bluuebunny/crossref_metadata_2025 huggingface dataset:
Software Development of Co-Simulation of Algebraically Coupled Dynamic Subsystems Without Disclosure of Proprietary Subsystem Models
Authors: Gu Bei , Asada H. Harry , He Xiangdong
Published: May 2008

This paper presents a software environment for Co-Simulation using a special Differential Algebraic Equation (DAE) solution method, which is based on the discrete-time sliding control methodology. This algorithm does not require the detailed information from subsystems to resolve causal conflict. The problem formulation and the computational algorithm will be briefly introduced. The algebraic constraint is handled by a special subsystem simulator, Boundary Condition Coordinator (BCC). All subsystem simulators run as independent processes in the Co-Simulation environment. Class templates containing all necessary functions for the different types of subsystems are defined. Subsystem engineers can easily build a subsystem simulator by simply providing the mathematical model, which will be hidden after the subsystem simulator is compiled. Integration engineers can assemble subsystem simulators into simulation of large coupled systems by simply connecting subsystems. The object-oriented class design makes it feasible to extend the software to run Internet-based subsystem simulators or to compile subsystems into a single-process simulator.
A Dynamic Sizing Methodology in the Context of an Automotive Application
Authors: Mechin Olivier , Marquis-Favre Wilfrid , Scavarda Serge , Ferbach Pierre
Published: May 2008

This paper deals with the application of a dynamic sizing methodology for car suspensions for different given aims of dynamic behavior aims in braking situations. The methodology is based on the establishment of the inverse model from the bond graph representation of the system by using the bicausality concept. By means of an automotive car suspension example and for specific dynamic trajectories imposed on the inverse model, we show how information on the system variables can be obtained in a dynamical sizing phase.
Prediction of Swash Plate Moment Using the Simulation Tool CASPAR
Authors: Ivantysynova Monika , Grabbel Jo¨rg , Ossyra Jean-Claude
Published: May 2008

The paper presents a new method of prediction of the swash plate moment based on a complex simulation model of the rotating group of swash plate axial piston machines. Due to further important demands within the design of the next generation of displacement machines – the reduction of noise and an increase of efficiency – the optimization of pump and motor control becomes really difficult. The application of the computer aided design tool CASPAR, a simulation tool developed at the Technical University of Hamburg-Harburg for the design and optimization of swash plate axial piston machines, allows the calculation of swash plate moments dependent on time, design and operating parameters of the machine. Especially the valve plate design affects the generated swash plate moment. The paper presents results of a simulation study into the influence of swash plate moments on the valve plate design. The dependency on the instantaneous pressure behaviour in the displacement chamber is explained. The simulation results were compared with experimental results obtained by measurements of the instantaneous pressure behaviour in the displacement chamber for various valve plate designs.
Dynamic Emulation Using a Resistive Control Input
Authors: Zhang Rong , Alleyne Andrew G.
Published: May 2008

Dynamic load emulation using a resistive control input is a key topic of Hardware-In-The-Loop implementation. Three control configurations are available to design a load emulator. When the bandwidth of the reference system is low enough compared to the bandwidth of the actuator, a one degree-of-freedom (DOF) feedback emulator can be successful. When the reference loop has a very large bandwidth compared to the actuator, the one-DOF feedback design yields poor performance with a possible loss of stability. In this case, if accurate plant model parameters or, alternatively, online adaptation is available, a one-DOF feed forward design can secure stability and improve the performance; otherwise, a two-DOF emulator is the choice to utilize both feedback and feed forward signals and to obtain robust stability and robust performance. To emulate the load dynamics, the usage of a resistance as the control input imposes some fundamental limitations to the closed-loop performance. This paper presents the following: (i) Generalization of load emulation problems and control configurations, (ii) Analysis of performance limitations for resistively controlled systems, and (iii) Design examples including simulation and experimental results.
Some Experimental Considerations of Stage Control in Digital Valves
Authors: Ruan J. , Burton R. , Ukrainetz P.
Published: May 2008

Because of saturation and hysteresis of magnetic materials, nonlinear characteristics are commonly experienced in servo or proportional valves. These nonlinearities can substantially affect the performance of the valve in practical applications. In the presence of magnetic nonlinearities, the output signal (displacement or force) is dependent on the input current and the sign of its derivative. If the driving current to the electrical-to-mechanical interface device changes for a number of cycles, as in a stepper motor for example, then a series of reset points will occur as the current undergoes cyclic changes. At each reset point the original starting characteristics of the system are re-established. A large number of reset points across the full stroke of the spool results in a significant reduction in the nonlinear behavior; indeed, the characteristics of the valve approach those of a linear system. The approach in creating these multiple reset points has been defined by the authors as “stage control”. In this paper, stage control using variable reluctance and hybrid stepper motors is first discussed. For the variable reluctance stepper motor, the reset point occurs once at each step of the stepper motor, whereas it occurs twice in a single cycle in the hybrid types. Experiments using a spool valve as a load were designed to obtain the characteristics using stage control. It is demonstrated that with the introduction of stage control, nonlinearities, such as saturation and hysteresis, are greatly reduced, system stiffness is increased, and the positioning accuracy and resolution of the spool are improved. The effect of dither due to a “digital fragment” signal is also examined and found to be crucial in reducing the hysteresis and in improving the resolution accuracy.
Prediction of Hydraulic Inductance
Authors: Johnston D. Nigel
Published: May 2008

The dynamic response, stability and fluid-borne noise characteristics of fluid power components and systems can be strongly influenced by the inertia or ‘hydraulic inductance’ of the fluid in passageways, which are often of complex geometry. The hydraulic inductance is a parameter that has often proved to be very difficult to quantify accurately, either theoretically or experimentally. This paper presents a method of numerical calculation of the hydraulic inductance in a passageway. The method is simple to apply and can be applied to geometries of arbitrary complexity. A simple way of using a Computational Fluid Dynamics package for calculating hydraulic inductance is also demonstrated. Results are presented for a simple cylindrical orifice, a simple spool valve and a conical poppet valve. The effect of the inductance on the response of a poppet valve is demonstrated.
Accumulator-Charged Drive for a Hydraulic Boom to Save Energy
Authors: Liang Xingui , Virvalo Tapio
Published: May 2008

Improving energy utilization in hydraulic booms has been an important scheme for industries and designers due to energy cost, environmental requirements, etc. This paper presents accumulator-charged drive in a Loglift boom, which is driven by Electro-hydraulic Load-Sensing (ELS) system based a micro-controller. The practical measurement and simulation are carried out for different work situations. The energy transfer process for a typical duty cycle is calculated and compared. The experimental and theoretical results show that this drive can improve energy utilization. The validation of its experiment in an example hydraulic boom will encourage its further research for possible application.
An Analysis of the Melt Casting of Metallic Fuel Pins
Authors: Wu Xiaolong , Clarksean Randy , Chen Yitung , Pepper Darrell , Meyer Mitchell K.
Published: May 2008

A model is developed and analyses are conducted to analyze the casting of metallic fuels pins. The important physics of the model includes the flow of the melt into the mold, the heat transfer into the mold, the amount of preheating in the mold, and the rate of heat transfer from the melt to the mold. This paper discusses and presents preliminary modeling results for the casting of long, slender fuel rods. Parametric modeling results are presented and discussed.
Using FEA Simulations to Determine Advanced Process Parameters for Tailor Welded Blank Forming
Authors: Kinsey Brad , Krishnan Neil
Published: May 2008

In order to realize the potential of sheet metal forming and take advantage of new process control capabilities, innovative modifications to the traditional sheet metal forming process must be developed. These modifications are particularly important with respect to Tailor Welded Blank (TWB) forming, which offers an excellent opportunity to reduce manufacturing costs, decrease part weight, and improve the quality of sheet metal stampings. However, tearing near the weld seam and wrinkling in the formed wall area and die addendum of the part often occurs when a traditional forming process is used to form a TWB. Research and industrial experience has shown that these forming concerns can be alleviated through advanced forming techniques, for example using a segmented die process or a non-uniform binder force. The difficulty then becomes determining the key process parameters associated with these forming methods. In this paper, a methodology is presented to effectively and easily determine both the location of a segmented die and a non-uniform binder force by evaluating nodal reaction forces provided from FEA simulations. Also, using FEA simulations to determine the process parameters for another advanced forming process, strain path control tooling, is discussed. The advanced forming processes presented in this paper and the use of FEA to determine key process parameters are critical components to the continued evolution of sheet metal forming processes.
Tensile Behavior of Monazite Coated Nextel™ 720 Fibers and Tows
Authors: Pai D. , Yarmolenko S. , Kailasshankar B. , Sankar J. , Lua J. , Zawada L.
Published: May 2008

The tensile strengths of Nextel™ 720 fibers, both bare and coated with monazite, and tows made of these fibers, were measured to study the effects of coating and thermal exposure. Close agreement was observed between the Weibull modulus obtained from the statistical fracture distribution and the modulus obtained from a study of the gage length dependence of strength. Thermal soaking for 24h at 1000, 1100 and 1200°C revealed significant differences in the behavior of coated and uncoated fibers. Uncoated fibers subjected to soaking for 24h at 1200°C retained 91% of their unsoaked strength, while similarly soaked coated fibers retained only 61%. The effect of coating reversed in the case of tows, with the presence of coating enabling higher strength retention after thermal exposure.
Single-Phase Flow Characteristics and Effect of Dissolved Gases on Heat Transfer Near Saturation Conditions in Microchannels
Authors: Kandlikar Satish G. , Steinke Mark E. , Balasubramanian Prabhu
Published: May 2008

An experimental investigation is carried out to study the heat transfer and pressure drop in the single-phase flow of water in a microchannel. The effect of dissolved gases on heat transfer and pressure drop is studied as the wall temperature approaches the saturation temperature of water, causing air and water vapor mixture to form bubbles on the heater surface. A set of six parallel microchannels, each approximately 200 micrometers square in cross section and fabricated in copper, with a hydraulic diameter of 207 micrometers, is used as the test section. Starting with air-saturated water at atmospheric pressure and temperature, the air content in the water is varied by vigorously boiling the water at elevated saturation pressures to provide different levels of dissolved air concentrations. The single-phase friction factor and heat transfer results are presented and compared with the available theoretical values. The friction factors for adiabatic cases match closely with the laminar single-phase friction factor predictions available for conventional-sized channels. The diabatic friction factor, after applying the correction for temperature dependent properties, also agrees well with the theoretical predictions. The Nusselt numbers, after applying the property corrections, are found to be below the theoretical values available in literature for constant temperature heating on all four sides. The disagreement is believed to be due to the three-sided heating employed in the current experiments. The effect of gas content on the heat transfer for the three gas concentrations is investigated. Nucleation was observed at a surface temperature of 90.5°C, for the reference case of 8.0 ppm. For the degassed cases (5.4 ppm and 1.8 ppm), nucleation is not observed until the surface temperature reached close to 100°C. An increase in heat transfer coefficient for surface temperatures above saturation is observed. However, a slight reduction in heat transfer is noted as the bubbles begin to nucleate. The presence of an attached bubble layer on the heating surface is believed to be responsible for this effect.
Effect of Cylinder Aspect Ratio and Channel Dimensions on the Fluid Flow and Heat Transfer in Parallel-Plate Channel Heat Exchangers
Authors: Saha A. K. , Acharya Sumanta
Published: May 2008

A comparative numerical study has been carried out to analyze the unsteady three-dimensional flow and heat transfer in a parallel-plate channel heat exchangers with in-line arrays of periodically mounted square cylinders (pins) at various Reynolds number and geometrical configurations. The geometry considered represents the narrow trailing edge region of the blade where pin fins are used to serve both a structural and a heat transfer role. The three-dimensional unsteady Navier-Stokes and energy equations are solved using higher order temporal and spatial discretizations. The simulations have been carried out for a range of Reynolds number based on cylinder width (180–600) and a Prandtl number of 6.99 (corresponding to water). Conjugate heat transfer calculations have been employed to account for the conduction in the solid cylinder and convection in the fluid. The thermal performance factor (TPF) increases significantly when the flow becomes unsteady. The choice of aspect ratio of the cylinders is judged by their relative increase in friction factor and heat transfer at transitional Reynolds number. The TPF is found to increase with the increase in pitch of the cylinders. The increase in channel height enhances the TPF though the heat transfer decreases at higher channel height.
Assembly Reliability Evaluation Method (AREM)
Authors: Suzuki Tatsuya , Ohashi Toshijiro , Asano Masaaki
Published: May 2008

This paper introduces an effective new Design For Quality tool called the Assembly Reliability Evaluation Method (AREM) that visualizes assembly fault potential. The distinctive features of AREM are: (1) visualization of parts and operations having a high fault probability; (2) evaluation of shop reliability, as well as product reliability and, (3) easy data input by symbol selection as well as simultaneous assemblability evaluation; can be evaluated quantitatively. The method can be integrated with other DFX tools such as the Assemblability Evaluation Method (AEM), and the Recyclability/Disassemblability Evaluation Method (REM/DEM) to realize a comprehensive production design evaluation system.
Pursuing Mechanical Part Feature Recognition Through the Isolation of 3-D Features in Organic Shapes
Authors: Mohandas Suraj , Henderson Mark
Published: May 2008

The successful extraction of 3D features in mechanical parts has always been a challenging task and has yielded mixed results. Extracting features from organic shapes however is even more difficult. This is due to the fact that they are defined by both gradual and abrupt changes in surface curvature. The term curvature is explained in detail in section 4. Learning how to recognize organic shapes may give insights into better ways of performing feature recognition on mechanical parts. Determining the exact values of curvature, based on the underlying parameters can prove to be quite difficult. Curvature can be a good tool to identify features as most of the features are areas of slowly changing curvature bounded by sudden changes in curvature. The benefits of developing a generic algorithm that picks out curvature, and hence the organic features, are quite huge. This paper explains one approach taken to accomplish this task. This paper studies characteristics of the watershed algorithm[1] when applied to the features on bones. This algorithm is used to isolate features based on curvature gradients. This paper uses the knowledge from the field of anthropology and medicine to explore the sensitivity factor analysis of the watershed and its effectiveness in extracting the features on bones. The paper also compares the differences between the anatomists definition of a feature and the algorithm interpretation of the same feature.
Assessing the Effectiveness of Filters for Shape Matching
Authors: Sung R. , Rea H. J. , Corney J. R. , Clark D. E. R. , Pritchard J. , Breaks M. L. , MacLeod R. A.
Published: May 2008

Collaborative re-use of design and manufacturing data is one way that global e-commerce could significantly reduce development costs and lead times of new products. However the proliferation of web based catalogues for standard components (e.g. brochure-ware for nuts and washers etc.) only hints at the possible productivity gains if a 3D search engine could be created. Consequently the research reported here is motivated by the belief that shape matching technology is key to enabling a much deeper form of Internet-based collaborative commerce. This paper describes the coarse “shape” filters that support a 3D, Internet-based search engine, known as ShapeSifter, whose ultimate aim is to enable the location of parts already in production that have a shape similar to a desired “newly designed” part. The challenge of the research is to identify the key metrics that produce meaningful characterizations of 3D models for similarity comparison purposes. In this context the work reported focuses on the use of novel indices based on an object’s convex-hull and surface area distribution to carry out a coarse filtering of candidates prior to the application of more detailed analysis (e.g. the construction of multi-dimensional feature vectors). In doing this, the paper describes the crucial role played by a benchmark database of geometrical similar objects.
Recyclability Evaluation Method
Authors: Hiroshige Yuzo , Nishi Takayuki , Ohashi Toshijiro
Published: May 2008

Realization of successful recycling of end-of-life products greatly depends on, as well as environmentally conscious, whether the recycling process can be made economically feasible. We regard the ease of product recycling as indispensable in order to realize a feasible recycling process. In order to make products easier to recycle, it is necessary to take the ease of disassembly, processing and final treatment into consideration at the design stage. Therefore, an advanced evaluation method that can evaluate a product’s ease of recycling, with minimal prototyping and testing of the product is required at the early design stage. In answer to this, we have developed the Recyclability Evaluation Method (REM). In this paper, the theory of the method, procedure and the structure of the system are presented and a number of application examples are given.
Design of Horizontal Mechanical Presses for Deep Drawing and Ironing Process
Authors: Wang Jyhwen
Published: May 2008

This paper addresses the kinematics design and analysis of a special class of mechanical presses used for deep drawing and ironing process. The key design objectives are to obtain a longer stroke and a quicker punch return. From the kinematics equations, it is shown that the horizontal quick return mechanism exhibits the preferred characteristics. The behavior of the press is studied based on the placement of the links. The kinematics constraints are observed and the placement of press components to achieve better performance is summarized.
Teaching of Mechatronics Through an Elective Course
Authors: Habibi S. R. , Williams A.
Published: May 2008

A mechatronics course has been recently introduced as a 4th year elective at the University of Saskatchewan Department of Mechanical Engineering. The necessity and the rational for this training are reviewed. A curriculum for the course is proposed supported by student feedback following its first year of introduction. The curriculum and the structure of the course is such that training in mechatronics may be provided through an elective course. Notwithstanding, the merits of establishing a degree in mechatronics are discussed given the strong industrial demand for this topic.
Transient Thermal Investigation for a SmartMOS Based Airbag Circuit Driver
Authors: Chiriac Victor Adrian , Lee Tien-Yu Tom , Bennett Paul
Published: May 2008

A numerical study was conducted to model the transient thermal behavior of an airbag squib driver using commercially available software. The squib driver is part of an airbag deployment IC. The simulations were primarily used to predict the thermal gradient across the die for determining the optimal sensor location for thermal shutdown that would protect the device from destruction. The temperature sensor should be placed such that it gets hot enough for any electrical pulses that heat up the device close to the destruction point. The overall purpose is to provide a thermal detection circuit for disabling current prior to reaching a thermally destructive level. A preliminary wafer level study correlates the simulated and measured values and indicates that the junction temperature is lower for the case with thicker die and adiabatic boundary conditions; an opposite trend is observed for the cases with fixed temperature boundary condition attached to the domain bottom side. The study of the high IC side dissipating 80W for 5 ms indicates that the bottom and top center monitor points reach temperatures of 188.2°C and 130.5°C at the end of the 5 ms timeframe, corresponding to a peak source temperature of 294.6°C. A similar study with 30W uniform dissipation for 20 ms indicates that the peak junction temperature is lower than before (220°C vs. 294°C). The study of the low IC side reveals higher peak temperatures compared to the high side, due to the larger power density for these cases. The peak temperatures are 368.7°C for 50W/5 ms, and 301.8°C for 25W/20 ms. The left monitor point temperature ranges between 210°C–260°C while the right monitor point temperature ranges between 140°C–160°C. The thermal investigation of the package after the thermal shutdown predicted the time needed for the FETs to reach predetermined temperatures for different scenarios. The temperatures of the low side FETs drop by almost 50% within the 30 ms following the 20 ms of constant powering at 50W. When the high-side FETs are powered at 80W for 5 ms then cooled, the temperature rises then decays within 0.1 s.
Surface Temperature Measurement of Semi-Transparent Ceramics by Long-Wavelength Pyrometry
Authors: Pfefferkorn Frank E. , Incropera Frank P. , Shin Yung C.
Published: May 2008

A long-wavelength pyrometer is developed for the measurement of surface temperatures on materials that are semitransparent at lower wavelengths, and specific application is made to a dense zirconia ceramic (Mg-PSZ) undergoing laser-assisted machining (LAM). The pyrometer operates in a waveband between 11 and 14μm, and a detailed description of measurement uncertainties is provided. The largest uncertainties relate to knowledge of the surface emissivity and the large temperature gradients generated by the LAM process. Repeatability of the measurements is demonstrated, and a parametric study of three LAM parameters reveals expected trends, with good agreement between the measurements and predictions based on a model of the LAM process.
A Hybrid-Inverse Method for Predicting the Temperature Profile Along a Blackbody Optical Fiber Thermometer
Authors: Barker David G. , Jones Matthew R.
Published: May 2008

A blackbody optical fiber thermometer consists of an optical fiber whose sensing tip is given a metallic coating. The sensing tip of the fiber forms an isothermal cavity, and the emission from this cavity is approximately equal to the emission from a blackbody. Temperature readings are obtained by measuring the spectral intensity at the end of the fiber at two wavelengths. The ratio of these measurements is used to infer the temperature at the sensing tip. However, readings from blackbody optical fiber thermometers are corrupted by self-emission when extended portions of the fiber are exposed to elevated temperatures. The error due to self-emission by the fiber may be eliminated using spectral remote sensing. In this method, the radiation exiting the fiber is measured in portions of the visible and infrared spectrum, and the measured spectral intensities are used to reconstruct the temperature profile along the fiber. One method of reconstructing the temperature profile along the fiber is to use a genetic algorithm. Genetic algorithms are, however, computationally expensive. This paper describes a method for decreasing the computational time by implementing a hybrid inversion algorithm. This hybrid algorithm first uses a genetic algorithm to narrow the search space. A gradient-based method is then used to complete the inversion process. Results from the genetic algorithm alone, the gradient-based method alone and the hybrid method are presented.
Gas-Liquid Two-Phase Flow Regimes in Microchannels
Authors: Akbar M. K. , Plummer D. A. , Ghiaasiaan S. M.
Published: May 2008

Recent experimental data dealing with gas-liquid two-phase flow regimes and their transitions in microchannels with circular and near-circular cross-sections are reviewed and compared. It is shown that, for microchannels with hydraulic diameters close to 1 mm, the available data are in good agreement. These data are used as the basis for the development of a simple Weber number-based flow regime map that divides the entire flow map into four zones: a surface tension dominated zone including bubbly and plug flow patterns; an inertia dominated zone representing the annular flow regime; a dispersed/churn flow zone; and a transition zone that consists of other intermittent flow patterns. Comparison is als o made with the limited available data representing channels with slightly larger hydraulic diameters or different cross-sectional geometries, and the effects of channel cross-sectional geometry and size are examined and discussed. The areas in need of further systematic experimental investigation are identified.
The Heat Transfer Characteristics of Exhaust Gas Recirculation (EGR) Cooling Devices
Authors: Ismail B. I. , Zhang R. , Ewing D. , Cotton J. S. , Chang J.-S.
Published: May 2008

A one-dimensional steady state model was developed to predict the heat transfer performance of a shell (liquid)-and-tube (gas) heat exchanger used as a cooling device for exhaust gas recirculation (EGR) application where there is a significant temperature drop across the device. The predictions of the model results were compared with experimental measurements and the trends were found to be in good agreement for most of the transitional and turbulent regimes. The results showed that the exit gas temperature increases with increasing gas mass flow rate at fixed gas inlet temperature and coolant flow rate. It was also found that the exit gas temperature was essentially independent of the coolant flow rate for the typical operating range but did depend on the coolant inlet temperature. It was observed that the pressure drop across the cooling device was not a strong function of the gas inlet temperature. The heat-transfer effectiveness of the cooling device was found to slightly depend on the gas mass flow rate and inlet gas temperature. A preliminary analysis showed that fouling in the EGR cooling device can have a significant effect on both the thermal and hydraulic performance of the cooling device.
Avoiding Failures During Assembly of a Trunnion-Hub-Girder for Bascule Bridges
Authors: Besterfield Glen H. , Nichani Sanjeev , Kaw Autar K. , Eason Thomas , Cherukara Thomas
Published: May 2008

This paper is a study of avoiding failures during the assembly of a trunnion-hub-girder (THG) for bascule bridges. The currently used assembly procedure, AP#1, cools the trunnion for a shrink fit into the hub, followed by cooling of the trunnion-hub assembly to shrink fit it into the girder. During assembly, using AP#1, development of cracks on the hub was observed in one THG assembly. Yet, during another assembly, the trunnion got stuck in the hub before it could be fully inserted. A complete analytical, numerical, and experimental study was conducted to understand these failures, and the results were used to develop specifications and recommendations for assembly. The causes of failures include development of high stresses at low temperatures during assembly, while noting that fracture toughness of THG material decreases with temperature. Recommended specifications included following an alternative assembly procedure that doubled allowable crack length, and lower cooling temperatures to avoid trunnions sticking in the hub.
Effect of Inlet Geometry on the Turbine Blade Tip Region Heat Transfer Coefficient and Effectiveness
Authors: Yoon J. H. , Martinez-Botas R. F.
Published: May 2008

An experimental investigation of the local film cooling effectiveness and heat transfer coefficient downstream of a row of elongated holes in a simulated axial turbine blade tip is presented. Film cooling is needed to protect the turbine blade tip region from high heat transfer rates, especially when cooling by convection is insufficient to keep the temperature distribution of the blade within the limits required. Accurate heat transfer predictions in this region of the blade are particularly difficult given the dimensionality of the flow and the narrow passage typical of turbine blades. The effect of inlet geometry, film cooling injection point, and blowing ratio are examined for an injection on the blade tip itself close to the pressure surface corner. Additionally, the corner radii between the pressure surface and the tip were varied. The experimental method uses the steady state liquid crystal technique. Film cooling injection provides the tip with a blanket of protection from the hot leakage flow. This extends far downstream of the holes at higher blowing ratios. Inlet curvature provides greater local film cooling effectiveness but it lacks streamwise film cooling coverage. It is important to have direct injection onto the separation bubble for greater lateral film cooling coverage.
Bubble Detachment in Variable Gravity Under the Influence of Electric Fields
Authors: Herman Cila , Chang Shinan , Iacona Estelle
Published: May 2008

The objective of the research is to investigate the behavior of individual air bubbles injected through an orifice into an electrically insulating liquid under the influence of a static electric field. Situations were considered with both uniform and nonuniform electric fields. Bubble formation and detachment were visualized in terrestrial gravity as well as for several levels of reduced gravity (lunar, martian and microgravity) using a high-speed video camera. Bubble volume, dimensions and contact angles at detachment were measured. In addition to the experimental studies, a simple model, predicting bubble characteristics at detachment in an initially uniform electric field was developed. The model, based on thermodynamic considerations, accounts for the level of gravity as well as the magnitude of the uniform electric field. The results of the study indicate that the level of gravity and the electric field magnitude significantly affect bubble behavior as well as shape, volume and dimensions.
Static and Fatigue Strength of Resin Transfer Molded Composites
Authors: Hamidi Youssef , Aktas Levent , Bladwin J. David , Altan M. Cengiz
Published: May 2008

Fiber reinforced polymer composites are preferred in many structural applications for their ease of production and high specific strengths. Although fatigue loading is commonly encountered in structural applications, behavior of composites under cyclic loading is less understood compared to fatigue behavior of more conventional metals and their alloys. In this work, the response of resin transfer molded (RTM) glass/epoxy composites to static tensile and fatigue loading is investigated. Center-gated, disk shaped composites are fabricated using EPON 815C epoxy resin and EPICURE 3282 curing agent. A randomly oriented, planar glass fiber preform with 0.459kg/m2 surface density is used as the reinforcement material. Two and six layers of preforms are used to achieve 7.9 and 28.9% fiber volume fractions respectively. In addition, neat polymer parts are molded without performs to study the effect of fiber content on the tensile and fatigue behavior. Initially, ultimate tensile strength (UTS) and stiffness for three different fiber volume fractions (i.e., 0, 7.9, and 28.9%) are reported. Then, fatigue tests are conducted for stress level (σmax/UTS) of 0.5 and stress ratio (σmax/σmin) of 0.1 at a test frequency of 10 Hz. Loss of stiffness and cycles to failure are the two fatigue properties investigated. As the fiber volume fraction increased from 7.9 to 28.9%, the ultimate tensile strength and stiffness increased by 140 and 100%, respectively. During fatigue loading, the stiffness gradually dropped by approximately 13% for 7.9% and 28.9% fiber volume fractions. However, neat polymer samples did not show considerable decrease in stiffness during cycling. It is also shown that the number of cycles before failure significantly increased with the fiber content.
Use of Resin Transfer Molding Simulation to Predict Flow, Saturation and Compaction in the VARTM Process
Authors: Correia N. C. , Robitaille F. , Long A. C. , Rudd C. D. , Sˇima´cˇek P. , Advani S. G.
Published: May 2008

Vacuum Assisted Resin Transfer Molding (VARTM) and Resin Transfer Molding (RTM) are among the most significant and widely used Liquid Composite manufacturing processes. In RTM preformed-reinforcement materials are placed in a mold cavity, which is subsequently closed and infused with resin. RTM numerical simulations have been developed and used for a number of years for gate assessment and optimization purposes. Available simulation packages are capable of describing/predicting flow patterns and fill times in geometrically complex parts manufactured by the resin transfer molding process. Unlike RTM, the VARTM process uses only one sided molds (tool surfaces) where performs are placed and enclosed by a sealed vacuum bag. To improve the delivery of the resin, a distribution media is sometimes used to cover the preform during the injection process. Attempts to extend the usability of the existing RTM algorithms and software packages to the VARTM domain have been made but there are some fundamental differences between the two processes. Most significant of these are 1) the thickness variations in VARTM due to changes in compaction force during resin flow 2) fiber tow saturation, which may be significant in the VARTM process. This paper presents examples on how existing RTM filling simulation codes can be adapted and used to predict flow, thickness of the preform during the filling stage and permeability changes during the VARTM filling process. The results are compared with results obtained from an analytic model as well as with limited experimental results. The similarities and differences between the modeling of RTM and VARTM process are highlighted.
Molecular Characterization and Epidemiology of Extended-Spectrum- β-Lactamase-Producing
Escherichia coli
and
Klebsiella pneumoniae
Isolates Causing Health Care-Associated Infection in Thailand, Where the CTX-M Family Is Endemic
Authors: Kiratisin Pattarachai , Apisarnthanarak Anucha , Laesripa Chaitat , Saifon Piyawan
Published: May 2008

Extended-spectrum β-lactamase (ESBL)-producing
Escherichia coli
and
Klebsiella pneumoniae
have rapidly spread worldwide and pose a serious threat for health care-associated (HA) infection. We conducted molecular detection and characterization of ESBL-related
bla
genes, including
bla
TEM
,
bla
SHV
,
bla
CTX-M
,
bla
VEB
,
bla
OXA
,
bla
PER
, and
bla
GES
, among 362 isolates of ESBL-producing
E. coli
(
n
= 235) and ESBL-producing
K. pneumoniae
(
n
= 127) collected from patients who met the definition of HA infection at two major university hospitals in Thailand from December 2004 to May 2005. The prevalence of ESBL-producing
E. coli
and ESBL-producing
K. pneumoniae
, patient demographics and the susceptibilities of these bacteria to various antimicrobial agents were described. A total of 87.3% of isolates carried several
bla
genes. The prevalence of
bla
CTX-M
was strikingly high: 99.6% for ESBL-producing
E. coli
(CTX-M-14, -15, -27, -40, and -55) and 99.2% for ESBL-producing
K. pneumoniae
(CTX-M-3, -14, -15, -27, and -55). IS
Ecp1
was found in the upstream region of
bla
CTX-M
in most isolates. Up to 77.0% and 71.7% of ESBL-producing
E. coli
and ESBL-producing
K. pneumoniae
, respectively, carried
bla
TEM
; all of them encoded TEM-1. ESBL-producing
K. pneumoniae
carried
bla
SHV
at 87.4% (SHV-1, -2a, -11, -12, -27, -71, and -75) but only at 3.8% for ESBL-producing
E. coli
(SHV-11 and -12).
bla
genes encoding VEB-1 and OXA-10 were found in both ESBL-producing
E. coli
(8.5% and 8.1%, respectively) and ESBL-producing
K. pneumoniae
(10.2% and 11.8%, respectively). None of the isolates were positive for
bla
PER
and
bla
GES
. Pulsed-field gel electrophoresis analysis demonstrated that there was no major clonal relationship among these ESBL producers. This is the first study to report CTX-M-3, CTX-M-27, CTX-M-40, SHV-27, SHV-71, and SHV-75 in Thailand and to show that CTX-M ESBL is highly endemic in the country.
Quantitative Assessment of Combination Antimicrobial Therapy against Multidrug-Resistant
Acinetobacter baumannii
Authors: Lim Tze-Peng , Ledesma Kimberly R. , Chang Kai-Tai , Hou Jing-Guo , Kwa Andrea L. , Nikolaou Michael , Quinn John P. , Prince Randall A. , Tam Vincent H.
Published: May 2008

Treatment of multidrug-resistant bacterial infections poses a therapeutic challenge to clinicians; combination therapy is often the only viable option for multidrug-resistant infections. A quantitative method was developed to assess the combined killing abilities of antimicrobial agents. Time-kill studies (TKS) were performed using a multidrug-resistant clinical isolate of
Acinetobacter baumannii
with escalating concentrations of cefepime (0 to 512 mg/liter), amikacin (0 to 256 mg/liter), and levofloxacin (0 to 64 mg/liter). The bacterial burden data in single and combined (two of the three agents with clinically achievable concentrations in serum) TKS at 24 h were mathematically modeled to provide an objective basis for comparing various antimicrobial agent combinations. Synergy and antagonism were defined as interaction indices of <1 and >1, respectively. A hollow-fiber infection model (HFIM) simulating various clinical (fluctuating concentrations over time) dosing exposures was used to selectively validate our quantitative assessment of the combined killing effect. Model fits in all single-agent TKS were satisfactory (
r
2
> 0.97). An enhanced combined overall killing effect was seen in the cefepime-amikacin combination (interactive index, 0.698; 95% confidence interval [CI], 0.675 to 0.722) and the cefepime-levofloxacin combination (interactive index, 0.929; 95% CI, 0.903 to 0.956), but no significant difference in the combined overall killing effect for the levofloxacin-amikacin combination was observed (interactive index, 0.994; 95% CI, 0.982 to 1.005). These assessments were consistent with observations in HFIM validation studies. Our method could be used to objectively rank the combined killing activities of two antimicrobial agents when used together against a multidrug-resistant
A. baumannii
isolate. It may offer better insights into the effectiveness of various antimicrobial combinations and warrants further investigations.
Effective Plague Vaccination via Oral Delivery of Plant Cells Expressing F1-V Antigens in Chloroplasts
Authors: Arlen Philip A. , Singleton Michael , Adamovicz Jeffrey J. , Ding Yi , Davoodi-Semiromi Abdolreza , Daniell Henry
Published: May 2008

The chloroplast bioreactor is an alternative to fermentation-based systems for production of vaccine antigens and biopharmaceuticals. We report here expression of the plague F1-V fusion antigen in chloroplasts. Site-specific transgene integration and homoplasmy were confirmed by PCR and Southern blotting. Mature leaves showed the highest level of transgene expression on the third day of continuous illumination, with a maximum level of 14.8% of the total soluble protein. Swiss Webster mice were primed with adjuvant-containing subcutaneous (s.c.) doses of F1-V and then boosted with either adjuvanted s.c. doses (s.c. F1-V mice) or unadjuvanted oral doses (oral F1-V mice). Oral F1-V mice had higher prechallenge serum immunoglobulin G1 (IgG1) titers than s.c. F1-V mice. The corresponding serum levels of antigen-specific IgG2a and IgA were 2 and 3 orders of magnitude lower, respectively. After vaccination, mice were exposed to an inhaled dose of 1.02 × 106CFU of aerosolizedYersinia pestisCO92 (50% lethal dose, 6.8 × 104CFU). All control animals died within 3 days. F1-V given s.c. (with adjuvant) protected 33% of the immunized mice, while 88% of the oral F1-V mice survived aerosolizedY. pestischallenge. A comparison of splenicY. pestisCFU counts showed that there was a 7- to 10-log reduction in the mean bacterial burden in survivors. Taken together, these data indicate that oral booster doses effectively elicit protective immune responses in vivo. In addition, this is the first report of a plant-derived oral vaccine that protected animals from liveY. pestischallenge, bringing the likelihood of lower-cost vaccines closer to reality.
Temporal and Spatial Distribution of
Toxoplasma gondii
Differentiation into Bradyzoites and Tissue Cyst Formation In Vivo
Authors: Di Cristina Manlio , Marocco Daniela , Galizi Roberto , Proietti Carla , Spaccapelo Roberta , Crisanti Andrea
Published: May 2008

During
Toxoplasma gondii
infection, a fraction of the multiplying parasites, the tachyzoites, converts into bradyzoites, a dormant stage, which form tissue cysts localized mainly in brain, heart, and skeletal muscles that persist for several years after infection. At this stage the parasite is protected from the immune system, and it is believed to be inaccessible to drugs. While the long persistence of tissue cysts does not represent a medical problem for healthy individuals, this condition represents a major risk for patients with a compromised immune system, who can develop recrudescent life-threatening
T. gondii
infections. We have investigated for the first time the dynamics and the kinetics of tachyzoite-to-bradyzoite interconversion and cyst formation in vivo by using stage-specific bioluminescent parasites in a mouse model. Our findings provide a new framework for understanding the process of bradyzoite differentiation in vivo. We have also demonstrated that complex molecules such as
d
-luciferin have access to tissue cysts and are metabolically processed, thus providing a rationale for developing drugs that attack the parasite at this developmental stage.
Interleukin-12 (IL-12) and IL-23 Induction of Substance P Synthesis in Murine T Cells and Macrophages Is Subject to IL-10 and Transforming Growth Factor β Regulation
Authors: Blum Arthur , Setiawan Tommy , Hang Long , Stoyanoff Korynn , Weinstock Joel V.
Published: May 2008

Substance P is a tachykinin that enhances pathways of inflammation. Leukocytes at sites of intestinal inflammation make substance P. This study explored the role of interleukin-12 (IL-12), IL-23, and the regulatory cytokines IL-10 and transforming growth factor β (TGF-β) in controlling leukocyte substance P production. In murine schistosomiasis, it was found that IL-12 and IL-23 drive substance P gene expression and peptide synthesis in murine splenic T cells and macrophages, respectively. Cytokine induction of substance P synthesis both in T cells and in macrophages depends on intracellular NF-κB activation and is Stat4 independent. IL-10 inhibits T-cell substance P production, while TGF-β blocks macrophage substance P expression. Intestinal macrophages also produce substance P, subject mostly to IL-23 and TGF-β regulation. Hemokinin is another tachykinin with homology to substance P. Macrophages and T cells make hemokinin, but hemokinin production is not subject to IL-12 or IL-23 regulation.
Noncytotoxic
Clostridium perfringens
Enterotoxin (CPE) Variants Localize CPE Intestinal Binding and Demonstrate a Relationship between CPE-Induced Cytotoxicity and Enterotoxicity
Authors: Smedley James G. , Saputo Juliann , Parker Jacquelyn C. , Fernandez-Miyakawa Mariano E. , Robertson Susan L. , McClane Bruce A. , Uzal Francisco A.
Published: May 2008

Clostridium perfringens
enterotoxin (CPE) causes the symptoms of a very common food poisoning. To assess whether CPE-induced cytotoxicity is necessary for enterotoxicity, a rabbit ileal loop model was used to compare the in vivo effects of native CPE or recombinant CPE (rCPE), both of which are cytotoxic, with those of the noncytotoxic rCPE variants rCPE D48A and rCPE
168-319
. Both CPE and rCPE elicited significant fluid accumulation in rabbit ileal loops, along with severe mucosal damage that starts at villus tips and then progressively affects the entire villus, including necrosis of epithelium and lamina propria, villus blunting and fusion, and transmural edema and hemorrhage. Similar treatment of ileal loops with either of the noncytotoxic rCPE variants produced no visible histologic damage or fluid transport changes. Immunohistochemistry revealed strong CPE or rCPE
168-319
binding to villus tips, which correlated with the abundant presence of claudin-4, a known CPE receptor, in this villus region. These results support (i) cytotoxicity being necessary for CPE-induced enterotoxicity, (ii) the CPE sensitivity of villus tips being at least partially attributable to the abundant presence of receptors in this villus region, and (iii) claudin-4 being an important intestinal receptor for CPE. Finally, rCPE
168-319
was able to partially inhibit CPE-induced histologic damage, suggesting that noncytotoxic rCPE variants might be useful for protecting against some intestinal effects of CPE.