Dissertations / Theses on the topic 'Attenuator'

Variable attenuators are important circuits that can be employed in many radio frequency (RF) applications, e.g., in automatic gain control (AGC) amplifiers, broadband gain-control blocks at RF frequencies or as broadband vector modulators. For any applications, low insertion phase shift and low power consumption are of interest. A way to implement variable attenuators is using the RF PIN diode. The PIN diode is characterized by a low doped (I = intrinsic) semiconductor region between p- (P) and n-type (N) semiconductor regions. Besides the variable attenuators, the PIN-diode is used in other RF circuits, such as RF switches, limiters and phase shifters. This project presents the design of variable attenuators at 7.5 GHz and 500 MHz frequency bandwidth for ultra-wideband (UWB) applications using two different PIN diodes. The variable attenuators have a topology based on 90° hybrid couplers. The design is performed using Advance Design Systems (ADS) from Agilent Technologies Inc. After presenting the PIN diode and its equivalent circuit, the theory of the 90° passive directional branch line coupler and the operation principle of the variable attenuators are presented. As the selection of the appropriate PIN diode is a critical step in the design, special attention is dedicated to this aspect. It follows the design of the variable attenuators with extensive descriptions of the simulations in ADS. Firstly, both series and shunt attenuators are presented. However, as these circuits normally offer narrow band variable attenuation, the 900 directional branch line coupler is used in the attenuator for broader band operation. At the end, a double hybrid coupler is found to eliminate the ripple in the high attenuation state of the single hybrid coupled attenuator. So the final topology of the variable attenuator is a double hybrid coupler variable attenuator- Moreover, in this project, different PIN diodes are investigated for variable attenuator applications. Different manufacture companies are currently providing different kinds of PIN diodes in terms of parameters and packages. Every type of PIN diodes are providing different sort of advantages to the designers. That is why it has become more difficult for the RF designers to choose the right device for the specified application. Beside the design of the variable attenuator using PIN diodes, some considerations in form of a guide line to the designers while they are using the PIN diode for designing the variable attenuator. In this work, the used PIN diodes are a beam lead PIN diode and chip PIN diode. The beam lead PIN diode is used because it is manufactured for high frequency and it produces excellent electrical performance and isolation at high frequencies. On the other hand, the chip PIN diode eliminates the problem of package parasitics. However, printed circuit board (PCB) manufacturing limitations at the university laboratory incline the balance in the favor of the beam lead PIN diode, HPND- 4005 from Avagotech, instead of the also considered chip diode MA-COM MA4P202.

This paper deals with the possibilities of designing the module for control of the attenuation of the optical signal. The paper describes basics of ber optic transmission and beam e ects. Variants of attenuation cells are characterized in this paper and based on the ndings a solution of the module for control of the attenuation of the optical signal is proposed. Practical section of the thesis deals with the design and physical construction of module for control of the attenuation of the optical signal using MEMS variable optical attenuator.

All solid-state switches and attenuators are becoming increasingly popular over their mechanical counterparts. Their advantages include smaller size, no moving parts, and faster response times. The device presented here is a silicon on insulator waveguide attenuator, its operation is based on free-carrier absorption of photons. Free-carriers are provided by forward biasing a PIN diode structure integrated in a single mode rib waveguide where the guided mode propagates in the intrinsic region. The device was optimized optically using CAD tools to provide off-state losses of less than 1dB. The PIN diode electrical structure was also optimized to for a maximum power consumption of 1W at maximum attenuation. Good agreement of the theory developed was found when compared to experimental measurements of fabricated prototypes of similar structure. Fabrication and testing of devices according to the specifications arrived at in this thesis is suggested for future work.

Le travail effectué dans le cadre de cette thèse porte sur l'étude d'un atténuateur de rayonnement X à gaz et du plasma produit à l'intérieur. Un atténuateur à gaz est composé d'une chambre remplie du gaz, généralement argon ou krypton à quelques centaines de millibars, qui absorbe la partie de basse énergie d'un spectre de rayonnement X de synchrotron, en réduisant la puissance reçu par les éléments optiques en aval sans affecter les propriétés de la partie de haute énergie du spectre. L'absorption des photons crée une région de gaz chaud et ionisé autour du parcours du faisceau X, en réduisant la densité du gaz localement. A détaillé bilan énergétique entre tous les processus impliqués c'est nécessaire pour être capable de prédire l'absorption et opérer et dessiner atténuateurs a gaz efficacement. Un modèle hybride que combine techniques de modélisation Monte Carlo et fluides à été développé pour déterminer le bilan énergétique et simuler l'absorption de rayonnement X. Le modèle a été valide expérimentalement pas études incluant absorption de puissance, spectroscopie optique d'émission et spectroscopie d'absorption par laser à diodes. Les résultats des simulation et expériences montre un plasma confiné autour du parcours du faisceau X, recombinant dans le volume de gaz et avec une température maximale de plusieurs centaines de Kelvin. Le modèle a été capable de prédire l'absorption de rayons X avec un erreur de entre 10 et 20%, qui permettre son utilisation comme première approximation pour le dessin et opération de atténuateurs a gaz et aussi comme point de partie pour modèles plus affinées
The work done in the context of this thesis focuses in the study of an X-ray gas attenuator and the plasma produced within. An X-ray gas attenuator consists on a vessel filled with gas, usually argon or krypton at a few hundreds millibars, that absorbs the low energy fraction of a synchrotron X-ray spectrum, reducing the power received by downstream optical elements without affecting the properties of the high energy part of the spectrum. The absorption of the photons creates a region of hot, ionized gas around the X-ray beam path, decreasing locally the gas density. A detailed energy balance between all the involved processes is required to be able to predict the absorption and operate and design gas attenuators efficiently. A hybrid model combining Monte Carlo and fluid modelling techniques has been developed to determine the energy balance and simulate the X-ray absorption. The model has been validated by experimental studies including power absorption, optical emission spectroscopy and tunable laser absorption spectroscopy. The results of both simulation and experiments show a plasma confined around the X-ray beam path, recombining in the bulk of the gas and with a maximum temperature of several hundreds of Kelvin. The model was able to predict the X-ray absorption within a 10-20% of error, which allows its use as a first approximation for the design and operation of gas attenuators, and also provides a starting point for more refined models

In wavelength division multiplexed (WDM) optical communication networks, signals are amplified periodically by optical amplifiers. Since the gain profiles of optical amplifiers are not flat, equalizers are usually used to maintain signal powers at different wavelengths in equal to avoid crosstalk and data loss. However, fixed attenuation can only compensate fixed input power and amplification. In active network, input power and amplifier gain change with time. Active level compensation at each wavelength is needed. An adaptive attenuator is a device with a chromatically variable transmissivity used to equalize channel powers in wavelength-division multiplexing (WDM) fiber-optic communication lines. In this thesis, a method of Fourier analysis of multi-beam interference is developed. It is shown that the total electric field and relative phase delay of each beam form a Fourier transform pair. Thus methods and properties of Fourier analysis are applicable in multi-beam interference analysis and design. Fourier transform based design is presented. Novel devices that apply such design principles are introduced. Principles and structures of novel adaptive attenuators based on various technologies such as segment deformable mirror, liquid crystal, phase modulation array are given. Simulation results for segment deformable mirror based adaptive attenuator are presented.
Master of Science

Fatty acids are an essential component of the phospholipids of the inner and outer membranes of Escherichia coli. The synthesis of both fatty acids and phospholipids is regulated. Synthesis increases when growth rate increases, is inhibited when starvation occurs, and the fatty acid composition of the membrane changes with growth temperature. Several genes encoding enzymes involved in membrane synthesis are located in the rpmF-plsX-fab operon. In this operon, a gene encoding a phospholipid synthetic gene of unknown function, plsX, lies just downstream of the ribosomal protein gene rpmF and upstream of five fatty acid biosynthetic genes, fabH, fabD, fabG, acpP, and fabF. The operon is also complex; transcription is initiated from at least eight promoters. In addition, some transcripts produced by the operon are cleaved by RNases while others terminate at one of three specific points at the 5' end of plsX. This work demonstrates that a weak transcriptional terminator (an attenuator) lies at the 5' end of plsX. The attenuator was localized to a 200 bp segment. Analysis of the secondary structure of the attenuator mRNA has lead to a model which includes four stem-loop structures. In this model, the plsX start codon lies within the loop of the second stem. Two tandem stems are located directly upstream of the mapped 3' endpoints. Mutational analysis shows that all four stem-loops play a role in attenuator activity. Regulation of the attenuator and the attenuator's mechanism of controlling downstream gene expression were investigated. Ribosome binding to attenuator mRNA, the PlsX protein, ppGpp concentration, and rate of lipid synthesis all appear to have no effect on attenuator activity. Interestingly, growth temperature appears to have an effect on both attenuator activity and the activity of one or more of the promoters upstream of rpmF, P₁, P₂, and P₃. Activity of the three promoters is 4.5-fold higher at 28°C as compared with 42°C. The attenuator also appears to increase expression of downstream genes 2-fold as temperature decreases. Though the attenuator region terminates transcription, growth temperature-regulation of attenuator activity is apparently mediated by a change in stability of the mRNA. These data demonstrate that transcriptional expression of plsX is 9-fold higher at 28°C as compared with 42°C. The striking dependence on temperature of plsX expression suggests a role for PlsX in the temperature modulation of fatty acid incorporation into the membrane phospholipids.
Ph. D.

Thesis (M.S. in electrical engineering)--Washington State University, December 2009.
Title from PDF title page (viewed on Dec. 28, 2009). "School of Electrical Engineering and Computer Science." Includes bibliographical references (p. 49-51).

The correct development of multicellular organisms is dependent upon the communication of individual cells by signalling. Negative feedback loops are often key, as once a signalling pathway has been activated, and the resulting changes in gene expression implemented, the pathway must be attenuated. Misregulation of these processes can lead to diseases such as cancer. The Ras pathway is a well-characterised example, being overactive in many types of cancer. In C. elegans, it has been proposed that attenuation of Ras can occur through the action of sumoylation on chromatin factors. To this end, we performed an RNAi screen in a SUMO-sensitised background, in which we targeted predicted C. elegans chromatin factors. We identified BET-1, a double bromodomain protein, and subsequently showed that it interacts genetically and physically with the sumoylation pathway to prevent hyperactivation of Ras signalling. Loss of BET-1 caused phenotypes consistent with excessive Ras signalling in the vulva and germline, and led to increased Ras signalling at a global level in the worm. Loss of both BET-1 and SUMO led to a striking effect on fluid homeostasis, and loss of muscle mass, in adult worms. This synthetic phenotype was found to be caused in part by overexpression of the FGF receptor, EGL-15. To summarise, the RNAi screen successfully identified BET-1 and other candidates as novel regulators of Ras signalling. We have shown that BET-1 alone has a role in preventing excessive Ras signalling in C. elegans, and that BET-1 and SUMO work together to maintain fluid homeostasis and muscle mass. In conclusion, the work presented in this thesis shows that BET-1 and SUMO cooperate to prevent excessive Ras signalling, and is consistent with a model in which BET-1 and SUMO perform this function by acting as part of a negative feedback loop.

The Hashin failure criteria and damage evolution model for laminated fiber reinforced polymers are explored. A series of tensile coupon finite element analyses are run to characterize the variables in the physical model as well as modeling techniques for using an explicit dynamic solver for a quasi-static problem. An attempt to validate the model on an axial tube crush is presented. It was found that fiber buckling was not occurring at the impactor-tube interface. Results and speculation as to why the failure initiation is incorrect are discussed. Lessons learned from the tube crush are applied successfully to the quasi-static Formula SAE nosecone crush test. The model is validated by experimental data and the impact metrics between the test and model are within 5%. Future work and possible optimization techniques are discussed.

In this master degree work, a digital attenuator and a low noise amplifier (LNA) have been designed and integrated with the RF front-end receiver for IEEE 802.11b Wireless LAN standard. Firstly, the 4-bit digitally controlled attenuator has been designed with theattenuation range of 50 to 80 dB and reflection coefficient less than -25 dB. Next, the single stage wide band low noise amplifier with voltage gain larger than 14 dB and noise figure below 4 dB has been designed to operate at frequency 2.4 GHz. Finally, the integration with a down-conversion mixer has been done and evaluated its performance.

The attenuator and low noise amplifier desired in this thesis have been implemented using standard CMOS 0.35µm technology and validated by the simulation tools Cadence Spectre-RF.

The onset of an explosion in an underground mining environment is a threat that has over years attracted a lot of attention. Much of this attention has focused on either arresting the explosion after it has been initiated or preventing the initiation. The methods devised have proved successful in most cases, but on the odd occasion that they fail, the end results can be disastrous. There have been fatalities from underground mining explosions as a result of fires burning and sapping all the oxygen in the atmosphere leading to asphyxiation. A different approach to arresting these explosions would enhance safety in the face of increased productivity. A novel method using an explosion door with a porous media acting as a shock wave attenuator and arresting the flames has been introduced. This research investigates the ability of the porous media used in the explosion door to withstand explosions. The performance of the porous media is crucial, as its failure would render the explosion door useless. In order to assess the performance of the porous media, a shock tube was built capable of generating shock waves with a Mach number of 1.5. By placing samples of the porous media within the test section of the shock tube, pressure measurements were taken fore and aft of the porous media as it was impinged upon by the shock wave. Tests were also conducted using thin orifice plates to provide data for comparing the performance characteristics of the porous media. Computational fluid dynamics (CFD) simulations of the porous media and the orifice plates were performed to validate the experimental work as well providing graphic detail of the flow around the test specimen. The work presented in this thesis makes a contribution to the efforts towards the provision of a safe underground environment. This contribution is achieved by investigating the performance of the porous media to be used in an explosion door and correlating the performance of the porous media with thin orifice plates. The porous media in the work presented here is currently used in the castings industry and its application as a shock wave attenuator and fire arrester would contribute greatly to the well being of all people working underground.

Les paramètres S constituent l'une des grandeurs de base de l'électricité-magnétisme dans le domaine radiofréquence. Ils sont normalisés par rapport à une valeur d'impédance dite de référence et sont mesurés à l'aide d'un analyseur de réseau vectoriel (Vector Network Analyzer (VNA)). La précision des paramètres S des composants micro-ondes avec un analyseur de réseau vectoriel (VNA) dépend de l'exactitude du calibrage utilisé pour corriger les erreurs inhérentes au système. Le calibrage consiste à mesurer des dispositifs particuliers plus ou moins bien connus, que l'on appelle étalons, afin de déterminer les erreurs systématiques du système avant la mesure du composant. Les coefficients d'erreurs calculés à partir de l'étalonnage seront utilisés pour caractériser les vrais paramètres S du dispositif. La procédure de calibrage LAR (Line-Attenuator-Reflect), intégrée dans les analyseurs de réseau modernes et qui permet une large bande de mesure avec un nombre limité d'étalons de référence sur wafer, est particulièrement attractive. Par contre, peu d'études sont réalisées pour évaluer sa traçabilité. C'est pourquoi le LNE (Laboratoire National de Métrologie et d'Essais) a décidé de mener des études afin d'évaluer la traçabilité et la précision de mesure quand la méthode de calibrage LAR est utilisée. Dans ce contexte, nos travaux de thèse se résument comme suit : 1)Réalisation d'un kit de calibrage sur Wafer pour exécuter à la fois le calibrage LAR et le calibrage Multiline TRL qui constitue le calibrage de référence pour les mesures sur wafer. 2)Proposition d'une méthode originale basée sur un calcul d'erreur pour tenir compte du fait que les impédances d'entrée et de sortie de l'atténuateur étalon sont différentes de 50 Ω. Outre sa précision, l'avantage de cette méthode est qu'elle ne nécessite pas la détermination précise de l'impédance de référence du calibrage LAR. 3)Proposition d'une méthode originale analytique pour déterminer l'impédance d'entrée et de sortie de calibrage et donc l'impédance de référence. 4)Réalisation d'un kit de calibrage large bande pour les utilisateurs, dont l'impédance de référence du calibrage LAR est peut être obtenue par trois moyens :. ● Modélisation électrique de l'atténuateur. ● Modélisation de l'impédance de référence par interpolation polynomiale. ● Mise au point d'une méthode simplifiée : la procédure LAR-L. 5)Analyse des erreurs dans le cas ou le substrat du kit de calibrage est différent du substrat du dispositif à caractériser. Pour déterminer cette capacité, une solution consiste à graver sur le wafer du dispositif sous test une ligne de transmission dont les dimensions doivent être connues, et dont on mesure les paramètres S après calibrage du VNA.

La procédure de calibrage LAR (Line-Attenuator-Reflect), intégrée dans les analyseurs de réseau modernes et qui permet une large bande de mesure avec un nombre limité d’étalons de référence sur wafer, est particulièrement attractive. Par contre, peu d’études sont réalisées pour évaluer sa traçabilité. C’est pourquoi le LNE (Laboratoire National de Métrologie et d’Essais) a décidé de mener des études afin d’évaluer la traçabilité et la précision de mesure quand la méthode de calibrage LAR est utilisée. Dans ce contexte, nos travaux de thèse se résument comme suit : 1) Réalisation d’un kit de calibrage sur Wafer pour exécuter à la fois le calibrage LAR et le calibrage Multiline TRL qui constitue le calibrage de référence pour les mesures sur wafer. 2) Proposition d’une méthode originale basée sur un calcul d’erreur pour tenir compte du fait que les impédances d’entrée et de sortie de l’atténuateur étalon sont différentes de 50 Ω. Outre sa précision, l’avantage de cette méthode est qu’elle ne nécessite pas la détermination précise de l’impédance de référence du calibrage LAR. 3) Proposition d’une méthode originale analytique pour déterminer l’impédance d’entrée et de sortie de calibrage et donc l’impédance de référence. 4) Réalisation d’un kit de calibrage large bande pour les utilisateurs, dont l’impédance de référence du calibrage LAR est peut être obtenue par trois moyens :. ● Modélisation électrique de l’atténuateur. ● Modélisation de l’impédance de référence par interpolation polynomiale. ● Mise au point d’une méthode simplifiée : la procédure LAR-L. 5) Analyse des erreurs dans le cas ou le substrat du kit de calibrage est différent du substrat du DST à mesuré
The LAR (Line-Attenuator-Reflect) calibration procedure is particularly attractive because it is already integrated into modern VNAs and it enables broadband measurements with a limited number of standards. On the other hand, only a few studies concern the traceability assessment of this method. That is the reason why the LNE (Laboratoire National de Métrologie) decided to estimate the traceability and accuracy of S parameters measurement when the LAR calibration method is used. In this context, the thesis can be summarized as follows: 1) Realization of a on wafer calibration kit allowing to execute both the LAR calibration and the Multiline TRL calibration which is considered as the reference calibration for on wafer measurements. 2) Development of a new method in order to estimate the errors due to the fact that the input and output impedances of the standard attenuator is different from 50 Ω. This solution is very efficient and it does not require an accurate determination of the reference impedance of the LAR calibration technique. 3) Development of an original method for determining the input and output impedances of the LAR calibration procedure leading to a precise measurement of the reference impedance. 4) Realization of a calibration kit for users, with three different methods to determine the reference impedance. ● Electrical model of the standard attenuator. ● Polynomial interpolation of the reference impedance measurement. ● Development of a new simplified and low cost technique named the LAR-L procedure. 5) Analysis of errors when the substrate of the calibration kit is different from the substrate of the device under test

This master's thesis is engage in suggestion of low noise 70 cm band amplifier with filter and diode attenuator. At first the thesis describes the basic parameters of amplifier, for example gain, noise figure and dynamic extent. Later in detail describes individual parts, which are the device consist of. At every part of system is mentioned the diagram of connection and values of components, which are ascertained from calculation, simulation and recommendation of producer. The characteristic parameters of amplifier were measured after construction.

The diploma thesis deals with Formula Student Impact Attenuator design of TU Brno Racing team. The aim of the thesis is the design, the dynamic tests and the production of Impact Attenuator of racing formulas called Dragon 4 and Dragon 5, so to meet the Formula Student rules. The thesis deals further with FEM dynamic analysis of Impact Attenuator.

With  the  continuous  advances  in  microwave  technology,  microwave  components  and  related magnetic materials become more important in industrial environment. In order to further develop the microwave components, it is of interest to find new kinds of technologies and materials. Here, we  introduce  a  new  kind  of  material  --  amorphous  metallic  wires  which  could  be  used  in microwave  components,  and  use  these  wires  to  design  new  kinds  of  attenuators.  Based  on  the fundamental  magnetic  properties  of  amorphous  wires  and  transmission  line  theory,  we  design  a series of experiments focusing on these wires, and analyze all the experimental results.    Experimental  results  show  that  incident  and  reflected  signals  produce  interference  and  generate standing  waves  along  the  wire.  At  given  frequency,  the  insertion  attenuation  S21 [dB]  of  an amorphous wire increases monotonically with dc bias current. The glass cover will influence the  magnetic  domain  structure  in  amorphous  metallic  wires.  Therefore,  it  will  affect  the circumference  permeability  and  change  the  signal  attenuation.  It  is  necessary  to  achieve  the impedance  matching  by  coupling  to  an  inductor  and  a  capacitor  in  the  circuit.  The  impedance matching  makes  the  load  impedance  close  to  the  characteristic  impedance  of  transmission  line. The magnetic wire-based attenuator designed in this thesis work are characterized and compared to conventional pin-diode attenuator.

This Master´s thesis focuses on design and implementation of programmable attenuator. The main aim of this thesis is to create an electronical device that provide continuous setting of attenuation value in the range between 0–150 dB. Setting a value from the range can be performed using buttons and set values are shown on display. For this thesis an attenuator with working frequency between 0–6 GHz was chosen and four–layer printed circuit board was designed. As a result the device is fitted with an 8bit microcontroller ATmega328P–PU using five 6bit digital attenuators connected in series with manual and program settings of attenuation from 0–157,5 dB with step of 0,5 dB. Data are shown on a build–in display. The application for remote settings and value reading over integrated USB (Universal Serial Bus) interface, was created in C#. In conclusion of this thesis there is a measurement evaluation of attenuation measurement performed on the device.

As a clean, abundant, and renewable source of energy with a strategic location in close proximity to global population regions, ocean wave energy shows major promise. Although much wave energy converter development has focused on large-scale power generation, there is also increasing interest in small-scale applications for powering the blue economy. In this thesis, the objective was to optimize the performance of small-sized, portable, oscillating-body wave energy converters (WECs). Two types of oscillating body WECs were studied: bottom hinged and two-body attenuator. For the bottom-hinged device, the goal was to show the feasibility of an oscillating surge WEC and desalination system using numerical modeling to estimate the system performance. For a 5-day test period, the model estimated 517 L of freshwater production with 711 ppm concentration and showed effective brine discharge, agreeing well with preliminary experimental results. The objective for the two-body attenuator was to develop a method of power maximization through resonance tuning and numerical simulation. Three different geometries of body cross sections were used for the study with four different drag coefficients for each geometry. Power generation was maximized by adjusting body dimensions to match the natural frequency with the wave frequency. Based on the time domain simulation results, there was not a significant difference in power between the geometries when variation in drag was not considered, but the elliptical geometry had the highest power when using approximate drag coefficients. Using the two degree-of-freedom (2DOF) model with approximate drag coefficients, the elliptical cross section had a max power of 27.1 W and 7.36% capture width ratio (CWR) for regular waves and a max power of 8.32 W and 2.26% CWR for irregular waves. Using the three degree-of-freedom (3DOF) model with approximate drag coefficients, the elliptical cross section had a max power of 22.5 W and 6.12% CWR for regular waves and 6.18 W and 1.68% CWR for irregular waves. A mooring stiffness study was performed with the 3DOF model, showing that mooring stiffness can be increased to increase relative motion and therefore increase power.
Master of Science
As a clean, abundant, and renewable source of energy with a strategic location in close proximity to global population centers, ocean wave energy shows major promise. Although much wave energy converter development has focused on large-scale power generation, there is also increasing interest in small-scale applications for powering the blue economy. There are many situations where large-scale wave energy converter (WEC) devices are not necessary or practical, but easily-portable, small-sized WECs are suitable, including navigation signs, illumination, sensors, survival kits, electronics charging, and portable desalination. In this thesis, the objective was to optimize the performance of small-sized, oscillating body wave energy converters. Oscillating body WECs function by converting a device's wave-driven oscillating motion into useful power. Two types of oscillating body WECs were studied: bottom hinged and two-body attenuator. For the bottom-hinged device, the goal was to show the feasibility of a WEC and desalination system using numerical modeling to estimate the system performance. Based on the model results, the system will produce desirable amounts of fresh water with suitably low concentration and be effective at discharging brine. The objective for the two-body attenuator was to develop a method of power maximization through resonance tuning and numerical simulation. Based on the two- and three-degree-of-freedom model results with approximate drag coefficients, the elliptical cross section had the largest power absorption out of three different geometries of body cross sections. A mooring stiffness study with the three-degree-of-freedom model showed that mooring stiffness can be increased to increase power absorption.

Designing CMOS linear transmitter front-end, specially the power amplifiers (PAs), in multi-band wireless transceivers is a major challenge for the single-chip integration of a CMOS radio. In some of the linear PA systems, for example, polar- or predistortion-PA system, amplitude and phase control circuits are used to suppress the distortion produces by the PA core. The requirements of these controlling circuits are much different from their conventional role in a receiver or a phase array system. In this dissertation, the special design issues will be addressed, and the circuit topologies of the amplitude and phase controllers will be proposed. In attempt to control the high-power input signal of a PA system, a highly linear variable attenuator with adaptive body biasing is first introduced. The voltage swing on the signal path is intentionally coupled to the body terminal of the triple-well NMOS devices to reduce their impedance variation. The fabricated variable attenuator shows a significant improvement on linearity as compared to previous CMOS works. The results of this research are then used to build a variable gain amplifier for linear PA systems that requires gain of its amplitude tuning circuits. Different from the conventional attenuator-based VGAs, the high linearity of the suggested attenuator allows it to be put after the gain stage in the presented VGA topology. This arrangement along with the current boosting technique gives the VGA a better noise performance while having a linear-in-dB tuning curve and better worst-case linearity. The following part of the dissertation is about a compact, linear-in-degree tuned variable phase shifter as the phase controller in the PA system. This design uses a modified RC poly-phase filter to produce a set of an orthogonal phase vectors with smaller loss. A specially designed control circuit combines these vectors and generates an output signal with different phases, while having very small gain mismatches at different phase setting. The proposed amplitude and phase control circuits are then verified with a system level analysis. The results show that the proposed designs successfully reduce the non-linear effect of a wireless transmitter.

In the chemistry branch of science is often a chromatograph usedto separate and purify substances in a solution. In achromatograph, different detectors are used to analyse the samplesconstituents. Some detectors destroy the sample during analysis.Because it is undesirable to destroy the entire flow of sample, asmall mass is transferred to a second flow by a flow splitter. Inthis report, four principles to divert a small mass from one flowto another are developed and evaluated. The basic principles todivert the flows is tested and principal mock-ups are designed andmanufactured. A brief survey of the market is conducted and aproblem related to flow spitting is investigated. The problem isthe influence on yield through a chromatograph due to flowretaining. Designing and testing of different retaining systems isalso included in this report. All four initial principles proved to be plausible splittingtechniques. However, only two principles appeared to be feasiblefor direct implementation in devices comparable withchromatographs. One of the less feasible principle is covered byseveral patents. The other is difficult to manufacture in order tomeet the strict requirements associated with e.g. chromatographs.The testing of different retaining systems showed that smallertube inner diameter and how the tube is winded can reduce theretaining system influence on the yield significantly. The splitting techniques in this report are all feasible splittingtechniques, and the report can be used as a solid foundation fordevelopment future laboratory instruments.
Inom kemin förekommer ofta kromatografer för att rena och separera kemiska substanser iett prov. De separerade substanserna kan detekteras och analyseras av olika detektorer, därvissa detektorer förstör provet i analysprocessen. Då det oftast är önskvärt att bevara såmycket som möjligt av ett prov, för vidare studier, avleds därför en liten mängd av deseparerade substanserna till detektorn då en förstörande detektor används. I denna studieutvecklades och undersöktes fyra principer för att avleda mycket små volymer från ett flödetill ett annat. Flödesdelning och sammanförning med de grundläggande flödesdelningsprincipernatestades, principiella modeller konstruerades och tillverkades. Enmarknadsundersökning samt en undersökning av ett flödesdelningsassocierat probleminkluderas också i rapporten. Problemet består i minskning av utbyte på grund avbandbreddning i flödesfördröjningssystem. Bandbreddning studerades således i olika formerav flödesfördröjningssystem. Alla fyra principer visade sig vara möjliga flödesdelningstekniker varav två av sådan karaktäratt de skulle kunna realiseras i ett instrument såsom en kromatograf. Av de två andra omfattasden ena av flertalet patent och den andra skulle vara tillverkningstekniks svår att förverkligamed vedertagna tillverkningstekniker. Tester på olika typer avflödesfördröjningssystemutformningar visade att slangdimension och hur slangen är lindadhar stor inverkan på bandbreddning. Det återstår en hel del konceptuell utveckling då principerna bara behandlats pågrundläggande nivå. Genom de principiella modellerna ges en bild av hur principerna skullekunna förverkligas, men vidare ställningstaganden måste tas till bland annat materialval samtmonitorering och anpassning av flöden. Rapporten ger en god grund för framtidaproduktutveckling.

This diploma thesis deals with Formula Student Impact Attenuator design. The aim of the thesis is to select suitable material and put it to the test of deformation. From results to suggest dimensions of Impact Attenuator and then perform its test. Next aim of the thesis is to perform FEM analysis of Anti-Intrusion plate and supporting rack.

Questo lavoro affronta gli aspetti riguardanti le metodologie e tecniche di analisi e progettazione per alcune funzionalità in front-end ricevitori a radiofrequenza ad elevata sensibilità e riconfigurabili. Tali funzionalità sono: l’amplificazione a basso rumore e il controllo dell’ampiezza di un segnale a RF. Infine, un’ulteriore investigazione ha focalizzato gli aspetti e le criticità in circuiti multi-funzione a elevata integrazione. E’ stata mostrata una metodologia per progettazione di amplificatori a basso rumore a microonde che ha portato a definire le relazioni di adattamento simultaneamente ottenibile in ingresso e uscita in un LNA. Il principale risultato di tale investigazione è l’individuazione di un grafico che permette di valutare in modo sinottico il guadagno di trasduzione e gli adattamenti I/O di una rete 2-porte amplificatrice una volta fissata l’impedenza di sorgente, e quindi il fattore di rumore del LNA. Sull’argomento degli amplificatori a basso rumore a onde millimetriche, è stato proposto un insieme di metodi analitici e sintetici che coprono le tematiche dalla scelta della tecnologia del dispositivo attivo al test del LNA realizzato. E’ stato ripreso il significato della Misura di Rumore nella progettazione a basso rumore a onde millimetriche investigando anche le tematiche della simulazione EM planare e 3D a onde millimetriche. All’interno della tematica sul controllo dell’ampiezza di un segnale a RF è stato investigato in profondità lo sfasamento parassita connesso al cambio di stato in attenuatori digitali a commutazione. E’ stata suggerita una tecnica circuitale e sono state ricavate equazioni di progetto che permettono di compensare tale sfasamento indesiderato, fornendo una relazione che consente di dimensionare l’elemento reattivo che compensa tale effetto sgradito. Infine, sulla materia della progettazione di circuiti-multi funzione a elevata integrazione è stata investigata la realizzabilità di un modulo contenente diverse funzionalità: controllo dell’ampiezza del segnale, amplificazione, scelta del modo T/R, controllo della fase del segnale e conversione seriale/parallelo dei dati di comando. Sono state presentate le procedure di progetto di alcuni sottosistemi nonché i criteri e i passi seguiti nella fase di integrazione.
This work deals with aspects relating to analysis and design methodologies and techniques for some circuits in high sensitivity and reconfigurable front-end RF receivers. These circuits are: low noise amplifier and RF attenuators. Finally, further investigation has focused aspects and issues of multi-function high integration circuits. A methodology for designing microwave low noise amplifiers is reported. The latter has led to define the I/O matching relationships simultaneously achievable in an LNA. The main result of this investigation is the identification of a chart that allows to synoptically evaluating the achievable gain and I/O matching of a 2-port amplifier, once the source impedance is fixed and consequently the LNA noise factor. A set of analytical and synthetic methods on millimetre wave low noise amplifiers has been proposed, covering topics from the active device technology selection to test the realized LNA. The meaning of the noise measure parameter is reprised for designing millimetre wave low-noise. The issues of and 3D planar EM millimetre wave simulation is also investigated. The parasitic phase shift in digital attenuators has been investigated in depth. Such parasitic effect is related to the change of state in digital switched attenuators. A technique has been suggested and circuit equations were derived that allow to compensate such unwanted phase shift, providing design relations that allows to estimate the value of the reactive element that compensates for this undesirable effect. Finally, in the field of multi-function high-integration circuits design, the feasibility of a module containing several functionalities has been investigated. The latter are: control of the signal amplitude, amplification, selection of Tx/Rx mode, control the phase of the signal and serial to parallel control data conversion. The design procedures of some sub-modules, together with the criteria and the steps followed in the process of integration, have been reported.

Stato dell’arte: I microrganismi probiotici negli alimenti potrebbero causare cambiamenti significativi nel sapore e nella reologia, a causa del loro metabolismo attivo. È importante, quindi, controllare il metabolismo dei microrganismi probiotici negli alimenti, senza influenzare negativamente la vitalità e le caratteristiche funzionali. Un modo per superare questo problema è l'utilizzo di colture starter attenuate attraverso l’utilizzo di metodi fisici o chimici. Alcuni autori hanno studiato l'omogeneizzazione come metodo per attenuare/modulare il metabolismo delle colture starter nei prodotti caseari (Lanciotti et al., 2004, 2006, 2007); in questo progetto di tesi ho utilizzato una nuova tecnologia emergente, gli ultrasuoni. (i) È stato effettuato uno screening delle combinazioni possibili di ultrasuoni (US) (potenza/durata) su diversi microrganismi probiotici e sono state studiate le caratteristiche probiotiche e tecnologiche dopo l'esposizione agli US. (ii) Sono stati studiati gli effetti degli US sul rilascio di componenti intracellulari. (iii) È stata valutata l'interazione dei ceppi attenuati con il microbiota intestinale utilizzando la fermentazione in vitro (batch culture fermentation). Problematiche: (i) Non si conoscono gli effetti dell’attenuazione mediante US sulle caratteristiche tecnologiche/probiotiche dei microrganismi; (ii) non è chiara la risposta delle cellule microbiche al trattamento con gli US e il danno che ne deriva, in quanto in letteratura sono disponibili pochi dati; (iii) non sono disponibili dati sull'interazione di ceppi attenuati con il microbiota intestinale. Obiettivi: (i) Scelta della migliore combinazione di ultrasuoni (potenza/durata), in grado di evitare la post-acidificazione senza compromettere la vitalità dei ceppi, studio dei cambiamenti delle caratteristiche probiotiche e tecnologiche che i microrganismi potrebbero subire a seguito dell’attenuazione; (ii) valutazione del rilascio di componenti intracellulari (acidi nucleici e proteine) dopo l'applicazione degli ultrasuoni; e (iii) studio dell’effetto di ceppi attenuati sul microbiota intestinale. Pianificazione della ricerca: Nella prima parte sono stati usati tre diversi generi di microrganismi probiotici: Lactobacillus, Bifidobacterium, Propionibacterium. I ceppi sono stati trattati con ultrasuoni e sono state studiate le caratteristiche tecnologiche e probiotiche. Nella seconda parte, sono stati studiati gli effetti degli US sul rilascio di componenti intracellulari. I ceppi sono stati studiati a seguito del trattamento fisico per valutare il rilascio di costituenti intracellulari (acidi nucleici, proteine) ed eventuali lesioni della membrana cellulare. Nell'ultima parte, è stata studiata l'interazione di ceppi attenuati con il microbiota intestinale. Questo studio è stato condotto presso l'Università di Roehampton (Regno Unito). Materiali e metodi: (i) Caratteristiche tecnologiche: Prove di acidificazione in mezzo di laboratorio, crescita a diverse temperature, pH e contenuto di sale; caratteristiche probiotiche: antibiotico resistenza, sopravvivenza a pH 2,5 e in presenza di sali biliari (0,3%), idrofobicità e formazione di biofilm. (ii) La valutazione del danno sulle cellule microbiche è stato determinato attraverso letture spettrofotometriche a 260 e 280 nm per quantificare il rilascio di DNA e proteine. (iii) L'interazione dei ceppi attenuati con il microbiota intestinale è stata valutata utilizzando la fermentazione in vitro (batch culture fermentation). Risultati: (i) Le migliori combinazioni in grado di evitare la post-acidificazione sono state le seguenti: potenza, 60%; tempo, 6 minuti; impulsi, 2 s per Lactobacillus e Bifidobacterium, 40%, 8 min P. jensenii; 60%, 4 min P. freudenreichii subsp. freudenreichii. Gli US non hanno influenzato la vitalità a 45 °C e a pH 9, ma hanno determinato una diminuzione della crescita microbica a pH 4 (lattobacilli e bifidobatteri). Tuttavia, gli US non hanno influenzato il GI dei propionibatteri. L'effetto dell'attenuazione potrebbe essere migliorato con la refrigerazione. Il trattamento con gli US non ha influenzato la maggior parte dei tratti tecnologici, ma ha causato un aumento della suscettibilità ad alcuni antibiotici. Per quanto riguarda i tratti probiotici, gli US hanno causato un aumento di idrofobicità per L. reuteri e P. freudenreichii spp. freudenreichii. Questi risultati sono stati confermati con l'adesione alle cellule Caco-2 per L. reuteri. L. reuteri attenuato ha registrato un significativo aumento di idrofobicità (dal 3 al 25%) e una maggiore adesione alle cellule Caco-2. Inoltre, gli US hanno migliorato la stabilità dei biofilm nel tempo e questo risultato ha confermato i dati ottenuti con l'idrofobicità. (ii) Il rilascio di acidi nucleici e proteine, evidenzia che la membrana cellulare potrebbe essere un altro target del trattamento fisico. (iii) Per quanto riguarda gli effetti degli US sul microbiota intestinale: i ceppi attenuati non hanno influenzato il microbiota intestinale, ma in alcuni casi sono stati evidenziati effetti positivi. Importanza e impatto della ricerca di dottorato: Il metabolismo attivo dei microrganismi probiotici potrebbe costituire un problema quando questi ultimi vengono aggiunti agli alimenti. Infatti alcuni ceppi di batteri lattici continuano a produrre acido lattico e causano post-acidificazione (diminuzione del pH durante la conservazione). Pertanto, è importante controllare il loro metabolismo. Un modo possibile per controllare il metabolismo dei probiotici negli alimenti è l'attenuazione attraverso metodi fisici o chimici. Una delle tecnologie emergenti sono gli ultrasuoni (US). Questo approccio è stato utilizzato per evitare la post-acidificazione in una bevanda commerciale di riso (Bevilacqua et al., 2016). La presente tesi di dottorato ha contribuito a valutare gli effetti dell'attenuazione mediante ultrasuoni, su alcune caratteristiche tecnologiche e probiotiche, testando tre diversi generi di ceppi probiotici. Inoltre, questo progetto di dottorato ha studiato i cambiamenti in termini di caratteristiche tecnologiche e probiotiche che i microrganismi probiotici potrebbero subire a seguito dell'attenuazione; il rilascio di proteine, acidi nucleici. Infine, la novità di questa tesi di dottorato è stata lo studio degli effetti di ceppi attenuati sul microbiota intestinale. Proposte future: una prospettiva futura potrebbe essere focalizzata sull'uso degli US per migliorare o modulare l'adesione dei ceppi probiotici, considerando l'aumento di idrofobicità e la maggiore adesione alle cellule Caco-2. È importante studiare gli effetti di altri ceppi attenuati sul microbiota intestinale modulando le variabili del trattamento.
Scientific background: Probiotics in foods could lead to significant changes in food flavor and rheology, due to their active metabolism. A possible way to overcome this problem is the attenuation of probiotics through a physical or chemical method. Some authors studied homogenization as a way to attenuate/modulate the metabolism of starter cultures in dairy products (Lanciotti et al., 2004, 2006, 2007); in this project I have used a new emerging technology, the ultrasounds. (i) A screening of the ultrasound (US) (power/duration) on different probiotic microorganisms was perfomed, and were studied the probiotic and technological characteristics after US-exposure. (ii) The effects of US on the release of intracellular components, was investigate. (iii) The interaction of attenuated strains with gut microbiota was evaluated, using in vitro batch culture fermentation. Open questions: (i) Few data are available on effects of US on probiotics and technological characteristics of probiotic strains; (ii) few data are available on the effect of attenuation with ultrasound on the sub-lethal injury; (iii) no data are available on the interaction of attenuated strains with gut microbiota. Aims: (i) Choice of the best combination of ultrasound to avoid post-acidification without affecting the viability of the strains, and study of the probiotic and technological characteristics to evaluate if attenuation could change them; (ii) study the release of intracellular components (nucleic acids and proteins) after the application of ultrasound; and (iii) evaluation the effects of attenuated strains on gut microbiota. Planning of the research: In the first part three different genera of probiotics were used: Lactobacillus, Bifidobacterium, Propionibacterium. The strains were treated with ultrasound and studied for technological and probiotic characteristics. In the second part, the effects of US on the release of intracellular components, was investigated. The strains were studied after physical treatment to assess the release of intra-cellular constituents (nucleic acids, proteins) and injury of the membrane. In the last part, the interaction of attenuated strains with gut microbiota, was studied. This study was carried out at University of Roehampton (UK). Materials and Methods: (i) Technological traits: acidification in lab medium, growth at different temperatures, pHs and salt content; probiotic traits: antibiotic-resistance, survival at pH 2.5 and in the presence of 0.3% bile salt, hydrophobicity, and biofilm formation. (ii) Injury characterization was evaluated by leakage of UV-absorbing substances. (iii) The interaction of attenuated strains with gut microbiota was evaluated, using in vitro batch culture fermentation. Results: (i) The best combinations to avoid post-acidification were the following: power, 60%; time, 6 min; pulse, 2 s for Lactobacillus and Bifidobacterium, 40%, 8 min P. jensenii; 60%, 4 min P. freudenreichii subsp. freudenreichii. US did not affect viability at 45 °C or at pH 9, but it determined a decrease of microbial growth to pH 4 (lactobacilli and bifidobacteria). However, the US did not affect the GI of propionibacteria. The effect of attenuation could be enhanced by the storage under refrigeration. US-treatment did not affect most of the technological traits, but generally caused an increase of susceptibility to some antibiotics. Concerning probiotic traits, US caused an increase of hydrophobicity for L. reuteri and P. freudenreichii spp. freudenreichii, after US-exposure. These results were confirmed with adhesion to Caco-2 cells for L. reuteri. US-attenuated L. reuteri experienced a significant increase of hydrophobicity (from 3 to 25%) and a higher adhesion to Caco-2 cells. Moreover, US improved the stability of the biofilm over the time, and this result confirmed the data obtained with hydrophobicity. (ii) The release of nucleic acids and proteins was found, highlighting that cell membrane could be another target physical treatments. (iii) Concerning the effects of US on gut microbiota, the ultrasound didn’t affect the gut microbiota, but in some cases, it could have a positive effect. Significance and Impact of PhD research: A main drawback of probiotics in foods can relate to their active metabolism, some strains of lactic acid bacteria continue to produce lactic acid and cause post-acidification (the decrease of pH within the storage). Therefore, it is important to control their metabolism. A possible way to control the metabolism of probiotic in foods is the attenuation through physical or chemical methods. One of the emerging technologies is ultrasound (US). This approach was used to avoid post-acidification in a commercial rice drink (Bevilacqua et al., 2016). The present PhD thesis contributed to evaluate the effects of attenuation with ultrasound, on some technological and probiotic strains, testing three different genera of probiotic strains. Moreover, this PhD project has investigate the changes that may affect probiotic strains after attenuation; the release of proteins, nucleic acids. Finally, the novelty of this PhD thesis was the study of the effects of attenuated strains on gut microbiota. Future trends: A future perspective could be a focus on the use of US to improve or modulate the adhesion of probiotic strains, considering the increase of hydrophobicity and the higher adhesion to Caco-2-cells. It is important to investigate the effects of other attenuated strains on gut microbiota by modulating the variables of the treatment. Key words: Hydrophobicity, acidification, growth, attenuation, gut-microbiota, proteins, nucleic acid, ultrasound, attenuated microorganisms, probiotics, lactic acid bacteria.

The aim of this thesis is to introduce to reader the application and use of optical EDFA amplifiers in optical transmission and to show wiring and practical test, including measurements on amplifier. The aim of this thesis is to propose the use of optical amplifier in laboratory practice for subject Optical networks. The thesis briefly introduces the problems of data transmissions through optical fibers with a focus on the use of optical amplifiers. The basic characteristic of optical transmission paths and the reasons for the use of optical amplifiers are described here. One entire chapter is devoted to distinction of optical amplifiers. Amplifiers can be divided according to location in the transmission path to the booster, in-line and pre-amplifiers and according to the used of amplifying technology to optical amplifiers with subsidies, semiconductor optical amplifiers and Raman optical amplifiers. The factors affecting the efficiency of optical amplifiers, such as noise and the level of saturated power are mentioned here too. The different types of optical amplifiers from the two producers are also described. From these amplifiers was chosen EDFA CzechLight Amplifier from Optokon to be used for the laboratory exercise in the subject of Optical networks. The use of EDFA optical amplifiers in optical transmission lines is mentioned here too. These amplifiers can be used in telecommunications transmission systems and for data transmission over long distances. They will find use in WDM transmission systems and cable TV distribution through the optical fiber to the end users. Practical measurements were performed on optical amplifier CLA-PB01F. In the transmission route was located attenuator and the dependence of output power to input signal power was measured. The amplification course was linear in the range of input values provided by the manufacturer. Laboratory exercise for the subject of Optical networks is aimed at preacquaintance of students with problems EDFA optical amplifiers and practical measurements with the optical amplifier CLA-PB01F. Students acquire basic theoretical knowledge of the issue and verify the functionality of optical amplifiers on a specific exercise. This work is destined for all who wish to get basic knowledge of optical amplifiers, their characteristics and possibilities of their use in optical transmission lines.

Standards exist to unify requirements and to make it possible to make sure that equipment is tested in the same way, even when several different test labs perform the test. But as new technology comes to market, and old technology evolves, so must the standards. The International Organization for Standardization are continuously developing new standards and updating existing standards, and sometimes the specified tests changes, rendering old test equipment obsolete. In this thesis, we will look at the differences between the old and the current versions of the ISO 7637 standards as well as how we can verify if older test equipment lives up to the new requirements. A verification method will be designed, partly implemented and evaluated. Several of the aspects for automating the verification will be considered. The results will show that older equipment most likely will be usable with the newer version of the standard, as well as point out some of the difficulties of verifying that this is the case.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1998.
Includes bibliographical references (leaves 55-56).
by Hafiz Jaman Alshammery.
S.M.

La commande optique de dispositifs microondes, qui exploite l'injection optique des porteurs dans un semiconducteur, apporte de nombreux avantages vis-a-vis de l'electronique conventionnelle. La presente etude avait pour objectif d'etendre cette commande a des dispositifs, realisant des fonctions complexes, tels que les attenuateurs, resonateurs et filtres microondes. Les structures etudiees ont ete realisees sur du silicium en technologie ligne microruban. Nous avons exploite principalement la charge complexe induite entre le ruban et le plan de masse par illumination optique. Nous avons demontre que la lumiere cree principalement une charge resistive aux faibles puissances, mais qu'une composante reactive apparait aussi d'une maniere nette pour les puissances optiques elevees. L'effet resistif a ete mis en application dans la realisation d'un attenuateur microondes en technologie microruban, reglable par la simple commande optique. Nous avons demontre sur un premier prototype une plage d'attenuation superieure a 10db dans la bande c. Quant a l'effet reactif, nous avons introduit une commande supplementaire qui permet de le renforcer. Il s'agit de polariser le plasma photo-induit par une tension continue qui se superpose au signal hyperfrequences. Nous avons accorde la frequence de differents resonateurs par cette nouvelle double commande optoelectronique. Ces accords, sont, a notre connaissance, de loin les plus larges jamais reportes parmi les accords electriques. En effet, nous avons mesure des deplacements de la frequence de resonance de l'ordre de 30% en dessous de la frequence de resonance en l'absence d'illumination. L'etude est plutot de nature experimentale, mais des modeles theoriques simples ont ete developpes pour tenter d'expliquer les differents phenomenes nouveaux mis en evidence experimentalement. Nous avons reussi a etablir, d'une maniere satisfaisante en premiere approche, le lien entre les parametres physiques du semiconducteur d'une part et le schema equivalent du plasma photo-induit deduit de la reponse microondes du dispositif d'autre part

The effect of hypoxemia on coronary autoregulation was investigated in nine anesthetized, open-chest dogs. The anterior descending coronary artery (LAD) was cannulated and perfused with normoxic arterial blood and with moderately hypoxic blood (0₂ content = 10 + 1 ml 0₂ /dl). LAD blood flow was measured as perfusion pressure was varied from 140 to 40 mmHg. At perfusion pressures at and above 40 mmHg, hypoxemia significantly increased LAD flow. During normoxia, the autoregulatory closed-loop gain (Gc) was significantly greater than zero at perfusion pressures from 60 to 120 mmHg. During hypoxemia, Gc was greater than zero only at perfusion pressures from 80 to 100 mmHg. During hypoxemia, LAD blood flow increased sufficiently to maintain oxygen delivery and consumption constant, but the range and potency of autoregulation was attenuated.

Human norovirus is a major cause of viral gastroenteritis worldwide, yet there are no licensed antivirals or a vaccine. This is mainly due to the lack of an efficient cell culture system for human norovirus which has prevented full understanding of norovirus replication. Murine norovirus (MNV), which can be grown in permissive cells and manipulated by reverse genetics, now provides a model for studying norovirus replication. Here, to firstly identify the essential viral factors required for replication, the entire MNV genome was subjected to transposon-mediated insertional mutagenesis and insertion profiling. Validation of the technique and genome-wide profiling of over 2000 insertions revealed the essential regions of each protein and probed the importance of known functional motifs. Identification of tolerated insertion sites led to the generation of the first epitope-tagged noroviruses, carrying the FLAG tag in three proteins of unknown function. This facilitated SILAC-based proteomic studies to identify host cell factors involved in norovirus replication, which may represent potential antiviral targets. With the availability of a small animal model of infection, MNV also provides the opportunity to develop rational approaches to norovirus attenuation. One approach that has been successful for attenuating other RNA viruses involves harnessing the regulatory capacity of the cellular microRNA machinery to control viral replication and tropism. This approach was applied to MNV by inserting a microglial-specific microRNA target sequence into the MNV genome which successfully attenuated norovirus replication in permissive cell lines expressing the cognate microRNA. A second rational approach to attenuation was based on manipulating the rate and fidelity of the viral polymerase, which has been shown to affect RNA virus pathogenesis and can lead to attenuation. To this aim a panel of MNV polymerase mutants were engineered and characterised for their growth and fidelity and their ability to establish acute and persistent infections in vivo.

Avec plus de 20% de morts annuels dus aux maladies infectieuses, celles-ci restent un sujet majeur de santé publique. Des maladies d’origine virale (ré)émergent suite aux changements environnementaux, climatiques et sociétaux : le virus Ebola, la Dengue ou, plus récemment, le virus Zika. Dans ce contexte, il est donc aujourd’hui crucial de développer des vaccins efficaces et sûrs contre les infections virales émergentes. Ce projet de thèse vise à mettre en place une nouvelle stratégie de production de vaccins vivants atténués ciblant les virus à ARN en travaillant sur le virus de la fièvre jaune (genre Flavivirus). Après une analyse génomique qui a permis d’approfondir une technique de modification des virus appelée « ré-encodage », des mutants de la fièvre jaune ont été produits puis caractérisés in vitro et in vivo. En parallèle, un modèle rongeur de la fièvre jaune a été développé et a permis de tester in vivo à la fois l’innocuité et l’efficacité vaccinale des virus ré-encodés
Despite recent considerable improvements, infectious diseases remain a major issue for public health, with an estimated 20% of annual deaths caused by infections. Among them, viral diseases (re)emerge following environmental, climatic and societal changes: Ebola, Dengue and Zika viruses have recently been the object of special attention. The development of safe and efficient vaccines against emerging viruses is a major challenge for global public health. This thesis work is in line with this issue. Using the yellow fever virus (YFV, genus Flavivirus) as a model, we tried to define new strategies for the design of live-attenuated vaccines for viral infections prevention. After a genomic analysis that allowed to go further into a procedure for virus modification named “re-encoding”, we generated and characterised both in vitro and in vivo mutant strains of YFV. In parallel, a rodent model was set up to test in vivo both the safety and the protective efficiency of the re-encoded viruses

An important research topic in engineering and science is the miniaturization of systems and components, where small size and weight, low power consumption and low manufacturing cost can offer new functionalities. In recent years the fields of optics and fluidics have merged to create the area of research known as "optofluidics". The unique properties of fluids (compression, flow, and variable refractive index) can be combined with optical devices to create systems with advantages in optical measuring, communication and imaging areas. Variable optical attenuators (VOAs) are components in optical communication networks for managing optical power levels. This thesis is focused on the design, fabrication and characterization of two novel optofluidics based single-mode fibre VOAs ("continuous fibre" type VOA and "fibre gap" type VOA). The first VOA is constructed from a side-polished optical fibre which is characterized by a sloping shape profile of the external cladding thickness. The fibre is positioned on top of a platform which exploits electrowetting-on-dielectric (EWOD) techniques to move a liquid droplet. By moving a liquid droplet across EWOD platform (and along the polished region of the fibre), optical attenuation can be obtained. The droplet, whose refractive index is equal to or higher than the refractive index of the fibre core, is accessing and leaking radiation from the optical evanescent field of the polished fibre which then modifies the optical attenuation. The level of attenuation depends on the position of the droplet; the attenuation increases as the cladding thickness reduces and the droplet moves closer to the fibre core. The second VOA is a fibre gap device, where a ferrofluid shutter/actuator is located in the gap between lensed single mode optical fibres. The ferrofluid shutter movement is controlled by a magnetic field and changes the light propagation between fibres. The level of attenuation is defined by the shutter position.

The presented master’s thesis deals with the acoustics, specifically with the selected characteristics of the sound. It focuses on the anatomy of the auditory system and its function. The work describes the testing approaches for an evaluation of the auditory organ function and introduces modern methods used for the hearing tests, especially pure tone audiometry. A part of the thesis is dedicated to a concept of an audiometer for pure tone audiometry, which is presented in a detailed block diagram along with a description of its working components. Included chapters describe the partial circuits of the audiometer supplemented by the calcuations of its individual elements. The concluding part of the thesis deals with the evaluation of the device’s functionality.

It has been proposed that, in order to enhance sensitivity to novel information, the brain removes predictable components of sensory input. This thesis describes a series of psychophysical and behavioural studies investigating predictive filtering in the perception of touch. Using a novel force-matching paradigm, we demonstrate that self-generated tactile sensations are perceived as weaker than the same stimuli externally imposed. This attenuation is shown to be temporally tuned to the expected time of contact and modulated by the certainty with which a sensation can be attributed to self-action. We confirm experimentally that this attenuation results from a predictive, rather than postdictive, mechanism. Such a mechanism may predict the sensory consequences of action based on an internal model of the environment and an efference copy of the motor command. We investigate how prediction is acquired in a new environment and the coordinate systems in which the new environment is internally represented. Using a novel protocol of transcranial magnetic stimulation, we find evidence to suggest that the efference copy signal underlying the prediction arises upstream of primary motor cortex. Patients with schizophrenia are found to show less attenuation than healthy controls, consistent with models of the disease that propose an underlying deficit in sensory prediction. These experimental findings are discussed in relation to potential neural mechanisms of sensory filtering, and the many proposed roles for predictive mechanisms in human sensory and motor systems are reviewed.

Thesis (M.S.)--Civil and Environmental Engineering, Georgia Institute of Technology, 2005.
Laurence J. Jacobs, Committee Chair ; Reginald DesRoches, Committee Member ; Jianmin Qu, Committee Member. Includes bibliographical references.

Low frequency volcanic earthquakes, characterised by slowly decaying harmonic codas of 0.5-5Hz, have been observed on many volcanoes and are considered key tools in monitoring and eruption forecasting. The common element in a variety of models proposed for the origin of these earthquakes is resonance of a fluid body within a volcanic edifice. The source of the resonance is believed to consist of dispersive interface waves, trapped at the fluid-solid boundaries. The amplitude decay or attenuation of these earthquake signals can be decomposed into radiative and intrinsic components, and in this way yield information about both the geometry and fluid properties of the resonating source body. This thesis presents a study of the attenuation of low-frequency volcanic earthquakes, with particular emphasis on quantitatively linking seismic signals to magmatic processes and properties. The effect of the intrinsic attenuation of the fluid on the amplitude decay of low-frequency volcanic earthquakes is examined using a viscoelastic finite-difference model of seismic wave propagation. It is shown that the viscosity of the fluid contributes 23.6±2.26% less than previously thought to the apparent attenuation, and that its effect may have been substantially overestimated in previous studies. A physical explanation for this lies in understanding the fundamental differences between acoustic and interface waves. An analytical approach demonstrates that, for a set of realistic volcanic parameters, interface waves can be attenuated less than acoustic waves in a pure melt, if the longitudinal viscosity is at least 107 Pas. These results widen the set of possible resonators and imply that resonating volcanic conduits filled with high viscosity magma are viable sources for low-frequency seismicity. An automated method to measure the apparent attenuation of seismic signals is developed, tested, and applied to a dataset of low-frequency earthquakes from Soufri`ere Hills Volcano, Montserrat. Temporal trends in attenuation are observed and quantitatively interpreted as changes in magma viscosity. An estimate of the magma shear viscosity of 2.3 ± 2 × 105 Pas is obtained, demonstrating the ability of seismological data to place constraints on the magma properties.

Seismic multiples are a serious hindrance to hydrocarbon exploration in Australia. In particular, water bottom multiples can be very difficult to attenuate. This is because there often exists a strongly reflective sea floor which gives multiples large amplitudes when compared with the primary events they overlay, and secondly, because of a widely occurring velocity inversion, which seriously reduces the effectiveness of a very important class of multiple attenuation techniques.Multiple attenuation techniques can be classified according to the characteristic of the data which is used to discriminate against the multiples in conjunction with the operation behind the demultiple process. Common multiple attenuation processes include FK demultiple, Radon Demultiple, predictive deconvolution, wave equation based demultiple procedures and the family of techniques which come under the umbrella of Surface Multiple Attenuation (SMA). All of these techniques, given the right conditions, can be very effective. They also vary in price from very cheap (FK demultiple) through to expensive (wave equation based demultiple procedures).However, despite these procedures, and fifty odd years of research, there is no effective general solution to multiple problems off the coast of Western Australia and indeed in many regions around the world.Two new wavefield transformations, Multiple MoveOut (MMO) and IsoStretch Radial Trace (ISR), have been developed in this research to precondition data prior to the removal of surface related multiples by existing techniques. These form the basis of a new multiple attenuating procedure.MMO shifts the data so that the water bottom primary event is flattened and the simple water bottom multiples are also flat and periodic. Water bottom peg leg multiples are made approximately periodic.To solve the stretch problem introduced by the MMO transform, ISR interpolates oblique traces of constant stretch, which also map constant shot emergence angles. The water bottom primary and multiple events form a stationary time series after MMO and ISR. They are then amenable to removal by autoconvolution and predictive deconvolution.The results of the new procedure are demonstrated on two case studies from offshore Western Australia. It is shown to be more effective at removing both simple and peg leg water bottom multiples than traditional techniques. Finally, it is an inexpensive procedure, which does not require velocity analysis prior to its application.

Seismic multiples are a serious hindrance to hydrocarbon exploration in Australia. In particular, water bottom multiples can be very difficult to attenuate. This is because there often exists a strongly reflective sea floor which gives multiples large amplitudes when compared with the primary events they overlay, and secondly, because of a widely occurring velocity inversion, which seriously reduces the effectiveness of a very important class of multiple attenuation techniques.Multiple attenuation techniques can be classified according to the characteristic of the data which is used to discriminate against the multiples in conjunction with the operation behind the demultiple process. Common multiple attenuation processes include FK demultiple, Radon Demultiple, predictive deconvolution, wave equation based demultiple procedures and the family of techniques which come under the umbrella of Surface Multiple Attenuation (SMA). All of these techniques, given the right conditions, can be very effective. They also vary in price from very cheap (FK demultiple) through to expensive (wave equation based demultiple procedures).However, despite these procedures, and fifty odd years of research, there is no effective general solution to multiple problems off the coast of Western Australia and indeed in many regions around the world.Two new wavefield transformations, Multiple MoveOut (MMO) and IsoStretch Radial Trace (ISR), have been developed in this research to precondition data prior to the removal of surface related multiples by existing techniques. These form the basis of a new multiple attenuating procedure.MMO shifts the data so that the water bottom primary event is flattened and the simple water bottom multiples are also flat and periodic. Water bottom peg leg multiples are made approximately periodic.To solve the stretch problem introduced by the MMO transform, ISR ++
interpolates oblique traces of constant stretch, which also map constant shot emergence angles. The water bottom primary and multiple events form a stationary time series after MMO and ISR. They are then amenable to removal by autoconvolution and predictive deconvolution.The results of the new procedure are demonstrated on two case studies from offshore Western Australia. It is shown to be more effective at removing both simple and peg leg water bottom multiples than traditional techniques. Finally, it is an inexpensive procedure, which does not require velocity analysis prior to its application.