Midbrain raphe cell firing and hippocampal theta rhythm in urethane-anaesthetized rats

This study aimed to examine the functional coupling between midbrain raphe and the septohippocampal system at the level of neuronal firing. Raphe unit activity and hippocampal EEG were simultaneously recorded in urethane-anaesthetized rats and their relationship was examined in the frequency domain. Subsets of presumably non-serotonergic neurones in both the dorsal and median raphe nuclei fired rhythmically in synchrony with hippocampal theta activity. Theta cells in the median raphe showed higher coherence than those in dorsal raphe and formed a more homogeneous group of cells, according to their firing rates. Since the raphe-septal serotonergic system is known to desynchronize the hippocampal EEG, activation of a subset of nonserotonergic cells during theta in this nucleus indicates a feedback from the limbic circuitry on the ascending raphe control of forebrain activity.     

Scandinavian Thins on Top of Cake: New and Improved Algorithms for Stacking and Packing

We show how to compute the smallest rectangle that can enclose any polygon, from a given set of polygons, in nearly linear time; we also present a PTAS for the problem, as well as a linear-time algorithm for the case when the polygons are rectangles themselves. We prove that finding a smallest convex polygon that encloses any of the given polygons is NP-hard, and give a PTAS for minimizing the perimeter of the convex enclosure. We also give efficient algorithms to find the smallest rectangle simultaneously enclosing a given pair of convex polygons.     

The Topology of Transportation Networks: A Comparison Between Different Economies

This paper presents an analysis of the topology of transportation networks within different systems of cities. Urban entities and their components are complex systems by their nature; there is no central force that affects their spatial structure. Thus, we study transportation networks within different countries as complex networks. Based on the above, we consider cities as nodes, while direct air and railways routes represent the links. We present characteristics of these networks including their degree and clustering coefficient. Transportation networks can be used as an indicator of economic activity between cities. Cities with strong economic relationship are characterized by high volume of connectivity. Our findings suggest that the topology of the analyzed transportation networks can be used to classify the countries they belong to based on their economic development.

Efficient Regular Data Structures and Algorithms for Dilation, Location, and Proximity Problems

In this paper we investigate data structures obtained by a recursive partitioning of the multi- dimensional input domain into regions of equal size. One of the best known examples of such a structure is the quadtree . It is used here as a basis for more complex data structures. We also provide multidimensional versions of the stratified tree by van Emde Boas [vEB]. We show that under the assumption that the input points have limited precision (i.e., are drawn from the integer grid of size u ) these data structures yield efficient solutions to many important problems. In particular, they allow us to achieve O(log log u) time per operation for dynamic approximate nearest neighbor (under insertions and deletions) and exact on-line closest pair (under insertions only) in any constant number of dimensions. They allow O(log log u) point location in a given planar shape or in its expansion (dilation by a ball of a given radius). Finally, we provide a linear time (optimal) algorithm for computing the expansion of a shape represented by a region quadtree. This result shows that the spatial order imposed by this regular data structure is sufficient to optimize the operation of dilation by a ball. Received January 19, 1999; revised November 4, 1999.     

Perceived density of road maps

Maps should be designed so that users can comprehend and use the information. Display decisions, such as choosing the scale at which an area is shown, depend on properties of the displayed information such as the perceived density (PD) of the information. Taking a psychophysical approach we suggest that the PD of information in a road map is related to the scale and properties of the mapped area. 54 participants rated the PD of 60 maps from different regions. We provide a simple model that predicts the PD of electronic road map displays, using the logarithm of the number of roads, the logarithm of the number of junctions and the length of the shown roads. The PD model was cross-validated using a different set of 60 maps (n = 44). The model can be used for automatically adjusting display scales and for evaluating map designs, considering the required PD to perform a map-related task.     

Limits to the evolution of dispersal kernels under rapid fragmentation

Adaptive evolution of dispersal strategies is one mechanism by which species can respond to rapid environmental changes. However, under rapid anthropogenic fragmentation, the evolution of dispersal may be limited, and species may be unable to adequately adapt to fragmented landscapes. Here, we develop a spatially explicit model to investigate the evolution of dispersal kernels under various combinations of fragmentation dynamics and initial conditions. We also study the consequences of modelling an evolutionary process in which dispersal phenotypes continuously and gradually shift in phenotype space in a manner corresponding to a polygenic underlying genetic architecture. With rapid fragmentation rates, we observed the emergence of long-term transient states in which dispersal strategies are not well suited to fragmented landscapes. We also show that the extent and length of these transient states depend on the pre-fragmentation dispersal strategy of the species, as well as on the rate of the fragmentation process leading to the fragmented landscape. In an increasingly fragmented world, understanding the ability of populations to adapt, and the effects that rapid fragmentation has on the evolution of dispersal, is critical for an informed assessment of species viability in the Anthropocene.     

Computing the fault tolerance of multi-agent deployment

A deployment of a multi-agent system on a network refers to the placement of one or more copies of each agent on network hosts, in such a manner that the memory constraints of each node are satisfied. Finding the deployment that is most likely to tolerate faults (i.e. have at least one copy of each agent functioning and in communication with other agents) is a challenge. In this paper, we address the problem of finding the probability of survival of a deployment (i.e. the probability that a deployment will tolerate faults), under the assumption that node failures are independent. We show that the problem of computing the survival probability of a deployment is at least NP-hard. Moreover, it is hard to approximate. We produce two algorithms to accurately compute the probability of survival of a deployment—these algorithms are expectedly exponential. We also produce five heuristic algorithms to estimate survival probabilities—these algorithms work in acceptable time frames. We report on a detailed set of experiments to determine the conditions under which some of these algorithms perform better than the others.     

Self‐Assembly of Perovskite for Fabrication of Semitransparent Perovskite Solar Cells

This work reports on the preparation of semitransparent perovskite solar cells. The cells transparency is achieved through a unique wet deposition technique that creates perovskite grids with various dimensions. The perovskite grid is deposited on a mesoporous TiO₂ layer, followed by hole transport material deposition and evaporation of a semitransparent gold film. Control of the transparency of the solar cells is achieved by changing the perovskite solution concentration and the mesh openings. The semitransparent cells demonstrate 20–70% transparency with a power conversion efficiency of 5% at 20% transparency. This is the first demonstration of the possibility to create a controlled perovskite pattern using a direct mesh‐assisted assembly deposition method for fabrication of a semitransparent perovskite‐based solar cell.