LPG (liquid propane gas) is, as the name implies, a liquid. Only a small part of it evaporates and thus exerts a pressure on the container, which is why you could not put it into, say, a plastic container.
On the other hand, CNG (compressed natural gas) is, as the name implies, a gas. There is no liquid part to it. It is all gas.
My car (a Honda Civic GX), has a CNG tank that has a 100 liter volume, but the quantity of CNG you can get into it at 3600 psi pressure is only about 7 GGE (gasoline gallon equivalent).
7 gallons equals about 26.5 liters.
Since "GGE" tries to establish an equivalence based on energy content, this means that, at 3600 psi pressure, one GGE of CNG occupies roughly 4 times the volume than liquid gasoline.
Hence, you need a 100 liter pressure tank for something that, in liquid form, would only occupy about 26 liters of volume.
So why not jack up the pressure even more?
Two answers:
- Cost of and experience in building pressure tanks
- Cost of and experience in building compressors
About pressure tanks:
3600 psi is well understood, after all, this is roughly the same pressure that your avarage scuba diver uses.
In other words, hundreds of thousands of such tanks are in operation - not as CNG tanks, but as scuba tanks.
Upping the pressure to, say, 7200 psi would go into rather unexplored and unproven territory.
About compressors:
Compressing natural gas or air to 3600 psi already requires 3 or 4 compressor stages. That's right, not just one compressor, but a cascade of 3 or 4.
Compressing gas to, say, 7200 psi would probably require 6 compressor stages or so, more than doubling the cost of the compressor and reducing its reliability.
Also: As you compress gas, it gets hot. Compress it more, it gets even hotter. Thus, you would have to design in a few cooling stages into your 7200 psi compressor.
Yes, it is CNG only.
If it ran on both gasoline and CNG, it would not be eligible for California's carpool lane decal == the sticker that tells a cop, who is not as dumb as those that pulled me over, that this is a car that may be driven on the carpool lane with only one person (the driver) in it.
As for pricing, here in California CNG is NOT less expensive than gasoline.
On the contrary: Right now in winter when demand for natural gas is up, CNG is actually more expensive ($2.25 per GGE, GGE being an acronym for "gasoline gallon equivalent") than regular gasoline (which costs around $2 per gallon right now).
Then again, with an octane rating of 128 (!), CNG should probably compared to PREMIUM gasoline, and yes, it is (and always has been) SLIGHTLY less expensive than premium gasoline.
It runs only on CNG.
If it ran on both gasoline and CNG, it would not be eligible for California's carpool lane decal == the sticker that tells a cop, who is not so dumb as those that pulled me over, that this is a car that can drive on the carpool lane with only one person (the driver) in it.
...not on hydrogen, and a little-known law allows me to drive solo on carpool (HOV) lanes in California.
Disadvantages:
- short range (only about 180 to 185 miles)
- higher purchase price (about $5000 more for a new car)
- limited number of CNG refueling stations (have to plan refueling stops ahead)
- cannot use the car for cross-country trips due to insufficient network of CNG stations
- There is the occasional moron who thinks I'm a carpool lane violator and turns on the high beams behind me
- There is the occasional dumb cop who thinks I'm a carpool lane violator and pulls me over, only to let me go 2 minutes later
I expect a hydrogen car to have similar advantages and similar disadvantages.
As I said, in Dreamweaver you can edit in BOTH views, not merely in the HTML view.
You cannot do that in a web browser.
In many cases, your development cycle looks like this with Dreamweaver:
Repeat until happy:
Change "real world" view a little bit.
And only occasionally:
Change HTML a little bit and see how "real world view" looks like.
When using "vi" or "notepad", your development cycle looks more like:
Repeat until happy:
Make a change in HTML
Save the file (don't forget!)
Hit "refresh" in the browser window
Observe whether you like the new look.
A big monitor helps.
You basically see two views of your website:
The HTML code and a "real world" view.
You can make changes in both views and the other view will be updated accordingly.
400 bucks sounds like a lot, but think of it in terms of time saved, not of money spent.
Highly recommended.
No, I'm not affiliated with Macromedia in any way - I just have a small web-based business and created the website myself.
Because a Qbit (quantum bit) is both 0 and 1 at the same time, until observation forces it to a known state.
Hence, a register built out of 512 Qbits represents 2^512 states at once and you can brute-force RSA or DSA encryption algorithms.
However, right now it is not yet feasible to build a quantum computer with 512 Qbits.
Athlon64 + motherboard at Fry's (on sale)... $200
120GB harddisk... $70
case and power supply... $30
512 MB RAM... $80
video card... $120 (I refuse to buy $400 video cards, sorry)
The satisfaction of having built your own computer... priceless
When we have open positions, we put the applicants
on
Who Needs Harvard?
·
· Score: 2, Insightful
through a series of grueling interviews and don't really take the name of the university into account too much.
Nothing worse than hiring an ivy-league graduate who cannot do the job very well and then proceeds to display an arrogant attitude towards his or her non-ivy-league coworkers who can.
One cannot, while remaining TCP standard compliant, continue to initiate (with SYN) and terminate (with FIN) tens of thousands of [short] TCP connections to the same destination without either:
1. slowing down to a crawl because all available ephemeral source ports are already in TIME_WAIT state (and thus not available for the new connection)
or
2. "reaping" such source ports that are in TIME_WAIT state prematurely, thereby violating the TIME_WAIT mandate of the TCP standard.
With faster and faster network cards (think 10 Gigabit) now readily available, this issue is getting worse and worse.
Most manufacturers choose to workaround number 2, by the way, undoubtedly in order not to jeopardize benchmarks.
Having 32 bit port numbers in TCP would alleviate this problem somewhat, at the expense of memory (all these 4-tuples in TIME_WAIT state obviously occupy memory). But this argument is moot, since port numbers are just 16 bits.
(Why would you want to continuously open short connections to the same host over and over again? Think two back-to-back application level firewalls. Think eCommerce credit card authorization. There are many situations where this may be necessary.)
Slashdot Mirror
On the other hand, CNG (compressed natural gas) is, as the name implies, a gas. There is no liquid part to it. It is all gas.
My car (a Honda Civic GX), has a CNG tank that has a 100 liter volume, but the quantity of CNG you can get into it at 3600 psi pressure is only about 7 GGE (gasoline gallon equivalent).
7 gallons equals about 26.5 liters.
Since "GGE" tries to establish an equivalence based on energy content, this means that, at 3600 psi pressure, one GGE of CNG occupies roughly 4 times the volume than liquid gasoline.
Hence, you need a 100 liter pressure tank for something that, in liquid form, would only occupy about 26 liters of volume.
So why not jack up the pressure even more?
Two answers:
- Cost of and experience in building pressure tanks
- Cost of and experience in building compressors
About pressure tanks:
3600 psi is well understood, after all, this is roughly the same pressure that your avarage scuba diver uses.
In other words, hundreds of thousands of such tanks are in operation - not as CNG tanks, but as scuba tanks.
Upping the pressure to, say, 7200 psi would go into rather unexplored and unproven territory.
About compressors:
Compressing natural gas or air to 3600 psi already requires 3 or 4 compressor stages. That's right, not just one compressor, but a cascade of 3 or 4.
Compressing gas to, say, 7200 psi would probably require 6 compressor stages or so, more than doubling the cost of the compressor and reducing its reliability.
Also: As you compress gas, it gets hot. Compress it more, it gets even hotter. Thus, you would have to design in a few cooling stages into your 7200 psi compressor.
If it ran on both gasoline and CNG, it would not be eligible for California's carpool lane decal == the sticker that tells a cop, who is not as dumb as those that pulled me over, that this is a car that may be driven on the carpool lane with only one person (the driver) in it.
As for pricing, here in California CNG is NOT less expensive than gasoline.
On the contrary: Right now in winter when demand for natural gas is up, CNG is actually more expensive ($2.25 per GGE, GGE being an acronym for "gasoline gallon equivalent") than regular gasoline (which costs around $2 per gallon right now).
Then again, with an octane rating of 128 (!), CNG should probably compared to PREMIUM gasoline, and yes, it is (and always has been) SLIGHTLY less expensive than premium gasoline.
It runs only on CNG.
If it ran on both gasoline and CNG, it would not be eligible for California's carpool lane decal == the sticker that tells a cop, who is not so dumb as those that pulled me over, that this is a car that can drive on the carpool lane with only one person (the driver) in it.
Disadvantages:
- short range (only about 180 to 185 miles)
- higher purchase price (about $5000 more for a new car)
- limited number of CNG refueling stations (have to plan refueling stops ahead)
- cannot use the car for cross-country trips due to insufficient network of CNG stations
- There is the occasional moron who thinks I'm a carpool lane violator and turns on the high beams behind me
- There is the occasional dumb cop who thinks I'm a carpool lane violator and pulls me over, only to let me go 2 minutes later
I expect a hydrogen car to have similar advantages and similar disadvantages.
You cannot do that in a web browser.
In many cases, your development cycle looks like this with Dreamweaver:
Repeat until happy:
Change "real world" view a little bit.
And only occasionally:
Change HTML a little bit and see how "real world view" looks like.
When using "vi" or "notepad", your development cycle looks more like:
Repeat until happy:
Make a change in HTML
Save the file (don't forget!)
Hit "refresh" in the browser window
Observe whether you like the new look.
A big monitor helps.
You basically see two views of your website:
The HTML code and a "real world" view.
You can make changes in both views and the other view will be updated accordingly.
400 bucks sounds like a lot, but think of it in terms of time saved, not of money spent.
Highly recommended.
No, I'm not affiliated with Macromedia in any way - I just have a small web-based business and created the website myself.
...there's not much to do in Beaverton besides staying indoors and writing open source software.
...street gangs have been reported to tote Bluetooth-enabled notebook computers instead of firearms.
Because a Qbit (quantum bit) is both 0 and 1 at the same time, until observation forces it to a known state.
Hence, a register built out of 512 Qbits represents 2^512 states at once and you can brute-force RSA or DSA encryption algorithms.
However, right now it is not yet feasible to build a quantum computer with 512 Qbits.
120GB harddisk
case and power supply
512 MB RAM
video card
The satisfaction of having built your own computer ... priceless
Nothing worse than hiring an ivy-league graduate who cannot do the job very well and then proceeds to display an arrogant attitude towards his or her non-ivy-league coworkers who can.
1. slowing down to a crawl because all available ephemeral source ports are already in TIME_WAIT state (and thus not available for the new connection)
or
2. "reaping" such source ports that are in TIME_WAIT state prematurely, thereby violating the TIME_WAIT mandate of the TCP standard.
With faster and faster network cards (think 10 Gigabit) now readily available, this issue is getting worse and worse.
Most manufacturers choose to workaround number 2, by the way, undoubtedly in order not to jeopardize benchmarks.
Having 32 bit port numbers in TCP would alleviate this problem somewhat, at the expense of memory (all these 4-tuples in TIME_WAIT state obviously occupy memory). But this argument is moot, since port numbers are just 16 bits.
(Why would you want to continuously open short connections to the same host over and over again? Think two back-to-back application level firewalls. Think eCommerce credit card authorization. There are many situations where this may be necessary.)
For instructions on how to use it under Linux, see (for instance): http://modular.fas.harvard.edu/sprint_merlin/
http://www.nwfusion.com/reviews/2004/110804rev.htm l/
Scanning for vulnerabilities on a regular basis is as pro-active as it gets, isn't it?