Slope ratio calibration for analysis of plant leaves by laser-induced breakdown spectroscopy

A new calibration strategy based on the increase of the ablated mass with the number of accumulated laser pulses on a single solid calibration standard is proposed for laser-induced breakdown spectroscopy (LIBS).

How cores grow by pebble accretion

Context. Planet formation by pebble accretion is an alternative to planetesimal-driven core accretion. In this scenario, planets grow by the accretion of cm- to m-sized pebbles instead of km-sized planetesimals. One of the main differences with planetesimal-driven core accretion is the increased thermal ablation experienced by pebbles. This can provide early enrichment to the planet’s envelope, which influences its subsequent evolution and changes the process of core growth. Aims. We aim to predict core masses and envelope compositions of planets that form by pebble accretion and compare mass deposition of pebbles to planetesimals. Specifically, we calculate the core mass where pebbles completely evaporate and are absorbed before reaching the core, which signifies the end of direct core growth. Methods. We model the early growth of a protoplanet by calculating the structure of its envelope, taking into account the fate of impacting pebbles or planetesimals. The region where high-Z material can exist in vapor form is determined by the temperature-dependent vapor pressure. We include enrichment effects by locally modifying the mean molecular weight of the envelope. Results. In the pebble case, three phases of core growth can be identified. In the first phase (Mcore < 0.23–0.39 M⊕), pebbles impact the core without significant ablation. During the second phase (Mcore < 0.5M⊕), ablation becomes increasingly severe. A layer of high-Z vapor starts to form around the core that absorbs a small fraction of the ablated mass. The rest of the material either rains out to the core or instead mixes outwards, slowing core growth. In the third phase (Mcore > 0.5M⊕), the high-Z inner region expands outwards, absorbing an increasing fraction of the ablated material as vapor. Rainout ends before the core mass reaches 0.6 M⊕, terminating direct core growth. In the case of icy H2O pebbles, this happens before 0.1 M⊕. Conclusions. Our results indicate that pebble accretion can directly form rocky cores up to only 0.6 M⊕, and is unable to form similarly sized icy cores. Subsequent core growth can proceed indirectly when the planet cools, provided it is able to retain its high-Z material.

Interaction of High Power Laser with Carbon Doped PVC

To measure the propulsion characters of PVC(poly vinyl chloride) doped with carbon ablated by high power density laser, torsion pendulum is used to measure the micro impulse. Laser interference is used to detect the vibration of the pendulum which is caused by the ablating jet. The measurement error is 2.6 according to the calibration. Nd:YAG laser is used as the laser source. Mettler-Toledo XS105DU analytical balance is used to measure the ablated mass. The results indicate that the performance of PVC+2C is better as an alternate target. Both the specific impulse(Isp) and energy transforming efficiency() increase with laser power density(I0), while momentum coupling coefficient(Cm) decreases. The maximum measured Cm is 557N/W. Isp and  reach to 204s and 46 respectively.

Influence of Electrode Flare Angle on the Performance of Pulsed Plasma Thruster

In order to study the influence of electrode flare angle on the performance of Ablation Pulsed Plasma Thruster. Discharge character, plasma velocity and performance over different electrode flare angles of the Pulsed Plasma Thruster at 13.5J initial energy are measured experimentally, the effect of electrode flare angle on the electrode inductance gradient, equivalent circuit parameters and energy transfer efficiency are analyzed. It can be seen that the circuit parameters and inductance distribution are changed with electrode flare angle, the impulse bit, specific impulse, thruster efficiency and mean exhaust velocity increase non-linearly with flare angle increasing from 0 degree to 27 degree and the Pulsed Plasma Thruster gets the maximum thruster performance at 27 degree flare angle. It shows that with the increase of electrode flare angle the fraction of ablated mass accelerated magnetically and the impulse bit created by Lorentz force decrease are the reasons inducing the change in thruster performance.