Quantifying kinematics of purposeful movements to real, imagined, or absent functional objects: Implications for modelling trajectories for robot-assisted ADL tasks**

BACKGROUND: Robotic therapy is at the forefront of stroke rehabilitation. The Activities of Daily Living Exercise Robot (ADLER) was developed to improve carryover of gains after training by combining the benefits of Activities of Daily Living (ADL) training (motivation and functional task practice with real objects), with the benefits of robot mediated therapy (repeatability and reliability). In combining these two therapy techniques, we seek to develop a new model for trajectory generation that will support functional movements to real objects during robot training. We studied natural movements to real objects and report on how initial reaching movements are affected by real objects and how these movements deviate from the straight line paths predicted by the minimum jerk model, typically used to generate trajectories in robot training environments. We highlight key issues that to be considered in modelling natural trajectories. METHODS: Movement data was collected as eight normal subjects completed ADLs such as drinking and eating. Three conditions were considered: object absent, imagined, and present. This data was compared to predicted trajectories generated from implementing the minimum jerk model. The deviations in both the plane of the table (XY) and the saggital plane of torso (XZ) were examined for both reaches to a cup and to a spoon. Velocity profiles and curvature were also quantified for all trajectories. RESULTS: We hypothesized that movements performed with functional task constraints and objects would deviate from the minimum jerk trajectory model more than those performed under imaginary or object absent conditions. Trajectory deviations from the predicted minimum jerk model for these reaches were shown to depend on three variables: object presence, object orientation, and plane of movement. When subjects completed the cup reach their movements were more curved than for the spoon reach. The object present condition for the cup reach showed more curvature than in the object imagined and absent conditions. Curvature in the XZ plane of movement was greater than curvature in the XY plane for all movements. CONCLUSION: The implemented minimum jerk trajectory model was not adequate for generating functional trajectories for these ADLs. The deviations caused by object affordance and functional task constraints must be accounted for in order to allow subjects to perform functional task training in robotic therapy environments. The major differences that we have highlighted include trajectory dependence on: object presence, object orientation, and the plane of movement. With the ability to practice ADLs on the ADLER environment we hope to provide patients with a therapy paradigm that will produce optimal results and recovery

Optical Nonlinearity in Cu2CdSnS4 and α/β-Cu2ZnSiS4: Diamond-like Semiconductors with High Laser-Damage Thresholds

Cu2CdSnS4 and α/β-Cu2ZnSiS4 meet several criteria for promising nonlinear optical materials for use in the infrared (IR) region. Both are air-stable, crystallize in noncentrosymmetric space groups, and possess high thermal stabilities. Cu2CdSnS4 and α/β-Cu2ZnSiS4 display wide ranges of optical transparency, 1.4–25 and 0.7–25 μm, respectively, and have relatively large second-order nonlinearity as well as phase matchability for wide regions in the IR. The laser-damage threshold (LDT) for Cu2CdSnS4 is 0.2 GW/cm2, whereas α/β-Cu2ZnSiS4 has a LDT of 2.0 GW/cm2 for picosecond near-IR excitation. Both compounds also exhibit efficient third-order nonlinearity. Electronic structure calculations provide insight into the variation in properties

Optical Nonlinearity in Cu₂CdSnS₄ and α/β-Cu₂ZnSiS₄: Diamond-like Semiconductors with High Laser-Damage Thresholds

Cu₂CdSnS₄ and α/β-Cu₂ZnSiS₄ meet several criteria for promising nonlinear optical materials for use in the infrared (IR) region. Both are air-stable, crystallize in noncentrosymmetric space groups, and possess high thermal stabilities. Cu₂CdSnS₄ and α/β-Cu₂ZnSiS₄ display wide ranges of optical transparency, 1.4–25 and 0.7–25 μm, respectively, and have relatively large second-order nonlinearity as well as phase matchability for wide regions in the IR. The laser-damage threshold (LDT) for Cu₂CdSnS₄ is 0.2 GW/cm², whereas α/β-Cu₂ZnSiS₄ has a LDT of 2.0 GW/cm² for picosecond near-IR excitation. Both compounds also exhibit efficient third-order nonlinearity. Electronic structure calculations provide insight into the variation in properties

Optical Nonlinearity in Cu₂CdSnS₄ and α/β-Cu₂ZnSiS₄: Diamond-like Semiconductors with High Laser-Damage Thresholds

Cu₂CdSnS₄ and α/β-Cu₂ZnSiS₄ meet several criteria for promising nonlinear optical materials for use in the infrared (IR) region. Both are air-stable, crystallize in noncentrosymmetric space groups, and possess high thermal stabilities. Cu₂CdSnS₄ and α/β-Cu₂ZnSiS₄ display wide ranges of optical transparency, 1.4–25 and 0.7–25 μm, respectively, and have relatively large second-order nonlinearity as well as phase matchability for wide regions in the IR. The laser-damage threshold (LDT) for Cu₂CdSnS₄ is 0.2 GW/cm², whereas α/β-Cu₂ZnSiS₄ has a LDT of 2.0 GW/cm² for picosecond near-IR excitation. Both compounds also exhibit efficient third-order nonlinearity. Electronic structure calculations provide insight into the variation in properties