bluuebunny/crossref_metadata_2025 huggingface dataset:
Why you should consider object‐oriented programming techniques for finite element methods
Authors: Cross J.T. , Masters I. , Lewis R.W.
Published: July 2002

Object‐oriented programming, as an alternative to traditional, procedural programming methods for finite element analysis, is growing rapidly in importance as algorithms and programs become more complex. This paper reviews some of the literature and seeks to explain some of the concepts of object‐oriented thinking most useful to the finite element programmer, using as an example a C++ implementation of a heat transfer and solidification program.
The challenge of ISO 9000 certification in higher education
Authors: Shutler Paul M.E. , Crawford Lachlan E.D.
Published: July 2002

Addresses the question of how ISO 9000, the international standard for quality management systems, may best be applied to higher education. Begins with a concise but systematic description of the requirements of ISO 9000 for industry in terms of a simplified model of a factory. Argues that the product of higher education must be the actual learning of the students and not merely the provision of learning opportunities. Hence shows how the requirements of ISO 9000 for higher education may be interpreted in terms of a simplified model of a university. Highlights the key educational management issues raised and reviews how they are currently being addressed in practice.
Influence of microgravity on astronauts' sympathetic and vagal responses to Valsalva's manoeuvre
Authors: Cox James F. , Tahvanainen Kari U.O. , Kuusela Tom A. , Levine Benjamin D. , Cooke William H. , Mano Tadaaki , Iwase Satoshi , Saito Mitsuru , Sugiyama Yoshiki , Ertl Andrew C. , Biaggioni Italo , Diedrich André , Robertson Rose Marie , Zuckerman Julie H. , Lane Lynda D. , Ray Chester A. , White Ronald J. , Pawelczyk James A. , Buckey Jay C. , Baisch Friedhelm J. , Bomqvist C. Gunnar , Robertson David , Eckberg Dwain L.
Published: July 2002

When astronauts return to Earth and stand, their heart rates may speed inordinately, their blood pressures may fall, and some may experience frank syncope. We studied brief autonomic and haemodynamic transients provoked by graded Valsalva manoeuvres in astronauts on Earth and in space, and tested the hypothesis that exposure to microgravity impairs sympathetic as well as vagal baroreflex responses. We recorded the electrocardiogram, finger photoplethysmographic arterial pressure, respiration and peroneal nerve muscle sympathetic activity in four healthy male astronauts (aged 38–44 years) before, during and after the 16 day Neurolab space shuttle mission. Astronauts performed two 15 s Valsalva manoeuvres at each pressure, 15 and 30 mmHg, in random order. Although no astronaut experienced presyncope after the mission, microgravity provoked major changes. For example, the average systolic pressure reduction during 30 mmHg straining was 27 mmHg pre‐flight and 49 mmHg in flight. Increases in muscle sympathetic nerve activity during straining were also much greater in space than on Earth. For example, mean normalized sympathetic activity increased 445 % during 30 mmHg straining on earth and 792 % in space. However, sympathetic baroreflex gain, taken as the integrated sympathetic response divided by the maximum diastolic pressure reduction during straining, was the same in space and on Earth. In contrast, vagal baroreflex gain, particularly during arterial pressure reductions, was diminished in space. This and earlier research suggest that exposure of healthy humans to microgravity augments arterial pressure and sympathetic responses to Valsalva straining and differentially reduces vagal, but not sympathetic baroreflex gain.
Differential effect of angiotensin II on blood circulation in the renal medulla and cortex of anaesthetised rats
Authors: Ba̧dzyńska Bożena , Grzelec‐Mojzesowicz Monika , Dobrowolski Leszek , Sadowski Janusz
Published: July 2002

The renal medulla is sensitive to hypoxia, and a depression of medullary circulation, e.g. in response to angiotensin II (Ang II), could endanger the function of this zone. Earlier data on Ang II effects on medullary vasculature were contradictory. The effects of Ang II on total renal blood flow (RBF), and cortical and medullary blood flow (CBF and MBF: by laser‐Doppler flux) were studied in anaesthetised rats. Ang II infusion (30 ng kg−1 min−1i.v.) decreased RBF 27 ± 2 % (mean ±s.e.m.), whereas MBF increased 12 ± 2 % (both P < 0.001). Non‐selective blockade of Ang II receptors with saralasin (3 μg kg−1 min−1i.v.) increased RBF 12 ± 2 % and decreased MBF 8 ± 2 % (P < 0.001). Blockade of AT1 receptors with losartan (10 mg kg−1) increased CBF 10 ± 2 % (P < 0.002) and did not change MBF. Losartan given during Ang II infusion significantly increased RBF (53 ± 7 %) and decreased MBF (27 ± 7 %). Blockade of AT2 receptors with PD 123319 (50 μg kg−1 min−1i.v.) did not change CBF or MBF. Intramedullary infusion of PD 123319 (10 μg min−1) superimposed on intravenous Ang II infusion did not change RBF, but slightly decreased MBF (4 ± 2 %, P < 0.05). We conclude that in anaesthetised surgically prepared rats, exogenous or endogenous Ang II may not depress medullary circulation. In contrast to the usual vasoconstriction in the cortex, vasodilatation was observed, possibly related to secondary activation of vasodilator paracrine agents rather than to a direct action via AT2 receptors.
Slow removal of Na+ channel inactivation underlies the temporal filtering property in the teleost thalamic neurons
Authors: Tsutsui Hidekazu , Oka Yoshitaka
Published: July 2002

It has been previously shown that the ‘large cell’ in the corpus glomerulosum (CG) of a teleost brain has a low‐pass temporal filtering property. It fires a single spike only in response to temporally sparse synaptic inputs and thus extracts temporal aspects of afferent activities. To explore the ionic mechanisms underlying this property, we quantitatively studied voltage‐gated Na+ channels of the large cell in the CG slice preparation of the marine filefish by means of whole‐cell patch clamp recordings in the voltage‐clamp mode. Recorded Na+ current was well described using the Hodgkin‐Huxley ‘m3h’ model. It was revealed that the Na+ channels have a novel feature: remarkably slow recovery from inactivation. In other words, the time constant for the ‘h’ gate was extremely large (∼100 ms at −80 to −50 mV). In order to test whether the analysed Na+ current serves as a mechanism for filtering, the behaviour of the membrane model incorporating the Na+ channel was simulated using a computer program called NEURON. In response to current injections, the membrane model displayed low‐pass filtering and firing properties similar to those reported in real cells. The present results suggest that slow removal of Na+ channel inactivation serves as a crucial mechanism for the low‐pass temporal filtering property of the large cell. The simulation study also suggested that velocity and/or amplitude of a spike propagating though an axon expressing Na+ channels of this type could potentially be modulated depending on the preceding activities of the cells.
Stress Relaxation Testing of Service Exposed IN738 for Creep Strength Evaluation
Authors: Woodford David A.
Published: July 2002

Standard size and miniature specimens of IN738 were taken from a service exposed turbine blade and vane for comparative stress relaxation testing at 800C, 850C, and 900C. Base data taken from root section material were used to construct stress versus creep rate parametric curves which could be used directly in design. Up to five decades in creep rates were obtained at each temperature from tests lasting less than one day. The data were also presented in the form of stress versus predicted times to 0.5 percent creep which compared well with available long time creep data. Differences were noted in specimens taken from different locations in the airfoil regions which probably resulted from differences in grain size or orientation. Based on these measurements it was concluded that there was no significant effect of section size on creep strength as defined by this test, and that the alloy was quite insensitive to prior deformation and thermal exposures. A life management procedure, using a combination of creep strength evaluation based on the stress relaxation test and a separate fracture evaluation measurement, is outlined in which end of useful life is defined in terms of minimum acceptable performance levels. [S0742-4795(00)01803-2]
Effects of Moving Three-Dimensional Nano-Textured Disk Surfaces on Thin Film Gas Lubrication Characteristics for Flying Head Slider Bearings in Magnetic Disk Storage
Authors: Tagawa Norio , Hayashi Takefumi , Mori Atsunobu
Published: July 2002

This paper describes the effects of moving three-dimensional nano-textured or patterned disk surfaces on thin film gas lubrication characteristics for flying head slider bearings in magnetic disk storage. In order to perform the most realistic simulation of slider flying characteristics over the textured disk surfaces, the direct numerical simulation method is used, instead of using various averaging techniques. Therefore, a deterministic description of the texture is adopted in this study. A dynamic analysis of the slider responses can be carried out, by solving the air bearing equation based on the linearized Boltzmann equation with the equations of motion of the slider under the excitation of the moving texture simultaneously. The slider’s dynamic responses to moving spaced bumps disk surfaces, including both the circumferentially and radially ridged disk surfaces, are computed systematically and basic slider dynamics over patterned disk surfaces is investigated. The effects of the texture area ratios (= texture width/texture pitch) in the circumferential and radial directions on the slider spacing dynamic modulations as well as the slider static flying characteristics are also studied. Furthermore, the effects of three kinds of texture patterns on the slider flying characteristics are investigated. Considering those simulation results, the design optimization for the texture pattern that minimizes not only the slider static flying height increase but also spacing dynamic modulations is discussed in order to achieve ultra-high density proximity magnetic recording.
Influence of Compressibility on the Helical Viscous Compressor
Authors: Pan Coda H. T.
Published: July 2002

The pressurization-flow characteristic of a helical viscous compressor is basic to the design of precision air bearings and non-contact gas seals which make use of the spiral-grooved surface feature. The method of Compressible Narrow Groove Analysis (CNGA) makes possible mapping of the pressurization-flow characteristic of a helical viscous compressor for a wide range of the compressibility number. In this manner, design features previously established by Quasi-Incompressible Narrow Groove Analysis (QINGA) are examined with respect to the influence of local compressibility.
Dynamic Characteristics of an In-Contact Headslider Considering Meniscus Force: Part 2—Application to the Disk With Random Undulation and Design Conditions
Authors: Kato Takahisa , Watanabe Souta , Matsuoka Hiroshige
Published: July 2002

In Part 1, the authors presented a three-degrees-of-freedom (3-DOF) model of an in-contact headslider/disk interface (HDI) system and the equations of motion of the in-contact headslider considering the meniscus force. Dynamic characteristics of the in-contact headslider over sinusoidal disk surface were made clear. In Part 2, using the equations of motion obtained in Part 1, the calculation results for the disk with random undulation and design conditions for the in-contact HDI system are described.
On-Line Monitoring of Tool Wear and Control of Dimensional Inaccuracy in Turning
Authors: Choudhury S. K. , Jain V. K. , Rama Krishna S.
Published: July 2002

The present work deals with on-line monitoring of tool wear and control of workpiece diameter so as to avoid the formation of taper in the machined job. A noncontact, displacement optical fiber transducer is developed to monitor the tool wear indirectly by constantly monitoring the change in the workpiece diameter due to the tool wear. The results show that the dimensional inaccuracy can be maintained below 0.03 mm using the developed system.
Performance Analysis and Optimization of Annular Fin With a Step Change in Thickness
Authors: Kundu B. , Das P. K.
Published: July 2002

The temperature distribution in a concentric annular fin with a step change in thickness (AFST) has been obtained analytically. The optimum design of such fins has been performed using Lagrange multiplier technique considering either the fin volume or the rate of heat transfer as the constraint. It has been demonstrated that the optimum AFSTs transfer more heat compared to optimum annular disc fins for a given fin volume as well as for given fin volume and fin length.
Optimal Fiber Orientation in Locally Transversely Isotropic Creeping Structures
Authors: Robinson D. N. , Binienda W. K.
Published: July 2002

An approximate method is developed for comparing various fiber configurations in a composite structure with the objective of achieving optimal resistance to creep failure. The class of composite structures addressed has a single family of long or continuous strong fibers embedded in a creeping matrix material, e.g., a polymer, metal, etc. Thus, the structure is locally transversely isotropic with the fiber orientation generally varying throughout the structure. The proposed method, intended as an early design tool, is based on an upper bound on creep rupture time and an associated representative failure stress. The latter is evaluated and compared for different fiber configurations, thereby identifying that with optimal creep rupture resistance. This approach allows a substantial saving in computational time by avoiding a detailed analysis of the actual failure process. Application is made to a fiber-reinforced thick-walled cylindrical pressure vessel.
Effects of Jet Reynolds Number on the Performance of Axisymmetric and Nonaxisymmetric Gas Burner Flames
Authors: Kamal Azfar , Gollahalli S. R.
Published: July 2002

An investigation of the effects of burner exit Reynolds number on the relative effects of burner geometry (circular and elliptic with an aspect ratio 2:4) in a propane jet flame is presented. Circular and elliptic burners of the equivalent area of a circular burner of diameter 5.2 mm were studied. Air entrainment into the nonreacting jets, emission indices of NO, NO2, and CO, visible flame length, flame temperature profiles, radiative fraction of heat release, and soot concentration were measured. Results show that an increase in Re decreases the benefits of higher air entrainment into the flame due to elliptic burner geometry. Similarly, the effects of changes in NO and CO emission indices level off at higher burner Re. The measurements of visible flame length, radiative fraction of heat release, temperature profiles, and soot concentrations corroborate the observed emission index results.
A New Method for Roundness Control in Taper Turning Using FCC Techniques
Authors: Fung Eric H. K. , Yang S. M.
Published: July 2002

This paper describes a methodology of online measuring and compensating spindle error motions without using a precalibrated master. The method is based on a combination of forecasting compensatory control (FCC) and error separation techniques. The real time recursive ARMA modeling technique is used for the modeling and forecasting of workpiece errors while the error compensation is performed by means of two-dimensional piezo-actuated tool movements. Experimental results have shown that an improvement of 42–47 percent was achieved for the roundness error of workpieces in the taper turning operations.
On the Existence of a Solution for a Solid Circular Plate Bilaterally Supported Along Two Antipodal Boundary Arcs and Loaded by a Central Transverse Concentrated Force
Authors: Monegato G. , Strozzi A.
Published: July 2002

A purely flexural mechanical analysis is presented for a thin, solid, circular plate, deflected by a central transverse concentrated force, and bilaterally supported along two antipodal periphery arcs, the remaining part of the boundary being free. This problem is modeled in terms of a singular integral equation of the Prandtl type, which possesses a unique solution expressed in terms of a reaction force containing a factor exhibiting square root endpoint singularities. This solution is then shown not to respect the requested boundary constraints. It is therefore concluded that, within the framework of the purely flexural plate theory, the title problem cannot admit the weighted L2 solution here examined. It cannot, however, be excluded that a solution to the title problem exists, which possesses stronger endpoint singularities than those examined in this paper, or is of a more general form than the one considered here.
Modeling and Validation of a Lean Burn Natural Gas Engine
Authors: Gangopadhyay Anupam , Meckl Peter
Published: July 2002

In this paper, a control-oriented model of a medium-duty throttle-body natural gas engine is developed. The natural gas engine uses lean-burn technology without exhaust gas recirculation (EGR). The dynamic engine model differs from models of gasoline engines by including the natural gas fuel dynamics in the intake manifold. The model is based on a mean value concept and has three state variables: intake manifold pressure, fuel fraction in the intake manifold and the engine rotational speed. The resulting model has been validated in steady-state and transient operation over the usual operating range of the engine between 800 rpm and 2600 rpm with air/fuel ratios ranging between 18.0 and 24.0.
Microfiltration of Polyoxyalkylene Metalworking Fluid Lubricant Additives Using Aluminum Oxide Membranes
Authors: Skerlos Steven J. , Rajagopalan N. , DeVor Richard E. , Kapoor Shiv G. , Angspatt V. Don
Published: July 2002

Microfiltration is capable of reducing health hazards and environmental pollution associated with metalworking fluids (MWFs) by enabling recycling and microbial removal. This paper investigates chemical characteristics of MWFs that can lead to flux decline during microfiltration using aluminum oxide membranes by studying the family of polyoxyalkylene diblock copolymers comprised of ethylene oxide and propylene oxide. These copolymers are commonly used as lubricant additives in metalworking fluids and serve as a model for beginning to understand the relationship between metalworking fluid formulation and microfiltration flux. It is found that increasing the hydrophobic content of the copolymers can lead to reduced flux. Anionic modification and increasing molecular weight of the copolymers can also lead to reduced flux. Insufficient cleaning of anionic copolymers from the membrane leads to pH-dependent flux of deionized water during subsequent filtration. The pH-dependence of flux arises due to swelling caused by electrostatic repulsions between the aluminum oxide surface and anionic copolymers that remain adsorbed to the surface of the membrane. This swelling serves to resist permeate flow above the isoelectric point of aluminum oxide. This phenomenon is observed directly using Field Emission Environmental Scanning Electron Microscopy (FE-ESEM).
Slip Flow Convection in Isoflux Rectangular Microchannels
Authors: Yu Shiping , Ameel Timothy A.
Published: July 2002

Laminar forced convection in thermally developing slip flow through isoflux rectangular microchannels is analytically investigated. Local and fully developed Nusselt numbers, fluid temperatures, and wall temperatures are obtained by solving the continuum energy equation for hydrodynamically fully developed slip flow with the velocity slip and temperature jump condition at the walls. It is found that heat transfer may increase, decrease, or remain unchanged, compared to nonslip flow conditions, depending on aspect ratios and two-dimensionless variables that include effects of the microchannel size or rarefaction and the fluid/wall interaction. The transition points that separate heat transfer enhancement from reduction are acquired for different aspect ratios.
Experimental Study on the Avoidance and Suppression Criteria for the Vortex-Induced Vibration of a Cantilever Cylinder
Authors: Sakai Takaaki , Morishita Masaki , Iwata Koji , Kitamura Seiji
Published: July 2002

Experimental validation of the design guideline to prevent the failure of a thermometer well by vortex-induced vibration is presented, clarifying the effect of structure damping on displacement amplitudes of a cantilever cylinder. The available experimental data in piping are limited to those with small damping in water flow, because of the difficulty in increasing structure damping of the cantilever cylinders in experiments. In the present experiment, high-viscosity oil within cylinders is used to control their structure damping. Resulting values of reduced damping Cn are 0.49, 0.96, 1.23, 1.98, and 2.22. The tip displacements of the cylinder induced by vortex vibration were measured in the range of reduced velocity Vr from 0.7 to 5 (Reynolds number is 7.8×104 at Vr=1). Cylinders with reduced damping 0.49 and 0.96 showed vortex-induced vibration in the flow direction in the Vr>1 region. However, in cases of reduced damping of 1.23, 1.98, and 2.22, the vibration was suppressed to less than 1 percent diameter. It is confirmed that the criteria of “Vr<3.3 and Cn>1.2” for the prevention of vortex-induced vibration is reasonably applicable to a cantilever cylinder in a water flow pipe.
Laminar Flow Heat Transfer and Pressure Drop Characteristics of
Power-Law Fluids Inside Tubes With Varying Width Twisted Tape Inserts
Authors: Patil A. G.
Published: July 2002

Results of an experimental investigation of heat transfer and flow friction of a generalized power-law fluid in tape generated swirl flow inside a 25.0 mm i.d. circular tube, are presented. In order to reduce excessive pressure drops associated with full width twisted tapes, with less corresponding reduction in heat transfer coefficients, reduced width twisted tapes of widths ranging from 11.0 to 23.8 mm, which are lower than the tube inside diameter are used. Reduced width twisted tape inserts give 18 percent–56 percent lower isothermal friction factors than the full width tapes. Uniform wall temperature Nusselt numbers decrease only slightly by 5 percent–25 percent, for tape widths of 19.7 and 11.0 mm, respectively. Based on the constant pumping power criterion, the tapes of width 19.7 mm perform more or less like full width tapes. Correlations are presented for isothermal and heating friction factors and Nusselt numbers (under uniform wall temperature condition) for a fully developed laminar swirl flow, which are applicable to full width as well as reduced width twisted tapes, using a modified twist ratio as pitch to width ratio of the tape. The reduced width tapes offer 20 percent–50 percent savings in the tape material as compared to the full width tapes. [S0022-1481(00)01401-8]
Computational Study of Horizontal Axis Wind Turbines
Authors: Xu Guanpeng , Sankar Lakshmi N.
Published: July 2002

A hybrid Navier-Stokes potential flow methodology for modeling three-dimensional unsteady viscous flow over horizontal axis wind turbine configurations is presented. In this approach, the costly viscous flow equations are solved only in a small viscous flow region surrounding the rotor. The rest of the flow field is modeled using a potential flow methodology. The tip vortices are modeled using a free wake approach, which allows the vortices to deform and interact with each other. Sample results are presented for two rotor configurations tested by the National Renewable Energy Laboratory. Comparisons with experimental data, full Navier-Stokes simulations and blade element momentum theory are given to establish the efficiency and accuracy of the present scheme. [S0199-6231(00)00601-8]
Graphite-Filled Poly(vinylidene fluoride) (PVdF) by XPS
Authors: Militello Maria C. , Gaarenstroom Stephen W.
Published: July 2002

XPS spectra of graphite-filled poly(vinylidene fluoride) (PVdF) are presented. The specimen consists of 17 wt % PVdF and 83 wt % graphite. A freshly cut surface was examined using monochromated Al Kα x-rays. Spectra include a survey scan, C 1s and F 1s regions, and the F KLL Auger transitions.
Scanning tunneling microscopy study of the Er/Ge(111) c(2×8) interface
Authors: Pelletier S. , Ehret E. , Gautier B. , Palmino F. , Labrune J. C.
Published: July 2002

Scanning tunneling microscopy (STM) is used to study the Er interaction on the Ge(111) substrate reconstructed c(2×8). In the submonolayer range, a homogeneous two-dimensional (2D) (1×1) reconstructed island distribution is observed for an Er deposit at room temperature with an additional annealing at 500 °C. However, when Er is deposited on substrate held at 500 °C, a significant modification in the surface morphology has been observed: 2D islands are accumulated at the step edges due to the high Ge and Er atom mobility. Moreover, for temperature under 500 °C, STM images have revealed the presence of metastable rod-shaped islands. Above 1 ML Er deposit, the interface displays a thin film reconstructed √3×√3R30° with a layer-by-layer growth mode.
E
′
centers and leakage currents in the gate oxides of metal oxide silicon devices
Authors: Lenahan P. M. , Mele J. J.
Published: July 2002

We have made electron spin resonance and current density versus voltage measurements on a variety of thin SiO2 films on silicon. In some of the films we have generated fairly high (⩾1018 cm3) densities of neutral E′ centers near the Si/SiO2 interface. Neutral E′ centers are paramagnetic defects in which an unpaired electron resides in a high p-character wave function primarily located on a silicon atom bonded to three oxygen atoms. We find that the generation of these centers is consistently accompanied by the generation of large leakage currents in the oxide. We also find that the annihilation of these E′ centers by a low temperature (200 °C) anneal in air is consistently accompanied by the annihilation of the large leakage currents. Many investigations have established that high electric field stressing creates leakage currents in thin oxide films on silicon. Studies of at least two independent groups have also established that high electric field stressing generates significant E′ density within the stressed oxides. Our study demonstrates a strong link between E′ center density and oxide leakage currents. Our results, combined with the results of the earlier aforementioned studies, strongly indicate an important role for E′ centers in stress induced leakage currents. These leakage currents are a fundamental problem in the very thin SiO2 films on silicon utilized in present day metal oxide silicon devices.
High speed anisotropic dry etching of CoNbZr for next generation magnetic recording
Authors: Andriesse M. S. P. , Zijlstra T. , van der Drift E.
Published: July 2002

Dry etch behavior of CoNbZr in an inductively coupled plasma of Cl2/BCl3 at elevated temperatures has been studied. Etch behavior of the alloy is ion induced with a strong chemical enhancement. The etch rate shows nonstoichiometric behavior when compared with the constituting elements. The increase by about 35% is attributed to interactive effects. A further enhancement up to about 40% is obtained under simultaneous exposure of deep ultraviolet irradiation. A fast anisotropic dry patterning process for CoNbZr has been developed, with etch rates up to 300 nm/min at 220 °C.
Studies on plasma-nitrided iron by scanning electron microscopy, glancing angle x-ray diffraction, and x-ray photoelectron spectroscopy
Authors: Miola Eduardo J. , de Souza Sylvio D. , Nascente Pedro A. P. , Olzon-Dionysio Maristela , Olivieri Carlos A. , Spinelli Dirceu
Published: July 2002

The tribological and mechanical properties of several iron alloys are improved by nitriding processes. In this work the plasma process was employed because it offers various advantages as compared to other methods used in surface modifications. For example, it is a nonpollutant method and the nitriding times are reduced. Four samples were prepared by nitriding the iron substrates in a gas mixture of 80% of H2 and 20% of N2 under a pressure of 900 Pa, discharge frequency of 10 kHz and temperature of 500 °C, for 1, 2, 4, and 6 h. The samples were analyzed by optical microscopy, scanning electron microscopy (SEM), microhardness technique, glancing angle x-ray diffraction (GXRD), and x-ray photoelectron spectroscopy (XPS). SEM and GXRD results showed the presence of γ′-Fe4N and a small amount of ε-Fe3N phase. XPS was employed in order to obtain the chemical-state and quantitative informations on the plasma-nitrided iron surfaces. The surface N/Fe atomic ratios obtained by XPS were close to the ideal value of 0.25 for Fe4N. The nitrogen concentration close to the surface is lower than that found in the bulk for all samples. This effect is explained by the presence of H2 in the gas mixture, which not only cleans the surface but also removes nitrogen by sputtering.
Silicon-on-Sapphire Epitaxy by Vacuum Sublimation: LEED–Auger Studies and Electronic Properties of the Films
Authors: Chang Chuan C.
Published: July 2002

Epitaxy of silicon on sapphire was studied by growing films up to 20 μ thick using high-temperature sublimation in 10−10 Torr vacuum on the (1̄012), (112̄3), (0001), and (112̄0) substrate surfaces. The surface structure and chemistry of both substrate and film could be monitored using LEED and Auger electron spectroscopy. The epitaxial relationships and the electrical properties were found to depend on deposit-substrate interactions, substrate temperature, and surface structure. A range of epitaxial temperatures could be defined for each substrate orientation within which the proper surface structure could be maintained during film growth. The behavior outside the epitaxial range was explored, revealing several causes for breakdown of optimum growth. The (1̄012) substrate was found to have the largest epitaxial temperature range. Silicon films of (100), (111), and, under special circumstances, the (110) orientations could be produced. Films thicker than 2 μ could be grown with essentially bulk values for carrier mobility (carrier concentration between 5×1015 and 8×1018/cm3). Film type (n or p), resistivity, and carrier concentration could be controlled by the choice of proper source material, and were reproducible within a factor of 2. Minority carrier lifetimes were about 10−9 sec; this short lifetime is probably due to the presence of defects, especially within the first micron of growth.
Pressure Considerations Associated with Ion Sampling from Glow Discharges
Authors: Coburn J. W. , Kay Eric
Published: July 2002

A discussion is presented of the influence of ion-neutral collisions downstream from an orifice through which ions from a glow discharge are being extracted. The effective pressure on the low pressure side of the orifice is treated as the sum of a static pressure (determined from pumping speed and orifice conductance considerations) and a localized beam pressure which is due to the neutral species effusing through the orifice with the ions. It is shown that in most experimental situations the beam pressure has a much greater influence on a collimated ion beam than does the static pressure. Some experimental results which support this conclusion are presented.
The Reactivity of Vanadium and Some Vanadium Alloys with Low-Pressure Oxygen and Nitrogen
Authors: Svedberg R. C.
Published: July 2002

The reactivity of pure vanadium (<350 ppm total impurity content) and the alloys vanadium–10.5-wt% chromium, vanadium–9.5-wt% molybdenum, and VANSTAR-7 (V–9 wt% Cr–3 wt% Fe–l.3 wt% Zr–0.05-wt%) with oxygen and nitrogen at low partial pressures in the temperature range of 600–800 °C was determined utilizing a hot-wall ultrahigh vacuum microbalance system. The rate of reactivity was determined from continuous weight-gain measurements as a function of both temperature and pressure, for oxygen partial pressures of 10−5 to 10−7 Torr and nitrogen partial pressures of 10−4 to 10−6 Torr. Linear kinetics were observed, indicative of a process controlled by gas transport to the metal surface. The sticking probability for oxygen of 0.185±0.040 was found to be independent of temperature, pressure, and alloying additions. The rate of reaction with nitrogen was a function of alloying additions, with VANSTAR-7 and V-10.5Cr exhibiting the lowest reactivity. The sticking probabilities were compared with those reported in the literature. These results indicate that the sticking probabilities of low-pressure gases on refractory metals are not well defined and seem to be a function of the particular experimental apparatus utilized.
Influence of Vacuum Environment on the Composition, Structure, and Mechanical Behavior of the Tantalum Tungsten Hafnium Alloy T-111
Authors: Sheffler K. D.
Published: July 2002

Various heats of a tantalum base alloy containing 8% tungsten and 2% hafnium together with 30 to 130 ppm oxygen as a residual impurity were creep tested in a vacuum environment of less than 1 × 10−8 Torr. Analyses of the residual gas composition indicated that the major constituents of the vacuum environment were carbon monoxide, hydrogen, argon, and water. Loads and temperatures were selected to provide approximately 1% creep strain in times ranging between 1000 and 40 000 h. Chemical analysis of the test materials before and after creep testing indicated that the exposure to the 10−8 Torr environment caused a significant decrease in the amount of oxygen present in the tantalum alloy. This decrease was accompanied by the disappearance of a grain boundary network of hafnium oxide inclusions which was shown by electron microprobe studies to be present in the material prior to testing. This loss of oxygen during testing had a pronounced influence on creep behavior of the T-111 alloy in the 1600–2200 °F temperature range where an oxygen-associated dynamic strain aging effect has been noted. The strain aging behavior appeared to cause an anomalously low creep rate in the early stages of T-111 creep testing; for example, creep rates below 10−8/h were measured at 1600 °F and 35 ksi. This period of very slow creep was followed by a transition to a much higher creep rate and this transition was thought to occur as a result of the loss of the oxygen from the test material. Analysis of the creep rates measured after the rate transition provided an activation energy value which was the same order as the self-diffusion coefficient for pure tantalum, indicating after the oxygen was lost that creep proceeded by a conventional diffusion controlled process.
Sulfur—Its Effects, Removal, or Modification in Vacuum Melting
Authors: Cremisio Richard S. , Cannon Joseph G. , Elliott C. Frank
Published: July 2002

Sulfur has long been recognized as one of several elements causing considerable property, difficulty in vacuum melting. Once introduced, usually via raw materials, traditional vacuum melting techniques must be modified to reduce sulfur to acceptable levels. Individual effects of sulfur on certain nickel, cobalt, and iron base alloys were discussed. Techniques for the removal of sulfur during vacuum melting were discussed including some thoughts on the kinetics of desulfurization. Among the sulfur removal techniques indicated are the following: Slag Base Metal Reactions Gaseous Purge Techniques Rare Earth Metal or Alloy Innoculation.

The paper gives some new data with regard to the desulfurization of nickel base superalloys (notably Inco 901) by addition of elemental cerium in vacuum induction melting. Desulfurization levels to 0.001 wt% were achieved without any loss in property response or microstructural degradation.
Miniseptor—A Modular Approach to Susceptor Design
Authors: Raufer Henry F.
Published: July 2002

MINISEPTOR is a susceptor for vacuum hear-treat and melting applications which is made up of a number of multisided polygons, (almost circular rings) primarily of graphite, stacked concentric with the axis of an induction coil. Its modular construction makes feasible hot zones, as large as 11 ft in diameter by 1712 ft high, for operating temperatures to 2750 °C (5000 °F). The reduced mass of the susceptor greatly reduces the stored energy in the susceptor resulting in brisk, temperature cycling. In addition, initial costs and operating costs are lower than for conventional systems. The modular construction of the susceptor and its thermal insulation allows replacement in sections as required, without complete removal, which simplifies maintenance and lowers the required minimum stock of spare parts. Variable configuration of the bars, pins, fit, and grade of the graphite used affect the overall resistance of each ring, the number and configuration of rings determining the power delivered to the susceptor at any given voltage and frequency. The multiplicity of independent concentric “rings” permits altering the spacing between “rings” so that it is possible to control the temperature gradient by distribution of the power along the length of the hot zone. Performance characteristics observed on a hot zone 35 in. in diameter and 51 in. tall are discussed. Uniformity of the temperature gradient across the hot zone and holding temperatures observed on this scale model of the large hot zone described above are reviewed.
Analysis of Thin Films Utilizing Mass Spectrometric Techniques
Authors: Socha A. J.
Published: July 2002

Mass spectrometry offers several techniques for analyzing thin films. The primary differences between these techniques is the manner in which the sample is ionized. The spark source, coupled with various probe techniques, has been very successful. Laser source instruments have been used with limited success. The sputter gas ion source, combined with a mass spectrometer which has imaging capabilities is a recent development and shows great promise for the analysis of thin films.
Vacuum Breakdown Voltages of Dispersion-Strengthened Copper vs Oxygen-Free, High-Conductivity Copper
Authors: Bouchard K. G.
Published: July 2002

Pairs of electrodes in vacuo at 10−9 Torr were tested at various gap spacings to find the amount of applied voltage needed to cause electrical breakdown, with a view to determining whether dispersion-strengthened (DS) copper has a higher breakdown voltage than standard, oxygen-free, high-conductivity (OFHC) copper. All anodes were made of OFHC copper. Half of these were paired with cathodes of OFHC copper, half with cathodes of DS copper. Voltage breakdown was determined for all pairs at gap spacings between 0.003 in. and 0.007 in. The group-average voltage breakdown of all DS/OFHC pairs was found to be 21% higher than that of OFHC/OFHC pairs. It is speculated that the relatively hard surface of DS copper may inhibit the growth of microprojections. In the softer-surface OFHC copper, microprojections might grow more easily and thus enhance the prebreakdown electrical field, leading to earlier breakdown.
Restoration of Optical Properties of Surfaces by Radiofrequency-Excited Oxygen
Authors: Gillette Roger B. , Hollahan John R. , Carlson George L.
Published: July 2002

Surfaces of mirrors or other optical devices employed in satellite programs will in time become contaminated with thin layers of polymer films. These films orginate most probably from outgassing followed by polymerization by uv radiation. The contaminant films degrade the reflectance of mirrors and the performance of critical optical surfaces. Atomic oxygen from an rf plasma restores optical surfaces to their original properties by rapid noncontaminating, nondestructive oxidation of the polymer film.
Interactions between Chemisorbed Species: H2 and N2 on (100) Tungsten
Authors: Yates John T. , Madey Theodore E.
Published: July 2002

The interactions between hydrogen and nitrogen adsorbed species on a (100) tungsten crystal have been investigated by flash desorption methods. When the crystal covered with a monolayer of hydrogen is exposed to gaseous N2, the nitrogen slowly replaces the two chemisorbed hydrogen β states by means of a slight lowering of the hydrogen desorption energy. This displacement process occurs via slow thermal desorption of hydrogen in the presence of gaseous N2 when the surface temperature is ≳300 K no such replacement is observed at 273 K. Coverage measurements indicate that there is a stoichiometric ratio between N atoms adsorbed and H atoms displaced from the crystal at ∼300 K. Although virtually no hydrogen will adsorb on the nitrogen-covered surface at 300 K, several weakly bound hydrogen states are populated at 100 K on this surface. No chemical difference between the β1 and β2 hydrogen species was detected, suggesting that both states originate from adsorbed atoms.
Inelastic Low-Energy Electron Diffraction Measurements on Al (111)
Authors: Porteus J. O. , Faith W. N.
Published: July 2002

An experimental study has been made of electrons in the energy range 40–80 eV, inelastically scattered and diffracted from a clean Al(111) surface. The surface is prepared by epitaxial vapor deposition on a Si(111) single-crystal surface in ultrahigh vacuum immediately preceding the measurements. The inelastic electron intensity at a given energy loss and angle is obtained as the energy derivative of the amplified electron current from a Faraday collector having a retarding field analyzer and limited angular acceptance. The energy derivative comes from the digitally computed average of a repeatedly measured difference in dc signal accompanying a fixed increment in retarding field. Using this method inelastic angular and loss profiles at 15° incidence have been obtained in the vicinity of a Bragg maximum of the 00 elastic beam. The profiles show structure related to the surface and volume plasmon momenta by a two-step model of inelastic diffraction. Dispersion data inferred by applying this model to the “loss-before-diffraction” structure are compared with results from other sources. The surface plasmon dispersion obtained from inelastic low energy electron diffraction measurements shows promise as a new means of characterizing solid crystalline surfaces.
Silver Chloride Vacuum Seals
Authors: Aslam Mohammad
Published: July 2002

Silver chloride has been successfully used in vacuum seals and vacuum valves. Sealing procedures are reviewed and a comprehensive bibliography on the subject presented. A method to improve the operating speed of silver chloride vacuum valves is suggested. Another use of silver chloride seals for electrical feed-throughs in the laboratory is briefly mentioned. A modified technique for seal formation is reported and its usefulness is briefly described.
Two Kilometers at 10−10 Torr. The CERN Intersecting Storage Rings for Protons
Authors: Fischer E.
Published: July 2002

The Intersecting Storage Rings (ISR) in Geneva are a new research facility for experiments with colliding proton beams of energies of up to 28 GeV and intensities of up to 20 A. The ISR vacuum system consists of two interlacing doughnuts formed by ellipitical pipes 160 × 50 mm and circular pipes of 160 mm diameter, of a total length of 2 km. The chambers are made out of stainless steel and can be baked in situ at 200–300 °C. An average pressure of 10−10 Torr has been attained. This is necessary in order to achieve the required beam life of several days. At the intersecting regions where the proton-proton collisions are being observed and where proton-gas collisions produce a disturbing background, equivalent nitrogen pressures of 10−11 Torr are required and have been actually achieved. Experiences are reported on the construction, commissioning and operation of this vacuum system.
Instrumental Method for High-Vacuum Handling
Authors: Guerrero J. Martínez , Rodríguez Gil
Published: July 2002

A manipulator is described, especially constructed to be connected to a high-vacuum multi-rotator, with the aim of proving that the system may be used to develop maneuvers within a high vacuum. The resultant device may be managed after a few moments of instruction and it is possible to program it so that it acts in a robotlike manner to carry out routine operations.
Self-Consistent Screening of Charges Embedded in a Metal Surface
Authors: Ying S. C. , Smith J. R. , Kohn W.
Published: July 2002

This paper first develops a general theory of the screening change induced in an inhomogeneous electron gas by a small perturbing charge. This theory is applied to the screening of a point charge embedded in a metal surface. The first stage of this program which is reported here, uses the jellium model for the unperturbed metal surface and treats both the unperturbed and perturbed systems in the Thomas–Fermi approximation. Self-consistency, which is maintained in the present paper, leads to results which differ significantly from earlier results obtained with infinite barriers, which are by their nature not self-consistent.
Phase Transitions in Two-Dimensional Absorbed Layers on Copper Investigated by LEED and Auger Spectroscopy
Authors: Domange J. L.
Published: July 2002

The equilibrium between one adsorbed phase of sulfur ions (loosely packed) and a reconstructed two-dimensional copper sulfide phase, is studied in ultrahigh vacuum on low index faces of copper. The nucleation from the loosely packed phase of nuclei of the two-dimensional sulfide is characterized under conditions for which sulfur dissolution or evaporation is negligible. The domain of the temperature-coverage diagram for which adsorbed sulfur is present at equilibrium in the two phases is determined. The data lead to an interpretation of adsorption isotherms at low temperature and point to the existence of a critical temperature above which the evolution of surface structure towards saturation proceeds without discontinuity.
Elastic and Inelastic Low-Energy Electron Diffraction (ELEED, ILEED) from an Al(100) Surface
Authors: Burkstrand J. M. , Propst F. M.
Published: July 2002

Elastic and inelastic low-energy electron diffraction (ELEED, ILEED) observations have been made on a clean surface of Al (100). Measurements on the (10) and (11) elastic diffraction beams were made using normally incident electrons in the energy range 30≤E≤170 eV. Peaks in the energy loss distribution are seen near 5.5, 10, 15, 26, and 31 eV, the dominant peaks near 10 and 15 eV corresponding to surface and bulk plasmon excitations, respectively. Two types of structure are observed in the inelastic angular profiles: one closely correlated with the structure in the elastic angular profile and the second being substructure corresponding to different ILEED conditions. Intensity profiles (as a function of incident energy) for the (10) and (11) elastic and inelastic diffraction beams have been measured. These profiles also show primary and secondary structure. The experimental results agree with the theoretical predictions of Duke et al.
Properties of 0.01-eV Helium Atoms Scattered Inelastically from Silver (111)
Authors: Subbarao R. B. , Miller David R.
Published: July 2002

Out-of-plane density distribution and in-plane velocity distribution measurements for low-energy (0.01-eV) helium scattering inelastically from 550 K silver (111) are presented. The data suggest that surface phonon interactions have a negligible effect on the observed scattering.