A view from above : changing seas, seabirds and food sources

In this review we summarize what is known about mechanisms by which climate change may be affecting the populations of seabirds around the UK. Breeding success and adult survival are the key factors affecting changes in seabird populations, and food intake is implicated as a major determinant of both. The diet of most UK seabird species is almost exclusively sandeels, small clupeoid fish or zooplankton and it is clear that the marine pelagic food web is the key ecological system determining food supply. Hence, we develop the review by first considering how climate changes may affect primary production, and then examine how this propagates through the food web to zooplankton and fish culminating in fluctuations in seabird numbers. A trend of increasing numbers of many seabird species since 1970, particularly puffins, guillemots and razorbills, appears to have been reversed since 2000. The proximate cause of the recent declines seems to be a succession of 5 years of low breeding success for a range of species due to a shortage of food, especially sandeels. However, the connection with climate change remains uncertain, though there are indications that declines in the productivity of sandeel populations may be linked in some complex way to warming sea temperatures. The main conclusion is that no part of the marine food web, including fisheries, can be considered in isolation when trying to understand and predict the consequences of climate change for seabirds. Impacts can be expected in all parts of the system, and all parts of the system are interconnected

Leading-edge flow criticality as a governing factor in leading-edge-vortex initiation in unsteady airfoil flows

A leading-edge suction parameter (LESP) that is derived from potential flow theory as a measure of suction at the airfoil leading edge is used to study initiation of leading-edge vortex (LEV) formation in this article. The LESP hypothesis is presented, which states that LEV formation in unsteady flows for specified airfoil shape and Reynolds number occurs at a critical constant value of LESP, regardless of motion kinematics. This hypothesis is tested and validated against a large set of data from CFD and experimental studies of flows with LEV formation. The hypothesis is seen to hold except in cases with slow-rate kinematics which evince significant trailing-edge separation (which refers here to separation leading to reversed flow on the aft portion of the upper surface), thereby establishing the envelope of validity. The implication is that the critical LESP value for an airfoil–Reynolds number combination may be calibrated using CFD or experiment for just one motion and then employed to predict LEV initiation for any other (fast-rate) motion. It is also shown that the LESP concept may be used in an inverse mode to generate motion kinematics that would either prevent LEV formation or trigger the same as per aerodynamic requirements

Observations of Short Period Mesospheric Wave Patterns: In Situ or Tropospheric Wave Generation

Near infrared images showing wave structure in the hydroxyl (OH) nightglow emission have been obtained from Maui, Hawaii during the ALOHA‐90 campaign. Analysis of two nights during this campaign (25 and 31 March) indicate extensive, highly coherent, linear wave patterns of very short apparent period (∼5 and 10 min respectively). Both displays exhibited several features characteristic of the in situ breakdown of a large scale, long period, upper atmospheric wave disturbance. Data in support of this mechanism was found by other ALOHA instruments which detected concurrent long period (1–2 hour) mesospheric wave disturbances on both occasions. However, a tropospheric source for these waves cannot be ruled out. At least on 25 March a weather front occurred at ∼1400 km range with a favourable orientation and location. Although its range was relatively large, background winds may have substantially increased the path length of the waves through the intervening atmosphere

Baryon operators and spectroscopy in lattice QCD

The construction of the operators and correlators required to determine the excited baryon spectrum is presented, with the aim of exploring the spatial and spin structure of the states while minimizing the number of propagator inversions. The method used to construct operators that transform irreducibly under the symmetries of the lattice is detailed, and the properties of example operators are studied using domain-wall fermion valence propagators computed on MILC asqtad dynamical lattices.Comment: 7 pages, 2 figures, to appear in Proceedings of Workshop on Lattice Hadron Physics 2003, Cairns, Australia, July 22 - July 30, 200

Improved Pseudofermion Approach for All-Point Propagators

Quark propagators with arbitrary sources and sinks can be obtained more efficiently using a pseudofermion method with a mode-shifted action. Mode-shifting solves the problem of critical slowing down (for light quarks) induced by low eigenmodes of the Dirac operator. The method allows the full physical content of every gauge configuration to be extracted, and should be especially helpful for unquenched QCD calculations. The method can be applied for all the conventional quark actions: Wilson, Sheikoleslami-Wohlert, Kogut-Susskind, as well as Ginsparg-Wilson compliant overlap actions. The statistical properties of the method are examined and examples of physical processes under study are presented.Comment: LateX, 26 pages, 10 eps figure

Finite sample performance of optimal treatment rule estimators with right-censored outcomes

Patient care may be improved by recommending treatments based on patient characteristics when there is treatment effect heterogeneity. Recently, there has been a great deal of attention focused on the estimation of optimal treatment rules that maximize expected outcomes. However, there has been comparatively less attention given to settings where the outcome is right-censored, especially with regard to the practical use of estimators. In this study, simulations were undertaken to assess the finite-sample performance of estimators for optimal treatment rules and estimators for the expected outcome under treatment rules. The simulations were motivated by the common setting in biomedical and public health research where the data is observational, survival times may be right-censored, and there is interest in estimating baseline treatment decisions to maximize survival probability. A variety of outcome regression and direct search estimation methods were compared for optimal treatment rule estimation across a range of simulation scenarios. Methods that flexibly model the outcome performed comparatively well, including in settings where the treatment rule was non-linear. R code to reproduce this study's results are available on Github