bluuebunny/crossref_metadata_2025 huggingface dataset:
CTCC Cogeneration Systems and Steam Supply Availability: An Investigation of Dynamic Availability
Authors: Franceschi J. M.
Published: April 2008

The ability of an industrial cogeneration project to satisfy its steam supply contract was investigated using dynamic simulation. This study of unit behavior performance focused on steam capacity control during expected operational transients, from the trigger event to system recovery. Transients specified in the project steam sale contract include the conditions of unit upset and the dynamic interruption criteria. Performance is measured by the quantitative steam supply variables of pressure, flow, temperature, enthalpy (at the battery limit) and response time following the disturbance of a combustion turbine (CT) trip. A unit especially configured for steam supply uses an availability strategy for response to a CT loss, which requires back-up equipment in the boiler island to activate in time to compensate for disturbance effects without loss of steam-sale continuity as defined in the contract. Dynamic simulation was used to validate seamless transitions of plant alignments from one mode to another during the specified scenarios. A discussion of steadystate availability and facility power block structure sets the context for the investigation.
Detonation-Wave Technique for On-Load Deposit Removal From Surfaces Exposed to Fouling: Part II—Full-Scale Application
Authors: Hanjalic´ K. , Smajevic´ I.
Published: April 2008

The paper reports on the full-scale application and testing of the detonation-wave technique in two boilers, fired with pulverized coal, of total thermal power of 600 MW. Continuous monitoring over a period of several years confirmed earlier laboratory findings, reported in the companion Part I of the paper. The testing proved that the technique is efficient and reliable, with a number of advantages in comparison with various conventional cleaning methods. In spite of the fact that the lining of one of the boilers is made of classic refractory material, careful records and inspection over several years of daily application of the detonation wave technique showed no signs of any undesirable effects. The method was officially adopted as a routine deposit removal technique in the Power Plant “Kakanj” in Bosnia.
Powder Metallurgy Repair of Turbine Components
Authors: Ellison K. A. , Lowden P. , Liburdi J.
Published: April 2008

An advanced powder metallurgy repair process called Liburdi Powder Metallurgy (LPM) has been developed for the repair, overlay or joining of nickel and cobalt-based high-temperature alloys. This process involves mechanical cleaning, followed by the application and consolidation of a filler metal powder, which has substantially the same composition as the base metal, and produces joints with mechanical properties similar to those of the parent material. While previously activated braze or “wide-gap” repair processes have been limited to clearances of approximately 1 mm, the LPM technique has the ability to bridge larger gaps of over 5 mm. In addition, the LPM joints contain significantly lower concentrations of melting point depressants such as silicon and boron than conventional wide-gap repair techniques and exhibit superior microstructural features. The characteristics and typical applications of the LPM process for blade and vane repairs are highlighted and the results of laboratory and engine tests are discussed.
The Evolution of Thermal Barrier Coatings in Gas Turbine Engine Applications
Authors: Meier S. M. , Gupta D. K.
Published: April 2008

Thermal barrier coatings (TBCs) have been used for almost three decades to extend the life of combustors and augmentors and, more recently, stationary turbine components. Plasma-sprayed yttria-stabilized zirconia TBC currently is bill-of-material on many commercial jet engine parts. A more durable electron beam-physical vapor deposited (EB-PVD) ceramic coating recently has been developed for more demanding rotating as well as stationary turbine components. This ceramic EB-PVD is bill-of-material on turbine blades and vanes in current high thrust engine models and is being considered for newer developmental engines as well. To take maximum advantage of potential TBC benefits, the thermal effect of the TBC ceramic layer must become an integral element of the hot section component design system. To do this with acceptable reliability requires a suitable analytical life prediction model calibrated to engine experience. The latest efforts in thermal barrier coatings are directed toward correlating such models to measured engine performance.
Optimal Sizing of a Gas Turbine Cogeneration Plant in Consideration of Its Operational Strategy
Authors: Yokoyama R. , Ito K. , Matsumoto Y.
Published: April 2008

An optimal planning method is proposed for the fundamental design of cogeneration plants. Equipment capacities and utility maximum demands are determined so as to minimize the annual total cost in consideration of the plants’ annual operational strategies for the variations of both electricity and thermal energy demands. These sizing and operational planning problems are formulated as a nonlinear programming problem and a mixed-integer linear programming problem, respectively. They are solved efficiently in consideration of their hierarchical relationship by a penalty method. A numerical example about a gas turbine plant is given to ascertain the validity and effectiveness of the proposed method.
Performance and Emission Levels in Gas Turbine Plants
Authors: Bozza F. , Tuccillo R. , Fontana G.
Published: April 2008

The rise in gas turbine combustion chamber temperatures requires optimal choices to be made with regard not only to performance parameters but also with a view to resolving pollutant emission problems. For this reason, the authors have set up a gas turbine cycle model, which performs an accurate analysis of several processes, in terms of operating fluid chemical and thermodynamic properties. The model also enables prediction of NOx formation based upon chemical kinetics and is able to relate the amount of pollutants to a number of operating parameters (e.g., cycle pressure ratio, fuel-to-air equivalence ratio, residence time in combustion chamber, etc.). It can also predict the effect of most usual NOx reduction systems, such as water or steam injection. A comparison of several possible choices for the gas and combined cycles is then presented, in terms of thermodynamic performance (e.g., first and second law analysis) and nitric and carbon dioxide emissions. In order to find the best compromise between performance improvement and limitation of pollutant emission, enhanced gas cycles are also considered, such as STIG or intercooled-reheat cycles. Examples also refer to medium or low Btu gases, obtained from coal gasification, in order to show not only the possible advantages in terms of thermal NOx reduction, but also the significant amounts of “fuel NOx” that can arise from ammonia contained in the fuel.
Development of Gas Turbine Steam Injection Water Recovery (SIWR) System
Authors: Nguyen H. B. , den Otter A.
Published: April 2008

This paper describes and discusses a “closed-loop” steam injection water recovery (SIWR) cycle that was developed for steam-injected gas turbine applications. This process is needed to support gas turbine steam injection especially in areas where water cannot be wasted and complex water treatment is discouraged. The development of the SIWR was initiated by NOVA in an effort to reduce the environmental impact of operating gas turbines and to find suitable solutions for its expanding gas transmission system to meet future air emission restrictions. While turbine steam injection provides many benefits, it has not been considered for remote, less supported environments such as gas transmission applications due to its high water consumption. The SIWR process can alleviate this problem regardless of the amount of injection required. The paper also covers conceptual designs of a prototype SIWR system on a small gas turbine unit. However, because of relatively high costs, it is generally believed that the system is more attractive to larger size turbines and especially when it is used in conjunction with cogeneration or combined cycle applications.
Engineering-Economic Optimization of a Fuel Cell Cogeneration Plant
Authors: Matsumoto Y. , Yokoyama R. , Ito K.
Published: April 2008

The feasibility of fuel cells in cogeneration applications is studied from engineering and economic viewpoints by using an optimization approach. Capacities of fuel cell cogeneration units and auxiliary devices are determined together with maximum utility demands so as to minimize the annual total cost by considering the plant’s annual operational strategy. This optimization problem is solved efficiently by considering the hierarchical relationship between unit sizing and operational planning problems. Through a numerical study on a plant for installation in a hotel and office building with a maximum electrical demand of 1000 kW, the effect of initial capital cost of fuel cell cogeneration units is examined from the perspective of the plant capacity, economics, and energy savings. The results show that a fuel cell cogeneration plant may have better economic and energy-saving characteristics than a conventional gas engine cogeneration plant with a reduction in the capital cost of fuel cell.
Flow Separation in Shock Wave Boundary Layer Interactions
Authors: Hamed A. , Kumar A.
Published: April 2008

This work presents an assessment of the experimental data on separated flow in shock wave turbulent boundary layer interactions at hypersonic and supersonic speeds. The data base consists of selected configurations where the only characteristic length in the iteration is the incoming boundary layer thickness. It consists of two-dimensional and axisymmetric interactions in compression corners or cylinder-flares, and externally generated oblique shock interactions with boundary layers over flat plates or cylindrical surfaces. The conditions leading to flow separation and the empirical correlations for incipient separation are reviewed. The effects of Mach number, Reynolds number, surface cooling, and the methods of detecting separation are discussed.
Exergy Analysis: Principles and Practice
Authors: Moran M. J. , Sciubba E.
Published: April 2008

The importance of the goal of developing systems that effectively use nonrenewable energy resources such as oil, natural gas, and coal is apparent. The method of exergy analysis is well suited for furthering this goal, for it enables the location, type and true magnitude of waste and loss to be determined. Such information can be used to design new systems and to reduce the inefficiency of existing systems. This paper provides a brief survey of both exergy principles and the current literature of exergy analysis with emphasis on areas of application.
Comments on the Development of the Early Westinghouse Turbojets, 1941-1946
Authors: Way S.
Published: April 2008

The early thinking leading to the American Turbojet engine is reviewed. This included ideas pertaining to ramjets and rockets, and culminated in the axial flow turbojet engine concept. The role of the NACA Subcommittee on Jet Propulsion under the leadership of Dr. W. F. Durand is stressed. Early problems with the new engine are mentioned, including flame tube light-off, interconnecting tubes, and fuel injection problems. An early major design innovation was the change to a single annular combustion chamber, replacing the 24 cans. This change culminated in the 19XB engine. The purposes of this paper are to show the magnitude of the problems encountered, and to give credit to the many dedicated persons who made the American Axial Flow Turbojet Engine a success.
Materials Performance in Advanced Combustion Systems
Authors: Natesan K.
Published: April 2008

A number of advanced technologies are being developed to convert coal into clean fuels for use as feedstock in chemical plants and for power generation. From the standpoint of component materials, the environments created by coal conversion and combustion in these technologies and their interactions with materials are of interest. The trend in the new or advanced systems is to improve thermal efficiency and reduce the environmental impact of the process effluents. This paper discusses several systems that are under development and identifies requirements for materials application in those systems. Available data on the performance of materials in several of the environments are used to examine the performance envelopes for materials for several of the systems and to identify needs for additional work in different areas.
Effect of Pressure on Second-Generation Pressurized Fluidized Bed Combustion Plants
Authors: Robertson A. , Bonk D.
Published: April 2008

In the search for a more efficient, less costly, and more environmentally responsible method for generating electrical power from coal, research and development has turned to advanced pressurized fluidized bed combustion (PFBC) and coal gasification technologies. A logical extension of this work is the second-generation PFBC plant, which incorporates key components of each of these technologies. In this new type of plant, coal is devolatilized/carbonized before it is injected into the PFB combustor bed, and the low-Btu fuel gas produced by this process is burned in a gas turbine topping combustor. By integrating coal carbonization with PFB coal/char combustion, gas turbine inlet temperatures higher than 1149°C (2100°F) can be achieved. The carbonizer, PFB combustor, and particulate-capturing hot gas cleanup systems operate at 871°C (1600°F), permitting sulfur capture by time-based sorbents and minimizing the release of coal contaminants to the gases. This paper presents the performance and economics of this new type of plant and provides a brief overview of the pilot plant test programs being conducted to support its development.
An Assessment of Weighted-Least-Squares-Based Gas Path Analysis
Authors: Doel D. L.
Published: April 2008

Manufacturers of gas turbines have searched for three decades for a reliable way to use gas path measurements to determine the health of jet engine components. They have been hindered in this pursuit by the quality of the measurements used to carry out the analysis. Engine manufacturers have chosen weighted-least-squares techniques to reduce the inaccuracy caused by sensor error. While these algorithms are clearly an improvement over the previous generation of gas path analysis programs, they still fail in many situations. This paper describes some of the failures and explores their relationship to the underlying analysis technique. It also describes difficulties in implementing a gas path analysis program. The paper concludes with an appraisal of weighted-least-squares-based gas path analysis.
Fault Diagnosis in Gas Turbines Using a Model-Based Technique
Authors: Merrington G. L.
Published: April 2008

Reliable methods for diagnosing faults and detecting degraded performance in gas turbine engines are continually being sought. In this paper, a model-based technique is applied to the problem of detecting degraded performance in a military turbofan engine from take-off acceleration-type transients. In the past, difficulty has been experienced in isolating the effects of some of the physical processes involved. One such effect is the influence of the bulk metal temperature on the measured engine parameters during large power excursions. It will be shown that the model-based technique provides a simple and convenient way of separating this effect from the faster dynamic components. The important conclusion from this work is that good fault coverage can be gleaned from the resultant pseudo-steady-state gain estimates derived in this way.
Influence of High Rotational Speeds on Heat Transfer and Oil Film Thickness in Aero-Engine Bearing Chambers
Authors: Wittig S. , Glahn A. , Himmelsbach J.
Published: April 2008

Increasing the thermal loading of bearing chambers in modern aero-engines requires advanced techniques for the determination of heat transfer characteristics. In the present study, film thickness and heat transfer measurements have been carried out for the complex two-phase oil/air flow in bearing chambers. In order to ensure real engine conditions, a new test facility has been built up, designed for rotational speeds up to n = 16,000 rpm and maximum flow temperatures of Tmax = 473 K. Sealing air and lubrication oil flow can be varied nearly in the whole range of aero-engine applications. Special interest is directed toward the development of an ultrasonic oil film thickness measuring technique, which can be used without any reaction on the flow inside the chamber. The determination of local heat transfer at the bearing chamber housing is based on a well-known temperature gradient method using surface temperature measurements and a finite element code to determine temperature distributions within the bearing chamber housing. The influence of high rotational speed on the local heat transfer and the oil film thickness is discussed.
Induced Draft Fan Innovation for Heat Recovery Steam Generators
Authors: Beasley O. W. , Hutchins E. C. , Predick P. R. , Vavrek J. M.
Published: April 2008

A first of its kind, induced draft (ID) heat recovery steam generators (HRSG) have been in service at a cogeneration facility since 1991. A preliminary engineering study considered a forced draft (FD) fan to supply combustion air to the HRSG duct burners (when the combustion turbine (CT) is out of service) as a traditional design; however, the study indicated that the FD fan may require the HRSG duct burner to be shut off following a CT trip and re-ignited after the FD fan was in service. Although the induced draft HRSG design cost more than the FD fan design, the induced draft design has improved the cogeneration facility’s steam generation reliability by enabling the HRSG to remain in service following a CT trip. This paper briefly summarizes the preliminary engineering study that supported the decision to select the ID fan design. The paper also discusses the control system that operates the fresh-air louvers, duct burners, HRSG, and ID fan during a CT trip. Startup and operating experiences are presented that demonstrate the effectiveness of the design. Lessons learned are also summarized for input into future induced draft HRSG designs.
The Increased Use of Gas Turbines as Commercial Marine Engines
Authors: Brady C. O. , Luck D. L.
Published: April 2008

Over the last three decades, aeroderivative gas turbines have become established naval ship propulsion engines, but use in the commercial marine field has been more limited. Today, aeroderivative gas turbines are being increasingly utilized as commercial marine engines. The primary reason for the increased use of gas turbines is discussed and several recent GE aeroderivative gas turbine commercial marine applications are described with particular aspects of the gas turbine engine installations detailed. Finally, the potential for future commercial marine aeroderivative gas turbine applications is presented.
Development of a Method to Evaluate the Design Performance of a Feedwater Heater With a Short Drain Cooler
Authors: Weber G. E. , Worek W. M.
Published: April 2008

A method is developed to determine the shell and tube side heat transfer performance of a feedwater heater with a short drain cooler. The desuperheating, condensing, and drain cooling zones are discussed and analyzed by deriving a modified version of the Delaware Method of Shell-Side Design.
Some Aspects of Erosion Prediction of Steam Turbine Blading
Authors: Krzyzanowski J. A. , Kowalski A. E. , Shubenko A. L.
Published: April 2008

This paper deals with an issue of paramount importance for the turbine manufacturer today: the mathematical modeling of erosive wear at the inlet rotor blade edges by streams of coarsely dispersed liquid droplets. In the methodology of blade material wear an important element is the erosion model or material response Y = Y (τ) to the droplet impact intensity. On the background of this erosion model development the approaches of Szprengiel and Weigle (1983), Szprengiel (1985), and Shubenko and Kovalsky (1987) are presented and applied for erosion calculation of some real turbine blade profiles. There are, however, several factors that affect the erosion prediction quality as well as the field experimental data. Hence a procedure for verifying the methodology of the erosion prediction by experimental data is necessary. Krzyzanowski (1987, 1988, 1991) used for that purpose the calculated and measured erodet area of various turbine blade profiles. Here the comparison of the calculated and measured erosion width ηB ≡ z has been used to verify the prediction methodology of erosion. The use of ηB instead of erosion area looked promising since acquiring ηB experimental values seemed easier than any other geometric characteristics of the blade erosion wear. It has been shown, however, that the prediction of ηB underestimates the blade erosion wear for both material response models. To cope with the scatter of experimental data, statistics have been used. Reasons for this scatter and differences between the calculated (ηBcalc) and measured (ηBm) values of the erosion field width have been suggested. The list of factors that affect the erosion prediction quality may be looked upon as a list of promising topics of further research on the subject.
Second-Law Analysis of Vapor Compression Heat Pumps With Solution Circuit
Authors: Amrane K. , Radermacher R.
Published: April 2008

A second-law analysis is conducted on both the single-stage vapor compression heat pump with solution circuit (VCHSC) and its modified version, the cycle with a preheater and additional desorber. The results are compared to a conventional heat pump cycle operating with pure ammonia. The location and magnitude of the irreversibilities of the individual components constituting the cycles are determined. The entropic average temperature is used in computing the irreversibilities. The total work input to the heat pumps is then conveniently decomposed into two parts: the minimum work input or the work of a reversible cycle operating between the desorber and absorber entropic average temperatures, plus an additional input of work caused by the irreversibilities of the different processes of the cycles. The analysis reveals that the compressor is the most inefficient component of the heat pumps with losses accounting for about one fourth of the work input. The irreversibilities in the desorber and absorber are found to be minimum when there is a good match in both the solution and heat transfer fluid temperature glides. By adding a preheater and an additional desorber, the irreversibilities in the single-stage VCHSC are considerably reduced. However, it is shown that it is the preheater and not the additional desorber that has by far the most significant impact on the heat pump’s efficiency improvements. Compared to a conventional ammonia vapor compression cycle, the modified VCHSC, which has twice as many sources of irreversibility, shows nevertheless a maximum improvement of 56.1 percent in second-law efficiency.
Aircraft Gas Turbine Emissions Challenge
Authors: Koff B. L.
Published: April 2008

The new generation of jet powered aircraft faces a significant challenge to reduce pollutant emissions while increasing fuel efficiency. Carbon monoxide (CO) and unburned hydrocarbon (HC) emissions are already very low and continued control of these pollutants is expected as engine temperatures and pressure ratios are increased. In contrast, significant system design improvements are needed to reduce oxides of nitrogen (NOx) emissions because of their harmful effect on the earth’s ozone layer. This paper discusses the prospects and technical approaches for significant NOx reductions in current and future subsonic and supersonic aircraft.
Nitrogen Oxide Emissions Characteristics of Augmented Turbofan Engines
Authors: Seto S. P. , Lyon T. F.
Published: April 2008

The exhaust plumes of modern military engines can be rendered visible at low augmentor power operation by the presence of nitrogen dioxide (NO2). Visible plumes have also been observed from some industrial gas turbines that have duct burners downstream of the power turbines. In 1986, gaseous emissions measurements were taken behind two F101 turbofan engines to determine the effect of reheat level on the degree of conversion of nitric oxide (NO) to nitrogen dioxide and to relate the plume visibility to nitrogen dioxide concentration.
Test Results of Low NOx Catalytic Combustors for Gas Turbines
Authors: Ozawa Y. , Hirano J. , Sato M. , Saiga M. , Watanabe S.
Published: April 2008

Catalytic combustion is an ultralow NOx combustion method, so it is expected that this method will be applied to a gas turbine combustor. However, it is difficult to develop a catalytic combustor because catalytic reliability at high temperature is still insufficient. To overcome this difficulty, we designed a catalytic combustor in which premixed combustion was combined. By this device, it is possible to obtain combustion gas at a combustion temperature of 1300°C while keeping the catalytic temperature below 1000°C. After performing preliminary tests using LPG, we designed two types of combustor for natural gas with a capacity equivalent to one combustor used in a 20 MW class multican-type gas turbine. Combustion tests were conducted at atmospheric pressure using natural gas. As a result, it was confirmed that a combustor in which catalytic combustor segments were arranged alternately with premixing nozzles could achieve low NOx and high combustion efficiency in the range from 1000°C to 1300°C of the combustor exit gas temperature.
Detailed Performance Comparison of a Dump and Short Faired Combustor Diffuser System
Authors: Carrotte J. F. , Denman P. A. , Wray A. P. , Fry P.
Published: April 2008

A rectangular model simulating four sectors of a combustion chamber was used to compare the performance of a standard dump diffuser, of overall length 180 mm, with that of a faired design 25.5 mm shorter. The performance of each system was assessed in terms of total pressure loss and static pressure recovery between prediffuser inlet and the annuli surrounding the flame tube. Since the program objective was to test design concepts only, no allowance was made for the presence of burner feed arms or flame tube support pins. In addition, tests were performed with relatively low levels of inlet turbulence and no wake mixing effects from upstream compressor blades. Relative to the dump design, the mass weighted total pressure loss to the outer and inner annuli was reduced by 30 and 40 percent, respectively, for the faired diffuser. Measurements around the flame tube head were used to identify regions of high loss within each system and account for the differences in performance. Within a dump diffuser the flow separates at prediffuser exit resulting in a free surface diffusion around the flame tube head and a recirculating flow in the dump cavity. This source of loss is eliminated in the faired system where the flow remains attached to the casings. Furthermore, the faired system exhibited similar velocity magnitudes and gradients around the combustor head despite its shorter length.
Control Requirements for the RB 211 Low-Emission Combustion System
Authors: Corbett N. C. , Lines N. P.
Published: April 2008

The RB 211 DLE series staged, premix, lean burn combustor demands total integration of control system and combustion hardware. The controls design process is described from the conception of the Engine Management System (EMS), which provides protection and control in separate environments, through to implementation of engine development testing. The process of devising an acceptable fueling strategy to each combustion stage is discussed. This identified the requirements for the computation of complex routines in order to control combustion zone temperatures. The sensitivity of the control design to external conditions of humidity, ambient temperature, and fuel composition is explored. Extensive simulation was used to determine necessary instrumentation accuracies. The paper concludes with a review of the development testing and the final control system configuration.
Development of an Aeroderivative Gas Turbine Dry Low Emissions Combustion System
Authors: Leonard G. , Stegmaier J.
Published: April 2008

This paper gives the development status of GE’s new aeroderivative premixed combustion system. This system consists of a new fuel staged annular combustor, compressor rear frame, first-stage turbine nozzle, electronic staging controller, and fuel delivery system. Component test results along with a description of the combustion system are presented. This new system will reduce NOx emissions by 90 percent relative to the original aircraft engine combustion system while maintaining low emissions of CO and UHCs. Tests of a LM6000 gas turbine equipped with the new system are planned for early 1994.
Effect of Pressure on Combustion Characteristics in LBG-Fueled 1300°C-Class Gas Turbine
Authors: Nakata T. , Sato M. , Ninomiya T. , Yoshine T. , Yamada M.
Published: April 2008

Developing integrated coal gasification combined cycle systems ensures that Japan will have cost-effective and environmentally sound options for supplying future power generation needs. Reduction of NOx emissions and increasing the inlet temperature of gas turbines are the most significant issues in gas turbine development in IGCC. The coal gasified fuel, which is produced in a coal gasifier of air blown entrained-flow type has a calorific value as low as 1/10 of natural gas. Furthermore, the fuel gas contains ammonia when a gas cleaning system is a hot type, and ammonia will be converted to nitrogen oxides in the combustion process of a gas turbine. The study is performed in 1300°C-class gas turbine combustor firing coal-gasifier fuel in IGCC power generation systems. In the previous study [1] the advanced rich-lean combustor of 150-MW class gas turbine was designed to hold stable combustion burning low-Btu gas fuel and to reduce fuel NOx emission that is produced from the ammonia in the fuel. By testing it under atmospheric pressure conditions, we have studied the effects of fuel parameters on combustor performances and listed the basic data for development applications. In this study, by testing it under pressurized conditions, we have obtained a very significant result through investigating the effect of pressure on combustion characteristics and wish to provide herein a summary of our findings.
Contribution of Thermal Radiation to the Temperature Profile of Ceramic Composite Materials
Authors: Tremante A. , Malpica F.
Published: April 2008

The steady energy transfer equation for simultaneous conduction and radiation in an absorbing, emitting, and nonscattering gray planar medium is studied theoretically. For extremely high-temperature applications, where radiative transfer plays an important role, ceramic-matrix composites, considered as semitransparent materials, are being explored for potential use in turbine and compressor components, spacecraft structures, engine control systems, and nuclear reactors. Exact solution of the above-mentioned radiative problems is seldom possible and time-consuming numerical approximations are then used. A technique combining an accurate physical formulation, the two-flux model, coupled to a fast numerical procedure for the calculation of the temperature and heat fluxes is described.
Computed Tomography Evaluation of Metal-Matrix Composites for Aeropropulsion Engine Applications
Authors: Yancey R. N. , Baaklini G. Y.
Published: April 2008

Computed tomography (CT) is a powerful evaluation tool for advanced propulsion engine materials and components. CT uses X-rays nondestructively to produce images of two-dimensional slices or planes through an object. This paper will present data from CT investigations of metal-matrix composite (MMC) ring, rod, and coupon structures. Moderate resolution CT data identified density variations within reinforced sections, which were correlated with fiber packing densities. Also, some composite lay-up features were also imaged. High-resolution CT data provided information on fiber spacing and distribution. Correlation with other NDE techniques and destructive analysis was good. CT proved to provide valuable information on the internal state of these metal-matrix composite components. Use of CT during process development of MMCs and the components made from MMCs is encouraged given the results of this study.
On Curve Veering and Flutter of Rotating Blades
Authors: Afolabi D. , Mehmed O.
Published: April 2008

The eigenvalues of rotating blades usually change with rotation speed according to the Stodola-Southwell criterion. Under certain circumstances, the loci of eigenvalues belonging to two distinct modes of vibration approach each other very closely, and it may appear as if the loci cross each other. However, our study indicates that the observable frequency loci of an undamped rotating blade do not cross, but must either repel each other (leading to “curve veering”), or attract each other (leading to “frequency coalescence”). Our results are reached by using standard arguments from algebraic geometry—the theory of algebraic curves and catastrophe theory. We conclude that it is important to resolve an apparent crossing of eigenvalue loci into either a frequency coalescence or a curve veering, because frequency coalescence is dangerous since it leads to flutter, whereas curve veering does not precipitate flutter and is, therefore, harmless with respect to elastic stability.
Performance Evaluation of Low Heat Rejection Engines
Authors: Sun X. , Wang W. G. , Bata R. M. , Gao X.
Published: April 2008

Improving the performance of the Chinese B135 six-cylinder direct injection turbocharged and turbocompounded Low Heat Rejection Engine (LHRE) was based on experimental and analytical studies. The studies were primarily applied on a B1135 single-cylinder LHR engine and a conventional water-cooled B1135 single cylinder engine. Performance of the B1135 LHRE was worse than that of the conventional B1135 due to a deterioration in the combustion process of the B1135 LHRE. The combustion process was improved and the fuel injection system was redesigned and applied to the B135 six-cylinder LHRE. The new design improved the performance of the LHRE and better fuel economy was realized by the thermal energy recovered from the exhaust gases by the turbocompounding system.
Human-Induced Arctic Moistening
Authors: Min Seung-Ki , Zhang Xuebin , Zwiers Francis
Published: April 2008

The Arctic and northern subpolar regions are critical for climate change. Ice-albedo feedback amplifies warming in the Arctic, and fluctuations of regional fresh water inflow to the Arctic Ocean modulate the deep ocean circulation and thus exert a strong global influence. By comparing observations to simulations from 22 coupled climate models, we find influence from anthropogenic greenhouse gases and sulfate aerosols in the space-time pattern of precipitation change over high-latitude land areas north of 55°N during the second half of the 20th century. The human-induced Arctic moistening is consistent with observed increases in Arctic river discharge and freshening of Arctic water masses. This result provides new evidence that human activity has contributed to Arctic hydrological change.
Cell Identity Mediates the Response of
Arabidopsis
Roots to Abiotic Stress
Authors: Dinneny José R. , Long Terri A. , Wang Jean Y. , Jung Jee W. , Mace Daniel , Pointer Solomon , Barron Christa , Brady Siobhan M. , Schiefelbein John , Benfey Philip N.
Published: April 2008

Little is known about the way developmental cues affect how cells interpret their environment. We characterized the transcriptional response to high salinity of different cell layers and developmental stages of the
Arabidopsis
root and found that transcriptional responses are highly constrained by developmental parameters. These transcriptional changes lead to the differential regulation of specific biological functions in subsets of cell layers, several of which correspond to observable physiological changes. We showed that known stress pathways primarily control semiubiquitous responses and used mutants that disrupt epidermal patterning to reveal cell-layer–specific and inter–cell-layer effects. By performing a similar analysis using iron deprivation, we identified common cell-type–specific stress responses and revealed the crucial role the environment plays in defining the transcriptional outcome of cell-fate decisions.
The Sensitivity of Polar Ozone Depletion to Proposed Geoengineering Schemes
Authors: Tilmes Simone , Müller Rolf , Salawitch Ross
Published: April 2008

The large burden of sulfate aerosols injected into the stratosphere by the eruption of Mount Pinatubo in 1991 cooled Earth and enhanced the destruction of polar ozone in the subsequent few years. The continuous injection of sulfur into the stratosphere has been suggested as a “geoengineering” scheme to counteract global warming. We use an empirical relationship between ozone depletion and chlorine activation to estimate how this approach might influence polar ozone. An injection of sulfur large enough to compensate for surface warming caused by the doubling of atmospheric CO
2
would strongly increase the extent of Arctic ozone depletion during the present century for cold winters and would cause a considerable delay, between 30 and 70 years, in the expected recovery of the Antarctic ozone hole.
Near-Field Plates: Subdiffraction Focusing with Patterned Surfaces
Authors: Grbic Anthony , Jiang Lei , Merlin Roberto
Published: April 2008

Using a patterned, grating-like plate to control the electromagnetic near field, we demonstrate focusing well beyond the diffraction limit at ∼ 1 gigahertz. The near-field plate consists of only capacitive elements and focuses microwaves emanating from a cylindrical source to a spot of size ≈ λ/20 (half-power beamwidth), where λ is the free-space wavelength. These plates will find application in antennas, beam-shaping devices, nonradiative wireless power-transfer systems, microscopy, and lithography.
Charge Distribution and Conformations of Weak Polyelectrolyte Chains in Poor Solvents
Authors: Košovan Peter , Limpouchová Zuzana , Procházka Karel
Published: April 2008

In this work we study the effect of mobility of charges in annealed polyelectrolytes on their conformational behavior in poor solvents. A combination of molecular dynamics and Monte Carlo simulation techniques was used to take the dissociation into account. We investigated the relation between the conformation of the polyelectrolyte and the distribution of charges along the chain. The results suggest that in sufficiently poor solvents the local degree of charging differs significantly from the average. When a pearl-necklace conformation is formed, the degree of charging of the pearls is significantly lower than that of the strings. The redistribution of charges stabilizes the pearl-necklace conformation and enables the formation of asymmetric conformations with a single pearl at one chain end and a string at the other end.
Handling Electrostatic Interactions in Molecular Simulations: A Systematic Study
Authors: Kolafa Jiří , Moučka Filip , Nezbeda Ivo
Published: April 2008

Two qualitatively different models with strong long-range electrostatic interactions, Lennard-Jones diatomics with an embedded dipole moment and TIP4P/2005 water, are considered in extensive Monte Carlo and molecular dynamics simulations to systematically study the differences in results caused by different treatments of the long-range electrostatic interactions. In addition to the standard Ewald summation and reaction field methods, we consider also two variants of short-range approximations. Both thermodynamic and structural properties, and both homogeneous and inhomogeneous phases are considered. It is shown that the accuracy of the short-range approximations with carefully selected parameters may be sufficient for a number of applications; however, in some cases one can encounter accuracy limits or structural or other artifacts.
A Polarizable Three-Site Water Model with Intramolecular Polarizability
Authors: Kolafa Jiří
Published: April 2008

The forgotten "atom dipole interaction model" in which several induced dipoles in a molecule can interact is investigated. This model leads to an anisotropic (tensor) polarizability of a molecule using only isotropic (scalar) atomic contributions. A three-site model of water reproducing the experimental tensor polarizability is developed and tested using molecular dynamics calculations.
The satiety hormone peptide YY as a regulator of appetite
Authors: Vincent R P , le Roux C W
Published: April 2008

Obesity is a major cause of premature death in the UK, and may contribute to as many as 30 000 deaths a year in the UK. Although effective treatment for obesity is still awaited, many developments have occurred to improve our understanding of neuroendocrine regulation of food intake and weight gain, especially regarding the role of gut hormones. One such gut hormone is peptide tyrosine-tyrosine also known as PYY where Y depicts the abbreviation for tyrosine. PYY is a 36 amino acid hormone, first isolated from porcine intestine. PYY, along with few other gut hormones, has been suggested as a potential therapeutic agent for obesity. This review examines the relationship of PYY to appetite regulation, energy homeostasis and the relevant neuroendocrine feedback mechanism.
The cell biology of bone metabolism
Authors: Datta H K , Ng W F , Walker J A , Tuck S P , Varanasi S S
Published: April 2008

Contrary to the commonly held misconception, bone is a relatively dynamic organ that undergoes significant turnover as compared to other organs in the body. This review details how complex intercellular signalling, between the osteoprogenitor cells and mature osteoblasts, osteocytes and osteoclasts, regulates and balances activities of bone cells during remodelling and growth. Both systemic, as well as local autocrine and paracrine factors are discussed. A number of recent important advances in cell biology of bone have led to a new paradigm in understanding of the subject. In this regard, the interaction between the immune system and bone cells is of particular interest, leading to the emergence of a new discipline termed osteoimmunology. The role of lymphocytes and a number of key cytokines in the regulation of osteoclastogenesis and osteoblast function is critically examined. The intracellular signalling regulating key cellular pathways involved in cell differentiation and activity are outlined. The emerging evidence of osteocytes as mechanosensors as well as regulators of mineralisation is discussed.
Categorisation of pleural fluids in routine clinical practice: analysis of pleural fluid protein and lactate dehydrogenase alone compared with modified Light’s criteria
Authors: Murphy M J , Jenkinson F
Published: April 2008

Modified Light’s criteria are widely used to categorise pleural fluids as either exudates or transudates. These criteria include fluid/serum ratios and therefore require a blood sample. It is not clear whether analysis of pleural fluid alone would alter pleural fluid categorisation in routine clinical practice. In this study, pleural fluids were categorised using cut-off values for pleural fluid protein (⩾30 g/l) and lactate dehydrogenase (>0.45 of upper limit of the serum reference interval) recommended as providing optimal discrimination between transudates and exudates. The resultant categorisations were compared with those produced by application of modified Light’s criteria. 77 pleural fluid specimens were included for analysis. Using modified Light’s criteria, 32 fluids were categorised as transudates and 45 as exudates. Applying the pleural fluid cut-off values as outlined above, 26 fluids were categorised as transudates and 51 as exudates. Agreement was observed in 71/77 or 92.2% (95% confidence interval 86.2 to 98.2). It was concluded that in most cases, analysis of pleural fluid protein and lactate dehydrogenase alone produces the same categorisation as modified Light’s criteria. Omission of a blood sample rarely affects the categorisation of pleural fluids in routine clinical practice.
Expression of connective tissue growth factor (CTGF/CCN2) in head and neck squamous cell carcinoma
Authors: Mullis T C , Tang X , Chong K T
Published: April 2008

Background:

Connective tissue growth factor (CTGF/CCN2), a multifunctional protein that regulates cell growth and differentiation, is known to play an important role in tumourigenesis of several human malignancies. However, CCN2 expression or its potential role in head and neck squamous cell carcinoma (HNSCC) is not known, even though HNSCC is one of the most common cancers worldwide.

Aims:

To investigate CCN2 expression in primary HNSCC and to correlate CCN2 mRNA expression level with one of its upstream regulators, transforming growth factor-β1 (TGF-β1).

Methods:

Tissue specimens of HNSCC (n = 22) and normal oral mucosa (n = 8) were analysed by real-time, quantitative PCR assays for CCN2 and TGF-β1 expression. Tissue localisation of CCN2 protein was analysed by immunohistochemistry.

Results:

Primary HNSCC expressed high levels of CCN2 mRNA. CCN2 protein was localised in stromal fibroblasts, tumour and vascular endothelial cells.

Conclusions:

Results show that CCN2 mRNA and protein are overexpressed in HNSCC, suggesting that CCN2 expression should be further evaluated for a possible role in HNSCC growth and progression.
Trace Element Loadings to Sediments of Fourteen Ontario Lakes and Correlations with Concentrations in Fish
Authors: Johnson Murray G.
Published: April 2008

Present, background, and anthropogenic loading rates of Cu, Ni, Zn, Pb, Cd, Cr, Hg, As, and Se to lake sediments were calculated from210Pb dated cores, and present loading rates were compared with concentrations in several fishes. Present loadings of Pb averaged 17 times background loadings and all lakes had statistically significant anthropogenic inputs. The majority of lakes had anthropogenic loadings of Zn, Cd, Hg, and As, which were presently 1.8–2.6 times background loadings. For Ni, Cu, Se, and Cr, only seven, five, two, and one lake(s), respectively, had significant anthropogenic inputs, and the means of present: background loadings for all lakes were not significantly different from 1.0. Enrichment by Zn, Cd, As, and especially Pb was greater closer to industrialized regions, while Hg enrichment was more widespread. Anthropogenic and precipitation loadings for Zn, Pb, Cd, and As were similar, suggesting that anthropogenic inputs are atmospheric and that current atmospheric loadings are mostly anthropogenic. [Hg] and [Cd] in fish were correlated with loadings to sediments, but [Cu] and [Zn] in fish were relatively constant within species, supporting the hypothesis that contaminants in fish would be correlated with inputs to sediments, while trace nutrients in ample supply would be unrelated to loading. [Cr] and [Se] in fish were intermediate in response to loading, but correlation between [Pb] in fish and loadings was not detected.