999 research outputs found
The developmental dynamics of terrorist organizations
We identify robust statistical patterns in the frequency and severity of
violent attacks by terrorist organizations as they grow and age. Using
group-level static and dynamic analyses of terrorist events worldwide from
1968-2008 and a simulation model of organizational dynamics, we show that the
production of violent events tends to accelerate with increasing size and
experience. This coupling of frequency, experience and size arises from a
fundamental positive feedback loop in which attacks lead to growth which leads
to increased production of new attacks. In contrast, event severity is
independent of both size and experience. Thus larger, more experienced
organizations are more deadly because they attack more frequently, not because
their attacks are more deadly, and large events are equally likely to come from
large and small organizations. These results hold across political ideologies
and time, suggesting that the frequency and severity of terrorism may be
constrained by fundamental processes.Comment: 28 pages, 8 figures, 4 tables, supplementary materia
Forecasting in the light of Big Data
Predicting the future state of a system has always been a natural motivation
for science and practical applications. Such a topic, beyond its obvious
technical and societal relevance, is also interesting from a conceptual point
of view. This owes to the fact that forecasting lends itself to two equally
radical, yet opposite methodologies. A reductionist one, based on the first
principles, and the naive inductivist one, based only on data. This latter view
has recently gained some attention in response to the availability of
unprecedented amounts of data and increasingly sophisticated algorithmic
analytic techniques. The purpose of this note is to assess critically the role
of big data in reshaping the key aspects of forecasting and in particular the
claim that bigger data leads to better predictions. Drawing on the
representative example of weather forecasts we argue that this is not generally
the case. We conclude by suggesting that a clever and context-dependent
compromise between modelling and quantitative analysis stands out as the best
forecasting strategy, as anticipated nearly a century ago by Richardson and von
Neumann
A Universal Model of Global Civil Unrest
Civil unrest is a powerful form of collective human dynamics, which has led
to major transitions of societies in modern history. The study of collective
human dynamics, including collective aggression, has been the focus of much
discussion in the context of modeling and identification of universal patterns
of behavior. In contrast, the possibility that civil unrest activities, across
countries and over long time periods, are governed by universal mechanisms has
not been explored. Here, we analyze records of civil unrest of 170 countries
during the period 1919-2008. We demonstrate that the distributions of the
number of unrest events per year are robustly reproduced by a nonlinear,
spatially extended dynamical model, which reflects the spread of civil disorder
between geographic regions connected through social and communication networks.
The results also expose the similarity between global social instability and
the dynamics of natural hazards and epidemics.Comment: 8 pages, 3 figure
ERCC1 expression and RAD51B activity correlate with cell cycle response to platinum drug treatment not DNA repair
Background: The H69CIS200 and H69OX400 cell lines are novel models of low-level platinum-drug resistance. Resistance was not associated with increased cellular glutathione or decreased accumulation of platinum, rather the resistant cell lines have a cell cycle alteration allowing them to rapidly proliferate post drug treatment. Results: A decrease in ERCC1 protein expression and an increase in RAD51B foci activity was observed in association with the platinum induced cell cycle arrest but these changes did not correlate with resistance or altered DNA repair capacity. The H69 cells and resistant cell lines have a p53 mutation and consequently decrease expression of p21 in response to platinum drug treatment, promoting progression of the cell cycle instead of increasing p21 to maintain the arrest.
Conclusion: Decreased ERCC1 protein and increased RAD51B foci may in part be mediating the maintenance of the cell cycle arrest in the sensitive cells. Resistance in the H69CIS200 and H69OX400 cells may therefore involve the regulation of ERCC1 and RAD51B independent of their roles in DNA repair. The novel mechanism of platinum resistance in the H69CIS200 and H69OX400 cells demonstrates the multifactorial nature of platinum resistance which can occur independently of alterations in DNA repair capacity and changes in ERCC1
Macroscopic effects of the spectral structure in turbulent flows
Two aspects of turbulent flows have been the subject of extensive, split
research efforts: macroscopic properties, such as the frictional drag
experienced by a flow past a wall, and the turbulent spectrum. The turbulent
spectrum may be said to represent the fabric of a turbulent state; in practice
it is a power law of exponent \alpha (the "spectral exponent") that gives the
revolving velocity of a turbulent fluctuation (or "eddy") of size s as a
function of s. The link, if any, between macroscopic properties and the
turbulent spectrum remains missing. Might it be found by contrasting the
frictional drag in flows with differing types of spectra? Here we perform
unprecedented measurements of the frictional drag in soap-film flows, where the
spectral exponent \alpha = 3 and compare the results with the frictional drag
in pipe flows, where the spectral exponent \alpha = 5/3. For moderate values of
the Reynolds number Re (a measure of the strength of the turbulence), we find
that in soap-film flows the frictional drag scales as Re^{-1/2}, whereas in
pipe flows the frictional drag scales as Re^{-1/4} . Each of these scalings may
be predicted from the attendant value of \alpha by using a new theory, in which
the frictional drag is explicitly linked to the turbulent spectrum. Our work
indicates that in turbulence, as in continuous phase transitions, macroscopic
properties are governed by the spectral structure of the fluctuations.Comment: 6 pages, 3 figure
Managing Incidental Genomic Findings in Clinical Trials: Fulfillment of the Principle of Justice
<p>Managing Incidental Genomic Findings in Clinical Trials: Fulfillment of the Principle of Justice</p
Family composition and age at menarche: findings from the international Health Behaviour in School-Aged Children Study
This research was funded by The University of St Andrews and NHS Health Scotland.Background Early menarche has been associated with father absence, stepfather presence and adverse health consequences in later life. This article assesses the association of different family compositions with the age at menarche. Pathways are explored which may explain any association between family characteristics and pubertal timing. Methods Cross-sectional, international data on the age at menarche, family structure and covariates (age, psychosomatic complaints, media consumption, physical activity) were collected from the 2009–2010 Health Behaviour in School-aged Children (HBSC) survey. The sample focuses on 15-year old girls comprising 36,175 individuals across 40 countries in Europe and North America (N = 21,075 for age at menarche). The study examined the association of different family characteristics with age at menarche. Regression and path analyses were applied incorporating multilevel techniques to adjust for the nested nature of data within countries. Results Living with mother (Cohen’s d = .12), father (d = .08), brothers (d = .04) and sisters (d = .06) are independently associated with later age at menarche. Living in a foster home (d = −.16), with ‘someone else’ (d = −.11), stepmother (d = −.10) or stepfather (d = −.06) was associated with earlier menarche. Path models show that up to 89% of these effects can be explained through lifestyle and psychological variables. Conclusions Earlier menarche is reported amongst those with living conditions other than a family consisting of two biological parents. This can partly be explained by girls’ higher Body Mass Index in these families which is a biological determinant of early menarche. Lower physical activity and elevated psychosomatic complaints were also more often found in girls in these family environments.Publisher PDFPeer reviewe
Energy- and flux-budget (EFB) turbulence closure model for the stably stratified flows. Part I: Steady-state, homogeneous regimes
We propose a new turbulence closure model based on the budget equations for
the key second moments: turbulent kinetic and potential energies: TKE and TPE
(comprising the turbulent total energy: TTE = TKE + TPE) and vertical turbulent
fluxes of momentum and buoyancy (proportional to potential temperature).
Besides the concept of TTE, we take into account the non-gradient correction to
the traditional buoyancy flux formulation. The proposed model grants the
existence of turbulence at any gradient Richardson number, Ri. Instead of its
critical value separating - as usually assumed - the turbulent and the laminar
regimes, it reveals a transition interval, 0.1< Ri <1, which separates two
regimes of essentially different nature but both turbulent: strong turbulence
at Ri<<1; and weak turbulence, capable of transporting momentum but much less
efficient in transporting heat, at Ri>1. Predictions from this model are
consistent with available data from atmospheric and lab experiments, direct
numerical simulation (DNS) and large-eddy simulation (LES).Comment: 40 pages, 6 figures, Boundary-layer Meteorology, resubmitted, revised
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