Early peripheral perfusion index predicts 28-day outcome in patients with septic shock

BACKGROUND:To investigate the prognostic value of the peripheral perfusion index(PPI)in patients with septic shock.METHODS:This prospective cohort study,conducted at the emergency intensive care unit of Peking University People's Hospital,recruited 200 patients with septic shock between January 2023 and August 2023.These patients were divided into survival(n=84)and death(n=116)groups based on 28-day outcomes.Clinical evaluations included laboratory tests and clinical scores,with lactate and PPI values assessed upon admission to the emergency room and at 6 h and 12 h after admission.Risk factors associated with mortality were analyzed using univariate and multivariate Cox regression analyses.Receiver operator characteristic(ROC)curve was used to assess predictive performance.Mortality rates were compared,and Kaplan-Meier survival plots were created.RESULTS:Compared to the survival group,patients in the death group were older and had more severe liver damage and coagulation dysfunction,necessitating higher norepinephrine doses and increased fl uid replacement.Higher lactate levels and lower PPI levels at 0 h,6 h,and 12 h were observed in the death group.Multivariate Cox regression identifi ed prolonged prothrombin time(PT),decreased 6-h PPI and 12-h PPI as independent risk factors for death.The area under the curves for 6-h PPI and 12-h PPI were 0.802(95%CI 0.742-0.863,P<0.001)and 0.945(95%CI 0.915-0.974,P<0.001),respectively,which were superior to Glasgow Coma Scale(GCS),Sequential Organ Failure Assessment(SOFA)scores(0.864 and 0.928).Cumulative mortality in the low PPI groups at 6 h and 12 h was signifi cantly higher than in the high PPI groups(6-h PPI:77.52%vs.22.54%;12-h PPI:92.04%vs.13.79%,P<0.001).CONCLUSION:PPI may have value in predicting 28-day mortality in patients with septic shock.

Knowledge,management,and complications of sepsis and septic shock:A significant therapeutic challenge in the intensive care unit

Sepsis and septic shock are life-threatening conditions that are globally responsible for almost 20%of mortality,especially in low and middle-income countries.This review was conducted on PubMed and Google Scholar databases with keywords sepsis,septic shock,sepsis management,and sepsis complications.Articles published up to July 2023 in English were included.Diagnosis and management should be carried out without unnecessary delay.Cooperation between various medical specialties including intensive care doctors,neurologists,hepatologists,cardiologists,and pediatric doctors is needed if a child is affected.New strategies have to be implemented in low and middle-income countries to decrease the sepsis incidence and reduce mortality in the population.

Systematic review with expert consensus on use of extracorporeal hemoadsorption in septic shock:An Indian perspective

BACKGROUND Septic shock is a severe form of sepsis characterised by deterioration in circulatory and cellular-metabolic parameters.Despite standard therapy,the outcomes are poor.Newer adjuvant therapy,such as CytoSorb®extracorporeal haemoadsorption device,has been investigated and shown promising outcome.However,there is a lack of some guidance to make clinical decisions on the use of CytoSorb®haemoadsorption as an adjuvant therapy in septic shock in Indian Setting.Therefore,this expert consensus was formulated.AIM To formulate/establish specific consensus statements on the use of CytoSorb®haemoadsorption treatment based on the best available evidence and contextualised to the Indian scenario.METHODS We performed a comprehensive literature on CytoSorb®haemoadsorption in sepsis,septic shock in PubMed selecting papers published between January 2011 and March 20232021 in English language.The statements for a consensus document were developed based on the summarised literature analysis and identification of knowledge gaps.Using a modified Delphi approach combining evidence appraisal and expert opinion,the following topics related to CytoSorb®in septic shock were addressed:need for adjuvant therapy,initiation timeline,need for Interleukin-6 levels,duration of therapy,change of adsorbers,safety,prerequisite condition,efficacy endpoints and management flowchart.Eleven expert members from critical care,emergency medicine,and the intensive care participated and voted on nine statements and one open-ended question.RESULTS Eleven expert members from critical care,emergency medicine,and the intensive care participated and voted on nine statements and one open-ended question.All 11 experts in the consensus group(100%)participated in the first,second and third round of voting.After three iterative voting rounds and adapting two statements,consensus was achieved on nine statements out of nine statements.The consensus expert panel also recognised the necessity to form an association or society that can keep a registry regarding the use of CytoSorb®for all indications in the open-ended question(Q10)focusing on“future recommendations for CytoSorb®therapy”.CONCLUSION This Indian perspective consensus statement supports and provides guidance on the use of CytoSorb®haemoadsorption as an adjuvant treatment in patients with septic shock to achieve optimal outcomes.

Low T3 vs low T3T4 euthyroid sick syndrome in septic shock patients:A prospective observational cohort study

BACKGROUND Both phases of euthyroid sick syndrome(ESS)are associated with worse prognosis in septic shock patients.Although there are still no indications for supplementation therapy,there is no evidence that both phases(initial and prolonged)are adaptive or that only prolonged is maladaptive and requires supplementation.AIM To analyze clinical,hemodynamic and laboratory differences in two groups of septic shock patients with ESS.METHODS A total of 47 septic shock patients with ESS were divided according to values of their thyroid hormones into low T3 and low T3T4 groups.The analysis included demographic data,mortality scores,intensive care unit stay,mechanical ventilation length and 28-day survival and laboratory with hemodynamics.RESULTS The Simplified Acute Physiology Score II score(P=0.029),dobutamine(P=0.003)and epinephrine requirement(P=0.000)and the incidence of renal failure and multiple organ failure(MOF)(P=0.000)were significantly higher for the low T3T4.Hypoalbuminemia(P=0.047),neutrophilia(P=0.038),lymphopenia(P=0.013)and lactatemia(P=0.013)were more pronounced on T2 for the low T3T4 group compared to the low T3 group.Diastolic blood pressure at T0(P=0.017)and T1(P=0.007),as well as mean arterial pressure at T0(P=0.037)and T2(P=0.033)was higher for the low T3 group.CONCLUSION The low T3T4 population is associated with higher frequency of renal insufficiency and MOF,with worse laboratory and hemodynamic parameters.These findings suggest potentially maladaptive changes in the chronic phase of septic shock.

Efficacy and safety of ulinastatin in the treatment of septic shock:a systematic review and meta-analysis

Background:Septic shock is a common systemic inflammatory response syndrome for critical patients in the intensive care unit.Ulinastatin is currently used for the treatment of septic shock.Our study sought to evaluate the efficacy and safety of ulinastatin in the treatment of septic shock patients.Methods:Three English databases(Embase,Medline,and Cochrane Library)and four Chinese databases(China National Knowledge Infrastructure,Wanfang data,SinoMed,and VIP)were searched for published randomized controlled trials.Stata 16.0 software was used to conduct the meta-analysis.Results:A total of 48 articles were included(Chinese article 47,1 in English).The results show that the treatment of ulinastatin could reduce mortality(risk ratio=0.63,95%confidence interval(CI)(0.55,0.72)),multiple organ dysfunction syndrome(risk ratio=0.6,95%CI(0.53,0.68)),length of intensive care unit stay(mean difference(MD)=-3.92,95%CI(-4.65,-3.18)),length of hospital stay(MD=-4.39,95%CI(-6.63,-2.15))and decrease Acute Physiology and Chronic Health Evaluation II score(MD=-4.55,95%CI(-5.63,-3.47))and Sequential Organ Failure Assessment score(MD=-2.02,95%CI(-2.59,-1.44))with P<0.001.Moreover,it lowers TNF-α(standardized mean difference(SMD)=-1.78,95%CI(-2.24,-1.32)),Interleukin-6(SMD=-1.17,95%CI(-1.55,-0.8)),C reactive protein(SMD=-1.49,95%CI(-1.99,-0.99)),hypersensitive C-reactive protein(SMD=-1.9,95%CI(-2.87,-0.94))and procalcitonin(SMD=-0.89,95%CI(-1.12,-0.67))levels in the body.Conclusions:Available evidence shows that ulinastatin reduces case mortality rate,multiple organ dysfunction syndrome,length of intensive care unit stay,and length of hospital stay and decreases Acute Physiology and Chronic Health Evaluation II score and Sequential Organ Failure Assessment score.Moreover,it also lowers TNF-α,Interleukin-6,C reactive protein,hypersensitive C-reactive protein,and procalcitonin levels in the body.

Predictive value of thrombocytopenia for bloodstream infection in patients with sepsis and septic shock

BACKGROUND Thrombocytopenia is common in patients with sepsis and septic shock.AIM To analyse the decrease in the number of platelets for predicting bloodstream infection in patients with sepsis and septic shock in the intensive care unit.METHODS A retrospective analysis of patients admitted with sepsis and septic shock in Xingtai People Hospital was revisited.Patient population characteristics and laboratory data were collected for analysis.RESULTS The study group consisted of 85(39%)inpatients with bloodstream infection,and the control group consisted of 133(61%)with negative results or contamination.The percentage decline in platelet counts(PPCs)in patients positive for pathogens[57.1(41.3-74.6)]was distinctly higher than that in the control group[18.2(5.1–43.1)](P<0.001),whereas the PPCs were not significantly different among those with gram-positive bacteraemia,gram-negative bacteraemia,and fungal infection.Using receiver operating characteristic curves,the area under the curve of the platelet drop rate was 0.839(95%CI:0.783-0.895).CONCLUSION The percentage decline in platelet counts is sensitive in predicting bloodstream infection in patients with sepsis and septic shock.However,it cannot identify gram-positive bacteraemia,gram-negative bacteraemia,and fungal infection.

Combining Serum Procalcitonin Level,Thromboelastography,and Platelet Count to Predict Short-term Development of Septic Shock in Intensive Care Unit

Objective Despite the recent advances in diagnosis and treatment,sepsis continues to lead to high morbidity and mortality.Early diagnosis and prompt treatment are essential to save lives.However,most biomarkers can only help to diagnose sepsis,but cannot predict the development of septic shock in high-risk patients.The present study determined whether the combined measurement of procalcitonin(PCT),thromboelastography(TEG)and platelet(PLT)count can predict the development of septic shock.Methods A retrospective study was conducted on 175 septic patients who were admitted to the intensive care unit between January 2017 and February 2021.These patients were divided into two groups:73 patients who developed septic shock were assigned to the septic shock group,while the remaining 102 patients were assigned to the sepsis group.Then,the demographic,clinical and laboratory data were recorded,and the predictive values of PCT,TEG and PLT count for the development of septic shock were analyzed.Results Compared to the sepsis group,the septic shock group had statistically lower PLT count and TEG measurements in the R value,K value,αangle,maximum amplitude,and coagulation index,but had longer prothrombin time(DT),longer activated partial thromboplastin time(APTT),and higher PCT levels.Furthermore,the Sequential Organ Failure Assessment(SOFA)score was higher in the septic shock group.The multivariate logistic regression analysis revealed that PCT,TEG and PLT count were associated with the development of septic shock.The area under the curve analysis revealed that the combined measurement of PCT,TEG and PLT count can be used to predict the development of septic shock with higher accuracy,when compared to individual measurements.Conclusion The combined measurement of PCT,TEG and PLT count is a novel approach to predict the development of septic shock in high-risk patients.

Emerging concepts in the care of patients with cirrhosis and septic shock

Septic shock impacts approximately 6% of hospitalized patients with cirrhosis and is associated with high rates of morbidity and mortality. Although a number of landmark clinical trials have paved the way for incremental improvements in the diagnosis and management of septic shock in the general population, patients with cirrhosis have largely been excluded from these studies and critical knowledge gaps continue to impact the care of these individuals. In this review,we discuss nuances in the care of patients with cirrhosis and septic shock using a pathophysiology-based approach. We illustrate that septic shock may be challenging to diagnose in this population in the context of factors such as chronic hypotension, impaired lactate metabolism, and concomitant hepatic encephalopathy. Furthermore, we demonstrate that the application of routine interventions such as intravenous fluids, vasopressors, antibiotics, and steroids should be carefully considered among those with decompensated cirrhosis in light of hemodynamic, metabolic, hormonal, and immunologic disturbances. We propose that future research should include and characterize patients with cirrhosis in a systematic manner, and clinical practice guidelines may need to be refined accordingly.

Hypoperfusion context as a predictor of 28-d all-cause mortality in septic shock patients:A comparative observational study

BACKGROUND As per the latest Surviving Sepsis Campaign guidelines,fluid resuscitation should be guided by repeated measurements of blood lactate levels until normalization.Nevertheless,raised lactate levels should be interpreted in the clinical context,as there may be other causes of elevated lactate levels.Thus,it may not be the best tool for real-time assessment of the effect of hemodynamic resuscitation,and exploring alternative resuscitation targets should be an essential research priority in sepsis.AIM To compare the 28-d mortality in two clinical patterns of septic shock:hyperlactatemic patients with hypoperfusion context and hyperlactatemic patients without hypoperfusion context.METHODS This prospective comparative observational study carried out on 135 adult patients with septic shock that met Sepsis-3 definitions compared patients with hyperlactatemia in a hypoperfusion context(Group 1,n=95)and patients with hyperlactatemia in a non-hypoperfusion context(Group 2,n=40).Hypoperfusion context was defined by a central venous saturation less than 70%,central venousarterial PCO_(2)gradient[P(cv-a)CO_(2)]≥6 mmHg,and capillary refilling time(CRT)≥4 s.The patients were observed for various macro and micro hemodynamic parameters at regular intervals of 0 h,3 h,and 6 h.All-cause 28-d mortality and all other secondary objective parameters were observed at specified intervals.Nominal categorical data were compared using theχ^(2)or Fisher’s exact test.Nonnormally distributed continuous variables were compared using the Mann-Whitney U test.Receiver operating characteristic curve analysis with the Youden index determined the cutoff values of lactate,CRT,and metabolic perfusion parameters to predict the 28-d all-cause mortality.A P value of<0.05 was considered significant.RESULTS Patient demographics,comorbidities,baseline laboratory,vital parameters,source of infection,baseline lactate levels,and lactate clearance at 3 h and 6 h,Sequential Organ Failure scores,need for invasive mechanical ventilation,days on mechanical ventilation,and renal replacement therapy-free days within 28 d,duration of intensive care unit stay,and hospital stay were comparable between the two groups.The stratification of patients into hypoperfusion and nonhypoperfusion context did not result in a significantly different 28-d mortality(24%vs 15%,respectively;P=0.234).However,the patients within the hypoperfusion context with high P(cva)CO_(2)and CRT(P=0.022)at baseline had significantly higher mortality than Group 2.The norepinephrine dose was higher in Group 1 but did not achieve statistical significance with a P>0.05 at all measured intervals.Group 1 had a higher proportion of patients requiring vasopressin and the mean vasopressor-free days out of the total 28 d were lower in patients with hypoperfusion(18.88±9.04 vs 21.08±8.76;P=0.011).The mean lactate levels and lactate clearance at 3 h and 6 h,CRT,P(cv-a)CO_(2)at 0 h,3 h,and 6 h were found to be associated with 28-d mortality in patients with septic shock,with lactate levels at 6 h having the best predictive value(area under the curve lactate at 6 h:0.845).CONCLUSION Septic shock patients fulfilling the hypoperfusion and non-hypoperfusion context exhibited similar 28-d all-cause hospital mortality,although patients with hypoperfusion displayed a more severe circulatory dysfunction.Lactate levels at 6 h had a better predictive value in predicting 28-d mortality than other parameters.Persistently high P(cv-a)CO_(2)(>6 mmHg)or increased CRT(>4 s)at 3 h and 6 h during early resuscitation can be a valuable additional aid for prognostication of septic shock patients.

Continuous renal replacement therapy with oXiris®in patients with hematologically malignant septic shock:A retrospective study

BACKGROUND The mortality rate from septic shock in patients with hematological malignancies(HMs)remains significantly higher than that in patients without HMs.A longer resuscitation time would definitely be harmful because of the irreversibly immunocompromised status of the patients.Shortening the resuscitation time through continuous renal replacement therapy(CRRT)with oXiris^(■)would be an attractive strategy in managing such patients.AIM To explore the effects of CRRT and oXiris^(■)in shortening the resuscitation time and modifying the host response by reducing inflammation mediator levels.METHODS Forty-five patients with HM were diagnosed with septic shock and underwent CRRT between 2018 and 2022.Patients were divided into two groups based on the hemofilter used for CRRT(oXiris^(■)group,n=26;M150 group,n=19).We compared the number of days of negative and total fluid balance after 7 d of CRRT between the groups.The heart rate,norepinephrine dose,Sequential Organ Failure Assessment(SOFA)score,and blood lactic acid levels at different time points in the two groups were also compared.Blood levels of inflammatory mediators in the 26 patients in the oXiris^(■)group were measured to further infer the possible mechanism.RESULTS The average total fluid balance after 7 d of CRRT in the oXiris^(■)group was significantly lower than that of patients in the M150 hemofilter group.The SOFA scores of patients after CRRT with oXiris^(■)therapy were significantly lower than those before treatment on day 1(d1),d3 and d7 after CRRT;these parameters were also significantly lower than those of the control group on d7.The lac level after oXiris^(■)therapy was significantly lower than that before treatment on d3 and d7 after CRRT.There were no significant differences in the above parameters between the two groups at the other time points.In the oXiris^(■)group,procalcitonin levels decreased on d7,whereas interleukin-6 and tumor necrosis factor levels decreased significantly on d3 and d7 after treatment.CONCLUSION CRRT with oXiris^(■)hemofilter may improve hemodynamics by reducing inflammatory mediators and playing a role in shortening the resuscitation period and decreasing total fluid balance in the resuscitation phases.

Should we initiate vasopressors earlier in patients with septic shock: A mini systemic review

Septic shock treatment remains a major challenge for intensive care units,despite the recent prominent advances in both management and outcomes.Vasopressors serve as a cornerstone of septic shock therapy,but there is still controversy over the timing of administration.Specifically,it remains unclear whether vasopressors should be used early in the course of treatment.Here,we provide a systematic review of the literature on the timing of vasopressor administration.Research was systematically identified through PubMed,Embase and Cochrane searching according to PRISMA guidelines.Fourteen studies met the eligibility criteria and were included in the review.The pathophysiological basis for early vasopressor use was classified,with the exploration on indications for the early administration of mono-vasopressors or their combination with vasopressin or angiotensinII.We found that mortality was 28.1%-47.7%in the early vasopressors group,and 33.6%-54.5%in the control group.We also investigated the issue of vasopressor responsiveness.Furthermore,we acknowledged the subsequent challenge of administration of high-dose norepinephrine via peripheral veins with early vasopressor use.Based on the literature review,we propose a possible protocol for the early initiation of vasopressors in septic shock resuscitation.

Osteoarticular Lesions of the Shoulder Girdle by Hippopotamus Bite: Highly Septic Lesion

Hippopotamus bites are rare in medical consultations, despite several studies exposing their aggressive character. A case of a hippopotamus bite on the shoulder of a fisherman has been reported. In addition to the osteoarticular aspect representing a therapeutic problem, the infectious aspect was marked by sepsis, with a death in less than 48 hours. Based on this observation, a protocol for the initial management of large animal bites was submitted.

Demonstrating grating-based phase-contrast imaging of laser-driven shock waves

Single-shot X-ray phase-contrast imaging is used to take high-resolution images of laser-driven strong shock waves.Employing a two-grating Talbot interferometer,we successfully acquire standard absorption,differential phase-contrast,and dark-field images of the shocked target.Good agreement is demonstrated between experimental data and the results of two-dimensional radiation hydrodynamics simulations of the laser-plasma interaction.The main sources of image noise are identified through a thorough assessment of the interferometer’s performance.The acquired images demonstrate that grating-based phase-contrast imaging is a powerful diagnostic tool for high-energy-density science.In addition,we make a novel attempt at using the dark-field image as a signal modality of Talbot interferometry to identify the microstructure of a foam target.

Strong shock propagation for the finite-source circular blast in a confined domain

The circular explosion wave produced by the abrupt discharge of gas from a high-temperature heat source serves as a crucial model for addressing explosion phenomena in compressible flow.The reflection of the primary shock and its propagation within a confined domain are studied both theoretically and numerically in this research.Under the assumption of strong shock,the scaling law governing propagation of the main shock is proposed.The dimensionless frequency of reflected shock propagation is associated with the confined distance.The numerical simulation for the circular explosion problem in a confined domain is performed for validation.Under the influence of confinement,the principal shock wave systematically undergoes reflection within the domain until it weakens,leading to the non-monotonic attenuation of kinetic energy in the explosion fireball and periodic oscillations of the fireball volume with a certain frequency.The simulation results indicate that the frequency of kinetic energy attenuation and the volume oscillation of the explosive fireball align consistently with the scaling law.

Dynamic convergent shock compression initiated by return current in high-intensity laser-solid interactions

We investigate the dynamics of convergent shock compression in solid cylindrical targets irradiated by an ultrafast relativistic laser pulse.Our particle-in-cell simulations and coupled hydrodynamic simulations reveal that the compression process is initiated by both magnetic pressure and surface ablation associated with a strong transient surface return current with density of the order of 10^(17) A/m^(2) and lifetime of 100 fs.The results show that the dominant compression mechanism is governed by the plasma β,i.e.,the ratio of thermal pressure to magnetic pressure.For targets with small radius and low atomic number Z,the magnetic pressure is the dominant shock compression mechanism.According to a scaling law,as the target radius and Z increase,the surface ablation pressure becomes the main mechanism generating convergent shocks.Furthermore,an indirect experimental indication of shocked hydrogen compression is provided by optical shadowgraphy measurements of the evolution of the plasma expansion diameter.The results presented here provide a novel basis for the generation of extremely high pressures exceeding Gbar(100 TPa)to enable the investigation of high-pressure physics using femtosecond J-level laser pulses,offering an alternative to nanosecond kJ-laser pulse-driven and pulsed power Z-pinch compression methods.

A rat model of multicompartmental traumatic injury and hemorrhagic shock induces bone marrow dysfunction and profound anemia

Background:Severe trauma is associated with systemic inflammation and organ dysfunction.Preclinical rodent trauma models are the mainstay of postinjury research but have been criticized for not fully replicating severe human trauma.The aim of this study was to create a rat model of multicompartmental injury which recreates profound traumatic injury.Methods:Male Sprague-Dawley rats were subjected to unilateral lung contusion and hemorrhagic shock(LCHS),multicompartmental polytrauma(PT)(unilateral lung contusion,hemorrhagic shock,cecectomy,bifemoral pseudofracture),or na?ve controls.Weight,plasma toll-l ike receptor 4(TLR4),hemoglobin,spleen to body weight ratio,bone marrow(BM)erythroid progenitor(CFU-GEMM,BFU-E,and CFU-E)growth,plasma granulocyte colony-stimulating factor(G-CSF)and right lung histologic injury were assessed on day 7,with significance defined as p values<0.05(*).Results:Polytrauma resulted in markedly more profound inhibition of weight gain compared to LCHS(p=0.0002)along with elevated plasma TLR4(p<0.0001),lower hemoglobin(p<0.0001),and enlarged spleen to body weight ratios(p=0.004).Both LCHS and PT demonstrated suppression of CFU-E and BFU-E growth compared to naive(p<0.03,p<0.01).Plasma G-CSF was elevated in PT compared to both na?ve and LCHS(p<0.0001,p=0.02).LCHS and PT demonstrated significant histologic right lung injury with poor alveolar wall integrity and interstitial edema.Conclusions:Multicompartmental injury as described here establishes a reproducible model of multicompartmental injury with worsened anemia,splenic tissue enlargement,weight loss,and increased inflammatory activity compared to a less severe model.This may serve as a more effective model to recreate profound traumatic injury to replicate the human inflammatory response postinjury.

Experimental and numerical study on protective effect of RC blast wall against air shock wave

Prototype experiments were carried out on the explosion-proof performance of the RC blast wall.The mass of TNT detonated in the experiments is 5 kg and 20 kg respectively.The shock wave overpressure was tested in different regions.The above experiments were numerically simulated,and the simulated shock wave overpressure waveforms were compared with that tested and given by CONWEP program.The results show that the numerically simulated waveform is slightly different from the test waveform,but similar to CONWEP waveform.Through dimensional analysis and numerical simulation under different working conditions,the equation for the attenuation rate of the diffraction overpressure behind the blast wall was obtained.According to the corresponding standards,the degree of casualties and the damage degree of the brick concrete building at a certain distance behind the wall can be determined when parameters are set.The above results can provide a reference for the design and construction of the reinforced concrete blast wall.

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.

Evolution of molecular structure of TATB under shock loading from transient Raman spectroscopic technique

By combination of the transient Raman spectroscopic measurement and the density functional theoretical calculations,the structural evolution and stability of TATB under shock compression was investigated.Due to the improvement in synchronization control between two-stage light gas gun and the transient Raman spectra acquisition,as well as the sample preparation,the Raman peak of the N-O mode of TATB was firstly observed under shock pressure up to 13.6 GPa,noticeably higher than the upper limit of 8.5 GPa reported in available literatures.By taking into account of the continuous shift of the main peak and other observed Raman peaks,we did not distinguish any structural transition or any new species.Moreover,both the present Raman spectra and the time-resolved radiation of TATB during shock loading showed that TATB exhibits higher chemical stability than previous declaration.To reveal the detailed structural response and evolution of TATB under compression,the density functional theoretical calculations were conducted,and it was found that the pressure make N-O bond lengths shorter,nitro bond angles larger,and intermolecular and intra-molecular hydrogen bond interactions enhanced.The observed red shift of Raman peak was ascribed to the abnormal enhancement of H-bound effect on the scissor vibration mode of the nitro group.

Propagation Properties of Shock Waves in Polyurethane Foam based on Atomistic Simulations

Porous materials are widely used in the field of protection because of their excellent energy absorption characteristics.In this work,a series of polyurethane microscopic models are established and the effect of porosity on the shock waves is studied with classical molecular dynamics simulations.Firstly,shock Hugoniot relations for different porosities are obtained,which compare well with the experimental data.The pores collapse and form local stress wave,which results in the complex multi-wave structure of the shock wave.The microstructure analysis shows that the local stress increases and the local velocity decreases gradually during the process of pore collapse to complete compaction.Finally,it leads to stress relaxation and velocity homogenization.The shock stress peaks can be fitted with two exponential functions,and the amplitude of attenuation coefficient decreases with the increase of density.Besides,the pore collapse under shock or non-shock are discussed by the entropy increase rate of the system.The energy is dissipated mainly through the multiple interactions of the waves under shock.The energy is dissipated mainly by the friction between atoms under non-shock.