National Magnetics Resonance Facility at Madison, University of Wisconsin-Madison, Madison, WI 53706, USA. whlee@nmrfam.wisc.edu|National Magnetics Resonance Facility at Madison, University of Wisconsin-Madison, Madison, WI 53706, USA. whlee@nmrfam.wisc.edu|National Magnetics Resonance Facility at Madison, University of Wisconsin-Madison, Madison, WI 53706, USA. whlee@nmrfam.wisc.edu