Dynamic odd-even effect in n-alkane systems: a molecular dynamics study.

Alternation in various properties of n-alkanes (CnH2n+2) as a function of carbon content (n) is termed 'odd-even effect'. Here, we report a comprehensive molecular dynamics simulation study on n-alkane systems carried out with n ranging between 3 (propane) and 8 (octane), examining the odd-even effect in melting point, density, intramolecular conformational ordering, translational and rotational motion. We observe an odd-even alternation in these properties, but with heptane (n = 7) exhibiting anomalous behavior for all except conformational ordering. Our simulations also show the presence of odd-even behavior in rotational and translational dynamics, below and above the melting point, respectively. The results highlight the role of both molecular shape and the variation in density and their interplay in the origins of the odd-even effect.

Structure and selected properties of Al-Cr-Fe alloys with the presence of structurally complex alloy phases.

The aim of the study was to supplement the data on the Al65Cr20Fe15 alloy with binary phase structure and the Al71Cr24Fe5 alloy with multiphase structure prepared with two different cooling rates from the liquid state. The presence of the structurally complex Al65Cr27Fe8 phase was confirmed by neutron diffraction, scanning electron microscopy with the analysis of chemical composition and transmission electron microscopy. Additionally, the Al8Cr5 phase with γ-brass structure was identified for Al71Cr24Fe5 alloy in both cooling rates from the liquid state. Due to the interesting features of structurally complex alloys, the wear resistance, magnetic properties, and corrosion products after performing electrochemical tests were examined. Based on pin-on-disc measurements, a lower friction coefficient was observed for the Al65Cr20Fe15 alloy (µ ≈ 0.55) compared to the Al71Cr24Fe5 multiphase alloy (µ ≈ 0.6). The average hardness of the binary phase Al65Cr20Fe5 alloy (HV0.1 = 917 ± 30) was higher compared to the multiphase Al71Cr24Fe5 alloy (HV0.1 = 728 ± 34) and the single phase Al-Cr-Fe alloys described in the literature. Moreover, the beneficial effect of rapid solidification on hardness was demonstrated. The alloys Al65Cr20Fe15 and Al71Cr24Fe5 showed paramagnetic behavior, however rapidly solidified Al71Cr24Fe5 alloy indicated an increase of magnetic properties. The studied alloys were characterized by the presence of passive layers after electrochemical tests. A higher amount of oxides on the surface of the Al71Cr24Fe5 alloy was recorded due to the positive effect of chromium on the stabilization of the passive layer.

Improving polarized neutron imaging for visualization of the Meissner effect in superconductors.

The polarized neutron imaging technique provides a non-invasive method of characterizing localized magnetic fields inside superconductors. However, complete understanding of the magnetic field distribution has yet to be realized experimentally due to the complexity of the interaction between neutron polarization and magnetic field. In this article, we show that a well-defined and controlled magnetic field through the neutron path contributes to simplify the data analysis and makes future quantitative polarized neutron imaging possible. This is demonstrated in a set of experiments that visualize the magnetic field distribution inside and around the superconductors. The experimental results demonstrate that proper guide field setup allows the visualization of the magnetic field expulsion at the surface of the superconductor in the zero-field cooling condition, as well as the magnetic field trapped inside the superconductor under field cooling condition.

Setup for polarized neutron imaging using in situ 3He cells at the Oak Ridge National Laboratory High Flux Isotope Reactor CG-1D beamline.

In the present study, we report a new setup for polarized neutron imaging at the ORNL High Flux Isotope Reactor CG-1D beamline using an in situ 3He polarizer and analyzer. This development is very important for extending the capabilities of the imaging instrument at ORNL providing a polarized beam with a large field-of-view, which can be further used in combination with optical devices like Wolter optics, focusing guides, or other lenses for the development of microscope arrangement. Such a setup can be of advantage for the existing and future imaging beamlines at the pulsed neutron sources. The first proof-of-concept experiment is performed to study the ferromagnetic phase transition in the Fe3Pt sample. We also demonstrate that the polychromatic neutron beam in combination with in situ 3He cells can be used as the initial step for the rapid measurement and qualitative analysis of radiographs.