Effect of the interval between two shocks on ejecta formation from the grooved aluminum surface

This work focuses on the effect of the interval between two shocks on the ejecta formation from the grooved aluminum(Al_(1100))surface by using smoothed particle hydrodynamics numerical simulation.Two unsupported shocks are obtained by the plate-impact between sample and two flyers at interval,with a peak pressure of approximately 30 GPa for each shock.When the shock interval varies from 2.11 to 7.67 times the groove depth,the bubble velocity reduces to a constant,and the micro jetting factor R_(J) from spike to bubble exhibits a non-monotonic change that decreases initially and then increases.At a shock interval of 3.6 times the groove depth,micro jetting factor R_(J) from spike to bubble reaches its minimum value of approximately 0.6.While,the micro jetting factor R_(F) from spike to free surface decreases linearly at first,and stabilizes around 0.25 once the shock interval surpasses 4.18 times the groove depth.When the shock interval is less than 4.18 times the groove depth,the unloading wave generated by the breakout of the first shock wave is superimpose with the unloading part of the second shock wave to form a large tensile area.

STABILITY OF TRANSONIC SHOCKS TO THE EULER-POISSON SYSTEM WITH VARYING BACKGROUND CHARGES

This paper is devoted to studying the stability of transonic shock solutions to the Euler-Poisson system in a one-dimensional nozzle of finite length.The background charge in the Poisson equation is a piecewise constant function.The structural stability of the steady transonic shock solution is obtained by the monotonicity argument.Furthermore,this transonic shock is proved to be dynamically and exponentially stable with respect to small perturbations of the initial data.One of the crucial ingredients of the analysis is to establish the global well-posedness of a free boundary problem for a quasilinear second order equation with nonlinear boundary conditions.

High-Order DG Schemes with Subcell Limiting Strategies for Simulations of Shocks,Vortices and Sound Waves in Materials Science Problems

Shock waves,characterized by abrupt changes in pressure,temperature,and density,play a significant role in various materials science processes involving fluids.These high-energy phenomena are utilized across multiple fields and applications to achieve unique material properties and facilitate advanced manufacturing techniques.Accurate simulations of these phenomena require numerical schemes that can represent shock waves without spurious oscillations and simultaneously capture acoustic waves for a wide range of wavelength scales.This work suggests a high-order discontinuous Galerkin(DG)method with a finite volume(FV)subcell limiting strategies to achieve better subcell resolution and lower numerical diffusion properties.By switching to the FV discretization on an embedded sub-cell grid,the method displays advantages with respect to both DG accuracy and FV shock-capturing ability.The FV scheme utilizes a class of high-fidelity schemes that are built upon the boundary variation diminishing(BVD)reconstruction paradigm.The method is therefore able to resolve discontinuities and multi-scale structures on the subcell level,while preserving the favorable properties of the high-order DG scheme.We have tested the present DG method up to the 6th-order accuracy for both smooth and discontinuous noise problems.

STABILIZATION EFFECT OF FRICTIONS FOR TRANSONIC SHOCKS IN STEADY COMPRESSIBLE EULER FLOWS PASSING THREE-DIMENSIONAL DUCTS

Transonic shocks play a pivotal role in designation of supersonic inlets and ramjets.For the three-dimensional steady non-isentropic compressible Euler system with frictions,we constructe a family of transonic shock solutions in rectilinear ducts with square cross-sections.In this article,we are devoted to proving rigorously that a large class of these transonic shock solutions are stable,under multidimensional small perturbations of the upcoming supersonic flows and back pressures at the exits of ducts in suitable function spaces.This manifests that frictions have a stabilization effect on transonic shocks in ducts,in consideration of previous works which shown that transonic shocks in purely steady Euler flows are not stable in such ducts.Except its implications to applications,because frictions lead to a stronger coupling between the elliptic and hyperbolic parts of the three-dimensional steady subsonic Euler system,we develop the framework established in previous works to study more complex and interesting Venttsel problems of nonlocal elliptic equations.

Dynamics of oil price shocks and stock market behavior in Pakistan:evidence from the 2007 financial crisis period

Background:The aim of this study is to investigate the effect of the oil price and its volatility on the stock market of Pakistan before and after the 2007 financial crisis period.Methods:The analyses are carried out on daily data for the period from July 31,2000 to July 31,2014.This study uses several econometric techniques for the analyses,namely,the Johansen-Juselius cointegration test,generalized autoregressive conditional heteroskedasticity(GARCH)model,exponential generalized autoregressive conditional heteroskedasticity(EGARCH)model,variance decomposition method,and impulse response function.Results:The results of the cointegration method indicate a significant long-run association between stock market and oil prices in the pre-crisis period.The EGARCH model shows that oil price returns have a significant effect on stock market returns in both sub-periods,while the result for the GARCH model is significant only in the postcrisis period.We find a significant effect of oil price volatility on the stock market in both sub-periods from the GARCH model.Furthermore,the EGARCH model shows an asymmetric effect of oil price volatility on the stock market in the pre-crisis period.Variance decomposition shows that stock market variations are mostly explained by selfinnovation.Moreover,the impulse response function results show that oil price shocks affected the stock market adversely in the pre-crisis period but positively in the postcrisis period.Conclusions:This study suggests that economic policymakers and investors should consider the oil price as an important factor affecting stock market returns.

Remote monitoring of implantable defibrillators is associated with fewer inappropriate shocks and reduced time to medical assessment in a remote and rural area

BACKGROUND Implantable cardioverter defibrillators(ICDs)and cardiac resynchronisation therapy with defibrillators(CRT-D)reduce mortality in certain cardiac patient populations.However,inappropriate shocks pose a problem,having both adverse physical and psychological effects on the patient.The advances in device technology now allow remote monitoring(RM)of devices to replace clinic follow up appointments.This allows real time data to be analysed and actioned and this may improve patient care.AIM To determine if RM in patients with an ICD is associated with fewer inappropriate shocks and reduced time to medical assessment.METHODS This was a single centre,retrospective observational study,involving 156 patients implanted with an ICD or CRT-D,followed up for 2 years post implant.Both appropriate and inappropriate shocks were recorded along with cause for inappropriate shocks and time to medical assessment.RESULTS RM was associated with fewer inappropriate shocks(13.6%clinic vs 3.9%RM;P=0.030)and a reduced time to medical assessment(15.1±6.8 vs 1.0±0.0 d;P<0.001).CONCLUSION RM in patients with an ICD is associated with improved patient outcomes.

A Physical Method of Analyzing theMechanism of Continental StrongShocks from Crustal Movement

In order to analyze the mechanism of continental strong shocks from the angle of crustal movement using the data of repeated geodetic survey, this paper has proposed a physical method; it analyzes the mechanism of density change due to the occurrence of strong shocks by use of the physical quantity that reflects the time change of crustal density. (1) The general theory of the time change of density in the earth’ s interior and the theory of the time change of single layer density have been introduced, and an algorithm of stepwise iteration has been proposed; (2) The effect of the change of single layer density caused by fault dislocation has been analyzed in brief; (3) The characteristics of the time change of crustal density in the south of the seismogenic region before the 1996 Lijiang earthquake with M_L =7.0 have been studied; (4) The precursor model or causal mechanism of strong shocks possibly existing in the time change of crustal density has been investigated preliminarily.

Web software reliability modeling with random impulsive shocks

As the web-server based business is rapidly developed and popularized, how to evaluate and improve the reliability of web-servers has been extremely important. Although a large num- ber of software reliability growth models （SRGMs）, including those combined with multiple change-points （CPs）, have been available, these conventional SRGMs cannot be directly applied to web soft- ware reliability analysis because of the complex web operational profile. To characterize the web operational profile precisely, it should be realized that the workload of a web server is normally non-homogeneous and often observed with the pattern of random impulsive shocks. A web software reliability model with random im- pulsive shocks and its statistical analysis method are developed. In the proposed model, the web server workload is characterized by a geometric Brownian motion process. Based on a real data set from IIS server logs of ICRMS website （www.icrms.cn）, the proposed model is demonstrated to be powerful for estimating impulsive shocks and web software reliability.

Shocks and Solitons in Ultradense Degenerate Electron-Positron-Ion Plasmas

The formation and propagation of shocks and solitons are investigated in an unmagnetized, ultradense plasma containing degenerate Fermi gas of electrons and positrons, and classical ion gas by employing Thomas-Fermi model. For this purpose, a deformed Korteweg-de Vries-Berger （dKdVB） equation is derived using the reductive perturbative technique for cold, adiabatic, and isothermal ions. Localized analytical solutions of dKdVB equation in planar geometry are obtained for dispersion as well as dissipation dominant cases. For nonplanar （cylindrical and spherical） geometry, time varying numerical shock wave solution of dKdVB equation is found. Its dispersion dominant case leading to the soliton solution is also discussed. The effect of ion temperature, positron concentration and dissipation is found significant on these nonlinear structures. The relevance of the results to the systems of scientific interest is pointed out.

Facing Challenges and Shocks with Rationality

The Iraqi War breaking out on March 20, 2003 undoubtedly marks a turning point in current international relations. The international disputes around this war is not only an embodiment of differentbeliefs and positions on the issue of war and peace, but more importantly a demonstration of the deep skepticism and worry throughout the international community on the possible outcome of the war, as well as the future development of American diplomatic and military policies. All these will exert a profound and extensive influence on the trend of development of international relations in the future.

Empirical Evidence of Natural Shocks, Risk Perceptions and Resilience from Cameroon

Invariably, it is the poorest of the poor who are mostly affected by perverse disasters, policies and laws. A major concern in disaster research is to explore the relationship between shock experiences and victims＇ perceptions of risk, as well as their possible effect on victims＇ behavior for resilience and adaptation. We explore this relationship on victimized households of the 1986 Lake Nyos disaster, employing a quasi-experimental design. Matching was done with non-affected households. Both groups affected and non-affected households were of adequate size, and subject to the same questionnaire. Selection of （470） test and matching households was purposely limited to nine of the ten towns accommodating both survivors and non survivors of the examined disaster. A list constructed with traditional rulers in each village allowed for random sampling of non victims for comparative analysis. We then compare households affected by the disaster with those who were not. The results reveal differentiated perceptions of risk and management behavior contingent on whether households experienced the shock or not. However, solidarity and reciprocity remained extremely high and not significantly different amongst both household types, suggesting resilience of endogenous, informal risk response mechanisms to natural shocks. The article concludes that analyzing risk perceptions can help explain why some individuals, households or communities may be resilient to shocks and others not. We argue for a combination of subjective perceptions and objective shock analysis, especially if the analyst hopes to influence policy.

Coping with Shocks and Determinants among Indigenous Vegetable Smallholder Farmers in Kenya

Farm households in developing countries are faced with various challenges one of which is occurrence of unexpected negative events namely shocks. Shocks could be caused by extreme adverse natural events (droughts, storms, flood, and landslides) and market-related events (fuel, food, input and output price fluctuations, volatilities and price hikes). Most of these shocks affect production systems, food markets and local economies, all of which have direct effects on food security. This study explores the prevalence of shocks among indigenous vegetable farmers in Kenya followed by an assessment of the type of coping strategies in response to these shocks. We find that over two thirds of farmers have coping strategies that are not based on market-related insurance mechanisms;rather they use strategies such as working for more hours and selling assets. We analyze which socioeconomic and institutional factors determine households’ decision and extent of coping with shocks. The results showed that access to high-value markets and market information were the major factors informing their decision and extent of using coping strategies along with access to critical services such as credit, extension, and farmer groups. This has significant policy implications regarding the dissemination of information and promotion of credit markets through mobile phone-based platforms for easy accessibility in remote rural areas. Social capital should be encouraged because it acts as a necessary and sufficient conduit for information dissemination and mutual support to help farmers’ access critical services and resources needed for successful and sustainable implementation of relevant and appropriate coping strategies.

International Price Shocks Transmission： The Case of Rice in Togo

The objective of the paper was to examine the relationship between the world rice price and the rice price in Togo using the linear and nonlinear co-integration tests. The author used the monthly prices for Togo local rice market and international market. The results show that the rice prices on the local market are integrated to international market. The elasticity of the long-term transmission is high. The threshold autoregression （TAR） model reveals an asymmetric transmission with a magnitude that varies depending on the nature of shock. Price increases in international markets are transmitted more rapidly to the local markets than price reductions. These results might be explained by the market power of traders, transport costs and government intervention.

Testing the Proposed Municipality Resilience Index to Climate Change Shocks and Stresses in Mbale Municipality in Eastern Uganda

Since climate change shocks and stresses cannot be fully prevented, building resilient urban areas is gaining more attention in the global community. By building resilience, the negative impacts of climate change shocks and stresses can be alleviated. Several indices have been developed to measure urban resilience. Yet, most of these indices focus more on objective methods which require robust bio-physical and socio-economic data sets which are generally lacking in many developing countries. To reduce this challenge, the use of subjective methods has recently been suggested. This study proposed and tested a Municipality Resilience Index (MRI) which employed a subjective method to assess the resilience of Mbale municipality in Eastern Uganda against climate change shocks and stresses. The proposed MRI includes 46 variables describing the physical, social, economic and institutional dimensions. The MRI can be applied in any municipality in developing countries facing climate related shocks and stresses and with limited survey data. The application of this index to Mbale municipality shows that the municipality has a low resilience index of 0.2. Similarly, most variables in the four dimensions of resilience reflected very low resilience scores with other divisions being more resilient than the others. Furthermore, the social dimension has the lowest score as compared to the physical, economic and institutional dimensions. The findings indicate a spatial variability in the contribution of the resilience dimensions within this small geographic confine. Moreover, the findings show the strengths and weaknesses in the different dimensions of the proposed MRI. This can act as a guide for policy and practitioners on which sectors to target in order to enhance the resilience of Mbale municipality.

Do Oil Price Shocks and COVID-19 Lead to Policy Uncertainty?

This study examines the asymmetric effects of the structural oil price shocks and COVID-19 pandemic on four uncertainty indexes.The author used the SVAR approach for the period 31-Dec-2019 to 28-Jun-2020.The results indicate that the effects are asymmetric of oil price shocks.The author also finds that COVID-19 shocks lead to positive responses to the economic policy uncertainty index.In addition,oil prices(their shocks)have a negative impact on the four indicators of uncertainty.Consequently,governments should actively take effective measures to prevent crude oil prices from shocking and maintain stable economic policies.

VANISHING VISCOSITY FOR NON-ISENTROPIC GAS DYNAMICS WITH INTERACTING SHOCKS

In this paper, we study the vanishing viscosity limit for non-isentropic gas dy- namics with interacting shocks. Given any entropy solution of non-isentropic gas dynamics which consists of two different families of shocks interacting at some positive time, we show that such solution is the vanishing viscosity limit of a family of smooth global solutions for a viscous system of conservation law. We remark that, after the interacting time, not only shocks but also contact discontinuity are generated.

Experimental and numerical studies on interactions of a spherical flame with incident and reflected shocks

Observations are presented from experiments and calculations where a laminar spherical CH4/air flame is perturbed successively by incident and reflected shock waves. The experiments are performed in a standard shock tube arrangement, in which a high-speed shadowgraph imaging system is used to record evolutions of the flame. Numerical simulations are conducted by using second-order wave propagation algorithms, based on two-dimensional axisymmetric Navier-Stokes equations with detailed chemical reactions. Qualitative agreements are obtained between the experimental and numerical results. Under actions of incident shock waves, Richtmyer-Meshkov instability responsible for the flame deformation is induced in the flame, and the distoned flame takes a barrel shape. Then, under subsequent actions of the shock wave reflected from a planar wall, the flame takes an inclined non-symmetrical kidney shape in a symmetric cross section, which means a mushroom-like shape of the flame comes finally into being. The vorticity direction in the ring cap has been altered by the reflected shock＇s action, which makes the head of the mushroom-like flame extend quickly to the side wall.

Ejecta from periodic grooved Sn surface under unsupported shocks

Dynamic failure and ejection characteristics of a periodic grooved Sn surface under unsupported shock loading are studied using a smoothed particle hydrodynamics method. An ＂Eiffel Tower＂ spatial structure is observed, which is com- posed of high-speed jet tip, high-density jet slug, longitudinal tensile sparse zone, and complex broken zone between grooves. It is very different from the spike-bubble structure under supported shocks, and has been validated by detonation loading experiments. In comparison with that under supported shocks at the same peak pressure, the high-speed ejecta decreases obviously, whereas the truncated location of ejecta moves towards the interior of the sample and the total mass of ejecta increases due to the vast existence of low-speed broken materials. The shock wave profile determines mainly the total ejection amount, while the variation of V-groove angle will significantly alter the distribution of middle- and high-speed ejecta, and the maximum ejecta velocity has a linear corretation with the groove angle.

Numerical investigation of Richtmyer-Meshkov instability driven by cylindrical shocks

In this paper, a numerical method with high order accuracy and high resolution was developed to simulate the Richtmyer-Meshkov（RM） instability driven by cylindrical shock waves. Compressible Euler equations in cylindrical coordinate were adopted for the cylindrical geometry and a third order accurate group control scheme was adopted to discretize the equations. Moreover, an adaptive grid technique was developed to refine the grid near the moving interface to improve the resolution of numerical solutions. The results of simulation exhibited the evolution process of RM instability, and the effect of Atwood number was studied. The larger the absolute value of Atwood number, the larger the perturbation amplitude. The nonlinear effect manifests more evidently in cylindrical geometry. The shock reflected from the pole center accelerates the interface for the second time, considerably complicating the interface evolution process, and such phenomena of reshock and secondary shock were studied.