Excitation Threshold Research Articles

Highly Tuneable Photochromic Sodalites for Dosimetry, Security Marking and Imaging

AbstractPhotochromic sodalites are considered for a plethora of possible applications, such as UV indexing and X‐ray imaging, but for many of these the materials are yet to be optimized. UV indexing can be improved through incremental adjustment of the activation energy of coloration from 300 to 410 nm through replacement of sulfur with selenium. By combining this and other methods of tuning presented in the literature, the excitation threshold and photochromism color can be tuned independently of one another. The range of possible absorption maxima is expanded to 420–680 nm, or almost the entire visible spectrum. Mixing low‐cost and easy‐to‐synthesize sodalites further broadens the possible range of colors and facilitates development of a unique sodalite mix capable of quantifying the doses of two types of UV radiation simultaneously. Finally, the response to X‐rays of these highly tuned sodalites is investigated, and it is found that they can be sensitized to produce clear, high‐contrast X‐ray images at significantly lower doses of radiation than those required by classic photochromic sodalite, Na8(AlSiO4)6(Cl,S)2.

Effects of non-ideality of classical plasmas on the 1Se resonance states in H−

The effects of the non-ideality (NI) of the classical plasmas on the 1Se resonance states of the negative ion of hydrogen (H−) have been investigated theoretically by using the stabilization method. The organized effect of the plasma charged particles is represented by a pseudopotential, which depends on the Debye length D and the non-ideality parameter γ. Densities of the resonance states as a function of D and γ are calculated by employing a highly correlated and extensive basis set. Convergence of the resonance parameters (energy and width) is ensured by increasing the number of terms in the basis. Three 1Se resonance states are found to emerge below the H(4S) excitation threshold. Our present results for lowest lying resonance for plasma-free cases as well as in weakly coupled plasmas are in excellent agreement with the established results in the literature. An extensive study is carried out to explore the changes in the resonance parameters of the three states due to the effects of plasma NI. It is found that, for a given Debye length, the resonance energy increases, and the resonance width decreases with increasing plasma non-ideality.

Measurements and Modeling of a Monolithically Integrated Self-Spiking Two-Section Laser in InP

The self-spiking behavior of an integrated saturable absorber and gain section laser fabricated in an InP technology platform is analyzed. The gain, absorber and intensity dynamics are first inspected using the normalized Yamada model. This model shows excitable behavior as well as the relative refractory period, both of which are also present in biological neurons. Measurements of a two-section laser show irregular spike generation on the millisecond timescale, with a saturable absorber voltage controlled spike density. From our simulations, and from the quasi-random character and millisecond timescale at which these pulses occur, we conclude the laser is triggered by noise, an important characteristic in the operation of biological neurons. Simulations of the laser around the excitability threshold using a newly proposed model with an optical noise term show qualitatively similar self-spiking behavior as measured.

A mechanical-free designing method for tailoring nonlinearity in bi-stable piezoelectric energy harvesters

This paper presents a mechanical-free method for providing and tailoring the nonlinear force in bistable piezoelectric energy harvesters (BPEHs). The nonlinear force can be tailored to obtain a lower threshold for inter-well motions, or for the harvester to operate at various excitation levels and frequencies without changing the mechanical structure or the overall assembly. In BPEHs, the nonlinear force is tailored to match a specific excitation level and frequency, and the mechanical structure is designed to achieve higher strain (and thus higher output power). The design of nonlinearity can be separated from the design of the mechanical structure by using magnetic interactions. Hence, the design of nonlinearity is the arrangement of the external magnetic field of the harvester. In this paper, arranging the external magnetic field is achieved by arranging the magnetization distribution of one external magnet. With the locally demagnetizing technique, a uniformly magnetized permanent magnet can be locally demagnetized with desired patterns. The external magnetic field is provided by a locally demagnetized permanent magnet (LDPM). The nonlinear force can be tailored by simply altering the properties of the LDPM. This method converts the design of providing and tailoring the nonlinear force into the design of the LDPMs. For demonstration, we show that without increasing the distance between magnets, the potential barrier of the bistable system is dramatically reduced by using LDPMs. Melnikov’s method is utilized to show that the energy harvesters with LDPMs possess a lower threshold for homoclinic tangency than energy harvesters with a normal magnet. The influence of the parameters of the LDPMs on the energy harvesting performance is studied via simulations and experiments. Results show that without violating the mechanical part, changing the locally demagnetizing patterns can effectively change the harvester’s working frequency and excitation threshold.

ANALYSIS OF BIOELECTRIC CHANGES IN THE NERVE – MUSCULAR COMPLEX UNDER THE CONDITIONS OF SHOCK WAVE INFLUENCE

Abstract. Recently, multimodal neurophysiological monitoring has been widely implemented in medical practice, thanks to which a powerful diagnostic base, additional possibilities of intensive therapy, surgical treatment and signifi cant improvement of its results are provided.In our experiment, as a result of the analysis of bioelectrical changes in the neuromuscular complex under the conditions of shock wave exposure, distinct changes in the functioning of the neuromuscular complex were observed, which were manifested in an increase in the excitation threshold under conditions of both direct and indirect stimulation of the calf muscle, reduction of the latent period and chronaxia with indirect stimulation and increase in the amplitude of the action potential. Blast injury leads to changes in refractoriness phases, there is a signifi cant increase in the amplitude of the action potential in response to the second stimulus. Under the conditions of simulation of the action of the shock wave, reliable changes in the conditioned bioelectric activity of the calf muscle develop, which is manifested in increased excitability, a decrease in the degree of synchronization of the response of the muscle under study, and a slowing of its response to indirect stimulation.On the day of the explosive injury, a more than two-fold increase in the amplitude of the evoked response of the calf muscle was observed, after a week this indicator showed a tendency to normalize, and after two weeks of the model’s existence it was only 140 % of the average value in the control group.Progressive changes in the bioelectrical activity of the neuromuscular apparatus reach a maximum after one week and do not level off completely after two weeks after the injury. In addition, primary damage, such as microvascular damage and neuroinfl ammation, do not play a major role in the occurrence of neurophysiological disorders, as they are present only in the initial period after the injury, but almost disappear after fourteen days.

The effect of prolonged emotional and pain stress on the expression of the <i>bdnf</i> gene in the brain of rats with contrast excitability of the nervous system

BACKGROUND: The neurotrophic factor BDNF performs important functions in synaptic plasticity and functional activity of neurons, involve in the stress response and the pathogenesis of post-stress disorders. The specificity of post-stress changes in the bdnf mRNA level due to genetically determined features of excitability of the nervous system has not been studied.
 AIM: To study the level of bdnf mRNA in the prefrontal cortex, hippocampus and amygdala of rats of two strains with contrasting excitability of the nervous system in normal condition and at different times after prolonged emotional and painful stress exposure (after 24 hours, 7, 24, 60 days).
 MATERIALS AND METHODS: The study was carried out on adult male rats of two strains with a different level of excitability of the nervous system (HT high threshold and LT low threshold of excitability). As a model of chronic stress, a long-term emotional and painful exposure according to Hecht was used. The bdnf mRNA level was determined using quantitative real-time PCR. Changes in the level of bdnf mRNA in the prefrontal cortex, hippocampus and amygdala of control and experimental groups of rats of two strains were studied at different time points (24 hours, 7, 24 days, 2 months) after prolonged emotional and painful stress exposure.
 RESULTS: It was found that in highly excitable LT rats, a decrease in the expression of the bdnf gene in the prefrontal cortex occurs 24 hours and persists up to 7 days after exposure, in the hippocampus 2 months after exposure. In rats of the low-excitable HT strain, the decrease in bdnf mRNA was not detected.
 CONCLUSIONS: In highly excitable LT rats, prolonged emotional and painful stress causes a decrease in the expression of the bdnf gene in the prefrontal cortex and hippocampus. In low-excitable rats of the HT strain, no significant decrease in the mRNA level of this neurotrophin was found in any of the studied brain regions. The possible association of this specificity of changes in the level of bdnf mRNA with a greater severity of post-stress anxiety-like behavior disorders in highly excitable rats compared with low-excitable ones is discussed.

Optical Gain Switching by Thermo‐Responsive Light‐Emitting Nanofibers through Moisture Sorption Swelling

AbstractThe development of intelligent photonic systems made of stimuli‐responsive materials, i.e., with features tunable and switchable by environmental signals, is gaining increasing attention. Here, the study reports on switchable optical gain based on complex arrays of nanofibers made of thermo‐responsive poly(2‐n‐propyl‐2‐oxazoline), incorporating a blue‐emitting chromophore. The fluorescent component endows the nanofibers with optical gain in addition to the moisture absorption capability of the polymer. Light amplification is found with temperature‐ and humidity‐dependent excitation threshold. The threshold value is halved close to the polymer cloud point temperature, enabling reversible switching of the emission intensity upon temperature change. Waveguiding analysis by back‐focal plane imaging on individual fibers allows the switching mechanisms to be rationalized, in terms of moisture sorption swelling‐induced morphological changes. These responsive light‐emitting nanofibers may find application in a novel class of lasers with dynamically‐controlled properties, environmentally‐switchable optoelectronics, and smart sensors.

Study on excitation threshold of strong modulation response and vibration suppression performance of bistable nonlinear energy sink

The dynamics and vibration reduction performance of bistable nonlinear energy sink (BNES) are studied in this paper. First, the negative stiffness of BNES is realized by geometric nonlinearity, and the dynamics model of the system is established. The slow flow equation of the system under 1:1 main resonance is analyzed based on the complexification-averaging (CX-A) method, and the boundary conditions of saddle node bifurcation and Hopf bifurcation are analyzed. Second, the slow invariant manifold (SIM) of the BNES is studied based on multiscale analysis, and the excitation threshold of strongly modulated response (SMR) is analyzed; the analysis results are verified by the numerical method. The results show that the analytical solution is highly consistent with the numerical solution, and the error is less than 1%. Finally, the influence of structural parameters on the vibration reduction performance is analyzed and optimized. The vibration reduction performance of BNES and CNES is compared, and the results show that the BNES has better vibration reduction performance in the full frequency band.

The potential role of astroglial GABAA receptors in autoimmune encephalitis associated with GABAA receptor antibodies and seizures.

The γ-aminobutyric acid (GABA) is the main inhibitory transmitter in the central nervous system and GABA receptors mediate the inhibitory synaptic transmission. GABA binding to neuronal GABAA R leads to a rapid hyperpolarization and a higher excitation threshold due to an increase in membrane Cl- permeability. The synaptic GABAA R is mostly composed of two α(1-3), two β, and one γ subunit with the most abundant configuration α1β2γ2. Recently, antibodies (Abs) against α1, β3, and γ2 subunits of GABAA R were detected in a severe form of autoimmune encephalitis with refractory seizures, status epilepticus, and multifocal brain lesions, affecting gray and white matter. Experimental studies confirmed multiple mechanisms and direct functional effects of GABAA R Abs on neurons with decreased GABAergic synaptic transmission and increased neuronal excitability. The expression of GABAA R on astrocytes is well established. However, extensive studies about the effects of autoimmune GABAA R Abs on astrocytic GABAA R are missing. We hypothesize that GABAA R Abs may lead additionally to blocking astrocytic GABAA Rs with impaired Ca2+ homeostasis/spreading, astrocytic Cl- imbalance, dysfunction of astrocyte-mediated gliotransmission (e.g., decreased adenosine levels) and accumulation of excitatory neurotransmission, all this contributing to seizures, variable clinical/MRI presentations, and severity. The most abundant expressed GABAA R subunits in rodent astrocytes are α1, α2, β1, β3, and γ1 localized in both white and gray matter. Data about GABAA R subunits in human astrocytes are even more limited, comprising α2, β1, and γ1. Overlapping binding of GABAA R Abs to neuronal and astroglial receptors is still possible. In vitro and in vivo animal models can be helpful to test the effects of GABAA R Abs on glia. This is from an epileptological point of view relevant because of the increasing evidence, confirming the glial involvement in the pathogenesis of epilepsy. Taken together, autoimmune disorders are complex and multiple mechanisms including glia could contribute to the pathogenesis of GABAA R encephalitis with seizures.

Rapid, activity-dependent co-release of GABA and glycine in the mouse brainstem

Presympathetic neurons in the ventrolateral and ventromedial medulla (VLM/VMM) control the sympathetic tone, and GABA was identified as a primary mechanism for sympathoinhibition. Intriguingly, there is evidence that both GABA and glycine efficiently inhibit sympathetic tone; however, the mechanism of glycine release is unknown. In this study, we tested the hypothesis that GABA and glycine are co-released in the VLM/VMM. Glycine is recycled by glycine transporter 2 (GlyT2), which is a reliable marker of glycinergic neurons. Therefore, we crossed heterozygous GlyT2Cre mice with floxed channelrhodopsin 2 (ChR2-EYFP) mice to generate GlyT2 reporter mice (GlyT2ChR2/EYFP), which were used to determine the mechanism of glycine release and reveal the location of glycinergic neurons. Whole-cell patch-clamp recordings from presympathetic VLM/VMM neurons revealed that GABA mediates most spontaneous inhibitory postsynaptic currents (sIPSCs); whereas increased activity of inhibitory inputs promotes the release of glycine. Light stimulation of glycinergic fibers expressing ChR2 in GlyT2ChR2/EYFP mice evoked IPSCs (eIPSCs) with glycinergic and GABAergic components. Bath application of GABAA receptors antagonist (bicuculline, 10 μM) decreased the amplitude of eIPSCs, suggesting that approximately 70% of the eIPSCs are generated by glycine. Moreover, blockade of GlyT2 partially diminished the glycinergic component of the light-evoked IPSCs. Using GlyT2ChR2/EYFP mice, we found that glycinergic fibers are abundant throughout the rostral brainstem, and GlyT2-expressing neurons were distributed within the ventral gigantocellular nucleus and medial reticular formation. Immunofluorescence labeling of glycine receptor subunits in the VLM/VMM revealed the expression of two prevalent forms of glycine receptors formed by α1 and α3. In summary, we found that GABA and glycine are co-released in the VLM/VMM, and blockage of GlyT2 decreased the amplitude of light-evoked IPSCs, suggesting that GABA and glycine are likely located in separate vesicles. Our data provide evidence for the co-inhibition of presympathetic neurons in the VLM/VMM by GABA and glycine and suggest that GABA controls the threshold excitability, while glycine is released on demand to increase the strength of inhibition. Supported by: NIDDK122842 and Tulane Brain Institute Marko Spark Innovation Research Fund This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Artificial Ducts Created via High-Power HF Radio Waves at EISCAT

Ducts (field-aligned plasma density enhancements) provide a link into the magnetosphere and can guide whistler waves. Inside ducts, wave-particle interactions occur efficiently; therefore, their presence contributes to the removal of energetic particles from the magnetosphere. We present experimental results concerning the characteristics, behavior, and excitation thresholds of ducts induced by extraordinary (X-mode) polarized high-power HF radio waves emitted towards the magnetic zenith (MZ) into the upper ionosphere at EISCAT (European Incoherent SCATter). The features and behavior of ducts were diagnosed by the EISCAT incoherent scatter radar (ISR) at Tromsø and the CUTLASS (SuperDARN) Finland radar at Hankasalmi. The state of the ionosphere was monitored by the Dynasonde in Tromsø. It was found that the electron density Ne enhancements inside ducts were of 50–80% above the background Ne values and their transverse size (normal to the magnetic flux tube) corresponded to about 3–4° in the north–south direction. They were generated during magnetically quiet periods and extended from ~300 to 320 km up to the upper altitude limit of the EISCAT radar measurements (600–700 km), when heater frequencies were both below and above the critical frequency of the F2 layer (fH ≤ foF2 and fH > foF2), regardless of whether HF-induced plasma and ion lines were generated or not. Comparing the O-/X-mode effects from the EISCAT radar observations, it was shown that the creation of the strong Ne ducts is a typical characteristic of the X-mode pulses. As a rule, electron density enhancements were not observed during O-mode pulses. A plausible mechanism for the creation of X-mode artificial ducts is discussed.

Bound states in nonuniform superconductors

This paper shows that the WKB quantization rule is suitable for the Andreev bound states in nonuniform superconductors. We consider nonhomogeneous superconductivity gap functions $\mathrm{\ensuremath{\Delta}}(x)$ in superconductors with the Bogoliubov quasiparticle energy $E$, the Fermi level ${E}_{F}$, and the total momentum $\mathbf{p}$ at ${E}_{F}+E$. The Andreev bound states in the well of slowly varying $|\mathrm{\ensuremath{\Delta}}(x)|$ are studied, and the well may also be induced by the phase variation of $\mathrm{\ensuremath{\Delta}}(x)$ for massless Dirac fermions. By applying the WKB method to the Bogoliubov--de Gennes equation, we obtain two main results: (i) For ${E}_{F}\ensuremath{\sim}0$, the bound states are determined by ${\ensuremath{\int}}_{{L}_{E}}^{{R}_{E}}|\mathbf{p}\phantom{\rule{0.16em}{0ex}}d\mathbf{x}|=(\frac{1}{2}+n)\ensuremath{\pi}\ensuremath{\hbar}$, where $n\ensuremath{\in}{\mathbb{N}}_{0}$ and ${L}_{E}$ and ${R}_{E}$ are the boundary points between the classically allowed region and forbidden regions, and (ii) for ${E}_{F}\ensuremath{\gg}E$ and $|\mathrm{\ensuremath{\Delta}}(x)|$, the bound states are given by ${\ensuremath{\int}}_{{L}_{E}}^{{R}_{E}}|\mathbf{p}\ifmmode\pm\else\textpm\fi{}{\mathbf{p}}_{F}|dx=(\frac{1}{2}+n)\ensuremath{\pi}\ensuremath{\hbar}$ with small ${p}_{y(z)}$. Empirical quantization conditions are provided for broader parameter regions. In addition to applying the traditional WKB method, we also develop a generalized WKB method to tackle semimetals with parabolic dispersion relationships. The applications of our results are discussed, for example, Dirac $\ensuremath{\pi}$ junctions or nonchiral Majorana wires, SNS junctions, the excitation threshold, and the tunneling rate in NSN junctions. In the $\ensuremath{\pi}$ junction, the Majorana zero modes correspond to the zero-point energy in the WKB formalism. This observation may provide insights into the Majorana bound state in a vortex and the Majorana fermions in high-energy physics.

Spectroscopic investigation of atmospheric pressure cold plasma jet produced in dielectric barrier discharge

Non-thermal cold atmospheric pressure plasma jet (APPJ) produced in multi-pulse dielectric barrier discharge (DBD) preferentially heats the electrons that subsequently transfer their energy to the other plasma species converting them into reactive species. Therefore the characterization of different energy groups of electrons is essential for efficient production and control of reactive plasma species contributing to surface modifications. Here we present the spectroscopic investigations of the APPJ produced in multi-pulse DBD using pin electrode configuration. Boltzmann plot relates the emission intensities of the several Ar–I spectral lines to their corresponding threshold excitation energies to give the electron temperature more precisely. The Stark broadening of the Ar–I (696.54 nm) line profile gives the electron number density after de-convoluting the contributions of the Doppler and instrumental broadenings. Plasma measurements correlate the gas flow rate, applied jet power across the electrodes, and a group of electrons contributing to optical emission. Sequential imaging correlates the size of the plasma bullets momentarily with the discharge pulse for different argon flow rates and applied jet powers. With an increasing flow rate of up to 1.4 L/min, the plasma plume of the jet becomes more elongated, intense, and spatially uniform. However, the glow intensity and size of the plume start reducing with a further increase in gas flow rate. Experimental findings propose plasma processing for small-scale localized plasma surface treatments.

Localized Bound Multiexcitons in Engineered Quasi-2D Perovskites Grains at Room Temperature for Efficient Lasers.

Reducing the excitation threshold to minimize the Joule heating is critical for the realization of perovskite laser diodes. Although bound excitons are promising for low threshold laser, how to generate them at room temperature for laser applications is still unclear in quasi-2D perovskite-based devices. In this work, via engineering quasi-2D perovskite PEA2 (CH3 NH3 )n -1 Pbn Br3 n +1 microscopic grains by the anti-solvent method, room-temperature multiexciton radiative recombination is successfully demonstrated at a remarkably low pump density of 0.97 µJ cm-2 , which is only one-fourth of that required in 2D CdSe nanosheets. In addition, the well-defined translational momentum in quasi-2D perovskite grains can restrict the Auger recombination which is detrimental to radiative emission. Furthermore, the quasi-2D perovskite grains are favorable for increasing binding energies of excitons and biexcitons and so as the related radiative recombination. Consequently, the prepared <n= 8> phase quasi-2D perovskite film renders a threshold of room-temperature stimulated emission as low as 13.7 µJ cm-2 , reduced by 58.6% relative to the amorphous counterpart with larger grains. The findings in this work are expected to facilitate the development of solution-processable perovskite multiexcitonic laser diodes.

Non-Parametric Nonlinear Parameter-Varying Parallel-Cascade Identification of Dynamic Joint Stiffness.

The paper presents a method to identify ankle joint dynamic stiffness during functional tasks where intrinsic and reflex stiffness change with a time-varying scheduling variable (SV), such as joint position or torque. The method models joint stiffness with two pathways: (1) A parameter-varying (PV) impulse response function (IRF) describing intrinsic stiffness; and (2) a reflex stiffness model comprising a PV static nonlinearity followed by a PV linear element. Monte-Carlo simulations demonstrated that the method accurately estimated all elements of the intrinsic and reflex pathways as they changed with a SV. Experimental results with a healthy individual subjected to large, imposed ankle movements demonstrated that: (a) Intrinsic stiffness changed substantially as a function of ankle position; elasticity was lowest near the mid-position and increased with either dorsiflexion or plantarflexion. (b) Reflex gain increased and the velocity threshold for reflex excitation decreased monotonically with ankle dorsiflexion. (c) Reflex dynamics resembled a second-order, low-pass system that was invariant with ankle position. (d) The identified PV Parallel-Cascade (PC) model accurately predicted the torque response to novel trajectories of ankle movement. The PV-PC method can accurately and reliably estimate how intrinsic and reflex stiffness change with a time-varying SV. The method is novel with multiple advantages: (a) It provides a unified algorithm that characterizes the changes in the parameters of all joint stiffness elements needed to understand their role in postural/movement control; (b) It is efficient requiring only two trials; (c) The models identified can predict the joint stiffness response to novel movements informing orthoses and prostheses design.

The Effect of Prolonged Emotional and Painful Stress on the Expression of Proinflammatory Cytokine Genes in Rats with High and Low Excitability of the Nervous System

Stress plays an important role in the pathogenesis of anxiety and depressive disorders. Neuroinflammation is considered as one of the mechanisms by which stress alters the molecular and cellular plasticity in the nervous tissue, which leads to a violation of the functions of the central nervous system. The contribution of genetically determined features of the nervous system to the development of post-stress neuroinflammation has not been sufficiently studied. In this study, the dynamics of poststress changes in the mRNA levels of the il1ß and tnf genes of proinflammatory cytokines interleukin-1-beta (IL-1ß) and tumor necrosis factor (TNF) in the blood and in the brain in two rat strains with high and low excitability thresholds of the nervous system (HT and LT) was evaluated. Changes in IL-1ß and TNF mRNA levels were assessed by real-time PCR 24 h, 7, 24 and 60 days after prolonged emotional and painful stress in the blood and three brain structures involved in the development of post-stress pathology (prefrontal cortex, hippocampus, amygdala). In highly excitable rats of the LT strain, the level of IL-1ß mRNA in the hippocampus and amygdala increased compared to the control 24 days after the end of stress, in low-excitable animals of the HT strain, an increase in the level of IL-1ß mRNA was detected only in the hippocampus at the same time. The TNF mRNA level did not change in any of the strains at any of the time points after stress. Genetically determined excitability of the nervous system is a promising marker of individual vulnerability to stress, manifested in post-stress disorders associated with the characteristics of the formation and dynamics of neuroinflammation.

Retinal ganglion cells adapt to ionic stress in experimental glaucoma.

Identification of early adaptive and maladaptive neuronal stress responses is an important step in developing targeted neuroprotective therapies for degenerative disease. In glaucoma, retinal ganglion cells (RGCs) and their axons undergo progressive degeneration resulting from stress driven by sensitivity to intraocular pressure (IOP). Despite therapies that can effectively manage IOP many patients progress to vision loss, necessitating development of neuronal-based therapies. Evidence from experimental models of glaucoma indicates that early in the disease RGCs experience altered excitability and are challenged with dysregulated potassium (K+) homeostasis. Previously we demonstrated that certain RGC types have distinct excitability profiles and thresholds for depolarization block, which are associated with sensitivity to extracellular K+. Here, we used our inducible mouse model of glaucoma to investigate how RGC sensitivity to K+ changes with exposure to elevated IOP. In controls, conditions of increased K+ enhanced membrane depolarization, reduced action potential generation, and widened action potentials. Consistent with our previous work, 4 weeks of IOP elevation diminished RGC light-and current-evoked responses. Compared to controls, we found that IOP elevation reduced the effects of increased K+ on depolarization block threshold, with IOP-exposed cells maintaining greater excitability. Finally, IOP elevation did not alter axon initial segment dimensions, suggesting that structural plasticity alone cannot explain decreased K+ sensitivity. Thus, in response to prolonged IOP elevation RGCs undergo an adaptive process that reduces sensitivity to changes in K+ while diminishing excitability. These experiments give insight into the RGC response to IOP stress and lay the groundwork for mechanistic investigation into targets for neuroprotective therapy.

Oscillator strengths and cross sections of the valence-shell excitations of CH[formula omitted]I studied by fast electron scattering

Oscillator strengths and cross sections of the valence-shell excitations in CH3I are important for studying molecular photodissociation and monitoring the destruction of ozone in the Earth’s atmosphere. Based on the relative flow technique, absolute generalized oscillator strengths of the valence-shell excitations in CH3I have been determined by using an angle-resolved electron energy loss spectrometer. The measurement was carried out at an incident electron energy of 1.5 keV and an energy resolution of 80 meV. Optical oscillator strengths for the dipole-allowed transitions have been obtained at the zero limit of the squared momentum transfer, providing an independent cross check with the previous experimental results. The integral cross sections from the excitation threshold to 5000 eV have also been obtained by means of the BE-scaling method. The present experimental oscillator strengths and cross sections can supplement the fundamental spectroscopic data of CH3I and will play an important role in the studies of molecular photodissociation dynamics.

Influence of low temperature on white light emission from graphene-based microchip

The laser-induced white emission of the graphene-based microchip was investigated under near-infrared region laser irradiation. The emission was characterized by an excitation threshold and an exponential dependence on the pump laser power. A decrease in temperature caused an increase in both the number of absorbed photons and the emission threshold. This dependence can be explained by the multiphoton ionization process in (sp2, sp3) hybridized domains.

Laser induced emission of NdAlO3 nanocrystals in vacuum, air, and liquid N2

The broadband laser induced white emission (LIWE) spectra of NdAlO3 nanocrystals in vacuum, air, and liquid N2 were explored. In particular, their dependence on excitation laser power was investigated. It was found that the LIWE spectra intensity increased exponentially the with laser power above the excitation threshold in all three cases. The process for NdAlO3 nanocrystals was discussed in terms of multiphoton ionization assisted by ejection of hot electrons. Two differences were observed depending on the conditions: the number of photons involved in the emission was higher in liquid N2 due to additional multiphoton ionization contribution of N2. Also, threshold value for LIWE showed an increasing behavior in air and liquid N2, discussed in terms of relative permittivity and thermal dissipation.