Nanosecond Scale Research Articles

Corrosion Behavior of a Laser Surface-Treated Alpha–Beta 6/4 Titanium Alloy

Laser surface treatment of Ti–6Al–4V alloy was carried out by means of a Q-switched Nd:YAG laser. Different laser exposure times were attempted aiming to get the optimal conditions for promising mechanical and electrochemical properties. The microstructure was examined using scanning electron microscopy attached with energy dispersive spectrometer for chemical composition analysis, and the electrochemical behavior of the treated samples was tested by means of polarization test. The corrosion resistance was investigated in Ringer´s solution. The results were compared with those obtained from untreated alloys tested in same conditions. Laser treatment produced a transformed layer with acicular martensite α′-Ti as a result of the recrystallization of the fully lamellar α + β microstructure of the substrate. The results indicate that ultra-short pulses (in nanosecond scale) from Nd:YAG laser effectively enhanced the corrosion resistance of this alloy in acidic media (Ringer’ s solution). A notable enhancement of hardness was reached as well.

Simulations of photothermal effects and thermodynamics induced by optical resonance in a fiber metallic Fabry-Perot cavity.

Our simulations revealed that a highly localized optic-thermal transformation can lead to high temperatures in the fiber-based metallic Fabry-Perot cavity (FMFP) due to optical resonance. Both the transfer matrix method and finite difference time domain (FDTD) method are used for optical analysis of FMFP. Empirical formulas of maximum temperature were derived based on the superposition principle. Despite the fact that the derivation of the resonance condition for FMFP is usually discarded due to its complexity, we propose a simple resonance condition for a metallic Fabry-Perot cavity. In addition, suddenly tuning on the incident light will cause fast-decaying air pressure and velocity, which are also solved from nanosecond scale to equilibrium. This paper is useful for estimating the heat tolerance threshold of nanostructures on fiber end surfaces. Photothermal conversion in FMFP provides an excellent miniature heat source for applications that require high-efficiency photothermal conversion, and FMFP is particularly suitable for optofluidics.

Design of a High Voltage Pulse Generator with Large Width Adjusting Range for Tumor Treatment

The unique biological effects stimulated by short pulsed electric field have many applications in tumor treatment, such as irreversible electroporation, electrochemotherapy, gene transfection and immune therapy. These biological effects require high voltage pulses with different pulse width in the range from nanoseconds to hundreds of microseconds. To fulfill this requirement, a compact high voltage pulse generator has been designed based on a switchable capacitor array and a SiC MOSFET switching array. The proposed pulse generator has one output channel with an adjustable pulse width from 100 ns to 100 µs, an amplitude range from 0 kV to 2 kV, a repetition rate less than 1.2 kHz and a voltage drop less than 5%. The mechanism of the stacked switches circuit was investigated, in connection with a switchable capacitor array. The introduction of a switchable capacitor array extends the pulse width from nanosecond scale and microsecond scale compared with other similar design methods. The pulse generator has been designed in simulation and implemented in experiment. The developed pulse generator provides a convenient and economical tool for the further studies of the unique biological effects stimulated by different pulsed electric fields for tumor treatment.

Pump-Color Selective Control of Ultrafast All-Optical Switching Dynamics in Metaphotonic Devices.

Incorporating active materials into metamaterials is expected to yield exciting advancements in the unprecedented versatility of dynamically controlling optical properties, which sheds new light on the future optoelectronics. The exploration of emerging semiconductors into terahertz (THz) meta‐atoms potentially allows achieving ultrafast nanodevices driven by various applications, such as biomedical sensing/imaging, ultrawide‐band communications and security scanners. However, ultrafast optical switching of THz radiation is currently limited to a single level of tuning speed, which is a main hurdle to achieve multifunctionalities. Here, a hybrid metadevice which can realize the pump‐wavelength controlled ultrafast switching response by the functionalization of double photoactive layers is demonstrated experimentally. A whole cycle of electromagnetically induced transparency switching with a half‐recovery state changes from 0.78 ns to 8.8 ps as pump wavelength varies from near infrared to near ultraviolet regions. The observed pump‐color selective switching speed changing from nanosecond scale to picosecond scale is ascribed to the wavelength‐dependent penetration length of Ge and the contrasting defect states between noncrystalline Ge and epitaxial Si layers. It is believed that the schemes regarding pump‐color controllable ultrafast switching behavior introduced here can inspire more innovations across the field of ultrafast photonics and can boost the reconfigurable metamaterial applications.

Numerical simulations of stable, high-electron-density atmospheric pressure argon plasma under pin-to-plane electrode geometry: effects of applied voltage polarity

When applying high-voltage direct current to a pin-to-plane electrode geometry with a distance of 2 mm under atmospheric pressure in argon gas, electrical breakdown forms primary then secondary streamers. The polarity of the applied voltage affects this streamer-propagating phenomenon. Properties such as propagation speed, streamer head size, and plasma generation are parameterized at nanosecond scales by computational simulations of a self-consistent, multi-species, multi-temperature plasma fluid modeling approach. For positive polarity on the pin electrode, streamer-head propagation speeds up and streamer head size increases with increasing applied voltages. However, local electron density at the head decreases. For negative polarity, corona-like discharges form around the pin electrode under low applied voltages, and diffusive steamers form under high applied voltages. Secondary streamers re-propagate from the pin after primary streamer propagation, forming a plasma with a high electron density of 1021 m−3 for the positive polarity. We show that low-voltage operations with positive polarity are useful for stable high-electron-density discharges under atmospheric pressure argon.

Review of developments on polymers’ breakdown characteristics and mechanisms on a nanosecond time scale

The breakdown of polymer insulators at a nanosecond scale is a serious problem for high-voltage devices and pulsed power systems. This paper reviews recent developments in research on the mechanisms and characteristics of the breakdown of polymers at a nanosecond scale at the Northwest Institute of Nuclear Technology. An improved avalanche breakdown model is proposed, and a formula for the strength of the electric breakdown (EBD) is formulated based on it. The formative time lag of the avalanche breakdown model is then developed to verify it. Two research groups were formed to study the characteristics of the breakdown. One focused on the characteristics of single-pulse breakdown, such as the effects of size, polymer type, electrode, pulse width, and pulse polarity on EBD, with the aim of deriving expressions for EBD. The other research group examined cumulative (multi-pulse) characteristics of the breakdown with the aim of deriving a formula for the lifetime of the polymer. A method to design solid insulation structures is finally proposed.

Molecular dynamics simulation on the dissolution process of Kaempferol cluster

Abstract The solid-liquid extraction is an effective method to extract bioactive components from crude medicinal herbs. The dissolution of bioactive molecules is the key to efficient solid-liquid extraction. In this work, a five-nanosecond molecular dynamics simulation was carried out to study the dissolution mechanism of a cluster, including 15 kaempferol molecules in a cubic solvent box of 6 nm. The theoretical and experimental infrared and Raman spectra were taken to confirm the low-energy kaempferol conformers for building the cluster. The effects of ethanol concentration and temperature on the kaempferol dispersion efficiency are investigated. The simulation results show that different concentration of ethanol solution has different dissolution behavior. Because of the intermolecular interaction between kaempferol and solvent, the kaempferol cluster can be decomposed gradually. In order to quantitatively describe the diffusion process of kaempferol cluster, the radial distribution function of the barycenter of the cluster around kaempferol molecules, the number of H-bond between kaempferol molecules, the solvent accessible area of the cluster, the dissolution free energy and the diffusion constant are analyzed. The results show that the optimal dispersion condition is at 80–90% of the ethanol concentration and 323.15 K of the system temperature, which agree with the experiment of extraction. This research provides new insight into the dissolution process of kaempferol on the nanosecond scale. Also, the result of molecular dynamics (MD) can effectively predict the extraction conditions of the actual experiment.

Ultra-Fast (ns-Scale) Characterization of NBTI Behaviors in Si pFinFETs

In this paper, NBTI behaviors of Si pFinFETs are characterized with the measurement time down to ns-scale utilizing the fast $\text{V}_{\mathrm{ th }}$ measurement (FVM) technique. It is found that the NBTI behaviors in terms of $\text{V}_{\mathrm{ th}}$ shift is strongly influenced by the measurement speed even in the nano-second scale (ns-scale). The measurement phase itself during the NBTI characterization could bring in an additional $\text{V}_{\mathrm{ th}}$ shift ( ${\Delta }\text{V}_{\mathrm{ th}}$ ) or ${\Delta }\text{V}_{\mathrm{ th}}$ recovery. From the ns-scale characterization results in different stress and temperature, it is shown that the rapid recoverable components of NBTI should be attributable to the rapid hole trapping/detrapping, which are related to the defects with time constants of ns-scale.

Real-time laser induced chemical derivatizations of peptide N-Terminus for in-situ mass spectrometric sequencing at sub-picomole and nanosecond scale

Distinguishing b- and y-ions is essential to compute amino acid sequences from either N- or C-terminus in mass spectrometry. We described herein a solvent free and real time on-plate derivatization approach that can tag N-terminus of peptides at microliter level with p-chlorobenzaldehyde or 2-hydroxy-5-methylisophthalaldehyde for matrix assisted laser desorption ionization mass spectrometry (MALDI MS). Less than 1 μL of sample solutions can be directly mixed with equal volumes of p-chlorobenzaldehyde or 2-hydroxy-5-methylisophthalaldehyde and α-cyano-4-hydroxycinnamic acid (CHCA), a matrix compound to co-crystalize with analytes for efficient absorption of laser energy and peptide ionization. When the mixture spotted on the sample plate is irradiated with the 3rd harmonic (355 nm) of Nd3+:YAG laser pulses (3 ns width), N-terminal amine groups of peptides instantly react with carbonyl groups of chlorobenzaldehyde or 2-hydroxy-5-methylisophthalaldehyde. Resultant peptides carrying with on-plate formed azomethine group (-CN-) are simultaneously protonated and isolated as precursor ions for subsequent collision-activated dissociation. The mass shift with unique Cl isotopic signature unambiguously distinguishes b ions from y ions and other ions. This method does not need extensive sample preparation and is useful for those samples with limited quantities down to sub-picomole level in sub-microliter volumes. The efficiency was demonstrated with synthetic peptides and tryptic peptides of model proteins. It was found that 2-hydroxy-5-methylisophthalaldehyde provides improved yield for peptides containing lysine residues. Unknown proteins of human saliva and bovine milk as well as phosphopeptides have been identified.

Vibrational Energy Redistribution between CH Stretching Modes in Alkyl Chain Monolayers Revealed by Time-Resolved Two-Color Pump-Probe Sum Frequency Spectroscopy.

The vibrational dynamics of the various CH stretching modes in a fatty acid Langmuir-Blodgett film was studied using a resonant narrowband infrared (IR) laser pulse for pumping and a broadband femtosecond IR visible pulse pair for detection in a sum frequency spectroscopy setup. The resulting two-dimensional spectra indicate that pumping either the antisymmetric methyl or methylene stretch results in the transfer of energy to the other modes on a time scale faster than 2 ps. This rapid process is followed by energy redistribution to other modes, presumably the bending and internal rotational modes, with a time constant of approximately 85 ps. The formation of gauche defects is not observed within the first 250 ps. The whole spectrum recovers on a time scale of several nanoseconds, indicating dissipation of the excitation energy into the substrate.

Physical reservoir computing using magnetic skyrmion memristor and spin torque nano-oscillator

Spintronic nanodevices have ultrafast nonlinear dynamic and recurrence behaviors on a nanosecond scale that promises to enable a high-performance spintronic reservoir computing (RC) system. Here, two physical RC systems based on one single magnetic skyrmion memristor (MSM) and 24 spin-torque nano-oscillators (STNOs) are numerically modeled to process image classification task and nonlinear dynamic system prediction, respectively. Based on the nonlinear responses of the MSM and STNO with current pulse stimulation, our results demonstrate that the MSM-based RC system exhibits excellent performance on image classification, while the STNO-based RC system does well in solving the complex unknown nonlinear dynamic problems, e.g., a second-order nonlinear dynamic system and NARMA10. Our result and analysis of the current-dependent nonlinear dynamic properties of the MSM and STNO provide the strategy to optimize the experimental parameters in building the better spintronic-based brainlike devices for machine learning based computing.

Optical Limiting and Femtosecond Pump-Probe Transient Absorbance Properties of a 3,5-distyrylBODIPY Dye.

The optical limiting (OL) properties of a 3,5-di-p-benzyloxystyrylBODIPY dye with an p-acetamidophenyl moiety at the meso-position have been investigated by using the open-aperture Z-scan technique at 532 nm with 10 ns laser pulses. There is a ca. 140 nm red shift of the main spectral band to 644 nm relative to the corresponding BODIPY core dye, due to the incorporation of p-benzyloxystyryl groups at the 3,5-positions. As a result, there is relatively weak absorbance across most of the visible region under ambient light conditions. Analysis of the observed reverse saturable absorbance (RSA) profiles demonstrates that the dye is potentially suitable for use in optical limiting applications as has been reported previously for other 3,5-distyrylBODIPY dyes. Time-resolved transient absorption spectroscopy and kinetic studies with femtosecond and nanosecond scale laser pulses provide the first direct spectral evidence that excited state absorption (ESA) from the S1 state is responsible for the observed OL properties.

A diagnostic system toward high-resolution measurement of wavefront profile

Analysis of wavefront is vital in the process of the inertial confinement fusion (ICF), but there is lack of accurate method to achieve the wavefront image with a high resolution of up to the picosecond (ps) level. The two-dimensional imaging velocity interferometer system for any reflectors (2D-VISAR) can only realize two-dimensional images with a temporal resolution in a nanosecond scale or one two-dimensional image, leading to the difficulties in recovering the high-speed changing process. Although the line-imaging VISAR with a streak camera has a higher temporal resolution of 5 ps, it hardly offers two-dimensional images. In this study, we design a diagnostic system by coupling the line-imaging VISAR and compressed sensing theory to recover the wavefront profile, by which both the two-dimensional and high-temporal resolution wavefront are obtained. A series of original fringe images are firstly processed, and then acquiring data and reconstructing images are simulated, which results in corresponding reconstructed fringe images. The deviation of the resulting images is evaluated to be below 2.1% for the reconstructed shock wave velocities compared to the original shock wave velocities, much lower than the initial velocity, suggesting that the wavefront profile change is successfully recovered, which indicates the diagnostic system for more accurate measurements of the wavefront profile is feasible. This new system is expected to be applied in the field of implosion to provide more extensive information.

Extreme Scalability of DFT-Based QM/MM MD Simulations Using MiMiC.

We present a highly scalable DFT-based QM/MM implementation developed within MiMiC, a recently introduced multiscale modeling framework that uses a loose-coupling strategy in conjunction with a multiple-program multiple-data (MPMD) approach. The computation of electrostatic QM/MM interactions is parallelized exploiting both distributed- and shared-memory strategies. Here, we use the efficient CPMD and GROMACS programs as QM and MM engines, respectively. The scalability is demonstrated through large-scale benchmark simulations of realistic biomolecular systems employing non-hybrid and hybrid GGA exchange-correlation functionals. We show that the loose-coupling strategy adopted in MiMiC, with its inherent high flexibility, does not carry any significant computational overhead compared to a tight-coupling scheme. Furthermore, we demonstrate that the adopted parallelization strategy enables scaling up to 13,000 CPU cores with efficiency above 70%, thus making DFT-based QM/MM MD simulations using hybrid functionals at the nanosecond scale accessible.

Influences of voltage shape and discharge gas on the temporally and spatially resolved emission characteristics of tin in a planar dielectric barrier discharge

Choosing a suitable power supply concerning the shape of the excitation voltage and the type of discharge gas for elemental analysis with a dielectric barrier discharge is not trivial. Both significantly affect the analyte signal. By means of conventional methods such as inductively coupled plasma mass spectrometry or atomic absorption spectrometry optimal conditions can be found, however the reason why the specific parameter set results in ideal signals is hidden in the detailed characteristics of the DBD. These phenomena occur on a narrow time scale of nanoseconds to microseconds and are challenging to observe. Therefore, the emission profiles of tin in a planar dielectric barrier discharge atomizer were studied by means of temporally and spatially resolved optical emission spectroscopy by varying the type of discharge gas and the shape of the excitation voltage. The latter was realized by applying either a sinusoidal or a square wave power supply. The temporally resolved emission profile showed that in case of sinusoidal excitation the power is distributed over a longer time in several discharge events, whereas with square wave excitation the power is coupled to the dielectric barrier discharge in one intensive pulse. The spatially resolved emission signals indicated a different point of excitation of Sn within the dielectric barrier discharge for each power source. The Sn emission in a plasma, which was sustained by the square wave power supply, was not significantly influenced by the change of the discharge gas from argon to helium. However, for the emission signal in a plasma excited by the sinusoidal power supply, helium had an adverse effect.

Understanding the Radio Spectrum of Thunderstorm Narrow Bipolar Events

AbstractThis paper reports a study to understand the radio spectrum of thunderstorm narrow bipolar events (NBEs) or compact intracloud discharges, which are powerful sources of high‐frequency (HF) and very high frequency (VHF) electromagnetic radiation. The radio spectra from 10 kHz to about 100 MHz are obtained for three NBEs, including one caused by fast positive breakdown and two by fast negative breakdown. The results indicate that the two polarities of fast breakdown have similar spectra, with a relatively flat spectrum in the HF and VHF band. The ratio of energy spectral densities in the very low frequency and HF bands is (0.9–5) × 105. We develop a statistical modeling approach to investigate if a system of streamers can explain the main features of fast breakdown. Assuming that the current moment peak and charge moment change of individual streamers vary in the ranges of 5–10 A‐m and 5–20 μC‐m, respectively, the modeling results indicate that a system of 107–108 streamers can reproduce the current moment, charge transfer, and radio spectrum of fast breakdown. The rapid current variation on a time scale of nanoseconds required for fast breakdown to produce strong HF/VHF emissions is provided by exponentially accelerating and expanding streamers. Our study therefore supports the hypothesis that fast breakdown is a system of streamers. Finally, suggestions are given regarding future streamer simulations and NBE measurements in order to further develop our understanding of NBEs and lightning initiation.

Rotational correlation times of proteins determined by 111mCd PAC spectroscopy

Molecules in solution experience rotational diffusion. For large biomolecules such as proteins, the rotational correlation times, τc, are often on the nanosecond time scale. PAC isotopes exhibit lifetimes of the intermediate nuclear level on the time scale of nanoseconds, and the hyperfine interactions measured by PAC spectroscopy are therefore sensitive to dynamics on this time scale. With this work we have compiled experimentally determined rotational correlation times, τcexp, reported in the literature in the slow reorientation limit, and compared to calculated rotational correlations times, τccalc, using the simple Stoke-Einstein-Debye approximation. In a number of cases τcexp agrees with the calculated value within the experimental error, including proteins which are expected to be rigid. In several cases, however, τcexp is smaller than the theoretical value, presumably due to local dynamics at the PAC probe site. In support of this interpretation, τcexp < τccalc is observed for many enzymes, which are expected to display dynamics at the PAC probe site due to water coordination to the active site metal.

Homology modeling and 3D–QSAR study of benzhydrylpiperazine δ opioid receptor agonists

The binding affinity of a series of benzhydrylpiperazine δ opioid receptor agonists were pooled and evaluated by using 3D-QSAR and homology modeling/molecular docking methods. Ligand-based CoMFA and CoMSIA 3D-QSAR analyses with 46 compounds were performed on benzhydrylpiperazine analogues by taking the most active compound BW373U86 as the template. The models were generated successfully with q2 value of 0.508 and r2 value of 0.964 for CoMFA, and q2 value of 0.530 and r2 value of 0.927 for CoMSIA. The predictive capabilities of the two models were validated on the test set with R2pred value of 0.720 and 0.814, respectively. The CoMSIA model appeared to work better in this case. A homology model of active form of δ opioid receptor was established by Swiss-Model using a reported crystal structure of active μ opioid receptor as a template, and was further optimized using nanosecond scale molecular dynamics simulation. The most active compound BW373U86 was docked to the active site of δ opioid receptor and the lowest energy binding pose was then used to identify binding residues such as s Gln105, Lys108, Leu125, Asp128, Tyr129, Leu200, Met132, Met199, Lys214, Trp274, Ile277, Ile304 and Tyr308. The docking and 3D-QSAR results showed that hydrogen bond and hydrophobic interactions played major roles in ligand-receptor interactions. Our results highlight that an approach combining structure-based homology modeling/molecular docking and ligand-based 3D-QSAR methods could be useful in designing of new opioid receptor agonists.

Ultrafast measurements of polarization switching dynamics on ferroelectric and anti-ferroelectric hafnium zirconium oxide.

The ultrafast measurements of polarization switching dynamics on ferroelectric (FE) and antiferroelectric (AFE) hafnium zirconium oxide (HZO) are studied. The transient current during the polarization switching process is probed directly on the nanosecond scale. The switching time is determined to be as fast as 10 ns to reach fully switched polarization with characteristic switching times of 5.4 ns for FE HZO and 4.5 ns for AFE HZO by the nucleation limited switching model. The limitation by the parasitic effect on capacitor charging is found to be critical in the correct and accurate measurements of intrinsic polarization switching speed of HZO.

Molecular dynamics simulations on RORγt: insights into its functional agonism and inverse agonism.

The retinoic acid receptor-related orphan receptor (ROR) γt receptor is a member of nuclear receptors, which is indispensable for the expression of pro-inflammatory cytokine IL-17. RORγt has been established as a drug target to design and discover novel treatments for multiple inflammatory and immunological diseases. It is important to elucidate the molecular mechanisms of how RORγt is activated by an agonist, and how the transcription function of RORγt is interrupted by an inverse agonist. In this study we performed molecular dynamics simulations on four different RORγt systems, i.e., the apo protein, protein bound with agonist, protein bound with inverse agonist in the orthosteric-binding pocket, and protein bound with inverse agonist in the allosteric-binding pocket. We found that the orthosteric-binding pocket in the apo-form RORγt was mostly open, confirming that apo-form RORγt was constitutively active and could be readily activated (ca. tens of nanoseconds scale). The tracked data from MD simulations supported that RORγt could be activated by an agonist binding at the orthosteric-binding pocket, because the bound agonist helped to enhance the triplet His479-Tyr502-Phe506 interactions and stabilized H12 structure. The stabilized H12 helped RORγt to form the protein-binding site, and therefore made the receptor ready to recruit a coactivator molecule. We also showed that transcription function of RORγt could be interrupted by the binding of inverse agonist at the orthosteric-binding pocket or at the allosteric-binding site. After the inverse agonist was bound, H12 either structurally collapsed, or reorientated to a different position, at which the presumed protein-binding site was not able to be formed.