681 research outputs found
More Than 50 Subtypes of Soft Tissue Sarcoma: Paving the Path for Histology-Driven Treatments
No full text Sarcomas are a diverse group of cancers with mesenchymal origin. Although sarcomas comprise less than 1% of cancers, there are more than 50 different subtypes that are quite different from one another in terms of both their biology and clinical behavior. Historically, the need for adequate patient numbers in clinical trials has pushed sarcoma researchers to lump these very different malignancies together and treat the patients using a “one-size-fits-all” approach. However, with improvements in our scientific understanding, we are finally ready for a histology-tailored therapeutic approach to these complex diseases. In this review, we discuss key advances in our understanding of the biology underlying selected sarcoma subtypes and how targeting these subtypes is relevant therapeutically with respect to both molecularly targeted agents as well as immunotherapy. </jats:p
Uncertainty principles connected with the Mobius inversion formula
No full textWe say that two arithmetic functions and form a \emph{M\"{o}bius pair} if for all natural numbers . In that case, can be expressed in terms of by the familiar M\"{o}bius inversion formula of elementary number theory. In a previous paper, the first-named author showed that if the members and of a M\"{o}bius pair are both finitely supported, then both functions vanish identically. Here we prove two significantly stronger versions of this uncertainty principle. A corollary of our results is that in a nonzero M\"{o}bius pair, one cannot have both $\sum_{f(n) \neq 0}\frac{1}{n
Levins and the lure of artificial worlds
No full textWhat is it about simulation models that has led some practitioners to treat them as potential sources of empirical data on the real-world systems being simulated; that is, to treat simulations as ‘artificial worlds’ within which to perform computational ‘experiments’? Here we use the work of Richard Levins as a starting point in identifying the appeal of this model building strategy, and proceed to account for why this appeal is strongest for computational modellers. This analysis suggests a perspective on simulation modelling that makes room for ‘artificial worlds’ as legitimate science without having to accept that they should be treated as sources of empirical dat
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On the Fourier-Jacobi Expansion of Quaternionic Modular Forms on Spin(8)
No full textIn this dissertation, we study a class of non-holomorphic, cohomological automorphic functions on the split, simply connected, spin group G=Spin(4,4). Following ideas of Gross-Wallach, Gan-Gross-Savin, M. Weissman, and A. Pollack, we term these automorphic functions quaternionic modular forms on G, and analyze a theory of scalar-valued Fourier coefficients associated to them. Our results build parallels between the theory of quaternionic modular forms on G, and the arithmetically rich theory of genus two Siegel modular forms. The main result states that a level one quaternionic modular form on G is determined by its primitive Fourier coefficients. As an input to this result, we develop a theory of Fourier-Jacobi expansions for quaternionic modular forms, in which the non-degenerate coefficients are themselves genus two Siegel modular forms. Our primary application strengthens earlier joint work of the author with J. Johnson-Leung, I. Negrini, M. Roy, and A. Pollack. More precisely, in this dissertation we show that the level one quaternionic modular forms on SO(4,4) that arise as theta lifts from Sp(4) admit an elementary Fourier coefficient theoretic characterization, which is akin to a characterization of the classical Saito-Kurokawa subspace proven by D. Zagier
The role of logistic constraints on termite construction of chambers and tunnels
No full textIn previous models of the building behaviour of termites, physical and logistic constraints that limit the movement of termites andpheromones have been neglected. Here, we present an individual-based mo del of termite construction that includes idealized constraints on the diffusion of pheromones, the movement of termites, and the integrity of the architecture that they construct. The model allows us to explore the extent to which the results of previous idealized models (typically realised in one or two dimensions via a set of coupled partial differential equations) generalize to a physical, 3-D environment. Moreover we are able to investigate new processes and architectures that rely upon these features. We explore the role of stigmergic recruitment in pillar formation, wall building, and the construction of royal chambers, tunnels and intersections. In addition, for the first time, we demonstrate the way in which the physicality of partially built structures can help termites to achieve efficient tunnel structures and to establish and maintain entrances in royal chambers. As such we show that, in at least some cases, logistic constraints can be important or even necessary in order for termites to achieve efficient, effective constructions
Empiricism in artificial life
No full textStrong artificial life research is often thought to rely on Alife systems as sources of novel empirical data. It is hoped that by augmenting our observations of natural life, this novel data can help settle empirical questions, and thereby separate fundamental properties of living systems from those aspects that are merely contingent on the idiosyncrasies of terrestrial evolution. Some authors have questioned whether this approach can be pursued soundly in the absence of a prior, agreed-upon definition of life. Here we compare Alife’s position to that of more orthodox empirical tools that nevertheless suffer from strong theory-dependence. Drawing on these examples, we consider what kind of justification might be needed to underwrite artificial life as empirical enquir
Combating coevolutionary disengagement by reducing parasite virulence
No full textWhile standard evolutionary algorithms employ a static, absolute fitness metric, coevolutionary algorithms assess individuals by their performance relative to populations of opponents that are themselves evolving. Although this arrangement offers the possibility of avoiding long-standing difficulties such as premature convergence, it suffers from its own unique problems, cycling, over-focusing and disengagement. Here, we introduce a novel technique for dealing with the third and least explored of these problems. Inspired by studies of natural host-parasite systems, we show that disengagement can be avoided by selecting for individuals that exhibit reduced levels of "virulence", rather than maximum ability to defeat coevolutionary adversaries. Experiments in both simple and complex domains are used to explain how this counterintuitive approach may be used to improve the success of coevolutionary algorithms
Wasps, termites and waspmites: Distinguishing competence from performance in collective construction
No full textWe introduce a distinction between algorithm performance and algorithm competence and argue that bio-inpsired computing should characterise the former rather than the latter. To exemplify this, we explore and extend a bio-inspired algorithm for collective construction influenced by paper wasp behaviour. Despite being provably general in its competence we demonstrate limitations on the algorithm's performance. We explain these limitations, and extend the algorithm to include pheromone-mediated behaviour typical of termites. The resulting hybrid "waspmite" algorithm shares the generality of the original wasp algorithm, but exhibits improved performance and scalability
Logistic constraints on 3D termite construction
No full textAbstract. The building behaviour of termites has previously been modelled mathematically in two dimensions. However, physical and logistic constraints were not taken into account in these models. Here, we develop and test a three-dimensional agent-based model of this process that places realistic constraints on the diffusion of pheromones, the movement of termites, and the integrity of the architecture that they construct. The following scenarios are modelled: the use of a pheromone template in the construction of a simple royal chamber, the effect of wind on this process, and the construction of covered pathways. We consider the role of the third dimension and the effect of logistic constraints on termite behaviour and, reciprocally, the structures that they create. For instance, when agents find it difficult to reach some elevated or exterior areas of the growing structure, building proceeds at a reduced rate in these areas, ultimately influencing the range of termite-buildable architectures
The long-wavelength view of GG Tau A: rocks in the ring world
No full textWe present the first detection of GG Tau A at centimetre wavelengths, made with the Arcminute Microkelvin Imager Large Array at a frequency of 16 GHz (λ = 1.8 cm). The source is detected at >6 σrms with an integrated flux density of S16GHz = 249 ± 45 µJy. We use these new centimetre-wave data, in conjunction with additional measurements compiled from the literature, to investigate the long-wavelength tail of the dust emission from this unusual protoplanetary system. We use an MCMC-based method to determine maximum likelihood parameters for a simple parametric spectral model and consider the opacity and mass of the dust contributing to the microwave emission. We derive a dust mass of Md ~ 0.1 Msun, constrain the dimensions of the emitting region and find that the opacity index at λ > 7 mm is less than unity, implying a contribution to the dust population from grains exceeding ~4 cm in size. We suggest that this indicates coagulation within the GG Tau A system has proceeded to the point where dust grains have grown to the size of small rocks with dimensions of a few centimetres. Considering the relatively young age of the GG Tau association in combination with the low derived disc mass, we suggest that this system may provide a useful test case for rapid core accretion planet formation models
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