Study and simulation of spatial video compression for remotely piloted vehicles

Techniques of video compression applicable to remotely piloted vehicles (RPVs) are investigated. One approach is to reduce the frame rate, the other is to reduce the number of bits per sample needed to represent static picture detail by means of digital video compression. Hadamard transforms of 8 x 8 subpictures, with adaptive and nonadaptive quantization of transform coefficients, were investigated for the latter technique. Tapes of typical RPV video, processed by Aeronautronic Ford to simulate four frame rates, were again processed by the Ames real-time video system to obtain a variety of compressions of each of the four frame rates

Computing metric hulls in graphs

We prove that, given a closure function the smallest preimage of a closed set can be calculated in polynomial time in the number of closed sets. This confirms a conjecture of Albenque and Knauer and implies that there is a polynomial time algorithm to compute the convex hull-number of a graph, when all its convex subgraphs are given as input. We then show that computing if the smallest preimage of a closed set is logarithmic in the size of the ground set is LOGSNP-complete if only the ground set is given. A special instance of this problem is computing the dimension of a poset given its linear extension graph, that was conjectured to be in P. The intent to show that the latter problem is LOGSNP-complete leads to several interesting questions and to the definition of the isometric hull, i.e., a smallest isometric subgraph containing a given set of vertices $S$. While for $|S|=2$ an isometric hull is just a shortest path, we show that computing the isometric hull of a set of vertices is NP-complete even if $|S|=3$. Finally, we consider the problem of computing the isometric hull-number of a graph and show that computing it is $\Sigma^P_2$ complete.Comment: 13 pages, 3 figure

Cuts in matchings of 3-connected cubic graphs

We discuss conjectures on Hamiltonicity in cubic graphs (Tait, Barnette, Tutte), on the dichromatic number of planar oriented graphs (Neumann-Lara), and on even graphs in digraphs whose contraction is strongly connected (Hochst\"attler). We show that all of them fit into the same framework related to cuts in matchings. This allows us to find a counterexample to the conjecture of Hochst\"attler and show that the conjecture of Neumann-Lara holds for all planar graphs on at most 26 vertices. Finally, we state a new conjecture on bipartite cubic oriented graphs, that naturally arises in this setting.Comment: 12 pages, 5 figures, 1 table. Improved expositio

Chomp on numerical semigroups

We consider the two-player game chomp on posets associated to numerical semigroups and show that the analysis of strategies for chomp is strongly related to classical properties of semigroups. We characterize, which player has a winning-strategy for symmetric semigroups, semigroups of maximal embedding dimension and several families of numerical semigroups generated by arithmetic sequences. Furthermore, we show that which player wins on a given numerical semigroup is a decidable question. Finally, we extend several of our results to the more general setting of subsemigroups of $\mathbb{N} \times T$, where $T$ is a finite abelian group.Comment: 22 pages, 14 figures, 1 table (improved exposition

Discharge chamber studies for mercury bombardment ion thrusters Semiannual report

Discharge chamber studies for mercury bombardment ion thrustors - discharge properties effects on magnetic field configuration, cathode location and type, and method of propellant introductio

Low work function cathode development Summary report

Low work function cathode configurations and nickel encapsulated powder for withstanding intensive ion bombardmen

A General Approach for the Analysis of Habitat Selection

Investigating habitat selection of animals aims at the detection of preferred and avoided habitat types as well as at the identification of covariates influencing the choice of certain habitat types. The final goal of such analyses is an improvement of the conservation of animals. Usually, habitat selection by larger animals is assessed by radio-tracking or visual observation studies, where the chosen habitat is determined for a number of animals at a set of time points. Hence the resulting data often have the following structure: A categorical variable indicating the habitat type selected by an animal at a specific time point is repeatedly observed and shall be explained by covariates. These may either describe properties of the habitat types currently available and / or properties of the animal. In this paper, we present a general approach for the analysis of such data in a categorical regression setup. The proposed model generalises and improves upon several of the approaches previously discussed in the literature and in particular allows to account for changing habitat availability due to the movement of animals within the observation area. It incorporates both habitat- and animal-specific covariates, and includes individual-specific random effects in order to account for correlations introduced by the repeated measurements on single animals. The methodology is implemented in a freely available software package. We demonstrate the general applicability and the capabilities of the proposed approach in two case studies: The analysis of a songbird in South-America and a study on brown bears in Central Europe