| 1. |
- Bernhard-Oettel, Claudia, 1977-
(författare)
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Alternative employment and well-being : Contract heterogeneity and differences among individuals
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The increasing use of temporary and part-time employment in recent decades was initially expected to lead to negative effects for the individual. The empirical evidence, however, has been equivocal and the consequences are therefore still unclear. This thesis adopts a psychological approach to alternative employment by investigating how heterogeneity in employment contracts together with individual differences associate with work attitudes and subjective well-being. It comprises four studies in which questionnaire data is used to study differences among temporary workers (Study I & II) and differences in the alternative workforce (fixed-term, on-call, and part-time workers) compared to permanent full-time workers (Study III & IV), in order to analyze the impact of different types of contracts together with individual differences. Study I found that attitudes, role stress, and health varied across different patterns in individuals’ backgrounds and contract forms. Study II demonstrated that distinct patterns of voluntary and involuntary contract motives and of work involvement associated with differences in reported work-related and general well-being. Study III showed that well-being and organizational attitudes were related to individuals’ job and contract preferences and, to some degree, heterogeneity in contract types. Study IV revealed that individuals’ perceptions of job conditions (control, demands, and job insecurity) predicted well-being, whereas type of employment contract was found to be less important. Employment contract forms, however, interacted with individual diversity in Study III and IV. The thesis concludes that differences among individuals are important for understanding the implications of different types of alternative employment contracts. Future research should focus on these interactive mechanisms to better understand the consequences of alternative employment forms.
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| 2. |
- Masud, Nauman
(författare)
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About Physical Human Robotic Interaction for Assistive Exoskeletons
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The thesis work has contributed to the field of assistive robotics. The physical interaction between the exoskeleton and human has been studied by considering performance both at the joint as well as task space level of the exoskeleton. For ensuring safe and enhancing physical human interactions for elderly persons, special consideration has been given to problems due to the weight and number of actuators of the exoskeleton. Specific scenarios have been formulated to investigate fundamental requirements and where innovations have been developed for originality and academic content after the initial phases of the investigations.Research on the lower active degree of freedom serial robotic manipulators has hence gained importance from the perspective of developing assistive exoskeletons that are light and can provide effective assistance to the user despite being less dexterous as compared to the high degree of freedom counterparts. Control methodologies have been investigated and developed for low active degrees of freedom exoskeleton that can ensure stable and safe human interaction. With this focus in mind, a specific strategy has been proposed to compensate for the nonlinear dynamics of the human exoskeleton system at the joint level. Furthermore, active compliance through impedance control in conjunction with passive compliance has been proposed to provide safe human interaction. The interactive human-machine-impedance-loop with a human as a dynamic environment (which contrasts with the existing approaches) and exoskeleton as a controlled impedance has also been investigated for stability and performance. This, in turn, has provided the sound-realistic basis for the development of cascaded strategies to ensure safe interaction between humans and the exoskeleton. A Hybrid switching control strategy has also been developed to simultaneously improve the load torque compensation performance as well as the stability of the human-exoskeleton system in case of actuator saturation. Methodology for proper selection of joint actuators along with a framework for finding the desired assistive forces based on the actual end-user group data has also been developed. A distributive controller area network-based control architecture has also been proposed for a lower-body exoskeleton. Lower and upper body exoskeleton test rigs and prototypes along with the associated hardware have been developed in tandem to verify the proposed strategies both at the joint and task space level. A new control strategy capable of imparting simultaneous impedance-based force tracking control for both the compliant contact supports of the lower-body exoskeleton(in task-space) using DOB-based-DLTC (at joint-space) has also has also been proposed
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| 3. |
- Zenteno, Efrain, 1983-
(författare)
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Digital Compensation Techniques for Transmitters inWireless Communications Networks
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Since they appeared, wireless technologies have deeply transformed our society. Today, wireless internet access and other wireless applications demandincreasingly more traffic. However, the continuous traffic increase can be unbearableand requires rethinking and redesigning the wireless technologies inmany different aspects. Aiming to respond to the increasing needs of wirelesstraffic, we are witnessing a rapidly evolving wireless technology scenario.This thesis addresses various aspects of the transmitters used in wireless communications.Transmitters present several hardware (HW) impairments thatcreate distortions, polluting the radio spectrum and decreasing the achievabletraffic in the network. Digital platforms are now flexible, robust and cheapenough to enable compensation of HW impairments at the digital base-bandsignal. This has been coined as ’dirty radio’. Dirty radio is expected in future transmitters where HW impairments may arise to reduce transmitter cost or to enhance power efficiency. This thesis covers the software (SW) compensation schemes of dirty radio developed for wireless transmitters. As describedin the thesis, these schemes can be further enhanced with knowledge of thespecific signal transmission or scenarios, e.g., developing cognitive digital compensationschemes. This can be valuable in today’s rapidly evolving scenarioswhere multiple signals may co-exist, sharing the resources at the same radiofrequency (RF) front-end. In the first part, this thesis focuses on the instrumentation challenges andHWimpairments encountered at the transmitter. A synthetic instrument (SI)that performs network analysis is designed to suit the instrumentation needs.Furthermore, how to perform nonlinear network analysis using the developedinstrument is discussed. Two transmitter HW impairments are studied: themeasurement noise and the load impedance mismatch at the transmitter, asis their coupling with the state-of-the-art digital compensation techniques.These two studied impairments are inherent to measurement systems and areexpected in future wireless transmitters. In the second part, the thesis surveys the area of behavioral modeling and digital compensation techniques for wireless transmitters. Emphasis is placed on low computational complexity techniques. The low complexity is motivated by a predicted increase in the number of transmitters deployed in the network, from base stations (BS), access points and hand-held devices. A modeling methodology is developed that allows modeling transmitters to achieve both reduced computational complexity and low modeling error. Finally, the thesis discusses the emerging architectures of multi-channel transmittersand describes their digital compensation techniques. It revises the MIMOVolterra series formulation to address the general modeling problem anddrafts possible solutions to tackle its dimensionality. In the framework of multi-channel transmitters, a technique to compensate nonlinear multi-carrier satellite transponders is presented. This technique is cognitive because it uses the frequency link planning and the pulse-shaping filters of the individual carriers. This technique shows enhanced compensation ability at reduced computational complexity compared to the state-of-the-art techniques and enables the efficient operation of satellite transponders.
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| 4. |
- Isaksson, Magnus, 1975-
(författare)
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Initiation of Autoimmunity in Experimental Autoimmune Encephalomyelitis
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The events that trigger an autoimmune disease remain largely unknown. To study these events animal models are necessary because symptoms of autoimmune diseases are preceded by a long asymptomatic period in humans.Experimental autoimmune encephalomyelitis (EAE) is the best characterized model for cell mediated autoimmunity and an animal model for the human disease multiple sclerosis. EAE is induced in rodents by immunization with myelin antigens (Ags) together with adjuvants. After immunization, T cells are primed in the periphery by Ag presenting cells and subsequently invade the central nervous system where they mediate parenchymal inflammation, resulting in demyelination and clinical symptoms of an ascending paralysis. It is now generally recognised that the main cell type mediating EAE is the T helper type 17 (Th17) cell.Tolerance to EAE can be attained by DNA vaccination, but how the immune response against the myelin Ags is abrogated after DNA vaccination is not known. By employing short interfering RNA technology, induction of the innate immune signalling molecule interferon (IFN) -β was found to be necessary for the protective effect of DNA vaccination in EAE. In addition, DNA vaccination inhibited subsequent autoimmune Th17 cell responses.The Toll-like receptors (TLRs) of the innate immune system have evolved to recognise conserved molecular structures on microbes and signalling through them almost exclusively converge on the molecule MyD88. Signalling via MyD88 was found to be required for induction of EAE since mice deficient in this molecule did not develop disease. Upstream signalling via TLR4 and TLR9 had tolerogenic properties.In studies of Ag presentation in EAE, two major subtypes of dendritic cells (DCs) were examined. Plasmacytoid DCs were found to have a promoting role in the induction of EAE, partly via type 1 IFNs. Myeloid DCs had a redundant role in the induction phase of EAE, neither disease severity nor encephalitogenic Th17 responses were affected by their absence during priming.These studies further demonstrate that the cells and molecules of the innate immune system exhibit a crucial role in controlling the adaptive immune system which mediates tissue damage in autoimmune diseases.
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| 5. |
- Landin, Per, 1983-
(författare)
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Digital Baseband Modeling and Correction of Radio Frequency Power Amplifiers
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Aspects related to behavioral modeling and correction of distortions for radio frequency (RF) power amplifiers (PAs) are treated in the thesis. When evaluating the performance of a behavioral model it is important to, first of all, use an evaluation criterion, and second, make sure that the criterion actually tells something about the behavior one wishes to describe. This is used in the weighted error spectral power ratio (WESPR) criterion by means of a frequency dependent weighting function. When the parameters of the models are estimated a suitable error criterion should likewise be used. The frequency weighting function in the WESPR is used in the extraction of the parameters. It is shown on two types of PAs that the model performance measured as WESPR can be improved while the model complexity is reduced compared to the standard frequency neutral criterion. When building a model of a system it is advantageous to take account of the physical structure and incorporate this knowledge into the model. It can improve model performance and possibly reduce the number of parameters. By starting from a physically motivated nonlinear model of a RF PA, the commonly used memory polynomial (MP) models are derived. Additionally, three novel MP model structures are derived. Using data measured on a PA it is found that two of these model structures have lower model errors while using fewer parameters than models previously published in the literature. Methods to increase the power efficiency and the linearity of RF PAs have been investigated. One of these methods is digital predistortion (DPD) which improves the linearity, thus facilitating operation at higher power levels which improves power efficiency. The other method is a signal shaping method that makes the signal more favorable to the PA by reducing the highest peaks to lower values. It is experimentally shown that the combination of DPD and signal shaping results in an increase of power efficiency in the order of 2-4 times. An instability in the feedback loop that updates the parameters of the DPD was also identified and two solutions were proposed. One solution changes the parameters of the DPD in such a way that the instability is avoided and the other changes the signal to avoid high amplitudes. The nonlinear effects of class-D outphasing amplifiers are considered. Four model structures are proposed and evaluated on data measured from two amplifiers. In order to reduce the distortions in the output signal from the amplifiers an algorithm using constant envelope amplitude (purely phase-modulated) signals is proposed. The DPD is evaluated and found to reduce the distortions in a state-of-the-art 32 dBm class-D outphasing PA to make it fulfill the linearity requirements for downlink signals used in the universal mobile telecommunications system (UMTS).
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| 6. |
- Isaksson, Magnus, 1978-
(författare)
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Extracting Genomic Variations using Selector Technology
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis describes the development and use of a new class of molecular tools called Selector probes, and its potential for investigations of genetic variation. The Selector technology provides multiplex amplification of targeted DNA sequences with a high specificity, and an enrichment factor in the same order of magnitude as PCR. A common feature in this thesis work is to focus the analysis on DNA regions of interest. For example, this technique can be implemented in analysing candidate regions found by whole genome studies that need validation (global to local analysis), and applications requiring detection of rare alleles (common to rare allele), important in for example cancer samples. An assay is presented that allows for fast and simple quantification of relative copy-number variations. The method was proven to be able to detect aneuploidy in chromosome 13, 18, 21 and X, with a resolution enough to distinguish between 4 and 5 copies. The method was successfully applied to solve a biological question regarding a copy-number variation, that explains the Ridge phenotype typical for the dog bread Rhodesian Ridgebacks. The Selector strategy was able to detect and map a tandem duplication with a size of 133 kb, which was characterized with base-pair resolution. A readout platform that facilitates simultaneous digital quantitative analysis of a large numbers of biomolecules is further introduced. The work involves arraying amplified product from successful selection and decoding each molecule by hybridization of fluorophore labeled oligonucleotides. Finally, a genome partitioning method which is applied upstream of next generation sequencing platforms is presented. It is shown that the method provides successful enrichment with 98 % coverage and 94 % specificity and high enrichment uniformity. The technique was applied for mutation analysis of 26 cancer-related genes in tumor cell-lines and tissue.
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| 7. |
- Khan, Zain Ahmed, 1987-
(författare)
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Characterization and Compensation of Hardware Impairments in Transmitters for Wireless Communications
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Increasing demands for data rate, energy efficiency and reliability in wireless communications have resulted in the introduction of radio frequency (RF) multiple input multiple output (MIMO) transmitters. However, MIMO transmitters suffer from additional crosstalk impairments along with the power amplifier (PA) and I/Q imbalance distortions observed in single input single output (SISO) transmitters. Therefore, this thesis focuses on the characterization and compensation of these hardware impairments in RF SISO and MIMO transmitters.PA distortions are often compensated using the Volterra series, but it suffers from high computational complexity. Therefore, a non-parametric method based on density estimation has been proposed in this thesis to estimate the PA transfer function, from which pruned Volterra models can be developed. The method is validated for a Doherty PA and achieves competitive error performance at a lower complexity than its competitors.For MIMO transmitters, a characterization technique that uses multitone excitation signals has been proposed. Multitone signals yield non-overlapping tones at the outputs of the MIMO Volterra kernels. These kernel outputs are used to identify the dominant crosstalk impairments, from which block structure and base-band behavioral models are developed. The method is validated for 2x2 and 3x3 MIMO transmitters and it is shown that the derived models achieve a better complexity accuracy trade-off than the other pruned MIMO Volterra models considered in this thesis.Finally, the thesis presents compensation models for joint static I/Q imbalance and MIMO PA distortions based on conjugate pair and real-valued basis functions. The models are augmented with sub-sample resolution to compensate for dynamic I/Q imbalance distortions. The proposed models are validated for a 2x2 RF MIMO transmitter and achieve a better complexity accuracy trade-off than the other state-of-the-art models considered in this thesis.
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| 8. |
- Landin, Per N.
(författare)
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On Radio Frequency Behavioral Modeling : Measurement Techniques, Devices and Validation Aspects
- 2009
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Effektförstärkare för radiofrekvensapplikationer utgör fortfarande ett av de största problemen i trådlösa kommunikationssystem. Detta beror på att dessa förstärkare är ickelinjära, har låg energieffektivitet och ger mycket distortioner. Bättre verktyg för att förstå och korrigera dessa beteenden är nödvändiga. Ett sådant verktyg är beteendemodellering. En beteendemodell kan ses som en svart låda med insignal(er) och utsignal(er). In detta fall är dessa signaler samplade basbandssignaler och den svarta lådan är en matematisk relation mellan en insignal och en utsignal. Avhandlingen behandlar några krav för beteendemodellering av nämnda system genom att presentera metoder för utvärdering och förbättring av modellernas prestanda. Detta åstadkoms genom att betrakta ett frekvensviktat felkriterium. Ett högpresterande mätsystem är också nödvändigt för experimenten. Prestandan hos det tillgängliga systemet jämförs med prestandan hos ett allmänt erkänt mätsystem, en s.k. storsignalsnätverksanalysator, genom att betrakta prestandan hos beteendemodellerna som extraheras och valideras med data från respektive mätsystem. Resultatet visar att det existerande mätsystemet har god prestanda. Ett stort problem vid beteendemodellering är att kunna sampla med tillräckligt hög hastighet. Genom att använda Zhu-Franks generaliserade samplingsteorem vid beteendemodellering kan en del av detta problem undvikas. Teoremet medför att man kan sampla med en väsentligt lägre samlingsfrekvens än vad Nyquistteoremet säger. Modeller extraheras och prestandan utvärderas genom att använda kriteriet normalized mean square error (NMSE). För stabil prediktion och korrektion av utsignalen måste robustheten hos de använda modellerna verifieras. En sådan studie som berör robustheten mot variationer i lastimpedansen har genomförts. Prestandan på direkta modeller försämras med 7 dB mätt som adjacent channel error power ratio (ACEPR). Prestanda på inversmodellen, implementerad som digital predistortion, försämras med upp till 13 dB mätt som adjacent channel power ratio (ACPR).
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| 9. |
- Marti Bigorra, Anna, 1990-
(författare)
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Customer-focused data-driven target setting
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- To develop products through a customer-centric strategy, early stages of product development such as target setting play an important role. In the target setting stage Customer Needs (CN) are gathered and translated into Design Requirements (DR) in order to subsequently set product targets that fit cost constraints and at the same time result in high Customer Satisfaction (CS). Continuous advances in information technology create new opportunities for companies to gather information about the customer, for example, for marketing purposes, or to assess customer reactions after the launch of new products. In addition, products are becoming complex systems that are successively equipped with more software and sensors offering opportunities for collecting data on how they are used. Knowing how customers use the product enhances a company’s ability to segment customers and customize products.Despite customer information availability from different sources (sensors, social media, etc.), surveys and focus groups are considered today as the main data source to derive the set of CN statements during target setting. Further, the team’s interpretation of CNs, which are often described in abstract language, must be translated into DRs, which are described in a more technical language. Hence, the translation process of CNs into DRs is said to be subjective. To set product targets, CS sensitivity to changes in DR levels is also considered. Surveys and benchmarking data containing customer perceptions on competitors’ performance are often the main customer data input into the process. While insightful information may be obtained, surveys are costly and time consuming and only encompass a small part of the market population.The research presented in this doctoral thesis explores how customer information obtained from sensors (e.g. product usage data) and text data (e.g. from websites, open-survey questionnaires) can be factored in the target setting process before concept generation to enhance customer focus without compromising product development time. The aim is to increase designers’ awareness of target population and in turn increase the quality of the design decisions on product targets. For this purpose, a customer-focused data-driven target setting methodology is proposed. The presented methodology changes the actual target setting methodology by means of indicators and autonomous activities on those parts of the process where marketing or design decisions are needed. The proposed methodology gives the incentive for a more integrated product development where marketing and designers need to work closely. This further allows a sustainable customer information gathering strategy that strives for missing customer information that is required for setting product targets. The indicators act as feedback channels for continuous product improvement. The use of such indicators and autonomous activities highlights the potential of a more efficient, less subjective and higher-quality target setting process.
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| 10. |
- Zenteno, Efrain, 1983-
(författare)
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Vector Measurements for Wireless Network Devices
- 2013
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Wireless networks are an iconic technology of today’s modern era, theyare present in our daily activities as can be exemplified by cellular communications,wi-fi, bluetooth, and others. Vector measurements play an importantrole in the design, simulation, and testing of wireless networks and are usedto characterize key devices operating in the radio interface, such as amplifiers,filters, and mixers.Accurate characterization is the key for improving the capacity and efficiencyof wireless networks. As the demand for network capacity continuouslyincreases, the accuracy of vector measurements must also improve. Further,it is anticipated that such trends will continue in the years to come. Consequently,the wireless industry needs to include nonlinear behavior in theircharacterization and analysis, to assess and guaranty the operation of the devices,and to comply to the specifications from governmental regulations. Incontrast to linear behavior, nonlinear behavior presents an additional bandwidthrequirement because the signal bandwidth grows when it passes throughnonlinear devices. In this thesis, vector measurements for devices operatingin wireless networks are studied, emphasizing a synthetic approach for theinstrumentation. This approach enables the use of digital post-processing algorithms,which enhances the measurement accuracy and/or speed and canovercome hardware impairments. This thesis presents the design of a vectorialmeasurement system for wireless devices considering the aforementionedtrends and requirements. It also explores the advantages of the proposedapproach, describes its limitations, and discusses the digital signal processingalgorithms used to reach its final functionality. Finally, measurement resultsof the proposed setup are presented, analyzed and compared to those of modernindustrial instruments.
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