Search results for "Trap"
showing 10 items of 2144 documents
Trapped ion density distribution in the presence of He-buffer gas
1981
The spatial density distribution of Ba+ ions, confined in a rf quadrupole trap, has been measured by laser scanning across the trap. This allows to determine the ion temperature, assuming thermal equilibrium. Under UHV conditions the average ion energy has been found to be one tenth of the trap potential well depth. Collisions with He at pressures up to 5×10−6 mbar reduce the ion temperature by a factor of 3.
Feasibility of In-Trap Conversion Electron Spectroscopy
2001
We have used REXTRAP at ISOLDE to test the feasibility of in-trap electron spectroscopy. The results of calculations, experiments with various electron sources as well as a first test with trapped radioactive ions are presented.
Spin dependence of low energy charge exchange between H 2 + and Na
1987
The difference in charge exchange rate in collisions between spin oriented sodium atoms and H 2 + ions has been measured at an energy of about 1 eV. H 2 + was stored in a Penning trap and polarized by spin exchange with Na beam atoms from a hexapole magnet. The ion loss from the trap due to charge exchange was different as we depolarized the atomic beam. From the data we obtain a ratio of cross sections for singlet and triplet collisionsQ 1/Q 3=1.5±0.2 andQ 3=1.2·10−15 cm2.
Ion traps in nuclear physics : recent results and achievements
2016
Ion traps offer a way to determine nuclear binding energies through atomic mass measurements with a high accuracy and they are routinely used to provide isotopically or even isomerically pure beams of short-living ions for post-trap decay spectroscopy experiments. In this review, different ion-trapping techniques and progresses in recent nuclear physics experiments employing low-energy ion traps are discussed. The main focus in this review is on the benefit of recent high accuracy mass measurements to solve some key problems in physics related to nuclear structure, nuclear astrophysics as well as neutrinos. Also, several cases of decay spectroscopy experiments utilizing trap-purified ion sa…
Trapping and mobilization of residual fluid during capillary desaturation in porous media
1998
We discuss the problem of trapping and mobilization of nonwetting fluids during immiscible two-phase displacement processes in porous media. Capillary desaturation curves give residual saturations as a function of capillary number. Interpreting capillary numbers as the ratio of viscous to capillary forces the breakpoint in experimental curves contradicts the theoretically predicted force balance. We show that replotting the data against a novel macroscopic capillary number resolves the problem for discontinuous mode displacement.
Direct to Indirect Crossover in III-VI Layered Compounds and Alloys under Pressure
1999
The pressure dependence of the optical absorption edge of In1± xGaxSe (0 < x < 0.2) and GaTe has been investigated in order to determine the direct to indirect crossover pressure and the energy difference between the absolute and subsidiary minima of the conduction band at ambient pressure. In the In1± xGaxSe alloy, the crossover pressure decreases with increasing Ga proportion. For InSe, from the extrapolation to x = 0 the band crossover is found to occur at 4.3 GPa and the subsidiary minimum of the conduction band is located, at ambient pressure, (0.32 0.02) eV above the absolute minimum. In addition, the energy difference between the conduction band minima is shown to decrease linearly w…
Critical phenomena in colloid-polymer mixtures: interfacial tension, order parameter, susceptibility, and coexistence diameter.
2004
The critical behavior of a model colloid-polymer mixture, the so-called AO model, is studied using computer simulations and finite size scaling techniques. Investigated are the interfacial tension, the order parameter, the susceptibility and the coexistence diameter. Our results clearly show that the interfacial tension vanishes at the critical point with exponent 2\nu ~ 1.26. This is in good agreement with the 3D Ising exponent. Also calculated are critical amplitude ratios, which are shown to be compatible with the corresponding 3D Ising values. We additionally identify a number of subtleties that are encountered when finite size scaling is applied to the AO model. In particular, we find …
Natura e caratteristiche del consenso al prelievo di organi e tessuti da cadavere. Un raffronto tra Italia ed Inghilterra
2018
Il saggio affronta il tema del prelievo degli organi e tessuti da cadavere, al fine di destinarli ai trapianti. Il fuoco dell’indagine è concentrato sulla natura e sulle caratteristiche del consenso che legittima il prelievo stesso, in modo da valutare il rapporto tra la volontà del potenziale donatore e l’interesse sociale alla disponibilità, più ampia possibile, di parti anatomiche utili al beneficio altrui. Lo studio, dopo avere affrontato le questioni poste dalla disciplina italiana, prende in esame le soluzioni adottate nel contesto giuridico inglese, al fine di valutarne le potenzialità applicative in seno al diritto interno. The essay deals with the deceased donor organ donations and…
High Order Extrapolation Techniques for WENO Finite-Difference Schemes Applied to NACA Airfoil Profiles
2017
Finite-difference WENO schemes are capable of approximating accurately and efficiently weak solutions of hyperbolic conservation laws. In this context high order numerical boundary conditions have been proven to increase significantly the resolution of the numerical solutions. In this paper a finite-difference WENO scheme is combined with a high order boundary extrapolation technique at ghost cells to solve problems involving NACA airfoil profiles. The results obtained are comparable with those obtained through other techniques involving unstructured meshes.