Local Search in Unstructured Networks

We review a number of message-passing algorithms that can be used to search through power-law networks. Most of these algorithms are meant to be improvements for peer-to-peer file sharing systems, and some may also shed some light on how unstructured social networks with certain topologies might function relatively efficiently with local information. Like the networks that they are designed for, these algorithms are completely decentralized, and they exploit the power-law link distribution in the node degree. We demonstrate that some of these search algorithms can work well on real Gnutella networks, scale sub-linearly with the number of nodes, and may help reduce the network search traffic that tends to cripple such networks.Comment: v2 includes minor revisions: corrections to Fig. 8's caption and references. 23 pages, 10 figures, a review of local search strategies in unstructured networks, a contribution to `Handbook of Graphs and Networks: From the Genome to the Internet', eds. S. Bornholdt and H.G. Schuster (Wiley-VCH, Berlin, 2002), to be publishe

Searching for the Sunk Cost Fallacy

We seek to isolate in the laboratory factors that encourage and discourage the sunk cost fallacy. Subjects play a computer game in which they decide whether to keep digging for treasure on an island or to sink a cost (which will turn out to be either high or low) to move to another island. The research hypothesis is that subjects will stay longer on islands that were more costly to find. Nine treatment variables are considered, e.g. alternative visual displays, whether the treasure value of an island is shown on arrival or discovered by trial and error, and alternative parameters for sunk costs. The data reveal a surprisingly small and erratic sunk cost effect that is generally insensitive to the proposed psychological drivers.sunk cost fallacy

Searching for the Sunk Cost Fallacy

We seek to isolate in the laboratory factors that encourage and discourage the sunk cost fallacy. Subjects play a computer game in which they decide whether to keep digging for treasure on an island or to sink a cost (which will turn out to be either high or low) to move to another island. The research hypothesis is that subjects will stay longer on islands that were more costly to find. Nine treatment variables are considered, e.g. alternative visual displays, whether the treasure value of an island is shown on arrival or discovered by trial and error, and alternative parameters for sunk costs. The data reveal a surprisingly small and erratic sunk cost effect that is generally insensitive to the proposed psychological drivers.sunk cost fallacy, experimental economics

Economics-Based Optimization of Unstable Flows

As an example for the optimization of unstable flows, we present an economics-based method for deciding the optimal rates at which vehicles are allowed to enter a highway. It exploits the naturally occuring fluctuations of traffic flow and is flexible enough to adapt in real time to the transient flow characteristics of road traffic. Simulations based on realistic parameter values show that this strategy is feasible for naturally occurring traffic, and that even far from optimality, injection policies can improve traffic flow. Moreover, the same method can be applied to the optimization of flows of gases and granular media.Comment: Revised version of ``Optimizing Traffic Flow'' (cond-mat/9809397). For related work see http://www.parc.xerox.com/dynamics/ and http://www.theo2.physik.uni-stuttgart.de/helbing.htm

Intermittent exploration on a scale-free network

We study an intermittent random walk on a random network of scale-free degree distribution. The walk is a combination of simple random walks of duration $t_w$ and random long-range jumps. While the time the walker needs to cover all the nodes increases with $t_w$, the corresponding time for the edges displays a non monotonic behavior with a minimum for some nontrivial value of $t_w$. This is a heterogeneity-induced effect that is not observed in homogeneous small-world networks. The optimal $t_w$ increases with the degree of assortativity in the network. Depending on the nature of degree correlations and the elapsed time the walker finds an over/under-estimate of the degree distribution exponent.Comment: 12 pages, 3 figures, 1 table, published versio

Laparoscopic removal of transmigrated intrauterine contraceptive device from abdomen in an asymptomatic patient

Uterine perforation followed by transmigration of intrauterine contraceptive device to the abdominal cavity is one of the rarest, but most dangerous complication of Copper T. These displaced Copper containing devices can cause chronic inflammatory reaction leading to adhesions, intestinal obstruction and even bowel perforation. Hence removal of these devices once found outside the uterus is recommended. Traditionally, a laparotomy used to be performed owing to the associated inflammation, adhesions and the risks of bowel injury. Laparoscopic removal of these displaced devices is a minimally invasive surgical approach with good results in skilled hands. Authors reported a rare case of misplaced transmigrated intrauterine contraceptive device in a 43-year-old asymptomatic lady. The Copper T had migrated after silent perforation of the uterus and was impacted in the greater omentum. There was evidence of chronic inflammation and small pockets of pus surrounding it. There were flimsy bowel adhesions. The dislodged device was successfully removed laparoscopically along with partial omentectomy without any complications. Regular follow up of patients who have had Copper T insertions and teaching them to feel the thread and report if not felt is essential to diagnose complications early. A transmigrated intrauterine device can be successfully removed laparoscopically

Geochemistry, textural studies and its environmental implications on the core sediment of Kadalundi estuary, Kerala

1536-1544The study area Kadalundi estuary is fully occupied with mangroves, and conserved as a bird sanctuary. In this estuary, systematic studies on sedimentological and geochemical aspects are not done so far. Hence, an attempt has been made in this area to infer the paleoenvironmental significance in this region. A core of length 185 cm was taken and subsampled in 5 cm intervals. The sand-silt-clay analyses indicate higher concentration of sand in the core and overall low calcium carbonate content. The organic matter content is highly concentrated at the top and bottom core, whereas in the middle core it is slightly decreased. The sorting values depict poor sorting which indicates mixed environment condition.i.e, one derived from riverine/aeolian environment and the other derived from marine environment. This is due to the widely varying nature of sediments and change in gradients of the coastaline. The heavy mineral assemblage of the study area shows the distribution of low and high ranked metamorphic and some basic igneous rocks.The presence of a little amount of zircon in the top core implies the influence of marine inputs by reworked sediments. XRF data resembles a sudden rise in the concentration towards the bottom core suggests that the trace elements show a positive relation with silt, clay and organic matter in the sediments. XRD analysis projects the presence of Illite in all the samples suggesting the emergence of estuary into Arabian Sea and the reworking of waves. From the overall study it is concluded that the river discharge from Kadalundi, deposits an additional sub-population of sand with a mean size of sediments from medium to fine grained, where low-energy conditons prevails and accretionary processes are taking place with mixed environments

Search in Power-Law Networks

Many communication and social networks have power-law link distributions, containing a few nodes which have a very high degree and many with low degree. The high connectivity nodes play the important role of hubs in communication and networking, a fact which can be exploited when designing efficient search algorithms. We introduce a number of local search strategies which utilize high degree nodes in power-law graphs and which have costs which scale sub-linearly with the size of the graph. We also demonstrate the utility of these strategies on the Gnutella peer-to-peer network.Comment: 17 pages, 14 figure