Danijel Gorupec

On 4/29/2020 at 4:48 PM, taeto said:

Since there apparently exists a good estimate of the mass of the asteroid that hit 65M years ago, is there also a good estimate of its velocity? After all the energy depends only linearly on mass, but quadratically on speed.

From Wikipedia (https://en.wikipedia.org/wiki/Chicxulub_impactor - first paragraph) the estimation is about 20km/s. But I am suspicious with the wikipedia  as their size estimation is very strange (11 to 81 km - wide range, but precise limits), while velocity and angle are given without ranges.

The 'Dark side' can be geographical location if that is how we decide to name the other side of the Moon. For sure it is not always dark, but language moves in mysterious ways (Greenland is not always green)... In fact, the 'Dark side' seems to be so widespread that we might start putting it into dictionaries.

...

I understand there are constantly dark spots on the bottom of some deep craters on the Moon. Did we confirm ice there? Is this in form of ice sheets or something that I wouldn't recognize as ice when looking at it?

On 1/19/2021 at 6:58 PM, Externet said:

Support?  it is a factual radio frequency.   A microwave oven cooks cells with 2.4GHz.  WiFi emits 2.4GHz at much lower power level;  but is there all the time. 

Hmm... I would say that with the soft radiation, the power level is important, not the 'total dose'' (that is, it is not like with the hard radiation where the damage is proportional to total dose)... Human body has means to regulate its temperature and can keep the temperature within safe limits despite of varying external influences. At least up to the power level where the regulation mechanism gets overwhelmed - only then the temperature can rise and the damage can occur.

[Note that some body parts, like eyeballs, might have less effective temperature regulation ability than some other body parts, like brain. Still, with such low power levels involved, I would not expect problems with temperature regulation.... even inside eyeballs.]

Hmm... In this case, I wonder if freedom of speech includes a right to create spamming bots. After all, spamming bots are just an information technology that I should be able to use to spread my speech. Or otherwise, where is that important line between spamming manually and making a script that does the same - I guess, they didn't explain this in their proposition?

...

(Btw, maybe we should also take a quick look at search engines and rights of their owners to moderate search results - like result ranking.  I just read Google did something particular in Australia.)

Did you measure already how much and where the energy is being lost in your car? If you are studying  you should have some picture how much energy is lost in batteries (charge/discharge cycle, self-discharging), how much is lost in inverter (if any), how much is lost in motor (resistance, eddy currents, hysteresis), how much is lost in transmission (if any), rolling resistance, air resistance, accessories power consumption... If you have this data then you can compare with other electric vehicles and check where you should be able to make an improvement.

If you didn't do such part-by-part measurements already, then I think you should.

My understanding: the way a privately controlled company moderates its social platform is a from of speech - that is, moderation is speaking. Companies are responsible about their moderation policies in the same way as speakers are responsible for their speech. Companies should have freedom in choosing their moderation policies under same rules as for the public speech itself.

(Btw, I am not that much impressed with actions big companies did last few days...  I hope you also agree that these came too late to be praised for either bravery, morals or foresight.)

Is there such thing as a paint that looks like a glossy metal (like stainless steel or nickel-plated steel). For example, a cheaper sink tap might have a plastic handle, but 'painted' to look like metal - is this a paint or what? Is it something that I can simply buy in a store (I have no experience... maybe it is just that easy)?

I need to make some ordinary carbon steel parts look shiny. I am thinking about nickel-electroplating but it seems a bit expensive where I am (and I am also afraid that there are different steel grades welded together in these parts and I am not sure if this can cause problems when electroplating). So, do I have a paint or some other option instead? (to be used indoors, occasionally touched by hands).

8 hours ago, Sensei said:

I would instantly dismiss idea of getting chair without armrest..

I actually prefer chairs without armrest - so I guess it is individual (It is because I tend to pull my legs up, sit on a leg and perform other unsightly poses - armrests limit this. Another unhappy thing about armrests is that I sometimes like to pull myself and the chair almost under the desk, and armrests prevent this. In any case, I am a person who constantly wiggles on his seat.)

Fiveworlds, I wouldn't dare to buy an expensive chair without testing it. It is one thing that you should not choose by just surfing the web (and/or asking other people - chairs are individual). But if something (corona?) prevents you from going out and testing chairs, I am  pretty sure that whatever you choose it will be much better for you than a kitchen chair. So, go for it in any case.

lol, anything discussed on this forum has a purpose... to be discussed on the forum.

Seriously, don't you think the word 'purpose' is has a funny purpose - it is a word that actually tells something about a subject, while disguised as if it tells something about an object.

I think that the strongest benefit of modern renewables (solar and wind) is that these technologies are compatible with private entrepreneurship. This drives efficiencies and lowers prices.

Likewise, the biggest weakness of nuclear (fission) is that this technology is inherently under heavy government control (among else, due to possible plutonium production). For most countries this almost guarantees sluggish development, inefficiencies and high prices.

I personally would accept to have underground nuclear power stations so that the surface remains uncluttered with wind towers and solar panels. At the moment it is not at all bad, but erecting 10 or 20 times more wind towers is a worrying thought to me.

1 hour ago, OldChemE said:

In a sense, Nuclear gave us a bridge to the days of efficient renewables.

Can you be more specific on the Switzerland example. Is there enough wind power? Is there enough infertile land for solar power? I ask because Switzerland is not a very large country, yet it uses about 35MWh per capita (if I found correct data). Makes me wondering if Switzerland at all has a non-nuclear option if it would want to achieve energy independence?

20 hours ago, John Cuthber said:

I think the Arecibo one was spherical too.
It' might be something to do with the lack of steering.
With a sphere it points in all directions- you just need to move the receiver.

But a paraboloid has a single axis that you have to line up with the target.

Yes, this is also my understanding. In fact, as I understand, the PingTang telescope can never use its whole dish to listen a single (point) source.

But I don't understand what is the advantage, if any, in comparison to a synchronized array of small movable-dish telescopes? The price?

2 hours ago, Area54 said:

If I have properly understood some of the reports I've seen then this is definitely a possibility and is actively hoped for.

Thanks.... Can you hint a possible mechanism? Just to get an idea. I understand a vaccine shot can protect from multiple strains of viruses, but I guess this is not the case with the corona vaccine.

I still didn't read anywhere if we have an estimation how long the vaccine protection might last(*). Do you know?

More generally, is it at all possible that a vaccine protection lasts longer than the protection obtained after getting over an actual illness?

Finally, the controversial question, do manufacturers have a technology to program vaccine protection time? You know, like when you buy an iPhone and then it slows down once it suits the manufacturer.

(* It does happen to me that sometimes I expect some information to have high visibility, but newspapers do not show much interest in it.)

I guess there is some hope that some hydrothermal vents organisms from Earth could find a nice spot also in Europa ocean. Sure, I would support doing this only if we prove, beyond reasonable doubt, that the chosen world is sterile. And I still very much hope that Europa is not sterile.

Another guess is that organisms that are left to evolve on another planet would soon turn inedible* - or better said, not directly edible, but with some advanced scientific cooking we should still be able to derive some nutrients and energy from them.

(* pigs probably can never turn inedible, no reason to panic. But other, less palatable animals, probably will incorporate some poisonous chemistry into their metabolism as an adaptation to foreign worlds)

I would much prefer a modern telescope than the wall between USA and Mexico. But i guess the US congress could still find valuable to debate about it.

23 minutes ago, iNow said:

Why not? Time is a savage mistress that deteriorates all things. Despite regular maintenance, the dish is quite old and in a very difficult location to service and tend. There's no need to assume malice or ill intent when nature herself is the most likely cause. 

I don't assume malice, but I would accept only few reasons for the wreckage:

- an earlier decision that maintenance expenses are too heavy and the telescope is to be left-on-its-own

- a beyond-design-basis event

If a maintenance program was in operation, then it was inadequate. Maintenance should maintain.

The reason I mention this is because the above photo can be used by anti-scientists for their agenda ("look how they spend your money"). If the telescope was intentionally abandoned, that must be clearly communicated to the public.

Why the antenna broke - funds withdrawal or incompetent/malicious management? It does not look like an accident to me.

45 minutes ago, MigL said:

Of the people involved in the study, who got infected with Coronavirus, 90-95% received the placebo.
But 5 -10 people who received the actual vaccine treatment were also infected.

After how long? I guess they have reason to believe that the protection is not only temporary?

24 minutes ago, Markus Hanke said:

Yes...but on these scales the effects of gravity are so small as to be negligible.

Hmm... I have no doubt gravity exists even at atomic scales, but the question was about 'classical gravity'. In my understanding, 'classical gravity' would be a 'smooth' (non-quantum) thing that behaves perfectly predictable. Sure, it could be that at the atomic scale the gravity is (still) pretty much classical, but do we know this?

2 hours ago, Bufofrog said:

Dinosaurs could certainly live in many areas of the earth today.

Supposing that those areas remain stable as it is now. But I am not sure this is the case... Some people think that we are going through a mass-extinction phase right now, caused by rapidly changing environment due to human activity.

In any case, it might be that at the moment the environment is changing too fast on the global scope that very large animals could thrive. My understanding is that large animals have difficulties in rapidly changing environments because they are generally slow to reproduce (and thus adapt by evolutionary change). Humans might be an exception because we have a technology that we can adapt instead of our own bodies.

On 10/22/2020 at 12:42 AM, MigL said:

The galaxy is, of course, rotating with a period of approx. 200 000 years...

I guess, you forgot to add three more zeros.

4 hours ago, Enthalpy said:

More fusion reactions exist, yes. But D-T is the only accessible to tokamaks presently. It's far less difficult than any other one because only one proton in D repels one proton in T. D-D reacts too but produces little heat as it releases the less stable ³He or T, and the reaction rate is 100 times less than D-T. Other fuels like Li or ³He are hugely more difficult. They work in hydrogen bombs, in some inertial confinement setups, but as a means of controlled net energy production they are out of reach.

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After ITER got >10 years late because of Covid-19, some sort of assembly was celebrated recently (2020, who cares about the month meanwhile).

As for the cost, present figures by the promoters fluctuate between 20 and 30G€. But the DOE, not significantly involved in this huge squandering, includes also the hardware developed by the participating countries and brought to ITER, to get >60G€ instead.

For an energy source as polluting as uranium fission and available half a century after wind turbines, ITER is an expensive scam.

 If it is a scam, that might tell us more about European Union than about nuclear fusion. From this single failure (of ITER) my first thought is that governments are incompetent, and only then that fusion might be a scam.... It will take several failures coming from different parties to convince me that fusion does not pay.

Very nice, Moontanman... as you once proposed and I accepted as more logical.

Thinking out loud... At the time, Einstein did not have to feel embarrassed because he didn't know how to reconcile his theory with QM. If one would be developing GR some 40 years later, he would be under some pressure to provide a theory that includes QM. Some guys/girls might abandon their work out of frustration... So maybe, we won't ever have GR as it is now, but we would directly have (eventually) a version given with QM in mind.

@studiot Thanks. I obtained the book (obviously a different edition than yours). Looks fine, will try to read some interesting chapters in my spare time.

I am considering electric and magnetic fields because I know them better. The gravitational field might be simpler from the potential energy point of view, but I wouldn't know how to handle its filed energy. Furthermore, the ultimate problem I am considering (what does it mean when we say that electron shifts its energy in magnetic field, like in the Zeeman effect) is related to electric and magnetic fields.

@swansont Great that you introduced the capacitor example - it is simple enough that I can make some calculations (see below). But first to answer your 'philosophical' question...

18 hours ago, swansont said:

If, as you say, the change in field energy is the same thing, then why does this matter? It would simply be a second way of doing the calculation.

Yes, these are two ways of doing calculations. But, imo, not equivalent... The 'field energy' is more precise. Specifically, it precisely defines how the energy is distributed in space (energy density distribution). The 'potential energy' obscures this information.

The energy distribution is important for the local energy conservation idea. Imo, if you cannot tell the energy distribution, then the idea of local energy conservation becomes moot. As I take the local energy conservation as a strong requirement, so I think that, at least in principle, we should be able to describe each form of energy by its energy density distribution... It is for this reason that I expect that each forms of potential energy is describable by field energy (or at least by some other way that does not obscure the energy distribution information).

As you know from my other thread, I found one example (spin magnetic moment in external magnetic field) where I cannot relate the potential energy change to the field energy change and this itches me.

Now the computations... they are striking... We consider a charged plate capacitor. During the experiment, the plates are moved from the starting distance d1 to the ending distance d2. We compute the potential energy change (first line of equations) and field energy change (second line of equations).

CASE 1 - constant charge. Everything is clear here and everything fits nicely. The PE change equals the field energy change.

CASE 2 - constant voltage. This is interesting. When we look at the system from the potential energy viewpoint, the total energy of the world does not fit! But when we look from the field energy viewpoint, everything fits nicely. Note that in the total energy of the world must include the energy in the idealistic battery that is used to ensure the constant voltage on the capacitor.

Note that in the constant-V case the field energy decreases as we are separating the plates. However the energy that is 'pumped' back into the battery is twice the work done... The potential energy viewpoint would give balanced energy only if you avoid looking into the energy change of the battery. Once you peek inside your battery,  your energy balance falls apart.

So, if I didn't do any major mistake in my reasoning, it seems that the field energy is more precise and more fundamental than the potential energy. If one really, really wants to give a precise answer to the question 'and where is the energy stored' he/she should give the answer from the field energy viewpoint and should avoid the potential energy viewpoint. What do you think?