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Transverse Oscillations in a Cylindrical Combustion Chamber

Description: Note presenting a study of certain features of transverse resonance in an idealized combustion chamber. Modes of weak oscillation are described with average Mach number neglected but with the effect of axial gradient of mean temperature considered. The nature of finite transverse periodic waves is also analyzed.
Date: October 1954
Creator: Moore, Franklin K. & Maslen, Stephen H.
Partner: UNT Libraries Government Documents Department

Science Drivers and Technical Challenges for Advanced Magnetic Resonance

Description: This report recaps the "Science Drivers and Technical Challenges for Advanced Magnetic Resonance" workshop, held in late 2011. This exploratory workshop's goal was to discuss and address challenges for the next generation of magnetic resonance experimentation. During the workshop, participants from throughout the world outlined the science drivers and instrumentation demands for high-field dynamic nuclear polarization (DNP) and associated magnetic resonance techniques, discussed barriers to their advancement, and deliberated the path forward for significant and impactful advances in the field.
Date: March 7, 2013
Creator: Mueller, Karl T.; Pruski, Marek; Washton, Nancy M. & Lipton, Andrew S.
Partner: UNT Libraries Government Documents Department

Suppression of probe background signals via B1 field inhomogeneity

Description: A new approach combining a long pulse with the DEPTH sequence (Cory and Ritchey, Journal of Magnetic Resonance, 1988) greatly improves the efficiency for suppressing probe background signals arising from spinning modules. By applying a long initial excitation pulse in the DEPTH sequence, instead of a {pi}/2 pulse, the inhomogeneous B{sub 1} fields outside the coil can dephase the background coherence in the nutation frame. The initial long pulse and the following two consecutive EXORCYCLE {pi} pulses function complementarily and prove most effective in removing background signals from both strong and weak B{sub 1} fields. Experimentally, the length of the long pulse can be optimized around odd multiples of the {pi}/2 pulse, depending on the individual probe design, to preserve signals inside the coil while minimizing those from probe hardware. This method extends the applicability of the DEPTH sequence to probes with small differences in B{sub 1} field strength between the inside and outside of the coil, and can readily combine with well-developed double resonance experiments for quantitative measurement. In general, spin systems with weak internal interactions are required to attain efficient and uniform excitation for powder samples, and the principles to determine the applicability are discussed qualitatively in terms of the relative strength of spin interactions, r.f. power and spinning rate.
Date: January 27, 2011
Creator: Feng, Jian & Reimer, Jeffrey
Partner: UNT Libraries Government Documents Department

Nuclear Magnetic Resonance Spectra of Some 1,2,4-triazoles

Description: In the work undertaken here, NMR has been used to ascertain the structure of some 1,2,4-triazoles. The investigation provides information concerning the structure of potentially tautomeric triazoles such as hydroxy- and aminotriazole. Connected with this aspect of triazole chemistry is the larger problem of mesohydric tautomerism. The present study also yields information for a comparison of substituent effects in triazoles, N-heteroaromatic substances and benzene.
Date: January 1967
Creator: Creagh, Linda Truitt
Partner: UNT Libraries

Multimode-diode-pumped gas (alkali-vapor) laser

Description: We report the first demonstration of a multimode-diode-pumped gas laser--Rb vapor operating on the 795 nm resonance transition. Peak output of {approx}1 Watt was obtained using a volume-Bragg-grating stabilized pump diode array. The laser's output radiance exceeded the pump radiance by a factor greater than 2000. Power scaling (by pumping with larger diode arrays) is therefore possible.
Date: August 22, 2005
Creator: Page, R H; Beach, R J & Kanz, V K
Partner: UNT Libraries Government Documents Department

Tunneling rate fluctuations induced by nonlinear resonances: A quantitative treatment based on semiclassical arguments

Description: This article discusses tunneling rate fluctuations induced by nonlinear resonances. The authors investigate the tunneling process between two symmetric stable islands of a forced pendulum Hamiltonian in the weak chaos regime.
Date: November 1998
Creator: Bonci, Luca; Farusi, Andrea; Grigolini, Paolo & Roncaglia, Roberto
Partner: UNT College of Arts and Sciences

Cyclotron Resonance Heating of a Deuterium Plasma

Description: Abstract: "The energy gained by a deuterium plasma, from a three megacycle per second radiofrequency field, was studied experimentally. A static magnetic field, in the form of a "mirror", was used. The coil of an rf resonant circuit, placed at the center of the machine produced a time-varying magnetic field parallel to the static field. This, in turn, induced an electrical field, in an azmuthal direction, which acted on the ions. When this was in synchronism with the cyclotron frequency, the ions could pick up energy. At this resonance the light intensity from the plasma increased markedly. This effect was used as evidence for the transfer of energy to the ions."
Date: October 28, 1957
Creator: Chambers, Edmund S.; Lamb, William A. S. & Kippenhan, Dean O.
Partner: UNT Libraries Government Documents Department

Raman and NMR Relaxation Studies of Molecular Dynamics in Liquids

Description: Raman vibrational bands are sensitive to fluctuations in the molecular environment. Variations in the bandwidth and peak position can then be utilized to monitor molecular forces and interactions present in condense phases. Nuclear Magnetic Resonance (NMR) provides a convenient probe for the study of molecular reorientation in liquids since nuclear spin relaxation times are dependent on the details of molecular motion. Presented here is the solvent study of the Raman bandwidths and frequency displacements of the mode of the compounds CH3MCI3 (M = C, Si, Ge, Sn) in a number of solvents of widely varying molecular structure. Also, a detailed isotope dilution study of the modes in CH2CI2/CD2CI2 mixtures is presented. In this set of experiments, I observed broadening of the v1 mode of CH2C12 upon dilution,which is the first experimental observation of such behavior. The temperature-dependent carbon-13 relaxation times and nuclear Overhauser enhancements in neat dichloromethane were measured. In this study we found that the molecular reorientation of this molecule was highly anisotropic, but could be well characterized assuming quasi-symmetric top behavior. In addition, in order to gain a more complete understanding of the reorientational dynamics in dichloromethane, we analyzed the 13-C NMR relaxation of CH2CI2 both in "inert" solvents of differing viscosities and in interactive solvents of varying Lewis basicities. Various theoretical models were also applied in order to characterize dichloromethane1s reorientational dynamics.
Date: August 1987
Creator: Rodriguez, Arturo A. (Arturo Angel)
Partner: UNT Libraries

Magnetic Resonance Facility (Fact Sheet)

Description: This fact sheet provides information about Magnetic Resonance Facility capabilities and applications at NREL's National Bioenergy Center. Liquid and solid-state analysis capability for a variety of biomass, photovoltaic, and materials characterization applications across NREL. NREL scientists analyze solid and liquid samples on three nuclear magnetic resonance (NMR) spectrometers as well as an electron paramagnetic resonance (EPR) spectrometer.
Date: March 1, 2012
Partner: UNT Libraries Government Documents Department

Least Squares Magnetic-Field Optimization for Portable Nuclear Magnetic Resonance Magnet Design

Description: Single-sided and mobile nuclear magnetic resonance (NMR) sensors have the advantages of portability, low cost, and low power consumption compared to conventional high-field NMR and magnetic resonance imaging (MRI) systems. We present fast, flexible, and easy-to-implement target field algorithms for mobile NMR and MRI magnet design. The optimization finds a global optimum ina cost function that minimizes the error in the target magnetic field in the sense of least squares. When the technique is tested on a ring array of permanent-magnet elements, the solution matches the classical dipole Halbach solution. For a single-sided handheld NMR sensor, the algorithm yields a 640 G field homogeneous to 16 100 ppm across a 1.9 cc volume located 1.5 cm above the top of the magnets and homogeneous to 32 200 ppm over a 7.6 cc volume. This regime is adequate for MRI applications. We demonstrate that the homogeneous region can be continuously moved away from the sensor by rotating magnet rod elements, opening the way for NMR sensors with adjustable"sensitive volumes."
Date: March 27, 2008
Creator: Paulsen, Jeffrey L; Franck, John; Demas, Vasiliki & Bouchard, Louis-S.
Partner: UNT Libraries Government Documents Department

High performance single stage operation of the LBL ECR and the design of an advanced ECR ion source

Description: A new mode of operation using only the second stage of the LBL ECR has been developed. This single stage mode produces charge states and currents equal to or better than the traditional two stage operation of the LBL ECR for a variety of gases such as nitrogen, oxygen, and argon. The critical parameter for this mode appears to be conditioning the plasma chamber walls with a coating of SiO/sub 2/. Various models to explain this effect will be discussed along with implications for ECR ion source design. A new Advanced ECR ion source which will operate at 14 GHz is being designed for the 88-Inch Cyclotron. Construction is scheduled to begin in the fall of 1988 and test operation should begin in the fall of 1989. The design includes hollow core copper wire solenoids, iron yoke, a Nd-Fe-B sextupole, radial pumping, and access to the plasma chamber. 8 refs., 4 figs., 1 tab.
Date: September 1, 1988
Creator: Lyneis, C.M.
Partner: UNT Libraries Government Documents Department

NMR DOUBLE QUANTUM SPIN DECOUPLING IN SOLIDS

Description: The problem of spin decoupling spin I = 1 nuclei with large quadrupolar splittings {omega}{sub Q} (e.g. deuterium) from dilute S spins via double quantum transitions is dealt with. The normal two spin-1/2 single quantum decoupling problem (I = 1/2, S = 1/2) is first dealt with as a reminder of the coherent averaging approach and to understand the dependence of the S resonance linewidth on the I rf field intensity ({omega}{sub 1}) and resonance offset ({Delta}{omega}). The double quantum problem (I = 1, S = 1/2) is then treated analogously by introducting fictitious spin-1/2 operators for the I double quantum transition. The decoupling condition is found to be very sensitive to the spin-I resonance condition and to go as {approx} 1/4 with the spin I rf field intensity at resonance in the double quantum regime ({omega}{sub 1} << {omega}{sub Q}). Experimental examples on heavy ice, dimethyl-sulfoxide-d{sub 6} and benzene-d{sub 6} are presented verifying the quantitative theoretical predictions. Extensions to higher order multiple quantum effects for spin I > I and for several coupled spin-1/2 nuclei are discussed.
Date: October 1, 1977
Creator: Pines, A.; Vega, S. & Mehring, M.
Partner: UNT Libraries Government Documents Department

Resonantly excited high-density exciton gas studiedvia broadbandTHz spectroscopy

Description: We report the density-dependent crossover of a resonantly photoexcited exciton gas from insulating to conducting phases. Broadband terahertz spectroscopy gives direct access to the exciton binding energy via intra-excitonic 1s-2p transitions. A strong shift, broadening, and ultimately the disappearance of this resonance occurs with decreasing inter-particle distance. Densities of excitons and unbound electron-hole pairs are followed quantitatively using a model of the composite free-carrier and exciton terahertz conductivity. Comparison with near-infrared absorption changes illustrates a significantly enhanced energy shift and broadening of the intra-excitonic resonance.
Date: June 25, 2005
Creator: Huber, Rupert; Kaindl, Robert A.; Schmid, Ben A. & Chemla, Daniel S.
Partner: UNT Libraries Government Documents Department

GLOBAL AND LOCAL COUPLING COMPENSATION EXPERIMENTS IN RHIC USING AC DIPOLES.

Description: Compensation of transverse coupling during the RHIC energy ramp has been proven to be non-trivial and tedious. The lack of accurate knowledge of the coupling sources has initiated several efforts to develop fast techniques using turn-by-turn BPM data to identify and compensate these sources. This paper aims to summarize the beam experiments performed to measure the coupling, matrix and resonance driving terms with the aid of RHIC ac dipoles at injection energy.
Date: June 26, 2006
Creator: CALAGA, R. & FRANCHI, A. (GSI), TOMAS, R.(CERN)
Partner: UNT Libraries Government Documents Department

Solution studies of ⁶Li enriched organolithium compounds using new NMR techniques

Description: With the values of 6Li T1 measured and the literature values of J(13C-6Li) for these compounds, three new 13C NMR techniques are developed for the analysis of organolithium compounds. Modifications to the spectrometer are discussed, as well as calibrations of the 6Li decoupler channel needed to set up these new experiments.
Date: May 1990
Creator: Ellington, Donald H. (Donald Howard)
Partner: UNT Libraries

Cyclotron resonance absorption by a hydrogen plasma

Description: From introduction: "The work described in this report was undertaken as part of an experimental study to determine the effectiveness of radiofrequency field in heating the ions of a hydrogen or deuterium plasma. The ultimate aim is to find a method of heating a deuterium plasma until an appreciable rate of nuclear reaction takes place."
Date: August 30, 1957
Creator: Chambers, Edmund S.
Partner: UNT Libraries Government Documents Department

Chlorine Nuclear Quadrupole Resonance Absorption of 3, 4, 5, 6 - Tetrachlorophthalimide and 1, 3, 6, 8 - Tetrachloropyrene

Description: In this study frequency modulation was used with a regenerative spectrometer and a super-regenerative spectrometer to detect the nuclear quadrupole resonance frequencies of chlorine in two commercially available compounds, 1, 3, 6, 8 - tetrachlorophyrene and 3, 4, 5, 6 - tetrachlorophthalimide.
Date: January 1968
Creator: Reeves, Jerry Byron
Partner: UNT Libraries