Intracellular transport driven by cytoskeletal motors: General mechanisms and defects

Cells are strongly out-of-equilibrium systems driven by continuous energy supply. They carry out many vital functions requiring active transport of various ingredients and organelles, some being small, others being large. The cytoskeleton, composed of three types of filaments, determines the shape of the cell and plays a role in cell motion. It also serves as a road network for the so-called cytoskeletal motors. These molecules can attach to a cytoskeletal filament, perform directed motion, possibly carrying along some cargo, and then detach. It is a central issue to understand how intracellular transport driven by molecular motors is regulated, in particular because its breakdown is one of the signatures of some neuronal diseases like the Alzheimer. We give a survey of the current knowledge on microtubule based intracellular transport. We first review some biological facts obtained from experiments, and present some modeling attempts based on cellular automata. We start with background knowledge on the original and variants of the TASEP (Totally Asymmetric Simple Exclusion Process), before turning to more application oriented models. After addressing microtubule based transport in general, with a focus on in vitro experiments, and on cooperative effects in the transportation of large cargos by multiple motors, we concentrate on axonal transport, because of its relevance for neuronal diseases. It is a challenge to understand how this transport is organized, given that it takes place in a confined environment and that several types of motors moving in opposite directions are involved. We review several features that could contribute to the efficiency of this transport, including the role of motor-motor interactions and of the dynamics of the underlying microtubule network. Finally, we discuss some still open questions.Comment: 74 pages, 43 figure

Design of 10 Gb/s burst-mode receivers for high-split extended reach PONs

The continuous stream of new applications for the internet, increases the need for higher access speed in the currently deployed communication networks. Most networks in use today still consist of twisted copper wires, inherited from the telephone network. The disadvantages of reusing the existing telephone network are twofold. Firstly, the bandwidth of twisted copper wires is limited and secondly, a large number of switches and routers are needed throughout the network leading to an excessive power consumption. The hybrid fiber coax network that reuses the television distribution network is not free from these drawbacks. The bandwidth is also limited and power hungry amplifiers are needed to bridge the distance to and from the user. The future of broadband access lies in optical fiber networks. The optical fiber has a virtually unlimited bandwidth and the lower attenuation leads to less switches and amplifiers in the network, reducing the power consumption of the complete infrastructure. This dissertation describes the design of a 10 Gb/s burst-mode receiver for high-split extended reach passive optical networks (PONs). The designed receiver incorporates two very advanced features. Firstly, the burst-mode receiver locks its gain setting within 6 ns avoiding packet loss due to gain switching during data payload reception. Secondly, the burst-mode receiver detects both burst start and burst end, making it the first burst-mode receiver of its kind to operate without any time critical signal requirements from outside the burst-mode receiver. The presented work covers the chip-level architecture study and design of a 10 Gb/s burst-mode transimpedance amplifier and a 10 Gb/s post-amplifier, which are the two most critical components of a burst-mode receiver

Annual General Assembly of the International Association of Maritime Universities

978-84-947311-7-

An investigation of stress wave propagation through rock joints and rock masses

Tese de doutoramento. Engenharia Civil. Faculdade de Engenharia. Universidade do Porto, Laboratório Nacional de Engenharia Civil. 201

Advanced Testing and Characterization of Bituminous Materials, Two Volume Set

Bituminous materials are used to build durable roads that sustain diverse environmental conditions. However, due to their complexity and a global shortage of these materials, their design and technical development present several challenges. Advanced Testing and Characterisation of Bituminous Materials focuses on fundamental and performance testin

Characterization of turbulent exchange processes in real urban street canyons with and without vegetation

Recent studies on turbulent exchange processes between the urban canopy layer and the atmosphere above have focused primarily on mechanical effects and less so on thermal ones, mostly by means of laboratory and numerical investigations and rarely in the real environment. More recently, these studies have been adopted to investigate city breathability, urban comfort and citizen health, with the aim to find new mitigation or adaptation solutions to air pollution and urban heat island, to enhance the citizen wellness. To investigate the small-scale processes characterizing vegetative and non-vegetative urban canopies, two field campaigns have been carried out within the city of Bologna, Italy. New mechanical and thermal time scales, and their ratios (rates), associated with inertial and thermal flow circulations, have been derived to this scope. In the non-vegetated canopy, mechanical time scales are found to describe fast exchanges at the rooftop and slow within the canopy, while thermal ones to describe fast mixing in the whole canopy. Faster processes are found in the vegetative canopy, with rapidly mixed mechanical time scales and varying thermal ones. The exchange rates are found to identify favorable mixing conditions in the 50−75% of the investigated period, but extreme disadvantageous events can totally suppress the exchanges. The exchange rates are also found to drive the pollutant removal from vegetated and non-vegetated canopies, with an efficacy which depends on the in-canyon circulation. The impacts of real trees in a real neighborhood of the city is tackled with a simplified fluid-dynamics model, where mean flow and turbulence are studied with different vegetation cofigurations, topological and morphological characteristics. Vegetation is found to increase both blocking and channeling effects on the mean flow and to modify the production/dissipation rate of turbulence, depending on the wind direction and topology. Nevertheless, buildings maintain a predominant impact on the atmospheric flows