Planets are common. Planets within the habitable zone look like they are common. So, is this evidence of the Great Filter - https://en.wikipedia.org/wiki/... ?
That's not because of shelf life. That's because of overcharge and/or over-discharge - laptop vendors tend to create charge/discharge profiles that abuse the cells in the interest of quoting more hours of operation per charge. If you were to detach your laptop's battery from all electronics (including a battery monitor / BMS) you would find that it retains its charge for months or even years.
First, lead-acid has a shelf life even if you do not discharge the battery - the lead plates sulfate over time, reducing capacity. It is only partially reversible by occasional special charge/discharge cycles. This shelf life is something like 3-5 years, depending on how much capacity you are willing to lose.
Second, lead-acid self-discharges. This means, unless you use the battery very close in time to when you charge it, you've wasted some of the energy you put into it. Trickle-charging only makes this worse, since you will always be dropping energy into the battery without getting most of it out.
Third, lead-acid discharge voltages are strongly impacted by the current at which you discharge them - look up the Peukert exponent for the golf cart batteries you were quoting - it will be over 1.2, and probably higher, meaning that high current discharge will drain the battery much faster than expected.
Finally, even deep cycle lead-acid batteries are slowly degraded even by the 50% discharge you quote. It only takes a few hundred cycles for capacity to be diminished by double-digit percentages. This is caused by plate erosion.
Existing lithium cells don't have a known shelf-life (they probably have one, but we don't know what it is) - it could be 10 years or more. They have expected 80% discharge cycle counts of *thousands* rather than hundreds. And their Peukert exponent is very close to 1.00 since they don't have the same variable internal resistance characteristics of lead-acid.
I have first-hand experience of this - I have used all three of deep-cycle flooded, deep-cycle sealed (AGM), and now Lithium Iron Phosphate (LiFePO4) cells in my home-built electric vehicle conversions. My lead-acid shelf lives were right along with that 3-5 year expectations. The LiFePO4 cells are going on 2 years now with no measurable decrease in capacity.
To make your own Dobsonian, just add a diagonal and stalk, a cardboard tube, plywood, a bit of Ebony Star formica, and some teflon pads and miscellaneous hardware.
This advice is almost exactly the opposite of "good". You might be interested to learn that James Dobson, of Dobsonian fame, specifically designed the telescope to be simple to construct and use. The OP talked about the moon and Saturn. Both of those objects are very easy to see with the naked eye, and therefore very easy to point an alt-azimuth telescope at. An equatorial mount or motor drive is actually harder for a beginner to use than just a simple push-to-go-to alt-az mount. And any motorized drive you could get for anywhere near $100 is just junk.
All that said, you probably won't find a new Dobsonian scope for $100. There are some inexpensive alt-az refractors for about $120 - the Orion StarBlast 70mm for example. It has a finderscope, an erect-image diagonal, and a standard 1.25"-diameter focuser and two eyepieces. Might be worth a peek.
Alternatively, if you are interested in really learning a lot about telescopes, you could build one, starting with grinding your own mirror. You might get that done for about $100 for a 4.25" reflector.
If I were personally going to use one of Tesla's patents in my business, I'd want a signed zero-cost GPL-like license agreement with Tesla. For example, Musk's good will is nice, but what if someone else were to acquire Tesla's IP?
Eris is just 2326 kilometers across—possibly smaller than Pluto, whose diameter is somewhere between 2300 and 2400 kilometers. The uncertainty arises because Pluto, unlike Eris, has air that complicates the interpretation of observational data.
The university is welcoming four renowned curators from Carnegie Museum into its classrooms to teach seminars and use the museum collection, which is considered one of the world's premiere displays of natural history artifacts, for demonstrations. Included in the collection is a 150-million-year-old fossilized dinosaur bone complete with a tumor.
I would not be surprised if there are even older amphibian tumor fossils out there somewhere.
It's not the *cost* of the iPhone. It's the *black market resale value* that drives theft.
It's uncomfortable allowing a third party to be able to permanently brick your phone or other device, but if that were a commonly-used option, the resale value would quickly drop down close to zero.
As always - back up your data, and don't store important personal information on your easily-stolen device...
Possibly the most exciting physics news of the year. Although the detection of the Higgs boson was big, it mostly confirmed what existing theory predicted. Interesting, important - but, to some physics, perhaps a bit boring.
If further measurements continue to verify this effect, there are some very interesting new physics to discover.
How many sticks of dynamite would it take at 15 times per second, to eventually push the stated goal of 200MW into the power grid?
1 stick of dynamite == 2.1MJ, if you can believe Wikipedia 15 sticks per second == 32MJ/S = 32MW 200MW/32MW = 6.3 sticks of dynamite exploded 15 times per second.
This assumes 100% efficiency to electricity, of course.
Spend a little time thinking about it, and you will realize that distilled water urban legend is silly. In your mouth, it is mixed with saliva and mucous and whatever else is stuck to your teeth, gums, and tongue. The instant it hits your stomach, it is mixed with stomach acids and whatever you ate recently. I.e. it is no longer pure distilled water. From there, the molecules wander through your body like any other water molecule. Distilling water does not give its component molecules magic properties.
For every action, there is an equal an opposite reaction. So, when your monster torque motor is spinning the input shaft, surely it is pushing against the counterspinning shafts with exactly that amount of power? In other words - won't the mechanism (electric motor, flywheel, etc.) that keeps the counterspinning shafts running at the desired speed ratios have to overcome this reaction? It's possible that the frictional and mass inertia of the system helps some, but how much?
I'm not an ME, but the explanation of what the required control motor power is relative to input motor power is very thin here. Be very interesting to see what the detailed input / output / control torque & power measurements end up being.
The bureaucrats really need to stop harrassing the customers with these ineffectual yet apparent methods, and start using the effective yet discrete but more expensive methods. Even then, nothing will ever be absolute, it's the nature of security.
It can only see half the sky due to being very close to the South Pole. Near-equatorial telescopes can see 80% or more of the sky over the course of the year. A polar telescope would be useful for statistical surveys, etc. but would miss, on average, 50% of observations unique to one point in the sky.
Slashdot Mirror
I know it's from TFA's headline, but GFA is "Generative Adversarial Networks", not what they said.
Planets are common. Planets within the habitable zone look like they are common. So, is this evidence of the Great Filter - https://en.wikipedia.org/wiki/... ?
That's not because of shelf life. That's because of overcharge and/or over-discharge - laptop vendors tend to create charge/discharge profiles that abuse the cells in the interest of quoting more hours of operation per charge. If you were to detach your laptop's battery from all electronics (including a battery monitor / BMS) you would find that it retains its charge for months or even years.
Lead is cheap but you get what you pay for.
First, lead-acid has a shelf life even if you do not discharge the battery - the lead plates sulfate over time, reducing capacity. It is only partially reversible by occasional special charge/discharge cycles. This shelf life is something like 3-5 years, depending on how much capacity you are willing to lose.
Second, lead-acid self-discharges. This means, unless you use the battery very close in time to when you charge it, you've wasted some of the energy you put into it. Trickle-charging only makes this worse, since you will always be dropping energy into the battery without getting most of it out.
Third, lead-acid discharge voltages are strongly impacted by the current at which you discharge them - look up the Peukert exponent for the golf cart batteries you were quoting - it will be over 1.2, and probably higher, meaning that high current discharge will drain the battery much faster than expected.
Finally, even deep cycle lead-acid batteries are slowly degraded even by the 50% discharge you quote. It only takes a few hundred cycles for capacity to be diminished by double-digit percentages. This is caused by plate erosion.
Existing lithium cells don't have a known shelf-life (they probably have one, but we don't know what it is) - it could be 10 years or more. They have expected 80% discharge cycle counts of *thousands* rather than hundreds. And their Peukert exponent is very close to 1.00 since they don't have the same variable internal resistance characteristics of lead-acid.
I have first-hand experience of this - I have used all three of deep-cycle flooded, deep-cycle sealed (AGM), and now Lithium Iron Phosphate (LiFePO4) cells in my home-built electric vehicle conversions. My lead-acid shelf lives were right along with that 3-5 year expectations. The LiFePO4 cells are going on 2 years now with no measurable decrease in capacity.
As penance, here is a $65 mirror grinding kit, for a 4.25" mirror: http://firsthanddiscovery.com/...
To make your own Dobsonian, just add a diagonal and stalk, a cardboard tube, plywood, a bit of Ebony Star formica, and some teflon pads and miscellaneous hardware.
Derp. Yes.
This advice is almost exactly the opposite of "good". You might be interested to learn that James Dobson, of Dobsonian fame, specifically designed the telescope to be simple to construct and use. The OP talked about the moon and Saturn. Both of those objects are very easy to see with the naked eye, and therefore very easy to point an alt-azimuth telescope at. An equatorial mount or motor drive is actually harder for a beginner to use than just a simple push-to-go-to alt-az mount. And any motorized drive you could get for anywhere near $100 is just junk.
All that said, you probably won't find a new Dobsonian scope for $100. There are some inexpensive alt-az refractors for about $120 - the Orion StarBlast 70mm for example. It has a finderscope, an erect-image diagonal, and a standard 1.25"-diameter focuser and two eyepieces. Might be worth a peek.
Alternatively, if you are interested in really learning a lot about telescopes, you could build one, starting with grinding your own mirror. You might get that done for about $100 for a 4.25" reflector.
If I were personally going to use one of Tesla's patents in my business, I'd want a signed zero-cost GPL-like license agreement with Tesla. For example, Musk's good will is nice, but what if someone else were to acquire Tesla's IP?
From TFA:
Eris is just 2326 kilometers across—possibly smaller than Pluto, whose diameter is somewhere between 2300 and 2400 kilometers. The uncertainty arises because Pluto, unlike Eris, has air that complicates the interpretation of observational data.
...then what we have now are clearly leftovers.
Paleontologists have found 150-million-year-old dino tumors, see http://www.livescience.com/4013-dinosaur-tumor-studied-human-cancer-clues.html
The university is welcoming four renowned curators from Carnegie Museum into its classrooms to teach seminars and use the museum collection, which is considered one of the world's premiere displays of natural history artifacts, for demonstrations. Included in the collection is a 150-million-year-old fossilized dinosaur bone complete with a tumor.
I would not be surprised if there are even older amphibian tumor fossils out there somewhere.
Now get off my lawn
It's not the *cost* of the iPhone. It's the *black market resale value* that drives theft.
It's uncomfortable allowing a third party to be able to permanently brick your phone or other device, but if that were a commonly-used option, the resale value would quickly drop down close to zero.
As always - back up your data, and don't store important personal information on your easily-stolen device...
Well, it could be sedimentary rock layers. But volcanos can also cause layering - consult the oracle about "welded tuff" (example image from Idaho)
It's here. Let's deal with it.
but, to some physics, perhaps a bit boring.
Err, make that, "but, to some *physicists", perhaps a bit boring."
Possibly the most exciting physics news of the year. Although the detection of the Higgs boson was big, it mostly confirmed what existing theory predicted. Interesting, important - but, to some physics, perhaps a bit boring.
If further measurements continue to verify this effect, there are some very interesting new physics to discover.
How many sticks of dynamite would it take at 15 times per second, to eventually push the stated goal of 200MW into the power grid?
1 stick of dynamite == 2.1MJ, if you can believe Wikipedia
15 sticks per second == 32MJ/S = 32MW
200MW/32MW = 6.3 sticks of dynamite exploded 15 times per second.
This assumes 100% efficiency to electricity, of course.
Spend a little time thinking about it, and you will realize that distilled water urban legend is silly. In your mouth, it is mixed with saliva and mucous and whatever else is stuck to your teeth, gums, and tongue. The instant it hits your stomach, it is mixed with stomach acids and whatever you ate recently. I.e. it is no longer pure distilled water. From there, the molecules wander through your body like any other water molecule. Distilling water does not give its component molecules magic properties.
I noticed that too. My guess: they've found a currently active or very recently active volcano
Call Yukon Cornelius!
Close - I bet they get their funds by broadcasting the humanoids as they wear / hold / use various retail items. For a fee.
For every action, there is an equal an opposite reaction. So, when your monster torque motor is spinning the input shaft, surely it is pushing against the counterspinning shafts with exactly that amount of power? In other words - won't the mechanism (electric motor, flywheel, etc.) that keeps the counterspinning shafts running at the desired speed ratios have to overcome this reaction? It's possible that the frictional and mass inertia of the system helps some, but how much?
I'm not an ME, but the explanation of what the required control motor power is relative to input motor power is very thin here. Be very interesting to see what the detailed input / output / control torque & power measurements end up being.
The bureaucrats really need to stop harrassing the customers with these ineffectual yet apparent methods, and start using the effective yet discrete but more expensive methods. Even then, nothing will ever be absolute, it's the nature of security.
Fixed that for you.
It can only see half the sky due to being very close to the South Pole. Near-equatorial telescopes can see 80% or more of the sky over the course of the year. A polar telescope would be useful for statistical surveys, etc. but would miss, on average, 50% of observations unique to one point in the sky.