A multiphase model describing vascular tumour growth

In this paper we present a new model framework for studying vascular tumour growth, in which the blood vessel density is explicitly considered. Our continuum model comprises conservation of mass and momentum equations for the volume fractions of tumour cells, extracellular material and blood vessels. We include the physical mechanisms that we believe to be dominant, namely birth and death of tumour cells, supply and removal of extracellular fluid via the blood and lymph drainage vessels, angiogenesis and blood vessel occlusion. We suppose that the tumour cells move in order to relieve the increase in mechanical stress caused by their proliferation. We show how to reduce the model to a system of coupled partial differential equations for the volume fraction of tumour cells and blood vessels and the phase averaged velocity of the mixture. We consider possible parameter regimes of the resulting model. We solve the equations numerically in these cases, and discuss the resulting behaviour. The model is able to reproduce tumour structure that is found `in vivo' in certain cases. Our framework can be easily modified to incorporate the effect of other phases, or to include the effect of drugs

The population of propellers in Saturn's A Ring

We present an extensive data set of ~150 localized features from Cassini images of Saturn's Ring A, a third of which are demonstrated to be persistent by their appearance in multiple images, and half of which are resolved well enough to reveal a characteristic "propeller" shape. We interpret these features as the signatures of small moonlets embedded within the ring, with diameters between 40 and 500 meters. The lack of significant brightening at high phase angle indicates that they are likely composed primarily of macroscopic particles, rather than dust. With the exception of two features found exterior to the Encke Gap, these objects are concentrated entirely within three narrow (~1000 km) bands in the mid-A Ring that happen to be free from local disturbances from strong density waves. However, other nearby regions are similarly free of major disturbances but contain no propellers. It is unclear whether these bands are due to specific events in which a parent body or bodies broke up into the current moonlets, or whether a larger initial moonlet population has been sculpted into bands by other ring processes.Comment: 31 pages, 10 figures; Accepted at A

Microwave resonance of the reentrant insulating quantum Hall phases in the 1st excited Landau Level

We present measurements of the real diagonal microwave conductivity of the reentrant insulating quantum Hall phases in the first excited Landau level at temperatures below 50 mK. A resonance is detected around filling factor $\nu=2.58$ and weaker frequency dependence is seen at $\nu=2.42$ and 2.28. These measurements are consistent with the formation of a bubble phase crystal centered around these $\nu$ at very low temperatures

Ion-ion dynamic structure factor, acoustic modes and equation of state of two-temperature warm dense aluminum

The ion-ion dynamical structure factor and the equation of state of warm dense aluminum in a two-temperature quasi-equilibrium state, with the electron temperature higher than the ion temperature, are investigated using molecular-dynamics simulations based on ion-ion pair potentials constructed from a neutral pseudoatom model. Such pair potentials based on density functional theory are parameter-free and depend directly on the electron temperature and indirectly on the ion temperature, enabling efficient computation of two-temperature properties. Comparison with ab initio simulations and with other average-atom calculations for equilibrium aluminum shows good agreement, justifying a study of quasi-equilibrium situations. Analyzing the van Hove function, we find that ion-ion correlations vanish in a time significantly smaller than the electron-ion relaxation time so that dynamical properties have a physical meaning for the quasi-equilibrium state. A significant increase in the speed of sound is predicted from the modification of the dispersion relation of the ion acoustic mode as the electron temperature is increased. The two-temperature equation of state including the free energy, internal energy and pressure is also presented

Isochoric, isobaric and ultrafast conductivities of aluminum, lithium and carbon in the warm dense matter (WDM) regime

We study the conductivities $\sigma$ of (i) the equilibrium isochoric state ($\sigma_{\rm is}$), (ii) the equilibrium isobaric state ($\sigma_{\rm ib}$), and also the (iii) non-equilibrium ultrafast matter (UFM) state ($\sigma_{\rm uf}$) with the ion temperature $T_i$ less than the the electron temperature $T_e$. Aluminum, lithium and carbon are considered, being increasingly complex warm dense matter (WDM) systems, with carbon having transient covalent bonds. First-principles calculations, i.e., neutral-pseudoatom (NPA) calculations and density-functional theory (DFT) with molecular-dynamics (MD) simulations, are compared where possible with experimental data to characterize $\sigma_{\rm ic}, \sigma_{\rm ib}$ and $\sigma_{\rm uf}$. The NPA $\sigma_{\rm ib}$ are closest to the available experimental data when compared to results from DFT+MD, where simulations of about 64-125 atoms are typically used. The published conductivities for Li are reviewed and the value at a temperature of 4.5 eV is examined using supporting X-ray Thomson scattering calculations. A physical picture of the variations of $\sigma$ with temperature and density applicable to these materials is given. The insensitivity of $\sigma$ to $T_e$ below 10 eV for carbon, compared to Al and Li, is clarified.Comment: 10 figure

Pilot interaction with automated airborne decision making systems

Two project areas were pursued: the intelligent cockpit and human problem solving. The first area involves an investigation of the use of advanced software engineering methods to aid aircraft crews in procedure selection and execution. The second area is focused on human problem solving in dynamic environments, particulary in terms of identification of rule-based models land alternative approaches to training and aiding. Progress in each area is discussed

Paradoxical Leadership to Enable Strategic Agility

Strategic agility evokes contradictions, such as stability-flexibility, commitment-change, and established routines-novel approaches. These competing demands pose challenges that require paradoxical leadership—practices seeking creative, both/and solutions that can enable fast-paced, adaptable decision making. Why is managing paradox critical to strategic agility? And which practices enable leaders to effectively manage tensions? This article describes the paradoxical nature of strategic agility. Drawing from data from five firms, Astro Studios, Digital Divide Data, IBM Global Services Canada, Lego, and Unilever, it proposes leadership practices to effectively respond to these challenges