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Yarkovsky effect

The Yarkovsky effect is a force acting on a rotating body in space caused by the anisotropic emission of thermal photons, which carry momentum. It is considered in relation to meteoroids or small asteroids, as its influence is most significant for these bodies; the effect was discovered by the Polish civil engineer Ivan Osipovich Yarkovsky, who worked in Russia on scientific problems in his spare time. Writing in a pamphlet around the year 1900, Yarkovsky noted that the daily heating of a rotating object in space would cause it to experience a force that, while tiny, could lead to large long-term effects in the orbits of small bodies meteoroids and small asteroids. Yarkovsky's insight would have been forgotten had it not been for the Estonian astronomer Ernst J. Öpik, who read Yarkovsky's pamphlet sometime around 1909. Decades Öpik, recalling the pamphlet from memory, discussed the possible importance of the Yarkovsky effect on movement of meteoroids about the Solar System; the Yarkovsky effect is a consequence of the fact that change in the temperature of an object warmed by radiation lags behind changes in the incoming radiation.

That is, the surface of the object takes time to become warm when first illuminated, takes time to cool down when illumination stops. In general there are two components to the effect: Diurnal effect: On a rotating body illuminated by the Sun, the surface is warmed by solar radiation during the day, cools at night. Due to the thermal properties of the surface, there is a lag between the absorption of radiation from the Sun, the emission of that same radiation as heat, so the warmest point on a rotating body occurs around the "2 PM" site on the surface, or after noon; this results in a difference between the directions of absorption and re-emission of radiation, which yields a net force along the direction of motion of the orbit. If the object is a prograde rotator, the force is in the direction of motion of the orbit, causes the semi-major axis of the orbit to increase steadily. A retrograde rotator spirals inward; the diurnal effect is the dominant component for bodies with diameter greater than about 100 m.

Seasonal effect: This is easiest to understand for the idealised case of a non-rotating body orbiting the Sun, for which each "year" consists of one "day". As it travels around its orbit, the "dusk" hemisphere, heated over a long preceding time period is invariably in the direction of orbital motion; the excess of thermal radiation in this direction causes a braking force that always causes spiraling inward toward the Sun. In practice, for rotating bodies, this seasonal effect increases along with the axial tilt, it dominates. This may occur because of rapid rotation, small size or an axial tilt close to 90°; the seasonal effect is more important for smaller asteroid fragments, provided their surfaces are not covered by an insulating regolith layer and they do not have exceedingly slow rotations. Additionally, on long timescales over which the spin axis of the body may be changed due to collisions, the seasonal effect will tend to dominate. In general, the effect is size-dependent, will affect the semi-major axis of smaller asteroids, while leaving large asteroids unaffected.

For kilometre-sized asteroids, the Yarkovsky effect is minuscule over short periods: the force on asteroid 6489 Golevka has been estimated at about 0.25 newtons, for a net acceleration of 10−12 m/s2. But it is steady; the above details can become more complicated for bodies in eccentric orbits. The effect was first measured in 1991–2003 on the asteroid 6489 Golevka; the asteroid drifted 15 km from its predicted position over twelve years. Without direct measurement, it is hard to predict the exact result of the Yarkovsky effect on a given asteroid's orbit; this is because the magnitude of the effect depends on many variables that are hard to determine from the limited observational information, available. These include the exact shape of the asteroid, its orientation, its albedo. Calculations are further complicated by the effects of shadowing and thermal "reillumination", whether caused by local craters or a possible overall concave shape; the Yarkovsky effect competes with radiation pressure, whose net effect may cause similar small long-term forces for bodies with albedo variations or non-spherical shapes.

As an example for the simple case of the pure seasonal Yarkovsky effect on a spherical body in a circular orbit with 90° obliquity, semi-major axis changes could differ by as much as a factor of two between the case of a uniform albedo and the case of a strong north/south albedo asymmetry. Depending on the object's orbit and spin axis, the Yarkovsky change of the semi-major axis may be reversed by changing from a spherical to a non-spherical shape. Despite these difficulties, utilizing the Yarkovsky effect is one scenario under investigation to alter the course of Earth-impacting near-Earth asteroids. Possible asteroid deflection strategies include "painting" the surface of th

Susong County

Susong County is a county in the southwest of Anhui Province, situated on the northwest bank of the Yangtze, bordering the provinces of Hubei to the west and Jiangxi to the south. It is located in the southwest of the jurisdiction of the prefecture-level city of Anqing and is its southernmost county-level division, it has population of 800,000 and an area of 2,394 km2. The government of Susong County is located in Fuyu Town. Susong County has jurisdiction over fourteen townships. Fuyu, Xuling, Erlang, Susong County, Poliang, Huikou Chenhan Township, Aikou Township, Zuoba Township, Qianling Township, Jiugu Township, Chengling Township, Zhoutou Township, Wujie Township, Beiyu Township, Liuping Township, Zhifeng Township, Heta Township, Gaoling Township Little Orphan, a rock in the middle of the Yangtze in the county

Cliff effect

In telecommunications, the cliff effect or brickwall effect is a sudden loss of digital signal reception. Unlike analog signals, which fade when signal strength decreases or electromagnetic interference or multipath increases, a digital signal provides data, either perfect or non-existent at the receiving end, it is named for a graph of reception quality versus signal quality, where the digital signal "falls off a cliff" instead of having a gradual rolloff. This is an example of an EXIT chart; the phenomenon is seen in broadcasting, where signal strength is liable to vary, rather than in recorded media, which have a good signal. However, it may be seen in damaged media, at the edge of readability; the term is used in economics for an unrelated phenomenon. This effect can most be seen on digital television, including both satellite TV and over-the-air terrestrial TV. While forward error correction is applied to the broadcast, when a minimum threshold of signal quality is reached it is no longer enough for the decoder to recover.

The picture may lock on a freeze frame, or go blank. Causes include rain fade or solar transit on satellites, temperature inversions and other weather or atmospheric conditions causing anomalous propagation on the ground. Three particular issues manifest the cliff effect. Firstly, anomalous conditions will cause occasional signal degradation. Secondly, if one is located in a fringe area, where the antenna is just strong enough to receive the signal usual variation in signal quality will cause frequent signal degradation, a small change in overall signal quality can have a dramatic impact on the frequency of signal degradation – one incident per hour versus problems every few seconds or continuous problems. Thirdly, in some cases, where the signal is beyond the cliff, viewers who were once able to receive a degraded signal from analog stations will find after digital transition that there is no available signal in rural, fringe or mountainous regions; the cliff effect is a serious issue for mobile TV, as signal quality may vary particularly if the receiver is moving as in a car.

Hierarchical modulation and coding can provide a compromise by supporting two or more streams with different robustness parameters and allowing receivers to scale back to a lower definition before dropping out completely. Two-level hierarchical modulation is supported in principle by the European DVB-T digital terrestrial television standard. However, layered source coding, such as provided by Scalable Video Coding, is not supported. HD Radio broadcasting used only in the United States, is one system designed to have an analog fallback. Receivers are designed to switch to the analog signal upon losing a lock on digital, but only as long as the tuned station operates in hybrid digital mode. In the future all-digital mode, there is no analog to fall back to at the edge of the digital cliff; this applies only to the main channel simulcast, not to any subchannels, because they have nothing to fall back to. It is important for the station's broadcast engineer to make sure that the audio signal is synchronized between analog and digital, or the cliff effect will still cause a jump forward or backward in the radio program.

The cliff effect is heard on mobile phones, where one or both sides of the conversation may break up resulting in a dropped call. Other forms of digital radio suffer from this. In economics, the "cliff effect" is a positive feedback loop, where downgrading a single security can have a disproportionate cascading effect; this has become pronounced with respect to the assessment of credit risk in a bank's portfolio. If a credit rating agency has the expectation that the credit risk of a position rises, it will downgrade its rating; as a consequence, a bank faces additional capital charges in order to comply with national capital requirements. During the subprime mortgage crisis banks had to increase their capital because many ratings were downgraded. In time banks needed their capital most to cope with high losses, this term emerged in the consultative process on reforms regarding existing capital requirements, namely criticizing the procyclical "cliff effect". Digital television transition Link adaptation

Benin at the 2016 Summer Paralympics

Benin competed at the 2016 Summer Paralympics in Rio de Janeiro, from 7 September to 18 September 2016. The country was represented by one sportsperson, Cosme Akpovi, competing in the men's javelin F57 event where he finished thirteenth; the Games were not broadcast in Benin. The country sent Cosme Akpovi, to the 2016 Summer Paralympics, he served as the country's flag bearer during the opening ceremony. Benin's delegation in Rio included three other people, the national teacm coach, the secretary general of the Benin Paralympic Committee and a representative of the Ministry of Sports Ahead of the 2016 Games, Benin's National Paralympic Committee launched a talent identification program, with the goal of identifying more athletes who could represent the country at the 2020 Games. Akpovi took up athletics in 2003, he had competed at the 2013 IPC Athletics World Championships, finishing fourteenth in the men's Javelin Throw F57/58 with a best throw of 22.60m. In Rio, he finished thirteenth in the men's javelin F57 event with a best throw of 27.37 meters.

Men's Field There were no broadcast rights holders for the 2016 Games in Benin. People who wanted to watch them had to watch them via the live stream provided by the International Paralympic Committee. Benin at the 2016 Summer Olympics

Ken Watters

Ken Watters is an American jazz trumpeter residing in Huntsville, Alabama. He is the brother of Harry Watters. Ken is a member of several noted performing groups, including Tabou Combo, Natalie Cole Band, the Magic City Jazz Orchestra, Ray Reach and Friends and the W. C. Handy Jazz All-Stars, he attended the University of North Texas, where he participated in the famed Lab Band program and studied trumpet with internationally renowned teacher Leonard Candelaria. Ken pursued further trumpet studies in New York City with Lew Soloff and Wynton Marsalis. Ken's most recent CD release was by his own Haitian-Caribbean influenced jazz septet, RIYEL; the group's self-titled debut CD was released internationally on Summit Records. His latest musical project is an ongoing venture co-led alongside vocalist Ingrid Felts, called "Watters-Felts Project; the jazz-oriented sextet, based in Huntsville, Alabama, is made up of six of the most in-demand musicians in the southeast, including pianist Keith Taylor, bassist Abe Becker, percussionist Darrell Tibbs, drummer Marcus Pope, plus Felts & Watters.

Ken is an adjunct professor at University of Alabama in Huntsville, where he directs the UAH Jazz Ensemble I. The Jungle Brothers* Brothers II* Southern Exposure Brothers III* RIYEL Watters Brothers website Ken Watters at

Moulin, Scotland

Moulin is a village in Perthshire in central Scotland. It is located in the Tummel valley, 1 kilometre north of Pitlochry, 40 kilometres north of Perth; the Black Castle of Moulin is the ruined remains of a 14th-century castle, built on a former island. The castle was burned down in 1512. Moulin Kirk was the parish church of the area from the Middle Ages; the church was granted to the monks of Dunfermline Abbey by William the Lion, King of the Scots from 1165 to 1214. In 1873 the church was gutted by fire and the present building was constructed. In 1989 the church was closed, the parish church is now Pitlochry Church of Scotland. Robert Louis Stevenson stayed at Fishers Hotel in Pitlochry in June 1881 with his wife Fanny and his mother; the party moved to Kinnaird Cottage in Moulin. Here Stevenson worked on “Thrawn Janet”, “The Merry Men” and “The Body Snatcher” Moulin Kirk Trust