M4 Sherman

The M4 Sherman Medium Tank, M4, was the most used medium tank by the United States and Western Allies in World War II. The M4 Sherman proved to be reliable cheap to produce, available in great numbers, it was the basis of several successful tank destroyers, such as the M10, Achilles and M36. Tens of thousands were distributed through the Lend-Lease program to the British Commonwealth and Soviet Union; the tank was named by the British for the American Civil War general William Tecumseh Sherman. The M4 Sherman evolved from the M3 Medium Tank, which had its main armament in a side sponson mount; the M4 retained much of the previous mechanical design, but moved the main 75 mm gun into a traversing central turret. One feature, a one-axis gyrostabilizer, was not precise enough to allow firing when moving but did help keep the reticle on target, so that when the tank did stop to fire, the gun would be aimed in the right direction; the designers stressed mechanical reliability, ease of production and maintenance, standardization of parts and ammunition in a limited number of variants, moderate size and weight.

These factors, combined with the Sherman's then-superior armor and armament, outclassed German light and medium tanks fielded in 1939–42. The M4 went on to be produced in large numbers, being the most produced tank in American history: The Soviets' T-34 medium tank was the only tank design produced in larger numbers during World War II; the Sherman spearheaded many offensives by the Western Allies after 1942. When the M4 tank went into combat in North Africa with the British Army at El Alamein in late 1942, it increased the advantage of Allied armor over Axis armor and was superior to the lighter German and Italian tank designs. For this reason, the US Army believed that the M4 would be adequate to win the war, little pressure was exerted for further tank development. Logistical and transport restrictions, such as limitations imposed by roads and bridges complicated the introduction of a more capable but heavier tank. Tank destroyer battalions using vehicles built on the M4 hull and chassis, but with open-topped turrets and more potent high-velocity guns entered widespread use in the Allied armies.

By 1944, most M4 Shermans kept their dual-purpose 75 mm gun. By the M4 was inferior in firepower and armor to increasing numbers of German heavy tanks, but was able to fight on with the help of considerable numerical superiority, greater mechanical reliability, better logistical support, support from growing numbers of fighter-bombers and artillery pieces; some Shermans were produced with a more capable gun, the 76 mm gun M1, or refitted with a 76.2mm calibre Ordnance QF 17-pounder gun by the British. The relative ease of production allowed large numbers of the M4 to be manufactured, significant investment in tank recovery and repair units allowed disabled vehicles to be repaired and returned to service quickly; these factors combined to give the Allies numerical superiority in most battles, many infantry divisions were provided with M4s and tank destroyers. After World War II, the Sherman the many improved and upgraded versions, continued to see combat service in many conflicts around the world, including the UN forces in the Korean War, with Israel in the Arab–Israeli wars with South Vietnam in the Vietnam War, on both sides of the Indo-Pakistani War of 1965.

The U. S. Army Ordnance Department designed the M4 medium tank as a replacement for the M3 medium tank; the M3 was an up-gunned development of the M2 Medium Tank of 1939, in turn derived from the M2 light tank of 1935. The M3 was developed as a stopgap measure. While it was a big improvement when tried by the British in Africa against early German tanks, the placement of a 37 mm gun turret on top gave it a high profile, the unusual side-sponson mounted main gun, with limited traverse, could not be aimed across the other side of the tank. Though reluctant to adopt British weapons into their arsenal, the American designers were prepared to accept proven British ideas. British ideas, as embodied in a tank designed by the Canadian General Staff influenced the development of the American Sherman tank. Before long American military agencies and designers had accumulated sufficient experience to forge ahead on several points. In the field of tank armament the American 75 mm and 76 mm dual-purpose tank guns won the acknowledgement of British tank experts.

Detailed design characteristics for the M4 were submitted by the Ordnance Department on 31 August 1940, but development of a prototype was delayed while the final production designs of the M3 were finished and the M3 entered full-scale production. On 18 April 1941, the U. S. Armored Force Board chose the simplest of five designs. Known as the T6, the design was a modified M3 hull and chassis, carrying a newly designed turret mounting the M3's 75 mm gun; this would become the Sherman. The Sherman's reliability resulted from many features developed for U. S. light tanks during the 1930s, including vertical volute spring suspension, rubber-bushed tracks, a rear-mounted radial engine with drive sprockets in front. The goals were to produce a fast, dependable medium tank able to support infantry, provide breakthrough striking capacity, defeat any tank in use by the Axis nations; the T6 prototype was completed on 2 September 1941. The upper hull of the T6 was a single large casting, it featured a single overhead hatch for the driver, a hatch in the side of the hull.

In the M4A1 production model, this large castin


Polypyrrole is a type of organic polymer formed by the polymerization of pyrrole. It is a solid with the formula HnH. Upon oxidation, polypyrrole converts to a conducting polymer; some of the first examples of polypyrroles were reported in 1963 by Weiss and coworkers. These workers described the pyrolysis of tetraiodopyrrole to produce conductive materials; the Nobel Prize in Chemistry was awarded in 2000 for work on conductive polymers including polypyrrole, polythiophene and polyacetylene. Polypyrrole is prepared by oxidation of pyrrole: n C4H2NH + 2n FeCl3 → n + 2n FeCl2 + 2n HClThe process is thought to occur via the formation of the pi-radical cation C4H4NH+; this electrophile attacks the C-2 carbon of an unoxidized molecule of pyrrole to give a dimeric cation 2]++. The process repeats itself many times. Conductive forms of PPy are prepared by oxidation of the polymer: n + 0.2 X → The polymerization and p-doping can be effected electrochemically. The resulting conductive polymer are peeled off of the anode.

Cyclic voltammetry and chronocoulometry methods can be used for electrochemical synthesis of polypyrrole. Films of PPy are yellow but darken in air due to some oxidation. Doped films are blue or black depending on the degree of polymerization and film thickness, they are amorphous, showing only weak diffraction. PPy is described as "quasi-unidimensional" vs one-dimensional since there is some crosslinking and chain hopping. Undoped and doped films are insoluble in solvents but swellable. Doping makes the materials brittle, they are stable in air up to 150 °C at which temperature the dopant starts to evolve. PPy is an insulator, but its oxidized derivatives are good electrical conductors; the conductivity of the material depends on the conditions and reagents used in the oxidation. Conductivities range from 2 to 100 S/cm. Higher conductivities are associated with larger anions, such as tosylate. Doping the polymer requires that the material swell to accommodate the charge-compensating anions; the physical changes associated with this charging and discharging has been discussed as a form of artificial muscle.

The surface of polypyrrole films present fractal properties and ionic diffusion through them show anomalous diffusion pattern. PPy and related conductive polymers have two main application in electronic devices and for chemical sensors. PPy is a potential vehicle for drug delivery; the polymer matrix serves as a container for proteins. Polypyrrole has been investigated as a catalyst support for fuel cells and to sensitize cathode electrocatalysts. Together with other conjugated polymers such as polyaniline, poly etc. polypyrrole has been studied as a material for "artificial muscles", a technology that offers advantages relative to traditional motor actuating elements. Polypyrrole was used to coat silica and reverse phase silica to yield a material capable of anion exchange and exhibiting hydrophobic interactions. Polypyrrole was used in the microwave fabrication of multiwalled carbon nanotubes, a rapid method to grow CNT's. A water-resistant polyurethane sponge coated with a thin layer of polypyrrole absorbs 20 times its weight in oil and is reusable.

The wet-spun polypyrrole fibre can be prepared chemical polymerization pyrrole and DEHS as dopant. Organic semiconductor Tetrapyrroles

Papilio antonio

Papilio antonio is a butterfly of the family Papilionidae. It is endemic to the Philippines; the wingspan is 90–110 mm. There are two recognised subspecies: Papilio antonio antonio Papilio antonio negrosiana Schröder & Treadaway Papilio antonio is a member of the noblei species-group; the members of this clade are Papilio antonio Hewitson, Papilio noblei de Nicéville, Collins, N. Mark. Threatened Swallowtail Butterflies of the World: The IUCN Red Data Book. Gland & Cambridge: IUCN. ISBN 978-2-88032-603-6 – via Biodiversity Heritage Library. William C. Hewitson: Illustrations of new species of exotic butterflies, selected chiefly from the Collections of W. Wilson Saunders and William C. Hewitson. Bd.1, John Van Voorst, 1866 PDF Page M. G. P & Treadaway,C. G. 2003 Schmetterlinge der Erde, Butterflies of the world Part XVII, Papilionidae IX Papilionidae of the Philippine Islands. Edited by Erich Bauer and Thomas Frankenbach Keltern: Goecke & Evers. ISBN 978-3-931374-45-7