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Nuclear medicine uses radioactive pharmaceuticals for diagnostic or therapeutic purposes. The ionizing radiation emitted from the radiopharmaceutical is partially absorbed within the patient's body and internal dosimetry is the method to estimate the absorbed dose to a tumour or risk organ. This is of special importance in radiopharmaceutical therapy (RPT), where particle-emitting radionuclides are utilized for their therapeutic effect. A better understanding of where and to what extent the radiation energy is deposited, i.e. dosimetry, in combination with a better understanding of the irradiation-induced biological processes in tissues and tumours, i.e., radiobiology, is the foundation to establish an absorbed dose-effect relationship. This thesis comprises quantitative methods and modelling within dosimetry and radiobiology, with a special focus on quantitative methods for activity concentration, absorbed dose calculation and quantification of biological effects after nuclear medicine exposures. Nonuniformity of activity distribution and the biological effect of internal irradiation is considered in Paper I and Paper II. When a radiopharmaceutical primarily localizes within specific tissue substructures of an organ, the average absorbed dose to the whole organ may become insufficient for dosimetric analysis. Hence, the nonuniformities of the distribution of activity need to be considered and absorbed dose calculations to part of an organ, cellular, or a sub-cellular structure may be a better predictor of the therapy outcome or normal tissue toxicity. In Paper I, a small-scale anatomical dosimetry model of the liver tissue structure addressed the issue of activity nonuniformity. Monte Carlo simulations were performed to simulate the particle transport from various substructure sources within the organ model for some clinically available radionuclides. The model enabled comparison between the average absorbed dose to the entire organ and the local absorbed dose close to the source region, which for particle emitting radionuclides differed significantly. To address the resulting biological effect after internal irradiation, an ex vivo method using the γH2AX surrogate marker to visualize and quantify DNA double-strand breaks in in vivo-irradiated tissues was developed. The method was demonstrated to be useful for γH2AX-foci quantification in both the fast proliferating, radiosensitive testis tissue and the slow proliferating and more radioresistant liver tissue. Image-based activity quantification and absorbed dose estimation are considered in Paper III and Paper IV, using somatostatin receptor targeting agents for both diagnostic and therapeutic applications for neuroendocrine tumours. In Paper III, the quantitative accuracy of pre-therapeutic 111In-Octreoscan® SPECT/CT and [68Ga]Ga-DOTA-TATE PET/CT images was investigated due to the change in clinical method to use PET- instead of SPECT-imaging. Further, the quantitative relationship between the theragnostic pair of DOTA-TATE was investigated in Paper IV. The relationship between activity uptakes observed at [68Ga]Ga-DOTA-TATE PET imaging and absorbed doses at subsequent [177Lu]Lu-DOTA-TATE therapy was studied. The study demonstrated that on a group level, a higher tumour uptake measured from pretherapeutic PET images is associated with higher absorbed doses in subsequent therapy with [177Lu]Lu-DOTA-TATE. However, on the individual level, there are limitations of using the 68Ga PET as a predictor for therapy absorbed dose.

A hybrid photovoltaic-thermal (PVT) system combines photovoltaic (PV) and photo-thermal (PT) energy collection into a single structure, enhancing the potential to achieve greater solar energy conversion efficiencies. Such enhanced efficiencies can result in greater economic returns and could promote a larger uptake of PVT devices in cold and temperate climate countries. Through the utilization of a Monte Carlo ray-tracing model, this work provides new insights into the optical, electrical, and thermal characteristics of PVT devices. In particular, the work focuses on evaluating the behaviour of novel luminescent imidazole-phenanthroline-based working fluids that were previously experimentally investigated as liquid spectral beam splitters (SBS). The modelling procedure outlined here is able of providing an in-depth analysis of various categories of photons undergoing events such as transmission, absorption, parasitic absorption, and luminescent downshifting (LDS) which, otherwise, are difficult or impossible to detect experimentally. Evaluating such photon characteristics provides the possibility to estimate the direct contribution of the luminophore (embedded within the working fluid) to the enhanced conversion efficiencies reported for PVT systems. In addition, the model can also allow for better tuning of the luminophore properties to match the main factors that are influencing the energy conversion dynamics of these systems. The current results indicate that the embedded luminophore is able of providing direct contributions of up to 91% for thermal power generation and 77% towards electrical power generation for the various concentrations of the liquid filters when compared with the individual performances of the independent PV or PT systems.

Past studies have repeatedly demonstrated the technical feasibility to produce polyhydroxyalkanoate (PHA) using bacterial biomass of mixed microbial cultures (MMCs). Commercial quality grades of poly(3-hydroxybutyrate-co-3-hydroxyvalerate), PHBV, can be produced with control of average monomer composition. However, demonstration of PHBV production and recovery with quality control of molecular weight (MW) distribution has been lacking in the research literature. Towards this goal, a workflow has been developed for characterizing molecular weight control by thermal treatment pre-processing of dried PHA-rich biomass before solvent extraction. Dimethyl carbonate (DMC) was a suitable solvent in this workflow in the routine evaluation of extractable PHA. From assessments of DMC extraction using differential scanning calorimetry, 125 °C was selected for nominally 100 percent extraction yield independent of polymer 3-hydroxyvalerate (3HV) content (2 to 41 wt.% 3HV) and molecular weight (100 to 1400 kDa). Intrinsic viscosity measurements of PHBV in DMC at 60 °C was used for molecular weight monitoring. Mark-Houwink constants, α (0.738 ± 0.010) and LogK (-2.016 ± 0.025), were estimated for a PHBV co-polymer blend having 36 wt.% 3HV. A model of random scission supported that weight average molecular weight (Mw) was a more robust metric, compared to number average molecular weight (Mn), for assessing the polymer scission rates. During isothermal heat treatment for a given biomass batch, interpreted scission rate was reproducible and commonly, but not always, constant in time. Scission rates between biomass batches were also variable. Measured properties of the polymer in the biomass (thermal stability, biomass PHA content, PHBV grade, initial moisture content) could not be correlated to this observed batch-to-batch variation of scission rate. Molecular weight loss before extraction did not influence the melting temperatures of the co-polymer blends of PHBV evaluated over a wide sub-eutectic range of average 3HV content. Molecular weight changes for these PHBV co-polymer blends were considered to have likely influenced the nature of blend 3HV distribution, and consequently, crystallization behaviour. Molecular weight loss effects on crystallization behaviour at constant PHBV average 3HV wt.% content could then have contributed to the observed variability for glass transition temperatures and melting enthalpies. However, a reproducible correlation between this variability and MW change was not observed.

This paper addresses the influence of land topography and cover on 3D radiative effects under cloudless skies in the Hornsund area, Spitsbergen, Svalbard. The authors used Monte Carlo simulations of solar radiation transfer over a heterogeneous surface to study the impact of a non-uniform surface on: (1) the spatial distribution of irradiance transmittance at the fjord surface under cloudless skies; (2) the spectral shortwave aerosol radiative forcing at the fjord surface; (3) normalized nadir radiance at the Top Of the Atmosphere (TOA) over the fjord. The modelled transmittances and radiances over the fjord are compared to the transmittances and radiances over the open ocean under the same conditions. The dependence of the 3D radiative effects on aerosol optical thickness, aerosol type, surface albedo distribution, solar azimuth and zenith angle and spectral channel is discussed. The analysis was done for channels 3 (459-479 nm) and 2 (841-876 nm) of the MODIS radiometer. In the simulations a flat water surface was assumed. The study shows that snow-covered land surrounding the fjord strongly modifies the radiation environment over the fjord surface. The enhancement of the mean irradiance transmittance over the fjord with respect to the open ocean is up to 0.06 for channel 3. The enhancement exceeds 0.11 in the vicinity of sunlit cliffs. The influence of the snow-covered land on the TOA radiance over the fjord in channel 3 is comparable to the impact of an increase in aerosol optical thickness of over 100%, and in lateral fjords of up to several hundred percent. The increase in TOA radiance is wavelength dependent. These effects may affect retrievals of aerosol optical thickness.

Ti-V-based body-centered cubic (BCC) alloys have potential for large-scale hydrogen storage if expensive vanadium is substituted with much cheaper Fe-containing ferrovanadium. Use of ferrovanadium reduces the alloys’ hydrogen storage capacity. This is puzzling since the amount of Fe is low and hydrogen atoms are accommodated in interstitial sites which are partly coordinated by Fe in many intermetallic compounds. The present work is aimed at finding a structural explanation for Fe-induced capacity loss in Ti-V alloys. Since such alloys and their hydrides are highly disordered without long-range occupational order of the different metal species, it was necessary to employ a technique which is sensitive to local structure. Neutron total scattering coupled with reverse Monte Carlo modelling was thus employed to elucidate short-range atomic correlations in Ti0.63V0.27Fe0.10D1.73 from the pair distribution function. It was found that Fe atoms form clusters and that the majority of the vacant interstitial sites are within these clusters. These clusters take the same face-centered cubic structure as the Ti-V matrix in the deuteride and thus they are not simply unreacted Fe which has a BCC structure. The presence of Fe clusters is confirmed by transmission electron microscopy. Density functional theory calculations indicate that the clustering is driven by thermodynamics.

Scintillator based coded-aperture imaging has proven to be effective when applied for X- and gamma-ray detection. Adaptation of the same method for neutron imaging has resulted in a number of propitious systems, which could be potentially employed for neutron detection in security and nuclear decommissioning applications. Recently developed scintillator based coded-aperture imagers reveal that localisation of neutron sources using this technique may be feasible, since pulse shape discrimination algorithms implemented in the digital domain can reliably separate gamma-rays from fast neutron interactions occurring within an organic scintillator. Moreover, recent advancements in the development of solid organic scintillators make them a viable solution for nuclear decommissioning applications as they present less hazardous characteristics than currently dominating liquid scintillation detectors. In this paper existing applications of coded-apertures for radiation detection are critically reviewed, highlighting potential improvements for coded-aperture based neutron source localisation. Further, the suitability of coded-apertures for neutron imaging in nuclear decommissioning is also assessed using Monte-Carlo modelling.

Transport of cellular cargo by molecular motors requires directionality to ensure proper biological functioning. During sporulation in Bacillus subtilis, directionality of chromosome transport is mediated by the interaction between the membrane-bound DNA translocase SpoIIIE and specific octameric sequences (SRS). Whether SRS regulate directionality by recruiting and orienting SpoIIIE or by simply catalyzing its translocation activity is still unclear. By using atomic force microscopy and single-round fast kinetics translocation assays we determined the localization and dynamics of diffusing and translocating SpoIIIE complexes on DNA with or without SRS. Our findings combined with mathematical modelling revealed that SpoIIIE directionality is not regulated by protein recruitment to SRS but rather by a fine-tuned balance among the rates governing SpoIIIE-DNA interactions and the probability of starting translocation modulated by SRS. Additionally, we found that SpoIIIE can start translocation from non-specific DNA, providing an alternative active search mechanism for SRS located beyond the exploratory length defined by 1D diffusion. These findings are relevant in vivo in the context of chromosome transport through an open channel, where SpoIIIE can rapidly explore DNA while directionality is modulated by the probability of translocation initiation upon interaction with SRS versus non-specific DNA., Instituto de Física de Líquidos y Sistemas Biológicos

Paired cosmogenic nuclides are often used to constrain the exposure/burial history of landforms repeatedly covered by ice during the Quaternary, including tors, high-elevation surfaces, and steep alpine summits in the circum-Arctic regions. The approach generally exploits the different production rates and half-lives of 10Be and 26Al to infer past exposure/burial histories. However, the two-stage minimum-limiting exposure and burial model regularly used to interpret the nuclides ignores the effect of variable erosion rates, which potentially may bias the interpretation. In this study, we use a Monte Carlo model approach to investigate systematically how the exposure/burial and erosion history, including variable erosion and the timing of erosion events, influence concentrations of 10Be and 26Al. The results show that low 26Al/10Be ratios are not uniquely associated with prolonged burial under ice, but may as well reflect ice covers that were limited to the coldest part of the late Pleistocene combined with recent exhumation of the sample, e.g. due to glacial plucking during the last glacial period. As an example, we simulate published 26Al/10Be data from Svalbard and show that it is possible that the steep alpine summits experienced ice-free conditions during large parts of the late Pleistocene and varying amounts of glacial erosion. This scenario, which contrasts with the original interpretation of more-or-less continuous burial under non-erosive ice over the last ∼1 Myr, thus challenge the conventional interpretation of such data. On the other hand, high 26Al/10Be ratios do not necessarily reflect limited burial under ice, which is the common interpretation of high ratios. In fact, high 26Al/10Be ratios may also reflect extensive burial under ice, combined with a change from burial under erosive ice, which brought the sample close to the surface, to burial under non-erosive ice at some point during the mid-Pleistocene. Importantly, by allowing for variable erosion rates, the model results may reconcile spatially varying 26Al/10Be data from bedrock surfaces preserved over multiple glacial cycles, suggesting that samples from the same high-elevation surface or neighbouring alpine summits may have experienced similar long-term burial under ice, but varying amounts of glacial erosion.

Comunicação em painel apresentada no E-MRS 2013 - Symposium B, To improve the efficiency of organic solar cells is necessary, for instance, to increase the open-circuit voltage or increase sun-light absorption by covering complementary regions of the solar spectrum. This can be achieved by using a donor-acceptor system composed of two polymers. The versatility of these materials has the advantage of enabling the control of morphology at nanoscale, and thus the design of an adequate interface to improve the device efficiency, using for instance nanoimprint lithography. However, proper control of the molecular organization of both polymers at polymer-polymer interface is difficult and strongly depends on the experimental conditions used. Polymer chains can present different conformations relative to the interface, creating different conjugated strand arrangements whose disorder degree can affect energy and charge transfer. Thus, understanding this effect is of utmost importance to improve the efficiency of excitonic solar cells. In this work we present a Monte Carlo model that uses a proper description of polymer-polymer interface nanomorpholy and considers the main physical processes that mediate excitons and charges dynamics. Our results show that the amount of charge extracted from the interface is sensible to polymer strand orientation and to the presence of the diffusive layer formed by the mixture of both polymers., Fundação para a Ciência e a Tecnologia (FCT)

C L Campbell acknowledges financial support from an UK EPSRC PhD studentship (EP/K503162/1) and the Alfred Stewart Trust. Most existing theoretical models of photodynamic therapy (PDT) assume a uniform initial distribution of the photosensitive molecule, Protoporphyrin IX (PpIX). This is an adequate assumption when the prodrug is systematically administered; however for topical PDT this is no longer a valid assumption. Topical application and subsequent diffusion of the prodrug results in an inhomogeneous distribution of PpIX, especially after short incubation times, prior to light illumination. In this work a theoretical simulation of PDT where the PpIX distribution depends on the incubation time and the treatment modality is described. Three steps of the PpIX production are considered. The first is the distribution of the topically applied prodrug, the second in the conversion from the prodrug to PpIX and the third is the light distribution which affects the PpIX distribution through photobleaching. The light distribution is modelled using a Monte Carlo radiation transfer model and indicates treatment depths of around 2 mm during daylight PDT and approximately 3 mm during conventional PDT. The results suggest that treatment depths are not only limited by the light penetration but also by the PpIX distribution Postprint

C L Campbell acknowledges financial support from an UK EPSRC PhD studentship (EP/K503162/1) and the Alfred Stewart Trust. We explore the effects of three dimensional (3D) tumour structures on depth dependent fluence rates, photodynamic doses (PDD) and fluorescence images through Monte Carlo radiation transfer modelling of photodynamic therapy. The aim with this work was to compare the commonly used uniform tumour densities with non-uniform densities to determine the importance of including 3D models in theoretical investigations. It was found that fractal 3D models resulted in deeper penetration on average of therapeutic radiation and higher PDD. An increase in effective treatment depth of 1 mm was observed for one of the investigated fractal structures, when comparing to the equivalent smooth model. Wide field fluorescence images were simulated, revealing information about the relationship between tumour structure and the appearance of the fluorescence intensity. Our models indicate that the 3D tumour structure strongly affects the spatial distribution of therapeutic light, the PDD and the wide field appearance of surface fluorescence images. Postprint

Introduction: Ireland had one of the highest pharmaceutical spends per capita in the EU in 2012. The General Medical Services (GMS) scheme is the largest community drug scheme in Ireland with approximately 40% of the population eligible for free drugs and appliances in 2012. The total cost of GMS prescriptions increased by 414% between 1998 and 2012. This paper projects Irish GMS cost from 2016 to 2026 and examines the implications of the estimated impact on GMS expenditure. Method: Central Statistics Office (CSO) population projections (2013) and HSE-PCRS GMS population prescription data (2012) were used to develop four variables; population, GMS coverage, average cost per claimant and claims rate. A Monte Carlo Simulation (MCS) model simulated the effect of these four variables on GMS costs, by health board region, age cohort and sex. Results: Irish population is projected to grow by approximately 10% between 2012 and 2026. The over 70s population is estimated to grow by 64% with the proportion of males growing by 72%. GMS expenditure is estimated to increase by 64%, from €1.1 billion in 2016 to €1.8 billion by 2026. Age is a key driver of GMS expenditure, specifically those aged under 11 and over 70. The MCS results project that males, the Mid-Western and South- Eastern regions are driving GMS costs in the under 11s. Females, Midlands and Southern regions are driving GMS costs in the over 70s. Conclusion: Population growth coupled with an aging population will impact future GMS costs. Targeted GMS policy changes such as co-payment charges, reference pricing, and generic substitution can help to contain future GMS expenditure.

This thesis was submitted for the degree of Master of Philosophy and awarded by Brunel University With the increasing of risks in the financial market, the models of risk management are developing quickly. The standard of the accuracy and effect of the models is improved continuously. This thesis investigates Value at Risk (VaR) which is an important method for measuring the market risk. It reviews the three methods which can be used to quantify VaR. These methods are parameter method, historical data processing method and Monte Carlo simulation method. Monte Carlo simulation has been widely employed for finance risk analysis. One challenge in Monte Carlo simulation is its computation complexity. For this purpose, this thesis researches into multithreading technique for high performance.

Because of their high alkalinity, Portland cement (OPC)-based materials may have deleterious effects in an underground waste repository. A solution would be to use low-alkalinity cements (also referred as low-pH cements) generating interstitial solutions with a reduced pH (11 instead of 13.5 for OPC), and thus showing an improved chemical compatibility with the repository environment. In this work, the investigated formulations were based on binary (OPC / silica fume) or ternary (OPC / silica fume / slag or fly ash) blends, with high substitution levels of CEM I (from 30% to 80%). This research project met two main objectives: (i) study the chemical evolution of low-pH cements at 50°C or 80°C, since such temperatures could be encoutered in certain zones of the waste repositories, and (ii) determine the mechanisms of alkali retention by hydrated low-pH cements. (i) Investigation of low-pH cement pastes with ongoing hydration over one year showed that increasing the temperature from 20°C to 80°C accelerated cement hydration and favoured the depletion of portlandite. A lengthening of the C-A-S-H silicate chains was also detected by 27Al and 29Si NMR analyses. Besides, ettringite precipitated at 20°C, but was destabilised at higher temperature. The released sulphates were partly adsorbed on the C-A-S-H and dissolved in the interstitial solution. The pH of this solution was reduced from 1.7 to 2.2 units depending on the formulations. The soluble fractions of alkalis did not significantly change with temperature. Among the five investigated blends, ternary binder T1 (37.5% CEM I, 32.5% silica fume, 30% fly ash) was the only one giving a pore solution pH lower than 11 at 20, 50 and 80°C (curing time of 6 months and 1 year). Its long-term evolution was simulated by model systems reproducing its chemical composition with reactive oxides. At equilibrium, the hydrate assemblage comprised C-A-S-H (Ca/Si and Al/Si ratios of 0.75 and 0.15 respectively), amorphous silica and aluminium hydroxide. It led to a pH of 10.3 at 20°C. (ii) C-A-S-H hydrates played a major role in the retention of alkalis. Sorption of potassium was higher than that of sodium and mainly resulted from electrostatic interactions with C-A-S-H. Monte Carlo modelling of these interactions showed that the difference of solvated radii between these ions could not explain by itself the sorption selectivity experimentally observed., Dans un site de stockage profond de déchets radioactifs, l’utilisation de matériaux à base de ciment Portland en association avec de l’argile pourrait se révéler inadaptée en raison de leur forte alcalinité. Une alternative serait de mettre en œuvre des ciments générant des solutions interstitielles de pH réduit (de l’ordre de 11 au lieu de 13,5 pour un CEM I). Les formulations étudiées dans cette thèse font appel à des ciments composés (également appelés « liant bas pH ») élaborés à partir de mélanges binaires (CEM I / fumée de silice) ou ternaires (CEM I / fumée de silice / cendres volantes ou laitier), avec de forts taux de substitution du CEM I (de 30% à 80%). Le travail réalisé répond à un double objectif : (i) étudier l’évolution chimique des liants bas pH à 50°C ou 80°C, températures qui pourraient être rencontrées dans certaines zones du stockage, et (ii) préciser les mécanismes à l’origine de la bonne rétention des alcalins par ces liants hydratés. (i) Le suivi sur une période d’un an de pâtes de liant bas pH montre que l’accroissement de la température de 20 à 80°C accélère l’hydratation des liants et favorise la consommation de la portlandite. L’allongement et la réticulation des chaînes de silicates des C-A-S-H est mise en évidence par RMN de l’27Al et du 29Si. L’ettringite observée dans les pâtes conservées à 20°C est par ailleurs déstabilisée. Les sulfates ainsi relâchés sont pour partie adsorbés sur les C-A-S-H et dissous dans la solution interstitielle. Le pH de cette dernière est réduit de 1,7 à 2,2 unités selon les formulations. En revanche, les fractions solubles d’alcalins n’évoluent pas de façon importante. Le liant ternaire T1 composé de 37,5% de CEM I, 32,5% de fumée de silice et 30% de cendres volantes est le seul des ciments étudiés à conduire à un pH de solution interstitielle inférieur à 11 aux trois températures considérées (20, 50 et 80°C - échéances 6 mois et 1 an). Son évolution à plus long terme a pu être simulée à l’aide de systèmes modèles reproduisant sa composition chimique à partir d’oxydes réactifs. A l’équilibre thermodynamique, l’assemblage minéralogique est constitué de C-A-S-H (rapports Ca/Si et Al/Si de 0,75 et 0,15 respectivement) ainsi que d’hydroxyde d’aluminium et de silice amorphes, et il impose un pH de 10,3 à 20°C. (ii) Ce sont les C-A-S-H qui jouent le rôle essentiel dans la rétention des alcalins. Le mécanisme mis en jeu est celui d’une compensation des charges négatives des C-A-S-H par interaction électrostatique. Il existe une sélectivité de sorption : le potassium est mieux retenu que le sodium. Celle-ci pourrait être attribuée en première approche à la différence de rayon solvaté entre ces ions. Une modélisation Monte Carlo des interactions électrostatiques entre des particules de C-S-H et un électrolyte contenant des ions sodium et potassium montre cependant que cette hypothèse ne suffit pas à elle seule à expliquer la sélectivité observée expérimentalement.

A near-infrared spectroscopic method and measurement system for moisture depth profiling is presented in this thesis. The measurement system is based on a fibre-optic light source and probes, and a hyperspectral imaging spectrograph. The probes feature six different measurement geometries, including a specular reflection measurement, and diffuse reflection and transmission measurements, all of which are measured in seven positions simultaneously. A theoretical analysis of the depth profiling capabilities of the system is presented, as well as laboratory tests of the system performance. Based on these, the analysis depth of the reflection moisture measurement in a 75 µm thick uncoated paper is estimated to be about 40 µm. It is also shown that the depth profiling properties depend on the average moisture content of the paper, and that the inclusion of a coating layer complicates the depth profiling. The use of the theoretical analysis results in the interpretation of the measurement results is also discussed. As the main application, the measurement system was installed on a pilot-scale paper coating machine. The feasibility of semi-quantitative moisture depth profiling during the coating process is shown. The determination of the first and second critical concentrations of the coating colour consolidation process is also discussed. Detailed results from the extensive programme of trial runs are presented, along with discussion of the physics behind the measurements. It is found that the water transport characteristics measured during the coating process are not in accordance with mass and heat transfer theories in some respects. Also, the specular reflection measurement results do not behave as expected, making the determination of the first critical concentration impossible in some cases. Instead, the second critical concentration is easily detected, but does not always behave as expected. Reasons for the unexpected behaviour of the measurements are discussed, and conclusions drawn about the water transport during the coating process.

This paper estimates the influence of land topography and cover on 3D radiative effects under overcast skies in the Arctic coastal environment, in particular in the Hornsund fjord region, Spitsbergen. The authors focus on the impact of a non-uniform surface on: (1) the spatial distribution of solar fluxes reaching the fjord surface, (2) spectral shortwave cloud radiative forcing at the fjord surface, (3) the solar flux anomaly at the domain surface resulting from the assumption of a uniform surface, i.e. the error due to plane parallel assumptions in climate models, and (4) remote sensing of cloud optical thickness over the fjord. Their dependence on spectral channel, cloud optical thickness, cloud type, cloud base height, surface albedo and solar zenith angle is discussed. The analysis is based on Monte Carlo simulations of solar radiation transfer over a heterogeneous surface for selected channels of the MODIS radiometer. The simulations showed a considerable impact of the land surrounding the fjord on the solar radiation over the fjord. The biggest differences between atmospheric transmittances over the fjord surface and over the ocean were found for a cloud optical thickness τ=12, low solar zenith angle ϑ, high cloud base and snow-covered land. For τ=12, ϑ=53°, cloud base height 1.8km and wavelength λ=469nm, the enhancement in irradiance transmittance over the fjord was 0.19 for the inner fjords and 0.10 for the whole fjord (λ=469nm). The land surrounding the Hornsund fjord also had a considerable impact on the spectral cloud radiative forcing on the fjord surface and the solar flux anomaly at the domain surface due to the uniform surface assumption. For the mouth and central part of the fjord the error due to the use of channel 2 of the MODIS radiometer (λ=858nm) for cloud optical thickness retrieval was 3 for τ=5 and by>5 for τ=20.

Ce papier présente une étude expérimentale et une analyse par simulation Monte-Carlo de Transistors Bipolaires à Hétérojonctions InGaAlAs/InGaAs/InGaAlAs avec et sans espaceurs. Ces espaceurs, destinés à séparer les jonctions électriques et métallurgiques, permettent de diminuer les hauteurs de barrière vues par les électrons tout en conservant celles vues par les trous. L'injection, de nature thermoïonique pour les hétérojonctions abruptes, se fait par effet diffusif lorsque l'on introduit un espaceur, et ainsi le coefficient d'injection est augmenté. D'autre part les espaceurs au collecteur conduisent à une meilleure collection des électrons, cette collection étant facilitée par une injection d'électrons chauds dans le cas d'une hétéro jonction émetteur-base abrupte. Les gains en courant en émetteur commun obtenus sont supérieurs à 100.