Anticipatory Online Compensation of Tool Deflection Using a Priori Information from Process Planning

Removing excess material from build-up welding by milling is a critical step in the repair of blades from aircraft engines. This so-called recontouring is a very challenging machining task. Shape deviations often result from the deflection of tool and workpiece due to process forces. Considering the individuality of repair cases, compensation of those deflections by process force measurement and online tool path adaption is a very suitable method. However, there is one caveat to this reactive approach. Due to causality, a corrective movement, following a force variation, is always delayed by a finite reaction time. At this moment, though, the displacement has already manifested itself as a deviation in the machined surface. To overcome those limitations and to improve compensation beyond the reduction of control delays, this study proposes a novel approach of anticipatory online compensation. Flank-milling experiments with abrupt changes in the tool-workpiece engagement conditions are conducted to investigate the limitations of reactive compensation and to explore the potential of the new anticipatory approach.

Primary Evaluation of Shape Recovery of Orthodontic Aligners Fabricated from Shape Memory Polymer (A Typodont Study)

As an innovative approach to overcome the rate-limiting staging of conventional aligners, using shape memory polymers (SMPs) as aligners’ materials was investigated in this in vitro study. The ability of SMPs to shape recover and consequently move tooth, upon appropriate stimuli, was evaluated on a typodont model before clinical application. The study design was to achieve 1.9 mm correction movement of an upper central incisor by one aligner after multiple steps/activation. A custom-made aligned typodont model with a movable upper central incisor was scanned. Using an orthodontic software and a 3D printer, resin-models were generated. Seven aligners of ClearX sheets (SMPs) were fabricated by thermoforming on the resin aligned model. Each aligner was tested for repositioning of the central incisor in the typodont model. The model was scanned after each step and the corrective movement was measured through the superimposition of scans. Results showed that the total correction efficiency of the SMPs’ aligner was ≈93% (1.76 mm). The corrective movement was 0.94 ± 0.04 mm after the reforming step, 0.66 ± 0.07 mm after the first activation step, and 0.15 ± 0.10 mm after the second activation step. It was concluded that aligners made of SMPs could have a promising future-use in orthodontic aesthetic treatment.

Blink-associated contralateral eccentric saccades as a rare sign of unilateral brain injury

Objective:To describe a rare sign of unilateral brain injury as a form of unwanted blink-associated contralateral eccentric saccades.Methods:A 62-year-old patient who underwent an ischemic stroke affecting the entire right middle cerebral artery territory came to our attention 1 year after stroke, manifesting with transient contralateral conjugate gaze deviations associated with spontaneous blinking. We complemented the regular neurologic evaluation with brain MRI, study of evoked potentials, electroneurography of the facial nerve, and infrared video-oculoscopy.Results:The patient had left-sided hemiparesis, hypoesthesia, hemianopia, and hemispatial neglect. He also showed the occurrence of a rapid leftward conjugate deviation of the eyes, followed by a corrective movement to the primary ocular position. MRI showed a wide malacic area spanning the right frontal, temporal, and parietal cortical and subcortical regions, with signs of wallerian degeneration of the descending right corticospinal tract. Motor and somatosensory evoked potentials were centrally altered on the right side. Electroneurography of the facial nerves was normal. Infrared video-oculoscopy indicated persistence of the same blink-related saccades even in darkness.Conclusions:It is known that unilateral cerebral lesions may manifest with a contralateral conjugate gaze deviation evoked by closure of the lids. This sign, known as spasticity of conjugate gaze, may be due to the suppression of the fixation reflex. In our case, the persistence of this sign in the darkness allowed us to exclude this diagnosis. We hypothesized that the blink-related neural pathways may improperly activate the oculomotor circuitry at both the cortical and subcortical levels.

Maintenance of Lateral Stability During Standing and Walking in the Cat

During free behaviors animals often experience lateral forces, such as collisions with obstacles or interactions with other animals. We studied postural reactions to lateral pulses of force (pushes) in the cat during standing and walking. During standing, a push applied to the hip region caused a lateral deviation of the caudal trunk, followed by a return to the initial position. The corrective hindlimb electromyographic (EMG) pattern included an initial wave of excitation in most extensors of the hindlimb contralateral to push and inhibition of those in the ipsilateral limb. In cats walking on a treadmill with only hindlimbs, application of force also caused lateral deviation of the caudal trunk, with subsequent return to the initial position. The type of corrective movement depended on the pulse timing relative to the step cycle. If the force was applied at the end of the stance phase of one of the limbs or during its swing phase, a lateral component appeared in the swing trajectory of this limb. The corrective step was directed either inward (when the corrective limb was ipsilateral to force application) or outward (when it was contralateral). The EMG pattern in the corrective limb was characterized by considerable modification of the hip abductor and adductor activity in the perturbed step. Thus the basic mechanisms for balance control in these two forms of behavior are different. They perform a redistribution of muscle activity between symmetrical limbs (in standing) and a reconfiguration of the base of support during a corrective lateral step (in walking).

Syria under Asad, 1970–78: The Centres of Power

NO OTHER MIDDLE EASTERN COUNTRY COULD MATCH THE TURBULENT post-independence history that Syria has experienced. Gaining its independence from France in April 1946, Syria moved uncertainly through the bewildering web of inter-Arab politics until the first military coup in March 1949 propelled it towards the long period of instability that was to follow. Indeed, the coup of November 1970, popularly known as the ‘Corrective Movement’, which installed the Asad regime in power constituted the twenty-first change of government in the twenty-four years of the country's independence. This persistent political turmoil, particularly during the fifties and sixties, contrasts sharply with the stability that Syria enjoyed in the first eight years of this decade.