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Experimental Tests of the GDH and Other Sum Rules at SLAC (open access)

Experimental Tests of the GDH and Other Sum Rules at SLAC

Recent measurements from SLAC of the polarized nucleon structure functions g{sub 1} and g{sub 2} have been used to experimentally test the Bjorken, Ellis-Jaffe, Burkhardt-Cottingham, and Efremov-Leader-Teryaev sum rules. In the future, the SLAC E159 experiment will extend structure function measurements using real photons to 40 GeV, enabling a definitive test of the high energy convergence of the GDH sum rule for both proton and deuteron targets.
Date: June 14, 2005
Creator: Bosted, P.E.
System: The UNT Digital Library
Burst Martensitic Transformations in a Steel and in a Pu-Ga Alloy (open access)

Burst Martensitic Transformations in a Steel and in a Pu-Ga Alloy

Upon cooling a Pu-2.0 at% Ga alloy from the ambient temperature, the metastable delta phase partially transforms martensitically to the alpha-prime phase. Because this transformation involves a 25% volume contraction, plastic accommodation by the delta matrix must occur. When the material is isochronally heated or isothermally annealed above ambient temperatures, the reversion of alpha-prime to delta is likely to occur by the alpha-prime/delta interface moving to consume the alpha-prime particles. This reversion exhibits a burst martensitic mode and is observed as sharp spikes in differential scanning calorimetry data and as steps in resistometry data. These large bursts appear to be the result of an interplay between the autocatalytically driven transformation of individual alpha-prime particles and self-quenching caused by small changes in temperature and/or stress accompanying each burst. The behavior of this Pu-Ga alloy is compared to that of a steel referred to as a ''burst martensite'' in the literature, which also exhibits bursts during both thermal cycling and isothermal holds.
Date: June 14, 2005
Creator: Blobaum, K; Krenn, C; Wall, M & Schwartz, A
System: The UNT Digital Library
Direct Observations of Sigma Phase Growth and Dissolution in 2205 Duplex Stainless Steel (open access)

Direct Observations of Sigma Phase Growth and Dissolution in 2205 Duplex Stainless Steel

The formation and growth of sigma ({sigma}) phase in a 2205 duplex stainless steel is monitored during an 850 C isothermal heat treatment using an in situ synchrotron x-ray diffraction technique. At this temperature, {sigma} phase is first observed within approximately 40 seconds of the start of the isothermal heat treatment and grows rapidly over the course of the 3600 second heat treatment to a volume fraction of approximately 13%. A simultaneous increase in the austenite ({gamma}) volume fraction and a decrease in the ferrite ({delta}) volume fraction are observed. The {sigma} phase formed at this temperature is rapidly dissolved within approximately 200 seconds when the temperature is increased to 1000 C. Accompanying this rapid dissolution of the {sigma} phase, the {delta} and {gamma} volume fractions both approach the balanced (50/50) level observed in the as-received material.
Date: June 14, 2005
Creator: Palmer, T.; Elmer, J.; Babu, S. & Specht, E.
System: The UNT Digital Library