The impact of the domain boundary on an inhibitory system: Interior discs and boundary half discs

Xiaofeng Ren; David Shoup

doi:10.3934/dcds.2020048

Article Contents

2020, Volume 40, Issue 6: 3957-3979. Doi: 10.3934/dcds.2020048 open access

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The impact of the domain boundary on an inhibitory system: Interior discs and boundary half discs

Xiaofeng Ren^1, , and
David Shoup^2,

1.
The George Washington University, Washington, DC 20052, USA
2.
Alvernia University, Reading, PA 19607, USA

^* Corresponding author. Phone: 1 202 994-6791; Fax: 1 202 994-6760
^* Corresponding author. Phone: 1 202 994-6791; Fax: 1 202 994-6760

Received: March 2019

Revised: August 2019

Published: March 2020

Xiaofeng Ren is supported in part by NSF grant DMS-1714371

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Abstract

When the Ohta-Kawasaki theory for diblock copolymers is applied to a bounded domain with the Neumann boundary condition, one faces the possibility of micro-domain interfaces intersecting the system boundary. In a particular parameter range, there exist stationary assemblies, stable in some sense, that consist of both perturbed discs in the interior of the system and perturbed half discs attached to the boundary of the system. The circular arcs of the half discs meet the system boundary perpendicularly. The number of the interior discs and the number of the boundary half discs are arbitrarily prescribed and their radii are asymptotically the same. The locations of these discs and half discs are determined by the minimization of a function related to the Green's function of the Laplace operator with the Neumann boundary condition. Numerical calculations based on the theoretical findings show that boundary half discs help lower the energy of stationary assemblies.

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Mathematics Subject Classification: 82B24, 82D60, 92C15.

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Figure 1. From the left of the first row with $ n_i = 10 $ and $ n_b = 0 $ to the right of the last row with $ n_i = 0 $ and $ n_b = 20 $, these assemblies, of $ n_i + \frac{n_b}{2} = 10 $, minimize $ F $. Among them, the right one on the first row has the least $ F $ value. Here $ \omega = 0.2 $

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Table 1. Stationary assemblies with $ n_i+\frac{n_b}{2} $ less than or equal to 4

$ n_i + \frac{n_b}{2} $	$ n_i $	$ n_b $	Minimum $ F $
1	1	0	-0.0796
1	0	2	-0.0307
1.5	1	1	-0.1365
1.5	0	3	-0.1131
2	2	0	-0.2221
2	1	2	-0.2333
2	0	4	-0.2025
2.5	2	1	-0.3440
2.5	1	3	-0.3374
2.5	0	5	-0.2922
3	3	0	-0.4619
3	2	2	-0.4706
3	1	4	-0.4421
3	0	6	-0.3780
3.5	3	1	-0.5955
3.5	2	3	-0.5890
3.5	1	5	-0.5707
3.5	0	7	-0.4573
4	4	0	-0.7301
4	3	2	-0.7287
4	2	4	-0.6783
4	1	6	-0.6963
4	0	8	-0.5280

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Table 2. Stationary assemblies with $ n_i+\frac{n_b}{2} = 10 $

$ n_i + \frac{n_b}{2} $	$ n_i $	$ n_b $	Minimum $ F $
10	10	0	-2.5781
10	9	2	-2.5819
10	8	4	-2.5885
10	7	6	-2.5793
10	6	8	-2.5644
10	5	10	-2.5433
10	4	12	-2.4791
10	3	14	-2.2864
10	2	16	-1.9222
10	1	18	-1.3549
10	0	20	-0.3911

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