Particle-in-cell simulations of rf breakdown

Breakdown voltages of a capacitively coupled radio frequency argon discharge at 27 MHz are studied. We use a one-dimensional electrostatic PIC code to investigate the effect of changing the secondary emission properties of the electrodes on the breakdown voltage, particularly at low pd values. Simulation results are compared with the available experimental results and a satisfactory agreement is found.Comment: 12th International Congress on Plasma Physics, 25-29 October 2004, Nice (France

Cosmological gas accretion history onto the stellar discs of Milky Way-like galaxies in the Auriga simulations -- (I) Temporal dependency

We use the 30 simulations of the Auriga Project to estimate the temporal dependency of the inflow, outflow and net accretion rates onto the discs of Milky Way-like galaxies. The net accretion rates are found to be similar for all galaxies at early times, increasing rapidly up to $\sim 10~\mathrm{M}_\odot \, \mathrm{yr}^{-1}$. After $\sim 6~\mathrm{Gyr}$ of evolution, however, the net accretion rates are diverse: in most galaxies, these exhibit an exponential-like decay, but some systems instead present increasing or approximately constant levels up to the present time. An exponential fit to the net accretion rates averaged over the MW analogues yields typical decay time-scale of $7.2~\mathrm{Gyr}$. The analysis of the time-evolution of the inflow and outflow rates, and their relation to the star formation rate (SFR) in the discs, confirms the close connection between these quantities. First, the inflow$/$outflow ratio stays approximately constant, with typical values of $\dot{M}_\mathrm{out}/ \dot{M}_\mathrm{in} \sim 0.75$, indicating that the gas mass involved in outflows is of the order of 25% lower compared to that involved in inflows. A similar behaviour is found for the SFR$/$inflow rate ratio, with typical values between 0.1 and 0.3, and for the outflow rate$/$SFR which varies in the range $3.5$--$5.5$. Our results show that continuous inflow is key to the SFR levels in disc galaxies, and that the star formation activity and the subsequent feedback in the discs is able to produce mass-loaded galaxy winds in the disc-halo interface.Comment: 21 pages, 15 figure

Cosmological gas accretion history on to the stellar discs of Milky Way-like galaxies in the Auriga simulations – II. The inside–out growth of discs

We investigate the growth of stellar discs in Milky Way-mass galaxies using the magnetohydrodynamical simulations of the Auriga Project in a full cosmological context. We focus on the gas accretion process along the discs, calculating the net, infall and outflow rates as a function of galactocentric distance, and investigate the relation between them and the star formation activity. The stellar distributions of around 70 per cent of the simulated galaxies exhibit an ‘inside–out’ pattern, with older (younger) stellar populations preferentially located in the inner (outer) disc regions. In all cases, we find a very tight correlation between the infall, outflow, and net accretion rates, as well as between these three quantities and the star formation rate. This is because the amount of gas which is ultimately available for star formation in each radial ring depends not only on the infall rates, but also on the amount of gas leaving the disc in outflows, which directly relates to the local star formation level. Therefore, any of these rates can be used to identify galaxies with inside–out growth. For these galaxies, the correlation between the dominant times of accretion/star formation and disc radius is well fitted by a linear function. We also find that, when averaged over galaxies with formation histories similar to the Milky Way, the simulated accretion rates show a similar evolution (both temporally and radially integrated) to the usual accretion prescriptions used in chemical evolution models, although some major differences arise at early times and in the inner disc regions

The mechanism of striation formation in plasma display panels

This article was published in the journal, Journal of applied physics [© American Institute of Physics] and is also available at: http://jap.aip.orgDespite the high pressure employed in plasma display panels, the energy balance of low-energy electrons is found to be dominated by inelastic collisions, and the resulting nonlocal electron kinetics plays a key role in the striation formation. Surface charge accumulation on the anode dielectric, however, is also needed for striations to form. It is the combined effect of surface charges and nonlocal electron kinetics that results in the striation formation in plasma display panel cells. Two-dimensional fluid simulations, which assume local electron kinetics, and two-dimensional particle-in-cell Monte Carlo collision simulations with a bare conducting anode show that striations do not form if either the nonlocal electron kinetics or the surface charge accumulation is not considered

Efficiency Droop Of InGaN/GaN Led With Different Indium Composition

III-nitride light emitting diodes (LEDs) have attracted considerable attraction due to their various applications in displays and illumination lighting. Nevertheless, the majority of InGaN/GaN LEDs suffer from the efficiency droop. This droop would limit the potential of the LEDs in high current applications. As widely reported, high indium content in InGaN/GaN multiquantum well active region of the LED promotes indium fluctuation that degrades the efficiency of the LED. In this work, we will present results of the efficiency droop for InGaN/GaN LED with indium content of 18% and 8%, respectively. The efficiency droop of the LED with 18% of indium shows higher efficiency droop than the LED with 8% of indium content

Effect Of Nucleation Time With TMAl Preflow Assistance On Reducing Dislocation Density Of Aln Layer For

AlGaN-based UVC LEDs have now received numerous attentions due to their ability to eliminate coronaviruses which cause COVID-19 disease. It is therefore essential to improve the efficiency of the LEDs to make them compatible for large scale applications. One of the major challenges to improve the efficiency is to reduce the dislocation density in AlN layer; the base layer for the LEDs, to be below 109 cm-2. Thus far, many works have been proposed to reduce the dislocation in the AlN layer. However, by properly adjusting the AlN nucleation time in the growth of the AlN layer, the dislocation can be reduced. The effect might be more significant with TMAl preflow assistance, which is applied after the growth of the nucleation. In this work, we will present the effect of the nucleation time with the assistance of TMAl preflow on reducing the dislocation density in the overgrown AlN layer. With 60 seconds of nucleation, the density of the dislocation in the AlN layer can be as low as 9.0 x 108 cm-2. In addition. the role of the TMAl preflow assistance will be justified. The AlN layer was subsequently used to grow a 255 nm UVC LED. The diode characteristic and CL emission of the LED will be discussed towards the endof the presentation

Effect Of Nucleation Time With Tmal Preflow Assistance On Reducing Dislocation Density Of Aln Layer For AlGaN-Based UVC LED

AlGaN-based UVC LEDs have now received numerous attentions due to their ability to eliminate coronaviruses which cause COVID-19 disease. It is therefore essential to improve the efficiency of the LEDs to make them compatible for large scale applications. One of the major challenges to improve the efficiency is to reduce the dislocation density in AlN layer; the base layer for the LEDs, to be below 109 cm-2 . Thus far, many works have been proposed to reduce the dislocation in the AlN layer. However, by properly adjusting the AlN nucleation time in the growth of the AlN layer, the dislocation can be reduced. The effect might be more significant with TMAl preflow assistance, which is applied after the growth of the nucleation. In this work, we will present the effect of the nucleation time with the assistance of TMAl preflow on reducing the dislocation density in the overgrown AlN layer. With 60 seconds of nucleation, the density of the dislocation in the AlN layer can be as low as 9.0 x 108 cm-2 . In addition. the role of the TMAl preflow assistance will be justified. The AlN layer was subsequently used to grow a 255 nm UVC LED. The diode characteristic and CL emission of the LED will be discussed towards the end of the presentation

Use of a Cholera Rapid Diagnostic Test during a Mass Vaccination Campaign in Response to an Epidemic in Guinea, 2012

During the 2012 cholera outbreak in the Republic of Guinea, the Ministry of Health, supported by Médecins Sans Frontières - Operational Center Geneva, used the oral cholera vaccine Shanchol as a part of the emergency response. The rapid diagnostic test (RDT) Crystal VC, widely used during outbreaks, detects lipopolysaccharide antigens of Vibrio cholerae O1 and O139, both included in Shanchol. In the context of reactive use of a whole-cell cholera vaccine in a region where cholera cases have been reported, it is essential to know what proportion of vaccinated individuals would be reactive to the RDT and for how long after vaccination