Good addition, I'll add a clarifying note to my post. I have a neuroscience background so all the receptor stuff I learned about was based on structural change.

Proteins can* be very rigid, and that rigidity comes mostly from four forces:

• hydrophobic and hydrophilic interactions (some amino acids will stay away from water and twist to the inside of the protein, others will be attracted to the water and be on the outside of the protein)

• hydrogen bonding in the protein (some substituents make strong dipole interactions with each other, these forces also exist in the backbone of the protein, making sub-structures)

• electrostatic interactions (parts of the protein carry positive and negative charges, which help hold the protein together)

• disulfide bridges formed from two cysteines which are actual covalent bonds between two parts of the chain

Here's the important part: when something binds to the protein, the electrical and chemical environment around the protein changes, and the protein will* change shape. For example, if a signal peptide with a lot of charged side chains lands on the receptor site, amino acids with charged side chains in the receptor will try to twist towards or away from it. This will change the shape of the protein, potentially opening new receptor sites or setting off other signalling.

A great example is this animation of a G-protein coupled receptor. Watch it change shape as things bind and unbind to it (the good part starts at 4:15) https://youtu.be/ZmrDWIeX0Tc

*Per /u/danby, below, the hydrogen bonding network is quite flexible, so we can't really call the protein a rigid body.

*Again, per /u/danby, there are examples of binding without structural change.

Starship for sure, but I'm also hoping Blue Origin surprises us with a New Glenn launch this year. I doubt it will happen but it would be nice to see some competition in reusable launchers.

Try it yourself!... although it probably won't work as described.

The wave would mostly regain the speed after the ping pong ball area, but it would be much reduced in height. A lot of energy would be lost to ripples going everywhere. My analogy just serves to illustrate the general concept of particles reacting to the approach and passing of the wave and generating interfering waves of their own.

However, a similar effect can be seen in wave tanks when you change the depth of the water: https://youtu.be/4_VejGC0DMM?t=261

In this case the interfering waves are bouncing from the new lower bottom of the tank, slowing down the wave.

I like this Fermilab video for explaining light slowing in a medium: https://youtu.be/CUjt36SD3h8

You can think of it as a wave moving through water with a bunch of ping pong balls. As the wave lifts and drops the ping pong balls they resist the acceleration, and that makes a little inverse ripple within the bigger wave. The big wave and the little ripples stack together into a slower wave, but the energy doesn't change, so once the wave moves past the ping pong balls it goes back to the same speed and height.

A human version of sort of the same technique is used to make three-parent babies: https://www.nature.com/articles/nature.2017.21761

This avoids mitochondrial diseases by transferring a nucleus from a fertilized egg to a donor fertilized egg that had the nucleus removed. The baby ends up with the nuclear DNA of its biological parents but the mitochondrial DNA from the donor, hence three parents.

You said it yourself in your first reply - it makes the ice melt earlier. The relevant concept is Gibbs free energy, where endo/exothermic is only part of the equation.

The only reason ice melts at 0 degrees in pure water is that that's the point where the gain in entropy from turning into a liquid balances out the increase in potential energy from turning into a liquid.

When you add salt to the water, you change the entropy part, making it more entropic to melt, which decreases the equilibrium temperature at which ice turns into water. The ice will melt faster when surrounded by salt, absorbing energy (and quite a bit of it! 334 J/g) until it hits the new depressed equilibrium temperature. Then it'll maintain that temperature by melting slowly, just like ice in pure water.

It's still the same total energy. You'll lose ice getting down to minus whatever degrees, so while you're colder to start, you also have less ice.

Ignoring all the extra stuff that can happen (e.g. condensation on the outside of the colder cooler dumping extra energy into it, or freezing and making an insulating layer), a sealed ice+salt cooler should hit 1 degree Celcius before a sealed cooler with ice alone would.

The phase change is endothermic, so ice near zero degrees will cool the surrounding ice down as it melts into colder water. You're right that the total energy won't change just by adding salt, but you will reduce thermal energy in the system to gain that potential energy in the liquid.

Your second point is dead on though, if anything, it should warm up faster because there's more temperature differential now.

I would absolutely buy that print. Got a link to the shop?

I really dig the paper airplane on a bombing run!

Molecular oxygen is 21% of the atmosphere on Earth thanks to the presence of life. There are many geological processes that remove molecular oxygen, so without life replenishing it it would go away over a relatively short geological timeframe.

There are some ways to maintain molecular oxygen in an atmosphere without life getting involved, but as far as we know that much molecular oxygen in an atmosphere is rare in the universe.

There's research being done to automate the process for large trucks so that they move together as a 'platoon', communicating with each other for semi-autonomous braking and accelerating. It would save a whole lot of fuel on long-haul drives.

https://highways.dot.gov/research/laboratories/saxton-transportation-operations-laboratory/Truck-Platooning

The biochemical explanation is that mercury messes with the 3D shape of your proteins (section 4.1.1). It does this mostly by disrupting the disulfide bridges, which are very important to the final shape of many proteins.

Proteins are involved in pretty much every process in your body, and their 3D shape is very important to their mode of action. The brain is particularly vulnerable because it uses a lot of energy (i.e. lots of reactions going on) and has a limited capacity for repair.

Edit for a bit more detail: One set of proteins that are particularly badly affected are the selenoproteins that help fight oxidative damage. The brain is prone to oxidative damage because of its high energy needs. Mercury binds to the selenocysteine in the selenoenzyme, basically deactivating it.