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"Warburton, P."
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Space chimps
A trio of chimpanzees are recruited to retrieve a wayward space probe and find themselves having to save the peaceful inhabitants of a distant planet from an evil dictator.
DVD
Velocity of Greenland's Helheim Glacier Controlled Both by Terminus Effects and Subglacial Hydrology With Distinct Realms of Influence
Two outstanding questions for the future of the Greenland Ice Sheet are (a) how enhanced meltwater draining beneath the ice will impact the behavior of large tidewater glaciers, and (b) to what extent tidewater glacier velocity is driven by changes at the terminus versus changes in sliding velocity due to meltwater. We present a two‐way coupled framework to simulate the nonlinear feedbacks of evolving subglacial hydrology and ice dynamics using the Subglacial Hydrology And Kinetic, Transient Interactions (SHAKTI) model within the Ice‐sheet and Sea‐level System Model (ISSM). Through coupled simulations of Helheim Glacier, we find that terminus effects dominate the seasonal velocity pattern up to 15 km from the terminus, while hydrology drives the velocity response upstream. With increased melt, the hydrology influence yields seasonal acceleration of several hundred meters per year in the interior, suggesting that hydrology will play an important role in future mass balance of tidewater glaciers. Plain Language Summary Water draining under glaciers and ice sheets affects the friction between the ice and the bed, and controls how fast the ice can slide into the ocean, contributing to sea‐level rise. We present a framework for simulating the feedbacks between hydrology and ice flow. We investigate the relative influence of changes at the terminus of the glacier where it meets the ocean, versus changes in meltwater drainage, in determining how fast the glacier moves. Our modeling of Helheim Glacier in southeast Greenland highlights the importance of terminus effects up to 15 km from the terminus, and hydrology farther upstream, with increased melt yielding higher inland acceleration. These results suggest that meltwater will play an increasingly important role in the future behavior of glaciers. Key Points We couple a subglacial hydrology model with an ice flow model to simulate the relationship between sliding velocity and effective pressure Terminus effects at Helheim Glacier drive velocity up to 15 km upstream, but seasonal hydrology controls velocity patterns further inland Increased melt accelerates ice inland of the main trunk, implying importance of hydrology in tidewater glacier future mass balance
Journal Article
Presence of Frozen Fringe Impacts Soft‐Bedded Slip Relationship
Glaciers and ice streams flowing over sediment beds commonly have a layer of ice‐rich debris adhered to their base, known as a “frozen fringe,” but its impact on basal friction is unknown. We simulated basal slip over granular beds with a cryogenic ring shear device while ice infiltrated the bed to grow a fringe, and measured the frictional response under different effective stresses and slip speeds. Frictional resistance increased with increasing slip speed until it plateaued at the frictional strength of the till, closely resembling the regularized Coulomb slip law associated with clean ice over deformable beds. We hypothesize that this arises from deformation in a previously unidentified zone of weakly frozen sediments at the fringe's base, which is highly sensitive to temperature and stress gradients. We show how a rheologic model for ice‐rich debris coupled with the thermomechanics of fringe growth can account for the regularized Coulomb behavior. Plain Language Summary Many glaciers move by sliding over sediment beds. As the glacier flows downslope, ice can infiltrate the underlying sediments, forming a layer of ice‐rich debris attached at the glacier's base. We investigated how this frozen fringe impacts glacier motion by simulating glacier slip in a cold‐room facility with a specialized ring shear device. We recreated glacier conditions, sliding ice over granular beds to form the fringe, and then assessed how frictional resistance at the slip interface varied under different stresses and ice speeds. We found that frozen fringe influences the relationship between ice speed and frictional resistance, known as the “slip law.” As ice speed increased, basal friction increased to a threshold that matches the strength of the ice‐free sediment bed—mirroring the “regularized Coulomb slip law” inferred for clean ice over soft beds. We attribute this behavior to deformation in a weakly frozen zone at the base of the frozen fringe and show how this behavior can be incorporated into existing parameterizations of glacier slip. Key Points Ring shear experiments show frozen fringe alters basal slip dynamics for soft‐bedded glaciers Deformation in a zone of weakly frozen sediments within the fringe leads to a regularized Coulomb slip response
Journal Article
Circuit design for multi-body interactions in superconducting quantum annealing systems with applications to a scalable architecture
Quantum annealing provides a way of solving optimization problems by encoding them as Ising spin models which are implemented using physical qubits. The solution of the optimization problem then corresponds to the ground state of the system. Quantum tunneling is harnessed to enable the system to move to the ground state in a potentially high non-convex energy landscape. A major difficulty in encoding optimization problems in physical quantum annealing devices is the fact that many real world optimization problems require interactions of higher connectivity, as well as multi-body terms beyond the limitations of the physical hardware. In this work we address the question of how to implement multi-body interactions using hardware which natively only provides two-body interactions. The main result is an efficient circuit design of such multi-body terms using superconducting flux qubits in which effective
N
-body interactions are implemented using
N
ancilla qubits and only two inductive couplers. It is then shown how this circuit can be used as the unit cell of a scalable architecture by applying it to a recently proposed embedding technique for constructing an architecture of logical qubits with arbitrary connectivity using physical qubits which have nearest-neighbor four-body interactions. It is further shown that this design is robust to non-linear effects in the coupling loops, as well as mismatches in some of the circuit parameters.
Quantum computing: Superconducting multi-qubit interaction circuits
A new method to build devices which implement interactions between more than two qubits in quantum annealing systems similar to those produced by D-Wave Systems has been proposed by a collaboration from UCL, Durham University, and the University of Oxford led by Paul Warburton. Such interactions occur naturally in many real world optimization problems. They demonstrate that constructing these circuits is experimentally feasible in the near term, and discuss how additional degrees of freedom included in their technique could help solve problems more efficiently. This new coupler design opens up a wide array of new architectural possibilities for these devices, as well as new ways in which they could solve problems, potentially leading to a new generation of more efficient quantum annealers.
Journal Article
A Direct Mapping of Max k-SAT and High Order Parity Checks to a Chimera Graph
We demonstrate a direct mapping of max
k
-SAT problems (and weighted max
k
-SAT) to a Chimera graph, which is the non-planar hardware graph of the devices built by D-Wave Systems Inc. We further show that this mapping can be used to map a similar class of maximum satisfiability problems where the clauses are replaced by parity checks over potentially large numbers of bits. The latter is of specific interest for applications in decoding for communication. We discuss an example in which the decoding of a turbo code, which has been demonstrated to perform near the Shannon limit, can be mapped to a Chimera graph. The weighted max
k
-SAT problem is the most general class of satisfiability problems, so our result effectively demonstrates how any satisfiability problem may be directly mapped to a Chimera graph. Our methods faithfully reproduce the low energy spectrum of the target problems, so therefore may also be used for maximum entropy inference.
Journal Article
Association of the arterial access site at angioplasty with transfusion and mortality: the M.O.R.T.A.L study (Mortality benefit Of Reduced Transfusion after percutaneous coronary intervention via the Arm or Leg)
Background: Bleeding and transfusion after percutaneous coronary intervention (PCI) are known predictors of mortality. Transradial arterial access reduces bleeding and transfusion related to femoral access complications, although its association with mortality is unknown. Objective: To determine the association of arterial access site (radial or femoral) with transfusion and mortality in unselected PCIs. Design, setting and patients: By data linkage of three prospectively collated provincial registries, 38 872 procedures in 32 822 patients in British Columbia were analysed. The association between access site, transfusion and outcomes was assessed by logistic regression, propensity score matching and probit regression. Main outcome measures: 30-Day and 1-year mortality. Results: 1134 (3.5%) patients had at least one blood transfusion. Transfused patients had a significantly increased 30-day and 1-year mortality, adjusted odds ratio (95% CI) 4.01 (3.08 to 5.22) and 3.58 (2.94 to 4.36), respectively. By probit regression the absolute increase in risk of death at 1 year associated with receiving a transfusion was 6.78%. The number needed to treat was 14.74 (prevention of 15 transfusions required to “avoid” one death). Radial access halved the transfusion rate. After adjustment for all variables, radial access was associated with a significant reduction in 30-day and 1-year mortality, odds ratio = 0.71 (95% CI 0.61 to 0.82) and 0.83 (0.71 to 0.98), respectively (all p<0.001). Conclusions: In a registry of all comers to PCI, transradial access was associated with a halving of the transfusion rate and a reduction in 30-day and 1-year mortality.
Journal Article
A shallow approximation for ice streams sliding over strong beds
Ice streams are regions of rapid ice sheet flow characterised by a high degree of sliding over a deforming bed. The shallow shelf approximation (SSA) provides a convenient way to obtain closed-form approximations of the velocity and flux in a rapidly sliding ice stream when the basal drag is much less than the driving stress. However, the validity of the SSA approximation breaks down when the magnitude of the basal drag increases. Here we find a more accurate expression for the velocity and flux in this transitional regime before vertical deformation fully dominates, in agreement with numerical results. The closed-form expressions we derive can be incorporated into wider modelling efforts to yield a better characterisation of ice stream dynamics, and inform the use of the SSA in large-scale simulations.
Journal Article
Towards modelling of corrugation ridges at ice-sheet grounding lines
Improvements in the resolution of sea-floor mapping techniques have revealed extremely regular, sub-metre-scale ridge landforms produced by the tidal flexure of ice-shelf grounding lines as they retreated very rapidly (i.e. at rates of several kilometres per year). Guided by such novel sea-floor observations from Thwaites Glacier, West Antarctica, we present three mathematical models for the formation of these corrugation ridges at a tidally migrating grounding line (that is retreating at a constant rate), where each ridge is formed by either constant till flux to the grounding line, till extrusion from the grounding line, or the resuspension and transport of grains from the grounding-zone bed. We find that both till extrusion (squeezing out till like toothpaste as the ice sheet re-settles on the sea floor) and resuspension and transport of material can qualitatively reproduce regular, delicate ridges at a retreating grounding line, as described by sea-floor observations. By considering the known properties of subglacial sediments, we agree with existing schematic models that the most likely mechanism for ridge formation is till extrusion at each low-tide position, essentially preserving an imprint of the ice-sheet grounding line as it retreated. However, when realistic (shallow) bed slopes are used in the simulations, ridges start to overprint one another, suggesting that, to preserve the regular ridges that have been observed, grounding line retreat rates (driven by dynamic thinning?) may be even higher than previously thought.
Journal Article
The comparative effect of propolis and chlorhexidine mouthwash on oral nitrite-producing bacteria and blood pressure regulation
Propolis mouthwash (PROP-M) has demonstrated antibacterial properties like those of chlorhexidine mouthwash (CHX-M). However, its impact on the abundance of oral nitrite-producing species (NPS) and nitrite-producing activity (NPA) remains unexplored.
Forty-five healthy individuals were randomised into 2 groups to rinse their mouth twice a day for seven days with either CHX-M (
= 21) or PROP-M (
= 24). Metagenomic sequencing (16S rRNA) was performed on saliva samples collected before and after each treatment. Additionally, salivary biomarkers and blood pressure were measured.
CHX-M increased the relative abundance of NPS (
< 0.001) but significantly impaired the NPA (
< 0.001) compared to baseline and PROP-M. No significant differences in the relative abundance of NPS and NPA were observed in the PROP-M group. However, a significant increase of plasma nitrate (+7 µmol/L,
= 0.047) and a decrease in systolic BP (-2 mmHg,
= 0.022) was observed in this group compared to the baseline.
The results indicate that PROP-M had a smaller effect on the abundance of NPS and NPA compared to CHX-M. Additionally, PROP-M reduced blood pressure in healthy individuals, but this effect was not associated with changes in the oral microbiome.
Journal Article
Verification of tolerance to infection by Ceratocystis manginecans in clones of Acacia mangium
Ceratocystis canker and wilt disease has had a devastating impact on plantations of Acacia mangium in Sabah, Malaysia effectively resulting in its discontinuation in the region. The immediate future of industrial tree plantations in Malaysia relies on alternative species, such as Eucalyptus pellita, which are suited to the environment and market opportunities. However, identifying A. mangium planting stock with high levels of tolerance to Ceratocystis manginecans provides substantial opportunities for its large scale planting and sustainability in the future. The aim of this study was to verify tolerance to C. manginecans in over 100 putatively tolerant A. mangium clones selected from a family screening trial consisting of 100 wild families. Selections from the family screening trial were based on either short-lesion length measured six weeks after inoculation or survival 12 months post inoculation. Six clonal trials were established under field conditions over two years with more than five ramets of most clones tested in at least two separate trials. The trees were inoculated with C. manginecans 12 months after trial establishment, and assessments of crown health and survival as well as the presence or absence of sunken bark, gummosis or stem borer infestation were carried out 12 months post inoculation. Narrow-sense heritability estimates were moderate for external variables and for crown health (0.14–0.24) and survival (0.14–0.22). Genetic correlation estimates between trials were generally high, indicating that assessments were repeatable across trials. Correlations between traits used to assess damage following inoculation indicated that different traits may be used to identify clones that tolerate infection. The accuracy of the screening showed that resistant clones can be identified and used to produce A. mangium tolerant to infection by C. manginecans.
Journal Article