1,640 research outputs found
Linear response of east Greenland's tidewater glaciers to ocean/atmosphere warming.
Predicting the retreat of tidewater outlet glaciers forms a major obstacle to forecasting the rate of mass loss from the Greenland Ice Sheet. This reflects the challenges of modeling the highly dynamic, topographically complex, and data-poor environment of the glacier-fjord systems that link the ice sheet to the ocean. To avoid these difficulties, we investigate the extent to which tidewater glacier retreat can be explained by simple variables: air temperature, meltwater runoff, ocean temperature, and two simple parameterizations of "ocean/atmosphere" forcing based on the combined influence of runoff and ocean temperature. Over a 20-y period at 10 large tidewater outlet glaciers along the east coast of Greenland, we find that ocean/atmosphere forcing can explain up to 76% of the variability in terminus position at individual glaciers and 54% of variation in terminus position across all 10 glaciers. Our findings indicate that (i) the retreat of east Greenland's tidewater glaciers is best explained as a product of both oceanic and atmospheric warming and (ii) despite the complexity of tidewater glacier behavior, over multiyear timescales a significant proportion of terminus position change can be explained as a simple function of this forcing. These findings thus demonstrate that simple parameterizations can play an important role in predicting the response of the ice sheet to future climate warming
Flavour Physics in the Soft Wall Model
We extend the description of flavour that exists in the Randall-Sundrum (RS)
model to the soft wall (SW) model in which the IR brane is removed and the
Higgs is free to propagate in the bulk. It is demonstrated that, like the RS
model, one can generate the hierarchy of fermion masses by localising the
fermions at different locations throughout the space. However, there are two
significant differences. Firstly the possible fermion masses scale down, from
the electroweak scale, less steeply than in the RS model and secondly there now
exists a minimum fermion mass for fermions sitting towards the UV brane. With a
quadratic Higgs VEV, this minimum mass is about fifteen orders of magnitude
lower than the electroweak scale. We derive the gauge propagator and despite
the KK masses scaling as , it is demonstrated that the
coefficients of four fermion operators are not divergent at tree level. FCNC's
amongst kaons and leptons are considered and compared to calculations in the RS
model, with a brane localised Higgs and equivalent levels of tuning. It is
found that since the gauge fermion couplings are slightly more universal and
the SM fermions typically sit slightly further towards the UV brane, the
contributions to observables such as and , from the
exchange of KK gauge fields, are significantly reduced.Comment: 33 pages, 15 figures, 5 tables; v2: references added; v3:
modifications to figures 4,5 and 6. version to appear in JHE
Developing and applying heterogeneous phylogenetic models with XRate
Modeling sequence evolution on phylogenetic trees is a useful technique in
computational biology. Especially powerful are models which take account of the
heterogeneous nature of sequence evolution according to the "grammar" of the
encoded gene features. However, beyond a modest level of model complexity,
manual coding of models becomes prohibitively labor-intensive. We demonstrate,
via a set of case studies, the new built-in model-prototyping capabilities of
XRate (macros and Scheme extensions). These features allow rapid implementation
of phylogenetic models which would have previously been far more
labor-intensive. XRate's new capabilities for lineage-specific models,
ancestral sequence reconstruction, and improved annotation output are also
discussed. XRate's flexible model-specification capabilities and computational
efficiency make it well-suited to developing and prototyping phylogenetic
grammar models. XRate is available as part of the DART software package:
http://biowiki.org/DART .Comment: 34 pages, 3 figures, glossary of XRate model terminolog
Pauli's Principle in Probe Microscopy
Exceptionally clear images of intramolecular structure can be attained in
dynamic force microscopy through the combination of a passivated tip apex and
operation in what has become known as the "Pauli exclusion regime" of the
tip-sample interaction. We discuss, from an experimentalist's perspective, a
number of aspects of the exclusion principle which underpin this ability to
achieve submolecular resolution. Our particular focus is on the origins,
history, and interpretation of Pauli's principle in the context of interatomic
and intermolecular interactions.Comment: This is a chapter from "Imaging and Manipulation of Adsorbates using
Dynamic Force Microscopy", a book which is part of the "Advances in Atom and
Single Molecule Machines" series published by Springer
[http://www.springer.com/series/10425]. To be published late 201
Reemergence of anthropogenic carbon into the ocean's mixed layer strongly amplifies transient climate sensitivity
A positive marine chemistryâclimate feedback was originally proposed by Revelle and Suess (1957, https://doi.org/10.3402/tellusa.v9i1.9075), whereby the invasion flux of anthropogenic carbon into the ocean serves to inhibit future marine CO2 uptake through reductions to the buffering capacity of surface seawater. Here we use an ocean circulationâcarbon cycle model to identify an upper limit on the impact of reemergence of anthropogenic carbon into the ocean's mixed layer on the cumulative airborne fraction of CO2 in the atmosphere. We find under an RCP8.5 emissions pathway (with steady circulation) that the cumulative airborne fraction of CO2 has a sevenfold reduction by 2100 when the CO2 buffering capacity of surface seawater is maintained at preindustrial levels. Our results indicate that the effect of reemergence of anthropogenic carbon into the mixed layer on the buffering capacity of CO2 amplifies the transient climate sensitivity of the Earth system
Silicon-based spin and charge quantum computation
Silicon-based quantum-computer architectures have attracted attention because
of their promise for scalability and their potential for synergetically
utilizing the available resources associated with the existing Si technology
infrastructure. Electronic and nuclear spins of shallow donors (e.g.
phosphorus) in Si are ideal candidates for qubits in such proposals due to the
relatively long spin coherence times. For these spin qubits, donor electron
charge manipulation by external gates is a key ingredient for control and
read-out of single-qubit operations, while shallow donor exchange gates are
frequently invoked to perform two-qubit operations. More recently, charge
qubits based on tunnel coupling in P substitutional molecular ions in Si
have also been proposed. We discuss the feasibility of the building blocks
involved in shallow donor quantum computation in silicon, taking into account
the peculiarities of silicon electronic structure, in particular the six
degenerate states at the conduction band edge. We show that quantum
interference among these states does not significantly affect operations
involving a single donor, but leads to fast oscillations in electron exchange
coupling and on tunnel-coupling strength when the donor pair relative position
is changed on a lattice-parameter scale. These studies illustrate the
considerable potential as well as the tremendous challenges posed by donor spin
and charge as candidates for qubits in silicon.Comment: Review paper (invited) - to appear in Annals of the Brazilian Academy
of Science
Prevalence of Disorders Recorded in Dogs Attending Primary-Care Veterinary Practices in England
Purebred dog health is thought to be compromised by an increasing occurence of inherited diseases but inadequate prevalence data on common disorders have hampered efforts to prioritise health reforms. Analysis of primary veterinary practice clinical data has been proposed for reliable estimation of disorder prevalence in dogs. Electronic patient record (EPR) data were collected on 148,741 dogs attending 93 clinics across central and south-eastern England. Analysis in detail of a random sample of EPRs relating to 3,884 dogs from 89 clinics identified the most frequently recorded disorders as otitis externa (prevalence 10.2%, 95% CI: 9.1-11.3), periodontal disease (9.3%, 95% CI: 8.3-10.3) and anal sac impaction (7.1%, 95% CI: 6.1-8.1). Using syndromic classification, the most prevalent body location affected was the head-and-neck (32.8%, 95% CI: 30.7-34.9), the most prevalent organ system affected was the integument (36.3%, 95% CI: 33.9-38.6) and the most prevalent pathophysiologic process diagnosed was inflammation (32.1%, 95% CI: 29.8-34.3). Among the twenty most-frequently recorded disorders, purebred dogs had a significantly higher prevalence compared with crossbreds for three: otitis externa (Pâ=â0.001), obesity (Pâ=â0.006) and skin mass lesion (Pâ=â0.033), and popular breeds differed significantly from each other in their prevalence for five: periodontal disease (Pâ=â0.002), overgrown nails (Pâ=â0.004), degenerative joint disease (Pâ=â0.005), obesity (Pâ=â0.001) and lipoma (Pâ=â0.003). These results fill a crucial data gap in disorder prevalence information and assist with disorder prioritisation. The results suggest that, for maximal impact, breeding reforms should target commonly-diagnosed complex disorders that are amenable to genetic improvement and should place special focus on at-risk breeds. Future studies evaluating disorder severity and duration will augment the usefulness of the disorder prevalence information reported herein
Ethanol reversal of tolerance to the respiratory depressant effects of morphine
Opioids are the most common drugs associated with unintentional drug overdose. Death results from respiratory depression. Prolonged use of opioids results in the development of tolerance but the degree of tolerance is thought to vary between different effects of the drugs. Many opioid addicts regularly consume alcohol (ethanol), and post-mortem analyses of opioid overdose deaths have revealed an inverse correlation between blood morphine and ethanol levels. In the present study, we determined whether ethanol reduced tolerance to the respiratory depressant effects of opioids. Mice were treated with opioids (morphine, methadone, or buprenorphine) for up to 6 days. Respiration was measured in freely moving animals breathing 5% CO(2) in air in plethysmograph chambers. Antinociception (analgesia) was measured as the latency to remove the tail from a thermal stimulus. Opioid tolerance was assessed by measuring the response to a challenge dose of morphine (10âmg/kg i.p.). Tolerance developed to the respiratory depressant effect of morphine but at a slower rate than tolerance to its antinociceptive effect. A low dose of ethanol (0.3âmg/kg) alone did not depress respiration but in prolonged morphine-treated animals respiratory depression was observed when ethanol was co-administered with the morphine challenge. Ethanol did not alter the brain levels of morphine. In contrast, in methadone- or buprenorphine-treated animals no respiratory depression was observed when ethanol was co-administered along with the morphine challenge. As heroin is converted to morphine in man, selective reversal of morphine tolerance by ethanol may be a contributory factor in heroin overdose deaths
Nutrition Strategies for Triathlon
Contemporary sports nutrition guidelines recommend that each athlete develop a personalised, periodised and practical approach to eating that allows him or her to train hard, recover and adapt optimally, stay free of illness and injury and compete at their best at peak races. Competitive triathletes undertake a heavy training programme to prepare for three different sports while undertaking races varying in duration from 20 min to 10 h. The everyday diet should be adequate in energy availability, provide CHO in varying amounts and timing around workouts according to the benefits of training with low or high CHO availability and spread high-quality protein over the day to maximise the adaptive response to each session. Race nutrition requires a targeted and well-practised plan that maintains fuel and hydration goals over the duration of the specific event, according to the opportunities provided by the race and other challenges, such as a hot environment. Supplements and sports foods can make a small contribution to a sports nutrition plan, when medical supplements are used under supervision to prevent/treat nutrient deficiencies (e.g. iron or vitamin D) or when sports foods provide a convenient source of nutrients when it is impractical to eat whole foods. Finally, a few evidence-based performance supplements may contribute to optimal race performance when used according to best practice protocols to suit the triathleteâs goals and individual responsiveness
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