texplore is a reinforcement learning ( rl ) algorithm, or a method for agents to learn to perform sequential decision making tasks through interaction with their environment. this research is focused on applying rl to more real - world problems, particularly learning on robots. enabling robots to learn will make them generally more useful, as they will not require pre - programming for every task and environment. in rl, an agent is in some state in the world ( e. g. a particular chess board configuration or a location in a city ) and has some set of actions it can take ( e. g. chess moves, turns at an intersection ). upon taking an action, it reaches a new state, and receives a scalar reward ( e. g. + 1 for winning the chess game, - 1 for losing, and 0 otherwise ; or minus the time each road segment took ). the goal of the agent is to learn which action to take in each state to maximize its reward over time. there are a number of issues with applying rl to real - world problems such as robots. first, learning must happen with a limited number of actions. methods that take thousands or millions of actions to learn are not feasible for a robot, as the robot is likely to break, wear out, run out of battery power, or overheat before that many actions can be taken. second, learning must take place in real - time. we would like the rl agent to be in continual control of the robot, not controlling it for short periods of time followed by long pauses for it to compute what action it should take next. finally, there are issues with handling the continuous state space of robots, and dealing with the delays many mechanical actuators have. to address these issues, we have developed an algorithm called texplore. it is a model - based rl algorithm, which means it learns a model of the state transition and reward dynamics of the domain and then uses its model to plan a policy, enabling it to learn in fewer actions than many model - free approaches. it also utilizes a real - time architecture which performs the model learning and planning in parallel threads, so the agent can act in real - time. i ' ve released a ros package with the texplore source code that can be easily applied to any robots running ros :


boeing is frantically trying to save face in the wake of several electrical failures and at least one fire on several of its its much ballyhooed 787 dreamliner airliners. authorities in the u. s. and japan are currently investigating the fires, and now one of the world ’ s best known inventors has chimed in by criticizing the battery technology onboard the planes. in the quest for better energy storage, researchers have investigated all manner of thin, flexible battery technology, power sources based on kinetic energy, and even batteries integrated into clothing. how about batteries you can paint onto any surface? according to research published in the june 28 issue of scientific reports, new “ spray - on ” battery technology could potentially turn any surface into an energy storage device. continue reading we ’ re always happy to hear about any advancements that can improve the performance of rechargeable batteries — particularly if those advancements could make lithium ion batteries robust enough for transportation and renewable energy storage applications. a group of researchers at stanford published a paper in march in the journal nature nanotechnology describing their work using silicon, as opposed to graphene, as an anode material in lithium ion batteries. while silicon has a larger charge storage capacity, it has inherent properties that make it less stable than graphene, which limits the lifecycle of silicon anodes to hundreds of cycles. continue reading


the divergence of perceptions and the need for interaction and communication to solve these problems ( edelenbos et al. 2003 ). because for complex, unstructured problems a purely content - directed approach is not possible, a process - directed approach should be adopted ( de bruijn et al. 2002 ). criticism to the process management approach is that it neglects substantive aspects. recent literature on process or network management pays explicit attention to the importance of interweaving process and content. although a process management approach assumes that an objective problem formulation and knowledge does not exist, this does not imply that substance does not matter in this approach ( de bruijn et al. 2002 ; edelenbos et al. 2003 ; koppenjan and 2004 ). the shift towards a more process - directed approach resulted in the development of empirical, descriptive models. these models aim to provide an alternative for the widely used phase - model. the phase - model describes policy processes as subsequent, interrelated phases with a clear beginning and end. common phases of policy formation are problem formulation, generating alternative solutions, and policy design. teisman ( 1992 ) developed an alternative model, the rounds model. actors are the focal point of analysis in the rounds model. problems and solutions are only relevant to the policy process if they are presented by an actor. policy formation does not stem from an intended course of action formulated by one actor, but results from a series of decisions taken by different actors in different rounds of interaction. rounds of decision - making can only be determined in retrospective by determining the most crucial decisions. decision - making rounds are characterized by dynamic combinations of sets of problems and solutions, represented by different actor. thus, problem formulation always refers to a problem - solution combination ( teisman 2000 ). the basic principles of the rounds model provide useful insights to understand problem structuring. the rounds model is also used as a basis to explain problem solving as a policy game in a network context ( koppenjan and 2004 ) and to explain the function of knowledge in decision - making processes ( van buuren 2006 ). hisschemoller ( 1993 ) uses the term problem structuring in the context of policy processes to refer to an approach which focuses on the integration of the most divergent views with respect to the problem situation. problem structuring prevents from addressing the wrong problem, because it is not solution oriented but oriented to problem finding. instead of using the term problem structuring to develop a normative framework, we developed a conceptual


with respect to the problem situation. problem structuring prevents from addressing the wrong problem, because it is not solution oriented but oriented to problem finding. instead of using the term problem structuring to develop a normative framework, we developed a conceptual model to describe problem formulation in the context of participatory policy processes. this conceptual model bases on insights about problem typologies, policy processes, process management and problem structuring. if problems are unstructured, no clear problem formulation exists. because different stakeholders behold different perceptions about the problem and knowledge is uncertain, interaction between stakeholders is necessary to formulate a joint problem and its solutions. complex, unstructured problems are characterized by uncertainty and diverging perceptions. uncertainty might result from a lack of knowledge, but also because different people interpret and value information differently ( ambiguity ) ( koppenjan and 2004 ). formulating a problem and its solutions implies that uncertainty, ambiguity and disagreement need to be reduced. the development of stakeholders ’ perceptions and knowledge are central elements to create a joint problem formulation. ideally, the outcome of problem structuring is ‘ negotiated knowledge ’, this is knowledge which is agreed upon and valid ( de bruijn et al. 2002 ; van de riet 2003 ). the content developed during a participatory process should not be seen as final or permanent. adoption is the consolidation of a problem formulation over a longer period of several decision rounds ( teisman 2000 ). how problem structuring develops is also summarized in figure 1. experiences from case study research indicate that the presented framework is very useful to analyze the development of substantive outcomes for participatory processes. important lessons are that problem structuring is not a clear - cut process which takes place in a vacuum. furthermore, it appears to be mainly useful to interactive policy - making processes which are open to all problem formulations and in which stakeholders ( i. e. not the general public ) are involved. an example of problem structuring is described in the section with experiences of evaluation and case studies. more information on the design of problem structuring processes and evaluation can be found in literature from m. hisschemoller. a variety of problem structuring methods ( psm ) have been analyzed and developed by j. rosenhead. the presented theory is used to analyze two case studies. for these case studies, see also : de kruijf, j. ( 2007 ). problem structuring in interactive decision - making processes : how interaction, problem


. rosenhead. the presented theory is used to analyze two case studies. for these case studies, see also : de kruijf, j. ( 2007 ). problem structuring in interactive decision - making processes : how interaction, problem perceptions and knowledge contribute to a joint formulation of a problem and its solutions, master ' s thesis, university of twente, enschede. this report is also available as tno - report, ref. nr 2007 - i & r - 065 - kfj - pem. for more information on interactive water management, see e. g. work from j. a. van ast. - ↑ kolkman, m. j. ( 2005 ), controversies in water management : frames and mental models. febodruk bv, enschede, the netherlands - ↑ geldof, g. d. ( 2001 ). omgaan met complexiteit bij integraal waterbeheer, phd thesis, university of twente, the netherlands, tauw bv, deventer - ↑ 3. 0 3. 1 van de graaf, h., and hoppe, r. ( 1996 ). beleid en politiek : een inleiding tot de beleidswetenschap en de beleidskunde coutinho, bussum - ↑ hisschemoller, m., and hoppe, r. ( 2001 ). coping with intractable controversies : the case for problem structuring in policy design and analysis. in : knowledge, power, and participation in environmental policy analysis, m. hisschemoller, r. hoppe, w. n. dunn, and j. r. ravetz, eds., transaction publishers, new brunswick and london, 47 - 72 - ↑ dery, d. ( 1984 ). problem definition in policy analysis, lawrence, kansas : university press of kansas. - ↑ 6. 0 6. 1 6. 2 6. 3 koppenjan, j. f. m., and, e. ( 2004 ). managing uncertainties in networks : a network approach to problem solving and decision making routledge, london [ etc. ] - ↑ 7. 0 7. 1 edelenbos, j., monnikhof, r., and van de riet, o. ( 2003 ). a double helix approach : a proposal to forge a better integration of analysis and policy development. international


receive - only transmission ) or two - way ( telephone channels ). shf - super high frequency ; any radio frequency in the 3, 000 - to 30, 000 - mhz range. shortwave - radio frequencies ( from 1. 605 to 30 mhz ) that fall above the commercial broadcast band and are used for communication over long distances. solidaridad - geosynchronous satellites in mexico ' s system of international telecommunications in the western hemisphere. statsionar - russia ' s geostationary system for satellite telecommunications. submarine cable - a cable designed for service under water. tat - trans - atlantic telephone ; any of a number of high - capacity submarine coaxial telephone cables linking europe with north america. telefax - facsimile service between subscriber stations via the public switched telephone network or the international datel network. telegraph - a telecommunications system designed for unmodulated electric impulse transmission. telex - a communication service involving teletypewriters connected by wire through automatic exchanges. tropospheric scatter - a form of microwave radio transmission in which the troposphere is used to scatter and reflect a fraction of the incident radio waves back to earth ; powerful, highly directional antennas are used to transmit and receive the microwave signals ; reliable over - the - horizon communications are realized for distances up to 600 miles in a single hop ; additional hops can extend the range of this system for very long distances. trunk network - a network of switching centers, connected by multichannel trunk lines. uhf - ultra high frequency ; any radio frequency in the 300 - to 3, 000 - mhz range. vhf - very high frequency ; any radio frequency in the 30 - to 300 - mhz range. source : cia world factbook - unless otherwise noted, information in this page is accurate as of april 17, 2003


- : password hacking : - password cracking is the process of recovering secret passwords from data that has been stored in or transmitted by a computer system. a common approach is to repeatedly try guesses for the password. most passwords can be cracked by using following techniques : 1 ) hashing : - here we will refer to the one way function ( which may be either an encryption function or cryptographic hash ) employed as a hash and its output as a hashed password. if a system uses a reversible function to obscure stored passwords, exploiting that weakness can recover even ' well - chosen ' passwords. one example is the lm hash that microsoft windows uses by default to store user passwords that are less than 15 characters in length. lm hash breaks the password into two 7 - character fields which are then hashed separately, allowing each half to be attacked separately. | | hash functions like sha - 512, sha - 1, and md5 are considered impossible to invert when used correctly. | 2 ) guessing : - many passwords can be guessed either by humans or by sophisticated cracking programs armed with dictionaries ( dictionary based ) and the user ' s personal not surprisingly, many users choose weak passwords, usually one related to themselves in some way. repeated research over some 40 years has demonstrated that around 40 % of user - chosen passwords are readily guessable by programs. examples of insecure choices * blank ( none ) * the word " password ", " passcode ", " admin " and their derivatives * the user ' s name or login name * the name of their significant other or another person ( loved one ) * their birthplace or date of birth * a pet ' s name * a dictionary word in any language * automobile licence plate number * a row of letters from a standard keyboard layout ( eg, the qwerty keyboard - - qwerty itself, asdf, or qwertyuiop ) * a simple modification of one of the preceding, such as suffixing a digit or reversing the order of the letters. and so on.... in one survery of myspace passwords which had been phished, 3. 8 percent of passwords were a single word found in a dictionary, and another 12 percent were a word plus a final digit ; two - thirds of the time that digit was. | | a password containing both uppercase & lowercase characters, numbers and special characters too ; is a strong password and can never 3 ) default


’ s own world of chemistry : “ speaking to many... at the same time. that ’ s what teaching is all about. ” but how does one speak chemical knowledge? chemistry as a study of molecular transformation — the physical actions of atoms colliding, electrons moving in space — is one for which representation in words is inadequate. so chemists draw pictures instead, symbolic codes that inform the basis of chemical thought. the chemical structure, with all its meanings attached, “ enters the conscience of a chemist directly... and the chemist manipulates that little picture mentally in a multiplicity of ways. ” manipulations of these thought - pictures make up underlying concepts in organic chemistry, to which we then can assign terms like “ steric hinderance ” and “ stereochemistry. ” how the chemical structure relates to language, to art, and to modes of thinking are ever - present themes in hoffmann ’ s work. through his exploration of these subjects, we are exposed to a dizzying amount of knowledge about history and philosophy and chemistry. we are taken on a tour that can link derrida ’ s concern with writing to new allotropes of carbon ( geometric arrangements of carbon atoms bonded together ). the examples and references themselves raise provocative questions. take, for example, printing history and its relationship to the structure of the organic compound norbornane, which hoffmann considers in “ representations in chemistry ” : chemistry journals up through the 1950s did not print lines at an angle ( for reasons of cost ), rendering the drawings of chemical structures two - dimensional. the structure of norbornane, a seven carbon molecule with six of its carbons bonded in a ring, was depicted as two connected squares, with a carbon atom at each corner, and the lines of the squares representing their bonds. but the structure of bonding around carbon is tetrahedral — in other words, carbons bonded together as they are in norbornane do not lie on the same plane. the physical structure of norbornane has carbon atoms in three dimensions of space ; these positions affect nonbornane ’ s ability to interact with other atoms, and thus whether and how a chemical transformation can proceed. so understanding the shape of a compound is vitally important for understanding a reaction. but this information gets lost when pictured as a flat figure. and if this presents a challenge to manipulating the thought - picture of norbornane, if the flat image conjured up by the word “ norbornane ” changes how one imagines a chemical reaction occurring, what


when pictured as a flat figure. and if this presents a challenge to manipulating the thought - picture of norbornane, if the flat image conjured up by the word “ norbornane ” changes how one imagines a chemical reaction occurring, what might it suggest about the cognitive process of linguistic relativity, or saussure ’ s ideas about the relationship of word - things? a story about the chemical world unfolds through its symbols, and the story is one that elucidates the principles by which electrons move around, breaking and forming new bonds to make new compounds. this is the narrative that molecular representations are meant to tell. but this is only chemical knowledge, and not the whole story of chemistry itself. the practice, the history, the connections — these other narratives are too often lost when we talk only of the mechanisms and the data and the formulas as what transpires in chemistry. for hoffmann, “ this leads to real crimes against the humanity of the scientist. in order to present a sanitized, pragmatic account of a chemical study, one suppresses many of the truly creative acts. among these are the ‘ fortuitous circumstance ’ — all of the elements of serendipity, of creative intuition at work. ” these elements are always at work in science. a story about the discovery of sucralose, perhaps apocryphal, tells of the graduate student who mistakenly believed that he had been asked to taste rather than to test what he had made. the mistake proved a happy one ( not usually the case when one tastes things one makes in a chemistry lab ) : today sucralose is found ubiquitously as the compound used in many artificial sweeteners. but the discovery makes for a much less interesting retelling when published with the human element omitted. to construct a narrative — why a goes to b, or how to get from a to b — is a natural way to make sense of things. telling the whole story can strengthen connections, or reveal gaps in thinking, and be used to improve what logic is used when we do science. the beauty of narrative is that it simplifies, but therein lies danger too, because what if the world is not simple? “ ockham ’ s razor and chemistry ” and “ how should chemists think? ” are two of hoffmann ’ s finest essays on the nature of thought in science. though we must have the knowledge and acumen to rationalize the world and order our ideas, we must also remember that


” and “ how should chemists think? ” are two of hoffmann ’ s finest essays on the nature of thought in science. though we must have the knowledge and acumen to rationalize the world and order our ideas, we must also remember that the pathways to a conclusion are infinite, the possibilities endless. “ time and again the process of discovery in science reveals that what was thought simple is really wondrously complicated.... but... one should beware of the inherent weaknesses of the beautiful human mind. the most prominent shortcoming is not weak logic, but prejudice, preferring simple solutions. ” we must work to think about how to approach that weakness. for a collection of works that addresses the concerns of audience, logic, and narrative structure within the framework of science, the structure of hoffmann ’ s book is strangely obtuse. the order the editors chose to present these essays gives no sense of coherent narrative or the themes the essays articulate so well. the book is divided into five parts : chemical reasoning and explanation, writing and communication in chemistry, art and science, chemical education, and ethics in science. they are rather shallow categories to divide along, and do not illuminate or build upon hoffmann ’ s insights in a compelling way. true, it is difficult to edit a volume with its contents meant for different audiences — pieces from angewandte chemie, a specialized journal, are reprinted next to ones from social research, and the language in things written for american scientist differs vastly from the language in journal of aesthetics and art criticism. but this is precisely one of the problems hoffmann wants to address. a reader unfamiliar with chemistry would certainly stop after the first few essays, put off by the unfamiliar figures and references, with little reason to care about “ why buy that theory? ” or “ near circular reasoning. ” for those familiar with chemistry, this is perhaps not a problem, and it is easier to approach the many enlightening points in hoffmann ’ s writing. but chemists are always looking for the next step of the chain, building upon a foundation to reach something new. here, excellent foundations are presented, but we are never allowed to make the connections and construct greater ideas from one essay to another, because the logic has been scrambled out of continuity. how the story of science is told to us matters ; because it informs how we think about science, how we practice it, how we advance it, and how human it is. roald hoffmann has done much to reveal and to celebrate the beauty and


gravitational waves were predicted by einstein ' s general theory of relativity, published in 1916. however, although astronomers have indirect evidence of their existence, none have yet been detected directly. uk scientists are at the forefront of the search for these elusive ripples in spacetime, with involvement in two ground - based experiments : the uk / german geo 600 project and the us ligo experiment ( laser interferometer gravitational - wave observatory ). now, uk industry has also been given a major role to play. on wednesday, 23 june, eads astrium in stevenage will be awarded the contract for the lisa pathfinder spacecraft by the european space agency ( esa ). " whilst eads astrium has led most of esa ' s space exploration projects over recent years, such as rosetta, mars express and venus express, this is the first space science contract for many years to be primed from the uk, " said dr. mike healy, uk director for earth observation, navigation and science, eads astrium. " it ' s a fantastic opportunity for our team at stevenage and follows on from similar recent successes like aeolus, an earth science project to provide global measurements of wind speed, and galileo, europe ' s satellite navigation system. " lisa pathfinder is a demonstration mission that is designed to test the advanced technologies required by the esa - nasa laser interferometer space antenna ( lisa ), a complex, multi - spacecraft mission that is scheduled for launch in the first half of the next decade. over a period of at least 2 years, lisa will detect gravitational waves from a variety of compact objects, ranging from massive black holes at great distances from the earth to sub - solar mass white dwarfs - extremely dense, glowing remnants of dead stars - in our galaxy. the mission will consist of three spacecraft flying 5 million kilometres ( 3 million miles ) apart in an equilateral triangle formation. laser beams traveling between the spacecraft will be reflected from two test masses in each satellite. by obtaining extremely accurate measurements of the distance between the spacecraft, it will be possible to determine whether the fabric of spacetime in which they are traveling has been distorted by passing gravitational waves. the formation of 3 spacecraft will face the sun and lie in a plane that is tilted at 60 degrees to the earth ' s orbit. the trio will orbit the sun following 20 degrees behind the earth, and will rotate once per year. this orbital motion will help to detect the direction of each source of gravitational radiation. although lisa will not be affected by vibrations found


stars produce energy through nuclear fusion, producing heavier elements from lighter ones. the heat generated from these reactions prevents gravitational collapse of the star. over time, the star builds up a central core which consists of elements which the temperature at the center of the star is not sufficient to fuse. for main - sequence stars with a mass below approximately 8 solar masses, the mass of this core will remain below the chandrasekhar limit, and they will eventually lose mass ( as planetary nebulae ) until only the core, which becomes a white dwarf, remains. stars with higher mass will develop a degenerate core whose mass will grow until it exceeds the limit. at this point the star will explode in a core - collapse supernova, leaving behind either a neutron star or a black hole. computed values for the limit will vary depending on the approximations used, the nuclear composition of the mass, and the temperature. chandrasekhar, eq. ( 36 ),, eq. ( 58 ),, eq. ( 43 ) gives a value of electron degeneracy pressure is a quantum - mechanical effect arising from the pauli exclusion principle. since electrons are fermions, no two electrons can be in the same state, so not all electrons can be in the minimum - energy level. rather, electrons must occupy a band of energy levels. compression of the electron gas increases the number of electrons in a given volume and raises the maximum energy level in the occupied band. therefore, the energy of the electrons will increase upon compression, so pressure must be exerted on the electron gas to compress it. this is the origin of electron degeneracy pressure. in the nonrelativistic case, electron degeneracy pressure gives rise to an equation of state of the form p = k1ρ5 / 3. solving the hydrostatic equation leads to a model white dwarf which is a polytrope of index 3 / 2 and therefore has radius inversely proportional to the cube root of its mass, and volume inversely proportional to its mass. as the mass of a model white dwarf increases, the typical energies to which degeneracy pressure forces the electrons are no longer negligible relative to their rest masses. the velocities of the electrons approach the speed of light, and special relativity must be taken into account. in the strongly relativistic limit, we find that the equation of state takes the form p = k2ρ4 / 3. this will yield a polytrope of index 3


of light, and special relativity must be taken into account. in the strongly relativistic limit, we find that the equation of state takes the form p = k2ρ4 / 3. this will yield a polytrope of index 3, which will have a total mass, mlimit say, depending only on k2. for a fully relativistic treatment, the equation of state used will interpolate between the equations p = k1ρ5 / 3 for small ρ and p = k2ρ4 / 3 for large ρ. when this is done, the model radius still decreases with mass, but becomes zero at mlimit. this is the chandrasekhar limit. the curves of radius against mass for the non - relativistic and relativistic models are shown in the graph. they are colored blue and green, respectively. μe has been set equal to 2. radius is measured in standard solar radii or kilometers, and mass in standard solar masses. a more accurate value of the limit than that given by this simple model requires adjusting for various factors, including electrostatic interactions between the electrons and nuclei and effects caused by nonzero temperature. lieb and yau have given a rigorous derivation of the limit from a relativistic many - particle schrodinger equation. in 1926, the british physicist ralph h. fowler observed that the relationship between the density, energy and temperature of white dwarfs could be explained by viewing them as a gas of nonrelativistic, non - interacting electrons and nuclei which obeyed fermi - dirac statistics. this fermi gas model was then used by the british physicist e. c. stoner in 1929 to calculate the relationship between the mass, radius, and density of white dwarfs, assuming them to be homogenous spheres. wilhelm anderson applied a relativistic correction to this model, giving rise to a maximum possible mass of approximately 1. 37 kg. in 1930, stoner derived the internal energy - density equation of state for a fermi gas, and was then able to treat the mass - radius relationship in a fully relativistic manner, giving a limiting mass of approximately ( for μe = 2. 5 ) 2. 19 · 1030 kg. stoner went on to derive the pressure - density equation of state, which he published in 1932. these equations of state were also previously published by the russian physicist yakov frenkel in 1928, together with some other remarks on the physics of de


jan. 19, 2007 researchers at the university of rochester have made an optics breakthrough that allows them to encode an entire image ' s worth of data into a photon, slow the image down for storage, and then retrieve the image intact. while the initial test image consists of only a few hundred pixels, a tremendous amount of information can be stored with the new technique. the image, a " ur " for the university of rochester, was made using a single pulse of light and the team can fit as many as a hundred of these pulses at once into a tiny, four - inch cell. squeezing that much information into so small a space and retrieving it intact opens the door to optical buffering - - storing information as light. " it sort of sounds impossible, but instead of storing just ones and zeros, we ' re storing an entire image, " says john howell, associate professor of physics and leader of the team that created the device, which is revealed in today ' s online issue of the journal physical review letters. " it ' s analogous to the difference between snapping a picture with a single pixel and doing it with a camera - - this is like a 6 - megapixel camera. " " you can have a tremendous amount of information in a pulse of light, but normally if you try to buffer it, you can lose much of that information, " says ryan camacho, howell ' s graduate student and lead author on the article. " we ' re showing it ' s possible to pull out an enormous amount of information with an extremely high signal - to - noise ratio even with very low light levels. " optical buffering is a particularly hot field right now because engineers are trying to speed up computer processing and network speeds using light, but their systems bog down when they have to convert light signals to electronic signals to store information, even for a short while. " the parallel amount of information john has sent all at once in an image is enormous in comparison to what anyone else has done before. " howell ' s group used a completely new approach that preserves all the properties of the pulse. the buffered pulse is essentially a perfect original ; there is almost no distortion, no additional diffraction, and the phase and amplitude of the original signal are all preserved. howell is even working to demonstrate that quantum entanglement remains unscathed. to produce the ur image, howell simply shone a beam of light through a stencil with the u and r etched out. anyone who has made shadow puppets knows how


howell is even working to demonstrate that quantum entanglement remains unscathed. to produce the ur image, howell simply shone a beam of light through a stencil with the u and r etched out. anyone who has made shadow puppets knows how this works, but howell turned down the light so much that a single photon was all that passed through the stencil. quantum mechanics dictates some strange things at that scale, so that bit of light could be thought of as both a particle and a wave. as a wave, it passed through all parts of the stencil at once, carrying the " shadow " of the ur with it. the pulse of light then entered a four - inch cell of cesium gas at a warm 100 degrees celsius, where it was slowed and compressed, allowing many pulses to fit inside the small tube at the same time. " the parallel amount of information john has sent all at once in an image is enormous in comparison to what anyone else has done before, " says alan willner, professor of electrical engineering at the university of southern california and president of the ieee lasers and optical society. " to do that and be able to maintain the integrity of the signal - - it ' s a wonderful achievement. " howell has so far been able to delay light pulses 100 nanoseconds and compress them to 1 percent of their original length. he is now working toward delaying dozens of pulses for as long as several milliseconds, and as many as 10, 000 pulses for up to a nanosecond. " now i want to see if we can delay something almost permanently, even at the single photon level, " says howell. " if we can do that, we ' re looking at storing incredible amounts of information in just a few photons. " other social bookmarking and sharing tools : note : materials may be edited for content and length. for further information, please contact the source cited above. note : if no author is given, the source is cited instead.


a mapreduce program comprises a map ( ) procedure that performs filtering and sorting ( such as sorting students by first name into queues, one queue for each name ) and a reduce ( ) procedure that performs a summary operation ( such as counting the number of students in each queue, yielding name frequencies ). the " mapreduce system " ( also called " infrastructure ", " framework " ) orchestrates by marshaling the distributed servers, running the various tasks in parallel, managing all communications and data transfers between the various parts of the system, providing for redundancy and failures, and overall management of the whole process. mapreduce libraries have been written in many programming languages. a popular free implementation is apache hadoop. the name mapreduce originally referred to the proprietary google technology and has since been genericized. mapreduce is a framework for processing parallelizable problems across huge datasets using a large number of computers ( nodes ), collectively referred to as a cluster ( if all nodes are on the same local network and use similar hardware ) or a grid ( if the nodes are shared across geographically and administratively distributed systems, and use more heterogenous hardware ). computational processing can occur on data stored either in a filesystem ( unstructured ) or in a database ( structured ). mapreduce can take advantage of locality of data, processing data on or near the storage assets to decrease transmission of data. the first complete end - to - end framework for mapreduce on top of apache hadoop was done within the advanced research group of unisys under dr. sumeet malhotra. " map " step : the master node takes the input, divides it into smaller sub - problems, and distributes them to worker nodes. a worker node may do this again in turn, leading to a multi - level tree structure. the worker node processes the smaller problem, and passes the answer back to its master node. " reduce " step : the master node then collects the answers to all the sub - problems and combines them in some way to form the output – the answer to the problem it was originally trying to solve. mapreduce allows for distributed processing of the map and reduction operations. provided each mapping operation is independent of the others, all maps can be performed in parallel – though in practice it is limited by the number of independent data sources and / or the number of cpus near each source. similarly, a set of ' reducers ' can perform the reduction phase - provided all outputs of


word : a word / / partialcounts : a list of aggregated partial counts sum = 0 for each pc in partialcounts : sum + = parseint ( pc ) emit ( word, sum ) here, each document is split into words, and each word is counted by the map function, using the word as the result key. the framework puts together all the pairs with the same key and feeds them to the same call to reduce, thus this function just needs to sum all of its input values to find the total appearances of that word. as another example, imagine that for a database of 1. 1 billion people, one would like to compute the average number of social contacts a person has according to age. in sql such a query could be expressed as : select age as y, avg ( contacts ) as a from social. person group by age order by age using mapreduce, the k1 key values could be the integers 1 through 1, 100, each representing a batch of 1 million records, the k2 key value could be a person ’ s age in years, and this computation could be achieved using the following functions : function map is input : integer k1 between 1 and 1100, representing a batch of 1 million social. person records for each social. person record in the k1 batch do let y be the person ' s age let n be the number of contacts the person has produce one output record < y, n > repeat end function function reduce is input : age ( in years ) y for each input record < y, n > do accumulate in s the sum of n accumulate in c the count of records so far repeat let a be s / c produce one output record < y, a > end function the mapreduce system would line up the 1, 100 map processors, and would provide each with its corresponding 1 million input records. the map step would produce 1. 1 billion < y, n > records, with y values ranging between, say, 8 and 103. the mapreduce system would then line up the 96 reduce processors by performing shuffling operation of the key / value pairs due to the fact that we need average per age, and provide each with its millions of corresponding input records. the reduce step would result in the much reduced set of only 96 output records < y, a >, which would be put in the final result file, sorted by y. the frozen part of the mapreduce framework is a large distributed sort. the hot spots, which the


materials scientists develop and test new materials that do certain jobs better than existing materials, or are easier or cheaper to make. scientists use their knowledge of how molecules form to combine atoms in new ways. they also apply heat and pressure to existing materials to create materials with new properties. they can even create materials with smart properties that respond to their environment. in freezing conditions, climbers need clothes that are extremely warm and lightweight, so they can move easily. aerogel is a new, super - light insulating material used to line extreme weather coats. it is made from silicon dioxide, the same material that glass is made from. however, aerogel is 99 per cent air, so it is 1, 000 times less dense than glass. one of the lightest substances on earth, aerogel can even float on air in its pure form. it also has amazing insulation properties and can protect skin from the heat of a blowtorch. aerogel is made by mixing a silicon compound with other chemicals to make a wet gel. the gel is dried at a high temperature and pressure. nasa has used cells of aerogel on a spacecraft called stardust to collect dust from a comet called wild 2. the comet dust collector contains rectangular cells, which are lined with aerogel. the panels of aerogel cells are placed into position on stardust. the spongy texture of aerogel means that comet dust particles travelling at six times the speed of a bullet can be slowed down and captured without being squashed or altered. stardust reached comet wild 2 in january 2004. the dust collector has trapped grains of comet dust the size of a grain of sand. by studying the particles, scientists hope to learn more about comets and the early solar system. this prototype computer is made from a fabric that conducts electricity. the fabric, called elektex™, contains fibres that have a thin coating of silver or copper – these metals are good electrical conductors. microchips woven into the fabric translate the electrical impulses from the fibres into digital data, which can be viewed on the computer ’ s screen. prototype mobile phones made from elektex™ are lightweight and water - resistant. they can also be folded up and crumpled without breaking. these properties make them a lot more hard - wearing than traditional mobile phones. a smart material senses a change to its environment and responds by altering in some way. each type of smart material has a different property that changes, such as stiffness, colour, shape, or conductivity ( ability to conduct electricity ).


especially for long distance transportation. ( dw : the horns of nimon ) the shalka were able to convert black holes into wormholes for them to travel through. to dispose of waste as well as enemies, the shalka can change the wormhole back into a black hole. ( wc : scream of the shalka ) during the year that never happened, the master created a fleet of toclafane rockets, each holding a black hole converter so that he could activate all of them and destroy earth. the rockets did, however, fade away when time was reversed. ( dw : last of the time lords ) a quantum singularity, or black hole, is an incredibly dense remnant of a star which has collapsed in on itself with such a force of gravity it pulls in everything in the electromagnetic spectrum, including light. the formation of a black hole could sometimes be observed in a supernova. people in the federation sometimes referred to them as hawking black holes after the 20th century earth scientist, professor stephen hawking. ( tos novel : the entropy effect ) the uss voyager became trapped by a black hole in the year 2371 where they experienced both unusual temporal as well as spatial distortions. they were, however, able to to escape through the use of dekyon beams to open a hole in the event horizon. ( voy episode : " parallax " ) as early as the 2260s, starfleet had been using artificial quantum singularities as power sources, though only in a limited number of ships and planetary defense systems, and under license. this technology, though, did make its way into other vessels, such as the rigellian registry vessel queen mary. ( tos novel : prime directive ) planetary based versions were known as singularity plants. ( tng video game : birth of the federation ) by the mid 24th century, the romulan star empire used artificial quantum singularities to power the warp cores of their starships, including the massive d ' deridex - class warbirds. sometimes these quantum singularities were detectable by sensors. ( tng episode : " timescape ", ds9 episode : " visionary " ) similarly, the ancient communication relay in the delta quadrant was powered by an artificial quantum singularity. ( voy episode : " hunter " ) also, scientists at the mertens orbital research station drew inspiration from the romulans and had created a singularity as part of a complex power source in the station. ( tng video game : a final unity )


better meets cost, performance, and other constraints. no physical prototype need be created until the design nears completion, allowing hundreds or thousands of designs to be evaluated, instead of a relative few. in addition, cae analysis programs can model complicated physical phenomena which cannot be solved by hand, such as viscoelasticity, complex contact between mating parts, or non - newtonian flows. as mechanical engineering begins to merge with other disciplines, as seen in mechatronics, multidisciplinary design optimization ( mdo ) is being used with other cae programs to automate and improve the iterative design process. mdo tools wrap around existing cae processes, allowing product evaluation to continue even after the analyst goes home for the day. they also utilize sophisticated optimization algorithms to more intelligently explore possible designs, often finding better, innovative solutions to difficult multidisciplinary design problems. the field of mechanical engineering can be thought of as a collection of many mechanical engineering science disciplines. several of these subdisciplines which are typically taught at the undergraduate level are listed below, with a brief explanation and the most common application of each. some of these subdisciplines are unique to mechanical engineering, while others are a combination of mechanical engineering and one or more other disciplines. most work that a mechanical engineer does uses skills and techniques from several of these subdisciplines, as well as specialized subdisciplines. specialized subdisciplines, as used in this article, are more likely to be the subject of graduate studies or on - the - job training than undergraduate research. several specialized subdisciplines are discussed in this section. mechanics is, in the most general sense, the study of forces and their effect upon matter. typically, engineering mechanics is used to analyze and predict the acceleration and deformation ( both elastic and plastic ) of objects under known forces ( also called loads ) or stresses. subdisciplines of mechanics include - statics, the study of non - moving bodies under known loads, how forces affect static bodies - dynamics ( or kinetics ), the study of how forces affect moving bodies - mechanics of materials, the study of how different materials deform under various types of stress - fluid mechanics, the study of how fluids react to forces - kinematics, the study of the motion of bodies ( objects ) and systems ( groups of objects ), while ignoring the forces that cause the motion. kinematics is often used in the design and analysis of mechanisms.


fluids react to forces - kinematics, the study of the motion of bodies ( objects ) and systems ( groups of objects ), while ignoring the forces that cause the motion. kinematics is often used in the design and analysis of mechanisms. - continuum mechanics, a method of applying mechanics that assumes that objects are continuous ( rather than discrete ) mechanical engineers typically use mechanics in the design or analysis phases of engineering. if the engineering project were the design of a vehicle, statics might be employed to design the frame of the vehicle, in order to evaluate where the stresses will be most intense. dynamics might be used when designing the car ' s engine, to evaluate the forces in the pistons and cams as the engine cycles. mechanics of materials might be used to choose appropriate materials for the frame and engine. fluid mechanics might be used to design a ventilation system for the vehicle ( see hvac ), or to design the intake system for the engine. mechatronics and robotics mechatronics is an interdisciplinary branch of mechanical engineering, electrical engineering and software engineering that is concerned with integrating electrical and mechanical engineering to create hybrid systems. in this way, machines can be automated through the use of electric motors, servo - mechanisms, and other electrical systems in conjunction with special software. a common example of a mechatronics system is a cd - rom drive. mechanical systems open and close the drive, spin the cd and move the laser, while an optical system reads the data on the cd and converts it to bits. integrated software controls the process and communicates the contents of the cd to the computer. robotics is the application of mechatronics to create robots, which are often used in industry to perform tasks that are dangerous, unpleasant, or repetitive. these robots may be of any shape and size, but all are preprogrammed and interact physically with the world. to create a robot, an engineer typically employs kinematics ( to determine the robot ' s range of motion ) and mechanics ( to determine the stresses within the robot ). robots are used extensively in industrial engineering. they allow businesses to save money on labor, perform tasks that are either too dangerous or too precise for humans to perform them economically, and to ensure better quality. many companies employ assembly lines of robots, especially in automotive industries and some factories are so robotized that they can run by themselves. outside the factory, robots have been employed in bomb disposal, space exploration, and many other fields. robots are also sold for various residential applications, from recreation


, especially in automotive industries and some factories are so robotized that they can run by themselves. outside the factory, robots have been employed in bomb disposal, space exploration, and many other fields. robots are also sold for various residential applications, from recreation to domestic applications. structural analysis structural analysis is the branch of mechanical engineering ( and also civil engineering ) devoted to examining why and how objects fail and to fix the objects and their performance. structural failures occur in two general modes : static failure, and fatigue failure. static structural failure occurs when, upon being loaded ( having a force applied ) the object being analyzed either breaks or is deformed plastically, depending on the criterion for failure. fatigue failure occurs when an object fails after a number of repeated loading and unloading cycles. fatigue failure occurs because of imperfections in the object : a microscopic crack on the surface of the object, for instance, will grow slightly with each cycle ( propagation ) until the crack is large enough to cause ultimate failure. failure is not simply defined as when a part breaks, however ; it is defined as when a part does not operate as intended. some systems, such as the perforated top sections of some plastic bags, are designed to break. if these systems do not break, failure analysis might be employed to determine the cause. structural analysis is often used by mechanical engineers after a failure has occurred, or when designing to prevent failure. engineers often use online documents and books such as those published by asm to aid them in determining the type of failure and possible causes. structural analysis may be used in the office when designing parts, in the field to analyze failed parts, or in laboratories where parts might undergo controlled failure tests. thermodynamics and thermo - science thermodynamics is an applied science used in several branches of engineering, including mechanical and chemical engineering. at its simplest, thermodynamics is the study of energy, its use and transformation through a system. typically, engineering thermodynamics is concerned with changing energy from one form to another. as an example, automotive engines convert chemical energy ( enthalpy ) from the fuel into heat, and then into mechanical work that eventually turns the wheels. thermodynamics principles are used by mechanical engineers in the fields of heat transfer, thermofluids, and energy conversion. mechanical engineers use thermo - science to design engines and power plants, heating, ventilation, and air - conditioning ( hvac ) systems, heat exchangers, heat sinks


fields of heat transfer, thermofluids, and energy conversion. mechanical engineers use thermo - science to design engines and power plants, heating, ventilation, and air - conditioning ( hvac ) systems, heat exchangers, heat sinks, radiators, refrigeration, insulation, and others. design and drafting drafting or technical drawing is the means by which mechanical engineers design products and create instructions for manufacturing parts. a technical drawing can be a computer model or hand - drawn schematic showing all the dimensions necessary to manufacture a part, as well as assembly notes, a list of required materials, and other pertinent information. a u. s. mechanical engineer or skilled worker who creates technical drawings may be referred to as a drafter or draftsman. drafting has historically been a two - dimensional process, but computer - aided design ( cad ) programs now allow the designer to create in three dimensions. instructions for manufacturing a part must be fed to the necessary machinery, either manually, through programmed instructions, or through the use of a computer - aided manufacturing ( cam ) or combined cad / cam program. optionally, an engineer may also manually manufacture a part using the technical drawings, but this is becoming an increasing rarity, with the advent of computer numerically controlled ( cnc ) manufacturing. engineers primarily manually manufacture parts in the areas of applied spray coatings, finishes, and other processes that cannot economically or practically be done by a machine. drafting is used in nearly every subdiscipline of mechanical engineering, and by many other branches of engineering and architecture. three - dimensional models created using cad software are also commonly used in finite element analysis ( fea ) and computational fluid dynamics ( cfd ). frontiers of research mechanical engineers are constantly pushing the boundaries of what is physically possible in order to produce safer, cheaper, and more efficient machines and mechanical systems. some technologies at the cutting edge of mechanical engineering are listed below ( see also exploratory engineering ). micro electro - mechanical systems ( mems ) micron - scale mechanical components such as springs, gears, fluidic and heat transfer devices are fabricated from a variety of substrate materials such as silicon, glass and polymers like su8. examples of mems components are the accelerometers that are used as car airbag sensors, modern cell phones, gyroscopes for precise positioning and microfluidic devices used in biomedical applications. friction stir welding ( fsw ) friction stir welding, a new type of welding, was discovered


are used as car airbag sensors, modern cell phones, gyroscopes for precise positioning and microfluidic devices used in biomedical applications. friction stir welding ( fsw ) friction stir welding, a new type of welding, was discovered in 1991 by the welding institute ( twi ). the innovative steady state ( non - fusion ) welding technique joins materials previously un - weldable, including several aluminum alloys. it plays an important role in the future construction of airplanes, potentially replacing rivets. current uses of this technology to date include welding the seams of the aluminum main space shuttle external tank, orion crew vehicle test article, boeing delta ii and delta iv expendable launch vehicles and the spacex falcon 1 rocket, armor plating for amphibious assault ships, and welding the wings and fuselage panels of the new eclipse 500 aircraft from eclipse aviation among an increasingly growing pool of uses. composites or composite materials are a combination of materials which provide different physical characteristics than either material separately. composite material research within mechanical engineering typically focuses on designing ( and, subsequently, finding applications for ) stronger or more rigid materials while attempting to reduce weight, susceptibility to corrosion, and other undesirable factors. carbon fiber reinforced composites, for instance, have been used in such diverse applications as spacecraft and fishing rods. mechatronics is the synergistic combination of mechanical engineering, electronic engineering, and software engineering. the purpose of this interdisciplinary engineering field is the study of automation from an engineering perspective and serves the purposes of controlling advanced hybrid systems. at the smallest scales, mechanical engineering becomes nanotechnology — one speculative goal of which is to create a molecular assembler to build molecules and materials via mechanosynthesis. for now that goal remains within exploratory engineering. areas of current mechanical engineering research in nanotechnology include nanofilters, nanofilms, and nanostructures, among others. finite element analysis this field is not new, as the basis of finite element analysis ( fea ) or finite element method ( fem ) dates back to 1941. but evolution of computers has made fea / fem a viable option for analysis of structural problems. many commercial codes such as ansys, nastran and abaqus are widely used in industry for research and design of components. calculix is an open source and free finite element program. some 3d modeling and cad software packages have added fea modules. other techniques such as finite difference method ( f


- biomedical optics & medical imaging - defense & security - electronic imaging & signal processing - illumination & displays - lasers & sources - micro / nano lithography - optical design & engineering - optoelectronics & communications - remote sensing - sensing & measurement - solar & alternative energy - sign up for newsroom e - alerts - information for : using a nano light source to investigate small - scale composite materials a new raman spectroscopy technique reveals both the chemical composition and spatial resolution of nanomaterials. 12 march 2008, spie newsroom. doi : 10. 1117 / 2. 1200802. 1070 we are currently witnessing a strong trend toward developing artificial materials with nanoscale structures. for example, single - walled carbon nanotubes ( swnts ) doped with organic molecules are useful for controlling electrical conductivity, optical switching, and nonlinear media. 1 – 3 because such materials consist of two or more different molecular components ( hence the term ‘ nanocomposites ’ ), characterizing them requires a technique that combines chemical analysis with nanometer - scale spatial resolution. a variety of methods exist for investigating and characterizing nanoscale structures, but few are suitable for molecular analysis. for instance, transmission electron microscopy enables visualization of objects inside swnts, 4 but it cannot identify molecular species. one alternative is vibrational spectroscopy, including raman spectroscopy. in addition to molecular identification, vibrational energy analysis provides detailed structural information for each species, such as intermolecular interactions, molecular orientation, and symmetry distortions. 5 this makes raman spectroscopy a powerful tool for studying the chemical composition of matter. by the same token, conventional confocal raman spectroscopy techniques cannot attain spatial resolution on the nanoscale. we have overcome this limitation through an approach we call tip - enhanced raman spectroscopy ( ters ). by introducing a sharp metal tip to the focus of a laser beam, we were able to localize raman excitation to an area of 30nm2. 6, 7 the apex acts as a nanoscale light source, which couples with surface plasmon polaritons ( charge density waves propagating along the metal surface ) to increase both the incident light field and the raman scattering signal. to demonstrate the technique we used samples of β−carotene encapsulated in swnts. 8 figure 1 shows a schematic experimental setup for ters. the optical layout is a combination of raman spectroscopy and scanning probe microscopy. ters


the technique we used samples of β−carotene encapsulated in swnts. 8 figure 1 shows a schematic experimental setup for ters. the optical layout is a combination of raman spectroscopy and scanning probe microscopy. ters profiles were measured using a silver tip positioned close to the sample, and reference spectra were also obtained at the same position without the silver tip. the detailed experimental setup has been described elsewhere. 8 figure 2 ( a ) shows atomic force microscopy images of the samples. although the images appear to be of single tubes, they are actually bundles of several tens of tubes aligned parallel to each other, as shown by the 15nm average heights of the samples detected. we chose two different bundles that were completely separated. the crosses ( a – g ) indicate the position of the tip during the ters, which was performed in 100nm steps along the bundles. figure 1. schematic illustration of the experimental setup. the inset shows β - carotene molecules encapsulated in carbon nanotubes. figure 2. ( a ) atomic force microscopy image of β−carotene−encapsulated carbon nanotubes. the scale bars indicate 50nm. ( b ) near−field spectra of the sample measured at positions a – g, respectively. figure 2 ( b ) shows near−field raman spectra of the difference between having the silver tip in contact with the sample and without the tip. spectra a – g correspond to the sample positions in figure 2 ( a ). the interesting feature of raman spectroscopy is that we can simultaneously obtain data from the swnts and β−carotene. figure 2 ( b ) illustrates the frequency region, including both ν1 ( 1523cm−1 conjugated c = c mode ) from β - carotene and the g - band ( 1592cm - 1 graphite mode ) from carbon nanotubes. the most predominant feature among the spectra a – g is the absence of the encapsulated β−carotene in spectrum f. this means that the rate of encapsulation of β−carotene in the swnts was not uniform. the extremely low rate at position f could have occurred if the tubes were twisted during encapsulation or were filled with impurities. another feature is that in spectrum c, the intensity of encapsulated β−carotene is higher compared with other spectra. figure 2 ( a ) shows the presence of another thin bundle entangled with


##ation or were filled with impurities. another feature is that in spectrum c, the intensity of encapsulated β−carotene is higher compared with other spectra. figure 2 ( a ) shows the presence of another thin bundle entangled with a thicker one. this example demonstrates that ters is useful for avoiding the averaging of raman spectra of nanocomposite materials that are not spatially uniform. the principle of this method is to use tip enhancement, which provides both spectral and topological information. this technique can be applied not only to surfaces but also to molecules enclosed inside nanostructures. frontier research center yuika saito has carried out basic and applied research in near - field raman spectroscopy at riken ( institute of physical and chemical research ) and osaka university since 2003. nanotechnology research institute national institute of advanced industrial science and technology ( aist ) kazuhiro yanagi has carried out fundamental research on swnts and nanocomposite materials at aist since 2005. 1. t. takenobu, t. takano, m. shiraishi, y. murakami, m. ata, h. kataura, y. achiba, y. iwasa, stable and controlled amphoteric doping by encapsulation of organic molecules inside carbon nanotubes, nat. mater. 2, no. 10, pp. 683 - 688, 2003. doi : 10. 1038 / nmat976 3. k. yanagi, k. iakoubovskii, s. kazaoui, n. minami, y. maniwa, y. miyata, h. kataura, light - harvesting function of beta - carotene inside carbon nanotubes, phys. rev. b 74, no. 15, pp. 155420, 2006. doi : 10. 1103 / physrevb. 74. 155420 8. y. saito, k. yanagi, n. hayazawa, k. ishitobi, a. ono, h. kataura, s. kawata, tip - enhanced raman spectroscopy of organic molecules encapsulated in carbon nanotubes, jap. j. appl. phys. 45, no. 12, pp. 9286 - 9289, 2006. doi : 10. 1143 / jjap. 45. 9286


a strange new family of algorithms probes the boundary between easy and hard problems why are some computational problems so hard and others easy? this may sound like a childish, whining question, to be dismissed with a shrug or a wisecrack, but if you dress it up in the fancy jargon of computational complexity theory, it becomes quite a serious and grownup question : is p equal to np? an answer — accompanied by a proof — will get you a million bucks from the clay mathematics institute. i ' ll return in a moment to p and np, but first an example, which offers a glimpse of the mystery lurking beneath the surface of hard and easy problems. consider a mathematical graph, a collection of vertices ( represented by dots ) and edges ( lines that connect the dots ). here ' s a nicely symmetrical example : is it possible to construct a path that traverses each edge exactly once and returns to the starting point? for any graph with a finite number of edges, we could answer such a question by brute force : simply list all possible paths and check to see whether any of them meet the stated conditions. but there ' s a better way. in 1736 leonhard euler proved that the desired path ( now called an eulerian circuit ) exists if and only if every vertex is the end point of an even number of edges. we can check whether a graph has this property without any laborious enumeration of pathways. now take the same graph and ask a slightly different question : is there a circuit that passes through every vertex exactly once? this problem was posed in 1858 by william rowan hamilton, and the path is called a hamiltonian circuit. again we can get the answer by brute force. but in this case there is no trick like euler ' s ; no one knows any method that gives the correct answer for all graphs and does so substantially quicker than exhaustive search. superficially, the two problems look almost identical, but hamilton ' s version is far harder. why? is it because no shortcut solution exists, or have we not yet been clever enough to find one? most computer scientists and mathematicians believe that hamilton ' s problem really is harder, and no shortcut algorithm will ever be found — but that ' s just a conjecture, supported by experience and intuition but not by proof. contrarians argue that we ' ve hardly begun to explore the space of all possible algorithms, and new problem - solving techniques could turn up at any time. before 1736, the eulerian - circuit problem also looked


the process by which one signal is used to modify another. the controlled signal is referred to as the ’ carrier ’, and the controlling signal as the ’ modulator ’. it is of the greatest importance in both sound synthesis and signal processing. the two main parameters of a sound to which modulation is commonly applied are those of amplitude ( loudness ) and frequency. amplitude modulation of a signal causes changes in loudness in that signal. if the control signal is a slow regular waveform ( e. g. a sine wave ) the result is a tremolo - similar to ( and often confused with ) vibrato, except that there is no pitch deviation. once the frequency of the modulator is raised above 10 to 15 hz the tremolo amalgamates into a complex sound with added frequency components derived from the pitches of carrier and modulator. an irregular or transient control signal is generally associated with envelope generation. frequency modulation causes the pitch of the carrier to rise and fall according to the shape of the modulating waveform. if this is, as above, a slow regular waveform, the result is vibrato if the depth of the modulation is low, otherwise becoming a wide siren - like effect. if the modulating waveform is a series of discrete steps, the result is a series of discrete pitches. particularly complex sounds arise when the frequency of the modulator is close to or even higher than that of the carrier. ( source - richard dobson ( 1992 ). a dictionary of electronic and computer music technology. oxford university press. ) ring modulation allows for the sum and difference of two input frequencies to be combined to create a new sound. often one of these frequencies is at a sub - audio level allowing the creation of a sound of two similar frequencies, frequently with noisy textural characteristics. see also : amplitude, frequency, frequency modulation synthesis


< storage > ( or " magtape ", " tape " - paper tape is now obsolete ) a data storage medium consisting of a magnetisable oxide coating on a thin plastic strip, commonly used for backup and archiving. early industry - standard magnetic tape was half an inch wide and wound on removable reels 10. 5 inches in diameter. different lengths were available with 2400 feet and 4800 feet being common. dectape was a variation on this " round tape ". in modern magnetic tape systems the reels are much smaller and are fixed inside a cartridge to protect the tape and for ease of handling ( " square tape " - though it ' s really rectangular ). cartridge formats include qic, dat, and exabyte. tape is read and written on a tape drive ( or " deck " ) which winds the tape from one reel to the other causing it to move past a read / write head. early tape had seven parallel tracks of data along the length of the tape allowing six bit characters plus parity written across the tape. a typical recording density was 556 characters per inch. the tape had reflective marks near its end which signaled beginning of tape ( bot ) and end of tape ( eot ) to the hardware. data is written to tape in blocks with inter - block gaps between them. each block is typically written in a single operation with the tape running continuously during the write. the larger the block the larger the data buffer required in order to supply or receive the data written to or read from the tape. the smaller the block the more tape is wasted as inter - block gaps. several logical records may be combined into one physical block to reduce wastage ( " blocked records " ). finding a certain block on the tape generally involved reading sequentially from the beginning, in contrast to magnetic disks. tape is not suitable for random access. the exception to this is that some systems allow tape marks to be written which can be detected while winding the tape forward or rewinding it at high speed. these are typically used to separate logical files on a tape. most tape drives now include some kind of data compression. there are several algorithms which provide similar results : lz ( most ), idrc ( exabyte ), aldc ( ibm, qic ) and dlz1 ( dlt ). see also cut a tape, flap, group code recording, spool, macrotape, microtape, non return to zero inverted, phase encoded.


errorin statistics an error is a difference between a computed, estimated, or measured value and the true, specified, or theoretically correct value. see also error function. in engineering an error is a difference between desired and actual performance. engineers often seek to design systems in such a way as to mitigate or even avoid the effects of error. in telecommunication, an error is a deviation from a correct value caused by a malfunction in a system or a functional unit. an example would be the occurrence of a wrong bit caused by an equipment malfunction. ( sources : federal standard 1037c and mil - std - 188 ) in linguistics, an individual language user ' s deviations from standard language paradigms are sometimes referred to as errors. at present, this usage is not widely used, as it connotes a value judgement about what what linguistic forms should and should not be used, something many modern linguists seek to avoid. in biology, an error is said to occur when perfect fidelity is lost in the copying of information. for example, in an asexually reproducing species, an error has occurred for each dna nucleotide that differs between the child and the parent. errors in this sense are not judged as " good " or " bad ", although an error may make an organism either more or less adapted to its environment. in baseball an error is judged by the official scorer when a runner advances a base because of a fielding mistake ; perfect play would have prevented the advancement ; and the mistake was physical. mental misjudgements are not errors. failing to get more than one out on given play is not an error. the enforcment of this rule is necessarily subjective.


new graphene - based material could revolutionise electronics industry 30 april 2012 the most transparent, lightweight and flexible material ever for conducting electricity has been invented by a team from the university of exeter. called graphexeter, the material could revolutionise the creation of wearable electronic devices, such as clothing containing computers, phones and mp3 players. graphexeter could also be used for the creation of ‘ smart ’ mirrors or windows, with computerised interactive features. since this material is also transparent over a wide light spectrum, it could enhance by more than 30 % the efficiency of solar panels. adapted from graphene, graphexeter is much more flexible than indium tin oxide ( ito ), the main conductive material currently used in electronics. ito is becoming increasingly expensive and is a finite resource, expected to run out in 2017. at just one - atom - thick, graphene is the thinnest substance capable of conducting electricity. it is very flexible and is one of the strongest known materials. the race has been on for scientists and engineers to adapt graphene for flexible electronics. this has been a challenge because of its sheet resistance, which limits its conductivity. until now, no - one has been able to produce a viable alternative to ito. to create graphexeter, the exeter team sandwiched molecules of ferric chloride between two layers of graphene. ferric chloride enhances the electrical conductivity of graphene, without affecting the material ’ s transparency. the material was produced by a team from the university of exeter ’ s centre for graphene science. the research team is now developing a spray - on version of graphexeter, which could be applied straight onto fabrics, mirrors and windows. lead researcher, university of exeter engineer dr. monica craciun said : “ graphexeter could revolutionise the electronics industry. it outperforms any other carbon - based transparent conductor used in electronics and could be used for a range of applications, from solar panels to ‘ smart ’ t - shirts. we are very excited about the potential of this material and look forward to seeing where it can take the electronics industry in the future. ” the centre for graphene science brings together the universities of exeter and bath in internationally leading research in graphene. the centre is bridging the gap between the scientific development and industrial application of this revolutionary new technology. this research was funded by the epsrc and royal society. contact details and archive...


new infrared camera delivers significantly better resolution by grant banks december 12, 2010 researchers at northwestern university have developed a new infrared imaging system that delivers a 16 - fold increase in resolution over long wavelength infrared radiation ( lwir ) cameras currently used in industrial, security and nighttime surveillance applications. based on a type of semiconductor called a type - ii inas / gasb superlattice, the ir camera is mercury - free, more robust, cheaper to produce and can collect 78 percent of the light showing temperature differences as small as 0. 02° c. superlattices, or quantum well structures as they are also known, have been known about for many years, but it has taken until now for the materials to be better understood and utilized. superlattices are a layered periodic structure of two or more semiconducting elements each with a thickness of only a couple of nanometers. they are thermal conductors that use photon diffusion and scattering to determine heat variations. superlattices are broken into three types according to their chemical composition with type - ii formed from layers of indium ( in ), arsenic ( as ), gallium ( ga ) and antinomy ( sb ). " type - ii [ superlattice ] is a very interesting and promising new material for infrared detection, " professor manijeh razeghi from the center for quantum devices in the mccormick school of engineering and applied science said. " everything is there to support its future : the beautiful physics, the practicality of experimental realization of the material. it has just taken time to prove itself, but now, the time has come. " using the type - ii inas / gasb superlattices as an alternative to existing lwir cameras the researchers have been able to achieve a 16 - fold increase in the number of pixels in an ir image. current lwir cameras are based on mercury cadmium telluride ( mct ) materials, but the type - ii superlattice is mercury - free, more durable, and stands to reduce camera cost once the technology is commercially manufactured. " not only does it prove type - ii superlattices as a viable alternative to mct, but also it widens the field of applications for infrared cameras, " razeghi said. " the importance of this work is similar to that of the realization of mega - pixel visible cameras in the last decade, which shaped the world ' s favor for digital cameras. " their results were recently published in the journal applied physics letters


something having a polished surface for reflecting light or heat, as a mirror, a speculum, etc. a reflecting telescope. the portion of a light fixture that shrouds the lamps and directs the light emitted from the lamps. or reflecting telescope a telescope which uses a curved mirror to focus the light rays entering the telescope. all the largest telescopes in the world, as well as the space telescope, are basically reflecting telescopes. any surface that reflects light. reflectors can be constructed of cardboard, metal, cloth, or other material. in motion picture projection, primarily the lamphouse mirror and the screen. a surface used reflect light onto the subject, usually made of shiny metal, white cloth. or cardboard. a surface, such as white cardboard, used to redirect light into shadow areas of a scene or subject. a piece of material with a reflective surface that directs light in a desired direction. reflectors are frequently specular, but may also be glossy, diffuse or matte. shiny device used to alter the path of light ; a mirror is a reflector any surface from which light can be reflected. used to reflect light from a main source into the shadow areas. ( see lastolite ) the part of a luminaire which controls the light emitted by the lamp ( e. g. cat2 reflector ) material used to reflect light onto a subject. a flash reflector is a shiny surface situated behind the flash tube that reflects light in a specific direction. mirror - based telescope in which a mirror at the bottom of the tube directs light up towards the front of the tube. most economical of the major telescope designs. a surface, usually a rock or sediment layer, that strongly reflects seismic ( sound ) waves. a " bounce " as mentioned above or a dish - shaped item that surrounds the back of a light source, ensuring no light " escapes " and it is all directed at the subject. a telescope that uses mirrors for its optics. a surface that reflects light, heat, a polished surface controlling light output by means of reflection ( mirror ). the part of a luminaire that redirects by reflection some light emitted from the lamp. telescope that uses a mirror - instead of a lens - to collect and focus the light coming from astronomical objects. the term ' reflector ' is also used for the mirror itself. a tool for redirecting light onto the subject. usually white, metallic, a cloth or any light - reflecting board. a shiny material used at the back of a luminaire to reduce


that directs most of the light to the intended location. a telescope that uses a concave mirror to gather light and form an image at a focal plane. a device that reflects light, to be located at the front, and back of the bike along with both tires. to make yourself more visible. the part of a light fixture that shrouds the lamps and redirects some of the light emitted from the lamp. a telescope whose objective is a mirror. surrounds the lamp and directs and focuses the light rays in one direction. any mirrored surface, often blown mercury glass, or concaved metal surface designed to increase light output by reflection. a telescope that uses a mirror to collect light. also called a newtonian a white, silver, or other reflective object used to reflect light into the shadow areas of a subject, especially in direct sunlight where contrast is high. reflectors can be bought or easily improvised, and are especially essential at model shoots. lighting accessory helpful for spreading light as well as filling in shadows. often made of white poster board or foamcore, lightweight reflective metal, or poster board covered with metallic foil. a built in reflective surface on a fixture. a telescope that uses a polished, curved mirror to gather light and reflect it to a focus. a piece of material with a reflective surface that directs radiant energy ( light ) in a desired direction. device designed to reflect light ( usually the headlights of an approaching vehicle ) back to the driver as a form of indication or warning ; used at front ( amber ), front side ( amber ), rear side ( red ) and rear ( red ) to signal overall dimensions of truck or trailer to approaching driver. a device for reflecting light in a chosen direction from its surface. depending on the brightness desired, these may be either diffuse, glossy, matte, or specular. ( see diffused lighting, gloss, matte and specular ). any substance from which light can be reflected. it also describes a white or gray card used to reflect from a main light source into shadow areas. a reflector is something that is used to reflect light onto an object. a flash reflector is a shiny surface that is behind the flash tube which reflects the light in a specific direction. the lcd has a smooth silver piece of aluminium foil, bonded to the rear polarizer that reflects incoming ambient light. backlighting cannot be used with reflective lcds. 1. ) a reflective surface, such as a piece of white cardboard, that can be positioned to redirect length, especially


interesting refraction phenomena most of our discussion of refraction in this unit has pertained to the refraction of light at a distinct boundary. as light is transmitted across the boundary from one material to another, there is a change in speed, which causes a change in direction of the light wave. the boundaries that we have been focusing on have been distinct interfaces between two recognizably different materials. the boundary between the glass of a fish tank and the surrounding air or the boundary between the water in a pool and the surrounding air are examples of distinct interfaces between two recognizably different materials. it has been mentioned in our discussion that the refraction or bending of light occurs at the boundary between two materials ; and once a light wave has crossed the boundary it travels in a straight line. the discussion has presumed that the medium is a uniform medium. a uniform medium is a medium whose optical density is everywhere the same within the medium. a uniform medium is the same everywhere from its top boundary to its bottom boundary and from its left boundary to its right boundary. but not every medium is a uniform medium, and the fact that air can sometimes form a non - uniform medium leads to an interesting refraction phenomenon - the formation of mirages. a mirage is an optical phenomenon that creates the illusion of water and results from the refraction of light through a non - uniform medium. mirages are most commonly observed on sunny days when driving down a roadway. as you drive down the roadway, there appears to be a puddle of water on the road several yards ( maybe one - hundred yards ) in front of the car. of course, when you arrive at the perceived location of the puddle, you recognize that the puddle is not there. instead, the puddle of water appears to be another one - hundred yards in front of you. you could carefully match the perceived location of the water to a roadside object ; but when you arrive at that object, the puddle of water is still not on the roadway. the appearance of the water is simply an illusion. mirages occur on sunny days. the role of the sun is to heat the roadway to high temperatures. this heated roadway in turn heats the surrounding air, keeping the air just above the roadway at higher temperatures than that day ' s average air temperature. hot air tends to be less optically dense than cooler air. as such, a non - uniform medium has been created by the heating of the roadway and the air just above it. while light will travel in a straight line through a uniform medium,


hot air tends to be less optically dense than cooler air. as such, a non - uniform medium has been created by the heating of the roadway and the air just above it. while light will travel in a straight line through a uniform medium, it will refract when traveling through a non - uniform medium. if a driver looks down at the roadway at a very low angle ( that is, at a position nearly one hundred yards away ), light from objects above the roadway will follow a curved path to the driver ' s eye as shown in the diagram below. light that is traveling downward into this less optically dense air begins to speed up. though there isn ' t a distinct boundary between two media, there is a change in speed of a light wave. as expected, a change in speed is accompanied by a change in direction. if there were a distinct boundary between two media, then there would be a bending of this light ray away from the normal. for this light ray to bend away from the normal ( towards the boundary ), the ray would begin to bend more parallel to the roadway and then bend upwards towards the cooler air. as such, a person in a car sighting downward at the roadway will see an object located above the roadway. of course, this is not a usual event. when was the last time that you looked downward at a surface and saw an object above the surface? while not a usual event, it does happen. for instance, suppose you place a mirror on the floor and look downward at the floor ; you will see objects located above the floor due to the reflection of light by the mirror. even a glass window placed on the floor will reflect light from objects above the floor. if you look downward at the glass window at a low enough angle, then you will see objects located above the floor. or suppose that you are standing on the shore of a calm pond and look downward at the water ; you might see objects above the pond due to the reflection of light by the water. so when you experience this sunny day phenomenon, your mind must quickly make sense of how you can look downward at the roadway and see an object located above the road. in the process of making sense of this event, your mind draws upon past experiences. searching the database of stored experiences, your mind is interested in an explanation of why the eye can sight downward at a surface and see an object that is located above the surface. in the process of searching, it comes up with three possible explanations based upon past experiences. your mind


experiences, your mind is interested in an explanation of why the eye can sight downward at a surface and see an object that is located above the surface. in the process of searching, it comes up with three possible explanations based upon past experiences. your mind subtly ponders these three options. - there is a mirror on the road. someone must have for some reason placed a mirror on the road. the mirror is reflecting light and that is why i see an image of the oncoming truck when i look downward at the road. - there is a glass window on the road. my gosh, do you believe it! someone has left a glass window on the road. the glass window is reflecting light and that is why i see an image of the oncoming truck when i look downward at the road. - there is water on the road. it must have rained last night and there is a puddle of water left on the road. the water is reflecting light and that is why i see an image of the oncoming truck when i look downward at the road. of the three possible explanations of the image of the truck, only one makes a lot of sense to the mind - there is water on the road. after all, while both glass windows and mirrors can reflect light, nowhere in your mind ' s database of past experiences is there an account of a mirror or glass window being seen on a roadway. yet there are plenty of times that a water puddle has been observed to be present on a roadway. smart person that you are, you then conclude that there is a puddle of water on the road that is causing you to see objects located above the road when you sight downward at the road. the illusion is complete.


implementation results of bloom filters for string matching abstract network intrusion detection and prevention systems ( idps ) use string matching to scan internet packets for malicious content. bloom filters offer a mechanism to search for a large number of strings efficiently and concurrently when implemented with field programmable gate array ( fpga ) technology. a string matching circuit has been implemented within the fpx platform using bloom filters. using 155 block rams on a single xilinx virtexe 2000 fpga, the circuit scans for 35, 475 unique signatures. mobile information systems. 01 / 2008 ; 4 : 33 - 49. ieee communications surveys and tutorials. 01 / 2011 ; 13 : 541 - 561. article : realizing a sub - linear time string - matching algorithm with a hardware accelerator using bloom filters [ show abstract ] [ hide abstract ] abstract : many network security applications rely on string matching to detect intrusions, viruses, spam, and so on. since software implementation may not keep pace with the high - speed demand, turning to hardware - based solutions becomes promising. this work presents an innovative architecture to realize string matching in sub - linear time based on algorithmic heuristics, which come from parallel queries to a set of space - efficient bloom filters. the algorithm allows skipping characters not in a match in the text, and in turn simultaneously inspect multiple characters in effect. the techniques to reduce the impact of certain bad situations on performance are also proposed : the bad - block heuristic, a linear worst - case time method and a non - blocking interface to hand over the verification job to a verification module. this architecture is simulated with both behavior simulation in c and timing simulation in hdl for antivirus applications. the simulation shows that the throughput of scanning windows executable files for more than 10000 virus signatures can achieve 5. 64 gb / s, while the worst - case performance is 1. 2 gb / s if the signatures are properly specified. ieee transactions on very large scale integration ( vlsi ) systems 09 / 2009 ; · 1. 22 impact factor


apr. 22, 2008 a new computer simulation has revealed a self - healing behavior in a common ceramic that may lead to development of radiation - resistant materials for nuclear power plants and waste storage. researchers at the department of energy ' s pacific northwest national laboratory found that the restless movement of oxygen atoms heals radiation - induced damage in the engineered ceramic yttria - stabilized zirconia. scientists ram devanathan and bill weber modeled how well that ceramic and other materials stand up to radiation. " if you want a material to withstand radiation over millennia, you can ' t expect it to just sit there and take it. there must be a mechanism for self - healing, " said devanathan. " this research raises the possibility of engineering mobile defects in ceramics to enhance radiation tolerance, " weber said. he noted that materials capable of handling high - radiation doses also " could improve the durability of key equipment and reduce the costs of replacements. " the researchers approached their investigation in three steps. first, they analyzed yttria - stabilized zirconia, a compound of yttrium and zirconium oxides that contains random structural defects called " vacancies. " the defects occur because yttrium has a smaller electrical charge than zirconium. to correct the charge imbalance, zirconia gives up oxygen atoms. but the loss of these oxygen atoms leaves empty oxygen sites. the remaining oxygen atoms constantly jump in and out of those sites. " it is like a classroom full of fidgety kids, " said devanathan. " when the teacher turns her back, the kids constantly jump into empty chairs, leaving their own chairs vacant until another kid leaps into the seat. " next, the scientists simulated an atom undergoing alpha decay. an alpha particle shoots out of the atomic nucleus with such force that the remainder of the atom recoils in the opposite direction. the recoiling atom can cause significant damage to surrounding atomic structures. finally, the researchers used data analysis algorithms developed at pnnl to look for atoms knocked out of place. the results showed that displaced oxygen atoms in the yttria - stabilized zirconia " found seats " in the pre - existing vacancies throughout the ceramic. although the self - healing activity does not completely repair the material, the defects are less apt to cause problems because they are spread out. this characteristic indicates that yttria - stabilized zirconia, which is used today in such items as solid oxide fuel cells and oxygen sensors, might be


repair the material, the defects are less apt to cause problems because they are spread out. this characteristic indicates that yttria - stabilized zirconia, which is used today in such items as solid oxide fuel cells and oxygen sensors, might be suitable for nuclear applications. the researchers also simulated the impact of radiation on zircon, a ceramic that is a candidate for immobilizing high - level nuclear waste. the simulation defects clustered together in simulations of zircon, changing the properties of the material. " clustered defects are much more difficult to repair than isolated defects, devanathan said. the scientists now are refining the simulations and applying them to other materials. doe ' s office of basic energy sciences funded the research, which was performed on massively parallel supercomputers in the william r. wiley environmental molecular sciences laboratory ( emsl ) at pnnl, and the national energy research scientific computer center at lawrence berkeley national laboratory. reference : ram devanathan and william j. weber. " dynamic annealing of defects in irradiated zirconia - based ceramics, " published in the journal of materials research, march 2008, 23 ( 3 ) : 593 - 597. other social bookmarking and sharing tools : note : materials may be edited for content and length. for further information, please contact the source cited above. note : if no author is given, the source is cited instead.


jan. 23, 2009 a team of physicists and engineers has demonstrated an optical device that filters two particles of light ( or photons ) based on the correlations between their polarisation that are only allowed in the seemingly bizarre quantum world. this so called " entanglement filter " passes the pair of photons only if they inhabit the same quantum state, without the user ( or anything else ) ever knowing what that state is. this device will have many important applications to quantum technologies, including computers, communication and advanced measurement. jeremy o ' brien, professor of physics and electrical engineering at bristol university, together with his collaborators in japan, has realised an entanglement filter made by combining two state - of - the - art developments in optical technologies with single photons : a special type of mirror that is sensitive to the polarisation of light ; and an optical device that enables stability at the billionth ' s of a meter level. the team reports its results in the latest issue of science [ 23 january 2009 ]. professor o ' brien speaking about the research, said : " this is a very exciting development in quantum information science. because our entanglement filter acts on photonic qubits, it is promising for quantum technologies because photons are the logical choice for communication, metrology and lithography and are a leading approach to information processing. " the filter can be used for the creation as well as the purification of entanglement, which will be important in realising quantum relays and repeaters for long - distance quantum communication. " an entanglement filter filters are one of the most powerful tools available in science and technology, while entanglement is the defining characteristic of quantum information science. an entanglement filter is of fundamental interest and will likely find wide application in quantum information science and technology. filters that act on the quantum correlations associated with entanglement must operate nonlocally on multiple quantum systems, typically two - level " qubits ". such a device has been proposed for photonic qubits, but the technical requirements to build such a device, an optical circuit with two extra photons and multiple quantum gates, requiring both quantum interference and classical interference in several nested interferomters, have been lacking. the entanglement filter will be a key element in the control of multiphoton quantum states, with a wide range of applications in entanglement - based quantum communication and quantum information processing. quantum technologies with photons quantum technologies aim to exploit the unique properties of quantum mechanics,