Technical University of Berlin

About: Technical University of Berlin is a education organization based out in Berlin, Germany. It is known for research contribution in the topics: Laser & Catalysis. The organization has 27292 authors who have published 59342 publications receiving 1414623 citations. The organization is also known as: Technische Universität Berlin & TU Berlin.

Electrochemical water splitting by layered and 3D cross-linked manganese oxides: correlating structural motifs and catalytic activity

Abstract: Manganese based precious metal-free electrocatalysts for the oxygen evolution reaction (OER) are promising materials for energy storage systems based on dark or photo-coupled water electrolysis, because they are active, inexpensive and of low toxicity. In this work, atomic scale structure–activity relationships of two different nano-structured manganese oxides, MnOx, are established using a combination of X-ray absorption, diffraction and electrochemistry. Prepared by chemical symproportionation (s-MnOx) and impregnation (i-MnOx), the s-MnOx catalyst consisted of a layered structure similar to δ-MnO2 while the i-MnOx catalyst displayed a mixture of tunnelled, 3D cross-linked β- and defective γ-MnO2 structures. During electrocatalytic oxygen evolution the structural motifs of both MnOx remain largely unchanged, but the oxidation state of Mn increases from 3.5 to 3.9–4. Kinetic parameters of the electrocatalytic oxygen evolution reaction were extracted using Tafel slope analysis and pH titration experiment, and the role of the protons abstracted was analyzed. The study reveals fundamental differences of general importance in the catalytic activity between layered and cross-linked structures. The exclusive presence of di-μ-oxo-bridged Mn ions in the layered structure is coupled to a pronounced redox and charge capacity behaviour. This ensured efficient use of surface and bulk active sites, and resulted in a relatively large Tafel slope. Consequently, the intrinsic OER activity is especially high in s-MnOx. In contrast, 3D cross-linked structures with both mono- and di-μ-oxo-bridged Mn ions resulted in lower intrinsic activity but smaller Tafel slope, and thus favourable activity at technological water-splitting rates. The insights from this comparative study will provide guidance in the structural design and optimization of other non precious metal oxide OER catalysts.

Generalized Hartree-Fock theory and the Hubbard model

Abstract: The familiar unrestricted Hartree-Fock variational principles is generalized to include quasi-free states. As we show, these are in one-to-one correspondence with the one-particle density matrices and these, in turn, provide a convenient formulation of a generalized Hartree-Fock variational principle, which includes the BCS theory as a special case. While this generalization is not new, it is not well known and we begin by elucidating it. The Hubbard model, with its particle-hole symmetry, is well suited to exploring this theory because BCS states for the attractive model turn into usual HF states for the repulsive model. We rigorously determine the true, unrestricted minimizers for zero and for nonzero temperature in several cases, notably the half-filled band. For the cases treated here, we can exactly determine all broken and unbroken spatial and gauge symmetries of the Hamiltonian.

Multiple-image radiography

Abstract: Conventional radiography produces a single image of an object by measuring the attenuation of an x-ray beam passing through it When imaging weakly absorbing tissues, x-ray attenuation may be a suboptimal signature of diseaserelated information In this paper we describe a new phase-sensitive imaging method, called multiple-image radiography (MIR), which is an improvement on a prior technique called diffraction-enhanced imaging (DEI) This paper elaborates on our initial presentation of the idea in Wernick et al (2002 Proc Int SympBiomedImaging pp 129–32) MIR simultaneously produces several images from a set of measurements made with a single x-ray beam Specifically, MIR yields three images depicting separately the effects of refraction, ultrasmall-angle scatter and attenuation by the object All three images have good contrast, in part because they are virtually immune from degradation due to scatter at higher angles MIR also yields a very comprehensive object description, consisting of the angular intensity spectrum of a transmitted x-ray beam at every image pixel, within a narrow angular range Our experiments are based on data acquired using a synchrotron light source; however, in preparation for more practical implementations using conventional x-ray sources, we develop and evaluate algorithms designed for Poisson noise, which is characteristic of photon-limited imaging The results suggest that MIR is capable of operating at low photon count levels, therefore the method

Nanorod-coated PNIPAM microgels: thermoresponsive optical properties.

Abstract: Nanoparticles and in particular gold nanorods have interesting optical properties arising from two well-differentiated plasmon modes. The frequency of such modes can be altered by their chemical environment and coupling with neighboring rods. This study investigates new composite materials made of gold nanorods adsorbed on thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) microgels. It is shown that the thermally induced collapse of the polymer network inside the particles leads to a red shift of the longitudinal plasmon band of the gold rods, which is found to be fully reversible.

Enabling IoT Ecosystems through Platform Interoperability

Abstract: Today, the Internet of Things (IoT) comprises vertically oriented platforms for things. Developers who want to use them need to negotiate access individually and adapt to the platform-specific API and information models. Having to perform these actions for each platform often outweighs the possible gains from adapting applications to multiple platforms. This fragmentation of the IoT and the missing interoperability result in high entry barriers for developers and prevent the emergence of broadly accepted IoT ecosystems. The BIG IoT (Bridging the Interoperability Gap of the IoT) project aims to ignite an IoT ecosystem as part of the European Platforms Initiative. As part of the project, researchers have devised an IoT ecosystem architecture. It employs five interoperability patterns that enable cross-platform interoperability and can help establish successful IoT ecosystems.