Maximum Hands-Off Control: A Paradigm of Control Effort Minimization

In this paper, we propose a new paradigm of control, called a maximum hands-off control. A hands-off control is defined as a control that has a short support per unit time. The maximum hands-off control is the minimum support (or sparsest) per unit time among all controls that achieve control objectives. For finite horizon control, we show the equivalence between the maximum hands-off control and L1-optimal control under a uniqueness assumption called normality. This result rationalizes the use of L1 optimality in computing a maximum hands-off control. We also propose an L1/L2-optimal control to obtain a smooth hands-off control. Furthermore, we give a self-triggered feedback control algorithm for linear time-invariant systems, which achieves a given sparsity rate and practical stability in the case of plant disturbances. An example is included to illustrate the effectiveness of the proposed control.Comment: IEEE Transactions on Automatic Control, 2015 (to appear

Atomic resolved material displacement on graphite surfaces by scanning tunnelling microscopy

Atomic scale modifications and subsequent atomic resolution imaging has been achieved on the highly oriented pyrolytic graphite surface in air. Application of short pulse voltages, above a minimum threshold voltage of 3.5 V, across the tunneling gap results in the displacement of a layer or more of atoms to form a hole and create a neighboring mound or ‘‘nanodot’’ from the displaced atoms. We have found a correlation between the hole and ‘‘nanodot’’ volume at the atomic level and observe an asymmetric displacement of material in all cases of feature creation. Nanofeatures as small as four carbon atoms at beta sites have been created. Our experimental observations are consistent with the modification process depending on the gradient in the electric field induced by the rise time of the bias pulse voltage and not the pulse duration. Interesting faceting behavior has also been observed around some hole edges. Tip bias pulsing sometimes induced a tip, and not a surface modification, resulting in a change in the observed tunneling image

Direction Detector on an Excitable Field: Field Computation with Coincidence Detection

Living organisms process information without any central control unit and without any ruling clock. We have been studying a novel computational strategy that uses a geometrically arranged excitable field, i.e., "field computation." As an extension of this research, in the present article we report the construction of a "direction detector" on an excitable field. Using a numerical simulation, we show that the direction of a input source signal can be detected by applying the characteristic as a "coincidence detector" embedded on an excitable field. In addition, we show that this direction detection actually works in an experiment using an excitable chemical system. These results are discussed in relation to the future development of "field computation."Comment: 6 pages, 3 figure

Monitoring of post-match fatigue in professional soccer: Welcome to the real world

Participation in soccer match-play leads to acute and transient subjective, biochemical, metabolic and physical disturbances in players over subsequent hours and days. Inadequate time for rest and regeneration between matches can expose players to the risk of training and competing whilst not entirely recovered. In professional soccer, contemporary competitive schedules can require teams to compete in-excess of 60 matches over the course of the season while periods of fixture congestion occur prompting much attention from researchers and practitioners to the monitoring of fatigue and readiness to play. A comprehensive body of research has investigated post-match acute and residual fatigue responses. Yet the relevance of the research for professional soccer contexts is debatable notably in relation to the study populations and designs employed. Monitoring can indeed be invasive, expensive, time-inefficient and difficult to perform routinely and simultaneously in a large squad of regularly competing players. Uncertainty also exists regarding the meaningfulness and interpretation of changes in fatigue response values and their functional relevance, and practical applicability in the field. The real-world need and cost-benefit of monitoring must be carefully weighed up. In relation to professional soccer contexts, this opinion paper intends to: 1) debate the need for PMF monitoring, 2) critique the real-world relevance of the current research literature, 3) discuss the practical burden relating to measurement tools and protocols and the collection, interpretation and application of data in the field, and, 4) propose future research perspectives

The protective role of the 3-mercaptopyruvate sulfurtransferase (3-MST)-hydrogen sulfide (H₂S) pathway against experimental osteoarthritis.

Osteoarthritis (OA) is characterized by the formation and deposition of calcium-containing crystals in joint tissues, but the underlying mechanisms are poorly understood. The gasotransmitter hydrogen sulfide (H <sub>2</sub> S) has been implicated in mineralization but has never been studied in OA. Here, we investigated the role of the H <sub>2</sub> S-producing enzyme 3-mercaptopyruvate sulfurtransferase (3-MST) in cartilage calcification and OA development. 3-MST expression was analyzed in cartilage from patients with different OA degrees, and in cartilage stimulated with hydroxyapatite (HA) crystals. The modulation of 3-MST expression in vivo was studied in the meniscectomy (MNX) model of murine OA, by comparing sham-operated to MNX knee cartilage. The role of 3-MST was investigated by quantifying joint calcification and cartilage degradation in WT and 3-MST <sup>-/-</sup> meniscectomized knees. Chondrocyte mineralization in vitro was measured in WT and 3-MST <sup>-/-</sup> cells. Finally, the effect of oxidative stress on 3-MST expression and chondrocyte mineralization was investigated. 3-MST expression in human cartilage negatively correlated with calcification and OA severity, and diminished upon HA stimulation. In accordance, cartilage from menisectomized OA knees revealed decreased 3-MST if compared to sham-operated healthy knees. Moreover, 3-MST <sup>-/-</sup> mice showed exacerbated joint calcification and OA severity if compared to WT mice. In vitro, genetic or pharmacologic inhibition of 3-MST in chondrocytes resulted in enhanced mineralization and IL-6 secretion. Finally, oxidative stress decreased 3-MST expression and increased chondrocyte mineralization, maybe via induction of pro-mineralizing genes. 3-MST-generated H <sub>2</sub> S protects against joint calcification and experimental OA. Enhancing H <sub>2</sub> S production in chondrocytes may represent a potential disease modifier to treat OA

Limbic-thalamo-cortical projections and reward-related circuitry integrity affects eating behavior: A longitudinal DTI study in adolescents with restrictive eating disorders.

Few studies have used diffusion tensor imaging (DTI) to investigate the micro-structural alterations of WM in patients with restrictive eating disorders (rED), and longitudinal data are lacking. Twelve patients with rED were scanned at diagnosis and after one year of family-based treatment, and compared to twenty-four healthy controls (HCs) through DTI analysis. A tract-based spatial statistics procedure was used to investigate diffusivity parameters: fractional anisotropy (FA) and mean, radial and axial diffusivities (MD, RD and AD, respectively). Reduced FA and increased RD were found in patients at baseline in the corpus callosum, corona radiata and posterior thalamic radiation compared with controls. However, no differences were found between follow-up patients and controls, suggesting a partial normalization of the diffusivity parameters. In patients, trends for a negative correlation were found between the baseline FA of the right anterior corona radiata and the Eating Disorder Examination Questionnaire total score, while a positive trend was found between the baseline FA in the splenium of corpus callosum and the weight loss occurred between maximal documented weight and time of admission. A positive trend for correlation was also found between baseline FA in the right anterior corona radiata and the decrease in the Obsessive-Compulsive Inventory Revised total score over time. Our results suggest that the integrity of the limbic-thalamo-cortical projections and the reward-related circuitry are important for cognitive control processes and reward responsiveness in regulating eating behavior

H2S biosynthesis and catabolism: new insights from molecular studies

Hydrogen sulfide (H2S) has profound biological effects within living organisms and is now increasingly being considered alongside other gaseous signalling molecules, such as nitric oxide (NO) and carbon monoxide (CO). Conventional use of pharmacological and molecular approaches has spawned a rapidly growing research field that has identified H2S as playing a functional role in cell-signalling and post-translational modifications. Recently, a number of laboratories have reported the use of siRNA methodologies and genetic mouse models to mimic the loss of function of genes involved in the biosynthesis and degradation of H2S within tissues. Studies utilising these systems are revealing new insights into the biology of H2S within the cardiovascular system, inflammatory disease, and in cell signalling. In light of this work, the current review will describe recent advances in H2S research made possible by the use of molecular approaches and genetic mouse models with perturbed capacities to generate or detoxify physiological levels of H2S gas within tissue

Wearable resistance sprint running is superior to training with no load for retaining performance in pre-season training for rugby athletes

This study determined the effects of a six-week lower-limb wearable resistance training (WRT) intervention on sprint running time, velocity, and horizontal force-velocity mechanical variables. Twenty-two collegiate/semi-professional rugby athletes completed pre- and post-intervention testing of three maximal effort 30 m sprints. A radar device was used to measure sprint running velocity from which horizontal force-velocity mechanical profiling variables were calculated. All athletes completed two dedicated sprint training sessions a week for six-weeks during pre-season. The intervention (wearable resistance, WR) group completed the sessions with 1% body mass load attached to the left and right shanks (i.e. 0.50% body mass load on each limb), whilst the control group completed the same sessions unloaded. For the control group, all variables were found to detrain significantly (p ≤ 0.05) over the training period with large detraining effects (ES > 0.80) for theoretical maximal horizontal force, slope of the force-velocity profile, maximal ratio of force, index of force application, 5 m and 10 m times. For the WR group, there were no significant changes to any recorded variables (all p > 0.05) and all effects of training were trivial or small (ES 0.80) except theoretical maximal velocity, 30 m time, and maximal velocity. The addition of light wearable resistance to sprint training during a six-week pre-season block enables the maintenance of sprint performance and mechanical output qualities that otherwise would detrain due to inadequate training frequencies

Aerogel as a Soft Acoustic Metamaterial for Airborne Sound

Soft acoustic metamaterials utilizing mesoporous structures have been proposed recently as a means for tuning the overall effective properties of the metamaterial and providing better coupling to the surrounding air. In this paper, the use of silica aerogel is examined theoretically and experimentally as part of a compact soft acoustic metamaterial structure, which enables a wide range of exotic effective macroscopic properties to be demonstrated, including negative density, density near zero, and nonresonant broadband slow-sound propagation. Experimental data are obtained on the effective density and sound speed using an air-filled acoustic impedance tube for flexural metamaterial elements, which have been investigated previously only indirectly due to the large contrast in acoustic impedance compared to that of air. Experimental results are presented for silica aerogel arranged in parallel with either one or two acoustic ports and are in very good agreement with the theoretical model.This work is supported by the U.S. Office of Naval Research. M. D. G., V. M. G.-C. and J. S.-D. also acknowledge the support by the Spanish Ministerio de Economia y Competitividad, and the European Union Fondo Europeo de Desarrollo Regional (FEDER) through Project No. TEC2014-53088-C3-1-R. The authors wish to acknowledge Encarna G. Villora and Kiyoshi Shimamura for their help in aerogel fabrication and handling.Guild, M.; García Chocano, VM.; Sánchez-Dehesa Moreno-Cid, J.; Martin, TP.; Calvo, DC.; Orris, GJ. (2016). Aerogel as a Soft Acoustic Metamaterial for Airborne Sound. Physical Review Applied. 5(3):034012-1-034012-13. https://doi.org/10.1103/PhysRevApplied.5.034012S034012-1034012-135

An Optimization Approach to Weak Approximation of Lévy-Driven Stochastic Differential Equations

We propose an optimization approach to weak approximation of Lévy-driven stochastic differential equations. We employ a mathematical programming framework to obtain numerically upper and lower bound estimates of the target expectation, where the optimization procedure ends up with a polynomial programming problem. An advantage of our approach is that all we need is a closed form of the Lévy measure, not the exact simulation knowledge of the increments or of a shot noise representation for the time discretization approximation. We also investigate methods for approximation at some different intermediate time points simultaneously