Particle-and droplet-laden flows are central to many problems in mechanics and transport.They occur in sedimentladen boundary layers,gas-solid and gas-liquid dispersions,and surface-water films driven by external forc...Particle-and droplet-laden flows are central to many problems in mechanics and transport.They occur in sedimentladen boundary layers,gas-solid and gas-liquid dispersions,and surface-water films driven by external forcing.They also underpin practical applications ranging from environmental transport to high-speed and aerothermal systems.Despite decades of progress,prediction remains difficult.The physics spans a wide range of scales and often couples turbulence,interphase momentum exchange,collisions,and interfacial transport.Reliable computation therefore requires both robust numerical methodology and careful physical interpretation.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
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
This study presents a theoretical and experimental analysis of laminar flow behavior of high-viscous non-Newtonian power-law and Bingham fluids in multiple structural bifurcation channel distributors.Theoretical model...This study presents a theoretical and experimental analysis of laminar flow behavior of high-viscous non-Newtonian power-law and Bingham fluids in multiple structural bifurcation channel distributors.Theoretical models are derived to describe velocity profiles,shear rate distribution,and pressure drop across specific channels.Modified pressure drop models are proposed based on experiments on 6 kinds of non-Newtonian fluids and 3 types of bifurcation channel distributors with different transition areas.Specifically,the deviations between the theoretical models and the experimental results are systematically analyzed,and models were modified with correction coefficients based on Reynolds number and dimensionless shape factor.The theoretical results,modified results and experimental data are compared and discussed to ensure the accuracy of the modified models,demonstrating a significant improvement in the prediction of pressure drops for high-viscous non-Newtonian fluids in certain types of bifurcation channels.Additional experiments and analyses were carried out to validate the modified models and the results suggest that the models offer a certain degree of universal applicability in bifurcation channel designs.It implies that for other types of bifurcation channel distributors,similar correction methods based on Reynolds number and shape factor may also be applicable even with different coefficients.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
This study presents a systematic investigation of pressure drop and gas holdup in an upward-flow fixedbed reactor,examining the effects of bubble size,bed height,particle shape,superficial gas velocity(SGV),and superf...This study presents a systematic investigation of pressure drop and gas holdup in an upward-flow fixedbed reactor,examining the effects of bubble size,bed height,particle shape,superficial gas velocity(SGV),and superficial liquid velocity(SLV)based on experimental measurements and empirical correlations.Two bubble generators,namely ring tube generator(RTG)and porous sintered film generator(PSG),are used.Key findings reveal that for the PSG,increasing SGV decreases small-bubble population while promoting large-bubble formation,with the bubbles stabilizing at a Sauter mean diameter(d_(32))of~3 mm.The RTG produces stable large bubbles(d_(32)=6—7 mm)with minimal size variations across the range of tested SGVs.The pressure drop decreases with an increase in SGV but increases with higher SLV and bed height,primarily due to the reduced liquid holdup and the dominance of static pressure.Smaller bubbles reduce the pressure drop by slowing rise velocity and minimizing frictional resistance.Clover-shaped particles exhibit the highest pressure drop owing to large porosity,while 3-mm toothed spheres show higher pressure drop than 5-mm spheres at high SGV because of intensified capillary forces.The gas holdup increases with increasing SGV and bed height but decreases slightly with increasing SLV.Smaller bubbles enhance gas holdup by improving bed distribution and residence time.The 3-mm toothed spheres show the highest gas holdup due to stronger capillary trapping,whereas the clover-shaped particles exhibit the lowest.Empirical correlations for pressure drop and gas holdup are developed,yielding calculation errors within±1%and±20%of the experimental values,respectively.展开更多
Many researchers have focused on the behavior of fiber-reinforced concrete(FRC)in the construction of various defensive structures to resist against impact forces resulting from explosions and projectiles.However,the ...Many researchers have focused on the behavior of fiber-reinforced concrete(FRC)in the construction of various defensive structures to resist against impact forces resulting from explosions and projectiles.However,the lack of sufficient research regarding the resistance of functionally graded fiber-reinforced concrete against projectile impacts has resulted in a limited understanding of the performance of this concrete type,which is necessary for the design and construction of structures requiring great resistance against external threats.Here,the performance of functionally graded fiber-reinforced concrete against projectile impacts was investigated experimentally using a(two-stage light)gas gun and a drop weight testing machine.For this objective,12 mix designs,with which 35 cylindrical specimens and 30 slab specimens were made,were prepared,and the main variables were the magnetite aggregate vol%(55%)replacing natural coarse aggregate,steel fiber vol%,and steel fiber type(3D and 5D).The fibers were added at six vol%of 0%,0.5%,0.75%,1%,1.25%,and 1.5%in 10 specimen series(three identical specimens per each series)with dimensions of 40×40×7.5 cm and functional grading(three layers),and the manufactured specimens were subjected to the drop weight impact and projectile penetration tests by the drop weight testing machine and gas gun,respectively,to assess their performance.Parameters under study included the compressive strength,destruction level,and penetration depth.The experimental results demonstrate that using the magnetite aggregate instead of the natural coarse aggregate elevated the compressive strength of the concrete by 61%.In the tests by the drop weight machine,it was observed that by increasing the total vol%of the fibers,especially by increasing the fiber content in the outer layers(impact surface),the cracking resistance and energy absorption increased by around 100%.Note that the fiber geometry had little effect on the energy absorption in the drop weight test.Investigating the optimum specimens showed that using 3D steel fibers at a total fiber content of 1 vol%,consisting of a layered grading of 1.5 vol%,0 vol%,and 1.5 vol%,improved the penetration depth by 76%and lowered the destruction level by 85%.In addition,incorporating the 5D steel fibers at a total fiber content of 1 vol%,consisting of the layered fiber contents of 1.5%,0%,and 1.5%,improved the projectile penetration depth by 50%and lowered the damage level by 61%compared with the case of using the 3D fibers.展开更多
The current quality standard for polyvinyl alcohol eye drops lacks an impurity assessment,despite the potential impact of raw material impurities on product safety.To strengthen quality control and ensure drug safety,...The current quality standard for polyvinyl alcohol eye drops lacks an impurity assessment,despite the potential impact of raw material impurities on product safety.To strengthen quality control and ensure drug safety,an investigation into the impurity profile of the formulation was conducted,and an HPLC-UV method was developed for impurity quantification.The method validation was performed using an H-type cation exchange column.A total of 116 batches of polyvinyl alcohol eye drops from four manufacturers and two batches of the innovator drug were analyzed.Formic acid was detected exclusively in 0.4 mL samples from Company A and the innovator drug,with concentrations below 0.002%in both cases.Acetic acid was identified in samples from all manufacturers,with levels not exceeding 0.1%.The method demonstrated high specificity and sensitivity,making it well-suited for the quantification of formic and acetic acids in polyvinyl alcohol eye drops.The presence of formic acid was attributed to excipients,whereas acetic acid originated from raw materials and was further generated during pH adjustment in manufacturing.Although the overall impurity levels were low and posed minimal risk to drug safety,manufacturers should remain vigilant regarding impurity control to maintain product quality.展开更多
Diabetic retinopathy(DR)is one of the common complications in patients with diabetes,which seriously aff ects the patient’s vision and quality of life.With the increase in the number of patients with diabetes,the pre...Diabetic retinopathy(DR)is one of the common complications in patients with diabetes,which seriously aff ects the patient’s vision and quality of life.With the increase in the number of patients with diabetes,the prevention and treatment of DR has become an urgent clinical problem to be solved.In recent years,Danshen dripping pills,as a traditional Chinese medicine preparation,have received widespread attention for its unique pharmacological eff ects.Studies have shown that Danshen Dropping Pills has a signifi cant regulatory eff ect on retinal vascular damage,oxidative stress,infl ammatory response and cell apoptosis.Current research results show that Danshen Dropping Pills can reduce retinal damage and improve the vision of diabetic patients through multiple mechanisms.However,in-depth research on its specifi c mechanism of action is still needed to better understand its potential application in the prevention and treatment of DR.This article aims to explore the mechanism of action of Danshen Dropping Pills in diabetic retinopathy by reviewing relevant literature and provide a theoretical basis for clinical application.展开更多
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 dynamics of vapor−liquid−solid(V−L−S)flow boiling in fluidized bed evaporators exhibit inherent complexity and chaotic behavior,hindering accurate prediction of pressure drop signals.To address this challenge,this...The dynamics of vapor−liquid−solid(V−L−S)flow boiling in fluidized bed evaporators exhibit inherent complexity and chaotic behavior,hindering accurate prediction of pressure drop signals.To address this challenge,this study proposes an innovative hybrid approach that integrates wavelet neural network(WNN)with chaos analysis.By leveraging the Cross-Correlation(C−C)method,the minimum embedding dimension for phase space reconstruction is systematically calculated and then adopted as the input node configuration for the WNN.Simulation results demonstrate the remarkable effectiveness of this integrated method in predicting pressure drop signals,advancing our understanding of the intricate dynamic phenomena occurring with V−L−S fluidized bed evaporators.Moreover,this study offers a novel perspective on applying advanced data-driven techniques to handle the complexities of multi-phase flow systems and highlights the potential for improved operational prediction and control in industrial settings.展开更多
Objective:To investigate the clinical efficacy of Shexiang Tongxin Dropping Pills combined with rosuvastatin calcium and clopidogrel bisulfate tablets in treating phlegm-heat and blood stasis type angina pectoris of c...Objective:To investigate the clinical efficacy of Shexiang Tongxin Dropping Pills combined with rosuvastatin calcium and clopidogrel bisulfate tablets in treating phlegm-heat and blood stasis type angina pectoris of coronary heart disease.Methods:Sixty-four patients with phlegm-heat and blood stasis type angina pectoris of coronary heart disease,hospitalized at Lin’an District Hospital of Traditional Chinese Medicine from January 2024 to April 2025,were selected and randomly divided into a control group(administered 10mg of rosuvastatin calcium and 75mg of clopidogrel bisulfate once daily)and an observation group(administered 2 Shexiang Tongxin Dropping Pills three times daily in addition to the control group’s treatment regimen),with 32 patients in each group.The therapeutic effects of the two groups were compared.Results:After 56 days of treatment,the angina pectoris score in the observation group was significantly lower than that in the control group(4.49±0.39 vs 4.88±0.47,p<0.05);the Seattle Angina Questionnaire(SAQ)score indicated improvement in the frequency of angina pectoris attacks.(SAQ-AF:71.35±5.29 vs.64.25±7.55,p<0.05)and treatment satisfaction(SAQ-TS:58.79±6.22 vs.54.16±5.02,p<0.05)were more significantly improved in the observation group.The total effective rate(96.87%vs.90.62%,p<0.05)and marked effective rate(62.50%vs.31.25%)were higher in the observation group than in the control group.The Traditional Chinese Medicine(TCM)syndrome score(4.49±0.39 vs.4.88±0.47,p<0.05)and lipid index(LDL-C:1.79±0.31 vs.1.99±0.33 mmol/L,p<0.05)decreased more significantly in the observation group.Conclusion:Shexiang Tongxin Dropping Pills combined with rosuvastatin calcium and clopidogrel bisulfate tablets demonstrated good efficacy and high safety in the treatment of phlegm-heat and blood stasis type angina pectoris associated with coronary heart disease.展开更多
The evaporation ofmicrometer and millimeter liquid drops,involving a liquid-to-vapor phase transition accompanied by mass and energy transfer through the liquid-vapor interface,is encountered in many natural and indus...The evaporation ofmicrometer and millimeter liquid drops,involving a liquid-to-vapor phase transition accompanied by mass and energy transfer through the liquid-vapor interface,is encountered in many natural and industrial processes as well as in numerous engineering applications.Therefore,understanding and predicting the dynamics of evaporating flows have become of primary importance.Recent efforts have been addressed using the method of Smoothed Particle Hydrodynamics(SPH),which has proven to be very efficient in correctly handling the intrinsic complexity introduced by the multiscale nature of the evaporation process.This paper aims to provide an overview of published work on SPH-based simulations related to the evaporation of drops suspended in static and convective environments and impacting on heated solid surfaces.After a brief theoretical account of the main ingredients necessary for the modeling of drop evaporation,the fundamental aspects of SPH are revisited along with the various existing formulations that have been implemented to address the challenges imposed by the physics of evaporating flows.In the following sections,the paper summarizes the results of SPH-based simulations of drop evaporation and ends with a few comments on the limitations of the current state-of-the-art SPHsimulations and future lines of research.展开更多
The water drop penetration time(WDPT)test consists of placing water drops on a material's surface in order to evaluate how long it takes to penetrate the pores.It is used to evaluate the hydrophobicity of material...The water drop penetration time(WDPT)test consists of placing water drops on a material's surface in order to evaluate how long it takes to penetrate the pores.It is used to evaluate the hydrophobicity of materials.This study aims at investigating in more detail the soil-water interaction during the test,exposing its mechanism.For that,a model soil named Hamburg Sand was coated with a hydrophobic fluoropolymer and then a WDPT test was performed while computed tomography(CT)images were taken.Tomography experiments were performed at the P07 high-energy materials science(HEMS)beamline,operated by Helmholtz–Zentrum Hereon,at the storage ring PETRA III at the Deutsches Elektronen-Synchrotron(DESY)in Hamburg.Using synchrotron radiation,a tomogram can be obtained in about 10 min,way less time than regular laboratory X-ray sources usually owned by universities.The faster imaging enables the observation of the drop penetration during time and thus provides insight into the dynamics of the process.After that,digital discrete image correlation is performed to track the displacement of the grains throughout time.From the results one can observe that,as the drop is absorbed at the material's surface,the grains directly around the droplet base are dragged to the liquid-air interface around the drop,revealing grain kinematics during capillary interactions of the penetrating liquid and sand grains.展开更多
Objective:To investigate the potential protective effect of Shexiang Tongxin dropping pills(STDP)on ischemia-reperfusion injury and its underlying mechanisms in improving endothelial cell function in coronary microvas...Objective:To investigate the potential protective effect of Shexiang Tongxin dropping pills(STDP)on ischemia-reperfusion injury and its underlying mechanisms in improving endothelial cell function in coronary microvascular disease(CMVD).Methods:A rat model of myocardial ischemia-reperfusion injury with CMVD was established using ligation and reperfusion of the left anterior descending artery.The effect of STDP(21.6 mg/kg)on cardiac function was evaluated using echocardiography,hematoxylin-eosin staining,and Evans blue staining.The effects of STDP on the microvascular endothelial barrier were assessed based on nitric oxide production,endothelial nitric oxide synthase expression,structural variety of tight junctions(TJs),and the expression of zonula occludens-1(ZO-1),claudin-5,occludin,and vascular endothelial(VE)-cadherin proteins.The mechanisms of STDP(50 and 100 ng/mL)were evaluated by examining the expression of sphingosine 1-phosphate receptor 2(S1PR2),Ras Homolog family member A(RhoA),and Rho-associated coiled-coil-containing protein kinase(ROCK)proteins and the distribution of ZO-1,VE-cadherin,and Factin proteins in an oxygen and glucose deprivation/reoxygenation model.Results:The administration of STDP on CMVD rat model significantly improved cardiac and microvascular endothelial cell barrier functions(all P<.05).STDP enhanced the structural integrity of coronary microvascular positioning and distribution by clarifying and completing TJs and increasing the expression of ZO-1,occludin,claudin-5,and VE-cadherin in vivo(all P<.05).The S1PR2/RhoA/ROCK pathway was inhibited by STDP in vitro,leading to the regulation of endothelial cell TJs,adhesion junctions,and cytoskeletal morphology.Conclusion:STDP showed protective effects on cardiac impairment and microvascular endothelial barrier injury in CMVD model rats induced by myocardial ischemia-reperfusion injury through the modulation of the S1PR2/RhoA/ROCK pathway.展开更多
Pollen morphology and hydration, ovule development, formation of pollination drop and the pollination process of Taxus chinensis (Pilg.) Rehd were investigated in detail. The results showed that mature pollen was ...Pollen morphology and hydration, ovule development, formation of pollination drop and the pollination process of Taxus chinensis (Pilg.) Rehd were investigated in detail. The results showed that mature pollen was one_celled, irregular in shape, nonsaccate, and the surface was covered with orbicules. When pollen became hydrated, the intine swelled and the exine bursted. The exine usually remained on the surface of water or on the pollination drop all the time, while the rest portion of the pollen sank into the drop of water or the pollination drop. In the late August, the down_curved female buds could be observed in the field trees. The downturning of the female buds was an characteristic feature discriminating from the vegetative buds. At this stage ovular primordium was present in the female bud with a dome_shaped nucellar primordium encircled by a rudimentary integument. The integument grew fast and overgrew the nucellus. In the March of the following year, the ovule formed a micropylar canal about 1?000 μm in length, 200-300 μm in width. Except the micropyle, the other part of the ovule was enclosed by 20-25 scales. During the early stage of the ovule development, the nucellar surface clearly showed cell configuration; but a membrane_like structure covering the nucellar apex appeared in the late stage of the ovule development, and subsequently broke down with nucellar cell disintegration before pollen shedding. The disintegrated cell products might partake in the formation of the pollination drop. Before and during pollination, the nucellar cells contained abundant mitochondria, endospermic reticulum and dictysomes with vesicles; the plasma membrane was undulated and there was no accumulation of electron_dense substances in the pericytoplasm. Pollination drops usually occurred at night, and disappeared by noon in the field tree. 15 days before pollination, the in vitro ovules from the field trees already had the capability of producing pollination drops, which could last for 4-5 days indoors. However, after these drops received pollen, they did not withdraw noticeably compared with the unpollinated ones. The retraction of the pollination drop was presumed not to be a nonmetabolic outcome but rather a result of evaporation.展开更多
To reveal the drop failure modes of the wafer level chip scale packages （WLCSPs） with Sn-3.0Ag-0.5Cu solder joints, board level drop tests were performed according to the JEDEC standard. Six failure modes were iden...To reveal the drop failure modes of the wafer level chip scale packages （WLCSPs） with Sn-3.0Ag-0.5Cu solder joints, board level drop tests were performed according to the JEDEC standard. Six failure modes were identified, i.e., short FR-4 cracks and complete FR-4 cracks at the printing circuit board （PCB） side, split between redistribution layer （RDL） and Cu under bump metallization （UBM）, RDL fracture, bulk cracks and partial bulk and intermetallic compound （IMC） cracks at the chip side. For the outmost solder joints, complete FR-4 cracks tended to occur, due to large deformation of PCB and low strength of FR-4 dielectric layer. The formation of complete FR-4 cracks largely absorbed the impact energy, resulting in the absence of other failure modes. For the inner solder joints, the absorption of impact energy by the short FR-4 cracks was limited, resulting in other failure modes at the chip side.展开更多
This article studies numerically a familiar important phenomenon in spray combustion which is deformation and breakup of liquid drops in gas flow. The SIMPLER method is used to solve the two-dimensional （2D） unstead...This article studies numerically a familiar important phenomenon in spray combustion which is deformation and breakup of liquid drops in gas flow. The SIMPLER method is used to solve the two-dimensional （2D） unsteady axisymmetric Navier-Stokes equations for both the drop and the ambient gas flow. The level set method is applied to capturing the liquid/gas interface. Through calculation are obtained four typical breakup modes--oscillation, bag breakup, sheet stripping breakup and shear breakup governed by four non-dimensional numbers which are gas Weber number （Weg）, liquid Reynolds number （Rel）, gas Reynolds number （Reg） and density ratio （γ）. Their effects upon each mode are analyzed. The results indicate that among the four numbers, Weg is of the highest importance with Rel, Reg and γfollowing up. By widening the range of the density ratio up to 1 000, the breakup mode is discovered to be so complicated that a new one called multimode breakup mode turns up. This mode contains the shearing breakup and piercing breakup, which successively happen. The calculation results agree well with what is observed from the experiments.展开更多
文摘Particle-and droplet-laden flows are central to many problems in mechanics and transport.They occur in sedimentladen boundary layers,gas-solid and gas-liquid dispersions,and surface-water films driven by external forcing.They also underpin practical applications ranging from environmental transport to high-speed and aerothermal systems.Despite decades of progress,prediction remains difficult.The physics spans a wide range of scales and often couples turbulence,interphase momentum exchange,collisions,and interfacial transport.Reliable computation therefore requires both robust numerical methodology and careful physical interpretation.
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.
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the financial support from the National Science and Technology Major Project of China(2024XXXXX2700)the National Natural Science Foundation of China (22408099)+1 种基金the Key Research and Development Program of Xinjiang Uygur Autonomous Region (2022B01032)the National Ten Thousand Talents Program。
文摘This study presents a theoretical and experimental analysis of laminar flow behavior of high-viscous non-Newtonian power-law and Bingham fluids in multiple structural bifurcation channel distributors.Theoretical models are derived to describe velocity profiles,shear rate distribution,and pressure drop across specific channels.Modified pressure drop models are proposed based on experiments on 6 kinds of non-Newtonian fluids and 3 types of bifurcation channel distributors with different transition areas.Specifically,the deviations between the theoretical models and the experimental results are systematically analyzed,and models were modified with correction coefficients based on Reynolds number and dimensionless shape factor.The theoretical results,modified results and experimental data are compared and discussed to ensure the accuracy of the modified models,demonstrating a significant improvement in the prediction of pressure drops for high-viscous non-Newtonian fluids in certain types of bifurcation channels.Additional experiments and analyses were carried out to validate the modified models and the results suggest that the models offer a certain degree of universal applicability in bifurcation channel designs.It implies that for other types of bifurcation channel distributors,similar correction methods based on Reynolds number and shape factor may also be applicable even with different coefficients.
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.
基金financially supported by the National Natural Science Foundation of China(52025103)。
文摘This study presents a systematic investigation of pressure drop and gas holdup in an upward-flow fixedbed reactor,examining the effects of bubble size,bed height,particle shape,superficial gas velocity(SGV),and superficial liquid velocity(SLV)based on experimental measurements and empirical correlations.Two bubble generators,namely ring tube generator(RTG)and porous sintered film generator(PSG),are used.Key findings reveal that for the PSG,increasing SGV decreases small-bubble population while promoting large-bubble formation,with the bubbles stabilizing at a Sauter mean diameter(d_(32))of~3 mm.The RTG produces stable large bubbles(d_(32)=6—7 mm)with minimal size variations across the range of tested SGVs.The pressure drop decreases with an increase in SGV but increases with higher SLV and bed height,primarily due to the reduced liquid holdup and the dominance of static pressure.Smaller bubbles reduce the pressure drop by slowing rise velocity and minimizing frictional resistance.Clover-shaped particles exhibit the highest pressure drop owing to large porosity,while 3-mm toothed spheres show higher pressure drop than 5-mm spheres at high SGV because of intensified capillary forces.The gas holdup increases with increasing SGV and bed height but decreases slightly with increasing SLV.Smaller bubbles enhance gas holdup by improving bed distribution and residence time.The 3-mm toothed spheres show the highest gas holdup due to stronger capillary trapping,whereas the clover-shaped particles exhibit the lowest.Empirical correlations for pressure drop and gas holdup are developed,yielding calculation errors within±1%and±20%of the experimental values,respectively.
文摘Many researchers have focused on the behavior of fiber-reinforced concrete(FRC)in the construction of various defensive structures to resist against impact forces resulting from explosions and projectiles.However,the lack of sufficient research regarding the resistance of functionally graded fiber-reinforced concrete against projectile impacts has resulted in a limited understanding of the performance of this concrete type,which is necessary for the design and construction of structures requiring great resistance against external threats.Here,the performance of functionally graded fiber-reinforced concrete against projectile impacts was investigated experimentally using a(two-stage light)gas gun and a drop weight testing machine.For this objective,12 mix designs,with which 35 cylindrical specimens and 30 slab specimens were made,were prepared,and the main variables were the magnetite aggregate vol%(55%)replacing natural coarse aggregate,steel fiber vol%,and steel fiber type(3D and 5D).The fibers were added at six vol%of 0%,0.5%,0.75%,1%,1.25%,and 1.5%in 10 specimen series(three identical specimens per each series)with dimensions of 40×40×7.5 cm and functional grading(three layers),and the manufactured specimens were subjected to the drop weight impact and projectile penetration tests by the drop weight testing machine and gas gun,respectively,to assess their performance.Parameters under study included the compressive strength,destruction level,and penetration depth.The experimental results demonstrate that using the magnetite aggregate instead of the natural coarse aggregate elevated the compressive strength of the concrete by 61%.In the tests by the drop weight machine,it was observed that by increasing the total vol%of the fibers,especially by increasing the fiber content in the outer layers(impact surface),the cracking resistance and energy absorption increased by around 100%.Note that the fiber geometry had little effect on the energy absorption in the drop weight test.Investigating the optimum specimens showed that using 3D steel fibers at a total fiber content of 1 vol%,consisting of a layered grading of 1.5 vol%,0 vol%,and 1.5 vol%,improved the penetration depth by 76%and lowered the destruction level by 85%.In addition,incorporating the 5D steel fibers at a total fiber content of 1 vol%,consisting of the layered fiber contents of 1.5%,0%,and 1.5%,improved the projectile penetration depth by 50%and lowered the damage level by 61%compared with the case of using the 3D fibers.
基金National Drug Sampling Inspection Project(No.NMPA Drug Admin[2024]1).
文摘The current quality standard for polyvinyl alcohol eye drops lacks an impurity assessment,despite the potential impact of raw material impurities on product safety.To strengthen quality control and ensure drug safety,an investigation into the impurity profile of the formulation was conducted,and an HPLC-UV method was developed for impurity quantification.The method validation was performed using an H-type cation exchange column.A total of 116 batches of polyvinyl alcohol eye drops from four manufacturers and two batches of the innovator drug were analyzed.Formic acid was detected exclusively in 0.4 mL samples from Company A and the innovator drug,with concentrations below 0.002%in both cases.Acetic acid was identified in samples from all manufacturers,with levels not exceeding 0.1%.The method demonstrated high specificity and sensitivity,making it well-suited for the quantification of formic and acetic acids in polyvinyl alcohol eye drops.The presence of formic acid was attributed to excipients,whereas acetic acid originated from raw materials and was further generated during pH adjustment in manufacturing.Although the overall impurity levels were low and posed minimal risk to drug safety,manufacturers should remain vigilant regarding impurity control to maintain product quality.
文摘Diabetic retinopathy(DR)is one of the common complications in patients with diabetes,which seriously aff ects the patient’s vision and quality of life.With the increase in the number of patients with diabetes,the prevention and treatment of DR has become an urgent clinical problem to be solved.In recent years,Danshen dripping pills,as a traditional Chinese medicine preparation,have received widespread attention for its unique pharmacological eff ects.Studies have shown that Danshen Dropping Pills has a signifi cant regulatory eff ect on retinal vascular damage,oxidative stress,infl ammatory response and cell apoptosis.Current research results show that Danshen Dropping Pills can reduce retinal damage and improve the vision of diabetic patients through multiple mechanisms.However,in-depth research on its specifi c mechanism of action is still needed to better understand its potential application in the prevention and treatment of DR.This article aims to explore the mechanism of action of Danshen Dropping Pills in diabetic retinopathy by reviewing relevant literature and provide a theoretical basis for clinical application.
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 open foundation of State Key Laboratory of Chemical Engineering(SKL-ChE-22B01)the Natural Science Foundation of China(22008169).
文摘The dynamics of vapor−liquid−solid(V−L−S)flow boiling in fluidized bed evaporators exhibit inherent complexity and chaotic behavior,hindering accurate prediction of pressure drop signals.To address this challenge,this study proposes an innovative hybrid approach that integrates wavelet neural network(WNN)with chaos analysis.By leveraging the Cross-Correlation(C−C)method,the minimum embedding dimension for phase space reconstruction is systematically calculated and then adopted as the input node configuration for the WNN.Simulation results demonstrate the remarkable effectiveness of this integrated method in predicting pressure drop signals,advancing our understanding of the intricate dynamic phenomena occurring with V−L−S fluidized bed evaporators.Moreover,this study offers a novel perspective on applying advanced data-driven techniques to handle the complexities of multi-phase flow systems and highlights the potential for improved operational prediction and control in industrial settings.
基金2023 Special Scientific Research Funding Project for Hospital Pharmacy by the Zhejiang Pharmaceutical Association(Project No.:2023ZYY33)。
文摘Objective:To investigate the clinical efficacy of Shexiang Tongxin Dropping Pills combined with rosuvastatin calcium and clopidogrel bisulfate tablets in treating phlegm-heat and blood stasis type angina pectoris of coronary heart disease.Methods:Sixty-four patients with phlegm-heat and blood stasis type angina pectoris of coronary heart disease,hospitalized at Lin’an District Hospital of Traditional Chinese Medicine from January 2024 to April 2025,were selected and randomly divided into a control group(administered 10mg of rosuvastatin calcium and 75mg of clopidogrel bisulfate once daily)and an observation group(administered 2 Shexiang Tongxin Dropping Pills three times daily in addition to the control group’s treatment regimen),with 32 patients in each group.The therapeutic effects of the two groups were compared.Results:After 56 days of treatment,the angina pectoris score in the observation group was significantly lower than that in the control group(4.49±0.39 vs 4.88±0.47,p<0.05);the Seattle Angina Questionnaire(SAQ)score indicated improvement in the frequency of angina pectoris attacks.(SAQ-AF:71.35±5.29 vs.64.25±7.55,p<0.05)and treatment satisfaction(SAQ-TS:58.79±6.22 vs.54.16±5.02,p<0.05)were more significantly improved in the observation group.The total effective rate(96.87%vs.90.62%,p<0.05)and marked effective rate(62.50%vs.31.25%)were higher in the observation group than in the control group.The Traditional Chinese Medicine(TCM)syndrome score(4.49±0.39 vs.4.88±0.47,p<0.05)and lipid index(LDL-C:1.79±0.31 vs.1.99±0.33 mmol/L,p<0.05)decreased more significantly in the observation group.Conclusion:Shexiang Tongxin Dropping Pills combined with rosuvastatin calcium and clopidogrel bisulfate tablets demonstrated good efficacy and high safety in the treatment of phlegm-heat and blood stasis type angina pectoris associated with coronary heart disease.
文摘The evaporation ofmicrometer and millimeter liquid drops,involving a liquid-to-vapor phase transition accompanied by mass and energy transfer through the liquid-vapor interface,is encountered in many natural and industrial processes as well as in numerous engineering applications.Therefore,understanding and predicting the dynamics of evaporating flows have become of primary importance.Recent efforts have been addressed using the method of Smoothed Particle Hydrodynamics(SPH),which has proven to be very efficient in correctly handling the intrinsic complexity introduced by the multiscale nature of the evaporation process.This paper aims to provide an overview of published work on SPH-based simulations related to the evaporation of drops suspended in static and convective environments and impacting on heated solid surfaces.After a brief theoretical account of the main ingredients necessary for the modeling of drop evaporation,the fundamental aspects of SPH are revisited along with the various existing formulations that have been implemented to address the challenges imposed by the physics of evaporating flows.In the following sections,the paper summarizes the results of SPH-based simulations of drop evaporation and ends with a few comments on the limitations of the current state-of-the-art SPHsimulations and future lines of research.
基金funding of this research by the German Research Foundation(Deutsche Forschungsgemeinschaft,DFG)in the framework of Research Training Group GRK 2462:Processes in natural and technical Particle-Fluid-Systems at Hamburg University of Technology(TUHH).
文摘The water drop penetration time(WDPT)test consists of placing water drops on a material's surface in order to evaluate how long it takes to penetrate the pores.It is used to evaluate the hydrophobicity of materials.This study aims at investigating in more detail the soil-water interaction during the test,exposing its mechanism.For that,a model soil named Hamburg Sand was coated with a hydrophobic fluoropolymer and then a WDPT test was performed while computed tomography(CT)images were taken.Tomography experiments were performed at the P07 high-energy materials science(HEMS)beamline,operated by Helmholtz–Zentrum Hereon,at the storage ring PETRA III at the Deutsches Elektronen-Synchrotron(DESY)in Hamburg.Using synchrotron radiation,a tomogram can be obtained in about 10 min,way less time than regular laboratory X-ray sources usually owned by universities.The faster imaging enables the observation of the drop penetration during time and thus provides insight into the dynamics of the process.After that,digital discrete image correlation is performed to track the displacement of the grains throughout time.From the results one can observe that,as the drop is absorbed at the material's surface,the grains directly around the droplet base are dragged to the liquid-air interface around the drop,revealing grain kinematics during capillary interactions of the penetrating liquid and sand grains.
基金supported the National Natural Science Foundation of China(81930113).
文摘Objective:To investigate the potential protective effect of Shexiang Tongxin dropping pills(STDP)on ischemia-reperfusion injury and its underlying mechanisms in improving endothelial cell function in coronary microvascular disease(CMVD).Methods:A rat model of myocardial ischemia-reperfusion injury with CMVD was established using ligation and reperfusion of the left anterior descending artery.The effect of STDP(21.6 mg/kg)on cardiac function was evaluated using echocardiography,hematoxylin-eosin staining,and Evans blue staining.The effects of STDP on the microvascular endothelial barrier were assessed based on nitric oxide production,endothelial nitric oxide synthase expression,structural variety of tight junctions(TJs),and the expression of zonula occludens-1(ZO-1),claudin-5,occludin,and vascular endothelial(VE)-cadherin proteins.The mechanisms of STDP(50 and 100 ng/mL)were evaluated by examining the expression of sphingosine 1-phosphate receptor 2(S1PR2),Ras Homolog family member A(RhoA),and Rho-associated coiled-coil-containing protein kinase(ROCK)proteins and the distribution of ZO-1,VE-cadherin,and Factin proteins in an oxygen and glucose deprivation/reoxygenation model.Results:The administration of STDP on CMVD rat model significantly improved cardiac and microvascular endothelial cell barrier functions(all P<.05).STDP enhanced the structural integrity of coronary microvascular positioning and distribution by clarifying and completing TJs and increasing the expression of ZO-1,occludin,claudin-5,and VE-cadherin in vivo(all P<.05).The S1PR2/RhoA/ROCK pathway was inhibited by STDP in vitro,leading to the regulation of endothelial cell TJs,adhesion junctions,and cytoskeletal morphology.Conclusion:STDP showed protective effects on cardiac impairment and microvascular endothelial barrier injury in CMVD model rats induced by myocardial ischemia-reperfusion injury through the modulation of the S1PR2/RhoA/ROCK pathway.
文摘Pollen morphology and hydration, ovule development, formation of pollination drop and the pollination process of Taxus chinensis (Pilg.) Rehd were investigated in detail. The results showed that mature pollen was one_celled, irregular in shape, nonsaccate, and the surface was covered with orbicules. When pollen became hydrated, the intine swelled and the exine bursted. The exine usually remained on the surface of water or on the pollination drop all the time, while the rest portion of the pollen sank into the drop of water or the pollination drop. In the late August, the down_curved female buds could be observed in the field trees. The downturning of the female buds was an characteristic feature discriminating from the vegetative buds. At this stage ovular primordium was present in the female bud with a dome_shaped nucellar primordium encircled by a rudimentary integument. The integument grew fast and overgrew the nucellus. In the March of the following year, the ovule formed a micropylar canal about 1?000 μm in length, 200-300 μm in width. Except the micropyle, the other part of the ovule was enclosed by 20-25 scales. During the early stage of the ovule development, the nucellar surface clearly showed cell configuration; but a membrane_like structure covering the nucellar apex appeared in the late stage of the ovule development, and subsequently broke down with nucellar cell disintegration before pollen shedding. The disintegrated cell products might partake in the formation of the pollination drop. Before and during pollination, the nucellar cells contained abundant mitochondria, endospermic reticulum and dictysomes with vesicles; the plasma membrane was undulated and there was no accumulation of electron_dense substances in the pericytoplasm. Pollination drops usually occurred at night, and disappeared by noon in the field tree. 15 days before pollination, the in vitro ovules from the field trees already had the capability of producing pollination drops, which could last for 4-5 days indoors. However, after these drops received pollen, they did not withdraw noticeably compared with the unpollinated ones. The retraction of the pollination drop was presumed not to be a nonmetabolic outcome but rather a result of evaporation.
基金Projects(51475072,51171036)supported by the National Natural Science Foundation of China
文摘To reveal the drop failure modes of the wafer level chip scale packages （WLCSPs） with Sn-3.0Ag-0.5Cu solder joints, board level drop tests were performed according to the JEDEC standard. Six failure modes were identified, i.e., short FR-4 cracks and complete FR-4 cracks at the printing circuit board （PCB） side, split between redistribution layer （RDL） and Cu under bump metallization （UBM）, RDL fracture, bulk cracks and partial bulk and intermetallic compound （IMC） cracks at the chip side. For the outmost solder joints, complete FR-4 cracks tended to occur, due to large deformation of PCB and low strength of FR-4 dielectric layer. The formation of complete FR-4 cracks largely absorbed the impact energy, resulting in the absence of other failure modes. For the inner solder joints, the absorption of impact energy by the short FR-4 cracks was limited, resulting in other failure modes at the chip side.
文摘This article studies numerically a familiar important phenomenon in spray combustion which is deformation and breakup of liquid drops in gas flow. The SIMPLER method is used to solve the two-dimensional （2D） unsteady axisymmetric Navier-Stokes equations for both the drop and the ambient gas flow. The level set method is applied to capturing the liquid/gas interface. Through calculation are obtained four typical breakup modes--oscillation, bag breakup, sheet stripping breakup and shear breakup governed by four non-dimensional numbers which are gas Weber number （Weg）, liquid Reynolds number （Rel）, gas Reynolds number （Reg） and density ratio （γ）. Their effects upon each mode are analyzed. The results indicate that among the four numbers, Weg is of the highest importance with Rel, Reg and γfollowing up. By widening the range of the density ratio up to 1 000, the breakup mode is discovered to be so complicated that a new one called multimode breakup mode turns up. This mode contains the shearing breakup and piercing breakup, which successively happen. The calculation results agree well with what is observed from the experiments.
