Hasil untuk "Explosives and pyrotechnics"

Ruixuan Xu, Zhihua Xue, Danfeng Yang et al.

Achieving high energy release of aluminum (Al) and ammonium perchlorate (AP) is of significant importance in the realm of energy materials. In this work, integrated Al@AP/GO‐CHZ‐M (M = Co2+ or Ni2+) composites are successfully synthesized through an integrated design and precise catalysis approach. The integrated Al@AP/Co composites exhibit fast decomposition, with a 76.6 °C reduction in decomposition temperature and a 66.0% increase in heat release compared to Al+AP mixture counterpart. From a kinetic perspective, the decomposition activation energy for Al@AP/Co is largely decreased by 215.5 kJ mol−1 (−67.4%) and its kinetics shifted to an autocatalytic model. Transition metals in GO‐CHZ‐M facilitate the proton transfer during the decomposition of AP, significantly increasing the yield of low‐valence nitrogen oxides. The ignition of the Al@AP/M composites is enhanced, with a 37.2 ms (−40.2%) reduction in ignition delay and a 6.6‐fold increase in radiation intensity over Al+AP. The change from deflagration for the physical mixture to detonation for integrated Al@AP/M composites further suggests high energy release. Furthermore, the mechanism of the integrated design and precise catalysis on the energy release enhancement of Al@AP composites is elucidated. This approach holds broad application prospects in the fields of solid propellants, aluminized explosives, micro‐thrusters, and pyrotechnics systems.

M. Samsonov, Jakub Mikuláštík, R. Matyáš et al.

The safe stockpiling of high-energy combustible and explosive materials is important for environmental and human population protection, particularly in mining and military areas. MTX-1 (2-(tetrazol-5-yl-diazenyl)guanidine) is used in percussion primer compositions that react rapidly with the hydroxides of alkali or alkaline earth metals to form complexes of diverse composition. These are insensitive to mechanical stimuli and to intense heat under high confinement. The most stable complexes were found to be those with ions having the smallest effective ion radii (Mg2+ and Ca2+), followed by Li+. These complexes form discrete mononuclear (Mg2+ and Ca2+) or dimeric (Li+) structures in the solid state. One-dimensional (1D) (Na+, Sr2+, and Ba2+), 2D (K+ and Rb+), and 3D (Cs+) coordination polymeric structures were found for the remaining complexes with larger ions. Detailed topological analysis of the electron density and quantitative estimation of π-π stacking interactions were performed. Complexes could be used for intense flame coloring in pyrotechnics. Upon thermal treatment of complexes over ∼200 °C, water is lost from the coordination sphere of the metal ion, which leads to materials that are slightly sensitive and rehydrate in moist air. Recovery of insoluble MTX-1 is possible when these complexes are treated with an aqueous acid.

André Anders

Ever since they have been studied, gas discharges have been classified by their visual appearance as well as by their current and voltage levels. Glow and arc discharges are the most prominent and well-known modes of discharges involving electrodes. In a first approximation, they are distinguished by their current and voltage levels, and current–voltage characteristics are a common way to display their relations. In this review, glow discharges are defined by their individual electron emission mechanism such as secondary electron emission by photons and primary ions, and arcs by their respective collective mechanism such as thermionic or explosive electron emission. Emitted electrons are accelerated in the cathode sheath and play an important role in sustaining the discharge plasma. In some cases, however, electron emission is not important for sustaining the plasma, and consequently we have neither a glow nor an arc discharge but a third type of discharge, the ohmic discharge. In part 1 of this review, these relationships are explained for quasi-stationary discharges, culminating with updated graphical presentations of I–V characteristics (Figs. 15 and 16). In part 2, further examples are reviewed to include time-dependent discharges, discharges with electron trapping (hollow cathode, E×B discharges) and active anode effects.

Syed M. Hamedoon, J. N. Chattha, Umair Rashid et al.

Internet of Things (IoT) is playing a significant role in wireless communication for future applications such as smart home, smart cities, intelligent transportation, telecare, and various other applications. However, the emergence of IoT on a large scale has introduced numerous challenges to current wireless communication system connectivity, coverage and energy dissipation. We propose a Reconfigurable Intelligent Surface (RIS)-assisted downlink Non-Orthogonal Multiple Access (NOMA) for Internet of Things (IoT) network, where we address the challenge of optimizing power allocation, RIS phase shifts, and energy efficiency. In our approach, users are first clustered based on channel gain differences and then performed optimization of resources. The primary objective is to maximize system performance through a series of optimization techniques. Initially, joint optimization of power allocation and RIS phase shifts is carried out to enhance energy efficiency, addressing the non-convexity of the problem through alternating optimization and fractional programming. Subsequently, an alternative optimization strategy is employed using the Karush-Kuhn-Tucker (KKT) conditions to further refine power allocation and RIS phase shifts, aiming to maximize the effective throughput across the transmission period. The deployment of machine learning (ML) is critically important for addressing the challenges posed by the explosive growth in data volume and computational complexity, particularly in the optimization of smart 6G networks. In the final phase, we introduce a deep learning (DL) and reinforcement learning (RL) approach to jointly optimize power allocation and RIS phase shifts in dynamic environments. The DL approach demonstrates superior performance in terms of system sum rate, especially under varying network conditions, while the RL approach excels in long-term reward optimization. Numerical results validate the proposed framework, showing significant improvements in both sum rate and energy efficiency.

Yuvaraja Dibdalli, Héctor Pérez, Alejandro López-Telgie et al.

Xue-Mei Li, Kexing Ying

We establish a non-explosion result for rough differential equations (RDEs) in which the noise and drift coefficients, together with their derivatives, may grow unboundedly at infinity. In addition, we prove the existence of a global bi-continuous solution flow for stochastic differential equations (SDEs). Finally, the non-explosion results for RDEs are shown to be sharp by constructing counterexamples.

Eduardo Abi Jaber, Paul Gassiat, Dimitri Sotnikov

We study the martingale property and moment explosions of a signature volatility model, where the volatility process of the log-price is given by a linear form of the signature of a time-extended Brownian motion. Excluding trivial cases, we demonstrate that the price process is a true martingale if and only if the order of the linear form is odd and a correlation parameter is negative. The proof involves a fine analysis of the explosion time of a signature stochastic differential equation. This result is of key practical relevance, as it highlights that, when used for approximation purposes, the linear combination of signature elements must be taken of odd order to preserve the martingale property. Once martingality is established, we also characterize the existence of higher moments of the price process in terms of a condition on a correlation parameter.

David León, Isabel Amez, Roberto Paredes et al.

Flash powder, an explosive compound widely used in flash bangers and pyrotechnic shells, among others, has emerged as a critical point in discussions about the negative effects of its use. Currently, fireworks present significant challenges due to their adverse impacts on the environment and the generation of acoustic disturbances in residential and urban areas due, among other compounds, to flash powder. This powder, mainly composed of potassium perchlorate and metallic compounds such as aluminium or magnesium, is crucial to achieve the opening and bursting of pyrotechnic devices. Therefore, it is necessary to develop alternatives that solve the flash powder associated problems to give a sustainable future to the pyrotechnic sector. This study proposes compositions that could be possible alternatives to reduce emissions and sound pressure levels, whit the intention of ensuring suitable performance for these pyrotechnic articles. F2 category flash bangers from different manufacturers were collected. The operation of these bangers was compared in different tests, by adding inert materials such as sodium bicarbonate (NaHCO3) and recycled glass, at 10 % and 20 % (w/w), and by replacing the flash powder with nitrocellulose ([C6H7(NO2)3O5]n), with a nitrogen percentage of less than 12.6 %, as stated in the European pyrotechnics regulation. The samples were subjected to sound pressure level measurements according to EN 15947-4:2022 standard, but also CO and CO2 emissions were evaluated. It was observed that the compositions studied could lead to a significant reduction in both pollutant emissions and the noise level generated by the pyrotechnic articles. After studying the explosion pressure generated for their substitution in pyrotechnic shells, it is concluded that the addition of inert compounds can be a real alternative. However, the nitrocellulose does not achieve a correct operation as a substitute for flash powder, and nitrocellulose with a higher nitrogen content must be studied.

B. V. Baal, A. Jerkstrand

In the nebular phase, supernovae are powered by radioactive decay and continuously fade, while their densities have decreased enough such that the expanding nebula becomes (largely) optically thin and the entire structure can be studied. Models for the nebular phase need to take Non-Local Thermodynamic Equilibrium (NLTE) effects into account, while at the same time radiative transfer effects often cannot be ignored. To account for the asymmetric morphologies of SNe, 3D input ejecta models must be used. In this work, we present the \texttt{ExTraSS} (EXplosive TRAnsient Spectral Simulator) code, which has been upgraded to be fully capable of 3D NLTE radiative transfer calculations in order to generate synthetic spectra for explosive transients in the nebular phase, with a focus on supernovae. We solve the long-standing difficulty of 3D NLTE radiative transfer -- to manage generation and storage of millions of photoexcitation rates over $\sim10^{5}$ of cells -- by developing a new Domain Decomposition algorithm. We describe this new methodology and general code operations in detail, and verify convergence and accuracy.

A. Jerkstrand, Dan Milisavjlevic, B. Muller

Core-collapse supernovae (CCSNe) are the explosive end-points of stellar evolution for $M_{ZAMS} \gtrsim 8$ $M_\odot$ stars. The cores of these stars collapse to neutron stars, a process in which high neutrino luminosity drives off the overlying stellar layers, which get ejected with thousands of kilometers per second. These supernovae enrich their host galaxies with elements made both during the star's life and in the explosion, providing the main cosmic source of elements such as oxygen, neon and silicon. Their high luminosities ($\sim$ $10^{42}$ erg s$^{-1}$ at peak) make SNe beacons to large distances, and their light curves and spectra provide rich information on single and binary stellar evolution, nucleosynthesis, and a diverse set of high-energy physical processes. As the SN ejecta sweep up circumstellar and interstellar matter, it eventually enters a supernova remnant phase, exemplified by nearby, spatially resolved remnants such as Cas A and the Crab Nebula. In this phase, shocks and pulsar winds continue to light up the interior of the exploded stars, giving detailed information about their 3D structure. We review the central concepts of CCSNe, from the late stages of evolution of massive stars, through collapse, explosion, and electromagnetic display, to the final remnant phase. We briefly discuss still open questions, and current and future research avenues.

B. V. Baal, A. Jerkstrand, D. Kresse et al.

The nebular phase of a supernova (SN) occurs several months to years after the explosion, when the ejecta become mostly optically thin yet there still is sufficient radioactive material to keep the supernova bright. The asymmetries created by the explosion are encoded into the line profiles of the emission lines which appear in the nebular phase. In order to make accurate predictions for these line profiles, Non-Local Thermodynamic Equilibrium (NLTE) radiative transfer calculations need to be carried out. In this work, we use \texttt{ExTraSS} (EXplosive TRAnsient Spectral Simulator) -- which was recently upgraded into a full 3D NLTE radiative transfer code (including photoionization and line-by-line transfer effects) -- to carry out such calculations. \texttt{ExTraSS} is applied to a 3D explosion model of a $9.0\,M_\odot$ H-rich progenitor which is evolved into the homologous phase. Synthetic spectra are computed and the lines from different elements are studied for varying viewing angles. The model spectra are also compared against observations of SN 1997D and SN 2016bkv. The model is capable of creating good line profile matches for both SNe, and reasonable luminosity matches for He, C, O, and Mg lines for SN 1997D -- however H$\alpha$ and Fe I lines are too strong.

Anders Borkenhagen, A. Babic

Igor Panov, Anton Ignatovskiy, Andrey Yudin

The pattern of nucleosynthesis during the explosion of a low-mass neutron star formed in a close binary system in the stripping scenario is considered. In the scenario considered the shock arising during the explosion is shown to strongly heat the expanding neutron star matter. The heavy nuclei produced at the preceding stage of nucleosynthesis are partially destroyed as a result of a sharp increase in the role of photonuclear reactions. It is shown that even short-term heating of the matter by the shock can exert a noticeable influence on the results of the synthesis of elements in the r-process in the inner crust matter, while explosive nucleosynthesis gives rise to new elements in the outer crust matter with mass numbers A from 50 to 130.

E. A. Zimmerman, I. Irani, P. Chen et al.

Observing a supernova explosion shortly after it occurs can reveal important information about the physics of stellar explosions and the nature of the progenitor stars of supernovae (SNe). When a star with a well-defined edge explodes in vacuum, the first photons to escape from its surface appear as a brief shock-breakout flare. The duration of this flare can extend to at most a few hours even for nonspherical breakouts from supergiant stars, after which the explosion ejecta should expand and cool. Alternatively, for stars exploding within a distribution of sufficiently dense optically thick circumstellar material, the first photons escape from the material beyond the stellar edge, and the duration of the initial flare can extend to several days, during which the escaping emission indicates photospheric heating. The difficulty in detecting SN explosions promptly after the event has so far limited data regarding supergiant stellar explosions mostly to serendipitous observations that, owing to the lack of ultraviolet (UV) data, were unable to determine whether the early emission is heating or cooling, and hence the nature of the early explosion event. Here, we report observations of SN 2023ixf in the nearby galaxy M101, covering the early days of the event. Using UV spectroscopy from the Hubble Space Telescope (HST) as well as a comprehensive set of additional multiwavelength observations, we trace the photometric and spectroscopic evolution of the event and are able to temporally resolve the emergence and evolution of the SN emission.

Inyoung Paik, Jaesik Choi

Deep neural networks, which employ batch normalization and ReLU-like activation functions, suffer from instability in the early stages of training due to the high gradient induced by temporal gradient explosion. In this study, we analyze the occurrence and mitigation of gradient explosion both theoretically and empirically, and discover that the correlation between activations plays a key role in preventing the gradient explosion from persisting throughout the training. Finally, based on our observations, we propose an improved adaptive learning rate algorithm to effectively control the training instability.

Pierre-Henri Chavanis, Bruno Denet, Martine Le Berre et al.

Supernovae explosions of massive stars are nowadays believed to result from a two-step process, with an initial gravitational core collapse followed by an expansion of matter after a bouncing on the core. This scenario meets several difficulties. We show that it is not the only possible one: a simple model based on fluid mechanics and stability properties of the equilibrium state shows that one can have also a simultaneous inward/outward motion in the early stage of the instability of the supernova. This shows up in the slow sweeping across a saddle-center bifurcation found when considering equilibrium states associated to the constraint of energy conservation. We first discuss the weakly nonlinear regime in terms of a Painlevé I equation. We then show that the strongly nonlinear regime displays a self-similar behavior of the core collapse. Finally, the expansion of the remnants is revisited as an isentropic process leading to shocks formation.

Svetlana V. Gurevich, Christian Schelte, Julien Javaloyes

We investigate the impact of higher-order nonlinear and dispersive effects on the onset of soliton explosions in the complex cubic-quintic Ginzburg-Landau equation. We show how the interplay of the high order effects (HOEs) results in the splitting of symmetric explosion modes and to the formation of right- or left-side periodic explosions. In addition, we demonstrate that HOEs induce a series of pulsating instabilities, leading to a significant reduction of the stability region of the single soliton solution.

Stefan Richter, Weining Wang, Wei Biao Wu

We develop a uniform test for detecting and dating explosive behavior of a strictly stationary GARCH$(r,s)$ (generalized autoregressive conditional heteroskedasticity) process. Namely, we test the null hypothesis of a globally stable GARCH process with constant parameters against an alternative where there is an 'abnormal' period with changed parameter values. During this period, the change may lead to an explosive behavior of the volatility process. It is assumed that both the magnitude and the timing of the breaks are unknown. We develop a double supreme test for the existence of a break, and then provide an algorithm to identify the period of change. Our theoretical results hold under mild moment assumptions on the innovations of the GARCH process. Technically, the existing properties for the QMLE in the GARCH model need to be reinvestigated to hold uniformly over all possible periods of change. The key results involve a uniform weak Bahadur representation for the estimated parameters, which leads to weak convergence of the test statistic to the supreme of a Gaussian Process. In simulations we show that the test has good size and power for reasonably large time series lengths. We apply the test to Apple asset returns and Bitcoin returns.

Roland Diehl

Gamma ray lines are expected to be emitted as part of the afterglow of supernova explosions, because radioactive decay of freshly synthesised nuclei occurs. Significant radioactive gamma ray line emission is expected from 56Ni and 44Ti decay on time scales of the initial explosion (56Ni, tau~days) and the young supernova remnant (44Ti,tau~90 years). Less specific, and rather informative for the supernova population as a whole, are lessons from longer lived isotopes such as 26Al and 60Fe. From isotopes of elements heavier than iron group elements, any interesting gamma-ray line emission is too faint to be observable. Measurements with space-based gamma-ray telescopes have obtained interesting gamma ray line emissions from two core collapse events, Cas A and SN1987A, and one thermonuclear event, SN2014J. We discuss INTEGRAL data from all above isotopes, including all line and continuum signatures from these two objects, and the surveys for more supernovae, that have been performed by gamma ray spectrometry. Our objective here is to illustrate what can be learned from gamma-ray line emission properties about the explosions and their astrophysics.

Noam Soker

I use recent observational and theoretical studies of type Ia supernovae (SNe Ia) to further constrain the viable SN Ia scenarios and to argue that there must be a substantial time delay between the end of the merger of the white dwarf (WD) with a companion or the end of mass accretion on to the WD and its terminal explosion. This merger/accretion to explosion delay (MED) is required to allow the binary system to lead to a more or less spherical explosion and to prevent a pre-explosion ionizing radiation. Considering these recent results and the required MED, I conclude that the core degenerate scenario is somewhat more favorable over the other scenarios, followed by the double degenerate scenario. Although the single degenerate scenario is viable as well, it is less likely to account for common (normal) SN Ia. As all scenarios require substantial MED, the MED has turned from a disadvantage of the core degenerate scenario to a challenge that theory should overcome. I hope that the requirement for a MED will stimulate the discussion of the different SN Ia scenarios and the comparison of the scenarios to each other.