Ferromagnetism of ultrathin films.

We discuss the nature of ferromagnetism in ultrathin films of magnetic ions, here regarded as two-dimensional Heisenberg ferromagnets subject to uniaxial anisotropy with the easy axis normal to the film. We show that a phase transition to ferromagnetism occurs always for arbitrarily small anisotropy. Renormalization-group scaling relations for the transition temperature and the temperature variation of the correlation length are obtained. Implications of these results are discussed. © 1988 The American Physical Society

Association of maternal serum PAPP-A levels, nuchal translucency and crown rump length in first trimester with adverse pregnancy outcomes: Retrospective cohort study.

OBJECTIVE: Are first trimester serum pregnancy-associated plasma protein-A (PAPP-A), nuchal translucency (NT) and crown rump length (CRL) prognostic factors for adverse pregnancy outcomes? METHOD: Retrospective cohort women, singleton pregnancies (UK 2011-2015). Unadjusted and multivariable logistic regression, outcomes: small for gestational age (SGA), pre-eclampsia (PE), pre-term birth (PTB), miscarriage, stillbirth, perinatal mortality and neonatal death (NND). RESULTS: 12,592 pregnancies: 852 (6.8%) PTB, 352 (2.8%) PE, 1824 (14.5%) SGA, 73 (0.6%) miscarriages, 37(0.3%) stillbirths, 73 perinatal deaths (0.6%) and 38 (0.30%) NND. Multivariable analysis: lower odds of SGA [adjusted odds ratio (aOR) 0.88 (95% CI 0.85,0.91)], PTB [0.92 (95%CI 0.88,0.97)], PE [0.91 (95% CI 0.85,0.97)] and stillbirth [ 0.71 (95% CI 0.52,0.98)] as PAPP-A increases. Lower odds of SGA [aOR 0.79 (95% CI 0.70,0.89)] but higher odds of miscarriage [aOR 1.75 95% CI (1.12,2.72)] as NT increases, and lower odds of stillbirth as CRL increases [aOR 0.94 95% CI (0.89,0.99)]. Multivariable analysis of three factors together demonstrated strong associations: a) PAPP-A, NT, CRL and SGA, b) PAPP-A and PTB, c) PAPP-A, CRL and PE, d) NT and miscarriage. CONCLUSIONS: PAPP-A, NT and CRL independent prognostic factor for adverse pregnancy outcomes, especially PAPP-A and SGA with lower PAPP-A associated with increased risk

Monitoring Partially Synchronous Distributed Systems using SMT Solvers

In this paper, we discuss the feasibility of monitoring partially synchronous distributed systems to detect latent bugs, i.e., errors caused by concurrency and race conditions among concurrent processes. We present a monitoring framework where we model both system constraints and latent bugs as Satisfiability Modulo Theories (SMT) formulas, and we detect the presence of latent bugs using an SMT solver. We demonstrate the feasibility of our framework using both synthetic applications where latent bugs occur at any time with random probability and an application involving exclusive access to a shared resource with a subtle timing bug. We illustrate how the time required for verification is affected by parameters such as communication frequency, latency, and clock skew. Our results show that our framework can be used for real-life applications, and because our framework uses SMT solvers, the range of appropriate applications will increase as these solvers become more efficient over time.Comment: Technical Report corresponding to the paper accepted at Runtime Verification (RV) 201

Dynamical Axion Field in Topological Magnetic Insulators

Axions are very light, very weakly interacting particles postulated more than 30 years ago in the context of the Standard Model of particle physics. Their existence could explain the missing dark matter of the universe. However, despite intensive searches, they have yet to be detected. In this work, we show that magnetic fluctuations of topological insulators couple to the electromagnetic fields exactly like the axions, and propose several experiments to detect this dynamical axion field. In particular, we show that the axion coupling enables a nonlinear modulation of the electromagnetic field, leading to attenuated total reflection. We propose a novel optical modulators device based on this principle.Comment: 5 pages, 3 figure

Teaching Evidence-Based Complementary and Alternative Medicine (EBCAM); Changing behaviours in the face of reticence: A cross-over trial

BACKGROUND: The effectiveness of teaching critical appraisal to students of Complementary and Alternative Medicine (CAM) has not been studied. In this study we attempt to determine if a workshop for final year students at a naturopathic college improved their ability to utilize critical appraisal concepts. METHODS: We assigned 83 Naturopathic Interns to two groups: Group A (n = 47) or Group B (n = 36). We conducted a baseline assessment of all subjects' critical appraisal skills. Group A was assigned to receive a 3 ½ hour workshop on Evidence Based Medicine (EBM) and Group B received a workshop on bioethics (control intervention). The groups critical appraisal skills were re-evaluated at this time. We then crossed over the intervention so that Group B received the EBM workshop while Group A received the bioethics workshop. Assessment of critical appraisal skills of the two groups was again performed. RESULTS: The students mean scores were similar in Group A (14.8) and Group B (15.0) after Group A had received the intervention and Group B had received the control (p = 0.75). Group scores were not significantly improved at the end of the trial compared to at the beginning of the study (Group A: 15.1 to 16.1) (Group B 15.6 to 15.9). Student's confidence in reading research papers also did not improve throughout the course of the study. CONCLUSION: The final year is a difficult but important time to teach critical appraisal and evidence skills. Single, short intervention programs will likely yield negligible results. A multi-factorial approach may be better suited to implementing EBCAM than single short interventions

Density of Healthcare Providers and Patient Outcomes: Evidence from a Nationally Representative Multi-Site HIV Treatment Program in Uganda

This study examined the association between density of healthcare providers and patient outcomes using a large nationally representative cohort of patients receiving combination antiretroviral therapy (cART) in Uganda.Objective: We examined the association between density of healthcare providers and patient outcomes using a large nationally representative cohort of patients receiving combination antiretroviral therapy (cART) in Uganda. Design: We obtained data from The AIDS Support Organization (TASO) in Uganda. Patients 18 years of age and older who initiated cART at TASO between 2004 and 2008 contributed to this analysis. The number of healthcare providers per 100 patients, the number of patients lost to follow-up per 100 person years and number of deaths per 100 person years were calculated. Spearman correlation was used to identify associations between patient loss to follow-up and mortality with the healthcare provider-patient ratios. Results: We found no significant associations between the number of patients lost to follow-up and physicians (p = 0.45), nurses (p = 0.93), clinical officers (p = 0.80), field officers (p = 0.56), and healthcare providers overall (p = 0.83). Similarly, no significant associations were observed between mortality and physicians (p = 0.65), nurses (p = 0.49), clinical officers (p = 0.73), field officers (p = 0.78), and healthcare providers overall (p = 0.73). Conclusions: Patient outcomes, as measured by loss to follow-up and mortality, were not significantly associated with the number of doctors, nurses, clinical officers, field officers, or healthcare providers overall. This may suggest that that other factors, such as the presence of volunteer patient supporters or broader political or socioeconomic influences, may be more closely associated with outcomes of care among patients on cART in Uganda

An extragalactic supernebula confined by gravity

Little is known about the origins of the giant star clusters known as globular clusters. How can hundreds of thousands of stars form simultaneously in a volume only a few light years across the distance of the sun to its nearest neighbor? Radiation pressure and winds from luminous young stars should disperse the star-forming gas and disrupt the formation of the cluster. Globular clusters in our Galaxy cannot provide answers; they are billions of years old. Here we report the measurement of infrared hydrogen recombination lines from a young, forming super star cluster in the dwarf galaxy, NGC 5253. The lines arise in gas heated by a cluster of an estimated million stars, so young that it is still enshrouded in gas and dust, hidden from optical view. We verify that the cluster contains 4000-6000 massive, hot "O" stars. Our discovery that the gases within the cluster are bound by gravity may explain why these windy and luminous O stars have not yet blown away the gases to allow the cluster to emerge from its birth cocoon. Young clusters in "starbursting" galaxies in the local and distant universe may be similarly gravitationally confined and cloaked from view.Comment: Letter to Natur

Electrically-driven phase transition in magnetite nanostructures

Magnetite (Fe$_{3}$O$_{4}$), an archetypal transition metal oxide, has been used for thousands of years, from lodestones in primitive compasses[1] to a candidate material for magnetoelectronic devices.[2] In 1939 Verwey[3] found that bulk magnetite undergoes a transition at T$_{V}$ $\approx$ 120 K from a high temperature "bad metal" conducting phase to a low-temperature insulating phase. He suggested[4] that high temperature conduction is via the fluctuating and correlated valences of the octahedral iron atoms, and that the transition is the onset of charge ordering upon cooling. The Verwey transition mechanism and the question of charge ordering remain highly controversial.[5-11] Here we show that magnetite nanocrystals and single-crystal thin films exhibit an electrically driven phase transition below the Verwey temperature. The signature of this transition is the onset of sharp conductance switching in high electric fields, hysteretic in voltage. We demonstrate that this transition is not due to local heating, but instead is due to the breakdown of the correlated insulating state when driven out of equilibrium by electrical bias. We anticipate that further studies of this newly observed transition and its low-temperature conducting phase will shed light on how charge ordering and vibrational degrees of freedom determine the ground state of this important compound.Comment: 17 pages, 4 figure

Star formation in a high-pressure environment: An SMA view of the Galactic centre dust ridge

The star formation rate in the Central Molecular Zone (CMZ) is an order of magnitude lower than predicted according to star formation relations that have been calibrated in the disc of our own and nearby galaxies. Understanding how and why star formation appears to be different in this region is crucial if we are to understand the environmental dependence of the star formation process. Here, we present the detection of a sample of high-mass cores in the CMZ's "dust ridge" that have been discovered with the Submillimeter Array as part of the CMZoom survey. These cores range in mass from ~ 50 - 2150 Msun within radii of 0.1 - 0.25 pc. All appear to be young (pre-UCHII), meaning that they are prime candidates for representing the initial conditions of high-mass stars and sub-clusters. We report that at least two of these cores ('c1' and 'e1') contain young, high-mass protostars. We compare all of the detected cores with high-mass cores in the Galactic disc and find that they are broadly similar in terms of their masses and sizes, despite being subjected to external pressures that are several orders of magnitude greater - ~ 10^8 K/cm^3, as opposed to ~ 10^5 K/cm^3. The fact that > 80% of these cores do not show any signs of star-forming activity in such a high-pressure environment leads us to conclude that this is further evidence for an increased critical density threshold for star formation in the CMZ due to turbulence