Three-dimensional pattern formation, multiple homogeneous soft modes, and nonlinear dielectric electroconvection

Patterns forming spontaneously in extended, three-dimensional, dissipative systems are likely to excite several homogeneous soft modes ($\approx$ hydrodynamic modes) of the underlying physical system, much more than quasi one- and two-dimensional patterns are. The reason is the lack of damping boundaries. This paper compares two analytic techniques to derive the patten dynamics from hydrodynamics, which are usually equivalent but lead to different results when applied to multiple homogeneous soft modes. Dielectric electroconvection in nematic liquid crystals is introduced as a model for three-dimensional pattern formation. The 3D pattern dynamics including soft modes are derived. For slabs of large but finite thickness the description is reduced further to a two-dimensional one. It is argued that the range of validity of 2D descriptions is limited to a very small region above threshold. The transition from 2D to 3D pattern dynamics is discussed. Experimentally testable predictions for the stable range of ideal patterns and the electric Nusselt numbers are made. For most results analytic approximations in terms of material parameters are given.Comment: 29 pages, 2 figure

Phase synchronization from noisy univariate signals

We present methods for detecting phase synchronization of two unidirectionally coupled, self-sustained noisy oscillators from a signal of the driven oscillator alone. One method detects soft, another hard phase locking. Both are applied to the problem of detecting phase synchronization in von Karman vortex flow meters.Comment: 4 pages, 4 figure

Biodiversity in Marine Ecosystems—European Developments toward Robust Assessments

Sustainability of marine ecosystems and their services are dependent on marine biodiversity, which is threatened worldwide. Biodiversity protection is a major target of the EU Marine Strategy Framework Directive, requiring assessment of the status of biodiversity on the level of species, habitats, and ecosystems including genetic diversity and the role of biodiversity in food web functioning and structure. This paper provides a summary of the development of new indicators and refinement of existing ones in order to address some of the observed gaps in indicator availability for marine biodiversity assessments considering genetic, species, habitat, and ecosystem levels. Promising new indicators are available addressing genetic diversity of microbial and benthic communities. Novel indicators to assess biodiversity and food webs associated with habitats formed by keystone species (such as macroalgae) as well as to map benthic habitats (such as biogenic reefs) using high resolution habitat characterization were developed. We also discuss the advances made on indicators for detecting impacts of non-native invasive species and assessing the structure and functioning of marine food-webs. The latter are based on indicators showing the effects of fishing on trophic level and size distribution of fish and elasmobranch communities well as phytoplankton and zooplankton community structure as food web indicators. New and refined indicators are ranked based on quality criteria). Their applicability for various EU and global biodiversity assessments and the need for further development of new indicators and refinement of the existing ones is discussed

Let's Train More Theoretical Ecologists - Here Is Why

A tangled web of vicious circles, driven by cultural issues, has prevented ecology from growing strong theoretical roots. Now this hinders development of effective conservation policies. To overcome these barriers in view of urgent societal needs, we propose a global network of postgraduate theoretical training programs

Understanding the local structure of Eu3+- and Y3+-stabilized zirconia: insights from luminescence and X-ray absorption spectroscopic investigations

This study combines bulk structural and spectroscopic investigations of Eu$^{3+}$- or Y$^{3+}$/Eu$^{3+}$ co-doped tetragonal and cubic zirconia polymorphs to gain an indepth understanding of the solid solution formation process. Our bulk structural characterizations show that the dopant is homogenously distributed in the ZrO$_{2}$ host structure resulting in an increase of the bulk symmetry with increasing dopant substitution (from 8 to 26 mol%). The local site symmetry around the Eu$^{3+}$ dopant, however, determined with luminescence spectroscopy (TRLFS), remains low in all samples. Results obtained with X-ray pair distribution function and X-ray absorption spectroscopy show that the average coordination environment in the stabilized zirconia structures remains practically unchanged. Despite this very constant average dopant environment, siteselective TRLFS data show the presence of three nonequivalent Eu$^{3+}$ environments in the ZrO$_{2}$ solid structures. These Eu$^{3+}$ environments are assumed to arise from Eu$^{3+}$ incorporation at superficial sites, which increase in abundance as the size of the crystallites decrease, and incorporation on two bulk sites differing in the location of the oxygen vacancies with respect to the dopant cation

Continuing WebAssembly with Effect Handlers

WebAssembly (Wasm) is a low-level portable code format offering near native performance. It is intended as a compilation target for a wide variety of source languages. However, Wasm provides no direct support for non-local control flow features such as async/await, generators/iterators, lightweight threads, first-class continuations, etc. This means that compilers for source languages with such features must ceremoniously transform whole source programs in order to target Wasm. We present WasmFX an extension to Wasm which provides a universal target for non-local control features via effect handlers, enabling compilers to translate such features directly into Wasm. Our extension is minimal and only adds three main instructions for creating, suspending, and resuming continuations. Moreover, our primitive instructions are type-safe providing typed continuations which are well-aligned with the design principles of Wasm whose stacks are typed. We present a formal specification of WasmFX and show that the extension is sound. We have implemented WasmFX as an extension to the Wasm reference interpreter and also built a prototype WasmFX extension for Wasmtime, a production-grade Wasm engine, piggybacking on Wasmtime's existing fibers API. The preliminary performance results for our prototype are encouraging, and we outline future plans to realise a native implementation

Immobilization of technetium by iron corrosion phases: lessons learned and future perspectives

Technetium-99 (99Tc) is a long-lived fission product (2.13×105 years) of uranium-235 (235U) and plutonium-239 (239Pu) and, therefore, of great concern for the long-term safe management of nuclear waste. The migration of Tc in the environment is highly influenced by the redox conditions, since Tc may be present in various oxidation states. Depending on the chemical properties of environmentally relevant systems, Tc is expected to mainly occur as Tc(VII) and as Tc(IV) under oxidizing and reducing conditions, respectively. The anion pertechnetate (Tc(VII)O ) is known to barely interact with mineral surfaces; this, in turn, enhances its migration in groundwater and favors its entry into the biosphere. On the contrary, the formation of Tc(IV) limits the migration of Tc, since it forms a low soluble solid (TcO2) and/or species, whose interaction with minerals is more favorable. In the last few decades Tc migration has been focused on the reduction of Tc(VII) to Tc(IV) by various reductants, such as Fe(II), Sn(II), or S(-II), which are either present in solution, taking part in mineral structures (Pearce et al., 2019), or metabolically induced by microbial cascades (Newsome et al., 2014). We have studied the immobilization of technetium (Tc) by various Fe(II)-containing phases, including Fe2+ pre-sorbed on alumina nanoparticles (Mayordomo et al., 2020), Fe(II)-Al(III)-layered double hydroxide (Mayordomo et al., 2021), and Fe(II) sulfides (Rodríguez et al., 2020; Rodríguez et al., 2021). We have combined sorption experiments with microscopic and spectroscopic techniques (scanning electron microscopy, Raman microscopy, X-ray photoelectron spectroscopy, infrared spectroscopy, and X-ray absorption spectroscopy) to elucidate the mechanisms responsible for Tc(VII) reductive immobilization. Those works have been focused on binary systems (i.e., studies of the interaction of Tc with a given reductant). However, the environment is a complex system, where different components often depend on and modify each other. Thus, Tc migration is susceptible and varies, depending on environmental conditions, and should not be studied in an isolated manner. The young investigator group TecRad (HZDR, 2022), funded by the German Federal Ministry of Education and Research, aims at analyzing Tc chemistry from a wider perspective. Our goal is to study the biogeochemical behavior of Tc when it interacts with (i) microorganisms, (ii) metabolites, (iii) Fe(II) minerals, and (iv) Fe(II) minerals in presence of metabolites. An important part of this project deals with implementing new spectro-electrochemical methods to monitor the in situ the behavior of Tc in solution and at interfaces as a function of the redox potential. With these tools, we aspire to characterize the molecular structures of Tc species under a variable range of redox conditions to broaden the understanding of the chemical behavior of the pollutant. We aim at generating valuable thermodynamic data (complex formation constants, solubility constants of minerals, redox potentials, and Tc distribution coefficients) that will be used to implement a geochemical modeling able to explain Tc\u27s environmental fate, even under different redox conditions

A Grassmann integral equation

The present study introduces and investigates a new type of equation which is called Grassmann integral equation in analogy to integral equations studied in real analysis. A Grassmann integral equation is an equation which involves Grassmann integrations and which is to be obeyed by an unknown function over a (finite-dimensional) Grassmann algebra G_m. A particular type of Grassmann integral equations is explicitly studied for certain low-dimensional Grassmann algebras. The choice of the equation under investigation is motivated by the effective action formalism of (lattice) quantum field theory. In a very general setting, for the Grassmann algebras G_2n, n = 2,3,4, the finite-dimensional analogues of the generating functionals of the Green functions are worked out explicitly by solving a coupled system of nonlinear matrix equations. Finally, by imposing the condition G[{\bar\Psi},{\Psi}] = G_0[{\lambda\bar\Psi}, {\lambda\Psi}] + const., 0<\lambda\in R (\bar\Psi_k, \Psi_k, k=1,...,n, are the generators of the Grassmann algebra G_2n), between the finite-dimensional analogues G_0 and G of the (``classical'') action and effective action functionals, respectively, a special Grassmann integral equation is being established and solved which also is equivalent to a coupled system of nonlinear matrix equations. If \lambda \not= 1, solutions to this Grassmann integral equation exist for n=2 (and consequently, also for any even value of n, specifically, for n=4) but not for n=3. If \lambda=1, the considered Grassmann integral equation has always a solution which corresponds to a Gaussian integral, but remarkably in the case n=4 a further solution is found which corresponds to a non-Gaussian integral. The investigation sheds light on the structures to be met for Grassmann algebras G_2n with arbitrarily chosen n.Comment: 58 pages LaTeX (v2: mainly, minor updates and corrections to the reference section; v3: references [4], [17]-[21], [39], [46], [49]-[54], [61], [64], [139] added

Structural defects in Hg1−xCdxI2 layers grown on CdTe substrates by vapor phase epitaxy

Hg1−xCdxI2 20–25-μm-thick layers with a uniform composition in the range of x = 0.1–0.2 were grown on CdTe substrates by vapor phase epitaxy (VPE). The growth was carried out using an α-HgI2 polycrystalline source at 200 °C and in the time range of 30–100 h. The layers were studied by scanning electron microscopy (SEM) and high resolution synchrotron x-ray topography (SXRT). The SEM and SXRT images of Hg1−xCdxI2 VPE layers allow one to identify the defects affecting the layer structure. The two main types of structural defects in the layers are subgrain boundaries and densely spaced striations similar to those referred generally to as vapor grown HgI2 bulk crystals. The effect of the growth time on these defects has been analyzed and on the basis of this it has been possible to grow Hg1−xCdxI2 layers with low defect [email protected]