Majorized iPADMM for Nonseparable Convex Minimization Models with Quadratic Coupling Terms

In this paper, we consider nonseparable convex minimization models with quadratic coupling terms arised in many practical applications. We use a majorized indefinite proximal alternating direction method of multipliers (iPADMM) to solve this model. The indefiniteness of proximal matrices allows the function we actually solved to be no longer the majorization of the original function in each subproblem. While the convergence still can be guaranteed and larger stepsize is permitted which can speed up convergence. For this model, we analyze the global convergence of majorized iPADMM with two different techniques and the sublinear convergence rate in the nonergodic sense. Numerical experiments illustrate the advantages of the indefinite proximal matrices over the positive definite or the semi-definite proximal matrices.

Sign-changing solutions for Schrödinger system with critical growth

<abstract><p>We consider the following Schrödinger system</p> <p><disp-formula> <label/> <tex-math id="FE1"> \begin{document}$ \begin{equation*} \left\{ \begin{aligned} &amp;-\Delta u_j = \sum\limits_{i = 1}^k \beta_{ij}|u_i|^3|u_j|u_j+\lambda_j|u_j|^{q-2}u_j, \ \ \ \text{in}\, \, \Omega, \\ &amp;u_j = 0\quad\text{on}\, \, \partial\Omega, \, \, j = 1, \cdots, k \end{aligned} \right. \end{equation*} $\end{document} </tex-math></disp-formula></p> <p>where $ \Omega\subset\mathbb{R}^3 $ is a bounded domain with smooth boundary. Assume $ 5 &lt; q &lt; 6, \, \lambda_j &gt; 0, \, \beta_{jj} &gt; 0, \, j = 1, \cdots, k $, $ \beta_{ij} = \beta_{ji}, \, i\neq j, i, j = 1, \cdots, k $. Note that the nonlinear coupling terms are of critical Sobolev growth in dimension $ 3 $. We prove that under an additional condition on the coupling matrix the problem has infinitely many sign-changing solutions. The result is obtained by combining the method of invariant sets of descending flow with the approach of using approximation of systems of subcritical growth.</p></abstract>

On the structure of non-planar strong coupling corrections to correlators of BPS Wilson loops and chiral primary operators

Starting with some known localization (matrix model) representations for correlators involving 1/2 BPS circular Wilson loop $$ \mathcal{W} $$ W in $$ \mathcal{N} $$ N = 4 SYM theory we work out their 1/N expansions in the limit of large ’t Hooft coupling λ. Motivated by a possibility of eventual matching to higher genus corrections in dual string theory we follow arXiv:2007.08512 and express the result in terms of the string coupling $$ {g}_{\mathrm{s}}\sim {g}_{\mathrm{YM}}^2\sim \lambda /N $$ g s ∼ g YM 2 ∼ λ / N and string tension $$ T\sim \sqrt{\lambda } $$ T ∼ λ . Keeping only the leading in 1/T term at each order in gs we observe that while the expansion of $$ \left\langle \mathcal{W}\right\rangle $$ W is a series in $$ {g}_{\mathrm{s}}^2/T $$ g s 2 / T , the correlator of the Wilson loop with chiral primary operators $$ {\mathcal{O}}_J $$ O J has expansion in powers of $$ {g}_{\mathrm{s}}^2/{T}^2 $$ g s 2 / T 2 . Like in the case of $$ \left\langle \mathcal{W}\right\rangle $$ W where these leading terms are known to resum into an exponential of a “one-handle” contribution $$ \sim {g}_{\mathrm{s}}^2/T $$ ∼ g s 2 / T , the leading strong coupling terms in $$ \left\langle {\mathcal{WO}}_J\right\rangle $$ WO J sum up to a simple square root function of $$ {g}_{\mathrm{s}}^2/{T}^2 $$ g s 2 / T 2 . Analogous expansions in powers of $$ {g}_{\mathrm{s}}^2/T $$ g s 2 / T are found for correlators of several coincident Wilson loops and they again have a simple resummed form. We also find similar expansions for correlators of coincident 1/2 BPS Wilson loops in the ABJM theory.

Strongly dispersive internal solitary waves transformation over slope-shelf topography

The evolution of strongly dispersive internal solitary waves (ISWs) over slope-shelf topography is studied in a two-layer system of finite depth. We consider the high-order vmeKdV model extending the Korteweg-de Vries (KdV) equation with coupling terms of [Formula: see text] order to treat the strong dispersion in the problem which has variable coefficients to adapt the varying bottom topography. The strongly dispersive initial ISW is characterized by the meKdV equation according to the comparison with experiments and can be propagated by the vmeKdV equation according to the comparison between vmeKdV and vKdV theories. The vmeKdV equation is numerically implemented adopting the finite difference scheme. Three dimensionless ISW amplitudes [Formula: see text], 1.136, 1.41 and two slope inclinations [Formula: see text], 1/10 are considered. The deformation of the ISW is observed when a wave propagates past over the slope. The balancing of shoaling effect and energy dispersion determine the amplitude variation. In the cases of mild or steeper slopes, the terminal wave has a stable profile and amplitude, commonly consistent to the meKdV profile with smaller amplitude. In a particular case of mild slope with very small initial amplitude, the terminal wave amplitude grows larger than the original value.

Diffusion phenomenon for indirectly damped hyperbolic systems coupled by velocities in exterior domains

We consider a system of two coupled wave equations in an exterior domain, where only one equation is directly damped. We prove that the solutions are [Formula: see text]-approximated by special functions, classified into three patterns depending on the values of the damping and the coupling terms, as well as on the speeds of the waves. In particular, when the damping term is sufficiently large, the waves are asymptotically equal to solutions of parabolic-type equations as [Formula: see text]. This result generalizes the standard diffusion phenomenon for directly damped hyperbolic systems.

Aerodynamic Roll-Yaw Instabilities of Floating Offshore Wind Turbines

This paper presents an investigation of a newly discovered motion instability phenomenon for floating wind turbines. The instability is due to anti-symmetric coupling terms in roll and yaw caused by the turbine thrust force. For floaters with small separation between the uncoupled roll and yaw natural periods these coupling forces may result in rigid body roll and yaw oscillations. The paper explains the theory and the physics of the instability phenomenon, and analytical expressions for these stiffness coupling terms (K46 and K64) are derived. The instability phenomenon is demonstrated using several points of attack, by using time domain simulations, conservation of energy flow and eigenvalue stability analysis. The problem is stripped down to a simplified two degree of freedom roll-yaw model where analytical stability criteria are developed. The instability is also demonstrated in tailor made six degree of freedom time domain simulations, and in simulations using a fully coupled aero-hydro-servo elastic simulation tool including a BEM model. An important finding is that damping forces are needed to fully understand the observed instability. It is demonstrated, quite counter-intuitively, that damping reduces the stability margin. This is explained by considering the effect damping forces has on roll-yaw phasing, for the typical damping values relevant for a floating offshore wind turbine.