Gross N-cycling rates in ephemeral wetlands

Non-Peer ReviewedEphemeral wetlands or depressions in hummocky landscapes have high levels of C, N, and soil moisture, often leading to high nutrient cycling activity. However, measuring soil nitrate and ammonium pools is typically a poor indication of N-cycling activity or of the soil N that is available for other processes such as N2O emissions. This study used stable 15N isotope dilution techniques in cultivated and uncultivated ephemeral wetlands in central Saskatchewan to quantify land use effects on gross mineralization and nitrification rates. In-field incubation experiments were repeated in early May, mid-June and late July. There was a clear land use effect on inorganic soil N levels, with significantly less NH4+ and more NO3- in the cultivated wetland soils. However, the rates of NH4+ mineralization and NO3 - nitrification were similar for both land uses, indicating similar substrate availability but different N-consuming processes. Both N pools turned over in as little as 1-2 d, highlighting the ineffectuality of measuring inorganic N pools as a predictor for N availability in these soils

Quantifying changes in biomass and soil organic carbon after abandonment of croplands in Saskatchewan

Non-Peer Reviewe

Variability of ammonium and nitrate in disturbed and undisturbed forest soils

Non-Peer ReviewedThe spatial distribution of NH4+- and N03--N in forest soils, as affected by site disturbance, was studied at the landscape-scale. A sampling grid, consisting of 169 points, was established at an undisturbed site located in Prince Albert National Park. Additional grids, consisting of 36 and 49 sampling points, were established at a burned and a clear-cut site, respectively. Similar levels of inorganic-N at the undisturbed and disturbed sites suggests that management practices had little effect on the availability of inorganic-N. Similarly, the spatial distribution of inorganic-N was not related to landform element complexes, suggesting that hydrologic processes were not the primary factor controlling the distribution of inorganic-N at the scale studied. The occurrence of NH4+ -N as the dominant inorganic-N form suggests that nitrification was strictly limited in these forest soils. This contrasts agricultural soils in which nitrification often proceeds swiftly in the presence of NH4+-N

Increased intraventricular velocities An unrecognized cause of systolic murmur in adults

AbstractObjectives. The purpose of this study was to determine the frequency, clinical features and echocardiographic characteristics of increased intraventricular velocities (IIVs) in patients referred to the echocardiography laboratory for systolic murmur.Background. A subset of patients referred to the echocardiography laboratory for evaluation of a systolic murmur have IIVs in the absence of other recognized causes of systolic murmur.Methods. We prospectively studied echocardiograms from 108 consecutive patients referred for evaluation of a systolic murmur. Clinical data were obtained from patient examinations and medical records.Results. The sole explanation for systolic murmur was IIVs in 16.7% of referred patients. Compared with those without IIVs, patients with IIVs had a higher ejection fraction (EF) (58.7 ± 7.8% vs. 51.1 ± 12.5%, p < 0.001), percent fractional shortening (42.3 ± 9.7% vs. 31.0 ± 11.4%, p < 0.0001), left ventricular (LV) mass index (181 ± 70 vs. 152 ± 48 g/m2, p = 0.046) and prevalence of hypertension (73.3% vs. 51.7%, p = 0.043) and a lower prevalence of segmental wall motion abnormalities (2.2% vs. 39.3%, p < 0.001).Conclusions. Increased intraventricular velocities are a common cause of systolic murmur in this group of patients and should be included in the differential diagnosis of systolic murmurs in adults. The association of IIVs with LV hypertrophy should be a clinical consideration when these murmurs are identified

A stochastic model for the evolution of the web allowing link deletion

Recently several authors have proposed stochastic evolutionary models for the growth of the web graph and other networks that give rise to power-law distributions. These models are based on the notion of preferential attachment leading to the ``rich get richer'' phenomenon. We present a generalisation of the basic model by allowing deletion of individual links and show that it also gives rise to a power-law distribution. We derive the mean-field equations for this stochastic model and show that by examining a snapshot of the distribution at the steady state of the model, we are able to tell whether any link deletion has taken place and estimate the link deletion probability. Our model enables us to gain some insight into the distribution of inlinks in the web graph, in particular it suggests a power-law exponent of approximately 2.15 rather than the widely published exponent of 2.1

Noise characteristics of upper surface blown configurations. Experimental program and results

An experimental data base was developed from the model upper surface blowing (USB) propulsive lift system hardware. While the emphasis was on far field noise data, a considerable amount of relevant flow field data were also obtained. The data were derived from experiments in four different facilities resulting in: (1) small scale static flow field data; (2) small scale static noise data; (3) small scale simulated forward speed noise and load data; and (4) limited larger-scale static noise flow field and load data. All of the small scale tests used the same USB flap parts. Operational and geometrical variables covered in the test program included jet velocity, nozzle shape, nozzle area, nozzle impingement angle, nozzle vertical and horizontal location, flap length, flap deflection angle, and flap radius of curvature

The Relevance of Grain Dissection for Grain Size Reduction in Polar Ice: Insights from Numerical Models and Ice Core Microstructure Analysis

The flow of ice depends on the properties of the aggregate of individual ice crystals, such as grain size or lattice orientation distributions. Therefore, an understanding of the processes controlling ice micro-dynamics is needed to ultimately develop a physically based macroscopic ice flow law. We investigated the relevance of the process of grain dissection as a grain-size-modifying process in natural ice. For that purpose, we performed numerical multi-process microstructure modelling and analysed microstructure and crystallographic orientation maps from natural deep ice-core samples from the North Greenland Eemian Ice Drilling (NEEM) project. Full crystallographic orientations measured by electron backscatter diffraction (EBSD) have been used together with c-axis orientations using an optical technique (Fabric Analyser). Grain dissection is a feature of strain-induced grain boundary migration. During grain dissection, grain boundaries bulge into a neighbouring grain in an area of high dislocation energy and merge with the opposite grain boundary. This splits the high dislocation-energy grain into two parts, effectively decreasing the local grain size. Currently, grain size reduction in ice is thought to be achieved by either the progressive transformation from dislocation walls into new high-angle grain boundaries, called subgrain rotation or polygonisation, or bulging nucleation that is assisted by subgrain rotation. Both our time-resolved numerical modelling and NEEM ice core samples show that grain dissection is a common mechanism during ice deformation and can provide an efficient process to reduce grain sizes and counter-act dynamic grain-growth in addition to polygonisation or bulging nucleation. Thus, our results show that solely strain-induced boundary migration, in absence of subgrain rotation, can reduce grain sizes in polar ice, in particular if strain energy gradients are high. We describe the microstructural characteristics that can be used to identify grain dissection in natural microstructures