407 research outputs found
Close encounters of the cell kind: The impact of contact inhibition on tumour growth and cancer models
Cancer is a complex phenomenon, and the sheer variation in behaviour across different types renders it difficult to ascertain underlying biological mechanisms. Experimental approaches frequently yield conflicting results for myriad reasons, and mathematical modelling of cancer is a vital tool to explore what we cannot readily measure, and ultimately improve treatment and prognosis. Like experiments, models are underpinned by certain biological assumptions, variation of which can lead to divergent predictions. An outstanding and important question concerns contact inhibition of proliferation (CIP), the observation that proliferation ceases when cells are spatially confined by their neighbours. CIP is a characteristic of many healthy adult tissues, but it remains unclear to which extent it holds in solid tumours, which exhibit regions of hyper-proliferation, and apparent breakdown of CIP. What precisely occurs in tumour tissue remains an open question, which mathematical modelling can help shed light on. In this perspective piece, we explore the implications of different hypotheses and available experimental evidence to elucidate the implications of these scenarios. We also outline how erroneous conclusions about the nature of tumour growth may be arrived at by looking selectively at biological data in isolation, and how this might be circumvented
Movement of Coconut Crabs, Birgus latro, in a Rainforest Habitat in Vanuatu
Patterns of movement in the coconut crab, Birgus latro (L.), were
studied using mark-recapture and radio-tracking techniques at a number of
sites in the rainforest regions of eastern Santo, Republic of Vanuatu (South
Pacific). Movement was assessed both for crabs caught and released in one place
(indigenous) and for crabs caught and then released at a new location
(introduced). Recapture rates in eastern Santo were very small ( < I%), whereas
on the small islet sites (area <2 ha) the rate approached 20%. There were no
significant relationships between distance moved and either time at liberty or
size of the individuals for introduced crabs. But for indigenous crabs, size of
individual was negatively correlated with distance moved. Recapture rates of
introduced and indigenous crabs were similar , but introduced crabs moved
significantly further from their point of release. Almost all radio-tagged crabs
moved from their point of release; smaller crabs tended to move further. On
eastern Santo, only two of five radio-tagged crabs were located again ; both had
moved over 250-m away from their release point. On the islet sites, all radiotagged
crabs were found again at least once; some of these returned to a number
of different sites, indicating that B. latro seems to be able to home to particular
locations. Nonetheless, dispersal of animals from an area, at least after handling,
is a common feature
Two-subband electron transport in nonideal quantum wells
Electron transport in nonideal quantum wells (QW) with large-scale variations
of energy levels is studied when two subbands are occupied. Although the mean
fluctuations of these two levels are screened by the in-plane redistribution of
electrons, the energies of both levels remain nonuniform over the plane. The
effect of random inhomogeneities on the classical transport is studied within
the framework of a local response approach for weak disorder. Both short-range
and small-angle scattering mechanisms are considered. Magnetotransport
characteristics and the modulation of the effective conductivity by transverse
voltage are evaluated for different kinds of confinement potentials (hard wall
QW, parabolic QW, and stepped QW).Comment: 10 pages, 6 figure
The Volume of some Non-spherical Horizons and the AdS/CFT Correspondence
We calculate the volumes of a large class of Einstein manifolds, namely
Sasaki-Einstein manifolds which are the bases of Ricci-flat affine cones
described by polynomial embedding relations in C^n. These volumes are important
because they allow us to extend and test the AdS/CFT correspondence. We use
these volumes to extend the central charge calculation of Gubser (1998) to the
generalized conifolds of Gubser, Shatashvili, and Nekrasov (1999). These
volumes also allow one to quantize precisely the D-brane flux of the AdS
supergravity solution. We end by demonstrating a relationship between the
volumes of these Einstein spaces and the number of holomorphic polynomials
(which correspond to chiral primary operators in the field theory dual) on the
corresponding affine cone.Comment: 25 pp, LaTeX, 1 figure, v2: refs adde
A weakly stable algorithm for general Toeplitz systems
We show that a fast algorithm for the QR factorization of a Toeplitz or
Hankel matrix A is weakly stable in the sense that R^T.R is close to A^T.A.
Thus, when the algorithm is used to solve the semi-normal equations R^T.Rx =
A^Tb, we obtain a weakly stable method for the solution of a nonsingular
Toeplitz or Hankel linear system Ax = b. The algorithm also applies to the
solution of the full-rank Toeplitz or Hankel least squares problem.Comment: 17 pages. An old Technical Report with postscript added. For further
details, see http://wwwmaths.anu.edu.au/~brent/pub/pub143.htm
Dibaryon Spectroscopy
The AdS/CFT correspondence relates dibaryons in superconformal gauge theories
to holomorphic curves in Kaehler-Einstein surfaces. The degree of the
holomorphic curves is proportional to the gauge theory conformal dimension of
the dibaryons. Moreover, the number of holomorphic curves should match, in an
appropriately defined sense, the number of dibaryons. Using AdS/CFT backgrounds
built from the generalized conifolds of Gubser, Shatashvili, and Nekrasov
(1999), we show that the gauge theory prediction for the dimension of
dibaryonic operators does indeed match the degree of the corresponding
holomorphic curves. For AdS/CFT backgrounds built from cones over del Pezzo
surfaces, we are able to match the degree of the curves to the conformal
dimension of dibaryons for the n'th del Pezzo surface, n=1,2,...,6. Also, for
the del Pezzos and the A_k type generalized conifolds, for the dibaryons of
smallest conformal dimension, we are able to match the number of holomorphic
curves with the number of possible dibaryon operators from gauge theory.Comment: 30 pages, 6 figures, corrected refs; v3 typos correcte
Job searching with a history of drugs and crime
This article explores the experiences and aspirations of offenders with histories of substance misuse in job searching. The analysis is based upon qualitative data from a localised study of 27 men and two women who were undertaking community-based court orders in Scotland. Their perspectives on job searching, job-readiness and aspirations for sustained employment including the role of self-employment are presented. The article concludes that with adequate support, greater tolerance and flexibility by employers and job searchers could contribute to reducing the vicious cycle of suspicion and dishonesty. Policy action needs to be sustained and possibly augmented to include enterprise training
Extreme Ultra-Violet Spectroscopy of the Lower Solar Atmosphere During Solar Flares
The extreme ultraviolet portion of the solar spectrum contains a wealth of
diagnostic tools for probing the lower solar atmosphere in response to an
injection of energy, particularly during the impulsive phase of solar flares.
These include temperature and density sensitive line ratios, Doppler shifted
emission lines and nonthermal broadening, abundance measurements, differential
emission measure profiles, and continuum temperatures and energetics, among
others. In this paper I shall review some of the advances made in recent years
using these techniques, focusing primarily on studies that have utilized data
from Hinode/EIS and SDO/EVE, while also providing some historical background
and a summary of future spectroscopic instrumentation.Comment: 34 pages, 8 figures. Submitted to Solar Physics as part of the
Topical Issue on Solar and Stellar Flare
Total photoproduction cross-section at very high energy
In this paper we apply to photoproduction total cross-section a model we have
proposed for purely hadronic processes and which is based on QCD mini-jets and
soft gluon re-summation. We compare the predictions of our model with the HERA
data as well as with other models. For cosmic rays, our model predicts
substantially higher cross-sections at TeV energies than models based on
factorization but lower than models based on mini-jets alone, without soft
gluons. We discuss the origin of this difference.Comment: 13 pages, 9 figures. Accepted for publication in EPJC. Changes
concern added references, clarifications of the Soft Gluon Resummation method
used in the paper, and other changes requested by the Journal referee which
do not change the results of the original versio
MultiCellDS : a community-developed standard for curating microenvironment-dependent multicellular data
Exchanging and understanding scientific data and their context represents a significant barrier to advancing research, especially with respect to information siloing. Maintaining information provenance and providing data curation and quality control help overcome common concerns and barriers to the effective sharing of scientific data. To address these problems in and the unique challenges of multicellular systems, we assembled a panel composed of investigators from several disciplines to create the MultiCellular Data Standard (MultiCellDS) with a use-case driven development process. The standard includes (1) digital cell lines, which are analogous to traditional biological cell lines, to record metadata, cellular microenvironment, and cellular phenotype variables of a biological cell line, (2) digital snapshots to consistently record simulation, experimental, and clinical data for multicellular systems, and (3) collections that can logically group digital cell lines and snapshots. We have created a MultiCellular DataBase (MultiCellDB) to store digital snapshots and the 200+ digital cell lines we have generated. MultiCellDS, by having a fixed standard, enables discoverability, extensibility, maintainability, searchability, and sustainability of data, creating biological applicability and clinical utility that permits us to identify upcoming challenges to uplift biology and strategies and therapies for improving human health
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