Vacuum is space devoid of matter. The word stems from the Latin adjective vacuus for "vacant" or "void". An approximation to such vacuum is a region with a gaseous pressure much less than atmospheric pressure. Physicists discuss ideal test results that would occur in a perfect vacuum, which they sometimes call "vacuum" or free space, use the term partial vacuum to refer to an actual imperfect vacuum as one might have in a laboratory or in space. In engineering and applied physics on the other hand, vacuum refers to any space in which the pressure is lower than atmospheric pressure; the Latin term in vacuo is used to describe an object, surrounded by a vacuum. The quality of a partial vacuum refers to how it approaches a perfect vacuum. Other things equal, lower gas pressure means higher-quality vacuum. For example, a typical vacuum cleaner produces enough suction to reduce air pressure by around 20%, but higher-quality vacuums are possible. Ultra-high vacuum chambers, common in chemistry and engineering, operate below one trillionth of atmospheric pressure, can reach around 100 particles/cm3.

Outer space is an higher-quality vacuum, with the equivalent of just a few hydrogen atoms per cubic meter on average in intergalactic space. According to modern understanding if all matter could be removed from a volume, it would still not be "empty" due to vacuum fluctuations, dark energy, transiting gamma rays, cosmic rays and other phenomena in quantum physics. In the study of electromagnetism in the 19th century, vacuum was thought to be filled with a medium called aether. In modern particle physics, the vacuum state is considered the ground state of a field. Vacuum has been a frequent topic of philosophical debate since ancient Greek times, but was not studied empirically until the 17th century. Evangelista Torricelli produced the first laboratory vacuum in 1643, other experimental techniques were developed as a result of his theories of atmospheric pressure. A torricellian vacuum is created by filling a tall glass container closed at one end with mercury, inverting it in a bowl to contain the mercury.

Vacuum became a valuable industrial tool in the 20th century with the introduction of incandescent light bulbs and vacuum tubes, a wide array of vacuum technologies has since become available. The recent development of human spaceflight has raised interest in the impact of vacuum on human health, on life forms in general; the word vacuum comes from Latin, meaning'an empty space, void', noun use of neuter of vacuus, meaning "empty", related to vacare, meaning "to be empty". Vacuum is one of the few words in the English language that contains two consecutive letters u. Historically, there has been much dispute over whether such a thing as a vacuum can exist. Ancient Greek philosophers debated the existence of a vacuum, or void, in the context of atomism, which posited void and atom as the fundamental explanatory elements of physics. Following Plato the abstract concept of a featureless void faced considerable skepticism: it could not be apprehended by the senses, it could not, provide additional explanatory power beyond the physical volume with which it was commensurate and, by definition, it was quite nothing at all, which cannot rightly be said to exist.

Aristotle believed that no void could occur because the denser surrounding material continuum would fill any incipient rarity that might give rise to a void. In his Physics, book IV, Aristotle offered numerous arguments against the void: for example, that motion through a medium which offered no impediment could continue ad infinitum, there being no reason that something would come to rest anywhere in particular. Although Lucretius argued for the existence of vacuum in the first century BC and Hero of Alexandria tried unsuccessfully to create an artificial vacuum in the first century AD. In the medieval Muslim world, the physicist and Islamic scholar, Al-Farabi, conducted a small experiment concerning the existence of vacuum, in which he investigated handheld plungers in water, he concluded that air's volume can expand to fill available space, he suggested that the concept of perfect vacuum was incoherent. According to Nader El-Bizri, the physicist Ibn al-Haytham and the Mu'tazili theologians disagreed with Aristotle and Al-Farabi, they supported the existence of a void.

Using geometry, Ibn al-Haytham mathematically demonstrated that place is the imagined three-dimensional void between the inner surfaces of a containing body. According to Ahmad Dallal, Abū Rayhān al-Bīrūnī states that "there is no observable evidence that rules out the possibility of vacuum"; the suction pump was described by Arab engineer Al-Jazari in the 13th century, appeared in Europe from the 15th century. European scholars such as Roger Bacon, Blasius of Parma and Walter Burley in the 13th and 14th century focused considerable attention on issues concerning the concept of a vacuum. Following Stoic physics in this instance, scholars from the 14th century onward departed from the Aristotelian perspective in favor of a supernatural void beyond the confines of the cosmos itself, a conclusion acknowledged by the 17th century, which helped to segregate natural and theological concerns. Two thousand years after Plato, René Descartes proposed a geometrically based alternative theory of atomism, without the problematic nothing–everything dichotomy of void and atom.

Although Descartes agreed with the contemporary position, that a vacuum does not occur in nature, the success of his namesake coordinate system and more implicitly, the spatial–corporeal component of his metaphysics would come t

NZL 32

NZL 32, or Black Magic, is an International Americas Cup Class yacht which won the 1995 America's Cup by defeating the American defender Young America in a 5–0 victory off San Diego, California. NZL 32 was, in many ways, the complete opposite of her predecessor NZL 20 which contested the 1992 edition of the Louis Vuitton Cup. Instead of being the brainchild of one man she was designed by a team of Tom Schnackenberg, Doug Peterson, Laurie Davidson, David Egan, Peter Jackson, Maury Leyland, David Alan-Williams, Anthony Lehmann, Richard Karn, Wayne Smith, Mike Drumond, Chris Mitchell and Neil Wilkinson; the idea was to produce a yacht that suited the crew, catering to their specific needs. NZL 32 was built of carbon fibre by the McMullen & Wing yard, Auckland, in 1994, her sister yacht, NZL 38, or Black Magic II, was used in the initial stages of the Louis Vuitton Cup in San Diego winning all but one race. However, Team New Zealand believed NZL 32 to be faster than NZL 38 and so retired her early, before the Louis Vuitton Cup semi-finals.

NZL 38 became a trial horse for Team New Zealand's 2000 defence of the America's Cup in Auckland, was purchased for the 2003 Cup by the Swedish Victory Challenge. She was renamed Cristina. With NZL 38 now retired, NZL 32 was brought out for the final stages of the Louis Vuitton Cup, she proved to be faster than NZL 38, winning 9 of 11 races in the semi-finals and 5 out of 6 in the finals against oneAustralia. As the winner of the Louis Vuitton Cup, she now had the right to challenge for the America's Cup itself. By this stage, it was clear NZL 32 was far superior to any of her rivals, including the winner of the defender series Stars & Stripes. With that knowledge, Stars & Stripes skipper Dennis Conner swapped boats for the Cup matches, taking the helm of Young America. While Young America didn't win the Defender's Series, she was believed to be faster than Stars & Stripes. Young America was however no match for NZL 32. In what became known as a "blackwash", Black Magic trounced Young America 5–0 in the Cup match, thus remains unbeaten in an America's Cup race.

NZL 32 was used as a trial boat for the 2003 challenge of China Team. In July 2002, she was donated to the Museum of New Zealand, however there was much debate over how she should be displayed to the nation; the initial proposal was for a'glass case' with the yacht placed inside – a giant "ship in a bottle" – however this was likened to a "glass coffin" by many and as such was abandoned. Following the murder of Team New Zealand's inspirational leader Sir Peter Blake, it was decided NZL 32 would form the centrepiece of a tribute to him; this was constructed at the National Maritime Museum in Auckland and was named'Blue Water Black Magic' – an interactive exhibit and tribute to Sir Peter. NZL 32 is suspended from the ceiling and can be viewed from all angles, with much of Sir Peter's yachting memorabilia exhibited around it. List of IACC yachts

List of state leaders in 955

This is a list of heads of state, heads of governments, other rulers in the year 955. Fatimid Caliphate – Maʻād al-Muʻizz li Dīn Allāh, Caliph Byzantine EmpireConstantine VII ChinaLater ZhouShizong, Emperor of Later Zhou Dingnan – Li Yixing, Dingnan Jiedushi JingnanGao Baorong, King of Nanping Later ShuMeng Chang, Emperor of Later Shu Northern HanLiu Chengjun, Emperor of Northern Han QingyuanLiu Congxiao, Qingyuan Jiedushi Southern HanLiu Sheng, Emperor of Southern Han Southern TangYuanzong, Emperor of Southern Tang.