Varian Associates

About: Varian Associates is a based out in . It is known for research contribution in the topics: Beam (structure) & Wafer. The organization has 2160 authors who have published 2591 publications receiving 46002 citations.

Multinuclear two-dimensional NMR: Assignments of natural abundance polypeptide 13C, 1H and 15N chemical shifts and demonstration of isomer interconversion

Abstract: The polypeptide carbobenzoxy-glycyl-L-prolyl-L-leucyl-L-alanyl-L-proline (0.2 M in DMSO-d6) was investigated using 13C, 1H and 15N NMR in natural abundance at 4.7 tesla. The existence of cis–trans-Gly-Pro and -Ala-Pro bonds permits up to four isomers, and all four were observed (in a 60:30:7:3 ratio). 13C shifts of the proline β-CH2 resonances are consistent only with the 60% form being trans–trans. The 30% form is either trans–cis or cis–trans (order as above) and was tentatively assigned as cis-trans on the basis of relaxation behavior. Refocused INEPT studies aided the 13C assignments. The 15N data were obtained using both NOE and INEPT excitation, with signals evident for the three major isomers. The spectra were analysed by starting from the 13C data, which were assigned based on known regularities in peptide spectra. A 13C1H heteronuclear two-dimensional chemical shift correlation experiment allowed direct assignment of proton shifts for major and minor isomers. The NH proton shifts were assigned by running a homonuclear two-dimensional chemical shift correlation experiment and noting the correlation with the previously assigned α-CH protons. The 15N resonances were then assigned from a 15N1H heteronuclear two-dimensional chemical shift correlation experiment, relating the 15N signals directly to the NH proton resonances. Isomer interconversion between the two major isomers was demonstrated by performing a magnetization transfer homonuclear 2D experiment. Off-diagonal intensity was noted relating the major and minor isomer alanine NH proton, as well as for the major and minor isomer leucine NH protons.

Slow-wave circuit for traveling-wave tubes

Abstract: In a travelling-wave tube for very high frequencies the slow-wave circuit is formed of four metal combs having teeth pointed toward the electron beam. The combs are arranged in two pairs. The teeth of the two combs in each pair extend inward from opposite sides of the beam and are axially aligned to form the electrical equivalent of a half-wave bar or ladder structure. They may or may not be joined at the tips because those are low-current points. The teeth of one pair are at right angles to those of the other pair and are displaced axially to interleave with them. Each comb is preferably made from a single piece of copper to provide better dimensional precision, low circuit loss, mechanical durability and high thermal capability.

Microwave applicator with distributed feed to a resonator

Abstract: A microwave applicator is disclosed which employs an elongated hollow resonator dimensioned to be cut off for the dominant waveguide mode at the frequency of the applicator. A hollow waveguide feed extends along and adjacent the resonator and includes a distributed coupling means providing a distributed wave energy feed path from the waveguide to the resonator. The distributed coupling means is arranged for exciting a transverse TEM mode in the resonator to produce standing wave microwave electric fields in the plane of a relatively thin elongated treatment zone within the resonator. The resonator includes a pair of elongated openings in registration with the treatment zone for passage of thin webs of material through the treatment zone. The distributed coupling means is preferably arranged to provide an increasing coefficient of coupling taken in the direction of power flow through the feed waveguide. Thus, the power is distributed to the resonator uniformly.

Fourier transform nuclear magnetic resonance spectrometer employing means for generating random pulse intervals to avoid anomalies due to net transverse magnetization

Abstract: Means for eliminating phase and intensity anomalies in high resolution nuclear magnetic resonance spectra particularly useful in impulse Fourier spectrometers wherein free induction decay signals are obtained from a sample under analysis, the demodulated free precession signals being averaged in a time-averaging computer and then Fourier-transformed and displayed as a resonance frequency spectrum. Phase and intensity anomalies are avoidable by not permitting establishment of a finite net transverse component of magnetization in the steady state regime by introducing a delay into each recycle time. Alternatively, net transverse magnetization may be permitted to occur for a set of pulses but the phase and intensity anomalies may be avoided by changing the pulse rate for each set and by time-averaging the responses of the sets of pulses, each set of pulses being a predetermined number of pulses at a fixed pulse interval for each set, the pulse intervals for each set being different from the pulse interval of said first set by a random period.

Microwave spectrometer employing a bimodal cavity resonator

Abstract: A pulsed electron paramagnetic resonance spectrometer employs a bimodal sample cavity. Coherent microwave power from a common source is applied to the cavity for exciting and observing resonance of the sample via separate pumping and observing microwave channels. An automatic frequency control circuit locks the frequency of the common source to the resonant frequency of the observing mode of the bimodal cavity. All modulating frequencies, delays, pulse repetition rates, etc. are derived from a master clock. Free induction decay resonance signals are separated from saturation-recovery resonance signals in the observing channel by proper adjustment of the relative phases at a detector crystal in the observing channel of a reference microwave signal, a cross-coupled pump signal, and a signal reflected from the observing cavity mode, and by furthermore adjusting the polarizing magnetic field to the center of a resonance line. The proper phase adjustment yields a dispersion free induction decay signal and an absorption saturation recovery signal. Alternatively or in combination with the first method, saturation recovery signals are separated from the free induction decay signals detected in the observing channel by modulating the observing power level from a nonsaturating microwave power level to a still lower power level at a low modulation frequency. The detected resonance signal is then phase sensitive detected at the modulation frequency to detect the saturation recovery signal to the exclusion of the free induction decay signal.