食品安全风险评估中的不确定性

食品安全风险评估的整个过程始终伴随着不确定性,其来源大致可分为两类,即结果外推和数据局限性。不确定系数是处理这些不确定性的常用方法,相关组织或机构均推荐了用于制定健康指导值的默认不确定系数,但基准剂量法和化学物特异性调整系数法等方法可更好地处理风险评估中的不确定性。     

Studies on thermal degradation kinetics and dielectric properties of polyether imide foam/nanosilica-based nanocomposites

ABSTRACT

In this paper, polyether imide (PEI) having properties such as a high glass transition temperature of 216°C, high heat resistance, high flame resistance, low smoke generation and a high melting point within the range of 400°C, having low thermal conductivity and low dielectric constant was chosen to be a polymeric foam. Water vapor-induced phase separation method was used to prepare PEI foams. PEI foams were reinforced with nano-silica (weight 1, 3 and 5%) in order to alter the dielectric properties, thermal conductivity and degradation kinetics of foamed polymer. The tested samples showed a reduction in dielectric constant than that of solid PEI but at a higher loading, it showed a higher value due to threshold percolation and a reduction in thermal conductivity was observed for foamed PEI. From thermogravimetric analysis, we can conclude that PEI with 3% filler loading showed better thermal stability compared to other PEI foam compositions.     

A novel and effective PECVD SiO2/SiN antireflectioncoating for Si solar cells

It is shown that sequential plasma-enhanced chemical vapor deposition (PECVD) of SiN and SiO₂ can produce a very effective double-layer antireflection (AR) coating. This AR coating is compared with the frequently used and highly efficient MgF₂/ZnS double layer coating. The SiO₂/SiN coating improves the short-circuit current (J_SC) by 47%, open-circuit voltage (V_OC) by 3.7%, and efficiency (Eff) by 55% for silicon cells with oxide surface passivation. The counterpart MgF₂/ZnS coating gives similar but slightly smaller improvement in V_OC and Eff. However, if silicon cells do not have the oxide passivation, the PECVD SiO₂/SiN gives much greater improvement in the cell parameters, 57% in J_SC, 8% in V_OC, and 66% in efficiency, compared to the MgF₂/ZnS coating which improves J_SC by 50%, V_OC by 2%, and cell efficiency by 54%. This significant additional improvement results from the PECVD deposition-induced surface/defect passivation. The internal quantum efficiency (IQE) measurements showed that the PECVD SiO₂/SiN coating a absorbs fair amount of photons in the short-wavelength range (<500 nm); however, the improved surface/defect passivation more than compensates for the loss in J_SC and gives higher improvement in the cell efficiency compared to the MgF₂/ZnS coating     

Modeling and Simulation of a PMSG-based Marine Current Turbine System under Faulty Rectifier Conditions

This paper deals with the modeling and simulation of a permanent magnet synchronous generator (PMSG)-based marine current turbine (MCT) under faulty rectifier conditions. The modeling of the generator is established in the synchronous rotating d-q reference frame. The control of the speed, the d-axis current, and the q-axis current are achieved using proportional integral (PI) correctors. The faulty mode deals with the study of single and multiple open-switch damages appearing in the pulse width modulation (PWM) power rectifier. Simulations are carried out to highlight the proposed PMSG-based MCT performance in both cases using MATLAB/Simulink environment.     

Spectrum Occupancy Statistics and Time Series Models for Cognitive Radio

While dedicated spectrum occupancy monitoring provides vital information for frequency planning and management, it usually cannot tell the common properties in spectrum occupancy. As a complement, the models approach can be used to describe and compare the occupancy situations under similar conditions. Time series analysis has been applied to modeling the radio spectrum occupancy. This paper categorizes different time series models to different occupancy patterns. Occupancy analysis of the Global System for Mobile communications (GSM) band is given as an example.     

Crosstalk between Ca2+ Signaling and Cancer Stemness: The Link to Cisplatin Resistance

In the fight against cancer, therapeutic strategies using cisplatin are severely limited by the appearance of a resistant phenotype. While cisplatin is usually efficient at the beginning of the treatment, several patients endure resistance to this agent and face relapse. One of the reasons for this resistant phenotype is the emergence of a cell subpopulation known as cancer stem cells (CSCs). Due to their quiescent phenotype and self-renewal abilities, these cells have recently been recognized as a crucial field of investigation in cancer and treatment resistance. Changes in intracellular calcium (Ca²⁺) through Ca²⁺ channel activity are essential for many cellular processes such as proliferation, migration, differentiation, and survival in various cell types. It is now proved that altered Ca²⁺ signaling is a hallmark of cancer, and several Ca²⁺ channels have been linked to CSC functions and therapy resistance. Moreover, cisplatin was shown to interfere with Ca²⁺ homeostasis; thus, it is considered likely that cisplatin-induced aberrant Ca²⁺ signaling is linked to CSCs biology and, therefore, therapy failure. The molecular signature defining the resistant phenotype varies between tumors, and the number of resistance mechanisms activated in response to a range of pressures dictates the global degree of cisplatin resistance. However, if we can understand the molecular mechanisms linking Ca²⁺ to cisplatin-induced resistance and CSC behaviors, alternative and novel therapeutic strategies could be considered. In this review, we examine how cisplatin interferes with Ca²⁺ homeostasis in tumor cells. We also summarize how cisplatin induces CSC markers in cancer. Finally, we highlight the role of Ca²⁺ in cancer stemness and focus on how they are involved in cisplatin-induced resistance through the increase of cancer stem cell populations and via specific pathways.     

Effect of CuO-, SiO2-, and Al2O3-based nanofluids on automotive cooling systems from laminar to turbulent flow regime—A CFD study

In recent studies, much attention has been given to nanofluids suggesting that adding nanoparticles in base fluids offers a higher heat transfer rate compared with conventional fluids. This study is based on the numerical investigation of different types of nanofluids, consisting of CuO (50 nm), SiO₂ (40 nm), and Al₂O₃ (15 nm) nanoparticles at different volume concentrations. Several simulations were performed from low to high Reynolds numbers, corresponding to laminar and turbulent flow regimes using ANSYS-Fluent CFD solver. Results suggest that under a laminar flow regime with the same Reynolds number of 2000, CuO-based nanofluids perform better as compared with SiO₂ and Al₂O₃-based nanofluids with Nusselt number (Nu) having percentage increase of 90% and 60% comparing with SiO₂- and Al₂O₃-based nanofluids, respectively. However, at higher Reynolds numbers when the flow is turbulent, Al₂O₃-based nanofluids demonstrate better performance having a percentage increase in Nusselt numbers equal to 40% and 23% as compared with CuO and SiO₂-based nanofluids respectively under the same Reynolds number of 15,000. This implies that turbulence has a significant effect on heat transfer rate, and is not only related to thermal conductivity. This study will help in designing more compact cooling systems for engines and the internal environment of motor vehicles.