bluuebunny/crossref_metadata_2025 huggingface dataset:
A Model of the Enhancement of Coal Combustion Using High-Intensity Acoustic Fields
Authors: Yavuzkurt S. , Ha M. Y. , Koopmann G. , Scaroni A. W.
Published: April 2008

A model for the enhancement of coal combustion in the presence of high-intensity acoustic fields has been developed. A high-intensity acoustic field induces an oscillating velocity over pulverized coal particles otherwise entrained in the main gas stream, resulting in increased heat and mass transfer. The augmented heat and mass transfer coefficients, expressed as space and time-averaged Nusselt and Sherwood numbers for the oscillating flow, were implemented in an existing computer code (PCGC-2) capable of predicting various aspects of pulverized coal combustion and gasification. Increases in the Nusselt and Sherwood numbers about 45, 60 and 82.5 percent at sound pressure levels of 160, 165 and 170 dB for 100-μm coal particles were obtained due to increase in the acoustic slip velocity associated with the increased sound pressure levels. The main effect of the acoustic field was observed during the char combustion phase in a diffusionally controlled situation. A decrease in the char burn-out length (time) of 15.7 percent at 160 dB and 30.2 percent at 170 dB was obtained compared to the case with no sound for the 100-μm coal particles.
Selection of Expert System Development Tools for Engineering Applications
Authors: Mills S. , Erbas C. , Hurmuzlu Y. , Tanik M. M.
Published: April 2008

The problems associated with engineering tasks are often too large and complex for application of conventional software methods, but are suitable to application of expert system methods. Development of custom expert system applications is expensive and difficult, but expert system development tools provide the basic components needed to construct an expert system. Such tools enable engineers to implement expert system applications by entering knowledge specific to the particular problem they are attempting to solve. Because the choice of a development tool can determine the success of the resulting expert system application, the characteristics of these tools and of the target problem must be clearly understood before a selection is made. An overview of expert systems and development tools is given, characteristics of some common engineering problems are discussed, and selection criteria for tools well suited to these problems are presented. Implementation of a rule-based advisor to assist with tool selection is discussed briefly.
Effect of Drag Forces on Bit Weight in High-Curvature Well Bores
Authors: Rocheleau D. N. , Dareing D. W.
Published: April 2008

This paper gives a method of analysis for determining drill string weight required to develop a given bit force while drilling through and out of high-curvature well bores. The analysis is directed at medium radius well bores having radii of curvature ranging between 286 ft (87 m) and 955 ft (291 m), which are typically found in horizontal drilling. Sample calculations show how friction within the angle building portion of the well affect bit force.
The Optimum Design of Stratified Thermal Energy Storage Systems—Part II: Completion of the Analytical Model, Presentation and Interpretation of the Results
Authors: Krane R. J. , Krane M. J. M.
Published: April 2008

This investigation is presented in two parts. The basic analytical model is developed in Part I. Part II includes the completion of the analytical model and the results of an optimization study performed with this model. The results show that: 1) Significant performance gains, that is, reductions in the entropy generation number on the order of 10 percent, are possible by employing perfectly stratified thermal energy storage systems that are designed on the basis of the second law of thermodynamics. 2) These performance gains are mainly due to the complete elimination of the entropy generation due to heat transfer through finite temperature differences within the storage element. 3) In general, the optimum design of a perfectly stratified thermal energy storage system requires the use of a very large heat exchanger; however, it is possible to employ a much smaller than optimum heat exchanger without seriously degrading the superior performance of the system. 4) The operation of a stratified system is quite flexible because it has no optimum storage time. 5) The optimum values of the capacity rate ratios, (φR)opt and (φR)opt, for a perfectly stratified thermal energy storage system are in general not equal to unity; however, this finding is shown to be in concert with Bejan’s theory of “remanent” irreversibilities for a heat exchanger.
Flame Structure and Pollutant Emission Characteristics of a Burning Kerosene Spray With Injection of Diluents
Authors: Gollahalli S. R. , Puri R.
Published: April 2008

An experimental study of the effects of diluent gas injection on the structure and pollutant emissions of a kerosene spray from a twin fluid atomizer is presented. Nitrogen and carbon dioxide were used as the diluents. Flame length, radiation emission, axial and radial temperature profiles, and the radial profiles of carbon monoxide, oxygen, nitric oxide, and soot in flame gas samples were studied. The emission index, defined as the mass ratio of the rate of the species emitted to the fuel input rate, was determined from the experimental data. Results show, at a diluent injection rate approximately equal to the atomizing air flow rate, nitrogen was more effective than carbon dioxide in reducing flame length, flame radiation, and the emission indices of carbon monoxide and soot. Although both diluents increased nitric oxide emission, the effect of carbon dioxide was weaker.
Nuclear Hydrogen Production Based on Sulfuric Acid Decomposition Process
Authors: Hammache A. , Bilgen E.
Published: April 2008

A thermochemical nuclear hydrogen producing process has been developed and evaluated from thermodynamics and engineering points of view. The cycle is based on sulfuric acid decomposition process developed earlier, which produces mechanical power using additional primary energy as well as excess process heat generated within the cycle. The sulfuric acid decomposition process has been closed using a sulfur dioxide electrochemical oxidizer cell and feasibility of its energy self-sufficient operation has been demonstrated. The first law efficiency of the cycle has been determined as 34.14 percent and the second law efficiency as 43.32 percent. It is found that the modified sulfuric acid decomposition section is improved by 14.8 percent compared to the basic process used in the sulfur family cycles. For a plant size producing 8.94 × 106 GJ H2 per year, the typical levelized costs of hydrogen are $20.15(1988) per GJ energy and $24.47(1988) per GJ exergy.
A Method for Improving the Quality of Bituminous Froth From Water Extraction of Oil Sands
Authors: Rajan V. S. V. , Tipman R.
Published: April 2008

Bituminous froths produced from the water extraction of oil sands contain significant quantities of sand and water which must be removed prior to upgrading the bitumen to synthetic crude oil. This paper presents a summary of the study of a simple twostep process for removing most of the solid and water contaminants from the bituminous froth. Low-quality froths containing 10–30 percent bitumen at temperatures of 40–70°C were improved in quality to 50–60 percent bitumen by heating the raw froth to ~ 90°C and settling the product in a gravity settler. The gravity settling vessel incorporated unique features for the introduction of the hot froth into the vessel. Two types of froth heaters were tested: a column heater containing a structured grid packing which used live steam injection, and a shell and tube heat exchanger. Heat transfer data were obtained for both types of heaters in the range of froth flow conditions available in the pilot plant. There was no apparent difference between the two heating modes in terms of the froth quality improvement, but the direct contact heater had the benefit of deaerating the froth. Evaluation of the separation efficiency showed that the gravity separation vessel design performed very well, and hence was incorporated into a commercial froth cleaning plant design. The bitumen separation efficiency was the best for froths containing about 20 percent bitumen. There was no apparent improvement in the froth quality for froths containing over 65 percent bitumen.
Formation of Flammable Zones Due to the Action of Diffusional Mass Transfer—A Simplified Approach
Authors: Badr O. , Karim G. A.
Published: April 2008

The transient concentration profiles of a fuel or a toxic gas were examined following its release into air within a long confined volume with either an open or a closed end. The exact one-dimensional solution with its limitations for cases of molecular and convective diffusion was presented and discussed. Two approximate solutions simplifying the exact one were developed. Their results were compared to those of the exact one and an error analysis was given. It was shown that despite its simple mathematical form, the second approximate solution would predict the concentration profiles with a reasonable accuracy. Comparison of some of the calculated values of the concentration with the corresponding experimental values was also made.
Friction and Wear in Threaded Surfaces of Rotary Drill Collars
Authors: Thornton H. R. , Bailey E. I. , Williamson J. S.
Published: April 2008

Two surfaces, under high normal stress, in sliding contact provide the basis for friction and wear studies within rotary drill collars. Flat and ring specimens, considering three (3) different contact areas, were rotated to determine the effect of surface finish, coatings, lubricants and normal stress on friction and wear. The 4145 steel specimens were heat-treated to a yield strength of 124,000 lb/in2 (855 MPa) and a Rc hardness of 28. The torque required to rotate the ring specimen was measured as a function of the rotation angle. The friction coefficient was calculated. Seizure and galling were common for metal-to-metal contact. Rust and phosphate coatings break down under the high normal stress. Metal-filled lubricants produce static coefficients of friction (μs) between 0.03 and 0.25 and dynamic coefficients between 0.04 and 0.26. Seizure and galling were not observed.
Emf, Maximum Power and Efficiency of Fuel Cells
Authors: Gaggioli R. A. , Dunbar W. R.
Published: April 2008

The ideal voltage of steady-flow fuel cells is usually expressed by Emf = −ΔG°/nF where ΔG° is the “Gibbs free energy of reaction” for the oxidation of the fuel at the supposed temperature of operation of the cell. Furthermore, the ideal power of the cell is expressed as the product of the fuel flow rate with this emf. Such viewpoints are flawed in several respects. While it is true that if a cell operates isothermally, the maximum conceivable electrical work output is equal to the difference between the Gibbs free energy of the incoming reactants and that of the leaving products; nevertheless, even if the cell operates isothermally, the use of the conventional ΔG° of reaction (a) assumes that the products of reaction leave separately from one another (and from any unused fuel); and (b) when ΔS of reaction is positive, it assumes that a free heat source exists at the operating temperature, whereas if ΔS is negative, it neglects the potential power which theoretically could be obtained from the heat released during oxidation. Moveover, (c) the usual cell does not operate isothermally, but (virtually) adiabatically. Comment (a) is often accounted for by employing the Nernst equation to correct for the dilution of reactants and/or products. Nevertheless, comments (b) and (c) remain pertinent. Rather than with emf, the proper starting place is with power output. The ideal power is that which would be obtained if the fuel were oxidized without irreversible entropy generation. Among other factors, this ideal power output depends upon the ratio of oxidant to fuel flow rate (e.g., air-fuel ratio) and the percentage of fuel oxidation. The ideal voltage is deduced from the ideal power, because it is defined as electrical work output per unit of charge delivered. It is a local characteristic which varies with the percent of fuel oxidized. Therefore, (d) ideal power is not equal to the product of emf with current (unless the amount of fuel utilized is infinitesimal). Examples are presented which illustrate such affects and their importance for the evaluation of ideal power and of efficiency.
The Effect of the Fuel-Cell Unit Size on the Efficiency of a Fuel- Cell-Topped Rankine Power Cycle
Authors: Dunbar W. R. , Lior N. , Gaggioli R. A.
Published: April 2008

Dunbar, Lior and Gaggioli (1991) proposed a configuration of a fuel-cell-topped electrical Rankine power generating station and analyzed its performance. That study revealed that the fuel-cell topping improved plant efficiency to values up to 62 percent, versus the conventional plant efficiency of 41.5 percent. This work lays the foundation for a thermoeconomic analysis of such systems by relating exergy consumption to fuel-cell unit size, as follows: 1) the relationship between system efficiency (and hence fuel consumption) and fuel-cell unit size is presented for a number of fuel-cell operating conditions; 2) the relationship between fuel flow rate and fuel-cell unit size is shown; and 3) the exergetic effects of the major plant components are discussed as a function of fuel-cell unit size. The results reveal that specific fuel consumption may be reduced by as much as 32 percent when incorporating fuel-cell units into electrical power plants.
The Drilling Experience of K6-2, the High-Temperature and Crooked Geothermal Well in Kakkonda, Japan
Authors: Saito S.
Published: April 2008

Well K6-2 was drilled for geothermal production for the Kakkonda No. 2 Power Plant (to be built in 1995) at the Kakkonda geothermal field, northern Honshu Island, Japan from 1988 through 1989. The well was planned to be vertical and the target area was a 100-m radius of 2800 m. Mainly, because of the formation inclination, strong bit walk tendency was encountered below 1200 m. Even with packed-hole bottom-hole assemblies (BHA), the well inclination buildup rate was over 1 deg per 30 m. With this buildup rate, the well inclination would be over 50 deg at 2800 m, and not only miss the target area, but could not reach total depth because of severe rotation drag in the very abrasive formation (tertiary: shale, dacitic tuff and andesitic tuff-breccia; pre-tertiary: slate, sandstone and andesitic tuff). Because a pendulum BHA did not help to drop the inclination, downhole motors with bent subs were employed. Totals of six and seven downhole motors for 12 1/4 and 8 1/2-in. hole sections, respectively, were run. The estimated formation temperature was over 350°C below 1900 m, so two mud cooling towers and 500 m3 pit were used to cool the returned mud. These systems worked well, but at 2245 m the estimated mud circulation temperature on bottom went up to 150°C and the stator rubber of the downhole motors unbonded and broke up after a 1-h run. Below that depth, only a packed hole BHA was employed, and the inclination increased from 6 deg at 2300 m to 14 deg at 2800 m. At 2799 m, lost circulation was encountered and drilling terminated at 2818 m.
Heat Generation in Ferrous Metal Piles
Authors: Gollahalli S. R. , Francis J. E. , Varshney D.
Published: April 2008

A laboratory-scale experimental study of the basic processes and controlling parameters involved in the spontaneous heating of a pile of ferrous metal turnings during their marine transport is presented. The results indicate that the salinity of seawater, the amount of moisture coming in contact with the turnings, the surface area of turnings, the volume of container, and the bulk density of the pile affect the temperature rise in the ferrous material.
A Quasi-Three-Dimensional Approach to Predict the Performance of
Steam Surface Condensers
Authors: Zhang C. , Zhang Y.
Published: April 2008

A quasi-three-dimensional numerical procedure is proposed to simulate the fluid flow and heat transfer in the shell-side of steam surface condensers. The proposed procedure is applied to an experimental steam surface condenser to evaluate its predictive capability. The predicted results give good general agreement with the experimental data. The governing equations are solved in primitive variable form using a semi-implicit consistent control-volume formulation in which a segregated pressure correction linked algorithm is employed. The modeling of the geometries of condensers, including tube bundles and baffle plates, is carried out based on porous media concepts using flow, heat and mass transfer resistances.
Binary-Flashing Geothermal Power Plants
Authors: Yuan Z. , Michaelides E. E.
Published: April 2008

Binary-flashing units utilize new types of geothermal power cycles, which may be used with resources of relatively low temperatures (less than 150°C) where other cycles result in very low efficiencies. The thermodynamic cycles for the binary flashing units are combinations of the geothermal binary and flashing cycles. They have most of the advantages of these two conventionally used cycles, but avoid the high irreversibilities associated with some of their processes. Any fluid with suitable thermodynamic properties may be used in the secondary Rankine cycle. At the optimum design conditions binary-flashing geothermal power plants may provide up to 25 percent more power than the conventional geothermal units.
Three-Dimensional Hydraulic Fracture Simulation Using Fixed Grid Finite Element Algorithms
Authors: Lee T. S. , Advani S. H. , Pak C. K.
Published: April 2008

A three-dimensional hydraulic fracture simulator (HYFFIX) is reformulated using finite element methodology and a newly adapted fixed grid. The numerical procedures for the coupled equations governing the fracture width, fluid pressure, and evolution of equilibrium planar crack in layered media are summarized. Fixed grid mesh control algorithms for the efficient tracking of the moving crack/fracture fluid front are detailed. The introduction of these novel algorithms in the simulator makes it numerically efficient and stable, in comparison to previously reported models which utilize migrating mesh techniques. Due to the enhanced numerical efficiency and compactness of the refined code, the model can also be readily implemented on a workstation or microcomputer.
Optimal Operation of a Cogeneration Plant in Combination With Electric Heat Pumps
Authors: Ito K. , Shiba T. , Yokoyama R.
Published: April 2008

An operational problem is discussed for a gas turbine cogeneration plant in combination with a heat pump/thermal storage system that utilizes time-of-use pricing of the electrical utility. An optimal planning method is presented by which the operational policy of constituent equipment is determined so as to minimize the daily operational cost. An algorithm is proposed to solve this optimization problem efficiently by combining the dynamic programming method with the mixed-integer programming one. A case study is carried out to investigate the effect of introducing a heat pump system into a cogeneration plant.
Experimental Testing and Thermoeconomic Analysis of an Incineration Plant Postcombustor With Oxycombustion
Authors: De Lucia M. , Lanfranchi C.
Published: April 2008

Experimental testing was performed on a prototype postcombustor fueled by pure oxygen and designed to treat exhaust gases from industrial waste incineration. The tests validated the technical feasibility of the small-size oxycombustion incinerator, which not only proved to be more flexible and compact than conventional systems of the same rating, but also faster in reaching operating conditions. The thermoeconomic analysis which followed was based on an exergy balance developed from the system’s operating conditions measured in the previous experimental phase. A subsequent comparison with conventional air-fueled solutions has shown that oxycombustion offers considerable energy savings and, as a result, economic benefits.
What is Diffusion?
Authors: Gyftopoulos E. P. , Flik M. I. , Beretta G. P.
Published: April 2008

In earlier publications, heat Q← is defined as an interaction that is entirely distinguishable from work W→. The energy exchanged Q← is TQ times the entropy exchanged S←, where TQ is the almost common temperature of the interacting systems. Here, we define diffusion as another interaction that is entirely distinguishable from both work and heat, and that involves exchanges of energy, entropy, and amount of a constituent. It is an interaction between two systems A and B that pass through stable equilibrium states while their respective parameters remain fixed, and that have almost equal temperatures TA ≈ TB ≈ TD and almost equal total potentials μA ≈ μB ≈ μD of the diffusing constituent. The exchanges of entropy S→, energy E→, and amount of constituent n→ out of one system satisfy the relation S→ = (E→ −μDn→)/TD. In the limit of n→ = 0, a diffusion interaction becomes heat.
Local Entropy Generation Analysis of a Rotary Magnetic Heat Pump Regenerator
Authors: Drost M. K. , White M. D.
Published: April 2008

The rotary magnetic heat pump has attractive thermodynamic performance, but it is strongly influenced by the effectiveness of the regenerator. This study uses local entropy generation analysis to evaluate the regenerator design and to suggest design improvements. The results show that performance of the proposed design is dominated by heat-transfer-related entropy generation. This suggests that enhancement concepts that improve heat transfer should be considered, even if the enhancement causes a significant increase in viscous losses (pressure drop). One enhancement technique, the use of flow disruptors, was evaluated and the results showed that flow disruptors can significantly reduce thermodynamic losses. The results of this study also suggest that, in this case, the widely used efficiency index is an inappropriate thermodynamic measure of the performance of a heat transfer enhancement technique and that a figure-of-merit based on second law considerations should be used.
An Investigation of Water as a Refrigerant
Authors: Van Orshoven D. , Klein S. A. , Beckman W. A.
Published: April 2008

This paper explores some of the basic thermodynamic and technical considerations involved in using water as a working fluid for refrigeration and heat pump cycles down to its freezing point of 0°C. It is first shown how the integration of the functions of refrigerant and heat transfer fluid can lead to energy savings, especially for the case of ice production. Next, the two fundamental requirements that the compressor must fulfill—handling a very large volume flow and achieving a large compression ratio—are described. A thermodynamic analysis of multistage compression follows to investigate the adiabatic head requirements and the large desuperheating irreversibility. It is concluded that a radically new type of vacuum compressor must be developed in order for water to be used as working fluid in vapor compression refrigeration cycles.
Modular Repowering of Power Plants With Nominal Ratings Lower Than 180 MW: A Rational Design Approach and Its Application to the Italian Utility System
Authors: Melli R. , Naso V. , Sciubba E.
Published: April 2008

The paper describes the rationale, the technical/economical details and the results of a study which is part of a large-scale energy conservation program enacted by the Italian Public Utility (ENEL), within a broader framework of structural interventions on the national electricity production/transportation/utilization network. The objective of the larger, long-term plan is to increase by a significant percentage (>5 percent) the net conversion efficiency of the national system. The purpose of the present study is to “recover” a large number of nearly obsolete steam power plants by converting them to a combined cycle configuration. The expression “generalized repowering” has been used to synthetically describe this plant reconfiguration plan, and will be employed in this paper. After giving a brief description of the existing Italian electricity generation situation, we list some possible criteria for repowering and describe in detail the configurations which were considered to be feasible. Finally, the proposed options are comparatively analyzed, and the major parameters which can be of importance in the actual decision-making process on the part of the Public Utility are computed and presented in tabular form. In the conclusions we try to put the present work in the broader perspective of a largescale (supernational), economically sound and ecologically acceptable energy conservation program.
Designing Surface-Mounted Components for High Reliability
Authors: Rasty J. , Kolarik W. , Chen B.
Published: April 2008

Recent emphasis of the Department of Defense (DOD) on the reliability and integrity of avionics has spurred a new wave of research on this subject. This paper presents the results of a parametric investigation conducted to study the effect of vibration direction, boundary conditions, stiffeners and/or point supports, lead type, lead height, and the layout of the components on the natural frequencies and stresses exerted on a typical printed circuit board (PCB) used in avionics. The “robust design” procedure was adopted using a series of computer-simulated experiments. A finite element software, EMRC-FEAP, was utilized to estimate the maximum von Mises stresses within the critical leads, while the statistical analysis system (SAS) software was employed to analyze the natural frequency responses of the system and the signal-to-noise ratio (SNR) of the stresses induced at critical leads.
The Phase Analysis of Coal Combustion Ashes
Authors: Iribarne A. P. , Iribarne J. V. , Anthony E. J. , Blondin J.
Published: April 2008

The phase composition of coal combustion ashes is important in regard to their potential uses. Here it is shown that a combination of phase separation techniques with X-ray diffraction, thermogravimetric analysis, and conventional chemical analysis, including elemental analysis and wet chemistry, can be used to obtain a fairly complete phase composition. The application of these techniques is illustrated with an FBC ash sample, indicating the procedures used to achieve the identification of calcium silicates, aluminates and ferrites, and their quantitative estimates. A new method for the quantitative determination of CaO in presence of large amounts of Ca(OH)2 has been developed which uses phase separation as a previous step to chemical titration.
Carbon nanotube cold cathodes for application in low current x-ray tubes
Authors: Tolt Zhidan Li , Mckenzie Chris , Espinosa Robert , Snyder Scott , Munson Marjorie
Published: April 2008

Low current x-ray tubes operating at 25–40kV have been developed using monolithic carbon nanotube (CNT) cold cathodes as electron sources. The authors have tested CNT cathodes from various sources. They were systematically evaluated and conditioned in a vacuum chamber and then went through high temperature baking and high voltage processing of standard tube production processes. Acceptance criteria were developed for each step in order to ensure that the final tube will meet the performance requirement of a commercial product. The tubes were subsequently operated continuously for an extended amount of time for life and reliability measurements. It was found that it is possible to use individually selected and preconditioned CNT cathodes in a commercial x-ray tube product. However, to find wide application and, particularly, to compete with existing hot filament thermionic cathodes, CNT cathodes need dramatic improvement in reproducibility and robustness. In addition, an empirical mathematical model for monolithic CNT cathodes has been developed for simulating the electron optics required in x-ray tubes. The model led to a successful design of a magnetically focused x-ray tube with a spot size of about 80μm.
Energy exchange in field emission from semiconductors
Authors: Chung M. S. , Jang Y. J. , Mayer A. , Cutler P. H. , Miskovsky N. M. , Weis B. L.
Published: April 2008

Field emission from semiconductors has been theoretically investigated by describing the energy transfer of electron. The authors developed a theory for the replacement process to calculate the energy exchange Δε between the electrons outgoing from and incoming to the semiconductor cathode. The obtained Δε is found to increase with increasing T and decreasing field F but to be almost independent of doping. It is also found that Δε is always positive, implying the cooling effect of field emission from the semiconductors for all temperatures.
Fabrication and characterization of InGaAsP∕InP double shallow-ridge rectangular ring laser photonic integration circuits by cascade reactive ion etching/inductively coupled plasma etching
Authors: Zhang R. , Ren Z. , Yu S.
Published: April 2008

The authors report the fabrication and characterization of InGaAsP∕InP rectangular ring laser photonic integration circuits based on active vertical-coupler structure by cascade reactive ion etching/inductively coupled plasma etching technology. This novel etching scheme can efficiently balance the photolithography, masking, and semiconductor etching requirements when several etching depths are demanded. For the 920μm circumference of ring lasers with coupler length (Lc) of 300μm, the smallest total threshold current (Ic+Id) of 75mA is achieved. Varying threshold situation and its sensitivity to the coupling parameters predict that the performance of such devices is not dominated by the nonideal fabrication loss, even though total internal-reflection mirrors are formed by etching twice. Such successful fabrication indicates that this can be widely employed to fabricate the other photonic integrated circuit components where multilevel deep etching is required.
Effects of Mo seeding on the formation of Si nanodots during low-energy ion bombardment
Authors: Ozaydin Gozde , Ludwig Karl F. , Zhou Hua , Headrick Randall L.
Published: April 2008

Effects of seed atoms on the formation of nanodots on silicon surfaces during normal incidence Ar+ ion bombardment at room temperature are studied with real-time grazing-incidence small-angle x-ray scattering (GISAXS), real-time wafer curvature stress measurements and ex situ atomic force microscopy. Although Si surfaces remain smooth during bombardment at room temperature, when a small amount of Mo atoms is supplied to the surface during ion bombardment, the development of correlated structures (“dots”) is observed. Stress measurements show that initially a compressive stress develops during bombardment, likely due to amorphization of the surface and insertion of argon. However, seeding causes a larger tensile stress to develop with further bombardment, possibly due to the formation of higher density regions around the Mo seed atoms on the surface. Detailed fits of the GISAXS evolution during nanostructure growth show that the instability is larger than predicted by the Bradley-Harper theory of curvature-dependent sputter yield. These results suggest that the tensile stress is playing a dominant role in driving the nanodot formation.
Comparative study on temperature-dependent characteristics of InP∕InGaAs single- and double-heterojunction bipolar transistors
Authors: Chen Wei-Hsin , Chen Tzu-Pin , Lee Chi-Jhung , Hung Ching-Wen , Chu Kuei-Yi , Chen Li-Yang , Tsai Tsung-Han , Liu Wen-Chau
Published: April 2008

Interesting temperature-dependent characteristics of InP∕InGaAs-based single-heterojunction bipolar transistor (SHBT) and double-heterojunction bipolar transistor (DHBT) devices are compared and studied. Experimentally, both studied devices show wider collector current (IC) operation regions, with over 11 decades in magnitude of collector current (IC=10−12to10−1A). However, the studied DHBT exhibits improved breakdown characteristics [common-emitter breakdown voltage (BVCEO)=8.05V and common-base breakdown voltage (BVCBO)=11.3V] and low output conductance at high temperature. Moreover, the undesired current-blocking effect, switching, hysteresis phenomenon usually found in an InP∕InGaAs conventional DHBT are not observed in the DHBT device. As compared with the studied SHBT, the studied DHBT shows a lower multiplication factor and weaker temperature dependence. Therefore, it is known that, based on experimental results, the studied DHBT device provides the promise for low-voltage and low-power circuit applications.
Nanoimprint lithography: An old story in modern times? A review
Authors: Schift Helmut
Published: April 2008

Nanoimprint lithography (NIL) is a high throughput, high-resolution parallel patterning method in which a surface pattern of a stamp is replicated into a material by mechanical contact and three dimensional material displacement. This can be done by shaping a liquid followed by a curing process for hardening, by variation of the thermomechanical properties of a film by heating and cooling, or by any other kind of shaping process using the difference in hardness of a mold and a moldable material. The local thickness contrast of the resulting thin molded film can be used as a means to pattern an underlying substrate on wafer level by standard pattern transfer methods, but also directly in applications where a bulk modified functional layer is needed. Therefore it is mainly aimed toward fields in which electron beam and high-end photolithography are costly and do not provide sufficient resolution at reasonable throughput. The aim of this review is to play between two poles: the need to establish standard processes and tools for research and industry, and the issues that make NIL a scientific endeavor. It is not the author’s intention to duplicate the content of the reviews already published, but to look on the NIL process as a whole. The author will also address some issues, which are not covered by the other reviews, e.g., the origin of NIL and the misconceptions, which sometimes dominate the debate about problems of NIL, and guide the reader to issues, which are often forgotten or overlooked.
Development of a super-high-sensitivity image sensor using 640×480 pixel active-matrix high-efficiency electron emission device
Authors: Negishi Nobuyasu , Sato Takanobu , Matsuba Youhei , Tanaka Ryota , Nakada Tomonari , Sakemura Kazuto , Okuda Yoshiyuki , Watanabe Atsushi , Yoshikawa Takamasa , Ogasawara Kiyohide , Nanba Masakazu , Okazaki Saburo , Tanioka Kenkichi , Egami Norifumi , Koshida Nobuyoshi
Published: April 2008

An extremely high-sensitivity image sensor has been developed with a combination of an active-matrix high-efficiency electron emission device (HEED) array and a high-gain avalanche rushing amorphous photoconductor (HARP) target. Following the description of the requirements for the use of the electron emitter as an image-sensing probe, the characteristics of a fabricated 640×480 pixel active-matrix HEED image sensor with a HARP target are presented by image-pickup experiments under a dark condition. The emission current density of the experimental HEED under an active-matrix drive was 4 A/cm2 corresponding to a practical level. A clear image observed in the prototype compact camera demonstrates that the surface-emitting HEED is useful for image sensing based on HARP with high sensitivity and sufficient definition.
Characteristics of an InGaP/AlXGa1−XAs/GaAs composite-emitter heterojunction bipolar transistor (CEHBT)
Authors: Cheng Shiou-Ying , Chu Kuei-Yi , Chen Li-Yang , Chen Lu-An , Liu Wen-Chau
Published: April 2008

The characteristics of an interesting InGaP/AlXGa1−XAs/GaAs composite-emitter heterojunction bipolar transistor (CEHBT) are studied and demonstrated. By employing an AlXGa1−XAs graded layer between an InGaP emitter and GaAs base layer, a nearly zero conduction-band discontinuity can be obtained. Owing to the complete disappearance of the potential spike at the emitter/base hetero-interface, our CEHBT with AlXGa1−XAs graded layer exhibited good dc performance with current gains of 280 and 11 at collector currents of IC=12.6 mA and 0.2 nA, respectively. Furthermore, our CEHBT also shows a lower offset voltage and collector and base current ideality factors. In microwave characteristics, for a 3×20 μm2 device, the unit current gain cutoff frequency fT and maximum oscillation frequency fmax are 41.3 and 35.4 GHz, respectively. Consequently, this work provides promise for high-performance analog, digital, and microwave device applications.
Generalized Voice-Leading Spaces
Authors: Callender Clifton , Quinn Ian , Tymoczko Dmitri
Published: April 2008

Western musicians traditionally classify pitch sequences by disregarding the effects of five musical transformations: octave shift, permutation, transposition, inversion, and cardinality change. We model this process mathematically, showing that it produces 32 equivalence relations on chords, 243 equivalence relations on chord sequences, and 32 families of geometrical quotient spaces, in which both chords and chord sequences are represented. This model reveals connections between music-theoretical concepts, yields new analytical tools, unifies existing geometrical representations, and suggests a way to understand similarity between chord types.
The Movement of Aquatic Mercury Through Terrestrial Food Webs
Authors: Cristol Daniel A. , Brasso Rebecka L. , Condon Anne M. , Fovargue Rachel E. , Friedman Scott L. , Hallinger Kelly K. , Monroe Adrian P. , White Ariel E.
Published: April 2008

Mercury has contaminated rivers worldwide, with health consequences for aquatic organisms and humans who consume them. Researchers have focused on aquatic birds as sentinels for mercury. However, trophic transfer between adjacent ecosystems could lead to the export of aquatic mercury to terrestrial habitats. Along a mercury-contaminated river in Virginia, United States, terrestrial birds had significantly elevated levels of mercury in their blood, similar to their aquatic-feeding counterparts. Diet analysis revealed that spiders delivered much of the dietary mercury. We conclude that aquatic mercury pollution can move into terrestrial habitats, where it biomagnifies to levels in songbirds that may cause adverse effects. Rivers contaminated with mercury may pose a threat to the many bird species that feed on predatory invertebrates in adjacent riparian habitats.
Scientists, We Need Your Swords!
Authors: Bohannon John
Published: April 2008

Put on your tabard and join troll huntress Gonzorina (a.k.a. the Gonzo Scientist) and her fearsome pet, Darwin, at the first scientific conference in
World of Warcraft
, to be held 9 to 11 May.
Identification of a Porcine Calicivirus Related Genetically to Human Sapoviruses
Authors: Martella V. , Lorusso E. , Banyai K. , Decaro N. , Corrente M. , Elia G. , Cavalli A. , Radogna A. , Costantini V. , Saif L. J. , Lavazza A. , Di Trani L. , Buonavoglia C.
Published: April 2008

Whether animals may act as reservoirs for human caliciviruses is unclear. By sequence analysis of a short fragment of the RNA-dependent RNA polymerase (RdRp) region, porcine sapovirus (SaV) strains that genetically resemble human SaVs have been detected in piglets, but more-informative sequences (capsid gene) were not available for a precise characterization. In this study, the 3′ terminus (the 3′ end of open reading frame 1 [ORF1], including the polymerase complex and the complete capsid; ORF2; and the 3′ untranslated region) of one such human SaV-like strain, 43/06-18p3/2006/It, was determined, revealing that these viruses are more related genetically to human (47.4 to 54.9% amino acid identity) than to animal (35.2 to 44.7% amino acid identity) SaVs in the capsid gene. In addition, the recombination-prone RdRp-capsid junction region was highly conserved with those of human SaVs of genogroup GI. The presence of porcine viruses similar to human SaVs is a significant finding because of the potential for zoonotic infections or generation of porcine/human recombinants.
Evaluation of New Commercial Real-Time PCR Quantification Assay for Prenatal Diagnosis of Cytomegalovirus Congenital Infection
Authors: Ducroux Aurélie , Cherid Samira , Benachi Alexandra , Ville Yves , Leruez-Ville Marianne
Published: April 2008

A new commercial real-time human cytomegalovirus (HCMV) PCR kit was evaluated after automated DNA extraction of 153 amniotic fluids in parallel with an in-house real-time PCR assay. The commercial kit displayed 100% sensitivity/specificity compared to the “in-house” assay and was suitable for prenatal diagnosis of HCMV congenital infection.
Priming of CD8+T Cells during Central Nervous System Infection with a Murine Coronavirus Is Strain Dependent
Authors: MacNamara Katherine C. , Bender Susan J. , Chua Ming Ming , Watson Richard , Weiss Susan R.
Published: April 2008

Virus-specific CD8+T cells are critical for protection against neurotropic coronaviruses; however, central nervous system (CNS) infection with the recombinant JHM (RJHM) strain of mouse hepatitis virus (MHV) elicits a weak CD8+T-cell response in the brain and causes lethal encephalomyelitis. An adoptive transfer model was used to elucidate the kinetics of CD8+T-cell priming during CNS infection with RJHM as well as with two MHV strains that induce a robust CD8+T-cell response (RA59 and SJHM/RA59, a recombinant A59 virus expressing the JHM spike). While RA59 and SJHM/RA59 infections resulted in CD8+T-cell priming within the first 2 days postinfection, RJHM infection did not lead to proliferation of naïve CD8+T cells. While all three viruses replicated efficiently in the brain, only RA59 and SJHM/RA59 replicated to appreciable levels in the cervical lymph nodes (CLN), the site of T-cell priming during acute CNS infection. RJHM was unable to suppress the CD8+T-cell response elicited by RA59 in mice simultaneously infected with both strains, suggesting that RJHM does not cause generalized immunosuppression. RJHM was also unable to elicit a secondary CD8+T-cell response in the brain following peripheral immunization against a viral epitope. Notably, the weak CD8+T-cell response elicited by RJHM was unique to CNS infection, since peripheral inoculation induced a robust CD8+T-cell response in the spleen. These findings suggest that the failure of RJHM to prime a robust CD8+T-cell response during CNS infection is likely due to its failure to replicate in the CLN.
Rapid Sequence Change and Geographical Spread of Human Parvovirus B19: Comparison of B19 Virus Evolution in Acute and Persistent Infections
Authors: Norja Päivi , Eis-Hübinger Anna Maria , Söderlund-Venermo Maria , Hedman Klaus , Simmonds Peter
Published: April 2008

Parvovirus B19 is a common human pathogen maintained by horizontal transmission between acutely infected individuals. However, B19 virus can also be detected in tissues throughout the life of the host, although little is understood about the nature of such persistence. In the current study, we created large VP1/2 sequence data sets of plasma- and tissue (autopsy)-derived variants of B19 virus with known sample dates to compare the rates of sequence change in exogenous virus populations with those in persistently infected individuals. By using linear regression and likelihood-based methods (such as the BEAST program), we found that plasma-derived B19 virus showed a substitution rate of 4 × 10
−4
and an unconstrained (synonymous)-substitution rate of 18 × 10
−4
per site per year, several times higher than previously estimated and within the range of values for mammalian RNA viruses. The underlying high mutation frequency implied by these substitution rates may enable rapid adaptive changes that are more commonly ascribed to RNA virus populations. These revised estimates predict that the last common ancestor for currently circulating genotype 1 variants of B19 virus existed around 1956 to 1959, fitting well with previous analyses of the B19 virus “bioportfolio” that support a complete cessation of genotype 2 infections and their replacement by genotype 1 infections in the 1960s. In contrast, the evolution of B19 virus amplified from tissue samples was best modeled by using estimated dates of primary infection rather than sample dates, consistent with slow or absent sequence change during persistence. Determining what epidemiological or biological factors led to such a complete and geographically extensive population replacement over this short period is central to further understanding the nature of parvovirus evolution.
Vesicular Stomatitis Virus Oncolysis of T Lymphocytes Requires Cell Cycle Entry and Translation Initiation
Authors: Oliere Stephanie , Arguello Meztli , Mesplede Thibault , Tumilasci Vanessa , Nakhaei Peyman , Stojdl David , Sonenberg Nahum , Bell John , Hiscott John
Published: April 2008

Vesicular stomatitis virus (VSV) is a candidate oncolytic virus that replicates and induces cell death in cancer cells while sparing normal cells. Although defects in the interferon antiviral response facilitate VSV oncolysis, other host factors, including translational and growth regulatory mechanisms, also appear to influence oncolytic virus activity. We previously demonstrated that VSV infection induces apoptosis in proliferating CD4+T lymphocytes from adult T-cell leukemia samples but not in resting T lymphocytes or primary chronic lymphocytic leukemia cells that remain arrested in G0. Activation of primary CD4+T lymphocytes with anti-CD3/CD28 is sufficient to induce VSV replication and cell death in a manner dependent on activation of the MEK1/2, c-Jun NH2-terminal kinase, or phosphatidylinositol 3-kinase pathway but not p38. VSV replication is specifically impaired by the cell cycle inhibitor olomoucine or rapamycin, which induces early G1arrest, but not by aphidicolin or Taxol, which blocks at the G11S or G21M phase, respectively; this result suggests a requirement for cell cycle entry for efficient VSV replication. The relationship between increased protein translation following G0/G1transition and VSV permissiveness is highlighted by the absence of mTOR and/or eIF4E phosphorylation whenever VSV replication is impaired. Furthermore, VSV protein production in activated T cells is diminished by small interfering RNA-mediated eIF4E knockdown. These results demonstrate that VSV replication in primary T lymphocytes relies on cell cycle transition from the G0phase to the G1phase, which is characterized by a sharp increase in ribogenesis and protein synthesis.
A randomised controlled trial on whether a participatory ergonomics intervention could prevent musculoskeletal disorders
Authors: Haukka E , Leino-Arjas P , Viikari-Juntura E , Takala E-P , Malmivaara A , Hopsu L , Mutanen P , Ketola R , Virtanen T , Pehkonen I , Holtari-Leino M , Nykänen J , Stenholm S , Nykyri E , Riihimäki H
Published: April 2008

Objectives:

To examine the efficacy of a participatory ergonomics intervention in preventing musculoskeletal disorders among kitchen workers. Participatory ergonomics is commonly recommended to reduce musculoskeletal disorders, but evidence for its effectiveness is sparse.

Methods:

A cluster randomised controlled trial among the 504 workers of 119 kitchens in Finland was conducted during 2002–2005. Kitchens were randomised to an intervention (n = 59) and control (n = 60) group. The duration of the intervention that guided the workers to identify strenuous work tasks and to seek solutions for decreasing physical and mental workload, was 11 to 14 months. In total, 402 ergonomic changes were implemented. The main outcome measures were the occurrence of and trouble caused by musculoskeletal pain in seven anatomical sites, local fatigue after work, and sick leave due to musculoskeletal disorders. Individual level data were collected by a questionnaire at baseline and every 3 months during the intervention and 1-year follow-up period. All response rates exceeded 92%.

Results:

No systematic differences in any outcome variable were found between the intervention and control groups during the intervention or during the 1-year follow-up.

Conclusions:

The intervention did not reduce perceived physical work load and no evidence was found for the efficacy of the intervention in preventing musculoskeletal disorders among kitchen workers. It may be that a more comprehensive redesign of work organisation and processes is needed, taking more account of workers’ physical and mental resources.