Electrons bound in highly charged heavy ions such as hydrogen-like bismuth 209Bi82+ experience electromagnetic fields that are a million times stronger than in light atoms. Measuring the wavelength of light emitted and absorbed by these ions is therefore a sensitive testing ground for quantum electrodynamical (QED) effects and especially the electron–nucleus interaction under such extreme conditions. However, insufficient knowledge of the nuclear structure has prevented a rigorous test of strong-field QED. Here we present a measurement of the so-called specific difference between the hyperfine splittings in hydrogen-like and lithium-like bismuth 209Bi82+,80+ with a precision that is improved by more than an order of magnitude. Even though this quantity is believed to be largely insensitive to nuclear structure and therefore the most decisive test of QED in the strong magnetic field regime, we find a 7-σ discrepancy compared with the theoretical prediction.
Theoretical as well as experimental examples concerning the evolution of the two-time distribution S2‖0 (ω1,ω2 ;tm) as a function of the mixing time tm are presented, where S2‖0 is identical with the two-dimensional (2D) absorption spectrum rendered by 2D exchange NMR spectroscopy of static powder samples. The model calculations comprise standard models like isotropic rotational diffusion or overall isotropic reorientation combined with discrete internal rotational jumps to simulate the chain dynamics of polymers. In any case, the 2D spectrum directly reflects the main aspects of the underlying motional mechanism. An axially symmetric coupling (η=0) between spin and lattice is assumed throughout. Thus, the angular information contained in a 2D spectrum is completely specified by a one-dimensional jump angle distribution supplied with each spectrum. In connection with the simulations the numerical mapping of a discrete distribution function into a space of new variables is discussed. In the experimental section 2H NMR spectra of chain deuterated linear polystyrene above its glass transition temperature are shown, which are compared with the model calculations.
2H NMR results from 2D exchange, solid echo, and wide-line absorption spectra as well as spin-lattice relaxation times are analyzed in terms of different reorientation models applied to the C-2H bond directions of chain-deuterated polystyrene. The dominant mechanism is rotational diffusion by small angular steps where the mean rotational correlation time agrees with relaxation times from dynamic mechanical experiments over a dynamic range of 10 decades. However, the width of the correlation time distribution extracted from the NMR results varies from about 5 decades at Tg to not more than 1 decade at T £ Tt + 40 K, whereas other relaxation techniques yield constant correlation time distributions. The results of the different methods employed for the study of chain motion are compared. It is shown that the motions of well-defined C-H bond directions which are probed by NMR are tightly coupled to the cooperative motion of the o-process. Moreover, they also monitor the separation of the fast 3-process from the slow a-process when approaching Tg by cooling down from the melt.
The two-dimensional (2D) exchange nuclear magnetic resonance (NMR) experiment is applied to study ultraslow as well as faster motions in powdered solids. The theoretical framework required for the simulation of 2D exchange of the faster motions, and for the evaluation of the experimental data, is developed. Calculations are presented for two standard models: two-site jump and isotropic rotational diffusion. For discrete jump motion, anisotropic spin-lattice relaxation during the mixing time is also considered. The resulting, simulated 2D line shapes show new characteristics in the intermediate dynamic range. Experimental data are presented for two-site exchange in the model compound polycrystalline dimethylsulphone. The technique is then applied to study the chain dynamics of linear polystyrene in the glass transition range. Close to Tg the correlation times extracted from 2D exchange NMR exhibit strong non-Arrhenius behavior. This data together with correlation times obtained at higher temperatures from conventional T1 data follows the WLF equation over 11 orders of magnitude, from 10−6 to 1000 s. It is shown that 2D exchange NMR and spin-lattice relaxation probe the α and the β process, respectively, of the chain dynamics in the glass transition region.
Tin is the chemical element with the largest number of stable isotopes. Its complete proton shell, comparable with the closed electron shells in the chemically inert noble gases, is not a mere precursor to extended stability; since the protons carry the nuclear charge, their spatial arrangement also drives the nuclear electromagnetism. We report high-precision measurements of the electromagnetic moments and isomeric differences in charge radii between the lowest 1/2+, 3/2+, and 11/2− states in 117–131Sn, obtained by collinear laser spectroscopy. Supported by state-of-the-art atomic-structure calculations, the data accurately show a considerable attenuation of the quadrupole moments in the closed-shell tin isotopes relative to those of cadmium, with two protons less. Linear and quadratic mass-dependent trends are observed. While microscopic density functional theory explains the global behaviour of the measured quantities, interpretation of the local patterns demands higher-fidelity modelling.
Implementing smart metering is an important field for energy policy to successfully meet energy efficiency targets. From an integrated social acceptance and customerperceived value theory perspective we model the importance of customer value of smart metering in this regard. We further shape the model on a choice-based conjoint experiment with Swiss private electricity customers. The study finds that overall customers perceive a positive value from smart metering and are willing to pay for it. Further, based on a cluster analysis of customers' value perceptions, we identify four customer segments, each with a distinct value perception profile for smart metering. We find that energy policy and management should integrate a solid understanding of customer value for smart metering in their initiatives and consider different smart metering market segments within their measures.
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