Real-time monitoring of wellbore stability during drilling is crucial for the early detection of instability and timely interventions.The cause and type of wellbore instability can be identified by analyzing the dropp...Real-time monitoring of wellbore stability during drilling is crucial for the early detection of instability and timely interventions.The cause and type of wellbore instability can be identified by analyzing the dropped blocks brought to the surface by the drilling fluid,enabling preventive measures to be taken.In this study,an image capture system with fully automated sorting and 3D scanning was developed to obtain the complete 3D point cloud data of dropping blocks.The raw data obtained were preprocessed using methods such as format conversion,down sampling,coordinate transformation,statistical filtering,and clustering.Feature extraction algorithms,including the principal component analysis bounding box method,triangular meshing method,triaxial projection method,local curvature method,and model segmentation projection method,were employed,which resulted in the extraction of 32 feature parameters from the point cloud data.An optimal machine learning algorithm was developed by training it with 10 machine learning algorithms and the block data collected in the field.The XGBoost algorithm was then used to optimize the feature parameters and improve the classification model.An intelligent,fully automated feature parameter extraction and classification system was developed and applied to classify the types of falling blocks in 12 sets of drilling field and laboratory experiments and to identify the causes of wellbore instability.An average accuracy of 93.9%was achieved.This system can thus enable the timely diagnosis and implementation of preventive and control measures for wellbore instability in the field.展开更多
The Adaptive Dropped Hinge Flap(ADHF) is a novel trailing edge high-lift device characterized by the integration of downward deflection spoiler and simple hinge flap, with excellent aerodynamic and mechanism performan...The Adaptive Dropped Hinge Flap(ADHF) is a novel trailing edge high-lift device characterized by the integration of downward deflection spoiler and simple hinge flap, with excellent aerodynamic and mechanism performance. In this paper, aerodynamic optimization design of an ADHF high-lift system is conducted considering the mechanism performance. Shape and settings of both takeoff and landing configurations are optimized and analyzed, with considering the kinematic constraints of ADHF mechanism, and the desired optimization results were obtained after optimization. Sensitivity analysis proves the robustness of the optimal design. Comparison shows that the ADHF design has better comprehensive performance of both mechanism and aerodynamics than the conventional Fowler flap and simple hinge flap design.展开更多
Marine pipeline damage subjected to dropped objects from platforms or supply vessels is analyzed to introduce an easy and applicable approach to investigating the damage induced by impact load from drop weight. A prac...Marine pipeline damage subjected to dropped objects from platforms or supply vessels is analyzed to introduce an easy and applicable approach to investigating the damage induced by impact load from drop weight. A practical engineering example was presented and analyzed using the commercial program 'ANSYS/LS-DYNA', which is a powerful tool with an explicit dynamic solver. And rational agreement of the results with previous works was obtained. The suggested procedure might be taken as a checking analysis of the protection measures of pipelines in addition to the general risk assessment method.展开更多
Background: Cataract surgery is the most frequently performed surgery worldwide. Posterior capsule rupture (PCR) remains one of the most common complications of cataract surgery and a major risk factor for poor visual...Background: Cataract surgery is the most frequently performed surgery worldwide. Posterior capsule rupture (PCR) remains one of the most common complications of cataract surgery and a major risk factor for poor visual outcomes. Cataract surgeries complicated by PCR and vitreous loss are managed with anterior vitrectomy at the time of surgery. However, the situation can be further complicated by dropping lens particles into the vitreous cavity necessitating a secondary pars plana vitrectomy (PPV). Purpose: To compare the visual outcomes and risk of rhegmatogenous retinal detachment (RRD) between eyes that required anterior vitrectomy (AV) alone for the management of vitreous loss and eyes that required AV and subsequent PPV for the management of dropped nuclear lens fragments (DNLF) following cataract surgery complicated by PCR in a tertiary care teaching hospital in Saudi Arabia. Methods: Medical records of patients in whom PCR occurred during phacoemulsification cataract surgery requiring AV or subsequent PPV for DNLF were retrospectively reviewed over a 6-year period from January 2016 to December 2021. Results: PCR occurred in 183 (2.3%) of 7757 consecutive eyes that underwent phacoemulsification cataract surgery during the study period. Seven eyes were excluded from analysis for missing data or short follow-up. Of the 176 eyes, 147 eyes (83.5%) were managed with AV alone, and the remaining 29 eyes (16.5%) underwent a secondary PPV for DNLF. After excluding eyes with pre-existing ocular pathology, final best-corrected visual acuity (BCVA) was similar in both groups with a mean of 0.32 logMAR (P = 0.99). Two of 147 eyes (1.4%) in the AV group developed RRD with poor final BCVA whereas none of the eyes in DNLF group developed RRD. Conclusion: The risk of RRD is lower in eyes that required PPV for DNLF than in eyes that were managed with AV alone following PCR during cataract surgery. The poor visual outcomes in eyes that suffered RRD underscore the importance of postoperative retinal examination and early detection of retinal breaks.展开更多
Muscle Specific Receptor Thyrosine Kinase (MuSK) Myasthenia Gravis (MG) is a rare auto-immune disorder of the neuromuscular junction. The clinical presentation of MG is dominated by fluctuating weakness of the extra-o...Muscle Specific Receptor Thyrosine Kinase (MuSK) Myasthenia Gravis (MG) is a rare auto-immune disorder of the neuromuscular junction. The clinical presentation of MG is dominated by fluctuating weakness of the extra-ocular, orofacial and limb muscles. The clinical presentation of MuSK MG can vary, which may delay diagnostic procedures. We present a patient who initially presented with severe weight loss and slowly progressive developing neck extensor weakness and diplopia. A single fiber EMG led to the diagnosis MG and antibodies directed towards MuSK were detected. He was treated with prednisone and the steroid sparing agent azathioprine after which he made full recovery.展开更多
Dropped pronouns (DPs) are ubiquitous in pro-drop languages like Chinese, Japanese etc. Previous work mainly focused on painstakingly exploring the empirical features for DPs recovery. In this paper, we propose a neur...Dropped pronouns (DPs) are ubiquitous in pro-drop languages like Chinese, Japanese etc. Previous work mainly focused on painstakingly exploring the empirical features for DPs recovery. In this paper, we propose a neural recovery machine (NRM) to model and recover DPs in Chinese to avoid the non-trivial feature engineering process. The experimental results show that the proposed NRM significantly outperforms the state-of-the-art approaches on two heterogeneous datasets. Further experimental results of Chinese zero pronoun (ZP) resolution show that the performance of ZP resolution can also be improved by recovering the ZPs to DPs.展开更多
Coiled tube heat exchangers are widely preferred in shell structures due to their superior heat transfer performance,driven by favorable flow characteristics.This study investigates the effect of modifying coil and sh...Coiled tube heat exchangers are widely preferred in shell structures due to their superior heat transfer performance,driven by favorable flow characteristics.This study investigates the effect of modifying coil and shell configurations on heat transfer efficiency.Two key enhancements were examined:adding fins to the outer coil surface and integrating longitudinal slots within a hollowed shell.These modifications promote turbulence and extend heat transfer duration,thereby improving performance.However,they also introduce challenges,including increased pressure loss andmanufacturing complexity.Numerical simulationswere conducted usingANSYS Fluent 2024R1 under identical boundary conditions.With a fixed cold-side flow rate of 3 L/min,the input temperatures for the hot and cold fluids were 333.15 and 291.65 K,respectively.The hot-side flow rate varied between 2 and 6 L/min.Simulation outcomes were reported for the objectives of the study that included the improvement in heat exchangers’heat transfer enhancement.As it was indicated in the study outcomes,the average heat transfer rate increased by 15.56%,the overall heat transfer coefficient enhanced by about 29.51%,and the convective heat transfer coefficient improved by about 75.96%compared to the conventional shell-and-coil tube heat exchanger model.However,the modified technique resulted in a significant pressure drop.展开更多
According to Beijing Commercial Information Consultation Center, sales value of men’s suits in Beijing 18 mid-to-high range department stores in April 2013 was CNY 19.22 million. e data was 15.89% lower than last month
From the sales situation in March, since this year, sales of the high-end clothing fell signiicantly, while prices of the high-end clothing increased signiicantly. Sales volume of mid-range clothing was declining in a...From the sales situation in March, since this year, sales of the high-end clothing fell signiicantly, while prices of the high-end clothing increased signiicantly. Sales volume of mid-range clothing was declining in a downturn. he consumption of medium to low-end clothing has steadily expanded. his also indicates that price展开更多
In the mobile environment, the dropped calls can be resulted from shadowing and rapid signal loss. As the cells shrink to accommodate an increasingly large demand for services, the dropped-call recovery procedure will...In the mobile environment, the dropped calls can be resulted from shadowing and rapid signal loss. As the cells shrink to accommodate an increasingly large demand for services, the dropped-call recovery procedure will become more important over the air interface. But in the current protocols, the recovery procedure is too simple to demonstrate the procedure. In this paper, we present a Transparent Reconnection Procedure (TRP) which is an efficient algorithm that can be adapted easily to the benefit of decreased dropped calls. In the simulation of a typical cellular system, it is shown that there are fewer dropped calls using TRP compared to the conventional procedure. This benefit comes at the expense of a slight increase (less than percent 1) in blocked call percentage. It depends on some relevant system parameters, the values of which are decided by the operators accordingly.展开更多
This retrospective case study investigates the clinical presentation of a 53-year-old female who underwent mantle field radiotherapy roughly 26 years ago. This patient presents with diffuse muscle atrophy and weakness...This retrospective case study investigates the clinical presentation of a 53-year-old female who underwent mantle field radiotherapy roughly 26 years ago. This patient presents with diffuse muscle atrophy and weakness in the cervical musculature, as well as sensory deficits in the upper extremities. We sought to compare our patient’s symptoms with other patients who had been formally diagnosed with Dropped Head Syndrome (DHS) by reviewing the existing literature. We found that the clinical presentation under investigation was consistent with other patients who had received radiotherapy for Hodgkins’s disease and were then diagnosed with DHS. Electromyography (EMG), nerve conduction studies, and a cervical MRI were unable to identify a separate neurological cause for the symptoms, but the MRI did confirm the presence of diffuse muscle atrophy in the cervical musculature. After reviewing the existing literature and imaging results, we compared our patient’s symptoms to those that define DHS, and both the time of onset, presenting symptoms, and progressing course are consistent with a diagnosis of Dropped Head Syndrome.展开更多
The stability and fracture behavior of a goaf roof beneath an open-pit bench are critical concerns,especially under impact loading.However,the effect of the thickness-to-span ratio on dynamic failure modes remains lar...The stability and fracture behavior of a goaf roof beneath an open-pit bench are critical concerns,especially under impact loading.However,the effect of the thickness-to-span ratio on dynamic failure modes remains largely unexplored,as existing research focuses mainly on static stability.Energy dissipation and instability evolution under impact loading require further study.To address this gap,this study conducts drop-weight impact experiments on specimens with circular perforations,complemented by numerical simulations.By integrating dimensional analysis,cusp catastrophe theory,and strength reduction techniques,the dynamic instability mechanism of goaf roofs with varying thickness-to-span ratios is revealed.Results show that the thickness-to-span ratio significantly influences energy accumulation and dissipation during roof failure.A higher ratio increases both the magnitude and rate of energy dissipation,particularly during crack initiation and stable propagation,while its impact diminishes in the final failure stage.Optimizing the thickness-to-span ratio within a critical range enhances structural stability,improving the safety factor by up to 83%.However,beyond a certain threshold,additional thickness yields diminishing benefits.This study provides new insights into the energy-based instability mechanism of goaf roofs under impact loads,establishing a theoretical foundation for early warning systems and optimized safety design.展开更多
With the change of the main influencing factors such as structural configuration and impact conditions,reinforced concrete slabs exhibit different mechanical behaviors with different failure patterns,and the failure m...With the change of the main influencing factors such as structural configuration and impact conditions,reinforced concrete slabs exhibit different mechanical behaviors with different failure patterns,and the failure modes are transformed.In order to reveal the failure mode and transformation rule of reinforced concrete slabs under impact loads,a dynamic impact response test was carried out using a drop hammer test device.The dynamic data pertaining to the impact force,support reaction force,structural displacement,and reinforcement strain were obtained through the use of digital image correlation technology(DIC),impact force measurement,and strain measurement.The analysis of the ultimate damage state of the reinforced concrete slab identified four distinct types of impact failure modes:local failure by stamping,overall failure by stamping,local-overall coupling failure,and local failure by punching.Additionally,the influence laws of hammerhead shape,hammer height,and reinforcement ratio on the dynamic response and failure mode transformation of the slab were revealed.The results indicate that:(1)The local damage to the slab by the plane hammer is readily apparent,while the overall damage by the spherical hammer is more pronounced.(2)In comparison to the high reinforcement ratio slabs,the overall bending resistance of the low reinforcement ratio slabs is significantly inferior,and the slab back exhibits further cracks.(3)As the hammer height increases,the slab failure mode undergoes a transformation,shifting from local failure by stamping and overall failure by stamping to local-overall coupling failure and local failure by punching.(4)Three failure mode thresholds have been established,and by comparing the peak impact force with the failure thresholds,the failure mode of the slab can be effectively determined.展开更多
The ratio of the pressure drop force to the drag force,C_(P),is concerned for a non-closely fitting spherical particle settling along the central line in long rectangular tubes with different A_(r)(A_(r)is W/H,where W...The ratio of the pressure drop force to the drag force,C_(P),is concerned for a non-closely fitting spherical particle settling along the central line in long rectangular tubes with different A_(r)(A_(r)is W/H,where W,H is length of the longer and shorter side of the rectangle respectively).Under Stokes flow conditions,C_(P0)for an infinitely small sphere in long rectangular tubes and C_(P)for a sphere in a long channel between two parallel layered barriers are both calculated.Then C_(P)of a sphere settling in long rectangular tubes are conducted with the direct-forcing fictitious domain(DF/FD)method.At large Reynolds number,the sphere settles unstably with a fluctuating velocity and C_(P).The fluctuation of Cp is much stronger than that of velocity and both fluctuations are stronger for less confined sphere.The influences of the particle Reynolds number(Re_(p))on C_(P)is similar to the existing experimental results in long circular tubes.At low Re_(p),C_(P)is a determined value and is calculated.For a given d/H(d sphere diameter),Cp gets its maximum value at one A_(r)in the range of[1,1.5].For a given A_(r),C_(P)is a quadratic function of d/H similar to that in a circular tube,and parameters of the quadratic function are got by curve fitting from numerical data.The constant term coefficients got have almost no difference with C_(P0)and are furtherly replaced by the latter to get new quadratic coefficients C_(P1).Lastly,an algebraic correlation of C_(P1)to A_(r)is developed.The predictions of Cp are good with a maximum relative error about 1.5%for a sphere with d/H not greater than0.7,compared to numerical results.展开更多
The sessile drop method combined with a capillary purification procedure was used,for thefirst time,to analyze the high-temperature behavior of molten Mg on three dissimilar substrates:1)molybdenum,2)tantalum and 3)AISI...The sessile drop method combined with a capillary purification procedure was used,for thefirst time,to analyze the high-temperature behavior of molten Mg on three dissimilar substrates:1)molybdenum,2)tantalum and 3)AISI 316L stainless steel.All tests were performed under isothermal conditions at 720℃ in a protective atmosphere(Ar+5 wt.%H2).Images of Mg/substrate couples recorded during the experiments were used to calculate the contact angles(θ)formed between the liquid Mg drop and the selected substrates.After the sessile drop tests,the Mg/Mo,Mg/Ta,and Mg/AISI 316L couples were subjected to in-depth microstructural characterization using scanning electron microscopy(SEM)and energy-dispersive X-ray spectroscopy(EDS).Under the employed experimental conditions,oxide-free Mg drops on all tested couples presented non-wetting behavior(θ>90°).The average values of the calculated contact angles after 40 s of liquid Mg deposition wereθMg/Mo=124°,θMg/Ta=125°,andθMg/AISI 316L=126°,respectively.The SEM/EDS analysis showed no mass transfer and no bonding between solidified drops and the substrates.This non-reactive and non-wetting behavior of investigated couples can be associated with the immiscible nature of the Mg-Mo,Mg-Ta,and Mg-Fe systems,where the solubility of liquid Mg with all tested materials is negligible,and Mg does not form any compounds with them.展开更多
With the increasing miniaturization of systems and surging demand for power density,accurate prediction and control of two-phase flow pressure drop have become a core challenge restricting the performance of microchan...With the increasing miniaturization of systems and surging demand for power density,accurate prediction and control of two-phase flow pressure drop have become a core challenge restricting the performance of microchannel heat exchangers.Pressure drop,a critical hydraulic characteristic,serves as both a natural constraint for cooling systems and determines the power required to pump the working fluid through microchannels.This paper reviews the characteristics,prediction models,and optimization measures of two-phase flow pressure drop for low-boiling-point working fluids in microchannels.It systematically analyzes key influencing factors such as fluid physical properties,operating conditions,channel geometry,and flow patterns,and discusses the complex mechanisms of pressure drop under the coupling effect of multi-physical fields.Mainstream prediction models are reviewed:the homogeneous flow model simplifies calculations but shows large deviations at low quality;the separated flow model considers interphase interactions and can be applied to micro-scales after modification;the flow-pattern-based model performs zoned modeling but relies on subjective classification;machine learning improves prediction accuracy but faces the“black-box”problem.In terms of optimization,channel designs are improved through porous structures and micro-rib arrays,and flow rate distribution is optimized using splitters to balance pressure drop and heat transfer performance.This study provides theoretical support for microchannel thermal management in high-power-density devices.展开更多
The evaporation behaviors are crucial for the flame location estimation in liquid rocketengines.This work,for the first time,experimentally reports the sub-millimeter droplet evaporationcharacteristics of the corrosiv...The evaporation behaviors are crucial for the flame location estimation in liquid rocketengines.This work,for the first time,experimentally reports the sub-millimeter droplet evaporationcharacteristics of the corrosive dinitrogen tetroxide(NTO,one prevailing hypergolic oxidizer)athigh ambient pressure up to 4.5 MPa.An in-house corrosion-resistant droplet generator is usedto generate isolated flying droplets of sub-millimeter size,which are then exposed in a gas environ-ment with temperatures between 1010 K and 1210 K and pressures in the range between 2.0 MPaand 4.5 MPa,provided by an optical rapid compression machine.Parallelly,a theoretical modelconsidering both the droplet ambient convection and the NTO dissociation is developed.Resultsindicate that firstly,the present theoretical model that considers the transient droplet-ambient con-vection as well as the temperature and pressure dependent rate of dissociation shows good agree-ment with the experimentally observed droplet lifetime.In addition,the flying droplets velocityregress gradually due to momentum exchange with the ambient,which is more prominent at higherpressure.The evaporation caused droplet size reduction is consistent with the classical D^(2)-law pre-diction,in the present temperature and pressure range.Finally,higher temperature and pressureaccelerate the evaporation and an empirical correlation for the temperature and pressure dependentevaporation rate constant is proposed,which shows good agreement with experiment and simula-tion results.展开更多
The energy consumption of a Split air conditioning unit(ACU)inside a building is extremely large,and efforts to decrease this issue are ongoing.The current work aims to experimentally investigate the thermal performan...The energy consumption of a Split air conditioning unit(ACU)inside a building is extremely large,and efforts to decrease this issue are ongoing.The current work aims to experimentally investigate the thermal performance of ACU using an external cooling-water loop for pre-cooling the condenser to improve the efficiency and to reduce energy consumption by reducing refrigerant temperature before entering the condenser,thereby reducing the coefficient of performance.The experiments are performed on ACU with and without using an external cooling-water loop under different climate conditions.By using the experimental data,the systems’performances for both cases are evaluated based on the energy,exergy,and pressure drop analysis.Effects of several parameters,e.g.,ambient temperature,inlet water temperature,and water volume flow rate,on the energy and exergy performances of ACU systems are presented for the purpose of comparison.The outcomes display that the use of an external cooling water loop system has a significant impact on the system performance as compared to conventional ACU.The results display that the addition of an external cooling-water loop leads to a reduction in the compressor power consumption and to an increase in the coefficient of performance(COP)as compared to a normal ACU.The maximum reduction in compressor power consumption is obtained equal 37%at T_(w)=15℃and 11 L/min,whereas the maximum enhancement in COP is obtained equal 21.5%at T_(w)=30℃,11 L/min,and T_(amb)=45℃.The modified model shows an increase in exergy efficiency with the maximum enhancement of about 17%at T_(w)=30℃and 15.8 L/min.The use of an external cooling water loop leads to a reduction in the irreversibility process of the compressor,evaporator and expansion valve and to an increase in the condenser losses.The outcomes show that the pressure drop is reduced by using a cooling water loop as compared to a normal ACU,where the reduction becomes more evident with a reduction in water volume flow rate and inlet temperature.Finally,the present study reveals that the use of an external cooling water loop system leads to an improvement in the performance of ACUs.展开更多
In this study,the flow boiling characteristics of R1234yf in parallel microchannels were experimentally investigated.The experiments were conducted with heat flux from 0 to 550 kW/m^(2),mass flux of 434,727,and 1015 k...In this study,the flow boiling characteristics of R1234yf in parallel microchannels were experimentally investigated.The experiments were conducted with heat flux from 0 to 550 kW/m^(2),mass flux of 434,727,and 1015 kg/(m2 s),saturation temperatures of 293,298,and 303 K,and inlet sub-cooling of 5,10,and 15 K.The analysis of the experimental results provides the following conclusions:a reduced mass flux and lower subcooling correspond to a diminished degree of superheat at the boiling inception wall;conversely,an elevated saturation temperature results in a reduced amount of superheat at the boiling inception wall.Furthermore,an increase in sub-cooling and saturation temperature will enhance heat transfer efficiency.The wall temperature is mostly influenced by variations in saturation temperature and is minimally related to changes in mass flux and subcooling degree.An increase in mass flux results in a greater pressure drop attributed to heightened frictional pressure loss.The variation in pressure drop with respect to sub-cooling is minimal,while an increased saturation temperature correlates with a reduced pressure drop due to the formation of smaller bubbles and lowered frictional pressure loss at high saturation pressures.This study thoroughly examines and summarizes the effects of mass flow rate,saturation temperature,and subcooling on the flow-boiling heat transfer and pressure drop characteristics of R1234yf.Furthermore,the new correlation has 93.42%of the predicted values fall within a 15%mean absolute error,exhibiting a mean absolute error of 5.75%.It provides a superior method for predicting the flow-boiling heat transfer coefficients of R1234yf in the heat sink of parallel microchannels compared to existing correlations.展开更多
基金supported by the Scientific research and technology development projects of CNPC“Research on Key Technologies and Equipment for Drilling and Completion of 10000-m Ultra-deep Oil and Gas Resources”(No.2022ZG06)“Development of a Complete Set of 70 MPa Intelligent Managed Pressure Drilling Equipment”(No.2024ZG35).
文摘Real-time monitoring of wellbore stability during drilling is crucial for the early detection of instability and timely interventions.The cause and type of wellbore instability can be identified by analyzing the dropped blocks brought to the surface by the drilling fluid,enabling preventive measures to be taken.In this study,an image capture system with fully automated sorting and 3D scanning was developed to obtain the complete 3D point cloud data of dropping blocks.The raw data obtained were preprocessed using methods such as format conversion,down sampling,coordinate transformation,statistical filtering,and clustering.Feature extraction algorithms,including the principal component analysis bounding box method,triangular meshing method,triaxial projection method,local curvature method,and model segmentation projection method,were employed,which resulted in the extraction of 32 feature parameters from the point cloud data.An optimal machine learning algorithm was developed by training it with 10 machine learning algorithms and the block data collected in the field.The XGBoost algorithm was then used to optimize the feature parameters and improve the classification model.An intelligent,fully automated feature parameter extraction and classification system was developed and applied to classify the types of falling blocks in 12 sets of drilling field and laboratory experiments and to identify the causes of wellbore instability.An average accuracy of 93.9%was achieved.This system can thus enable the timely diagnosis and implementation of preventive and control measures for wellbore instability in the field.
基金supported by the National Natural Science Foundation of China(Nos.11872230,91852108,91952302,92052203)the Aeronautical Science Foundation of China(No.2020Z006058002)。
文摘The Adaptive Dropped Hinge Flap(ADHF) is a novel trailing edge high-lift device characterized by the integration of downward deflection spoiler and simple hinge flap, with excellent aerodynamic and mechanism performance. In this paper, aerodynamic optimization design of an ADHF high-lift system is conducted considering the mechanism performance. Shape and settings of both takeoff and landing configurations are optimized and analyzed, with considering the kinematic constraints of ADHF mechanism, and the desired optimization results were obtained after optimization. Sensitivity analysis proves the robustness of the optimal design. Comparison shows that the ADHF design has better comprehensive performance of both mechanism and aerodynamics than the conventional Fowler flap and simple hinge flap design.
文摘Marine pipeline damage subjected to dropped objects from platforms or supply vessels is analyzed to introduce an easy and applicable approach to investigating the damage induced by impact load from drop weight. A practical engineering example was presented and analyzed using the commercial program 'ANSYS/LS-DYNA', which is a powerful tool with an explicit dynamic solver. And rational agreement of the results with previous works was obtained. The suggested procedure might be taken as a checking analysis of the protection measures of pipelines in addition to the general risk assessment method.
文摘Background: Cataract surgery is the most frequently performed surgery worldwide. Posterior capsule rupture (PCR) remains one of the most common complications of cataract surgery and a major risk factor for poor visual outcomes. Cataract surgeries complicated by PCR and vitreous loss are managed with anterior vitrectomy at the time of surgery. However, the situation can be further complicated by dropping lens particles into the vitreous cavity necessitating a secondary pars plana vitrectomy (PPV). Purpose: To compare the visual outcomes and risk of rhegmatogenous retinal detachment (RRD) between eyes that required anterior vitrectomy (AV) alone for the management of vitreous loss and eyes that required AV and subsequent PPV for the management of dropped nuclear lens fragments (DNLF) following cataract surgery complicated by PCR in a tertiary care teaching hospital in Saudi Arabia. Methods: Medical records of patients in whom PCR occurred during phacoemulsification cataract surgery requiring AV or subsequent PPV for DNLF were retrospectively reviewed over a 6-year period from January 2016 to December 2021. Results: PCR occurred in 183 (2.3%) of 7757 consecutive eyes that underwent phacoemulsification cataract surgery during the study period. Seven eyes were excluded from analysis for missing data or short follow-up. Of the 176 eyes, 147 eyes (83.5%) were managed with AV alone, and the remaining 29 eyes (16.5%) underwent a secondary PPV for DNLF. After excluding eyes with pre-existing ocular pathology, final best-corrected visual acuity (BCVA) was similar in both groups with a mean of 0.32 logMAR (P = 0.99). Two of 147 eyes (1.4%) in the AV group developed RRD with poor final BCVA whereas none of the eyes in DNLF group developed RRD. Conclusion: The risk of RRD is lower in eyes that required PPV for DNLF than in eyes that were managed with AV alone following PCR during cataract surgery. The poor visual outcomes in eyes that suffered RRD underscore the importance of postoperative retinal examination and early detection of retinal breaks.
文摘Muscle Specific Receptor Thyrosine Kinase (MuSK) Myasthenia Gravis (MG) is a rare auto-immune disorder of the neuromuscular junction. The clinical presentation of MG is dominated by fluctuating weakness of the extra-ocular, orofacial and limb muscles. The clinical presentation of MuSK MG can vary, which may delay diagnostic procedures. We present a patient who initially presented with severe weight loss and slowly progressive developing neck extensor weakness and diplopia. A single fiber EMG led to the diagnosis MG and antibodies directed towards MuSK were detected. He was treated with prednisone and the steroid sparing agent azathioprine after which he made full recovery.
基金This paper was supported by the National Natural Science Foundation of China (Grant Nos. 61502120, 61472105, 61772153)Heilongjiang philosophy and social science research project (16TQD03)+1 种基金Young research foundation of Harbin University (HUYF2013-002)the project of university library work committee of Heilongjiang (2013-B-065).
文摘Dropped pronouns (DPs) are ubiquitous in pro-drop languages like Chinese, Japanese etc. Previous work mainly focused on painstakingly exploring the empirical features for DPs recovery. In this paper, we propose a neural recovery machine (NRM) to model and recover DPs in Chinese to avoid the non-trivial feature engineering process. The experimental results show that the proposed NRM significantly outperforms the state-of-the-art approaches on two heterogeneous datasets. Further experimental results of Chinese zero pronoun (ZP) resolution show that the performance of ZP resolution can also be improved by recovering the ZPs to DPs.
文摘Coiled tube heat exchangers are widely preferred in shell structures due to their superior heat transfer performance,driven by favorable flow characteristics.This study investigates the effect of modifying coil and shell configurations on heat transfer efficiency.Two key enhancements were examined:adding fins to the outer coil surface and integrating longitudinal slots within a hollowed shell.These modifications promote turbulence and extend heat transfer duration,thereby improving performance.However,they also introduce challenges,including increased pressure loss andmanufacturing complexity.Numerical simulationswere conducted usingANSYS Fluent 2024R1 under identical boundary conditions.With a fixed cold-side flow rate of 3 L/min,the input temperatures for the hot and cold fluids were 333.15 and 291.65 K,respectively.The hot-side flow rate varied between 2 and 6 L/min.Simulation outcomes were reported for the objectives of the study that included the improvement in heat exchangers’heat transfer enhancement.As it was indicated in the study outcomes,the average heat transfer rate increased by 15.56%,the overall heat transfer coefficient enhanced by about 29.51%,and the convective heat transfer coefficient improved by about 75.96%compared to the conventional shell-and-coil tube heat exchanger model.However,the modified technique resulted in a significant pressure drop.
文摘According to Beijing Commercial Information Consultation Center, sales value of men’s suits in Beijing 18 mid-to-high range department stores in April 2013 was CNY 19.22 million. e data was 15.89% lower than last month
文摘From the sales situation in March, since this year, sales of the high-end clothing fell signiicantly, while prices of the high-end clothing increased signiicantly. Sales volume of mid-range clothing was declining in a downturn. he consumption of medium to low-end clothing has steadily expanded. his also indicates that price
基金Supported by the National Foundation of Science (NFS-69872008)
文摘In the mobile environment, the dropped calls can be resulted from shadowing and rapid signal loss. As the cells shrink to accommodate an increasingly large demand for services, the dropped-call recovery procedure will become more important over the air interface. But in the current protocols, the recovery procedure is too simple to demonstrate the procedure. In this paper, we present a Transparent Reconnection Procedure (TRP) which is an efficient algorithm that can be adapted easily to the benefit of decreased dropped calls. In the simulation of a typical cellular system, it is shown that there are fewer dropped calls using TRP compared to the conventional procedure. This benefit comes at the expense of a slight increase (less than percent 1) in blocked call percentage. It depends on some relevant system parameters, the values of which are decided by the operators accordingly.
文摘This retrospective case study investigates the clinical presentation of a 53-year-old female who underwent mantle field radiotherapy roughly 26 years ago. This patient presents with diffuse muscle atrophy and weakness in the cervical musculature, as well as sensory deficits in the upper extremities. We sought to compare our patient’s symptoms with other patients who had been formally diagnosed with Dropped Head Syndrome (DHS) by reviewing the existing literature. We found that the clinical presentation under investigation was consistent with other patients who had received radiotherapy for Hodgkins’s disease and were then diagnosed with DHS. Electromyography (EMG), nerve conduction studies, and a cervical MRI were unable to identify a separate neurological cause for the symptoms, but the MRI did confirm the presence of diffuse muscle atrophy in the cervical musculature. After reviewing the existing literature and imaging results, we compared our patient’s symptoms to those that define DHS, and both the time of onset, presenting symptoms, and progressing course are consistent with a diagnosis of Dropped Head Syndrome.
基金support from the Natural Science Foundation of Jiangsu Province(Grant No.BK20242059)the Collaborative Innovation Center for Prevention and Control of Mountain Geological Hazards of Zhejiang Province(PCMGH-2023-02)the opening fund of State Key Laboratory of Coal Mine Disaster Dynamics and Control(2011DA105827-FW202209)are gratefully acknowledged.
文摘The stability and fracture behavior of a goaf roof beneath an open-pit bench are critical concerns,especially under impact loading.However,the effect of the thickness-to-span ratio on dynamic failure modes remains largely unexplored,as existing research focuses mainly on static stability.Energy dissipation and instability evolution under impact loading require further study.To address this gap,this study conducts drop-weight impact experiments on specimens with circular perforations,complemented by numerical simulations.By integrating dimensional analysis,cusp catastrophe theory,and strength reduction techniques,the dynamic instability mechanism of goaf roofs with varying thickness-to-span ratios is revealed.Results show that the thickness-to-span ratio significantly influences energy accumulation and dissipation during roof failure.A higher ratio increases both the magnitude and rate of energy dissipation,particularly during crack initiation and stable propagation,while its impact diminishes in the final failure stage.Optimizing the thickness-to-span ratio within a critical range enhances structural stability,improving the safety factor by up to 83%.However,beyond a certain threshold,additional thickness yields diminishing benefits.This study provides new insights into the energy-based instability mechanism of goaf roofs under impact loads,establishing a theoretical foundation for early warning systems and optimized safety design.
基金Supported by the National Natural Science Foundation of China(Grant No.52078283)Shandong Provincial Natural Science Foundation(Project No.ZR2024MA094)。
文摘With the change of the main influencing factors such as structural configuration and impact conditions,reinforced concrete slabs exhibit different mechanical behaviors with different failure patterns,and the failure modes are transformed.In order to reveal the failure mode and transformation rule of reinforced concrete slabs under impact loads,a dynamic impact response test was carried out using a drop hammer test device.The dynamic data pertaining to the impact force,support reaction force,structural displacement,and reinforcement strain were obtained through the use of digital image correlation technology(DIC),impact force measurement,and strain measurement.The analysis of the ultimate damage state of the reinforced concrete slab identified four distinct types of impact failure modes:local failure by stamping,overall failure by stamping,local-overall coupling failure,and local failure by punching.Additionally,the influence laws of hammerhead shape,hammer height,and reinforcement ratio on the dynamic response and failure mode transformation of the slab were revealed.The results indicate that:(1)The local damage to the slab by the plane hammer is readily apparent,while the overall damage by the spherical hammer is more pronounced.(2)In comparison to the high reinforcement ratio slabs,the overall bending resistance of the low reinforcement ratio slabs is significantly inferior,and the slab back exhibits further cracks.(3)As the hammer height increases,the slab failure mode undergoes a transformation,shifting from local failure by stamping and overall failure by stamping to local-overall coupling failure and local failure by punching.(4)Three failure mode thresholds have been established,and by comparing the peak impact force with the failure thresholds,the failure mode of the slab can be effectively determined.
基金supported by the National Natural Science Foundation of China(12132015,12332015)。
文摘The ratio of the pressure drop force to the drag force,C_(P),is concerned for a non-closely fitting spherical particle settling along the central line in long rectangular tubes with different A_(r)(A_(r)is W/H,where W,H is length of the longer and shorter side of the rectangle respectively).Under Stokes flow conditions,C_(P0)for an infinitely small sphere in long rectangular tubes and C_(P)for a sphere in a long channel between two parallel layered barriers are both calculated.Then C_(P)of a sphere settling in long rectangular tubes are conducted with the direct-forcing fictitious domain(DF/FD)method.At large Reynolds number,the sphere settles unstably with a fluctuating velocity and C_(P).The fluctuation of Cp is much stronger than that of velocity and both fluctuations are stronger for less confined sphere.The influences of the particle Reynolds number(Re_(p))on C_(P)is similar to the existing experimental results in long circular tubes.At low Re_(p),C_(P)is a determined value and is calculated.For a given d/H(d sphere diameter),Cp gets its maximum value at one A_(r)in the range of[1,1.5].For a given A_(r),C_(P)is a quadratic function of d/H similar to that in a circular tube,and parameters of the quadratic function are got by curve fitting from numerical data.The constant term coefficients got have almost no difference with C_(P0)and are furtherly replaced by the latter to get new quadratic coefficients C_(P1).Lastly,an algebraic correlation of C_(P1)to A_(r)is developed.The predictions of Cp are good with a maximum relative error about 1.5%for a sphere with d/H not greater than0.7,compared to numerical results.
文摘The sessile drop method combined with a capillary purification procedure was used,for thefirst time,to analyze the high-temperature behavior of molten Mg on three dissimilar substrates:1)molybdenum,2)tantalum and 3)AISI 316L stainless steel.All tests were performed under isothermal conditions at 720℃ in a protective atmosphere(Ar+5 wt.%H2).Images of Mg/substrate couples recorded during the experiments were used to calculate the contact angles(θ)formed between the liquid Mg drop and the selected substrates.After the sessile drop tests,the Mg/Mo,Mg/Ta,and Mg/AISI 316L couples were subjected to in-depth microstructural characterization using scanning electron microscopy(SEM)and energy-dispersive X-ray spectroscopy(EDS).Under the employed experimental conditions,oxide-free Mg drops on all tested couples presented non-wetting behavior(θ>90°).The average values of the calculated contact angles after 40 s of liquid Mg deposition wereθMg/Mo=124°,θMg/Ta=125°,andθMg/AISI 316L=126°,respectively.The SEM/EDS analysis showed no mass transfer and no bonding between solidified drops and the substrates.This non-reactive and non-wetting behavior of investigated couples can be associated with the immiscible nature of the Mg-Mo,Mg-Ta,and Mg-Fe systems,where the solubility of liquid Mg with all tested materials is negligible,and Mg does not form any compounds with them.
基金supported by the Beijing Municipal Science&Technology Commission(Z231100006123010).
文摘With the increasing miniaturization of systems and surging demand for power density,accurate prediction and control of two-phase flow pressure drop have become a core challenge restricting the performance of microchannel heat exchangers.Pressure drop,a critical hydraulic characteristic,serves as both a natural constraint for cooling systems and determines the power required to pump the working fluid through microchannels.This paper reviews the characteristics,prediction models,and optimization measures of two-phase flow pressure drop for low-boiling-point working fluids in microchannels.It systematically analyzes key influencing factors such as fluid physical properties,operating conditions,channel geometry,and flow patterns,and discusses the complex mechanisms of pressure drop under the coupling effect of multi-physical fields.Mainstream prediction models are reviewed:the homogeneous flow model simplifies calculations but shows large deviations at low quality;the separated flow model considers interphase interactions and can be applied to micro-scales after modification;the flow-pattern-based model performs zoned modeling but relies on subjective classification;machine learning improves prediction accuracy but faces the“black-box”problem.In terms of optimization,channel designs are improved through porous structures and micro-rib arrays,and flow rate distribution is optimized using splitters to balance pressure drop and heat transfer performance.This study provides theoretical support for microchannel thermal management in high-power-density devices.
基金supported by the Natural Science Foundation of China(No.52236001)The support from Research Grants Council of Hong Kong,China(No.CityU 15218820)was also appreciated。
文摘The evaporation behaviors are crucial for the flame location estimation in liquid rocketengines.This work,for the first time,experimentally reports the sub-millimeter droplet evaporationcharacteristics of the corrosive dinitrogen tetroxide(NTO,one prevailing hypergolic oxidizer)athigh ambient pressure up to 4.5 MPa.An in-house corrosion-resistant droplet generator is usedto generate isolated flying droplets of sub-millimeter size,which are then exposed in a gas environ-ment with temperatures between 1010 K and 1210 K and pressures in the range between 2.0 MPaand 4.5 MPa,provided by an optical rapid compression machine.Parallelly,a theoretical modelconsidering both the droplet ambient convection and the NTO dissociation is developed.Resultsindicate that firstly,the present theoretical model that considers the transient droplet-ambient con-vection as well as the temperature and pressure dependent rate of dissociation shows good agree-ment with the experimentally observed droplet lifetime.In addition,the flying droplets velocityregress gradually due to momentum exchange with the ambient,which is more prominent at higherpressure.The evaporation caused droplet size reduction is consistent with the classical D^(2)-law pre-diction,in the present temperature and pressure range.Finally,higher temperature and pressureaccelerate the evaporation and an empirical correlation for the temperature and pressure dependentevaporation rate constant is proposed,which shows good agreement with experiment and simula-tion results.
文摘The energy consumption of a Split air conditioning unit(ACU)inside a building is extremely large,and efforts to decrease this issue are ongoing.The current work aims to experimentally investigate the thermal performance of ACU using an external cooling-water loop for pre-cooling the condenser to improve the efficiency and to reduce energy consumption by reducing refrigerant temperature before entering the condenser,thereby reducing the coefficient of performance.The experiments are performed on ACU with and without using an external cooling-water loop under different climate conditions.By using the experimental data,the systems’performances for both cases are evaluated based on the energy,exergy,and pressure drop analysis.Effects of several parameters,e.g.,ambient temperature,inlet water temperature,and water volume flow rate,on the energy and exergy performances of ACU systems are presented for the purpose of comparison.The outcomes display that the use of an external cooling water loop system has a significant impact on the system performance as compared to conventional ACU.The results display that the addition of an external cooling-water loop leads to a reduction in the compressor power consumption and to an increase in the coefficient of performance(COP)as compared to a normal ACU.The maximum reduction in compressor power consumption is obtained equal 37%at T_(w)=15℃and 11 L/min,whereas the maximum enhancement in COP is obtained equal 21.5%at T_(w)=30℃,11 L/min,and T_(amb)=45℃.The modified model shows an increase in exergy efficiency with the maximum enhancement of about 17%at T_(w)=30℃and 15.8 L/min.The use of an external cooling water loop leads to a reduction in the irreversibility process of the compressor,evaporator and expansion valve and to an increase in the condenser losses.The outcomes show that the pressure drop is reduced by using a cooling water loop as compared to a normal ACU,where the reduction becomes more evident with a reduction in water volume flow rate and inlet temperature.Finally,the present study reveals that the use of an external cooling water loop system leads to an improvement in the performance of ACUs.
基金supported by the Beijing Municipal Science&Technology Commission(Z231100006123010).
文摘In this study,the flow boiling characteristics of R1234yf in parallel microchannels were experimentally investigated.The experiments were conducted with heat flux from 0 to 550 kW/m^(2),mass flux of 434,727,and 1015 kg/(m2 s),saturation temperatures of 293,298,and 303 K,and inlet sub-cooling of 5,10,and 15 K.The analysis of the experimental results provides the following conclusions:a reduced mass flux and lower subcooling correspond to a diminished degree of superheat at the boiling inception wall;conversely,an elevated saturation temperature results in a reduced amount of superheat at the boiling inception wall.Furthermore,an increase in sub-cooling and saturation temperature will enhance heat transfer efficiency.The wall temperature is mostly influenced by variations in saturation temperature and is minimally related to changes in mass flux and subcooling degree.An increase in mass flux results in a greater pressure drop attributed to heightened frictional pressure loss.The variation in pressure drop with respect to sub-cooling is minimal,while an increased saturation temperature correlates with a reduced pressure drop due to the formation of smaller bubbles and lowered frictional pressure loss at high saturation pressures.This study thoroughly examines and summarizes the effects of mass flow rate,saturation temperature,and subcooling on the flow-boiling heat transfer and pressure drop characteristics of R1234yf.Furthermore,the new correlation has 93.42%of the predicted values fall within a 15%mean absolute error,exhibiting a mean absolute error of 5.75%.It provides a superior method for predicting the flow-boiling heat transfer coefficients of R1234yf in the heat sink of parallel microchannels compared to existing correlations.
