Dynamic transformation above the A_(e3) in a 0.06%C low carbon steel

A 0.06%C low carbon steel was deformed in torsion over the temperature range 877-917℃in a 2% H_2 - Ar gas atmosphere.Strains of 0.25 -5.0 were applied at strain rates ofε= 0.04 s^(-1) andε= 0.4 s^(-1) to study the formation of ferrite by dynamic transformation(DT) at temperatures above the A_(e3).The critical strain for ferrite formation by DT was aboutε= 0.2 and its volume fraction increased with strain and decreased with temperature above the A_(e3).Average ferrite grain sizes of 1.5μm to 5μm were produced,which decreased with strain rate.At the lower strain rate(ε= 0.04 s^(-1)) reverse transformation(RT) took place during deformation once an incubation time of about 40 s,was exceeded.An increase in strain rate fromε= 0.04 s^(-1) toε= 0.4 s^(-1) arrested RT during testing at all temperatures as the total test times did not exceed 13 s.The present work shows that DT is favored at higher strain rates by increasing the driving force(i.e.stored energy ) and by suppressing RT.

Relationship between β→α dynamic transformation and dynamic recrystallization under thermomechanical coupling in Ti-5Al-5Mo-5V-1Cr-1Fe alloy

The thermal simulation compression tests of near-β titanium alloy Ti-5Al-5Mo-5V-1Cr-1Fe were per-formed within the range of deformation temperatures of 710-860 ℃ and strain rates of 0.001-1 s^(-1).Based on electron backscatter diffraction(EBSD)characterization and analysis technology,the inter-action between dynamic phase transformation(DPT)of β-to-α and dynamic recrystallization(DRX)under thermal-mechanical coupling is deeply and systematically explored.We clarify the effects of temperatures and strain rates on the orientation relationship during dynamic precipitation of α-phase within β grain interiors possessing special orientation.The results show that the intragranular α-phase precipitated on the subgrain boundaries near {001}β with a high degree of dynamic recovery(DRV)deviates more from Burgers Orientation Relationship(BOR)than the α-phase that precipitates near{111}βas temperature increases.The proportion of α-phase precipitated by strain-induced on β recrys-tallized equiaxed grains for the deviating angle from BOR(θBoR)in the range of 20°-30° increases to 40%with the increase of strain rates below 800 ℃.In addition,the α-phase is dynamically precipitated on the grain boundaries with {110}β orientation,which undergoes continuous dynamic recrystallization(CDRX),exhibiting epitaxial recrystallization,namely {110}β//{0001 }α.Furthermore,the morphology of grain boundaries α phase(αGBs)precipitated by strain-induced phase transformation(SIPT)on specific types of β grain boundaries(βGBs),as well as the crystallographic orientation relationship and variant selection effect between adjacent α-variant within β grains are elucidated.The orientation relationships between α variants in {111}β grain are related with each other by 50°-60°/<-12-10>and 60°-70°/<-48-43>rotation.The"necklace"αGBs of recrystallization exhibit mainly the rotation of 50°-70° around the<2-310>zone axis,while the adjacent α-variant in the grain interiors is mainly 60° or 90°/<12-30>.In summary,the study has contributed to a deeper understanding of the deformation behavior and DPT laws of β-to-αp in near-β titanium alloy,which lays a foundation for the optimization of the hot deformation process and mechanical properties.

Cryo-EM structures reveal the dynamic transformation of human alpha-2-macroglobulin working as a protease inhibitor

Human alpha-2-macroglobulin is a well-known inhibitor of a broad spectrum of proteases and plays important roles in immunity,inflammation,and infections.Here,we report the cryo-EM structures of human alpha-2-macroglobulin in its native state,induced state transformed by its authentic substrate,human trypsin,and serial intermediate states between the native and fully induced states.These structures exhibit distinct conformations,which reveal the dynamic transformation of alpha-2-macroglobulin that acts as a protease inhibitor.The results shed light on the molecular mechanism of alpha-2-macroglobulin in entrapping substrates.

NANOSCALE CUTTING OF MONOCRYSTALLINE SILICON USING MOLECULAR DYNAMICS SIMULATION

It has been found that the brittle material, monocrystalline silicon, can be machined in ductile mode in nanoscale cutting when the tool cutting edge radius is reduced to nanoscale and the undeformed chip thickness is smaller than the tool edge radius. In order to better understand the mechanism of ductile mode cutting of silicon, the molecular dynamics （MD） method is employed to simulate the nanoscale cutting of monocrystalline silicon. The simulated variation of the cutting forces with the tool cutting edge radius is compared with the cutting force results from experimental cutting tests and they show a good agreement. The results also indicate that there is silicon phase transformation from monocrystalline to amorphous in the chip formation zone that can be used to explain the cause of ductile mode cutting. Moreover, from the simulated stress results, the two necessary conditions of ductile mode cutting, the tool cutting edge radius are reduced to nanoscale and the undeformed chip thickness should be smaller than the tool cutting edge radius, have been explained.

Fast speedometer identification in dynamic scene based on phase correlation

Speedometer identification has been researched for many years.The common approaches to that problem are usually based on image subtraction,which does not adapt to image offsets caused by camera vibration.To cope with the rapidity,robust and accurate requirements of this kind of work in dynamic scene,a fast speedometer identification algorithm is proposed,it utilizes phase correlation method based on regional entire template translation to estimate the offset between images.In order to effectively reduce unnecessary computation and false detection rate,an improved linear Hough transform method with two optimization strategies is presented for pointer line detection.Based on VC＋＋ 6.0 software platform with OpenCV library,the algorithm performance under experiments has shown that it celerity and precision.

Dynamic Rheological Behavior of Low Water-to-binder Ratio Mortars under Large Amplitude Oscillatory Shear(LAOS)

This work focuses on the dynamic rheological behavior of low water-to-binder ratio cement mortars blended with fly ash microspheres（FAM） or silica fume（SF）. The initial slump flow of each group has been controlled at similar values by adjusting the superplasticizer dosages. With the help of a coaxial cylinder rheometer, the dynamic rheological behaviors of these mortars are investigated by frequency sweeping in the range of 0-2 Hz under large amplitude oscillatory shear（LAOS）. Based on the systematical elaboration of dynamic rheological testing theory, the experimental data are processed according to Lissajous plot fitting to reveal the viscoelastic characteristics. The nonlinearity of response signals is further assessed with Fourier transform（FT） analysis. The parameters, storage modulus G＇, loss modulus G＂ and relative amplitude I3/I1 are proposed to clarify the influences of FAM and SF on the stability and energy consumption of local structures and nonlinearity of response torques. The hydration characteristics of various groups well confirmed the rheological phenomenon. This study is beneficial for the preparation and optimization of flow state concrete such as pumping concrete and self-compacting concrete.

An efficient technique for recovering responses of parameterized structural dynamic problems

In this article,an effective technique is developed to efficiently obtain the output responses of parameterized structural dynamic problems.This technique is based on the conception of reduced basis method and the usage of linear interpolation principle.The original problem is projected onto the reduced basis space by linear interpolation projection,and subsequently an associated interpolation matrix is generated.To ensure the largest nonsingularity,the interpolation matrix needs to go through a timenode choosing process,which is developed by applying the angle of vector spaces.As a part of this technique,error estimation is recommended for achieving the computational error bound.To ensure the successful performance of this technique,the offline-online computational procedures are conducted in practical engineering.Two numerical examples demonstrate the accuracy and efficiency of the presented method.

Formation of adiabatic shearing band for high-strength Ti-5553 alloy:A dramatic thermoplastic microstructural evolution

By using split Hopkinson pressure bar, optical microscopy and electronic microscopy, we investigate the influence of initial microstructures on the adiabatic shear behavior of high-strength Ti-5Al-5V-5Mo-3Cr(Ti-5553) alloy with lamellar microstructure and bimodal microstructure. Lamellar alloy tends to form adiabatic shearing band(ASB) at low compression strain, while bimodal alloy is considerably ASBresistant. Comparing with the initial microstructure of Ti-5553 alloy, we find that the microstructure of the ASB changes dramatically. Adiabatic shear of lamellar Ti-5553 alloy not only results in the formation of recrystallized β nano-grains within the ASB, but also leads to the chemical redistribution of the alloying elements such as Al, V, Cr and Mo. As a result, the alloying elements distribute evenly in the ASB.In contrast, the dramatic adiabatic shear of bimodal alloy might give rise to the complete lamination of the globular primary a grain and the equiaxial prior β grain, which is accompanied by the dynamic recrystallization of a lamellae and β lamellae. As a result, ASB of bimodal alloy is composed of a/β nanomultilayers. Chemical redistribution does not occur in ASB of bimodal alloy. Bimodal Ti-5553 alloy should be a promising candidate for high performance armors with high mass efficiency due to the processes high dynamic flow stress and excellent ASB-resistance.

Carbene-catalyzed activation of cyclopropylcarbaldehydes for mannich reaction andδ-lactam formation:remote enantioselecitvity control and dynamic kinetic asymmetric transformation

An N-heterocyclic carbene(NHC)-catalyzed enantioselective Mannich reaction of the remoteγ-carbon of cyclopropylcarbaldehydes is disclosed for the first time.Diastereo-and enantiomerically enriched multicyclicδ-lactam compound is afforded as the main product from 8 possible stereo-specific isomers through dynamic kinetic asymmetric transformation(DYKAT)processes.Multiple chiral functional molecules can be afforded from the lactam products through simple protocols with retentions of the optical purities.

Characterizations of Dynamic Strain-induced Transformation in Low Carbon Steel

Dynamic strain-induced transformation of the low carbon steel Q（235） at 770℃ and 850℃ leads to fine ferrite grains. The microstructure characterization and mechanism of the fine ferrite grain were studied by scanning electron microscopy （SEM）, transmission electron microscopy （TEM） and electron backscattered diffraction （EBSD） technique. The results show that strain-induced microstructure is the mixed microstructure of ferrite and pearlite, with cementite randomly distributed on ferrite grain boundaries and the grains interiors. EBSD images of grain boundaries demonstrate that high angle grain boundaries （HAGBs） are dominant in both of the deformation induced microstructures occurring below and above A（e3） , with only a few low angle grain boundaries （LAGBs） existing in the grain interiors. It implies that the dynamic strain-induced transformation （DSIT） happens above and below A（e3） temperature and has the same phase transition mechanisms. The refinement of ferrite is the cooperative effect of DSIT and continuous dynamic recrystallization （CDRX） of ferrite. Besides, DSIT is deemed as an incomplete carbon diffusion phase transition through the analysis of microstructure and the previous simulated results. The strengths of the Q（235） steel with refined ferrite and pearlite structure get doubled than the initial state without treated by DSIT and the residual stress in the refined structure is partly responsible for the ductility loss.

Oscillation criteria for second order neutral dynamic equations of Emden-Fowler type with positive and negative coefficients on time scales

We investigate oscillation of certain second order neutral dynamic equations of Emden-Fowler type with positive and negative coefficients. We use some different techniques and apply Riccati transformation to establish new oscillatory criteria which include two necessary and sufficient conditions. Moreover, we point out that how the power γ plays its role. Some interesting examples are given to illustrate the versatility of our results.

Experimental realization of a switchable filter based on a dynamically transformable array

We introduce a geometrically reconfigurable metasurface whose artificial ＂atoms＂ will reorient within unit ceils in response to a thermal stimulus in the microwave spectrum. It can alternate between two contrasting behaviors under different temperatures and serve as a switchable filter that allows the incident energy to be selectively transmitted or reflected with an excess of 10 dB isolation at certain frequencies for both polarizations. The ex- perimental results are consistent with the theoretical simulations, verifying the availability of an innovative method for manipulating electromagnetic waves with the merits of higher controllability for dynamic behavior and greater flexibility in the design process.

Microstructure Evolving Behaviors of Undercooled Ultrafine Austenite Grains During Deformation

Samples with ultrafine grained austenite were prepared by repetitive rapid heating and quenching for three times and were used to investigate the dynamic microstructural evolving behaviors at different temperatures. A sim- ultaneous development of dynamic straiminduced transformation （DSIT） and austenite grain growth was detected at the deformation temperatures above At3 , while only DSIT happened as the deformation proceeded at lower temperatures close to and below At3. In addition, a reverse ferrite-to-austenite transformation was also observed. Most of the strain induced ferrite nucleated on the boundaries of ultrafine prior austenite grains, especially at the corners and no evidence about intragranular nucleus was obviously obtained.

Analysis on hot deformation and following cooling technology of 25Cr2Ni4MoVA steel

The true stress–true strain curves of 25Cr2Ni4MoVA steel were obtained by uniaxial compression experiments at 850–1200℃ in the strain rate range of 0.001–10.0 s^(−1).And the dynamic continuous cooling transformation curves were obtained at the cooling rate range of 0.5–15.0℃ s^(−1) from the austenitization temperature of 1000℃ to the room temperature by pre-strain of 0.2 as well.The power dissipation map and the dynamic continuous cooling transformation diagram were constructed based on the data provided by these curves.Compared with the optical micrographs of the compressed samples,the full dynamic recrystallization region is located between 1000 and 1200℃ and at the strain rate range from 0.01 to 10.0 s^(−1) with the power dissipation efficiency not less than 0.33.In the full dynamic recrystallization region,the power dissipation efficiency increases and the dynamic recrystallization activation energy decreases with the temperature increasing.With the strain rate decreasing,the power dissipation efficiency increases firstly and then starts to decrease as the strain rate is less than 0.1 s^(−1),and dynamic recrystallization activation energy changes on the contrary.According to the dynamic continuous cooling transformation diagram,slow cooling is a better way for the hot-deformed piece with large size or complex shape to avoid cracking as the temperature of the piece is lower than 400℃,and different cooling ways can be used for the hot-deformed piece with small size and simple shapes to obtain certain microstructure and meet good compressive properties.

LEGENDRE TRANSFORM-DUAL SOLUTION FOR INVESTMENT AND CONSUMPTION PROBLEM UNDER THE VASICEK MODEL

This paper studies an investment and consumption problem with stochastic interest rate,where interest rate is governed by the Vasicek model.The financial market is composed of one riskfree asset and one risky asset,in which stock price dynamics is assumed to be generally correlated with interest rate dynamics.The aim is to maximize expected utility of consumption and terminal wealth in the finite horizon.Legendre transform is used to deal with this investment and consumption problem and the explicit solutions of the optimal investment and consumption strategies with power and logarithm preference are achieved.Finally,the authors add a numerical example to analyze the effect of market parameters on the optimal investment and consumption strategy and provide some economic implications.

Effect of Hot Torsion Parameters on Development of Ultrafine Ferrite Grains in Microalloyed Steel

Hot torsion testing was performed on a low carbon Nb-Ti microalloyed steel to study the effects of hot tor- sion parameters, strain and strain rate, on ultrafine ferrite grains production through dynamic strain-induced trans- formation, at a deformation temperature just above At3. The initiation and evolution of ultrafine ferrite grains were studied. The results show that the amount of strain and strain rate has conversely effect on the volume fraction and grain size of ultrafine ferrite grains. With increasing strain, the interior of austenite grains become activated as nucle- ation sites for fine ferrite grains. As a result, ferrite grains continuously nucleate not only at the former austenite grain boundaries but also inside the austenite grains which leads to a rapid increase in volume fraction of ultrafine grains. Increasing of strain rate reduces the tendency of ferrite grains coarsening so that ultrafine ferrite grains are achieved, while the volume fraction of ultrafine grains decreases at the same strain level.

Rashba Effect in Presence of Time-Dependent Interaction

Rashba effect in presence of a time-dependent interaction has been considered.Then time-evolution of such a system has been studied by using Lewis–Riesenfeld dynamical invariant and unitary transformation method.So appropriate dynamical invariant and unitary transformation according the considered system have been constructed as well as some special cases have come into this article which are common in physics.