We apply network flow techniques to find good exit selections for evacuees in an emergency evacuation. More precisely, we present two algorithms for computing exit distributions using both classical flows and flows over time which are well known from combinatorial optimization. The performance of these new proposals is compared to a simple shortest path approach and to a best response dynamics approach by using a cellular automaton model.
In chloralosed, non-vagotomized, spontaneously breathing cats the peripheral arterial chemoreceptors were stimulated by intravenous infusion of almitrine bismesylate (Vectarion, 0.20 mg/kg). Within 5 h after administration of the drug, a decline of both the mean systemic arterial blood pressure and the effective renal plasma flow, as well as an increase of the plasma renin activity (PRA) and the plasma aldosterone concentration (PAC) was observed. But as the PAC increase was less than that of PRA, a highly significant suppression of the PAC to PRA ratio was noted. The results indicate that not only whole body altitude hypoxia, but also stimulation of the peripheral arterial chemoreceptors in normoxic animals lowers the PAC-to-PRA ratio. It remains to be verified experimentally whether there exists a specific reflex influence of the peripheral arterial chemoreceptors on the renin-aldosterone relationship.
We study $k$-clustering problems with lower bounds, including $k$-median and $k$-means clustering with lower bounds. In addition to the point set $P$ and the number of centers $k$, a $k$-clustering problem with (uniform) lower bounds gets a number $B$. The solution space is restricted to clusterings where every cluster has at least $B$ points. We demonstrate how to approximate $k$-median with lower bounds via a reduction to facility location with lower bounds, for which $O(1)$-approximation algorithms are known. Then we propose a new constrained clustering problem with lower bounds where we allow points to be assigned multiple times (to different centers). This means that for every point, the clustering specifies a set of centers to which it is assigned. We call this clustering with weak lower bounds. We give a $(6.5+ε)$-approximation for $k$-median clustering with weak lower bounds and an $O(1)$-approximation for $k$-means with weak lower bounds. We conclude by showing that at a constant increase in the approximation factor, we can restrict the number of assignments of every point to $2$ (or, if we allow fractional assignments, to $1+ε$). This also leads to the first bicritera approximation algorithm for $k$-means with (standard) lower bounds where bicriteria is interpreted in the sense that the lower bounds are violated by a constant factor. All algorithms in this paper run in time that is polynomial in $n$ and $k$ (and $d$ for the Euclidean variants considered).
The k-center problem is a classical combinatorial optimization problem which asks to find k centers such that the maximum distance of any input point in a set P to its assigned center is minimized. The problem allows for elegant 2-approximations. However, the situation becomes significantly more difficult when constraints are added to the problem. We raise the question whether general methods can be derived to turn an approximation algorithm for a clustering problem with some constraints into an approximation algorithm that respects one constraint more. Our constraint of choice is privacy: Here, we are asked to only open a center when at least l clients will be assigned to it. We show how to combine privacy with several other constraints.
Size, anatomical position and blood supply of the carotid bodies were studied by light microscopic methods in spontaneously hypertensive rats of the Okamoto-strain (SHR) and in normotensive Wistar rats (NWR) of a random-bred strain. In both groups of animals the single carotid body was usually supplied by only one glomic artery which most frequently derived from the external carotid artery, more rarely from the occipital artery and very seldom from the internal carotid artery. In general the carotid bodies were of ellipsoide shape and compact structure and as a rule closely located to the internal carotid artery. In the NWR at the origins of their glomic arteries almost regularly circular intraarterial cushions were found; in the SHR such cushions were only seen in a few cases, and if so than they were less clearly developed. In the SHR, never in the NWR, within the carotid body the lumen of some branches of the glomic arteries was narrowed by pad-like structures. When compared with the NWR the SHR showed enlarged carotid bodies and a respiratory alcalosis, suggesting that systemic hypertension leads to morphologically and functionally detectable alterations of both carotid body structure and function.
