Leibniz University of Hanover

About: Leibniz University of Hanover is a education organization based out in Hanover, Niedersachsen, Germany. It is known for research contribution in the topics: Finite element method & Population. The organization has 14283 authors who have published 29845 publications receiving 682152 citations.

Melting of isolated tin nanoparticles

Abstract: The melting of isolated neutral tin cluster distributions with mean sizes of about 500 atoms has been investigated in a molecular beam experiment by calorimetrically measuring the clusters' formation energies as a function of their internal temperature. For this purpose the possibility to adjust the temperature of the clusters' internal degrees of freedom by means of the temperature of the cluster source's nozzle was exploited. The melting point of the investigated tin clusters was found to be lowered by 125 K and the latent heat of fusion per atom is reduced by 35% compared to bulk tin. The melting behavior of the isolated tin clusters is discussed with respect to the occurrence of surface premelting.

A nonlocal operator method for partial differential equations with application to electromagnetic waveguide problem

Abstract: A novel nonlocal operator theory based on the variational principle is proposed for the solution of partial differential equations. Common differential operators as well as the variational forms are defined within the context of nonlocal operators. The present nonlocal formulation allows the assembling of the tangent stiffness matrix with ease and simplicity, which is necessary for the eigenvalue analysis such as the waveguide problem. The present formulation is applied to solve the differential electromagnetic vector wave equations based on electric fields. The governing equations are converted into nonlocal integral form. An hourglass energy functional is introduced for the elimination of zeroenergy modes. Finally, the proposed method is validated by testing three classical benchmark problems.

Routes towards Anderson-like localization of Bose-Einstein condensates in disordered optical lattices.

Abstract: We investigate, both experimentally and theoretically, possible routes towards Anderson-like localization of Bose-Einstein condensates in disordered potentials. The dependence of this quantum interference effect on the nonlinear interactions and the shape of the disorder potential is investigated. Experiments with an optical lattice and a superimposed disordered potential reveal the lack of Anderson localization. A theoretical analysis shows that this absence is due to the large length scale of the disorder potential as well as its screening by the nonlinear interactions. Further analysis shows that incommensurable superlattices should allow for the observation of the crossover from the nonlinear screening regime to the Anderson localized case within realistic experimental parameters.

Robust Superhydrophobic/Superoleophilic Wrinkled Microspherical MOF@rGO Composites for Efficient Oil–Water Separation

Abstract: Graphene/MOF-based composite materials in three-dimensional (3D) architectures are promising for the treatment of oil-containing wastewater by absorption owing to their intrinsic properties of graphene and metal-organic frameworks (MOFs), such as high porosity, ultralow density, and facilely tailored superwettability. In this study, novel wrinkled 3D microspherical MOF@rGO composites with both superhydrophobic and superoleophilic properties were developed by embedding MOF nanoparticles between graphene oxide (GO) nanosheets, followed by high-temperature reduction self-assembly. The microspherical composites feature a unique micro/nano hierarchy consisting of crumpled reduced GO (rGO) nanosheets intercalated with well-dispersed MOF nanoparticles. Combined with the superwettability and abundant meso/microporosity, the peculiar architectures of wrinkled ZIF-8@rGO microspheres show very fast absorption rates and high sorption selectivity for organic solvents and oils from water.