Titel: Off-resonance T1rho using adiabatic rotations

Description: (see also Mulder et al. (1998) JMR 131, p.351-357)
Pulse sequence to measure off-resonance relaxation of 15N nuclei
to quantify chemical exchange contributions. Sequence is based
on a 15N T1 experiment, using gradients for coherence selection
in conjunction with sensitivity enhancement. The operator Sz is
rotated adiabatically by simultaneous amplitude and frequency
modulation. At the end of the 1st adiabatic passage the nuclear
spin magnetization is aligned with the effective field of the
subsequent spin-lock period and relaxation takes place for a certain
T1rho relaxation delay. A 2nd adiabatic rotation restores the
magnetization along the z-axis.

Notes about the specific use of the sequence:
Spectrometer: Bruker AMX/2 600 MHz, BLTX-300 amplifier (15N=F2).
Frequency swithing has been done explicitly by use of an F2list.
Alternatively, DPOFFS1 can be used to execute the entire
off-resonance pulse at the desired offset. All adiabatic pulses
have been programmed as AHP on-resonance, in this way you can use
the same pulse for all offsets. For each individual T1rho delay
time a different shape is created, as well as a different pulse
program. On our spectrometer this is the only way to ensure
the correct synchronization of high power 1H pulse -to suppress
relaxation interference effects- with the 15N shaped SL pulse.
!! NOTE !! The gradient include file gradients.def is unique to our
hardware setup and the way gradients are applied on your system
will require their adjustment, you may want to use your own way
of doing this and change the pulse sequence accordingly !! NOTE !!
In the file 'gradientfile' it is explained exactly how the gradients
are executed on our system.

Literature reference: Mulder, F.A.A., de Graaf, R.A., Kaptein, R.
and Boelens, R., J. Magn. Reson. 131, 351-357 (1998)

Parameters: A list of parameters 'param.list' and a gradient file 
'N_8shape8.r' is included for guidance

Shaped pulses: The source code of a small C program is added,
which can be used to generate the desired adiabatic pulse shapes.