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Displaying 1201 - 1225 of 1321

Subsolidus Phase Relations and Dielectric Properties in the SrO-Al 2 O 3 -Nb 2 O 5 System

February 1, 2000
Author(s)
Julia Y. Chan, Igor Levin, Terrell A. Vanderah, Richard G. Geyer, Robert S. Roth
Subsolidus phase equilibria in the SrO-Al 2O 3-Nb 2O 5 system were determined by synthesis of 75 compositions in air in the temperaturerange 1200-1600 C. Phase assemblages were determined by X-ray powder diffraction at room temperature. Two new ternary

Temperature Dependence of Molecular Orientation on the Surfaces of Semi-Fluorinated Polymer Thin Films

February 1, 2000
Author(s)
Jan Genzer, E Sivaniah, E K. Kramer, J G. Wang, H Koerner, K Char, Christopher K. Ober, B M. DeKoven, Robert A. Bubeck, Daniel A. Fischer, S Sambasivan
Near-edge X-ray absorption fine structure is used to investigate the temperature dependence of molecular orientation of semi-fluorinated liquid crystalline (SF-LC) mesogens, which are attached to the modified isoprene backbone of i) a polyisoprene

The Elastic Constants of Single Crystal Beta-Si 3 N 4

February 1, 2000
Author(s)
R Vogelgesang, M Grimsditch, Jay S. Wallace
Using Brillouin scattering, we have determined the five independent elastic constants of Β-Si 3N 4 single crystals. They are (in units of GPa) c 11 = 433(3), C 33=574(3), c 13 = 127(5), c 44 = 108(2), C 66 =119(4), and C 12 = C 11-2c 66 = 195(8), giving a

Orientation of Surface Bound Proteins Studied by Near Edge X-Ray Absorption Fine Structure

January 25, 2000
Author(s)
L Gamble, J R. Long, P S. Stayton, Daniel A. Fischer, S Sambasivan, David G. Castner
The orientation of surface bound proteins may play an important role in the function and properties of materials to which they are adsorbed. Near edge absorption fine structure (NEXAFS) is a technique which allows the user to determine the presence of

Ab-Initio Energetics of Transition Metal Ordering in Decagonal Al-Co-Cu

January 21, 2000
Author(s)
M Widom, I Al-Lehyani, Yijun Wang, Eric J. Cockayne
We perform ab-initio total energy calculations for approximants to a model of decagonal A1CoCu. These calculations support previously proposed chemical ordering of Co and Cu atoms along tile edges. Preferred arrow orientations are identified and shown to

Generation of Quasicrystals Via a Single Cluster

January 21, 2000
Author(s)
Eric J. Cockayne
We present a columnar cluster with 46 atoms per repeat distance which forces a quasicrystal when space is filled by interpenetrating copies of itself. The atomic positions in the resultant quasicrystal are remarkably similar to those in models for real

Pressure Dependence of Instabilities in Perovskite PbZrO 3

January 21, 2000
Author(s)
Eric J. Cockayne, K M. Rabe
We have computed the frequencies of selected normal modes in perovskite PbZrO 3 (PZ) as a function of lattice parameter using local density functional theory variational linear response. The most significant instabilities that freeze in to give the

In Situ Characterization of Catalytic Propylene Oxidation on the Pt (111) Surface

January 17, 2000
Author(s)
A M. Gabelnick, A T. Capitano, D J. Burnett, Daniel A. Fischer, J L. Gland
The catalytic oxidation of propylene with both propylene and oxygen in the gas phase has been characterized on the Pt(111) surface. In situ soft x-ray kinetic and spectroscopic measurements using fluorescence detection have been used to characterize this

Comparison of Tensile and Compressive Creep Behavior in Silicon Nitride

January 1, 2000
Author(s)
K J. Yoon, Sheldon M. Wiederhorn, William E. Luecke
The creep behavior of most commercial grade of Si 3N 4 was studied at 1350 and 1400 C. Stresses ranged from 10 to 200 Mpa in tension and from 30 to 300 Mpa in compression. In tension, the creep rate increased linearly with stress at low stresses and

Direct Measurement of Valence-Charge Asymmetry by X-Ray Standing Waves

January 1, 2000
Author(s)
Joseph C. Woicik, E Nelson, P Pianetta
By detecting valence-photoelectron under condition of strong x-ray Bragg reflection, we have determined that a majority of GaAs valence charge resides on the anion sites of this heteropolar crystal, in quantitative agreement with the Ga-As bond polarity as

Layer Perfection in Ultrathin InAS Quantum Wells in GaAs(001)

January 1, 2000
Author(s)
J A. Gupta, S P. Watkins, E D. Crozier, Joseph Woicik, D A. Harrison, D Jiang, I J. Pickering, B A. Karlin
X-ray diffraction (XRD), X-ray standing wave (XSW) and X-ray absorption fine structure (XAFS) measurements were used to assess the layer perfection and positions of 1 and 2 monolayer (ML) InAs quantum wells buried in GaAs(001). Photoluminescence (PL)

Model of Fatigue Damage in Strain Rate-Sensitive Composite Materials

January 1, 2000
Author(s)
S K. Lee, Tinh Nguyen, Tze J. Chuang
A Fatigue damage accumulation model based on the Paris law has been proposed for strain rate-sensitive polymer composite materials. A pre-exponent factor c 2/f and strain-rate sensitive exponent n is introduced. Numerical analysis of the model has been

Ordering/Displacive Phase Transformations in Ca 4 Nb 2 O 9

December 17, 1999
Author(s)
Igor Levin, Leonid A. Bendersky, Robert S. Roth, Terrell A. Vanderah
Four Ca 4Nb 2O 9=Ca(Ca1/3Nb 2/3)O 3 polymorphs based on ABO 3 perovskite-like structure were identified. These polymorphs feature three different arrangements of Ca/Nb cations on B-sites of perovskite. In three of the polymorphs, cation ordering is

Modeling Wear of Ceramics Based on Wear Maps

December 2, 1999
Author(s)
Stephen M. Hsu, M C. Shen
Ceramics are increasingly being considered for wear resistant applications. The design and prediction of ceramics wear, however are lacking behind metals. This paper addresses the ability to predict wear of ceramics by examining a large data base of four

A Novel Multiaxial Wear Tester for Accelerated Testing of Materials

December 1, 1999
Author(s)
M C. Shen, Stephen M. Hsu, John A. Tesk, A Christou
A versatile wear tester has been designed and built. The initial study showed that that with this tester, tes procedures can be developed to achieve clinically relevant simulations in a short time. With the continuously monitored force traces, this tester

Combined EXAFS and First-Principles Theory Study of Pb 1-x Ge x Te

December 1, 1999
Author(s)
Bruce D. Ravel, Eric J. Cockayne, E Newville, K M. Rabe
The narrow band-gap semiconductor Pb 1-xGe xTe has a low-temperature ferroelectric rhombohedral phase whose average structure is a distorted rocksalt structure. We have measured the Extended X-Ray-Absorption Fine-Structure (EXAFS) spectra of Pb 1-xGe xTe

Cyclic Fatigue of Intrinsically Brittle Ceramics in Contact with Spheres

December 1, 1999
Author(s)
D K. Kim, Yeon-Gil G. Jung, I M. Peterson, Brian R. Lawn
Contact damage modes in cyclic loading with spheres are investigated in three relatively brittle ceramics, soda-lime glass, porcelain and fine-grain silicon nitride, in moist environments. Initial damage at small numbers of cycles and low loads consists of

Determination of Texture From Individual Grain Orientation Measurements

November 17, 1999
Author(s)
J Blendell, Mark D. Vaudin, Lin-Sien H. Lum
We present a technique for determining the texture of a polycrystalline material based on the measurement of the orientation of a number of individual grains. We assume that the sample has fiber texture and that the texture can be characterized by a
Displaying 1201 - 1225 of 1321
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