Full-width At Half-maximum Duration Research Articles

Proton energy enhancement by optimizing a laser pulse profile

Based on current laboratory laser parameters and the low density target that is induced by the inevitable prepulse, we propose what we believe to be a new scheme to enhance the proton energy by employing a laser pulse with two different peak intensities. Initially, the lower-intensity peak of the laser pulse P1, irradiates the low-density plasma target induced by the prepulse to form a significantly denser plasma target. Such a compressed high-density target is critical for supporting the subsequent main pulse P2 with higher peak intensity to drive proton acceleration. As an example, particle-in-cell (PIC) simulations reveal that when using a circularly polarized (CP) flat-top P1 with a peak intensity of approximately 1.71 × 10 19 W/cm2, full-width at half-maximum(FWHM) duration of 325 fs and a CP P2 with a peak intensity of 1.54 × 10 22 W/cm2, FWHM duration of 26.5 fs, and focal spot radius of 4 µm successively acting on a target with an initial density of 8nc, protons with cut-off energy of 940 MeV can be obtained from the cascaded acceleration scheme. Compared with the case without P1, the cutoff energy increased by 340 MeV. Owing to the intervention of P1, this scheme overcomes the limitation of laser contrast and is more feasible to be implemented experimentally.

Optical imaging of stimulation-evoked cortical activity using GCaMP6f and jRGECO1a.

Genetically encoded calcium indicators (GECIs), especially the GCaMP-based green fluorescence GECIs have been widely used for in vivo detection of neuronal activity in rodents by measuring intracellular neuronal Ca2+ changes. More recently, jRGECO1a, a red shifted GECI, has been reported to detect neuronal Ca2+ activation. This opens the possibility of using dual-color GECIs for simultaneous interrogation of different cell populations. However, there has been no report to compare the functional difference between these two GECIs for in vivo imaging. Here, a comparative study is reported on neuronal responses to sensory stimulation using GCaMP6f and jRGECO1a that were virally delivered into the neurons in the somatosensory cortex of two different groups of animals, respectively. GCaMP6f and jRGECO1a GECI were virally delivered to sensory cortex. After 3-4 weeks, the animals were imaged to capture the spatiotemporal changes of neuronal Ca2+ and the hemodynamic responses to forepaw electrical stimulation (0.3 mA, 0.3 ms/pulse, 0.03 Hz). The stimulation-evoked neuronal Ca2+ transients expressed with GCaMP6f or jRGECO1a were recorded during the baseline period and after an acute cocaine administration (1 mg/kg, i.v.). Histology confirmed that the efficiency of jRGECO1a and GCaMP6f expression into the cortical neurons was similar, i.e., 34%±3% and 32.7%±1.6%, respectively. Our imaging in vivo showed that the hemodynamic responses to the stimulation were the same between jRGECO1a and GCaMP6f expressed groups. Although the stimulation-evoked fluorescence change (∆F/F) and the time-to-peak of the neuronal Ca2+ transients were not significantly different between these two indicators, the full-width-half-maximum (FWHM) duration of the ∆F/F rise in the jRGECO1a-expressed group (0.16±0.02 s) was ~50 ms or 46% longer than that of the GCaMP6f group (0.11±0.003 s), indicating a longer recovery time in jRGECO1a than in GCaMP6f transients (P<0.01). This is likely due to the longer off rate of jRGECO1a than that of GCaMP6f. After cocaine, the time-to-peak of Ca2+ transients was delayed and their FWHM duration was prolonged for both expression groups, indicating that these are cocaine's effects on neuronal Ca2+ signaling and not artifacts due to the property differences of the GCEIs. This study shows that both jRGECO1a and GCaMP6f have sufficient sensitivity for tracking single-stimulation-evoked Ca2+ transients to detect neuronal activities from the brain. Since these GECIs are emitted at the different wavelengths, it will be possible to use them together to characterize the activity of different cell types (e.g., neurons and astrocytes) to study brain activation and brain functional changes in normal or diseased brains.

X-ray radiation and runaway electron beams generated during discharges in atmospheric-pressure air at rise times of voltage pulse of 500 and 50 ns

AbstractThe parameters of X-ray radiation and runaway electron beams (RAEBs) generated at long-pulse discharges in atmospheric-pressure air were investigated. In the experiments, high-voltage pulses with the rise times of 500 and 50 ns were applied to an interelectrode gap. The gap geometry provided non-uniform distribution of the electric field strength. It was founded that at the voltage pulse rise time of 500 ns and the maximum breakdown voltage Um for 1 cm-length gap, a duration [full width at half maximum (FWHM)] of a RAEB current pulse shrinks to 0.1 ns. A decrease in the breakdown voltage under conditions of a diffuse discharge leads to an increase in the FWHM duration of the electron beam current pulse up to several nanoseconds. It was shown that when the rise time of the voltage pulse is of 500 ns and the diffuse discharge occurs in the gap, the FWHM duration of the X-ray radiation pulse can reach ≈100 ns. It was established that at a pulse-periodic diffuse discharge fed by high-voltage pulses with the rise time of 50 ns, an energy of X-ray quanta and their number increase with increasing breakdown voltage. Wherein the parameter Um/pd is saved.

A quantitative study of the forbidden and intercombination transitions arising from the Li-like Al autoionizing levels

This work presents results from detailed quantitative description of the level population kinetics responsible for the relatively high line-intensity of the forbidden and intercombination transitions arising from autoionization states. The goal is to investigate the influence of different atomic processes on the emission spectrum of the laser-produced aluminum plasma obtained at the nhelix-laser test bed facility at GSI (PRA 63, 032716). In the experiment a Nd-glass YAG laser beam having 50 J pulse energy, 15 ns full width half maximum duration and 1.064 μm wavelength is focused on a massive Al target. To simulate the experimental reported spectrum, the population kinetics is investigated based on a collisional radiative model. The theoretical spectroscopic investigation reported here indicates the existence of anomalous high intensity X-ray intercombination and two-electron transitions arising from autoionizing states in Li-like Al ion. Detailed atomic structure calculation and kinetics modeling is performed to find out the individual states involved, and the population density distribution over them. Presented results are useful for femtosecond-laser produced plasma experiments and diagnostics.

Nanoparticle ζ-potential measurements using tunable resistive pulse sensing with variable pressure

Modern resistive pulse sensing techniques can be used to measure nanoparticle electrophoretic mobility, and hence ζ-potential. In contrast to conventional light scattering methods, resistive pulse sensing produces particle-by-particle data. We have used tunable resistive pulse sensing (TRPS) to compare methods for measuring the ζ-potential of carboxylated polystyrene nanoparticles. The five particle sets studied had nominal surface charge density (σ) between 0 and −0.67Cm−2, and diameters in the range 160–230nm. Data were collected with pressure in the range ±500Pa applied across a tunable pore. In each experiment, pressure was varied either continuously or in discrete steps. Calculations of the ζ-potential were obtained by analysing both the rate and the full-width half maximum duration of resistive pulses. Data obtained from duration analyses were more reproducible than rate methods, yielding typical variations smaller than ±5mV. When σ was greater (less negative) than −0.32Cm−2, all of the analysis methods studied yielded a monotonic relationship between ζ-potential and σ. Complicated pulse data were observed near the pressure at which the net particle flux is zero, and these observations have been explored by examining competition between electrokinetic and pressure-driven transport. The typical difference between ζ-potentials obtained using TRPS and phase analysis light scattering was 15% (<5mV), with an experimental error of ∼10% attributable to both techniques.

Electron emission from La-Doped lead zirconate stannate titanate antiferroelectric ceramic under fast electric field pulses

High current density pulsed-electron emission is observed from a lead zirconate stannate titanate lanthanum-doped (PLZST) antiferroelectric ceramic disc on application of positive or negative triggering voltage pulses. Electron-emission pulse with a peak current density 1,400 A/cm2 and a full-width at half-maximum (FWHM) duration of 560 ns was recorded in the presence of a 3.5 kV dc extraction voltage. It is higher than the various earlier results obtained using lead zirconate titanate ferroelectric ceramic. Self emission of electrons with a current density of 1.3 A/cm2 and the FWHM duration of about 100 ns were also observed. Strong electrons emission was the co-effect of surface plasma and noncompensated charges at the surface of the antiferroelectric. Field-induced local phase transition in the vicinity close to triple junction results in primary electron emission from these areas. These primary emission electrons ignited surface plasma and then led to the strong emission.

Monte Carlo analysis of MEGA microlensing events towards M 31

We perform an analytical study and a Monte Carlo (MC) analysis of the main features for microlensing events in pixel lensing observations towards M31. Our main aim is to investigate the lens nature and location of the 14 candidate events found by the MEGA collaboration. Assuming a reference model for the mass distribution in M31 and the standard model for our galaxy, we estimate the MACHO-to-self lensing probability and the event time duration towards M31. Reproducing the MEGA observing conditions, as a result we get the MC event number density distribution as a function of the event full-width half-maximum duration t1/2 and the magnitude at maximum Rmax. For a MACHO mass of 0.5 M⊙ we find typical values of t1/2 ≃ 20 day and Rmax ≃ 22, for both MACHO-lensing and self-lensing events occurring beyond about 10 arcminutes from the M31 center. A comparison of the observed features (t1/2 and Rmax) with our MC results shows that for a MACHO mass > 0.1 M⊙ the four innermost MEGA events are most likely self-lensing events, whereas the six outermost events must be genuine MACHO-lensing events.