Objective: to observe the practical effect of amoxicillin and clavulanate potassium plus tinidazole in the clinical treatment of infantile gastritis. Methods: 88 cases of infantile gastritis were included and divided ...Objective: to observe the practical effect of amoxicillin and clavulanate potassium plus tinidazole in the clinical treatment of infantile gastritis. Methods: 88 cases of infantile gastritis were included and divided into group ①: Control group and group ②: Observation group according to the "single and double number allocation of treatment number". Both groups were given amoxicillin and potassium clavulanate. On this basis, the observation group was given tinidazole. Results: the total effective rate and eradication rate of Hp in the observation group were higher than those in the control group (P < 0.05). After the implementation of various treatments, the clinical symptoms, gastric function index, inflammatory factor index and immune function index were all improved by horizontal measurement, and the change range in the observation group was larger (P < 0.05). There was no significant difference between the two groups (P > 0.05). Conclusion: the application of amoxicillin and clavulanate potassium combined with tinidazole in children with gastritis is more beneficial to improve the clinical total effective rate, eradication rate of helicobacter pylori (Hp), immune function, and promote the improvement of symptoms and gastric function, without increasing adverse reactions.展开更多
This paper focuses on a common problem for entrepreneurs and investors:the uncertainty around the actual tax rate,which is the percent of net income that a corporation pays in taxes.This uncertainty results from a dif...This paper focuses on a common problem for entrepreneurs and investors:the uncertainty around the actual tax rate,which is the percent of net income that a corporation pays in taxes.This uncertainty results from a difference(i.e.,a gap)between the statutory and the effective tax rate,which is the actual tax rate.This gap results from the legal framework which provides that certain types of incomes and expenses are not considered income.This gap causes significant uncertainty and may hinder entrepreneurship.This paper studies this gap in seven OECD countries(Austria,Canada,France,Germany,Italy,UK,and USA)and Brazil.We selected the 10 top-listed companies of each country and calculated the gaps for the period 2016-2019.Our findings proved that these gaps are unstable and may differ between companies of the same country and between countries.In addition,gaps of specific companies may change over time.The key outcome of this paper is the proposal of a new derivative tax rate swap.Using this derivative,governments will be able to eliminate the gap of specific companies,attract new investment,and increase entrepreneurship.展开更多
Natural cemented calcareous sand and limestone are highly complex and not well understood in terms of the me-chanical behavior due to the difficulty of obtaining undisturbed samples from far sea.This paper proposes an...Natural cemented calcareous sand and limestone are highly complex and not well understood in terms of the me-chanical behavior due to the difficulty of obtaining undisturbed samples from far sea.This paper proposes an artificial method in a laboratory setting using microbial-induced carbonate precipitation(MICP)to simulate the natural process of cementation of limestone.The artificially cemented sand has a high degree of similarity with the natural weakly limestone in three aspects:(1)the mineral composition of the cemented material is also granular calcite and acicular aragonite;(2)the microstructure in interconnected open pore network can be gradually closed and contracted with cementation.The porosity reaches to approximately 9.2%;(3)both the stress-strain relationship and the unconfined strength closely resemble that of natural weakly limestone.Furthermore,both static and dynamic behaviors of artificial limestone were studied by quasi-static compression tests and Split Hopkinson Pressure Bar(SHPB)tests,finding that the unconfined strength of weakly artifical limestone exponentially increases with increasing strain rate.A rate-dependent bond strength was proposed and implemented in software to reveal the mechanism of strain rate effects.It is found that the loading velocity is too high to keep in sync with the initiation and propagation of cracks under impact loading.This delay-induced viscosity may restrict the movement of the surrounding balls,thus increasing resistance.展开更多
It seems that an effective way of how to make the right choice of Various investment projects is based on the theory of average internal income rate, or the theory of weight-added internal income rate. With several ex...It seems that an effective way of how to make the right choice of Various investment projects is based on the theory of average internal income rate, or the theory of weight-added internal income rate. With several examples of numerical value, this paper proves that this method is not as effective as expected, but indirectly testifies that only with the principle of maximization of NPV that independent projects can be the best combination of projects with limited investment that is achieved.展开更多
The tensile properties and deformation mechanisms of the reduced activation ferritic/martensitic steel—China low activation martensitic(CLAM)steel are determined from tests carried out over a wider range of strain ra...The tensile properties and deformation mechanisms of the reduced activation ferritic/martensitic steel—China low activation martensitic(CLAM)steel are determined from tests carried out over a wider range of strain rate and temperature.During high-temperature deformation,the plastic deformation modes involve dynamic recrystallization(DRX)and dynamic recovery(DRV)processes,which govern the mechanical behaviors of CLAM steel under different loading conditions.This work systematically explored the effects of increasing strain rates and temperatures,finding that the microstructure evolution process is facilitated by nano-sized M_(23)C_(6)precipitates and the grain boundaries of the initial microstructure.Under quasi-static loading conditions,DRX grains preferentially nucleate around M_(23)C_(6) precipitates,and the dominant deformation mechanism is DRX.However,under dynamic loading conditions,the number of DRX grains decreases significantly,and the dominant deformation mechanism converts to DRV.It was concluded that the coupling effects of strain rates and temperatures strongly influence DRX and DRV processes,which ultimately determine the mechanical properties and microstructure evolution.Moreover,dynamic deformation at elevated temperatures achieves much finer grain sizes,offering a novel method for grain refinement through dynamic straining processes.展开更多
The plastic flow behaviors of AA6061-T4 sheets at different temperatures(21-300°C)and strain rates(0.002-4 s^(-1))were studied.Significant nonlinear effects of temperature and strain rate on flow behaviors were r...The plastic flow behaviors of AA6061-T4 sheets at different temperatures(21-300°C)and strain rates(0.002-4 s^(-1))were studied.Significant nonlinear effects of temperature and strain rate on flow behaviors were revealed,as well as underlying micromechanical factors.Phenomenology and machine learning-based constitutive models were developed.Both models were formulated in the framework of a temperature-dependent linear combination regulated by a transition function to capture the evolution of strain-hardening behavior with increasing temperature.Novel mathematical functions for describing temperature and strain rate sensitivities were formulated for the phenomenological constitutive model.The threshold temperature related to microstructure evolution was considered in the modeling.A data-enrichment strategy based on extrapolating experimental data via classical strain hardening laws was adopted to improve neural network training.An efficient inverse identification strategy,focusing solely on the transition function,was proposed to enhance the prediction accuracy of post-necking deformation by both constitutive models.展开更多
Objective:To investigate the effectiveness and efficiency of combining levamlodipine besylate and valsartan in the treatment of hypertension.Methods:This study selected 28 patients with hypertension as observation sub...Objective:To investigate the effectiveness and efficiency of combining levamlodipine besylate and valsartan in the treatment of hypertension.Methods:This study selected 28 patients with hypertension as observation subjects.The treatment duration ranged from January 2020 to June 2023.Using the random number table method,patients were divided into two groups.The control group received treatment with valsartan,while the observation group received a combination of valsartan and levamlodipine besylate.Therapeutic effects and safety were compared between the groups,and changes in the patient’s blood pressure and renal function index levels were assessed.Results:The total clinical effective rate of the observation group was significantly higher than that of the control group(P<0.05).The observation group demonstrated better diastolic blood pressure,systolic blood pressure,and renal function indicators compared to the control group(P<0.05).There was no significant difference in the incidence of adverse reactions between the two groups(P>0.05).Conclusion:The combined treatment of levamlodipine besylate and valsartan in patients with hypertension showed significant clinical efficacy and holds broad application value.展开更多
Objective: to discuss the curative effect of combined traditional Chinese and western medicine on recurrent oral ulcer. Methods: the data of 92 patients with recurrent oral ulcer were reviewed and randomly divided int...Objective: to discuss the curative effect of combined traditional Chinese and western medicine on recurrent oral ulcer. Methods: the data of 92 patients with recurrent oral ulcer were reviewed and randomly divided into two groups. Different treatment methods were used to compare the clinical effects. Results: the indexes of the study group were better than those of the control group (P < 0.05). Conclusion: combination of traditional Chinese and western medicine has significant effect on recurrent oral ulcer.展开更多
The advance speed of the working face in coal mines can significantly affect the fluctuation frequency of abutment pressure in front of the coal body.Moreover,it has a certain correlation with the change of axial load...The advance speed of the working face in coal mines can significantly affect the fluctuation frequency of abutment pressure in front of the coal body.Moreover,it has a certain correlation with the change of axial loading rate in coal and rock mechanics test.Therefore,uniaxial compression tests under various loading rates of 0.05,0.1,0.15,0.25,0.5 MPa/s were conducted using 2000 kN triaxial testing machine and PCI-2 acoustic emission test system to study the loading rate effect on the mechanical properties of deep sandstones.The results show that 1)the peak strength and elastic modulus of the deep sandstone increase with the loading rate increasing;2)with the loading rate increasing,the deep sandstone transforms from plastic-elastic-plastic to plastic-elastic and moreover,the failure mode gradually transfers from type I to type III;3)With the loading rate increasing,the total input strain energy,elastic strain energy,and dissipated strain energy generally increase;4)the damage variable presents the evolution characteristics of inverted“S”shape with time,and with the loading rate increasing,the damage degree of the deep sandstone is aggravated.The conclusion obtained can provide the theoretical basis for the stability control of the surrounding rock in deep engineering.展开更多
The seemingly contradictory understandings of the initial crush stress of cellular materials under dynamic loadings exist in the literature, and a comprehensive analysis of this issue is carried out with using direct ...The seemingly contradictory understandings of the initial crush stress of cellular materials under dynamic loadings exist in the literature, and a comprehensive analysis of this issue is carried out with using direct information of local stress and strain. Local stress/strain calculation methods are applied to determine the initial crush stresses and the strain rates at initial crush from a cell-based finite element model of irregular honeycomb under dynamic loadings. The initial crush stress under constant-velocity compression is identical to the quasi-static one, but less than the one under direct impact, i.e. the initial crush stresses under different dynamic loadings could be very different even though there is no strain-rate effect of matrix material. A power-law relation between the initial crush stress and the strain rate is explored to describe the strain-rate effect on the initial crush stress of irregular honeycomb when the local strain rate exceeds a critical value, below which there is no strain-rate effect of irregular honeycomb. Deformation mechanisms of the initial crush behavior under dynamic loadings are also explored.The deformation modes of the initial crush region in the front of plastic compaction wave are different under different dynamic loadings.展开更多
The code for calculating the crown effect rate of hot strip steel Was developed using the effect function method. The effect of the initial crown on the crown of the product in hot strip rolling was investigated. The ...The code for calculating the crown effect rate of hot strip steel Was developed using the effect function method. The effect of the initial crown on the crown of the product in hot strip rolling was investigated. The coefficients of a polynomial of degree six for calculating the base value of initial crown effect rate in 4-high mill were determined and the compensation factors of per unit width rolling force, bending force, work roll crown and draft on the initial crown effect rate were given. The difference between the calculation result by established model and theoretical value obtained by effect function method was 4.88 μm when the strip width was 1.85 m.展开更多
The controlling plastic deformation mechanisms(i.e.slip or twinning)and the structural crash performance of Mg alloys are strongly influenced by loading mode,texture and microstructure.This paper summarizes the main r...The controlling plastic deformation mechanisms(i.e.slip or twinning)and the structural crash performance of Mg alloys are strongly influenced by loading mode,texture and microstructure.This paper summarizes the main results from an experimental program to assess these effects for commercial Mg alloy extrusions(AM30 and AZ31),sheet(AZ31),and high pressure die castings(HPDC,AM50 and AM60).Uniaxial tensile and compressive tests were performed over a wide range of strain rate and temperature(i.e.0.00075–2800 s^(−1) and 100℃ to−150℃)using conventional servo-hydraulic and high-strain-rate universal test machines and a split-Hopkinson-bar(SHB)apparatus.In primarily-slip-dominant deformation,the true stress–strain curves showed approximate power-law behavior,and the effects of strain rate and temperature on yield strength could be approximately described by constitutive equations linearly dependent on the rate parameter,Tln(5.3×10^(7)/ɛ˙)where T is test temperature in Kelvin andɛ˙is strain rate in s^(−1).In primarily-twin-dominant deformation,the effects of strain rate and temperature on yield and initial flow stress were negligible or small from quasi-static to 2800 s^(−1) owing to the athermal characteristics of mechanical twinning;the effects may become more pronounced with exhaustion of twinning and increasing proportion of slip.展开更多
In this paper, numerical method is used als. A typical unit of masonry is selected to serve merical model of RVE is established with detailed to study the strain rate effect on masonry materias a representative volume...In this paper, numerical method is used als. A typical unit of masonry is selected to serve merical model of RVE is established with detailed to study the strain rate effect on masonry materias a representative volume element （RVE）. Nudistinctive modeling of brick and mortar with their respective dynamic material properties obtained from laboratory tests. The behavior of brick and mortar are characterized by a dynamic damage model that accounts for rate-sensitive and pressuredependent properties of masonry materials. Dynamic loads of different loading rates are applied to RVE. The equivalent homogenized uniaxial compressive strength, threshold strain and elastic modulus in three directions of the masonry are derived from the simulated responses of the RVE. The strain rate effect on the masonry material with clay brick and mortar, such as the dynamic increase factor （DIF） of the ultimate strength and elastic modulus as a function of strain rate are derived from the numerical results.展开更多
To study the dynamic properties of the concrete subjected to impulsive loading, stress-time curves of concrete in different velocities were measured using split Hopkinson pressure bar (SHPB).Effects of temperature and...To study the dynamic properties of the concrete subjected to impulsive loading, stress-time curves of concrete in different velocities were measured using split Hopkinson pressure bar (SHPB).Effects of temperature and strain rate on the dynamic yield strength and constitutive relation of the con-crete were analyzed. The dynamic mechanical properties of the reinforced concrete are subjected to high strain rates when it is at a relatively low temperature. But with temperature increasing, the temperature softening effect makes the strength of the concrete weaken and the impact toughness of the concrete is saliently relative to strain rate effect. So, strain rate effect, strain hardening and temperature softening work together on the dynamic mechanical capability of concrete and the relation between them is relatively complex.展开更多
Software for calculating the strip profile in 4-high hot rolling mill was developed using influence coefficient method. Regularity of backup roller diameter effect rate was studied systematically using the software. T...Software for calculating the strip profile in 4-high hot rolling mill was developed using influence coefficient method. Regularity of backup roller diameter effect rate was studied systematically using the software. The results show that backup roller diameter effect rates decrease versus the increase of strip width, increase significantly versus the increase of backup roller diameter and obscurely increase versus the increase of reduction. The difference between backup roller diameter effect rate and it is reference value increases versus strip width increasing. When backup rollers diameter is set to be 1.64 m and strip width is 1.85 m, the error of strip profile calculated using the model of backup roller diameter effect rate reference value will be 3.55μm. Based on the results, reference values of roller diameter effect rate and six power polynomial fitting coefficients of modification coefficients were determined considering coherent parameters. The high precision model of backup roller diameter effect rate was established. When the model is used to predict strip profile, the accuracy is less than 5.0 μm.展开更多
The influence of strain rate on the mechanics of particles is well documented.However,a comprehensive understanding of the strain rate effect on calcareous particles,particularly in the transition from static to dynam...The influence of strain rate on the mechanics of particles is well documented.However,a comprehensive understanding of the strain rate effect on calcareous particles,particularly in the transition from static to dynamic loading,is still lacking in current literature.This study conducted 720 quasi-static and impact tests on irregular calcareous particles to investigate the macroscopic strain rate effect,and performed numerical simulations on spherical particles to explore the underlying microscopic mechanisms.The strain rate effect on the characteristic particle strength was found to exhibit three regimes:in Regime 1,the particle strength gradually improves when the strain rate is lower than approximately 10^(2)s^(-1);in Regime 2,the particle strength sharply enhances when the strain rate increases from 10^(2)s^(-1)to 10^(4)s^(-1);and in Regime 3,the particle strength remains almost constant when the strain rate is higher than 10^(4)s^(-1).The three-regime strain rate effect is an inherent property of the material and independent of particle shape.The asynchrony between loading and deformation plays a dominant role in these behaviors,leading to a thermoactivation-dominated effect in Regime 1,a macroscopic viscosity-dominated effect in Regime 2,and a combined thermoactivation and macroscopic viscosity-dominated effect in Regime 3.These mechanisms induce a transition in the failure mode from splitting to exploding and then smashing,which increases the energy required to rupture a single bond and,consequently,enhances the particle strength.展开更多
Based on the structural characteristics of the high-speed loading tester,a four-point bending test device was designed to carry out the four-point bending strength test of glass under the action of static load and dif...Based on the structural characteristics of the high-speed loading tester,a four-point bending test device was designed to carry out the four-point bending strength test of glass under the action of static load and different impact velocities,and the formulae for calculating the maximum dynamic stress and strain rate of glass specimens under the action of impact loads were derived.The experimental results show that the bending strength values of the glass under dynamic impact loading are all higher than those under static loading.With the increase of impact speed,the bending strength value of glass specimens generally tends to increase,and the bending strength value increases more obviously when the impact speed exceeds 0.5 m/s or higher.By increasing the impact velocity,higher tensile strain rate of glass specimens can be obtained because the load action time becomes shorter.The bending strength of the glass material increases with its tensile strain rate,and when the tensile strain rate is between 0 and 2 s^(-1),the bending strength of the glass specimen grows more obviously with the strain rate,indicating that the glass bending strength is particularly sensitive to the tensile strain rate in this interval.As the strain rate increases,the number of cracks formed after glass breakage increases significantly,thus requiring more energy to drive the crack formation and expansion,and showing the strain rate effect of bending strength at the macroscopic level.The results of the study can provide a reference for the load bearing and structural design of glass materials under dynamic loading.展开更多
Rocks are heterogeneous from the point of dynamic failure behavior. Both the compressive and microstructure which is of significance to their tensile strength of rock-like materials is regarded different from the stat...Rocks are heterogeneous from the point of dynamic failure behavior. Both the compressive and microstructure which is of significance to their tensile strength of rock-like materials is regarded different from the static strength. The present study adopts smoothed particle hydrodynamics （SPH） which is a virtual particle based meshfree method to investigate strain rate effect for heterogeneous brittle materials. The SPH method is capable of simulating rock fracture, free of the mesh constraint of the traditional FEM and FDM models. A pressure dependent J-H constitutive model involving heterogeneity is employed in the numerical modeling. The results show the compressive strength increases with the increase of strain rate as well as the tensile strength, which is important to the engineering design.展开更多
The effects of 1 Me V electron irradiation in air at a fixed accumulated dose and dose rates of 393.8,196.9,78.8,and 39.4 Gy s^(-1)on a shape memory epoxy(SMEP)resin were studied.Under low-dose-rate irradiation,accele...The effects of 1 Me V electron irradiation in air at a fixed accumulated dose and dose rates of 393.8,196.9,78.8,and 39.4 Gy s^(-1)on a shape memory epoxy(SMEP)resin were studied.Under low-dose-rate irradiation,accelerated degradation of the shape memory performance was observed;specifically,the shape recovery ratio decreased exponentially with increasing irradiation time(that is,with decreasing dose rate).In addition,the glass transition temperature of the SMEP,as measured by dynamic mechanical analysis,decreased overall with decreasing dose rate.The dose rate effects of 1 Me V electron irradiation on the SMEP were confirmed by structural analysis using electron paramagnetic resonance(EPR)spectroscopy and Fourier transform infrared(FTIR)spectroscopy.The EPR spectra showed that the concentration of free radicals increased exponentially with increasing irradiation time.Moreover,the FTIR spectra showed higher intensities of the peaks at 1660 and 1720 cm^(-1),which are attributed to stretching vibrations of amide C=O and ketone/acid C=O,at lower dose rates.The intensities of the IR peaks at 1660 and 1720 cm^(-1) increased exponentially with increasing irradiation time,and the relative intensity of the IR peak at 2926 cm^(-1)decreased exponentially with increasing irradiation time.The solid-state13 C nuclear magnetic resonance(NMR)spectra of the SMEP before and after 1 Me V electron irradiation at a dose of 1970 k Gy and a dose rate of 78.8 Gy s^(-1) indicated damage to the CH_(2)–N groups and aliphatic isopropanol segment.This result is consistent with the detection of nitrogenous free radicals,a phenoxy-type free radical,and several types of pyrolytic carbon radicals by EPR.During the subsequent propagation process,the free radicals produced at lower dose rates were more likely to react with oxygen,which was present at higher concentrations,and form the more destructive peroxy free radicals and oxidation products such as acids,amides,and ketones.The increase in peroxy free radicals at lower dose rates was thought to accelerate the degradation of the macroscopic performance of the SMEP.展开更多
Partial drainage often occurs during piezocone penetration testing on Yellow River Delta silt because of its intermediate physical and mechanical properties between those of sand and clay.Yet,there is no accurate unde...Partial drainage often occurs during piezocone penetration testing on Yellow River Delta silt because of its intermediate physical and mechanical properties between those of sand and clay.Yet,there is no accurate understanding for the range of penetra-tion rates to trigger the partial drainage of silt soils.In order to fully investigate cone penetration rate effects under partial drainage condi-tions,indoor 1 g penetration model tests and numerical simulations of cavity expansion at variable penetration rates were carried out on the Yellow River Delta silt.The boundary effect of the model tests and the variation of key parameters at the different cavity ex-pansion rates were analyzed.The 1 g penetration model test results and numerical simulations results consistently indicated that the penetration rate to trigger the partially drainage of typical silt varied at least three orders of magnitude.The numerical simulations also provide the reference values for the penetration resistance corresponding to zero dilation and zero viscosity at any given normalized penetration rate for silt in Yellow River Delta.These geotechnical properties can be used for the design of offshore platforms in Yel-low River Delta,and the understanding of cone penetration rate effects under the partially drained conditions would provide some technical support for geohazard evaluation of offshore platforms.展开更多
文摘Objective: to observe the practical effect of amoxicillin and clavulanate potassium plus tinidazole in the clinical treatment of infantile gastritis. Methods: 88 cases of infantile gastritis were included and divided into group ①: Control group and group ②: Observation group according to the "single and double number allocation of treatment number". Both groups were given amoxicillin and potassium clavulanate. On this basis, the observation group was given tinidazole. Results: the total effective rate and eradication rate of Hp in the observation group were higher than those in the control group (P < 0.05). After the implementation of various treatments, the clinical symptoms, gastric function index, inflammatory factor index and immune function index were all improved by horizontal measurement, and the change range in the observation group was larger (P < 0.05). There was no significant difference between the two groups (P > 0.05). Conclusion: the application of amoxicillin and clavulanate potassium combined with tinidazole in children with gastritis is more beneficial to improve the clinical total effective rate, eradication rate of helicobacter pylori (Hp), immune function, and promote the improvement of symptoms and gastric function, without increasing adverse reactions.
文摘This paper focuses on a common problem for entrepreneurs and investors:the uncertainty around the actual tax rate,which is the percent of net income that a corporation pays in taxes.This uncertainty results from a difference(i.e.,a gap)between the statutory and the effective tax rate,which is the actual tax rate.This gap results from the legal framework which provides that certain types of incomes and expenses are not considered income.This gap causes significant uncertainty and may hinder entrepreneurship.This paper studies this gap in seven OECD countries(Austria,Canada,France,Germany,Italy,UK,and USA)and Brazil.We selected the 10 top-listed companies of each country and calculated the gaps for the period 2016-2019.Our findings proved that these gaps are unstable and may differ between companies of the same country and between countries.In addition,gaps of specific companies may change over time.The key outcome of this paper is the proposal of a new derivative tax rate swap.Using this derivative,governments will be able to eliminate the gap of specific companies,attract new investment,and increase entrepreneurship.
基金The authors would like to acknowledge the support of the National Natural Science Foundation of China(No.52279097,No.51779264)Blue and Green Project of Jiangsu Province.
文摘Natural cemented calcareous sand and limestone are highly complex and not well understood in terms of the me-chanical behavior due to the difficulty of obtaining undisturbed samples from far sea.This paper proposes an artificial method in a laboratory setting using microbial-induced carbonate precipitation(MICP)to simulate the natural process of cementation of limestone.The artificially cemented sand has a high degree of similarity with the natural weakly limestone in three aspects:(1)the mineral composition of the cemented material is also granular calcite and acicular aragonite;(2)the microstructure in interconnected open pore network can be gradually closed and contracted with cementation.The porosity reaches to approximately 9.2%;(3)both the stress-strain relationship and the unconfined strength closely resemble that of natural weakly limestone.Furthermore,both static and dynamic behaviors of artificial limestone were studied by quasi-static compression tests and Split Hopkinson Pressure Bar(SHPB)tests,finding that the unconfined strength of weakly artifical limestone exponentially increases with increasing strain rate.A rate-dependent bond strength was proposed and implemented in software to reveal the mechanism of strain rate effects.It is found that the loading velocity is too high to keep in sync with the initiation and propagation of cracks under impact loading.This delay-induced viscosity may restrict the movement of the surrounding balls,thus increasing resistance.
文摘It seems that an effective way of how to make the right choice of Various investment projects is based on the theory of average internal income rate, or the theory of weight-added internal income rate. With several examples of numerical value, this paper proves that this method is not as effective as expected, but indirectly testifies that only with the principle of maximization of NPV that independent projects can be the best combination of projects with limited investment that is achieved.
基金financially supported by National Natural Science Foundation of China(Grant Nos.12025205 and 12141203)Natural Science Basic Research Program of Shaanxi(Program No.S2023-JC-QN-0614)Fund for Basic Research(No.2021T019)from the Analytical&Testing Center of Northwestern Polytechnical University.
文摘The tensile properties and deformation mechanisms of the reduced activation ferritic/martensitic steel—China low activation martensitic(CLAM)steel are determined from tests carried out over a wider range of strain rate and temperature.During high-temperature deformation,the plastic deformation modes involve dynamic recrystallization(DRX)and dynamic recovery(DRV)processes,which govern the mechanical behaviors of CLAM steel under different loading conditions.This work systematically explored the effects of increasing strain rates and temperatures,finding that the microstructure evolution process is facilitated by nano-sized M_(23)C_(6)precipitates and the grain boundaries of the initial microstructure.Under quasi-static loading conditions,DRX grains preferentially nucleate around M_(23)C_(6) precipitates,and the dominant deformation mechanism is DRX.However,under dynamic loading conditions,the number of DRX grains decreases significantly,and the dominant deformation mechanism converts to DRV.It was concluded that the coupling effects of strain rates and temperatures strongly influence DRX and DRV processes,which ultimately determine the mechanical properties and microstructure evolution.Moreover,dynamic deformation at elevated temperatures achieves much finer grain sizes,offering a novel method for grain refinement through dynamic straining processes.
文摘The plastic flow behaviors of AA6061-T4 sheets at different temperatures(21-300°C)and strain rates(0.002-4 s^(-1))were studied.Significant nonlinear effects of temperature and strain rate on flow behaviors were revealed,as well as underlying micromechanical factors.Phenomenology and machine learning-based constitutive models were developed.Both models were formulated in the framework of a temperature-dependent linear combination regulated by a transition function to capture the evolution of strain-hardening behavior with increasing temperature.Novel mathematical functions for describing temperature and strain rate sensitivities were formulated for the phenomenological constitutive model.The threshold temperature related to microstructure evolution was considered in the modeling.A data-enrichment strategy based on extrapolating experimental data via classical strain hardening laws was adopted to improve neural network training.An efficient inverse identification strategy,focusing solely on the transition function,was proposed to enhance the prediction accuracy of post-necking deformation by both constitutive models.
文摘Objective:To investigate the effectiveness and efficiency of combining levamlodipine besylate and valsartan in the treatment of hypertension.Methods:This study selected 28 patients with hypertension as observation subjects.The treatment duration ranged from January 2020 to June 2023.Using the random number table method,patients were divided into two groups.The control group received treatment with valsartan,while the observation group received a combination of valsartan and levamlodipine besylate.Therapeutic effects and safety were compared between the groups,and changes in the patient’s blood pressure and renal function index levels were assessed.Results:The total clinical effective rate of the observation group was significantly higher than that of the control group(P<0.05).The observation group demonstrated better diastolic blood pressure,systolic blood pressure,and renal function indicators compared to the control group(P<0.05).There was no significant difference in the incidence of adverse reactions between the two groups(P>0.05).Conclusion:The combined treatment of levamlodipine besylate and valsartan in patients with hypertension showed significant clinical efficacy and holds broad application value.
文摘Objective: to discuss the curative effect of combined traditional Chinese and western medicine on recurrent oral ulcer. Methods: the data of 92 patients with recurrent oral ulcer were reviewed and randomly divided into two groups. Different treatment methods were used to compare the clinical effects. Results: the indexes of the study group were better than those of the control group (P < 0.05). Conclusion: combination of traditional Chinese and western medicine has significant effect on recurrent oral ulcer.
基金Projects(52034009, 51974319) supported by the National Natural Science Foundation of ChinaProject(2020JCB01)supported by the Yue Qi Distinguished Scholar Project of China。
文摘The advance speed of the working face in coal mines can significantly affect the fluctuation frequency of abutment pressure in front of the coal body.Moreover,it has a certain correlation with the change of axial loading rate in coal and rock mechanics test.Therefore,uniaxial compression tests under various loading rates of 0.05,0.1,0.15,0.25,0.5 MPa/s were conducted using 2000 kN triaxial testing machine and PCI-2 acoustic emission test system to study the loading rate effect on the mechanical properties of deep sandstones.The results show that 1)the peak strength and elastic modulus of the deep sandstone increase with the loading rate increasing;2)with the loading rate increasing,the deep sandstone transforms from plastic-elastic-plastic to plastic-elastic and moreover,the failure mode gradually transfers from type I to type III;3)With the loading rate increasing,the total input strain energy,elastic strain energy,and dissipated strain energy generally increase;4)the damage variable presents the evolution characteristics of inverted“S”shape with time,and with the loading rate increasing,the damage degree of the deep sandstone is aggravated.The conclusion obtained can provide the theoretical basis for the stability control of the surrounding rock in deep engineering.
基金supported by the National Natural Science Foundation of China (Grants 11372308, 11372307)the Fundamental Research Funds for the Central Universities (Grant WK2480000001)
文摘The seemingly contradictory understandings of the initial crush stress of cellular materials under dynamic loadings exist in the literature, and a comprehensive analysis of this issue is carried out with using direct information of local stress and strain. Local stress/strain calculation methods are applied to determine the initial crush stresses and the strain rates at initial crush from a cell-based finite element model of irregular honeycomb under dynamic loadings. The initial crush stress under constant-velocity compression is identical to the quasi-static one, but less than the one under direct impact, i.e. the initial crush stresses under different dynamic loadings could be very different even though there is no strain-rate effect of matrix material. A power-law relation between the initial crush stress and the strain rate is explored to describe the strain-rate effect on the initial crush stress of irregular honeycomb when the local strain rate exceeds a critical value, below which there is no strain-rate effect of irregular honeycomb. Deformation mechanisms of the initial crush behavior under dynamic loadings are also explored.The deformation modes of the initial crush region in the front of plastic compaction wave are different under different dynamic loadings.
基金This study was financially supported by the National Nat-ural Science Foundation of China under grant No.59995440the State Key Development Programming Research under grant No.G2000027208-4the Natural Science Foundar tion of Liaoning Province under grant No.2001101021.
文摘The code for calculating the crown effect rate of hot strip steel Was developed using the effect function method. The effect of the initial crown on the crown of the product in hot strip rolling was investigated. The coefficients of a polynomial of degree six for calculating the base value of initial crown effect rate in 4-high mill were determined and the compensation factors of per unit width rolling force, bending force, work roll crown and draft on the initial crown effect rate were given. The difference between the calculation result by established model and theoretical value obtained by effect function method was 4.88 μm when the strip width was 1.85 m.
基金This work is part of the crashworthiness R&D task of an on-going Canada-China-US Magnesium Front-End Research and Development(MFERD)project.The Canadian task is funded by the CCT&I and ASM-NGV programs,Govemment of Canada.
文摘The controlling plastic deformation mechanisms(i.e.slip or twinning)and the structural crash performance of Mg alloys are strongly influenced by loading mode,texture and microstructure.This paper summarizes the main results from an experimental program to assess these effects for commercial Mg alloy extrusions(AM30 and AZ31),sheet(AZ31),and high pressure die castings(HPDC,AM50 and AM60).Uniaxial tensile and compressive tests were performed over a wide range of strain rate and temperature(i.e.0.00075–2800 s^(−1) and 100℃ to−150℃)using conventional servo-hydraulic and high-strain-rate universal test machines and a split-Hopkinson-bar(SHB)apparatus.In primarily-slip-dominant deformation,the true stress–strain curves showed approximate power-law behavior,and the effects of strain rate and temperature on yield strength could be approximately described by constitutive equations linearly dependent on the rate parameter,Tln(5.3×10^(7)/ɛ˙)where T is test temperature in Kelvin andɛ˙is strain rate in s^(−1).In primarily-twin-dominant deformation,the effects of strain rate and temperature on yield and initial flow stress were negligible or small from quasi-static to 2800 s^(−1) owing to the athermal characteristics of mechanical twinning;the effects may become more pronounced with exhaustion of twinning and increasing proportion of slip.
基金Supported by Australia Research Council(No.DP0451966)
文摘In this paper, numerical method is used als. A typical unit of masonry is selected to serve merical model of RVE is established with detailed to study the strain rate effect on masonry materias a representative volume element （RVE）. Nudistinctive modeling of brick and mortar with their respective dynamic material properties obtained from laboratory tests. The behavior of brick and mortar are characterized by a dynamic damage model that accounts for rate-sensitive and pressuredependent properties of masonry materials. Dynamic loads of different loading rates are applied to RVE. The equivalent homogenized uniaxial compressive strength, threshold strain and elastic modulus in three directions of the masonry are derived from the simulated responses of the RVE. The strain rate effect on the masonry material with clay brick and mortar, such as the dynamic increase factor （DIF） of the ultimate strength and elastic modulus as a function of strain rate are derived from the numerical results.
基金Supported by National Natural Science Foundation of China(No.10602048)
文摘To study the dynamic properties of the concrete subjected to impulsive loading, stress-time curves of concrete in different velocities were measured using split Hopkinson pressure bar (SHPB).Effects of temperature and strain rate on the dynamic yield strength and constitutive relation of the con-crete were analyzed. The dynamic mechanical properties of the reinforced concrete are subjected to high strain rates when it is at a relatively low temperature. But with temperature increasing, the temperature softening effect makes the strength of the concrete weaken and the impact toughness of the concrete is saliently relative to strain rate effect. So, strain rate effect, strain hardening and temperature softening work together on the dynamic mechanical capability of concrete and the relation between them is relatively complex.
基金the National Natu-ral Science Foundation of China,under the contract No.59995440the State Key Development Prograrmming Research under the contract No.G2000027208-4 the Natural Science Foundation ofLiaoning Province,under the contract No.2001101021.
文摘Software for calculating the strip profile in 4-high hot rolling mill was developed using influence coefficient method. Regularity of backup roller diameter effect rate was studied systematically using the software. The results show that backup roller diameter effect rates decrease versus the increase of strip width, increase significantly versus the increase of backup roller diameter and obscurely increase versus the increase of reduction. The difference between backup roller diameter effect rate and it is reference value increases versus strip width increasing. When backup rollers diameter is set to be 1.64 m and strip width is 1.85 m, the error of strip profile calculated using the model of backup roller diameter effect rate reference value will be 3.55μm. Based on the results, reference values of roller diameter effect rate and six power polynomial fitting coefficients of modification coefficients were determined considering coherent parameters. The high precision model of backup roller diameter effect rate was established. When the model is used to predict strip profile, the accuracy is less than 5.0 μm.
基金support of the National Natural Science Foundation of China(Grant Nos.52279097 and 51779264)the China Scholarships Council(Grant No.202306710072)and Blue and Green Project of Jiangsu Province.
文摘The influence of strain rate on the mechanics of particles is well documented.However,a comprehensive understanding of the strain rate effect on calcareous particles,particularly in the transition from static to dynamic loading,is still lacking in current literature.This study conducted 720 quasi-static and impact tests on irregular calcareous particles to investigate the macroscopic strain rate effect,and performed numerical simulations on spherical particles to explore the underlying microscopic mechanisms.The strain rate effect on the characteristic particle strength was found to exhibit three regimes:in Regime 1,the particle strength gradually improves when the strain rate is lower than approximately 10^(2)s^(-1);in Regime 2,the particle strength sharply enhances when the strain rate increases from 10^(2)s^(-1)to 10^(4)s^(-1);and in Regime 3,the particle strength remains almost constant when the strain rate is higher than 10^(4)s^(-1).The three-regime strain rate effect is an inherent property of the material and independent of particle shape.The asynchrony between loading and deformation plays a dominant role in these behaviors,leading to a thermoactivation-dominated effect in Regime 1,a macroscopic viscosity-dominated effect in Regime 2,and a combined thermoactivation and macroscopic viscosity-dominated effect in Regime 3.These mechanisms induce a transition in the failure mode from splitting to exploding and then smashing,which increases the energy required to rupture a single bond and,consequently,enhances the particle strength.
基金Found by the National Natural Science Foundation of China(Nos.52072356 and 52032011)the Shandong Province Science and Technology Small and Medium-sized Enterprises Innovation Ability Improvement Project(No.2022TSGC1194)。
文摘Based on the structural characteristics of the high-speed loading tester,a four-point bending test device was designed to carry out the four-point bending strength test of glass under the action of static load and different impact velocities,and the formulae for calculating the maximum dynamic stress and strain rate of glass specimens under the action of impact loads were derived.The experimental results show that the bending strength values of the glass under dynamic impact loading are all higher than those under static loading.With the increase of impact speed,the bending strength value of glass specimens generally tends to increase,and the bending strength value increases more obviously when the impact speed exceeds 0.5 m/s or higher.By increasing the impact velocity,higher tensile strain rate of glass specimens can be obtained because the load action time becomes shorter.The bending strength of the glass material increases with its tensile strain rate,and when the tensile strain rate is between 0 and 2 s^(-1),the bending strength of the glass specimen grows more obviously with the strain rate,indicating that the glass bending strength is particularly sensitive to the tensile strain rate in this interval.As the strain rate increases,the number of cracks formed after glass breakage increases significantly,thus requiring more energy to drive the crack formation and expansion,and showing the strain rate effect of bending strength at the macroscopic level.The results of the study can provide a reference for the load bearing and structural design of glass materials under dynamic loading.
文摘Rocks are heterogeneous from the point of dynamic failure behavior. Both the compressive and microstructure which is of significance to their tensile strength of rock-like materials is regarded different from the static strength. The present study adopts smoothed particle hydrodynamics （SPH） which is a virtual particle based meshfree method to investigate strain rate effect for heterogeneous brittle materials. The SPH method is capable of simulating rock fracture, free of the mesh constraint of the traditional FEM and FDM models. A pressure dependent J-H constitutive model involving heterogeneity is employed in the numerical modeling. The results show the compressive strength increases with the increase of strain rate as well as the tensile strength, which is important to the engineering design.
基金support of the 111 Project(No.B18017)the National Equipment Pre-Research Project of the 13th Five-Year Plan(No.30508040601)。
文摘The effects of 1 Me V electron irradiation in air at a fixed accumulated dose and dose rates of 393.8,196.9,78.8,and 39.4 Gy s^(-1)on a shape memory epoxy(SMEP)resin were studied.Under low-dose-rate irradiation,accelerated degradation of the shape memory performance was observed;specifically,the shape recovery ratio decreased exponentially with increasing irradiation time(that is,with decreasing dose rate).In addition,the glass transition temperature of the SMEP,as measured by dynamic mechanical analysis,decreased overall with decreasing dose rate.The dose rate effects of 1 Me V electron irradiation on the SMEP were confirmed by structural analysis using electron paramagnetic resonance(EPR)spectroscopy and Fourier transform infrared(FTIR)spectroscopy.The EPR spectra showed that the concentration of free radicals increased exponentially with increasing irradiation time.Moreover,the FTIR spectra showed higher intensities of the peaks at 1660 and 1720 cm^(-1),which are attributed to stretching vibrations of amide C=O and ketone/acid C=O,at lower dose rates.The intensities of the IR peaks at 1660 and 1720 cm^(-1) increased exponentially with increasing irradiation time,and the relative intensity of the IR peak at 2926 cm^(-1)decreased exponentially with increasing irradiation time.The solid-state13 C nuclear magnetic resonance(NMR)spectra of the SMEP before and after 1 Me V electron irradiation at a dose of 1970 k Gy and a dose rate of 78.8 Gy s^(-1) indicated damage to the CH_(2)–N groups and aliphatic isopropanol segment.This result is consistent with the detection of nitrogenous free radicals,a phenoxy-type free radical,and several types of pyrolytic carbon radicals by EPR.During the subsequent propagation process,the free radicals produced at lower dose rates were more likely to react with oxygen,which was present at higher concentrations,and form the more destructive peroxy free radicals and oxidation products such as acids,amides,and ketones.The increase in peroxy free radicals at lower dose rates was thought to accelerate the degradation of the macroscopic performance of the SMEP.
基金supported by the National Natural Science Foundation of China(Nos.U1806230,U2006213),and the Fundamental Research Funds for the Central Univer-sities(No.201962011).
文摘Partial drainage often occurs during piezocone penetration testing on Yellow River Delta silt because of its intermediate physical and mechanical properties between those of sand and clay.Yet,there is no accurate understanding for the range of penetra-tion rates to trigger the partial drainage of silt soils.In order to fully investigate cone penetration rate effects under partial drainage condi-tions,indoor 1 g penetration model tests and numerical simulations of cavity expansion at variable penetration rates were carried out on the Yellow River Delta silt.The boundary effect of the model tests and the variation of key parameters at the different cavity ex-pansion rates were analyzed.The 1 g penetration model test results and numerical simulations results consistently indicated that the penetration rate to trigger the partially drainage of typical silt varied at least three orders of magnitude.The numerical simulations also provide the reference values for the penetration resistance corresponding to zero dilation and zero viscosity at any given normalized penetration rate for silt in Yellow River Delta.These geotechnical properties can be used for the design of offshore platforms in Yel-low River Delta,and the understanding of cone penetration rate effects under the partially drained conditions would provide some technical support for geohazard evaluation of offshore platforms.
