ScienceIQ.com

The Self-less Gene?

The dictionary defines altruism as 'an unselfish concern for the welfare of others.' That's the kind of behavior that rescue workers showed in the 9-11 attack on the World Trade Center, and many of those rescuers sacrificed their lives so that the lives of others could be saved. Every culture has altruists. But altruistic behavior has long posed an ...

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SelflessGene
Astronomy

Not Quite A Planet

Astronomers have dubbed it 'Quaoar' (pronounced kwa-whar) after a Native American god. It lies a billion kilometers beyond Pluto and moves around the Sun every 288 years in a near-perfect circle. ... Continue reading

Quaoar
Biology

Our Brains: A Wasted Resource?

Have you ever heard people say, 'Human beings use only 10 percent of their brains?' It implies that some gifted scientist has already been able to accurately calibrate the brain's maximum operational ... Continue reading

WastedBrains
Geology

Natural Gas - The Blue Flame

It is colorless, shapeless, and in its pure form, odorless. For many years, it was discarded as worthless. Even today, some countries (although not the United States) still get rid of it by burning it ... Continue reading

NaturalGasTheBlueFlame
Engineering

What Are Composite Materials?

A composite material is one in which two or more separate materials have been combined to make a single construct having more desirable properties. What many people don't realize is that composites ... Continue reading

CompositeMaterials

Unit Of Luminous Intensity (candela)

CandelaOriginally, each country had its own, and rather poorly reproducible, unit of luminous intensity; it was necessary to wait until 1909 to see a beginning of unification on the international level, when the national laboratories of the United States of America, France, and Great Britain decided to adopt the international candle represented by carbon filament lamps. Germany, at the same time, stayed with the Hefner candle, defined by a flame standard, and equal to about nine-tenths of an international candle. But a standard based on incandescent lamps, and consequently dependent upon their stability, would never have been fully satisfactory and could therefore be only provisional; on the other hand, the properties of a blackbody provided a theoretically perfect solution and, as early as 1933, the principle was adopted that new photometric units would be based on the luminous emission of a blackbody at the freezing temperature of platinum (2045 K).

The units of luminous intensity based on flame or incandescent filament standards in use in various countries before 1948 were replaced initially by the 'new candle' based on the luminance of a Planckian radiator (a blackbody) at the temperature of freezing platinum. This modification had been prepared by the International Commission on Illumination (CIE) and by the CIPM before 1937, and was promulgated by the CIPM in 1946. It was then ratified in 1948 by the 9th CGPM which adopted a new international name for this unit, the candela (symbol cd); in 1967 the 13th CGPM gave an amended version of the 1946 definition.

In 1979, because of the experimental difficulties in realizing a Planck radiator at high temperatures and the new possibilities offered by radiometry, i.e., the measurement of optical radiation power, the 16th CGPM (1979) adopted a new definition of the candela: the candela is the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540 x 1012 hertz and that has a radiant intensity in that direction of 1/683 watt per steradian.