Millisecond Time Domain Research Articles

Dodecanogram (DDG): Advancing EEG technology with a high- frequency brain activity measurement device

EEG measures electric potential changes in the scalp. Even though it has been associated with human thoughts, there has been no direct evidence. The problem with EEG is that it measures variations in current or electric potential in the millisecond time domain, where muscle movement strongly affects the readings. The millisecond time domain is equivalent to the kHz resonance signal generated by any dielectric resonator, and every single cell membrane resonates in this time range. So, the measurement of EEG could come simply from the skin and not from the brain. Therefore, we have advanced EEG technology with the dodecanogram (DDG), which reveals 12 frequency bands or 12 discrete time regions where brain activities are most significant. We measure brain activity using a stream of pulses and a logic analyzer that counts ultra-short pulses needed to emulate brain scalp potential changes. We have created another version of DDG where, using an array of RLC (resistor-inductor-capacitor) resonators, we sense the ultra-low-power electromagnetic radiation from different locations on the brain's surface. Since we measure signals from Hz to THz, covering 12 orders of time ranges as a property of dielectric resonance, unlike EEG, there is a high probability that the DDG signal may truly originate from the brain. We have monitored DDG on an artificial organic brain replica 24/7 for over a year and on multiple human subjects, before and after meditation and concluded that most cognitive, perceptive, and emotional bursts occur around 200-700 nanoseconds, not milliseconds, as it was believed for 150 years of EEG era.

Identification of a Functionally Efficient and Thermally Stable Outward Sodium-Pumping Rhodopsin (BeNaR) from a Thermophilic Bacterium.

Rhodopsins are transmembrane proteins with retinal chromophores that are involved in photo-energy conversion and photo-signal transduction in diverse organisms. In this study, we newly identified and characterized a rhodopsin from a thermophilic bacterium, Bellilinea sp. Recombinant Escherichia coli cells expressing the rhodopsin showed light-induced alkalization of the medium only in the presence of sodium ions (Na+), and the alkalization signal was enhanced by addition of a protonophore, indicating an outward Na+ pump function across the cellular membrane. Thus, we named the protein Bellilinea Na+-pumping rhodopsin, BeNaR. Of note, its Na+-pumping activity is significantly greater than that of the known Na+-pumping rhodopsin, KR2. We further characterized its photochemical properties as follows: (i) Visible spectroscopy and HPLC revealed that BeNaR has an absorption maximum at 524 nm with predominantly (>96%) the all-trans retinal conformer. (ii) Time-dependent thermal denaturation experiments revealed that BeNaR showed high thermal stability. (iii) The time-resolved flash-photolysis in the nanosecond to millisecond time domains revealed the presence of four kinetically distinctive photointermediates, K, L, M and O. (iv) Mutational analysis revealed that Asp101, which acts as a counterion, and Asp230 around the retinal were essential for the Na+-pumping activity. From the results, we propose a model for the outward Na+-pumping mechanism of BeNaR. The efficient Na+-pumping activity of BeNaR and its high stability make it a useful model both for ion transporters and optogenetics tools.

The effect of low temperature on the explosion characteristics of a methane/air mixtures

Prevention and mitigation of unwanted explosions require knowledge of explosion characteristics. Available explosion data are not always adequate for use in a particular application. For example, predicting the behavior of gas explosions at a lower temperature should be based on the explosion data obtained at these temperatures and not atmospheric. Basic knowledge of the methane explosions at low temperatures is desirable for a thorough understanding of this gas that cannot be found in the literature. In the presented research, the methane/air deflagrations were studied in the millisecond time domain. The standard 20-L deflagration chamber was adopted to produce consistent and reproducible data for the comparison of atmospheric and low initial temperature measurements. Methane/air mixtures were studied experimentally for concentrations between 4.6 vol.% and 16.6 vol.% and two initial temperatures of 20 and −5 °C. More than three hundred and fifty pressure–time curves were recorded and analyzed. Twenty-five deflagration curves of the methane/air mixtures were studied in 20-L volume for the first time, including thirteen pressure–time curves at −5 °C. The effects of temperature on the maximum rate of pressure rise and deflagration index were investigated. The evaluated experiments’ results are the maximum pressure rise rate of 261 bar/s at −5 °C. This work allowed potential hazards involving the handling and storing of fuels. Many pieces of knowledge must be collected to advance the phenomenological understanding of low-temperature deflagrations to make realistic theoretical predictions and correlations.

Boost in Solid‐State Photon Upconversion Efficiency through Combined Approach of Melt‐Processing and Purification

Realization of efficient photon upconversion (UC) mediated by triplet–triplet annihilation (TTA) in a solid state is a great challenge, even though order of magnitude higher efficiencies are routinely reported in a solution/liquid state. To address this issue in a typical emitter/sensitizer UC system, a combined approach is introduced based on 1) thorough emitter purification for reduced exciton quenching and 2) UC film fabrication via melt‐processing for attaining large emitter concentrations with suppressed aggregation. Emitter purification via vacuum sublimation is shown to reduce the number of both singlet and triplet quenchers as confirmed by fluorescence and UC quantum yield measurements along with the respective transient measurements performed on nanosecond and millisecond time domains. Application of this approach to the benchmark TTA‐UC system DPA/PtOEP is demonstrated to yield a record‐high UC efficiency (=8 ± 1%, out of maximum 50%) achieved at 40 wt% of DPA homogeneously dispersed in the PMMA host. Importantly, such high efficiency is accomplished in large‐area amorphous films, the most preferred for practical applications, and featuring low UC threshold (=5 mW cm−2) that is close to the solar irradiance. The presented approach describes the guidelines for boosting UC efficiency in the solid state, and generally, is applicable to any conventional TTA‐UC system.

Microsecond-Resolved Infrared Spectroscopy on Nonrepetitive Protein Reactions by Applying Caged Compounds and Quantum Cascade Laser Frequency Combs.

Infrared spectroscopy is ideally suited for the investigation of protein reactions at the atomic level. Many systems were investigated successfully by applying Fourier transform infrared (FTIR) spectroscopy. While rapid-scan FTIR spectroscopy is limited by time resolution (about 10 ms with 16 cm-1 resolution), step-scan FTIR spectroscopy reaches a time resolution of about 10 ns but is limited to cyclic reactions that can be repeated hundreds of times under identical conditions. Consequently, FTIR with high time resolution was only possible with photoactivable proteins that undergo a photocycle. The huge number of nonrepetitive reactions, e.g., induced by caged compounds, were limited to the millisecond time domain. The advent of dual-comb quantum cascade laser now allows for a rapid reaction monitoring in the microsecond time domain. Here, we investigate the potential to apply such an instrument to the huge class of G-proteins. We compare caged-compound-induced reactions monitored by FTIR and dual-comb spectroscopy by applying the new technique to the α subunit of the inhibiting Gi protein and to the larger protein-protein complex of Gαi with its cognate regulator of G-protein signaling (RGS). We observe good data quality with a 4 μs time resolution with a wavelength resolution comparable to FTIR. This is more than three orders of magnitude faster than any FTIR measurement on G-proteins in the literature. This study paves the way for infrared spectroscopic studies in the so far unresolvable microsecond time regime for nonrepetitive biological systems including all GTPases and ATPases.

Photochemistry of hexachloroosmate(IV) in ethanol.

The photochemistry of the OsIVCl62- complex in ethanol was studied by means of stationary photolysis, nanosecond laser flash photolysis, ultrafast pump-probe spectroscopy and quantum chemistry. The direction of the photochemical process was found to be wavelength-dependent. Irradiation in the region of the d-d and LMCT bands results in the photosolvation (with the wavelength-dependent quantum yield) and photoreduction of Os(iv) to Os(iii), correspondingly. The characteristic time of photosolvation is ca. 40 ps. Photoreduction occurs in the micro- and millisecond time domains via several Os(iii) intermediates. The nature of intermediates and the possible mechanisms of photoreduction are discussed. We believe that the lability of the photochemically produced Os(iv) and Os(iii) intermediates determines the synthetic potential of OsIVCl62- photochemistry.

Potential Step for Double-Layer Capacitances Obeying the Power Law.

Potential-step chronoamperometry was made at a platinum wire electrode in KCl aqueous solution at the aim of finding the behavior of the power law of the time or the constant phase element for the double-layer (DL) capacitances. The logarithmic current decays linearly with the time shorter than 0.1 ms, and then it obeys the power law in which it has a linear relation with the logarithmic time in the millisecond time domain. The transition from the exponential decay to the power law was expressed theoretically for the model of a series combination of the resistance and the DL capacitance. The expression predicts that the double logarithmic plots of the current–time provide a capacitance value at 1 s from the intercept, independent of the resistance. This prediction was demonstrated experimentally in KCl solutions of which concentrations ranged from 1 mM to 0.5 M. The capacitance can be evaluated simply by chronoamperometry on a 1 s time scale without considering any resistance effect. The capacitance values did not vary with the applied potential.

Generation of 8-oxo-7,8-dihydroguanine in G-Quadruplexes Models of Human Telomere Sequences by One-electron Oxidation.

The mechanistic aspects of one-electron oxidation of G-quadruplexes in the basket (Na+ ions) and hybrid (K+ ions) conformations were investigated by transient absorption laser kinetic spectroscopy and HPLC detection of the 8-oxo-7,8-dihydroguanine (8-oxoG) oxidation product. The photo-induced one-electron abstraction from G-quadruplexes was initiated by sulfate radical anions (SO4 ˙- ) derived from the photolysis of persulfate ions by 308nm excimer laser pulses. In neutral aqueous solutions (pH 7.0), the transient absorbance of neutral guanine radicals, G(-H)˙, is observed following the complete decay of SO4 ˙- radicals (~10μs after the actinic laser flash). In both basket and hybrid conformations, the G(-H)˙ decay is biphasic with one component decaying with a lifetime of ~0.1ms, and the other with a lifetime of 20-30ms. The fast decay component (~0.1ms) in G-quadruplexes is correlated with the formation of 8-oxoG lesions. We propose that in G-quadruplexes, G(-H)˙ radicals retain radical cation character by sharing the N1-proton with the O6 -atom of G in the [G˙+ : G] Hoogsteen base pair; this [G(-H)˙: H+ G G˙+ : G] leads to the hydration of G˙+ radical cation within the millisecond time domain, and is followed by the formation of the 8-oxoG lesions.

Demonstration of a Light-Driven SO42- Transporter and Its Spectroscopic Characteristics.

In organisms, ion transporters play essential roles in the generation and dissipation of ion gradients across cell membranes. Microbial rhodopsins selectively transport cognate ions using solar energy, in which the substrate ions identified to date have been confined to monovalent ions such as H+, Na+, and Cl-. Here we report a novel rhodopsin from the cyanobacterium Synechocystis sp. PCC 7509, which inwardly transports a polyatomic divalent sulfate ion, SO42-, with changes of its spectroscopic properties in both unphotolyzed and photolyzed states. Upon illumination, cells expressing the novel rhodopsin, named Synechocystis halorhodopsin (SyHR), showed alkalization of the medium only in the presence of Cl- or SO42-. That alkalization signal was enhanced by addition of a protonophore, indicating an inward transport of Cl- and SO42- with a subsequent secondary inward H+ movement across the membrane. The anion binding to SyHR was suggested by absorption spectral shifts from 542 to 536 nm for Cl- and from 542 to 556 nm for SO42-, and the affinities of Cl- and SO42- were estimated as 0.112 and 5.81 mM, respectively. We then performed time-resolved spectroscopic measurements ranging from femtosecond to millisecond time domains to elucidate the structure and structural changes of SyHR during the photoreaction. Based on the results, we propose a photocycle model for SyHR in the absence or presence of substrate ions with the timing of their uptake and release. Thus, we demonstrate SyHR as the first light-driven polyatomic divalent anion (SO42-) transporter and report its spectroscopic characteristics.

N- and L-Type Voltage-Gated Calcium Channels Mediate Fast Calcium Transients in Axonal Shafts of Mouse Peripheral Nerve.

In the peripheral nervous system (PNS) a vast number of axons are accommodated within fiber bundles that constitute peripheral nerves. A major function of peripheral axons is to propagate action potentials along their length, and hence they are equipped with Na+ and K+ channels, which ensure successful generation, conduction and termination of each action potential. However little is known about Ca2+ ion channels expressed along peripheral axons and their possible functional significance. The goal of the present study was to test whether voltage-gated Ca2+ channels (VGCCs) are present along peripheral nerve axons in situ and mediate rapid activity-dependent Ca2+ elevations under physiological circumstances. To address this question we used mouse sciatic nerve slices, Ca2+ indicator Oregon Green BAPTA-1, and 2-photon Ca2+ imaging in fast line scan mode (500 Hz). We report that transient increases in intra-axonal Ca2+ concentration take place along peripheral nerve axons in situ when axons are stimulated electrically with single pulses. Furthermore, we show for the first time that Ca2+ transients in peripheral nerves are fast, i.e., occur in a millisecond time-domain. Combining Ca2+ imaging and pharmacology with specific blockers of different VGCCs subtypes we demonstrate that Ca2+ transients in peripheral nerves are mediated mainly by N-type and L-type VGCCs. Discovery of fast Ca2+ entry into the axonal shafts through VGCCs in peripheral nerves suggests that Ca2+ may be involved in regulation of action potential propagation and/or properties in this system, or mediate neurotransmitter release along peripheral axons as it occurs in the optic nerve and white matter of the central nervous system (CNS).

Electrophysiological Indicators of the Age-Related Deterioration in the Sensitivity to Auditory Duration Deviance

The present study investigates age-related changes in duration discrimination in millisecond time domain. We tested young (N = 20, mean age = 24.5, SD = 2.97) and elderly (N = 20, mean age = 65.2, SD = 2.94) subjects using the mismatch negativity (MMN) paradigm. White-noise bursts of two different durations (50 and 10 ms) were presented in two oddball blocks. In one block (Increment Condition), the repetitive sequence of 10 ms standards was interspersed by occasional 50 ms deviants. In the Decrement Condition, the roles of the two stimuli were reversed. We analyzed the P1-N1 complex, MMN and P3a and found the effect of age for all these components. Moreover, the impact of stimulus presentation condition (increment/decrement) was observed for MMN and P3a. Our results confirmed the previous evidence for deteriorated duration discrimination in elderly people. Additionally, we found that this effect may be influenced by procedural factors.

Photon emission induced by brittle fracture of borosilicate glasses

Photon emission (PE) at wavelength ranges of 430–490nm (B-PE), 500–600nm (G-PE) and 610–680nm (R-PE) caused by brittle fracture was simultaneously measured in the nanosecond-to-microsecond and millisecond time domains for two types of borosilicate glasses: Pyrex-type Tempax glass and BK7 glass. The results were compared to those for silica and soda lime glasses. The time dependence of the PE of Tempax glass was similar to that of silica glass, while the PE intensity was lower. Because Tempax glass contains both silica-rich and borate-rich amorphous phases, the PE must be mainly produced by the fracture of the silica-rich phase. Moreover, the proportion of B-PE of Tempax glass was higher than that of silica glass. This suggests that the measured B-PE might also include very weak PE caused by the fracture of the borate-rich phase. The PE time dependence of BK7 glass was similar to that of soda lime glass, which was different from the case for Tempax glass. The PE intensity of BK7 glass was slightly higher than that of soda lime glass, but much lower than that of Tempax glass. The result indicates that non-bridging oxygen in the glasses affects crack propagation behavior and reduces the PE.

Investigating the position of the hairpin loop in New Delhi metallo-β-lactamase, NDM-1, during catalysis and inhibitor binding

In an effort to examine the relative position of a hairpin loop in New Delhi metallo-β-lactamase, NDM-1, during catalysis, rapid freeze quench double electron electron resonance (RFQ-DEER) spectroscopy was used. A doubly-labeled mutant of NDM-1, which had one spin label on the invariant loop at position 69 and another label at position 235, was prepared and characterized. The reaction of the doubly spin labeled mutant with chromacef was freeze quenched at 500μs and 10ms. DEER results showed that the average distance between labels decreased by 4Å in the 500μs quenched sample and by 2Å in the 10ms quenched sample, as compared to the distance in the unreacted enzyme, although the peaks corresponding to distance distributions were very broad. DEER spectra with the doubly spin labeled enzyme with two inhibitors showed that the distance between the loop residue at position 69 and the spin label at position 235 does not change upon inhibitor binding. This study suggests that the hairpin loop in NDM-1 moves over the metal ion during the catalysis and then moves back to its original position after hydrolysis, which is consistent with a previous hypothesis based on NMR solution studies on a related metallo-β-lactamase. This study also demonstrates that this loop motion occurs in the millisecond time domain.

Mechanism and elimination of bending effect in femtosecond laser deep-hole drilling.

In this work, a comprehensive study of the bending effect, which remains one of the most critical challenges during deep-hole drilling, was conducted. The experimental statistics indicate that polarization is not the main factor in bending, but the deviation of the hole tends to be perpendicular to the polarization direction. Also, the dynamic ablated material/plasma was studied. Straight microholes were obtained by extending the interval between laser pulses to avoid dynamic ablated material existing in the millisecond time domain. Therefore, we speculated that the disturbance of the laser beam at the dynamic ablated aerosol, which have not sufficiently dispersed in the millisecond domain, is the main mechanism of bending. However, to more efficiently reduce the disturbance factor, a rough vacuum environment was applied; and the bending effect was also eliminated. The critical pressure for eliminating bending was about 2 × 10(4) Pa that is about one order of magnitude lower than the atmosphere. The fabricated high-quality microhole arrays without bending show that the proposed drilling method is convenient and efficient with high repeatability and controllability.

Size influence on the fluorescence decay time of ZnS:Mn2+ nanocrystals

ZnS:Mn2+ nanocrystals (NCs) with particle size from 1.9 nm to 3.2 nm are synthesized via chemical precipitation method with different [S2−]/[Zn2+] ratios. The size dependent decay for Mn emission exhibits a double exponential behavior. And two lifetime values, in millisecond time domain, can both be shortened with size increasing, which is attributed to enhanced interaction between host and Mn2+ impurity. A molecular structure model is proposed to interpret the tendency of two lifetime components, which is correlated to the number of S vacancy (Vs) defects around Mn2+.

Delayed responses of analyte emission in a pulse-modulated direct-current argon arc at atmospheric pressure

A pulse-modulated direct-current argon arc burning at atmospheric pressure has been investigated by analyzing temporally and spatially resolved analyte emission responses in a millisecond time domain. The arc current was a rectangular pulse modulated between 9 and 3.5 A with a modulation period of 250 ms and a low current interval of up to 50 ms. Both positive and negative step modulation in current strongly affected the analyte emission. Delayed responses of representative analytes with ionization energies ranging from 6.5 to 10 eV have been studied. Depending on the analyte ionization energy and the plasma zone observed, a sudden current change was in most cases followed by a line intensity increase. The magnitude of this increase is correlated with changes in the ionization–recombination balance, the extent of demixing and the gas dynamics processes invoked by a current modulation. For analytes with medium and low ionization energies a current drop is accompanied by a large increase in signal-to-background ratio, which opens up the possibility of the use of arc current modulation for sensitivity improvement.

Emission properties of Tb3 + ions in LYSO: evidence of a cross relaxation mechanism explained by a kineticmodel

The optical properties of Tb3 + ions in oxyorthosilicates of lutetium and yttrium (LYSO) are reported. The introduction ofa small number of terbium ions (nominal content 10 ppm) generates, in the otherwisetransparent absorption spectrum of the matrix, an ultraviolet absorption bandpeaked at about 240 nm. By exciting within the reported UV band, line shapedemissions in the 350–600 nm range are detected. These transitions are related to the 5D3 and 5D4 levelsof the Tb3 + ions and are characterized by decay times in the millisecond time domain. Analysis of thedecay time measurements allows us to individuate a cross relaxation mechanism amongterbium ions even at the low dopant concentration investigated. We propose a three-levelkinetic model which is able to successfully reproduce the experimental data, allowing us todiscriminate among the radiative and non-radiative contributions to the observedemissions.

Real time monitoring of the crystallization process during the plasma annealing of amorphous silicon

AbstractThe transient surface temperature and optical transmissivity profiles during the plasma annealing of amorphous silicon (a‐Si) on quartz substrate was studied using a radio‐frequency (rf) thermal plasma torch (TPT). The film crystallization promoted through solid‐phase crystallization (SPC) at surface temperature of 750 °C, followed by a lateral crystalline grain growth at above 900 °C within millisecond time domain. The spectroscopic ellipsometry study revealed that the film crystallization by a TPT annealing promoted from near the bottom surface due to the sufficient thermal storage in the bulk rather than the top surface. The average crystalline grain size extended to 200–300 nm by adjusting the stage velocity and substrate distance.

Partial Reactions of the ATP Synthesis Reaction in the E. Coli βD380C Mutant F1Fo-ATP Synthase

The initial stage of ATP synthesis by the E. coli wild type (WT) and mutant βD380C F1Fo-ATPase was compared at saturating substrate concentrations and a proton-motive force (pmf) of ∼315 mV. The enzymes catalyze both ATP hydrolysis (Baylis Scanlon et al., 2008, J. Biol. Chem. 283, 26228-26240) and ATP synthesis with similar steady-state parameters. ATP synthesis by the WT enzyme proceeded with neither burst nor lag-phase while ATP synthesis by βD380C (+DTT) showed a burst phase with a stoichiometry of ATP/F1Fo equal to 1. The burst was simulated using a kinetic model in which the βD380C mutant has a less than 10-fold increase in Pi binding rate in combination with a less than 10-fold decrease in ATP release rate compared to WT. Resolution of the burst allows us to distinguish the partial reactions of the ATP synthesis pathway.Comparison of the ATP release rates in ATP hydrolysis (Baylis Scanlon et al., 2007, Biochemistry 46, 8785-8797) and ATP synthesis suggest differences in the cooperative behavior in the two directions of the reaction. In ATP hydrolysis, positive cooperativity in catalysis is induced by nucleotide (ATP) only, while in ATP synthesis it is induced by both nucleotide (ADP) and the pmf. Fast steady-state ATP hydrolysis proceeds through a trisite mechanism, while ATP synthesis uses a bisite mechanism.We further analyzed the effects of the mutation by forming a stator-rotor disulfide cross-link, βD380C-γC87 induced by DTNB. The cross-linked enzyme catalyzed absolutely no ATP synthesis in the millisecond time domain after inducing a pmf. This result suggests that γ subunit mobility is required for the ATP synthetic reaction to occur and is consistent with the model that high affinity Pi binding cannot be achieved without ΔμH+-dependent γ-subunit rotation.

Microsecond Light-Induced Proton Transfer to Flavin in the Blue Light Sensor Plant Cryptochrome

Plant cryptochromes are blue light photoreceptors that regulate key responses in growth and daily rhythm of plants and might be involved in magnetoreception. They show structural homology to the DNA repair enzyme photolyase and bind flavin adenine dinucleotide as chromophore. Blue light absorption initiates the photoreduction from the oxidized dark state of flavin to the flavin neutral radical, which is the signaling state of the sensor. Previous time-resolved studies of the photoreduction process have been limited to observation of the decay of the radical in the millisecond time domain. We monitored faster, light-induced changes in absorption of an algal cryptochrome covering a spectral range of 375-750 nm with a streak camera setup. Electron transfer from tryptophan to flavin is completed before 100 ns under formation of the flavin anion radical. Proton transfer takes place with a time constant of 1.7 micros leading to the flavin neutral radical. Finally, the flavin radical and a tryptophan neutral radical decay with a time constant >200 micros in the millisecond and second time domain. The microsecond proton transfer has not been observed in animal cryptochromes from insects or photolyases. Furthermore, the strict separation in time of electron and proton transfer is novel in the field of flavin-containing photoreceptors. The reaction rate implies that the proton donor is not in hydrogen bonding distance to the flavin N5. Potential candidates for the proton donor and the involvement of the tryptophan triad are discussed.