Hartree-Fock Many-Body Perturbation Theory for Nuclear Ground-States

We investigate the order-by-order convergence behavior of many-body perturbation theory (MBPT) as a simple and efficient tool to approximate the ground-state energy of closed-shell nuclei. To address the convergence properties directly, we explore perturbative corrections up to 30th order and highlight the role of the partitioning for convergence. The use of a simple Hartree-Fock solution to construct the unperturbed basis leads to a convergent MBPT series for soft interactions, in contrast to, e.g., a harmonic oscillator basis. For larger model spaces and heavier nuclei, where a direct high-order MBPT calculation in not feasible, we perform third-order calculation and compare to advanced ab initio coupled-cluster calculations for the same interactions and model spaces. We demonstrate that third-order MBPT provides ground-state energies for nuclei up into tin isotopic chain that are in excellent agreement with the best available coupled-cluster results at a fraction of the computational cost.Comment: 6 pages, 5 figures, 1 tabl

Ab Initio Path to Heavy Nuclei

We present the first ab initio calculations of nuclear ground states up into the domain of heavy nuclei, spanning the range from 16-O to 132-Sn based on two- plus three-nucleon interactions derived within chiral effective field theory. We employ the similarity renormalization group for preparing the Hamiltonian and use coupled-cluster theory to solve the many-body problem for nuclei with closed sub-shells. Through an analysis of theoretical uncertainties resulting from various truncations in this framework, we identify and eliminate the technical hurdles that previously inhibited the step beyond medium-mass nuclei, allowing for reliable validations of nuclear Hamiltonians in the heavy regime. Following this path we show that chiral Hamiltonians qualitatively reproduce the systematics of nuclear ground-state energies up to the neutron-rich Sn isotopes.Comment: 5 pages, 5 figure

The red fluorescent protein eqFP611: application in subcellular localization studies in higher plants

<p>Abstract</p> <p>Background</p> <p>Intrinsically fluorescent proteins have revolutionized studies in molecular cell biology. The parallel application of these proteins in dual- or multilabeling experiments such as subcellular localization studies requires non-overlapping emission spectra for unambiguous detection of each label. In the red spectral range, almost exclusively DsRed and derivatives thereof are used today. To test the suitability of the red fluorescent protein eqFP611 as an alternative in higher plants, the behavior of this protein was analyzed in terms of expression, subcellular targeting and compatibility with GFP in tobacco.</p> <p>Results</p> <p>When expressed transiently in tobacco protoplasts, eqFP611 accumulated over night to levels easily detectable by fluorescence microscopy. The native protein was found in the nucleus and in the cytosol and no detrimental effects on cell viability were observed. When fused to N-terminal mitochondrial and peroxisomal targeting sequences, the red fluorescence was located exclusively in the corresponding organelles in transfected protoplasts. Upon co-expression with GFP in the same cells, fluorescence of both eqFP611 and GFP could be easily distinguished, demonstrating the potential of eqFP611 in dual-labeling experiments with GFP. A series of plasmids was constructed for expression of eqFP611 in plants and for simultaneous expression of this fluorescent protein together with GFP. Transgenic tobacco plants constitutively expressing mitochondrially targeted eqFP611 were generated. The red fluorescence was stably transmitted to the following generations, making these plants a convenient source for protoplasts containing an internal marker for mitochondria.</p> <p>Conclusion</p> <p>In plants, eqFP611 is a suitable fluorescent reporter protein. The unmodified protein can be expressed to levels easily detectable by epifluorescence microscopy without adverse affect on the viability of plant cells. Its subcellular localization can be manipulated by N-terminal signal sequences. eqFP611 and GFP are fully compatible in dual-labeling experiments.</p

Ab Initio Calculations of Medium-Mass Nuclei with Explicit Chiral 3N Interactions

We present the first ab initio coupled-cluster calculations of medium-mass nuclei with explicit chiral three-nucleon (3N) interactions. Using a spherical formulation of coupled cluster with singles and doubles excitations including explicit 3N contributions, we study ground states of 16,24-O, 40,48-Ca and 56-Ni. We employ chiral NN plus 3N interactions softened through a similarity renormalization group (SRG) transformation at the three-body level. We investigate the impact of all truncations and quantify the resulting uncertainties---this includes the contributions from triples excitations, the truncation of the set of three-body matrix elements, and the omission of SRG-induced four-body interactions. Furthermore, we assess the quality of a normal-ordering approximation of the 3N interaction beyond light nuclei. Our study points towards the predictive power of chiral Hamiltonians in the medium-mass regime.Comment: 6 pages, 3 figures, 2 table

Extension of coupled-cluster theory with a non-iterative treatment of connected triply excited clusters to three-body Hamiltonians

We generalize the coupled-cluster (CC) approach with singles, doubles, and the non-iterative treatment of triples termed $\Lambda$CCSD(T) to Hamiltonians containing three-body interactions. The resulting method and the underlying CC approach with singles and doubles only (CCSD) are applied to the medium-mass closed-shell nuclei O16, O24, and Ca40. By comparing the results of CCSD and $\Lambda$CCSD(T) calculations with explicit treatment of three-nucleon interactions to those obtained using an approximate treatment in which they are included effectively via the zero-, one-, and two-body components of the Hamiltonian in normal-ordered form, we quantify the contributions of the residual three-body interactions neglected in the approximate treatment. We find these residual normal-ordered three-body contributions negligible for the $\Lambda$CCSD(T) method, although they can become significant in the lower-level CCSD approach, particularly when the nucleon-nucleon interactions are soft.Comment: 21 pages, 3 figure

Tracing structural changes in energy materials: A novel multi sample capillary setup for in house powder X‐ray diffraction

Lithium ion batteries (LIBs) are currently a major subject of applied electrochemical research as there is a fast growing demand of electrochemical energy storage, driven by the transformation of the automotive sector and the expansion of renewable energies. One of the key strategies to improve LIBs is the optimization of the cathode active materials (CAMs). Therefore, in order to find structure property relations, both crystallographic and electrochemical properties need to be investigated and well understood. However, standard laboratory powder X-ray diffraction (PXRD) possibly comes to its limit when minor structural variations such as atomic defects, cation order, or minor impurity phases are addressed. In order to focus on such minor structural changes and to find decisive differences in crystalline properties of battery materials, a multi-sample capillary setup for a multipurpose in-house PXRD setup was developed. The latter is made up from a six-circle diffractometer, a microfocus molybdenum rotating anode, and a 2D area detector. The capillary spinner itself is made from commercial components and simple custom-made adapters. A goniometer head is installed on a rotary module and sample spinning is enabled by a 12 V gear motor. Mounted on a xyz-stage of the diffractometer, the position of the rotating capillary exposed to the primary beam can be varied while remaining perfectly aligned in the center of the diffractometer. Hence, by packing up to 10 different powder samples separated from each other into a single glass capillary, subsequent measurements of all samples can be carried out without remounting or readjustment. Within a series of samples, the setup is extremely reliable, precise, and accurate, while errors originating from sample displacement, misalignment, or calibration are minimized

Impact of Particle and Crystallite Size of Ba0.6_{0.6}Sr0.4_{0.4}TiO3_3 on the Dielectric Properties of BST/P(VDF-TrFE) Composites in Fully Printed Varactors

In the field of printed electronics, electronic components such as varactors are of special interest. As ferroelectric materials, Ba$_{0.6}$Sr$_{0.4}$TiO$_3$ (BST) and poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)) are promising compounds to be used in functional inks for the fabrication of fully inkjet-printed dielectric layers. In BST/P(VDF-TrFE) composite inks, the influence of the particle and crystallite size is investigated by using different grinding media sizes and thermal treatments at varying temperatures. It was found that with an increasing particle and crystallite size, both the relative permittivity and tunability increase as well. However, the thermal treatment which impacts both the particle and crystallite size has a greater effect on the dielectric properties. An additional approach is the reduction in the dielectric layer thickness, which has a significant effect on the maximal tunability. Here, with a thickness of 0.9 µm, a tunability of 29.6% could be achieved in an external electric field of 34 V µm$^{−1}$

Enhancing the Stability of LiNio.5_{o.5}0Mn1.5_{1.5}O4_{4} by Coating with LiNbO3_{3} Solid-State Electrolyte: Novel Chemically Activated Coating Process versus Sol-Gel Method

LiNbO$_{3}$-coated LiNi$_{0.5}$Mn$_{1.5}$O$_{4}$ spinel was fabricated by two methods: using hydrogen-peroxide as activating agent and sol-gel method. The structure of the obtained cathode materials was investigated using a scanning electron microscope (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and the electrochemical properties of the prepared cathodes were probed by charge-discharge studies. The morphology of the coating material on the surface and the degree of coverage of the coated particles were investigated by SEM, which showed that the surface of LiNi$_{0.5}$Mn$_{1.5}$O$_{4}$ particles is uniformly encapsulated by lithium innovate coating. The influence of the LiNbO3 coating layer on the spinel’s properties was explored, including its effect on the crystal structure and electrochemical performance. XRD studies of the obtained coated active materials revealed very small expansion or contraction of the unit cell. From the capacity retention tests a significant improvement of the electrochemical properties resulted when a novel chemically activated coating process was used. Poorer results, however, were obtained using the sol-gel method. The results also revealed that the coated materials by the new method exhibit enhanced reversibility and stability compared to the pristine and reference ones. It was shown that the morphology of the coating material and possible improvement of communication between the substrates play an important role