SUMMARY / RELATED TOPICS

Microstructure

Microstructure is the small scale structure of a material, defined as the structure of a prepared surface of material as revealed by an optical microscope above 25× magnification. The microstructure of a material can influence physical properties such as strength, ductility, corrosion resistance, high/low temperature behaviour or wear resistance; these properties in turn govern the application of these materials in industrial practice. Microstructure at scales smaller than can be viewed with optical microscopes is called nanostructure, while the structure in which individual atoms are arranged is known as crystal structure; the nanostructure of biological specimens is referred to as ultrastructure. A microstructure’s influence on the mechanical and physical properties of a material is governed by the different defects present or absent of the structure; these defects can take many forms but the primary ones are the pores. If those pores play a important role in the definition of the characteristics of a material, so does its composition.

In fact, for many materials, different phases can exist at the same time. These phases have different properties and if managed can prevent the fracture of the material; the atoms and molecules comprising minerals and living matter are bound by six types of bonds with different intensities and properties. Examples include metallic bonds, covalent bonds, ionic bonds, weak bonds. Among the weak bonds, there is a distinction between polar bonds or hydrophilic bonds and nonpolar or hydrophobic bonds. From these properties will come the spatial form of the associated atoms and the molecules and at a larger scale, of the crystal, of the organism as a whole. Metallic bonds are formed by the sharing of electrons in the outer layer of the atom in an electron cloud, where they are free and delocalized; this free-electron gas ensures the cohesion of the remaining cations and enables electrical conduction in metals and alloys. Covalent bonds are formed by the sharing of pairs of valence electrons in order to fill the outer electron shells of each atom.

They are strong bonds that are found in non-metals such as semiconductors, certain ceramics and biological materials. Ionic bonds are formed by the transfer of an electron from one atom to the other, they are strong bonds that appear, for example, between a metal atom that has released an electron and a non-metal atom that has captured the free electron. After bonding, both atoms become charged; these bonds are found in minerals, biological materials, certain polymers. Weak polar bonds are electrostatic and correspond to simple attractions between dipoles in compounds or molecules with inhomogeneous or polarizable charges, they act with less intensity than strong bonds. Among them, for example, are van der Waals bonds between molecules and hydrogen bonds between water molecules in liquid water and ice; these bonds are found in all biological materials, certain hydrated minerals and some mixed–composite materials. Weak nonpolar bonds or hydrophobic bonds are formed by repulsion. In a polar liquid, the molecules try to establish a maximum number of bonds between each other.

If nonpolar molecules are added to the solution, their presence disrupts the formation of this network of bonds, they will be rejected. Uniquely nonpolar molecules are rare for the most part are found in hydrocarbons. Fatty acids are amphiphilic molecules, containing a nonpolar end; these molecules will form complex structures, with the polar end on the outside in contact with the water and the nonpolar end on the inside isolated from the water. Depending on the nature of the molecule, these structures will either be small globules called micelles or be membranes; these bonds are found in all biological materials. The concept of microstructure is observable in macrostructural features in commonplace objects. Galvanized steel, such as the casing of a lamp post or road divider, exhibits a non-uniformly colored patchwork of interlocking polygons of different shades of grey or silver; each polygon is a single crystal of zinc adhering to the surface of the steel beneath. Zinc and lead are two common metals.

The atoms in each grain are organized into one of seven 3d stacking arrangements or crystal lattices. The direction of alignment of the matrices differ between adjacent crystals, leading to variance in the reflectivity of each presented face of the interlocked grains on the galvanized surface; the average grain size can be controlled by processing conditions and composition, most alloys consist of much smaller grains not visible to the naked eye. This is to increase the strength of the material. To quantify microstructural features, both morphological and material property must be characterized. Image processing is a robust technique for determination of morphological features such as volume fraction, inclusion morphology and crystal orientations. To acquire micrographs, optical as well as electron microscopy are used. To determine material property, Nanoindentation is a robust technique for determination of properties in micron and submicron level for which conventional testing are not feasible.

Conventional mechanical testing such as tensile testing or dynamic mechanical analysis can only return macroscopic properties without any indication of microstructural properties. However, nanoindentation can be used for determination of local microstru

Canada (1786 ship)

Canada was launched at King's Yard in 1779 for the Royal Navy, which sold her at the end of the war. Her name while in Royal Navy service is unknown. John St Barbe purchased her and named her Adriatic, but renamed her Canada c.1786. She made three seal hunting and whaling voyages between 1791 and 1799 under that name, was lost at South Georgia in 1800 on her fourth. Adriatic entered Lloyd's Register in 1783, her master was K. St Barbe and her trade was London-Ancona. In 1786 her master was Cole, her name changed to Canada, her trade became London-Quebec.1st whaling voyage: Captain Alexander Muirhead left Britain on 15 July 1791. In August 1793 Lloyd's List reported that the French privateer Ajax, of Bordeaux, armed with twenty-six 12-pounder guns and having a crew of 286 men, had captured Canada at 27°0′N 35°0′W as Canada was returning from the South Seas fishery. However, Prince of Wales, of Greenock, recaptured Canada and took her into Greenock.2nd whaling voyage: Captain Muirhead left late in 1793 for New Holland and Africa.

He returned in 1794 with 15 tuns of sperm oil, seven tuns of whale oil, 7000 seal skins. Smyrna trade: Lloyd's Register for 1794 shows Canada, still with Muirhead, changing her trade from London-South Seas to London-Smyrna; this entry continues until 1797 when J. Cundall replaces Muirhead and her trade becomes London-Jamaica.3rd whaling voyage: In 1798 Canada's owner changed from J. Cundall to J. Hill, her master from J. Cundall to J. French, her trade changed from London-Jamaica to London—South Seas. Her armament increased. Captain John French received a letter of marque on 11 June 1798, he left Britain on 25 June for South Georgia, returned on 16 July 1799. Canada left Britain on 2 September 1799, it is not clear who her master was. Lloyd's Register for 1799 reports. On 6 June 1800 Lloyd's List reported Canada, master, lost at South Georgia. Notes Citations References Clayton, Jane M. Ships employed in the South Sea Whale Fishery from Britain: 1775-1815: An alphabetical list of ships.. ISBN 978-1908616524 Demerliac, Alain.

La Marine de la Révolution: Nomenclature des Navires Français de 1792 A 1799. Éditions Ancre. ISBN 2-906381-24-1

Icaricia icarioides blackmorei

Icaricia icarioides blackmorei, the Puget blue, is a butterfly native to the Puget Sound area in the northwestern U. S. state of Washington. It is a subspecies of Boisduval's blue; the Puget blue is a small blue and grey butterfly with a wingspan of around 1.8 inches in the family Lycaenidae. The male has dorsal wings; the female is grey brown with diffuse blue patches at the base of the wings, with chocolate brown inner wings. The range of this subspecies spans from Vancouver Island and the Olympic Mountains in alpine to subalpine habitat to the lowland prairies of the South Puget Sound. At this time, the Puget blue has not yet been designated endangered or threatened by the federal government, but it is a candidate subspecies for restoration in the state of Washington. Populations in the prairies have declined due to the loss of prairies as well as the encroachment of woody vegetation such as Douglas-fir and Scotch broom. Scotch broom out-competes the host plants of this butterfly subspecies and as a nitrogen fixer it alters the natural nutrient balance in the soils.

Because many prairie species, such as their host plant, the lupine, have adapted to thrive on much lower nutrient levels the increased nutrient loading inhibits the lupines ability to thrive. The subalpine populations have increased as logging activities have cleared land allowing the expansion of the lupine; the biggest threat to the subalpine populations is climate change, while the prairie populations are most threatened by habitat loss and fragmentation. Land management techniques used to maintain prairies such as controlled burns, can either help or hurt populations of native butterflies. If timed controlled burns can increase that year's lupine crop, giving the Puget blue a better chance of success