bluuebunny/crossref_metadata_2025 huggingface dataset:
Eucalypt NADP-Dependent Isocitrate Dehydrogenase1
Authors: Boiffin Vincent , Hodges Michael , Gálvez Susana , Balestrini Raffaella , Bonfante Paola , Gadal Pierre , Martin Francis
Published: July 2002

NADP-dependent isocitrate dehydrogenase (NADP-ICDH) activity is increased in roots ofEucalyptus globulus subsp. bicostata ex Maiden Kirkp. during colonization by the ectomycorrhizal fungusPisolithus tinctorius Coker and Couch. To investigate the regulation of the enzyme expression, a cDNA (EgIcdh) encoding the NADP-ICDH was isolated from a cDNA library of E. globulus-P. tinctorius ectomycorrhizae. The putative polypeptide sequence of EgIcdh showed a high amino acid similarity with plant NADP-ICDHs. Because the deduced EgICDH protein lacks an amino-terminal targeting sequence and shows highest similarity to plant cytosolic ICDHs, it probably represents a cytoplasmic isoform. RNA analysis showed that the steady-state level ofEgIcdh transcripts was enhanced nearly 2-fold in ectomycorrhizal roots compared with nonmycorrhizal roots. Increased accumulation of NADP-ICDH transcripts occurred as early as 2 d after contact and likely led to the observed increased enzyme activity. Indirect immunofluorescence microscopy indicated that NADP-ICDH was preferentially accumulated in the epidermis and stele parenchyma of nonmycorrhizal and ectomycorrhizal lateral roots. The putative role of cytosolic NADP-ICDH in ectomycorrhizae is discussed.
Calmodulin Activation of an Endoplasmic Reticulum-Located Calcium Pump Involves an Interaction with the N-Terminal Autoinhibitory Domain
Authors: Hwang Ildoo , Harper Jeffrey F. , Liang Feng , Sze Heven
Published: July 2002

To investigate how calmodulin regulates a unique subfamily of Ca2+ pumps found in plants, we examined the kinetic properties of isoform ACA2 identified in Arabidopsis. A recombinant ACA2 was expressed in a yeast K616 mutant deficient in two endogenous Ca2+ pumps. Orthovanadate-sensitive45Ca2+ transport into vesicles isolated from transformants demonstrated that ACA2 is a Ca2+ pump. Ca2+ pumping by the full-length protein (ACA2-1) was 4- to 10-fold lower than that of the N-terminal truncated ACA2-2 (Δ2–80), indicating that the N-terminal domain normally acts to inhibit the pump. An inhibitory sequence (IC50 = 4 μm) was localized to a region within valine-20 to leucine-44, because a peptide corresponding to this sequence lowered the V  max and increased theK  m for Ca2+ of the constitutively active ACA2-2 to values comparable to the full-length pump. The peptide also blocked the activity (IC50 = 7 μm) of a Ca2+ pump (AtECA1) belonging to a second family of Ca2+ pumps. This inhibitory sequence appears to overlap with a calmodulin-binding site in ACA2, previously mapped between asparatate-19 and arginine-36 (J.F. Harper, B. Hong, I. Hwang, H.Q. Guo, R. Stoddard, J.F. Huang, M.G. Palmgren, H. Sze [1998] J Biol Chem 273: 1099–1106). These results support a model in which the pump is kept “unactivated” by an intramolecular interaction between an autoinhibitory sequence located between residues 20 and 44 and a site in the Ca2+ pump core that is highly conserved between different Ca2+ pump families. Results further support a model in which activation occurs as a result of Ca2+-induced binding of calmodulin to a site overlapping or immediately adjacent to the autoinhibitory sequence.
Overexpression of the ArabidopsisCBF3Transcriptional Activator Mimics Multiple Biochemical Changes Associated with Cold Acclimation
Authors: Gilmour Sarah J. , Sebolt Audrey M. , Salazar Maite P. , Everard John D. , Thomashow Michael F.
Published: July 2002

We further investigated the role of the ArabidopsisCBF regulatory genes in cold acclimation, the process whereby certain plants increase in freezing tolerance upon exposure to low temperature. The CBF genes, which are rapidly induced in response to low temperature, encode transcriptional activators that control the expression of genes containing the C-repeat/dehydration responsive element DNA regulatory element in their promoters. Constitutive expression of either CBF1 orCBF3 (also known as DREB1b andDREB1a, respectively) in transgenic Arabidopsis plants has been shown to induce the expression of target COR(cold-regulated) genes and to enhance freezing tolerance in nonacclimated plants. Here we demonstrate that overexpression ofCBF3 in Arabidopsis also increases the freezing tolerance of cold-acclimated plants. Moreover, we show that it results in multiple biochemical changes associated with cold acclimation:CBF3-expressing plants had elevated levels of proline (Pro) and total soluble sugars, including sucrose, raffinose, glucose, and fructose. Plants overexpressing CBF3 also had elevated P5CS transcript levels suggesting that the increase in Pro levels resulted, at least in part, from increased expression of the key Pro biosynthetic enzyme Δ1-pyrroline-5-carboxylate synthase. These results lead us to propose that CBF3 integrates the activation of multiple components of the cold acclimation response.
Disentangling organizational commitment
Authors: Benkhoff Birgit
Published: July 2002

Much of commitment research is based on the belief that the concept consists of three different aspects: identification, desire to stay and extra effort. Shows that the three‐dimensional concept is misleading. Confirmatory factor analysis suggests that the organizational commitment questionnaire (OCQ) is not homogenous, but consists of three separate concepts. This is confirmed by correlational analysis with theoretically relevant variables which reveals that identification, desire to stay and extra effort are associated with different antecedents. The poor research output to date on organizational commitment can be explained by reference to the small weight given to discretionary effort in the OCQ, the most widely used commitment scale. Discusses implications for research and management policies.
Integral attachment using snap‐fit features: a key to assembly automation. Part 1 ‐ introduction to integral attachment using snap‐fit features
Authors: Messler Robert W. , Genc Suat , Gabriele Gary A.
Published: July 2002

This first part of a comprehensive six‐part series of articles on integral attachment using snap‐fit features familiarizes the reader with the key terms relating to the subject. Every area of study and practice must have associated with it a language to express objects, actions, and ideas. To understand any subject, understanding the language is essential. Developing clear, concise, unambiguous definitions of key terms is a tedious but necessary and critical first step to promoting understanding by allowing effective and efficient communication. These terms and definitions have been carefully compiled and thoughtfully refined from a broad industrial base, published literature, and university‐based research. They are the beginning of a lexicon for the embryonic but promising technology of integral attachment using snap‐fit features.
Application of wavelets in Doppler ultrasound
Authors: Keeton P.I.J. , Schlindwein F.S.
Published: July 2002

Provides an introduction into wavelets and illustrates their application with two examples. The wavelet transform provides the analyst with a scaleable time‐frequency representation of the signal, which may uncover details not evidenced by conventional signal processing techniques. The signals used in this paper are Doppler ultrasound recordings of blood flow velocity taken from the internal carotid artery and the femoral artery. Shows how wavelets can be used as an alternative signal processing tool to the short time Fourier transform for the extraction of the time‐frequency distribution of Doppler ultrasound signals. Implements wavelet‐based adaptive filtering for the extraction of maximum blood velocity envelopes in the post processing of Doppler signals.
The meanings of competency
Authors: Hoffmann Terrence
Published: July 2002

The term “competency” has not been clearly defined in the literature. Two main meanings of the term have been identified, one referring to the outputs, or results of training – that is, competent performance. The other definition referring to the inputs, or underlying attributes, required of a person to achieve competent performance. Each definition has been used to describe both individual and organisational competencies. A typology of the meanings of competency has been developed to show that the term has several meanings depending on the purpose for which it is used. The implications developed in this paper are directed toward reducing the confusion over the meaning of the term competency.
Numerical prediction of enhanced heat flux due to shock‐on‐shock interaction in hypersonic nonequilibrium flow
Authors: Lee Min G.
Published: July 2002

This paper describes the numerical solutions of type‐IV shock‐on‐shock interactions in hypersonic thermochemical nonequilibrium air flows around blunt bodies. The Navier‐Stokes equation solver for a chemically reacting and vibrationally relaxing gas mixture was applied to the present problem, where the concepts of the Advection Upstream Splitting Method (AUSM) and the Lower‐Upper Symmetric Gauss‐Seidel (LU‐SGS) method were basically employed along with the two‐temperature thermochemical model of Park. The aerodynamic heating with or without the shock‐on‐shock interaction to a sphere and circular cylinders are simulated for a hypersonic nonequilibrium flow. The numerical results show that typical type‐IV shock‐on‐shock interaction pattern with a supersonic jet structure is also formed in a high‐enthalpy thermochemical nonequilibrium flow, and that the contribution of convective heat flux in the translational/rotational mode to the total heat flux is dominant. Furthermore, the inherent unsteadiness of nonequilibrium type‐IV shock‐on‐shock interaction flowfield is discussed briefly.
Managing information resources and environmental turbulence
Authors: Karake Zeinab A.
Published: July 2002

Using a sample of large industrial firms from two industries with differing external turbulence ‐ commercial banking and pharmaceutical ‐ hypothesizes that the need for a senior manager of information technology is essential in high‐turbulence industries (commercial banking). This hypothesis was tested by evaluating the performance (as measured by return on investment (ROI) of 50 commercial banking firms and 39 pharmaceutical firms, and the presence of a top level information manager. In the commercial banking industry, statistical analysis did not support the hypothesis of significant differences in performance between those companies with a top‐level information manager and those without. States that, in the pharmaceutical industry, the statistical test supported the hypothesis of significant differences in performance between companies with top‐level information managers and those without.
Characterization of the mesostructure of fused‐deposition acrylonitrile‐butadiene‐styrene materials
Authors: Rodriguez Jose F. , Thomas James P. , Renaud John E.
Published: July 2002

Fused‐deposition (FD) is a robotically controlled “fiber” extrusion process that produces a new class of materials with a variety of controllable mesostructural features related to fiber layout and the presence of voids. Mesostructural features of importance to the stiffness and strength of unidirectionally extruded materials were characterized as a function of the processing variables. Samples were made using the Stratasys FDM1600 Modeler with the P400 acrylonitrile‐butadiene‐styrene plastic. Results showed that the void geometry/density and the extent of bonding between contiguous fibers depended strongly on the fiber gap and extrusion flow rate. Settings for minimum void and maximum fiber‐to‐fiber bonding were determined. Void and bond length densities in the plane transverse to the fiber extrusion direction varied from 4 to 16 per cent and 39 to 73 per cent respectively. The results quantify the important mesostructural features as a function of the FD process variables and are expected to find use with other FD materials.
A novel approach for hybrid optoelectronic circuits: thick‐film on glass (TOG)
Authors: Köhler Achim , Dullenkopf Peter
Published: July 2002

The realization of thick‐film circuits on glass substrates is discussed. Within the large number of commercially available thick‐film pastes, suitable pastes for thick‐film conductors, resistors and dielectrics on glass substrates have been found. Experimental results for these pastes are presented. Finally two applications for thick‐film on glass technology are demonstrated.
Entropy—enthalpy compensation: Fact or artifact?
Authors: Sharp Kim
Published: July 2002

The phenomenon of entropy–enthalpy (S‐H) compensation is widely invoked as an explanatory principle in thermodynamic analyses of proteins, ligands, and nucleic acids. It has been suggested that this compensation is an intrinsic property of either complex, fluctuating, or aqueous systems. The questions examined here are whether the observed compensation is extra‐thermodynamic (i.e., reflects anything more than the well‐known laws of statistical thermodynamics) and if so, what does it reveal about the system? Compensation is rather variably defined in the literature and different usages are discussed. The most precise and interesting one, which is considered here, is a linear relationship between ΔH and ΔS for some series of perturbations or changes in experimental variable. Some recent thermodynamic data on proteins purporting to show compensation is analyzed and shown to be better explained by other causes. A general statistical mechanical model of a complex system is analyzed to explore whether and under what conditions extra‐thermodynamic compensation can occur and what it reveals about the system. This model shows that the most likely behavior to be seen is linear S‐H compensation over a rather limited range of perturbations with a compensation temperature Tc = dΔH/dΔS within 20% of the experimental temperature. This behavior is insensitive to the details of the model, thus revealing little extra‐thermodynamic or causal information about the system. In addition, it will likely be difficult to distinguish this from more trivial forms of compensation in real experimental systems.
Effects of insulin on adipose tissue blood flow in man
Authors: Karpe Fredrik , Fielding Barbara A. , Ardilouze Jean‐Luc , Ilic Vera , Macdonald Ian A. , Frayn Keith N.
Published: July 2002

Adipose tissue blood flow (ATBF) rises after nutrient ingestion. It is not clear whether this is due to insulin. The aim of this study was to investigate the role of insulin in the regulation of subcutaneous ATBF. We have investigated the role of insulin in the regulation of ATBF in normal, healthy subjects in a three‐step procedure to determine the functional level at which insulin may potentially exert its effect. Fifteen subjects were studied on two occasions. On the first visit, 75 g oral glucose was given. In the second, similar plasma concentrations of insulin and glucose were achieved by dynamic intravenous infusions of insulin and glucose. The increase in ATBF after oral glucose (4.2 ± 1.4 ml min−1 (100 g tissue)−1, P= 0.01) was significantly greater (P < 0.05) than that after intravenous infusions (1.5 ± 0.6 ml min−1 (100 g tissue)−1P < 0.05). For the local delivery of potentially vasoactive substances and simultaneous measurement of ATBF, we describe a novel combination of methods, which we have called ‘microinfusion’. We have used this technique to show that locally infused insulin, even at pharmacological concentrations, had no demonstrable effect on ATBF in nine subjects. We conclude that whilst insulin does not have a direct effect on ATBF, it is likely to be an important mediator, possibly acting via sympathetic activation. In the postprandial state, other candidate peptides and hormones are also likely to play important roles.
A High Performance Pneumatic Force Actuator System: Part II—Nonlinear Controller Design
Authors: Richer Edmond , Hurmuzlu Yildirim
Published: July 2002

In this article we present two nonlinear force controllers based on the sliding mode control theory. For this purpose we use the detailed mathematical model of the pneumatic system developed in the first part of the paper. The first controller is based on the complete model, and exhibits superior performance both in the numerical simulation and experiments, but requires complex online computations for the control law. The second controller neglects the valve dynamics and the time delay due to connecting tubes. The performance of this controller exhibits slight degradation for configurations with relatively short tubes, and at frequencies up to 20 Hz. At higher frequencies or when long connecting tubes are used, however, the performance exhibits significant degradation compared to the one provided by the full order controller. [S0022-0434(00)00703-6]
Predictions of Mechanical Output of the Human M. Triceps Surae on the Basis of Electromyographic Signals: The Role of Stimulation Dynamics
Authors: van Zandwijk J. P. , Bobbert M. F. , Harlaar J.
Published: July 2002

In order to assess the significance of the dynamics of neural control signals for the rise time of muscle moment, simulations of isometric and dynamic plantar flexion contractions were performed using electromyographic signals (EMG signals) of m. triceps surae as input. When excitation dynamics of the muscle model was optimized for an M-wave of the medial head of m. gastrocnemius (GM), the model was able to make reasonable predictions of the rise time of muscle moment during voluntary isometric plantar flexion contractions on the basis of voluntary GM EMG signals. The rise time of muscle moment in the model was for the greater part determined by the amplitude of the first EMG burst. For dynamic jumplike movements of the ankle joint, however, no relationship between rise time of muscle moment in the experiment and muscle moment predicted by the model on the basis of GM EMG signals was found. Since rise time of muscle moment varied over a small range for this movement, it cannot be completely excluded that stimulation dynamics plays a role in control of these simple single-joint movements. [S0148-0731(00)01104-3]
Free Vibration of Orthotropic Skew Plates
Authors: Farag A. M. , Ashour A. S.
Published: July 2002

The main purpose of this paper is to develop a fast converging semianalytical method for assessing the vibration effect on thin orthotropic skew (or parallelogram/oblique) plates. Since the geometry of the skew plate is not helpful in the mathematical treatments, the analysis is often performed by more complicated and laborious methods. A successive conjunction of the Kantorovich method and the transition matrix is exploited herein to develop a new modification of the finite strip method to reduce the complexity of the problem. The displacement function is expressed as the product of a basic trigonometric series function in the longitudinal direction and an unknown function that has to be determined in the other direction. Using the new transition matrix, after necessary simplification and the satisfaction of the boundary conditions, yields a set of simultaneous equations that leads to the characteristic matrix of vibration. The influence of the skew angle, the aspect ratio, the properties of orthotropy, and the prescribed boundary conditions are investigated. Convergence of the solution is investigated and the accuracy of the results is compared with that available from other numerical methods. The numerical results show that the convergence is rapidly deduced and the comparisons agree very well with known results. [S0739-3717(00)00202-6]
Closure to “Discussion of ‘The Impact of the Model of the Environment in Exergy Analyses,’ ” (2000, ASME J. Energy Resour. Technol., 122, No. 4, p. 248)
Authors: Michaelides Efstathios E.
Published: July 2002

[S0195-0738(00)00204-1]
Transmission Error in Helical Timing Belt Drives (Case of a Period of Pulley Pitch)
Authors: Kagotani Masanori , Ueda Hiroyuki , Koyama Tomio
Published: July 2002

Helical timing belts have been developed in order to reduce the noise that occurs when conventional timing belts are driven. Helical timing belts are characterized by synchronous rotation. Although several studies have been performed to clarify the noise characteristics and belt life of helical timing belts, the transmission error of these belts remains unclear. In the present study, the transmission error having a period of one pitch of the pulley was investigated both theoretically and experimentally for helical timing belt drives. Experimental conditions were such that the transmission force acts on the helical timing belts under quasi-static conditions and the belt incurs belt climbing at the beginning of meshing and at the end of meshing. Experimental results obtained for the transmission error agreed closely with the computed results. The computed results revealed that helical timing belts can be analyzed as a set of very narrow belts for which the helix angle is zero. The transmission error was found to decrease when the helix angle or the belt width increase within a range defined such that the face advance is less than one belt pitch. In addition, there exists an appropriate installation tension that reduces the transmission error.
Kinematic Analysis of 3-D Swept Shock Surfaces in Axial Flow Compressors
Authors: Shan Peng
Published: July 2002

This paper is part II of a comprehensive study on the blade leading edge sweep/bend of supersonic and transonic axial compressors. The paper explores and analyzes the kinematic characteristic variables of three-dimensional (3-D) swept shock surfaces. In the research field studying the sweep aerodynamics of axial flow compressors and fans, many types of high loading swept blades are under intensive study. So, in both direct and inverse design methods and experimental validations, an accurate grasp of the sweep characteristic of the blade’s 3-D swept shock surface becomes of more concern than before. Associated with relevant blading variables, this paper studies the forward and zero and backward sweeps of shock surfaces, defines and resolves every kind of useful sweep angle, obtains dimensionless sweep similarity factors, suggests a kind of method for the quantitative classification of 3-D shock structures, and proposes the principle of 3-D shock structure measurements. Two rotor blade leading edge shock surfaces from two high loading single stage fans are analyzed and contrasted. This study is the foundation of the kinematic design of swept shock surfaces.
Three-Dimensional Dynamic Simulation of Total Knee Replacement Motion During a Step-Up Task
Authors: Piazza Stephen J. , Delp Scott L.
Published: July 2002

A three-dimensional, dynamic model of the tibiofemoral and patellofemoral articulations was developed to predict the motions of knee implants during a step-up activity. Patterns of muscle activity, initial joint angles and velocities, and kinematics of the hip and ankle were measured experimentally and used as inputs to the simulation. Prosthetic knee kinematics were determined by integration of dynamic equations of motion subject to forces generated by muscles, ligaments, and contact at both the tibiofemoral and patellofemoral articulations. The modeling of contacts between implants did not rely upon explicit constraint equations; thus, changes in the number of contact points were allowed without modification to the model formulation. The simulation reproduced experimentally measured flexion–extension angle of the knee (within one standard deviation), but translations at the tibiofemoral articulations were larger during the simulated step-up task than those reported for patients with total knee replacements.
A Switching Scheme for Mixed PZT-Based/Jet Thrusters Control of a Large Flexible Structure
Authors: Ferrara, A. , Magnani, and L. , Scattolini R.
Published: July 2002

Vibration suppression of a large space structure is achieved by switching between different actuators in order to optimize control performance and to reduce energy consumption. The theoretical properties of the proposed control strategy are reported together with some experimental results.
Triple Cycle: A Conceptual Arrangement of Multiple Cycle Toward
Optimal Energy Conversion
Authors: Hung T. C.
Published: July 2002

The purpose of this study is to find a maximum work output from various combinations of thermodynamic cycles from a viewpoint of the cycle systems. Three systems were discussed in this study: a fundamental combined cycle and two other cycles evolved from the fundamental dual combined cycle: series-type and parallel-type triple cycles. In each system, parametric studies were carried out in order to find optimal configurations of the cycle combinations based on the influences of tested parameters on the systems. The study shows that the series-type triple cycle exhibits no significant difference as compared with the combined cycle. On the other hand, the efficiency of the parallel-type triple cycle can be raised, especially in the application of recovering low-enthalpy-content waste heat. Therefore, by properly combining with a steam Rankine cycle, the organic Rankine cycle is expected to efficiently utilize residual yet available energy to an optimal extent. The present study has pointed out a conceptual design in multiple-cycle energy conversion systems.
The Effects of Compression and Pore Size Variations on the Liquid Flow Characteristics in Metal Foams
Authors: Boomsma K. , Poulikakos D.
Published: July 2002

Open-cell aluminum foams were investigated using water to determine their hydraulic characteristics. Maximum fluid flow velocities achieved were 1.042 m/s. The permeability and form coefficient varied from 2.46×10−10 m2 and 8701 m−1 to 3529×10−10 m2 and 120 m−1, respectively. It was determined that the flowrate range influenced these calculated parameters, especially in the transitional regime where the permeability based Reynolds number varied between unity and 26.5. Beyond the transition regime where ReK≳30, the permeability and form coefficient monotonically approached values which were reported as being calculated at the maximum flow velocities attained. The results obtained in this study are relevant to engineering applications employing metal foams ranging from convection heat sinks to filters and flow straightening devices.
Flow Characteristics of the Molecular Pump of Holweck Type in the Slip Regime
Authors: Tsui Yeng-Yung , Su Yuan-Sheng , Cheng Hong-Ping
Published: July 2002

A computational method is used to analyze the viscous flow in the spiral grooves of the molecular drag pump of Holweck type. The flow is assumed in the slip flow regime and, thus, the slip boundary condition is imposed at walls. Tests are conducted to examine the effects of clearance gap, spiral angle, channel height, number of channels, and rotating speed. The appearance of clearance brings about lower pressure gradient between side walls of the channel and, thus, reduces the pressure rise in the channel. Testing on spiral angle and channel height indicates that these parameters need to be optimized to achieve better performance. Results also reveal that increase of rotating speed is an effective way to promote compression ratio. In calculations, pressure rise is enhanced when the number of channel is decreased. However, it should be understood that by reducing channel number the cross-sectional area of the channel is decreased, which has the effects of reducing the pressure rise.
Thermal Transport Mechanisms at Nanoscale Point Contacts
Authors: Shi Li , Majumdar Arunava
Published: July 2002

We have experimentally investigated the heat transfer mechanisms at a 90±10 nm diameter point contact between a sample and a probe tip of a scanning thermal microscope (SThM). For large heated regions on the sample, air conduction is the dominant tip-sample heat transfer mechanism. For micro/nano devices with a submicron localized heated region, the air conduction contribution decreases, whereas conduction through the solid-solid contact and a liquid meniscus bridging the tip-sample junction become important, resulting in the sub-100 nm spatial resolution found in the SThM images. Using a one dimensional heat transfer model, we extracted from experimental data a liquid film thermal conductance of 6.7±1.5 nW/K. Solid-solid conduction increased linearly as contact force increased, with a contact conductance of 0.76±0.38W/m2-K-Pa, and saturated for contact forces larger than 38±11 nN. This is most likely due to the elastic-plastic contact between the sample and an asperity at the tip end.
Development of a Molten-Salt Thermocline Thermal Storage System for Parabolic Trough Plants
Authors: Pacheco James E. , Showalter Steven K. , Kolb William J.
Published: July 2002

Thermal storage improves the dispatchability and marketability of parabolic trough power plants allowing them to produce electricity on demand independent of solar collection. One such thermal storage system, a thermocline, uses a single tank containing a fluid with a thermal gradient running vertically through the tank, where hotter fluid (lower density) is at the top of the tank and colder fluid is at the base of the tank. The thermal gradient separates the two temperature potentials. A low-cost filler material provides the bulk of the thermal capacitance of the thermal storage, prevents convective mixing, and reduces the amount of fluid required. In this paper, development of a thermocline system that uses molten-nitrate salt as the heat transfer fluid is described and compared to a two-tank molten salt system. Results of isothermal and thermal cycling tests on candidate materials and salt safety tests are presented as well as results from a small pilot-scale (2.3 MWh) thermocline.
An Alternative to API 14E Erosional Velocity Limits for Sand-Laden Fluids
Authors: Salama Mamdouh M.
Published: July 2002

The current practice for eliminating erosional problems in piping systems is to limit the flow velocity Ve to that established by the recommended practice API RP 14E based on an empirical constant (C-factor) and the fluid mixture density ρm as follows: Ve=C/ρm. The API criterion is specified for clean service (noncorrosive and sand-free), and it is noted that the C-factor should be reduced if sand or corrosive conditions are present. The validity of the equation has been challenged on the basis that the API RP 14E limits on the C-factor can be very conservative for clean service and is not applicable for conditions when corrosion or sand are present. Extensive effort has been devoted to develop an alternative approach for establishing erosional velocity limits for sand-laden fluids. Unfortunately, none of these proposals have been adopted as a standard practice because of their complexity. This paper will review the results of these studies and proposes an alternative equation that is as simple as the API 14E equation. This alternative equation has the following form: Ve=SDρm/W. The value of the S-factor depends on the pipe geometry, i.e., bend, tee, contraction, expansion, etc. Using the units for mixture flow velocity Ve in m/s, fluid mixture density ρm in kg/m3, pipe diameter (D) in mm and sand production W in kg/day, the value of the S-factor is 0.05 for pipe bends. The accuracy of the proposed equation for predicting erosion in pipe bends for fluids containing sand is demonstrated by a comparison with several multi-phase flow loop tests that cover a broad range of liquid-gas ratios and sand concentrations. [S0195-0738(00)00202-8]
Introduction to the Surface Spectra of Oxides
Authors: Baer D. R. , Henrich V. E.
Published: July 2002

Due to their technological importance and an increasing scientific interest, a set of data from oxide surfaces has been collected for publication in two special issues of Surface Science Spectra. This Introduction to these two special issues summarizes the data to be presented and provides short overviews of trends in both the physics and chemistry of metal-oxide surfaces and of some important aspects of the techniques used to examine these surfaces. The surface spectroscopies discussed in relation to oxides include: valence band photoemission (ultraviolet photoelectron spectroscopy and synchrotron based), core level photoemission (x-ray photoelectron spectroscopy, XPS), Auger electron spectroscopy (AES), (reflection) electron energy loss spectroscopy (R)EELS, high-resolution electron energy loss spectroscopy (HREELS), scanning probe methods, and ion scattering spectroscopy (ISS). Brief sections also discuss the nature of stoichiometric oxide surfaces, the physics and chemistry of defects on these surfaces, and adsorption on metal-oxide surfaces.
Activation Energy for the Desorption of Carbon Dioxide from Oxygen-Covered Silver
Authors: Czanderna A. W. , Biegen J. R.
Published: July 2002

The thermal desorption of carbon dioxide from an oxygen-covered silver powder was studied from 25 ° to 150 °C by applying a nominal heating rate of 2 °C/min and measuring the mass lost with a vacuum microbalance. A maximum rate of desorption was reached at 49 °C and the desorption was completed at about 100 °C. The temperature at which the maximum rate of desorption occurred was independent of the initial coverage of carbon dioxide to within 2 °C. However, the data could not be simply explained by a fit to the first order Wigner–Polanyi desorption equation, in which it is assumed that the frequency factor (ν) and the desorption energy (E) are independent of coverage and temperature. Beyond the maximum, a slow decrease in the experimental rate of desorption, which was found in contrast to the usual sharp cutoff for a first order process, was attributed to desorbing oxygen, readsorption of carbon dioxide, or a variation of E at low coverages. Parallel studies with a residual gas analyzer showed that small quantities of oxygen were desorbed in addition to the carbon dioxide. The experimental desorption curve could be fit to the Wigner–Polanyi equation by assuming that the desorption consisted of all the adsorbed carbon dioxide and a small amount of oxygen. The desorption parameters for carbon dioxide which were obtained ranged from E = 20 to 24 kcal/mol and ν = 1011 to 1013  sec−1.
Effect of Mg content in Cu(Mg)/SiO2/Si multilayers on the resistivity after annealing in an oxygen ambient
Authors: Lee Wonhee , Cho Heunglyul , Cho Bumseok , Kim Jiyoung , Kim Yong-suk , Jung Woo-Gwang , Kwon Hoon , Lee Jinhyung , Lee Chongmu , Reucroft P. J. , Lee Jaegab
Published: July 2002

The formation mechanism of self-aligned MgO layers obtained from Cu(Mg) alloys has been investigated. Self-aligned surface and interfacial MgO layers were formed upon annealing Cu(Mg)/SiO2/Si multilayer films in an oxygen ambient, resulting in a structure of MgO/Cu/MgO/SiO2/Si. Upon annealing at 300 °C or higher in an oxygen ambient, Mg segregates preferentially to the Cu surface until a dense, uniform MgO layer is formed. A growth limited thickness of the surface MgO was found to be about 150 Å , providing substantial passivation of the exposed Cu surface. After a dense MgO layer forms, substantial Mg segregation to the SiO2 surface takes place. However, the formation of the interfacial MgO caused a sudden increase in resistivity after annealing for about 20 min, which can be due to the release of free Si being diffused into the Cu film by the reaction of Mg with Si in the SiO2. The optimum Mg contents in Cu(Mg) alloy films with various thickness were thus estimated to obtain the Cu(Mg) alloy multilayer film with substantially lower resistivity while retaining the beneficial properties of Cu passivation in an oxygen ambient.
Multiple Twinning and Pentagonal Structures in Germanium
Authors: Mader S.
Published: July 2002

Based on diffraction analysis of amorphous Ge, pentagonal structure elements have been proposed. In a search for evidence other than diffraction from amorphous films for such structure elements, small (100 Å) particles of Ge were evaporated onto cleaved NaCl under almost epitaxial conditions and examined by electron microscopy and diffraction. These particles contain numerous primary and secondary twins. Each (100) oriented nucleus can, in principle, give rise to four primary and 12 secondary twins; however, only four of the possible 12 secondary twin orientations are observed. With crystallographic structure models one can extrapolate the boundaries between the observed twin orientations to a common line of intersection where indeed regions with pentagonal stacking sequence occur. Based on this result, a model for an idealized structural unit in amorphous Ge is proposed.
Behavior of Hydrogen on Nickel
Authors: Gilbreath W. P. , Wilson D. E.
Published: July 2002

An electron-impact desorption (EID)–flash-filament system incorporating a gas-phase and a surface-ion spectrometer, and a means of vapor-depositing clean surfaces has been used to study the adsorption behavior of hydrogen on polycrystalline nickel surfaces with several surface treatments. The desorption activation energy, coverage, and sticking coefficient varied from 98 kJ mole−1, 5×1014 molecules cm−2 and 0.19, respectively, for freshly deposited nickel films, to 50 kJ mole−1, 2×1014 molecules cm−2 and 0.002, respectively, for nickel foils with no prior cleaning treatment. The results indicate a low number (less than 1% of the surface sites) of active sites for EID of H3+ and a preferential filling of these sites by surface diffusion.
A Process for Delubrication, Presintering, Sintering, and Rapid Cooling in a Vacuum Induction Furnace
Authors: Hallemeier J. F.
Published: July 2002

Delubrication, presintering, and sintering are major steps in the manufacture of many products in the powder metallurgy field. The quality of the final product, to a great extent, depends on the quality, accuracy, and reliability of the sintering equipment used. The vacuum induction furnace for delubrication, presintering, sintering, and rapid cooling described below offers the possibility of delubricating the charge under vacuum and protective or reactive gas atmospheres at reduced pressures and to sinter the material in the same furnace, eliminating charge handling and transfer between the delubrication and sintering processes. All components of the furnace chamber and manifolds which come in contact with lubricant vapors are heated during the delubrication cycle and thus it is impossible to accumulate any traces of condensed wax in critical areas of the furnace. This eliminates the possibility that during sintering the charge is contaminated by lubricant decomposition products. The performance of the total cycle from delubrication to cooling in one furnace and the application of forced gas cooling improve the economic picture of the sintering process. Elaborate controls and programmers provide precise process control and generation of valuable records. The design of the furnace results in reduced maintenance and service costs.
Vacuum Deposition of Alloys—Theoretical and Practical Considerations
Authors: Foster James S. , Pfeifer W. H.
Published: July 2002

The conditions necessary for successful steady-state vacuum deposition of a binary alloy from a single continuously fed source are examined and used to relate the compositions of the source and the deposit. This relationship involves the vapor pressures, atomic weights, activity coefficients, and weight percentages of the elements in the alloy. Extensions to prediction of the behavior of impurities and to ternary and higher order systems are discussed. The temperature sensitivities of single and multiple sources are qualitatively compared. A method of approximating the time required to reach steady state conditions is presented. Practical problems associated with the use of poor quality source materials are reviewed and recommendations are given for use in selecting source materials.
Investigation of the Effect of Vacuum Environment on the Fatigue and Fracture Behavior of 7075–T6
Authors: Hudson C. Michael
Published: July 2002

Axial-load fatigue-life, fatigue-crack-propagation, and fracture-toughness experiments were conducted on sheet specimens made of 7075-T6 aluminum alloy. These experiments were conducted at air pressures ranging from 101kN/m2 to 7 μN/m2 to determine the effect of air pressure on fatigue behavior. Analysis of the results from the fatigue-life experiments indicated that for a given stress level, the lower the air pressure was the longer the fatigue life. At a pressure of 7 μN/m2, fatigue lives were 15–30 times longer than at 101 kN/m2. Analysis of the results from the fatigue-crack-growth experiments indicates that at low values of stress-intensity range, the fatigue-crack-growth rates were approximately twice as high at atmospheric pressure as in vacuum. However, at higher values of stress-intensity range, the fatigue-crack-growth rates were nominally the same in vacuum and at atmospheric pressure. An empirical equation developed by Forman, Kearney, and Engle was fitted to the crack-propagation data using least-squares techniques. This equation gave an excellent fit to the data generated both in vacuum and at atmospheric pressure. Analysis of the fracture-toughness data showed there was essentially no difference between the fracture toughness of 7075-T6 in vacuum and at atmospheric pressure
Studies of the Catalytic Reaction of C2H4 and O2 on Ag(111) Surfaces
Authors: Smith Joe N. , Palmer R. L. , Vroom D. A.
Published: July 2002

A molecular beam study of the reaction of C2H4 with O2 on Ag(111) was attempted and supplemented with data obtained using an isotropic source (IS) configuration. In the beam configuration, the possible product signals at 18 amu (H2O) or 44 amu (C2H4O, CO2) could not be discerned. In the IS configuration, a product signal at 44 amu (CO2) was observed. An estimate of the collision reaction probability of 9×10−3, obtained from the IS data, confirmed that the product signal would not be readily observable in the beam configuration due to signal-to-noise considerations. From C2H4 beam scattering data, coupled with the experimental ion spectrum obtained from C2H4 by electron impact, it was possible to estimate that roughly about 15% of the incident C2H4 fragmented upon collision with the surface; 10% going to C2H3 and 5% to C2H2. From the surface temperature dependence in the IS configuration, an activation energy of ∼8 kcal/mole was obtained for the mass 44 product.
Plasmon Angular Profiles in Low Energy Electron Diffraction from Single Crystals
Authors: Stein R. J. , Stern R. M.
Published: July 2002

Measurement of surface and bulk plasma peaks in the secondary electron distribution from Ni(100) and W(110) provides confirmation of two-step inelastic diffraction. Angular profiles are made in the neighborhood of selected prominent elastic diffraction maxima. Momentum conservation parallel to the surface leads to the prediction of a doublet structure in the angular distribution of diffracted electrons having lost the surface plasmon energy. This structure is observed. The observed structure in the bulk plasmon loss angular profile is more complex and is indicative of other conservation laws.
Thin dielectric films for integrated optics
Authors: Ulrich R.
Published: July 2002

After a brief review of some fundamentals of thin-film light guides, the dispersion and the attenuation of an ideally smooth light-guiding dielectric film are presented as weighted averages of the bulk dielectric properties of the three materials forming the guide (substrate, film, and superstrate). The weights entering here are essentially the fractions of the electric field energy travelling in each of the materials. In a real guide, the light-guiding properties are also affected by any nonuniformities of the film thickness. These considerations are applied to the light-guiding films required for various purposes of integrated optics. Conversely, it is shown how measurements of the light-guiding properties of a film may help to determine other characteristic parameters of the film. In the last section the numerous methods are reviewed that have been used for the preparation of light-guiding films.
Site control of InAs quantum dots on GaAs surfaces patterned by in situ electron-beam lithography
Authors: Ishikawa T. , Kohmoto S. , Nishikawa S. , Nishimura T. , Asakawa K.
Published: July 2002

We studied a site-control technique for InAs quantum dots (QDs) on GaAs substrates using a combination of in situ electron-beam (EB) lithography and self-organized molecular-beam epitaxy. On prepatterned square-mesa structures with a dimension of several tens of microns, we were able to control the average density of Stranski–Krastanow QDs. On these mesa structures, submicron holes in an array were formed as preferential growth sites of QDs by EB writing and Cl2 gas etching. By supplying 1.8 monolayer (ML) of InAs, QDs were formed in the patterned holes without any formation on the flat region between them. The QD concentration in each hole was dependent on the hole depth, that is, on the density of atomic steps inside holes. In the holes deeper than 50 Å, QDs were so densely formed that carrier tunneling occurred between them. In the shallow holes with 5–6 ML steps, on the other hand, single QDs were formed.
Calculated energetics for adsorption and desorption steps during etching of Si(110) surface by Cl
Authors: Halicioglu Timur
Published: July 2002

Energetics and the configurational aspects related to the adsorption of Cl on the (110) index plane of Si and the subsequent desorption of SiClx species from the surface (leading to etching) were investigated. Calculations were conducted for varying surface Cl concentrations. First and second chlorination steps for surface Si atoms were analyzed and the role played by surface vacancies was investigated. On the Si(110) surface, steric effects coming from repulsive forces among the adsorbed Cl atoms, were found to be quite significant. Results indicate that the second chlorination step which leads to the formation of attached SiCl2 species, is very important in the overall eching process.
Wide-band gap semiconductors for noncontact thermometry
Authors: Salvatori S.
Published: July 2002

The advantages achieved in two-color optical pyrometry using wide-band gap semiconductors (e.g., silicon carbide, gallium arsenide) and silicon-based photosensors for short- and long-wavelength light detection, respectively, are demonstrated here. Spectral responsivities of Si-, SiC-, and GaN-based photodiodes are used to evaluate the performances of a simple ratio pyrometer. Compared to conventional near-infrared ratio pyrometers, it is shown that high-energy photon detection is able to reduce temperature measurement errors—mainly induced by spectral variation of the target emissivity—by more than 1 order of magnitude and allows increased output dynamics of the pyrometer of up to 4 orders of magnitude.
Tin-oxide overlayer formation by oxidation of Pt–Sn(111) surface alloys
Authors: Batzill Matthias , Beck David E. , Jerdev Dmitri , Koel Bruce E.
Published: July 2002

Ordered (2×2) and (√3×√3)R30° Pt–Sn(111) surface alloys were oxidized by NO2 exposure at 400 K under ultrahigh vacuum conditions. The evolution of the surface morphology with annealing temperature was characterized by using low energy electron diffraction (LEED), scanning tunneling microscopy, Auger electron spectroscopy, and x-ray photoelectron spectroscopy. Both oxidized surface alloys form a SnOx overlayer that wets the substrate. However, the SnOx film does not completely cover the surface for the oxidized (2×2) surface alloy. For the oxidized (√3×√3)R30° surface alloy, an ordered (4×4) LEED pattern is formed upon flash annealing above 900 K. The formation of this ordered SnOx adlayer coincides with Sn segregation from the bulk to the interface region. A model for the (4×4) structure is discussed. The SnOx overlayer formed by oxidation of the (2×2) surface alloy is significantly less thermally stable than the oxidized (√3×√3)R30° surface alloy. Exothermic alloying of Sn with Pt may facilitate the decomposition of the oxide overlayers. Differences in the amount of subsurface tin and its segregation to the surface is proposed to explain the thermal stabilities of the oxide layers. The incompleteness of the SnOx overlayer and less subsurface tin for the oxidized (2×2) surface alloy is proposed to explain its significant lower thermal stability.