944 research outputs found
Hyperpolarization of 3-fluoropyridine via Signal Amplification by Reversible Exchange
Abstract. In nuclear magnetic resonance (NMR), inductive detection has been the only essential signal acquisition mechanism for decades. Recently, a fundamentally new way of detecting NMR, by observing nuclear spin-induced optical rotation (NSOR), was discovered. However, NSOR suffers from a poor signal-to-noise ratio (SNR), hindering its applications. One compelling way of improving the SNR by orders of magnitude is to use a relatively new hyperpolarization method called signal amplification by reversible exchange (SABRE).
The purpose of this thesis was to see whether SABRE could enable the NSOR signal detection of fluorine and to find ways to optimize an existing continuous-flow NSOR system. This involved studying the polarization transfer process in SABRE by performing several experiments with a 3-fluoropyridine sample.
The levels of obtained hyperpolarization were measured at different magnetic fields. Fluorine received the greatest levels of polarization at ultralow fields, whereas proton was hyperpolarized most effectively at milli-Tesla fields. This was attributed to the coherent polarization transfer at level anti-crossings (LACs). At magnetic field strengths where LACs are not present, the polarization transfer mechanism could not be unambiguously determined.
Measured relaxation times at different magnetic fields proved to be similar for fluorine and proton. At ultralow fields, the relaxation was rather quick (~ 3 s), whereas at low and high fields, slower relaxation was observed (~ 10 s). Therefore, having a well-defined magnetic field during the sample transfer would minimize the effects of relaxation and result in better levels of polarization.
Polarization build-up constants were measured at different magnetic fields. They were also quite comparable between the fluorine and the proton, while also being similar to the relaxation time constants. At ultralow fields, the polarization builds up fastest, which is a favourable result considering the continuous-flow NSOR system, as the sample is continuously pumped from the polarizing cell. Additionally, the fast build-up enables the use of faster pumping speeds to minimize the effects of relaxation during sample transfer
Wear properties of thermally sprayed tungsten-carbide coatings in paper machine environments
Thermally sprayed tungsten-carbide (WC) coatings have proven to be one of the most wear resistant coatings available and a respectable replacement for hard-chromium coatings. They are used in paper machine parts such as calender rolls. However, improved lifetime and performance are continuing considerations, as well as finding more economical alternatives. This study researched the wear phenomena of tungsten-carbide coatings in a paper machine environment. To achieve this, five different feedstock materials and coatings manufactured from these were compared by electron microscopy as well as dry abrasion-, high-speed slurry abrasion- and cavitation erosion tests. Improvements in ductility by changing the matrix material were found, while changing the particle strength had no effect on the behavior of the coatings. The findings suggest further research on altering the matrix of the feedstock could lead to overall improvements in coating quality and component lifetime
A comparison of estimates of mean annual precipitation from different proxies: a pilot study for the European Neogene
Peer reviewe
Frisbeegolfkiekon muodon vaikutus sen lentorataan
TiivistelmÀ. TÀssÀ tutkielmassa otetaan selvÀÀ, minkÀlaisia fysikaalisia ilmiöitÀ frisbeegolfkiekon lentÀmiseen liittyy, ja kuinka kiekon muoto vaikuttaa sen lentorataan. Ilmiöt, joihin tutkielmassa perehdytÀÀn, ovat aerodynaaminen noste, ilmanvastus ja gyroskooppinen vakaus. LisÀksi lukijalle tulee tutuksi frisbeegolfin historia sekÀ eri heitto- ja kiekkotyypit
Q_EC values of the Superallowed beta-Emitters 10-C, 34-Ar, 38-Ca and 46-V
The Q_EC values of the superallowed beta+ emitters 10-C, 34-Ar, 38-Ca and
46-V have been measured with a Penning-trap mass spectrometer to be 3648.12(8),
6061.83(8), 6612.12(7) and 7052.44(10) keV, respectively. All four values are
substantially improved in precision over previous results.Comment: 9 pages, 7 figures, 5 table
Isomeric states close to doubly magic Sn studied with JYFLTRAP
The double Penning trap mass spectrometer JYFLTRAP has been employed to
measure masses and excitation energies for isomers in Cd,
Cd, Cd and Te, for isomers in In and
In, and for isomers in Sn and Sb. These first
direct mass measurements of the Cd and In isomers reveal deviations to the
excitation energies based on results from beta-decay experiments and yield new
information on neutron- and proton-hole states close to Sn. A new
excitation energy of 144(4) keV has been determined for Cd. A good
agreement with the precisely known excitation energies of Cd,
Sn, and Sb has been found.Comment: 10 pages, 6 figures, submitted to Phys. Rev.
Beta-decay branching ratios of 62Ga
Beta-decay branching ratios of 62Ga have been measured at the IGISOL facility
of the Accelerator Laboratory of the University of Jyvaskyla. 62Ga is one of
the heavier Tz = 0, 0+ -> 0+ beta-emitting nuclides used to determine the
vector coupling constant of the weak interaction and the Vud quark-mixing
matrix element. For part of the experimental studies presented here, the
JYFLTRAP facility has been employed to prepare isotopically pure beams of 62Ga.
The branching ratio obtained, BR= 99.893(24)%, for the super-allowed branch is
in agreement with previous measurements and allows to determine the ft value
and the universal Ft value for the super-allowed beta decay of 62Ga
Precision mass measurements of radioactive nuclei at JYFLTRAP
The Penning trap mass spectrometer JYFLTRAP was used to measure the atomic
masses of radioactive nuclei with an uncertainty better than 10 keV. The atomic
masses of the neutron-deficient nuclei around the N = Z line were measured to
improve the understanding of the rp-process path and the SbSnTe cycle.
Furthermore, the masses of the neutron-rich gallium (Z = 31) to palladium (Z =
46) nuclei have been measured. The physics impacts on the nuclear structure and
the r-process paths are reviewed. A better understanding of the nuclear
deformation is presented by studying the pairing energy around A = 100.Comment: 4 pages and 4 figures, RNB7 conf. pro
Laser Spectroscopy of Niobium Fission Fragments: First Use of Optical Pumping in an Ion Beam Cooler Buncher
A new method of optical pumping in an ion beam cooler buncher has been developed to selectively enhance ionic metastable state populations. The technique permits the study of elements previously inaccessible to laser spectroscopy and has been applied here to the study of Nb. Model independent mean-square charge radii and nuclear moments have been studied for Nb to cover the region of the N=50 shell closure and Nâ60 sudden onset of deformation. The increase in mean-square charge radius is observed to be less than that for Y, with a substantial degree of ÎČ softness observed before and after N=60
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