Structure formation under steady-state isothermal planar elongational flow of n-eicosane: A comparison between simulation and experiment

We use nonequilibrium molecular dynamics simulations to investigate the structural properties of an oriented melt of n-eicosane under steady-state planar elongational flow. The flow-induced structure was evaluated using the structure factor sk taken as the Fourier transform of the total pair correlation function gr. We found that the equilibrium liquid structure factor is in excellent agreement with the one determined via x-ray diffraction. Moreover, a new x-ray diffraction experiment has been performed on a crystalline n-eicosane sample. The resulting intramolecular contribution to the structure factor was found to be in very good agreement with the simulated one at a high elongation rate, indicating the existence of a possible crystalline precursor structure.open11

The ORNL beamline at the National Synchrotron Light Source

The Oak Ridge National Laboratory's (ORNL) beamline at the National Synchrotron Light Source (NSLS) incorporates several novel features including x-ray optics based on sagittal focusing with crystals and a cantilevered mirror whose center becomes the pivot for all downstream optical elements. Crystal focusing accepts a much larger horizontal divergence of radiation than a mirror while maintaining excellent momentum transfer and energy resolution. This sagittally bent crystal serves as the second element of a two-crystal, nondispersive monochromator. The cantilevered mirror provides a simple design for vertical focusing of the radiation. The beamline is suitable for both x-ray scattering and spectroscopy experiments requiring good energy resolution and high intensity in the energy range from 2.5 to 40 keV. This paper describes the optics of the ORNL beamline and reports their performance to date

X-Ray Diffraction From Ion Implanted Zones

Measurements of x-ray profiles and diffuse scattering from (111), (100) single crystal Niobium films implanted with Nitrogen to average levels of 5 and 0.5 atomic percent are discussed. Theoretical analysis of the asymmetric profiles are used to determine the strain profile in the implanted films. The measured strain profile results from two factors: (1) depth distribution of implants and knock-on damage and (2) elastic constraints. Residual elastic strains develop due to the constraints imposed by a sapphire substrate. Comparison of the diffraction results with theoretical predictions of TRIM indicates the presence of measurable knock-on damage in the films. Huang and Stokes-Wilson scattering measurements made using synchrotron radiation at the ORNL beamline, Brookhaven National Laboratory, were used to reveal the identity of defects formed during the knock-on process

Synchrotron Studies of the First-Order Melting Transitions of Hexatic Monolayers and Multilayers in Freely Suspended Liquid-Crystal Films

Synchrotron x-ray diffraction has been used to study the surface and the interior hexatic-to-liquid (smectic-I to smectic-C) melting transitions of freely suspended liquid-crystal films of N-[4'-(n-heptyl)benzylidene]-4-(n-heptyl)aniline (7O.7) five molecular layers thick. Both the surface hexatic monolayers and the interior hexatic layers melt via hysteretic first-order transitions. After the two surface layers undergo a first-order transition to the smectic-I phase, the surface hexatic correlation length $\xi$ evolves smoothly from $\sim 100 to \sim 300 \mathring{A}$ with a roughly square-root form, $\xi \sim \mid T-T_c \mid ^{1/2}$.Engineering and Applied Science

Thermodynamic systematics of oxides of americium, curium, and neighboring elements

Recently-obtained calorimetric data on the sesquioxides and dioxides of americium and curium are summarized. These data are combined with other properties of the actinide elements to elucidate the stability relationships among these oxides and to predict the behavior of neighboring actinide oxides. 45 references, 4 figures, 5 tables

The Variation in the Standard Entropies of Aqueous Tripositive Lanthanide Ions

Previous published entropies of solid lanthanide trichloride hydrates are reviewed and revised by taking account of the Kramers degeneracy of ground states with half-integral values of J. The revised values necessitate corrections to the standard entropies of the aqueous tripositive lanthanide ions which display an irregular variation with both atomic number and ionic radius. These irregularities can be smoothed out by taking account of contributions from the electronic or magnetic entropy, from structural changes in the coordination that have been revealed by EXAFS and XANES measurements and X-ray crystallography, and from an increasing intrusion of eight coordination across the series. When these contributions are removed, the entropies of the aqueous ions refer to a hypothetical nine-coordinate state in trigonal triprismatic coordination. Within experimental error, they then vary uniformly across the lanthanide series and there is a good linear correlation with the reciprocal of the metal–oxygen distance in the nine-coordinate aqua complexes

Structure Formation under Steady-State Isothermal Planar Elongational Flow of \u3cem\u3en\u3c/em\u3e-Eicosane: A Comparison between Simulation and Experiment

We use nonequilibrium molecular dynamics simulations to investigate the structural properties of an oriented melt of n-eicosane under steady-state planar elongational flow. The flow-induced structure was evaluated using the structure factor s(k) taken as the Fourier transform of the total pair correlation function g(r). We found that the equilibrium liquid structure factor is in excellent agreement with the one determined via x-ray diffraction. Moreover, a new x-ray diffraction experiment has been performed on a crystalline n-eicosane sample. The resulting intramolecular contribution to the structure factor was found to be in very good agreement with the simulated one at a high elongation rate, indicating the existence of a possible crystalline precursor structure