bluuebunny/crossref_metadata_2025 huggingface dataset:
Sensitivity of macaque retinal ganglion cells to chromatic and luminance flicker.
Authors: Lee B B , Martin P R , Valberg A
Published: December 2014

1. We have studied the sensitivity of macaque retinal ganglion cells to sinusoidal flicker. Contrast thresholds were compared for stimuli which alternated only in luminance ('luminance flicker') or chromaticity ('chromatic flicker'), or which modulated only the middle‐ or long‐wavelength‐sensitive cones ('silent substitution'). 2. For luminance flicker, the lowest thresholds were those of phasic, non‐opponent ganglion cells. Sensitivity was maximal near 10 Hz. 3. Tonic, cone‐opponent ganglion cells were relatively insensitive to luminance flicker, especially at low temporal frequencies, but were sensitive to chromatic flicker, thresholds changing little from 1 to 20 Hz. Those with antagonistic input from middle‐ and long‐wavelength‐sensitive (M‐ and L‐) cones had a low threshold to chromatic flicker between red and green lights. Those with input from short‐wavelength‐sensitive (S‐) cones had a low threshold to chromatic flicker between blue and green. Expressed in terms of cone contrast, the S‐cone inputs to blue on‐centre cells had higher thresholds than M‐ and L‐cone inputs to other cell types. 4. Phasic, non‐opponent cells responded to high‐contrast red‐green chromatic flicker at twice the flicker frequency. This frequency‐doubled response is due to a non‐linearity of summation of M‐ and L‐cone mechanisms. It was only apparent at cone contrasts which were above threshold for most tonic cells. 5. M‐ or L‐cones were stimulated selectively using silent substitution. Thresholds of M‐ and L‐cone inputs to both red and green on‐centre cells were similar. This implies that these cells' sensitivity to chromatic flicker is derived in equal measure from centre and surround. Thresholds of the isolated cone inputs could be used to predict sensitivity to chromatic flicker. The high threshold of these cells to achromatic contrast is thus, at least in part, due to mutual cancellation by opponent inputs rather than intrinsically low sensitivity. 6. Thresholds of M‐ and L‐cone inputs to phasic cells were similar at 10 Hz, and were comparable to those of tonic cells, suggesting that at 1400 td cone inputs to both cell groups are of similar strength. 7. The modulation transfer function of phasic cells to luminance flicker was similar to the detection sensitivity curve of human observers who viewed the same stimulus. For chromatic flicker, at low temporal frequencies thresholds of tonic cells (red or green on‐centre cells in the case of red‐green flicker or blue on‐centre cells in the case of blue‐green flicker) approached that of human observers. We propose the different cell types are the substrate of different channels which have been postulated on the basis of psychophysical experiments. 8. At frequencies of chromatic flicker above 2 Hz, human sensitivity falls off steeply whereas tonic cell sensitivity remained the same or increased. This implies that high‐frequency signals in the chromatic, tonic cell pathway are not available to the central pathway respons
Serotonin‐induced bistability of turtle motoneurones caused by a nifedipine‐sensitive calcium plateau potential.
Authors: Hounsgaard J , Kiehn O
Published: December 2014

1. The effect of serotonin on the firing properties of motoneurones was studied in transverse sections of the adult turtle spinal cord in vitro with intracellular recording techniques. 2. In normal medium, turtle motoneurones adapt from an initial high frequency to a low steady firing during a depolarizing current pulse. In the presence of serotonin (4‐100 microM) motoneurones responded with accelerated firing and a frequency jump during a depolarizing current pulse followed by an after‐depolarization outlasting the stimulus. From a depolarized holding potential motoneuronal activity was shifted between two stable states by brief depolarizing and hyperpolarizing current pulses. As an expression of this bistable firing behaviour, the frequency‐current relation in response to a triangular current injection was counter‐clockwise in serotonin while clockwise in normal medium. 3. The delay to onset of the frequency jump was shortened as the amplitude of the activation pulse was increased. From a positive holding potential the after‐depolarization exceeded spike threshold and its duration increased with an increase in steady bias current. The effect of serotonin on turtle motoneurones could be blocked by methysergide (10 microM). 4. When action potentials were depressed by tetrodotoxin, a voltage‐dependent, non‐inactivating plateau potential, intrinsic to the motoneurone, was revealed. Activation of this voltage plateau provides the motoneurones with two stable states of firing. The apparent input resistance was 2‐4‐fold lower during the plateau than at rest. 5. The serotonin‐induced plateau potential was Ca2+‐dependent and was blocked when Ca2+ was replaced by either Co2+ (3 mM) or Mn2+ (3 mM). 6. The Ca2+ plateau was blocked by nifedipine (1‐15 microM). 7. Serotonin reduced the slow after‐hyperpolarization following action potentials. The change in balance between inward and outward currents seems to be sufficient to reveal the plateau response. 8. Although a small plateau response was induced by Bay K 8644 (1‐15 microM), this L‐channel agonist could not reproduce the pronounced effect of serotonin. 9. It is concluded that serotonin induces a Ca2+‐dependent and nifedipine‐sensitive plateau potential in turtle motoneurones primarily by reducing a K+‐current responsible for the slow after‐hyperpolarization.
Increased sodium pump activity following repetitive stimulation of rat soleus muscles.
Authors: Hicks A , McComas A J
Published: December 2014

1. Soleus muscles of anaesthetized rats were stimulated tetanically (4 s at 20 Hz every 5 s for 5 min), following which the resting and action potentials were measured in surface fibres. 2. At the end of the stimulation period, the mean resting potential was found to have increased from a control value of ‐79.5 +/‐ 4.8 mV (mean +/‐ S.D.) to ‐90.5 +/‐ 6.3 mV. The hyperpolarization started to decline after 9 min but was still present at 15 min. 3. Associated with the membrane hyperpolarization was an increase in the mean amplitude of the muscle fibre action potential, from 82.2 +/‐ 10.8 to 96.8 +/‐ 10.0 mV. 4. Both the hyperpolarization and the enlargement of the muscle fibre action potential were abolished by 1.25 X 10(‐4) M‐ouabain, cooling the bathing fluid to 19 degrees C or removing K+ from the bathing fluid. 5. The results are explained in terms of an increase in electrogenic sodium pump activity resulting from tetanic stimulation. When the bathing fluid contained 20 mM‐K+, the mean resting potential of stimulated fibres was approximately ‐30 mV greater than that calculated from the Goldman‐Hodgkin‐Katz equation. 6. The increase in sodium pumping not only acts to restore the concentrations of Na+ and K+ on either side of the muscle fibre membrane, but, through its electrogenic effect, enables fibres to remain excitable during continuous contractile activity.
ATP requirement of the sodium‐dependent magnesium extrusion from human red blood cells.
Authors: Frenkel E J , Graziani M , Schatzmann H J
Published: December 2014

1. Competitive behaviour detectable in the stimulatory action of external sodium (Nao+) and internal magnesium (Mgi2+) corroborates the idea that Nao+‐dependent Mg2+ extrusion is a Mgi2+‐Nao+ exchange. 2. Mg2+‐loaded resealed cells made from metabolically starved cells (with less than 5 mumols/l cells of ATP), show hardly any Nao+‐dependent Mg2+ outflow. Incorporation of ATP during lysis‐resealing restores this Mg2+ transport. Half‐saturation for the effect is reached at an initial ATP concentration of about 150 mumols/l cells. 3. Adenylyl(beta, gamma‐methylene) diphosphonate (AMP‐PCP) and AMP had no restituting effect, indicating that in order to act ATP must be hydrolysed. 4. Nao+‐dependent Mg2+ outflow is not inhibited by vanadate concentrations that completely block the Ca2+ or Na+ pump. Therefore, the Nao+‐Mgi2+ exchange does not fall into the class of cation pumps of the E1E2 type. 5. Yet the fact that reversal of the Na+ gradient fails to reverse the direction of the Na+‐dependent Mg2+ transport in human red cells (Lüdi & Schatzmann, 1987) and that at equal Na+ concentration inside and outside the rate of Mg2+ transport is still 50% of that at a Na+ concentration difference of approximately 100 mM across the membrane suggests that the Na+ gradient, or the cation gradients in general, are not the only driving forces for Mg2+ movement. The assumption that there is energy input from ATP hydrolysis is compatible with these observations, whereas proposing the action of a protein kinase fails to explain them. 6. It is concluded that the Nao+‐Mgi2+ exchange system has an absolute requirement for ATP and that it is more probable that ATP is supplying energy for transport rather than activating transport by protein phosphorylation or simply by binding.
Indirect evidence for the presence of non‐specific anion channels in rabbit mandibular salivary gland acinar cells.
Authors: Brown P D , Elliott A C , Lau K R
Published: December 2014

1. Intracellular pH (pHi) was measured using the fluorescent pH‐sensitive dye 2',7'‐bis(carboxyethyl)‐5(6)‐carboxyfluorescein in acini isolated from the rabbit mandibular salivary gland. 2. Stimulation of the acinar cells with acetylcholine (ACh) evoked an intracellular acidosis, the size of which was dependent on the HCO3‐concentration in the bathing medium. A half‐maximal acidosis was observed at approximately 10 mM‐HCO3‐. ACh also evoked an acidosis in HCO3(‐)‐free solutions containing acetate; a half‐maximal acidosis was observed at about 10 mM‐acetate. 3. Propionate, lactate and butyrate were also able to support the ACh‐evoked acidosis to varying extents. In contrast, formate, pyruvate and salicylate did not support the ACh‐induced acidosis to any great extent. 4. Acetazolamide greatly reduced the size of the acidosis in HCO3(‐)‐buffered medium, but had no effect in acetate‐buffered medium, suggesting that the inhibitory effect of acetazolamide was due to a specific inhibition of carbonic anhydrase activity. 5. The Cl‐ channel blockers diphenylamine‐2‐carboxylic acid (DPC, 1 mM) and 5‐nitro‐2‐(3‐phenylpropylamino)‐benzoic acid (0.5 mM) abolished the ACh‐evoked acidosis in both HCO3(‐) ‐and acetate‐buffered media. 6. The data are consistent with the presence in the acinar cell of relatively non‐specific anion channels sensitive to DPC and its derivatives. Such channels, activated on stimulation with ACh, would allow HCO3‐ and other weak acid ions to leave the cell, leading to the observed acidosis. The existence of such channels, located in the apical membrane, could explain why HCO3‐ or acetate can sustain fluid secretion in the intact perfused rabbit mandibular gland in the absence of Cl‐.
Tension‐independent heat in rabbit papillary muscle.
Authors: Alpert N R , Blanchard E M , Mulieri L A
Published: December 2014

1. Heat and force were measured from isometrically contracting (0.2 Hz) rabbit papillary muscles at 21 degrees C during a single contraction‐relaxation cycle using antimony‐bismuth thermopiles and a capacitance force transducer. 2. Tension‐independent heat (TIH) associated with excitation‐contraction coupling was isolated from the initial heat by eliminating tension and tension‐dependent heat with a Krebs‐Ringer solution containing 2,3‐butanedione monoxime (BDM) and mannitol. 3. A strategy for testing the validity of this new method for measuring TIH in heart muscle is described and the test confirms that the BDM‐hypertonic solution partitioning method properly estimates the magnitude of the TIH component of initial heat. 4. TIH at the time of complete mechanical relaxation is 1.00 +/‐ 0.17 mJ/g wet weight and the data suggest that calcium cycling is complete by this time. Conversion of TIH to calcium cycled, assuming that 87% of TIH is due to calcium pumping by the sarcoplasmic reticulum, indicates that approximately 52 nmol calcium/g wet weight are required to support a single cycle of mechanical activity (0.2 Hz, 21 degrees C). 5. The length and frequency dependence of excitation‐contraction coupling were demonstrated. TIH is reduced by shortening muscle length and by increasing the interval between stimuli. These steady‐state data suggest that only a portion (approximately 40%) of TIH is directly related to activation of the contractile apparatus. 6. TIH in the first twitch following a 45 min rest period is significantly reduced by approximately 30%. 7. With subsequent twitches in the positive treppe following the rest period, TIH does not increase as steeply as expected suggesting that tension rise in twitches 1‐10 may be modulated by competitive binding of calcium rather than increased calcium delivery.
Ca2(+)‐activated K+ channels in human B lymphocytes and rat thymocytes.
Authors: Mahaut‐Smith M P , Schlichter L C
Published: December 2014

1. Previous evidence for the existence of Ca2(+)‐activated K+ channels in lymphocytes comes from measurements using voltage‐sensitive dyes and from tracer flux studies. We have now directly measured these channels in human tonsillar B lymphocytes and rat thymocytes in single‐channel recordings from cell‐attached and excised patches. 2. In cell‐attached recordings, intracellular Ca2+ was raised by either ionomycin or replacement of external Ca2+ following incubation in Ca2(+)‐free medium. Indo‐1 measurements during the Ca2(+)‐replacement technique showed that [Ca2+]i rose from approximately 90 to 260 nM. Both techniques activated two channels of approximately 25 and 8 pS (slope conductance at 0 mV applied, with 140 mM‐K+ in the pipette). Over 90% of patches displayed this activity, indicating a high density of these channels in the membrane. 3. Both channels reversed near the K+ equilibrium potential with either KCl or potassium aspartate in the pipette, when the cells were bathed in normal or high‐K+ saline. Therefore, these channels are selective for K+. 4. The larger channel was studied in more detail. It displayed inward rectification in symmetrical K+ solutions. The open‐channel probability was weakly dependent on membrane potential. 5. Ca2(+)‐dependent K+ channels were also recorded from excised, inside‐out membrane patches. The threshold for activation was 200‐300 nM [Ca2+i]. 6. Patch excision altered some characteristics of IK(Ca). Channels were activated in fewer than 50% of patches and the main conductance level was approximately 34 pS (at ‐80 mV). The duration of single‐channel events was shorter than in cell‐attached patches; kinetic analysis suggested that this was due to the loss of an open state in excised patches. 7. We conclude that B and T lymphocytes have K(+)‐selective channels which are activated by internal [Ca2+] in the physiological range and which will influence the membrane potential during cell activation.
Electrophysiological properties of rat CA1 pyramidal neurones in vitro modified by changes in extracellular bicarbonate.
Authors: Church J , McLennan H
Published: December 2014

1. Intracellular recordings were made from the somata of CA1b hippocampal pyramidal neurones in vitro and the concentration of bicarbonate ion ([HCO3‐]o) in the artificial cerebrospinal fluid (ACSF) was varied by substitution for Cl‐. 2. Reducing [HCO3‐]o from 26 mM (standard ACSF) to 8.6 mM or raising it to 72 mM had only minor effects on resting membrane potential but input resistance was reduced and increased, respectively. Threshold for Na(+)‐dependent action potential generation was raised during the perfusion with low‐HCO3‐ ACSF and lowered during perfusion with high‐HCO3‐ ACSF. In tetrodotoxin‐poisoned neurones where presumed Ca2(+)‐dependent potentials could be elicited in standard ACSF, perfusion with high‐HCO3‐ ACSF lowered the activation threshold. Where no Ca2(+)‐dependent spikes could be elicited in standard ACSF, perfusion with high‐HCO3‐ ACSF caused their appearance. Ca2(+)‐dependent spikes could not be evoked during perfusion with low‐HCO3‐ ACSF. 3. Depolarizing current pulses evoked two basic patterns of action potential discharge under standard [HCO3‐]o conditions. Conversion between the two types was possible by varying [HCO3‐]o. In those neurones which fired a train of fast Na(+)‐dependent spikes in standard ACSF, perfusion with high‐HCO3‐ ACSF usually led to the development of burst discharges. A smaller number of neurones responded to depolarizing current with an initial burst of three to six action potentials; the bursts were attenuated in low‐HCO3‐ ACSF and replaced by a repetitive spike discharge. Frequency accommodation of spike discharge in response to depolarizing current pulses and the after‐hyperpolarization following a current‐evoked discharge were usually both attenuated in low‐HCO3‐ ACSF and enhanced in high‐HCO3‐ ACSF. 4. Orthodromically evoked excitatory postsynaptic potentials (EPSPs) and early and late inhibitory postsynaptic potentials (IPSPs) were reduced in amplitude during perfusion with low‐HCO3‐ ACSF. In high‐HCO3‐ ACSF, EPSP amplitude and duration increased, the latter reflecting a positive shift in the reversal potential of the early IPSP consequent upon reduced [Cl‐] in high‐HCO3‐ ACSF. The late IPSP was, however, unaffected. 5. Responses to ionophoretically applied excitatory amino acids were enhanced in high‐HCO3‐ ACSF and depressed in low‐HCO3‐ ACSF. 6. Perfusion with high‐HCO3‐ ACSF was associated with the development of epileptiform activity. Spontaneous or synaptically evoked bursts of action potentials were indistinguishable and could be blocked by N‐methyl‐D‐aspartate antagonists.(ABSTRACT TRUNCATED AT 400 WORDS)
Electrophysiological properties of three types of granulocytes in circulating blood of the newt.
Authors: Kawa K
Published: December 2014

1. The electrophysiological properties of three subtypes of granulocytes obtained from the circulating blood of the newt, Triturus pyrrhogaster, were studied using the whole‐cell variation of the patch‐electrode voltage‐clamp technique. 2. Neutrophils were identified by their multilobulated nucleus in the cytoplasm. Basophils and eosinophils, having characteristic granular structures in their cells, could definitely be distinguished from other leucocytes. The reliability of cellular identification using phase‐contrast microscopy was confirmed by fixing and staining the granulocytes with Wright's solution. 3. In neutrophils under current‐clamp conditions, a hyperpolarization‐induced conductance increase was observed. With depolarization, however, no changes in regenerative potential were detected. When voltage clamped in standard saline (containing 96 mM‐NaCl), hyperpolarizing voltage pulses to a potential more negative than ‐90 mV evoked slowly decaying inward currents. 4. The hyperpolarization‐evoked membrane currents in neutrophils were identified as anomalous rectifying K+ currents, since (1) externally applied Cs+ (0.1 or 1 mM) or Ba2+ (1 mM) produced suppressive effects on the currents, (2) replacement of external Na+ with choline ions eliminated the decay of macroscopically observed currents, and (3) both the amplitude and kinetic properties of the currents were strongly dependent on membrane potential as well as on external K+ concentration; the activation of the conductance depended on the electrochemical force for K+ rather than on membrane potential alone. The magnitude of steady‐state conductance was roughly proportional to the square root of the external K+ concentration. 5. In basophils and eosinophils, no major time‐ or voltage‐dependent increase in conductance was detected at voltages between +20 and ‐130 mV. However, under current‐clamp conditions, spontaneous fluctuation of zero‐current potentials was clearly apparent, presumably due to the activities of some ion channels generating a small amount of current flux through the membranes of these cells. 6. It was concluded that the three subtypes of granulocytes in the newt differ considerably not only in appearance and structure but also in the electrical properties of their membranes. The anomalous rectifying K+ channels in neutrophils may serve to determine the resting potential of the cell at K+ equilibrium potential. The closure of the channels at depolarization might facilitate the maintenance of depolarization triggered by stimuli accompanying current influx.
Single sodium channels from canine ventricular myocytes: voltage dependence and relative rates of activation and inactivation.
Authors: Berman M F , Camardo J S , Robinson R B , Siegelbaum S A
Published: December 2014

1. Single sodium channel currents were recorded from canine ventricular myocytes in cell‐attached patches. The relative rates of single‐channel activation vs. inactivation as well as the voltage dependence of the rate of open‐channel inactivation were studied. 2. Ensemble‐averaged sodium currents showed relatively normal activation and inactivation kinetics, although the mid‐point of the steady‐state inactivation (h infinity) curve was shifted by 20‐30 mV in the hyperpolarizing direction. This shift was due to the bath solution, which contained isotonic KCl to depolarize the cell to 0 mV. 3. Steady‐state activation showed less of a voltage shift. The threshold for eliciting channel opening was around ‐70 mV and the mid‐point of activation occurred near ‐50 mV. 4. The decline of the ensemble‐averaged sodium current during a maintained depolarization was fitted by a single exponential function characterizing the apparent time constant of inactivation (tau h). The apparent rate of inactivation was voltage dependent, with tau h decreasing e‐fold for a 15.4 mV depolarization. 5. The relative contributions of the rates of single‐channel activation and inactivation in determining the time course of current decay (tau h) were examined using the approach of Aldrich, Corey & Stevens (1983). Mean channel open time (tau o) showed significant voltage dependence, increasing from 0.5 ms at ‐70 mV to around 0.8 ms at ‐40 mV. At ‐70 mV tau h was much greater than tau o, while at ‐40 mV the two time constants were similar. 6. The degree to which the kinetics of single‐channel activation contribute to tau h was studied using the first latency distribution. The first latency function was fitted by two exponentials. The slow component was voltage dependent, decreasing from 19 ms at ‐70 mV to 0.5 ms at ‐40 mV. The fast component (0.1‐0.5 ms) was not well resolved. 7. Comparing the first latency distribution with the time course of the ensemble‐averaged sodium current at ‐40 mV showed that activation is nearly complete by the time of peak inward sodium current. However, at ‐70 mV, activation overlaps significantly with the apparent time course of inactivation of the ensemble‐averaged current. 8. Using the methods of Aldrich et al. (1983) we also measured the apparent rate of open‐channel closing (a) and open‐channel inactivation (b). Both rates were voltage dependent, with a showing an e‐fold decrease for an 11 mV depolarization and b showing an e‐fold increase for a 30 mV depolarization.(ABSTRACT TRUNCATED AT 400 WORDS)
Whole‐cell current noise produced by excitatory and inhibitory amino acids in large cerebellar neurones of the rat.
Authors: Cull‐Candy S G , Usowicz M M
Published: December 2014

1. Membrane noise and current changes produced by glutamate and related excitatory amino acids have been examined in cultured large cerebellar neurones (including Purkinje cells), with whole‐cell patch‐clamp methods. The sensitivity of these neurones to the inhibitory amino acids gamma‐aminobutyric acid (GABA) and glycine has also been studied. 2. The neurones formed inhibitory synapses in culture, and displayed spontaneous synaptic currents. Reducing the pipette Cl‐ concentration (i.e. intracellular synaptic currents. Reducing the pipette Cl‐ concentration (i.e. intracellular concentration) caused a negative shift in their reversal potential, and the currents could be blocked with bicuculline (10 microM), suggesting that they were mediated by GABAA receptors. Spontaneous synaptic activity was also considerably reduced in the presence of 3 microM‐tetrodotoxin. 3. Analysis of the increase in whole‐cell current noise produced by the application of GABA (3 microM) gave noise spectra that were fitted by two Lorentzian components with slow and fast time constants of 23.6 and 1.9 ms at a membrane potential (Vm) of ‐110 mV. The mean single‐channel conductance estimated from GABA noise was gamma noise = 12 pS. Glycine (10 microM) whole‐cell current responses were Cl(‐)‐mediated and reversibly abolished by 1 microM‐strychnine. 4. Bath application of excitatory amino acids gave whole‐cell current changes accompanied by an increase in synaptic activity. Postsynaptic responses to the excitatory amino acids were more readily seen after the inhibitory synaptic currents had been abolished by bicuculline. Membrane current changes were obtained in response to the putative transmitters glutamate and aspartate, and the agonists NMDA (N‐methyl‐D‐aspartate), ibotenate, quisqualate and kainate. Their reversal potential was approximately ‐5 mV. 5. A majority of noise spectra produced by the various glutamate receptor agonists were fitted by two Lorentzian components; the rest were fitted with a single Lorentzian component. The noise time constants were apparently not dependent on the type of glutamate agonist used to activate the receptor channels. Pooling data for all agonists gave a mean time constant for single‐component spectra of tau noise = 4.8 +/‐ 0.3 ms; for two‐component spectra the time constants were tau 1 = 22.7 +/‐ 1.8 ms and tau 2 = 2.2 +/‐ 0.12 ms (Vm = ‐110 to ‐50 mV). It is likely that the two components present in whole‐cell noise spectra reflect complex kinetics of glutamate receptor channels. 6. The mean single‐channel conductance was estimated from whole‐cell noise for the various excitatory amino acids.(ABSTRACT TRUNCATED AT 400 WORDS)
Independent purinergic mechanisms of central and peripheral chemoreception in the rostral ventrolateral medulla
Authors: Moreira Thiago S. , Wenker Ian C. , Sobrinho Cleyton R. , Barna Barbara F. , Takakura Ana C. , Mulkey Daniel K.
Published: December 2014

The rostral ventrolateral medulla oblongata (RVLM) contains two functionally distinct types of neurons that control and orchestrate cardiovascular and respiratory responses to hypoxia and hypercapnia. One group is composed of the central chemoreceptor neurons of the retrotrapezoid nucleus, which provides a CO2/H+‐dependent drive to breathe and serves as an integration centre and a point of convergence of chemosensory information from other central and peripheral sites, including the carotid bodies. The second cluster of RVLM cells forms a population of neurons belonging to the C1 catecholaminergic group that controls sympathetic vasomotor tone in resting conditions and in conditions of hypoxia and hypercapnia. Recent evidence suggests that ATP‐mediated purinergic signalling at the level of the RVLM co‐ordinates cardiovascular and respiratory responses triggered by hypoxia and hypercapnia by activating retrotrapezoid nucleus and C1 neurons, respectively. The role of ATP‐mediated signalling in the RVLM mechanisms of cardiovascular and respiratory activities is the main subject of this short review.
Studies of Mechanical Properties of Multiwall Nanotube Based Polymer Composites
Authors: Gupta A. K. , Harsha S. P.
Published: December 2014

The two phase polymer composites have been extensively used in various structural applications; however, there is need to further enhance the strength and stiffness of these polymer composites. Carbon nanotubes (CNTs) can be effectively used as secondary reinforcement material in polymer based composites due to their superlative mechanical properties. In this paper, effects of multiwall nanotubes (MWNTs) reinforcement on epoxy–carbon polymer composites are investigated using experiments. MWNTs synthesized by chemical vapor deposition (CVD) technique and amino-functionalization are achieved through acid-thionyl chloride route. Diglycidyl ether of bisphenol-A (DGEBA) epoxy resin with diethyl toluene diamine (DETDA) hardener has been used as matrix. T-300 carbon fabric is used as the primary reinforcement. Three types of test specimen of epoxy–carbon composite are prepared with MWNT reinforcement as 0%, 1%, and 2% MWNT (by weight). The resultant three phase nanocomposites are subjected to tensile test. It has been found that both tensile strength and strain at failure are substantially enhanced with the small addition of MWNT. The analytical results obtained from rule of mixture theory (ROM) shows good agreement with the experimental results. The proposed three phase polymer nanocomposites can find applications in composite structures, ballistic missiles, unmanned arial vehicles, helicopters, and aircrafts.
Response Sensitivity and the Assessment of Nonlinear Vibration Using a Nonlinear Lateral–Torsional Coupling Model of Vehicle Transmission System
Authors: Xiang Chang L. , Huang Yi , Liu Hui
Published: December 2014

The eigensensitivity analysis does not meet the increasing industrial requirements of the dynamic performance of a vehicle transmission system. To reduce vibration, it is necessary to include response sensitivity in the guideline in the design stage. In this study, we developed a nonlinear lateral–torsional coupling spur gear system model considering the effect of time-varying mesh stiffness, clearance, mass eccentricity, and transmission error. Then the dynamic response sensitivity to system parameters was systematically analyzed by taking the shaft torsional stiffness, for example. The equation of response sensitivity was deduced by a direct method (DM) based on the fitting of the clearance function curve using a polynomial function. In allusion to the characteristic of the aperiodicity of response sensitivity curves of the nonlinear system in the time domain, a novel assessment method—differential sensitivity based on the root mean square (RMS) of response is proposed. This method provides statistical results in a certain range, thus avoiding the inaccuracy of the partial amplitude. The vibrational energy of modified system (MS) can also be estimated. All the abovementioned characteristics make it possible to provide the theoretical support for dynamic modification, model updating, and optimal design.
Assessing Significance of Information Flow in High Dimensional Dynamical Systems With Few Data
Authors: Anderson Ross P. , Porfiri Maurizio
Published: December 2014

Information-theoretical notions of causality provide a model-free approach to identification of the magnitude and direction of influence among sub-components of a stochastic dynamical system. In addition to detecting causal influences, any effective test should also report the level of statistical significance of the finding. Here, we focus on transfer entropy, which has recently been considered for causality detection in a variety of fields based on statistical significance tests that are valid only in the asymptotic regime, that is, with enormous amounts of data. In the interest of applications with limited available data, we develop a non-asymptotic theory for the probability distribution of the difference between the empirically-estimated transfer entropy and the true transfer entropy. Based on this result, we additionally demonstrate an approach for statistical hypothesis testing for directed information flow in dynamical systems with a given number of observed time steps.
Integrated Trajectory Planning and Tracking Control of Underactuated Surface Vessels
Authors: Mahini Farshad , Ashrafiuon Hashem
Published: December 2014

A novel nonlinear trajectory tracking controller for underactuated unmanned surface vessels is presented. A comprehensive planar model of the vessel with two control inputs is considered such that the system is represented by the equations of motion comprised of two double integrators subject to a second-order nonholonomic constraint. Given a target trajectory, a transitional desired trajectory is generated that uniformly satisfies the nonholonomic constraint and actuator saturation constraints. The system error dynamics is then modeled using the equations of motion and the transitional desired trajectory. A finite time sliding mode control law is developed to stabilize the yaw rotation which is robust to model uncertainties and disturbances. Consequently, the resulting reduced-order system is asymptotically stabilized via the surge force. Examples are presented and demonstrate that the approach provides trajectories and tracking control inputs which are suitable for real world applications.
UAV Coordinated Decision Making and Mission Management
Authors: Garcia Eloy , Casbeer David W.
Published: December 2014

A cooperative control problem where N Unmanned Aerial Vehicles (UAVs) are assigned to eliminate M main targets is studied in this paper. The environment where these assignments are performed also includes T >> M threats that pose a risk to the group of UAVs. A decentralized optimization problem is presented where agents try to minimize a total cost that combines distance to reach main targets and exposure to threats. The main novelty here is the use of limited resources by the UAVs to eliminate threats while on their way to reach main targets. This option improves the trajectories of vehicles by further reducing total cost but it adds complexity to the optimization problem. The solution to this extended problem provides optimal decisions regarding the selection of threats to eliminate, and the corresponding trajectories to follow, in order to minimize total cost. Due to constraints imposed by communication topologies, agents implement a decentralized auction scheme in order to assign UAVs to threats while avoiding conflicts on those assignments. This paper describes the specific constraints concerning the decentralized decision process and its effects in recomputing new costs. The paper also offers preliminary results that provide coordinated selection of UAV paths and choice of threats to attack.
Stability and Control of a Thermoacoustic Device: The Rijke’s Tube
Authors: Olgac Nejat , Zalluhoglu Umut , Kammer Ayhan S.
Published: December 2014

This study presents an intersection of two seemingly separate areas of research frontiers, “prediction and control of thermoacoustic instability” and “stability analysis of neutral-class linear-time-invariant (LTI) and time-delayed systems (TDS)”. The former is a coveted capability which has been elusive to the scientific community over 1½ centuries. Analytical capabilities have been limited due to the complex physics invoking the “combustion” phenomenon. Most available results rely on accumulated empirical knowledge. In this paper we consider a benchmark combustion test platform, which is known as Rijke’s tube. Its representation is simplified to an LTI neutral TDS, stability of which is assessed using a recent mathematical paradigm called the Cluster Treatment of Characteristic Roots (CTCR). CTCR provides a unique non-conservative and exhaustive stability declaration for a Rijke’s tube within the space of its parameters, naturally, under some simplifying assumptions. For those operating conditions which induce instability, we also propose a conventional and simple control strategy which can recover stability. This method is also analyzed using the CTCR paradigm for the first time.
Application of Linear Observers to Estimate States of a Roll Simulator
Authors: Zagorski Scott B. , Heydinger Gary J. , Guenther Dennis A.
Published: December 2014

In this research, a variety of Kalman Filters are implemented in an effort to estimate sled speed of a Roll Simulator. An Extended Kalman Filter (EKF) is incorporated to capture the nonlinear dynamics of the sled-platform assembly to estimate sled speed for the entire motion, as a linear Kalman Filter was found to be inadequate. When applied to experimental data, the EKF over-estimates sled speed, which is due to a disturbance force and/or uncertainty in system parameters. In combination with the disturbance observer, the Kalman Filter adequately estimates sled speed for experimental data. For lower speed/payload applications, a Kalman Filter using an accelerometer and measured drum speed is able to accurately track sled speed when a gain scheduling scheme is employed.
Dynamic Analysis and Controller Design of the Balloon Point Control System of Gamma-Ray Imager/Polarimeter for Solar Flares
Authors: Mao Yao-Ting , Auslander David , Wiputra Eduardo , Dokko Ben , Pankow David , Saint Hilaire Pascal
Published: December 2014

A pointing control system is developed for the Gamma-Ray Imager/Polarimeter for Solar flares (GRIPS) balloon-borne instrument which provides a near-optimal combination of high-resolution imaging, spectroscopy, and polarimetry of solar-flare gamma-ray/hard X-ray emissions from ∼20 keV to ∼10 MeV. Within the narrow field of view of its sun sensor, the telescope must track the sun with a 0.5 degrees rms accuracy. This paper introduces the mechanical structure of the pointing control system and investigates the dynamics and control strategy and presents the simulation and experimental results.
Development and Full-Scale Experimental Validation of a Rapid Prototyping Environment for Plant and Control Design of Airborne Wind Energy Systems
Authors: Vermillion Chris , Glass Ben , Szalai Balazs
Published: December 2014

Airborne wind energy systems present great promise for inexpensive, clean energy at remote locations, but have only been demonstrated through short-duration flights in very limited wind conditions. Because of the time and money that is required to implement full-scale airborne wind energy prototypes, convergence toward designs that achieve longer-duration flight in adverse weather has been slow. This paper presents an inexpensive rapid prototyping approach for improving the flight dynamics and control of airborne wind energy systems, which has been implemented and validated on Altaeros Energies most recent full-scale flight prototype. The approach involves the 3d printing of lab-scale water channel models of airborne wind energy lifting bodies, which enable prediction of dynamic flight characteristics, rapid iteration between the designs, identification of unknown or poorly known parameters, and improved control design. By applying this approach to its last prototype design cycle, Altaeros demonstrated robust operation in double the wind speeds sustained by its previous prototype (reaching a maximum of 21.2 m/s, with sustained 10–15 m/s winds), with demonstrably improved flight characteristics.
Modeling and Control of a Novel Power Split Hybrid Electric Vehicle
Authors: Ahmed Qadeer , Cai Haiwei , Rizzoni Giorgio , Xu Longya
Published: December 2014

This paper presents a novel dual-clutch, transmission-less hybrid electric powertrain architecture using Dual Mechanical Port Machine (DMPM). The proposed architecture offers the vehicle to operate in four different modes i.e. charge depleting mode, charge sustaining mode, highway mode and braking mode. Power/energy flow in each operating mode is explored and operating characteristics of each prime mover in all four modes are analyzed. A detailed system level modeling is conducted for the proposed powertrain. The power split HEV offers a variety of control problems to insure its optimal performance. In this paper, a rule based control has been designed to meet some of the outlined control objectives. The simulation results show that the proposed HEV architecture with a rule based energy management scheme offers high fuel efficiency as compared to its conventional counterpart.
Model Predictive Control of Integrated Hybrid Electric Powertrains Coupled With Aftertreatment Systems
Authors: Zhao Junfeng , Wang Junmin
Published: December 2014

For hybrid electric vehicles (HEVs), especially for diesel-electric hybrid vehicles, the low exhaust gas temperature induced by the hybridization and fuel economy optimization will bring significant impact on the performance of the exhaust gas aftertreatment systems, and may consequently lead to violation of the tailpipe emission constraints. To investigate the influence of diesel powertrain hybridization on the aftertreatment system and tailpipe emissions, an integrated HEV model is established by incorporating the thermodynamics models of the aftertreatment systems. This comprehensive model is able to predict engine-out nitrogen oxides (NOx) concentration, exhaust gas temperature, and to describe the temperature dynamics in the aftertreatment systems. A static map of selective catalytic reduction (SCR) system temperature-dependent de-NOx efficiency is utilized, so that the tailpipe NOx can be predicted. To investigate the tradeoff between fuel consumption and emissions for diesel HEV with aftertreatment systems, a preliminary study is carried out on optimally balancing both aspects via a model predictive control scheme. This controller is designed with an explicit consideration of HEV tailpipe NOx emission constraint. The simulation results show that the HEV tailpipe NOx emissions can be regulated by slightly sacrificing the fuel economy.
Observer Design for State Estimation of UV Curing Processes
Authors: Yebi Adamu , Ayalew Beshah , Dey Satadru
Published: December 2014

This article discusses the challenges of non-intrusive state measurement for the purposes of online monitoring and control of Ultraviolet (UV) curing processes. It then proposes a two-step observer design scheme involving the estimation of distributed temperature from boundary sensing cascaded with nonlinear cure state observers. For the temperature observer, backstepping techniques are applied to derive the observer partial differential equations along with the gain kernels. For subsequent cure state estimation, a nonlinear observer is derived along with analysis of its convergence characteristics. While illustrative simulation results are included for a composite laminate curing application, it is apparent that the approach can also be adopted for other UV processing applications in advanced manufacturing.
Comparison of Velocity Forecasting Strategies for Predictive Control in HEVs
Authors: Sun Chao , Hu Xiaosong , Moura Scott J. , Sun Fengchun
Published: December 2014

The performance of model predictive control (MPC) for energy management in hybrid electric vehicles (HEVS) is strongly dependent on the projected future driving profile. This paper proposes a novel velocity forecasting method based on artificial neural networks (ANN). The objective is to improve the fuel economy of a power-split HEV in a nonlinear MPC framework. In this study, no telemetry or on-board sensor information is required. A comparative study is conducted between the ANN-based method and two other velocity predictors: generalized exponentially varying and Markov-chain models. The sensitivity of the prediction precision and computational cost on tuning parameters in examined for each forecasting strategy. Validation results show that the ANN-based velocity predictor exhibits the best overall performance with respect to minimizing fuel consumption.
Multi-Model Adaptive Regulation for Aircraft Dynamics With Different Zero Structures
Authors: Peterson Eric D. , Kwatny Harry G.
Published: December 2014

An adaptive regulator is designed for parameter dependent families of systems subject to changes in the zero structure. Since continuous adaptive regulation is limited by relative degree and right half plane zeros, a multiple model adaptive regulator is implemented. The two multiple model design subproblems, covering and switching, are addressed with LQR state feedback and Lyapunov function switch logic respectively. These two subproblems are combined into a set of Linear Matrix Inequalities (LMI) and concurrently solved. The multiple model design method is applied to longitudinal aircraft dynamics.
Model Predictive Control of Commercial Office Plug-Loads and Battery Storage Systems
Authors: Sankur Michael D. , Arnold Daniel , Auslander David M.
Published: December 2014

Commercial demand response (DR) has traditionally relied on HVAC and lighting systems as load-shed resources in buildings. However, improvements in technologies such as Energy Information Gateways and smart power strips are making it possible to incorporate distributed plug-loads as an actionable resource. In this paper we explore the addition of a battery storage system (BSS) as a load-shed resource to supplement plug-loads in an office setting. Furthermore we investigate the value of control of BSS battery charging. We develop a model predictive control (MPC) framework for office plug-loads and a BSS. An experimentally derived model of a BSS is presented along with numerical methods for solving the MPC optimization program. Simulations demonstrate the efficacy of a BSS as a load-shed resource. Simulation results also quantify the benefit of BSS controllable charging for DR and load-following scenarios.
Drillstring Vibration Observation, Modeling and Prevention in the Oil and Gas Industry
Authors: Shor Roman J. , Pryor Mitch , van Oort Eric
Published: December 2014

As well designs become increasingly complicated, a complete understanding of drillstring vibrations is key to maximize drilling efficiency and reduce bit wear as well as prevent drillstring, tool, and borehole damage. This paper presents a review of the past fifty years of work on drillstring dynamics models and the proposed and accepted vibration mitigation applications within the drilling industry. Early modeling began with simplistic models in efforts to understand downhole processes. Once downhole sensors were deployed and the basic modes of vibration were understood, proprietary systems were developed and — only recently — successfully deployed to detect and mitigate the effects of certain undesired vibrational modes, specifically stick-slip torsional vibrations. Future systems and their effectiveness will depend on a refined understanding of the various modes of vibration and their interaction, as well as improved real-time downhole sensing techniques. Implementation of high-fidelity models to deduce and correct the downhole drillstring state will subsequently improve the operational drilling efficiency.
Functional Electrical Stimulation for Equilibrium-Point Control of Human Ankle Movement: Frequency Domain System Identification of Human Ankle Dynamics
Authors: Yamashita Yuto , Maegaki Kazuya , Matsui Kazuhiro , Oku Takanori , Uno Kanna , Koba Keitaro , Phatiwuttipat Pipatthana , Murakami Kenta , Uemura Mitsunori , Hirai Hiroaki , Miyazaki Fumio
Published: December 2014

This paper presents a novel method for creating an electrical stimulation pattern to control the equilibrium-point (EP) of human ankle movement. Focusing on the synergetic activation of agonist–antagonist (AA) muscles, the proposed method employs the ES-AA ratio (the ratio of the electrical stimulation levels for AA muscles) and the ES-AA sum (the sum of the electrical stimulation levels for AA muscles), which are based on the AA ratio (the ratio of the electromyography (EMG) voltage levels for AA muscles) and the AA sum (the sum of the EMG voltage levels for AA muscles) used in human movement analysis [1, 2]. The ES-AA ratio is related to the EP of the joint whereas the ES-AA sum is associated with mechanical stiffness of the joint. Using the AA concepts, we estimated the transfer function between the input ES-AA ratio (for the tibialis anterior (TA ) and gastrocnemius (GC)) and the force output of the endpoint in the ankle joint in an isometric environment by investigating the frequency characteristics, and finally found that the ankle-joint system was a second-order system with dead time in terms of the ES-AA ratio and foot force.