An approach for complex activity recognition by key frames

A new method for complex activity recognition in videos by key frames was presented. The progressive bisection strategy(PBS) was employed to divide the complex activity into a series of simple activities and the key frames representing the simple activities were extracted by the self-splitting competitive learning(SSCL) algorithm. A new similarity criterion of complex activities was defined. Besides the regular visual factor, the order factor and the interference factor measuring the timing matching relationship of the simple activities and the discontinuous matching relationship of the simple activities respectively were considered. On these bases, the complex human activity recognition could be achieved by calculating their similarities. The recognition error was reduced compared with other methods when ignoring the recognition of simple activities. The proposed method was tested and evaluated on the self-built broadcast gymnastic database and the dancing database. The experimental results prove the superior efficiency.

Hot deformation behavior of TC11/Ti-22Al-25Nb dual-alloy in isothermal compression

The high-temperature flow behavior of TCll/Ti-22Al-25 Nb electron beam（EB） weldments was investigated by the isothermal compression tests at the temperature of 900-1060℃ and the strain rate of 0.001-10 s-（-1）.Based on the experimental data,the constitutive equation that describes the flow stress as a function of strain rate and deformation temperature is obtained.The apparent activation energy of deformation is calculated,which decreases with increasing the strain and the value is 334 kJ/mol at strain of 0.90.The efficiency of power dissipation η changes obviously with the variation of deformation conditions.Under the strain rates of 0.01,0.1 and 1 s-（-1）,the value of η increases with increasing the true strain for different deformation temperatures.While the value of η decreases with increasing the strain under the strain rates of 0.001 and 10 s-（-1）.The optimum processing condition is（t（opi）=1060℃,ε（opi）=0.1 s-（-1）） with the peak efficiency of 0.51.Under this deformation,dynamic recrystallization（DRX） is observed obviously in the microstructure of welding zone.Under the condition of 1060℃ and 0.001 s-（-1）,the deformation mechanism is dominated by dynamic recovery（DRV） and the value of η decreases sharply（η=0.02）.The flow instability is predicted to occur since the instability parameter ξ（ε）becomes negative.The hot working process can be carried out safely in the domain with the strain rate of 0.001-0.6 s-（-1） and the temperature of 900-1060℃.

Microstructure and mechanical properties of Fe_3Al alloys prepared by MA-PAS and MA-HP

Fe3Al alloys with nearly full density were fabricated by plasma activated sintering（PAS） and hot pressing（HP） from mechanical alloyed Fe-28%Al（mole fraction） powders,respectively.It is found that A2-type Fe3Al alloys were obtained by PAS,and they had a heterogeneous grain size distribution,most areas had a grain size smaller than 500 nm,and other areas had a grain size of about 1 μm.Different to PAS,D03-type Fe3Al alloys with a grain size of of 1-2 μm were obtained by HP.The compression testing results show that yield strength values of Fe3Al alloys fabricated by PAS and HP are almost equal at an elevated temperature,and the compression yield strength was about 100 MPa for all at 800 ℃.The room temperature compression ductility of Fe3Al alloys by PAS was about 20%,which was superior to that of Fe3Al alloys prepared by HP and casting.

Thermal activation parameters of V-5Cr-5Ti alloy under hot compression

In order to well understand the elementary mechanisms that govern the hot working process of a V？5Cr？5Ti alloy （mass fraction, %）, thermal activation parameters under compression were measured in a temperature range of 1373？1673 K by a Gleeble？3800 system. The results show that the stress exponentn is 4.87 and the activation energyQis 375.89 kJ/mol for the power law equation. The activation energy is determined as 288.34 kJ/mol, which is close to the self-diffusion energy of alloy （270？300 kJ/mol） by introducing a threshold stress（σ0） variable. The typical values of physical activation volume （Vp） and strain rate sensitivity （m） are measured as （120？700）b3 and 0.075？0.122, respectively, by the repeated stress relaxation tests. These activation parameters indicate that the rate controlling mechanism for V？5Cr？5Ti alloy compressed in ranges of 1373？1673 K and 0.001？1.0 s？1 is the dislocation climb by overcoming of forest dislocations.

Hot deformation behavior of Mg-7.22Gd-4.84Y-1.26Nd-0.58Zr magnesium alloy

The behavior evolvement of Mg-7.22Gd-4.84Y-1.26Nd-0.58Zr（GWN751K） magnesium alloy during the hot deformation process was discussed.The flow stress behavior of the magnesium alloy over the strain rate range of 0.002 to 2.000 s^-1 and in the temperature range of 623 to 773 K was studied on a Gleeble-1500D hot simulator under the maximum deformation degree of 60%.The experimental results showed that the relationship between stress and strain was obviously affected by strain rate and deformation temperature.The flow stress of GWN751K magnesium alloy during high temperature deformation could be represented by the Zener-Hollomon parameter in the hyperbolic Arrhenius-type equation.The stress exponent n and deformation activation energy Q were evaluated by linear regression analysis.The stress exponent n was fitted to be 3.16.The hot deformation activation energy of the alloy during hot deformation was 230.03 kJ/mol.The microstructures of hot deformation were also influenced by strain rate and compression temperature strongly.It was found that the alloy could be extruded at 723 K with the mechanical properties of σ0.2 = 260 MPa,σb = 320 MPa,and δ = 18%.

Simple physically-based constitutive equations for hot deformation of 2024 and 7075 aluminum alloys

The hot working behaviors of 2024 and 7075 aluminum alloys were studied through constitutive analysis based on a physically-based approach which accounts for the dependence of the elastic modulus and the self-diffusion coefficient of aluminum on temperature. It was demonstrated that the lattice self-diffusion activation energy of aluminum（142 k J/mol） can be used in the Zener-Hollomon parameter＇s formula as the deformation activation energy and the theoretical exponent of 5 can be set in the modified hyperbolic sine law to describe the peak flow stresses. By consideration of physically-based material＇s parameters, it was possible to conduct a comparative study on the hot flow stress of 2024 and 7075 aluminum alloys. It was concluded that the used approach in the current work can be considered as a versatile tool in future comparative hot working studies, especially in studies dedicated to alloy development.

Hot deformation behavior of FGH96 superalloys

The hot deformation behavior of FGH96 superalloys at 1070-1170℃ and 5×10^-4-2×10^-1 s^-1 were investigated by means of the isothermal compression tests at a Gleeble-1500 thermal mechanical simulator. The results show that dynamic recovery acts as the main softening mechanism below 2×10^-3 s^-1, whereas dynamic recrystallization acts as the main softening mechanism above 2× 10^-3 s^-1 during deformation; the temperature increase caused by the deformation and the corresponding softening stress is negligible; the thermal-mechanical constitutive model to describe the hot deformation behavior is given, and the value of the apparent deformation activation energy （Qdef） is determined to be 354.93 kJ/mol.

A comparative study on the hot flow stress of Mg-Al-Zn magnesium alloys using a simple physically-based approach

A comparative study was carried out on the hot flow stress of AZ31,AZ61,and AZ91 magnesium alloys.Their hot working behaviors were studied through constitutive analysis based on a simple physically-based approach which accounts for the dependence of the Young's modulus and the self-diffusion coefficient of magnesium on temperature.Since the main difference between these alloys is the difference in their amount of aluminum,the differences in constitutive behavior were quantitatively characterized by relating the hot flow stress to amount of Al,which was not possible without the consideration of physically-based parameters.It was concluded that the used approach in the current work can be considered as a versatile tool in future hot working and alloy development studies.

Dynamic recrystallization and precipitation in high manganese austenitic stainless steel during hot compression

Dynamic recrystallization and precipitation in a high manganese austenitic stainless steel were investigated by hot compression tests over temperatures of 950-1150~C at strain rates of 0.001 s-1-1 s-1. All the flow curves within the studied deformation regimes were typ- ical of dynamic recrystallization. A window was constructed to determine the value of apparent activation energy as a function of strain rate and deformation temperature. The kinetics of dynamic recrystallization was analyzed using the Avrami kinetics equation. A range of apparent activation energy for hot deformation from 303 kJ/mol to 477 kJ/mol is obtained at different deformation regimes. Microscopic characterization confirms that under a certain deformation condition （medium Zener-Hollomon parameter （Z） values）, dynamic recrystalliza- tion appears at first, but large particles can not inhibit the recrystallization. At low or high Z values, dynamic recrystallization may occur be- fore dynamic precipitation and proceeds faster. In both cases, secondary phase precipitation is observed along prior austenite grain bounda- ries. Stress relaxation tests at the same deformation temperatures also confirm the possibility of dynamic precipitation. Unexpectedly, the Avrami＇s exponent value increases with the increase of Z value. It is associated with the priority of dynamic recrystallization to dynamic precipitation at higher Z values.

Hot deformation behavior of Fe–27.34Mn–8.63Al–1.03C lightweight steel

Hot compression tests were performed to investigate the hot deformation behavior of Fe–27.34Mn–8.63Al–1.03C lightweight steel and optimize the hot workability parameters. The temperature range was 900–1150℃ and the strain rate range was 0.01–5 s^(-1)on a Gleeble-3800 thermal simulator machine. The results showed that the flow stress increased with decreasing deformation temperature and increasing strain rate. According to the constitutive equation, the activation energy of hot deformation was 422.88 kJ·mol^(-1). The relationship between the critical stress and peak stress of the tested steel was established, and a dynamic recrystallization kinetic model was thus obtained. Based on this model, the effects of strain rate and deformation temperature on the volume fraction of dynamically recrystallized grains were explored. The microstructural examination and processing map results revealed that the tested steel exhibited a good hot workability at deformation temperatures of 1010–1100℃ and strain rate of 0.01 s^(-1).

Modeling of metadynamic recrystallization kinetics after hot deformation of low-alloy steel Q345B

Based on the steady-state strain measured by single-pass hot compression tests,the method by a double-pass hot compression testing was developed to measure the metadynamic-recrystallization kinetics.The metadynamic recrystallization behavior of low-alloy steel Q345B during hot compression deformation was investigated in the temperature range of 1 000-1 100℃,the strain rate range of 0.01-0.10 s -1 and the interpass time range of 0.5-50 s on a Gleeble-3500 thermo-simulation machine.The results show that metadynamic recrystallization during the interpass time can be observed.As the deformation temperature and strain rate increase,softening caused by metadynamic recrystallization is obvious.According to the data of thermo-simulation,the metadynamic recrystallization activation energy is obtained to be Qmd=100.674 kJ/mol and metadynamic recrystallization kinetics model is set up.Finally,the error analysis of metadynamic recrystallization kinetics model proves that the model has high accuracy(correlation coefficient R=0.988 6).

Microstructure, properties and hot workability of M300 grade maraging steel

This paper presents isothermal uniaxial compression test results of M300 grade maraging steel over a wide range of temperatures(900 e1200℃) and strain rates(0.001 e100 s^(-1)) to examine hot deformability and concurrent microstructural evolution. Processing map is generated and indicated the optimum processing parameters in the temperature range of 1125℃-1200℃ and strain rate range of 0.001 e0.1 s^(-1). High values of the efficiency of power dissipation, microstructural observations and EBSD results indicate softening mechanism to be the occurrence of dynamic recrystallisation. Material constants in a constitutive relation are evaluated from the flow stress data useful in computer modelling.

Hot Deformation Characteristics for a Nickel-base Superalloy GH742y

The hot deformation characteristics of as-cast nickel-base superalloy GH742y after hot isostatic pressing （HIP）（hereafter referred to as-cast alloy） have been investigated by hot compression tests in the temperature range of 1050 to 1140℃, strain rate range of 0.01 s^-1 to 10 s^-1 and strain range of 35% to 50% by means of Gleeble-3500 thermal mechanical simulator. The results show that the as-cast alloy exhibits the poor deformability, and shows wedge-shaped cracking beyond the strain of 35%. At strain rates less than 1.0 s^-1, the stress-strain curves exhibit nearly steady-state behavior, while at strain rate of 10 s^-1, a yield drop and serrated yielding occur. The activation energy values developed on the basis of the experimental data are divided into three domains. The first domain appears at lower strain rate （≤1.0 s^-1） and lower temperature （≤1080℃）, with the lowest mean value of activation energy about 261.4 kJ/mol. The second domain appears at the same strain rate as the first domain, but higher temperature （〉1080℃）, with the intermediate mean value of activation energy about 328.8 k J/tool. The third domain appears at higher strain rate （10 s^-1） and temperature range of 1050 to 1140℃, with the largest mean value of activation energy about 605.05 kJ/mol. Three different constitutive equations are established in corresponding to domains. Microstructural observations in the third domain reveal non-uniform dynamic recrystallization （DRX） of homogeneous γ phase, which leads to the poor deformability and the highest Q value. In contrast, microstructures in the first domain show fully DRX of homogeneous γ phase, leading to the better deformability and the lowest Q value. It is noted that the grain size increases with the increment of strain rate or temperature. These results suggest that bulk metal working of this material may be carried out in the first domain where fully DRX of γ homogeneous occurred.

Deformation behavior and microstructural evolution during hot compression of an a+b Ti-6.5Al-3.5Mo-1.5Zr-0.3Si alloy

The effect of processing parameters on the flow response and microstructural evolution of the a＋b titanium alloy Ti-6.5Al-3.5Mo-1.5Zr-0.3Si has been studied by conducting isothermal hot compressive tests at a strain rate of 0.01-10 s-1 at 860-1100°C. The true stress-true strain curves of the sample hot-compressed in the a＋b phase region exhibit a peak stress followed by continuous flow softening, whereas in the b region, the flow stress attains a steady-state regime. At a strain rate of 10 s-1, the alloy exhibits plastic flow insta-bilities. According to the kinetic rate equation, the apparent activation energies are estimated to be about 674-705 kJ/mol in the a＋b region and 308-335 kJ/mol in the b region, respectively. When deformed in the a＋b region, the globularization process of the a colony structure occurs, and a dynamic recrystallized microstructures are observed to show bimodal. Dynamic recrystallization can take place in the b region irrespective of starting deformed structures.

Synergistic Influence of Pre-Harvest Calcium Sprays and Postharvest Hot Water Treatment on Fruit Firmness, Decay, Bitter Pit Incidence and Postharvest Quality of Royal Delicious Apples (<i>Malus x domestica</i>Borkh)

Experiments were conducted to observe the effect of pre-harvest calcium (Ca) applied as calcium chloride (1% W/V) and postharvest hot water treatment (HWT) on “Royal Delicious” apples. For this, apples were divided in 4 lots viz., untreated (neither Ca nor HWT), Ca alone (pre-harvest 3 sprays of CaCl2 (1.0% w/v) in the orchard), HWT (42℃ for 2 h). Apples of all four lots were stored in cold storage maintained at 0℃ ± 1℃ and 90% - 95% relative humidity for 6 months. After storage, fruits were removed to ambient conditions for 5 days, and then observations on decay area and incidence, bitter pit incidence, fruit Ca content, lipoxygenase (LOX) and antioxidant (AOX) activity, fruit firmness and fruit quality parameters were recorded. After 6 months in cold storage plus 5 day at 22℃ ± 2℃ and 70% + 4% RH, apples, which received Ca as pre-harvest spray or those which received postharvest hot water treatment or Ca + HWT had significantly lesser decay area (decay lesions) caused by Penicillium expansum or Botrytis cinerea than untreated ones (control). Ca + HWT treatment was significantly more effective on B. cinerea than P. expansum. Untreated apples exhibited higher incidence of bitter pit (18.2%) than those treated with Ca or HWT or both. Fruit Ca content (2.92% DM) were significantly lower and conversely the LOX activity (6.9 μmoles min–1×g–1FW) was higher in untreated apples. Similarly, total phenolics and AOX activity were also lower in the untreated apples than Ca or HWT treated. HWT or Ca treated apples have beneficial effects on fruit firmness, peel colour and quality parameters like TSS and ascorbic acid content. Thus, it is concluded that pre-harvest sprays of calcium chloride with postharvest HWT is highly useful for “Royal Delicious” for reducing decay loss, maintaining firmness, high levels of antioxidants and fruit quality.

Survival,growth and immune activity of scallop Chlamys farreri cultured at different depths in Haizhou Bay(Yellow Sea,China) during hot season

Survival, growth and immune response of the scallop, Chlamys farreri, cultured in lantern nets at five different depths (2, 5, 10, 15, and 20 m below the sea surface) were studied in Haizhou Bay during the hot season (summer and autumn) of 2007. Survival and growth rates were quantified bimonthly. Immune activities in hemolymph (superoxide dismutase (SOD) and acid phosphatase (ACP)) were measured to evaluate the health of scallops at the end of the study. Environmental parameters at the five depths were also monitored during the experiment. Mortalities mainly occurred during summer. Survival of scallops suspended at 15 m (78.0%) and 20 m (86.7%) was significantly higher than at 2 m (62.9%), 5 m (60.8%) or 10 m (66.8%) at the end of the study. Mean shell height grew significantly faster at 10 m (205.0 μm/d) and 20 m (236.9 μm/d) than at 2, 5 or 15 m in summer (July 9 to September 1); however, shell growth rate at 20 m was significantly lower than at the other four depths in autumn (September 2 to November 6). In contrast to summer, scallops at 5 m grew faster (262.9 μm/d) during autumn. The growth of soft tissue at different depths showed a similar trend to the shell. Growth rates of shell height and soft tissue were faster in autumn than in summer, with the exception of shell height at 20 m. SOD activity of scallops increased with depth, and ACP activity was significantly higher at 15 and 20 m than at other depths, which suggests that scallops were healthier near the bottom. Factors explaining the depth-related mortality and growth of scallops are also discussed. We conclude that the mass mortality of scallop, C. farreri, during summer can be prevented by moving the culture area to deeper water and yield can be maximized by suspending the scallops in deep water during summer and then transferring them to shallow water in autumn.

Flow behavior and microstructure evolution of TB8 alloy during hot deformation process

Hot compression tests of metastable β titanium alloy TB8 were carried out using a Gleeble-1500 thermal simulation testing machine in the temperature range of 750-1100 ℃, at constant strain rate from 0.01 s-1 to 1 s-1 and with height direction reduction of 60%. Flow stress behavior and microstructure evolution during hot compression of TB8 alloy were investigated. The hyperbolic-sine-type constitutive model of TB8 alloy was obtained to provide basic data for determining reasonable forming process. The results indicate that hot deformation behavior of TB8 alloy is highly sensitive to the temperature and strain rate. An analysis of the flow stress dependence on strain rate and temperature gives a stress exponent of n≈3.416 19 and a deformation activation energy of Q≈227.074 4 kJ/mol. According to the deformation microstructure, no dynamic recrystallization happens below β-phase transus temperature and as a result dynamic recovery is the predominant softening mechanism. On the other hand, the main softening mechanism is characterized as dynamic recrystallization at a slow strain rate above β-phase transus temperature.

Effects of contents of Nb and C on hot deformation behaviors of high Nb X80 pipeline steels

The behavior of the flow deformation and the effects of contents of Nb and C on deformation behaviors of high Nb X80 pipeline steels during hot compression deformation were studied by thermal simulation test. The content of solid solution Nb was quantificationally studied during the reheating and hot deformation process, and the effects of change of solid solution Nb in steels on hot deformation behaviors were discussed. The results show that the contents of Nb and C have great effects on the flow stress behaviors of high Nb X80 pipeline steels. When the C content in steels is constant, the recrystallization activation energy increases from 387 to 481 kJ/mol with increasing the Nb from 0.082% to 0.13% (mass fraction). However, the effect of Nb is correlative to the C content, i.e. w(Nb)/w(C). When w(Nb)/w(C) decreases from 3.61 to 2.18, the recrystallization activation energy decreases from 481 to 434 kJ/mol.

Characteristics of Late Quaternary Activity of the Luhuatai Buried Fault Revealed by Drilling

The Luhuatai fault is one of the important buried tectonics in the Yinchuan basin. Based on the results of shallow seismic exploration, we conducted composite drilling section exploration and dating of the samples from boreholes. Some useful data was obtained, such as the depth of the upper breaking point, the latest activity age, displacement in the late Quaternary, and slip rates, etc. This study shows that the activity is different between the north and south segment along the Luhuatai fault. The north segment is a Holocene fault, while the south segment is a late mid-Pleistocene fault. From north to south along the north segment of Luhuatai fault, the activity has been enhanced, and the faulting is stronger in late Pleistocene than Holocene.