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Physics, Astronomy & Cosmology / Re: Is this the first direct observation of 2 neutron stars colliding?

« on: 16/10/2017 18:55:20 »

My understanding is that the light slows down a little bit as it travels (space is not a perfect vacuum, so the light interacts with the ions, atoms and dust in the cosmos, leading to a decrease in the velocity. I guess the effect is more subtle  for gravity(or nonexistant? is there such thing as permeability/permitivity for gravity?)

Given that it was about 150 Mly away, and the delay was only 20 seconds, that means the space in between has an index of refraction of about 1.0000000000000000000000001 (that's *very* close to 1)

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General Science / Re: How do atomic models correlate with electron microscope observations?

« on: 11/10/2017 14:50:41 »

Protons and neutrons make up the nucleus. The "shell" is the electrons.

See the attached image which my colleague captured using TEM (transmission electron microscopy). This is about as high resolution as can be achieved using these types of techniques. As far as I understand the physics involved, electron microscopy cannot have the precision required to see the subatomic structure for essentially the same reasons that atoms are the size they are (both are determined by the quantum mechanical properties of electrons). However, the resolution is clear enough to see which parts of my sample are crystalline (where all the atoms are in neat rows) and where it is amorphous (random, but still with more order than the empty field on the right, which just looks kinda like static on an old tv). Note you can also see diffraction patterns appearing as halos around the edge of the particle being looked at.
14 lattice burned.jpg (228.33 kB . 668x692 - viewed 221 times)

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Physics, Astronomy & Cosmology / Re: What causes light reflection?

« on: 29/09/2017 21:09:03 »

A detail that was new to me is that the photons are not just bouncing off the reflector.  They are being absorbed and then re-emitted.  The articles I've found so far haven't described why (in the case of a sliver mirror, for example) the silver atoms are able to re-emit a photon that is exactly the same frequency as the absorbed photon.  I know energy must be conserved, but the electrons in a high-energy, excited atom can only fall back down to specific shells, meaning the energy in the emitted photon corresponds to a specific frequency.

Atoms within a metallic object cannot be considered individually. One must look at the electronic structure of the whole materials (metals have delocalized orbitals throughout the entire material). Instead of talking about "energy levels" we must talk about "bands." (and for metals specifically, there is no "band gap" between occupied and unoccupied levels, so they can interact with light over a very broad (and effectively continuous) range. https://en.wikipedia.org/wiki/Electronic_band_structure

I can't help with an atomic-scale reason for the angles of reflection (specular over diffuse), but my suspicion is that it has something to do with conservation of momentum.

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New Theories / Re: Are all atoms transparent?

« on: 29/09/2017 20:00:24 »

If air doesn't interact with light then how does the air look funny above a hot fire or over the road ahead on a hot day? (see attached pix if you don't know what I'm talking about)
wavey fire.jpg (8.52 kB . 275x183 - viewed 358 times)
wavey road.jpg (6.26 kB . 320x157 - viewed 358 times)

And in the picture, you shared of the Earth from space: I clearly see a fuzzy blue layer at the edge of the horizon (as pointed out by others, this IS the atmosphere), and also the "sky" above is black, even though it is clearly "daytime" whereas "daytime" without clouds means blue sky on Earth...

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That CAN'T be true! / Re: Is Hurricane Harvey evidence of geoengineering? (NO, IT ISN'T!)

« on: 12/09/2017 21:17:16 »

I have decided to lock this thread. Nothing good can come of it at this point.

The consensus (with the notable exception of the original poster) is that:
• There is no evidence of "tampering" with Harvey
and
• The scientific principles involved with storm engineering are well beyond our ken, and even if we knew what we were doing, the sheer size and energy involved would dwarf our technological capabilities

None of the conspiracy theories, conjectures, or claims relating to storm engineering have any basis in scientifically established (establishable) fact, and largely depends on misrepresentation of selected and unrelated studies

Since this discussion stalled out long ago but still appears to be taking oxygen from the rest of the forum, I am locking the thread.

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Physics, Astronomy & Cosmology / Re: Does the velocity of electrically attracted particles depend upon mass?

« on: 12/09/2017 02:17:57 »

Does the hypothetical field change the mass into kinetic energy that the remaining particle?

Energy and mass can be interchanged by Einstein's famous formula, but you cannot change one without changing the other (in a closed system).

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Physics, Astronomy & Cosmology / Re: Does the velocity of electrically attracted particles depend upon mass?

« on: 10/09/2017 21:37:27 »

The electron will move much more than the proton.

Why?

Because the forces acting on the particles are equal in magnitude, and the proton has 1836 times the mass of the electron. Since F=ma, the electron must be accelerating 1836 times as much as the proton.

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Plant Sciences, Zoology & Evolution / Re: How do poison arrow frogs obtain their toxins?

« on: 07/09/2017 17:50:59 »

Actually, I will take this opportunity to point out that most of the highly bioactive molecules we have discovered are, in fact, produced by bacteria, algae, and funguses (plants have produced some impressive alkaloids, like strychnine and aconitine, and some animals can make some impressive peptidic toxins, like snake and snail venoms, but they just don't hold a candle to the agents developed by single-celled organisms that have been involved in constant chemical warfare with each other for billions of years). The brevetoxins (red tide), tetrodotoxin (adopted by fugu and blue ringed octopus, among species, see below) and aflatoxins (aspergillus molds) are truly awesome in the biblical sense of the word.

Most of the natural products isolated from marine organisms are believed to be derived from bacteria or algae. These little "bugs" either have a symbiotic relationship with a host animal that benefits from their toxins, or they are eaten by the animal, which then accumulates their toxins.

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Plant Sciences, Zoology & Evolution / Re: How do poison arrow frogs obtain their toxins?

« on: 07/09/2017 16:31:45 »

I remember an article from a few years back that claimed to show that poison dart frogs obtain their toxins from ants (which themselves might rely on bacteria to produce them).

I was able to relocate the article ( https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1187980/ ) from a more accessible news release: https://news.mongabay.com/2005/08/study-discovers-why-poison-dart-frogs-are-toxic/#study

(This article is a dozen years old now, and I don't know if this is still the prevailing theory)

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Physics, Astronomy & Cosmology / Re: Can we use the moon as a launch platform for spacecraft?

« on: 05/09/2017 17:25:28 »

Just to add my two cents:

Where are we sending these spacecraft? And how would launching from the moon help?

If, in the not-so-distant future there is an active space-travel/transport industry, presumably Earth would be one node (we will want to send people and robots and perhaps raw materials from Earth, and we will want to bring precious metals, samples, etc. back to Earth.)

The moon doesn't seem like that much of a destination yet, but perhaps there could be a base there and people would go back and forth. For traveling anywhere except perhaps within the inner solar system, there really isn't much benefit to leaving from the moon rather than from the earth. The gravity well is still quite substantial to get off the surface of the moon, and then you still have to climb the rest of the way out of Earth's well. And if you are going to the outer solar system, climbing against the sun will be the primary challenge, and the moon doesn't help there at all.

Some have proposed building a base on one of the Martian moons, both of which are significantly smaller than our moon, and starting from a Martian orbit does make it significantly easier to send ships to the asteroid belt, and Jupiter (from which a slingshot maneuver can get you anywhere within the solar system if you time it right.)

Others say we should build in the asteroid belt. Maybe make a base on Ceres, which we know has water and organic matter and less than 20% the surface gravity of our moon, and is very close to some asteroids with high precious metal content.

Others argue that we should make bases closer to the sun to take advantage of the solar energy. Sending ships out into the cold, dark reaches of the outer solar system is probably not the best way to start. A large space station in orbit around Venus could be pretty awesome! Some even have suggested floating cities in the atmosphere of Venus (supposedly there is a certain altitude where the temperatures and pressures are not terribly far from liveable, but you would still need to have a perfectly contained system to keep the toxic/corrosive atmosphere out)...

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Physiology & Medicine / Re: Can nicotine addiction influence our psychological behaviour?

« on: 30/08/2017 14:45:22 »

Withdrawal from nicotine will negatively affect a lot of your bodily functions (GI tract, musculoskeletal system, attention span, thought processes, etc.). The good news is it's temporary. Your body will eventually readjust to a nicotine-free equilibrium, but it will take some time. Some people switch to nicotine gum or patch with very low doses of nicotine to wean themselves off slowly, but that only seems to draw out the process, and many have better luck just quitting cold turkey. I don't know what will work best for you, but best of luck--it's the good fight!

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General Science / Re: Can science create more eco-friendly farming practices?

« on: 25/08/2017 18:47:22 »

Now to address the OP:

Alan gives a pretty good summary. I will distill some of this down, and add a few points of my own in a short list of action steps that can be taken to reduce the impact of our agriculture on the environment:

Ranked by impact:
1) Reduce the human population to feasible levels. We can argue about what is feasible, but 7 billion (going on 10) is clearly not. Personally, I think that 2 billion is a reasonable upper limit. At any rate, the smaller the population is, the less we need to worry about the following actions.
2) Reduce food waste. Currently less than half of the food produced ever makes it onto a plate, let alone eaten.
3) Reduce or eliminate meat consumption. Yeah, I know meat is good, and we are omnivores. But, as pointed out in the OP, it is very wasteful and environmentally harmful. I have limited myself to three meat-containing meals per week for the last year or so, and am trying to get to only one per week.
4) Improve farming efficiency. We need to decrease the use of water, fertilizers, and pesticides to produce a given amount of food. I think the most promising things that science can offer here is GMO foods. While there are some legitimate concerns about cross-pollination, and the economics of GMO seed production, most arguments against GMO foods are rooted in ignorant fear. (I believe I have ranted about this elsewhere on the forum, so I will leave it at that for now).

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Physiology & Medicine / Re: How can we design a synthetic naloxone derivative?

« on: 22/08/2017 15:23:43 »

Naloxone availability is only limited by policy. It is neither terribly expensive to manufacture nor particularly hard to transport/store/distribute. In the US (I can only speak about the US, because that's where I am), it is a scheduled drug and requires a prescription. However, there is a push to remove this barrier, and allow it to be sold over the counter or included in standard first aid kits (opiate overdoses now supposedly kill more Americans per year than gun violence and car crashes combined!)

would like your input on designing a synthetic and functional opioid antagonist for medical purposes. The design of this medication could be of tremendous help for people struggling with opioid overdose. Can we use the power of the internet to gather collective knowledge on the synthesis of novel opioid receptor antagonists?

This is probably not a very effective mode of drug discovery. Even assuming you are able to bring together hundreds of the most knowledgeable and creative minds in the world, you will never successfully discover a new drug by thought experiment alone.

Actual experimentation is required to find structures that bind to the desired targets, and then iterative experimentation to improve binding, bioavailability, and clearance, as well as limiting toxicity and side effects. You also have to figure out how to make and distribute these compounds in an economically feasible way on scale. Pharmaceutical companies typically spend more than $1,000,000,000 on research for each new drug that comes to market, and the whole process takes at least a decade from conception to prescription.

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Physics, Astronomy & Cosmology / Re: Which one would move faster, an electron or a snail?

« on: 22/08/2017 15:10:22 »

Electrons don't have a set speed, though most have enough energy to move significantly faster than a snail. Classically, kinetic energy and velocity of an electron are related by the equation:
E_k = ½ × m_e x v²
where E_k is kinetic energy in J, m_e is the mass of the electron (9.1×10^–31 kg), and v is the velocity of the electron in m/s.

In many cases electrons are traveling fast enough that relativistic equations are required (electrons in a TEM can move at about 70% the speed of light.) If you are interested in these more complex equations, see more here: http://advanced-microscopy.utah.edu/education/electron-micro/

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Physics, Astronomy & Cosmology / Re: Why is the structure of an atom depicted as spherical?

« on: 18/08/2017 16:44:46 »

A single atom is best considered as spherical. The positively charged nucleus is at the very center, and the negatively charged electrons are distributed around it. The electrons are attracted to the nucleus and repel each other. Because the nucleus is so incomprehensibly small, even compared to the size of an atom, it can be thought of as a single point (from the perspective of an electron). In the absence of any external influence (like an electric or magnetic field, or other nearby atoms) a sphere is the only reasonable shape for such a thing to have, because the only interactions are within the atom (between the point-like nucleus and the electrons), none of which have any way to define a special direction (atoms are isotropic, and spheres are isotropic).

Even orbitals, as mentioned above by Kryptid, are actually spherical in an isolated atom. For the purposes of intuition and making the math easier, we can break the orbitals up into linear combinations of sub-orbitals. Depending on which linear combinations are used, each suborbital can have a shape that is different from spherical, but sum of all of the sub-orbitals will form a spherically symmetric orbital in a lone atom.

Once we go to an atom that is interacting with anything else, the assumptions of sphericality all go out the window. For instance, if we place an atom in a strong electric field, the atom will distort into an ellipsoid (elongating along the axis parallel to the electric field lines).

Then, once we consider molecules, which have many nuclei (at least two), molecular orbitals become the important construct (sometimes one can think of this in terms of hybrid atomic orbitals), and these come in all types of shapes (none of which are spherical).