2,395 research outputs found
Weakly nonlocal fluid mechanics - the Schrodinger equation
A weakly nonlocal extension of ideal fluid dynamics is derived from the
Second Law of thermodynamics. It is proved that in the reversible limit the
additional pressure term can be derived from a potential. The requirement of
the additivity of the specific entropy function determines the quantum
potential uniquely. The relation to other known derivations of Schr\"odinger
equation (stochastic, Fisher information, exact uncertainty) is clarified.Comment: major extension and revisio
Treatment of missing data in Bayesian network structure learning : an application to linked biomedical and social survey data
The authors acknowledge the Research/Scientific Computing teams at The James Hutton Institute and NIAB for providing computational resources and technical support for the âUKâs Crop Diversity Bioinformatics HPCâ (BBSRC grant BB/S019669/1), use of which has contributed to the results reported within this paper. Access to this was provided via the University of St Andrews Bioinformatics Unit which is funded by a Wellcome Trust ISSF award (grant 105621/Z/14/Z and 204821/Z/16/Z). XK was supported by a World-Leading PhD Scholarship from St Leonardâs Postgraduate School of the University of St Andrews. VAS and KK were partially supported by HATUA, The Holistic Approach to Unravel Antibacterial Resistance in East Africa, a three-year Global Context Consortia Award (MR/S004785/1) funded by the National Institute for Health Research, Medical Research Council and the Department of Health and Social Care. KK is supported by the Academy of Medical Sciences, the Wellcome Trust, the Government Department of Business, Energy and Industrial Strategy, the British Heart Foundation Diabetes UK, and the Global Challenges Research Fund [Grant number SBF004\1093]. KK is additionally supported by the Economic and Social Research Council HIGHLIGHT CPC- Connecting Generations Centre [Grant number ES/W002116/1].Background Availability of linked biomedical and social science data has risen dramatically in past decades, facilitating holistic and systems-based analyses. Among these, Bayesian networks have great potential to tackle complex interdisciplinary problems, because they can easily model inter-relations between variables. They work by encoding conditional independence relationships discovered via advanced inference algorithms. One challenge is dealing with missing data, ubiquitous in survey or biomedical datasets. Missing data is rarely addressed in an advanced way in Bayesian networks; the most common approach is to discard all samples containing missing measurements. This can lead to biased estimates. Here, we examine how Bayesian network structure learning can incorporate missing data. Methods We use a simulation approach to compare a commonly used method in frequentist statistics, multiple imputation by chained equations (MICE), with one specific for Bayesian network learning, structural expectation-maximization (SEM). We simulate multiple incomplete categorical (discrete) data sets with different missingness mechanisms, variable numbers, data amount, and missingness proportions. We evaluate performance of MICE and SEM in capturing network structure. We then apply SEM combined with community analysis to a real-world dataset of linked biomedical and social data to investigate associations between socio-demographic factors and multiple chronic conditions in the US elderly population. Results We find that applying either method (MICE or SEM) provides better structure recovery than doing nothing, and SEM in general outperforms MICE. This finding is robust across missingness mechanisms, variable numbers, data amount and missingness proportions. We also find that imputed data from SEM is more accurate than from MICE. Our real-world application recovers known inter-relationships among socio-demographic factors and common multimorbidities. This network analysis also highlights potential areas of investigation, such as links between cancer and cognitive impairment and disconnect between self-assessed memory decline and standard cognitive impairment measurement. Conclusion Our simulation results suggest taking advantage of the additional information provided by network structure during SEM improves the performance of Bayesian networks; this might be especially useful for social science and other interdisciplinary analyses. Our case study show that comorbidities of different diseases interact with each other and are closely associated with socio-demographic factors.PostprintPublisher PDFPeer reviewe
Low energy neutron propagation in MCNPX and GEANT4
Simulations of neutron background from rock for underground experiments are
presented. Neutron propagation through two types of rock, lead and hydrocarbon
material is discussed. The results show a reasonably good agreement between
GEANT4, MCNPX and GEANT3 in transporting low-energy neutrons.Comment: 9 Figure
Pausanias in Athens: an archaeological commentary on the Agora of Athens
Pausanias' eye-witness description of Greece has been used as an essential tool by
scholars and laymen alike to clarify Greek sites to explain archaeological findings. This
commentary analyses what Pausanias described, and reassesses his work in the light of
new evidence and arguments. Thus the process is reversed, archaeology is taken to
Pausanias, which regularly verifies his account. This method has resulted in possible
answers to some outstanding archaeological problems: such as the location of the
Enneakrounos as well as the Aphrodite Ourania sanctuary. In the same way, just
analysing the language Pausanias uses alongside the archaeological record, possible
solutions can be found to questions unanswered so far by archaeology alone, for instance
the position of the Eleusinion. By analysing other ancient sources in conjunction with
Pausanias' description it appears that the exact area the name Kerameikos covered
changed in different periods. Also a virtual 'silence' in his text may reveal the location of
the long lost Leokoreion. Since arguably the most important artefacts to come from the
ancient world are inscriptions, the weight of epigraphical evidence used in such a
commentary should reflect this wherever possible. There are also photographs and line
drawings of relevant architectural elements, foundations, monuments, sculpture, plans
and inscriptions. The proposed route possibly taken by Pausanias is illustrated, which
combined with the interdisciplinary material covered in this thesis allow access not only
to Pausanias' description but also to the site of the Agora itself
KinoCuban: the significance of Soviet and East European cinemas for the Cuban moving image
Kinocuban: the significance of Soviet and East European cinemas for the Cuban moving image examines a piece of evidence that has been misunderstood in the existing body of Cuban film studies. The first revolutionary legislation concerning the arts was the creation of the ICAIC in 1959, a fact that demonstrates the importance of cinema for the new cultural project. This thesis argues that the moving image was radically affected by the proclamation of the socialist character of the Revolution on 16 April 1961. What was it that the distant audiovisual culture, film theories and practices of the Soviet-bloc offered Cubans? Is it not the case that Soviet-bloc cinemas had an influence upon the shaping of the Cuban moving image, if one takes into consideration the very few films co-produced in 30 years? It should be stressed that during this period, the moving image was the direct or indirect effect of the different waves that arrived in Cuba from âthe otherâ Europe, which were born at the same time as the first films that were co-produced in the 1960s, particularly from the unique experience of Mikhail Kalatozovâs masterpiece Soy Cuba. The present study reveals that the most important outcome from that influence was the conceptualisation of the cinematic discourse of the Revolution, so well represented in ICAIC and its socialist films of commitment. The experience included the introduction of new practices in television in order âto de-colonizeâ the moving image. KinoCuban analyses the impact on four main subjects: film theory and criticism; film administration; the filmmakersâ works (films, videos, and television practices) and the spectator. KinoCuban works within the area of postcolonial studies and takes Ortizâs transculturation as its starting point. KinoCuban argues that the experience was a process of give and take, thus âlo exacto es hablar de continuidadâ
Tree amplitudes at multiparticle threshold in a model with softly broken symmetry
Tree amplitudes of the production of two kinds of scalar particles at
threshold from one virtual particle are calculated in a model of two scalar
fields with symmetric quartic interaction and unequal masses. These
amplitudes exhibit interesting factorial and exponential behaviour at large
multiplicities. As a by-product we observe that the kinematically allowed decay
of one real particle into real particles of another kind, all at rest, has
zero tree amplitude in this model for .Comment: 17 pages. Preprint INR-823/9
Two-pathogen model with competition on clustered networks
Networks provide a mathematically rich framework to represent social contacts sufficient for the transmission of disease. Social networks are often highly clustered and fail to be locally tree-like. In this paper, we study the effects of clustering on the spread of sequential strains of a pathogen using the generating function formulation under a complete cross-immunity coupling, deriving conditions for the threshold of coexistence of the second strain. We show that clustering reduces the coexistence threshold of the second strain and its outbreak size in Poisson networks, whilst exhibiting the opposite effects on uniform-degree models. We conclude that clustering within a population must increase the ability of the second wave of an epidemic to spread over a network. We apply our model to the study of multilayer clustered networks and observe the fracturing of the residual graph at two distinct transmissibilities.Publisher PDFPeer reviewe
Degree correlations in graphs with clique clustering
Funding: This work was partially supported by the UK Engineering and Physical Sciences Research Council under grant number EP/N007565/1 (Science of Sensor Systems Software).Correlations among the degrees of nodes in random graphs often occur when clustering is present. In this paper we define a joint-degree correlation function for nodes in the giant component of clustered configuration model networks which are comprised of higher-order subgraphs. We use this model to investigate, in detail, the organisation among nearest-neighbour subgraphs for random graphs as a function of subgraph topology as well as clustering. We find an expression for the average joint degree of a neighbour in the giant component at the critical point for these networks. Finally, we introduce a novel edge-disjoint clique decomposition algorithm and investigate the correlations between the subgraphs of empirical networks.PostprintPeer reviewe
First measurement of low intensity fast neutron background from rock at the Boulby Underground Laboratory
A technique to measure low intensity fast neutron flux has been developed.
The design, calibrations, procedure for data analysis and interpretation of the
results are discussed in detail. The technique has been applied to measure the
neutron background from rock at the Boulby Underground Laboratory, a site used
for dark matter and other experiments, requiring shielding from cosmic ray
muons. The experiment was performed using a liquid scintillation detector. A
6.1 litre volume stainless steel cell was filled with an in-house made liquid
scintillator loaded with Gd to enhance neutron capture. A two-pulse signature
(proton recoils followed by gammas from neutron capture) was used to identify
the neutron events from much larger gamma background from PMTs. Suppression of
gammas from the rock was achieved by surrounding the detector with high-purity
lead and copper. Calibrations of the detector were performed with various gamma
and neutron sources. Special care was taken to eliminate PMT afterpulses and
correlated background events from the delayed coincidences of two pulses in the
Bi-Po decay chain. A four month run revealed a neutron-induced event rate of
1.84 +- 0.65 (stat.) events/day. Monte Carlo simulations based on the GEANT4
toolkit were carried out to estimate the efficiency of the detector and the
energy spectra of the expected proton recoils. From comparison of the measured
rate with Monte Carlo simulations the flux of fast neutrons from rock was
estimated as (1.72 +- 0.61 (stat.) +- 0.38 (syst.))*10^(-6) cm^(-2) s^(-1)
above 0.5 MeV.Comment: 37 pages, 24 figures, to be published in Astroparticle Physic
CsI(Tl) for WIMP dark matter searches
We report a study of CsI(Tl) scintillator to assess its applicability in
experiments to search for dark matter particles. Measurements of the mean
scintillation pulse shapes due to nuclear and electron recoils have been
performed. We find that, as with NaI(Tl), pulse shape analysis can be used to
discriminate between electron and nuclear recoils down to 4 keV. However, the
discrimination factor is typically (10-15)% better than in NaI(Tl) above 4 keV.
The quenching factor for caesium and iodine recoils was measured and found to
increase from 11% to ~17% with decreasing recoil energy from 60 to 12 keV.
Based on these results, the potential sensitivity of CsI(Tl) to dark matter
particles in the form of neutralinos was calculated. We find an improvement
over NaI(Tl) for the spin independent WIMP-nucleon interactions up to a factor
of 5 assuming comparable electron background levels in the two scintillators.Comment: 16 pages, 8 figures, to be published in Nucl. Instrum. and Meth. in
Phys. Res.
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