Ultra-Precise Mass Measurements Using the UW-PTMS

Based on the use of a single ion, isolated at the center of a cryogenically cooled Penning trap, an environment is produced which makes this mass spectrometer remarkably free of systematic errors. The most notable developments in our quest for an ultra-high accuracy instrument were (a) the compensation of the trapping potential, (b) the discovery that motional sidebands could manipulate radial energies, (c) the use of multiply-charged ions that could improve signal-to-noise, and (d) the use of an ultra-stable superconducting magnet/cryostat system with drift <0.010 ppb/h. The dominant systematic errors are associated with radial electric fields caused by image charges in the trap electrodes and with the rf-electrical drive field used to determine the harmonic axial resonance. To illustrate the potential of this improved spectrometer, the four-fold improved measurement of the proton's mass and the eight-fold improved measurement of oxygen's atomic mass will be described. This revised version was published online in July 2006 with corrections to the Cover Date.     

Preconditioned iterative methods for coupled discretizations of fluid flow problems

Computational fluid dynamics, where simulations require largecomputation times, is one of the areas of application of highperformance computing. Schemes such as the SIMPLE (semi-implicitmethod for pressure-linked equations) algorithm are often usedto solve the discrete Navier-Stokes equations. Generally theseschemes take a short time per iteration but require a largenumber of iterations. For simple geometries (or coarser grids)the overall CPU time is small. However, for finer grids or morecomplex geometries the increase in the number of iterationsmay be a drawback and the decoupling of the differential equationsinvolved implies a slow convergence of rotationally dominatedproblems that can be very time consuming for realistic applications.So we analyze here another approach, DIRECTO, that solves theequations in a coupled way. With recent advances in hardwaretechnology and software design, it became possible to solvecoupled Navier-Stokes systems, which are more robust but implyincreasing computational requirements (both in terms of memoryand CPU time). Two approaches are described here (band blockLU factorization and preconditioned GMRES) for the linear solverrequired by the DIRECTO algorithm that solves the fluid flowequations as a coupled system. Comparisons of the effectivenessof incomplete factorization preconditioners applied to the GMRES(generalized minimum residual) method are shown. Some numericalresults are presented showing that it is possible to minimizeconsiderably the CPU time of the coupled approach so that itcan be faster than the decoupled one.     

Preparation, structural analysis and dielectric properties of Bi x La1−x FeO3 perovskite

Rare earth element substituted bismuth ferrites (BiFeO₃) are of enormous importance as magnetoelectric materials. The polycrystalline samples of Bi _x La_1−x FeO₃ (x=0, 0.2, 0.4, 0.6, 0.8) were prepared by solid-state reaction using standard ceramic method. The single-phase formation of these compounds was confirmed by X-ray diffraction (XRD) studies. The samples with x=0, 0.2, 0.4, 0.6 are found to be orthorhombic while the sample with x=0.8 is triclinic. The dielectric constant (ε′) and dissipation factor (tan δ) were measured in the frequency range 100 Hz to 1 MHz at room temperature and as a function of temperature at certain fixed frequencies (1 kHz, 10 kHz, 100 kHz, 1 MHz). All the samples showed dielectric dispersion. The dielectric constant with temperature shows a broad peak; the peak temperature shifts with frequency which reflects the relaxor-type behavior. The peak above 600 K in the measured temperature range corresponds to antiferromagnetic ordering temperature (Néel temperature). The broadness of the peak changes with composition. The ac conductivity as well as ε′ are found to be maximum for the sample x=0.2 at room temperature.     

Impurity analysis of gentamicin bulk samples by improved liquid chromatography-ion trap mass spectrometry

Several gentamicin bulk samples from different origins were investigated using an LC/MS method.LC equipped with ion trap MS with positive ionization was performed on a Capcell Pak C18(AQ) column with the mobile phase containing 50 mM trifluoroacetic(TFA) and methanol.Impurities present in batches of gentamicin bulk samples were elucidated and compared according to their fragmentation behavior.In total seventeen impurities present in samples,five impurities were not elucidated and two compounds were identifi...     

Ultraprecise atomic mass measurement of the alpha particle and 4He

The atomic masses of the alpha particle and 4He have been measured by means of a Penning trap mass spectrometer which utilizes a frequency-shift detector to observe single-ion cyclotron resonances in an extremely stable 6.0 T magnetic field. The present resolution of this instrument approaches 0.01 ppb [10 ppt (parts per trillion)] and is limited primarily by the effective stability (<5 ppt/h) of the magnet over hundreds of hours of observation. The leading systematic shift [at -202(9) ppt] is due to the image charge located in the trap electrodes. The new value for the atomic mass of the alpha particle is 4 001 506 179.147(64) nu and the corresponding value for the mass of 4He is 4 002 603 254.153(64) nu (nu=10(-9) u). The 16 ppt uncertainty is at least 20 times smaller than any previous determination.