Maize, commonly known as corn, is a large grain plant domesticated by indigenous peoples in Mexico in prehistoric times about 10,000 years ago. The six major types of corn are dent corn, flint corn, pod corn, popcorn, flour corn, and sweet corn.

The leafy stalk of the plant produces separate pollen and ovuliferous inflorescences or ears, which are fruits, yielding kernels (often erroneously called seeds). Maize kernels are often used in cooking as a starch.

Many forms of maize are used for food, sometimes classified as various subspecies related to the amount of starch each has:

• Flour corn: Zea mays var. amylacea
• Popcorn: Zea mays var. everta
• Dent corn : Zea mays var. indentata\
• Flint corn: Zea mays var. indurata
• Sweet corn: Zea mays var. saccharata and Zea mays var. rugosa
• Waxy corn: Zea mays var. ceratina
• Amylomaize: Zea mays
• Pod corn: Zea mays var. tunicata Larrañaga ex A. St. Hil.
• Striped maize: Zea mays var. japonica

This system has been replaced (though not entirely displaced) over the last 60 years by multivariable classifications based on ever more data. Agronomic data were supplemented by botanical traits for a robust initial classification, then genetic, cytological, protein and DNA evidence was added. Now, the categories are forms (little used), races, racial complexes, and recently branches.

Maize is a diploid with 20 chromosomes (n=10). The combined length of the chromosomes is 1500 cM. Some of the maize chromosomes have what are known as “chromosomal knobs”: highly repetitive heterochromatic domains that stain darkly. Individual knobs are polymorphic among strains of both maize and teosinte.

Barbara McClintock used these knob markers to validate her transposon theory of “jumping genes”, for which she won the 1983 Nobel Prize in Physiology or Medicine. Maize is still an important model organism for genetics and developmental biology today.

The Maize Genetics Cooperation Stock Center, funded by the USDA Agricultural Research Service and located in the Department of Crop Sciences at the University of Illinois at Urbana-Champaign, is a stock center of maize mutants. The total collection has nearly 80,000 samples. The bulk of the collection consists of several hundred named genes, plus additional gene combinations and other heritable variants. There are about 1000 chromosomal aberrations (e.g., translocations and inversions) and stocks with abnormal chromosome numbers (e.g., tetraploids). Genetic data describing the maize mutant stocks as well as myriad other data about maize genetics can be accessed at MaizeGDB, the Maize Genetics and Genomics Database.

Petroleum refining processes are the chemical engineering processes and other facilities used in petroleum refineries (also referred to as oil refineries) to transform crude oil into useful products such as liquefied petroleum gas (LPG), gasoline or petrol, kerosene, jet fuel, diesel oil and fuel oils.

Petroleum refineries are very large industrial complexes that involve many different processing units and auxiliary facilities such as utility units and storage tanks. Each refinery has its own unique arrangement and combination of refining processes largely determined by the refinery location, desired products and economic considerations.

Some modern petroleum refineries process as much as 800,000 to 900,000 barrels (127,000 to 143,000 cubic meters) per day of crude oil.

Auxiliary facilities required in refineries

• Steam reforming unit: Converts natural gas into hydrogen for the hydrotreaters and/or the hydrocracker.
  Sour water stripper unit: Uses steam to remove hydrogen sulfide gas from various wastewater streams for subsequent conversion into end-product sulfur in the Claus unit.
• Utility units such as cooling towers for furnishing circulating cooling water, steam generators, instrument air systems for pneumatically operated control valves and an electrical substation.
  Wastewater collection and treating systems consisting of API separators, dissolved air flotation (DAF) units and some type of further treatment (such as an activated sludge biotreater) to make the wastewaters suitable for reuse or for disposal.
• Liquified gas (LPG) storage vessels for propane and similar gaseous fuels at a pressure sufficient to maintain them in liquid form. These are usually spherical vessels or bullets (horizontal vessels with rounded ends).
  Storage tanks for crude oil and finished products, usually vertical, cylindrical vessels with some sort of vapour emission control and surrounded by an earthen berm to contain liquid spills.

A solar cell, or photovoltaic cell, is an electrical device that converts the energy of light directly into electricity by the photovoltaic effect, which is a physical and chemical phenomenon. It is a form of photoelectric cell, defined as a device whose electrical characteristics, such as current, voltage, or resistance, vary when exposed to light. Solar cells are the building blocks of photovoltaic modules, otherwise known as solar panels.

Solar cells are described as being photovoltaic irrespective of whether the source is sunlight or an artificial light. They are used as a photodetector (for example infrared detectors), detecting light or other electromagnetic radiation near the visible range, or measuring light intensity.

The operation of a photovoltaic (PV) cell requires 3 basic attributes:

• The absorption of light, generating either electron-hole pairs or excitons.
• The separation of charge carriers of opposite types.
• The separate extraction of those carriers to an external circuit.

In contrast, a solar thermal collector supplies heat by absorbing sunlight, for the purpose of either direct heating or indirect electrical power generation from heat. A “photoelectrolytic cell” (photoelectrochemical cell), on the other hand, refers either to a type of photovoltaic cell (like that developed by Edmond Becquerel and modern dye-sensitized solar cells), or to a device that splits water directly into hydrogen and oxygen using only solar illumination.

Carbon fiber is most notably used to reinforce composite materials, particularly the class of materials known as carbon fiber or graphite reinforced polymers. Non-polymer materials can also be used as the matrix for carbon fibers. Due to the formation of metal carbides and corrosion considerations, carbon has seen limited success in metal matrix composite applications. Reinforced carbon-carbon (RCC) consists of carbon fiber-reinforced graphite, and is used structurally in high-temperature applications. The fiber also finds use in filtration of high-temperature gases, as an electrode with high surface area and impeccable corrosion resistance, and as an anti-static component. Molding a thin layer of carbon fibers significantly improves fire resistance of polymers or thermoset composites because a dense, compact layer of carbon fibers efficiently reflects heat.

The increasing use of carbon fiber composites is displacing aluminum from aerospace applications in favor of other metals because of galvanic corrosion issues.

Carbon fibers are used for fabrication of carbon-fiber microelectrodes. In this application typically a single carbon fiber with diameter of 5–7 μm is sealed in a glass capillary. At the tip the capillary is either sealed with epoxy and polished to make carbon-fiber disk microelectrode or the fiber is cut to a length of 75–150 μm to make carbon-fiber cylinder electrode. Carbon-fiber microelectrodes are used either in amperometry or fast-scan cyclic voltammetry for detection of biochemical signaling.

A roof is part of a building envelope. It is the covering on the uppermost part of a building or shelter which provides protection from animals and weather, notably rain or snow, but also heat, wind and sunlight. The word also denotes the framing or structure which supports that covering.

The characteristics of a roof are dependent upon the purpose of the building that it covers, the available roofing materials and the local traditions of construction and wider concepts of architectural design and practice and may also be governed by local or national legislation. In most countries a roof protects primarily against rain. A verandah may be roofed with material that protects against sunlight but admits the other elements. The roof of a garden conservatory protects plants from cold, wind, and rain, but admits light.
Shack made of date palm branches at Neot Semadar, Israel

A roof may also provide additional living space, for example a roof garden.

The elements in the design of a roof are:

• the material
• the construction
• the durability

The material of a roof may range from banana leaves, wheaten straw or seagrass to laminated glass, copper (see: copper roofing), aluminium sheeting and pre-cast concrete. In many parts of the world ceramic tiles have been the predominant roofing material for centuries, if not millennia. Other roofing materials include asphalt, coal tar pitch, EPDM rubber, Hypalon, polyurethane foam, PVC, slate, Teflon fabric, TPO, and wood shakes and shingles.

The construction of a roof is determined by its method of support and how the underneath space is bridged and whether or not the roof is pitched. The pitch is the angle at which the roof rises from its lowest to highest point. Most US domestic architecture, except in very dry regions, has roofs that are sloped, or pitched. Although modern construction elements such as drainpipes may remove the need for pitch, roofs are pitched for reasons of tradition and aesthetics. So the pitch is partly dependent upon stylistic factors, and partially to do with practicalities.

Some types of roofing, for example thatch, require a steep pitch in order to be waterproof and durable. Other types of roofing, for example pantiles, are unstable on a steeply pitched roof but provide excellent weather protection at a relatively low angle. In regions where there is little rain, an almost flat roof with a slight run-off provides adequate protection against an occasional downpour. Drainpipes also remove the need for a sloping roof.

A person that specializes in roof construction is called a roofer.

The durability of a roof is a matter of concern because the roof is often the least accessible part of a building for purposes of repair and renewal, while its damage or destruction can have serious effects.

Aluminium (or aluminum; see different endings) is a chemical element in the boron group with symbol Al and atomic number 13. It is a silvery-white, soft, nonmagnetic, ductile metal. Aluminium is the third most abundant element (after oxygen and silicon), and the most abundant metal, in the Earth’s crust. It makes up about 8% by mass of the crust, though it is less common in the mantle below. Aluminium metal is so chemically reactive that native specimens are rare and limited to extreme reducing environments. Instead, it is found combined in over 270 different minerals. The chief ore of aluminium is bauxite.

Aluminium is remarkable for the metal’s low density and for its ability to resist corrosion due to the phenomenon of passivation. Structural components made from aluminium and its alloys are vital to the aerospace industry and are important in other areas of transportation and structural materials, such as building facades and window frames.[clarification needed] The most useful compounds of aluminium, at least on a weight basis, are the oxides and sulfates.
Despite its prevalence in the environment, no known form of life uses aluminium salts metabolically. In keeping with its pervasiveness, aluminium is well tolerated by plants and animals. Owing to their prevalence, the potential beneficial (or otherwise) biological roles of aluminium compounds are of continuing interest.

If you’re deep into gardening and self-sufficiency, sooner or later you’ll want to try growing wheat. Among other benefits, it allows you to get away from the commercial process that grows a perfectly good grain, then scrapes off the bran, peels out the germ, bleaches the flour, and sells all those things back to you separately.

If you try, you will discover wheat is easy to grow almost anywhere in the United States, even as a wide-row crop in your garden. One gardener in Vermont attests to having planted 30 pounds of winter wheat on one-eighth of an acre and harvesting 250 pounds of grain in July. On a somewhat smaller scale, even if you have a front yard that’s 20 feet by 50 feet, you could plant 6 pounds of wheat and harvest nearly 50 pounds of grain.

Before you enthusiastically plan to put in enough wheat to make all your bread for the next year, start with a small trial area the first year. This test run will allow you to learn how the grain behaves, what its cultivation problems are, how long it takes you to handle it, how it’s affected by varying climate conditions, and more.
Different Types of Wheat

After you’ve decided how much wheat to plant, you’ll need to decide which type to plant. It’s easy to get confused about types of wheat. Winter wheat is planted in the fall and harvested from mid-May in the South to late July in the North. Spring wheat is planted in the spring and harvested in the fall. Both spring and winter wheat are further divided into soft wheat (lacking a high gluten content and used primarily for pastries and crackers), hard wheat (with a high gluten content and used for breads), and durum wheat (used for pasta). The variety you select will depend on where you live. Check with your local cooperative extension agent to learn which varieties are best for your region. (To find sources for small quantities of wheat seeds, try our Seed and Plant Finder, or check with your local farm stores.)
Planting Wheat

Plant winter wheat in fall to allow for six to eight weeks of growth before the soil freezes. This allows time for good root development. If the wheat is planted too early, it may smother itself the following spring and it could be vulnerable to some late-summer insects that won’t be an issue in the cooler fall weather. If winter wheat is planted too late, it will not overwinter well.

Spring wheat should be planted as early as the ground can be worked in spring. Do the initial plowing in the fall, then till and sow in the spring. To ensure an evenly distributed crop, figure out the amount of seed you’ll need, divide it into two piles, and broadcast one part in one direction, such as from east to west. Then broadcast the remainder from north to south. A cyclone crank seeder will do an even job, but broadcasting by hand is fine for a small plot. You also can plant it in rows like other crops.

The wind systems that exist over the earth’s surface are a result of variations in air pressure. These are in turn due to the variations in solar heating. Warm air rises and cooler air rushes in to take its place. Wind is merely the movement of air from one place to another. There are global wind patterns related to large scale solar heating of different regions of the earth’s surface and seasonal variations in solar incidence. There are also localised wind patterns due the effects of temperature differences between land and seas, or mountains and valleys. Wind speed generally increases with height above ground. This is because the roughness of ground features such as vegetation and houses cause the wind to be slowed.