Force control of a very lightweight single-link flexible arm based on coupling torque feedback

In this paper, a feedback control law is proposed for regulating the contact force exerted by a very lightweight single-link flexible manipulator when it comes into contact with a motionless object. This control law is based on a lumped-parameter model. The tracking of the desired contact force is obtained by using a feedback loop control of the coupling torque between the motor and the flexible arm. To achieve a good performance on the force control it is only necessary to measure the coupling torque at the root of the arm. Neither the contact force sensor nor the angular position sensor of the motor are used in the control method. A modified PID controller is proposed for this control law. In this work the force control problem is studied for both free and constrained motions of the flexible manipulator, and a collision detection algorithm is also described.     

Metabolic pathways of the colonic metabolism of procyanidins (monomers and dimers) and alkaloids

Procyanidins are metabolised by endogenous gastrointestinal microflora into several small molecules that may exert systemic effects. However, the metabolic pathways of procyanidins are still largely uncharacterised. The aim of this study was to evaluate the colonic metabolism of procyanidins (catechin, epicatechin, epicatechin gallate, epigallocatechin gallate and dimer B2) and alkaloids (theobromine and caffeine) by an in vitro colonic fermentation model using rat colonic microflora. Simultaneously, a nuts-cocoa cream was incubated and the colonic metabolism of procyanidins and alkaloids was evaluated. Results showed that most of the procyanidins tested were catabolised after 24–48 h of fermentation. Fermentation of the dimer B2 did not produce the same catabolic compounds as epicatechin fermentation and differences were observed between the fermentation of catechin and epicatechin. The alkaloids were not metabolised by the colonic microflora and this fact was verified in vivo. The results showed an intense metabolism of procyanidins and poor metabolism of alkaloids.     

mTOR Knockdown in the Infralimbic Cortex Evokes A Depressive-like State in Mouse

Fast and sustained antidepressant effects of ketamine identified the mammalian target of rapamycin (mTOR) signaling pathway as the main modulator of its antidepressive effects. Thus, mTOR signaling has become integral for the preclinical evaluation of novel compounds to treat depression. However, causality between mTOR and depression has yet to be determined. To address this, we knocked down mTOR expression in mice using an acute intracerebral infusion of small interfering RNAs (siRNA) in the infralimbic (IL) or prelimbic (PrL) cortices of the medial prefrontal cortex (mPFC), and evaluated depressive- and anxious-like behaviors. mTOR knockdown in IL, but not PrL, cortex produced a robust depressive-like phenotype in mice, as assessed in the forced swimming test (FST) and the tail suspension test (TST). This phenotype was associated with significant reductions of mTOR mRNA and protein levels 48 h post-infusion. In parallel, decreased brain-derived neurotrophic factor (BDNF) expression was found bilaterally in both IL and PrL cortices along with a dysregulation of serotonin (5-HT) and glutamate (Glu) release in the dorsal raphe nucleus (DRN). Overall, our results demonstrate causality between mTOR expression in the IL cortex and depressive-like behaviors, but not in anxiety.     

Whole cell electrochemistry of electricity-producing microorganisms evidence an adaptation for optimal exocellular electron transport

The mechanism(s) by which electricity-producing microorganisms interact with an electrode is poorly understood. Outer membrane cytochromes and conductive pili are being considered as possible players, but the available information does not concur to a consensus mechanism yet. In this work we demonstrate that Geobacter sulfurreducens cells are able to change the way in which they exchange electrons with an electrode as a response to changes in the applied electrode potential. After several hours of polarization at 0.1 V Ag/AgCl-KCl (saturated), the voltammetric signature of the attached cells showed a single redox pair with a formal redox potential of about -0.08 V as calculated from chronopotentiometric analysis. A similar signal was obtained from cells adapted to 0.4 V. However, new redox couples were detected after conditioning at 0.6 V. A large oxidation process beyond 0.5 V transferring a higher current than that obtained at 0.1 V was found to be associated with two reduction waves at 0.23 and 0.50 V. The apparent equilibrium potential of these new processes was estimated to be at about 0.48 V from programmed current potentiometric results. Importantly, when polarization was lowered again to 0.1 V for 18 additional hours, the signals obtained at 0.6 V were found to greatly diminish in amplitude, whereas those previously found at the lower conditioning potential were recovered. Results clearly show the reversibility of cell adaptation to the electrode potential and pointto the polarization potential as a key variable to optimize energy production from an electricity producing population.     

Prediction of the effect of second phases embedded in a lead matrix on anodic corrosion

After referring to the research carried out on composite specimens formed by lamellae of “reactive” metals embedded in a lead matrix, an attempt is made to apply the data obtained on penetration of attack into these lamellae to the real case of the anodic corrosion of several two-phase Pb---Sb and Pb---Ag alloys in the as-cast condition.To this end, a theoretical treatment of the effect of a “reactive” second phase on the stability of an alloy is presented. Emphasis is laid on the role which material disintegration may play, provided the second phase particles supply routes for a fast penetration of the localized attack into the alloy structure.     

A New Control Scheme of Single-link Flexible Manipulators Robust to Payload Changes

A new scheme is presented in this paper to control single-link flexiblemanipulators. The objective is to control the tip position of the flexiblearm in the presence of joint friction and payload changes. The controlscheme is based on two nested loops: an inner feedback loop to control themotor position which is robust to joint friction, and an outer loop tocontrol the tip position which is robust to payload changes. This outer loopis composed of a feedforward term and a feedback term. This results in asimple control law that needs minimal computing effort and, thus, can beused for real time control of flexible arms. The proposed method is generalin the sense that it can be applied to very different arm structures anddiverse sensor systems configurations. Results corresponding to twodifferent arm setups are presented.     

The structural plasticity of the C terminus of p21Cip1 is a determinant for target protein recognition

The cyclin-dependent kinase inhibitory protein p21(Cip1) might play multiple roles in cell-cycle regulation through interaction of its C-terminal domain with a defined set of cellular proteins such as proliferating cell nuclear antigen (PCNA), calmodulin (CaM), and the oncoprotein SET. p21(Cip1) could be described as an intrinsically unstructured protein in solution although the C-terminal domain adopts a well-defined extended conformation when bound to PCNA. However, the molecular mechanism of the interaction with CaM and the oncoprotein SET is not well understood, partly because of the lack of structural information. In this work, a peptide derived from the C-terminal domain of p21(Cip1) that covers the binding domain of the three above-mentioned proteins was used to demonstrate that the C-terminal domain of p21 recognizes multiple ligands through its ability to adopt multiple conformations. The conformation is dictated by tertiary contacts rather than by the primary sequence of the protein. Our results suggest that the C-terminal domain of p21(Cip1) adopts an extended structure when bound to PCNA and probably when bound to the oncoprotein SET, but an alpha helix when bound to CaM.     

Experimental Testing of a Gauge Based Collision Detection Mechanism for a New Three‐Degree‐of‐Freedom Flexible Robot

The use of flexible robots can be easily justified in two main cases: (1) when the weight of the robot has to be minimized and (2) when collisions between the robot and the environment are foreseen, since a flexible, lightweight robot implies less impact energy. The position control of these robots has already been analyzed in previous communications. However, the second of these cases justifying the use of flexible robots requires further consideration, leading to the development of a force controller. Inmost up to date analysis the force control is studied beginning from a known contact point at a given collision time. In a more realistic approach, however, an accurate detection of the collision would be needed prior to dealing with the force control. After developing a reliable position controller for a three‐degree‐of‐freedom flexible robot using strain gauges placed over the robot structure, in this paper we deal with the possibility of carrying out the collision detection for the same prototype. This has been easily achieved by analyzing some estimated signals such as tip position and tip velocity. However, a complete analysis of the information obtained with the sensors has been required to obtain those estimates and a signal processing scheme had to be devised for a previous filtering of the original signals from the sensors (encoders and strain gauges). This work has been carried out as a first step towards the position/force control. Experimental results on a three‐degree‐of‐freedom flexible arm prototype are presented to verify how well this method performs. © 2003 Wiley Periodicals, Inc.     

Fertilizer characterization: isotopic data (N, S, O, C, and Sr)

A detailed isotopic characterization (delta15N(Ntotal), delta15N(NO3), delta18O(NO3), delta34S(SO4), delta18O(SO4), (delta13C(Ctotal), and 87Sr/86Sr) of 27 commercial fertilizers used in Spain is presented in this paper. Results together with a compilation of fertilizer isotopic published data are used for two purposes: (i) to identify the origin of the primary constituents and raw materials used in fertilizer manufacture and relate these data with their heavy metals and rare earth elements (REE) contents; (ii) to compare the fertilizer isotopic signatures with natural values and other anthropogenic pollutants and evaluate the usefulness of multi-isotopic analyses to trace fertilizer contaminations in future study cases. Isotope data permit us to know, in most cases, the origin of the primary constituents of fertilizers, and the 87Sr/86Sr ratio distinguishes the origin of the phosphate content--phosphorites or carbonatites--which in turn implies a qualitatively defined and potentially contaminant presence of REE and heavy metals in fertilizers. Delta15N, delta34S, and 87Sr/86Sr have already been used to trace fertilizer contaminations. Their utility can be improved by the coupled use of delta15N(NO3)-delta18O(NO3) and delta34S(SO4)-delta18O(SO4) to evaluate the fractionation processes that can affect contaminants. Moreover, multi-isotopic analyses, using heavy isotopes, allow us to see beyond the fractionation effects to the fertilizer stable isotope signatures and a better distinction from other anthropogenic contaminants.     

Dimethoxymethane electrooxidation on low index planes of platinum single crystal in acid media

Conventional electrochemical methods have been applied to study the oxidation of a possible alternative fuel for a direct oxidation fuel cell. The electrooxidation of dimethoxymethane (DMM) was investigated on the three low index planes, (1 0 0), (1 1 0) and (1 1 1) of platinum single crystals and compared with its oxidation on a platinum polycrystalline electrode. Among platinum electrodes, electroreactivity of DMM observed is Pt(1 1 1) > Pt(1 0 0) > Pt(1 1 0) ∼ Pt poly. Hydrogen adsorption is limited by the presence of DMM, except for Pt(1 1 1) plane. In situ IR experiments show the presence of bands of CO_ads with all electrodes except Pt(1 1 1). This work shows that the mechanism of DMM electrooxidation is structure sensitive. A path takes place on Pt(1 0 0) and Pt(1 1 0) which is favourable to the formation of CO_ads. Another path proceeds on Pt(1 1 1), where CO_ads is not present and reaction does not occur at low potential. Results indicate that peak intensities are higher in perchloric acid than in sulphuric acid. So DMM adsorption is dependent on the specific adsorption of the anions. In situ IR reflectance spectroscopy identified some intermediates and reaction products of DMM adsorption and electrooxidation on Pt electrodes: CO_L (linearly bonded) and CO_B (bridge bonded), adsorbed CHO and CH₃O species, methanol and CO₂. The electrochemical and spectroelectrochemical experiments suggest a complex mechanism of DMM electrooxidation.