Accuracy of circular contact area measurements with thin-film pressure sensors

Contact area is often used to characterize the biomechanical properties of joints, especially in testing of injury and joint replacement. Several methods have been developed to measure contact area, including piezo-resistive thin-film arrays. The purpose of this study was to determine the accuracy with which one of these systems (Tekscan, Inc., South Boston, MA) could measure the contact area of flat-ended circular indenters of varying known sizes. Static loads ranging from 1000 to 7000 N were applied to four flat, circular indenters (1140, 2027, 3167, and 4560 mm(2)) and the contact areas were recorded with Tekscan 5076 sensor. Similar testing was carried out on a 4000 sensor. I-scan software (Tekscan Inc., South Boston, MA) was used to analyze the Tekscan-recorded area measurements. The Tekscan data were also post-processed to filter out sensel signal intensity values that were at least two standard deviations from the average sensel signal intensity values of the sensor matrix. Unprocessed Tekscan measurements with the 5076 sensor had area percent errors ranging from 5% to 27%. The filtering algorithm reduced most errors to less than 1%. Similar trends of improved accuracy with post-filtering were found with the 4000 sensor. While this method of thresholding out the sensels with the lowest signal intensity values may not work for all surfaces and indenter shapes, it provides a new approach to improve the accuracy of contact area measurements collected with the Tekscan system.     

The significant features of Japanese macaque coo sounds: a psychophysical study

Japanese macaques, Macaca fuscata, were trained with a positive reinforcement operant procedure to discriminate smooth early high and smooth late high coo sounds recorded during Green's (1975) field study of the speices' vocal repertoire. Subjects labelled the various tokens by maintaining contact with a response device for calls from one category and by breaking contact for those of the second call type. After the completion of discrimination training, the generalization of the operant behaviour to novel natural and synthetic vocalizations was measured. Initial generalization tests established that macaques would respond appropriately both to natural vocalizations and to computer-synthesized prototypes representing the smooth early high-smooth late high contrast. In subsequent tests, individual acoustic features were removed from the synthetic prototypes to determine the minimal elements of functional coo sounds. These tests suggested that those sounds are distinguished by the predominant direction of their frequency change which, in turn, is determined by the temporal position of their highest frequency.     

The comparative activity of the Australian and united states strains of Culicinomyces clavosporus bioassayed in mosquito larvae of three different genera

Anopheles hilli, Culex quinquefasciatus, and Aedes aegypti were used as test insects to compare the activity of the Australian and United States strains of Culicinomyces clavosporus. To minimize the variability incurred by using different larval batches, both strains were bioassayed at the same time using one batch of larvae. Six pairs of assays for each of the three test species were conducted in this manner. It was found that there was no difference in potency of the two strains in any one of the three species. A between species comparison, with the data pooled for both strains, showed that A. aegypti was more susceptible to the fungus than A. hilli. The susceptibility of C. Quinquefasciatus appeared to be intermediate but the fiducial limits of the weighted mean LC₅₀ overlapped with those of the other two species. From the results of these experiments it would seem that, with regard to potency, both strains of Culicinomyces may be equally promising for the biological control of mosquitoes.     

Simultaneous prediction of muscle and contact forces in the knee during gait

Musculoskeletal models are currently the primary means for estimating in vivo muscle and contact forces in the knee during gait. These models typically couple a dynamic skeletal model with individual muscle models but rarely include articular contact models due to their high computational cost. This study evaluates a novel method for predicting muscle and contact forces simultaneously in the knee during gait. The method utilizes a 12 degree-of-freedom knee model (femur, tibia, and patella) combining muscle, articular contact, and dynamic skeletal models. Eight static optimization problems were formulated using two cost functions (one based on muscle activations and one based on contact forces) and four constraints sets (each composed of different combinations of inverse dynamic loads). The estimated muscle and contact forces were evaluated using in vivo tibial contact force data collected from a patient with a force-measuring knee implant. When the eight optimization problems were solved with added constraints to match the in vivo contact force measurements, root-mean-square errors in predicted contact forces were less than 10 N. Furthermore, muscle and patellar contact forces predicted by the two cost functions became more similar as more inverse dynamic loads were used as constraints. When the contact force constraints were removed, estimated medial contact forces were similar and lateral contact forces lower in magnitude compared to measured contact forces, with estimated muscle forces being sensitive and estimated patellar contact forces relatively insensitive to the choice of cost function and constraint set. These results suggest that optimization problem formulation coupled with knee model complexity can significantly affect predicted muscle and contact forces in the knee during gait. Further research using a complete lower limb model is needed to assess the importance of this finding to the muscle and contact force estimation process.     

Force Outputs during Squats Performed Using a Rotational Inertia Device under Stable versus Unstable Conditions with Different Loads

The purpose of the study was to compare the force outputs achieved during a squat exercise using a rotational inertia device in stable versus unstable conditions with different loads and in concentric and eccentric phases. Thirteen male athletes (mean ± SD: age 23.7 ± 3.0 years, height 1.80 ± 0.08 m, body mass 77.4 ± 7.9 kg) were assessed while squatting, performing one set of three repetitions with four different loads under stable and unstable conditions at maximum concentric effort. Overall, there were no significant differences between the stable and unstable conditions at each of the loads for any of the dependent variables. Mean force showed significant differences between some of the loads in stable and unstable conditions (P < 0.010) and peak force output differed between all loads for each condition (P < 0.045). Mean force outputs were greater in the concentric than in the eccentric phase under both conditions and with all loads (P < 0.001). There were no significant differences in peak force between concentric and eccentric phases at any load in either stable or unstable conditions. In conclusion, squatting with a rotational inertia device allowed the generation of similar force outputs under stable and unstable conditions at each of the four loads. The study also provides empirical evidence of the different force outputs achieved by adjusting load conditions on the rotational inertia device when performing squats, especially in the case of peak force. Concentric force outputs were significantly higher than eccentric outputs, except for peak force under both conditions. These findings support the use of the rotational inertia device to train the squatting exercise under unstable conditions for strength and conditioning trainers. The device could also be included in injury prevention programs for muscle lesions and ankle and knee joint injuries.     

Sensitivity of medial and lateral knee contact force predictions to frontal plane alignment and contact locations

Musculoskeletal models are increasingly used to estimate medial and lateral knee contact forces, which are difficult to measure in vivo. The sensitivity of contact force predictions to modeling parameters is important to the interpretation and implication of results generated by the model. The purpose of this study was to quantify the sensitivity of knee contact force predictions to simultaneous errors in frontal plane knee alignment and contact locations under different dynamic conditions. We scaled a generic musculoskeletal model for N = 23 subjects’ stature and radiographic knee alignment, then perturbed frontal plane alignment and mediolateral contact locations within experimentally-possible ranges of 10° to −10° and 10 to −10 mm, respectively. The sensitivity of first peak, second peak, and mean medial and lateral knee contact forces to knee adduction angle and contact locations was modeled using linear regression. Medial loads increased, and lateral loads decreased, by between 3% and 6% bodyweight for each degree of varus perturbation. Shifting the medial contact point medially increased medial loads and decreased lateral loads by between 1% and 4% bodyweight per millimeter. This study demonstrates that realistic measurement errors of 5 mm (contact distance) or 5° (frontal plane alignment) could result in a combined 50% BW error in subject specific contact force estimates. We also show that model sensitivity varies between subjects as a result of differences in gait dynamics. These results demonstrate that predicted knee joint contact forces should be considered as a range of possible values determined by model uncertainty.     

Chemical mimicry and host specificity in the butterfly Maculinea rebeli,a social parasite of Myrmica ant colonies

Although it has always been assumed that chemical mimicry and camouflage play a major role in the penetration of ant societies by social parasites, this paper provides the first direct evidence for such a mechanism between the larvae of the parasitic butterfly Maculinea rebeli and its ant host Myrmica schencki. In the wild, freshly moulted fourth-instar caterpillars, which have no previous contact with ants, appear to be recognized as ant larvae by foraging Myrmica workers, which return them to their nest brood chambers. Three hypotheses concerning the mechanism controlling this behaviour were tested: (i) the caterpillars produce surface chemicals that allow them to be treated as ant larvae; (ii) mimetic compounds would include hydrocarbons similar to those employed by Myrmica to recognize conspecifics and brood; and (iii) the caterpillars'' secretions would more closely mimic the profile of their main host in the wild, M. schencki, than that of other species of Myrmica. Results of behavioural bioassays and chemical analyses confirmed all three hypotheses, and explained the high degree of host specificity found in this type of highly specialized myrmecophile. Furthermore, although caterpillars biosynthesized many of the recognition pheromones of their host species (chemical mimicry), they later acquired additional hydrocarbons within the ant nest (chemical camouflage), making them near-perfect mimics of their individual host colony''s odour.     

Gait alterations in rats following attachment of a device and application of altered knee loading

Animal models are widely used to study cartilage degeneration. Experimental interventions to alter contact mechanics in articular joints may also affect the loads borne by the leg during gait and consequently affect the overall loading experienced in the joint. In this study, force plate analyses were utilized to measure parameters of gait in the rear legs of adult rats following application of a varus loading device that altered loading in the knee. Adult rats were assigned to Control, Sham, or Loaded groups (n≥4/each). Varus loading devices were surgically attached to rats in the Sham and Loaded groups. In the Loaded group, this device applied a controlled compressive overload to the medial compartment of the knee during periods of engagement. Peak ground reaction forces during walking were recorded for each rear leg of each group. Analyses of variance were used to compare outcomes across groups (Control, Sham, and Loaded), leg (contralateral, experimental) and device status (disengaged, engaged) to determine the effects of surgically attaching the device and applying a compressive overload to the joint with the device. The mean peak vertical force in the experimental leg was reduced to 30% in the Sham group in comparison to the contralateral leg and the Control group, indicating an effect of attaching the device to the leg (p<0.01). No differences were found in ground reaction forces between the Sham and Loaded groups with application of compressive overloads with the device. The significant reduction in vertical force due to the surgical attachment of the varus loading device must be considered and accounted for in future studies.     

Effect of micromechanical stimulations on osteoblasts: development of a device simulating the mechanical situation at the bone-implant interface

Many experimental models have been developed to investigate the effects of mechanical stimulation of cells, but none of the existing devices can simulate micromotions at the cellular-mechanical interface with varying amplitudes and loads. Osteoblasts are sensitive to mechanical stimuli, so to study the bone-implant interface it would be important to quantify their reaction in a situation mimicking the mechanical situation arising at that interface. In this study, we present the development of a new device allowing the application of micromotions and load on cells in vitro. The new device allowed the cells to be stimulated with sinusoidal motions of amplitudes comprised between +/- 5 and +/- 50 microm, frequencies between 0.5 and 2 Hz, and loads between 50 and 1000 Pa. The device, with a total length of 20 cm, was designed to work in an incubator at 37 degrees C and 100% humidity. Expression of various bone important genes was monitored by real-time RT-PCR. Micromotions and load were shown to affect the behavior of osteoblasts by down-regulating the expression of genes necessary for the creation of organic extracellular matrix (collagen type I) as well as for genes involved in the mineralization process (osteocalcin, osteonectin). The developed device could then be used to simulate different mechanical situations at the bone-implant interface.     

Honey bee handling behaviour on the papilionate flower of Robinia pseudoacacia L.

Papilionate flowers, such as those of Robinia pseudoacacia L., show tripping mechanisms that prevent pollen release: only those bees which apply the right force on petals induce pollen to be deposited on their bodies. Apis mellifera is considered a poor visitor of such flowers, since individuals are usually too weak to trip the mechanism. Despite this, the honey bee pays frequent visits to flowers of R. pseudoacacia and produces a much appreciated unifloral honey. We investigated how bees manipulate R. pseudoacacia flowers, whether they contact the plant’s reproductive core and if there is any appreciable difference related to the manipulation of individual flowers. Honey bees showed two strategies for resource collection, namely legitimate visits and robberies. Legitimate visits were more frequent and about 63 % entailed contact with the flower’s reproductive core. We distinguished two behaviours, one to achieve successful positioning on the flower and the other for nectar intake. These behaviours were clearly perceptible and described by different curves of time frequency distribution. From the beginning to the end of anthesis, flowers were classified into four types on the basis of their morphological and phenological traits. Positioning time differed significantly depending on the flower type, with less time needed for more ageing flowers. Time spent in nectar intake was instead highly variable and independent of flower ageing. Selecting the right flower type would appear to lead to obtaining the R. pseudoacacia reward, overcoming species-specific physical inability. Moreover, the role of honey bees as pollinators of R. pseudoacacia is considered. Finally, the relations between petal characteristics and strength needed to trip the mechanism in papilionate flowers is also discussed in the light of nectar foragers.     

How rhesus monkey infants budget their time between mothers and peers

Social play between two rhesus monkey (Macaca mulatta) infants takes place mainly when they are both not in body contact with their mothers. This suggests that social play and mother-infant body contact are potential competitors in the infants' time budgets. We investigated whether the presence of a playmate changed the duration of mother-infant body contact during the first 6 months of life. A decrease in contact would favour play opportunity. Mother-infant pairs were observed alternately alone and together with another pair. Resting, which always occurs during on-mother, was not reduced in the presence of a peer. Body contact during activity phases was reduced in most playing pairs, but only to a large extent in pairs which showed relatively high levels of contact in the situation without a peer. Play opportunity was further increased by synchronization of the rest-activity cycles of the two infants; this occurred without a reduction in mother-infant interactions. No influences by mothers on play opportunity were demonstrated, except that strong maternal interference with resting reduced activity synchronization.     

Can captive-bred American bullfrogs learn to avoid a model avian predator?

Animals that are isolated from their natural predators may lose the ability to express antipredator behavior. The aim of this study was to test whether it would be possible to train captive-bred North American bullfrogs (Rana catesbeiana) to avoid a model avian predator and to measure their behavioral responses to this predator. We used 18 animals divided into two groups, trained (N?=?6) and control (N?=?12); these individuals were from a line that has been bred in captivity for at least 20 generations without predator contact. The trained group was exposed, individually, to 20 sequential antipredator training sessions, during which the presence of a model avian predator was paired with an aversive stimulus. The control group was exposed, individually, once only to the same model avian predator, but without the association of the aversive stimulus. Both groups were observed for 10 min after the presentation of the avian predator, during which their behavior was recorded using instantaneous recording of behavior. The results showed that, after only two training sessions, the trained bullfrogs started to express proper antipredator behavior: diving to the bottom of the tank, lying still, and eventually, learning to cover themselves in substrate (mud). However, continued training sessions provoked a varied response to antipredator training, which was undesirable as the effectiveness of their antipredator response varied. This study has shown that captive-bred bullfrogs were capable of learning antipredator behavior, despite having been bred for many generations in captivity with no predator contact.     

Cell Electrofusion Visualized with Fluorescence Microscopy

Cell electrofusion is a safe, non-viral and non-chemical method that can be used for preparing hybrid cells for human therapy. Electrofusion involves application of short high-voltage electric pulses to cells that are in close contact. Application of short, high-voltage electric pulses causes destabilization of cell plasma membranes. Destabilized membranes are more permeable for different molecules and also prone to fusion with any neighboring destabilized membranes. Electrofusion is thus a convenient method to achieve a non-specific fusion of very different cells in vitro. In order to obtain fusion, cell membranes, destabilized by electric field, must be in a close contact to allow merging of their lipid bilayers and consequently their cytoplasm. In this video, we demonstrate efficient electrofusion of cells in vitro by means of modified adherence method. In this method, cells are allowed to attach only slightly to the surface of the well, so that medium can be exchanged and cells still preserve their spherical shape. Fusion visualization is assessed by pre-labeling of the cytoplasm of cells with different fluorescent cell tracker dyes; half of the cells are labeled with orange CMRA and the other half with green CMFDA. Fusion yield is determined as the number of dually fluorescent cells divided with the number of all cells multiplied by two.     

Parameter estimation and sensitivity analysis in an agent-based model of Leishmania major infection

Computer models of disease take a systems biology approach toward understanding host-pathogen interactions. In particular, data driven computer model calibration is the basis for inference of immunological and pathogen parameters, assessment of model validity, and comparison between alternative models of immune or pathogen behavior. In this paper we describe the calibration and analysis of an agent-based model of Leishmania major infection. A model of macrophage loss following uptake of necrotic tissue is proposed to explain macrophage depletion following peak infection. Using Gaussian processes to approximate the computer code, we perform a sensitivity analysis to identify important parameters and to characterize their influence on the simulated infection. The analysis indicates that increasing growth rate can favor or suppress pathogen loads, depending on the infection stage and the pathogen's ability to avoid detection. Subsequent calibration of the model against previously published biological observations suggests that L. major has a relatively slow growth rate and can replicate for an extended period of time before damaging the host cell.     

Radioligand assays — Methods and applications. IV. Uniform regression of hyperbolic and linear radioimmunoassay calibration curves

In order to handle all types of radioimmunoassay (RIA) calibration curves obtained in our laboratory in the same way, we tried to find a non-linear expression for their regression which allows calibration curves with different degrees of curvature to be fitted. Considering the two boundary cases of the incubation protocol we derived a hyperbolic inverse regression function: x = a₁ya₀ + a_?1y^?1, where x is the total concentration of antigen, a_i constants, and y is the specifically bound radioactivity. An RIA evaluation procedure based on this function is described providing a fitted inverse RIA calibration curve and some statistical quality parameters. The latter are on an order which is normal for RIA systems. There is an excellent agreement between fitted and experimentally obtained calibration curves having a different degree of curvature.     

Giving your daughters the edge: bequeathing reproductive dominance in a primitively social bee

The fitness associated with behavioural strategies is usually estimated in terms of offspring number and size. However, in group-living animals the reproductive value of offspring may also depend on their social rank. We show here that in an allodapine bee Exoneura robusta, dominant mothers can behaviourally influence their daughters'' reproductive rank by controlling insemination of other potential mothers. In E. robusta, group living is near mandatory and reproductive dominance among female nestmates is determined by order of adult emergence. Nests are single, undivided burrows and the dominant female assumes a guarding position closest to the nest entrance. We show that before the egg-laying period, subordinate females who have been absent from the nest are ''screened'' by the reproductive guard upon attempted re-entry. Those who have been in contact with foreign males are less likely to be granted access back into the nest than those who have been in contact with foreign females or with no bees at all. We argue that by controlling insemination patterns of their nestmates, dominant females ensure that their own daughters eclose first and are therefore more likely to assume dominance in the next generation. This presents a situation where dominance is bequeathed to daughters by behavioural means. The ability of mothers to influence social hierarchies in subsequent generations introduces a fitness component additional to the number and size of offspring produced.     

Flexible approach to amperometric oxygen determination

In vitro and in vivo results obtained from a novel flexible amperometric oxygen sensor are reported. The sensor is fabricated using thin film deposition techniques and is operated by the application of a pulsed waveform. Development of the sensor was undertaken in order to produce a device that is capable of being sited at the interface of a wound and an overlying wound dressing. Oxygen determinations in such an environment would aid in gaining an undertanding of the role of oxygen in wound healing and the type of wound dressing that would provide an environment conducive towards wound healing. In vitro data indicate that linearity of response is good although other performance characteristics are irreproducible. In vivo response to oxygen has been observed 50 h after insertion into a porcine sham wound. Expected trends were followed when changes to the oxygen regime of the wound space were effected, but absolute values of oxygen tension are difficult to state with certainty. This may be due to poor calibration stability and inadequate sealing of the sensor from the surrounding environment.     

Improving SARS-CoV-2 structures: Peer review by early coordinate release

This work builds upon the record-breaking speed and generous immediate release of new experimental three-dimensional structures of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) proteins and complexes, which are crucial to downstream vaccine and drug development. We have surveyed those structures to catch the occasional errors that could be significant for those important uses and for which we were able to provide demonstrably higher-accuracy corrections. This process relied on new validation and correction methods such as CaBLAM and ISOLDE, which are not yet in routine use. We found such important and correctable problems in seven early SARS-CoV-2 structures. Two of the structures were soon superseded by new higher-resolution data, confirming our proposed changes. For the other five, we emailed the depositors a documented and illustrated report and encouraged them to make the model corrections themselves and use the new option at the worldwide Protein Data Bank for depositors to re-version their coordinates without changing the Protein Data Bank code. This quickly and easily makes the better-accuracy coordinates available to anyone who examines or downloads their structure, even before formal publication. The changes have involved sequence misalignments, incorrect RNA conformations near a bound inhibitor, incorrect metal ligands, and cis-trans or peptide flips that prevent good contact at interaction sites. These improvements have propagated into nearly all related structures done afterward. This process constitutes a new form of highly rigorous peer review, which is actually faster and more strict than standard publication review because it has access to coordinates and maps; journal peer review would also be strengthened by such access.     

A hub dynamometer for measurement of wheel forces in off-road bicycling

A dynamometric hubset that measures the two ground contact force components acting on a bicycle wheel in the plane of the bicycle during off-road riding while either coasting or braking was designed, constructed, and evaluated. To maintain compatibility with standard mountain bike construction, the hubs use commercially available shells with modified, strain gage-equipped axles. The axle strain gages are sensitive to forces acting in the radial and tangential directions, while minimizing sensitivity to transverse forces, steering moments, and variations in the lateral location of the center of pressure. Static calibration and a subsequent accuracy check that computed differences between applied and apparent loads developed during coasting revealed root mean squared errors of 1 percent full-scale or less (full-scale load = 4500 N). The natural frequency of the rear hub with the wheel attached exceeded 350 Hz. These performance capabilities make the dynamometer useful for its intended purpose during coasting. To demonstrate this usefulness, sample ground contact forces are presented for a subject who coasted downhill over rough terrain. The dynamometric hubset can also be used to determine ground contact forces during braking providing that the brake reaction force components are known. However, compliance of the fork can lead to high cross-sensitivity and corresponding large (> 5 percent FS) measurement errors at the front wheel.     

Neuromuscular responses to different resistance loading protocols using pneumatic and weight stack devices

The purpose of this study was to examine single repetition characteristics and acute neuromuscular responses to typical hypertrophic (HL), maximal strength (MSL), and power (PL) loadings performed with two of the most common resistance modes; pneumatic and weight stack. Acute responses were assessed by measuring maximal voluntary contraction (MVC), corresponding quadriceps-EMG and resting and superimposed twitch torques. Activation level was calculated from the twitch torques.Decreases in MVC were greater during HL and MSL than during PL. During HL, resting twitch force decreased 8% (P < 0.05) more on the weight stack than on the pneumatic device. Furthermore, loading using the weight stack caused reduced resting twitch force, activation level, and EMG-amplitude after MSL and PL (P < 0.05–0.01).PL on the pneumatic device decreased MVC and rapid force production, while the respective PL on the weight stack device was specific to decreased rapid force production only. However, mean angular velocities and power of the repetitions were higher on the pneumatic device when using light loads.The present study showed that, at least in untrained subjects, the weight stack device induced greater levels of peripheral fatigue during HL. It also led to large central fatigue during MSL and PL. On the other hand, on the pneumatic device contraction velocity with low loads was higher compared to the weight stack device.Therefore, it is recommended that the resistance mode should be chosen according to the specific training goal.