This isn’t exactly my area of expertise, but I have some information that might be helpful. Here’s the description of the frame selection from a paper on a lucky imaging system:
The frame selection algorithm, implemented (currently) as a post-processing step, is summarised below:
A Point Spread Function (PSF) guide star is selected as a reference to the turbulence induced blurring of each frame.
The guide star image in each frame is sinc-resampled by a factor of 4 to give a sub-pixel estimate of the position of the brightest speckle.
A quality factor (currently the fraction of light concentrated in the brightest pixel of the PSF) is calculated for each frame.
A fraction of the frames are then selected according to their quality factors. The fraction is chosen to optimise the trade- off between the resolution and the target signal-to-noise ra- tio required.
The selected frames are shifted-and-added to align their brightest speckle positions.
If you want all the gory details, the best place to look is probably the thesis the same author wrote on this work. That’s available here PDF warning.
Thanks, I’ll take a look at that! I think I actually already skimmed it, because those 5 points are familiar.
I wasn’t sure what was meant by the PSF guide star. Is that just the function that selects the speckle in each frame use to shift/align the frames?
Also I wasn’t sure what “sync-resampled” means. Shifted-and-upscaled?
Reading this had given me an idea on how I might implement it myself, but I wasn’t familiar enough with the terminology to know if my algorithm was the same as the one described.
I’ll try reading further into the paper to see if it clears anything up
I believe the idea is that a single bright star in the frame (the guide star) is used for selecting the frames. The point spread function (PSF) is just going to be some function that describes the blurred shape you would observe with the detector for an input point source. You then select frames in which the guide star is well centered, compared to its overall distribution.
I think your guess on “sync-resampled” is correct. They increased the “resolution” by a factor of 4, so that when they realign the chosen frames to center the guide star, they can do so at a sub-pixel precision.
You may want to check out chapter 3 in the thesis, particularly section 3.5.3. The give a lot more detail on the process than you’ll be able to find in the paper. A well-written PhD thesis can be 1000x more valuable than the journal article it ultimately produces, because it contains all the specific details that can be glossed over in the final paper.
Hollow bones and in some cases spaces within their bodies that were just filled up with air. The end result being that dinosaurs were a lot lighter than their frame would suggest, which is what allowed them to get so big in volume.
Being big is advantageous as long as the animal is able to find enough food to sustain itself. Food was plentiful at the time, so dinosaurs grew quite large.
In modern times, most mega fauna is gone because Humans hunted them to extinction.
They weren’t all big, but anyway, they (probably) evolved like giraffes to reach for food and as protection against physical damage from predators. The climate was also different and they had plenty of food.
Anyway, evolution does not select. It’s not survival of the coolest features… it’s only reproduction of those that manage to reproduce.
First, not all dinosaurs were huge. It’s not a trait of dinosaurs in general. Rather, the environmental factors in the past and some factors that are true for reptiles, allowed being huge as an acceptable evolutionary niche, more than today!
Why would some of them grow so big:
In evolution, it’s always a bit of a hen and egg problem. And there is between species competition called “Red Queen Hypothesis”.
So a likely explanation is that, due to high CO2 atmosphere, plants grew larger which lead to having a long neck or being tall being an advantage. And for carnivorous species bigger herbivores meant that being bigger is an advantage. That, again, meant their prey had pressure to grow bigger (and/or faster), and so on and on.
How could some of them grow that much:
Dinosaurs are reptiles, so they were poikilothermic. Since temperatures have been higher and more stable at their time, a bigger body allowed to keep body temperature stable as well. It doesn’t cool off as fast which allowed more activity which allowed eating more which allowed a bigger body.
There was also significantly more oxygen in the atmosphere which is associated with bigger growth in all species since our metabolism depends on it.
This is especially true for Arthropoda btw, some of them were huge in the time of dinosaurs because they breath through their exosceleton. The biggest centipede found (yet) was 2.5 m long! The difference in size between insects in the past and insects today is much bigger than between reptiles today and in the past. All due to bigger plants and more oxygen and the interaction spiral between prey and predator.
Maybe we look at the ratio of country perimeter to area? Counting the number of exclaves could also be a factor. And maybe a ratio of the distance to cover all the exclaves divided by their area?
So if a country were a perfect circle it’s perimeter to area ratio would be 2/r, it has zero exclaves and then it’s width would be the diameter.
If a country were two perfect circles of the same diameter, separated by a distance of the same diameter, it’s area ratio would be 2/r, exclaves would be one, and it’s width would be three times it’s diameter.
So now you can imagine a country like Chile, modeled as a really skinny rectangle, has a pretty large perimeter to area ratio, no exclaves, and a width roughly the length of the rectangle.
I guess you’d have to decide if archipelago nations are measured as the geometry of the sea they own, or as discrete islands.
Thanks for the proposal. That gets us somewhere already, although only for non-landlocked countries. Using the perimeter also opens us up to the coastline paradox.
I guess you’d have to decide if archipelago nations are measured as the geometry of the sea they own, or as discrete islands.
I think that it might serve us better to consider them as distinct islands, to keep the measures comparable with landlocked countries.
You didn’t really mention how this is all being tabulated. Just in theory? Do you have access to data sets or are you making them? The coastline paradox only really exists for smaller and smaller measuring devices. If for example your method is using satellite images of a given resolution, or another consistent measuring tool, the measurements should be comparable between country borders and therefore the error or the paradox should come out in the wash.
I would imagine using some sort of shapefile that I can run calculations in a scripted manner. So, in that case it will depend on the resolution of the shapefile.
I would do perimeter^2/area, to avoid biasing toward small countries. Divide one circular country into two circles with the same total area and p^2/A goes from 4 pi to 8 pi. Divide a square country in two and p^2/A goes from 4 to 6.
I did this all in my head. I think you are right. Point being, small simple algebraic expressions stacked as a a polynomial can be used to create relative scores for this type of analysis.
I think it would ultimately depend on a use case for that metric, otherwise you're putting the cart before the horse. There are many measurements and calculations you could come up with, but no obvious (to me, anyway) interpretation of "most discontinuous": something is either in one piece or not. If you needed a metric like this for a practical purpose, your specific needs would be a starting point for designing one. If it's more of a shower thought, you sort of have "too much freedom" to be able to define anything that's necessarily meaningful.
Simple examples would be just "number of 'discrete parts'", "minimal area needed to span all territories" and things like that. Maybe you're more interested in "total distance from all satellites to wherever the capital is" or something, in a different context. The point is they'd all tell you radically different things, so it's important to know which one to ask for.
You could argue that something like Hawaii and Alaska's distance from the rest of the US makes the US score highly.
You could argue that any number of island nations score highly because after all, most of e.g. the US is in one part.
You could argue e.g. Norway's territories near both poles make it pretty high-scoring too.
You could argue that for whatever reason, distribution of area and population matter, and so on.
SI is great, but if you reset everything (and lose all tech and most of knowledge), just create a new system. Embrace what makes SI great (easy conversions and a the nature-based properties) and do it over.
For length, use Hydrogen line when you advance your society enough. It’s more universal than using 🌎 as a 📏.
Step 1: Find the area of each chunk. The biggest chunk is your main chunk.
Step 2: Find the distance between the closest edge of main chunk and the center of each other chunk individually.
Step 3: Discontinuity of each chunk is area of chunk * distance from main chunk / total area.
Step 4: Total discontinuity is sum of each chunk’s discontinuity.
Bolded parts are important. If you use the center of the main chunk, larger main chunk radii make other chunks seem more discontinuous than they should be. If you use the closest edge of other chunk’s, you don’t account for the entire area of the other chunk.
This will give you a number that is bigger when there are more and/or bigger pieces that are further away, and smaller when the opposite is true, normalized for the total area of the country so bigger countries aren’t penalized just because they’re bigger.
The metre was originally defined in 1791 (…) as one ten-millionth of the distance from the equator to the North Pole along a great circle, so the Earth’s circumference is approximately 40000 km. en.m.wikipedia.org/wiki/Metre
The kilogram was originally defined in 1795 during the French Revolution as the mass of one litre (1/1000 m³) of water. en.m.wikipedia.org/wiki/Kilogram
… and the last major SI unit is the second which of course you know is (originally was) 1/86400 day.
Please notice about the Celsius scale : the second reference point isn’t a mixture of ice and salt but rather pure water freezing point.
Now how can we as naked humans develop technology to figure this out is something of historical proportion, that’s a quite amazing story !
Can we improve things a bit? Hoping we can get a calendar with no leap year, even number of days in each month, no daylight savings, etc
Edit: obviously no one got what i meant. We can base the day of the year on whatever the fuck you want, but for the love of god can we not split it into twelve randomly numbered chunks, i hate how our months are!!
This would need the Earth to make one complete rotation around the Sun in an exact whole number of times it rotates around itself. …which is not the case right now and extremely difficult (meaning near impossible) to change.
…no daylight savings…
Okay but now we have a greater problem : we have to change (twice, a year) the time when business, school , stores etc… open and close, for it to be convenient with outside natural light. So, in my opinion, this is not an improvement.
Nah fuck it, change something, its all made up anyways!! The whole idea of our “years” doesn’t make any sense on other planets, so we potentially could define some arbitrary system to it.
Not sure if you’re joking or just having a slow day, but neither the length of a day nor the length of a year are arbitrary. One is the length of a revolution of the earth around its own axis, the other is the time the earth takes to complete a full run around the sun. Those two aren’t fully in sync, and to line them up would require a major feat of astroengineering. Given sufficient advances in science, we might get there in a few millennia, if we’re still around by then, but until then leap years are here to stay.
Look, i know what it is based on now, I am saying we should change it. Obviously I am not being super serious, but it would be nice to have even numbers instead of how it is now
There is a calendar that proposes to have 13 months, each with 28 days. That gives you 364 days. Day 365 is new years day and is not part of any month. There are still leap years because as stated, the Earth goes around the sun in 365.24… days. To not need leap years we’d need that to be a whole number.
Well pretty much everyone likes defining a day based on the position of the sun in the sky. While sun rise and sunset might change over the course of the year, nearly everyone agrees that noon is when the sun is the highest in the sky (ignoring day light savings and time zone effects). Turns out people don’t like it when noon occurs in the middle of the night (which would happen if we changes it to any other length of time).
Likewise, nearly everyone has agreed for millenia that a year is defined by earth’s position within its orbit. We know that based on where the stars are at night. Again, people didn’t like having snow during July (which actually happened because the calendar was so far off).
These are not definitions that we can change or have any control over. Additionally, the length of a year (to get earth back to the same spot in its orbit) divided by the length of a day (the time between the sun reaching its apex one day and the next) is not an integer and there’s nothing that says it has to be.
We can’t change it, so if thats important to you, you’ll have to find another planet to live on.
I know what “we like”. I am saying we should change it in a hypothetical post-apocalyptic scenario where humanity joins hands together and demand a yearly calendar that makes more sense. Don’t know why this is getting downvoted, guess you’re all taking me wayy too seriously lol
I’m personally not voting on your comments, but you are probably being down voted because you are either being purposefully ignorant or you are continuing to insist on a “better system” that is physically impossible.
How is a better system impossible? Lets say you are on a star ship, heading away from earth, no reference points besides distant stars. How do you determine time? How do you determine anything? Even if we knew and simulated exactly how fast the earth is spinning and how much it is rotating around the sun, it means nothing out there. We have decided that time works the way it does, all I am asking is to take the extra .24 days in a year and make them disappear. There are several inconvenient ways to do this but it is possible to break it down further so we do not need the extra day. We could round it off to the nearest day every few years, shrug our shoulders and move on with our lives without tacking on another 29th day in some random month? Maybe there is some other way we haven’t thought of? I guess I just thought more people would respond positively to “impossible future scenario where a calendar that makes sense is used” :/
Sure, in that scenario, such a system would be possible. Hopefully, there is still an earth to communicate with however. So we’d have to keep using earth days and years to enable effective communication. Also, the entire ship would have been built using earth based units, so it might be easier to use the system we’ve already got.
We’re not on a space ship though. We’re on Earth, so what happens on this planet matters. You may care more about not having leap years, but the majority of us care about knowing approximately what the weather will look like at a given point in time and how much sunlight to expect, since those things actually affect our daily lives, whereas an extra day in a given month does not.
What about when in the future if we needed to, say, sync time between here and mars, it would make it easier if we had some “frame of reference” outside of the sun maybe. There would basically just need to be a slight redefinition of what a day is, to account for the extra quarter of a day each year, its only a minute each day, ~86,460 seconds in a day instead of 86,400. Not exactly gonna throw the weather/sun off, no?
oh i know the answer. Since a mars day is about 15 minutes longer and out rover there are solar powered it was important that the human operators of them knew what time it was on mars. Nasa’s answer, make a watch that runs about 2% slower. that git the mars watch an extra 15 minutes and so it syncs to the martian sun.
you just have the ship day be the same length as an earth day and start count from day 0. So the ship launches and it clock starts ticking. Now you do need to ask is this going fast enough that time dilation is a thing? That will change how well it can ever sync up to earth.
I really like that one! Guess there’s really no easy way around leap day, but i was thinking you could add an extra ~60.684 seconds to each day and pretend its the same thing? Even increasing the second to be slightly longer could make it possible i think, since we are restarting from scratch it would be easier to adjust it slightly
Your definition of the meter leaves out the most interesting part. Yes, it was 1,000, 000th the distance of the equator to the North Pole, but how far is that? That wasn’t known accurately in the 18th Century. So, two Frenchmen, Delambre and Mechain conducted the longest meridian survey every attempted. They also did so while half of Europe was at war with one another. It was an amazingly dangerous endeavor. There is also significant evidence they totally flubbed and hand-waived their results. So, although their science ended up being questioned, the process and method was accepted and the Meter was defined.
Re Celsius 0 °: the reason I thought perhaps Fahrenheit’s Weird Brine might be a more absolute thing to take de novo temperature from was because I don’t actually know the answer to “how can you ensure water is exactly freezing temperature?” If it’s solid ice it could be colder, if it’s liquid it’s probably warmer, and even if it’s a bucket of cold distilled water with distilled water ice in it, isn’t it still likely hotter than 0 ° C? I feel like there’s probably something involving equilibrium between solid and liquid water that would be difficult to sus out
if you have both liquid and solid water at equilibrium then you have zero degrees Celsius. Pressure has minimal effects …at plus or minus 0.5 atmosphere. of course if you go to a hundred or a thousand atmosphere then there is an effect of pressure.
Small pieces of ice will equilibrate their temperature faster in water.
Surface tension has minimal effect on melting temperature unless you go to extremely small pieces of ice meaning less than one micron, …which is not possible to achieve anyway because such small ice pellet with fuse rapidly to form larger ones.
Yes a bucket of a mixture of small ice pellets, say a few millimeter size, plus water, (this bucket being enveloped with some insulation) would be a great zero degrees Celsius reference point.
… “the actual melting point of ice is very slightly (less than a thousandth of a degree) below 0 °C.” …
isotopic distribution of heavy and light elements in water also has a very slight effect on melting point. So, rainwater and water distilled from ocean will not melt at the (exact) same temperature.
Now, about small particle fusing together this is true not only of ice but of any material.
it’s called sinteringand it is caused by diffusion and a lowering of the surface energy.
This process is faster when the material is near it’s melting temperature and faster yet if in contact with any miscible liquid phase.
If the sphere of destruction is propagating at the speed of light, then any observable effect reaches you at the same time as the sphere itself. Either you don’t observe it because you’re far enough away to be safe, or you don’t observe it because you’re dead the instant it becomes observable.
Incidentally, you might be interested in looking up the idea of false vacuum decay - although if you tend to get anxious about end-of-the-world hypotheticals you might prefer to give it a miss.
askscience
Active
This magazine is from a federated server and may be incomplete. Browse more on the original instance.