Rate Of Change In Parameters Research Articles

Abstract Number ‐ 58: Effects of Neck Geometry on Reccurence in CFD Analysis for Aneurysms after Low VER Coiling

Introduction Although low volume embolization ratio is known as risk factor of aneurysmal recanalization, stable occlusion can be achieved in limited cases. Evaluation of hemodynamic parameters at the neck surface has usually been performed with a flat surface rather than a curved surface following the actual coil shape. In this study, we investigated the effect of the geometry of the neck surface on hemodynamics related to aneurysm recanalization after coil embolization in low volume embolization ratio. Methods We focused on aneurysms of 5–10 mm in size that were conducted coil embolization with 15–20% volume embolization ratio (low‐VER). Aneurysms that were recanalized after coil embolization and conducted additional coil deployment were defined as the recanalized case. We identified 25 aneurysms (7 recanalized and 18 stable). We randomly selected 3 recanalized cases and 6 stable cases. For each case, the three‐dimensional vascular geometry including aneurysm was reconstructed by preoperative angiographic images. To divide the aneurysm from the parent artery, two types of neck surfaces (flat neck surface and curved neck surface) were generated for each case. The embolized coil was modeled in the enclosed area with the neck plane and aneurysmal wall by our original virtual coiling simulation. CFD analyses were conducted with the flat neck surface and the curved neck surface. We estimated 6 morphological parameters and 35 hemodynamic parameters, and the mean values of hemodynamic parameters were compared between the flat neck surface and the curved neck surface. The change rate of each parameter in the curved neck was calculated based on that in the flat neck. Results Since the velocity and pressure were involved in recanalization factors by the previous studies, as illustrative hemodynamic parameters, the mean values and change rate of the spatially averaged velocity normal to the neck surface into the cerebral aneurysm (NVneck) and the pressure difference between the average pressure on the surface of control volume and the maximum pressure at the neck surface (PDneck) were summarized in Table 1. These parameters were higher with the curved neck surface geometry case than with the flat neck surface geometry case. Furthermore, the change rates were higher in the recanalized cases compared to those in the stable cases. Conclusions In the CFD analysis with the curved surface, the averaged inflow velocity and pressure difference at the neck surface were higher than those with the flat surface. In addition, the change rates of hemodynamic parameters in recanalized cases were higher than those of stable cases. Therefore, the hemodynamic parameters are changed depending on the geometry of the neck surface, which may affect the prediction accuracy for recanalization using CFD.

Comparison of channel geometry changes in Inner Mongolian reach of the Yellow River before and after joint operation of large upstream reservoirs

The impact of reservoirs on downstream river channel change has been a scientific issue in fluvial geomorphology during the last few decades. However, it is still a difficult issue as to how to express quantitatively the channel adjustment in the Inner Mongolian reach of the Yellow River induced by the joint operation of upstream reservoirs. Based on the shape parameters of channel cross-sections at four gauging stations in this river reach over a flooding season in two periods, 1978–1982 and 2008–2012, the present work investigated the channel changes in terms of shape parameter change rate under the same controlling water level in each flooding season at the channel cross-sections. Results showed that most of the change rates of the parameters evidently increased over a flooding season in both periods. However, the change rate of each parameter at the cross-sections decreased evidently in the latter period, compared with the former period. At the same time, the distribution pattern of the change rate of the shape parameters along the cross-sections thus changed from a convex curve in the former period to an S-shaped curve in the latter period. The obvious decrease of the change rates is related to the joint operation of the Liujiaxia and Longyangxia reservoirs. The reservoirs stored a large volume of water and decreased the peak discharge and maximum velocity in the flooding season; as a result, the erosion ability of the flood decreased accordingly. With the joint operation of the large reservoirs, the Inner Mongolian channel shrunk markedly. Therefore, the channel will present the possibility of an extreme flood in the future. Consequently, it is reasonable to adjust the function of the reservoirs in future. The total water and sediment discharges and the peak discharge in flooding seasons should be effectively controlled. Continuous shrinkage of the channel can thus be avoided and it can be ready for a potential extreme flood.

A hybrid approach to the synthesis of simply structured robust and gain-scheduled controllers

Abstract Frequently in engineering applications, simply structured controllers are required for plants whose dynamics are either not fully known or varies with time. The problem of designing such structurally constrained controllers is known to be NP-hard. This paper presents a method for designing such controllers for both continuous-time and discrete-time uncertain or linear parameter varying (LPV) systems. The method relies on sufficient linear matrix inequalities (LMI) conditions also presented here. These LMIs are used to evaluate performance of a given controller in terms of the worst-case induced L 2 -norm for complete operational envelope. The strength of this LMI formulation lies in the fact that the robust performance evaluation condition is less conservative than standard results because it is based on a parameter-dependent Lypunov function and full block multipliers which allows to consider a bound on the rate of change in parameters. The LMI conditions are used in a hybrid evolutionary-LMI algorithm. The proposed algorithm employs evolutionary search to span the solution space and LMI solvers to find the worst case performance. The algorithm is independent of the controller structure, which allows to design simply structured controllers for complex systems in a systematic way. To illustrate the approach, two applications are presented: a distillation column and a spark ignition (SI) engine. For the distillation column, simple PI controllers with first order pre-filters are designed to achieve time and frequency domain control objectives in the presence of 20% input uncertainty. For the SI engine example, gain-scheduled PID controllers are designed and tuned. these examples illustrate that the proposed approach can be used to systematically design simply structured low-order controllers, while satisfying all performance requirements in terms of the worst-case induced L 2 -norm.

Plus Disease in Retinopathy of Prematurity: Quantitative Analysis of Vascular Change

To examine the relationship between rate of vascular change and plus disease diagnosis. Retrospective observational case-control study. Wide-angle images were taken bilaterally from 37 infants at 31 to 33 weeks and 35 to 37 weeks postmenstrual age (PMA). The semi-automated Retinal Image multiScale Analysis system was used to measure parameters for all arteries and veins: integrated curvature, diameter, and tortuosity index. A reference standard diagnosis (plus vs not plus) was defined for each eye by consensus of 5 experts at 35 to 37 weeks PMA. Weekly rate of change in parameters was compared in eyes with plus vs not plus disease. Receiver operating characteristic area under the curve (AUC) was calculated for plus disease detection based on 1) weekly rates of parameter change between 31 to 33 weeks and 35 to 37 weeks PMA and 2) parameter values at 35 to 37 weeks only. Weekly rates of change in all venous parameters were significantly different in eyes with plus vs not plus disease, particularly for tortuosity index (P < .0004) and diameter (P = .018). Using weekly rate of change, AUC for plus disease detection was highest for venous tortuosity index (0.819) and venous diameter (0.712). Using the 35 to 37-week PMA image only, AUC was highest for venous integrated curvature (0.952) and diameter (0.789). Rate of change in venous, but not arterial, parameters is correlated with plus disease development in this data set. This did not appear to contribute information beyond analysis of an image at 35 to 37 weeks PMA only.

Towards understanding the capability of adaptation for time-varying systems

The primary function of adaptation is to deal with systems with uncertain and time-varying dynamics. However, a natural question is: how fast must the rate of change of the uncertain dynamics be, before it can no longer be captured by adaptation? In order to initiate an understanding of this problem, we consider in this paper a first-order linear system with time-varying unknown parameters modeled as a finite state hidden Markov chain. It is shown that the key factor inherent in characterizing the capability of adaptation is the information uncertainty coupled with the structural complexity of the systems under control, rather than the existence of a certain critical rate of parameter changes that has been conjectured by many in the area.