High dynamic range pseudo–two-level digital pulse-width modulation for power-efficient RF transmitters

Radio frequency (RF) power amplification based on pulse-width modulation (PWM) has been widely discussed as a potential solution to achieve higher efficiency in RF transmitters. A digitally implemented PWM introduces a large amount of in-band distortion due to spectral aliasing. In this paper, a novel memoryless PWM modulator with a built-in anti-aliasing filter is proposed that effectively reduces the in-band distortion in digital implementation. The spectral characteristics of the proposed PWM modulator as well as the statistical properties of its output PWM signal are analytically studied. The pseudo–two-level output of the proposed modulator provides the capability to compromise between the efficiency, linearity, and complexity of transmitter, based on the given design targets. The proposed PWM method benefits from a simple circuit implementation in both digital and RF sections of the transmitter. Moreover, it preserves the low distortion property at low oversampling ratios of digital baseband. Simulations, as well as measurements, verify the performance of the proposed method.     

Bounded output feedback tracking control of fully actuated Euler-Lagrange systems

In this short note we deal with the problem of trajectory tracking control of fully actuated Euler-Lagrange systems with unmeasurable velocities and bounded control inputs. In order to avoid the use of velocity measurements we introduce a nonlinear dynamic extension for the plant which renders the closed-loop system semi-globally asymptotically stable, hence, we prove that by increasing some of the dynamic extension parameters it is possible to enlarge the domain of attraction and to maintain the control inputs bounded.     

Global uniform asymptotic stabilization of an underactuated surface vessel

Explicit formulas of smooth time-varying state feedbacks, which make the origin of an underactuated surface vessel globally uniformly asymptotically stable, are proposed. The construction of the feedback extensively relies on the backstepping approach. The feedbacks constructed are time-periodic functions.     

Coordination of two robot manipulators based on position measurements only

In this note we propose a controller that solves the problem of coordination of two (or more) robots, under a master-slave scheme, in the case when only position measurements are available. The controller consists of a feedback control law, and two non-linear observers. It is shown that the controller yields ultimate uniformly boundedness of the closed loop errors, a relation between this bound and the gains on the controller is established. Simulation results on two twolink robot systems show the predicted convergence performance.     

Input-output decoupling of Hamiltonian systems: The linear case

In this note we give necessary and sufficient conditions for a linear Hamiltonian system to be input-output decouplable by Hamiltonian feedback, i.e. feedback that preserves the Hamiltonian structure. In a second paper we treat the same problem for nonlinear Hamiltonian systems.     

Tetracycline hydrochloride-containing poly (ε-caprolactone)/poly lactic acid scaffold for bone tissue engineering application: in vitro and in vivo study

In the current study, tetracycline hydrochloride (TCH), an antibiotic against most of the medically relevant bacteria, was incorporated into poly (ε-caprolactone)/poly lactic acid solution in order to develop a composite scaffold with both antibacterial and osteoinductive properties for the repair of infected bone defects. The composite scaffolds were produced from poly (ε-caprolactone) (PCL) and poly lactic acid (PLA) solution (1:1 (w/w)) incorporated with 3, 5, and 10% (w/w) of TCH by thermally induced phase separation technique. The scaffolds were evaluated regarding their morphology, wettability, porosity, degradation, mechanical properties, and cellular response. The scaffold containing 10% of TCH (PCL/PLA/TCH10%) was chosen as the optimum scaffold for further investigation in a rat femoral defect model. The study showed that after eight weeks, the bone formation was relatively higher in PCL/PLA/TCH10%-treated group with completely filled defect when compared with control (PCL/PLA scaffold without TCH). Histopathological evaluation showed that the defect in PCL/PLA/TCH10%-treated group was fully replaced by new bone and connective tissue. Our results provide evidence supporting the possible applicability of TCH-containing scaffolds for successful bone regeneration.     

Molecular dynamics study of the growth of optical fibers

We have carried out molecular dynamics simulations that model a special growth technique for optical fibers, the so-called laser heated pedestal growth. Although the simulations are a crude representation of the experimental process, they demonstrate that it is possible to simulate such experiments on a microscopic scale. We measure properties of both the growth process and the resulting fibers and find some of those properties to match our intuitive expectations while others show a more complicated behavior.     

An addendum on “Robust control of robots by the computed torque method”

We reinterprete and improve recent results on robust control of robots by the computed method. The methods and ideas used are inspired by ‘passivity based’ control methods for robot manipulators and lead to a significant increase in freedom of controller implementation, thereby providing more flexibility to the designer of robot control systems.