Features of Melt Droplet Formation during Electrical Destruction Aluminum Films on the Semiconductor Surface

The work is devoted to processes during melting of thin aluminium film on silicon surface in pulse current mode. An experiment was conducted to study the dynamics during the onset of the liquid phase on a metal film. Besides, the process of formation droplet localization zones is considered. The experimental part revealed critical current values ​ during an electrical explosion of thin metal films near the thermal shock source. Using the oscillographic method, the temperature profile of the metallization track is calculated.

New bow-shock source with bipolar morphology in the vicinity of Sgr A*

Context. We find an extended source in the direct vicinity of Sgr A* with an approximate projected mean distance of 425 ± 26 mas. Its sky-projected elongated shape can be described by an averaged spatial extension ofx = 110 ± 20 mas andy = 180 ± 20 mas. With this, the observed object points in the analyzed SINFONI data sets between 2006 and 2016 directly toward the supermassive black hole. We discuss different possible scenarios that could explain the detected blueshifted line emission source.Aims. Here we present a detailed and extensive analysis of the adaptive optics corrected SINFONI data between 2006 and 2016 with a spatial pixel scale of 0.″025 and a corresponding field of view of 0.″8 × 0.″8 per single data cube with the focus on the newly discovered source. We spectroscopically identify the source, which we name X8, in the blueshifted Brγline maps. Additionally, an upper limit for the continuum magnitude can be derived from the close-by S-star S41.Methods. We applied the standard reduction procedure with the SINFONI/EsoRex pipeline for the analysis. We applied pre- and post-data correction in order to establish various calibration procedures. For the sharpened images, we used the Lucy–Richardson algorithm with a low iteration number. For the high-pass filtered images, we used the smooth-subtracting process in order to increase the signal-to-noise ratio.Results. We are able to detect the elongated line emission source in quantified data sets between 2006 and 2016. We find a lower limit for the infrared continuum magnitude ofKs ≳ 17.0 ± 0.1. The alignment of X8 toward Sgr A* can be detected in data sets that fulfill a sufficient number of observations with a defined quality level. A more detailed analysis of the results shows indications of a bipolar outflow source that might be associated with either a young stellar object, or with a post-AGB star or young planetary nebula.Conclusions. The near-infrared excess source X8 close to S24, S25, and S41 can be detected between 2006 and 2016. In addition to an apparent bow-shock morphology, the source shows clear signatures of a bipolar outflow that is consistent with both a young stellar object and a post-AGB star. If confirmed, this would be the closest ever detected bipolar outflow source to the supermassive black hole. Similar to the case of the DSO/G2 source and other dusty sources, it further supports the in situ star formation in the direct vicinity of Sgr A*. If X8 were a bow-shock source, it would be the third object of this type that can be found in projection in the mini-cavity. This scenario would support the idea that the cavity is created by a wind from Sgr A*.

Numerical Study of Separation Characteristics of Piston-Type Explosive Bolt

An explosive bolt is a simple, highly reliable, and efficient pyrotechnic release device widely used in spacecraft and rocket launchers. High shock transient response is generated during the separation of a release device, which tends to damage the nearby micromechanism and hardware. The purpose of this article is to predict the shock response of an explosive bolt. In this paper, the separation process of a piston-type explosive bolt is simulated by using a hydrocode named AUTODYN and the influence of the charge amount on separation time, separation speed, and separation shock is analyzed. Results show that piston-type explosive bolts obey a tensile fracture mechanism and that the critical charge amount for separation is 354–398 mg of PETN. The separation shock of such an explosive bolt mainly includes two aspects: the shock caused by explosive detonations and the impact of the piston at the end of the stroke. As the charge amount increases, the separation time decreases, the speed of the piston and screw increases first and then decreases, and the separation shock first increases and then stabilizes. On a simple aluminum plate, the shock response decreases as the distance from the shock source increases, obeying the power function attenuation law.

Identification of Pyrotechnic Shock Sources for Shear Type Explosive Bolt

To identify the shock generated sources of shear type explosive bolt, five kinds of explosive bolts with different states, including high preload, low preload, no preload, no piston shear, and only propellant combustion, were designed. The decoupling of four kinds of shock sources, including the collision of propellant combustion, piston shear weak surface, end of piston stroke, and preload release, was realized. Their acceleration responses at 15 cm from the shock source center on 60 cm × 60 cm × 1 cm equivalent aluminum plate were measured by using the piezoresistive accelerometer. On this account, the relative contribution values along with frequency and the mean relative values without regard to frequency of various sources were calculated in high and low preload. Results show that the characteristics of different shock sources are different, and the shock induced by propellant combustion is mainly caused by high frequency, while piston shear and piston impact are concentrated in medium and low frequency. In the high preload condition, the preload release is major contributor to the overall shock response output, accounting for approximately 57.51%, while the contributions of the three shock sources of propellant combustion, piston shear, and piston impact are equivalent, but they are significant contributors in the low preload condition. This study provides design reference to reduce the pyrotechnic shock of shear type explosive bolt.

A new MIR bow shock source in the Galactic center

We find a convex-like feature at a distance of 0.68 pc (17″) from the position of the supermassive black hole, Sgr A*, at the center of the nuclear stellar cluster. This feature resembles a stellar bow shock with a symmetry axis pointing to the center. We discuss the possible nature of the feature and the implications of its alignment with other dusty comet-like objects inside the central parsec.