Intrinsic viscosity of a suspension of weakly Brownian ellipsoids in shear

We analyze the angular dynamics of triaxial ellipsoids in a shear flow subject to weak thermal noise. By numerically integrating an overdamped angular Langevin equation, we find the steady angular probability distribution for a range of triaxial particle shapes. From this distribution we compute the intrinsic viscosity of a dilute suspension of triaxial particles. We determine how the viscosity depends on particle shape in the limit of weak thermal noise. While the deterministic angular dynamics depends very sensitively on particle shape, we find that the shape dependence of the intrinsic viscosity is weaker, in general, and that suspensions of rod-like particles are the most sensitive to breaking of axisymmetry. The intrinsic viscosity of a dilute suspension of triaxial particles is smaller than that of a suspension of axisymmetric particles with the same volume, and the same ratio of major to minor axis lengths.Comment: 14 pages, 6 figures, 1 table, revised versio

The Ising phase in the J1-J2 Heisenberg Model

The two dimensional Heisenberg antiferromagnet on the square lattice with nearest (J1) and next-nearest (J2) neighbor couplings is investigated in the strong frustration regime (J2/J1>1/2). A new effective field theory describing the long wavelength physics of the model is derived from the quantum hamiltonian. The structure of the resulting non linear sigma model allows to recover the known spin wave results in the collinear regime, supports the presence of an Ising phase transition at finite temperature and suggests the possible occurrence of a non-magnetic ground state breaking rotational symmetry. By means of Lanczos diagonalizations we investigate the spin system at T=0, focusing our attention on the region where the collinear order parameter is strongly suppressed by quantum fluctuations and a transition to a non-magnetic state occurs. Correlation functions display a remarkable size independence and allow to identify the transition between the magnetic and non-magnetic region of the phase diagram. The numerical results support the presence of a non-magnetic phase with orientational ordering.Comment: 6 pages, 4 figures, to be published in PR

Bit error evaluation of optically preamplified direct detection receiver with Fabry-Perot optical filters

The error performance of a preamplified, direct detection receiver with an optical filter of the Lorentzian type is studied. The analysis takes into account the influence of the optical intersymbol interference (ISI). A closed-form expression of the moment generating function (MGF) of the decision variable is derived. Error probabilities are evaluated from the MGF using a saddlepoint approximation. The Gaussian approximation is also examined. The detection sensitivity in terms of a quantum limit is calculated. The results show that there exists an optimum optical bandwidth, the reason being a tradeoff between the effect of ISI and the spontaneous emission noise. It is also shown that the Gaussian approximation gives a good estimate of the error probability, allowing to find in a simple manner the optimum parameters of optically preamplified, direct detection receive

A stratified transect approach captures reef complexity with canopy-forming organisms

On the Great Barrier Reef (GBR), persistent changes to reef communities have begun to be documented, and on inshore reefs these shifts may favour the proliferation of macroalgae. Critical to understanding changes to reef community structure in response to anthropogenic impacts is developing effective methods to accurately document the abundance of different reef organisms. Effective monitoring must be time and cost efficient, replicable, and able to sufficiently and accurately detect disturbances to allow development of strategies to mitigate their impacts. Traditional techniques to document coral reef communities (i.e. photo-quadrats, benthic intercept transects) rely on planar views, which tend to either over- or under-represent canopy-forming organisms. As canopy-forming organisms are likely to be affected by anthropogenic influences (corals negatively, algae positively), it is essential for monitoring programs to implement methods sufficient to document changes to the vertical dimension of coral reefs. Here we build on previous work to document the canopy effect in coral-dominated ecosystems and propose a new survey approach suitable for implementation in algal-dominated systems. A vertically stratified transect, modified from a traditional point intercept transect, captures benthic and canopy-forming members of reef communities and provides information on three-dimensional complexity. To test the capability of the new method to detect changes in vertical reef structure, seaweed was removed from experimental quadrats and monitoring techniques were applied before and after four months of regrowth. A stratified method more accurately captured the three-dimensional change resulting from algal canopy growth, while resolving the over- and under-representation of algal biomass in two traditional techniques. We propose that a stratified transect method improves abundance estimates of canopy-forming organisms whilst maintaining data compatibility with traditional methods

A Severe Throat Infection - Case Report

Neðst á síðunni er hægt að nálgast greinina í heild sinni með því að smella á hlekkinn View/OpenWe report a case of Lemierre?s syndrome or, human necrobacillosis, in a 33 year old icelandic male. A severe clinical picture, fulfilling all the criteria for this syndrome, is described. With antibiotic therapy, and critical care, the outcome was successful. A brief overview of infections due to Fusobacterium necro phorum, with special emphasis on Lemierre?s syndrome, is presented. Etiology, clinical symptoms, treatment and prognosis of this syndrome are dis cussed. We believe this to be the first case of human necrobacillosis to be reported in Iceland.Sjúkrasaga Þrjátíu og þriggja ára gamall bóndi, áður hraust­ur, kom á bráðamóttöku Fjórðungssjúkrahússins á Akureyri (FSA). Hann hafði veikst sex dögum áður með háum hita, miklum slappleika og verkjum aftan í hálsi. Hann var alveg rúmfastur, kastaði mikið upp en var ekki með niðurgang. Allan tímann var hann með óstöðv­andi hiksta. Kona hans tók eftir að hann var móður og svaf illa. Hann mældist með hita um 40° C og fór að lokum til heilsugæslulæknis sem sá að hann var gulur og fárveikur og sendi hann á bráðamóttöku FSA. Við komu á FSA var hann fárveikur (septískur), lá á bekk, vakandi og áttaður, mjög þvoglumæltur, og skalf mikið. Blóðþrýstingur var 140/85 mmHg liggj­andi og 128/64 mmHg sitjandi. Púls 119/mín, reglu­legur. Öndunartíðni 36/mín. Hiti 39,8°C í enda­þarmi. Hann var gulur á húð og í augnhvítu. Mikil þreifi­eymsli voru í hnakka og aftan á hálsi en ekki hnakkastífleiki. Hann var mjög þurr á vörum, með blóð­skorpur í munni og brúnleita, að því er virt­ist, fláka af yfirborðsdrepi á tungu. Hann var mjög bólginn í koki. Fíngert brak heyrðist yfir hægra lunga. Við hjartahlustun heyrðust eðlilegir hjartatónar og slagbilsóhljóð (systólískt). Kviður var aumur undir hægri rifjaboga en engar líffærastækkanir né aðrar fyrirferðaraukningar fundust. Hann var með kylfufingur (talið vera meðfætt) og flísablæðingar sáust undir nöglum. Nöglin á hægri stórutá var inngróin og talsvert sár og bólguholdgun (granulation) umhverfis en ekki merki um bráða sýkingu. Maðurinn var að nálgast sýkingalost án augljósrar orsakar

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

Strike-slip faulting during the 2014 Bároarbunga-Holuhraun dike intrusion, central Iceland

Over a 13 day period magma propagated laterally from the subglacial Bárðarbunga volcano in the northern rift zone, Iceland. It created > 30,000 earthquakes at 5–7 km depth along a 48 km path before erupting on 29 August 2014. The seismicity, which tracked the dike propagation, advanced in short bursts at 0.3–4.7 km/h separated by pauses of up to 81 h. During each surge forward, seismicity behind the dike tip dropped. Moment tensor solutions from the leading edge show exclusively left-lateral strike-slip faulting subparallel to the advancing dike tip, releasing accumulated strain deficit in the brittle layer of the rift zone. Behind the leading edge, both left- and right-lateral strike-slip earthquakes are observed. The lack of non-double-couple earthquakes implies that the dike opening was aseismic.Seismometers were borrowed from the Natural Environment Research Council (NERC) SEIS-UK (loans 968 and 1022),with funding by research grants from the NERC and the European Community’s Seventh Framework Programme grant 308377 (Project FUTUREVOLC), and graduate studentships from the NERC and Shell. We thank Ágúst Þór Gunnlaugsson and others who assisted with fieldwork in Iceland and Nigel Woodcock for his helpful discussions. M.T. Gudmundsson, H. Reynolds, and Þ. Högnadóttir supplied ice cauldron coordinates. The Icelandic Meteorological Office, Chris Bean (University College Dublin), and the British Geological Survey kindly provided additional data from seismometers in northeast Iceland, data delivery from IMO seismic database 20151001/01. We thank the two anonymous reviewers for their constructive comments. Hypocenter locations in Figure 1 are listed in Tables S2 and S3. (Department of Earth Sciences, Cambridge contribution ESC3539).This is the final version of the article. It first appeared from Wiley via http://dx.doi.org/10.1002/2015GL06742

Weakly frustrated two-dimensional Heisenberg antiferromagnets: thermodynamic properties from a non-perturbative approach

We analyze the thermodynamic properties of the spin-S two-dimensional quantum Heisenberg antiferromagnet on a square lattice with nearest and next-nearest neighbor couplings in the Neel phase (J_2/J_1<0.4) employing the quantum hierarchical reference theory (QHRT), a non-perturbative implementation of the renormalization group method to quantum systems. We investigate the staggered susceptibility, the structure factors and the correlation length at finite temperature and for different values of the frustration ratio. From the finite temperature results, we also extrapolate ground state properties, such as spin stiffness and spontaneous staggered magnetization, providing an estimate of the extent of quantum corrections. The behavior of these quantities as a function of frustration may provide some hint on the breakdown of the Neel phase at zero temperature for larger values of J_2