29 Matching Results

Search Results

Advanced search parameters have been applied.

Solid-state NMR studies for DC 745: April--May 2000

Description: Powles et al. reported in 1961 that pdydimethyl siloxane melts exhibit a transverse decay of nuclear spin magnetization (T{sub 2}) that is nonexponential. This observation was interpreted in terms of the proton NMR signal from the melt having characteristics of a broad line. Since then, similar findings were obtained for other polymer melts too. Accordingly to Powles et al. this peculiar proton line shape was the result of an intramolecular direct dipole-dipole interaction between a pair of protons. They also suggested that this dipolar interaction was weak because the dipolar interaction was motionally averaged since the orientation-dependent local dipolar field is modulated by molecular dynamics. In sum, the consequences and the origins of nuclear spin correlations in viscous polymer melts were recognized almost 4 decades ago. In the 1970s, Cohen-Addad suggested that these weak proton dipolar interactions could be used to characterize polymer melts and networks. In this work, we have used some of these ideas to probe the effects of thermal treatments on the proton spin-spin relaxation times for DC745.
Date: December 1, 2000
Creator: Stephens, T. & Labouriau, A.
Partner: UNT Libraries Government Documents Department

Azimuthal and single spin asymmetry in deep-inelasticlepton-nucleon scattering

Description: The collinear expansion technique is generalized to thefactorization of unintegrated parton distributions and other higher twistparton correlations from the corresponding collinear hard parts thatinvolve multiple parton final state interaction. Such a generalizedfactorization provides a consistent approach to the calculation ofinclusive and semi-inclusive cross sections of deep-inelasticlepton-nucleon scattering. As an example, the azimuthal asymmetry iscalculated to the order of 1/Q in semi-inclusive deeply inelasticlepton-nucleon scattering with transversely polarized target. Anon-vanishing single-spin asymmetry in the "triggered inclusive process"is predicted to be 1/Q suppressed with a part of the coefficient relatedto a moment of the Sivers function.
Date: September 21, 2006
Creator: Liang, Zuo-tang & Wang, Xin-Nian
Partner: UNT Libraries Government Documents Department

Viscosity of black liquor project

Description: The discussion of magnetic resonance in this report is confined to nuclides with a spin quantum number of 1/2. Included is a basic discussion of magnetic resonance; magnetic resonance relaxation and viscosity; and rhometers and viscometers. Many other effects are ignored for the sake of clarity.
Date: June 1, 1998
Creator: Barrall, G.A.
Partner: UNT Libraries Government Documents Department

Chemical and Physical Changes in a Hydrolyzed Poly(ester urethane)

Description: Hydrolytic degradation has been shown to be a significant problem for poly(ester urethane) elastomers exposed to high humidity environments. The ester group in the soft segment is particularly susceptible to hydrolysis. One of the products of this reaction is a carboxylic acid group that catalyses further hydrolysis. The resulting reduction in molecular weight leads to deterioration of the elastomer's mechanical properties. In this paper we have measured the extent of the hydrolysis reaction by {sup 13}C NMR spectroscopy. In addition we have measured the spin-spin relaxation time of the soft phase and followed the increase in mobility of these segments. Both measurements were performed on the solid polymer. These measurements provide an excellent monitoring tool of the chemical and physical state of polymer during the aging process.
Date: November 3, 1999
Creator: ASSINK,ROGER A.; CELINA,MATHIAS C. & LANG,DAVID P.
Partner: UNT Libraries Government Documents Department

Effect of the Nuclear Hyperfine Field on the 2D Electron Conductivity in the Quantum Hall Regime

Description: The effect of the nuclear hyperfine interaction on the dc conductivity of 2D electrons under quantum Hall effect conditions at filling factor v= 1 is observed for the first time. The local hyperfine field enhanced by dynamic nuclear polarization is monitored via the Overhauser shift of the 2D conduction electron spin resonance in AlGaAs/GaAs multiquantum-well samples. The experimentally observed change in the dc conductivity resulting from dynamic nuclear polarization is in agreement with a thermal activation model incorporating the Zeeman energy change due to the hyperfine interaction. The relaxation decay time of the dc conductivity is, within experimental error, the same as the relaxation time of the nuclear spin polarization determined from the Overhauser shift. These findings unequivocally establish the nuclear spin origins of the observed conductivity change.
Date: July 13, 2000
Creator: VITKALOV,S.A.; BOWERS,C.R.; SIMMONS,JERRY A. & RENO,JOHN L.
Partner: UNT Libraries Government Documents Department

Spin Spectrometer at the ALS and APS

Description: A spin-resolving photoelectron spectrometer, the"Spin Spectrometer," has been designed and built. It has been utilized at both the Advanced Light Source in Berkeley, CA, and the Advanced Photon Source in Argonne, IL. Technical details and an example of experimental results are presented here.
Date: April 20, 2007
Creator: Laboratory, Lawrence Livermore National; Missouri-Rolla, University of; Technologies, Boyd; Morton, Simon A; Morton, Simon A; Tobin, James G et al.
Partner: UNT Libraries Government Documents Department

New method for the determination of diffusion constants from partially narrowed NMR lines

Description: The effect of atomic and molecular motions on the NMR free-induction decay (FID) and lineshape is investigated theoretically in the intermediate temperature range in which the NMR line is only partially narrowed. It is shown that the FID may be decomposed into the weighted sum of a rigid-lattice (background) contribution and an exponentially decaying part containing all the information on the diffusive or reorientational motions in the crystal in terms of the spin-spin relaxation time T/sub 2/.
Date: January 1, 1980
Creator: Wolf, D.
Partner: UNT Libraries Government Documents Department

Muon spin relaxation study of exchange coupling in dilute AgMn alloys

Description: We have observed for the first time conduction-electron mediated muon-impurity coupling, and deduced the strength of the conduction electron-Mn exchange coupling. Our results are marginally consistent with a wave-vector dependent exchange model. 16 refs.
Date: January 1, 1985
Creator: Heffner, R.H.; Cooke, D.W.; Hutson, R.L.; Schillaci, M.E.; Dodds, S.A.; Gist, G.A. et al.
Partner: UNT Libraries Government Documents Department

Theory and applications of maps on SO(3) in nuclear magnetic resonance

Description: Theoretical approaches and experimental work in the design of multiple pulse sequences in Nuclear Magnetic Resonance (NMR) are the subjects of this dissertation. Sequences of discrete pulses which reproduce the nominal effect of single pulses, but over substantially broader, narrower, or more selective ranges of transition frequencies, radiofrequency field amplitudes, and spin-spin couplings than the single pulses they replace, are developed and demonstrated. 107 refs., 86 figs., 6 tabs.
Date: February 1, 1987
Creator: Cho, H.M.
Partner: UNT Libraries Government Documents Department

Possibility of studying crystal-field levels and excitations by. mu. /sup +/SR spectroscopy

Description: We point out that ..mu../sup +/SR relaxation times T/sub 1/ and T/sub 2/ measured in metallic magnetic materials can sometimes be expressed in terms of the spin-spin correlation functions of the magnetic ions. We calculate these functions in a random phase approximation and notice they can strongly depend on the crystal field levels and excitations of the magnetic ions. The shortcomings of this approximation are discussed.
Date: January 1, 1983
Creator: Yaouanc, A.
Partner: UNT Libraries Government Documents Department

A New Spin on Photoemission Spectroscopy

Description: The electronic spin degree of freedom is of general fundamental importance to all matter. Understanding its complex roles and behavior in the solid state, particularly in highly correlated and magnetic materials, has grown increasingly desirable as technology demands advanced devices and materials based on ever stricter comprehension and control of the electron spin. However, direct and efficient spin dependent probes of electronic structure are currently lacking. Angle Resolved Photoemission Spectroscopy (ARPES) has become one of the most successful experimental tools for elucidating solid state electronic structures, bolstered by-continual breakthroughs in efficient instrumentation. In contrast, spin-resolved photoemission spectroscopy has lagged behind due to a lack of similar instrumental advances. The power of photoemission spectroscopy and the pertinence of electronic spin in the current research climate combine to make breakthroughs in Spin and Angle Resolved Photoemission Spectroscopy (SARPES) a high priority . This thesis details the development of a unique instrument for efficient SARPES and represents a radical departure from conventional methods. A custom designed spin polarimeter based on low energy exchange scattering is developed, with projected efficiency gains of two orders of magnitude over current state-of-the-art polarimeters. For energy analysis, the popular hemispherical analyzer is eschewed for a custom Time-of-Flight (TOF) analyzer offering an additional order of magnitude gain in efficiency. The combined instrument signifies the breakthrough needed to perform the high resolution SARPES experiments necessary for untangling the complex spin-dependent electronic structures central to today's condensed matter physics.
Date: December 1, 2008
Creator: Jozwiak, Chris
Partner: UNT Libraries Government Documents Department

Relaxation nuclear magnetic resonance imaging (R-NMRI) of desiccation in M9787 silicone pads.

Description: The production and aging of silicone materials remains an important issue in the weapons stockpile due to their utilization in a wide variety of components and systems within the stockpile. Changes in the physical characteristics of silicone materials due to long term desiccation has been identified as one of the major aging effects observed in silicone pad components. Here we report relaxation nuclear magnetic resonance imaging (R-NMRI) spectroscopy characterization of the silica-filled and unfilled polydimethylsiloxane (PDMS) and polydiphenylsiloxane (PDPS) copolymer (M9787) silicone pads within desiccating environments. These studies were directed at providing additional details about the heterogeneity of the desiccation process. Uniform NMR spin-spin relaxation time (T2) images were observed across the pad thickness indicating that the drying process is approximately uniform, and that the desiccation of the M9787 silicone pad is not a H2O diffusion limited process. In a P2O5 desiccation environment, significant reduction of T2 was observed for the silica-filled and unfilled M9787 silicone pad for desiccation up to 225 days. A very small reduction in T2 was observed for the unfilled copolymer between 225 and 487 days. The increase in relative stiffness with desiccation was found to be higher for the unfilled copolymer. These R-NMRI results are correlated to local changes in the modulus of the material
Date: June 1, 2004
Creator: Alam, Todd M; Cherry, Brian Ray & Alam, Mary Kathleen
Partner: UNT Libraries Government Documents Department

Investigation of the deswelling characteristics of Illinois No. 6 coal by nuclear magnetic resonance imaging (NMRI) and NMR techniques

Description: NMRI can observe the internal and external physical structural changes of a sample as well as the solvent penetration process without physical handing. Although the spatial resolution achievable in NMRI of coal samples is only 20--40 {mu}m swelling of coal can be measured because a polar solvent expands the coal to almost twice its original volume. NMR can also monitor the change of solvent concentration m a swollen coal (by integrating the peak areas of the NMR spectra), and can also examine solvent mobility (by measuring spin-lattice and spin-spin relaxation times). This paper reports results on application of NMR and NMRI for study of solvent induced-deswelling in an Illinois No. 6 coal.
Date: September 1, 1993
Creator: Hou, L.; Hatcher, P. G.; French, D. C. & Botto, R. E.
Partner: UNT Libraries Government Documents Department

Thin film coatings which inhibit spin relaxation of polarized potassium atoms

Description: A prototype of a polarized deuterium target which employs the spin exchange method is being developed. The mixing cell for mixing deuterium atoms and potassium vapor requires a surface that will reflect these atoms without being destroyed by the corrosive potassium. Thin film coating methods and a technique for coating pyrex are described. Results of spin relaxation measurements are given. (LEW)
Date: January 1, 1986
Creator: Thomas, G.E.; Holt, R.J.; Boyer, D.; Green, M.C.; Kowalczyk, R.S. & Young, L.
Partner: UNT Libraries Government Documents Department

Nuclear relaxation rates at copper and oxygen sites in YBa/sub 2/Cu/sub 3/O/sub 7/

Description: We report NMR measurements of the nuclear relaxation rate at all copper and oxygen sites in magnetically aligned powder samples of YBa/sub 2/Cu/sub 3/O/sub 7/. There is no peak in the oxygen relaxation rate below T/sub c/ at any oxygen site supporting the possibility that d-wave pairs are formed in the superconducting state. Comparison of the oxygen and copper rates in the planes reveals a characteristic temperature greater than T/sub c/. 6 refs., 2 figs.
Date: January 1, 1989
Creator: Hammel, P.C.; Takigawa, M.; Heffner, R.H.; Fisk, Z. & Ott, K.C.
Partner: UNT Libraries Government Documents Department

Single crystal NMR studies of high temperature superconductors

Description: The authors report Cu NMR studies in the normal state of a single crystal of the T/sub c/ = 90 K superconductor YBa/sub 2/Cu/sub 3/O/sub 7/minus/delta/. The authors have measured the magnetic shift tensor, the electric field gradient tensor, the nuclear spin-lattice relaxation rate tensor, and the time dependence and functional form of the transverse decay. From these data they obtain information about the charge state and magnetic state of the Cu atoms, and the existence and size of the electronic exchange coupling between spins of adjacent Cu atoms. 18 refs., 3 figs., 2 tabs.
Date: January 1, 1989
Creator: Pennington, C.H.; Durand, D.J.; Zax, D.B.; Slichter, C.P.; Rice, J.P.; Bukowski, E.D. et al.
Partner: UNT Libraries Government Documents Department

Neutron scattering experiments on the magnetism in Cu-Mn single crystals

Description: Neutron polarization analysis experiments, and unpolarized neutron scattering experiments, were made on annealed single crystal Cu-Mn samples of 5, 10, 15, and 25 at. % Mn. Peaks in the magnetic diffuse scattering are found at the (1, 1/2 +- delta, 0)-type positions in reciprocal space, where delta = 0.34, 0.29, 0.25 and 0.19 for the 5, 10, 15 and 25% Mn samples respectively. This magnetic scattering is symmetry-related to the diffuse nuclear scattering centered at the (1, 1/2, 0)-type positions arising from atomic short range order. The intensity of this diffuse magnetic scattering in all of the alloys decreases smoothly with temperature, approaching zero in the range 300 to 350/sup 0/K. The spin-spin correlation range, as judged from the width of the magnetic diffuse peaks, also decreases smoothly with temperature. Neither the width nor the intensity of this magnetic scattering gives any hint of a freezing transition at lower temperatures.
Date: October 1, 1980
Creator: Werner, S.A. & Cable, J.W.
Partner: UNT Libraries Government Documents Department

Proton NMR relaxation in hydrous melts

Description: Pulse and continuous wave NMR measurements are reported for protons in hydrous melts of calcium nitrate at temperatures between -4 and 120/sup 0/C. Although measured in different temperature ranges, spin-lattice (T/sub 1/) and spin-spin (T/sub 2/) relaxation times appear to be nearly equal to each other and proportional to the self-diffusion coefficients of solute metal cations such as Cd/sup 2 +/. At temperatures near 50/sup 0/C, mean Arrhenius coefficients ..delta.. H/sub T/sub 1// (kcal/mol) are 7.9, 7.3, and 4.8, respectively, for melts containing 2.8, 4.0, and 8.0 moles of water per mole of calcium nitrate, compared to 4.6 kcal/mol for pure water. Temperature dependence of T/sub 1/ and T/sub 2/ in Ca(NO/sub 3/)/sub 2/-2.8 H/sub 2/O between -4 and 120/sup 0/C are non-Arrhenius and can be represented by a Fulcher-type equation with a ''zero mobility temperature'' (T/sub 0/) of 225/sup 0/K, close to the value of T/sub 0/ for solute diffusion, electrical conductance and viscosity. Resolution of the relaxation rates into correlation times for intramolecular (rotational) and intermolecular (translational) diffusional motion is discussed in terms of the Bloembergen-Purcell-Pound and more recent models for dipolar relaxation. (auth)
Date: January 1, 1976
Creator: Braunstein, J.; Bacarella, A. L.; Benjamin, B. M.; Brown, L. L. & Girard, C.
Partner: UNT Libraries Government Documents Department

NMR of small platinum particles

Description: /sup 195/Pt NMR lineshapes as well as relaxation data are presented in three different samples of platinum metal particles (46%, 26%, and 15% dispersion) supported on alumina. The electronic properties of these particles are very much different from that of bulk Pt metal. A prominent peak in the lineshape has been identified as a surface resonance which arises from Pt nuclei on the surface of the Pt particles. We find that these surface Pt atoms are non-metallic when coated with adsorbed molecules.
Date: January 1, 1980
Creator: Stokes, H. T.; Rhodes, H. E.; Wang, P. K; Slichter, C. P. & Sinfelt, J. H.
Partner: UNT Libraries Government Documents Department

NMR study of cluster-assembled nanophase copper

Description: {sup 63}Cu and {sup 65}Cu NMR spectra from cluster-assembled nanophase copper with an average grain size between 5 and 10mn show a broadened peak, at the normal Knight-shifted frequency for copper meta which arises from only the central 1/2 to -1/2 transition. A very broad background is observed on either side of that peak. Some samples exhibit a second broad peak at a position normally associated with non-metallic copper. Pulsed NMR measurements of the central peak show that virtually all the copper signals are significantly broadened and have a spin-spin relaxation time longer than larger grained copper samples. Line shape measurements, using spin echoes, as a function of delay between rf excitation and measurement show there are a number of copper sites with longer relaxation times which have a significantly larger broadening. Those sites are tentatively identified as being at or near a grain boundary or free surface. A small orientation effect is observed indicating an anisotropy within the samples. An isochronal anneal of one sample showed significant, but not complete, line narrowing after an anneal at 450C consistent with other nanophase metals which show grain growth above 40--50% of the melting temperature.
Date: December 1, 1992
Creator: Suits, B. H.; Meng, M.; Siegel, R. W. & Liao, Y. X.
Partner: UNT Libraries Government Documents Department

/sup 7/Li NMR relaxation in superionic. beta. -lithium aluminum

Description: NMR measurements have been carried out on stoichiometric ..beta..-LiAl samples as a function of temperature and frequency. The /sup 7/Li spin-lattice relaxation was found to be predominantly dipolar. Data were analyzed using several diffusion models. The results show that a fraction of the constitutional Li vacancies in ..beta..-LiAl is bound to the vicinity of a Li antisite defect. The remaining free vacancies are responsible for the fact that LiAl is a superionic Li conductor. The spin-spin relaxation results support this picture of two different vacancy environments. The high temperature results demonstrate still another type of Li diffusion related to thermally generated defects. 41 refs., 6 figs., 2 tabs.
Date: March 1, 1986
Creator: Tokuhiro, Tadashi; Susman, S.; Brun, T.O. & Volin, K.J.
Partner: UNT Libraries Government Documents Department

Measurement of pair interactions in neodymium ethyl sulfate

Description: The EPR spectrum of single ions of /sup 143/Nd in a crystal of Neodymium Ethyl Sulfate, predominantly of isotope /sup 142/Nd, was observed under condition of very high Boltzmann factor, i.e., high fields and low temperatures. It was found that the interactions with neighboring ions displaced the hyperfine lines from uniform spacing, and that by measuring the deviation it was possible to find the nearest neighbor interaction. The departure from a purely magnetic dipolar interaction is smaller than previous measurements would indicate. It was found that EPR resonance at large values of H/T in magnetically concentrated crystals can yield accurate values of spin-spin interactions.
Date: August 1, 1970
Creator: King, A.R. & Jeffries, C.D.
Partner: UNT Libraries Government Documents Department