Large Decay Time Research Articles

Modulation of large rhythmic depolarizations in human large basket cells by norepinephrine and acetylcholine

Rhythmic brain activity is critical to many brain functions and is sensitive to neuromodulation, but so far very few studies have investigated this activity on the cellular level in vitro in human brain tissue samples. This study reveals and characterizes a novel rhythmic network activity in the human neocortex. Using intracellular patch-clamp recordings of human cortical neurons, we identify large rhythmic depolarizations (LRDs) driven by glutamate release but not by GABA. These LRDs are intricate events made up of multiple depolarizing phases, occurring at ~0.3 Hz, have large amplitudes and long decay times. Unlike human tissue, rat neocortex layers 2/3 exhibit no such activity under identical conditions. LRDs are mainly observed in a subset of L2/3 interneurons that receive substantial excitatory inputs and are likely large basket cells based on their morphology. LRDs are highly sensitive to norepinephrine (NE) and acetylcholine (ACh), two neuromodulators that affect network dynamics. NE increases LRD frequency through β-adrenergic receptor activity while ACh decreases it via M4 muscarinic receptor activation. Multi-electrode array recordings show that NE enhances and synchronizes oscillatory network activity, whereas ACh causes desynchronization. Thus, NE and ACh distinctly modulate LRDs, exerting specific control over human neocortical activity.

Direction of arrival estimation in reverberant environments using a single vibration sensor on an elastic panel

The vibrational response of an elastic panel to an incoming acoustic pressure wave is dependent on the coupling between the incident angle and the panel’s bending modes. By examining the relative modal excitations recorded by a single structural vibration sensor affixed to the panel, the direction of arrival (DOA) of the incident wave may be inferred. In reverberant environments, determination of the DOA of a sound source is complicated by acoustic reflections. Panel microphones may be particularly susceptible to this effect due to their large surface areas and finite modal decay times. A study on the impact of reverberation on DOA estimation using panel microphones was conducted. The panel’s response to wake word utterances was recorded in eight spaces, with reverberation times (RT60s) ranging from 0.27 to 3.00 s. These responses were used to train neural networks for DOA estimation. Results indicate an inverse relationship between RT60 and DOA estimation reliability. Within ±5°, DOA estimation reliability was measured at 95% in the least reverberant space and decreased to 78% in the most reverberant space. Results also suggest that DOA estimation using panel microphones can adapt to diverse acoustic environments by training the system with data from multiple spaces with different RT60s.

Continuation analysis of overhung rotor bouncing cycles with smooth and contact nonlinearities

Time simulation has been widely used when investigating the nonlinear response of rotating machines, due to its relative simplicity. However, this approach is computationally inefficient due to large transient decay times and the need to repeat the analysis for multiple drive speeds and initial conditions, and is incomplete because of its inability to give information about unstable responses. Alternatively, the numerical continuation method can be used to explore the nonlinear behaviour of such systems in a more systematic and efficient way. In rotating machinery, tighter tolerances are valued for efficiency, making the rotor–stator contact phenomenon a priority for research. Various cases including rigid and very compliant contact stiffness models have been investigated in the literature, in many cases showing responses similar to that of smooth nonlinearities such as cubic stiffness. This knowledge has been used in the present study to transform the bifurcation diagram of a simpler nonlinearity (cubic) to a more complex one (contact represented by bilinear stiffness approximated using a tanh formulation) through a homotopy of the nonlinear restoring forces present in the system definition. A 2-dof overhung rotor with gyroscopic effects is used in the investigation of quasiperiodic bouncing cycles that appear periodic in the rotating frame. This work not only provides more insight into the behaviour of nonlinear rotor–stator contact responses, but also demonstrates the numerical continuation method as a potential tool to explore the nonlinear rotating system’s response in a more structured manner.

Parametric Simulation Studies on the Wave Propagation of Solar Radio Emission: The Source Size, Duration, and Position

Abstract The observed features of the radio source indicate that the waves of solar radio bursts are convoluted with complex propagation effects. In this work, we perform ray-tracing simulations on radio wave transport in the corona and interplanetary region with anisotropic electron density fluctuations. For the first time, the variation of the apparent source size, burst duration, and source position for the fundamental emission and harmonic emission at the frequency of 35 MHz are simulated as a function of the anisotropic parameter α and the angular scattering rate coefficient η = ϵ 2/h 0, where ϵ 2 = 〈δ n 2〉/n 2 is the density fluctuation level and h 0 is its correlation length near the wave excitation site. It is found that isotropic fluctuations produce a much larger decay time than a highly anisotropic fluctuation for fundamental emission. By comparing the observed duration and source size with the simulation results in the parameter space, we can estimate the scattering coefficient and the anisotropic parameter η = 8.9 × 10−5 km−1 and α = 0.719 with a point pulse source assumption. Position offsets due to wave scattering and refraction can produce the co-spatial of the fundamental and harmonic waves in the observation of some type III radio bursts. The visual speed due to the wave propagation effect can reach 1.5c for η = 2.4 × 10−4 km−1 and α = 0.2 for the fundamental emission in the sky plane, accompanied with large expansion rate of the source size. The direction of the visual speed is mostly identical to the direction of the offset, thus, for the observation aimed at obtaining the source position, the source centroid at the starting time is closer to the wave excitation site.

Fluorescent 1-hydroxy-10-alkylacridin-9(10H)-one BF2-chelates: Large Stokes shift and long emission decay times

New 1-hydroxy-10-alkylacridin-9(10H)-one BF2-chelates absorb in the blue-green part of the electromagnetic spectrum and emit fluorescence with moderate quantum yields of 8–45% in toluene. The dyes show large Stokes shifts about 4300 cm−1, decay times between 5 ns and 15 ns in toluene and high photostabilities. Introduction of a fluorine atom into the acridone cycle results in an increase of the fluorescence quantum yield and decay time whereas immobilization in a rigid polymer matrix (polystyrene) further extends the lifetime up to 18 ns. Large Stokes shifts and long emission decay time make this dye class an interesting platform for time-resolved imaging and sensing applications.

Band Gap Adjustment in Perovskite-type Eu1−xCaxTiO3via Ammonolysis

AbstractPerovskite-type oxynitridesAB(O,N)3are potential candidates for photoelectrode materials in solar water splitting. A drawback of these materials is their low sintering tendency resulting in low electrical conductivities. Typically, they are prepared by ammonia treatment of insulating, wide band gap oxides. In this study, we propose an approach starting from small band gap oxides Eu1−xCaxTiO3−δand then widen the band gaps in a controlled way by ammonolysis and partial Ca2+substitution. Both together induced a distortion of the octahedral network and dilution of the Eu4fand N2plevels in the valence band. The effect is the stronger the more Ca2+is present. Within the series of samples, Eu0.4Ca0.6Ti(O,N)3had the most suitable optical band gap (EG≈ 2.2 eV) for water oxidation. However, its higher Eu content compared to Eu0.1Ca0.9Ti(O,N)3slowed down the charge carrier dynamics due to enhanced trapping and recombination as expressed by large accumulation (τon) and decay (τoff) times of the photovoltage of up to 109 s and 486 s, respectively. In contrast, the highly Ca2+-substituted samples (x≥ 0.7) were more prone to formation of TiN and oxygen vacancies also leading to Ti3+donor levels below the conduction band. Therefore, a precise control of the ammonolysis temperature is essential, since even small amounts of TiN can suppress the photovoltage generation by fast recombination processes. Water oxidation tests on Eu0.4Ca0.6Ti(O,N)3revealed a formation of 7.5 μmol O2from 50 mg powder together with significant photocorrosion of the bare material. Combining crystal structure, chemical composition, and optical and electronical band gap data, a first simplified model of the electronical band structure of Eu1−xCaxTi(O,N)3could be proposed.

Air-Coupled and Resonant Pulse-Echo Ultrasonic Technique.

An ultrasonic, resonant, pulse-echo, and air-coupled nondestructive testing (NDT) technique is presented. It is intended for components, with regular geometries where it is possible to excite resonant modes, made of materials that have a high acoustic impedance (Z) and low attenuation coefficient (α). Under these conditions, these resonances will present a very large quality factor (Q) and decay time (τ). This feature is used to avoid the dead zone, produced by the echo coming from the first wall, by receiving the resonant echo from the whole specimen over a longer period of time. This echo is analyzed in the frequency domain to determine specimen resonant frequency, which can be further used to determine either velocity or thickness. Using wideband air-coupled transducers, we tested the technique on plates (steel, aluminum, and silicone rubber) by exciting the mode of the first thickness. As expected, the higher the Z and the lower the α, the better the technique performed. Sensitivity to deviations of the angle of incidence away from normal (±2°) and the possibility to generate shear waves were also studied. Then, it was tested on steel cylindrical pipes that had different wall thicknesses and diameters. Finally, the use of this technique to generate C-Scan images of steel plates with different thicknesses was demonstrated.

Temporal disorder in discontinuous nonequilibrium phase transitions: General results

We develop a general theory for discontinuous non-equilibrium phase transitions into an absorbing state in the presence of temporal disorder. We focus in two paradigmatic models for discontinuous transitions: the quadratic contact process (in which activation is only spread when two nearest- neighbor sites are both active) and the contact process with long-range interactions. Using simple stability arguments (supported by Monte Carlo simulations), we show that temporal disorder does not destroy the discontinuous transition in the former model. For the latter one, the first-order transition is turned into a continuous one only in the strong-disorder limit, with critical behavior belonging to the infinite-noise universality class of the contact process model. Finally, we have found that rare temporal fluctuations dramatically changes the behavior of metastable phase turning it into a temporal Griffiths inactive phase characterized by an exponentially large decay time.

Synthesis, characterization and mechanoluminescence properties of europium doped (1-x) MgO.xBaO-Al2O3:0.1 Eu (x = 0, 0.2, 0.4, 0.5, 0.6, 0.8, and 1.0) phosphor

A series of phosphor sample powders with varying concentrations of Magnesium and Barium concentration were prepared by high temperature solid state reaction method in air atmosphere. The phase formation of the calcined samples were confirmed by taking powder XRD and particle size of the sample powders were identified using SEM picture. The mechanoluminescent (ML) studies of each sample in the series were carried out via impact method. Variations in mechanoluminescence intensities were observed due to the variations in percentage compositions of magnesium and barium in the powder phosphors. The role of barium as sensitizer for enhancing ML intensities was undoubtfully proved and effort was taken to investigate about optimum concentration of barium for observing highest ML activity. The significant variations observed in ML intensities with stress variations and large decay time indicates the future scope of the sample for stress sensing applications. The Photoluminescence (PL) of the samples was studied using PL spectrum. The appreciable value of decay time and significant ML intensity variations of the sample with change in impact velocities highlights the future scope of the phosphor for stress sensing applications.

Electric Field-effect-assisted Persistent Photoconductivity In CZTS

CZTS thin film was deposited by co-sputtering metal targets and post deposition sulfurization in H2S. Temperature dependent electrical conductivity and photo conductivity effects in CZTS are studied. The low temperature electrical conductivity measurement shows acceptor level energy value as 36.85 meV. A large decay time of 108 s at 300K, 99 s at 200K and 94 s at 100K after switching off the light source was observed. The decay behavior of this persistent photoconductivity (PPC) in CZTS follows the double exponential function. The results show that defects are responsible for the observed PPC in CZTS. The combined measurements of low temperature electrical conductivity and photoconductivity give account of the defect level. Control of these defects can improve the quality of material and thus the resulting device. Copyright © 2015 VBRI press.

Noninstantaneous polarization dynamics in dielectric media

Third-order optical nonlinearities play a vital role for the generation and characterization of ultrashort optical pulses. One particular characterization method is frequency-resolved optical gating, which can be based on a large variety of third-order nonlinear effects. Any of these variants presupposes an instantaneous temporal response, as it is expected off resonance. In this paper we show that resonant excitation of the third harmonic gives rise to surprisingly large decay times, which are on the order of the duration of the shortest oscillator pulses generated to date. To this end, we measured interferometric third-harmonic frequency-resolved optical gating traces in TiO2 and SiO2, corroborating polarization decay times up to 6.5 fs in TiO2. This effect is among the fastest effects observed in ultrafast spectroscopy. Numerical solutions of the time-dependent Schrodinger equation are in excellent agreement with experimental observations. Our work (experiments and simulations) corroborates that a noninstantaneous polarization decay may appear in the presence of a 3-photon resonance. In turn, pulse generation and characterization in the ultraviolet may be severely affected by this previously unreported effect.

Splay states in networks of identical integrate-and-fire neurons

We develop an analytic framework to investigate the stability of splay states in infinite networks of identical integrate-and-fire neurons coupled through synaptic pulses. More specifically we perform a linear stability analysis of the splay state probability distribution whose dynamics is governed by an appropriate Fokker Planck equation. For exponentially decaying synaptic pulses the splay state is unstable for excitation and stable for inhibition. For excitatory alpha-function pulses the splay state becomes stable for sufficiently large decay times and we find an analytic expression for the boundary of stability. This large decay time stability is analogous to the stability of synchronous states for inhibition studied by van Vreeswijk, Abbott and Ermentrout [1]. For inhibitory alpha-function pulses the splay state is unstable, but for smaller decay times (when there is no stable synchronous state) the splay state exhibits a remarkable attracting meta-stable transient. We complement our analytic framework with numerical simulations on finite networks.

Assessment of ${\rm Lu}_{1.8}{\rm Gd}_{0.2}{\rm SiO}_{5}$ (LGSO) Scintillators With APD Readout for PET/SPECT/CT Detectors

Fusion of functional PET or SPECT images and anatomical X-ray CT images would ideally be performed using data recorded concurrently with the same detection system under all three modalities to avoid inaccurate co-registration due to patient movements and normal physiological processes like respiratory motion. One possible approach to achieve this goal is to use an avalanche photodiode (APD) based scintillation detection system. Requirements on scintillators for such an application are high density and high timing resolution for PET, good energy resolution for SPECT, large light output and fast scintillation decay time for counting mode X-ray CT. The purpose of this work is to investigate new Lu1.8Gd0.2SiO5:Ce (LGSO) scintillators with improved performance developed purposely for PET applications, but having suitable characteristics for SPECT and CT detection. LGSO with 90% Lu content has high density (7.3 g/cc), large light output (90-120% of Nal), good energy resolution (~10 - 12% @ 511 keV), and fast decay time that can be adjusted from 34 to 45 ns by varying Ce concentration. In this work, LGSO with 0.025, 0.15 and 0.75 mol% Ce was assessed with APD readout for PET/SPECT/CT applications by measuring energy spectra at 511 keV (PET), 140 keV (SPECT) and 60 keV (CT), and timing resolution in reference to a fast plastic scintillator. LGSO-APD detectors can be considered as promising candidates for combined multimodality imaging scanners.

High Dielectric Titanium Dioxide Doped Holographic PDLC

Conventional formulation of holographic polymer dispersed liquid crystal (HPDLC) has been doped with TiO2 nanoparticles. It was found that local electric field across the LC domain was effectively increased by the TiO2 inclusion in polymer, and the film was electrically driven. Typical inverted sigmoidal decrease to a constant value was obtained with and above 0.1 wt% TiO2. On the other hand TiO2 increased formulation viscosity, giving rise to slow grating formation, low saturation diffraction efficiency, and large decay time of the film. It was also found that resin composition of polyurethane acrylate (PUA)/N‐vinyl‐pyrrollidinone (NVP) = 1.5:1 (by weight) gave closer solubility parameter to TiO2, rapid grating formation, and lower switching voltage than PUA/NVP = 1:1 due to the high reactivity and closer solubility parameter of the resin to TiO2.

Photoinduced charge separation in pyrenedicarboxamide-linked DNA hairpins

The synthesis and photophysical properties of the dihydroxypropylamide derivative of pyrene-1,6-dicaboxamide, its aniline dyad, and DNA conjugates are reported. The dicarboxamide serves as a hairpin linker for bis(oligonucleotide) conjugates having short base pair stems. The dihydroxypropyl derivative has a large fluorescence quantum yield and long singlet decay time, as determined by fluorescence and time-resolved broad band pump-probe spectroscopy. The aniline dyad undergoes exergonic charge separation with formation of a radical ion pair which decays via charge recombination. The highly characteristic transient absorption spectrum of the pyrene anion radical is used to monitor the dynamics of its formation and decay. The dicarboxamide-linked hairpin conjugates undergo charge separation with adjacent guanine and adenine bases. Charge separation with guanine is accompanied by efficient pyrene fluorescence quenching. In contrast, reversible charge separation with adenine results in multiple exponential fluorescence decay. The energetics and dynamics of charge separation are compared with those of other arenedicarboxamide DNA hairpin linkers.

Modeling of a radial-flow moving-bed reactor for dehydrogenation of isobutane

A mathematical model for the performance of a radial-flow moving-bed reactor for dehydrogenation of light paraffins was developed. Assuming relevant kinetic expressions for the main reaction and catalyst deactivation, the kinetic parameters were obtained through lab-scale fixed-bed reactor testing using the integral method of analysis. The conversion was found to be a function of a dimensionless decay time, i.e., the ratio of a “catalyst deactivation time constant” to the residence time of the catalyst within the reactor. For a large dimensionless decay time (negligible catalyst decay), the performance equation approached that of a simple packed-bed reactor. The predictions of the model were compared with those of a commercial unit, and fair agreements were observed.

Stroboscopic detection of the 181Ta-Mössbauer resonance with synchrotron radiation

Stroboscopic detection of nuclear forward scattered synchrotron radiation is used to detect the high-resolution 6.2keV Mössbauer resonance of 181Ta in tantalum metal. It is shown that synchrotron timing modes with a bunch interval ideal for 57Fe (typically around 150ns) are perfectly suited for the investigation of systems with a much larger decay time.

Luminescence study on exciton relaxation in single crystals of symmetric diacetylenes

We have measured photoluminescence of the single crystals of symmetric diacetylenes with alkyl end groups. We found that the luminescence bands peaking around 2.6 eV are induced irrespective of the type of the end group. The 2.6-eV luminescence are characterized by large Stokes shifts and long decay time constants of 110 ms at 6 K. These characteristics are analogous to the 2.85-eV luminescence in 5,7-dodecadiyne-1,12-diole bis[phenyl carbamate] (DA-4Ph), in which it has been attributed to the recombination of the triplet self-trapped excitons. The results suggest that the excitons relax into the self-trapped exciton dominantly localized on the triple bonds. The 4.2-eV luminescence, which was tentatively assigned to the recombination luminescence of singlet self-trapped excitons in DA-4Ph, was not observed in the crystals used in the present study. It is inferred that the 4.2-eV luminescence is arising from the relaxed excited state localized at a phenyl ring.

Dephasing of a Superconducting Qubit Induced by Photon Noise

We have studied the dephasing of a superconducting flux qubit coupled to a dc-SQUID based oscillator. By varying the bias conditions of both circuits we were able to tune their effective coupling strength. This allowed us to measure the effect of such a controllable and well-characterized environment on the qubit coherence. We can quantitatively account for our data with a simple model in which thermal fluctuations of the photon number in the oscillator are the limiting factor. In particular, we observe a strong reduction of the dephasing rate whenever the coupling is tuned to zero. At the optimal point we find a large spin-echo decay time of .

The Influence of Drying on Quantitative Laser Fluorescence and Optical Pathlengths in Incipient Natural Caries Lesions

Drying effects in 14 natural lesions were studied with quantitative light-induced fluorescence and optical pathlength spectroscopy. Results were compared with clinical judgments of the lesion surface and microradiographical characterizations of the lesions. Relative fluorescence and average pathlength decreased as a function of drying time with a decay time ranging from 35.5 to <1 min. Depth and mineral loss correlated with average pathlength total changes (r = –0.79/–0.60, respectively) and poorly with total fluorescence changes (r 0.3). The decay time of the drying process for the relative fluorescence correlated well with a theoretical model based on water diffusion in lesion and surface layer, but only for large decay times. Clinical judgments could not be related to the surface layer properties or the changes in the average pathlength, but were weakly related to the changes in the relative fluorescence. We conclude that (i) fluorescence effects are mostly due to the screening by the lesion of the fluorescence from the dentin and enamel-dentin junction; (ii) water evaporation in lesions conforms to the diffusion laws only in large lesions with low surface layer penetrability; (iii) the evaporation process is controlled by the surface layer only for small surface penetrabilities (≈ 0.1 vol% µm^–1).