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This paper investigates the possibility of reducing the energy use for cooling as well as improving the thermal comfort in lightweight buildings by associating new heat thermal energy storage (HTES) to the building HVAC system. The numerical model of the so-called “phase-shifter” HTES has been implemented on the SimSpark platform and validated against the analytical solution for the constant airflow and harmonic temperature profile. The experimental data has been used to assess its predictive capability with non-constant airflow. Using reduced ventilation periods has been numerically studied regarding the environmental air resource and thermal storage efficiency of the system. The size and electricity consumption were optimized by this way. Particularly, a comfort analysis based on the adaptive model was carried out on several combined building thermal inertia and HVAC configuration. The building energy simulation results demonstrate that the low-inertia building equipped with a phase-shifter presents the similar internal thermal conditions to those of a more massive night-ventilated structure. The proposed optimization can reduce significantly the size of the system (by 30%) and the electricity consumption (by at least 38%) while the temperature is out of the comfort range for an extra 5% of the total estimation period.

Sponges are among the dominant benthic organisms on coral reefs, representing important spatial competitors for reef-building corals. Coral reefs have experienced drastic declines in coral cover and corresponding increases in the abundance of other spatial competitors, such as macroalgae, corallimorpharians and sponges, due to a combination of global and local stressors. The ability of sponges to chemically defend themselves against predators, microbes and other competitors may partially explain their high abundance on reefs worldwide. Nonetheless, studies investigating sponge abundance and chemical ecology are rare, particularly in the Western Indian Ocean, which is considered a hotspot of coral and sponge biodiversity. Thus, this thesis is the first study that provides insights into the chemical ecology of sponges from the Western Indian Ocean. The thesis consists of a general introduction, three chapters investigating in detail different aspects of chemical defence mechanisms in sponges from Zanzibar and a general discussion. In Chapter 1 I assessed the benthic community composition of the reef at Bawe, an island on Zanzibara s West Coast. This reef was dominated by reef-building corals, but sponges also represented a diverse and abundant component of the reef fauna. Moreover, laboratory experiments were conducted to investigate if predation was a key factor in structuring the sponge community. Findings revealed that the reef was dominated by palatable rather than chemically defended sponge species, demonstrating a lack of predatory control on the sponge community likely due to overfishing. In the absence of predation, palatable sponges could potentially undergo uncontrolled growth in the future and thus subject reef-building corals to greater competitive pressure. Chapter 2 focused on the antimicrobial and cytotoxic activities of secondary metabolites extracted from the most abundant sponges at the reef around Bawe. The experiments revealed that the most abundant sponges were remarkably well defended against co-occurring marine bacteria and in particular against potential pathogens. Moreover, the majority of the sponge extracts also displayed cytotoxic activities. Metabolites with either antimicrobial or cytotoxic properties can provide sponges with a competitive advantage over corals. Antimicrobial compounds could alter the coral microbiota while cytotoxic compounds are able to impair the cell division of corals. Consequently, the potential allelopathic properties of sponge crude extracts from the three most abundant and bioactive sponges were further examined in field experiments under natural conditions in Chapter 3. These experiments showed that the extracts of all three sponges possessed allelopathic compounds that adversely affected the photosynthetic efficiency of the corals symbiotic zooxanthellae. Despite this, experiments with live sponge fragments were unable to detect significant impairments on the physiology of corals. However, the presence of allelopathic compounds, and their significantly negative effect on coral photo-efficiency, suggests that allelopathy by sponges does play a role in spatial competition with corals. As a result, sponges might be able to exert negative effects on the corala s fecundity, their reproduction or even their associated microbiome making corals more vulnerable towards further natural or anthropogenic disturbances and pathogenesis. Collectively, the present study demonstrated that sponges on reefs in Zanzibar are serious spatial competitors against reef-building corals. The increased sewage input in combination with other local stressors, such as destructive fishing practices or damage to the reef through tourism activities, will most likely result in more frequently occurring sponge-coral interactions. Thus, management strategies for Zanzibarian reefs should focus on minimizing anthropogenic stressors, like the establishment of a sewage water treatment facility to minimize stress on the benthic community, in order to reduce the risks to coral reef health. Fisheries regulations should also be enforced as an important component of coral reef management plans in order to restore healthy herbivorous as well as spongivorous fish populations on the reefs, which limit the proliferation of competing macroalgae and sponges.

To improve the understanding of high-latitude rain microphysics and its implications for the remote sensing of rainfall by ground-based and spaceborne radars, raindrop size measurements have been analyzed that were collected over five years with a Joss–Waldvogel disdrometer located in Järvenpää, Finland. The analysis shows that the regional climate is characterized by light rain and small drop size with narrow size distributions and that the mutual relations of drop size distribution parameters differ from those reported at lower latitudes. Radar parameters computed from the distributions demonstrate that the high latitudes are a challenging target for weather radar observations, particularly those employing polarimetric and dual-frequency techniques. Nevertheless, the findings imply that polarimetric ground radars can produce reliable “ground truth” estimates for space observations and identify dual-frequency radars utilizing a W-band channel as promising tools for observing rainfall in the high-latitude climate.

The phase error in a high quality accelerometer was investigated on the basis of systematic experiments on a prototype platform permitting controlled vertical harmonic oscillations. The recordings of an accelerometer and of an ultra-high frequency GPS fixed on this platform were compared with those of a LVDT transducer, controlling the platform movement. All sensors were supported by independent GPS timing. The output of this study is that the recordings of accelerometers are characterized by a random phase error, which, however, decreases with the increase of the oscillation frequency, as dictated from the laws of mechanics. Such errors are important given the increasing use of combinations of accelerometers with various sensors for a wide range of applications. A simple method for the correction of such errors is proposed.

The sinusoidal oscillator (Wien-Bridge,Phase-shift, quadrature, and Bubba) based on theoperational amplifier of the type (TL082-JFET) havebeen studied under the influence of differentenvironmental conditions. Considering the effect oftemperature on the operation of the four types ofoscillator circuits, their oscillation frequencies wereshown to decrease from 37.6, 19.3, 79.5 and 54 kHz,down to 34, 16.8, 76.6 and 46.6 kHz, respectively, withincreasing temperature up to 110 ºC. The signal pk-pkvoltage of Wien-bridge and phase shift oscillatorsdecreases as a function of temperature. On the otherhand, signal pk-pk voltage of Bubba oscillator (forexample at the fourth stage) and quadrature oscillatorwere shown to be slightly increase with increasingtemperature. Concerning the phase difference betweenthe first and the fourth stages output signals of Bubba- and phase shift - oscillators, their values decreasefrom 170º and 162º down to 146º and 142º,respectively, with increasing temperature up to 110ºC.The operation of the proposed four types ofoscillator circuits under the influence of gammaradiation environment was studied. It was clearlyshown that, the oscillation frequency of Wien-bridge,phase shift, quadrature and Bubba oscillators decreasefrom 38, 19.3, 85.6 and 48.7 kHz down to 31, 16.2, 60and 8.5 kHz, respectively, with increasing gammairradiation dose up to 600 kGy. Also, the signal pk-pkvoltage of the first three types of oscillator circuits wasshown to decrease as a function of γ-dose, while for thefourth one (quadrature oscillator) it is clear that thechange in signal pk-pk voltage was less affected by γ-radiation dose.

The Lee metric measures the circular distance between two elements in a cyclic group and is particularly appropriate as a measure of distance for data transmission under phase-shift-keying modulation over a white noise channel. In this paper, using newly derived properties on Newton's identities, we initially investigate the Lee distance properties of a class of BCH codes and show that (for an appropriate range of parameters) their minimum Lee distance is at least twice their designed Hamming distance. We then make use of properties of these codes to devise an efficient algebraic decoding algorithm that successfully decodes within the above lower bound of the Lee error-correction capability. Finally, we propose an attractive design for the corresponding VLSI architecture that is only mildly more complex than popular decoder architectures under the Hamming metric; since the proposed architecture can also be used for decoding under the Hamming metric without extra hardware, one can use the proposed architecture to decode under both distance metrics (Lee and Hamming). © 2008 IEEE. 56 12 2050 2059

The inspection of functional elements is a crucial part of modern production cycles. However, with higher integration of production machinery and products, the accessibility for measurement systems is more and more limited. A solution for this problem can be found in endoscopy techniques, which are able to transport the image information for optical measurement methods. In this paper, an optical inspection system based on the fringe projection proifllometry technique is presented. The iflber-optic fringe projection system uses two high-resolution image iflbers to connect a compact sensor head to the pattern generation and camera unit. In order to keep inspection times low, the system is developed with particular focus on fast projection times. This can be achieved by using a digital micro-mirror device, which is capable of projecting grey-scale patterns at a rate of more than 10 images per second. However, due to the low numerical aperture of the optical iflbers, a limiting factor for the pattern rate is the illumination path of the pattern generator. Two different designs of the illumination path are presented, which are based on a LASER light source as well as a LED light source. Due to low beam divergence and high intensities LASERs are well suited for iflber coupling. Unfortunately, the coherent property of the light has negative effects in certain measurement applications, as interference patterns, the so called speckle, appear on rough surfaces. Although speckle reducing methods are employed in the LASER beam path, the emergence of interference cannot be prevented completely. As an alternative, an illumination path based on a LED light source is demonstrated. To compare the effects of the speckle, based on measurements on a planar calibration standard both designs are compared in terms of phase noise, which is directly related to the noise in the reconstructed 3-D point data. Additionally, optical power measurements of both methods are compared to give an estimation of coupling eiflciency. Finally, the capabilities of the system are shown based on measurements of a micro-contour standard. © 2016 SPIE. DFG/CRC/TR 73

Entrainment may involve responses to dawn, to dusk, and to the light in between these transitions. Previous studies showed that the circadian system responds to only 2 light pulses, one at the beginning and one at the end of the day, in a similar way as to a full photoperiod, as long as the photoperiod is less than approximately 1/2 τ. The authors used a double 1-h light pulse protocol with different intervals of darkness in between (1, 2, 4, 7, 10, and 16 h) to study the phase responses of mice. The phase response curves obtained were compared to full light pulse PRCs of corresponding durations. Up to 6 hours, phase responses induced by double light pulses are virtually the same as by a corresponding full light pulse. The authors made a simple phase-only model to estimate the response reduction due to light exposure and response restoration due to dark exposure of the system. In this model, they assumed a 100% contribution of the first 1-h light pulse and fitted the reduction factor for the second light pulse to yield the best fit to the observations. The results suggest that after 1 h of light followed by less than 4 h of darkness, there is a considerable reduction in response to the second light pulse. Full response restoration requires more than 10 h of darkness. To investigate the influence of the duration of light on the response saturation, the authors performed a second series of experiments where the duration of the 2 light pulses was varied from 4 to 60 min each with a fixed duration of the stimulus (4 h). The response to 2 light pulses saturates when they are between 30 and 60 min long. In conclusion, double pulses replace single full light pulses of a corresponding duration of up to 6 h due to a response reduction during light, combined with response restoration during darkness. By the combined response reduction and response restoration, mice can maintain stable entrainment to the external LD cycle without being continuously exposed to it.

We discuss a real-space and a Fourier-space technique to compute numerically, the phase images observed by electron holography of nanoscale particles. An assessment of the applicability and accuracy of these techniques is made by calculating numerical results for simple geometries for which analytical solutions are available. We employ the numerical techniques to compute the electron holography phase images of slabs with surface roughness and slabs containing magnetic domain walls.

Although undulatory swimming is observed in many organisms, the neuromuscular basis for undulatory movement patterns is not well understood. To better understand the basis for the generation of these movement patterns, we studied muscle activity in the nematodeCaenorhabditis elegans. Caenorhabditis elegansexhibits a range of locomotion patterns: in low viscosity fluids the undulation has a wavelength longer than the body and propagates rapidly, while in high viscosity fluids or on agar media the undulatory waves are shorter and slower. Theoretical treatment of observed behaviour has suggested a large change in force–posture relationships at different viscosities, but analysis of bend propagation suggests that short-range proprioceptive feedback is used to control and generate body bends. How muscles could be activated in a way consistent with both these results is unclear. We therefore combined automated worm tracking with calcium imaging to determine muscle activation strategy in a variety of external substrates. Remarkably, we observed that across locomotion patterns spanning a threefold change in wavelength, peak muscle activation occurs approximately 45° (1/8th of a cycle) ahead of peak midline curvature. Although the location of peak force is predicted to vary widely, the activation pattern is consistent with required force in a model incorporating putative length- and velocity-dependence of muscle strength. Furthermore, a linear combination of local curvature and velocity can match the pattern of activation. This suggests that proprioception can enable the worm to swim effectively while working within the limitations of muscle biomechanics and neural control.

The characterization of canopy structure is crucial for modeling eco-physiological processes. Two commonly used metrics for characterizing canopy structure are the gap fraction and the effective Plant Area Index (PAIe). Both have been successfully retrieved with terrestrial laser scanning. However, a systematic assessment of the influence of the laser scan properties on the retrieval of these metrics is still lacking. This study investigated the effects of resolution, measurement speed, and noise compression on the retrieval of gap fraction and PAIe from phase-shift FARO Photon 120 laser scans. We demonstrate that FARO’s noise compression yields gap fractions and PAIe that deviate significantly from those based on scans without noise compression and strongly overestimate Leaf Area Index (LAI) estimates based on litter trap measurements. Scan resolution and measurement speed were also shown to impact gap fraction and PAIe, but this depended on leaf development phase, stand structure, and LAI calculation method. Nevertheless, PAIe estimates based on various scan parameter combinations without noise compression proved to be quite stable.

A pronounced, widespread and persistent regime shift among marine ecosystems is observable on temperate rocky reefs as a result of sea urchin overgrazing. Here, we empirically define regime-shift dynamics for this grazing system which transitions between productive macroalgal beds and impoverished urchin barrens. Catastrophic in nature, urchin overgrazing in a well-studied Australian system demonstrates a discontinuous regime shift, which is of particular management concern as recovery of desirable macroalgal beds requires reducing grazers to well below the initial threshold of overgrazing. Generality of this regime-shift dynamic is explored across 13 rocky reef systems (spanning 11 different regions from both hemispheres) by compiling available survey data (totalling 10 901 quadrats surveyed in situ) plus experimental regime-shift responses (observed during a total of 57 in situ manipulations). The emergent and globally coherent pattern shows urchin grazing to cause a discontinuous ‘catastrophic’ regime shift, with hysteresis effect of approximately one order of magnitude in urchin biomass between critical thresholds of overgrazing and recovery. Different life-history traits appear to create asymmetry in the pace of overgrazing versus recovery. Once shifted, strong feedback mechanisms provide resilience for each alternative state thus defining the catastrophic nature of this regime shift. Importantly, human-derived stressors can act to erode resilience of desirable macroalgal beds while strengthening resilience of urchin barrens, thus exacerbating the risk, spatial extent and irreversibility of an unwanted regime shift for marine ecosystems.

In this thesis a design of a Coriolis mass flow-meter is chosen by considering all advantages and disadvantages and the project requirements. The chosen geometry is imported into COMSOL, because modelling is implemented by FEM and two different physics should be coupled. To consider both applications of the device include measuring density and flow rate, modeling is divided into two parts: Coriolis density meter and Coriolis mass flow-meter. Both applications are based on Fluid Structure Interaction. The results are compared to existing setup’s experimental data. Keywords: Coriolis mass flowmeter, Fluid Structure Interaction, Modal order, FEM, Acoustic Shell Interaction, Phase-shift, Disposable and Polymer. +46-737260449

Control of the flow rate of liquid metals is required in a number of technological processes such as the cooling of nuclear reactors, transmutation systems and the dosing and casting of liquid metals. Electromagnetic flow meters play an important role in the diagnostics and automatic control of such processes. For example, the electromagnetic control of casting processes can be used to improve the quality of products by reducing their brittleness and increasing durability at high production efficiency, especially for complex shape components. A number of different electromagnetic flow meter designs have been developed starting from the end of the forties of the last century. One such flowmeter - themagnetic flywheel,which is described in the textbook of Shercliff uses the electromagnetic force exerted by the flow on a close magnet. Commercial electromagnetic flow meters are typically based on the flow-induced electrical voltage measurements by electrodes in direct contact to the melt in a steady magnetic field. In view of the typical problems coming along with applications at liquid metal flows such as high temperatures, interfacial effects and corrosion, the main disadvantage of this type of flow meter is the electrical contact to the liquidmetal, which is necessary to measure the electric potential difference. Therefore, contactless operating measurement techniques are very attractive for liquid metal applications.

Using calculated phase- shift values, for pp, nn, and np elastic scattering in the energy range 1MeV to 350MeV, the charge independence breaking of nucleon-nucleon interaction is investigated. We have used Darboux transformation to calculate phase-shift for the first three values of, {"references":["R. Machleidt and I. Slaus, \"The nucleon-nucleon Interaction\", J.Phys.G:Nucl.Part.Phys.27, R69 (2001).","G. Q. Li and R. Machleidt, \"Charge-dependence of nucleon-nucleon Interaction\", phys. Rev.C58, 3135(1998).","J. L. Friar and U. van Kolck, \"Charge- Independence Breaking in the Two-pion-Exchange Nucleon- Nucleon force\", Phys. Rev.C 60, 034006(1999).","K. S. Kran, \"Introduction Nuclear Physics\", John Wiley & Sons, New York (1988).","Samuel S. M. Wong, \"Introduction Nuclear Physics\", Prentice- Hall International, Inc., Englewood Cli®s, N.J. (1990).","P. Swan, \"Asymptotic phase-shifts and bound states for two-body central interactions\", Nucl.Phys.46, 669(1963).","R. G. Newton \"Scattering theory of waves and particles\", McGraw-Hill, New York, 1966.","B. F. Samsonov and F1.Stancu, \"Phase equivalent chains of Darboux transformations in scattering theory\", phys.Rev.C66, 034001(2002).","V. G. J. Stoks, et al., \"Construction of high-quality NN potential models\", Phys.Rev.C49, 2950(1994).\n[10]\tH. P. Noyes and D. Y. Wong, \"Modification of the Effective-Rang formula for Nucleon-Nucleon Scattering\", Phys.Rev.Lett.3, 191(1959).\n[11]\tL. Mathelitsch and B. J. Ver West, \"Effective range Parameters in Nucleon-Nucleon Scattering\", Phys.Rev.C29, 739(1984)."]}

Predictions concerning the consequences of the oceanic uptake of increasing atmospheric carbon dioxide (CO2) have been primarily occupied with the effects of ocean acidification on calcifying organisms, particularly those critical to the formation of habitats (e.g. coral reefs) or their maintenance (e.g. grazing echinoderms). This focus overlooks direct and indirect effects of CO2 on non-calcareous taxa that play critical roles in ecosystem shifts (e.g. competitors). We present the model that future atmospheric [CO2] may act as a resource for mat-forming algae, a diverse and widespread group known to reduce the resilience of kelp forests and coral reefs. We test this hypothesis by combining laboratory and field CO2 experiments and data from 'natural' volcanic CO2 vents. We show that mats have enhanced productivity in experiments and more expansive covers in situ under projected near-future CO2 conditions both in temperate and tropical conditions. The benefits of CO2 are likely to vary among species of producers, potentially leading to shifts in species dominance in a high CO2 world. We explore how ocean acidification combines with other environmental changes across a number of scales, and raise awareness of CO2 as a resource whose change in availability could have wide-ranging community consequences beyond its direct effects.

Renewable energy and distributed generation are getting more and more popular, including photovoltaic modules (PV), wind turbines, and fuel cells. The renewable energy sources need the power electronics interface to the utility grid because of different characteristics between the sources and the grid. No matter what renewable energy source is utilized, inverters are essential in the microgrid system. Thanks to flexible modular design, transformerless connection, extended voltage and power output, less maintenance and higher fault tolerance, the cascade inverters are good candidates for utility interface of various renewable energy sources. This dissertation proposes a new type of cascade inverters based on dual-buck topology and phase-shift control scheme. Compared to traditional cascade inverters, they have enhanced system reliability thanks to no shoot-through problems and lower switching loss with the help of using power MOSFETs. With phase-shift control, it theoretically eliminates the inherent current zero-crossing distortion of the single-unit dual-buck type inverter. In addition, phase-shift control can greatly reduce the ripple current or cut down the size of passive components by increasing the equivalent switching frequency. An asymmetrical half-cycle unipolar (AHCU) PWM technique is proposed for dual-buck full-bridge inverter. The proposed approach is to cut down the switching loss of power MOSFETs by half. At the same time, this AHCU PWM leads to current ripple reduction, and thus reducing ripple-related loss in filter components. Therefore, the proposed PWM strategy results in significant efficiency improvement. Additionally, the AHCU PWM also compensates for the zero-crossing distortion problem of dual-buck full-bridge inverter. Several PWM techniques are analyzed and compared, including bipolar PWM, unipolar PWM and phase-shifted PWM, when applied to the proposed cascade dual-buck full-bridge inverter. It has been found out that a PWM combination technique with the use of two out of the three PWMs leads to better performance in terms of less output current ripple and harmonics, no zero-crossing distortion, and higher efficiency. A grid-tie control system is proposed for cascade dual-buck inverter with both active and reactive power flow capability in a wide range under two types of renewable energy and distributed generation sources. Fuel cell power conditioning system (PCS) is Type I system with active power command generated by balance of plant (BOP) of each unit; and photovoltaic or wind PCS is Type II system with active power harvested by each front-end unit through maximum power point tracking (MPPT). Reactive power command is generated by distributed generation (DG) control site for both systems. Selective harmonic proportional resonant (PR) controller and admittance compensation controller are first introduced to cascade inverter grid-tie control to achieve better steady-state and dynamic performances. Ph. D.

Coral reefs are experiencing increased frequency, intensity, and diversity of disturbances that threaten not only the corals themselves, but many associated species as well. The reefs located in the Society archipelago, French Polynesia, recently underwent two major disturbances: an outbreak of the corallivorous sea star Acanthaster planci and a cyclone. This investigation focuses on the dynamics of coral populations and of the major associated communities of the outer reef slopes of the islands Moorea and Raiatea in the context of these two disturbances.Coral population dynamics, as well as reef community dynamics, are governed by a combination of intrinsic factors specific to species (e.g., recruitment, growth, and mortality rates, and susceptibilities to various regulations) and extrinsic factors characteristic of their environment (e.g., quality of habitats, levels of biotic and abiotic stress, frequency andintensity of disturbances). In French Polynesia, these dynamics are strongly influenced by natural disturbances that affect the size, the structure, and the composition of communities.The first section of this PhD estimates the impact of two successive disturbances, the aforementioned Acanthaster outbreak and cyclone, on the dynamics of reef communities, and evaluates their consequences for species diversity and abundance by detailing the progression of these disturbances and quantifying their effects, including their spatial and temporal scales. For the sea star outbreak, on both studied islands Acanthaster densities were first observed in relatively restricted locations situated at the bottom of the outer reef slopes, where these predators greatly depleted coral populations before moving successively to adjacent sites, progressively spreading the outbreak to the whole insular reef system. Aside from this mode of progression, Acanthaster displayed strong feeding preferences among coral taxa, with the genera Acropora, Montipora, other scleractinians, and Pocillopora hierarchically preyed upon before these predators significantly impacted the genus Porites. While the cyclone did not display a significant impact on the coral cover of these reefs, which had already been highly impacted by Acanthaster; however, the cyclone did strongly damage the physical structure of the reef habitats upon which many species rely. Overall, the decline of corals resulted in an increase in the cover of turf algae, enabled by the relaxed competition for space, and it indirectly affected the trophic chain leading to a collapse of corallivorous fish assemblages (family Chaetodontidae) and a relative increase of herbivore fish assemblages (family Scaridae). This response of the ecosystem, with respect to consumer pressures which favor algae regulation and coral recovery, seems to characterize an ecosystem with high resilience potential; however, the exceptional severity of recent disturbances and the progressive drift in the structure of coral communities facing recurrent perturbations are of concern for the maintenance of the ecological services and the diversity of reefs in French Polynesia.The second section of this thesis investigates the spatial and temporal variability of coral population dynamics and their link with species life history traits and environmental conditions. This second part qualifies the size structure and quantifies the recruitment, growth, and mortality rates of the dominant coral species in French Polynesia, and identifies the life strategies of these taxa. Pocillopora displays an opportunistic strategy, with high production and dispersion of larvae, and small, relatively short-lived colonies. In contrast, Porites engages in a strategy based on the persistence of colonies on the reef, with a low rate of habitat colonization counterbalanced by elevated longevity and high resistance todisturbances. Acropora engages in a different strategy from both Pocillopora and Porites, which is based on competition and which displays an intermediate recruitment rate and relatively fast growth, but also high susceptibility to disturbances. Considering their respective life strategies, these coral taxa must rely on different environmental scenarios for their maintenance and for dominating reef habitats. The third section of this doctoral investigation focuses on the elaboration of a mathematical model that allows predicting the trajectory of coral assemblages under various environmental scenarios. This third part simulates the population dynamics of the major scleractinian taxa in French Polynesia both (1) during the colonization of the reef habitat, and (2) in the face of a hypothetical increase in the frequency of Acanthaster outbreaks. In accordance with the life strategies identified in the second section of this thesis, Pocillopora appears as the best colonizer of reef habitats, Acropora dominates the assemblages in a relatively stable environment, and Porites is the less impacted by repeated disturbances. The recurrence of disturbances affects the structure and the perennity of coral assemblages.Thanks to the relatively low and spatially restricted anthropic pressures in French Polynesia, coral reefs in this region are among the most resilient on our planet. As on many reefs, however, long term monitoring programs show an increase in the frequency and intensity of disturbances that threaten the maintenance of corals, as well as their associated communities. Today, coral reefs are in decline globally, and they seem to be heralds of a dynamic shared by many natural ecosystems. In the present era of anthropic disturbances and global climate change, the investigation of community regulation and resilience processes appears crucial for the durable management of these valuable ecosystems., Les récifs coralliens sont soumis à une augmentation de la fréquence, de l’intensité et de la diversité des perturbations qui menacent la persistance des populations de coraux, ainsi que celle des espèces qui y sont associées. Les récifs de l’archipel de la Société en Polynésie française ont récemment connu deux perturbations majeures, une explosion démographique de l’étoile de mer corallivore Acanthaster planci et un cyclone. Dans ce contexte, ce programme de recherche a porté sur l’étude de la dynamique des populations de coraux et des principales communautés qui y sont associées sur la pente externe des îles de Moorea et de Raiatea.Les dynamiques des populations coralliennes et des communautés récifales sont gouvernées par une combinaison de facteurs intrinsèques propres aux espèces (e.g., taux de recrutement, vitesse de croissance, taux de mortalité, et susceptibilité aux facteurs de régulation) et de facteurs extrinsèques caractéristiques de leur environnement (e.g., qualité de l’habitat, degré de stress biotique et abiotique, fréquence et intensité des perturbations). En Polynésie française, ces dynamiques sont fortement orientées par les perturbations naturelles de grandes ampleurs qui influencent fortement la taille, la structure et la composition des communautés.Le premier volet de ce doctorat évalue l’impact de deux perturbations successives, l’explosion démographique d’Acanthaster et le cyclone, sur la dynamique des communautés récifales, et les conséquences sur la diversité et l’abondance des espèces. Cette première partie permet notamment de qualifier les modalités d’action de ces perturbations, ainsi que de quantifier leurs effets à différentes échelles spatiales et temporelles. Sur chacune des îles étudiées, les densités d’Acanthaster ont d’abord été observées sur une localité relativement restreinte à la base du récif de la pente externe, où les prédateurs ont fortement extirpé les populations coralliennes avant de se propager successivement aux sites et profondeurs adjacents, propageant ainsi progressivement la prolifération à l’ensemble du système récifal insulaire. De même, les Acanthaster ont montré des préférences alimentaires marquées selon les taxa coralliens, avec les genres Acropora, Montipora, autres genres scléractiniaires et Pocillopora ont été préférentiellement dévorés avant que ces prédateurs n’impactent significativement le genre Porites. Le passage du cyclone a montré relativement peu d’impact sur le recouvrement corallien sur des récifs déjà fortement affectés par les Acanthaster, mais a cependant fortement dégradé la structure physique des habitats récifaux auxquels sont inféodées de nombreuses espèces. Dans l’ensemble, le déclin corallien a résulté en une augmentation de la couverture en turf algal suite à une libération de la pression de compétition sur le substrat, et s’est répercuté dans le réseau trophique avec un effondrement des assemblages de poissons corallivores (famille Chaetodontidae) et, à l’inverse, un certain essor des assemblages de poissons herbivores (famille Scaridae). Cette réponse de l’écosystème, en termes de remaniement des assemblages de consommateurs en faveur de la régulation algale et la récupération corallienne, semble caractériser un écosystème à fort potentiel de résilience. Cependant, l’ampleur exceptionnelle des deux récentes perturbations, et la dérive progressive de la structure des communautés coralliennes face à la récurrence des perturbations, s’avèrent préoccupantes quant au maintien des services écologiques et de la diversité des récifs de la Polynésie française.Le second volet de ce manuscrit examine plus spécifiquement la dynamique des populations de coraux, sa variabilité spatiale et temporelle, et son lien avec les traits d’histoire de vie des espèces et avec les conditions environnementales. Cette seconde partie permet notamment de qualifier la structure de taille et de quantifier les taux de recrutement, de croissance et de mortalité des espèces dominantes du paysage corallien en Polynésie française, et d’identifier les stratégies de vie de ces taxa. Pocillopora montre une stratégie de type opportuniste, avec un fort investissement dans la production et la dispersion larvaire, et une taille et une durée de vie relativement limitée des colonies. A l’inverse, Porites montre une stratégie basée sur la persistance des colonies sur le récif, avec un faible taux de colonisation des habitats, mais en contrepartie une longévité importante et une forte résistance face aux perturbations. Acropora montre une stratégie encore distincte et basée sur la compétition, avec un taux de recrutement intermédiaire et une forte vitesse de croissance, mais cependant une susceptibilité importante aux perturbations. Avec leurs traits d’histoire de vie respectifs, ces différents taxa coralliens montrent des habilités variées à se maintenir et à dominer l’habitat récifal selon différents scénarios environnementaux.Le troisième volet de ce programme de recherche doctoral se concentre sur l’élaboration d’un modèle mathématique qui permet de prédire la trajectoire des assemblages coralliens sous divers scénarios environnementaux. Cette troisième partie permet notamment de simuler la dynamique des populations des principaux taxa scléractiniaires de Polynésie française, (1) lors d’une phase de colonisation de l’habitat récifal, et (2) face à une augmentation hypothétique de la fréquence des proliférations du prédateur Acanthaster. En concordance avec les stratégies de vie des espèces telles qu’identifiées au second volet de cemanuscrit, Pocillopora s’avère être le meilleur colonisateur des habitats, Acropora domine les assemblages sous un environnement relativement stable, et Porites est le moins affecté par les perturbations répétitives. La récurrence des perturbations affecte la structure et la pérennité des assemblages coralliens.Grâce à une pression anthropique relativement faible et restreinte à quelques sites particuliers, les récifs coralliens de la Polynésie française figurent parmi les plus résilients de notre planète. Cependant, à l’image d’autres récifs, les suivis à long terme montrent une augmentation de la fréquence et de l’intensité des perturbations qui en viennent à menacer le maintien des coraux, ainsi que des communautés récifales qui y sont associées. Aujourd’hui, les récifs coralliens sont globalement en déclin, et semblent être les précurseurs d’une dynamique partagée par de nombreux écosystèmes naturels. Dans l’ère actuelle des perturbations anthropiques et des changements climatiques globaux, l’investigation des processus de régulation des communautés et des capacités de résilience s’avère primordiale pour une gestion durable de ces écosystèmes si précieux.

A comparison of the community structure of juvenile hermatypic corals of 2 to 37 m depth at the fringing reefs of Curaçao between 1975 and 2005 shows a decline of 54.7% in juvenile coral abundance and a shift in species composition. Agaricia species and Helioseris cucullata, the most common juveniles in 1975, showed the largest decline in juvenile abundance (a 9 and 120 fold decrease in density respectively) with Helioseris cucullata being nearly extirpated locally. In 2005, Porites astreoides contributed most colonies to the juvenile coral community, increasing from 8.2% (in 1975) to 19.9% of the total juvenile community. Between 1975 and 2005, juveniles of brooding species decreased in relative abundance while the abundance of juveniles of broadcast spawning species increased or remained the same. These data illustrate the magnitude of the changes that have occurred in only three decades in the composition of juvenile coral communities.

Ensemble Monte Carlo simulations have been carried out to investigate the effects of upper valleys on the characteristics of wurtzite GaN MESFETs. Electronic states within the conduction band valleys at the Γ1, U, M, Γ3 and K are represented by non-parabolic ellipsoidal valleys centred on important symmetry points of the Brillouin zone. The following scattering mechanisims, i.e, impurity, polar optical phonon, acoustic phonon, alloy and piezoelectric are inculded in the calculation. Ionized imurity scattering has been treated beyound the Born approximation using the phase-shift analysis. The simulation results show that on the drain side of the gate region, hot electrons attained enough energy to be scattered into the upper satellite conduction valleys. Approximately %20 of the electrons occupy the higher valleys (mainly U and M valley). The simulated device geometries and doping are matched to the nominal parameters described for the experimental structures as closely as possible, and the predicted drain current and other electrical characteristics for the simulated device including upper valleys show much closer agreement with the available experimantal data.

Waveguide-based cavity ring-down spectroscopy (CRD) can be used for quantitative measurements of chemical concentrations in small amounts of liquid, in gases or in films. The change in ring-down time can be correlated to analyte concentration when using fiber optic sensing elements that change their attenuation in dependence of either sample absorption or refractive index. Two types of fiber cavities, i.e., fiber loops and fiber strands containing reflective elements, are distinguished. Both types of cavities were coupled to a variety of chemical sensor elements, which are discussed and compared.

Fibre Bragg gratings (FBGs) are key components for a vast number of applications in optical communication systems, microwave photonics systems, and optical sensors, etc. The main topic of this thesis is fibre Bragg grating fabrication and applications in direct microwave optical filtering, high speed switching and switchable dual-wavelength fibre lasers. First, a brief overview is given about the photosensitivity in optical fibre, basic FBG fabrication techniques, the popular coupled-mode theory for describing fundamental characteristics of FBGs and the Transfer Matrix method for the numerical simulations of complex-structured FBGs. An advanced FBG fabrication system based on the technique of multiple printing in fibre (with a continuous-wave source) has been used to write complex FBGs incorporating phase shifts, apodization and chirp. A single double-peaked superimposed grating working in reflection can be employed as a direct optical filter for millimetre-wave signals. Bit error rate measurements confirmed that the filter exhibited nearly on-off behaviour in the passband with a 3-dB bandwidth of 2 GHz for a central frequency of 20 GHz, as expected from the optical spectrum reflection. The presented technique can be used in radio-over-fibre systems or simultaneous up-conversion of ultra-wide band signals and filtering. This thesis focused mostly on the research of two 4-cm long Hamming-apodized gratings written in side-hole fibres with internal electrodes. The temperature dependence measurements showed that the birefringence of the component increased with the temperature. Dynamic measurement has shown nanosecond full off-on and on-off switching. During the electrical pulse action, the grating wavelength was blue-shifted for the x-polarization and red-shifted for the y-polarization due to the mechanical stress. Both peaks subsequently experienced a red-shift due to the relaxation of mechanical stress and the increasing core temperature transferred from the metal in many microseconds. All the wavelength shifts of the two polarizations depend quadratically on the electrical pulse voltage and linearly on the pulse duration. Numerical simulations gave accurate description of the experimental results and were useful to understand the physics behind the birefringence switching. Finally, two switchable dual-wavelength erbium-doped fibre lasers based on FBG feedback were proposed. In one method, an overlapping cavity for the two lasing wavelengths and hybrid gain medium in the fibre laser were introduced. Dual-wavelength switching was achieved by controlling the Raman pump power. The other method employed an injection technique and the dual-wavelength switching was controlled by the power of the injection laser. The switching time was measured to be ~50 ms. Detailed characteristics of the dual-wavelength switching in the two fibre lasers were experimentally studied and corresponding principles were physically explained. QC 20100922

A phase-shifting Sagnac interferometer that uses wavelength tunability of the laser diode is proposed. A Sagnac interferometer itself is robust for the mechanical disturbances because it has a common path configuration and requires no special reference. Unbalanced optical path introduced between p- and s-polarized beams enables us to implement easy phase-shift by the direct current modulation. Several experimental results indicate that the proposed system is useful for the disturbance-free precise measurement., Advanced materials and devices for sensing and imaging 3 : 12-14 November 2007 : Beijing, China.

Este trabalho propõe uma técnica do tipo rotação de fase (PSM - Phase-Shift Method), para migração em profundidade de dados sísmicos para meios localmente transversalmente isotrópicos (LTI), nos quais a direção do eixo de simetria varia continuamente ao longo das camadas. Para a modelagem em meios LTI, onde cada ponto da malha tem suas características definidas pelas velocidades de fase P e SV, parâmetros de Thomsen, densidade e inclinação do eixo de simetria, desenvolveu-se um método baseado na solução da equação elástica da onda por diferenças finitas. Na separação dos modos de onda qP e qSV dos sismogramas, implementou-se um algoritmo baseado na solução da equação de Christoffel. A migração para cada família de tiro comum é realizada somente por PSM. Nos resultados das migrações usando reflexões dos tipos qP-qP e qP-qSV, os horizontes foram localizados precisamente e verificou-se que o processo é estável em relação à variação do eixo de simetria. O método proposto é para aquisições sísmicas multicomponentes podendo ser aplicado em dados sísmicos marítimos convencionais, como também em dados provenientes de aquisições do tipo cabo de fundo e cabo vertical. Como o método proposto se baseia em algoritmos que utilizam PSM a sua implementação paralela pode ser altamente eficiente. This paper shows a technique based on the phase-shift method (PSM) to implement pre-stack depth migration on locally transverse isotropic media (LTI), with the symmetry axis direction varies continually along the layers. For seismic modeling, a generalization of the finite differences method for the solution of the elastic wave equation was used. With this procedure, it was possible to accommodate seismic modeling on LTI media defined by six parameters at each grid point, i.e. , density, P and S wave propagation velocities along the local symmetry axis, Thomsen parameters and the direction of the local symmetry axis itself. In order to separate from the seismograms the qP and qSV wavefields, an algorithm based on the Christoffel equation was implemented. The migration for each common shot gather is implemented solely by phase-shift based algorithms, which means that not only the depropagation of the registered wavefield, but also the generation of the time matrices involved in the imaging condition were obtained in this manner for each set of parameters at each depth level. The migration results using qP-qP and qP-qSV reflections show that the horizons were located precisely, and that the process is stable in relation to the symmetry axis variations. The proposed method is for multicomponent seismic acquisitions and might be applied to marine seismic data using streamers, or Ocean Bottom Cables or vertical cables. Since the proposed method uses phase-shift algorithms, its parallel implementation can be highly efficient.

Fuel cells are a clean, high-efficiency source for power generation. This innovative technology is going to penetrate all aspects in our life, from utility distributed power, transportation applications, down to power sources for portable devices such as laptop computer and cell phones. To enable the usage of fuel cell, developing power converters dedicated for fuel cells becomes imminent. Currently, the full-bridge converter is the dominating topology in high power dc/dc applications. Although multiphase converters have been proposed, most of them are dealing with high input-voltage systems, and their device characteristic is not suitable for a low voltage source such as a fuel cell. For a high power fuel cell system, high voltage conversion ratios and high input currents are the major obstacles to achieving high-efficiency power conversions. This dissertation proposes a novel 3-phase 6-leg dc/dc power converter with transformer isolation to overcome these obstacles. Major features of the proposed converter include: (1) Increase converter power rating by paralleling phases, not by paralleling multiple devices; (2) Double the output voltage by transformer delta-wye connection, thus lowering the turns-ratio; (3) Reduce the size of output filter and input dc bus capacitor with interleaved control; (4) Achieve Zero-Voltage Zero-Current Switching (ZVZCS) over a wide load range without auxiliary circuitry. High conversion efficiency above 96% is verified with different measurement approaches in experiments. This dissertation also presents the power stage and control design for the proposed converter. Control design guideline is provided and the design result is confirmed with both simulation and hardware experiments. When using the fuel cell for stationary utility power applications, a low-frequency ripple interaction was identified among fuel cell, dc/dc converter and dc/ac inverter. This low frequency ripple tends to not only damage the fuel cell, but also reduce the source capability. This dissertation also investigates the mechanism of ripple current propagation and exploits the solutions. A linearized ac model is derived and used to explain the ripple propagation. An active ripple reduction technique by the use of the current loop control is proposed. This active current loop control does not add extra converters or expensive energy storage components. Rather, it allows a reduction in capacitance because the ripple current flowing into the capacitor is substantially reduced, and less capacitance can be used while maintaining a clean dc bus voltage. The design process and guideline for the proposed control is suggested, and the effectiveness of this active control is validated by both simulation and experimental results. Ph. D.

An internet-based, real-time, Global Positioning System (GPS) ---synchronized relative to the wide-area frequency-monitoring network (FNET) ---has been developed at Virginia Tech. In this FNET system, an algorithm that employs the relationship between phasor angles and deviated frequency [13] is used to calculate both frequency and its rate of change. Tests of the algorithm disclose that, for non-pure sinusoidal input (as compared to pure sinusoidal input), significant errors in the output frequency will result. Three approaches for increasing the accuracy of the output frequency were compared. The first---increasing the number of samples per cycle N---proved ineffective. The second---using the average of the first estimated frequencies rather than the instant first estimated frequency as the resampling frequency---produces a moderate increase in accuracy of the frequency estimation. The third---multiple resampling---significantly increased accuracy. But both the second and the third become ineffective to the extent the input is not pure sinusoidal. From a practical standpoint, attention needs to be paid toward eliminating noise in the input data from the power grid so as to make it more purely sinusoidal. Therefore, it will be worthwhile to test more sophisticated digital filters for processing the input data before feeding it to the algorithm. Master of Science

A guide to the composition of the enigmatic f0(980) and a0(980) states is their formation in φ-radiative decays. Precision data are becoming available from the KLOE experiment at the DAΦNE machine at Frascati, as well as results from SND and CMD-2 at VEPP-2M at Novosibirsk. We show how the coupling of the f0(980) to this channel can be extracted from these, independently of the background provided by σ production. To do this we use the fact that the behaviour of both the f0(980) and σ cannot be determined by these data alone, but is strongly constrained by experimental results from other hadronic processes as required by unitarity. We find that the resulting coupling for the φ → γf0(980) is ∼ 10−4 GeV with a background that is quite unlike that assumed if unitarity is neglected. This provides an object lesson in how unitarity teaches us to add resonances. Not surprisingly the result is crucially dependent on the pole position of the f0(980), for which there are still sizeable uncertainties. At present this leads to an uncertainty in the φ → γf0 branching ratio which can only be fixed by further precision data on the f0(980). Nevertheless, the BR(φ → γf0) is now the same order of magnitude as the experimental BR(φ → γa0).

We report on the development of a contactless measurement technique for torsional shear stress τ in ferromagnetic axles or hollow shafts, based on the magneto-elastic effect. In general two different measuring principles for ferromagnetic materials can be realised, based on: the evaluation of the change of magnetic polarisation influenced by mechanical stress ΔJ(τ ) or, the change of the magnetic susceptibility ΔχA(τ). The comprehension of the magnetic polarisation or the magnetic susceptibility in a sensor concept requires an external magnetic field. Preferably alternating magnetic fields were used as mechanical stress can disturb the amplitude but also the phase distribution of the applied magnetic field. As a result of a torsional moment acting on an axle or hollow shaft an angle of twist η appears, which is constant over the length of the twisted object. This angle of twist can be understood as a shift of infinitesimal thin cross-sections in which the whole length of the axle is separated. Beside the macroscopic deformation effect, shear forces taking also effect on the Weiss domains in the microscale of the ferromagnetic material. The effects in the microscale are the base of the magneto-eleastic effect. The combination of the deformation effect in the macro-scale with the deformation of the Weiss domains in the microscale leading to a sophisticated measurement principle for torsional stress in axles or hollow shafts. Magneto-sensitive detectors along or around the measurement object open the possibility for a contactless detection of torsional stress in ferromagnetic materials. Beside a strong measuring signal, free from electromagnetic interference, the introduced contactless measurement principle offers different advantages, like an independence from compression strength, nominal tensile stress, impact load, ferromagnetic hysteresis effects and an independence from the temperature dependent electrical conductivity of the axle or hollow shaft. The characteristics of such a type of sensor are analysed by an electrotechnical model based on Maxwells equations. Beside the chosen design of a contactless torsion sensor and an experimental set-up, the obtained test results are illustrated and reported in the present paper.

We study solitons in one-dimensional quadratic nonlinear photonic crystals with modulation of both the linear and nonlinear susceptibilities. We derive averaged equations that include induced cubic nonlinearities and numerically find previously unknown soliton families. The inclusion of the induced cubic terms enables us to show that solitons still exist even when the effective quadratic nonlinearity vanishes and conventional theory predicts that there can be no soliton. We demonstrate that both bright and dark forms of these solitons are stable under propagation., 4 pages with 6 figures

SHORT NOTES

Background Physical activity as measured by activity counts over short time intervals across a 24 h period are often used to assess circadian variation. We are interested in characterizing circadian patterns in activity among adolescents and examining how these patterns vary by obesity status. New statistical approaches are needed to examine how factors affect different features of the circadian pattern and to make appropriate covariate adjustments when the outcomes are longitudinal count data. Methods We develop a statistical model for longitudinal or repeated activity count data that is used to examine differences in the overall activity level, amplitude (defined as the difference between the lowest and highest activity level over a 24 hour period), and phase shift. Using seven days of continuous activity monitoring, we characterize the circadian patterns and compare them between obese and non-obese adolescent girls. Results We find a statistically significant phase delay in adolescent girls who were obese compared with their non-obese counterparts. After the appropriate adjustment for measured potential confounders, we did not find differences in mean activity level between the two groups. Conclusion New statistical methodology was developed to identify a phase delay in obese compared with non-obese adolescents. This new approach for analyzing longitudinal circadian rhythm count data provides a useful statistical technique to add to the repertoire for those analyzing circadian rhythm data.