High-voltage pulse rise time decreasing using transmission coaxial and spiral lines with ferrite

This article presents the results of a study of the formation of a short rise time of a powerful nanosecond 410 kV pulse. Ferrite filled coaxial transmission lines with standard inner conductor and construction in the form of a spiral are designed. The sharpening of the pulse occurs due to the appearance of an electromagnetic shock wave in the ferrite. The value of the rise time at the level of 0.1 - 0.9 has been decreased from 4.5 to 2.5 ns.

SN 2019muj – a well-observed Type Iax supernova that bridges the luminosity gap of the class

ABSTRACT We present early-time (t < +50 d) observations of SN 2019muj (=ASASSN-19tr), one of the best-observed members of the peculiar SN Iax class. Ultraviolet and optical photometric and optical and near-infrared spectroscopic follow-up started from ∼5 d before maximum light [tmax(B) on $58707.8$ MJD] and covers the photospheric phase. The early observations allow us to estimate the physical properties of the ejecta and characterize the possible divergence from a uniform chemical abundance structure. The estimated bolometric light-curve peaks at 1.05 × 1042 erg s−1 and indicates that only 0.031 M⊙ of 56Ni was produced, making SN 2019muj a moderate luminosity object in the Iax class with peak absolute magnitude of $M_\rm {V} = -16.4$ mag. The estimated date of explosion is t0 = $58698.2$ MJD and implies a short rise time of trise = 9.6 d in B band. We fit of the spectroscopic data by synthetic spectra, calculated via the radiative transfer code tardis. Adopting the partially stratified abundance template based on brighter SNe Iax provides a good match with SN 2019muj. However, without earlier spectra, the need for stratification cannot be stated in most of the elements, except carbon, which is allowed to appear in the outer layers only. SN 2019muj provides a unique opportunity to link extremely low-luminosity SNe Iax to well-studied, brighter SNe Iax.

Power Efficient Current Driver Based on Negative Boosting for High-Speed Lasers

Vertical-cavity surface-emitting lasers (VCSELs) are commonly used in high-speed optical communication and 3D sensing applications. Both of these applications require high switching frequency and a short rise time of the VCSEL current. The parasitic inductance of the wire (connecting the driver with VCSEL) makes it challenging to achieve a short rise time, which often incur increased supply voltage and excessive power consumption. This paper utilizes a momentary boosting in supply voltage to overcome the parasitic inductance of the wire with minimal power overhead. The proposed technique uses a precalculated boosting capacitance to produce negative voltage for common-anode VCSELs. The boosting capacitance provides the required amount of charge during the rising transition and automatically disconnects itself in steady-state. Circuit simulations reveal up to three times shorter rise time at the negligible cost of less than 10% power overhead.

Dynamic Mechanical Simulation of Miniature Silicon Membrane during Air Blast for Pressure Measurement

The development of new ultra-fast sensors for pressure air blast monitoring requires taking into account the very short rise time of pressure occurring during explosion. Simulations show here that the dynamic mechanical behavior of membrane-based sensors depends significantly on this rise time when the fundamental mechanical resonant frequency of the membrane is higher than 10 MHz.

Collector Conductivity Modulation in 1200-V 4H-SiC BJTs (Modeling)

The resistance of the BJT collector layer can be sharply reduced by the effective injection of minority carriers (holes) from base to collector. As a result, the voltage drop across the BJT becomes substantially lower. The conditions under which this process can occur are the short rise time and the high amplitude of the base pulse.

Electron energy spectrum produced by stochastic acceleration in the laser–plasma interaction

In this paper, the electrons energy spectrum produced by stochastic acceleration in the interaction of an intense laser pulse with the underdense plasma is described by employing the fully kinetic 1D-3 V particle-in-cell simulation. In this way, two finite laser pulses with the same length 200 fs and with two different rise times 30 and 60 fs are typically selected. It is shown that the maximum energy of electrons in the laser pulse with the short rise time (30 fs) is about eight times greater than the maximum energy of the electrons with the long rise time (60 fs). Furthermore, unlike the pulse with the short rise time, the shape of energy spectrum and the electrons temperature in the long rise time laser pulse are approximately unchanged over the time. These results originated from the fact that in the case of long rise time laser pulse, all electrons are accelerated by the one chaotic mechanism because of the scattered fields generated in the plasma, but in the case of short rise time laser pulse, three different mechanisms accelerate the electrons: first, the stochastic acceleration because of the nonlinear wave breaking via plasma-vacuum boundary effect; second, the stochastic acceleration initiated by the wave breaking; and third, the direct laser acceleration of the released electrons.