25 research outputs found

    Nuclear Spin-Lattice Relaxation in Taurine

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    The temperature dependence of the spin-lattice relaxation time Ti in taurine was studied between - 130° C and + 12° C. A value of (T1)min = 24 msec was obtained in quite good agreement witlp. some other results. The difference between this and the theor~tical value of (T1 )min was explained by the relaxation of CH2 protons via the NH3 protons. An activation energy Ea. = 4.6 kcal/rriole has been .calculated. This value was ascribed to the NH; gr9up motion

    A Proton Magnetic Resonance Study of Rotational Motion of NH3 Group in Solids

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    The variations in PMR line parameters of taurine [NH; CH2CH2so; J and E-aminocaproic acid [NH; (CH2)5Coo-1 were studied in a wide temperature region. They were explained in terms of rotational motion of NH; group. The energy barriers hindering such a motion were calculated, and they are V 0 = 5.0 kcal mo1e-1 for taurine, and V0 = 9.0 kcal mo1e-1 for E-aminocaproic acid. The influence of hydrogen bond length N - H . . . O and position of NH; group in a molecule upon the extent of hindering, were shown

    The photo-neutrino process in astrophysical systems

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    Explicit expressions for the differential and total rates and emissivities of neutrino pairs from the photo-neutrino process e±+γe±+ν+νˉe^\pm + \gamma \to e^\pm + \nu + \bar\nu in hot and dense matter are derived. Full information about the emitted neutrinos is retained by evaluating the squared matrix elements for this process which was hitherto bypassed through the use of Lenard's identity in obtaining the total neutrino emissivities. Accurate numerical results are presented for widely varying conditions of temperature and density. Analytical results helpful in understanding the qualitative behaviors of the rates and emissivities in limiting situations are derived. The corresponding production and absorption kernels in the source term of the Boltzmann equation for neutrino transport are developed. The appropriate Legendre coefficients of these kernels, in forms suitable for multigroup flux-limited diffusion schemes are also provided.Comment: 26 pages and 7 figures. Version as accepted in Phys. Rev. D; three figures and related discussion revise

    Differential Neutrino Rates and Emissivities from the Plasma Process in Astrophysical Systems

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    The differential rates and emissivities of neutrino pairs from an equilibrium plasma are calculated for the wide range of density and temperature encountered in astrophysical systems. New analytical expressions are derived for the differential emissivities which yield total emissivities in full agreement with those previously calculated. The photon and plasmon pair production and absorption kernels in the source term of the Boltzmann equation for neutrino transport are provided. The appropriate Legendre coefficients of these kernels, in forms suitable for multi-group flux-limited diffusion schemes are also computed.Comment: 27 pages and 10 figures. Submitted to Phys. Rev.

    1H and 31P NMR investigation of gadolinium uptake in maize roots

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    Low-resolution 1H NMR and high-resolution 31P NMR were used to study the absorption of gadolinium (Gd) by the root tissues of maize seedlings. Gd was supplied as either Gd3+ or Gd(DTPA)2-, and its presence in the tissue caused changes in the relaxation properties of the tissue water and of various phosphorylated metabolites. 1H NMR relaxation measurements indicated that soluble Gd accumulated in the tissue more rapidly with Gd(DTPA)2- than with Gd3+, and this was attributed to the precipitation of Gd3+ in the root. Electron microscopy and x-ray microanalysis confirmed the presence of deposits containing Gd and phosphorus (P) in the extracellular space of the tissue. 31P NMR showed the presence of soluble Gd in both the cytoplasm and the vacuole of roots treated with Gd3+ and, thus, proved that Gd3+ can reach the symplast, contrary to the usual assumption about the lanthanides. Evidence for the immobilization of P by Gd3+ and for the vacuolar breakdown of Gd(DTPA)2- was also obtained from the 31P NMR spectra. © 1990

    H-1 AND P-31 NMR INVESTIGATION OF GADOLINIUM UPTAKE IN MAIZE ROOTS

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    Low-resolution 1H NMR and high-resolution 31P NMR were used to study the absorption of gadolinium (Gd) by the root tissues of maize seedlings. Gd was supplied as either Gd3+ or Gd(DTPA)2-, and its presence in the tissue caused changes in the relaxation properties of the tissue water and of various phosphorylated metabolites. 1H NMR relaxation measurements indicated that soluble Gd accumulated in the tissue more rapidly with Gd(DTPA)2- than with Gd3+, and this was attributed to the precipitation of Gd3+ in the root. Electron microscopy and x-ray microanalysis confirmed the presence of deposits containing Gd and phosphorus (P) in the extracellular space of the tissue. 31P NMR showed the presence of soluble Gd in both the cytoplasm and the vacuole of roots treated with Gd3+ and, thus, proved that Gd3+ can reach the symplast, contrary to the usual assumption about the lanthanides. Evidence for the immobilization of P by Gd3+ and for the vacuolar breakdown of Gd(DTPA)2- was also obtained from the 31P NMR spectra. © 1990

    Water exchange in plant tissue studied by proton NMR in the presence of paramagnetic centers.

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    The proton NMR relaxation of water in maize roots in the presence of paramagnetic centers, Mn2+, Mn- EDTA2 -, and dextran-magnetite was measured. It was shown that the NMR method of Conlon and Outhred (1972, Biochem. Biophys. Acta. 288:354-361) can be applied to a heterogenous multicellular system, and the water exchange time between cortical cells and the extracellular space can be calculated. The water exchange is presumably controlled by the intracellular unstirred layers. The Mn- EDTA2 - complex is a suitable paramagnetic compound for complex tissue, while the application of dextran-magnetite is probably restricted to studies of water exchange in cell suspensions. The water free space of the root and viscosity of the cells cytoplasm was estimated with the use of Mn- EDTA2 -. The convenience of proton NMR for studying the multiphase uptake of paramagnetic ions by plant root as well as their transport to leaves is demonstrated. A simple and rapid NMR technique (spin-echo recovery) for continuous measurement of the uptake process is presented

    Enhancing capacity for social justice work within the academy: Building critical consciousness

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    In this article, we explore our experience of carving out space within an academic program where we were able to engage in learning and teaching that enhanced our capacity to understand foundational literature in the Socio/Cultural Field of Study and work towards our social justice goals. The doctoral course described provided the conditions (environmental and social) we needed to support our questioning of disciplinary and personal knowledge and experience and ‘to see the limitations and lacunae in our understandings’ (Burbules and Berk 1999, 61). Data collected during the course included: audio-taped class sessions, weekly written responses/reflections, and final papers
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