522 research outputs found
From attachment to damage : defined genes of Candida albicans mediate adhesion, invasion and damage during interaction with oral epithelial cells
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Characterizing photocatalysts for water splitting: from atoms to bulk and from slow to ultrafast processes
Research on light-driven catalysis has gained tremendous importance due to the ever-increasing power consumption and the threatening situation of global warming related to burning fossil fuels. Significant efforts have been dedicated to artificial photosynthesis mimicking nature to split H2O into H2 and O2 by solar energy. Novel semiconductor und molecular photocatalysts focusing on one-step excitation processes via single component photocatalysts or via two-step excitation processes mimicking the Z-scheme of natural photosynthesis are currently developed. Analytical and physicochemical methods, which provide information at different time and length scales, are used to gain fundamental understanding of all processes leading to catalytic activity, i.e., light absorption, charge separation, transfer of charges to the reaction centres and catalytic turnover, but also understanding degradation processes of the photocatalytic active material. Especially, molecular photocatalysts still suffer from limited long-Term stability due to the formation of reactive intermediates, which may lead to degradation. Although there is an overwhelming number of research articles and reviews focussing on various materials for photocatalytic water splitting, to date only few reviews have been published providing a comprehensive overview on methods for characterizing such materials. This review will highlight spectroscopic, spectroelectrochemical, and electrochemical approaches in respect to their potential in studying processes in semiconductor and (supra)molecular photocatalysts. Special emphasis will be on spectroscopic methods to investigate light-induced processes in intermediates of sequential electron transfer chains. Further, microscopic characterization methods, which are predominantly used for semiconducting and hybrid photocatalytic materials will be reviewed as surface area, structure, facets, defects, and bulk properties such as crystallinity and crystal size are key parameters for charge separation, transfer processes and suppression of charge recombination. Recent developments in scanning probe microscopy will also be highlighted as such techniques are highly suited for studying photocatalytic active material. © The Royal Society of Chemistry
Topological synchronization of quantum van der Pol oscillators
To observe synchronization in a large network of classical or quantum systems
demands both excellent control of the interactions between the nodes and very
accurate preparation of the initial conditions due to the involved
nonlinearities and dissipation. This limits the applicability of this
phenomenon for future devices. Here, we demonstrate a route towards
significantly enhancing the robustness of synchronized behavior in open
nonlinear systems that utilizes the power of topology. In a lattice of quantum
van der Pol oscillators with topologically motivated couplings, boundary
synchronization emerges in the classical mean field as well as the quantum
model. In addition to its robustness against disorder and initial state
perturbations, the observed dynamics is independent of the underlying
topological insulator model provided the existence of zero-energy modes. Our
work extends the notion of topology to the general nonlinear dynamics and open
quantum system realm with applications to networks where specific nodes need
special protection like power grids or quantum networks.Comment: Comments are very welcome (14+5 pages, 12+1 figures
Topological synchronization of fractionalized spins
The gapped symmetric phase of the Affleck-Kennedy-Lieb-Tasaki (AKLT) model
exhibits fractionalized spins at the ends of an open chain. We show that
breaking SU(2) symmetry and applying a global spin-lowering dissipator achieves
synchronization of these fractionalized spins. Additional local dissipators
ensure convergence to the ground state manifold. In order to understand which
aspects of this synchronization are robust within the entire Haldane-gap phase,
we reduce the biquadratic term which eliminates the need for an external field
but destabilizes synchronization. Within the ground state subspace, stability
is regained using only the global lowering dissipator. These results
demonstrate that fractionalized degrees of freedom can be synchronized in
extended systems with a significant degree of robustness arising from
topological protection.Comment: 5+1 pages, 2 figures, comments are welcom
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