lunar and mars landing is a crucial part of any exploration mission. its importance is manifested by the considerable interest in the past couple of decades. solution of lunar descent can be either numerical or analytical. numerical solutions are iterative and computationally demanding and some of them might not be suitable for on-board implementation. on the other hand, analytical solutions ar...

‎In this paper‎, ‎we study translation invariant surfaces in the‎ ‎3-dimensional Heisenberg group $rm Nil_3$‎. ‎In particular‎, ‎we‎ ‎completely classify translation invariant surfaces in $rm Nil_3$‎ ‎whose position vector $x$ satisfies the equation $Delta x = Ax$‎, ‎where $Delta$ is the Laplacian operator of the surface and $A$‎ ‎is a $3 times 3$-real matrix‎.

Background Background: Mammalian spermatogenesis is regulated through paracrine and endocrine activity, specific cell signaling, and local control mechanisms. These highly specific signaling interactions are effectively absent upon placing testicular cells into two-dimensional primary culture. The specific changes that occur between key cell types and involved spermatogenesis signaling pathways...

We prove the existence and uniqueness, for wave speeds sufficiently large, of monotone traveling wave solutions connecting 0 and 1 for a class of N -dimensional lattice differential equations with unidirectional coupling. We also obtain a variational characterization of the minimum wave speed. The class of systems that we study includes as a special case the one-dimensional lattice equation un ...

We show that history-preserving bisimilarity for higher-dimensional automata has a simple characterization directly in terms of higher-dimensional transitions. This implies that it is decidable for finite higher-dimensional automata. To arrive at our characterization, we apply the open-maps framework of Joyal, Nielsen and Winskel in the category of unfoldings of precubical sets.

The paper shows that there is no finite set of forbidden minors which characterizes classes of independence models that are representable by Gaussian, discrete and binary distributions, respectively. In addition, a way to prove the nonexistence of a finite characterization for any other class of independence models is suggested. MSC 2000: 60A99, 68T30, 94A15

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In this paper, we obtain a forbidden-minor characterization of the class of binary gammoids M such that, for every pair of elements x, y of M, both the splitting matroid Mx,y and the element splitting matroid M ′ x,y are binary gammoids.