Trigger Position Research Articles

A Deep Learning Method for AGILE-GRID Gamma-Ray Burst Detection

Abstract The follow-up of external science alerts received from gamma-ray burst (GRB) and gravitational wave detectors is one of the AGILE Team’s current major activities. The AGILE team developed an automated real-time analysis pipeline to analyze AGILE Gamma-Ray Imaging Detector (GRID) data to detect possible counterparts in the energy range 0.1–10 GeV. This work presents a new approach for detecting GRBs using a convolutional neural network (CNN) to classify the AGILE-GRID intensity maps by improving the GRB detection capability over the Li & Ma method, currently used by the AGILE team. The CNN is trained with large simulated data sets of intensity maps. The AGILE complex observing pattern due to the so-called “spinning mode” is studied to prepare data sets to test and evaluate the CNN. A GRB emission model is defined from the second Fermi-LAT GRB catalog and convoluted with the AGILE observing pattern. Different p-value distributions are calculated, evaluating, using the CNN, millions of background-only maps simulated by varying the background level. The CNN is then used on real data to analyze the AGILE-GRID data archive, searching for GRB detections using the trigger time and position taken from the Swift-BAT, Fermi-GBM, and Fermi-LAT GRB catalogs. From these catalogs, the CNN detects 21 GRBs with a significance of ≥3σ, while the Li & Ma method detects only two GRBs. The results shown in this work demonstrate that the CNN is more effective in detecting GRBs than the Li & Ma method in this context and can be implemented into the AGILE-GRID real-time analysis pipeline.

Simulation study of local thermal runaway of 18650 lithium battery module under multi-point thermal trigger

The thermal runaway of lithium power battery is the key problem of battery safety, according to the standard SAE J2464–2009 single point heating key position, the proposed multi-point trigger based thermal runaway of lithium power battery module simulation method and battery module thermal runaway battery monomer ratio PN, thermal runaway trigger time tn two indicators, the thermal runaway rule of 18650 lithium power battery module under different trigger position, trigger points. The results show that considering the external thermal insulation conditions of the power lithium battery module, the geometric angular position in the module is the most dangerous position, and the number of thermal trigger points is positively correlated with PN.

Picosecond pulse pumped supercontinuum generation in silicon waveguide with a weak continuous wave trigger

We numerically demonstrate that picosecond pulse pumped supercontinuum (SC) generation in a silicon waveguide can be enhanced with the assistance of a weak continuous-wave (CW) trigger. The bandwidth of the resulting SC is greatly improved. The effects of two-photon absorption, free-carrier absorption, and free-carrier dispersion on SC generation in the silicon waveguide are studied. The optimized trigger position is close to the modulation instability peak. The results help us understand the details of SC generation in silicon waveguides in the presence of a CW trigger and noise. By tuning the wavelength of the CW trigger, we reach a good temporal coherence and intensity stability in the picosecond pulse pumped SC generation in a silicon waveguide.

Low-rate firing limit for neurons with axon, soma and dendrites driven by spatially distributed stochastic synapses.

Analytical forms for neuronal firing rates are important theoretical tools for the analysis of network states. Since the 1960s, the majority of approaches have treated neurons as being electrically compact and therefore isopotential. These approaches have yielded considerable insight into how single-cell properties affect network activity; however, many neuronal classes, such as cortical pyramidal cells, are electrically extended objects. Calculation of the complex flow of electrical activity driven by stochastic spatio-temporal synaptic input streams in these structures has presented a significant analytical challenge. Here we demonstrate that an extension of the level-crossing method of Rice, previously used for compact cells, provides a general framework for approximating the firing rate of neurons with spatial structure. Even for simple models, the analytical approximations derived demonstrate a surprising richness including: independence of the firing rate to the electrotonic length for certain models, but with a form distinct to the point-like leaky integrate-and-fire model; a non-monotonic dependence of the firing rate on the number of dendrites receiving synaptic drive; a significant effect of the axonal and somatic load on the firing rate; and the role that the trigger position on the axon for spike initiation has on firing properties. The approach necessitates only calculating the mean and variances of the non-thresholded voltage and its rate of change in neuronal structures subject to spatio-temporal synaptic fluctuations. The combination of simplicity and generality promises a framework that can be built upon to incorporate increasing levels of biophysical detail and extend beyond the low-rate firing limit treated in this paper.

Investigation of Synchronous Induction Coilgun With Stepped Coil Launcher and Stepped Armature

Synchronous induction coilgun (SICG) typically includes an array of drive coils and a conductive armature. The structure of the drive coil and armature can greatly affect the launching performance of SICG. The traditional drive coils and armatures have a cylinder-shaped structure for simplicity and ease of fabrication. In this article, a novel structural SICG with stepped drive coil and stepped armature (SA) is proposed and investigated. As a comparison, four structural SICGs are researched by static and transient simulations. The static simulation results show that the stepped drive coil makes the magnetic field larger and the center of the magnetic field moves backward toward the tail end. The transient simulation results indicate that the SA improves the eddy current distribution and the positive propulsion force and weakens the reverse electromagnetic force and the armature capture effect at the same time. As a result of integrating the above characteristics, the new structural SICG with stepped drive coil and SA makes the optimal trigger position of armature move backward by 7 mm and improves the muzzle velocity by 4.79% and the launch efficiency by 9.82%.

Study on Multi-Segment Asynchronous Induction Coilgun Launcher

This article studies a multi-segment capacitively driven asynchronous induction coil launcher. First, a segment with six-stage asynchronous induction coil launcher is studied. Based on the results of the single-segment induction coil launcher and the orthogonal design method, a six-factor and five-level orthogonal table is established. The factors are, namely, trigger position, armature thickness, initial capacitance voltage, inner radius of coil, turns of coil, and coil axial length. The results of the orthogonal test show that the influencing factors from large to small are coil turns, coil axial length, initial capacitance voltage, coil radius, trigger position, and armature thickness. Based on the above results, a two-segment asynchronous induction coil launcher is designed. The coil parameters of the second section are the same as those of the first section, and the number of coils is twice that of the first section. By studying the trigger position, capacitance, and voltage combination of the second stage, the optimal trigger position is 163 mm, capacitance value is 1125 μF, and capacitance voltage is 4 kV. On account of the above research results, a four-segment induction coil launcher with two armatures is proposed. The parameters of the first and third segments are the same, and the parameters of the second and fourth segments are the same. The first and second segments drive armature 1, and the third and fourth segments drive armature 2. In the case of cross ignition, the standard deviation of armature force is 18.62 kN, while the standard deviation of armature force for sequential ignition is 25 kN. Through cross ignition, higher armature muzzle velocity and smaller acceleration jitter can be obtained.

Modeling and analysis of triggering pulse to thermoacoustic instability in an end-burning-grain model solid rocket motor

Occurrences of pulse-triggered instabilities in combustion chambers always trouble solid rocket motors (SRMs) in application. This paper performs numerical simulation of the pulse-triggered nonlinear instabilities in the end-burning-grain SRM, in use of the pressure-coupled response function to describe the spatiotemporal burning rate of AP-HTPB composite propellant grains. A high-order numerical solver realizes the cooperation of the burning rate model into the axisymmetric internal ballistic simulation of SRMs via the source terms in gas-phase governing equations. The analysis of high-amplitude pressure oscillations, which are the primary symptom of nonlinear thermoacoustic instabilities, provides the insight into the nature of the longitudinal instability growth process after the pulse triggering. The change rate of pressure fluctuation over the pressure fluctuation in the chamber is independent of the pulse intensity and triggering position. The growth characteristics of pressure oscillations for the present combustor system is neither affected by the pressure pulse intensity nor by the imposed regions in the flow field, while the higher pressure-coupled response function of the propellant promotes the growth process evidently. The present study is expected for the guidance of grain design in SRMs.

Dynamics study of a microsensor for perceiving unsafe acceleration and angular speed

A micro-trigger sensor that can perceive unsafe acceleration and angular speed is proposed in this study. This sensor can send an alarm message regarding the excessive speed of rotating machinery or activate the automobile airbag during emergencies. A mathematical and mechanical model with size-dependent is established through generalized elasticity theory and Euler–Bernoulli beam hypothesis. The governing equations of motion are deduced using Hamilton’s principle and solved using a modal superposition method. The influence of the degree of freedom (DOF) on the dynamics response is analyzed, and the result converges when the DOF is 5. Meanwhile, the dynamics response of the microcantilever under instantaneous impact and centrifugal force are evaluated along with the engineering background. Oscillation is observed in dynamics response results, but oscillation is not obvious when the deflection change rate is minimal. Furthermore, the scale effect of the dynamics response is examined, and the obvious scale effect is noted in the calculation results. Lastly, the trigger position of the circular ring is ascertained via the graphical method in cases of specified and unspecified trigger time.

Determination Method of Optimal Trigger Position for Induction Coil Launcher Based on the Reverse Point of Electromagnetic Force on Armature

The optimal trigger position of the induction coil launcher is difficult to determine, which can affect the design efficiency of the induction coil launcher. Accordingly, the characteristics of the induction current and the reverse point of electromagnetic force for an armature are analyzed based on the electromagnetic force equation and the electromagnetic induction law. Then, the relative position of the electromagnetic force and the discharge current curves are analyzed, and the intrinsic characteristic of the optimal trigger position is obtained. After that, the determination method for the optimal trigger position and the calculation equation are given based on the reverse point of the electromagnetic force. At last, taking the armature whose initial velocity is 200 m/s, for instance, the validity of the determination method for the optimal trigger position is verified by calculation instance and numerical simulations. Meanwhile, the determination method is also verified by experimental results. One can draw the conclusion that the essence of the optimal trigger position is to make the peak zone of the discharge current located just in the acceleration zone of the electromagnetic force, which can improve the launching efficiency of the coil launcher. Furthermore, the optimal trigger position of the driving coil can be determined rapidly when the curve of the electromagnetic force for the armature at a certain initial velocity is obtained. Thus, it is unnecessary to obtain the optimal trigger position by a large number of simulations and experiments, which can improve the efficiency of the simulation and the experiment for the coil launcher.

Investigation of steam explosion duration in stratified configuration

A steam explosion is an energetic fuel-coolant interaction process, which may occur during a severe reactor accident when the molten core comes into contact with the coolant water. In the stratified melt-coolant configurations, where the corium melt is released in a shallow water pool or in an initially dry cavity later flooded with coolant water, the melt-water interaction may occur on the interface between the bottom melt layer and the upper water layer. It was long believed that stratified melt-water conditions cannot generate strong explosive interactions, because it was assumed that there is no significant premixing of melt and coolant water prior to the shock wave propagation. However, the recently performed experiments in the PULiMS and SES (KTH, Sweden) facilities with corium simulant materials revealed that strong steam explosions may spontaneously develop also in a stratified melt-water configuration, where a formation of a considerable melt-water premixed layer was observed. Understanding the premixture formation mechanisms is crucial for predicting the stratified steam explosion energetics. One of the external indicators of the way the melt and water are mixed during the stratified steam explosion process is the explosion duration.In the article, the duration of the stratified steam explosion is studied by the analysis of experimental observations in the PULiMS and SES tests using simulation results obtained with the MC3D code (IRSN, France). The explosion characteristics are analysed by varying the available melt mass in the premixed layer, the triggering position, the melt droplet diameter, the void fraction in the premixed layer, the void fraction in the water above the premixed layer and the size of the fine fragments. The analysis showed that longer explosion duration for the experiments with strong explosions cannot be predicted solely by varying the premixed layer conditions. A significant increase of the explosion duration could be obtained only by increasing the size of the fine fragments, which depends on the nature of the explosion. Thus the observed discrepancies between the experimental results and simulations can be explained by the fact that in strong stratified steam explosions there is also significant melt-water layer mixing during the explosion propagation.

Study on the Best Trigger Position of Multistage Induction Coil Launcher

A mathematical electromechanical model of the multistage induction coil launcher was established based on the current filament model. According to the model, the armature force is determined by the current of the drive coil and the armature together with the mutual inductance gradient between them. Except that the current waveform of the drive coil is determined by the given electrical parameters, the current waveform induced by the armature and the mutual inductance gradient waveform is determined by the position of the drive coil and armature. Therefore, after simulating and comparing, the acceleration performance and efficiency of the matching situation of drive coil current waveform and the mutual inductance gradient waveform can be obtained under limit conditions, and the following results are concluded: 1) the current pulse time is much longer than the mutual inductance gradient time and 2) the current pulse waveform is much smaller than the mutual inductance gradient waveform. Therefore, the current pulse time shall be consistent with the mutual inductance gradient time to achieve smoother acceleration curve and higher efficiency. According to the above-mentioned principles, the current pulse time and mutual inductance gradient time were calculated quantitatively, and the position of drive coil and armature were considered; thus, the armature trigger formula of the multistage induction coil launcher was given, which would lay a theoretical foundation for the performance optimization of the multistage induction coil launcher.

Design of an Electromagnetic Induction Coilgun Using the Taguchi Method

Electromagnetic induction coilgun systems have been receiving great attention, recently, due to the advantage of noncontact between the stator and armature coils. Several studies present the simulation and analysis of the coilgun system by using the finite-element method. However, there are still deficiencies in current modeling studies of the coilgun system. This paper presents a design of a multistage pulsed power induction coilgun system using the Taguchi method to maximize its efficiency and reduce the time and cost of the design process. A coilgun system is analyzed and designed using a state-space equation system. The Taguchi method is applied in order to evaluate and determine the geometric variables, the layer, turn layer numbers for both the stator and armature coils, and the trigger positions of each stage. Then, a 2-D finite-element model of the coilgun system using the MagNet program was developed to compare the design and analysis results. The energy efficiency of the three-stage coilgun system is 31.3% and this is expected to increase with the increase in the number of stages.

Using a novel shear apparatus coupled with acoustic emission to investigate shear fracture evolution of cement-based materials in macro- and micro-views

It is difficult to investigate the shear fracture triggering position and subsequent fracture propagation using traditional direct shear testing due to its closed-shear-box design. To examine the fracture evolution of cement-based materials subjected to shear stresses, a novel shear apparatus with an opened-shear-box and crack displacement control coupled with a non-destructive technique of acoustic emission (AE) was developed in this study. The complete loading curve in the macro-view and corresponding AE event (micro-crack) development were then obtained. The fracture behaviors affected by the shear angle and the aggregate shape of cement mortar were also investigated. The test results showed that the stiffness and peak shear stress decreased with an increase in the shear angle. The stiffness of the specimen with angular-shaped aggregate was higher than that of the specimen with rounded-shaped aggregate. The localization of AE events occurred before the peak and were located near the middle of the specimen. The position of the AE localization was related to that of the macro-crack initiation. After localization, the AE events then propagated following the shear direction. A comparison of the distribution of AE events before the peak with the position of the macro-crack showed good agreement. The results obtained in this study provide a better understanding of the shear fracture mechanism of cement-based material.

Shear fracture evolution in rocks examined using a novel shear device associated with acoustic emissions

This study constructs a new shear test method composed of an open-box-style shear device with a crack-opening-displacement (COD) extensometer associated with a non-destructive acoustic emission (AE) detection system for examining the complete load behavior and the shear fracture triggering position and subsequent fracture propagation of two rock types (Charcoal granite and Berea sandstone). The complete macroscopic view loading curve presents that the pre-peak shear stiffness and shear strength of granite are higher than those for sandstone. The post-peak load behavior of both rocks trend towards the unstable fracture type (Class II), whereas in the microscopic view, the localization of AE events occurred before the peak and is located near the middle of the specimen. The AE localization spatial distribution is in good agreement with the macro-crack position. This suggests that the AE localization distribution is related to the macro-crack initiation position. After localization, the AE events then propagate following the shear direction. The results obtained in this study provide a better understanding of the shear fracture mechanism of brittle rock material.

Experiment and Analysis on the New Structure of the Coilgun With Stepped Coil Winding

In this paper, a new structure of coilgun with stepped coil winding was designed. The performance of this structure was investigated and compared to the conventional coilgun with uniform diameter stator coil (UDSC) winding. It can be seen from the results that the trigger position of this new structure moves forward with respect to the conventional coilgun. In order to compare the results, the inductance of the two coils is set to the same. If the initial voltage of the capacitor is lower, as the armature at the optimum trigger position, the muzzle velocity of armature in the conventional UDSC coilgun is relatively larger. Conversely, if the initial voltage of the capacitor is higher, the muzzle velocity of armature in the new structure coilgun is relatively larger. According to the simulation results with the increase of voltage, the difference is more and more obvious. Through the single-stage preliminary experiment in our laboratory, the results were in good agreement with the simulation results. And the trigger position is more forward, so the interaction time between the armature and the coil will be longer. Besides, the coil with stepped structure will increase the efficiency of the coilgun when the voltage level is higher.

The LOFT mission concept

The Large Observatory For x-ray Timing (LOFT) is a mission concept exploiting a novel detector solution and constitutes the base for a series of subsequent projects in various states of advancement. Thanks to the unprecedented combination of effective area and spectral resolution of its main instrument and the uniquely large field of view of its wide field monitor, LOFT will be able to study the behavior of matter in extreme conditions such as the strong gravitational field in the innermost regions close to black holes and neutron stars and the supra-nuclear densities in the interiors of neutron stars. The science payload is based on a Large Area Detector (LAD, >8m2 effective area, 2–30 keV, 240 eV spectral resolution, 1 degree collimated field of view) and a Wide Field Monitor (WFM, 2–50 keV, 4 steradian field of view, 1 arcmin source location accuracy, 300 eV spectral resolution). The WFM is equipped with an on-board system for bright events (e.g., GRB) localization. The trigger time and position of these events are broadcast to the ground within 30 s from discovery. In this paper we present the structure of the mission concept.

An Experimental Study on LT-GaAs Photoconductive Antenna Breakdown Mechanism

In this paper, an experimental study on the low-temperature-grown gallium arsenide (LT-GaAs) photoconductive antenna (PCA) breakdown mechanism is presented. A terahertz (THz) PCA is an important device for the THz wave generation. Due to that the typical LT-GaAs PCA breakdown scenarios, different trigger positions and different bias voltages, have been studied. Breakdown mechanism analysis has shown that when the trigger position was on the antenna electrode edge, the PCA breakdown was more probable to happen, because the electrode edge electric field was nearly 3 times greater than the electric field of the electrode center. Moreover, it has been shown that the thermal effect was the main cause of the LT-GaAs PCA breakdown. Last, the PCA lifetime has been calculated using the current waveform and the thermal effect analysis.

Investigation of Magnetic Field Arrangement on Launching Performance of Multistage Synchronous Induction Coilgun

For the multistage induction coilgun, many researchers pay great attention to improving the system efficiency. The directions of magnetic field generated by the driving coils are consistent for conventional coilgun, because it is convenient to analyze acceleration characteristic and stress status for the armature in the barrel. In this paper, the launching performance of multistage induction coilgun is investigated in terms of different directions of magnetic field in order to improve the system efficiency. A field-circuit coupled model for a 6-stage coilgun is built. The simulation for the consistent direction of magnetic field is calculated. For the same parameter setup, the directions of magnetic field generated by the last three stages current are changed. The simulation results show that the armature endures a large braking force when going through the last three stages, and the velocity drop is obvious. Meanwhile, the currents in the last three stages are very large. The distribution of the current density and the magnetic field during the transition process of magnetic field are analyzed. The reason for velocity drop when changing the direction of magnetic field is discussed. A method that the trigger position is adjusted for the armature is proposed. The simulation results show that the armature can be accelerated to a higher speed on condition of inconsistent direction of magnetic field with adjusting the trigger position. It is feasible to improve the system launching performance through changing the direction of magnetic field. A 15-stage coilgun is built to validate the method. The experimental results show that the velocity and system efficiency are increased dramatically through changing the direction of magnetic field. It provides valuable reference for multistage induction design.

Trigger control characteristics of fuze-recoil simulation system based on electromagnetic launcher

Fuze is the information processing and control unit of the ammunition, so the quality of the fuze becomes one of the most important aspects of ammunition detection. Since using recoil force is a common method to the arm fuze, its dynamic simulation test has always been the focus of the fuze test research. A new fuze recoil environmental simulation method is proposed based on the electromagnetic launcher. Then the trigger control characteristics of the fuze recoil simulation system and the influence of the trigger position on the recoil force are studied. The results of the study show that although the pulse width of the armature force curve can be changed by adjusting the trigger position, due to the limit of the range, there also exists the contradiction that the electromagnetic pulse width gets narrow with the increase of electromagnetic force peak. Thus, it cannot meet the requirements of the fuze launch recoil simulation. In order to make the recoil force close to the actual environment, the multi-stage trigger control characteristics are analyzed, and the influence of trigger position on recoil environmental force characteristics is studied. Then a fuze launch recoil environmental simulation platform is established and continuous electromagnetic force is achieved by using the trigger strategy. Finally, the experiment is performed to simulate the fuze launch recoil environment and show the feasibility and effectiveness of the proposed theoretical analysis. The major research work of this paper includes studying the composition and basic principle of the simulation system, establishing a launch model to analyze the single-stage and multi-stage coil fuze launch recoil characteristics, designing the test device to verify the correctness and validity of the research. This paper draws the conclusions that the feasibility of the fuze launch environmental simulation based on the electromagnetic launcher is verified, the trigger position has a great influence on force peak continuity, the problems of low maximum overload peak and short peak duration in the multi-stage coil fuze launch environmental simulation can be effectively solved through adjusting the trigger position, the system has creative and extensive application prospects.

Cathode configuration influence on low-inductance vacuum spark plasma dynamics

The results of studies of cathode configuration influence on high current low- inductance vacuum spark (HLVS) plasma dynamics are presented in this work. The research was carried out on “PION” installation using shadowgraphy method. Molecular nitrogen laser (λ = 337 nm) was used as a radiation source. It was determined that the HLVS behavior changes with the increase of number of discharges. In a fresh electrode system (less than 200 discharges) the dependence of constriction position on the discharge trigger position is observed during HLVS development. Also, high gradients of plasma density and secondary constrictions are observed. In a previously exploited electrode system (more than 300 discharges) HLVS behavior changes: plasma density gradients become less expressed, secondary constrictions disappear. In electrode systems with highly developed cathode surface plasma density gradient distribution pattern only slightly changes from discharge to discharge, e.g. the discharge becomes more stable.