A set of isothermally melt-crystallized polyethylene samples was examined using small-angle x-ray scattering (SAXS). Time and temperature of crystallization were the variable parameters used to create the set of sampl...
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A set of isothermally melt-crystallized polyethylene samples was examined using small-angle x-ray scattering (SAXS). Time and temperature of crystallization were the variable parameters used to create the set of samples. Following background subtraction, desmearing, and application of the Lorentz factor to the raw SAXS data it is possible to see many orders of reflection. This suggests that much higher degrees of order are present in isothermally melt-crystallized samples than had previously been thought possible. A combination of SAXS and DSC data indicates that there is no evidence for isothermal thickening in these samples. This study, coupled with data obtained from PE single crystals, produced information concerning the extrapolation of single-crystal data to fit bulk systems. In addition, the equilibrium melting point T determined is somewhat lower than previously claimed. This study also suggests that the surface energy of the mature crystals is always lower than that of the nucleated state and/or the nucleation factor K σ en increases with decreasing supercooling.
There are many methods currently producing high modulus and high strength films and fibers in industry. This publication examines the results of a hot nip drawing process to produce high modulus PP films at a relative...
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There are many methods currently producing high modulus and high strength films and fibers in industry. This publication examines the results of a hot nip drawing process to produce high modulus PP films at a relatively rapid production rate. The effects of both temperature and rate of draw on the drawn material will also be examined.
Annealing studies of the calcium salt of an ethylene-methacrylic acid copolymer are reported. Fourier-transform infrared spectroscopy and differential scanning calorimetry were applied to the investigation of the effe...
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Annealing studies of the calcium salt of an ethylene-methacrylic acid copolymer are reported. Fourier-transform infrared spectroscopy and differential scanning calorimetry were applied to the investigation of the effect of polyethylene crystallization on ionic structure as a function of annealing temperature and time. The spectroscopic changes observed in the spectra of the calcium salt annealed at 80°C differ from those seen in the spectra of the calcium salt annealed at room temperature. These changes are interpreted in terms of the multiplet-cluster model and the effect of the polyethylene-type crystallinity on the ionic microstructure.
A systematic study of the sodium and calcium salts of an ethylene–methacrylic acid copolymer is reported. Fourier-transform infrared spectroscopy (in the midinfrared region) is applied to the characterization of stru...
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A systematic study of the sodium and calcium salts of an ethylene–methacrylic acid copolymer is reported. Fourier-transform infrared spectroscopy (in the midinfrared region) is applied to the characterization of structural changes as a function of temperature and time of annealing. In the spectra of calcium ionomers, bands associated with carboxylate dimers are identified and assignments of specific spectral features to multiplets and clusters are discussed. The spectroscopic changes observed in the spectra of sodium ionomers differ somewhat from their calcium counterparts in that a single infrared band attributed to isolated carboxylate groups is observed. Assignments of specific bands to multiplets and clusters can, however, be made in a manner consistent with the interpretation of the spectra of calcium ionomers.
Sexual selection is thought to play a major role in the evolution of color due to the correlation between a signaler’s physiological state and the displayed *** such,researchers often investigate how color correlates...
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Sexual selection is thought to play a major role in the evolution of color due to the correlation between a signaler’s physiological state and the displayed *** such,researchers often investigate how color correlates to the quality of the ***,research on the relationship between color and individual quality is often taxonomically limited and researchers typically investigate how color phenotypes relate to one index of quality,such as a linear measure of body ***,we investigated the relationship among body size,claw size,claw muscle mass,lipid content,and the color of the claw in male fiddler crabs(Leptuca uruguayensis)which wield an exaggerated claw that varies in color from brown to *** hypothesized that if the color was correlated to one or more indices of male quality,the color displayed on the claws of male *** could be under sexual *** found *** claw color varies substantially among the individuals we ***,we did not find a correlation between claw color and indices of quality;neither brightness nor hue correlated to the indices of quality we *** findings suggest that claw color in *** is unlikely to have evolved to signal quality,but may instead function as a species identity or as a non-indicator sexual signal.
Molecular dynamics simulations of the crack-tip f.c.c. --> b.c.c. martensitic transformation in Fe-20Ni and Fe-40Ni (at.%) were carried out. Embedded atom method potential functions were used to represent the inter...
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Molecular dynamics simulations of the crack-tip f.c.c. --> b.c.c. martensitic transformation in Fe-20Ni and Fe-40Ni (at.%) were carried out. Embedded atom method potential functions were used to represent the interaction between the atoms in both crystal structures. The results show that in both alloys the crack-tip stresses are relaxed owing to formation of the b.c.c. phase which is twinned to help accommodate the transformation strain associated with the f.c.c. --> b.c.c. transformation. As a result of the transformation, the crack tip becomes blunted which, in turn, enhances the material toughness. To quantify the effect of the crack-tip f.c.c. --> b.c.c. transformation on material toughness, components of Eshelby's F conservation integral were evaluated in the two alloys. It was found that the F-1 component of the integral which represents the force acting to propagate the crack tip has become negative owing to the transformation. As a result, crack propagation has ceased. Comparison of the two alloys showed that in Fe-40Ni dislocation emission in addition to the transformation can take place at the crack tip, causing additional crack blunting.
Known weights of Cd and Te in a silica optical cell of known volume were reacted and the partial pressure of Te-2 determined by measuring the optical density of the vapor in the visible. The composition of the condens...
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Known weights of Cd and Te in a silica optical cell of known volume were reacted and the partial pressure of Te-2 determined by measuring the optical density of the vapor in the visible. The composition of the condensed phase or phases was calculated from the original weights and the amount of material in the vapor phase. The partial pressure measurements showed that the condensed phase was within the CdTe(s) homogeneity range at high temperatures and so Te-rich solidus points could be established as well as X(Te)-T-P-Te2 data. The values of 10(5)(X(Te) - 1/2) are in the 1-10 range between 960 and 1320 K and are in fair agreement with the findings of Greenberg el al. [J. Solid State Chem. 102, 382 (1993)].
The heteroepitaxy in DyMnO3/Er1Ba2Cu3O7-delta bilayer thin films on LaAlO3 (100) substrates was characterized by four-circle X-ray diffractometry. The Er1Ba2CU3O7-delta thin films on LaAlO3 (100) substrates were prepa...
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The heteroepitaxy in DyMnO3/Er1Ba2Cu3O7-delta bilayer thin films on LaAlO3 (100) substrates was characterized by four-circle X-ray diffractometry. The Er1Ba2CU3O7-delta thin films on LaAlO3 (100) substrates were prepared by molecular-beam deposition (MBD) and post-growth annealing in wet and dry O2 at 880-degrees-C, whereas the DyMnO3 thin films OD the Er1Ba2Cu3O7-delta/LaAlO3 (100) heterostructure were deposited by MBD and post-growth annealing in dry O2 at 750-degrees-C. The conventional X-ray diffraction (XRD) patterns as well as pole figures (phi-scans) for specific (hkl) reflections were acquired. The Er1Ba2Cu3O7-delta thin film in the DyMnO3/Er1Ba2Cu3O7-delta/LaAlO3 (100) heterostructure showed [001] oriented epitaxial growth, as expected. The DyMnO3 thin film on the Er1Ba2Cu3O7-delta epilayer in the heterostructure grew with (110) epitaxy in its metastable orthorhombic phase (lattice constants: a0 = 5.272 angstrom, b0 = 5.795 angstrom and c0 = 7.38 angstrom). The heteroepitaxial relationships at the orthorhombic-DyMnO3 (110)/Er1Ba2Cu3O7-delta (001) interface was determined as the following: DyMnO3 (110) parallel-to Er1Ba2Cu3O7-delta (001), DyMnO3 [110BAR] parallel-to Er1Ba2Cu3O7-delta [100] or Er1Ba2Cu3O7-delta [010], and DyMnO3 [001] parallel-to Er1Ba2Cu3O7-delta [010] or Er1Ba2Cu3O7-delta [100].
The dry sliding wear performance of discontinuously reinforced aluminum (DRA) as investigated by numerous studies during the last two decades is reviewed and discussed. In general DRAs feature substantially better wea...
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The dry sliding wear performance of discontinuously reinforced aluminum (DRA) as investigated by numerous studies during the last two decades is reviewed and discussed. In general DRAs feature substantially better wear resistance than their respective unreinforced matrix. However, under particular conditions and wear mechanisms, the wear performance of the overall DRA-metal couple is similar to or lower than its respective unreinforced alloy-metal couple. Furthermore conflicting results regarding the effect of the different tribological parameters on the wear performance of DRAs are noted among the reviewed studies, thereby increasing the difficulty in achieving the optimization of DRA-metal couples. It is shown that parameter interactions exist and are responsible for these conflicting results. The development of a general framework identifying groups of interactive parameters and assessing wear material performance through investigating these groups of parameter is therefore presented. It is suggested that material loss can be rationalized from the understanding and description of the three wear precursors which delineate these groups of parameters, the wear precursors being surface, subsurface and third body behavior. It is proposed that optimization of a tribosystem can be done through optimizing the three behaviors independently, thus allowing consideration of a reduced number of parameters while providing a higher degree of practical extrapolation.
The F.C.C. --> B.C.C. martensitic transformation in Fe-Ni alloys containing between 20 and 40 at.% Ni was studied using molecular dynamics simulations. The interatomic interactions were represented using the embedd...
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The F.C.C. --> B.C.C. martensitic transformation in Fe-Ni alloys containing between 20 and 40 at.% Ni was studied using molecular dynamics simulations. The interatomic interactions were represented using the embedded atom method pseudo-monoatomic potentials, which were shown to represent correctly the relative stability of the F.C.C. and B.C.C. structures as a function of the nickel content. The simulation results dearly demonstrate the important role that crystal defects, such as the free surface or grain boundary, play in the formation of martensite. This is consistent with the experimental observations, which suggest that the martensitic nucleation is of a heterogeneous nature. The simulation results further indicate the need for lattice invariant deformation, such as twinning and slip, for the continued growth of martensite.
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