Greedy Routing Enables Network Navigation Without a Map

first_img Algorithm explains how ants create and repair trail networks This correlation between a node’s distance to the destination in metric space, the node’s overall reach, and its degree is what makes the greedy routing strategy efficient at determining the shortest paths. In most cases of transferring information with greedy routing, information first travels to nodes with high degrees. Then, when the distance to the destination decreases, the pattern changes so that the information reaches its destination in a few small hops, regardless of node degree.As the researchers explain, complex networks have a peculiar structure that makes them navigable and that guarantees that information can flow along the shortest routes even without knowledge of the network’s global topology. Regardless of the specifics of the hidden metric space, greedy paths are the shortest paths in synthetic networks with the topologies of real complex networks. Still, the study leaves open some questions, such as the possibility that real networks may tend to evolve to become navigable, as well as determining which networks have hidden metric spaces and which do not. Using the greedy routing strategy to find the shortest paths for the Internet could greatly improve the efficiency of routing in the Internet, Today, Internet routers must continually update their global topology knowledge, presenting a major scalability bottleneck in Internet growth.“Routing in the Internet today requires global topological awareness for all routers, which involves enormous and ever-growing inter-router communication overhead,” Krioukov explained. “Routers are constantly detecting, distributing, processing, and recalculating information needed to compute the shortest paths. For example, as soon as a link fails, the adjacent routers send messages to their neighboring routers about this event, those send messages to their neighbors, and so on, resulting in huge and never-abating cascades of routing updates and recalculations. Routers are getting overwhelmed with this overhead. They can’t keep up with it, they fail, and black holes – unreachable islands of the Internet – are appearing everywhere.“With greedy routing, global topology knowledge is not needed, so that this overhead would be removed, and routing would scale and work much better,” he said.More information: Boguna, Marián; and Krioukov, Dmitri. “Navigating Ultrasmall Worlds in Ultrashort Time.” Physical Review Letters 102, 058701 (2009).Copyright 2009 PhysOrg.com. All rights reserved. This material may not be published, broadcast, rewritten or redistributed in whole or part without the express written permission of PhysOrg.com. However, a navigation technique called greedy routing has shown that it can find the shortest paths between nodes using only local information, without knowledge of the network’s global topology. Marián Boguna from the University of Barcelona and Dmitri Krioukov from the University of California, San Diego, have shown in a recent study that random, scale-free networks such as the Internet have a peculiar structure that enables information to flow along the shortest routes without global topology knowledge. The surprising results are published in a recent issue of Physical Review Letters.“As common sense suggests, the computation of shortest paths is commonly believed to require the full and precise knowledge of the full topology, and here we are showing that it’s in fact not true – not true for the topologies of real complex networks,” Krioukov told PhysOrg.com.In greedy routing, a node passes information to the neighboring node that is closest to the final destination in an abstract space called hidden metric space. This space underlies the real network, and distances in this space abstract intrinsic similarities between nodes. The existence of hidden metric spaces under real networks is a conjecture, although researchers have found evidence of their existence for some real networks, including the Internet.As the researchers explain, some types of networks are not navigable. For instance, if the probability that two nodes are linked doesn’t depend on the metric distance between them, then such networks are difficult to navigate, as there is no way to choose one node over another based on distance. But when there is a connection between the link existence probability and the hidden distance between nodes, metric distances can help to navigate the network, i.e., such networks are “navigable.”As the scientists explain, an ideal navigating strategy should first pass the information to high-degree nodes, since their numerous connections likely cover long distances, getting closer to the destination node. However, greedy routing doesn’t check nodes’ degrees, but only compares the underlying metric distances between various neighbor nodes and the destination node. Fortunately, as the researchers show for navigable networks, node degree is positively correlated with the distances that the node covers by its links. So the closer to the destination a node is, the more distance it likely reaches, and the higher the degree of the node. Citation: Greedy Routing Enables Network Navigation Without a ‘Map’ (2009, February 17) retrieved 18 August 2019 from https://phys.org/news/2009-02-greedy-routing-enables-network.html Explore furthercenter_img This illustration shows the path of greedy routing, a navigation strategy in which a node passes information to the neighboring node that is closest to the final destination in hidden metric space. Image credit: Marián Boguna and Dmitri Krioukov. This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only. (PhysOrg.com) — How does an e-mail get routed so quickly to its recipient’s inbox, or a search query generate relevant Web pages from servers from around the world? Navigating the Internet – or any similar network – generally works most efficiently when routers have knowledge of the network’s global topology. Without knowing the links between nodes, it’s difficult to determine the shortest path between two nodes.last_img read more

Why the sandfish lizard wriggles as it does w Video

first_imgImage credit: Daniel Goldman Study Reveals Small Lizard Tucks Legs and Swims Like a Snake Through Desert Sand (w/ Video) Citation: Why the sandfish lizard wriggles as it does (w/ Video) (2011, February 25) retrieved 18 August 2019 from https://phys.org/news/2011-02-sandfish-lizard-video.html PausePlay% buffered00:0000:00UnmuteMuteDisable captionsEnable captionsSettingsCaptionsDisabledQuality0SpeedNormalCaptionsGo back to previous menuQualityGo back to previous menuSpeedGo back to previous menu0.5×0.75×Normal1.25×1.5×1.75×2×Exit fullscreenEnter fullscreen Image credit: Daniel Goldman © 2010 PhysOrg.com (PhysOrg.com) — The sandfish lizard (Scincus scincus) lives in the desert sands of North Africa and burrows through the sand by wriggling. Now scientists in the US have created a computer model that emulates the physics of the lizard and other burrowing animals. Play Video credit: Daniel Goldman Goldman’s team then built a snake-like robot capable of moving in a similar way to the living lizard, and were able to control the extent of bending and wriggling as the robot moved. They filmed the robot moving through sand to determine how the amount of curling affected their movements.The team followed with computer simulations of the lizards swimming through a field of beads 3mm in diameter. Even with 3 mm beads rather than tiny grains of sand, the simulations needed the computing power of 20-30 ordinary PCs to run, and still took several days. They used the simulation to analyze the movement of every bead affected by the passing lizard. Both the living lizard and robot swam through the glass beads in the same way as they did through sand.The simulation and robotic tests both gave the same answer: if the lizards curl too little they cannot provide enough power to push through the sand, while if they curl too much they do not move very far forward as they wriggle. The movements of the living lizard are close to optimum. Dr Goldman also said the studies suggest that sandfish lizards dive into the sand and wriggle down into it to escape from predators as fast as possible. Burrowing into the sand also enables them to escape the scorching heat of the desert.As a result of their experiments Goldman’s team were able to derive a mathematical theory and highly predictive computer model capable of emulating the physics of sand and objects or animals moving through it. Dr Goldman said the model is the first really detailed, quantitative and accurate model of objects moving through an environment other than air or water.The research could find applications in a number of fields involving objects beneath the surface, such as earthquake monitoring and landmine detection. It could also lead to robots designed to wriggle into the sub-surface on other planets, and the team is already talking to NASA representatives about the possibilities. Explore further Professor Daniel Goldman of the Complex Rheology And Biomechanics Laboratory (CRAB Lab) at the Georgia Institute of Technology in Atlanta, said it is not easy to study the movements of burrowing animals because sand grains bounce off each other wildly rather than creating the kind of flowing movements found when animals move through water or air.Previous studies using X-rays revealed that the sandfish lizard moves through the sand by wriggling in S-shaped curves with their legs tucked in. Dr. Goldman said the wriggling movements of the lizard enable it to move at great speed, since it can cover two body lengths every second, but it was unclear at that time exactly how they achieve those speeds in sand. More information: Mechanical models of sandfish locomotion reveal principles of high performance subsurface sand-swimming, Ryan D. Maladen, Yang Ding, Paul B. Umbanhowar, Adam Kamor, and Daniel I. Goldman, Journal of the Royal Society Interface, in press (2011). This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.last_img read more

Couple finds evidence indicating earliest humans lived by rivers and streams

first_img © 2011 PhysOrg.com Journal information: Nature Communications This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only. More information: River-margin habitat of Ardipithecus ramidus at Aramis, Ethiopia 4.4 million years ago, Nature Communications 2, Article number: 602 doi:10.1038/ncomms1610AbstractThe nature and type of landscape that hominins (early humans) frequented has been of considerable interest. The recent works on Ardipithecus ramidus, a 4.4 million years old hominin found at Middle Awash, Ethiopia, provided critical information about the early part of human evolution. However, habitat characterization of this basal hominin has been highly contested. Here we present new sedimentological and stable isotopic (carbon and oxygen) data from Aramis, where the in situ, partial skeleton of Ar. ramidus (nicknamed ‘Ardi’) was excavated. These data are interpreted to indicate the presence of major rivers and associated mixed vegetations (grasses and trees) in adjacent floodplains. Our finding suggests that, in contrast to a woodland habitat far from a river, Ar. ramidus lived in a river-margin forest in an otherwise savanna (wooded grassland) landscape at Aramis, Ethiopia. Correct interpretation of habitat of Ar. ramidus is crucial for proper assessment of causes and mechanisms of early hominin evolution, including the development of bipedalism. Image: USGS Explore furthercenter_img Now new evidence has come to light that suggests the former might be more likely. Husband and wife team Royhan and Nahid Gani have been studying the sediments surrounding the place where Ardipithecus ramidus, aka, “Ardi,” was found in Ethiopia, and have, as they describe in their paper published in Nature Communications, found that most of the evidence in the area points to a group of people that lived near a very large river.Ardi is believed to have lived some four and half million years ago in what is now Aramis, a hot and dry part of Ethiopia, but until now, no serious study had been done on the dirt in which the skeletal remains were found. After doing so, the Gani’s discovered that the dirt was actually layers of sandstone that appear most likely to have been the result of an ancient stream overflowing it’s banks periodically, leaving behind layers of sand. Branching out, the team discovered that the sediments indicated that such a stream was actually a river, likely twenty six feet deep and over twelve hundred feet wide.Next they turned their attention to plant material that had been preserved in the sandstone, measuring their isotopes, and found that the material had come from grassy plants, suggesting a savannah type environment. But once again, widening their area of study, they also found that there were wide changes in the types of plant material in the area. This caused them to surmise that there were patches of forests near the rivers and streams.Based on these two pieces of information, the team suggests that it appears Ardi, who many researchers believe is our oldest found ancestor, lived in a savannah, near fresh flowing water. Some suggest that such an environment would be consistent with learning to walk upright to see over the tall grasses. (PhysOrg.com) — When many people think of our earliest human ancestors, they think of the hot dried out dusty environments in Africa in which many of their remains were found. Unfortunately, such images don’t take into account the changes in environment that have occurred since those times when early peoples walked the Earth. Archeologists of course have thought of such things and for many years have tossed ideas back and forth debating whether such people lived by rivers and streams, as did those that came later and built civilization along such places as the Nile or whether they lived in woodlands. Out Of The Woods For ‘Ardi’: Scientists Rip Habitat Claim for ‘Breakthrough of the Year’ Citation: Couple finds evidence indicating earliest humans lived by rivers and streams (2011, December 26) retrieved 18 August 2019 from https://phys.org/news/2011-12-couple-evidence-indicating-earliest-humans.htmllast_img read more

Astronomers study star formation and gas flows in the galaxy NGC 1365

first_img Ultra-luminous infrared galaxy with strong ionized-gas outflow discovered Located some 56 million light years away in the Fornax cluster, NGC 1365, dubbed the Great Barred Spiral Galaxy, is a barred spiral and ringed galaxy of Seyfert type. Although many observations of NGC 1365 have been conducted to date, it has not been yet thoroughly studied at mid-infrared wavelengths.In general, mid-infrared observations have the potential to uncover crucial details about molecular gas clouds and ionized gas, which is key to study the distribution and kinematics of the mass-dominating old stellar population in galaxies. Such observations could also provide important information on star formation history and properties of central engines of galaxies.A team of European astronomers led by Nastaran Fazeli of University of Cologne in Germany performed near-infrared observations of NGC 1365 hoping to learn more insights into gas and stellar kinematics in this galaxy. In their observational campaign, the researchers concentrated on the approximately 2,600-light-year-wide circumnuclear region of NGC 1365, studying it using the Spectrograph for INtegral Field Observations in the Near Infrared (SINFONI) instrument on VLT in Chile.”In the framework of understanding the gas and stellar kinematics and their relations to AGNs [active galactic nuclei] and galaxy evolution scenarios, we present spatially resolved distributions and kinematics of the stars and gas in the central ~800-pc radius of the nearby Seyfert galaxy NGC 1365,” the astronomers wrote in the paper.SINFONI observations resulted in detecting parts of the starburst circumnuclear ring (with a radius of about 3,260 light years) and resolving some weaker starburst regions within the inner ring and the nucleus (radius of approximately 1,000 light years). The researchers found that the circumnuclear ring has strong emitting “hot spots” in optical wavelengths, which have starburst ages below 10 million years with an age gradient on the west side of the ring. The study also revealed strong broad and narrow emission-line components of ionized gas in the nuclear region, as well as hot dust with a temperature of approximately 1,300 K. The researchers noted that these properties are typical for type 1 AGN.Observations indicate that the stellar velocity field of NGC 1365 shows an overall rotation. Moreover, ionized and molecular gas show an overall rotation in the general orientation with the stellar velocity.The astronomers calculated that the galaxy’s black hole mass is from five to 10 million times greater than the mass of our sun. They found that the hot molecular gas is around 615 solar masses, what corresponds to a cold molecular gas mass at a level between 200 and 800 million solar masses. Additionally, the ionized gas mass was estimated to be about 5.3 million solar masses. Using European Southern Observatory’s Very Large Telescope (VLT), astronomers have investigated the galaxy NGC 1365. The study, presented in a paper published January 18 on the arXiv.org pre-print server, reveals essential insights about star formation processes and gas flows in this galaxy. A three-color optical image of NGC 1365 combined from three exposures with the FORS1 multi-mode instrument at VLT UT1, in the B (blue), V (green), and R (red) optical bands. Credit: ESO Citation: Astronomers study star formation and gas flows in the galaxy NGC 1365 (2019, February 4) retrieved 18 August 2019 from https://phys.org/news/2019-02-astronomers-star-formation-gas-galaxy.html Explore further More information: Nastaran Fazeli et al. Near-infrared observations of star formation and gas flows in the NUGA galaxy NGC 1365. arXiv:1901.06241 [astro-ph.GA]. arxiv.org/abs/1901.06241 This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only. © 2019 Science X Networklast_img read more

A cause to run

first_imgMilind Soman and Gul Panag announced the launch of the 2nd Edition of Pinkathon Delhi, 2014 which is the biggest multi-city women’s running event to encourage and promote fitness and health among women and create awareness for Breast Cancer.The run is scheduled on 14 September at Jawaharlal Nehru Stadium. Giving out the message of Each One Kheench One; Pinkathon urges all men to encourage at least one special woman in their life to participate. Registrations for the annual women’s run are open for all three categories – 10 km, 5 km and 3 km. The first edition of the run marked more than 2500 participants including women from corporates, colleges and social platforms under various categories. It is now spread across six cities. Soman said, ‘After the encouraging response from last year, Pinkathon is back in the capital. Also Read – ‘Playing Jojo was emotionally exhausting’I personally urge all the men to show their support by encouraging the special women in their life to participate. And I am confident this time also the capital will come together with full vigour to help spread the awareness about breast cancer’.Panag noted, ‘It’s a pleasure to be associated with Pinkathon for two consecutive years. I feel that a platform like Pinkathon is very important in today’s age not just to create awareness about the much neglected disease but also encourage women to come out of their shell and talk about it. I wish Milind all the success in this noble endeavour and urge the citizens of Delhi to participate’.last_img read more

Order not to be construed as internal affairs of any party HC

first_imgThe Patna High Court on Thursday said its order for legal examination of the Assembly Secretary’s letter recognising Nitish Kumar as JD(U)LP leader should not be construed as interference in the internal affairs of any party. “The order should not be construed as any interference in the internal affairs of any party, including JD(U),” a division bench comprising Chief Justice L N Reddy and Justice Vikash Jain said. This was said during the hearing of a review petition by former JD(U) minister PK Shahi this morning on Wednesday’s order of the same bench.last_img read more

Sculpting thoughts

first_imgSangeet Natak Akademi is hosting a show titled Yoga Chakra: Tradition and Modernity by Seema Kohli’s iconography and philosophy of the Yogini cult that inspires her work and life, with constant references to the various form of yoginis and matrikas in her paintings. It will be showcased in an art exhibition and multimedia project with evocative metal sculptures, video performances, tea stains inks and watercolour on arche’s paper. The show will commence on June 21 and will be on till June 28.  Kohli who received the prestigious Gold Award at the Florence Biennale for her video installation, Swayamsiddha — Myth, Mind and Movement, says: “It is both the iconography as well as the philosophy of the Yogini cult that inspires my work and my life. There are constant references to the various forms of yoginis and matrikas in my paintings. The idea of yoginis becomes very fascinating in today’s Kalyuga because yogini is not simply a thought and neither is her message or a sermon.”  Also Read – ‘Playing Jojo was emotionally exhausting’She further adds: “She is experimenting on herself through kriya and yoga through which she enters our blood, vein, bones and our soul. She comes down to subliminal levels and starts her own journey, her khel — her play with herself which takes us to new mystical heights. My work I believe then becomes an exploration into these realms of the self and the relationship of the self with the larger cosmos that seeks an identity, symbol and meaning.last_img read more

One held from Rajarhat on charges of smuggling drugs

first_imgKolkata: Bidhannagar Police arrested one person from Rajarhat on Thursday on charges of smuggling drugs.Acting on a tip off, the police conducted a raid and arrested 42-year-old Sahudul Molla in wee hours of Thursday. He is a resident of Khalusada area at Haroa. Sources said police caught him red handed when he was carrying codine phosphate mixture weighing around 6 litre.A police officer said he was also involved in many other antisocial activities. He used to mainly operate in areas — Haroa, Madhyamgram, New Town, Kolkata Leather Complex, Rajarhat and it’s adjoining areas. He was also involved in bike theft racket. A case has been started in this connection with Rajarhat Police station under section 21(c) of the NDPS Act.In another case, a 21-year-old youth Anik Sarkar was arrested with 47 kg of ganja.He is a resident of Dhanirampur Kandipara and he was arrested while smuggling ganja in a car. He was bringing the consignment from Baliura in Odisha in a car and one Muntu was accompanying him.They also changed the registration number of the vehicle. Muntu has, however, managed to flee.last_img read more

Education dept puts teacher recruitment on hold in Daribhit High School till

first_imgKolkata: In the wake of the incident at Daribhit High School in Islampur in North Dinajpur district, the state Education department has decided to stall recruitment process of teachers till October 5.”The minister has directed all the DIs to submit a report to the department by October 5, stating the student and teacher strength, the infrastructure of the schools under their respective jurisdiction and other details. Till then, there will be no recruitment of teachers. We will examine the vacancies at the schools on the basis of the report and then the recruitment process will start,” a senior official of the Education department said. Also Read – Rain batters Kolkata, cripples normal lifeIn Islampur, two students were killed in a clash that broke out over the recruitment of Urdu teachers on Friday. It may be mentioned that the School Service Commission has already completed the counselling for 6,000 teachers on September 19. The Education department, in collaboration with the West Bengal Board of Secondary Education, was in the process of handing over the appointment letters, amidst which the Daribhit incident occurred. “We are hopeful that the process of handing over appointment letters will be completed before the pujas,” a senior official in the department said. Also Read – Speeding Jaguar crashes into Mercedes car in Kolkata, 2 pedestrians killedIt may be mentioned that state Education minister Partha Chatterjee, in his meeting with the District Inspectors (DI) on Monday, had expressed his displeasure over the decision of shuffling teachers at Daribhit High School in Islampur and reprimanded some DIs for their aggressive role in the recruitment or shuffling of teachers. According to sources, Daribhit High School had no vacancy. Among its 22 sanctioned posts, five are para-teachers. “The act is heinous and nobody involved in the incident will be spared,” Chatterjee had said after the meeting.last_img read more

ER to run four pairs of special trains to tackle Kali Puja

first_imgKOLKATA: To tackle passenger rush on Kali Puja/Deepavali nights, Eastern Railway will run 4 pairs of suburban EMU special trains in Sealdah Division on the nights of November 6/7 & 7/8, 2018. Among these special trains, one pair each will run between Sealdah & Dankuni , Sealdah & Barasat, Sealdah & Ranaghat and between Sealdah (South) & Baruipur stations. The Sealdah-Dankuni Suburban EMU Special will leave Sealdah at 11.30pm and reach Dankuni at 00:15 am and in return journey, the Dankuni-Sealdah Special will Dankuni at 00:25 am and arrive at Sealdah at 1:05 am. The Sealdah-Barasat Suburban EMU Special will leave Sealdah at 00:10 am and reach Barasat at 00:55 am and in the return journey, the Barasat-Sealdah Special will leave at 01:10 am and arrive at 1:55 am. The Sealdah-Ranaghat Suburban EMU Special will leave Sealdah at 00:40 am and reach Ranaghat at 2:30 am and the Ranaghat-Sealdah Special while coming back will leave Ranaghat station at 11:45 am and arrive at 1:40 pm. Also Read – Rain batters Kolkata, cripples normal lifeThe Sealdah (South)-Baruipur Suburban EMU Special will Sealdah at 00:30 am and reach Baruipur at 01:15 am and while returning, the Baruipur-Sealdah Special will leave Baruipur station at 01:25 am and arrive at Sealdah (South) station at 02:10 am. One Passenger Special Train for Baruipur will be run from Sealdah leaving Sealdah (South) station at 5.35pm on November 6. All suburban train services in Sealdah Division will follow Sundays’ schedule up to 2 pm on November 6 and after 2pm, all suburban train services will continue scheduled services with stoppages at all stations including flag & halt stations enroute.last_img read more