A variable star is a star whose brightness as seen from Earth fluctuates. This variation may be caused by a change in emitted light or by something blocking the light, so variable stars are classified as either: Intrinsic variables, whose luminosity changes. Extrinsic variables, whose apparent changes in brightness are due to changes in the amount of their light that can reach Earth. Many most, stars have at least some variation in luminosity: the energy output of our Sun, for example, varies by about 0.1% over an 11-year solar cycle. An ancient Egyptian calendar of lucky and unlucky days composed some 3,200 years ago may be the oldest preserved historical document of the discovery of a variable star, the eclipsing binary Algol. Of the modern astronomers, the first variable star was identified in 1638 when Johannes Holwarda noticed that Omicron Ceti pulsated in a cycle taking 11 months; this discovery, combined with supernovae observed in 1572 and 1604, proved that the starry sky was not eternally invariable as Aristotle and other ancient philosophers had taught.
In this way, the discovery of variable stars contributed to the astronomical revolution of the sixteenth and early seventeenth centuries. The second variable star to be described was the eclipsing variable Algol, by Geminiano Montanari in 1669. Chi Cygni was identified in 1686 by G. Kirch R Hydrae in 1704 by G. D. Maraldi. By 1786 ten variable stars were known. John Goodricke himself discovered Beta Lyrae. Since 1850 the number of known variable stars has increased especially after 1890 when it became possible to identify variable stars by means of photography; the latest edition of the General Catalogue of Variable Stars lists more than 46,000 variable stars in the Milky Way, as well as 10,000 in other galaxies, over 10,000'suspected' variables. The most common kinds of variability involve changes in brightness, but other types of variability occur, in particular changes in the spectrum. By combining light curve data with observed spectral changes, astronomers are able to explain why a particular star is variable.
Variable stars are analysed using photometry, spectrophotometry and spectroscopy. Measurements of their changes in brightness can be plotted to produce light curves. For regular variables, the period of variation and its amplitude can be well established. Peak brightnesses in the light curve are known as maxima. Amateur astronomers can do useful scientific study of variable stars by visually comparing the star with other stars within the same telescopic field of view of which the magnitudes are known and constant. By estimating the variable's magnitude and noting the time of observation a visual lightcurve can be constructed; the American Association of Variable Star Observers collects such observations from participants around the world and shares the data with the scientific community. From the light curve the following data are derived: are the brightness variations periodical, irregular, or unique? What is the period of the brightness fluctuations? What is the shape of the light curve? From the spectrum the following data are derived: what kind of star is it: what is its temperature, its luminosity class? is it a single star, or a binary? does the spectrum change with time?
Changes in brightness may depend on the part of the spectrum, observed if the wavelengths of spectral lines are shifted this points to movements strong magnetic fields on the star betray themselves in the spectrum abnormal emission or absorption lines may be indication of a hot stellar atmosphere, or gas clouds surrounding the star. In few cases it is possible to make pictures of a stellar disk; these may show darker spots on its surface. Combining light curves with spectral data gives a clue as to the changes that occur in a variable star. For example, evidence for a pulsating star is found in its shifting spectrum because its surface periodically moves toward and away from us, with the same frequency as its changing brightness. About two-thirds of all variable stars appear to be pulsating. In the 1930s astronomer Arthur Stanley Eddington showed that the mathematical equations that describe the interior of a star may lead to instabilities that cause a star to pulsate; the most common type of instability is related to oscillations in the degree of ionization in outer, convective layers of the star.
Suppose the star is in the swelling phase. Its outer layers expand; because of the decreasing temperature the degree of ionization decreases. This makes the gas more transparent, thus makes it easier for the star to radiate its energy; this in turn will make the star start to contract. As the gas is thereby compressed, it is heated and the degree of ionization again increases. Thi
In computer science, a software agent is a computer program that acts for a user or other program in a relationship of agency, which derives from the Latin agere: an agreement to act on one's behalf. Such "action on behalf of" implies the authority to decide. Agents are colloquially known from robot, they may be embodied, as when execution is paired with a robot body, or as software such as a chatbot executing on a phone or other computing device. Software agents may work together with other agents or people. Software agents interacting with people may possess human-like qualities such as natural language understanding and speech, personality or embody humanoid form. Related and derived concepts include intelligent agents, autonomous agents, distributed agents, multi-agent systems, mobile agents; the basic attributes of an autonomous software agent are that agents are not invoked for a task, but activate themselves, may reside in wait status on a host, perceiving context, may get to run status on a host upon starting conditions, do not require interaction of user, may invoke other tasks including communication.
The term "agent" describes a software abstraction, an idea, or a concept, similar to OOP terms such as methods and objects. The concept of an agent provides a convenient and powerful way to describe a complex software entity, capable of acting with a certain degree of autonomy in order to accomplish tasks on behalf of its host, but unlike objects, which are defined in terms of methods and attributes, an agent is defined in terms of its behavior. Various authors have proposed different definitions of agents, these include concepts such as persistence autonomy social ability reactivity. All agents are programs. Contrasting the term with related concepts may help clarify its meaning. Franklin & Graesser discuss four key notions that distinguish agents from arbitrary programs: reaction to the environment, goal-orientation and persistence. Agents are more autonomous than objects. Agents have flexible behaviour: reactive, social. Agents may have more. Expert systems are not coupled to their environment.
Expert systems are not designed for proactive behavior. Expert systems do not consider social ability. Intelligent agents are not just computer programs: they may be machines, human beings, communities of human beings or anything, capable of goal-directed behavior. Software agents may offer various benefits to their end users by automating complex or repetitive tasks. However, there are organizational and cultural impacts of this technology that need to be considered prior to implementing software agents. People like to perform easy tasks providing the sensation of success unless the repetition of the simple tasking is affecting the overall output. In general implementing software agents to perform administrative requirements provides a substantial increase in work contentment, as administering their own work does never please the worker; the effort freed up serves for a higher degree of engagement in the substantial tasks of individual work. Hence, software agents may provide the basics to implement self-controlled work, relieved from hierarchical controls and interference.
Such conditions may be secured by application of software agents for required formal support. The cultural effects of the implementation of software agents include trust affliction, skills erosion, privacy attrition and social detachment; some users may not feel comfortable delegating important tasks to software applications. Those who start relying on intelligent agents may lose important skills, for example, relating to information literacy. In order to act on a user’s behalf, a software agent needs to have a complete understanding of a user’s profile, including his/her personal preferences. This, in turn, may lead to unpredictable privacy issues; when users start relying on their software agents more for communication activities, they may lose contact with other human users and look at the world with the eyes of their agents. These consequences are what agent researchers and users must consider when dealing with intelligent agent technologies; the concept of an agent can be traced back to Hewitt's Actor Model - "A self-contained and concurrently-executing object, possessing internal state and communication capability."
To be more academic, software agent systems are a direct evolution of Multi-Agent Systems. MAS evolved from Distributed Artificial Intelligence, Distributed Problem Solving and Parallel AI, thus inheriting all characteristics from DAI and AI. John Sculley’s 1987 “Knowledge Navigator”
Hawaii is the 50th and most recent state to have joined the United States, having received statehood on August 21, 1959. Hawaii is the only U. S. state located in Oceania, the only U. S. state located outside North America, the only one composed of islands. It is the northernmost island group in Polynesia, occupying most of an archipelago in the central Pacific Ocean; the state encompasses nearly the entire volcanic Hawaiian archipelago, which comprises hundreds of islands spread over 1,500 miles. At the southeastern end of the archipelago, the eight main islands are—in order from northwest to southeast: Niʻihau, Kauaʻi, Oʻahu, Molokaʻi, Lānaʻi, Kahoʻolawe and the Island of Hawaiʻi; the last is the largest island in the group. The archipelago is ethnologically part of the Polynesian subregion of Oceania. Hawaii's diverse natural scenery, warm tropical climate, abundance of public beaches, oceanic surroundings, active volcanoes make it a popular destination for tourists, surfers and volcanologists.
Because of its central location in the Pacific and 19th-century labor migration, Hawaii's culture is influenced by North American and East Asian cultures, in addition to its indigenous Hawaiian culture. Hawaii has over a million permanent residents, along with many visitors and U. S. military personnel. Its capital is Honolulu on the island of Oʻahu. Hawaii is the 8th-smallest and the 11th-least populous, but the 13th-most densely populated of the 50 U. S. states. It is the only state with an Asian plurality; the state's oceanic coastline is about 750 miles long, the fourth longest in the U. S. after the coastlines of Alaska and California. The state of Hawaii derives its name from the name of Hawaiʻi. A common Hawaiian explanation of the name of Hawaiʻi is that it was named for Hawaiʻiloa, a legendary figure from Hawaiian myth, he is said to have discovered the islands. The Hawaiian language word Hawaiʻi is similar to Proto-Polynesian *Sawaiki, with the reconstructed meaning "homeland". Cognates of Hawaiʻi are found in other Polynesian languages, including Māori and Samoan.
According to linguists Pukui and Elbert, "lsewhere in Polynesia, Hawaiʻi or a cognate is the name of the underworld or of the ancestral home, but in Hawaii, the name has no meaning". A somewhat divisive political issue arose in 1978 when the Constitution of the State of Hawaii added Hawaiian as a second official state language; the title of the state constitution is The Constitution of the State of Hawaii. Article XV, Section 1 of the Constitution uses The State of Hawaii. Diacritics were not used because the document, drafted in 1949, predates the use of the ʻokina and the kahakō in modern Hawaiian orthography; the exact spelling of the state's name in the Hawaiian language is Hawaiʻi. In the Hawaii Admission Act that granted Hawaiian statehood, the federal government recognized Hawaii as the official state name. Official government publications and office titles, the Seal of Hawaii use the traditional spelling with no symbols for glottal stops or vowel length. In contrast, the National and State Parks Services, the University of Hawaiʻi and some private enterprises implement these symbols.
No precedent for changes to U. S. state names exists since the adoption of the United States Constitution in 1789. However, the Constitution of Massachusetts formally changed the Province of Massachusetts Bay to the Commonwealth of Massachusetts in 1780, in 1819, the Territory of Arkansaw was created but was admitted to statehood as the State of Arkansas. There are eight main Hawaiian islands; the island of Niʻihau is managed by brothers Bruce and Keith Robinson. Access to uninhabited Kahoʻolawe island is restricted; the Hawaiian archipelago is located 2,000 mi southwest of the contiguous United States. Hawaii is the southernmost U. S. the second westernmost after Alaska. Hawaii, like Alaska, does not border any other U. S. state. It is the only U. S. state, not geographically located in North America, the only state surrounded by water and, an archipelago, the only state in which coffee is commercially cultivable. In addition to the eight main islands, the state has many smaller islets. Kaʻula is a small island near Niʻihau.
The Northwest Hawaiian Islands is a group of nine small, older islands to the northwest of Kauaʻi that extend from Nihoa to Kure Atoll. Across the archipelago are around 130 small rocks and islets, such as Molokini, which are either volcanic, marine sedimentary or erosional in origin. Hawaii's tallest mountain Mauna Kea is 13,796 ft above mean sea level; the Hawaiian islands were formed by volcanic activity initiated at an undersea magma source called the Hawaii hotspot. The process is continuing to build islands; because of the hotspot's location, all active land volcanoes are located on the southern half of Hawaii Island. The newest volcano, Lōʻihi Seamount, is located south of the coast of Hawaii Island; the last volcanic eruption outside Hawaii Island occurred
Gravitational microlensing is an astronomical phenomenon due to the gravitational lens effect. It can be used to detect objects that range from the mass of a planet to the mass of a star, regardless of the light they emit. Astronomers can only detect bright objects that emit much light or large objects that block background light; these objects make up only a minor portion of the mass of a galaxy. Microlensing allows the study of objects that emit no light; when a distant star or quasar gets sufficiently aligned with a massive compact foreground object, the bending of light due to its gravitational field, as discussed by Einstein in 1915, leads to two distorted unresolved images resulting in an observable magnification. The time-scale of the transient brightening depends on the mass of the foreground object as well as on the relative proper motion between the background'source' and the foreground'lens' object. Since microlensing observations do not rely on radiation received from the lens object, this effect therefore allows astronomers to study massive objects no matter how faint.
It is thus an ideal technique to study the galactic population of such faint or dark objects as brown dwarfs, red dwarfs, white dwarfs, neutron stars, black holes, massive compact halo objects. Moreover, the microlensing effect is wavelength-independent, allowing use of distant source objects that emit any kind of electromagnetic radiation. Microlensing by an isolated object was first detected in 1989. Since microlensing has been used to constrain the nature of the dark matter, detect exoplanets, study limb darkening in distant stars, constrain the binary star population, constrain the structure of the Milky Way's disk. Microlensing has been proposed as a means to find dark objects like brown dwarfs and black holes, study starspots, measure stellar rotation, probe quasars including their accretion disks.. Microlensing was used in 2018 to detect Icarus, the most distant star observed. Microlensing is based on the gravitational lens effect. A massive object will bend the light of a bright background object.
This can generate multiple distorted and brightened images of the background source. Microlensing is caused by the same physical effect as strong lensing and weak lensing, but it is studied using different observational techniques. In strong and weak lensing, the mass of the lens is large enough that the displacement of light by the lens can be resolved with a high resolution telescope such as the Hubble Space Telescope. With microlensing, the lens mass is too low for the displacement of light to be observed but the apparent brightening of the source may still be detected. In such a situation, the lens will pass by the source in a reasonable amount of time, seconds to years instead of millions of years; as the alignment changes, the source's apparent brightness changes, this can be monitored to detect and study the event. Thus, unlike with strong and weak gravitational lenses, a microlensing event is a transient phenomenon from a human timescale perspective. Unlike with strong and weak lensing, no single observation can establish that microlensing is occurring.
Instead, the rise and fall of the source brightness must be monitored over time using photometry. This function of brightness versus time is known as a light curve. A typical microlensing light curve is shown below: A typical microlensing event like this one has a simple shape, only one physical parameter can be extracted: the time scale, related to the lens mass and velocity. There are several effects, that contribute to the shape of more atypical lensing events: Lens mass distribution. If the lens mass is not concentrated in a single point, the light curve can be different with caustic-crossing events, which may exhibit strong spikes in the light curve. In microlensing, this can be seen when the lens is a planetary system. Finite source size. In bright or quickly-changing microlensing events, like caustic-crossing events, the source star cannot be treated as an infinitesimally small point of light: the size of the star's disk and limb darkening can modify extreme features. Parallax. For events lasting for months, the motion of the Earth around the Sun can cause the alignment to change affecting the light curve.
Most focus is on the more unusual microlensing events those that might lead to the discovery of extrasolar planets. Although it has not yet been observed, another way to get more information from microlensing events that may soon be feasible involves measuring the astrometric shifts in the source position during the course of the event and resolving the separate images with interferometry. In practice, because the alignment needed is so precise and difficult to predict, microlensing is rare. Events, are found with surveys, which photometrically monitor tens of millions of potential source stars, every few days for several years. Dense background fields suitable for such surveys are nearby galaxies, such as the Magellanic Clouds and the Andromeda galaxy, the Milky Way bulge. In each case, the lens population studied comprises the objects between Earth and the source field: for the bulge, the lens population is the Milky Way disk stars, for external galaxies, the lens population is the Milky Way halo, as well as objects in the other galaxy itself.
The density and location of the objects in these lens populations determines the frequency of microlensing along that line of sight, characterized by a value known as the optical depth due to microlensing. (This
A multi-agent system is a computerized system composed of multiple interacting intelligent agents. Multi-agent systems can solve problems that are difficult or impossible for an individual agent or a monolithic system to solve. Intelligence may include methodic, procedural approaches, algorithmic search or reinforcement learning. Despite considerable overlap, a multi-agent system is not always the same as an agent-based model; the goal of an ABM is to search for explanatory insight into the collective behavior of agents obeying simple rules in natural systems, rather than in solving specific practical or engineering problems. The terminology of ABM tends to be used more in the science, MAS in engineering and technology. Applications where multi-agent systems research may deliver an appropriate approach include online trading, disaster response and social structure modelling. Multi-agent systems consist of their environment. Multi-agent systems research refers to software agents. However, the agents in a multi-agent system could well be robots, humans or human teams.
A multi-agent system may contain combined human-agent teams. Agents can be divided into types spanning simple to complex. Categories include: Passive agents or "agent without goals" Active agents with simple goals Cognitive agents Agent environments can be divided into: Virtual Discrete ContinuousAgent environments can be organized according to properties such as accessibility, dynamics, discreteness and dimensionality. Agent actions are mediated via an appropriate middleware; this middleware offers a first-class design abstraction for multi-agent systems, providing means to govern resource access and agent coordination. The agents in a multi-agent system have several important characteristics: Autonomy: agents at least independent, self-aware, autonomous Local views: no agent has a full global view, or the system is too complex for an agent to exploit such knowledge Decentralisation: no agent is designated as controlling Multi-agent systems can manifest self-organisation as well as self-direction and other control paradigms and related complex behaviors when the individual strategies of all their agents are simple.
When agents can share knowledge using any agreed language, within the constraints of the system's communication protocol, the approach may lead to a common improvement. Example languages are Agent Communication Language. Many MAS are implemented in computer simulations, stepping the system through discrete "time steps"; the MAS components communicate using a weighted request matrix, e.g. Speed-VERY_IMPORTANT: min=45 mph, Path length-MEDIUM_IMPORTANCE: max=60 expectedMax=40, Max-Weight-UNIMPORTANT Contract Priority-REGULAR and a weighted response matrix, e.g. Speed-min:50 but only if weather sunny, Path length:25 for sunny / 46 for rainy Contract Priority-REGULAR note – ambulance will override this priority and you'll have to wait A challenge-response-contract scheme is common in MAS systems, where First a "Who can?" Question is distributed. Only the relevant components respond: "I can, at this price". A contract is set up in several short communication steps between sides,also considering other components, evolving "contracts" and the restriction sets of the component algorithms.
Another paradigm used with MAS is the "pheromone", where components leave information for other nearby components. These pheromones may evaporate/concentrate with time, their values may decrease. MAS tend to find the best solution for their problems without intervention. There is high similarity here to physical phenomena, such as energy minimizing, where physical objects tend to reach the lowest energy possible within the physically constrained world. For example: many of the cars entering a metropolis in the morning will be available for leaving that same metropolis in the evening; the systems tend to prevent propagation of faults, self-recover and be fault tolerant due to the redundancy of components. The study of multi-agent systems is "concerned with the development and analysis of sophisticated AI problem-solving and control architectures for both single-agent and multiple-agent systems." Research topics include: agent-oriented software engineering beliefs and intentions cooperation and coordination distributed constraint optimization organization communication negotiation distributed problem solving multi-agent learning agent mining scientific communities dependability and fault-tolerance robotics, multi-robot systems, robotic clusters Frameworks have emerged that implement common standards.
These frameworks e.g. JADE, save aid in the standardization of MAS development. Though, no standard is maintained from FIPA or OMG. Efforts for further development of software agents in indu
Liverpool John Moores University
Liverpool John Moores University is a public research university in the city of Liverpool, England. The university can trace its origins to the Liverpool Mechanics' School of Arts, established in 1823; this merged to become Liverpool Polytechnic. In 1992, following an Act of Parliament the Liverpool Polytechnic became what is now Liverpool John Moores University, it is named after Sir John Moores, a local businessman and philanthropist, who donated to the university's precursor institutions. It has 22,445 students, of which 18,325 are undergraduate students and 4,115 are postgraduate, making it the 35th largest university in the UK by total student population, it is a member of the University Alliance, the Northern Consortium and the European University Association. Founded as a small mechanics institution in 1823, the institution grew over the centuries by converging and amalgamating with different colleges, including the F. L. Calder School of Domestic Science, the City of Liverpool C. F. Mott Training College, before becoming Liverpool Polytechnic in 1970.
The University has a long history of providing training and research to the maritime industry, dating back to the formation of the Liverpool Nautical College in 1892. The institution became a university under the terms of the Further and Higher Education Act 1992 under the new title of "Liverpool John Moores University"; this new title was approved by the Privy Council on 15 September 1992. The university took its name from the founder of the Littlewoods empire. Moores was a great believer in the creation of opportunity for all, which embodies the ethos of LJMU in providing educational routes for people of all ages and from all backgrounds; this belief led Sir John Moores to invest in the institution and facilities, such as the John Foster Building, designed by and named after leading architect John Foster. With the institution's backgrounds dating back as far as 1823, many of the university buildings date back with aesthetically pleasing Georgian and Victorian buildings found on a few of the campuses.
LJMU now has more than 24,000 students. LJMU was awarded the Queen's Anniversary Prize in 2005. Liverpool John Moores University is receiving more applications than seen. On 14 April 2008, Brian May was inducted into the university as the fourth Chancellor of Liverpool John Moores University. May is the lead guitarist for the rock band Queen, he replaced wife of former Prime Minister Tony Blair. Honorary fellows in attendance at the ceremony included Pete Postlethwaite. May was succeeded as Chancellor in 2013 by Sir Brian Leveson. LJMU is a founding member of the Northern Consortium, an educational charity, owned by eleven universities in the north of England; the university is based on three campuses: City Campus, housing buildings from many faculties in and around Liverpool city centre Mount Pleasant Campus, in the city centre, home to the faculty of Business and Law I M Marsh Campus, in Aigburth housing the Education and Leisure faculty There are three libraries based at the three campus sites operated by LJMU.
The two largest and more modern LRC facilities are the Avril Robarts library, based on the City campus and used by students studying on the city campus, in particular the Byrom Street and Marybone students. The Aldham Robarts LRC is used by students at the Mount Pleasant campus, this campus includes the faculty of Business and Law but student based to the LRC on a range of courses use this facility; the third LRC is sited on the IM Marsh campus in Aigburth and is used by student at this campus. There are more than 68,500 books in the LRCs' collections, with 1,630 work spaces available for students 24 hours a day. In addition to this there are over 16,000 e-books and 5,000 e-journals available, it is a member of the Libraries Together: Liverpool Learning Partnership which formed in 1990. Under which, a registered reader at any of the member libraries can have access rights to the other libraries within the partnership; the Aldham Robarts library is situated on Maryland Street at the heart of the Mount Pleasant Campus and right opposite the Student's Union, Aldham Robarts caters for the Faculty of Business and Law and the Faculty of Media and Social Science.
Avril Robarts Library is located on Tithebarn Street on City Campus, covers three faculties: Faculty of Health and Applied Social Sciences, the Faculty of Science and the Faculty of Technology and Environment, IM Marsh Campus library services the IM Marsh campus at Aigburth and covers the Faculty of Education and Leisure, situated at this site. The Tom Reilly Building houses the School of Sports and Exercise Sciences and the School of Natural Sciences and Psychology, which are both part of the Faculty of Science; some 8,000 students use the building, located at LJMU's City Campus on Byrom Street. The five storey, 6,493 m2 building was completed in November 2009 and opened in March 2010 by Liverpool F. C. captain Steven Gerrard. The building provides sports and science facilities including; the university is organised into five faculties (which are each split into s