Relaxation to persistent currents in a Hubbard trimer coupled to fermionic baths

We consider a ring of fermionic quantum sites, modeled by the Fermi-Hubbard Hamiltonian, in which electrons can move and interact strongly via the Coulomb repulsion. The system is coupled to fermionic cold baths which by the exchange of particles and energy induce relaxation in the system. We eliminate the baths and describe the system effectively by the Lindblad master equations in various versions valid for different coupling parameter regimes. The early relaxation phase proceeds in a universal way, irrespective of the relative couplings and approximations. The system settles down to its low-energy sector and is consecutively well approximated by the Heisenberg model. In the late relaxation, different Lindblad approaches push the system towards different final states with opposite, extreme spin orders, from ferromagenetic to antiferromagnetic. Due to spin frustration in the trimer (a three site ring), degenerate ground states are formed by spin waves (magnons). The system described by the global coherent version of the Lindblad operators relaxes towards the final states carrying directed persistent spin currents. We numerically confirm these predictions.Comment: 24 pages, 14 figure

Neue Wege für die Einbindung des Schienengüterverkehrs in die Wertschöpfungsketten der Logistik: Neue Wege für die Einbindung des Schienengüterverkehrs in die Wertschöpfungsketten der Logistik

Der Schienengüterverkehr in Deutschland weist nach langer Stagnation erstmals wieder eine höhere Wachstumsrate als der Straßengüterverkehr auf. Die hierbei erreichten Positionen können jedoch langfristig nur ausgebaut werden, wenn es gelingt, die Zukunftsfähigkeit des Schienengüterverkehrs in den Lieferketten der Industrie und des Handels zu sichern. Der Überwindung existierender und neuer Engpässe bei der Nutzung der notwendigen Ressourcen, wie zum Beispiel der Gleisinfrastruktur, kommt dabei eine herausragende Bedeutung zu. Kurz- und mittelfristig gefragt sind daher Ansätze für eine effizientere Nutzung der vorhandenen Ressourcen. Im Beitrag werden dazu an den Schnittstellen zwischen Schienengüterverkehr und Logistik neue strategische und operative Ansätze für ein prozess- und strukturübergreifendes Ressourcenmanagement vorgestellt.For the first time after years of decline, rail freight transport in Germany is returning a higher growth rate than road transport. The success of recent years can only be perpetuated, however, if the growing demands of consignors can be fulfilled under conditions of increasing cost pressure. Meanwhile, the recent dynamic growth in transport volume is leading to first bottlenecks regarding the necessary resources for rail freight operation, e.g. railway infrastructure. New paths and solutions are thus required, with a strong focus on more efficient use of the existing resources. This paper presents new approaches to process and cross-company resource management, based on existing potentials at the interfaces between the operational concepts of freight railways, logistics and production

Casting of Gold Nanoparticles with High Aspect Ratios inside DNA Molds

DNA nanostructures provide a powerful platform for the programmable assembly of nanomaterials. Here this approach is extended to synthesize rod-like gold nanoparticles in a full DNA controlled manner. The approach is based on DNA molds containing elongated cavities. Gold is deposited inside the molds using a seeded-growth procedure. By carefully exploring the growth parameters it is shown that gold nanostructures with aspect ratios of up to 7 can be grown from single seeds. The highly anisotropic growth is in this case controlled only by the rather soft and porous DNA walls. The optimized seeded growth procedure provides a robust and simple routine to achieve continuous gold nanostructures using DNA templating

Smart Chips for Smart Surroundings -- 4S

The overall mission of the 4S project (Smart Chips for Smart Surroundings) was to define and develop efficient flexible, reconfigurable core building blocks, including the supporting tools, for future Ambient System Devices. Reconfigurability offers the needed flexibility and adaptability, it provides the efficiency needed for these systems, it enables systems that can adapt to rapidly changing environmental conditions, it enables communication over heterogeneous wireless networks, and it reduces risks: reconfigurable systems can adapt to standards that may vary from place to place or standards that have changed during and after product development. In 4S we focused on heterogeneous building blocks such as analogue, hardwired functions, fine and coarse grain reconfigurable tiles and microprocessors. Such a platform can adapt to a wide application space without the need for specialized ASICs. A novel power aware design flow and runtime system was developed. The runtime system decides dynamically about the near-optimal application mapping to the given hardware platform. The overall concept was verified on hardware platforms based on an existing SoC and in a second step with novel silicon. DRM (Digital Radio Mondiale) and MPEG4 Video applications have been implemented on the platforms demonstrating the adaptability of the 4S concept

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