1 For automobiles a taxpayer uses for business purposes, the portion of the business standard mileage rate treated as depreciation is 23 cents per mile for 2013, the same as in 2012. 2  The IRS also publishes a standard mileage rate for the use of a vehicle for medical or moving purposes.
What causes continuous rolling thunder when no lightning visible? Thunder is caused by the rapid expansion of super-heated air as electrical spark passes through. What causes the long (ie some several seconds) of rumbling when no lightning is visible even at night during tropical downpours?
When this happens, a stream of negative charges pours down towards a high point where positive charges have clustered due to the pull of the thunderhead. The connection is made and the protons rush up to meet the electrons. It is at that point that we see lightning and hear thunder. A bolt of lightning heats the air along its path causing it to expand rapidly. Thunder is the sound caused by rapidly expanding air.