Dynamic modeling of an upper limb hybrid exoskeleton for simulations of load-lifting assistance

Work-related musculoskeletal disorders (MSDs) are among the most commonly reported issue in Europe. Using robotic exoskeletons to support users in performing heavy industrial tasks can effectively mitigate the work-related MSDs. In this paper, a dynamic model of a hybrid exoskeleton is presented to analyze the assistive effect. The exoskeleton in this study is able to passively support the human shoulder joint and actively support the human forearm movements by providing different levels of assistive torque. With the model, two different tasks are simulated, i.e., an overhead lifting task and a static load transferring task. The results show that the assistive torque provided by the passive spring-loaded mechanism reduces the maximum human upper arm effort by 22.65%. Moreover, the exoskeleton elbow joint’s assistive torque reduces the peak torque of human forearm from [Formula: see text] Nm to [Formula: see text] Nm. All these results demonstrate the efficacy of the model developed in the simulation and analysis of human-exoskeleton systems.

Mechanism of duplex unwinding by coronavirus nsp13 helicases

The current COVID-19 pandemic urges in-depth investigation into proteins encoded with coronavirus (CoV), especially conserved CoV replicases. The nsp13 of highly pathogenic MERS-CoV, SARS-CoV-2, and SARS-CoV exhibit the most conserved CoV replicases. Using single-molecule FRET, we observed that MERS-CoV nsp13 unwound DNA in discrete steps of approximately 9 bp when ATP was used. If another NTP was used, then the steps were only 4 to 5 bp. In dwell time analysis, we detected 3 or 4 hidden steps in each unwinding process, which indicated the hydrolysis of 3 or 4 dTTP. Based on crystallographic and biochemical studies of CoV nsp13 helicases, we modeled an unwinding mechanism similar to the spring-loaded mechanism of HCV NS3 helicase, although our model proposes that flexible 1B and stalk domains, by allowing a lag greater than 4 bp during unwinding, cause the accumulated tension on the nsp13-DNA complex. The hinge region between two RecA-like domains in SARS-CoV-2 nsp13 is intrinsically more flexible than in MERS-CoV nsp13 due to the difference of a single amino acid, which causes the former to induce significantly greater NTP hydrolysis. Our findings thus establish a blueprint for determining the unwinding mechanism of a unique helicase family.When dTTP was used as the energy source, 4 hidden steps in each individual unwinding step after 3 - 4 NTP hydrolysis were observed.An unwinding model of MERS-CoV-nsp13 which is similar to the spring-loaded mechanism of HCV NS3 helicase, except the accumulation of tension on nsp13/DNA complex is caused by the flexible 1B and stalk domains that allow a lag of 4-bp in unwinding.Comparing to MERS-CoV nsp13, the hinge region between two RecA-like domains in SARS-CoV-2 nsp13 is intrinsically more flexible due to a single amino acid difference, which contributes to the significantly higher NTP hydrolysis by SARS-CoV-2 nsp13.

Oscillations in a nonlinear spring mechanism with one degree of freedom

A new method for studying dynamics in a nonlinear spring- loaded mechanism is described, which consists in describing a spring as an elastic solid rod with conditional density and elastic modulus. When studying vibrations in such a rod, instead of the well-known second-order differential equation, two derived first-order equations are used that relate the acceleration and gradient of speed to the velocity and gradient of the change in the voltage of the particles of a given body. The frequency characteristic of the linear mechanism is given. The behavior of the mechanism in the presence of significant nonlinearity is considered. The self-oscillation parameters are determined that make it possible to estimate the design life.

Myoelectric Prosthetic Hand with Air Muscles

Prosthesis development was historically been done in order to find a matching replacement for a human hand which is unique in exhibiting its dexterous properties. Prosthesis controls that are established with the help of heavy motors make it a very complex actuation mechanism with relatively less power and efficiency. This paper describes an EMG – activated, tendon-driven, air muscle mechanism which delivers, relatively high power to weight ratio with higher efficiency by mimicking human muscle motion. The EMG signal is acquired from the skin surface by surface EMG electrodes and is conditioned using the basic techniques. Using a spring-loaded mechanism the weight of the hand prosthesis is kept to a minimum. Air muscles are used in for better control and to improve power to weight ratio. The flexion movements are achieved with a nylon string (tendon).

Repetitive DNA reeling by the Cascade-Cas3 complex in nucleotide unwinding steps

CRISPR-Cas loci provide an RNA-guided adaptive immune system against invading genetic elements. Interference in type I systems relies on the RNA-guided surveillance complex Cascade for target DNA recognition and the trans-acting Cas3 helicase/nuclease protein for target degradation. Even though the biochemistry of CRISPR interference has been largely covered, the biophysics of DNA unwinding and coupling of the helicase and nuclease domains of Cas3 remains elusive. Here we employed single-molecule FRET to probe the helicase activity with a high spatiotemporal resolution. We show that Cas3 remains tightly associated with the target-bound Cascade complex while reeling in the target DNA using a spring-loaded mechanism. This spring-loaded reeling occurs in distinct bursts of three base pairs, that each underlie three successive 1-nt unwinding events. Reeling is highly repetitive, compensating for inefficient nicking activity of the nuclease domain. Our study reveals that the discontinuous helicase properties of Cas3 and its tight interaction with Cascade ensure well controlled degradation of target DNA only.

Damage limitation

A spring-loaded mechanism can explain the activation process for a protein that has a crucial role in maintaining the genomic integrity of immature eggs cells