1,338 research outputs found
Effect of B-y in three-dimensional reconnection at the dayside magnetopause
No full textAsymmetric magnetic reconnection with a non-zero B-y component is studied using a three-dimensional magnetohydrodynamic simulation and the results are interpreted in terms of the dayside reconnection at the magnetopause. The B-y component is implemented by rotating the magnetosheath field. It is seen that a magnetic bulge is formed in the magnetosheath region but displaced in the y direction due to the tilted magnetic field line geometry of reconnection. The bulge moves away from the reconnection region along the magnetopause with a speed significantly slower than that of the symmetric case. In fact, the reconnection rate is seen much slower than the symmetric case. It is also seen that the reconnection rate decreases as the angle of rotation increases. The discontinuity associated with magnetic reconnection geometry is identified as a slow shock with Alfven waves attached to it on the magnetospheric side, while on the magnetosheath side an intermediate shock is seen, which evolves into a slow shock and a rotational discontinuity near the center of the bulge and near the y-directional edges of the current disruption region. A large B-y component is generated on the open field lines, exceeding the initial sheath B-y near the center of the bulge. The inflow mass flux into the reconnection region from the magnetosheath is seven times larger than that from the magnetosphere in the present study, while the outflow mass flux into the magnetosphere is five times larger than that into the magnetosheath, implying that a significant mass transfer occurs from the magnetosheath into the magnetosphere. The outflow plasmas move mostly along the magnetic field lines in the downstream and transported toward the polar region. (C) 2002 American Institute of Physics
Polymeric micelles and the Dy-166/Ho-166 generator: A study of the loading mechanism of Dy/Dy-166 and Ho-166 into PCL-b-PEO polymeric micelles for imaging and cancer treatment
No full textA radioisotope used in radionuclide therapy is Holmium-166 (Ho-166). The treatment effectiveness of Ho-166 could be improved by the use of a so called in vivo Dysprosium-166(Dy-166)/Ho-166 generator. The application of this generator is hindered by an effect called internal conversion (IC). This affect can arise after the decay of Dy-166 to Ho-166, which can cause separation of Ho-166 from its carrier.Polymeric micelles might form a solution in the application of the Dy-166/Ho-166 generator in radionuclide therapy. The main goal of this thesis was to investigate and understand the loading mechanism of metallic species and polymeric micelles with a focus on the loading of Dy/Dy-166 and Ho-166. It was found that it was not effective to load metallic species (Dy/Dy-166) as free ions or as solid precipitates. Loading metallic species as aqueous hydroxides showed to be crucial for achieving a good loading and high stability. The second goal was to study if polymeric micelles were able to retain Ho-166 inside their core under the effects of internal conversion. No additional losses of Ho-166 were found when Dy/Dy-166 and Ho-166 were loaded into the micelles. It was concluded that the PCL-PEO micelles prevented the loss of Ho-166 under internal conversion effects.Applied Science
How are storm time injections different from nonstorm time injections?
No full textOne of the key elements of storms and substorms is the injection of energetic particles into the region of near geosynchronous orbit, that is, the sudden flux enhancement in the energy range of tens to hundreds of KeV. This paper reports the observational results on how such injection features during storm times are different from those of nonstorm times. We particularly focus on the difference between proton injections and electron in injections. Based on a number of storm time injection events that meet our strict selection criteria, we find a notable difference between proton injections and electron injections in the energy-spectral dependence of the flux enhancement averaged over the first 30min after the injection onset: The average flux enhancement of many protons injections tends to be bigger at higher energy channels than at lower energy channels, but electron injections exhibit the opposite tendency for the energy-spectral dependence of flux enhancement, i.e., average flux enhancement decreasing with increasing energy. We show that this feature is almost unique only for the injection events during the storm main and early recovery phase. It is suggested that any successful scenario intended to model storm time injections should be able to explain this difference between proton injections and electron injections. (C) 2004 Elsevier Ltd. All rights reserved
beta-delayed proton decays and spin assignments for Tb-140, Dy-141 and Dy-143
No full textThe proton-rich isotopes Tb-140 and Dy-141 were produced via the fusion evaporation reaction Ca-40+ Cd-106. Their beta-delayed proton decays were studied by p-gamma coincidence in combination with a He-jet tape transport system, and half-lives, proton energy spectra, gamma-transitions following the proton emission, as well as beta-delayed proton branching ratios to the low-lying states in the grand-daughter nuclei were determined. Comparing the experimental data with statistical model calculations, the ground-state spins of Tb-140 and Dy-141 were found to be consistent with 7 and 9/2, respectively. The configuration-constrained nuclear potential energy surfaces (NPES) of Tb-140 and Dy-141 were calculated using the Woods-Saxon-Strutinsky method, which suggest the ground-state spins and parities of Tb-140 and Dy-141 to be 7(+) and 9/2(-), respectively. In addition, the configuration-constrained NPES of Dy-143 were calculated, which predict a 1/2(+) ground state and a 11/2(-) isomer with excitation energy of 198 keV. These findings are consistent with our previous experimental data on Dy-143 reported in Eur. Phys. J. A 16, 347 (2003).Physics, NuclearPhysics, Particles & FieldsSCI(E)3ARTICLE137-402
Direct numerical simulation of turbulent Couette-Poiseuille flow with zero skin friction
No full textThe near-wall scaling of mean velocity U(y) is addressed for the case of zero skin friction on one wall of a fully turbulent channel flow. The present DNS results can be added to the evidence in support of the conjecture that U is proportional to √yw in the region just above the wall at which the mean shear dU/dy = 0
Iron oxide nanoparticles as carriers for the Dy-166/Ho-166 in vivo generator: A study into the characteristics and retention of Dy and Ho in iron oxide nanoparticles
No full textBackground:Cancer is one of the leading causes of death worldwide. Targeted radionuclide therapy has become a important treatment, this is when a carrier molecule is attached to a radionuclide to deliver cytotoxic radiation levels to diseased cells. β− emitters are frequently used in RNT because they have a long penetration depth, such as the dysprosium-166/holmium-166 (166Dy/166Ho) in vivo generator. The 166Dy/166Ho in vivo generator shows great potential for large tumors because of the long half-life time of the mother nuclide 166Dy and the emission of high energy β− from the daughter nuclide 166Ho. Previous research shows the release of 72 % of the 166Ho when 166Ho is bound to conventional chelators due to internal conversion after the β− decay. The aim of this thesis is to synthesize an iron oxide nanoparticle as carrier for the 166Dy/166Ho in vivo generator. This iron oxide nanoparticles (SPIONs) should prevent internal conversion and thus the loss of the daughter nuclide 166Ho.Results:The dysprosium doped iron oxide nanoparticles were synthesized successfully with an average diameter of 6.1 ± 1.5 nm, measured with TEM. The DLS and TEM results showed that the SPIONs were aggregating. The labeling efficiency represents how much Dy is retained in the Dy doped SPIONs, for the non-radioactive Dy this was measured with the ICP/OES. The labelling efficiency was 3.21 ± 0.8 %. The 166Dy doped iron oxide nanoparticles were also synthesized successfully with a radiolabelling efficiency of 3.12 ± 2.2 %, measured with a 2480 Wizard 2 Gamma counter. The retention of 166Dy + 166Ho was 79.2 ± 1.8 % after 96 h.Conclusion:The retention of 166Dy + 166Ho in iron oxide nanoparticles was 79.2±1.8 % after 96 hours. This is much higher than the retention of 28% by conventional chelators. This means that the iron oxide nanoparticls is a safer carrier for the 166Dy/166Ho in vivo generator than the conventional chelator.Applied Physic
Carrier recombination processes and divalent lanthanide spectroscopy in YPO4:Ce3+;L3+ (L=Sm,Dy,Tm)
No full textWe studied charge carrier trapping, detrapping, and recombination phenomena in Ce3+ doped YPO4, codoped with Sm3+, Dy3+, or Tm3+. Ce ions trap the holes and Sm, Dy, and Tm trap electrons created during x-ray irradiation. By means of red to infrared stimulation, the trapped electrons can be back transferred to Ce leading to shorter wavelength Ce3+?5d-4f luminescence. Excitation spectra for this recombination luminescence were recorded from 10 K to room temperature. It provides information on the excited state energies of divalent Sm, Dy, and Tm with respect to the lanthanide ground state energy and with respect to the mobility edge energy of YPO4. From the temperature dependence, insight is obtained on the carrier recombination pathways. We will identify temperature independent tunneling recombination, recombination by thermal excitation to the conduction band, and phonon-assisted delocalization of electrons from impurity states within the conduction band.QN/Quantum NanoscienceApplied Science
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