Slashdot is powered by your submissions, so send in your scoop

 



Forgot your password?
typodupeerror
×

Comment Comparing electric oranges and gasoline apples (Score 2) 172

A fuel efficient gasoline car these days is EPA-city rated at, what, 30 MPG? The Nissan Leaf and Chevy Volt are EPA-city rated at about 100 eMPG (electric-equivalent MPG)?

Bear with me now. A gallon of gasoline, depending on blending and the amount of ethanol has a high heating value (HHV) of about 120,000 BTU per gallon. At 100 percent conversion efficiency, 3400 BTUs gives you 1 kWHr, so 100% conversion of a gallon of gas gives 35.3 kWHr. That is what the EPA means by "eMPG" -- the EPA is assuming 100% conversion efficiency, but that is counteracted by the eMPG rating being artificially high because of that assumption.

Apart from arguments on whether EPA mileage reflects actual mileage, and whether an electric vehicle (EV) takes a "bigger hit" in efficiency in cold weather than a gasoline car, the gasoline MPG combined with the MPG gives you the cents-per-mile; the same holds true for eMPG combined with the kWHr rate according to how eMPG translates into kWHr -- as supplied to the plug connection to the EV. Thus we have "real word" fuel consumption numbers on current-gen gas cars, "real world" kWHr consumption on current-gen EV's, and we don't have to get tied up in knots over figuring all the energy losses in gasoline cars and in EVs.

That Enerdel battery "costs" 18 cents/kWHr, and my Midwestern power company sells me electricity at 14 cents/kWHr. That is, the electric cost is 32 center/kWHr or $11.30 per "electric gallon", but for an EV getting 100 eMPG, that works out to 11 cents/mile.

For gasoline at 4 dollars/gallon (it is cheaper now but will probably climb in price next summer), that works out to 13 cents/mile.

OK, I am sold, that at least from a policy perspective, that if this price on batteries holds up or improves, and if gasoline keeps getting more expensive, a given but you never know for sure, and if electric rates don't increase, not really a given with current policies, or if through Smart Grid that EV owners are given a "deal" for charging at night or other off-peak times, this new battery tech is at least putting the EV "in play."

The other consideration is that $4/gallon is what I pay at the filling station and 14 cents/kWHr is what I pay at home as a retail electric customer. Is this $711 the retail price of that battery pack, or is it the wholesale price to an automobile manufacturer? If I want to replace a 30 kWHr battery pack in a LEAF, do I pay 21 grand or do I pay twice that amount at the Nissan parts counter?

Comment Silicon Valley driven by military requirements (Score 2, Insightful) 382

The whole of Silicon Valley and the Fairchild Instruments-planar-process birth of the modern semiconductor industry was driven by massive infusions of Federal money, military money. The whole integrated circuit thing was motivated by a solid-state guidance system for ICBMs and other military systems.

The whole of large-scale funding of science and engineering came out of WW-II -- the Manhatten Project and microwave radar.

It is kinda like the early commenters don't know who is paying the bills and why. Oh, noes, the Republicans are making us put some boilerplate sentences into our NSF proposals?

I think people funded through NSF should just chill.

Comment Open season on pedestrians (Score 2) 947

If all cyclists did was inconvenience motorists by "sharing" the road, either by following traffic laws or being a little fast and loose with those laws, that is one thing. But I see cyclists not regarding any need to grant right-of-way to pedestrians.

I am driving in a congested city area with a cyclist tailgating me. A pedestrian is not yet in the cross walk but showing signs of entering a marked cross walk so I start to slow down. Pedestrian enters the walk, the cyclist pulls out from behind me to pass on the right, accelerating as the pedestrian dodges the cyclist.

Yeah, these are only the "rude" cyclists, but you all know about No True Scotsman. "A man with red hair on a bike wearing a kilt almost clobbered a pedestrian in Aberdeen the other day." "No true Scotsman would ride a bike that way!"

Comment Quantifying Java performance (Score 1) 465

I tried various Java profilers and they seemed to offer too much "instrumentation overhead" for what I was doing.

For Java, I use System.nanoTime(). For C++, I use the Windows-specific QueryPerformance() call. So

The technique profilers claim to use is to calibrate the overhead of something like System.nanoTime() with a loop and then subtract the estimated overhead from your instrumented code. The overhead to the nanoTime() calls can even be larger than the execution time of code segments you are trying to measure, but if your estimate is accurate, this works.

I am doing plain add-subract-multiply-divide in a mix of scalar and looped operations on arrays -- if you are doing largely trig or calls into a numeric library, you are timing loops and library calls, not the intrinisic performance of your language.

I am also doing a lot of the OO version of using global variables. Java is supposed to do "escape analysis" where if you allocate inside a method and don't let a reference pass outside, the JIT is supposed to recognize that as a local-context stack allocation, but I am not using an advanced Java version or the right set of JVM flags to get that to work.

Comment Java Java! (Score 3, Interesting) 465

For research engineering, I use Java to run the numerical examples of the algorithms I develop although most of the authors in the journals I publish in are using Matlab for this purpose (ewwwwww!). Long time ago I was a Turbo Pascal person as were engineering colleagues who crossed over to Matlab seeking the same kind of ease-of-use. Me, I transitioned to Delphi but now I am with Java and Eclipse -- the Turbo Pascal of the 21st century.

For numeric-intensive work, I can get within 20% of the speed of C++ using the usual techniques -- minimize garbage collection by allocating variables once, use the "server" VM, perform "warmup" iterations in benchmark code to stabilize the JIT. I use the Eclipse IDE, copy and paste numeric results from the Console View into a spreadsheet program, and voila, instant journal article tables.

Comment Maxwell Equations (Score 1) 377

Um, electricity is only indirectly related to the flow of electrons. Current density is proportional to the time rate-of-change of the electric field. That's it

This definition of current, Maxwell's "displacement current" term not only explains the current flow through the insulator separating the plates of a capacitor, it also defines current in nano-scale circuits where only one electron is moving.

An electron is a point source of an electric field, and if you move the electron, you move the electric field, which means that current flows across boundaries some distance from the exact location of the electron. Yes, there is quantum mechanics and no "exact location of the electron", even more the reason to define current in terms of the change in the electric field.

Comment A deal at twice the price (Score 4, Insightful) 497

In light of the importance of this project, the thing is cheap at 600 million -- if they can get it to work. A pretty big if, it seems right now.

In other words, the issue right now is not the cost of the thing but whether any amount of money can make it healthy in the required time.

If this thing doesn't get right, "they" might have to wave the fine/penalty/tax to be payed by people who didn't sign up, which is why there is a political fight right now "shutting down the government"?

Comment Ground point five (Score 1) 249

I guess the one thing you need to know about the radio is the international distress channel of 121.5? I am told that this channel is monitored, even by pilots in the air in case someone is in trouble and they need to relay instructions?

For a more complex aircraft, maybe the next thing is a pencil and paper to copy some checklists? For all but the simplest GA aircraft, you are probably going to need to have a bunch of switches in the right positions?

Slashdot Top Deals

Too many people are thinking of security instead of opportunity. They seem more afraid of life than death. -- James F. Byrnes

Working...