Differential energy measurement between He- and Li-like uranium intra-shell transitions

We present the first clear identification and highly accurate measurement of the intra-shell transition 1s2p\, ^3P_2 \to 1s2s\, ^3S_1 of He-like uranium performed via X-ray spectroscopy. The present experiment has been conducted at the gas-jet target of the ESR storage ring in GSI (Darmstadt, Germany) where a Bragg spectrometer, with a bent germanium crystal, and a Ge(i) detector were mounted. Using the ESR deceleration capabilities, we performed a differential measurement between the 1s2p\, ^3P_2 \to 1s2s\, ^3S_1 He-like U transition energy, at 4510 eV, and the 1s^22p\ ^2P_{3/2} \to 1s^22s\, ^2S_{1/2} Li-like U transition energy, at 4460 eV. By a proper choice of the ion velocities, the X-ray energies from the He- and Li-like ions could be measured, in the laboratory frame, at the same photon energy. This allowed for a drastic reduction of the experimental systematic uncertainties, principally due to the Doppler effect, and for a comparison with the theory without the uncertainties arising from one-photon QED predictions and nuclear size corrections

Observation of the 2p3/2 -> 2s1/2 intra-shell transition in He-like uranium

We present the first observation of the 1s2p 3P2 ? 1s2s 3S1 transition in He-like uranium. The experiment was performed at the internal gas-jet target of the ESR storage ring at GSI exploiting a Bragg crystal spectrometer and a germanium solid state detector. Using the 1s2 2p 2P3/2 ? 1s2 2s 2S1/2 transition in Li-like uranium as reference and the deceleration capabilities of the ESR storage rings, we obtained the first evaluation of the He-like heavy ion intra-shell transition energy

Testing quantum electrodynamics in extreme fields using helium-like uranium

Funding Information: The results presented here are based on the experiment E125, which is performed at the infrastructure ESR at the GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt, in the framework of FAIR Phase-0 and SPARC collaboration. This work is supported by the Horizon 2020 research and innovation programme of the European Union and grant agreement no. 6544002. We acknowledge the support provided by ErUM FSP T05-‘Aufbau von APPA bei FAIR’ (BMBF nos. 05P19SJFAA and 05P21SJFA1). We thank A. Malyshev, V. Shabaev and Y. Kozhedub for providing previously unknown theoretical results and also for the discussions on theoretical uncertainties. M.T. thanks the ExtreMe Matter Institute EMMI and Alexander von Humboldt Foundation for their support for the stays at the GSI for the preparation and data acquisition. L.D. acknowledges funding support from the Initiative Physique des Infinis (IPI), a research training programme of the Idex SUPER at Sorbonne Université. Funding Information: The results presented here are based on the experiment E125, which is performed at the infrastructure ESR at the GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt, in the framework of FAIR Phase-0 and SPARC collaboration. This work is supported by the Horizon 2020 research and innovation programme of the European Union and grant agreement no. 6544002. We acknowledge the support provided by ErUM FSP T05-‘Aufbau von APPA bei FAIR’ (BMBF nos. 05P19SJFAA and 05P21SJFA1). We thank A. Malyshev, V. Shabaev and Y. Kozhedub for providing previously unknown theoretical results and also for the discussions on theoretical uncertainties. M.T. thanks the ExtreMe Matter Institute EMMI and Alexander von Humboldt Foundation for their support for the stays at the GSI for the preparation and data acquisition. L.D. acknowledges funding support from the Initiative Physique des Infinis (IPI), a research training programme of the Idex SUPER at Sorbonne Université. Publisher Copyright: © 2024, The Author(s).Quantum electrodynamics (QED), the quantum field theory that describes the interaction between light and matter, is commonly regarded as the best-tested quantum theory in modern physics. However, this claim is mostly based on extremely precise studies performed in the domain of relatively low field strengths and light atoms and ions 1–6. In the realm of very strong electromagnetic fields such as in the heaviest highly charged ions (with nuclear charge Z ≫ 1), QED calculations enter a qualitatively different, non-perturbative regime. Yet, the corresponding experimental studies are very challenging, and theoretical predictions are only partially tested. Here we present an experiment sensitive to higher-order QED effects and electron–electron interactions in the high-Z regime. This is achieved by using a multi-reference method based on Doppler-tuned X-ray emission from stored relativistic uranium ions with different charge states. The energy of the 1s 1/22p 3/2 J = 2 → 1s 1/22s 1/2 J = 1 intrashell transition in the heaviest two-electron ion (U90+) is obtained with an accuracy of 37 ppm. Furthermore, a comparison of uranium ions with different numbers of bound electrons enables us to disentangle and to test separately the one-electron higher-order QED effects and the bound electron–electron interaction terms without the uncertainty related to the nuclear radius. Moreover, our experimental result can discriminate between several state-of-the-art theoretical approaches and provides an important benchmark for calculations in the strong-field domain.publishersversionpublishe

Stability of the Wurtzite Structure

An analysis of available data for 20 wurtzite compounds of the ANB8-N type shows that the stability as compared with zinc blende is closely connected with deviations of the c / a ratio from the ideal value of 1.633. A simple qualitative model is proposed to account for this feature. The variation in c / a is then correlated with the charge parameter ZC / ℏωp, where Z is the (effective) valence, C Phillips's electronegativity difference, and ℏωp the plasma energy of the free-valence-electron gas. The results indicate that c / a may be predicted with an uncertainty of 0.1%

TRY plant trait database - enhanced coverage and open access

Plant traits-the morphological, anatomical, physiological, biochemical and phenological characteristics of plants-determine how plants respond to environmental factors, affect other trophic levels, and influence ecosystem properties and their benefits and detriments to people. Plant trait data thus represent the basis for a vast area of research spanning from evolutionary biology, community and functional ecology, to biodiversity conservation, ecosystem and landscape management, restoration, biogeography and earth system modelling. Since its foundation in 2007, the TRY database of plant traits has grown continuously. It now provides unprecedented data coverage under an open access data policy and is the main plant trait database used by the research community worldwide. Increasingly, the TRY database also supports new frontiers of trait-based plant research, including the identification of data gaps and the subsequent mobilization or measurement of new data. To support this development, in this article we evaluate the extent of the trait data compiled in TRY and analyse emerging patterns of data coverage and representativeness. Best species coverage is achieved for categorical traits-almost complete coverage for 'plant growth form'. However, most traits relevant for ecology and vegetation modelling are characterized by continuous intraspecific variation and trait-environmental relationships. These traits have to be measured on individual plants in their respective environment. Despite unprecedented data coverage, we observe a humbling lack of completeness and representativeness of these continuous traits in many aspects. We, therefore, conclude that reducing data gaps and biases in the TRY database remains a key challenge and requires a coordinated approach to data mobilization and trait measurements. This can only be achieved in collaboration with other initiatives

Reliability of low-energy electron diffraction for studies of surface order-disorder phenomena

It is shown that a determination of critical exponents in surface phase transformations based on a kinematic analysis of LEED peak intensities is subject to errors caused by multiple scattering that are large enough to prevent a clear assignment to a known universality class. The multiple-scattering contribution arises from short-range flucutations and has its maximum value at the transition temperature. The specific-heat exponent of the surface phase can be measured directly from the variation of the integral-order-beam intensity with temperature that is caused by the multiple scattering

Connective Tissue Growth Factor in Regulation of RhoA Mediated Cytoskeletal Tension Associated Osteogenesis of Mouse Adipose-Derived Stromal Cells

Background: Cytoskeletal tension is an intracellular mechanism through which cells convert a mechanical signal into a biochemical response, including production of cytokines and activation of various signaling pathways. Methods/Principal Findings: Adipose-derived stromal cells (ASCs) were allowed to spread into large cells by seeding them at a low-density (1,250 cells/cm 2), which was observed to induce osteogenesis. Conversely, ASCs seeded at a high-density (25,000 cells/cm 2) featured small cells that promoted adipogenesis. RhoA and actin filaments were altered by changes in cell size. Blocking actin polymerization by Cytochalasin D influenced cytoskeletal tension and differentiation of ASCs. To understand the potential regulatory mechanisms leading to actin cytoskeletal tension, cDNA microarray was performed on large and small ASCs. Connective tissue growth factor (CTGF) was identified as a major regulator of osteogenesis associated with RhoA mediated cytoskeletal tension. Subsequently, knock-down of CTGF by siRNA in ASCs inhibited this osteogenesis. Conclusions/Significance: We conclude that CTGF is important in the regulation of cytoskeletal tension mediated AS