Excitation Threshold Research Articles

Структурные и функциональные параметры кишечника у крыс с различной возбудимостью нервной системы

The paper reports the results of the study on structural parameters of the intestine and the activity of a number of intestinal membrane enzymes in rat lines with high and low thresholds of nervous system excitability (HP, LP, low excitable and highly excitable, respectively) under normal conditions. It was found that the number of enterocytes and intraepithelial lymphocytes on the villi of the ileum increased in HP rats compared to LP animals. These changes in HP rats were accompanied by an increase in the activity of maltase in the ileum mucosa. In addition, HP rats showed a reduction in the activity of alkaline phosphatase in the mucosa and chyme of the large intestine. Compared to the LP line, HP rats also showed an increase in the mass of chyme in this part of the intestine. The latter may indicate a higher sensitivity of the intestine to inflammation and a lower motor activity of the colon in HP rats. The study revealed patterns in the relationship between the genetically determined level of excitability of the nervous system and the structural and functional characteristics of the intestine in adult animals. It allows us to conclude that low excitability of the nervous system may be related to an increased risk of developing inflammatory bowel disease.

Relaxation and polarization oscillations in a wide-aperture bistable laser with a saturable absorber

The regions of stability of homogeneous generation regimes in a wide-aperture laser with a saturable absorber, including a semiconductor laser with a vertical output of radiation, are determined depending on the relative relaxation rate of carriers in active and passive media and on the frequency detunings of working transitions in these media with a resonant frequency of radiation, taking into account its polarization state. The excitation thresholds for relaxation and polarization oscillations are determined within the four-level model. Keywords: wide-aperture laser, saturable absorber, relaxation and polarization oscillations

Optic chiasmatic potential by endoscopically implanted skull base microinvasive biosensor: a brain-machine interface approach for anterior visual pathway assessment.

Background: Visually evoked potential (VEP) is widely used to detect optic neuropathy in basic research and clinical practice. Traditionally, VEP is recorded non-invasively from the surface of the skull over the visual cortex. However, its trace amplitude is highly variable, largely due to intracranial modulation and artifacts. Therefore, a safe test with a strong and stable signal is highly desirable to assess optic nerve function, particularly in neurosurgical settings and animal experiments.Methods: Minimally invasive trans-sphenoidal endoscopic recording of optic chiasmatic potential (OCP) was carried out with a titanium screw implanted onto the sphenoid bone beneath the optic chiasm in the goat, whose sphenoidal anatomy is more human-like than non-human primates.Results: The implantation procedure was swift (within 30 min) and did not cause any detectable abnormality in fetching/moving behaviors, skull CT scans and ophthalmic tests after surgery. Compared with traditional VEP, the amplitude of OCP was 5-10 times stronger, more sensitive to weak light stimulus and its subtle changes, and was more repeatable, even under extremely low general anesthesia. Moreover, the OCP signal relied on ipsilateral light stimulation, and was abolished immediately after complete optic nerve (ON) transection. Through proof-of-concept experiments, we demonstrated several potential applications of the OCP device: (1) real-time detector of ON function, (2) detector of region-biased retinal sensitivity, and (3) therapeutic electrical stimulator for the optic nerve with low and thus safe excitation threshold.Conclusions: OCP developed in this study will be valuable for both vision research and clinical practice. This study also provides a safe endoscopic approach to implant skull base brain-machine interface, and a feasible in vivo testbed (goat) for evaluating safety and efficacy of skull base brain-machine interface.

Релаксационные и поляризационные колебания в широкоапертурном бистабильном лазере с насыщающимся поглотителем

The regions of stability of homogeneous generation regimes in a wide-aperture laser with a saturable absorber, including a semiconductor laser with a vertical output of radiation, are determined depending on the relative relaxation rate of carriers in active and passive media and on the frequency detunings of working transitions in these media with a resonant frequency of radiation, taking into account its polarization state. The excitation thresholds for relaxation and polarization oscillations are determined within the four-level model.

Certain calcium channel inhibitors exhibit a number of secondary effects on the physiological properties in Nitellopsis obtusa: a voltage clamp approach.

An unsolved problem of contemporary plant electrophysiology is the identity of Ca2+ channels responsible for the initiation of the action potential. We took a pharmacological approach and applied several Ca2+ channel blockers (verapamil, tetrandrine, and NED-19) on a Characean (Nitellopsis obtusa ) algae model system. The impact of the selected pharmaceuticals on the parameters of excitation transients of a single cell was analysed employing the two-electrode voltage clamp technique. It was revealed that tetrandrine exerted no effect, while both verapamil and NED-19 prolonged activation and inactivation durations of the excitatory Cl- current. NED-19 also significantly depolarised the excitation threshold membrane potential and shifted Ca2+ current reversal potential. Thus, NED-19 most specifically targeted Ca2+ channels. A viability assay paired with observations of cytoplasmic streaming revealed that verapamil affected not only Ca2+ channels but also exhibited non-specific effects, which eventually lead to cell death. Since many potential Ca2+ channel blockers exert additional undesirable non-specific effects, our study underlines the necessity to search for new more specific modulators of plant Ca2+ transport systems.

Nerve excitability study – a method to assess the pathophysiology of peripheral nervous system disorders

Nerve excitability study is an interesting extension of classical neurography. The principle of the test is to stimulate the nerve with a long-term depolarising or hyperpolarising stimulus, followed by a test stimulus that induces a complex motor or sensory potential of a given amplitude. The analysis of the intensity of the test stimulus used in chronic depolarisation or hyperpolarisation of the nerve fibre allows for the assessment of changes in nerve excitability. The median nerve is stimulated, and it is possible to assess the excitability of sensory or motor fibres. Nerve excitability study is the only method to evaluate the function of neuronal membrane ion channels in vivo. Test results are impacted by the following membrane-related factors: voltage-gated sodium and potassium ion channels, sodium and potassium ATPase, as well as the degree of fibre myelination and the levels of extracellular and intracellular electrolytes. Nerve excitability study yields a result in the form of a series of complex peripheral nerve excitability parameters, such as the relationship between the stimulus and the excitation threshold, rheobase, fibre chronaxie, threshold electrotonus, and reactivation after action potential. Nerve excitability study helps assess the pathophysiology of nerve fibre damage in various disorders of the peripheral nervous system, such as hereditary polyneuropathies, neurodegenerative or metabolic diseases. The test is highly sensitive, e.g. it shows pre-symptomatic excitability changes. It can also be used to monitor treatment outcomes in metabolic and drug-induced polyneuropathies and to search for peripheral markers of central nervous system channelopathies.

Threshold increase and lasing inhibition due to hexagonal-pyramid-shaped hillocks in AlGaN-based DUV laser diodes on single-crystal AlN substrate

The presence of hexagonal-pyramid-shaped hillocks (HPHs) in AlGaN epitaxial films affects device characteristics; this effect is significant in DUV laser diodes (LDs) on AlN substrates, where the presence of HPHs under the p-electrode increases the threshold current density and inhibits the lasing. In this study, we investigated the difference between the lasing characteristics of LDs with and without HPHs. It was found that in the presence of HPHs, the threshold excitation power density increased and the slope efficiency decreased by optical excitation. To investigate the cause of these phenomena, we performed structural, optical, and electrical analyses of the HPHs. Various imaging techniques were used to directly capture the characteristics of the HPHs. As a result, we concluded that HPHs cause the degradation of LD characteristics due to a combination of structural, optical, and electrical factors.

Infrared stimulated emission with an ultralow threshold from low-dislocation-density InN films grown on a vicinal GaN substrate

Near-infrared stimulated emission from a high-quality InN layer under optical pumping was observed with a threshold excitation power density of 0.3 and 4 kW cm−2 at T = 8 and 77 K, respectively. To achieve such a low threshold power density, vicinal GaN substrates were used to reduce the edge-component threading dislocation (ETD) density of the InN film. Cross-sectional transmission electron microscopy images reveal that the annihilation of ETDs can be divided into two steps, and the ETD density can be reduced to approximately 5 × 108 cm−2 near the surface of the 5-µm-thick film. The well-resolved phonon replica of the band-to-band emission in the photoluminescence spectra at 9 K confirm the high quality of the InN film. As a result, the feasibility of InN-based photonic structures and the underlying physics of their growth and emission properties are demonstrated.

Valence Band Dispersion Embedded in Resonant Auger Electrons

Resonant photoelectron spectroscopy highlights certain elemental components of the valence band by adjusting the photon energy to a core-level excitation threshold, allowing the study of the elemen...

Textronics spacer knitted material tests as a key element of the diagnostic system that monitors above the proper level of seat vibration

This research is focused on the construction and examination of a prototype of a spacer knitted material with integrated sensors. The combination of textiles with elements of electronics, computer science, and a knowledge of automation is called textronics. This type of material has been proposed as a component of diagnostic systems to monitor the extension level of vibration in employee seats at selected workstations or in children’s chairs. The purpose of the diagnostic system is to improve personal protective equipment (PPE) and increase employee safety. The spacer knitted material was tested with vibration frequencies in the range of 0–40 Hz to develop metrological properties under reproducible and repeatable conditions. The tested spacer knitted material meets the requirements of sensory properties such as vibration. The tested material is characterized by the following metrological parameters: total uncertainty U = 4.5%, sensitivity Sa = 0.64 [V/s2/m] and excitability threshold of 5 Pa with simultaneous high coefficient of low-frequency vibration damping of effective amplitude transmissibility (SEAT) = 2.3. Spacer knitted materials are modern constructs that enable the creation of new hybrid structures that have other properties, e.g., sensory suppression, in addition to spatial form.

Drive-Induced Backward-Wave Oscillations in Helix Traveling-Wave Tubes—A Case Study

The output section of helix traveling-wave tubes (TWTs) usually features a tapered delay line to enhance the amplifier performance. This alters the phase velocity of the circuit waves, which, in particular, disturbs the narrowband synchronism between the backward wave (BW) and the electron beam. As a result, the excitation threshold of BW oscillations (BWOs) increases. Large-signal operation significantly alters beam-wave synchronism, as the electrons loose kinetic energy during the amplification process, i.e., toward the TWT output. As a result, beam and BW may interact over a larger distance, thus lowering the threshold for the onset of BWOs. These would thus be drive-induced in contrast to the zero-drive BWOs mentioned above. The following investigates the occurrence of such drive-induced BWOs as a case study of several different TWT models and proposes a theory for the large-signal instability. As the simulation process is quite involved and time-consuming, a heuristic approach for the fast prediction of the oscillation is presented as well.

High-frequency stimulation induces axonal conduction block without generating initial action potentials.

The purpose of this modeling study is to develop a novel method to block nerve conduction by high frequency biphasic stimulation (HFBS) without generating initial action potentials. An axonal conduction model including both ion concentrations and membrane ion pumps is used to analyze the axonal response to 1kHz HFBS. The intensity of HFBS is increased in multiple steps while maintaining the intensity at a sub-threshold level to avoid generating an action potential. Axonal conduction block by HFBS is defined as the failure of action potential propagation at the site of HFBS. The simulation analysis shows that step-increases in sub-threshold intensity during HFBS can successfully block axonal conduction without generating an initial response because the excitation threshold of the axon can be gradually increased by the sub-threshold HFBS. The mechanisms underlying the increase in excitation threshold involve changes in intracellular and extracellular sodium and potassium concentration, change in the resting potential, partial inactivation of the sodium channel and partial activation of the potassium channel by HFBS. When the excitation threshold reaches a sufficient level, an acute block occurs first and after additional sub-threshold HFBS it is followed by a post-stimulation block. This study indicates that step-increases in sub-threshold HFBS intensity induces a gradual increase in axonal excitation threshold that may allow HFBS to block nerve conduction without generating an initial response. If this finding is proven to be true in human, it will significantly impact clinical applications of HFBS to treat chronic pain.

Influence of Vibrational Excitation and Nuclear Dynamics in Multiphoton Photoelectron Circular Dichroism of Fenchone.

We report photoelectron circular dichroism of S-(+)-fenchone enantiomers recorded with state-state vibrational level resolution using picosecond laser (2 + 1) resonance enhanced multiphoton ionization via 3s and 3p Rydberg intermediate states. The 3p state decays to the 3s state on a picosecond time scale so that, above the 3p Rydberg excitation threshold, ionization of vibrationally hot 3s states competes with direct 3p-1 ionization. Complex vibronic dynamics of the 3p → 3s internal conversion weaken the Rydberg Δv = 0 propensity rule in both the 3p-1 and 3s-1 ionization channels. Large variations of the forward-backward chiral asymmetry factors are observed between the Δv = 0 and Δv > 0 vibrational transitions, including dramatic swings from up to ±17%. Such changes of sign indicate complete reversal of the preferred direction for photoelectron emission in the laboratory frame, associated with vibrational motion. These asymmetry switches easily exceed the amplitude and frequency of such vibrationally induced flips previously observed in single photon ionization.

Is electric field strength deterministic in cortical neurons' response to transcranial electrical stimulation?

Transcranial electrical stimulation (tES), which modulates cortical excitability via electric currents, has attracted increasing attention because of its application in treating neurologic and psychiatric disorders. To obtain a better understanding of the brain areas affected and stimulation's cellular effects, a multi-scale model was proposed that combines multi-compartmental neuronal models and a head model. While one multi-scale model of tES that used straight axons reported that the direction of electric field (EF) is a determining factor in a neuronal response, another model of transcranial magnetic stimulation (TMS) that used arborized axons reported that EF magnitude is more crucial than EF direction because of arborized axons' reduced sensitivity to the latter. Our goal was to investigate whether EF magnitude remains a crucial factor in the neuronal response in a multi-scale model of tES into which an arborized axon is integrated. To achieve this goal, we constructed a multi-scale model that integrated three types of neurons and a realistic head model, and then simulated the neuronal response to realistic EF. We found that EF magnitude was correlated with excitation threshold, and thus, it may be one of the determining factors in cortical neurons' response to tES.Clinical Relevance-This multi-scale model based on biophysical and morphological properties and realistic brain geometry may help elucidate tES's neural mechanisms. Moreover, given its clinical applications, this model may help predict a patient's neuronal response to brain stimulation effectively.

Peripheral GABAA receptor signaling contributes to visceral hypersensitivity in a mouse model of colitis.

Pain is a common and debilitating symptom of inflammatory bowel disease (IBD). Based on evidence that peripheral GABAA receptor (GAR) inhibition plays an important role in establishing colonic afferent excitability and nociceptive threshold, we hypothesized that the increase in pain associated with IBD is due to, at least in part, a decrease in peripheral GAR-mediated inhibition. Acute colitis was induced with 5 days of dextran sodium sulfate (DSS, 3%) in the drinking water. Visceral sensitivity was assessed with the visceromotor response (VMR) evoked with balloon distention of the colon in control and DSS-treated mice before and after intracolonic administration of GAR agonist muscimol, the high-affinity GAR preferring agonist 4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridine-3-ol (THIP), the GAR positive allosteric modulator diazepam, or the GAR antagonists gabazine and bicuculline. Low concentrations of muscimol or THIP increased the VMR in DSS-treated mice but not in control mice. However, high concentrations of muscimol decreased the VMR in both control and DSS-treated mice. Diazepam decreased the VMR in both DSS-treated and control mice. By contrast, at a concentration of gabazine that blocks only low-affinity GAR, there was no effect on the VMR in either DSS-treated or control mice, but at concentrations of the antagonist that block low-affinity and high-affinity GAR, the VMR was increased in control mice and decreased in DSS-treated mice. Furthermore, bicuculline increased the VMR in control mice but decreased it in DSS-treated mice. These data suggest that activating of low-affinity GAR or blocking high-affinity GAR may be effective therapeutic strategies for the management of pain in IBD.

Resonant behavior of the electron component of the plasma and stratification of the positive column of a gas discharge

A new point of view on the appearance of S-, P- and R-striations in a positive column of inert gases is proposed, based on a dynamic analysis of the resonance properties of phase trajectories of electrons in spatially periodic fields. The area of applicability is focused on DC discharge in inert gases at low pressures. The motion of electrons associated with the gain of energy in the field E 0 up to the excitation threshold ɛ ex and the abrupt loss of this quantum of energy leads to the appearance of a spatial scale L 0 = ɛ ex/(eE 0). Analysis of motion in sinusoidally modulated fields shows the presence of resonant fields containing the fundamental mode L 0, which corresponds to the S-striation, and higher harmonics associated with integer and non-integer resonances. In particular, a resonant field with a period length L P = L 0/2 corresponds to a P-striation, and a resonant field L R = 2/3L 0 to an R-striation. Thus, the positive column can be viewed as a resonator containing a set of resonant fields. Like a tuning fork, it responds to a disturbance of one of the modes, in particular, by the appearance of S-, P-, or R-striations, depending on the discharge conditions. The acuity of the resonances is analyzed as a function of the detuning from the resonant fields. The spectrum of integer and non-integer resonances is given. It is shown that resonances corresponding to S-, P-, and R- striations have the highest amplitude. The dynamic and kinetic approaches to the description of striations are compared. The dynamic approach to some extent eliminates the difficulties of the kinetic theory associated with the long settling length of the solution to the Boltzmann equation, which is much larger than the length of the positive column.

Vasovagal syncope as a specific side effect of rTMS: A frontal-vagal dose-finding study

Abstract In the treatment of depression using repetitive Transcranial Magnetic Stimulation (rTMS), the intensity of stimulation is established based on the motor threshold (MT). Neuro-Cardiac-Guided TMS (NCG-TMS) is a newly developed method to optimize and individualize target location and to determine the intensity of treatment. In this method, the frontal threshold is established by evaluating the effect of stimulation of the DLPFC on heart rate variability and may be a better proxy for frontal excitability thresholds. In our pilot study (n=10), aimed at further optimizing NCG-TMS, one of the subjects experienced a syncope during the stimulation. In this case 10Hz stimulation (ITI 11 sec) was applied to the left Beam-F3 site in increasing intensities. Intensity was started at a low intensity and was increased in 5% points of machine output in 7 consequent steps, where the 5th intensity corresponded to 100% of the MT. ECG was measured simultaneously using a Brainquiry PET EEG device and BioExplorer software. ECG data were analyzed offline using Kubios software. During the assessment the resting heart rate dropped from 80BPM to 60BPM and HRV increased. The first cardiac effects already appeared at a stimulation intensity of 45% machine output, which represented 75% of the individual MT. The subject experienced feelings of dizziness and lightheadedness during the stimulation. The HR-data of the subject’s Fitbit collected over the prior month demonstrated an average HR of 67.6 BPM and a minimum HR of 65 BPM. This suggests that the DLPFC-rTMS specifically induced a HR-deceleration below the subject’s minimum HR. Presumably, the syncope was caused by overstimulation relative to the frontal excitability threshold. This may suggest that vasovagal syncope is a specific side effect of applying rTMS over the DLPFC. To avoid unwanted side effects of over stimulation, future studies should focus on frontal thresholding when applying rTMS. Keywords: Frontal Thresholding, Syncope, NCG-TMS, rTMS

Impact of potential fluctuation on temperature dependence of optical gain characteristics in InGaN quantum-well laser diodes

The effects of the potential fluctuation (alloy compositional fluctuation and/or well-width fluctuation) in InGaN quantum wells (QWs) on the characteristics of InGaN-QW lasers, have been theoretically investigated, and it is found that the temperature dependence of the lasing threshold is strongly affected by the degree of fluctuation. Furthermore, we have experimentally measured the temperature dependence of stimulated-emission threshold excitation power density in photo-pump measurements, and have observed the predicted behavior of temperature dependence. It is considered that the temperature dependence of the lasing threshold could be used for the evaluation of the degree of the potential fluctuation in active layers of InGaN QW lasers.

Theoretical foundations for the evanescent mode oscillator (EMO) as a high-efficiency source of millimeter-wave and terahertz radiations

Evanescent mode oscillators (EMO) are investigated as high-efficiency sources of millimeter-waves and low-frequency parts of terahertz radiation. EMO can be considered a high-efficiency version of the extended interaction oscillator (EIO) using the evanescent resonance mode (ERM) of a slow-wave structure. It has been shown quantitatively that the efficiency of the EMO is superior to that of the conventional EIO having the same periodic unit cell. The condition to have an evanescent resonant mode in a chain is derived in this article. EMO threshold excitation condition is expressed in terms of the beam and RF mode parameters. A Typical EMO is systematically modeled, and its performance is checked with a particle-in-cell simulation software package. The excitation of the ERM modes is illustrated, with the results being close to the prediction of the non-linear model used in the paper.

Investigations on magnetic bistable PZT-based absorber for concurrent energy harvesting and vibration mitigation: Numerical and analytical approaches

Bistable systems possess broadband characteristics and can have large-amplitude oscillations under low amplitude excitations. This work is aimed to investigate the potential of a bistable piezoelectric-based absorber (BPA) for the purpose of simultaneous energy harvesting and vibration suppression. The BPA composed of a cantilever beam with PZT layers and two permanent magnets. The interactions due to magnets generate bistability in the BPA. Furthermore, the absorber is connected to a main vibrating beam. The governing nonlinear equations are obtained using the Hamilton's principle and a recently developed magnetic force model. Next, numerical analyses in time and frequency domains are performed to characterize the BPA performance in various dynamical regimes. It is found that, the best performance occurs when the BPA exhibits chaotic inter-well oscillations, which lead to strongly modulated response (SMR). Furthermore, approximate-analytical investigations based on the complexification-averaging and multiple scales methods are carried out. Using these, the excitation threshold corresponding to SMR is obtained. The performance of the proposed BPA in terms of harvested power and dissipated energy are examined comprehensively. The results reveal that, the BPA efficiently suppresses the vibration and harvests power over a wide frequency band, and it outperforms a linear absorber and nonlinear energy sink.