Danijel Gorupec

I have questions about local conservation of energy. I am trying to better understand consequences that follow from it. How I understand it, the 'local conservation' means that not only energy is conserved, but is conserved in every local region. It cannot just at once decrease in one region, and increase in a region far away without anything happening in between. So, is the local conservation of energy a true law? It seems correct to me, but I cannot remember if I ever heard about it during my formal education (looong time ago)... [BTW, is it also valid regarding quantum mechanic? Specifically what I have in my mind is the wave function collapse - does the collapse has at all anything to do with energy distribution?] Next... My understanding is that one of direct consequences of the law of local conservation of energy is that we are then capable to define a value of 'energy flow' (through space) and a value of 'energy density' (in space). Am I correct? I have troubles understanding this 'energy density'. How much is this distribution of energy throughout space a physical thing. Should I expect that with a very sensitive equipment I should be able to measure a curvature of space that this energy density is producing... thus actually measuring energy density? (I understand that energy density should curve the space as well as mass do). Is energy density tied to one frame of reference or is it the same in all frames of reference? It seems to me that if you change the frame of reference, the energy density distribution changes too. Take for example a kinetic energy. Really, "where" is the kinetic energy? I mean, how is its density distributed in space? Where is gravitational potential energy? Where is electrostatic potential energy? I guess, If the energy density is for real, it should be possible to answer these questions. No? I guess energy density could be in fields. For example, kinetic energy could be distributed in gravitational field of a massive object (its mass increases with speed). For electrostatic potential energy I even know some formulas that say how energy is distributed in electric field... But what do you say?

Germany, I am afraid. As I am getting older, I am only hoping to see some good moves and good players (like 2014. James Rodriguez goal). I do not attach much to national team any more.

What about nuclear waste - do you guys believe that after 10M years it will still be possible to tell that a nuclear waste site is clearly of an artificial origin? My opinion is that it strongly depends on the circumstances. As far as I know, there is almost nothing that would surely last 10M years. However, even very fragile things can last that long under right circumstances (like a mosquito in amber). My opinion about OP is then: we know that happy circumstances happen and some artifacts do get preserved for amazingly long time. I therefore find it very unlikely that there was any industrial pre-human civilization - for sure we would find something. We didn't even find fossilized biological remains of an 'animal' that would look like a candidate (and it seems that to make an climate-changing industrial civilization you need quite a sizable population). Concluding industrial civilizations just from a rapid temperature rise is indeed a 'creepier conclusion'.

Sorry, this took a wrong turn... I was only making a joke... I found it amusing how you constructed your sentence saying that 'engineers never noticed devices that did not work'. I, on the other hand, noticed that almost all my first (and second) tries did not work. Still have some of them hidden in my garage. Going on-topic... ummm.... ummm.... nope.

Hey Bender.... But many do not work. We tend to hide them (in embarrassment). We only put forward those that do work

Inappropriate (at best) and short-sighted (even if well-intended) politicians, sure... But are you sure that you mean 'politicians' and not 'Venezuelan voters'? [ I ask because I think that sometimes posters are trying to be polite blaming politicians when they actually think people. ] High politics in Venezuela was, in my opinion, plainly wrong. But this is nothing new for me. It is the non-existence of any effective corrective action coming from the society that I find intriguing. In fact, I am afraid that the opposite is happening - the movements are such that the society undermines itself. The fluctuations on oil market, being an external factor, can be attributed as a trigger, but again no coping mechanism is being established, as far as I can see. How not? One would expect that societies adjust. [ Venezuelans are a large group of people, not just a few individuals, and for sure they are neither smarter nor stupider than any other nation in average. I am sure that an average citizen just does whatever he/she can to improve his/her own life and surrounding and also the life of those he/she cares about... Maybe we can say "they got what they asked for", but probably we cannot claim that we would make better choices. ]

Maybe it is a boring theme, but if someone wants to comment, I will be happy to read. What do you think is happening to Venezuelan society? Can this be called a degradation? Or is this only a fluctuation on path of progress? Or is this actually a progress when looked from a different perspective? Or is it just a logical consequence of some external pressure? To me, Venezuela is an interesting example to study as it has plenty of natural resources. My personal opinion is that this already can be called degradation. When I look at individuals in this society I understand that the each individual strives for the better. Yet, the society as a whole spirals downward. I find this fascinating... What is the 'invisible hand' that governs this process? Is there some sort if bad ideology that individuals pursue leading them in wrong direction? Or is it that most individuals just make logical and reasonable decisions at personal level and it still pushes the society in the wrong direction? Maybe you think that what happens in Venezuela is a progress (on society level). How come? I don't see it. Some societies in north Africa did turn toward democracy, and for those societies I could accept such argumentation (barely) despite the fact that currently they are in quite a chaos - but I just don't see it for Venezuela. Do you think that it is actually external pressure of some sort that causes present society movements in Venezuela (I guess, some Venezuelans would say this is true blaming greedy Americans for disruption of their society). But I myself don't see much of some external pressure (is there more behind scenes that I can imagine?). External pressure is always present, and most societies can cope with this. I have no connections with Venezuela. My interest is academic (but also personal because I find historical events like Fall of Rome quite upsetting).

In any case, I will have sensors at both ends so it is only the matter of weighting factors. Normally the regulation will be agonizingly slow, but there might be situations (after power interruption, for example) when a quick re-establishment of air flow will be needed - and this is when latency could be an issue. (There are 4 fans of 0.8MW always working in parallel as a single unit - it would be cumbersome to transport a single 3MW unit and it would lack redundancy. I however think that not even half of the installed power will ever be needed.)

Thanks Studiot... In my application there is a 3MW fan pushing air into tubes that feeds the air toward tunnel boring machines (TBM). I was puzzled because there was a claim that an air-speed sensor nearer to the fan will be able to sense air-flow changes much sooner (faster response regarding the fan speed) than if it is placed at the far end of the tube. I however tend to believe there will be no relevant difference (it is a slow regulation process anyway), and you seem to confirm this.

Probably I should know the answer, but I have doubts... There is a very long tube (pipe), say 2 km long and 3 meters in diameter. The tube is open at one end and there is a stationary air inside and outside the tube at normal pressure and temperature. At the other end of the tube there is a piston. At one moment the piston starts moving with some constant velocity (much lower than the speed of sound) something like 5m/s. My question is how long does it take that the air at the open end of the tube starts moving at speed comparable to the piston speed? My guess is that this would happen quickly (comparable to the time sound needs to travel the distance). Am I right? Will there be oscillations of air speed at the open tube end (if yes, on what will oscillation frequency depend)? More difficult question for me to guess... There is the same setting as above but the piston is not moving at constant velocity, but is pressing the air with some constant force (that is, it creates constant local pressure of the air). How will now look the air-speed curve (speed-vs-time) at the open end of the tube? Will it lag significantly to the air-speed curve near the piston? No need to make actual calculations - I am only trying to qualitatively understand what is happening. No need to consider high piston velocities either. Thanks.

Cat's speed This one happens when I was just a small kid (one of my earliest meaningful memories). My parents were building our home and most of the rooms in the house were still unfinished. I was playing in one almost empty room. There was a carpet rolled next to the wall. At one moment I saw a mouse running into the hole (a tunnel) formed between the carpet and the wall. The hole/tunnel had a small cross-section, just ideal for a mouse. I knew that the mouse can only exit the same way it entered inside, as the other end of the carpet was pressed to the other wall. I had an idea... I knew where my cat was sleeping so I quickly ran out and got my still sleeping cat. I placed it just half foot away from the opening, wondering what the cat will do in order to catch the mouse. I was quite disappointed. My cat was not excited at all - she just continued napping where I put her... And then, suddenly, it happened... For whatever reason the mouse decided to break through - it ran from the tunnel at the high speed several inches from the cat's nose. In exactly that instant (I am talking milliseconds) the cat wake up and hit the running mouse with her paw. As a result, the mouse flew off vertically some two feet (over 50cm) high in the air. Before the mouse fell to the ground the cat caught it with its teeth and ran through the door.... I will always remember this episode as it demonstrates reflexes ways above any human can produce. Cat's courage Many years later and involving different cat... It was summer and it was hot and my home is in a rural setting. All the doors were open wide. I was working in a living room on my computer when suddenly out of the corner of my eye I saw something small (but larger than a mouse) quickly ran through the living room and into the kitchen. My cat followed, at full speed, about one second later. (Somehow the cat knew exactly where to go although I am not sure she was able to see that the chased animal turned into the kitchen.) Then, coming from somewhere under the kitchen bench, I heard some fighting noise and a most incredible sound... like a high-pitched scream that freezes blood in your veins. The fight lasted only 4-5 seconds. My cat was victorious and it ran off the same way it entered, carrying something in her mouth... Later I was examining the body of the animal my cat killed. It was a weasel (of some sort, cannot tell the exact species). The weasel had teeth so sharp and scary that I would never go near it if it was not dead already. But my cat did not care about them. Dog's determination (or dog vs cat) This is a sad story... I don't consider dogs to be very determined animals. Dogs always look at their owners, guessing if owners are pleased or pissed with their behavior... One day I was in my backyard and my medium-sized dog was in my vicinity, completely relaxed. At once, I saw, my dog froze in place, intensively looking at one spot some ten-twelve meters away. All the muscles in dog's body were tense, and I am pretty sure that at that moment his owner (me) ceased to exist in his mind. I looked in the same direction and saw an unfamiliar cat sleeping in the grass. Very, very stupid cat... Before I could react in any way, in just a few jumps my dog was there. The cat woke up but it was too late (the cat tried to fly away, not to fight back). My dog grabbed it into his teeth. The cat was dead after less than two seconds of shaking... This part of dog's nature is something that most people don't see very often. It is also funny to me when I hear people wonder if a cat is a match to a dog in a fight - only to a playful dog maybe, certainly not to a determined one.

Great, great argumentation Sensei... +1... (I myself have a simple stance that we can have morality issues when switching off an AI only if that AI has a will to live.)

Thank you guys for your helpful comments. I solved the problem within 24h by buying a second-hand laptop similar to the one I had (Lenovo; similar specifications; similar age; the dead laptop was 'L' line, the current laptop is 'T' line) and migrating the hard drive into it. Finished successfully, after some manual driver installations. Windows is working good; all other important licenses also seem to work. Prior to this, I bought external HD enclosure and made backup (as StringJunky suggested) just in case something goes wrong. I also tried to boot my HD from a newer (more recently manufactured) laptop, but this did not finish good as this newer laptop model required something called UEFI boot. I see now that this second-hand laptop that I obtained has a very poor battery... nevertheless, my software is running and I am as happy as a pig

I hope my software licenses (rockwell automation, for example) are tied to hard drve. At least some od them. Replacing the motherboard may cause windows license problem then, if i underatood correctly? I still have to confirm that i can find mb replacement. I was trying to find the same laptop. No success for the moment.

Yes, this is my secondary option. My prmary is to boot from my old disk as i have some hard to replace software licenses on it.

Motherboard died on my laptop (lenovo think pad). If I buy new laptop and replace its hard drive with the one from my old laptop, is there a chance that it will boot? Is it worth a try? How to increase my chances?

Maybe... when it asks you not to do it (or shows other signs that it does not want to be switched off, like fighting for its 'life').

Not bad... I am reading this on a big screen - a design is a bit too wide for my taste. I am missing side content (list of new posts and user feeds) - is there any way to have them again? Where can I read user feeds? Also, I look a bit too pale on my avatar picture. I actually have a bit grayish complexion.

Just some ideas: - you might 'invent' a new type of battery that is extensively used in electric cars. The new battery has all the benefits (gasoline cars being quickly replaced, even banned for years) but also one drawback - sensitiveness to EMP (military should avoid its use in military vehicles). - you might consider that smaller batteries of that type (cell phones) are less sensitive to EMP. Or maybe, it is still possible to find and use classic-type batteries for replacement in cell phones (no such replacements for electric cars). - There could exist microwave (or whatever) energy links between Moon and Earth (sort of power lines) that actually directed and maybe amplified the effect of the Moon-originated EMP. - Flying a space shuttle becomes a heroic mission due to all the debris (satellite network being all crushed generating lots of space garbage).

I also don't analyse the show while I am watching it. It is only after the show that I enjoy thinking about 'how would I do it'. If ever the actual way is revealed to me, I sometimes get impressed by how much simpler it is than I was thinking. However, I strongly dislike if it is revealed that the actual show involves fake neutral audience.

This thread is a stub. You can help SFN by expanding it This is definitely not my field, but as far as I understand, various 'germs' have various means to extract benefits from our body. For most of them, human body is the natural environment where they develop. Intestine parasites and bacteria, I guess, take advantage of already half-processed food, moisture and temperature regulation provided by human body. Most intestine bacteria are 'not evil' and will not kill the host. Some other bacteria and parasites might tend to live inside human tissues (I don't know if any nasty bacteria tend to live inside a living cell?). I guess they are feeding on inter-cellular fluids - taking out energy (sugars?) and proteins. But I am purely guessing and hope that someone else will give more precise answer. Viruses "live" inside human cells. They are very dependent as they don't have complete reproduction means. For their reproduction viruses must use our cell infrastructure and energy. You might also read more about mitochondria. They live inside human cell and are very welcome there. Parasites often can be simpler organisms than non-parasites as they don't need to have all organs (systems) developed - instead they are using their host infrastructure. This is one biological (or evolutionary) benefit of being a parasite, I guess. In a way, living inside host is an easier way to live. Host body being a simpler (more steady) environment. You asked how come that germs might kill their host. This happens, sure... My view is that such 'germs' often cannot be called a perfect fit. Note that beings are not always perfect fit - just good enough fit. Many animals (locust, humans...), not only germs, can overcrowd their environment causing harm to themselves. I hope some other poster will expand on it.

BTW, we already had a somewhat similar thread: http://www.scienceforums.net/topic/83094-the-ethics-of-de-extinction/

So, why can this extracellular toxin removal process only happen during unconscious state? Accidental evolutionary path or deeper reasons?

[ Off-topic, but because you are the original poster: When I have an opportunity, I like to read mythology. I am mostly familiar with Croatian and Serbian mythology, much less so Russian (yesterday I read a synopsis of the "Tsarevitch Ivan, the firebird and the gray wolf" which is a pale example, but still contains motives of revenge). A hero is often on a revenge mission, although sometimes the act of revenge can be executed by nature or super-nature. The revenge is often bloody and can be worse than the original sin... There are many other motives, including forgiveness, in mythological stories, but somehow I noticed this revenge. This got me thinking if revenge is regarded in higher esteem in some cultures than in others... If one would need to estimate how high the revenge (or forgiveness) is regarded in a certain culture, I think that analyzing myths and legends of that culture would be a good way to go.]