Theory of Broensted acidity in zeolites

The nature of the chem. bond of protons in a zeolite is analyzed from theor. and spectroscopic results. Of interest is the dependence on zeolite structure as well as compn. The zeolitic OH bond is mainly covalent. Proton attachment to the zeolite lattice causes a weakening of neighboring Si-O and Al-O bonds. The effective increase in vol. of the bridging O atom causes a local deformation, that changes the strength of the lattice-chem. bonds over a few bond distances. Proton concn. effects as well as lattice-compn. effects can be understood from the lattice-relaxation model. The energetics of proton transfer is controlled by the need to stabilize the resulting Zwitter-ion. The pos. charge on the cation becomes stabilized by contact with basic lattice-O atom

Interaction of vortices in superconductors with kappa close to 2^(-1/2)

Using a perturbative approach to the infinitely degenerate Bogomolnyi vortex state for a superconductor with kappa = 2^(-1/2), T -> T_c, we calculate the interaction of vortices in a superconductor with kappa close to 2^(-1/2). We find, numerically and analytically, that depending on the material the interaction potential between the vortices varies with decreasing kappa from purely repulsive (as in a type-II superconductor) to purely attractive (as in a type-I superconductor) in two different ways: either vortices form a bound state and the distance between them changes gradually from infinity to zero, or this transition occurs in a discontinuous way as a result of a competition between minima at infinity and zero. We study the discontinuous transition between the vortex and Meissner states caused by the non-monotonous vortex interaction and calculate the corresponding magnetization jump.Comment: v1:original submit v2:changed formate of images (gave problems to some) v3:corrected fig v4v6 (was -v4v6) orthographic corrections (and U_lat/int) mismatch v4:more small orthographic corrections v5:converted to revtex4 and bibTex v6:Renamed images to submit to pr

On the validity of tidal turbine array configurations obtained from steady-state adjoint optimisation

Extracting the optimal amount of power from an array of tidal turbines requires an intricate understanding of tidal dynamics and the effects of turbine placement on the local and regional scale flow. Numerical models have contributed significantly towards this understanding, and more recently, adjoint-based modelling has been employed to optimise the positioning of the turbines in an array in an automated way and improve on simple, regular man-made configurations. Adjoint-based optimisation of high-resolution and ideally 3D transient models is generally a very computationally expensive problem. As a result, existing work on the adjoint optimisation of tidal turbine placement has been mostly limited to steady-state simulations in which very high, non-physical values of the background viscosity are required to ensure that a steady-state solution exists. However, such compromises may affect the reliability of the modelled turbines, their wakes and interactions, and thus bring into question the validity of the computed optimal turbine positions. This work considers a suite of idealised simulations of flow past tidal turbine arrays in a 2D channel. It compares four regular array configurations, detailed by Divett et al. (2013), with the configuration found through adjoint optimisation in a steady-state, high-viscosity setup. The optimised configuration produces considerably more power. The same configurations are then used to produce a suite of transient simulations that do not use constant high-viscosity, and instead use large eddy simulation (LES) to parameterise the resulting turbulent structures. It is shown that the LES simulations produce less power than that predicted by the constant high-viscosity runs. Nevertheless, they still follow the same trends in the power curve throughout time, with optimised layouts continuing to perform significantly better than simplified configuration

Preclinical Applications of 3'-Deoxy-3'-[18F]Fluorothymidine in Oncology - A Systematic Review

The positron emission tomography (PET) tracer 3'-deoxy-3'-[18F]fluorothymidine ([18F]FLT) has been proposed to measure cell proliferation non-invasively in vivo. Hence, it should provide valuable information for response assessment to tumor therapies. To date, [18F]FLT uptake has found limited use as a response biomarker in clinical trials in part because a better understanding is needed of the determinants of [18F]FLT uptake and therapy-induced changes of its retention in the tumor. In this systematic review of preclinical [18F]FLT studies, comprising 174 reports, we identify the factors governing [18F]FLT uptake in tumors, among which thymidine kinase 1 plays a primary role. The majority of publications (83 %) report that decreased [18F]FLT uptake reflects the effects of anticancer therapies. 144 times [18F]FLT uptake was related to changes in proliferation as determined by ex vivo analyses. Of these approaches, 77 % describe a positive relation, implying a good concordance of tracer accumulation and tumor biology. These preclinical data indicate that [18F]FLT uptake holds promise as an imaging biomarker for response assessment in clinical studies. Understanding of the parameters which influence cellular [18F]FLT uptake and retention as well as the mechanism of changes induced by therapy is essential for successful implementation of this PET tracer. Hence, our systematic review provides the background for the use of [18F]FLT in future clinical studies

Reliability Evaluation of Drivetrains: Challenges for Off‐ Highway Machines

Downtime of mobile machinery used in fields like construction, earthmoving or mining usually leads to an instant halt of an entire process and can even endanger entire operations. To meet the customer’s requirement for high availabilities of their equipment, safeguarding the reliability of overall systems and components is necessary. Since life expectancy of systems and its components strongly depends on the experienced load history, this information needs to be available as accurately as possible to allow reliable lifetime calculation results. Due to the wide range of machines and applications of off‐highway machines, determining representative loads is especially challenging. The challenges, in determining both load cycles for the entire system and local component loads, are discussed in this work, along with approaches to face them. Additionally, a method is described, which allows users to quantitatively calculate life expectancy of technical systems in both the concept phase and the later stages of the product life cycle. In the end, two examples are presented in which exemplary challenges are faced

Lattice-relaxation of zeolites

Quantum-chemical cluster calculations as well as solid-state chemical lattice-calculations indicate that zeolitic SiO2- and AlPO4-structures are flexible structures. The structures reflect the subtle balance of electrostatic and covalent interactions. The different electrostatic interactions lower the symmetry of layered AlPO4-structures compared to that of the corresponding SiO2-compounds. The result is a smaller zeolite-channel dimension for the AlPO4-structure compared to that of the corresponding SiO2-network. Deprotonation of the zeolite-lattice leads to large local changes in geometry that changes acidity compared to that predicted for a non-flexible lattice. Changes in lattice vibrational frequencies are consistent with the theoretically predicted relaxation of the zeolite-lattic

Bogomol'nyi Limit For Magnetic Vortices In Rotating Superconductor

This work is the sequel of a previous investigation of stationary and cylindrically symmetric vortex configurations for simple models representing an incompressible non-relativistic superconductor in a rigidly rotating background. In the present paper, we carry out our analysis with a generalized Ginzburg-Landau description of the superconductor, which provides a prescription for the radial profile of the normal density within the vortex. Within this framework, it is shown that the Bogomol'nyi limit condition marking the boundary between type I and type II behavior is unaffected by the rotation of the background.Comment: 7 pages, uses RevTeX, submitted to Phys.Rev.

The structure of hot gas in Cepheus B

By observing radiation-affected gas in the Cepheus B molecular cloud we probe whether the sequential star formation in this source is triggered by the radiation from newly formed stars. We used the dual band receiver GREAT onboard SOFIA to map [C II] and CO 13--12 and 11--10 in Cep B and compared the spatial distribution and the spectral profiles with complementary ground-based data of low-$J$ transitions of CO isotopes, atomic carbon, and the radio continuum. The interaction of the radiation from the neighboring OB association creates a large photon-dominated region (PDR) at the surface of the molecular cloud traced through the photoevaporation of C^+. Bright internal PDRs of hot gas are created around the embedded young stars, where we detect evidence of the compression of material and local velocity changes; however, on the global scale we find no indications that the dense molecular material is dynamically affected.Comment: Accepted for publication in A&A (SOFIA/GREAT special issue