Basic life support for cardiac arrest associates cardiopulmonary resuscitation(CPR)and defibrillation.CPR relies on chest compressions(CC)and ventilation.Current guidelines on CPR recommend a depth of 5-6 cm at a rhyt...Basic life support for cardiac arrest associates cardiopulmonary resuscitation(CPR)and defibrillation.CPR relies on chest compressions(CC)and ventilation.Current guidelines on CPR recommend a depth of 5-6 cm at a rhythm of 100-120 times/min for CC.[1,2]Interruptions of the CC must be as short as possible and are related to ventilation,defibrillation and turnover of the rescuers.Most of the automated external defibrillators(AEDs)require interruptions of the CC to perform rhythm analysis.Among the numerous marketed models of AEDs,some provide real-time feedback about the quality of the CC.展开更多
BACKGROUND It remains unclear whether video aids can improve the quality of bystander cardiopulmonary resuscitation(CPR).AIM To summarize simulation-based studies aiming at improving bystander CPR associated with the ...BACKGROUND It remains unclear whether video aids can improve the quality of bystander cardiopulmonary resuscitation(CPR).AIM To summarize simulation-based studies aiming at improving bystander CPR associated with the quality of chest compression and time-related quality parameters.METHODS The systematic review was conducted according to the PRISMA guidelines.All relevant studies were searched through PubMed,EMBASE,Medline and Cochrane Library databases.The risk of bias was evaluated using the Cochrane collaboration tool.RESULTS A total of 259 studies were eligible for inclusion,and 6 randomised controlled trial studies were ultimately included.The results of meta-analysis indicated that video-assisted CPR(V-CPR)was significantly associated with the improved mean chest compression rate[OR=0.66(0.49-0.82),P<0.001],and the proportion of chest compression with correct hand positioning[OR=1.63(0.71-2.55),P<0.001].However,the difference in mean chest compression depth was not statistically significant[OR=0.18(-0.07-0.42),P=0.15],and V-CPR was not associated with the time to first chest compression compared to telecommunicator CPR[OR=-0.12(-0.88-0.63),P=0.75].CONCLUSION Video real-time guidance by the dispatcher can improve the quality of bystander CPR to a certain extent.However,the quality is still not ideal,and there is a lack of guidance caused by poor video signal or inadequate interaction.展开更多
Objectives: The aim of this study was to analyze the quality of chest compressions in different working situations pertaining to ambulance crews using either standard chest compressions (S-CC) or LUCAS mechanical ches...Objectives: The aim of this study was to analyze the quality of chest compressions in different working situations pertaining to ambulance crews using either standard chest compressions (S-CC) or LUCAS mechanical chest compressions (L-CC) in a manikin setting. Participants and Methods: Cardiopulmonary resuscitation (CPR) was performed using a compression to ventilation ratio of 30:2 with both S-CC and L-CC. Quality parameters were collected using a modified manikin enabling impedance measurements. The evaluation was performed in two manikin scenarios: Scenario 1 evaluated ten minutes of CPR on the ground and Scenario 2 assessed six minutes of CPR in different settings relevant to work in the ambulance. Quality parameters compared were: time to apply LUCAS, hands-off fraction, number of correct chest compressions and the rate of compressions. Results: In Scenario 1 the hands-off fraction was higher when S-CC was performed (S-CC group 29% vs. L-CC 16%, P = 0.003). We found a higher number of chest compressions (S-CC = 913 vs. L-CC = 831, P = 0.0049) and a higher rate of chest compressions (S-CC = 118 vs. L-CC = 99, P < 0.0001) in the S-CC group. In Scenario 2 we noted a higher hands-off fraction for S-CC (39% vs. L-CC = 19%, P = 0.003), but a higher number of compressions given during S-CC ((n = 504) vs. L-CC (n = 396) P = 0.0002). Conclusion: Mechanical chest compression with the LUCAS 2TM device enables ambulance personnel to provide high quality chest compression even while transporting the patient.展开更多
Flow softening behavior of a homogenized Mg-7Gd-4Y-1Nd-0.5Zr alloy under compression to a final strain of∼1.8 at elevated temperatures of 450∼550℃ and a constant strain rate of 2s^(−1) has been investigated by opti...Flow softening behavior of a homogenized Mg-7Gd-4Y-1Nd-0.5Zr alloy under compression to a final strain of∼1.8 at elevated temperatures of 450∼550℃ and a constant strain rate of 2s^(−1) has been investigated by optical microscopy,scanning electron microscopy,electron back-scattered diffraction and transmission electron microscopy.The results show that true stress first rises to the peak point and then drops to the bottom value and increases again with further increasing strain at each temperature.Twinning dynamic recrystallization(DRX)and continuous DRX contribute to the formation of new fine grains at temperatures 450∼475℃ when the restoration is caused by both DRX and texture change due to extension twinning,resulting in the larger softening degrees compared with the softening effects owing to continuous DRX and discontinuous DRX at 500∼550℃ when twinning activation is suppressed.500℃ is the transition temperature denoting a significant decline in the contribution of twinning and TDRX to the strain with increasing temperature.The cuboid-shape phase exists in both homogenized and compressed samples,while the compositions are varied.展开更多
Three-dimensional(3D)mesostructures with distinct compressive deformation behaviors and tunable mechanical responses have gained increasing interest in recent years.3D cage-shaped mesostructures are representative fra...Three-dimensional(3D)mesostructures with distinct compressive deformation behaviors and tunable mechanical responses have gained increasing interest in recent years.3D cage-shaped mesostructures are representative framework structures widely exploited in 3D flexible electronics,owing to their unique cellular geometry and unusual mechanical responses.The snap-through behavior of cage-shaped mesostructures could potentially result in the performance degradation of electronics,while it could also be harnessed to design reconfigurable electronics.Due to the complicated deformation modes and random characteristics in experiments,the snap-through behavior of cage-shaped mesostructures remains largely unexplored,espe-cially in terms of probability-based analyses.In this work,we present a systematic study on the configuration evolution and snap-through of 3D cage-shaped mesostructures under out-of-plane compressions.Experimental and computational studies show the existence of two distinct deformation modes associated with the snap-through,which is controlled by the energy barrier based on the energetic analyses.Phase diagrams of the deformation modes decode how key geometric parameters and assembly strain affect the snap-through.Compressive experiments based on periodic arrays(10 × 10)of mesostructures provided a large amount of deformation data,allowing for statistical analyses of the snap-through behavior.These results provide new insights and useful guidelines for the design of 3D reconfigurable devices and multistable metamaterials based on 3D cage-shaped mesostructures.展开更多
Purpose: According to guideline recommendations, chest compressions (CC) during cardiopulmonary resuscitation (CPR) should be performed at a rate of 100 - 120 per minute, with a CC fraction (CCF) of ≥80%. The aim of ...Purpose: According to guideline recommendations, chest compressions (CC) during cardiopulmonary resuscitation (CPR) should be performed at a rate of 100 - 120 per minute, with a CC fraction (CCF) of ≥80%. The aim of this work is to explore whether CC quality differs between advanced life support (ALS) and basic life support (BLS) performed by two rescuers. Method: Cardiopulmonary resuscitation was performed by two ambulance personnel in ten ALS and ten BLS manikin scenarios. Data from these scenarios were then compared with data on ten ALS cases from the clinical setting, all with non-shockable rhythms. Data from the first two 5-minute periods of CC were evaluated from impedance data (LIFEPAK 12 defibrillator monitors) using a modified Laerdal Skillmaster manikin. Quality parameters compared were: number of CC pauses (CCPs), total time of CC (%), number of CC given and CC rate/min. Results: During the first 5 minutes, the BLS manikin scenarios had the highest number of CCPs, 15 (14 - 16), compared with the ALS manikin scenario, 14 (13 - 15), and the clinical ALS cases, 12 (10 - 15). The BLS scenario also had the highest CCFs, 81% (77% - 85%), and number of CC, 450 (435 - 495), compared with the ALS manikin scenario, 75% (64% - 81%) and 400 (365 - 444) respectively, and the clinical ALS cases, 63% (50% - 74%) and 408 (306 - 489). The median rate of CC/min in the BLS scenario was 115 (110 - 120) compared with the ALS manikin scenario, 110 (106 - 115), and the clinical ALS cases, 130 (118 - 146). During the second 5-minute period, the BLS scenario had the highest number of CCPs, 16 (15 - 17), compared with 15 (14 - 16) for the ALS manikin scenario and 11 (11 - 12) for the clinical ALS cases. The CCF in the BLS setting was 79% (75% - 83%), and the number of CC 455 (430 - 480), compared with the ALS manikin scenario, 79% (74% - 84%) and 435 (395 - 480) respectively, and the clinical ALS cases, 71% (57% - 77%) and 388 (321 - 469) respectively. The median CC rate was 118 (113 - 124) for BLS, 111 (105 - 120) for ALS manikins and 123 (103 - 128) CC/min for clinical ALS cases. Conclusion: None of the groups being studied could deliver CC at a rate of 100 - 120 CC/min or a CCF of ≥80% over the whole 10-minute period in any of the resuscitation scenarios analyzed. However, BLS had the best compliance with CC quality recommendations according to the 2010 guidelines.展开更多
The sandwich structure of cushioning packaging has an important influence on the cushioning performance.Mathematical fractal theory is an important graphic expression.Based on Hilbert fractal theory,a new sandwich str...The sandwich structure of cushioning packaging has an important influence on the cushioning performance.Mathematical fractal theory is an important graphic expression.Based on Hilbert fractal theory,a new sandwich structure was designed.The generation mechanism and recurrence formula of theHilbert fractal were expressed by Lin’s language,and the second-orderHilbert sandwich structure was constructed fromthermoplastic polyurethane.The constitutive model of the hyperelastic body was established by using the finite element method.With the unit mass energy absorption as the optimization goal,the fractal sandwich structure was optimized,and the best result was obtained when the order was 2.5 and the unit layer thickness was 0.75 mm.TheHilbert sandwich structure was compared with the rice-shaped sandwich structure commonly used in industry,and the Hilbert fractal structure had better energy absorption.This has practical significance for the development and application of newcushioning packaging structures.展开更多
Slow spinal compressions are due to the development of an expansive process in the spinal canal. It is a very common pathology, the diagnosis of which is mainly clinical. However, magnetic resonance imaging occupies a...Slow spinal compressions are due to the development of an expansive process in the spinal canal. It is a very common pathology, the diagnosis of which is mainly clinical. However, magnetic resonance imaging occupies an essential place in the site diagnosis and etiological research in the management. Non-traumatic spinal cord compression is a diagnostic and therapeutic emergency, requiring early and appropriate management. MRI is the benchmark imaging examination for this pathology. No similar previous MRI study in Mali. We undertook this work with the aim to determine the place of MRI in the diagnosis of spinal cord compressions in Mali hospital. <strong>Method and Patients:</strong> This was a descriptive retrospective study, carried out at the hospital’s medical imaging department from January 1, 2017 to December 31, 2018 (02 years). It involved all patients, regardless of sex and age, sent for an MRI examination of the spine, and in whom spinal cord compression was diagnosed. We used a 0.35T low-field MRI machine with solid-state antennas. <strong>Results:</strong> We collected 179 cases of spinal cord compression MRI out of 585 spinal MRI performed, (frequency of 30.59%). The average age was 53.5 years with a male predominance (sex ratio 3.7). Motor disorders were the most common reason for examination (41%). We used the T1 T2 sagittal and T2 axial sequences. IV injection of gadolinium was performed in 48% of patients. The topographic lesions were: cervical (54.7%), thoracic (31.3%) and several segments (9.5%). The lesions concerned the compartments: extradural (79.3%), intradural (4.5%), and intramedullary (16.2%). The processes were degenerative (57.5%). tumorous (29.6%), infectious (12.3%) and vascular (0.6%). <strong>Conclusion:</strong> MRI is the benchmark imaging test for the management of non-traumatic spinal cord injury. Myelo-CT can be an alternative in the absence or in case of MRI contraindication.展开更多
In 1997 and 1998, hundreds of specimens of megascopic carbonaceous compressions or algal fossils were found from - 1800-million-year old Changzhougou Formation, which is the lowermost unit of the latest Palaeoproteroz...In 1997 and 1998, hundreds of specimens of megascopic carbonaceous compressions or algal fossils were found from - 1800-million-year old Changzhougou Formation, which is the lowermost unit of the latest Palaeoproterozoic Changcheng Group (~1 600-1 800 Ma) in the Xinglong-Kuancheng areas at the middle Yanshan Range, North China. They are discoid, ellipsoid and sausage-like, namely shaped like Chuaria Shouhsiennia (Ellipsophyta) and Tawuia. By adopting HF acid-resistant maceration coupled with scanning electron microscope and petrologic section, the authors made a preliminary research on the histology for some circular and ellipsoid carbonaceous compressions, namely Chuaria- and Shouhsienia-llke forms, in addition to their morphology. The following three types of multicellular tissues have been found in the fragments of them: colony-like, pseudoparenchyma-like and parenchyma-like. All of the new data about multicelluar tissues not only supply a very important basis in histology to determine the展开更多
Background The effects of chest compressions to hemodynamic and respiratory parameters during hands-only cardiopulmonary resuscitation （CPR） in a non-arrested patient who suddenly collapses are confusing.In this res...Background The effects of chest compressions to hemodynamic and respiratory parameters during hands-only cardiopulmonary resuscitation （CPR） in a non-arrested patient who suddenly collapses are confusing.In this research,we investigated the effects of chest compressions in a non-arrested porcine model.Methods Fourteen male domestic pigs were randomized into sham control group （SHAM group,only anesthetized and instrumented without chest compression,n=6） or chest compression group （CC group,2 minutes of chest compressions,n=8）.Continuous hemodynamic parameters,dynamic lung compliance （Cdyn）,and blood gas analysis outcomes were recorded.Serum levels of catecholamine were measured at baseline and 2 minutes,30 minutes,4 hours,and 24 hours after chest compressions.Chest computed tomography （CT） was performed at 30 minutes and 24 hours.Conventional histopathology evaluation was performed.Results After two minutes of chest compressions in the CC group,heart rate and extravascular lung water increased significantly; mean arterial pressure,stroke volume,and global ejection fraction significantly decreased.Cdyn significantly decreased to valley levels at 30 minutes and slowly recovered.Compared with the baseline,serum levels of catecholamine significantly increased at 2 minutes and rapidly decreased 24 hours later.At 30 minutes after chest compressions,chest CT showed local exudation,which was absorbed 24 hours later.Conclusions This research showed that 2 minutes of chest compressions causes various heart and lung tissue damage in the normal a normal porcine model.It also impacts the hemodynamic and Cdyn.展开更多
Polyurethane foam,when used as a compressible layer in deep soft rock tunnels,offers a feasible solution to reduce the support pressure on the secondary lining.The foam spraying method using sprayed polyurethane mater...Polyurethane foam,when used as a compressible layer in deep soft rock tunnels,offers a feasible solution to reduce the support pressure on the secondary lining.The foam spraying method using sprayed polyurethane material is convenient for engineering applications;however,the compressive behaviour and feasibility of sprayed polyurethane material as a compressible layer remain unclear.To address this gap,this study conducts uniaxial compression tests and scanning electron microscope(SEM)tests to investigate the compressive behaviour of the rigid foams fabricated from a self-developed polyurethane spray material.A peridynamics model for the composite lining with a polyurethane compressible layer is then established.After validating the proposed method by comparison with two tests,a parametric study is carried out to investigate the damage evolution of the composite lining with a polyurethane compressible layer under various combinations of large deformations and compressible layer parameters.The results indicate that the polyurethane compressible layer effectively reduces the radial deformation and damage index of the secondary lining while increasing the damage susceptibility of the primary lining.The thickness of the polyurethane compressible layer significantly influences the prevention effect of large deformation-induced damage to the secondary lining within the density range of 50e100 kg/m^(3).In accordance with the experimental and simulation results,a simple,yet reasonable and convenient approach for determining the key parameters of the polyurethane compressible layer is proposed,along with a classification scheme for the parameters of the polyurethane compressible layer.展开更多
The selection of an appropriate basic detonation wave flow field is crucial for improving the performance and geometric design of standing detonation vehicles.This paper employs a detailed chemical reaction model and ...The selection of an appropriate basic detonation wave flow field is crucial for improving the performance and geometric design of standing detonation vehicles.This paper employs a detailed chemical reaction model and solves the unsteady axisymmetric Euler equation to study the characteristics of the Axisymmetric Inward Turning Curved Detonation Wave(AIT-CDW)flow field and the parameters affecting the stability of the wave system structure of AIT-CDW flow field.The numerical results demonstrate a radial compression effect in the AIT-CDW flow field.This effect causes the detonation wave to have a shorter initiation length than oblique detonation wave flow field and the detonation wave angle to gradually increase with the flow direction postdetonation.The AIT-CDW flow field is confined space,making it prone to normal detonation waves when the detonation wave reflects from the wall.This phenomenon is detrimental to the stability of the wave system structure in the flow field.It has been observed that increasing the center body radius and decreasing the fuel equivalent ratio can effectively reduce the height of the normal detonation wave or even eliminate it.Additionally,a well-designed generatrix shape of the center body can enhance airflow,reduce choked flow,and promote the stability of the wave structure in the flow field.展开更多
Along with the proliferating research interest in semantic communication(Sem Com),joint source channel coding(JSCC)has dominated the attention due to the widely assumed existence in efficiently delivering information ...Along with the proliferating research interest in semantic communication(Sem Com),joint source channel coding(JSCC)has dominated the attention due to the widely assumed existence in efficiently delivering information semantics.Nevertheless,this paper challenges the conventional JSCC paradigm and advocates for adopting separate source channel coding(SSCC)to enjoy a more underlying degree of freedom for optimization.We demonstrate that SSCC,after leveraging the strengths of the Large Language Model(LLM)for source coding and Error Correction Code Transformer(ECCT)complemented for channel coding,offers superior performance over JSCC.Our proposed framework also effectively highlights the compatibility challenges between Sem Com approaches and digital communication systems,particularly concerning the resource costs associated with the transmission of high-precision floating point numbers.Through comprehensive evaluations,we establish that assisted by LLM-based compression and ECCT-enhanced error correction,SSCC remains a viable and effective solution for modern communication systems.In other words,separate source channel coding is still what we need.展开更多
BACKGROUND Magnetic compression anastomosis(MCA)offers a simple and reliable technique for inducing anastomoses at any point along the digestive tract.Evidence regarding whether the design of the MCA device influences...BACKGROUND Magnetic compression anastomosis(MCA)offers a simple and reliable technique for inducing anastomoses at any point along the digestive tract.Evidence regarding whether the design of the MCA device influences the anastomosis effect is lacking.AIM To investigate any difference in the side-to-side colonic anastomosis effect achieved with cylindrical vs circular ring magnets.METHODS We designed cylindrical and circular ring magnets suitable for side-to-side colonic anastomosis in rats.Thirty Sprague-Dawley rats were randomly divided into a cylindrical group,circular ring group,and cylindrical–circular ring group(n=10/group).Side-to-side colonic anastomosis was completed by transanal insertion of the magnets without incision of the colon.Operation time,perioperative complications,and magnet discharge time were recorded.Rats were euthanized 4 weeks postoperatively,and anastomotic specimens were obtained.The burst pressure and anastomotic diameter were measured sequentially,and anastomosis formation was observed by naked eye.Histological results were observed by light microscopy.RESULTS In all 30 rats,side-to-side colonic anastomosis was completed,for an operation success rate of 100%.No postoperative complications of bleeding and intestinal obstruction occurred,and the postoperative survival rate were 100%.The operation time,magnet discharge time,anastomotic bursting pressure,and anastomotic diameter did not differ significantly among the three designs(P>0.05).Healing was similar across the groups,with gross specimens showing good anastomotic healing and good mucosal continuity observed on histological analysis.CONCLUSION This study found no significant difference in the establishment of rat side-to-side colonic anastomosis with the use of cylindrical vs circular ring magnets.展开更多
Hot deformation with high strain rate has been paid more attention due to its high efficiency and low cost,however,the strain rate dependent dynamic recrystallization(DRX)and texture evolution in hot deformation proce...Hot deformation with high strain rate has been paid more attention due to its high efficiency and low cost,however,the strain rate dependent dynamic recrystallization(DRX)and texture evolution in hot deformation process,which affect the formability of metals,are lack of study.In this work,the DRX behavior and texture evolution of Mg-8Gd-1Er-0.5Zr alloy hot compressed with strain rates of 0.1 s^(−1),1 s^(−1),10 s^(−1) and 50 s^(−1) are studied,and the corresponding dominant mechanisms for DRX and texture weakening are discussed.Results indicated the DRX fraction was 20%and the whole texture intensity was 16.89 MRD when the strain rate was 0.1 s^(−1),but they were 76%and 6.55 MRD,respectively,when the strain rate increased to 50 s^(−1).The increment of DRX fraction is suggested to result from the reduced DRX critical strain and the increased dislocation density as well as velocity,while the weakened whole texture is attributed to the increased DRX grains.At the low strain rate of 0.1 s^(−1),discontinuous DRX(DDRX)was the dominant,but the whole texture was controlled by the deformed grains with the preferred orientation of{0001}⊥CD,because the number of DDRX grains was limited.At the high strain rate of 50 s^(−1),continuous DRX(CDRX)and twin-induced DRX(TDRX)were promoted,and more DRX grains resulted in orientation randomization.The whole texture was mainly weakened by CDRX and TDRX grains,in which CDRX plays a major role.The results of present work are significant for understanding the hot workability of Mg-RE alloys with a high strain rate.展开更多
Using cemented rockfill to replace coal pillars offers an effective solution for reducing solid waste while ensuring the safety of gob-side entries.However,achieving the balance among low cost,high waste recycling rat...Using cemented rockfill to replace coal pillars offers an effective solution for reducing solid waste while ensuring the safety of gob-side entries.However,achieving the balance among low cost,high waste recycling rates,and adequate strength remains a significant challenge for cemented rockfill.This study used a composite alkali activator to activate gangue cemented rockfill.The compressive strength,scanning electron microscopy,energy dispersive spectrometer,mercury intrusion porosimetry,X-ray diffraction,and thermogra-vimetric tests were carried out to investigate the effect of the composite alkali activator proportion on the compressive strength,micro-structure,and composition of the cemented rockfill.The calcium silicate hydrate(C–S–H)molecular model of cemented rockfill was con-structed to explore the fracture evolution of the nucleated molecular structure under tension.The results show that compressive strength initially increased and then decreased with the activator proportion,the optimal activator proportion of 1:2 resulted in a 31.25%increase in strength at 3 d.This reasonable activator proportion strengthens the pozzolanic effect of gangue,and consumes more calcium hydroxide to inhibit its agglomeration,ultimately achieving the densification of microstructure.The activator proportion inevitably substitutes calcium ions with sodium ions in the C–S–H molecular model.The 12%substitution of calcium ions increases the adhesion between silicon chain layers,which is beneficial to the interlayer stress transfer.This work proposes a method for preparing low-cost cemented rockfill from al-kali-activated gangue,which can be used for solid waste recycling and reducing cement consumption to achieve low-carbon goals.展开更多
Research on the mechanical–electrical properties is crucial for designing and preparing high-temperature superconducting(HTS)cables.Various winding core structures can influence the mechanical–electrical behavior of...Research on the mechanical–electrical properties is crucial for designing and preparing high-temperature superconducting(HTS)cables.Various winding core structures can influence the mechanical–electrical behavior of cables,but the impact of alterations in the winding core structure on the mechanical–electrical behavior of superconducting cables remains unclear.This paper presents a 3D finite element model to predict the performance of three cables with different core structures when subjected to transverse compression and axial tension.The three cables analyzed are CORC(conductor-on-round-core),CORT(conductor-on-round-tube),and HFRC(conductor-on-spiral-tube).A parametric analysis is carried out by varying the core diameter and inner-to-outer diameter ratio.Results indicate that the CORT cable demonstrates better performance in transverse compression compared to the CORC cable,aligning with experimental data.Among the three cables,the HFRC cables exhibit the weakest resistance to transverse deformation.However,the HFRC cable demonstrates superior tensile deformation resistance compared to the CORT cable,provided that the transverse compression properties are maintained.Finite element results also show that the optimum inner-to-outer diameter ratios for achieving the best transverse compression performance are approximately 0.8 for CORT cables and 0.6 for HFRC cables.Meanwhile,the study explores the effect of structural changes in HTS cable winding cores on their electromagnetic properties.It recommends utilizing small tape gaps,lower frequencies,and spiral core construction to minimize eddy losses.The findings presented in this paper offer valuable insights for the commercialization and practical manufacturing of HTS cables.展开更多
This study tested the electrical conductivity and pressure sensitivity of lime⁃improved silty sand reinforced with Carbon Fiber Powder(CFP)as the conductive medium.The influence of CFP dosage,moisture content and curi...This study tested the electrical conductivity and pressure sensitivity of lime⁃improved silty sand reinforced with Carbon Fiber Powder(CFP)as the conductive medium.The influence of CFP dosage,moisture content and curing duration on the unconfined compressive strength,initial resistivity and pressure sensitivity of the improved soil was systematically analysed.The results showed that the unconfined compressive strength varied non⁃monotonically with increasing CFP dosage,reaching a peak at a dosage of 1.6%.Furthermore,the initial resistivity showed slight variations under different moisture conditions but eventually converged towards the conductive percolation threshold at a dosage of 2.4%.It is worth noting that CFP reinforced lime⁃improved silty sand(CRLS)exhibit a clear dynamic synchronization of strain with stress and resistivity rate of variation.The pressure sensitivity was optimized with CFP dosages ranging from 1.6%to 2.0%.Both insufficient and excessive dosages had a negative impact on pressure sensitivity.It is important to consider the weakening effect of high moisture content on the pressure sensitivity of the specimens in practical applications.展开更多
Against the background of“carbon peak and carbon neutrality,”it is of great practical significance to develop non-blast furnace ironmaking technology for the sustainable development of steel industry.Carbon-bearing ...Against the background of“carbon peak and carbon neutrality,”it is of great practical significance to develop non-blast furnace ironmaking technology for the sustainable development of steel industry.Carbon-bearing iron ore pellet is an innovative burden of direct reduction ironmaking due to its excellent self-reducing property,and the thermal strength of pellet is a crucial metallurgical property that affects its wide application.The carbon-bearing iron ore pellet without binders(CIPWB)was prepared using iron concentrate and anthracite,and the effects of reducing agent addition amount,size of pellet,reduction temperature and time on the thermal compressive strength of CIPWB during the reduction process were studied.Simultaneously,the mechanism of the thermal strength evolution of CIPWB was revealed.The results showed that during the low-temperature reduction process(300-500℃),the thermal compressive strength of CIPWB linearly increases with increasing the size of pellet,while it gradually decreases with increasing the anthracite ratio.When the CIPWB with 8%anthracite is reduced at 300℃for 60 min,the thermal strength of pellet is enhanced from 13.24 to 31.88 N as the size of pellet increases from 8.04 to 12.78 mm.Meanwhile,as the temperature is 500℃,with increasing the anthracite ratio from 2%to 8%,the thermal compressive strength of pellet under reduction for 60 min remarkably decreases from 41.47 to 8.94 N.Furthermore,in the high-temperature reduction process(600-1150℃),the thermal compressive strength of CIPWB firstly increases and then reduces with increasing the temperature,while it as well as the temperature corresponding to the maximum strength decreases with increasing the anthracite ratio.With adding 18%anthracite,the thermal compressive strength of pellet reaches the maximum value at 800℃,namely 35.00 N,and obtains the minimum value at 1050℃,namely 8.60 N.The thermal compressive strength of CIPWB significantly depends on the temperature,reducing agent dosage,and pellet size.展开更多
The undrained mechanical behavior of unsaturated completely weathered granite(CWG)is highly susceptible to alterations in the hydraulic environment,particularly under uniaxial loading conditions,due to the unique natu...The undrained mechanical behavior of unsaturated completely weathered granite(CWG)is highly susceptible to alterations in the hydraulic environment,particularly under uniaxial loading conditions,due to the unique nature of this soil type.In this study,a series of unconfined compression tests were carried out on unsaturated CWG soil in an underground engineering site,and the effects of varying the environmental variables on the main undrained mechanical properties were analyzed.Based on the experimental results,a novel constitutive model was then established using the damage mechanics theory and the undetermined coefficient method.The results demonstrate that the curves of remolded CWG specimens with different moisture contents and dry densities exhibited diverse characteristics,including brittleness,significant softening,and ductility.As a typical indicator,the unconfined compression strength of soil specimens initially increased with an increase in moisture content and then decreased.Meanwhile,an optimal moisture content of approximately 10.5%could be observed,while a critical moisture content value of 13.0%was identified,beyond which the strength of the specimen decreases sharply.Moreover,the deformation and fracture of CWG specimens were predominantly caused by shear failure,and the ultimate failure modes were primarily influenced by moisture content rather than dry density.Furthermore,by comparing several similar models and the experimental data,the proposed model could accurately replicate the undrained mechanical characteristics of unsaturated CWG soil,and quantitatively describe the key mechanical indexes.These findings offer a valuable reference point for understanding the underlying mechanisms,anticipating potential risks,and implementing effective control measures in similar underground engineering projects.展开更多
文摘Basic life support for cardiac arrest associates cardiopulmonary resuscitation(CPR)and defibrillation.CPR relies on chest compressions(CC)and ventilation.Current guidelines on CPR recommend a depth of 5-6 cm at a rhythm of 100-120 times/min for CC.[1,2]Interruptions of the CC must be as short as possible and are related to ventilation,defibrillation and turnover of the rescuers.Most of the automated external defibrillators(AEDs)require interruptions of the CC to perform rhythm analysis.Among the numerous marketed models of AEDs,some provide real-time feedback about the quality of the CC.
基金Supported by the Fundamental Research Funds for the Central Universities,Northwest Minzu University,Grant No.31920170180.
文摘BACKGROUND It remains unclear whether video aids can improve the quality of bystander cardiopulmonary resuscitation(CPR).AIM To summarize simulation-based studies aiming at improving bystander CPR associated with the quality of chest compression and time-related quality parameters.METHODS The systematic review was conducted according to the PRISMA guidelines.All relevant studies were searched through PubMed,EMBASE,Medline and Cochrane Library databases.The risk of bias was evaluated using the Cochrane collaboration tool.RESULTS A total of 259 studies were eligible for inclusion,and 6 randomised controlled trial studies were ultimately included.The results of meta-analysis indicated that video-assisted CPR(V-CPR)was significantly associated with the improved mean chest compression rate[OR=0.66(0.49-0.82),P<0.001],and the proportion of chest compression with correct hand positioning[OR=1.63(0.71-2.55),P<0.001].However,the difference in mean chest compression depth was not statistically significant[OR=0.18(-0.07-0.42),P=0.15],and V-CPR was not associated with the time to first chest compression compared to telecommunicator CPR[OR=-0.12(-0.88-0.63),P=0.75].CONCLUSION Video real-time guidance by the dispatcher can improve the quality of bystander CPR to a certain extent.However,the quality is still not ideal,and there is a lack of guidance caused by poor video signal or inadequate interaction.
文摘Objectives: The aim of this study was to analyze the quality of chest compressions in different working situations pertaining to ambulance crews using either standard chest compressions (S-CC) or LUCAS mechanical chest compressions (L-CC) in a manikin setting. Participants and Methods: Cardiopulmonary resuscitation (CPR) was performed using a compression to ventilation ratio of 30:2 with both S-CC and L-CC. Quality parameters were collected using a modified manikin enabling impedance measurements. The evaluation was performed in two manikin scenarios: Scenario 1 evaluated ten minutes of CPR on the ground and Scenario 2 assessed six minutes of CPR in different settings relevant to work in the ambulance. Quality parameters compared were: time to apply LUCAS, hands-off fraction, number of correct chest compressions and the rate of compressions. Results: In Scenario 1 the hands-off fraction was higher when S-CC was performed (S-CC group 29% vs. L-CC 16%, P = 0.003). We found a higher number of chest compressions (S-CC = 913 vs. L-CC = 831, P = 0.0049) and a higher rate of chest compressions (S-CC = 118 vs. L-CC = 99, P < 0.0001) in the S-CC group. In Scenario 2 we noted a higher hands-off fraction for S-CC (39% vs. L-CC = 19%, P = 0.003), but a higher number of compressions given during S-CC ((n = 504) vs. L-CC (n = 396) P = 0.0002). Conclusion: Mechanical chest compression with the LUCAS 2TM device enables ambulance personnel to provide high quality chest compression even while transporting the patient.
基金This work was supported by the Changsha University Talent Introduction Project(50800-92808)the Excellent youth project of Hunan Provincial Department of Education(19B055,18B418,19C0156)the Natural Science Foundation of Hunan Province of China(2020JJ4645).
文摘Flow softening behavior of a homogenized Mg-7Gd-4Y-1Nd-0.5Zr alloy under compression to a final strain of∼1.8 at elevated temperatures of 450∼550℃ and a constant strain rate of 2s^(−1) has been investigated by optical microscopy,scanning electron microscopy,electron back-scattered diffraction and transmission electron microscopy.The results show that true stress first rises to the peak point and then drops to the bottom value and increases again with further increasing strain at each temperature.Twinning dynamic recrystallization(DRX)and continuous DRX contribute to the formation of new fine grains at temperatures 450∼475℃ when the restoration is caused by both DRX and texture change due to extension twinning,resulting in the larger softening degrees compared with the softening effects owing to continuous DRX and discontinuous DRX at 500∼550℃ when twinning activation is suppressed.500℃ is the transition temperature denoting a significant decline in the contribution of twinning and TDRX to the strain with increasing temperature.The cuboid-shape phase exists in both homogenized and compressed samples,while the compositions are varied.
基金National Natural Science Foundation of China,12225206,Yihui Zhang,12050004,Yihui Zhang,11921002,Yihui Zhangthe Tsinghua National Laboratory for Information Science and Technology,the Henry Fok Education Foundation,171003,Yihui Zhangthe Institute for Guo Qiang,Tsinghua University,2019GQG1012,Yihui Zhang.
文摘Three-dimensional(3D)mesostructures with distinct compressive deformation behaviors and tunable mechanical responses have gained increasing interest in recent years.3D cage-shaped mesostructures are representative framework structures widely exploited in 3D flexible electronics,owing to their unique cellular geometry and unusual mechanical responses.The snap-through behavior of cage-shaped mesostructures could potentially result in the performance degradation of electronics,while it could also be harnessed to design reconfigurable electronics.Due to the complicated deformation modes and random characteristics in experiments,the snap-through behavior of cage-shaped mesostructures remains largely unexplored,espe-cially in terms of probability-based analyses.In this work,we present a systematic study on the configuration evolution and snap-through of 3D cage-shaped mesostructures under out-of-plane compressions.Experimental and computational studies show the existence of two distinct deformation modes associated with the snap-through,which is controlled by the energy barrier based on the energetic analyses.Phase diagrams of the deformation modes decode how key geometric parameters and assembly strain affect the snap-through.Compressive experiments based on periodic arrays(10 × 10)of mesostructures provided a large amount of deformation data,allowing for statistical analyses of the snap-through behavior.These results provide new insights and useful guidelines for the design of 3D reconfigurable devices and multistable metamaterials based on 3D cage-shaped mesostructures.
文摘Purpose: According to guideline recommendations, chest compressions (CC) during cardiopulmonary resuscitation (CPR) should be performed at a rate of 100 - 120 per minute, with a CC fraction (CCF) of ≥80%. The aim of this work is to explore whether CC quality differs between advanced life support (ALS) and basic life support (BLS) performed by two rescuers. Method: Cardiopulmonary resuscitation was performed by two ambulance personnel in ten ALS and ten BLS manikin scenarios. Data from these scenarios were then compared with data on ten ALS cases from the clinical setting, all with non-shockable rhythms. Data from the first two 5-minute periods of CC were evaluated from impedance data (LIFEPAK 12 defibrillator monitors) using a modified Laerdal Skillmaster manikin. Quality parameters compared were: number of CC pauses (CCPs), total time of CC (%), number of CC given and CC rate/min. Results: During the first 5 minutes, the BLS manikin scenarios had the highest number of CCPs, 15 (14 - 16), compared with the ALS manikin scenario, 14 (13 - 15), and the clinical ALS cases, 12 (10 - 15). The BLS scenario also had the highest CCFs, 81% (77% - 85%), and number of CC, 450 (435 - 495), compared with the ALS manikin scenario, 75% (64% - 81%) and 400 (365 - 444) respectively, and the clinical ALS cases, 63% (50% - 74%) and 408 (306 - 489). The median rate of CC/min in the BLS scenario was 115 (110 - 120) compared with the ALS manikin scenario, 110 (106 - 115), and the clinical ALS cases, 130 (118 - 146). During the second 5-minute period, the BLS scenario had the highest number of CCPs, 16 (15 - 17), compared with 15 (14 - 16) for the ALS manikin scenario and 11 (11 - 12) for the clinical ALS cases. The CCF in the BLS setting was 79% (75% - 83%), and the number of CC 455 (430 - 480), compared with the ALS manikin scenario, 79% (74% - 84%) and 435 (395 - 480) respectively, and the clinical ALS cases, 71% (57% - 77%) and 388 (321 - 469) respectively. The median CC rate was 118 (113 - 124) for BLS, 111 (105 - 120) for ALS manikins and 123 (103 - 128) CC/min for clinical ALS cases. Conclusion: None of the groups being studied could deliver CC at a rate of 100 - 120 CC/min or a CCF of ≥80% over the whole 10-minute period in any of the resuscitation scenarios analyzed. However, BLS had the best compliance with CC quality recommendations according to the 2010 guidelines.
基金supported by the Natural Science Foundation of Tianjin Munici-pality[21YDTPJC00480]the Science and Technology Project of Tianjin[20YDTPJC00830].
文摘The sandwich structure of cushioning packaging has an important influence on the cushioning performance.Mathematical fractal theory is an important graphic expression.Based on Hilbert fractal theory,a new sandwich structure was designed.The generation mechanism and recurrence formula of theHilbert fractal were expressed by Lin’s language,and the second-orderHilbert sandwich structure was constructed fromthermoplastic polyurethane.The constitutive model of the hyperelastic body was established by using the finite element method.With the unit mass energy absorption as the optimization goal,the fractal sandwich structure was optimized,and the best result was obtained when the order was 2.5 and the unit layer thickness was 0.75 mm.TheHilbert sandwich structure was compared with the rice-shaped sandwich structure commonly used in industry,and the Hilbert fractal structure had better energy absorption.This has practical significance for the development and application of newcushioning packaging structures.
文摘Slow spinal compressions are due to the development of an expansive process in the spinal canal. It is a very common pathology, the diagnosis of which is mainly clinical. However, magnetic resonance imaging occupies an essential place in the site diagnosis and etiological research in the management. Non-traumatic spinal cord compression is a diagnostic and therapeutic emergency, requiring early and appropriate management. MRI is the benchmark imaging examination for this pathology. No similar previous MRI study in Mali. We undertook this work with the aim to determine the place of MRI in the diagnosis of spinal cord compressions in Mali hospital. <strong>Method and Patients:</strong> This was a descriptive retrospective study, carried out at the hospital’s medical imaging department from January 1, 2017 to December 31, 2018 (02 years). It involved all patients, regardless of sex and age, sent for an MRI examination of the spine, and in whom spinal cord compression was diagnosed. We used a 0.35T low-field MRI machine with solid-state antennas. <strong>Results:</strong> We collected 179 cases of spinal cord compression MRI out of 585 spinal MRI performed, (frequency of 30.59%). The average age was 53.5 years with a male predominance (sex ratio 3.7). Motor disorders were the most common reason for examination (41%). We used the T1 T2 sagittal and T2 axial sequences. IV injection of gadolinium was performed in 48% of patients. The topographic lesions were: cervical (54.7%), thoracic (31.3%) and several segments (9.5%). The lesions concerned the compartments: extradural (79.3%), intradural (4.5%), and intramedullary (16.2%). The processes were degenerative (57.5%). tumorous (29.6%), infectious (12.3%) and vascular (0.6%). <strong>Conclusion:</strong> MRI is the benchmark imaging test for the management of non-traumatic spinal cord injury. Myelo-CT can be an alternative in the absence or in case of MRI contraindication.
文摘In 1997 and 1998, hundreds of specimens of megascopic carbonaceous compressions or algal fossils were found from - 1800-million-year old Changzhougou Formation, which is the lowermost unit of the latest Palaeoproterozoic Changcheng Group (~1 600-1 800 Ma) in the Xinglong-Kuancheng areas at the middle Yanshan Range, North China. They are discoid, ellipsoid and sausage-like, namely shaped like Chuaria Shouhsiennia (Ellipsophyta) and Tawuia. By adopting HF acid-resistant maceration coupled with scanning electron microscope and petrologic section, the authors made a preliminary research on the histology for some circular and ellipsoid carbonaceous compressions, namely Chuaria- and Shouhsienia-llke forms, in addition to their morphology. The following three types of multicellular tissues have been found in the fragments of them: colony-like, pseudoparenchyma-like and parenchyma-like. All of the new data about multicelluar tissues not only supply a very important basis in histology to determine the
文摘Background The effects of chest compressions to hemodynamic and respiratory parameters during hands-only cardiopulmonary resuscitation （CPR） in a non-arrested patient who suddenly collapses are confusing.In this research,we investigated the effects of chest compressions in a non-arrested porcine model.Methods Fourteen male domestic pigs were randomized into sham control group （SHAM group,only anesthetized and instrumented without chest compression,n=6） or chest compression group （CC group,2 minutes of chest compressions,n=8）.Continuous hemodynamic parameters,dynamic lung compliance （Cdyn）,and blood gas analysis outcomes were recorded.Serum levels of catecholamine were measured at baseline and 2 minutes,30 minutes,4 hours,and 24 hours after chest compressions.Chest computed tomography （CT） was performed at 30 minutes and 24 hours.Conventional histopathology evaluation was performed.Results After two minutes of chest compressions in the CC group,heart rate and extravascular lung water increased significantly; mean arterial pressure,stroke volume,and global ejection fraction significantly decreased.Cdyn significantly decreased to valley levels at 30 minutes and slowly recovered.Compared with the baseline,serum levels of catecholamine significantly increased at 2 minutes and rapidly decreased 24 hours later.At 30 minutes after chest compressions,chest CT showed local exudation,which was absorbed 24 hours later.Conclusions This research showed that 2 minutes of chest compressions causes various heart and lung tissue damage in the normal a normal porcine model.It also impacts the hemodynamic and Cdyn.
基金financially supported by the National Key Research and Development Program of China(Grant Nos.2023YFB2604005)the National Key Research and Development 451 Program of China(Grant No.2021YFC3100803)the Yangtze River Water Science Research Joint Fund Key Project of National Natural Science Foundation of China(Grant No.U2340231).
文摘Polyurethane foam,when used as a compressible layer in deep soft rock tunnels,offers a feasible solution to reduce the support pressure on the secondary lining.The foam spraying method using sprayed polyurethane material is convenient for engineering applications;however,the compressive behaviour and feasibility of sprayed polyurethane material as a compressible layer remain unclear.To address this gap,this study conducts uniaxial compression tests and scanning electron microscope(SEM)tests to investigate the compressive behaviour of the rigid foams fabricated from a self-developed polyurethane spray material.A peridynamics model for the composite lining with a polyurethane compressible layer is then established.After validating the proposed method by comparison with two tests,a parametric study is carried out to investigate the damage evolution of the composite lining with a polyurethane compressible layer under various combinations of large deformations and compressible layer parameters.The results indicate that the polyurethane compressible layer effectively reduces the radial deformation and damage index of the secondary lining while increasing the damage susceptibility of the primary lining.The thickness of the polyurethane compressible layer significantly influences the prevention effect of large deformation-induced damage to the secondary lining within the density range of 50e100 kg/m^(3).In accordance with the experimental and simulation results,a simple,yet reasonable and convenient approach for determining the key parameters of the polyurethane compressible layer is proposed,along with a classification scheme for the parameters of the polyurethane compressible layer.
基金supported by the National Natural Science Foundation of China(Nos.U20A2069,62376234 and 123B2037)the Advanced Aero-Power Innovation Workstation,China(No.HKCX2024-01-017)。
文摘The selection of an appropriate basic detonation wave flow field is crucial for improving the performance and geometric design of standing detonation vehicles.This paper employs a detailed chemical reaction model and solves the unsteady axisymmetric Euler equation to study the characteristics of the Axisymmetric Inward Turning Curved Detonation Wave(AIT-CDW)flow field and the parameters affecting the stability of the wave system structure of AIT-CDW flow field.The numerical results demonstrate a radial compression effect in the AIT-CDW flow field.This effect causes the detonation wave to have a shorter initiation length than oblique detonation wave flow field and the detonation wave angle to gradually increase with the flow direction postdetonation.The AIT-CDW flow field is confined space,making it prone to normal detonation waves when the detonation wave reflects from the wall.This phenomenon is detrimental to the stability of the wave system structure in the flow field.It has been observed that increasing the center body radius and decreasing the fuel equivalent ratio can effectively reduce the height of the normal detonation wave or even eliminate it.Additionally,a well-designed generatrix shape of the center body can enhance airflow,reduce choked flow,and promote the stability of the wave structure in the flow field.
基金supported in part by the National Key Research and Development Program of China under Grant No.2024YFE0200600the Zhejiang Provincial Natural Science Foundation of China under Grant No.LR23F010005the Huawei Cooperation Project under Grant No.TC20240829036。
文摘Along with the proliferating research interest in semantic communication(Sem Com),joint source channel coding(JSCC)has dominated the attention due to the widely assumed existence in efficiently delivering information semantics.Nevertheless,this paper challenges the conventional JSCC paradigm and advocates for adopting separate source channel coding(SSCC)to enjoy a more underlying degree of freedom for optimization.We demonstrate that SSCC,after leveraging the strengths of the Large Language Model(LLM)for source coding and Error Correction Code Transformer(ECCT)complemented for channel coding,offers superior performance over JSCC.Our proposed framework also effectively highlights the compatibility challenges between Sem Com approaches and digital communication systems,particularly concerning the resource costs associated with the transmission of high-precision floating point numbers.Through comprehensive evaluations,we establish that assisted by LLM-based compression and ECCT-enhanced error correction,SSCC remains a viable and effective solution for modern communication systems.In other words,separate source channel coding is still what we need.
基金Supported by the Key Research and Development Program of Shaanxi,No.2024SF-YBXM-447the Institutional Foundation of The First Affiliated Hospital of Xi’an Jiaotong University,No.2022MS-07the Fundamental Research Funds for the Central Universities,No.xzy022023068.
文摘BACKGROUND Magnetic compression anastomosis(MCA)offers a simple and reliable technique for inducing anastomoses at any point along the digestive tract.Evidence regarding whether the design of the MCA device influences the anastomosis effect is lacking.AIM To investigate any difference in the side-to-side colonic anastomosis effect achieved with cylindrical vs circular ring magnets.METHODS We designed cylindrical and circular ring magnets suitable for side-to-side colonic anastomosis in rats.Thirty Sprague-Dawley rats were randomly divided into a cylindrical group,circular ring group,and cylindrical–circular ring group(n=10/group).Side-to-side colonic anastomosis was completed by transanal insertion of the magnets without incision of the colon.Operation time,perioperative complications,and magnet discharge time were recorded.Rats were euthanized 4 weeks postoperatively,and anastomotic specimens were obtained.The burst pressure and anastomotic diameter were measured sequentially,and anastomosis formation was observed by naked eye.Histological results were observed by light microscopy.RESULTS In all 30 rats,side-to-side colonic anastomosis was completed,for an operation success rate of 100%.No postoperative complications of bleeding and intestinal obstruction occurred,and the postoperative survival rate were 100%.The operation time,magnet discharge time,anastomotic bursting pressure,and anastomotic diameter did not differ significantly among the three designs(P>0.05).Healing was similar across the groups,with gross specimens showing good anastomotic healing and good mucosal continuity observed on histological analysis.CONCLUSION This study found no significant difference in the establishment of rat side-to-side colonic anastomosis with the use of cylindrical vs circular ring magnets.
基金supported by the Nation Key Research and Development Program of China(No.2021YFB3701100).
文摘Hot deformation with high strain rate has been paid more attention due to its high efficiency and low cost,however,the strain rate dependent dynamic recrystallization(DRX)and texture evolution in hot deformation process,which affect the formability of metals,are lack of study.In this work,the DRX behavior and texture evolution of Mg-8Gd-1Er-0.5Zr alloy hot compressed with strain rates of 0.1 s^(−1),1 s^(−1),10 s^(−1) and 50 s^(−1) are studied,and the corresponding dominant mechanisms for DRX and texture weakening are discussed.Results indicated the DRX fraction was 20%and the whole texture intensity was 16.89 MRD when the strain rate was 0.1 s^(−1),but they were 76%and 6.55 MRD,respectively,when the strain rate increased to 50 s^(−1).The increment of DRX fraction is suggested to result from the reduced DRX critical strain and the increased dislocation density as well as velocity,while the weakened whole texture is attributed to the increased DRX grains.At the low strain rate of 0.1 s^(−1),discontinuous DRX(DDRX)was the dominant,but the whole texture was controlled by the deformed grains with the preferred orientation of{0001}⊥CD,because the number of DDRX grains was limited.At the high strain rate of 50 s^(−1),continuous DRX(CDRX)and twin-induced DRX(TDRX)were promoted,and more DRX grains resulted in orientation randomization.The whole texture was mainly weakened by CDRX and TDRX grains,in which CDRX plays a major role.The results of present work are significant for understanding the hot workability of Mg-RE alloys with a high strain rate.
基金supported by the Key Research and Development Special Tasks of Xinjiang,China (No.2022B01051-2)the National Natural Science Foundation of China (Nos.U23B2091,42372328,and 52478253)+1 种基金the Natural Science Foundation of Jiangsu Province,China (No.BK20240209)the Science and Technology Program Special Fund of Jiangsu Province (Frontier Leading Technology Basic Research) Major projects,China (No.BK 20222004)
文摘Using cemented rockfill to replace coal pillars offers an effective solution for reducing solid waste while ensuring the safety of gob-side entries.However,achieving the balance among low cost,high waste recycling rates,and adequate strength remains a significant challenge for cemented rockfill.This study used a composite alkali activator to activate gangue cemented rockfill.The compressive strength,scanning electron microscopy,energy dispersive spectrometer,mercury intrusion porosimetry,X-ray diffraction,and thermogra-vimetric tests were carried out to investigate the effect of the composite alkali activator proportion on the compressive strength,micro-structure,and composition of the cemented rockfill.The calcium silicate hydrate(C–S–H)molecular model of cemented rockfill was con-structed to explore the fracture evolution of the nucleated molecular structure under tension.The results show that compressive strength initially increased and then decreased with the activator proportion,the optimal activator proportion of 1:2 resulted in a 31.25%increase in strength at 3 d.This reasonable activator proportion strengthens the pozzolanic effect of gangue,and consumes more calcium hydroxide to inhibit its agglomeration,ultimately achieving the densification of microstructure.The activator proportion inevitably substitutes calcium ions with sodium ions in the C–S–H molecular model.The 12%substitution of calcium ions increases the adhesion between silicon chain layers,which is beneficial to the interlayer stress transfer.This work proposes a method for preparing low-cost cemented rockfill from al-kali-activated gangue,which can be used for solid waste recycling and reducing cement consumption to achieve low-carbon goals.
基金supported by the National Natural Science Foundation of China(12072136).
文摘Research on the mechanical–electrical properties is crucial for designing and preparing high-temperature superconducting(HTS)cables.Various winding core structures can influence the mechanical–electrical behavior of cables,but the impact of alterations in the winding core structure on the mechanical–electrical behavior of superconducting cables remains unclear.This paper presents a 3D finite element model to predict the performance of three cables with different core structures when subjected to transverse compression and axial tension.The three cables analyzed are CORC(conductor-on-round-core),CORT(conductor-on-round-tube),and HFRC(conductor-on-spiral-tube).A parametric analysis is carried out by varying the core diameter and inner-to-outer diameter ratio.Results indicate that the CORT cable demonstrates better performance in transverse compression compared to the CORC cable,aligning with experimental data.Among the three cables,the HFRC cables exhibit the weakest resistance to transverse deformation.However,the HFRC cable demonstrates superior tensile deformation resistance compared to the CORT cable,provided that the transverse compression properties are maintained.Finite element results also show that the optimum inner-to-outer diameter ratios for achieving the best transverse compression performance are approximately 0.8 for CORT cables and 0.6 for HFRC cables.Meanwhile,the study explores the effect of structural changes in HTS cable winding cores on their electromagnetic properties.It recommends utilizing small tape gaps,lower frequencies,and spiral core construction to minimize eddy losses.The findings presented in this paper offer valuable insights for the commercialization and practical manufacturing of HTS cables.
基金Sponsored by Jilin Provincial Department of Education Scientific Research Project(Grant Nos.JJKH20190875KJ,JJKH20230348KJ).
文摘This study tested the electrical conductivity and pressure sensitivity of lime⁃improved silty sand reinforced with Carbon Fiber Powder(CFP)as the conductive medium.The influence of CFP dosage,moisture content and curing duration on the unconfined compressive strength,initial resistivity and pressure sensitivity of the improved soil was systematically analysed.The results showed that the unconfined compressive strength varied non⁃monotonically with increasing CFP dosage,reaching a peak at a dosage of 1.6%.Furthermore,the initial resistivity showed slight variations under different moisture conditions but eventually converged towards the conductive percolation threshold at a dosage of 2.4%.It is worth noting that CFP reinforced lime⁃improved silty sand(CRLS)exhibit a clear dynamic synchronization of strain with stress and resistivity rate of variation.The pressure sensitivity was optimized with CFP dosages ranging from 1.6%to 2.0%.Both insufficient and excessive dosages had a negative impact on pressure sensitivity.It is important to consider the weakening effect of high moisture content on the pressure sensitivity of the specimens in practical applications.
基金support of the National Natural Science Foundation of China(52074080,52004001,and 51574002).
文摘Against the background of“carbon peak and carbon neutrality,”it is of great practical significance to develop non-blast furnace ironmaking technology for the sustainable development of steel industry.Carbon-bearing iron ore pellet is an innovative burden of direct reduction ironmaking due to its excellent self-reducing property,and the thermal strength of pellet is a crucial metallurgical property that affects its wide application.The carbon-bearing iron ore pellet without binders(CIPWB)was prepared using iron concentrate and anthracite,and the effects of reducing agent addition amount,size of pellet,reduction temperature and time on the thermal compressive strength of CIPWB during the reduction process were studied.Simultaneously,the mechanism of the thermal strength evolution of CIPWB was revealed.The results showed that during the low-temperature reduction process(300-500℃),the thermal compressive strength of CIPWB linearly increases with increasing the size of pellet,while it gradually decreases with increasing the anthracite ratio.When the CIPWB with 8%anthracite is reduced at 300℃for 60 min,the thermal strength of pellet is enhanced from 13.24 to 31.88 N as the size of pellet increases from 8.04 to 12.78 mm.Meanwhile,as the temperature is 500℃,with increasing the anthracite ratio from 2%to 8%,the thermal compressive strength of pellet under reduction for 60 min remarkably decreases from 41.47 to 8.94 N.Furthermore,in the high-temperature reduction process(600-1150℃),the thermal compressive strength of CIPWB firstly increases and then reduces with increasing the temperature,while it as well as the temperature corresponding to the maximum strength decreases with increasing the anthracite ratio.With adding 18%anthracite,the thermal compressive strength of pellet reaches the maximum value at 800℃,namely 35.00 N,and obtains the minimum value at 1050℃,namely 8.60 N.The thermal compressive strength of CIPWB significantly depends on the temperature,reducing agent dosage,and pellet size.
基金Project(42202318)supported by the National Natural Science Foundation of ChinaProject(252300421199)supported by the Natural Science Foundation of Henan Province,ChinaProject(2024JJ6219)supported by the Hunan Provincial Natural Science Foundation of China。
文摘The undrained mechanical behavior of unsaturated completely weathered granite(CWG)is highly susceptible to alterations in the hydraulic environment,particularly under uniaxial loading conditions,due to the unique nature of this soil type.In this study,a series of unconfined compression tests were carried out on unsaturated CWG soil in an underground engineering site,and the effects of varying the environmental variables on the main undrained mechanical properties were analyzed.Based on the experimental results,a novel constitutive model was then established using the damage mechanics theory and the undetermined coefficient method.The results demonstrate that the curves of remolded CWG specimens with different moisture contents and dry densities exhibited diverse characteristics,including brittleness,significant softening,and ductility.As a typical indicator,the unconfined compression strength of soil specimens initially increased with an increase in moisture content and then decreased.Meanwhile,an optimal moisture content of approximately 10.5%could be observed,while a critical moisture content value of 13.0%was identified,beyond which the strength of the specimen decreases sharply.Moreover,the deformation and fracture of CWG specimens were predominantly caused by shear failure,and the ultimate failure modes were primarily influenced by moisture content rather than dry density.Furthermore,by comparing several similar models and the experimental data,the proposed model could accurately replicate the undrained mechanical characteristics of unsaturated CWG soil,and quantitatively describe the key mechanical indexes.These findings offer a valuable reference point for understanding the underlying mechanisms,anticipating potential risks,and implementing effective control measures in similar underground engineering projects.
