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Spin Relaxation Times (spin + relaxation_time)
Selected AbstractsWide-ranging molecular mobilities of water in active pharmaceutical ingredient (API) hydrates as determined by NMR relaxation timesJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 10 2008Sumie Yoshioka Abstract In order to examine the possibility of determining the molecular mobility of hydration water in active pharmaceutical ingredient (API) hydrates by NMR relaxation measurement, spin,spin relaxation and spin,lattice relaxation were measured for the 11 API hydrates listed in the Japanese Pharmacopeia using pulsed 1H-NMR. For hydration water that has relatively high mobility and shows Lorentzian decay, molecular mobility as determined by spin,spin relaxation time (T2) was correlated with ease of evaporation under both nonisothermal and isothermal conditions, as determined by DSC and water vapor sorption isotherm analysis, respectively. Thus, T2 may be considered a useful parameter which indicates the molecular mobility of hydration water. In contrast, for hydration water that has low mobility and shows Gaussian decay, T2 was found not to correlate with ease of evaporation under nonisothermal conditions, which suggests that in this case, the molecular mobility of hydration water was too low to be determined by T2. A wide range of water mobilities was found among API hydrates, from low mobility that could not be evaluated by NMR relaxation time, such as that of the water molecules in pipemidic acid hydrate, to high mobility that could be evaluated by this method, such as that of the water molecules in ceftazidime hydrate. © 2008 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 97:4258,4268, 2008 [source] Synthesis and Evaluation of Water-Soluble Fluorinated Dendritic Block-Copolymer Nanoparticles as a 19F-MRI Contrast AgentMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 14 2010Michihiro Ogawa Abstract Well-defined water-soluble fluorinated polymer nanoparticles (PNPs) with a high fluorine content and biocompatibility were successfully prepared by living radical polymerization (LRP) of 2,2,3,3-tetrafluoropropyl methacrylate (TFPMA) from the polyamidoamine dendrimer macroinitiator (PAMAM-Br), and successive block polymerization of carboxybetaine monomer (CMB). The obtained core,shell type PNPs (PAMAM- g -PTFPMA- b -PCMB) showed high solubility in water and a sphere-like structure with a diameter in the range of 15,80,nm in water. The short 19F-NMR spin,lattice relaxation time (T1) (<250,ms) of PAMAM- g -PTFPMA- b -PCMB allowed the use of fast repetition time. The spin,spin relaxation time (T2) was evaluated to be as low as 10 ms. 19F-MRI in vitro signals can be detectable even at concentrations lower than 1 µM (particle concentration). These results demonstrate that a new type of 19F-MRI contrast agent can be developed by the molecular design using the dendrimer-initiated LRP method. [source] Hysteretic magnetoresistance in polymeric diodesPHYSICA STATUS SOLIDI - RAPID RESEARCH LETTERS, Issue 7-8 2009Sayani Majumdar Abstract We report on hysteretic organic magnetoresistance (OMAR) in polymeric diodes. We found that magnitude and lineshape of OMAR depend strongly on the scan speed of the magnetic field and on the time delay between two successive measurements. The time-dependent OMAR phenomenon is universal for diodes made with various polymers. However, the width and magnitude of OMAR varied with the polymeric material. The suggestive reason for this hysteretic behavior is trapped carriers, which in presence of a magnetic field change the ferromagnetic ground-state of the polymer leading to a long spin relaxation time. These experimental observations are significant for clarification of the OMAR phenomenon. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Spin polarization of a non-magnetic high g-factor semiconductor at low magnetic fieldPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 12 2007J. Lee Abstract We have studied the spin polarization of HgCdTe by measuring Shubnikov-de Haas oscillations. The magnetic field have been applied in parallel and perpendicular to the current. Relatively long spin relaxation time was observed since only spin conserved transition is allowed by selection rules. The electronic spin is completely polarized when the applied magnetic field is larger than 0.5 Tesla, which can be easily generated by micromagnets deposited on the surface of the specimen. Thus, the spin-manipulation such as spin up/down junction can be realized with this semiconductor. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Measurements by MRI of the settling and packing of solid particles from aqueous suspensionsAICHE JOURNAL, Issue 6 2009Julio Acosta-Cabronero Abstract This study extends the application of existing magnetic resonance imaging methods to measure the settling of solid particles from aqueous suspensions. The acquisition of one-dimensional multiecho projections allowed the direct measurement of initial magnetizations (M0), from which solid volume fractions along the sedimentation column were inferred. For polystyrene beads, it was found that monoexponential curves accurately fitted the transverse relaxation decays. In contrast, for the other four solids investigated (activated carbon, talc, calcium carbonate, and glass beads), the single exponential model did not suffice and additional terms in the fitting function significantly improved the calculation of solid concentrations. Additional information about particle sizes was obtained by comparing volume fractions with the spin,spin relaxation times of the hydrogen protons as a function of the vertical height through the sedimenting suspensions of activated carbon and polystyrene beads. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] 17O relaxation time and NMR sensitivity of cerebral water and their field dependenceMAGNETIC RESONANCE IN MEDICINE, Issue 4 2001Xiao-Hong Zhu Abstract 17O spin relaxation times and sensitivity of detection were measured for natural abundance H217O in the rat brain at 4.7 and 9.4 Tesla. The relaxation times were found to be magnetic field independent (T2 = 3.03 ± 0.08 ms, T = 1.79 ± 0.04 ms, and T1 = 4.47 ± 0.14 ms at 4.7T (N = 5); T2 = 3.03 ± 0.09 ms, T = 1.80 ± 0.06 ms, and T1 = 4.84 ± 0.18 ms at 9.4T (N = 5)), consistent with the concept that the dominant relaxation mechanism is the quadrupolar interaction for this nucleus. The 17O NMR sensitivity was more than fourfold higher at 9.4T than at 4.7T, for both the rat brain and a sodium chloride solution. With this sensitivity gain, it was possible to obtain localized 17O spectra with an excellent signal-to-noise ratio (SNR) within 15 s of data acquisition despite the relatively low gyromagnetic ratio of this nucleus. Such a 15-s 2D 17O-MRS imaging data set obtained for natural abundance H217O in the rat brain yielded an SNR greater than 40:1 for a ,16,l voxel. This approach was employed to measure cerebral blood flow using a bolus injection of H217O via one internal carotid artery. These results demonstrate the ability of 17O-MRS imaging to reliably map the H217O dynamics in the brain tissue, and its potential for determining tissue blood flow and oxygen consumption rate changes in vivo. Magn Reson Med 45:543,549, 2001. © 2001 Wiley-Liss, Inc. [source] 23Na and 87Rb relaxation study of the structural phase transitions in the Tutton salts Na2Zn(SO4)2·6H2O and Rb2Zn(SO4)2·6H2O single crystalsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 5 2010Ae Ran Lim Abstract The NMR spectrum, spin,lattice relaxation times, T1, and the spin,spin relaxation times, T2, for the 23Na and 87Rb nuclei in Tutton salts Na2Zn(SO4)2·6H2O and Rb2Zn(SO4)2·6H2O single crystals were determined by using an FT NMR spectrometer. The NMR spectrum and relaxation times for the 23Na and 87Rb nuclei in two crystals undergo significant changes near TC. These changes close to TC were the only detectable result of the structural transformation; the change is due to the fact that the electric field gradient value becomes 0. Especially, T1 and T2 for 87Rb in the Rb2Zn(SO4)2·6H2O crystals at high temperature have similar values on the order of milliseconds, which is indicative of a liquid-like system. The motion giving rise to this liquid-like behavior is probably related to superionic motion at high temperature. [source] Nanosecond spin memory of electrons in CdTe/CdMgTe quantum wellsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 4 2006G. V. Astakhov Abstract We report on spin memory relaxation time ,s of free electrons in CdTe-based quantum wells which is found to be in the nanosecond range. In these studies two different techniques have been exploited: (i) the Hanle effect under cw excitation and (ii) the time-resolved pump-&-probe Kerr rotation measured under excitation by 1.8-ps optical pulses. These independent techniques give very close results ,s ns and ,s = 14 ns, respectively. To our knowledge this is by two orders of magnitude longer than the electron spin relaxation times reported for CdTe-based quantum wells so far. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Tuning the magnetic properties of ZnCdSe/ZnSe quantum dots by thermal annealingPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 11 2006E. Margapoti Abstract Photoluminescence of ZnCdSe/ZnSe quantum dots treated by thermal annealing is investigated in magnetic fields up to 6 T. Thermal annealing leads to considerable changes of the circular polarization properties, which we attribute to different spin relaxation times and exciton lifetimes. A negative diamagnetic shift is observed for quantum dots showing the largest TA-induced shift of 80 meV. Possible origins are discussed. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | |||||||||||||