Bruce Schneier makes a good point in this article on Movie Plot Threats:

I wonder why he thinks that "schools, churches and government or medical facilities" are terrorist targets worth protecting, and movie theaters, stadiums, concert halls, restaurants, train stations, shopping malls, Toys-R-Us stores on the day after Thanksgiving, train stations, and theme parks are not. After all, "there's got to be some common sense."

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Yes, and the same technology that allows people to call their friends can be used by terrorists to choose targets and plan attacks. And the same technology that allows people to commute to work can be used by terrorists to plan and execute attacks. And the same technology that allows you to read this blog post...repeat until tired.

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Ok, here's the situation:

Say you have a hot water tank (boiler here) that holds 80 liters of water.  You want to heat that water to 70 degrees C.  Assume the temp of the water in the tank (and the incoming water) is room temperature--20 deg celcius.  Also assume that during the day, electric costs 4 times what it does at night.

Now, is it better to heat all 80 liters of water at night (with cheap electric) or are you better off to heat it a bit at a time as it comes into the tank when you use it?  Assume 90% of the hot water usage is during the expensive time.

You'll have to look up the formulas as I don't have them handy right now (sorry).  My hypothesis is that it will be cheaper to heat the water at night all at once instead of during the day time as you use it.  Why?  Just because 1 cubic cm of water ALWAYS takes the same amount of energy to heat it up a given number of degrees.  But, I could be wrong.  What do you think?

Image from akirsa via flickr

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A few friends and I went to see Terminator Salvation yesterday.  For a 4th, it was good.  It seemed like they made a few things force fit the rest of the story.  All in all, it was ok though.

Image from alfredituzz on flickr

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This event happened 20 years ago tomorrow (5 June)

Read more about it here, here, and here.

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