The polarization of positrons in the decay of14O

The polarization of positrons in the decay of¹⁴O (pure Fermi) has been measured relative to that of¹⁰C (pure Gamow-Teller) using a new technique based on the time-resolved spectroscopy of hyperfine positronium decay. Combined with the absolute experimental value for Gamow-Teller decay polarization, the result is P(¹⁴O)=(1.02±0.056). This constitutes the first use of this technique in an online configuration, and demonstrates its ability for reaching eventual precisions of 0.1% in relative polarization measurements.     

Chemical synthesis inside the collision cell of a MS/MS system: 1—Formation of adduct ions between protonated esters and ammonia

An evaluation of the TAGA 6000 tandem quadrupole MS/MS capabilities for the study of the formation of adduct ions is presented. It is shown that under chemical ionization conditions the protonated molecular ions of esters react with neutral ammonia inside the collision cell of the instrument to yield adduct ions. Under the same reaction conditions the molecular ions obtained under electron impact conditions do not yield any adduct. Although it is not yet clear whether the adduct structure is of the cluster or covalently bonded type, the experimental results argue mainly in favor of the latter. The center-of-mass energy range usable for the formation of adduct ions is narrow and an order of magnitude lower than the energy required for collision-induced dissociation. However, despite the weak parent ion center-of-mass energies used, the spectra exhibit fragments characteristic of the adduct ion structures. Finally, by controlling the parent ion center-of-mass axial kinetic energy, the number of parent ions and the target thickness, it is possible to measure and control all the usual physicochemical parameters for adduct ion formation.     

N-point spatial phase-measurement techniques for non-destructive testing

Spatial phase-measurement interferometry techniques commonly used in non-destructive testing are affected by a number of fundamental error sources. This paper focuses on the major limitations for phase calculations using standard N-point algorithms. These limitations include: the wrong carrier frequency, unequally spaced fringes, detector non-linearities and variations in the dc fringe intensity. The character and magnitude of these errors are quantified by using computer simulations. A displacement measurement of a bent plate using different algorithms on the same data shows that practical limitations are unequally-spaced fringes and variations in dc intensity and fringe visibility. These errors limit the resolution of this type of measurement to about a tenth of a wave r.m.s.     

Controlling hot electrons by wave amplification and decay in compressing plasma

Through particle-in-cell simulations, it is demonstrated that a part of the mechanical energy of compressing plasma can be controllably transferred to hot electrons by preseeding the plasma with a Langmuir wave that is compressed together with the medium. Initially, a wave is undamped, so it is amplified under compression due to plasmon conservation. Later, as the phase velocity also changes under compression, Landau damping can be induced at a predetermined instant of time. Then the wave energy is transferred to hot electrons, shaping the particle distribution over a controllable velocity interval, which is wider than that in stationary plasma. For multiple excited modes, the transition between the adiabatic amplification and the damping occurs at different moments; thus, individual modes can deposit their energy independently, each at its own prescribed time.     

Electrostatics and aggregation: how charge can turn a crystal into a gel

The crystallization of proteins or colloids is often hindered by the appearance of aggregates of low fractal dimension called gels. Here we study the effect of electrostatics upon crystal and gel formation using an analytic model of hard spheres bearing point charges and short range attractive interactions. We find that the chief electrostatic free energy cost of forming assemblies comes from the entropic loss of counterions that render assemblies charge-neutral. Because there exists more accessible volume for these counterions around an open gel than a dense crystal, there exists an electrostatic entropic driving force favoring the gel over the crystal. This driving force increases with increasing sphere charge, but can be counteracted by increasing counterion concentration. We show that these effects cannot be fully captured by pairwise-additive macroion interactions of the kind often used in simulations, and we show where on the phase diagram to go in order to suppress gel formation.     

Vicinal alkylation of alkynes. A short route toward Δα,β butenolides,furans and cyclopentenones.

Cyclobutenones 1 which are readily prepared from alkynes and keteniminium salts 2 were-regiospecifically converted into Δ^α,β butenolides 4 or cyclopentenones 7. Reaction of 4 with diisobutylaluminum hydride yielded the corresponding substituted furans.     

Radial oscillations of neutron stars in strong magnetic fields

The eigen frequencies of radial pulsations of neutron stars are calculated in a strong magnetic field. At low densities we use the magnetic BPS equation of state (EOS) similar to that obtained by Lai and Shapiro while at high densities the EOS obtained from the relativistic nuclear mean field theory is taken and extended to include strong magnetic field. It is found that magnetized neutron stars support higher maximum mass whereas the effect of magnetic field on radial stability for observed neutron star masses is minimal.