Recent comments in /f/askscience

ronflair t1_jds7p7s wrote

Reply to comment by mcnessa32 in Around 550 million years ago the earth's magnetic field almost collapsed, but then strengthened a few million years later. Scientists say this may have been due to the formation of the inner core. But why exactly would that cause the magnetic field to get stronger? by somethingX

On the contrary, coincidentally it corresponds with the Cambrian Explosion, when all multicellular organisms and phyla arose. Before that, for billions of years, everything was mainly unicellular, such as cyanobacteria; afterwards, dinosaurs, trees, mammals, humans etc.

https://en.m.wikipedia.org/wiki/Cambrian_explosion

Could a severely weakened magnetic field have lead to a massive increase in mutagenesis globally, essentially jumpstarting a new evolutionary arms race? Maybe. We do use radiation and other mutagens to do just that in the laboratory.

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Chalkarts t1_jds7f2j wrote

Reply to comment by acfox13 in Around 550 million years ago the earth's magnetic field almost collapsed, but then strengthened a few million years later. Scientists say this may have been due to the formation of the inner core. But why exactly would that cause the magnetic field to get stronger? by somethingX

I was recently contemplating how similar fast moving river water with its swirls and waves looks a lot like atmosphere of a gas giant, or the formation of galaxies. Made me wonder if magnetism and gravity were the only forms of “drag” giving the swirling galaxies their shape since there are no shorelines or rock to provide it in space.

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UnchainedSora t1_jdrxo24 wrote

Reply to Is there a difference in effect when dosing antibiotics? by Strong_Camel_4468

Answering as a microbiologist, not a pharmacist or MD.

Different bacteria are able to survive different concentrations of antibiotics before they are killed. We call the lowest concentration that is enough to kill them the Minimum Inhibitory Concentration (MIC). In order to treat a patient, we want to make sure they have at least the MIC of the antibiotic, otherwise the bacteria will survive. Additionally, an antibiotic concentration below the MIC won't kill bacteria, but will still provide a stress and create a selective pressure for resistance. Then, upping the concentration to the original MIC won't matter - the bacteria will already be resistant to it, and the new MIC will be higher.

Now the other thing to consider is that once an antibiotic enters the body, it is gradually broken down. This means that if a patient is given a dose of exactly the MIC, the concentration will quickly drop to the point where it won't be helpful, and thus won't be cured. The idea to counter this is to give a higher dose than is needed, and to take a new dose around when the concentration would drop to the MIC. That way, there is always a lethal concentration of antibiotics in the patient's body until all of the disease-causing bacteria are dead (or at least, enough dead that the immune system can take care of any stragglers).

The last consideration is that most antibiotics can have a toxic effect on humans at a high enough concentration. So we want to plan a dose that is high enough to always be above the MIC, but low enough that it doesn't actually harm the patient.

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BeneficialWarrant t1_jdrx8pt wrote

Reply to Is there a difference in effect when dosing antibiotics? by Strong_Camel_4468

There are many factors that go into choosing dosing intervals. Some drugs are described as "bactericidal" vs "bacteriostatic". Some bactericidal drugs have a "concentration-dependent" response rather than a "time-dependent" response, which means that they are more effective when given a large dose for a short duration rather than a smaller dose for a longer time. Some drugs also continue to inhibit bacterial growth even when it is no longer detectable in blood (postantibiotic effect)

There is a class of drugs called aminoglycosides (tobramycin, streptomycin, amikacin) that are often taken at long intervals. They have an initial concentration-dependent bactericidal effect when first taken, then continue to provide bacteriostatic effect for many hours. Infrequent dosing also helps reduce toxic side-effects (hearing damage).

Also drug makers try to make drugs which can be taken as infrequently as possible while still being effective in order to improve patient compliance. They want you to take the drug as directed and not create a resistant super-bug. If the drug is effective when only taken once or twice per day, particularly in oral medication for an outpatient, this is preferable to a drug that is taken multiple times per day. Its just human nature to forget a dose here or there and to be less motivated to remember doses on time once you start feeling better.

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Xiphoideush t1_jdrwbl8 wrote

Reply to Is there a difference in effect when dosing antibiotics? by Strong_Camel_4468

Most antibiotics are bacteriostatic, meaning they inhibit the replication of bacteria. To achieve this effect you have to maintain a sufficient concentration of antibiotics over time. Taking double the recommended dosage would put you way over that concentration, but it wouldn’t achieve a greater inhibition on bacterial replication. As your body breaks down the substance, dosing with half the recommended frequency would put you below the minimal inhibitory concentration before your next dose, allowing some regrowth of the bacterial colony every day.

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mcnessa32 t1_jdruaz1 wrote

Reply to comment by wazoheat in Around 550 million years ago the earth's magnetic field almost collapsed, but then strengthened a few million years later. Scientists say this may have been due to the formation of the inner core. But why exactly would that cause the magnetic field to get stronger? by somethingX

What impact would a near collapse of the magnetic field have on the planet? Does 550M years ago coincide with any known extinction periods?

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Coomb t1_jdrsw29 wrote

Reply to comment by Fenrisvitnir in The two retinas are tied/linked together in the brain. Are they tied 1:1, so that each retinal point corresponds to the same retinal point in the other eye? I.e., each retinal point from one eye shares the same binocular neuron with its counterpoint in the other eye? by ch1214ch

Did anyone say that the matrix operation of convolution, or the idea of smearing it across an image, was invented via inspiration from experimental explication of image processing as performed by animals? I don't think they did, and I would be surprised if that were true. But those references do show that the "neocognitron" was explicitly inspired by actual physical neural networks used by animals for image processing, because among other things they include the original neocognitron paper, which is very clear about its inspiration. This is relevant because review papers of convolutional neural networks like this one from University College London almost universally identify the neocognitron as the direct precursor to modern convolutional neural networks.

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Constant_Breadfruit t1_jdrrnkf wrote

Reply to comment by [deleted] in Can elephants canter or gallop? by [deleted]

This is not very satisfying but it does not have a name. Elephants are unique in their size. I watched the video closely a number of times. For part of the charge, the footfall pattern indeed matches a gallop. But you’re only halfway there because all 4 feet need to be off the ground at some point and that can’t happen. This gait as far as I can tell does not have a name in English.

noun: gallop the fastest pace of a horse or other quadruped, with all the feet off the ground together in each stride.

https://www.scientificamerican.com/article/elephant-locomotion/

https://www.animatornotebook.com/learn/quadrupeds-gaits

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