maltolate against Staphylococci in Logarithmic, Stationary, and Biofilm Growth Phases: Comparison of Conventional and Calorimetric Susceptibility Testing Methods
Authors: Baldoni Daniela , Steinhuber Andrea , Zimmerli Werner , Trampuz Andrej
Published: October 2009

Ga3+is a semimetal element that competes for the iron-binding sites of transporters and enzymes. We investigated the activity of gallium maltolate (GaM), an organic gallium salt with high solubility, against laboratory and clinical strains of methicillin-susceptibleStaphylococcus aureus(MSSA), methicillin-resistantS. aureus(MRSA), methicillin-susceptibleStaphylococcus epidermidis(MSSE), and methicillin-resistantS. epidermidis(MRSE) in logarithmic or stationary phase and in biofilms. The MICs of GaM were higher forS. aureus(375 to 2000 μg/ml) thanS. epidermidis(94 to 200 μg/ml). Minimal biofilm inhibitory concentrations were 3,000 to ≥6,000 μg/ml (S. aureus) and 94 to 3,000 μg/ml (S. epidermidis). In time-kill studies, GaM exhibited a slow and dose-dependent killing, with maximal action at 24 h againstS. aureusof 1.9 log10CFU/ml (MSSA) and 3.3 log10CFU/ml (MRSA) at 3× MIC and 2.9 log10CFU/ml (MSSE) and 4.0 log10CFU/ml (MRSE) againstS. epidermidisat 10× MIC. In calorimetric studies, growth-related heat production was inhibited by GaM at subinhibitory concentrations; and the minimal heat inhibition concentrations were 188 to 4,500 μg/ml (MSSA), 94 to 1,500 μg/ml (MRSA), and 94 to 375 μg/ml (MSSE and MRSE), which correlated well with the MICs. Thus, calorimetry was a fast, accurate, and simple method useful for investigation of antimicrobial activity at subinhibitory concentrations. In conclusion, GaM exhibited activity against staphylococci in different growth phases, including in stationary phase and biofilms, but high concentrations were required. These data support the potential topical use of GaM, including its use for the treatment of wound infections, MRSA decolonization, and coating of implants.
Transcriptomic Profiling of theSaccharomyces cerevisiaeResponse to Quinine Reveals a Glucose Limitation Response Attributable to Drug-Induced Inhibition of Glucose Uptake
Authors: dos Santos Sandra C. , Tenreiro Sandra , Palma Margarida , Becker Jorg , Sá-Correia Isabel
Published: October 2009

Quinine has been employed in the treatment of malaria for centuries and is still used against severePlasmodium falciparummalaria. However, its interactions with the parasite remain poorly understood and subject to debate. In this study, we used theSaccharomyces cerevisiaeeukaryotic model to better understand quinine's mode of action and the mechanisms underlying the cell response to the drug. We obtained a transcriptomic profile of the yeast's early response to quinine, evidencing a marked activation of genes involved in the low-glucose response (e.g.,CAT8,ADR1,MAL33,MTH1, andSNF3). We used a low inhibitory quinine concentration with no detectable effect on plasma membrane function, consistent with the absence of a general nutrient starvation response and suggesting that quinine-induced glucose limitation is a specific response. We have further shown that transport of [14C]glucose is inhibited by quinine, with kinetic data indicating competitive inhibition. Also, tested mutant strains deleted for genes encoding high- and low-affinity hexose transporters (HXT1toHXT5,HXT8, andHXT10) exhibit resistance phenotypes, correlating with reduced levels of quinine accumulation in the mutants examined. These results suggest that the hexose transporters are facilitators of quinine uptake inS. cerevisiae, possibly through a competitive inhibition mechanism. Interestingly,P. falciparumis highly dependent on glucose uptake, which is mediated by the single-copy transporter PfHT1, a protein with high homology to yeast's hexose transporters. We propose that PfHT1 is an interesting candidate quinine target possibly involved in quinine import inP. falciparum, an uptake mechanism postulated in recent studies to occur through a still-unidentified importer(s).
Clindamycin-Induced CovS-Mediated Regulation of the Production of Virulent Exoproteins Streptolysin O, NAD Glycohydrolase, and Streptokinase in
Streptococcus pyogenes
Authors: Minami Masaaki , Kamimura Takuya , Isaka Masanori , Tatsuno Ichiro , Ohta Michio , Hasegawa Tadao
Published: October 2009

The administration of high-dose clindamycin (CLI) along with penicillin is recommended for the treatment of streptococcal toxic shock syndrome. However, the prevalence of CLI-resistant
Streptococcus pyogenes
strains is increasing worldwide, and the effect of CLI on CLI-resistant
S. pyogenes
strains remains unknown. We aimed to evaluate the effect of CLI on the in vitro production of three major virulent exoproteins, namely, streptolysin O (Slo), NAD glycohydrolase (Nga), and streptokinase (Ska), by CLI-resistant
S. pyogenes
strains. After the incubation of M1 serotype CLI-resistant
S. pyogenes
D2TY in the presence of 1 μg/ml CLI, the amounts of Slo, Nga, and Ska and the levels of
slo
,
nga
, and
ska
mRNA in the supernatant were analyzed by Northern blotting and Western blotting, respectively. The results of both assays showed that the production of Slo, Nga, and Ska was higher with CLI treatment than without CLI treatment. We evaluated the role of the sensor kinase CovS, which is involved in the two-component system of
S. pyogenes
, in the CLI-induced production of these three exoproteins. Northern blotting analysis revealed that CLI induced the expression of
covS
mRNA in wild-type strain D2TY. Furthermore, both Northern blotting and Western blotting analyses showed that CLI decreased the levels of expression of Slo, Nga, and Ska in isogenic
covS
mutant D2TYcovS. These results suggest that CLI increases the production of three virulent exoproteins in CLI-resistant
S. pyogenes
strains via the action of CovS.
Mitochondrial DNA Depletion and Respiratory Chain Activity in Primary Human Subcutaneous Adipocytes Treated with Nucleoside Analogue Reverse Transcriptase Inhibitors
Authors: Stankov Metodi V. , Lücke Thomas , Das Anibh M. , Schmidt Reinhold E. , Behrens Georg M. N.
Published: October 2009

Mitochondrial dysfunction as a consequence of mitochondrial DNA (mtDNA) depletion due to therapy with nucleoside analogue reverse transcriptase inhibitors (NRTI) has been proposed as a pathogenic mechanism leading to lipoatrophy in HIV-infected patients. The aim of our study was to investigate the impact of NRTI treatment on mtDNA abundance and the activities of respiratory chain complexes in primary human subcutaneous preadipocytes (phsPA). We studied adipocyte phenotypes, viability, and differentiation (CCAAT/enhancer-binding protein α [C/EBPα] and peroxisome proliferator-activated receptor γ [PPARγ] expression) and adiponectin production, mtDNA content, mitochondrial membrane potential, mitochondrial mass, and respiratory chain enzyme and citrate synthase activities in both proliferating and differentiating phsPA. Cells were exposed to zidovudine (6 μM), stavudine (d4T; 3 μM), and zalcitabine (ddC; 0.1 μM) for 8 weeks. NRTI-induced mtDNA depletion occurred in proliferating and differentiating phsPA after exposure to therapeutic drug concentrations of d4T and ddC. At these concentrations, ddC and d4T led to an almost 50% decrease in the number of mtDNA copies per cell without major impact on adipocyte differentiation. Despite mtDNA depletion by NRTI, the activities of the respiratory chain complexes, the mitochondrial membrane potential, and the mitochondrial mass were found to be unaffected. Severe NRTI-mediated mtDNA depletion in phsPA is not inevitably associated with impaired respiratory chain activity or altered mitochondrial membrane potential.
Prevention and Treatment ofStaphylococcus aureusPneumonia with a β-Cyclodextrin Derivative
Authors: Ragle Brook E. , Karginov Vladimir A. , Bubeck Wardenburg Juliane
Published: October 2009

Staphylococcus aureuspneumonia is a common, potentially life-threatening infection caused by this human pathogen. The only therapies available to treatS. aureuspneumonia are antibiotics, a modality that is jeopardized by the organism's remarkable ability to acquire antimicrobial resistance.S. aureusalpha-hemolysin is a pore-forming cytotoxin that is essential for the pathogenesis of pneumonia. Strains lacking this cytotoxin are avirulent in a murine model of pneumonia; likewise, vaccine-based strategies that antagonize the toxin afford protection against lethal disease. Disruption of the function of this toxin therefore provides a potent mechanism to prevent and/or treatS. aureuspneumonia. β-Cyclodextrin derivatives are small molecules with a sevenfold symmetry that mirrors the heptameric alpha-hemolysin. These compounds block the assembled alpha-hemolysin pore, compromising toxin function. We report that a modified β-cyclodextrin compound, IB201, prevents alpha-hemolysin-induced lysis of human alveolar epithelial cells. This protective effect does not result from the ability of the β-cyclodextrin to impair formation of the oligomeric alpha-hemolysin on the cell surface, supporting a role for this molecule in blockade of the lytic pore. An examination of IB201 in murineS. aureuspneumonia demonstrated that administration of this compound prevents and treats disease, protecting against mortality. Consistent with the vital importance of alpha-hemolysin in pneumonia caused by methicillin-sensitive and highly virulent methicillin-resistantS. aureusstrains, IB201 protects against lethal challenge with both types of isolates. These observations, coupled with a favorable safety profile of β-cyclodextrin compounds, provide a novel strategy that may be developed to combatS. aureuspneumonia.
Global Challenge of Antibiotic-Resistant
Treponema pallidum
Authors: Stamm Lola V.
Published: October 2009

Syphilis is a multistage infectious disease that is usually transmitted through contact with active lesions of a sexual partner or from an infected pregnant woman to her fetus. Despite elimination efforts, syphilis remains endemic in many developing countries and has reemerged in several developed countries, including China, where a widespread epidemic recently occurred. In the absence of a vaccine, syphilis control is largely dependent upon identification of infected individuals and treatment of these individuals and their contacts with antibiotics. Although penicillin is still effective, clinically significant resistance to macrolides, a second-line alternative to penicillin, has emerged. Macrolide-resistant strains of
Treponema pallidum
are now prevalent in several developed countries. An understanding of the genetic basis of
T. pallidum
antibiotic resistance is essential to enable molecular surveillance. This review discusses the genetic basis of
T. pallidum
macrolide resistance and the potential of this spirochete to develop additional antibiotic resistance that could seriously compromise syphilis treatment and control.
The Sca2 Autotransporter Protein from
Rickettsia conorii
Is Sufficient To Mediate Adherence to and Invasion of Cultured Mammalian Cells
Authors: Cardwell Marissa M. , Martinez Juan J.
Published: October 2009

Obligate intracellular bacteria of the genus
Rickettsia
must adhere to and invade the host endothelium in order to establish an infection. These processes require the interaction of rickettsial surface proteins with mammalian host cell receptors. A previous bioinformatic analysis of sequenced rickettsial species identified a family of at least 17 predicted “surface cell antigen” (
sca
) genes whose products resemble autotransporter proteins. Two members of this family, rOmpA and rOmpB of spotted fever group (SFG) rickettsiae have been identified as adhesion and invasion factors, respectively; however, little is known about the putative functions of the other
sca
gene products. An intact
sca2
gene is found in the majority of pathogenic SFG rickettsiae and, due to its sequence conservation among these species, we predict that Sca2 may play an important function at the rickettsial surface. Here we have shown that
sca2
is transcribed and expressed in
Rickettsia conorii
and have used a heterologous gain-of-function assay in
E. coli
to determine the putative role of Sca2. Using this system, we have demonstrated that expression of Sca2 at the outer membrane of nonadherent, noninvasive
E. coli
is sufficient to mediate adherence to and invasion of a panel of mammalian cells, including endothelial cells. Furthermore, soluble Sca2 protein is capable of diminishing
R. conorii
invasion of cultured mammalian cells. This is the first evidence that Sca2 participates in the interaction between SFG rickettsiae and host cells and suggests that in addition to other surface proteins, Sca2 may play a critical role in rickettsial pathogenesis.
Inescapable Need for Neutrophils as Mediators of Cellular Innate Immunity to Acute
Pseudomonas aeruginosa
Pneumonia
Authors: Koh Andrew Y. , Priebe Gregory P. , Ray Christopher , Van Rooijen Nico , Pier Gerald B.
Published: October 2009

Pseudomonas aeruginosa
is a leading cause of pneumonia, and many components of the innate immune system have been proposed to exert important effects in preventing lung infection. However, a vigorous experimental system to identify an overriding, key effector mediating innate immunity to lung infection has not been utilized. As many of the important components of innate immunity are involved in recruitment and activation of polymorphonuclear neutrophils (PMNs) to infected tissues, we hypothesized that the cells and factors needed for their proper recruitment to the lung comprised the major mediators of innate immunity. In neutropenic mice, intranasal (i.n.) doses of
P. aeruginosa
as low as 10 to 100 CFU/mouse produced a fatal lung infection, compared with 10
7
to >10
8
CFU for nonneutropenic mice. There was only a very modest increased mortality in mice lacking mature lymphocytes and no increased mortality in mice depleted of alveolar macrophages when administered i.n.
P. aeruginosa
. Recombinant mouse granulocyte colony-stimulating factor increased survival of neutropenic mice after i.n.
P. aeruginosa
inoculation. MyD88
−/−
mice, which cannot recruit PMNs to the lungs, were highly susceptible to fatal
P. aeruginosa
lung infection, with bacterial doses of <120 CFU being lethal. Activation of a MyD88-independent pathway for PMN recruitment to the lungs in MyD88
−/−
mice resulted in enhanced protection against
P. aeruginosa
lung infection. Overall, in the absence of PMNs, mice cannot resist
P. aeruginosa
lung infection from extremely small bacterial doses. There is an inescapable requirement for local PMN recruitment and activation to mediate innate immunity to
P. aeruginosa
lung infection.
Leptospira interrogans
Binds to Human Cell Surface Receptors Including Proteoglycans
Authors: Breiner Deborah D. , Fahey Mark , Salvador Ryan , Novakova Jana , Coburn Jenifer
Published: October 2009

Leptospirosis is a global public health problem, primarily in the tropical developing world. The pathogenic mechanisms of the causative agents, several members of the genus
Leptospira
, have been underinvestigated. The exception to this trend has been the demonstration of the binding of pathogenic leptospires to the extracellular matrix (ECM) and its components. In this work, interactions of
Leptospira interrogans
bacteria with mammalian cells, rather than the ECM, were examined. The bacteria bound more efficiently to the cells than to the ECM, and a portion of this cell-binding activity was attributable to attachment to glycosaminoglycan (GAG) chains of proteoglycans (PGs). Chondroitin sulfate B PGs appeared to be the primary targets of
L. interrogans
attachment, while heparan sulfate PGs were much less important. Inhibition of GAG/PG-mediated attachment resulted in partial inhibition of bacterial attachment, suggesting that additional receptors for
L. interrogans
await identification. GAG binding may participate in the pathogenesis of leptospirosis within the host animal. In addition, because GAGs are expressed on the luminal aspects of epithelial cells in the proximal tubules of the kidneys, this activity may play a role in targeting the bacteria to this critical site. Because GAGs are shed in the urine, GAG binding may also be important for transmission to new hosts through the environment.
Enterococcus faecalis
Capsular Polysaccharide Serotypes C and D and Their Contributions to Host Innate Immune Evasion
Authors: Thurlow Lance R. , Thomas Vinai Chittezham , Fleming Sherry D. , Hancock Lynn E.
Published: October 2009

It has become increasingly difficult to treat infections caused by
Enterococcus faecalis
due to its high levels of intrinsic and acquired antibiotic resistance. However, few studies have explored the mechanisms that
E. faecalis
employs to circumvent the host innate immune response and establish infection. Capsular polysaccharides are important virulence factors that are associated with innate immune evasion. We demonstrate, using cultured macrophages (RAW 264.7), that capsule-producing
E. faecalis
strains of either serotype C or D are more resistant to complement-mediated opsonophagocytosis than unencapsulated strains. We show that differences in opsonophagocytosis are not due to variations in C3 deposition but are due to the ability of capsule to mask bound C3 from detection on the surface of
E. faecalis
. Similarly,
E. faecalis
capsule masks lipoteichoic acid from detection, which correlates with decreased tumor necrosis factor alpha production by cultured macrophages in the presence of encapsulated strains compared to that in the presence of unencapsulated strains. Our studies confirm the important role of the capsule as a virulence factor of
E. faecalis
and provide several mechanisms by which the presence of the capsule influences evasion of the innate immune response and suggest that the capsule could be a potential target for developing alternative therapies to treat
E. faecalis
infections.
Instantaneous Within-Patient Diversity of
Pseudomonas aeruginosa
Quorum-Sensing Populations from Cystic Fibrosis Lung Infections
Authors: Wilder Cara N. , Allada Gopal , Schuster Martin
Published: October 2009

In the opportunistic pathogen
Pseudomonas aeruginosa
, acyl-homoserine lactone (acyl-HSL) quorum sensing (QS) regulates biofilm formation and expression of many extracellular virulence factors. Curiously, QS-deficient variants, often carrying mutations in the central QS regulator LasR, are frequently isolated from infections, particularly from cystic fibrosis (CF) lung infections. Very little is known about the proportion and diversity of these QS variants in individual infections. Such information is desirable to better understand the selective forces that drive the evolution of QS phenotypes, including social cheating and innate (nonsocial) benefits. To obtain insight into the instantaneous within-patient diversity of QS, we assayed a panel of 135 concurrent
P. aeruginosa
isolates from eight different adult CF patients (9 to 20 isolates per patient) for various QS-controlled phenotypes. Most patients contained complex mixtures of QS-proficient and -deficient isolates. Among all patients, deficiency in individual phenotypes ranged from 0 to about 90%. Acyl-HSL, sequencing, and complementation analyses of variants with global loss-of-function phenotypes revealed dependency upon the central QS circuitry genes
lasR
,
lasI
, and
rhlI
. Deficient and proficient isolates were clonally related, implying evolution from a common ancestor in vivo. Our results show that the diversity of QS types is high within and among patients, suggesting diverse selection pressures in the CF lung. A single selective mechanism, be it of a social or nonsocial nature, is unlikely to account for such heterogeneity. The observed diversity also shows that conclusions about the properties of
P. aeruginosa
QS populations in individual CF infections cannot be drawn from the characterization of one or a few selected isolates.