22,884 research outputs found

    Solar irradiance models and measurements: a comparison in the 220 nm to 240 nm wavelength band

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    Solar irradiance models that assume solar irradiance variations to be due to changes in the solar surface magnetic flux have been successfully used to reconstruct total solar irradiance on rotational as well as cyclical and secular time scales. Modelling spectral solar irradiance is not yet as advanced, and also suffers from a lack of comparison data, in particular on solar-cycle time scales. Here we compare solar irradiance in the 220 nm to 240 nm band as modelled with SATIRE-S and measured by different instruments on the UARS and SORCE satellites. We find good agreement between the model and measurements on rotational time scales. The long-term trends, however, show significant differences. Both SORCE instruments, in particular, show a much steeper gradient over the decaying part of cycle 23 than the modelled irradiance or that measured by UARS/SUSIM.Comment: 8 pages, 2 figures, conference proceedings to appear in Surveys in Geophysic

    Critical Dynamical Exponent of the Two-Dimensional Scalar Ļ•4\phi^4 Model with Local Moves

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    We study the scalar one-component two-dimensional (2D) Ļ•4\phi^4 model by computer simulations, with local Metropolis moves. The equilibrium exponents of this model are well-established, e.g. for the 2D Ļ•4\phi^4 model Ī³=1.75\gamma= 1.75 and Ī½=1\nu= 1. The model has also been conjectured to belong to the Ising universality class. However, the value of the critical dynamical exponent zcz_c is not settled. In this paper, we obtain zcz_c for the 2D Ļ•4\phi^4 model using two independent methods: (a) by calculating the relative terminal exponential decay time Ļ„\tau for the correlation function āŸØĻ•(t)Ļ•(0)āŸ©\langle \phi(t)\phi(0)\rangle, and thereafter fitting the data as Ļ„āˆ¼Lzc\tau \sim L^{z_c}, where LL is the system size, and (b) by measuring the anomalous diffusion exponent for the order parameter, viz., the mean-square displacement (MSD) āŸØĪ”Ļ•2(t)āŸ©āˆ¼tc\langle \Delta \phi^2(t)\rangle\sim t^c as c=Ī³/(Ī½zc)c=\gamma/(\nu z_c), and from the numerically obtained value cā‰ˆ0.80c\approx 0.80, we calculate zcz_c. For different values of the coupling constant Ī»\lambda, we report that zc=2.17Ā±0.03z_c=2.17\pm0.03 and zc=2.19Ā±0.03z_c=2.19\pm0.03 for the two methods respectively. Our results indicate that zcz_c is independent of Ī»\lambda, and is likely identical to that for the 2D Ising model. Additionally, we demonstrate that the Generalised Langevin Equation (GLE) formulation with a memory kernel, identical to those applicable for the Ising model and polymeric systems, consistently capture the observed anomalous diffusion behavior.Comment: 14 pages, 4 figures, 6 figure files, to appear in Phys. Rev.

    The social geography of childcare: 'making up' the middle class child

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    Childcare is a condensate of disparate social forces and social processes. It is gendered and classed. It is subject to an excess of policy and political discourse. It is increasingly a focus for commercial exploitation. This is a paper reporting on work in progress in an ESRC funded research project (R000239232) on the choice and provision of pre-school childcare by middle class (service class) families in two contrasting London locations. Drawing on recent work in class analysis the paper examines the relationships between childcare choice, middle class fractions and locality. It suggests that on the evidence of the findings to date, there is some evidence of systematic differences between fractions in terms of values, perspectives and preferences for childcare, but a more powerful case for intra-class similarities, particularly when it comes to putting preferences into practice in the 'making up of a middle class child' through care and education

    Diffusion-limited aggregation as branched growth

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    I present a first-principles theory of diffusion-limited aggregation in two dimensions. A renormalized mean-field approximation gives the form of the unstable manifold for branch competition, following the method of Halsey and Leibig [Phys. Rev. A {\bf 46}, 7793 (1992)]. This leads to a result for the cluster dimensionality, D \approx 1.66, which is close to numerically obtained values. In addition, the multifractal exponent \tau(3) = D in this theory, in agreement with a proposed `electrostatic' scaling law.Comment: 13 pages, one figure not included (available by request, by ordinary mail), Plain Te

    Making co-enrolment feasible for randomised controlled trials in paediatric intensive care.

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    Enrolling children into several trials could increase recruitment and lead to quicker delivery of optimal care in paediatric intensive care units (PICU). We evaluated decisions taken by clinicians and parents in PICU on co-enrolment for two large pragmatic trials: the CATCH trial (CATheters in CHildren) comparing impregnated with standard central venous catheters (CVCs) for reducing bloodstream infection in PICU and the CHIP trial comparing tight versus standard control of hyperglycaemia

    Experimental quantum verification in the presence of temporally correlated noise

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    Growth in the complexity and capabilities of quantum information hardware mandates access to practical techniques for performance verification that function under realistic laboratory conditions. Here we experimentally characterise the impact of common temporally correlated noise processes on both randomised benchmarking (RB) and gate-set tomography (GST). We study these using an analytic toolkit based on a formalism mapping noise to errors for arbitrary sequences of unitary operations. This analysis highlights the role of sequence structure in enhancing or suppressing the sensitivity of quantum verification protocols to either slowly or rapidly varying noise, which we treat in the limiting cases of quasi-DC miscalibration and white noise power spectra. We perform experiments with a single trapped 171^{171}Yb+^{+} ion as a qubit and inject engineered noise (āˆĻƒz\propto \sigma^z) to probe protocol performance. Experiments on RB validate predictions that the distribution of measured fidelities over sequences is described by a gamma distribution varying between approximately Gaussian for rapidly varying noise, and a broad, highly skewed distribution for the slowly varying case. Similarly we find a strong gate set dependence of GST in the presence of correlated errors, leading to significant deviations between estimated and calculated diamond distances in the presence of correlated Ļƒz\sigma^z errors. Numerical simulations demonstrate that expansion of the gate set to include negative rotations can suppress these discrepancies and increase reported diamond distances by orders of magnitude for the same error processes. Similar effects do not occur for correlated Ļƒx\sigma^x or Ļƒy\sigma^y errors or rapidly varying noise processes, highlighting the critical interplay of selected gate set and the gauge optimisation process on the meaning of the reported diamond norm in correlated noise environments.Comment: Expanded and updated analysis of GST, including detailed examination of the role of gauge optimization in GST. Full GST data sets and supplementary information available on request from the authors. Related results available from http://www.physics.usyd.edu.au/~mbiercuk/Publications.htm

    Pore-blockade Times for Field-Driven Polymer Translocation

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    We study pore blockade times for a translocating polymer of length NN, driven by a field EE across the pore in three dimensions. The polymer performs Rouse dynamics, i.e., we consider polymer dynamics in the absence of hydrodynamical interactions. We find that the typical time the pore remains blocked during a translocation event scales as āˆ¼N(1+2Ī½)/(1+Ī½)/E\sim N^{(1+2\nu)/(1+\nu)}/E, where Ī½ā‰ƒ0.588\nu\simeq0.588 is the Flory exponent for the polymer. In line with our previous work, we show that this scaling behaviour stems from the polymer dynamics at the immediate vicinity of the pore -- in particular, the memory effects in the polymer chain tension imbalance across the pore. This result, along with the numerical results by several other groups, violates the lower bound āˆ¼N1+Ī½/E\sim N^{1+\nu}/E suggested earlier in the literature. We discuss why this lower bound is incorrect and show, based on conservation of energy, that the correct lower bound for the pore-blockade time for field-driven translocation is given by Ī·N2Ī½/E\eta N^{2\nu}/E, where Ī·\eta is the viscosity of the medium surrounding the polymer.Comment: 14 pages, 6 figures, slightly shorter than the previous version; to appear in J. Phys.: Cond. Ma
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