Numerical and experimental evaluation for density-related thermal insulation capability of entangled porous metallic wire material

Entangled porous metallic wire material(EPMWM)has the potential as a thermal insulation material in defence and engineering.In order to optimize its thermophysical properties at the design stage,it is of great significance to reveal the thermal response mechanism of EPMWM based on its complex structural effects.In the present work,virtual manufacturing technology(VMT)was developed to restore the physics-based 3D model of EPMWM.On this basis,the transient thermal analysis is carried out to explore the contact-relevant thermal behavior of EPMWM,and then the spiral unit containing unique structural information are further extracted and counted.In particular,the thermal resistance network is numerically constructed based on the spiral unit through the thermoelectric analogy method to accurately predict the effective thermal conductivity(ETC)of EPMWM.Finally,the thermal diffusivity and specific heat of the samples were obtained by the laser thermal analyzer to calculate the ETC and thermal insulation factor of interest.The results show that the ETC of EPMWM increases with increasing temperature or reducing density under the experimental conditions.The numerical prediction is consistent with the experimental result and the average error is less than 4%.

A Detailed Thermal Resistance Network Analysis of FCBGA Package

Using thermal models to describe the heat dissipation process of FCBGA is a significant topic in the field of packaging.However,the thermal resistance model considering the structure of each part of the chip is still ambiguous and rare,but it is quite desirable in engineering.In this work,we propose a detailed thermal resistance network model,and describe it by using thermal conduction resistance and thermal spreading resistance.For a striking FCBGA case,we calculated the thermal resistance of each part of the structure according to the temperature field simulated by COMSOL.The thermal resistance network can be used to predict the temperatures in the chip under different conditions.For example,when the power changes by 40%,the relative error of junction temperature prediction is only 0.24%.The function of the detailed thermal resistance network in evaluating the optimization space and determining the optimization direction is clarified.This work illustrates a potential thermal resistance analysis method for electronic devices such as FCBGA.

Thermal Analysis of Vehicular Twin-Tube Hydraulic Gas-Precharged Shock Absorbers

In this study of temperature rising in vehicular twin-tube hydraulic gas-precharged shock absorbers,thermodynamic analyses were conducted via simulations.Equations on heat conduction,heat convection as well as radiation were derived by applying certain laws governing heat transfer;an equivalent thermal resistance network model of a shock absorber undergoing heat transfer was established innovatively;moreover,the shock absorber’s thermodynamic model of control volume system was built by using the first law of thermodynamics;and finally,time required for shock absorber to reach thermal equilibrium and corresponding value of steady temperature were calculated by programming.In this way,a lower thermal equilibrium temperature will be achieved,hence help to improve reliability of shock absorbers in work by offering low ambient temperature,by reducing amplitudes and frequencies of external incentives exerted on them and by increasing flow rate of ambient air passing around them.

Resistivity-temperature Characteristics of Conductive Asphalt Concrete

The changes of resistivity of conductive asphalt concrete at different temperatures were studied,and positive temperature coefficient（PTC）modelwas established to estimate the influence of temperature on the resistivity quantitatively,which eliminated the interference with conductivity evaluation brought by temperature variation.Finally,the analysis of temperature cycling test results proves that the changes of percolation network structure caused by temperature variation prompt the emergence of PTC of conductive asphalt concrete.

Calculating current and temperature fields of HVDC grounding electrodes

Current field calculation based on the resistance network method (RNM) and temperature field calculation based on the finite volume method (FVM) can be used to evaluate the performance of high-voltage direct-current(HVDC) grounding electrodes.The main idea of the two methods is to transform an electric and temperature field problems to equivalent circuit problems by dividing the 3D soil space near the grounding electrode into a suitable number of contiguous and non-overlapped cells.Each cell is represented as a central node connecting to the adjacent cells.The resistance network formed by connecting all the adjacent cells together can be solved to calculate the current field.Under the same conditions,the results calculated by the RNM are consistent with the result by CDEGS,a widely used software package for current distribution and electromagnetic field calculation.Based on the finite volume method,the temperature field results are also calculated using time domain simulation.

Global antimicrobial resistance:a system-wide comprehensive investigation using the Global One Health Index

Background:Antimicrobial resistance(AMR)is one of the top ten global public health challenges.However,given the lack of a comprehensive assessment of worldwide AMR status,our objective is to develop a One Health-based system-wide evaluation tool on global AMR.Methods:We have further developed the three-hierarchical Global One Health Index(GOHI)-AMR indicator scheme,which consists of five key indicators,17 indicators,and 49 sub-indicators,by incorporating 146 countries'data from diverse authoritative databases,including WHO's Global Antimicrobial Resistance and Use Surveillance System(GLASS)and the European CDC.We investigated the overall-or sub-rankings of GOHI-AMR at the international/regional/national levels for data preprocessing and score calculation utilizing the existing GOHI methodology.Additionally,a correlation analysis was conducted between the GOHI-AMR and other socioeconomic factors.Results:The average GOHI-AMR score for 146 countries is 38.45.As expected,high-income countries(HICs)outperform the other three income groups on overall rankings and all five key indicators of GOHI-AMR,whereas lowincome countries unexpectedly outperform upper-middle-income countries and lower-middle-income countries on the antibiotics-resistant key indicator(ARR)and ARR-subordinate indicators,including carbapenem-,β-lactam-,and quinolone resistance,and even HICs on aminoglycoside resistance.There were no significant differences among the four groups on the environmental-monitoring indicator(P>0.05).GOHI-AMR was positively correlated with gross domestic product,life expectancy,and AMR-related publications,but negatively with natural growth rate and chronic respiratory disease.In contrast to Cyprus,the remarkably lower prevalence of"ESKAPE pathogens"in high-scoring Sweden and Denmark highlights Europe's huge gaps.China and Russia outperformed the other three BRICS countries on all key indicators,particularly India's ARR and Brazil's AMR laboratory network and coordination capacity.Furthermore,significant internal disparities in carbapenem-resistant Klebsiella pneumoniae(CRKP)and methicillin-resistant Staphylococcus aureus(MRSA)prevalence were observed between China and the USA,with MRSA prevalence both gradually declining,whereas CRKP prevalence has been declining in the USA but increasing in China,consistent with higher carbapenems-related indicator'performance in USA.Conclusions:GOHI-AMR is the most comprehensive tool currently available for the assessment of AMR status worldwide.We discovered unique features impacting AMR in each country and offered precise recommendations to improve the capacity to tackle AMR in low-ranking countries.

Application analysis of efficient heat dissipation of electronic equipment based on flexible nanocomposites

The efficient heat dissipation of electronic equipment is very important,its heat dissipation performance directly determines the life of the equipment itself.A hand-held electronic communications equipment,when used in surface temperature is exorbitant,need to heat dissipation equipment efficiently,to ensure that the use of comfort in the handheld.In accordance with this requirement,this article presents a flexible composite material based on nano-efficient cooling methods that can keep the layout,through the improvement of internal thermal path,it can achieve the effective heat dissipation.The network thermal resistance method is used to analyze the heat transfer in the equipment,and the thermal analysis of the local thermal resistance is carried out.At the same time,through the modeling of electronic equipment and the analysis of finite elements,the temperature drop of the equipment after improvement is accurately judged.Finally,the device experimental performance comparison before and after the optimization of the standby mode and working mode is verified.The results show that the optimized equipment heat source temperature can be reduced by up to 8.5℃,the surface temperature of the equipment can be reduced by about 5℃~7℃,and the final control equipment in the steady standby state of the temperature of about 39±0.5℃,to ensure the comfort of use,and also improved the service life of the equipment.The efficient thermal design of electronic equipment based on flexible nanocomposites can provide a convenient and reliable cooling solution for high-heat flow density devices.

Spacing optimization of high power LED arrays for solid state lighting

This paper provides an analytical approach to determine the optimum pitch by utilizing a thermal resistance network, under the assumption of constant luminous efficiency. This work allows an LED array design which is mounted on a printed circuit board （PCB） attached with a heat sink subject to the natural convection cooling. Being validated by finite element （FE） models, the current approach can be shown as an effective method for the determination of optimal component spacing in an LED array assembly for SSL.