Mechanical Systems with Symmetry, Variational Principles, and Integration Algorithms

This paper studies variational principles for mechanical systems with symmetry and their applications to integration algorithms. We recall some general features of how to reduce variational principles in the presence of a symmetry group along with general features of integration algorithms for mechanical systems. Then we describe some integration algorithms based directly on variational principles using a discretization technique of Veselov. The general idea for these variational integrators is to directly discretize Hamilton’s principle rather than the equations of motion in a way that preserves the original systems invariants, notably the symplectic form and, via a discrete version of Noether’s theorem, the momentum map. The resulting mechanical integrators are second-order accurate, implicit, symplectic-momentum algorithms. We apply these integrators to the rigid body and the double spherical pendulum to show that the techniques are competitive with existing integrators

High tide or riptide on the cosmic shoreline? A water-rich atmosphere or stellar contamination for the warm super-Earth GJ 486b from JWST observations

Planets orbiting M-dwarf stars are prime targets in the search for rocky exoplanet atmospheres. The small size of M dwarfs renders their planets exceptional targets for transmission spectroscopy, facilitating atmospheric characterization. However, it remains unknown whether their host stars' highly variable extreme-UV radiation environments allow atmospheres to persist. With JWST, we have begun to determine whether or not the most favorable rocky worlds orbiting M dwarfs have detectable atmospheres. Here, we present a 2.8–5.2 μm JWST NIRSpec/G395H transmission spectrum of the warm (700 K, 40.3× Earth's insolation) super-Earth GJ 486b (1.3 R⊕ and 3.0 M⊕). The measured spectrum from our two transits of GJ 486b deviates from a flat line at 2.2σ − 3.3σ, based on three independent reductions. Through a combination of forward and retrieval models, we determine that GJ 486b either has a water-rich atmosphere (with the most stringent constraint on the retrieved water abundance of H2O > 10% to 2σ) or the transmission spectrum is contaminated by water present in cool unocculted starspots. We also find that the measured stellar spectrum is best fit by a stellar model with cool starspots and hot faculae. While both retrieval scenarios provide equal quality fits (${\chi }_{\nu }^{2}=1.0$) to our NIRSpec/G395H observations, shorter wavelength observations can break this degeneracy and reveal if GJ 486b sustains a water-rich atmosphere

Drowning is an apparent and unexpected recurrent cause of mass mortality of Common starlings (Sturnus vulgaris

Drowning is infrequently reported as a cause of death of wild birds and such incidents typically involve individual, rather than multiple, birds. Over a 21-year period (1993 to 2013 inclusive), we investigated 12 incidents of mortality of multiple (2 − 80+) Common starlings (Sturnus vulgaris) in Great Britain that appeared to be due to drowning. More than ten birds were affected in ten of these reported incidents. These incidents always occurred during the spring and early summer months and usually involved juvenile birds. In all cases, circumstantial evidence and post-mortem examinations indicated drowning to be the most likely cause of death with no underlying disease found. A behavioural explanation seems likely, possibly related to the gregarious nature of this species combined with juvenile inexperience in identifying water hazards. A review of data from the ringed bird recovery scheme across Great Britain (1909–2013 inclusive) of both starlings and Common blackbirds (Turdus merula), also a common garden visitor, identified additional suspected drowning incidents, which were significantly more common in the former species, supporting a species predisposition to drowning. For each species there was a marked seasonal peak from April to August. Drowning should be included as a differential diagnosis when investigating incidents of multiple starling mortality, especially of juveniles

Pandemic Influenza A H1N1 2009 Infection versus Vaccination: A Cohort Study Comparing Immune Responses in Pregnancy

Background: With the emergence of H1N1 pandemic (pH1N1) influenza, the CDC recommended that pregnant women be one of five initial target groups to receive the 2009 monovalent H1N1 vaccine, regardless of prior infection with this influenza strain. We sought to compare the immune response of pregnant women to H1N1 infection versus vaccination and to determine the extent of passive immunity conferred to the newborn. Methods/Findings: During the 2009-2010 influenza season, we enrolled a cohort of women who either had confirmed pH1N1 infection during pregnancy, did not have pH1N1 during pregnancy but were vaccinated against pH1N1, or did not have illness or vaccination. Maternal and umbilical cord venous blood samples were collected at delivery. Hemagglutination inhibition assays (HAI) for pH1N1 were performed. Data were analyzed using linear regression analyses. HAIs were performed for matched maternal/cord blood pairs for 16 women with confirmed pH1N1 infection, 14 women vaccinated against pH1N1, and 10 women without infection or vaccination. We found that pH1N1 vaccination and wild-type infection during pregnancy did not differ with respect to (1) HAI titers at delivery, (2) HAI antibody decay slopes over time, and (3) HAI titers in the cord blood. Conclusions: Vaccination against pH1N1 confers a similar HAI antibody response as compared to pH1N1 infection durin

Search for pair-produced long-lived neutral particles decaying to jets in the ATLAS hadronic calorimeter in ppcollisions at √s=8TeV

The ATLAS detector at the Large Hadron Collider at CERN is used to search for the decay of a scalar boson to a pair of long-lived particles, neutral under the Standard Model gauge group, in 20.3fb−1of data collected in proton–proton collisions at √s=8TeV. This search is sensitive to long-lived particles that decay to Standard Model particles producing jets at the outer edge of the ATLAS electromagnetic calorimeter or inside the hadronic calorimeter. No significant excess of events is observed. Limits are reported on the product of the scalar boson production cross section times branching ratio into long-lived neutral particles as a function of the proper lifetime of the particles. Limits are reported for boson masses from 100 GeVto 900 GeV, and a long-lived neutral particle mass from 10 GeVto 150 GeV

Search for direct pair production of the top squark in all-hadronic final states in proton-proton collisions at s√=8 TeV with the ATLAS detector

The results of a search for direct pair production of the scalar partner to the top quark using an integrated luminosity of 20.1fb−1 of proton–proton collision data at √s = 8 TeV recorded with the ATLAS detector at the LHC are reported. The top squark is assumed to decay via t˜→tχ˜01 or t˜→ bχ˜±1 →bW(∗)χ˜01 , where χ˜01 (χ˜±1 ) denotes the lightest neutralino (chargino) in supersymmetric models. The search targets a fully-hadronic final state in events with four or more jets and large missing transverse momentum. No significant excess over the Standard Model background prediction is observed, and exclusion limits are reported in terms of the top squark and neutralino masses and as a function of the branching fraction of t˜ → tχ˜01 . For a branching fraction of 100%, top squark masses in the range 270–645 GeV are excluded for χ˜01 masses below 30 GeV. For a branching fraction of 50% to either t˜ → tχ˜01 or t˜ → bχ˜±1 , and assuming the χ˜±1 mass to be twice the χ˜01 mass, top squark masses in the range 250–550 GeV are excluded for χ˜01 masses below 60 GeV

Alpine bogs of southern Spain show human-induced environmental change superimposed on long-term natural variations

Recent studies have proved that high elevation environments, especially remote wetlands, are exceptional ecological sensors of global change. For example, European glaciers have retreated during the 20th century while the Sierra Nevada National Park in southern Spain witnessed the first complete disappearance of modern glaciers in Europe. Given that the effects of climatic fluctuations on local ecosystems are complex in these sensitive alpine areas, it is crucial to identify their long-term natural trends, ecological thresholds, and responses to human impact. In this study, the geochemical records from two adjacent alpine bogs in the protected Sierra Nevada National Park reveal different sensitivities and long-term environmental responses, despite similar natural forcings, such as solar radiation and the North Atlantic Oscillation, during the late Holocene. After the Industrial Revolution both bogs registered an independent, abrupt and enhanced response to the anthropogenic forcing, at the same time that the last glaciers disappeared. The different response recorded at each site suggests that the National Park and land managers of similar regions need to consider landscape and environmental evolution in addition to changing climate to fully understand implications of climate and human influence.This study was supported by the project P11-RNM 7332 of the “Junta de Andalucía”, the projects CGL2013-47038-R and CGL2015-67130-C2-1-R of the “Ministerio de Economía y Competitividad of Spain and Fondo Europeo de Desarrollo Regional FEDER” and the research group RNM0190 and RNM309 (Junta de Andalucía). A.G.-A. was also supported by a Marie Curie Intra-European Fellowship of the 7th Framework Programme for Research, Technological Development and Demonstration of the European Commission (NAOSIPUK. Grant Number: PIEF-GA-2012-623027) and by a Ramón y Cajal Fellowship RYC-2015-18966 of the Spanish Government (Ministerio de Economía y Competividad). J.L.T. was also supported by a Small Research Grant by the Carnegie Trust for the Universities of Scotland and hosted the NAOSIPUK project (PIEF-GA-2012-623027). M. J. R-R acknowledges the PhD funding provided by Consejería de Economía, Innovación, Ciencia y Empleo de la Junta de Andalucía (P11-RNM 7332)

Dopaminergic D1 receptor signalling is necessary, but not sufficient for cued fear memory destabilisation

Rationale. Pharmacological targeting of memory reconsolidation is a promising therapeutic strategy for the treatment of fear memory-related disorders. However, the success of reconsolidation-based approaches depends upon the effective destabilisation of the fear memory by memory reactivation. Objectives. Here, we aimed to determine the functional involvement of dopamine D1 receptors in cued fear memory destabilisation, using systemic drug administration. Results. We observed that direct D1 receptor agonism was not sufficient to stimulate tone fear memory destabilisation to facilitate reconsolidation disruption by the glucocorticoid receptor antagonist mifepristone. Instead, administration of the nootropic nefiracetam did facilitate mifepristone-induced amnesia, in a manner that was dependent upon dopamine D1 receptor activation, although. Finally, while the combined treatment with nefiracetam and mifepristone did not confer fear-reducing effects under conditions of extinction learning, there was some evidence that mifepristone reduces fear expression irrespective of memory reactivation parameters. Conclusions. The use of combination pharmacological treatment to stimulate memory destabilisation and impair reconsolidation has potential therapeutic benefits, without risking a maladaptive increase of fear