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Calculate the number 2420

NUMBERMANIA: Calculate the number 2420 using numbers [2, 2, 5, 1, 97, 582] and basic arithmetic operations (+, -, *, /). Each of the numbers can be used only once.

Correct answers: 1

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Todd Barry: Hearing Aid

Saw a great product advertised -- it was a hearing aid made to look like a Bluetooth headset. Its for people who are embarrassed about wearing a hearing aid but not about wearing a Bluetooth headset.

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Crystal rectifier

In 1874, a paper by Ferdinand Braun (1850-1918) was published in the Annalen der Physik und Chemie describing his discovery of the electrical rectifier effect. He observed that certain crystals of metal sulphides have a larger or smaller resistance to an electric current, depending on its direction of flow. He used a galena crystal, a semiconductor material composed of lead sulfide. He found the rectifying effect especially true if at least one of the electrodes was a pointed wire. Thus, he had discovered the point-contact rectifier effect, the first semiconductor device. This effect wasn't used until over 30 years later in the form of the “cat's whisker”crystal radio detector which ultimately led to the point-contact transistor first produced in 1948.

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