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Data compression

In signal processing, data compression, source coding, or bit-rate reduction is the process of encoding information using fewer bits than the original representation. Any particular compression is either lossless. Lossless compression reduces bits by eliminating statistical redundancy. No information is lost in lossless compression. Lossy compression reduces bits by removing less important information. A device that performs data compression is referred to as an encoder, one that performs the reversal of the process as a decoder; the process of reducing the size of a data file is referred to as data compression. In the context of data transmission, it is called source coding. Source coding should not be confused with channel coding, for error detection and correction or line coding, the means for mapping data onto a signal. Compression is useful because it reduces resources required to transmit data. Computational resources are consumed in the decompression processes. Data compression is subject to a space–time complexity trade-off.

For instance, a compression scheme for video may require expensive hardware for the video to be decompressed fast enough to be viewed as it is being decompressed, the option to decompress the video in full before watching it may be inconvenient or require additional storage. The design of data compression schemes involves trade-offs among various factors, including the degree of compression, the amount of distortion introduced, the computational resources required to compress and decompress the data. Lossless data compression algorithms exploit statistical redundancy to represent data without losing any information, so that the process is reversible. Lossless compression is possible. For example, an image may have areas of color; this is a basic example of run-length encoding. The Lempel–Ziv compression methods are among the most popular algorithms for lossless storage. DEFLATE is a variation on LZ optimized for decompression speed and compression ratio, but compression can be slow. In the mid-1980s, following work by Terry Welch, the Lempel–Ziv–Welch algorithm became the method of choice for most general-purpose compression systems.

LZW is used in GIF images, programs such as PKZIP, hardware devices such as modems. LZ methods use a table-based compression model where table entries are substituted for repeated strings of data. For most LZ methods, this table is generated dynamically from earlier data in the input; the table itself is Huffman encoded. Grammar-based codes like this can compress repetitive input effectively, for instance, a biological data collection of the same or related species, a huge versioned document collection, internet archival, etc; the basic task of grammar-based codes is constructing a context-free grammar deriving a single string. Other practical grammar compression algorithms include Re-Pair; the strongest modern lossless compressors use probabilistic models, such as prediction by partial matching. The Burrows–Wheeler transform can be viewed as an indirect form of statistical modelling. In a further refinement of the direct use of probabilistic modelling, statistical estimates can be coupled to an algorithm called arithmetic coding.

Arithmetic coding is a more modern coding technique that uses the mathematical calculations of a finite-state machine to produce a string of encoded bits from a series of input data symbols. It can achieve superior compression compared to other techniques such as the better-known Huffman algorithm, it uses an internal memory state to avoid the need to perform a one-to-one mapping of individual input symbols to distinct representations that use an integer number of bits, it clears out the internal memory only after encoding the entire string of data symbols. Arithmetic coding applies well to adaptive data compression tasks where the statistics vary and are context-dependent, as it can be coupled with an adaptive model of the probability distribution of the input data. An early example of the use of arithmetic coding was in an optional feature of the JPEG image coding standard, it has since been applied in various other designs including H.263, H.264/MPEG-4 AVC and HEVC for video coding. In the late 1980s, digital images became more common, standards for lossless image compression emerged.

In the early 1990s, lossy compression methods began to be used. In these schemes, some loss of information is accepted as dropping nonessential detail can save storage space. There is a corresponding trade-off between reducing size. Lossy data compression schemes are designed by research on. For example, the human eye is more sensitive to subtle variations in luminance than it is to the variations in color. JPEG image compression works in part by rounding off nonessential bits of information. A number of popular compression formats exploit these perceptual differences, including psychoacoustics for sound, psychovisuals for images and video. Most forms of lossy compression are based on transform coding the discrete cosine transform, it was first proposed in 1972 by Nasir Ahmed, who developed a working algorithm with T. Natarajan and K. R. Rao in 1973, before introducing it in January 1974. DCT is the most used l

Polícia de Segurança Pública

The Polícia de Segurança Pública is the national civil preventive police force of Portugal. Part of the Portuguese security forces, the mission of the PSP is to defend Republican democracy, safeguarding internal security and the rights of its citizens. Despite many other functions, the force is known for policing urban areas with uniformed police officers, while rural areas are policed by National Republican Guard, a gendarmerie force. PSP is focused in the preventive policing. Investigation of serious crimes falls under the Judicial Police responsibility, a separate agency. Like most of Europe, until the Middle Ages the defense of public order was the responsible of local communities, under the authority of feudal lords and courts. In Portugal, there are few references to the administration of justice until the second half of the 15th century. With the reign of King Afonso V came the first ordinances and penal codes, known as the Ordenações Afonsinas; these ordinances were reissued during the reign of King John I in 1514, after various changes under Manuel I.

Some of the early judicial measures came from the early nobles. Afonso Henriques ordered the incarceration of women who lived with elements of the clergy, while in the era of Afonso II, under the influence of Visigothic codes and Roman law, resulted in the appearance of the first general laws. Afonso III punished anyone who assaulted and robbed the home of another. King Pedro I, the Just, decreed that anyone who falsified coins, gold or silver objects would have their hands and feet amputated. However, criminals were provided shelters by which to flee justice: the churches, monasteries and "privileged" lands; these privileged lands became areas of thieves and criminals, which resulted in King John extinguishing these areas. This was something that King Fernando did with bairros, only churches and convents became sanctuaries; the first corps of police agents, the Quadrilheiros, was created by Fernando I, on 12 September 1383, consisting of 20 members, who were recruited by force from the strongest physical men, to serve Lisbon.

These men were subject to the town council for three years, required to swear fealty and carry a weapon, which they would display at their homes, representing a symbol of their authority to arrest and direct criminals to the Corregedores. Since these men never received payment for their services, since these activities were dangerous, most chose to escape the responsibility. For most, these services were intolerable, with little prestige, at various times resulting in bruises and wounds in the execution of their tasks. Owing to this, by 1418, these constables were not required to circle the town. Afonso V provided the Quadrilheiros, on 10 June 1460, with several social and economic privileges. However, these would disappear over time; as Afonso V put into action other laws, regulations and ordinances, many were ineffective. King Sebastian promulgated laws on 31 January 1559, 17 January 1570, 12 July and 13 August 1571, to reinforce the laws of Fernando I, Edward and Afonso V. In order to compensate the diminishing benefits of their service, the Quadrilheiros were exempt from paying taxes or military service.

Sebastian ordered that Lisbon be divided into barrios, that each should be administered by an official of justice, with discretionary powers. On 12 March 1603, King Philip II ordered new regulations for the Quadrilheiros in order to reinforce their authority; the Lisbon council, on 30 January 1617, determined that Quadrilheiros should have a label over their doors to identify them, that the King should confer on them special privileges, such as sitting at the council table. King John IV of Portugal provided a new charter, a decree on 29 November 1644, forced them to serve the public, working in the day and evenings. By the first half of the 18th century, little had improved. There continued to be a lack of policing, resulting in leis in 1701, 1702 and 1714; as new circuits were created to blanket the city, many of the criminals were aware that the laws transformed the situation into forgettable enclaves. The Quadrilheiros continued to be a poor class, due to their limitations, resulting in poor public order.

After the 1755 Lisbon earthquake new laws and resolutions were established to maintain public order and reduce anarchy. Sebastião José de Carvalho e Melo, the Marquess of Pombal, found it necessary to create an organism to centralize all laws. By law, on 25 June 1760, he created the Intendência da Polícia da Corte e do Reino, the position of Intendente-Geral da Polícia da Corte e do Reino, with unlimited jurisdiction; the first Quartermaster-General was Inácio Ferreira Souto, at the same time that the term polícia was used, the Quadrilheiros were relegated to the evenings. However, this foundation did little resolve criminal issues, locks on doors, grades on windows and blunderbusses beside the bed continued to be important; the Intendente-Geral was preoccupied with pursuing those who spoke badly of the King, Government or Pombal himself. Between 1760 and 1780, chaos persisted. By decree, on 18 January 1780, Queen Maria I of Portugal named the old Criminal Judge for the Bairro do Castelo de S. Jorge, Diogo Inácio de Pina Manique, Intendente-Geral.

Instructed in laws at the University of Coimbra, he became a powerful chief: he began by expunging the police services of criminal elements, took advantage of all laws to arrest all criminals or suspects in the Alfama, Bairro Alto and Madragoa, reorganizing the services and bringing a level of

Dolphin drive hunting

Dolphin drive hunting called dolphin drive fishing, is a method of hunting dolphins and other small cetaceans by driving them together with boats and usually into a bay or onto a beach. Their escape is prevented by closing off the route to the open ocean with boats and nets. Dolphins are hunted this way in several places around the world, including the Solomon Islands, the Faroe Islands and Japan, the most well-known practitioner of this method. By numbers, dolphins are hunted for their meat. Despite the controversial nature of the hunt resulting in international criticism, the possible health risk that the polluted meat causes, tens of thousands of dolphins are caught in drive hunts each year. Whaling in the Faroe Islands takes the form of beaching and slaughtering long-finned pilot whales, it has been practiced since about the time of the first Norse settlements on these North Atlantic islands, thus can be considered aboriginal whaling. It is mentioned in the Sheep Letter, a Faroese law from 1298, a supplement to the Norwegian Gulating law.

It is regulated by the Faroese authorities. Around 800 long-finned pilot whales and some Atlantic white-sided dolphins are slaughtered annually during the summer; the hunts, called grindadráp in Faroese, are organized on a community level. Anyone who has a special training certificate on slaughtering a pilot whale with the spinal-cord lance can participate; this was not necessary earlier, but because of constant criticism from animal welfare organizations, the Faroese people try to improve the slaughtering methods in order to make them more humane. The Grind law was updated in 2015, where one of the regulations demanded that the whalers followed a course on how to slaughter a pilot whale with the spinal-cord lance; the police and Grindaformenn are allowed to remove people from the grind area. The hunters first surround the pilot whales with a wide semicircle of boats; the boats drive the pilot whales into a bay or to the bottom of a fjord. Not all bays are certified, the slaughter will only take place on a certified beach.

Many Faroese consider the whale meat an important part of their food history. Animal rights groups criticize the slaughter as being unnecessary. In November 2008, Høgni Debes Joensen, chief medical officer of the Faroe Islands and Pál Weihe, have recommended in a letter to the Faroese government that pilot whales should no longer be considered fit for human consumption because of the high level of mercury, PCB and DDT derivatives. However, the Faroese government did not forbid whaling. On 1 July 2011 the Faroese Food and Veterinary Authority announced their recommendation regarding the safety of eating meat and blubber from the pilot whale, not as strict as the one of the chief medical officer; the new recommendation says only one dinner with whale meat and blubber per month, with a special recommendation for younger women, pregnant women and breastfeeding women. From 2002 to 2009 the PCB concentration in whale meat has fallen by 75%, DDT values in the same time period have fallen by 70% and mercury levels have fallen.

In mid-1950s, fishermen in Iceland requested assistance from the government to remove killer whales from Icelandic waters as they damaged fishing equipment. With fisheries accounting for 20% of Iceland's employment at the time, the perceived economic impact was significant; the Icelandic government asked the United States for assistance. As a NATO ally with an air base in Iceland, the US Navy deployed Patrol Squadrons VP-18 and VP-7 to achieve this task. According to the US Navy, hundreds of animals were killed with machineguns and depth charges. In the late 1970s, after the Marine Mammal Protection Act of 1972 and the ban on hunting killer whales in Washington in 1976 as discussed in this article, the hunting of killer whales in Iceland resumed, this time aiming to capture live animals for the entertainment industry; the first two killer whales captured went to Dolfinarium Harderwijk in the Netherlands. One of these animals was soon after transferred to SeaWorld; these captures continued until 1989, with the additional animals going to SeaWorld, Marineland Antibes, Marineland of Canada, Kamogawa Sea World, Ocean Park Hong Kong and Conny-Land.

Although commercial whaling does still take place in Icelandic waters today, dolphins are no longer hunted and whale watching is popular amongst tourists. The Taiji dolphin drive hunt captures small cetaceans for their meat and, for sale to dolphinariums. Taiji has a long connection to Japanese whaling; the 2009 documentary film The Cove drew international attention to the hunt. Taiji is the only town in Japan. Concern is majority through the methodology of the hunt. An article by National Geographic refers to The Japanese Association of Zoos and Aquariums' decision to no longer support the Taiji hunt. In 2015, it was announced that there would be a ban in the buying and selling of dolphins through the means of this hunt. Similar drive hunting existed in Kiribati at least until the mid-20th century. Though it is forbidden under Peruvian law to hunt dolphins or eat their meat, a large number of dolphins are still killed illegally by fishermen each year. To catch the dolphins, they are driven together with boats and encircled with nets harpooned, dragged on to the boat, clubbed to death if still alive.

Various species are hunted, such as the dusky dolphin. According to estimates from local animal welfare organisation Mundo Azul released in October 2013, between 1,000 and 2,000 dolphins are killed annually for cons