Multiple Brain Abscesses Complicating Enterobacter Cloacae Sepsis in a Preterm Neonate with Atypical MRI Appearance: A Case Report

Multiple brain abscesses in neonates are extremely rare and occur as an unusual complication of bacterial meningitis or sepsis. There are many bacterial pathogens reported to cause brain abscesses in newborns; however, brain abscess caused by Enterobacter cloacae has rarely been described previously in neonates and only a few reports exist in English literature. After 4 weeks in the neonatal intensive care unit, a preterm neonate developed multiple brain abscesses as a complication of E. cloacae sepsis which were revealed on TFU and confirmed on MRI. Consequently, a limited craniotomy was performed for the biggest abscess for evacuation of pus and followed by aspiration of other abscesses

Multidimensional Optimized Optical Modulation Formats

This chapter overviews the relatively large body of work (experimental and theoretical) on modulation formats for optical coherent links. It first gives basic definitions and performance metrics for modulation formats that are common in the literature. Then, the chapter discusses optimization of modulation formats in coded systems. It distinguishes between three cases, depending on the type of decoder employed, which pose quite different requirements on the choice of modulation format. The three cases are soft-decision decoding, hard-decision decoding, and iterative decoding, which loosely correspond to weak, medium, and strong coding, respectively. The chapter also discusses the realizations of the transmitter and transmission link properties and the receiver algorithms, including DSP and decoding. It further explains how to simply determine the transmitted symbol from the received 4D vector, without resorting to a full search of the Euclidean distances to all points in the whole constellation

Mehrdimensionale Modulationsformate für optische Übertragungssysteme

The ever-increasing demand for bandwidth is constantly driving deployment of new strategies to enable the upgrading of current optical transmission systems. Therefore, next generation optical networks are required to be elastic and more efficiently utilize the available optical spectrum; this in turn increases spectral efficiency and overall network capacity. To this end, future optical transceivers need to be able to adapt the bit rate and reach in a flexible manner based on actual network demand. Moreover, the cost and complexity of these transceivers should be kept as low as possible for practical implementation. In this thesis, multidimensional (multi­D) optical modulation formats are studied as a promising approach to realize flexible and cost-efficient optical transceivers. The first part of the thesis discusses the coding gain that can be obtained by designing a signal constellation based on a dense lattice of arbitrary dimension. In particular, four-dimensional (4­D) signal constellations are considered for coherent optical communication systems. Various optimized 4-D modulation formats are studied showing their potential coding gain advantage over conventional 2-D modulation formats. In addition, novel digital signal processing (DSP) algorithms for some 4­D modulation formats are proposed and tested by numerical simulation and in transmission experiments. In the second part of the thesis, the advantages of combining advanced modulation formats and forward error correction (FEC) codes, so-called coded modulation, are explored. The idea of 2­D trellis coded modulation (TCM) is first reviewed. Afterwards, the benefits of extending the dimensionality to multi-D space are explained. Following this, different partitioning schemes for multi­D signal sets are reviewed, and from this the Multilevel coding (MLC) scheme is described in detail. Moreover, the principle of operation of the turbo TCM (TTCM) scheme is discussed as a means to enhance the coding gain and close the gap to the channel capacity. The last part of the thesis presents two experimental realizations concerning multi­D modulation formats. In the first experimental study, an optimized 4-D modulation format, namely 128­SP­QAM, is implemented and tested in a Nyquist­wavelength division multiplexing (NWDM) system. The performance of 128­SP­QAM is first compared with PDM-16QAM in back-to-back (b2b) setup and after transmission. In addition, two different soft-decision (SD-) FEC codes are experimentally evaluated for the 128­SP­QAM modulation format. In the second experiment, 4-D TCM based on PDM­MQAM formats are experimentally realized. The coding gain advantages of 4-D TCM over conventional PDM­MQAM are demonstrated in the b2b configuration and in WDM transmission system. In addition, the impact of burst error events, induced by the fiber nonlinearities, on the performance of 4-D TCM is experimentally analyzed. A multi­rate optical transceiver with a bitrate granularity of 25 Gb/s is realized by a single encoder/decoder structure. Furthermore, tolerance toward cycle­slip events is enabled by the rotational invariant feature of the 4-D TCM scheme. Moreover, the performance of 4-D TTCM schemes is experimentally evaluated and their superior coding gains over 4-D TCM are validated. Finally, the performance of 4-D TCM and TTCM is compared with standard PDM-MQAM formats in presence FEC codes. Here it is shown that 4-D TCM concatenated with a low complexity HD­FEC could be an alternative approach to SD-FE codes for complexity-performance tradeoff.Die stetig ansteigende Nachfrage für zusätzliche Übertragungsbandbreite drängt nach dem Einsatz neuer Strategien, die Erweiterungen existierender optischer Übertragungssysteme ermöglichen. An die kommende Generation optischer Netzwerke wird folglich der Anspruch von Elastizität und einer effizienteren Nutzung des verfügbaren Spektrums gestellt, was zu einer Erhöhung der Gesamtnetzwerkkapazität führt. Künftige optische Transceiver werden daher ihre Datenraten und Reichweiten flexibel an vorliegende Netzwerke anpassen müssen, wobei in deren Implementierungen ein besonderes Augenmerk auf geringe Kosten und Komplexität gerichtet werden muss. In dieser Dissertation werden mehrdimensionale (multi-dimensional, multi-D) optische Modulationsformate als vielversprechende Ansätze für flexible und kosteneffizienten Transceiverentwürfe untersucht. Der erste Teil dieser Arbeit untersucht den Codierungsgewinn, der sich durch das Design von Signalkonstellationen auf dichten mehrdimensionalen Gittern ergibt. Besondere Beachtung finden hier vier dimensionale (4-D) Signalkonstellationen für kohärent optische Übertragungssysteme. Zuerst wird der Kodierungsgewinn einer Vielzahl von 4-D Modulationsformaten gegenüber herkömmlichen 2-D Modulationsformaten untersucht. Zusätzlich werden neue Algorithmen der digitalen Signalverarbeitung (digital signal processing, DSP) einiger 4-D Modulationsformate vorgeschlagen und sowohl numerisch, als auch experimentell getestet. Im zweiten Teil dieser Arbeit werden die Vorteile von codierte Modulation, d.h. einer Kombination fortschrittlicher Modulationsformate mit Vorwärtsfehlerkorrektur (forward error correction, FEC) Codes, erforscht. Nach einer Einführung des Ansatzes von 2-D trellis codierter Modulation (TCM), werden die Vorteile der Erweiterung des Signalraums zu einem multi-D Raum erläutert. Es folgt eine Übersicht zu verschiedenen Partinionierungsschemata für multi-D Signalmengen, von aus denen Multilevel coding (MLC) im Detail diskutiert wird. Zusätzlich wird das Verfahren von turbo TCM (TTCM) als Mittel zur Verbesserung des Codiergewinns und somit zur Schließung der Lücke zur Kanalkapazität betrachtet. Der letzte Teil der Arbeit präsentiert zwei experimentelle Realisierungen, die sich mit mutli-D Modulationsformaten beschäftigen. In der ersten experimentellen untersuchung wird ein optimiertes 4-D Modulationsformat namens 128-SP-QAM implementiert und in einem Nyquist Wellenlaengenmultiplex (Nyquist wavelength division multiplexing, NWDM) System getestet. Die Performanz von 128-SP-QAM wird zuerst mit PDM-16QAM in einem Rücken-an-Rücken (back-to-back, b2b) und nach einer optischen Übertragungsstrecke verglichen. Zusaetzlich werden zwei unterschiedliche soft-decision (SD-) FEC Codes experimentell für 128-SP-QAM evaluiert. Das zweite Experiment beschäftigt sich mit der Realisierung von 4-D TCM, welches auf PDM-MQAM basiert. Der Vorteil im Codiergewinn von 4-D TCM über herkömmlichem PDM-MQAM werden in einer b2b Konfiguration und einer WDM Übertragung demonstriert. Der Einfluss durch Fasernichtlinearitäten hervorgerufenen, gebündelten Bitfehlerereignissen auf die Performanz von 4-D TCM wird zusätzlich experimentell untersucht. Es wird ein mehrratiger optischer Transceiver mit einer einzigen Codier-/Decodierstruktur, einer Bitraten Granularität von 25 Gb/s und einer Toleranz gegenüber Zyklusschlupfereignissen durch die Rotationsinvarianz des 4-D TCM Schemas vorgestellt. Zusätzlich wird die Performanz von 4-D TTCM experimentell evaluiert und deren Vorteil erhöhter Codiergewinne im Vergleich zu 4-D TCM validiert. Abschliessend wird die Performanz von 4-D TCM und TTCM mit den herkömmlichen PDM-MQAM Formaten mit FEC Kodierung verglichen. Es wird gezeigt, dass das Zusammenspiel von 4-D TCM mit einer einfachen HD-FEC ein alternativer Ansatz zu SD-FEC Codes darstellen

High-Temperature Growth of Bulk Gallium Nitride by the Sodium Flux Method

The progress in optoelectronics and power electronics devices and their industrial applications has been remarkable since the beginning of the 21st century. Gallium nitride (GaN) based devices have shown high efficiency and good reliability, but their full potential is hindered by the shortage of native substrates. The Na-flux technique has the ability to produce high quality and low cost bulk GaN. At UCSB, a novel Na-flux system was designed by Von Dollen et al. to monitor GaN growth in-situ.‎ In addition, they demonstrated the fastest growth rate (>50 μm/h) reported for this technique. However, the main challenges such as low structural quality, high impurity, and opaqueness were usually noticed in the grown GaN. Furthermore, the poor control of growth and the low reproducibility of experiments limited the reliability of the system. The focus of this dissertation is on understanding the reasons behind these challenges, finding possible solutions, and testing the capability of the system to monitor and control the growth in-situ.Higher structural quality and lower impurity transparent GaN growth was noticed on some regions of the seed related to its position within the system. First, higher structural quality was linked to the switch from 3D to 2D growth mode as was evident from the optical microscope images. For 2D growth, the full width half maximum (FWHM) of the (0002) and (112 ̅0) rocking curves were as low as 89 and 44 arcseconds respectively. This switch – from 3D to 2D – occurred at a late growth stage and the reason for the observed crystal quality improvement is speculated to be decreased thermodynamic driving force as growth progressed. Second, in optically transparent regions, concentrations of oxygen, sodium, and carbon were as low as 7×1016, 2×1016, and 5×1016 atoms/cm3, respectively, while the concentration of molybdenum was below the detection limit. In addition, the area, the thickness, and the reproducibility of transparent regions were increased by controlling the seed position and omitting the addition of carbon (a common additive in the Na-flux method). Furthermore, the opaqueness was found to correlate with oxygen impurity as it was established by secondary ion mass spectrometry (SIMS) analysis. GaN growths which contain oxygen concentrations above 1019 atoms/cm3 were highly absorbing regardless of the presence of other impurities. Thus, the effect of three oxygen getters – i.e. magnesium, aluminum, and titanium – on the GaN transparency was investigated but was not significant. However, polycrystalline GaN was found to preferentially form on titanium sheets; and the reproducibility of growth conditions was enhanced with titanium sheets in the Na flux reactor. The effective solution to grow transparent GaN was by depleting oxygen impurity in the system via extended GaN growths. Extended growth typically consisted of two consecutive single growth experiments; and it was found that the all second experiments were thermodynamically limited in contrast with many of the first or single experiments. Third, the second experiments of extended growths were used to inspect the thermodynamics of GaN growth in-situ using the UCSB system. The ability of the system to determine equilibrium pressure and temperature for a specific sodium-gallium melt composition was demonstrated. Furthermore, positive deviation of the melt from ideality was noticed and the gallium activity and activity coefficient were calculated based on experimental data. Finally, some changes and improvements to the system – based on the outcomes of this dissertation – were suggested for better monitoring and controlling of GaN crystal growth

Firm performance through online engagement: The role of experience and customer inspiraton

This research aims to assess the current status of online trade relations between Kuwait and Portugal. To do so, we examine how firm managers from Portugal and Kuwait use online platforms to engage customers to enhance firm performance. A set of existing constructs was chosen (Online Experience, Customer Inspiration, Online Customer Engagement, Firm Performance, National Culture), which were included in a proposed model of structural equations, in order to assess the contribution of Online Experience and Customer inspiration to the current status of online trade relations (through Online Customer Engagement), and how these can be improved to the further development of e-commerce between the two countriesinfo:eu-repo/semantics/publishedVersio

High-Temperature Growth of Bulk Gallium Nitride by the Sodium Flux Method

The progress in optoelectronics and power electronics devices and their industrial applications has been remarkable since the beginning of the 21st century. Gallium nitride (GaN) based devices have shown high efficiency and good reliability, but their full potential is hindered by the shortage of native substrates. The Na-flux technique has the ability to produce high quality and low cost bulk GaN. At UCSB, a novel Na-flux system was designed by Von Dollen et al. to monitor GaN growth in-situ.‎ In addition, they demonstrated the fastest growth rate (>50 μm/h) reported for this technique. However, the main challenges such as low structural quality, high impurity, and opaqueness were usually noticed in the grown GaN. Furthermore, the poor control of growth and the low reproducibility of experiments limited the reliability of the system. The focus of this dissertation is on understanding the reasons behind these challenges, finding possible solutions, and testing the capability of the system to monitor and control the growth in-situ.Higher structural quality and lower impurity transparent GaN growth was noticed on some regions of the seed related to its position within the system. First, higher structural quality was linked to the switch from 3D to 2D growth mode as was evident from the optical microscope images. For 2D growth, the full width half maximum (FWHM) of the (0002) and (112 ̅0) rocking curves were as low as 89 and 44 arcseconds respectively. This switch – from 3D to 2D – occurred at a late growth stage and the reason for the observed crystal quality improvement is speculated to be decreased thermodynamic driving force as growth progressed. Second, in optically transparent regions, concentrations of oxygen, sodium, and carbon were as low as 7×1016, 2×1016, and 5×1016 atoms/cm3, respectively, while the concentration of molybdenum was below the detection limit. In addition, the area, the thickness, and the reproducibility of transparent regions were increased by controlling the seed position and omitting the addition of carbon (a common additive in the Na-flux method). Furthermore, the opaqueness was found to correlate with oxygen impurity as it was established by secondary ion mass spectrometry (SIMS) analysis. GaN growths which contain oxygen concentrations above 1019 atoms/cm3 were highly absorbing regardless of the presence of other impurities. Thus, the effect of three oxygen getters – i.e. magnesium, aluminum, and titanium – on the GaN transparency was investigated but was not significant. However, polycrystalline GaN was found to preferentially form on titanium sheets; and the reproducibility of growth conditions was enhanced with titanium sheets in the Na flux reactor. The effective solution to grow transparent GaN was by depleting oxygen impurity in the system via extended GaN growths. Extended growth typically consisted of two consecutive single growth experiments; and it was found that the all second experiments were thermodynamically limited in contrast with many of the first or single experiments. Third, the second experiments of extended growths were used to inspect the thermodynamics of GaN growth in-situ using the UCSB system. The ability of the system to determine equilibrium pressure and temperature for a specific sodium-gallium melt composition was demonstrated. Furthermore, positive deviation of the melt from ideality was noticed and the gallium activity and activity coefficient were calculated based on experimental data. Finally, some changes and improvements to the system – based on the outcomes of this dissertation – were suggested for better monitoring and controlling of GaN crystal growth

GPS Navigation and Tracking Device

Since the introduction of GPS Navigation systems in the marketplace, consumers and businesses have been coming up with innovative ways to use the technology in their everyday life. GPS Navigation and Tracking systems keep us from getting lost when we are in strange locations, they monitor children when they are away from home, keep track of business vehicles and can even let us know where a philandering partner is at all times. Because of this we attend to build a GPS tracking device to solve the mentioned problems. Our work consists of the GPS module that collects data from satellites and calculates the position information before transmitting them to the user’s PC (of Navigation system) or observers (of Tracking System) using wireless technology (GSM)

Four-dimensional trellis coded modulation for flexible optical transponders

We experimentally demonstrate 4-D TCM based on PDM-16QAM, PDM-32QAM and PDM-64QAM formats. A multi-rate optical transponder is enabled by only a single encoder/decoder structure. The scheme is resilient to cycle-slip events due to its 90° phase rotation invariant property

A new system for sodium flux growth of bulk GaN

Though several methods exist to produce bulk crystals of gallium nitride (GaN), none have been commercialized on a large scale. The sodium flux method, which involves precipitation of GaN from a sodium-gallium melt supersaturated with nitrogen, offers potentially lower cost production due to relatively mild process conditions while maintaining high crystal quality. We successfully developed a novel apparatus for conducting crystal growth of bulk GaN using the sodium flux method which has advantages with respect to prior reports. A key task was to prevent sodium loss or migration from the growth environment while permitting N2 to access the growing crystal. We accomplished this by implementing a reflux condensing stem along with a reusable capsule containing a hermetic seal. The reflux condensing stem also enabled direct monitoring of the melt temperature, which has not been previously reported for the sodium flux method. Furthermore, we identified and utilized molybdenum and the molybdenum alloy TZM as a material capable of directly containing the corrosive sodium-gallium melt. This allowed implementation of a crucible-free system, which may improve process control and potentially lower crystal impurity levels. Nucleation and growth of parasitic GaN ("PolyGaN") on non-seed surfaces occurred in early designs. However, the addition of carbon in later designs suppressed PolyGaN formation and allowed growth of single crystal GaN. Growth rates for the (0001) Ga face (+c-plane) were up to 14μm/h while X-ray omega rocking (ω-XRC) curve full width half-max values were 731″ for crystals grown using a later system design. Oxygen levels were high, >1019 atoms/cm3, possibly due to reactor cleaning and handling procedures.Peer reviewe