(The Human Brain Book, by Rita Carter)
Aug 30, 2014
Aug 23, 2014
Three types of blood vessels form a complex network of tubes throughout the body. Arteries carry blood away from the heart, and veins carry it toward the heart. Capillaries are the tiny links between the arteries and the veins where oxygen and nutrients diffuse to body tissues. The inner layer of blood vessels is lined with endothelial cells that create a smooth passage for the transit of blood. This inner layer is surrounded by connective tissue and smooth muscle that enable the blood vessel to expand or contract. Blood vessels expand during exercise to meet the increased demand for blood and to cool the body. Blood vessels contract after an injury to reduce bleeding and also to conserve body heat.
Arteries have thicker walls than veins to withstand the pressure of blood being pumped from the heart. Blood in the veins is at a lower pressure, so veins have one-way valves to prevent blood from flowing backwards away from the heart. Capillaries, the smallest of blood vessels, are only visible by microscope—ten capillaries lying side by side are barely as thick as a human hair. If all the arteries, veins, and capillaries in the human body were placed end to end, the total length would equal more than 100,000 km (more than 60,000 miles—they could stretch around the earth nearly two and a half times.
The arteries, veins, and capillaries are divided into two systems of circulation: systemic and pulmonary. The systemic circulation carries oxygenated blood from the heart to all the tissues in the body except the lungs and returns deoxygenated blood carrying waste products, such as carbon dioxide, back to the heart. The pulmonary circulation carries this spent blood from the heart to the lungs. In the lungs, the blood releases its carbon dioxide and absorbs oxygen. The oxygenated blood then returns to the heart before transferring to the systemic circulation.
Aug 16, 2014
There could be as many as 40 billion Earth-sized planets orbiting in the habitable zones of sun-like stars and red dwarf stars within the Milky Way Galaxy
Earth is the only place in the universe known to harbor life. However, recent advances in planetary science have changed fundamental assumptions about the possibility of life in the universe, raising the estimates of habitable zones around other stars, along with the discovery of hundreds of extrasolar planets and new insights into the extreme habitats here on Earth, suggesting that there may be many more habitable places in the universe than considered possible until very recently. On 4 November 2013, astronomers reported, based on Kepler space mission data, that there could be as many as 40 billion Earth-sized planets orbiting in the habitable zones of sun-like stars and red dwarf stars within the Milky Way Galaxy -- 11 billion of these estimated planets may be orbiting sun-like stars. The nearest such planet may be 12 light-years away, according to the scientists.
Aug 9, 2014
As of 2010, Mandarin was the mother language of 14.4% of the world’s population, Spanish 6.15%, and English 5.43%.
Although English ranks only third among the world's most spoken languages, it is on its way to becoming the first truly global language - used throughout the world as the language of commerce, diplomacy, and science. English is the mother tongue for some 450 million people, and a further 1.5 billion people use it as a second language to some degree. Beginning in the 17th century, the language spread throughout the British Empire to the Americas, Africa, India, and Oceana. Today 70 countries designate English as an official language (although it does not have that status in the United States), and it is an official language of the United Nations, the European Union, Nafta, NATO, and the Organization of American States.
(Adapted from ‘The New York Times ‘Smarter by Sunday – 52 Weekends of Essential Knowledge for the Curious Mind’ and Wikipedia)
Aug 2, 2014
Kilauea is located on central Hawaii Island, Hawaii. It is situated on the southeastern slope of the great volcanic mountain Mauna Loa, at an elevation of 1,247 m (4,090 ft) above sea level, which is more than 3000 m (almost 10,000 ft) below the summit of the mountain. The crater, which forms a great cavity in the side of the mountain, has an area of about 10 sq km (about 4 sq mi); the walls of the crater are from 60 to 210 m (about 200 to 700 ft) high. Except for occasional lava flows across the floor of the crater, volcanic activity in recent times has been restricted to an inner crater called Halemaumau, which measures more than 900 m (about 3000 ft) across and has a depth of about 400 m (about 1300 ft).