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Physics, Astronomy & Cosmology / Re: Will refinement of measurement standards alter how we think of uncertainty?

« on: 21/11/2018 16:37:44 »

To expand a bit (now that my internet connection is a bit faster!)

If we measure something, we know that there are some uncertainties associated with the procedure itself, which will produce a different number if we repeat the experiment: these are random uncertainties. If we can separate out the random uncertainties to a set of independent uncertainties a, b, c in different parts of the measurement, we add them as though they are random noise, so the amplitude of the overall random or experimental uncertainty is √(a² + b² +c²...)

We also know that there are small discrepancies between the national standards or laboratory sub-standards of length, time, voltage, or whatever against which you and I make our individual measurements These contribute to the systematic uncertainty √x²+ y²+z²....) of our measurements.

Defining the units of measurement in terms of fundamental constants means that the systematic uncertainty of anyone's measurement is now reduced to the random uncertainty with which we have determined those constants, and the universal value is now fixed by definition and consensus rather than by reference to a lump of metal or whatever.

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Just Chat! / Re: The DOGMA of science........

« on: 19/11/2018 00:00:14 »

It hardly matter , this forum  lies  just  like every other forum.   I am deleting my account never to return  to  science, they can kiss my ......I would not help them even if the earth was at stake.

Here much evidence of great sanity I see. Much learning done you have. No clothes the emperor has, and clothes-having-not being told, he likes not.

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General Science / Re: What do nerves do in a human?

« on: 25/08/2018 19:25:10 »

Hey. Do not quite understand what exactly you asked. Information about this a lot on the Internet.
The human nervous system is, perhaps, the most complex system of any organism. Only the human brain contains more than 100 billion nerve cells, and each nerve cell can have up to 10,000 connections to other nerve cells.
This means that the nerve impulse is an electrochemical signal or from the brain can travel along 1015 possible routes. The nervous system has two main departments: the central nervous system (CNS) and the peripheral nervous system (PNS).
The peripheral nervous system includes nerves that carry sensory messages into the central nervous system and nerves that send information from the central nervous system to the muscles and glands.
There are three types of nerves in the human body, called sensory nerves, motor nerves and mixed nerves.
Sensory nerves. These are the nerves that send messages to the brain or spinal cord from the senses. They are enclosed in the form of bundles, like structures or nerve fibers in the peripheral nervous system. They are information from PNS to CNS.
Motor nerves - motor nerves - are those nerves that carry messages in the form of a response from the brain or spinal cord to other parts of the body, such as muscles and glands. They are responsible for the transmission of information from the CNS to the PNC
Mixed nerves are nerves that perform both sensory nerve action and motor nerve. Spinal nerves are functionally mixed and carry both sensory and motor fibers.
The neuron itself has a primary structure with an axon or soma body, a bunch of squiggles on a soma, called dendrites, and a long unfortunate structure called an axon, with synaptic pens on the other side of the axon. Nerve fiber is a set of axons that extends from the body of the cell to the point where it innervates. The nerve fiber also contains other cells, such as Schwann cells, which create a layer around the nerve, called the myelin sheath.
Based on what the nerves do and what they transport, they can be classified.
These can be nerves that arise from the brain itself, called the cranial nerves or those that arise from a spinal column called the spinal nerves.
Thanks for reading.

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Technology / Re: How do batteries work?

« on: 14/07/2018 23:14:42 »

The most important thing to grasp is the electrochemical series: https://en.wikipedia.org/wiki/Standard_electrode_potential_(data_page)

Batteries (really galvanic cells) and fuel cells are essentially the same thing. Each employs two "half reactions," one at each electrode: one that releases electrons, and one that receives them. The series can be used to determine which pairs of reactions will provide energetically favorable reactions, and what the maximum theoretical energy can be.

For instance, a galvanic cell can employ these two reactions:
Cu²⁺ + 2e^– --> Cu (+0.337 V)
and
Mg --> Mg²⁺ + 2e^– (+2.70 V)

(I have chosen these because they are both 2-electron reactions, which simplifies the considerations).

Together the total reaction is Mg + Cu²⁺ --> Mg²⁺ + Cu (3.037 V)

The maximum theoretical voltage this cell can produce is 3.037 V, but it is likely to be less due to internal resistance.

For current to flow, the circuit must be closed. Electrons must be allowed to flow from the Mg to the Cu²⁺ through wires (and electronic devices) and ions must be able to flow through the battery (either negative ions from Cu²⁺ to Mg, or positive ions going the other way.)

That's it! The rest is just details...

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Physics, Astronomy & Cosmology / Re: How does a geostationary orbit work?

« on: 08/02/2018 16:47:02 »

As long as the satellite has a small mass with respect to the Earth (as are any of the ones we have put up), then the non-rotating Earth centered frame is what one measures the sattelite's velocity with respect to.   In fact, in the formula V= sqrt(GM/R) for orbital velocity, R is the distance between the centers of the orbiting mass and the primary body.

This changes as the mass of the satellite increases. At some point(when this is depends on just how accurate of an answer you require), you have to start including the mass of the satellite into the calculation.  At this point you no longer use the Earth's center as the focus of the orbit, but rather the "barycenter",  which is the center of  mass of the two bodies combined.
You also consider both bodies as orbiting this point. (this is not to say that small satellites don't orbit a barycenter, but that is is so close to the center of the Earth as to make no practical difference.) 
An example is the Earth-Moon pair. the Moon is massive enough and far enough away that the Earth-Moon barycenter is some 4267 km from the Earth's center and 2111 km below it surface.  The Earth's center orbits around this point with the same period as the Moon does.   (With many astronomical resources, it is common to use the E-M barycenter as the reference upon which our orbit around the Sun is based rather than the Earth's center.)
The Sun-Jupiter barycenter is just above the Sun's surface.(The earliest detection of extra-solar planets were based on this. The planets detected this way were so massive that they caused a large enough shift in the position of its star as it orbited the barycenter that we were able to measure it. This is also how the first black hole candidate was discovered. )

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Technology / Re: Is the speed of a hard drive invariant?

« on: 18/03/2016 16:50:25 »

Speed is very specific to the particular drive. While the platters inside are rotating at a constant angular velocity, the modern hard drive tries to record data at a constant data density per unit length of head travel along the track, so the data rate varies as the head moves from inside of the disc, where the lowest block numbers are, to the higher numbered blocks that are at the edge. The data rate further is going to be varied by the encoding applied to the data so it can be recorded reliably, with forward error correction and spectrum spreading data added, along with the encryption if used on the drive, so the rate will be varying around a small value that is compensated for by the buffer built into the drive, typically something like 64k, 128k or 256k, depending on the drive type and desired application.

Then you get variations caused by the drive having to move the heads, and after moving it has to check it is on the correct track, by reading some sector data, then writing when the right sector is below the head, and then reading the next sector data before the write. Also complicating things id the drive remapping bad sectors, so that you can have the next logical block to be read or written not being actually in the next physical sector, but it has been relocated to a spare block ( interspersed through the drive surface during manufacture and hidden, like so many of the internal operations, from the outside, so the drive appears as a perfect drive while in reality it is very unreliable, relying heavily on error detection and correction to get the data back and show it to the outside) so there has to be a head movement and then a few cycles to get the correct track. Tracks are so close together that the only way to get the correct one is to go to the approximate position and then move slowly while reading to get the correct track and then wait for the right block to go under the head.

Reading can be worse, as the drive often has to use error correction to get the data back despite noise, or do multiple reads to reconstruct the data from best guesses from the reads. Too many and it ( secret sauce again) will decide to reallocate the data on the block to a spare track when idle, and mark the block internally as relocated and not usable. Thus a drive which appears as perfect can go from working to unreadable very fast as the spares are used up, and the drive no longer can swap out growing defects.

But to the original question, so long as the data is coming in at a lower rate than the worst write ability the drive can keep up and write it, if it comes in the drive will buffer to the point where the buffer is full, then simply discard some data ( mostly the last lot) and return an error code of it not being able to write the data. Reading the data rate will be set by the drive, requesting faster will simply result in the drive returning as not ready until the buffer is filled with data, and the read will stall.

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Radio Show & Podcast Feedback / Re: Why do dogs turn in circles before lying down?

« on: 04/03/2016 05:34:35 »

If you ever watched a dog sleeping in the cold, they will ball up in a circle to conserve body heat. Another possible answer is as they circle, they spiral downward into their resting circle, with little waste of motion. This action may also adjust the sleeping surface to allow the best insulation R-value.

I really just have to say here that that's simply the most adorable picture I think I've ever seen posted in a "Cells, Microbes & Viruses" science forum!

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New Theories / Re: Does sight work the way we think it works?

« on: 16/02/2016 16:07:46 »

Maybe stars are the same size, and distance gives the sense of a difference.

Incredible..................Now Mr. Box, you're showing us your abject ignorance. I'm wasting my time with you sir.

You asked me a question, I can only guess at a way to know, that is not ignorant that is me thinking of an answer to give you. 

Mr. Box, we have a star in our own solar system, it's referred to as the Sun. From this evidence alone, we know that stars come in different sizes. This is evidence that your answer was hasty and lacked credibility, thus the use of the term "ignorant". Ignorance does not mean stupid, ignorance is a word that defines lack of knowledge or the impetuous use of the knowledge one presently possesses.

Listen my friend, we all recognize that you're not stupid. Your mind is searching for answers and that is admirable. However, until you are willing to learn from others, your hunger for scientific knowledge will suffer greatly. We offer our answers and you continually seek to either ignore them or brush them off as insufficient and or flawed.

None of us are perfect but IMHO, the answers you'll receive here are worthy of consideration and you insult us with your cavalier attitude. I have just about had it with your obstinate positions Mr. Box. If you continue to gloss over and minimize the worthiness of my answers, I will eventually acquaint you with my ignore list.

If you continue to be disenchanted with the answers you receive from us, you might consider just not asking in the first place. Enough said......................

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New Theories / Re: All my ideas in one basket.

« on: 23/10/2015 17:05:23 »

The flaw with your theory is that you assume light has a color, when it doesn't.

Inside your eyes are these things called "cone cells" and "rod cells" which act as photoreceptors. Rod cells are in the peripheral vision of the eye and are 100 times more sensitive than cone cells, so sensitive that they can respond to a single photon; but they cannot distinguish color. Cone cells come in 3 kinds, S-cones, M-cones, and L-cones. S-cones respond to wavelengths between ~400-500nm. M-cones respond to wavelengths between ~400nm-675nm, and L-cones respond to wavelengths between ~400-700nm.



S-cones are what we perceive as blue light, M-cones are what we perceive as green light, and L-cones are what we perceive as red light. The peak responsiveness of these cones is at ~420nm, ~534nm, and ~564nm respectively.

Combining waves is done by adding the waves together. When 2 positive or 2 negative peaks hit each other, the absolute value of the peak increases. When a positive and a negative peak hit each other, they cancel out.

+

=

So as you can see, white is not the combination (read: addition) of red, green, and blue (all subjective) waves of light; it's the presence of all these waves of light. If you actually combined them, you'd just get a single wave that stimulates one type of your cone cells more than the others, which would probably just appear orange.

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Geology, Palaeontology & Archaeology / Re: When during human evolution did the first scientist appear?

« on: 22/10/2015 23:59:10 »

In 1983 I watched a gorilla at Chessington Zoo discover the principle of universal gravitation. He had two apples, one considerably larger than the other, one in each hand. He dropped them and noticed that they hit the ground at the same time.  He repeated the test, twice, then changed hands and did it again. Perfect null experimental technique: observe, repeat, change one parameter.

On the presumption that gorillas don't read books or have much of an oral tradition of scientific knowledge, this chap discovered, by the application of best scientific practice and in the space of five minutes, what took humans several million years and and a fair bit of bloodshed. Indeed there is no historical evidence that Galileo actually did his  "leaning tower" experiment, and if you read some of the bizarre submissions to this forum, it's quite clear that very few humans appreciate even the simplest principles of scientific investigation. Of course the gorilla didn't have to shake off centuries of superstition and the threat of excommunication, which gave him a huge advantage over Bruno et al.

Having seen birds, rats and chimpanzees deduce causal relationships from observation, and having marvelled at the gullibility of humans (including verbatim acceptance of garbage like Genesis) for many years, I fear that scientific thought in homo sapiens is something of a rarity compared with other species. Worse: when it appears, the herd generally tries to stamp it out, always preferring consensus and superstition to the demonstrable truth - unlike blue tits.

 

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General Science / Re: What would be the most likely cause of WW3?

« on: 12/08/2015 18:08:48 »

Individual terrorist acts or actual human suffering don't generally start world wars.

And WW I started how?

True, the official war started when nations (empires) declared war on each other. And yes, the world needs a certain amount of political tension for anything to turn into a large war, but given the right (wrong) circumstances, a single terrorist event can trigger a world war (for instance the assassination of a certain Archduke set everything into motion, and the actual war started one month later).

I think of it rather like a chemical reaction. There needs to be enough stored energy (tension/will to fight) for a war to happen. There also needs to be an initiation that supplies enough energy (anger?) to get the reaction (fighting) started, then as long as the fighting leads to an increased bloodlust and there is enough materiel to fight with, the war will continue. Eventually someone surrenders (or is defeated/destroyed), the war ends, and tensions begin to rise again...