bluuebunny/crossref_metadata_2025 huggingface dataset:
Relationship of Crack Growth Between Thermal-Mechanical and Isothermal Low-Cycle Fatigue at Elevated Temperatures
Authors: Okazaki Masakazu , Koizumi Takashi
Published: October 2009

The surface and through crack growth behaviors of some steels in thermal-mechanical and isothermal low-cycle fatigue at elevated temperatures were investigated. It was shown that the crack growth rate under each test condition was successfully correlated with the cyclic J-integral range by the simple power law equation, regardless of crack configurations and test controlling modes. Based on the results thus obtained, the relationship between the crack growth rates of the two types of fatigue was discussed. When the crack growth rates in thermal-mechanical and isothermal low-cycle fatigue at elevated temperatures were correlated with the parameter of which the range of cyclic J-integral was divided by the equivalent flow stress defined in this work, they could be represented by a single curve approximately. The crack growth rates in isothermal fatigue under various test temperatures could be also represented by the same single crack growth curve described above, regardless of the test materials. From the above result, it was found that the difference of crack growth rate in both types of fatigue merely resulted from the difference of equivalent flow stress.
Effect of Prior Deformation on the 76-K Fracture Toughness of AISI 304L and AWS 308L Stainless Steels
Authors: Purtscher P. T. , Read D. T.
Published: October 2009

In this study, the effect of service-induced deformation on the toughness of AISI 304L and its weld metal, A WS 308L was determined. Low temperature compressive loading in the laboratory produced larger deformations. Crack initiation toughness, KIC(J), and tearing resistance, dJ/da, at 76 K were evaluated as a function of martensite content, a measure of the deformation in these steels. The results showed that the toughness properties of the 304L decrease gradually as the martensite content increases from the 5 to 8 percent level found in the service condition to the 45 percent level obtained by compressive loading. The decrease was less than that expected on the basis of the increased flow stress. The toughness properties of the 308L weld metal decreased more sharply with increased martensite content than those of the 304L. The sharp decrease is associated with a degradation of the properties of the delta ferrite rather than that of the austenite.
Techniques to Predict Dislocation Generation During Growth of Silicon Ribbon
Authors: Tsai C. T. , Dillon O. W. , De Angelis R. J.
Published: October 2009

This paper describes the numerical techniques that are used to predict stresses, strains, dislocation densities, and buckling during the growth of flat plate silicon. High quality silicon ribbon would be an ideal starting material for manufacturing solar cells for electrical power generation. The techniques developed are uniquely related to the material model that is used which is a generalization of the silicon model reported by Hassen in Germany, Sumino in Japan and their co-workers. The novelty of the model is that it accounts for a changing dislocation density and through this, the plastic strain rate also changes with the dislocation density. The rate of dislocation generation depends on the stresses, temperature as well as the existing dislocation density. The numerical techniques that are discussed incorporate this novel material model in the analysis of the silicon ribbon growing process. This approach requires that the stresses and dislocation density due to a complex thermal field be determined. The details of these techniques are the main feature of this paper.
Crack-Tip-Acuity Effect on Crack Growth Initiation
Authors: Gu Inhoy
Published: October 2009

For a stationary crack of an initially finite root radius in plane-strain tension, the strain fields around the smoothly blunted crack-tip are calculated for each deformation stage using the slipline field method for nonhardening plastic material. The crack growth initiation from the blunt crack-tip in small-scale yielding, with a full triaxiality ahead of the crack-line, is predicted based on the fracture criterion of the fracture strain at a characteristic distance, obtained by applying the criterion to the case of a sharp crack-tip, in which the effect of the initial root radius on the strain distribution can be neglected. The predicted toughness for mild steel is in reasonable agreement with an experiment. For other materials, the observed J-integral value at fracture initiation, consistent with the present analysis, increases linearly with the initial root radius, but its rate shows a large deviation from the model, which is discussed due to the shear band development. The analysis also predicts that the toughness of a cracked low-ductility material does not increase by making the initial crack-root profile round, and that the reduced triaxiality at the crack-tip brings about a toughness increase.
Factors Influencing the Fatigue Behavior of Ferrous Laminates
Authors: Wittenauer J. , Sherby O. D.
Published: October 2009

Laminates based on ultrahigh carbon steel were prepared and found to exhibit enhanced fatigue life as compared to a monolithic reference material. This result was achieved through the insertion of weak interlaminar regions of copper into the layered material during preparation of the laminates. The presence of these regions allowed for the operation of a delamination mechanism in advance of the propagating fatigue crack. The result was interlaminar separation and associated crack blunting. Stress-life curves show that an increase in life by as much as a factor of four is achieved for these materials when compared to monolithic specimens of similar processing history.
Development of a Coal Ash Corrosivity Index for High Temperature Corrosion
Authors: Shigeta Jun-Ichi , Hamao Yoshio , Aoki Hiroshi , Kajigaya Ichiro
Published: October 2009

Current development of Advanced Steam Cycle coal-fired power plants requires superheater and reheater tubing alloys which can withstand severe conditions for high temperature corrosion. A corrosion equation to predict corrosion rates for candidate alloys has been developed by a study of deposits removed from steam generator tubes and from test probes installed in a boiler, supplemented by laboratory studies using synthetic coal ash. The corrosion equation predicts corrosion for a particular coal as a function of its content of sulfur, acid-soluble alkalies, and acid-soluble aklaline earths. Good agreement was obtained between the corrosion equation and 6000-hour tests using probes of TP347H and 17-14 CuMo.
A New Method for Measurement of Residual Axial Stresses Applied to a Multi-Pass Butt-Welded Cylinder
Authors: Cheng Weili , Finnie Iain
Published: October 2009

A method based on fracture mechanics solutions for a circumferential crack is used to measure the distribution of axial residual stresses in the circumferential weld between two cylinders. The case considered is a 22 pass weld and the residual stress is obtained in the form of a Legendre polynomial series. The results are in general agreement with published values for multi-pass welds on similar material. However, the present approach appears to be considerably simpler and easier to implement than existing experimental methods.
Temperature Distribution in a Slab During Hot Rolling
Authors: Karagiozis A. N. , Lenard J. G.
Published: October 2009

The dependence of the temperature distribution during hot rolling of a steel slab on the speed of rolling, reduction and initial temperature is investigated. It is observed that while the center of the slab cools, the surface loses heat at a much higher rate following which significant reheating occurs. Because of that different parts of the slab receive significantly different thermal-mechanical treatments, possibly resulting in a nonhomogeneous product.
Biaxial Low Cycle Fatigue for Notched, Cracked, and Smooth Specimens at High Temperatures
Authors: Sakane Masao , Ohnami Masateru , Hamada Naomi
Published: October 2009

Push-pull and reversed torsion tests were carried out for notched, precracked, and smooth hollow cylindrical specimens of type 304 stainless steel at 923K in air. This paper describes the crack direction in the three types of specimens and the parameter that correlates the biaxial low cycle fatigue failure data. All types of specimens, except the smooth specimen in the reversed torsion test, failed by mode I cracking. Failure life of the specimens was discussed in connection with the crack mode. The equivalent stress based on COD could correlate the biaxial fatigue data whereas the Mises’ equivalent stress and the maximum principal stress could not.
Modelling Stiffness Loss in Quasi-Isotropic Laminates Due to Microstructural Damage
Authors: Harris C. E. , Allen D. H. , Nottorf E. W. , Groves S. E.
Published: October 2009

Continuous fiber laminated composites are known to undergo substantial load induced damage in the form of matrix cracking, interior delamination, fiber fracture, etc. These damage modes produce significant losses in component performance measures such as stiffness, residual strength, and life. The authors have previously constructed a general model for predicting the response of laminated composites with damage. The current paper utilizes the model to predict stiffness loss as a function of damage in quasi-isotropic and angle-ply laminates with matrix cracks. It is shown that the model is capable of predicting the stiffness loss for any layup by utilizing the same input data, thus producing a model which is independent of stacking sequence. The favorable comparisons of the model to experimental results reported herein support the validity of the model.
Load Interaction Effects on Compression Fatigue Crack Growth in Ductile Solids
Authors: Aswath P. B. , Suresh S. , Holm D. K. , Blom A. F.
Published: October 2009

The influence of the very first compression cycle on subsequent Mode I crack growth in notched plates of ductile solids subject to fully compressive cyclic loads has been examined in this work. Whereas stable crack growth occurs from the root of the notch over hundreds of thousands of compression cycles, the amplitude of the very first compression cycle is found to have a decisive effect on the total distance of crack advance. Specifically, a three-fold increase in the stress amplitude during the first compression cycle alone leads to more than a ten-fold increase in the total distance of crack growth during subsequent cycles. Finite element calculations of the crack closure stress levels during cyclic compression are in concurrence with the experimental results of closure stresses (measured from changes in compliance) for a lower strength steel. A brief discussion is also presented of the effects of periodic compressive overloads on crack growth behavior under far-field cyclic compression.
New Measuring Method of Three-Dimensional Residual Stresses in Long Welded Joints Using Inherent Strains as Parameters—Lz Method
Authors: Ueda Yukio , Fukuda Keiji
Published: October 2009

In this paper, a new measuring method of three-dimensional residual stresses induced in a butt welded joint is presented. The proposed method is based on a general approach developed by the authors, in which inherent strains (the source of residual stresses) are dealt with as parameters. In the present report, three-dimensional residual stresses in a long body, in which the residual stress distribution is uniform in longitudinal direction, is considered as a special case. It is shown that the measurement of the three-dimensional residual stress, in this case, can be reduced to a combination of two sets of measurements of two-dimensional residual stresses. This method is applied to determine the residual stresses in an actual welded joint and its reliability and practicability are also demonstrated.
The Effect of Several Finishing Processes on the Fatigue Resistance of Hole Surfaces
Authors: Lai M. O. , Nee A. Y. C.
Published: October 2009

This investigation examines the effects of different finishing processes on the fatigue life of premachined holes in Assab 760 steel plates. The finishing processes studied were reaming, ballizing, and emery polishing. A general decrease in fatigue life with increase in surface roughness is observed for all the processes employed. In comparing the different processes, for a constant surface roughness, polishing is generally found to give the longest fatigue life while ballizing, in spite of the greater compressive residual stresses induced on the surface of the finished hole, the shortest. The surprising phenomenon was found to be attributed to the amount of plastic deformation occurred before fatigue loading. For Assab 760 steel, a prestrain in the radial direction of less than about 2.5 percent appeared to reduce the fatigue resistance of the material.
On the Mechanics of Microcracking in Fiber Composite Laminates Under Combined Stress
Authors: Swanson S. R.
Published: October 2009

The formation of matrix microcracks in fiber composite laminates has been widely observed. The present paper addresses the mechanics of this microcracking by means of a shear lag model in conjunction with a Weibull failure criterion for further cracking. This shear lag model considers both shear loading as well as cross-fiber tension in the cracked ply. The reduction in inplane shear and tensile modulus of the cracked ply is computed directly from the model. The increase in applied load required to produce new cracks is computed and shows general agreement with previous experimental results. A general approximate relationship between the applied strain levels and the modulus reduction is presented.
Extensive Theory of Force-Approach Relations of Elastic Spheres in Compression and in Impact
Authors: Tatara Yoichi
Published: October 2009

The prevailing Hertz theory in contact and in impact is based on the total compressive displacement of a semi-infinite elastic body. This paper considers displacements of finite elastic medium in each of elastic spheres and presents analytically extensive force-approach relations of the Hertz theory for two elastic spheres in statical compression and in impact. In the statical conditions, expansive displacements of the mutual surf ace of contact due to compressive displacements by the reactions, which act on the opposite surfaces in a distance equal to each diameter, are considered analytically in two approximate cases. The force-approach relations obtained here are much closer than the Hertz’s one in a wide range of deformations to one experimental result carried out for one rubber sphere. In impact, it is considered that relative position of each center of mass of the impacting spheres accompanying asymmetrical deformations is shifted from the initial position. The force-approach relation has another extensive term different from the Hertz’s relation and from the above relations in the statical conditions. In the case of very small deformations for hard spheres, the extensive terms can be neglected and the Hertz theory is valid in compression and in impact. The present force-approach relations can be applicable to the cases of large deformations in compression and in impact.
Slow Strain Rate Fracture Characteristics of Steel and Aluminum Alloys Tested in Mercury Environments
Authors: Krupowicz J. J.
Published: October 2009

Slow strain rate tensile tests performed on Type 304 stainless steel, A516 Grade 70 C-Mn steel, and aluminum alloy 5083 revealed that all three materials were susceptible to varying degrees of mercury liquid metal embrittlement (LME) at ambient conditions. Both Type 304 stainless and A516 Grade 70 C-Mn steels exhibited significant strain rate sensitivity to LME, while aluminum alloy 5083 embrittlement was independent of strain rate over the range tested (8.3 × 10−3 to 5.0 × 10−7 s−1). Ductility (reduction in area) and toughness losses for tests in mercury compared to respective tests in air indicated that aluminum alloy 5083 embrittlement was more acute than either steel. Crack arrest (secondary cracking) characteristics and reactions to different mercury species also suggested that Type 304 stainless and A516 Grade 70 C-Mn steels were less susceptible to mercury LME than aluminum alloy 5083.
Crack Instability in Pipes Containing Internal Surface Flaw
Authors: Rajab M. D. , Zahoor A.
Published: October 2009

Crack associated pipe axial displacement and tearing modulus solutions are derived for pipes containing internal circumferential part-through wall surface flaw under axial tension loading. The tearing modulus solution is derived for both load control and displacement control loadings. The solutions are useful for practical applications involving contained yielding in the crack section. The analytical solutions can be readily applied to pipe radius-to-thickness ratio ranging from 5 to 20. A sensitivity study was performed to assess the influence of flaw size, pipe radius and wall thickness, pipe length, and axial tension load on the applied tearing modulus. Numerical results are presented for critical stress as a function of flaw size for 4130 carbon steel pipe.
Ultrasonic Wave Considerations for the Development of an NDE Feature Matrix for Anisotropic Media
Authors: Rose J. L. , Pilarski A. , Balasubramaniam K. , Tverdokhlebov A. , Ditri J.
Published: October 2009

The problem of ultrasonic surface and bulk wave propagation in an anisotropic media and/or a composite material is addressed so that applications in Nondestructive Evaluation can be considered, emphasis in this paper being placed on bulk wave propagation. Global material property determination is considered in an inverse wave velocity computation of stiffness coefficients based on principles of anisotropic elasticity. A one-sided inspection technique based on practical considerations of a field environment is developed. The concept of a feature matrix, based on the stiffness coefficients, is then introduced as a means of both material characterization and defect analysis in composite materials. A brief discussion on a test protocol and an interpretation of the elements in the feature matrix from an NDE point of view is also presented. The conclusions of a previous theoretical investigation of wave propagation in anisotropic media are considered from an experimental point of view by way of the bulk wave technique. A result of fundamental value is that the actual propagation of quasilongitudinal waves, generated by a standard broad band pulsed transducer, is indeed well matched with the theoretical approximation obtained earlier. This approximation was based on the generalized retarded potential principle with variable energy velocity of the quasilongitudinal mode in an anisotropic medium as the substitute for the constant longitudinal velocity used in the retarded potential scheme for an isotropic medium.
Effects of Amplitude-History and Temperature-History on Multiaxial Cyclic Behavior of Type 316 Stainless Steel
Authors: Murakami S. , Kawai M. , Ohmi Y.
Published: October 2009

The effects of the history in strain-amplitude and temperature variation on the multiaxial cyclic behavior of type 316 stainless steel were discussed by performing a series of total-strain controlled cyclic tests under uniaxial tension-compression and circular strain paths. Constant strain rate of 0.2 percent/min was specified throughout the tests. The effects of strain amplitude history were examined by changing the strain amplitude between 0.2 percent and 0.4 percent (step-up and step-down tests) at room temperature, 400°C and 600°C. For temperature history dependence tests, the temperature was changed between 200°C and 600°C, 400°C and 600°C, 500°C and 600°C, by specifying a constant strain amplitude of 0.3 percent. It was observed that for the step-up change in strain amplitude the prior cycle showed apparently no influence on the subsequent cyclic accommodation for the uniaxial and the multiaxial cycles at room temperature, 400°C and 600°C. For the decrease in strain amplitude, however, the definite effect of the prior cycle was observed at 400°C, while at higher temperature it disappeared. The effect of the temperature history, on the other hand, appeared only in the case of the temperature-decrease during the uniaxial cycle.
Fracture Mechanics Applied to Elevated Temperature Crack Growth
Authors: Jordan E. H. , Meyers G. J.
Published: October 2009

Twenty-six isothermal crack growth tests were performed on Hastelloy-X tubular specimens at a variety of temperatures and strain ranges. Conditions were selected to include nominally elastic and nominally plastic conditions. A number of parameters including the stress intensity factor, strain intensity factor, J-integral, Crack Opening Displacement, and Tompkins model were examined for their ability to correlate the data. Test conditions were selected such that growth rates at a single value of the parameter were obtained at radically different crack lengths, thus exploring the geometry independence of the correlating parameter. None of the parameters were fully satisfactory. However, COD calculated from J-integral appeared to be the most successful.
A Contact Model of Nominally Flat Rough Surfaces Based on a Visco-Elasto-Adhesive Interaction
Authors: Cheng W. , Farhang K.
Published: October 2009

Approximate closed-form equations are derived for normal contact force between nominally flat rough surfaces in dry contact. The formulation is based on the asperity-level interaction in which adhesive forces between two asperities and elastic and rate-dependent forces are included. The elastic and time rate-dependent portion of force is derived using a viscoelastic interaction of the two asperities. Statistical consideration of rough surfaces then furnishes the mathematical formulation of total normal force due to adhesion, elastic, and rate-dependent properties of the solids in contact. The probabilistic formulation of contact force leads to integral equations. From these are derived approximate closed-form expressions that relate the microscale properties of the surfaces to the macroscale behavior in the form of the total normal contact force between the surfaces. The approximate equations for visco-elasto-adhesive contact of rough surfaces illustrate the dependence of the contact force on the time rate of approach based on a combination of 1/6, 1/3, and 1 power laws.
Mechanisms of Acute Angle Laser Drilling Induced Thermal Barrier Coating Delamination
Authors: Sezer H. K. , Li L.
Published: October 2009

Laser fabrication of cooling holes in certain parts of the aero-engine components involves percussion or trepan drilling at acute angles (e.g., 16–30 deg) to the surface. These parts are often covered with plasma sprayed ceramic thermal barrier coatings (TBCs) to protect them from reaching excessive temperatures in hot engine environments. Delamination of the TBC is the main problem of laser drilling acute angled holes in the coated components. The present study investigates the mechanisms involved in the development of the delamination cracks. A significant role of melt ejection in the formation of cracks and the delamination at the coating/coating interface of the leading edge of a laser-drilled inclined hole was identified. It is shown that the delamination mechanisms at the TBC coating/bond coating and the bond coating/substrate interfaces are different. Melt ejection induced stresses were identified as the key mechanisms for the former type, while the thermal effects dominates the latter type.
A New Method for Identification and Modeling of Process Damping in Machining
Authors: Budak E. , Tunc L. T.
Published: October 2009

Although process damping has a strong effect on cutting dynamics and stability, it has been mostly ignored in chatter analysis as there is no practical model for estimation of the damping coefficient and very limited data are available. This is mainly because of the fact that complicated test setups were used in order to measure the damping force in the past. In this study, a practical identification and modeling method for the process damping is presented. In this approach, the process damping is identified directly from the chatter tests using experimental and analytical stability limits. Once the process damping coefficient is identified, it is related to the instantaneous indentation volume by a coefficient which can be used for different cutting conditions and tool geometries. In determining the indentation coefficient, chatter test results, energy, and tool indentation geometry analyses are used. The determined coefficients are then used for the stability limit and process damping prediction in different cases, and verified using time-domain simulations and experimental results. The presented method can be used to determine chatter-free cutting depths under the influence of process damping for increased productivity.
Bacterial Strain-to-Strain Variation in Pharmacodynamic Index Magnitude, a Hitherto Unconsidered Factor in Establishing Antibiotic Clinical Breakpoints
Authors: MacGowan Alasdair P. , Reynolds Rosy , Noel Alan R. , Bowker Karen E.
Published: October 2009

Antibiotic pharmacodynamic modeling allows variations in pathogen susceptibility and human pharmacokinetics to be accounted for when considering antibiotic doses, potential bacterial pathogen targets for therapy, and clinical susceptibility breakpoints. Variation in the pharmacodynamic index (area-under-the-concentration curve to 24 h [AUC
24
]/MIC; maximum serum concentration of drug in the serum/MIC; time the serum concentration remains higher than the MIC [
T
> MIC]) is not usually considered. In an in vitro pharmacokinetic model of infection using a dose-ranging design, we established the relationship between AUC
24
/MIC and the antibacterial effect for moxifloxacin against 10 strains of
Staphylococcus aureus
. The distributions of AUC
24
/MIC targets for 24-h bacteriostatic effect and 1-log, 2-log, and 3-log drops in bacterial counts were used to calculate potential clinical breakpoint values, and these were compared with those obtained by the more conventional approach of taking a single AUC
24
/MIC target. Consideration of the AUC
24
/MIC as a distribution rather than a single value resulted in a lower clinical breakpoint.
In Vitro Pharmacodynamics of Levofloxacin and Other Aerosolized Antibiotics under Multiple Conditions Relevant to Chronic Pulmonary Infection in Cystic Fibrosis
Authors: King Paula , Lomovskaya Olga , Griffith David C. , Burns Jane L. , Dudley Michael N.
Published: October 2009

The inhalational administration of antibiotics can provide high concentrations locally in the lungs of cystic fibrosis patients and, thus, can be useful for the treatment of chronic bacterial infections. The present study evaluated the in vitro activities of levofloxacin, ciprofloxacin, tobramycin, amikacin, and aztreonam against clinical isolates of
Pseudomonas aeruginosa
,
Burkholderia cepacia
complex,
Stenotrophomonas maltophilia
,
Alcaligenes xylosoxidans
, and
Staphylococcus aureus
from cystic fibrosis patients. Levofloxacin was the most potent antibiotic against all cystic fibrosis isolates tested, with MIC
90
s ranging from 8 to 32 μg/ml. Levofloxacin was more potent than the aminoglycosides and aztreonam against
P. aeruginosa
biofilms. Time-kill assays with drug concentrations achievable in sputum following aerosol administration showed that levofloxacin had the most rapid rate of killing among mucoid and nonmucoid isolates of
P. aeruginosa
. In contrast to tobramycin, the bactericidal activity of levofloxacin was not affected by sputum from cystic fibrosis patients. The results of the study show that the high concentrations of levofloxacin readily achievable in the lung following aerosol delivery may be useful for the management of pulmonary infections in patients with cystic fibrosis.
Effects of Subinhibitory Concentrations of Antibiotics on Colonization Factor Expression by Moxifloxacin-Susceptible and Moxifloxacin-Resistant
Clostridium difficile
Strains
Authors: Denève Cécile , Bouttier Sylvie , Dupuy Bruno , Barbut Frédéric , Collignon Anne , Janoir Claire
Published: October 2009

Recent outbreaks of
Clostridium difficile
infection have been related to the emergence of the NAP1/027 epidemic strain. This strain demonstrates increased virulence and resistance to the C-8-methoxyfluoroquinolones gatifloxacin and moxifloxacin. These antibiotics have been implicated as major
C. difficile
infection-inducing agents. We investigated by real-time reverse transcription-PCR the impact of subinhibitory concentrations of ampicillin, clindamycin, ofloxacin, and moxifloxacin on the expression of genes encoding three colonization factors, the protease Cwp84, the high-molecular-weight S-layer protein, and the fibronectin-binding protein Fbp68. We have previously shown in six non-NAP1/027 moxifloxacin-susceptible strains that the presence of ampicillin or clindamycin induced an upregulation of these genes, whereas the presence of fluoroquinolones did not. The objective of this study was to analyze the expression of these genes under the same conditions in four NAP1/027 strains, one moxifloxacin susceptible and three moxifloxacin resistant. Two in vitro-selected moxifloxacin-resistant mutants were also analyzed. Moxifloxacin resistance was associated with the Thr82→Ile substitution in GyrA in all but one of the moxifloxacin-resistant strains. The expression of
cwp84
and
slpA
was strongly increased after culture with ampicillin or clindamycin in NAP1/027 strains. Interestingly, after culture with fluoroquinolones, the expression of
cwp84
and
slpA
was only increased in four moxifloxacin-resistant strains, including the NAP1/027 strains and one of the in vitro-selected mutants. The overexpression of
cwp84
was correlated with increased production of the protease Cwp84. The historical NAP1/027 moxifloxacin-susceptible strain and its mutant appear to be differently regulated by fluoroquinolones. Overall, fluoroquinolones appear to favor the expression of some colonization factor-encoding genes in resistant
C. difficile
strains. The fluoroquinolone resistance of the NAP1/027 epidemic strains could be considered an ecological advantage. This could also increase their colonization fitness and promote the infection.
New Small-Molecule Inhibitor Class Targeting Human Immunodeficiency Virus Type 1 Virion Maturation
Authors: Blair Wade S. , Cao Joan , Fok-Seang Juin , Griffin Paul , Isaacson Jason , Jackson R. Lynn , Murray Edward , Patick Amy K. , Peng Qinghai , Perros Manos , Pickford Chris , Wu Hua , Butler Scott L.
Published: October 2009

A new small-molecule inhibitor class that targets virion maturation was identified from a human immunodeficiency virus type 1 (HIV-1) antiviral screen. PF-46396, a representative molecule, exhibits antiviral activity against HIV-1 laboratory strains and clinical isolates in T-cell lines and peripheral blood mononuclear cells (PBMCs). PF-46396 specifically inhibits the processing of capsid (CA)/spacer peptide 1 (SP1) (p25), resulting in the accumulation of CA/SP1 (p25) precursor proteins and blocked maturation of the viral core particle. Viral variants resistant to PF-46396 contain a single amino acid substitution in HIV-1 CA sequences (CAI201V), distal to the CA/SP1 cleavage site in the primary structure, which we demonstrate is sufficient to confer significant resistance to PF-46396 and 3-
O
-(3′,3′-dimethylsuccinyl) betulinic acid (DSB), a previously described maturation inhibitor. Conversely, a single amino substitution in SP1 (SP1A1V), which was previously associated with DSB in vitro resistance, was sufficient to confer resistance to DSB and PF-46396. Further, the CAI201V substitution restored CA/SP1 processing in HIV-1-infected cells treated with PF-46396 or DSB. Our results demonstrate that PF-46396 acts through a mechanism that is similar to DSB to inhibit the maturation of HIV-1 virions. To our knowledge, PF-46396 represents the first small-molecule HIV-1 maturation inhibitor that is distinct in chemical class from betulinic acid-derived maturation inhibitors (e.g., DSB), demonstrating that molecules of diverse chemical classes can inhibit this mechanism.
Mutations in Ribosomal Protein L3 Are Associated with Oxazolidinone Resistance in Staphylococci of Clinical Origin
Authors: Locke Jeffrey B. , Hilgers Mark , Shaw Karen Joy
Published: October 2009

Following recent reports of ribosomal protein L3 mutations in laboratory-derived linezolid-resistant (LZD
r
)
Staphylococcus aureus
, we investigated whether similar mutations were present in LZD
r
staphylococci of clinical origin. Sequence analysis of a variety of LZD
r
isolates revealed two L3 mutations, ΔSer145 (
S. aureus
NRS127) and Ala157Arg (
Staphylococcus epidermidis
1653059), both occurring proximal to the oxazolidinone binding site in the peptidyl transferase center. The oxazolidinone torezolid maintained a ≥8-fold potency advantage over linezolid for both strains.
Phenotypic and Genotypic Characterization of
Enterobacteriaceae
with Decreased Susceptibility to Carbapenems: Results from Large Hospital-Based Surveillance Studies in China
Authors: Yang Qiwen , Wang Hui , Sun Hongli , Chen Hongbin , Xu Yingchun , Chen Minjun
Published: October 2009

The resistance mechanism of 49
Enterobacteriaceae
isolates with decreased susceptibility to carbapenems collected from 2004 to 2008 at 16 teaching hospitals in China was investigated. Moderate- to high-level carbapenem resistance in most isolates was more closely associated with loss or decreased expression of both major porins combined with production of AmpC or extended-spectrum β-lactamase enzymes, while KPC-2, IMP-4, and IMP-8 carbapenemase production may lead to a low to moderate level of carbapenem resistance in
Enterobacteriaceae
in China.
Development of a Test System To Evaluate Procedures for Decontamination of Respirators Containing Viral Droplets
Authors: Vo Evanly , Rengasamy Samy , Shaffer Ronald
Published: October 2009

The aim of this study was to develop a test system to evaluate the effectiveness of procedures for decontamination of respirators contaminated with viral droplets. MS2 coliphage was used as a surrogate for pathogenic viruses. A viral droplet test system was constructed, and the size distribution of viral droplets loaded directly onto respirators was characterized using an aerodynamic particle sizer. The sizes ranged from 0.5 to 15 μm, and the sizes of the majority of the droplets were the range from 0.74 to 3.5 μm. The results also showed that the droplet test system generated similar droplet concentrations (particle counts) at different respirator locations. The test system was validated by studying the relative efficiencies of decontamination of sodium hypochlorite (bleach) and UV irradiation with droplets containing MS2 virus on filtering facepiece respirators. It was hypothesized that more potent decontamination treatments would result in corresponding larger decreases in the number of viable viruses recovered from the respirators. Sodium hypochlorite doses of 2.75 to 5.50 mg/liter with a 10-min decontamination period resulted in approximately 3- to 4-log reductions in the level of MS2 coliphage. When higher sodium hypochlorite doses (≥8.25 mg/liter) were used with the same contact time that was used for the dilute solutions containing 2.75 to 5.50 mg/liter, all MS2 was inactivated. For UV decontamination at a wavelength of 254 nm, an approximately 3-log reduction in the level of MS2 virus was achieved with dose of 4.32 J/cm
2
(3 h of contact time with a UV intensity of 0.4 mW/cm
2
), while with higher doses of UV irradiation (≥7.20 J/cm
2
; UV intensity, 0.4 mW/cm
2
; contact times, ≥5 h), all MS2 was inactivated. These findings may lead to development of a standard method to test decontamination of respirators challenged by viral droplets.
Glycoprofiling Bifidobacterial Consumption of Galacto-Oligosaccharides by Mass Spectrometry Reveals Strain-Specific, Preferential Consumption of Glycans
Authors: Barboza Mariana , Sela David A. , Pirim Claire , LoCascio Riccardo G. , Freeman Samara L. , German J. Bruce , Mills David A. , Lebrilla Carlito B.
Published: October 2009

Galacto-oligosaccharides (GOS) are versatile food ingredients that possess prebiotic properties. However, at present there is a lack of precise analytical methods to demonstrate specific GOS consumption by bifidobacteria. To better understand the role of GOS as prebiotics, purified GOS (pGOS) without disaccharides and monosaccharides was prepared and used in bacterial fermentation experiments. Growth curves showed that all bifidobacteria assayed utilized and grew on pGOS preparations. We used a novel mass spectrometry approach involving matrix-assisted laser desorption ionization-Fourier transform ion cyclotron resonance (MALDI-FTICR) to determine the composition of oligosaccharides in GOS syrup preparations. MALDI-FTICR analysis of spent fermentation media demonstrated that there was preferential consumption of selected pGOS species by different bifidobacteria. The approach described here demonstrates that MALDI-FTICR is a rapid-throughput tool for comprehensive profiling of oligosaccharides in GOS mixtures. In addition, the selective consumption of certain GOS species by different bifidobacteria suggests a means for targeting prebiotics to enrich select bifidobacterial species.
Longitudinal Characterization of Resistant
Escherichia coli
in Fecal Deposits from Cattle Fed Subtherapeutic Levels of Antimicrobials
Authors: Alexander T. W. , Reuter T. , Sharma R. , Yanke L. J. , Topp E. , McAllister T. A.
Published: October 2009

Model fecal deposits from cattle fed or not fed antimicrobial growth promoters were examined over 175 days in the field for growth and persistence of total
Escherichia coli
and numbers and proportions of ampicillin-resistant (Amp
r
) and tetracycline-resistant (Tet
r
)
E. coli
. In addition, genotypic diversity and the frequency of genetic determinants encoded by Amp
r
and Tet
r
E. coli
were investigated. Cattle were fed diets containing chlortetracycline (44 ppm; A44 treatment group), chlortetracycline plus sulfamethazine (both at 44 ppm; AS700 treatment group), or no antibiotics (control). Fecal deposits were sampled 12 times over 175 days. Numbers of Tet
r
E. coli
in A44 and AS700 deposits were higher (
P
< 0.001) than those of controls and represented up to 35.6% and 20.2% of total
E. coli
, respectively. A time-by-treatment interaction (
P
< 0.001) was observed for the numbers of Tet
r
and Amp
r
E. coli.
Except for Amp
r
E. coli
in control deposits, all
E. coli
numbers increased (
P
< 0.001) in deposits up to day 56. Even after 175 days, high Tet
r
E. coli
numbers were detected in A44 and AS700 deposits [5.9 log
10
CFU (g dry matter)
−
1
and 5.4 log
10
CFU (g dry matter)
−
1
, respectively].
E. coli
genotypes, as determined by pulsed-field gel electrophoresis, were diverse and were influenced by the antimicrobial growth promoter and the sampling time. Of the determinants screened,
bla
TEM1
,
tetA
,
tetB
,
tetC
,
sul1
, and
sul2
were frequently detected. Occurrence of determinants was influenced by the feeding of antimicrobials. Fecal deposits remain a source of resistant
E. coli
even after a considerable period of environmental exposure.
Distribution and Diversity of Archaeal and Bacterial Ammonia Oxidizers in Salt Marsh Sediments
Authors: Moin Nicole S. , Nelson Katelyn A. , Bush Alexander , Bernhard Anne E.
Published: October 2009

Diversity and abundance of ammonia-oxidizing
Betaproteobacteria
(β-AOB) and archaea (AOA) were investigated in a New England salt marsh at sites dominated by short or tall
Spartina alterniflora
(SAS and SAT sites, respectively) or
Spartina patens
(SP site). AOA
amoA
gene richness was higher than β-AOB
amoA
richness at SAT and SP, but AOA and β-AOB richness were similar at SAS. β-AOB
amoA
clone libraries were composed exclusively of
Nitrosospira
-like
amoA
genes. AOA
amoA
genes at SAT and SP were equally distributed between the water column/sediment and soil/sediment clades, while AOA
amoA
sequences at SAS were primarily affiliated with the water column/sediment clade. At all three site types, AOA were always more abundant than β-AOB based on quantitative PCR of
amoA
genes. At some sites, we detected 10
9
AOA
amoA
gene copies g of sediment
−1
. Ratios of AOA to β-AOB varied over 2 orders of magnitude among sites and sampling dates. Nevertheless, abundances of AOA and β-AOB
amoA
genes were highly correlated. Abundance of 16S rRNA genes affiliated with
Nitrosopumilus maritimus
,
Crenarchaeota
group I.1b, and pSL12 were positively correlated with AOA
amoA
abundance, but ratios of
amoA
to 16S rRNA genes varied among sites. We also observed a significant effect of pH on AOA abundance and a significant salinity effect on both AOA and β-ΑΟΒ abundance. Our results expand the distribution of AOA to salt marshes, and the high numbers of AOA at some sites suggest that salt marsh sediments serve as an important habitat for AOA.
Impact of an 8-Year-Old Transgenic Poplar Plantation on the Ectomycorrhizal Fungal Community
Authors: Stefani Franck O. P. , Moncalvo Jean-Marc , Séguin Armand , Bérubé Jean A. , Hamelin Richard C.
Published: October 2009

The long-term impact of field-deployed genetically modified trees on soil mutualistic organisms is not well known. This study aimed at evaluating the impact of poplars transformed with a binary vector containing the selectable
nptII
marker and β-glucuronidase reporter genes on ectomycorrhizal (EM) fungi 8 years after field deployment. We generated 2,229 fungal internal transcribed spacer (ITS) PCR products from 1,150 EM root tips and 1,079 fungal soil clones obtained from the organic and mineral soil horizons within the rhizosphere of three control and three transformed poplars. Fifty EM fungal operational taxonomic units were identified from the 1,706 EM fungal ITS amplicons retrieved. Rarefaction curves from both the root tips and soil clones were close to saturation, indicating that most of the EM species present were recovered. Based on qualitative and/or quantitative α- and β-diversity measurements, statistical analyses did not reveal significant differences between EM fungal communities associated with transformed poplars and the untransformed controls. However, EM communities recovered from the root tips and soil cloning analyses differed significantly from each other. We found no evidence of difference in the EM fungal community structure linked to the long-term presence of the transgenic poplars studied, and we showed that coupling root tip analysis with a soil DNA cloning strategy is a complementary approach to better document EM fungal diversity.
Functional Tomographic Fluorescence Imaging of pH Microenvironments in Microbial Biofilms by Use of Silica Nanoparticle Sensors
Authors: Hidalgo Gabriela , Burns Andrew , Herz Erik , Hay Anthony G. , Houston Paul L. , Wiesner Ulrich , Lion Leonard W.
Published: October 2009

Attached bacterial communities can generate three-dimensional (3D) physicochemical gradients that create microenvironments where local conditions are substantially different from those in the surrounding solution. Given their ubiquity in nature and their impacts on issues ranging from water quality to human health, better tools for understanding biofilms and the gradients they create are needed. Here we demonstrate the use of functional tomographic imaging via confocal fluorescence microscopy of ratiometric core-shell silica nanoparticle sensors (C dot sensors) to study the morphology and temporal evolution of pH microenvironments in axenic
Escherichia coli
PHL628 and mixed-culture wastewater biofilms. Testing of 70-, 30-, and 10-nm-diameter sensor particles reveals a critical size for homogeneous biofilm staining, with only the 10-nm-diameter particles capable of successfully generating high-resolution maps of biofilm pH and distinct local heterogeneities. Our measurements revealed pH values that ranged from 5 to >7, confirming the heterogeneity of the pH profiles within these biofilms. pH was also analyzed following glucose addition to both suspended and attached cultures. In both cases, the pH became more acidic, likely due to glucose metabolism causing the release of tricarboxylic acid cycle acids and CO
2
. These studies demonstrate that the combination of 3D functional fluorescence imaging with well-designed nanoparticle sensors provides a powerful tool for in situ characterization of chemical microenvironments in complex biofilms.
Novel Electrochemically Active Bacterium Phylogenetically Related to
Arcobacter butzleri
, Isolated from a Microbial Fuel Cell
Authors: Fedorovich Viatcheslav , Knighton Matthew C. , Pagaling Eulyn , Ward F. Bruce , Free Andrew , Goryanin Igor
Published: October 2009

Exoelectrogenic bacteria are organisms that can transfer electrons to extracellular insoluble electron acceptors and have the potential to be used in devices such as microbial fuel cells (MFCs). Currently, exoelectrogens have been identified in the
Alpha
-,
Beta
-,
Gamma
- and
Deltaproteobacteria
, as well as in the
Firmicutes
and
Acidobacteria
. Here, we describe use of culture-independent methods to identify two members of the genus
Arcobacter
in the
Epsilon
p
roteobacteria
that are selectively enriched in an acetate-fed MFC. One of these organisms,
Arcobacter butzleri
strain ED-1, associates with the electrode and rapidly generates a strong electronegative potential as a pure culture when it is supplied with acetate. A mixed-community MFC in which ∼90% of the population is comprised of the two
Arcobacter
species generates a maximal power density of 296 mW/liter. This demonstration of exoelectrogenesis by strain ED-1 is the first time that this property has been shown for members of this genus.
Long-Term Survival of
Campylobacter jejuni
at Low Temperatures Is Dependent on Polynucleotide Phosphorylase Activity
Authors: Haddad Nabila , Burns Christopher M. , Bolla Jean Michel , Prévost Hervé , Fédérighi Michel , Drider Djamel , Cappelier Jean Michel
Published: October 2009

Campylobacter jejuni
is a leading cause of bacterial gastroenteritis worldwide. Infection generally occurs after ingestion of contaminated poultry products, usually conserved at low temperatures. The mechanisms promoting survival of
C. jejuni
in the cold remain poorly understood despite several investigations. The present study provides insight into the survival mechanism by establishing the involvement of polynucleotide phosphorylase (PNPase), a 3′-5′ exoribonuclease with multiple biological functions in cold survival. The role of PNPase was demonstrated genetically using strains with altered
pnp
genes (which encode PNPase) created in
C. jejuni
F38011 and
C. jejuni
81-76 backgrounds. Survival assays carried out at low temperatures (4 and 10°C) revealed a difference of 3 log CFU/ml between the wild-type and the
pnp
deletion (Δ
pnp
) strains. This did not result from a general requirement for PNPase because survival rates of the strains were similar at higher growth temperatures (37 or 42°C).
trans
-Complementation with plasmid pNH04 carrying the
pnp
gene under the control of its natural promoter restored the cold survival phenotype to the
pnp
deletion strains (at 4 and 10°C) but not to the same level as the wild type. In this study we demonstrate the role of PNPase in low-temperature survival of
C. jejuni
and therefore attribute a novel biological function to PNPase directly related to human health.