Opposite Legs Research Articles

Weak Bonding and Anharmonicity in Thermoelectric ZnSb

AbstractThe Zn─Sb binary system contains two high‐performing thermoelectric materials, namely the ordered ZnSb and the disordered Zn13Sb10. Both systems exhibit low thermal conductivity, which is speculated to originate from multicentre bonding within Zn2Sb2‐rhombi. Here, the electron density of ZnSb is reported based on multipole modelling of accurate X‐ray diffraction data measured at 20 K. Topological analysis reveals that the bond paths in the rhombus are endocyclically strained and that electron density is concentrated within the rhombus rather than along its geometric bonds consistent with a multicentre bond description. However, the electron density is not equally shared between the geometric bonds of the rhombus. Electron density analysis and modelling of low‐temperature anharmonicity reveal that one Zn–Sb interaction is weaker than the other. Taken together with the orientation of bonds external to the rhombus structure, an alternative description emerges wherein the multicentre bond is more partially localised along one set of the opposite legs of the rhombus. In this description, the stronger bond can be considered a traditional 2‐centre‐2‐electron bond, while the weaker interaction is coordinative to the covalent bond. The anharmonicity and low thermal conductivity may consequently be understood as Zn rattling along the coordinative interaction.

The deviation angle for one-lane roundabouts: A general mathematical formulation and application

Properly designed roundabouts may lead to safety improvements based on both reducing approaching speeds and controlling traffic. Measurements of deflection of vehicle trajectories are commonly used to estimate roundabout speed control. One of these measurements is the deviation angle, which is mentioned in both the Italian and Swiss road standards and, in specific conditions, can be more effective than other methods. This article presents a general mathematical formulation for linking several geometric parameters with the deviation angle in different rural and urban one-lane roundabout configurations, which is currently missing in the literature. For urban roundabouts, refuge islands for pedestrians and cyclists were considered. Based on the proposed formulation, a sensitivity analysis of the influential geometric parameters was conducted. Results suggest that an insufficient deflection of trajectories (deviation angle less than 45°) is always present for roundabouts with inscribed circle diameter less than 25 m; for urban roundabouts with refuge islands for pedestrians and cyclists having inscribed circle diameter less than 34 m and orthogonal legs; and for roundabouts with angles between opposite legs smaller than 140°. The main parameters which are responsible for a decrease in the deviation angle are: a decrease in the inscribed circle diameter; a decrease in the angle between opposite legs; and an increase in the width of the circulatory lane. Some optimized procedures for roundabout design, the generalized application of the deviation angle method and alternative speed control measures in cases of small deviation angles are discussed. • The deviation angle is an effective measure of the deflection of trajectories and speed reduction at roundabouts. • A mathematical formulation for linking geometric parameters with the deviation angle in one-lane roundabouts is proposed. • The general framework is applicable for both rural/urban one-lane roundabouts, considering the presence of vulnerable users. • The most influential parameters on the deflection of trajectories were discussed through a detailed sensitivity analysis. • Some measures were proposed, alternative to the geometrically-induced deflection of trajectories, in different cases.

Corrosion behavior of stirrups in corroded concrete beams exposed to chloride environment under sustained loading

This paper discusses the corrosion behavior of stirrups in two concrete beams under sustained loading, exposed to a chloride environment for 9 years. The cracking maps of concrete beams were recorded after 28 days and after 9 years, respectively. The corrosion maps of the stirrups were drawn and the cross-sectional losses of stirrups were measured after destroying the beams. The experimental results show that the horizontal legs of stirrups mainly corroded at the mid span of the tensile zone and at the ends of the compressive zone of the reinforced concrete beams regardless of the exposure conditions, while the opposite horizontal legs were protected. The corrosion of vertical legs of stirrups, which was slight, was not impacted by the load-induced cracks. In the present study, it is difficult to find the correlation of corrosion degree between stirrups and the main reinforcing steels in the reinforced concrete beams. The corrosion behavior of the intersection between stirrups and main bars was controlled by the interfacial conditions between them. Cathodic protection occurred at the ends of the top-cast side and the mid-span of bottom-cast side of reinforced concrete beams when the compressive rebars and tensile rebars were placed at the top- and bottom- cast sides, respectively.

Estimation of Ground Reaction Force for Quadruped Robot Control Using a High-Gain Observer

Ground reaction force is one of the most important information for legged-locomotion control. This paper presents a novel design of an observer for estimating the ground reaction force of a quadruped robot without force sensors. Simple dynamics model of a general quadruped robot is derived by assuming that the robot’s fore and hind legs can be treated separately, and they can support force provided by opposite legs and the ground reaction force are considered as external disturbance force to be estimated by a disturbance observer. Simulation results show that the proposed observer can successfully estimate the ground reaction force even though the leg is in its swing phase. The estimation of the ground reaction force by the proposed observer may be applied to the controller design using the ground reaction force such as Zero-Moment Point and Central Pattern Generator modulated by the ground reaction force.

The use of clamping grips and friction pads by tree frogs for climbing curved surfaces.

Most studies on the adhesive mechanisms of climbing animals have addressed attachment against flat surfaces, yet many animals can climb highly curved surfaces, like twigs and small branches. Here we investigated whether tree frogs use a clamping grip by recording the ground reaction forces on a cylindrical object with either a smooth or anti-adhesive, rough surface. Furthermore, we measured the contact area of fore and hindlimbs against differently sized transparent cylinders and the forces of individual pads and subarticular tubercles in restrained animals. Our study revealed that frogs use friction and normal forces of roughly a similar magnitude for holding on to cylindrical objects. When challenged with climbing a non-adhesive surface, the compressive forces between opposite legs nearly doubled, indicating a stronger clamping grip. In contrast to climbing flat surfaces, frogs increased the contact area on all limbs by engaging not just adhesive pads but also subarticular tubercles on curved surfaces. Our force measurements showed that tubercles can withstand larger shear stresses than pads. SEM images of tubercles revealed a similar structure to that of toe pads including the presence of nanopillars, though channels surrounding epithelial cells were less pronounced. The tubercles' smaller size, proximal location on the toes and shallow cells make them probably less prone to buckling and thus ideal for gripping curved surfaces.

Mitochondrial Bioenergetics and Fiber Type Assessments in Microbiopsy vs. Bergstrom Percutaneous Sampling of Human Skeletal Muscle.

Microbiopsies of human skeletal muscle are increasingly adopted by physiologists for a variety of experimental assays given the reduced invasiveness of this procedure compared to the classic Bergstrom percutaneous biopsy technique. However, a recent report demonstrated lower mitochondrial respiration in saponin-permeabilized muscle fiber bundles (PmFB) prepared from microbiopsies vs. Bergstrom biopsies. We hypothesized that ADP-induced contraction (rigor) of smaller length microbiopsy PmFB causes a greater reduction in maximal respiration vs. Bergstrom, such that respiration could be increased by a myosin II ATPase-inhibitor (Blebbistatin; BLEB). Eleven males and females each received a 2 mm diameter percutaneous microbiopsy and a 5 mm diameter Bergstrom percutaneous biopsy in opposite legs. Glutamate/malate (5/0.5 mM)—supported respiration in microbiopsy PmFB was lower than Bergstrom at submaximal concentrations of ADP. 5 μM BLEB reduced this impairment such that there were no differences relative to Bergstrom ± BLEB. Surprisingly, pyruvate (5 mM)-supported respiration was not different between either biopsy technique ±BLEB, whereas BLEB increased succinate-supported respiration in Bergstrom only. H2O2 emission was lower in microbiopsy PmFB compared to Bergstrom PmFB in the presence of BLEB. Microbiopsies contained fewer type I fibers (37 vs. 47%) and more type IIX fibers (20 vs. 8%) compared to Bergstrom possibly due to sampling site depth and/or longitudinal location. These findings suggest that smaller diameter percutaneous biopsies yield lower glutamate-supported mitochondrial respiratory kinetics which is increased by preventing ADP-induced rigor with myosin inhibition. Microbiopsies of human skeletal muscle can be utilized for assessing mitochondrial respiratory kinetics in PmFB when assay conditions are supplemented with BLEB, but fiber type differences with this method should be considered.

Fault tolerance criteria and walking capability analysis of a novel parallel-parallel hexapod break walking robot

SUMMARYFault tolerance is a very important issue for legged robots, especially in some harsh environments. One of the most fragile parts is the actuation system. There are two common faults of robot actuators: (1) the motor is locked and could not move anymore; (2) the motor is uncontrollable and can be treated as a passive joint. In this paper, we first discuss all fault combinations of a single leg of a hexapod walking robot with parallel-parallel mechanism topology. Then, the leg tolerable criterion is brought out, which defines whether a leg is fault tolerant. After that, the fault tolerance of the whole robot is researched, and we found that the robot can walk with one tolerable leg or two opposite tolerable legs. Finally, relative simulation results are given, which show the robot walk with one or two broken legs.

Advanced rehabilitation ergometer (ARES): A technical introduction

To optimize training relating to the coordinative skills of athletes, a special cycle ergometer ARES with decoupled cranks was developed. The system is equipped with a measurement system to measure radial and tangential forces on the pedals, additionally to the acquisition of angle velocities of the two crank wheels. Due to the decoupled cranks, every leg performs its own revolution, and has to be active even at the pulling phase, without direct support of the opposite legs downstroke. To explore the unique possibilities of ARES, 4 subjects were tested on the ergometer in a first trial. After a short acclimatization phase to get familiar with the characteristics of the bike, the following tests were performed: (1) normal biking at different numbers of revolution with the challenge to keep a 180° phase angle, and (2) special coordination tasks: a) biking with 0° phase angle, b) Stop-and-go procedures with re-synchronization of the movement, c) counter-movement with both legs moving into opposite direction, and d) a lower half circle swing. During the exercises, forces on the pedals, the crank positions and current cadence were acquired. Out of this data, torque, power, angle velocities and an efficiency parameter were determined for the left and right leg. Variations in cadence, forces and torque as a function of pedal angle are clearly visible. A dependency on number of revolutions seems to be evident, caused by the higher coordinative challenge at high velocities.

Structure and mechanics of the tarsal chain in the hornet, Vespa crabro (Hymenoptera: Vespidae): implications on the attachment mechanism

Two combined mechanisms on the hornet tarsus are adapted to attachment to the substrate: a friction-based (claws and spines) and an adhesion-based one (arolium). There are two ranges of substrate roughness optimal for attachment, either very smooth or very rough. There is an intermediate range of substrate grains of small but non-zero size, where both of these mechanisms fail. The optimal size of substrate grains for hornet grasping was 50–100 μm. Maximal hold to the substrate was achieved when surface irregularities were clamped between the claws of opposite legs. In such a position, the insect could withstand an external force which was almost 25 times larger than its own weight. The tarsal chain is an important part of the entire attachment mechanism. The articulations in the kinematic chain of tibia-tarsus-pretarsus are monocondylar. Three tarsal muscles and one head of the claw retractor muscle originate in the tibia. On pull to the retractor tendon, the tarsus bends in a plane. All elements of the tarsal kinematic chain have one active degree of freedom. The distance between the intertarsomeric articulation point and the tendon of the claw retractor (75–194 μm) corresponds to an efficiency of 1° per 1–3 μm of pulling distance travelled by the tendon. The claw turns about 1° per 4.3–5.0 μm of pulling distance travelled by the unguitractor. The arolium turns forward and downward simultaneously with flexion of the claws. The kinematic chain of the arolium lacks real condylar joints except the joint at the base of the manubrium. Other components are tied by flexible transmissions of the membranous cuticle. The walking hornet rests on distal tarsomeres of extended tarsi. If the retractor tendon inside the tarsus is fixed, passive extension of the tarsomeres might be replaced by claw flexion. Tarsal chain rigidity, measured with the force tester, increased when the retractor tendon was tightened. Probably, pull to the tendon compresses the tarsomeres, increasing friction within contacting areas of rippled surfaces surrounding condyles within articulations.

Ligand binding on ladder lattices

The ligand binding problems on two-dimensional ladders, which model many important binding phenomena in molecular biology, are studied in details. The model is represented by four parameters, the interactions between ligands when bound to adjacent sites on opposite legs of the ladder (τ), the interactions between bound ligands in the longitudinal direction of the ladder (σ), the number of binding sites that are covered by a bound ligand ( m), and the intrinsic binding constant ( K). The partition functions of ring ladders are approached with the transfer matrix method. A general relation is derived which connects the partition function of a linear ladder with that of a ring ladder. The results obtained apply to the general situation of multivalent binding, in which m>1. Special attention is paid to the case where the ligand covers one site ( m=1). In this case explicit formulas are given for the partition functions of ring and linear ladders. Closed-form expressions are obtained for various properties of the system, including the degree of binding (θ), the midpoint in the binding isotherm (1/√τσ), the initial and end slopes of the Scatchard plots (2σ+τ−4 and −σ 2τ, respectively). From these closed-form formulas, σ and τ may be extracted from experimental data. The model reveals certain features which do not exist in one-dimensional models. Using the general method discussed in Kong (submitted), the recurrence relation is found for the partition functions. The analytical solution found for this model provides test cases to verify the numerical results for more complex two-dimensional models.

A simple nonlinear model for pendular chaotic oscillations of reactor core barrel

We propose a non-linear model reproducing the unidirectional (quasi)pendular motion of pressurized water reactor (PWR) core barrel (CB), which is in intermittent contact with reactor pressure vessel (RPV) in places of lower fastenings. Analytic formulae are obtained, which allow one to elucidate the influence of reactor parameters on the character of motion. We show by the example of the WWER-1000 reactor that, in the framework of our model, there exists a possibility of chaotic pendular oscillations in the certain region of three parameters, namely, (i) the pendular oscillation frequency, (ii) the resulting force acting on the CB at the main circulation pump (MCP) frequency from the coolant flows of opposite legs, and (iii) the clearance between the CB and RPV. Vibratory monitoring, which is realized in modern diagnostic systems, in principle, allows one to distinguish between regular and chaotic regimes, thus giving information about the state of fastenings in the lower part of the CB and RPV. We also demonstrate the possibility of stabilizing chaotic oscillations by applying recently proposed control technique.

The Effect of Eccentricity on Brace-to-gusset Angles

Claw angles are used in many bracing connections as shown in Figure 1. Normally these angles and their connections are designed for direct load only without consideration of the fact that the connections are to opposite legs of the angles and of the eccentricities thereby induced. It is the purpose of this note to demonstrate that this practice is generally acceptable, and to produce some guidance as to when it is not.

Studies on the regenerative recovery of long-term denervated muscle in rats

Denervated extensor digitorum longus (EDL) muscles in rats rapidly lose mass and contractile force. After two months of denervation, mass and maximum tetanic force have fallen to 31% and 2% of the values of contralateral control muscles. Our purpose was to determine if grafting a long-term denervated muscle into an innervated site provides an effective means of restoring its structure and function. EDL muscles that had been denervated for periods of 2-12 months were freely grafted into innervated sites of EDL muscles in 4-month inbred host animals. Contralateral normally innervated EDL muscles from the same donors were implanted into the opposite legs of the same hosts. Two months after grafting, the muscles were removed and measurements were made in vitro of isometric contractile properties. The grafts were then prepared for morphological analysts. In all cases, the maximum forces generated by innervated grafts of denervated muscles were greater than those generated by denervated muscles. However, when compared with grafts of control muscles in the contralateral limb, grafts of previously denervated muscles showed a steady decline in structural and functional recovery corresponding to the time of previous denervation. The decline was especially pronounced for muscles denervated between 2 and 7 months prior to grafting. Grafts of 7-month denervated muscles were restored to only 17% of the maximum tetanic force of contralateral control grafts compared with 83% for grafts of 2-month denervated muscles. The longer a muscle had been denervated prior to grafting, the higher proportion of thin atrophic muscle fibers it contained. We conclude that grafting into an innervated site improves the mass and maximum force of a muscle over the denervated state, but the longer the period of prior denervation the poorer the recovery of the grafted muscles.

Magnetic field sensors using GMR multilayer

Wheatstone bridge magnetic field sensors using giant magnetoresistive ratio (GMR) multilayers were designed, fabricated, and evaluated. The GMR ranged from 10% to 20% with saturation fields of 60 Oe to 300 Oe. The multilater resistances decreased linearly with magnetic field and showed little hysteresis. In one sensor configuration, a permanent magnet bias was placed between two pairs of magnetoresistors, each pair representing opposite legs of the bridge. This sensor gave a bipolar bridge output whose output range was approximately GMR times the bridge source voltage. The second sensor configuration used shielding on one resistor pair, and it gave a bridge output dependent on the magnetic field magnitude, but not polarity, and the output range was approximately one half GMR tines the bridge source voltage. Field amplifications of 3 to 6 were accomplished by creating a gap in a low reluctance magnetic path, thus providing the full range of outputs with 1/3 to 1/6 of the intrinsic saturation fields of the GMR multilayers. >

Precision and variability of hindlimb representation in cat dorsal horn and implications for tactile localization.

1. One hundred fifty-eight cells were recorded extracellularly in rows of tracks spanning both left and right dorsal horns, at segmental boundaries and midsegment in segments L5-S1, in six anesthetized cats. For each cell the low-threshold cutaneous mechano-receptive field was determined with the use of hand-held probes, and the recording site was marked with a microlesion. Recording sites were reconstructed, and the mediolateral (ML) and rostrocaudal (RC) locations of each cell were recorded along with the location of the cell's receptive field, expressed as distance from tips of toes (D). 2. Ninety-five percent of pairs of cells recorded from bilaterally symmetric locations (+/- 10%) in the same animal had receptive fields on opposite legs that had components that were mirror symmetric. Only 42% of cell pairs deviating from bilateral symmetry by approximately +/- 240 microns had receptive fields with overlapping components. This indicated that there was a substantial bilateral symmetry that was not simply due to large receptive fields. 3. The trajectories of receptive fields of cells in a single row of tracks were plotted in order of mediolateral recording site, going from medial to lateral, combining both sides. These trajectories followed a distoproximal course on the leg. Of 144 adjacent cells used to plot these trajectories, with an average spacing of approximately 120 microns, only 6 reversals of the distoproximal gradient polarity were observed within animals. 4. Data from individual animals were shifted rostrally and caudally, to obtain best agreement of mediolateral somatotopic gradients with the combined data from the other animals in the sample. Best agreement was obtained with shifts ranging from 0.3 segment rostral to 0.4 segment caudal, with an average absolute value shift of 0.22 segment. 5. By comparing cell pairs within the same dorsal horn, on opposite sides of the same animal, and across animals, variability in cell placement given the average map and the receptive field could be calculated. Interanimal variability and bilateral asymmetry were approximately +/- 60 microns, and within-dorsal horn variability was approximately +/- 35 microns. The interanimal variability is equivalent to a variability of distoproximal receptive-field location on the leg of +/- 13 mm, with a smaller variability in areas of high magnification (e.g., the toes), and a larger variability in areas with small magnification (e.g., the thigh). This degree of variability is consistent with the ability of animals with transected dorsal columns to localize tactile stimuli with a normal degree of precision.

Effects of eccentric and concentric exercise on muscle glycogen replenishment

Eccentric contractions appear to reduce muscle glycogen replenishment during the 1- to 10-day period after exercise. The main purpose of this study was to determine whether consuming a large amount of carbohydrate (1.6 g.kg-1.h-1) during the 4 h after glycogen-reducing exercise would produce different patterns of glycogen replenishment in human muscle that had undergone either eccentric or concentric contractions approximately 2 or 48 h earlier. Subjects cycled for 75 min and undertook interval exercise to deplete glycogen on days 1 and 3. After cycling exercise on day 1 only, subjects performed 10 sets of 10 repetitions of either concentric or eccentric contractions in opposite legs. During the 4 h after exercise, subjects consumed 0.4 g carbohydrate/kg body wt every 15 min. Biopsies were obtained immediately before the feedings and 4 h later, and blood was sampled every 15 min. For days 1 and 3 combined, total integrated areas for the glucose and insulin response curves averaged 1,683 mumol.ml-1.240 min-1 and 21,450 microU.ml-1.240 min-1, respectively. For days 1 and 3 combined, muscle glycogen replenishment after concentric exercise averaged 10 mmol.kg-1.h-1. On day 1 glycogen replenishment was similar for subjects performing either concentric or eccentric contractions. On day 3, however, glycogen replenishment was 25% lower (P < 0.05) in muscle that had undertaken eccentric contractions 48 h earlier than in concentrically exercised muscle. In conclusion, glycogen replenishment can be stimulated to a high rate when a large amount of carbohydrate is consumed after glycogen-depleting concentric exercise.(ABSTRACT TRUNCATED AT 250 WORDS)

A case-control study of lameness in dairy cows

A case-control study was conducted to compare the physical hoof properties of digits responsible for clinical lameness with those of other digits on the same cows and with those of equivalent digits on non-lame control cows. The control cows were herd-mates matched by age, breed and stage of lactation. Hoof moisture, hoof hardness and sole concavity were measured on-farm. The resilience, compressive strength and elastic modulus of both sole and wall hoof were measured on biophys samples collected from both case and control digits. White line disease, sole bruising and septic pododermatitis accounted for 92% of the clinical lameness lesions in the case digits examined. Less severe forms of white line disease and hoof haemorrhage were also observed frequently in the non-lame digits of both the case and control cows. Independent variables were screened for unconditional associations with case-control status using Student's paired t-test and Wilcoxon's matched pairs test. Conditional logistic regression analysis was finally used to identify which risk factors were associated with lameness. When equivalent digits on the matched cows were used as controls, sole and heel moisture, sole haedness, sole concavity and wall colour were selected for inclusion in the model derived to explain differences between the physical properties of lame and control digits. Values for each of these properties were lower in the lame digits than in the controls. The control digits had a higher percentage of black coloration than the lame digits. Sole hardness and sole concavity (both lower in the lame digits) were also selected for inclusion in the conditional logistic regression model derived when the adjoining digits on the same legs of the lame cows were used as controls. None of the physical hoof properties measured were associated with lameness when attempts were made to fit a model using the equivalent digits on the opposite legs of the lame cows as controls. Production of the lame cows was also compared with that of matched herd-mates. Total lactation yields of milk, milk fat and milk protein were lower for the lame cows than for the control cows ( P < 0.05).

The thermal defect of A-150 plastic and graphite for low-energy protons

The thermal defects of A-150 plastic and graphite referenced to aluminium were determined for 800 keV protons scattered by a 2 mu m nickel foil (mean transmitted energy=550 keV). Composite cores of Al/A-150, graphite/A-150 and Al/graphite which could be irradiated from one side or the other were employed. The temperature increase of a core caused by 30-100 s of irradiation (3-6 nA of proton beam current) was detected by two thermistors mounted in opposite legs of a Wheatstone bridge. The thermal defect of A-150 plastic was determined to be 0.0421+or-0.0036 (SE) referenced to aluminium and 0.0402+or-0.0034 referenced to graphite. The thermal defect of graphite referenced to aluminium is 0.0043+or-0.0034. No change in the thermal defect of A-150 plastic was detected for accumulated doses up to 8*105 Gy.

Natural convection in a two-dimensional square loop

The present investigation deals with the steady-state natural convective flow inside a two-dimensional square loop. Opposite legs of the loop are held at constant but different temperatures and therefore, due to the presence of gravity, fluid motion ensues; viscous effects resist the motion and a steady-state flow is reached. The geometry of the loop is fixed but several temperature differences have been considered. Also, the effect of the tilt angle on the flow patterns has been analyzed. Local recirculating motions are the dominant features of the flow when the upper walls are at higher temperature than the lower ones. In contrast, a single global cell appears when the loop is tilted. Double solutions have been found for tilt angles close to zero (high temperature at the bottom walls); the size of the tilt angle interval where double solutions exist has been determined as a function of the Rayleigh number. One-dimensional models have predicted multiple steady-state solutions in systems similar to the one studied here; in the present paper, the existence of multiple solutions in a two-dimensional model has been demonstrated.

Genetic differentiation associated with gait within American standardbred horses.

American Standardbred horses are divided into two groups based upon gait: the trot and the pace. The tendency to trot (diagonally opposite legs moving forward together) or pace (the two legs on the same side of the body moving forward together) appears to be genetically determined, although no formal genetic analysis has been undertaken. There is nearly complete assortative mating for gait; however, about 20% of the offspring sired by trotters are registered as pacers, while fewer than 1% of those sired by pacers are registered as trotters. Electrophoretically detectable genic variation at 13 protein loci has been analysed for 371 trotters and 856 pacers, and 10 blood group loci have been examined for 600 trotters and 1227 pacers. Trotters and pacers shared common alleles at 20 of the 23 loci; however, there were significant differences in allele frequencies at 21 of the 23 loci. Highly significant fixation indices (FSTS) were observed for 17 of the loci. The extent of genetic difference between Standardbred trotters and pacers was as great as or greater than that seen between some distinct horse breeds.