A collection of Letters to the Editor from magazine readers.

This month's Computing section includes "Girls and Video Games," "Bikes in the Right Place" and "Virtual Space."

The CIA carried out 118 drone strikes last year, costing more than $1 million each. Because of the large cost and the low rate of “high-value target” hits, many are questioning the drone campaign.

The April 2011 News & Notes section includes "Clear Skies to Cool the Planet" and "Jets' Smaller Vortices Save 2.5 Billion Gallons."

The April 2011 Tech Focus section features "Online Troubleshooting" and "Plug-and-Play for Medical Implants."

A collection of recently released publications that should be of interest to those working in the engineering profession.

The San Joaquin Air Pollution Control Board had been looking at greenhouse gas emissions emanating from dairy farms, and there was talk that methane digesters might be made mandatory.

Unmanned aerial vehicles have changed the face of warfare, but UAVs can do even more when they fly in flocks.

The demand is there, but to fill it, companies have to know how to build mass-customized products on demand.

Stacking processing chips can make for more compact computers. But it will take advances in microfluidics to make such dense number crunching practical.

Focus on Power & Energy: Thermodynamics puts limits on the efficiency of thermal power plants. Cleverly reconfiguring cooling towers can lead to a way of recapturing some of that waste heat.

Focus on Power & Energy: It's time to reevaluate the way we think about the size of power plants.

Focus on Power & Energy: During the first two months of the year, the spot price for Brent crude on the New York Mercantile Exchange shot past $110 a barrel.

A new report calls for the United States to take steps to secure supplies of materials critical to future energy technologies.

Autodesk Tinkerbox and GrafiCalc Elements 2011 are among the products examined in Software Exchange this month.

This month's New Products include conductive epoxy, a thermocouple connector, and a hydraulic rod clamp.