Passivation of underactuated systems with physical damping

In recent works, IDA-PBC has been succesfully applied to mechanical control problems with no physical damping present. In some cases, the friction terms can be obviated without compromising stability in closed loop. However in methods that modify the kinetic energy, a controller designed for stabilizing the undamped system might loose passivity, a key property for stabilization, when damping is introduced. This paper presents a necessary and sufficient condition, namely the dissipation condition, for recovering passivity (and hence stability) in such cases. If the dissipation condition is fulfilled, an IDA-PBC redesign is necessary in general, and with this goal two different methods for passivating the damped system are presented

Electroproduction of the d* dibaryon

The unpolarized cross section for the electroproduction of the isoscalar $J^\pi = 3^+$ di-delta dibaryon $d^*$ is calculated for deuteron target using a simple picture of elastic electron-baryon scattering from the $\Delta \Delta (^7D_1)$ and the $NN (^3S_1)$ components of the deuteron. The calculated differential cross section at the electron lab energy of 1 GeV has the value of about 0.24 (0.05) nb/sr at the lab angle of 10$^\circ$ (30$^\circ$) for the Bonn B potential when the dibaryon mass is taken to be 2.1 GeV. The cross section decreases rapidly with increasing dibaryon mass. A large calculated width of 40 MeV for $d^*(\Delta\Delta ^7S_3)$ combined with a small experimental upper bound of 0.08 MeV for the $d^*$ decay width appears to have excluded any low-mass $d^*$ model containing a significant admixture of the $\Delta\Delta (^7S_3)$ configuration.Comment: 11 journal-style pages, 8 figure

Characterization of cork and cork agglomerates under compressive loads by means of energy absorption diagrams

Cork and cork agglomerates could be suitable replacements for petroleum-based polymeric foams due to their similar internal structure of cells and grains. Additionally, cork products have a renewable origin and are recyclable. Despite these notable properties, few studies have analysed the mechanical properties, especially the specific properties, of these materials under compressive loads. Moreover, although efficiency, ideality, and energy-normalized stress diagrams are commonly used for polymeric foams and 3D-printed lattice structures, these types of diagrams are not yet applied to cork products. It must be highlighted that efficiency diagrams are plotted only against nonspecific properties so, this article proposes additionally the use of nonspecific properties to compare materials not only in terms of properties per unit volume instead but also in terms of properties per unit mass that is more suitable for certain applications in which the weight is crucial. The materials studied herein include three different white cork agglomerates, a brown cork agglomerate, a black cork agglomerate, natural cork, and expanded polystyrene foam, which are subjected to quasi-static compressive loads

Numerical model of the inhomogeneous scattering by the human lens

We present in this work a numerical model for characterizing the scattering properties of the human lens. After analyzing the scattering properties of two main scattering particles actually described in the literature through FEM (finite element method) simulations, we have modified a Monte Carlo''s bulk scattering algorithm for computing ray scattering in non-sequential ray tracing. We have implemented this ray scattering algorithm in a layered model of the human lens in order to calculate the scattering properties of the whole lens. We have tested our algorithm by simulating the classic experiment carried out by Van der Berg et al for measuring "in vitro" the angular distribution of forward scattered light by the human lens. The results show the ability of our model to simulate accurately the scattering properties of the human lens. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreemen

Mechanical properties of diamond lattice structures based on main parameters and strain rate

The diamond triply periodic minimal surface structure has a high mechanical property–weight ratio. They can be modified by changing their internal parameters or the material. They are generated using the additive manufacturing (AM) that possibilities the use of various materials for generating zones with different mechanical properties or by modifying their internal parameters. However, the effects of internal parameters in the mechanical properties have not been defined in detail. Furthermore, the strain rate modifies these mechanical properties. In this study, the effects of the internal parameters and strain rate were evaluated and additionally, the failure mechanism of the structures

The finger flexors occlusion threshold in sport-climbers: an exploratory study on its indirect approximation

Blood flow partially determines specific climbing endurance (SCE) as it mediates oxygen bio-availability in the finger flexors. Blood flow is related to occlusion threshold (OT), which is defined as the contraction intensity at which intramuscular pressure exceeds perfusion blood pressure resulting in the cessation of local blood flow. The OT is represented as an inflection point on a force-time graph when isometric force is registered and applied through maximal and continuous tests. Endurance time (ET) to exhaustion is influenced by the relative isometric applied force and is different for each climber. The aim of this study was to explore whether an approximation of the finger flexors OT in sport climbers through records of ET to exhaustion at different isometric relative intensities was possible. We measured maximum finger hang ETs at 6 intensities ranging from 85% to 35% maximal force in 34 sport climbers of advanced and elite level. The values obtained were analysed by two different methods in an attempt to determine a change in the shape of the curve in the intensity-ET relationship graphs that approximated the OT for each climber. The results suggest that the finger flexors OT could be different among climbers, regardless of their strength and ability level. The presented methods do not accurately reflect the OT, but could indicate the intensity at which blood flow is restored in the active muscles. This is the first study to indirectly approximate the finger flexors OT in sport-climbers, a parameter that could be essential to assess SCE

Rapid in vivo PGC-1 mRNA upregulation in brown adipose tissue of Wistar rats by a beta(3)-adrenergic agonist and lack of effect of leptin.

Peroxisome proliferator-activated receptor-γ coactivator-1 (PGC-1) is highly expressed in brown adipose tissue (BAT) and plays an important role in adaptive thermogenesis. The aim of this study was to assess the acute effect of a β3-adrenergic agonist (Trecadrine) and leptin on the expression of PGC-1 and PPARγ2 mRNA in BAT. Trecadrine produced a marked increase (4.5-fold) in PGC-1 mRNA compared to controls (P<0.001) without changes in PPARγ2 mRNA, whereas leptin administration did not alter either PGC-1 or PPARγ2 expression. These results show that selective stimulation of the β3-adrenoceptor rapidly upregulates the expression of PGC-1 in brown adipocytes without a concomitant increase in PPARγ2. Moreover, our results show that PGC-1 and PPARγ2 expression in BAT seems not to be acutely regulated by leptin

Longitudinal effects of swimming on bone in adolescents: A pQCT and DXA study

The aims of the present study were, firstly, to evaluate areal bone mineral density (aBMD), bone strength and structure during a swimming season and compare them to those of normo-active controls (CG), and secondly to ascertain whether practising an additional weight-bearing sport other than swimming might improve bone. Twenty-three swimmers who only swam (SWI-PURE; 14 males, 9 females), 11 swimmers who combined swimming with an additional weight-bearing sport (SWI-SPORT; 8 males, 3 females) and 28 controls (CG; 16 males, 12 females) participated in the present study. aBMD was assessed with dual energy X-ray (DXA). Bone mass, area, structure and strength of the non-dominant tibia and radius were measured with peripheral quantitative computed tomography (pQCT). Measurements were performed at the beginning of the swimming season and 8 months later. The only difference among groups for DXA and pQCT variables was found for arm aBMD, which was higher in the SWI-SPORT than in the CG group at both pre- and post-evaluation. Group by time interactions (GxT) were found for trochanter aBMD when comparing SWI-SPORT to CG and SWI-SPORT to SWI-PURE, favouring in both cases SWI-SPORT. No GxT were found for the radius. For the tibia, GxT were found between SWI-SPORT and CG and between SWI-PURE and CG, in both cases favouring the swimmers. A season of swimming does not confer any additional benefits to aBMD, but may confer minor benefits to structure and mass. Complementing swimming with a weight-bearing activity is beneficial to bone

Chiral Perturbation Theory and the f2(1270) resonance

Within Chiral Perturbation Theory, we study elastic pion scattering in the I=0, J=2, channel, whose main features are the f2(1270) resonance and the vanishing of the lowest order. By means of a chiral model that includes an explicit resonance coupled to pions, we describe the data and calculate the resonance contribution to the O(p^4) and O(p^6) chiral parameters. We also generalize the Inverse Amplitude Method to higher orders, which allows us to study channels with vanishing lowest order. In particular, we apply it to the I=0,J=2 case, finding a good description of the f2(1270) resonance, as a pole in the second Riemann sheet.Comment: 4 pages,1 figur

A new performance threshold in sport climbing: A change in how climbing trainers work?

Objectives: Previous research has shown that the finger flexor's occlusion threshold (OT) could be different among sport climbers when expressed as a percentage of their maximum finger force (OT%), and that there is no association between the OT% and the climberś ability level. The aim of the present study was to evaluate the possible association between the relative finger force applied at the OT% (rff-OT%) and climbing ability level. Equipment and methods: WWe approximated the finger flexor's OT of 34 sport climbers by finger hang endurance test analyses at different intensities between 35% and 85% of their individual maximum finger force on a previously individually adapted edge depth, and we valued their rff-OT% as the relative force they could perform at that intensity. Results: We found a high correlation between the rff-OT% and climbing ability in elite climbers. These findings suggest that having an OT at the highest possible percentage is critical, in addition to having a high relative finger force, as this would enable climbers to express relative force at a wider range of intensities with favorable metabolic conditions