bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Study of Residual Stresses and Microstructure in 2024-T3 Aluminum
Friction Stir Butt Welds
Authors: Sutton M. A. , Reynolds A. P. , Wang D.-Q. , Hubbard C. R. 
Published: July 2002

Abstract
Three-dimensional residual stress mapping of an aluminum 2024-T3 arcan specimen, butt-welded by the friction stir technique, was performed by neutron diffraction. Results indicate that the residual stress distribution profiles across the weld region are asymmetric with respect to the weld centerline, with the largest gradients in the measured residual stress components occurring on the advancing side of the weld, with the longitudinal stress, σL, oriented along the weld line, as the largest stress. Within the region inside the shoulder diameter, the through-thickness stress, σZ, is entirely compressive, with large gradients occurring along the transverse direction just beyond the shoulder region. In addition, results indicate a significant reduction in the observed residual stresses for a transverse section that was somewhat closer to the free edge of an Arcan specimen. Microstructural studies indicate that the grain size in the weld nugget, is approximately 6.4 microns, with the maximum extent of the recrystallized zone extending to 6 mm on each side of the weld centerline. Outside of this region, the plate material has an unrecrystallized grain structure that consists of pancake shaped grains ranging up to several mm in size in two dimensions and 10 microns in through-thickness dimension.
A Technique for Deducing In-Plane Modulus and Coefficient of Thermal
Expansion of a Supported Thin Film
Authors: Chiang Martin Y. M. , Chiang Chwan K. , Wu Wen-li 
Published: July 2002

Abstract
A technique for determining the in-plane modulus and the coefficient of thermal expansion (CTE) of supported thin films has been developed. The modulus and CTE are calculated by solving two coupled equations that relate the curvature of film samples deposited on two different substrates to the thermal and mechanical properties of the constituents. In contrast with the conventional method used to calculate modulus and CTE, which involves differentiation of the thermal stress in the film, this new technique does not require the differentiation of the thermal stress, and can also provide the temperature-dependence of the in-plane CTE and elastic modulus of supported thin films. The data reduction scheme used for deducing CTE and elastic modulus is direct and reliable.
A Comparative Study of Two Practical Methods for Estimating the
Hydrodynamic Loads and Motions of a Semi-Submersible
Authors: Söylemez M. , Atlar M. 
Published: July 2002

Abstract
This article presents a comparative study of two practical methods for the estimation of the hydrodynamic loads and motion responses of a semisubmersible to demonstrate some important shortcomings inherent with each method. These methods are: Morison’s equation with constant hydrodynamic coefficients, and panel method based on two-dimensional (2-D) Green’s function integral equation technique. The article includes a brief formulation of each method dedicated to a twin-hull semisubmersible and presents the results of the comparative calculations with each method performed on a twin-circular hull of eight-column semisubmersible model. The results of the calculations are discussed by emphasizing relative importance of these shortcomings and recommendations are made to the designers to be aware of them in the use of both methods. [S0892-7219(00)00401-5]
Interaction of Gases with a Condensed Phase
Authors: Yu J. S. , Soo S. L. 
Published: July 2002

By use of a classical model, the phenomenon of trapping of a gas particle at the surface of a cold solid is investigated. The equation of motion is solved by the adoption of a semirepulsive potential of interaction and the equations determining the critical kinetic energy for trapping which is essential for the evaluation of the capture coefficient are obtained. These equations are simplified for the case that a gas particle collides on its own crystalline phase on account of the long “regression time” and the critical kinetic energy is thereby obtained. The regression time is the total time during which an initially free gas particle becomes trapped by the crystal surface before it is reevaporated again. It is long as compared to the period of lattice vibration.
The cryopumping of condensable nonpolar gases is investigated. The existence of an adsorbed, mobile phase is taken into account in the derivation. The capture coefficients obtained for N2 and CO2 based on the geometric area of the cryosurface are quite satisfactory as compared with those derived from experimental data. Pressures as functions of flow rates were measured for CO2 at a cryosurface temperature of 77.4 °K. The results are in good agreement with that calculated from the present simple theory.
Kinetics of N2 Desorption from the Surfaces of Iron–Nitrogen Solid Solutions
Authors: Podgurski H. H. , Davis F. N. , Smith R. P. 
Published: July 2002

The kinetics of nitrogen desorption from iron surfaces was studied between 400 ° and 550 °C. The nitrogen desorbed isothermally into the gas phase was made available to the surface by diffusion from within the iron at the desorption temperature. The method of rate measurement involved the collection and volumetric measurement of gas samples at low pressures from specimens only a few square centimeters in area. Specimens were prepared by nitrogenizing zone-refined iron with NH3–H2 mixtures having a range of N2 fugacity between 10 and 3000 atm. The surfaces were then cleaned by ion bombardment in a bakeable high-vacuum system.
The kinetics of nitrogen desorption from iron was observed to be a surface-controlled process, which showed first-order dependence upon the nitrogen concentration in the iron when conventional ion-bombardment cleaning procedures were employed. However, it was discovered that carbon monoxide is generated in glass systems during ion bombardment and can contaminate the iron surface. When this contamination was reduced, the nitrogen-desorption process was observed to be diffusion controlled at temperatures as low as 400 °C.
Abstract: Electromask generator
Authors: Beasley J. P. , Squire D. G. 
Published: July 2002

An electron-beam pattern generator has been made for mask fabrication, either for conventional photolithography or more specifically for making electromasks for use in an image projection system. The maskmaker draws the pattern required at the final size in electron-sensitive resist which in turn defines the pattern in an opaque metal film on a transparent substrate. A 50-mm -square mask covered with detail down to at least 1 μm can be made in less than three hours. To achieve this speed of working two stages of beam deflection are used together with mechanical movement of the substrate. The high-speed deflection system runs at a 10-MHz stepping rate over a maximum amplitude of 32 μm. The slow-speed system covers an area of 2×2 mm.
An array of markers predefined over the substrate is used to obtain a pattern accuracy of ±1/8 μm relative to these markers. They are also used to check and, if necessary, correct the beam focus after each mechanical movement of the table. The pattern drawing, positioning, and beam focusing are entirely automatic.
An integrated-circuit mask-generation program is used on a larger computer to prepare the data for the patterns to be drawn. Magnetic tape is used to transfer this data to the maskmaker’s small computer.
Hydrogen pumping and release by graphite under high-flux plasma bombardment
Authors: Hirooka Y. , Leung W. K. , Conn R. W. , Goebel D. M. , Labombard B. , Nygren R. , Wilson K. L. 
Published: July 2002

Inert gas (helium or argon) plasma bombardment has been found to increase the surface gas adsorptivity of isotropic graphite (POCO-graphite), which can then getter residual gases in a high-vacuum system. The inert gas plasma bombardment was carried out at a flux ≊1×1018 ions s−1 cm−2 to a fluence of the order of 1021 ions/cm2 and at temperatures around 800 °C. The plasma bombarding energy was varied between 100 and 200 eV. The gettering speed of the activated graphite surface is estimated to be as large as 25 l s−1 cm−2 at total pressures between 10−6 and 10−7 Torr. The gettering capacity estimated is 0.025 Torr l/cm2 at room temperature. The gettering capability of graphite can be easily recovered by repeating inert gas plasma bombardment. The activated graphite surface exhibits a smooth, spongelike morphology with significantly increased pore openings, which correlates with the observed increase in the surface gas adsorptivity. The activated graphite surface has been observed to pump hydrogen plasma particles as well. From calibrated H-alpha measurements, the dynamic hydrogen retention capacity is evaluated to be as large as 2×1018 H/cm2 at temperatures below 100 °C and at a plasma bombarding energy of 300 eV. The graphite temperature was varied between 15 and 480 °C.
Due to the plasma particle pumping capability, hydrogen recycling from the activated graphite surface is significantly reduced, relative to that from a presaturated surface. A presaturated surface was also observed to reproducibly pump a hydrogen plasma to a concentration of 9.5×1017 H/cm2. The hydrogen retention capacity of graphite is found to decrease with increasing temperature. At temperatures between 450 and 480 °C, the hydrogen retention estimated for the activated surface and presaturated surface is 7.9×1017 and 2.7×1017 H/cm2, respectively. A transient pumping mechanism associated with the spongelike surface morphology is conjectured to explain the large hydrogen retention capacity. Hydrogen release behavior under helium and argon plasma bombardment was also investigated, and the result indicated the possibility of some in-pore retrapping effect. The effective plasma impact desorption cross sections are evaluated in the plasma bombarding energy range from 15 to 300 eV. A significant fraction (70%–80%) of preimplanted hydrogen was observed to release under inert gas plasma bombardment to a fluence of 6×1019 ions/cm2. The graphite surface, once saturated, can be reactivated via plasma-impact hydrogen desorption, regardless of the helium and argon bombarding energy in the range examined here.
Some aspects of adsorption, diffusion, and thermal desorption properties of a La–Mo system
Authors: Sreenivasa Rao G. , Dharmadhikari C. V. , Nigavekar A. S. 
Published: July 2002

Thin films of lanthanum on polycrystalline molybdenum surfaces have been investigated using a variety of techniques such as the Auger electron spectroscopy (AES)–Ar+ sputtering combination, quadrupole mass spectrometry (QMS), neutron activation analysis (NAA), small-angle x-ray diffraction (SAXRD), field emission microscopy (FEM), and scanning electron microscopy (SEM) with a view of understanding the interaction in a La–Mo system. The experiments with AES consisted of evaporating La from a LaB6 source onto polycrystalline Mo and heating it at different temperatures. The variation of adsorbate (substrate) signal as a function of surface coverage suggests that the growth at room temperature takes place in the form of clusters. FEM and SEM investigations of these films suggest cluster sizes of 35- to 100-Å diameter with average spacings of the same order. Annealing of thick (∼35 Å) films at 400 K for 30 s results in redistribution leading to uniform thickness of La. Further heating of the same at higher temperatures caused considerable penetration of La into Mo. The detailed analysis of depth profiles in the temperature range 800–1300 K indicated that this could be attributed to both bulk and grain boundary diffusion. The temperature dependence of diffusion coefficients in this temperature range could be expressed by the following equations: Db=1.9×10−8 exp(−1.7/kBT) and Dgb=1.2×10−6 exp(−1.07/kBT), where Db,Dgb correspond to the bulk and grain boundary diffusion coefficients and kB, the Boltzmann constant. Further heating of these films at still higher temperatures resulted in depletion of La. Isothermal desorption studies in the temperature range 1673–1913 K yielded values of 3.8 eV and 109 s−1 for the activation energy of desorption and the prefactor, respectively. The low value of prefactor suggested a complex desorption mechanism involving a surface precursor molecule with a very low degree of freedom as compared to a single atom adsorbed on the
surface. The diffusion and desorption are compared with available relevant information by other techniques. The evaporation kinetics of the blue colored LaB6 compound which constituted La source in our work has also been investigated and existing controversy in this field has been critically but briefly reviewed. The results are believed to be important in the context of development of La–Mo cathodes.
Detection of reactions and changes in thin film morphology using stress measurements
Authors: Gardner Donald S. , Longworth Hai P. , Flinn Paul A. 
Published: July 2002

Mechanical stresses in thin films arise from thermal expansion differences
Mechanical stresses in thin films arise from thermal expansion differences between the film and substrate, structural changes within the films, and intrinsic stresses from the deposition process. These stresses can lead to open circuit failures from voiding in interconnections, short circuits from hillocks, or delamination. Measurement of this stress in situ as a function of temperature have proven to be an easy and powerful technique for obtaining information on the temperature, time, rate, and extent of formation of both solid-state reactions and changes in morphology and structure. This information is helpful in obtaining an understanding and finding solutions for stress-induced voiding. A theoretical model is developed for the stress change when precipitation occurs from elements in solid solution. The stress during thermal cycling was measured for aluminum and copper on oxidized silicon substrates and for several aluminum alloys and layered films consisting of Si, Cu, Ti, W, Ta, V, Cu–Cr, and/or TiSi2. Correlating these changes using hot-stage transmission electron microscopy and x-ray diffraction has demonstrated that some stress changes do correspond to reactions and structural changes. In most multielement films, there were changes in stress that correlated to phase changes. Morphological changes such as during secondary grain growth of ultralarge grains (50–100 μm) in Al/Cu/Cr films can also be detected using stress measurements. Finally, pure copper and Mo/Cu films exhibited several differences in stress behavior as compared to aluminum.
Cold beam tube photodesorption and related experiments for the Superconducting Super Collider Laboratory 20 TeV proton collider
Authors: Anashin V. V. , Derevyankin G. , Dudnikov V. G. , Malyshev O. B. , Osipov V. N. , Foerster C. L. , Jacobsen F. M. , Ruckman M. W. , Strongin M. , Kersevan R. , Maslennikov I. L. , Turner W. C. , Lanford W. A. 
Published: July 2002

The next generation of proton colliders that has been contemplated—the Superconducting Super Collider (SSC) in the U.S. and the Large Hadron Collider (LHC) at CERN—will be the first to encounter significant intensities of synchrotron radiation within the cold bore tube of superconducting magnets. Aside from removal of the synchrotron radiation heat load, the main problem encountered is how to deal with the magnitudes of photodesorbed gases. Choosing the beam tube to coincide with the cryosorbing magnet bore tube has the advantages of simplicity and, in principle, of providing very high pumping speed. Tightly bound H, C, and O in the near-surface layer (∼100 Å) are converted by photodesorption to a steadily increasing surface density of physisorbed molecules. However, the effective pumping by the bore tube is greatly reduced by the photodesorption of relatively weakly bound physisorbed molecules. In addition, the saturation vapor density of H2 at the ∼4.2 K temperature of the SSC cryostats exceeds, by a factor of fifty, the upper bound allowed by the nuclear scattering deposition of energy in the magnet cryostats. Consequently, accumulation of a monolayer of physisorbed H2 must be avoided even locally. An alternative approach is to install a coaxial perforated tube or liner inside the magnet bore tube which allows the photodesorbed gases to be pumped out of the view of the synchrotron radiation photons. The purpose of the work described in this paper is to develop a methodology that will allow prediction of the SSC beam tube vacuum for simple, 4.2 K beam tubes and for distributed pump or liner configurations—and to provide the technical data required for choosing among the alternative possibilities.
The first photodesorption experiments have been completed on the VEPP2M storage ring at the Budker Institute of Nuclear Physics (BINP). Additional photodesorption experiments are underway at BINP and are being planned for a beamline at the UV ring of the Brookhaven National Laboratory National Synchrotron Light Source (BNL NSLS). Related experiments at BNL measuring molecular sticking coefficients and at the State University of New York-Albany (SUNY-Albany) measuring the depth profile of hydrogen on beam tube surfaces are also beginning to yield data. New ideas for directly measuring molecular density inside a cryosorbing beam tube are under development—neutralization of H− and H+ beams at BINP and positron annihilation at BNL. A status report of these activities is given in this paper.
Vacancy first and second neighbor hopping at a compound semiconductor interface: Insights from computer simulation
Authors: Van Vechten J. A. , Schmid U. 
Published: July 2002

We have now demonstrated that the ratio of the activation enthalpies for nearest neighbor hopping of the two types of vacancy in InP are in the 4 to 1 ratio of the masses of the atoms that hop and are in good agreement with the values predicted by the ballistic model (BM), which identifies the activation enthalpy as a kinetic energy. A consequence is that relatively light atoms should hop to second neighbor vacancy sites as easily as heavy atoms hop to nearest neighbor vacancies, and do so without the complication of forming or annihilating antisites. For example, in GaAs B, C, N, Al, Si, and P are predicted to hop to second neighbor sites as easily as As hops to a first neighbor site. Of course, they hop to nearest neighbor sites even more readily. The import of this on the array of point defects predicted to occur as a heterojunction anneals is rather complex. Experiment supports our contention of complexity. For example, in As rich, n-type AlGaAs Mei et al. report D(Al)∝n1  exp(−2.9 eV/kT) if the doping is with Te but D(Al) ∝n3  exp(−4 eV/kT) if the doping is with Si, where n is the free electron density. We have studied the Al diffusion in AlGaAs with the aid of a microcomputer simulation that works out the complex consequences of one’s assumptions re thermochemical parameters at the atomic level. Our previously published BM assumptions lead to the conclusion that Si promotes the conversion of Ga vacancies to trivacancies while Te does not; they also identify 2.9 eV as the sum of the Ga second-neighbor hopping enthalpy and the enthalpy of formation of single negative Ga vacancy in n-type GaAs and identify 4 eV as the sum of the enthalpy of formation of the trivacancy plus its nearest neighbor hopping energy in GaAs. The simulation also finds that Al by itself converts As vacancies to trivacancies plus metal antisite. It shows the trivacancies to diffuse very rapidly and to entrain Al.
We propose that the cation sublattice dominance of Si induced host interdiffusion follows from this entrainment. We also suggest these complexes are related to DX and account for the anomalous variation of the parameters of that defect with Al concentration. Except for the assumption that the hopping kinetic energy be proportional to the mass of the hopping atom, the conclusions stated above are insensitive to the precise values of atomic level parameters assumed. Quantities such as activation energies for macroscopic diffusion are sensitive to the precise values and some of these are either poorly determined or controversial. More simulation than we have accomplished to date is required to establish the relation between precise atomic level values and observable macroscopic quantities.
In Vivo Activity of Amphotericin B Lipid Complex in Immunocompromised Mice against Fluconazole-Resistant or Fluconazole-Susceptible
Candida tropicalis
Authors: Warn P. A. , Morrissey J. , Moore C. B. , Denning D. W. 
Published: July 2002

ABSTRACT

We compared four doses of amphotericin B lipid complex (ABLC) with three doses of fluconazole in temporarily neutropenic mice in a murine model of disseminated candidiasis due to four different isolates of
Candida tropicalis
. The mice were infected with a 90% lethal dose of four strains of
C. tropicalis
for which the fluconazole MICs ranged from 1 to >125 mg/liter 3 days after receiving 200 mg of cyclophosphamide/kg of body weight. Treatment was started 18 h after infection and lasted for 7 days. ABLC (1, 2, 5, and 10 mg/kg) was administered once a day intravenously, fluconazole was administered by oral gavage once daily (25 and 50 mg/kg/day) or twice daily (125 mg/kg). MICs determined in five different ways with 24- and 48-h endpoints were also compared. The overall survival rates were controls, 14%; fluconazole, 64%; and ABLC, 82%. Treatment with ABLC at 2 to 10 mg/kg increased survival compared to controls (
P
= <0.0001) and was also superior to fluconazole at 25 and 50 mg/kg (
P
= 0.006). In the fluconazole-resistant
C. tropicalis
model (MIC, 128 μg/ml), ABLC at 2 to 10 mg/kg was superior to fluconazole at 250 mg/kg and ABLC at 10 mg/kg was superior to all fluconazole doses (
P
= <0.05). Fluconazole at 250 mg/kg daily was superior to both 25 and 50 mg/kg at reducing mortality with most isolates. ABLC was superior to fluconazole (
P
= <0.01), and fluconazole at 250 mg/kg was superior to fluconazole at both 25 and 50 mg/kg (
P
= 0.02) in all models at reducing
C. tropicalis
counts in the kidneys. Neither drug consistently sterilized the brain or kidneys. A 48-h endpoint reading with the NCCLS susceptibility testing microtiter variation overestimates resistance to fluconazole. ABLC is an effective treatment for fluconazole-resistant
C. tropicalis
at all doses tested.