Effect of slow shot speed on externally solidified crystal,porosity and tensile property in a newly developed high-pressure die-cast Al-Si alloy

The effect of slow shot speed on externally solidified crystal(ESC),porosity and tensile property in a newly developed high-pressure die-cast Al-Si alloy was investigated by optical microscopy(OM),scanning electron microscopy(SEM)and laboratory computed tomography(CT).Results showed that the newly developed AlSi9MnMoV alloy exhibited improved mechanical properties when compared to the AlSi10MnMg alloy.The AlSi9MnMoV alloy,which was designed with trace multicomponent additions,displays a notable grain refining effect in comparison to the AlSi10MnMg alloy.Refining elements Ti,Zr,V,Nb,B promote heterogeneous nucleation and reduce the grain size of primaryα-Al.At a lower slow shot speed,the large ESCs are easier to form and gather,developing into the dendrite net and net-shrinkage.With an increase in slow shot speed,the size and number of ESCs and porosities significantly reduce.In addition,the distribution of ESCs is more dispersed and the net-shrinkage disappears.The tensile property is greatly improved by adopting a higher slow shot speed.The ultimate tensile strength is enhanced from 260.31 MPa to 290.31 MPa(increased by 11.52%),and the elongation is enhanced from 3.72%to 6.34%(increased by 70.52%).

An externally perceivable smart leaky-wave antenna based on spoof surface plasmon polaritons

Smart antennas have received great attention for their potentials to enable communication and perception functions at the same time.However,realizing the function synthesis remains an open challenge,and most existing system solutions are limited to narrow operating bands and high complexity and cost.Here,we propose an externally perceivable leakywave antenna(LWA)based on spoof surface plasmon polaritons(SSPPs),which can realize adaptive real-time switching between the“radiating”and“non-radiating”states and beam tracking at different frequencies.With the assistance of computer vision,the smart SSPP-LWA is able to detect the external target user or jammer,and intelligently track the target by self-adjusting the operating frequency.The proposed scheme helps to reduce the power consumption through dynamically controlling the radiating state of the antenna,and improve spectrum utilization and avoid spectrum conflicts through intelligently deciding the radiating frequency.On the other hand,it is also helpful for the physical layer communication security through switching the antenna working state according to the presence of the target and target beam tracking in real time.In addition,the proposed smart antenna can be generalized to other metamaterial systems and could be a candidate for synaesthesia integration in future smart antenna systems.

Effect of Manufacturing Errors on Static Characteristics of Externally Pressurized Spherical Air Bearings

Externally pressurized spherical air bearings are the key component of the three-axis air bearing table, and the manufacturing errors of the bearing affects the performance of the air bearing table. However, the manufacturing errors are unavoidable, and the pursuit to enhance the manufacturing accuracy will increase the cost greatly. In order to provide some theoretical guideline for the tolerance choice in the design of the externally pressurized spherical air bearings with inherent compensation, the effects of several manufacturing errors on the static characteristics of the air bearing are studied. Due to the complex geometry of the computational domain, an unstructured meshing technology is used for mesh generation. A finite-volume method is adopted to discretize the three-dimensional steady-state compressible Navier-Stokes equations. A modified SIMPLE algorithm which is suitable for compressible flows is applied to solve the discretized governing equations. The effects of the dimension error and the roundness error of the ball head and the ball socket on the static characteristics are investigated. The investigation result shows that the positive dimension error and the oblate spheroid-type roundness error of the ball head as well as the negative dimension error and the prolate spheroid-type roundness error of the ball socket can improve the bearing capacity and static stiffness of the air bearings by reducing the mass flow. The calculation method proposed in this paper fits well for the general principle, which can be extended to the characteristics analysis of other air bearings.

Theoretical analysis of natural frequency of externally prestressed concrete beam based on rigidity correction

A dynamic test on externally prestressed simply supported concrete beams separately with three typical types of tendon distributions was conducted. The results show that the natural frequencies of the beams increase with the increase in the prestressing force at the tensioning stage, and the natural frequencies decrease after the cracks occur in the beams. Following the calculation formula of natural frequency of externally prestressed beam, which was reported in a literature, the natural frequencies of the experimental beams are calculated, and big errors are found between the test results and the calculated ones of natural frequency values. As a result, this paper has tried to adopt two methods to correct the rigidity parameter of the concrete beam in the formula for natural frequency calculation, and to use the corrected formula to calculate the frequencies of the experimental beams. The calculation results indicate a good consistency with the experimental ones, which verifies the feasibility of the corrected formula.

Effects of process parameters on morphology and distribution of externally solidified crystals in microstructure of magnesium alloy die castings

During the cold-chamber high pressure die casting(HPDC) process, samples were produced to investigate the microstructure characteristics of AM60B magnesium alloy. Special attention was paid to the effects of process parameters on the morphology and distribution of externally solidified crystals(ESCs) in the microstructure of magnesium alloy die castings, such as slow shot phase plunger velocity, delay time of pouring and fast shot phase plunger velocity. On the basis of metallographic observation and quantitative statistics, it is concluded that a lower slow shot phase plunger velocity and a longer delay time of pouring both lead to an increment of the size and percentage of the ESCs, due to the fact that a longer holding time of the melt in the shot sleeve will cause a more severe loss of the superheat. The impingement of the melt flow on the ESCs is more intensive with a higher fast shot phase plunger velocity, in such case the ESCs reveal a more granular and roundish morphology and are dispersed throughout the cross section of the castings. Based on analysis of the filling and solidification processes of the melt during the HPDC process, reasonable explanations were proposed in terms of the nucleation, growth, remelting and fragmentation of the ESCs to interpret the effects of process parameters on the morphology and distribution of the ESCs in the microstructure of magnesium alloy die castings.

The detrimental effect of autofrettage on externally cracked modern tank gun barrels

Overstraining gun tubes has a twofold advantage. First, it enables the increase of the Safe Maximum Pressure(SMP) in the tube, resulting in a higher muzzle velocity which extends the gun's range and its projectile kinetic energy. Second, it reduces the tube's susceptibility to internal cracking which prolongs its fatigue life. Unfortunately, autofrettage also bears an inherent detrimental effect as it considerably increases the tensile hoop stress at the outer portion of the barrel's wall, which enhances external cracking of the tube by increasing the prevailing Stress Intensity Factor(SIF). In order to quantify this disadvantageous effect, 3-D Mode I SIFs distributions along the front of a single external radial semielliptical crack initiating from the outer surface of an autofrettaged modern gun barrel, overstrained by either the Swage or the Hydraulic autofrettage processes, are evaluated. The analysis is performed by the finite element(FE) method, using singular elements along the crack front. Innovative residual stress fields(RSFs), incorporating the Bauschinger effect for both types of autofrettage are applied to the barrel.Hill's [1] RSF is also applied to the tube for comparison reasons. All three RSFs are incorporated in the FE analysis, using equivalent temperature fields, Values for K_(IA)-the SIF resulting from the tensile residual stresses induced by autofrettage are evaluated for: a typical barrel of radii ratio R_o/R_i = 2, crack depth to wall-thickness ratios(a/t = 0.005-0.1),crack ellipticities(a/c = 0.2-1.0),and five levels of Swage,Hydraulic and Hill's autofrettage(e = 40%,60%,70%,80%,and 100%). In total,375 different 3-D cases are analyzed. The analysis demonstrates undoubtedly the detrimental effect of all types of autofrettage in increasing the prevailing effective stress intensity factor of external cracks, resulting in crack initiation enhancement and crack growth rate acceleration which considerably shortens the total fatigue life of the barrel. Nonetheless, the detrimental effect is autofrettage-type dependent. Swage and Hydraulic autofrettage RSFs differ substantially from each other. The disadvantageous effect of Swage autofrettage is much greater than that resulting from Hydraulic autofrettage. The results also emphasize the significance of the Bauschinger effect and the importance of the 3-D analysis.

The use of traditional Chinese medicine internally and externally combined with auricular acupuncture point bloodletting in the treatment of vulvar leukoplakia

Vulvar leukoplakia refers to the chronic disease of degeneration and hypopigmentation of the skin and mucous membrane of the vulva with unbearable itching in women, seriously affecting the quality of life. The main treatment of western medicine for vulvar leukoplakia is the external use of glucocorticoids or estrogen, resulting to the high recurrence rate and side effects. Traditional Chinese medicine (TCM) has the characteristics of the overall concept and dialectical treatment with a variety of ways. Literature review in recent years found that the treatment of TCM decoction combined with external therapies, such as external fumigation, acupuncture and other treatments, or the combination of TCM decoction and external western medicine hormone ointment, can obtain good effects in vulvar leukoplakia. During the clinical practice, we found that the use of TCM internally and externally combined with auricular acupuncture point bloodletting was highly effective with unique advantages in the treatment of vulvar leukoplakia, providing the ideas guidance for clinicians.

The Effects of Externally Paced Exercise on Executive Function and Stress in College-Aged Students

Purpose The purpose of the study was to investigate the acute effect of a beginner martial art class and aerobic exercise on executive function(EF)in college-aged young adults.There is overwhelming evidence that demonstrates acute as well as long-term aerobic exercise improves EF.Nevertheless,there is limited research comparing externally paced exercise(EPE)to self-paced exercise(SPE)such as walking on improving EF.EPE requires greater cortical demand than SPE to execute a motor plan.Methods Eight men and eight women,aged 24.2±2.8 years,participated in a Repeated Measures Crossover Design.Pre-and post-testing of EF with the Stroop and Tower of London(ToL)and stress level were measured after each of the two 1-h conditions:the SPE consisted of a walk(aerobic exercise)and the EPE was a beginner martial art class.Results There were significant main effects for the martial art class for the Stroop’s mean reaction time for congruent trials(P=0.01)with a large-effect size.The mean reaction time for incongruent trials was significant(P=0.05)with a medium-effect size.The ToL’s mean solution time(P=0.003)and mean execution time(P=0.002)were also significant with large-effect sizes.Stress levels were not significantly improved following either condition.Conclusion The martial art class significantly improved all the major domains of EF,while aerobic exercise of a similar intensity did not demonstrate any measured significant changes.The physiological benefits of physical exercise are well documented;however,the cognitive enhancing capability of EPE should also be appreciated given the results of this study.

Mechanical Performance of Bio-inspired Bidirectional Corrugated Sandwich Pressure Shell Under External Hydrostatic Pressure

This paper aims to enhance the compression capacity of underwater cylindrical shells by adopting the corrugated sandwich structure of cuttlebone.The cuttlebone suffers uniaxial external compression,while underwater cylindrical shells are in a biaxial compressive stress state.To suit the biaxial compressive stress state,a novel bidirectional corrugated sandwich structure is proposed to improve the bearing capacity of cylindrical shells.The static and buckling analysis for the sandwich shell and the unstiffened cylindrical shell with the same volume-weight ratio are studied by numerical simulation.It is indicated that the proposed sandwich shell can effectively reduce the ratio between circumferential and axial stress from 2 to 1.25 and improve the critical buckling load by about 1.63 times.Numerical simulation shows that optimizing and adjusting the structural parameters could significantly improve the advantage of the sandwich shell.Then,the hydrostatic pressure tests for shell models fabricated by 3D printing are carried out.According to the experimental results,the overall failure position of the sandwich shell is at the center part of the sandwich shell.It has been found the average critical load of the proposed sandwich shell models exceeds two times that of the unstiffened shell models.Hence,the proposed bio-inspired bidirectional corrugated sandwich structure can significantly enhance the pressure resistance capability of cylindrical shells.

Regional Climate Effects of Internally and Externally Mixed Aerosols over China

A regional climate model is employed to simulate the aerosols （dust, sulfate, black carbon, and organic carbon） and their direct effect on the climate over China. The emphasis is on the direct radiative forcing due to the change in mixing state of aerosols. The results show that direct radiative forcing is significantly different between externally and internally mixed aerosols. At the top of the atmosphere （TOA）, the radiative forcing of externally mixed aerosols is larger than that of internally mixed ones, especially in the Tarim desert region where the difference is about 0.7 W m-2. At the surface, however, the situation becomes opposite, especially in the Sichuan basin where the difference is about 1.4 W m-2. Nonetheless, either externally or internally mixed aerosols in China can result in a significant cooling effect, except for the warming in South China in winter and the slight warming in North China in February. The cooling effect induced by externally mixed aerosols is weaker than that induced by internally mixed aerosols, and this is more obvious in spring and winter than in summer and autumn. In spring and summer, the inhibiting effect of externally mixed aerosols on precipitation is less than that of internally mixed aerosols, whereas in autumn and winter the difference is not obvious.

Impacts of Internally and Externally Mixed Anthropogenic Sulfate and Carbonaceous Aerosols on East Asian Climate

A coupled regional climate and aerosol-chemistry model, RIEMS 2.0 （Regional Integrated Environmental Model System for Asia）, in which anthropogenic sulfate, black carbon, and organic carbon were assumed to be externally mixed （EM）, internally mixed （IM） or partially internally mixed （IEM）, was used to simulate the impacts of these anthropogenic aerosols on East Asian climate for the entire year of 2006. The distributions of aerosol mass concentration, radiative forcing and hence the surface air temperature and precipitation variations under three mixing assumptions of aerosols were analyzed. The results indicated that the mass concentration of sulfate was sensitive to mixing assumptions, but carbonaceous aerosols were much less sensitive to the mixing types. Modeled results were compared with observations in a variety of sites in East Asia. It was found that the simulated concentrations of sulfate and carbonaceous aerosols were in accord with the observations in terms of magnitude. The simulated aerosol concentrations in IM case were closest to observation results. The regional average column burdens of sulfate, black carbon, and organic carbon, if internally mixed, were 11.49, 0.47, and 2.17 mg m 2 , respectively. The radiative forcing of anthropogenic aerosols at the top of the atmosphere increased from –1.27 （EM） to –1.97 W m 2 （IM） while the normalized radiative forcing （NRF） decreased from –0.145 （EM） to –0.139 W mg 1 （IM）. The radiative forcing and NRF were –1.82 W m 2 and –0.141 W mg 1 for IEM, respectively. The surface air temperature changes over the domain due to the anthropogenic sulfate and carbonaceous aerosols were –0.067, –0.078, and –0.072 K, with maxima of –0.47, –0.50, and –0.49 K, for EM, IM, and IEM, respectively. Meanwhile, the annual precipitation variations were –8.0 （EM）, –20.6 （IM）, and –21.9 mm （IEM）, with maxima of 148, 122, and 102 mm, respectively, indicating that the climate effects were stronger if the sulfate and carbonaceous aerosols were internally mixed.

Discovery of the Significant Impacts of Swell Propagation on Global Wave Climate Change

This study compared the differences in the wave climate in the South China Sea and North Indian Ocean under these two datasets:ERA-40 wave reanalysis and Mei’s hindcast wave data.In the numerical calculation of regional ocean waves,the wave climate characteristics exhibited significant bias if the influence of external swells(swells from afar)was not fully considered,which may provide an incorrect basis for global climate change analysis.1)The trends of the significant wave height(SWH)obtained from the two datasets showed significant differences,such as those of the Bay of Bengal and the Java Sea in June-July-August.For the past 45 years,SWH from ERA-40(SWH-ERA)exhibited a significant annual increase in low-latitude waters of the North Indian Ocean(0.2-0.6 cm yr^(-1))and South China Sea(0.2-0.8 cm yr^(-1)).2)In the Bay of Bengal,the SWH-ERA in each month was generally 0.5 m higher than the SWH from Mei’s hindcast wave data(SWH-Mei)and can reach 1.0 m higher in some months.3)In the Bay of Bengal,SWH-ERA and SWH-Mei increased significantly at annual rates of 0.13 and 0.27 cm yr^(-1),respectively.This increasing trend was mainly reflected after 1978.SWH-ERA showed a trough in 1975(1.33 m)and a crest in 1992(1.83 m),which were not reflected in SWH-Mei.

Effect of external magnetic field on the instability of THz plasma waves in nanoscale graphene field-effect transistors

The instability of plasma waves in the channel of field-effect transistors will cause the electromagnetic waves with THz frequency.Based on a self-consistent quantum hydrodynamic model,the instability of THz plasmas waves in the channel of graphene field-effect transistors has been investigated with external magnetic field and quantum effects.We analyzed the influence of weak magnetic fields,quantum effects,device size,and temperature on the instability of plasma waves under asymmetric boundary conditions numerically.The results show that the magnetic fields,quantum effects,and the thickness of the dielectric layer between the gate and the channel can increase the radiation frequency.Additionally,we observed that increase in temperature leads to a decrease in both oscillation frequency and instability increment.The numerical results and accompanying images obtained from our simulations provide support for the above conclusions.

Transient Experiments on a Prototype Pump with an Atypical Open Impeller for Different Discharge Valve Openings

In order to obtain the transient characteristics of a low-speed centrifugal pump during the start-up and shutdown stages,dedicated experimental tests were conducted with eight different valve opening conditions.The Pearson correlation coefficient was used to reveal the linear correlation between variables.According to the results,the stable rotational speed decreases with increasing valve opening(rotational speed decreases from approximately 1472 to 1453 r/min),while the stable shaft power exhibits an increasing trend(shaft power increases from approximately 0.242 to 0.390 kW).The stable time and zeroing time of each parameter during start-up and shutdown processes vary,with the flow zeroing time significantly increasing with the relative flow,reaching up to 10.468 s,while the shaft power zeroing time is roughly between 1.219 and 1.375 s.The results demonstrate that with increasing valve opening,the stable and zeroing time of flow significantly increase(|r|greater than 0.95),while the stable and zeroing time of rotational speed,power,and head display a smaller sensitivity on the valve opening(|r|less than 0.6).

Experimental Analysis of Radial Centrifugal Pump Shutdown

Centrifugal pumps are widely used in the metallurgy,coal,and building sectors.In order to study the hydraulic characteristics of a closed impeller centrifugal pump during its shutdown in the so-called power frequency and frequency conversion modes,experiments were carried to determine the characteristic evolution of parameters such as speed,inlet and outlet pressure,head,flow rate and shaft power.A quasi-steady-state method was also used to further investigate these transient behaviors.The results show that,compared to the power frequency input,the performance parameter curves for the frequency conversion input are less volatile and smoother.The characteristic time is longer and the response to shutdown is slower.The quasi-steady-state theoretical head-flow curves match the experimental head-flow curves more closely at low flow rates when the frequency conversion input is considered.Moreover,in this case,the similarity law predicts the hydraulic performance more accurately.

Magneto-optical Kerr Effect of Mono-layer NiX_(2)(X=Cl,Br,I):A Density Functional Theory Study

The full-potential linearized augmented plane wave plus local orbital method is utilized for exploring the electronic,magnetic,and magneto-optical properties of the NiX_(2)(X=Cl,Br,and I)single layer.The first-principles calculation demonstrates that these compounds are ferromagnetic indirect semiconductors,and the energy band gaps of NiX_(2)for X=Cl,Br,and I are 3.888,3.134,and 2.157 eV,respectively.The magnetic moments of Ni atoms in NiX_(2)monolayer are 1.656,1.588,1.449μB,and their magneto-crystalline anisotropy energies are 0.167,0.029,0.090 meV,respectively.Based on the macro-linear response theory,we systematically studied the influences of the external magnetic field and out-of-plane strain on the magneto-optical Kerr effect(MOKE)spectrum of the NiX_(2)single layer.It is found that,when the external magnetic field is perpendicular to the sample plane,the value of the Kerr rotation angle reaches the maximum,and the single-layer NiI_(2)material has a Kerr rotation angle of 1.89°at the photon energy of 1.986 eV.Besides,the Kerr rotation spectrum of NiCl_(2)and NiBr_(2)monolayers redshift as the out-of-plane strain increases,while NiI_(2)monolayer blueshifts.Accurate computation of the MOKE spectrum of NiX_(2)materials provides an opportunity for applications of 2D magnetic material ranging from sensing to data storing.

Comparison of the effect of different external electrodes on discharge plasma-assisted diffusion flame stabilization

To optimize the design of plasma injectors,the influence of different external electrodes on plasma-assisted flame stabilization was assessed by using a nonequilibrium plasma injector flame control setup.The electrical characteristics of the injector,flame structure parameters,flame intensity,discharge power,and cost-to-effectiveness ratio under different external electrodes(four mesh electrodes and one copper foil electrode)were analyzed using electrical and optical methods.The results show that reducing the mesh size of the external electrode leads to a decrease in breakdown voltage.Compared with a ceramic dielectric barrier-based injector,an injector with a quartz dielectric barrier produces a higher breakdown voltage under the same conditions.For the same actuation voltage,the discharge current increases as the mesh size of the external electrode decreases,and combustion is enhanced by the discharge plasma;therefore,it is better to adopt a smaller mesh hole size to realize good flame stabilization under a lower actuation voltage.However,under the studied working conditions,reducing the mesh hole size of the external electrode increases the cost-to-effectiveness ratio of plasma injector-based flame stabilization.Thus,considering the cost-to-effectiveness ratio and the weight of the injector,an external electrode with a larger mesh hole size should be chosen,which contradicts the above rule.

Effects of vacancy and external electric field on the electronic properties of the MoSi_(2)N_(4)/graphene heterostructure

Recently,the newly synthesized septuple-atomic layer two-dimensional(2D)material MoSi_(2)N_(4)(MSN)has attracted attention worldwide.Our work delves into the effect of vacancies and external electric fields on the electronic properties of the MSN/graphene(Gr)heterostructure using first-principles calculation.We find that four types of defective structures,N-in,N-out,Si and Mo vacancy defects of monolayer MSN and MSN/Gr heterostructure are stable in air.Moreover,vacancy defects can effectively modulate the charge transfer at the interface of the MSN/Gr heterostructure as well as the work function of the pristine monolayer MSN and MSN/Gr heterostructure.Finally,the application of an external electric field enables the dynamic switching between n-type and p-type Schottky contacts.Our work may offer the possibility of exceeding the capabilities of conventional Schottky diodes based on MSN/Gr heterostructures.

Smoothed-Particle Hydrodynamics Simulation of Ship Motion and Tank Sloshing under the Effect of Regular Waves

Predicting the response of liquefied natural gas(LNG)contained in vessels subjected to external waves is extremely important to ensure the safety of the transportation process.In this study,the coupled behavior due to ship motion and liquid tank sloshing has been simulated by the Smoothed-Particle Hydrodynamics(SPH)method.Firstly,the sloshing flow in a rectangular tank was simulated and the related loads were analyzed to verify and validate the accuracy of the present SPH solver.Then,a three-dimensional simplified LNG carrier model,including two prismatic liquid tanks and a wave tank,was introduced.Different conditions were examined corresponding to different wave lengths,wave heights,wave heading angles,and tank loading rates.Finally,the effects of liquid tank loading rate on LNG ship motions and sloshing loading were analyzed,thereby showing that the SPH method can effectively provide useful indications for the design of liquid cargo ships.

An Investigation of Moxibustion Treatment for Abscesses in the Song Dynasty:Focusing on the“Jiu Ai Tu”

Jiu Ai Tu(The Moxa Treatment)from the Song dynasty is the earliest surviving painting that focuses on the subject of acupuncture and moxibustion.This paper takes the medical activities depicted in the artwork as its research object and systematically analyzes the external treatment methods for abscesses during the Song dynasty reflected in Jiu Ai Tu.By examining the understanding of abscesses during that period,the paper explores the level of development in external medicine techniques.By analyzing the medical awareness and behaviors of patients when facing such severe illnesses,it aims to explore the societal cognition and experiences regarding health and disease.The paper attempts to present the folk medical ecology of the Song dynasty represented by Jiu Ai Tu.