Latitudinal gradient of nestedness and its potential drivers in stream detritivores

Understanding what mechanisms shape the diversity and composition of biological assemblages across broad-scale gradients is central to ecology. Litter-consuming detritivorous invertebrates in streams show an unusual diversity gradient, with α-diversity increasing towards high latitudes but no trend in γ -diversity. We hypothesized this pattern to be related to shifts in nestedness and several ecological processes shaping their assemblages (dispersal, environmental filtering and competition). We tested this hypothesis, using a global dataset, by examining latitudinal trends in nestedness and several indicators of the above processes along the latitudinal gradient. Our results suggest that strong environmental filtering and low dispersal in the tropics lead to often species-poor local detritivore assemblages, nested in richer regional assemblages. At higher latitudes, dispersal becomes stronger, disrupting the nested assemblage structure and resulting in local assemblages that are generally more species-rich and non-nested subsets of the regional species pools. Our results provide evidence that mechanisms underlying assemblage composition and diversity of stream litter-consuming detritivores shift across latitudes, and provide an explanation for their unusual pattern of increasing α-diversity with latitude. When we repeated these analyses for whole invertebrate assemblages of leaf litter and for abundant taxa showing reverse or no diversity gradients we found no latitudinal patterns, suggesting that function-based rather than taxon-based analyses of assemblages may help elucidate the mechanisms behind diversity gradients

Heart Rate Recovery After Exercise Is Associated With Arrhythmic Events in Patients With Catecholaminergic Polymorphic Ventricular Tachycardia

BACKGROUND: Risk stratification in catecholaminergic polymorphic ventricular tachycardia remains ill defined. Heart rate recovery (HRR) immediately after exercise is regulated by autonomic reflexes, particularly vagal tone, and may be associated with symptoms and ventricular arrhythmias in patients with catecholaminergic polymorphic ventricular tachycardia. Our objective was to evaluate whether HRR after maximal exercise on the exercise stress test (EST) is associated with symptoms and ventricular arrhythmias. METHODS: In this retrospective observational study, we included patients ≤65 years of age with an EST without antiarrhythmic drugs who attained at least 80% of their age- and sex-predicted maximal HR. HRR in the recovery phase was calculated as the difference in heart rate (HR) at maximal exercise and at 1 minute in the recovery phase (ΔHRR1'). RESULTS: We included 187 patients (median age, 36 years; 68 [36%] symptomatic before diagnosis). Pre-EST HR and maximal HR were equal among symptomatic and asymptomatic patients. Patients who were symptomatic before diagnosis had a greater ΔHRR1' after maximal exercise (43 [interquartile range, 25-58] versus 25 [interquartile range, 19-34] beats/min; P<0.001). Corrected for age, sex, and relatedness, patients in the upper tertile for ΔHRR1' had an odds ratio of 3.4 (95% CI, 1.6-7.4) of being symptomatic before diagnosis (P<0.001). In addition, ΔHRR1' was higher in patients with complex ventricular arrhythmias at EST off antiarrhythmic drugs (33 [interquartile range, 22-48] versus 27 [interquartile range, 20-36] beats/min; P=0.01). After diagnosis, patients with a ΔHRR1' in the upper tertile of its distribution had significantly more arrhythmic events as compared with patients in the other tertiles (P=0.045). CONCLUSIONS: Catecholaminergic polymorphic ventricular tachycardia patients with a larger HRR following exercise are more likely to be symptomatic and have complex ventricular arrhythmias during the first EST off antiarrhythmic drug

Predicting the large-scale consequences of offshore wind turbine array development on a North Sea ecosystem

This paper was accepted for publication in the journal Continental Shelf Research and the definitive published version is available at http://dx.doi.org/10.1016/j.csr.2014.05.018.Three models were applied to obtaina first assessment of some of the potential impacts of large-scale operational wind turbine arrays on the marine ecosystem in a well-mixed area in a shelf sea: a biogeochemical model,a wave propagation model and an a coustic energy flux model.The results of the models are discussed separately and together to elucidate the combined effects. Overall,all three models suggested relatively weak environmental changes for the mechanisms included in this study, however these are only a subset of all the potential impacts,and a number of assumptions had to be made. Further work is required to address these assumptions and additional mechanisms. All three models suggested most of the changes with in the wind turbine array,and small changes up to several tens of km outside the array. Within the array, the acoustic model indicated the most concentrated, spatially repetitive changes to the environment,followed by the SWAN wave model,and the biogeochemical model being the most diffuse. Because of the different spatial scales of the response of the three models,the combined results suggested a spectrum of combinations of environmental changes with in the wind turbine array that marine organism smight respond to. The SWAN wave model and the acoustic model suggested a reduction in changes with increasing distance between turbines. The SWAN wave model suggested that the biogeochemical model, because of the in ability of its simple wave model to simulate wave propagation,over-estimated the biogeochemical changes by a factor of 2 or more. The biogeochemical model suggested that the benthic system was more sensitive to the environmental changes than the pelagic system

Design and performance of the PEP-II B-Factory HER QDA quadrupole magnet

The High Energy Ring (HER) in Stanford Linear Accelerator Center`s PEP-II B-Factory employs two high field quality quadrupole magnets, labeled QD4, for final horizontal beam de-focusing at a gradient of {approximately}75.65 kG/m. An asymmetric, septum quadrupole design is required for QD4. Due to space constraints, the magnetic field is shaped with both the iron and the coil. Each coil has fifteen conductors. A perturbation analysis was performed using the Poisson code in order to locate the ideal position of the individual conductors. Manufacturing and assembly tolerances of +/- 0.5 mm of each conductor were required to maintain an integrated field quality of multipole content of b{sub n}/b{sub 2}{le}0.0001 for n=3-15 at a radius of 59.0 mm. The steel core of the magnet is 1.425 m long and is comprised of 1.5 mm thick laminations. A cut out in the steel core is required to allow the Low Energy Ring beam to pass through the side of the magnet. A double shield is in place to allow the LER beam to remain field free. The pole tip shape is a simple hyperbola without any end contours. The design and performance of the QD4 magnet is presented