With the increase in egg production rate and the coming of peak laying period, some metabolic disorders usually emerge in layers. The current study was conducted to compare the physiological difference between the early laying stage (around 30% laying rate) and peak laying stage (more than 95% laying rate) of laying hens based on hepatic transcriptome, serum metabolomics and caecal microbiota. The results showed that the egg weight and yolk weight were significantly higher in peak laying hens. Further, serum malondialdehyde and total bile acid concentrations were higher, but total anti-oxidant capacity, total bilirubin and low-density lipoprotein cholesterol (LDL-c) concentrations were significantly lower in peak laying hens. Hepatic transcriptome analysis identified 540 up-regulated and 269 down-regulated genes. Consistently, fatty acid biosynthesis, PPAR and insulin signalling pathways were significantly enriched. Subsequently, the result of serum metabolomics identified 74 up- and 77 down-regulated metabolites. Among down-regulated metabolites, hesperetin, apigenin and betaine related to anti-oxidant function were down-regulated. In addition, western blotting result showed BCL2 and p53 proteins expressions were decreased in the peak laying period, whereas hepatic CEBPα protein level was increased. On the other hand, gut microbiota analysis revealed that Chao index was decreased in peak laying hens. And the LEfSe analysis showed the dominant microflora including Ruminococcus, Oxalobacter, Paracoccus and so on was found in peak laying hens. These findings indicated that the hepatic lipid metabolism of peak laying hens is enhanced and the decline in anti-oxidant performance of hens also implies its importance during the early stage of egg production.

Based on social norms theory, we examine the impact of local gambling culture, an unexpected result of government-permitted lotteries, on enterprise bribery. We propose that local gambling cultures can promote active enterprise involvement in bribery activities by reinforcing the speculative psychology of enterprise decision-makers. In addition, we argue that local gambling culture is less likely to lead female (returnee) chairpersons to develop speculative psychology than male (nonreturnee) chairpersons. This, in turn, allows female (returnee) chairpersons to undermine the positive impact of local gambling culture on involvement in enterprise bribery. Based on 11 years of empirical data obtained from privately listed Chinese companies (including 2,637 listed companies with 15,036 firm-year data points), we obtain empirical evidence to support most of these views. This study is the first to explore the relationship between local gambling culture and enterprise bribery, and important insights are provided for shareholders and policy-makers to better curb enterprise bribery.

Compared to the streamwise instability, the cross-flow instability in high-enthalpy flows has received relatively less attention, but the latter is of vital importance in the flow transition for practical configurations. This work aims to investigate the cross-flow primary and secondary instabilities in hypersonic and high-enthalpy boundary layers, considering thermochemical non-equilibrium (TCNE) effects. The numerical tools adopted include a high-order shock-fitting solver, nonlinear parabolized stability equations and secondary instability theory (SIT). The flow over a swept parabola is calculated at a free-stream Mach number of 16. It is found that TCNE has a destabilizing effect on the cross-flow mode with a non-catalytic wall. Two important non-dimensional parameters are summarized to explain this effect. One is the ratio between the wall and boundary-layer edge temperatures, and the other is the cross-flow Mach number. Due to nonlinear effects, the stationary cross-flow vortices evolve and exhibit the classic rollover structures as in lower-speed flows. Two different disturbance energy norms are used in the energy budget analysis to classify the secondary cross-flow instability modes. The results from SIT highlight the importance of type-IV modes in TCNE flows at the downwash region of the vortex. The type-IV modes arise with the combined contribution from the wall-normal (on top and trough of the vortex) and spanwise (in the downwash region) production terms. The type-I mode is dominant in the calorically perfect gas case with an adiabatic wall, whereas the type-IV mode has the largest growth rate in the TCNE cases irrespective of wall temperature variation.

This study performs global stability/receptivity analyses of hypersonic flows over a swept blunt body with infinite span. For the first time, we obtain the characteristics of the leading attachment-line mode to the variation of sweep angles from $20^{\circ }$ to $70^{\circ }$. The global eigenfunctions exhibit the characteristics of the attachment-line instability at the leading edge. At the same time, cross-flow (at small sweep angles) or second Mack mode (at larger sweep angles) dominates further downstream. We establish an adjoint-based bi-orthogonal eigenfunction system to address the receptivity problem of such flows to any external forces and boundary perturbations. The receptivity analyses indicate that the global modes are the most responsive to external forces and surface perturbations applied in the vicinity of the attachment line, regardless of the sweep angles. It is also proven that the present global extension of the bi-orthogonal eigenfunction system can be successfully applied to complex hypersonic flows.

This study aims to shed light on hypersonic attachment-line instabilities with large sweep Mach numbers. Highly swept flows over a cold cylinder that give rise to large sweep Mach numbers are studied. High-fidelity basic flows are obtained by solving full Navier–Stokes equations with a high-order shock-fitting method. Using local and global stability theories, an attachment-line mode is found to be dominant for the laminar–turbulent transition along the leading edge that agrees qualitatively with the experimental observations (Gaillard et al., Exp. Fluids, vol. 26, 1999, pp. 169–176). The behaviour of this mode explains the reason for the transition occurring earlier as the sweep Mach number is above 5. In addition, this attachment-line mode is absent if the basic flow is calculated with boundary layer assumptions, indicating that the influence of inviscid flow outside the boundary layer cannot be ignored as is normally done. It is clearly demonstrated that the global modes display the features of both attachment-line modes, as in sweep Hiemenz flow, and the second Mack modes further downstream along the surface. In the large sweep Mach number regime, the attachment-line mode is inviscid in nature and its growth rate increases with the sweep angle. In contrast, in the lower sweep Mach number regime, the attachment-line instability exhibits the features of viscous Tollmien–Schlichting waves, and the sweep angle first increases but then decreases the maximum growth rate.

The development of free-stream disturbances in flow over a vertically vibrating flat plate with a slender leading edge is investigated. The evolution of the optimal inflow perturbation that results in the maximum amplification is computed to investigate the effect of the plate vibration on the development of free-stream disturbance, secondary instability of streaks and subsequently the bypass transition to turbulence. It is observed that the plate vibration leads to periodic change of the angle of attack, shifting the free-stream disturbance to the upper or lower side of the plate. Therefore, the development of steady inflow perturbations, which receive the largest amplification, is interrupted by the vibration, and the perturbation amplification via the lift-up mechanism is weakened. The vibration brings a second peak of perturbation growth at the vibration frequency, leading to high-frequency free-stream perturbations penetrating into the base boundary layer, which is not observed in flow over a stationary plate owing to the sheltering mechanism. This resonance of the flow perturbation and the vibrating plate is explained by the staggering effect of the leading edge. Further, the direct numerical simulations with the optimal inflow perturbation imposed on the inflow boundary show that the vertical vibration of the plate leads to streamwise periodic vorticity near the edge of the boundary layer. This inhomogeneity of the streamwise vorticity brings about streamwisely localized distortion of the low-speed streaks and, thus, an intermittent secondary instability. Therefore, before the streaks break down to turbulence, they undergo several rounds of secondary instabilities, resulting in an elongated bypass transition process.

We present an experimental study on controlling the number of vortices and the torque in a Taylor–Couette flow of water for Reynolds numbers from 660 to 1320. Different flow states are achieved in the annulus of width $d$ between the inner rotating and outer stationary cylinders through manipulating the initial height of the water annulus. We show that the torque exerted on the inner cylinder of the Taylor–Couette system can be reduced by up to 20 % by controlling the flow at a state where fewer than the nominal number of vortices develop between the cylinders. This flow state is achieved by starting the system with an initial water annulus height $h_0$ (which nominally corresponds to $h_0/d$ vortices), then gradually adding water into the annulus while the inner cylinder keeps rotating. During this filling process the flow topology is so persistent that the number of vortices does not increase; instead, the vortices are greatly stretched in the axial (vertical) direction. We show that this state with stretched vortices is sustainable until the vortices are stretched to around 2.05 times their nominal size. Our experiments reveal that by manipulating the initial height of the liquid annulus we are able to generate different flow states and demonstrate how the different flow states manifest themselves in global momentum transport.

Polydopamine (PDA) is a biopolymer, which can form uniform thin films on almost all solid substrates as well as at the liquid/air interface. Carbonized polydopamine possesses graphite-like structure and exhibits high electrical conductivity, which makes it a potential carbon-based thin film conductor. However, studies on mechanical behavior of PDA and its derived materials are very limited. In this study, PDA samples were synthesized through self-assembly of dopamine in aqueous solution. Elastic modulus of thin films was measured using the nanoindentation technique. It is shown that the Young’s modulus of PDA thin film increased with increasing heat treatment temperature (up to 600°C). Doping with Cu ions also increased the Young’s modulus of PDA. Furthermore, all PDA thin films, with and without Cu, exhibited creep behavior.

In this paper, the design of a graded honeycomb radar absorbing structure (RAS) is presented to realize both a wide bandwidth and absorption over a wide range of angles. For both transverse-electric and transverse-magnetic polarization, a fractional bandwidth of more than 118.6% is achieved for at least a 10 dB reflectivity reduction when the incident angle is <45°, an 8 dB reduction when the incident angle is <55° and a 5 dB reduction when the incident angle is <70°. Meanwhile the 10 dB reduction upper angle limit is approximately 30° for the uniform coating honeycomb RAS in the literature, which loses its absorbing ability when the incident angle is larger than 55°. Furthermore, the total thickness of our design is 10.7 mm, which is only approximately 1.29 times that of the theoretical limitation. The good agreement between the calculated, simulated, and measured results demonstrates the validity of this optimization.

Dynamics and instability of a vortex ring impinging on a wall were investigated by means of large eddy simulation for two vortex core thicknesses corresponding to thin and thick vortex rings. Various fundamental mechanisms dictating the flow behaviors, such as evolution of vortical structures, formation of vortices wrapping around vortex rings, instability and breakdown of vortex rings, and transition from laminar to turbulent state, have been studied systematically. The evolution of vortical structures is elucidated and the formation of the loop-like and hair-pin vortices wrapping around the vortex rings (called briefly wrapping vortices) is clarified. Analysis of the enstrophy of wrapping vortices and turbulent kinetic energy (TKE) in flow field indicates that the formation and evolution of wrapping vortices are closely associated with the flow transition to turbulent state. It is found that the temporal development of wrapping vortices and the growth rate of axial flow generated around the circumference of the core region for the thin ring are faster than those for the thick ring. The azimuthal instabilities of primary and secondary vortex rings are analyzed and the development of modal energies is investigated to reveal the flow transition to turbulent state. The modal energy decay follows a characteristic –5/3 power law, indicating that the vortical flow has become turbulence. Moreover, it is identified that the TKE with a major contribution of the azimuthal component is mainly distributed in the core region of vortex rings. The results obtained in this study provide physical insight of the mechanisms relevant to the vortical flow evolution from laminar to turbulent state.

The effects of an axial high magnetic field on the growth of the α-Al dendrites and the alignment of the iron-intermetallics (β-AlSiFe phases) in directionally solidified Al–7 wt% Si and Al–7 wt% Si–1 wt% Fe alloys were investigated experimentally. The results showed that the application of a high magnetic field changed the α-Al dendrite morphology significantly. Indeed, a high magnetic field caused the deformation of the α-Al dendrites and induced the occurrence of the columnar-to-equiaxed transition (CET). It was also found that a high magnetic field was capable of aligning the β-AlSiFe phases with the <001>-crystal direction along the solidification direction. Further, the Seebeck thermoelectric signal at the liquid/solid interface in the Al–7 wt% Si alloys was measured in situ and the results indicated that the value of the Seebeck signal was of the order of 10 µV. The modification of the α-Al dendrite morphology under the magnetic field should be attributed to the thermoelectric magnetic force acting on the α-Al dendrites. The magnetization force may be responsible for the alignment of the β-AlSiFe phases under the magnetic field.

A vortex ring impacting a three-dimensional bump is studied using large eddy simulation for a Reynolds number Re = 4 × 104 based on the initial diameter and translational speed of the vortex ring. The effects of bump height and vortex core thickness for thin and thick vortex rings on the vortical flow phenomena and the underlying physical mechanisms are investigated. Based on the analysis of the evolution of vortical structures, two typical kinds of vortical structures, i.e., the wrapping vortices and the hair-pin vortices, are identified and play an important role in the flow state evolution. The boundary vorticity flux is analyzed to reveal the mechanism of the vorticity generation on the bump surface. The circulation of the primary vortex ring reasonably elucidates some typical phases of flow evolution. Further, the analysis of turbulent kinetic energy reveals the transition from laminar to turbulent state. The results obtained in this study provide physical insight into the understanding of the mechanisms relevant to the flow evolution and the flow transition to turbulent state.

The effect of a strong magnetic field on the solid solubility and the microsegregation during directional solidification of Al–Cu alloy at lower growth speeds (1–10 μm/s) has been investigated experimentally. Results indicate that the magnetic field causes the reduction of the grain boundary and promotes the amalgamation of the grains. Further, measurement results reveal that the magnetic field increases the solid solubility and decreases the microsegregation. It is also found that the value of the solid solubility increases as the magnetic field and the temperature gradient increase. The modification of the solid solubility and the microsegregation under the magnetic field is attributed to the thermoelectric magnetic force acting on the solid and the interdendritic thermoelectric magnetic convection. The present work may initiate a new method to enhance the solid solubility and to eliminate the microsegregation in Al-based alloys via an applied strong magnetic field during directional solidification.

Molecular films have been extensively used for crystal growth. The Langmuir–Blodgett (LB) technique allows the oriented molecules film to be produced in a controllable manner. By controlling the LB film surface pressure and tuning quenching temperature of the supersaturated solution, single NaCl (100) crystal planes are successfully produced under the surface pressure of 30 mN/m with quenching temperature 5 °C of the NaCl supersaturated solution. The mechanism of single NaCl (100) crystal growth can be further explained based on the best matching between NaCl (100) crystal plane distance and the lattice parameter of LB film among all other crystal planes.

Poly(vinylidene fluoride) (PVDF) is well known for its ferroelectric and piezoelectric properties. Currently, this polymer is used in applications in the form of films. PVDF fibers are expected to open up exciting new opportunities such as design and use of active textiles and composites. It is well-known that synthetic fiber properties improve substantially with the decrease of their diameter. However, conventional mechanical fiber spinning processes usually produce fibers with diameters in the range from tens to hundreds of microns. In this work, ultrafine, submicron-diameter continuous PVDF nanofibers were fabricated by electrospinning method. The method consists of spinning polymer solutions in high electric fields. Effects of process parameters on nanofiber diameter and morphology were studied. XRD and FTIR analyses of PVDF nanofibers were performed. The latter indicated that the initial á phase of the raw material was converted to â phase PVDF during electrospinning. As â phase is primarily responsible for the piezo- and ferroelectric properties of PVDF, the latter result is very encouraging. The demonstrated novel continuous PVDF nanofibers can be used in nanostructured active textiles and composites and can lead to unusual new designs for actuators and sensors.

A refractory silicon nitride joint, which contains β–Si3N4 grains and grain boundary amorphous phase in the joined layer, was developed with the aid of a ceramic adhesive based on the system Si3N4–Y2O3–SiO2–Al2O3. The similarity in chemistry and microstructure between the parent ceramic and the joint zone indicates that the joining mechanism is the same as that involved in the sintering of Si3N4. The resultant joint exhibits a high bond strength of 550 MPa at 25 °C and retains a strength of 332 MPa at 1000 °C. Post-joining hot-isostatic pressing was applied to strengthen the joint, resulting in increased strengths of 668 MPa at room temperature and 464 MPa at 1000 °C.

We derive formulas for the first- and higher-order derivatives of the steady state performance measures for changes in transition matrices of irreducible and aperiodic Markov chains. Using these formulas, we obtain a Maclaurin series for the performance measures of such Markov chains. The convergence range of the Maclaurin series can be determined. We show that the derivatives and the coefficients of the Maclaurin series can be easily estimated by analysing a single sample path of the Markov chain. Algorithms for estimating these quantities are provided. Markov chains consisting of transient states and multiple chains are also studied. The results can be easily extended to Markov processes. The derivation of the results is closely related to some fundamental concepts, such as group inverse, potentials, and realization factors in perturbation analysis. Simulation results are provided to illustrate the accuracy of the single sample path based estimation. Possible applications to engineering problems are discussed.