Pitting of zirconium alloys in NH4 HF2, comments on ‘The relationship between deuterium and fluorine uptake by thin foils of Zr and its alloys etched with a weak solution of NH4HF2 in D2O’ by J.R. Leslie et al., J. Nucl. Mater. 218 (1995) 314

1996 ◽  
Vol 228 (2) ◽  
pp. 248-249
Author(s):  
B. Cox
1992 ◽  
Vol 285 ◽  
Author(s):  
G.A. Bickel ◽  
G.A. Mcrae ◽  
L.W. Green

ABSTRACTElemental distributions in the bulk and metal oxide surface layers of zirconium alloys play key roles in the fracture toughness of the alloys. In particular, localized hydrogen build-up leads to hydride formation and delayed hydride cracking. Parts per million levels of H in Zr have been detected using the 1.06 μm or 355 nm output of a Nd:YAG laser for ablation followed by 2+1 resonance ionization detection of H and D. Analysis of the ablation plume has shown that it consists predominately of atomic species in thermal equilibrium between 2000 and 3600°C. Ablation of thin foils has shown that the ablation rate is on the order of mono-layers per shot and increases exponentially with increasing fluence. Laser ablation depth profiling results of H distributions in an anodically grown oxide film compare qualitatively with nuclear-reaction-analysis profiling of the same sample.


Author(s):  
M. G. Chu ◽  
R. J. Rioja ◽  
G. J. Hildeman ◽  
D. K. Denzer

Al-Fe-Ce alloys produced from gas atomized powders exhibit greater strength at 150°-315°C than conventional aluminum alloys. This higher strength can be attributed to small dispersoids that form during the rapid solidification and precipitates that form after solidification and during consolidation. Understanding the powder microstructure is essential to establishing the relationship between wrought product microstructures and properties. Microstructures present in Al-8 wt% Fe-4 wt% Ce and Al-7 wt% Fe-6 wt% Ce powders (-325 mesh) are presented; in addition, a solidification sequence for atomized droplets is proposed.Analyses include: SEM, TEM, and Chemical Analyses from thin foils via EDXS. Powder samples were compacted into wafers at 200 ksi and subsequently electropolished via the window technique.


Author(s):  
Huang Gao ◽  
Chang Ye ◽  
Gary J. Cheng

Microscale laser dynamic forming (μLDF) is a novel microfabrication technique to introduce complex 3D profiles in thin films. This process utilizes pulse laser to generate plasma to induce shockwave pressure into the thin film, which is placed above a microsized mold. The strain rate in μLDF reaches 106–107 S−1. Under these ultrahigh strain rates in microscale, deformation behaviors of materials are very complicated and almost impossible to be measured in situ experimentally. In this paper, a finite element method model is built to simulate the μLDF process. An improved Johnson–Cook model was used to calculate the flow stress, and the Johnson–Cook failure criterion was employed to simulate failure during μLDF. The simulation results are validated by experiments, in which the deformation of Cu thin foils after μLDF experiments are characterized by scanning electron microscopy and compared with simulation results. With the verified model, the ultrafast μLDF process is generally discussed first. A series of numerical simulations are conducted to investigate the effects of critical parameters on deformation behaviors. These critical parameters include the ratio of the fillet radius to film thickness, the aspect ratio of mold, as well as laser intensities. The relationship of laser pulse energy and the deformation depth is also verified by a series of μLDF experiments.


1967 ◽  
Vol 31 ◽  
pp. 239-251 ◽  
Author(s):  
F. J. Kerr

A review is given of information on the galactic-centre region obtained from recent observations of the 21-cm line from neutral hydrogen, the 18-cm group of OH lines, a hydrogen recombination line at 6 cm wavelength, and the continuum emission from ionized hydrogen.Both inward and outward motions are important in this region, in addition to rotation. Several types of observation indicate the presence of material in features inclined to the galactic plane. The relationship between the H and OH concentrations is not yet clear, but a rough picture of the central region can be proposed.


Paleobiology ◽  
1980 ◽  
Vol 6 (02) ◽  
pp. 146-160 ◽  
Author(s):  
William A. Oliver

The Mesozoic-Cenozoic coral Order Scleractinia has been suggested to have originated or evolved (1) by direct descent from the Paleozoic Order Rugosa or (2) by the development of a skeleton in members of one of the anemone groups that probably have existed throughout Phanerozoic time. In spite of much work on the subject, advocates of the direct descent hypothesis have failed to find convincing evidence of this relationship. Critical points are:(1) Rugosan septal insertion is serial; Scleractinian insertion is cyclic; no intermediate stages have been demonstrated. Apparent intermediates are Scleractinia having bilateral cyclic insertion or teratological Rugosa.(2) There is convincing evidence that the skeletons of many Rugosa were calcitic and none are known to be or to have been aragonitic. In contrast, the skeletons of all living Scleractinia are aragonitic and there is evidence that fossil Scleractinia were aragonitic also. The mineralogic difference is almost certainly due to intrinsic biologic factors.(3) No early Triassic corals of either group are known. This fact is not compelling (by itself) but is important in connection with points 1 and 2, because, given direct descent, both changes took place during this only stage in the history of the two groups in which there are no known corals.


2020 ◽  
Vol 43 ◽  
Author(s):  
Thomas Parr

Abstract This commentary focuses upon the relationship between two themes in the target article: the ways in which a Markov blanket may be defined and the role of precision and salience in mediating the interactions between what is internal and external to a system. These each rest upon the different perspectives we might take while “choosing” a Markov blanket.


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