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We have developed an efficient method for the atomistic determination of the conductance of a biological ion channel model by applying an external field to the conducting ions only. The underlying theory is discussed and demonstrated in a simple test system consisting of two ions in a box of water. Finally, the theory is applied to the experimentally… (More)

We recorded from Purkinje cells in the anterior and posterior lobes of the cerebellar vermis in anesthetized cats during passive flexion and extension of the ipsilateral hind foot. Nearly 60% of the 302 cells recorded in lobules I-IV anterior and VII-IX posterior responded to this stimulus. In lobule V, generally considered to be the forelimb projection… (More)

We present new results for three problems dealing with a set <i>P</i> of <i>n</i> convex constant-complexity fat polyhedra in 3-space. (i) We describe a data structure for vertical ray shooting in <i>P</i> that has <i>O</i>(log<sup>2</sup> <i>n</i>) query time and uses <i>O</i>(<i>n</i> log<sup>2</sup> <i>n</i>) storage. (ii) We give an algorithm to compute… (More)

We show that finding the optimistic shortest path on an uncertain terrain is NP-hard using a reduction similar to Canny and Reif's reduction of 3SAT to 3D Euclidean shortest path. Shortest path problems are a well-studied class of problems in theoretical computer science. One particularly applicable type of shortest path problem is to find the geodesic… (More)

In this paper we consider imprecise terrains, that is, triangulated terrains with a vertical error interval in the vertices. In particular, we study the problem of removing as many local extrema (minima and maxima) as possible from the terrain. We show that removing only minima or only maxima can be done optimally in O(n log n) time, for a terrain with n… (More)

We examine the nature of the stationary character of the Hamilton action S for a space-time trajectory ͑worldline͒ x͑t͒ of a single particle moving in one dimension with a general time-dependent potential energy function U͑x , t͒. We show that the action is a local minimum for sufficiently short worldlines for all potentials and for worldlines of any length… (More)

We present a data structure for ray-shooting queries in a set of convex fat polyhedra of total complexity <i>n</i> in <i>R</i><sup>3</sup>. The data structure uses <i>O(n</i><sup>2+ε</sup>) storage and preprocessing time, and queries can be answered in <i>O</i>(log<sup>2</sup> <i>n</i>) time. A trade-off between storage and query time is also possible:… (More)

We study optimization problems for polyhedral terrains in the presence of data imprecision. An imprecise terrain is given by a triangulated point set where the height component of the vertices is specified by an interval of possible values. We restrict ourselves to terrains with a one-dimensional projection, usually referred to as 1.5-dimensional terrains,… (More)

Ion channel conductance can be influenced by electrostatic effects originating from fixed "surface" charges that are remote from the selectivity filter. To explore whether surface charges contribute to the conductance properties of Kir2.1 channels, unitary conductance was measured in cell-attached recordings of Chinese hamster ovary (CHO) cells transfected… (More)