The longitudinal dispersion of the projectile in shooting tests of two-dimensional trajectory corrections fused with fixed canards is extremely large that it sometimes exceeds the correction ability of the correction ...The longitudinal dispersion of the projectile in shooting tests of two-dimensional trajectory corrections fused with fixed canards is extremely large that it sometimes exceeds the correction ability of the correction fuse actuator.The impact point easily deviates from the target,and thus the correction result cannot be readily evaluated.However,the cost of shooting tests is considerably high to conduct many tests for data collection.To address this issue,this study proposes an aiming method for shooting tests based on small sample size.The proposed method uses the Bootstrap method to expand the test data;repeatedly iterates and corrects the position of the simulated theoretical impact points through an improved compatibility test method;and dynamically adjusts the weight of the prior distribution of simulation results based on Kullback-Leibler divergence,which to some extent avoids the real data being"submerged"by the simulation data and achieves the fusion Bayesian estimation of the dispersion center.The experimental results show that when the simulation accuracy is sufficiently high,the proposed method yields a smaller mean-square deviation in estimating the dispersion center and higher shooting accuracy than those of the three comparison methods,which is more conducive to reflecting the effect of the control algorithm and facilitating test personnel to iterate their proposed structures and algorithms.;in addition,this study provides a knowledge base for further comprehensive studies in the future.展开更多
The Sichuan-Tibet transportation corridor is prone to numerous active faults and frequent strong earthquakes.While extensive studies have individually explored the effect of active faults and strong earthquakes on dif...The Sichuan-Tibet transportation corridor is prone to numerous active faults and frequent strong earthquakes.While extensive studies have individually explored the effect of active faults and strong earthquakes on different engineering structures,their combined effect remains unclear.This research employed multiple physical model tests to investigate the dynamic response of various engineering structures,including tunnels,bridges,and embankments,under the simultaneous influence of cumulative earthquakes and stick-slip misalignment of an active fault.The prototype selected for this study was the Kanding No.2 tunnel,which crosses the Yunongxi fault zone within the Sichuan-Tibet transportation corridor.The results demonstrated that the tunnel,bridge,and embankment exhibited amplification in response to the input seismic wave,with the amplification effect gradually decreasing as the input peak ground acceleration(PGA)increased.The PGAs of different engineering structures were weakened by the fault rupture zone.Nevertheless,the misalignment of the active fault may decrease the overall stiffness of the engineering structure,leading to more severe damage,with a small contribution from seismic vibration.Additionally,the seismic vibration effect might be enlarged with the height of the engineering structure,and the tunnel is supposed to have a smaller PGA and lower dynamic earth pressure compared to bridges and embankments in strong earthquake zones crossing active faults.The findings contribute valuable insights for evaluating the dynamic response of various engineering structures crossing an active fault and provide an experimental reference for secure engineering design in the challenging conditions of the Sichuan-Tibet transportation corridor.展开更多
BACKGROUND Premature ovarian insufficiency(POI)is a condition that causes secondary amenorrhea owing to ovarian hypofunction at an early stage.Early follicular depletion results in intractable infertility,thereby cons...BACKGROUND Premature ovarian insufficiency(POI)is a condition that causes secondary amenorrhea owing to ovarian hypofunction at an early stage.Early follicular depletion results in intractable infertility,thereby considerably reducing the quality of life of females.Given the continuum in weakened ovarian function,progressing from incipient ovarian failure(IOF)to transitional ovarian failure and further to POI,it is necessary to develop biomarkers for predicting POI.The oxidative stress states in IOF and POI were comprehensively evaluated via oxidative stress[diacron-reactive oxygen metabolites(d-ROMs)]test and anti-oxidant capacity[biological antioxidant potential(BAP)].METHODS Females presenting with secondary amenorrhea over 4 mo and a follicle stimulating hormone level of>40 mIU/mL were categorized into the POI group.Females presenting with a normal menstrual cycle and a follicle stimulating hormone level of>10.2 mIU/mL were categorized into the IOF group.Healthy females without ovarian hypofunction were categorized into the control group.Among females aged<40 years who visited our hospital from January 2021 to June 2022,we recruited 11 patients into both POI and IOF groups.For the potential antioxidant capacity,the relative oxidative stress index(BAP/d-ROMs×100)was calculated,and the oxidative stress defense system was comprehensively evaluated.RESULTS d-ROMs were significantly higher in the POI and IOF groups than in the control group,(478.2±58.7 U.CARR,434.5±60.6 U.CARR,and 341.1±35.1 U.CARR,respectively)(U.CARR is equivalent to 0.08 mg/dL of hydrogen peroxide).However,no significant difference was found between the POI and IOF groups.Regarding BAP,no significant difference was found between the control,IOF,and POI groups(2078.5±157.4μmol/L,2116.2±240.2μmol/L,and 2029.0±186.4μmol/L,respectively).The oxidative stress index was significantly higher in the POI and IOF groups than in the control group(23.7±3.3,20.7±3.6,and 16.5±2.1,respectively).However,no significant difference was found between the POI and IOF groups.CONCLUSION High levels of oxidative stress suggest that evaluating the oxidative stress state may be a useful indicator for the early detection of POI.展开更多
BACKGROUND A reliable test is essential for diagnosing Helicobacter pylori(H.pylori)infection,and crucial for managing H.pylori-related diseases.Serving as an excellent method for detecting H.pylori infection,histolog...BACKGROUND A reliable test is essential for diagnosing Helicobacter pylori(H.pylori)infection,and crucial for managing H.pylori-related diseases.Serving as an excellent method for detecting H.pylori infection,histologic examination is a test that clinicians heavily rely on,especially when complemented with immunohistochemistry(IHC).Additionally,other diagnostic tests for H.pylori,such as the rapid urease test(CLO test)and stool antigen test(SA),are also highly sensitive and specific.Typically,the results of histology and other tests align with each other.However,on rare occasions,discrepancy between histopathology and other H.pylori diagnostic tests occurs.AIM To investigate the discordance between histology and other H.pylori tests,the underlying causes,and the impact on clinical management.METHODS Pathology reports of gastric biopsies were retrieved spanning August 2013 and July 2018.Reports were included in the study only if there were other H.pylori tests within seven days of the biopsy.These additional tests include CLO test,SA,and H.pylori culture.Concordance between histopathology and other tests was determined based on the consistency of results.In instances where histology results were negative while other tests were positive,the slides were retrieved for re-assessment,and the clinical chart was reviewed.RESULTS Of 1396 pathology reports were identified,each accompanied by one additional H.pylori test.The concordance rates in detecting H.pylori infection between biopsy and other tests did not exhibit significant differences based on the number of biopsy fragments.117 discrepant cases were identified.Only 20 cases(9 with CLO test and 11 with SA)had negative biopsy but positive results in other tests.Four cases initially stained with Warthin-Starry turned out to be positive for H.pylori with subsequent IHC staining.Among the remaining 16 true discrepant cases,10 patients were on proton pump inhibitors before the biopsy and/or other tests.Most patients underwent treatment,except for two who were untreated,and two patients who were lost to follow-up.CONCLUSION There are rare discrepant cases with negative biopsy but positive in SA or CLO test.Various factors may contribute to this inconsistency.Most patients in such cases had undergone treatment.展开更多
P omegranate(Punica granatum L.)has attracted considerable attention in world markets due to its valuable nutrients and highly appreciated sensory properties.The aroma profiles of 4 varieties of pomegranate juice,incl...P omegranate(Punica granatum L.)has attracted considerable attention in world markets due to its valuable nutrients and highly appreciated sensory properties.The aroma profiles of 4 varieties of pomegranate juice,including Dahongtian(DP),Jingpitian(JP),Luyudan(LP),and Tianhonngdan(TP),were investigated via gas chromatography-mass spectrometry(GC-MS)and gas chromatography-olfactometry(GC-O)analyses.A total of 43 volatile compounds were identified by using GC-MS.Among these compounds,16 were considered as potential aroma-active compounds as detected by GC-O.These compounds belonged to the classes of terpinenes,alcohols,and aldehydes.Eleven volatile compounds were defined as the main contributors to the overall aroma of pomegranate juice due to their high odor activity values(OAVs≥1).Aroma recombination and omission tests confirmed thatβ-myrcene,1-hexanol,and(Z)-3-hexen-1-ol were the key aroma compounds,and limonene,1-octen-3-ol,linalool,and hexanal were important aroma-active compounds in DP samples.展开更多
The Stinger PDC cutter has high rock-breaking efficiency and excellent impact and wear resistance, which can significantly increase the rate of penetration (ROP) and extend PDC bit life for drilling hard and abrasive ...The Stinger PDC cutter has high rock-breaking efficiency and excellent impact and wear resistance, which can significantly increase the rate of penetration (ROP) and extend PDC bit life for drilling hard and abrasive formation. The knowledge of force response and mechanical specific energy (MSE) for the Stinger PDC cutter is of great importance for improving the cutter's performance and optimizing the hybrid PDC bit design. In this paper, 87 single cutter tests were conducted on the granite. A new method for precisely obtaining the rock broken volume was proposed. The influences of cutting depth, cutting angle, and cutting speed on cutting force and MSE were analyzed. Besides, a phenomenological cutting force model of the Stinger PDC cutter was established by regression of experimental data. Moreover, the surface topography and fracture morphology of the cutting groove and large size cuttings were measured by a 3D profilometer and a scanning electron microscope (SEM). Finally, the rock-breaking mechanism of the Stinger PDC cutter was illustrated. The results indicated that the cutting depth has the greatest influence on the cutting force and MSE, while the cutting speed has no obvious effects, especially at low cutting speeds. As the increase of cutting depth, the cutting force increases linearly, and MSE reduces with a quadratic polynomial relationship. When the cutting angle raises from 10° to 30°, the cutting force increases linearly, and the MSE firstly decreases and then increases. The optimal cutting angle for breaking rock is approximately 20°. The Stinger PDC cutter breaks granite mainly by high concentrated point loading and tensile failure, which can observably improve the rock breaking efficiency. The key findings of this work will help to reveal the rock-breaking mechanisms and optimize the cutter arrangement for the Stinger PDC cutter.展开更多
When building geotechnical constructions like retaining walls and dams is of interest,one of the most important factors to consider is the soil’s shear strength parameters.This study makes an effort to propose a nove...When building geotechnical constructions like retaining walls and dams is of interest,one of the most important factors to consider is the soil’s shear strength parameters.This study makes an effort to propose a novel predictive model of shear strength.The study implements an extreme gradient boosting(XGBoost)technique coupled with a powerful optimization algorithm,the salp swarm algorithm(SSA),to predict the shear strength of various soils.To do this,a database consisting of 152 sets of data is prepared where the shear strength(τ)of the soil is considered as the model output and some soil index tests(e.g.,dry unit weight,water content,and plasticity index)are set as model inputs.Themodel is designed and tuned using both effective parameters of XGBoost and SSA,and themost accuratemodel is introduced in this study.Thepredictionperformanceof theSSA-XGBoostmodel is assessedbased on the coefficient of determination(R2)and variance account for(VAF).Overall,the obtained values of R^(2) and VAF(0.977 and 0.849)and(97.714%and 84.936%)for training and testing sets,respectively,confirm the workability of the developed model in forecasting the soil shear strength.To investigate the model generalization,the prediction performance of the model is tested for another 30 sets of data(validation data).The validation results(e.g.,R^(2) of 0.805)suggest the workability of the proposed model.Overall,findings suggest that when the shear strength of the soil cannot be determined directly,the proposed hybrid XGBoost-SSA model can be utilized to assess this parameter.展开更多
To address the problem of conventional approaches for mechanical property determination requiring destructive sampling, which may be unsuitable for in-service structures, the authors proposed a method for determining ...To address the problem of conventional approaches for mechanical property determination requiring destructive sampling, which may be unsuitable for in-service structures, the authors proposed a method for determining the quasi-static fracture toughness and impact absorbed energy of ductile metals from spherical indentation tests (SITs). The stress status and damage mechanism of SIT, mode I fracture, Charpy impact tests, and related tests were frst investigated through fnite element (FE) calculations and scanning electron microscopy (SEM) observations, respectively. It was found that the damage mechanism of SITs is diferent from that of mode I fractures, while mode I fractures and Charpy impact tests share the same damage mechanism. Considering the diference between SIT and mode I fractures, uniaxial tension and pure shear were introduced to correlate SIT with mode I fractures. Based on this, the widely used critical indentation energy (CIE) model for fracture toughness determination using SITs was modifed. The quasi-static fracture toughness determined from the modifed CIE model was used to evaluate the impact absorbed energy using the dynamic fracture toughness and energy for crack initiation. The efectiveness of the newly proposed method was verifed through experiments on four types of steels: Q345R, SA508-3, 18MnMoNbR, and S30408.展开更多
Most studies on liquefaction have addressed homogeneous soil strata using sand or sand with fine content without considering soil stratification.In this study,cyclic triaxial tests were conducted on the stratified san...Most studies on liquefaction have addressed homogeneous soil strata using sand or sand with fine content without considering soil stratification.In this study,cyclic triaxial tests were conducted on the stratified sand specimens embedded with the silt layers to investigate the liquefaction failures and void-redistribution at confining stress of 100 kPa under stress-controlled mode.The loosening of underlying sand mass and hindrance to pore-water flow caused localized bulging at the sand-silt interface.It is observed that at a silt thickness of 0.2H(H is the height of the specimen),nearly 187 load cycles were required to attain liquefaction,which was the highest among all the silt thicknesses with a single silt layer.Therefore,0.2H is assumed as the optimum silt thickness(t_(opt)).The silt was placed at the top,middle and bottom of the specimen to understand the effect of silt layer location.Due to the increase in depth of the silt layer from the top position(capped soil state)to the bottom,the cycles to reach liquefaction(N_(cyc,L))increased 2.18 times.Also,when the number of silt layers increased from single to triple,there was an increase of about 880%in N_(cyc,L).The micro-characterization analysis of the soil specimens indicated silty materials transported in upper sections of the specimen due to the dissipated pore pressure.The main parameters,including thickness(t),location(z),cyclic stress ratio(CSR),number of silt layers(n)and modified relative density(D_(r,m)),performed significantly in governing the lique-faction resistance.For this,a multilinear regression model is developed based on critical parameters for prediction of N_(cyc,L).Furthermore,the developed constitutive model has been validated using the data from the present study and earlier findings.展开更多
BACKGROUND Upper gastrointestinal(GI)bleeding is a life-threatening condition with high mortality rates.AIM To compare the performance of pre-endoscopic risk scores in predicting the following primary outcomes:In-hosp...BACKGROUND Upper gastrointestinal(GI)bleeding is a life-threatening condition with high mortality rates.AIM To compare the performance of pre-endoscopic risk scores in predicting the following primary outcomes:In-hospital mortality,intervention(endoscopic or surgical)and length of admission(≥7 d).METHODS We performed a retrospective analysis of 363 patients presenting with upper GI bleeding from December 2020 to January 2021.We calculated and compared the area under the receiver operating characteristics curves(AUROCs)of Glasgow-Blatchford score(GBS),pre-endoscopic Rockall score(PERS),albumin,international normalized ratio,altered mental status,systolic blood pressure,age older than 65(AIMS65)and age,blood tests and comorbidities(ABC),including their optimal cut-off in variceal and non-variceal upper GI bleeding cohorts.We subsequently analyzed through a logistic binary regression model,if addition of lactate increased the score performance.RESULTS All scores had discriminative ability in predicting in-hospital mortality irrespective of study group.AIMS65 score had the best performance in the variceal bleeding group(AUROC=0.772;P<0.001),and ABC score(AUROC=0.775;P<0.001)in the non-variceal bleeding group.However,ABC score,at a cut-off value of 5.5,was the best predictor(AUROC=0.770,P=0.001)of inhospital mortality in both populations.PERS score was a good predictor for endoscopic treatment(AUC=0.604;P=0.046)in the variceal population,while GBS score,(AUROC=0.722;P=0.024),outperformed the other scores in predicting surgical intervention.Addition of lactate to AIMS65 score,increases by 5-fold the probability of in-hospital mortality(P<0.05)and by 12-fold if added to GBS score(P<0.003).No score proved to be a good predictor for length of admission.CONCLUSION ABC score is the most accurate in predicting in-hospital mortality in both mixed and non-variceal bleeding population.PERS and GBS should be used to determine need for endoscopic and surgical intervention,respectively.Lactate can be used as an additional tool to risk scores for predicting inhospital mortality.展开更多
Choosing appropriate statistical tests is crucial but deciding which tests to use can be challenging. Different tests suit different types of data and research questions, so it is important to choose the right one. Kn...Choosing appropriate statistical tests is crucial but deciding which tests to use can be challenging. Different tests suit different types of data and research questions, so it is important to choose the right one. Knowing how to select an appropriate test can lead to more accurate results. Invalid results and misleading conclusions may be drawn from a study if an incorrect statistical test is used. Therefore, to avoid these it is essential to understand the nature of the data, the research question, and the assumptions of the tests before selecting one. This is because there are a wide variety of tests available. This paper provides a step-by-step approach to selecting the right statistical test for any study, with an explanation of when it is appropriate to use it and relevant examples of each statistical test. Furthermore, this guide provides a comprehensive overview of the assumptions of each test and what to do if these assumptions are violated.展开更多
Choosing appropriate statistical tests is crucial but deciding which tests to use can be challenging. Different tests suit different types of data and research questions, so it is important to choose the right one. Kn...Choosing appropriate statistical tests is crucial but deciding which tests to use can be challenging. Different tests suit different types of data and research questions, so it is important to choose the right one. Knowing how to select an appropriate test can lead to more accurate results. Invalid results and misleading conclusions may be drawn from a study if an incorrect statistical test is used. Therefore, to avoid these it is essential to understand the nature of the data, the research question, and the assumptions of the tests before selecting one. This is because there are a wide variety of tests available. This paper provides a step-by-step approach to selecting the right statistical test for any study, with an explanation of when it is appropriate to use it and relevant examples of each statistical test. Furthermore, this guide provides a comprehensive overview of the assumptions of each test and what to do if these assumptions are violated.展开更多
The engagement of students is a recognised challenge for teachers.Technology offers some practical student engagement tools,and this paper examines the use of low-stakes online tests and immediate dialogic feedback to...The engagement of students is a recognised challenge for teachers.Technology offers some practical student engagement tools,and this paper examines the use of low-stakes online tests and immediate dialogic feedback to improve behavioural engagement.The academic exploration of low-stakes tests and dialogic feedback has been extensive,and they are credible teaching tools.In this study,we explore the learning benefit of their combination.Postgraduate engineering students’self-reported and learning analytics data shows conclusive evidence of improved behavioural engagement.We measured a 500%increase in the Learning Management System(LMS)page views on the days when we ran the low-stakes tests(each worth 2%of the marks for the subject)and engaged in immediate dialogic feedback.To interpret these results,we draw on theories of behavioural engagement,low-stakes tests,and feedback.We conclude that the combination of low-stakes tests and immediate feedback improves student behavioural engagement.展开更多
Unlike most animals,plants fail to move bodily at will.However,movements also occur in every single part of plants out of energy and nutrients needs,spanning from milliseconds to hours on a time scale.And with the gro...Unlike most animals,plants fail to move bodily at will.However,movements also occur in every single part of plants out of energy and nutrients needs,spanning from milliseconds to hours on a time scale.And with the growing understanding of plant movement in the academic community,bionic soft robots based on plant movement principles are increasingly studied and are considered by scientists as a source of inspiration for innovative engineering solutions.In this paper,through the study of the biological morphology,microstructure,and motion mechanism of the flytrap,we developed chambered design rules,and designed and fabricated a gas-driven bionic flytrap blade,intending to investigate its feasibility of performing complex bending deformation.The experimental result shows that the bionic flytrap blade can achieve multi-dimensional bending deformation,and complete the bending and closing action within 2 s.The performance of the bionic flytrap blade fabricated is in high agreement with the real flytrap blade in terms of bending and deformation,achieving an excellent bionic design effect.In this study,the chambered design rules of the bionic flytrap blade were proposed and developed,and the possibility of its deformation was investigated.The effects of different chamber types and different flow channel design precepts on the bending deformation of the bionic flytrap blade were revealed,together with the relationship between the response time and flow rate of the bionic flytrap blade.At last,this study provides new ideas for the study of plant blade motion mechanism in a hope to expand the application fields of bionic robots,especially hope to offer solutions for plant-type robotics.展开更多
A novel adaptive multiple dependent state sampling plan(AMDSSP)was designed to inspect products from a continuous manufacturing process under the accelerated life test(ALT)using both double sampling plan(DSP)and multi...A novel adaptive multiple dependent state sampling plan(AMDSSP)was designed to inspect products from a continuous manufacturing process under the accelerated life test(ALT)using both double sampling plan(DSP)and multiple dependent state sampling plan(MDSSP)concepts.Under accelerated conditions,the lifetime of a product follows the Weibull distribution with a known shape parameter,while the scale parameter can be determined using the acceleration factor(AF).The Arrhenius model is used to estimate AF when the damaging process is temperature-sensitive.An economic design of the proposed sampling plan was also considered for the ALT.A genetic algorithm with nonlinear optimization was used to estimate optimal plan parameters to minimize the average sample number(ASN)and total cost of inspection(TC)under both producer’s and consumer’s risks.Numerical results are presented to support the AMDSSP for the ALT,while performance comparisons between the AMDSSP,the MDSSP and a single sampling plan(SSP)for the ALT are discussed.Results indicated that the AMDSSP was more flexible and efficient for ASN and TC than the MDSSP and SSP plans under accelerated conditions.The AMDSSP also had a higher operating characteristic(OC)curve than both the existing sampling plans.Two real datasets of electronic devices for the ALT at high temperatures demonstrated the practicality and usefulness of the proposed sampling plan.展开更多
Objectives: The study aimed to determine the most appropriate hearing screening test to identify disabling hearing loss for adults aged 65 years or older.Methods: This study included 577 older adults. Four hearing scr...Objectives: The study aimed to determine the most appropriate hearing screening test to identify disabling hearing loss for adults aged 65 years or older.Methods: This study included 577 older adults. Four hearing screening tests were considered in the study, including the Hearing Handicap Inventory for Elderly Screening(HHIE-s), three single question tests, the whisper test, and the finger rub test. The sensitivity and specificity of these tests referenced to the hearing threshold of disabling hearing loss were estimated.Results: Among all tests, only the single self-perception question(0.7064 for sensitivity;0.7225 for specificity) and whisper test(0.7833 for sensitivity;0.7708 for specificity) could obtain both sensitivity and specificity higher than 70% for adults aged ≥65 years.Conclusion: Overall, we suggest using the whisper test to identify disabling hearing loss(>40 dB HL at the better ear) for adults aged 65 years or older. However, if the conditions do not permit, the single selfperception question is also acceptable. Moreover, HHIE-s might not be a good test to detect disabling hearing loss for adults aged 80 years or older.展开更多
Suction foundations are generally installed with negative pressures to overcome the resistance of soils and complete the penetration,but excessive negative pressures are also avoided to cause seepage damages.In this p...Suction foundations are generally installed with negative pressures to overcome the resistance of soils and complete the penetration,but excessive negative pressures are also avoided to cause seepage damages.In this paper,the model test method was used to analyze the movement characteristics of multi-bucket foundations in the process of sinking in sand,and the common calculation methods of sinking resistances are verified.The critical negative pressure corresponding to the seepage failure of foundation was determined under the action of increasing negative pressure step by step and the characteristics of soil failure were studied.The calculation formula of critical suction in sand was verified in application,and according to the test results,the value of seepage coefficient was modified,which provides an example for the study of suction foundation in sand soils.展开更多
Rock anchors are a common safety measure for stabilising large-scale infrastructure,such as bridge towers,retaining walls,rock slopes and windmills.There are four principal failure modes for rock anchors:(a)tensile fa...Rock anchors are a common safety measure for stabilising large-scale infrastructure,such as bridge towers,retaining walls,rock slopes and windmills.There are four principal failure modes for rock anchors:(a)tensile failure of the steel anchor,(b)anchor-grout interface failure,(c)grout-rock interface failure,and(d)rock mass uplift.Field tests were performed in a limestone quarry.These tests were designed to test failure modes B and C through pullout.In the tests of failure mode B,the shear stress on the anchor-grout interface is the largest at the top of the grout column and attenuates towards the distal end for small loads.The shear stress becomes uniformly distributed when the applied load is approximately 50%of the ultimate pullout load.The anchors designed to test failure mode C were installed with an endplate and had a higher toughness than the straight bar anchors.The shear stress on the grout-rock interface is the largest at the endplate and attenuates upward before slip starts along the interface.When the ultimate pullout load is reached,and the grout column starts to slip,the shear stress is approximately constant.The bond shear strength on the anchor-grout interface was approximately 20%of the uniaxial compressive strength of the grout,and the bond strength of the grout-rock interface was around 5%for that of the grout.The grout-rock interface is likely determined by whichever is weaker,the grout or the rock.展开更多
Lime-treatment of clayey soil significantly increases its shear and tensile strengths.Consequently,the tensile strength of lime-treated soils deserves careful investigation because it may provide an appreciable benefi...Lime-treatment of clayey soil significantly increases its shear and tensile strengths.Consequently,the tensile strength of lime-treated soils deserves careful investigation because it may provide an appreciable benefit for the stability of earth structures.This study investigates the tensile and shear strengths of an untreated and lime-treated(3%of lime)plastic clay at different curing times(7 d,56 d and 300 d),through triaxial tension and compression tests.Triaxial tension tests are performed using“diabolo-shaped”soil samples with reduced central section,such that the central part of the specimen can be under axial tension while both end-sections remain in axial compression.Consolidated undrained(CU)conditions with measurement of pore water pressure allow analyzing the failure conditions through effective stress and total stress approaches.The results of triaxial tension tests reveal that the failure occurs under tensile mode at low confining pressure while extensional shear failure mode is observed under higher confining pressure.Consequently,a classical Mohr-Coulomb shear failure criterion must be combined with a cut-off tensile strength criterion that is not affected by the confining pressure.When comparing shear failure under compression and tension,a slight anisotropy is observed.展开更多
The unsupported sleeper can change the load characteristics of ballast particles and thus affect the dynamic stability of a ballasted bed.In this work,a laboratory test was constructed on a ballasted track containing ...The unsupported sleeper can change the load characteristics of ballast particles and thus affect the dynamic stability of a ballasted bed.In this work,a laboratory test was constructed on a ballasted track containing unsupported sleepers.The ballasted track was excited by a wheelset,and the influence of unsupported sleepers on the dynamic stability of a ballasted bed was studied.The results show that the main frequency of the sleeper vibration appeared at 670 Hz,and the first-order rigid vibration mode at the frequency of 101 Hz had a significant effect on the condition without the unsupported sleeper.When the sleepers were continuously unsupported,the vibration damping effect of ballasted bed within the frequency range of 0–450 Hz was better than that at higher frequencies.Within the frequency range of 70–250 Hz,the vibration damping effect of the ballasted bed with unsupported sleepers was better than that without the unsupported sleeper.Owing to the excitation from the wheelset impact,the lateral resistance of the ballasted bed with unsupported sleepers whose hanging heights were 30,60,and 90 mm increased by 37.43%,12.25%,and 18.23%,respectively,while the lateral resistance of the ballasted bed without the unsupported sleeper remained basically unchanged.The unsupported sleeper could increase the difference in the quality of the ballasted bed between two adjacent sleepers.In addition,test results show that the hanging height of the unsupported sleeper had little effect on the lateral resistance of a ballasted bed without external excitation,but had an obvious effect on the rate of change of the lateral resistance of a ballasted bed and the acceleration amplitude of the sleeper vibration under the wheelset impact.展开更多
基金the National Natural Science Foundation of China(Grant No.61973033)Preliminary Research of Equipment(Grant No.9090102010305)for funding the experiments。
文摘The longitudinal dispersion of the projectile in shooting tests of two-dimensional trajectory corrections fused with fixed canards is extremely large that it sometimes exceeds the correction ability of the correction fuse actuator.The impact point easily deviates from the target,and thus the correction result cannot be readily evaluated.However,the cost of shooting tests is considerably high to conduct many tests for data collection.To address this issue,this study proposes an aiming method for shooting tests based on small sample size.The proposed method uses the Bootstrap method to expand the test data;repeatedly iterates and corrects the position of the simulated theoretical impact points through an improved compatibility test method;and dynamically adjusts the weight of the prior distribution of simulation results based on Kullback-Leibler divergence,which to some extent avoids the real data being"submerged"by the simulation data and achieves the fusion Bayesian estimation of the dispersion center.The experimental results show that when the simulation accuracy is sufficiently high,the proposed method yields a smaller mean-square deviation in estimating the dispersion center and higher shooting accuracy than those of the three comparison methods,which is more conducive to reflecting the effect of the control algorithm and facilitating test personnel to iterate their proposed structures and algorithms.;in addition,this study provides a knowledge base for further comprehensive studies in the future.
基金supported by the National Natural Science Foundation of China(Grant Nos.41825018,41977248,42207219)the Second Tibetan Plateau Scientific Expedition and Research Program(STEP)(Grant No.2019QZKK0904)。
文摘The Sichuan-Tibet transportation corridor is prone to numerous active faults and frequent strong earthquakes.While extensive studies have individually explored the effect of active faults and strong earthquakes on different engineering structures,their combined effect remains unclear.This research employed multiple physical model tests to investigate the dynamic response of various engineering structures,including tunnels,bridges,and embankments,under the simultaneous influence of cumulative earthquakes and stick-slip misalignment of an active fault.The prototype selected for this study was the Kanding No.2 tunnel,which crosses the Yunongxi fault zone within the Sichuan-Tibet transportation corridor.The results demonstrated that the tunnel,bridge,and embankment exhibited amplification in response to the input seismic wave,with the amplification effect gradually decreasing as the input peak ground acceleration(PGA)increased.The PGAs of different engineering structures were weakened by the fault rupture zone.Nevertheless,the misalignment of the active fault may decrease the overall stiffness of the engineering structure,leading to more severe damage,with a small contribution from seismic vibration.Additionally,the seismic vibration effect might be enlarged with the height of the engineering structure,and the tunnel is supposed to have a smaller PGA and lower dynamic earth pressure compared to bridges and embankments in strong earthquake zones crossing active faults.The findings contribute valuable insights for evaluating the dynamic response of various engineering structures crossing an active fault and provide an experimental reference for secure engineering design in the challenging conditions of the Sichuan-Tibet transportation corridor.
文摘BACKGROUND Premature ovarian insufficiency(POI)is a condition that causes secondary amenorrhea owing to ovarian hypofunction at an early stage.Early follicular depletion results in intractable infertility,thereby considerably reducing the quality of life of females.Given the continuum in weakened ovarian function,progressing from incipient ovarian failure(IOF)to transitional ovarian failure and further to POI,it is necessary to develop biomarkers for predicting POI.The oxidative stress states in IOF and POI were comprehensively evaluated via oxidative stress[diacron-reactive oxygen metabolites(d-ROMs)]test and anti-oxidant capacity[biological antioxidant potential(BAP)].METHODS Females presenting with secondary amenorrhea over 4 mo and a follicle stimulating hormone level of>40 mIU/mL were categorized into the POI group.Females presenting with a normal menstrual cycle and a follicle stimulating hormone level of>10.2 mIU/mL were categorized into the IOF group.Healthy females without ovarian hypofunction were categorized into the control group.Among females aged<40 years who visited our hospital from January 2021 to June 2022,we recruited 11 patients into both POI and IOF groups.For the potential antioxidant capacity,the relative oxidative stress index(BAP/d-ROMs×100)was calculated,and the oxidative stress defense system was comprehensively evaluated.RESULTS d-ROMs were significantly higher in the POI and IOF groups than in the control group,(478.2±58.7 U.CARR,434.5±60.6 U.CARR,and 341.1±35.1 U.CARR,respectively)(U.CARR is equivalent to 0.08 mg/dL of hydrogen peroxide).However,no significant difference was found between the POI and IOF groups.Regarding BAP,no significant difference was found between the control,IOF,and POI groups(2078.5±157.4μmol/L,2116.2±240.2μmol/L,and 2029.0±186.4μmol/L,respectively).The oxidative stress index was significantly higher in the POI and IOF groups than in the control group(23.7±3.3,20.7±3.6,and 16.5±2.1,respectively).However,no significant difference was found between the POI and IOF groups.CONCLUSION High levels of oxidative stress suggest that evaluating the oxidative stress state may be a useful indicator for the early detection of POI.
文摘BACKGROUND A reliable test is essential for diagnosing Helicobacter pylori(H.pylori)infection,and crucial for managing H.pylori-related diseases.Serving as an excellent method for detecting H.pylori infection,histologic examination is a test that clinicians heavily rely on,especially when complemented with immunohistochemistry(IHC).Additionally,other diagnostic tests for H.pylori,such as the rapid urease test(CLO test)and stool antigen test(SA),are also highly sensitive and specific.Typically,the results of histology and other tests align with each other.However,on rare occasions,discrepancy between histopathology and other H.pylori diagnostic tests occurs.AIM To investigate the discordance between histology and other H.pylori tests,the underlying causes,and the impact on clinical management.METHODS Pathology reports of gastric biopsies were retrieved spanning August 2013 and July 2018.Reports were included in the study only if there were other H.pylori tests within seven days of the biopsy.These additional tests include CLO test,SA,and H.pylori culture.Concordance between histopathology and other tests was determined based on the consistency of results.In instances where histology results were negative while other tests were positive,the slides were retrieved for re-assessment,and the clinical chart was reviewed.RESULTS Of 1396 pathology reports were identified,each accompanied by one additional H.pylori test.The concordance rates in detecting H.pylori infection between biopsy and other tests did not exhibit significant differences based on the number of biopsy fragments.117 discrepant cases were identified.Only 20 cases(9 with CLO test and 11 with SA)had negative biopsy but positive results in other tests.Four cases initially stained with Warthin-Starry turned out to be positive for H.pylori with subsequent IHC staining.Among the remaining 16 true discrepant cases,10 patients were on proton pump inhibitors before the biopsy and/or other tests.Most patients underwent treatment,except for two who were untreated,and two patients who were lost to follow-up.CONCLUSION There are rare discrepant cases with negative biopsy but positive in SA or CLO test.Various factors may contribute to this inconsistency.Most patients in such cases had undergone treatment.
基金funded by Shaanxi Natural Science Foundation (2019JQ-665)Xi’an Agricultural Science and Technology Project (20NYYF0021)supported by the Open Project Program of Beijing Key Laboratory of Flavor Chemistry, Beijing Technology and Business University (BTBU), Beijing 100048, China (SPFW2020YB12)
文摘P omegranate(Punica granatum L.)has attracted considerable attention in world markets due to its valuable nutrients and highly appreciated sensory properties.The aroma profiles of 4 varieties of pomegranate juice,including Dahongtian(DP),Jingpitian(JP),Luyudan(LP),and Tianhonngdan(TP),were investigated via gas chromatography-mass spectrometry(GC-MS)and gas chromatography-olfactometry(GC-O)analyses.A total of 43 volatile compounds were identified by using GC-MS.Among these compounds,16 were considered as potential aroma-active compounds as detected by GC-O.These compounds belonged to the classes of terpinenes,alcohols,and aldehydes.Eleven volatile compounds were defined as the main contributors to the overall aroma of pomegranate juice due to their high odor activity values(OAVs≥1).Aroma recombination and omission tests confirmed thatβ-myrcene,1-hexanol,and(Z)-3-hexen-1-ol were the key aroma compounds,and limonene,1-octen-3-ol,linalool,and hexanal were important aroma-active compounds in DP samples.
基金supported by the Joint Funds of The National Natural Science Foundation of China(Grant No.U19B6003-05)the National Key Research and Development Program of China(No.2019YFA0708302)+2 种基金the National Science Fund for Distinguished Young Scholars(Grant No.51725404)the Beijing Outstanding Young Scientist Program(Grant No.BJJWZYJH01201911414038)the Strategic Cooperation Technology Projects of CNPC and CUPB(Grant No.ZLZX2020-01).
文摘The Stinger PDC cutter has high rock-breaking efficiency and excellent impact and wear resistance, which can significantly increase the rate of penetration (ROP) and extend PDC bit life for drilling hard and abrasive formation. The knowledge of force response and mechanical specific energy (MSE) for the Stinger PDC cutter is of great importance for improving the cutter's performance and optimizing the hybrid PDC bit design. In this paper, 87 single cutter tests were conducted on the granite. A new method for precisely obtaining the rock broken volume was proposed. The influences of cutting depth, cutting angle, and cutting speed on cutting force and MSE were analyzed. Besides, a phenomenological cutting force model of the Stinger PDC cutter was established by regression of experimental data. Moreover, the surface topography and fracture morphology of the cutting groove and large size cuttings were measured by a 3D profilometer and a scanning electron microscope (SEM). Finally, the rock-breaking mechanism of the Stinger PDC cutter was illustrated. The results indicated that the cutting depth has the greatest influence on the cutting force and MSE, while the cutting speed has no obvious effects, especially at low cutting speeds. As the increase of cutting depth, the cutting force increases linearly, and MSE reduces with a quadratic polynomial relationship. When the cutting angle raises from 10° to 30°, the cutting force increases linearly, and the MSE firstly decreases and then increases. The optimal cutting angle for breaking rock is approximately 20°. The Stinger PDC cutter breaks granite mainly by high concentrated point loading and tensile failure, which can observably improve the rock breaking efficiency. The key findings of this work will help to reveal the rock-breaking mechanisms and optimize the cutter arrangement for the Stinger PDC cutter.
文摘When building geotechnical constructions like retaining walls and dams is of interest,one of the most important factors to consider is the soil’s shear strength parameters.This study makes an effort to propose a novel predictive model of shear strength.The study implements an extreme gradient boosting(XGBoost)technique coupled with a powerful optimization algorithm,the salp swarm algorithm(SSA),to predict the shear strength of various soils.To do this,a database consisting of 152 sets of data is prepared where the shear strength(τ)of the soil is considered as the model output and some soil index tests(e.g.,dry unit weight,water content,and plasticity index)are set as model inputs.Themodel is designed and tuned using both effective parameters of XGBoost and SSA,and themost accuratemodel is introduced in this study.Thepredictionperformanceof theSSA-XGBoostmodel is assessedbased on the coefficient of determination(R2)and variance account for(VAF).Overall,the obtained values of R^(2) and VAF(0.977 and 0.849)and(97.714%and 84.936%)for training and testing sets,respectively,confirm the workability of the developed model in forecasting the soil shear strength.To investigate the model generalization,the prediction performance of the model is tested for another 30 sets of data(validation data).The validation results(e.g.,R^(2) of 0.805)suggest the workability of the proposed model.Overall,findings suggest that when the shear strength of the soil cannot be determined directly,the proposed hybrid XGBoost-SSA model can be utilized to assess this parameter.
基金Supported by National Natural Science Foundation of China(Grant No.52275154)National Key Research and Development Project of China(Grant No.2016YFF0203005).
文摘To address the problem of conventional approaches for mechanical property determination requiring destructive sampling, which may be unsuitable for in-service structures, the authors proposed a method for determining the quasi-static fracture toughness and impact absorbed energy of ductile metals from spherical indentation tests (SITs). The stress status and damage mechanism of SIT, mode I fracture, Charpy impact tests, and related tests were frst investigated through fnite element (FE) calculations and scanning electron microscopy (SEM) observations, respectively. It was found that the damage mechanism of SITs is diferent from that of mode I fractures, while mode I fractures and Charpy impact tests share the same damage mechanism. Considering the diference between SIT and mode I fractures, uniaxial tension and pure shear were introduced to correlate SIT with mode I fractures. Based on this, the widely used critical indentation energy (CIE) model for fracture toughness determination using SITs was modifed. The quasi-static fracture toughness determined from the modifed CIE model was used to evaluate the impact absorbed energy using the dynamic fracture toughness and energy for crack initiation. The efectiveness of the newly proposed method was verifed through experiments on four types of steels: Q345R, SA508-3, 18MnMoNbR, and S30408.
基金performed at Geotechnical engineering lab,Indian Institute of Technology,Roorkee,India.Ministry of Human Resource Development,Government of India,New Delhi supported this work(Grant No.MHR 002).
文摘Most studies on liquefaction have addressed homogeneous soil strata using sand or sand with fine content without considering soil stratification.In this study,cyclic triaxial tests were conducted on the stratified sand specimens embedded with the silt layers to investigate the liquefaction failures and void-redistribution at confining stress of 100 kPa under stress-controlled mode.The loosening of underlying sand mass and hindrance to pore-water flow caused localized bulging at the sand-silt interface.It is observed that at a silt thickness of 0.2H(H is the height of the specimen),nearly 187 load cycles were required to attain liquefaction,which was the highest among all the silt thicknesses with a single silt layer.Therefore,0.2H is assumed as the optimum silt thickness(t_(opt)).The silt was placed at the top,middle and bottom of the specimen to understand the effect of silt layer location.Due to the increase in depth of the silt layer from the top position(capped soil state)to the bottom,the cycles to reach liquefaction(N_(cyc,L))increased 2.18 times.Also,when the number of silt layers increased from single to triple,there was an increase of about 880%in N_(cyc,L).The micro-characterization analysis of the soil specimens indicated silty materials transported in upper sections of the specimen due to the dissipated pore pressure.The main parameters,including thickness(t),location(z),cyclic stress ratio(CSR),number of silt layers(n)and modified relative density(D_(r,m)),performed significantly in governing the lique-faction resistance.For this,a multilinear regression model is developed based on critical parameters for prediction of N_(cyc,L).Furthermore,the developed constitutive model has been validated using the data from the present study and earlier findings.
文摘BACKGROUND Upper gastrointestinal(GI)bleeding is a life-threatening condition with high mortality rates.AIM To compare the performance of pre-endoscopic risk scores in predicting the following primary outcomes:In-hospital mortality,intervention(endoscopic or surgical)and length of admission(≥7 d).METHODS We performed a retrospective analysis of 363 patients presenting with upper GI bleeding from December 2020 to January 2021.We calculated and compared the area under the receiver operating characteristics curves(AUROCs)of Glasgow-Blatchford score(GBS),pre-endoscopic Rockall score(PERS),albumin,international normalized ratio,altered mental status,systolic blood pressure,age older than 65(AIMS65)and age,blood tests and comorbidities(ABC),including their optimal cut-off in variceal and non-variceal upper GI bleeding cohorts.We subsequently analyzed through a logistic binary regression model,if addition of lactate increased the score performance.RESULTS All scores had discriminative ability in predicting in-hospital mortality irrespective of study group.AIMS65 score had the best performance in the variceal bleeding group(AUROC=0.772;P<0.001),and ABC score(AUROC=0.775;P<0.001)in the non-variceal bleeding group.However,ABC score,at a cut-off value of 5.5,was the best predictor(AUROC=0.770,P=0.001)of inhospital mortality in both populations.PERS score was a good predictor for endoscopic treatment(AUC=0.604;P=0.046)in the variceal population,while GBS score,(AUROC=0.722;P=0.024),outperformed the other scores in predicting surgical intervention.Addition of lactate to AIMS65 score,increases by 5-fold the probability of in-hospital mortality(P<0.05)and by 12-fold if added to GBS score(P<0.003).No score proved to be a good predictor for length of admission.CONCLUSION ABC score is the most accurate in predicting in-hospital mortality in both mixed and non-variceal bleeding population.PERS and GBS should be used to determine need for endoscopic and surgical intervention,respectively.Lactate can be used as an additional tool to risk scores for predicting inhospital mortality.
文摘Choosing appropriate statistical tests is crucial but deciding which tests to use can be challenging. Different tests suit different types of data and research questions, so it is important to choose the right one. Knowing how to select an appropriate test can lead to more accurate results. Invalid results and misleading conclusions may be drawn from a study if an incorrect statistical test is used. Therefore, to avoid these it is essential to understand the nature of the data, the research question, and the assumptions of the tests before selecting one. This is because there are a wide variety of tests available. This paper provides a step-by-step approach to selecting the right statistical test for any study, with an explanation of when it is appropriate to use it and relevant examples of each statistical test. Furthermore, this guide provides a comprehensive overview of the assumptions of each test and what to do if these assumptions are violated.
文摘Choosing appropriate statistical tests is crucial but deciding which tests to use can be challenging. Different tests suit different types of data and research questions, so it is important to choose the right one. Knowing how to select an appropriate test can lead to more accurate results. Invalid results and misleading conclusions may be drawn from a study if an incorrect statistical test is used. Therefore, to avoid these it is essential to understand the nature of the data, the research question, and the assumptions of the tests before selecting one. This is because there are a wide variety of tests available. This paper provides a step-by-step approach to selecting the right statistical test for any study, with an explanation of when it is appropriate to use it and relevant examples of each statistical test. Furthermore, this guide provides a comprehensive overview of the assumptions of each test and what to do if these assumptions are violated.
文摘The engagement of students is a recognised challenge for teachers.Technology offers some practical student engagement tools,and this paper examines the use of low-stakes online tests and immediate dialogic feedback to improve behavioural engagement.The academic exploration of low-stakes tests and dialogic feedback has been extensive,and they are credible teaching tools.In this study,we explore the learning benefit of their combination.Postgraduate engineering students’self-reported and learning analytics data shows conclusive evidence of improved behavioural engagement.We measured a 500%increase in the Learning Management System(LMS)page views on the days when we ran the low-stakes tests(each worth 2%of the marks for the subject)and engaged in immediate dialogic feedback.To interpret these results,we draw on theories of behavioural engagement,low-stakes tests,and feedback.We conclude that the combination of low-stakes tests and immediate feedback improves student behavioural engagement.
基金the National Natural Science Foundation of China,51905084the Natural Science Foundation of Heilongjiang Province,YQ2021E002.
文摘Unlike most animals,plants fail to move bodily at will.However,movements also occur in every single part of plants out of energy and nutrients needs,spanning from milliseconds to hours on a time scale.And with the growing understanding of plant movement in the academic community,bionic soft robots based on plant movement principles are increasingly studied and are considered by scientists as a source of inspiration for innovative engineering solutions.In this paper,through the study of the biological morphology,microstructure,and motion mechanism of the flytrap,we developed chambered design rules,and designed and fabricated a gas-driven bionic flytrap blade,intending to investigate its feasibility of performing complex bending deformation.The experimental result shows that the bionic flytrap blade can achieve multi-dimensional bending deformation,and complete the bending and closing action within 2 s.The performance of the bionic flytrap blade fabricated is in high agreement with the real flytrap blade in terms of bending and deformation,achieving an excellent bionic design effect.In this study,the chambered design rules of the bionic flytrap blade were proposed and developed,and the possibility of its deformation was investigated.The effects of different chamber types and different flow channel design precepts on the bending deformation of the bionic flytrap blade were revealed,together with the relationship between the response time and flow rate of the bionic flytrap blade.At last,this study provides new ideas for the study of plant blade motion mechanism in a hope to expand the application fields of bionic robots,especially hope to offer solutions for plant-type robotics.
基金This research was supported by The Science,Research and Innovation Promotion Funding(TSRI)(Grant No.FRB650070/0168)This research block grants was managed under Rajamangala University of Technology Thanyaburi(FRB65E0634M.3).
文摘A novel adaptive multiple dependent state sampling plan(AMDSSP)was designed to inspect products from a continuous manufacturing process under the accelerated life test(ALT)using both double sampling plan(DSP)and multiple dependent state sampling plan(MDSSP)concepts.Under accelerated conditions,the lifetime of a product follows the Weibull distribution with a known shape parameter,while the scale parameter can be determined using the acceleration factor(AF).The Arrhenius model is used to estimate AF when the damaging process is temperature-sensitive.An economic design of the proposed sampling plan was also considered for the ALT.A genetic algorithm with nonlinear optimization was used to estimate optimal plan parameters to minimize the average sample number(ASN)and total cost of inspection(TC)under both producer’s and consumer’s risks.Numerical results are presented to support the AMDSSP for the ALT,while performance comparisons between the AMDSSP,the MDSSP and a single sampling plan(SSP)for the ALT are discussed.Results indicated that the AMDSSP was more flexible and efficient for ASN and TC than the MDSSP and SSP plans under accelerated conditions.The AMDSSP also had a higher operating characteristic(OC)curve than both the existing sampling plans.Two real datasets of electronic devices for the ALT at high temperatures demonstrated the practicality and usefulness of the proposed sampling plan.
文摘Objectives: The study aimed to determine the most appropriate hearing screening test to identify disabling hearing loss for adults aged 65 years or older.Methods: This study included 577 older adults. Four hearing screening tests were considered in the study, including the Hearing Handicap Inventory for Elderly Screening(HHIE-s), three single question tests, the whisper test, and the finger rub test. The sensitivity and specificity of these tests referenced to the hearing threshold of disabling hearing loss were estimated.Results: Among all tests, only the single self-perception question(0.7064 for sensitivity;0.7225 for specificity) and whisper test(0.7833 for sensitivity;0.7708 for specificity) could obtain both sensitivity and specificity higher than 70% for adults aged ≥65 years.Conclusion: Overall, we suggest using the whisper test to identify disabling hearing loss(>40 dB HL at the better ear) for adults aged 65 years or older. However, if the conditions do not permit, the single selfperception question is also acceptable. Moreover, HHIE-s might not be a good test to detect disabling hearing loss for adults aged 80 years or older.
基金The authors would like to acknowledge the support from the National Natural Science Foundation of China(No.52171274).
文摘Suction foundations are generally installed with negative pressures to overcome the resistance of soils and complete the penetration,but excessive negative pressures are also avoided to cause seepage damages.In this paper,the model test method was used to analyze the movement characteristics of multi-bucket foundations in the process of sinking in sand,and the common calculation methods of sinking resistances are verified.The critical negative pressure corresponding to the seepage failure of foundation was determined under the action of increasing negative pressure step by step and the characteristics of soil failure were studied.The calculation formula of critical suction in sand was verified in application,and according to the test results,the value of seepage coefficient was modified,which provides an example for the study of suction foundation in sand soils.
文摘Rock anchors are a common safety measure for stabilising large-scale infrastructure,such as bridge towers,retaining walls,rock slopes and windmills.There are four principal failure modes for rock anchors:(a)tensile failure of the steel anchor,(b)anchor-grout interface failure,(c)grout-rock interface failure,and(d)rock mass uplift.Field tests were performed in a limestone quarry.These tests were designed to test failure modes B and C through pullout.In the tests of failure mode B,the shear stress on the anchor-grout interface is the largest at the top of the grout column and attenuates towards the distal end for small loads.The shear stress becomes uniformly distributed when the applied load is approximately 50%of the ultimate pullout load.The anchors designed to test failure mode C were installed with an endplate and had a higher toughness than the straight bar anchors.The shear stress on the grout-rock interface is the largest at the endplate and attenuates upward before slip starts along the interface.When the ultimate pullout load is reached,and the grout column starts to slip,the shear stress is approximately constant.The bond shear strength on the anchor-grout interface was approximately 20%of the uniaxial compressive strength of the grout,and the bond strength of the grout-rock interface was around 5%for that of the grout.The grout-rock interface is likely determined by whichever is weaker,the grout or the rock.
文摘Lime-treatment of clayey soil significantly increases its shear and tensile strengths.Consequently,the tensile strength of lime-treated soils deserves careful investigation because it may provide an appreciable benefit for the stability of earth structures.This study investigates the tensile and shear strengths of an untreated and lime-treated(3%of lime)plastic clay at different curing times(7 d,56 d and 300 d),through triaxial tension and compression tests.Triaxial tension tests are performed using“diabolo-shaped”soil samples with reduced central section,such that the central part of the specimen can be under axial tension while both end-sections remain in axial compression.Consolidated undrained(CU)conditions with measurement of pore water pressure allow analyzing the failure conditions through effective stress and total stress approaches.The results of triaxial tension tests reveal that the failure occurs under tensile mode at low confining pressure while extensional shear failure mode is observed under higher confining pressure.Consequently,a classical Mohr-Coulomb shear failure criterion must be combined with a cut-off tensile strength criterion that is not affected by the confining pressure.When comparing shear failure under compression and tension,a slight anisotropy is observed.
基金The present work was supported by the National Natural Science Foundation of China(No.52008395).
文摘The unsupported sleeper can change the load characteristics of ballast particles and thus affect the dynamic stability of a ballasted bed.In this work,a laboratory test was constructed on a ballasted track containing unsupported sleepers.The ballasted track was excited by a wheelset,and the influence of unsupported sleepers on the dynamic stability of a ballasted bed was studied.The results show that the main frequency of the sleeper vibration appeared at 670 Hz,and the first-order rigid vibration mode at the frequency of 101 Hz had a significant effect on the condition without the unsupported sleeper.When the sleepers were continuously unsupported,the vibration damping effect of ballasted bed within the frequency range of 0–450 Hz was better than that at higher frequencies.Within the frequency range of 70–250 Hz,the vibration damping effect of the ballasted bed with unsupported sleepers was better than that without the unsupported sleeper.Owing to the excitation from the wheelset impact,the lateral resistance of the ballasted bed with unsupported sleepers whose hanging heights were 30,60,and 90 mm increased by 37.43%,12.25%,and 18.23%,respectively,while the lateral resistance of the ballasted bed without the unsupported sleeper remained basically unchanged.The unsupported sleeper could increase the difference in the quality of the ballasted bed between two adjacent sleepers.In addition,test results show that the hanging height of the unsupported sleeper had little effect on the lateral resistance of a ballasted bed without external excitation,but had an obvious effect on the rate of change of the lateral resistance of a ballasted bed and the acceleration amplitude of the sleeper vibration under the wheelset impact.
