Incorporation of the Spatial Correlation of Arias Intensity Within Earthquake Loss Estimation

Arias Intensity (Ia) has been identified as an efficient intensity measure for the purpose of estimating the likelihood and extent of landslides. This efficiency implies that Arias intensity may logically be used within earthquake loss estimation applications in order to ultimately estimate the damage to spatially-distributed systems or portfolios. In order to estimate the effects of ground motions on such spatially-distributed systems it is important to take into account the spatial correlation of the intensity measure. However, existing landslide loss-estimation models, which use Ia as an input, do not take this aspect of the ground motion into account. Due to the areal nature of landslides, accounting for the spatial distribution of Ia is important if one wishes to accurately predict the probability of landslides occurring, and their subsequent displacements. In this paper, a model for the spatial correlation of Arias intensity is proposed. In order to obtain this model, a new empirical prediction equation for Arias intensity is first developed. The empirical predictive model is developed using recordings from the PEER NGA database while the model for spatial correlation makes use of the well-recorded events from this database, i.e. the Northridge and Chi-Chi earthquakes

Physical Conditions in Circumstellar Gas surrounding SN 1987A 12 Years After Outburst

Two-dimensional spectra of Supernova 1987A were obtained on 1998 November 14-15 (4282 days after outburst) with the Space Telescope Imaging Spectrograph (STIS) on board the Hubble Space Telescope (HST). The slit sampled portions of the inner circumstellar ring at the east and west ansae as well as small sections of both the northern and southern outer rings. The temperature and density at these locations are estimated by nebular analysis of [N II], [O III], and [S II] emission line ratios, and with time-dependent photoionization/recombination models. The results from these two methods are mutually consistent. The electron density in the inner ring is ~ 4000 cm-3 for S II, with progressively lower densities for N II and O III. The electron temperatures determined from [N II] and [O III] line ratios are ~11,000 K and \~22,000 K, respectively. These results are consistent with evolutionary trends in the circumstellar gas from similar measurements at earlier epochs. We find that emission lines from the outer rings come from gas of lower density (n_e \la 2000 cm-3) than that which emits the same line in the inner ring. The N/O ratio appears to be the same in all three rings. Our results also suggest that the CNO abundances in the northern outer ring are the same as in the inner ring, contrary to earlier results of Panagia et al. (1996). Physical conditions in the southern outer ring are less certain because of poorer signal-to-noise data. The STIS spectra also reveal a weak Ha emission redshifted by ~100 km s-1 at p.a. 103\arcdeg that coincides with the recently discovered new regions that are brightening (Lawrence et al. 2000). This indicates that the shock interaction in the SE section of the inner ring commenced over a year before it became apparent in HST images.Comment: 25 pages, 6 figures, to appear in December 1, 2000 Astrophysical Journa

Ganglionic Plexus Ablation During Pulmonary Vein Isolation - Predisposing to Ventricular Arrhythmias?

Catheter ablation is increasingly used to treat patients with atrial fibrillation (AF). Ablation of ganglionic plexi is often performed to reduce vagal innervation and has been shown to confer a better long-term outcome in terms of AF recurrence. We report a case of a patient having AF ablation with a profound vagal response, suggesting ganglionic plexus ablation, who subsequently developed ventricular fibrillation after programmed ventricular stimulation. Reduced vagal modulation is known to predispose to ventricular arrhythmias and vagal denervation following AF ablation may predispose to ventricular arrhythmias and requires further study

Pulmonary Vein Isolation using a High Density Mesh Ablator Catheter: Incorporation of three-Dimensional Navigation and Mappin

Background: We evaluated the use of a novel High Density Mesh Ablator (HDMA) catheter in combination with three-dimensional navigation for the treatment of paroxysmal atrial fibrillation. Methods: The HDMA catheter was used to carry out pulmonary vein isolation in a consecutive series of patients. Three-dimensional geometry of the left atrial-pulmonary vein (LA-PV) junctions were first created with the HDMA catheter. Ostial, proximal and distal sites within the pulmonary veins were tagged with catheter shadows on the created geometry to allow for re-interrogation of these exact sites after ablation. Results: The HDMA catheter was successfully used to create three dimensional geometry of the LA-PV junction in a total of 20 pulmonary veins which involved 5 patients. In all cases, ostial ablation alone was sufficient to achieve electrical isolation. No significant pulmonary vein stenosis was seen acutely after ablation. Conclusion: We describe the successful use of the novel HDMA catheter to create three-dimensional geometry of the LA-PV junction to assist with pulmonary vein isolation

Increase in organization index predicts atrial fibrillation termination with flecainide post-ablation: spectral analysis of intracardiac electrograms

Aims: The mechanism of the action of flecainide in the termination of human atrial fibrillation (AF) is not fully understood. We studied the acute effects of flecainide on AF electrograms in the time and frequency domain to identify factors associated with AF termination. Methods and results: Patients who were still in AF at the end of catheter ablation for AF were given intravenous flecainide. Dominant frequency (DF) and organization index (OI) were obtained by fast Fourier transform of electrograms from the coronary sinus catheter over 10 s in AF, before and after flecainide infusion. Mean AF cycle length (CL) was also calculated. Twenty-six patients were studied (16 paroxysmal AF and 10 persistent AF). Seven converted to sinus rhythm (SR) with flecainide. In all patients, mean CL increased from 211 ± 44 to 321 ± 85 ms ( P \u3c 0.001). Mean DF decreased from 5.2 ± 1.03 to 3.6 ± 1.04 Hz ( P \u3c 0.001). Mean OI was 0.33 ± 0.13 before and 0.32 ± 0.11 after flecainide ( P = 0.90). Comparing patients who converted to SR with those who did not, OI post-flecainide was 0.41 ± 0.12 vs. 0.29 ± 0.10 ( P = 0.013), and the relative change in OI was 29 ± 33 vs. −3.9 ± 27% ( P = 0.016), respectively. No significant difference was noted in the change in CL and DF in the two groups. Conclusion: Increase in OI, independent of changes to CL and DF, appears critical to AF termination with flecainide. Increase in OI holds promise as a sensitive predictor of AF termination