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Zigbee network is a popular choice for deploying low power personal area network (LoWPAN). The application areas vary but the most popular are industrial area monitoring and home automation. But Zigbee has been identified to have weak security and is not applicable for industrial implementation. This paper is collaboration with Ericsson to investigate Zigbee network security and implementation. This paper will cover security solutions for Zigbee and touch on how to configure Zigbee network such that it can operate for a long period of time without battery changes. The security solutions will demonstrate how public-key respective symmetric key algorithm can be used for enhancing Zigbee security such that it provide authentication and authorization of joining devices while maintaining confidentiality and integrity of the network communication. Security solutions will also take regards to the power consumption of each proposed solution. For the network configuration part of the thesis, it will present node lifetime for different network configuration, i.e. how polling period between each message will affect the total cur- rent consumption of a node and how the joining procedure, depending on the security solution will affect the total node lifetime. Achieving longer node lifetime is desired because it is assumed that the network will be deployed in remote and unfavorable areas. The result of this paper compares different solutions for enhancing the security. Further, it concludes that Zigbee security with authentication and authorization of joining devices is reached through secret-splitting key establishment - which is the best solution. This is possible while maintaining low power consumption in the network. / Zigbee nätverk är ett populärt val vid uppsättning av ett nätverk med låg strömförbrukning. Zigbees användningsområde är olika men den är väldigt populär inom industriell områdesövervakning och hemautomation. Däremot har Zigbees säkerhet varit en nackdel, då det har framkommit att den inte möter kraven för industriell användning. Arbetet kom till genom ett samarbete med Ericsson och KTH för att undersöka Zigbee nätverks implementation och säkerhet. Arbetet bearbetar olika säkerhetslösningar för Zigbee nätverk och hur den kan implementeras för att uppnå långtidsanvändning utan batteribyte. Säkerhetslösningar bygger på public-key samt symmetric key kryptografi algoritmer för att förbättra och öka Zigbees säkerhet genom autentisering och tillåtelse av noder som ansluter sig till nätverket. Nätverkets konfiguration för långtidsanvändning redovisas genom att jämföra olika polling tidsintervaller mellan meddelanden. Långtidsanvändning utan batteribyte är viktigt för att nätverket kommer implementeras i ett avlägset område som är svåråtkomlig. Arbetet redovisar och jämföra olika lösningar för att öka säkerheten för Zigbee nätverk. Den optimala lösningen för att uppnå autentisering samt tillåtelse av noder som ansluter sig uppnås med nyckel skapande genom secret-splitting metoden. Metoden följer NIST rekommendationer och anses vara säker, därav uppfyller den kraven för industriell implementation. Nätverkets säkerhet ökar samt bibehåller ett nätverk med låg strömförbrukning.

Three testing methods are proposed to characterize properties of fuel cell materials that affect the mechanical durability of proton exchange membranes (PEMs). The first two methods involved measuring the in-plane biaxial strength of PEMs and the biaxial hygrothermal stresses that occur in PEMs during hygrothermal cycles. The third method investigated the nonuniform thickness and compressibility of gas diffusion media which can lead to concentrated compressive stresses in the PEM in the through-plane direction. Fatigue and creep to leak tests using multi-cell pressure-loaded blister fixtures were conducted to obtain the lifetimes of PEMs before reaching a threshold value of gas leakage. These tests are believed to be more relevant than quasi-static uniaxial tensile to rupture tests because of the introduction of biaxial cyclic and sustained loading and the use of gas leakage as the failure criterion. They also have advantages over relative humidity cycling test because of the controllable mechanical loading. Nafion® NRE-211 membrane was tested at three different temperatures and the time-temperature superposition principle was used to construct a stress-lifetime master curve. Tested at 90°C, extruded Ion Power® N111-IP membrane was found to have longer lifetime than Gore™-Select® 57 and Nafion NRE-211 membranes under the same blister pressure profiles. Bimaterial specimens fabricated by bonding a piece of PEM to a substrate material were used to measure the hygral stresses, compressive and tensile, in the PEM during relative humidity cycles. The substrate material and its thickness were carefully chosen so that stresses in the PEM could be obtained directly from the curvature of the bimaterial specimen without knowing the constitutive properties of the PEM. Three commercial PEMs were tested at 80°C by cycling the relative humidity between 90% and 0% and by drying the membrane to 0%RH after submersion in liquid water. Stress histories for all three membranes show strong time-dependencies and Nafion® NRE-211 exhibited the largest tensile stress upon drying. Besides in-plane stresses, hard spots in gas diffusion media (GDM) can locally overcompress PEMs in the out-of-plane direction and cause electrical shorting. In this study, GDM samples sealed with an impermeable Kapton® film on the surface were compressed with uniform air pressure and the nonuniform displacement field was measured with a three-dimensional digital image correlation technique. Hard spots as a result of the nonuniform thickness and compressibility of the GDM were found and their severities as stress risers are evident. Locally, a nominal platen compression (similar to bipolar plate land compression) of 0.68 MPa can lead to compressive stress as large as 2.30 MPa in various hard spots that are in the order of 100s µm to 1 mm in size. / Ph. D.

Vissa yrkesofficerare slutar alltför tidigt i Försvarsmakten. Andra börjar för sent. Yrkesofficeren är idag inte bunden av något tidskontrakt, vilket skapar oreda när den enskilda medarbetaren kan välja att sluta när som helst. Denna experimentella studie avhandlar vad som skulle förmå en yrkesofficer vid Livregementets husarer (K3) att skriva på ett kontrakt som binder individen till förbandet under sju års tid. Kontraktet som stipuleras innehåller bl a följande delar: det gäller för sju år, regementschefen har full handlingsfrihet med yrkesofficeren men man är fortfarande arbetstidsreglerad. Vissa förmåner tar man del av direkt, medan andra utfaller efter ett fullgjort kontrakt. Vår forskning utgår från ett hermeneutiskt paradigm med en experimentell ansats. Metoden som används för insamling av empiri är en fokusgrupp med respondenter ur K3. Referensramen utgörs av tre olika teorier: Etzionis styrformer för organisationer, Pinks X- och I-teori, samt Deci och Ryans självbestämmandeteori. Slutsatserna innehåller tre delar: Det behövs nya villkor samt förmåner för att yrkesofficeren ska vilja skriva på kontraktet.Yrkesofficer måste inte vara en tillsvidareanställning.Gemenskapen, kulturen och samhällsnyttan är det som attraherar till yrket, men det är de varierande arbetsuppgifterna och möjligheten att planera sitt liv som skapar fortsatt motivation. Studien avslutas med rekommendationer till både Försvarsmakten och till Livregementets husarer, eftersom det skiljer sig i hur komplexa rekommendationerna vore i införande. / Some officers quit their career within the Swedish Armed Forces too early. Others enter theirs too late. The Swedish officer is not bound by a contract, thus s/he can quit at any time they choose. This experimental study asks the question of what would induce an officer at the Life Regiment Hussars (K3) to sign a seven year long binding contract. The contract would span seven years, would grant the regimental commanding officer full freedom of action with the officer, who would still be subdued to regulations considering work hours. Some benefits would be provided throughout the contract time, while others would occur after fulfillment of the contract. Our research springs from a hermeneutic paradigm with an experimental approach. The method used to gather data is a focus group, with participants from Life Regiment Hussars (K3). Our frame of reference is based on three theories: the organizational powers by Etzioni, the X- and I-theories by Pink, and the Self-determination theory by Deci and Ryan. We have come to the following three conclusions: New terms and benefits are required to induce the officer to sign the contract.Being an officer does not require permanent employment, which it does today.The camaraderie, the culture and the higher purpose are what attracts people to become officers, but it is the variation of tasks and the possibility to organize one’s life which contribute to continued motivation. The study ends with recommendations divided between the Swedish Armed Forces and the Life Regiment Hussars, because they differ in how complex they would be to introduce.

In the last 10-15 years there has been a renewed interest in amorphous Se (a-Se) and its alloys due to their application as photoconductor materials in the new fully digital direct conversion flat panel x-ray medical image detectors. For a number of reasons, the a-Se photoconductor layer in such x-ray detectors has to be operated at very high electric fields (up to 10 Volts per micron) and one of the most difficult problems related to such applications of a Se is the problem of the dark current (the current in the absence of any radiation) minimization in the photoconductor layer. <p>This PhD work has been devoted to researching the possibilities for dark current minimization in a-Se x-ray photoconductors devices through a systematic study of the charge transport (carrier mobility and carrier lifetimes) and dark currents in single and multilayered a-Se devices as a function of alloying, doping, deposition condition and other fabrication factors. The results of the studies are extensively discussed in the thesis. We have proposed a new technological method for dark current reduction in single and multilayered a-Se based photoconductor for x-ray detector applications. The new technology is based on original experimental findings which demonstrate that both hole transport and the dark currents in a-Se films are a very strong function of the substrate temperature (Tsubstrate) during the film deposition process. We have shown that the new technique reduces the dark currents to approximately the same levels as achievable with the previously existing methods for dark current reduction. However, the new method is simpler to implement, and offers some potential advantages, especially in cases when a very high image resolution (20 cycles/mm) and/or fast pixel readout (more than 30 times per second) are needed. <p>Using the new technology we have fabricated simple single and double (ni-like) photoconductor layers on prototype x-ray image detectors with CCD (Charge Coupled Device) readout circuits. Dark currents in the a-Se photoconductor layer were not a problem for detector operation at all tested electric fields. Compared to the currently available commercial systems for mammography, the prototype detectors have demonstrated an excellent imaging performance, in particular superior spatial resolution (20 cycles/mm). Thus, the newly proposed technology for dark current reduction has shown a potential for commercialization.

In the last 10-15 years there has been a renewed interest in amorphous Se (a-Se) and its alloys due to their application as photoconductor materials in the new fully digital direct conversion flat panel x-ray medical image detectors. For a number of reasons, the a-Se photoconductor layer in such x-ray detectors has to be operated at very high electric fields (up to 10 Volts per micron) and one of the most difficult problems related to such applications of a Se is the problem of the dark current (the current in the absence of any radiation) minimization in the photoconductor layer. <p>This PhD work has been devoted to researching the possibilities for dark current minimization in a-Se x-ray photoconductors devices through a systematic study of the charge transport (carrier mobility and carrier lifetimes) and dark currents in single and multilayered a-Se devices as a function of alloying, doping, deposition condition and other fabrication factors. The results of the studies are extensively discussed in the thesis. We have proposed a new technological method for dark current reduction in single and multilayered a-Se based photoconductor for x-ray detector applications. The new technology is based on original experimental findings which demonstrate that both hole transport and the dark currents in a-Se films are a very strong function of the substrate temperature (Tsubstrate) during the film deposition process. We have shown that the new technique reduces the dark currents to approximately the same levels as achievable with the previously existing methods for dark current reduction. However, the new method is simpler to implement, and offers some potential advantages, especially in cases when a very high image resolution (20 cycles/mm) and/or fast pixel readout (more than 30 times per second) are needed. <p>Using the new technology we have fabricated simple single and double (ni-like) photoconductor layers on prototype x-ray image detectors with CCD (Charge Coupled Device) readout circuits. Dark currents in the a-Se photoconductor layer were not a problem for detector operation at all tested electric fields. Compared to the currently available commercial systems for mammography, the prototype detectors have demonstrated an excellent imaging performance, in particular superior spatial resolution (20 cycles/mm). Thus, the newly proposed technology for dark current reduction has shown a potential for commercialization.

Cavity ring-down spectroscopy has been used over the last twenty years as a highly sensitive absorption spectroscopic technique to measure light attenuation in gases, liquids, and solid samples. An optical cavity is used as a multi-pass cell, and the decay time of the light intensity in the cavity is measured, thereby rendering the techniques insensitive to light intensity fluctuations. Optical waveguides are used to build the optical cavities presented in this work. The geometries of such waveguides permit the use of very small liquid sample volumes while retaining the advantages of cavity ring-down spectroscopy. In this thesis cavity ring-down measurements are conducted, both, in the time domain and by measuring phase-shifts of sinusoidally modulated light, and the two methods are theoretically connected using a simple mathematical model, which is then experimentally confirmed. A new laser driver, that is compatible with high powered diode lasers, has to be designed to be able to switch from time domain to frequency domain measurements. A sample path length enhancement within the optical cavity is explored with the use of liquid core waveguides. The setup was optimised with respect to the matrix liquid, the geometrical matching of waveguide geometries, and the shape of liquid core waveguide ends. Additionally, a new technique of producing concave lenses at fibre ends has been developed and the output of a general fibre lens is simulated. Finally, liquid core waveguides are incorporated into a fibre-loop ring-down spectroscopy setup to measure the attenuation of two model dyes in a sample volume of <1 µL. The setup is characterized by measuring concentrations of Allura Red AC and Congo Red from 1 µM to a limit of detection of 5 nM. The performance of the setup is compared to other absorption techniques measuring liquid samples. / Thesis (Ph.D, Chemistry) -- Queen's University, 2013-04-23 14:08:16.33

This thesis is concerned with the influence of nanoscale boundaries and interfaces upon the electronic processes that occur within the inorganic semiconductors. Inorganic semiconductor nanowires and their blends with semiconducting polymers have been investigated using state-of-the-art ultrafast optical techniques to provide information on the sub-picosecond to nanosecond photoexcitation dynamics in these systems. Chapters 1 and 2 introduce the theory and background behind the work and present a literature review of previous work utilising nanowires in hybrid organic photovoltaic devices, revealing the performances to date. The experimental methods used during the thesis are detailed in Chapter 3. Chapter 4 describes the crucial roles of surface passivation on the ultrafast dynamics of exciton formation in gallium arsenide (GaAs) nanowires. By passivating the surface states of nanowires, exciton formation via the bimolecular conversion of electron-hole plasma can observed over few hundred picoseconds, in-contrast to the fast carrier trapping in 10 ps observed in the uncoated nanowires. Chapter 5 presents a novel method to passivate the surface-states of GaAs nanowires using semiconducting polymer. The carrier lifetime in the nanowires can be strongly enhanced when the ionization potential of the overcoated semiconducting polymer is smaller than the work function of the nanowires and the surface native oxide layers of nanowires are removed. Finally, Chapter 6 shows that the carrier cooling in the type-II wurtzite-zincblend InP nanowires is reduced by order-of magnitude during the spatial charge-transfer across the type-II heterojunction. The works decribed in this thesis reveals the crucial role of surface-states and bulk defects on the carrier dynamics of semiconductor nanowires. In-addition, a novel approach to passivate the surface defect states of nanowires using semiconducting polymers was developed.

La philosophie ricœurienne indique qu’il n’est pas de compréhension de soi qui ne soit médiatisée par des signes, des symboles, des textes ; elle peut donc être interprétée comme une chance pour la philosophie africaine. En effet, si on estime que le champ éthique s’étend à tous les domaines de la vie, si on admet avec Ricœur que l’existence est synonyme d’action, à savoir que « dire ‘’je suis’’, c’est dire ‘’je veux, je meus, je fais’’ », alors l’Africain traditionnel qui n’a pas une pensée systématique comme l’exige la philosophie grecque, mais a plutôt développé une pensée de ce qu’il fait, peut apporter au discours éthique sa modeste contribution. En effet, ses mythes, ses contes et même quelquefois ses chants, contiennent un enseignement à la fois pratique, symbolique et philosophique, à caractère universel. Entrer à l’intérieur d’un conte, c’est comme entrer à l’intérieur de soi-même. / Ricoeur’s philosophy shows us that there is not any comprehension of self without it being mediated by signs, symbols and texts; it can be, therefore, interpreted as a chance given to the African philosophy. In fact, if we estimate that the ethical field extends to all human domains and if we admit, like Ricoeur does, the synonymy between action and existence – “to say I am, means I want, I move, I do” – thus the traditional African, who hasn’t a systematical thinking as required by the Greek philosophy, but instead has developed a thinking of what he can do, can bring into the ethical discourse his modest contribution. In reality, his myths, his tales and sometimes his chants, all contain a message that is at the same time: practical, symbolical and philosophical, with a universal character. To enter into a tail is like entering inside one’s self.