The reversibility of sea ice loss in a state-of-the-art climate model

Rapid Arctic sea ice retreat has fueled speculation about the possibility of threshold (or ‘tipping point’) behavior and irreversible loss of the sea ice cover. We test sea ice reversibility within a state-of-the-art atmosphere–ocean global climate model by increasing atmospheric carbon dioxide until the Arctic Ocean becomes ice-free throughout the year and subsequently decreasing it until the initial ice cover returns. Evidence for irreversibility in the form of hysteresis outside the envelope of natural variability is explored for the loss of summer and winter ice in both hemispheres. We find no evidence of irreversibility or multiple ice-cover states over the full range of simulated sea ice conditions between the modern climate and that with an annually ice-free Arctic Ocean. Summer sea ice area recovers as hemispheric temperature cools along a trajectory that is indistinguishable from the trajectory of summer sea ice loss, while the recovery of winter ice area appears to be slowed due to the long response times of the ocean near the modern winter ice edge. The results are discussed in the context of previous studies that assess the plausibility of sea ice tipping points by other methods. The findings serve as evidence against the existence of threshold behavior in the summer or winter ice cover in either hemisphere

The potential role for a pharmacist in a multidisciplinary general practitioner super clinic

© 2015, AMJ. All rights reserved. Background The Australian government’s General Practitioner (GP) super clinics programme aims to provide well-integrated, multidisciplinary, patient-centred care for people with chronic disease. However, there is no research into the current role of pharmacists in this setting. Aims To explore the perspectives of GP super clinic staff on current and potential (future) pharmacist-led services provided in this setting. Methods Individual interviews (facilitated using a semi-structured interview guide and thematically analysed) were conducted with purposively sampled staff of a GP super clinic in a semirural location in the state of New South Wales, until theme saturation. Participating staff included (n=9): three GPs, one pharmacist, one nurse, one business manager, and three reception staff. Results Three themes emerged conveying perspectives on: working relationships between staff; a pharmacist’s current role; and potential future roles for a pharmacist. All clinic staff actively engaged the pharmacist in their “team approach”. Currently established roles for home medicines reviews (HMRs) and drug information were well supported, but needed to be expanded, for example, with formalised case conferences between GPs, pharmacists, and other staff. New roles needed be explored in auditing medication use, optimising medication records, specialised drug information, dispensing, and prescribing. Although GPs had differing views about opportunities for pharmacists’ prescribing in this setting, they saw several benefits to this service, such as reducing the time pressure on GPs to enable more effective consultations. Conclusion Results suggest a pharmacist’s services can potentially be better used within the multidisciplinary super clinic model of care to address current gaps within the semi-rural practice setting. Any future role for the pharmacist could be addressed as part of a formalised, strategic approach to creating an integrated healthcare team, with attention to funding and government legislation

Noise properties of two single electron transistors coupled by a nanomechanical resonator

We analyze the noise properties of two single electron transistors (SETs) coupled via a shared voltage gate consisting of a nanomechanical resonator. Working in the regime where the resonator can be treated as a classical system, we find that the SETs act on the resonator like two independent heat baths. The coupling to the resonator generates positive correlations in the currents flowing through each of the SETs as well as between the two currents. In the regime where the dynamics of the resonator is dominated by the back-action of the SETs, these positive correlations can lead to parametrically large enhancements of the low frequency current noise. These noise properties can be understood in terms of the effects on the SET currents of fluctuations in the state of a resonator in thermal equilibrium which persist for times of order the resonator damping time.Comment: Accepted for publication in Phys. Rev.

The location of re-entry tears affects false lumen thrombosis in aortic dissection following TEVAR

Purpose. Thoracic endovascular aortic repair (TEVAR) has been shown to be an effective treatment method for acute type B aortic dissection. However, it remains unclear which factors determine false lumen thrombosis (FLT) after TEVAR. In this study we assess the influence of the distance between the distal end of the stent graft and first re-entry tear (SG-FET)on the progression of FLT.Methods.Three post-operative patient-specific models were reconstructed from computed tomography scans. Two additional models were created byartificially changing the SG-FET distance in patient 1 and 2. In all five models, computational fluid dynamics simulations coupled with thrombus formation modelling were performed at physiological flow conditions.Predicted FLT was compared with follow-up scans.Results.Ourresults showed reduced false lumen flow and low time-averaged wall shear stress (TAWSS) inpatients withlarge SG-FET distances. Predicted thrombus formation and growth were consistent with follow-up scansfor all patients. Reducingthe SG-FET distanceby 30 mm in patient 1 increased flowandTAWSS in the upper abdominal false lumen, reducing the thrombus volume by 9.6%. Increasingthe SG-FET distance inpatient 2 resulted in fasterthoracic thrombosis and increased total thrombus volume.Conclusion.The location of re-entry tears can influencethe progression of FLT following TEVAR. The more distal the re-entry tear in the aorta the more likely FLTis. Hence, the distal landing zone of the stent graft should be chosen carefully to ensure a sufficient SG-FET distance

Dissipation due to tunneling two-level systems in gold nanomechanical resonators

We present measurements of the dissipation and frequency shift in nanomechanical gold resonators at temperatures down to 10 mK. The resonators were fabricated as doubly-clamped beams above a GaAs substrate and actuated magnetomotively. Measurements on beams with frequencies 7.95 MHz and 3.87 MHz revealed that from 30 mK to 500 mK the dissipation increases with temperature as $T^{0.5}$, with saturation occurring at higher temperatures. The relative frequency shift of the resonators increases logarithmically with temperature up to at least 400 mK. Similarities with the behavior of bulk amorphous solids suggest that the dissipation in our resonators is dominated by two-level systems

Dynamics of a two-level system strongly coupled to a high-frequency quantum oscillator

Recent experiments on quantum behavior in microfabricated solid-state systems suggest tantalizing connections to quantum optics. Several of these experiments address the prototypical problem of cavity quantum electrodynamics: a two-level system coupled to a quantum harmonic oscillator. Such devices may allow the exploration of parameter regimes outside the near-resonance and weak-coupling assumptions of the ubiquitous rotating-wave approximation (RWA), necessitating other theoretical approaches. One such approach is an adiabatic approximation in the limit that the oscillator frequency is much larger than the characteristic frequency of the two-level system. A derivation of the approximation is presented and the time evolution of the two-level-system occupation probability is calculated using both thermal- and coherent-state initial conditions for the oscillator. Closed-form evaluation of the time evolution in the weak-coupling limit provides insight into the differences between the thermal- and coherent-state models. Finally, potential experimental observations in solid-state systems, particularly the Cooper-pair box--nanomechanical resonator system, are discussed and found to be promising.Comment: 16 pages, 11 figures; revised abstract; some text revisions; added two figures and combined others; added references. Submitted to Phys. Rev.

Contributions of greenhouse gas forcing and the Southern Annular Mode to historical Southern Ocean surface temperature trends

We examine the 1979-2014 Southern Ocean (SO) sea surface temperature (SST) trends simulated in an ensemble of coupled general circulation models and evaluate possible causes of the models’ inability to reproduce the observed 1979-2014 SO cooling. For each model we estimate the response of SO SST to step changes in greenhouse gas (GHG) forcing and in the seasonal indices of the Southern Annular Mode (SAM). Using these step-response functions, we skillfully reconstruct the models’ 1979-2014 SO SST trends. Consistent with the seasonal signature of the Antarctic ozone hole and the seasonality of SO stratification, the summer and fall SAM exert a large impact on the simulated SO SST trends. We further identify conditions that favor multidecadal SO cooling: 1) a weak SO warming response to GHG forcing; 2) a strong multidecadal SO cooling response to a positive SAM trend; 3) a historical SAM trend as strong as in observations

Nonlinear modal coupling in a high-stress doubly-clamped nanomechanical resonator

We present results from a study of the nonlinear intermodal coupling between different flexural vibrational modes of a single high-stress, doubly-clamped silicon nitride nanomechanical beam. The measurements were carried out at 100 mK and the beam was actuated using the magnetomotive technique. We observed the nonlinear behavior of the modes individually and also measured the coupling between them by driving the beam at multiple frequencies. We demonstrate that the different modes of the resonator are coupled to each other by the displacement induced tension in the beam, which also leads to the well known Duffing nonlinearity in doubly-clamped beams.Comment: 15 pages, 7 figure

Distribution and abundance of fish and crayfish in a Waikato stream in relation to basin area

The aim of this study was to relate the longitudinal distribution of fish and crayfish to increasing basin area and physical site characteristics in the Mangaotama Stream, Waikato region, North Island, New Zealand. Fish and crayfish were captured with two-pass removal electroshocking at 11 sites located in hill-country with pasture, native forest, and mixed land uses within the 21.6 km2 basin. Number of fish species and lineal biomass of fish increased with increasing basin area, but barriers to upstream fish migration also influenced fish distribution; only climbing and non-migratory species were present above a series of small waterfalls. Fish biomass increased in direct proportion to stream width, suggesting that fish used much of the available channel, and stream width was closely related to basin area. Conversely, the abundance of crayfish was related to the amount of edge habitat, and therefore crayfish did not increase in abundance as basin area increased. Densities of all fish species combined ranged from 17 to 459 fish 100 m-2, and biomass ranged from 14 to 206 g m-2. Eels dominated the fish assemblages, comprising 85-100% of the total biomass; longfinned eels the majority of the biomass at most sites. Despite the open access of the lower sites to introduced brown trout, native species dominated all the fish communities sampled