Chip-to-chip bottlenecks have long been a vexing challenge for computer designers, who have explored many ways of increasing the overall speed of systems that are composed of hundreds of chips.

For Mr. Keller the most vexing challenges are neither labor costs nor technology.

However, proper implementation of these policies has become a vexing challenge especially in countries like Japan, where banks are playing an increasingly proactive role in fulfilling national security goals to obtain extractive and energy resources.

For journalists and world leaders, however, the month has historically presented more vexing challenges.

Oversensitivity of the trip wires proved to be a vexing challenge throughout the service life of the SM-70.

Though Mr. Corzine's fellow Democrats control both branches of the Legislature, managing his relationship with party leaders may be his most vexing challenge.

The most vexing challenge, though, is what fuel cars will run on in a future where oil is too scarce or tailpipe emissions too dangerous on account of global warming.

Professor Clark told me that one of her most vexing challenges was contending with what she called the "fully aware narcissism" of young Americans abroad.

Stemming the flow of illegal guns is a vexing challenge, police officials say.

One participant, Dr. Michael T. Osterholm, a professor of public health at the University of Minnesota, said the anthrax investigations were a far more vexing challenge than traditional disease detective work.