Of course! This is something I’m mostly familiar with from the popular press, so I’ll leave it to someone else to dig up the more technical papers but:

Here’s an article in Science about recent projects and results.

Here’s a more technical article from Nature Medicine from the research team that pioneered this technique

Here’s a human interest story from a hospital network that performed one of these operations which gives a look at what this is like for a patient.

Thank you for the correction!

First off, there are lots of causes that could lead to someone not being able to walk, and severed nerves or damaged neural pathways are only one of them.

Nerves cannot be naturally regrown by the body, and are delicate and difficult to work with. So far it hasn’t really been possible to do the kind of reconnection you’re thinking of. But there are groups working on that! For example there are projects that implant sensors “upstream” of the break to measure signals and then stimulating electrodes “downstream” of the break to match those measures signals. They’ve started having some pretty remarkable success too.

To give a direct example from your own body: the heat is capable of beating on its own without any signals from the brain. A region of the heart called the pacemaker generates a rhythmic signal which starts a wave of muscle contraction which runs across the heart and causes it to beat in a sequence which pumps blood (random or disorganized contraction of cardiac muscle is called fibrillation, pumps little to no blood, and is what those paddles you see in ever medical show are for). The heart is only involved in sending signals which tell the pacemaker to speed up or slow down. But the basic function of the heart itself runs on its own.

No worries. I actually appreciate the correction! Ironically I was enervated when I wrote this so I mistyped the word lol

There are animals that have no centralized brain, like a jellyfish or a sea anemone. So without a brain at all (but still with some neurons) they would by definition fit your criteria.

But “has no brain” feels like kind of a cop out. I think your best bet for an organism with a true brain might be a cephalopod. They have big brains, but also extremely complex and highly enervated arms.

Sorry, brain fart above and I typed the wrong thing: I means that a photon does not have kinetic energy because a photon has no mass.

Hopefully someone with more knowledge can jump in, but I don’t know that there’s an intuitive reason why Planck’s Relation is true. I think it’s a relationship derived from the Schrödinger Equation and Einstein’s work on relativity and then extensively measured and confirmed since then.

Basically is it backlit or lit from the front. If you backlight the cup you are looking at the light that has passed from the light source through the cup and then reaches your eyes. If you put the light on the same side of the cup as you, then you are looking at light which hits the cup, reflects or scatters off the glass and gold and then reaches your eyes.

Ok, it’s been a while since it took physics so if I’m wrong someone can correct me:

No, moving charge doesn’t have kinetic energy because it has no mass. The link between photon frequency and energy is called the Planck Relation.

Key distinction: the color of something is based on the spectrum of light (how much light at each wavelength in the visible range) reaches our eye. Absorption is a big part in that, but it’s not all of it. For example: an apple won’t appear red if the light illuminating it doesn’t include any red light since there’s no red light there to reach our eyes. And there are plenty of situations where optical effects other than absorption are dominant. A great practical example is the Lycurgus Cup. It’s a glass cup full of gold nano particles. When light shines through it, absorption dominates and so only red light passes through and it appears red. When light shines on it, scattering dominates, and those same particles scatter green light, but not red or blue, so it appears green since the scattered green light is reaching our eye.

Also, up until now we’ve been talking about the light itself. How we perceive that light and turn it into our sense of color is a whole other part of this. Very simplified explanation but: our eyes contain two types of light sensitive cells, rods and cones. Rods are great in low light conditions but can only see black and white. Cones are less sensitive to light, but they come in three variants, red, blue, and green. Red cones most strongly absorb red light, blue cones most strongly absorb blue and green absorbs green. When a cone absorbs light, it sends a signal to our brain. Based on how many of the RGB cones are triggered our brain mixes those signals together to form a perceived color. So complimentary colors have to do with how our eye and brain perceive colors. I don’t think there’s anything inherent to the photons that makes, say, blue the complement of red. It’s the way our sense of color works that makes those have high contrast.

Emission specta (or scattering spectra, or transmission spectra, etc) are basically the same yeah. You read the wavelength (or frequency) of light along the x axis and the y value tells you how much is emitted/scattered etc for that wavelength. It’s been a while but I think for an emission spectrum you need to specify the conditions under which the object is emitting.

Like I said in my final paragraph, I was glossing over a lot :P

So any given molecule has a lot of energy levels. And for each of those transitions, there is actually a narrow range of acceptable wavelengths that will be absorbed. Start adding all of those together and what you end up with is that pretty much any wavelength of light can be absorbed, some are just much more strongly absorbed than others.

So an absorption spectrum is showing how strongly light is absorbed. The higher on the y axis, the more of that light gets absorbed by the material and the less is available to reach your eye.

Looking at water, it strongly absorbs UV (high energy light) and then there is a big drop and it has a minima right around 420 nm, which is blue. From there are the wavelength gets longer (redder) the graph ticks back up until it passes into the IR. So this tells us that water passes blue light and absorbs red light. So if you shine a red light through water, it will go away much faster than if you shine a blue light. From the graph we can (successfully) guess that water will appear blue or blue-green because it more easily allows blue light to pass (and reach our eyes) than it does yellow/orange/red light.

Complementary colors have more to do with how we perceive color than with how light works. It’s about which colors look good together rather than how those colors are made.

The shortest answer to your question is: physics and chemistry!

Ok so just a couple quick things: you are correct that the color we perceive is based on the spectrum of light which reaches our eyes. But there are a lot of other factors beyond the pure absorption of the object. For example, the spectrum of the source (eg a lightbulb has a different “color” of light than the sun) as well as the intervening medium (air interacts with light differently than glass, and dusty air is different than pure air). And there are ways for light to interact with an material beyond absorption (like scattering). But generally speaking you’re on the right track.

So, light comes in discrete packets called photons which have an energy. Because of quantum mechanics that energy is directly linked to the wavelength. In other words, different wavelengths of light have different energies. When light hits an object, light is so tiny that what we’re really talking about is light hitting the molecules which make up that object. Now, again due to quantum mechanics, each molecule (and each part of the molecule) can only have different set energy states. Making up numbers but let’s say it can be 1, 2, or 2.5. But it can’t be say, 1.7 or 2.8. So going back to the light, let’s say the molecule is generally in state 1, which physicists call the ground state. If the photon has an energy of 0.7 it can’t interact* with the molecule, but if it’s 1 it can boost the molecule up to 2 and if it’s 1.5 it can boost the molecule to 2.5. Now, remember that each energy of photon is tied to a wavelength? This is the mechanism by which some wavelengths get absorbed but others do not. For a given material this is expressed as an absorption spectrum, which is a graph that shows how strongly different wavelengths of light are absorbed. Add together a weighted average of the absorption spectra for all the materials in the skin of an apple, and you get the overall absorption spectra which determines what color the apple’s skin is. In the case of a red apple, shorter (bluer) wavelengths are more strongly absorbed than longer (redder) wavelengths.

As to where that extra energy goes, the molecule will eventually return to its ground state. In most situations for light in the visible spectrum, the energy ends up lost to heat (at a molecular level, the molecule wiggles a bit faster). In other words if you shine a light on a thing, it’ll get hot over time and that heat is the energy coming from absorbed photons.

Now, I’m glossing over a whole lot here, and the reality is more complicated than I’m describing in a lot of important ways. For example most molecules have tons and tons of different energy states, eg vibrational, rotational, electron energy levels, chemical bonds, etc. And in practice there’s usually a narrow range of acceptable energies that mean you don’t get a perfectly sharp peak. But hopefully this is enough to get you started.

Perhaps a more instructive version of your metaphor might be a fire extinguisher which emits a flame retardant for the first second which explodes when it contacts a certain chemical. Would it be better if it didn’t do that? Sure. But the flame retardant which doesn’t explode is expensive and changing the design of the fire extinguisher is even more expensive. Besides, the fire extinguisher would still work fine, you just have to not use it on that one particular type of chemical fire.

As others have covered in a lot more detail, the operators of reactor four had to take a number of extraordinary measures to put the reactor into a state where the graphite tipped control rods could cause a catastrophic failure. Worse, they didn’t even know there was a catastrophic failure state they needed to look out for. To go back to the fire extinguisher metaphor, no one ever warned them about the chemical.

That’s supposed to be the big revelation at the end of the show. Legasov knew about the potential for an RBMK reactor to explode, but the people running Chernobyl that night didn’t. Even though the operators where running the reactor in reckless and dangerous manner, they only thought they were risking a shutdown. They didn’t know they were courting utter disaster because they had never been told that was a possibility.

There actually are some ways you can tell cancer cells from non-cancerous cells using color/appearance! Cancer cells generally have a higher nuclear/cytoplasmic ratio than non-cancerous cells. In other words, in cancer cells the cell nuclei are larger compared to the size of cell they’re in. This can be seen under a microscope, but the difference between nucleus and cytoplasm is hard to see with its ‘natural’ colors. But you can see the difference if you use dyes which color the nucleus one color and the cytoplasm another.

The cell also has various optical properties which are subtle or otherwise not visible to the naked eye which can be used to visually distinguish cancerous and normal cells. For example, human tissues is fluorescent. If you shine light at a specific wavelength (often in the UV) the tissue lights up (fluoresces) at a different wavelength (color). Cancer cells have different fluorescent properties than normal cells, and this can be seen using a specialized microscope.

You can also apply dyes to make cells and their structures more easily visible. There are certain dyes which will stick to cancer cells but not non-cancer cells. These can be used to make it relatively easy to spot cancerous tissue. However this requires a dye to be applied which can be impractical depending on how toxic the dye is, where the site is in the body (inside of the mouth is way easier to get a microscope and dye in than inside the heart for example)

You can also administer carcinogens to cause the specimen to develop cancer on its own, without the need to culture and graft the cells. Based on the type of carcinogen and where/how it is administered you end up with different types of cancer.

Back when I was in grad school one of my colleagues injected a carcinogen via catheter to promote bladder cancer for example.

As to your questions about ethics: in my experience at least yes, researchers take the ethics of what they are doing extremely seriously, and the university has an elaborate oversight and approval system which monitors for ethical lapses. We were taught that an animal could only be used if there was no other way to collect the data we needed, and that the study should always be designed to minimize the animal’s suffering

Sure, but I’m not an expert by any stretch of the imagination. So the cell is surrounded by a membrane. That membrane is absolutely covered in tons and tons and tons of proteins which stick out above the surface of the membrane. We call these surface proteins because they extend above the surface. Those proteins can be used to mark what type of cell the cell is, interact with chemicals floating around outside the cell, bind the cell to various structural components or other cells etc. These are sometimes called surface antigens, because antibodies can be bind to them.

The normal blood group markers, the ABO system, represent a set of surface antigens. The ABO and Rh (that’s the +/- part) happen to be particularly important to how the body recognizes self vs foreign cells. So it’s really important to match those correctly.

But the blood cells have hundreds of different antigens. And just because the ABO and Rh groups are particularly important for recognition doesn’t mean those other antigens aren’t also used. And to make it even more complicated, different people seem to respond more or less strongly to different groups (although ABO seems to be close to universally important)

Here’s an article I found on the topic

Depending on how you dye/stain the cell, yes. The surface proteins are distributed all across the surface. So if you use a dye which only sticks to those proteins it would color the whole surface of the cell.

There are ways of binding dyes to targeting moeties, like antibodies, that only stick to one type of target. So you could theoretically make different batches with different colors of dyes and bind them to different targeting moeties so only blood cells with that group get stained that color.

There are way, way, way easier and more practical ways to type blood though. So I don’t know that anyone would actually go through the work to do this or what it would accomplish. Just saying this is a way to achieve what the OP asked about and actually see a clear difference under the microscope.

Very tiny. A blood cell is around 7-8um across (there are 1000 um, micrometers or microns, in every millimeter). A surface protein is probably around the 10s of nm (nanometers, there are 1000 nm in every um) large. So roughly a thousand times smaller.

It is relatively easy to see cells with a microscope. With a light microscope you generally cannot see proteins because they are too small. Microscopes are limited by something called the diffraction limit, which is usually around 0.25um (or 250nm).

However you can see much smaller structures with an electron microscope and could presumably “see” surface proteins in that manner.

You could also use a stain or dye which colors the cell based on what surface proteins are present. You wouldn’t directly see the proteins, but you could differentiate blood type based on an indirect visualization (the color)

You’re both over and under thinking this lol. So, your DNA encode a ton of information that ultimately determines a lot about your body’s morphology. But that information isn’t a “picture” of what you’ll look like. There’s no coordinate system and your DNA doesn’t “know” where the tip of your nose will be or what your eye color is, etc. Generally speaking your DNA doesn’t know anything about macroscopic space or encode any information about it. DNA directly encodes tiny little parts and machines, and those parts and machines work together in a way that is vastly more complex than the DNA “knows” about.

To give a simple view: DNA codes for proteins in units called codons. Each codon is three bases of the DNA chain (the A, C, G, and T letters you’ve probably seen) and which of those bases appear in what order defines the meaning of the codon. Through a process called transcription and translation, the codon is used to pick a chemical called an amino acid. There are 20 possible amino acids (in humans). The DNA tells the cell which amino acids to assemble in what order. The chain of assembled amino acids folds into a protein (often along with other chains) based on what amino acids go in what order. The proteins do all kinds of things but they’re not smart, they’re structural building blocks or simple machines. But the interplay of simple machines can lead to extremely complex behaviors (like “grow a nose”).

Imagine we have a first protein that sits on the surface of the cell. It bends one way if it’s touching something and bends another if it’s not. We have a second protein that checks the bend of those first proteins and triggers a signal to grow if it’s bent touching something. Now we have a simple little system which means that the cells will grow across an object (like the bottom of a Petri dish) but stop when they run out of room for each cell to be touching the dish. A relatively complex spatial behavior from two simple parts*

And cells are way, way, way more complicated than this, with tons and tons of interlocking signal pathways.

*to be clear: I made the parts and their functions up for my example to just illustrate how the proteins can lead to a spatial behavior without the DNA knowing anything about space. Growing to confluence is a real behavior in many cells, but frankly it’s been a long time since I took cell bio and I don’t remember the exact mechanism.

No. The tests generally use antibodies to test for your antibodies. The only antigen would come from you. And as noted by others, even if the test did contain antigen, it would 1) likely not be infectious on its own and 2) not enter your body.

The type of test you’re thinking of is a lateral flow immunoassay or dipstick test. They perform a type of test (assay in fancy scientist speak) called a sandwich assay. The strip is prepared with three things:

1. a loading pad that includes an antibody which binds to the target analyte (the thing you are testing for). We will call this antibody A. For the type of test you describe, an antibody test for HIV, the analyte is human anti-HIV antibodies. The Antibody-A’s are bound to something that generates a visible color, often a metal particle such as gold.
2. A test line, which is a line we’ve drawn across the strip and chemically glued another set of Antiboy-A’s down so they are stuck to the strip
3. A control line which has a second type of antibody (Antibody-B) which will bind to Antibody-A

When we add a sample to the loading pad, it will start flowing down the strip. If analyte is present it will bind the loose Antibody-A’s and become colored as it flows down the strip. When it hits the test like those Antibody-A’s will bind the analyte too. So if analyte is present we form a “sandwich” with two Antibody-A’s as the bread (one bound to a colored marker and one bound to the strip) and the analyte as our filling. If there’s no analyte (or if there is and there are extra Antibody-A’s) they will get grabbed by the Antibody-B’s at the control line.

PS: Antigen not Antigene. Antigen just means something an antibody binds to. Doesn’t have to be (and usually isn’t) anything genetic.

Ok, my NASA friends have got your back! Here is the official NASA roadmap for research about mitigating bone loss related fracture risks, and here is the specific section that discusses prevention mitigation.

Regarding medication they say that since there is a very low chance of a bone breaking on current missions, pharmaceuticals are currently considered a plan B for use on future exploration/longer term missions and their use will be reconsidered/researched as those become more likely.

Ok, I got interested enough that I reached out to my friend who does spacesuit engineering for NASA. She says she’s not aware* of any drugs they take for that purpose while in space. They focus on exercise instead. She speculates this could be an interesting clinical trial.

*Although she adds that what meds the astronauts take wouldn’t really be her area so it’s possible they do and she doesn’t know about it. A different friend in that chat who works in healthcare points out that a lot of anti-osteoporotic meds can cause kidney stones, which would be really bad in space.

Edit: I noticed after typing this that your question is about prophylaxis. So presumably you mean before they launch. My bad.

I don’t know what current practice was, but when I was in university one of the professors I worked for was working with NASA on a stimulation device to prevent osteoporosis. They had found that small amounts of vibration help stave off bone loss more than high impact so he developed a belt/harness you could wear covered in small vibrating motors to help reduce bone loss. As far as muscle loss, the astronauts already undergo an exercise regime to help reduce muscle (and bone) loss.

Informed consent and legal ability to make certain decisions are different concepts. And in the cases you list the key difference is giving consent for a medical procedure which may have drawbacks but which may have upsides too, and asking the patient to weigh those aspects before deciding. Whereas the things you listed that a teenager cannot do are generally not seen as having a benefit to the teen.

Informed consent is more or less exactly what it sounds like. It’s the idea that a thing is explained to you in a manner you can understand and then you agree to it. It’s a thing that can be given even by very young children for example. It’s also a thing that an adult may not be able to give, for example if they have certain developmental disabilities. A large chunk of medicine and medical research is built around the idea of informed consent. The idea that the patient needs to have medical procedures explained to them in a manner they can understand before they agree so that they can make their own judgements about if the risk is worth the potential gain.

The other things you mention have to do with legality, which is a policy rather than scientific construct. For the examples you listed the idea is that those are things we generally don’t want children doing because they are 1) addictive and 2) bad for you. The age cutoff is the age at which we as a society will let you make your own self-destructive choices.