×

Announcing: Slashdot Deals - Explore geek apps, games, gadgets and more. (what is this?)

Thank you!

We are sorry to see you leave - Beta is different and we value the time you took to try it out. Before you decide to go, please take a look at some value-adds for Beta and learn more about it. Thank you for reading Slashdot, and for making the site better!

Comments

top

Tesla About To Start Battery-Swap Pilot Program

Solandri Re:3 minutes is slow? (89 comments)

For comparison, 3 minutes is about how long it takes to fill a tank of gas (including stuff like removing the gas cap, inserting the hose, swiping your credit card, and putting the hose back on the hook). It's a good time to reference against.

3 hours ago
top

Tesla About To Start Battery-Swap Pilot Program

Solandri Re:even better (89 comments)

My take on this is if they put up wind or solar arrays, it would work better than trying to charge people's cars live off it.

Have you ever calculated how big a solar array it would take to charge a Tesla battery?

Solar constant on the ground at U.S. latitudes is about 750 Watts/m^2.
High-efficiency panels are about 22% efficient. Commercially, 18% is more realistic, but let's go with 22%.
Solar capacity factor for the desert Southwest U.S. is about 0.18. Multiply by 2 to account for night.
The big Tesla S battery has a 85 kWh.

750 Watts/m^2 * 22% efficiency = 165 W/m^2
times 0.36 capacity factor (average for the day) = 59.4 W/m^2 average generation during the 12 hours of daylight

Assume 90% charging efficiency. Real-life measurements put it at about 85%, but solar would charge it a lot slower so let's be generous and say 90%. At 90% charging efficiency, you need 94.4 kWh to fill the 85 kWh battery.

To charge the battery in 12 hours would thus take:
94,400 Wh / (12 hours * 59.4 W/m^2) = 132.5 m^2 of solar panels

A car parking space is about 9' x 18', or about 15 square meters. So you'd need roughly 9 car parking spaces worth of solar panels to charge one big Tesla S battery per day in the desert Southwest U.S.

Costs of implementing a PV Solar generation system are about $3.30/Watt in the U.S. on a utility-level scale. Technically this is commercial scale, but let's go with best case. 1 m^2 of these panels would be rated at 165 Watts peak capacity. At a price of $3.30/Watt, this would be $544.50/m^2 * 132.5 m^2 = $72,146.25 worth of PV to be able to charge 1 Tesla battery per day.

The amount of electricity used by a busy Tesla battery charging station would put it into the industrial category. The average U.S. electricity price for industrial customers was $0.07/kWh for 2014. At $0.07/kWh, the panels would essentially be charging the battery with $6.61 worth of electricity per day. It would take 10,913 days, or 29.9 years for the PV system to pay for themselves.

I won't go through the math in detail, but if you use more realistic figures of 18% efficient panels, 0.145 capacity factor (average for the U.S. overall), 85% charging efficiency, and the $4.50/Watt cost of commercial PV installations, the numbers end up 213 m^2 (14.2 parking spaces) of panels to charge one battery per day, and 61.9 years before the panels pay for themselves.

The costs are coming down, and we will eventually get to the point where it's cost-effective. But please do a reality check on the notion that you'll be able to prop up a few square meters of solar panels and charge your car for free.

3 hours ago
top

Sony Leaks Reveal Hollywood Is Trying To Break DNS

Solandri Re:comcast (378 comments)

1) Yet another reason why it should be illegal for cities/municipalities to award a monopoly cable contract. The folks living in such an area (90%+ of Comcast's network) cannot choose not to do business with Comcast if they want broadband Internet.

2) Yet another reason to set the primary DNS of every router you set up for a friend to a public DNS server.

2 days ago
top

Backblaze's 6 TB Hard Drive Face-Off

Solandri Re:Long story short (ad-less) (172 comments)

- Energy Use â" The Seagate drives were 7200 rpm and used slightly more electricity than the Western Digital drives which were 5400 rpm. This small difference adds up when you place 45 drives in a Storage Pod and then stack 10 Storage Pods in a cabinet.
- Loading speed â" Edge to Western Digital, by a little over 1 TB per day on average.

That didn't really make sense to me that the 5400 RPM drive beat out the 7200 RPM drive, so I did a bit of research.

The WD drives were the WD60EFRX. It's a 5-platter 6TB drive, or 1.2 TB/platter. It has 64MB cache.

The Seagate drives were the STBD6000100. It's a 6-platter drive, or 1 TB/platter. It has 128MB cache. Googling for it brings up contradictory information, listing it as both 7200 RPM and 5900 RPM. (Note: It's pathetic that Seagate doesn't list basic information like RPM on their website.)

So apparently the higher areal density on the WD (meaning more data can be written per rotation, and shorter r/w head strokes to move to a given number of cylinder tracks) is enough to overcome its RPM disadvantage. Given the results, it's likely the Seagate STBD6000100 is 5900 RPM drive, as 7200/5400 = 1.33 which would've exceeded the WD's higher areal density.

I'd caution though that Backblaze's application seems to be a highly sequential task. Peak transfer rates were over 7 TB/day, which is more than 80 MB/s. Given the larger cache and higher RPM (whether 5900 or 7200), I'd expect the Seagate drive to perform better under random read/writes.

2 days ago
top

Microsoft Gets Industry Support Against US Search Of Data In Ireland

Solandri Re:Probably cruel but... (137 comments)

If the US get their way, no company on this planet would touch a data center that is remotely in league with a US based company with a 10 foot pole.

Which is precisely what companies should have been doing as soon as America passed the PATRIOT Act, which pretty much spelled out their claim to be able to do this.

That's the really sad/pathetic thing about all this. Everyone knows how the PATRIOT Act, NSA eavesdropping, warrants approved by secret courts, etc have damaged the trustworthiness of U.S. communications traffic companies within the international community . Rather than learn from that experience and realize that overreaching government invasion of privacy is bad for business and the economy, the U.S. government is eagerly rushing to do it all over again, this time to U.S. data hosting companies. The U.S. government isn't just shooting itself in the foot, it's blasting a basketball-sized hole in its chest (crippling its own tech economy).

2 days ago
top

Waze Causing Anger Among LA Residents

Solandri Re:Sympton of a bigger problem (593 comments)

App or no app, traffic in cities and suburbs is something that is going to need to be dealt with somehow. Cities like Boston or New York at least have a workable public transit system to keep some cars off the roads. LA is totally different -- it was built around cars and is only now getting a very small set of public transit choices.

Actually most of the highways and major roads in Los Angeles are laid out in a more or less straight North-South East-West grid system, and it's fairly easy to get off the highway to take a local road to bypass an accident or excessive traffic.

Interstates 5 and 405 are the exception. They're diagonal, heading Northwest to Southeast. The roads they intersect are still North-South East-West. Not coincidentally, they also happen to be the LA freeways with the worst traffic.

Public transportation needs high population density to be effective. Los Angeles' population density isn't anywhere near as high as New York or Chicago. While you're correct that the city was built around cars and freeways, that's not the only reason for the sprawl. The other major factor was earthquakes. It was a lot riskier to build high-rises in L.A. until about the 1970s when materials and structural engineering improved. The landing flight path to LAX actually goes right over the "densest" residential part of Los Angeles outside of downtown. Look out the window next time you fly in - it's all singly story housing.

4 days ago
top

Vinyl Record Pressing Plants Struggle To Keep Up With Demand

Solandri Re:Not really missing vinyl (433 comments)

The little "steps" in digital audio are so small and so fast, that no one can hear them.

No, those steps don't exist. The digital sample is basically the minimum information needed to code the original smooth analog signal. The DAC takes that minimum digital info and can convert it back into the complete and smooth original analog signal.

You're thinking of the digital signal as discrete but continuous steps in time. It's not continuous. It's an instantaneous measurement of the analog signal at regular time intervals. The digital signal at any point in time says nothing about the signal immediately before or after that point in time. The DAC "fills in the gaps" by interpolating a smooth and analog signal. If the frequency limit is half the sampling rate, that interpolation is perfect and there is only one unique analog solution to any set of digital samples. And that unique solution is a perfect reproduction of the original analog signal (within the frequency limit).

Watch the first 10 min of this video. It explains it technically, graphically, and experimentally using an oscilloscope and both analog and digital signal generators.

5 days ago
top

Vinyl Record Pressing Plants Struggle To Keep Up With Demand

Solandri Re:Not really missing vinyl (433 comments)

The analog waves looked like regular osilloscope waves but the digital ones looked like tiny sets of a thousand stairs going up and down. He claimed this difference may be perceivable by some people.

Sigh. This is the misconception that keeps millions of non-technical people mired in the stone age of audio.

When you play back digital audio, that stairstep pattern isn't sent to the speakers. A DAC (digital to audio converter) finds the unique mathematical signal which passes through all those stairsteps given a certain frequency limit. I repeat - the solution is unique. For a given audio signal and sampling rate, a given stairstep digital pattern converts into a unique and perfectly smooth analog pattern. That smooth analog pattern is what's sent to the speakers, and is every bit as smooth as the analog waves you saw on your oscilloscope.

Watch this video. The meat of it is in the first 10 minutes and will save you a lifetime of misunderstanding about digital sampling.

5 days ago
top

Blade Runner 2 Script Done, Harrison Ford Says "the Best Ever"

Solandri Re:Why do I care what Harrison Ford thinks? (297 comments)

Actually, I think most of his success stems from the fact that half the population thinks he's devastatingly handsome. There's a saying about James Earl Jones - that if he did a performance reading a phone book, it would sell out. Same thing for actors like Harrison Ford in the visual sense. His image helped make the movies successful as much as the other way around.

5 days ago
top

Microsoft To US Gov't: the World's Servers Are Not Yours For the Taking

Solandri Re:Hiding evidence (192 comments)

The New York Times is a wholly American company.
The New York Times reporter is presumed to be an American citizen. If the "New York Times" were a wholly owned subsidiary of Deutche Bank and the New York Times employee was instead a German citizen and an employee of Deutche Bank ... THEN it would be equivalent.

That's an even more dangerous line of thinking. It would result in every major corporation in the U.S. immediately moving their HQ to a more warrant-friendly country and reincorporating there. Your citizenship has nothing to do with any activities you conduct abroad. When you do things in other countries, their laws take precedence, not the laws of your country of citizenship.

The core issue is that in the past, when you did things, you did them in the country you were currently in. So if I traveled to Macau and gambled, I was not subject to U.S. or my home state's gambling laws. Heck, if I traveled there and killed someone, the U.S. can't file murder charges against me. Physical location was an easy way to determine legal jurisdiction.

But in our modern networked world, it is now possible to do things outside the country you are in. I can now gamble in Macau over the Internet from the comfort of my living room. Physical location is no longer adequate to determine jurisdiction. It hasn't happened yet, but eventually some hacker is going to mess up some hospital's ICU computers in another country and kill someone. This issue needs to be resolved somehow by the International community in a manner which is consistent and reciprocal without being destructive.

Microsoft is correctly pointing out that the Justice Dept. unilaterally declaring that it is privy to any documents held abroad simply because the company holding those documents happens to be HQed in the U.S. is self-destructive because of its broad overreach. If the Justice Dept. gets their way, basically no non-U.S. entity would ever want to house records with a U.S. company even if those records are kept in their country, because of the U.S. government's overreaching powers to obtain those records. Those companies would be forced to reincorporate outside the U.S. if they wished to continue keep international customers.

A much more constructive approach would be like extradition treaties - countries develop treaties where they agree to respect each others' search warrants under certain circumstances.

about two weeks ago
top

French Publishers Prepare Lawsuit Against Adblock Plus

Solandri Re:They can go bite a donkey (698 comments)

If a site wants to serve ads, then they should do like I did when I was running a largish (over 1M unique users a day) website. Sell your own ad space. Ad networks who host obtrusive ads need to go away.

Yeah, that's the real root issue here. The publishers were unwilling to pay for development costs so they can host their own ad space, and pay marketing costs to sell that space to potential advertisers. Instead, they wanted someone else to pay for the development work and to find advertisers, and have them given them ads to embed. Embedding ads is a technological solution to this economic problem. Adblockers exist because of a flaw with this technological solution.

Part of living in a capitalist system is that bad ideas die. The rise of adblockers means that ad servers are a bad idea, and need to die. Bringing a lawsuit to try to stave off that death not only thwarts capitalism, but allows a non-optimal solution to persist longer than it should. The real solution is to solve the initial economic problem - pay the extra money to give yourself the capability to sell your own ad space.

about two weeks ago
top

A Case Against Further Government Spectrum Auctions

Solandri Spectrum auctions are anti-capitalism (66 comments)

Spectrum is a natural monopoly (for that particular spectrum). Much in the way that real estate is a natural monopoly (for that particular patch of land). Giving a private party ownership in perpetuity of a natural monopoly breaks capitalism. A recurring cost needs to be added to encourage effective use. Property taxes accomplish that for real estate (when used properly, and not hijacked by the government as a source of revenue). If the property taxes are appropriate for the location, people making effective use of the land are able to pay it with little pain. People not making effective use of the land (e.g. a strawberry farm in the middle of a city) are unable to pay, and thus are encouraged to either change how they're using the land to generate revenue more appropriate for the location's potential, or to sell the land to someone who can/plans to generate such revenue.

The same needs to happen with spectrum. The government shouldn't be selling it. It should be leasing it. Every 5-10 years, it should reappraise how much revenue all spectrum is generating, and the annual lease amount raised to something commensurate with that revenue potential. Companies which are doing a thriving business with that spectrum will be able to pay the increased lease. Companies sitting on the spectrum just to keep it out of the hands of their competitors will indirectly be paying their competitors (via the government, which should use the funds for enforcement and to encourage development of technologies that use spectrum). And companies struggling will be forced to adopt newer (hopefully better) business models to use the spectrum, or be forced to sell to someone else who can. If they can't make it work, someone else should be given the chance.

You can even get fancy to thwart corner cases. e.g. To discourage sitting on spectrum to block competitors, tie the annual lease to the amount that the spectrum is used. If it's utilized 75% or more, you get the normal lease. If it's 50%-75% utilization, you pay 1.5x the rate. If it's 25%-50% utilization you pay 2x the rate. Less than 25% utilization and you pay 5x the rate. To discourage monopolization of large amounts of spectrum by a few companies, increase the annual lease depending on how many blocks you're leasing. But it all hinges on leasing spectrum instead of auctioning it off.

about two weeks ago
top

Apple DRM Lawsuit Might Be Dismissed: Plaintiffs Didn't Own Affected iPods

Solandri Re:Not unexpected. (141 comments)

Yeah, factually untrue. Industry statistics show Apple products to be consistently the most dependable you can buy.

That's a myth. It's only true if you rely on subjective surveys which are vulnerable to self-bias. Owners of Apple products basically like to believe their products are more reliable, so report them as such. Same reason BMW and Mercedes owners rate their vehicles so highly, when the repair rates show them to be average or below average in dependability.

If you use objective data like extended warranty insurance claim rates or repair rates at a computer repair shop, while Apple is top tier, they are hardly the best. (Their repair rates are probably biased low too, because a larger percentage of Mac owners first think to take their Macbook to an Apple store, rather than a generic computer repair store.)

http://www.squaretrade.com/htm/pdf/SquareTrade_laptop_reliability_1109.pdf
http://www.rescuecom.com/news-press-releases/computer-reliability-report-2014-q3.aspx
http://www.rescuecom.com/news-press-releases/computer-reliability-report-2014-q2.aspx
http://www.rescuecom.com/news-press-releases/computer-reliability-report-2014.aspx
http://www.rescuecom.com/news-press-releases/computer-reliability-report-2013-q3.aspx
http://www.rescuecom.com/news-press-releases/computer-reliability-report-2013-q2.aspx
http://www.rescuecom.com/news-press-releases/computer-reliability-report-2013-q1.aspx
http://www.rescuecom.com/news-press-releases/computer-reliability-report-2012-q3.aspx
http://www.rescuecom.com/news-press-releases/computer-reliability-report-2012-q2.aspx
http://www.rescuecom.com/news-press-releases/computer-reliability-report-2012.aspx

And if you don't yet know, Apple doesn't make the Macbooks. They're made by Quanta. Quanta is an ODM - original design manufacturer. Like an OEM except they also design the product. Quanta also happens to make most of HP's laptops. The vast majority of laptops sold are made by ODMs, not the brand names you see on the box. While the brand name exhibits some executive control over acceptable quality control criteria, it's really the ODM which determines build quality.

about two weeks ago
top

Renewables Are Now Scotland's Biggest Energy Source

Solandri Re:Numbers in summary contradict headline (235 comments)

If you drill down into the source numbers (Scotland Qtr tab), it breaks down as:

31.0% - 7.8 TWh - Nuclear
25.1% - 6.325 TWh - * Wind
22.2% - 5.6 TWh - Coal
12.4% - 3.108 TWh - * Hydro
5.6% - 1.4 TWh - Gas
2.3% - 0.585 TWh - * Other biomass including co-firing (this usually means wood burning)
1.1% - 0.277 TWh - * Landfill gas
0.2% - 0.054 TWh - * Solar
0.06% - 0.014 TWh - * Sewage sludge

Sources preceded by a * are classified as renewable.

about three weeks ago
top

Mathematicians Study Effects of Gerrymandering On 2012 Election

Solandri Re:Don't hear that it's just the Republicans at th (413 comments)

Senators can't be gerrymandered because they represent the entire state. A pre-set geographic boundary which (usually) can't be changed. Gerrymandering happens after each Census (2010, 2000, 1990, 1980, etc) when the House seats are reapportioned and redrawn to be relatively equal in population.

If you want a recent Democrat example, just look at California. In the 2014 House elections, Democrat candidates got 57.7% of the votes relative to Republicans (4.06m vs 2.98m). Yet they won 73.6% of the races (39 of 53). Of the 9 races where the winner got fewer than 57.7% of the votes, Democrats won 8, Republicans just 1.

Anyway, this is nothing new. The term Gerrymandering dates back to 1812. Letting the State legislatures draw the election districts is literally letting the foxes guard the henhouse (gerrymandering isn't just about helping your own party, it's also about making "safe" districts so incumbents have an easier time getting re-elected). In the 1990 election, California ended up with a Democrat-controlled legislature and a Republican governor. The Democrats gerrymandered the districts, and the governor vetoed it. The boundaries ended up being drawn by the State Supreme Court, and for the next 8 years California had probably the fairest elections in its history.

There were two California ballot initiatives in 1990 for taking control of redrawing the districts away from the legislature. They were both winning until about a month before the election. Basically every special interest out there realized fairer districts would add unpredictability by increasing the chances of incumbents losing. So they all ran ads against them (including several groups I had previously thought were "honest" like the Sierra Club and NOW). And both initiatives were defeated.

about three weeks ago
top

Uber's Android App Caught Reporting Data Back Without Permission

Solandri Re:Spoofing (234 comments)

As others have pointed out, XPrivacy does exactly that. Unfortunately, it runs on top of the Xposed Framework, which was coded assuming Dalvik. ART breaks it, and Lollipop has switched over entirely to ART. According to the developer it's going to be a monumental task rewriting it to work under ART, and not to expect anything until 2015.

I've fallen back to my old standby - Droidwall. It's an iptables firewall. Doesn't help with the apps which need Internet access to function, but works on everything else. They can collect all the information they want. It's useless to them if the app can't phone home.

about three weeks ago
top

Health Advisor: Ebola Still Spreading, Worst Outbreak We've Ever Seen

Solandri Re:Actually doubles in 60 days (244 comments)

Your graph shows Sierra Leone and Guinea cases growing at about the same exponential rate as in the past. Most of the "slowdown" is due to Liberia cases tapering off, but there's a huge comment in the middle of the graphic saying this is likely due to a breakdown in Liberia's ability to accurately track the number of cases, rather than an actual slowdown.

about three weeks ago
top

Consortium Roadmap Shows 100TB Hard Drives Possible By 2025

Solandri Re:How about transfer rate and reliability? (215 comments)

Transfer rate is proportional to areal density. If the areal density increases 10x, then for each rotation of the platter 10x as many bits pass under the read/write heads, and (sequential) transfer rate increases by 10x as well.

The problem for HDDs is and always has been random seek times - the time it takes to move the read/write heads to a new location and wait for the proper part of the platter to spin underneath. Look at this 7200 RPM HDD reivew from 2003. The sequential read/write speeds (45/27 MB/sec) are about a third what a modern drive gets. But the IOPS is exactly the same because it depends platter rotation speed.

about three weeks ago
top

WaveNET – the Floating, Flexible Wave Energy Generator

Solandri Re:Niche energy (90 comments)

I am wondering why you think the energy density is low? I think it is huge, a lot more kinetic energy per square meter than faster moving, but lighter, air.(wind)

That's the problem - you can't really tap into the kinetic energy of the wave from the surface. The up-down motion of the wave is just a boundary layer height change due to a transient lateral pressure differential in the water. i.e. The water pressure is higher at this point than at a point 1 meter away, while the air pressure is the same in both spots. So the water is higher at this point, creating the height differential we call a wave. The vast majority of the energy is transmitted under the surface - even if you covered the ocean surface with a solid 100% energy-absorbing material, the wave would still propagate. The amount that'd be lost to the surface (due to harvesting) is just the difference in cross sectional area of the wave front from one end of the harvesting device to the other if the wavefront were allowed to expand upwards. Unless you're in very shallow water, the vast majority of the energy simply passes underneath your device.

So a floating structure is a terribly inefficient way to extract energy from the wave. It'd be like trying to extract wind energy using balloons which flop around in the wind. A turbine is a much more efficient way to harvest the kinetic energy, except underwater turbines tend not to last very long due to corrosion, biological fouling, and experience higher wear due to the incompressibility of water.

If you don't believe me, ask yourself why sailing ships were designed to use wind energy instead of wave energy. Waves are more consistent than wind - even when there is no wind there are frequently ocean swells which could've provided energy to propel ships. It's because average wind energy is denser than the fraction of wave energy you can extract from something bobbing on the surface.

about three weeks ago
top

Ask Slashdot: Why Is the Power Grid So Crummy In So Many Places?

Solandri Re:In Finland (516 comments)

And we have underground wiring. Areas with above ground wiring sees more outages.

This is also what annoys me whenever I have been visiting the US - the air is filled with wires high and low, which definitely destroys the scenery of the otherwise picturesque towns that are common in New England among other places.

It boils down to average population density and cost. It's worth paying to put wires underground if they're going to be servicing a thousand homes on one block. But it's not worth it if you're going to be servicing just a few dozen homes spread out over a square mile. That's why the cities tend to have underground wiring, and suburban and rural areas tend to have above ground wiring. Europe tends to have more of the former, the U.S. more of the latter.

As for home building materials, that again boils down to cost. The U.S. and Canada had (still have) vast tracts of forests and lumber is relatively cheap. Europeans cut down most of their forests centuries ago, so brick and stone tend to be cheaper.

about three weeks ago

Submissions

top

Students figure out how to unlock school-issued iPads

Solandri Solandri writes  |  about a year ago

Solandri (704621) writes "The Los Angeles Times reports that the LA Unified School District's plans to assign an iPad to every student in the district are on hold after students figured out how to unlock the iPads. Once unlocked, the iPads can be used for decidedly non-academic activities such as surfing the web and accessing social media sites. According to students, unlocking the devices is simple — just delete your personal profile info."

Journals

Solandri has no journal entries.

Slashdot Login

Need an Account?

Forgot your password?