Dec 28, 2013

Heavy Water

Heavy water contains heavy hydrogen, or deuterium, instead of normal hydrogen.  Deuterium is the stable, nonradioactive isotope of hydrogen with atomic weight 2.01363 and symbol D, or 2H. It is commonly called heavy hydrogen because its atomic weight is approximately double that of ordinary hydrogen, but it has identical chemical properties. Deuterium has about twice the atomic weight of normal hydrogen because its nucleus contains a proton and a neutron, instead of just a proton. Hydrogen as it occurs in nature contains approximately 0.02 percent of deuterium. The boiling point of deuterium is -249.49° C (-417.08° F), or 3.28° C (5.90° F) higher than that of ordinary hydrogen. Heavy water (deuterium oxide, D2O) boils at 101.42° C (214.56° F) as compared to 100° C (212° F), the boiling point of ordinary water. It freezes at 3.81° C (38.86° F) as compared to 0° C (32° F) for ordinary water. Its density at room temperature is 10.79 percent greater than that of ordinary water.

Deuterium, which was discovered by the American chemist Harold Urey and his associates in 1932, was the first isotope to be separated in a pure form from an element. Several methods have been used to separate the isotope from natural hydrogen. The two processes that have been most successful have been fractional distillation of water and a catalytic exchange process between hydrogen and water. In the latter system, when water and hydrogen are brought together in the presence of a suitable catalyst, about three times as much deuterium appears in the water as in hydrogen. Deuterium has also been concentrated by electrolysis, centrifuging, and fractional distillation of liquid hydrogen.

Dec 21, 2013

Book of the Dead

The name generally given to a large collection of funerary texts of various dates, containing magical formulas, hymns, and prayers believed by the ancient Egyptians to guide and protect the soul (Ka) in its journey into the region of the dead (Amenti). Egyptians believed that the knowledge of these texts enabled the soul to ward off demons attempting to impede its progress, and to pass the tests set by the 42 judges in the hall of Osiris, god of the underworld. These texts also indicated that happiness in the afterlife was dependent on the deceased's having led a virtuous life on earth. The earliest religious (funerary) texts known were found cut in hieroglyphs on the walls inside the pyramids of the kings of the 5th and 6th Dynasties of the Old Kingdom; these became known as the Pyramid Texts. A famous example is found in the pyramid of Unas (reigned about 2356-2323 BC), the last king of the 5th Dynasty. In the first Intermediate Period and in the Middle Kingdom private individuals had these texts painted on coffins, from which the alternate name Coffin Texts is derived. By the 18th Dynasty the texts were inscribed on papyri placed in the mummy case; these papyri were frequently from 15 to 30 m (50 to 100 ft) long and illustrated in color.

Dec 14, 2013

Solar-terrestrial effects

Besides providing light and heat, the Sun affects the Earth through its ultraviolet radiation, the steady stream of the solar wind, and the particle storms of great flares. The near-ultraviolet radiation from the Sun produces the ozone layer, which in turn shields the planet from such radiation. The soft (long-wavelength) X rays from the solar corona produce those layers of the ionosphere that make short-wave radio communication possible. The harder (shorter-wavelength) X-ray pulses from flares ionize the lowest ionospheric layer, producing radio fadeouts. The Earth's rotating magnetic field is strong enough to block the solar wind, forming the magnetosphere, around which the solar particles and fields flow. On the side opposite to the Sun, the field lines stretch out in a structure called the magnetotail. When shocks arrive in the solar wind, a short, sharp increase in the field of the Earth is produced. When the interplanetary field switches to a direction opposite the Earth's field, or when big clouds of particles enter it, the fields in the magnetotail reconnect and energy is released, producing the aurora borealis (northern lights). Big flares or coronal mass ejections bring clouds of energetic particles that form a ring current around the magnetosphere, which produces sharp fluctuations in the Earth's field called geomagnetic storms. These phenomena disturb radio communication and produce voltage surges in long-distance transmission lines and other long conductors.

Dec 6, 2013

Population growth in Paris and New York

It is estimated that in 1800 the population of Paris was about 550,000 and New York’s about 60,000. In 1931, however, these numbers increased to 2,800,000 for Paris and 7,400,000 for New York. (Adapted from 'The Timetables of History', by Bernard Grun, based upon Werner Stein’s Kulturfahrplan)

Dec 1, 2013

The Splice of Life

Dr. James Watson, left, and Dr. Francis Crick with their 
Nobel Prize-winning model of the DNA molecule
Genetic engineering is the process that inserts genes from one living organism into the cells of another, thereby custom-tailoring them to do work they weren't designed for. For example, thanks to genetic engineering, or recombinant-DNA technique, millions of bacteria are kept busy churning out precious human insulin. Scientists built the micro-factories by slipping the human gene responsible for the creation of insulin into E. coli, a mild-mannered bacterium found in our intestinal tract. So far, genetic engineering has been most successful with microorganisms, plants, mice (whose immune systems have been made to mimic those of human beings), and-Stephen King, take note -- livestock: pigs that gain weight faster, cows that give more milk. Science is still working on the problem of getting genetically altered DNA back into a human cell and, we're told, isn't even close to a solution. Someday, however, we may be able to replace or repair bad genes, like the ones responsible for such diseases as cystic fibrosis, sickle-cell anemia, and perhaps even cancer.