Дисертації з теми "Neutral modes"

Axisymmetric radial Bernstein modes are known to exist in non-neutral plasmas and have been studied theoretically and computationally in 1D, but detection of these modes has still proven to be difficult due to self-shielding. To help advance the work on this front we created a 2D particle-in-cell (PIC) code that simulates a non-neutral plasma in a Malmberg-Penning trap. A detailed description of the PIC code itself has been included that highlights the benefits of using an $r^2$--$z$ grid and how it can be tested. The focus of the PIC simulation was to discover how best to drive and detect these modes. While it is improbable that radial Bernstein modes will be detected in long plasmas, we show that it may be a possible due to the axial nodal structure in the potential and electric field generated by confining plasmas of any finite-length. Additionally, we find that for a short plasma the strongest detection signal along the trap wall occurs at the plasma's midpoint rather than near the ends. Results show that oscillating the confinement potentials is sufficient to excite the fundamental radial Bernstein mode, but not any of the higher order modes. The higher order modes can be seen in the simulation, however, by sinusoidally driving the radial electric field. Unfortunately, the individual modes are difficult to isolate which we suspect is due to mode mixing. Finally, we report frequencies and mode shapes for the fundamental mode and the (lower) first higher order mode.

Neutral particles, particularly neutrons, gammas and neutrinos are difficult to detect and measure due to their lack of electric charge. Noble fluids are a powerful medium when detecting such particles due to their ability to collect charge and scintillation light. The LAGUNA-LBNO and MODES-SNM projects are two independent projects that focus on using this concept to detect neutral particles of interest. The two projects are consecutively discussed in this thesis. A study on a potential near detector design to be used within the proposed LAGUNA-LBNO experiment is presented. We introduce a novel design for the near detector based on a pressurised gas Argon TPC at 20 bar surrounded by layers of plastic scintillator, encompassed in a pressurised gas chamber. Monte Carlo studies form the basis of the study with focus on detector interaction rates and assessment of the basic detector properties and parameterisation. Based on a 2 × 2 × 2 × m3 TPC we estimate 0.1785 ± 0.0003 (stat) neutrinos p.p.p interactions for a 400 GeV neutrino beam in positive focusing and 0.0628 ± 0.0002 (stat) muon neutrinos p.p.p interactions for energies 0-10 GeV in a 1.8 × 1.8 × 1.8 × m3 fiducial volume. Conversely we can expect high muon backgrounds in the TPC at 44.5 ± 0.5 μ (stat) p.p.p, arising from neutrino interactions with external detector components (non TPC) and surrounding rock interactions. With the inclusion of the muons arising from the beam directly at 70 p.p.p (estimated) we can expect ∼1-2 μ tracks in the TPC / 700 cm2 / spill. Within the MODES-SNM section of the thesis a prototype system is designed, tested and analysed using He4, instead of the commonly favourable He3, for fast neutron detection. A neutron-gamma discrimination analysis is performed based on a pulse shape discrimination technique from the collected scintillation light of PuBe and Co60 sources in laboratory conditions. For high levels of gamma contamination (up to 76%) detection efficiencies exceeding 96% can be achieved with the prototype system while maintaining reasonable false alarm rates (< 1 per hour).

Дипломний проєкт складається із пояснювальної записки та графічної частини. Пояснювальну записку виконано на 98 сторінках формату А4, вона містить 25 рисунків, 45 таблиць та 8 посилань на джерела інформації. Графічну частину складають три аркуші (формату А1) креслень. У першому розділі синтезовано п’ять варіантів конфігурації електричної мережі номінальної напруги 110 кВ та внаслідок порівняння техніко-економічних показників обрано оптимальний. Вибрано трансформатори на підстанціях та перерізи дротів ліній електропередачі. Розраховано режими електричної мережі – максимальних навантажень та післяаварійний. Вибрано регулювальні відгалуження РПН та ПБЗ силових трансформаторів. У другому розділі виконано аналіз режимів нейтралі електричних мереж номінальної напруги 110 кВ.
The diploma project consists of an explanatory note and a graphic part. The explanatory note is made on 98 pages (A4 format), it contains 25 pictures, 45 tables and 8 references. The graphic part consists of three sheets (A1 format) of drawings. The aim of the diploma project is the development of an electrical network of nominal voltage 110 kV and analysis of its neutral modes. In the first section, five variants of the configuration of the electric network of nominal voltage of 110 kV are synthesized and as a result of comparison of technical and economic indicators the optimal one is chosen. Transformers at substations and wires sections of power lines are selected. The modes of the electric network are calculated - maximum loads and post-accident. The control branches of on-load tap-changers and off-load tap-changers of power transformers are selected. In the second section the analysis of the modes of neutral of electric networks of nominal voltage of 110 kV is performed.

The electroweak standard model (Salam-Weinberg) is well-known to be a satisfactory and consistent theoretical description of all the experimental data we have obtained so far. In this thesis, we discuss possible phenomenology which goes beyond the standard model, with particular emphasis on the neutral current effects. First of all, the left-right symmetric extension of the standard model is discussed and we find limits on its parameters. We show that this model cannot explain certain newly reported and highly speculative events at the CERN collider [3], which in principle could be caused by the decay into two W's of a new heavy Z. We then discuss composite models where there is a strong expectation that there should be two neutral Z's of similar mass. We study the effects of these on neutral current phenomenology and show that in general the extra Z would be very hard to detect. A comparison of our model with a particular superstring model [6] is also made.

A better understanding of how biodiversity forms and is maintained is critical for informing our conservation efforts. Useful tools for achieving this are models of community assembly which help identify the dominant processes in different ecosystems. Neutral models in particular, have the benefit of being simple, tractable, mechanistic models that can produce good fits to empirical data for many different ecological communities.

In this thesis I present an in-depth study of the distribution of various neutral species in Titan’s upper atmosphere, at altitudes between 950 and 1,500 km for abundant species (N₂, CH₄ as well as their isotopes) and between 950 and 1,200 km for most minor species. However, the study of the H2 distribution on Titan is extended to an altitude as high as 6,000 km in the exosphere. The analysis is based on a large sample of Cassini/INMS (Ion Neutral Mass Spectrometer) measurements in the CSN (Closed Source Neutral) mode, obtained during 15 close flybys of Titan. The densities of abundant species including N₂, CH₄ and H₂ are determined directly from their main channels. However, to untangle the overlapping cracking patterns of minor species, the technique of Singular Value Decomposition (SVD) is used to determine simultaneously the densities of various hydrocarbons, nitriles and oxygen compounds. All minor species except for ⁴⁰Ar present density enhancements measured during the outbound legs. This can be interpreted as a result of wall effects, which could be either adsorption/desorption or heterogeneous surface chemistry on the chamber walls. In the thesis, I use a simple model to describe the observed time behavior of minor species. Results on their atmospheric abundances are provided both in terms of direct inbound measurements assuming ram pressure enhancement and values corrected for wall adsorption/desorption. Among all minor species of photochemical interest, the INMS data provide direct observational evidences for C₂H₂, C₂H₄, C₂H₆, CH₃C₂H, C₄H₂, C₆H₆, HC₃N and C₂N₂ in Titan’s upper atmosphere. Upper limits are put for other minor species. The globally averaged distribution of N₂, CH₄ and H₂ are each modeled with the diffusion approximation. The N₂ profile suggests an average thermospheric temperature of 154 K. The CH₄ and H₂ distribution constrains their fluxes to be 3.0×10⁹ cm⁻² s⁻¹ and 1.3×10¹⁰ cm⁻² s⁻¹, referred to Titan’s surface. The H₂ escape flux is about a factor of ∼3 higher than the Jeans value, which is interpreted as enhanced thermal escape driven primarily by an upward conductive heat flux. Such a conclusion is based on kinetic model calculations in the 13-moment approximation that require energy continuity at the upper boundary. On the other hand, a proper interpretation of the observed CH4 escape has to rely on the detailed nonthermal processes, which are still unknown at the present time. The INMS observations of the nitrogen isotope ratio implies ¹⁴N/¹⁵N= 131.6 near Titan’s surface. The profile of carbon isotope ratio combining INMS and GCMS results implies that both CH₄ and its isotope escape from Titan’s exobase with roughly the same drift velocity, in contrast to the Jeans case which requires that CH₄ escapes with a much larger velocity due to its smaller mass. The INMS data also suggest horizontal/diurnal variations of temperature and neutral gas distribution in Titan’s thermosphere. The equatorial regions, the ramside, as well as the nightside hemisphere of Titan appear to be warmer and present some evidences for the depletion of light species such as CH₄. Meridional variations of most heavy species are also observed, with a trend of depletion toward the north pole. Though some of the above variations might be interpreted by either the solardriven models or plasma-driven models, a physical scenario that reconciles all the observed horizontal/diurnal variations in a consistent way is still missing, With a careful evaluation of the effect of restricted sampling, some of the features shown in the INMS data are more likely to be observational biases.

Energy demand forecasting, and specifically electricity demand forecasting, is a fun-damental feature in both industry and research. Forecasting techniques assist all electricity market participants in accurate planning, selling and purchasing decisions and strategies. Generation and distribution of electricity require appropriate, precise and accurate forecasting methods. Also accurate forecasting models assist producers, researchers and economists to make proper and beneficial future decisions. There are several research papers, which investigate this fundamental aspect and attempt var-ious statistical techniques. Although weather and economic effects have significant influences on electricity demand, in this study they are purposely eliminated from investigation. This research considers calendar-related effects such as months of the year, weekdays and holidays (that is, public holidays, the day before a public holiday, the day after a public holiday, school holidays, university holidays, Easter holidays and major religious holidays) and includes university exams, general election days, day after elections, and municipal elections in the analysis. Regression analysis, cate-gorical regression and auto-regression are used to illustrate the relationships between response variable and explanatory variables. The main objective of the investigation was to build forecasting models based on this calendar data only and to observe how accurate the models can be without taking into account weather effects and economic effects, hence weather neutral models. Weather and economic factors have to be forecasted, and these forecasts are not so accurate and calendar events are known for sure (error-free). Collecting data for weather and economic factors is costly and time consuming, while obtaining calendar data is relatively easy.

Since the default of Lehman Brothers in 2008, it has become increasingly important to measure, manage and price the default risk in financial derivatives. Default risk in financial derivatives is referred to as counterparty credit risk (CCR). The price of CCR is captured in Credit Valuation Adjustment (CVA). This adjustment should in principle always enter the valuation of a derivative traded over-the-counter (OTC). To calculate CVA, one needs to know the probability of default of the counterparty. Since CVA is a price, what one needs is the risk-neutral probability of default. The typical way of obtaining risk-neutral default probabilities is to build credit curves calibrated using Credit Default Swaps (CDS). However, for a majority of a bank's counterparties there are no CDSs liquidly traded. This constitutes a major challenge. How does one model the risk-neutral default probability in the absence of observable CDS spreads? A number of methods for constructing proxy credit curves have been proposed previously. A particularly popular choice is the so-called Nomura (or cross-section) model. In studying this model, we find some weaknesses, which in some instances lead to degenerate proxy credit curves. In this thesis we propose an altered model, where the modelling quantity is changed from the CDS spread to the hazard rate. This ensures that the obtained proxy curves are valid by construction. We find that in practice, the Nomura model in many cases gives degenerate proxy credit curves. We find no such issues for the altered model. In some cases, we see that the differences between the models are minor. The conclusion is that the altered model is a better choice since it is theoretically sound and robust.
Sedan Lehman Brothers konkurs 2008 har det blivit allt viktigare att mäta, hantera och prissätta kreditrisken i finansiella derivat. Kreditrisk i finansiella derivat benämns ofta motpartsrisk (CCR). Priset på motpartsrisk fångas i kreditvärderingsjustering (CVA). Denna justering bör i princip alltid ingå i värderingen av ett derivat som handlas över disk (eng. over-the-counter, OTC). För att beräkna CVA behöver man veta sannolikheten för fallissemang (konkurs) hos motparten. Eftersom CVA är ett pris, behöver man den riskneutrala sannolikheten för fallissemang. Det typiska tillvägagångsättet för att erhålla riskneutrala sannolikheter är att bygga kreditkurvor kalibrerade med hjälp av kreditswappar (CDS:er). För en majoritet av en banks motparter finns emellertid ingen likvid handel i CDS:er. Detta utgör en stor utmaning. Hur ska man modellera riskneutrala fallissemangssannolikheter vid avsaknad av observerbara CDS-spreadar? Ett antal metoder för att konstruera proxykreditkurvor har föreslagits tidigare. Ett särskilt populärt val är den så kallade Nomura- (eller cross-section) modellen. När vi studerar denna modell hittar vi ett par svagheter, som i vissa fall leder till degenererade proxykreditkurvor. I den här uppsatsen föreslår vi en förändrad modell, där den modellerade kvantiteten byts från CDS-spreaden till riskfrekvensen (eng. hazard rate). Därmed säkerställs att de erhållna proxykurvorna är giltiga, per konstruktion. Vi finner att Nomura-modellen i praktiken i många fall ger degenererade proxykreditkurvor. Vi finner inga sådana problem för den förändrade modellen. I andra fall ser vi att skillnaderna mellan modellerna är små. Slutsatsen är att den förändrade modellen är ett bättre val eftersom den är teoretiskt sund och robust.

In this study, neutral real interest rate gap and output gap are estimated jointly under two different multivariate unobserved components models with the motivation to provide empirical measures that can be used to analyze the amount of stimulus that monetary policy is passing on to the economy, and to understand historical macroeconomic developments. In the analyses, Kalman filter technique is applied to a small-scale macroeconomic model of the Turkish economy to estimate the unobserved variables for the period 1989-2005. In addition, two alternative specifications for neutral real interest rate are used in the analyses. The first model uses a random walk model for the neutral real interest rate, whereas the second one employs more structural specification, which specifically links the neutral real rate with the trend growth rate and the long-term course of the risk premium. Comparison of the models developed by using various performance criteria clearly indicates the use of more structural specification against random walk specification. Results suggest that though there is relatively high uncertainty surrounding the neutral real interest rate estimates to use them directly in the policy-making process, estimates appear to be very useful for ex-post monetary policy evaluations.

CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO
O apreçamento de opções é um assunto muito importante nos dias de hoje. Métodos probabilisticos são necessários para fazer o apreçamento neutro ao risco. Usaremos o método de Siu et al. para duas classes de GARCHs, o FC-GARCH e a mistura de GARCHs Em ambos os modelos nós encontramos a versão neutra ao risco do modelo que é necessária para a precificação de contratos, em dois diferentes casos, quando o ruído é normal e quando é shifted gamma. Fizemos também simulações para ilustrar e comparamos os resultados com o valor de Black Scholes, verificamos a existência de smile e fizemos uma análise de sensibilidade nos parâmetros.
Option pricing is a very important issue nowadays. The use of probabilistic methods is required for risk neutral pricing. Here we apply the method of Siu et al. for two classes of GARCHs, viz., the FC-GARCH and the Mixture of GARCHs. In both models we derive the risk neutral version of the model which is essential for pricing contracts, in two different cases, when the noise is normal as well as when it is shifted gamma. We also performed simulations with both models and compared to the benchmark Black Scholes model, checked for the smile effect and made some sensibility analysis in the parameters.

In questo lavoro di tesi sono stati studiati modelli stocastici per ecosistemi basati su equazioni di tipo Lotka-Volterra con componenti fluttuanti. E' stato affrontato per primo il modello preda-predatore aggiungendo un rumore additivo ed è stata risolta l'equazione linearizzata attorno all'equilibrio. Con una limitazione alla crescita delle prede e rumore moltiplicativo si è proposto poi un modello più completo di cui si può calcolare la distribuzione di probabilità all'equilibrio. Nel caso deterministico si è fatto un confronto con dati raccolti sull’Isle Royale. Il secondo passo è stato quello di considerare specie in competizione, nell'ambito delle teorie di nicchia, e le fluttuazioni dovute alla scarsa numerosità in presenza di immigrazione, nell'ambito delle teorie neutrali. La master equation è stata analizzata in dettaglio per una popolazione con crescita limitata e immigrazione. Il passaggio da una distribuzione Gaussiana a quella di Pareto mostra come sia cruciale la scelta della forma della fluttuazione. La teoria di nicchia è stata sviluppata per due popolazioni a crescita limitata in competizione tra loro e con immigrazione, studiando gli equilibri, la loro stabilità e le biforcazioni nel caso deterministico. Si è anche indicato come formulare la master equation per combinare teoria neutrale e di nicchia in un unico modello, come proposto da Haegeman. Si è infine delineato il caso più generale di N specie, composte sia da prede in competizione sia da predatori, presenti nello stesso ambiente. Si è studiato in dettaglio un ecosistema costituito da due prede e un predatore senza competizione tra le prede caratterizzando completamente gli equilibri e la loro natura. Un confronto con dati empirici su microrganismi ha mostrato un ottimo accordo con le predizioni del modello, aprendo la possibilità per una sua estensione che includa la competizione tra le prede al fine di descrivere anche il comportamento caotico osservato sperimentalmente.

Diese Arbeit beschreibt die Suche nach dem Higgs Boson, welches in vielen theoretischen Modellen der Teilchenphysik vorhergesagt wird. Das Higgs Boson ist die Konsequenz der spontanen Symmetriebrechung, welche den Teilchen Masse verleiht. Zur Suche werden e+e- Annihilationen bei Schwerpunktenergien bis 209 GeV analysiert, welche vom Experiment L3 am Speicherring LEP in den Jahren 1998 bis 2000 registriert wurden. Die Suche erfolgte in allen relevanten Endzustaenden, wobei der Endzustand mit vier hadronischen Jets im Detail behandelt wird. Die Daten werden mit den Erwartungen eines Signals in verschiedenen Modellen bei Beruecksichtigung der bekannten Untergrundprozesse verglichen oder es wird modellunabhaengig nach der Erzeugung skalarer Teilchen gesucht. Die Produktion von Higgs Bosonen konnte nicht nachgewiesen werde. Die Daten wurden daher benutzt, um neue Grenzen fuer Parameter der Modelle oder der Kopplungen zu setzen. Als erstes wird die Suche nach dem Higgs Boson im Standard Modell der elektroschwachen Wechselwirkung beschrieben. Die Produktion des Higgs Bosons wird bei LEP Energien ueber die Higgs-Strahlung und der Zerfall des Higgs Bosons in ein Paar von b-Quarks vorhergesagt. Die Analysen beruhen daher wesentlich auf der Erkennung von B-Hadronen. Der HZ->qqqq Endzustand wird im Detail untersucht, und die Ergebnisse werden mit den anderen Kanaelen : HZ->qqvv, HZ->qql+l- und HZ->tau+tau- qq kombiniert. Die untere Massengrenze fuer das Higgs Boson wird zu mH > 112.0 GeV auf 95% Vertrauensniveau, bestimmt. Ausserdem werden Grenzen auf die HZZ Kopplung abgeleitet. Im minimalen supersymmetrischen Modell (MSSM) werden fuenf Higgs Bosonen vorhergesagt. Zur Higgs-Strahlung kommt die Paarproduktion von Higgs Bosonen, e+e- -> hA , hinzu. Die Ergebnisse der Suche im Standard Modell werden durch die Suche in den Endzustaenden bb tau+tau- (tau+tau- bb), bbbb und hZ->AAqq ergaenzt. Im Rahmen von drei Standard-Szenarien, benannt als "mh-max", "no mixing" und "large-mu" werden untere Grenzen auf die Higgs Boson Massen von mh > 84.5 GeV und mA > 86.3 GeV fuer tan(beta) > 0.7 abgeleitet. Weiterhin werden im "mh-max" Szenario 0.55 < tan(beta) < 2.2, im "no mixing" Szenario 0.4 < tan(beta) < 4.9, und im "large-mu" Szenario 0.7 < tan(beta) < 6.2 ausgeschlossen. Eine modellunabhaengige Suche nach dem Prozess e+e- -> hZ wird fuer den vier-Jet Endzustand durchgefuehrt. In Kombination mit den Ergebnissen von den anderen Kanaelen werden Grenzen fuer die hZZ Kopplung bestimmt. Wird die hZZ Kopplung auf den Wert im Standard Modell gesetzt und der Zerfall des Higgs Bosons zu 100% in Hadronen angenommen, ergibt sich als Grenze der Higgs Boson Masse, mh > 97 GeV. Modellunabhaengige obere Grenzen fuer die hAZ Kopplung werden aus der Suche nach der Paarerzeugung von Higgs Bosonen in den Kanaelen hA->qqqq und hA->qq tau+tau- in Abhaengigkeit von den Higgs Boson Massen abgeleitet. Die Resultate aus der Kombination aller LEP Experimente werden fuer die oben genannten Analysen vorgestellt. Die Perspektiven der Higgs Boson Suche an den TEVATRON und LHC Speicherringen werden diskutiert und die Higgs Boson Physik an kuenftigen e+e- Linearbeschleunigern behandelt. Ein Linearbeschleuniger wie TESLA waere ideal fuer Untersuchungen eines leichten Higgs Bosons. Fuer ein Higgs Boson mit einer Masse zwischen 120 und 180 GeV kann mH mit einer Praezision von 40 bis 70 MeV bestimmt werden. Im gleichen Massenbereich ist die Messung des Wirkungsquerschnitts, weitgehend modellunabhaengig, mit einem relativen Fehler von 2.6 bis 3.8% moeglich. In vier-Fermion und sechs-Fermion Endzustaenden werden topologische Wirkungsquerschnitte, definiert als Produkt des totalen Wirkungsquerschnitts fuer e+e- -> HZ mit dem Verzweigungsverhaeltnis eines Zerfallskanals, untersucht. Fuer den Messfehler werden 1.1% fuer HZ->bbqq und 13% fuer HZ->W+W-l+l- bei mH = 120 GeV abgeschaetzt. Die Gesamtheit dieser und weiterer Messungen erlaubt eine genaue Bestimmung des Higgs Boson Profils und gibt Aufschluss ueber die Struktur des Higgs Sektors in der Natur.
This thesis is devoted to the search for neutral Higgs bosons predicted by various theoretical models. The Higgs boson arises as a result of spontaneous breaking of SU(2) symmetry leading to the generation of masses of fermions and weak bosons. The search is done in all experimentally related channels using the data collected at center-of-mass energies up to 209 GeV in the years 1998-2000 with the L3 detector at the Large Electron Positron collider, LEP. Here the study of the final states characterised by four jets is described in detail. For other final states the analyses are briefly reviewed and the results are reported. The data are compared with the expectation from the Standard Model background processes and with various signal hypotheses. A model independent search for neutral Higgs bosons is also performed. No evidence for the production of Higgs bosons is found. New mass limits are determined superseding previous mass limits established by L3 and other experiments. First I describe the analysis searching for the Standard Model Higgs Boson. Its production at LEP is expected mainly via the Higgs-strahlung process. In the mass range accessible at LEP the Standard Model Higgs Boson is predicted to decay dominantly into a pair of b and anti-b quarks, hence the dedicated analyses are optimised for the H->bb decay mode. The four-jet signal topology is investigated and then combined with the other search channels leading to a lower mass limit of mH > 112.0 GeV at 95% C.L.. The results of the search are also interpreted in terms of limits on the HZZ coupling. In the Minimal Supersymmetric Standard Model (MSSM) the Higgs sector is extended to five physical states. The Higgs-strahlung process is complemented by the mechanism of the Higgs boson pair production e+e- -> hA. Therefore, for the interpretation of the results in the framework of the MSSM the Standard Model analyses are combined with the hA -> bb tau+tau-, hA -> bbbb and hZ->AAqq channels. Three benchmark MSSM scenarios denoted "mh-max", "no mixing" and "large-mu" are considered. Using L3 data the lower bounds on the Higgs boson masses mh > 84.5 GeV mA > 86.3 GeV are derived at 95% C.L. for tan(beta) > 0.7. For the "mh-max", "no mixing" and "large-mu" scenarios, ranges 0.55 < tan(beta) < 2.2, 0.4 < tan(beta) < 4.9 and 0.7 < tan(beta) < 6.2, respectively, are ruled out. A model independent search for the Higgs-strahlung process with subsequent decay of h into hadrons is carried out in the four-jet channel. The results of the analysis are then combined with the other channels. A limit on the hZZ coupling as a function of the Higgs boson mass is derived. The results of L3 combined search establish a 95% C.L. lower mass limit, mh > 97 GeV, for a hadronically decaying Higgs boson assuming the cross section of the Higgs-strahlung process to be equal to the value predicted by the Standard Model and the branching fraction of the Higgs boson into hadrons equal to 100%. Analyses are developed to search exclusively for the hA -> bbbb, hA -> qqqq, hA -> bb tau+tau- and hA -> qq tau+tau- final states. Results of these analyses are translated into a 95% C.L. upper limit on the hAZ coupling as a function of Higgs boson masses. Searches for neutral Higgs bosons carried out by the L3 collaboration are combined with searches performed in other LEP experiments. The results of this combination are reported. The perspectives of Higgs boson searches at TEVATRON and LHC are briefly reviewed. The prospects of Higgs physics at a future linear e+e- collider are discussed. The potential of the TESLA detector foreseen at the TESLA linear collider for the determination of Higgs boson properties is studied. The Higgs boson masses 120, 150 and 180 GeV are considered. It is shown that a precision of 40 - 70 MeV in the measurement of the Higgs boson mass can be achieved. A model independent method to measure the e+e- -> HZ cross section is proposed. The method is based on the study of the inclusive HZ -> X e+e- and X mu+mu- channels. The relative error in the determination of the cross section varies between 2.6% and 3.8% for Higgs boson mass ranging from 120 GeV to 180 GeV. For the four-fermion and six-fermion final states arising from the Higgs-strahlung process the accuracy of the measurement of a topological cross section, defined as the product of the Higgs-strahlung cross section and the branching fraction of the specific final state, is investigated. The relative uncertainty of this measurement varies from 1.1% and 13%, depending on final state and Higgs boson mass. These and other measurements will allow to determine the profile of the Higgs boson and give insight into the structure of the Higgs sector in nature.

We focus on the two-dimensional Falicov-Kimball model in the neutral case with U >> 0. We determine the ground state ion configurations for all rational densities in (1/3, 2/5), as well as densities 1/6 and 2/11. We also determine the ground states for a sequence of densities starting at 1/5 and converging to 0. On the interval (1/3, 2/5) we show that the ground states are periodic, having the same structure as the one-dimensional ground states. For densities between 1/6 and 2/11 we show that the ground states exhibit a phase separation.

A physical model for redox flow batteries is developed to estimate performance for any chemistry using parameters such as electrolyte conductivity and kinetic rate constants. The model returns the performance as a function of flow rate, current density, and state of charge. Two different models are developed to estimate the current density distribution throughout the electrode in order to evaluate physical performance of the battery. This is done using electrochemical parameters such as conductivity and kinetic rate constant. The models are analytical in order to produce a computationally cheap algorithm that can be used in optimization routines. This allows for evaluating the economic performance of redox flow batteries, and optimization of cost. The models are validated vs data and found to accurately predict performance in a V-V system for a wide variety of operating conditions.

Effective understanding of gas flow is important to ensure efficient operation of gas neutralizer systems such as those used at the Joint European Torus (JET), which form part of invaluable heating systems for nuclear fusion experiments. Computational fluid dynamics modelling of the neutral gas flow in the JET neutraliser has been undertaken, motivated by the shortfall in neutralisation efficiency and apparent loss of gas target observed in the JET neutraliser system. This has presented a challenging modelling endeavour due to the interaction of beam, background plasma and rarefied neutral gas. Utilising the continuum flow approximation, the Navier-Stokes and Augmented Burnett equations have been implemented and applied in conjunction with secondorder slip boundary conditions to form a gas solver accurate within the continuum-transition regime. Simulations in the presence of the ionic beam and background neutraliser plasma encountered during tokamak heating operations have been achieved via the development of a coupled beamplasma- gas solver. The gas flow governing equations have been supplemented by a series of source/sink terms for mass/energy that describe the complex web of interactions between the neutraliser constituents. The developed solver has been validated against experimental data, both in the absence and presence of beam. The design of future gas neutraliser systems has also been considered, with variation of several model and geometry parameters in order to better understand the loss of neutralisation efficiency and how future systems might be optimised. The neutraliser design for the forthcoming International Thermonuclear Experimental Reactor (ITER) has also been evaluated.

The Neutral Indel Model is able to predict accurately the distribution of indel events in alignments of neutrally evolving genomic sequence. Here, I apply this model to a diverse range of metazoan species pairs, to a number of ends. First, I apply the Neutral Indel Model to alignments of genome sequences for species within the mammalian clade in order to estimate the quantities of functional DNA shared between species pairs. I demonstrate that as the evolutionary divergence between species pairs increases, estimates of functional sequence drop off dramatically. This pattern is not replicated in extensive simulations of genome sequence alignments, suggesting that functional (and mostly non-coding) sequence is turning over at a rapid rate. I also estimate that between 200 and 300 Mb (6.5-10%) of the human genome is under evolutionary constraint, a considerably higher quantity of sequence than has been estimated by previous whole genome analyses. Second, extending my analyses to consider more diverse metazoan species, I provide estimates for functional bases within organisms’ genomes that appear to mirror our conceptions of organismal complexity. Thirdly, I develop the Neutral Indel Model as a method for assessing genome sequence quality, by quantifying indel errors within alignments of closely related (ds < 0.1) species pairs. Applying this method to six primate genome sequence assemblies, I demonstrate that the frequency of indel error events per base varies up to six-fold. Further to this, I show that second generation sequencing technologies can be used to create high quality genome sequence assemblies and to ameliorate errors in pre-existing assemblies. Finally, I analyse patterns of indel mutations in primate transposable elements and show that indels are not randomly distributed within these sequences due to regularly spaced homo-nucleotide motifs.

The demand for computational tools that are capable to reliably predict the behavior of a nuclear reactor core in a variety of static and dynamic conditions does inevitably require a proper qualification of these tools for the intended purposes. One of the qualification methods is the verification of the code in question. Hereby, the correct implementation of the applied model as well as its flawless implementation in the code are scrutinized. The present work concerns with benchmarking as a substantial part of the verification of the three-dimensional, multigroup neutron kinetics model employed in the transient code POLCA-T. The benchmarking is done by solving some specified and widely used space-time kinetics benchmark problems and comparing the results to those of other, established and well-proven spatial kinetics codes. It is shown that the obtained results are accurate and consistent with corresponding solutions of other codes. In addition, a sensitivity analysis is carried out with the objective to study the sensitivity of the POLCA-T neutronics to variations in different numerical options. It is demonstrated that the model is numerically stable and provide reproducible results for a wide range of various numerical settings. Thus, the model is shown to be rather insensitive to significant variations in input, for example. The other consequence of this analysis is that, depending on the treated transient, the computing costs can be reduced by, for instance, employing larger time-steps during the time-integration process or using a reduced number of iterations. Based on the outcome of this study, one can finally conclude that the POLCA-T neutron kinetics is modeled and implemented correctly and thus, the model is fully capable to perform the assigned tasks.

The aim of this thesis is to predict the column densities of various neutral and ionised molecular species that are formed, or are likely to be formed, in the neutral envelope of a planetary nebula (PN). To this end a computer program has been constructed based on existing code (Abgrall et al. 1992) that considers a large set of chemical reactions covering the formation and destruction of the chemical species considered in the model. The rate coefficient of a chemical reaction will either depend on the local gas kinetic temperature if it is a gas phase reaction, or on the local radiation field spectrum if it is a photoreaction. To model the reaction network it is therefore also required to model the heating and cooling processes in the nebula to determine the kinetic temperature and also to solve the radiative transfer equation to determine the energy spectrum of ultraviolet radiation. Formation of the H2 molecule on the surface of dust grains and cosmic ray interactions are also considered. The ultraviolet absorption spectrum of the dominant molecules H2 and CO and the photodissociation rates are both functions of the rotational population. Rate coefficients for collisional cooling also depend on the rotational state. For these reasons, to model the thermal processes and the radiative transfer accurately it is also required to model the processes contributing to rotational excitation and de-excitation of H2 and CO to determine the distribution amongst their various rotational levels. Dust grains play a significant role in much of the physics occurring in the nebula, not least because they represent the catalyst for the formation of molecular hydrogen. Dust also represents the most important source of opacity for the ultraviolet radiation field and hence a significant part of the thesis is devoted to a consideration of the probable dust composition and optical properties. The results of the model are shown and a comparison is made between the predictions of the model and recent computations of molecular column densities based on astronomical observations of planetary nebulae. The probable sources of large discrepancies are discussed within the context of assumptions and possible omissions in the physical model.

A stochastic backscatter (SB) approach to subgrid-scale (SGS) modelling for large-eddy simulation (LES) of the neutral atmospheric boundary layer (ABL) has previously been shown to reduce excessive velocity shear, as seen with the popular Smagorinsky SGS model, in the under-resolved surface layer. However, previous SB models exhibit unwanted grid-dependency issues, and the range of atmospheric flows tested remains limited. Here, a new SB model is proposed that uses a grid-adaptive filter to control the length-scale, anisotropy and momentum flux of the backscatter fluctuations, independently of the model grid. Model performance is confirmed to be grid-independent in simulations of the neutral ABL, in which an 80% reduction in excessive near-surface velocity shear is achieved. The model is also applied to street canyon flow, where the shear layer that separates the recirculating vortex within the canyon from the external flow is again typically under-resolved in most LES set-ups. The backscatter acts to increase momentum transfer across the shear layer, bringing the simulated vortex intensity significantly closer towards wind-tunnel observations. A passive tracer is also released to model traffic emissions, and the pollutant exchange velocity between the canyon and the external flow is again found in better agreement with wind-tunnel data. This information can be used to improve operational urban dispersion models.

This thesis investigates a novel DC/AC resonant inverter of Induction Heating (IH) system presenting a Multilevel Neutral Point Clamped (MNPCI) topology, as a new part of power supply design. The main function of the prototype is to provide a maximum and steady state power transfer from converter to the resonant load tank, by achieving zero current switching (ZCS) with selecting the best design of load tank topology, and utilizing the advantage aspects of both the Voltage Fed Inverter (VFI) and Current Fed Inverter (CFI) kinds, therefore it can considered as a hybrid-inverter (HVCFI) category . The new design benefits from series resonant inverter design through using two bulk voltage source capacitors to feed a constant voltage delivery to the MNPCI inverter with half the DC rail voltage to decrease the switching losses and mitigate the over voltage surge occurred in inverter switches during operation which may cause damage when dealing with high power systems. Besides, the design profits from the resonant load topology of parallel resonant inverter, through using the LLC resonant load tank. The design gives the advantage of having an output current gain value of about Quality Factor (Q) times the inverter current and absorbs the parasitic components. On the contrary, decreasing inverter current means decreasing the switching frequency and thus, decreasing the switching losses of the system. This aspect increases the output power, which increases the heating efficiency. In order for the proposed system to be more reliable and matches the characteristics of IH process , the prototype is modelled with a variable LLC topology instead of fixed load parameters with achieving soft switching mode of ZCS and zero voltage switching (ZVS) at all load conditions and a tiny phase shift angle between output current and voltage, which might be neglected. To achieve the goal of reducing harmonic distortion, a new harmonic control modulation is introduced, by controlling the ON switching time to obtain minimum Total Harmonic Distortion (THD) content accompanied with optimum power for heating energy.

The advent of X-ray astronomy has turned the study of compact objects into one of the most active research fields in modern-day physics. Diverse luminosity phenomena have been remarked upon in neutron stars and it is believed that in many of them the neutron star crust plays a critical role. This work presents a steady-state model for the neutron star crust that describes, in particular, the profiles of temperature and flux along this region. It is divided as follows: First, a review of observational phenomena in neutron stars, where crust characteristics are thought to be crucial, are presented, alongside general aspects of the theoretical models applied. Second, the different elements that are needed to construct this model are considered. Third, the set of structure equations to be resolved and the calculations of the components of these equations are provided. Finally, the results are shown and discussed and the conclusion is presented.
L'avènement de l'astronomie des rayons X a transformé l'étude des objets compacts en un des champs de recherche des plus actifs en physique moderne. Divers phénomènes de luminosité ont été observés dans les étoiles neutron et on estime que la croûte de l'étoile neutron joue un rôle important dans beaucoup de ces phénomènes. Cet ouvrage présente un modèle d'équilibre stable pour la croûte de l'étoile neutron qui décrit, en particulier, les profiles de température et flux dans cette région. L'ouvrage est divisé comme suit: Premièrement, une révision des phénomènes observés dans les étoiles neutron, où les caractéristiques de la croûte sont supposées être cruciaux, est présentée, avec les aspects généraux des modèles théoriques utilisés. Deuxièmement, les différents éléments nécessaires pour construire ce modèle sont examinés. Troisièmement, l'ensemble des équations de structure à résoudre et les calculs des composantes de ces équations sont présentés. Finalement, les résultats sont montrés et discutés et la conclusion est présentée.

Over the last several decades, there has been consistent growth in the research and development of multilevel voltage-source inverter-based adjustable speed motor drives (ASDs) as a result of low cost, high reliability power semiconductors. The three-level neutral-point-clamped (NPC) ASD is a popular multilevel inverter used in low and medium voltage applications because of its ability to produce lower levels of total harmonic distortion (THD) and withstand higher voltages while preserving the rated output power compared to two-level ASDs.

As with other voltage-source inverters, three-level NPC ASDs produce common-mode voltage (CMV) that can cause motor shaft voltages, bearing currents, and excess voltage stresses on motor windings, resulting in the deterioration of motor bearings and insulation. Furthermore, the CMV and resultant currents can generate electromagnetic interference that can hinder the operation of sensitive control electronics. In this thesis, three carrier-based, three-level pulse-width-modulation (PWM) strategies were investigated to examine the levels of CMV, common-mode current, and dv/dt produced by the three-level NPC ASD. Additionally, the effects that each PWM strategy has on the THD in the output waveforms, as well as the total switching and conduction losses were analyzed through software simulation programs using a resistive-inductive load over a range of modulation indices. The first of the three methods, in-phase disposition sub-harmonic PWM (PD-SPWM), was verified experimentally using a laboratory-scale, 7.5 kVA three-level NPC ASD prototype.

It was determined that PD-SPWM produced the highest CMV amplitude of one-third the dc bus voltage, but the lowest values of differential-mode dv/dt, THD, and drive losses. The second strategy, phase-opposition (PO)-SPWM, reduced the CMV amplitude to one-sixth the dc bus voltage, at the cost of higher THD and drive losses and a doubling of the differential-mode dv/dt. The final strategy, zero common-mode (ZCM)-SPWM, was modified (MZCM-SPWM) to accommodate IGBT dead-time by delaying the output voltage transitions based on the polarity of the output currents and the direction of the commanded voltage transitions. The MZCM-SPWM method nearly eliminated all CMV pulses while maintaining comparable levels of THD, but produced twice the switching losses compared to PD- and PO- SPWM, and twice the differential-mode dv/dt compared to PD-SPWM.

It is widely believed that the Standard Model (SM) can not be a fundamental theory of the basic interactions. Originated from this fact, many new physics models have been proposed. Among them, the two Higgs doublet model (2HDM), the SM enlarged by adding one extra scalar doublet, is considered as the simplest extension of the SM. In this work, within the framework of the model III version of the 2HDM, the exclusive decay the branching ratio is calculated and discussed in various physical regions determined by model parameters. It is observed that it is possible to reach present experimental upper limits in model Finally, the avor changing top quark decay,

The accumulation of xenobiotics, such as halogenated phenols, in soils, sediments, and living organisms is primarily a partitioning process between an aquatic and organic phase. It is traditional to use a bulk octanol-water system to model the partitioning of a compound between complex biological lipid membranes and aqueous media. The octanol-water partition coefficient Kow successfully approximates the lipid membrane-water partition coefficient Ki;pw of neutral compounds. However, the ionized species of substituted phenols were shown (Smejtek, et al. 1993; Escher, et al. 1996) to have a higher affinity for lipid membranes than predicted from octanol-water results. Data on the octanol-water partition coefficients of molecular ions is limited. In order to compare the partitioning of neutral and charged species of halogenated phenols between the lipid membrane-water and octanol-water systems, we measured the pH dependent distribution of ionized and neutral 2,3,4,6-tetrachlorophenol (TeCP), pentafluorphenol (PFP), pentachlorophenol (PCP), and pentabromophenol (PBP). For the neutral (HA) species of each phenol, log Kow was found to be 4.28 (TeCP), 2.79 (PFP), 4.77 (PCP), and approximately 4.67 (PBP). For the ionized (A-) species of each phenol, log Kow was found to be 0.48 (TeCP), -0.85 (PFP), 1.16 (PCP), and 1.77 (PBP). These results are compared with sorption data on halophenols in a lipid membrane-water system (Smejtek, et al. 1996). This study shows that ionized halophenols have an affinity for lipid membranes about two to three orders of magnitude greater than for octanol. The usefulness of the octanol-water model as a predictor of lipid membrane-water partitioning for ionizable compounds, such as halogenated phenols, is questioned in view of the present results. Two thermodynamic Kow prediction models based on molecular properties are discussed in the context of the octanol-water partitioning of ionized and neutral compounds. The partition coefficients predicted by the molar volume based model (Gobas, et al. 1988) correlates with the experimental Kow results of this study better than Kow results predicted from the molecular surface area based model (Smejtek, et al. 1996). Results of this study support the hypothesis that partitioning of xenobiotics in the octanol-water system is fundamentally different than partitioning in lipid membrane-water systems.

In this thesis we consider three different problems in the domain of portfolio optimisation. The first problem we consider is that of selecting an Absolute Return Portfolio (ARP). ARPs are usually seen as financial portfolios that aim to produce a good return regardless of how the underlying market performs, but our literature review shows that there is little agreement on what constitutes an ARP. We present a clear definition via a three-stage mixed-integer zero-one program for the problem of selecting an ARP. The second problem considered is that of designing a Market Neutral Portfolio (MNP). MNPs are generally defined as financial portfolios that (ideally)exhibit performance independent from that of an underlying market, but, once again, the existing literature is very fragmented. We consider the problem of constructing a MNP as a mixed-integer non-linear program (MINLP) which minimises the absolute value of the correlation between portfolio return and underlying benchmark return. The third problem is related to Exchange-Traded Funds (ETFs). ETFs are funds traded on the open market which typically have their performance tied to a benchmark index. They are composed of a basket of assets; most attempt to reproduce the returns of an index, but a growing number try to achieve a multiple of the benchmark return, such as two times or the negative of the return. We present a detailed performance study of the current ETF market and we find, among other conclusions, constant underperformance among ETFs that aim to do more than simply track an index. We present a MINLP for the problem of selecting the basket of assets that compose an ETF, which, to the best of our knowledge, is the first in the literature. For all three models we present extensive computational results for portfolios derived from universes defined by S&P international equity indices with up to 1200 stocks. We use CPLEX to solve the ARP problem and the software package Minotaur for both our MINLPs for MNP and an ETF.

The hydrogen and helium accreted by X-ray bursting neutron stars is periodically consumed in runaway thermonuclear reactions that cause the entire surface to glow brightly in X-rays for a few seconds. With models of the emission, the mass and radius of the neutron star can be inferred from the observations. By simultaneously probing neutron star masses and radii, X-ray bursts (XRBs) are one of the strongest diagnostics of the nature of matter at extremely high densities. Accurate determinations of these parameters are difficult, however, due to the highly non-ideal nature of the atmospheres where XRBs occur. Observations from X-ray telescopes such as RXTE and NuStar can potentially place strong constraints on nuclear matter once uncertainties in atmosphere models have been reduced. Here we discuss current progress on modeling atmospheres of X-ray bursting neutron stars and some of the challenges still to be overcome.

Oscillating single neutron stars are considered to be important quasi-continuous sources for gravitational wave emission and detection at the Laser Interferometer Gravitational-Wave Observatory (LIGO). In order to detect these oscillations above the noise level in the detector, LIGO data must be compared to theoretical templates of the signal, which means predicting the signal amplitude and frequency range. In this thesis, we compute the two most important eigenfrequencies of superfluid neutron stars where the signal might be peaked. To calculate this spectrum, we first construct the background structure of the neutron star using realistic microscopic models of dense and interacting nuclear matter. For this purpose, we use the CompOSE database which provides an array of such models with thermodynamically consistent interpolation. The fluid pertubation equations of the equilibrium configuration, including superfluidity in a two-fluid model, are solved numerically in the non-relativistic limit, yielding the eigenfrequencies upon imposing suitable boundary conditions. We find that the modes of the superfluid star support modes that are very close to the corresponding normal fluid star, but there also appear one or two purely superfluid modes, the lower one of which is intermediate between the two lowest order modes of the normal fluid. Thus, in the event that these oscillation modes can be observed, we can confirm the theoretical prediction of neutron superfluidity in neutron stars. A part of the results presented in this thesis have been published as a proceedings article in Jaikumar, Monroy and Klaehn, Universe 4, 58 (2018).

The thesis focuses on methods of option prices calculations using two different pricing models which are Heston and Black-Scholes models. The first part describes theory of these two models and conlcudes with a comparison of the risk-neutral measures of these two models. In the second part, the relations between input parameters and the option price generated by these models are clarified. This part ends up with an analysis of the market data and it answers the question which model predicts better.

Fission yields represent the probability of producing a certain nuclide in a fission event, and are important observables for fission research. For applications, accurate knowledge of the yields is fundamental at all stages of the fuel cycle of nuclear reactors, e.g., for reactivity calculations, or to estimate (spent) fuel inventory. Fission yields also help in the basic understanding of the fission process, for nucleosynthesis models, and for radioactive ion beam production. This thesis was developed in the framework of the AlFONS project, the objective of which was to measure neutron-induced fission yields of relevance for partitioning and transmutation of spent fuel. The work is performed at the IGISOL-4 facility in JYFL (University of Jyväskylä). The first part of this thesis work is dedicated to the development and characterisation of a suitable 9Be(p(30MeV),nx) neutron source for IGISOL-4. The neutron energy spectrum and the neutron yield from a 5mm thick converter were studied with Monte Carlo simulations. Two characterisation campaigns that validated the MCNPX code were also performed. At the maximum current available from the cyclotron at JYFL, a total neutron yield between 2 and 5×1012 neutrons/(sr s) can be obtained. This satisfies the design goal for studies of fission yields. The neutron source was used in the measurement of fission yields from high-energy neutron-induced fission of natU at IGISOL-4, discussed in the second part of this thesis. The fission products were online-separated with a dipole magnet. The isobars, with masses in the range A = 128-133, were identified using γ-spectroscopy. Data for the relative yields of tin and antimony, as well as isomeric yield ratios for five nuclides will be reported. The yields show trends not observed in the ENDF/B-VII.1 evaluation, and only in part confirmed by the GEF model. The final part of this thesis concerns a study of the performance of different nuclear model codes, that aim at describing the states of the fission fragments right after scission. Reproduction of experimental data serves to benchmark the models and it indicates, to some extent, how reliably the results can be extrapolated to regions where no data exist. A methodology to compare and test these models has been developed, which was implemented in the DEℓFIN code. DEℓFIN takes the excited fission fragments, defined by the model under test, and de-excites them in a standardised way using the nuclear model code TALYS. Eliminating any variability in the way the final observables are extracted helps focusing on each model's assumptions. DEℓFIN was tested on five models, and interesting features in the prompt neutron multiplicity were found for some of them. This study will promote a better understanding of the ideas used in the development of fission models.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2016.
Cataloged from PDF version of thesis.
Includes bibliographical references.
Charge-containing polymers are used in a wide variety of commercial products including fuel cell membranes, heat sealing packages, and golf ball covers. Traditionally made as random copolymers of charged and uncharged monomers, morphological understanding and control is limited due to the lack of long range order and small length scale of the structural inhomogeneities. Moreover, the charge functionality is typically introduced in a permanent way that is not modifiable after synthesis, locking in a chemistry and structure that may not be optimal for the ultimate application. This thesis develops and studies the morphologies of a model block copolymer which is controllably charged in a novel way: by protonating a weak base. This polymer is composed of one hydrophilic but uncharged block, poly(oligoethylene glycol methyl ether methacrylate) (POEGMA), and one weak polyelectrolyte, poly(2-vinylpyridine) (P2VP) which can be controllably charged by varying the amount of acid to which it is exposed. This thesis presents the synthesis and morphological characterization of this polymer using scanning probe microscopy and small angle X-ray scattering. First, the ability of P2VP protonation to change the morphology of the diblock is demonstrated; while miscible in the absence of charge, the diblock undergoes a disorder to order transition upon protonation by a variety of acids. Thin films with varying levels of polyelectrolyte protonation are created and the efficacy of several polar aqueous and organic annealing solvents are presented. The introduction of acid in either the vapor or liquid phase is also shown to induce microphase separation. This is followed by a thorough treatment of the bulk morphologies of POEGMA-P2VP as a function of acid content, temperature, and minority block volume fraction. For all diblocks, protonation is found to increase the segregation strength between the two blocks and disorder to order transitions are observed with increasing protonation and temperature. Polymers with minority block volume fractions closest to 0.5 are the most immiscible, while those richer in majority block require more acid and higher temperatures to demix. Finally, the effect of acid type is investigated in detail by the comparison of two monoprotic with one diprotic acid. The diprotic acid is found to be more efficient at inducing microphase separation than either monoprotic acid for two diblocks of differing composition.
by Charlotte Roberta Stewart-Sloan.
Ph. D.

Adsorption of proteins at interfaces has an important role in biotechnological and pharmaceutical applications. Indeed, several undesirable processes are related to protein adsorption, as for example: fouling of contact lenses, clotting on blood contacting devices, triggering inflammation around artificial organs, diminished circulation time of therapeutic proteins and drug bearing liposomes. Neutral water soluble polymers, such as poly(ethylene glycol) (PEG), are used to repress protein adsorption: by coating the surface with a polymer brush, a "cushion" is created between the protein and the surface, that can reduce, or even completely repress the adsorption. Understanding the mechanism that inhibits the adsorption at interfaces is an active field of research, and could lead to relevant improvements in biomaterials performances and design.

A clear understanding of the mechanism of protein adsorption onto polymer brushes is still missing. The first models describing the interactions of a polymer brush with adsorbing particles predicted two adsorption modes: primary adsorption at the grafting surface, and secondary adsorption at the outer edge of the brush (occurring for large cylindrical proteins). Primary adsorption can be repressed by increasing the grafting density of the brush, and secondary adsorption by increasing its thickness, in agreement with the experiments reported in the literature. But experimental evidences (a maximum in the adsorbed amount observed for long brushes) suggested then the existence of a third mode: ternary adsorption within the brush itself, due to attractive interactions between the protein and the brush. Standard techniques can in general only probe the total adsorbed amount. The aim of this work was to separate primary and ternary adsorption isotherms, by using neutron reflectivity and deuterated proteins. As neutrons interact differently with hydrogen and deuterium atoms, the contrast between the hydrogenated brush and the deuterated protein is high enough to separate the two contributions.

We studied the adsorption of deuterated myoglobin on PEG brushes with different degrees of polymerisation (N = 56, 146 and 770), and as a function of the area per grafted chain. The contribution of primary and ternary adsorption was separated for the different systems, and the adsorbed amount was extracted and the adsorption isotherms compared to the theoretical predictions. The ability to distinguish between the different adsorption modes, and the quantification of their relative contribution to the overall amount of adsorbed proteins, represents a major advance in optimising surface properties. In particular, the occurrence of ternary adsorption onto PEG brushes affects their status as tool for repressing protein adsorption.

L’adsorption de protéines aux interfaces a un rôle important pour certaines applications pharmaceutiques ou biotechnologiques. En effet, plusieurs processus indésirables sont liés à l’adsorption de protéines, par exemple l’encrassement de lentilles de contact, la coagulation dans des appareils contenant du sang, l’inflammation d’organes artificiels ou encore la diminution du temps de circulation dans le corps de protéines ou liposomes thérapeutiques. Certains polymères, tels que le polyéthylène glycol (PEG), sont utilisés pour réprimer l’adsorption de protéines :en greffant une brosse de PEG sur la surface, une couche est créée entre la protéine et celle-ci qui diminue, voire même réprime complètement l’adsorption. Comprendre le mécanisme qui entrave l’adsorption aux interfaces est un sujet de recherche actif, qui pourrait mener à des améliorations significatives dans la conception de biomatériaux.

À ce jour, la compréhension du mécanisme d’adsorption de protéines sur des brosses de polymère n’est pas claire. Les premiers modèles décrivant les interactions entre brosses de polymères et particules adsorbantes prédisaient deux modes d’adsorption :l’adsorption primaire sur la surface de greffage, et l’adsorption secondaire à l’extérieur de la brosse (pour les grandes protéines cylindriques uniquement). L’adsorption primaire peut-être réprimée en augmentant la densité de greffage de la brosse, et l’adsorption secondaire en augmentant son épaisseur, en accord avec les expériences reportées dans la littérature. Mais d’autres évidences expérimentales (un maximum dans la quantité adsorbée observé pour les brosses longues) ont ensuite suggéré l’existence d’un troisième mode :l’adsorption ternaire à l’intérieur même de la brosse, due aux interactions attractives entre la protéine et la brosse.

Les techniques standards peuvent en général mesurer la quantité adsorbée totale. Le but de ce travail était de séparer les isothermes d’adsorption primaire et ternaire, en utilisant la réflectivité de neutrons et des protéines deutérées. Comme les neutrons interagissent différemment avec les atomes d’hydrogène ou de deutérium, le contraste entre la brosse hydrogénée et la protéine deutérée est ainsi suffisant pour séparer les deux contributions.

Nous avons étudié l’adsorption de myoglobine deutérée sur des brosses de PEG avec différents degrés de polymérisation (N = 56, 146 and 770), en fonction de l’aire par chaîne Σ. La contribution des adsorptions primaire et ternaire put être séparée pour les différents systèmes, et les quantités adsorbées extraites pour finalement comparer les isothermes d’adsorption aux prédictions théoriques. La possibilité de distinguer les différents modes d’adsorption, et la quantification de leur contribution relative à la quantité totale de protéines adsorbées représente une avancée majeure dans l’optimisation des propriétés des surfaces. L’adsorption ternaire dans les brosses de PEG en particulier remet en question leur utilisation pour réprimer l’adsorption de protéines.
Doctorat en Sciences
info:eu-repo/semantics/nonPublished

Cultural evolutionary models that relate spatial and temporal patterning in artifact sequences to human social learning processes and history have made many recent advances. Specifically, these models connect evolutionary forces and social leaning mechanisms along cultural pathways with expectations that can be assessed using material culture. In this dissertation, I use an historical archaeology case study of carved New England gravestones to evaluate three different aspects of cultural transmission and artifact patterns. First, I study the role of social network structure in the transmission of cultural information among carvers organized in workshops that were principally comprised of a carver and his apprentices. The results of this study suggest that the motifs reflect widespread similarity that transcends workshop organization. However, the finer grained decorative elements that make up these motifs correspond with cultural lineages of gravestone carvers. Second, I examine the relationship between the diffusion of innovations and cultural transmission mechanisms that result in spatiotemporal patterning. The spatial patterning suggests that social contagion among consumers created brief instances of wave-like diffusion from a distinct workshop, highlighting the role of consumer choice. A review of probate payments shows that gravestones were rarely purchased from distance sources, as transport costs could be prohibitive. The spatial patterning and historic record suggest that carvers also learned from other carvers creating a hierarchical diffusion process. These two populations created a feedback mechanism that leads to complex emergent phenomena, as illustrated by the rapid and widespread adoption of the cherub motif. Third, the neutral model of stylistic variation is applied to gravestone data to examine the ways that increased consumption and an expanding carving industry led to dominant decorative motifs. This study shows that neutrality can be a fleeting and transitional state between the dominance of single decorative styles. These three studies use New England gravestones to illustrate the evolutionary forces and cultural transmission mechanisms among artifact producers and consumers, which generated the stylistic patterning we observe in the archaeological record.

In recent years, the discontinuous Galerkin (DG) method has been successfully applied to solving hyperbolic conservation laws. Due to its compactness, high order accuracy, and versatility, the DG method has been extensively applied to convection-diffusion problems. In this dissertation, a numerical package, texttt{PHORCE}, is introduced to solve a number of convection-diffusion problems in neutral fluids and plasmas. Unstructured grids are used in order to randomize grid errors, which is especially important for complex geometries. texttt{PHORCE} is written in texttt{C++} and fully parallelized using the texttt{MPI} library. Memory optimization has been considered in this work to achieve improved efficiency. DG algorithms for hyperbolic terms are well studied. However, an accurate and efficient diffusion solver still constitutes ongoing research, especially for a nodal representation of the discontinuous Galerkin (NDG) method. An affine reconstructed discontinuous Galerkin (aRDG) algorithm is developed in this work to solve the diffusive operator using an unstructured NDG method. Unlike other reconstructed/recovery algorithms, all computations can be performed on a reference domain, which promotes efficiency in computation and storage. In addition, to the best of the authors' knowledge, this is the first practical guideline that has been proposed for applying the reconstruction algorithm on a nodal discontinuous Galerkin method. TVB type and WENO type limiters are also studied to deal with numerical oscillations in regions with strong physical gradients in state variables. A high-order positivity-preserving limiter is also extended in this work to prevent negative densities and pressure. A new interface tracking method, mass of fluid (MOF), along with its bound limiter has been proposed in this work to compute the mass fractions of different fluids over time. Hydrodynamic models, such as Euler and Navier-Stokes equations, and plasma models, such as ideal-magnetohydrodynamics (MHD) and two-fluid plasma equations, are studied and benchmarked with various applications using this DG framework. Numerical computations of Rayleigh-Taylor instability growth with experimentally relevant parameters are performed using hydrodynamic and MHD models on planar and radially converging domains. Discussions of the suppression mechanisms of Rayleigh-Taylor instabilities due to magnetic fields, viscosity, resistivity, and thermal conductivity are also included. This work was partially supported by the US Department of Energy under grant number DE-SC0016515. The author acknowledges Advanced Research Computing at Virginia Tech for providing computational resources and technical support that have contributed to the results reported within this work. URL: http://www.arc.vt.edu
Doctor of Philosophy
High-energy density (HED) plasma science is an important area in studying astrophysical phenomena as well as laboratory phenomena such as those applicable to inertial confinement fusion (ICF). ICF plasmas undergo radial compression, with an aim of achieving fusion ignition, and are subject to a number of hydrodynamic instabilities that can significantly alter the implosion and prevent sufficient fusion reactions. An understanding of these instabilities and their mitigation mechanisms is important allow for a stable implosion in ICF experiments. This work aims to provide a high order accurate and robust numerical framework that can be used to study these instabilities through simulations. The first half of this work aims to provide a detailed description of the numerical framework, texttt{PHORCE}. texttt{PHORCE} is a high order numerical package that can be used in solving convection-diffusion problems in neutral fluids and plasmas. Outstanding challenges exist in simulating high energy density (HED) hydrodynamics, where very large gradients exist in density, temperature, and transport coefficients (such as viscosity), and numerical instabilities arise from these region if there is no intervention. These instabilities may lead to inaccurate results or cause simulations to fail, especially for high-order numerical methods. Substantial work has been done in texttt{PHORCE} to improve its robustness in dealing with numerical instabilities. This includes the implementation and design of several high-order limiters. An novel algorithm is also proposed in this work to solve the diffusion term accurately and efficiently, which further enriches the physics that texttt{PHORCE} can investigate. The second half of this work involves rigorous benchmarks and experimentally relevant simulations of hydrodynamic instabilities. Both advection and diffusion solvers are well verified through convergence studies. Hydrodynamic and plasma models implemented are also validated against results in existing literature. Rayleigh-Taylor instability growth with experimentally relevant parameters are performed on both planar and radially converging domains. Although this work is motivated by physics in HED hydrodynamics, the emphasis is placed on numerical models that are generally applicable across a wide variety of fields and disciplines.