Primary Shock Research Articles

Underexpanded jet impingement in near vacuum environment

Understanding the dynamics of rocket plume impingement on flat surfaces is critical for designing effective and sustainable landing pads. The current near vacuum study measures the surface pressures and temperature profiles arising on a flat surface due to highly underexpanded, axisymmetric plume impingement. The experiments were conducted in a dedicated, large-volume plume-regolith facility situated at the University of Glasgow. A total of eight tests were conducted, comprising of both constant and pulsed firing modes. The impingement plate is located at stand-off distances equal to 4 and 16 times the nozzle exit diameters and plate inclinations of 0° and 30°. Reduced stand-off distance increases impingement pressure, with a transient peak in the early stages of impingement indicating the presence of a primary shock wave. Higher stand-off distance resulted in decreased impingement pressure without an initial peak, but with a spike at the end of impingement once the nozzle had stopped firing. For inclined plates, the centerline impingement pressure magnitude decreased by around 40% compared with the 0° inclination. The measured pressures at lower stand-off height are then compared with the results of both a two-way coupled direct simulation Monte Carlo/Navier–Stokes–Fourier solver and an analytical theory. The results from all methods are in good agreement with each other, with the simulation and experimental centerline pressures being within 1% of each other. As the optical thickness of the gas is very low in the experimental case, the numerical method is used to generate a Schlieren image to analyze the shock structure.

Formation of a spherical plasma liner for plasma-jet-driven magneto-inertial fusion

Plasma-jet-driven magneto-inertial fusion is an alternative approach to controlled nuclear fusion, which aims to utilize a line-replaceable dense plasma liner as a repetitive spherical compression driver. In this experiment, first measurements of the formation of a spherical argon plasma liner formed from 36 discrete pulsed plasma jets are obtained on the Plasma Liner Experiment. Properties including liner uniformity and morphology, plasma density, temperature, and ram pressure are assessed as a function of time throughout the implosion process and indicate an apparent transition from initial kinetic inter-jet interpenetration to collisional regime near stagnation times, in accordance with theoretical expectation. A lack of primary shock structures between adjacent jets during flight implies that arbitrarily smooth liners may be formed by way of corresponding improvements in jet parameters and control. The measurements facilitate the benchmarking of computational models and understanding the scaling of plasma liners toward fusion-relevant energy density.

Physical mechanism for prolonged test duration in shock tubes

The main challenge in the operation of shock tubes is the very short test time. Hence, this work was carried out to optimize the ratio of driver section to driven section length and to investigate its effect on the test time in a shock tube. Three different cases were tested in this paper for driver to driven tube length ratio of 2, 1, and 0.5. The study was conducted numerically using ANSYS Fluent CFD solver and k-epsilon realizable turbulent model. The shock wave strength and speed were monitored at two different locations downstream the driven tube for diaphragm pressure ratio of 10. The numerical model was verified with experimental measurements in a shock tube apparatus at the College of Engineering, Universiti Tenaga Nasional, Malaysia (UNITEN). From the numerical and experimental data, the primary shock strength was very comparable, while using low pressure ratio of 10. Subsequently, higher pressure ratio of 20 and 30 were implemented and the results were compared to select the longest test time. A driver section to driven section ratio of 2 resulted in a longer test time of approximately of 20 ms. In addition, insignificant reduction in the test duration of about 5 % was observed after increasing the driver tube pressure to 30 kPa. In contrast, higher peak pressure was recorded for pressure ratio of 30 for all three cases.

The rise of Soybean in international commodity markets: A quantile investigation

The complex interplay between agricultural and energy commodities has been a subject of interest in past research, gaining more relevance recently due to geopolitical events such as the conflict between Ukraine and Russia. This conflict has systematically driven up the prices of both energy and agricultural commodities. Deeply understanding the dynamic interconnections between these commodities and the cascading events resulting from the war is crucial for comprehensive market analysis. Our study leverages the connectedness or risk of spillover based on a Quantile Vector Autoregression (QVAR) model, allowing us to track connectedness over time through the examination of extreme quantiles. This approach facilitates the identification of shocks triggered by exogenous events, such as the Russian-Ukrainian war, which are often observable in these extreme quantiles or tails. The investigation encompasses several agricultural commodities: Wheat, Barley, Soybean, Soybean Oil, Soybean Meal, and Sunflower Oil, along with energy commodities represented by Crude Oil and Natural Gas. Furthermore, we considered the prices of crucial fertilizers, DAP & Urea, given their significance in agricultural production. The timeframe for our study extends from January 2010 to January 2023, providing a comprehensive review of market trends during various geopolitical scenarios. This research contributes valuable insights into the intersection of global events, agricultural trends, and energy commodity markets. The study revealed that Soybean and its derivatives consistently play a leading role in the market, with Soybean being the primary shock transmitter. This is particularly true for the upper Quantile, where Soybean and Soybean Meal's influence remains stable. On the other hand, Soybean Oil's, Barley, and Wheat risk of spillover has increased, especially during the Ukraine-Russia conflict. Finally, spillover appears symmetric, with both extreme tails exhibiting around 91–87 % connectedness, while the median Quantile is under 49 %. We observed a diminution in network complexity, manifested as a decline in network connectedness, in correlation with extreme quantiles. Policymakers can use this information to draft proactive measures, ensuring stability and sustainability in both domestic and international markets.

Analysis of the building on the air shock wave by direct dy-namic method (with LIRA-FEM soft-ware)

Calculation of the impact of air shock waves on buildings is extremely important for our country, which is in a state of war. Studying the structural safety and survivability of load-bearing reinforced concrete structures under influence is an important task, especially for critical infrastructure facilities. A blast scenario can be carried out directly in an FEA program as a time history analysis evaluate varying levels of structural damage and to minimize loss of life.The article is devoted to the features of the calcula-tion of buildings under the influence of air shock waves using the finite element method using the LIRA-FEM software complex. The features of ex-plosive loads, typical shock wave parameters, and the order of analysis for explosive loads are taken into consideration. The primary distinctions be-tween shock or explosion impacts and regular loads are explained. In-depth consideration is given to the problems of determining shock wave parameters and how they affect structures. Also included are the techniques for evaluating structures for explosive impacts.Using LIRA-FEM software, a preliminary analysis of the explosion resistance of a one-story building with a metal frame and sheet metal wall infill is carried out. It is demonstrated how to define impulse loads from a shock wave to the side walls, roofs, rear walls, and walls facing the explosion. The article describes the peculiarities of the "Time History Analysis" system in the LIRA-FEM program for ex-plosion dynamics problems.This analysis helps in the assessment of risks in the design of protective structures, development of pro-ject solutions and conducting research in the field of explosion safety.

How does inflation propagate among CPI components? Evidence from the euro area

This study employs a time-varying parameter vector autoregressive (TVP-VAR) model to investigate infla- tion propagation and spillovers among twelve major Consumer Price Index (CPI) components across eleven euro area countries from 1999 to 2023. We uncover empirical regularities in the transmission channels of inflation, noting Transport and Clothing and Footwear as primary shock transmitters, whereas Communi- cation, Alcohol and Tobacco consistently absorb shocks. These insights, consistent across various contexts and countries, contribute to understanding inflation persistence and households’ inflation experiences in the Euro area.

Earthquake Detection and Alerting system using ANN and IOT

Earthquakes are one of the deadliest natural disasters. The damage caused by earthquakes is very destructive and the number of deaths are at a very large scale. The National Earthquake Information Centre now detects about 20,000 earthquakes around the globe each year, or approximately 55 per day. Many of the Earth’s earthquake zones coincide with areas of high population density. When a large earthquake occurs in such areas, the results can be catastrophic. The basic parameter to determine an earthquake before it was going to occur is the p wave or primary shock wave which is not destructive to infrastructure because it travels parallel to the propagation of seismic wave. A series of destructive waves that follows p waves are s waves or secondary waves which has a speed of about 60% that of p waves. The movement of the s wave is perpendicular to the direction of propagation of the seismic wave and hence it is extremely risky to infrastructures and cause a lot of damage. This research aims to build an earthquake detection and alerting system using a low-cost accelerometer, ESP32 Wi-Fi module, and ANN algorithm. The input earthquake data is taken by the accelerometer and with the help of the ESP32 Wi-Fi module the data is sent to a system that processes the ANN algorithm with Multi layered perceptron trained with stochastic gradient descent learning algorithm and detects whether an earthquake is going to occur or not and alerts users with ESP32 Wi-Fi module. Key Words: Artificial Neural Networks, ESP32, Accelerometer, Earthquake, Multi-layer perceptron, Sigmoid function, Stochastic Gradient Descent.

Green bonds and traditional and emerging investments: Understanding connectedness during crises

This paper investigates dynamic connectedness between US green bonds and major implied volatility indices from stock, crude oil, gold, exchange rate and cryptocurrency markets through the application of a novel TVP-VAR frequency connectedness approach of Chatziantoniou et al. (2023) for the first time. The specific goal of this paper is to explore how uncertainty from different financial markets could affect the US green bonds during three major events that resulted in substantial financial market instability, such as the US–China trade war, the COVID-19 pandemic, and the Russia–Ukraine conflict. Firstly, there is a relatively low connectedness between green bonds and all implied volatility indices. Secondly, the degree of transmission is notably influenced by such extreme events. Thirdly, the US green bond market is a receiver of each of the analysed stock, oil, and gold markets, while it is a transmitter of exchange rate and cryptocurrency markets. Fourthly, the US green bond functioned as the primary shock transmitter for the cryptocurrency market during the COVID-19 outbreak, but it shifted to being a receiver of shocks during the Russia–Ukraine conflict. Lastly, connectedness between the green bond market and other financial markets is predominantly driven by short-term frequencies. Our results are crucial for understanding the evolution of green bonds, especially during turbulent periods, and assessing green bonds’ classification as safe assets. Such findings also show that black swan events have been deeply disruptive to the green transition, with specific relevance to policymakers and market participants.

Analysis of the combustion modes in a rocket-based combined cycle combustor using unsupervised machine learning methodology

Combustion mode analysis is essential to a rocket-based combined cycle (RBCC) combustor because it may experience multiple combustion modes during the operation. In this study, a method based on an autoencoder and a K-means algorithm was proposed for combustion mode analysis. Flame chemiluminescence images and schlieren images of three combustion modes observed in an RBCC combustor were used to evaluate this method. Two autoencoders that followed the same encoder–decoder architecture were developed separately to generate the latent space representations of flame chemiluminescence images and schlieren images. In the latent space, the centroids and boundaries of different combustion modes were determined using the K-means algorithm. Each autoencoder was trained using 750 images and tested using another 3000 images. The method achieved an accuracy up to 99% on both flame chemiluminescence images and schlieren images. The images generated by the decoder suggested that the autoencoder captured the important features (e.g., primary reaction zone and shock wave) of the reacting flow field. The autoencoder developed for flame chemiluminescence images also successfully detected the combustion mode transition during an ignition process, which suggested that it had the potential to monitor the combustion mode in a real time manner. However, the autoencoder failed on monitoring combustion mode transition when it came to the schlieren images because the optical access of the training data was not exactly the same. Therefore, it is essential to ensure that the optical accesses of different combustion modes are exactly the same when schlieren images are employed for combustion mode analysis.

Tác động lan truyền giữa tăng trưởng tín dụng và giá tài sản tài chính: Bằng chứng từ mô hình TVP-VAR

The article assesses the spillover effects among credit growth, stock, and bond returns through a dynamic network model with time-varying parameters, TVP-VAR, from 2010 to 2023Q2. The findings reveal a dynamic interconnection among credit growth, stock price volatility, and bond prices over time. Notably, credit growth emerges as the primary shock spillover to the system. However, credit growth spillover effects are mainly toward stock returns dynamics, while the connection between credit growth and bond returns is much less clear. Conversely, stock return exhibits spillover effects on bond return, indicating changes in risk appetite among market participants during various financial market cycles. Based on the empirical results, the authors propose some policy implications

Clinical impact and efficacy of bedside echocardiography on patient management in pediatric intensive care unit: A single center study

BackgroundCritically ill pediatric patients often have multi-system involvement that can overlap different clinical diagnoses, making proper assessment and management challenging. Using echocardiography is increasing as a bedside and noninvasive tool for accurate hemodynamic assessment and guiding treatment. ObjectivesThis study aimed to determine the indication and value of bedside echocardiography in patient management in the pediatric intensive care unit (PICU) at Fayoum University Hospital and the relationship to the Pediatric Risk of Mortality Score III (PRISM). MethodsA total of 200 critically ill pediatric patients admitted to the PICUs of Fayoum University Hospital between January 2020 and January 2021 were prospectively evaluated. Detailed clinical examinations and requested echocardiography were conducted by intensivists and cardiologists. Results200 critically ill pediatric patients had an age range of 0.2–12 years, with 134 patients (67 %) under two years old. The most common admission diagnosis was pulmonary disease in 51 patients (26 %), followed by cardiac disease in 44 (22 %). The most common indication for echocardiography was left ventricle function assessment in 68 patients (34 %). Among the 108 patients (54 %) who underwent echocardiographic assessment, no difference in the management was found, while in the remaining 92 patients (46 %), supplemental information or decision help in management was obtained. There was a positive correlation between the effective value of echocardiography in the management of patients with primary cardiac disease (p-value = 0.001), shock (p-value = 0.001), and hypoxia (p-value = 0.009). Additionally, there was no correlation between the PRISM score and the effectiveness of echocardiographic assessment. ConclusionThe most common clinical indication for bedside echocardiography is assessing cardiac function. Echocardiography is an effective tool in PICU patient management, particularly in cases with primary cardiac disease, hypoxia, and shock, but its effectiveness does not increase according to the severity of the disease.

Supersonic Flow over Elliptic Cone with Different Ellipticity Ratio

This study investigates supersonic flow characteristics over circular and elliptic cones at various angles of attack. Simulations were conducted on the cones with the same base area and length-to-diameter ratio. The elliptic cones considered had axis ratios of 1.5 and 3. The angle of attack varied from 0o to 50o, with two different Mach numbers (1.97 and 2.94) employed for the analysis. The numerical results were compared with the experimental and theoretical findings from existing literature. The results revealed that increasing the ellipticity ratio of the cones resulted in higher lift generation. The pressure distributions on the windward and leeward sides of the cones were also examined. The results demonstrated that elliptic cones outperformed circular cones in terms of lift production, and this advantage increased with higher ellipticity ratios. Specifically, when the ellipticity ratio was increased from 1 to 3, the maximum increase in lift coefficient was 96% and 100% at Mach numbers 2.94 and 1.97, respectively. Additionally, by changing the ellipticity ratio from 1 to 1.5, the maximum gain in the lift-drag ratio was 16% and 22% at Mach numbers 1.97 and 2.94, respectively. Notably, an elliptic cone with an ellipticity ratio of 3 achieved a remarkable 46% gain in lift-to-drag ratio compared to a circular cone. However, as the angle of attack increased, a primary bow shock formed on the windward side of the cone, with an embedded shock appearing on the leeward side.

Shock interactions and heating predictions on a V-shaped blunt leading edge at Mach 6–12

V-shaped blunt leading edges (VSBLEs) are usually found at the inlet lips of air-breathing hypersonic vehicles and irregular shape flows. In this work, the VSBLE flows are investigated using numerical simulations and theoretical analysis from Mach 6 to Mach 12. The simulation results show that complex shock–shock interactions around the VSBLE cause extremely high heat flux peaks, which nonlinearly increase with the freestream Mach numbers. To theoretically study the flow mechanism, the shock interactions are divided into large-scale primary shock interactions (PSIs) and micro-scale secondary shock interactions (SSIs). The PSIs are constant, but the SSIs experience a transition from Mach reflection to regular reflection with the Mach number increasing. A transition criterion for the SSIs is established by the shock interaction theory. Furthermore, the increase in the heat flux peaks is proved to be caused by the SSI transition. A semi-empirical heat flux prediction method that relates the shock intensity and heat flux amplification is established. Finally, the transition criterion and the heat flux prediction method are verified by simulations at higher Mach numbers and experiments of VSBLEs with different geometric parameters. This paper develops a theoretical analysis approach for quickly predicting the shock interaction types and heat flux peaks of the VSBLEs under a wide range of Mach numbers.

Experimental study of load characteristics caused by underwater explosion bubble collapsing in the neighborhood of a rigid wall

In this paper, a series of underwater explosion (UNDEX) experiments were carried out in a cubical explosion tank, to investigate the complex behaviors of one bubble collapsing near a vertical rigid wall. The evolution of the bubble was captured by a high-speed camera and the pressure caused by both the primary shock wave and the bubble collapse on the surface of the wall was measured by several sensors installed on the wall surface. Experimental results of the measured wall pressure and the resultant load impulse are compared with theoretical results that are calculated from the corrected empirical formula. A good agreement between the experimental and theoretical results is achieved. On this basis, the effects of the bubble-wall distance on the bubble behaviors and the corresponding explosion load characteristics on the rigid surface are analyzed and discussed. The result aims to provide a feasible reference for the study of near-field UNDEX bubble dynamics and the resultant load on structures nearby.

Density deficit of Earth's core revealed by a multimegabar primary pressure scale.

An accurate pressure scale is a fundamental requirement to understand planetary interiors. Here, we establish a primary pressure scale extending to the multimegabar pressures of Earth's core, by combined measurement of the acoustic velocities and the density from a rhenium sample in a diamond anvil cell using inelastic x-ray scattering and x-ray diffraction. Our scale agrees well with previous primary scales and shock Hugoniots in each experimental pressure range and reveals that previous scales have overestimated laboratory pressures by at least 20% at 230 gigapascals. It suggests that the light element content in Earth's inner core (the density deficit relative to iron) is likely to be double what was previously estimated, or Earth's inner core temperature is much higher than expected, or some combination thereof.

Оценка изменения безопасных расстояний при нарушениях регламента испытаний газопроводов

Accidents occurring during the process of gas pipelines testing are characterized by the impossibility of the occurrence of thermal radiation of jet flames and fire in the pit-damaging factors dominating the operation stage of the facility. In addition, what is happening cannot be accompanied by the baric effect of chemical explosions. However, taking into account the significant increase in pressure in the gas pipeline during pneumatic tests, such damaging factors of the accident as the scattering of fragments, the pressure effect of a high-speed jet and the baric effect of the primary shock wave are amplified. The issue of ensuring the safety of personnel present near the test site becomes relevant. As a result, the need occurs to determine precisely the safe distances to the gas pipeline. Protective zones for the population are also established based on the identified safe distances. Within the framework of the risk-oriented approach, the procedure for determining safe distances is reduced to calculating the distances at which damaging factors lose their damaging properties. When assigning protective zones, it is required to consider the possibility of changing the indicator under consideration, due to probable errors of personnel in the preparation and conduct of tests. Even non-critical miscalculations can significantly affect the determination of a safe distance. The article presents an assessment of the relative values of safe distances, taking into account possible violations of the regulations regarding backfilling and filling with water or air, during hydraulic or pneumatic tests of gas pipelines. Relative values of safe distances are also established in terms of the scattering of fragments and the impact of an air shock wave of a physical explosion on people and building objects.

Damage Rule of Marine Isolator under Secondary Shock Vibration

To study the damage of the shock vibration generated by the ship hull to the internal equipment of the ship under the secondary explosion impact, a three-dimensional simulation model of the BE rubber isolator was established. The signal of the impact vibration load was loaded by the AUTODYN software. And the relationship between the damage of the isolator under the primary vibration impact and the frequency, amplitude, and attenuation of the loading signal was found. It is revealed that the damage law curve of the isolator under the secondary shock vibration conforms to a rational function. Based on this discovery, a mathematical model of the secondary shock vibration signal that can predict the isolator damage through the primary shock vibration is established.

Defining TLR4-independent molecular pathways activated during endotoxemia

Abstract Sepsis is the leading cause of nosocomial mortality, accounting for almost 20% of annual global deaths. Patients who recover from septic shock maintain a significantly increased risk for mortality due to secondary infection. Toll-like receptor 4 (TLR4) recognizes Gram-negative bacterial lipopolysaccharides (LPS) and initiates robust immune activation that can be detrimental to the host. Towards the end of septicemia, cells self-regulate and remove surface TLR4 which contributes to immune ataxia. TLR4 deficient (TLR4 −/−) C57BL6 mice are used as a model for the immune refractory period following septic shock and compared to wildtype (WT) mice. In the serum of both WT and TLR4 −/−mice, 51 proteins were previously found to be dysregulated over the course of endotoxemia. We hypothesize that these 51 proteins represent TLR4 independent activation mechanisms. This study further investigates protein and mRNA distribution during endotoxemia. Liver, spleen, kidney, heart, and brain were collected at 0, 6, 12, and 18 hours post-intraperitoneal injection of 30 mg/kg E. coli LPS. Using qPCR and Western Blot to quantify gene and protein expression, we observed down regulation of genes involved with metabolism (Adsl, Mdh1) and erythrocyte cytoskeleton stabilization (Dmtn). In the same samples we observe activation of genes and proteins involved in T-cell function (Coro1a), and the complement cascades (Masp1, C1qb, Cfd, F5). These results further define TLR4 independent activation during endotoxemia as a model for immune ataxia that occurs after primary septic shock. This project could provide proof of principle to support the development of more targeted treatments to address immune activation during secondary infection after septic shock. This project was supported by a Towson University FDRC grant to EMH and a Fisher College of Science and Mathematics undergraduate research award to JCH, HA, PC, and AA.

Two-temperature accretion flows around strongly magnetized stars and their spectral analysis

ABSTRACT We investigate two-temperature accretion flows onto strongly magnetized compact stars. Matter is accreted in the form of an accretion disc upto the disc radius (rd), where, the magnetic pressure exceeds both the gas and ram pressure and thereafter the matter is channelled along the field lines onto the poles. We solve the equations of motion self-consistently along the field lines, incorporating radiative processes like bremsstrahlung, synchrotron, and inverse-comptonization. For a given set of constants of motion, the equations of motion do not produce unique transonic solution. Following the second law of thermodynamics, the solution with the highest entropy is selected and thereby eliminating the degeneracy in solution. We study the properties of these solutions and obtain corresponding spectra as a function of the magnetic field (B*), spin period (P) and accretion rate of the star ($\dot{M}$ ). A primary shock is always formed just near the surface. The enhanced radiative processes in this post-shock region slows down the matter and it finally settles on the surface of the star. This post-shock region contributes to ${\gtrsim}99.99~{{\ \rm per\ cent}}$ of the total luminosity obtained from the accretion flow. It is still important to study the full accretion flow because secondary shocks may be present for some combination of B*, P, and $\dot{M}$ in addition to primary shocks. We find that secondary shocks, if present, produce an extended emission at higher energies in the spectra.

Numerical investigation of shock-induced bubble collapse dynamics and fluid–solid interactions during shock-wave lithotripsy

In this paper we investigate the bubble collapse dynamics under shock-induced loading near soft and rigid bio-materials, during shock wave lithotripsy. A novel numerical framework was developed, that employs a Diffuse Interface Method (DIM) accounting for the interaction across fluid–solid-gas interfaces. For the resolution of the extended variety of length scales, due to the dynamic and fine interfacial structures, an Adaptive Mesh Refinement (AMR) framework for unstructured grids was incorporated. This multi-material multi-scale approach aims to reduce the numerical diffusion and preserve sharp interfaces. The presented numerical framework is validated for cases of bubble dynamics, under high and low ambient pressure ratios, shock-induced collapses, and wave transmission problems across a fluid–solid interface, against theoretical and numerical results. Three different configurations of shock-induced collapse applications near a kidney stone and soft tissue have been simulated for different stand-off distances and bubble attachment configurations. The obtained results reveal the detailed collapse dynamics, jet formation, solid deformation, rebound, primary and secondary shock wave emissions, and secondary collapse that govern the near-solid collapse and penetration mechanisms. Significant correlations of the problem configuration to the overall collapse mechanisms were found, stemming from the contact angle/attachment of the bubble and from the properties of solid material. In general, bubbles with their center closer to the kidney stone surface produce more violent collapses. For the soft tissue, the bubble movement prior to the collapse is of great importance as new structures can emerge which can trap the liquid jet into induced crevices. Finally, the tissue penetration is examined for these cases and a novel tension-driven tissue injury mechanism is elucidated, emanating from the complex interaction of the bubble/tissue interaction during the secondary collapse phase of an entrapped bubble in an induced crevice with the liquid jet.