Consider a nonlinear Kirchhoff type equation as follows \begin{equation*} \begin{cases} \displaystyle - \Big ( a\int_{\mathbb{R}^{N}}|\nabla u|^{2}dx+b \Big ) \Delta u+u=f(x)\left\vert u\right\vert ^{p-2}u & \text{ in }\mathbb{R}^{N}, \\[2mm] u\in H^{1}(\mathbb{R}^{N}), & \end{cases} \end{equation*} where $N\geq 1,a,b > 0, 2 < p < \min \left\{ 4,2^{\ast }\right\}$($2^{\ast }=\infty $ for $N=1,2$ and $2^{\ast }=2N/(N-2)$ for $N\geq 3)$ and the function $f \in C(\mathbb{R}^{N})\cap L^{\infty }(\mathbb{R}^{N})$. Unlike the existing results in the literature, we are more interested in the geometric properties of the energy functional related to the above problem on $H^{1}( \mathbb{R}^{N})$. As a consequence, we prove the nonexistence, existence and multiplicity of positive solutions, respectively, depending on the parameter $a$ and the dimension $N$. In particular, for the autonomous case, we conclude that a unique positive solution exists for $1\leq N\leq4$ while at least two positive solutions are permitted for $N\geq5$.

Let $\Omega$ be a bounded domain in $\mathbb{R}^2$ with smooth boundary, we study the following elliptic Dirichlet problem $$ \begin{cases} -\Delta\upsilon= e^{\upsilon}-s\phi_1-4\pi\alpha\delta_p-h(x)\,\,\,\, \,\textrm{in}\,\,\,\,\,\Omega,\\ \upsilon=0 \quad\quad\quad\quad\quad\quad \qquad\qquad\quad\quad\,\,\,\, \textrm{on}\,\ \,\partial\Omega, \end{cases} $$ where $s > 0$ is a large parameter, $h\in C^{0,\gamma}(\overline{\Omega})$, $p\in\Omega$, $\alpha\in(-1,+\infty)\setminus\mathbb{N}$, $\delta_p$ denotes the Dirac measure supported at point $p$ and $\phi_1$ is a positive first eigenfunction of the problem $-\Delta\phi=\lambda\phi$ under Dirichlet boundary condition in $\Omega$. If $p$ is a strict local maximum point of $\phi_1$, we show that such a problem has a family of solutions $\upsilon_s$ with arbitrary $m$ bubbles accumulating to $p$, and the quantity $$ \int_{\Omega}e^{\upsilon_s} \rightarrow8\pi(m+1+\alpha)\phi_1(p) \ \text{ as $s\rightarrow+\infty$.} $$

In Euclidean 3-space endowed with a Cartesian reference system, we consider a class of surfaces, called Delaunay tori, constructed by bending segments of Delaunay cylinders with neck-size $a$ and $n$ lobes along circumferences centered at the origin. Such surfaces are complete and compact, have genus one and almost constant, say 1, mean curvature, when $n$ is large. Considering a class of mappings $H\colon\mathbb{R}^{3}\to\mathbb{R}$ such that $H(X)\to 1$ as $|X|\to\infty$ with some decay of inverse-power type, we show that for $n$ large and $|a|$ small, in a suitable neighborhood of any Delaunay torus with $n$ lobes and neck-size $a$ there is no parametric surface constructed as normal graph over the Delaunay torus and whose mean curvature equals $H$ at every point.