Z-Curve: A Time Difference of Arrivals (TDOA) Based Model for Global Navigation Satellite Systems (GNSS) Signals

Jmjd3, a histone H3K27 demethylase, regulates macrophage and T-cell differentiation, but its role in T-cell trafficking and persistence remains largely unknown. In this dissertation, I show that Jmjd3 deficiency in CD4^+ T cells limits CD4^+ T-cell egress out of the thymus, leading to thymic T-cell accumulation, and Jmjd3 deletion limits peripheral CD4^+ T-cell migration, leading to a reduced number of T cells in secondary lymphoid organs. Further investigation identified Pdlim4 as a novel Jmjd3 target gene that affects T-cell trafficking by cooperating with S1P1. Jmjd3 deficiency also enables T-cell persistence due to an increase in proliferation and a decrease in apoptosis, suggesting that the H3K27 demethylase Jmjd3 may be a good therapeutic target for adoptive immunotherapy for the generation of superior T cell grafts

Flower constellation optimization and implementation

Satellite constellations provide the infrastructure to implement some of the most important global services of our times both in civilian and military applications, ranging from telecommunications to global positioning, and to observation systems. Flower Constellations constitute a set of satellite constellations characterized by periodic dynamics. They have been introduced while trying to augment the existing design methodologies for satellite constellations. The dynamics of a Flower Constellation identify a set of implicit rotating reference frames on which the satellites follow the same closed-loop relative trajectory. In particular, when one of these rotating reference frames is “Planet Centered, Planet Fixed”, then all the orbits become compatible (or resonant) with the planet; consequently, the projection of the relative path on the planet results in a repeating ground track. The satellite constellations design methodology currently most utilized is the Walker Delta Pattern or, more generally, Walker Constellations. The set of orbital planes and initial spacecraft positions are represented by a set of only three integers and two real parameters rather than by all the orbital elements; Flower Constellations provide a more general framework in which most of the former restrictions are removed, by allowing the use of resonant elliptical orbits. Flower Constellations can represent hundreds of spacecraft with a set of 6 integers and 5 real parameters only and existing constellations can be easily reproduced. How to design a Flower Constellation to satisfy specific mission requirements is an important problem for promoting the acceptance of this novel concept by the space community. Therefore one of the main goals of this work is that of proposing design techniques that can be applied to satisfy practical mission requirements. The results obtained by applying Global optimization techniques, such as Genetic Algorithms, to some relevant navigation and Earth observation space-based systems show that the Flower Constellations not only are as effective asWalker Constellations, but can also be applied to non-traditional constellation problem domains, such as regional coverage and reconnaissance

Establishment of GPS Reference Network in Ghana

The quest for the use of GNSS in developing countries is on the rise following the realization of its numerous advantages over the conventional methods of positioning, navigation and timing. Africa's attempt to harness this technology has made it imperative to investigate the regional problems associated with its implementation by its member states, which constitute the AFREF. This study goes beyond the establishment of a GNSS reference network in Ghana by investigating and finding solutions to some of the regional problems associated with its implementation. The problem of turbulent atmospheric conditions which includes the severe ionospheric fluctuations and the erratic tropospheric conditions coupled with the sparsely populated base stations has led to the development of a new concept of correction, the Corridor Correction, which is able to correct the atmospheric effect comparable with the established concepts like the Virtual Reference Station, VRS, Flaechen-Korrektur-Parameter, FKP and Master Auxiliary Concept, MAC. In spite of the ionospheric problems in the equatorial region, the number of single frequency receivers in use for precise positioning is on the increase as compared with the relatively few multiple frequency receivers. This has necessitated the investigation of the code-plus-carrier processing approach which uses the idea of opposite signs of the propagation delay of the ionosphere in the code and carrier signals to eliminate the ionospheric delay, which normally requires dual frequency receivers to do same. This improved processing technique has led to the achievement of an accuracy of 5 cm with single frequency over a distance of 194 km. Sub-decimeter is generally achieved after 12 hours and 18 hours of observation for a distance of 200 km and 1200 km respectively with this technique as shown in this study. In addition to the improved processing techniques, the ambiguity that characterizes the use of mean-sea-level for the definition of vertical references as a result of either the sea level change or movement of the earth crust can be resolved with the use of GNSS which is independent of these two phenomena. This is achieved by collocating a GPS base station at the reference tide gauge located at Takoradi. The orthometric height derived from the tide gauge and the corresponding ellipsoidal height at the collocated GNSS base station is used to determine the local quasi-geoid. This is compared with the global geoid derived from EGM96, the global model from NGA, to obtain a difference that can be applied as a correction factor to obtain orthometric heights. The release of EGM2008 which has undergone remarkable improvement over EGM96 in terms of resolution makes it important to investigate into how it can be used to improve the orthometric height determination using ellipsoidal heights from GNSS observation. This can be achieved by following up what has been derived with EGM96 at the Takoradi tide gauge with this newly released EGM2008. To be able to move through a smooth transition from the existing geodetic reference system based on the War Office Ellipsoid to the newly established system based on the geocentric ITRF05, a set of seven parameter transformation has been derived for the project area, the Golden Triangle of Ghana.Das Bestreben GNSS in Entwicklungsländern zu nutzen nimmt stetig zu, da man die zahlreichen Vorteile gegenüber herkömmlichen Verfahren der Positionierung, Navigation und Zeitübertragung erkannt hat. Afrikas Versuch, diese Technologie zu nutzen, gebietet es, die regionalen Probleme im Zusammenhang mit der Umsetzung durch die AFREF Mitgliedsstaaten zu untersuchen. Diese Abhandlung geht über die Errichtung eines GNSS Referenznetzwerks in Ghana hinaus, indem sie Lösungen zu einigen regionalen Problemen in der Umsetzung aufzeigt und untersucht. Das Problem der turbulenten Atmosphäre, die schweren ionospärische Fluktuationen und sprunghafte troposphärische Bedingungen verbunden mit den sehr spärlich gestreuten Referenzstationen, hat zu der Entwicklung eines neuen Konzeptes von Korrekturverfahren, der Corridor Correction, geführt, die es ermöglicht, atmosphärische Einflüsse ähnlich wie etablierte Verfahren wie Virtual Reference Station, VRS, Flaechen-Korrektur-Paramter, FKP and Master Auxiliary Concept, MAC, zu korrigieren. Trotz der Probleme mit der Ionosphäre in der Äquatorregion, übersteigt die Anzahl der Ein-Frequenz-Empfänger für die präzise Positionierung die der relativ wenigen Mehrfrequenzempfänger. Dies machte die Untersuchung des Code-plus-Carrier Prozessierungsansatzes notwendig. Dieser nutzt den Effekt von unterschiedlichen Vorzeichen bei der Änderung der Ausbreitungsgeschwindigkeit von Code- und Trägersignalen durch die Ionosphäre um den ionosphärischen Effekt zu eliminieren, was in der herkömmlichen Prozessierung Zweifrequenzempfänger benötigt. Diese verbesserte Prozessierungstechnik hat zur Erzielung von Genauigkeiten von 5 cm mit Einfrequenzempfängern über eine Basislinienlänge von 194 km geführt. Damit werden im Allgemeinen Sub-Dezimeter Genauigkeiten nach 12 Stunden Beobachtungsdauer für Basislinienlängen von 200 km bzw. 18 Stunden für Basislinien von 1200 km erreicht, wie diese Abhandlung zeigt. Zusätzlich zu den oben genannten Verbesserungen in der Prozessierung, wird eine Methode aufgezeigt, die die Unsicherheit durch Meeresspiegeländerungen oder Bewegungen der Erdkruste, die der Gebrauch des mittleren Meeresspiegels als Definition des vertikalen Datums in sich birgt, durch den Gebrauch von GNSS, das von diesen beiden Phänomenen unberührt ist. Dies wird dadurch erreicht, dass GPS Basisstationen an Orten mit einer Pegelstation eingerichtet werden. Die orthometrische Höhe des Referenzpegels und die ellipsoidische Höhe der Basisstation werden dann zur Bestimmung eines lokalen Geoids verwendet. Das in dieser Abhandlung verwendete lokale Geoid ist an das globale Geoid angeschlossen worden, das aus dem EGM96, dem Modell der NGA, abgeleitet ist. Die Veröffentlichung des EGM2008, das gegenüber dem EGM96 im Hinblick auf die Auflösung erfahren hat bedeutende Verbesserungen, erfordert es, zu untersuchen, wie es Ghana zur Bestimmung von orthometrischen Höhen durch GNSS Beobachtungen nutzen kann. Das kann durch eine Weiterentwicklung des Ansatzes erreicht werden, der in dieser Studie schon mit dem EGM96 für Ghana bei Takoradi begonnen wurde. Das hierbei aufgebaute GNSS Referenznetzwerk wurde an den Pegel von Takoradi angeschlossen, einem der ältesten Level auf dem afrikanischen Kontinent. Um einen glatten Übergang vom vorhandenen Referenzsystem, das auf dem War Office Ellipsoid basiert, zum neuen, auf dem ITRF05 basierendem System zu ermöglichen, wurde ein Satz von sieben Transformationsparametern abgeleitet, die auf den Messungen im Projektgebiet „Goldenes Dreieck“ in Ghana basieren

The Effects of Using Solar Radiation Pressure to Alleviate Fuel Requirements for Orbit Changing and Maintenance of the DSCS II F-13 Satellite

Orbit disposal and maintenance of aging satellites has become a significant concern over the past few years, as the increasing number of orbiting objects threatens to limit the launching of future satellites. Many of the satellites currently in orbit, however, were not built with disposal considerations. The DSCS II series was launched into orbit beginning in the 1970s, and many satellites are now without the fuel required to conventionally transition to a sanctioned disposal orbit. In GEO orbit the largest non-gravitational perturbation is solar radiation pressure. By adjusting the attitude of a satellite with a controller to maximize the perturbing acceleration due to the force of SRP, the satellite can be slowly raised into a disposal orbit. The results from this study, along with validation results propagated with STK, are presented. After making several simplifying assumptions, the time required to raise the modelled DSCS II F-13 satellite 400 km into a disposal orbit is approximately 33 years. This time-to-disposal can be reduced by using a larger area-to-mass ratio and more reflective surface materials

Simulator Networking Handbook: Distributed Interactive Simulation Testbed

Report is an attempt to collect and organize a large body of knowledge regarding the design and development of simulation networks, particularly distributed interactive simulation

Advanced multilateration theory, software development, and data processing: The MICRODOT system

The process of geometric parameter estimation to accuracies of one centimeter, i.e., multilateration, is defined and applications are listed. A brief functional explanation of the theory is presented. Next, various multilateration systems are described in order of increasing system complexity. Expected systems accuracy is discussed from a general point of view and a summary of the errors is listed. An outline of the design of a software processing system for multilateration, called MICRODOT, is presented next. The links of this software, which can be used for multilateration data simulations or operational data reduction, are examined on an individual basis. Functional flow diagrams are presented to aid in understanding the software capability. MICRODOT capability is described with respect to vehicle configurations, interstation coordinate reduction, geophysical parameter estimation, and orbit determination. Numerical results obtained from MICRODOT via data simulations are displayed both for hypothetical and real world vehicle/station configurations such as used in the GEOS-3 Project. These simulations show the inherent power of the multilateration procedure

A microcomputer-based position updating system for general aviation utilizing Loran-C

Modern digital electronic technology is used to produce a device to convert LORAN C to useful pilot information using a simple software algebra and low cost microprocessor devices. Results indicate that the processor based LORAN C navigator has an accuracy of 1.0 nm or less over an area typically covered by a triad of Loran C stations and can execute a position update in less than 0.2 seconds. The system was tested in 30 hours of flight and proved that it can give reliable and accurate navigation information. Methods of converting time differences to position, design considerations for the microcomputer system, and the system for coordinate conversion are discussed. Testing with predetermined points and possible fixes for errors are also considered

Terrain Referenced Navigation Using SIFT Features in LiDAR Range-Based Data

The use of GNSS in aiding navigation has become widespread in aircraft. The long term accuracy of INS are enhanced by frequent updates of the highly precise position estimations GNSS provide. Unfortunately, operational environments exist where constant signal or the requisite number of satellites are unavailable, significantly degraded, or intentionally denied. This thesis describes a novel algorithm that uses scanning LiDAR range data, computer vision features, and a reference database to generate aircraft position estimations to update drifting INS estimates. The algorithm uses a single calibrated scanning LiDAR to sample the range and angle to the ground as an aircraft flies, forming a point cloud. The point cloud is orthorectified into a coordinate system common to a previously recorded reference of the flyover region. The point cloud is then interpolated into a Digital Elevation Model (DEM) of the ground. Range-based SIFT features are then extracted from both the airborne and reference DEMs. Features common to both the collected and reference range images are selected using a SIFT descriptor search. Geometrically inconsistent features are filtered out using RANSAC outlier removal, and surviving features are projected back to their source coordinates in the original point cloud. The point cloud features are used to calculate a least squares correspondence transform that aligns the collected features to the reference features. Applying the correspondence that best aligns the ground features is then applied to the nominal aircraft position, creating a new position estimate. The algorithm was tested on legacy flight data and typically produces position estimates within 10 meters of truth using threshold conditions