Accuracy Study of a Single Frequency Receiver Using a Combined GPS/GALILEO Constellation

As the date of availability of GALILEO approaches, more and more interest appears to pre-evaluate the accuracy of GALILEO and combined GPS+ GALILEO receivers. The majority of simulations made are based on the general use of UERE (often presented as a function of the elevation angle of the satellite) multiplied by the GDOP (Geometric Dilution Of Precision) matrix. This is a too approximate approach to state for the real position error distributions. Therefore, the concept of an Instantaneous Pseudo Range Error (IPRE) is defined and is implemented into NAVSIM the DLR’s end to end GNSS simulator. This new module coupled with the other modules of the simulator permit to lead complete End-to-End simulations. This new functionality has the advantage to augment the field of applications and to couple the generation of errors already implemented in NAVSIM with error distributions coming from real measurements. This study is a good first approach to compare constellations between each other regarding the accuracy issue. The IPRE concept multiplies the functionalities thanks to its ability to generate real distributions of errors. The application to a combined existing constellation (GPS) for which real measurements can be used with a not yet existing constellation (GALILEO) for which only simulated data can be used is an interesting approach. These results can directly be used to test the impact of correction models, of filtering techniques, of antenna types to a combined GPS/GALILEO system thanks to the time series of IPRE and the instantaneous individual errors output from NAVSIM. The best strategy of error mitigation technique can be tested and the result can be used for receiver design before the launch of GALILEO system

Electro-thermal Transport in Non-homogenous Network

Nano-structured networks have drawn attention as potential replacements for bulk-material approaches in applications including transparent conducting electrodes (TCEs). As TCEs, these systems can provide relatively low sheet resistances in the high optical transmission regime along with excellent mechanical flexibility. While percolation models have been developed to describe the general trends in sheet resistance and transmittance on nanowire density, prior experiments have not yielded details such as distributions of junction resistances and current pathways through the networks. Most experimental studies on nanostructured TCE properties have focused on large area steady state exploration of electrical and optical properties or more microscopic studies of single/few junctions within the networks. A more detailed and microscopic understanding of the conduction pathways is necessary to more completely understand the percolating transport in these network systems. In this thesis, we fabricate high quality graphene-silver nanowire (NW) based hybrid TCE and use transient thermoreflectance (TR) imaging technique with high temporal (200 ns) and spatial resolution (~ 200 - 400 nm) that allows simultaneous characterization of time and spatial dependence of the local self-heating around NW-NW junctions. Hotspots arise from self-heating associated with applied bias and are spatially correlated with current pathways through the network. Moreover, these hotspots can potentially redistribute and/or turn off percolating conductive current pathways due to elevated temperatures and thus impose reliability concerns. The ability to image the formation of the microscopic hotspots due to local self-heating (i.e. associated with local current pathways through the microscopic regions) provides a means to semi-quantitatively infer current pathways in these percolating systems. First, we investigate time dependent temperature rise at hotspots in hybrid network at low spatial resolution (i.e. each hotspot comprises multiple NW-NW junctions) that allows analysis of multiple hotspots residing in between the electrical contacts. We quantitatively determine the thermal time constants of the hotspots and show their dependence on different spatial locations within the network. Collectively, we decouple the temperature rise into separate contributions from local self-heating and heat spreading from the electrical contacts. As we identify the time regime when local self-heating at the hotspots is predominant, we focus on local self-heating (rather than heat spreading from contacts) for subsequent electro-thermal studies. Next, using high-resolution TR imaging in case of a silver NW network, we study microscopic hotspots corresponding to individual NW-NW junctions and show the temporal and spatial evolution of the temperature profiles along two crossing NWs. We quantify the local power generated at a hotspot (i.e. an individual junction) at steady state and the fraction of this power propagating along each constituent NW. We also compare material/composition dependence of hotspots (each containing multiple junctions) characteristics in terms of their transient electro-thermal response, number, average temperature, and spatial distribution by considering two random 2-D networks where different transport mechanism prevails: silver NW network (percolation) and graphene-silver NW hybrid network (copercolation). Finally, we do an extended study of temperature distributions (which can be described by Weibull distributions) in silver NW network that shows distinctive signatures (i.e. evolution of shape parameter with time) of local self-heating vs heat spreading through network. The ability to resolve the local self-heating with high temporal and spatial resolution uniquely enables a comprehensive understanding of electro-thermal response and current pathways in the distributed conductors

Experimental Evaluation of Effect of Length of Stone Column on Load Carrying Capacity of Cohesive Soil

Stone column technique is widely used to improve load bearing capacity and to reduce settlement in case of soft clayey soil and loose silty soil. Stone column helps to improve the properties of soil by densifying, reinforcing the soil forming stiff fused soil mass. More over stone column provides good drainage path and diminishes the excess pore pressure. This paper discuss the effect of length of stone column on the performance of stone column through a lab study