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As an important moving element in the machine structure, the crossbeam determines the dynamic characteristics of the machine in X or Y axis, which directly affects the machining efficiency and quality of the machine. The most typical expression of dynamic characteristics is acceleration, and the acceleration is inversely proportional to the mass of the moving parts, so reducing the mass of the moving parts while ensuring the stiffness is an important part of optimizing the machine structure. To address the problem that the cross beam of HIMT50 vertical machining center has structural redundancy, which leads to bad dynamic characteristics, the cross beam is firstly modeled in 3D, and its static and dynamic characteristics are analyzed by Abaqus software, and the data are applied to the optimization module to optimize the structure by topology optimization method. The optimization results show that the deformation and low-order amplitude of the crossbeam are improved with the reduction of its mass, which provides a theoretical basis and reference value for optimizing the crossbeam structure, reducing the overall manufacturing cost and improving the machining efficiency of the machine tool.

Lobes and clefts are characteristic structures at the front of sand storms. In this paper, their original formation mechanism and geometric features are studied experimentally and theoretically. A rotatable lock-exchange tank is utilized to avoid the strong local disturbances existing in the conventional horizontal apparatus, and the original lobe size is selected as the dominant spanwise wavelength by a statistical method instead of the mean lobe size used in the literature. It is shown that at the initial formation stage, the measured lobe sizes for different tank geometries and density differences (or Atwood numbers) have a 1/3 scaling law with the Grashof number (Gr) as predicted by a Rayleigh–Taylor (RT) model, especially at moderate Gr range, and substantially depend on the diffusion effect represented by the Schmidt number. Furthermore, using turbulent Schmidt number and eddy viscosity for atmosphere in the RT model predicts large scale dominant lobes, whose sizes agree qualitatively with those observed in a real sand storm, revealing that the underlying control mechanism for these lobe and cleft structures is intrinsically related to the RT instability.

In this paper, the decay and growth of localized wave packet (LWP) in a two-dimensional plane-Poiseuille flow are studied numerically and theoretically. When the Reynolds number (Re) is less than a critical value [Formula: see text], the disturbance kinetic energy Ek of LWP decreases monotonically with time and experiences three decay periods, i.e., the initial and the final steep descent periods and the middle plateau period. Higher initial Ek of a decaying LWP corresponds to longer lifetime. According to the simulations, the lifetime scales as [Formula: see text], indicating a divergence of lifetime as Re approaches [Formula: see text], a phenomenon known as “critical slowing-down.” By proposing a pattern preservation approximation, i.e., the integral kinematic properties (e.g., the disturbance enstrophy) of an evolving LWP are independent of Re and single valued functions of Ek, the disturbance kinetic energy equation can be transformed into the classical differential equation for saddle-node bifurcation, by which the lifetimes of decaying LWPs can be derived, supporting the [Formula: see text] scaling law. Furthermore, by applying the pattern preservation approximation and the integral kinematic properties obtained as [Formula: see text], the Reynolds number and the corresponding Ek of the whole lower branch, the turning point, and the upper-branch LWPs with [Formula: see text] are predicted successfully with the disturbance kinetic energy equation, indicating that the pattern preservation is an intrinsic feature of this localized transitional structure.

Effects of the Ohnesorge ( Oh) number and contact angle on the instability of a sessile rivulet are theoretically studied in this paper for both the pinned contact line (PCL) and moving contact line with invariant contact angle (MCL) conditions. Inviscid dispersion relations of unstable modes for rivulets with different static contact angles are shown to be transformed analytically into a unified form for both PCL and MCL conditions, reflecting the same intrinsic instability mechanism. The growth rate becomes lower at higher Oh due to the stabilization effect of viscosity. It is found for both PCL and MCL conditions that the deviation of the maximum growth rate from its inviscid counterpart varies as [Formula: see text] when Oh is so small that the viscous effect mainly exists in a thin layer near the wall. For the MCL condition, the maximum growth rate of the unstable mode decreases and increases monotonically with the augment of the static contact angle at low and high Oh, respectively, while at moderate Ohnesorge numbers, increasing the static contact angle will first enlarge and then decrease the maximum growth rate for cases with hydrophilic bottom walls.

By direct numerical simulations of the plane Couette flow (PCF) in a large computational domain, it is shown that an isolated turbulent band decays monotonically at low Reynolds numbers but experiences transient growth before the eventual relaminarization at moderate Reynolds numbers. The lower bound Reynolds number of the transient-growth regime is determined as 286. The width, length, and tilt angle of the isolated band structure are defined based on the disturbance kinetic energy in the mid-plane, and the geometric characteristics of the band can be described with a tilted rectangle. It is illustrated that before its eventual fragmentation, the isolated turbulent band decays in a style of longitudinal contraction, where the center, width, and tilt angle of the band keep almost constant but the band length contracts with a statistically constant velocity.

In this paper, the rotational part of the disturbance flow field caused by viscous Rayleigh-Taylor instability (RTI) at the cylindrical interface is considered, and the most unstable mode is revealed to be three-dimensional for interfaces of small radii $R$. With an increase in $R$, the azimuthal wave number of the most unstable mode increases step by step, and the corresponding axial wave number increases as well at each step of the azimuthal wave number. When the amplitude of the wave-number vector is much larger or much smaller than $1/R$, the cylindrical RTI is close to the semi-infinite planar viscous RTI limit or the finite-thickness creeping-flow RTI limit, respectively. The effect of the viscosity ratio is double-edged; it may enhance or suppress the cylindrical RTI, depending on $R$ and the amplitude range of the wave-number vector.

We show that when linear azimuthal perturbations on the surfaces of a fluid shell are regrouped according to ${\ensuremath{\alpha}}^{m}$, they can be divided into Bell model terms, coupling terms, and the newly identified thin-shell correction terms, where $\ensuremath{\alpha}$ is the ratio of ${R}_{\text{out}}$ to ${R}_{\text{in}}$, and $m$ is the mode number of a given unstable mode on the surfaces. It is also revealed that ${\ensuremath{\alpha}}^{m}$ is a convenient index variable of coupling effects, with which we show that the evolution of instability is composed of three stages, i.e., strongly coupled stage, transition stage, and uncoupled stage. Roughly, when ${\ensuremath{\alpha}}^{m}l6$, the fluid shell is in the strongly coupled stage, where both coupling effects and the newly identified thin-shell corrections play important roles. Strong feed through is expected to be observed. The uncoupled stage is reached at ${\ensuremath{\alpha}}^{m}\ensuremath{\sim}36$, where Bell's model of independent surface holds. In between is the transition stage, where mode competitions on the two surfaces are expected to be observed. These results afford an intuitive picture which is easy to use in guiding the design of experiments. They may also help to quickly grasp major features of instability experiments of this kind.

The instabilities of a pendent viscous thin film underneath two corrugated ceilings are studied numerically and theoretically in comparison with the case of a flat wall. With the same initial interface perturbations, it is shown numerically that both the supercritical instability and the subcritical instability can be retarded by the in-phase corrugated ceilings. The lubrication approximation is used to explain the retardation effect of the corrugated ceiling on the supercritical instability of the pendant film, where the linear growth rate is revealed to be power three of the initial film thickness.

BACKGROUND To determine the association between serum 25(OH)D and dry eye syndrome (DES) incidence. This study was also designed to determine whether serum 25(OH)D levels were associated with ocular parameter of DES patients. MATERIAL AND METHODS This is a case-control study with 70 DES cases and 70 healthy controls. Clinical data included body mass index (BMI, kg/m²), smoking history, diabetes, and blood pressure. Serum 25(OH)D was chosen as the main parameter and reflected the level of vitamin D. The DES parameters included ocular surface disease index (OSDI) scales, tear film breakup time (TBUT) and Schirmer test I. The differences in each parameter between case and control groups were detected and the association of serum 25(OH)D and DES parameter were detected. RESULTS It was shown that 25(OH)D levels were lower in patients with DES than in healthy controls. When the 25(OH)D levels was stratified, vitamin D deficiency was more common in the DES cases. In advanced studies, it was found that there were statistically significant associations between serum 25(OH) D levels and the Schimer test, TBUT, and OSDI scales. CONCLUSIONS A significant association between serum 25(OH)D level and DES incidence was detected in this study. Considering the relatively small sample size of this study, larger studies are needed in the future.

The relationship between stabilities of the buoyancy boundary layers along an inclined plate and a vertical plate immersed in a stratified medium is studied theoretically and numerically. The eigenvalue problem of energy stability is solved with the method of descending exponentials. The disturbance energy is found to be able to grow to 11.62 times as large as the initial disturbance energy for Pr = 0.72 when the Grashof number is between the critical Grashof numbers of the energy stability and the linear stability. We prove that, with a weighted energy method, the basic flow of the vertical buoyancy boundary layer is stable to finite-amplitude streamwise-independent disturbances.

The approximate but analytical solution of the viscous Rayleigh-Taylor instability (RTI) has been widely used recently in theoretical and numerical investigations due to its clarity. In this paper, a modified analytical solution of the growth rate for the viscous RTI of incompressible fluids is obtained based on an approximate method. Its accuracy is verified numerically to be significantly improved in comparison with the previous one in the whole wave number range for different viscosity ratios and Atwood numbers. Furthermore, this solution is expanded for viscous RTI including the concentration-diffusion effect.

In this Rapid Communication, the Rayleigh-Taylor instability (RTI) along the density interfaces of gravity current fronts is analyzed. Both the location and the spanwise wave number of the most unstable mode determined by the local dispersion relation agree with those of the strongest perturbation obtained from numerical simulations, suggesting that the original formation mechanism of lobes and clefts at the current front is RTI. Furthermore, the predictions of the semi-infinite RTI model, i.e., the original dominating spanwise wave number of the Boussinesq current substantially depends on the Prandtl number and has a 1/3 scaling law with the Grashof number, are confirmed by the three-dimensional numerical simulations.

The two-dimensional natural convection of air in upper and a lower square cavities connected with a vertical vent is studied numerically and theoretically. At high Rayleigh numbers (Ra), it is revealed by the dynamic-mode-decomposition method that the plumes yield to a new sway mode, where the plumes oscillate in the azimuthal direction around the vent ends. In particular, when Ra is high enough, a reversal convection occurs, i.e., the dominating large-scale circulation changes its flow direction quasiperiodically. A van der Pol--type model is developed based on the momentum and the energy equations, and the reversal phenomenon is explained in terms of the relaxation oscillation caused by the competition between the nonlinear advection and the thermal diffusion.

The identification of hyperaccumulators is a key step for the phytoextraction of contaminated soils. However, few cadmium (Cd) hyperaccumulators have been identified in the plant kingdom. In our previous field investigations, Lantana camara L. plants exhibited some traits of hyperaccumulators. To confirm whether this species is a Cd hyperaccumulator, laboratory dose-gradient experiments and field sample analysis experiments were first designed and implemented in an integrated manner. The results showed that lantana plants did not exhibit any visible damage or marked reduction in shoot biomass when grown in Cd-contaminated soil with less than 100 mg kg−1 Cd. Moreover, the lantana plants exhibited high Cd tolerance with effective coordination of photosynthesis and rapid reactive oxygen species scavenging. Most importantly, the bioaccumulation factors (BFs) and translocation factors (TFs) were greater than 1.0 in all the Cd treatments, while the Cd concentrations in the shoots were all greater than those in the roots and were also greater than 100 mg kg−1, the threshold value for a Cd hyperaccumulator. Our data provide comprehensive evidence that lantana plants have the typical characteristics of a Cd hyperaccumulator and thus can be regarded as potential Cd-hyperaccumulating plants for the restoration of Cd-polluted soils.

In the previous studies of Rayleigh-Taylor instability, different methods were used to consider the effects of elasticity, viscosity, and magnetic fields. In this paper, a unified method, which was first used for fluids, is validated for different physical models, where the unstable mode is decomposed into an irrotational part and a rotational part, and the latter one includes the effects of nonconservative forces and constitutive relations. Previous results of solid and liquid with or without the effects of magnetic fields and finite thickness can be easily recovered after applying the corresponding interface boundary conditions. In addition, new approximate but analytical solutions of the growth rates for a semi-infinite solid-solid interface and solid-fluid interface are obtained with substantially improved accuracy in comparison with the previous ones.

The stabilities of an annulus flow between the rotating inner and outer cylinders with an external helical magnetic field are studied by using the quasistatic approximation. It is shown numerically that for the spiral base flow with a zero axial pressure gradient, the helical magnetic field yields a helical traveling wave at a critical Reynolds number. This wave mode is revealed to be the most unstable mode by linear stability analysis. At higher Reynolds numbers, the first wave mode is superposed by a second antisymmetric helical wave mode, which travels with a higher phase velocity than the first mode. When the Reynolds number is increased further, the flow becomes turbulent, but the key features of the flow structure are still dominated by the first and the second wave modes. Furthermore, when a finite axial pressure gradient is applied to guarantee a zero axial flow rate, the annulus flow is found to be more unstable than the case with zero axial pressure gradient.

Aiming at 45-element adaptive optics system, the model of 45-element deformable mirror is truly built by COMSOL Multiphysics, and every actuator’s influence function is acquired by finite element method. The process of this system correcting optical aberration is simulated by making use of procedure, and aiming for Strehl ratio of corrected diffraction facula, in the condition of existing different translation and rotation error between Hartmann-Shack sensor and deformable mirror, the system’s correction ability for 3-20 Zernike polynomial wave aberration is analyzed. The computed result shows: the system’s correction ability for 3-9 Zernike polynomial wave aberration is higher than that of 10-20 Zernike polynomial wave aberration. The correction ability for 3-20 Zernike polynomial wave aberration does not change with misalignment error changing. With rotation error between Hartmann-Shack sensor and deformable mirror increasing, the correction ability for 3-20 Zernike polynomial wave aberration gradually goes down, and with translation error increasing, the correction ability for 3-9 Zernike polynomial wave aberration gradually goes down, but the correction ability for 10-20 Zernike polynomial wave aberration behave up-and-down depression.

In this letter, it is shown numerically that in plane Poiseuille flow and before the threshold of equilibrium turbulence defined by the directed-percolation universality class, a sparse turbulent state in form of localized turbulent band can sustain either by continuous increase of the turbulence fraction due to band extension when the flow domain is large enough, or by a dynamic balance between the band extension and the band breaking and decay caused by the band interaction in a finite domain. The width and tilt angle of the band keep statistically invariant during its oblique extension, a process which is not sensitive to random disturbances., Comment: 4 figures

By using a linear symmetric Conditional Instability of Second Kind (CISK) model containing basic flow, we study the interactions between basic flow and mesoscale disturbances in typhoon. The result shows that in the early stage of typhoon formation, the combined action of vertical shear of basic flow at low level and CISK impels the disturbances to grow rapidly and to move toward the center of typhoon. The development of disturbances, likewise, influences on typhoon’s development and structure. Analysis of the mesoscale disturbances’ development and propagation indicates that the maximum wind region moves toward the center, wind velocity increases, and circulation features of an eye appear. Similarly, when a typhoon decays, the increase of low-level vertical wind shear facilitates the development of mesoscale disturbances. In turn, these mesoscale disturbances will provide typhoon with energy and make the typhoon intensify again. Therefore, it can be said that typhoon has the renewable or self-repair function.

Recent experimental and numerical investigations reveal that the onset of turbulence in plane-Poiseuille flow and plane-Couette flow has some similar stages separated with different threshold Reynolds numbers. Based on these observations and the energy equation of a disturbed fluid element, a local Reynolds number ReL is derived to represent the maximum ratio of the energy supplement to the energy dissipation in a cross section. It is shown that along the sequence of transition stages, which include transient localized turbulence, “equilibrium” localized turbulence, spatially intermittent but temporally persistent turbulence and uniform turbulence, the corresponding thresholds of ReL for plane-Couette flow, Hagen-Poiseuille flow and plane-Poiseuille flow are consistent, indicating that the critical (threshold) states during the laminar-turbulent transition are determined by the local properties of the base flow and are independent of global features, such as flow geometries (pipe or channel) and types of driving forces (shear driving or pressure driving).

The Rayleigh-Taylor (RT) mixing induced by random interface disturbances between two incompressible viscous fluids is simulated numerically. The ensemble averaged spike velocity is found to be remarkably retarded when the random interface disturbances are superimposed with an optimized additional mode. The mode's wavenumber is selected to be large enough to avoid enhancing the dominance of long-wavelength modes, but not so large that its saturated spike and bubble velocities are too small to stimulate a growing effective density-gradient layer suppressing the long-wavelength modes. Such an optimized suppressing mode is expected to be found in the RT mixing including other diffusion processes, e.g., concentration diffusion and thermal diffusion.

A stability analysis is carried out to investigate the onset of thermosolutal convection in a horizontal porous layer when the solid and fluid phases are not in a local thermal equilibrium, and the solubility of the dissolved component depends on temperature. To study how the reaction and thermal non-equilibrium affect the double-diffusive convection, the effects of scaled inter-phase heat transfer coefficient H and dimensionless reaction rate k on thermosolutal convection are discussed . The critical Rayleigh number and the corresponding wave number for the stability and overstability convections are obtained. Specially, asymptotic analysis for both small and large values of H and k is presented, and the corresponding asymptotic solutions are compared with numerical results. At last, a nonlinear stability analysis is presented to study how H and k affect the Nusselt number.

When an inclined plate is heated in a stably stratified fluid, a buoyancy-driven boundary-layer flow will be generated. According to previous studies, such a layer is mainly subjected to two instability mechanisms: the transverse traveling (TS) waves and the stationary longitudinal (SL) rolls. In present paper we identify a novel oblique roll (OR) instability. The oblique rolls are more unstable than SL rolls in fluids with Prandtl numbers P of the order unity or less for all angles of inclination χ with respect to the horizontal except those close to 0°. The OR mode has smaller critical Grashof numbers than the TS waves in some regions of the P – χ -parameter space. This feature is surprising because the transverse TS wave has been reported as the most unstable infinitesimal disturbances in boundary-layer flows. In comparison with TS waves, oblique rolls have a lower critical frequency, which coincides with the Brunt–Vaisala frequency of internal waves when the surface temperature is fixed and the tilt angle is large. Another important feature of the OR mode is that its amplitude decreases less rapidly with distance from the plate than the amplitudes of SL rolls and TS waves. As a result, OR mode disturbances penetrate into the stably stratified region for nearly three times the thickness of the boundary layer. Further investigation reveals that in low Prandtl number fluids with a uniform-heat-flux boundary the preference for onset of oblique rolls instead of TS waves is even stronger than in the case of a fixed temperature at the plate.

A theoretical study is presented of convection in a horizontal fluid layer heated from below or above which is periodically accelerated in its plane. The analysis is based on Galerkin methods as well as on direct numerical simulations of the underlying Boussinesq equations.Shaking in a fixed direction breaks the original isotropy of the layer. At onset of convection and at small acceleration, we find longitudinal rolls, where the roll axis aligns parallel to the acceleration direction. With increasing acceleration amplitude, a shear instability takes over and transverse rolls with the axis perpendicular to the shaking direction nucleate at onset. In the nonlinear regime, the longitudinal rolls become unstable against transverse modulations very close to onset which leads to a kind of domain chaos between patches of symmetry degenerated oblique rolls.In the case of circular shaking, the system is isotropic in the time average sense, however, with a broken chiral symmetry. The onset of convection corresponds to the transverse roll case studied before with the roll axis selected spontaneously. With increasing Rayleigh number, a heteroclinic cycle is observed with the roll changing its orientation periodically in time. At even higher Rayleigh number, this heteroclinic cycle becomes chaotic similarly to the case of the Küppers–Lortz instability.

Despite numerous reports implicating nitric oxide (NO) in the environmental-stress responses of plants, the specific metabolic and ionic mechanisms of NO-mediated adaptation to metal stress remain unclear. Here, the impacts of copper (Cu) and NO donor (SNP, 50 μM) alone or in combination on the well-known medicinal plant Catharanthus roseus L. were investigated. Our results showed that Cu markedly increased Cu 2+ accumulation, decreased NO production, and disrupted mineral equilibrium and proton pumps, thereby stimulating a burst of ROS; in addition, SNP ameliorates the negative toxicity of Cu, and cPTIO reverses this action. Furthermore, the accumulations of ROS and NO resulted in reciprocal changes. Interestingly, nearly all of the investigated amino acids and the total phenolic content in the roots were promoted by the SNP treatment but were depleted by the Cu + SNP treatment, which is consistent with the self-evident increases in phenylalanine ammonia-lyase activity and total soluble phenol content induced by SNP. Unexpectedly, leaf vincristine and vinblastine as well as the total alkaloid content (ca. 1.5-fold) were decreased by Cu but markedly increased by SNP (+38% and +49% of the control levels). This study provides the first evidence of the beneficial behavior of NO, rather than other compounds, in depleting Cu toxicity by regulating mineral absorption, reestablishing ATPase activities, and stimulating secondary metabolites.

To investigate the traits contributing to the invasiveness of Alnus formosana and the mechanisms underlying its invasiveness, we compared A. formosana with its native congener (Alnus cremastogyne) under three light treatments (13%, 56%, and 100%). The consistently higher plant height, total leaf area, light-saturated photosynthetic rate (A(max)), light saturation point (LSP), light compensation point (LCP), respiration efficiency (RE), and non-photochemical quenching coefficient (NPQ) but lower root mass fraction (RMF) and specific leaf area (SLA) of the invader than of its native congener contributed to the higher RGR and total biomass of A. formosana across light regimes. The total biomass and RGR of the invader increased markedly with increased RMF, A(max), LSP, LCP, RE, stomatal conductance (G(s)) and total leaf area. Furthermore, compared with the native species, the higher plasticity index in plant height, RMF, leaf mass fraction (LMF), SMF, SLA, A(max) and dark respiration rate (R(d)) within the range of total light contributed to the higher performance of the invader. In addition, the activities of antioxidant enzymes were higher in the invader compared to the native, contributing to its invasion success under high/low light via photoprotection. With a decrease in light level, superoxide dismutase (SOD) and catalase (CAT) activities increased significantly, whereas total carotenoid (Car) and total chlorophyll (Chl) decreased; ascorbate peroxidase (APX) and glutathione reductase (GR) activities remained unchanged. These responses may help the invader to spread and invade a wide range of habitats and form dense monocultures, displacing native plant species. The results suggest that both resource capture-related traits (morphological and photosynthetic) and adaptation-related traits (antioxidant protection) contribute to the competitive advantage of the invader.

This paper investigates the spatio-temporal instability of the natural-convection boundary-layer flow adjacent to a vertical heated flat plate immersed in a thermally stratified ambient medium. The temperature on the plate surface is distributed linearly. By introducing a temperature gradient radio and Prandtl number on the global frequency are discussed as well.

We use a finite-difference algorithm to simulate the shear flow of nematic liquid crystals based on the Leslie–Ericksen theory, and investigate how unequal elastic constants affect the formation, oscillation, and breakup of roll cells, the nucleation of defects, and the coarsening of texture upon cessation of flow. With elastic anisotropy, the so-called Ericksen number (Er) cascade comprises the same regimes previously documented for isotropic elasticity: stable simple shear, steady roll cells, oscillatory roll cells, and an irregular pattern with thick disclinations. The onset of roll cells is most sensitive to K3, the elastic constant for bend. Increasing K3 stabilizes the shear flow against the formation of rolls. For reduced K3, a second Er cascade may appear for higher Er, with regularization and eventual reappearance of the defect-laden irregular pattern. The twist constant K2 is the most important for defect formation; a weaker K2 causes roll cells to breakup and pairs of ±1 defects to nucleate at lower Er. The defects show distinctive structures depending on the elastic anisotropy; typically a weaker elastic constant gives rise to patterns that incur greater distortion in the corresponding mode. After cessation of shear, all textures relax completely to a monodomain. The longest-lasting orientational pattern is again attributable to the weakest of the elastic constants. By analyzing the amount of distortion in each mode and the associated free energy, we are able to elucidate the role of elastic anisotropy in defining the orientational patterns in sheared nematics.

In this letter, the concentration of particles with size less than 10 μm (PM10) and flow velocities are measured synchronously at different heights in a sand storm, a high-Reynolds number multi-phase turbulent boundary layer. It is revealed that the low-speed very large scale motions (VLSMs) are recurrent with a frequency dominating the streamwise velocity power spectra and modulate the streamwise distribution of PM10 concentration. In the logarithmic layer, the low-speed VLSMs correspond to weak shear stress on the bottom surface and hence decrease the PM10 upward flux. In the higher region, the high-speed VLSMs enhance both the streamwise and the upward transportation of PM10 because of the positive correlation between the velocity and the particle concentration perturbations.

Transition from a Taylor-Couette turbulent flow to a completely two-dimensional axisymmetric turbulent state is realized numerically by increasing gradually the strength of the azimuthal magnetic field produced by electric current flowing through the axial rod. With the increase of the Hartmann number, the Taylor-vortex-like structures shrink, move closer to the inner cylinder, and turn into unsteady but perfect tori at sufficiently high Hartmann numbers.

The spatiotemporal instability of a natural convection flow in vertical heated slot is studied theoretically. The two unstable modes, secondary cell and traveling wave, are illustrated to be absolute and convective instabilities, respectively. Using a model to simulate the temperature gradient in the center of the slot, we propose an interpretation of the mechanism controlling the reverse transition of flow patterns, and explain the temperature fluctuation observed after the reverse transition in terms of the traveling wave mode.

Convective and absolute instabilities in the conduction regime of a vertical heated slot are investigated. It is found that in a large range of Prandtl number (0 12, a secondary instability appears with stationary mode, and it is proven that even at large Prandtl numbers the stationary mode still exists.

In this study, we investigated the biochemical composition and digestive enzyme activity during embryonic development in the marine crab, Charybdis japonica. Water, protein, and ash content increased, while levels of lipids and carbohydrates decreased significantly during embryonic development, and a marked correlation between water content and egg volume (r = 0.97; P < 0.01) was recorded. The utilization percentages of lipids and carbohydrates were 32.72% and 91.56%, respectively. The predominant essential amino acids (EAA) were lysine, leucine, arginine and valine, and the major nonessential amino acids (NEAA) were glutamic acid and aspartic acid. From the fertilized egg stage to the protozoea stage, total amino acid (TAA) concentration increased from 52.18% to 55.11% on a dry weight basis, but the ratio of EAA/TAA decreased from 52.57% to 48.90%. The quantitatively more important fatty acids were C16:0, C18:1n-9c, C16:1, C22:6n-3 (docosahexaenoic acid, DHA), and C22:2. Polyunsaturates (PUFA) and monounsaturated (MUFA) were consumed at similar rates (34.20% and 36.70%, respectively); both were consumed at higher rates than saturates (SFA) (26.56%). In particuler, n-3 fatty acids decreased significantly, with a high consumption rate of 43.74%. Activities of trypsin and pepsin increased during both the early and later embryonic stages, but decreased during the middle stages. Lipase activity increased gradually during embryonic development, except in the protozoea stage with a significant decrease, while activities of amylase and cellulase showed an ascending trend after an initial decline. The activity of all digestive enzymes increased, except for that of lipase, from the heartbeat stage to the protozoea stage.