Anisotropic Outflows and IGM Enrichment

We have designed an analytical model for the evolution of anisotropic galactic outflows. These outflows follow the path of least resistance, and thus travel preferentially into low-density regions, away from cosmological structures where galaxies form. We show that anisotropic outflows can significantly enrich low-density systems with metals.Comment: Proceedings of Chemodynamics 2006, Lyon, 2 pages, 1 figure, style file include

Anisotropic Galactic Outflows and Enrichment of the Intergalactic Medium. I: Monte Carlo Simulations

We have developed an analytical model to describe the evolution of anisotropic galactic outflows. With it, we investigate the impact of varying opening angle on galaxy formation and the evolution of the IGM. We have implemented this model in a Monte Carlo algorithm to simulate galaxy formation and outflows in a cosmological context. Using this algorithm, we have simulated the evolution of a comoving volume of size [12h^(-1)Mpc]^3 in the LCDM universe. Starting from a Gaussian density field at redshift z=24, we follow the formation of ~20,000 galaxies, and simulate the galactic outflows produced by these galaxies. When these outflows collide with density peaks, ram pressure stripping of the gas inside the peak may result. This occurs in around half the cases and prevents the formation of galaxies. Anisotropic outflows follow the path of least resistance, and thus travel preferentially into low-density regions, away from cosmological structures (filaments and pancakes) where galaxies form. As a result, the number of collisions is reduced, leading to the formation of a larger number of galaxies. Anisotropic outflows can significantly enrich low-density systems with metals. Conversely, the cross-pollution in metals of objects located in a common cosmological structure, like a filament, is significantly reduced. Highly anisotropic outflows can travel across cosmological voids and deposit metals in other, unrelated cosmological structures.Comment: 32 pages, 9 figures (2 color). Revised version accepted in Ap

Q-Band Millimeter-Wave Antennas: An Enabling Technology for MultiGigabit Wireless Backhaul

[EN] The bandwidth demands in mobile communication systems are growing exponentially day by day as the number of users has increased drastically over the last five years. This mobile data explosion, together with the fixed service limitations, requires a new approach to support this increase in bandwidth demand. Solutions based on lower-frequency microwave wireless systems may be able to meet the bandwidth demand in a short term. However, with the small-cell mass deployment requiring total capacities of 1 Gb/s/km2, scalable, multigigabit backhaul systems are required. Millimeter-wave technology fits nicely into these new backhaul scenarios as it provides extended bandwidth for high-capacity links and adaptive throughput rate, which allows efficient and flexible deployment. Besides these advantages, millimeter-wave solutions become even more attractive when the cost of backhaul solutions and the cost of spectrum licenses are factored in. Compared to the cost of laying fiber to a cell base station, which is the only other scalable solution, the millimeter-wave solution becomes the most appropriate approach.The research leading to these results received funding from the European Commission's seventh Framework Programme under grant agreement 288267.Vilar Mateo, R.; Czarny, R.; Lee, ML.; Loiseaux, B.; Sypek, M.; Makowski, M.; Martel, C.... (2014). Q-Band Millimeter-Wave Antennas: An Enabling Technology for MultiGigabit Wireless Backhaul. IEEE Microwave Magazine. 15(4):121-130. https://doi.org/10.1109/MMM.2014.2308769S12113015

Identification of molecular signatures specific for distinct cranial sensory ganglia in the developing chick

Background The cranial sensory ganglia represent populations of neurons with distinct functions, or sensory modalities. The production of individual ganglia from distinct neurogenic placodes with different developmental pathways provides a powerful model to investigate the acquisition of specific sensory modalities. To date there is a limited range of gene markers available to examine the molecular pathways underlying this process. Results Transcriptional profiles were generated for populations of differentiated neurons purified from distinct cranial sensory ganglia using microdissection in embryonic chicken followed by FAC-sorting and RNAseq. Whole transcriptome analysis confirmed the division into somato- versus viscerosensory neurons, with additional evidence for subdivision of the somatic class into general and special somatosensory neurons. Cross-comparison of distinct ganglia transcriptomes identified a total of 134 markers, 113 of which are novel, which can be used to distinguish trigeminal, vestibulo-acoustic and epibranchial neuronal populations. In situ hybridisation analysis provided validation for 20/26 tested markers, and showed related expression in the target region of the hindbrain in many cases. Results One hundred thirty-four high-confidence markers have been identified for placode-derived cranial sensory ganglia which can now be used to address the acquisition of specific cranial sensory modalities.</p

Modelling and Design of Antennas For Ground-Penetrating Radar Systems.

This thesis addresses the problem of stand-off ground-penetrating radar (GPR) antenna systems, which are principally used in demining applications. The detection of buried target is difficult due to fundamental limitations. Electromagnetic signals are highly attenuated in soil and the attenuation increases with frequency. Depth resolution on the target can only be achieved with broadband systems. As a consequence, the requirements on the antenna are severe. Antennas having a large bandwidth and a clean radiated response are needed to achieve depth resolution of the target. Moreover, stand-off systems such as the one used in demining applications require sufficient gain characteristics and mobility. The physics behind the GPR problem is complicated due to the large number of parameters affecting the radiation and reception of electromagnetic signals. Natural soils are often inhomogeneous and the close environment creates a considerable amount of clutter. Modelling techniques play an important role in understanding the electromagnetic wave propagation in natural ground. They are very useful in the design of antenna systems. The above issues are addressed in two different investigation routes. One route of investigation looks at the design of directive broadband antennas. The other route of investigation concerns the way of enhancing the modelling capabilities of GPR antenna problems. A novel stand-off antenna is proposed. The structure is resistively loaded and resembles a skeleton TEM horn. The design of the TEM horn antenna is undertaken by using an equivalent transmission line model. The structure is optimised to meet the design goals. Prototypes of the derived antenna are built and used within a real GPR system. GPR images of mines are obtained using the prototypes. Additionally, the agreement between measurements and predictions is good. Concerning the second route of investigation of this project, a hybrid method based on plane wave spectra interactions is introduced. The method enables field prediction of a GPR situation. It is based on splitting the complete problem into two sub-geometries. One geometry represents the antenna and the other represents the ground with buried targets. Each sub-geometry is analysed independently. Field prediction is undertaken by merging the two sub-geometries via a plane wave spectra formulation. The proposed hybrid method is validated with a dipole and a TEM horn antenna problem. Good agreement is found between the Method of Moment results and the hybrid method results

Modelling and design of antennas for ground penetrating radar systems

SIGLEAvailable from British Library Document Supply Centre- DSC:DXN055102 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Modelling and Design of Antennas for Ground-Penetrating Radar Systems

This thesis addresses the problem of stand-off ground-penetrating radar (GPR) antenna systems, which are principally used in demining applications. The detection of buried target is difficult due to fundamental limitations. Electromagnetic signals are highly attenuated in soil and the attenuation increases with frequency. Depth resolution on the target can only be achieved with broadband systems. As a consequence, the requirements on the antenna are severe. Antennas having a large bandwidth and a clean radiated response are needed to achieve depth resolution of the target. Moreover, stand-off systems such as the one used in demining applications require sufficient gain characteristics and mobility. The physics behind the GPR problem is complicated due to the large number of parameters affecting the radiation and reception of electromagnetic signals. Natural soils are often inhomogeneous and the close environment creates a considerable amount of clutter. Modelling techniques play an important role in understanding the electromagnetic wave propagation in natural ground. They are very useful in the design of antenna systems. The above issues are addressed in two different investigation routes. One route of investigation looks at the design of directive broadband antennas. The other route of investigation concerns the way of enhancing the modelling capabilities of GPR antenna problems. A novel stand-off antenna is proposed. The structure is resistively loaded and resembles a skeleton TEM horn. The design of the TEM horn antenna is undertaken by using an equivalent transmission line model. The structure is optimised to meet the design goals. Prototypes of the derived antenna are built and used within a real GPR system. GPR images of mines are obtained using the prototypes. Additionally, the agreement between measurements and predictions is good. Concerning the second route of investigation of this project, a hybrid method based on plane wave spectra interactions is introduced. The method enables field prediction of a GPR situation. It is based on splitting the complete problem into two sub-geometries. One geometry represents the antenna and the other represents the ground with buried targets. Each sub-geometry is analysed independently. Field prediction is undertaken by merging the two sub-geometries via a plane wave spectra formulation. The proposed hybrid method is validated with a dipole and a TEM horn antenna problem. Good agreement is found between the Method of Moment results and the hybrid method results

Antenna-based Multipath and Interference Mitigation for Aeronautical Applications: Present and Future

Vulnerability to radio interference and multipath is a wellknown drawback of satellite-based navigation systems. This is widely accepted as a critical issue for safety-of-life applications such as precision approach operations in aviation. Interference and multipath signals enter the navigation receiver through the antenna which, in order to minimise such signals, can be used as a spatial- and frequency-domain filter provided that some critical antenna parameters are controlled. The most important parameters are the shape of the antenna pattern with associated cross-polar levels and polarisation purity as well as an appropriate in and out-of-band frequency response. This paper aims at giving an overview of existing and future antenna technologies to be used with satellite navigation receivers. Also, we will consider some auxiliary technologies like resistive or high impedance ground planes which can be used in combination with antenna methods for both the above mentioned categories. Firstly, interference and multipath encountered by an aviation receiver of a Global Navigation Satellite System (GNSS) are briefly discussed. The objective is to set the scene and to identify the most significant sources of radio interference, like DME (Distance Measuerment Equipment) and TACAN (Tactical Air Navigation) systems, and multipath for which some antenna solutions may be provided. The critical antenna parameters for each type of interference will be identified. Secondly, existing antenna solutions and techniques used nowadays with an airborne GPS receiver are reviewed. The majority of existing GNSS antenna solutions are single element based, which usually provide low costs and low implementation complexity. We summarise the main technologies used with single antennas including helical antennas, patch antennas, stacked patch antennas and cavity backed antennas. The compatibility of the reviewed structures with the requirements to critical antenna parameters determined above will be discussed in detail. Advanced antenna systems including antenna arrays and auxiliary technologies will be presented in the paper. Such technologies are based on the use of absorbing materials or borrow from the concept of choked antennas commonly used in ground based geodesy applications. These will be discussed and assessed in view of combating interference and multipath. Array system methodologies currently used in GNSS anti-jam systems will be described and assessed. Array GNSS systems offer advanced capabilities to overcome interference at the expense of size, cost and manufacturing complexity. They are mostly used in military applications to combat intentional interference by shaping the antenna radiation pattern and placing nulls in the direction of interference. These types of antennas are commonly called CRPA´s (Controlled Radiation Pattern Arrays) due to their abilities to tailor their radiation patterns as a function of the interference threats. In this paper, we will analyse conformal array geometries with rectangular and circular grids adjusted to the airframe curvature

Multi path and jam resistant antennas for GNSS receivers

In GNSS applications, multipath errors and jamming threats are still one of the major error sources or service unavailability in conventional receivers. Antenna array algorithms are introduced as a possible solution to both these threats. Nevertheless, the performances of such techniques are degraded when considering technological defects and especially mutual coupling. To face this limitation, a HIS based antenna array design is presented. This design aims at minimizing the array mutual coupling coefficients while not increasing the size of the arra

Interference and Multipath Mitigation Study Report

This document reports results obtained within the first of two phases of WP 3.2.1 “Interference and multipath mitigation study”. The objective of the first phase is to study and define new techniques for mitigating interference and short-delay multipath threats which are required for the design of improved reliability and accuracy navigation platforms. The investigated techniques are both at the antenna level using single antenna or antenna array solutions with conformal or planar geometries and at the receiver level using new specific digital signal processing. Also the possibility of interference and multipath mitigation with the utilization of INS/GNSS hybridisation is investigated