bluuebunny/crossref_metadata_2025 huggingface dataset:
Orthogonal Microcutting of Thin Workpieces
Authors: Kushendarsyah Saptaji , Sathyan Subbiah
Published: July 2013

With a broader intention of producing thin sheet embossing molds, orthogonal cutting experiments of thin workpieces are conducted. Challenges in machining thin workpieces are many: machining induced stress and deformation, fixturing challenges, and substrate effects. A setup involving continuous orthogonal cutting with a single crystal diamond toolof an aluminum alloy (Al6061-T6) workpiece fixtured using an adhesive to reduce its thickness is used to study trends in forces, chip thickness, and to understand to what level of thickness we can machine the workpiece down to and in what form the adhesive fails. There are no significant changes observed in the forces and chip thickness between thick and thin workpieces during the experiments, meaning that the cutting energy required is the same in cutting thick or thin workpieces. The limitation to achieve thinner workpiece is attributed mainly due to the detachment of the thin workpiece by peel-off induced by adhesive failure mode, which occurs during initial chip formation as the tool initially engages with the workpiece. We use a finite element model to understand the stresses in the workpiece during this initial tool engagement when it is thick and when it is thin, as well as the effect of the adhesive itself and the effect of adhesive thickness. Simulation results show that the tensile stress induced by the tool at the workpiece-adhesive interface is higher for a thinner workpiece (45 μm) than a thicker workpiece (150 μm) and higher at the entrance. As such, a thinner workpiece is more susceptible to peel-off. The peeling of thin workpiece is induced when the high tensile stress at the interface exceeds the tensile-at-break value of the adhesive.
Continuous Dry Cylindrical and Rectangular Deep Drawing by Electroconductive Ceramic Dies
Authors: Tamaoki Kenji , Manabe Ken-ichi , Kataoka Seiji , Aizawa Tatsuhiko
Published: July 2013

Two types of electroconductive ceramic tools are employed in this study to describe the dry deep drawing behavior of cold rolled steel sheets into cylindrical and rectangular cups. Each of electroconductive ceramic tools is machined by die sinking electric discharge. Four experimental setups are also prepared to investigate the effect of the surface roughness on the quality of dry deep drawing: the unlapped and the lapped electroconductive ceramic dies in dry condition and the unlubricated and the lubricated SKD11 die. Even without lubricating oils, cylindrical and rectangular cups are successfully deep drawn over 10,000 by the present tooling. Furthermore, compared to the lubricated SKD11 tooling, surface roughness of deep drawn cups is reduced by the present ceramic tooling. Fine finishing in ceramic tooling never leads to low surface roughness in the deep drawn cups since the work materials make unconstrained plastic flow in the direction of thickness. Hence, the unlapped electroconductive ceramic tooling is favored for practical ceramic tooling to preserve well-defined contact interface between metallic work sheets and ceramic tools in dry deep drawing. In addition, the rectangular cup drawing is evaluated by more severe conditions than the cylindrical cup drawing because the stress concentrates on the corner parts. Through this test, it is demonstrated that the electroconductive ceramic tooling has a potential of practical dry deep drawing.
Computational Coupled Method for Multiscale and Phase Analysis
Authors: Tak Moonho , Park Duhee , Park Taehyo
Published: July 2013

On micro scale the constitutions of porous media are effected by other constitutions, so their behaviors are very complex and it is hard to derive theoretical formulations as well as to simulate on macro scale. For decades, in order to escape this complication, the phenomenological approaches in a field of multiscale methods have been extensively researched by many material scientists and engineers. Their theoretical approaches are based on the hierarchical multiscale methods using a priori knowledge on a smaller scale; however it has a drawback that an information loss can be occurred. Recently, according to a development of the core technologies of computer, the ways of multiscale are extended to a direct multiscale approach called the concurrent multiscale method. This approach is not necessary to deal with complex mathematical formulations, but it is noted as an important factor: development of computational coupling algorithms between constitutions in a porous medium. In this work, we attempt to develop coupling algorithms in different numerical methods finite element method (FEM), smoothed particle hydrodynamics (SPH) and discrete element method (DEM). Using this coupling algorithm, fluid flow, movement of solid particle, and contact forces between solid domains are computed via proposed discrete element which is based on SPH, FEM, and DEM. In addition, a mixed FEM on continuum level and discrete element model with SPH particles on discontinuum level is introduced, and proposed coupling algorithm is verified through numerical simulation.
Ab Initio Investigation of Strain Dependent Atomistic Interactions at Two Tropocollagen-Hydroxyapatite Interfaces
Authors: Dubey Devendra K. , Tomar Vikas
Published: July 2013

Tropocollagen (TC) and hydroxyapatite (HAP) interfaces are one of the main load bearing entities in bone family of materials. Atomistic interactions in such interfaces occur in a variety of chemical environments under a range of biomechanical loading conditions. It is challenging to investigate such interactions using traditional analytical or using classical molecular simulation approaches owing to their limitations in predicting bond strength change as a function of change in chemical environment. In the present work, 3D ab initio molecular dynamics simulations are used to understand such atomistic interactions by analyzing tensile strain dependent deformation mechanism and strength of two structurally distinct idealized TC-HAP interfaces in hydrated as well as unhydrated environments. Analyses suggest that the presence of water molecules leads to modification of H-bond density at the interfaces that also depends upon the level of strain. TC molecules become stiffer in the presence of water due to the presence of H-bonds. Bond forming-and-breaking cycle change as a function of H-bond density lies at the heart of TC-HAP interfacial shear deformation. Consequently, interfaces with TC molecule placed flat on the HAP crystal surface experience significantly higher shear stress during deformation in comparison to the interfaces with TC molecule placed with their axes perpendicular to the HAP surface.
Preliminary Assessment of the Importance of Platform–Tendon Coupling in a Tension Leg Platform
Authors: Masciola Marco , Nahon Meyer , Driscoll Frederick
Published: July 2013

This paper presents performance metrics that can be used to evaluate the response sensitivity of a tension leg platform (TLP) to its tendons. An uncoupled TLP model ignores the intrinsic dynamics and environmental loads on the cables by treating each tendon as an ideal massless spring. A coupled TLP system, in contrast, considers the effects of distributed mass and drag along the tendon. Under certain operating conditions, an uncoupled dynamics model can produce results comparable to its coupled counterpart. This paper defines the conditions under which it is acceptable to model a TLP tendon as a linear spring, as opposed to one that considers the cable dynamics. The analysis is performed in the frequency domain and, for generality, the results are nondimensionalized. The findings indicate that a more elaborate set of conditions than the platform–to–cable mass ratio must be satisfied for the two models to provide similar results. To conclude this study, two simulations are performed and compared against the performance metrics derived in this paper.
Fundamental Gas Turbine Heat Transfer
Authors: Han Je-Chin
Published: July 2013

Gas turbines are used for aircraft propulsion and land-based power generation or industrial applications. Thermal efficiency and power output of gas turbines increase with increasing turbine rotor inlet temperatures (RIT). Current advanced gas turbine engines operate at turbine RIT (1700 °C) far higher than the melting point of the blade material (1000 °C); therefore, turbine blades are cooled by compressor discharge air (700 °C). To design an efficient cooling system, it is a great need to increase the understanding of gas turbine heat transfer behaviors within complex 3D high-turbulence unsteady engine-flow environments. Moreover, recent research focuses on aircraft gas turbines operating at even higher RIT with limited cooling air and land-based gas turbines burn coal-gasified fuels with a higher heat load. It is important to understand and solve gas turbine heat transfer problems under new harsh working environments. The advanced cooling technology and durable thermal barrier coatings play critical roles for the development of advanced gas turbines with near zero emissions for safe and long-life operation. This paper reviews fundamental gas turbine heat transfer research topics and documents important relevant papers for future research.
Effects of the Dispersed Phase on Oil/Water Wax Deposition
Authors: Wang Pengyu , Wang Wei , Gong Jing , Zhou Yuanxin , Yang Wei
Published: July 2013

In the study of the foundation of the oil / water wax deposition experiment, the emulsification characteristics of crude oil emulsion with high wax content have gradually become the hot research area. In the current research of emulsification characteristics of oil/water emulsion, the attention has been focused on the study of the effects of water cut, stirring speed, particle size distribution on the viscosity of waxy crude oil emulsion in the experiment, in which heavy oil and simulated oil are adopted as the working fluids. In this study, the emulsion with different water cut and stirred by different speed was prepared under three different temperature conditions, the temperature above the wax appearance temperature (WAT), near the WAT, and below the WAT. The polarization microscope and rotary viscometer were applied to measure the effects of the particle size of the dispersed phase and waxy crystal distribution on the oil/water emulsion viscosity. The results suggest that preparing the temperature for crude oil emulsion with high wax content has an important influence on the emulsion microstructure. This study lays the foundation for further study of oil/water two phase dynamic wax deposition experiments.
Stochastic Modeling of Microgrinding Wheel Topography
Authors: Kunz Jacob A. , Mayor J. Rhett
Published: July 2013

Superabrasive microgrinding wheels are used for jig grinding of microstructures using various grinding approaches. The desire for increased final geometric accuracy in microgrinding leads to the need for improved process modeling and understanding. An improved understanding of the source of wheel topography characteristics leads to better knowledge of the interaction between the individual grits on the wheel and the grinding workpiece. Analytic stochastic modeling of the abrasives in a general grinding wheel is presented as a method to stochastically predict the wheel topography. The approach predicts the probability of the number of grits within a grind wheel, the individual grit locations within a given wheel structure, and the static grit density within the wheel. The stochastic model is compared to numerical simulations that imitate both the assumptions of the analytic model where grits are allowed to overlap and the more realistic scenario of a grind wheel where grits cannot overlap. A new technique of grit relocation through collective rearrangement is used to limit grit overlap. The results show that the stochastic model can accurately predict the probability of the static grit density while providing results two orders of magnitude faster than the numerical simulation techniques. It is also seen that grit overlap does not significantly impact the static grit density allowing for the simpler, faster analytic model to be utilized without sacrificing accuracy.
Acoustic Emission Monitoring for Ultrasonic Cavitation Based Dispersion Process
Authors: Wu Jianguo , Zhou Shiyu , Li Xiaochun
Published: July 2013

In the manufacturing of micro/nanocomposite materials, micro/nanoparticles need to be dispersed evenly into the base materials. However, due to their high surface-to-volume ratio and high surface energy, the micro/nanoparticles tend to agglomerate and cluster together. Ultrasonic cavitation is effective to disperse micro/nanoparticles. However, works on correlating the cavitation parameters with the micro/nanoparticle dispersion are limited. This paper presents a real-time acoustic monitoring method based on cavitation noises to monitor the micro/nanoparticle dispersion status. In this paper, two types of cavitation noise power indices computed based on the raw cavitation noise signals are used to monitor the cavitation status. Both off-line and on-line steady state detection algorithms are developed. These algorithms can be used to determine the critical process parameters including the power of the ultrasonic sound and the dispersion time. Extensive experiments have been conducted to illustrate the effectiveness of the developed methods.
Numerical Study of Two-Dimensional Circular Cylinders in Tandem at Moderate Reynolds Numbers
Authors: Vakil Ali , Green Sheldon I.
Published: July 2013

Computer simulations of the flow around a pair of two-dimensional, tandem circular cylinders in a flow, for Reynolds numbers in the range 1–40, are described. Cylinder surface-to-surface separations in the range 0.1<s/D<400 (D = cylinder diameter) were considered. The computed wake of a single cylinder at these low to moderate Reynolds numbers was in surprisingly good agreement with the laminar wake approximation, and a simple theory is presented to explain this agreement. With tandem cylinders, the drag on the downstream cylinder is a monotonic function of the cylinder separation. The laminar wake approximation can be used to explain reasonably well the variation in drag. The drag on the upstream cylinder is also a monotonic function of separation distance provided that the Reynolds number is less than about 10. For Reynolds numbers between 10 and 40, the upstream cylinder drag first decreases as separation increases up to a few diameters and then increases monotonically with separation distance.
Analysis of Friction and Stabilized Wear in the Area of Mechanical Energy Dissipation
Authors: Maciąg Maria
Published: July 2013

Friction, its concomitant thermal processes and wear are analyzed in a tribological system which is formed by a separate fragment of a friction pair element where mechanical energy is dissipated. A phenomenological (macroscopic) interpretation of stationary processes in a thermodynamic perspective is proposed. The tribological system is assumed to form an open thermodynamic system. An original model of a frictional source of heat is formulated. Balancing of mass and energy, especially the first law of thermodynamics, is employed in the discussion. Analytical dependences are found between work of friction, wear, heat of friction, heat carried away to the environment, and physical properties of the system material are determined. Variation of the system temperature and dimensions of the energy dissipation region are taken into consideration. The proposed model is illustrated by means of selected tests. Reference is made to an earlier, energetic interpretation of friction and its associated processes (Maciąg, M., 2010, “Thermodynamic Model of the Metallic Friction Process,” ASME J. Tribol., 132(3), pp. 1–7). A method of defining a tribological system and a new mechanism of frictional heating are some of the original elements. Introduction of these elements to equations of mass and energy balances resulted in new analytical dependences characterizing properties of a tribological system.
The Influence of Cryogenic Coolants in Machining of Ti–6Al–4V
Authors: Jerold B. Dilip , Kumar M. Pradeep
Published: July 2013

Machining of titanium alloy Ti–6Al–4V is a challenging task because of the greatly increased cutting temperature that results in short tool life. Numerous attempts have been made in the past by employing various cutting fluids for machining purpose, including liquid nitrogen (LN2) as the cryogenic coolant. This study deals with the influence of cryogenic coolants, especially LN2 and carbon dioxide (CO2), in machining of Ti–6Al–4V and its effects on cutting temperature, cutting forces, surface roughness, chip morphology, and tool wear. The results obtained in cryogenic machining are compared with that of dry and wet machining. Cutting temperature was reduced to an extent of 36% and 47% in cryogenic CO2 machining and cryogenic LN2 machining in comparison with wet machining. The application of CO2 produced reduced cutting forces up to 24% and improved surface finish up to 48% compared to cryogenic LN2 machining. It also produced better chip control and minimized tool wear than dry, wet, and LN2 machining.
Fabrication Technology of Low-Adhesive Superhydrophobic and Superamphiphobic Surfaces Based on Electrochemical Machining Method
Authors: Song Jinlong , Xu Wenji , Lu Yao , Luo Limei , Liu Xin , Wei Zefei
Published: July 2013

Low-adhesive superhydrophobic and superamphiphobic (both superhydrophobic and superoleophobic) surfaces with a liquid contact angle larger than 150 deg and rolling angle less than 10 deg have attracted great interest for fundamental research and potential application. However, the existing methods to fabricate the aforementioned surfaces are contaminative, dangerous, expensive, and time-consuming. Low-adhesive superhydrophobic surfaces on aluminum substrates and steel substrates were fabricated via electrochemical etching method and electrochemical deposition method, respectively. Low-adhesive superamphiphobic surfaces on magnesium alloy substrates were fabricated via one-step electrochemical etching method. The sample surfaces were investigated using electron microscopy, energy-dispersive X-ray spectroscopy (EDS), Fourier-transform infrared spectrophotometry (FTIR), X-ray diffraction (XRD), optical contact angle measurements, and digital roughness and microhardness measurements. The SEM results show that the hierarchical rough structures composed of micrometer-scale pits, protrusions, rectangular-shaped plateaus, and smaller step-like structures and particles are present on the aluminum surfaces after electrochemical etching; meanwhile, the hierarchical micro/nanometer-scale rough structures composed of micrometer-scale globular structures and nanometer-scale SiO2 particles are present on the steel surfaces. After being modified with a low surface energy material, superhydrophobic surfaces on aluminum substrates with 167.0 deg water contact angle and 2 deg rolling angle and superhydrophobic surfaces on steel substrates with 172.9 deg water contact angle and 1 deg rolling angle are obtained. For magnesium alloy, the hierarchical micro/nanometer-scale rough structures composed of micrometer-scale, grain-like structures, protrusions, pits, globular structures, lump-like structures, and nanometer-scale sheets and needles are present on the magnesium alloy surfaces. After obtaining the hierarchical micro/nanometer-scale rough structures, the magnesium alloy surfaces directly show a superamphiphobicity without any chemical modification. The hierarchical rough structures are essential to fabricate superhydrophobic surfaces. In addition, the re-entrant structures are important to fabricate superamphiphobic surfaces. Furthermore, the proposed electrochemical machining method is simple, economic, and highly effective.
Technical Challenges and Opportunities for Concentrating Solar Power With Thermal Energy Storage
Authors: Stekli Joseph , Irwin Levi , Pitchumani Ranga
Published: July 2013

Concentrating solar power (CSP) provides the ability to incorporate simple, efficient, and cost-effective thermal energy storage (TES) by virtue of converting sunlight to heat as an intermediate step to generating electricity. Thermal energy storage for use in CSP systems can be one of sensible heat storage, latent heat storage using phase change materials (PCMs) or thermochemical storage. Commercially deployed CSP TES systems have been achieved in recent years, with two-tank TES using molten salt as a storage medium and steam accumulators being the system configurations deployed to date. Sensible energy thermocline systems and PCM systems have been deployed on a pilot-scale level and considerable research effort continues to be funded, by the United States Department of Energy (DOE) and others, in developing TES systems utilizing any one of the three categories of TES. This paper discusses technoeconomic challenges associated with the various TES technologies and opportunities for advancing the scientific knowledge relating to the critical questions still remaining for each technology.
Experimental Research on Film Pressure Distribution of Water-Lubricated Rubber Bearing With Multiaxial Grooves
Authors: Wang Nan , Meng Qingfeng , Wang Pengpeng , Geng Tao , Yuan Xiaoyang
Published: July 2013

In order to obtain the entire continuous circumferential film pressure distribution of a water-lubricated rubber bearing with multiaxial grooves, and further to study the bearing properties, an experimental research was conducted. The wireless measurement scheme was proposed, which can make the measurement process simple, convenient, and accurate. The unique design of the shaft and the installation methods for the pressure sensors are described. The time-domain averaging (TDA) algorithm was presented to suppress the random noises of the film pressure signal. By contrastive analysis on experimental results, some bearing properties, and working mechanism have been found and demonstrated.
Numerical Analysis of Circular Graphene Bubbles
Authors: Wang Peng , Gao Wei , Cao Zhiyi , Liechti Kenneth M. , Huang Rui
Published: July 2013

Pressurized graphene bubbles have been observed in experiments, which can be used to determine the mechanical and adhesive properties of graphene. A nonlinear plate theory is adapted to describe the deformation of a graphene monolayer subject to lateral loads, where the bending moduli of monolayer graphene are independent of the in-plane Young's modulus and Poisson's ratio. A numerical method is developed to solve the nonlinear equations for circular graphene bubbles, and the results are compared to approximate solutions by analytical methods. Molecular dynamics simulations of nanoscale graphene bubbles are performed, and it is found that the continuum plate theory is suitable only within the limit of linear elasticity. Moreover, the effect of van der Waals interactions between graphene and its underlying substrate is analyzed, including large-scale interaction for nanoscale graphene bubbles subject to relatively low pressures.
Failure of Graphdiyne: Structurally Directed Delocalized Crack Propagation
Authors: Brommer Dieter B. , Buehler Markus J.
Published: July 2013

Among the many potential two-dimensional carbon allotropes inspired by graphene, graphynes have received exceptional attention recently. Graphynes exhibit remarkable mechanical properties depending on their structure. The similar structure and two-dimensional nature of these materials yield many properties that are similar to those of graphene, but the presence of heterogeneous bond types is expected to lead to distinct properties. The main subject of this work is graphdiyne, one of the few graphynes that has been fabricated in large quantities. In this paper, we perform fracture analysis on graphdiyne and find a delocalized failure mechanism in which a crack propagates along a diagonal with respect its original direction. The covalence of the material allows for this simple but intriguing phenomenon to be investigated. Graphene is also tested to compare the behavior. This mechanism has implications for the toughness and robustness of this material, which is topical for many device applications recently proposed in the literature. Further, connections of such delocalized failure mechanisms are made to that of hidden length and sacrificial bonding in some biological systems such as proteins, bone, and nacre.
Characterization of Cavitation Fields From Measured Pressure Signals of Cavitating Jets and Ultrasonic Horns
Authors: Singh Sowmitra , Choi Jin-Keun , Chahine Georges L.
Published: July 2013

Cavitation pressure fields under a cavitating jet and an ultrasonic horn were recorded for different conditions using high frequency response pressure transducers. This was aimed at characterizing the impulsive pressures generated by cavitation at different intensities. The pressure signals were analyzed and statistics of the amplitudes and widths of the impulsive pressure peaks were extracted. Plots of number densities and cumulative numbers of peaks as functions of peak amplitude, peak width, and the power of the ultrasonic horn or the jet were generated. The analysis revealed the dominance of pulses with smaller amplitudes and larger durations at lower cavitation intensities and the increase of the amplitudes and reduction of the pulse widths at higher intensities. The ratio of the most probable peak amplitude to peak width was computed. A representative Gaussian curve was then generated for each signal using a characteristic peak amplitude and the corresponding most probable peak duration/width. This resulted in a proposed statistical representation of a cavitation field, useful to characterize cavitation fields of various intensities.
Optimization of Constraint Location, Orientation, and Quantity in Mechanical Assembly
Authors: Rusli Leonard , Luscher Anthony , Schmiedeler James
Published: July 2013

A mechanical assembly aims to remove 6 degree-of-freedom (DOF) motion between two or more parts using features such as fasteners, integral attachments, and mating surfaces, all of which act as constraints. The locations, orientations, and quantity of these constraints directly influence the effectiveness of a constraint configuration to eliminate DOF; therefore, constraint design decisions are crucial to the performance of a mechanical assembly. The design tool presented in this paper uses an analysis tool developed by the authors to explore a user-specified constraint design space and help the designer make informed decisions based on quantitative data so as to optimize constraint locations and orientations. The utility of the design tool is demonstrated with an assembly case study that contains both threaded fasteners and integral attachments. The results identify the opportunity for significant improvements by separately exploring individual design spaces associated with some constraints and further gains through a search of a multidimensional design space that leverages interaction effects between the location and orientation variables. The example also highlights how the tool can help identify nonintuitive solutions such as nonrectilinear, nonplanar parting lines. A trade-off study demonstrates how the design tool can quantitatively aid in optimizing the total number of constraints. Adding constraints generally improves an assembly's performance at the expense of increased redundancy, which can cause locked-in stresses and assembly inaccuracies, so the design tools helps identify new/removable constraints that offer the greatest/least contribution to the overall part constraint configuration. Through these capabilities, this design tool provides useful data to optimize and understand mechanical assembly performance variables.
Evaluation of the Influence of a Planned Interference Fit on the Expected Fatigue Life of a Conjugate Cam Mechanism- A Case Study
Authors: Català Pau , De los Santos Maria Antònia , Veciana Joaquim M. , Cardona Salvador
Published: July 2013

Due to dynamic effects, clearances, manufacturing and assembly errors in form-closed cam mechanisms, the follower jump can also occur. For conjugate cam mechanisms a technique to avoid the follower jump without the use of a spring involves making the conjugate cam profiles bigger than the kinematical ones by adding an external offset. This strategy produces an interference fit between the conjugate cam profiles and the follower train. This paper presents an ordered procedure to study the influence that the planned interference fit has on the evaluation of the contact forces, the expected fatigue life of the rollers, contact pressures and the lubrication conditions. The study is based on a conjugate cam mechanism with translational roller followers used in a real automatic process for manufacturing muselets. A three-degree-of-freedom dynamic model is proposed and the Hertzian theory for general profiles is used to model the nonlinear contact stiffness between the cams and the crowned rollers. The dynamic model predicts that it is difficult to obtain conjugate cam mechanisms with an infinite expected fatigue life of the rollers just by considering typical achievable manufacturing errors or clearances, and as happens in reality, a set-up process is highly recommended. The procedure is also tested with measured manufacturing errors on a coordinate measure machine—CMM—and with measured radial internal clearances for the rollers measured by an experimental apparatus. Also, to evaluate lubrication conditions, surface finishing measurements have been taken of the cams and the rollers with a surface profiler.
Rhodococcus jostii Porin A (RjpA) Functions in Cholate Uptake
Authors: Somalinga Vijayakumar , Mohn William W.
Published: July 2013

RjpA in
Rhodococcus jostii
is the ortholog of a channel-forming porin, MspA. Deletion of
rjpA
delayed growth of
R. jostii
on cholate but not on cholesterol. Eventual growth on cholate involved increased expression of other porins, namely, RjpB, RjpC, and RjpD. Porins appear essential for the uptake of bile acids by mycolic acid bacteria.
The Peptidoglycan Hydrolase of Staphylococcus aureus Bacteriophage ϕ11 Plays a Structural Role in the Viral Particle
Authors: Rodríguez-Rubio Lorena , Quiles-Puchalt Nuria , Martínez Beatriz , Rodríguez Ana , Penadés José R. , García Pilar
Published: July 2013

The role of virion-associated peptidoglycan hydrolases (VAPGHs) in the phage infection cycle is not clear. gp49, the VAPGH from
Staphylococcus aureus
phage ϕ11, is not essential for phage growth but stabilizes the viral particles. ϕ11Δ49 phages showed a reduced burst size and delayed host lysis. Complementation of gp49 with HydH5 from bacteriophage vB_SauS-phiIPLA88 restored the wild-type phenotype.
New Methods for Analysis of Spatial Distribution and Coaggregation of Microbial Populations in Complex Biofilms
Authors: Almstrand Robert , Daims Holger , Persson Frank , Sörensson Fred , Hermansson Malte
Published: July 2013

In biofilms, microbial activities form gradients of substrates and electron acceptors, creating a complex landscape of microhabitats, often resulting in structured localization of the microbial populations present. To understand the dynamic interplay between and within these populations, quantitative measurements and statistical analysis of their localization patterns within the biofilms are necessary, and adequate automated tools for such analyses are needed. We have designed and applied new methods for fluorescencein situhybridization (FISH) and digital image analysis of directionally dependent (anisotropic) multispecies biofilms. A sequential-FISH approach allowed multiple populations to be detected in a biofilm sample. This was combined with an automated tool for vertical-distribution analysis by generatingin silicobiofilm slices and the recently developed Inflate algorithm for coaggregation analysis of microbial populations in anisotropic biofilms. As a proof of principle, we show distinct stratification patterns of the ammonia oxidizersNitrosomonas oligotrophasubclusters I and II and the nitrite oxidizerNitrospirasublineage I in three different types of wastewater biofilms, suggesting niche differentiation between theN. oligotrophasubclusters, which could explain their coexistence in the same biofilms. Coaggregation analysis showed thatN. oligotrophasubcluster II aggregated closer toNitrospirathan didN. oligotrophasubcluster I in a pilot plant nitrifying trickling filter (NTF) and a moving-bed biofilm reactor (MBBR), but not in a full-scale NTF, indicating important ecophysiological differences between these phylogenetically closely related subclusters. By using high-resolution quantitative methods applicable to any multispecies biofilm in general, the ecological interactions of these complex ecosystems can be understood in more detail.
Variation in Consumption of Human Milk Oligosaccharides by Infant Gut-Associated Strains of Bifidobacterium breve
Authors: Ruiz-Moyano Santiago , Totten Sarah M. , Garrido Daniel A. , Smilowitz Jennifer T. , German J. Bruce , Lebrilla Carlito B. , Mills David A.
Published: July 2013

Human milk contains a high concentration of complex oligosaccharides that influence the composition of the intestinal microbiota in breast-fed infants. Previous studies have indicated that select species such as
Bifidobacterium longum
subsp.
infantis
and
Bifidobacterium bifidum
can utilize human milk oligosaccharides (HMO)
in vitro
as the sole carbon source, while the relatively few
B. longum
subsp.
longum
and
Bifidobacterium breve
isolates tested appear less adapted to these substrates. Considering the high frequency at which
B. breve
is isolated from breast-fed infant feces, we postulated that some
B. breve
strains can more vigorously consume HMO and thus are enriched in the breast-fed infant gastrointestinal tract. To examine this, a number of
B. breve
isolates from breast-fed infant feces were characterized for the presence of different glycosyl hydrolases that participate in HMO utilization, as well as by their ability to grow on HMO or specific HMO species such as lacto-
N
-tetraose (LNT) and fucosyllactose. All
B. breve
strains showed high levels of growth on LNT and lacto-
N
-neotetraose (LNnT), and, in general, growth on total HMO was moderate for most of the strains, with several strain differences. Growth and consumption of fucosylated HMO were strain dependent, mostly in isolates possessing a glycosyl hydrolase family 29 α-fucosidase. Glycoprofiling of the spent supernatant after HMO fermentation by select strains revealed that all
B. breve
strains can utilize sialylated HMO to a certain extent, especially sialyl-lacto-
N
-tetraose. Interestingly, this specific oligosaccharide was depleted before neutral LNT by strain SC95. In aggregate, this work indicates that the HMO consumption phenotype in
B. breve
is variable; however, some strains display specific adaptations to these substrates, enabling more vigorous consumption of fucosylated and sialylated HMO. These results provide a rationale for the predominance of this species in breast-fed infant feces and contribute to a more accurate picture of the ecology of the developing infant intestinal microbiota.
The Oxygenase CAO-1 of Neurospora crassa Is a Resveratrol Cleavage Enzyme
Authors: Díaz-Sánchez Violeta , F. Estrada Alejandro , Limón M. Carmen , Al-Babili Salim , Avalos Javier
Published: July 2013

The genome of the ascomycete
Neurospora crassa
encodes CAO-1 and CAO-2, two members of the carotenoid cleavage oxygenase family that target double bonds in different substrates. Previous studies demonstrated the role of CAO-2 in cleaving the C
40
carotene torulene, a key step in the synthesis of the C
35
apocarotenoid pigment neurosporaxanthin. In this work, we investigated the activity of CAO-1, assuming that it may provide retinal, the chromophore of the NOP-1 rhodopsin, by cleaving β-carotene. For this purpose, we tested CAO-1 activity with carotenoid substrates that were, however, not converted. In contrast and consistent with its sequence similarity to family members that act on stilbenes, CAO-1 cleaved the interphenyl Cα-Cβ double bond of resveratrol and its derivative piceatannol. CAO-1 did not convert five other similar stilbenes, indicating a requirement for a minimal number of unmodified hydroxyl groups in the stilbene background. Confirming its biological function in converting stilbenes, adding resveratrol led to a pronounced increase in
cao-1
mRNA levels, while light, a key regulator of carotenoid metabolism, did not alter them. Targeted Δ
cao-1
mutants were not impaired by the presence of resveratrol, a phytoalexin active against different fungi, which did not significantly affect the growth and development of wild-type
Neurospora
. However, under partial sorbose toxicity, the Δ
cao-1
colonies exhibited faster radial growth than control strains in the presence of resveratrol, suggesting a moderate toxic effect of resveratrol cleavage products.
Characterization of Pneumocystis Major Surface Glycoprotein Gene (msg) Promoter Activity in Saccharomyces cerevisiae
Authors: Kutty Geetha , Shroff Robert , Kovacs Joseph A.
Published: July 2013

Major surface glycoprotein (Msg), the most abundant cell surface protein ofPneumocystis, plays an important role in the interaction of this opportunistic pathogen with host cells, and its potential for antigenic variation may facilitate evasion of host immune responses. In the present study, we have identified and characterized the promoter region ofmsgin 3 species ofPneumocystis:P. carinii,P. jirovecii, andP. murina. BecausePneumocystiscannot be cultured, promoter activity was measured inSaccharomyces cerevisiae, a related fungus, using a yeast vector modified to utilize the gene coding forRenillaluciferase as a reporter gene. The 5′-flanking sequences ofmsgfrom all threePneumocystisspecies showed considerable promoter activity, with increases in luciferase activity up to 15- to 44-fold above baseline. Progressive deletions helped define an ∼13-bp sequence in eachPneumocystisspecies that appears to be critical for promoter activity. Electrophoretic mobility shift analysis usingP. carinii-specificmsgpromoter sequences demonstrated binding of nuclear proteins ofS. cerevisiae. The 144-bp 5′-flanking region ofP. murinamsgshowed 72% identity to that ofP. carinii. The 5′-flanking region ofP. jiroveciimsgshowed 58 and 61% identity to those ofP. murinaandP. carinii, respectively. Themsgpromoter is a good candidate for inclusion in a construct designed for genetic manipulation ofPneumocystisspecies.
Redox Regulation of an AP-1-Like Transcription Factor, YapA, in the Fungal Symbiont Epichloë festucae
Authors: Cartwright Gemma M. , Scott Barry
Published: July 2013

One of the central regulators of oxidative stress inSaccharomyces cerevisiaeis Yap1, a bZIP transcription factor of the AP-1 family. In unstressed cells, Yap1 is reduced and cytoplasmic, but in response to oxidative stress, it becomes oxidized and accumulates in the nucleus. To date, there have been no reports on the role of AP-1-like transcription factors in symbiotic fungi. An ortholog of Yap1, named YapA, was identified in the genome of the grass symbiontEpichloë festucaeand shown to complement anS. cerevisiaeΔyap1mutant. Hyphae of theE. festucaeΔyapAstrain were sensitive to menadione and diamide but resistant to H2O2, KO2, andtert-butyl hydroperoxide (t-BOOH). In contrast, conidia of the ΔyapAstrain were very sensitive to H2O2and failed to germinate. Using a PcatA-eGFPdegron-tagged reporter, YapA was shown to be required for expression of a spore-specific catalase gene,catA. Although YapA-EGFP localized to the nucleus in response to host reactive oxygen species during seedling infection, there was no difference in whole-plant and cellular phenotypes of plants infected with the ΔyapAstrain compared to the wild-type strain. Homologs of theS. cerevisiaeandSchizosaccharomyces pomberedox-sensing proteins (Gpx3 and Tpx1, respectively) did not act as redox sensors for YapA inE. festucae. In response to oxidative stress, YapA-EGFP localized to the nuclei ofE. festucaeΔgpxC, ΔtpxA, and ΔgpxCΔtpxAcells to the same degree as that in wild-type cells. These results show thatE. festucaehas a robust system for countering oxidative stress in culture andin plantabut that Gpx3- or Tpx1-like thiol peroxidases are dispensable for activation of YapA.
Helicobacter pylori Salvages Purines from Extracellular Host Cell DNA Utilizing the Outer Membrane-Associated Nuclease NucT
Authors: Liechti George W. , Goldberg Joanna B.
Published: July 2013

Helicobacter pyloriis a bacterial pathogen that establishes life-long infections in humans, and its presence in the gastric epithelium is strongly associated with gastritis, peptic ulcer disease, and gastric cancer. Having evolved in this specific gastric niche for hundreds of thousands of years, this microbe has become dependent on its human host. Bioinformatic analysis reveals thatH. pylorihas lost several genes involved in thede novosynthesis of purine nucleotides, and without this pathway present,H. pylorimust salvage purines from its environment in order to grow. While the presence and abundance of free purines in various mammalian tissues has been loosely quantified, the concentration of purines present within the gastric mucosa remains unknown. There is evidence, however, that a significant amount of extracellular DNA is present in the human gastric mucosal layer as a result of epithelial cell turnover, and this DNA has the potential to serve as an adequate purine source for gastric purine auxotrophs. In this study, we characterize the ability ofH. pylorito grow utilizing only DNA as a purine source. We show that this ability is independent of the ComB DNA uptake system, and thatH. pyloriutilization of DNA as a purine source is largely influenced by the presence of an outer membrane-associated nuclease (NucT). A ΔnucTmutant exhibits significantly reduced extracellular nuclease activity and is deficient in growth when DNA is provided as the sole purine source in laboratory growth media. These growth defects are also evident when this nuclease mutant is grown in the presence of AGS cells or in purine-free tissue culture medium that has been conditioned by AGS cells in the absence of fetal bovine serum. Taken together, these results indicate that the salvage of purines from exogenous host cell DNA plays an important role in allowingH. pylorito meet its purine requirements for growth.
Eliminating a Set of Four Penicillin Binding Proteins Triggers the Rcs Phosphorelay and Cpx Stress Responses in Escherichia coli
Authors: Evans Kerry L. , Kannan Suresh , Li Gang , de Pedro Miguel A. , Young Kevin D.
Published: July 2013

Penicillin binding proteins (PBPs) are responsible for synthesizing and modifying the bacterial cell wall, and in
Escherichia coli
the loss of several nonessential low-molecular-weight PBPs gives rise to abnormalities in cell shape and division. To determine whether these proteins help connect the flagellar basal body to the peptidoglycan wall, we surveyed a set of PBP mutants and found that motility in an agar migration assay was compromised by the simultaneous absence of four enzymes: PBP4, PBP5, PBP7, and AmpH. A wild-type copy of any one of these restored migration, and complementation depended on the integrity of the PBP active-site serine. However, the migration defect was caused by the absence of flagella instead of improper flagellar assembly. Migration was restored if the
flhDC
genes were overexpressed or if the
rcsB
or
cpxR
genes were deleted. Thus, migration was inhibited because the Rcs and Cpx stress response systems were induced in the absence of these four specific PBPs. Furthermore, in this situation Rcs induction depended on the presence of CpxR. The results imply that small changes in peptidoglycan structure are sufficient to activate these stress responses, suggesting that a specific cell wall fragment may be the signal being sensed. The fact that four PBPs must be inactivated may explain why large perturbations to the envelope are required to induce stress responses.
Can a media campaign change health service use in a population with stroke symptoms? Examination of the first Irish stroke awareness campaign
Authors: Mellon Lisa , Hickey Anne , Doyle Frank , Dolan Eamon , Williams David
Published: July 2013

Background

Mass media campaigns for stroke awareness encourage the public to recognise stroke symptoms and respond to stroke in a timely manner. However, there is little evidence to suggest that media messages can influence behaviour after stroke onset. The F.A.S.T. (Face Arm Speech Time) test is a common stroke recognition tool used in public education campaigns.

Objective

To assess the impact of the F.A.S.T. campaign on health service use in Ireland, which has had no previous exposure to a F.A.S.T. media campaign.

Methods

An interrupted time series design was used to detect behaviour change after the introduction of the first Irish F.A.S.T. campaign in presentations of patients with suspected stroke to two emergency departments (EDs), serving a population of about 580 000.

Results

There was a significant change in ED attendance of patients with reported stroke symptoms after the introduction of the F.A.S.T. campaign (β=0.84, 95% CI 0.43 to 1.24; p<0.001), although this was not sustained. ED presentation within 3.5 h was associated with emergency medical services activation (OR=3.1, p<0.001) and self-referral to the ED (OR=2.67, p<0.001).

Conclusions

This first Irish F.A.S.T. campaign had an initial impact on ED attendance of patients with stroke symptoms. However, the campaign effects were not sustained in the long term. Results indicate that prehospital delay in accessing acute stroke services is a complex process with involvement of factors other than stroke knowledge and intention to call 911.
Defining combat helmet coverage for protection against explosively propelled fragments
Authors: Breeze John , Baxter D , Carr D , Midwinter M J
Published: July 2013

Introduction

Prevention against head wounds from explosively propelled fragments is currently the Mark 7 general service combat helmet, although only limited evidence exists to define the coverage required for the helmet to adequately protect against such a threat. The Royal Centre for Defence Medicine was tasked by Defence Equipment and Support to provide a framework for determining the optimum coverage of future combat helmets in order to inform the VIRTUS procurement programme.

Method

A systematic review of the literature was undertaken to identify potential solutions to three components felt necessary to define the ideal helmet coverage required for protection against explosively propelled fragments.

Results

The brain and brainstem were identified as the structures requiring coverage by a helmet. No papers were identified that directly defined the margins of these structures to anatomical landmarks, nor how these could be related to helmet coverage.

Conclusions

We recommend relating the margins of the brain to three identifiable anatomical landmarks (nasion, external auditory meatus and superior nuchal line), which can in turn be related to the coverage provided by the helmet. Early assessments using an anatomical mannequin indicate that the current helmet covers the majority of the brain and brainstem from projectiles with a horizontal trajectory but not from ones that originate from the ground. Protection from projectiles with ground-originating trajectories is reduced by helmets with increased stand-off from the skin. Future helmet coverage assessments should use a finite element numerical modelling approach with representative material properties assigned to intracranial anatomical structures to enable differences in projectile trajectory and helmet coverage to be objectively compared.