Metal surface can repel electric charges

first_img Explore further The electric charge packet investigated here is a transverse packet, which is elongated in the direction perpendicular to its motion (motion is indicated by the v arrow). Unlike point charges and longitudinal packets, a fast-moving transverse packet that travels parallel to a metal surface can be repelled by that surface. Credit: Primož Rebernik Ribič ©2012 American Physical Society (—Metals are known for being good electrical conductors. Due to this property, a stationary electric point charge placed outside a metal will cause the electrons in the metal to redistribute in such a way that the point charge will always be attracted toward the metal surface. However, a new study shows that a metal surface will repel an electric charge packet moving parallel to it when the charge packet has a certain geometry and travels at a sufficiently high energy. It’s not just metal surfaces that repel electric charges; any surface will repel this kind of charge packet since the repulsion is caused by the properties of the packet, not the surface. The counterintuitive phenomenon could have implications for improving particle accelerator experiments. Citation: Metal surface can repel electric charges (2013, January 8) retrieved 18 August 2019 from Journal information: Physical Review Letters Primož Rebernik Ribič, a physicist at Ecole Polytechnique Fédérale de Lausanne (EPFL) in Lausanne, Switzerland, has published his study on metal and other surfaces repelling electric charges in a recent issue of Physical Review Letters.As Ribič explains, the interaction between solid surfaces and point charges has been extensively studied, with a classic article by Bolotovskii on the subject published in 1962. More recently, scientists have thoroughly studied the interaction between solid surfaces and charge packets that are elongated in the longitudinal direction (parallel to their motion). However, much less is known about transverse packets, which are elongated in the direction perpendicular to their motion. Ribič has found that the behavior of these packets unexpectedly departs from that of the other two charge geometries.Ribič explains that the phenomenon is easier to understand if one considers the special case of a charge packet moving parallel to the surface of a dielectric. In this case, the packet experiences a force due to two kinds of electromagnetic waves excited in the solid: evanescent waves and Čerenkov waves. Evanescent waves, which exist very close to the surface of the solid, always contribute an attractive force to the charges at all energies. However, the contribution from Čerenkov waves, which travel into the solid, is zero or attractive at low energies, but becomes repulsive at high energies. The reason for this change at high energies is that radiating Čerenkov waves carry a certain momentum into the solid. This momentum has to be balanced by the charge packet, which results in a repulsive force.So at low energies, the attractive components dominate the transverse force, regardless of the charge packet geometry. But even though the Čerenkov contribution becomes repulsive at high energies, previous research has shown that, for point charges, the total force remains attractive at all energies. Electric charge disorder: A key to biological order? More information: Primož Rebernik Ribič. “Can a Metal Surface Repel Electric Charges?” Physical Review Letters 109, 244801 (2012). DOI: 10.1103/PhysRevLett.109244801 Copyright 2013 All rights reserved. This material may not be published, broadcast, rewritten or redistributed in whole or part without the express written permission of When investigating transverse charges, however, Ribič discovered a different result. He found that the geometry of the transverse charges suppresses the evanescent waves, which decreases their attractive contribution and allows the Čerenkov wave repulsion to dominate at high energies to produce an overall repulsive force. This effect is due to the fact that a “long” charge packet, i.e., one with a high ratio of transverse to longitudinal size, will suppress evanescent waves propagating at large angles with respect to the packet velocity. When this ratio is increased infinitely, resulting in a line charge with infinite transverse length, the range of angles is reduced to zero. In other words, all waves except those propagating in the forward direction, i.e., Čerenkov waves, are suppressed. Ribič showed that repulsion can occur between a transverse charge packet and either a dielectric or a metal surface, implying that the repulsive interaction is caused by the geometry of the packet. However, the case with the metal surface is the most interesting. Ribič explained that the finding that a metal surface can repel certain kinds of electric charges will change the way scientists solve problems involving electric charges.”In electrostatics, one is used to solving problems with simple charge geometries using the so-called method of images,” Ribič told “For a single point charge above a metal surface, the force between the charge and the metal is equal to the force between the original charge and an opposite charge placed at twice the distance of the original charge from the surface. This also works for line charges and sheets. This method will always give you an attractive force. The method doesn’t work anymore for charges moving at relativistic speeds, which the paper demonstrates. Besides the standard attractive interaction, which is due to evanescent waves, there is also repulsive interaction due to propagating Čerenkov waves. One has to take this into account whenever dealing with charge distributions other than point charges.”The results not only add to scientists’ understanding of fundamental electrodynamics, but could also prove useful for designing particle accelerator experiments. When a high-energy charge gets close to the surface of an accelerator wall, it produces transverse and longitudinal wakefields that can negatively affect the beam properties. Ribič predicts that manipulating the packet geometry may help alleviate this effect.In the future, Ribič hopes that further investigations into the largely neglected effects of charge geometry will have even greater fundamental and practical consequences.”We will probably also check what happens with other geometries,” he said. “One interesting example would be a ring of charge with a large radius. For an infinitely large ring, one should also get repulsion between a ring that is placed into a guiding tube of an accelerator. Then the question is how the ring and tube radius affect the interaction. We are also planning to explore the interaction between charges and anisotropic media (such as uniaxial dielectrics).” 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

How does complex behavior spontaneously emerge in the brain

first_img Citation: How does complex behavior spontaneously emerge in the brain? (2013, August 26) retrieved 18 August 2019 from A spatial representation of the background avalanche activity in a circular culture with a 2.5-mm radius and density of 300 neurons per mm. Only the top 1% of the most active connections is shown. Different colors correspond to different neuron communities, according to a community detection algorithm. Credit: Javier G. Orlandi, et al. ©2013 Macmillan Publishers Limited In a new study published in Nature Physics, a team of researchers from Spain has shown that emergence in neuronal networks can be explained as a noise-driven phenomenon that is controlled by the interplay between network topology and intrinsic neuronal dynamics. In this scenario, a randomly fired pulse propagates through the network and is amplified by noise focusing, which the researchers describe as an implosive concentration of spontaneous activity. “From the experimental point of view, we show that in neuronal cultures, the emergence early in the development of collective spontaneous activity is dominated by the presence of activity waves that initiate in specific regions of the culture, in a similar way as it happens in vivo,” lead author Javier G. Orlandi at the University of Barcelona told “And with the help of simulations, we also show that you don’t need any special mechanism to explain this behavior, just the right combination of network structure and dynamics. These waves emerge naturally from the noise focusing effect, in which individual firings propagate and concentrate in specific regions to later generate these activity waves.”The researchers arrived at this explanation by combining high-resolution calcium imaging experiments of rat cortical neurons with simulations. The experiments revealed that bursts of neuronal pulses are controlled by waves that originate at small areas called nucleation sites. Although previous research has hinted at the existence of such waves, this study is the first that provides sufficiently high resolution to measure the wave velocity for the first time. The random nature of the wave initiation from spontaneous neuronal firing also supports the idea that it is a noise-driven phenomenon, in which the waves are later amplified to become global bursts.The view of emergence in neural networks as a noise-driven phenomenon differs from the common view in which the bursts of neuronal pulses are controlled by specific leader neurons assisted by the network architecture. In the noise-driven explanation, the nucleation sites do not actively initiate the firing process, but collect and amplify the firing activity that originated elsewhere.As the researchers explain, understanding the full implications of noise focusing in the brain remains a question for future research.”The mechanism of noise focusing emerges naturally in any system with interconnected integrate-and-fire units (like neurons), so its effect should also be present in the brain,” Orlandi said. “If this effect is important in the brain, or by contrast, if the brain has other mechanisms to counter its effect, is still an open question. It could be that noise focusing is responsible for the generation of waves of activity during development, like in the retina, and that it helps the maturation of specific neuronal pathways.”In the future, the researchers plan to further investigate neuronal activity through more in-depth investigations.”We want to see what happens in more complex neuronal systems, like slices or electrode recordings from anaesthetized animals, and see if we find the same effect in there,” Orlandi said. “We know that activity waves are present in these systems, but we still need to see how these waves form exactly, if it is also due to noise focusing or due to something else. It would also be extremely interesting to check what role noise focusing plays in social networks, for example in rumor spreading.”In this analogy, the points of a rumor’s origins can be compared to the nucleation sites where waves originate, and the spreading of a rumor to the brain’s collective neuronal firing. More information: Javier G. Orlandi, et al. “Noise focusing and the emergence of coherent activity in neuronal cultures.” Nature Physics. DOI: 10.1038/NPHYS2686 Journal information: Nature Physics Coherence activity in neuronal cultures from noise focusinglast_img read more

Fossil find shows ancient beaked whale hunted fish in shallow waters

first_img © 2015 Rarely-seen whale washes up on Massachusetts beach Modern Ziphiidae dive down to great depths to find prey such as fish and squid—their dolphin-like snouts and teeth allow them to capture prey and eat it, a marked difference from other whales that suck in huge amounts of water and filter the small creatures in it as their means of sustenance. The fossil that was found, the group claims, is the first known example of a ziphiid eating fish near the surface.The researchers believe the whale captured and consumed a large number of sardine-like fish, then a very short time later, died, possibly due to also ingesting a toxin of some sort, fell to the ocean floor and was entombed—but not before disgorging some of the contents of its belly. The fossil was found embedded in rock with multiple small fish inside of its body and in the immediate area surrounding it. Dating of material in the rock placed the age of the whale and surrounding fish to approximately nine to ten million years ago, placing them in the Late Miocene.The fossils were all in remarkably good shape—the team could make out scales on the fish, which is why they believe that they had not had much time to be digested before the whale that ate them died. More importantly, the fish were not deep sea dwellers, which indicated that the whale hunted near the surface at least part of the time. The number of fish, 40 to 60 of them, and their average size of 39 centimeters, the team notes, is in line with a bellyful of fish caught by the whales’ modern cousins. They note also that dolphins moved into the area not much later, displacing the whales, forcing them to seek food in deeper waters. Explore further Life reconstruction of three individuals of the extinct beaked whale Messapicetus gregarius preying upon a school of aged sardines Sardinops sp. (average body length 38.8 cm) in the upper part of the water column along the coast of nowadays Peru. The front individual is an adult male, whereas the last in the background is a female. Illustration by A. Gennari. Credit: Proceedings of the Royal Society B, Published 9 September 2015.DOI: 10.1098/rspb.2015.1530 (—A team of researchers from several institutions in Europe and Peru has found evidence of an ancient ziphiid (toothed beaked whale) that unlike its modern ancestors, hunted near the surface of the sea. In their paper published in Proceedings of the Royal Society B, the group describes their study of the whale fossil found in a dolomite concretion beneath the sea bed off the coast of Peru last year.last_img read more

Latest study of Tabbys star offers more weirdness

center_img Journal information: arXiv More information: 8462852 is a superficially ordinary main sequence F star for which Kepler detected an unusual series of brief dimming events. We obtain accurate relative photometry of KIC 8462852 from the Kepler full frame images, finding that the brightness of KIC 8462852 monotonically decreased over the four years it was observed by Kepler. Over the first ~1000 days, KIC 8462852 faded approximately linearly at a rate of 0.341 +/- 0.041 percent per year, for a total decline of 0.9%. KIC 8462852 then dimmed much more rapidly in the next ~200 days, with its flux dropping by more than 2%. For the final ~200 days of Kepler photometry the magnitude remained approximately constant, although the data are also consistent with the decline rate measured for the first 2.7 yr. Of a sample of 193 nearby comparison stars and 355 stars with similar stellar parameters, 0.6% change brightness at a rate as fast as 0.341 +/- 0.041 percent per year, and none exhibit either the rapid decline by >2% or the cumulative fading by 3% of KIC 8462852. We examine whether the rapid decline could be caused by a cloud of transiting circumstellar material, finding while such a cloud could evade detection in sub-mm observations, the transit ingress and duration cannot be explained by a simple cloud model. Moreover, this model cannot account for the observed longer-term dimming. No known or proposed stellar phenomena can fully explain all aspects of the observed light curve. New study supports natural causes, not alien activity, explain mystery star’s behavior The tale of Tabby’s Star began in September of last year when Louisiana State University astronomer Tabetha Boyajian reported anomalies in the unusual light curve of star KIC 8462852—over the years 2009 to 2013, its light appeared to dip in ways that did not conform to what would be expected if it were due to a planet passing in front of it, temporarily blocking some of its light. Her paper led to observations, commentaries and theories from others in the space community, though no one was able to come up with a reasonable explanation for what she had found. One researcher actually proposed that it might be due to alien activity. Then, earlier this year, Bradley Schaefer with Louisiana State University published results of his efforts studying photographic plates that had captured the star going back to the 19th century—he reported that the light from the star had dimmed 19 percent over just the past century. His report was not received warmly by all, as many suggested his data or approach was likely flawed.But now, another team has found something similar. Montet and Simon studied images from the space-based Kepler observatory and found that light from Tabby’s Star had decreased in brightness by approximately .34 percent a year for 1000 days starting in 2009, which was actually twice the rate that Schaefer had found. Even stranger, they found that over the next 200 days, the brightness of the star dimmed by another 2.5 percent before it finally leveled out.Various scientists have offered possible explanations for the strange behavior of Tabby’s star—from comet swarms to planetary remnants to the construction of a Dyson Sphere-like structure around the star to capture its energy by aliens—but so far, none of the theories has been able to take into account all of the odd observations. That may change soon, however, as Boyajian, the astronomer who first noticed the star’s strange behavior, ran a successful crowdsourcing campaign to pay for time at the Las Cumbres Observatory Global Telescope Network over the course of a year—this will give her a chance to catch the star in the act of blinking, allowing her to alert the rest of the astronomy community, which will presumably its sights on the star at once, and in so doing, perhaps solve the mystery.last_img read more

Exfoliate Hyderate and Glow

first_imgExfoliating the skin with body a scrub and hydrating it with a good summer lotion are important things that can help your skin to get a glow and look younger.Dead cells can be knocked off to get radiant skin by following few basic steps religiously, says Manoj Khanna of Enhance Cosmetic and Aesthetic Studio. Exfoliate your body: It’s very important to exfoliate your skin. No matter how much lotion you use, you’re never going to have glowing skin if you don’t exfoliate. Grab a body scrub and hit the shower. Gently rub your exfoliator in circular movements on your entire body from the shoulders down and rinse clean. Also Read – ‘Playing Jojo was emotionally exhausting’Continue to do this two- three times a week for year-round beautiful skin. Go for fresh sunscreen: Throw away last year’s unused sunscreen for a new bottle. Buy a new sunscreen that has Ultraviolet aging and Ultraviolet burning products and comes in SPF 30 and SPF 70.Reapply every one to two hours that you are in the sun to ensure a summer full of safe sun fun. Hydrate your body with a summer-scented lotion: Find a fruity summery lotion, which is light and fast absorbing. Gels and purees are perfect fast absorbers. Make sure you apply it right after you dry off from your shower. Also Read – Leslie doing new comedy special with NetflixDon’t forget your feet: Winter boots have long since been packed away; it’s sandal season ladies! Either go and get a pedicure, or give yourself an at-home pedicure. Scrub off the dead dry skin to reveal your sandal ready feet. Keep a foot scrub and file in your shower, and scrub your feet a few times a week. Avoid makeup: During summer, less makeup is best. If you intend to use foundation, then also apply face powder with SPF to avoid patchy skin. To protect your lips, always use a gloss or a lip balm with an SPF 15 to make them feel fresh. Avoid eye makeup in summer. Exfoliating is a good idea during summer because it unclogs  sweat pores as well allowing the body to breathe.last_img read more

Flying high

first_imgAakashan is a fusion of Australian and Indian traditional aerial acrobatics arts. The show was developed and directed by Catherine Daniel an Australian physical theater practitioner in collaboration with Indian choreographer Vikram Mohan, Carly Sheppard, an indigenous Australian contemporary and tradition dancer and the Kalakar Trust.Aakashan was presented and performed by young artists who belong to traditional artist families having low- income backgrounds. The show’s daring aerial acrobatics feats performed include the aptly named gazelle split, half angel, mermaid, bow and arrow & sleeping beauty.  All these elements require incredible stamina and endurance to perform. Also Read – ‘Playing Jojo was emotionally exhausting’Speaking on the occasion Sterre Sharma, founder Kalakar Trust said, ‘I am proud that the youngsters in this show showed the strength to succeed in spite of the challenges they have faced every day of their life.’Founded by 1992 by Sharma, The Kalakar Trust has grown to benefit more than 1200 families of mostly puppeteers, dancers, musicians, acrobats, and magicians.  The funding for the Trust comes from the sale of Sharma’s paintings.  The basic aim of the Trust is to keep the traditional art of these communities alive by providing education, health services, drinking water, income generation arts and community management.The Kalakar Trust is an NGO working for the up-liftment of underprivileged artists living in Delhi slums. The major project is in Katputli colony, West Delhi. The basic aim of the trust is to keep the traditional art of these communities alive by providing education, health services, drinking water, income generation arts and community management.last_img read more

3 injured in DalitJat clash

first_imgThree persons, including a minor, were injured after a clash broke out between members of two communities in Jat Mujhera village, police said on Saturday.A panchayat was convened under New Mandi Police Station on Friday evening to resolve some dispute between Jaat and Dalit communities when the discussions turned violent as the two sides resorted to stones pelting and firing, SP city Sarvan Kumar said.Three persons — Ravish (32), Pradeep (28) and Andnaveen (17), who belonged to the Dalit community were shot at and injured in the incident, he said. The victims were shifted to a nearby hospital and are in a critical condition.Police have registered a case against nine persons and have arrested two accused in this connection.last_img

Governor to meet SEC chief today take stock of poll prep

first_imgKolkata: Governor Keshari Nath Tripathi will hold a meeting with state Election Commissioner A K Singh on Wednesday, to take stock of the preparations for the ensuing Panchayat elections, the dates for which was announced by the state Election Commission (SEC) on Saturday.Sources in the Raj Bhavan said that Singh had sought the time from the Governor, to discuss certain aspects of security and other things related to poll-preparedness. “The stand of the state government in various matters related to the polls and the allegations made by the Opposition will also come up for discussion in the meeting,” a top official of SEC said. Also Read – Heavy rain hits traffic, flightsMeanwhile, the state government once again engaged in a shadow duel with the Governor, over BJP state President Dilip Ghosh’s comment that the Governor was reportedly “worried about violence in Bengal and wanted Central forces in the state during the Panchayat polls.” State Education minister and Trinamool Congress secretary general Partha Chatterjee told mediapersons: “People of Bengal have stopped considering the Governor as a neutral person. We have never heard from the Governor that he wants Central Forces. But Dilip babu (Dilip Ghosh) has said so. Why should things said to a delegation come out in public? Why are the Opposition scared of the rule of law?” Also Read – Speeding Jaguar crashes into Merc, 2 B’deshi bystanders killedGhosh, along with BJP leader Mukul Roy, led a delegation and met Tripathi on Tuesday afternoon. It may be mentioned that one person has died in alleged clashes over submission of nomination forms ahead of the Panchayat polls. The filing of nominations had started on Monday, soon after the SEC put forth the notification, declaring the election dates. Clashes were reported from Bankura’s Onda, Lalbagh in Murshidabad, Arambagh in Hooghly district, Suri and Labhpur in Birbhum.”The Opposition has started visiting the Governor with an attempt to disturb the smooth poll process and the development taken up by the government under the leadership of Mamata Banerjee,” Chatterjee said.last_img read more

Cops use body lights to increase visibility in beaches

first_imgKolkata: Taking a unique initiative to help tourists easily identify policemen and civic volunteers even after sunset, the policemen on Digha and Mandarmani beaches have been provided with uniforms fitted with LED lights.The LED lights of blue and red colour are fitted on the shoulder of the uniform and are visible even from a distance. The lights are commonly called “body lights” by the police.It may be recalled that similar LED lights were first introduced by Kolkata Traffic Police and on-duty traffic constables and sergeants put the lights on after sunset while performing duty on road. It helps to identify them easily. Also Read – Speeding Jaguar crashes into Merc, 2 B’deshi bystanders killedAt present, Digha and Mandarmani are the most famous seaside destinations at East Midnapore. Lakhs of people visit Digha every year and on almost every day, thousands of people gather at the sea beach after sunset. Similarly, many people also prefer to visit Mandarmani for its serenity. The district police have taken several steps to ensure safety and security of the visitors at both the tourist spots.There are around 65 policemen and civic volunteers who are provided with body lights. Fifty of them are posted at Digha while 15 are at Mandarmani. Also Read – Naihati: 10 councillors return to TMC from BJPThe policemen and civic volunteers keep patrolling the sea beach to avoid any untoward incident. They keep watch to ensure that no tourist goes close to the sea after sunset, as it may lead to an accident. They also ensure that the tourists are not disturbed by anyone else.Often tourists need to approach police to seek some sort of help. Since the LED lights are visible even from a distance, a tourist can directly reach an on-duty policeman or a civic volunteer, instead of searching here and there.V Solomon Nesakumar, Superintendent of Police of East Midnapore district, said: “The basic idea is to help tourists as much as possible and the body lights will help them easily identify policemen in case they need any help. At the same time, manpower has also been increased to avoid any untoward incident at the beaches.”last_img read more