Found in oceans worldwide, orcas display sophisticated hunting techniques and social behaviors that have been described by experts as manifestations of a shared culture. Like other dolphins, orcas produce a variety of vocalizations used for communication and echolocation. Orca mothers have even been observed training their young in the group’s dialect, and it is said that groups that share ancestors are likely to have a similar set of call types. What does this suggest about orca vocal behavior? Discuss
Source: The Free Dictionary
An exabyte is a unit of information or computer storage equal to one quintillion bytes—an amount roughly represented by the number 1 followed by 18 zeros. Though the term is rarely encountered in any practical context, a popular, hotly contested assertion, which often cites as support a project at the UC Berkeley School of Information, is that “all words ever spoken by human beings” can be represented by approximately 5 exabytes of data. What is meant by the related term “exaflood”? 
Some claim that mail art, an art form that uses the postal system as a medium, began when Cleopatra had herself delivered to Julius Caesar in a rolled-up carpet, but the thousands-strong, international network of mail artists as it exists today is a more recent development, evolving between the 1950s and 90s. Mail artists typically exchange ephemera in the form of decorated envelopes, illustrated letters, artist trading cards, and many other items. Who is deemed the pioneer of modern mail art? 
If the universe is assumed to contain an infinite number of uniformly distributed luminous stars, then every point in the sky should be as bright as a star. So why is the sky dark at night? That is the question posed by Olbers’s paradox, named for astronomer Heinrich Wilhelm Olbers, who described it in 1823, more than 200 years after Johannes Kepler first posed the question as an argument against the notion of a limitless universe with infinite stars. How has the paradox since been resolved? 
Informally labeled the “pain ray,” the Active Denial System (ADS) is a non-lethal weapon being developed by the US military. Designed for use in crowd control operations, the ADS emits electromagnetic radiation that excites water molecules in the epidermis, causing an intensely painful burning sensation. Though the device does not actually burn the skin, its effect is said to feel similar to a hot light bulb being pressed against it. How long do these painful effects last? 
Long thought to cause feelings of fear or awe, infrasound is sound that is able to cover long distances with little dissipation at a frequency too low to be detected by the human ear. It is created by natural phenomena such as ocean waves and earthquakes and can be artificially produced by explosions or machines. Infrasound is used by some animals to communicate over long distances and by predators to “freeze” their prey. Why do some scientists believe infrasound is related to ghost sightings? 
Used in machine guns since World War I, tracer ammunition contains modified bullets packed with a pyrotechnic charge that ignites upon firing, illuminating the bullets. This technology enables a shooter to check a bullet’s trajectory and adjust his or her aim accordingly. Since the tracer path can also betray a shooter’s position, many modern tracers are designed to become visible only once they have traveled a set distance. Why were tracers especially useful against Zeppelins in World War I? 
A molecular machine is a minute mechanism consisting of molecular components that perform mechanical-like movements in response to specific stimuli. Chemists have synthesized a number of simple molecular machines, including molecular propellers and molecular motors, the latter of which are powered by light or reactions with other molecules and are capable of unidirectional rotation. Far more complex biological versions of these artificial nanomachines are found in living cells. What do they do? 
On November 20, 1979, approximately 200 armed Islamic fundamentalist dissidents opposed to the Saudi ruling family took over Islam’s holiest place, the Al-Masjid al-Haram in Mecca, Saudi Arabia. After 127 Saudi Arabian National Guard members were killed in an unsuccessful attempt to regain control, the nervous Saudi government called in French and Pakistani forces, which retook the shrine in a battle that left approximately 250 dead and 600 wounded. What happened to the surviving militants? 
Travelers who fail to familiarize themselves with a region’s customs before visiting that area risk inadvertently offending or insulting their hosts. For example, in Iraq and Iran, the “thumbs up” gesture—a Western expression of approval—is considered an offensive insult. In the Middle East, where Islam is the predominant religion, modesty and hospitality are strongly valued traits, but their practice varies across ethnic groups. How do Middle Easterners show their respect for the elderly?