The FlowSimulator framework for massively parallel CFD applications

In this paper the FlowSimulator framework for multi- disciplinary computational fluid dynamics simulations on high performance computer platforms is described. An overview of the provided functionality is given and possible benefits for tool developers as well as design engineers are presented

A microfluidic device for the study of the orientational dynamics of microrods

We describe a microfluidic device for studying the orientational dynamics of microrods. The device enables us to experimentally investigate the tumbling of microrods immersed in the shear flow in a microfluidic channel with a depth of 400 mu and a width of 2.5 mm. The orientational dynamics was recorded using a 20 X microscopic objective and a CCD camera. The microrods were produced by shearing microdroplets of photocurable epoxy resin. We show different examples of empirically observed tumbling. On the one hand we find that short stretches of the experimentally determined time series are well described by fits to solutions of Jeffery's approximate equation of motion [Jeffery, Proc. R. Soc. London. 102 (1922), 161-179]. On the other hand we find that the empirically observed trajectories drift between different solutions of Jeffery's equation. We discuss possible causes of this orbit drift.Comment: 11 pages, 8 figure

Individual risk assessment and information technology to optimise screening frequency for diabetic retinopathy.

To access publisher full text version of this article. Please click on the hyperlink in Additional Links field.AIMS/HYPOTHESIS: The aim of this study was to reduce the frequency of diabetic eye-screening visits, while maintaining safety, by using information technology and individualised risk assessment to determine screening intervals. METHODS: A mathematical algorithm was created based on epidemiological data on risk factors for diabetic retinopathy. Through a website, www.risk.is , the algorithm receives clinical data, including type and duration of diabetes, HbA(1c) or mean blood glucose, blood pressure and the presence and grade of retinopathy. These data are used to calculate risk for sight-threatening retinopathy for each individual's worse eye over time. A risk margin is defined and the algorithm recommends the screening interval for each patient with standardised risk of developing sight-threatening retinopathy (STR) within the screening interval. We set the risk margin so that the same number of patients develop STR within the screening interval with either fixed annual screening or our individualised screening system. The database for diabetic retinopathy at the Department of Ophthalmology, Aarhus University Hospital, Denmark, was used to empirically test the efficacy of the algorithm. Clinical data exist for 5,199 patients for 20 years and this allows testing of the algorithm in a prospective manner. RESULTS: In the Danish diabetes database, the algorithm recommends screening intervals ranging from 6 to 60 months with a mean of 29 months. This is 59% fewer visits than with fixed annual screening. This amounts to 41 annual visits per 100 patients. CONCLUSION: Information technology based on epidemiological data may facilitate individualised determination of screening intervals for diabetic eye disease. Empirical testing suggests that this approach may be less expensive than conventional annual screening, while not compromising safety. The algorithm determines individual risk and the screening interval is individually determined based on each person's risk profile. The algorithm has potential to save on healthcare resources and patients' working hours by reducing the number of screening visits for an ever increasing number of diabetic patients in the world

Prevalence of atrial fibrillation and use of warfarin among patients with ischemic stroke

Neðst á síðunni er hægt að nálgast greinina í heild sinni með því að smella á hlekkinn View/OpenObjective: Atrial fibrillation (AF) is the most common sustained cardiac arrythmia and a significant cause of morbidity. Stroke and transient ischemic attack (TIA) are well known serious complications of AF. In the last decade, a number of studies have shown that the risk of stroke in patients with AF is reduced by anticoagulation therapy with warfarin. The aim of this study was to assess the prevalence of AF in patients with acute ischemic stroke or TIA and to look at the use of anticoagulation therapy in patients who either had a previously known AF or were diagnosed to have AF during hospitalisation for ischemic stroke or TIA. Methods: Medical records of 918 patients admitted to Landspitali University Hospital in Iceland in 1997-2000 with the diagnosis of TIA or ischemic stroke were reviewed to detect a subgroup with AF. In addition to demographic data and cardiac function studies, information was collected about other possible coexisting stroke risk factors. Results: A total of 159 patients (17%) had AF in 124 (78%) of whom the AF was previously known. In 35 patients AF was diagnosed during the hospitalisation.The majority of those patients also had at least one other risk factor for stroke. On admission, 27 patients (22%) of those with previously known AF were being treated with warfarin. In eleven (41%) the anticoagulation was subtherapeutic as the INR was found to be lower than 2,0. At discharge, 74 patients of those 131 (56%) who were alive were receiving warfarin anticoagulation. Conclusion: The prevalence of AF in patients with TIA or ischemic stroke was somewhat high in this study. AF and other risk factors for stroke were found to commonly coexist. Despite the well documented effect of warfarin in such patients, this therapy was underused for both primary and secondary stroke prevention.Tilgangur: Gáttatif er algengasta viðvarandi hjartsláttartruflunin og getur haft afgerandi áhrif á lífs­gæði. Heiladrep er einn alvarlegasti fylgikvilli gáttatifs og fjölmargar rannsóknir á síðasta áratug sýna að draga má úr tíðni þessa fylgikvilla með warfarín blóðþynningarmeðferð. Tilgangur þessarar rannsóknar var að kanna algengi gáttatifs hjá sjúklingum með heiladrep og skammvinnt blóðþurrðarkast í heila og hvernig staðið var að blóðþynningu hjá þeim sem höfðu áður þekkt gáttatif. Efniviður og aðferðir: Upplýsinga var aflað á aftur­skyggnan hátt um alla sjúklinga sem komu á Land­spítala vegna heiladreps eða skammvinnrar blóðþurrðar í heila á fjögurra ára tímabili (1997-2000). Þessar upplýsingar höfðu verið skráðar á framvirkan kerfisbundinn hátt í Heilablóðfallsskrá. Í þessari rannsókn var litið sérstaklega á gögn sjúklinga sem jafnframt voru greindir með gáttatif, ýmist áður eða í sjúkrahúslegunni eftir heilablóðfallið. Niðurstöður: Á meðal 918 sjúklinga með heiladrep eða skammvinnna blóðþurrð í heila sem gögn voru til um reyndust 124 (13,5%) hafa þekkt gáttatif fyrir greiningu heilaáfallsins. Þrjátíu og fimm til viðbótar greindust með gáttatif í legunni og hjartsláttartruflun því til staðar hjá 159 (17%) þeirra sem greindust með heiladrep eða blóðþurrðarkast. Af þeim sem voru með þekkt gáttatif fyrir voru aðeins 27 (22%) á blóðþynningarmeðferð með warfaríni við greiningu heilaáfallsins og aðeins 16 af 27 (59%) höfðu INR gildi (International Normalized Ratio) yfir 2,0 við innlögn. Tuttugu og átta sjúklingar létust í legunni. Alls útskrifuðust 74 af 131 (56%) sjúklingi á warfarínmeðferð. Velflestir sjúklinganna höfðu að minnsta kosti einn viðbótaráhættuþátt fyrir blóðþurrðarsjúkdómi í heila auk gáttatifs. Ályktun: Gáttatif er algengt meðal sjúklinga sem fá heiladrep eða skammvinna heilablóðþurrð en margir þeirra hafa aðra áhættuþætti heila­blóð­þurrð­ar­sjúk­dóms að auki. Erfitt er því að átta sig á beinu orsakasamhengi gáttatifs og heilaáfalls hjá stórum hluta þessara sjúklinga. Niðurstöður þessarar rann­sókn­ar benda til þess að notkun warfaríns hafi ver­ið ábótavant bæði fyrir og eftir heilablóðþurrð á rann­sóknartímabilin

Individualised risk assessment for diabetic retinopathy and optimisation of screening intervals: a scientific approach to reducing healthcare costs.

To access publisher's full text version of this article, please click on the hyperlink in Additional Links field or click on the hyperlink at the top of the page marked Files. This article is open access.To validate a mathematical algorithm that calculates risk of diabetic retinopathy progression in a diabetic population with UK staging (R0-3; M1) of diabetic retinopathy. To establish the utility of the algorithm to reduce screening frequency in this cohort, while maintaining safety standards.The cohort of 9690 diabetic individuals in England, followed for 2 years. The algorithms calculated individual risk for development of preproliferative retinopathy (R2), active proliferative retinopathy (R3A) and diabetic maculopathy (M1) based on clinical data. Screening intervals were determined such that the increase in risk of developing certain stages of retinopathy between screenings was the same for all patients and identical to mean risk in fixed annual screening. Receiver operating characteristic curves were drawn and area under the curve calculated to estimate the prediction capability.The algorithm predicts the occurrence of the given diabetic retinopathy stages with area under the curve =80% for patients with type II diabetes (CI 0.78 to 0.81). Of the cohort 64% is at less than 5% risk of progression to R2, R3A or M1 within 2 years. By applying a 2 year ceiling to the screening interval, patients with type II diabetes are screened on average every 20 months, which is a 40% reduction in frequency compared with annual screening.The algorithm reliably identifies patients at high risk of developing advanced stages of diabetic retinopathy, including preproliferative R2, active proliferative R3A and maculopathy M1. Majority of patients have less than 5% risk of progression between stages within a year and a small high-risk group is identified. Screening visit frequency and presumably costs in a diabetic retinopathy screening system can be reduced by 40% by using a 2 year ceiling. Individualised risk assessment with 2 year ceiling on screening intervals may be a pragmatic next step in diabetic retinopathy screening in UK, in that safety is maximised and cost reduced by about 40%.Icelandic Research Counci

Novel spin-liquid states in the frustrated Heisenberg antiferromagnet on the honeycomb lattice

Recent experiment on a honeycomb-lattice Heisenberg antiferromagnet (AF) Bi$_3$Mn$_4$O$_{12}$(NO$_3$) revealed a novel spin-liquid-like behavior down to low temperature, which was ascribed to the frustration effect due to the competition between the AF nearest- and next-nearest-neighbor interactions $J_1$ and $J_2$. Motivated by the experiment, we study the ordering of the $J_1$ -$J_2$ frustrated classical Heisenberg AF on a honeycomb lattice both by a low-temperature expansion and a Monte Carlo simulation. The model has been known to possess a massive degeneracy of the ground state, which, however, might be lifted due to thermal fluctuations leading to a unique ordered state, the effect known as 'order-by-disorder'. We find that the model exhibits an intriguing ordering behavior, particularly near the AF phase boundary. The energy scale of the order-by-disorder is suppressed there down to extremely low temperatures, giving rise to exotic spin-liquid states like a "ring-liquid" or a "pancake-liquid" state accompanied by the characteristic spin structure factor and the field-induced antiferromagnetism. We argue that the recent experimental data are explicable if the system is in such exotic spin-liquid states

Schwinger-boson approach to quantum spin systems: Gaussian fluctuactions in the "natural" gauge

We compute the Gaussian-fluctuation corrections to the saddle-point Schwinger-boson results using collective coordinate methods. Concrete application to investigate the frustrated J1-J2 antiferromagnet on the square lattice shows that, unlike the saddle-point predictions, there is a quantum nonmagnetic phase for 0.53 < J2/J1 < 0.64. This result is obtained by considering the corrections to the spin stiffness on large lattices and extrapolating to the thermodynamic limit, which avoids the infinite-lattice infrared divergencies associated to Bose condensation. The very good agreement of our results with exact numerical values on finite clusters lends support to the calculational scheme employed.Comment: 4 pages, Latex, 3 figures included as eps files,minor correction

Elevated visual dependency in young adults after chemotherapy in childhood

Chemotherapy in childhood can result in long-term neurophysiological side-effects, which could extend to visual processing, specifically the degree to which a person relies on vision to determine vertical and horizontal (visual dependency). We investigated whether adults treated with chemotherapy in childhood experience elevated visual dependency compared to controls and whether any difference is associated with the age at which subjects were treated. Visual dependency was measured in 23 subjects (mean age 25.3 years) treated in childhood with chemotherapy (CTS) for malignant, solid, non-CNS tumors. We also stratified CTS into two groups: those treated before 12 years of age and those treated from 12 years of age and older. Results were compared to 25 healthy, age-matched controls. The subjective visual horizontal (SVH) and vertical (SVV) orientations was recorded by having subjects position an illuminated rod to their perceived horizontal and vertical with and without a surrounding frame tilted clockwise and counter-clockwise 20° from vertical. There was no significant difference in rod accuracy between any CTS groups and controls without a frame. However, when assessing visual dependency using a frame, CTS in general (p = 0.006) and especially CTS treated before 12 years of age (p = 0.001) tilted the rod significantly further in the direction of the frame compared to controls. Our findings suggest that chemotherapy treatment before 12 years of age is associated with elevated visual dependency compared to controls, implying a visual bias during spatial activities. Clinicians should be aware of symptoms such as visual vertigo in adults treated with chemotherapy in childhood

Spin Liquid Phases in 2D Frustrated XY Model

In this paper we consider the $J_1-J_2-J_3$ classical and quantum 2D XY model. Spin wave calculations show that a spin liquid phase still exists in the quantum case as for Heisenberg models. We formulate a semiclassical approach of these models based on spin wave action and use a variational method to study the role played by vortices. Liquid and crystal phases of vortex could emerge in this description. These phases seem to be directly correlated with the spin liquid one and to its crystalline interpretation.Comment: 16 pages, Latex, 4 figures. To be published in Phys. Rev.

Association between different methods of assessing blood pressure variability and incident cardiovascular disease, cardiovascular mortality and all-cause mortality : a systematic review

Dr Smith is supported by the National Institute for Health Research (NIHR) Oxford Biomedical Research Centre (BRC). The views expressed are those of the author(s) and not necessarily those of the NHS, the NIHR or the Department of Health. Dr Choon-Hian Goh is supported by the University of Malaya Post Doctoral Research Fellowship scheme. No funding was received to undertake the conduct of this study.Peer reviewedPostprin