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This paper presents a global finite difference time domain (FDTD) analysis of a silicon nonlinear transmission line (NLTL) using optimized varactors. The simulation is based on the FDTD method also including transmission line losses and the drift-diffusion model for the semiconductor devices solved by means of finite differences (FD). The diodes are included in the FDTD scheme as lumped elements. The fall time of 74 ps of a 4 GHz sinewave was compressed to approximately 15 ps at the output of a 20 mm long NLTL with 40 diodes. Comparing the measured output signal to the simulation, a good agreement could be achieved.

When pressure vessels are exposed to external fire impingement, high wall temperatures can result and these can lead to material degradation and the ultimate failure of the vessel. To protect against this possibility, vessels can be protected by means of pressure relief devices, external thermal barriers or external water spray cooling. This paper deals with a device that cools the walls of fire-impinged vessels carrying pressurized liquids by directing 2-phase fluid along the upper internal surface of the vessel when the vessel pressure relief valve is in action. The device consists of a concentric secondary internal shell that partitions the interior into a core region and an annulus. The bottom of the internal shell is open to allow communication between the two regions. When vapor is vented from the annulus, it results in significant fluid swelling in the annular space. This swelling results in large areas of the wall being wetted and cooled by liquid. Experimental results are presented for the case of a short electrically heated cylindrical vessel with and without the cooling device installed. From the limited tests conducted, it was shown that the device cools areas of the vessel wall that would normally have experienced high wall temperatures and possible material degradation.

When a pressure vessel is exposed to an engulfing fire, the vessel can fail due to a combination of high internal pressure and material degradation due to high wall temperatures. In fire-engulfed vessels containing pressurized liquids in equilibrium with their vapors, high wall temperatures will occur in the upper regions of the vessel where the wall is in contact with vapor. Several methods exist for thermal protection of vessels, including thermal insulation and external water spray cooling. Recent tests have shown internal spray cooling to be potentially effective as thermal protection. The present paper presents a theoretical evaluation of a new concept in thermal protection which involves cooling the upper regions of vessel during fire engulfment by directing 2-phase fluid along the upper regions of the vessel wall during pressure relief. Based on observations of the internal cooling device from small-scale tests, a model was formulated and integrated with an existing vessel-in-fire computer model. This model was then used to study the effectiveness of internal spray cooling on an example system consisting of a rail tank-car carrying propane. Simulation results indicate that internal wall cooling could be effective at reducing the risk of thermal ruptures of vessels. The simulation results for internally cooled vessels are compared with previously validated simulations of an uninsulated tank-car filled with propane exposed to engulfing fires.

DERACS (Derailment Accident Computer Simulation) is a computer program developed to simulate some of the consequences of train derailment accidents involving fires and accidental releases of dangerous commodities. The present paper shows the results of two sample simulations that were performed using the prototype DERACS program. Technical details of the DERACS program are presented in Reference [1]. Because of the limitations of the prototype version of DERACS the sample simulations only approximate the Mississauga rail accident of November 1979. The results presented have not been validated in any way and should not be considered as accurate representations of the Mississauga accident. They were generated for discussion purposes only so that future applications of the DERACS program could be illustrated, and areas within DERACS requiring further development could be identified.

Summary The merchantable timber yield from Pinus radiata plantations established on former pastures is reduced compared with stands on ex-native forest sites in comparable areas because the trees develop numerous defects including sinuous stems, multiple leaders and heavy branches. The causative factors have not been identified, but deformation is most severe on highly improved sites where the soils have a high nitrification potential. In NSW, other site-specific nutritional factors including boron and sulphur deficiencies also appear to be involved in the development of “poor form” on ex-pastures. The availability to trees of several elements including phosphorus, boron, sulphur, aluminium and manganese is affected by previous land use. Most plantations on previous pastures in NSW are of pre-commercial age so the major impact on timber yields has yet to be realized. Over the past decade there has been a steady increase in the area and proportion of plantations established each year on pasture country. Of...

A prototype computer program has been developed which is capable of simulating some of the consequences of a train derailment accident. The program is made up from a number of models which account for train derailment mechanics, flammable liquid spills, fire effects on remote targets, fire impingement on tank cars carrying dangerous commodities, explosion blast over-pressure and thermal radiation, and heavy plume and puff dispersion. Most of these sub-models have previously been developed and are available in the open literature. The overall program consists of a pre-processor for inputting the surroundings data and train consist data, a simulation module containing the various models and a post-processor which presents the results of the simulation in graphical form. The present paper briefly describes the overall organization of the program and the technical basis of the simulation models.

This paper describes an experimental investigation into optimizing the performance of air-air ejectors with triangular tabbed driving nozzles. Mixing tabs have been shown to improve ejector performance, but at the cost of increased back-pressure. Ejector performance was evaluated on the basis of pumping, mixing, and back-pressure. It was discovered that mixing-tube inlet treatment influenced the ability of ejectors to entrain ambient air. It was also found that although mixing improved as a function of increased mixingtube length, maximum pumping occurred when the mixing-tube was approximately four nozzle diameters in length. Lastly, for a given overall ejector length, increased standoff was found to be more beneficial than increased mixing-tube length. Optimal ejector geometry was defined by the configuration that generated maximum mixing and maximum pumping for minimal increases in back-pressure.Copyright © 2007 by ASME

Even though the notion that high customer satisfaction leads to high repurchase rates is one of the fundamental assumptions of relationship marketing, empirical evidence concerning the satisfaction–retention link is mixed. Studies who investigated the satisfaction–retention link have shown that the relationship is weak and that customers repeatedly defect even though they state to be highly satisfied. Recent research has successfully been able to identify variables that moderate the link between satisfaction and repurchase behavior and can partially explain the weak overall relationship. However, almost all of previous research has been conducted in single brand, business-to-consumer contexts. In contrast to these studies, we investigate the differential effect of the manufacturer on the satisfaction–retention link in a business-to-business setting. Results show, that the satisfaction–retention link is moderated by demographic characteristics of a decider in a buying center, characteristics of the purchasing company and the manufacturer. Moreover several effects of demographic and company characteristics are specific to the manufacturer. Implications of the results for relationship management and customer lifetime value are discussed.

This paper draws upon categorization theory and applies it to segmentation and strategic group research. In contrast to existing approaches that have investigated the categorizations of managers and industry experts, we investigate customers' patterns of brand categorization. Customer groups defined by their pattern of brand categorization can be conceptualized as the demand-side counterpart of strategic groups. Characterising customer segments or strategic groups by their respective probabilities of brand categorization (brand consideration, brand neutrality, brand rejection) helps to understand the competitive structure of a market and preference barriers that exist for brands (i.e. it is very difficult for a firm to enter a segment/strategic group where its brand is rejected). These preference barriers in effect represent mobility barriers for firms and are crucial for understanding the dynamics of competition in a given market. Conceiving brand categorization as a goal-derived categorization process, we propose and show that product category goals and category-specific benefits differ across brand categorization segments. Applying our approach in the automotive industry helps to explain market phenomena that are difficult to account for with solely a traditional resource based perspective on strategic groups.

This paper presents experimental and CFD data for the performance of a round straight air-air ejector with a 4-ring entraining diffuser. The effects of inlet swirl angle and flow temperature on the ejector pumping, back pressure, wall pressure distribution, and diffuser pressure recovery were studied. The ejector experiments were carried out on a hot flow wind tunnel that can provide primary flow rates up to 2.2 kg/s at ambient temperature and 1.8 kg/s at 500°C. Velocity, pressure and temperature measurements were taken in the annulus upstream of the primary nozzle, on the mixing tube and diffuser walls, and at the mixing tube and diffuser ring exits. A parallel computational study was conducted along with the experimental study. A commercial CFD solver, Fluent 6.216, was used for simulation. The Realizable k-ε turbulence model and non-equilibrium wall functions were implemented on the cases. The CFD inlet boundary conditions were chosen to replicate the experimental configuration.

This paper presents the results of an experimental study on the performance of oblong ejectors with a bend in the mixing tube. In the aerospace industry, space limitations can lead to the design of exhaust ducts of oblong cross section. These ducts can also include ejectors for engine space ventilation or exhaust cooling or infrared signature suppression. In some cases these systems require bends after the primary driving nozzle. Each ejector consisted of a nozzle and a constant area mixing tube. A series of bent mixing tubes with the same radius of curvature was tested and the results were compared with the baseline straight ejector. A hot flow wind tunnel was used to provide the primary air flow at temperatures up to 450°C and mass flow rates up to 2 kg/s. Ambient air from the surroundings was allowed to enter the mixing tubes and mix with the primary air issuing from the primary nozzle. Velocity, pressure and temperature measurements were taken upstream of the nozzle, at the mixing tube inlet and at the exit of the mixing tube. Seven-hole probes were used to resolve the velocity vector at the exit of the mixing tube to identify large-scale flow structures. Mass flow ratio, temperature distribution and the losses in the different ejectors were compared to estimate the degradation of ejector performance with the degree of bend. Significant reduction in the performance was observed with the degree of bend in the ejector.Copyright © 2007 by ASME

Introduction Surgical manipulations at C7 level present the most difficulty during a posterior cervicothoracic fusion where instrumentation across the cervicothoracic junction is required. There is increased risk of vascular injury, neurological injury, and possibility of postoperative instability because of the surgical complications at this site. Placement of C7 instrumentation also poses additional difficulty during rod placement. Vertebral artery (when present) and C8 nerve roots are the most important structures susceptible to the surgical injury at C7 level. Our clinical observations suggested that skipping instrumentation at C7 in a multiple level posterior cervicothoracic fusion will result in minimal intraoperative complications, decreased surgical time, while still maintaining fixation, sagittal balance parameters, and successful rates of fusion. Methods This was a retrospective chart review of 49 patients (mean age: 62 years; range: 45–87 years) undergoing multilevel posterior cervicothoracic fusion between November 2010 and October 2014. Of the 49 patients, 42 had no screws placed at C7 level and 7 patients had instrumentation done at C7 and served as a control group. Assessment of the safety and efficacy of skipping C7 instrumentation were based on intraoperative complications, operative time, estimated blood loss (EBL), and radiographic evidence of fusion and spine stability. Results There were no intraoperative complications though two patients (one skipped and one not skipped) required extended time under anesthesia because of the difficulty in patient positioning and intubation. Skipping C7 resulted in reduced average operative time compared with those patients instrumented at C7 (203 vs. 171 minutes, respectively). In addition, skipping C7 reduced average EBL compared with patients instrumented at C7 (531 vs. 445 mL, respectively). In addition, patients skipped at C7 maintained sagittal balance with fusion rates identical to control patients at follow-up with a very low incidence of pseudarthrosis. Conclusion Skipping instrumentation at C7 in a multilevel posterior cervicothoracic fusion demonstrates lower EBL and faster operative times compared with performing instrumentation at the C7 level. In addition, in a postoperative assessment of patients undergoing posterior cervicothoracic fusion identical rates of fusion were achieved. Serious negative outcomes of skipping C7 were not found in this retrospective study. The results of this study point to the clinical benefits of skipping C7 to minimize surgical risk and complications in patients undergoing posterior cervical fusion across the cervicothoracic junction.

Nonlinear transmission lines (NLTLs) have so far only been fabricated on GaAs. Here, an NLTL was monolithically integrated on a 2000-/spl Omega//spl middot/cm silicon substrate, demonstrating the applicability of the NLTL concept to silicon millimeter-wave integrated circuits (SIMMWICs). The fall time of 74 ps of a 4-GHz sinewave was compressed to 32 ps at the output of the NLTL, in accordance with theory. This is the first working NLTL on silicon to our knowledge.

TELIS (TErahertz and sub millimeter LImb Sounder) is a three-channel balloon-borne cryogenic heterodyne receiver on which a number of novel features are tested. It flies together with the MIPAS-B2 instrument and the combination can yield the most complete map of atmospheric species ever measured from one platform. The three channels are selected at 500 GHz, tunable between 500 and 650 GHz and at 1.8 THz, and employ a SIS mixer, a Superconducting Integrated Receiver and a HEBM. The first flight is foreseen in 2006.

Objectives: Surgical simulation has been shown to enhance the training of general surgery residents. Since catheter-based techniques have become an important part of the vascular surgeon's armamentarium, we explored whether simulation might impact the acquisition of catheter skills by surgical residents. Methods: Twenty general surgery residents received didactic training in the techniques of catheter intervention. Residents were then randomized with 10 receiving additional training with the Procedicus, computer-based, haptic simulator. All 20 residents then participated in 2 consecutive mentored catheter-based interventions for lower extremity occlusive disease in an OR/angiography suite. Resident performance was graded by attending surgeons blinded to the resident's training status, using 18 procedural steps as well as a global rating scale. Results: There were no differences between the 2 resident groups with regard to demographics or scores on a visuospatial test administered at study outset. Overall, residents exposed to simulation scored higher than controls during the first angio/OR intervention: procedural steps (simulation/control) (50 ± 6 vs. 33 ± 9, P = 0.0015); global rating scale (30 ± 7 vs. 19 ± 5, P = 0.0052). The advantage provided by simulator training persisted with the second intervention (53 ± 6 vs. 36 ± 7, P = 0.0006); global rating scale (33 ± 6 vs. 21 ± 6, P = 0.0015). Moreover, simulation training, particularly for the second intervention, led to enhancement in almost all of the individual measures of performance. Conclusion: Simulation is a valid tool for instructing surgical residents and fellows in basic endovascular techniques and should be incorporated into surgical training programs. Moreover, simulators may also benefit the large number of vascular surgeons who seek retraining in catheter-based intervention.

Calculations of N 2 -, O 2- broadened half-widths, ?, of water vapor transitions in the 3.2 to 17.76 ?m spectral region were made at 225 and 296 K with the mean relative thermal velocity approximation of the complex Robert-Bonamy (CRB) formalism. Five thousand four hundred and forty two transitions belonging to 11 vibrational bands were studied. From these data air-broadened half-widths were determined at the two temperatures and the temperature dependence of the half-width was evaluated using the standard formula (See PDF for formula) For a limited number of transitions CRB calculations doing the velocity integral were made at 7 temperatures in the range 200-980 K. The mechanisms in the broadening process are discussed and the effects on ? and on the temperature dependence of the half-width as a function of the quantum states of the transitions are shown. Where possible this work is compared with measurement. It is shown that the standard temperature dependence model for the half-width is not correct for a number of transitions.

Once in groundwater, chlorinated solvents, nitrate, perchlorate and dissolved metals from acid rock drainage pose serious water quality threats. Options for clea nup of these contaminants vary, but many have high capital costs that need long -term maintenance, continuing attention, and are not appropriate for lightly contaminated areas or where the source area is poorly defined. The introduction of emulsified edible oil substrate (EOS®) to the aquifer has been shown to accelerate anaerobic biodegradation and biotransformations of these widespread contaminants (U.S. Patent #6,398,960).

An experimental study has been undertaken on a 3-stage entraining diffuser with a distorted inlet flow. Two different circular-to-slot transition ducts were used as driving nozzles. Both transition ducts included a 90 degree bend. Varying degrees of inlet swirl were also considered. A 7-hole pressure probe was used to traverse the diffuser outlets. With a longitudinal duct the measured flows showed severe impingement of the primary flow on the walls of the entraining diffuser. Similar outlet flow distributions were observed for all cases of inlet swirl considered. In contrast, only minimal primary flow impingement was observed with a transverse duct. The use of the transverse duct also resulted in significant secondary flows including multiple large-scale vortices. These secondary flows intensified when swirl was added. Four performance parameters were calculated: the entrainment ratio, back pressure coefficient, pressure recovery coefficient and the entraining diffuser efficiency. The results showed that peak performance was attained at 20° of inlet swirl for both configurations. The addition of an entraining diffuser was found to result in minimal improvements of performance for the longitudinal duct configuration and significant improvements for the transverse orientation.Copyright © 2006 by ASME

An experimental investigation into the overall influence of struts spanning a double divergent annular diffuser followed by a straight cored annular diffuser has been undertaken in order to determine the performance of various strut configurations over a wide range of inlet swirl conditions. Two strut profiles have been investigated in four and eight strut configurations. Results have shown that the presence of struts under no swirl conditions have a relatively small effect on the overall total pressure loss. Increasing the inlet swirl angle to 20° has shown that the struts are able to assist in recovery of the swirling flow such that the pressure recovery nearly approaches that without struts, despite increased total pressure losses. Performance at 40° swirl is highly dependent on strut profile; the higher thickness-to-chord ratio strut configurations show minimal decrease in pressure recovery compared to 20° swirl, while the lower thickness-to-chord ratio configurations experiences a significant decrease as the result of significant flow separation from the struts. The exit swirl number has been shown to correlate strongly with the strut profile shape, while the number of struts had only a secondary influence. The exit velocity profiles show significant distortions at 40° swirl, and as a result the ideal pressure recovery calculated from the inlet and exit profiles change with strut configuration at 40° swirl.Copyright © 2006 by ASME

In the predicted future of distributed power generation, a large number of users will operate gas turbine powered cogeneration systems. These systems will be small, relatively inexpensive, and installed in locations without ready access to experts in gas turbine maintenance. Consequently, an automated system to monitor the engine and diagnose the health of the system is required. To remain compatible with the low cost of the overall system, the diagnostic system must also be relatively inexpensive to install and operate. Therefore, a minimum number of extra sensors and computing power should be used. A statistical technique is presented that compares the engine operation over time to the expected trends for particular faults. The technique ranks the probability that each fault is occurring on the engine. The technique can be used online, with daily data from the engine forming a trend for comparison, or, with less accuracy, based on a single operating point. The use of transient operating data with this technique is also examined. This technique has the advantage of providing an automated numerical result of the probability of a particular mode of degradation occurring, but can also produce visual plots of the engine operation. This allows maintenance staff to remain involved in the process, if they wish, rather than the system operating purely as a black box, and provides an easy to understand aid for discussions with operators. The technique is compared to an off the shelf neural network to determine its usefulness in comparison to other diagnostic methods. The test bed was a micro turbojet engine. The data to test the system was obtained from both experiment and computer modeling of the test engine.Copyright © 2006 by ASME

A large number of papers have been published on transient modeling of large industrial and military gas turbines. Few, however, have examined micro turbines. The decrease in size affects the relative rates of change of shaft speed, gas dynamics and heat soak. This paper compares the modeled transient effects of a micro turbojet engine comprised of a single stage of radial compression and a single stage of axial expansion, with a diameter of 12cm. The model was validated with experimental data. Several forms of the model were produced starting with the shaft and fuel transients. Conservation of mass, and then energy, was subsequently added for the compressor, combustor and turbine, and a large inlet plenum that was part of the experimental apparatus. Heat soak to the engine body was incorporated into both the shaft and energy models. Heat soak was considered in the compressor, combustor and turbine. Since the engine diameter appears in the differential equations to different powers, the relative rates of change vary with diameter. The rate of change of shaft speed is very strongly influenced. The responses of the different transient effects are compared. The relative solution times are also discussed, since the relative size of the required time steps changes when compared to a large engine.Copyright © 2006 by ASME

The potential extensive use of micro turbines in distributed power generation will produce a requirement for maintenance scheduling. The wide variety of operating environments and loads will demand that simple hour counters be overly conservative. Additionally, more advanced techniques, such as producing databases of the engine history or metallography, would have expenditures that far outweigh the benefit for such low cost engines. The technique presented in this paper predicts the remaining life of the engine based on operating data since the last overhaul. The technique is independent of the component degrading and uses specific fuel consumption as the determinant of failure, but does not require the measurement of fuel flow or power. The prime advantages of this technique are the requirement for few additional sensors beyond those needed for engine control, and the ability to predict the time until failure without knowledge of the fault occurring or input from the engine user. The system utilizes an algorithm to determine the form of the trend the path to failure is taking and applies exponential smoothing, which is then extrapolated forward to the failure conditions. Since the prediction is based on the operating data since the last overhaul, it initially performs very poorly, but as the engine approaches failure it improves. Depending on the form of the trend, good predictions begin between 30% and 70% through the life of the engine. The system was tested with a computer model of a micro turbojet engine with five different faults ranging from blockage of inlet filters to turbine degradation. Both single and combined faults were tested with similar success. The engine model, including healthy baseline and degraded operation, was validated with an experimental program.Copyright © 2006 by ASME

Laser transmission welding (LTW) is a relatively new technology for joining plastic parts. This paper presents a three-dimensional (3-D) transient thermal model of LTW solved with the finite element method (FEM). A lap-joint geometry was modelled for unreinforced nylon 6 specimens. This thermal model addressed the heating and cooling stages in a laser welding process with a stationary laser beam. This paper compares the temperature distribution of a lap-joint geometry exposed to a stationary diode laser beam, obtained from 3-D thermal modelling with thermal imaging observations. It is shown that the thermal model is capable of accurately predicting the temperature distribution when laser beam scattering during transmission through the polymer is included in the model. The weld dimensions obtained from the model have been compared with the experimental data and are in good agreement.Copyright © 2006 by ASME

This paper describes an experimental investigation into the effects of geometrical variations on ejector system performance when the driving nozzle includes delta mixing tabs. Mixing tabs have been shown to provide good mixing performance with comparable back-pressure penalties to other types of enhanced mixing nozzles. The performance parameters of most interest are pumping, mixing, and back-pressure. Geometric parameters studied include standoff distance, mixing-tube diameter, and tab angle. Experimental testing showed significant performance improvements in mixing and pumping with a decrease in tab angle. Maximum mixing was found to occur with tab angles positioned at 120°. Exceptional mixing was also observed with increased standoff. Back-pressure was shown to increase with increasing standoff and decreasing tab angle, but was not affected by mixing-tube diameter. In addition, a zone of recirculation was identified at the entrance to the mixing-tube. This zone is thought to have an influence on ejector performance.Copyright © 2006 by ASME

A composition for the bioremediation of soil or groundwater includes 35 to 60% by weight of an emulsifiable C4-C22 vegetable oil such as soybean or corn oil, about 60-35% by weight of a non-ionic surfactant/co-surfactant blend such as Tween 80®/Labrafil® mixed with Kolliphor EL®/Waglinol®, and about 0-12% by weight water.

Recent years have seen wider application of laser transmission welding (LTW) as a means for joining plastic parts. This paper presents a two-dimensional (2-D) thermal model of LTW solved with finite element method (FEM). A modified T-like joint geometry is modelled for unreinforced nylon 6 specimens. This thermal model addresses heating and cooling stages in a laser welding process. The 2-D model is capable of predicting the molten zone depth as well as transient temperature distribution along the weld line.Recent years have seen wider application of laser transmission welding (LTW) as a means for joining plastic parts. This paper presents a two-dimensional (2-D) thermal model of LTW solved with finite element method (FEM). A modified T-like joint geometry is modelled for unreinforced nylon 6 specimens. This thermal model addresses heating and cooling stages in a laser welding process. The 2-D model is capable of predicting the molten zone depth as well as transient temperature distribution along the weld line.

A computational study of an air-air ejector system, utilizing a primary S-bend transition duct, was compared with experimental results. Two primary ducts, differing in offset, consisted of an annular-to-circular-to-oblong transition which incorporated a total area increase of 62.4% with the duct performing 16% diffusion. The ducts were analyzed both alone and in ejector configuration under varying degrees of inlet swirl. The ejector geometry consisted of the duct with a downstream mixing tube. Several mixing tubes, of oblong cross sectional shape, differing in both length and area, were tested in various parametric configurations. Ejector performance was established on the basis of pumping capability, duct back pressure, and outlet effective area. Experimental work commenced on a cold flow test rig, with duct inlet conditions being measured with four 3-hole pitot probes. The duct outlet profiles were measured using a 7-hole probe which traversed the entire exit area. Three conditions of inlet swirl were analyzed: 0°, 20° and 40°. Experimental results showed an increase in pumping performance with increased inlet swirl, mixing tube length, area ratio and standoff. An optimum standoff value of 0.25Dh2 was observed. CFD simulations were based on experimental mass flow inlet conditions utilizing the realizable k-e turbulence model. CFD results showed that the realizable k-e turbulence model was quite capable of modeling the complex flow for the associated geometry, and correctly predicted flow features as well as performance trends for all geometrical configurations tested. However, the CFD was unable to properly predict the duct inlet static pressure leading to erroneous back pressure results.Copyright © 2005 by ASME

This paper presents preliminary results of a study performed on bent ejectors having applications in the aerospace industry. The ejectors consisted of a simple round primary nozzle and a bent mixing tube. The effects of bend angles on pumping characteristics were studied. A cold flow wind tunnel was used to provide the primary flow of air at ambient temperature at a maximum mass flow rate of 1.6 kg/sec. Velocity and pressure measurements were taken upstream of the nozzle and at the exit of mixing tube. The study was done with and without swirl in the primary flow. It was observed that swirl in primary flow improved the pumping performance of the bent. CFD analysis was performed using a commercial CFD code and the results were compared with the experiments. It was observed that the bend in the ejector had a significant effect on the pumping performance. The entrainment ratio decreased and then increased with the degree of bend. An ejector with a 45° bend in the geometry had 28% less entrainment ratio than a same size straight ejector. It was found that swirl in the primary flow improves the performance of the bent ejector. A maximum 17% increase in the entrainment ratio was observed with swirl in the case of a 67.5° bent ejector. In both 22.5° and 67.5° bent ejectors the pressure rise was slightly improved by 20° swirl in the primary flow. CFD was generally successful in predicting the trends as observed in the experiment results. CFD predictions of pumping were within ± 7% of the experiments.Copyright © 2005 by ASME

Objectives To investigate the prevalence of GB virus C (GBV-C) viraemia and GBV-C antibodies in a cohort of HIV-infected mothers and their infants between 1987 and 1994. Methods GBV-C viraemia and antibodies were determined by polymerase chain reaction (PCR) and enzyme-linked immunosorbent assay (ELISA) in 52 HIV-infected mothers and their 53 infants, who were born before antiretroviral prophylaxis for reduction of HIV transmission was introduced at the end of 1994. Ten of these children acquired HIV. Results Mothers of three children had GBV-C viraemia and mothers of another 14 children carried antibodies against GBV-C. No mother had GBV-C antibodies and GBV-C viraemia simultaneously. GBV-C viraemia was detected in only one infant. This child was delivered by the vaginal route to a mother with GBV-C viraemia, and was not HIV-infected. No vertical transmission of GBV-C occurred from mothers with GBV-C antibodies. However, four of 10 children who were infected with HIV had a mother with past or ongoing GBV-C infection. Conclusion Our findings suggest that the risk of vertical transmission of GBV-C is not elevated in HIV-infected mothers. Furthermore, although the number of HIV-1-infected children was low, we saw no evidence that the presence of ongoing or past GBV-C infection influenced the probability of vertical HIV transmission.

In some gas turbine applications, it is desirable to redirect the exhaust flow through 90 degrees and mix this flow with the ambient air for the purposes of structural integrity and heat signature suppression. A method to achieve this is to transform the flow from a circular profile to a rectangular slot of high aspect ratio. The increase in wetted perimeter allows for greater mixing with the ambient air; however the shape of such a duct causes significant amounts of flow distortion and poor pressure recovery. This paper presents preliminary experimental results of the performance of such a duct and discusses the ability of a commercial CFD software package to numerically predict this performance. Significant crossflows and reversed flows were observed at the duct outlet leading to inefficient use of the outlet area, high back pressure and consequently a high loss coefficient. These trends are exacerbated with an increasing inlet swirl angle. The preliminary numerical predictions captured the general trends of the flow but could not capture the extent of the reversed flow, leading to over-prediction of the effective area ratio, E, and under-prediction of the loss coefficient, k.Copyright © 2004 by ASME

Set up and operation of a mid to large size gas turbine requires a significant investment in the engine and the test cell. The continuing cost of operation and maintenance is also substantial. Both the capital and operating costs are well outside the budget of many educational institutions, and small research centres. Micro-turbines, in particular engines used for model aircraft, are a viable alternative. Their capital costs are low and existing facilities can often be modified to support them. Micro-turbines are complete turbojets often utilizing a centrifugal compressor from a turbo-charger and an axial turbine. This work utilized a micro-jet engine commonly used to propel remote control aircraft. The engine has been set up for research into component degradation and as a laboratory for an upper year engineering course in turbomachinery. It is rated by the manufacturer to produce 150 N of thrust at 132,000 RPM. This paper examines some of the problems encountered in installing small total pressure and temperature probes in a micro engine. The entire test rig, including measurement of thrust and mass flow is presented. As well, the addition of a PC based control system is discussed. Operating data is presented and compared to larger engines to demonstrate the viability of this engine as a test bed. Some problems encountered in using an engine such as this beyond its normal operating envelope, along with some solutions, are presented.Copyright © 2004 by ASME

Steady state and transient computer models of a micro turbine were produced. The engine under study was a micro-jet engine that when tested at 126,000 RPM provided 95 N thrust. The aero-thermal model uses generic performance maps for the compressor and turbine which were modified, based on operating data, to represent the components in the engine under study. The model also includes the inlet ducting connected to the engine. It simulates engine operation from idle to full power over the expected operating range of ambient temperature, pressure and humidity. A comparison of steady state model results to actual engine operating data is presented over the full range of speeds. The effect of ambient humidity on the engine operating point is examined for a micro-engine, in particular at temperatures above 30° Celsius. The techniques for introducing component faults are given and their effect on the engine operation is presented. The degraded components are the turbine and inlet flow passages. The methods for modeling the transient behavior of the engine are also presented. Results are presented for both acceleration and deceleration of the engine between steady state operating point. These results are also compared to the operating engine.Copyright © 2004 by ASME

An experimental and computational study of an air-air ejector system applicable to aerospace applications was conducted. The geometry of the ejector consists of a primary S-bend duct that expels into an oblong mixing tube. The focus of this study was to determine the performance and practicality of an ejector implemented downstream of an S-bend duct. Experimental and computational results were compared to determine computational adequacy. The experimental apparatus utilized a cold flow blower delivering air through an annulus to an S-bend duct that incorporated a downstream mixing tube. Flow measurements were made at the inlet and outlet of the duct as well as at the outlet of the mixing tube. This allowed losses of the primary duct as well as ejector pumping performance to be evaluated. The computational work involved using a commercial CFD package implementing k-e turbulence modeling and non-equilibrium wall functions.Copyright © 2004 by ASME

In the 1999 addenda to the 1998 ASME pressure vessel code, Section VIII, Div. 1 there was a change in design margin for unfired pressure vessels from 4.0 to 3.5. This has resulted in the manufacture of propane and LPG tanks with thinner walls. For example, the author has purchased some new 500 gallon ASME code propane tanks for testing purposes. These tanks had the wall thickness reduced from 7.7 mm in 2000 to 7.1 mm in 2002 and now to 6.5 mm in 2004. These changes were partly due to the code change and partly due to other factors such as steel plate availability. In any case, the changes in wall thickness significantly affects the fire survivability of these tanks. This paper presents both experimental and computational results that show the effect of wall thickness on tank survivability to fire impingement. The results show that for the same dank diameter, tank material, and pressure relief valve setting, the thinner wall tanks are more likely to fail in a given fire situation. In severe fires, the thinner walled tanks will fail earlier. An earlier failure usually means the tank will fail with a higher fill level, because the pressure relief system has had less time to vent material from the tank. A higher liquid fill level at failure also means more energy is in the tank and this means the failure will be more violent. The worst failure scenario is known as a boiling liquid expanding vapor explosion and this mode of failure is also more likely with the thinner walled tanks. The results of this work suggest that certain applications of pressure vessels such as propane transport and storage may require higher design margins than required by Section VIII ASME code.

A short range broad band noise radar system using an electrically tunable true-time-delay line in silicon is presented. The delay line has to cover the interested scanning range (here 2.3 m) and show low dispersion. The delay line consists of discrete switchable lines realized in hybrid form and a on chip continual tunable coplanar delay line. The noise radar operates at the X-band (10.7 GHz-12 GHz). Measurements are presented with a fixed obstacle in the scanned range.

Nanosecond routing in a 64/spl times/64 optical phased array switch is reported. Further testing of the switch shows transmission capability of four 40 Gb/s WDM channels through a single switch path, with power penalty of 0.3 dB per channel. The optical path performance at high bit rate and data rate scalability of the switch is demonstrated for the first time. This performance indicates the possibility of switch implementation in Terabit routing systems. Furthermore, the results presented demonstrate the wavelength, data rate and format transparency of the switch, opening the possibility for the switch to be used in optical IP networks.

In summary, we demonstrated a large-scale MEMS PXC with performance capabilities consistent with needs for realistic carrier network applications. Careful attention needs to be given to interoperating PXCs with other network equipment, including WDM systems.

We have fabricated and measured a sampling circuit on high resistivity silicon substrate. The circuit incorporates a nonlinear transmission line to provide the sampling pulses. The sampling circuit was measured up to 50 GHz, with a voltage conversion loss lower than 11 dB and varying in this range by just 2.3 dB. This is the first presentation of a sampling circuit on silicon substrate with a corner frequency beyond 50 GHz.

Nonlinear transmission lines (NLTL) use the voltage-dependent reverse-biased capacitance of Schottky diodes distributed along a high impedance transmission line to introduce nonlinear wave propagation effects. The shockwave NLTL, as described in this paper, steepens the leading or falling edge of a large time-domain signal, just like the wave-breaking effect of water on beaches. While traditionally NLTLs were monolithically integrated on GaAs, with the best reported results being the generation of 480 fs and 680 fs transients, we integrate these lines on high resistivity silicon. The advantages include the combination of silicon millimeter wave integrated circuits (SIMMWIC) with the nonlinear transmission line for high frequency applications, such as sampling circuits or high-order frequency multiplication. Integration with Si-SiGe heterostructure bipolar transistors for frequencies above 30 GHz yields new design alternatives.

Semiconductor Schottky diodes are key elements in nonlinear transmission lines (NLTL) with their doping profiles optimized for performance. Several reports have used doping profiles other than homogeneous doping. However, to date, no work has been reported on the direct comparison of those different doping compositions. In this report, we present a complete study on composition profiles (homogeneous, double homogeneous, pulse, exponential and gaussian doping profiles) with GaAs as the semiconductor material of choice. With our analytical diode model originally demonstrated for NLTL on silicon substrates, the diode maximum value of cutoff frequency was achieved by varying parameters such as the doping concentrations and layer thicknesses while keeping constant the breakdown voltage and capacitance swing.

Summary form only given. Nonlinear Transmission Lines (NLTL) have been fabricated so far on GaAs substrates only. Recently, we were able to demonstrate a working nonlinear transmission line for the first time on high resistivity silicon proving the applicability of the NLTL concept to silicon millimeter wave integrated circuits (SIMMWICs). We have significantly improved our previous results by integrating the NLTL into a Si/SiGe Heterostructure Bipolar Transistor (HBT) process. The falltime of 74 ps of a 4 GHz sine wave was compressed to 12 ps, 4 V amplitude at the output of the NLTL.

If a pressure vessel containing a pressure liquefied gas (PLG) is exposed to a severe fire, there is a chance the tank will rupture and possibility even explode. It has been shown that the energy stored in the liquid phase is important in the outcome of such an accident. In order to better understand tank failure and energy storage, it is desired to understand the complex thermo-hydraulic response of the lading prior to a thermally induced rupture. In the summers of 2000 and 2001, a series of controlled fire tests were conducted on horizontal 1890 litre (500 US gallon) propane tanks. The test tanks were instrumented with pressure transducers, lading and wall thermocouples, and an instrumented flow nozzle in place of a pressure relief valve (PRV). A computer controlled PRV was used to control pressure, while high momentum, liquid propane utility torches were used to heat the tank. PRV blowdown and fire conditions were varied in this test series while all other input parameters were held constant. It was found that the lading response and energy storage varied according to the fire conditions and PRV operation. The location and quantity of the burners affected the thermal stratification within the liquid, and the swelling and frothing at the liquid/vapour interface. The blowdown of the PRV affected average tank pressure, average liquid temperature and time to destratify. PRV operation caused enhanced convective cooling on the vapour space wall. The degree of blowdown dictated the pressure drop, and thus the liquid flashing and subsequent swelling were affected. This paper will discuss these thermohydraulic responses and their role in the tank failure.Copyright © 2002 by ASME

In one possible model of distributed power generation a large number of users will operate individual, gas turbine powered, cogeneration systems. These systems will be small, relatively inexpensive, and installed in locations without ready access to gas turbine maintenance experts. Consequently an automated method to monitor the engine and diagnose its health is required. To remain compatible with the low cost of the power system the diagnostics must also be relatively inexpensive to install and operate. Accordingly a minimum number of extra sensors should be used and the analysis performed by a common personal computer system. The current work automates the diagnosis of component faults by comparing the engine’s operating trends to the trends for known faults. This allows the relative percentage chance of each fault occurring to be determined. The likelihood of each fault is then compared, to determine which component is degrading. The technique can be adapted to compare the engines historic operating trend or a single operating point. In this initial work a computer model was used as a test bed and 5 faults were introduced individually. The technique successfully diagnosed the faulty component using either the operating trend or a single operating point.Copyright © 2002 by ASME

A series of fire tests were conducted on nine, 1.8 m 3 (500 US gal) ASME code propane pressure vessels to study the significance of pressure relief valve behavior on tank survivability to fire impingement. In these tests three tanks ruptured (i.e., finite failure) and six boiling liquid expanding vapor explosion (BLEVEd) (total loss of containment). The difference between the BLEVE and non-BLEVE failures was due to a difference in the fire conditions. It is believed that these tests show some insight into the BLEVE process. In all tests the fire consisted of an array of nominal 590 kW (2 MBTU/h) liquid propane burners. A pool fire was not used because of the uncontrolled nature of open pool fires. It was believed that very repeatable fire conditions could be achieved by using a series of burners. In the tests where the outcome was a non-BLEVE there were two burners mounted 30 cm above the tank on the tank vapor space. These burners were used to weaken the steel and to initiate a failure. To heat the liquid, there were between 4 and 12 burners applied below the liquid level. When one burner was added on the vapor space, all of the remaining tanks BLEVEd. This was true over a range of fill levels (at failure) of between 10% and 50% by volume. It is believed this added burner was just enough to weaken the tank so that any initial rupture would grow towards a total loss of containment and BLEVE. This paper presents the details of this test series and shows how severely heated length and liquid energy affected the outcome.

When highly non-symmetric exhaust ducts are installed on a gas turbine engine, the asymmetries result in a non-uniform circumferential total pressure condition at the inlet of the duct. When testing these ducts experimentally or computationally the correct inlet conditions are often not known or cannot be reproduced. To study the sensitivity of duct performance to inlet conditions, an experimental and computational study of a non-symmetric gas turbine exhaust duct that includes a 160° turn with an annular to rectangular transition, has been carried out over a range of inlet conditions. The inlet conditions varied include circumferential total pressure profiles and swirl. The experimental studies have been carried out in cold flow with several non-uniform total pressure inlet conditions. Computational fluid dynamic (CFD) techniques validated against the experimental results, have been used to extend the range of inlet conditions beyond the range that could be obtained experimentally to those typical of an engine installation. Results show that the total pressure inlet conditions have a significant effect on the flow structure in the exhaust duct and that the performance of the exhaust duct degrades as the level of circumferential non-uniformities increase. However, trends in geometric optimization identified experimentally using cold flow and uniform total pressure inlet conditions are confirmed computationally with circumferential non-uniformities typical of actual engine operations. This suggests that although inlet conditions are important for determining the level of performance, the configuration of the optimized geometry is somewhat independent of the inlet conditions.Copyright © 2002 by ASME

A computer model of a gas turbine auxiliary power unit was produced to develop techniques for fault diagnosis and prediction of remaining life in small gas turbine engines. Due to the relatively low capital cost of small engines it is important that the techniques have both low capital and operating costs. Failing engine components were identified with fault maps, and an algorithm was developed for predicting the time to failure, based on the engine’s past operation. Simulating daily engine operation over a maintenance cycle tested the techniques for identification and prediction. The simulation included daily variations in ambient conditions, operating time, load, engine speed and operating environment, to determine the amount of degradation per day. The algorithm successfully adapted to the daily changes and corrected the operating point back to standard conditions to predict the time to failure.