Article: As with the minerals discussed above, some vitamins are recognized as organic essential nutrients, necessary in the diet for good health. (Vitamin D is the exception: it can be synthesized in the skin, in the presence of UVB radiation.) Certain vitamin-like compounds that are recommended in the diet, such as carnitine, are thought useful for survival and health, but these are not "essential" dietary nutrients because the human body has some capacity to produce them from other compounds. Moreover, thousands of different phytochemicals have recently been discovered in food (particularly in fresh vegetables), which may have desirable properties including antioxidant activity (see below); however, experimental demonstration has been suggestive but inconclusive. Other essential nutrients that are not classified as vitamins include essential amino acids (see above), choline, essential fatty acids (see above), and the minerals discussed in the preceding section.

Question: What is choline not an example of?
Ans: vitamins

Article: There are several types of multi-color white LEDs: di-, tri-, and tetrachromatic white LEDs. Several key factors that play among these different methods, include color stability, color rendering capability, and luminous efficacy. Often, higher efficiency will mean lower color rendering, presenting a trade-off between the luminous efficacy and color rendering. For example, the dichromatic white LEDs have the best luminous efficacy (120 lm/W), but the lowest color rendering capability. However, although tetrachromatic white LEDs have excellent color rendering capability, they often have poor luminous efficacy. Trichromatic white LEDs are in between, having both good luminous efficacy (>70 lm/W) and fair color rendering capability.

Question: Higher efficiency in multi-color white LEDs may mean what?
Ans: lower color rendering

Article: Observing that face-to-face communication of the type that online videos convey has been "fine-tuned by millions of years of evolution", TED curator Chris Anderson referred to several YouTube contributors and asserted that "what Gutenberg did for writing, online video can now do for face-to-face communication". Anderson asserted that it's not far-fetched to say that online video will dramatically accelerate scientific advance, and that video contributors may be about to launch "the biggest learning cycle in human history." In education, for example, the Khan Academy grew from YouTube video tutoring sessions for founder Salman Khan's cousin into what Forbes' Michael Noer called "the largest school in the world", with technology poised to disrupt how people learn.

Question: Who is the TED curator?
Ans: Chris Anderson

Article: where a single prime denotes the real part and a double prime the imaginary part, Z() is the complex impedance with the dielectric present, Ccmplx() is the so-called complex capacitance with the dielectric present, and C0 is the capacitance without the dielectric. (Measurement "without the dielectric" in principle means measurement in free space, an unattainable goal inasmuch as even the quantum vacuum is predicted to exhibit nonideal behavior, such as dichroism. For practical purposes, when measurement errors are taken into account, often a measurement in terrestrial vacuum, or simply a calculation of C0, is sufficiently accurate.)

Question: Under what condition is the approximation C0 sufficiently accurate for calculation purposes?
Ans:
in terrestrial vacuum