Muscle activation patterns for voluntary isometric stiffness in human index finger

Humans can voluntarily control their finger stiffness for grasping and manipulation tasks. A long standing question in biomechanics is aimed at understanding the criterion used by the cenrtal nervous system to control the motor output of human limbs. Humans are known to voluntarily control their limb posture, end-tip force and stiffness. This thesis concerns itself with controlling stiffness in isometric conditions only. This work examines the variability of voluntary isometric stiffness modulation for the index finger at constant fingertip force. Previous studies either investigated muscle synergies responsible for different force-stiffness conditions or only measured behavioral measures of stiffness. However, the variability of stiffness for constant force condition was not explained. In this study, the stiffness of the index finger was modulated while maintaining a constant isometric fingertip force at 4 different force magnitudes and 2 different force directions. The muscle activations of 7 muscles that are related to the index finger were measured using surface electromyography (sEMG) sensors. Synergies estimated from a principal component analysis (PCA) using the recorded sEMG showed that the contribution of one synergy explains 80-95% of the variation in the data. The degree of alignment was used to analyze these stiffness synergies for different force conditions. The minimum mean value of degree of alignment was found for the comparison between synergies at high forces. However, comparison of synergies at lower forces showed that the stiffness synergy varies more with the forcing direction than it does with force magnitude. These results show the existence of a stiffness synergy to modulate the stiffness for individual force direction regardless of the magnitude of force level. Although the results at higher forces do not agree with this conclusion, stiffness modulation is prominent only at lower forces. This result gives an insight into what muscle synergies are important for modulating the fingertip stiffness. It can prove useful in robotics applications to simplify stiffness modulation without explicitly calculating inverse kinematics and also in restoring stiffness modulation after hand injuryMechanical Engineerin

Adaptive algorithms for identification of symmetric and positive definite matrices

Adaptive estimation and identification algorithms involving unknown symmetric and positive definite (SPD) matrix-valued parameters are ubiquitous in engineering applications. The problem of estimating the noise covariance matrices in estimation algorithms is considered first. An adaptive Kalman filter to estimate the noise covariance matrix of the noises entering a linear time invariant system is introduced first. The convergence of the estimates as well as the states is guaranteed with mild assumptions on the system. Conditions of estimability of the noise covariance matrix are discussed. The generalization of the adaptive Kalman fitler to the linear time varying case is introduced next. To maintain positive definiteness of the noise covariance estimates a differential geometric approach is adopted. The geometry of the manifold of SPD matrices is used to develop a Riemannian optimization based adaptive Kalman filter that ensure positive definiteness of the estimate. The convergence of the Riemannian optimization-based estimate and the adaptive Kalman filter is established under mild conditions of uniform observability and uniform controllability of the system. An adaptive control problem with an unknown SPD matrix is considered next. A novel projection scheme is introduced that ensures that the estimates of the unknown SPD matrix are SPD. Adaptive update laws for identifying the SPD matrix are also presented. The adaptive control laws are shown to globally stabilize systems in problems such as the adaptive angular velocity tracking, adaptive attitude control, and the adaptive trajectory tracking of robotic manipulators with parameter uncertainties within the generalized mass matrix. In general, such a method can be applied to estimation of symmetric matrices with eigenvalue constraints.Aerospace Engineerin

Effect of vesicular encapsulation on in-vitro cytotoxicity of ciclopirox olamine

Context: Ciclopirox olamine (CPO), an antifungal has recently been cited as a drug repurposed for cancer treatment.  Vesicular drug delivery systems like liposomes and niosomes have proven to increase the efficacy of anticancer drugs. Objective: The purpose of this paper was to evaluate the effect of two vesicular delivery systems liposome and niosome on the anticancer potential of CPO using in vitro cytotoxicity assays. Materials and methods: CPO was encapsulated in liposomes (prepared from Phospholipon®90H) and niosomes (prepared from Span 60) by ethanol injection method.  The cytotoxic effect of liposomal and niosomal CPO was evaluated on KB (oral cancer), PC3 (prostate cancer), Siha (cervical cancer) and Vero (kidney epithelial) cell lines using MTT assay. The IC50 values were compared with free drug CPO and with standard anticancer drug doxorubicin Results: CPO exhibited cytotoxicity to all the cell lines studied. The niosomal encapsulation of CPO favored its cytotoxicity on the cancer cell lines. Much lower IC50 values were obtained in comparison to the liposomal and free form of CPO. The enhancement in the cytotoxic effect on the non-cancer cell line Vero was not noted. Discussion: CPO demonstrated marginal difference in the concentration required to produce cytotoxic effect on cancer and normal cell lines. The difference was enhanced by niosomal CPO as much lower concentration was required to produce cytotoxic effect on cancer cells while rendering no effect on normal cells. Conclusion: Enhanced cytotoxicity selectively to cancer cells in the present study demonstrates the pharmacological significance of niosomal drug delivery system of CPO