Abstract-A sliding window filter (SWF) is an appealing smoothing algorithm for nonlinear estimation problems such as simultaneous localization and mapping (SLAM), since it is resource-adaptive by controlling the size of the sliding window, and can better address the nonlinearity of the problem by relinearizing available measurements. However, due to the marginalization employed to discard old states from the sliding window, the standard SWF has different parameter observability properties from the optimal batch maximum-aposterior (MAP) estimator. Specifically, the nullspace of the Fisher information matrix (or Hessian) has lower dimension than that of the batch MAP estimator. This implies that the standard SWF acquires spurious information, which can lead to inconsistency. To address this problem, we propose an observability-constrained (OC)-SWF where the linearization points are selected so as to ensure the correct dimension of the nullspace of the Hessian, as well as minimize the linearization errors. We present both Monte Carlo simulations and realworld experimental results which show that the OC-SWF's performance is superior to the standard SWF, in terms of both accuracy and consistency.

Objectives: The non-penetrating Vascular Clip System (VCS) was tested experimentally and compared with the conventional suture method on the venous system. Materials and Methods: In five pigs, 30 transverse venotomies were carried out in the jugular and renal veins, and vena cava. Fifteen venotomies were reconstructed using autosuture clips and 15 using the standard needle and suture method. Eight weeks later, following phlebography, the specimens were examined macro- and microscopically. Results: For both methods, the veins remained patent; however, significant stenosis of 8.9% (95% CI: 0.6–17.1) for the renal vein and 8.5% (95% CI: 1.2–15.7) for the vena cava occurred when the suture technique was used. The intima to media height ratio remained the same. The anastomosis time with the clips was significantly shorter ( p<0.05), while the endothelium remained intact without any hyperplasia or inflammatory changes, which are usual findings of the suture technique. Conclusion: Early and mid-term results show that the VCS clipped anastomotic technique seems to be effective and acceptable for venous reconstructions.

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