# If oxygen masks on airlines have empty bags, where is the oxygen stored?

If oxygen masks on airlines have empty bags, where is the oxygen stored? by @CStuartHardwick

Excellent sciency question!

Humans and airplanes both need oxygen, but high speed airliners operate much more efficiently at high altitudes where the air is thinner. The lack of oxygen doesn’t bother them because jet engines compress their intake air anyway, but above about 8,000 feet, the lack of oxygen would start making passengers woozy, and at higher altitudes still, would be fatal.

That’s why airliners carry emergency oxygen. The cabin is normally pressurized to about 8,000 feet, but if pressurization ever fails above about 14,000 feet, some passengers would be unable to absorb sufficient oxygen from the rarefied air and would grow faint, even ill—especially those who are old or infirm, and those accustomed to near sea level pressure, which is a third of the global population.

We can tolerate much higher altitudes, though, if we have pure oxygen to breath instead of the 21% oxygen in ordinary air. Breathing supplemental oxygen, we can go up to about 35,000 feet (40,000 with a full face mask ensuring 100% undiluted oxygen). Much higher than that and we risk passing out or asphyxiation even with 100% oxygen. That’s why few airliners fly higher—passengers would need pressure suits or at least full face masks as backup life support. Were it not for that, planes would happily fly at 50-, 60- even 70,000 feet.

If you’ve ever gone scuba diving (or seen it on TV) you know that divers only get air when they draw a breath—their rig doesn’t just continually belch out air (unless the regulator is busted) because that would waste air.

That’s what the bag is for. The oxygen generator over your seat in an airliner DOES just continually belch out oxygen. There is no tank or regulator—just a canister containing chemical reactants which, once started, produce a continuous stream of oxygen until the reactants are used up (a few minutes, long enough to descend to thicker air).

The flimsy little bag is there to catch the stream of oxygen in between your breaths so it isn’t wasted. That’s it. It only inflates while you are exhaling, provided you are breathing slowly enough. That’s why it might not inflate (you might not give it a chance you panicky rascal).

If you like science, you might enjoy my free award-winning scifi sampler.

If oxygen masks on airlines have empty bags, where is the oxygen stored?

# What if I requested the last room at the Hilbert’s Hotel?

What if I requested the last room at the Hilbert's Hotel? by Alon Amit

“Welcome to Hilbert’s Hotel, transfinitely serving your needs since 1883! How may we be of service?”

“Yes, I’d like to have a room, please.”

“Very good, sir. Which room would you prefer? Our rooms are numbered 1, 2, 3, and so on – in fact we have a room for every natural number! Our prime rooms are, well, prime, and we also have a special tonight for rooms 1,729 and 196,884, if you care to…”

“So, all rooms are available? The place is… empty?”

“Oh no, sir, funny you should ask! In fact quite the opposite is true. All our rooms are currently occupied! But, we pride ourselves on our efficiency, so if you choose to stay in room 1,729 for example – which as I mentioned we have a truly unique special for tonight, sir, I warmly suggest you consider it – we simply move all of our guests in rooms 1,729, 1,730, 1,731 and so on, we move them all one room up, vacating room 1,729. It's no hassle at all.”

“So… you can put me in any room I wish?”

“Absolutely sir, and I especially recommend room 1,729, and did I also mention room 196…”

“Yes yes. So, I’d like the last room please.”

“Excuse me?”

“I’d like to stay in the last room.”

“The last room?”

“Yes.”

“You mean room 1?”

“No, that's the first room. I want the last one, please.”

“But… sir, as I've explained, we have a room for every natural number. I'm not aware of a last natural number, and, um, I don’t think there is one. Would you like to hear about our specials…?”

“Look, I don't have time for this. I prefer not to have anyone in a room with a number greater than mine, and if you can't accommodate I'll take my business to the Sheraton Interuniversal down the street. Thank you.”

“Wait! Sir, please, I'm just an undergrad here. Please let me fetch my manager, I'm sure she’ll be able to help.”

“Hi, my name is Julia. I understand you require the last room, Mr…?”

“Zzyzzek. Zwawoy Zzyzzek.”

“Well then, that explains a few things. Alright, Mr. Zzyzzek, we pride ourselves on our transfinite service, and I can accommodate your request, it won’t be a problem. You’ll reside in the last room at the Hilbert Hotel. Just give us a few moments to get it set up.”

“Excellent. What would be my room number?”

“Ah, of course. You’ll be in room $\omega$. I apologize that our undergrad receptionist here wasn’t able to help you out; you see, they are only trained to understand the cardinality aspects of our hotel, so they know how to handle, for instance, a busload of infinitely many tourists arriving from Xanadu, by shifting all our current guests from their room to the room with twice the number, freeing up all the odd-numbered rooms.

But they’re not aware that the natural numbers aren’t just a set: they are an ordered set, with order $1<2<3<\ldots$, and that order clearly has no last element. However, it’s perfectly fine to establish another number, $\omega$, and declare it greater than all natural numbers:

$1<2<3<\ldots<\omega$.

Your request wasn’t merely to accommodate a room for you, but rather to consider the order aspects of that room, asking for it to be last. So, by now, our staff has had time to put room $\omega$ together and it is ready for you. Would you be requiring WiFi?”

Mr. Zzyzzek turned out not to be so easy to placate.

“What if I want my wife in the next room? Her room number needs to be yet greater than my own.”

“Sure. She’ll be in room $\omega+1$.”

“And my kids need also to be next to us, but in a lower numbered room.”

“Ok, I can move you guys to $\omega+1$ and $\omega+2$ and put them in $\omega$.”

“What if I have infinitely many friends, all asking to be greater than us?”

“They’ll stay in $\omega+3$, $\omega+4$, and so on. We’ll have a room $\omega+n$ for every friend numbered $n$.”

“I actually have infinitely many cohorts of friends, each with infinitely many people.”

“So far we’ve only gone up to $\omega+\omega=\omega\cdot 2$. We can introduce $\omega\cdot 2, \omega\cdot 3, \omega\cdot 4$ and so on and place your friends in room $\omega\cdot c+i$, for the $i$th person in cohort $c$.”

“Ok, now I think I’m going to stump you. We also have infinitely many relatives, and they all need to stay in rooms between me and my wife.”

“Of course. They can stay in rooms $\omega+1/2, \omega+1/3, \omega+1/4$ and so on, meaning there will be no first among them, but there will be a greatest.”

“And if they don’t want that? They’ll fight endlessly over who gets the largest room.”

“Easy. We can add $\omega+2/3, \omega+3/4, \omega+4/5$ and so on. There are still infinitely many rooms between $\omega$ and $\omega+1$, and those infinitely many rooms have neither a smallest nor a greatest one.”

There was a moment of silence.

“Can you handle anything?”

“Yes and No. I can handle any combination of crazy relative orders, with infinitely many infinities intertwined in any way you want. I can make it so there’s a room between every pair of rooms. I can make infinitely many sets of infinitely many rooms between every pair of rooms. I can fit $\omega^3+\omega+7$ of your friends between rooms $22$ and $23$. I can, in short, handle any linear order of a countable number of people.”

“Yet, the number of rooms in our hotel is only countable. If you have all the real numbers as your business associates, for example, I won’t be able to fit them even if they don’t have any order requirements at all. For that, you’ll want to check with the new Hyatt Uncountable that’s being built on the other side of town. But I hear that making reservations there is a nightmare. It takes an infinite amount of time just to describe the guest list!”

The countable orders that can be handled by the Hilbert Hotel and its manager, Julia Robinson, are simply all orders that fit inside the rational numbers. The rational numbers form a dense linear order, and any order whatsoever on any countable set can be placed inside the rationals.

In fact, it wasn’t even necessary to introduce the countable ordinals $\omega, \omega\cdot 2$ etc.: Ms. Robinson could have just renamed the same rooms she already has with rational numbers instead of natural numbers. Presumably this would have somewhat inconvenienced her guests, so it’s understandable she chose to give Mr. Zzyzzek a brand new room, but she could have simply moved all guests one room up, vacating room $1$, and then renaming rooms $2, 3, 4, \ldots$ to $\frac{1}{2}, \frac{1}{3}, \frac{1}{4}, \ldots$. This would have made room $1$ available for Mr. Zzyzzek as the room with the largest number.

Any countable ordinal can be fit inside the rational numbers. In fact, any countable total order can fit in this way, and they are not necessarily ordinals (meaning, well-ordered). The rationals can easily accommodate sets with no first element, such as the renumbered rooms we just considered.

Furthermore, it is possible to fit even uncountable ordered sets into larger structures than the rationals, most beautifully the Surreal numbers. But that’s a story for another trip.

What if I requested the last room at the Hilbert's Hotel?

# What inspired you to go from zero to pro in programming?

What inspired you to go from zero to pro in programming? by Bhagwati Malav

I got rejected by one of my dream company because i was not able to answer few algorithms questions. I felt bad that time, and i immediately bought one monitor and started learning ds and algo. Now i solve 3–4 problems everyday. I started few month back(1–2), i have reached to algorithms level 3, and percentile is 61+.

I think you can not be pro at anything unless you love it. As a programmer love your job, love your work and be perfect at your work.

You should learn ds and algo, it changes the way you write code or approach any problem.

Thank you so much guys for upvotes !!!

There are many good books on algorithms, i would suggest Cracking the Coding Interview book.

Topcoder – Data Science Tutorials

InterviewBit – Coding Interview Questions (you can find questions for specific company here)

Keep checking stackoverflow data structure/ algorithms tag – Newest 'data-structures' Questions (You will find many new questions here, try to answer those, try to understand others’ answer.)

Data Structures and Algorithms

What inspired you to go from zero to pro in programming?

# What are some motivational wallpapers?

What are some motivational wallpapers? by @aadeshchandra01

• If you end up with a boring miserable life because you listened to your mom, your dad, your teacher, your priest or some guy on television telling you how to do your shit, then you deserve it.

-Frank Zappa

• In the end we only regret the chances we didn't take.
• Some people die at 25 but aren't buried till 75.

Benjamin Franklin

• I've got a dream that's worth more than my sleep.
• The Devil Whispers :

You can’t withstand the storm.”

The Warrior Replied :

“I am the storm.”

• Pain is temporary, quitting lasts forever.
• Today I would do what others won't, so tomorrow I can do what others can't.

Cheers !!!

Edit : Adding some more of them.

• It comes down to one simple thing : How bad do you want it ?
• When you want to succeed as bad as you want to breathe, then you will be successful.
• Forget all the reasons it won't work and believe the one reason it will !
• It takes bravery to dream big, it takes passion to turn a big dream into a plan, it takes persistence to turn a plan into reality, but it will take forever to regret the dreams that you let go.

Carpe Diem !!!

Edit 2 :

• You can never cross the ocean until you have the courage to lose sight of the shore.

Christopher Columbus

• Work like there is someone working 24 hours a day to take it away from you.

Mark Cuban

• You can't have million dollar dreams with a minimum wage work ethic.

What are some motivational wallpapers?

# What are some motivational wallpapers?

What are some motivational wallpapers? by Shubham Darak

• If it excites you and scare you at the same time, its worth trying.
• The only thing standing between you and your goal is the bullshit story you keep telling yourself as to why you can't achieve it.
• If your parents still need to work for your living, keep grinding.
• Be strong enough to stand alone, smart enough to know when you need help, and brave enough to ask for it.
• A lion and Tiger may be powerful but a wolf doesn't perform in a circus.
• The expert in anything was once a beginner.
• I've always hated Maths but I've always loved counting money.
• If you're searching for that one person who will change your life, look into the mirror.
• If you salute your duty, you no need to salute anybody, but if you pollute your duty, you have to salute everybody.
• Take care of home first before impressing the streets.
• Don't quit your job just because you're unhappy. Your bills don't care if you're happy or not.
• Maturity comes with experience not age !

What are some motivational wallpapers?

# How do scientists measure the speed of light?

How do scientists measure the speed of light? by Jack Fraser

We don't.

No, seriously, we don't measure the speed of light (which always refers to the speed in a vacuum).

We know exactly what the speed of light is.

It is:

$c =$$299792458$$ms^{-1}$

And that is absolutely 100% accurate, with no measurement errors.

But Jack, I hear you say, what the bloody hell are you talking about?

The reason we know that that's exactly the speed of light, is that we defined it to be that number.

We then take our definition of a second (the length of time for a certain number of periods of the radiation emitted in hyperfine transitions in caesium-133), and from that we define a metre.

So the thing we would be measuring is what a metre is!

We use the speed of light as a fixed velocity, from which all observers can define their own length scale.

To measure the speed of light would require an external definition of what a metre is – and since about the 1970s, we don't have one!

And if you did want to measure the speed of light using this external distance reference, it's easy to test – you just release a light pulse at t=0, towards a mirror – and then time how long it takes to get back to you. This is the exact principle that Radar/Sonar work on (although again, they measure the distance knowing the speed – but it works either way round).

Some background:

The metre was originally defined after the French Revolution, in about 1799. It was defined as $\frac{1}{10,000,000}$ the distance between the equator and the pole.

The “metre” was formally defined from 1889 as the length of a platinum rod, held in a vault in Paris.

From this definition of a metre (and an old definition of a second – I forget what that was), we measured (using the mirror-timing method, or based on astronomical observations) the speed of light to be about $299792458$, plus a non-integer bit, and error bars from the measurement errors.

Eventually, we realised that having a metre defined by something there was only one of was a bit annoying. So, we attempted to define it in a way that anyone could replicate – without having to refer to a “standard object”.

Therefore, we redefined the metre – using the speed of light.

The official definition of a metre today is:

$\frac{1}{299792458}$of the distance travelled by light in a vacuum, in 1 second$.$

Using the caesium definition of a second.

Therefore, this was exactly equivalent to defining the speed of light to be the number given above.

We chose that number (and not a more convenient number like 300,000,000), because that number changed the definition of a metre by only a fraction of a fraction of a percent – but made everything all nice and integer-y.

A consequence of using this definition is that any attempt to measure the speed of light is cyclical – you must use a “metre” to measure it at some point – which relies on the speed of light.

Therefore what you actually do now, when you “measure” the speed of light (in a vacuum), is actually “measure how accurate your measuring instruments are”!

How do scientists measure the speed of light?

# Why is Christopher Nolan considered great?

Why is Christopher Nolan considered great? by Ashok Kumar

1.Technology achievements

Inception gravity sequence

Nolan always inventing new menthol in film making .Example is Inception hallway fight sequence Instead of CGI they created whole set and actors tied to ropes for the required output

Dark knight Rises plane crash

They placed this aircraft model on the ground and filmed the fight sequence ,late used minimal CGI to look like a moving plane scene

interstellar film shoot

While the film shoot took place in many countries they modified the locations as per the requirement.See they wearing customized boots for easy walking as they modified the surface of the location

2.he is a master Dialogue writer – some of quotes from his movies

below quote tells us that how guilt can destroy.Many of relationships fail because of the guilt of mistakes they did

3.A great screen writer -although he is collaborated with David s goer and his brother Jonathan nolan for most of his movies (thanks to the people who researched and put in images)

interstellar time line

inception levels explained

memento movie chart

the reverse screenplay is very hard to write

Why is Christopher Nolan considered great?