Disturbance-Observer-Based PD Control of Electro-Hydrostatically Actuated Flexible Joint Robots

A position-based proportional derivative (PD) controller is a well-known controller to be able to render compliant behaviors to a robot and it is usually used with a friction compensator for control performance improvement. Despite the previous methods are effective to the actuation systems with mechanical transmissions, they cannot be applied to the actuation systems that use fluid transmissions owing to their characteristics caused by fluid parameters. To solve this problem, this paper proposes a stability-guaranteed PD control methods incorporating two observers; one is for the observation of friction and the other is for the observation of flexible joint effects caused by fluid compliance and internal leakage. This allows the robots with fluid transmissions to asymptotically converge to the desired position. The proposed approach was verified through simulations and experiments

Asymptotically Stable Disturbance Observer-Based Compliance Control of Electro-Hydrostatic Actuators

This paper proposes a disturbance observer (DOB)-based compliance control strategy for electro-hydrostatic actu-ators (EHAs), particularly those with high gear reductions andlong hydraulic pipelines, which could lead to a high performanceinteractive robot system. EHAs suffer significantly from internal leakage and friction, which hampers the application of existing compliance control methods to EHAs. Therefore, a two-degree-of-freedom DOB is introduced to compensate for both undesirable effects separately; one degree of freedom handles friction observations and the other monitors internal leakage. Then, a compliance controller is designed without affecting the closed-loop stability. To this end, the state of the nominal plant, not the real plant, is used in the designs of the internal leakage observer and the compliance controller as it guarantees closed-loop stability. The asymptotic convergence of the closed-loop system is evaluated via simulations and experiments

Strengths and Limitations of Commercial Tests for Hepatitis C Virus RNA Quantification

The sensitivity of the Roche COBAS Monitor v.2.0 test was slightly better than that of the Bayer bDNA 3.0 test, but the Monitor test underquantified specimens by 2.5- to 10.6-fold even at relatively low hepatitis C virus RNA concentrations. Dilution prior to assay minimally decreased the reproducibility of the Monitor assay, leading to the recommendation for all specimens to be diluted 1:100 prior to testing by this assay

A Passivity-based Nonlinear Admittance Control with Application to Powered Upper-limb Control under Unknown Environmental Interactions

This paper presents an admittance controller based on the passivity theory for a powered upper-limb exoskeleton robot, which is governed by the nonlinear equation of motion. Passivity allows us to include a human operator and environmental interaction in the control loop. The robot interacts with the human operator via force/torque (F/T) sensor and interacts with the environment mainly via end-effectors. Although the environmental interaction cannot be detected by any sensors (hence unknown), passivity allows us to have natural interaction. An analysis shows that the behavior of the actual system mimics that of a nominal model as the control gain goes to infinity, which implies that the proposed approach is an admittance controller. However, because the control gain cannot grow infinitely in practice, the performance limitation according to the achievable control gain is also analyzed. The result of this analysis indicates that the performance in the sense of infinite norm increases linearly with the control gain. In the experiments, the proposed properties were verified using 1-DoF testbench, and an actual powered upper-limb exoskeleton was used to lift and maneuver the unknown payload

Rhodium-molybdenum oxide electrocatalyst with dual active sites for electrochemical ammonia synthesis under neutral pH condition

Electrochemical nitrogen reduction reaction (NRR) process has attracted significant attention recently as an alternative route for green ammonia (NH3) production to replace conventional, energy intensive Haber-Bosh process. However, a major challenge in NRR process is the relatively poor selectivity of NRR process over its competing hydrogen evolution reaction (HER) process. Herein, we report the synthesis of molybdenum oxide decorated on the rhodium (RhMoOx/C) catalyst for an efficient NRR with high selectivity. RhMoOx/C catalyst exhibits an outstanding NH3 yield rate of 57.2 μg h−1 mgcat−1 at −0.6 V vs. RHE and a high faradaic efficiency of 22% at −0.2 V vs. RHE in 0.1 M Na2SO4 electrolyte. This study reveals the interdependent relationship between the catalyst structure, operating conditions, and the reaction selectivity in the electrochemical NH3 synthesis. Moreover, this study also demonstrates the effectiveness of the bimetallic materials in enhancing the NRR process which is an important finding for designing a future electrocatalyst for electrochemical NH3 production.</p

Gradient index lens based combined two-photon microscopy and optical coherence tomography

We report a miniaturized probe-based combined two-photon microscopy (TPM) and optical coherence tomography (OCT) system. This system is to study the colorectal cancer in mouse models by visualizing both cellular and structural information of the colon in 3D with TPM and OCT respectively. The probe consisted of gradient index (GRIN) lenses and a 90 degrees reflecting prism at its distal end for side-viewing, and it was added onto an objective lens-based TPM and OCT system. The probe was 2.2 mm in diameter and 60 mm in length. TPM imaging was performed by raster scanning of the excitation focus at the imaging speed of 15.4 frames/s. OCT imaging was performed by combining the linear sample translation and probe rotation along its axis. This miniaturized probe based dual-modal system was characterized with tissue phantoms containing fluorescent microspheres, and applied to image mouse colonic tissues ex vivo as a demonstration. As OCT and TPM provided structural and cellular information of the tissues respectively, this probe based multi-modal imaging system can be helpful for in vivo studies of preclinical animal models such as mouse colonic tumorigenesis. (C) 2014 Optical Society of AmericaX11109sciescopu

Investigation of Putative Multisubtype Hepatitis C Virus Infections In Vivo by Heteroduplex Mobility Analysis of Core/Envelope Subgenomes▿

The frequency that multiple different subtypes of hepatitis C virus (HCV) simultaneously infect a given individual is controversial. To address this question, heteroduplex mobility analysis (HMA) of portions of the HCV core and envelope 1 region was optimized for sensitive and specific detection of mixtures of HCV genomes of different genotype or subtype. Using the standard HCV genotyping approach of 5′-untranslated region (UTR) analysis, 28 of 374 (7.5%) chronic hepatitis C research subjects were classified as having either multiple-subtype HCV infections (n = 21) or switching HCV subtypes over time (n = 7), the latter pattern implying viral superinfection. Upon retesting of specimens by HMA, 25 of 28 multiple-subtype results could not be reproduced. All three patients with positive results were injection drug users with potential multiple HCV exposures. To address the hypothesis of tissue sequestration of multiple-subtype HCV infections, liver (n = 22), peripheral blood mononuclear cell (n = 13), perihepatic lymph node (n = 16), and serum (n = 19) specimens from 23 subjects with end-stage hepatitis C were collected and analyzed by the HMA technique. Whereas 5′-UTR results implicated mixed-subtype HCV infections in 2 subjects, HMA testing revealed no evidence of a second HCV subtype in any tissue compartment (0 of 70 compartments [0%]) or within any given subject (0 of 23 subjects [0%]). In summary, a large proportion of mixed-genotype and switching-genotype patterns generated by 5′-UTR analysis were not reproducible using the HMA approach, emphasizing the need for additional study

Experimental observation of the non-diffusive avalanche-like electron heat transport events and their dynamical interaction with the shear flow structure

We present experimental observations suggesting that non-diffusive avalanche-like transport events are a prevalent and universal process in the electron heat transport of tokamak plasmas. They are observed in the low confinement mode and the weak internal transport barrier plasmas in the absence of magnetohydrodynamic instabilities. In addition, the electron temperature profile corrugation, which indicates the existence of the E x B shear flow layers, is clearly demonstrated as well as their dynamical interaction with the avalanche-like events. The measured width of the profile corrugation is around 45(rho i), implying the mesoscale nature of the structure