Formation energy of Stone–Wales defects in carbon nanotubes

2003-2004 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe

Calculation of tunnel splitting in a biaxial spin particle with an applied magnetic field

The level splitting formulae of excited states as well as ground state for a biaxial spin particle in the presence of an applied magnetic field are obtained in a simple way from Schrödinger theory. Considering the boundary condition of the wave function, we obtain the tunneling splitting of the energy levels for half-integral spins as well as for the integral spins. The results obtained are compared with those previously derived by complicated pseudoparticle methods and numerical calculation values.postprin

Multiqubit maximally entangled states in the NMR model

A single step operation to produce a multiqubit maximally entangled states in the nuclear magnetic resonance was presented. A single pulse of a multifrequency coherent magnetic radiation was applied to manipulate simultaneously the active states to satisfy the resonant condition. An effective Hamiltonian to predict the time evolution of active states generated by the magnetic pulse was derived. The magnetic pulse parameters such as frequencies, phases, amplitudes and duration time were obtained to implement a Bell state of two qubits and a Greenberger-Horne-Zeilinger state of three qubits.published_or_final_versio

Quantum-classical crossover for biaxial antiferromagnetic particles with a magnetic field along the hard axis

Quantum-classical crossover of the escape rate is studied for biaxial antiferromagnetic particles with a magnetic field along the hard axis. The phase boundary line between first- and second-order transitions is calculated, and the phase diagrams are presented. Comparing with the results of different directed fields, the qualitative behavior of the phase diagram for the magnetic field along the hard axis is different from the case of the field along the medium axis. For the hard axis the phase boundary lines k(y) shift downwards with increasing h, but upwards for the medium axis. It is shown that the magnetic field along the hard axis favors the occurrence of the first-order transition in the range of parameters under the certain constraint condition. The results can be tested experimentally for molecular magnets Fe 8 and Fe 4.published_or_final_versio

Interference in transport through double barriers in interacting quantum wires

We investigate interference effects of the backscattering current through a double-barrier structure in an interacting quantum wire attached to noninteracting leads. Depending on the interaction strength and the location of the barriers, the backscattering current exhibits different oscillation and scaling characteristics with the applied voltage in the strong and weak interaction cases. However, in both cases, the oscillation behaviors of the backscattering current are mainly determined by the quantum mechanical interference due to the existence of the double barriers.Comment: 6 pages, 3 fig

A MUSIC-based method for SSVEP signal processing

The research on brain computer interfaces (BCIs) has become a hotspot in recent years because it offers benefit to disabled people to communicate with the outside world. Steady state visual evoked potential (SSVEP)-based BCIs are more widely used because of higher signal to noise ratio and greater information transfer rate compared with other BCI techniques. In this paper, a multiple signal classification based method was proposed for multi-dimensional SSVEP feature extraction. 2-second data epochs from four electrodes achieved excellent accuracy rates including idle state detection. In some asynchronous mode experiments, the recognition accuracy reached up to 100 %. The experimental results showed that the proposed method attained good frequency resolution. In most situations, the recognition accuracy was higher than canonical correlation analysis, which is a typical method for multi-channel SSVEP signal processing. Also, a virtual keyboard was successfully controlled by different subjects in an unshielded environment, which proved the feasibility of the proposed method for multi-dimensional SSVEP signal processing in practical applications

Coupling Disturbance Compensated MIMO Control of Parallel Ankle Rehabilitation Robot Actuated by Pneumatic Muscles

To solve the poor compliance and safety problems in current rehabilitation robots, a novel two-degrees-offreedom (2-DOF) soft ankle rehabilitation robot driven by pneumatic muscles (PMs) is presented, taking advantages of the PM’s inherent compliance and the parallel structure’s high stiffness and payload capacity. However, the PM’s nonlinear, time-varying and hysteresis characteristics, and the coupling interference from parallel structure, as well as the unpredicted disturbance caused by arbitrary human behavior all raise difficulties in achieving high-precision control of the robot. In this paper, a multi-input-multi-output disturbance compensated sliding mode controller (MIMO-DCSMC) is proposed to tackle these problems. The proposed control method can tackle the un-modeled uncertainties and the coupling interference existed in multiple PMs’ synchronous movement, even with the subject’s participation. Experiment results on a healthy subject confirmed that the PMs-actuated ankle rehabilitation robot controlled by the proposed MIMO-DCSMC is able to assist patients to perform high-accuracy rehabilitation tasks by tracking the desired trajectory in a compliant manner

Design and control of a robotic wrist orthosis for joint rehabilitation

Ageing society in many countries has led to an increasing number of stroke and cerebral palsy patients who require rehabilitation therapy. Affected wrist joints often show an increased spasticity and stiffness, caused by impairments of surrounding muscles and tendons. However, the medical devices for wrist joint assessment and rehabilitation are lacking. This paper proposes a robotic orthosis to assist the patient's wrist to perform rehabilitation exercise in a compliant way. A 1-DOF robotic device with parallel mechanism is designed for the wrist joint by utilising pneumatic artificial muscles (PAMs) that are compliant and lightweight. The mechanical design of the wrist orthosis and the corresponding development of pneumatic control system will be also presented. A model-based pressure close-loop control strategy is implemented for the PAMs in order to track the trajectory in high-performance. Experiments on the orthosis demonstrated that the robot could assist the hand to move along a torque-sensitive trajectory with relatively small errors and the differential forces were also kept stable