I've seen most of my friends drive (I don't drive myself so I can be a more objective 3rd party observer) and I have to say I'd welcome self driving cars any day. Most people frequently are distracted while driving. In 99.9% of the time (yes statistic made up on the fly) nothing happens because nothing out of the ordinary happened at that particular moment. Our built-in autopilot copes very well with the routine events. But change that in any significant manner and accidents are imminent. I have no doubt that self-driving cars are more effetively aware of their surroundings most of the time.

It's funny how most of my family and friends consider themselves good drivers. Having been in close calls the very few times I have been riding with each of them I find it quite scary. It's actually quite amazing that there are no more accidents on the road each day. i have sample only an infinitesimely small amount of each of those people's driving time, and the frequency of the close calls doesn't fill me with confidence about their general level of distraction. And, I repeat, ALL of them consider themselves good drivers. Food for thought.

I for one welcome our self-driving vehicles. The roads can't possibly be less safe with them.

Maybe it was not "woment" but "youngsters" doing the cave paintings. Putting graffiti wherever they could, just like today's kids. :D

Meh. I just use Google streetview. Don't even need a poweful mind for that.

Well, why don't you test the official story? It's easy, go to your computer and google search "pressure cooker" and a few minutes later "back pack". Make sure to let us know if the MIB go visit you. Here on /., we like to know.

Just in time for Transformers. That movie really looked like a formula movie (without a plot). Interesting to note it came in 2007 and felt like junk right of the bad. It had all the elements of "successful" movie, the inadequate boy... who meets the hot girl, pointles fights here and there. Oh yeah, did we mention the hot girl bending over the open hood of a car? Shouldn't miss that. So the bullied boy... oh yeah and the awkward parents who are actually happy to see that he'd been sneaking a girl in his room.... a puppy peeing on somebody. Oh, yeah car chases, you can't have a blockbuster without at least one car chase. And of course, giant fighting robots to add what most wouldn't have.

All they missed was a plot. But they definitely had everything else in the recipe book.

I never understood its success given the lack of plot, but apparently the book was right. Form trumps content anytime. (but really, was a little bit of a plot linking the different ingredients that much to ask? I didn need an Oscar winning plot, just the kind of plot that gets childrens books going).

P.S.
I know the continuity (or lack thereof) will offend some sensibilities. I appologize for this, but I was trying to convey my state of mind as I was watching that disaster unravelling before my eyes.

Were you being sarcastic?

To answer your question as to "rebar corrodes", I should point out that cement is generally basic. Actually, Portland Cement can be quite basic which tengs to cause some unwanted reactions with the silicate aggregates. Still, a high PH will generally tend to protect the steel from corrosion. The salts used in de-icing salts will tend to have a low pH which will foster corrosion of the reinforcement make it expand, which causes cracking of the concrete and accelerates the influx of water to the steel which accelerates corrosion etc.

Recipes such as those used by Romans are already known (the contribution of t he paper is more as to why that is, than that it is the case as various types of ashes are used in different mixes). Replacing cement by addititives can give some properties that are good in some cases, but may make it take longer to cure, and/or reduce its ultimate strength (depending on the additives). Choosing the peroper mix depends on the usage and the cost.

As to why reinforce at all, it's because we need reinforcement for tensile strength. Concrete has a fraction of the tensile strength than compressive strength (think of a chalk) . As mentionned in a previous post, Roman works relied more on compressive strength than tensile strength. There are advantages to that approach, but definitely many practical disadvantages.

From the press release: "The resulting calcium-aluminum-silicate-hydrate (C-A-S-H) is an exceptionally stable binder."

Now, if they could only make it transparent...

Yup. It's about the shashdot summary which sucks and completely misses the point. The press release focuses on the differences in the chemical composition of the hydrated cement (chiefly the presence of aluminium atoms in the Roman cement) and how those differences may affect durability.

Roman works relied strictly on compression (arches and domes are good examples). There is no doubt that compression works can be more durable than tension structures because by the nature of the beast they require much more material to build. Because of this, they have much more material to wear off (redundancy) and so they can better resist the passage of time (and erosion).

Of course, as in everything, there are tradeoffs. One of them being the shear mass of materials required for construction. Engineering is about efficiency, and so for a structure of a lifespan of 50 years (typical design lifespan) roman-style strucures would be way over-engineered. Not only in terms of cost to build but in terms of energy consumption of the process. You are also limited in the freespan of a bridge you can build this way. Imagine the size of the arch that would be required to match modern suspended bridges spans... and the corresponding amount of rock and/or concrete needed and you start getting an idea of what efficiency means in those terms. Some things would just be impossible to build the roman way.

Of course, if one of your key requirement is 2000+ years design lifespan, then using a compression design the roman way does make sense for many things. It's all about the design objectives.

From the headline one would think that this is the "secret ingredient" to the Roman concrete: "The lime was hydrated — incorporating water molecules into its structure — and reacted with the ash to cement the whole mixture together"

However, this is pretty much how portland cement (the modern binder in concrete) reacts with water to form the concrete with the agregate. Reading the article, however this is what matters:

"One is the kind of glue that binds the concrete’s components together. In concrete made with Portland cement this is a compound of calcium, silicates, and hydrates (C-S-H). Roman concrete produces a significantly different compound, with added aluminum and less silicon. The resulting calcium-aluminum-silicate-hydrate (C-A-S-H) is an exceptionally stable binder."

"At ALS beamlines 5.3.2.1 and 5.3.2.2, x-ray spectroscopy showed that the specific way the aluminum substitutes for silicon in the C-A-S-H may be the key to the cohesion and stability of the seawater concrete."

"Another striking contribution of the Monteiro team concerns the hydration products in concrete. In theory, C-S-H in concrete made with Portland cement resembles a combination of naturally occurring layered minerals, called tobermorite and jennite. Unfortunately these ideal crystalline structures are nowhere to be found in conventional modern concrete."

"Tobermorite does occur in the mortar of ancient seawater concrete, however. High-pressure x-ray diffraction experiments at ALS beamline 12.2.2 measured its mechanical properties and, for the first time, clarified the role of aluminum in its crystal lattice. Al-tobermorite (Al for aluminum) has a greater stiffness than poorly crystalline C-A-S-H and provides a model for concrete strength and durability in the future."

So basically, there is alimunium in the crystaline structure of Roman cement that contributes to the differences in performance over time (not raw strength). Another factor that may impact durability that is not covered here but that civil engineers will know well is the fact that modern cements are more alkaline than even early Portland Cement productions. As a result, they tend to react with the silicates in the aggregates of the cement (phenomenon known as alkali-aggregate reaction). If you see concrete with cracks that look wet even when it's not raining, that's a symptom of this effect. The reaction with the aggregates causes an expansion within the concrete which builds ups stresses locally and result in those cracks, with obviously unfortunate effects on the longevity of concrete structures.

Even without prestressing, (which reinforced concrete does allow) reinforcement provides additional tensile strength. Concrete's tensile strength is no more than 10% of its compressive strength which means it's nothing to write home about. You can get reinforcement from fibres (which is why the ancients would add straw to clay to make bricks).

The point is that while pretensioning does give you added tensile resistance (by converting the inital tension to a reduction of the pre-imposed compression), reinforced concrete does not require pre-tensioning to reinforce concrete in tension, and in most cases just the presence of rebar is enough to provide the required tensile resistance. Pretensioning will be used when larger spans (and therefore larger tensile stresses in some parts of the beams) are required.

Actually, I'd say unless you have a government bent on controlling the news, state media usually provides the most neutral less "hyped" information. I know in the US it's all about "nothing should be state owned" but beyond the rethoric in many instances state media have provided the best quality TV, certainly in terms of information. Too much of private TV news is entertainment. The CNNisation of news is a terrible tragedy.

I cannot say what the situation was in Greece, but if it is similar to what I have experienced when I have been in Western Europe, greeks have probably lost their best source of news.

I'm still running Debian on 64 MB of RAM. With Xwindows and icewm. I can even browse the interwebs for a while with firefox until I hit a page with javascript requirements that beat the OS requirements. Sadly that is becoming the norm (I'm looking at you gmail)

I don't think that anthropology deals much with fossils anyways. I don't know how long it takes for remains to fossilize, but I'd be willing to bet that it takes more than the few hundred millenia associated with ancient human studies. Anthropology deals more with actual bones than fossils, though even then, wood is probably usually one of the first casualties of time.