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231.
M.L. Bissell K.T. Flanagan M.D. Gardner M. Avgoulea J. Billowes P. Campbell B. Cheal T. Eronen D.H. Forest J. Huikari A. Jokinen I.D. Moore A. Nieminen H. Penttilä S. Rinta-Antila B. Tordoff G. Tungate J. Äystö 《Physics letters. [Part B]》2007
We report changes in mean-square charge radii, δ〈r2〉, magnetic moments and quadrupole moments for three multi-quasi particle isomers; 97m2Y, 176mYb and 178m1Hf. All the isomers are observed to display a decrease in 〈r2〉 compared to the lower-lying nuclear state on which the isomer is built. The decreases in 〈r2〉 occur despite the isomers showing increases in quadrupole moment. Possible mechanisms for the effect, which is now seen for six multi-quasi particle isomers, are discussed. 相似文献
232.
Busygin I Nieminen V Taskinen A Sinkkonen J Toukoniitty E Sillanpää R Murzin DY Leino R 《The Journal of organic chemistry》2008,73(17):6559-6569
Structures and conformational behavior of several cinchona alkaloid O-ethers in the solid state (X-ray), in solution (NMR and DFT), and in the gas phase (DFT) were investigated. In the crystal, O-phenylcinchonidine adopts the Open(3) conformation similar to cinchonidine, whereas the O-methyl ether derivatives of both cinchonidine and cinchonine are packed in the Closed(1) conformation. Dynamic equilibria in solutions of the alkaloids were revealed by combined experimental-theoretical spin simulation/iteration techniques for the first time. In the (1)H NMR spectra in CDCl3 and toluene-d8 at room temperature, Closed(1) conformation was observed for the O-silyl ethers as a separate set of signals. For O-methyl ether derivatives Closed(1) could be separated only at -30 degrees C in CDCl3 or toluene-d8 and for O-phenylcinchonidine at -70 degrees C in CDCl3/CD2Cl2. The ratio between the Closed(2) and Open(3) conformers was estimated by analyzing the vicinal coupling constant (3)J(H9,H8) at ambient and low temperatures. The observed conformational equilibria of O-(tert-butyldimethylsilyl)cinchonidine in CDCl 3 and toluene-d8 are in good agreement with the theoretically estimated equilibrium populations of the conformations according to Boltzmann statistics. The conformational equilibria of four cinchona alkaloid O-ether solutes in CDCl3 and toluene-d8 are discussed in the light of their relevance to the mechanism of 1-phenyl-1,2-propanedione (PPD) hydrogenation over cinchona alkaloid modified heterogeneous platinum catalysts. It was demonstrated that the conformation found to be abundant in the liquid phase has no direct correlation with the enantioselectivity of the PPD hydrogenation reaction. 相似文献
233.
Calculation and optical measurement of laser trapping forces on non-spherical particles 总被引:1,自引:0,他引:1
T. A. Nieminen H. Rubinsztein-Dunlop N. R. Heckenberg 《Journal of Quantitative Spectroscopy & Radiative Transfer》2001,70(4-6):627-637
Optical trapping, where microscopic particles are trapped and manipulated by light is a powerful and widespread technique, with the single-beam gradient trap (also known as optical tweezers) in use for a large number of biological and other applications. The forces and torques acting on a trapped particle result from the transfer of momentum and angular momentum from the trapping beam to the particle. Despite the apparent simplicity of a laser trap, with a single particle in a single beam, exact calculation of the optical forces and torques acting on particles is difficult. Calculations can be performed using approximate methods, but are only applicable within their ranges of validity, such as for particles much larger than, or much smaller than, the trapping wavelength, and for spherical isotropic particles. This leaves unfortunate gaps, since wavelength-scale particles are of great practical interest because they are readily and strongly trapped and are used to probe interesting microscopic and macroscopic phenomena, and non-spherical or anisotropic particles, biological, crystalline, or other, due to their frequent occurance in nature, and the possibility of rotating such objects or controlling or sensing their orientation. The systematic application of electromagnetic scattering theory can provide a general theory of laser trapping, and render results missing from existing theory. We present here calculations of force and torque on a trapped particle obtained from this theory and discuss the possible applications, including the optical measurement of the force and torque. 相似文献
234.
M. Leino H. Kankaanpää R.-D. Herzberg A.J. Chewter F.P. Heßberger Y. Le Coz F. Becker P.A. Butler J.F.C. Cocks O. Dorvaux K. Eskola J. Gerl P.T. Greenlees K. Helariutta M. Houry G.D. Jones P. Jones R. Julin S. Juutinen H. Kettunen T.L. Khoo A. Kleinböhl W. Korten P. Kuusiniemi R. Lucas M. Muikku P. Nieminen R.D. Page P. Rahkila P. Reiter A. Savelius Ch. Schlegel Ch. Theisen W.H. Trzaska H.-J. Wollersheim 《The European Physical Journal A - Hadrons and Nuclei》1999,6(1):63-69
235.
G. Lhersonneau P. Dendooven G. Canchel J. Huikari P. Jardin A. Jokinen V. Kolhinen C. Lau L. Lebreton A.C. Mueller A. Nieminen S. Nummela H. Penttilä K. Peräjärvi Z. Radivojevic V. Rubchenya M.-G. Saint-Laurent W.H. Trzaska D. Vakhtin J. Vervier A.C.C. Villari J.C. Wang J. Äystö 《The European Physical Journal A - Hadrons and Nuclei》2000,9(3):385-396
In the context of a parameter study conducted by several laboratories for future European radioactive beam facilities based
on fast-neutron induced fission, in particular for the SPIRAL-II project at GANIL, we have measured the yields of neutron-rich
isotopes in the mass range of 88 to 144. These nuclei were obtained as fission products of natural uranium bombarded by neutrons
of 20 MeV average energy emitted by a thick carbon target irradiated by 50 MeV deuterons. Yields have been measured using
on-line mass separation with the ion-guide method. Compared with proton-induced fission at 25 MeV the magnitude of cross-sections,
except for the symmetric region, is similar. Z-distributions of isobars have the same width, 0.7 charge units, but their maxima are shifted by about 0.8 charge units, favouring
production of the neutron-richer isobars. Our data allow calculations of absolute cross-sections for fission of natural uranium
induced by neutrons of about 20 MeV.
Received: 10 July 2000 / Accepted: 27 October 2000 相似文献
236.
J. Kurpeta A. Andreyev J. Äystö A.-H. Evensen M. Huhta M. Huyse A. Jokinen M. Karny E. Kugler J. Lettry A. Nieminen A. Płochocki M. Ramdhane H.L. Ravn K. Rykaczewski J. Szerypo P. Van Duppen G. Walter A. Wöhr 《The European Physical Journal A - Hadrons and Nuclei》2000,7(1):49-54
The decay of the neutron–rich isotope 216Bi, produced by proton–induced spallation at the PS Booster–ISOLDE facility, was investigated by β-γγ, αγ coincidence and
spectrum-multiscaling measurements. A new method for reducing isobaric contamination enabled to cover the unknown region “east”
of 208Pb for the isobaric chain A=216. The half-life of the β decay of 216Bi was found as T1/2= 135 ± 5 s. Its decay scheme was extended and the possible shell model configurations are proposed.
Received: 13 July 1999 / Revised version: 22 September 1999 相似文献
237.
Abstract In earlier studies on the oxidation of monosaccharides, we measured the rates of the oxidation of three aldohexoses, two ketohexoses and three aldopentoses with V(V),1 Ce(IV)2Cr(VI)3 and MII(VII).4We now report on the corresponding oxidations with bromate ion and N-bromosuccinimide (NBS) as oxidants. To our knowledge, only kinetic studies of oxidations of ribose with BrO3-in aqueous H2O4 5 and aldoses with NBS in 10% AcOH - H2SO4 6 have been reported. Because oxidation of carbohydrates is subject to HSO4- ion catalysis, HClO4 was used, as in our earlier studies, in the present investigation to minimize the number of different catalyzing species. 相似文献
238.
Calculations of positron and positronium atom work functions in transition metals are described with an analysis of the surface and internal contributions. Negative work functions are obtained for elements towards the centre of the transition series, in qualitative agreement with experimental observations. 相似文献
239.
Diffusion tensor imaging (DTI) is potentially sensitive to collagen degeneration in cartilage. In this study, DTI was measured on human cartilage samples with interventions of trypsin and collagenase. The measured preferred diffusion direction was consistent with the zonal structure of collagen network. The glycosaminoglycan concentration decreased and apparent diffusion coefficient increased with both interventions. The fractional anisotropy (FA) was not affected by trypsin and showed a slight increase with combined trypsin and collagenase intervention. DTI in cartilage is technically challenging due to the low FA and the almost undetectable change with collagen disruption seen here. 相似文献
240.
H. Saarikoski A. Harju M.J. Puska R.M. Nieminen 《Physica E: Low-dimensional Systems and Nanostructures》2005,26(1-4):317
We study electronic structures of two-dimensional quantum dots in high magnetic fields using the density-functional theory (DFT) and the exact diagonalization (ED). With increasing magnetic field, beyond the formation of the totally spin-polarized maximum density droplet (MDD) state, the DFT gives the ground-state total angular momentum as a continuous function with well-defined plateaus. The plateaus agree well with the magic angular momenta of the ED calculation. By constructing a conditional wave function from the Kohn–Sham states we show that vortices enter the quantum dot one-by-one at the transition to the state with the adjacent magic angular momentum. Vortices are also observed outside the high-density region of the quantum dot. These findings are compared to the ED results and we report a significant agreement. We also study interpretations and limitations of the density functional approach in these calculations. 相似文献