bluuebunny/crossref_metadata_2025 huggingface dataset:
Excitatory synaptic responses in turtle cerebellar Purkinje cells.
Authors: Chan C Y , Hounsgaard J , Midtgaard J
Published: December 2014

1. Climbing fibre responses (CFRs) and parallel fibre responses (PFRs) in Purkinje cells have been analysed in intracellular recordings obtained at various levels from cell body to terminal dendrites in the turtle cerebellum in vitro. 2. With increasing stimulus intensity, the PFR recorded in distal dendrites displayed an early regenerative component which was graded at rest and at hyperpolarized membrane potentials, but was all‐or‐none at depolarized membrane potentials. 3. The all‐or‐none component had the same characteristics as Ca2+ spikes triggered by passing depolarizing current through the recording electrode. 4. The repolarizing phase of the PFR had a fast component enhanced by depolarization and diminished by hyperpolarization. 5. In the mid‐molecular layer the PFR also included a plateau component which was increasingly prolonged by depolarization and abolished by hyperpolarization. 6. CFRs recorded in the soma had a plateau component, prolonged by local depolarization and abolished by local hyperpolarization. 7. The CFR in distal dendrites included a regenerative component. In some cells this component appeared in an all‐or‐none manner with local depolarization. In other cells it was smoothly graded with local polarization. 8. In mid‐molecular records the CFR was prolonged by local depolarization and presumably electrotonically affected by the configuration of the response more distally and proximally in the cell. 9. It is concluded that excitatory synaptic responses in Purkinje cells include a regenerative Ca2+‐mediated spike component in the spiny dendrites and a plateau component located in the proximal dendrites and/or the cell body. It is shown that both responses are modulated in configuration by the local membrane potential. In the spiny dendrites activation and inactivation of the transient hyperpolarizing potential appear to govern the Ca2+ influx during the CFR.
An after‐hyperpolarization of medium duration in rat hippocampal pyramidal cells.
Authors: Storm J F
Published: December 2014

1. In hippocampal pyramidal cells, action potentials are followed by three after‐hyperpolarizations (AHPs): a fast AHP (fAHP) lasting 2‐5 ms, a medium AHP (mAHP) lasting 50‐100 ms, and a slow AHP (sAHP) lasting more than 1 s. The mechanism underlying the mAHP was studied in CA1 cells (n = 46) in rat hippocampal slices, using injection of depolarizing current to elicit discharge. 2. The current underlying the mAHP was studied by single‐electrode voltage clamp in two ways. Either the voltage clamp was activated following a burst of spikes, thus recording the early tail current underlying the mAHP (hybrid clamp), or, after blocking the spikes with tetrodotoxin, the early tail current following a depolarizing voltage clamp command (to ‐20 to ‐45 mV for 100‐400 ms) was measured. In both cases, the early tail current (measured at ‐60 mV) showed the following characteristics: (a) it decayed exponentially with a time constant of about 50 ms; (b) it was substantially reduced by the muscarinic agonist carbachol (40‐50 microM); (c) it was moderately reduced (by 20% or less) by Ca2+‐free medium and Ca2+ channel blockers (Cd2+, Mn2+), which abolished the fAHP and the sAHP; (d) it was partly blocked by tetraethylammonium (TEA, 1‐10 mM) both before and during Ca2+ channel blockade; (e) it was resistant to noradrenaline (5‐10 microM), which blocked the sAHP, and to apamin (100 nM). 3. The mAHP itself, recorded under current clamp, showed properties corresponding to those of the early tail current. 4. Unlike the current underlying the sAHP, which was reduced and reversed by hyperpolarization, the early tail current appeared to be reduced only at potentials down to ‐80 mV, and to increase at more negative potentials. The early tail current and mAHP‐like undershoot at hyperpolarized potentials was blocked by external Cs+, but not by carbachol, in contrast to the early tail current and mAHP at ‐60 mV. 5. It was concluded that two currents contribute to the mAHP: IM (a voltage‐gated muscarine‐sensitive K+ current) and IC (a Ca2+‐dependent TEA‐sensitive K+ current). TEA reduced both the IM (5 mM) and the IC (1 mM) component of the mAHP. When the cell is hyperpolarized, a third current, IQ (a Ca+‐sensitive mixed Na+‐K+ inward current activated by hyperpolarization), masks the reversal of the mAHP by causing a depolarizing sag which resembles the decay of the mAHP.
Selective recruitment of high‐threshold human motor units during voluntary isotonic lengthening of active muscles.
Authors: Nardone A , Romanò C , Schieppati M
Published: December 2014

1. We have investigated the possibility that voluntary muscle lengthening contractions can be performed by selective recruitment of fast‐twitch motor units, accompanied by derecruitment of slow‐twitch motor units. 2. The behaviour of motor units in soleus, gastrocnemius lateralis and gastrocnemius medialis muscles was studied during (a) controlled isotonic plantar flexion against a constant load (shortening contraction, S), maintained plantar flexion, or dorsal flexion resisting the load and gradually yielding to it (lengthening contraction, L), (b) isometric increasing or decreasing plantar torque accomplished by graded contraction or relaxation of the triceps surae muscles, (c) isometric or isotonic ballistic contractions, and (d) periodic, quasi‐sinusoidal isotonic contractions at different velocities. The above tasks were performed under visual control of foot position, without activation of antagonist muscles. The motor units discharging during foot rotation were grouped on the basis of the phase(s) during which they were active as S, S + L and L. The units were also characterized according to both the level of isometric ramp plantar torque at which they were first recruited and the amplitude of their action potential. 3. S units were never active during dorsal flexion; some of them were active during the sustained contraction between plantar and dorsal flexion. Most S + L units were active also during the maintenance phase and were slowly derecruited during lengthening; their behaviour during foot rotations was similar to that during isometric contractions or relaxations. L units were never active during either plantar or maintained flexion, but discharged during lengthening contraction in a given range of rotation velocities; the velocity of lengthening consistently influenced the firing frequency of these units. Such dependence on velocity was not observed in S + L units. 4. A correlation was found between the amplitude of the action potential and the threshold torque of recruitment among all the units. In addition, the amplitudes of both the action potential and the threshold torque were higher in the case of L units than in the case of S and S + L units. Most L units could be voluntarily recruited only in the case of ballistic isometric or isotonic contraction. 5. Occasionally, L units were directly activated by electrical stimulation of motor fibres and their conduction velocity was in the higher range for alpha‐axons. In contrast, nerve stimulation could induce a reflex activation of S and S + L units.(ABSTRACT TRUNCATED AT 400 WORDS)
Maximum tension and force‐velocity properties of fatigued, single Xenopus muscle fibres studied by caffeine and high K+.
Authors: Lännergren J , Westerblad H
Published: December 2014

1. The importance of reduced maximum force‐generating capacity in the development of skeletal muscle fatigue has been studied using potassium and caffeine contractures as tools. 2. Single, intact fibres isolated from the lumbrical and iliofibularis muscles of Xenopus were fatigued by repeated tetanic stimulations until they produced close to 40% of the original tetanic tension (P0). Using this stimulation scheme three major types of fibres can be distinguished: easily fatigued (type 1), fatigue resistant (type 2), and very fatigue‐resistant (type 3) fibres (Westerblad & Lännergren, 1986). 3. When activated by 8‐15 mM‐caffeine‐Ringer solutions fatigued fibres of all three types developed tensions similar to those of controls (81.0 +/‐ 6.6 vs. 83.9 +/‐ 4.2% of P0, respectively; means +/‐ S.D.). 4. Tension output also increased markedly when fatigued fibres were depolarized by 190 mM‐K+ solution. The tension produced was in this case fibre type dependent: 71.4 +/‐ 6.6, 81.3 +/‐ 2.5 and 95.0 +/‐ 4.4% of P0 in fibre types 1, 2 and 3, respectively. 5. Force‐velocity measurements were performed during caffeine contractures in fatigued iliofibularis fibres (types 1 and 2) to obtain more information about the functional state of cross‐bridges. 6. In fatigued type 1 fibres the shortening velocity was reduced to about 25% of that in controls, while it was not significantly depressed in type 2 fibres. 7. It is concluded that cross‐bridges of fatigued fibres can produce nearly full tension, but they may work at a much slower rate in this state. 8. Fibre types 1 and 2 mostly display a long‐lasting, reversible state of severely depressed tension production during the recovery period, which has been named post‐contractile depression, PCD (Westerblad & Lännergren, 1986). Fibres tested in this state generated full caffeine‐activated tension and the shortening velocity was not significantly reduced. The tension output during K+ contractures was, however, markedly depressed (12.4 +/‐ 4.1% of P0). 9. In conclusion, cross‐bridges are able to produce close to full tension during PCD as well as in the fatigued state if they are fully activated. The form of functional impairment seems, however, not to be the same in the two cases.
Some electrical properties of the endothelium‐dependent hyperpolarization recorded from rat arterial smooth muscle cells.
Authors: Chen G , Suzuki H
Published: December 2014

1. Electrical responses produced by acetylcholine (ACh) and histamine were recorded from smooth muscle cells of the intralobular small pulmonary artery (SPA), main pulmonary artery (MPA) and thoracic aorta of rats. 2. In MPA and SPA, ACh and histamine produced a transient hyperpolarization of the membrane, and the potential decayed exponentially with a time constant of 2‐3 min. In aorta, ACh produced a sustained and histamine produced a transient hyperpolarization. 3. The ACh‐ and histamine‐induced hyperpolarizations were blocked by atropine and mepyramine, respectively, or by removing the endothelial cells. 4. The amplitude of the hyperpolarization was increased in low [K+]o solutions and decreased in high [K+]o solutions. The ionic conductance of the membrane was increased during the hyperpolarization, suggesting an involvement of the increased potassium conductance. 5. A reproducible amplitude of hyperpolarization was generated when ACh or histamine was applied at intervals of over 10 or 30 min, respectively. 6. In aorta, after the transient hyperpolarization had ceased during continued application of histamine, ACh again produced a hyperpolarization, i.e. the transient nature of the hyperpolarization was not due to desensitization of the receptor upon which the hyperpolarizing substance acted, assuming histamine and ACh release the same hyperpolarizing substance. 7. ACh and histamine relaxed the tissues from SPA, MPA and aorta during the noradrenaline (NA)‐ or high [K+]o solution‐induced contraction, in a concentration‐dependent manner, only when the endothelial cells were intact. Both ACh and histamine were potent relaxants in MPA and aorta, but showed weak relaxing actions in SPA. 8. In aorta, ACh and histamine produced a sustained relaxation for up to 10 min, and Methylene Blue diminished and altered it to a transient relaxation (for histamine) or an initial large, followed by a small sustained (for ACh), relaxation. 9. In the presence of NA and NA plus Methylene Blue, ACh and histamine also produced a hyperpolarization similar to that seen in the control. 10. It is concluded that in arteries of the rat, ACh and histamine release a hyperpolarizing substance from the endothelial cells. This substance may be different from the endothelium‐derived relaxing factor (EDRF), and is released mainly transiently. The hyperpolarization is generated by an increase in potassium conductance of the membrane, and this has some contribution to the endothelium‐dependent relaxation.
A Na+‐activated K+ current in cultured brain stem neurones from chicks.
Authors: Dryer S E , Fujii J T , Martin A R
Published: December 2014

1. Patch‐clamp techniques were used to study the properties of a Na+‐activated K+ current (IK(Na) in neurones cultured from embryonic chick brain stem. 2. With whole‐cell clamp, a depolarizing voltage command evoked an inward current that was followed by an outward current with two components, the first transient, the second sustained. 3. Tetrodotoxin (TTX, 1 microM) eliminated the inward current and the transient component of the outward current, without affecting the sustained outward current. In addition, the transient outward current was attenuated when all external Na+ was replaced by Li+, suggesting that it was activated specifically by Na+ entry into the cell. 4. The time course of the transient outward current was obtained by subtracting records obtained in Li+ solution from those obtained in Na+ solution. There was significant overlap between the decay of the inward current and the onset of the transient outward current. 5. When just after the peak of the transient outward current, the membrane was stepped to progressively more hyperpolarized levels, the tail currents associated with the current reversed polarity near the calculated K+ equilibrium potential. 6. 4‐Aminopyridine (4‐AP, 4 mM) abolished the transient outward current and approximately half of the sustained late current. Tetraethylammonium (TEA, 2 mM) had no effect on the transient current, but reduced the sustained current slightly. 7. Inside‐out patches, made in LiCl bathing solutions, contained channels that were activated by exposing the cytoplasmic face of the patch to Na+. Channel activity continued as long as Na+ was present. 8. The single‐channel currents reversed at the K+ equilibrium potential, and were associated with a main conductance that depended upon K+ concentration (about 50 pS with [K+]o = 15 mM, [K+]i = 5 mM, and 100 pS when [K+]i was increased to 75 mM). 9. The open probability of the channels increased with increasing cytoplasmic Na+ concentration. At [Na+]i = 150 mM (the maximum concentration tested), channels were open almost continuously. Open probability was considerably less at 50 mM, and still measureable at 20 mM. 10. The magnitude of IK(Na) and its overlap with the inward Na+ current indicate that these channels contribute significantly to the repolarizing phase of the action potential. In addition, the relation between channel activity and Na+ concentration suggests that the channels may make a measurable contribution to membrane conductance at resting intracellular Na+ concentrations.
A T‐type Ca2+ current underlies low‐threshold Ca2+ potentials in cells of the cat and rat lateral geniculate nucleus.
Authors: Crunelli V , Lightowler S , Pollard C E
Published: December 2014

1. The characteristics of a transient inward Ca2+ current (IT) underlying low‐threshold Ca2+ potentials were studied in projection cells of the cat and rat dorsal lateral geniculate nucleus (LGN) in vitro using the single‐electrode voltage‐clamp technique. 2. In cat LGN slices perfused at 25 degrees C with a solution which included 1 mM‐Ca2+ and 3 mM‐Mg2+, IT could be evoked by depolarizing voltage steps to ‐55 mV from a holding potential (Vh) of ‐95 mV and was abolished by reducing [Ca2+]o from 1 to 0.1 mM. IT was also blocked by 8 mM‐Mg2+ and 500 microM‐Ni2+, but 500 microM‐Cd2+ was a significantly less effective antagonist. 3. The inactivation of IT, which occurred at Vh positive to ‐65 mV, was removed as Vh approached ‐100 mV. The process of inactivation removal was also time dependent, with 800‐1000 ms needed for total removal. Activation curves for IT showed a threshold of ‐70 mV and illustrated that IT was extremely voltage sensitive over the voltage range from ‐65 to ‐55 mV. 4. The decay phase of IT followed a single‐exponential time course with a time constant of decay which was voltage sensitive and ranged from 20 to 100 ms. The mean peak conductance increase associated with IT was 8.4 nS (+/‐0.9, S.E.M.). 5. In more ‘physiological’ conditions (35 degrees C and 1.5 mM‐Ca2+, 1 mM‐Mg2+) the voltage dependence of activation and inactivation were unaffected. However, the development and decay of IT proceeded more rapidly and only 500‐600 ms were needed for total removal of inactivation. Under these conditions, the use of voltage ramps showed that depolarization rates of greater than 30 mV/s were necessary for IT activation. 6. The use of multiple voltage‐step protocols illustrated that the process of inactivation removal was rapidly reversed by brief returns to a Vh of ‐50 mV. Furthermore, any delay in IT activation, once the LGN cell membrane potential was in the IT activation range, resulted in a current of reduced amplitude. 7. Although IT in rat LGN cells was briefer and had a shorter latency to peak, it was otherwise similar to that seen in cat LGN cells. 8. The characteristics of IT are very similar to those of the T‐type Ca2+ currents of other excitable membranes. The properties of IT are discussed with respect to its role in generating the low‐threshold Ca2+ potentials which are central to the oscillatory behaviour of thalamic projection cells.
Reciprocal inhibition following lesions of the spinal cord in man.
Authors: Ashby P , Wiens M
Published: December 2014

1. Reciprocal inhibition was studied in normal subjects and patients with spinal cord lesions by stimulating the posterior tibial nerve below the threshold of the soleus alpha‐motoneurone axons and recording the changes in firing probability of single tibialis anterior motor units activated by voluntary contraction. A short‐latency (about 35 ms) period of decreased firing probability was assumed to represent reciprocal inhibition. 2. For a given stimulus intensity this inhibition was greater in patients with spinal lesions than in normal subjects. 3. The stimulus intensities at which soleus motoneurones and the Ia inhibitory interneurones were brought to threshold provided an estimate of the relative excitability of these two neural populations. In the patients with spinal lesions the Ia inhibitory interneurones were more excitable than soleus motoneurones, whereas in normal subjects the excitabilities were approximately equal. 4. Stimulation of the posterior tibial nerve below the threshold of alpha‐motoneurone axons also resulted in a second period of inhibition with a latency of approximately 50 ms. This was less prominent in the patients with spinal cord lesions. 5. It is concluded that transmission through the pathways mediating reciprocal inhibition of flexor muscles during their voluntary contraction is enhanced following a spinal cord lesion in man but that a later inhibitory process is depressed.
Visual responses of neurones in cat superior colliculus in relation to fixation of targets.
Authors: Peck C K
Published: December 2014

1. Visually elicited discharges were recorded from single cells in the intermediate and deep layers of the superior colliculus of alert, trained cats. With the behavioural protocols used, vigorous and consistent visual responses to the onset and offset of small, stationary targets were encountered in all layers of the colliculus. In addition, the responses of many cells depended on the behavioural context in which the response occurred. Specifically, thirty‐nine cells were encountered in which discharge was contingent upon prolonged fixation of the visual stimulus. Thirty of these were located in the intermediate and deep layers and comprised 22% of the 134 isolated cells which were not related to saccadic eye movement. 2. Fixation‐related cells showed sustained increases or decreases in firing during fixation of a visual target. Responses to presentation of a visual target at the same retinal location, without active fixation by the animal, were either absent, much weaker, or had extremely variable latencies. 3. Changes in activity were well established by the end of the fixation saccade. The neuronal response was sustained if fixation was sustained. Moreover, the neuronal response began to decrease before the onset of the saccade which broke fixation even though the receptive field location of the target had not yet changed. 4. In these neurones, the discharge rate was not a function of the position of the eye in the orbit. 5. Neurones in which the discharge rate was suppressed during fixation had larger receptive fields than cells in which the discharge rate was enhanced during fixation. There were fewer fixation‐suppressed cells (n = 7, 5%) than fixation‐activated cells (n = 23, 17%).
The effects of vagal stimulation and applied acetylcholine on the sinus venosus of the toad.
Authors: Bywater R A , Campbell G , Edwards F R , Hirst G D , O'Shea J E
Published: December 2014

1. The effects of vagal stimulation and applied acetylcholine were compared on the isolated sinus venosus preparation of the toad, Bufo marinus. 2. The effects of applied acetylcholine and of low‐frequency, or short bursts of high‐frequency vagal stimulation were abolished by hyoscine. 3. When intracellular recordings were made from muscle cells of the sinus venosus, it was found that applied acetylcholine caused bradycardia and a cessation of the heart beat which was associated with membrane hyperpolarization and a reduction in the duration of the action potentials. Much of the effect of acetylcholine can be attributed to it causing an increase in potassium conductance, gK. 4. When slowing was produced by low‐frequency vagal stimulation, only a small increase in maximum diastolic potential was detected. During vagal arrest the membrane potential settled to a potential positive of the control maximum diastolic potential. 5. In the presence of barium, much of the bradycardia associated with vagal stimulation persisted. Although the bradycardia produced by added acetylcholine also persisted in the presence of barium, the effects of acetylcholine that could be attributed to an increase in gK were abolished. 6. Addition of caesium ions produced bradycardia with membrane potential changes similar to those seen during vagal stimulation. 7. The results are discussed in relation to the idea that neuronally released acetylcholine reduces inward current flow during diastole. In contrast applied acetylcholine as well as reducing inward current flow during diastole also increases outward current flow by increasing gK.
Desensitization of the acetylcholine receptor of frog end‐plates measured in a Vaseline‐gap voltage clamp.
Authors: Cachelin A B , Colquhoun D
Published: December 2014

1. Desensitization of the nicotinic acetylcholine receptor of the frog end‐plate was investigated in dissociated frog muscle fibres using the Vaseline‐gap clamp method so that a wide range of well‐defined agonist concentrations could be used without having to use alpha‐bungarotoxin to reduce currents, and so that the intracellular medium could be controlled. 2. Acetylcholine (ACh) concentrations between 1 and 1000 microM were used, after inactivation of acetylcholinesterase. The intracellular calcium concentration was usually kept near zero by using 80 mM‐K2EGTA as the intracellular solution. 3. When using the low intracellular calcium solution, desensitization proceeded as a biphasic process with estimates of fast and slow time constants of about 8 and 80 s at 4 degrees C and 20 microM‐ACh (the rates increased with concentration). In contrast, only one (fast) component of desensitization was detected when the intracellular calcium concentration was allowed to increase during ACh application. 4. Despite rapid application of ACh the time to peak response was 0.2 s (with 400 microM‐ACh) to 2 s (with 1 microM‐ACh); this slow rise was shown to result from diffusion delays. Nevertheless the peak current with 200 microM‐ACh corresponded to opening of most of the channels present, so there is probably not much desensitization in the millisecond time range. 5. Both fast and slow time constants for onset of desensitization showed only slight dependence on membrane potential when [Ca2+]i was buffered with 80 mM‐K2EGTA. 6. Increasing the intracellular cyclic AMP concentration directly, or indirectly with forskolin and IBMX, had no effect on the time course of desensitization. 7. Intracellular application of submicromolar concentrations of phorbol‐12,13‐dibutyrate (PDBu) and phorbol‐12‐myristate‐13‐acetate (PMA) yielded a small but reproducible reduction of the peak response to ACh. The time course of desensitization was, however, not modified by these substances. 8. The implications of these observations for the mechanism of desensitization, and their relationship to single‐channel observations, are discussed.
High Temperature Flow Behavior and Microstructure of Al-Cu/Mg2Si Metal Matrix Composite
Authors: Shafieizad A. H. , Zarei-Hanzaki A. , Ghambari M. , Abbasi-Bani A.
Published: December 2014

The present work deals with the high temperature flow behavior and the microstructure of the Al-Cu/Mg2Si metal matrix composite. Toward this end, a set of hot compression tests was performed in a wide range of temperature (573–773 K) and strain rate (0.001–0.1 s−1). The results indicated that the temperature and strain rate have a significant effect on the flow softening and hardening behavior of the material. The work hardening rate may be offset due to the occurrence of the restoration processes, the dynamic coarsening, and spheroidization of the second phase particles. In this regard, two phenomenological constitutive models, Johnson–Cook (JC) and Arrhenius-type equations, were employed to describe the high temperature deformation behavior of the composite. The JC equation diverged from experimental curves mainly in conditions which are far from its reference temperature and reference strain rate. This was justified considering the fact that JC model considers thermal softening, strain rate hardening, and strain hardening as three independent phenomena. In contrast, the Arrhenius-type model was more accurate in modeling of the flow behavior in wide range of temperature and strain rate. The minor deviation at some specified conditions was attributed to the negative strain rate sensitivity of the alloys at low temperature deformation regime.
The Effects of Anisotropic Transport Coefficients on Pore Pressure in Shale Formations
Authors: Dokhani Vahid , Yu Mengjiao , Miska Stefan Z. , Bloys James
Published: December 2014

This study investigates shale–fluid interactions through experimental approaches under simulated in situ conditions to determine the effects of bedding plane orientation on fluid flow through shale. Current wellbore stability models are developed based on isotropic conditions, where fluid transport coefficients are only considered in the radial direction. This paper also presents a novel mathematical method, which takes into account the three-dimensional coupled flow of water and solutes due to hydraulic, chemical, and electrical potential imposed by the drilling fluid and/or the shale formation. Numerical results indicate that the presence of microfissures can change the pore pressure distribution significantly around the wellbore and thus directly affect the mechanical strength of the shale.
Stochastic Estimation of Human Ankle Mechanical Impedance in Lateral/Medial Rotation
Authors: Ficanha Evandro M. , Rastgaar Mohammad
Published: December 2014

This article compares stochastic estimates of human ankle mechanical impedance when ankle muscles were fully relaxed and co-contracting antagonistically. We employed Anklebot, a rehabilitation robot for the ankle to provide torque perturbations. Surface electromyography (EMG) was used to monitor muscle activation levels and these EMG signals were displayed to subjects who attempted to maintain them constant. Time histories of ankle torques and angles in the lateral/medial (LM) directions were recorded. The results also compared with the ankle impedance in inversion-eversion (IE) and dorsiflexion-plantarflexion (DP). Linear time-invariant transfer functions between the measured torques and angles were estimated for the Anklebot alone and when a human subject wore it; the difference between these functions provided an estimate of ankle mechanical impedance. High coherence was observed over a frequency range up to 30 Hz. The main effect of muscle activation was to increase the magnitude of ankle mechanical impedance in all degrees of freedom of ankle.
Decentralized Sub-Optimal Minimum-Time Consensus
Authors: Garcia Eloy , Cao Yongcan , Casbeer David W.
Published: December 2014

In many multi-agent scenarios, agents must balance both local and global performance and collaboration objectives with the constraints of efficient resource utilization. Here, consensus problems with fixed communication graphs are considered, where agents strive to reach a common decision value in minimum time while simultaneously minimizing a performance cost that measures the deviation of the decision value from the desired value. The paper offers preliminary results on the selection of meaningful decision values that approximate optimal solutions. The proposed approach shows a fast convergence time and also reduces the overall number of information transmissions by the agents in the network.
Bio-Inspired Approach for Aircraft Health Assessment and Flight Envelope Estimation
Authors: Moguel Israel , Moncayo Hever , Perez Andres , Perhinschi Mario , Al Azzawi Dia , Togayev Adil
Published: December 2014

Based on the artificial immune system paradigm and a hierarchical multi-self strategy, a set of algorithms for aircraft sub-systems failure detection, identification, evaluation and flight envelope estimation have been developed and implemented. Data from a six degrees-of-freedom flight simulator were used to define a large set of 2-dimensional self/non-self projections as well as for the generation of antibodies and identifiers designated for health assessment of an aircraft under upset conditions. The methodology presented in this paper classifies and quantifies the type and severity of a broad number of aircraft actuators, sensors, engine and structural component failures. In addition, the impact of these upset conditions on the flight envelope is estimated using nominal test data. Based on immune negative and positive selection mechanisms, a heuristic selection of sub-selves and the formulation of a mapping-based algorithm capable of selectively capturing the dynamic fingerprint of upset conditions is implemented. The performance of the approach is assessed in terms of detection and identification rates, false alarms, and correct prediction of flight envelope reduction with respect to specific states.
Nonlinear Vibration Control of Flexible Structures Using Nonlinear Modified Positive Position Feedback Approach
Authors: Omidi Ehsan , Mahmoodi S. Nima
Published: December 2014

A new Nonlinear Modified Positive Position Feedback (NMPPF) controller is proposed in this paper to suppress the nonlinear resonant vibrations in flexible structures. The NMPPF uses a nonlinear second-order feedback compensator to overcome the vibrations at exact primary resonance frequency, and a first-order integrating term to lower the remaining peak amplitudes in the frequency domain. For the closed-loop system, an innovative implementation of the Method of Multiple Scales is employed to obtain the modulation equations. Results demonstrate the superior performance of the NMPPF controller compared to the conventional approach i.e. Positive Position Feedback (PPF), as the suppression performance is improved by 62% in the peak amplitude reduction. The presented parameter analysis of the NMPPF controller also proposes the optimal controller parameters to provide the highest suppression level in the nonlinear oscillatory system.
Resting State EEG Multiscale Entropy Dynamics in Mild Cognitive Impairment and Early Alzheimer’s Disease
Authors: McBride Joseph , Zhao Xiaopeng , Munro Nancy , Jicha Gregory , Smith Charles , Jiang Yang
Published: December 2014

Mild cognitive impairment (MCI) is a neurological condition related to early stages of dementia such as Alzheimer’s disease (AD). This study explores non-event-related multiscale entropy (MSE) measures as features for effectively discriminating between normal aging, MCI, and AD participants. Resting EEG records from 48 age-matched participants (mean age 75.7 years) — 15 normal controls (NC), 16 MCI, and 17 early AD — are examined. Multiscale entropy curves are computed for short EEG segments and averaged over the segments. Binary discriminations among the three groups are conducted using support vector machine models. Leave-one-out cross-validation accuracies of 80.7% (p-value <0.0018) for MCI vs. NC, 87.5% (p-value <1.322E−4) for AD vs. NC, and 90.9% (p-value <2.788E−5) for MCI vs. AD are achieved. Results demonstrate influence of cognitive deficits on multiscale entropy dynamics of non-event-related EEG.
Applying the Gale-Shapley Stable Matching Algorithm to Peer Human-Robot Task Allocation
Authors: Carano Elena L. , Liu Shih-Yuan , Hedrick J. Karl
Published: December 2014

When human and robotic agents work together, the challenge in assigning tasks lies in exploiting human strengths, such as expertise and intuition, while still managing the heterogeneous agent team in a near-optimal way. An extension to the Gale-Shapley stable matching algorithm that combines a sequential greedy approach is proposed to apply to task allocation missions. Conventional task features are modeled in the form of task preferences; agent inputs are modeled in the form of agent preferences. The algorithm is applied to a bomb defusal scenario, where bomb location is known but time for each agent to defuse each bomb is supplied through agent preferences. Simulation results are presented, and the sequential greedy Gale-Shapley algorithm is compared to a corresponding sequential single-item auction algorithm under three evaluation criteria — mission completion time, agent-task pair regret, and evenness of task distribution among agents.
Nonlinear Control of Floating Offshore Wind Turbines Using Input/Output Feedback Linearization and Sliding Control
Authors: Bagherieh Omid , Hedrick Karl , Horowitz Roberto
Published: December 2014

Input/ output feedback linearization and smoothed sliding control methods are used to control a floating offshore wind turbine on a barge platform in high wind speed in order to regulate the power capture. The model of the turbine has the blade pitch angle as the input, generator speed, platform pitch angle and its derivative as the measurements, and wind speed as a disturbance. The designed controllers have been applied to the simplified model of the plant which is used for controller design and also a more complex model which considers all six degrees of freedom for platform movements. Moreover, their performance is compared with the baseline controller for floating offshore wind turbines [1]. Both nonlinear controllers have improved the power fluctuation compared to the baseline controller. Also, sliding control has been shown to have better performance than the input/ output controller, since it can consider the uncertainty of the disturbance signal in the controller design.
Cooling Air Temperature and Mass Flow Rate Control for Hybrid Electric Vehicle Battery Thermal Management
Authors: Tao Xinran (William) , Wagner John
Published: December 2014

Lithium-Ion (Li-ion) batteries are widely used in electric and hybrid electric vehicles for energy storage. However, a Li-ion battery’s lifespan and performance is reduced if it’s overheated during operation. To maintain the battery’s temperature below established thresholds, the heat generated during charge/discharge must be removed and this requires an effective cooling system. This paper introduces a battery thermal management system (BTMS) based on a dynamic thermal-electric model of a cylindrical battery. The heat generation rate estimated by this model helps to actively control the air mass flow rate. A nonlinear back-stepping controller and a linear optimal controller are developed to identify the ideal cooling air temperature which stabilizes the battery core temperature. The simulation of two different operating scenarios and three control strategies has been conducted. Simulation results indicate that the proposed controllers can stabilize the battery core temperature with peak tracking errors smaller than 2.4°C by regulating the cooling air temperature and mass flow rate. Overall the controllers developed for the battery thermal management system show improvements in both temperature tracking and cooling system power conservation, in comparison to the classical controller. The next step in this study is to integrate these elements into a holistic cooling configuration with AC system compressor control to minimize the cooling power consumption.
Disturbance Attenuation Using Proportional-Integral-Observer for Wind Turbine Speed Regulation
Authors: Njiri Jackson G. , Liu Yan , Söffker Dirk
Published: December 2014

In this paper high-gain Proportional-Integral-Observer (PI-Observer) is used to estimate system states and wind disturbances. To guarantee the robustness and the desired performance, a disturbance rejection scheme is employed to compensate these disturbances. The proposed method realizes speed/power regulation during high wind regime. Control performance of the proposed scheme is evaluated against a baseline collective pitch controller (CPC). The results show that the proposed method can maintain fairly constant power/rotor speed without inducing extra load on the rotor.
Predictive Boundary Management Control of a Hybrid Powertrain
Authors: Yang Jie , Zhu Guoming G.
Published: December 2014

Hybrid Electric Vehicle (HEV) is capable of improving fuel economy with reduced emissions over traditional vehicles powered by the internal combustion engine alone. However the HEV durability is significantly limited by the battery useful life; and the battery life could be significantly reduced if it was operated over its allowed charging or discharging limits, which could occur especially at extremely low battery temperatures, leading to permanent battery damage and reduced battery life. In order to extend the battery life, this paper proposed a battery boundary management control strategy based upon the predicted desired torque to proactively make the engine power available to reduce future battery over-discharging. The proposed control strategy was validated in simulations and its performance was compared with the baseline control strategy under US06, and other four typical city and highway driving cycles. The simulation results show that the proposed control strategy is very effective when the battery temperature is under zero Celsius degree, and the over-discharged power is reduced more than 65% under aggressive US06 and ARB02 driving cycles, 45% under highway and city FTP and city NYCC driving cycles, and 30% under highway IM240 driving cycle, respectively.
Supernumerary Robotic Fingers: An Alternative Upper-Limb Prosthesis
Authors: Wu Faye , Asada Harry
Published: December 2014

Conventional prosthetic devices substitute lost human limbs with mechanical proxies to enable amputees perform daily chores. We present an alternative approach that may replace or supplement traditional upper-limb prostheses by utilizing and enhancing the functionality of the remaining healthy limb with a new type of wrist-mounted robot: the Supernumerary Robotic (SR) Fingers. These SR Fingers are naturally and implicitly coordinated with the motion of the human fingers to provide assistance in a variety of prehensile tasks that are usually too difficult to carry out with a single hand, such as grasping a large/oddly shaped object or taking the lid off a jar. A novel control algorithm, termed “Bio-Artificial Synergies”, is developed so the SR Fingers can share a work load and adapt to diverse task conditions just like the real fingers do. Through grasp experiments and data analysis, postural synergies were found for a seven-fingered hand comprised of two SR Fingers and five human fingers. The synergy-based control law was then extracted from the experimental data using Partial Least Squares Regression (PLSR) and tested on the SR Finger prototype on a number of common tasks to demonstrate the usefulness and effectiveness of this new class of prosthetic device.
Switching Adaptive Observer for Lithium-Ion Battery State of Charge Estimation
Authors: Li Yonghua , Anderson R. Dyche
Published: December 2014

A switching adaptive observer is proposed for estimation of state of charge (SOC) for lithium ion batteries used in electrified automotive propulsion systems. The base observer includes (i) a parameter estimation subsystem including a recursive parameter estimator for identifying battery parameters and (ii) an open circuit voltage (OCV) estimation subsystem including a nonlinear adaptive observer for estimating battery OCV. A timer as well as excitation level determination decides when the ampere-hour integration based SOC or estimated OCV based SOC is used as output. Using this approach, transient response of the adaptive SOC estimator is greatly improved. Examples are used to show the effectiveness of the proposed approach.
High Resolution Digital Elevation Modeling With On-Vehicle Sensors
Authors: Liang Mengyang , Xu Chi , Xie Yangmin , Alleyne Andrew
Published: December 2014

High resolution elevation mapping is useful for precise field operations. To achieve a good operation performance, the requirement of the field shape accuracy can be centimeter-level in some tasks. This paper presents a method of conducting high resolution elevation mapping with vehicle-borne sensors. To achieve this purpose, a laser range sensor obtains geometric information of the ground surface while an Inertial Navigation System (INS) and vision sensor provide high resolution measurements of the moving vehicle’s current location and attitude. The high frequency information from the INS captures the vehicle dynamics, and the low frequency vision sensor data enables vehicle self-localization by eliminating drift error in the INS measurements. A test run of this system was conducted experimentally. And the inclusion of vision-based measurements was shown to improve the accuracy of the ground elevation comparing with an INS-only method.
A State Synchronization Controller for Functional Electrical Stimulation-Based Telerehabilitation
Authors: Alibeji Naji A. , Kirsch Nicholas A. , Sethi Amit , Sharma Nitin
Published: December 2014

A position-synchronization controller for functional electrical stimulation (FES)-based telerehabilitation was designed. The developed controller synchronizes an FES-driven human limb with a remote physical therapist’s manipulator despite constant bilateral communication delays. The control design overcomes a major stability analysis challenge: the unknown and unstructured nonlinearities in the FES-driven musculoskeletal dynamics. To address this challenge, the nonlinear muscle model was estimated through two neural networks with online update laws. A Lyapunov-based stability analysis was used to prove the globally uniformly ultimately bounded tracking performance. The control performance of the state synchronization controller is depicted using a simulation of an FES-elicited elbow extension that is remotely controlled by a manipulator.
Model-Based Mode Transition Control Between SI and HCCI Combustion
Authors: Zhang Shupeng , Zhu Guoming G.
Published: December 2014

While the homogeneous charge compression ignition (HCCI) combustion has its advantages of high thermal efficiency with low emissions, its operational range is limited in both engine speed and load. To utilize the advantage of the HCCI combustion an HCCI capable SI (spark ignition) engine needs to be developed. One of the key challenges of developing such an engine is how to achieve smooth mode transition between SI and HCCI combustion, where the in-cylinder thermal conditions are quite different due to the distinct combustion characteristics. In this paper, an SI-HCCI mode transition control strategy was developed for an HCCI capable SI engine equipped with electrical variable valve timing (EVVT) systems with two step-lift valves and electronic throttle control (ETC) system, and the developed strategy was validated in hardware-in-the-loop (HIL) simulations. During the mode transition, a MAP (manifold air pressure) controller was used to track the desired intake manifold pressure for charge air management, and a fuel management controller is used to provide the desired engine torque. HIL simulation results show that the developed controller is able to achieve smooth combustion mode transition under unmodeled dynamics and external disturbance.
Stability Analysis of a Dynamic Surface Control for Piezoelectric Fuel Injection During Rate Shaping
Authors: Le Dat , Pietrzak Bradley W. , Shaver Gregory M.
Published: December 2014

Piezoelectric fuel injection provides a high bandwidth response that can be utilized in a common rail system to control injection during rate shaping. A model-based control is necessary to compensate for the nonlinearities, including the non-smoothness, in a piezoelectric fuel injector. Since the injector has a high order, a dynamic surface control was developed and simulated in MATLAB. In this paper, a stability analysis of the dynamic surface control is performed and show the stability and the guarantee of tracking performance.
Light Field Estimation and Control Using a Graphical Rendering Engine
Authors: Afshari Sina , Jia Li , Radke Richard J. , Mishra Sandipan
Published: December 2014

State-of-the-Art feedback control of lighting depends on point sensor measurements for light field generation. However, since the occupant’s perception depends on the entire light field in the room instead of the illumination at a limited set of points, the performance of these lighting control systems may be unsatisfactory. Therefore, it is critical to reconstruct the light field in the room from point sensor measurements and use it for feedback control of lights. This paper presents a framework for using graphical rendering tools along with point sensor measurements for the estimation of a light field and using these estimates for feedback control. Computer graphics software is used to efficiently and accurately model building spaces, while a game engine is used to render different lighting conditions for the space on the fly. These real-time renderings are then used together with sensor measurements to estimate and control the light field in the room using an optimization-based feedback control approach. We present a set of estimation algorithms for this purpose and analyze their convergence and performance limitations. Finally, we demonstrate closed loop lighting control systems that use these estimation algorithms and compare their relative performance, highlighting their benefits and disadvantages.
LMI Based Control of Stick-Slip Oscillations in Drilling
Authors: Harris Matthew W. , Açıkmeşe Behçet , van Oort Eric
Published: December 2014

This paper investigates control of stick-slip oscillations in drilling from a linear matrix inequality perspective. Stick-slip oscillations include a period of no angular motion at the bit caused by a large static friction torque followed by a period of rapid angular motion at the bit caused by a build up of torque in the drilling pipe. Many of the model parameters are uncertain but belong to convex sets, and the friction torques are not easily modeled. The linear matrix inequality approach facilitates design of state feedback controllers in the presence of polytopic uncertainties and can be optimized to reject disturbance effects relative to outputs. Results indicate that the linear matrix inequality approach leads to a simple controller, successfully alleviates the stick-slip problem, and is robust to uncertainties.