EyeScout: Active Eye Tracking for Position and Movement Independent Gaze Interaction with Large Public Displays

While gaze holds a lot of promise for hands-free interaction with public displays, remote eye trackers with their confined tracking box restrict users to a single stationary position in front of the display. We present EyeScout, an active eye tracking system that combines an eye tracker mounted on a rail system with a computational method to automatically detect and align the tracker with the user's lateral movement. EyeScout addresses key limitations of current gaze-enabled large public displays by offering two novel gaze-interaction modes for a single user: In "Walk then Interact" the user can walk up to an arbitrary position in front of the display and interact, while in "Walk and Interact" the user can interact even while on the move. We report on a user study that shows that EyeScout is well perceived by users, extends a public display's sweet spot into a sweet line, and reduces gaze interaction kick-off time to 3.5 seconds -- a 62% improvement over state of the art solutions. We discuss sample applications that demonstrate how EyeScout can enable position and movement-independent gaze interaction with large public displays

Supply modulated GaN HEMT power amplifiers - From transistor to system

Power amplifiers (PAs) for mobile communication applications are required to fulfil stringent requirements concerning linearity while keeping a high efficiency over a wide power range and bandwidth. To achieve this, a number of advanced PA topologies have been developed, mostly based on either load modulation, such as Doherty PAs or load modulation balanced PAs, or on supply modulation such as envelope tracking or envelope elimination and restoration. Supply modulation has an advantage over other topologies as the power range of high efficiency can be realised over arbitrary bandwidths, only limited by the bandwidth of the PA. This does, however, come at the cost of a significantly more complicated voltage supply. Instead of a static supply voltage, the PA needs to be provided with one which is rapidly changing, requiring a supply modulator capable of powering the PA while modulating its supply voltage. This thesis investigates a number of challenges in supply modulated power amplifiers, ranging from the transistor itself to circuit design and system level considerations and focusses on power levels up to 10 W and frequencies between 1 GHz and 4 GHz. Transistors, as the centre-piece of a PA, determine how well the PA reacts to a changing supply voltage. In this work, the traits that make GaN HEMTs suitable for supply modulated PAs were investigated, and gain variation with changing supply voltage was established as an important parameter. This gain variation is described in detail and its impacts on PA performance are discussed. By comparing transistors in literature, gain variation has been demonstrated to be a prevalent characteristic in transistors with GaN HEMTs showing a very wide range of gain variation. Using a small-signal model based on measurements, the voltage dependent behaviour of the feedback capacitance CGD is, for the first time, identified as the origin of small-signal gain variation. This is traced down to the gate field plate which is commonly used to combat surface trapping effects in GaN HEMTs. With this in mind, two different ways of changing the transistor geometry to reduce the impact of gain variation and thus optimise the transistor for operation in supply modulated PAs are discussed and demonstrated using a 250 nm GaN HEMT. As a result of the non-linearity of the feedback and gate-source capacitances, the input impedance of GaN HEMTs changes with supply voltage and drive power. This prevents the transistor from being matched at all supply voltages and input powers and introduces phase distortion. Using simulation and measurement, the impact of input impedance on linearity and efficiency of supply modulated power amplifiers is demonstrated on a 2.9 GHz 10 W PA. Careful selection of the input impedance allows improvement of AM/PM distortion of a supply modulated PA with little cost in terms of AM/AM and PAE. I Supply modulators have a significant impact on efficiency and linearity of the ET system. One supply modulator topology with the potential to generate a supply voltage with a high modulation bandwidth is the RF modulator in which the input DC voltage is turned into an RF signal and rectified, resulting in an output voltage which depends on the excitation of the PA. While PAs are well understood in every detail, there are gaps in the understanding of RF rectifiers. Using active load-pull/source-pull measurements, intrinsic gate and drain waveforms of a GaN HEMT operated as a rectifier are demonstrated for the first time. This allows in-detail evaluation of the impact of the gate termination in self-synchronous rectifiers. It also allows detailed analysis of the loss mechanisms in rectifiers and formulation of the required impedances to realise efficient self-synchronous operation, resulting in efficiencies exceeding 90% over wide power ranges. Using waveform engineering, a new type of RF modulator, with potentially very high bandwidths, based on even harmonic generation/injection is proposed. The necessary operating conditions of the rectifier part of the modulator are emulated using an active load-pull/source-pull system to successfully demonstrate that the rectifier behaves as predicted. Using a simple demonstrator, preliminary measurements were conducted and the RF modulator was shown to work, reaching efficiencies up to 78%. As PA and supply modulator are combined, they present impedances to each other. These impedances have a significant impact on the behaviour of both sub-systems. A simple way to characterise both the impedance presented to the PA by the modulator and the impedance presented to the modulator by the PA is described. Using a state-of-the-art modulator, these impedances are measured, the modulator impedance is demonstrated to be close to the simulated value. These measurements also demonstrate that the impedances change significantly with the operating conditions

Improving efficiency, linearity and linearisability of an asymmetric doherty power amplifier by modulating the peaking amplifier’s supply voltage

Envelope tracking and asymmetric Doherty power amplifiers are two techniques that can be used to achieve high average efficiencies when amplifying signals with high peak-toaverage power ratios, e.g. those employed in modern wireless communication standards. In this paper, a combination of the two techniques, the modulation of the drain voltage of the peaking amplifier in an asymmetric Doherty power amplifier, is described. It is demonstrated how this combination can increase the efficiency in the high-power range while reducing the AM/PM distortion of the DPA. Additionally, the degrees of freedom in terms of efficiency, linearity, and linearisability when designing the shaping function is discussed. Measurements of an asymmetric 2.4 GHz DPA using 10 W and 25 W GaN HEMTs prove the concept and demonstrate the achievable improvements in terms of efficiency, linearity, and linearisability

Supply modulator ripple in envelope tracking systems - effects and countermeasures

Envelope tracking power amplifiers (ET PAs) are one of the promising architectures to provide high efficiency amplification for future wireless communication systems. This is due to their ability to offer high efficiency over a wide output power range, by modulating the supply voltage applied to the PA. Generating this dynamic supply voltage with switching-mode modulators is highly efficient, but filtering the output remains a challenge, resulting in a residual `ripple' on the supply voltage. This paper presents an experimental investigation into the interaction between a PA and a supply modulator in the presence of this ripple. By adding a varying ripple magnitude to the modulated drain voltage of a 2.14 GHz GaN ET PA with a 10 MHz LTE signal, the effects on the linearity of the RFPA can be observed and analysed to allow the system designer an insight into the amount of ripple that is tolerable, while still being able to achieve linearity and efficiency targets. The mixing products of the ripple and RF signal are shown to be a potential issue in ET PAs. This paper shows, for the first time, the full impact of the ripple voltage magnitude on the output spectrum. Further more, the ripple sensitivity of two different ET PA linearisation approaches are explored; firstly applying generic memory polynomial digital pre-distortion (DPD) and secondly optimising the ET tracking signal shaping function to improve linearity. Measurements show that for the case where the ripple and RF are not synchronized, neither approach is able to significantly mitigate the ripple effect on the PA linearity

On the role of the time scale Delta t in Bose-Einstein correlations

The time scale $\Delta t$ parameter, which appears in the Bose-Einstein Correlations (BEC) treated in term of the Heisenberg uncertainty relations, is reexamined. Arguments are given for the role of $\Delta t$ as a measure of the particles' emission time rather than representing the strength property of the correlated particles. Thus in the analyzes of the $Z^0$ hadronic the $\Delta t$ given value of ~$10^{-24}$ seconds is the particles' emission time prescribed by the $Z^0$ lifetime. In heavy ion collisions $\Delta t$ measures the emission time duration of the particles produced from a nucleus of atomic number $A$ which is here shown to be equal to \Delta t =(m_{\pi}a^2)/(\hbar c^2})*A^{2/3} where a is about 1 fm, that is, proportional to the nucleus surface area. This dependence agrees rather well with the experimental $\Delta t$ values deduced from the BEC analyzes of heavy ion collisions.Comment: 8 pages, 5 figure

Characterising the baseband impedance of supply modulators using simple modulated signals

Envelope tracking is one of the promising technologies for 5G power amplifiers, providing high power efficiency over a wide output power range by modulating the supply voltage. Although the baseband impedance, the output impedance of the supply modulator, plays a crucial role in the linearity of the PA, it is often not measured or considered during the modulator design. This paper presents a new, simplified approach to characterising this impedance using a PA with a simple multi-tone modulation as a load. It describes the measurement setup and verifies the results by characterising the baseband impedance of a state-of-the-art buck converter and comparing this to its static model. The results demonstrate that multi-tone signals and complex modulations yield comparable results and are both suitable for measuring and modelling the baseband impedance. This shows that using simple multi-tone measurements and basic equipment, the full static impedance characteristic can be obtained

Ein optimierter Versorgungsprozess bei Patienten mit schlafbezogenen Atmungsstörungen – Pilotstudie

Background: To date, patients have been instructed in diagnostic polygraphy (PG) by a trained specialist. This process is time- and cost-intensive. In a pilot study, we tested an innovative procedure in sleep-disordered breathing (SDB) to achieve faster diagnoses and more effective referral for treatment. For this purpose, study participants had a PG device delivered at home directly from the provider. Methods: Patients self-administered the PGs independently using a manual, and, if necessary, received telephone support. After the night of recording, the device was sent back to the supplier. Diagnosis by a physician was done online via an encrypted portal. In addition, subjective satisfaction with the process was assessed using a questionnaire and PG results were compared with polysomnography (PSG) within a narrow timescale. Results: Fifty patients middle-aged (50.5 ± 13.7 years), male = 30/female = 20, with suspected SDB were included in the study. The study participants had a similar mean Apnea-Hypopnea Index (AHI; PSG) of M = 20.8 (SD 23.2) and a mean AHI measured using PG of M = 20.2 (SD 18.9) under both measurement methods. At AHI values between ≥15–30/h showed sensitivity of 88% and specificity of 91%. Conclusion: In assessing whether clinically relevant sleep apnea occurred, we found a weak to moderate match between the individual diagnostic categories of the measuring process, with the most frequent matches occurring in the highest and lowest diagnosis groups. However, these results do not allow for a prediction of feasibility in a general or multimorbid patient population because of the selective sample.Hintergrund: Die Einweisung der Patienten in die diagnostische Polygraphie wird bisher von einer medizinisch ausgebildeten Fachkraft durchgeführt. Dieser Prozess ist zeit- und ressourcenintensiv. In dieser Pilotstudie wurde ein innovativer Versorgungsweg bei schlafbezogenen Atmungsstörungen (SBAS) untersucht, um eine beschleunigte Diagnostik und effektivere Therapiezuweisung zu erreichen. Hierfür wurde den Studienteilnehmern ein Polygrafie (PG)-Gerät direkt von der versorgenden Firma nach Hause geliefert. Methodik: Der Patient legte die PG selbstständig nach einer Bedienungsanleitung an und erhielt bei Bedarf telefonische Unterstützung. Nach der Untersuchungsnacht wurde das Gerät zurückgesendet. Die ärztliche Befundung erfolgte online über ein verschlüsseltes Portal. Zusätzlich erfolgte eine Befragung zur subjektiven Zufriedenheit mit dem Ablaufprozess sowie ein Vergleich der PG-Ergebnisse mit einer zeitnahen Polysomnografie (PSG). Ergebnisse: Es wurden 50 Patienten (m = 30/w = 20) mit Verdacht auf SBAS im mittleren Alter von 50,5 ± 13,7 Jahren eingeschlossen. Die Probanden wiesen unter beiden Messverfahren einen ähnlichen mittleren Apnoe-Hypopnoe-Index (AHI) (PSG) von M = 20,8 (SD 23,2) und AHI (PG) von M = 20,2 (SD 18,9) auf. Bei AHI-Werten zwischen ≥15–30/h lag die Sensitivität bei 88 % und die Spezifität bei 91 %. Diskussion: In der Beurteilung, ob eine klinisch relevante Schlafapnoe vorliegt, zeigte sich eine eher schwache, moderate Übereinstimmung zwischen den einzelnen Diagnosekategorien der Messverfahren, wobei sich die häufigsten Übereinstimmungen in den höchsten und niedrigsten Diagnosegruppen zeigten. Die Ergebnisse lassen jedoch aufgrund der selektiven Stichprobe keine Prognosen hinsichtlich der Durchführbarkeit in einer allgemeinen oder multimorbiden Patientengruppe zu

Podoplanin immunopositive lymphatic vessels at the implant interface in a rat model of osteoporotic fractures

Insertion of bone substitution materials accelerates healing of osteoporotic fractures. Biodegradable materials are preferred for application in osteoporotic patients to avoid a second surgery for implant replacement. Degraded implant fragments are often absorbed by macrophages that are removed from the fracture side via passage through veins or lymphatic vessels. We investigated if lymphatic vessels occur in osteoporotic bone defects and whether they are regulated by the use of different materials. To address this issue osteoporosis was induced in rats using the classical method of bilateral ovariectomy and additional calcium and vitamin deficient diet. In addition, wedge-shaped defects of 3, 4, or 5 mm were generated in the distal metaphyseal area of femur via osteotomy. The 4 mm defects were subsequently used for implantation studies where bone substitution materials of calcium phosphate cement, composites of collagen and silica, and iron foams with interconnecting pores were inserted. Different materials were partly additionally functionalized by strontium or bisphosphonate whose positive effects in osteoporosis treatment are well known. The lymphatic vessels were identified by immunohistochemistry using an antibody against podoplanin. Podoplanin immunopositive lymphatic vessels were detected in the granulation tissue filling the fracture gap, surrounding the implant and growing into the iron foam through its interconnected pores. Significant more lymphatic capillaries were counted at the implant interface of composite, strontium and bisphosphonate functionalized iron foam. A significant increase was also observed in the number of lymphatics situated in the pores of strontium coated iron foam. In conclusion, our results indicate the occurrence of lymphatic vessels in osteoporotic bone. Our results show that lymphatic vessels are localized at the implant interface and in the fracture gap where they might be involved in the removal of lymphocytes, macrophages, debris and the implants degradation products. Therefore the lymphatic vessels are involved in implant integration and fracture healing

CFD-modeling and Experiments of insulation debris transport phenomena in water flow

The investigation of insulation debris generation, transport and sedimentation becomes important with regard to reactor safety research for PWR and BWR, when considering the long-term behavior of emergency core cooling systems during all types of loss of coolant accidents (LOCA). The insulation debris released near the break during a LOCA incident consists of a mixture of disparate particle population that varies with size, shape, consistency and other properties. Some fractions of the released insulation debris can be transported into the reactor sump, where it may perturb/impinge on the emergency core cooling systems. Open questions of generic interest are the sedimentation of the insulation debris in a water pool, its possible re-suspension and transport in the sump water flow and the particle load on strainers and corresponding pressure drop. A joint research project on such questions is being performed in cooperation between the University of Applied Sciences Zittau/Görlitz and the Forschungszentrum Dresden-Rossendorf. The project deals with the experimental investigation of particle transport phenomena in coolant flow and the development of CFD models for its description. While the experiments are performed at the University at Zittau/Görlitz, the theoretical modeling efforts are concentrated at Forschungszentrum Dresden-Rossendorf. In the current paper the basic concepts for CFD modeling are described and feasibility studies including the conceptual design of the experiments are presented