A hydrophone is a microphone designed to be used underwater for recording or listening to underwater sound. Most hydrophones are based on a piezoelectric transducer that generates an electric potential when subjected to a pressure change, such as a sound wave; some piezoelectric transducers can serve as a sound projector, but not all have this capability, some may be destroyed if used in such a manner. A hydrophone can detect airborne sounds, but will be insensitive because it is designed to match the acoustic impedance of water, a denser fluid than air. Sound travels 4.3 times faster in water than in air, a sound wave in water exerts a pressure 60 times that exerted by a wave of the same amplitude in air. A standard microphone can be buried in the ground, or immersed in water if it is put in a waterproof container, but will give poor performance due to the bad acoustic impedance match, it is considered a sensor. The first hydrophones consisted of a tube with a thin membrane covering the submerged end and the observer's ear on the other end.

The design of effective hydrophones must take into account the acoustic resistance of water, 3750 times that of air. The American Submarine Signaling Company developed a hydrophone to detect underwater bells rung from lighthouses and lightships. The case was a hollow brass disc 35 centimetres in diameter. On one face was a 1 millimetre thick brass diaphragm, coupled by a short brass rod to a carbon microphone. Early in the war, French President Raymond Poincaré, himself a physicist, provided Paul Langevin with the facilities needed to work on a method to locate submarines by the echos from sound pulses, they developed a piezoelectric hydrophone by increasing the power of the signal with a vacuum tube amplifier. The same piezoelectric plate could be vibrated by an electrical oscillator to produce the sound pulses. In the war, the British Admiralty belatedly convened a scientific panel to advise on how to combat U-boats. It included the Australian physicist William Henry Bragg and the New Zealand physicist Sir Ernest Rutherford.

They concluded. Rutherford's research produced his sole patent for a hydrophone. Bragg took the lead in July 1916 and he moved to the Admiralty hydrophone research establishment at Hawkcraig on the Firth of Forth. The scientists set two goals: to develop a hydrophone that could hear a submarine despite the racket produced by a patrol ship carrying the hydrophone and to develop a hydrophone that could reveal the bearing of the submarine. A bidirectional hydrophone was invented at East London College, they mounted a microphone on each side of a diaphragm in a cylindrical case. Bragg's laboratory made such a hydrophone directional by mounting a baffle in front of one side of the diaphragm, it took months to discover that effective baffles must contain a layer of air. In 1918, airships of the Royal Naval Air Service engaged in anti-submarine warfare experimented by trailing dipped hydrophones. Bragg found it inferior to British models. By the end of the war, the British had 38 hydrophone officers and 200 qualified listeners, paid an addition 4d per day.

From late in World War I until the introduction of active sonar in the early 1920s, hydrophones were the sole method for submarines to detect targets while submerged. A small single cylindrical ceramic transducer can achieve near perfect omnidirectional reception. Directional hydrophones increase sensitivity from one direction using two basic techniques: This device uses a single transducer element with a dish or conical-shaped sound reflector to focus the signals, in a similar manner to a reflecting telescope; this type of hydrophone can be produced from a low-cost omnidirectional type, but must be used while stationary, as the reflector impedes its movement through water. A new way to direct is to use a spherical body around the hydrophone; the advantage of directivity spheres is that the hydrophone can be moved within the water, ridding it of the interferences produced by a conical-shaped element. Multiple hydrophones can be arranged in an array so that it will add the signals from the desired direction while subtracting signals from other directions.

The array may be steered using a beamformer. Most hydrophones are arranged in a "line array" but may be in two- or three-dimensional arrangements. SOSUS hydrophones, laid on the seabed and connected by underwater cables, were used, beginning in the 1950s, by the U. S. Navy to track movement of Soviet submarines during the Cold War along a line from Greenland and the United Kingdom known as the GIUK gap; these are capable of recording low frequency infrasound, including many unexplained ocean sounds. Communication with submarines Geophone Underwater acoustics Sonar Reflection seismology John. SOSUS. Retrieved January 28, 2005. Watlington, Frank. How to build & use low-cost hydrophones. Unknown. Hydrophone. Retrieved January 28, 2005. Unknown. Schlumberger Oilfield Glossary: Term'hydrophone'. Retrieved January 28, 2005. Onda Corporation.'Hydrophone Handbook'. Report AIR 1/645/17/122/304 - National Archives Kew. Airship Hydrophone experiments. DOSITS—Hydrophone introduction at Discovery of Sound in the Sea orcasound.n

Stapleford Woods

Stapleford Woods are an area of ancient woodland and forest in Stapleford, England. The boundary of the ancient woods marks the county boundary between Lincolnshire and Nottinghamshire. Left in ancient times to Trinity College, the 750 acres site was clear-felled during the early stages of World War I to supply local industry. Left unplanted between the wars, the grounds were used as a British Army camp and training grounds during World War II. In September 1943 No. 239 Squadron RAF had moved to RAF Ayr to train as a night fighter unit, re-equipped with the De Havilland Mosquito. It moved to RAF West Raynham, Norfolk to join No. 100 Group, participating in night time operations against enemy Nazi-Luftwaffe fighters. On 27 October 1944 during fighter affiliation training with No. 49 Squadron RAF, a Mosquito piloted by F/Lt J. H. Roberts and accompanied by Flight Engineer Sgt. A. M. Ashcroft and crashed in the woods, with the immediate death of both pilot and passenger. After the cessation of hostilities, in late 1945 the woods were bought by the newly formed Forestry Commission.

Along with a lot of woodland within the River Trent valley, in the 1950s the site was extensively replanted with both Scots and Corsican pine, chosen to supply local industry. Now a managed working forest under the care of the Forestry Commission, surveys in 2004 found that the wood dated back at least 400 years, making it a designated ancient woodland. While many visitors are attracted by the Victorian era-plated Rhododendrons which are found throughout the wood at heights of up to 7 metres, the Forestry Commission and North Kesteven council have agreed to a 50-year plan to restore the forest to its original broad-leaf tree state. Initial clearance of a 75 acres area yielded a resultant crop of purple flowering heather, which germinated from seeds, buried for over 70 years; the Forestry Commission carpark grid reference SK861569, provides access to a marked.75 miles circular walk, which takes 30-40mins at a leisurely pace to complete. The car park can be access from Coddington Lane, is sign posted off of this road whilst travelling through the wood.

The woods were the main backdrop for the 2009 documentary film The Real Badlands produced by Current TV and Rockwood Pictures, by British filmmakers Tim Clark and Craig Ford. The film tells the story of a Newark-on-Trent couple, who fed up with modern day life, quit their jobs, sell all of their possessions, move into the woods; the film was shot in the woods and Kelham, near Newark, during the summer and winter of 2008. After release the film was controversial, due to claims that the film was in fact a mockumentary; the filmmakers publicly denied these claims in a written statement read out live on Current TV, minutes after the film was broadcast. In July 2012, the woods made national headlines after the Forestry Commission cleared undergrowth within the woods, which were said to be attracting large numbers of doggers, scaring families and ramblers. Police patrols by both Lincolnshire and Nottinghamshire Police have been increased, carparks closed by North Kesteven at night with warning signs applied.

Stapleford Woods at the Forestry Commission Stapleford Woods at Lincolnshire County Council

Correctional Education Association

The Correctional Education Association was founded in 1930 to provide educational services in correctional settings. This non-profit professional association is the largest affiliate of the American Correctional Association; the Correctional Education Association is the professional organization for educators who work in adult correctional and juvenile justice facilities internationally. Although based in the United States of America, where most of its members work, it has made great advances in encouraging members from outside the US to become active members from outside the US to become active members of the organization; the CEA provides a host of services to its members. These include the following: a peer-reviewed international journal, a quarterly newsletter, annual membership and resource directory, an accreditation system for prison and juvenile school programs, a website and listserves for its special interest groups, under-graduate and graduate online courses for educators, many more services.

Austin MacCormick wrote a book based on the results of his 1928 nationwide survey of prison education. MacCormick was influenced by Thomas Mott Osborne. MacCormick was Assistant Director of the U. S. Bureau of Prisons, organized in 1930 a standing committee on education within the American Prison Association; the Standing Committee on Education published its first journal from 1937 to 1940 entitled Correctional Education. In 1945, the Standing Committee on Education organized the Correctional Education Association at the 76th Congress of the American Prison Association. In 1946, CEA was formally recognized with Price Chenault elected as the first President. In 1949, The Journal of Correctional Education was reestablished with Chester D. Owens as editor. In 1981, the CEA hired its first Executive Director, Osa Coffey, established a national office. In 1986 CEA moved its national office to Maryland from DC where it remains today; the current address is 12625 Laurel Bowie Road #3430, Laurel, MD 20709.

Telephone is 443-459-3080 and the fax number is 443-459-3088. Website: The Acting Executive Director is Morris Dews and the Administrative Assistant is Kiara Wilson. CEA is divided into 8 regions encompassing Canada. There are two international representative seats open on the Executive Board of the CEA. There is one for the Rest of the World; the International Representatives relay the issues and subjects of concern from international members to the Executive Board at regular meetings. There are provincial chapters; these regions and state/provincial chapters host annual conferences and training seminars. The International CEA hosts an annual Spring Forum; the annual International conferences offer members an opportunity to exchange ideas with correctional and prison educators from around the world and dialogue about the experience of teaching in a unique pedagogical setting. Each year the Journal of Correctional Education devotes a special issue to a different subject; the June 2007 issue of the Journal was devoted to international issues in correctional education with contributions from other countries including Ireland and Israel.

The CEA is the largest professional organization dedicated to the mission of education for those students in the Adult and Juvenile Criminal Justice Systems. There are over 1300 members of CEA; the most current versions of the CEA Standards are listed below: Performance Standards for Correctional Education Programs in Adult Institutions, July 2016 Performance Standards for Correctional Education Programs in Juvenile Institutions, July 2010 Performance Standards for Correctional Education Programs in Jails and Detention Centers, July 2016 Prison education Correctional Education Association: Transforming Lives Center for the Study of Correctional Education