Search

Self-adaptive stage (SAS) is defined as the period between harvest and pre-cooling in this study, which is extremely neglected in the field of postharvest horticultural products. This study aimed to investigate resistant responses and wound-healing activities during the SAS. Broccoli heads that needed cut-harvest were used as experimental materials, and the indices related to storage quality, reactive oxygen species, and phenylpropanoid metabolism were determined during 12 h after the harvest. The results showed that the quality of broccoli heads did not change significantly within 12 h after cut-harvest compared with the normal-growth group. The rapid water loss indicated that measures should be taken for water prevention during SAS. The cut-harvest group showed a significant accumulation of H2O2 after 3 h, which acted as a signal in regulating the antioxidant enzyme system. The activities of phenylalanine ammonia-lyase, cinnamate 4-hydroxylase, and 4-coumarate coenzyme A ligase increased in cut-harvest broccoli stems during 0–6 h, 3–12 h, and 0–9 h, respectively, compared with those in normal-growth broccoli stems. The enhanced enzyme activity involved in phenylpropanoid metabolism and accumulated phenolic acids associated with wound healing at different time points during SAS demonstrated that the response time should be considered when regulating resistance and wound healing. This study focused on revealing the resistance and wound-healing activities of broccoli stems during independent growth after cut-harvest, thus providing a theoretical basis for the subsequent study and regulatory measurement in cut-harvest vegetables. [ABSTRACT FROM AUTHOR]

Consideration of transient effects is important for industrial applications of heat transfer structure optimisation studies; however, the huge computational cost associated with transient problems is a pressing concern. This paper proposes an extension of a previous reduced-dimensional model to transient conjugate heat transfer between a fluid flow and solid-heated plates in a plate heat exchanger. The extended reduced-dimensional model introduces the temperature field of the plate governed by the heat conduction equation, which is coupled to the temperature field of the fluid, governed by the convection-diffusion equation, through the heat flux balance equation at the contact surface. The model is based on assumptions of fully developed flow and constant temperature profile, reducing the three-dimensional problem to a planar problem and significantly reducing computational costs. The accuracy of the model for the simulation of transient heat transfer is verified by comparison with a three-dimensional model. In this paper, the topography of the heat exchanger plate is optimised for both steady-state and transient conditions by applying the reduced-dimensional model. The effectiveness of the optimised design was demonstrated by the cross-check of both the reduced-dimensional and full three-dimensional models. Furthermore, this work considers the effect of time-independent boundary conditions and time-dependent boundary conditions on transient optimisation. The transient and steady-state optimised designs are analysed and compared for both conditions, and the necessity of transient optimisation is discussed. [ABSTRACT FROM AUTHOR]

This paper proposes a reduced-dimensional model for the structural optimisation of conjugate heat transfer between parallel plates with constant temperature and a fluid channel of varying height. The model considers heat conduction and convection through a planar reduced-dimensional version of the convection-diffusion equation. To significantly reduce the computational time for the optimisation process, assumptions on the through-thickness velocity and temperature fields are made, allowing to transform a three-dimensional problem to a two-dimensional one. The accuracy and limitations of the model are investigated through an in-depth parametric analysis and are seen to be acceptable in the context of optimisation when considering the reduced computational cost. To allow for the optimisation of varying topology and topography, the local channel height is linearly interpolated based on the design field. The height parametrisation combined with the reduced-dimensional model provides physical meaning to intermediate design variables and removes the traditional requirement of 0–1 discrete solutions for topology optimisation. This allows the free switch between topology and topography optimisation, but it is illustrated through various examples that only topography changes are relevant for the treated problems. Two optimisation examples, a square heat exchanger and a manifold heat exchanger, demonstrate that the reduced-dimensional model is sufficiently accurate to be applied to structural optimisation. In comparison with shape optimisation using a full three-dimensional model, it is demonstrated that topography optimisation using the reduced-dimensional model can achieve equivalent optimised designs at a significantly lower computational cost. [ABSTRACT FROM AUTHOR]

Bentonite is a key material for engineering barriers to prevent groundwater and nuclide migration in the multi-barrier system of high-level radioactive waste (HLW) geological disposal. However, its barrier property will be degraded under the action of iron corrosion products of steel disposal containers. In this paper, the effects of iron corrosion products on the degradation of bentonite structure and properties were investigated in the simulated environments for HLW geological disposal. The results showed that Fe2+/Fe3+ dissolved from iron powder could enter montmorillonite (Mt) interlayer and substituted part of Na+, which caused the decrease of the volume and interlayer spacing of Mt, and the structural integrity of Mt was destroyed. Macroscopically, the water absorption and swelling property of bentonite were significantly decreased. The degradation mechanism of Mt structure was mainly that Fe2+/Fe3+ generated by iron corrosion entered the interlayer domain of Mt to compensate for the interlayer charge deficit. [ABSTRACT FROM AUTHOR]

Frequently, the shooting angles available to photograph an object are limited, and the resultant images contain perspective distortions. These distortions make more difficult to perform subsequent tasks like feature extraction and information identification. This paper suggested a perspective correction method that extracts automatically distortion features through edge detection. Results showed that this method is powerful in correcting images with perspective distortions. The corrected image has virtually little information missing, clear features and high recovery rate. [ABSTRACT FROM AUTHOR]

As functional components of machine tools, parallel mechanisms are widely used in high efficiency machining of aviation components, and accuracy is one of the critical technical indexes. Lots of researchers have focused on the accuracy problem of parallel mechanisms, but in terms of controlling the errors and improving the accuracy in the stage of design and manufacturing, further efforts are required. Aiming at the accuracy design of a 3-DOF parallel spindle head(A3 head), its error model, sensitivity analysis and tolerance allocation are investigated. Based on the inverse kinematic analysis, the error model of A3 head is established by using the first-order perturbation theory and vector chain method. According to the mapping property of motion and constraint Jacobian matrix, the compensatable and uncompensatable error sources which affect the accuracy in the end-effector are separated. Furthermore, sensitivity analysis is performed on the uncompensatable error sources. The sensitivity probabilistic model is established and the global sensitivity index is proposed to analyze the influence of the uncompensatable error sources on the accuracy in the end-effector of the mechanism. The results show that orientation error sources have bigger effect on the accuracy in the end-effector. Based upon the sensitivity analysis results, the tolerance design is converted into the issue of nonlinearly constrained optimization with the manufacturing cost minimum being the optimization objective. By utilizing the genetic algorithm, the allocation of the tolerances on each component is finally determined. According to the tolerance allocation results, the tolerance ranges of ten kinds of geometric error sources are obtained. These research achievements can provide fundamental guidelines for component manufacturing and assembly of this kind of parallel mechanisms. [ABSTRACT FROM AUTHOR]

Edge effects are predicted to significantly impact the properties of low dimensional materials with layered structures. The synthesis of low dimensional materials with copious edges is desired for exploring the effects of edges on the band structure and properties of these materials. Here we developed an approach for synthesizing MoS nanobelts terminated with vertically aligned edges by sulfurizing hydrothermally synthesized MoO nanobelts in the gas phase through a kinetically driven process; we then investigated the electrical and magnetic properties of these metastable materials. These edge-terminated MoS nanobelts were found to be metallic and ferromagnetic, and thus dramatically different from the semiconducting and nonmagnetic two-dimensional (2D) and three-dimensional (3D) 2H-MoS materials. The transitions in electrical and magnetic properties elucidate the fact that edges can tune the properties of low dimensional materials. The unique structure and properties of this one-dimensional (1D) MoS material will enable its applications in electronics, spintronics, and catalysis. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

An integrated transcriptome and metabolome profiling was used to investigate how exogenous H2O2 affects amino acid metabolism and its underlying regulatory mechanism involved in post-harvest broccoli’s yellowing and senescence processes. This approach found 86 differentially expressed genes (DEGs) and 28 differentially accumulated metabolites (DAMs) associated with amino acid metabolism during broccoli storage in the Control, H2O2, and DPI (diphenylene iodonium, an H2O2 inhibitor) treatments on 2 or 4 d. Furthermore, H2O2 treatment promoted the biosynthesis and accumulation of amino acids (e.g., tryptophan, valine, isoleucine, arginine, lysine, histidine, and glutamate) while inhibiting the degradation of seven amino acids (e.g., tyrosine, valine, leucine, isoleucine, β-alanine, glutamate, and proline) into tricarboxylic acid (TCA) cycle precursor (pyruvate) and intermediates (fumarate, acetyl-CoA, and 2-oxoglutarate). This inhibition alleviated metabolic disorders and ammonium-induced toxicity of post-harvest broccoli. Additionally, H2O2 treatment promoted the NH3 conversion into glutamine and the urea cycle, further mitigating ammonium-induced toxicity. H2O2 treatment also down-regulated the expressions of S-adenosylmethionine synthases (SAM), 1-aminocyclopropane-1-carboxylate synthases (ACS), and 1-aminocyclopropane-1-carboxylate oxidases (ACO), which reduced the S-adenosyl-L-methionine content, thereby inhibiting ethylene biosynthesis from methionine. Therefore, this study provides insights into the role and potential underlying regulatory mechanism of H2O2 on amino acid metabolism during broccoli senescence, thus offering a theoretical basis for delaying senescence in post-harvest horticultural products by regulating their amino acid metabolism. [ABSTRACT FROM AUTHOR]