Fluctuation on Brownian motor in the presence of entropic barrier

Transporting velocity of a loaded Brownian motor with entropic barrier is investigated in the presence of an asymmetric unbiased force. It is found that in the presence of the entropic barrier, the stall force of the Brownian motor does not change monotonously with temperature. The average velocity of the Brownian motor is a peaked function of thermal noise and amplitude of the asymmetric unbiased external force, which indicates that a definite fluctuation can facilitate the loaded Brownian motor moving. With the increase of the load, the range of temperature and amplitude of the asymmetric unbiased external force for Brownian motor working become smaller. The limited area for Brownian motor working is given on the load-temperature plane. The threshold of fluctuation for Brownian motor working is found, and the minimum of asymmetric parameter of unbiased external force for Brownian motor working is given.     

Entropy compensation in human motor adaptation

This experiment examined the changes in entropy of the coordination of isometric force output under different levels of task demands and feedback from the environment. The goal of the study was to examine the hypothesis that human motor adaptation can be characterized as a process of entropy conservation that is reflected in the compensation of entropy between the task, organism (motor output), and environment. Healthy young individuals produced two-finger force output to a total constant level under different task (error tolerance) and environmental (feedback frequency) conditions. Information entropy of the coordination dynamics (relative phase) of the motor output was made conditional on the idealized situation of human movement, for which the goal is always achieved. Conditional entropy of the motor output decreased as the error tolerance and feedback frequency were decreased. Thus, as the likelihood of meeting the task demands is decreased (increased task entropy) and/or the amount of information from the environment is reduced (increased environmental entropy), the subjects employed fewer coordination patterns in the force output to achieve the goal.     

Corticomuscular synchronization with small and large dynamic force output

Background  

Over the last few years much research has been devoted to investigating the synchronization between cortical motor and muscular activity as measured by EEG/MEG-EMG coherence. The main focus so far has been on corticomuscular coherence (CMC) during static force condition, for which coherence in beta-range has been described. In contrast, we showed in a recent study [1] that dynamic force condition is accompanied by gamma-range CMC. The modulation of the CMC by various dynamic force amplitudes, however, remained uninvestigated. The present study addresses this question. We examined eight healthy human subjects. EEG and surface EMG were recorded simultaneously. The visuomotor task consisted in isometric compensation for 3 forces (static, small and large dynamic) generated by a manipulandum. The CMC, the cortical EEG spectral power (SP), the EMG SP and the errors in motor performance (as the difference between target and exerted force) were analyzed.     

Mechanical properties of single motor units in speech musculature.

Electromyograms were recorded from three subjects during steady, low-rate discharge of single motor units of anterior belly of digastric, accompanying maintenance of isometric tension. The overall tension developed in muscles subserving mandibular depression was recorded from a force tansducer situated inferior to the mandibular symphysis. The force transducer output from the 90 ms period immediately following each of the several hundred discharges of a motor unit was averaged to obtain a characteristic tension curve for the contractile response (twitch) of that unit. Peak twitch tensions and time taken to develop peak tension (contraction time) were recorded for 27 motor units. The obtained median twitch tension of 0.26 g and contraction time of 29 ms were compared with values obtained for units in other human muscles and in animal muscles. As expected from the size principle, later recruited units possessed higher twitch tensions. Contrary to some statements of the size principle, contraction times were not shorter in later recruited units. Data on muscles elevating the mandible were also evaluated.     

Effect of gravitational force upon traffic flow with gradients

We study the effect of gravitational force upon traffic flow on a highway with sag, uphill, and downhill. We extend the optimal velocity model to take into account the gravitational force which acts on vehicles as an external force. We study the traffic states and jamming transitions induced by the slope of highway. We derive the fundamental diagrams (flow-density diagrams) for the traffic flow on the sag, the uphill, and downhill by using the extended optimal velocity model. We clarify where and when traffic jams occur on a highway with gradients. We show the relationship between densities before and after the jam. We derive the dependence of the fundamental diagram on the slope of gradients.     

Length-tension relationship of the feline thyroarytenoid muscle

Vocal fold tension during phonation is generated by coordinated contraction of the intrinsic laryngeal muscles. The thyroarytenoid muscle has been found to have increased stiffness at various levels of strain when compared with other intrinsic laryngeal muscles. The objective here is to test the hypothesis that the thyroarytenoid muscle exhibits high passive tension during maximal isometric tetanic force generation, and to test the hypothesis that the thyroarytenoid maintains the ability to generate contractile force at high levels of strain more effectively than other skeletal muscle. The thyroarytenoid muscles (n=9) and digastric muscle strips (n=7) were removed from adult random-bred cats. Maximal isometric tension and passive tension at optimum length were measured from each muscle in vitro. Active and passive length-tension curves were constructed for each muscle. The contractile properties of the thyroarytenoid group were compared with those of the digastric muscle group. The thyroarytenoid muscle group required on average 140 mN of passive tension to generate maximal isometric tetanic tension. This represented 39% of the average maximal isometric tetanic tension generated by the muscles. These results were significantly higher than the digastric muscle group, which required on average 28 mN of passive tension (9% of maximal isometric tetanic tension, p<0.05). At 110% of optimum length, the thyroarytenoid muscle maintained 89.8% of maximal isometric tetanic force, whereas the digastric muscle group maintained 67.7% of maximal isometric tetanic force (p<0.05). The thyroarytenoid muscle exhibits higher passive tension when generating maximal isometric tension than the digastric muscle control group. The thyroarytenoid muscle maintains higher levels of active tension at high strain than the digastric muscle control group. We conclude that these findings are related to the ability of the thyroarytenoid muscle to function as a fine tensor of the vocal fold in a high strain environment.     

Transport in a ratchet with spatial disorder and time-delayed feedback

A Brownian motor with Gaussian short-range correlated spatial disorder and time-delayed feedback is investigated. The effects of disorder intensity, correlation strength and delay time on the transport properties of an overdamped periodic ratchet are discussed for different driving force. For small driving force, the disorder intensity can induce a peak in the drift motion and a linear increasing function in diffusion motion. For large driving force, the disorder intensity can suppress the drift motion but enhance the diffusion motion. For both small and large driving forces, the correlation strength of the spatial disorder can enhance the drift motion but suppress the diffusion motion. While the delay time can reduce the drift motion to a small value and enhance the diffusion motion to a large value. The drift motion increases as the driving force increases. However, the diffusion motion is either decreases or only increases slightly when the driving force increases.     

Determining the optimal pre-tightening force of a sandwich transducer by measuring resonance resistance

The pre-tightening force applied on a sandwich transducer plays a key role on the transducer’s vibration performance. Typically, a transducer’s optimal pre-tightening force is not known during assembly. The objective of this study is to examine a method for determining the optimal pre-tightening force for a sandwich transducer. We propose that the transducer’s optimal pre-tightening force can be measured indirectly through the resonance resistance. Resonance resistance is an equivalent electric parameter which reflects the transducer’s mechanical energy loss, and can be measured easily using an impedance analyzer. The relationship between resonance resistance and the pre-tightening force is analyzed both theoretically and experimentally. Measurement of resonance resistance based on transducer’s admittance circle is studied. Experiments involving this relationship are conducted. Results indicate that the front-end surface amplitude of the sandwich transducer reaches a maximum when the pre-tightening force is optimal, the resonance resistance tends to a minimum, but with a small offset. This indicates that the minimum value of resonance resistance corresponds closely to the highest vibration amplitude of the transducer, but not exactly. Thus, by determining the minimum resonance resistance, the optimal pre-tightening force can be determined.     

The role of knowledge of results in performance and learning of a voice motor task

The relationship between the provision of Knowledge of Results and the performance and learning of a voice motor task was examined. Thirty adult subjects, randomly assigned to a 100%, 50%, or No Knowledge of Results group, practiced a novel vowel nasalization task. Measures of accuracy and variability obtained during the practice session indicated influence of knowledge of results schedule on the transient effects of motor performance. Deviations from the nasalance target during the retention phase, 5 minutes later, and during a transfer phase, 24 hours later, indicated influence of knowledge of results schedule on the permanent effects of motor learning. Collective results revealed that an increase in relative frequency of knowledge of results led to a decrease in motor performance and learning of a vowel nasalization task: Both accuracy and variability were degraded as knowledge of results increased, with those subjects in the 100% group exhibiting the poorest scores.     

Design and construction of shaft-driving type piezoceramic ultrasonic motor

A new approach in design of shaft-driving type piezoceramic ultrasonic motor is proposed. The stator of motor consisted of a commercial available buzzer disk in which a piezoceramic membrane is adhered to a metal sheet. The wave propagation on the metal sheet was generated by extended-shrunk force from piezoceramic oscillation. Driving energy came from the vibration modes by mechanical-electrical oscillation of the metal sheet in corresponding to converse piezoelectric effect using a single-phase AC voltage power. Where the relative elliptic motion was occurred between the bearing seat and rotor in order to kinematical delivery, the rotor being driven was connected directly on the bearing seat to transmit the dynamic power with frictional contact force. In analysis of dynamic features, the system transfer function of admittance and equivalent circuit was obtained. The rotating speed of the prototype motor could be reached as high as 2000 rpm on the driving condition of 72 kHz, +/-10 V(pp), and 0.2 A. The maximum torque was less than 0.003 Nm. It could be utilized in the driver of CD, or the cooling fan in the computer CPU.     

Effect of correlated noises on Brownian motor

The Brownian motor operating between two correlated Gaussian white noises was investigated. The expressions of the current and the energy conversion efficiency of the Brownian motor were analytically derived by exploiting adiabatic approximation. The results indicates that: (i) Regulating the correlation strength λ between the two noises and the ratio D₂/D₁ of the two noise intensities can change the rotational direction of the motor; (ii) For the smaller D₂/D₁, an optimal λ can make the positive current and the efficiency be maximal, and for the smaller λ, an optimal D₂/D₁ also let the positive current be maximal. The results were explained from a viewpoint of modified potentials. The study is of important significance in the aspect of controlling the operation of the Brownian motor.     

Deformation in cooperative molecular motors

We implement a model to represent the effect of the deformation of the backbone of a system of motor proteins while sliding on a track filament. This model incorporates a nearest neighbor interaction term among the motors for the deformation energy. Correlations induced by this term result in increased motor force for inter-particle distances small compared to the ratchet period. Received 20 February 2001 and Received in final form 31 May 2001     

Importance of punching and workability in non-oriented electrical steel sheets

In order to reduce energy loss in motors, the use of high-efficiency non-oriented electrical steel sheets and an optimal motor core design are important. It is also crucial to minimize the deterioration of magnetic properties during the motor core manufacturing process. Accordingly, this report evaluates the effects of cutting and clamping methods on the deterioration factors of motor cores. Magnetic properties are largely influenced by both cutting and clamping methods. While it is difficult to avoid cutting and clamping altogether, it is necessary to adopt suitable production conditions and minimize the deterioration involved.     

Bi-directional interhemispheric inhibition during unimanual sustained contractions

Background  

The interaction between homologous muscle representations in the right and left primary motor cortex was studied using a paired-pulse transcranial magnetic stimulation (TMS) protocol known to evoke interhemispheric inhibition (IHI). The timecourse and magnitude of IHI was studied in fifteen healthy right-handed adults at several interstimulus intervals between the conditioning stimulus and test stimulus (6, 8, 10, 12, 30, 40, 50 ms). IHI was studied in the motor dominant to non-dominant direction and vice versa while the right or left hand was at rest, performing isometric contraction of the first dorsal interosseous (FDI) muscle, and isometric contraction of the FDI muscle in the context of holding a pen.     

A linear piezoelectric inchworm motor using ultrasonic clamping vibrator

This paper reports a kind of linear piezoelectric inchworm motor us-ing ultrasonic clamping vibrator with ring-shaped three-pile piececonstruction.The clamping vibrator and guide shaft of the motor constitutethe friction pair.The ratio of moving friction coefficient to static one is about1:10,when the clamping vibrator is in resonance.The driving peak voltage ofthe clamping vibrator is only 120V(V_(p-p)).The velocities of the motor are0-2 mm/min,the driving force is about 0.2 kgf,and the mechanic resolvingpower is less than 50nm.The motor's technique is simple.     

A modeling investigation of articulatory variability and acoustic stability during American English /r/ production

This paper investigates the functional relationship between articulatory variability and stability of acoustic cues during American English /r/ production. The analysis of articulatory movement data on seven subjects shows that the extent of intrasubject articulatory variability along any given articulatory direction is strongly and inversely related to a measure of acoustic stability (the extent of acoustic variation that displacing the articulators in this direction would produce). The presence and direction of this relationship is consistent with a speech motor control mechanism that uses a third formant frequency (F3) target; i.e., the final articulatory variability is lower for those articulatory directions most relevant to determining the F3 value. In contrast, no consistent relationship across speakers and phonetic contexts was found between hypothesized vocal-tract target variables and articulatory variability. Furthermore, simulations of two speakers' productions using the DIVA model of speech production, in conjunction with a novel speaker-specific vocal-tract model derived from magnetic resonance imaging data, mimic the observed range of articulatory gestures for each subject, while exhibiting the same articulatory/acoustic relations as those observed experimentally. Overall these results provide evidence for a common control scheme that utilizes an acoustic, rather than articulatory, target specification for American English /r/.     

Energetics of molecular motor proteins: could it pay to take a free ride?

ABSTRACT

Molecular motor proteins are used in biological systems to generate directed motion. They consist of one end that can bind to and then move along a filament. The other end can then bind to a cargo that needs transporting and the motor then pulls it along. Here, we consider the energetics of this process allowing for the friction force exerted by the surrounding fluid, given that the process takes place in a confined geometry. In nature, not all motor/cargo complexes are bound to the filament, many are in solution. Here, we address the question of whether this can be energetically favourable given that the unbound complexes will be transported by the flow generated by those that are bound. A simple theory suggests that this is the case and that there exists an optimal coverage of bound complexes. Simulations of a model of this system that includes all the relevant hydrodynamic effects confirm that the assumptions in the theory are valid so long as the coverage of bound complexes is not too low. Using realistic values for the parameters involved yields an optimal coverage that is plausible for the biological systems involved.     

一种基于迈斯纳效应的超导电机的驱动力的计算

超导体的迈斯纳效应是超导体的特有的性质之一,超导驱动的电机正是利用超导体的这个性质而设计的一种新型电机,由于驱动原理与传统的电机有很大的不同,这种电机的驱动力的计算一直是这种超导电机设计中要解决的主要问题,针对一种结构的电机,利用理论分析和数值计算的方法计算了一种基于超导体迈斯纳效应的超导电机驱动力的大小,为这种电机的设计提供了主要依据。     

Single-molecule force spectroscopy: Practical limitations beyond Bell’s model

Single-molecule force spectroscopy experiments, and a number of other physical systems, are governed by thermally activated transitions out of a metastable state under the action of a steadily increasing external force. The main observable in such experiments is the distribution of the forces, at which the escape events occur. The challenge in interpreting the experimental data is to relate them to the microscopic system properties. We work out a maximum likelihood approach and show that it is the optimal method to tackle this problem. When fitting actual experimental data it is unavoidable to assume some functional form for the force-dependent escape rate. Focusing on escape processes over a single activation barrier, we consider a quite general and common such functional form and demonstrate by means of data from a realistic computer experiment that the maximum number of fit parameters that can be determined reliably is three. They are related to the force-free escape rate and the position and height of the activation barrier. Furthermore, the results for the first two of these fit parameters show little dependence on the assumption about the manner in which the barrier decreases with the applied force, while the last one, the barrier height in the absence of force, depends strongly on this assumption.