Linking and link complexity of geometrically constrained pairs of rings

We investigate and compare the effects of two different constraints on the geometrical properties and linking of pairs of polygons on the simple cubic lattice, using Monte Carlo methods. One constraint is to insist that the centres of mass of the two polygons are less than distance $d$ apart, and the other is to insist that the radius of gyration of the \emph{pair} of polygons is less than $R$. The second constraint results in links that are quite spherically symmetric, especially at small values of $R$, while the first constraint gives much less spherically symmetric pairs, prolate at large $d$ and becoming more oblate at smaller $d$. These effects have an influence on the observed values of the linking probability and link spectrum.

Measurement and theoretical analysis of sound absorption of simple cubic and hexagonal lattice granules

A structure that possesses a continuous pore space packed with a granular material exhibits acoustic characteristics based on the principle similar to that of a porous material. Such a structure is used in low-noise pavement and ballast track. Therefore, predicting the sound absorption characteristics of a clearance generated in a granular material from the particle diameter and the physical property of gas is useful for engineering. This article deals with two packing models, namely, the simple cubic lattice model and the hexagonal lattice model, to measure the sound absorption coefficient of the structure packed with a granular material whose particle diameter is a few mm. Furthermore, a simple and accurate theoretical analysis that uses a one-dimensional transfer matrix method, which does not require numerous parameters, was performed. Comparing experimental values, when the particle diameter of the granular material was 4 mm, the percentage of the boundary layer in the clearance was moderately larger than when the diameter was 8 mm; therefore, the effect of viscosity on it was larger, and its sound absorption coefficient peak was higher. Moreover, compared with the simple cubic lattice, the hexagonal lattice had a higher percentage of boundary layer in the clearance because of its smaller volume of pore space. Then, the influence of friction due to the viscosity on it was higher, and its sound absorption coefficient peak was higher. In addition, the theoretical values obtained by the proposed analysis method typically matched the experiment values.

Skyrmions and Spin Waves in Magneto–Ferroelectric Superlattices

We present in this paper the effects of Dzyaloshinskii–Moriya (DM) magneto–electric coupling between ferroelectric and magnetic interface atomic layers in a superlattice formed by alternate magnetic and ferroelectric films. We consider two cases: magnetic and ferroelectric films have the simple cubic lattice and the triangular lattice. In the two cases, magnetic films have Heisenberg spins interacting with each other via an exchange J and a DM interaction with the ferroelectric interface. The electrical polarizations of ±1 are assumed for the ferroelectric films. We determine the ground-state (GS) spin configuration in the magnetic film and study the phase transition in each case. In the simple cubic lattice case, in zero field, the GS is periodically non collinear (helical structure) and in an applied field H perpendicular to the layers, it shows the existence of skyrmions at the interface. Using the Green’s function method we study the spin waves (SW) excited in a monolayer and also in a bilayer sandwiched between ferroelectric films, in zero field. We show that the DM interaction strongly affects the long-wave length SW mode. We calculate also the magnetization at low temperatures. We use next Monte Carlo simulations to calculate various physical quantities at finite temperatures such as the critical temperature, the layer magnetization and the layer polarization, as functions of the magneto–electric DM coupling and the applied magnetic field. Phase transition to the disordered phase is studied. In the case of the triangular lattice, we show the formation of skyrmions even in zero field and a skyrmion crystal in an applied field when the interface coupling between the ferroelectric film and the ferromagnetic film is rather strong. The skyrmion crystal is stable in a large region of the external magnetic field. The phase transition is studied.

THE EFFECTIVENESS ANALYSIS OF FUEL BALL (KERNEL) DIMENSION SIZE AND URANIUM ENRICHMENT TO REACTOR REACTIVITY

Reactor reactivity does not only depend on reactor diameter but also radius and enrichment of fuel ball (kernel) to operate reactor optimally. This research analyses effectiveness of kernel radius and enrichment to achieve critical reactor condition. The HTR in this research adopts HTR-10 China and HTR of pebble bed. The calculations are performed by using MCNPX code in each kernel radii of 320-350 µm and enrichments of 5-10% Uranium. Kernel is composed of Uranium Dioxide coated by four outer layers: Carbon, IpyC (Inner Pyrolytic Coating), SiC (Silicon Carbides) and OpyC (Outer Pyrolytic Coating). It is called TRISO and it is distributed in pebble-bed ball using Simple Cubic Lattice whereas pebble-bed and moderator balls are distributed in the core zone using a Body Centred Cubic (BCC) lattice by ratio of 57:43. The research results are obtained that the reactor will be effective to achieve critical condition in kernel radius of 325-330 µm at 9% Uranium enrichment and will be in supercritical condition if the reactor uses more than 330 µm of kernel radius and 9% enrichment of Uranium but the reactor will be subcritical if Uranium enrichment is 5-8%.