Design,Analysis and Experimental Performance of a Bionic Piezoelectric Rotary Actuator

This study presents a piezoelectric rotary actuator which is equipped with a bionic driving mechanism imitating the centipede foot.The configuration and the operational principle are introduced in detail.The movement model is established to analyze the motion of the actuator.We establish a set of experimental system and corresponding experiments are conducted to evaluate the characteristics of the prototype.The results indicate that the prototype can be operated stably step by step and all steps have high reproducibility.The driving resolutions in forward and backward motions are 2.31 μrad and 1.83 μrad,respectively.The prototype can also output a relatively accurate circular motion and the maximum output torques in forward and backward directions are 76.4 Nmm and 70.6 Nmm,respectively.Under driving frequency of 1 Hz,the maximum angular velocities in forward and backward directions are 1029.3 μrad·s-1 and 1165 μrad·s-1 when the driving voltage is 120 V.Under driving voltage of 60 V,the angular velocities in forward and backward motions can be up to 235100 μtrad·s-1 and 153650 prad·s-1 when the driving frequency is 1024 Hz.We can obtain the satisfactory angular velocity by choosing a proper driving voltage and frequency for the actuator.     

A blood pressure-regulating device for inducing hemorrhagic shock.

An instrument for producing closely controlled and repeatable hemorrhagic shock in laboratory animals is described. A Sarns roller pump, controlled by an electronic device, is used to pump blood in and out of the animal at a constant rate. Photoelectric cells are used to sense pressure changes and depending on their configuration, the pump runs forward or backward or stops. Pressures are accurately maintained, bleeding and reinfusion rates are controlled, and a record of bleeding patterns is provided.     

Stepping backward can improve sprint performance over short distances

The use of a backward (false) step to initiate forward movement has been regarded as an inferior starting technique and detrimental to sprinting performance over short distances as it requires additional time to be completed, but little evidence exists to support or refute this claim. Therefore, we recruited 27 men to examine the temporal differences among three standing starts that employed either a step forward (F) or a step backward (B) to initiate movement. An audio cue was used to mark the commencement of each start and to activate the subsequent timing gates. Three trials of each starting style were performed, and movement (0 m), 2.5 m, and 5 m times were recorded. Despite similar performances to the first timing gate (0.80 and 0.81 s for F and B, respectively), utilizing a step forward to initiate movement resulted in significantly slower sprint times to both 2.5 and 5 m (6.4% and 5.3%, respectively). Furthermore, when the movement times were removed and performances were compared between gates 1 and 2, and 2 and 3, all significant differences were seen before reaching a distance of only 2.5 m. The results from this investigation question the advocacy of removing the false step to improve an athlete's sprint performance over short distances. In fact, if the distance to be traveled is as little as 0.5 m in the forward direction, adopting a starting technique in which a step backward is employed may result in superior performance.     

Elementary Energy Transfer Pathways in Allochromatium vinosum Photosynthetic Membranes

Allochromatium vinosum (formerly Chromatium vinosum) purple bacteria are known to adapt their light-harvesting strategy during growth according to environmental factors such as temperature and average light intensity. Under low light illumination or low ambient temperature conditions, most of the LH2 complexes in the photosynthetic membranes form a B820 exciton with reduced spectral overlap with LH1. To elucidate the reason for this light and temperature adaptation of the LH2 electronic structure, we performed broadband femtosecond transient absorption spectroscopy as a function of excitation wavelength in A. vinosum membranes. A target analysis of the acquired data yielded individual rate constants for all relevant elementary energy transfer (ET) processes. We found that the ET dynamics in high-light-grown membranes was well described by a homogeneous model, with forward and backward rate constants independent of the pump wavelength. Thus, the overall B800→B850→B890→ Reaction Center ET cascade is well described by simple triexponential kinetics. In the low-light-grown membranes, we found that the elementary backward transfer rate constant from B890 to B820 was strongly reduced compared with the corresponding constant from B890 to B850 in high-light-grown samples. The ET dynamics of low-light-grown membranes was strongly dependent on the pump wavelength, clearly showing that the excitation memory is not lost throughout the exciton lifetime. The observed pump energy dependence of the forward and backward ET rate constants suggests exciton diffusion via B850→ B850 transfer steps, making the overall ET dynamics nonexponential. Our results show that disorder plays a crucial role in our understanding of low-light adaptation in A. vinosum.     

Stepping behavior of two-headed kinesin motors

The stepping behavior of the dimeric kinesin is studied by using our model based on previous biochemical, X-ray crystallography and cryo-electron microscopy studies. It is shown that, when a Pi is released from the trailing head, a forward step is made under a backward load smaller than the stall force; while when a Pi is released from the leading head, no stepping is made under a forward load or no load, and a backward step is made under a backward load. The forward stepping time, i.e., the time from the release of Pi in the trailing head to the binding of the ADP head to next binding site, is much smaller than the dwell time even under the backward load near the stall force. Thus the movement velocity of the kinesin dimer can be considered to be only dependent on ATPase rates of the two heads. The duration of the rising phase, i.e., the actual time taken by the ADP head to transit from the trailing to leading positions, is on the time scale of microseconds under any backward load smaller than the stall force. This is consistent with available experimental results.     

Stepping behavior of two-headed kinesin motors

The stepping behavior of the dimeric kinesin is studied by using our model based on previous biochemical, X-ray crystallography and cryo-electron microscopy studies. It is shown that, when a Pi is released from the trailing head, a forward step is made under a backward load smaller than the stall force; while when a Pi is released from the leading head, no stepping is made under a forward load or no load, and a backward step is made under a backward load. The forward stepping time, i.e., the time from the release of Pi in the trailing head to the binding of the ADP head to next binding site, is much smaller than the dwell time even under the backward load near the stall force. Thus the movement velocity of the kinesin dimer can be considered to be only dependent on ATPase rates of the two heads. The duration of the rising phase, i.e., the actual time taken by the ADP head to transit from the trailing to leading positions, is on the time scale of microseconds under any backward load smaller than the stall force. This is consistent with available experimental results.     

Modeling of mixing in 96-well microplates observed with fluorescence indicators

Mixing in 96-well microplates was studied using soluble pH indicators and a fluorescence pH sensor. Small amounts of alkali were added with the aid of a multichannel pipet, a piston pump, and a piezoelectric actuator. Mixing patterns were observed visually using a video camera. Addition of drops each of about 1 nL with the piezoelectric actuator resulted in umbrella and double-disklike shapes. Convective mixing was mainly observed in the upper part of the well, whereas the lower part was only mixed quickly when using the multichannel pipet and the piston pump with an addition volume of 5 microL or larger. Estimated mixing times were between a few seconds and several minutes. Mixing by liquid dispensing was much more effective than by shaking. A mixing model consisting of 21 elements could describe mixing dynamics observed by the dissolved fluorescence dye and by the optical immobilized pH sensor. This model can be applied for designing pH control in microplates or for design of kinetic experiments with liquid addition.     

What Eye Movements Can Tell about Theory of Mind in a Strategic Game

This study investigates strategies in reasoning about mental states of others, a process that requires theory of mind. It is a first step in studying the cognitive basis of such reasoning, as strategies affect tradeoffs between cognitive resources. Participants were presented with a two-player game that required reasoning about the mental states of the opponent. Game theory literature discerns two candidate strategies that participants could use in this game: either forward reasoning or backward reasoning. Forward reasoning proceeds from the first decision point to the last, whereas backward reasoning proceeds in the opposite direction. Backward reasoning is the only optimal strategy, because the optimal outcome is known at each decision point. Nevertheless, we argue that participants prefer forward reasoning because it is similar to causal reasoning. Causal reasoning, in turn, is prevalent in human reasoning. Eye movements were measured to discern between forward and backward progressions of fixations. The observed fixation sequences corresponded best with forward reasoning. Early in games, the probability of observing a forward progression of fixations is higher than the probability of observing a backward progression. Later in games, the probabilities of forward and backward progressions are similar, which seems to imply that participants were either applying backward reasoning or jumping back to previous decision points while applying forward reasoning. Thus, the game-theoretical favorite strategy, backward reasoning, does seem to exist in human reasoning. However, participants preferred the more familiar, practiced, and prevalent strategy: forward reasoning.     

Forward and backward running waves in the arteries: analysis using the method of characteristics

The one-dimensional equations of flow in the elastic arteries are hyperbolic and admit nonlinear, wavelike solutions for the mean velocity, U, and the pressure, P. Neglecting dissipation, the solutions can be written in terms of wavelets defined as differences of the Riemann invariants across characteristics. This analysis shows that the product, dUdP, is positive definite for forward running wavelets and negative definite for backward running wavelets allowing the determination of the net magnitude and direction of propagating wavelets from pressure and velocity measured at a point in the artery. With the linearizing assumption that intersecting wavelets are additive, the forward and backward running wavelets can be separately calculated. This analysis, applied to measurements made in the ascending aorta of man, shows that forward running wavelets dominate during both the acceleration and deceleration phases of blood flow in the aorta. The forward and backward running waves calculated using the linearized analysis are similar to the results of an impedance analysis of the data. Unlike the impedance analysis, however, this is a time domain analysis which can be applied to nonperiodic or transient flow.     

Unsteady processes during stimulated emission from a relativistic electron beam in a quasi-longitudinal electrostatic pump field

The problem of stimulated emission from a relativistic electron beam in an external electrostatic pump field is studied. A set of nonlinear time-dependent equations for the spatiotemporal dynamics of the undulator radiation amplitude and the amplitude of the beam space charge field is derived. The beam electrons are described by a modified version of the macroparticle method. The regimes of the single-particle and collective Cherenkov effects during convective and absolute instabilities are considered. The nonlinear dynamics of radiation pulses emitted during the instabilities of the beam in its interaction with the forward and backward electromagnetic waves is investigated.     

Kinematic Comparison of Forward and Backward Swimming and Maneuvering in a Self-Propelled Sub-Carangiform Robotic Fish

We make a thorough kinematic comparison of forward and backward swimming and maneuvering on a self-propelled robot platform that uses sub-carangifbrm swimming as the primary propulsor. An improved Central Pattern Generator （CPG） model allowing free adjustment of phase relationship and directional bias is employed to achieve flexible swimming and smooth transition. Considering the characteristics of forward swimming in carangiform fish and backward swimming in anguilliform fish, various backward swimming patterns for the sub-carangiform robotic fish are suitably created by reversing the direction of propagating propulsive waves. Through a combined use of the CPG control and closed-loop swimming direction control strategy, flexible and precise turning maneuvers in both forward and backward swimming are implemented and compared. By contrast with forward swimming, backward swimming requires a higher frequency or an increased lateral displacement to reach the same relative swimming speed. Noticeably, the phase difference shows a greater impact on forward swimming than on backward swimming. Our observations also indicate that the robotic fish achieves a larger turning rate in forward maneuvering than in backward maneuvering, yet these two maneuvers display comparable turning precision.     

The role of backscattering in SHG tissue imaging

We investigate the properties of second-harmonic generation (SHG) tissue imaging for the functional biological unit fascia, skeletal muscle, and tendon. Fascia and Achilles tendon primarily consist of similar collagen type I arrays that can be imaged using SHG microscopy. For muscle, it is the myosin molecules represented within the A bands. For fascia and tendon tissue samples, we observe, in addition to a stronger signal in forward images, vastly different features for the backward versus the forward images. In vivo as well as intact ex vivo thick tissue imaging requires backward detection. The obtained image is a result of the direct backward components plus a certain fraction of the forward components that are redirected (backscattered) toward the objective as they propagate within the tissue block. As the forward and the backward images are significantly different from each other for the imaged collagen type I tissue, it is crucial to determine the fraction of the forward signal that contributes to the overall backward signal. For intact ex vivo SHG imaging of Achilles tendon, we observe a significant contribution of forward features in the resulting image. For fascia, the connective tissue immediately surrounding muscle, we only observe backward features, due to low backscattering in muscle.     

Torque generated by the bacterial flagellar motor close to stall.

In earlier work in which electrorotation was used to apply external torque to tethered cells of the bacterium Escherichia coli, it was found that the torque required to force flagellar motors backward was considerably larger than the torque required to stop them. That is, there appeared to be substantial barrier to backward rotation. Here, we show that in most, possibly all, cases this barrier is an artifact due to angular variation of the torque applied by electrorotation, of the motor torque, or both; the motor torque appears to be independent to speed or to vary linearly with speed up to speeds of tens of Hertz, in either direction. However, motors often break catastrophically when driven backward, so backward rotation is not equivalent to forward rotation. Also, cells can rotate backward while stalled, either in randomly timed jumps of 180 degrees or very slowly and smoothly. When cells rotate slowly and smoothly backward, the motor takes several seconds to recover after electrorotation is stopped, suggesting that some form of reversible damage has occurred. These findings do not affect the interpretation of electrorotation experiments in which motors are driven rapidly forward.     

Olfactory interference during inhibitory backward pairing in honey bees

Background

Restrained worker honey bees are a valuable model for studying the behavioral and neural bases of olfactory plasticity. The proboscis extension response (PER; the proboscis is the mouthpart of honey bees) is released in response to sucrose stimulation. If sucrose stimulation is preceded one or a few times by an odor (forward pairing), the bee will form a memory for this association, and subsequent presentations of the odor alone are sufficient to elicit the PER. However, backward pairing between the two stimuli (sucrose, then odor) has not been studied to any great extent in bees, although the vertebrate literature indicates that it elicits a form of inhibitory plasticity.

Methodology/Principal Findings

If hungry bees are fed with sucrose, they will release a long lasting PER; however, this PER can be interrupted if an odor is presented 15 seconds (but not 7 or 30 seconds) after the sucrose (backward pairing). We refer to this previously unreported process as olfactory interference. Bees receiving this 15 second backward pairing show reduced performance after a subsequent single forward pairing (excitatory conditioning) trial. Analysis of the results supported a relationship between olfactory interference and a form of backward pairing-induced inhibitory learning/memory. Injecting the drug cimetidine into the deutocerebrum impaired olfactory interference.

Conclusions/Significance

Olfactory interference depends on the associative link between odor and PER, rather than between odor and sucrose. Furthermore, pairing an odor with sucrose can lead either to association of this odor to PER or to the inhibition of PER by this odor. Olfactory interference may provide insight into processes that gate how excitatory and inhibitory memories for odor-PER associations are formed.     

Muscle contributions to specific biomechanical functions do not change in forward versus backward pedaling

Previous work had identified six biomechanical functions that need to be executed by each limb in order to produce a variety of pedaling tasks. The functions can be organized into three antagonistic pairs: an Ext/Flex pair that accelerates the foot into extension or flexion with respect to the pelvis, an Ant/Post pair that accelerates the foot anteriorly or posteriorly with respect to the pelvis, and a Plant/Dorsi pair that accelerates the foot into plantarflexion or dorsiflexion. Previous analyses of experimental data have inferred that muscles perform the same function during different pedaling tasks (e.g. forward versus backward pedaling) because the EMG timing was similar, but they did not present rigorous biomechanical analyses to assess whether a muscle performed the same biomechanical function, and if so, to what degree. Therefore, the objective of this study was to determine how individual muscles contribute to these biomechanical functions during two different motor tasks, forward and backward pedaling, through a theoretical analysis of experimental data. To achieve this objective, forward and backward pedaling simulations were generated and a mechanical energy analysis was used to examine how muscles generate, absorb or transfer energy to perform the pedaling tasks. The results showed that the muscles contributed to the same primary Biomechanical functions in both pedaling directions and that synergistic performance of certain functions effectively accelerated the crank. The gluteus maximus worked synergistically with the soleus, the hip flexors worked synergistically with the tibialis anterior, and the vasti and hamstrings functioned independently to accelerate the crank. The rectus femoris used complex biomechanical mechanisms including negative muscle work to accelerate the crank. The negative muscle work was used to transfer energy generated elsewhere (primarily from other muscles) to the pedal reaction force in order to accelerate the crank. Consistent with experimental data, a phase shift was required from those muscles contributing to the Ant/Post functions as a result of the different limb kinematics between forward and backward pedaling, although they performed the same biomechanical function. The pedaling simulations proved necessary to interpret the experimental data and identify motor control mechanisms used to accomplish specific motor tasks, as the mechanisms were often complex and not always intuitively obvious.     

Effect of arm swing direction on forward and backward jump performance

This study quantified and compared how the directional differences in arm swing affected mechanical and physiological parameters during forward and backward jumping. Seven subjects maximally performed three types of forward and backward squat jumps-no arm swing (FJ, BJ), forward arm swing (FJF, BJF), and backward arm swing (FJB, BJB) from a force platform. All performances were captured with a 3-D motion capture system. Electromyograms (EMGs) of the lower extremity muscles were obtained. Variables were calculated by combining kinematic and kinetic data. The jump displacement and center of mass velocity at take-off were significantly larger in FJF than in FJ or FJB and larger in BJB than in BJ or BJF, suggesting that the best performance was obtained by employing the same arm swing direction as a given jump direction. The total work by three lower and two upper extremity joints was significantly larger in FJF than in FJ or FJB and larger in BJB than in BJ or BJF. For the lower extremity joints, hip work was the greatest in FJF and BJB. The integrated EMG of the biceps femoris when the hip power was produced was significantly larger in FJF and BJB than under other conditions. These results suggest that if the arm swing direction is the same as a given jump direction, the activation level of the hip extensor is greater to counter large loads which make the hip joint flex during the push-off phase, which result in increased hip extension torque, power, and work.     

Complexity,symmetry and variability of forward and backward walking at different speeds and transfer effects on forward walking: Implications for neural control

This study aimed to investigate effects of walking direction and speed on gait complexity, symmetry and variability as indicators of neural control mechanisms, and if a period of backward walking has acute effects on forward walking. Twenty-two young adults attended 2 visits. In each visit participants walked forwards at preferred walking speed (PWS) for 3-minutes (pre) followed by 5-minutes walking each at 80%, 100% and 120% of PWS of either forward or backward walking then a further 3-minutes walking forward at PWS (post). The order of walking speed in each visit was randomised and walking direction of each visit was randomised. An inertial measurement unit was placed over L5 vertebra to record tri-axial accelerations. From the trunk accelerations multiscale entropy, harmonic ratio and stride time variability were calculated to measure complexity, symmetry and variability for each walk. Complexity increased with increasing walking speed for all axes in forward and backward walking, and backward walking was less complex than forward walking. Stride time variability was also greater in backward than forward walking. Anterio-posterior and medio-lateral complexity increased following forward and backward walking but there was no difference between forward and backward walking post effects. No effects were found for harmonic ratio. These results suggest during backward walking trunk motion is rigidly controlled but central pattern generators responsible for temporal gait patterns are less refined for backward walking. However, in both directions complexity increased as speed increased suggesting additional constraint of trunk motion, normally characterised by reduced complexity, is not applied as speed increases.     

Unidirectional Optical Transmission of a Dual Metallic Grating with Grooves

In this paper, a dual grating structure for unidirectional transmission is presented. The forward and backward transmission performances have been investigated by finite element method. To enhance the forward transmission and to suppress the backward transmission simultaneously, we suggested to cut grooves on the surfaces of one of the gratings, and the effects of the grooves on the optical transmission have been studied. The numerical simulation results reveal that the transmission contrast ratio and the optical unidirectional transmission of the structure can be improved markedly by properly arranging the size and the position of the grooves. The forward transmission can be more than 90%, while the backward transmission transmittance is less than 5%.

     

Backwrd population projection by a generalized inverse

The Leslie population projection matrix may be used to project forward in time the age distribution or age-sex distribution of a population. As it is a singular matrix, it does not have an inverse, and so it is not clear that there is a corresponding procedure for backward projection. In terms of the eigenvalues and eigenvectors of the Leslie matrix, certain generalized inverses are constructed that can sometimes be used advantageously for backward projection.     

Information, discrimination and divergence in cytology. V. General symmetry of total discrimination and total divergence.

Total discrimination and divergence are derived from Baye's theorem and based on backward (a posteriori) probabilities. Total forward (a priori) discrimination and divergence can be computed from a test matrix from which total backward discrimination and divergence were calculated for optimization of the classifications of gynecologic cytology (Papanicolaou smears) and quality control in a laboratory. The total forward discrimination and divergence appears to behave in parallel with the total backward discrimination and divergence, and the discrepancies in the backward and forward discrimination/divergence were the smallest near the optimum classification scheme. Conversely, the discrepancies between backward and forward discrimination and divergence may be helpful in finding the best classification scheme for gynecologic cytology. The general symmetries of the total backward and forward discrimination/divergence may be related to the human cognitive process of preferring symmetry and to the historic process in which cytologic classification followed histologic classification and continuously checked for matches in two directions--i.e., from histology to cytology and vice versa--thus resulting in the preservation of symmetry.