Context and question: The Downtown District is the home of the Third Street Promenade, a major outdoor pedestrian-only shopping district that stretches for three blocks between Wilshire Blvd. and Broadway (not the same Broadway in downtown and south Los Angeles). Third Street is closed to vehicles for those three blocks to allow people to stroll, congregate, shop and enjoy street performers. Santa Monica Place, featuring Bloomingdale's and Nordstrom in a three-level outdoor environment, is located at the south end of the Promenade. After a period of redevelopment, the mall reopened in the fall of 2010 as a modern shopping, entertainment and dining complex with more outdoor space.
What is Third Street access shut off from?
Answer: vehicles
Context and question: Time appears to have a direction—the past lies behind, fixed and immutable, while the future lies ahead and is not necessarily fixed. Yet for the most part the laws of physics do not specify an arrow of time, and allow any process to proceed both forward and in reverse. This is generally a consequence of time being modeled by a parameter in the system being analyzed, where there is no "proper time": the direction of the arrow of time is sometimes arbitrary. Examples of this include the Second law of thermodynamics, which states that entropy must increase over time (see Entropy); the cosmological arrow of time, which points away from the Big Bang, CPT symmetry, and the radiative arrow of time, caused by light only traveling forwards in time (see light cone). In particle physics, the violation of CP symmetry implies that there should be a small counterbalancing time asymmetry to preserve CPT symmetry as stated above. The standard description of measurement in quantum mechanics is also time asymmetric (see Measurement in quantum mechanics).
The direction of the past is sometimes what?
Answer: unanswerable
Context and question: Natural uranium consists of three major isotopes: uranium-238 (99.28% natural abundance), uranium-235 (0.71%), and uranium-234 (0.0054%). All three are radioactive, emitting alpha particles, with the exception that all three of these isotopes have small probabilities of undergoing spontaneous fission, rather than alpha emission. There are also five other trace isotopes: uranium-239, which is formed when 238U undergoes spontaneous fission, releasing neutrons that are captured by another 238U atom; uranium-237, which is formed when 238U captures a neutron but emits two more, which then decays to neptunium-237; uranium-233, which is formed in the decay chain of that neptunium-237; and finally, uranium-236 and -240, which appear in the decay chain of primordial plutonium-244. It is also expected that thorium-232 should be able to undergo double beta decay, which would produce uranium-232, but this has not yet been observed experimentally.
What isotope of uranium is formed when 238U experiences spontaneous fission?
Answer:
uranium-239