The range of potential applications of compact laser-plasma ion sources motivates the development of new acceleration schemes to increase achievable ion energies and conversion efficiencies. Whilst ...the evolving nature of laser-plasma interactions can limit the effectiveness of individual acceleration mechanisms, it can also enable the development of hybrid schemes, allowing additional degrees of control on the properties of the resulting ion beam. Here we report on an experimental demonstration of efficient proton acceleration to energies exceeding 94 MeV via a hybrid scheme of radiation pressure-sheath acceleration in an ultrathin foil irradiated by a linearly polarised laser pulse. This occurs via a double-peaked electrostatic field structure, which, at an optimum foil thickness, is significantly enhanced by relativistic transparency and an associated jet of super-thermal electrons. The range of parameters over which this hybrid scenario occurs is discussed and implications for ion acceleration driven by next-generation, multi-petawatt laser facilities are explored.
As antibiotic consumption grows, bacteria are becoming increasingly resistant to treatment. Antibiotic resistance undermines much of modern health care, which relies on access to effective ...antibiotics to prevent and treat infections associated with routine medical procedures. The resulting challenges have much in common with those posed by climate change, which economists have responded to with research that has informed and shaped public policy. Drawing on economic concepts such as externalities and the principal-agent relationship, we suggest how economics can help to solve the challenges arising from increasing resistance to antibiotics. We discuss solutions to the key economic issues, from incentivizing the development of effective new antibiotics to improving antibiotic stewardship through financial mechanisms and regulation.
Sustainable development requires the reconciliation of demands for biodiversity conservation and increased agricultural production. Assessing the impact of novel farming practices on biodiversity and ...ecosystem services is fundamental to this process. Using farmland birds as a model system, we present a generic risk assessment framework that accurately predicts each species' current conservation status and population growth rate associated with past changes in agriculture. We demonstrate its value by assessing the potential impact on biodiversity of two controversial land uses, genetically modified herbicide-tolerant crops and agri-environment schemes. This framework can be used to guide policy and land management decisions and to assess progress toward sustainability targets.
Abstract
This study aims to advance our knowledge about the role of public participation in formulating budgetary decisions of local governments. By focusing on participatory budgeting as a prominent ...form of public participation in the budgetary process, we posit that participatory budgeting serves two important roles in aligning the fiscal outcomes of local governments with citizen preferences: (1) increased transparency of the local budget and (2) improved budget literacy of citizens. This study investigates a link between participatory budgeting and the fiscal outcomes of local governments by utilizing data drawn from Korean local governments for seven fiscal years. Employing instrumental variable regression to address endogeneity, there is strong evidence that public participation and deliberation during the participatory budgeting process have a positive association with the fiscal balance. There is also weak evidence that the authority delegated to participatory budgeting participants affects the fiscal balance. The findings of this study imply that it is the quality of public participation that matters in holding the government accountable for its fiscal decisions.
Functional networks are comprised of neuronal ensembles bound through synchronization across multiple intrinsic oscillatory frequencies. Various coupled interactions between brain oscillators have ...been described (e.g., phase-amplitude coupling), but with little evidence that these interactions actually influence perceptual sensitivity. Here, electroencephalographic (EEG) recordings were made during a sustained-attention task to demonstrate that cross-frequency coupling has significant consequences for perceptual outcomes (i.e., whether participants detect a near-threshold visual target). The data reveal that phase-detection relationships at higher frequencies are dependent on the phase of lower frequencies, such that higher frequencies alternate between periods when their phase is either strongly or weakly predictive of visual-target detection. Moreover, the specific higher frequencies and scalp topographies linked to visual-target detection also alternate as a function of lower-frequency phase. Cross-frequency coupling between lower (i.e., delta and theta) and higher frequencies (e.g., low- and high-beta) thus results in dramatic fluctuations of visual-target detection.
► Cross-frequency coupling shapes visual perception. ► The phase of lower frequencies determines the influence of higher frequencies. ► The frequencies and scalp topographies linked with detection are not static. ► Oscillations at multiple frequencies are linked to visual-target detection.
We report the detection of two new planets from the Anglo-Australian Planet Search. These planets orbit two stars each previously known to host one planet. The new planet orbiting HD 142 has a period ...of 6005 + or - 427 days, and a minimum mass of 5.3 M sub(Jup). HD 142c is thus a new Jupiter analog: a gas-giant planet with a long period and low eccentricity (e = 0.21 + or - 0.07). The second planet in the HD 159868 system has a period of 352.3 + or - 1.3 days and m sin i = 0.73 + or - 0.05 M sub(Jup). In both of these systems, including the additional planets in the fitting process significantly reduced the eccentricity of the original planet. These systems are thus examples of how multiple-planet systems can masquerade as moderately eccentric single-planet systems.
Computing the velocity field is an expensive process for mantle convection codes. This has implications for particle methods used to model the advection of quantities such as temperature or ...composition. A common choice for the numerical treatment of particle trajectories is classical fourth‐order explicit Runge–Kutta (ERK4) integration, which involves a velocity computation at each of its four stages. To reduce the cost per time step, it is possible to evaluate the velocity for a subset of the four time integration stages. We explore two such alternative schemes, in which velocities are only computed for: (a) stage 1 on odd‐numbered time steps and stages 2–4 for even‐numbered time steps, and (b) stage 1 for all time steps. A theoretical analysis of stability and accuracy is presented for all schemes. It was found that the alternative schemes are first‐order accurate with stability regions different from that of ERK4. The efficiency and accuracy of the alternate schemes were compared against ERK4 in four test problems covering isothermal, thermal, and thermochemical flows. Exact solutions were used as reference solutions when available. In agreement with theory, the alternate schemes were observed to be first‐order accurate for all test problems. Accordingly, they may be used to efficiently compute solutions to within modest error tolerances. For small error tolerances, however, ERK4 was the most efficient.
Plain Language Summary
Computation of the flow velocity is an expensive process for mantle convection codes. For high‐velocity flows, tracer particle methods can be used to model the transport of mantle material while minimizing model errors such as artificial diffusion. A major element of tracer particle methods is the computation of particle trajectories, which is commonly done using Runge–Kutta (RK) methods. A popular choice is the classical fourth‐order accurate RK method, which is comprised of four stages per model time step. Strictly speaking, flow velocities are to be computed for each RK stage. However, flow velocities can be computed less often in order to reduce computation time. In this study, we examine the impact of how often the flow velocities are computed during time integration on accuracy and efficiency. We find that velocities can be computed less frequently to efficiently compute solutions to modest error tolerances. However, computing the velocities for every time integration stage is the most efficient way to find solutions with tight error tolerances. Specifically, highly accurate results can be achieved with less computation time using the classical fourth‐order explicit RK method with velocity updates at all four stages.
Key Points
Computation of the velocity field is expensive for mantle convection codes
Computing the velocity for a subset of Runge–Kutta stages can give acceptable results for modest error tolerances at reduced cost
The reduced cost from not updating the velocity at each time integration stage is not worth the accuracy lost for tight error tolerances
The purpose of this study was to investigate the influence that replacing natural coarse aggregate with recycled concrete aggregate (RCA) has on concrete bond strength with reinforcing steel. Two ...sources of RCA were used along with one natural aggregate source. Numerous aggregate properties were measured for all aggregate sources. Two types of concrete mixture proportions were developed replacing 100% of the natural aggregate with RCA. The first type maintained the same water–cement ratios while the second type was designed to achieve the same compressive strengths. Beam-end specimens were tested to determine the relative bond strength of RCA and natural aggregate concrete. On average, natural aggregate concrete specimens had bond strengths that were 9 to 19% higher than the equivalent RCA specimens. Bond strength and the aggregate crushing value seemed to correlate well for all concrete types.
ABSTRACT
Our understanding of planetary systems different to our own has grown dramatically in the past 30 yr. However, our efforts to ascertain the degree to which the Solar system is abnormal or ...unique have been hindered by the observational biases inherent to the methods that have yielded the greatest exoplanet hauls. On the basis of such surveys, one might consider our planetary system highly unusual – but the reality is that we are only now beginning to uncover the true picture. In this work, we use the full 18-yr archive of data from the Anglo-Australian Planet Search to examine the abundance of ‘cool Jupiters’ – analogues to the Solar system’s giant planets, Jupiter and Saturn. We find that such planets are intrinsically far more common through the cosmos than their siblings, the hot Jupiters. We find that the occurrence rate of such ‘cool Jupiters’ is $6.73^{+2.09}_{-1.13}$ per cent, almost an order of magnitude higher than the occurrence of hot Jupiters (at $0.84^{+0.70}_{-0.20}$ per cent). We also find that the occurrence rate of giant planets is essentially constant beyond orbital distances of ∼1 au. Our results reinforce the importance of legacy radial velocity surveys for the understanding of the Solar system’s place in the cosmos.
Using data from Truven Health MarketScan Commercial Claims and Encounters Database between 2009 and 2015, we studied the effects of medical and recreational marijuana laws on opioid prescribing in ...employer‐sponsored health insurance. We used a differences‐in‐differences (DD) approach and found that the implementation of medical marijuana laws (MMLs) and recreational marijuana laws (RMLs) reduced morphine milligram equivalents per enrollee by 7% and 13%, respectively. The reduction associated with MMLs was predominately in people aged 55–64, whereas the reduction associated with RMLs was largely in people aged 35–44 and aged 45–54. Our findings suggest that both MMLs and RMLs have the potential to reduce opioid prescribing in the privately insured population, especially for the middle‐aged population.