Integrated optics technology study

The status and near term potential of materials and processes available for the fabrication of single mode integrated electro-optical components are discussed. Issues discussed are host material and orientation, waveguide formation, optical loss mechanisms, wavelength selection, polarization effects and control, laser to integrated optics coupling fiber optic waveguides to integrated optics coupling, sources, and detectors. Recommendations of the best materials, technology, and processes for fabrication of integrated optical components for communications and fiber gyro applications are given

Integrated optics technology study

The materials and processes available for the fabrication of single mode integrated electrooptical components are described. Issues included in the study are: (1) host material and orientation, (2) waveguide formation, (3) optical loss mechanisms, (4) wavelength selection, (5) polarization effects and control, (6) laser to integrated optics coupling,(7) fiber optic waveguides to integrated optics coupling, (8) souces, (9) detectors. The best materials, technology and processes for fabrication of integrated optical components for communications and fiber gyro applications are recommended

MAC layer assisted localization in wireless environments with multiple sensors and multiple emitters

Extreme emitter density (EED) RF environments, defined as 10k-100k emitters within a footprint of less than 1 km squared, are becoming increasingly common with the proliferation of personal devices containing myriad communication standards (e.g. WLAN, Bluetooth, 4G, etc). Attendees at concerts, sporting events, and other such large-scale events desire to be connected at all times, creating tremendous spectrum management challenges, especially in unlicensed frequencies such as 2.4 GHz, 5 GHz, or 900 MHz Industrial, Scientific, and Medical (ISM) bands. In licensed bands, there are often critical communication systems such as two-way radios for emergency personnel which must be free from interference. Identification and localization of a non-conforming or interfering Emitter of Interest (EoI) is important for these critical systems. In this dissertation, research is conducted to improve localization for these EED RF environments by exploiting side information available at the Medium Access Control (MAC) layer. The primary contributions of this research are: (1) A testbed in Bobby Dodd football stadium consisting of three spatially distributed, time-synchronized RF Sensor Nodes (RFSN) collecting and archiving complex baseband samples for algorithm development and validation. (2) A modeling framework and analytical results on the benefits of exploiting the structure of the MAC layer for associating physical layer measurements, such as Time Difference of Arrivals (TDoA), to emitters. (3) A three stage localization algorithm exploiting time between packets and a constrained geometry to shrink the error ellipse of the emitter position estimate. The results are expected to improve localization accuracy in wireless environments when multiple sensors observe multiple emitters using a known communications protocol within a constrained geometry.Ph.D

Sensor array processing: localisation of wireless sources

In this thesis, various subspace array processing techniques for wireless source localisation are presented and investigated in the following three aspects. First, in the environment of indoor optical wireless communications, the paths of different sources and/or from different reflectors may impinge on the receiver from closely spaced directions with a high probability. In this case, the ranges of the paths, together with their directions, are important especially for isolating the desired source from the interferers. A blind multi-source localisation approach, which can be used as a channel estimator in the receiver of a communication system, is proposed for direction, range, and path gain estimation. Utilising the above channel parameter estimates, two subspace multibeam beamformers are also presented to achieve complete interference cancellation. Second, in applications such as wireless sensor networks and ubiquitous computing, both the location and orientation of an array are important parameters of interest to be estimated. Hence, array localisation and orientation estimation approaches are proposed for two cases. In the first case, a number of sources of known locations are employed to estimate these parameters of a receiver array. In the second case, a receiver array is utilised to estimate these parameters of multiple sources with each one being a transmitter array. Last, when sources operate in the near field of an array, the spherical wave propagation model needs to be considered. A problem associated with such a scenario is source localisation under the wideband assumption, where the wavefront of a baseband signal varies when traversing through the sensors of the array. Two novel approaches with the employment of the subcovariance of the received signal and the rotation of the array reference point are proposed to localise multiple sources under the wideband assumption. Throughout the thesis, computer simulation studies are presented for evaluating the performance of the proposed approaches.Open Acces

Contributions aux bornes inférieures de l’erreur quadratique moyenne en traitement du signal

A l’aide des bornes inférieures de l’erreur quadratique moyenne, la caractérisation du décrochement des estimateurs, l’analyse de la position optimale des capteurs dans un réseau ainsi que les limites de résolution statistiques sont étudiées dans le contexte du traitement d’antenne et du radar

Star Formation in Galaxies

Topics addressed include: star formation; galactic infrared emission; molecular clouds; OB star luminosity; dust grains; IRAS observations; galactic disks; stellar formation in Magellanic clouds; irregular galaxies; spiral galaxies; starbursts; morphology of galactic centers; and far-infrared observations

Proceedings of the International Workshop on Medical Ultrasound Tomography: 1.- 3. Nov. 2017, Speyer, Germany

Ultrasound Tomography is an emerging technology for medical imaging that is quickly approaching its clinical utility. Research groups around the globe are engaged in research spanning from theory to practical applications. The International Workshop on Medical Ultrasound Tomography (1.-3. November 2017, Speyer, Germany) brought together scientists to exchange their knowledge and discuss new ideas and results in order to boost the research in Ultrasound Tomography

Star formation and disk stability in nearby galaxies

Observations of apparent cutoffs in star formation in the disks of galaxies as well as apparent thresholds in empirical laws of star formation have led many workers in the field to seek out the drivers and regulators of star formation in galaxies. Although the intricate details of these drivers are yet to be untangled, one of the main theories put forward is the existence of a gravitational stability threshold, controlled by the balance between the pressure-forces and gravity in a galactic disk to determine where gas collapses to form stars. Studies on this have mainly focused on the radial variation of the gravitational stability parameter and how it relates to the radial variations in the star formation activity. In this study, we look at the two dimensional structure of this parameter across the disks of star forming galaxies and compare it with the two dimensional structure of the star formation activity. The gravitational stability of the disks was derived using two different models. (i) The thin gas-disk model (single-fluid disk criterion, Qg) was derived for each galaxy in our sample. We use atomic gas for the majority of the sample and we use molecular gas whenever available. (ii) A two-fluid disk criterion which models a galaxy disk with gas and stars as two distinct fluids each with single-fluid instabilities and together having the combined twofluid instabilities (QT ). Both models were compared to maps of star formation rate. Data from the Westerbork survey of Hi in Irregular and SPiral galaxies (WHISP) were used to trace the properties of the gas disk, while data from the Wide-field Infrared Survey Explorer (WISE) were used to derive the stellar disk and star formation properties. In the case of the single-fluid thin gas-disk model, we find that the star forming disks show typical values of 3 - 15, much higher than the theoretical threshold value of 1. The high values can be attributed to low Hi gas densities (ΣHi) in the central regions, although the general structure in the maps traces the local density enhancements. However, the structural variations in Qg do not correlate with local variations in the surface density of the star formation rate, except in 25% of the sample, which are late type and have high gas fractions relative to the rest of the sample. This result confirms previous findings of 1D studies that the single-fluid criterion is better suited for late type galaxies. This is because the low stellar surface densities coupled with high gas fractions make the thin gas disk approximation yield a close description of late types. In addition to the above, we find that the values of Qg along the edges of the star forming disks are generally lower than those inside the disk. In about half the sample, the values on the edges are found to be roughly constant with an overall average of 4.0, which is four times higher than the theoretical threshold but in agreement with previous studies of the radial variation of Qg. Incorporating the stellar disk (the two-fluid disk criterion) leads to lower stability for all the disks in the sample, which is consistent with the increased gravity budget of the disks. Nevertheless, the two-fluid consideration does not render the disks unstable. In fact, we see that 80% of the galaxies in the sample have QT ≈ 2 or higher. The QT values vary only slightly, yielding flat maps consistent with previous studies of the azimuthally-averaged QT parameter. The overall average value of QT is 2.5 both inside the star forming disks and at the edges. This is in agreement with previous studies which showed that the critical value of the two-fluid disk criterion lies between 2 - 3. In spite of the mostly flat featureless QT disks, four galaxies had some variations in QT across their disks which mapped lower stability values to local regions of enhanced star formation. It is interesting to note that these galaxies also had lower Qg values matching the locally enhanced SF regions, although the QT maps had lower stability values and more extended patches. All four galaxies are late types. This confirms previous findings that the single-fluid disk criterion may be a reliable predictor of star formation in late type galaxies. This is because the stellar surface density in late types is low, and if coupled with a high gas fraction as is the case for these four galaxies, the gas-disk predictions will be close to the predictions for a disk of gas+stars. Additionally, as part of characterization of our sample, we have also studied the scaling relations between atomic gas and star formation rate. We found general correlation between the the star formation rate and Hi surface densities on sub-kpc scales, defined by a non-linear power law relationship with index varying between 1.6 - 3.8