The specialized equipment utilized in long-line tunnel engineering is evolving towards large-scale,multifunctional,and complex orientations.The vibration caused by the high-frequency units during regular operation is ...The specialized equipment utilized in long-line tunnel engineering is evolving towards large-scale,multifunctional,and complex orientations.The vibration caused by the high-frequency units during regular operation is supported by the foundation of the units,and the magnitude of vibration and the operating frequency fluctuate in different engineering contexts,leading to variations in the dynamic response of the foundation.The high-frequency units yield significantly diverse outcomes under different startup conditions and times,resulting in failure to meet operational requirements,influencing the normal function of the tunnel,and causing harm to the foundation structure,personnel,and property in severe cases.This article formulates a finite element numerical computation model for solid elements using three-dimensional elastic body theory and integrates field measurements to substantiate and ascertain the crucial parameter configurations of the finite element model.By proposing a comprehensive startup timing function for high-frequency dynamic machines under different startup conditions,simulating the frequency andmagnitude variations during the startup process,and suggesting functions for changes in frequency and magnitude,a simulated startup schedule function for high-frequency machines is created through coupling.Taking into account the selection of the transient dynamic analysis step length,the dynamic response results for the lower dynamic foundation during its fundamental frequency crossing process are obtained.The validation checks if the structural magnitude surpasses the safety threshold during the critical phase of unit startup traversing the structural resonance region.The design recommendations for high-frequency units’dynamic foundations are provided,taking into account the startup process of the machine and ensuring the safe operation of the tunnel.展开更多
Electro-hydraulic vibration equipment(EHVE)is widely used in vibration environment simulation tests,such as vehicles,weapons,ships,aerospace,nuclear industries and seismic waves replication,etc.,due to its large outpu...Electro-hydraulic vibration equipment(EHVE)is widely used in vibration environment simulation tests,such as vehicles,weapons,ships,aerospace,nuclear industries and seismic waves replication,etc.,due to its large output power,displacement and thrust,as well as good workload adaptation and multi-controllable parameters.Based on the domestic and overseas development of high-frequency EHVE,dividing them into servo-valve controlled vibration equipment and rotary-valve controlled vibration equipment.The research status and progress of high-frequency electro-hydraulic vibration control technology(EHVCT)are discussed,from the perspective of vibration waveform control and vibration controller.The problems of current electro-hydraulic vibration system bandwidth and waveform distortion control,stability control,offset control and complex vibration waveform generation in high-frequency vibration conditions are pointed out.Combining the existing rotary-valve controlled high-frequency electro-hydraulic vibration method,a new twin-valve independently controlled high-frequency electro-hydraulic vibration method is proposed to break through the limitations of current electro-hydraulic vibration technology in terms of system frequency bandwidth and waveform distortion.The new method can realize independent adjustment and control of vibration waveform frequency,amplitude and offset under high-frequency vibration conditions,and provide a new idea for accurate simulation of high-frequency vibration waveform.展开更多
<b><span>Background:</span></b><span> With reports of higher mortality and complications occurring in patients with perioperative 2019 novel coronarvirus disease (COVID-19), most elective...<b><span>Background:</span></b><span> With reports of higher mortality and complications occurring in patients with perioperative 2019 novel coronarvirus disease (COVID-19), most elective surgeries have been postponed. However, evidence regarding emergency surgeries in patients with COVID-19 remains scarce. We report the case of a patient with asymptomatic perioperative COVID-19, presenting with an acute abdomen requiring surgery.</span><span> </span><b><span>Case:</span></b><span> A 25-year-old male, with a prior nasopharyngeal swab that was negative for SARS-CoV-2, presented with classical signs and symptoms of acute appendicitis. Clinical examination </span><span>and investigations were not suggestive of COVID-19 infection. He underwent</span><span> laparoscopic appendicectomy with infection control precautions. Post-</span><span>operatively, he was found to be positive for SARS-CoV-2 but remained asymptomatic and had an uneventful recovery.</span><span> </span><b><span>Conclusion: </span></b><span>In asymptomatic </span><span>individuals with higher risks, negative test results should be viewed cau</span><span>tiously. </span><span>The benefits of urgent surgical interventions must be weighed against the</span><span> risks of complications due to perioperative COVID-19 in these patients.</span>展开更多
The coronavirus disease 2019(COVID-19)pandemic has had a major impact on pediatric surgery.The infection is often asymptomatic and atypical in children,while overlapping presentations with other infectious diseases ge...The coronavirus disease 2019(COVID-19)pandemic has had a major impact on pediatric surgery.The infection is often asymptomatic and atypical in children,while overlapping presentations with other infectious diseases generate additional diagnostic challenges.The high probability of missed pediatric cases and the invasive nature of surgery generate great concern for widespread transmission in this setting.Current guidelines suggest that triage of cases should be made on a case-by-case basis by a multidisciplinary team of experts.Decisionmaking can be assisted by classifying cases as elective,urgent,or an emergency according to the risks of delaying their surgical management.A workflow diagram should ideally guide the management of all cases from admission to discharge.When surgery is necessary,all staff should use appropriate personal protective equipment,and high-risk practices,such as aerosol-generating tools or procedures,should be avoided if possible.Furthermore,carefully designed organizational protocols should be established to minimize transmission while ensuring the uninterrupted operation of pediatric surgery units.For example,surgical teams can be divided into small weekly rotating groups,and healthcare workers should be continuously monitored for COVID-19 symptoms.Additionally,team protocols in the operating room can optimize communication and improve adherence to personal protective equipment use.Isolated operating rooms,pediatric intensive care units,and surgical wards should be specifically designed for suspected or confirmed COVID-19 cases.Finally,transportation of patients should be minimal and follow designated short routes.All these measures can help mitigate the effects of the COVID-19 pandemic on pediatric surgery units.展开更多
基金Smart Integration Key Technologies and Application Demonstrations of Large Scale Underground Space Disaster Prevention and Reduction in Guangzhou International Financial City([2021]–KJ058).
文摘The specialized equipment utilized in long-line tunnel engineering is evolving towards large-scale,multifunctional,and complex orientations.The vibration caused by the high-frequency units during regular operation is supported by the foundation of the units,and the magnitude of vibration and the operating frequency fluctuate in different engineering contexts,leading to variations in the dynamic response of the foundation.The high-frequency units yield significantly diverse outcomes under different startup conditions and times,resulting in failure to meet operational requirements,influencing the normal function of the tunnel,and causing harm to the foundation structure,personnel,and property in severe cases.This article formulates a finite element numerical computation model for solid elements using three-dimensional elastic body theory and integrates field measurements to substantiate and ascertain the crucial parameter configurations of the finite element model.By proposing a comprehensive startup timing function for high-frequency dynamic machines under different startup conditions,simulating the frequency andmagnitude variations during the startup process,and suggesting functions for changes in frequency and magnitude,a simulated startup schedule function for high-frequency machines is created through coupling.Taking into account the selection of the transient dynamic analysis step length,the dynamic response results for the lower dynamic foundation during its fundamental frequency crossing process are obtained.The validation checks if the structural magnitude surpasses the safety threshold during the critical phase of unit startup traversing the structural resonance region.The design recommendations for high-frequency units’dynamic foundations are provided,taking into account the startup process of the machine and ensuring the safe operation of the tunnel.
基金Supported by National Natural Science Foundation of China.(Grant Nos.51605431,51675472)
文摘Electro-hydraulic vibration equipment(EHVE)is widely used in vibration environment simulation tests,such as vehicles,weapons,ships,aerospace,nuclear industries and seismic waves replication,etc.,due to its large output power,displacement and thrust,as well as good workload adaptation and multi-controllable parameters.Based on the domestic and overseas development of high-frequency EHVE,dividing them into servo-valve controlled vibration equipment and rotary-valve controlled vibration equipment.The research status and progress of high-frequency electro-hydraulic vibration control technology(EHVCT)are discussed,from the perspective of vibration waveform control and vibration controller.The problems of current electro-hydraulic vibration system bandwidth and waveform distortion control,stability control,offset control and complex vibration waveform generation in high-frequency vibration conditions are pointed out.Combining the existing rotary-valve controlled high-frequency electro-hydraulic vibration method,a new twin-valve independently controlled high-frequency electro-hydraulic vibration method is proposed to break through the limitations of current electro-hydraulic vibration technology in terms of system frequency bandwidth and waveform distortion.The new method can realize independent adjustment and control of vibration waveform frequency,amplitude and offset under high-frequency vibration conditions,and provide a new idea for accurate simulation of high-frequency vibration waveform.
文摘<b><span>Background:</span></b><span> With reports of higher mortality and complications occurring in patients with perioperative 2019 novel coronarvirus disease (COVID-19), most elective surgeries have been postponed. However, evidence regarding emergency surgeries in patients with COVID-19 remains scarce. We report the case of a patient with asymptomatic perioperative COVID-19, presenting with an acute abdomen requiring surgery.</span><span> </span><b><span>Case:</span></b><span> A 25-year-old male, with a prior nasopharyngeal swab that was negative for SARS-CoV-2, presented with classical signs and symptoms of acute appendicitis. Clinical examination </span><span>and investigations were not suggestive of COVID-19 infection. He underwent</span><span> laparoscopic appendicectomy with infection control precautions. Post-</span><span>operatively, he was found to be positive for SARS-CoV-2 but remained asymptomatic and had an uneventful recovery.</span><span> </span><b><span>Conclusion: </span></b><span>In asymptomatic </span><span>individuals with higher risks, negative test results should be viewed cau</span><span>tiously. </span><span>The benefits of urgent surgical interventions must be weighed against the</span><span> risks of complications due to perioperative COVID-19 in these patients.</span>
文摘The coronavirus disease 2019(COVID-19)pandemic has had a major impact on pediatric surgery.The infection is often asymptomatic and atypical in children,while overlapping presentations with other infectious diseases generate additional diagnostic challenges.The high probability of missed pediatric cases and the invasive nature of surgery generate great concern for widespread transmission in this setting.Current guidelines suggest that triage of cases should be made on a case-by-case basis by a multidisciplinary team of experts.Decisionmaking can be assisted by classifying cases as elective,urgent,or an emergency according to the risks of delaying their surgical management.A workflow diagram should ideally guide the management of all cases from admission to discharge.When surgery is necessary,all staff should use appropriate personal protective equipment,and high-risk practices,such as aerosol-generating tools or procedures,should be avoided if possible.Furthermore,carefully designed organizational protocols should be established to minimize transmission while ensuring the uninterrupted operation of pediatric surgery units.For example,surgical teams can be divided into small weekly rotating groups,and healthcare workers should be continuously monitored for COVID-19 symptoms.Additionally,team protocols in the operating room can optimize communication and improve adherence to personal protective equipment use.Isolated operating rooms,pediatric intensive care units,and surgical wards should be specifically designed for suspected or confirmed COVID-19 cases.Finally,transportation of patients should be minimal and follow designated short routes.All these measures can help mitigate the effects of the COVID-19 pandemic on pediatric surgery units.
