Shock Parameters Research Articles

Heliospheric 3-D MHD ENLIL simulations of multi-CME and multi-spacecraft events

Interpreting multi-spacecraft heliospheric observations of the evolving solar wind (SW) streams with propagating and interacting coronal mass ejections (CMEs) is challenging. Numerical simulations can provide global context and suggest what may and may not be observed. The heliospheric three-dimensional (3D) magnetohydrodynamic (MHD) ENLIL model can provide a near-real-time prediction of heliospheric space weather, and it is used at NASA Community Coordinated Modeling Center (CCMC), NOAA Space Weather Prediction Center (SWPC), and UK Meteorological Office (MetOffice). However, this version does not show its full potential, especially in the case of multi-CME events observed by various spacecraft. We describe tools developed to interpret remote observations and in-situ measurements better and apply them to multi-CME events observed by ACE, STEREO-A, Parker Solar Probe (PSP), BepiColombo, and Solar Orbiter. We present some results on 1) global structures of the SW speed and density at the ecliptic, 2) the evolution of SW parameters at the spacecraft, 3) magnetic field connectivity at the spacecraft, 4) automatic detection of shock parameters and alert plots, and 5) synthetic white-light (WL) imaging. This paper is not on model initialization or analyzing specific CME events, but it describes features not used at space weather prediction centers and provided by NASA/CCMC Run-On-Request service. This paper advertises new tools and shows their benefits when applied to selected heliospheric space weather events observed at near-Earth, PSP, Solar Orbiter, and STEREO-A spacecraft.

Fracture mechanics behavior of coarse-grained MgO–C at room and high temperature

The fracture mechanical properties of coarse-grained MgO–C were investigated in four-point bending tests at single-edge V-notched beams (SEVNB) at room and high temperature. For measurement of the crack mouth opening displacement (CMOD) an optical system was used. Room temperature tests were accompanied with microstructural observations of the crack path with the use of digital image correlation to investigate the mechanisms of crack propagation and to determine the crack length. MgO–C showed stable crack propagation at room temperature as well as up to 1500 °C. Increased fracture toughness KIc and work of fracture were observed in the temperature range from 700 °C to 1200 °C. This behavior was correlated with crack closure, quasi-plastic deformation as well as the activation of visco-plastic creep mechanisms above 1200 °C. Additionally, the results were discussed in terms of Hasselman's thermal shock parameters.

Scaling laws for bubble collapse driven by an impulsive shock wave

Upon interaction with underwater shock waves, bubbles can collapse and produce high-speed liquid jets in the direction of the wave propagation. This work experimentally investigates the impact of laser-induced underwater impulsive shock waves, i.e. shock waves with a short, finite width, of variable peak pressure on bubbles of radii in the range 10–500 $\mathrm {\mu }$ m. The high-speed visualisations provide new benchmarking of remarkable quality for the validation of numerical simulations and the derivation of scaling laws. The experimental results support scaling laws describing the collapse time and the jet speed of bubbles driven by impulsive shock waves as a function of the impulse provided by the wave. In particular, the collapse time and the jet speed are found to be, respectively, inversely and directly proportional to the time integral of the pressure waveform for bubbles with a collapse time longer than the duration of shock interaction and for shock amplitudes sufficient to trigger a nonlinear bubble collapse. These results provide a criterion for the shock parameters that delimits the jetting and non-jetting behaviour for bubbles having a shock width-to-bubble size ratio smaller than one. Jetting is, however, never observed below a peak pressure value of 14 MPa. This limit, where the pressure becomes insufficient to yield a nonlinear bubble collapse, is likely the result of the time scale of the shock wave passage over the bubble becoming very short with respect to the bubble collapse time scale, resulting in the bubble effectively feeling the shock wave as a spatially uniform change in pressure, and in an (almost) spherical bubble collapse.

Fracture mechanical behavior of fine-grained carbon-bonded alumina at room and high temperature

The fracture mechanical properties of fine-grained carbon-bonded alumina (Al2O3–C) were investigated in four-point bending tests at single edged V-notched beams (SEVNB) at room and high temperature. Graphite served as a reference material. For measurement of the crack mouth opening displacement (CMOD) an optical system was used. The fracture behavior of Al2O3–C changed from brittle at room temperature to a crack resistance behavior at 1400 °C due to visco-plastic phenomena. The fracture toughness KIc was determined as 0.69 ± 0.07 MPa m1/2 at room temperature and 0.55 ± 0.21 MPa m1/2 at 1400 °C. At room temperature, the work of fracture γwof was determined as 26.3 ± 6.3 J/m2, and Hasselman's thermal shock parameters Rst and R'''' were 8.6 K m1/2 and 0.9 mm, respectively. Although a quantitative analysis of the work of fracture at 1400 °C was hindered by heat shimmer within the chamber, the results indicated significant increases of this parameter as well as Hasselman's thermal shock parameters up to 1400 °C.

Prolonging the therapeutic window for valproic acid treatment in a swine model of traumatic brain injury and hemorrhagic shock.

It has previously been shown that administration of valproic acid (VPA) can improve outcomes if given within an hour following traumatic brain injury (TBI). This short therapeutic window (TW) limits its use in real-life situations. Based upon its pharmacokinetic data, we hypothesized that TW can be extended to 3 hours if a second dose of VPA is given 8 hours after the initial dose. Yorkshire swine (40-45 kg; n = 10) were subjected to TBI (controlled cortical impact) and 40% blood volume hemorrhage. After 2 hours of shock, they were randomized to either (1) normal saline resuscitation (control) or (2) normal saline-VPA (150 mg/kg × two doses). First dose of VPA was started 3 hours after the TBI, with a second dose 8 hours after the first dose. Neurologic severity scores (range, 0-36) were assessed daily for 14 days, and brain lesion size was measured via magnetic resonance imaging on postinjury day 3. Hemodynamic and laboratory parameters of shock were similar in both groups. Valproic acid-treated animals had significantly less neurologic impairment on days 2 (16.3 ± 2.0 vs. 7.3 ± 2.8) and 3 (10.9 ± 3.6 vs. 2.8 ± 1.1) postinjury and returned to baseline levels 54% faster. Magnetic resonance imaging showed no differences in brain lesion size on day 3. Pharmacokinetic data confirmed neuroprotective levels of VPA in the circulation. This is the first study to demonstrate that VPA can be neuroprotective even when given 3 hours after TBI. This expanded TW has significant implications for the design of the clinical trial.

Experimental investigation of nanosecond laser-induced shock waves in water using multiple excitation beams.

Revealing the expansion and interaction dynamics of multiple shock waves induced by a nanosecond laser is important for controlling laser surgery. However, the dynamic evolution of shock waves is a complex and ultrafast process, making it difficult to determine the specific laws. In this study, we conducted an experimental investigation into the formation, propagation, and interaction of underwater shock waves that are induced by nanosecond laser pulses. The effective energy carried by the shock wave is quantified by the Sedov-Taylor model fitting with experimental results. Numerical simulations with an analytic model using the distance between adjacent breakdown locations as input and effective energy as fit parameters provide insights into experimentally not accessible shock wave emission and parameters. A semi-empirical model is used to describe the pressure and temperature behind the shock wave taking into account the effective energy. The results of our analysis demonstrate that shock waves exhibit asymmetry in both their transverse and longitudinal velocity and pressure distributions. In addition, we compared the effect of the distance between adjacent excitation positions on the shock wave emission process. Furthermore, utilizing multi-point excitation offers a flexible approach to delve deeper into the physical mechanisms that cause optical tissue damage in nanosecond laser surgery, leading to a better comprehension of the subject.

High-energy (>40 MeV) Proton Intensity Enhancements Associated with the Passage of Interplanetary Shocks at 1 au

We analyze periods with elevated >40 MeV proton intensities observed near Earth over a time span of 43 yr (1973–2016) that coincide with the passage of interplanetary (IP) shocks. Typically, elevated proton intensities result from large solar energetic particle (SEP) events. The IP shocks observed during these elevated-intensity periods may or may not be related to the origin of the SEP events. By choosing those cases when the shocks can be confidently associated with the solar eruption that generated the SEP event, we analyze the components of these SEP events that are localized in the vicinity of the shock (so-called “energetic storm particles”, ESPs), focusing on those events where the ESP component exceeds 40 MeV. We examine the interdependence of these high-energy ESPs with (i) the properties of the solar eruptions that generated the shocks and the SEP events, and (ii) the parameters of the shocks at their arrival at 1 au. The solar eruptions at the origin of the shocks producing >40 MeV proton ESP intensity enhancements are within ±50° longitude of central meridian and are associated with fast coronal mass ejections (plane-of-sky speeds ≳1000 km s−1). The ESP events with the largest >40 MeV proton intensity increases tend to occur when there are structures such as intervening IP coronal mass ejections and other unrelated shocks present in the solar wind through which the shock is propagating. Among the various local shock parameters considered, only the shock speed shows a certain degree of correlation with the observed ESP intensity increase.

Investigating the Temperature Shock of a Plate in the Framework of a Static Two-Dimensional Formulation of the Thermoelasticity Problem

The paper investigates the stress–strain state of a homogeneous rectangular plate after a temperature shock. It is believed that the plate is the first approximation of the solar panel model of a small spacecraft. To study the stress–strain state of the plate, a two-dimensional thermoelasticity problem is posed. The problem has a static formulation, since it does not take into account the dynamics of the plate’s natural oscillations. These oscillations affect the stress–strain state through the initial deflection of the plate at the time of the temperature shock. This deflection changes the parameters of the temperature shock and does not allow the use of a one-dimensional formulation of the thermoelasticity problem. As a result of solving the static two-dimensional thermoelasticity problem, approximate solutions are obtained for the components of the plate point’s displacement vector after the temperature shock. An approximation of the temperature field is presented. A numerical simulation is carried out. The correspondence of the obtained approximate analytical dependencies of the components of the plate point’s displacement vector to the numerical simulation data is analyzed. The proposed method can be used to assess the significance of the influence of the small spacecraft’s solar panels temperature shock on the dynamics of its rotational motion.

Statistical Analysis of Interplanetary Shocks from Mercury to Jupiter

In situ observations of interplanetary (IP) coronal mass ejections (ICMEs) and IP shocks are important to study as they are the main components of solar activity. Hundreds of IP shocks have been detected by various space missions at different times and heliocentric distances. Some of these are followed by clearly identified drivers, while some others are not. In this study, we carry out a statistical analysis of the distributions of plasma and magnetic parameters of the IP shocks recorded at various distances to the Sun. We classify the shocks according to the heliocentric distance, namely from 0.29 to 0.99 AU (Helios-1/2); near 1 AU (Wind, ACE, and STEREO-A/B); and from 1.35 to 5.4 AU (Ulysses). We also differentiate the IP shocks into two populations, those with a detected ICME and those without one. As expected, we find that there are no significant differences in the results from spacecraft positioned at 1 AU. Moreover, the distributions of shock parameters, as well as the shock normal, have no significant variations with the heliocentric distance. Additionally, we investigate how the number of shocks associated with stream-interaction regions (SIRs) increases with distance in the proportion to ICME/shocks. From 1 to 5 AU, SIRs/ shock occurrence increases slightly from 21% to 34%; in contrast, ICME/shock occurrence decreases from 47% to 17%. We also find indication of an asymmetry induced by the Parker spiral for SIRs and none for ICMEs.

Use of hemodynamic and laboratory monitoring tools to reduce the risk of mortality from pediatric septic shock

Background Early recognition of septic shock in terms of clinical, macrocirculatory hemodynamic, and microcirculatory laboratory parameters is a fundamental challenge in the emergency room and intensive care unit for early identification, adequate management, prevention of disease progression, and reduction of mortality risk.
 Objective To evaluate for possible correlations between survival outcomes of post-resuscitation pediatric septic shock patients and parameters of clinical signs, macrocirculatory hemodynamics, as well as microcirculatory laboratory findings.
 Methods This prospective, study was conducted in the PICU at Saiful Anwar Hospital, Malang, East Java. Inclusion criteria were children diagnosed with septic shock according to the 2005 Surviving Sepsis Campaign (SSC) criteria, aged >30 days-18 years, who were followed up for 72h after resuscitation. The measured variables such as cardiac index (CI), systemic vascular resistance index (SVRI), stroke volume index (SVI) were obtained from ultrasonic cardiac output monitor (USCOM). Blood gas and lactate were obtained from laboratory findings. Heart rate, pulse strength, extremity temperature, mean arterial pressure (MAP), systolic blood pressure (SBP), capillary refill time (CRT), Glasgow coma scale (GCS), and diuretic used were obtained from hemodynamic monitoring tools. Survival outcomes of post-resuscitation pediatric septic shock patients were noted.
 Results There was a significant correlation between the outcomes of the pediatric septic shock patients 72h after fluid resuscitation and clinical, macrocirculatory hemodynamic, and microcirculatory laboratory parameters. After the 6th hour of observation, strong pulse was predictive of survival, with 88.2% area under the curve (AUC). At the 12th hour of observation, MAP >50th percentile for age was predictive of survival, with 94% AUC.
 Conclusion For pediatric patients with septic shock, the treatment target in the first 6 hours is to improve strength of pulse, and that in the first 12 hours is to improve MAP >50th percentile for age to limit mortality.

Postinjury multiple organ failure in polytrauma: more frequent and potentially less deadly with less crystalloid

BackgroundRecently, retrospective registry-based studies have reported the decreasing incidence and increasing mortality of postinjury multiple organ failure (MOF). We aimed to describe the current epidemiology of MOF following the introduction of haemostatic resuscitation.MethodsA 10-year prospective cohort study was undertaken at a Level-1 Trauma Centre-based ending in December 2015. Inclusion criteria age ≥ 16 years, Injury Severity Score (ISS) > 15, Abbreviated Injury Scale (AIS) Head < 3 and survived > 48 h. Demographics, physiological and shock resuscitation parameters were collected. The primary outcome was MOF defined by a Denver Score > 3. Secondary outcomes: intensive care unit length of stay (ICU LOS), ventilation days and mortality.ResultsThree hundred and forty-seven patients met inclusion criteria (age 48 ± 20; ISS 30 ± 11, 248 (71%) were males and 23 (6.6%) patients died. The 74 (21%) MOF patients (maximum Denver Score: 5.5 ± 1.8; Duration; 5.6 ± 5.8 days) had higher ISS (32 ± 11 versus 29 ± 11) and were older (54 ± 19 versus 46 ± 20 years) than non-MOF patients. Mean daily Denver scores adjusted for age, sex, MOF and ISS did not change over time. Crystalloid usage decreased over the 10-year period (p value < 0.01) and PRBC increased (p value < 0.01). Baseline cumulative incidence of MOF at 28 days was 9% and competing risk analyses showed that incidence of MOF increased over time (subdistribution hazard ratio 1.14, 95% CI 1.04 to 1.23, p value < 0.01). Mortality risk showed no temporal change. ICU LOS increased over time (subdistribution hazard ratio 0.95, 95% CI 0.92 to 0.98, p value < 0.01). Ventilator days increased over time (subdistribution hazard ratio 0.94, 95% CI 0.9 to 0.97, p value < 0.01).ConclusionThe epidemiology of MOF continues to evolve. Our prospective cohort suggests an ageing population with increasing incidence of MOF, particularly in males, with little changes in injury or shock parameters, who are being resuscitated with less crystalloids, stay longer on ICU without improvement in survival.

L-FABP and NGAL are novel biomarkers for detection of abdominal injury and hemorrhagic shock

IntroductionDelayed diagnosis of abdominal injuries and hemorrhagic shock leads to secondary complications and high late mortality in severely traumatized patients. The liver fatty acid-binding protein (L-FABP) is expressed in intestine, liver and kidney; the neutrophil gelatinase-associated lipocalin (NGAL) in colon and kidney. We hypothesized that l-FABP is an early biomarker for abdominal injury and hemorrhagic shock and that l-FABP and NGAL are specific markers for detection of liver and/or kidney injuries. Patients and MethodsTraumatized patients with an age ≥18 years and an abdominal injury (AISabd≥2), independently from Injury Severity Score (ISS), were prospectively included from 04/2018 to 05/2021. 68 patients had an abdominal injury (“Abd”) and 10 patients had an abdominal injury with hemorrhagic shock (“HS Abd”). 41 patients without abdominal injury and hemorrhagic shock but with an ISS ≥ 25 (“noAbd”) were included as control group. Four abdominal subgroups with isolated organ injuries were defined. Plasma l-FABP and NGAL levels were measured at admission (ER) and up to two days post-trauma. ResultsAll patient groups had a median ISS≥25. In ER, median l-FABP levels were significantly higher in “HS Abd” group (1209.2 ng/ml [IQR=575.2–1780.3]) compared to “noAbd” group (36.4 ng/ml [IQR=14.8–88.5]), and to “Abd” group (41.4 ng/ml [IQR=18.0–235.5]), p<0.001. In matched-pair-analysis l-FABP levels in the group “Abd” were significantly higher (108.3 ng/ml [IQR=31.4–540.9]) compared to “noAbd” (26.4 ng/ml [IQR=15.5–88.8]), p = 0.0016. l-FABP correlated significantly with clinical parameters of hemorrhagic shock; the optimal cut-off level of l-FABP for detection was 334.3 ng/ml (sensitivity: 90%, specificity: 78%). Median l-FABP-levels were significantly higher in patients with isolated liver or kidney injuries and correlated significantly with AST, ALT and creatinine value. Median NGAL levels in the ER were significantly higher in “HS Abd” group (115.9 ng/ml [IQR=90.6–163.8]) compared to “noAbd” group (58.5 ng/ml [IQR=41.0–89.6],p<0.001) and “Abd” group (70.5 ng/ml [IQR=53.3–115.5], p<0.05). The group “Abd” showed significant higher median NGAL levels compared to “noAbd”, p = 0.019. NGAL levels correlated significantly with clinical parameters of hemorrhagic shock. Conclusion:L-FABP and NGAL are novel biomarkers for detection of abdominal trauma and hemorrhagic shock. l-FABP may be a useful and promising parameter in diagnosis of liver and kidney injuries, NGAL failed to achieve the same.

The Efficiency of Electron Acceleration by ICME-driven Shocks

We present a study of the efficiency of the acceleration of suprathermal electrons at collisionless shock waves driven by interplanetary coronal mass ejections (ICMEs), with the data analysis from both the spacecraft observations and test-particle simulations. The observations are from the 3DP/EESA instrument on board Wind during the 74 shock events listed in Yang et al., and the test-particle simulations are carried out through 315 cases with different shock parameters. A total of seven energy channels ranging from 0.428–4.161 keV are selected. In the simulations, using a backward-in-time method, we calculate the average downstream flux in the 90° pitch angle. On the other hand, the average downstream and upstream fluxes in the 90° pitch angle can also be directly obtained from the 74 observational shock events. In addition, the variation in the event number ratio with the downstream to upstream flux ratio above a threshold value in terms of the shock angle (the angle between the shock normal and upstream magnetic field), upstream Alfvén Mach number, and shock compression ratio is statistically obtained. It is shown from both the observations and simulations that a large shock angle, upstream Alfvén Mach number, and shock compression ratio can enhance the efficiency of the shock acceleration. Our results suggest that shock drift acceleration is more efficient in the electron acceleration by ICME-driven shocks, which confirms the findings of Yang et al.

Secondary hyperperfusion injury following surgical evacuation for acute isolated epidural hematoma with concurrent cerebral herniation.

Hemispherical cerebral swelling or even encephalocele after head trauma is a common complication and has been well elucidated previously. However, few studies have focused on the secondary brain hemorrhage or edema occurring regionally but not hemispherically in the cerebral parenchyma just underneath the surgically evacuated hematoma during or at a very early stage post-surgery. In order to explore the characteristics, hemodynamic mechanisms, and optimized treatment of a novel peri-operative complication in patients with isolated acute epidural hematoma (EDH), clinical data of 157 patients with acute-isolated EDH who underwent surgical intervention were reviewed retrospectively. Risk factors including demographic characteristics, admission Glasgow Coma Score, preoperative hemorrhagic shock, anatomical location, and morphological parameters of epidural hematoma, as well as the extent and duration of cerebral herniation on physical examination and radiographic evaluation were considered. It suggested that secondary intracerebral hemorrhage or edema was determined in 12 of 157 patients within 6 h after surgical hematoma evacuation. It was featured by remarkable, regional hyperperfusion on the computed tomography (CT) perfusion images and associated with a relatively poor neurological prognosis. In addition to concurrent cerebral herniation, which was found to be a prerequisite for the development of this novel complication, multivariate logistic regression further showed four independent risk factors contributing to this type of secondary hyperperfusion injury: cerebral herniation that lasted longer than 2 h, hematomas that were located in the non-temporal region, hematomas that were thicker than 40 mm, and hematomas occurring in pediatric and elderly patients. Secondary brain hemorrhage or edema occurring within an early perioperative period of hematoma-evacuation craniotomy for acute-isolated EDH is a rarely described hyperperfusion injury. Because it plays an important prognostic influence on patients' neurological recovery, optimized treatment should be given to block or reduce the consequent secondary brain injuries.

The effect of shock wave properties on the release timings of solar energetic particles

Context. Fast and wide coronal mass ejections (CMEs) and CME-driven shock waves are capable of accelerating solar energetic particles (SEPs) and releasing them in very distant locations in the solar corona and near-Sun interplanetary space. SEP events have a variety of characteristics in their release times and particle anisotropies. In some events, specifics of the SEP release times are thought to be difficult to reconcile with the scenario that a propagating shock wave is responsible for the SEP release. Aims. Despite the apparent difficulties posed by the shock scenario, many studies have not considered the properties of the propagating shock waves when making a connection with SEP release. This could probably resolve some of the issues and would help us to delve into and understand more important issues such as the effect of the shock acceleration efficiency on the observed characteristics of the SEP timings and the role of particle transport. This study aims to approach these issues from the shock wave perspective and elucidate some of these aspects. Methods. We constructed a simple 2D geometrical model to describe the propagation and longitudinal extension of a disturbance. We used this model to examine the longitudinal extension of the wave front from the eruption site as a function of time, to calculate the connection times as a function of the longitudinal separation angle, and to determine the shock parameters at any connection point. We examined how the kinematic and geometric properties of the disturbance could affect the timings of the SEP releases at different heliolongitudes. Results. We show that the extension of a wave close to the solar surface may not always indicate when a magnetic connection is established for the first time. The first connection times depend on both the kinematics and geometry of the propagating wave. A shock-related SEP release process can produce a large event-to-event variation in the relationship between the connection and release times and the separation angle to the eruption site. The evolution of the shock geometry and shock strength at the field lines connected to an observer are important parameters for the observed characteristic of the release times.

Electrostatic Plasma Wave Excitations at the Interplanetary Shocks

Over the last few decades, different types of plasma waves (e.g., the ion acoustic waves (IAWs), electrostatic solitary waves, upper/lower hybrid waves, and Langmuir waves) have been observed in the upstream, downstream, and ramp regions of the collisionless interplanetary (IP) shocks. These waves may appear as short-duration (only a few milliseconds at 1 au) electric field signatures in the in-situ measurements, with typical frequencies of ∼1–10 kHz. A number of IAW features at the IP shocks seem to be unexplained by kinetic models and require a new modeling effort. Thus, this paper is dedicated to bridging this gap in understanding. In this paper, we model the linear IAWs inside the shock ramp by devising a novel linearization method for the two-fluid magnetohydrodynamic equations with spatially dependent shock parameters. It is found that, for parallel propagating waves, the linear dispersion relation leads to a finite growth rate, which is dependent on the shock density compression ratio, as Wind data suggest. Further analysis reveals that the wave frequency grows towards the downstream region within the shock ramp, and the wave growth rate is independent of the electron-to-ion temperature ratio, as Magnetospheric Multiscale (MMS) in-situ measurements suggest, and is uniform within the shock ramp. Thus, this study helps in understanding the characteristics of the IAWs at the collisionless IP shocks.

Hybrid simulations of the decay of reconnected structures downstream of the bow shock

Observations by Magnetospheric Multiscale have demonstrated that magnetic reconnection occurs at Earth's bow shock, typically at thin current sheets arising from plasma instabilities and turbulence in the shock transition region. Observational surveys of both the shock transition and the magnetosheath downstream suggest that the number of current sheets in these regions may not be strongly dependent on the shock Mach number MA or the angle between the upstream magnetic field and shock normal (θBn). This result is somewhat surprising given that quasi-parallel and high Mach number shocks tend to have a more disordered and non-stationary structure. In order to investigate how shock reconnection manifests across different parameters, we perform a series of hybrid (fluid electron, kinetic ion) particle-in-cell simulations across a range of Mach numbers and orientations. Given that hybrid simulations cannot resolve electron-scale current sheets and reconnection, these simulations isolate an ion-scale mechanism for shock reconnection driven by an ion–ion beam instability in the foot. We find that this mechanism is strongly constrained to quasi-parallel shocks across all simulated Mach numbers. By quantifying reconnection using the area occupied by plasma on closed magnetic field lines, we find the number of reconnecting structures and closed field area increase with MA and decrease with θBn in the upstream and ramp regions. Downstream of the shock, however, we find a similar result to observational surveys: within the subset of quasi-parallel shocks, the decay rate of the closed field area (and hence thin current sheets) is not strongly dependent on upstream shock parameters.

Optimizing Parameters with FEM Model for 20CrMnTi Laser Shocking

As a new surface treatment technology, laser shock peening (LSP) is a multi-point overlay process of single-point laser shock. In this study, the finite element method (FEM) was used to build a model of single-point laser shock, and the model was verified by experiments. The difference in residual stresses between the experimental and simulated results was less than 20%. Then, the effects of the stress field and deformation of 20CrMnTi with different laser shock parameters were simulated and analyzed. According to the mechanical response of 20CrMnTi to different laser shock parameters, the optimal shocking process parameters for single-point shocking via LSP were determined to be a shock energy of 5 J, a laser pulse width of 20 ns, and an impact number of 5. Lastly, a simulation of multi-point laser shock was performed with the optimal parameters, and the residual compressive stress values of multi-point impacts are close to those of single-point impacts under the same process conditions.

Electron acceleration in supernova remnants

Supernova remnants (SNRs) are believed to produce the majority of galactic cosmic rays (CRs). SNRs harbor non-relativistic collisionless shocks responsible for the acceleration of CRs via diffusive shock acceleration (DSA), in which particles gain their energy via repeated interactions with the shock front. Since the DSA theory involves pre-existing mildly energetic particles, a means of pre-acceleration is required, especially for electrons. Electron injection remains one of the most troublesome and still unresolved issues and our physical understanding of it is essential to fully comprehend the physics of SNRs. To study any electron-scale phenomena responsible for pre-acceleration, we require a method capable of resolving these small kinetic scales and particle-in-cell simulations that fulfill this criterion. Here, I report on the latest achievements made by utilizing kinetic simulations of non-relativistic high Mach number shocks. I discuss how the physics of SNR shocks depends on the shock parameters (e.g. the shock obliquity, Mach number, the ion-to-electron mass ratio) as well as the processes responsible for the electron heating and acceleration.

Parameters associated with successful weaning of veno-arterial extracorporeal membrane oxygenation: a systematic review

PurposeVeno-arterial (VA) extracorporeal membrane oxygenation (ECMO) can be used to restore organ perfusion in patients with cardiogenic shock until native heart recovery occurs. It may be challenging, however, to determine when patients can be weaned successfully from ECMO—surviving without requiring further mechanical support or heart transplant. We aimed to systematically review the medical literature to determine the biomarkers, hemodynamic and echocardiographic parameters associated with successful weaning of VA-ECMO in adults with cardiogenic shock and to present an evidence-based weaning algorithm incorporating key findings.MethodWe systematically searched PubMed, Embase, ProQuest, Google Scholars, Web of Science and the Grey literature for pertinent original research reports. We excluded studies limited to extracorporeal cardiopulmonary resuscitation (ECPR) as the neurological prognosis may significantly alter the decision-making process surrounding the device removal in this patient population. Studies with a mixed population of VA-ECMO for cardiogenic shock or cardiac arrest were included. We excluded studies limited to patients in which ECMO was only used as a bridge to VAD or heart transplant, as such patients are, by definition, never “successfully weaned.” We used the Risk of Bias Assessment tool for Non-Randomized Studies. The study was registered on the International prospective register of systematic reviews (PROSPERO CRD42020178641).ResultsWe screened 14,578 records and included 47 that met our pre-specified criteria. Signs of lower initial severity of shock and myocardial injury, early recovery of systemic perfusion, left and right ventricular recovery, hemodynamic and echocardiographic stability during flow reduction trial and/or pump-controlled retrograde trial off predicted successful weaning. The most widely used parameter was the left ventricular outflow tract velocity time integral, an indicator of stroke volume. Most studies had a moderate or high risk of bias. Heterogeneity in methods, timing, and conditions of measurements precluded any meta-analysis.ConclusionsIn adult patients on VA-ECMO for cardiogenic shock, multiple biomarkers, hemodynamic and echocardiographic parameters may be used to track resolution of systemic hypoperfusion and myocardial recovery in order to identify patients that can be successfully weaned.Graphical