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Comment Re:Still a bad value (Score 2) 130

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.

Comment Re:Still a bad value (Score 5, Interesting) 130

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.

Comment Re:Dobsonian (Score 3) 187

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.

Comment Re:And when Eris' atmosphere is measured... (Score 4, Informative) 138

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.

Submission One in five stars has an Earth-sized planet in its habitable zone->

cunniff writes: Remarkable statistics from the Keck Observatory on Mauna Kea, Hawaii — 22% (+/- 8%) of stars have an Earth-sized planet in its habitable zone. From the press release, UC Berkley graduate student Erik Petigura says, "What this means is, when you look up at the thousands of stars in the night sky, the nearest sun-like star with an Earth-size planet in its habitable zone is probably only 12 light years away and can be seen with the naked eye. That is amazing,"

This, of course, raises the Fermi paradox again — if alien life is common, why haven't we seen it yet? This study will be used to spark further investigation, including proposals for space telescopes which might be able to image nearby Earth-sized planets.

Link to Original Source

Comment Oldest *hominid* tumor, maybe (Score 5, Informative) 46

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.

Comment The real issue (Score 5, Insightful) 311

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...

Going the speed of light is bad for your age.