Search for heavy neutral leptons in e+e− annihilations at 29 GeV

A search was made in 29 GeV e⁺e^? annihilations for heavy, neutral leptons decaying to e^±X^?(ν), where X is a muon or charged meson. Six events with isolated e^±X^? pairs were found for an intergrated luminosity of 106 pb^?1. The expected background is 5.5 ± 2.2 events. Limits on $\text{σ}\text{s}\text{?}\text{B}$ depend on mass and range from 8 to 20 × 10^?5 nb.     

N@C60 and P@C60 as quantum bits

Due to their long electron spin relaxation times, the endohedral fullerenes N@C₆₀ and P@C₆₀ are good candidates for the implementation of qubits in an electron spin quantum computer. A central operation in this context is the rotation of the spin direction by an arbitrary angle. In the present experiment, this nutation behavior was studied in pulsed electron spin resonance measurements. We show that, even at room temperature, about 50 Rabi oscillations (about 100 qubit operations) can be performed without refocusing the spin system, although inhomogeneities are present. A special feature of the group V endohedral fullerenes is the electron spinS=3/2, which complicates the nutation behavior. The zero-field splitting at low temperature gives rise to different nutation frequencies for the (1/2,?1/2) transition and the (±3/2, ±1/2) transitions. The frequency ratio is 2/3^1/2.     

PIV/PLIF investigation of two-phase vortex–flame interactions: effects of vortex size and strength

The evolution of flame surface area and rate of CH layer extinction are measured during the interaction of a two-phase counterflow diffusion flame with fuel-side vortices of varying size and strength. Planar laser-induced fluorescence (PLIF) of CH is used to mark the flame front and particle-image velocimetry (PIV) is used to measure the strain rate field at various phases of the interaction process. Vortices of similar initial circulation but differing in size showed widely disparate peak strain rates and CH decay rates because of varying levels of flame-induced vortex dissipation. Vortex size is also found to have a significant effect on flame surface area evolution during and after extinction, with the presence of droplets playing a significant role in the latter. Implications of these results for the fundamental understanding of vortex–flame interactions are discussed.     

The nilsson-potential parameters for neutrons at A≃-100 and new deformation values for103Mo and105Mo

The half-lives of the first excited levels in odd-neutron nuclei¹⁰³Mo and¹⁰⁵Mo have been measured. From these data, values of the deformation parameter of?=0.31±0.05 and 0.29±0.06 for¹⁰³Mo and¹⁰⁵Mo, respectively, have been deduced assuming prolate spheroidal shapes. The present results in combination with previously determined properties of the ground-state bands of these nuclei are used to determineμ, the magnitude of the coefficient of the 1² term, in the Nilsson Hamiltonian, for the new region of deformation atA～-100.     

Improved predictability of two-dimensional turbulent flows using wavelet packet compression

We propose to use new orthonormal wavelet packet bases, more efficient than the Fourier basis, to compress two-dimensional turbulent flows. We define the “best basis” of wavelet packets as the one which, for a given enstrophy density, condenses the L² norm into a minimum number of non-negligible wavelet packet coefficients. Coefficients below a threshold are discarded, reducing the number of degrees of freedom. We then compare the predictability of the original flow evolution with several such reductions, varying the number of retained coefficients, either from a Fourier basis, or from the best-basis of wavelet packets. We show that for a compression ratio of 1/2, we still have a deterministic predictability using the wavelet packet best-basis, while it is lost when using the Fourier basis. Likewise, for compression ratios of 1/20 and 1/200 we still have statistical predictability using the wavelet packet best-basis, while it is lost when using the Fourier basis. In fact, the significant wavelet packet coefficients in the best-basis appear to correspond to coherent structures. The weak coefficients correspond to vorticity filaments, which are only passively advected by the coherent structures. In conclusion, the wavelet packet best-basis seems to distinguish the low-dimensional dynamically active part of the flow from the high-dimensional passive components. It gives us some hope of drastically reducing the number of degrees of freedom necessary to the computation of two-dimensional turbulent flows.     

Eine Strukturvariante zum NaErCl4/α-NiWO4-Typ für ternäre Selten-Erd-Chloride vom Typ NaMCl4: Synthese und Kristallstruktur von NaLuCl4

A Structural Variant to the NaErCl₄/α-NiWO₄ Type for Ternary Rare-Earth Halides NaMCl₄: Synthesis and Crystal Structure of NaLuCl₄ Single crystals of NaLuCl₄ (orthorhombic, Pbcn (Nr. 60), Z = 4, a = 618.6(1) pm, b = 1 592.2(2) pm, c = 657.0(1) pm) were grown for the first time from the binary components using the Bridgman technique. The crystal structure may be derived from a hexagonally closest packing of Cl^? spheres with one half of all octahedral sites occupied by the cations Na⁺ and Lu³⁺, respectively. The close relation of the structure to that of NaErCl₄ (α-NiWO₄) is discussed. NaScCl₄ was found to be isotypic to NaLuCl₄.