arXiv subjects
Publications and source records attributed to Wilson P. Álvarez-Samaniego.
Following closely the analysis performed by Andrew C. Fowler to derive the first canonical equation for nonlinear dune dynamics, but considering some appropriate changes of variables, suitable scalings, and by neglecting higher order terms, we obtain an adaptation of the aforementioned equation, which contains an additional term, to describe dune morphodynamics.
A useful result is that if a bounded complex-valued path is Riemann-integrable, then its modulus is also Riemann-integrable. The extension of this last result to bounded paths taking values in a normed space is affirmed, as being true, in [3]. However, we show that if a bounded path taking values in a normed space is barely Riemann-integrable, then it is not really guaranteed that the norm of this path is also Riemann-integrable.
We give some conditions under which the pressure term in the incompressible Navier-Stokes equations on the entire $d$-dimensional Euclidean space is determined by the formula $\displaystyle \nabla p = \nabla \left(\sum_{i,j=1}^d \mathcal{R}_i \mathcal{R}_j (u_i u_j - F_{i,j}) \right)$, where $d \in \{2, 3\}$, ${\textbf{u}} := (u_1, \ldots, u_d)$ is the fluid velocity, $\mathbb{F}:= (F_{i,j})_{1\le i,j\le d}$ is the forcing tensor, and for all $k \in \{1, \ldots, d\}$, $\mathcal{R}_k$ is the $k$-th Riesz transform.
From the Einstein field equations, in a weak-field approximation and for speeds small compared to the speed of light in vacuum, the following system is obtained \begin{align*} \nabla \times \overrightarrow{E_g} & = -\frac{1}{c} \frac{\partial \overrightarrow{B_g}}{\partial t}, \nabla \cdot \overrightarrow{E_g} \;\; & \approx -4πGρ_g, \nabla \times \overrightarrow{B_g} & \approx -\frac{4πG}{c^{2}}\overrightarrow{J_g}+ \frac{1}{c}\frac{\partial \overrightarrow{E_g}}{\partial t}, \nabla \cdot \overrightarrow{B_g} \;\; & = 0, \end{align*} where $\overrightarrow{E_g}$ is the gravitoelectric field, $\overrightarrow{B_g}$ is the gravitomagnetic field, $\overrightarrow{J_g}$ is the space-time-mass current density and $ρ_g$ is the space-time-mass density. This last gravitoelectromagnetic field system is similar to the Maxwell equations, thus showing an analogy between the electromagnetic theory and gravitation.
The existence of two different Cantor sets, one of them contained in the set of Liouville numbers and the other one inside the set of Diophantine numbers, is proved. Finally, a necessary and sufficient condition for the existence of a Cantor set contained in a subset of the real line is given.