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1. CMB Online first

Kalvin, Victor; Kokotov, Alexey
 Determinant of the Laplacian on tori of constant positive curvature with one conical point We find an explicit expression for the zeta-regularized determinant of (the Friedrichs extensions) of the Laplacians on a compact Riemann surface of genus one with conformal metric of curvature $1$ having a single conical singularity of angle $4\pi$. Keywords:determinant of Laplacian, moduli space, spectral zeta-function, curvature one, conical point, conical singularity, Riemann surface, compact Riemann surfaceCategories:47A10, 58J52, 30F45

2. CMB 2018 (vol 61 pp. 768)

Li, Liangliang; Tian, Jing; Chen, Goong
 Chaotic Vibration of a Two-dimensional Non-strictly Hyperbolic Equation The study of chaotic vibration for multidimensional PDEs due to nonlinear boundary conditions is challenging. In this paper, we mainly investigate the chaotic oscillation of a two-dimensional non-strictly hyperbolic equation due to an energy-injecting boundary condition and a distributed self-regulating boundary condition. By using the method of characteristics, we give a rigorous proof of the onset of the chaotic vibration phenomenon of the 2D non-strictly hyperbolic equation. We have also found a regime of the parameters when the chaotic vibration phenomenon occurs. Numerical simulations are also provided. Keywords:chaotic vibration, reflection boundary condition, period-doubling bifurcation, method of characteristicsCategories:32H50, 34C28, 37K50, 54H20, 58J45

3. CMB 2018 (vol 61 pp. 588)

Lang, Honglei; Sheng, Yunhe; Wade, Aissa
 $\mathsf{VB}$-Courant algebroids, $\mathsf{E}$-Courant algebroids and generalized geometry In this paper, we first discuss the relation between $\mathsf{VB}$-Courant algebroids and $\mathsf{E}$-Courant algebroids and construct some examples of $\mathsf{E}$-Courant algebroids. Then we introduce the notion of a generalized complex structure on an $\mathsf{E}$-Courant algebroid, unifying the usual generalized complex structures on even-dimensional manifolds and generalized contact structures on odd-dimensional manifolds. Moreover, we study generalized complex structures on an omni-Lie algebroid in detail. In particular, we show that generalized complex structures on an omni-Lie algebra $\operatorname{gl}(V)\oplus V$ correspond to complex Lie algebra structures on $V$. Keywords:$\mathsf{VB}$-Courant algebroid, $\mathsf{E}$-Courant algebroid, omni-Lie algebroid, generalized complex structure, algebroid-Nijenhuis structureCategories:53D17, 18B40, 58H05

4. CMB 2017 (vol 60 pp. 253)

Chen, Bin; Zhao, Lili
 On a Yamabe Type Problem in Finsler Geometry In this paper, a new notion of scalar curvature for a Finsler metric $F$ is introduced, and two conformal invariants $Y(M,F)$ and $C(M,F)$ are defined. We prove that there exists a Finsler metric with constant scalar curvature in the conformal class of $F$ if the Cartan torsion of $F$ is sufficiently small and $Y(M,F)C(M,F)\lt Y(\mathbb{S}^n)$ where $Y(\mathbb{S}^n)$ is the Yamabe constant of the standard sphere. Keywords:Finsler metric, scalar curvature, Yamabe problemCategories:53C60, 58B20

5. CMB 2016 (vol 60 pp. 122)

Ghanei, Mohammad Reza; Nasr-Isfahani, Rasoul; Nemati, Mehdi
 A Homological Property and Arens Regularity of Locally Compact Quantum Groups We characterize two important notions of amenability and compactness of a locally compact quantum group ${\mathbb G}$ in terms of certain homological properties. For this, we show that ${\mathbb G}$ is character amenable if and only if it is both amenable and co-amenable. We finally apply our results to Arens regularity problems of the quantum group algebra $L^1({\mathbb G})$; in particular, we improve an interesting result by Hu, Neufang and Ruan. Keywords:amenability, Arens regularity, co-amenability, locally compact quantum group, homological propertyCategories:46L89, 43A07, 46H20, 46M10, 58B32

6. CMB 2016 (vol 59 pp. 806)

Izumiya, Shyuichi
 Geometric Interpretation of Lagrangian Equivalence As an application of the theory of graph-like Legendrian unfoldings, relations of the hidden structures of caustics and wave front propagations are revealed. Keywords:wave front propagations, big wave fronts, graph-like Legendrian unfoldings, causticsCategories:58K05, 57R45, 58K60

7. CMB 2016 (vol 60 pp. 77)

Christ, Michael; Rieffel, Marc A.
 Nilpotent Group C*-algebras as Compact Quantum Metric Spaces Let $\mathbb{L}$ be a length function on a group $G$, and let $M_\mathbb{L}$ denote the operator of pointwise multiplication by $\mathbb{L}$ on $\lt(G)$. Following Connes, $M_\mathbb{L}$ can be used as a Dirac'' operator for the reduced group C*-algebra $C_r^*(G)$. It defines a Lipschitz seminorm on $C_r^*(G)$, which defines a metric on the state space of $C_r^*(G)$. We show that for any length function satisfying a strong form of polynomial growth on a discrete group, the topology from this metric coincides with the weak-$*$ topology (a key property for the definition of a compact quantum metric space''). In particular, this holds for all word-length functions on finitely generated nilpotent-by-finite groups. Keywords:group C*-algebra, Dirac operator, quantum metric space, discrete nilpotent group, polynomial growthCategories:46L87, 20F65, 22D15, 53C23, 58B34

8. CMB 2016 (vol 59 pp. 760)

Fichou, Goulwen; Quarez, Ronan; Shiota, Masahiro
 Artin Approximation Compatible with a Change of Variables We propose a version of the classical Artin approximation which allows to perturb the variables of the approximated solution. Namely, it is possible to approximate a formal solution of a Nash equation by a Nash solution in a compatible way with a given Nash change of variables. This result is closely related to the so-called nested Artin approximation and becomes false in the analytic setting. We provide local and global versions of this approximation in real and complex geometry together with an application to the Right-Left equivalence of Nash maps. Keywords:Artin approximation, global case, Nash functionsCategories:14P20, 58A07

9. CMB 2016 (vol 59 pp. 673)

Bačák, Miroslav; Kovalev, Leonid V.
 Lipschitz Retractions in Hadamard Spaces Via Gradient Flow Semigroups Let $X(n),$ for $n\in\mathbb{N},$ be the set of all subsets of a metric space $(X,d)$ of cardinality at most $n.$ The set $X(n)$ equipped with the Hausdorff metric is called a finite subset space. In this paper we are concerned with the existence of Lipschitz retractions $r\colon X(n)\to X(n-1)$ for $n\ge2.$ It is known that such retractions do not exist if $X$ is the one-dimensional sphere. On the other hand L. Kovalev has recently established their existence in case $X$ is a Hilbert space and he also posed a question as to whether or not such Lipschitz retractions exist for $X$ being a Hadamard space. In the present paper we answer this question in the positive. Keywords:finite subset space, gradient flow, Hadamard space, Lie-Trotter-Kato formula, Lipschitz retractionCategories:53C23, 47H20, 54E40, 58D07

10. CMB 2015 (vol 58 pp. 723)

Castro, Alfonso; Fischer, Emily
 Infinitely Many Rotationally Symmetric Solutions to a Class of Semilinear Laplace-Beltrami Equations on Spheres We show that a class of semilinear Laplace-Beltrami equations on the unit sphere in $\mathbb{R}^n$ has infinitely many rotationally symmetric solutions. The solutions to these equations are the solutions to a two point boundary value problem for a singular ordinary differential equation. We prove the existence of such solutions using energy and phase plane analysis. We derive a Pohozaev-type identity in order to prove that the energy to an associated initial value problem tends to infinity as the energy at the singularity tends to infinity. The nonlinearity is allowed to grow as fast as $|s|^{p-1}s$ for $|s|$ large with $1 \lt p \lt (n+5)/(n-3)$. Keywords:Laplace-Beltrami operator, semilinear equation, rotational solution, superlinear nonlinearity, sub-super critical nonlinearityCategories:58J05, 35A24

11. CMB 2015 (vol 58 pp. 846)

Sundar, S.
 A Computation with the Connes-Thom Isomorphism Let $A \in M_{n}(\mathbb{R})$ be an invertible matrix. Consider the semi-direct product $\mathbb{R}^{n} \rtimes \mathbb{Z}$ where the action of $\mathbb{Z}$ on $\mathbb{R}^{n}$ is induced by the left multiplication by $A$. Let $(\alpha,\tau)$ be a strongly continuous action of $\mathbb{R}^{n} \rtimes \mathbb{Z}$ on a $C^{*}$-algebra $B$ where $\alpha$ is a strongly continuous action of $\mathbb{R}^{n}$ and $\tau$ is an automorphism. The map $\tau$ induces a map $\widetilde{\tau}$ on $B \rtimes_{\alpha} \mathbb{R}^{n}$. We show that, at the $K$-theory level, $\tau$ commutes with the Connes-Thom map if $\det(A)\gt 0$ and anticommutes if $\det(A)\lt 0$. As an application, we recompute the $K$-groups of the Cuntz-Li algebra associated to an integer dilation matrix. Keywords:K-theory, Connes-Thom isomorphism, Cuntz-Li algebrasCategories:46L80, 58B34

12. CMB 2015 (vol 58 pp. 575)

Martinez-Torres, David
 The Diffeomorphism Type of Canonical Integrations Of Poisson Tensors on Surfaces A surface $\Sigma$ endowed with a Poisson tensor $\pi$ is known to admit canonical integration, $\mathcal{G}(\pi)$, which is a 4-dimensional manifold with a (symplectic) Lie groupoid structure. In this short note we show that if $\pi$ is not an area form on the 2-sphere, then $\mathcal{G}(\pi)$ is diffeomorphic to the cotangent bundle $T^*\Sigma$. This extends results by the author and by Bonechi, Ciccoli, Staffolani, and Tarlini. Keywords:Poisson tensor, Lie groupoid, cotangent bundleCategories:58H05, 55R10, 53D17

13. CMB 2015 (vol 58 pp. 285)

Karpukhin, Mikhail
 Spectral Properties of a Family of Minimal Tori of Revolution in Five-dimensional Sphere The normalized eigenvalues $\Lambda_i(M,g)$ of the Laplace-Beltrami operator can be considered as functionals on the space of all Riemannian metrics $g$ on a fixed surface $M$. In recent papers several explicit examples of extremal metrics were provided. These metrics are induced by minimal immersions of surfaces in $\mathbb{S}^3$ or $\mathbb{S}^4$. In the present paper a family of extremal metrics induced by minimal immersions in $\mathbb{S}^5$ is investigated. Keywords:extremal metric, minimal surfaceCategory:58J50

14. CMB 2015 (vol 58 pp. 281)

Kalus, Matthias
 On the Relation of Real and Complex Lie Supergroups A complex Lie supergroup can be described as a real Lie supergroup with integrable almost complex structure. The necessary and sufficient conditions on an almost complex structure on a real Lie supergroup for defining a complex Lie supergroup are deduced. The classification of real Lie supergroups with such almost complex structures yields a new approach to the known classification of complex Lie supergroups by complex Harish-Chandra superpairs. A universal complexification of a real Lie supergroup is constructed. Keywords:Lie supergroup, almost complex structure, Harish-Chandra pair, universal complexificationCategories:32C11, 58A50

15. CMB 2014 (vol 58 pp. 69)

Fulp, Ronald Owen
 Correction to "Infinite Dimensional DeWitt Supergroups and Their Bodies" The Theorem below is a correction to Theorem 3.5 in the article entitled " Infinite Dimensional DeWitt Supergroups and Their Bodies" published in Canad. Math. Bull. Vol. 57 (2) 2014 pp. 283-288. Only part (iii) of that Theorem requires correction. The proof of Theorem 3.5 in the original article failed to separate the proof of (ii) from the proof of (iii). The proof of (ii) is complete once it is established that $ad_a$ is quasi-nilpotent for each $a$ since it immediately follows that $K$ is quasi-nilpotent. The proof of (iii) is not complete in the original article. The revision appears as the proof of (iii) of the revised Theorem below. Keywords:super groups, body of super groups, Banach Lie groupsCategories:58B25, 17B65, 81R10, 57P99

16. CMB 2013 (vol 57 pp. 357)

Lauret, Emilio A.
 Representation Equivalent Bieberbach Groups and Strongly Isospectral Flat Manifolds Let $\Gamma_1$ and $\Gamma_2$ be Bieberbach groups contained in the full isometry group $G$ of $\mathbb{R}^n$. We prove that if the compact flat manifolds $\Gamma_1\backslash\mathbb{R}^n$ and $\Gamma_2\backslash\mathbb{R}^n$ are strongly isospectral then the Bieberbach groups $\Gamma_1$ and $\Gamma_2$ are representation equivalent, that is, the right regular representations $L^2(\Gamma_1\backslash G)$ and $L^2(\Gamma_2\backslash G)$ are unitarily equivalent. Keywords:representation equivalent, strongly isospectrality, compact flat manifoldsCategories:58J53, 22D10

17. CMB 2012 (vol 56 pp. 814)

Petridis, Yiannis N.; Raulf, Nicole; Risager, Morten S.
 Quantum Limits of Eisenstein Series and Scattering States We identify the quantum limits of scattering states for the modular surface. This is obtained through the study of quantum measures of non-holomorphic Eisenstein series away from the critical line. We provide a range of stability for the quantum unique ergodicity theorem of Luo and Sarnak. Keywords:quantum limits, Eisenstein series, scattering polesCategories:11F72, 58G25, 35P25

18. CMB 2011 (vol 56 pp. 127)

Li, Junfang
 Evolution of Eigenvalues along Rescaled Ricci Flow In this paper, we discuss monotonicity formulae of various entropy functionals under various rescaled versions of Ricci flow. As an application, we prove that the lowest eigenvalue of a family of geometric operators $-4\Delta + kR$ is monotonic along the normalized Ricci flow for all $k\ge 1$ provided the initial manifold has nonpositive total scalar curvature. Keywords:monotonicity formulas, Ricci flowCategories:58C40, 53C44

19. CMB 2011 (vol 56 pp. 3)

Aïssiou, Tayeb
 Semiclassical Limits of Eigenfunctions on Flat $n$-Dimensional Tori We provide a proof of a conjecture by Jakobson, Nadirashvili, and Toth stating that on an $n$-dimensional flat torus $\mathbb T^{n}$, and the Fourier transform of squares of the eigenfunctions $|\varphi_\lambda|^2$ of the Laplacian have uniform $l^n$ bounds that do not depend on the eigenvalue $\lambda$. The proof is a generalization of an argument by Jakobson, et al. for the lower dimensional cases. These results imply uniform bounds for semiclassical limits on $\mathbb T^{n+2}$. We also prove a geometric lemma that bounds the number of codimension-one simplices satisfying a certain restriction on an $n$-dimensional sphere $S^n(\lambda)$ of radius $\sqrt{\lambda}$, and we use it in the proof. Keywords:semiclassical limits, eigenfunctions of Laplacian on a torus, quantum limitsCategories:58G25, 81Q50, 35P20, 42B05

20. CMB 2011 (vol 56 pp. 366)

Kyritsi, Sophia Th.; Papageorgiou, Nikolaos S.
 Multiple Solutions for Nonlinear Periodic Problems We consider a nonlinear periodic problem driven by a nonlinear nonhomogeneous differential operator and a CarathÃ©odory reaction term $f(t,x)$ that exhibits a $(p-1)$-superlinear growth in $x \in \mathbb{R}$ near $\pm\infty$ and near zero. A special case of the differential operator is the scalar $p$-Laplacian. Using a combination of variational methods based on the critical point theory with Morse theory (critical groups), we show that the problem has three nontrivial solutions, two of which have constant sign (one positive, the other negative). Keywords:$C$-condition, mountain pass theorem, critical groups, strong deformation retract, contractible space, homotopy invarianceCategories:34B15, 34B18, 34C25, 58E05

21. CMB 2011 (vol 55 pp. 723)

Gigli, Nicola; Ohta, Shin-Ichi
 First Variation Formula in Wasserstein Spaces over Compact Alexandrov Spaces We extend results proved by the second author (Amer. J. Math., 2009) for nonnegatively curved Alexandrov spaces to general compact Alexandrov spaces $X$ with curvature bounded below. The gradient flow of a geodesically convex functional on the quadratic Wasserstein space $(\mathcal P(X),W_2)$ satisfies the evolution variational inequality. Moreover, the gradient flow enjoys uniqueness and contractivity. These results are obtained by proving a first variation formula for the Wasserstein distance. Keywords:Alexandrov spaces, Wasserstein spaces, first variation formula, gradient flowCategories:53C23, 28A35, 49Q20, 58A35

22. CMB 2011 (vol 54 pp. 396)

Cho, Jong Taek; Inoguchi, Jun-ichi; Lee, Ji-Eun
 Parabolic Geodesics in Sasakian $3$-Manifolds We give explicit parametrizations for all parabolic geodesics in 3-dimensional Sasakian space forms. Keywords:parabolic geodesics, pseudo-Hermitian geometry, Sasakian manifoldsCategory:58E20

23. CMB 2011 (vol 54 pp. 693)

Lusala, Tsasa; Śniatycki, Jędrzej
 Stratified Subcartesian Spaces We show that if the family $\mathcal{O}$ of orbits of all vector fields on a subcartesian space $P$ is locally finite and each orbit in $\mathcal{O}$ is locally closed, then $\mathcal{O}$ defines a smooth Whitney A stratification of $P$. We also show that the stratification by orbit type of the space of orbits $M/G$ of a proper action of a Lie group $G$ on a smooth manifold $M$ is given by orbits of the family of all vector fields on $M/G$. Keywords:Subcartesian spaces, orbits of vector fields, stratifications, Whitney ConditionsCategories:58A40, 57N80

24. CMB 2011 (vol 54 pp. 249)

Dattori da Silva, Paulo L.
 A Note about Analytic Solvability of Complex Planar Vector Fields with Degeneracies This paper deals with the analytic solvability of a special class of complex vector fields defined on the real plane, where they are tangent to a closed real curve, while off the real curve, they are elliptic. Keywords:semi-global solvability, analytic solvability, normalization, complex vector fields, condition~($\mathcal P$)Categories:35A01, 58Jxx

25. CMB 2010 (vol 53 pp. 674)

Kristály, Alexandru; Papageorgiou, Nikolaos S.; Varga, Csaba
 Multiple Solutions for a Class of Neumann Elliptic Problems on Compact Riemannian Manifolds with Boundary We study a semilinear elliptic problem on a compact Riemannian manifold with boundary, subject to an inhomogeneous Neumann boundary condition. Under various hypotheses on the nonlinear terms, depending on their behaviour in the origin and infinity, we prove multiplicity of solutions by using variational arguments. Keywords:Riemannian manifold with boundary, Neumann problem, sublinearity at infinity, multiple solutionsCategories:58J05, 35P30
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