ASSTG Articles
http://hdl.handle.net/2104/5502
2018-02-23T06:21:49ZThe magnetic field inside a protoplanetary disk gap opened by planets of different masses
http://hdl.handle.net/2104/10207
The magnetic field inside a protoplanetary disk gap opened by planets of different masses
Carballido, Augusto; Matthews, Lorin; Hyde, Truell W.
We perform magnetohydrodynamic simulations of protoplanetary disc gaps opened by planets
of various masses, with the aim of calculating the strength of the vertical magnetic field
threading such gaps. We introduce a gravitational potential at the centre of a shearing box to
compute the tidal interaction between the planets and the disc gas, which is turbulent due to
the magnetorotational instability. Two types of simulations are executed: 1) In type ‘Z’, the
initial magnetic field has only a uniform, vertical component, and ten planet masses between
0.66 and 6.64 thermal masses are used; 2) In type ‘YZ’, the initial magnetic field has both
toroidal and vertical components, and five planet masses covering the same mass range are
used. Our results show that, for low planet masses, higher values of the vertical magnetic field
occur inside the gaps than outside, in agreement with the previous work. However, for massive
planets, we find that the radial profiles of the field show dips near the gap centre. The interior
of the Hill sphere of the most massive planet in the Z runs contains more low-plasma β values
(i.e. high magnetic pressure) compared to lower-mass planets. Values of β at a distance of one
Hill radius from each planet show a moderate decrease with planet mass. These results are
relevant for the magnetic structure of circumplanetary discs and their possible outflows, and
may be refined to aid future observational efforts to infer planet masses from high-resolution
polarimetric observations of discs with gaps.
2017-01-01T00:00:00ZDelocalization in infinite disordered two-dimensional lattices of different geometry
http://hdl.handle.net/2104/10206
Delocalization in infinite disordered two-dimensional lattices of different geometry
Kostadinova, Eva; Busse, Kyle; Ellis, Naoki; Padgett, Josh; Liaw, Constanze; Matthews, Lorin S.; Hyde, Truell W.
The spectral approach to infinite disordered crystals is applied to anAnderson-type Hamiltonian to demonstrate the existence of extended states for nonzero disorder in 2D lattices of different geometries. The numerical simulations shown prove that extended states exist for disordered honeycomb, triangular, and square crystals. This observation stands in contrast to the predictions of scaling theory, and aligns with experiments in photonic lattices and electron systems. The method used is the only theoretical approach aimed at showing delocalization. A comparison of the results for the three geometries indicates that the triangular and honeycomb lattices experience transition in the transport behavior for similar levels of disorder, which is to be expected from the planar duality of the lattices. This provides justification for the use of artificially prepared triangular lattices as analogues for honeycomb materials, such as graphene. The analysis also shows that the transition in the honeycomb case happens more abruptly compared to the other two geometries, which can be attributed to the number of nearest neighbors.We outline the advantages of the spectral approach as a viable alternative to scaling theory and discuss its applicability to transport problems in both quantum and classical 2D systems.
2017-12-06T00:00:00ZPhysical interpretation of the spectral approach to delocalization in infinite disordered systems
http://hdl.handle.net/2104/9887
Physical interpretation of the spectral approach to delocalization in infinite disordered systems
Kostadinova, Eva; Liaw, Constanze; Matthews, Lorin; Hyde, Truell
In this paper we introduce the spectral approach to delocalization in infinite disordered systems and provide a physical interpretation in context of the classical model of Edwards and Thouless. We argue that spectral analysis is an important contribution to localization problems since it avoids issues related to the use of boundary conditions. Applying the method to 2D and 3D numerical simulations with various amount of disorder W shows that delocalization occurs for W ≤ 0.6 in 2D and for W ≤ 5 for 3D.
2016-12-05T00:00:00ZMultipole Expansions of Aggregate Charge: How Far to Go?
http://hdl.handle.net/2104/9881
Multipole Expansions of Aggregate Charge: How Far to Go?
Matthews, Lorin; Coleman, Douglas A.; Hyde, Truell W.
Aggregates immersed in a plasma or radiative environment will have charge distributed over their extended surface. Previous studies have modeled the aggregate charge using the monopole and dipole terms of a multipole expansion, with results indicating that the dipole-dipole interactions play an important role in increasing the aggregation rate and altering the morphology of the resultant aggregates. This study examines the effect that including the quadrupole terms has on the dynamics of aggregates interacting with each other and the confining electric fields in laboratory experiments. Results are compared to modeling aggregates as a collection of point charges located at the center of each spherical monomer comprising the aggregate.
2016-04-01T00:00:00Z