A Heuristic Based on the Intrinsic Dimensionality for Reducing the Number of Cyclic DTW Comparisons in Shape Classification and Retrieval Using AESA

Cyclic Dynamic Time Warping (CDTW) is a good dissimilarity of shape descriptors of high dimensionality based on contours, but it is computationally expensive. For this reason, to perform recognition tasks, a method to reduce the number of comparisons and avoid an exhaustive search is convenient. The Approximate and Eliminate Search Algorithm (AESA) is a relevant indexing method because of its drastic reduction of comparisons, however, this algorithm requires a metric distance and that is not the case of CDTW. In this paper, we introduce a heuristic based on the intrinsic dimensionality that allows to use CDTW and AESA together in classification and retrieval tasks over these shape descriptors. Experimental results show that, for descriptors of high dimensionality, our proposal is optimal in practice and significantly outperforms an exhaustive search, which is the only alternative for them and CDTW in these tasks

Sublinear Algorithms for Approximating String Compressibility

We raise the question of approximating the compressibility of a string with respect to a fixed compression scheme, in sublinear time. We study this question in detail for two popular lossless compression schemes: run-length encoding (RLE) and a variant of Lempel-Ziv (LZ77), and present sublinear algorithms for approximating compressibility with respect to both schemes. We also give several lower bounds that show that our algorithms for both schemes cannot be improved significantly. Our investigation of LZ77 yields results whose interest goes beyond the initial questions we set out to study. In particular, we prove combinatorial structural lemmas that relate the compressibility of a string with respect to LZ77 to the number of distinct short substrings contained in it (its ℓth subword complexity , for small ℓ). In addition, we show that approximating the compressibility with respect to LZ77 is related to approximating the support size of a distribution.National Science Foundation (U.S.) (Award CCF-1065125)National Science Foundation (U.S.) (Award CCF-0728645)Marie Curie International Reintegration Grant PIRG03-GA-2008-231077Israel Science Foundation (Grant 1147/09)Israel Science Foundation (Grant 1675/09

The physiology of penile erection

Erection of the penis results from increase in blood flow into the corpora. The blood flows through the corpus spongiosum and glans which increase in volume, whereas the blood becomes trapped in the corpus cavernosum which becomes rigid as the pressure increases. The protrusion of the penis may be aided by relaxation of the retractor penis muscle. The major erectile fibres lie in the pelvic nerve and anti-erectile fibres in the sacral sympathetic outflow. The hypogastric nerves may contain both nerve types but there is considerable species and individual variation. The neurotransmitters mediating erection have yet to be determined. There is some evidence that acetylcholine is involved in the increase in blood flow through the corpus spongiosum but not in the corpus cavernosum. Vasoactive intestinal peptide may also have a role. It is possible that these and other substances interact to control the complete process. Erection is inhibited by noradrenaline released from sympathetic nerves, and this acts mainly on alpha-1 adrenoceptors within the penis and on the retractor penis muscle. During tumescence blood flows into the sinusoids from the helicine arterioles which supply them. The sinusoids become dilated due to relaxation of smooth muscle within the trabeculae. Blood may also be redirected from anastomoses between the dorsal arteries and corpus spongiosum through other helicine arterioles supplying the sinusoids of the corpus cavernosum. The significance of polsters (smooth muscle projections into the blood vessel lumen) remains controversial. Occlusion of venous drainage from the corpora cavernosa is both passive (due to increased corpus cavernosum pressure) and active. Relaxation of trabecular smooth muscle may also modify blood flow through the corpora cavernosa

Autonomic control and vascular changes during penile erection in monkeys

The mean pressure in the unstimulated corpus cavernosum of monkeys was 12.1 mm Hg. Pelvic nerve stimulation at 8 to 10 Hz produced penile extension and the mean pressure increased to 64.3 mm Hg (47-84% of carotid artery pressure) after a latency of 10 s. On stopping stimulation, recovery to resting levels occurred within 2 min. The response was not blocked by atropine or propranolol. Blood flow through two 19 gauge needles inserted into the corpus cavernosum increased in parallel with the pressure changes, indicating that arterial inflow increased. Stimulation of either hypogastric nerves or the sympathetic chain produced penile retraction but increased corpus cavernosal pressure. The response to pelvic nerve stimulation was partially blocked. It was concluded that both of these nerves contract penile erectile tissue within the corpus cavernosum and constrict arterial inflow