All-optical routing and switching for three-dimensional photonic circuitry

The ability to efficiently transmit and rapidly process huge amounts of data has become almost indispensable to our daily lives. It turned out that all-optical networks provide a very promising platform to deal with this task. Within such networks opto-optical switches, where light is directed by light, are a crucial building block for an effective operation. In this article, we present an experimental analysis of the routing and switching behaviour of light in two-dimensional evanescently coupled waveguide arrays of Y- and T-junction geometries directly inscribed into fused silica using ultrashort laser pulses. These systems have the fundamental advantage of supporting three-dimensional network topologies, thereby breaking the limitations on complexity associated with planar structures while maintaining a high dirigibility of the light. Our results show how such arrays can be used to control the flow of optical signals within integrated photonic circuits

Diversifying molecular and topological space via a supramolecular solid-state synthesis: a purely organic mok net sustained by hydrogen bonds

A three-dimensional hydrogen-bonded network based on a rare mok topology has been constructed using an organic molecule synthesized in the solid state. The molecule is obtained using a supramolecular protecting-group strategy that is applied to a solid-state [2+2] photodimerization. The photodimerization affords a novel head-to-head cyclobutane product. The cyclobutane possesses tetrahedrally disposed cis-hydrogen-bond donor (phenolic) and cis-hydrogen- bond acceptor (pyridyl) groups. The product self-assembles in the solid state to form a mok network that exhibits twofold interpenetration. The cyclobutane adopts different conformations to provide combinations of hydrogen-bond donor and acceptor sites to conform to the structural requirements of the mok net

Automated Hardware Prototyping for 3D Network on Chips

Vor mehr als 50 Jahren stellte Intel® Mitbegründer Gordon Moore eine Prognose zum Entwicklungsprozess der Transistortechnologie auf. Er prognostizierte, dass sich die Zahl der Transistoren in integrierten Schaltungen alle zwei Jahre verdoppeln wird. Seine Aussage ist immer noch gültig, aber ein Ende von Moores Gesetz ist in Sicht. Mit dem Ende von Moore’s Gesetz müssen neue Aspekte untersucht werden, um weiterhin die Leistung von integrierten Schaltungen zu steigern. Zwei mögliche Ansätze für "More than Moore” sind 3D-Integrationsverfahren und heterogene Systeme. Gleichzeitig entwickelt sich ein Trend hin zu Multi-Core Prozessoren, basierend auf Networks on chips (NoCs). Neben dem Ende des Mooreschen Gesetzes ergeben sich bei immer kleiner werdenden Technologiegrößen, vor allem jenseits der 60 nm, neue Herausforderungen. Eine Schwierigkeit ist die Wärmeableitung in großskalierten integrierten Schaltkreisen und die daraus resultierende Überhitzung des Chips. Um diesem Problem in modernen Multi-Core Architekturen zu begegnen, muss auch die Verlustleistung der Netzwerkressourcen stark reduziert werden. Diese Arbeit umfasst eine durch Hardware gesteuerte Kombination aus Frequenzskalierung und Power Gating für 3D On-Chip Netzwerke, einschließlich eines FPGA Prototypen. Dafür wurde ein Takt-synchrones 2D Netzwerk auf ein dreidimensionales asynchrones Netzwerk mit mehreren Frequenzbereichen erweitert. Zusätzlich wurde ein skalierbares Online-Power-Management System mit geringem Ressourcenaufwand entwickelt. Die Verifikation neuer Hardwarekomponenten ist einer der zeitaufwendigsten Schritte im Entwicklungsprozess hochintegrierter digitaler Schaltkreise. Um diese Aufgabe zu beschleunigen und um eine parallele Softwareentwicklung zu ermöglichen, wurde im Rahmen dieser Arbeit ein automatisiertes und benutzerfreundliches Tool für den Entwurf neuer Hardware Projekte entwickelt. Eine grafische Benutzeroberfläche zum Erstellen des gesamten Designablaufs, vom Erstellen der Architektur, Parameter Deklaration, Simulation, Synthese und Test ist Teil dieses Werkzeugs. Zudem stellt die Größe der Architektur für die Erstellung eines Prototypen eine besondere Herausforderung dar. Frühere Arbeiten haben es versäumt, eine schnelles und unkompliziertes Prototyping, insbesondere von Architekturen mit mehr als 50 Prozessorkernen, zu realisieren. Diese Arbeit umfasst eine Design Space Exploration und FPGA-basierte Prototypen von verschiedenen 3D-NoC Implementierungen mit mehr als 80 Prozessoren

Commissural axon guidance in the developing spinal cord: from Cajal to the present day.

During neuronal development, the formation of neural circuits requires developing axons to traverse a diverse cellular and molecular environment to establish synaptic contacts with the appropriate postsynaptic partners. Essential to this process is the ability of developing axons to navigate guidance molecules presented by specialized populations of cells. These cells partition the distance traveled by growing axons into shorter intervals by serving as intermediate targets, orchestrating the arrival and departure of axons by providing attractive and repulsive guidance cues. The floor plate in the central nervous system (CNS) is a critical intermediate target during neuronal development, required for the extension of commissural axons across the ventral midline. In this review, we begin by giving a historical overview of the ventral commissure and the evolutionary purpose of decussation. We then review the axon guidance studies that have revealed a diverse assortment of midline guidance cues, as well as genetic and molecular regulatory mechanisms required for coordinating the commissural axon response to these cues. Finally, we examine the contribution of dysfunctional axon guidance to neurological diseases

System-Level Modeling and Optimization of the Energy Efficiency in Cellular Networks -- A Stochastic Geometry Framework

In this paper, we analyze and optimize the energy efficiency of downlink cellular networks. With the aid of tools from stochastic geometry, we introduce a new closed-form analytical expression of the potential spectral efficiency (bit/sec/m$^2$). In the interference-limited regime for data transmission, unlike currently available mathematical frameworks, the proposed analytical formulation depends on the transmit power and deployment density of the base stations. This is obtained by generalizing the definition of coverage probability and by accounting for the sensitivity of the receiver not only during the decoding of information data, but during the cell association phase as well. Based on the new formulation of the potential spectral efficiency, the energy efficiency (bit/Joule) is given in a tractable closed-form formula. An optimization problem is formulated and is comprehensively studied. It is mathematically proved, in particular, that the energy efficiency is a unimodal and strictly pseudo-concave function in the transmit power, given the density of the base stations, and in the density of the base stations, given the transmit power. Under these assumptions, therefore, a unique transmit power and density of the base stations exist, which maximize the energy efficiency. Numerical results are illustrated in order to confirm the obtained findings and to prove the usefulness of the proposed framework for optimizing the network planning and deployment of cellular networks from the energy efficiency standpoint.Comment: To appear in IEEE Transactions on Wireless Communication

Graphene-Based Aerogels for Biomedical Application

Aerogels are three-dimensional solid networks with incredibly low densities, high porosity, and large specific surface areas. These aerogels have both nanoscale and macroscopic interior structures. Combined with graphene, the aerogels show improved mechanical strength, electrical conductivity, surface area, and adsorption capacity, making them ideal for various biomedical applications. The graphene aerogel has a high drug-loading capacity due to its large surface area, and the porous structure enables controlled drug release over time. The presence of graphene makes it a suitable material for wound dressings, blood coagulation, and bilirubin adsorption. Additionally, graphene’s conductivity can help in the electrical stimulation of cells for improved tissue regeneration, and it is also appropriate for biosensors. In this review, we discuss the preparation and advantages of graphene-based aerogels in wound dressings, drug delivery systems, bone regeneration, and biosensors