DC Current Injection Research Articles

Excitability of jcBNST Neurons Is Reduced in Alcohol-Dependent Animals during Protracted Alcohol Withdrawal

Alcohol dependence and withdrawal has been shown to cause neuroadaptive changes at multiple levels of the nervous system. At the neuron level, adaptations of synaptic connections have been extensively studied in a number of brain areas and accumulating evidence also shows the importance of alcohol dependence-related changes in the intrinsic cellular properties of neurons. At the same time, it is still largely unknown how such neural adaptations impact the firing and integrative properties of neurons. To address these problems, here, we analyze physiological properties of neurons in the bed nucleus of stria terminalis (jcBNST) in animals with a history of alcohol dependence. As a comprehensive approach, first we measure passive and active membrane properties of neurons using conventional current clamp protocols and then analyze their firing responses under the action of simulated synaptic bombardment via dynamic clamp. We find that most physiological properties as measured by DC current injection are barely affected during protracted withdrawal. However, neuronal excitability as measured from firing responses under simulated synaptic inputs with the dynamic clamp is markedly reduced in all 3 types of jcBNST neurons. These results support the importance of studying the effects of alcohol and drugs of abuse on the firing properties of neurons with dynamic clamp protocols designed to bring the neurons into a high conductance state. Since the jcBNST integrates excitatory inputs from the basolateral amygdala (BLA) and cortical inputs from the infralimbic and the insular cortices and in turn is believed to contribute to the inhibitory input to the central nucleus of the amygdala (CeA) the reduced excitability of the jcBNST during protracted withdrawal in alcohol-dependent animals will likely affect ability of the jcBNST to shape the activity and output of the CeA.

Precise detection and elimination of grid injected DC from single phase inverters

Single-phase voltage source inverters are used for connecting small scale renewable energy sources to low voltage distribution networks. They operate to supply the network with sinusoidal current. If output transformers are not used, these inverters must prevent excessive dc current injection, which may cause detrimental effects in the network. In this study, the causes of dc current injection in a common inverter topology are analyzed. This work explains the design and test of a passive filter circuit precisely measuring the dc component in the inverter output current. The filtered dc signal is then used to control the single phase inverter for the objective to keep the dc injection low — below the standard limit. Characteristics of the proposed method are illustrated using simulation and experimental results.

Spike threshold dynamics reshape the phase response curve and increase the degree of synchronization among neurons coupled by excitatory synapses

The collective behavior of a neuronal population can often be illuminated by representing neurons as simple phase oscillators, where the response of each neuron to its synaptic input is given by an infinitesimal phase response curve (iPRC). This approach can, for example, predict whether neuronal activity will tend to synchronize across the population depending on the nature of the synaptic coupling and the shape of the iPRCs[1-3]. Despite the extreme simplicity of phase models, we have found that the response of subthalamic neurons to excitatory synaptic input is remarkably well described by iPRCs; this is probably true of many other cell types. However, one aspect of subthalamic neurons’ response to input may undermine the phase model description: spike threshold accommodation[4], a phenomenon also found in many other cell types. In spike threshold accommodation, spikes fired following more rapid depolarization are triggered at a lower voltage threshold. We developed a phenomenological model of spike threshold accommodation that treats the threshold itself as a dynamical variable; this model successfully accounted for the experimentally observed features of this phenomenon[4]. However, the introduction of a new dynamical variable raises the possibility that one-dimensional phase models will be unable to represent adequately the impact of spike threshold dynamics. This danger seems more pressing given that most of the threshold accommodation phenomenon arises from the fact that spikes are initiated in the axon at some distance from the soma[5,6], a factor that cannot be accounted for by standard methods for reducing a biophysical model to a phase model. We analyzed the effect of adding our phenomenological model of spike threshold dynamics to biophysical models that are otherwise well described by phase models. We discovered that spike threshold dynamics change the shape of the iPRC and that this effect alone accounts for much of this phenomenon’s impact on the response to synaptic input. Specifically, threshold dynamics increase the input sensitivity at late input phases, causing the iPRC to have higher values than one would otherwise predict. We show numerically that this alteration of the iPRC promotes synchronization of neurons coupled by excitation, even if those neurons have type I iPRCs. In addition to reshaping the iPRC itself, spike threshold dynamics also cause a deviation from the response predicted by the iPRC as the size of the stimulus grows; this effect further enhances the sensitivity to excitation at late input phases but suppresses the sensitivity to inhibition. We compare the results obtained with our phenomenological model of threshold dynamics to experimental data and to a full multicompartment biophysical model that exhibits spike threshold accommodation naturally, by virtue of the cable properties of the axon. We were able to explain some otherwise anomalous aspects of our data and predicted changes in iPRC shape as neurons are driven to fire at higher rates by DC current injection. We confirmed this effect experimentally in subthalamic neurons; a similar phenomenon has also been reported in cerebellar Purkinje neurons [7].

Chirality control of magnetic vortex in a square Py dot using current-induced Oersted field

We have proposed a method for controlling the vortex chirality in a squared permalloy dot by using the circular Oersted field locally induced by flowing a DC current across a small Py/Cu junctions. The reliability of the chirality control has been evaluated by measuring the nonlocal spin valve signal. The desired vortex chirality has been obtained when the injecting DC current has a moderate magnitude. However, the large DC current is found to reduce the control reliability. Another possibility for controlling the vortex structure using the large DC current injection was also discussed.

Analysis of broad emission direction in a spiral-shaped microcavity laser

Broad emission direction with two lobes is analyzed in a spiral-shaped microcavity laser. By pumping the boundary of the InGaAsP semiconductor laser with dc current injection, whispering-gallery-type modes emitting through a notch are obtained. By classifying the lasing modes into mode groups based on the equidistant mode spacing, it is shown that each mode group has its own emission direction with a narrow divergence angle and that a superposition of emission direction of dominant mode groups reproduces a far-field pattern of total intensity with two lobes, which is contrary to theoretical results.

Study on Restraining DC Neutral Current of Transformer During HVDC Monopolar Operation

HVDC transmission system operating in ground return mode often affects the neighboring ac power system seriously. This paper presented some field experimental results, including audible noise, voltage harmonics, and oscillation of the transformer while dc current passes through the neutral point. The relationship between the dc neutral current and those effects were discovered clearly by analyzing these data. Based on the analysis of the characteristics of the dc current distributed under ground and in the ac network, some useful measures to decrease or block the dc current through the neutral point of the transformer, such as the injection of reverse dc current, blocking capacitor, and series resistor are compared. And the series resistor method is chosen after carefully study of its feasibility in the ac power system. The parameters as well as the protection method of the resistor were selected by implementing several large current experiments. Finally, field experiments were carried out to observe the effect of reducing the neutral current with a series resistor device. Experimental results show that series resistor method is a simple structure, low cost, and of high reliability, which can restrain the neutral current effectively.

Effect of DC current injection on AC supercurrent carrying ability of ring shaped HTS thin films

The effect of DC current injection on the AC current carrying characteristics of superconducting thin film rings was analyzed because of the possibility for using similar ferromagnetic/high temperature superconducting (FM/HTS) structures for contactless investigation of the spin-injection process. It was shown, that the injection leads to decreasing of the critical current I C1, determined by using AC magnetic field. A superposition of AC and DC currents in the HTS ring and a breaking of Cooper pairs may cause this effect. The effect was investigated experimentally at 77 K in HTS Y 1Ba 2Cu 3O 7− x (YBCO) thin film samples with YBCO or La 0.7Sr 0.3MnO 3 (LSMO) current injecting electrodes: I C1 of the last sample was found to be more sensitive to the injection process. The results allow concluding, that a change of the I C1 caused by both mechanisms can be evaluated separately and the contactless method can be successfully used for the investigation of the spin-injection effect.

Electrical characterization of a-Si:H(n)/c-Si(p) structure

In this study, n-type hydrogenated amorphous silicon (a-Si:H) was fabricated on p-type crystalline silicon (c-Si) substrates to obtain heterojunction diodes. The amorphous films were obtained by the Plasma Enhanced Chemical Vapor Deposition (PECVD) technique. Temperature dependent current–voltage ( I– V– T) measurements and investigation of the dc current injection mechanism of a-Si:H(n)/c-Si(p) device structure have been performed. The series resistance (4.6–8.2 Ω) values displayed nearly temperature independent behavior and the ideality factor varied between 2.7 and 1.6 in the temperature range 100–320 K. The forward bias I– V– T characteristics of c-Si/a-Si:H heterojunctions are found to behave like the Schottky junctions where carrier injection is especially influenced by the carrier generation-recombination in the junction interface formed on the amorphous side. The temperature dependent ideality factor behavior shows that tunneling enhanced recombination is valid rather than thermionic emission theory. In the frame of this model, characteristic tunneling energy and characteristic temperature are found to be 9 meV and 1900 K, respectively. It is concluded that fabricate n-type hydrogenated amorphous silicon is a preferable semiconductor material layer with low interface state density because the temperature dependent interface state density calculations give values of the order of 10 14 eV −1 cm −2.

Approach to low-cost prevention of DC injection in transformerless grid connected inverters

With the growing popularity of distributed generation, there are concerns over the effects that distributed generators may have on power quality. One highly important aspect often overlooked when considering power quality is DC current and the effects that it may have on distribution components. This study considers the problems associated with DC current injection into the electricity distribution network from transformerless grid connected inverters. A new method of preventing differential mode DC injection from transformerless inverters is proposed which eliminates the need for a bulky and costly isolation transformer. This technique is experimentally validated and its benefits regarding DC injection reduction are shown.

High output power density from GaN-based two-dimensional nanorod light-emitting diode arrays

Here we propose and realize a scheme for making a direct contact to a two-dimensional nanorod light-emitting diode (LED) array using the oblique-angle deposition approach. And, more importantly, we demonstrate highly efficient electrical carrier injection into the nanorods. As a result, we show that at a 20 mA dc current injection, the light output power density of our nanorod LED array is 3700 mW cm−2. More general, this contact scheme will pave the ways for making direct contacts to other kinds of nanoscale optoelectronic devices.

Anesthetics Discriminate Between Tonic and Phasic γ-Aminobutyric Acid Receptors on Hippocampal CA1 Neurons

Anesthesia is produced by a depression of neuronal signaling in the central nervous system (CNS); however, the mechanism(s) of action underlying this depression remain unclear. Recent studies have indicated that anesthetics can enhance inhibition of CNS neurons by increasing current flow through tonic gamma-aminobutyric acid (GABA(A)) receptor gated chloride channels in their membranes. Enhanced tonic inhibition would contribute to CNS depression produced by anesthetics, but it remains to be determined to what extent anesthetic actions at these receptors contribute to CNS depression. In the present study, we compared and contrasted the involvement of tonic versus synaptic GABA(A) receptors in the functional depression of CNS neurons produced by isoflurane and thiopental. In rat hippocampal slices, whole cell patch clamp recordings were used to study anesthetic effects on CA1 neuron intrinsic excitability, and population spike recordings were used to investigate effects on synaptically evoked discharge. These responses were chosen to test whether anesthetic effects on GABA receptors alter single neuron discharge and/or circuit level synaptic functioning. Phasic (synaptic) GABA receptors were selectively blocked using the GABA(A) antagonist gabazine and tonic responses were blocked using the chloride channel blocker picrotoxin. Clinically relevant and equi-effective concentrations of thiopental and isoflurane depressed CA1 neuron synaptically evoked discharge. This depression was partially reversed by blocking synaptic GABA(A) receptors with gabazine (20 microM). The thiopental-induced depression was reversed by approximately 60%, but the isoflurane-induced depression was reversed by only approximately 20%. Blocking tonic GABA(A) receptors with the addition of 100 microM picrotoxin produced an additional 40% reversal of the thiopental-induced depression, but no additional reversal was seen for isoflurane-depressed responses. In response to direct DC current injection, CA1 neuron discharge was depressed by thiopental and membrane conductance was increased. Both of these effects were reversed by picrotoxin, but not by gabazine. Isoflurane, in contrast, neither depressed current-evoked discharge, nor altered the membrane conductance of CA1 neurons. These results indicate that general anesthetics discriminate between synaptic and tonic GABA(A) receptors. Effects on both phasic and tonic receptors combined to depress circuit responses produced by thiopental, whereas only effects on synaptic GABA receptors appeared to play an important role for isoflurane. Together with the other known sites of action for these two anesthetics, our results support a multisite, agent-specific mechanism for anesthetic actions.

Iberiotoxin-sensitive large conductance Ca 2+-dependent K + (BK) channels regulate the spike configuration in the burst firing of cerebellar Purkinje neurons

Cerebellar Purkinje cells (PCs) are the sole output neurons of the cerebellar cortex. Mature PCs discharge either tonically Na + spikes or bursts of Na + spikes ending to a Ca 2+ spike. These cells express inactivating and non-inactivating large conductance Ca 2+-dependent K + (BK) channels in their soma and dendrites. Somatic intracellular recording of acutely prepared brain slices was performed to examine the role of BK channels-mediated current in the tonic and burst firing of PCs. Continuous injection of a negative DC current was used to both suppress the spontaneous activity and stabilize the resting membrane potential around − 70 mV. Then, the short depolarizing current injection was used to evoke spike discharge. For establishing of the burst firing, 4-aminopyridine (4-AP) was bath applied to the bath solution. Blockade of BK channels with iberiotoxin (IbTx); a specific blocker of BK channels, did not affect the Na + spike configuration in the tonic firing but caused a remarkable change in the shape of Na + and Ca 2+ spikes in 4-AP-induced burst. Our results showed that during the burst firing, strong activation of IbTx-sensitive BK channels enhances the amplitude of fast afterhyperpolarization while decreases the duration of both Na + and Ca 2+ spikes. The current from these channels contributes to both the repolarizing of Na + spike in the burst and setting of the amplitude of post-pulse AHP that occurs immediately after a depolarizing pulse. These data reveal an important role of IbTx-sensitive BK current in regulating of the spike configuration during the burst firing of PCs.

Fabrication and Characterization of InGaN-Based Green Resonant-Cavity LEDs Using Hydrogen Ion-Implantation Techniques

The InGaN-based green resonant-cavity light-emitting diodes (RCLEDs) have been fabricated using hydrogen ion-implantation and laser liftoff techniques. The RCLEDs structure consisted of an multiple-quantum-well active layer between the top (5 pairs) and bottom (7.5 pairs) dielectric distributed Bragg reflectors with optical reflectance of 85% and 99.9%, respectively. The insulation layers of the RCLEDs with and without implantation were formed by the hydrogen ion-implantation layers of concentration and film, respectively. The corresponding forward turn-on voltage at dc current density injection were about and for the RCLEDs with and without implantation. The light output intensity of the RCLEDs with implantation is higher by a factor of 1.4 as compared to that of the similar structure without implantation at a current density of . The directionality of RCLEDs with implantation is superior to that of RCLEDs without implantation.

DC current injection into the network from PV inverters of

The present paper is focused on the study of DC current injection for low-voltage small grid-connected PV systems, which is one of the power quality requirements of utility companies. To achieve this aim, the existing status of guidelines and regulations in six selected countries where the development in the grid PV sector has evolved rapidly over the last decade (Australia, Germany, Japan, Spain, the United Kingdom and the United States) has been reviewed according to the DC current injection into the grid. Furthermore, a grid-connected system installed in Spain has been used to carry out measures concerning possible DC current injection into the grid. Thus, 12 single-phase inverters <5 kW (according to the transformer options: 50 Hz LF transformers, HF transformers or transformerless) from the European market have been tested. Many groups of measurements were made under different conditions. The results show that in all cases there is DC current injection, even if an LF transformer inverter is used.

Spin-current induced vortex displacement and annihilation in micro-scale Permalloy disk

The influence of the DC current injection on the magnetic vortex is investigated by measuring planar Hall resistance. We experimentally demonstrate that the vortex motion and annihilation can be induced by the DC current injection. The obtained result is quantitatively consistent with the recent theoretical study.

Auto-Calibrating DC Link Current Sensing Technique for Transformerless, Grid Connected, H-Bridge Inverter Systems

Power electronic inverters are commonly used for the interfacing of distributed generation systems to the electrical power network. These electronic inverters operate in a current controlled mode to inject unity power factor sinusoidal current into the network. To prevent possible dc current injection, a mains frequency isolation transformer is often employed at the inverter output. This isolation transformer is a costly component. An alternative approach is to use current sensing and control techniques to eliminate the dc current component. One method is to use a current controller to force the output dc current to zero. Current controllers are prone to errors associated with nonlinearity and offsets in the current transducers. This paper considers a novel auto-calibrating dc link current sensing technique that eliminates the errors associated with the current transducer, and helps avoid dc current injection into the grid when using a transformerless grid connect inverter system

Current-induced vortex displacement and annihilation in a single permalloy disk

The induced motion of a magnetic vortex in a micron-sized ferromagnetic disk due to the DC current injection is studied by measuring planar Hall effect. The DC current injection is found to induce the spin torque that sweeps the vortex out of the disk at the critical current while bias magnetic field are applied. The current-induced vortex core displacement deduced from the change in planar Hall resistance is quantitatively consistent with theoretical prediction. Peak structures similar to those originated from spin wave excitations are observed in the differential planar Hall resistance curve.

Current driven domain wall motion in magnetic U-pattern

We have studied the current induced domain wall motion by using patterned U geometry. The observation of two magnetic states of the U-pattern was evidenced. One is the vortex domain wall at the center of semicircular arc in U-pattern and the other is the continuous magnetic state without wall. We investigated the influence of the positive and negative dc current injection on domain wall motion before switching field with density on the order of ∼107A∕cm2⁠. The critical current varied dramatically as the bias field is close to the switching field and only gradually as the field is far away from the switching field.

Domain wall drag due to dc current injection into ferromagnetic nano-wires

Abstract We here experimentally demonstrate the domain wall depinning triggered by injecting the current into the domain wall. The domain wall is pinned at the connection of a large pad and a narrow wire prior to the current injection experiment. The pinned domain wall is freed and pushed into the wire at the critical current, only when the current is injected along the direction of the domain wall propagation. These results imply that the injection of the spin-polarized current into the domain wall causes additional magnetic pressure due to the spin-momentum transfer between the spin-polarized current and the localized magnetic moment.

K + currents produce P 1 in the RW CAP: evidence from DC current bias, K + channel blockade and recordings from cochlea and brainstem

Tone-burst-evoked compound action potentials (CAP) from the guinea pig round window (RW) are altered by DC current injection through the RW. The CAP waveform consists of a series of interleaved negative and positive peaks (N 1, P 1, N 2, P 2 etc.) of decreasing amplitude. During positive DC current injection (around +50 μA) the positive peaks are depressed substantially and there is an overall negative baseline shift of the waveform following the N 1. Negative current injection (around −50 μA) increased the positive peaks, in particular P 1, and produced an overall positive baseline shift following the N 1 peak. Results support our hypothesis that the first and dominant N 1 peak in the RW CAP is due to depolarising Na + currents into the primary afferent dendrites and axons within the cochlea, and that the P 1 potential is largely due to the exit of the hyperpolarising K + currents in the same cells. We have reached this conclusion on the basis of the sign and latency of the N 1 and P 1 components at the RW, beneath the myelin layers around the spiral ganglion cells, at the internal auditory meatus (IAM) within the brain case, and on the basis of the differential susceptibility of the various peaks to perfusion of lidocaine in the cochlear nucleus, sectioning of the cochlear nerve at the IAM, application of the K + channel blockers 4-amino-pyridine and tetraethylammonium within the cochlea, and DC current biasing at the RW.