Dynamic Reconfiguration of Redundant Haptic Interfaces for Rendering Soft and Hard Contacts.

There are conflicting objectives between required characteristics of haptic interfaces such as maximum force feedback capability versus back-drive friction, which can be optimally traded-off in a redundant haptic interface; a redundant haptic interface has more degrees of freedom than minimally required ones for a given task. In this article, a contact-aware null-space control approach for redundant haptic interfaces is proposed to address these trade-offs. First, we introduce a task-dependent null-space controller in which the internal motion of the redundant haptic interface is appropriately controlled to achieve a desired performance; i.e., low back-drive friction in case of free-space motion and soft contact or large force feedback capability in case of stiff contact. Next, a transition method is developed to facilitate the adaptation of the null-space controller's varying objectives according to the varying nature of the task. The transition method prevents discontinuities in the null-space control signal. This transition method is informed by a proposed actuator saturation observer that monitors the distance of joint torques from their saturation levels. The overall outcome is an ability to recreate the feelings of soft contacts and hard contacts with higher fidelity compared to what a conventional non-redundant haptic interface can achieve. Simulations are provided throughout the paper to illustrate the concepts. Moreover, experimental results are reported to verify the effectiveness of the proposed control strategies. It is shown that the proposed controller can perform well in the soft-contact, hard-contact, and transition phases.

Angiographic computed tomography with selective microcatheterization in delineating surgical anatomy in the case of a dural arteriovenous fistula. Technical note.

Intracranial dural arteriovenous fistulas (dAVFs) are commonly encountered in centers specializing in cerebrovascular diseases. Knowing the precise site of fistulous communication with the venous structures is essential in targeting the appropriate surgical or endovascular therapy once a decision to treat has been made. Such sites can usually be located with digital subtraction angiography alone. The authors describe a case in which localization was best performed using cone-beam volume CT in the angiography suite after selective microcatheterization of the feeding vessel and injection of a contrast agent in a dAVF related to the petrous temporal bone. Imaging studies showed the lesion was related to the inferior aspect of the tentorium, warranting a suboccipital surgical approach to treat the fistula.

13C-Labeled substrates and the cerebral metabolic compartmentalization of acetate and lactate.

[1-13C]Glucose, [2-13C]acetate and [3-13C]lactate were infused into male Sprague-Dawley rats (150-170 g) for periods of 3-100 min (n=4 per time) and neocortex extracts were analyzed using 13C-edited 1H magnetic resonance (MR) spectroscopy. The time dependence of the [4-13C]glutamine/[4-13C]glutamate labeling ratio was significantly different for all three substrates infused (p<0.001) and showed that acetate is primarily utilized by glia and lactate by neurons, whereas glucose is ubiquitous. The ratio of second- to first-turn TCA cycle labeling for glutamine was significantly lower for acetate (30-100 min infusion; p<0.02) and greater for lactate (10-30 min; p<0.02) than for glucose infusions, while the C-2/C-4 glutamate labeling ratio was similar for all the three substrates. This indicated that transfer of [2-13C]acetate-derived [4-13C]glutamine to neurons was preferred to reentry of label into the glial TCA cycle and that the neuronal TCA cycle turnover is significantly faster than that for glia. Fitting parameters of a function representing a pseudo-first-order process to the time dependence of labeling demonstrated that GABA labeling reaches steady state faster with glutamine labeled from [2-13C]acetate than with glutamate labeled from [3-13C]lactate. It is concluded that lactate represents a significant improvement over glucose in the study of neuronal metabolism and complements the use of acetate to study glial metabolism and glial/neuronal metabolic relationships.