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Refinement design of shock-wave high-pressure loading is needed to suppress the lateral rarefaction wave, which can potentially reduce the pressure and inhibit the occurrence of pressure-induced effects (e.g. phase transition). In this study, based on the numerical simulation of shock dynamics, an ideal one-dimensional stress state in a ferroelectric crystal could be achieved in the lateral rarefaction zone under shock-wave loading. The thermodynamic analysis and experimental tests showed that, at the same loading rate, compared with one-dimensional strain state in the non-lateral rarefaction zone, one-dimensional stress in the lateral rarefaction zone was more conducive to the occurrence of electromechanical coupling effects, such as ferroelectric phase transition and depolarization, thus releasing more charges. It was also indicated that lateral rarefaction protection may not be always necessary in the shock compression experiments.

This study investigated the effect of storage time on biochemical characteristics of hawk tea (Litsea coreana) and explored the correlation between the content of flavonoids and polyphenols and antioxidant activity. The antioxidant activity and the content of inclusions, amino acid, and mineral elements in hawk tea processed by boiling water fixation and packed in airtight polypropylene bags and stored in 0°C refrigerator under different storage time (one year, three years, and six years) were analyzed. Results indicated that the biochemical characteristics of hawk tea changed less within 12 months. The total content and types of amino acids in hawk tea reached the maximum in the third year, as well as the content of total trace elements. The water extracts, tea polyphenol, caffeine, lysine, valine, isoleucine, glycine, proline, Ca, and Zn decreased continuously in the storage period of 6 years, but the total flavonoids, Mg, and Ni changed just the opposite. Total polyphenol is the main antioxidant material in hawk tea. Results of the present study provided useful information for people to systematically understand the changes of tea in the storage process and to reasonably develop hawk tea product.

This study investigated the effect of storage time on biochemical characteristics of hawk tea (Litsea coreana) and explored the correlation between the content of flavonoids and polyphenols and antioxidant activity. The antioxidant activity and the content of inclusions, amino acid, and mineral elements in hawk tea processed by boiling water fixation and packed in airtight polypropylene bags and stored in 0°C refrigerator under different storage time (one year, three years, and six years) were analyzed. Results indicated that the biochemical characteristics of hawk tea changed less within 12 months. The total content and types of amino acids in hawk tea reached the maximum in the third year, as well as the content of total trace elements. The water extracts, tea polyphenol, caffeine, lysine, valine, isoleucine, glycine, proline, Ca, and Zn decreased continuously in the storage period of 6 years, but the total flavonoids, Mg, and Ni changed just the opposite. Total polyphenol is the main antioxidant material in hawk tea. Results of the present study provided useful information for people to systematically understand the changes of tea in the storage process and to reasonably develop hawk tea product., The biochemical characteristics of hawk tea processed by boiling water fixation changed less within 12 months. The total content and types of amino acids in hawk tea reached the maximum in the third year, as well as the content of total trace elements. The water extracts, tea polyphenol, caffeine, lysine, valine, isoleucine, glycine, proline, Ca, and Zn decreased continuously in the storage period of 6 years, but the total flavonoids, Mg, and Ni changed just the opposite. Total polyphenol is the main antioxidant material in hawk tea.

A critical damage degree model was established for spall fracture in high-purity ductile polycrystalline metals. Three critical characteristic damage degrees (i.e., nucleation, complete plasticity, and fracture damage) were used to divide the dynamics of damage evolution into four stages: void nucleation, elastoplastic growth, plastic growth, and coalescence. For each stage, a physical model was established based on the damage evolution regularities and mechanism. Simulated results of the proposed model coincided well with the experimental ones in terms of serious spall experiments for oxygen-free copper. Finally, the association between the characteristics of the pullback signal in the spall experiment and the dynamic properties of damage evolution is discussed, indicating that the three critical damage degrees in the model had definite physical meanings.

Under uniaxial shock compression, the steepness of the plastic shock front usually exhibits power law characteristics with the Hugoniot pressure, also known as the ``Swegle-Grady law.'' In this Letter, we show that the Swegle-Grady law can be described better by a third power law rather than the classical fourth power law at the strain rate between ${10}^{5}--{10}^{7}\text{ }\text{ }{\mathrm{s}}^{\ensuremath{-}1}$. A simple dislocation-based continuum model is developed, which reproduced the third power law and revealed very good agreement with recent experiments of multiple types of metals quantitatively. New insights into this unusual macroscopic phenomenon are presented through quantifying the connection between the macroscopic mechanical response and the collective dynamics of dislocation assembles. It is found that the Swegle-Grady law results from the particular stress dependence of the plasticity behaviors, and that the difference between the third power scaling and the classical fourth power scaling results from different shock dissipative actions.

The identification of the liquid–liquid phase transition (LLPT) in liquids under shock compression is a long-standing challenge. In this Letter, by designing shock-release experiments in shock-driven molten Ce, we observe a first-order LLPT along the release path. The volume change associated with the transition is less than 6%, much smaller than the one (14%) obtained in static compression experiments, indicating that the LLPT in molten Ce is strongly rate dependent. The identified timescale for the LLPT is on the order of 200 ns. Our results, therefore, provide kinetic information of the LLPT in an unprecedented manner, which is extremely valuable for the construction of a non-equilibrium phase diagram.

A dislocation-based constitutive model is applied to revisit the anomalous thermal hardening behavior of fcc metals under shock loading. Two scale-dependent dislocation motion mechanisms are found to dominate the thermal hardening behavior of fcc metals under shock loading. In particular, because of the shear stress decay with the propagation of the shock wave, the relativistic effect of dislocation motion is only significant near the impact surface, whereas the phonon drag mechanism dominates dislocation motion in a macroscopic fcc metal. Furthermore, we provide a detailed picture of the thermal hardening behavior on the continuum scale, in which the role of the newly generated stress wave from plastic deformation in the dynamic deformation process is highlighted. We show that the mechanical response at the elastic precursor is mainly controlled by the stress wave emanating from the plastic front.

Interpretation of the temperature dependence of the dynamic yield stress of shock-loaded metals has recently become a critical problem in shock wave physics. However, the temperature dependence of the dynamic yield stress of BCC metals is rarely investigated owing to the lack of an accurate description of the constitutive behavior of BCC metals subjected to high strain rate and high temperature. To unravel the underlying mechanism of the dynamic yield stress of BCC metals under such extreme conditions, we established a dislocation-based constitutive model in which the dislocation generation equation is proposed from the viewpoint of dissipation energy. When applied to shock-loaded BCC metals, this model reproduced the elastic–plastic wave characteristics observed in preheated plate-impact experiments quantitatively even at temperatures of >1000 K. It was found that forest hardening induced by thermally activated homogeneous nucleation (TA-HN) serves as the primary contributing factor to the thermal hardening behavior of vanadium at elevated temperature, while Peierls stress serves as the primary contributing factor to the thermal softening behaviors of other BCC metals. The novelty of this work lies in that the forest hardening mechanism, as a plastic hardening mechanism and usually regarded as temperature insensitive for BCC metals, has been proved to be temperature sensitive and influence dislocation motion significantly owing to TA-HN at high strain rate and high temperature. Based on this mechanism, we also predicted that the thermal hardening behavior would also occur in other BCC metals, e.g., molybdenum and tungsten, at temperature ranges beyond the limit of existing experiments.

In this study, we evaluated the effect of temperature on the development and reproductive biology of Serangium japonicum (Coleoptera: Coccinellidae) at seven constant temperature regimes (17, 20, 23, 26, 29, 32 and 35°C) for its effect as a predator of Bemisia tabaci (Homoptera: Aleyrodidae). Results indicated that the duration of the egg, larval and pupal stages were significantly affected by temperature. The developmental time gradually declined with the increase of temperature from 17 to 29°C, however an extension in the developmental periods was observed in the temperature range of 32 to 35°C. The survival rates of different insect stages were stable at temperatures between 20 and 32°C; however at extreme temperatures of 35°C, a sharp decrease was evident. The highest fecundity of the female (387.2 eggs per female) was recorded at 20°C. Based on these results, life tables of S. japonicum were constructed for temperatures in the range 20–35°C. The maximum reproductive rate (R 0=279.9) occurred...

Axinoscymnus cardilobus is an indigenous coccinellid predator in South China, which feeds on many whitefly species. Its development, consumption rate, survivorship, longevity and fecundity on a diet of eggs and nymphs of Bemisia tabaci were evaluated. Larval consumption decreased sharply as instars of B. tabaci become bigger, and development time of beetle larvae was significantly different when fed on different stages of B. tabaci. The sex ratio was 0.44. The performances were better after feeding on whitefly eggs than nymphs. Axinoscymnus cardilobus showed good potential for biological control of B. tabaci, especially in greenhouse situations.

A novel explanation of the quasielastic release phenomenon in shock compressed aluminum is presented. A dislocation-based model, taking into account dislocation substructures and evolution, is applied to simulate the elastic plastic response of both single crystal and poly crystalline aluminum. The calculated results are in good agreement with experimental results from not only the velocity profiles but also the shear strength and dislocation density, which demonstrates the accuracy of our simulations. Simulated results indicate that dislocation immobilization during dynamic deformation results in a smooth increase of yield stress, which leads to the quasi-elastic release, while the generation of dislocations caused by the plastic release wave results in the appearance of a transition point between the quasielastic release and the plastic release in the profile., 13 pages and 12 figures

The laboratory study on the predation of Axinoscymnus cardilobus to Bemisia tabaci showed that the functional response of A. cardilobus to B. tabaci was of Holling' s type II. With the increasing age of B. tabaci, the searching rate of A. cardilobus adult decreased, and its handling time became longer. The searching rate of A. cardilobus larva was increased with its age, and the handling time became shorter. The mutual interference in individual predator could be described by Hassell and Varley equation, and the relationship between predation ratio (E) and natural enemies density (P) was E =0. 5205P(-0 6631.) The predation efficiency (E) of predator varied with environmental temperature, and the effects of the temperature on search rate (a) and handling time ( T ) could be described by a = -0. 0002T(3)+ 0. 0166T(2) - 0. 3492T + 3. 2329 and Th = 4 x 10 (-7) T-( 3) x 10(-5) T(2) + 0.0006T 0.0009, respectively.

Serangiurm japonicum is an important predator of whiteflies in China. In this study, the Bemisia tabaci-attacking behavior of S. japonicum adults and larvae was observed by a videocassette recorder. The results showed that the predatory behavior of S. japonicum adults was characteristic with six events, i.e., walking, feeding, clearing, resting, vibrating wings, and excreting. The starved larvae of S. japonicum was fond spending all times in feeding and walking on host eggs, with no time in resting or clearing throughout the process. The time included in feeding and walking was not significant different among different instars of S. japonicum. The handing time per egg decreased with S. japonicum larvae developed from instar I to IV, but differed little between instar III and IV. The starved females of S. japonicum spent longer time on egg feeding, but less time on clearing, resting and walking than satiated females. The time for starved female to predate on B. tabaci nymphs and pupae increased as the host nymphs developed.