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First Pass (first + pass)
Selected AbstractsAnalysis of single rock blocks for general failure modes under conservative and non-conservative forcesINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 14 2007F. Tonon Abstract After describing the kinematics of a generic rigid block subjected to large rotations and displacements, the Udwadia's General Principle of Mechanics is applied to the dynamics of a rigid block with frictional constraints to show that the reaction forces and moments are indeterminate. Thus, the paper presents an incremental-iterative algorithm for analysing general failure modes of rock blocks subject to generic forces, including non-conservative forces such as water forces. Consistent stiffness matrices have been developed that fully exploit the quadratic convergence of the adopted Newton,Raphson iterative scheme. The algorithm takes into account large block displacements and rotations, which together with non-conservative forces make the stiffness matrix non-symmetric. Also included in the algorithm are in situ stress and fracture dilatancy, which introduces non-symmetric rank-one modifications to the stiffness matrix. Progressive failure is captured by the algorithm, which has proven capable of detecting numerically challenging failure modes, such as rotations about only one point. Failure modes may originate from a limit point or from dynamic instability (divergence or flutter); equilibrium paths emanating from bifurcation points are followed by the algorithm. The algorithm identifies both static and dynamic failure modes. The calculation of the factor of safety comes with no overhead. Examples show the equilibrium path of a rock block that undergoes slumping failure must first pass through a bifurcation point, unless the block is laterally constrained. Rock blocks subjected to water forces (or other non-conservative forces) may undergo flutter failure before reaching a limit point. Copyright © 2007 John Wiley & Sons, Ltd. [source] Dynamic T1 estimation of brain tumors using double-echo dynamic MR imagingJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 1 2003Yoshiyuki Ishimori RT Abstract Purpose To assess the clinical utility of a new method for real-time estimation of T1 during the first pass of contrast agent by using this method to examine brain tumors. Materials and Methods The multi-phase spoiled gradient-echo pulse sequence using the double-echo magnetic resonance (MR) technique was modified. In the first half of the pulse sequence, the flip angle was varied systematically. Then, static T1 values were calculated using differences in MR signal intensities between different flip angles. In the latter half of this sequence, changes in absolute T1 were calculated using differences in signal intensities before and after injection of contrast agent. The double-echo MR data were used to minimize the T2* effect. Five cases of neurinoma and seven cases of meningioma were examined. Changes in T1 during the first pass of contrast agent were compared between neurinoma and meningioma. Results Changes in absolute T1 were clearly demonstrated on the parametric map. Although the changes in absolute T1 during the first pass of contrast agent did not allow differentiation between the two types of tumors, the mean gradient after the first pass was statistically higher for neurinoma than for meningioma (P < 0.05; meningioma, 0.011 ± 0.012 second,1/second; neurinoma, 0.034 ± 0.020 second,1/second). Conclusion The present method appears to be useful for estimation of dynamic T1 changes in brain tumors in clinical settings. J. Magn. Reson. Imaging 2003;18:113,120. © 2003 Wiley-Liss, Inc. [source] Enrofloxacin and marbofloxacin in horses: comparison of pharmacokinetic parameters, use of urinary and metabolite data to estimate first-pass effect and absorbed fractionJOURNAL OF VETERINARY PHARMACOLOGY & THERAPEUTICS, Issue 5 2006M. PEYROU Enrofloxacin and marbofloxacin are two veterinary fluoroquinolones used to treat severe bacterial infections in horses. A repeated measures study has been designed to compare their pharmacokinetic parameters, to investigate their bioavailability and to estimate their absorbed fraction and first-pass effect by using plasma, urinary and metabolite data collected from five healthy mares. Clearance and Vd(ss) were greater for enrofloxacin (mean ± SD = 6.34 ± 1.5 mL/min/kg and 2.32 ± 0.32 L/kg, respectively) than for marbofloxacin (4.62 ± 0.67 mL/min/kg and 1.6 ± 0.25 L/kg, respectively). Variance of the AUC0-inf of marbofloxacin was lower than that for enrofloxacin, with, respectively, a CV = 15% and 26% intravenously and a CV = 31% and 55% after oral administration. Mean oral bioavailability was not significantly different between marbofloxacin (59%) and enrofloxacin (55%). The mean percentage of the dose eliminated unchanged in urine was significantly higher for marbofloxacin (39.7%) than that for enrofloxacin (3.4%). Absorbed fraction and first-pass effect were only determinable for enrofloxacin, whereas the percentage of the dose absorbed in the portal circulation was estimated to be 78% and the fraction not extracted during the first pass through the liver was 65%. Consequently, the moderate observed bioavailability of enrofloxacin appears to be mainly caused by hepatic first-pass effect. [source] Time-resolved, undersampled projection reconstruction imaging for high-resolution CE-MRA of the distal runoff vesselsMAGNETIC RESONANCE IN MEDICINE, Issue 3 2002J. Du Abstract Imaging of the blood vessels below the knee using contrast-enhanced (CE) MRI is challenging due to the need to coordinate image acquisition and arrival of the contrast in the targeted vessels. Time-resolved acquisitions have been successful in consistently capturing images of the arterial phase of the bolus of contrast agent in the distal extremities. Although time-resolved exams are robust in this respect, higher spatial resolution for the depiction of tight stenoses and the small vessels in the lower leg is desirable. A modification to a high-spatial-resolution T1 -weighted pulse sequence (projection reconstruction-time resolved imaging of contrast kinetics (PR-TRICKS)) that improves the through-plane spatial resolution by a factor of 2 and maintains a high frame rate is presented. The undersampled PR-TRICKS pulse sequence has been modified to double the spatial resolution in the slice direction by acquiring high-spatial-frequency slice data only after first pass of the bolus of contrast agent. The acquisition reported in the present work (PR-hyperTRICKS) has been used to image healthy volunteers and patients with known vascular disease. The temporal resolution was found to be beneficial in capturing arterial phase images in the presence of asymmetric filling of vessels. Magn Reson Med 48:516,522, 2002. © 2002 Wiley-Liss, Inc. [source] Assessing the performance of a consultant anaesthetist by control chart methodology,ANAESTHESIA, Issue 3 2009C. J. Runcie Summary The performance of trainee anaesthetists has been assessed by control chart methodology, but while assessment of consultants' performance has been suggested, published reports are rare. In order to test the value of control charts, I monitored my insertion of arterial and central venous cannulae over 3 years, documenting success or failure both for the first pass of the needle and for the intended site of cannulation. The resultant control charts clearly show episodes of changed performance. It was necessary to modify the technique used to assess trainees, specifically with relation to definitions of success, failure and ,acceptable' failure rates. The information obtained from these charts is well suited to inform an appraisal or revalidation discussion with both reflective and assessment elements. [source] Fault detection and isolation for dynamic processes using recursive principal component analysis (PCA) based on filtering of signalsASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 6 2007Jyh-Cheng Jeng Abstract A systematic procedure for the fault detection and isolation of dynamic systems is presented. The inputs of the process first pass through the dynamic filters which represent the process dynamics. Then, principal component analysis (PCA) is applied to the data matrix consisting of these filtered signals and the process outputs for fault detection. In case of a fault being detected, owing to an artificial linear relationship existing in the data matrix, the last principal component (LPC) is adopted for fault isolation. A recursive algorithm for PCA based on rank-one matrix update of the covariance is derived to compute the LPC on line. Patterns of the LPC are devised to isolate these faults, which include constant-bias and high-frequency noises originating from sensor measurement, errors resulting from input disturbance and change in the process gain. Furthermore, the magnitude of the fault can also be identified from the computed LPC. An illustrative example is used to verify the effectiveness of the proposed method. Copyright © 2007 Curtin University of Technology and John Wiley & Sons, Ltd. [source] | ||||||||||