Modelling and detecting tumour oxygenation levels.

Tumours that are low in oxygen (hypoxic) tend to be more aggressive and respond less well to treatment. Knowing the spatial distribution of oxygen within a tumour could therefore play an important role in treatment planning, enabling treatment to be targeted in such a way that higher doses of radiation are given to the more radioresistant tissue. Mapping the spatial distribution of oxygen in vivo is difficult. Radioactive tracers that are sensitive to different levels of oxygen are under development and in the early stages of clinical use. The concentration of these tracer chemicals can be detected via positron emission tomography resulting in a time dependent concentration profile known as a tissue activity curve (TAC). Pharmaco-kinetic models have then been used to deduce oxygen concentration from TACs. Some such models have included the fact that the spatial distribution of oxygen is often highly inhomogeneous and some have not. We show that the oxygen distribution has little impact on the form of a TAC; it is only the mean oxygen concentration that matters. This has significant consequences both in terms of the computational power needed, and in the amount of information that can be deduced from TACs

The Extended Overlap Alternate Arm Converter:A Voltage Source Converter with DC Fault Ride-Through Capability and a Compact Design

The Alternate Arm Converter (AAC) was one of the first modular converter topologies to feature DC-side fault ride-through capability with only a small penalty in power efficiency. However, the simple alternation of its arm conduction periods (with an additional short overlap period) resulted in (i) substantial 6-pulse ripples in the DC current waveform, (ii) large DC-side filter requirements, and (iii) limited operating area close to an energy sweet-spot. This paper presents a new mode of operation called Extended Overlap (EO) based on the extension of the overlap period to 60 ◦ which facilitates a fundamental redefinition of the working principles of the AAC. The EO-AAC has its DC current path decoupled from the AC current paths, a fact allowing (i) smooth DC current waveforms, (ii) elimination of DC filters, and (iii) restriction lifting on the feasible operating point. Analysis of this new mode and EO- AAC design criteria are presented and subsequently verified with tests on an experimental prototype. Finally, a comparison with other modular converters demonstrates that the EO-AAC is at least as power efficient as a hybrid MMC (i.e. a DC fault ride-through capable MMC) while offering a smaller converter footprint because of a reduced requirement for energy storage in the submodules and a reduced inductor volume

Tweet valence, volume of abuse, and observers’ dark tetrad personality factors influence victim-blaming and the perceived severity of Twitter cyberabuse

Previous research into Twitter cyberabuse has yielded several findings: victim-blaming (VB) was influenced by victims’ initial tweet-valence; perceived severity (PS) was influenced independently by tweet valence and abuse volume; VB and PS were predicted by observer narcissism and psychopathy. However, this previous research was limited by its narrow focus on celebrity victims, and lack of consideration of observer sadism. The current study investigated 125 observers’ VB and PS perceptions of lay-user cyberabuse, and influence of observers’ Dark Tetrad scores (psychopathy, narcissism, Machiavellianism, sadism). We manipulated initial-tweet valence (negative, neutral, positive) and received abuse volume (low, high). Our results indicated that VB was highest following negative initial tweets; VB was higher following high-volume abuse. PS did not differ across initial-tweet valences; PS was greater following a high abuse volume. Regression analyses revealed that observer sadism predicted VB across initial-tweet valences; psychopathy predicted PS when initial tweets were ‘emotive’ (negative, positive), whereas Machiavellianism predicted PS when they were neutral. Our results show that perceptions of lay-user abuse are influenced interactively by victim-generated content and received abuse volume. Our current results contrast with perceptions of celebrity-abuse, which is mostly determined by victim-generated content. Findings are contextualised within the Warranting Theory of impression formation

Characterisation of ocean island basalt sources : St. Helena

The extrusive and intrusive members of the St. Helena rock suite (SHRS) are formed in an intra-oceanic plate tectonic setting as part of two shield volcanoes. The SHRS vary from picrobasalts to phonofites. The former represent mantle derived melts, whereas the remainder of the suite have undergone differing degrees of crystal fractionation. A stratigraphic framework is developed to illustrate temporal geochemical variations over 2 Ma of subaerial activity. This is accomplished in conjunction with a detailed field study of the SHRS by Baker(1968) which is shown to be largely accurate. It is demonstrated that ascending magma batches are substantially modified by crystal fractionation and subsequent alteration processes. Petrogenetic modelling shows that the genesis of the SHRS is consistent with small degree (1-10%) melting of an olivine - clinopyroxene - orthopyroxene - garnet source containing a residual K-rich phase. Combined Sr-Nd-Pb isotope and fractionation corrected trace element data for fresh rocks enable consideration of changing thermal and chemical fluxes impinging on and interacting with the base of the lithosphere over a period of at least 2 Ma. The existence of two geochemically distinct components in the source region is indicated. A H/MU (high 238U /104Pb)c omponent has extremely radiogenic Pb isotopes (206Pb/104Pb> 20.8) with 143Nd/'44Nd and 87S8r,6 Sr displaced below the mantle array. The complementary depleted component has less radio genic Pb and Sr isotopic compositions and more radio genic Nd compositions. The limited variation of geochemical compositions in the SHRS (caused by mixing of these components) is attributed to the dissimilarity of the components in terms of their trace element abundance and their similarity in terms of ratios of highly incompatible elements. Coupled trace element and isotope variations are evident during the activity of each volcano. During shield development an increase in incompatible trace element enrichment occurs. This is coupled to a decrease in 143Nd/'44Nd, whilst Sr and Pb become progressively more radiogenic. The time dependent variations are thought to be consistent with mixing and melting processes occurring at the base of, or within the lithosphere. A decrease in the signature of the depleted component at the end of activity of the NE volcano and SW volcano is the inferred result of a decreasing thermal flux acting on the base of the lithosphere. With lower heat input less fusion of the depleted component (from the asthenosphere or lithosphere) occurs resulting in an increased H/MU signature in the erupted products through time. Previous explanations for the development of the dominant HIMU component are critically reviewed by considering shared isotope and trace element characteristics for HIMU OIB. U-Th-Pb systematics suggest the HIMU component has remained discrete from other mantle components for approximately 2 Ga. The fractionation event producing the H/MU component is shown to cause an increase in U/Pb and a decrease in Rb/Sr and Th/U.. This is thought to be consistent with a model suggested by Hofmann and White(1980,1982). in which HIMU represents ancient recycled altered oceanic crust. It is demonstrated that other models are less tenable. It is thought that the HIMU characteristics necessitate modification of oceanic crust in subduction zones in addition to the geochemical changes caused by hydrothermal alteration of oceanic crust

The effect of the G1-S transition checkpoint on an age structured cell cycle model.

Knowledge of how a population of cancerous cells progress through the cell cycle is vital if the population is to be treated effectively, as treatment outcome is dependent on the phase distributions of the population. Estimates on the phase distribution may be obtained experimentally however the errors present in these estimates may effect treatment efficacy and planning. If mathematical models are to be used to make accurate, quantitative predictions concerning treatments, whose efficacy is phase dependent, knowledge of the phase distribution is crucial. In this paper it is shown that two different transition rates at the G1-S checkpoint provide a good fit to a growth curve obtained experimentally. However, the different transition functions predict a different phase distribution for the population, but both lying within the bounds of experimental error. Since treatment outcome is effected by the phase distribution of the population this difference may be critical in treatment planning. Using an age-structured population balance approach the cell cycle is modelled with particular emphasis on the G1-S checkpoint. By considering the probability of cells transitioning at the G1-S checkpoint, different transition functions are obtained. A suitable finite difference scheme for the numerical simulation of the model is derived and shown to be stable. The model is then fitted using the different probability transition functions to experimental data and the effects of the different probability transition functions on the model's results are discussed

The effect of the G1-S transition checkpoint on an age structured cell cycle model.

Knowledge of how a population of cancerous cells progress through the cell cycle is vital if the population is to be treated effectively, as treatment outcome is dependent on the phase distributions of the population. Estimates on the phase distribution may be obtained experimentally however the errors present in these estimates may effect treatment efficacy and planning. If mathematical models are to be used to make accurate, quantitative predictions concerning treatments, whose efficacy is phase dependent, knowledge of the phase distribution is crucial. In this paper it is shown that two different transition rates at the G1-S checkpoint provide a good fit to a growth curve obtained experimentally. However, the different transition functions predict a different phase distribution for the population, but both lying within the bounds of experimental error. Since treatment outcome is effected by the phase distribution of the population this difference may be critical in treatment planning. Using an age-structured population balance approach the cell cycle is modelled with particular emphasis on the G1-S checkpoint. By considering the probability of cells transitioning at the G1-S checkpoint, different transition functions are obtained. A suitable finite difference scheme for the numerical simulation of the model is derived and shown to be stable. The model is then fitted using the different probability transition functions to experimental data and the effects of the different probability transition functions on the model's results are discussed

Entrepreneurship and marketing education: time for the road less travelled?

Three dimensions are proposed as a conceptual framework for entrepreneurship education: context, behaviours and process. Entrepreneurship educators have focussed more on the behaviours of entrepreneurs and less on the process of entrepreneurship. In doing so, they have also tended to avoid challenging the context of other disciplines such as marketing. If however we examine important aspects of marketing through the behaviours of entrepreneurs, we find that they do not conform to the standard concepts of marketing as portrayed in widely used learning materials. The increasingly well travelled �pragmatic� road, which encourages the development of enterprising behaviours ands kills, is contrasted with the less travelled �conceptual� road, where our understanding of the phenomenon of entrepreneurship in contexts such as marketing, is challenged and explained. We suggest that unlike the poet�s �traveller� � who cannot take both roads entrepreneurship education can benefit most by reaching the fork in the road and taking it