<p>Digital imaging systems for medical applications must bebased upon highly efficient detectors to ensure low patientdose. This is particularly important in screening mammographybecause of the large number healthy women that is examined. Amammography system must also provide high spatial and contrastresolution. Different approaches are compared in this thesis,and it is argued that a system based on photon countingdetectors in a scanned multi-slit geometry provides aperformance superior to established technologies.</p><p>The system is realized using silicon strip detectorsirradiated at a small angle relative to the wafer surface,thereby offering large absorption depth. A linear pixelarray isscanned across the breast to obtain the complete image.Pulse-processing electronics rejecting all detector andelectronics noise count the number of photons that aredetected, forming the pixel values of the image.</p><p>Optimization of the detector design is discussed in detail.The detector has been carefully simulated to investigate chargemotion and signal formation after photoninteraction. Based onthese simulations, the impact of the detector characteristicson the image quality has been evaluated.</p><p>Detectors have been manufactured and evaluated both assingle components and as part of experimental imaging devicesincluding custom readout electronics. Presented in this thesisare the measured detector characteristics including a verifi-cation of charge collection efficiency and confirmation thatthe quantum efficiency is 90% for a typical mammographyspectrum. Modulation transfer functions and noise power spectrawere recorded and the detective quantum efficiency calculated.A prototype mammography system was also assembled and themodulation transfer function recorded. The interpretation ofthe modulation transfer function and detective quantumefficiency is discussed for digital systems in general and fora scanned multi-slit system in particular.</p><p><b>Keywords:</b>x-ray, imaging, silicon, detector, digital,mammography, scanning, photon counting.</p>

<p>Vacuum insulation panels, VIPs, constitute a new insulation material, 6 to 8 times better than traditional insulation materials, which utilizes the positive influence vacuum has on the thermal properties of certain materials. A VIP is a composite with a flat core enclosed by an envelope preventing the core to fill with gas. The vacuum in the core is vital to reach thermal conductivities down to 0,0035 W/(m K), if the vacuum is lost the panel has reached the end of its service life time. Metal sheets would the preferred material to create an impermeable envelope but would creates a large thermal bridge at the edges of a panel when it folds over the edges of the panel.</p><p>A serpentine edge has been proposed in order to deal with this large thermal bridge. This serpentine edge has been evaluated first as a numeric model in software and then by measuring on a prototype edge element in a hot and cold plate instrument. Measured temperatures were used to validate the numerical model. Results show that a serpentine edge can greatly reduce the thermal bridge if designed correctly.</p><p>Another direction taken in the development of the VIP barrier is to use very thin metal layers, metallization layer or coating, incorporated into multi layered polymer composite film. This creates barrier films with very good barrier properties and only small thermal bridges. The modeling of gas flux through films with more than one coating has only just started. Existing models for flux through multi coated films all assume that flux is only taking place through defects in the coating layers, that all defects are of the same size and that all defects are positioned in square lattices. The model discussed herein use the same assumption of flux through pinholes only but it does take defect sizes and positions into account. Barrier film, from a regular vacuum insulation panel, with double coatings has been evaluated in light microscopy to characterize the defects in each of the coatings. The data found have been fed into the model and the results comply well with reported permeabilities of similar barrier films.</p>

<p>In today's GSM system there is a complex resource situation when it comes to the scarce TDMA channels in the air interface, the time slots. There are both voice call services that use one or a half time slot and there are packet data users, that may share time slots with other packet data users, and they can use multiple channels at the same time. Allocating time to users is a crucial part in the system and it may affect the performance for the end user substantially.</p><p>In the future there may be more types of services than just voice and packet data and that these services may have specific demands on their channels, time slots. That means they would not be able to use just any of the available channels. The way to "give" services channels is what is called channel allocation. In this thesis four different services and three different principles for channel allocation is implemented in a Matlab simulator and simulated. The thesis goal is to determine which principle is best for which mix of services.</p><p>The principles that have been investigated are Flexible Algorithm that lets all services use all channels, Fix Dedication Algorithm where all channels are dedicated to a service and only can be used by that one and finally Soft Dedication Algorithm where all channels are dedicated to a service but may be used by other services when it is not needed by the preferred one.</p><p>The conclusion is, simplified, that the Soft Dedication Algorithm generates low blocking rates, high bandwidth and that it is a quite robust principle although the borrowing user may be preempted. It may not always be the best one but over all it is the one to prefer.</p> / <p>Detta examensarbete är utfört på uppdrag av och i samarbete med Ericsson och rör kanal- och resurshantering i GSM-systemet.</p><p>Ett ständigt problem vid trådlös och mobil kommunikation är den begränsade mängd frekvenser som finns tillgängliga i radiogränssnittet och hur pass nära två radioresursers frekvenser kan ligga varandra. I GSM används TDMA (Time Division Multiple Access) för att få plats med många användare på ett smalt frekvensband. TDMA innebär förenklat att tiden delas upp i åtta tidsluckor och att varje användare får tillgång till en av radioresurserna under en sådan tidslucka (kanal). Detta gäller både i upp- och nedlänk.</p><p>I nuläget finns två tjänster, paketdata och tal, som använder tidsluckorna på olika sätt. En talanvändare använder en eller en halv lucka själv medan paketdataanvändare kan dela på en eller flera luckor. Det finns alltså en mängd olika sätt att allokera, "dela ut", dessa luckor till ett givet antal användare. I nuläget har man en väl fungerande algoritm för detta men man tror att det i framtiden kommer att finnas fler tjänster med mer specifika krav på sina tidsluckor (kanaler) och att man då inte längre kan använda samma princip för kanalallokeringen.</p><p>I detta exjobb har tre nya, enkla och renodlade principer för kanalallokering undersökts för fyra fiktiva tjänster. Det tre principerna är Flexible Algorithm, där alla tjänster tillåts använda alla kanaler, Fix Dedication Algorithm, där alla kanaler är dedicerade till någon tjänst och endast kan användas av just denna tjänst; och slutligen Soft Dedication Algorithm som fungerar liknande den föregående men här kan tjänster "låna" kanaler av andra tjänster så längs som de är lediga. I Soft Dedication Algorithm kan en eventuell "låntagare" bli avbruten om en användare av rätt tjänst inte hittar en ledig kanal.</p><p>Utvärdering har skett genom att simulera systemet i en, delvis egengjord, Matlabsimulator.</p><p>Resultaten visar, förenklat, att Soft Dedication Algorithm är den bästa vad gäller låg blockering, kanalutnyttjande och även bandbredder. Den är även förhållandevis robust mot variationer i last.</p>

In this thesis, we tackle the problem of designing and implementing a wireless video sensor network for a surveillance application. The goal was to design a low power content aware system that is able to take an image from an image sensor, determine blocks in the image that contain important information and encode those block for transmission thus reducing the overall transmission effort. At the same time, the encoder and the preprocessor must not consume so much computation power that the utility of this system is lost. We have implemented such a system which uses a combination of Edge Detection and Frame Differencing to determine useful information within an image. A JPEG encoder then encodes the important blocks for transmission. An implementation on a FPGA is presented in this work. This work demonstrates that preprocessing gives us a 48.6 % reduction in power for a single frame while maintaining a delivery ratio of above 85 % for the given set of test frames.

In this dissertation, multicarrier schemes are reviewed within the framework of Gabor Systems. Their fundamental elements; what to transmit, i.e., symbols, how to transmit, i.e., filters or pulse shape, and where/when to transmit, i.e., lattices are investigated extensively. The relations between different types of multicarrier schemes are discussed. Within the framework of Gabor systems, a new windowing approach, edge windowing, is developed to address the out-of-band (OOB) radiation problem of orthogonal frequency division multiplexing (OFDM) based multicarrier schemes. To the best of our knowledge, for the first time, the diversity on the range of the users is exploited to suppress the sidelobes of OFDM. In addition to that, the concept of using different filters in OFDM structure is proposed. Besides the improvement on the OOB radiation performance of OFDM via edge windowing, conventional lattice structure of OFDM frame is enhanced considering the diversity in the network. The lattice structure of an OFDM frame is designed based on the statistical characteristics of the range of the users and the mobility. The concept of channel-aware frame structure is developed, which allows more efficient and reliable transmission. In addition to the aforementioned improvements on OFDM, interference issues in uncoordinated networks are addressed in this dissertation considering different multicarrier schemes. It is stressed that the interference from other links in the network sharing the same spectrum might degrade the link performance between the devices in an uncoordinated network, significantly. Considering the degradation due to other-user interference, the concept of partially overlapping tones (POT) is proposed. With the concept of partially overlapping tones, the interference energy observed at the victim receiver is mitigated via an intentional frequency offset between the links. The usefulness of intentional frequency offset to combat with the asynchronous nature of other-user interference without any timing constraint between interfering signals is emphasized. To the best of our knowledge, for the first time, the efficacy of non-orthogonal schemes are shown along with POT to address the other-user interference, which relies on the fact that self-interference problem is easier than other-user interference problem in an uncoordinated network. In the last part of this dissertation, required number of equalizer taps for multicarrier schemes is investigated to address the potential self-interference problems (e.g. due to the non-orthogonal multicarrier schemes with the concept of POT). Composite impact of transmit pulse shape, communication medium, and receive filter on the characteristics of the interference among the symbols in time and frequency is analyzed. It is emphasized that while taking less number of taps into account for the channel estimation causes lack of description of the composite effect, using more number of taps folds the noise into the estimated channel. The number of interfering symbols and their locations are obtained in both time and frequency for a given multicarrier scheme and signal-to-noise ratio. It is shown that correct number of taps yields not only improvement on BER performance but also less complex equalizer structures in practice.

Steps on a high index metal or semiconductor surface may play a fundamental role for electronic structure, adsorption, film growth, chemical reaction and catalysis. The surface atomic and electronic structures of stepped W(110) surfaces have been investigated by a few research groups during the past 20 years. But there is still a lot of controversy. We use high resolution core level photoemission to study several different stepped tungsten surfaces. Curve fittings of the spectra permit tests of core-level binding- energy shift models that relate local atomic coordination to binding -energy differences associated with terrace and step-edge atoms. For the first time we find a well resolved W4f₂/₇ peak associated with step edge atoms. We attribute previous failure to directly detect the step-edge effects in core level photoemission to contamination by hydrogen. The well resolved peaks for surface atoms with different coordinations can serve as a “finger print” for specific atoms. Experiments in which stepped surfaces are systematically dosed by H₂ clarify the role played by H contamination. We also grow Ag nanowires on the stepped W(110) surface and use angle resolved photoemission to study the band structure. We find distinct dispersion for the nanowires along the step edge direction while there is only little dispersion perpendicular to the wires. The second part of the research is core level photoemission study on Cesium film growth on Cu(100) surface. We study the phonon broadening effect for Cs at different temperatures. We compare our data with previous theoretical models and get good results on surface and bulk Debye temperatures and zero temperature phonon broadening. The binding energy shifts for the Cs 5p₂/₇ at different temperatures have also been investigated. The results fit the lattice expansion model very well except at temperature higher than 200 K. The higher temperature deviation is caused by thermal evaporation of Cs films. This conclusion is checked by the following coverage dependent core level peaks study on the Cs/Cu(100) system. / text

The leading edge of a turbine vane is subject to some of the highest temperature loading within an engine, and an accurate understanding of leading edge film coolant behavior is essential to efficient engine design. Although there have been many investigations of the adiabatic effectiveness for showerhead film cooling within the leading edge region, there have been no previous studies in which individual rows of the showerhead were tested with the explicit intent of validating superposition models. For the current investigation, a series of adiabatic effectiveness experiments were performed with a five-row showerhead, wherein each row of holes was operated in isolation. This allowed evaluation of superposition on both the suction side of the vane, which was moderately convex, and the pressure side of the vane, which was mildly concave. Superposition was found to accurately predict performance on the suction side of the vane at lower momentum flux ratios, but not for higher momentum flux ratios. On the pressure side of the vane, the superposition predictions were consistently lower than measured values, with significant under-prediction of adiabatic effectiveness occurring at the higher mass flow rates. Possible reasons for the under-prediction of effectiveness by the superposition model are presented. / text

A viscous/inviscid interaction method for predicting the effect of viscosity on the performance of wetted and cavitating propulsors is presented. The emphasis is placed on steady wetted and cavitating propulsor flows. A three-dimensional low order potential based boundary element method is strongly coupled with a two dimensional integral boundary layer analysis method based on the strip theory assumption. The influence of viscosity on the outer inviscid flow is modeled through the wall transpiration model by distributing “blowing” sources on the propulsor blade and trailing wake surfaces. The boundary layer edge velocities are expressed as the sum of the inviscid edge velocity and a correction which depends only on the boundary layer variables. The influence of outer potential flow on the inner boundary layer flow is considered through the edge velocities. In the case of sheet cavitation, a “thin” cavity approach is employed and the viscous/inviscid interaction method is applied on the blade surface underneath the cavity. On the cavity surface, the friction force coefficient is forced to be zero. Numerical predictions by the present viscous/inviscid interaction method are presented for open, ducted, and water-jet propulsors. For water-jet propulsors, the flow is solved in an iterative manner by solving the rotor and stator problems separately and by considering the time-averaged effects of one component on the other. Predicted forces, pressure distributions, and boundary layer variables are compared with those predicted by other numerical methods and experimental measurements. / text

This thesis will describe the works had been done by the author in the Flying Crane aircraft group design project and the new design of a novel swing arm mechanism which can be applied in the trailing edge high lift devices for this aircraft concept. Flying Crane aircraft is a new generation commercial airliner concept as the result of group design project conducted by China Aviation Industry Corporation I (AVIC I) and Cranfield University. At the end of the group design project, parameters such as take-off and landing distance, trailing edge flap type and deflection in take-off and landing configuration of the Flying Crane concept have been determined. These parameters are design input of the novel trailing edge high lift device mechanism for this aircraft concept. The idea of this innovative mechanism comes from the research achievement of a previous MSc student, Thomas Baxter, which applied swing arm mechanism into a passenger aircraft's leading edge slat. This thesis applied this idea to trailing edge flap and modeled the mechanism on CATIA software to yield a kinematic simulation for the purpose of check motion trail and force transfer in this mechanism. Relevant works such as actuation, mass and stress analysis are also involved. As the result of this research project, it was found that swing arm mechanism trends to require relatively small fairings for supports and attachments due to its high stowed space utilizing efficiency. Initial mass estimation carried out in this thesis also indicates that the new design takes advantage in terms of weight comparing with traditional trailing edge flap mechanisms. Thus. swing arm mechanism is supposed to show great competitive potential for commercial airliner's trailing edge flaps after further analysis has been done in the detail design phase.

In 1960's Gordon Moore predicted that the increase in the number of components in integrated circuits would exponentially decrease the relative manufacturing cost per component with time. The semiconductor industry has managed to keep that pace for nearly 45 years and one of the main contributors to this phenomenal improvement in technology is advancement in the field of lithography. However, the technical challenges ahead are severe and the future roadmap laid by the International Technology Roadmap for Semiconductors looks mostly red (i.e. no solution has been found to specific problem). There are efforts in the industry and academia directed toward development of newer, alternative lithographic techniques. Step and Flash Imprint Lithography (SFIL) has recently emerged as one of the most promising alternatives, capable of producing high resolution patterns. While it has numerous advantages over conventional photolithography, several engineering challenges must be overcome to eliminate defects due to the nature of contact imprinting if SFIL is to be a viable alternative technique for manufacturing tomorrow's integrated circuits. The complete filling of template features is vital in order for the SFIL imprint process to truly replicate the template features. The feature filling phenomena for SFIL was analyzed by studying diffusion of a gas, entrapped in the features, through liquid imprint resist. A simulation of the dynamics of feature filling for different pattern configurations and process conditions during the SFIL imprint step is presented. Simulations show that initial filling is pressure-controlled and very rapid; while the rest of the feature filling is diffusion-controlled, but fast enough that diffusion of entrapped gas is not a cause for non-filling of features. A theory describing pinning of an air-liquid interface at the feature edge of a template during the SFIL imprint step was developed, which shows that pinning is the main cause of non-filling of features. Pinning occurs when the pressure at the air-liquid interface reaches the pressure of the bulk liquid. At this condition, there is no pressure gradient or driving force to move the liquid and fill the feature. The effect of several parameters on pinning was examined. A SFIL process window was established and template modifications are proposed that minimize the pinning at the feature edge while still preventing any extrusion along the mesa (pattern containing area on the template) edge. Part of semiconductor manufacturing community believes that optical lithography has the capability to drive this industry further and is committed to the continuous improvement of current optical patterning approaches. Some of the major challenges with shrinking critical dimensions (CDs) in coming years are the control of line-edge roughness (LER) and other related defects. The current CDs are such that the presence or absence of even a single polymer molecule can have a considerable impact on LER. Therefore molecular level understanding of each step in the patterning process is required. Computer simulations are a cost-effective approach to explore the huge process space. Mesoscale modeling is one promising approach to simulations because it captures the stochastic phenomena at a molecular level within reasonable computational time. The modeling and simulation of the post-exposure bake (PEB) and the photoresist dissolution steps are presented. The new simulator enables efficient exploration of the statistical excursions that lead to LER and the formation of insoluble residues during the dissolution process. The relative contributions of the PEB and the dissolution step to the LER have also been examined in the low/high frequency domain. The simulations were also used to assess the commonly proposed measures to reduce LER. The goal of the work was to achieve quantification of the effect of changes in resist composition, developer concentration, and process variables on LER and the associated defectivity. / text