Low temperature phase diagram and critical behaviour of the four-state chiral clock model

The low temperature behaviour of the four-state chiral clock ($CC_4$) model is reexamined using a systematic low temperature series expansion of the free energy. Previously obtained results for the low temperature phases are corrected and the low temperature phase diagram is derived. In addition, the phase transition from the modulated region to the high temperature paraphase is shown to belong to the universality class of the 3d-XY model.Comment: 17 pages in ioplppt style, 3 figure

Coarsening Dynamics of Crystalline Thin Films

The formation of pyramid-like structures in thin-film growth on substrates with a quadratic symmetry, e.g., {001} surfaces, is shown to exhibit anisotropic scaling as there exist two length scales with different time dependences. Analytical and numerical results indicate that for most realizations coarsening of mounds is described by an exponent n=0.2357. However, depending on material parameters, n may lie between 0 (logarithmic coarsening) and 1/3. In contrast, growth on substrates with triangular symmetries ({111} surfaces) is dominated by a single length scale and an exponent n=1/3.Comment: RevTeX, 4 pages, 3 figure

Reconstructing ice-sheet accumulation rates at ridge B, East Antarctica

Understanding how ice sheets responded to past climate change is fundamental to forecasting how they will respond in the future. Numerical models calculating the evolution of ice sheets depend upon accumulation data, which are principally available from ice cores. Here, we calculate past rates of ice accumulation using internal layering. The englacial structure of the East Antarctic ice divide at ridge B is extracted from airborne ice-penetrating radar. The isochronous surfaces are dated at their intersection with the Vostok ice-core site, where the depth–age relationship is known. The dated isochrons are used as input to a one-dimensional ice-flow model to investigate the spatial accumulation distribution. The calculations show that ice-accumulation rates generally increase from Vostok lake towards ridge B. The western flank of the ice divide experiences markedly more accumulation than in the east. Further, ice accumulation increases northwards along the ice divide. The results also show the variability of accumulation in time and space around the ridge B ice divide over the last 124 000 years

Strong Resonance of Light in a Cantor Set

The propagation of an electromagnetic wave in a one-dimensional fractal object, the Cantor set, is studied. The transfer matrix of the wave amplitude is formulated and its renormalization transformation is analyzed. The focus is on resonant states in the Cantor set. In Cantor sets of higher generations, some of the resonant states closely approach the real axis of the wave number, leaving between them a wide region free of resonant states. As a result, wide regions of nearly total reflection appear with sharp peaks of the transmission coefficient beside them. It is also revealed that the electromagnetic wave is strongly enhanced and localized in the cavity of the Cantor set near the resonant frequency. The enhancement factor of the wave amplitude at the resonant frequency is approximately $6/|\eta_\mathrm{r}|$, where $\eta_\mathrm{r}$ is the imaginary part of the corresponding resonant eigenvalue. For example, a resonant state of the lifetime $\tau_\mathrm{r}=4.3$ms and of the enhancement factor $M=7.8\times10^7$ is found at the resonant frequency $\omega_\mathrm{r}=367$GHz for the Cantor set of the fourth generation of length L=10cm made of a medium of the dielectric constant $\epsilon=10$.Comment: 20 pages, 11 figures, to be published in Journal of the Physical Society of Japa

Event generation with SHERPA 1.1

In this paper the current release of the Monte Carlo event generator Sherpa, version 1.1, is presented. Sherpa is a general-purpose tool for the simulation of particle collisions at high-energy colliders. It contains a very flexible tree-level matrix-element generator for the calculation of hard scattering processes within the Standard Model and various new physics models. The emission of additional QCD partons off the initial and final states is described through a parton-shower model. To consistently combine multi-parton matrix elements with the QCD parton cascades the approach of Catani, Krauss, Kuhn and Webber is employed. A simple model of multiple interactions is used to account for underlying events in hadron--hadron collisions. The fragmentation of partons into primary hadrons is described using a phenomenological cluster-hadronisation model. A comprehensive library for simulating tau-lepton and hadron decays is provided. Where available form-factor models and matrix elements are used, allowing for the inclusion of spin correlations; effects of virtual and real QED corrections are included using the approach of Yennie, Frautschi and Suura.Comment: 47 pages, 21 figure

The future of UK Antarctic science: strategic priorities essential needs and opportunities for international leadership

• The Antarctic region has been experiencing rapid change in recent decades due to human induced factors. Most notably, climate heating is causing ice sheet melting, leading to sea level rise and disruption in global ocean heat circulation, with far-reaching global consequences. • At the same time, this region holds unique research potential that can help address a range of critically important scientific priorities, including climate change impacts, ecosystem protection, the likelihood of extra-terrestrial life and monitoring of space debris. • Due to its long and impressive record of Antarctic research and its scientific, engineering and logistical capabilities in the region, the United Kingdom (UK) is strategically well-positioned to lead or play a key role in the delivery of these research priorities. • To achieve this potential, the UK must act collectively and in partnership with others, as the best and most urgent research benefits from collaboration, cooperation and cost sharing. Crucially, it must mobilise experts both from within the UK and internationally from a range of disciplines, including the social sciences. In the twenty-first century, Antarctic research must not exist within its own bubbl

Reconstructing glacier-based climates of LGM Europe and Russia ? Part 2: A dataset of LGM climates derived from degree-day modelling of palaeo glaciers

International audienceThe study of European and Russian Quaternary glacial-geological evidence during the last 15 years has generated sufficient to data to use former glacial extent as a proxy for Last Glacial Maximum (LGM) climate at a continental scale. Utilisation of such data is relevant for two reasons. First, continental to global scale proxy reconstructions of past climate are an important tool in the assessment of retrospective general circulation model (GCM) simulations. Second, the development of a multi-proxy approach will result in a more robust proxy based climate signal. A new and independent dataset of 36 LGM climate estimates derived from European and Russian mountain regions is presented in this paper. A simple glacier-climate model was used to establish the optimum LGM climate conditions for each region from a suite of over 4000 model climates using the principle of zero cumulative mass balance. Clear regional trends are present in the reconstructed LGM climates; temperature anomalies north of the Alps are 2°C and 5°C larger than those in the western and eastern Mediterranean, respectively. In Russia the model results suggest that both the Arctic Urals and Puterana Plateau were probably glaciated by small mountain glaciers during the LGM

Comment on "Indispensable Finite Time Correlations for Fokker-Planck Equations from Time Series Data"

Comment on "Indispensable Finite Time Correlations for Fokker-Planck Equations from Time Series Data"Comment: 2 pages, 1 figur

Reconstructing glacier-based climates of LGM Europe and Russia ? Part 3: Comparison with GCM and pollen-based climate reconstructions

International audienceUnderstanding past climates using GCM models is critical to confidently predicting future climate change. Although previous analysis of GCM simulations have shown them to under predicted European glacial temperature anomalies (the difference between modern and glacial temperatures) such analyses have focused primarily on results from glacial simulations alone. Here we compare glacial maximum GCM results with the palaeoenvironment derived from glacier-climate modelling. The comparison confirms that GCM anomalies are under predicted, and that this is due to modern conditions that are modelled too cold and glacial temperatures that are too warm. The result is that CGM results, if applied to a glacier mass balance model, over predict the extent of glaciers today, and under predict their extent at the last glacial (as depicted in glacial geological reconstructions). Effects such as seasonality and model parameterisation change the magnitude of the under prediction but still fail to match expected glacial conditions