Onyx was recently approved for the treatment of pial arteriovenous malformations, but its use to treat dural arteriovenous fistulas (DAVFs) is not yet well established. We now report on the treatment ...of intracranial DAVFs using this nonadhesive liquid embolic agent.
We performed a retrospective analysis of 12 consecutive patients with intracranial DAVFs who were treated with Onyx as the single treatment technique at our institution between March 2006 and February 2007.
A total of 17 procedures were performed in 12 patients. In all of the cases, transarterial microcatheterization was performed, and Onyx-18 or a combination of Onyx-18/Onyx-34 was used. Eight patients were men. The mean age was 56 +/- 12 years. Nine patients were symptomatic. There was an average of 5 feeders per DAVF (range, 1-9). Cortical venous reflux was present in all of the cases except for 1 of the symptomatic patients. Complete resolution of the DAVF on immediate posttreatment angiography was achieved in 10 patients. The remaining 2 patients had only minimal residual shunting postembolization, 1 of whom appeared cured on a follow-up angiogram 8 weeks later. The other patient has not yet had angiographic follow-up. Follow-up angiography (mean, 4.4 months) is currently available in 9 patients. There was 1 angiographic recurrence (asymptomatic), which was subsequently re-embolized with complete occlusion of the fistula and its draining vein. There was no significant morbidity or mortality.
In our experience, the endovascular treatment of intracranial DAVFs with Onyx is feasible, safe, and highly effective with a small recurrence rate in the short-term follow-up.
Spatiotemporal variability of fine particle concentrations in Indianapolis, Indiana is quantified using a combination of high temporal resolution measurements at four fixed sites and mobile ...measurements with instruments attached to bicycles during transects of the city. Average urban PM2.5 concentrations are an average of ∼3.9–5.1 μg m−3 above the regional background. The influence of atmospheric conditions on ambient PM2.5 concentrations is evident with the greatest temporal variability occurring at periods of one day and 5–10 days corresponding to diurnal and synoptic meteorological processes, and lower mean wind speeds are associated with episodes of high PM2.5 concentrations. An anthropogenic signal is also evident. Higher PM2.5 concentrations coincide with morning rush hour, the frequencies of PM2.5 variability co-occur with those for carbon monoxide, and higher extreme concentrations were observed mid-week compared to weekends. On shorter time scales (<one day), spatial variability is 2–3 times greater than temporal variability. Spatial variability along the transect (within 10 km of the fixed measurement sites) was within ±3.6 μg m−3 of the stationary measurements (once the temporal variability is removed). Localized extreme values of PM2.5 concentrations ranged in the spatial dimension from a few hundred meters up to 2 km, and contributed an average of 4.4 μg m−3 to ambient concentrations.
•PM2.5 measured in Indianapolis indicates a strong signature from mobile emissions.•Intra-urban PM2.5 variability is the same magnitude as between urban-rural differences.•Spatial variability is greater than temporal variability on short time scales.•∼1/3 of hours with high concentrations at one site were not observed at other sites.
Changes in near–surface wind speeds due to global climate change may have profound geophysical and societal impacts. However, Global Climate Models (GCMs) are unable to replicate the historically ...observed magnitude and spatial variability of wind speeds, so we apply a downscaling technique to generate probability distributions of wind speeds at sites in northern Europe for historical periods (1961–1990 and 1982–2000) and two future periods (2046–2065, 2081–2100). Projections for the twenty‐first century (C21st) indicate no evidence of substantial evolution relative to the end of the twentieth century (C20th), although there is increased divergence of results from downscaling of different GCMs toward the end of C21st. Predicted changes in the downscaled mean and 90th percentile wind speeds are small (<±15%) and are comparable to the current variability manifest in downscaling from different GCMs.
The Weather Research and Forecasting (WRF) Model has been extensively used for wind energy applications, and current releases include a scheme that can be applied to examine the effects of wind ...turbine arrays on the atmospheric flow and electricity generation from wind turbines. Herein we present a high-resolution simulation using two different wind farm parameterizations: 1) the “Fitch” parameterization that is included in WRF releases and 2) the recently developed Explicit Wake Parameterization (EWP) scheme. We compare the schemes using a single yearlong simulation for a domain centered on the highest density of current turbine deployments in the contiguous United States (Iowa). Pairwise analyses are applied to diagnose the downstream wake effects and impact of wind turbine arrays on near-surface climate conditions. On average, use of the EWP scheme results in small-magnitude wake effects within wind farm arrays and faster recovery of full WT array wakes. This in turn leads to smaller impacts on near-surface climate variables and reduced array–array interactions, which at a systemwide scale lead to summertime capacity factors (i.e., the electrical power produced relative to nameplate installed capacity) that are 2%–3% higher than those from the more commonly applied Fitch parameterization. It is currently not possible to make recommendations with regard to which wind farm parameterization exhibits higher fidelity or to draw inferences with regard to whether the relative performance may vary with prevailing climate conditions and/or wind turbine deployment configuration. However, the sensitivities documented herein to the wind farm parameterization are of sufficient magnitude to potentially influence wind turbine array siting decisions. Thus, our research findings imply high value in undertaking combined long-term high-fidelity observational studies in support of model validation and verification.
Assessing the ability of global and regional models to describe aerosol optical properties is essential to reducing uncertainty in aerosol direct radiative forcing in the contemporary climate and to ...improving confidence in future projections. Here we evaluate the performance of high-resolution simulations conducted using the Weather Research and Forecasting model with coupled with Chemistry (WRF-Chem) in capturing spatiotemporal variability of aerosol optical depth (AOD) and the Ångström exponent (AE) by comparison with ground- and space-based remotely sensed observations. WRF-Chem is run over eastern North America at a resolution of 12 km for a representative year (2008). A systematic positive bias in simulated AOD relative to observations is found (annual mean fractional bias (MFB) is 0.15 and 0.50 relative to MODIS (MODerate resolution Imaging Spectroradiometer) and AERONET, respectively), whereas the spatial variability is well captured during most months. The spatial correlation of observed and simulated AOD shows a clear seasonal cycle with highest correlation during summer months (r = 0.5–0.7) when the aerosol loading is large and more observations are available. The model is biased towards the simulation of coarse-mode aerosols (annual MFB for AE = −0.10 relative to MODIS and −0.59 for AERONET), but the spatial correlation for AE with observations is 0.3–0.5 during most months, despite the fact that AE is retrieved with higher uncertainty from the remote-sensing observations. WRF-Chem also exhibits high skill in identifying areas of extreme and non-extreme aerosol loading, and its ability to correctly simulate the location and relative intensity of extreme aerosol events (i.e., AOD > 75th percentile) varies between 30 and 70 % during winter and summer months, respectively.
Windstorms resulting from intense synoptic-scale cyclones are an important natural hazard in the current climate of the northeastern United States, but their likely response to global climate ...non-stationarity is poorly understood. This study investigates the ability of the Weather Research and Forecasting model applied at 3.3 km resolution to simulate historically important cold-season windstorms associated with Alberta Clippers (AC) and Colorado Lows (CL) and then examines how such events may evolve in the future using pseudo-global-warming (PGW) simulations. The simulations encompass approximately 14-day periods that include passage of both a primary-strong extratropical cyclone during which multiple stations exhibited 10-m wind speed observations > 20 ms
−1
, and a secondary-weak mid-latitude cyclone. The thermodynamics changes projected in the pseudo-global-warming (PGW) experiments lead to a modest decline in maximum wind speeds. The marginal probability of 10-m wind speeds > 14.3 ms
−1
drops from 6.6 to 5.3% during the intense AC and from 9 to 6.5% for the intense CL. Similarly, the probability of nonzero precipitation in any grid cell/3-h time interval declines from 2.44% in the control simulation of the intense AC to 1.59% in the PGW simulation, and from 3.39 to 2.67% for the intense CL. Virtually all snow during the CL that occurred during March 2018 is simulated as other hydrometeor types in the PGW experiment, and the spatial extent and location of very heavy precipitation are also greatly modified.
The behavior of flow close to a cliff at heights relevant to wind turbines is explored using observations and simulations from a field experiment conducted at the Wind Energy Institute of Canada ...Prince Edward Island field site. There are 4 wind turbines located approximately 100 m from a 12 m high cliff and a fifth turbine located 500 m inland. During the field experiment, ongoing mast‐based observations were supplemented with additional sonic anemometers and Doppler lidars. Consistent with wind tunnel measurements and previous model simulations, a small speedup in the flow (~3‐5%) at the turbine hub‐height (of 80 m) is observed when the flow is perpendicular to the cliff. The objective here is to determine the degree to which the magnitude of the speedup, or horizontal distance over which it is manifest, changes as the flow deviates from the perpendicular impingement angle (ie, for nonzero yaw angles). Results indicate that the zone of deceleration upwind of the cliff and the downwind acceleration zone are maintained with flow ±25° to the perpendicular. Further, there is little change in the relative magnitude of either the wind speed or the turbulence intensity with modest deviations from perpendicular flow. However, as the angle from the perpendicular increases (ie, flow becomes increasingly parallel to the coast), the impact on wind speed and turbulence intensity decreases and is manifest over narrow and spatially less coherent regions.
Consequences of possible changes in annual total precipitation are dictated, in part, by the timing of precipitation events and changes therein. Herein, we investigated historical changes in ...precipitation seasonality over the US using observed station precipitation records to compute a standard seasonality index (SI) and the day of year on which certain percentiles of the annual total precipitation were achieved (percentile day of year). The mean SI from the majority of stations exhibited no difference in 1971–2000 relative to 30‐year periods earlier in the century. However, analysis of the day of year on which certain percentiles of annual total precipitation were achieved indicated spatially coherent patterns of change. In some regions, the mean day of the year on which the 50th percentile of annual precipitation was achieved differed by 20–30 days between 1971–2000 and both 1911–1940 and 1941–1970. Output from the 10‐Atmosphere‐Ocean General Circulation Models (AOGCM) simulations of 1971–2000, 2046–2065, and 2081–2100 was used to determine whether AOGCMs are capable of representing the seasonal distribution of precipitation and to examine possible future changes. Many of the AOGCMs qualitatively captured spatial patterns of seasonality during 1971–2000, but there was considerable divergence between AOGCMs in terms of future changes. In both the west and southeast, 7 of 10 AOGCMs indicated later attainment of the 50th percentile accumulation in 2047–2065, implying a possible reversal of the twentieth‐century tendency toward relative increases in precipitation receipt during winter and early spring over the southeast. However, this is also a region characterized by considerable interannual variability in the percentile day of year during the historical period.
There is considerable interest in the potential impact of climate change on the feasibility and predictability of renewable energy sources including wind energy. This paper presents dynamically ...downscaled near-surface wind fields and examines the impact of climate change on near-surface flow and hence wind energy density across northern Europe. It is shown that: Simulated wind fields from the Rossby Centre coupled Regional Climate Model (RCM) (RCAO) with boundary conditions derived from ECHAM4/OPYC3 AOGCM and the HadAM3H atmosphere-only GCM exhibit reasonable and realistic features as documented in reanalysis data products during the control period (1961-1990). The near-surface wind speeds calculated for a climate change projection period of 2071-2100 are higher than during the control run for two IPCC emission scenarios (A2, B2) for simulations conducted using boundary conditions from ECHAM4/OPYC3. The RCAO simulations conducted using boundary conditions from ECHAM4/OPYC3 indicate evidence for a small increase in the annual wind energy resource over northern Europe between the control run and climate change projection period and for more substantial increases in energy density during the winter season. However, the differences between the RCAO simulations for the climate projection period and the control run are of similar magnitude to differences between the RCAO fields in the control period and the NCEP/NCAR reanalysis data. Additionally, the simulations show a high degree of sensitivity to the boundary conditions, and simulations conducted using boundary conditions from HadAM3H exhibit evidence of slight declines or no change in wind speed and energy density between 1961-1990 and 2071-2100. Hence, the uncertainty of the projected wind changes is relatively high.
Recent laboratory chamber studies indicate a significant role for highly oxidized low-volatility organics in new particle formation (NPF), but the actual role of these highly oxidized low-volatility ...organics in atmospheric NPF remains uncertain. Here, particle size distributions (PSDs) measured in nine forest areas in North America are used to characterize the occurrence and intensity of NPF and to evaluate model simulations using an empirical formulation in which formation rate is a function of the concentrations of sulfuric acid and low-volatility organics from alpha-pinene oxidation (Nucl-Org), and using an ion-mediated nucleation mechanism (excluding organics) (Nucl-IMN). On average, NPF occurred on ~ 70 % of days during March for the four forest sites with springtime PSD measurements, while NPF occurred on only ~ 10 % of days in July for all nine forest sites. Both Nucl-Org and Nucl-IMN schemes capture the observed high frequency of NPF in spring, but the Nucl-Org scheme significantly overpredicts while the Nucl-IMN scheme slightly underpredicts NPF and particle number concentrations in summer. Statistical analyses of observed and simulated ultrafine particle number concentrations and frequency of NPF events indicate that the scheme without organics agrees better overall with observations. The two schemes predict quite different nucleation rates (including their spatial patterns), concentrations of cloud condensation nuclei, and aerosol first indirect radiative forcing in North America, highlighting the need to reduce NPF uncertainties in regional and global earth system models.
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