231 research outputs found
Numerical treatment of the Filament Based Lamellipodium Model (FBLM)
We describe in this work the numerical treatment of the Filament Based
Lamellipodium Model (FBLM). The model itself is a two-phase two-dimensional
continuum model, describing the dynamics of two interacting families of locally
parallel F-actin filaments. It includes, among others, the bending stiffness of
the filaments, adhesion to the substrate, and the cross-links connecting the
two families. The numerical method proposed is a Finite Element Method (FEM)
developed specifically for the needs of these problem. It is comprised of
composite Lagrange-Hermite two dimensional elements defined over two
dimensional space. We present some elements of the FEM and emphasise in the
numerical treatment of the more complex terms. We also present novel numerical
simulations and compare to in-vitro experiments of moving cells
A Density Spike on Astrophysical Scales from an N-Field Waterfall Transition
Hybrid inflation models are especially interesting as they lead to a spike in
the density power spectrum on small scales, compared to the CMB, while also
satisfying current bounds on tensor modes. Here we study hybrid inflation with
waterfall fields sharing a global symmetry. The inclusion of many
waterfall fields has the obvious advantage of avoiding topologically stable
defects for . We find that it also has another advantage: it is easier to
engineer models that can simultaneously (i) be compatible with constraints on
the primordial spectral index, which tends to otherwise disfavor hybrid models,
and (ii) produce a spike on astrophysically large length scales. The latter may
have significant consequences, possibly seeding the formation of
astrophysically large black holes. We calculate correlation functions of the
time-delay, a measure of density perturbations, produced by the waterfall
fields, as a convergent power series in both and the field's correlation
function . We show that for large , the two-point function is
and the
three-point function is .
In accordance with the central limit theorem, the density perturbations on the
scale of the spike are Gaussian for large and non-Gaussian for small .Comment: 15 pages in double column format, 6 figures. V2: Further
clarifications, updated to coincide with version published in Physics Letters
A behavioral analysis of Greek strike activity
This work deals with the analysis of Greek strike activity during the period 1975-1994
based on the data collected by the National Statistical Service of Greece. The work is distinguished into two parts as follows: a. For the industry sector, b. For all the sectors.
Conventional strike equations are specified and estimated using the data for all strikes
and the effects of the explanatory variables are compared. The study includes several explanatory
variables, which have been used by many investigators of strikes. To analyze the
aforementioned data, the ARIMA procedure was also used to estimate and forecast models
using the methods prescribed by Box and Jenkins (1976). The logarithmic transformation
of the data has demonstrated a better behavior of the respective models, fact that it was
expected since in a previous work, which was presented in the Fourth Statistical Conference
of Greece in Patras 1991, the goodness of fit of the data in the lognormal distribution
has been proved.peer-reviewe
A hybrid multiscale model for cancer invasion of the extracellular matrix
The ability to locally degrade the extracellular matrix (ECM) and interact with the tumour microenvironment is a key process distinguishing cancer from normal cells, and is a critical step in the metastatic spread of the tumour. The invasion of the surrounding tissue involves the coordinated action between cancer cells, the ECM, the matrix degrading enzymes, and the epithelialto-mesenchymal transition. This is a regulatory process through which epithelial cells (ECs) acquire mesenchymal characteristics and transform to mesenchymal-like cells (MCs). In this paper, we present a new mathematical model which describes the transition from a collective invasion strategy for the ECs to an individual invasion strategy for the MCs. We achieve this by formulating a coupled hybrid system consisting of partial and stochastic di erential equations that describe the evolution of the ECs and the MCs, respectively. This approach allows one to reproduce in a very natural way fundamental qualitative features of the current biomedical understanding of cancer invasion that are not easily captured by classical modelling approaches, for example, the invasion of the ECM by self-generated gradients and the appearance of EC invasion islands outside of the main body of the tumour
Mathematical modelling of cancer invasion : phenotypic transitioning provides insight into multifocal foci formation
Funding: Z. Szymańska acknowledge the support from the National Science Centre, Poland – grant No. 2017/26/M/ST1/00783. N. Sfakianaki’s scientific visit to the University of Warsaw was partially supported by the Excellence Initiative Research University Programme at the University of Warsaw. M. Lachowicz is happy to acknowledge the support from the New Ideas Grant - ”Równania kinetyczne w opisie zjawisk samoorganizacji” funded by the Excellence Initiative Research University Programme at the University of Warsaw.The transition from the epithelial to mesenchymal phenotype and its reverse (from mesenchymal to epithelial) are crucial processes necessary for the progression and spread of cancer. In this paper, we investigate how phenotypic switching at the cancer cell level impacts on behaviour at the tissue level, specifically on the emergence of isolated foci of the invading solid tumour mass leading to a multifocal tumour. To this end, we propose a new mathematical model of cancer invasion that includes the influence of cancer cell phenotype on the rate of invasion and metastasis. The implications of model are explored through numerical simulations revealing that the plasticity of tumour cell phenotypes appears to be crucial for disease progression and local invasive spread. The computational simulations show the progression of the invasive spread of a primary cancer reminiscent of in vivo multifocal breast carcinomas, where multiple, synchronous, ipsilateral neoplastic foci are frequently observed and are associated with a poorer patient prognosis.Publisher PDFPeer reviewe
Encore: Lightweight Measurement of Web Censorship with Cross-Origin Requests
Despite the pervasiveness of Internet censorship, we have scant data on its
extent, mechanisms, and evolution. Measuring censorship is challenging: it
requires continual measurement of reachability to many target sites from
diverse vantage points. Amassing suitable vantage points for longitudinal
measurement is difficult; existing systems have achieved only small,
short-lived deployments. We observe, however, that most Internet users access
content via Web browsers, and the very nature of Web site design allows
browsers to make requests to domains with different origins than the main Web
page. We present Encore, a system that harnesses cross-origin requests to
measure Web filtering from a diverse set of vantage points without requiring
users to install custom software, enabling longitudinal measurements from many
vantage points. We explain how Encore induces Web clients to perform
cross-origin requests that measure Web filtering, design a distributed platform
for scheduling and collecting these measurements, show the feasibility of a
global-scale deployment with a pilot study and an analysis of potentially
censored Web content, identify several cases of filtering in six months of
measurements, and discuss ethical concerns that would arise with widespread
deployment
Developing a European grid infrastructure for cancer research: vision, architecture and services
Life sciences are currently at the centre of an information revolution. The nature and amount of information now available opens up areas of research that were once in the realm of science fiction. During this information revolution, the data-gathering capabilities have greatly surpassed the data-analysis techniques. Data integration across heterogeneous data sources and data aggregation across different aspects of the biomedical spectrum, therefore, is at the centre of current biomedical and pharmaceutical R&D
No-boundary measure and preference for large e-foldings in multi-field inflation
The no-boundary wave function of quantum gravity usually assigns only very
small probability to long periods of inflation. This was a reason to doubt
about the no-boundary wave function to explain the observational universe. We
study the no-boundary proposal in the context of multi-field inflation to see
whether the number of fields changes the situation. For a simple model, we find
that indeed the no-boundary wave function can give higher probability for
sufficient inflation, but the number of fields involved has to be very high.Comment: 16 pages, 2 figure
Non-invasive predictors of axillary lymph node burden in breast cancer: a single-institution retrospective analysis
Purpose: Axillary staging is an important prognostic factor in breast cancer. Sentinel lymph node biopsy (SNB) is currently used to stage patients who are clinically and radiologically node-negative. Since the establishment that axillary node clearance (ANC) does not improve overall survival in breast-conserving surgery for patients with low-risk biological cancers, axillary management has become increasingly conservative. This study aims to identify and assess the clinical predictive value of variables that could play a role in the quantification of axillary burden, including the accuracy of quantifying abnormal axillary nodes on ultrasound. Methods: A retrospective analysis was conducted of hospital data for female breast cancer patients receiving an ANC at our centre between January 2018 and January 2020. The reference standard for axillary burden was surgical histology following SNB and ANC, allowing categorisation of the patients under ‘low axillary burden’ (2 or fewer pathological macrometastases) or ‘high axillary burden’ (> 2). After exploratory univariate analysis, multivariate logistic regression was conducted to determine relationships between the outcome category and candidate predictor variables: patient age at diagnosis, tumour focality, tumour size on ultrasound and number of abnormal lymph nodes on axillary ultrasound. Results: One hundred and thirty-five patients were included in the analysis. Logistic regression showed that the number of abnormal lymph nodes on axillary ultrasound was the strongest predictor of axillary burden and statistically significant (P = 0.044), with a sensitivity of 66.7% and specificity of 86.8% (P = 0.011). Conclusion: Identifying the number of abnormal lymph nodes on preoperative ultrasound can help to quantify axillary nodal burden and identify patients with high axillary burden, and should be documented as standard in axillary ultrasound reports of patients with breast cancer
Further investigation of confirmed urinary tract infection (UTI) in children under five years: a systematic review.
Background: Further investigation of confirmed UTI in children aims to prevent renal scarring and future complications. Methods: We conducted a systematic review to determine the most effective approach to the further investigation of confirmed urinary tract infection (UTI) in children under five years of age. Results: 73 studies were included. Many studies had methodological limitations or were poorly reported. Effectiveness of further investigations: One study found that routine imaging did not lead to a reduction in recurrent UTIs or renal scarring. Diagnostic accuracy: The studies do not support the use of less invasive tests such as ultrasound as an alternative to renal scintigraphy, either to rule out infection of the upper urinary tract (LR- = 0.57, 95%CI: 0.47, 0.68) and thus to exclude patients from further investigation or to detect renal scarring (LR+ = 3.5, 95% CI: 2.5, 4.8). None of the tests investigated can accurately predict the development of renal scarring. The available evidence supports the consideration of contrast-enhanced ultrasound techniques for detecting vesico-ureteric reflux (VUR), as an alternative to micturating cystourethrography (MCUG) (LR+ = 14.1, 95% CI: 9.5, 20.8; LR- = 0.20, 95%CI: 0.13, 0.29); these techniques have the advantage of not requiring exposure to ionising radiation. Conclusion: There is no evidence to support the clinical effectiveness of routine investigation of children with confirmed UTI. Primary research on the effectiveness, in terms of improved patient outcome, of testing at all stages in the investigation of confirmed urinary tract infection is urgently required
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