Fast Sweep Rate Research Articles

Precise beam energy measurement using resonant spin depolarization in the SOLEIL storage ring

The average electron beam energy for the operational mode of 400mA in 416 bunches in the SOLEIL storage ring was measured to be 2.73724±0.00016GeV with an accuracy of 5.9×10−5 using the method of resonant spin depolarization (RSD). A Touschek-dominated electron beam was excited using a shaker magnet, and the beam polarization and depolarization were monitored using the change in beam lifetime and beam loss rate. To establish the primary condition that is required to perform energy measurement using the RSD method, the radiative beam polarization was first simulated using the SLIM beam dynamics code and then measured using the relative increase of beam lifetime for a Touschek-dominated electron beam. With a fast frequency sweep rate, the main depolarization resonance to be used to extract the beam energy, along with sidebands within the range of frequency sweep, was identified during our first trials. Sweeping the frequency of the excitation field around the main resonance with a slower frequency sweep rate, the beam energy measurement accuracy was increased from 1.7×10−4 to 5.9×10−5. Finally, the effects of closed orbit distortions on the radiative polarization and measured energy accuracy are discussed.

Effect of Graphene Fermi Level on the Raman Scattering Intensity of Molecules on Graphene

We studied the modulation of Raman scattering intensities of molecules on graphene by tuning the graphene Fermi level with electrical field effect (EFE). A series of metal phthalocyanine (M-Pc) molecules (M = Mn, Fe, Co, Ni, Cu, Zn), which have different molecular energy levels, were used as probe molecules. The Raman intensities of all these M-Pc molecules become weaker when the graphene Fermi level is up-shifted by applying a positive gate voltage, while they become stronger when the graphene Fermi level is down-shifted by applying a negative gate voltage. However, this Raman intensity modulation only occurs when applying the gate voltage with a fast sweep rate, while it is nearly absent when applying the gate voltage with a slow sweep rate, which is likely due to the arising of the hysteresis effect in the graphene EFE. In addition, the Raman modulation ability for M-Pc molecules with smaller energy gaps is larger than that with larger energy gaps due to the difference in the energy alignment between graphene and these M-Pc molecules. Furthermore, this modulation shows the greatest one on single-layer graphene and mainly comes from the first layer of molecules which are in direct contact with graphene. The Raman modulation of molecules in GERS with the EFE suggests that the Raman enhancement for GERS occurs through a chemical enhancement mechanism.

Detonation Nanodiamond and Onion‐Like‐Carbon‐Embedded Polyaniline for Supercapacitors

AbstractThe detonation nanodiamond is a versatile low‐cost nanomaterial with tunable properties and surface chemistry. In this work, it is shown how the application of nanodiamond (ND) can greatly increase the performance of electrochemically active polymers, such as polyaniline (PANI). Symmetric supercapacitors containing PANI‐ND nanocomposite electrodes with 3–28 wt% ND show dramatically improved cycle stability and higher capacitance retention at fast sweep rate than pure PANI electrodes. Contrary to other PANI‐carbon nanocomposites, specific capacitance of the selected PANI electrodes with embedded ND increases after 10 000 galvanostatic cycles and reaches 640 F g−1, when measured in a symmetric two‐electrode configuration with 1 M H2SO4 electrolyte. The demonstrated specific capacitance is 3–4 times higher than that of the activated carbons and more than 15 times higher than that of ND and onion‐like carbon (OLC).

An ansatz for the nonlinear Demkov-Kunike problem for cold molecule formation

We study nonlinear mean-field dynamics of ultracold molecule formation in the case when the external field configuration is defined by the level-crossing Demkov-Kunike model, characterized by a bell-shaped coupling and finite variation of the detuning. Analyzing the fast sweep rate regime of the strong interaction limit, which models a situation when the peak value of the coupling is large enough and the resonance crossing is sufficiently fast, we construct a highly accurate ansatz to describe the temporal dynamics of the molecule formation in the mentioned interaction regime. The absolute error of the constructed approximation is less than 3 × 10−6 for the final transition probability while at certain time points it might increase up to 10−3. Examining the role of the different terms in the constructed approximation, we prove that in the fast sweep rate regime of the strong interaction limit the temporal dynamics of the atom-molecule conversion effectively consists of the process of resonance crossing, which is governed by a nonlinear equation, followed by atom-molecular coherent oscillations which are basically described by a solution of the linear problem, associated with the considered nonlinear one.

Magnetic instability of MgB2 thin film triggered by the various sweeping rates of an applied magnetic field

Up to now, the vortex avalanche is known to depend critically on the changing of some external parameters, such as the applied magnetic field, the temperature, and the demagnetization factor. In this study, we found the sweeping rate (SR) of the applied magnetic field to be another parameter that contributed to the appearance of the vortex avalanche. For example, a fast SR 500 Oe/s enhanced the vortex avalanche quietly compared to the case of a slow SR of 3 Oe/s. The dependence of the appearance of the vortex avalanche on the SR was quite strong, especially at low temperatures. A H-T phase diagram that distinguishes the regions of magnetic stability and instability is drawn for each SR.

Brainstem correlates of temporal auditory processing in children with specific language impairment

Deficits in identification and discrimination of sounds with short inter-stimulus intervals or short formant transitions in children with specific language impairment (SLI) have been taken to reflect an underlying temporal auditory processing deficit. Using the sustained frequency following response (FFR) and the onset auditory brainstem responses (ABR) we evaluated if children with SLI show abnormalities at the brainstem level consistent with a temporal processing deficit. To this end, the neural encoding of tonal sweeps, as reflected in the FFR, for different rates of frequency change, and the effects of reducing inter-stimulus interval on the ABR components were evaluated in 10 4-11-year-old SLI children and their age-matched controls. Results for the SLI group showed degraded FFR phase-locked neural activity that failed to faithfully track the frequency change presented in the tonal sweeps, particularly at the faster sweep rates. SLI children also showed longer latencies for waves III and V of the ABR and a greater prolongation of wave III at high stimulus rates (>30/sec), suggesting greater susceptibility to neural adaptation. These results taken together appear to suggest a disruption in the temporal pattern of phase-locked neural activity necessary to encode rapid frequency change and an increased susceptibility to desynchronizing factors related to faster rates of stimulus presentation in children with SLI.

Laminated Thin Films of Titanate Nanosheets Obtained by Electrophoretic Deposition for High-Rate Capable Electrodes of Li-ion Batteries

Thin films of titanate were prepared by electrophoretic deposition (EPD) of a colloidal suspension of nanosheets, and their lithium intercalation properties were examined. Flat and dense films with relative density of approximately 95 % were obtained by EPD. Thickness of the obtained film increased approximately in proportion to the increase in deposition time. The reversible capacity for the obtained film was approximately 210 mA h g-1. The obtained thin films showed high capacity retention of more than 50 % even at a fast sweep rate of 30 mV sec-1. Thin films of titanate nanosheets prepared by EPD exhibited a relatively large capacity and excellent high-rate capability.

Employing fractional autocorrelation for fast detection and sweep rate estimation of pulse compression radar waveforms

Fractional autocorrelation of a signal defined for a fractional domain at an arbitrary angle of the time–frequency plane exactly corresponds to the radial slice of the radar ambiguity function (AF) of that signal at that particular angle. In other words, any radial cross-section of the radar AF, that itself serves as a two-dimensional correlation function, can be readily obtained by computing fractional autocorrelation, which is one-dimensional. In this manuscript, we employ a novel fast detection statistic derived utilizing this property of fractional autocorrelation for computationally efficient detection of pulse compression radar waveforms such as the step linear frequency modulated (SLFM) signal, Frank code, and P1 and P4 codes. As a byproduct, the detection algorithm also serves as an unbiased estimator of the sweep rate (chirp rate) of the considered radar waveforms. Through receiver operating characteristic (ROC) curves, we investigate the performance of the detection statistic and compare it against the matched filter and generalized likelihood ratio test (GLRT) detectors of the linear frequency modulated (LFM) signal. Performance of the accompanying sweep rate estimator is also demonstrated using mean square error (MSE) curves and compared with the optimum maximum likelihood (ML) estimator of the sweep rate parameter of the LFM signal.

Transient Hole Trapping in Individual GeSi Quantum Dot Grown on Si(001) Studied by Conductive Atomic Force Microscopy

Electrical properties of individual self-assembled GeSi quantum dots grown on Si substrates are investigated by using conductive atomic force microscopy at room temperature. By controlling the bias voltage sweep in a certain fast sweep rate range, a novel current peak is observed in the current–voltage characteristics of the quantum dots. The current peaks are detectable only during the backward voltage sweep immediately after a forward sweep. The current peak position and intensity are found to depend strongly on the voltage sweep conditions. This kind of current–voltage characteristic under fast sweep is very different from the ordinary steady state current behaviour of quantum dots measured previously. The origin of this phenomenon can be attributed to the transient hole trapping in the potential well formed by the quantum dot sandwiched between the native oxide layer and the bottom Si substrate.

Polarization Switching and Hysteresis of VCSELs With Time-Varying Optical Injection

We study the influence of time-varying orthogonal optical injection on polarization switching (PS) of vertical-cavity surface-emitting lasers (VCSELs). Three cases are considered: scanning injection strength, and scanning frequency detuning in two different reference ranges. In all the three cases, fast sweep rates make PSs happen at higher (lower) values for upward (downward) scans, and thus enlarge the hysteresis region. Furthermore, types of PS and the emission states of the laser can be controlled, if the scanning parameter and scanning range are chosen properly. Statistical analysis indicates PS for the third case is not so stable as that for the first two cases.

Transport properties of InAs nanowire field effect transistors: The effects of surface states

It is shown that interface trap states have pronounced effects on carrier transport and parameter extraction from top-gated InAs nanowire field effect transistors (NWFETs). Due to slow surface state charging and discharging, the NWFET characteristics are time dependent with time constants as long as ∼45s. This is also manifested in a time-dependent extrinsic transconductance that severely affects carrier mobility and carrier density determination from conventional three-terminal current-voltage characteristics. Slow gate voltage sweep rates result in charge balance between carrier capture and emission from interface states and lead to reduced hysteresis in the transfer curves. The gate transconductance is thus increased and intrinsic NW transport parameters can be isolated. In the InAs NWFETs, a carrier mobility value of ∼16000cm2∕Vs was obtained from the transfer curves at slow sweep rates, which is significantly higher than ∼1000cm2∕Vs obtained at fast sweep rates. A circuit model that takes into account the reduction in the extrinsic transconductance is used to estimate an interface state capacitance to be ∼2μF∕cm−2, a significant value that can lead to underestimation of carrier mobility.

Stability of poly(vinylidene fluoride- co-hexafluoropropylene)-based composite gel electrolytes with functionalized silicas

Various aspects of stability of composite polymer gel electrolytes based on poly(vinylidene fluoride- co-hexafluoropropylene) (PVdF/HFP) polymeric matrix and functionalized precipitated silicas have been studied. The silica fillers have been surface modified with methacryloxy or vinyl groups by partially replacing silanol groups, so that bi-functional (hydrophilic/hydrophobic) character of the inorganic fillers was created. Compatibility of the gel electrolytes with lithium electrode has been examined by means of EIS technique. Electrochemical stability window has been studied with the application of cyclic voltammetry technique with fast sweeping rate. Passive layer formation on graphite electrode has been investigated for all the gel electrolytes by means of cyclic voltammetry with slow scan rate and galvanostatic charging/discharging technique. It has been shown that stability of the interface between lithium and gel electrolyte is significantly improved when bi-functional silicas are used as fillers. The phenomenon has been ascribed to more effective scavenging of trace impurities as well as to better shielding of the electrode surfaces. Cyclic voltammetry on platinum has revealed excessive electrochemical redox processes upon prolonged cycling for all the gel electrolytes. It has been demonstrated that stable passive layers are formed on graphite electrodes upon electrochemical reduction in the presence of the studied composite polymer gel electrolytes.

Neural Mechanisms Underlying Selectivity for the Rate and Direction of Frequency-Modulated Sweeps in the Inferior Colliculus of the Pallid Bat

This study describes mechanisms that underlie neuronal selectivity for the direction and rate of frequency-modulated sweeps in the central nucleus of the inferior colliculus (ICC) of the pallid bat (Antrozous pallidus). This ICC contains a high percentage of neurons (66%) that respond selectively to the downward sweep direction of the bat's echolocation pulse. Some (19%) are specialists that respond only to downward sweeps. Most neurons (83%) are also tuned to sweep rates. A two-tone inhibition paradigm was used to describe inhibitory mechanisms that shape selectivity for sweep direction and rate. Two different mechanisms can create similar rate tuning. The first is an early on-best frequency inhibition that shapes duration tuning, which in turn determines rate tuning. In most neurons that are not duration tuned, a delayed high-frequency inhibition creates rate tuning. These neurons respond to fast sweep rates, but are inhibited as rate slows, and delayed inhibition overlaps excitation. In these neurons, starting a downward sweep within the excitatory tuning curve eliminates rate tuning. However, if rate tuning is shaped by duration tuning, this manipulation has no effect. Selectivity for the downward sweep direction is created by an early low-frequency inhibition that prevents responses to upward sweeps. In addition to this asymmetry in arrival times of low- and high-frequency inhibitions, the bandwidth of the low-frequency sideband was broader. Bandwidth influences the arrival time of inhibition during an FM sweep because a broader sideband will be encountered sooner. These findings show that similar spectrotemporal filters can be created by different mechanisms.

Development of a rapid screening test for SCC susceptibility of copper in disposal vault conditions

ABSTRACTStress corrosion cracking is a potential failure mechanism of the copper canister proposed to be the main corrosion barrier in the Scandinavian design of the final nuclear waste disposal vault. The main target in SCC-oriented research is to determine the limiting values for the critical concentration of harmful species, the potential range in which these species cause SCC and the threshold stress level required for SCC. The present paper attempts to redefine the criteria for SCC susceptibility of copper in acetate solutions through analysis of potentiodynamic curves using both rotating disc and thin plate electrodes insulated on one side. A potential range in which the current densities at a slow sweep rate are lower than those at a fast sweep rate exists for Cu in 0.001 M - 0.1 M acetate. However, the values of the current densities within this range are significantly smaller than those postulated for active anodic dissolution, implying dissolution mediated by a surface film. New criteria for the SCC susceptibility of pure copper in acetate solutions have been formulated through Stern-Geary analysis of the polarisation curves. Several electrochemical characteristics, such as the current density at the positive crossover potential, the ratio between the corrosion current densities determined from the slow and fast sweeps, as well as the anodic current density in a fast sweep show a clear jump for concentrations between 0.01 M and 0.05 M. This, however, cannot yet be considered as an indication of SCC susceptibility at higher acetate concentrations, as evidenced by complementary SSRT tests.

Electrochemical Behavior of Stimulation∕Sensing Materials for Pacemaker Electrode Applications: III. Nanoporous and Smooth Carbon Electrodes

The electrochemical behavior of nanoporous and smooth carbon electrodes was investigated in a phosphate-buffered saline solution. The interfacial properties were characterized by electrochemical impedance spectroscopy. The influence of charging∕discharging rate on the capacitive behavior was investigated by cyclic voltammetry between and at fast sweep rates. The transient processes taking place at the electrode upon stimulation pulse were also studied by using a pulse generator. For the nanoporous electrode at sufficiently high sweep rates, the charge-transfer characteristics change from capacitive to resistive, due to voltage drop down the pores. Only a small part of total available capacitance of the porous electrode can be utilized at high charging∕discharging rates. This is probably the reason for the observed relationship between pacing impedance and geometric electrode surface area. When subjected to stimulation pulses, compared to the smooth electrode, the nanoporous electrode delivers more charge due to lower pacing impedance. At high pulse potentials, some faradaic reaction seems to occur, which is more pronounced on the smooth electrode.

Investigation of Electrochemical Behavior of Stimulation/Sensing Materials for Pacemaker Electrode Applications II. Conducting Oxide Electrodes

The electrochemical behavior, interfacial properties, and stability of -, -, - and -coated electrodes for pacemaker applications were investigated in a phosphate buffered saline solution, by electrochemical impedance spectroscopy and cyclic voltammetry (CV). The psuedocapacitive properties of these conducting oxides and influence of coating roughness and porosity were examined, and accelerated aging of the electrode materials was simulated by fast sweep rate CV cycles between vs. . Changes in surface composition and structure due to the accelerated aging were investigated using X-ray photoelectron spectroscopy and scanning electron microscopy. The conducting oxides exhibit high interfacial capacitance. At high sweep rates, not all of total capacitance could be utilized due to voltage drop associated with resistance down the pores. Above a certain sweep rate, the charging/discharging mechanism changes from capacitive to resistive character. Showing the best performance among the investigated materials, the exhibits capacitive characteristics at sweep rates up to and excellent stability under the accelerated aging. The coating was not stable during the cycling. The mixed oxides experience limitations at high sweep rates due to the ohmic effects and some degradation due to the accelerated aging.

One-electron redox reaction of di- tert-butyl nitroxide at platinum electrode in acetonitrile

The electrochemical oxidation of di- tert-butyl nitroxide (DTBN) at a platinum electrode in acetonitrile was examined. The cyclic voltammogram indicated an irreversible response during a normal time scale measurement, whereas chemically reversible voltammograms were obtained during a shorter time using a micro disk electrode with relatively fast sweep rates. The apparent formal redox potential and heterogeneous electron transfer rate constant were estimated to be 0.218 V (versus Fc +|Fc) and 0.035 ± 0.015 cm s −1 from the digital simulation analysis.

EFFECTS OF MAGNETIC FIELD ON THE HYSTERESIS V-I CURVE

Hysteresis V-I curves were simulated based on flux creep model. The clockwise loop was found for a sample with homogenous flux pinning if a fast current sweeping rate is used. Moreover, it is shown that an applied magnetic field can suppress the loop. The results coincide qualitatively with the relevant measurements.

Effect of the leaving group on the electrodic reduction mechanism of anti- Helicobacter pylori metronidazole derivatives, in aprotic and protic media

Because redox properties are central to bioreductive drug activity and selectivity, six 2-methyl-5-nitroimidazole, substituted at the N1-ethyl side chain with I, Br, Cl, OAc, OMs and NH 3 + were synthesized and submitted to cyclic voltammetry and electrolyses, in order to define their electrodic reduction mechanism, in aprotic [dimethylsulphoxide (DMSO)+0.1 mol l −1 tetrabuthylammonium perchlorate (TBAP)] and phosphate-buffered media, on glassy carbon electrode, in comparison with metronidazole. Three of these compounds, namely, the iodo, bromo and ammonium salt derivatives showed significant anti- Helicobacter pylori (strain resistant to metronidazole) activity. All the cyclic voltammograms (CV), in aprotic medium, are similar to the one for metronidazole, except for −I, -Br and -NH 3 + derivatives. The CV of the N1-ethylhalide (-I, -Br) 5-nitroimidazole showed more intense and irreversible first waves, even at faster sweep rates ( ν<2 V s −1). The absence of the first wave anodic counterpart, along with analysis of the dependence of E p, I p and other parameters with ν, and results from electrolysis (consumption of two electrons) showed the process to be an ECE system, with halide release, after uptake of two electrons. This behaviour represents a case of dissociative electron transfer (ET). For the ammonium salt, self-protonation mechanism was evident. The facility of reduction represented by the first wave potential and concerning the substituents is NH 3 +>Br>I>Cl>OMs>OH>OAc. In aqueous phosphate-buffered medium, the electrochemical behaviour of all the compounds is similar to the one of metronidazole, represented by a unique and irreversible 4e −/4H + wave. The order of reduction ease is NH 3 +>Br∼OMs>I>OH>OAc. Aprotic medium allows a better discrimination between the substituents. Concerning biological activity, despite the impossibility of establishing a correlation, it has been observed that the more electrophilic compounds showed better anti- H. pylori activity.

Surface-enhanced infrared study of catalytic electrooxidation of formaldehyde, methyl formate, and dimethoxymethane on platinum electrodes in acidic solution

Surface-enhanced infrared absorption spectroscopy (SEIRAS) combined with cyclic voltammetry has been employed to investigate the electrooxidation of formaldehyde, methyl formate, and dimethoxymethane (byproducts in methanol oxidation) on platinum in acidic solution. Owing to the sensitivity of SEIRAS being much higher than that of infrared reflection–absorption spectroscopy (IR-RAS), the reactions could be studied during cyclic voltammetric measurements at relatively fast potential sweep rates (50 mV s −1 or faster). In the oxidation of formaldehyde, a weak band assigned to the symmetric O–C–O stretching mode of formate adsorbed on the Pt surface in a bridging configuration was observed for the first time in addition to those for linearly and bridge-bonded CO known to be poisons. The oxidation current was found to increase as the band intensity of formate increases. On the other hand, none of the other reactive intermediates claimed in earlier IR-RAS studies was detected. These results led us to propose that adsorbed formate is a reactive intermediate en route to CO 2 production and the oxidation of formate to CO 2 is the rate-determining step. Methyl formate and dimethoxymethane are also oxidized to CO 2 via formate.