ELI5: why doesn't the International Space Station (ISS) run out of air? Is it capable of making its own air? Do we presently have the technology to make a self-sustaining biosphere in space?

TwentyThousandLeague · 1年前

I love your subtle reference to the Haber process.

alexinboots · 1年前

The NOAA page on the Lituya Bay runup lists the source as an eyewitness measurement. The report also refers to other physical evidence such as the removal of soil, trees, and artificial structures.

In general, there are several methods that can be used to assess the height of a tsunami/runup. If you look at the historical distribution of measurement types (click distribution in the previous link), post-tsunami surveys of various kinds account for the majority, followed by eyewitness measurements, then tide and deep-ocean gauge measurements.

Most tsunamis, however, are relatively minor. Far more of these smaller tsunamis that would otherwise have been missed are now measured using tide and deep-ocean gauges: measurement types of 2 and 3 on this list of 2013's tsunamis. You can see that this year's list is heavily skewed towards gauge measurements.

DART (deep-ocean assessment and reporting of tsunamis) buoys are the current gold-standard in advance detection of tsunamis. They are generally deployed several kilometres deep, measure the height of the column of water above them using pressure sensors, and trigger when an event just a few centimetres (an inch) high is detected.

TL;DR: Most smaller tsunamis are measured using tide and deep-ocean gauges (such as DART buoys). Eyewitness measurements and post-tsunami surveys can be used for larger tsunamis.

jackmandood2 · 1年前

This post is correct, but the livescience article linked didn't research their facts when they proclaimed this 2013 event "the deepest earthquake ever recorded". A two-minute search (or less time than it took to write that livescience article) returns 1611 earthquakes of Mw 4+ deeper than this event since 1980.

The deepest in that list was a much smaller 2004 Mb 4.2 event at a depth of 736 +/- 70km (457 +/- 44 miles). There was also an Mw 7.7 event in 2002 at a depth of 675km (420 miles).

Fourgot · 1年前

My research is in processing seismic signals to detect tsunamis. My background is in signal processing and machine learning, but I've spent the last couple of years specialising in geophysics.

Fourgot · 1年前

This USGS FAQ does a good job of explaining why larger ruptures can't be prevented using smaller, harmless, "controlled" earthquakes.

The main reason is that you need thousands of smaller quakes to release the equivalent energy. For example, 32000 M3 earthquakes release equivalent energy to one M6 event. This scales to around one million M3 events if you want the equivalent energy of an M7 earthquake!

Secondly, how do you guarantee that the earthquakes you trigger will be minor enough to cause no damage? Now guarantee that for every one of the many thousands of quakes you will need to trigger.

UncertainHeisenberg · 1年前

If anyone is interested in a comprehensive and detailed list of nuclear tests, refer to the Nuclear Explosion Database.

kyarmentari · 1年前

Yep, this is a practical limitation. I posted the comment because the two deleted replies were suggesting that higher resistance for the heating element leads to greater power output.

TurtleCracker · 1年前

Wolfram alpha calculates that it will cause a grain of sand to jump 50nm (50 billionths of a metre or 2 millionths of an inch) into the air, which is about 1/400^th to 1/1600^th the width of a human hair. Sideways it would go further than this.

EDIT: It seems Wolfram Alpha has interpreted a "grain of sand" as 1 grain in weight measures (64mg). Looking at fine to coarse sands (0.063 - 2mm), a grain has a mass of between around 26ug to 84mg. The lightest grain would jump 0.126mm (0.005") at a speed of 50mm/s (0.2ft/s), while the heaviest would jump 40nm (2 millionths of an inch) at a speed of 0.9mm/s (0.03ft/s).

SwagMasterPimpNigga · 1年前

Chris is able to kick Steve due to the normal force of the air behind him .... So, the normal force from the air around the top free-faller allows him to kick the bottom free-faller

You are correct that you are able to kick someone while falling, but the "normal force" of the air as a reaction force isn't the correct explanation. Consider Chris kicking out his foot while floating around by himself.

First, the rest of his body is a lot heavier than the leg doing the kicking. Acceleration of the leg in one direction causes the rest of his body to accelerate in the opposite direction. Due to the difference in mass, however, the leg (and foot) ends up moving faster and further than the rest of his body.

Without external forces, you can model Chris as a centre of mass moving at a constant velocity (v=0 is nice and easy). Kicking out his foot shifts his centre of mass. But the shift in the centre of mass isn't as great as the movement of the leg (due to the relative mases of the leg and body), so the foot extends outwards from the centre of mass.

This would happen whether he was in air or a vacuum. The air would provide a small reaction force, but it's not the reason you can kick your foot out while falling.

kyarmentari · 1年前

therealdreykevins is correct. If you assume that all of the voltage is being dropped across the resistance (which you do, because the whole point is to drive the heating element), then power is:

P = V² / R

Given a fixed voltage, halving the resistance will double the power output.

ItsDijital · 1年前

The example given on that site is completely wrong. If they mean 0.1 in decimal form, it can be represented rationally in binary as 1/1010. If they mean 0.1 in binary form, it can be represented rationally in binary as 1/10.

TDaltonC · 1年前

Below is a repost of my original comment here. To address a little more about what you asked, plates aren't one solid inelastic chunk. They can deform and develop varying stresses in different regions.

Larger earthquakes aren't localised at a single point. The Mw 9+ 2004 Sumatran earthquake, for example, occurred over 1200km and 8-10 minutes. The rupture propagated at around 2.2 km/s (1.4 miles/s).

An earthquake's location is determined from the seismic wave arrival times at numerous seismic stations. The two types of body waves, P-waves (pressure or primary) and S-waves (shear or secondary), travel at around 8 and 5 km/s (5 and 3 miles/s) respectively in the upper mantle (this diagram tells a little more of the story).

Due to the inner structure of the Earth, these waves can arrive at a single station at various times via different routes. Given an earth velocity model and the phase arrival times at numerous stations, the location of the hypocentre (lat, lon, and depth) can be estimated.

Notice that the P and S-waves travel faster than the rupture propagates. This means that the first arrivals at seismometers will be the P-waves from the source rupture. The story is similar with each of the subsequent phase arrivals. These first arrivals from the source are the simplest to pick as they are most abrupt. Seismic waves generated from further rupture actually make subsequent phase arrivals more difficult to pick. In addition, different frequency components of the seismic waves travel at different velocities causing dispersion (the wavefront becomes "smeared"). These and other factors add up to a whole lot of noise that serve to mask the sought after arrivals.

TLDR: Fault ruptures can occur over long distances (over 1200km for the 2004 Sumatran earthquake), but the seismic wave arrivals from the source event are the simplest to pick. The times of these arrivals at numerous stations are used to determine the location of the earthquake's source.

UncertainHeisenberg · 1年前

A signal can be fully reconstructed if it is sampled at double its highest frequency component. Although if you plot the points of a sine or cosine wave sampled at double its frequency it may look like a triangular wave, when you reconstruct it you'll get the original back still.

A few quick plots to demonstrate this:

Note that sampling was timed to correspond to the maximums and minimums. If this wasn't the case, the reconstruction of a frequency component of Fs/2 (Fs is sampling frequency) may be phase-shifted and have it's amplitude reduced.

UncertainHeisenberg · 1年前

Aside from the benefits already mentioned, higher sampling rates allow the use of simpler anti-aliasing filters. A low-pass analogue filter is used to remove high frequency components prior to sampling. If you are sampling at 44.1kHz and want to retain frequencies up to 20kHz, your analogue filter needs to rolloff sharply between 20 and 22kHz.

If on the other hand you sample at 96kHz, you can use an analogue filter with a less precise cutoff frequency (due to component tolerances) and slower rolloff. This allows the use of cheaper components or improvement in passband ripple, phase response, stopband attenuation, etc at the expense of the slower rolloff.

A ~~high~~ low-pass digital filter, with more desirable properties than can be practically or economically achieved in analogue, can then be used to low-pass filter the signal prior to downsampling.

EDIT: high -> low

andyblu · 1年前

Calculating impact velocity using the simulation is a little more difficult, as acceleration is greatest when the bowling balls are closest. This means that a small error in impact time introduces a large error in the impact velocity. As a result, I had to alter the code to reduce the time step as the balls approached each other.

The calculated impact velocity is 4.72x10^-5 m/s (17cm/hr or 7"/hr). But impact velocity can also be calculated relatively easily using conservation of energy.

The kinetic energy gained by each bowling ball is equivalent to the integral of the force with respect to distance. If we define x as distance to the midpoint between the balls, then F = G m² / (2x)² , where 2x is the separation distance between the balls.

We need to integrate this with respect to x from 0.1085m (the radius of the ball) to 804.5m (the initial distance from the midpoint) to calculate the kinetic energy gained. This gives a value of 8.10x10^-9 Joules.

Since KE = 0.5mv² , we can calculate that the impact velocity is 4.72x10^-5 m/s.

EDIT: I should mention that both bowling balls are travelling at this velocity. So the relative impact velocity is double this.

andyblu · 1年前

I understood your original post and was providing a solution, using an alternate method, in support of your calculations. :)

andyblu · 1年前

It's been a few years since I've had to solve second-order differential equations, so I ran a simulation in MATLAB instead! I assumed a separation of 1609 metres and a mass of 7.26kg for each of the bowling balls.

I tried time steps from 10 to 100,000 seconds in the simulation, and all predicted a collision in 73.0 years.

Code for those who are interested:

G = 6.67e-11;
m = 7.26;

xi = [0 1609]; % Initial positions
xf = xi(2)/2;  % Final position
tS = 1000;     % Time step in seconds

% Initialise
x = xi;
t = 0;
v = 0;

% Increment until a collision occurs
while x(1)<xf
    a = G*m/(x(2)-x(1))^2;
    v = v + a*tS;
    x = x + [v*tS -v*tS];
    t = t + tS;
end

fprintf('Collision in %0.1f years\n',t/(86400*365));

myleskilloneous · 1年前

This is a factor, but I just wanted to point out that body waves don't travel in straight lines between the source and detector. They travel along curved paths through the Earth as a result of velocity changes with depth causing refraction.

This page has links to some basic videos that show the curved paths through the Earth and travel-time graphs plotted.

myleskilloneous · 1年前

The velocity of body waves through the Earth changes with depth. The second diagram on this page illustrates the relationship between depth and velocity for P and S-waves.

Waves that travel further also travel deeper, so their average velocity is faster. This assumes a direct path through the mantle without core phases, reflections, triplications, etc.

Dipping_Stick · 1年前

It depends how you define efficiency. A compressor-driven heat pump, such as a reverse-cycle air conditioner or refrigerator, can provide more cooling/heating power than the input power that runs the compressor. For example, a 2.1kW (electrical rating) Daiken FTKS71LVMA air conditioner can provide 7.1kW of cooling. The coefficient of performance relates input work to transferred heat.

This is achieved by moving thermal energy from a cold reservoir to a hot reservoir (heating the hot side and cooling the cold side). The energy additional to whatever is input to run the compressor is provided by thermal energy from the cold reservoir. So energy is still conserved overall.

jmdugan · 1年前

Larger earthquakes aren't localised at a single point. The Mw 9+ 2004 Sumatran earthquake, for example, occurred over 1200km and 8-10 minutes. The rupture propagated at around 2.2 km/s (1.4 miles/s).

An earthquake's location is determined from the seismic wave arrival times at numerous seismic stations. The two types of body waves, P-waves (pressure or primary) and S-waves (shear or secondary), travel at around 8 and 5 km/s (5 and 3 miles/s) respectively in the upper mantle (this diagram tells a little more of the story).

Due to the inner structure of the Earth, these waves can arrive at a single station at various times via different routes. Given an earth velocity model and the phase arrival times at numerous stations, the location of the hypocentre (lat, lon, and depth) can be estimated.

Notice that the P and S-waves travel faster than the rupture propagates. This means that the first arrivals at seismometers will be the P-waves from the source rupture. The story is similar with each of the subsequent phase arrivals. These first arrivals from the source are the simplest to pick as they are most abrupt. Seismic waves generated from further rupture actually make subsequent phase arrivals more difficult to pick. In addition, different frequency components of the seismic waves travel at different velocities causing dispersion (the wavefront becomes "smeared"). These and other factors add up to a whole lot of noise that serve to mask the sought after arrivals.

TLDR: Fault ruptures can occur over long distances (over 1200km for the 2004 Sumatran earthquake), but the seismic wave arrivals from the source event are the simplest to pick. The times of these arrivals at numerous stations are used to determine the location of the earthquake's source.

coniform · 1年前

You have an undergraduate degree in biochemistry. Do you have any relevant posts in this field that you can list?

coniform · 1年前

Can you please post a few comments, when an opportunity presents itself, and update your information? A moderator with expertise in your field may additionally ask you some questions.

coniform · 1年前

Can you please post a few comments, when an opportunity presents itself, and update your information? A moderator with expertise in your field may additionally ask you some questions.

coniform · 1年前

Can you please post a few comments, when an opportunity presents itself, and update your information? A moderator with expertise in your field may additionally ask you some questions.

UncertainHeisenberg

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