The game has a long history. Games that resemble it have been played for thousands of years. Archaeologists doing excavations at a place called "Burnt City" in modern-day Iran have found parts of a game that resembled backgammon. They have found 60 pieces to play with, and two dice. They could show that the game utensils date from around 3000 BC. These pieces around 100–200 years older than another set, found in Ur, in Mesopotamia.
Cell wall
A cell wall is the wall of a cell in plants, bacteria, fungi, algae, and some archaea. Animal cells do not have cell walls, nor do protozoa. Cell walls protect the cells from damage. It is also there to make the cell strong, to keep its shape, and to control the growing of the cell and plant.
The cell wall is the tough, usually flexible but sometimes fairly rigid layer that surrounds some types of cells. It is outside the cell membrane and gives these cells support and protection, as well as acting as a filter. The cell wall also acts as a pressure vessel, preventing over-expansion when water enters the cell by osmosis.
The material in the cell wall varies. In plants and algae, the cell wall is made of long molecules of cellulose, pectin, and hemicellulose. The cell wall has channels which let some proteins in and keeps others out. Water and small molecules can go through the cell wall and the cell membrane.
The cell wall has mechanical strength, and supports cell shape. This mechanical strength is its main function:
Although the plant cell wall is strong, it is not rigid or stiff. The flexibility of the cell walls is seen when plants wilt, so that the stems and leaves begin to droop.
Some plants add stiffening material to some of their cell walls. A "secondary" cell wall is an additional layer of cellulose which increases wall rigidity. More layers may be added containing lignin in xylem cell walls, or containing suberin in cork cell walls. These compounds are rigid and waterproof. They make the secondary wall stiff. Both wood and bark cells of trees have secondary walls. Other parts of plants such as the leaf stalk may get reinforcement to resist the strain of physical forces.
Small molecules, including small proteins, can easily get through the primary plant cell wall. Water and carbon dioxide are distributed throughout the plant. The pH is an important factor in the transport of molecules through cell walls.
Around the outside of the cell membrane is the bacterial cell wall. Bacterial cell walls are made of peptidoglycan, which is made from polysaccharide chains cross-linked by unusual peptides containing D-amino acids. Bacterial cell walls are different from the cell walls of plants and fungi which are made of cellulose and chitin, respectively.
The cell wall of bacteria is also distinct from that of Archaea, which do not contain peptidoglycan. The cell wall is essential to the survival of many bacteria. The antibiotic penicillin is able to kill bacteria by preventing the cross-linking of peptidoglycan and this causes the cell wall to weaken and lyse. The lysozyme enzyme can also damage bacterial cell walls.
The middle lamella gives the cell shape, support, and strength. It is made of calcium and magnesium. Even though it is called "middle" lanella, it is the outer part of the cell. The middle lamella is the first wall of the cell to give protection.
Animal cells do not have cell walls. They have microfilaments (the thinnest filaments of the cytoskeleton).
Friction
Friction is a force that acts to stop the movement of two touching things. The energy lost to friction is turned into sound and heat. Two kinds of friction are static and kinetic. Static friction is when the friction is strong enough to stop movement between two objects. Kinetic friction is used when the frictional force is not strong enough to stop all motion. An effect of kinetic friction is heat production.
Many everyday mechanisms that utilize friction include car brakes, suitcases, and shoes. Even a person sliding across the floor uses a form of friction.
Some facts about friction are:
Lima
Lima is the capital city (where the government works), and is considered the most important and largest city of Peru. 75% of the Peruvian economy is handled in Lima.
Lima is the industrial and financial center of Peru, and one of the most important financial centers in Latin America.
It is an important city of South America and the entrance to Peru. Lima is city in constant urban growth. It has a large population. Over 8 million people live in the metropolitan area, which includes Callao Seaport. Lima is the fifth largest city in Latin America, behind Mexico City, São Paulo, Buenos Aires and Rio de Janeiro.
The city was founded by the Spanish conquistador (conqueror) Francisco Pizarro on January 18, 1535. He called it 'La Ciudad de los Reyes' (the City of the Kings). It became the capital and most important city in the Spanish Viceroyalty of Perú. And after the Peruvian War of Independence, it became the capital of the Republic of Peru.
In the 1940s, Lima started a period of rapid growth, with the migration from the Andean regions of Peru, as rural people. They wanted to find better opportunities for work and education. The population, estimated at 0.6 million in 1940, reached 1.9M by 1960 and 4.8M by 1980.
Lima has developed an important tourism industry, characterized by its historic center, archeological sites, nightlife, museums, art galleries, festivals, popular traditions, and gastronomy. Lima is considered Americas's gastronomical capital.
Lima is made up of mainly Spanish speaking inhabitants with over 90% of the population speaking the language. Lima Province has 43 districts, including:
1 - Cercado de Lima
3 - Ate
4 - Barranco
5 - Brena
7 - Comas
9 - Chorrillos
10 - El Agustino
11 - Jesus Maria
12 - La Molina
13 - La Victoria
14 - Lince
17 - Magdalena del Mar
18 - Miraflores
21 - Pueblo Libre
22 - Puente Piedra
25 - Rimac
27 - San Isidro
28 - Independence
29 - San Juan de Miraflores
30 - San Luis
31 - San Martin de Porres
32 - San Miguel
33 - Santiago de Surco
34 - Surquillo
35 - Villa María del Triunfo
36 - San Juan de Lurigancho
38 - Santa Rosa
39 - Los Olivos
41 - San Borja
42 - Villa El Savador
43 - Santa Anita
Cleaner
A cleaner (or janitor) is someone who takes away garbage and cleans surfaces. Cleaners sometimes repair things, and maintain their equipment in good working order, as well as dusting, washing, waxing and polishing.
Heavy duty cleaners often move furniture, large containers of recycled materials and waste, and other objects, and operate large buffers and other weighty equipment. "Light" duty cleaners clean chalk boards, windows, shelves, desks, light fixtures, and ledges. Some duties, like using a vacuum cleaner, can be done by either "light" or "heavy" duty cleaners. Cleaners can clean offices, staircases, kitchens, bathrooms, hallways, sidewalks, elevators, escalators, and other areas. Cleaners can specialize in washing windows, or in cleaning carpets, hospitals, food processing plants, or construction sites. Cleaners who discover seriously damaged surfaces and equipment on their sites can notify specialists, like plumbers and carpenters, about the need for professional repairs.
Cleaners are also alert for security problems, like vandalism, signs of theft (forced windows or doors, missing computers or stock), blocked fire escape routes, lights or fire alarms not working, or trespassers. When these occur, the cleaners promptly notify their sites' Security Officers and Site Supervisors. Janitors know how to keep themselves and their sites safe, by immediately removing hazards like broken class, spilled fluids, and waste from kitchens and bathrooms, and by checking hand rails, floor mats, stairs, automated doors, escalators, elevators, intercoms, and plumbing.
Bovinae
Bovinae is a subfamily of the even-toed ungulate family Bovidae. About 26 species of bovines belong to this subfamily.