Number Of Active Units Research Articles

Optimization of the on/off status configuration of control units in an active vibration isolation system—experiment

Active vibration isolation (AVI) is an important measure to attenuate vibration transmission in underwater vehicles and multiple active control units are usually used to attenuate low frequency vibrations induced by power equipment. Under certain operation conditions, however, the pre-installed control units in an AVI system may be redundant. Hence, it is necessary to optimize the on/off status configuration of all the control units. An optimization approach is proposed for configuration optimization of control units and validated by experiments. The criterion of the proposed approach is derived from the vibration responses of the monitoring points. The involved optimization, formulated as a constrained 0–1 nonlinear programming problem, utilizes the on/off status of control units as the input variable and the number of active units as the constraint. Optimized configurations were obtained by solving the nonlinear programming problem and deployed to the experimental system. The test results have demonstrated that vibration of the monitoring points can be effectively suppressed by activating only a portion of control units, and the configurations corresponding to maximum vibration reduction vary with different excitations.

Sparse Antenna Array Based Positional Modulation Design With a Low-Complexity Metasurface

Positional modulation (PM) has been introduced recently where a given modulation pattern can only be received at certain desired positions. To achieve it, the multi-path effect is exploited for positional modulation with the aid of metasurface acting as a low-cost flexible reflecting surface. In this paper, sparse antenna array based positional modulation design is proposed for the first time; to reduce the implementation complexity of the metasurface, the number of active units is also minimised for a given PM design requirement. Design examples are provided to show the effectiveness of the proposed design.

Chiller Plant Operation Optimization: Energy-Efficient Primary-Only and Primary–Secondary Systems

A chiller plant consists of chiller, cooling tower, and pump subsystems. Two major configurations, primary-only and primary–secondary systems, are often used. Given the high energy costs of a plant, chiller plant operation optimization is important to save energy. For both configurations, chilled/condenser water supply temperatures are critical in improving chiller efficiency and should be considered as decision variables. However, nonlinearity of the problem is increased since chiller power consumption is a highly nonlinear function of these temperatures. Additionally, the problem is combinatorial considering the number of active units (e.g., chillers). In this paper, primary-only systems with identical units in each subsystem and primary–secondary systems with units of two sizes are studied, and both supply temperatures are optimized for energy savings. To obtain near-optimal solutions efficiently, a recent decomposition and coordination approach with little multiplier zigzagging and fast reduction of coupling constraint violations combining with sequential quadratic programming (SQP) is used. Penalties for the constraints that are difficult to be satisfied (e.g., mass balance constraints between fixed-speed pumps and variable-speed chillers) are added. After decomposition, complexity and nonlinearity of a subproblem are reduced drastically as compared with the original problem so that SQP is used. Numerical testing demonstrates that our approach is efficient in obtaining near-optimal solutions, and major energy savings are achieved as compared with benchmark strategies. The approach is scalable and can be used for chiller plant optimization and beyond. Note to Practitioners —Traditionally, chiller plant operation is often based on rules. For example, the number of active chillers is the minimum number that satisfies cooling requirements, and chilled water supply temperature is constant. Chiller power consumption is a nonlinear function of chiller cooling load and chilled/condenser water supply temperatures. Energy is wasted since chiller efficiency is low with fixed supply temperatures, and sometimes energy consumption of two chillers is less than that of one chiller. To save energy, chiller plant optimization with good decision variables such as the number of active units and chilled/condenser water supply temperatures is studied. The problem is challenging with high nonlinearity caused by considering such temperatures as decision variables. Furthermore, with discrete variables (e.g., the number of active chillers), the problem is combinatorial. To efficiently solve the problem for high-quality solutions, a novel decomposition and coordination approach is developed. Complexity and nonlinearity of a subproblem are reduced drastically after decomposition as compared with the original problem so that appropriate nonlinear methods are used to solve the subproblems. The results show that the solutions are near-optimal with short computational time and the approach is scalable. Additionally, major energy savings are achieved as compared with benchmark strategies. The approach provides a new and powerful way to solve chiller plant optimization problems and beyond.

Optimizing usage and maintenance decisions for k‐out‐of‐n systems of moving assets

AbstractWe consider an integrated usage and maintenance optimization problem for a k‐out‐of‐n system pertaining to a moving asset. The k‐out‐of‐n systems are commonly utilized in practice to increase availability, where n denotes the total number of parallel and identical units and k the number of units required to be active for a functional system. Moving assets such as aircraft, ships, and submarines are subject to different operating modes. Operating modes can dictate not only the number of system units that are needed to be active, but also where the moving asset physically is, and under which environmental conditions it operates. We use the intrinsic age concept to model the degradation process. The intrinsic age is analogous to an intrinsic clock which ticks on a different pace in different operating modes. In our problem setting, the number of active units, degradation rates of active and standby units, maintenance costs, and type of economic dependencies are functions of operating modes. In each operating mode, the decision maker should decide on the set of units to activate (usage decision) and the set of units to maintain (maintenance decision). Since the degradation rate differs for active and standby units, the units to be maintained depend on the units that have been activated, and vice versa. In order to minimize maintenance costs, usage and maintenance decisions should be jointly optimized. We formulate this problem as a Markov decision process and provide some structural properties of the optimal policy. Moreover, we assess the performance of usage policies that are commonly implemented for maritime systems. We show that the cost increase resulting from these policies is up to 27% for realistic settings. Our numerical experiments demonstrate the cases in which joint usage and maintenance optimization is more valuable. © 2017 Wiley Periodicals, Inc. Naval Research Logistics 64: 418–434, 2017

Short-term regulation of the proximal tubule Na+,K+-ATPase: increased/decreased Na+,K+-ATPase activity mediated by protein kinase C isoforms.

In different species and tissues, a great variety of hormones modulate Na+,K+-ATPase activity in a short-term fashion. Such regulation involves the activation of distinct intracellular signaling networks that are often hormone- and tissue-specific. This minireview focuses on our own experimental observations obtained by studying the regulation of the rodent proximal tubule Na+,K+-ATPase. We discuss evidence that hormones responsible for regulating kidney proximal tubule sodium reabsorption may not affect the intrinsic catalytic activity of the Na+,K+-ATPase, but rather the number of active units within the plasma membrane due to shuttling Na+,K+-ATPase molecules between intracellular compartments and the plasma membrane. These processes are mediated by different isoforms of protein kinase C and depend largely on variations in intracellular sodium concentrations.

Study of the effects of motor unit recruitment and firing statistics on the signal-to-noise ratio of a myoelectric control channel

An important measure of the performance of a myoelectric control channel for powered artificial limbs is the myoelectric signal processor output signal-to-noise ratio (SNR). The signal and noise in this context are, respectively, the mean and variance of the estimate of some signal parameter to be used for control purposes. These quantities are determined by the signal processor, motor unit recruitment and motor unit firing statistics. The paper investigates, through analytical, simulation and experimental work, the role and significance of recruitment and firing statistics in channel performance. Equations are derived which express, for the single and multi-unit cases, channel SNR as a function of the number of active units, firing rates, action potential amplitude variation and action potential moments. A computer-simulated myoelectric signal is generated in which these variables can be controlled and SNR measured. The simulation results are compared with the theoretical and found to agree very well. Limited experiments with wire intramuscular electrodes and surface electrodes are performed to measure in vivo SNR from the biceps brachii muscle. The results of the experiments agree well with those of the simulation and theoretical work. The significance of this work is that it provides insight into the roles of important physiological parameters in myoelectric channel performance. It will also provide data necessary for the development of SNR enhancement techniques.

The effects of intensity on the detection of interaural differences of time in high-frequency trains of clicks.

Threshold values of interaural differences of time (delta IDTs ) were measured for trains of dichotic clicks whose levels were 20, 40, or 60 dB SPL. All clicks were bandpass filtered at 4 kHz, and the number of clicks in the train (n) was 1, 2, 4, 8, 16, or 32. The interclick interval (ICI) was 5, 2, or 1 ms. Performance was compared to that of an ideal integrator of information, which produces slopes of - 0.5 when log delta IDT versus log n is plotted. The results showed that increases in level had no effect on the slopes of the log-log functions regardless of the ICI but did decrease the intercepts. Shortening the ICI caused the slopes to go from nearly - 0.5 towards 0.0. The improvement with level could be explained by either a decrease in the temporal variability of neural discharges, or by an increase in the number of samples of IDT at higher intensities brought on by increased firing rates or the activation of more auditory units. A review of the physiological literature found the most parsimonious explanation to be that the decline in threshold IDT was mediated by an increase in the number of active units, each possessing the same degree of adaptation.

The relationship between surface potentials and the number of active motor units

One of the assumptions inherent in a technique recently devised for enumerating motor units in human muscles is that the surface potentials from active motor units summate in a linear fashion. We present an electrical model of a muscle which predicts that a linear relationship between the number of active units and the electrical response recorded at the surface overlying the muscle would not be expected. The extent of the non-linearity, and hence the error in the calculation of the number of motor units in a given muscle, depends upon the ratio between the mean conductance of the motor units themselves and that of the external conduction pathway through which the electrical signal is fed ( G ̄ u G e ). The extent of non-linearity is assessed experimentally in human hypothenar muscles using a “collision” technique. The average underestimate introduced into the calculation of the number of motor units in this particular case was concluded to be 26%. The value of G ̄ u G e derived from these experiments, in 2 subjects, was checked by simulating an intramuscular action potential and determining the attenuation at the surface. The 2 independently obtained values were sufficiently close to suggest that the model may be a valid one. We conclude that caution should be employed in the interpretation of experiments which purport to determine the number of motor units in a muscle by means of surface recording.

Activity and habituation in the brain of the polyclad flatworm Freemania litoricola.

1. A variety of spontaneously active units was measured in the brain of the polyclad flatworm Freemania litoricola. Following application of MgCl2 there was both a decrease in number of active units and a decrease in frequency of firing of those cells which persisted in their activity. 2. Receptors which respond to vibration stimuli evoke potentials in the posterior part of the brain. Repetitive stimulation leads to habituation, the extent of which is dependent on both the number of times stimulated and the strength of the stimulus. Weaker stimuli habituate more rapidly than strong stimuli. Habituated responses can be dishabituated by tactile stimuli and also by stronger intensity stimuli of the same modality. The vibration-evoked potentials appear to occur in at least second-order cells, since vibration responses are abolished by the application of MgCl2. 3. Tactile responses can also be elicited from the posterior portion of the brain when the stimulus is applied to the periphery of the animal. These responses are insensitive to MgCl2. 4. Both vibration and tactile evoked responses are able to evoke further barrages of spike activity. 5. The presence of a dual sensitizing and inhibitory system during habituation is discussed.

Sensory activity of the mandibular muscle receptor organ ofHomarus gammarus(L)

The mandibular muscle receptor organ (Mand. M.R.O.) of Homarus gammarus (L) exhibits increased activity to receptor muscle (R.M.) contraction (decrease in length) and to stretch (increase in length). The sensory units of this receptor differ in their threshold to R.M. tension and in the frequency change they exhibit for a given increment in tension. The units fire tonically during maintained tension once their threshold has been reached. Both the number of active units and their frequency increase with R.M. tension. The Mand. M.R.O. is velocity sensitive and exhibits a higher degree of activity during rapid stretch. This dynamic response increases with rate of R.M. stretch. The activity of the Mand. M.R.O. sensory neurones is compared with that of other M.R.O.’s and the authenticity of some aberrant units is discussed.

Activity of interneurones in the arm of Octopus in response to tactile stimulation.

ABSTRACT A method for recording nervous activity from the nervous system of the arm of Octopus is given. Difficulties of mobility and vasoconstriction are reduced by brain lesions. Three areas were recorded : afferent sucker nerves, axial ganglia, and the dorsolateral axial cord. The sucker nerves include large tactile units corresponding to discrete parts of the sucker rim. These are fast-adapting, phasic, not very sensitive, and are located in the area of motor innervation of the same nerve. Two types of interneurones were found in the axial ganglia, responding to either tactile stimulation of their own or neighbouring suckers, or to proprioceptive input from their own sucker. Motor units to the sucker musculature were also found. Almost all recorded units in the dorsolateral axial cord were interneurones receiving tactile input. They have the following characteristics : they are rapidly adapting, often phasic, and show little or no ‘spontaneous’ activity. they habituate rapidly to even complex patterns of stimulation and discriminate between them, behaving as ‘novelty units’. different sites of stimulation are discriminated by change in both the number of active units and their temporal patterning. The smallest area shown to be separately represented is the rim of one sucker. prolonged activity can be initiated by a brief initial stimulus, which is without apparent correlated motor output. stimulation of areas outside a unit’s sensory field can lead to activity in that unit or to dehabituation in a previously active unit. No proprioceptive representation was found.

RC active networks

RC active networks are described which use a voltage or current amplifier of gain larger than unity. The amplifiers are made to (a) produce a negative one-port immittance, and (b) provide isolation between separate stages of the network. This effectively gives RC active networks synthetised by the same methods, with the same performance as conventional ±RC networks, but having only half their number of active units.

Patterned Activity of Co-Ordinated Motor Units, Studied in Flying Locusts

ABSTRACT A brief survey of the locust flight system is presented as background for this and future studies. Included are descriptions of the wing movements, the aerodynamic parameters and the pertinent muscle anatomy and physiology. A procedure has been designed which makes it possible to study a complex locomotory pattern in terms of the activities of single nervous and muscular units, in this case during normal flight of locusts. We have found a detailed repetitive pattern which is precisely correlated with the wing movements. Fig. 24 shows the pattern during normal flight. Variations in the details of the pattern are also correlated with significant variation in the movements. During average flight most of the flight motor units fire a single time per wing stroke. In low-powered flight numerous units are inactive. With increase in power additional units are recruited and active ones may fire twice or more during a specific phase of a single wingstroke. Increase in wingstroke frequency is correlated with increase in number of active units and with earlier onset of activity so that the wing movements are braked at top and bottom by muscular activity as well as by other restoring forces. Lift is controlled by changes in wing twisting which are mainly due to changes in activity of a single two-unit muscle for each wing, the subalar muscle.

ACTION POTENTIALS IN THE NERVOUS SYSTEM OF THE CRAYFISH

Increase in temperature elicits an increase in the number of nerve impulses arising spontaneously from deafferented crayfish ganglia. This alteration in gross frequency gives an apparent temperature characteristic of 27,000 calories. Changes in the number of active fibers and in the frequency of discharge of individual units account for the alterations in the gross frequency. The change in number of active units gives a n value of 17,500 calories. Individual fibers fall into two groups with respect to the effect of temperature on their frequency of discharge. One of these groups exhibits a micro value of 14,500 calories and the other yields a micro value of 7,000 calories.