Safety reliability optimal allocation of food cold chain

This paper applied the safety reliability of food cold chain logistics to establish reliability allocation model for cold chain systems, designed optimization algorithms, and made a case analysis. By applying system reliability allocation principle, this article firstly built safety reliability allocation model of food cold chain logistics system without cost constraint based on the safety reliability model of food cold chain logistics system, and then it set up optimal decision- making model of food cold chain logistics system with cost constraint using the functional relationship between the time, temperature of cold chain logistics and logistics costs. Next, according to the characteristics of the model, a heuristic algorithm was proposed to allocate safety reliability of the system to each cold chain unit so as to achieve the goal of operatingcosts optimization subject to assurance ofoverall safety reliability of the cold chain system. Taking the safety impact factor of food cold chain unit as a weight, the article also deduced the equation of reallocation of safety reliability of food cold chain system. In the end, these models were used to optimize the allocation of safety reliability in an example of Sushi cold chain process. It provided a new thought and method to optimally plan the unit safety of food cold chain system as well as reduce the cost of food cold chain.

Laser ablation mechanism of ZrC-SiC-MoSi_(2) ternary ceramic modified C/C

C/C composites were prepared by chemical vapor infiltration(CVI),and then were subjected to Si,Zr,and MoSi_(2) reactive melt infiltration(RMI)to obtain C/C-SiC,C/C-SiC-ZrC,and C/C-SiC-ZrC-MoSi_(2) com-posites.The ablation behavior of these three composites was evaluated by high-energy CO 2 laser irra-diation.The surface temperature distribution of composite materials was simulated by finite element analysis.The results show that the ablation resistance mechanisms of the three materials are entirely different.The C/C-SiC-ZrC-MoSi_(2) com posite showed the best ablation performance among them.It is at-tributed to the lower oxygen permeability and richer heat dissipation mechanism of the C/C-SiC-ZrC-MoSi_(2) composite within the total temperature threshold.

Damage behavior of atomic oxygen on CVD SiC coating-modified carbon/carbon composite in low earth orbit environment

In this work, samples of carbon/carbon(C/C) and chemical vapor deposited(CVD) SiC-coated C/C samples were investigated to understand the AO damage mechanism in low Earth orbit(LEO) environment. The ground-based simulated atomic oxygen(AO) generator was employed. Results indicate that the CVD SiC coating exhibited improved radiation resistance properties against AO radiation as evidenced by a 16%better strength retention ratio, 60% less mass ablation, and increased strength stability. The magnitude of these influences affected the surface morphology, as observed by scanning electron microscopy(SEM)and surface resistance meter test results. The variations in the surface constituents were confirmed by X-ray diffraction(XRD) and X-ray photoelectron spectroscopy(XPS) results. The main products left on surface after AO exposure are SiO2 and SiCxOyfilm. Additionally, Si atoms are found to be the preferential reacting element in the SiC coating, and this process is accompanied by graphite precipitation, grain growth, and crack necking. Also, the damage mechanism of the AO-exposed SiC coating was revealed and is discussed.