Want to read Slashdot from your mobile device? Point it at m.slashdot.org and keep reading!


Forgot your password?

Comment: Re:Darwin by proxy (Score 1) 616

by MattskEE (#49532325) Attached to: Bill To Require Vaccination of Children Advances In California

I don't understand why people who vaccinate are afraid of those that don't.

It's not fear, but there are several legitimate reasons to be concerned about people who choose not to vaccinate their children for personal non-medical reasons:

1) Some people have legitimate medical reasons why they cannot receive vaccines or it is harder for them to get vaccines, e.g. allergies.
2) Vaccines are not 100% effective but increasing vaccination rate provides greater protection to all.
3) We still care about kids who are not our own and we don't want them to catch easily preventable diseases like measles.

Comment: Re:Powdered alcohol is stupid. (Score 1) 421

by MattskEE (#49410429) Attached to: Powdered Alcohol Banned In Six States

Get yourself some 200 proof booze, put it in a flask, and if you want drink, then mix that with some amount of water because you really don't want to drink 200 proof booze straight unless you're completely crazy.

At least 15 states already ban 190 proof alcohol, in those states 150 proof is typically the maximum allowed by law.

Comment: Re:No they don't (Score 1) 226

by MattskEE (#49374113) Attached to: Chinese Scientists Plan Solar Power Station In Space

That does not change the fact that the math is pretty solid and it would work.

You haven't done the math or cited any.

There is a big efficiency problem in space-based solar with the double conversion from DC to RF/laser and back to DC. Total efficiency neglecting transmission loss is about 64% (80% twice). Then you have to invert it back to AC usually, but that is also needed for terrestrial solar.

So 35% power is thrown away, but since the sun is stronger in space without atmospheric attenuation, and there are no clouds, some of that will be made up.

So to a first approximation the power per unit of panel area is the same from space as it is on earth.

Now factor in launch costs which are tremendous (even if SpaceX succeeds in yet another 10x reduction in launch costs as claimed) and the difficulty performing maintenance in space versus on land, and I don't see a strong case. Installation costs on land are around $1/watt, I'd like to see you come within a factor of 10 of that in space.

Comment: Re:Waste of time (Score 1) 51

by MattskEE (#49269089) Attached to: Fujitsu Could Help Smartphone Chips Run Cooler

In undoped semiconductor resistance will usually decrease as temperature is raised because a higher temperature excites more electrons into the conduction band where they can carry current.

But for cases where there is already a lot of charge the opposite usually applies. In something like a MOSFET the electrons are supplied by the source contact or in a doped bulk semiconductor there will be lots of charge from dopants. In these cases increasing the temperature doesn't significantly increase the charge. However raising the temperature does increase the electron scattering rate which reduces the electron mobility and slows electrons down, so the resistance actually increases.

Comment: Re:I'm disappointed in my fellow geeks (Score 1) 214

by MattskEE (#49235755) Attached to: Billionaire Teams Up With NASA To Mine the Moon

I'm all for exploring space, but the premise of mining the moon sounds pretty shaky and its totally fair for geeks to want realistic goals because that's what attracts sustainable capital investment from public and private sources that are needed to realize the goal. It's not a zero-sum game, but putting private and public money into crazy unworkable ideas takes some money away from realistic ideas.

Moon mining sounds to me a lot like orbital solar power - it sounds great and cool until you actually think for a moment and realize that it has very little to no net benefit per panel area compared to terrestrial solar after you transmit the power back to earth, and the cost is astronomical to boot. What is the benefit of mining the moon aside from sounding cool? It doesn't seem like there's a particularly high concentration of any of these purported mineral riches and with the expense of mining the material in space I'm highly suspicious of it being in any way economical after shipping back to Earth. He-3 is a bust since there's currently no major use for it. Maybe moon mining would be viable for obtaining materials on the moon without launch costs, but the supposed mineral riches are mostly high priced specialty materials and not the boring metals like iron and aluminum that would be needed for building a spaceship or lunar colony.

Fuck off, some of us have dreams.

Some of us like to support our dreams with back of the envelope analyses to ensure viability before getting too invested in them.

Comment: Re:Spectrum is measured in Hz? (Score 1) 91

by MattskEE (#48943725) Attached to: US Wireless Spectrum Auction Raises $44.9 Billion

Nope, reread your link. Channel capacity (at a given signal to noise ratio) is proportional to bandwidth alone. 1.000GHz to 1.065GHz is as good as 20.000GHz to 20.065GHz.

But as you say higher frequencies often have worse propagation characteristics, especially through buildings, which reduces channel capacity by reducing the signal to noise ratio.

Comment: Re:TWT based (Score 1) 54

by MattskEE (#48880641) Attached to: TWEETHER Project Promises 10Gbps MmW 92-95GHz Based Wireless Broadband

To get tens of watts from solid state in W-band yes you need either spatial or corporate (or both) combining of individual chips. So the amp ends up being of similar size to a mm-wave TWT but you don't need an expensive and large HV power supply or water cooling. Chip level output powers in GaAs I think have been done up to about 500mW, and 1-2W in GaN.

GaN for mm-wave still has some yield and reliability problems (pick at least one depending on supplier), and performance is not yet up to the ideal levels. But that's the same thing that GaN went through at lower frequencies, and mm-wave GaN is improving.

Comment: Re:TWT based (Score 2) 54

by MattskEE (#48879835) Attached to: TWEETHER Project Promises 10Gbps MmW 92-95GHz Based Wireless Broadband

Solid state GaAs is slowly catching up to TWTAs at this frequency. They're not common but it is possible to buy a 30 watt solid state amplifier, probably for the same price you can get a TWTA that has a little bit more power. GaN still has lots of problems at this frequency but it's improving and will likely be competitive with tubes within 5-10 years.

But yes it seems like it would be much easier to do this at Ka band where solid state amps are now a better value than tubes for communication applications.

Comment: Re:Physics doesn't work like that. (Score 2) 54

by MattskEE (#48879743) Attached to: TWEETHER Project Promises 10Gbps MmW 92-95GHz Based Wireless Broadband

In addition to penetrating solids the range is challenging (or expensive anyway) just because of limited transmit power levels. Power is important because that gives you your range, your cell phone and home wireless router transmit up to about 1 watt. A 1 watt output solid-state power amplifier at this frequency would cost $5-10k, or at least that was the case about a year ago. This project seems to propose using travelling wave vacuum tube technology which provides lots of drive power (50-100 watts) but at a high price (over $100-250k).

Wherever you go...There you are. - Buckaroo Banzai