Given a document, find the main entity about whom the author is writing. Write the full name if mentioned in the text. Note that URLs in the text have been replaced with [Link].

Q: After enduring one too many maddeningly slow boarding experiences  Jason Steffen a professor of physics and astronomy at the University of Nevada Las Vegas  began digging into the unexpectedly complicated mechanics of efficiently ushering passengers onto planes.
In 2008   Steffen  created a computer simulation to evaluate existing boarding methods and ultimately design what  he  claims is the most efficient option for getting restless passengers into their seats. The results were published several years ago in the Journal of Air Transport Management (summarized here).
In  his  research   Steffen  identified the two most common factors responsible for slowing the boarding process to a painful crawl:
In fact  the most routine boarding process â from back to front â is actually the slowest of them all   Steffen âs argues  Itâs even less efficient than boarding a plane in a completely random order.
 Steffen  claims that  his  proposed method  which minimizes the former issue and eliminates the latter  could significantly reduce boarding times  thus cutting down on overall door-to-door flight lengths  and ultimately saving airlines hundreds of millions of dollars a year.

A: Jason Steffen
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Q: LONDON (Reuters) - Manchester City âs Argentine striker Sergio Aguero  has broken a rib in a road accident in the Netherlands and will miss Saturdayâs Premier League game at Chelsea with World Cup qualifiers also doubtful.
Manager Pep Guardiola  speaking to reporters before  Aguero  had seen club doctors  said the player was definitely out of Saturdayâs game between league leaders City and champions Chelsea.
He also cast doubt on  Aguero  travelling to Argentina for World Cup qualifiers next month.
âExactly how many days he will be off  I donât know right now â he said  adding that he had âno problemâ with  Aguero  being in Amsterdam.
Soccer Football - Champions League - Manchester City vs Shakhtar Donetsk - Etihad Stadium  Manchester  Britain - September 26  2017 Manchester City's Sergio Aguero Action Images via Reuters/Lee Smith
 Aguero  had earlier posted a picture of  himself  on  his  Instagram account seated in the back of a car thanking Colombian singer Maluma  who was also in the photo  for the invitation.
City are level on 16 points with Manchester United at the top of the table with Chelsea in third place on 13  and  Aguero  is one goal away from equalling Eric Brooksâ all-time club record of 177 goals in all competitions.
The international break follows the weekendâs Premier League matches with  Aguero  in Argentinaâs squad for their last two World Cup qualifiers against Peru and Ecuador on Oct. 5 and 10.

A: Sergio Aguero
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Q: As two officers reached a rear bedroom in the railroad-style apartment   69-year-old Mario Sanabria  emerged from the room holding a large  machete with a 2-foot blade in  his  hand and was ordered to drop  it  but did not comply  police said.
“They told  him  to drop the sword   he  advanced ” a high-ranking law enforcement source told The Post.
That’s when one of the officers shot  him .
“The uniformed officers ordered the subject to drop the weapon and  he  refused to comply … As the subject continued to approach the lead officer  the officer discharged one shot from his service firearm  striking the subject once in the chest ” said Chief of Patrol Terence Monahan during a press briefing at the scene.
 Sanabria  was rushed to Lincoln Hospital where  he  later died  officials said.
 Sanabria  was not the subject of the search warrant  according to Monahan.

A:
Mario Sanabria
****