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Recoil leaders develop in lightning flash decayed channels. The propagation of a recoil leader depends on the charges stored at its tip and the conductivity of the decayed channel. When the recoil leader propagates over the entire channel, a subsequent return stroke happens. Recoil leaders very often cease propagating before they reach the ground, that is, only part of the decayed channel is reionized. The present work aims to analyze the herein named secondary recoil leader that connect with the primary recoil leaders and cause them to start propagating again. We believe that the secondary recoil leader injects additional charge into the primary recoil leader, allowing the recoil leader reionize the whole decayed channel of the lightning flash. High‐speed videos analysis of upward lightning flashes shows that secondary recoil leaders play an important role on the formation and progression of dart leaders/subsequent return strokes. Plain Language Summary The recoil leader is a phenomenon that occurs in all types of lightning flashes (upward, downward and intracloud flashes). They arise in the remnants of decayed channels of positive leaders, partially or completely rebuilding these channels. The recoil leaders are responsible for some physical processes observed in lightning flashes. Thus, understanding how these physical processes originate is of significant importance. This work presents the role of secondary recoil leaders (recoil leaders that connect to preexisting recoil leaders) in the integral reconstruction of the decayed channels of the analyzed lightning flashes. Key Points Use of high‐speed cameras to study recoil leaders in upward lightning flashes Secondary recoil leaders boost the development of previous recoil leaders Secondary recoil leaders likely influence the development of dart leaders/subsequent return strokes

The parameter model of the full-open safety valve with different recoil disc convex angles is constructed. Additionally, the CFD software simulation and UDF dynamic mesh technology are used to analyze the change of the convex angle of the recoil disc of the spring full-open safety valve, the pressure distribution, and flow rate distribution of the front and rear areas of the valve disc and the recoil disc on the valve lift. The research results show that the valve lift curve of the recoil disc, convex at different side angles, exhibits clear proportional and protruding characteristics. The lift curve of the safety valve disc increases nonlinearly with the increase of the opening height, and the total lift appears at the maximum at the recoil disc convex angle of 72°. The main factor affecting the lift of the valve disc is the pressure in the front area of the recoil disc.

This paper investigates the influence of gun stock elasticity on the firing stability of a handheld automatic weapon during burst firing. The mechanical characteristics of the stock, including axial stiffness and damping, are analyzed in terms of their effect on muzzle deviation and controllability. A recoil dynamic model incorporating elastic deformation of the stock and its interaction with the shooter's shoulder was developed. Numerical simulations were performed and validated against experimental data obtained from single-shot and burst firing tests on an AKM assault rifle equipped with an elastic stock. The results show that the use of an elastic stock significantly reduces muzzle displacement amplitude. For a stock stiffness of 20,000 N/m, the amplitude decreases by 33.9% in the vertical plane and 32.9% in the horizontal plane compared to the rigid stock. However, the oscillation duration increases by 23.2% and 25.1%, respectively. These findings demonstrate that appropriate tuning of stock elasticity can effectively reduce vibration and off-axis motion, thereby improving firing stability during burst operation. The proposed approach provides a theoretical basis for the design and optimization of gun stocks in modern small arms.

Recoilless launch can improve the adaptability of unmanned platforms to weapons by eliminating recoil, but it has the disadvantage of reducing the initial velocity of the projectile. The initial velocity of the recoilless gun can be improved by increasing the charge mass, so research into the recoilless efficiency of recoilless firing with increasing charge mass is of great importance for future applications of recoilless weapons. Based on the combustible cartridge and induction ignition, the one-dimensional homogeneous flow internal ballistic of a recoilless gun with high initial velocity is established. The effect of the Laval nozzle diameter on the efficiency of the recoilless gun is then investigated. The results show that, compared to conventional guns, the recoil can be reduced to 1N-s without reducing the initial velocity of the projectile. A ballistic test on a slide-rail mount is carried out to verify the results of the analysis. The results should make an important contribution to the development of a recoilless rifle.

The PandaX-4T is a dark matter direct search experiment with a dual-phase xenon detector. It is located at Jinping underground laboratory in Sichuan, China. In 2.8-ton fiducial mass and energy region of interest (range from 1 to 10 keV), the total electron recoil and nuclear recoil backgrounds are estimated to be (4.9±0.5) × 10 −2 mDRU and (2.8±0.5) × 10 −4 mDRU. With an exposure of 5.6 ton-years, the expected sensitivity of PandaX-4T could reach a spin-independent dark matter-nucleon cross section of 6 × 10 −48 cm 2 at a dark matter mass of 40 GeV/c 2 . An overview of detector design, background control and current status will be presented in this paper.

Aiming at the requirement of a 30% reduction in the recoil of the automatic shotgun, the researchers investigated the various thicknesses of the stock rubber, the different hardness of the stock rubber, and the floating buffer mechanism of the gun body. Researchers also conducted the recoil test and comparison to determine the structural scheme for recoil reduction. The test results indicate that the recoil force of the automatic shotgun is reduced by 51.9% compared with that of a fixed shotgun when using NBR (nitrile rubber buna) with a thickness of 20 mm and a hardness of 20 Shore hardness. The technical measures adopted are effective and can meet the requirements of the specified technical indicators.

In order to model recoil motion of artillery elaborately, the pneumatic recuperator was modelled and analyzed by thermodynamic theory, and a recuperator force model based on energy equation was proposed. The thermal power, mechanical power and gas equation of state were considered. Comparison with the classical recuperator force model based on polytropic process, the change of gas state with time is directly considered in this model. The effectiveness of the model was verified based on firing experiment data of a soft recoil artillery, and numerical analysis was carried out based on a normal recoil artillery. The results show that the recuperator force model based on energy equation can describe the hysteretic nonlinear properties of the gas state, and can predict the changes of gas pressure and temperature at the end of firing process relative to the start.

The fine-structure constant, α, is a dimensionless constant that characterizes the strength of the electromagnetic interaction between charged elementary particles. Related by four fundamental constants, a precise determination of α allows for a test of the Standard Model of particle physics. Parker et al. used matter-wave interferometry with a cloud of cesium atoms to make the most accurate measurement of α to date. Determining the value of α to an accuracy of better than 1 part per billion provides an independent method for testing the accuracy of quantum electrodynamics and the Standard Model. It may also enable searches of the so-called “dark sector” for explanations of dark matter. Science , this issue p. 191 Atom interferometry provides a precise measurement of the fine-structure constant. Measurements of the fine-structure constant α require methods from across subfields and are thus powerful tests of the consistency of theory and experiment in physics. Using the recoil frequency of cesium-133 atoms in a matter-wave interferometer, we recorded the most accurate measurement of the fine-structure constant to date: α = 1/137.035999046(27) at 2.0 × 10 −10 accuracy. Using multiphoton interactions (Bragg diffraction and Bloch oscillations), we demonstrate the largest phase (12 million radians) of any Ramsey-Bordé interferometer and control systematic effects at a level of 0.12 part per billion. Comparison with Penning trap measurements of the electron gyromagnetic anomaly g e − 2 via the Standard Model of particle physics is now limited by the uncertainty in g e − 2; a 2.5σ tension rejects dark photons as the reason for the unexplained part of the muon’s magnetic moment at a 99% confidence level. Implications for dark-sector candidates and electron substructure may be a sign of physics beyond the Standard Model that warrants further investigation.

The purpose of this paper is to study the characteristics of recoil motion of a new suggested recoil system designed for the Russian 120- mm PM-38 mortar, rather than the conventional fixed-barrel mortar system. The new recoil system enables to reduce the total force imparted by the mortar system to the carriage, with the purpose of the mortar can be mounted on tracked/wheeled vehicles. The paper presents the suggestion of the new recoiling mortar system along with the discussion of the presentation of constructional considerations and constraints. The dynamic characteristics of recoil motion have been modelled with the aid of a new mathematical model that have been established using MATLAB software. As a result of the suggestion of the new recoiling mortar system, the maximum recoil resistance force is predicted to be reduced by more than 60% compared to that in the traditional fixed-barrel mortar system. In addition, the maximum recoil distance was predicted to be around 26 cm.

In this paper, we quantitatively characterise the kinetics of elastic recoil in the wings attached to the cicada Dundubia rufivena. We use high‐speed videography to deduce the velocities of recoil motion in both bending (B) and torsion (T), in downstroke and upstroke modes of flapping. Elastic recoil is faster in downstroke (DS) than it is in upstroke (US), reaching average velocities, v¯ v̄ , 244 ∘·s−1 ° ⋅ \\rm s⁻¹in DS‐B versus 6434 ∘·s−1 ° ⋅ \\rm s⁻¹in US‐B, and 5887 ∘·s−1 ° ⋅ \\rm s⁻¹in DS‐T versus 4545 ∘·s−1 ° ⋅ \\rm s⁻¹in US‐T. Our results also therefore evidence that bending velocities during elastic recoil are higher than the velocities in torsion, and conclude that this is a result of the necessary geometrical distances that need to be covered over a stroke. The wings do not act alone as biological springs, but rather, we find that the stiffnesses of the wings (1.7–3.6 GPa) are higher when attached to the cicada body than they are when detached. This evidences thoracical involvement as part of the biological spring enabling elastic recoil, indicating that elastic recoil of flapping wings should be approached from a systems perspective, rather than solely through a localised understanding of wing mechanics. We quantify elastic recoil in cicada wings using high‐speed videography, revealing faster bending than torsional recoil. Wing stiffness increases when attached to the thorax, demonstrating a body‐wing spring system and highlighting that elastic recoil must be understood through whole‐organism mechanics rather than isolated wing properties.