The Krein Matrix: General Theory and Concrete Applications in Atomic Bose-Einstein Condensates

When finding the nonzero eigenvalues for Hamiltonian eigenvalue problems it is especially important to locate not only the unstable eigenvalues (i.e., those with positive real part), but also those which are purely imaginary but have negative Krein signature. These latter eigenvalues have the property that they can become unstable upon collision with other purely imaginary eigenvalues, i.e., they are a necessary building block in the mechanism leading to the so-called Hamiltonian-Hopf bifurcation. In this paper we review a general theory for constructing a meromorphic matrix-valued function, the so-called Krein matrix, which has the property of not only locating the unstable eigenvalues, but also those with negative Krein signature. These eigenvalues are realized as zeros of the determinant. The resulting finite dimensional problem obtained by setting the determinant of the Krein matrix to zero presents a valuable simplification. In this paper the usefulness of the technique is illustrated through prototypical examples of spectral analysis of states that have arisen in recent experimental and theoretical studies of atomic Bose-Einstein condensates. In particular, we consider one-dimensional settings (the cigar trap) possessing real-valued multi-dark-soliton solutions, and two-dimensional settings (the pancake trap) admitting complex multi-vortex stationary waveforms.Comment: 26 pages, 16 figures (revised version on April 18 2013

Existence and stability of hole solutions to complex Ginzburg-Landau equations

We consider the existence and stability of the hole, or dark soliton, solution to a Ginzburg-Landau perturbation of the defocusing nonlinear Schroedinger equation (NLS), and to the nearly real complex Ginzburg-Landau equation (CGL). By using dynamical systems techniques, it is shown that the dark soliton can persist as either a regular perturbation or a singular perturbation of that which exists for the NLS. When considering the stability of the soliton, a major difficulty which must be overcome is that eigenvalues may bifurcate out of the continuous spectrum, i.e., an edge bifurcation may occur. Since the continuous spectrum for the NLS covers the imaginary axis, and since for the CGL it touches the origin, such a bifurcation may lead to an unstable wave. An additional important consideration is that an edge bifurcation can happen even if there are no eigenvalues embedded in the continuous spectrum. Building on and refining ideas first presented in Kapitula and Sandstede (Physica D, 1998) and Kapitula (SIAM J. Math. Anal., 1999), we show that when the wave persists as a regular perturbation, at most three eigenvalues will bifurcate out of the continuous spectrum. Furthermore, we precisely track these bifurcating eigenvalues, and thus are able to give conditions for which the perturbed wave will be stable. For the NLS the results are an improvement and refinement of previous work, while the results for the CGL are new. The techniques presented are very general and are therefore applicable to a much larger class of problems than those considered here.Comment: 41 pages, 4 figures, submitte

Stability analysis for pitchfork bifurcations of solitary waves in generalized nonlinear Schroedinger equations

Linear stability of both sign-definite (positive) and sign-indefinite solitary waves near pitchfork bifurcations is analyzed for the generalized nonlinear Schroedinger equations with arbitrary forms of nonlinearity and external potentials in arbitrary spatial dimensions. Bifurcations of linear-stability eigenvalues associated with pitchfork bifurcations are analytically calculated. It is shown that the smooth solution branch switches stability at the bifurcation point. In addition, the two bifurcated solution branches and the smooth branch have the opposite (same) stability when their power slopes have the same (opposite) sign. One unusual feature on the stability of these pitchfork bifurcations is that the smooth and bifurcated solution branches can be both stable or both unstable, which contrasts such bifurcations in finite-dimensional dynamical systems where the smooth and bifurcated branches generally have opposite stability. For the special case of positive solitary waves, stronger and more explicit stability results are also obtained. It is shown that for positive solitary waves, their linear stability near a bifurcation point can be read off directly from their power diagram. Lastly, various numerical examples are presented, and the numerical results confirm the analytical predictions both qualitatively and quantitatively.Comment: 28 pages, 6 figure

Stability criterion for bright solitary waves of the perturbed cubic-quintic Schroedinger equation

The stability of the bright solitary wave solution to the perturbed cubic-quintic Schroedinger equation is considered. It is shown that in a certain region of parameter space these solutions are unstable, with the instability being manifested as a small positive eigenvalue. Furthermore, it is shown that in the complimentary region of parameter space there are no small unstable eigenvalues. The proof involves a novel calculation of the Evans function, which is of interest in its own right. As a consequence of the eigenvalue calculation, it is additionally shown that N-bump bright solitary waves bifurcate from the primary wave.Comment: 28 pages, LaTeX, submitted; author info at http://www.math.unm.edu/~kapitul

Spectral stability of nonlinear waves in KdV-type evolution equations

This paper concerns spectral stability of nonlinear waves in KdV-type evolution equations. The relevant eigenvalue problem is defined by the composition of an unbounded self-adjoint operator with a finite number of negative eigenvalues and an unbounded non-invertible symplectic operator $\partial_x$. The instability index theorem is proven under a generic assumption on the self-adjoint operator both in the case of solitary waves and periodic waves. This result is reviewed in the context of other recent results on spectral stability of nonlinear waves in KdV-type evolution equations.Comment: 15 pages, no figure

Assessing Women\u27s Understanding of Mensuration: Knowledge Gaps and Educational Needs

The menstrual cycle is more complex than what seems to be taught in the education system. School systems focus on the basics of the menstrual cycle, like for example what to do when a young female gets her menstrual cycle for the first time and telling the young female that she can get pregnant but then do not go into detail on the timeframe when pregnancy can occur. It consists of more information than what is taught in the public school system and should be better taught to young females to prevent the unpreventable. The main objective of the study was to evaluate how much women know or think they know about the menstrual cycle, and where in their education they learned the information. In order to generate responses, a survey was created and sent out to women that asked multiple questions. The questions were regarding the menstrual cycle and were specific to the knowledge that they have obtained or have not obtained in their lifetime.https://digitalcommons.misericordia.edu/research_posters2023/1008/thumbnail.jp